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Pharmaceutical strategies of improving oral systemic bioavailability of curcumin for clinical application
Journal Pre-proof Pharmaceutical strategies of improving oral systemic bioavailability of curcumin for clinical application Ziwei Ma, Wang Na, Haibing He, Xing Tang
PII:
S0168-3659(19)30617-0
DOI:
https://doi.org/10.1016/j.jconrel.2019.10.053
Reference:
COREL 10002
To appear in: Received Date:
26 August 2019
Revised Date:
28 October 2019
Accepted Date:
29 October 2019
Please cite this article as: Ma Z, Na W, He H, Tang X, Pharmaceutical strategies of improving oral systemic bioavailability of curcumin for clinical application, Journal of Controlled Release (2019), doi: https://doi.org/10.1016/j.jconrel.2019.10.053
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Pharmaceutical strategies of improving oral systemic bioavailability of curcumin for clinical application Ziwei Maa, Wang Naa, Haibing Hea, Xing Tanga a
Department of Pharmaceutics, School of Pharmacy, Shenyang Pharmaceutical
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University, Shenyang 110016, Liaoning, PR China
Corresponding author. Xing Tang, E-mail address: [email protected]. Haibing He, Email address: [email protected].
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Graphical abstract
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Pharmaceutical strategies are developed to improve curcumin oral bioavailability. Curcumin oral bioavailability is enhanced by increasing curcumin solubility. Curcumin oral bioavailability is enhanced by improving curcumin intestinal stability. Curcumin oral bioavailability is enhanced by changing curcumin absorption route. Curcumin oral bioavailability is enhanced by coadministrating with other adjuvants.
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Highlights
Abstract
Curcumin (Cur), a natural compound from Curcuma longa Linn, has various pharmacological activities such as anti-cancer, anti-inflammatory, anti-oxidant, antiAlzheimer, anti-microbial and more. Curcumin also has nephroprotective, hepatoprotective, neuroprotective, antirheumatic and cardioprotective effects. However, its low aqueous solubility inhibits the oral bioavailability of curcumin. As well, curcumin can be metabolized rapidly by intestinal tract which can also result in low
oral bioavailability. In fact, the bioavailability of curcumin is low even through intraveneous administration routes. Various pharmaceutical strategies for oral administration including solid dispersions, nano/microparticles, polymeric micelles, nanosuspensions, lipid-based nanocarriers, cyclodextrins, conjugates, polymorphs have been developed in order to improve the oral bioavailability of curcumin. These pharmaceutical strategies can increase the solubility of curcumin, improve the intestinal stability of curcumin, change the absorption route of curcumin and allow for coadministration with other adjuvants. Here we discuss efficacy studies in vitro and in vivo of curcumin nanoformulations, as well as human clinical trials.
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Key words: Curcumin, Oral administration, Pharmaceutical strategy, Systemic bioavailability, Clinical studies.
1.Introduction
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Curcumin [1,7-bis(4-hydroxy-3-methoxyphenyl)-1, 6-heptadiene-3, 5-dione], a low molecular weight hydrophobic polyphenol derived from turmeric rhizomes (Curcuma longa Linn.), is used as a spice in many foods and as a coloring agent. Natural cur is composed of three hydrophobic curcuminoids: curcumin, bisdemethoxycurcumin and demethoxycurcumin in the proportion of 77:3:17 (Fig 1). Cur has the highest antidiabetic, dioprotective and neuroprotective effects out of the three curcuminoids. However, the mixture of curcuminoids has improved nematocidal activity compared to the individual compounds[1]. Cur has various pharmacological activities against chronic diseases such as Alzheimer’s disease, multiple sclerosis, rheumatoid arthritis, atherosclerosis and more. It also protects against cataract formation, liver injury, pulmonary toxicity and fibrosis, can inhibit thrombosis and suppress platelet aggregation and can enhance wound healing. Finally, cur also has anti-cancer activity and can treat various cancers such as melanoma, breast, gastrointestinal, genitonurinary, sarcoma and more. At the molecular level, cur can inhibit cell metastasis and induces cell apoptosis by regulating pro-inflammatory cell factors such as tumor necrosis, receptors such as epidermal growth factor receptor (EGFR), growth factors such as epidermal growth factor (EGF), transcription factors, apoptosis-related enzymes and proteins, cyclooxygenase-2 (COX2) and so on. An overview of cur pharmacological activities is shown in Fig 2.
Inflammatoy diseases
Lifestyle-related disease
Cancer
Others
Colorectal
β-Thalassemia
Ulcerative proctitis
Heart failure
cancer
Respiratory contraction
Crohn’s disease
Atherosclerosis
Pancreatic
Alcohol intoxication
Irritable bowel Syndrome
Alcoholism
cancer
Atherosclerosis
Rheumatoid arthritis
Liver dysfunction
Prostate cancer
Cadaveric
Chronic anterior
Kidney disease
Breast
Renal Transplantation
Uveitis
Myocardial infarction
Head and neck
Monoclonal gammopathy of
cancer
undefined significance (MGUS)
Cervical cancer
Depression
Skin cancer
Psoriasis Osteoporosis Muscular fatigue
Idiopathic
Curcumin
Inflammatory
Orbital
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Pepticulcer
Pseudotumors
Neurodegenerative diseases
Pancreatitis Allergy Malaria Bacterial infection
Dejerine-Sottas diseases
Metabolic diseases
Alzheimer’s diseases
Diabetes
Arterial diseases
Diabetic nephropathy
Parkinson’s disease
Fungal infection
Epilepsy
Diabetic microangiopathy Lupus nephritis
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HIV
Curcumi n
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Arthritis
cancer
Renal transplantation
Nematode infection
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Fig 2. An overview of different pharmacological activities of curcumin.
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Unfortunately, cur oral bioavailability is low due to its limited water solubility and rapid metabolism and excretion. Various types of nanocarriers including nanoparticles[2], phospholipid complexation[3], nanoemulsion[4], solid dispersions[5], liposome[6], adjuvant with piperine[7] etc have been developed in order to improve cur oral bioavailability. These nanocarriers are discussed in the following sections highlight that nanocarriers can increase cur solubility and thus oral bioavailability in order to effectively treat various diseases.
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This review focuses on the strategies of improving cur oral bioavailability, the development of various cur formulations, preclinical (including in vitro and in vivo) and clinical studies of cur. Previously employed strategies are presented in the following sections using specific examples.
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Fig. 1. Chemical structures of curcumin (A) demethoxycurcumin (B) and bisdemethoxycurcumin (C).
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2.Reasons of low oral bioavailability of curcumin
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As seen in Fig 3., when cur is orally administered, a large proportion of cur is excreted through the feces while only small proportion is absorbed in the intestine, followed by rapid metabolism in plasma and the liver. Cur is mostly absorbed in the small intestines.
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The poor oral bioavailability may be due to poor absorption, high metabolism rate, rapid clearance and elimination from the body. For cur oral delivery, three physiological barriers in the gastrointestinal tract are related to the low oral bioavailability of cur. Firstly, physical barriers such as the upper mucus and the intestinal epithelium can restrict drug transport. Tight junctions in the epithelial cells can inhibit the absorption of molecules[8]. The mucus layer which consists of negatively charged glycoproteinsmucins and water are on the surface of the epithelium, and can inhibit the diffusion of cur due to the high moisture[9]. Secondly, chemical barriers such as gastric acid, bile and various digestive enzymes can cause the cur degradation, which may also influence its absorption in the blood[10]. Biochemical obstacles such as metabolic enzymes and epithelial cell p-glycoprotein efflux may make cur inactive and deliver cur back to the gastrointestinal lumen, which may also limit the gasterinternal absorption of cur[11]. Finally, the liver first-pass effect can inhibit the oral absorption of cur.
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The oral absorption of cur is extremely low which also contributes to the low cur oral bioavailability. It was shown that orally administered cur at a dose of 500 mg/kg only had 0.06 μg/mL maximum serum concentration, indicating only 1% oral bioavailability[12]. This is likely the result of limited gastrointestinal absorption of cur because of the poor solubility in water [13]. Cur possesses three protons, two phenolic protons and an enolic proton, which are ionizable in water. The pKa of the two phenolic protons is 10-10.5 and the pKa of the enolic proton is 8.5. In neutral or acidic pH, cur has limited solubility (the maximum solubility in pH 5.0 aqueous buffer is 11 ng/ml), and is not stable in alkali pH and can be hydrolyzed within the intestinal (pH 6.8) conditions, also contributing to its low oral bioavailability and absorption. In order to predict cur oral bioavailability, its in vivo distribution has been studied in various groups. In the study of Ravindranath et al., when cur was administered at a dose of 400 mg to rats, 40% of cur was excreted in the feces, with none found in urine, heart and blood. After 30 min administration of cur, 90% of cur was in the small intestine and stomach, however only 1% remained after 24 h[14]. When cur is administered orally, rapid metabolism and clearance of cur from the body occurs through formation of glucuronide and sulphates by conjugation in the intestine, and it can also interact with bile salts. Cur blood concentrations are extremely low after oral administration due to this rapid metabolism in the intestinal wall and liver[15~17]. When cur was orally administered at a dose of 10 or 12 g, maximum plasma cur concentrations in humans was still as low as less than 160 nmol/L[18]. Only minute amounts of cur, the majority of which is excreted in the urine and feces, were detected in the blood circulation after high-dose oral administration.
Absorption from small intestine
Distribution
Elimination
Portal circulation of curcumin
Blood Circulation curcumin
Liver Degradation of curcumin
of
Coadministration
adjucants by inhibiting the
Increase the solubility of curcumin
Tissue Distribution curcumin
Lymphatic Transport of curcumin
Urinary Excretion of curcumin
of
Blood
Vessel
Lymphoid
Mucus
Tg
Enter
M
Nanoparticle s
cell
Targeted nanoparticles
-p
ocyte
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vessel
Increase the stability of curcumin in
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gastrointestinal tract
degration
curcumin.
Change the absorption route of curcumin
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Fig 3. Absorption, distribution, metabolism and elimination(ADME) of curcumin preparations following oral administration. The curcumin oral bioavailability is increased by enhancing curcumin solubility, improving curcumin gastrointestinal stability, changing the absorption route of curcumin, coadministrating with adjucants.
3.Pharmaceutical Strategies of improving oral bioavailability
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of Curcumin
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In order to enhance cur oral bioavailability, several drug delivery strategies have been employed. Firstly, pharmaceutical strategies are used in order to enhance cur solubility, and then cur absorption in the gastrointestinal tract is enhanced resulting in overall improved oral bioavailability. Secondly, several nanoformulations can increase cur oral bioavailability by improving its gastrointestinal stability. Thirdly, cur nanoformulations can change the absorption route of cur, also improving oral bioavailability. Finally, cur oral bioavailability can be enhanced by co–administration of with other adjuvants which can inhibit the metabolism of cur. 3.1 Increase the solubility of curcumin 3.1.1 Solubility of curcumin in solvents The cur log P value is 3.29, indicating that cur has very low water solubility (11 ng/mL).
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Cur is soluble in various polar solvents including methanol (4.44 mg/mL), 2-butanone (2.17 mg/mL), ethanol (5.6 mg/mL), isopropanol (3.93 mg/mL), acetone (7.75 mg/mL), and 1,2-dichloroethane (0.5125 mg/mL). Cur had the highest solubility in DMSO (20 mg/mL), and is therefore the best solvent for preparation of cur nanoformulations. For preparation of cur nanoemulsions, the cur solubility in various oils is essential. The cur solubility in surfactants and oils is listed in Table 1, giving the oils with the higher solubility of cur that can be chosen as oil phase.
Solubility
Oil/Surfactant
Solubility
Miglyol 812
3.56 mg/g
Peceol
1.67±0.09 mg/ml
Miglycol 840
11.12 ± 0.82mg/ml
Ethyl oleate
0.43±0.02 mg/ml
Soybean oil
5.5 ± 0.4 mg/ml
ODO
9.39 ± 0.24 mg/ml
Mineral oil
0.5 ± 0.2 mg/ml
IPP
Castor oil
8.8 ± 0.4 mg/ml
oleic acid
1.39 ± 0.030 mg/ml
Cotton seed oil
4.9 ± 0.5 mg/ml
WL 1349
12.60 ± 0.20 mg/ml
Olive oil
3.3 ± 0.4 mg/ml
Cremphor RH40
86.27 ± 3.01mg/ml
Sesame oil
2.8± 0.2 mg/ml
Cremorphor EL
37.04±7.86 mg/ml
Peanut oil
3.2± 0.3 mg/ml
transcutol P
66.66 ± 1.20 mg/ml
Corn oil
1.48±0.06 mg/ml
Glycerine
3.95 ± 0.12 mg/ml
PEG 7 glyceryl cocoate
41 mg/g
Labrafac PG
0.90±0.01 mg/ml
PEG 600
250 mg/ml
Capryol PGMC
13.93±0.07 mg/ml
PEG 400
95.07 ± 4.50 mg/ml
Lauroglycol 90
4.24±0.09 mg/ml
Propylene glycol
11.89 ± 2.03 mg/ml
Capryol 90
7.75±0.11 mg/ml
Labrafac ® CC
13.0 ± 0.6 mg/ml
Lauroglycol Fcc
8.20±0.08 mg/ml
Labrafil ® M 1944 CS
26.1 ± 1.8 mg/m
Isopropyl myristate
3.1 ± 0.2 mg/ml
Labrafil M 2125 CS
0.60±0.01 mg/ml
Tocopherol acetate
3.0 ± 0.3 mg/ml
Labrafac lipophile WL
2.63±0.03 mg/ml
Plurol ® Oleique CC
31.6 ± 2.6 mg/ml
Labrafac WL 2609 BS
4.43±0.11 mg/ml
SPAN 80
8.8± 0.4 mg/ml
Labrasol
52.15±1.67 mg/ml
Tween-80
34.38±0.78 mg/ml
2.64 mg/g
Trancutol HP
112.98±17.40 mg/ml
CRMEL
41 mg/g
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Oil/Surfactant
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Table 1. Solubility of curcumin in oil/surfactant phase[19].
9.18 ± 0.32 mg/ml
3.1.2 Pharmaceutical strategies of improving solubility of curcumin In the GI tract, insoluble cur can be excreted with the feces, while only soluble cur is absorbed through intestinal epithelial cells. Thus, in order to improve the cur GI tract absorption, cur solubility needs to be enhanced. Various pharmaceutical strategies to improve cur solubility have been applied to improve the oral bioavailability of cur, and
are listed in Table 2. Among these formulations, cur micelles (CUR-MM) prepared by Sharvil Patil et al.[42] had a relatively higher bioavailability with the higher Cmax(0.24 ± 0.04 μg/mL) and AUC (6.13 ± 0.22 μg h/mL ) than other formulations. By incorporating cur in micelles using Gelucire ® 44/14 (GL44) and Pluronic F-127 (PF-127) as surfactants by a solvent evaporation method, the cur aqueous solubility was increased to 104 or 103 fold with increasing surfactant concentration. Besides, both the solubility, stability, antioxidant activity and bioavailability of cur were improved by incorporating cur in mixed surfactant vesicles. Table 2. Solubility of curcumin in various of curcumin preparations. Formulation
Solid dispersion
Solubility
Cmax
AUC
(Preparation vs.
(Preparation vs.
control)
control)
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Preparation
Hydroxy-
1000
184 ± 14
20685 ± 836
propylmethyl
fold
vs.
vs.
(HPMC),
increased
27 ± 8 ng/ml
1615 ± 114
Lecithin, Isomalt
(20 mg/rat)
[23]
ng.min/ml
(20 mg/rat)
α-glucosyl stevia (Stevia-G),
fold
polyvinylpyrrolidone
increased
vs. 3.78μg/ml min
(100 mg/kg)
(100 mg/kg)
95.60 ± 53.8
72.84±36.4
(50 mg/kg)
(50mg/kg)
vs.
vs.
15.65 ± 12.6
15.31±19.7
ng/ml
ng/ml.h
(50 mg/kg)
(50 mg/kg)
6.75±1.54
2066±332
(100 mg/kg)
(100mg/kg) vs.
vs.
367±21
1.55±0.21 μg/mL
μg/ml min
(100 mg/kg)
(100 mg/kg)
/
/
[31]
8.9μg/ml
/
/
[32]
The solubility of cur in
0.0291±0.0078
9.5931±1.3731
[33]
MSN-A was 10-fold
(50 mg/kg)
(50mg/kg)
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560 μg/ml
(PVP)
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640-fold increased
PVA
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articles
PLGA,
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poly[2-hydroxypropyl
(PHPMA )
[24]
vs.
Polyvinylpyrrolidone
methacrylate]
5.06(20mg/kg)
35.0 ng/ml
(PVP)
Nano/microp
86.6(20 mg/kg)
-p
13000
PLGA,
1.23 mg/ml~1.76
poly(vinyl alcohol),
mg/ml
[28]
[30]
poly(L-lysine) Soy protein isolate (SPI) Mesoporous silica
and 2-fold
vs.
vs.
than free cur and
higher
0.0105±0.0016
2.6714±0.3832
MSM-A group.
μg/mL
μg/ml min
(50 mg/kg)
(100 mg/kg)
Tween 80
The solubility value of
440.68±31.39
1513.48±
SAS-processed
AcCFR3TN2
204.71
AcCFR3TN1,
(100 mg/kg)
AcCFR3TN2
AcCFR3TN2 and
vs.
(100 mg/kg)
AcCFR3 were
351.00 ± 25.69
vs.
71.2 ± 3.5, 483.2 ± 4.3
AcCFR3TN1
923.25 ±
and 4.3 ± 2.3 μg/mL in
(100 mg/kg)
131.85
vs.
AcCFR3TN1
and 473.6 ± 4.0, 687.9
186.68 ± 13.92
(100 mg/kg)
± 5.6 and 112.5 ±
AcCFR3
vs.
3.8μg/mL in SGF of
(100mg/kg)
378.74 ± 24.96
pH 1.2.
vs.
AcCFR3
51.33±5.03
(100mg/kg)
ng/mL
vs.
native cur
102.81 ± 10.22
(50 mg/kg)
ng/mL min
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distilled water
[34]
native cur
(50 mg/kg)
0.5 mg/ml
99.72±30.47
-p
AN–CS–Arg
s
(100mg/kg)
vs.
vs.
11.00±1.17
65.12±7.42
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Cyclodextrin
Water solubility at pH
lP
Cyclodextrin
295.47±82.44
(100 mg/kg)
[35]
mg/mL
mg/ mL h
(100 mg/kg)
(100 mg/kg)
/
/
[38]
/
/
[38]
0.701±0.308
79.48±12.37
[38]
(50 mg/kg)
(50mg/kg)
vs.
vs.
0.189±0.088
28.69±15.16
μg/mL
μg/ml min
(50 mg/kg)
(50 mg/kg)
5 was increased by a factor of 104
HP-βCD, M-βCD
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HP-β-CD
0.3830~0.6086 mg/mL
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Micelles
15.2 mg/mL
DiDDAB:DDAB
The aqueous solubility
0.24 ± 0.04
6.13 ± 0.22
DMDTAB:DDAB
of cur increases in the
(10 mg/kg)
(10 mg/kg)
vs.
vs.
0.08± 0.03μg/mL
0.11 ± 0.04
(10 mg/kg)
μg h/mL
DiCTAB:DDAB
order of
104 or
103
DODAB:DDAB
[42]
(10 mg/kg) Emulsion
OP:Cremorphor EL,
21 mg/g
/
/
/
/
[43]
PEG 400, ethyl oleate Polymorphs
/
The
solubility
was
[54]
enhanced by twice. /
The solubility of cur
86.3 ± 12.58
79.8 ± 15.30
polymorphs was 17-
(250 mg/kg)
(250mg/kg)
fold higher than native
vs.
vs.
43.7 ± 6.45ng/ml
43.7±6.45
(250 mg/kg)
ng.h/ml
cur.
[56]
(250 mg/kg) Triethylamine (TEA),
1-10mg/ml ,
/
/
[58]
4-dimethylamino-
1.6mg/ml
23.35 ± 0.96
223.52±5.25
[59]
pyridine (DMAP),
(50 mg/kg)
(50mg/kg)
N,N0-
vs.
vs.
dicyclohexylcarbodiim
6.85 ± 0.36ng/ml
23.98 ± 4.89
ide (DCC)
(50 mg/kg)
h ng/mL
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Conjugates
hydrophilic
(50 mg/kg)
poly(ethylene glycol)
-p
(PEG)
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Solid dispersions are (semi)crystalline or amorphous drug dispersions with drug dispersed in the inert matrix[20]. Solid dispersions can increase the dissolution rate and solubility of hydrophobic drugs [21,22]. Ai Mey Chuah et al. prepared a cur amorphous solid dispersion (ASD) consisting of hydroypropyl methyl cellulose (HPMC), isomalt and lecithin by the hot melt extrusion method which could enhance AUC0–∞ of cur by 13-fold and Cmax of cur by 7 fold compared with native cur. The Cmax of ASD cur(20 mg/rat) was 184 ± 14 ng/ml, while Cmax of native cur was 27 ± 8 ng/ml(20 mg/rat).Cur ASD had enhanced solubility over native cur (>1000 times). Besides, the anti-inflammatory activity of ASD cur was also improved compared to native cur[23]. Kazunori Kadota et al. prepared cur ASD composed of polyvinylpyrrolidone (PVP), αglucosyl stevia (Stevia-G) and cur by the freeze-drying method with a seven-fold increased relative bioavailability.The Cmax and AUC0-180 of cur ASD (20 mg/kg) were 86.6 ng/ml min and 5.06 μg/ml min, and 35.0 ng/ml and 3.78 μg/ml/min of native cur(100 mg/kg). The cur solubility in cur ASD was 13,000-fold higher than native cur equilibrium solubility[24]. Cur ASD had a 6.7 fold enhanced oral absorption compared to native cur. Besides, they also prepared a cur ternary ASD system composed of cur, polyvinylpyrrolidone (PVP) K-30 and α-glucosyl hesperidin (hesperidin-G) using the solvent evaporation method, and the solubility of cur in ASD was 2600-fold higher than native cur[25]. Anant Paradkar et al. prepared cur-PVP ASD using different ratios of PVP.[26]. The solid dispersion of cur had a complete dissolution characteristic within 30min, whereas the physical mixture of cur had negligible release characteristics after 90 min, suggesting a good oral bioavailability of the cur ASD. Satomin onoue et al. prepared a cur nanocrystal solid dispersion and an amorphous solid dispersion, which had significantly enhanced dissolution profiles and 9-fold improved oral bioavailability compared with native cur. The Cmax and AUC0–inf of cur(100 mg/kg) were 35±8.0
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ng/mL and 11.0±0.5 μg/ml min, and 147± 53ng/ml and 27.1±6.7μg/ml/min of native cur(20 mg/kg).[27] Hisham Al-Obaidi et al et al. prepared a cur ternary ASD composed of cur, PHPMA (poly[2-hydroxypropyl methacrylate]) and PVP (polyvinylpyrrolidone) using the spray drying method. By incorporating PHPMA to immiscible binary solid dispersions, the stability of the amorphous form of cur was improved[28]. Cur solubility was enhanced to 560 μg/m by forming a Solutol ® HS15 ASD. Cur ASD stability was studied in pH 1.2, 6.8 and 7.4 buffer media, and the cur solid dispersion formulations were stable over 3 months. Solutol ® HS15 had an enhanced stabilizing effect compared to Kollidon ® 30 and Cremophor ® RH40. In vitro release profiles suggested that 90% of the drug was improved within 1 h. Dissolution and pharmacokinetic characteristics were improved compared with pure cur.[29]. The cur solid dispersion composed of 10:1 Solutol ® HS15 and cur had a 5fold increased AUC 0–12h. The Cmax and AUC0–12 h were 15.65 ± 12.6 ng/mL and 15.31 ± 19.7 ng/mL h of native cur, 95.60 ± 53.8ng/mL and 72.84 ± 36.4 ng/mL h of ASD cur, respetively(50 mg/kg). Different polymers concluding PLGA, chitosan, mesoporous silica, protein and polymeric nanoparticles have been developed in order to prepare cur nanoparticles with enhanced solubility.
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PLGA (poly(D,L-lactic-co-glycolic) can delivery cur orally with enhanced solubility and bioavailability. Xiaoxia Xie et al. prepared cur PLGA nanoparticles using the solidin-oil-in-water (s/o/w) solvent evaporation method, and the final particle diameters were 200 nm. [30]. The entrapment efficiency and drug loading were 91.96% and 5.75%, respectively. The water solubility was 640-fold enhanced compared with unformulated cur. 77% of cur was released from cur nanoparticles while 48% of cur was released in artificial gastric juice. The relative oral bioavailability was 5.6-fold enhanced compared with unformulated native cur. The Cmax and AUC0–t was 1.55± 0.21μg/mL and 367±21μg/ mL min of native cur(100 mg/kg), 6.75±1.54 μg/mL and 2066 ± 332 μg/ mL min of cur PLGA nanoparticles, respectively(100 mg/kg).The improved cur PLGA nanoparticles oral bioavailability may be attributed to improved water solubility, fast release characteristics in the intestinal juice, enhanced permeability and residence time in the intestinal tract and P-glycoprotein (P-gp)mediated efflux effect. Murali Mohan Yallapu et al. prepared cur PLGA nanoparticles with poly(L-lysine) and poly(vinyl alcohol) as stabilizers using a nano-precipitation method[31]. The nanoparticles had sustained release characteristics and improved solubility in aqueous solution. By increasing the concentration of PVA from 0% to 1%, cur solubility in PBS was increased from 1.23 mg/ml to 1.76 mg/ml. The cur nanoparticles cellular uptake was 6-fold higher in metastatic MDA-MB-231 breast cancer cells and 2-fold enhanced in cisplatin resistant A2780CP ovarian cells, with enhanced cell apoptosis observed with cur nanoparticles. Arun Tapal et al. prepared a curcumin-soy protein isolate (SPI) complex with enhanced solubility of cur[32]. The solubility of cur in SPI-curcumin complex was 8.9 μ g/ml, while free cur was 11 ng/ml in water, which was an 812-fold enhancement compared with free cur. Fluorescence spectroscopy showed that the complex was formed through
hydrophobic interactions. The SPI–cur complex had improved antioxidant activity.
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Mesoporous silica has promising potential in oral drug delivery due to the solubility increasing effect of drugs. Sandy Budi Hartono et al. prepared cur-amine functionalized mesoporous silica nanoparticles (MSN)[33]. Cur loaded amine functionalized MSN (MSN-A-Cur) released better and had improved solubility characteristics compared with amine MSM (MSM-A-Cur). They found that the solubility of cur in MSN-A was 10-fold and 2-fold higher than free cur and MSM-A, which may be due to the reduced particle size of cur loaded MSM-A and MSN-A compared with free cur. The oral bioavailability of MSM-A-Cur and MSN-A-Cur was enhanced compared with free cur. The Cmax and AUC0–6 h was 0.0105 ± 0.0016 μg/mL and 2.6714 ± 0.3832 μg/ mL min of native cur(50 mg/kg), 0.0291 ± 0.0078 μg/mL and 9.5931 ± 1.3731μg/ mL min of MSM-A-Cur, respectively(50 mg/kg).
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In the study of Mohammed Anwar et al., cur nanoparticles were prepared with Tween 80 as a permeation enhancer and solubilizing agent by the supercritical anti-solvent (SAS) process[34]. Solubility and dissolution characteristics were enhanced compared with native cur. The solubility value of SAS-processed AcCFR3TN1, AcCFR3TN2 and AcCFR3 were 371.2 ± 3.5, 483.2 ± 4.3 and 94.3 ± 2.3 μg/mL in distilled water and 473.6 ± 4.0, 687.9 ± 5.6 and 112.5 ± 3.8μg/mL in SGF at pH 1.2, while cur was nearly insoluble in water and SGF. The increased solubility was likely due to the reduced particle size and hydrophilic coating of Tween 80, and the oral bioavailability of the cur nanoparticles was 11.6-fold enhanced compared with free cur. The Cmax and AUC0–t was 51.33 ± 5.03 ng/mL and 102.81 ± 10.22 ng/ mL min of native cur(50 mg/kg), 186.68 ± 13.92 ng/mL and 378.74 ± 24.96 ng/ mL min of AcCFR3(100 mg/kg), 351.00 ± 25.69 ng/mL and 923.25 ± 131.85 ng/ mL min of AcCFR3TN1(100 mg/kg), 440.68 ± 31.39 ng/mL and 1513.48 ± 204.71 ng/ mL min of AcCFR3TN2(100 mg/kg) , respectively.
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The oral bioavailability of cur chitosan nanoparticles was enhanced through enhancing cur solubility. Mazhar Ali Raja et al. prepared cur loaded AN–CS–Arg NPs (AN–CS– Arg/Cur NPs) (Acrylonitrile (AN), hydrophilic arginine (Arg), amphiphilic chitosan (CS)) with a particle size of 218 nm by a simple sonication method[35]. Cur aqueous solubility was improved compared with native cur, with the solubility of cur in AN– CS–Arg NPs 0.5 mg/ml compared to 11 ng/ml of native cur, nearly a 5×10 4 –fold increase. AN–CS–Arg NPs had sustained release characteristics, enhanced mucoadhesion effect, stronger cell uptake and improved cytotoxicity effect against HT29 cells. Furthermore, the oral bioavailability was also improved compared with native cur. The Cmax and AUC0–24 h was 99.72±30.47 mg/mL and 295.47±82.44 mg/ mL h of AN–CS–Arg/Cur NPs(100 mg/kg),11.00±1.17 mg/mL and 65.12±7.42 mg/ mL h of Cur solution, respectively(100 mg/kg). Cur was encapsulated in alginatechitosan-pluronic composite nanoparticles using ionotropic pre-gelation followed by
the polycationic cross-linking method[36]. Pluronic F127 was formulated in the nanoparticles to enhance the cur solubility. The particle size of the spherical nanoparticles was 100 nm, and cytotoxicity assays showed that 500 μg/mL of nanoparticles were nontoxic to HeLa cells. The IC50 of free cur and cur nanoparticles was 13.28 and 14.34 μM.
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Cyclodextrins are cyclic oligosaccharides with a hydrophilic surface and lipophilic cavity, and are used as stabilizing and solubilizing agents in pharmaceutical preparations to improve the solubility of hydrophobic drugs such as cur. Commonly used CDs are βCD, γCD, hydroxypropyl-β-cyclodextrin (HPβCD), methylβ-CD (MβCD) and more. Vivek R. Yadav et al. prepared a novel cyclodextrin complex of curcumin (CDC) by incorporating cur into γCD, HPβCD, MβCD and βCD in order to enhance cur solubility[37]. The ability of cur solubility enhancement was in the order of: HPβCD>MβCD>βCD>γCD. It was apparent that the bulky side group of the cur phenyl moiety could fit well within the HPβCD cavity, which is indicated in Fig 4. Compared with free cur, CDC demonstrated enhanced cellular uptake ability, longer half-life in cancer cell lines, an antiproliferative effect and anti-inflammatory effect. Hanne Hjorth Tønnesen et al. prepared cur cyclodextrin complexes, where the water solubility was enhanced to 104 at pH 5[38]. Besides, in alkaline conditions cur stability was enhanced and photodecomposition rate was also improved. In the study of Martin Purpura et al., they saw that their γ-cyclodextrin cur formulation had a significantly increased bioavailability in healthy humans compared with unformulated cur[39]. The Cmax and AUC0–12 h was 0.3 ng/mL and 19.7 ± 2.6 ng/ mL h of native cur, 1.2 ng/mL and 327.7 ± 58.1 ng/ mL h of Cur solution , respectively. Cur (CUR)-hydroxypropyl-β-cyclodextrin (HP-β-CD) inclusion complex (CUR-HP-β-CD) were prepared by Ning Li et al., with a mole ratio of cur to HP-β-CD of 1:7. The solubility of cur was enhanced, the cytotoxicity of cur was improved and the oral bioavailability of cur in CUR-HP-β-CD was 2.77-fold higher than native cur. The Cmax and AUC0–t of native cur(50 mg/kg) was 0.189±0.088 μg/mL and 28.69±15.16 μg min/mL, while 0.701±0.308 μg/mL and 79.48±12.37 μg min/mL of CUR/HP-β-CD inclusion(50 mg/kg)[40].
O
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H OCH3 OH
HO
Fig 4. The proposed structure of curcumin cyclodextrin complex. Self-assembled polymeric micelles (PMs) are a promising oral drug delivery system due to the advantages of improving drug solubility in water. It has been reported that
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cur can be solubilized in a micellar solution up to 40 times [41]. Thus, micelles are excellent drug delivery systems for the delivery of cur. Sharvil Patil et al. prepared cur micelles (CUR-MM) using Gelucire ® 44/14 (GL44) and Pluronic F-127 (PF-127) as surfactants by a solvent evaporation method. The particle size of CUR-MM was 188 ± 3 nm and EE of CUR-MM was 76.45 ± 1.18% w/w. Due to the solubilization effect of cur in the micelles and the PF-127 and GL-44 P-gp inhibition effect, the cytotoxic activity of CUR-MM was 3-fold enhanced and oral bioavailability was 55-fold increased compared with native cur.[42]. The solubility of cur was improved by incorporating cur in mixed surfactant vesicles composed of single and double chain ionic surfactants. The cur aqueous solubility was increased to 104 or 103 fold with increasing surfactant concentration. Mixed surfactant vesicles could decrease cur degradation in alkaline media. Both the solubility, stability and antioxidant activity of cur were improved by incorporating cur in mixed surfactant vesicles.The Cmax and AUC0–t of native cur(10 mg/kg) was 0.08 ± 0.03 μg/mL and 0.11 ± 0.04 μg h/mL, while 0.24 ± 0.04 μg/mL and 6.13 ± 0.22 μg h/mL of CUR-MM(10 mg/kg).
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Nanoemulsions are thermodynamically stable and transparent systems of oil and water, stabilized by a surfactant or mixture of surfactant and cosurfactant. It has been reported that cur nanoemulsions can enhance the bioavailability and oral absorption of cur.
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Over recent years, many emulsion curcumin formulations which can enhance cur bioavailability by increasing the solubility of cur have been developed and select studies are highlighted. In order to enhance cur oral absorption and solubility, a cur loaded self-microemulsifying drug delivery system (SMEDDS) was prepared by Jing Cui et al using ethyl oleate as the oil phase, OP and Cremorphor EL as surfactants and PEG-400 as co-surfactant. Cur solubility in SMEDDS was increased to 21 mg/g, and more than 95% of cur in the nanoemulsion was dissolved in 20min compared with 2% for unformulated cur within 60min. The cur absorption mechanism in the intestine was via passive transfer, and oral absorption was improved compared with its suspension[43]. Jinglei Li et al. prepared a chitosan coating cur nanoemulsion composed of lecithin, Tween 80 and MCT oil by the ultrasonication method, and the loading efficiency and ability was 95.10 % and 0.548 mg/ml, respectively[44]. The water dispersity of the cur nanoemulsion was increased by 1400 fold. High, middle and low molecular weight chitosan (190-310, 30, 3 kDa) was applied for coating nanoemulsions, and it was found that cur had different solubility varying from 13.97 to 22.14 mg/g, when the ratio of surfactant, co-surfactant and oil was changed. Cur was absorbed in the intestine through passive transfer, and the cur nanoemulsion oral absorption was improved compared with cur suspension. The solubility of cur in the oil phase of an emulsion is important for their preparation to improve the drug loading (Table 1). Dong-Jin Jang et al. prepared a cur dry emulsion for oral delivery of cur[45]. Cur has higher solubility in Plurol ® Oleique CC497 compared with other oils, and thus Plurol ® Oleique CC497 was chosen as the oil phase.
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The release of cur from the cur dry emulsion was enhanced compared with native cur, and the Cmax and AUC were 12.0 and 7.1 fold higher than native cur.The Cmax and AUC0–24h of native cur was 8.5 ± 2.4 μg/mL and 24.2 ± 7.6 ng h/mL, while 102.4 ± 32.7 μg/mL and 171.0 ± 45.1 ng h/mL of cur dry emulsion(50 mg/kg).Yi-Dong Yan et al. prepared cur liquid self-emulsifying drug delivery system (SEDDS) using Lauroglycol Fcc as the oil phase, Labrasol as the surfactant and Transcutol HP as the co-surfactant, the ratio of which was 15.0:70.8:14.2 [46]. Lauroglycol Fcc was chosen as the oil phase because of the high solubility of cur compared with other oil phases. The cur oral absorption was found to be higher than native cur. The Cmax and AUC of cur SEDDS was 33.97±9.84 ng/mL and 37.05±17.73 ng h/mL at the dose of 25 mg/kg, while155.56±18.34 ng/mL and 282.54±61.37 ng h/mL at the dose of 100 mg/kg. Chaonan Wang et al. prepared a cur loaded emulsion[47]. The oil phase was MCT containing 10% ethanol, which could further improve the cur solubility in the oil phase. The cur emulsion oral bioavailability was 4.8-fold higher compared with cur suspension. CUR@BD-1 emulsion had the Cmax and AUC0 – 24h of 270 ng/mL and 1511 ng h/mL(60 mg/kg), while the Cmax and AUC0–24h of CUR/Tween 20 suspension was 37 ng/mL and 317 ng h/mL (60 mg/kg).MEDDS also improves cur dissolution and bioavailability, therefore Xuemei Wu et al. prepared cur loaded self-microemulsifying drug delivery system (SMEDDS) composed of 20% isopropyl myristate, 20% ethanol and 60% Cremophor RH40 ®, and the cur concentration in SMEDDS was 50 mg/ml[48]. Cur had enhanced solubility with 1,2-propylene glycol, which was thus chosen as cosurfactant. The cur solubility in cremophor RH40 ® was 150 mg/g, showing a good solubilizing effect of cur. Cur released from SMEDDS completely within 10 minutes, and the relative oral bioavailability of cur SMEDDS was 1213% compared with cur suspension. The Cmax and AUC0–∞ of cur microemulsion were 196.56μg/L and 277.06 μg/L·h while that of cur suspension were 63.89μg/L and 21.76 μg/L·h. Kashif Ahmed et al. prepared a cur nanoemulsion using short, medium, and long chain triacylglycerols (SCT, MCT and LCT) as lipids[49]. The maximum solubilized amount of cur in SCT, MCT and LCT was 0.30 ± 0.10 wt.%, 0.79 ± 0.2 wt.%, 2.98 ± 0.18 wt.%, respectively. However, cur emulsion cannot be formed using pure SCT due to the Ostwald ripening effect, as SCT has a high solubility in water. Cur bioaccessibility decreased in the different medium in the order of: MCT > LCT >> SCT. The bioavailability was 41±4% of cur LCT nanoemulsion, 58 ± 6% of cur MCT nanoemulsion, 1 ± 1% of cur SCT nanoemulsion, 20 ± 3% of cur LCT:SCT nanoemulsion.Yanyu Xiao et al. prepared a curcuminoid-loaded microemulsion (CurME) with enhanced cur bioavailability[50]. Cremophor RH 40, labrafac lipophile WL 1349, and glycerine were used as the oil phase, cremorphor RH40 as surfactant and glycerine as cosurfactant, both of which had a better solubility than other vehicles. CurME had a 9.6-fold enhanced relative bioavailability compared with cur suspension. Cmax and AUC0-t of cur suspension were 5.39 ± 0.13 ng/mL and 18.66 ± 1.54 ng h /mL, while that of cur-ME were 66.19 ± 4.43 ng/mL and 180.97 ± 2.71 ng h /mL. Saujanya Gosangari et al. prepared a cur self-emulsifying formulation with different formulations using different polymers as precipitation inhibitors. It was found that by incorporating 10% polymer such as
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polyvinylpyrrolidone (PVP) or hydroxypropyl methyl cellulose (HPMC) into curcumin emulsions, the cur concentration was 100-fold higher than that of the formulation without added polymer. They found that the inhibition precipitation effect of polymers was in the order of PVP-K30 < PVP-K90 < HPMC[51]. Patcharawalai Jaisamut et al. prepared a cur loaded self-microemulsifying formulation by using Capryol 90 as the oil phase, Cremophor EL as surfactant, and Labrasol as co-surfactant[52]. Cur had higher solubility in the selected vehicles (Capryol 90: 6.71 mg/ml, Cremophor EL: 85.98 mg/ml, Labrasol: 62.99 mg/ml) than other solvents. The antioxidant activity, cytotoxic effect and oral bioavailability were enhanced compared with native cur. Saipin Setthacheewakul et al. formulated cur into liquid self-microemulsifying drug delivery systems (SMEDDS) and SMEDDS pellets[53]. In cur loaded SMEDDS, Cremophor EL (113.94 mg/ml) and Labrasol (88.26 mg/ml) (1:1) were used as surfactants, Labrafac PG (20.24 mg/ml) and Capryol 90 (42.34 mg/ml) (1:1) were used as the oil phase and PEG400 (153.07 mg/ml) was used as co-surfactant (the solubility of cur in vehicles is listed in parenthesis). The release rate of cur emulsion was 16-fold enhanced compared with native cur, and the oral absorption of liquid cur-SMEDDS and pellet cur-SMEDDS were 14- and 10-fold enhanced compared with cur suspension. The Cmax and AUC0– ∞ of cur--SMEDDS(50 mg/kg) were 4.38 ± 0.09 μg/mL and 537.90 ± 13.82 ng h/ml, that of Cur-SMEDDS pellets(50 mg/kg) were 4.17 ± 0.32 μg/mL and 408.13 ± 14.18 ng h/ml, while the Cmax and AUC0–∞ of cur suspension(50 mg/kg) were 0.25 ± 0.04 μg/L and 38.61 ± 10.61 ng h/ml. Palash Sanphui et al. reported two new cur crystalline polymorphs (Form 2 and Form 3, the original structure of which is Form I) and an amorphous cur [54]. The solubility of the polymorphs was twice enhanced. The intrinsic dissolution rates in 40% EtOH–water of Form 2 was nearly 4 times higher than Form I, and the amorphous was nearly twice higher than Form I. This suggests that new forms of cur crystalline polymorphs are suitable for oral administration in order to enhance cur bioavailability and solubility. In another study, cur co-crystals were synthesized with 5 coformers (nicotinamide, p-hydroxybenzoic acid, ferulic acid, hydroquinone, and L-tartaric acid)[55]. Both of the 5 cur co-crystals had lower melting points and dissolved faster than free cur, with curcumin-nicotinamide showing the fastest dissolution rate. Yogesh B. Pawar et al. investigated the phase behavior and oral bioavailability of the amorphous form of Cur (CRM-A)[56]. CRMA aqueous solubility was 17-fold higher than normal cur. AUC and Cmax were enhanced by 1.45-fold and 1.97-fold respectively, however the rapid devitrification may limit CRM-A oral bioavailability. The Cmax and AUC0–∞ of native cur (250 mg/kg) were 43.7 ± 6.45 ng/ml and 55.0 ± 10.41 ng.h/ml, that of CRM-A were 86.3 ± 12.58 ng/ml and 79.8 ± 15.30 ng.h/ml after oral administration. Cur can conjugate with small molecules such as amino acids and other hydrophilic polymers which can enhance cur aqueous solubility. Select amino acids including alanine, phenylalanine, proline, glycine, phenyl glycine and cysteine were coupled to cur[57]. K.S Parvathy et al. prepared cur-amino acid conjugates through conjugation of cur at the phenolic position with amino acids in dry dioxane using triethylamine (TEA) and (4dimethylamino-pyridine (DMAP) as catalysts, N,N 0 -dicyclohexylcarbodiimide (DCC) as the coupling agent, and finally purified by column chromatography[58]. Cur aqueous
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solubility was enhanced to 1-10 mg/ml. They found that the conjugates of cur with proline and glycine had the highest water solubility (10 mg/ml). In antioxidant assays experiments, cur derivatives conjugated with alkyl-substituted amino acid concluding alanine, valine, cysteine exhibited lower IC50 values compared with native cur. Hongzhi Qiao et al. prepared an amphiphilic curcumin polymer (PCur) composed of hydrophobic cur (Cur) and hydrophilic poly(ethylene glycol) (PEG) linked by a disulfide bond [59]. The water solubility of cur was improved to 1.6 mg/ml for the curPEG conjugate. The particle size of the cur-PEG conjugate was 134.4 nm and the zeta potential was -3.3 mv, both of which led to the accumulation of drug in the gut inflamed regions. Cur-PEG conjugates had a limited drug release profile under the gastrointestinal tract conditions (GIT), while a significant release characteristics were observed in the region of colon with reduced bacterials. Besides, cur-PEG conjugates also had increased transmembrane permeability and low cytotoxicity resulting in improved oral bioavailability. The Cmax and AUC0–∞ of PCur (50 mg/kg) were 23.35 ± 0.96 ng/mL and 223.52 ± 5.25 h ng/mL, and that of Cur suspension(50 mg/kg) was 6.85 ± 0.36 ng/mL and 23.98 ± 4.89 h ng/mL.Thus, cur-PEG conjugates are an excellent oral colon delivery system which have improved bioavailability.
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3.2 Increase the stability of curcumin preparations in gastrointestinal tract Various pharmaceutical strategies have been developed in order to enhance cur oral bioavailability by improving the gastrointestinal stability of cur (Table 3). By coupling to various of gastro-resistant polymers, cur can be protected from the harsh gastrointestinal environment against destruction, giving a higher solubility and controlled-release characteristics.
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Among these formulations, polymeric micelles prepared by Jiang Ni et al.had a higher bioavailability than other formulations with a higher Cmax(5.365 ± 1.246 μg/mL ) and AUC(77.261 ± 12.485 μg.h/mL) than other formulations at a dose of 15 mg/kg[61]. Carboxy methyl chitosan was used as a P-gp mediated efflux and gastrointestinal absorption enhancer, and heparin-all-trans-retinoid acid (LHR) as the loading material by a chemical bonding method, which could improve the stability of cur polymeric micelles in physiological pH and the oral bioavailability of cur.
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Silica is a gastro-resistant polymer which can improve the stability of liposomes in the harsh gastrointestinal track environment. It has been reported that the silica shell has enhanced stability at pH 1.2, which can protect the nanoformulation inner structure. The silica shell is hydrolysed at pH 7.4, thus controlling the release of cur. Chong Li et al. prepared cur silica-coated liposomes (CUR-SLs), which exhibited hjgher GIT stability compared with cur liposome. As well, the CUR-SLs oral bioavailability was 3.31 fold higher than cur liposome, the C max CUR-FL were higher than that of cur suspension(446.66 vs 71.35 ng .L−1 ) at a single dose of 50 mg/kg, suggesting that CURSLs was an excellent oral delivery system[60]. Chitosan, a natural polysaccharide, is widely applied for oral delivery of drugs, and can
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prolong the absorption of cur due to its mucoadhesive properties. Jiang Ni et al. developed mixed polymeric micelles made from carboxy methyl chitosan as a P-gp mediated efflux and gastrointestinal absorption enhancer, and heparin-all-trans-retinoid acid (LHR) as the loading material by a chemical bonding method, which could improve the stability of cur polymeric micelles in physiological pH and the oral bioavailability of cur. It has been reported that the Cmax and AUC0-48h of CsACNC/LHRMPMs-3 were 5.365 ± 1.246 μg/mL and 77.261 ± 12.485 μg.h/mL, while that of CsA suspension was 0.610 ± 0.109 μg/L and 5.107 ± 1.629 μg.h/mL after a single oral dose of 15 mg/kg.[61]. The chitosan coating prevented phase separation of the cur nanoemulsion and inhibited cur degradation. When cur nanoemulsion was treated with thermal treatment and UV irradiation, the degradation of cur could be inhibited when nanoparticles were coated with middle and high molecular weight chitosan. Jinglei Li et al. prepared a cur nanoemulsion which was composed of lecithin, Tween 80 and MCT oil[62]. The cur nanoemulsion was coated with low (3kDa), middle (30kDa) and high molecular weight (190-310kDa) chitosan, which could prevent the phase separation of cur nanoemulsion and inhibit cur degradation, thus improving the gastrointestinal stability of cur. Chitosan with middle and high molecular weight could promote the hydrolysis of cur nanoemulsion, which enhanced cur gastrointestinal tract stability, thus improving the oral bioavailability of cur. Warayuth Sajomsang et al. prepared cur micelles composed of pH responsive amphiphilic chitosan N-benzyl-N,O-succinyl chitosan (BSCS)[63]. They found that the release profile of cur in the stomach (pH 1.2) was slow, and the micelles were slowly release in the intestine (pH 5.5–7.4) without any burst effect, highlighting the stability of cur micelles. In the pH of the stomach (1.2), during the first 10 hours no more than 25% cur was released from cur micelles, while at pH 5.5, 6.8 and 7.4, 38%, 50% and 50% of cur were released from micelles within 10 h respectively. The pH-dependent release profile can be explained by the degree of succinic acid ionization on the BSCS micelles surface at different pH values. The pKa1 value of succinic acid is 4.21, thus when the pH in the medium is higher than the pKa1 value, the micelles are dissociated, and thus, cur micelles release faster at pH 5.5, 6.8 and 7.4 than at pH 1.2. Cytotoxicity, cellular uptake and apoptosis were also improved compared with unformulated cur, where cytotoxicity assays indicated that IC50 of cur micelles was 3.6-, 4.7-, 12.2- fold lower than that of free cur in SiHa, HeLa and C33a cells. Cur micelles cell uptake was 6-fold enhanced compared with unformulated cur in all cancer cells. Various polymers have been applied as gastroresistant polymers which have a mucoadhesion inhibition effect, resulting in a high stability of cur in the gastrointestinal tract. Among these polymers, Eudragit is a gastro-resistant polymer, which can protect cur from degradation in the gastrointestinal tract. Ana Catalan-Latorre et al. prepared freeze-dried eudragit-hyaluronan multicompartment liposomes using phospholipid, Eudragit-S100 and hyaluronan sodium salt. By incorporating different ratios of the gastroresistant polymer eudragit-hyaluronan in the liposome, cur was protected against GIT conditions with enhanced absorption in the intestinal region[64]. Elisabet Martí Coma-Cros et al. prepared cur loaded liposomes using the anionic copolymer Eudragit
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® S100 containing also either Nutriose ® FM06 (Eudragit-nutriosomes) or hyaluronan (Eudragit-hyaluronan liposomes)[65]. Under the condition of gastrointestinal fluids, Eudragit-nutriosomes were found to be more stable than Eudragit-hyaluronan liposomes. Sharvil Patil et al. prepared cur micelles (CUR-MM) using Pluronic F-127 (PF-127) and Gelucire ® 44/14 (GL44) as surfactants by a solvent evaporation method. The CUR-MM particle size was 188 ± 3 nm and CUR-MM EE was 76.45 ± 1.18% w/w. The cytotoxic activity of CUR-MM was 3-fold higher than native cur, and the oral bioavailability was 55-fold higher than unformulated cur, the Cmax(0.24 ± 0.04 vs 0.08 ± 0.03μg/ml) and AUC0-t (6.13 ± 0.22 vs 0.11 ± 0.04 h/μg/ml)of CUR-MM were much higher than that of native cur, after an oral administration dose of 10 mg/kg, likely due to solubilization of cur in micelles and the P-gp inhibit effect of PF127 and GL44[66]. Yuwei Duan et al. prepared cur-loaded methoxy poly(ethylene glycol)-poly(lactide) (mPEG-PLA)/Dα-tocopherol polyethylene glycol 1000 succinate (TPGS) mixed micelles (CUR-MPPTPGS-MMs) through the thin film diffusion method. The drug loading achieved was 16.1%, the particle size was 46.0 nm, and due to the low critical micelle concentration (CMC) and dilution stability, CUR-MPP-TPGS-MMs had enhanced stability in the gastrointestinal fluid conditions. The duodenum showed good absorption ability for CUR-MPP-TPGS-MMs. The Cmax of CUR-MPP-TPGS-MMs(75 mg/kg) was 197.88 ± 61.71ng/ml, while that of Cur suspension(75 mg/kg) was 27 ± 1.37 ng/ml. The AUC0–24 of CUR-MPP-TPGS-MMs was 9-fold higher than that of cur suspension.(1.02± 0.93 vs 0.11 ± 0.029 μg/ml h) with a relative bioavailability of 927.3%, suggesting that the oral bioavailability was also improved compared with unformulated cur[67]. Hamidreza Kheiri Manjili et al. prepared CUR-loaded mPEG-PCL (CUR/mPEG-PCL) micelles with a zeta potential of -11.5 mV, average size of 81.0nm and loading capacity of 20.65 ± 0.015% using a single-step nano-precipitation method. Pharmacokinetic profiles showed that CUR-loaded micelles had an excellent oral bioavailability.The Cmax of CUR-loaded micelles was much higher than that of CUR aqueous solution(29.97 ± 0.012 vs 3.99 ± 0.01 ng/mL), while the AUC0–t of CUR-loaded micelles and CUR aqueous solution were 452.695 ± 0.75 h ng/mL and 8.561 ± 0.872 h ng/mL after oral administration at a dose of 50 mg/kg[68]. Mixed surfactant vesicles were prepared, composing of single chain ionic surfactants and equimolar ionic surfactants, which could improve the solubility of the incorporated cur. The mixed surfactant vesicles could also reduce the degradation of cur in alkaline media. Both the stability, solubility and antioxidant activity of cur were improved by incorporating cur in mixed surfactant vesicles[69]. Cur pickering emulsion digestion and storage stability were investigated by Ali Marefati et al. [70]. During 24 h storage, heat treated curcumin Pickering emulsions had greater encapsulation stability than non-heat treated cur Pickering emulsions (78.2% vs. 38.3%), and in simulated in vitro digestion, intestinal (86.3%vs. 40.2%) and oral (95.3% vs. 69.6%), however there was no significant difference in simulated gastric in vitro digestion (82.4% vs 86.2%). The cur emulsion stability under in vitro simulated intestinal environment with or without bile salts was investigated, and while the changes were larger in samples with bile salts, the changes
were also slighter in heat-treated samples. The results showed that cur Pickering emulsions have great potential in cur drug delivery. Table 3.Pharmaceutical strategies for improving the oral bioavailability of curcumin by increasing the gastrointestinal stability. Cmax AUC Gastrore- Preparation Observation Refer (Preparation vs. (Preparation vs. sistant -ence control) control) polymers Silica
Liposome
446.66
673.79
CUR-SLs had significantly
vs
vs
higher gastrointestinal track
71.35 ng/.L
203.64
stability compared with cur
(50 mg/kg)
ng ⋅ h/ L
liposome.
[60]
Polymeric
5.365 ± 1.246
77.261±12.485
LHR can improve the stability of
micelles
vs.
vs.
cur micelles.
0.61± 0.109
5.107 ± 1.629
μg/mL (15 mg/kg)
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Nanoparticle
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Eudragit
Liposome
Chitosan coating can improve the gastrointestinal stability of cur.
[62]
Cur loaded micelles had
[63]
stability.
0.73 ± 0.31
4.98 ± 2.28
Cur SLNs have enhanced
vs.
vs.
stability, controlled release
0.29 ± 0.11
0.56 ± 0.14
characteristics in SIF, and
μg/L
μg.h/L
higher oral bioavailability.
(50 mg/kg)
(50 mg/kg)
/
/
Cur nanoparticle did not degrade
[77]
[74]
more rapidly than free cur in mouse plasma.
/
/
Cur is protected against harsh conditions of the gastro-intestinal
[64]
tract.
Liposome
/
/
Eudragit-nutriosomes had enhanced stability compared with Eudragit-hyaluronan liposomes under gastrointestinal fluids.
Pluronic F-
[61]
improved gastrointestinal track
na
(SLNs)
/
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micelles
/
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/
Polymeric
nanoparticles
(15 mg/kg)
/
Nanoemulsion
Solid lipid
μg.h/mL
re
Chitosan
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(50 mg/kg)
Micelles
0.24 ± 0.04
6.13 ± 0.22
The cytotoxic activity (3-folds)
[65]
127 (PF-
vs
vs
and oral bioavailability (around
127),
0.08±0.03
0.11 ± 0.04
55-folds) were also improved.
Gelucire ®
μg/ml
h/μg/ml
44/14 (GL44)
(10 mg/kg)
(10 mg/kg)
197.88± 61.71
1.02± 0.93
Cur solubility, stability and
vs.
vs.
antioxidant activity was
27 ± 1.37
0.11 ± 0.029
enhanced.
ng/ml.
μg/ml h
Micelles
(75 mg/kg) Solutol®HS1
Solid dispersion
5
[67]
(75 mg/kg)
95.60 ± 53.8
72.84±36.4
Oral bioavailability was
vs.
(50mg/kg)
enhanced compared with native
15.65 ± 12.6
vs.
cur;1.3% of cur was degraded pH
ng/ml
15.31±19.7
1.2 buffer,
(50 mg/kg)
ng/ml.h
while 2.4% of cur was degraded
(50 mg/kg)
in pH 6.8 buffer, 4.2% of cur was
[28]
ro of
mPEG-PCL
[66]
degraded in pH 7.4 buffer. 29.97 ± 0.012
452.695 ± 0.75
The oral bioavailability of cur
soy soluble
vs
vs.
emulsion was 11-fold higher than
polysacchari
3.99 ± 0.01
8.561 ± 0.872
cur suspension.
de
ng/mL
h ng/mL
(50 mg/kg)
(50 mg/kg)
Hydroxyprop
/
Emulsion
ylmethyl(HP MC) Liposome
Caseinate
Solid lipid
(NaCas),
nanoparticles (SLNs)
Eudragit-nutriosomes had
/
The physico-chemical stability of
[176]
[177]
cur SLNs was enhanced.
Nanosuspensions and
nanoparticles
vs.
vs.
CUR/TPGS nanosuspensions
(SLNs)
2.12 ± 0.34
14.29 ± 1.58
were 3.7 and 3.18-fold higher
μg/mL
μg.h/mL
than cur suspension.
(50 mg/kg)
(50 mg/kg)
/
[70]
enhanced stability
136.27 ± 10.85
Nanoparticle
[68]
enhanced.
7.51 ± 0.44
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bovine serum
The oral bioavailability was
Solid lipid
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TPGS /Brij78
/
/
na
Pectin
/
/
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Bile salts
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Emulsion
re
Casein,
/
albumin
The oral bioavailability of cur
[72]
[57]
was enhanced.
(BSA) Zein
Nanoparticle
/
/
In vitro gastrointestinal stability of cur nanoparticles was enhanced;
[179]
3.3 Change the absorption route of curcumin preparations Cur preparations can change the absorption route of cur, thus improving the oral bioavailability. Polymers with absorption-promoting effects have been applied in order to increase the oral bioavailability of cur, and these absorption mechanisms are summarized in Table 4. Among these formulations, cur micelles prepared by Jiang Ni et al. had a reletively higher bioavailability with a higher Cmax(5.365 ± 1.246 μg/mL)and AUC0-48h（77.261 ± 12.485) than other formulations[71]. Cur micelles were composed of a cur-carboxymethyl chitosan (CNC) conjugate and a lowmolecular-weight heparin-all-transretinoid acid (LHR) conjugate. CNC had the P-gp efflux inhibit effect, and can enhance the oral bioavailability of cur micelles.
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3.3.1 P-gp inhibit effect Several pharmaceutical strategies which have a P-gp inhibition effect have been developed in order to enhance cur oral bioavailability. Chitosan and its derivatives display a P-gp inhibitory effect, which may be applied for the delivery of cur. Jiang Ni et al. prepared cur micelles composed of a cur-carboxymethyl chitosan (CNC) conjugate and a low-molecular-weight heparin-all-transretinoid acid (LHR) conjugate[71]. CNC could inhibit the P-gp efflux effect and enhance the gastrointestinal absorption, and the oral absorption of cur MPMs was also enhanced by inhibiting the P-gp efflux effect (Fig 5). The oral bioavailability of CsA-CNC/LHRMPMs-3 was enhanced with a higher Cmax(5.365 ± 1.246 vs. 0.610 ± 0.109μg/mL) and AUC048h（77.261 ± 12.485 vs.5.107 ± 1.629μg.h/mL）than that of CsA suspension after oral administration at a single dose of 15 mg/kg. Cur solid lipid nanoparticles (CurSLNs) were prepared by Hongyu Ji et al. TPGS and Brij78 were used as P-gp inhibition excipients, which could both enhance the solubility of cur and the intestinal absorption.[72]. Surfactants can disrupt tight junctions in intestinal cells. The Cur-SLNs displayed a sustained release profile and 942.53 % relative bioavailability compared with cur suspension. It has been reported that the Cmax and AUC0–∞ of Cur-SLNs were 7.51 ± 0.44 μg/mL and 136.27 ± 10.85μg.h/mL, while that of Cur suspension was 2.12 ± 0.34 μg/mL and 14.29 ± 1.58 μg.h/mL after a single oral dose of 50 mg/kg. Sharvil Patil et al. prepared cur loaded mixed micelles (CUR-MM) using Pluronic F-127 (PF-127) and Gelucire ® 44/14 (GL44) as excipients through a solvent evaporation method. The particle size of CUR-MM was 188 ± 3 nm and EE was 76.45 ± 1.18% w/w. The cytotoxic activity of CUR-MM was 3-folds higher than native cur, while oral bioavailability was 55-fold enhanced compare with native cur, the Cmax(0.24 ± 0.04 vs. 0.08 ± 0.03 μg/mL) and AUC 0-t (6.13 ± 0.22 vs.0.11 ± 0.04 h/μg/mL) of CUR-MM(10 mg/kg) were higher than that of native cur(10 mg/kg), likely as a contribution of solubilization of cur in micelles and PF127 and GL44 P-gp inhibition effect [73].
Mixed polymeric micelles Low-molecular-weight heparin-all-trans-retinoidpolymeric acid micelles (MPMs) Cyclosporine A
P-gp pumps
Cur-carboxymethyl chitosan Enterocytes
Systemic
Circulation
M cells
ro of
Fig 5. Inhibit effect of curcumin-carboxymethyl chitosan (CNC) on P-gp mediated efflux effect.
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3.3.2 Modulate the integrity of epithelial tight junctions Several polymers which can encapsulate cur can also enhance cur intestinal absorption through modulating the integrity of epithelial tight junctions, as well as through mucoadhesive features. R. Shelma et al. prepared cur loaded submicroparticles composed of Lauroyl sulphated chitosan (LSCS)[74]. LSCS could penetrate Caco-2 cells tight junctions, and thus improve cur paracellular permeability and enhance cur oral bioavailability. Chitosan, a mucoadhesive polymer, can protect the drug from intestinal and enzymatic degradation and enhance the penetration of curcumin across mucosal barriers by interacting with epithelial tight junctions, enhancing oral bioavailability. R. Shelma et al. found that cur loaded acyl modified chitosan nanoparticles had a higher mucin interactions effect than unformulated cur, which could enhance cur intestinal absorption[75].
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In addition, lipid based nanoparticles are absorbed via lymphatic transport by intestine Peyer’s patches M cells. The oral bioavailability of cur can be enhanced through the lymphatic transport route, as lymphatic vessels can transport the drug into the thoracic duct, followed by transfer into systemic circulation, which can bypass the portal circulation. In this regard, Min Sun et al. prepared cur loaded polybutylcyanoacrylate nanoparticles (PBCNs) [76]. Cur nanoparticles were mostly absorbed in the ileum and colon, as there are more M cells and Peyer’s patches (PP) in these sites. PBCNs are mainly absorbed by M cells on the PP, and the oral bioavailability was 800% higher than unformulated cur. The Cmax(43.53 ± 25.57 vs. 35.46 ± 12.78 μg/L) and AUC0–∞(419.62 ± 102.74 vs.244.81 ± 76.52 μg/L h) of CUR–PBCN (50 mg/kg) were higher than that of CUR-suspension(250 mg/kg), suggesting a good oral bioavailability of CUR – PBCN. Jong-Suep Baek et al. formulated cur in Ncarboxymethyl chitosan (NCC) coated SLN (NCC-SLN). The burst release of cur in acid environments was inhibited compared with pure SLN[77]. In simulated gastric and intestinal fluid, the burst release of NCC-SLN was suppressed, and the formulation had
a sustained release characteristic. NCC-SLN had enhanced cytotoxicity and cellular uptake, with the lymphatic uptake 6.3-fold and oral bioavailability 9.5-fold enhanced compared with cur solution respectively. NCC-SLN had a higher Cmax(0.73 ± 0.31 vs.0.29 ± 0.11 μg/L) and AUC0–12 (4.98 ± 2.28 vs. 0.56 ± 0.14 μg.h/L) than that of cur solution at a dose of 50 mg/kg. In addition, surface modification of SLN with NCC can enhance the SLN lymphatic uptake.
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3.3.3 Various of intestinal absorption mechanism of curcumin preparations The mechanisms of intestinal absorption of cur preparations have been discussed. Jinling Wang et al. prepared cur polymeric micelles (Cur-PMs) with an enhanced absorption in the duodenum, jejunum and ileum. Cur-PMs were translated by energydependent, macropinocytic transcytosis and lymphatic transport pathways with a resultant enhanced cellular uptake (Fig 6). Cmax of Cur-PMs (342.33 ± 122.42 ng/mL) was 3.11-fold enhanced than that of Cur-Sol (109.84 ± 85.89 ng/mL). While, the AUC (0−t) of Cur-PMs (870.2 ± 466.78 mg/L × h) was 2.87 times enhanced than that of Cur-Sol (303.58 ± 294.31 mg/L ×h) at a dose of 50 mg/kg by oral administration.[78]. Bingchao Cheng et al. prepared a cur loaded D-α-tocopherol polyethylene glycol 1000 succinate (TPGS) decorated nanodiamond (ND) system with a particle size of 196.32 nm and drug loading of 81.59%[79]. The absorption mechanism of cur was as follows: (1) After oral administration, cur could be released from the preparations and absorbed by passive diffusion in intestinal epithelium. (2) Nanoparticles could penetrate the mucus layer and be absorbed by transcytosis or paracellular methods. The transcytosis mechanisms of cur nanoparticles were caveolinmediated, clathrin-mediated, clathrin- and caveolae-independent endocytosis and macropinocytosis. (3) After transport across the epithelium, cur nanoparticles could diffuse into lymphatic transport system or blood capillaries, and finally enter blood circulation. Cur nanoparticles had a higher Cmax (311.13 ± 78.52 vs.69.20 ± 15.92 ng/ml, 4.5 fold), longer MRT0-t (3.71 ± 0.66 vs.1.21 ± 0.22 h, 3.07 fold) and larger AUC 0–t (897.75 ± 258.81 vs. 84.12 ± 30.34 ng/mL·h, 10.67-fold) compared with cur suspension at a dose of 75 mg/kg. Yuwei Duan et al. formulated cur in micelles through the thin film diffusion method. The micelles was composed of methoxy poly(ethylene glycol)-poly(lactide) (mPEG-PLA) and D-α-tocopherol polyethylene glycol 1000 succinate (TPGS). The micelles had high drug-loading (16.1%) and small size (46.0 nm), and demonstrated excellent stability in gastrointestinal fluid due to the low critical micelle concentration (CMC) and dilution stability. The highest absorption segment was the duodenum, and cur micelles was mainly transferred through passive diffusion. The Cmax of CUR-MPP-TPGS-MMs(197.88 ± 61.71 vs.27 ± 1.37 ng/ml) was higher than that of cur suspension, while the AUC0–24 of CUR-MPP-TPGSMMs (1.02 ± 0.93 vs. 0.11 ± 0.029 μg/mL·h) was about 9 times enhanced than that of cur suspension after oral administration at the dose of 75 mg/kg , with a relative bioavailability of 927.3%. The oral bioavailability was also improved compared with unformulated cur[67]. Yan Gao prepared a cur nanosuspension (CUR-NS) with a diameter of 210.2 nm. By using an in situ single pass perfusion method, 9.20% CURNS was absorbed in the stomach within 2 h, and the main absorptive segments of cur
Table 4. Absorption mechanism of curcumin preparations. Cmax AUC Absorpti Preparation (Preparation vs. (Preparation vs. on control) control) mechanis m Chitosan-micelles
5.365 ± 1.246
effect
77.261 ± 12.485
vs.
vs.
Refe renc e
The oral absorption of cur
[71]
were enhanced.
5.107 ± 1.629
μg/mL
μg.h/mL
re
0.610±0.109
(15 mg/kg)
(15 mg/kg)
7.51 ± 0.44
136.27 ± 10.85
TPGS and Brij78 acted as
solid lipid nanoparticles
vs.
vs.
P-gp inhibitor by enhancing
14.29±1.58
absorption of cur.
lP
TPGS and Brij78-
2.12
± 0.34
μg/mL
(50 mg/kg)
GL44-
0.24 ± 0.04
na
PF-127 and
ur
micelles
(50 mg/kg) 6.13 ± 0.22
The cytotoxic activity (3-
vs.
vs.
folds) and oral
0.11 ± 0.04
bioavailability (around 55-
μg/mL
h/μg/mL
folds) were enhanced.
(10 mg/kg)
(10 mg/kg)
/
LSCS-
[72]
μg.h/mL
0.08 ± 0.03
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Modulate the
Observation
-p
P-gp inhibit
ro of
were the duodenum and jejunum through passive diffusion mechanisms. A pharmacokinetic study also showed CUR-NS had a relatively high bioavailability compared with native cur, the Cmax of CUR-NS(174.75 ± 49.05 vs. 12.58±4.28 ng/ml) was higher than that of cur suspension, AUC0–∞ for CUR-NS (612.82 ± 70.92 vs. 90.12 ± 16.85 μg/mL·h ) was 6.8-fold enhanced than that of cur suspension, after oral administartion at a dose of 250 mg/kg.[80]. Hailong Yu et al. prepared a cur nanoemulsion with enhanced oral bioavailability[81]. Caco-2 cell permeation experiments showed that the cur nanoemulsion absorption mechanism was a digestiondiffusion mechanism. The Cmax (29.9 ± 5.1 vs.1.6 ± 1.2 μg/mL) and AUC0-inf (210 vs.21.4 μg/mL·min) of cur-nanoemulsion(240 mg/ml) was enhanced compared with that of cur water dispersion(240 mg/ml). Cur oral bioavailability was 9-fold higher than unformulated cur.
/
submicroparticles
LSCS can open the tight
[73]
[74]
junctions in Caco 2 cells
integrityof epithelial
/
Chitosan-nanoparticles
/
Chitosan nanoparticles had
tight
higher mucin interactions
junctions
effect. PBCNs-nanoparticles
43.53 ± 25.57
419.62 ± 102.74
PBCNs are mainly
(50 mg/ml)
(50mg/ml)
absorbed by M cells on the
vs.
vs.
PP.
35.46 ± 12.78
244.81 ± 76.52
[75]
[76]
μg/L
μg/L h
(250 mg/ml)
(250 mg/ml)
N-carboxymethyl
0.73 ± 0.31
4.98 ± 2.28
The lymphatic uptake was
chitosan (NCC)
vs.
vs.
6.3-fold and oral
SLN
0.29 ± 0.11
0.56 ± 0.14
bioavailability was 9.5-fold
μg/L
μg.h/L
higher than cur solution.
(50 mg/ml) Macropinoc
Micelles
342.33±122.42
N-[ [77]
(50 mg/ml) 870.2 ± 466.78
Oral absorption of cur was enhanced.
ytic
vs.
vs.
transcytosis
109.84 ± 85.89
303.58± 294.31
and
ng/mL
mg/L × h
lymphatic
(50 mg/kg)
(50 mg/kg)
311.13 ± 78.52
897.75 ± 258.81
or
vs.
vs.
paracellular
69.20 ± 15.92
84.12 ± 30.34
ng/ml
ng/mL·h
(75 mg/kg)
(75 mg/kg)
[78]
Nanodiamond
Passive
Micelles
suspension.
vs.
enhanced.
27 ± 1.37
0.11 ± 0.029
ng/ml
μg/mL·h
(75 mg/kg)
(75 mg/kg)
174.75 ± 49.05
612.82 ± 70.92
Oral bioavailability was
vs.
vs.
enhanced.
12.58±4.28
90.12 ± 16.85
ng/ml
μg/mL·h
(250 mg/kg)
(250 mg/kg)
29.9 ± 5.1
210 vs.21.4
Cur bioavailability was 9-
vs.
μg/mL·min
fold enhanced compared
1.6 ± 1.2
（240mg/ml）
with unformulated cur.
μg/mL （240mg/ml ）
Endocytosis micelles
fold) compared with cur
vs.
Transcytosis
Cur
and larger AUC 0–t (10.67-
Oral bioavailability was
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diffusion
Nanoemulsion
longer MRT0-t(3.07 fold)
1.02 ± 0.93
na
Digestion-
[79]
higher Cmax(4.5 fold),
197.88 ± 61.71
diffusion
Nanosuspension
Cur nanoparticles had
[67]
re
Transcytosis
-p
pathways
ro of
transport
[80]
[81]
Macropinocytosis Caveolae and
Caveolae
Clathrin
Clathrin Independent Endosome junction
Blood system
ro of
Tight
Lymphatic capillary
cur
polymer
-p
Fig 6. Schematic diagram of proposed absorption mechanisms of cur micelles in order to improve the oral absorption and bioavailability of cur.
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3.4 Coadministration of curcumin with adjuctants
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Some absorption enhancers have the ability to improving cur bioavailability through inhibition of cur metabolism with several adjuvants which can interfere with metabolized enzymes of cur. Piperine and other adjuvants have been shown to enhance cur oral bioavailability in both preclinical studies and in humans[82]. Piperine can inhibit the metabolizing enzymes of cur and circumvent the first pass metabolism. Sesamin can also alter the metabolism and bioavailability by modulating the activities of catechol-O-methyltransferases and UGT[83]. Xanthohumol can inhibit the metabolism of cur by conjugating with sulphotransferases and UGT[84]. Other adjuvants such as etoposide, docetaxel, silibinin and so on have been coadministered with cur in order to enhance cur oral bioavailability (Table 5).
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Alex E. Grill et al. formulated cur with UGT inhibitors (piperine, silibinin, tangeretin, and quercetin) in a self-microemulsifying drug delivery system (SMEDDS)[85]. SMEDDS containing curcumin (100mg/kg) and either piperine (125mg/kg), quercetin (100mg/kg), or silibinin (100mg/kg) were orally administered to mice. They found that silibinin, tangeretin and quercetin had inhibitory effects on the metabolism of curcumin (20~30% inhibition of maximum concentration compared to native curcumin). Mouse liver microsome studies showed that quercetin and silibinin had a glucuronidation inhibition effect of cur. In vivo experiments showed that silibinin can enhanced cur bioavailability by 3.5-fold compared with cur SMEDDS by an enhanced Cmax(0.15 vs. 0.03 μM) than cur SMEDDS.
Table 5. Coadministration of curcumin and other adjuvants. Codelivery
Formulation
Drugs
/
Cur, Etoposide
Dose
Cmax
AUC
Observation
(mg/
(Codilivery vs.
(Codilivery vs.
kg)
control)
control)
0.4、
Cur(0.4, 2, 8mg/kg), Etoposide(6
Cur
2 or
mg/kg) vs.Etoposide(6 mg/kg)
bioavailability
8,6
Refer -ence
can
improve of
the
etoposide
oral by
[86]
inhibiting the activity of intestinal Pgp and CYP3A4; 635±121,
The oral bioavailability of etoposide in
365±71,
758±142,
cur etoposide coadministration was
375±74 vs. 276
846±169 vs.
52% higher than etoposide at the dose
±50 ng/ml
561±98 ng/ml
of 8 mg/kg.
/
Cytotoxicity
/
nanoemulsion
/
Paclitaxel
ro of
Cur,
305± 59,
was
enhanced
by
promoting apoptotic with the treatment
[87]
of paclitaxel and cur. Cur,
nanoemulsion
/
50,20
/
was 5.2-fold increased. self-
25 、
Cur (25, 50, 100 and 150 mg/kg),
The oral bioavailability of docetaxel
emulsifying
50 、
Docetaxel (30 mg/kg)
was improved
drug delivery
100
vs. Docetaxel (30 mg/kg)
system
and
202.4 ± 38.0,
638.2 ± 41.5,
150 ,
342.6 ± 81.6,
828.9 ± 143.6,
30
374.9 ± 58.2,
1,004.1 ± 183.4,
370.3 ± 123.1
941.4 ± 243.4
vs.
vs.
78.7 ±
10.6
micelles
adjuvants
80
ur
(sesamin,
therapy of cur.
264.5 ± 40.8
Cur( 98 mg) vs.
The micellar formulation can improve
Sesamin, ferulic acid, naringenin,
the oral bioavailability of cur (80mg)
xanthohumol (NCP) vs.
by 88-fold.
Micellar cur (MC) vs.
naringenin,
Micellar cur plus phytochemicals
xanthohumol)
(MCP).
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ferulic acid,
Quercetin
0.6 ± 1.3
/
with the combination
ng/ml
na
ng/ml
Cur,
[89]
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Docetaxel
[88]
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Cur,
Cur,
Relative bioavailability of paclitaxle
-p
Paclitaxel
/
vs.
6.5 ± 12.2 vs.
3.9 ± 2.3 vs.
49.6 ± 31.4 vs.
129.7 ± 61.4 vs.
574.7±144.3 vs.
104.9 ± 59.6
475.9 ± 204.8
nmol/L
nmol/L·h
/
[90]
/
Cur oral bioavailability was 8-fold improved through coadministration of cur and adjuvants; Combination of cur and quercetin was
[91]
effective
in
preventing
urinary
infections.
/
50 、
EVL (0.5 mg/kg) vs.
Oral intake of cur decreased the
Everolimus
100，
EVL + curcumin (50 mg/kg) vs.
bioavailability
(EVL)
0.5
EVL + curcumin (100 mg/kg)
of everolimus.
Cur,
6.0 ± 1.8 vs.
1637.7±256.8 vs.
1.4 ± 0.9 vs.
481.8 ± 327.8 vs.
1.4 ± 1.2 ng/mL
466.0± 330.2
[92]
ng·min/mL Cur,
/
nanoemulsion
/
/
5-Fluorouracil
Coadminsion of cur and 5-Fluorouracil nanoemulsion
had
[93]
improved
cytotocity and enhanced cell uptake.
/
nanoparticles
/
/
Dual drug loaded nanoparticles can
Cur-quercetin,
enhance the efficacy of curcumin in
Cur-silibinin
the treatment of cancers.
/
Cur, Norfloxacin
60,
Norfloxacin (100 mg/kg) vs.
The mean plasma concentration of
100
Norfloxacin
norfloxacin was improved in cur
(100
mg/kg)+Cur(60
[95]
pretreated rabbits.
/
-p
mg/kg)
[94]
ro of
Cur-piperine,
2.67 ± 0.42 vs. 4.06 ± 1.24
2Cur NPs(100 mg/kg) vs.
nanoparticles
Piperine
re
Cur,
250,
Cur + piperine suspension
10
(250 + 10 mg/kg) vs.
lP
Cur suspension(250 mg/kg)
Jo Cur,
Resveratrol
vs.121.2 ± 23.1
vs.872 ± 43
vs.90.3 ±15.5
vs.312 ± 9
ng/ml
ng/ml h
100,
Cur(100mg/kg),docetaxel(30mg/kg)
30
vs. docetaxel(30 mg/kg)
ur
Docetaxel
3224 ± 329
na /
Cur,
260.5 ± 26.4
1024.2± 121.7 vs.
102.5
11.5 ng/ml
liposomes
50, 50
/
±
2244.1 ± 68.0 vs282.6 ± 18.4 .ng h/ml
/
Coadministration incidence
reduced of
adenocarcinoma.
4.In vitro studies of curcumin oral nanoformulations
the
prostatic
[98]
ro of
The cell permeability, cell uptake and cytotoxicity of various cur nanoformulations have been studied against different cancer cells by many groups in recent years. Cur can inhibit cancer cells growth through various mechanisms. Cur is able to downregulate P-glycoprotein (P-gp) and multidrug resistance proteins (MDR), and can also overcome cancer cells multidrug resistance[99,100]. Cur has cytotoxic activities in lung squamous cell carcinoma H520 and small cell lung cancer H460 cell lines [101]. Pharmacological activities studies showed that cur can induce cell death as a result of interference with various cell signaling pathways, including cell cycle (cyclin-D1 and cyclin-E), survival (PI3K/Akt pathway), apoptosis (caspases activation and antiapoptotic gene products down-regulation), angiogenesis (VEGF), metastasis (CXCR-4), proliferation (AP-1, EGFR and HER-2), inflammation (5-LOX, COX-2, NFkB, IL-1, TNF, IL-6) and invasion (adhesion molecules and MMP-9)[102]. Besides, cur also induces apoptosis and cell proliferation in other cancer cells such as human prostate cancer, leukemia, and non-small cell lung cancer cell lines and more.
-p
4.1 Cell permeability of curcumin nanoformulations The poor oral bioavailability may be the result of poor permeability of cur in cancer cells. Wahlang B et al. detected cur permeability in Caco-2 cells. They found that cur had a poor permeability with a P app of 2.93±0.94×10 −6 cm/s[103]. Another study showed that the apparent permeability of cur in Caco-2 cells was < 0.1×10-6 cm/s[104].
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4.2 Cell uptake of curcumin nanoformulations Cell uptake of various cur nanoformulations has also been investigated. In order to facilitate the cellular uptake of cur, cur loaded propylene glycol liposomes (PGL) were developed. The liposomes were composed of hydrogenated egg yolk lecithin, cholesterol, Tween 80 and propylene glycol [105]. In vitro cell experiments showed that PGL exhibited higher cellular uptake than conventional liposomes and unformulated cur. In a recent study, cur loaded Pluronic/polycaprolactone (Pluronic/PCL) block copolymer micelles were prepared by Raveendran et al[106]. The uptake ability of micelles into Caco-2 cells was measured by fluorescence exploiting the intrinsic fluorescence of curcumin. The fluorescence intensity of cur micelles in cells was higher than that of native cur, indicating that the micelles had better cell internalization than free cur. Cellular uptake extent of cur was influenced by various factors including nanocarrier type, surface charge, particle size and cell lines. For example, cur PLGA nanoparticles with different particle size (76 nm to 560 nm) had different uptake patterns. With the decrease of particle size, the uptake was increased, likely as low particle size nanoparticles are more easily endocytosed than nanoparticles with higher particle sizes. In addition, coating the nanoparticle surfaces with poly(Llysine) (PLL) can make the nanoparticles positively charged, which can enhance nanoparticles uptake inside the cells[107]. Another comparative study was also conducted analyzing the cell uptake of dendrimer, β-cyclodextrin (β-CD), nanogel, PLGA and cellulose nanoformulations of cur in MDA-MB-231 (breast), SKBR-3, and HPAF-II (pancreatic) cancer cells [108]. The uptake ability was in the order of: MDAMB-231 > SKBR-3 > HPAF-II. Importantly, the uptake ability of cur preparations was
2~3 fold enhanced compared with unformulated cur.
5.In vivo studies of curcuimin oral nanoformulations
ro of
5.1 Absorption of curcumin oral nanoformulations Cur and preparations of cur have been investigated for their cur absorption and pharmacokinetic characteristics, which indicate the treatment effect of cur nanopreparations. The absorption of cur in humans was investigated, whereby 12 healthy volunteers were orally administered a cur C3-complexTM at a dose of 10-12 g[109]. Free cur, the Cmax of which is 50 ng/ml, was only detected in the plasma of one person. Cur sulphate had a Cmax of 1μg/ml, while the Cmax of cur glucuronide was 2 μg/ml. Alzheimer’s disease patients were orally administered with C3complex™, the dose of which was 2-4 g daily and the drug was administered for 24 weeks. Cmax of cur, cur glucuronide, tetrahydrocurcumin (THC) and THC-glucuronide were 7.76 ng/ml, 96.05 ng/ml, 3.73 ng/ml and 298.2 ng/ml, respectively[110].
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Yan Yang et al. found that when cur was orally administered at a dose of 100 mg/kg, the plasma concentration of cur was extremely low [111]. Oral administration of cur has an anti-arthritic effect through inhibiting somatostatin (SOM) secretion from small intestine endocrine cells via Ca2+ /CaMKII and cAMP/PKA signaling pathways. When the cur preparations were orally administered, Cmax and AUC were much higher than that of unformulated cur.
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Khalil et al. found that when cur was orally administered at a dose of 50 mg/kg, the pharmacokinetic characteristics of PLGA and PLGA-PEG nanoparticles were much improved over unformulated cur. The half-lives of cur loaded PLGA and PLGA-PEG nanoparticles were 4 h and 6 h, while the half-life of free cur was 1 h. As well, the AUCs and Cmax of the same formulations were 15.6 and 55.4 fold and 2.9 and 7.9 fold enhanced compared with free cur. Cur could release from the nanoparticles rapidly, thus the drug could be soon found in the plasma[112].
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Bhushan Munjal et al. compared the oral bioavailability of seven different preparations of cur including nanosuspension, micronized suspension, aqueous suspension, hydroxypropyl-β-cyclodextrin (HP-β-CD) inclusion complex, amorphous solid dispersion, combination with piperine, and spray-dried CRM–milk composite [113]. The aqueous suspension has a C max of 28.9 ng/ml, while the AUC is 26.9 ng/ml. For the nanosuspension and amorphous solid dispersion, the oral bioavailability was increased to 251%, 446%, 567% in AUC (0−t) and 405%, 270%, 415% in Cmax. For the micronized suspension and piperine, the Cmax and AUC were not increased significantly. The oral bioavailability of the milk composite was reduced (37% in Cmax and 10% in AUC (0−t)). Sophie P. Valentine et al. orally administered cur at doses of 200 mg/kg or 400 mg/kg,
and the cur preparations were administered for two weeks[114]. They found that CYP1A catalytic activity was decreased to 25%, however cur had no inhibition effect on hepatic UDP-glucuronosyltransferase, hepatic catechol-O-methyltransferase or ovarian aromatase. Additionally, the catalytic activity had a 20% decrease, and the CYP3A levels of polypeptide had a 28% decrease as a result of giving cur at 400 mg/kg for two weeks. Furthermore, when cur was orally administered at a dose of 400 mg/kg, glutathione S-transferase activity had a 20% increase. A combination of CYP1A, CYP3A and Glutathione S-transferase (GST) metabolic pathways could activate the cur chemopreventative action.
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Adjuvants such as piperine can also have an influence on cur pharmacokinetics in rats and humans by enhancing cur oral bioavailability. Piperine can enhance cur oral bioavailability through inhibiting hepatic and intestinal glucuronidation. Guido Shoba et al. studied the process of piperine enhancing of cur oral bioavailability [115]. When cur was orally administered in humans at a dose of 2g/kg combination with 20 mg/kg piperine, the AUC and Cmax were 20- and 30-fold higher than cur 2g/kg alone. In rats, the AUC and Cmax were only 1.5-fold increased after coadminstration of cur at 2g/kg and piperine at 20mg/kg compared with administration of cur at 2g/kg alone.
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5.2 Distribution of curcumin oral nanoformulations Uptake and distribution of cur in tissues is important, and various studies have addressed this issue. In vitro studies have shown that when rat intestines were incubated in 10 ml incubation medium with 50 ~750 µg cur, when the concentration of cur was 750 µg, no more than 3% of cur was detected in tissues. There was no cur in the serosal while 30~80% of cur couldn’t be found in the mucosal side[116].
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5.3 In vivo metabolism and excretion of curcumin oral nanoformulations The low cur oral bioavailability preparations may also due to the rapid cur metabolism and excretion from the gastrointestinal tract. Various studies of cur metabolism and excretion have been conducted in recent years.
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When cur is orally administered at a dose of 1 g/kg in rats, there was a limited amount of cur detected in the urine, while 75% of cur was excreted through the feces[117]. 89 % of [3H] cur was excreted in the feces while 6% was detected in the urine after oral administration of [3H] cur at a dose of 0.6 mg/rat.[118] Ravindranath and Chandrasekhara et al. detected that less than 5 μg/ml cur could be found in plasma after oral administration at a dose of 400 mg/rat[119]. The poor cur oral bioavailability is due to the rapid metabolism in the intestinal wall and liver. Several studies have showed that the liver and intestine are the major organs that can metabolize cur[120,121]. When cur was orally administered at a dose of 0.1 g/kg in mice, the peak plasma concentration of free cur was only 2.25 μg/mL[122]. When cur was orally administered at a dose of 500 mg/kg, the plasma concentration of
re
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free cur was only 1.8 ng/mL. Cur is metabolized as cur sulfate and cur glucuronide in rat plasma, and hexahydrocurcumin, hexahydrocurcumin glucuronide and hexahydrocurcuminol were also detected in minor amounts. Previous human studies showed that when cur was orally administered at a dose of 3.6g daily for four months, very low level of sulfate and glucuronide conjugates could be detected in plasma (3-6 ng/mL)[123]. The absorption, tissue distribution and metabolism of cur after oral administration of 10, 80 and 400 mg of [3H] cur were investigated[124~126]. At a dose of 400 mg, [3H] cur was detected in tissues even after 12 days, and 60%~66% of cur was absorbed regardless of the given dose. In another study, animals were orally administered with cur for 1 week. Cur tissue levels declined to a limited amount 3~6 h after administration [127]. Marczylo et al. evaluated the effect of phosphatidylcholine for the oral bioavailability and metabolic profile of cur[128]. After oral administration of either cur formulated with phosphatidylcholine (Meriva) or unformulated cur at a dose of 340 mg/kg, cur, curcuminoids desmethoxycurcumin and bisdesmethoxycurcumin, metabolites including hexahydrocurcumin, tetrahydrocurcumin, curcumin glucuronide, and curcumin sulfate were detected in plasma, liver and intestinal mucosa of the rats. After Meriva was given to rats, cur plasma concentration (33.4±7.1 nM) was 5-fold enhanced compared with native cur (6.5±4.5 nM), and liver levels of cur after receiving Meriva were also higher than native cur. However, cur concentrations in gastrointestinal mucosa after administration of Meriva was enhanced compared with native cur, suggesting that cur is formulated with phosphatidylcholine.
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Therefore, conjugating with adjuvants which can interact with cur metabolizing enzymes is an effective strategy to inhibit the metabolism of cur in order to enhance cur oral bioavailability. Phytochemicals can alter the cur metabolism, which in return improves the bioavailability of cur[129]. For example, ferulic acid, which is similar with cur in structure, can inhibit the xenobiotic enzymes of cur, and xanthohumol can inhibit cur metabolism by conjugating with the cur metabolism enzyme UGT and sulphotransferases. Piperine can inhibit the cur metabolizing enzymes and circumvent the first pass cur metabolism. Sesamin can modulate the activities of catechol-Omethyltransferases and UGT, thus alter the metabolism and bioavailability of cur. Other adjuvants which can improve the oral bioavailability of cur have already been discussed in this paper.
6.Clinical trials Nanoformulations and the free form of cur have been investigated in human clinical trials for treatment of various diseases such as cancer, inflammatory diseases, neurodegenerative diseases, metabolic diseases and more. In order to enhance cur oral bioavailability, cur has been formulated into capsules and tablets with high doses. At present, there are still several active clinical trials of cur with different formulations [http://www.clinicaltrials.gov/].
ro of
The clinical trials of cur which have been investigated are listed in Table 6, and here several clinical trials of cur are highlighted. There are a few clinical trials with positive outcomes. Several clinical observations suggested that cur had effective systemic biological activity even at low doses. For example, in a Phase II clinical trial on 25 patients with pancreatic cancer, when cur was administered at a dose of 8 g/day for 2 months, Cmax was 22 ~41ng/mL[130]. Cur oral administration is well tolerated with biological activity in pancreatic cancer by downregulating the cyclooxygenase-2, NFκB, phosphorylated signal transducer in patients, in spite of the limited absorption. When cur was orally administered at the dose of 0.45~1.8 g daily for 4 month in 15 patients, cur did not affect the PGE2 levels in leukocites, while cur affected the PGE2 levels at the dose of 3.6 g. In fact, when cur was administered at a dose of 3600 mg/day, the blood concentration of cur sulfate was 8.9 ± 0.7nmol/L, while that of cur glucuronide was 15.8 ±0.9nmol/L , which may inhibit PGE2 levels[131]. In another clinical trial, cur was administered at a dose of 0.45, 1.8 or 3.6 g per day for 1 week. When cur was administered at the dose of 3.6 g, M1G levels in colorectal tissue was affected while COX-2 protein expression was not decreased. And the effect was only be detected at the highest level(3.6 g/ per day)[132].
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There are several successful cur formulations which are reported in recent years with higher Cmax and bioavaialbility. Cur was orally administered in a nano-colloid dispersion THERACURMIN formulation at the dose of 30 mg, and it was found that the Cmax was 29 ng/ml, whereas the Cmax of the unformulated curcumin was only 1.8 ng/ml[133]. THERACURMIN was prepared by a high pressure homogenizer method using glycerin, gum ghatti and water. In addition, THERACURMIN was also administered at a dose of 150 mg and 210 mg, and the Cmax was found to be 189 ng/ml and 275 ng/ml, respectively. THERACURMIN can improve cur bioavailability and gastrointestinal absorption with limited toxicity [134]. It has been reported that the maximal cur plasma concentration in humans was 3228.0 ± 1408.2 ng/ml at a dose of 410mg when cur was formulated into liquid micelles[135]. Cur was excreted in its nonmetabolised form mostly through the feces after oral administration[136]. The absorbed cur could be converted into water-soluble sulfates and glucuronides metabolites[137]. In a phase I trial, after oral administration of cur at 3600 mg in patients, the cur plasma and urine concentrations were 11.1 nmol/L and 1.3 μmol/L respectively[138]. The concentration of cur administered at this dose in colorectal tissues were 7.7–12.7 nmol/g, while the concentration of cur in the liver could not be detected[139]. Peak plasma concentrations was 0.41-1.75μM after oral administration at a dose of 4-8 g cur. However, such examples are exceptional and most of the clinical trials had limited clinical trial effects which may due to the two factors concluding the low cur bioavailability and inadequate clinicals study quality.First pass and cur intestinal metabolism may contribute to the low bioavailability of cur oral administration. Most clinical trials had small amount patients and were not double blinded and not randomized. It has been reported that when cur was orally administered at a dose of 450–3600 mg/day in patients with colorectal cancer, the plasma concentration of cur
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was in the 10 -8 M range, which is around a hundredth of in vitro effective cur concentration in blood or colon cells[140].Vikram et al. detected the free cur plasma concentration in healthy volunteers after administration of cur in a solid lipid cur particle (SLCP) formulation compared with native cur. The mean plasma concentration of cur in SLCP (650 mg) was 22.43 ng/mL, while plasma cur was not detected in unformulated cur with the same dose. SLCP with doses of 2, 3, and 4 g were administered in 11 patients with osteosarcoma, and the Cmax was 33 ng/ml, 31 ng/ml and 41 ng/ml, respectively. It was found that a higher dose did not contribute significantly to a higher plasma concentration[141]. Sharma et al. detected cur plasma concentration after given cur at doses of 440~2200 mg/day for 4 months[142]. Clinical results showed that GST activity was decreased by 59% at a low dose(440 mg) instead of higher doses.Cur oral bioavailability was low although the Cmax was 64~1054 nmol/g at a dose of 2200 mg/day. Cur was metabolised by intestine. Metabolites were detected in the feces instead of the blood or urine. Thus, cur formulation with higher bioavailability and clinical therapeutic effect should be developed which need the hard working of ourselves.
re
Table 6. A list of clinical trials with oral administration of curcumin in different disease patients. Disease Dosage Dose Duration Pati Cmax Clinical Trail Results
Cancer Colorectal
Capsules
cancer
440– 2200
4 months
15
na
mg/day
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ents
144~ 519 nmol/g;
(1) The oral bioavailability of cur
(lower dose)
was low and cur was metabolised
64~1054 nmol/g
by intestine.
(higher dose)
(2) Metabolites were detected in
[143]
the feces instead of the blood or
ur
urine. (3) GST activity was decreased by 59% at a low dose(440 mg) instead of higher doses.
Jo Capsules
Reference
(4) Cur cause clinical benifit in patients of colon rectal cancer. (3)Larger dose of cur clinical trial is merited. 450–
4 months
15
8.9±0.7nmol/L (cur
(1) Compounds and conjugates
3600
sulfate)
were detectable
mg/day
15.8
±0.9nmol/L
in plasma and
urine after consumption of cur 3.6
cur glucuronide
g per day.
(3600 mg/day)
(2)Significantly decreased serum
[144]
PGE2 levels at the highest dose. Capsules
450,
7 days
12
12.7±5.7nmol/g
(1) Cur
levels
was
1800,
( normal mucosa )
pharmacologically efficacious by
3600
7.7±1.8 nmol/g
decreasing M 1 G levels instead of
mg/day
(tumor tissue)
COX-2 protein levels in the
(3600 mg/day)
colorectum with negligible cur
[145]
distribution outside the gut at a 19.6 ± 14.8nmol/g
dose of 3600 mg/day.
( normal mucosa )
(2) Cur
6.7 ± 1.6 nmol/g
malignant and normal colorectal
(tumor tissue)
tissue.
(1800 mg/day)
(3)Traces amount of cur was
was
detected
0.9±0.4 nmol/g (tumor tissue) (450 mg/day) 7 days
3600
10 −8M
Below 12
(1) Cur had low bioavailability, with
mg/day
The
administered cur was low.
-p
450–
blood.
by
systemic availability of orally
( normal mucosa )
/
the
up
ro of
0 nmol/g
in
taken
low
metabolites
[146]
in
circulation.
/
480 mg
3 months
Capsules
2,4
5
1 month
44
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na
g/day
/
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×3 / day
re
(2) M1G level was not decreased.
Capsules
1.08
10~30 days
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Capsules
cancer
[147]
quercetin decreased in polyps size(50.9%),
polyps
number(60.4%) without severe toxicity.
7.3±8.1 ng/mL
Decreased ACF levels with the 4g
cur
dose, while no decrease in 2g dose.
[148]
Increased body weight, decreased
[149]
15.±14.8 ng/mL cur conjugate (4 g/day) 126
/
g/day
Pancreatic
Combination therapy of cur and
serum
TNF-α,
induced
p53,
regulated apoptotic pathway of tumor cell.
500
/
42 days
mg/day
20
Decreased PhK (Phosphorylase kinase) activity in cur treated
(curcum
[150]
group.
in), 5
mg
(piperin e) Capsules
8 g/day
4, 8 weeks
25
22 ~41ng/mL
(1) Cur oral administration is well
[151]
tolerated with biological activity in pancreatic cancer, in spite of the limited absorption. (2) Cur
downregulated
the
NF- κ B,
cyclooxygenase-2,
phosphorylated signal transducer in patients. (3) The
trial
had
positive
outcomes with tumor regression and enhanced serum cytokines levels.
/
8 g/day
4 weeks
/
17
(1) Cur had low compliance at high dose(8 g/day)
[152]
ro of
(2) Gemcitabine in combination with cur had therapeutic effect in advanced
pancreatic
cancer
patients.
/
8 g/day
/
21
29 ~412 ng/ml
Gemcitabine in combination with
-p
cur was safe and feasible in
[153]
pancreatic cancer patients.
Prostate
cancer
Capsules
0.1
6 months
/
85
cancer
6 g/day
/
Tablets
3 weeks
/
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Head and
/
neck cancer
/
500~12
3 months
/
[154]
(1)The recomend dose for cur was 6,000 mg/day for 3 weeks in
[155]
combination with docetaxel. (2)
Clinical
responses
were
observed in patients for treatment of cur and docetaxel.
/
Cur inhibited IKKβ kinase activity
[156]
and IL-8 levels in head and neck cancer patients. 11
0.51±0.11μM/ml
(1) Cur is not toxic up to the dose
000
(4000 mg)
of 8000 mg/day for the treatment
mg/day
0.63±0.06μM/ml
of 3 months.
(6000 mg)
(2) Cur was not absorpted by
1.77±1.87μM/ml
gastrointestinal completely with
(8000 mg)
low Cmax(1.77±1.87 μ M/ml at
Jo
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Cervical
/
14
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Breast
with the
therapy of isoflavone and cur.
re
g/day
Reduced serum PSA
[157]
the dose of 8000 mg). (3) Cur had a biologic effect in cancer treatment.
Inflammatory diseases Ulcerative
Capsules
550 mg
proctitis
×2–3
Crohn’s disease
/day
/
2 months 5
Cur had reduced inflammatory response effect in patients.
[158]
360 mg
1 month
×3 / day 360 mg
2 months
×4 / day Irritable bowel
Tablets
Syndrome(IBS)
72–144
8 weeks
207
/
mg/day
Irritable bowel syndrome (IBS) prevalence
was
decreased;
[159]
Abdominal pain was reduced.
Capsules
arthritis
0.5
8 weeks
45
/
g/day
/
Chronic anterior
375mg×
Uveitis Tablets
anterior Uveitis
[160]
active rheumatoid arthritis (RA). 12 weeks
32
/
3 /day
Recurrent
Cur had the treatment effect of
Side effect is lack; Reccurrence
[161]
rate was 86%.
1.2
12-18
g/day
months
106
/
More than 80% patients had
ro of
Rheumatoid
reduced
eye discomfort after
[162]
treatment. Cur had therapeutic effect on eye relapsing diseases.
Peptic ulcer
Capsules
3 g/day
4 weeks
45
/
Cur had the therapeutic effect of
[163]
Idiopathic
375
6-22
Inflammatory
mg×3
months
Orbital
/day
4.5
1.5
4 months
12
/
/
2-4
Jo
/
500
related swelling. (2)Cur had therapeutic effect on healing of peptic ulcer.
(1) Cur with a dose of 4.5 g/day is
[165]
treatment effect for psoriasis. 1
/
Cur had efficacy and safety on treatment
of
[166]
dejerine-sottas
disease. 24 weeks
33
/
g/day
Arterial diseases
[164]
safe and well-tolerated;(2)Cur had
g/day
ur
Disease
12 weeks
na
/
Dejerine-Sottas
(1)Five patients completed the study, four patients recovered
re Capsules
g/day
disease
8
lP
Skin conditions
Alzheimer’s
/
completely, the fifth had tumor
Pseudotumors
Psoriasi
-p
peptic ulcer.
Cur had a therapeutic effect on
[167]
Alzheimer’s disease.
7 days
10
/
mg/day
Increased cholesterol(29%),
HDL
[168]
decreased
lipid peroxidase (33%), decreased total serum cholesterol(11.63%) were
detected
after
cur
administration.
Metabolic diseases Diabetes
Capsules
0.6
8 weeks
/
(1) NCB-02 and atorvastatincan
[169]
g/day
72
increased the endothelial function. (2) NCB-02 had more therapeutic effect on endothelial dysfunction compared with atorvastatincan.
Capsules
6g
15-120 min
/
14
(1) The
postprandial
serum
[170]
insulin levels were increased, plasma glucose levels or glycemic index was not increased after cur administration; (2) Cur had the effect of insulin secretion.
/
Diabetic
1.5
nephropathy
2 months
/
40
(1)TGF-β and IL-8 serum level
g/day
[171]
and urinary protein excretion were
ro of
decreased after cur administration; (2)No
adverse
effect
was
observed.
Diabetic
Tablets
1 g/day
4 weeks
/
40
microangiopathy
Decrease in skin resting flux, edema
score,
increase
[172]
in
-p
venoarteriolar response, PO 2 were observed.
Lupus nephritis
Capsules
500
3 months
/
24
Capsules
transplantation
480-960 mg/day
Others β-Thalassemia
Capsules
500
/
Respiratory
Alcohol
/
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intoxication
Atherosclerosis
Safety trials Phase I
3 g/day
ur
contraction
12 months
na
mg/day
1 month
Tablets
Tablets
0.03 g
/
43
lP
Renal
systolic
re
mg/day
Proteinuria,
4 weeks
single dose
21
10
/
hematuria,
blood
pressure
and
[173]
were
decreased. Enhanced effect in cadaveric renal
[174]
Transplantation.
Oxidative stress was increased
[175]
in β -thalassemia/Hb E patients after cur administration.
/
Reduced
infections
after
[176]
administration of lactoferrin and curcumin (LC) . 7
29.52±12.86ng/ml
The
bioavailability
of
(THERACURMIN)
THERACURMIN was higher than
1.84±2.03ng/ml
cur powder for the treatment of
(Cur powder)
human disorders.
[177]
(30 mg/kg) 10mg
28 days
12
/
Increased
ApoA
and
HDL,
/twice
decreased apoB and LDL after cur
day
administration.
500–
3 months
25
0.51±0.11μM/ml
(1)Cur is not toxic up to the dose
12,000
(4000 mg)
of 8000 mg/day for the treatment
mg/day
0.63±0.06μM/ml
of 3 months.
(6000 mg)
(2)Cur was not absorpted by
[178]
[157]
1.77±1.87μM/ml
gastrointestinal completely with
(8000 mg)
low Cmax(1.77±1.87 μ M/ml at the dose of 8000 mg). (3)Cur had a biologic effect in cancer treatment.
Cadaveric
Capsules
480
1 month
43
/
mg×1–
Increased renal function,
[179]
decreased neurotoxicity.
2/day(c urcumin ) 20mg (quercet in) Tablets
4 g/day
6 months
26
/
gammopathy of
Serum paraprotein and uNTx
ro of
monoclonal ,
levels were decreased in MGUS
undefined
patients after cur administration.
significance
7. Conclusions and prospects
-p
(MGUS)
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Several preclinical and clinical studies of cur have been developed in the last few decades, showing that cur is a good chemotherapeutic agent. Cur has a treatment effect in various diseases such as cancers (including colorectal cancer, pancreatic cancer, breast cancer and more), inflammatory diseases, neurodegenerative diseases, metabolic diseases and many others. Oral administration is an excellent administration route because of its good patient compliance characteristics. However, there are still various drawbacks of oral drug delivery systems because of the structure of the gastrointestinal tract and characteristics of the drug. For cur, the oral absorption is still low and various nanoformulations need to be developed in order to enhance cur oral bioavailability. In this review, cur nanoformulations for oral administration including solid dispersions, nano/microparticles, polymeric micelles, nanosuspensions, lipid-based nanocarriers, cyclodextrins, conjugates, polymorphs, coadministration of cur and other adjuctants are discussed. By incorporating cur in these formulations, the solubility and stability in the gastrointestinal system were enhanced, and the absorption route of cur nanoparticles could also be changed. As well, by coadministration of cur and other adjuvants, the metabolism of cur was inhibited, thus enhancing cur oral bioavailability. The in vitro and in vivo profiles of cur formulations were also discussed, which had a predictive effect on cur clinical treatments. Nanoformulations of cur consistently have a higher oral bioavailability compared to free cur. Various clinical treatments of orally administered cur have been investigated in order to establish their safety and effectiveness for the treatment of various diseases. Cur nanoformulations are promising drug delivery system for oral administration.
[180]
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Declaration of interest
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ro of
Although great progress has been achieved over the past few decades, there are still many questions and challenges for cur oral administration nanoformulations. First, cur can reverse drug resistance of cancer cells by inhibiting the three major cancer cells high drug efflux including P-glycoprotein (P-gp), mitoxantrone resistance protein (ABCG2) and multidrug resistance associated protein 1 (MRP-1). Thus, coadministration of cur with other chemotherapeutic drugs such as paclitaxel, docetaxel, doxorubicin, gemcitabine and cisplatin through formulation of these drugs in the same or different preparations can improve the antitumor effect and reduce toxicity, which may be a promising area for the development of cur nanoformulations. As well, although cur nanoformulations have good safety characteristics in humans and animals, the toxicity of cur oral nanoformulations still needs to be considered especially for high dose administrations. It has been reported that cur is safe by oral administration at a dose of 12 g/day. By formulating cur in nanoformulations for oral administration, the toxicity should be further reduced. Furthermore, most research has been developed on the lab scale, producing stable cur oral administration nanoformulations for clinical trials is also important. Cur oral bioavailability is extremely low, as a result of low systemic bioavailability, and therefore cur plasma concentration is low even by intravenous administration. Thus, a combination of various administration routes such as lipid lymphatic transport to achieve high cur nanoparticle absorption is essential in order to enhance cur oral bioavailability. With these promising progressions, various pharmaceutical strategies can be applied in order to enhance cur oral bioavailability without severe adverse effects, which still need focused research effort.
The authors have declared no conflicts of interest.
na
Acknowledgements
Amanda Pearce is gratefully thanked for correcting the manuscript.
ur
References
Jo
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DOI:
https://doi.org/10.1016/j.jconrel.2019.10.053
Reference:
COREL 10002
To appear in: Received Date:
26 August 2019
Revised Date:
28 October 2019
Accepted Date:
29 October 2019
Please cite this article as: Ma Z, Na W, He H, Tang X, Pharmaceutical strategies of improving oral systemic bioavailability of curcumin for clinical application, Journal of Controlled Release (2019), doi: https://doi.org/10.1016/j.jconrel.2019.10.053
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.
Pharmaceutical strategies of improving oral systemic bioavailability of curcumin for clinical application Ziwei Maa, Wang Naa, Haibing Hea, Xing Tanga a
Department of Pharmaceutics, School of Pharmacy, Shenyang Pharmaceutical
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University, Shenyang 110016, Liaoning, PR China
Corresponding author. Xing Tang, E-mail address: [email protected]. Haibing He, Email address: [email protected].
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Graphical abstract
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Pharmaceutical strategies are developed to improve curcumin oral bioavailability. Curcumin oral bioavailability is enhanced by increasing curcumin solubility. Curcumin oral bioavailability is enhanced by improving curcumin intestinal stability. Curcumin oral bioavailability is enhanced by changing curcumin absorption route. Curcumin oral bioavailability is enhanced by coadministrating with other adjuvants.
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Highlights
Abstract
Curcumin (Cur), a natural compound from Curcuma longa Linn, has various pharmacological activities such as anti-cancer, anti-inflammatory, anti-oxidant, antiAlzheimer, anti-microbial and more. Curcumin also has nephroprotective, hepatoprotective, neuroprotective, antirheumatic and cardioprotective effects. However, its low aqueous solubility inhibits the oral bioavailability of curcumin. As well, curcumin can be metabolized rapidly by intestinal tract which can also result in low
oral bioavailability. In fact, the bioavailability of curcumin is low even through intraveneous administration routes. Various pharmaceutical strategies for oral administration including solid dispersions, nano/microparticles, polymeric micelles, nanosuspensions, lipid-based nanocarriers, cyclodextrins, conjugates, polymorphs have been developed in order to improve the oral bioavailability of curcumin. These pharmaceutical strategies can increase the solubility of curcumin, improve the intestinal stability of curcumin, change the absorption route of curcumin and allow for coadministration with other adjuvants. Here we discuss efficacy studies in vitro and in vivo of curcumin nanoformulations, as well as human clinical trials.
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Key words: Curcumin, Oral administration, Pharmaceutical strategy, Systemic bioavailability, Clinical studies.
1.Introduction
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Curcumin [1,7-bis(4-hydroxy-3-methoxyphenyl)-1, 6-heptadiene-3, 5-dione], a low molecular weight hydrophobic polyphenol derived from turmeric rhizomes (Curcuma longa Linn.), is used as a spice in many foods and as a coloring agent. Natural cur is composed of three hydrophobic curcuminoids: curcumin, bisdemethoxycurcumin and demethoxycurcumin in the proportion of 77:3:17 (Fig 1). Cur has the highest antidiabetic, dioprotective and neuroprotective effects out of the three curcuminoids. However, the mixture of curcuminoids has improved nematocidal activity compared to the individual compounds[1]. Cur has various pharmacological activities against chronic diseases such as Alzheimer’s disease, multiple sclerosis, rheumatoid arthritis, atherosclerosis and more. It also protects against cataract formation, liver injury, pulmonary toxicity and fibrosis, can inhibit thrombosis and suppress platelet aggregation and can enhance wound healing. Finally, cur also has anti-cancer activity and can treat various cancers such as melanoma, breast, gastrointestinal, genitonurinary, sarcoma and more. At the molecular level, cur can inhibit cell metastasis and induces cell apoptosis by regulating pro-inflammatory cell factors such as tumor necrosis, receptors such as epidermal growth factor receptor (EGFR), growth factors such as epidermal growth factor (EGF), transcription factors, apoptosis-related enzymes and proteins, cyclooxygenase-2 (COX2) and so on. An overview of cur pharmacological activities is shown in Fig 2.
Inflammatoy diseases
Lifestyle-related disease
Cancer
Others
Colorectal
β-Thalassemia
Ulcerative proctitis
Heart failure
cancer
Respiratory contraction
Crohn’s disease
Atherosclerosis
Pancreatic
Alcohol intoxication
Irritable bowel Syndrome
Alcoholism
cancer
Atherosclerosis
Rheumatoid arthritis
Liver dysfunction
Prostate cancer
Cadaveric
Chronic anterior
Kidney disease
Breast
Renal Transplantation
Uveitis
Myocardial infarction
Head and neck
Monoclonal gammopathy of
cancer
undefined significance (MGUS)
Cervical cancer
Depression
Skin cancer
Psoriasis Osteoporosis Muscular fatigue
Idiopathic
Curcumin
Inflammatory
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Pseudotumors
Neurodegenerative diseases
Pancreatitis Allergy Malaria Bacterial infection
Dejerine-Sottas diseases
Metabolic diseases
Alzheimer’s diseases
Diabetes
Arterial diseases
Diabetic nephropathy
Parkinson’s disease
Fungal infection
Epilepsy
Diabetic microangiopathy Lupus nephritis
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cancer
Renal transplantation
Nematode infection
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Fig 2. An overview of different pharmacological activities of curcumin.
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Unfortunately, cur oral bioavailability is low due to its limited water solubility and rapid metabolism and excretion. Various types of nanocarriers including nanoparticles[2], phospholipid complexation[3], nanoemulsion[4], solid dispersions[5], liposome[6], adjuvant with piperine[7] etc have been developed in order to improve cur oral bioavailability. These nanocarriers are discussed in the following sections highlight that nanocarriers can increase cur solubility and thus oral bioavailability in order to effectively treat various diseases.
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This review focuses on the strategies of improving cur oral bioavailability, the development of various cur formulations, preclinical (including in vitro and in vivo) and clinical studies of cur. Previously employed strategies are presented in the following sections using specific examples.
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Fig. 1. Chemical structures of curcumin (A) demethoxycurcumin (B) and bisdemethoxycurcumin (C).
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2.Reasons of low oral bioavailability of curcumin
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As seen in Fig 3., when cur is orally administered, a large proportion of cur is excreted through the feces while only small proportion is absorbed in the intestine, followed by rapid metabolism in plasma and the liver. Cur is mostly absorbed in the small intestines.
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The poor oral bioavailability may be due to poor absorption, high metabolism rate, rapid clearance and elimination from the body. For cur oral delivery, three physiological barriers in the gastrointestinal tract are related to the low oral bioavailability of cur. Firstly, physical barriers such as the upper mucus and the intestinal epithelium can restrict drug transport. Tight junctions in the epithelial cells can inhibit the absorption of molecules[8]. The mucus layer which consists of negatively charged glycoproteinsmucins and water are on the surface of the epithelium, and can inhibit the diffusion of cur due to the high moisture[9]. Secondly, chemical barriers such as gastric acid, bile and various digestive enzymes can cause the cur degradation, which may also influence its absorption in the blood[10]. Biochemical obstacles such as metabolic enzymes and epithelial cell p-glycoprotein efflux may make cur inactive and deliver cur back to the gastrointestinal lumen, which may also limit the gasterinternal absorption of cur[11]. Finally, the liver first-pass effect can inhibit the oral absorption of cur.
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The oral absorption of cur is extremely low which also contributes to the low cur oral bioavailability. It was shown that orally administered cur at a dose of 500 mg/kg only had 0.06 μg/mL maximum serum concentration, indicating only 1% oral bioavailability[12]. This is likely the result of limited gastrointestinal absorption of cur because of the poor solubility in water [13]. Cur possesses three protons, two phenolic protons and an enolic proton, which are ionizable in water. The pKa of the two phenolic protons is 10-10.5 and the pKa of the enolic proton is 8.5. In neutral or acidic pH, cur has limited solubility (the maximum solubility in pH 5.0 aqueous buffer is 11 ng/ml), and is not stable in alkali pH and can be hydrolyzed within the intestinal (pH 6.8) conditions, also contributing to its low oral bioavailability and absorption. In order to predict cur oral bioavailability, its in vivo distribution has been studied in various groups. In the study of Ravindranath et al., when cur was administered at a dose of 400 mg to rats, 40% of cur was excreted in the feces, with none found in urine, heart and blood. After 30 min administration of cur, 90% of cur was in the small intestine and stomach, however only 1% remained after 24 h[14]. When cur is administered orally, rapid metabolism and clearance of cur from the body occurs through formation of glucuronide and sulphates by conjugation in the intestine, and it can also interact with bile salts. Cur blood concentrations are extremely low after oral administration due to this rapid metabolism in the intestinal wall and liver[15~17]. When cur was orally administered at a dose of 10 or 12 g, maximum plasma cur concentrations in humans was still as low as less than 160 nmol/L[18]. Only minute amounts of cur, the majority of which is excreted in the urine and feces, were detected in the blood circulation after high-dose oral administration.
Absorption from small intestine
Distribution
Elimination
Portal circulation of curcumin
Blood Circulation curcumin
Liver Degradation of curcumin
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Coadministration
adjucants by inhibiting the
Increase the solubility of curcumin
Tissue Distribution curcumin
Lymphatic Transport of curcumin
Urinary Excretion of curcumin
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Fig 3. Absorption, distribution, metabolism and elimination(ADME) of curcumin preparations following oral administration. The curcumin oral bioavailability is increased by enhancing curcumin solubility, improving curcumin gastrointestinal stability, changing the absorption route of curcumin, coadministrating with adjucants.
3.Pharmaceutical Strategies of improving oral bioavailability
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of Curcumin
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In order to enhance cur oral bioavailability, several drug delivery strategies have been employed. Firstly, pharmaceutical strategies are used in order to enhance cur solubility, and then cur absorption in the gastrointestinal tract is enhanced resulting in overall improved oral bioavailability. Secondly, several nanoformulations can increase cur oral bioavailability by improving its gastrointestinal stability. Thirdly, cur nanoformulations can change the absorption route of cur, also improving oral bioavailability. Finally, cur oral bioavailability can be enhanced by co–administration of with other adjuvants which can inhibit the metabolism of cur. 3.1 Increase the solubility of curcumin 3.1.1 Solubility of curcumin in solvents The cur log P value is 3.29, indicating that cur has very low water solubility (11 ng/mL).
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Cur is soluble in various polar solvents including methanol (4.44 mg/mL), 2-butanone (2.17 mg/mL), ethanol (5.6 mg/mL), isopropanol (3.93 mg/mL), acetone (7.75 mg/mL), and 1,2-dichloroethane (0.5125 mg/mL). Cur had the highest solubility in DMSO (20 mg/mL), and is therefore the best solvent for preparation of cur nanoformulations. For preparation of cur nanoemulsions, the cur solubility in various oils is essential. The cur solubility in surfactants and oils is listed in Table 1, giving the oils with the higher solubility of cur that can be chosen as oil phase.
Solubility
Oil/Surfactant
Solubility
Miglyol 812
3.56 mg/g
Peceol
1.67±0.09 mg/ml
Miglycol 840
11.12 ± 0.82mg/ml
Ethyl oleate
0.43±0.02 mg/ml
Soybean oil
5.5 ± 0.4 mg/ml
ODO
9.39 ± 0.24 mg/ml
Mineral oil
0.5 ± 0.2 mg/ml
IPP
Castor oil
8.8 ± 0.4 mg/ml
oleic acid
1.39 ± 0.030 mg/ml
Cotton seed oil
4.9 ± 0.5 mg/ml
WL 1349
12.60 ± 0.20 mg/ml
Olive oil
3.3 ± 0.4 mg/ml
Cremphor RH40
86.27 ± 3.01mg/ml
Sesame oil
2.8± 0.2 mg/ml
Cremorphor EL
37.04±7.86 mg/ml
Peanut oil
3.2± 0.3 mg/ml
transcutol P
66.66 ± 1.20 mg/ml
Corn oil
1.48±0.06 mg/ml
Glycerine
3.95 ± 0.12 mg/ml
PEG 7 glyceryl cocoate
41 mg/g
Labrafac PG
0.90±0.01 mg/ml
PEG 600
250 mg/ml
Capryol PGMC
13.93±0.07 mg/ml
PEG 400
95.07 ± 4.50 mg/ml
Lauroglycol 90
4.24±0.09 mg/ml
Propylene glycol
11.89 ± 2.03 mg/ml
Capryol 90
7.75±0.11 mg/ml
Labrafac ® CC
13.0 ± 0.6 mg/ml
Lauroglycol Fcc
8.20±0.08 mg/ml
Labrafil ® M 1944 CS
26.1 ± 1.8 mg/m
Isopropyl myristate
3.1 ± 0.2 mg/ml
Labrafil M 2125 CS
0.60±0.01 mg/ml
Tocopherol acetate
3.0 ± 0.3 mg/ml
Labrafac lipophile WL
2.63±0.03 mg/ml
Plurol ® Oleique CC
31.6 ± 2.6 mg/ml
Labrafac WL 2609 BS
4.43±0.11 mg/ml
SPAN 80
8.8± 0.4 mg/ml
Labrasol
52.15±1.67 mg/ml
Tween-80
34.38±0.78 mg/ml
2.64 mg/g
Trancutol HP
112.98±17.40 mg/ml
CRMEL
41 mg/g
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Oil/Surfactant
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Table 1. Solubility of curcumin in oil/surfactant phase[19].
9.18 ± 0.32 mg/ml
3.1.2 Pharmaceutical strategies of improving solubility of curcumin In the GI tract, insoluble cur can be excreted with the feces, while only soluble cur is absorbed through intestinal epithelial cells. Thus, in order to improve the cur GI tract absorption, cur solubility needs to be enhanced. Various pharmaceutical strategies to improve cur solubility have been applied to improve the oral bioavailability of cur, and
are listed in Table 2. Among these formulations, cur micelles (CUR-MM) prepared by Sharvil Patil et al.[42] had a relatively higher bioavailability with the higher Cmax(0.24 ± 0.04 μg/mL) and AUC (6.13 ± 0.22 μg h/mL ) than other formulations. By incorporating cur in micelles using Gelucire ® 44/14 (GL44) and Pluronic F-127 (PF-127) as surfactants by a solvent evaporation method, the cur aqueous solubility was increased to 104 or 103 fold with increasing surfactant concentration. Besides, both the solubility, stability, antioxidant activity and bioavailability of cur were improved by incorporating cur in mixed surfactant vesicles. Table 2. Solubility of curcumin in various of curcumin preparations. Formulation
Solid dispersion
Solubility
Cmax
AUC
(Preparation vs.
(Preparation vs.
control)
control)
Refe rence
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Preparation
Hydroxy-
1000
184 ± 14
20685 ± 836
propylmethyl
fold
vs.
vs.
(HPMC),
increased
27 ± 8 ng/ml
1615 ± 114
Lecithin, Isomalt
(20 mg/rat)
[23]
ng.min/ml
(20 mg/rat)
α-glucosyl stevia (Stevia-G),
fold
polyvinylpyrrolidone
increased
vs. 3.78μg/ml min
(100 mg/kg)
(100 mg/kg)
95.60 ± 53.8
72.84±36.4
(50 mg/kg)
(50mg/kg)
vs.
vs.
15.65 ± 12.6
15.31±19.7
ng/ml
ng/ml.h
(50 mg/kg)
(50 mg/kg)
6.75±1.54
2066±332
(100 mg/kg)
(100mg/kg) vs.
vs.
367±21
1.55±0.21 μg/mL
μg/ml min
(100 mg/kg)
(100 mg/kg)
/
/
[31]
8.9μg/ml
/
/
[32]
The solubility of cur in
0.0291±0.0078
9.5931±1.3731
[33]
MSN-A was 10-fold
(50 mg/kg)
(50mg/kg)
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560 μg/ml
(PVP)
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640-fold increased
PVA
ur
articles
PLGA,
lP
poly[2-hydroxypropyl
(PHPMA )
[24]
vs.
Polyvinylpyrrolidone
methacrylate]
5.06(20mg/kg)
35.0 ng/ml
(PVP)
Nano/microp
86.6(20 mg/kg)
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13000
PLGA,
1.23 mg/ml~1.76
poly(vinyl alcohol),
mg/ml
[28]
[30]
poly(L-lysine) Soy protein isolate (SPI) Mesoporous silica
and 2-fold
vs.
vs.
than free cur and
higher
0.0105±0.0016
2.6714±0.3832
MSM-A group.
μg/mL
μg/ml min
(50 mg/kg)
(100 mg/kg)
Tween 80
The solubility value of
440.68±31.39
1513.48±
SAS-processed
AcCFR3TN2
204.71
AcCFR3TN1,
(100 mg/kg)
AcCFR3TN2
AcCFR3TN2 and
vs.
(100 mg/kg)
AcCFR3 were
351.00 ± 25.69
vs.
71.2 ± 3.5, 483.2 ± 4.3
AcCFR3TN1
923.25 ±
and 4.3 ± 2.3 μg/mL in
(100 mg/kg)
131.85
vs.
AcCFR3TN1
and 473.6 ± 4.0, 687.9
186.68 ± 13.92
(100 mg/kg)
± 5.6 and 112.5 ±
AcCFR3
vs.
3.8μg/mL in SGF of
(100mg/kg)
378.74 ± 24.96
pH 1.2.
vs.
AcCFR3
51.33±5.03
(100mg/kg)
ng/mL
vs.
native cur
102.81 ± 10.22
(50 mg/kg)
ng/mL min
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distilled water
[34]
native cur
(50 mg/kg)
0.5 mg/ml
99.72±30.47
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AN–CS–Arg
s
(100mg/kg)
vs.
vs.
11.00±1.17
65.12±7.42
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Cyclodextrin
Water solubility at pH
lP
Cyclodextrin
295.47±82.44
(100 mg/kg)
[35]
mg/mL
mg/ mL h
(100 mg/kg)
(100 mg/kg)
/
/
[38]
/
/
[38]
0.701±0.308
79.48±12.37
[38]
(50 mg/kg)
(50mg/kg)
vs.
vs.
0.189±0.088
28.69±15.16
μg/mL
μg/ml min
(50 mg/kg)
(50 mg/kg)
5 was increased by a factor of 104
HP-βCD, M-βCD
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na
HP-β-CD
0.3830~0.6086 mg/mL
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Micelles
15.2 mg/mL
DiDDAB:DDAB
The aqueous solubility
0.24 ± 0.04
6.13 ± 0.22
DMDTAB:DDAB
of cur increases in the
(10 mg/kg)
(10 mg/kg)
vs.
vs.
0.08± 0.03μg/mL
0.11 ± 0.04
(10 mg/kg)
μg h/mL
DiCTAB:DDAB
order of
104 or
103
DODAB:DDAB
[42]
(10 mg/kg) Emulsion
OP:Cremorphor EL,
21 mg/g
/
/
/
/
[43]
PEG 400, ethyl oleate Polymorphs
/
The
solubility
was
[54]
enhanced by twice. /
The solubility of cur
86.3 ± 12.58
79.8 ± 15.30
polymorphs was 17-
(250 mg/kg)
(250mg/kg)
fold higher than native
vs.
vs.
43.7 ± 6.45ng/ml
43.7±6.45
(250 mg/kg)
ng.h/ml
cur.
[56]
(250 mg/kg) Triethylamine (TEA),
1-10mg/ml ,
/
/
[58]
4-dimethylamino-
1.6mg/ml
23.35 ± 0.96
223.52±5.25
[59]
pyridine (DMAP),
(50 mg/kg)
(50mg/kg)
N,N0-
vs.
vs.
dicyclohexylcarbodiim
6.85 ± 0.36ng/ml
23.98 ± 4.89
ide (DCC)
(50 mg/kg)
h ng/mL
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Conjugates
hydrophilic
(50 mg/kg)
poly(ethylene glycol)
-p
(PEG)
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Solid dispersions are (semi)crystalline or amorphous drug dispersions with drug dispersed in the inert matrix[20]. Solid dispersions can increase the dissolution rate and solubility of hydrophobic drugs [21,22]. Ai Mey Chuah et al. prepared a cur amorphous solid dispersion (ASD) consisting of hydroypropyl methyl cellulose (HPMC), isomalt and lecithin by the hot melt extrusion method which could enhance AUC0–∞ of cur by 13-fold and Cmax of cur by 7 fold compared with native cur. The Cmax of ASD cur(20 mg/rat) was 184 ± 14 ng/ml, while Cmax of native cur was 27 ± 8 ng/ml(20 mg/rat).Cur ASD had enhanced solubility over native cur (>1000 times). Besides, the anti-inflammatory activity of ASD cur was also improved compared to native cur[23]. Kazunori Kadota et al. prepared cur ASD composed of polyvinylpyrrolidone (PVP), αglucosyl stevia (Stevia-G) and cur by the freeze-drying method with a seven-fold increased relative bioavailability.The Cmax and AUC0-180 of cur ASD (20 mg/kg) were 86.6 ng/ml min and 5.06 μg/ml min, and 35.0 ng/ml and 3.78 μg/ml/min of native cur(100 mg/kg). The cur solubility in cur ASD was 13,000-fold higher than native cur equilibrium solubility[24]. Cur ASD had a 6.7 fold enhanced oral absorption compared to native cur. Besides, they also prepared a cur ternary ASD system composed of cur, polyvinylpyrrolidone (PVP) K-30 and α-glucosyl hesperidin (hesperidin-G) using the solvent evaporation method, and the solubility of cur in ASD was 2600-fold higher than native cur[25]. Anant Paradkar et al. prepared cur-PVP ASD using different ratios of PVP.[26]. The solid dispersion of cur had a complete dissolution characteristic within 30min, whereas the physical mixture of cur had negligible release characteristics after 90 min, suggesting a good oral bioavailability of the cur ASD. Satomin onoue et al. prepared a cur nanocrystal solid dispersion and an amorphous solid dispersion, which had significantly enhanced dissolution profiles and 9-fold improved oral bioavailability compared with native cur. The Cmax and AUC0–inf of cur(100 mg/kg) were 35±8.0
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ng/mL and 11.0±0.5 μg/ml min, and 147± 53ng/ml and 27.1±6.7μg/ml/min of native cur(20 mg/kg).[27] Hisham Al-Obaidi et al et al. prepared a cur ternary ASD composed of cur, PHPMA (poly[2-hydroxypropyl methacrylate]) and PVP (polyvinylpyrrolidone) using the spray drying method. By incorporating PHPMA to immiscible binary solid dispersions, the stability of the amorphous form of cur was improved[28]. Cur solubility was enhanced to 560 μg/m by forming a Solutol ® HS15 ASD. Cur ASD stability was studied in pH 1.2, 6.8 and 7.4 buffer media, and the cur solid dispersion formulations were stable over 3 months. Solutol ® HS15 had an enhanced stabilizing effect compared to Kollidon ® 30 and Cremophor ® RH40. In vitro release profiles suggested that 90% of the drug was improved within 1 h. Dissolution and pharmacokinetic characteristics were improved compared with pure cur.[29]. The cur solid dispersion composed of 10:1 Solutol ® HS15 and cur had a 5fold increased AUC 0–12h. The Cmax and AUC0–12 h were 15.65 ± 12.6 ng/mL and 15.31 ± 19.7 ng/mL h of native cur, 95.60 ± 53.8ng/mL and 72.84 ± 36.4 ng/mL h of ASD cur, respetively(50 mg/kg). Different polymers concluding PLGA, chitosan, mesoporous silica, protein and polymeric nanoparticles have been developed in order to prepare cur nanoparticles with enhanced solubility.
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PLGA (poly(D,L-lactic-co-glycolic) can delivery cur orally with enhanced solubility and bioavailability. Xiaoxia Xie et al. prepared cur PLGA nanoparticles using the solidin-oil-in-water (s/o/w) solvent evaporation method, and the final particle diameters were 200 nm. [30]. The entrapment efficiency and drug loading were 91.96% and 5.75%, respectively. The water solubility was 640-fold enhanced compared with unformulated cur. 77% of cur was released from cur nanoparticles while 48% of cur was released in artificial gastric juice. The relative oral bioavailability was 5.6-fold enhanced compared with unformulated native cur. The Cmax and AUC0–t was 1.55± 0.21μg/mL and 367±21μg/ mL min of native cur(100 mg/kg), 6.75±1.54 μg/mL and 2066 ± 332 μg/ mL min of cur PLGA nanoparticles, respectively(100 mg/kg).The improved cur PLGA nanoparticles oral bioavailability may be attributed to improved water solubility, fast release characteristics in the intestinal juice, enhanced permeability and residence time in the intestinal tract and P-glycoprotein (P-gp)mediated efflux effect. Murali Mohan Yallapu et al. prepared cur PLGA nanoparticles with poly(L-lysine) and poly(vinyl alcohol) as stabilizers using a nano-precipitation method[31]. The nanoparticles had sustained release characteristics and improved solubility in aqueous solution. By increasing the concentration of PVA from 0% to 1%, cur solubility in PBS was increased from 1.23 mg/ml to 1.76 mg/ml. The cur nanoparticles cellular uptake was 6-fold higher in metastatic MDA-MB-231 breast cancer cells and 2-fold enhanced in cisplatin resistant A2780CP ovarian cells, with enhanced cell apoptosis observed with cur nanoparticles. Arun Tapal et al. prepared a curcumin-soy protein isolate (SPI) complex with enhanced solubility of cur[32]. The solubility of cur in SPI-curcumin complex was 8.9 μ g/ml, while free cur was 11 ng/ml in water, which was an 812-fold enhancement compared with free cur. Fluorescence spectroscopy showed that the complex was formed through
hydrophobic interactions. The SPI–cur complex had improved antioxidant activity.
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Mesoporous silica has promising potential in oral drug delivery due to the solubility increasing effect of drugs. Sandy Budi Hartono et al. prepared cur-amine functionalized mesoporous silica nanoparticles (MSN)[33]. Cur loaded amine functionalized MSN (MSN-A-Cur) released better and had improved solubility characteristics compared with amine MSM (MSM-A-Cur). They found that the solubility of cur in MSN-A was 10-fold and 2-fold higher than free cur and MSM-A, which may be due to the reduced particle size of cur loaded MSM-A and MSN-A compared with free cur. The oral bioavailability of MSM-A-Cur and MSN-A-Cur was enhanced compared with free cur. The Cmax and AUC0–6 h was 0.0105 ± 0.0016 μg/mL and 2.6714 ± 0.3832 μg/ mL min of native cur(50 mg/kg), 0.0291 ± 0.0078 μg/mL and 9.5931 ± 1.3731μg/ mL min of MSM-A-Cur, respectively(50 mg/kg).
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lP
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-p
In the study of Mohammed Anwar et al., cur nanoparticles were prepared with Tween 80 as a permeation enhancer and solubilizing agent by the supercritical anti-solvent (SAS) process[34]. Solubility and dissolution characteristics were enhanced compared with native cur. The solubility value of SAS-processed AcCFR3TN1, AcCFR3TN2 and AcCFR3 were 371.2 ± 3.5, 483.2 ± 4.3 and 94.3 ± 2.3 μg/mL in distilled water and 473.6 ± 4.0, 687.9 ± 5.6 and 112.5 ± 3.8μg/mL in SGF at pH 1.2, while cur was nearly insoluble in water and SGF. The increased solubility was likely due to the reduced particle size and hydrophilic coating of Tween 80, and the oral bioavailability of the cur nanoparticles was 11.6-fold enhanced compared with free cur. The Cmax and AUC0–t was 51.33 ± 5.03 ng/mL and 102.81 ± 10.22 ng/ mL min of native cur(50 mg/kg), 186.68 ± 13.92 ng/mL and 378.74 ± 24.96 ng/ mL min of AcCFR3(100 mg/kg), 351.00 ± 25.69 ng/mL and 923.25 ± 131.85 ng/ mL min of AcCFR3TN1(100 mg/kg), 440.68 ± 31.39 ng/mL and 1513.48 ± 204.71 ng/ mL min of AcCFR3TN2(100 mg/kg) , respectively.
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The oral bioavailability of cur chitosan nanoparticles was enhanced through enhancing cur solubility. Mazhar Ali Raja et al. prepared cur loaded AN–CS–Arg NPs (AN–CS– Arg/Cur NPs) (Acrylonitrile (AN), hydrophilic arginine (Arg), amphiphilic chitosan (CS)) with a particle size of 218 nm by a simple sonication method[35]. Cur aqueous solubility was improved compared with native cur, with the solubility of cur in AN– CS–Arg NPs 0.5 mg/ml compared to 11 ng/ml of native cur, nearly a 5×10 4 –fold increase. AN–CS–Arg NPs had sustained release characteristics, enhanced mucoadhesion effect, stronger cell uptake and improved cytotoxicity effect against HT29 cells. Furthermore, the oral bioavailability was also improved compared with native cur. The Cmax and AUC0–24 h was 99.72±30.47 mg/mL and 295.47±82.44 mg/ mL h of AN–CS–Arg/Cur NPs(100 mg/kg),11.00±1.17 mg/mL and 65.12±7.42 mg/ mL h of Cur solution, respectively(100 mg/kg). Cur was encapsulated in alginatechitosan-pluronic composite nanoparticles using ionotropic pre-gelation followed by
the polycationic cross-linking method[36]. Pluronic F127 was formulated in the nanoparticles to enhance the cur solubility. The particle size of the spherical nanoparticles was 100 nm, and cytotoxicity assays showed that 500 μg/mL of nanoparticles were nontoxic to HeLa cells. The IC50 of free cur and cur nanoparticles was 13.28 and 14.34 μM.
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Cyclodextrins are cyclic oligosaccharides with a hydrophilic surface and lipophilic cavity, and are used as stabilizing and solubilizing agents in pharmaceutical preparations to improve the solubility of hydrophobic drugs such as cur. Commonly used CDs are βCD, γCD, hydroxypropyl-β-cyclodextrin (HPβCD), methylβ-CD (MβCD) and more. Vivek R. Yadav et al. prepared a novel cyclodextrin complex of curcumin (CDC) by incorporating cur into γCD, HPβCD, MβCD and βCD in order to enhance cur solubility[37]. The ability of cur solubility enhancement was in the order of: HPβCD>MβCD>βCD>γCD. It was apparent that the bulky side group of the cur phenyl moiety could fit well within the HPβCD cavity, which is indicated in Fig 4. Compared with free cur, CDC demonstrated enhanced cellular uptake ability, longer half-life in cancer cell lines, an antiproliferative effect and anti-inflammatory effect. Hanne Hjorth Tønnesen et al. prepared cur cyclodextrin complexes, where the water solubility was enhanced to 104 at pH 5[38]. Besides, in alkaline conditions cur stability was enhanced and photodecomposition rate was also improved. In the study of Martin Purpura et al., they saw that their γ-cyclodextrin cur formulation had a significantly increased bioavailability in healthy humans compared with unformulated cur[39]. The Cmax and AUC0–12 h was 0.3 ng/mL and 19.7 ± 2.6 ng/ mL h of native cur, 1.2 ng/mL and 327.7 ± 58.1 ng/ mL h of Cur solution , respectively. Cur (CUR)-hydroxypropyl-β-cyclodextrin (HP-β-CD) inclusion complex (CUR-HP-β-CD) were prepared by Ning Li et al., with a mole ratio of cur to HP-β-CD of 1:7. The solubility of cur was enhanced, the cytotoxicity of cur was improved and the oral bioavailability of cur in CUR-HP-β-CD was 2.77-fold higher than native cur. The Cmax and AUC0–t of native cur(50 mg/kg) was 0.189±0.088 μg/mL and 28.69±15.16 μg min/mL, while 0.701±0.308 μg/mL and 79.48±12.37 μg min/mL of CUR/HP-β-CD inclusion(50 mg/kg)[40].
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O
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H3CO
H OCH3 OH
HO
Fig 4. The proposed structure of curcumin cyclodextrin complex. Self-assembled polymeric micelles (PMs) are a promising oral drug delivery system due to the advantages of improving drug solubility in water. It has been reported that
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cur can be solubilized in a micellar solution up to 40 times [41]. Thus, micelles are excellent drug delivery systems for the delivery of cur. Sharvil Patil et al. prepared cur micelles (CUR-MM) using Gelucire ® 44/14 (GL44) and Pluronic F-127 (PF-127) as surfactants by a solvent evaporation method. The particle size of CUR-MM was 188 ± 3 nm and EE of CUR-MM was 76.45 ± 1.18% w/w. Due to the solubilization effect of cur in the micelles and the PF-127 and GL-44 P-gp inhibition effect, the cytotoxic activity of CUR-MM was 3-fold enhanced and oral bioavailability was 55-fold increased compared with native cur.[42]. The solubility of cur was improved by incorporating cur in mixed surfactant vesicles composed of single and double chain ionic surfactants. The cur aqueous solubility was increased to 104 or 103 fold with increasing surfactant concentration. Mixed surfactant vesicles could decrease cur degradation in alkaline media. Both the solubility, stability and antioxidant activity of cur were improved by incorporating cur in mixed surfactant vesicles.The Cmax and AUC0–t of native cur(10 mg/kg) was 0.08 ± 0.03 μg/mL and 0.11 ± 0.04 μg h/mL, while 0.24 ± 0.04 μg/mL and 6.13 ± 0.22 μg h/mL of CUR-MM(10 mg/kg).
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Nanoemulsions are thermodynamically stable and transparent systems of oil and water, stabilized by a surfactant or mixture of surfactant and cosurfactant. It has been reported that cur nanoemulsions can enhance the bioavailability and oral absorption of cur.
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Over recent years, many emulsion curcumin formulations which can enhance cur bioavailability by increasing the solubility of cur have been developed and select studies are highlighted. In order to enhance cur oral absorption and solubility, a cur loaded self-microemulsifying drug delivery system (SMEDDS) was prepared by Jing Cui et al using ethyl oleate as the oil phase, OP and Cremorphor EL as surfactants and PEG-400 as co-surfactant. Cur solubility in SMEDDS was increased to 21 mg/g, and more than 95% of cur in the nanoemulsion was dissolved in 20min compared with 2% for unformulated cur within 60min. The cur absorption mechanism in the intestine was via passive transfer, and oral absorption was improved compared with its suspension[43]. Jinglei Li et al. prepared a chitosan coating cur nanoemulsion composed of lecithin, Tween 80 and MCT oil by the ultrasonication method, and the loading efficiency and ability was 95.10 % and 0.548 mg/ml, respectively[44]. The water dispersity of the cur nanoemulsion was increased by 1400 fold. High, middle and low molecular weight chitosan (190-310, 30, 3 kDa) was applied for coating nanoemulsions, and it was found that cur had different solubility varying from 13.97 to 22.14 mg/g, when the ratio of surfactant, co-surfactant and oil was changed. Cur was absorbed in the intestine through passive transfer, and the cur nanoemulsion oral absorption was improved compared with cur suspension. The solubility of cur in the oil phase of an emulsion is important for their preparation to improve the drug loading (Table 1). Dong-Jin Jang et al. prepared a cur dry emulsion for oral delivery of cur[45]. Cur has higher solubility in Plurol ® Oleique CC497 compared with other oils, and thus Plurol ® Oleique CC497 was chosen as the oil phase.
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The release of cur from the cur dry emulsion was enhanced compared with native cur, and the Cmax and AUC were 12.0 and 7.1 fold higher than native cur.The Cmax and AUC0–24h of native cur was 8.5 ± 2.4 μg/mL and 24.2 ± 7.6 ng h/mL, while 102.4 ± 32.7 μg/mL and 171.0 ± 45.1 ng h/mL of cur dry emulsion(50 mg/kg).Yi-Dong Yan et al. prepared cur liquid self-emulsifying drug delivery system (SEDDS) using Lauroglycol Fcc as the oil phase, Labrasol as the surfactant and Transcutol HP as the co-surfactant, the ratio of which was 15.0:70.8:14.2 [46]. Lauroglycol Fcc was chosen as the oil phase because of the high solubility of cur compared with other oil phases. The cur oral absorption was found to be higher than native cur. The Cmax and AUC of cur SEDDS was 33.97±9.84 ng/mL and 37.05±17.73 ng h/mL at the dose of 25 mg/kg, while155.56±18.34 ng/mL and 282.54±61.37 ng h/mL at the dose of 100 mg/kg. Chaonan Wang et al. prepared a cur loaded emulsion[47]. The oil phase was MCT containing 10% ethanol, which could further improve the cur solubility in the oil phase. The cur emulsion oral bioavailability was 4.8-fold higher compared with cur suspension. CUR@BD-1 emulsion had the Cmax and AUC0 – 24h of 270 ng/mL and 1511 ng h/mL(60 mg/kg), while the Cmax and AUC0–24h of CUR/Tween 20 suspension was 37 ng/mL and 317 ng h/mL (60 mg/kg).MEDDS also improves cur dissolution and bioavailability, therefore Xuemei Wu et al. prepared cur loaded self-microemulsifying drug delivery system (SMEDDS) composed of 20% isopropyl myristate, 20% ethanol and 60% Cremophor RH40 ®, and the cur concentration in SMEDDS was 50 mg/ml[48]. Cur had enhanced solubility with 1,2-propylene glycol, which was thus chosen as cosurfactant. The cur solubility in cremophor RH40 ® was 150 mg/g, showing a good solubilizing effect of cur. Cur released from SMEDDS completely within 10 minutes, and the relative oral bioavailability of cur SMEDDS was 1213% compared with cur suspension. The Cmax and AUC0–∞ of cur microemulsion were 196.56μg/L and 277.06 μg/L·h while that of cur suspension were 63.89μg/L and 21.76 μg/L·h. Kashif Ahmed et al. prepared a cur nanoemulsion using short, medium, and long chain triacylglycerols (SCT, MCT and LCT) as lipids[49]. The maximum solubilized amount of cur in SCT, MCT and LCT was 0.30 ± 0.10 wt.%, 0.79 ± 0.2 wt.%, 2.98 ± 0.18 wt.%, respectively. However, cur emulsion cannot be formed using pure SCT due to the Ostwald ripening effect, as SCT has a high solubility in water. Cur bioaccessibility decreased in the different medium in the order of: MCT > LCT >> SCT. The bioavailability was 41±4% of cur LCT nanoemulsion, 58 ± 6% of cur MCT nanoemulsion, 1 ± 1% of cur SCT nanoemulsion, 20 ± 3% of cur LCT:SCT nanoemulsion.Yanyu Xiao et al. prepared a curcuminoid-loaded microemulsion (CurME) with enhanced cur bioavailability[50]. Cremophor RH 40, labrafac lipophile WL 1349, and glycerine were used as the oil phase, cremorphor RH40 as surfactant and glycerine as cosurfactant, both of which had a better solubility than other vehicles. CurME had a 9.6-fold enhanced relative bioavailability compared with cur suspension. Cmax and AUC0-t of cur suspension were 5.39 ± 0.13 ng/mL and 18.66 ± 1.54 ng h /mL, while that of cur-ME were 66.19 ± 4.43 ng/mL and 180.97 ± 2.71 ng h /mL. Saujanya Gosangari et al. prepared a cur self-emulsifying formulation with different formulations using different polymers as precipitation inhibitors. It was found that by incorporating 10% polymer such as
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polyvinylpyrrolidone (PVP) or hydroxypropyl methyl cellulose (HPMC) into curcumin emulsions, the cur concentration was 100-fold higher than that of the formulation without added polymer. They found that the inhibition precipitation effect of polymers was in the order of PVP-K30 < PVP-K90 < HPMC[51]. Patcharawalai Jaisamut et al. prepared a cur loaded self-microemulsifying formulation by using Capryol 90 as the oil phase, Cremophor EL as surfactant, and Labrasol as co-surfactant[52]. Cur had higher solubility in the selected vehicles (Capryol 90: 6.71 mg/ml, Cremophor EL: 85.98 mg/ml, Labrasol: 62.99 mg/ml) than other solvents. The antioxidant activity, cytotoxic effect and oral bioavailability were enhanced compared with native cur. Saipin Setthacheewakul et al. formulated cur into liquid self-microemulsifying drug delivery systems (SMEDDS) and SMEDDS pellets[53]. In cur loaded SMEDDS, Cremophor EL (113.94 mg/ml) and Labrasol (88.26 mg/ml) (1:1) were used as surfactants, Labrafac PG (20.24 mg/ml) and Capryol 90 (42.34 mg/ml) (1:1) were used as the oil phase and PEG400 (153.07 mg/ml) was used as co-surfactant (the solubility of cur in vehicles is listed in parenthesis). The release rate of cur emulsion was 16-fold enhanced compared with native cur, and the oral absorption of liquid cur-SMEDDS and pellet cur-SMEDDS were 14- and 10-fold enhanced compared with cur suspension. The Cmax and AUC0– ∞ of cur--SMEDDS(50 mg/kg) were 4.38 ± 0.09 μg/mL and 537.90 ± 13.82 ng h/ml, that of Cur-SMEDDS pellets(50 mg/kg) were 4.17 ± 0.32 μg/mL and 408.13 ± 14.18 ng h/ml, while the Cmax and AUC0–∞ of cur suspension(50 mg/kg) were 0.25 ± 0.04 μg/L and 38.61 ± 10.61 ng h/ml. Palash Sanphui et al. reported two new cur crystalline polymorphs (Form 2 and Form 3, the original structure of which is Form I) and an amorphous cur [54]. The solubility of the polymorphs was twice enhanced. The intrinsic dissolution rates in 40% EtOH–water of Form 2 was nearly 4 times higher than Form I, and the amorphous was nearly twice higher than Form I. This suggests that new forms of cur crystalline polymorphs are suitable for oral administration in order to enhance cur bioavailability and solubility. In another study, cur co-crystals were synthesized with 5 coformers (nicotinamide, p-hydroxybenzoic acid, ferulic acid, hydroquinone, and L-tartaric acid)[55]. Both of the 5 cur co-crystals had lower melting points and dissolved faster than free cur, with curcumin-nicotinamide showing the fastest dissolution rate. Yogesh B. Pawar et al. investigated the phase behavior and oral bioavailability of the amorphous form of Cur (CRM-A)[56]. CRMA aqueous solubility was 17-fold higher than normal cur. AUC and Cmax were enhanced by 1.45-fold and 1.97-fold respectively, however the rapid devitrification may limit CRM-A oral bioavailability. The Cmax and AUC0–∞ of native cur (250 mg/kg) were 43.7 ± 6.45 ng/ml and 55.0 ± 10.41 ng.h/ml, that of CRM-A were 86.3 ± 12.58 ng/ml and 79.8 ± 15.30 ng.h/ml after oral administration. Cur can conjugate with small molecules such as amino acids and other hydrophilic polymers which can enhance cur aqueous solubility. Select amino acids including alanine, phenylalanine, proline, glycine, phenyl glycine and cysteine were coupled to cur[57]. K.S Parvathy et al. prepared cur-amino acid conjugates through conjugation of cur at the phenolic position with amino acids in dry dioxane using triethylamine (TEA) and (4dimethylamino-pyridine (DMAP) as catalysts, N,N 0 -dicyclohexylcarbodiimide (DCC) as the coupling agent, and finally purified by column chromatography[58]. Cur aqueous
ro of
solubility was enhanced to 1-10 mg/ml. They found that the conjugates of cur with proline and glycine had the highest water solubility (10 mg/ml). In antioxidant assays experiments, cur derivatives conjugated with alkyl-substituted amino acid concluding alanine, valine, cysteine exhibited lower IC50 values compared with native cur. Hongzhi Qiao et al. prepared an amphiphilic curcumin polymer (PCur) composed of hydrophobic cur (Cur) and hydrophilic poly(ethylene glycol) (PEG) linked by a disulfide bond [59]. The water solubility of cur was improved to 1.6 mg/ml for the curPEG conjugate. The particle size of the cur-PEG conjugate was 134.4 nm and the zeta potential was -3.3 mv, both of which led to the accumulation of drug in the gut inflamed regions. Cur-PEG conjugates had a limited drug release profile under the gastrointestinal tract conditions (GIT), while a significant release characteristics were observed in the region of colon with reduced bacterials. Besides, cur-PEG conjugates also had increased transmembrane permeability and low cytotoxicity resulting in improved oral bioavailability. The Cmax and AUC0–∞ of PCur (50 mg/kg) were 23.35 ± 0.96 ng/mL and 223.52 ± 5.25 h ng/mL, and that of Cur suspension(50 mg/kg) was 6.85 ± 0.36 ng/mL and 23.98 ± 4.89 h ng/mL.Thus, cur-PEG conjugates are an excellent oral colon delivery system which have improved bioavailability.
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3.2 Increase the stability of curcumin preparations in gastrointestinal tract Various pharmaceutical strategies have been developed in order to enhance cur oral bioavailability by improving the gastrointestinal stability of cur (Table 3). By coupling to various of gastro-resistant polymers, cur can be protected from the harsh gastrointestinal environment against destruction, giving a higher solubility and controlled-release characteristics.
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Among these formulations, polymeric micelles prepared by Jiang Ni et al.had a higher bioavailability than other formulations with a higher Cmax(5.365 ± 1.246 μg/mL ) and AUC(77.261 ± 12.485 μg.h/mL) than other formulations at a dose of 15 mg/kg[61]. Carboxy methyl chitosan was used as a P-gp mediated efflux and gastrointestinal absorption enhancer, and heparin-all-trans-retinoid acid (LHR) as the loading material by a chemical bonding method, which could improve the stability of cur polymeric micelles in physiological pH and the oral bioavailability of cur.
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Silica is a gastro-resistant polymer which can improve the stability of liposomes in the harsh gastrointestinal track environment. It has been reported that the silica shell has enhanced stability at pH 1.2, which can protect the nanoformulation inner structure. The silica shell is hydrolysed at pH 7.4, thus controlling the release of cur. Chong Li et al. prepared cur silica-coated liposomes (CUR-SLs), which exhibited hjgher GIT stability compared with cur liposome. As well, the CUR-SLs oral bioavailability was 3.31 fold higher than cur liposome, the C max CUR-FL were higher than that of cur suspension(446.66 vs 71.35 ng .L−1 ) at a single dose of 50 mg/kg, suggesting that CURSLs was an excellent oral delivery system[60]. Chitosan, a natural polysaccharide, is widely applied for oral delivery of drugs, and can
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prolong the absorption of cur due to its mucoadhesive properties. Jiang Ni et al. developed mixed polymeric micelles made from carboxy methyl chitosan as a P-gp mediated efflux and gastrointestinal absorption enhancer, and heparin-all-trans-retinoid acid (LHR) as the loading material by a chemical bonding method, which could improve the stability of cur polymeric micelles in physiological pH and the oral bioavailability of cur. It has been reported that the Cmax and AUC0-48h of CsACNC/LHRMPMs-3 were 5.365 ± 1.246 μg/mL and 77.261 ± 12.485 μg.h/mL, while that of CsA suspension was 0.610 ± 0.109 μg/L and 5.107 ± 1.629 μg.h/mL after a single oral dose of 15 mg/kg.[61]. The chitosan coating prevented phase separation of the cur nanoemulsion and inhibited cur degradation. When cur nanoemulsion was treated with thermal treatment and UV irradiation, the degradation of cur could be inhibited when nanoparticles were coated with middle and high molecular weight chitosan. Jinglei Li et al. prepared a cur nanoemulsion which was composed of lecithin, Tween 80 and MCT oil[62]. The cur nanoemulsion was coated with low (3kDa), middle (30kDa) and high molecular weight (190-310kDa) chitosan, which could prevent the phase separation of cur nanoemulsion and inhibit cur degradation, thus improving the gastrointestinal stability of cur. Chitosan with middle and high molecular weight could promote the hydrolysis of cur nanoemulsion, which enhanced cur gastrointestinal tract stability, thus improving the oral bioavailability of cur. Warayuth Sajomsang et al. prepared cur micelles composed of pH responsive amphiphilic chitosan N-benzyl-N,O-succinyl chitosan (BSCS)[63]. They found that the release profile of cur in the stomach (pH 1.2) was slow, and the micelles were slowly release in the intestine (pH 5.5–7.4) without any burst effect, highlighting the stability of cur micelles. In the pH of the stomach (1.2), during the first 10 hours no more than 25% cur was released from cur micelles, while at pH 5.5, 6.8 and 7.4, 38%, 50% and 50% of cur were released from micelles within 10 h respectively. The pH-dependent release profile can be explained by the degree of succinic acid ionization on the BSCS micelles surface at different pH values. The pKa1 value of succinic acid is 4.21, thus when the pH in the medium is higher than the pKa1 value, the micelles are dissociated, and thus, cur micelles release faster at pH 5.5, 6.8 and 7.4 than at pH 1.2. Cytotoxicity, cellular uptake and apoptosis were also improved compared with unformulated cur, where cytotoxicity assays indicated that IC50 of cur micelles was 3.6-, 4.7-, 12.2- fold lower than that of free cur in SiHa, HeLa and C33a cells. Cur micelles cell uptake was 6-fold enhanced compared with unformulated cur in all cancer cells. Various polymers have been applied as gastroresistant polymers which have a mucoadhesion inhibition effect, resulting in a high stability of cur in the gastrointestinal tract. Among these polymers, Eudragit is a gastro-resistant polymer, which can protect cur from degradation in the gastrointestinal tract. Ana Catalan-Latorre et al. prepared freeze-dried eudragit-hyaluronan multicompartment liposomes using phospholipid, Eudragit-S100 and hyaluronan sodium salt. By incorporating different ratios of the gastroresistant polymer eudragit-hyaluronan in the liposome, cur was protected against GIT conditions with enhanced absorption in the intestinal region[64]. Elisabet Martí Coma-Cros et al. prepared cur loaded liposomes using the anionic copolymer Eudragit
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® S100 containing also either Nutriose ® FM06 (Eudragit-nutriosomes) or hyaluronan (Eudragit-hyaluronan liposomes)[65]. Under the condition of gastrointestinal fluids, Eudragit-nutriosomes were found to be more stable than Eudragit-hyaluronan liposomes. Sharvil Patil et al. prepared cur micelles (CUR-MM) using Pluronic F-127 (PF-127) and Gelucire ® 44/14 (GL44) as surfactants by a solvent evaporation method. The CUR-MM particle size was 188 ± 3 nm and CUR-MM EE was 76.45 ± 1.18% w/w. The cytotoxic activity of CUR-MM was 3-fold higher than native cur, and the oral bioavailability was 55-fold higher than unformulated cur, the Cmax(0.24 ± 0.04 vs 0.08 ± 0.03μg/ml) and AUC0-t (6.13 ± 0.22 vs 0.11 ± 0.04 h/μg/ml)of CUR-MM were much higher than that of native cur, after an oral administration dose of 10 mg/kg, likely due to solubilization of cur in micelles and the P-gp inhibit effect of PF127 and GL44[66]. Yuwei Duan et al. prepared cur-loaded methoxy poly(ethylene glycol)-poly(lactide) (mPEG-PLA)/Dα-tocopherol polyethylene glycol 1000 succinate (TPGS) mixed micelles (CUR-MPPTPGS-MMs) through the thin film diffusion method. The drug loading achieved was 16.1%, the particle size was 46.0 nm, and due to the low critical micelle concentration (CMC) and dilution stability, CUR-MPP-TPGS-MMs had enhanced stability in the gastrointestinal fluid conditions. The duodenum showed good absorption ability for CUR-MPP-TPGS-MMs. The Cmax of CUR-MPP-TPGS-MMs(75 mg/kg) was 197.88 ± 61.71ng/ml, while that of Cur suspension(75 mg/kg) was 27 ± 1.37 ng/ml. The AUC0–24 of CUR-MPP-TPGS-MMs was 9-fold higher than that of cur suspension.(1.02± 0.93 vs 0.11 ± 0.029 μg/ml h) with a relative bioavailability of 927.3%, suggesting that the oral bioavailability was also improved compared with unformulated cur[67]. Hamidreza Kheiri Manjili et al. prepared CUR-loaded mPEG-PCL (CUR/mPEG-PCL) micelles with a zeta potential of -11.5 mV, average size of 81.0nm and loading capacity of 20.65 ± 0.015% using a single-step nano-precipitation method. Pharmacokinetic profiles showed that CUR-loaded micelles had an excellent oral bioavailability.The Cmax of CUR-loaded micelles was much higher than that of CUR aqueous solution(29.97 ± 0.012 vs 3.99 ± 0.01 ng/mL), while the AUC0–t of CUR-loaded micelles and CUR aqueous solution were 452.695 ± 0.75 h ng/mL and 8.561 ± 0.872 h ng/mL after oral administration at a dose of 50 mg/kg[68]. Mixed surfactant vesicles were prepared, composing of single chain ionic surfactants and equimolar ionic surfactants, which could improve the solubility of the incorporated cur. The mixed surfactant vesicles could also reduce the degradation of cur in alkaline media. Both the stability, solubility and antioxidant activity of cur were improved by incorporating cur in mixed surfactant vesicles[69]. Cur pickering emulsion digestion and storage stability were investigated by Ali Marefati et al. [70]. During 24 h storage, heat treated curcumin Pickering emulsions had greater encapsulation stability than non-heat treated cur Pickering emulsions (78.2% vs. 38.3%), and in simulated in vitro digestion, intestinal (86.3%vs. 40.2%) and oral (95.3% vs. 69.6%), however there was no significant difference in simulated gastric in vitro digestion (82.4% vs 86.2%). The cur emulsion stability under in vitro simulated intestinal environment with or without bile salts was investigated, and while the changes were larger in samples with bile salts, the changes
were also slighter in heat-treated samples. The results showed that cur Pickering emulsions have great potential in cur drug delivery. Table 3.Pharmaceutical strategies for improving the oral bioavailability of curcumin by increasing the gastrointestinal stability. Cmax AUC Gastrore- Preparation Observation Refer (Preparation vs. (Preparation vs. sistant -ence control) control) polymers Silica
Liposome
446.66
673.79
CUR-SLs had significantly
vs
vs
higher gastrointestinal track
71.35 ng/.L
203.64
stability compared with cur
(50 mg/kg)
ng ⋅ h/ L
liposome.
[60]
Polymeric
5.365 ± 1.246
77.261±12.485
LHR can improve the stability of
micelles
vs.
vs.
cur micelles.
0.61± 0.109
5.107 ± 1.629
μg/mL (15 mg/kg)
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Nanoparticle
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Eudragit
Liposome
Chitosan coating can improve the gastrointestinal stability of cur.
[62]
Cur loaded micelles had
[63]
stability.
0.73 ± 0.31
4.98 ± 2.28
Cur SLNs have enhanced
vs.
vs.
stability, controlled release
0.29 ± 0.11
0.56 ± 0.14
characteristics in SIF, and
μg/L
μg.h/L
higher oral bioavailability.
(50 mg/kg)
(50 mg/kg)
/
/
Cur nanoparticle did not degrade
[77]
[74]
more rapidly than free cur in mouse plasma.
/
/
Cur is protected against harsh conditions of the gastro-intestinal
[64]
tract.
Liposome
/
/
Eudragit-nutriosomes had enhanced stability compared with Eudragit-hyaluronan liposomes under gastrointestinal fluids.
Pluronic F-
[61]
improved gastrointestinal track
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(SLNs)
/
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micelles
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/
Polymeric
nanoparticles
(15 mg/kg)
/
Nanoemulsion
Solid lipid
μg.h/mL
re
Chitosan
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(50 mg/kg)
Micelles
0.24 ± 0.04
6.13 ± 0.22
The cytotoxic activity (3-folds)
[65]
127 (PF-
vs
vs
and oral bioavailability (around
127),
0.08±0.03
0.11 ± 0.04
55-folds) were also improved.
Gelucire ®
μg/ml
h/μg/ml
44/14 (GL44)
(10 mg/kg)
(10 mg/kg)
197.88± 61.71
1.02± 0.93
Cur solubility, stability and
vs.
vs.
antioxidant activity was
27 ± 1.37
0.11 ± 0.029
enhanced.
ng/ml.
μg/ml h
Micelles
(75 mg/kg) Solutol®HS1
Solid dispersion
5
[67]
(75 mg/kg)
95.60 ± 53.8
72.84±36.4
Oral bioavailability was
vs.
(50mg/kg)
enhanced compared with native
15.65 ± 12.6
vs.
cur;1.3% of cur was degraded pH
ng/ml
15.31±19.7
1.2 buffer,
(50 mg/kg)
ng/ml.h
while 2.4% of cur was degraded
(50 mg/kg)
in pH 6.8 buffer, 4.2% of cur was
[28]
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mPEG-PCL
[66]
degraded in pH 7.4 buffer. 29.97 ± 0.012
452.695 ± 0.75
The oral bioavailability of cur
soy soluble
vs
vs.
emulsion was 11-fold higher than
polysacchari
3.99 ± 0.01
8.561 ± 0.872
cur suspension.
de
ng/mL
h ng/mL
(50 mg/kg)
(50 mg/kg)
Hydroxyprop
/
Emulsion
ylmethyl(HP MC) Liposome
Caseinate
Solid lipid
(NaCas),
nanoparticles (SLNs)
Eudragit-nutriosomes had
/
The physico-chemical stability of
[176]
[177]
cur SLNs was enhanced.
Nanosuspensions and
nanoparticles
vs.
vs.
CUR/TPGS nanosuspensions
(SLNs)
2.12 ± 0.34
14.29 ± 1.58
were 3.7 and 3.18-fold higher
μg/mL
μg.h/mL
than cur suspension.
(50 mg/kg)
(50 mg/kg)
/
[70]
enhanced stability
136.27 ± 10.85
Nanoparticle
[68]
enhanced.
7.51 ± 0.44
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bovine serum
The oral bioavailability was
Solid lipid
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TPGS /Brij78
/
/
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Pectin
/
/
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Bile salts
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Emulsion
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Casein,
/
albumin
The oral bioavailability of cur
[72]
[57]
was enhanced.
(BSA) Zein
Nanoparticle
/
/
In vitro gastrointestinal stability of cur nanoparticles was enhanced;
[179]
3.3 Change the absorption route of curcumin preparations Cur preparations can change the absorption route of cur, thus improving the oral bioavailability. Polymers with absorption-promoting effects have been applied in order to increase the oral bioavailability of cur, and these absorption mechanisms are summarized in Table 4. Among these formulations, cur micelles prepared by Jiang Ni et al. had a reletively higher bioavailability with a higher Cmax(5.365 ± 1.246 μg/mL)and AUC0-48h（77.261 ± 12.485) than other formulations[71]. Cur micelles were composed of a cur-carboxymethyl chitosan (CNC) conjugate and a lowmolecular-weight heparin-all-transretinoid acid (LHR) conjugate. CNC had the P-gp efflux inhibit effect, and can enhance the oral bioavailability of cur micelles.
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3.3.1 P-gp inhibit effect Several pharmaceutical strategies which have a P-gp inhibition effect have been developed in order to enhance cur oral bioavailability. Chitosan and its derivatives display a P-gp inhibitory effect, which may be applied for the delivery of cur. Jiang Ni et al. prepared cur micelles composed of a cur-carboxymethyl chitosan (CNC) conjugate and a low-molecular-weight heparin-all-transretinoid acid (LHR) conjugate[71]. CNC could inhibit the P-gp efflux effect and enhance the gastrointestinal absorption, and the oral absorption of cur MPMs was also enhanced by inhibiting the P-gp efflux effect (Fig 5). The oral bioavailability of CsA-CNC/LHRMPMs-3 was enhanced with a higher Cmax(5.365 ± 1.246 vs. 0.610 ± 0.109μg/mL) and AUC048h（77.261 ± 12.485 vs.5.107 ± 1.629μg.h/mL）than that of CsA suspension after oral administration at a single dose of 15 mg/kg. Cur solid lipid nanoparticles (CurSLNs) were prepared by Hongyu Ji et al. TPGS and Brij78 were used as P-gp inhibition excipients, which could both enhance the solubility of cur and the intestinal absorption.[72]. Surfactants can disrupt tight junctions in intestinal cells. The Cur-SLNs displayed a sustained release profile and 942.53 % relative bioavailability compared with cur suspension. It has been reported that the Cmax and AUC0–∞ of Cur-SLNs were 7.51 ± 0.44 μg/mL and 136.27 ± 10.85μg.h/mL, while that of Cur suspension was 2.12 ± 0.34 μg/mL and 14.29 ± 1.58 μg.h/mL after a single oral dose of 50 mg/kg. Sharvil Patil et al. prepared cur loaded mixed micelles (CUR-MM) using Pluronic F-127 (PF-127) and Gelucire ® 44/14 (GL44) as excipients through a solvent evaporation method. The particle size of CUR-MM was 188 ± 3 nm and EE was 76.45 ± 1.18% w/w. The cytotoxic activity of CUR-MM was 3-folds higher than native cur, while oral bioavailability was 55-fold enhanced compare with native cur, the Cmax(0.24 ± 0.04 vs. 0.08 ± 0.03 μg/mL) and AUC 0-t (6.13 ± 0.22 vs.0.11 ± 0.04 h/μg/mL) of CUR-MM(10 mg/kg) were higher than that of native cur(10 mg/kg), likely as a contribution of solubilization of cur in micelles and PF127 and GL44 P-gp inhibition effect [73].
Mixed polymeric micelles Low-molecular-weight heparin-all-trans-retinoidpolymeric acid micelles (MPMs) Cyclosporine A
P-gp pumps
Cur-carboxymethyl chitosan Enterocytes
Systemic
Circulation
M cells
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Fig 5. Inhibit effect of curcumin-carboxymethyl chitosan (CNC) on P-gp mediated efflux effect.
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3.3.2 Modulate the integrity of epithelial tight junctions Several polymers which can encapsulate cur can also enhance cur intestinal absorption through modulating the integrity of epithelial tight junctions, as well as through mucoadhesive features. R. Shelma et al. prepared cur loaded submicroparticles composed of Lauroyl sulphated chitosan (LSCS)[74]. LSCS could penetrate Caco-2 cells tight junctions, and thus improve cur paracellular permeability and enhance cur oral bioavailability. Chitosan, a mucoadhesive polymer, can protect the drug from intestinal and enzymatic degradation and enhance the penetration of curcumin across mucosal barriers by interacting with epithelial tight junctions, enhancing oral bioavailability. R. Shelma et al. found that cur loaded acyl modified chitosan nanoparticles had a higher mucin interactions effect than unformulated cur, which could enhance cur intestinal absorption[75].
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In addition, lipid based nanoparticles are absorbed via lymphatic transport by intestine Peyer’s patches M cells. The oral bioavailability of cur can be enhanced through the lymphatic transport route, as lymphatic vessels can transport the drug into the thoracic duct, followed by transfer into systemic circulation, which can bypass the portal circulation. In this regard, Min Sun et al. prepared cur loaded polybutylcyanoacrylate nanoparticles (PBCNs) [76]. Cur nanoparticles were mostly absorbed in the ileum and colon, as there are more M cells and Peyer’s patches (PP) in these sites. PBCNs are mainly absorbed by M cells on the PP, and the oral bioavailability was 800% higher than unformulated cur. The Cmax(43.53 ± 25.57 vs. 35.46 ± 12.78 μg/L) and AUC0–∞(419.62 ± 102.74 vs.244.81 ± 76.52 μg/L h) of CUR–PBCN (50 mg/kg) were higher than that of CUR-suspension(250 mg/kg), suggesting a good oral bioavailability of CUR – PBCN. Jong-Suep Baek et al. formulated cur in Ncarboxymethyl chitosan (NCC) coated SLN (NCC-SLN). The burst release of cur in acid environments was inhibited compared with pure SLN[77]. In simulated gastric and intestinal fluid, the burst release of NCC-SLN was suppressed, and the formulation had
a sustained release characteristic. NCC-SLN had enhanced cytotoxicity and cellular uptake, with the lymphatic uptake 6.3-fold and oral bioavailability 9.5-fold enhanced compared with cur solution respectively. NCC-SLN had a higher Cmax(0.73 ± 0.31 vs.0.29 ± 0.11 μg/L) and AUC0–12 (4.98 ± 2.28 vs. 0.56 ± 0.14 μg.h/L) than that of cur solution at a dose of 50 mg/kg. In addition, surface modification of SLN with NCC can enhance the SLN lymphatic uptake.
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3.3.3 Various of intestinal absorption mechanism of curcumin preparations The mechanisms of intestinal absorption of cur preparations have been discussed. Jinling Wang et al. prepared cur polymeric micelles (Cur-PMs) with an enhanced absorption in the duodenum, jejunum and ileum. Cur-PMs were translated by energydependent, macropinocytic transcytosis and lymphatic transport pathways with a resultant enhanced cellular uptake (Fig 6). Cmax of Cur-PMs (342.33 ± 122.42 ng/mL) was 3.11-fold enhanced than that of Cur-Sol (109.84 ± 85.89 ng/mL). While, the AUC (0−t) of Cur-PMs (870.2 ± 466.78 mg/L × h) was 2.87 times enhanced than that of Cur-Sol (303.58 ± 294.31 mg/L ×h) at a dose of 50 mg/kg by oral administration.[78]. Bingchao Cheng et al. prepared a cur loaded D-α-tocopherol polyethylene glycol 1000 succinate (TPGS) decorated nanodiamond (ND) system with a particle size of 196.32 nm and drug loading of 81.59%[79]. The absorption mechanism of cur was as follows: (1) After oral administration, cur could be released from the preparations and absorbed by passive diffusion in intestinal epithelium. (2) Nanoparticles could penetrate the mucus layer and be absorbed by transcytosis or paracellular methods. The transcytosis mechanisms of cur nanoparticles were caveolinmediated, clathrin-mediated, clathrin- and caveolae-independent endocytosis and macropinocytosis. (3) After transport across the epithelium, cur nanoparticles could diffuse into lymphatic transport system or blood capillaries, and finally enter blood circulation. Cur nanoparticles had a higher Cmax (311.13 ± 78.52 vs.69.20 ± 15.92 ng/ml, 4.5 fold), longer MRT0-t (3.71 ± 0.66 vs.1.21 ± 0.22 h, 3.07 fold) and larger AUC 0–t (897.75 ± 258.81 vs. 84.12 ± 30.34 ng/mL·h, 10.67-fold) compared with cur suspension at a dose of 75 mg/kg. Yuwei Duan et al. formulated cur in micelles through the thin film diffusion method. The micelles was composed of methoxy poly(ethylene glycol)-poly(lactide) (mPEG-PLA) and D-α-tocopherol polyethylene glycol 1000 succinate (TPGS). The micelles had high drug-loading (16.1%) and small size (46.0 nm), and demonstrated excellent stability in gastrointestinal fluid due to the low critical micelle concentration (CMC) and dilution stability. The highest absorption segment was the duodenum, and cur micelles was mainly transferred through passive diffusion. The Cmax of CUR-MPP-TPGS-MMs(197.88 ± 61.71 vs.27 ± 1.37 ng/ml) was higher than that of cur suspension, while the AUC0–24 of CUR-MPP-TPGSMMs (1.02 ± 0.93 vs. 0.11 ± 0.029 μg/mL·h) was about 9 times enhanced than that of cur suspension after oral administration at the dose of 75 mg/kg , with a relative bioavailability of 927.3%. The oral bioavailability was also improved compared with unformulated cur[67]. Yan Gao prepared a cur nanosuspension (CUR-NS) with a diameter of 210.2 nm. By using an in situ single pass perfusion method, 9.20% CURNS was absorbed in the stomach within 2 h, and the main absorptive segments of cur
Table 4. Absorption mechanism of curcumin preparations. Cmax AUC Absorpti Preparation (Preparation vs. (Preparation vs. on control) control) mechanis m Chitosan-micelles
5.365 ± 1.246
effect
77.261 ± 12.485
vs.
vs.
Refe renc e
The oral absorption of cur
[71]
were enhanced.
5.107 ± 1.629
μg/mL
μg.h/mL
re
0.610±0.109
(15 mg/kg)
(15 mg/kg)
7.51 ± 0.44
136.27 ± 10.85
TPGS and Brij78 acted as
solid lipid nanoparticles
vs.
vs.
P-gp inhibitor by enhancing
14.29±1.58
absorption of cur.
lP
TPGS and Brij78-
2.12
± 0.34
μg/mL
(50 mg/kg)
GL44-
0.24 ± 0.04
na
PF-127 and
ur
micelles
(50 mg/kg) 6.13 ± 0.22
The cytotoxic activity (3-
vs.
vs.
folds) and oral
0.11 ± 0.04
bioavailability (around 55-
μg/mL
h/μg/mL
folds) were enhanced.
(10 mg/kg)
(10 mg/kg)
/
LSCS-
[72]
μg.h/mL
0.08 ± 0.03
Jo
Modulate the
Observation
-p
P-gp inhibit
ro of
were the duodenum and jejunum through passive diffusion mechanisms. A pharmacokinetic study also showed CUR-NS had a relatively high bioavailability compared with native cur, the Cmax of CUR-NS(174.75 ± 49.05 vs. 12.58±4.28 ng/ml) was higher than that of cur suspension, AUC0–∞ for CUR-NS (612.82 ± 70.92 vs. 90.12 ± 16.85 μg/mL·h ) was 6.8-fold enhanced than that of cur suspension, after oral administartion at a dose of 250 mg/kg.[80]. Hailong Yu et al. prepared a cur nanoemulsion with enhanced oral bioavailability[81]. Caco-2 cell permeation experiments showed that the cur nanoemulsion absorption mechanism was a digestiondiffusion mechanism. The Cmax (29.9 ± 5.1 vs.1.6 ± 1.2 μg/mL) and AUC0-inf (210 vs.21.4 μg/mL·min) of cur-nanoemulsion(240 mg/ml) was enhanced compared with that of cur water dispersion(240 mg/ml). Cur oral bioavailability was 9-fold higher than unformulated cur.
/
submicroparticles
LSCS can open the tight
[73]
[74]
junctions in Caco 2 cells
integrityof epithelial
/
Chitosan-nanoparticles
/
Chitosan nanoparticles had
tight
higher mucin interactions
junctions
effect. PBCNs-nanoparticles
43.53 ± 25.57
419.62 ± 102.74
PBCNs are mainly
(50 mg/ml)
(50mg/ml)
absorbed by M cells on the
vs.
vs.
PP.
35.46 ± 12.78
244.81 ± 76.52
[75]
[76]
μg/L
μg/L h
(250 mg/ml)
(250 mg/ml)
N-carboxymethyl
0.73 ± 0.31
4.98 ± 2.28
The lymphatic uptake was
chitosan (NCC)
vs.
vs.
6.3-fold and oral
SLN
0.29 ± 0.11
0.56 ± 0.14
bioavailability was 9.5-fold
μg/L
μg.h/L
higher than cur solution.
(50 mg/ml) Macropinoc
Micelles
342.33±122.42
N-[ [77]
(50 mg/ml) 870.2 ± 466.78
Oral absorption of cur was enhanced.
ytic
vs.
vs.
transcytosis
109.84 ± 85.89
303.58± 294.31
and
ng/mL
mg/L × h
lymphatic
(50 mg/kg)
(50 mg/kg)
311.13 ± 78.52
897.75 ± 258.81
or
vs.
vs.
paracellular
69.20 ± 15.92
84.12 ± 30.34
ng/ml
ng/mL·h
(75 mg/kg)
(75 mg/kg)
[78]
Nanodiamond
Passive
Micelles
suspension.
vs.
enhanced.
27 ± 1.37
0.11 ± 0.029
ng/ml
μg/mL·h
(75 mg/kg)
(75 mg/kg)
174.75 ± 49.05
612.82 ± 70.92
Oral bioavailability was
vs.
vs.
enhanced.
12.58±4.28
90.12 ± 16.85
ng/ml
μg/mL·h
(250 mg/kg)
(250 mg/kg)
29.9 ± 5.1
210 vs.21.4
Cur bioavailability was 9-
vs.
μg/mL·min
fold enhanced compared
1.6 ± 1.2
（240mg/ml）
with unformulated cur.
μg/mL （240mg/ml ）
Endocytosis micelles
fold) compared with cur
vs.
Transcytosis
Cur
and larger AUC 0–t (10.67-
Oral bioavailability was
lP
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ur
diffusion
Nanoemulsion
longer MRT0-t(3.07 fold)
1.02 ± 0.93
na
Digestion-
[79]
higher Cmax(4.5 fold),
197.88 ± 61.71
diffusion
Nanosuspension
Cur nanoparticles had
[67]
re
Transcytosis
-p
pathways
ro of
transport
[80]
[81]
Macropinocytosis Caveolae and
Caveolae
Clathrin
Clathrin Independent Endosome junction
Blood system
ro of
Tight
Lymphatic capillary
cur
polymer
-p
Fig 6. Schematic diagram of proposed absorption mechanisms of cur micelles in order to improve the oral absorption and bioavailability of cur.
re
3.4 Coadministration of curcumin with adjuctants
ur
na
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Some absorption enhancers have the ability to improving cur bioavailability through inhibition of cur metabolism with several adjuvants which can interfere with metabolized enzymes of cur. Piperine and other adjuvants have been shown to enhance cur oral bioavailability in both preclinical studies and in humans[82]. Piperine can inhibit the metabolizing enzymes of cur and circumvent the first pass metabolism. Sesamin can also alter the metabolism and bioavailability by modulating the activities of catechol-O-methyltransferases and UGT[83]. Xanthohumol can inhibit the metabolism of cur by conjugating with sulphotransferases and UGT[84]. Other adjuvants such as etoposide, docetaxel, silibinin and so on have been coadministered with cur in order to enhance cur oral bioavailability (Table 5).
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Alex E. Grill et al. formulated cur with UGT inhibitors (piperine, silibinin, tangeretin, and quercetin) in a self-microemulsifying drug delivery system (SMEDDS)[85]. SMEDDS containing curcumin (100mg/kg) and either piperine (125mg/kg), quercetin (100mg/kg), or silibinin (100mg/kg) were orally administered to mice. They found that silibinin, tangeretin and quercetin had inhibitory effects on the metabolism of curcumin (20~30% inhibition of maximum concentration compared to native curcumin). Mouse liver microsome studies showed that quercetin and silibinin had a glucuronidation inhibition effect of cur. In vivo experiments showed that silibinin can enhanced cur bioavailability by 3.5-fold compared with cur SMEDDS by an enhanced Cmax(0.15 vs. 0.03 μM) than cur SMEDDS.
Table 5. Coadministration of curcumin and other adjuvants. Codelivery
Formulation
Drugs
/
Cur, Etoposide
Dose
Cmax
AUC
Observation
(mg/
(Codilivery vs.
(Codilivery vs.
kg)
control)
control)
0.4、
Cur(0.4, 2, 8mg/kg), Etoposide(6
Cur
2 or
mg/kg) vs.Etoposide(6 mg/kg)
bioavailability
8,6
Refer -ence
can
improve of
the
etoposide
oral by
[86]
inhibiting the activity of intestinal Pgp and CYP3A4; 635±121,
The oral bioavailability of etoposide in
365±71,
758±142,
cur etoposide coadministration was
375±74 vs. 276
846±169 vs.
52% higher than etoposide at the dose
±50 ng/ml
561±98 ng/ml
of 8 mg/kg.
/
Cytotoxicity
/
nanoemulsion
/
Paclitaxel
ro of
Cur,
305± 59,
was
enhanced
by
promoting apoptotic with the treatment
[87]
of paclitaxel and cur. Cur,
nanoemulsion
/
50,20
/
was 5.2-fold increased. self-
25 、
Cur (25, 50, 100 and 150 mg/kg),
The oral bioavailability of docetaxel
emulsifying
50 、
Docetaxel (30 mg/kg)
was improved
drug delivery
100
vs. Docetaxel (30 mg/kg)
system
and
202.4 ± 38.0,
638.2 ± 41.5,
150 ,
342.6 ± 81.6,
828.9 ± 143.6,
30
374.9 ± 58.2,
1,004.1 ± 183.4,
370.3 ± 123.1
941.4 ± 243.4
vs.
vs.
78.7 ±
10.6
micelles
adjuvants
80
ur
(sesamin,
therapy of cur.
264.5 ± 40.8
Cur( 98 mg) vs.
The micellar formulation can improve
Sesamin, ferulic acid, naringenin,
the oral bioavailability of cur (80mg)
xanthohumol (NCP) vs.
by 88-fold.
Micellar cur (MC) vs.
naringenin,
Micellar cur plus phytochemicals
xanthohumol)
(MCP).
Jo
ferulic acid,
Quercetin
0.6 ± 1.3
/
with the combination
ng/ml
na
ng/ml
Cur,
[89]
re
Docetaxel
[88]
lP
Cur,
Cur,
Relative bioavailability of paclitaxle
-p
Paclitaxel
/
vs.
6.5 ± 12.2 vs.
3.9 ± 2.3 vs.
49.6 ± 31.4 vs.
129.7 ± 61.4 vs.
574.7±144.3 vs.
104.9 ± 59.6
475.9 ± 204.8
nmol/L
nmol/L·h
/
[90]
/
Cur oral bioavailability was 8-fold improved through coadministration of cur and adjuvants; Combination of cur and quercetin was
[91]
effective
in
preventing
urinary
infections.
/
50 、
EVL (0.5 mg/kg) vs.
Oral intake of cur decreased the
Everolimus
100，
EVL + curcumin (50 mg/kg) vs.
bioavailability
(EVL)
0.5
EVL + curcumin (100 mg/kg)
of everolimus.
Cur,
6.0 ± 1.8 vs.
1637.7±256.8 vs.
1.4 ± 0.9 vs.
481.8 ± 327.8 vs.
1.4 ± 1.2 ng/mL
466.0± 330.2
[92]
ng·min/mL Cur,
/
nanoemulsion
/
/
5-Fluorouracil
Coadminsion of cur and 5-Fluorouracil nanoemulsion
had
[93]
improved
cytotocity and enhanced cell uptake.
/
nanoparticles
/
/
Dual drug loaded nanoparticles can
Cur-quercetin,
enhance the efficacy of curcumin in
Cur-silibinin
the treatment of cancers.
/
Cur, Norfloxacin
60,
Norfloxacin (100 mg/kg) vs.
The mean plasma concentration of
100
Norfloxacin
norfloxacin was improved in cur
(100
mg/kg)+Cur(60
[95]
pretreated rabbits.
/
-p
mg/kg)
[94]
ro of
Cur-piperine,
2.67 ± 0.42 vs. 4.06 ± 1.24
2Cur NPs(100 mg/kg) vs.
nanoparticles
Piperine
re
Cur,
250,
Cur + piperine suspension
10
(250 + 10 mg/kg) vs.
lP
Cur suspension(250 mg/kg)
Jo Cur,
Resveratrol
vs.121.2 ± 23.1
vs.872 ± 43
vs.90.3 ±15.5
vs.312 ± 9
ng/ml
ng/ml h
100,
Cur(100mg/kg),docetaxel(30mg/kg)
30
vs. docetaxel(30 mg/kg)
ur
Docetaxel
3224 ± 329
na /
Cur,
260.5 ± 26.4
1024.2± 121.7 vs.
102.5
11.5 ng/ml
liposomes
50, 50
/
±
2244.1 ± 68.0 vs282.6 ± 18.4 .ng h/ml
/
Coadministration incidence
reduced of
adenocarcinoma.
4.In vitro studies of curcumin oral nanoformulations
the
prostatic
[98]
ro of
The cell permeability, cell uptake and cytotoxicity of various cur nanoformulations have been studied against different cancer cells by many groups in recent years. Cur can inhibit cancer cells growth through various mechanisms. Cur is able to downregulate P-glycoprotein (P-gp) and multidrug resistance proteins (MDR), and can also overcome cancer cells multidrug resistance[99,100]. Cur has cytotoxic activities in lung squamous cell carcinoma H520 and small cell lung cancer H460 cell lines [101]. Pharmacological activities studies showed that cur can induce cell death as a result of interference with various cell signaling pathways, including cell cycle (cyclin-D1 and cyclin-E), survival (PI3K/Akt pathway), apoptosis (caspases activation and antiapoptotic gene products down-regulation), angiogenesis (VEGF), metastasis (CXCR-4), proliferation (AP-1, EGFR and HER-2), inflammation (5-LOX, COX-2, NFkB, IL-1, TNF, IL-6) and invasion (adhesion molecules and MMP-9)[102]. Besides, cur also induces apoptosis and cell proliferation in other cancer cells such as human prostate cancer, leukemia, and non-small cell lung cancer cell lines and more.
-p
4.1 Cell permeability of curcumin nanoformulations The poor oral bioavailability may be the result of poor permeability of cur in cancer cells. Wahlang B et al. detected cur permeability in Caco-2 cells. They found that cur had a poor permeability with a P app of 2.93±0.94×10 −6 cm/s[103]. Another study showed that the apparent permeability of cur in Caco-2 cells was < 0.1×10-6 cm/s[104].
Jo
ur
na
lP
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4.2 Cell uptake of curcumin nanoformulations Cell uptake of various cur nanoformulations has also been investigated. In order to facilitate the cellular uptake of cur, cur loaded propylene glycol liposomes (PGL) were developed. The liposomes were composed of hydrogenated egg yolk lecithin, cholesterol, Tween 80 and propylene glycol [105]. In vitro cell experiments showed that PGL exhibited higher cellular uptake than conventional liposomes and unformulated cur. In a recent study, cur loaded Pluronic/polycaprolactone (Pluronic/PCL) block copolymer micelles were prepared by Raveendran et al[106]. The uptake ability of micelles into Caco-2 cells was measured by fluorescence exploiting the intrinsic fluorescence of curcumin. The fluorescence intensity of cur micelles in cells was higher than that of native cur, indicating that the micelles had better cell internalization than free cur. Cellular uptake extent of cur was influenced by various factors including nanocarrier type, surface charge, particle size and cell lines. For example, cur PLGA nanoparticles with different particle size (76 nm to 560 nm) had different uptake patterns. With the decrease of particle size, the uptake was increased, likely as low particle size nanoparticles are more easily endocytosed than nanoparticles with higher particle sizes. In addition, coating the nanoparticle surfaces with poly(Llysine) (PLL) can make the nanoparticles positively charged, which can enhance nanoparticles uptake inside the cells[107]. Another comparative study was also conducted analyzing the cell uptake of dendrimer, β-cyclodextrin (β-CD), nanogel, PLGA and cellulose nanoformulations of cur in MDA-MB-231 (breast), SKBR-3, and HPAF-II (pancreatic) cancer cells [108]. The uptake ability was in the order of: MDAMB-231 > SKBR-3 > HPAF-II. Importantly, the uptake ability of cur preparations was
2~3 fold enhanced compared with unformulated cur.
5.In vivo studies of curcuimin oral nanoformulations
ro of
5.1 Absorption of curcumin oral nanoformulations Cur and preparations of cur have been investigated for their cur absorption and pharmacokinetic characteristics, which indicate the treatment effect of cur nanopreparations. The absorption of cur in humans was investigated, whereby 12 healthy volunteers were orally administered a cur C3-complexTM at a dose of 10-12 g[109]. Free cur, the Cmax of which is 50 ng/ml, was only detected in the plasma of one person. Cur sulphate had a Cmax of 1μg/ml, while the Cmax of cur glucuronide was 2 μg/ml. Alzheimer’s disease patients were orally administered with C3complex™, the dose of which was 2-4 g daily and the drug was administered for 24 weeks. Cmax of cur, cur glucuronide, tetrahydrocurcumin (THC) and THC-glucuronide were 7.76 ng/ml, 96.05 ng/ml, 3.73 ng/ml and 298.2 ng/ml, respectively[110].
re
-p
Yan Yang et al. found that when cur was orally administered at a dose of 100 mg/kg, the plasma concentration of cur was extremely low [111]. Oral administration of cur has an anti-arthritic effect through inhibiting somatostatin (SOM) secretion from small intestine endocrine cells via Ca2+ /CaMKII and cAMP/PKA signaling pathways. When the cur preparations were orally administered, Cmax and AUC were much higher than that of unformulated cur.
ur
na
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Khalil et al. found that when cur was orally administered at a dose of 50 mg/kg, the pharmacokinetic characteristics of PLGA and PLGA-PEG nanoparticles were much improved over unformulated cur. The half-lives of cur loaded PLGA and PLGA-PEG nanoparticles were 4 h and 6 h, while the half-life of free cur was 1 h. As well, the AUCs and Cmax of the same formulations were 15.6 and 55.4 fold and 2.9 and 7.9 fold enhanced compared with free cur. Cur could release from the nanoparticles rapidly, thus the drug could be soon found in the plasma[112].
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Bhushan Munjal et al. compared the oral bioavailability of seven different preparations of cur including nanosuspension, micronized suspension, aqueous suspension, hydroxypropyl-β-cyclodextrin (HP-β-CD) inclusion complex, amorphous solid dispersion, combination with piperine, and spray-dried CRM–milk composite [113]. The aqueous suspension has a C max of 28.9 ng/ml, while the AUC is 26.9 ng/ml. For the nanosuspension and amorphous solid dispersion, the oral bioavailability was increased to 251%, 446%, 567% in AUC (0−t) and 405%, 270%, 415% in Cmax. For the micronized suspension and piperine, the Cmax and AUC were not increased significantly. The oral bioavailability of the milk composite was reduced (37% in Cmax and 10% in AUC (0−t)). Sophie P. Valentine et al. orally administered cur at doses of 200 mg/kg or 400 mg/kg,
and the cur preparations were administered for two weeks[114]. They found that CYP1A catalytic activity was decreased to 25%, however cur had no inhibition effect on hepatic UDP-glucuronosyltransferase, hepatic catechol-O-methyltransferase or ovarian aromatase. Additionally, the catalytic activity had a 20% decrease, and the CYP3A levels of polypeptide had a 28% decrease as a result of giving cur at 400 mg/kg for two weeks. Furthermore, when cur was orally administered at a dose of 400 mg/kg, glutathione S-transferase activity had a 20% increase. A combination of CYP1A, CYP3A and Glutathione S-transferase (GST) metabolic pathways could activate the cur chemopreventative action.
-p
ro of
Adjuvants such as piperine can also have an influence on cur pharmacokinetics in rats and humans by enhancing cur oral bioavailability. Piperine can enhance cur oral bioavailability through inhibiting hepatic and intestinal glucuronidation. Guido Shoba et al. studied the process of piperine enhancing of cur oral bioavailability [115]. When cur was orally administered in humans at a dose of 2g/kg combination with 20 mg/kg piperine, the AUC and Cmax were 20- and 30-fold higher than cur 2g/kg alone. In rats, the AUC and Cmax were only 1.5-fold increased after coadminstration of cur at 2g/kg and piperine at 20mg/kg compared with administration of cur at 2g/kg alone.
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5.2 Distribution of curcumin oral nanoformulations Uptake and distribution of cur in tissues is important, and various studies have addressed this issue. In vitro studies have shown that when rat intestines were incubated in 10 ml incubation medium with 50 ~750 µg cur, when the concentration of cur was 750 µg, no more than 3% of cur was detected in tissues. There was no cur in the serosal while 30~80% of cur couldn’t be found in the mucosal side[116].
ur
na
5.3 In vivo metabolism and excretion of curcumin oral nanoformulations The low cur oral bioavailability preparations may also due to the rapid cur metabolism and excretion from the gastrointestinal tract. Various studies of cur metabolism and excretion have been conducted in recent years.
Jo
When cur is orally administered at a dose of 1 g/kg in rats, there was a limited amount of cur detected in the urine, while 75% of cur was excreted through the feces[117]. 89 % of [3H] cur was excreted in the feces while 6% was detected in the urine after oral administration of [3H] cur at a dose of 0.6 mg/rat.[118] Ravindranath and Chandrasekhara et al. detected that less than 5 μg/ml cur could be found in plasma after oral administration at a dose of 400 mg/rat[119]. The poor cur oral bioavailability is due to the rapid metabolism in the intestinal wall and liver. Several studies have showed that the liver and intestine are the major organs that can metabolize cur[120,121]. When cur was orally administered at a dose of 0.1 g/kg in mice, the peak plasma concentration of free cur was only 2.25 μg/mL[122]. When cur was orally administered at a dose of 500 mg/kg, the plasma concentration of
re
-p
ro of
free cur was only 1.8 ng/mL. Cur is metabolized as cur sulfate and cur glucuronide in rat plasma, and hexahydrocurcumin, hexahydrocurcumin glucuronide and hexahydrocurcuminol were also detected in minor amounts. Previous human studies showed that when cur was orally administered at a dose of 3.6g daily for four months, very low level of sulfate and glucuronide conjugates could be detected in plasma (3-6 ng/mL)[123]. The absorption, tissue distribution and metabolism of cur after oral administration of 10, 80 and 400 mg of [3H] cur were investigated[124~126]. At a dose of 400 mg, [3H] cur was detected in tissues even after 12 days, and 60%~66% of cur was absorbed regardless of the given dose. In another study, animals were orally administered with cur for 1 week. Cur tissue levels declined to a limited amount 3~6 h after administration [127]. Marczylo et al. evaluated the effect of phosphatidylcholine for the oral bioavailability and metabolic profile of cur[128]. After oral administration of either cur formulated with phosphatidylcholine (Meriva) or unformulated cur at a dose of 340 mg/kg, cur, curcuminoids desmethoxycurcumin and bisdesmethoxycurcumin, metabolites including hexahydrocurcumin, tetrahydrocurcumin, curcumin glucuronide, and curcumin sulfate were detected in plasma, liver and intestinal mucosa of the rats. After Meriva was given to rats, cur plasma concentration (33.4±7.1 nM) was 5-fold enhanced compared with native cur (6.5±4.5 nM), and liver levels of cur after receiving Meriva were also higher than native cur. However, cur concentrations in gastrointestinal mucosa after administration of Meriva was enhanced compared with native cur, suggesting that cur is formulated with phosphatidylcholine.
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ur
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Therefore, conjugating with adjuvants which can interact with cur metabolizing enzymes is an effective strategy to inhibit the metabolism of cur in order to enhance cur oral bioavailability. Phytochemicals can alter the cur metabolism, which in return improves the bioavailability of cur[129]. For example, ferulic acid, which is similar with cur in structure, can inhibit the xenobiotic enzymes of cur, and xanthohumol can inhibit cur metabolism by conjugating with the cur metabolism enzyme UGT and sulphotransferases. Piperine can inhibit the cur metabolizing enzymes and circumvent the first pass cur metabolism. Sesamin can modulate the activities of catechol-Omethyltransferases and UGT, thus alter the metabolism and bioavailability of cur. Other adjuvants which can improve the oral bioavailability of cur have already been discussed in this paper.
6.Clinical trials Nanoformulations and the free form of cur have been investigated in human clinical trials for treatment of various diseases such as cancer, inflammatory diseases, neurodegenerative diseases, metabolic diseases and more. In order to enhance cur oral bioavailability, cur has been formulated into capsules and tablets with high doses. At present, there are still several active clinical trials of cur with different formulations [http://www.clinicaltrials.gov/].
ro of
The clinical trials of cur which have been investigated are listed in Table 6, and here several clinical trials of cur are highlighted. There are a few clinical trials with positive outcomes. Several clinical observations suggested that cur had effective systemic biological activity even at low doses. For example, in a Phase II clinical trial on 25 patients with pancreatic cancer, when cur was administered at a dose of 8 g/day for 2 months, Cmax was 22 ~41ng/mL[130]. Cur oral administration is well tolerated with biological activity in pancreatic cancer by downregulating the cyclooxygenase-2, NFκB, phosphorylated signal transducer in patients, in spite of the limited absorption. When cur was orally administered at the dose of 0.45~1.8 g daily for 4 month in 15 patients, cur did not affect the PGE2 levels in leukocites, while cur affected the PGE2 levels at the dose of 3.6 g. In fact, when cur was administered at a dose of 3600 mg/day, the blood concentration of cur sulfate was 8.9 ± 0.7nmol/L, while that of cur glucuronide was 15.8 ±0.9nmol/L , which may inhibit PGE2 levels[131]. In another clinical trial, cur was administered at a dose of 0.45, 1.8 or 3.6 g per day for 1 week. When cur was administered at the dose of 3.6 g, M1G levels in colorectal tissue was affected while COX-2 protein expression was not decreased. And the effect was only be detected at the highest level(3.6 g/ per day)[132].
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There are several successful cur formulations which are reported in recent years with higher Cmax and bioavaialbility. Cur was orally administered in a nano-colloid dispersion THERACURMIN formulation at the dose of 30 mg, and it was found that the Cmax was 29 ng/ml, whereas the Cmax of the unformulated curcumin was only 1.8 ng/ml[133]. THERACURMIN was prepared by a high pressure homogenizer method using glycerin, gum ghatti and water. In addition, THERACURMIN was also administered at a dose of 150 mg and 210 mg, and the Cmax was found to be 189 ng/ml and 275 ng/ml, respectively. THERACURMIN can improve cur bioavailability and gastrointestinal absorption with limited toxicity [134]. It has been reported that the maximal cur plasma concentration in humans was 3228.0 ± 1408.2 ng/ml at a dose of 410mg when cur was formulated into liquid micelles[135]. Cur was excreted in its nonmetabolised form mostly through the feces after oral administration[136]. The absorbed cur could be converted into water-soluble sulfates and glucuronides metabolites[137]. In a phase I trial, after oral administration of cur at 3600 mg in patients, the cur plasma and urine concentrations were 11.1 nmol/L and 1.3 μmol/L respectively[138]. The concentration of cur administered at this dose in colorectal tissues were 7.7–12.7 nmol/g, while the concentration of cur in the liver could not be detected[139]. Peak plasma concentrations was 0.41-1.75μM after oral administration at a dose of 4-8 g cur. However, such examples are exceptional and most of the clinical trials had limited clinical trial effects which may due to the two factors concluding the low cur bioavailability and inadequate clinicals study quality.First pass and cur intestinal metabolism may contribute to the low bioavailability of cur oral administration. Most clinical trials had small amount patients and were not double blinded and not randomized. It has been reported that when cur was orally administered at a dose of 450–3600 mg/day in patients with colorectal cancer, the plasma concentration of cur
-p
ro of
was in the 10 -8 M range, which is around a hundredth of in vitro effective cur concentration in blood or colon cells[140].Vikram et al. detected the free cur plasma concentration in healthy volunteers after administration of cur in a solid lipid cur particle (SLCP) formulation compared with native cur. The mean plasma concentration of cur in SLCP (650 mg) was 22.43 ng/mL, while plasma cur was not detected in unformulated cur with the same dose. SLCP with doses of 2, 3, and 4 g were administered in 11 patients with osteosarcoma, and the Cmax was 33 ng/ml, 31 ng/ml and 41 ng/ml, respectively. It was found that a higher dose did not contribute significantly to a higher plasma concentration[141]. Sharma et al. detected cur plasma concentration after given cur at doses of 440~2200 mg/day for 4 months[142]. Clinical results showed that GST activity was decreased by 59% at a low dose(440 mg) instead of higher doses.Cur oral bioavailability was low although the Cmax was 64~1054 nmol/g at a dose of 2200 mg/day. Cur was metabolised by intestine. Metabolites were detected in the feces instead of the blood or urine. Thus, cur formulation with higher bioavailability and clinical therapeutic effect should be developed which need the hard working of ourselves.
re
Table 6. A list of clinical trials with oral administration of curcumin in different disease patients. Disease Dosage Dose Duration Pati Cmax Clinical Trail Results
Cancer Colorectal
Capsules
cancer
440– 2200
4 months
15
na
mg/day
lP
ents
144~ 519 nmol/g;
(1) The oral bioavailability of cur
(lower dose)
was low and cur was metabolised
64~1054 nmol/g
by intestine.
(higher dose)
(2) Metabolites were detected in
[143]
the feces instead of the blood or
ur
urine. (3) GST activity was decreased by 59% at a low dose(440 mg) instead of higher doses.
Jo Capsules
Reference
(4) Cur cause clinical benifit in patients of colon rectal cancer. (3)Larger dose of cur clinical trial is merited. 450–
4 months
15
8.9±0.7nmol/L (cur
(1) Compounds and conjugates
3600
sulfate)
were detectable
mg/day
15.8
±0.9nmol/L
in plasma and
urine after consumption of cur 3.6
cur glucuronide
g per day.
(3600 mg/day)
(2)Significantly decreased serum
[144]
PGE2 levels at the highest dose. Capsules
450,
7 days
12
12.7±5.7nmol/g
(1) Cur
levels
was
1800,
( normal mucosa )
pharmacologically efficacious by
3600
7.7±1.8 nmol/g
decreasing M 1 G levels instead of
mg/day
(tumor tissue)
COX-2 protein levels in the
(3600 mg/day)
colorectum with negligible cur
[145]
distribution outside the gut at a 19.6 ± 14.8nmol/g
dose of 3600 mg/day.
( normal mucosa )
(2) Cur
6.7 ± 1.6 nmol/g
malignant and normal colorectal
(tumor tissue)
tissue.
(1800 mg/day)
(3)Traces amount of cur was
was
detected
0.9±0.4 nmol/g (tumor tissue) (450 mg/day) 7 days
3600
10 −8M
Below 12
(1) Cur had low bioavailability, with
mg/day
The
administered cur was low.
-p
450–
blood.
by
systemic availability of orally
( normal mucosa )
/
the
up
ro of
0 nmol/g
in
taken
low
metabolites
[146]
in
circulation.
/
480 mg
3 months
Capsules
2,4
5
1 month
44
ur
na
g/day
/
lP
×3 / day
re
(2) M1G level was not decreased.
Capsules
1.08
10~30 days
Jo
Capsules
cancer
[147]
quercetin decreased in polyps size(50.9%),
polyps
number(60.4%) without severe toxicity.
7.3±8.1 ng/mL
Decreased ACF levels with the 4g
cur
dose, while no decrease in 2g dose.
[148]
Increased body weight, decreased
[149]
15.±14.8 ng/mL cur conjugate (4 g/day) 126
/
g/day
Pancreatic
Combination therapy of cur and
serum
TNF-α,
induced
p53,
regulated apoptotic pathway of tumor cell.
500
/
42 days
mg/day
20
Decreased PhK (Phosphorylase kinase) activity in cur treated
(curcum
[150]
group.
in), 5
mg
(piperin e) Capsules
8 g/day
4, 8 weeks
25
22 ~41ng/mL
(1) Cur oral administration is well
[151]
tolerated with biological activity in pancreatic cancer, in spite of the limited absorption. (2) Cur
downregulated
the
NF- κ B,
cyclooxygenase-2,
phosphorylated signal transducer in patients. (3) The
trial
had
positive
outcomes with tumor regression and enhanced serum cytokines levels.
/
8 g/day
4 weeks
/
17
(1) Cur had low compliance at high dose(8 g/day)
[152]
ro of
(2) Gemcitabine in combination with cur had therapeutic effect in advanced
pancreatic
cancer
patients.
/
8 g/day
/
21
29 ~412 ng/ml
Gemcitabine in combination with
-p
cur was safe and feasible in
[153]
pancreatic cancer patients.
Prostate
cancer
Capsules
0.1
6 months
/
85
cancer
6 g/day
/
Tablets
3 weeks
/
na
Head and
/
neck cancer
/
500~12
3 months
/
[154]
(1)The recomend dose for cur was 6,000 mg/day for 3 weeks in
[155]
combination with docetaxel. (2)
Clinical
responses
were
observed in patients for treatment of cur and docetaxel.
/
Cur inhibited IKKβ kinase activity
[156]
and IL-8 levels in head and neck cancer patients. 11
0.51±0.11μM/ml
(1) Cur is not toxic up to the dose
000
(4000 mg)
of 8000 mg/day for the treatment
mg/day
0.63±0.06μM/ml
of 3 months.
(6000 mg)
(2) Cur was not absorpted by
1.77±1.87μM/ml
gastrointestinal completely with
(8000 mg)
low Cmax(1.77±1.87 μ M/ml at
Jo
ur
Cervical
/
14
lP
Breast
with the
therapy of isoflavone and cur.
re
g/day
Reduced serum PSA
[157]
the dose of 8000 mg). (3) Cur had a biologic effect in cancer treatment.
Inflammatory diseases Ulcerative
Capsules
550 mg
proctitis
×2–3
Crohn’s disease
/day
/
2 months 5
Cur had reduced inflammatory response effect in patients.
[158]
360 mg
1 month
×3 / day 360 mg
2 months
×4 / day Irritable bowel
Tablets
Syndrome(IBS)
72–144
8 weeks
207
/
mg/day
Irritable bowel syndrome (IBS) prevalence
was
decreased;
[159]
Abdominal pain was reduced.
Capsules
arthritis
0.5
8 weeks
45
/
g/day
/
Chronic anterior
375mg×
Uveitis Tablets
anterior Uveitis
[160]
active rheumatoid arthritis (RA). 12 weeks
32
/
3 /day
Recurrent
Cur had the treatment effect of
Side effect is lack; Reccurrence
[161]
rate was 86%.
1.2
12-18
g/day
months
106
/
More than 80% patients had
ro of
Rheumatoid
reduced
eye discomfort after
[162]
treatment. Cur had therapeutic effect on eye relapsing diseases.
Peptic ulcer
Capsules
3 g/day
4 weeks
45
/
Cur had the therapeutic effect of
[163]
Idiopathic
375
6-22
Inflammatory
mg×3
months
Orbital
/day
4.5
1.5
4 months
12
/
/
2-4
Jo
/
500
related swelling. (2)Cur had therapeutic effect on healing of peptic ulcer.
(1) Cur with a dose of 4.5 g/day is
[165]
treatment effect for psoriasis. 1
/
Cur had efficacy and safety on treatment
of
[166]
dejerine-sottas
disease. 24 weeks
33
/
g/day
Arterial diseases
[164]
safe and well-tolerated;(2)Cur had
g/day
ur
Disease
12 weeks
na
/
Dejerine-Sottas
(1)Five patients completed the study, four patients recovered
re Capsules
g/day
disease
8
lP
Skin conditions
Alzheimer’s
/
completely, the fifth had tumor
Pseudotumors
Psoriasi
-p
peptic ulcer.
Cur had a therapeutic effect on
[167]
Alzheimer’s disease.
7 days
10
/
mg/day
Increased cholesterol(29%),
HDL
[168]
decreased
lipid peroxidase (33%), decreased total serum cholesterol(11.63%) were
detected
after
cur
administration.
Metabolic diseases Diabetes
Capsules
0.6
8 weeks
/
(1) NCB-02 and atorvastatincan
[169]
g/day
72
increased the endothelial function. (2) NCB-02 had more therapeutic effect on endothelial dysfunction compared with atorvastatincan.
Capsules
6g
15-120 min
/
14
(1) The
postprandial
serum
[170]
insulin levels were increased, plasma glucose levels or glycemic index was not increased after cur administration; (2) Cur had the effect of insulin secretion.
/
Diabetic
1.5
nephropathy
2 months
/
40
(1)TGF-β and IL-8 serum level
g/day
[171]
and urinary protein excretion were
ro of
decreased after cur administration; (2)No
adverse
effect
was
observed.
Diabetic
Tablets
1 g/day
4 weeks
/
40
microangiopathy
Decrease in skin resting flux, edema
score,
increase
[172]
in
-p
venoarteriolar response, PO 2 were observed.
Lupus nephritis
Capsules
500
3 months
/
24
Capsules
transplantation
480-960 mg/day
Others β-Thalassemia
Capsules
500
/
Respiratory
Alcohol
/
Jo
intoxication
Atherosclerosis
Safety trials Phase I
3 g/day
ur
contraction
12 months
na
mg/day
1 month
Tablets
Tablets
0.03 g
/
43
lP
Renal
systolic
re
mg/day
Proteinuria,
4 weeks
single dose
21
10
/
hematuria,
blood
pressure
and
[173]
were
decreased. Enhanced effect in cadaveric renal
[174]
Transplantation.
Oxidative stress was increased
[175]
in β -thalassemia/Hb E patients after cur administration.
/
Reduced
infections
after
[176]
administration of lactoferrin and curcumin (LC) . 7
29.52±12.86ng/ml
The
bioavailability
of
(THERACURMIN)
THERACURMIN was higher than
1.84±2.03ng/ml
cur powder for the treatment of
(Cur powder)
human disorders.
[177]
(30 mg/kg) 10mg
28 days
12
/
Increased
ApoA
and
HDL,
/twice
decreased apoB and LDL after cur
day
administration.
500–
3 months
25
0.51±0.11μM/ml
(1)Cur is not toxic up to the dose
12,000
(4000 mg)
of 8000 mg/day for the treatment
mg/day
0.63±0.06μM/ml
of 3 months.
(6000 mg)
(2)Cur was not absorpted by
[178]
[157]
1.77±1.87μM/ml
gastrointestinal completely with
(8000 mg)
low Cmax(1.77±1.87 μ M/ml at the dose of 8000 mg). (3)Cur had a biologic effect in cancer treatment.
Cadaveric
Capsules
480
1 month
43
/
mg×1–
Increased renal function,
[179]
decreased neurotoxicity.
2/day(c urcumin ) 20mg (quercet in) Tablets
4 g/day
6 months
26
/
gammopathy of
Serum paraprotein and uNTx
ro of
monoclonal ,
levels were decreased in MGUS
undefined
patients after cur administration.
significance
7. Conclusions and prospects
-p
(MGUS)
Jo
ur
na
lP
re
Several preclinical and clinical studies of cur have been developed in the last few decades, showing that cur is a good chemotherapeutic agent. Cur has a treatment effect in various diseases such as cancers (including colorectal cancer, pancreatic cancer, breast cancer and more), inflammatory diseases, neurodegenerative diseases, metabolic diseases and many others. Oral administration is an excellent administration route because of its good patient compliance characteristics. However, there are still various drawbacks of oral drug delivery systems because of the structure of the gastrointestinal tract and characteristics of the drug. For cur, the oral absorption is still low and various nanoformulations need to be developed in order to enhance cur oral bioavailability. In this review, cur nanoformulations for oral administration including solid dispersions, nano/microparticles, polymeric micelles, nanosuspensions, lipid-based nanocarriers, cyclodextrins, conjugates, polymorphs, coadministration of cur and other adjuctants are discussed. By incorporating cur in these formulations, the solubility and stability in the gastrointestinal system were enhanced, and the absorption route of cur nanoparticles could also be changed. As well, by coadministration of cur and other adjuvants, the metabolism of cur was inhibited, thus enhancing cur oral bioavailability. The in vitro and in vivo profiles of cur formulations were also discussed, which had a predictive effect on cur clinical treatments. Nanoformulations of cur consistently have a higher oral bioavailability compared to free cur. Various clinical treatments of orally administered cur have been investigated in order to establish their safety and effectiveness for the treatment of various diseases. Cur nanoformulations are promising drug delivery system for oral administration.
[180]
lP
Declaration of interest
re
-p
ro of
Although great progress has been achieved over the past few decades, there are still many questions and challenges for cur oral administration nanoformulations. First, cur can reverse drug resistance of cancer cells by inhibiting the three major cancer cells high drug efflux including P-glycoprotein (P-gp), mitoxantrone resistance protein (ABCG2) and multidrug resistance associated protein 1 (MRP-1). Thus, coadministration of cur with other chemotherapeutic drugs such as paclitaxel, docetaxel, doxorubicin, gemcitabine and cisplatin through formulation of these drugs in the same or different preparations can improve the antitumor effect and reduce toxicity, which may be a promising area for the development of cur nanoformulations. As well, although cur nanoformulations have good safety characteristics in humans and animals, the toxicity of cur oral nanoformulations still needs to be considered especially for high dose administrations. It has been reported that cur is safe by oral administration at a dose of 12 g/day. By formulating cur in nanoformulations for oral administration, the toxicity should be further reduced. Furthermore, most research has been developed on the lab scale, producing stable cur oral administration nanoformulations for clinical trials is also important. Cur oral bioavailability is extremely low, as a result of low systemic bioavailability, and therefore cur plasma concentration is low even by intravenous administration. Thus, a combination of various administration routes such as lipid lymphatic transport to achieve high cur nanoparticle absorption is essential in order to enhance cur oral bioavailability. With these promising progressions, various pharmaceutical strategies can be applied in order to enhance cur oral bioavailability without severe adverse effects, which still need focused research effort.
The authors have declared no conflicts of interest.
na
Acknowledgements
Amanda Pearce is gratefully thanked for correcting the manuscript.
ur
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Jo
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