Berberine pharmacology and the gut microbiota: A hidden therapeutic link

Journal Pre-proof Berberine Pharmacology and the Gut Microbiota: A Hidden Therapeutic Link Solomon Habtemariam

PII:

S1043-6618(20)30149-3

DOI:

https://doi.org/10.1016/j.phrs.2020.104722

Reference:

YPHRS 104722

To appear in:

Pharmacological Research

Received Date:

13 January 2020

Revised Date:

21 February 2020

Accepted Date:

23 February 2020

Please cite this article as: Habtemariam S, Berberine Pharmacology and the Gut Microbiota: A Hidden Therapeutic Link, Pharmacological Research (2020), doi: https://doi.org/10.1016/j.phrs.2020.104722

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Berberine Pharmacology and the Gut Microbiota: A Hidden Therapeutic Link Solomon Habtemariam Pharmacognosy Research Laboratories & Herbal Analysis Services UK, University of Greenwich, ChathamMaritime, Kent ME4 4TB, UK; [email protected]; Tel.: +44-208-331-8302 Received: 26 November 2019; Accepted: 11 December 2019; Published: date

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Graphical abstract

Abstract

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Berberine is a natural pentacyclic isoquinoline alkaloid that has been isolated as the principal component of many popular medicinal plants such as the genus Berberis, Coptis and Hydrastis. The multifunctional nature of berberine as a therapeutic agent is an attribute of its diverse effects on enzymes, receptors and cell signalling pathways. Through specific and general antioxidant and antiinflammatory mechanisms, its polypharmacology has been established. Intriguingly, this is despite the poor bioavailability of berberine in animal models and hence begging the question how it induces its reputed effects in vivo. A growing evidence now suggest the role of the gut microbiota, the so-called the hidden organ, as targets for the multifunctional role of berberine. Evidences are herein scrutinised to show that the structural and numerical changes in the gut microbiota under pathological conditions are reversed by berberine. Examples in the pharmacokinetics field, obesity, hyperlipidaemia, diabetes, cancer, inflammatory disease conditions, etc. are used to show the link between the gut microbiota and the polypharmacology of berberine. Keywords: Berberine, microbiota, diabetes, obesity, hyperlipidaemia, infection, inflammation, SCFA, Firmicutes-to-Bacteroidetes ratio.

1. Introduction

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Berberine (Figure 1) is a natural pentacyclic isoquinoline alkaloid which is abundantly found as a principal constituent of many medicinal plants. The classic examples of berberine sources are the stems and roots of Berberis species including B. aristata [1,2], B. darwinii [3,4], B. Petiolaris [5] and B. vulgaris [6]. These berberine-containing plants with high yield of up to 5% of their dry weight have been reported. Composition up to 8-9% berberine in the rhizomes of many medicinal plants have also been known with the most researched plants to date include Argemone mexicana, Coptis chinensis (Chinese goldthread), C. japonica, C. teeta, Eschscholzia californica and Hydrastis Canadensis or goldenseal, Mahonia aquifolium, Tinospora cordifolia, Xanthorhiza simplicissima, and Phellodendron amurense. One characteristic feature of berberine is its distinctive yellowish colour that gives the source plant materials their yellow to gold appearance (Figure 1).

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Figure 1. The structure of berberine and its deep yellow colour.

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In its chemically pure form, berberine is known to be first isolated from H. canadensis (goldenseal) in 1917 [7] but its use as a principal component of plants was dated to antiquity primarily as a dye (e.g., the textile industry) due to its deep yellow and yellow fluorescent characteristics. Its medicinal use was also dated for centuries as an active principle for numerous medicinal plants which are still in use to date including as ingredients of various food supplements. The pharmacology of berberine has been extensively studied and include anti-inflammatory [8,9], anticancer [10-12], antidiabetic [13-15], antiobesity and anti-hyperlipidaemic [14,16], cardioprotective [17,18] and spatial memory enhancement [19-21] effects. The plethora of pharmacological effects recorded for berberine attributes to some specific effects on enzymes, receptors and other biological targets along with other general effects such as antioxidant and anti-inflammatory properties. As with many natural products, the therapeutic potential of berberine could be explained by the polypharmacology principle of drug action [22] though research on the mechanisms of action that account to its diverse effects still continues. This article is designed to shade some light on the potential contribution of the gut microbiota to berberine’s multifunctional bioactivity.

2. Pharmacokinetics Even though berberine is a cationic alkaloid, its structure is by no means optimised for rapid absorption from the gut. It is sparingly soluble in water implying that it has poor intestinal absorption and/or bioavailability. In fact, the absolute bioavailability of berberine is far less than 1% given that even the absorbed berberine from the gut could be excreted back to the intestinal lumen through the action of P-glycoprotein. Chen et al. [23] reported absolute bioavailability from the oral route in rats as 0.68%, and as expected, inhibitors of P-glycoprotein could increase bioavailability from the intestine. Berberine absorption in rats could also be improved by up to 6-times by P-glycoprotein inhibitors

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suggesting the contribution of P-glycoprotein to the poor intestinal absorption of berberine [24]. An absolute oral bioavailability in rats of 0.36% has also been reported making intestinal first-pass elimination of berberine as the major barrier to its oral bioavailability [25]. With such poor degree of absorption from the gut, berberine ingested in hamsters is largely accumulated in the gut (not the circulation) and its bioavailability through intraperitoneal route is much better than the oral/intragastric route [26]. Based on HPLC analysis of human plasma following berberine oral dose, the absolute bioavailability was considered extremely low with the maximum plasma concentration of about 0.4 ng/ml obtained following 400 mg oral dose [27]. Despite all these, berberine has been shown to induce pharmacological effects in a plethora of animal models. Once absorbed, berberine has also shown to be distributed into all major organs with the highest amount obtained in the liver and readily excreted via the urine [28]. One of the emerging links between the expected poor bioavailability of berberine and its pharmacology is the gut microbiota that modulate both the pharmacokinetics profile and its biological effects. In beagle dogs, for example, oral administration of berberine leads to changes in the intestinal bacterial composition and butyrate (a product of bacteria) level in the gut [29]. In this case, treatment with berberine for seven days could increase the abundance of butyrate- and the nitroreductases-producing bacteria though the plasma level of berberine was still very low with the maximum level detected following an oral administration of 50 mg/kg was 37 ng/ml [29]. Earlier studies have also shown that berberine could enhance the oral bioavailability of other drugs. The bioavailability of ciclosporin A, for example, was shown to be augmented in healthy human volunteers resulting from the suspected decrease in liver and intestinal metabolism through inhibition of CYP3A4 [30]. Recent studies however pinpoint the role of the gut microbiota as a major target for modulation of drug pharmacokinetics by berberine. Accordingly, the pharmacokinetics interaction of berberine and metformin include the berberine-induced increase in metformin level coupled with decreased metformin degradation by rat and human intestinal bacteria [31]. Guo et al. [32] further showed that oral administration of berberine in mice could lead to increased expression of bile acidssynthetic enzymes (Cyp7a1 and 8b1) and uptake transporter (Ntcp) in the liver while the level of Bacteroides in the terminal ileum and large bowel were enhanced. An inspiring research on the role of the gut microbiota in the pharmacokinetics of berberine and potential variations between Chinese and Africans has been investigated by Alioga et al. [33]. The study revealed a higher abundance of the genera Prevotella, Bacteroides, and Megamonas (34.22, 13.88, and 10.68%, respectively) in the Chinese than the Africans subjects with more extensive metabolism was observed in the Chinese group. This study highlights that inter-individual and inter-racial differences in drug metabolism could be linked to variations in the gut microbiota. Dietary habits and antibiotics therapy are also likely to affect the state of the individual’s response in the pharmacokinetics and pharmacology of berberine. One mechanism for enhancing the biological activity of berberine by the gut microbiota lies in their ability to convert it into a better absorbable form, dihydroberberine. Feng et al. [34] reported a 5-fold increase in intestinal absorption rate for dihydroberberine than berberine in animals. In mice, the microbiota could reduce berberine to dihydroberberine which is absorbed into intestinal tissue and subsequently oxidised back to berberine to enter the blood stream. This process too could be ameliorated by treatment with antibiotics [34]. The dual effect of berberine in its pharmacology either by enhancing the gut microbiota or through its own specific mechanism of action was noted by the study of Wang et al. [35]. They have shown that some of the effect of berberine could be attributed to the increased butyrate production in the gut and increased abundance of such bacteria which has profound effect on blood lipid and glucose levels. The mechanism of butyrate itself on blood level of glucose and lipids was however different begging into a question of multiple mechanisms of action. The role of the gut microbiota as mediators of berberine’s polypharmacology is detailed further in the following sections. 3.

General effect on the gut microbiota

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Although the direct antibacterial effect of berberine in vitro is somehow weak, the compound is widely known as an antibacterial agent including in vivo. Not surprisingly, one of its known mechanism in ameliorating intestinal inflammation in humans is through direct antibacterial action [36]. This includes effects against Escherichia coli in vitro [37,38]; Clostridium difficile-induced intestinal injury model in mice [39] and anti-diarrhoeal effect in human [40]. The most important function of berberine related to the present communication is its ability to modify the composition of the gut microbiota. Earlier studies have shown that berberine can induce cell death in harmful gut bacteria while enhancing the composition of beneficial bacteria including Bifidobacterium adolescentis and Lactobacillus acidophilus [41,42]. The mechanism of berberine in modifying diseases is thus somehow similar with those of probiotics [43-46]. Hence, under disease conditions such as colitis, inflammatory bowel disease (IBD) or related pathologies associated with gut inflammation, berberine can reverse the increased prevalence of harmful bacteria such as E. coli and enterococci bacteria and the pathology-induced decreased Lactobacilli and Bifidobacteria. The mild diarrhoea induction under clinical condition by berberine is also shown to be coupled with gut microbiota dysbiosis such as increased abundances of the families Porphyromonadaceae and Prevotellaceae as well as the genera of Parabacteroides, Prevotellaceae_UCG-001 and Prevotellaceae_NK3B31_group [47]. Analysis of microbiota in the gut of broilers under high stocking density has further shown that treatment with berberine could lower the level of E. coli while increasing Lactobacillus in the cecum [48]. Most of the experiments conducted on berberine discussed in the following sections are based on changes on the profile of the gut microbiota population. While the composition of the human gut microbiota could change with diet and many other factors, studies on the bacterial 16S rRNA gene sequences from the faecal microbiota of humans and 59 other mammalian species have shown the prevalent groups as Firmicutes (65.7%) and to the Bacteroidetes (16.3%) and small proportion of Proteobacteria (8.8%), Actinobacteria (4.7%), Verrucomicrobia (2.2%), Fusobacteria (0.67%), and others [49]. The composition of these gut microbiota under pathological condition and their modulation by berberine is worth further scrutiny (see the following sections).

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3.1. Anti-obesity and antihyperlipidemic effects through regulation of the gut microbiota

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The antiobesity potential of berberine has been demonstrated in numerous experimental models. Through the AMP-Activated Protein Kinase (AMPK)-dependent and independent mechanisms, berberine can inhibit adipogenesis in experimental animals [50]. In obese mice, berberine administered through peripheral or central route can lower liver weight, hepatic and plasma triglycerides (TGs), and cholesterol contents by promoting AMPK activity and fatty acid oxidation and modulation of expression of genes involved in lipid metabolism. Some of the effects of berberine in obesity could be linked to its ability to modulation of microRNA (miRNA) as shown from its inhibitory effect on 3T3-L1 adipocytes cell differentiation and reduction of TGs contents via increased mRNA expression levels of miRNA-27a and miRNA-27b [51]. This in turn is linked to the negative regulation of the peroxisome proliferator-activated receptors (PPAR)-γ by these miRNA (miRNA-27a). Adipocyte differentiation has also been widely reported as a mechanism for the antiobesity effect of berberine through various distinct mechanisms including suppression of galectin-3 in mouse primary preadipocytes isolated from epididymal white adipose tissues [52]. It also suppresses the cAMPresponse element-binding protein (CREB) phosphorylation and CCAAT-enhancer-binding proteinβ(C/EBPβ) expression at the early stage of 3T3-L1 preadipocyte differentiation [53]. Berberine could also enhance thermogenesis in white adipose tissues [54]. Berberine further regulates lipid metabolism by upregulating hepatic low-density lipoprotein (LDL) receptors through the AMPK-dependent Raf-1 activation pathway [55]. One of the best researched experimental models for the antiobesity effect of berberine is the highfat diet-induced obesity in mice where it has been shown to inhibit adipogenesis [57]. The aniobesity (weight loss), lipid lowering effect of berberine as a function of TGs and cholesterol reduction have been demonstrated in both rats and humans [58]. Through both central and peripheral action that are

distinctly different from the statins, berberine is now known as a potent antiobesity and lipid lowering agent [59,60]. It is based on this plethora of evidences for berberine as weight, lipid and cholesterol lowering agent [26, 61-74] that its mechanism through modulation of the gut microbiota (Table 1) is scrutinised herein.

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Table 1. The antiobesity and antihyperlipidemic pharmacology of berberine via modulation of the gut microbiota Bioassay model Dosage Key finding References db/db mice 136.5 mg/kg, i.g. Increase SCFA content in faeces; modulate the Zhang et for 11 weeks ratio of Firmicutes-to-Bacteroidetes; increase al. [62] the proportions of Butyricimonas, Lactobacillus, Coprococcus, Ruminococcus, and Akkermansia; reduce the proportions of Prevotella and Proteus at the genus level. High-fat diet- Added to Increase the abundance of Akkermansia spp. Zhu et al. induced drinking water [63] atherosclerosis in (0.5 g/L) for 14 ApoE-/- mice weeks. High-fat diet- 50 mg/kg twice Enrich Firmicutes and Verrucomicrobia and Shi et al. induced weekly, i.g. for decrease Proteobacteria at the phylum level [64] atherosclerosis in 12 weeks when compared with the disease model. ApoE-/- mice Colorectal cancer Diet supplement Alter the structure of gut microbiota - inhibits Wang et al. development in with 500 ppm of the increase in Verrucomicrobia (phylum level); [65] Akkermansia and increase high-fat diet- berberine for 12 decrease Lachnospiraceae_incertae_ sedis (genus level); min/+ obese Apc weeks trends of increase in Bacteroidetes abundance; mice elevate some SCFAs-producing bacteria. High-fat diet- 100 mg/kg, p.o. Reverse the dysbiosis and a reduction in Sun et al. obese mice for 8 weeks SCFAs (butyric, acetic, propionic, isobutyric, [66] isovaleric, valeric acids), in the colon of obese mice; decrease the Firmicutes/Bacteroidetes ratio under obesity. High-fat diet 150 mg/kg, p.o. Reduce the richness and diversity of the gut Xu et al. obesity model in 6 weeks microbiota: increasing the abundance of [67] rats Fusobacteria and Proteobacteria, and decreasing the abundance of Firmicutes and Actinobacteria; no effect on the abundance of the Bacteroidetes phylum; At the genus level, those increased by berberine under obesity include Fusobacterium, Anaerostipes, Bacteroides and Phascolarctobacterium, Erysipelotrichaceae_Incertae_Sedis, Peptostreptococcaceae_Incertae_Sedis and Escherichia-Shigella; while those decreased include Roseburia, Allobaculum, Oscillibacter, Faecalibacterium, Prevotella Desulfovibrio, Coprococcus, Collinsella and Blautia. High-fat diet‐ 100 mg/kg, p.o. Increased berberine bioavailability correlate Wang et al. induced obese for 10 days in with increase in NR activity. [68] hamsters; animals; 500 mg

in

Sun et al. [69]

200 mg/kg, p.o. for 8 weeks

Reverse the decreased level of Bifidobacterum and Bacteroidete in obesity.

Cao et al. [70]

150 mg/kg containing a formulation with 24 mg/kg of oryzanol and 10 mg/kg of vitamin B6; p.o for 4 weeks 150 mg/kg, p.o. for 4 months

Enrich beneficial bacteria (e.g. Bacteroides, Blautia) and decrease the abundance of Escherichia at the genus level.

Li et al. [71]

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Increase conjugated bile acids in serum and their excretion in faeces; inhibits BSH activity in gut microbiota.

Increase the Bacteroidetes-to-Firmicutes (B/F) ratio in obese rats; At the genus level those enriched include Bacteriodes (SCFAproducing) as Bacteriodetes and those suppressed (Firmicutes) include Dorea, Roseburia, and Blautia; others increased include Anaerofilum, Bilophila (SCFAproducing), and Desulfovibrio. Modulate the gut microbiota (increased the proportion of Firmicutes and reduce the proportion of Bacteroidetes); inhibits the 7αdehydroxylation conversion of cholic acid to deoxycholic acid (decreased elimination of bile acids in the gut). Similar effect for both drugs reduce diversity of gut microbiota; of the 134 OTUs identified, sixty were decreased by both drugs; increase the abundance of those belonging to putative SCFAs-producing bacteria (Allobaculum, Bacteriodes, Blautia, Butyricoccus and Phascolarctobacterium). Reduce bacterial diversity with selective enrichment of putative short-chain fatty acid (SCFAs)-producing bacteria (Blautia and Allobaculum); increase elevations of faecal SCFAs concentration; bacterial list on the increase are Allobaculum, Bacteroides, Blautia, Butyricicoccus, Lactobacillus,

Sun et al. [72]

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100 mg/kg, i.g. for 2 weeks

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High-fat dietinduced hyperlipidaemia model in hamster

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High-fat-fed obese rats

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Hyperlipidaemic and normal subjects High-fat dietinduced obesity in wild type (WT) and FXR knockout (FXRint-/) mice High-fat dietinduced Steatohepatitis and dysbiosis of the gut microbiota in mice High-fat dietinduced hyperlipidaemia in rats

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High-fat dietinduced obesity in rats

High-fat diet-fed obese rats

100 or 200 mg/kg berberine or metformin, i.g. for 8 weeks

100 mg/kg, p.o. for 8 weeks

Gu et al. [26]

Zhang al. [73]

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Zhang al. [74]

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Phascolarctobacterium, Parasutterella, Dorea, Clostridium XVIII and Fusobacterium and Klebsiella; those suppressed include Clostridium XlVa, Flavonifractor, Lachnospiracea_incertae_sedis, Roseburia and Clostridium XI. Abbreviations: BSH, bile salt hydrolase; NR, nitroreductases; OTUs, operational taxonomic units; SCFAs, short chain fatty acids.

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The association between obesity and change in the gut microbiota has been shown to be the key to the effect of berberine as antiobesity agent. This in a way is also linked to the differential pharmacokinetics of berberine under normal and disease states in the gut microbiota. Wang et al. [68] have shown that berberine is more bioavailable in obese than lean animals owing to the differential microbiota composition. By using the high-fat diet-induced non-alcoholic steatohepatitis model in mice, Cao et al. [70] investigated the effect of berberine on the caecal content of proportions of Bacteroidetes, Firmicutes, Bifidobacteria and Lactobacillus species. The antiobesity effect of berberine in this model was established through the significant reduction in body weight and serum lipids (TG and TC). As a link between obesity and diabetes (see, Section 3.2), the anti-inflammatory mechanism of berberine in this model was also evident given the reduction in the level of proinflammatory cytokines such as IL-1, IL-6 and TNF-α which are known to be the major link between obesity and diabetes. Beyond amelioration of obesity and associated disease markers, berberine could reverse the diseaseassociated suppression of the Lactobacillus and Bifidobacterium levels. The obesity-mediated alteration of the microbial ecology [75] is thus a target for berberine. A similar experiment on the high-fat diet-induced hyperlipidaemia model was conducted in hamsters where berberine treatment effectively showed antihypercholesteraemic effect [26]. This is despite the poor pharmacokinetic profile of berberine through the oral route of administration discussed in Section 2. More importantly, treatment with berberine through an oral route could modulate the proportion of Firmicutes and Bacteroidetes in hypercholesteraemic hamsters. As a note of the Firmicutes-to-Bacteroideteratio (F/B) ratio, it was 1.43 in health animals while it was 0.95 in hypercholesteraemic hamsters before berberine treatment increased it to 1.6 [26]. In the hypocholestrolaemic activity study in rats, Li et al. [71] also demonstrated the ameliorative effects of changes in the serum, urine, liver and faecal metabolites. They noted a higher abundance of Bacteroides, Parabacteroides and Blautia after berberine treatment with a concomitant decrease in the genus Escherichia. The taxon-based analysis by Sun et al. [69,72] further showed that Firmicutes, Bacteroidetes, and Proteobacteria were the major phyla of faecal microbiota in rats while after high-fat-induced obesity, berberine could induce a decline in Firmicutes abundance and a moderately increase in Bacteroidetes ratios. Hence, a higher Bacteroidetes-to-Firmicutes (B/F) ratio was observed in obese animals treated by berberine. They also noted the enriching effects of berberine on Bacteroidaceae and Rikenellaceae families; both belonging to the Bacteroidetes phylum. In contrast, the elevated abundances of Christensenellaceae, Dehalobacteriaceae, Erysipelotrichaceae and Peptococcaceae (all belonging to the Firmicutes phylum) in in obese animals declined after treatment with berberine. This was in addition to the increased Alcaligenaceae (Proteobacteria Phylum) in obese animals after treatment with berberine. The effect of berberine as a lipid-lowering agent has been shown to be linked to the gut via modulation of the turnover of bile acids and subsequently the ileal Farnesoid X receptor (FXR) signalling pathway [69]. As receptors for bile acids and regulator of bile acid and their transporters synthesis, the FXR has close working relationship with the gut microbiota. For example, the gut microbiota is the source of the enzyme bile salt hydrolase (BSH) that hydrolyse bile acids conjugates [76]. Hence, the effect of berberine on FXR signalling is similar with the known effect of antibiotics and probiotics in lipid metabolism via microbial remodelling [77,78].

The study by Sun et al. [66] tried to determine the relationship between the bacteria-derived SCFAs with obesity-related markers. They have shown that the level of six types of SCFAs (butyric acid, acetic acid, propionic acid, isobutyric acid, isovaleric acid, and valeric acid) were reduced in obese mice with the most pronounced effect observed in butyric acid. The partial blockage of obesity and diabetes (see, Section 3.2) was associated with modulation of the gut microbiota (Table 1). Once again, Firmicutes and Bacteroidetes are the most abundant bacteria in the gut microflora at the phylum level but the general trend was for Firmicutes to increase and Bacteroidetes to decrease under obesity. Under this condition, the ratio of F/B in obese animals could be increased by up to 10-folds in obese mice which was suppressed by berberine treatment. At the genus level, berberine could also reverse the relative abundance of Clostridiales.g and Oscillospira under obesity condition [66].

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In obese animals, berberine has been shown to suppress weight gain along with critical effect on the gut microbiota. Zhang et al. [73], for example have shown treatment of high-fat diet-induced obese animals both by berberine and metformin led to an increase in the total relative abundance in 7 operational taxonomic units (OTUs) to 10–20% from less than 2%. Of the 7 OTUs, six were shown to be major SCFA-producing bacteria such as Blautia, Bacteriodes, Butyricoccus and Phascolarctobacterium. Unlike other studies, however, they reported that neither an increase of the F/B ratio after drug treatments nor any correlation between F/B ratio and body weight or adiposity index. The most recent experiment by Zhang et al. [62] using the db/db mouse model of obesity, diabetes, and dyslipidaemia showed similar effects (Table 1) where the microbiota modulation by berberine was shown to be involved in its antiobesity effect. The study by Zhang et al. [74] on the effect of berberine on obesity through the gut microbiota was among the most comprehensive since they included 3764 OTUs, contributing to 53.51% of all reads for the he most abundant phyla Firmicutes and 1753 OTUs, contributing to 34.83% of all reads for Bacteroidetes. Other phyla included the Proteobacteria (341 OTUs, contributing to 6.22% of all reads), and Actinobacteria (139 OTUs, contributing to 1.15% of all reads). While higher abundances of the phyla Actinobacteria and Verrucomicrobia were observed in the high-fat diet-obese group than normal animals, and trend was shown to be completely reversed by berberine. They also reported that berberine treatment could increase the faecal concentration of total SCFAs, particularly acetic acid and propionic acid, in obese rats. The trend of change for butyric acid was not significant suggesting some discrepancies among the different studies on the role of individual SCFA in obesity-related pathology. In the study of high-fat diet-induced atherosclerosis development in mice, Shi et al. [64] assessed the effect of berberine in the gut microbiota composition, which was dominated by the Firmicutes and Bacteroidetes, followed by Proteobacteria and Verrucomicrobia at the phyla level. The Firmicutes and Verrucomicrobia appeared to be enriched by berberine treatment while the level of Proteobacteria were suppressed when compared with the disease-model groups. The reduction of atherosclerosis score and inflammation by berberine in high-fat diet-induced atherosclerosis in ApoE-/- mice was similarly coupled with microbiota modulation by berberine: increase the abundance of Akkermansia spp. [63]. Hence, there seem to be an overwhelming evidence to suggest that the effect of berberine in obesity, hyperlipidaemia and cholesterol-induced pathologies could be in part linked to modulation of the gut microbiota. More evidences in other pathologies are discussed in the following sections.

3.2. Antidiabetic effects through gut microbiota regulation The efficacy of berberine in type-2 diabetes (T2D) patients have been effectively demonstrated in recent years [79-81]. Its direct effect on increasing the expression level of insulin receptors and to lower blood glucose level in T2D patients have been shown [82]. Hence, berberine is now known to act as antidiabetic agent through modulation of insulin signalling [83]. It is also often regarded as an insulin sensitizing and insulinotropic agent [84]. Meta-analysis of randomised clinical trial data further suggests the antidiabetic potential of berberine for diabetes [85]. In addition to the effect of berberine

in obesity and hyperlipidaemia states discussed in the previous section, it also acts through several other mechanisms including glucagon-like peptide-1 (GLP-1) release [13,86]. Through activation of the AMPK, berberine can also ameliorate the T2D-associated cardiac dysfunction both in cellular and animal models [87]. In high-fat diet-induced obese mice model and macrophages and 3T3-L1 adipocytes in vitro, berberine could ameliorate inflammation, improve glucose tolerance, reduce the increased expressions of inflammatory mediators (TNF-α, IL-6 and MCP-1) and ameliorate the phosphorylation of JNK and IKKβ, the expression of NF-κB p65 IRS-1 (Ser307). Furthermore, berberine inhibits the phosphorylation of IRS-1 (Ser307) while increasing the phosphorylation of AKT (Ser473) in adipose tissue and cultured adipocytes [88]. In addition, berberine can lower glucose level by inducing glycolysis [89] as well as inhibition of gluconeogenesis [90].

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The antidiabetic effect of berberine through its modulatory effect on the gut microbiota is summarised in Table 2 [56,61,62,67,70,74,91-97]. Some of these effects are similar with what is already known for the well-known antidiabetic agent, metformin, which has a profound effect on the microbial diversity (decrease) in high-fat diet-fed mice even more than in lean mice [98]. Table 2. Antidiabetic effect of berberine associated with alteration of microbiota.

In vivo - 200 mg/kg, p.o. for 10 weeks; in vitro - 10, 50 or 100 µM

na In vivo at 100 mg/kg for 5 days; or in vitro on isolated mouse cecal bacteria at 0.1, 1, and 10 mg/mL for 4 hours in an anaerobic chamber

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In vivo in mice or direct effect on bacteria in vitro

db/db mice

136.5 mg/kg metformin 113.75 mg/kg for 11 weeks

or at i.g

References Pan et al. [91]

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High-fat diet-fed mice; hepatocytes and 3T3-L1 adipocytes

Key finding Increase the composition of gut microbiota - the enriched OTUs mainly belong to Firmicutes; ameliorate the changes in dominance of Proteobacteria, Planctomycetes, Bacteroidetes, and Firmicutes; alter the decrease in the ratio of Firmicutes to Bacteroidetes; 32 berberine-OTUs negatively correlate with glucose level. Decrease the relative abundance of BCAA-producing bacteria (order Clostridiales; family Streptococcaceae and genera Streptococcus; Clostridiaceae, and Prevotellaceae (genera Prevotella); increased in abundance include Akkermansia (genus of the phylum Verrucomicrobia). In vivo - Alter intestinal bacteria by reducing Firmicutes and Clostridium cluster XIVa and BSH activity; In vitro alter bacterial physiology and bacterial community composition and function (reduce BSH-expressing bacteria like Clostridium spp); no effect on Bacteroidetes but reduce the Firmicutes/Bacteroidetes ratio. Increase SCFA content in faeces; modulate the ratio of Firmicutes-toBacteroidetes; increase the proportions of Butyricimonas, Lactobacillus, Coprococcus, Ruminococcus, and Akkermansia; reduce the proportions of Prevotella and Proteus.

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Dosage Diet supplementation at a dose of 30 mg/Kg

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Bioassay model Grass carp (Ctenopharyngodon idellus)

Yue [92]

et

al.

Tian et al. [93]

Zhang et al. [62]

200 mg/kg, p.o. for 8 weeks

High-fat obese mice

100 mg/kg, p.o. for 8 weeks; cellular model of CI-H716 cells treated with palmitic acid – berberine at 100 µM 150 mg/kg, p.o. 6 weeks

300 mg berberine three times daily, 0.5 h after each major meal for 8 weeks

200 mg/kg, p.o. for 8 weeks

ur

Patients aged 18-65 years with newly diagnosed T2D with (BMI) > 25 kg/m2 before and 8 weeks after treatment High-fat diet-dietinduced Steatohepatitis and dysbiosis of the gut microbiota in mice High-fat-fed obese rats STZ combined with high-fat diet in Rats High-fat diet-fed obese rats

Reduce the richness and diversity of the gut microbiota; increase the abundance of Fusobacteria and Proteobacteria, and decrease the abundance of Firmicutes and Actinobacteria; no effect on the abundance of the Bacteroidetes phylum. Increase in total Bifidobacterium level, Bifidobacterium longum, Bifidobacterium breve, Bifidobacterium adolescentis, and Bifidobacterium infantis in good correlation (except Bifidobacterium breve) with TNF-α and LPS levels.

Xu et al. [67]

Restore the relative level Bifidobacterium and Bacteroidate.

Cao [70]

150 mg/kg, p.o. for 4 months 100 mg/kg, p.o. for 2 weeks

of

Increase the Bacteroidetes-to-Firmicutes ratio in obese rats; see details in Table 1. Decrease in plasma LPS level by increasing tight junction protein (ZO1) expression. 100 mg/kg, p.o. for Reduce bacterial diversity while 8 weeks selectively enriching putative SCFAproducing bacteria (Blautia and Allobaculum); increase elevations of faecal SCFA concentration; see details in Table 1. Abbreviations: LPS, lipopolysaccharide; TNF-α tumour necrosis factor-α.

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Liu et al. [95]

Sun [66]

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Chen et al. [96]

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High-fat diet obesity model in rats

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High-fat diet obesity-induced diabetes in rats

Increase the populations of Bacteroidetes, Clostridia, Lactobacillales, Prevotellaceae, and Alloprevotella; reduce those of Bacteroidales, Lachnospiraceae, Rikenellaceae, and Desulfovibrio. Reverse the obesity-induced change in the gut microbiota composition – ameliorate the reduction in protective bacteria like Bifidobacterium and the increased gram negative bacteria like Escherichia coli; ameliorate the increased LPS release into plasma. Modulate the changes in dysbiosis and the diabetes-associated reduction in SCFAs in the colon of obese mice (see Table 1)

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500 mg/kg, i.g. for 4 weeks

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STZ-induced diabetic rats under high-fat, highsucrose diet

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Sun et al. [72] Shan et al. [97] Zhang et al. [74]

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In addition to the antiobesity and lipid lowering effect of berberine in the high-fat diet-induced non-alcoholic steatohepatitis model in mice (see, Section 3.1), Cao et al. [70] have shown a reduction in fasting blood glucose (FBG), insulin, and homeostasis model assessment of insulin resistance (HOMAIR) through alteration of the gut microbiota (Table 2). The link between diabetes and obesity being proinflammatyory cytokines and/or inflammation, the alteration of the structure and abundance of the microbiota in the gut was also associated with the observed anti-inflammatory effect. Moreover, berberine ameliorated the morphological and biochemical (ALT and AST) disease markers while the disease-associated suppression of Lactobacillus and Bifidobacterium levels were reversed. The effect of berberine in reversing the suppressed level of SCFAs in obese mice and increasing the ratio of F/B was coupled with its antidiabetic effect (Sun et al. [66]). In this connection, the more pronounced effect of berberine on butyric acid level was consistent with the effect of butyric acid on improvement of insulin sensitivity and increased energy expenditure in mice [99]. As with the antiobesity effect, the antidiabetic effect of probiotics has been shown to be mediated through butyrateinduced mechanism such as increased GLP-1 release [100]. The effect of berberine on diabetes, obesity, inflammation and microbiota modulation was also similar with metformin when assessed in the db/db mouse model of diabetes [62]. Chen et al. [96] studied the effect of berberine in newly diagnosed T2D and overweight patients. Although, the microbiota population studied was limited to the genus Bifidobacterium, four species (B. longum, B. breve, B. infantis and B. adolescentis) appeared to be enriched after berberine treatment. Moreover, the observed change in these group of bacteria, except for B. breve, were positively correlated with the reduction in the TNF-α and LPS levels induced by berberine. Hence, both the antidiabetic and antiobesity potentials of berberine are somehow linked to its anti-inflammatory effect which were all intern linked to changes in the microbiota population of the Bifidobacterium species. Cui et al. [94] recorded that several biochemical and morphological markers of diabetes could be suppressed by berberine (Table 2). These include increased level of antioxidants, insulin and GLP-1 together with reduction in the level of plasma glucose, lipids and insulin resistance. Along with inhibition of gluconeogenesis and enhanced glycolysis that all confer antidiabetic effect, there was an increase in the populations of Bacteroidetes, Clostridia, Lactobacillales, Prevotellaceae, and Alloprevotella while those of Bacteroidales, Lachnospiraceae, Rikenellaceae, and Desulfovibrio were reduced. They also reported the ratios of F/B in the normal, T2D, and berberine groups were 0.54, 1.09, and 0.73, respectively. Hence, the structural changes along with the F/B ratio in the intestines appears to be positively correlated with blood glucose concentrations in diabetic rats. The study by Cui et al. [94] further established that the Clostridiales and Bacteroidales were the dominant orders in the intestines of all treatment groups in rats: while the relative abundances of Clostridiales (35.91%) and Lactobacillales (2.46%) were lower than that of Bacteroidales (47.31%) in the T2D group, with berberine tended to abolish this order. The study by Liu et al. [95] did not find a significant effect on body weight, visceral fat mass or the visceral fat to body weight ratio following treatment of high-fat-fed obese rats with berberine. They have shown however that the inflammatory components of diabetes were ameliorated along with improvement in insulin resistance as well as insulin receptor and insulin receptor substrate-1 expression in the liver. These effects along with pathological markers such as hepatic steatosis was shown to be ameliorated by berberine together with reversal of the obesity-induced alteration of the gut microbiota composition. In particular, the reduction in protective bacteria like Bifidobacterium and increased gram-negative bacteria like E. coli in obesity and berberine’s ability to reverse this trend was suggested as potential mechanism for its antidiabetic properties. A randomized, double-blind and Placebo-controlled Study under the title “Effectiveness and Safety of Berberine Hydrochloride and Bifidobacterium in People with Abnormal Glucose Level” were conducted in China with 300 participants of newly diagnosed patients with pre-diabetes or T2D. Given Bifidobacterium, as a known probiotic that can modulate the gut microbiota and improve glucose and

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lipid metabolism in animal experiments, the 16-weeks study was designed to investigate the link between the antihyperglycaemic effect of berberine tablets by its own and in combination with bifidobacterium mimetic capsules. The primary outcome is the absolute value of fasting plasma glucose and the results are still awaiting. In fish, the study by Pan et al. [91] revealed that the effect of berberine in glucose level of the serum was associated with structural modulation of the gut microbiota. The enriched OTUs mainly belonging to Firmicutes altered to the dominance of Proteobacteria, Planctomycetes, Bacteroidetes, and Firmicutes during and after berberine feeding; decrease the ratio of F/B; 32 berberine-OTUs were significantly negative correlated with glucose level. Readers should bear in mind that this change was on healthy animals and the trend could be different in diabetic animals. The study by Shan et al. [97] did not directly aimed at the microbiota level but they have shown that fasting insulin, insulin resistance index, plasma LPS level, and ZO1 expression were significantly correlated with increased GLP-2 level. The association between bacterial endotoxemia from the gut origin and T2D/obesity has been routinely established by other studies. All the above-mentioned data for berberine is in line with the well-established role played by the gut microbiota in diabetes pathology. Any condition including sleep deprivation that alter the structure of the gut microbiota is thus associated with the development of inflammation in adipose tissues and insulin resistance in animal studies [101]. Accordingly, both obesity and glucose tolerance could be modulated by targeting the gut microbiota [102]. The high blood glucose level associated with obesity in elderly people was also shown to be linked to changes in the gut microbiota [103]. The differential structure and composition of the gut microbiota in normal and T2D diabetes patients observed in many studies [104-106] also appear to be the therapeutic target for berberine.

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Berberine is among the most potent natural products which ameliorate inflammatory bowel disease and associated disorders [36]. Some the key findings on the role of the gut microbiota modulation for its anti-inflammatory properties in the gut is summarised in Table 3 [62,107-109]. Berberine also ameliorate mucosal barrier alteration and dysfunction under diabetic and other pathological conditions. Gong et al. [110] have shown that diabetic rats are subjected to proinflammatory intestinal changes, altered gut-derived hormones, and 2.77-fold increase in intestinal permeability which were all reversed by berberine treatment. This effect was also associated with the known effect of berberine as anti-inflammatory agent via the TLR4/MyD88/NF-κB signalling pathways in intestinal tissue [110]. By activating the AMPK activity thereby suppressing IFN-γ- and Il-17A-producing lamina propria CD4+ T cells both in vitro and in vivo, berberine can suppress chronic inflammation including under IBD condition [111]. Berberine can modulate the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) signalling both in Caco-2 cells and rat model of colitis [112] as shown for many other antiinflammatory natural products [113]. Intestinal barrier function in nonalcoholic fat liver disease (NAFLD) in rats maintained under high-fat diet could also be reversed by berberine along with improvement on anti-inflammatory (LPS and cytokines) and lipid (cholesterol) dysregulation markers [114]. Table 3. Inhibition of gut inflammation by berberine via modulation of the gut microbiota. Bioassay model Diarrhoea from irritable bowel syndrome patients transplanted to rats

Dosage 200 mg/kg, p.o. weeks

for 2

Key finding Alter the level of Faecalibacterium, faecal formate, acetate, and propionate by modulating the gut microbiome composition; decrease

References Jia et al. [107]

DSS-induced colitis in mice

40 mg/kg BBR for 10 days

Zhang et al. [62]

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136.5 mg/kg or metformin at 113.75 mg/kg i.g for 11 weeks

Cui et al. [108]

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Sequencing on 253 faecal samples from consecutive ITP patients and healthy controls.

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Firmicutes-to-Bacteroidetes ratio at the phylum level; decrease at the genus level Bacteroides, Faecalibacterium, Ruminococcus, Gemmiger, Roseburia, Clostridium XI, and Lachnospiraceae_incertae_sedis. Reduce serum LPS levels; increase SCFA content in faeces; modulate the ratio of Firmicutes-to-Bacteroidetes; increase the proportions of Butyricimonas, Lactobacillus, Coprococcus, Ruminococcus, and Akkermansia; reduce the proportions of Prevotella and Proteus. Increase the relative abundance of Eubacterium while reducing Desulfovibrio in the disease model; Bacteroides abundance even higher than the level in healthy animals; effect on Treg/Th17 balance was ameliorated after the depletion (by combination of ciprofloxacin and metronidazole treatment) of gut microbiota. Improve the microbial dysbiosis of corticosteroid-resistant ITP patients; reverse the effect of L. bacterium colonization on gut microbiota structure.

Wang et al. [109]

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Abbreviations: ITP, Thrombocytopenia; Treg, regulatory T cells.

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The anti-inflammatory effect and amelioration of ulcerative colitis in rats by berberine was shown to be associated with modulation of the gut microbiota [108]. In this DSS-induced colitis model in mice, berberine treatment could recover body weight loss and decreased loss of colon length, mucosal necrosis and the associated inflammation. They also noted the ratio of CD4+IL17A+(Th17) cells in spleen lymphocytes were increased while the proportion of CD4+CD25+Foxp3+(Treg or regulatory T cells) cells in spleen lymphocytes were decreased by berberine treated animals with colitis. Hence, berberine treatment could improve the Treg/Th17 balance in the DSS-induced colitis model. Even though the most abundant phyla in all animal groups were Bacteroidetes, Firmicutes, and Proteobacteria, those treated with berberine have Proteobacteria, Streptococcaceae, Enterococcaceae, and Erysipelotrichale as predominant intestinal flora. While the relative abundance of various groups could be modified by berberine (Table 3), the effect of berberine on the Treg/Th17 balance was lost after the depletion (by combination of ciprofloxacin and metronidazole treatment) of the gut microbiota. Hence, the antiinflammatory effect of berberine in this colitis model was induced through modulation of the

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microbiota. Based on meta-analysis of twenty-three randomized controlled trials with a total of 1763 patients of active ulcerative colitis, probiotics have been shown to have additional benefit in inducing remission [115]. This is consistent with experimental data in animal studies where probiotics ameliorate colitis by increasing Treg [116]. In this direction, the role of SCFAs, as microbial product to regulate the size and function of the colonic Treg pool and protect against colitis in mice have been established [117]. When the faecal microbiota from diarrhoea-predominant irritable bowel syndrome patients were transplanted to rats, it was shown to induce significant Kupffer cell hyperplasia, hepatic sinusoid hypertrophy, and elevated levels of hepatic TNF-α and interferon-γ and a decrease in the synthesis of ALB [107]. Under this condition, berberine could partially reverse the Kupffer cell hyperplasia, Faecalibacterium, faecal formate, acetate, and propionate levels by modulating the gut microbiome composition. It was also shown that treatment with berberine can significantly change the structure and profile of the faecal microbiome of the disease group (Table 3). As discussed for obesity and diabetes conditions, Rajilić-Stojanović et al. [118] have shown that the microbiota of IBS patients when compared with controls, had a “2-fold increased ratio of the Firmicutes to Bacteroidetes resulting from an approximately 1.5-fold increase in numbers of Dorea, Ruminococcus, and Clostridium spp; a 2-fold decrease in the number of Bacteroidetes; a 1.5-fold decrease in numbers of Bifidobacterium and Faecalibacterium spp; and, when present, a 4-fold lower average number of methanogens”. While the degree of changes may depend on the severity of the diseases and doses of therapeutic agents, the effect of berberine appears to be in line with these observations. Wang et al. [109] have shown that dysbiosis was detected in the gut microbiome of Thrombocytopenia (ITP) patients with Lachnospiraceae bacterium, Clostridium asparagiforme were overrepresented while Bacteroides spp was depleted when compared with healthy controls. In this case, berberine treatment could improve the microbial dysbiosis of corticosteroid-resistant ITP patients (Table 3). Interestingly, berberine but not antibiotics, enhance the response to corticosteroid therapy by reversing the effect of L. bacterium colonization on gut microbiota structure. This of course needs further research to establish how modulation of L. bacterium could lead to the observed effect. In the antidiabetic activity studies using db/db mice, Zhang et al. [62] showed that berberine and metformin could reverse the disease-mediated reduction in the level of occludin and ZO1 tight junction proteins along with increased SCFA content in faeces and/or reversal of the altered microbiota composition (Table 3). 3.4. Other organoprotective effects

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Given the diverse pharmacological effects of berberine through multiple mechanisms including general anti-inflammatory and antioxidants properties, its organoprotective effect is not surprising. By regulating autophagic flux, berberine can induce hepatoprotective effect under high level of cholesterol [66]. Hence, it induces neuroprotective effects in cellular models such as SH-SY5Y and PC12 cells [119,120], in animal models [121,122] and under clinical conditions [123]. The hepatoprotective [124,125], cardioprotective including in humans [126-128] and nephroprotective [129,130] effects, among others, of berberine have been well-established. On these bases and the organoprtective effects under obesity, hyperepidemic and diabetes discussed in the preceding sections, it is interesting to see the link between its organoprotective and modulatory effects in the gut microbiota. Guan et al. [131] have studied the role played by the colon microbiota in the ameliorative effect of berberine on the bleomycin-induced pulmonary fibrosis (PF) in mice. While the mechanisms involved activation of PPAR-γ in lung tissues, they have shown that it was a result of hepatocyte growth factor (HGF) expression in colonic fibroblasts. In this connection, the LPS-induced hepatocyte proliferation via stimulation of HGF has been shown to be suggested as the link between the gut microbiota and liver regeneration [132]. In the gut of liver cirrhosis patients, potentially pathogenic bacteria including the Enterobacteriaceae and Streptococcaceae have been shown to be predominant while the beneficial

bacteria such as Lachnospiraceae exit at lower level [133]. Agents like berberine with a profound effect on the structure of the gut microbiota in health and diseases are thus likely to modulate diseases through such mechanisms. Evidence for the direct link was further provided by the study of Quin et al. [134] which showed that berberine could ameliorate the diethylnitrosamine-induced hepatotoxicity and intestinal damage induced by penicillin or DSS. They have also used faecal microbiota transplantation experiment to demonstrate that the observed beneficial effect of berberine was mediated by homeostatic alteration in the gut microbiota. These data are also consistent with those by Jia et al. [135] which revealed that berberine can alleviate some of the inflammatory damage in germfree rats subjected to faecal microbiota from IBS patients. Other effect of berberine linked to the gut microbiota is related to periodontal bone loss [136]. 3.5. Cancer

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Noting the high inter-individual variability in the mice gut microbial composition, Wang et al. [137] studied colorectal cancer development in high-fat obese Apc min/+ mice. As with other experiments discussed in the previous sections, the predominant gut microbiota of wild type mice taxa at the phylum level were Firmicutes (55.7%) and Bacteroidetes (42.28%); and on the lower scale, Proteobacteria (1.69%) and Verrucomicrobia (0.11%). The individual variation in these groups could be up to 55% (Bacteroidetes and Firmicutes) in the wild type mice, while the level of Verrucomicrobia increases (wild type and Apc min/+ mice) by high-fat diet, treatment with berberine appear to ameliorate both the structural changes in microbiota and colorectal cancer development. The association between the effect of berberine on colorectal cancer and microbiota regulation was also investigated by Gao et al. [138]. Their study characterized the faecal microbiota, also known as fungal signature, in 131 subjects, comprising polyp and colorectal cancer (CRC) patients. They reported a distinct fungal dysbiosis and an alteration in the fungal network in polyp and CRC pathogenesis. Whether this pattern could be reversed by natural products such as berberine remains to be investigated. The study by Yu et al. [139] employed a potent carcinogen, 1,2-dimethylhydrazine (DMH) or Fusobacterium nucleatum in mice in the presence or absence of berberine. Treatment with F. nucleatum, for example, could increase the level of opportunistic pathogens such as Tenericutes and Verrucomicrobia both in in wild-type and in mice treated with DMH. Berberine was able to ameliorate this bacterial compositional change along with modulation of inflammatory markers: IL-21/22/31, CD40L and the expression of p-STAT3, p-STAT5 and p-ERK1/2, when compared with mice fed with F. nucleatum alone. The levels of opportunistic pathogens, such as Fusobacterium, Streptococcus and Enterococcus spp. gradually increased during the colorectal adenoma-carcinoma sequence in human faecal and mucosal samples. Readers should note that berberine is by far one of the best studied natural products for direct toxicity to cancer cells such as breast cancer [140], colorectal [141], lung [142], hepatocarcinoma [143], leukaemia [144], etc. By interfering signalling pathways such as the AMPK [145], PI3K/AKT [146,147], miRNA [148,149], and prostaglandin [150], berberine has been shown to suppress cancer metastasis. As an adjuvant or combination therapy, berberine has also been shown to enhance the activity of anticancer drugs such as tamoxifen [151], vincristine [152], cisplatin [153], etc. On these bases and the observed effect of berberine on the gut microbiota, berberine is an example of a natural products that acts through polypharmacology principles. General Summary and Conclusion Berberine is a multifunctional natural product with diverse therapeutic applications. As a potent inhibitor of enzymes such as acetylcholinesterase and its ability to alter the amyloid β-induced pathological changes, its therapeutic potential in neurodegenerative diseases such as Alzheimer’s disease has been advocated [4]. Berberine also possesses antioxidant and anti-inflammatory effects in vivo and its plethora of pharmacological effects as organoprotective agent could be linked to such

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properties. The therapeutic potential of berberine is thus through acting on multiple targets of the polypharmacology principle that has been shown for many natural products [22]. Evidences presented in this paper now appear to also show that the effect of berberine is linked to the diverse effects of the gut microbiota in health and disease as depicted in Figure 2.

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Figure 2. Modulation of the gut microbiota by berberine in health and disease. The polypharmacology of berberine is associated with the diverse effect of the gut microbiota in health and disease. Berberine has a poor bioavailability and its metabolism and pharmacokinetics are related to the activity of the microbiota. Under normal conditions, the structure and composition of the gut microbiota, partly through increased production of SCFAs, promote health. The reduced level of infection and LPS means low level of inflammation both in the gut and in the circulation which has also implication to improved lipid metabolism and insulin sensitivity. Under pathological conditions, the gut microbiota composition is in favour of pathogenic bacteria proliferation and the resulting gut inflammation with compromised intestinal barrier allow high level of systemic LPS. Altered lipid metabolism and insulin sensitivity are associated with such changes leading to the development of diseases such as hyperlipidaemia-associated cardiovascular diseases, diabetes, neurodegenerative diseases and organ disfunction associated with inflammation and oxidative stress (e.g., liver, kidney, and pulmonary dysfunctions). While berberine has multiple effects through enzyme/receptor and cell signalling mechanisms, a growing evidence now also suggest that it acts through modulation of the gut microbiota structure and composition.

The evidences on the modulation of microbiota by berberine showed a great deal of variability to the extent of changes both in quantitative and qualitative manor. While some evidences show, alteration in F/B ratio, some studies show no effect on this ratio. Although the general trend is that

berberine reverses the suppressed level of SCFAs under pathological conditions, there is also data variability related to which individual SCFA is more affected by berberine. Most of these data variations are also attributed to the inter-individual variations in the composition of the gut microbiota. The effect of berberine on the gut microbiota appears to be similar with the general pharmacology associated with the therapeutic application of probiotics, dietary fibres and other drugs such as metformin. With the call for more scientific research on the above-mentioned data variations, the polypharmacology of berberine is in part explained by its role in modulation of the gut microbiota. Conflicts of Interest: The authors declare no conflict of interest.

Funding: This work did not receive any financial support from either internal or external sources.

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