Nanotechnological breakthroughs in the development of topical phytocompounds-based formulations

Journal Pre-proofs Review Nanotechnological breakthroughs in the development of topical phytocompounds-based formulations Ana Cláudia Santos, Dora Rodrigues, Joana A.D. Sequeira, Irina Pereira, Ana Simões, Diana Costa, Diana Peixoto, Gustavo Costa, Francisco Veiga PII: DOI: Reference:

S0378-5173(19)30832-4 https://doi.org/10.1016/j.ijpharm.2019.118787 IJP 118787

To appear in:

International Journal of Pharmaceutics

Received Date: Revised Date: Accepted Date:

18 July 2019 10 October 2019 11 October 2019

Please cite this article as: A. Cláudia Santos, D. Rodrigues, J.A.D. Sequeira, I. Pereira, A. Simões, D. Costa, D. Peixoto, G. Costa, F. Veiga, Nanotechnological breakthroughs in the development of topical phytocompoundsbased formulations, International Journal of Pharmaceutics (2019), doi: https://doi.org/10.1016/j.ijpharm. 2019.118787

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Nanotechnological breakthroughs in the development of topical phytocompounds-based formulations

Ana Cláudia Santosa,b*, Dora Rodriguesa, Joana A. D. Sequeiraa, Irina Pereiraa,b, Ana Simõesa,b, Diana Costaa, Diana Peixotoa, Gustavo Costac, Francisco Veigaa,b

a

Department of Pharmaceutical Technology, Faculty of Pharmacy, University of Coimbra, Coimbra,

Portugal b

REQUIMTE/LAQV, Group of Pharmaceutical Technology, Faculty of Pharmacy, University of Coimbra,

Coimbra, Portugal c

Coimbra Institute for Clinical and Biomedical Research (iCBR), Faculty of Medicine, University of

Coimbra, Coimbra, Portugal; CNC.IBILI Consortium & CIBB Consortium, University of Coimbra, Coimbra, Portugal

*CORRESPONDING AUTHOR: Ana Cláudia Santos, Pharm.D., Ph.D. Assistant Professor Department of Pharmaceutical Technology Faculty of Pharmacy, University of Coimbra (FFUC) Pólo das Ciências da Saúde, Azinhaga de Santa Comba, 3000-548 Coimbra, Portugal Phone number: +351 239 488 400 Fax number: +351 239 488 503 E-mail address: [email protected]

Abstract Cosmeceuticals are a type of cosmetic products distinguished by the presence of active ingredients that, in addition to their cosmetic effects, also hold therapeutic outcomes. This review is focused on phytocompounds (PHYTOCs)-based cosmeceuticals, an established segment of cosmetic industry, due to the great demand for vitamins and plant-derived products. PHYTOCs beauty and health-related applications are due to their anti-oxidant, anti-bacterial, wound-healing, anti-aging, sun protection, cytoprotective, anticarcinogenic and anti-inflammatory activities. However, PHYTOCs present disadvantages, precisely the poor solubility, instability, reduced skin permeation and low skin retention time, which strongly restrict their topical application. Therefore, and since the cosmetic industry constantly pursues groundbreaking technological products, nanotechnology emerges as an innovative strategy to tackle the PHYTOCs recognized limitations. Nanotechnology manipulates and reduces materials size to 1 and 100 nm, creating structures able to encapsulate active ingredients, such as PHYTOCs, with the purpose of overcoming their limitations and delivering them in a controlled manner to the skin. This review highlights the potential properties of PHYTOCs loaded in several types of nanocarriers (liposomes, niosomes, ethosomes, transferosomes, cubosomes, phytosomes, nanoemulsions, nanocrystals, polymeric nanoparticles, solid lipid nanoparticles, nanostructured lipid carriers, carbon nanotubes, fullerenes, and dendrimers) used to overcome PHYTOCs free form limitations and potentiate their cosmeceutical properties. An approach to the “green” chemical synthesis of metallic nanoparticles taking advantage of PHYTOCS as natural reducing agents is exposed as well. Nanocosmeceuticals toxicity concerns and regulatory aspects are also addressed.

Keywords Phytocompound Nanocarrier Cosmeceutical Topical administration Skin care

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1. Introduction Cosmetic industry is an huge and dynamic segment of the world economy that, due to the public stringent concerns about beauty and skin care, is always pursuing the best technological products. Currently, nanotechnology is the hot trend in the cosmetic market. Nanotechnology is a science focused in the manipulation and reduction of materials to the nanometer scale (1 to 100 nm), granting upgraded or new properties which enable the regulation of a variety of different aspects that influence skin diffusion (Mu and Sprando, 2010). Nanotechnology-based carriers, also known as nanocarriers, are able to encapsulate active ingredients that have low water or lipid solubility. Moreover, nanocarriers protect the active ingredients from physical and chemical degradation, enable a controlled and sustained release, subsequently, diminishing the number of administrations. Furthermore, the use of nanocarriers in cosmetic formulations may increase the product skin spreadability making it more enjoyable, thus, enhancing public adherence (Mu and Sprando, 2010). Cosmeceuticals are a niche of cosmetic products composed of active ingredients that, besides their cosmetic benefits, evidence therapeutic effects capable of changing skin function and structure. In fact, the denomination “cosmeceuticals” seems to be a combination of two words related to their definition: “cosmetic”, due to the cosmeceuticals capacity to change the appearance of an individual; and “pharmaceuticals”, because of the presence of active pharmaceutical ingredients (APIs) with therapeutic action in their composition. Overall, cosmeceuticals are being used for topical treatments of very common skin and hair conditions, like photo-aging, acne, wound-healing, hyperpigmentation and hair damage, just to name a few. Therefore, cosmeceuticals are functionalized cosmetics with beauty and health applications (Gao et al., 2008, Nagaich U., 2016, Sanjeewa et al., 2016). The term cosmeceutical is not recognized by the Food and Drug Administration (FDA) and the European Commission (EC), but it is commonly used by the cosmetic industry to identify and isolate these products from the conventional cosmetics and to embellish them to the consumer’s eyes. Although most cosmeceuticals contain synthetic ingredients in their composition, PHYTOCs are gaining more interest as components of these formulations attending to their reduced toxicity in comparison with synthetic ingredients, which add to their beauty and health beneficial properties (Bocca et al., 2014, Komane et al., 2017). The majority of cosmeceuticals do not need commercial approval; thus, their safety is sometimes questioned, which leads the consumer to prefer cosmetic products based on plant-based bioactive ingredients since these ingredients are generally accepted by the consumers as safe. Plants are being used for centuries by societies to preserve and improve natural beauty. This fact, for itself, is enough to recognize the existing and potential properties associated with plants. Since the PHYTOCs present in plants have a natural origin, they do not possess the artificial aspects of synthetic chemical ingredients that are reported, most of the times, as responsible for skin irritation side effects. Besides that, in general, PHYTOCs are

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environment-friendly and compatible with different skin types. The strong consumer interest and the evident beneficial features have led the cosmetic industry to heavily invest time and R&D resources in PHYTOCsbased cosmeceuticals development (Draelos Z.D., 2009, Salverda et al., 2013, Joshi and Pawar, 2015). Until now, the investigation has been focused on testing isolated PHYTOCs for biodegradability and emulsification properties, as well as their efficiency as sun protection, anti-aging, anti-oxidant, anti-irritant, anti-hyperpigmentation, moisturizing and antimicrobial agents (Chanchal and Swarnlata, 2008, Dorni et al., 2017). However, PHYTOCs also evidence some limitations that impair their full application in cosmeceutical products. These natural compounds show poor solubility, instability, reduced skin permeation and low skin retention time. Such limitations may be overcome by incorporating the PHYTOCs into nanocarriers, including distinct types of nanoparticles (NPs) (Kidd, 2009, Krausz et al., 2014, Xie et al., 2016). Despite of the eminent NPs advantages, their use in cosmetic products raises some concerns about their toxicity, giving rise to some regulatory issues, since there is a scarcity of studies regarding NPs longterm effects allied with the fact that NPs are not pre-approved for commercialization (Wang et al., 2014a). In this review, the potential properties of PHYTOCs, including curcumin (CUR), vitamin C (AA), resveratrol (RES), rutin (RU), ursolic acid (UA), baicalin (BAI), capsain (CAP), quercetin (QUE), betulin (BE), α-mangostin, auraptene (AUR), luteolin (LT), silymarin (SILYM), silibin (SILIB), epigallocatechin3-gallate (EGCG), as well as extracts of Aloe vera, Citrus auranticum, Glycyrrhiza glabra, and pomegranate peel, as antibacterial, anti-aging, anti-carcinogenic, wound-healing, sun blocking, photoprotective, cytoprotective and anti-inflammatory agents are exposed when encapsulated using nanocarriers for cosmeceutical applications. The use of the following nanocarriers, particularly liposomes, niosomes, ethosomes, transferosomes, cubosomes, phytosomes, nanoemulsions, nanocrystals, polymeric NPs, solid lipid nanoparticles (SLNs), nanostructured lipid carriers (NLCs), carbon nanotubes, fullerenes and dendrimers are presented herein as promising solutions already employed to overcome recognized PHYTOCs limitations and potentiate their beauty and medicinal merits. “Green” chemical synthesis of metallic NPs taking advantage of PHYTOCS as natural reducing agents is exposed, along with nanocosmeceuticals toxicity concerns and the inherent regulatory aspects.

2. Topical administration of active ingredients Skin is the largest organ of the human body and its most important function is the protection against external factors (e.g., microorganisms, temperature, among others) (Baroli, 2010, Lai-Cheong and McGrath, 2017). The skin is divided in three main layers: the epidermis, the dermis and the hypodermis, whose composition was detailed revised in (Benítez and Montáns, 2017, Bibi et al., 2017). Concerning topical administration,

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the transport of an active ingredient through the skin may be carried out through different pathways: (i) transepidermal intracellular route; the (ii) transepidermal intercellular route; and the (iii) transfollicular or transappendageal route. Moreover, the diffusion of active ingredients across the different skin layers is influenced by: molecular weight (MW) of the active ingredients; absorption channels; solubility; polarity; dermabrasion; ultrasound waves and electric currents (Benítez and Montáns, 2017, Bibi et al., 2017, Desai et al., 2010, Nafisi and Maibach, 2017). It is in the context of these requirements that nanotechnology plays a major role, since it can manipulate and reduce materials to the size of 1 to 100 nm, granting upgraded or new properties capable of enabling the regulation of the aforementioned aspects that influence skin diffusion, namely the encapsulated molecules solubility increase, just to refer an example (Mu and Sprando, 2010). Further aspects concerning the use of nanotechnology for the topical delivery of PHYTOCs will be thoroughly addressed in the following Section 3.

3. Nanotechnology for the topical delivery of phytocompounds For many years, synthetic-based cosmeceuticals were the main commercialized cosmetic products. However, more recently, due to a rise in health awareness by consumers, the toxicity associated with synthetic ingredients has been raising concerns. The solution to overcome this undesired toxicity concern seems to be the use of plant-derived PHYTOCs that already have proven to enhance beauty and to prevent, mitigate or treat some pathological conditions (Gismondi et al., 2014, Pandel et al., 2013). Therefore, PHYTOCs are a great promise to the cosmeceuticals pipeline. In order to overcome PHYTOCs constrains, such molecules may be encapsulated or conjugated with nanocarriers (Cheng et al., 2012, Kidd, 2009, Krausz et al., 2014, Xie et al., 2016). According to nanomaterial’s nature, it is possible to describe different nanocarriers. The organic nanocarriers, like liposomes, NLCs, SLNs, nanoemulsions and dendrimers are preferred to inorganic nanocarriers, as metallic NPs, due to their changeable properties and performance through the adjustment of their chemical composition, surface, shape and size (Conte et al., 2017). Nanoformulations containing nanosized PHYTOCs evidence markedly improved properties, such as controlled release, targeted delivery, as well as increased PHYTOCs loading capacity in a lower volume (Steichen et al., 2013). On the basis of these premises, nanotechnology has been universally investigated by the cosmetic industry due to its practical advantages in overcoming active ingredients limitations, showing, so far, to be a very efficient tool to

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encapsulate PHYTOCs. Such potential and technological evolution led to the origin of nanocosmeceuticals and, consequently, of PHYTOCs-based nanocosmeceuticals. Nevertheless, to consider nanocosmeceuticals as good candidates for PHYTOCs topical delivery, the nanocarriers have to possess optimal skin permeation features. In this context, the transport of an active ingredient through the skin may be carried out through different pathways, as referred. Such happens according to the active ingredient’s physicochemical properties, and to environmental factors, including the viscosity, and the tortuosity and the diffusional path length (Benítez and Montáns, 2017, Benson, 2012, Bibi et al., 2017, Desai et al., 2010, Nafisi and Maibach, 2017). Therefore, skin permeation is determined by the nanocarriers’ particle size, shape, surface charge, entrapment efficiency (EE); as well as the active ingredient physicochemical properties, such as the MW (Baroli, 2010), partition coefficient (log P), distribution coefficient (log D) (Kundi and Ho, 2019), permeability coefficient (Kp), acid dissociation coefficient (pKa); and the vehicle’s pH (Baroli, 2010). Regarding nanocarriers, the particle size and shape determine the transport of the active ingredients through the skin layers, having impact in the active ingredients’ stability, release and cellular uptake. For instance, in healthy individuals, particles with size under 5-7 nm can cross the stratum corneum (SC), the first layer of the epidermis, by the transepidermal intercellular pathway. Particles under 36 nm can cross SC through the aqueous pores; whereas larger particles, with a particle size between 10 and 210 nm, may enter through the transfollicular route. Particles above 600 nm stay in the SC without delivering their cargo into deeper layers of the skin. It is generally accepted that smaller nanocarriers are more likely to deliver the active ingredients through several skin permeation routes, thus promoting a superior therapeutic outcome (Baroli, 2010, Danaei et al., 2018, Geusens et al., 2011). Particle size measurements are commonly assessed by dynamic light scattering (DLS), and the shape is usually assessed by electron microscopy. Besides particle size and shape, the zeta potential, which corresponds to the electrokinetic potential of NPs, influence on skin permeation. Zeta potential measurements are extremely important to predict the NPs stability in colloidal dispersions, as it indicates the extent of electrostatic repulsion between equal charged NPs. Such potential is highly dependent of the combination of the nanomaterial and the surfactant chemical nature. When anionic or cationic surfactants are used in NPs production, a minimum zeta potential of |30| mV (absolute value) is achieved, leading to an adequate formulation stability due to the effective electrostatic repulsions between NPs. In the presence of non-ionic surfactants, zeta potential magnitude is obtained generally below |30| mV, which advocates that attractive forces may lead to NPs aggregation. However the dispersion stability is ensured by the presence of additional mechanisms of steric stabilization conferred by the nonionic surfactants. A major factor to have in consideration when measuring zeta potential is pH, which really influences it, as pH may be responsible for the deprotonation and protonation of the superficial groups (Pardeike and Müllera, 2010, Zielińska and Nowak, 2016, Wu et al., 2011). Zeta potential measurements

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are commonly assessed by electrophoretic light scattering (ELS) (Xu, 2008). The corneocytes (differentiated keratinocytes) cell membrane and NPs interact through electrostatic interactions. The corneocytes cell surface is composed by a broad of negatively charged domains, which are responsible for the negative skin charge. Generally, these domains would repel negatively charged NPs but, in fact, firstly, negatively charged NPs are absorbed to the cell membrane and, secondly, NPs clusters are formed and enter into the cell by endocytosis (Honary and Zahir, 2013). The surface charge and the surface modification of the nanocarriers is crucial to their adhesion and cellular uptake, determining the way of permeation (Patil et al., 2007, Uchechi,et al. 2014). Additionally, EE is important to assess how efficient the encapsulation of the active ingredient in the nanocarrier might be. The formulation of a nanocarrier presumes the attainment of a high value of EE, since it avoids the wastage of the encapsulated active ingredient, enhancing the clinical efficacy of the nanoformulation. This parameter must not be confused with the loading capacity, which is the amount of loaded compound per unit weight of the nanocarrier (Huang al., 2018, Rosenblatt and Bunjes, 2017). Furthermore, concerning the active ingredients to be encapsulated, the optimal MW of the active ingredient should be under 600 Da in order to provide an optimal percutaneous delivery. In addition, the log P of the nanosized active ingredient must be assessed to enable the design of an optimal nanoformulation (Bannan et al., 2016). The log P refers to the equilibrium distribution of an active ingredient in a system composed of two completely immiscible or partially miscible solvents, such as emulsions with an organic phase and a water phase. It is presented as the ratio of the concentrations of the active ingredient in the two solvents and it is used as a measure of the lipophilicity of the active ingredient. The log P differs from the log D, which takes into account all ionized and neutral forms of the active ingredient at a determined pH value (Kundi and Ho, 2019). Both parameters can be determined using the shake-flask method, which consists of the dissolution of the studied compound in a volume of octanol and water followed by the measure of the compound concentration in each solvent. Besides the shake-flask method, voltametric, or chromatographic methods, where the log P of a compound is determined by correlating its retention time with similar compounds with known log P values, are also possible methods for the same purpose (Andrés et al., 2015, Ulmeanu et al., 2003).Another important parameter for skin permeation is the Kp, that gives information about the aptitude of a nanosized active ingredient to be absorbed by the skin. It is calculated according to Fick's first law. Finally, considering that the majority molecules that diffuse through the lipophilic intercellular regions of the skin are usually not charged, the pKa of the nanosized active agent, as well as the vehicle’s pH are parameters of imperative setting (Baroli, 2010). Besides the physicochemical properties, there are also biological aspects to consider, in particular: (i) the skin area where the formulation is intended to be applied (considering the skin integrity); (ii) the local variation (different body regions have different skin thickness, and variation on the appendages density);

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and (iii) skin hydration (a high water content increases skin permeability) (van Smeden and Bouwstra, 2016, Vogt et al., 2005).

3.1. Nanocosmeceuticals A vast range of PHYTOCs have already been incorporated in nanocarriers. Hereinafter, examples of different PHYTOCs-loaded nanocarriers are presented. Table 1 resume all the following presented examples.

[Please, insert Table 1 about here]

3.1.1. Vesicular systems Vesicular systems constitute a group of nanocarriers made of amphiphilic molecules that evidence a selfassembly capacity under specific conditions. A vesicular system is a very organized structure that is able to encapsulate both lipophilic and hydrophilic compounds and offer higher compound delivery and protection, as well as, controlled and target release (Karami and Hamidi, 2016). Several types of PHYTOCs-loaded vesicular systems exist, including liposomes, niosomes, ethosomes, transfersomes, cubosomes and phytosomes (Figure 1 and 2).

3.1.1.1. Liposomes Liposomes are sphere-shaped vesicular structures made of a single or multiple concentric lipid bilayers of cholesterol and phospholipids arranged around an aqueous core (Figure 1). The number of bilayers allows liposomes to be classified as: i) unilamellar vesicles (ULVs) or ii) multilamellar vesicles (MLVs). The ULVs can also be classified according to their size as small unilamellar vesicles (SUVs), large unilamellar vesicles (LUVs) and giant unilamellar vesicles (GUVs), since the vesicles size can range from 25 nm to many micrometres (Akbarzadeh et al., 2013, Escobar-Chávez et al., 2012). Liposomes differ in shape and size depending on the preparation procedures and the process variables (Akbarzadeh et al., 2013). Liposomes are able to carry hydrophilic molecules in the aqueous core and hydrophobic molecules trapped inside the lipid bilayer. This aspect, along with their non-toxic nature and long circulation time, makes them a really efficient nanocarrier for cosmeceuticals delivery (Escobar-Chávez et al., 2012, Uchechi et al. 2014). In fact, liposomes may be composed by lipids and ceramides present in the SC, the ones responsible for the water impermeable barrier of skin and, thus be used as a strategy to increase the lipid composition of the SC, attenuate the water loss and deliver lipophilic substances, such as vitamins (e.g., vitamins A and E) and

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anti-oxidants (e.g., lycopene), to the skin. The encapsulation of vitamins and/or anti-oxidants in liposomes grants protection from the external environment, and improves the physicochemical properties of the encapsulated molecules, in particular, the aqueous solubility. Owing to such, this type of nanocarrier is used frequently in skin care products with moisturizing and anti-aging indications (Nuzhatun, 2015, Ramirez et al., 2009). CUR is the Curcuma longa (turmeric) active ingredient, which shows a wide range of beneficial properties, including anti-aging, moisturizing, anti-oxidant, antineoplastic, antibacterial, anti-inflammatory and woundhealing properties (Mahmood et al., 2015). However, its clinical application is impaired because of its poor stability and solubility, which lead to a low bioavailability (Jagannathan et al., 2012). These limitations may be surpassed by using strategic nanocarriers for its nanoencapsulation (Guorgui et al., 2018). In this context, CUR-loaded liposomes were prepared to study their permeation capacity and CUR anti-cancer action. As the phospholipids are one of the principal components of liposomes, their different typology may have an impact on the liposome’s properties, namely in its cellular permeability. In this study, the use of different phospholipids and how those influence the topical delivery of CUR were investigated. Natural phospholipids, soybean phospholipids (SPCs) and egg yolk phospholipids (EPCs), and synthetic phospholipids, hydrogenated soybean phospholipids (HSPCs), were used to formulate CUR-loaded liposomes. All the liposomes were of small size, precisely: 82.37 ± 2.19 nm for CUR-loaded SPC liposomes (CUR-SPC-Ls), 83.13 ± 4.89 nm for CUR-loaded EPC liposomes (CUR-EPC-Ls) and 92.42 ± 4.56 nm for CUR-loaded HSPC liposomes (CUR-HSPC-Ls). Although all of the liposomes formulated were effective at improving CUR skin permeation, CUR-SPC-Ls showed to be the most effective nanocarrier for CUR with a superior drug release of 67.38%, when compared to the drug release of the CUR-EPC-Ls (64.22%) and CUR-HSPC-Ls (34.14%); as well as, the higher EE value of 82.32 ± 3.91%, when compared with CUREPC-Ls (81.59 ± 2.38%) and CUR-HSPC-Ls (80.77 ± 4.12%). In addition, enhanced skin permeation and retention were evidenced by CUR-SPC-Ls, with 34.84 μg·cm-2 of amount of permeated CUR when compared with 31.97 μg·cm-2 for CUR-EPC-Ls and 21.87 μg·cm-2 for CUR-HSPC-Ls. The effect of the different phospholipids use in the permeation of the liposomes was found to be extremely relevant (Chen et al., 2012). Vitamin C, also known as AA, is a commonly known anti-oxidant present in plants that has been shown to play a significant role in anti-aging beauty treatments due to the promotion of collagen synthesis capability (Crisan et al., 2015). The stability of this vitamin is affected by heat, light and storage conditions, which can easily turn vitamin C into its inactive constituents. The low stability of vitamin C limits its cosmeceutical utilization (Sliem et al., 2017), and, again, nanotechnology can be used to engineer and properly deliver vitamin C, surpassing its handling and administration restrictions (Yang et al., 2013). Accordingly, in a research study, vitamin C-loaded liposomes coated with pectin were reported as showing better storage

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stability and superior skin permeation when compared with free vitamin C (Zhou et al., 2014). In another conducted study, the stability of vitamin C was enhanced by its incorporation into liposomes. The results showed a high EE, an improvement in the stability and a superior anti-oxidant activity of vitamin C conferred by the vitamin C-loaded liposomes (Yang et al., 2013). Aloe vera pulp is composed of polysaccharides that evidence skin healing properties, being used in the treatment of a wide range of skin conditions, in particular eczema and burns (Radha and Laxmipriya, 2015). The Aloe vera wound-healing properties are due to the plant ability to stimulate the synthesis of collagen and elastin fibers. Additionally, Aloe vera also exhibits anti-aging and moisturizing properties (Moriyama et al., 2016, Tabandeh et al., 2014). In this regard, Aloe vera leaf gel extract-loaded liposomes have shown to increment the bioavailability of the Aloe vera leaf gel extract as well as its skin care effects (Takahashi et al., 2009).

3.1.1.2. Niosomes Niosomes are vesicles, like liposomes but constituted by non-ionic surfactants (e.g. Tweens, Spans and Brijs). Non-ionic surfactants are structurally similar to the phospholipids used in liposomes, since these surfactants are also composed by a lipophilic tail and a hydrophilic head. Niosomes are formed due to the self-assembly capacity of the non-ionic surfactants in aqueous media (Figure 1). Besides the non-ionic surfactants, niosomes are also composed by cholesterol. These NPs can also be sorted in three categories: SUV and LUV, with sizes ranging from 10 to 100 nm and from 100 to 3000 nm, respectively; and MLV, when there is more than one bilayer. Niosomes have the capacity to encapsulate both lipophilic and/or hydrophilic molecules, thus showing the same cosmeceutical applications as liposomes. However, due to their different composition, these vesicles show superior stability, EE and skin penetration, controlled release patterns and are cost-effective when compared with liposomes (Moghassemi and Hadjizadeh, 2014). On account of the niosomes non-ionic surfactants composition, these nanocarriers are also biocompatible, biodegradable, non-irritant and non-immunogenic (Uchechi et al. 2014). Additionally, thanks to the niosomes hydration (proniosomes), these vesicles hold a notorious advantage regarding consumer compliance, since niosomes are less greasy in comparison with other oil-based systems (Rajera et al., 2011). Niosomes have shown an optimal anti-oxidants transdermal delivery efficiency, being effective in the delivery of CUR, RES and -tocopherol, which can be applied to prevent skin pathological conditions related to oxidative stress (Tavano et al., 2014). Ellagic acid (EA), an anti-oxidant and a potential skin-whitening agent with poor solubility in water and in some organic solvents, was formulated in EA-loaded niosomes by using Span 60 and Tween 60 (at 2:1) and the solubilizers polyethylene glycol 400, methanol and propylene glycol that were used to increase EA

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solubility. These niosomes showed higher EE and higher amount of EA delivery to the deeper skin layers when compared with an EA solution. It was concluded that the different types and compositions of surfactants and solubilizers impact significantly on the EE and the stability of EA-loaded niosomes (Junyaprasert et al., 2012). Niosomes were also reported to improve CUR bioavailability and have shown to be a more efficient nanocarrier in protecting CUR from deterioration when compared to other nanocarriers employing surfactants, due to the rigidity and composition of the niosomes membrane (Mandal et al., 2013). Niosomes were also investigated and have shown augment RES stability and solubility (Pando et al., 2015). RES is a natural polyphenol existent in red grapes and in red wine that is known for an extended range of health benefits, such as anti-aging, anti-inflammatory, skin-whitening and anti-acne activities (Docherty et al., 2007, Fan et al., 2018, Lee et al., 2014). RES exists in two isomeric forms, -trans and -cis, however, in comparison with the -cis isomer, the -trans isomer, is more biologically active. Nonetheless, the -trans isomer may undergo degradation easily when exposed to environmental factors, such as light. The rapid isomerization and auto-oxidation makes RES a very unstable compound (Ratz-Lyko and Arct, 2018). Such reasons render RES as a candidate for nanoencapsulation, in this case achieved successfully with niosomes that promoted a superior RES skin penetration. Despite the aforementioned advantages, both liposomes and niosomes have been revealing some disadvantages in terms of their use in topical delivery, as they are prone to fuse into higher-sized vesicles, consequently allowing the leakage of active ingredients. In order to overthrow these disadvantages, innovative vesicular systems have been tailored, namely: ethosomes, transfersomes, cubosomes and phytosomes (Kazi et al., 2010, Wang et al., 2014b), which are exposed below.

3.1.1.3. Ethosomes Ethosomes are elastic vesicles composed of phospholipids and ethanol (20-45 % of ethanol content) (Figure 1). Ethanol works as a permeation enhancer due to its ability to interact with lipid molecules, reducing the melting point of the lipids present in the SC and, consequently increasing the cell membrane lipid fluidity and permeability. Ethanol causes a change in the net charge of ethosomes, resulting in a steric stabilization, which decreases vesicle size and increases stability, thus, avoiding aggregation. Ethosomes vesicles size can be fine-tuned from tens of nanometers to microns (Touitou et al., 2000, Verma and Pathak, 2010). Thanks to their synergistic interaction with skin structures, ethosomes have a much higher delivery efficiency when it comes to the amount and depth of active ingredient vehiculation to the skin. RU is a glucoside flavonoid found in redwine, buckwheat, red pepper, and tomato commonly used as a nonprescription dietary supplement (Kızılbey, 2019). RU evidences a strong antioxidant activity and is used to

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prevent or to treat venous or lymphatic insufficiency, or capillary fragility and permeability, as well as to prevent the damage caused by UV radiation (Candido, et al., 2018). In this context, RU-loaded ethosomes were developed to improve the RU skin permeation rate, in order to reach deeper epidermis layers and overcome the SC barrier. The authors carried out an ex vivo study, using a tape stripping technique to study the permeation of RU-loaded ethosomes into the skin. Twenty strips were applied into human skin after application of RU-loaded ethosomes (F1) and free RU (F2), and the results were divided in three groups: 1 - tape 1; 2 - tape 2 to 10; 3 - tape 11 to 20; where the first group is the representative of the more superficial layer of SC and the group 3 is representative of the deeper skin layers. In tape 1, the permeation assay results showed a concentration of delivered RU of 0.135 ± 0.081 μg/mL for F1 and 0.471 ± 0.261 for F2; while in the tapes 11-20, the assay results showed RU concentrations of 0.090 ± 0.037 μg/mL to F1 and 0.027 ± 0.023 μg/mL to F2. Thus, the permeation study shows that free RU (F2) was retained at the superficial layers of the SC, while RU-loaded ethosomes were able to penetrate and deliver RU to deeper skin layers (Candido, et al., 2018). UA is a pentacyclic terpenoid present in numerous medicinal plants, like Rosmarinus offıcinalis, Eriobotrya japonica and Ocimum sanctum, as well as in the wax coating of fruits like apples and prunes. UA holds multiple health properties, as anti-oxidant, anti-aging, anti-inflammatory, cytotoxic, anti-microbial and cellular renewal promoter (Wozniak et al., 2015, Kashyap et al., 2016, Wiemann et al., 2016, Ahmad et al. 2018, Lopez-Hortas et al., 2018). However, it exhibits the common PHYTOCs limitation: the poor water solubility, resulting in low bioavailability. To improve UA physicochemical properties and to incorporate it in cosmeceutical products, studies using nanotechnological approaches have been performed (De Almeida et al., 2013). UA-loaded ethosomes were developed for transdermal application to enhance the UA skin penetration. An improved penetration was achieved when compared to a 10% isopropanolic solution of free UA in in vitro diffusion cell studies using rat skin (Chen et al., 2011).

3.1.1.4. Transfersomes Transfersomes (so-called transferosomes) are a different kind of vesicular systems, composed of an aqueous core surrounded by the lipid bilayer and surfactants, which act as edge activators (Figure 1). The edge activators are surfactant molecules that are responsible for the transfersomes deformability, making them able to pass through the SC intracellular lipids without significant depletion. Evidences show that transfersomes with sizes up to 500 nm are able to spontaneously penetrate into the SC. Therefore, transfersomes are very adaptable and can respond to stress conditions, making them eligible carriers for PHYTOCs delivery when compared with liposomes (Rajan et al., 2011).

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BAI-loaded transfersomes and BAI-loaded gellan tranfersomes efficacy was studied in terms of polyphenol anti-inflammatory action in inflamed skin and compared to Betnovate®, a commercial cream of betamethasone used to treat skin inflammatory conditions. To study the transfersomes efficacy, skin appearance and inflammation markers (e.g., edema and the tumor necrosis factor alfa (TNF-α)) were evaluated and measured. The Betnovate® TNF-α inhibition was 0%, while the BAI-loaded transfersomes and BAI gellan-transfersomes TNF-α inhibition was 67 ± 20% and 100 ± 21%, respectively. The difference between the two nanoformulations was explained by the higher absorption and retention of BAI on the skin by the application of BAI-loaded gellan transfersomes when compared to the BAI-loaded transfersomes. Betamethasone, a large lipophilic steroid molecule that constitutes the API on the conventional Betnovate® formulation, evidences difficulties to diffuse from the cream to the skin, showing much lower efficiency inhibiting TNF-α when compared to the BAI-loaded transfersomes and BAI-loaded gellan tranfersomes that, due to their deformable property, quickly diffuse to the skin and release BAI to the dermis, ultimately stimulating pro-inflammatory markers inhibition and, subsequently, promoting skin repair (Manconi et al., 2018).

3.1.1.5. Cubosomes As stated previously, the self-assembly of amphiphilic molecules in vesicular systems formation makes these molecules to rearrange in stable lamellar structures (resulting in liposomes). However, this rearrangement may occur also in hexagonal and bicontinuous cubic phases, giving rise to cubosomes (Figure 2). Thus, cubosomes are nanostructured liquid crystalline particles composed by particular amphiphilic lipids in precise proportions. Cubosomes are recognized as biocompatible carriers in drug delivery and possess a particle size that ranges from 100 to 500 nm. These NPs are composed by rounded bicontinuous lipid bilayers organized in a three-dimensional structure. This specific structure of cubosomes resembles a honeycomb architecture, which consist of two different hydrophilic channels that are separated by a lipid bilayer. Therefore, PHYTOCs of distinct polar properties might be incorporated. The cubosomes’ structure confers a notorious drug loading potential due to their high inner surface area, higher encapsulation capacity for amphiphilic, lipophilic and hydrophilic molecules, biodegradability, and controlled and targeted active ingredient release features (Duttagupta et al., 2016, Garg et al., 2007, Karami and Hamidi, 2016). Phytantriol-based cubosomes (F1) and glycerol monooleate-based cubosomes (F2) were formulated and characterized in order to find a sustained and targeted transdermal delivery carrier for CAP. CAP is a natural alkaloid with properties that have been used to treat skin conditions associated with psoriasis and pruritus. The EE of CAP-loaded cubosomes showed high values of EE; particularly, F1 exhibited an EE of 97.10 ± 0.54% and F2 depicted an EE of 97.58 ± 0.53%. The release study performed during a 36 h period accounted for 41% (F1) and 33% (F2) of released CAP, revealing a CAP sustained release profile. In addition, the

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diffusion study showed a CAP skin retention of 2.75 ± 0.22 μg (F1) and 4.32 ± 0.13 μg (F2) for CAP-loaded cubosomes, when compared with 0.72 ± 0.13 μg of a CAP free form-based cream. The data clearly emphasized the importance of the nanosystems for the transdermal administration of CAP (Peng et al., 2015).

3.1.1.6. Phytosomes Phytosomes are a combination of a phytocompound and a natural phospholipid, e.g., phosphatidylcholine. These nanocarriers are a patented technology that fits plant-derived active ingredients delivery, since phytosomes improve PHYTOCs absorption due to their lipid membranes crossing ability, which is reduced in poor water soluble PHYTOCs. Besides that, phytosomes enable PHYTOCs targeted delivery reducing the required dosage, because of PHYTOCs optimized bioavailability and minimized toxicity. Phytosomes differ from liposomes, since the PHYTOCs polar function groups react with the polar head of the phospholipids and become an integral member of the membrane, while, in liposomes, such reaction does not occur and PHYTOCs are just surrounded be the phospholipids (Figure 1). Contrary to liposomes, phytosomes have shown better applications in skin care products, since those are formed by fewer molecules, making them much more readily absorbed. Also, thanks to the strong covalent bonds between the PHYTOCs and the phospholipids, phytosomes are more stable than liposomes (Gnananath et al., 2017, Li et al., 2014b, Mirzaei et al., 2017). Citrus auranticum and Glycyrrhiza glabra are two plants, composed of anti-oxidant polyphenols, which have proven to augment skin hydration and skin viscoelastic properties, being helpful in preventing skin aging. In a study, the extracts of Citrus auranticum and Glycyrrhiza glabra were simultaneously used to develop a phytophospholipid complex (phytosome) loaded in a cream with increased skin absorption and retention that could lead, ultimately, to a polyherbal formulation with a synergetic skin anti-aging action. The complexes were arranged in extract:phospholipid ratios of 1:1, 1:2, 1:3 and 2:1. The ratio 1:1 presented the highest EE (93.22 ± 0.26 %). To test the complexes, a phenolic content diffusion and retention comparative study was performed on pig skin using an extract-based cream and a phytosome-based cream. The results showed that, in 24 h, the skin diffusion was faster for the extract cream in comparison with the phytosome-based cream. Moreover, the amount of phenolic content retained in the pig skin was higher for the phytosome-based cream (33.89 ± 2.46 micro-GA equivalent (μGAE) cm-2), in contrast to the extractbased cream (5.87 ± 1.56 μGAE cm-2). These findings confirmed that the PHYTOCs and phospholipids complexation may enhance PHYTOCs skin retention for prolonged periods (Damle and Mallya, 2016). Such data were in accordance with the previous suggested utility of phytosomes to delay intrinsic skin aging or natural aging processes related to solar radiation exposure (photo-aging) (Thring et al., 2009), reinforcing the high potential of these formulations as anti-aging cosmeceuticals.

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QUE is a flavonoid present frequently in several plants. QUE is known for its anti-oxidant, antiinflammatory and antimicrobial activities. When compared to other flavonoids, QUE revealed higher antioxidant activity, due to its content in hydroxyl (-OH) groups (Lee et al., 2016). However, like other PHYTOCs, QUE shows lack of stability and a reduced skin permeation and retention efficiency, thereby nanotechnology has been used to solve those known limitations. QUE-loaded phytosomes have successfully proved to reduce inflammatory redness and the itchy sensation caused by exposure to the UV radiation and the histamine prick test (Maramaldi et al., 2016).

[Please, insert Figure 1 about here]

[Please, insert Figure 2 about here] 3.1.2. Nanoemulsions An emulsion is a mixture of two immiscible liquids, in which a liquid (the dispersed phase) is dispersed into other (the continuous phase). An interfacial tension between these two liquids exists because of the attractive interactions discrepancy (Figure 3 (a)). In this way, to make the formulation structure last longer without coalescing, a soluble surfactant is usually added to the continuous phase (Gupta et al., 2016). Nanoemulsions can incorporate both lipophilic and hydrophilic ingredients, since those can be prepared as oil-in-water (O/W) and water-in-oil (W/O) emulsions. A nanoemulsion is based on the same principles as a macroemulsion, but with an important difference: the sizes of the droplets of the dispersed phase are much smaller, evidencing a size between 5 to 200 nm. Nanoemulsions have demonstrated to be appropriate to transport both lipophilic and hydrophilic ingredients into the skin, while improving skin penetration and enhancing the PHYTOCs concentration due to the higher loading, which is a consequence of the nanoemulsions small droplet size (Kaci et al., 2018, Nastiti et al., 2017). Pomegranate peel contains anti-oxidant polyphenols, like GA and EA. These polyphenols have shown photoprotection properties. The interest in developing an appropriate formulation for the topical delivery of these anti-oxidant polyphenols led to the execution of an in vitro permeation study using nanoemulsions entrapping an ethyl acetate fraction from a pomegranate peel extract. The results showed that EA and GA reached the viable epidermis and dermis only when formulated as nanoemulsions, with epidermis retention values of 1.36 and 1.78 μg cm-2 to EA and GA, respectively; and dermis retention values of 0.97 and 1.10 μg cm-2 to EA and GA, respectively. These data supported the ability of nanoemulsions to improve PHYTOCs concentration and their skin penetration (Baccarin and Lemos-Senna, 2017). Nanoemulsions containing RES have also shown to protect RES against UV radiation-induced deterioration (Kumar et al., 2017).

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BE, also known as betulinic alcohol or betulinol, is a pentacyclic triterpene found in the Betula sp. bark, which is known for its broad range of biological activities, including anticancer, antiviral and antiinflammatory effects (Dehelean, Feflea et al. 2013, Krol, Kielbus et al. 2015). These effects can be enhanced by taking advantage of the proper nanoformulation in order to improve its bioavailability by increasing skin penetration when applied topically. Topical application of a BE-loaded nanoemulsion based in 7,12dimethylbenz[a]anthracene (DMBA) and 12-O-tetradecanoylphorbol 13-acetate (TPA) was applied for 12 weeks in skin carcinoma-bearing Balb/c mice. It was found that BE acted as a prophylactic and curative antitumor agent in skin carcinoma; and that its formulation into a BE-loaded nanoemulsion inhibited skin tumor promotion and growth with low levels of toxicity to the skin, after applied topically over the carcinoma (Dehelean et al., 2013).

3.1.3. Nanocrystals Nanocrystals (Figure 3 (b)) are nanocarriers with a particle size usually ranging between 200 and 500 nm. Nanocrystals are solely composed by active ingredients in their pure state. Usually it is referred that nanocrystals have 100% of drug loading capacity attaining a higher active ingredient concentration when compared to polymeric NPs. Nanocrystals are prepared in water and lipid phases, as colloidal nanosuspensions, with surfactants or polymers used for stabilization. This kind of nanoparticulate system has been studied for topical purposes, since it can augment skin permeation due to the following factors: (i) the higher saturation solubility, which will raise the concentration gradient among the formulation and skin and, consequently, the molecule diffusion into the skin; (ii) the nanometer size, that will lead to a higher skin adhesion and to an enlargement of the surface area, which, subsequently, will increase the molecule dissolution velocity (Al Shaal et al., 2011, Lai, Schlich et al., 2015). SmartCrystals® are a second generation of nanocrystals produced by a combination of technological processes. For example, combination of lyophilization and high pressure homogenization makes possible to achieve smaller nanocrystals with superior physical stability (Keck et al., 2008). QUE was formulated into QUE-nanocrystals with the purpose of overcoming its inherent poor water solubility. QUE-nanocrystals presented a saturation solubility of 3.63 ± 0.67 g/mL when compared with QUE free form saturation solubility of 0.48 ± 0.12 g/mL. These results show that particle sizes in the nanorange incremented the kinetic solubility. Besides that, QUE-nanocrystals with Tween 80 in their composition, as surfactant, required 30 min to dissolve an amount of 79.1 ± 13.7%, in contrast with QUE free form that took 30 min to dissolve an amount of only 13.0 ± 4.7%. Taking into account that a faster dissolution and superior saturation solubility are required for a good transdermal delivery, the nanocrystals previously cited seem to be strongly suitable to topical deliver PHYTOCs, namely, flavonoids (with marked low water solubility) (Hatahe et al., 2016).

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3.1.4. Polymeric nanoparticles Polymeric NPs are nanocarriers made of polymers with a trustworthy record of human safe use. The organic phase constitution and the preparation method will determine the formation of nanocapsules or nanospheres. Regarding nanocapsules, the encapsulated molecules are confined in the aqueous or oily core enclosed by a polymeric shell. In the case of nanospheres (Figure 3 (c)), encapsulated molecules are uniformly dispersed with polymers in the polymeric matrix (Crucho and Barros, 2017). Those nanocarriers are suitable for drug delivery due to their high stability, high drug loading and EE, controlled release capability and low enzymatic degradation (Hussain et al., 2013). In addition, the surface of polymeric NPs may be easily modified and enable ligands complexation, thus allowing the development of customized carriers to a specific need, e.g., cell targeting (Patel et al., 2012). Several natural polymers are available (e.g., chitosan), and synthetic polymers including biodegradable, non-biodegradable and biocompatible polymers (e.g., (poly) glycolic acid (PGA) or (poly) lactic acid (PLA)). Among the biocompatible and biodegradable polymers, chitosan is a natural-based cationic polysaccharide of interest to fabricate polymeric NPs, because of its mucoadhesive properties alongside with its optimal transepidermal penetration capacity attained due to the opening capability of intercellular tight junctions (Hussain et al., 2013, Moritz and Geszke-Moritz, 2015). A study was performed to access the potential anti-Propionibacterium acnes (or P.acnes) activity of αmangostin, the principal active component of Garcinia mangostana L., vulgarly known as mangosteen fruit, in order to find an effective prevention or cure for acne. P.acnes is a part of the normal flora of sebaceous glands, thus, the delivery of α-mangostin-loaded nanocarriers through the transfollicular route could easily target the sebaceous glands promoting the direct release of α-mangostin and, consequently, enhancing the PHYTOCs anti-P.acnes activity. Towards that aim, ethyl cellulose-methyl cellulose (EC-MC) NPs loaded with α-mangostin were produced and characterized. The polymer mixture, EC-MC, was chosen to produce the polymeric NPs due to its high drug loading capacity. The obtained α-mangostin-loaded polymeric NPs revealed a particle size of 400 nm, which was considered as an optimal size for transfollicular administration. The α-mangostin-loaded polymeric NPs loading capacity value was 50%. The α-mangostinloaded EC-MC NPs showed anti-P. acnes activity in vitro, while the free form of α-mangostin suspended in water revealed no P.acnes activity in the cell lines used. The sustained release of α-mangostin from the α-mangostin-loaded EC-MC NPs was observed for 7 days. Additionally, the therapeutic outcome of αmangostin was evaluated in 10 patients with acne in a 4-week double-blind, randomized, split face assay. The α-mangostin-loaded EC-MC NPs revealed a positive anti-acne therapeutic outcome, which was observed in all the patients studied (Pan-In et al., 2015). Thus, this study, emphasizes the cosmeceutical potential of PHYTOCs-loaded polymeric NPs.

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In another study, RU was loaded in poly(lactic-co-glycolic acid) (PLGA) NPs. PLGA is a biodegradable, biocompatible, nontoxic, FDA and European Medicines Agency (EMA)-approved copolymer. RU-loaded PLGA NPs with a particle size of 252.6 ± 2.854 nm and a RU encapsulation efficiency of 81% protected RU from premature degradation and enabled its controlled release (Kızılbey 2019).

3.1.5. Lipid nanoparticles 3.1.5.1. Solid lipid nanoparticles SLNs are comparable to a nanoemulsion, as they have a hydrophilic shell and a lipid hydrophobic core with a standard size ranging from 40 to 1000 nm (Figure 3 (d)). The difference is in the hydrophobic core, which is solid at body and room temperatures. In this way, the melting point of the lipids that compose the NPs must be higher than the body and ambient temperatures (≥ 40 ºC) (Naseri et al., 2015). The lipids normally used are triglycerides, fatty acids, waxes or a mixture of the aforementioned. SLNs contain also in their composition water, co-surfactants and surfactants that work as lipid dispersion stabilizers. The surfactants typically used to produce SLNs are phospholipids, bile salts, fatty acids, sorbitan esters or a mixture of those. Moreover, since it is possible to avoid the use of organic solvents in SLNs production, these NPs are generally accepted as biocompatible and show reproducibility, constituting a suitable nanocarrier to encapsulate and deliver PHYTOCs (Mehnert and Mader, 2001). Hydrophobic molecules may be incorporated in the solid core of SLNs leading to an enhanced permeation, stability, target specificity, low toxicity, low degradation, as well as a controlled release. Thanks to the solid lipid matrix, SLNs evidence skin adhesive film-forming properties that may be advantageous in treating chronic atopic eczemas and additional skin disorders (Daneshmand et al., 2018). Besides that, SLNs show an additional occlusive behavior (Geszke-Moritz and Moritz, 2016). This occlusive behavior is the responsible reason for the application of nanocarriers, such as SLNs, in cosmeceuticals formulations, since this behavior enables the formation of a skin superficial film, reducing the transepidermal water loss and improving skin hydration (Garces et al., 2018). It is important to note that SLNs promote a higher occlusive effect in comparison with the second generation of lipid NPs, NLCs, attending mainly to the higher degree of crystallinity of the SLNs matrix, which is responsible for a consequent increment of the occlusion factor (Wissing and Muller, 2002). AUR is an anti-oxidant coumarin that exhibits anti-inflammatory effects, thus, having the potential to be applied in the treatment of inflammatory skin conditions. Nevertheless, AUR has poor water solubility and low skin permeation. To surpass AUR physicochemical limitations, AUR-loaded SLNs were prepared and characterized. Thereupon AUR encapsulation, the AUR-loaded SLNs presented an EE of 84.11 ± 3.30%. Subsequently, in the stability study held for over three months, the AUR-loaded SLNs dispersion preserved its odor, texture and color. In addition, the SLNs retained the particle size and EE, emphasizing the effective

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protection against AUR degradation conferred by the SLNs. Furthermore, in the performed release study, after 24 h, only ca. 11.84% of AUR was released from the AUR-loaded SLNs in contrast to the ca. 61.18% of AUR released from the free-AUR-based conventional cream, showing the sustained release capacity of AUR-loaded SLNs. In the skin retention study performed, there was a skin accumulation of ca. 44.64 µg cm−2 for the AUR-based conventional cream and ca. 133.77 µg cm−2 for the AUR-loaded SLNs, illustrating the potential of SLNs as AUR carriers, since these NPs enable an AUR controlled release (Daneshmand et al., 2018). Additionally, SLNs showed to be optimal nanocarriers to deliver RES, presenting high RES EE values (Nemen and Lemos-Senna, 2011). Three types of lipid-based nanocarriers, including nanoemulsions, SLNs and NLCs, were studied comparatively in terms of their capability to enhance RES delivery. All the lipidbased nanocarriers showed promising results regarding the topical delivery of RES; however, SLNs were considered the best nanocarriers for this purpose, since those provided a superior controlled release profile. In fact, authors have underpinned that the release rate of NLCs was possibly accelerated when the liquid lipid proportion was reduced (Sun et al., 2014). QUE-loaded SLNs evidenced the ability to permeate deeper into the skin layers, evidencing potential to treat inflammatory processes and psoriasis (Bose et al., 2013, Hatahet et al., 2018). LT (30,40,5,7-tetrahydroxyflavone) is a flavonoid present in medicinal herbs, vegetables and fruits that holds anti-oxidant, pro-oxidant, and estrogenic activity (since flavonoids are reported as phytoestrogens), anti-inflammatory, anti-allergic (Lin et al., 2008, Jeong et al., 2016), and skin anti-aging properties (Jeong et al., 2016). In a research study, triple-tailed cationic SLNs consisting of cationic lipids were prepared for the effective delivery of LT. Fvorable results suggested LT effective transdermal delivery with a desirable slow release kinetic without initial burst. Also, a high intracellular LT uptake was observed, resulting in high cytoprotective effects against UVA and H2O2 (Jeong et al., 2016). Notwithstanding, SLNs have some limitations particularly related to their crystallinity, which can lead to the reduction of the active ingredient loading capacity and active ingredient expulsion. These limitations have prompted the development of the second generation of lipid NPs: the NLCs (Ahmad et al., 2018, Mehnert and Mader, 2001).

3.1.5.2. Nanostructured lipid carriers NLCs appeared as a strategy to outweigh the disadvantages arising from SLNs. These NPs exhibit a different core lipid composition. NLCs are composed of both long and short chain lipids, resulting in a half solid and half liquid lipid mixture-based core, which, when crystalized, forms an imperfect matrix that enables the accommodation of higher amounts of lipophilic molecules (Sanad et al., 2010) (Figure 3 (e)). This feature

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allows for a higher loading capacity and lower active ingredient expulsion in relation to SLNs. Thus, NLCs can easily incorporate hydrophobic PHYTOCs into their core, e.g., RES, constituting a recommended nanocarrier for these poorly soluble compounds (Gokce et al., 2012). NLCs have been chosen to be the nanocarriers incorporated in several anti-aging and sunscreen formulations due to their controlled release and occlusive properties (Andreo-Filho et al., 2018, Montenegro et al., 2017). SILYM and its major constituent, SILIB, have been traditionally used for the treatment of liver diseases and, more recently, evidence was found for their anti-neoplastic effects, attributed to anti-oxidant and immunomodulatory activities, in a variety of in vitro and in vivo cancer models, including skin, breast, lung, colon, bladder, prostate and kidney carcinomas. Those are flavonoids present in the extracts from the medicinal plant Silybum marianum (milk thistle) (Cheung et al., 2010). SILYM has has been receiving, thereby, much attention for its application in the chemoprevention of UV-induced skin cancer. However, SILYM presents low water solubility, low chemical stability and poor biological membranes permeability. Bearing in mind such difficulties, a study was performed to formulate a SILYM-loaded NLCs-composed gel, aiming for an epidermal SILYM deposition improvement. Besides the suitability of NLCs for SILYM delivery, those nanocarriers exhibit the crucial capacity of UV-light scattering (just like titanium dioxide), conferring recognized sun-blocking properties (Iqbal et al., 2012). Two critical parameters were screened in order to achieve an optimal SILYM-loaded NLCs formulation: (i) lipid composition and (ii) lipid crystallinity. Lipid composition was found to have an important role in SILYM payload. The lipid crystallinity is determined by the melting point of the lipids used and appears to have an impact on the occlusive effect of the formulation, as well as in the drug release, drug EE and formulation stability. In NLCs, particle size and zeta potential were identified as critical features. The particle size influences skin permeation and retention, whereas the zeta potential ensures physical stability and a higher EE. The EE of SILYM-loaded NLCs suffered an increase of ca. 74.80% to ca. 90.50% when the lipid concentration increased from 0.8 to 2.2% w/w, respectively. This shows that SILYM solubilization is higher when higher amounts of the lipid phase are used. An ex vivo permeation study revealed that the skin permeation of SILYM-loaded NLCs-composed gel was 201.2 ± 1.1 μg/cm2 when compared to the SILYM permeation of a SIYM conventional gel (57.2 ± 1.5 μg/cm2). Results also revealed a Kp of 23.6 x 10-3 cm/h for SILYMloaded NLCs-composed gel, and 6.3 x 10-3 cm/h for the SILYM conventional gel. The findings of the permeation study revealed that, in comparison with the SILYM conventional gel (without NLCs), the incorporation of SILYM-loaded NLCs in the gel improved the skin permeation, attributing a major role to NLCs regarding the profitable obtained outcome (Iqbal et al., 2018). Ocimum sanctum L. leaf extract (OLE)-loaded NLCs were formulated for improved UA transdermal delivery. It was found that after topical application to Wistar rats with induced arthritis, OLE-loaded NLCs induced skin permeation of UA, present in the referred extract. Moreover, OLE-loaded NLCs were effective

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for the treatment of arthritis, with results equivalent to those obtained with the standard marketed formulation of diclofenac gel for topical application (Ahmad et al., 2018).

3.1.6. Carbon nanostructures 3.1.6.1. Carbon nanotubes Carbon nanotubes are carbon nanostructures with remarkably small sizes (under 100 nm). These nanotubes present a wide inner volume that allows the high loading of molecules and, at the same time, present an exterior surface that may be chemically functionalized to promote a targeted delivery (Figure 4 (a)). In addition, the highly stable carbon nanotubes have shown anti-oxidant and cytoprotective properties (Gupta et al., 2013), and have been used to topically deliver active ingredients thanks to their enhanced transdermal penetration, especially for hydrophobic drugs (Degim et al., 2010). CUR, a phytocompound with promising anti-neoplastic applications, evidences concerning drawbacks, namely the poor water solubility and high instability, as already mentioned. These limitations impair the attainment of specific CUR concentrations required for its anti-neoplastic activity. A study was performed by (Li et al., 2014a) to develop single wall carbon nanotubes (SWCNTs) to deliver CUR. The SWCNTs were chosen since these nanocarriers protect CUR from degradation and increase its solubility. The results showed that the loading efficiency of CUR-loaded SWCNTs was 94.00%, explained by the SWCNT vast surface area. The solubility of CUR suffered an increment of 1.88 mg/mL, when formulated using SWCNTs, in comparison to the considerably lower native CUR solubility (0.006–0.007 mg/mL). Additionally, in the CUR-loaded SWCNTs, only 5% of the CUR was degraded when compared to the high degradable native CUR, that, after 8 h in PBS, was degraded in 55% (Li et al., 2014a).

3.1.6.2. Fullerenes Fullerenes are a type of carbon allotrope containing odd-numbered rings of carbon resulting in a 3D spherical silhouette, which resembles a soccer ball, being also named as buckyballs (Figure 4 (b)). These nanocarriers assume the most stable structure in a typical carbon order of C60, the pristine fullerene. Initially, fullerenes exhibited some limitations due to their high hydrophobicity, however, nowadays, the use of surfactants and surface modifications are some of the selected tools to increase fullerenes water solubilization (Wu et al., 2011). In addition, fullerenes evidence a great anti-oxidant activity. Thus, fullerenes constitute a promising bioactive nanocarrier to be incorporated into hair and skin care (e.g., antiaging creams or sunscreens), as well as in additional dermatological products (Ngan et al., 2015). Once applied to the skin, fullerenes show a protective activity against keratinocyte apoptosis induced by the

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reactive oxygen species (ROSs) formed by the UV exposure (Murakami et al., 2013). Moreover, fullerenes also show an increased penetration into epidermis without causing skin irritation, which makes them a good option for the development of topical formulations to treat acne vulgaris (Inui et al., 2011). As a matter of fact, there is a fullerene derivate called fullerenol, C60(OH)24, that has shown anti-microbial properties against P.acnes and sebum production suppression (Aoshima et al., 2009, Inui et al., 2012). In addition, fullerenes have been reported to possess hair growth stimulation activity, but the responsible mechanism is not clear yet. However, hypotheses pointing to fullerenes anti-oxidant properties exist, since there is data suggesting a relation between oxidative stress and hair loss (Trueb, 2009, Zhou et al., 2009). In this regard, the co-administration of aqueous mixtures of 1% fullerenes and 2% of AA was performed, and the authors concluded that these mixtures provided better protection against oxidative skin damage caused by UVB irradiation than the administration of just fullerenes or AA to live rats whose skin was UVB irradiated. The results of this study suggested that fullerene, as well as AA, show ROS-reducing effects, but both effects are the result of different ROSs-scavenging mechanisms, resulting in a synergic protection effect between AA and fullerenes. Besides, the co-administration resulted in the spontaneous formation of bonds between fullerenes and AA. The authors suggested that fullerene is bonded to a high-electron-density oxygen atom of AA. This interaction impairs the AA-mediated Fenton reaction between iron (Fe) from hemoglobin and ROS, based on their observations of ascorbate-specific UV absorption quantifications (Ito et al., 2010).

3.1.7. Dendrimers Dendrimers are branched nanocarriers with particle size ranging between 2 to 20 nm. These nanocarriers are produced from a starting nitrogen element, to which a number of other elements, like carbons, are added in a step-by-step polymerization growth process, which leads to successive branches. Ultimately, dendrimers adopt an arborescent form (Figure 4 (c)). In the end of the process, the final dendrimers are composed by three components: (i) the initiator core; (ii) the inner layers, called “generations” (number of repeated branches added); and (iii) the exterior, which contains the terminal functional groups that are attached to the last inner layer. Both hydrophobic and hydrophilic molecules can be incorporated in dendrimers. The dendrimers structure allows the controlled delivery of entrapped molecules, which are bonded to the inner layers of dendrimers. These nanocarriers also provide a targeted molecular delivery to the site of action through the modification of the terminal groups present in the exterior of the dendritic structure (Rai et al., 2016). A study with SILIB, a lipophilic polyphenolic flavonoid, and EGCG, a hydrophilic polyphenolic catechin and the major component of green tea, was performed to analyze the skin permeation and retention effects

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of peptide dendrimers loaded with these PHYTOCs. Peptide dendrimers were chosen due to their reduced toxicity and biodegradability to simple amino acids in opposition to conventional dendrimers, as polyamidoamine (PAMAM), which is degraded to form acrylates. The permeation assay was performed using a rat skin ex vivo model and the diffusion of the polyphenols alone was compared to the diffusion of the polyphenol-dendrimer complex. The Kp of SILIB alone was 0.0055 cm/h and 0.0128 cm/h for EGCG alone. A Kp of 0.0221 cm/h was achieved by the SILIB-dendrimer complex, while the EGCG-dendrimer complex displayed a Kp of 0.1206 cm/h. Regarding the skin retention, in the non-complexed SILIB the skin deposition was 123.29 ± 3.85 μg/cm2, whereas in the non-complexed EGCG it was 90.83 ± 3.88 μg/cm2 for. When both polyphenols were complexed with dendrimers, the PHYTOCs skin retention results were the highest found, with 183.25 ± 6.96 μg/cm2 for the SILIB- dendrimer complex and 212.18 ± 8.68 μg/cm2 for the EGCG-dendrimer complex. This study highlighted the strong topical delivery enhancement that dendrimers display for both hydrophilic and hydrophobic PHYTOCs (Shetty et al., 2017).

[Please, insert Figure 3 about here]

[Please, insert Figure 4 about here]

4. Phytocompound-synthesis-based nanotechnology Metallic NPs, in particular silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) (Figure 4 (d) and Figure (e), respectively), have gained special attention in biomedical fields for applications as antimicrobial, antifungal and anti-inflammatory agents in cosmetics products, as well as in medical devices, constituting interesting nanocarriers for drug delivery, with special emphasis on cancer therapy, and diagnostics (Wang et al., 2016). Thereby, the antifungal and antibacterial properties of metallic NPs are exploited in cosmetics and topical administration (Kaul et al., 2018), even though the antibacterial mechanism has yet not been completely understood (Dizaj et al., 2014, Park et al., 2016). It is believed that the antibacterial AgNPs mechanism of action is linked with AgNPs binding to the disulfide and sulfhydryl groups of enzymes essential for bacteria survival, resulting in the inability of the bacteria to perform their essential metabolism. Another hypothesis for the antibacterial action is linked with the release of ions by the metallic NPs, damaging the bacterial membranes; or generation of ROSs by the metallic NPs, resulting in the inhibition of DNA replication, inducing protein denaturation, which ultimately leads to the disruption of the bacteria cell wall (Dizaj et al., 2014, Park et al., 2016). For the production of metallic NPs, environmentally friendly synthetic chemical methods, also known as green chemistry (Park et al., 2011), have been emerging. Green chemistry uses biosynthetic methods as

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simple and viable alternatives to the chemical and physical methods that use toxic compounds, like chemical reducing agents, such as hydrazine, sodium citrate and sodium borohydride. These toxic compounds are usually used to reduce the corresponding precursor metallic salts into uniform suspensions of metallic NPs (Chandran et al., 2006, Park et al., 2011). Alternatively, in green chemistry, the main premises to be followed in the preparation of metallic NPs consist of using an environmentally benign solvent, and a non-toxic material-based reducing agent for the stabilization of the NPs (Park et al., 2011). The latter premise is totally achieved by the use of plant extracts and natural products, which are receiving considerable attention for the synthesis of metallic NPs, by PHYTO-synthesis. 4.1. Metallic nanoparticles Numerous plants have been utilized for the PHYTO-synthesis of metallic NPs, including AgNPs and AuNPs (Mittal et al., 2013,Yadi et al., 2018). Particularly, polysaccharides show hydroxyl groups, a hemiacetal reducing end, and other functionalities that play important roles in both the reduction and the stabilization of metallic NPs (Shah et al., 2015). Water is commonly used as an environmentally benign solvent, replacing toxic organic solvents in the green synthesis of AgNPs and AuNPs (Shah et al., 2015). With that in mind, aqueous extracts of the brown algae Sargassum incisifolium were employed to synthesize AgNPs and AuNPs. The extracts are rich in sulfated polysaccharides known as “fucoidans”, polyphenols and phlorotannins. Such compounds also are reported to have antibacterial activity, cytotoxicity and antioxidant capacity. The antioxidant capacity enable the reducing power, resulting in the reducing of Ag+ to Ag and Au3+ to Au. The produced metallic NPs were assessed against two gram-negative bacteria: Enterococcus faecalis and Staphylococcus aureus subsp. Aureus; two gram-positive bacteria: Acinetobacter baumannii and Klebsiella pneumoniae subsp. pneumoniae; and one yeast strain: Candida albicans. It was found that AgNPs possess potent antimicrobial activities and were particularly toxic to Gram-negative bacteria, while AuNPs have shown only negligible bactericidal activity (Mmola et al., 2016). The authors also evaluated both metallic NPs cytotoxic activity against cancerous (HT-29, MCF-7) and non-cancerous (MCF-12a) cell lines. Good results regarding AgNPs were obtained, revealing selectivity for cancerous HT-29 cell line. AuNPs displayed negligible toxicity (Mmola et al., 2016). In another study, AuNPs and AgNPs were synthesized by a green synthetic route using only RES as reducing agent, and thus avoiding the involvement of additional noxious chemical reducing agents. The produced NPs showed potential for application as nano-antibacterial agents with greater antibacterial activity against Gram-positive and Gram-negative bacteria compared to that of RES alone. AuNPs displayed the highest antibacterial activity against Streptococcus pneumoniae. Another research group synthesized AuNPs and AgNPs using Aloe vera plant extract as the reducing agent, due to its carbonyl groups, which lead to the formation of very small spherical stable AgNPs with 15.2 ± 4.2 nm of particle size (Chandran et al., 2006).

24

Others have used Dendropanax morbifera (D. morbifera) Léveille, an oriental medicinal plant traditionally used for improving blood circulation, as reducing agent to stabilize AuNPs and AgNPs. Besides the reducing power, D. morbifera has been reported to contain acetylenes, saponin glycosides, terpenoids and volatile oils, being the latter linked to the reducion of total cholesterol, triglycerides, and low-density lipoprotein cholesterol levels, as weel as promotion of high-density lipoprotein cholesterol levels in mice. D. morbifera extract is also linked with the non-proliferation and non-migration of vascular smooth muscle cells and important antioxidant effects. D. morbifera crude leaf extract acted as both reducing and stabilizing agent, leading to a rapid synthesis of the metallic NPs (around an hour), avoiding additional steps of toxic solvents removal (Wang et al., 2016). The produced AgNPs and AuNPs were tested for cytotoxicity using two cell lines. Specifically, AgNPs exhibited lower cytotoxicity in the human keratinocyte (HaCaT) cell line at 100 μg/mL after 48 h than AuNPs, but exhibited a potent cytotoxicity in lung cancer cells (A459) at the same concentration after 48 h (Wang et al., 2016). The aforementioned data firmly emphasize the potential of natural compounds and plant extracts as a tool to obtain rapid, one-step, clean, nontoxic and ecologically methods for the production of stable metallic NPs, constituting a viable alternative to the chemical traditional synthesis methods.

5. Marketed nanocosmeceuticals The potential of PHYTOCs-based nanocosmeceuticals became so noticeable and believable that all the consequent investment in R&D by the cosmetic industry has been revealing positive outcomes regarding their commercialization. Several examples of commercialized nanocosmeceuticals are illustrated in Table 2.

[Please, insert Table 2 about here]

6. Nanocosmeceuticals toxicity Taking into account the major growth of the nanocosmeceuticals market, the amount of people exposed (not only consumers, but also industry workers involved in the production), as well as, the lack of toxicity studies, some concerning aspects associated with the nanocosmeceuticals potential toxicity exist. A list of these crucial points is disclosed below: 

The small size of nanocarriers allows their passage through cell membranes, subsequently, these nanocarriers reach sensible organs and interact with cells, proteins and DNA (Pourmand and Abdollahi, 2012). Some available reports refer that nanocarriers with a particle size inferior to10

25

nm can act like a gas and pass through human tissues, easily crossing the cell membranes and leading to disturbs in the cell chemistry (Bahadar et al., 2016). 

Nanocarriers can enter into human organisms through the skin, gastrointestinal and respiratory routes. There are evidences suggesting that nanocarriers that enter into the human body through inhalation can translocate to the brain (Mostafalou et al., 2013).



The reduced loading and encapsulation capacity of nanocarriers leads to an increase in the amount of surfactants added to their formulations. This can lead to potential adverse effects related to the surfactant, such as skin irritation and trauma, disruption of skin enzyme activity (leading to abnormal body physiological function) and potential toxicity, since the surfactants and inclusive the nanocarriers can accumulate in the body (Yuan et al., 2014).



Studies regarding the nanocarriers permeation into unhealthy skins are lacking. In unhealthy skin, the skin structure and its composition is different, thus, the nanocarriers effects may also be distinct (Wang et al., 2014a).



The need for long-term toxicity studies should be a present concern to disclose the effects of chronic exposure to nanocosmeceuticals (Wang et al., 2014a).

In response to the present boom of nanotechnology-based products, their increasing consumption and the concern about their safety, the EC, the FDA and additional governmental organizations developed guidance and guidelines to minimize the potential toxicity of nanomaterials in order to increase their safety. It can be concluded that this overall concern may be implied in upcoming changes. In fact, the EC already holds regulation towards nanomaterials used in the European Union (EU) cosmetics, where safety studies are required (European Commission, 2009). The Organization for Economic Co-operation and Development and the International Organization for Standardization have been making standards to be used by the industry by creating the ISO/TS 13830:2013 - Guidance for the Voluntary Labelling of Products with Nano Elements and, more recently, the ISO 19007:2018 - Nanotechnologies - In Vitro Assay for Measuring the Cytotoxic

Effect

of

Nanoparticles,

which

is

an

in

vitro

3-(4,5-dimethylthiazol-2-yl)-5-(3-

carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay to evaluate the aggregation and agglomeration of NPs and their effects (International Organization for Standardization, 2013, 2018). The FDA, so far, does not have specific regulation concerning nanocarriers, but, recently, this entity did release a draft entitled Guidance for Industry: Safety of Nanomaterials in Cosmetic Products (Food and Drug Administration, 2014). These efforts might lead to prevent the use of nanocarriers when pre-clinically evidence of involved toxicity may exist. Therefore, on account of these guidelines’ implementation, toxicity might be detected previously to the commercialization of the nanocosmeceuticals-based formulations. Nevertheless, the knowledge about the nanocarriers toxicity has a long way to pave and there is an imminent need for studies to understand the actual interaction between the nanocarriers and the biological systems.

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7. Nanocosmeceuticals regulatory aspects When we talk about regulation in cosmeceuticals there is a quick question that comes to our minds: are they a cosmetic or a drug? In the EU, United States of America (USA) and Japan the term cosmeceutical is not legally recognized, since it does not fully fit in the definition of cosmetics or drugs, which means that there is a lack of specific regulation to support such products. In the EU and the USA, depending on their quantitative and qualitative composition, as well as, their claims, cosmeceuticals can come into the market as a cosmetic or as a drug. In the EU, cosmeceuticals are distributed as cosmetic and body hygiene products (PCHC), which should legally obey to the Regulation (EC) No 1223/2009 of the European Parliament and of the Council of 30 November 2009 on Cosmetic Products (European Commission, 2009). In the USA, the existing cosmetics regulation lays in two laws: (i) Federal Food, Drug and Cosmetic Act and (ii) Fair Packing and Labeling Act (Food and Drug Administration, 2018). Here the definition of cosmetic is more restricted and products as antiperspirants, sunscreens and anti-dandruff shampoos are distributed as cosmetic drugs. In the USA the cosmetic products do not need the entities approval to be commercialized. However, those are regulated by the two referenced laws. In the EU, the responsible personal must grant the commitment to the Regulation (EC) No 1223/2009, where safety evaluation is required. In the USA, the companies which manufacture and/or market the cosmetic products are the ones legally responsible for the products safety, which means that the FDA laws do not require safety information from the companies. In Japan, beauty products are regulated by the Ministry of Health, Labor and Welfare and their regulation lays on the Pharmaceutical and Medical Devices Law, where there is a legal term “Quasi- Drugs” for products that are a combination of cosmetics and drugs, which have specific regulation and need to be pre-approved before commercialization (Ministry of Health, Labor and Welfare of Japan, EU-Japan, 2015). When the cosmeceuticals have nanomaterials in their composition and are marketed in the EU, those should also respect the article no. 16 from the Regulation (EC) No 1223/2009 of the European Parliament and of the Council of 30 November 2009 on Cosmetic Products, which is the main regulation for nanomaterials used in cosmetics. This regulation specifies that all nanomaterials ingredients must appear stated on the package with the suffix “nano”, and that cosmetic products containing nanomaterials must be notified to the commission by the established responsible person with their specific information: identification, quantity, specification, safety data, toxicological profile and foreseeable exposure conditions. The regulation also specifies that this notification must be done six months before the cosmetic products are placed in the market. If the EC raise safety concerns about the product notification or about the nanomaterial used, it can request the Scientific Committee on Consumer Safety (SCCS) opinion. This SCCS from the EC has published up a guidance document entitled Guidance on the Safety Assessment of Nanomaterials in Cosmetics to answer the need of specific guidance to help in the development of standardized safety evaluation dossiers of nanomaterials. Although they emphasize that this guidance is based in the current

27

available information, albeit the risk assessment of the nanomaterials is still evolving

(European

Commission, 2012). Meanwhile, in USA, so far, the FDA has not endorsed a regulatory definition for “nanotechnology”, “nanoscale” or “nanomaterial”, however, FDA has stated that “the current framework for safety assessment is sufficiently robust and flexible to be appropriate for a variety of materials, including nanomaterials”. In July of 2007, a report from Nanotechnology Task Force recommended guidance to manufactures to describe safety affairs in cosmetic products with nanomaterials, which FDA implemented by building up the draft Guidance for Industry: Safety of Nanomaterials in Cosmetic Products, which is stated by the FDA as a “current thinking on this topic. It does not create or confer any rights for or on any person and does not operate to bind FDA or the public. You can use an alternative approach if the approach satisfies the requirements of the applicable statutes and regulations” (European Commission, 2009). Thus, the FDA shows a much “lighter” regulation, when compared to the EU.

8. Conclusions and future remarks The public interest and adherence to products composed of natural compounds is growing. Therefore, a lot of investigations regarding PHYTOCs-based cosmeceuticals have been developed in the recent decades and it is expected that the number of these studies will increase in the near future, since, in nature, there are many PHYTOCs with a diversity of beauty and health attractive properties. Nanotechnology constitutes a distinctive and useful approach to overcome PHYTOCs physicochemical limitations,

which

restrict

their

application

in

cosmeceuticals.

Using

PHYTOCs-loaded

nanocosmeceuticals, the encapsulated PHYTOCs can permeate skin in higher amounts, more profoundly, for more time, and with higher stability, thus, improving the efficacy of their cosmetic or therapeutic properties. Notwithstanding, in the past years, the fast PHYTOCs-based nanocosmeceuticals globalization has been raising questions concerning their toxicity mostly because most of cosmetics do not need precommercialization approval and because there are still no long-term toxicity studies available regarding this matter. Although regulation about cosmetics and nanomaterials used in the cosmetic industry have been refreshed and adjusted to the outstanding growing of nanocosmeceuticals, there are still some rough edges to smooth about this promising and strongly sought-after sector. Overall, new developments and the finest output are expected regarding PHYTOCs-based nanocosmeceuticals application in the cosmetic market for the next stretch.

Acknowledgments

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Joana A. D. Sequeira gratefully acknowledges Fundacão para a Ciência e a Tecnologia (FCT-Portugal) for the PhD grant with reference PD/BDE/135148/2017 funded by Ministério da Ciência, Tecnologia e Ensino Superior of Portugal and Fundo Social Europeu, as well as Tecnimede S.A. Ana Simões acknowledges the PhD research grant PD/BDE/135074/2017, assigned by FCT from Research Drugs & Development Doctoral Program and Dendropharma – Investigação e Serviços de Intervenção Farmacêutica, Sociedade Unipessoal Lda. Irina Pereira acknowledges the PhD research grant SFRH/BD/136892/2018 funded by FCT and Programa Operacional Capital Humano (POCH).

Conflict of interest and disclosure The authors report no financial or personal interests.

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Figure Captions Figure 1 - Figurative comparison of a conventional liposome and derivative vesicular systems used to nanoencapsulate PHYTOCs. PHYTOC - Phytocompound.

Figure 2 - Schematic representation of the derivative vesicular system cubosome.

Figure 3 - Schematic representation of different nanocarriers: (a) Nanoemulsion (b) Nanocrystal (c) Polymeric nanoparticle (type: nanosphere) (d) SLN, and (e) NLC. SLN - Solid lipid nanoparticle; NLC - Nanostructured lipid carrier.

Figure 4 - Schematic representation of different nanocarriers: (a) Carbon nanotube (b) Fullerene (c) Dendrimer, and Metallic NPs: (d) Silver NP and (e) Gold NP. NP - Nanoparticle

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Table 1 - Examples of nanocarriers reported in the literature as PHYTOCs-based nanocosmeceuticals. Nanocarrier

Liposomes

PHYTOC(s)

PHYTOCs activity/function

Ref.

CUR

Anticancer

(Chen et al., 2012)

AA

Anti-oxidant

(Zhou et al., 2014) (Yang et al., 2013)

Aloe vera extract EA

CUR Niosomes

RES

RU Ethosomes UA

Wound-healing Moisturizing Anti-aging Anti-oxidant Skin-whitening Anti-oxidant Anti-ageing Moisturizing Anticancer Antibacterial Anti-inflammatory Wound-healing Anti-inflammatory skin-whitening Anti-acne Anti-aging Antioxidant Photoprotection Venotonic Anti-oxidant Anti-inflammatory Antimicrobial Cytotoxic Anti-aging Cellular renewal

(Takahashi et al., 2009) (Junyaprasert et al., 2012)

(Mandal et al., 2013)

(Pando et al., 2015)

(Candido et al., 2018)

(Chen et al., 2011

Transferosomes

BAI

Anti-inflammatory

(Manconi et al., 2018)

Cubosomes

CAP

Anti-inflammatory

(Peng et al., 2015)

Citrus auranticum and Glycyrrhiza glabra extracts

Anti-oxidant Anti-aging

(Damle and Mallya, 2016)

QUE

Anti-oxidant Anti-inflammatory

(Maramaldi et al., 2016)

Pomegranate peel extract

Photoprotection

(Baccarin and LemosSenna, 2017)

RES

Anti-inflammatory Skin-whitening Anti-acne Anti-aging

(Kumar et al., 2017)

BE

Anti-cancer

Phytosomes

Nanoemulsions

(Dehelean et al., 2013)

45

Nanocrystals

Polymeric nanoparticles

QUE

Anti-oxidant Anti-inflammatory Photoprotection

(Hatahe et al., 2016)

α-mangostin

Anti-acne

(Pan-In et al., 2015)

RU

Anti-oxidant Photoprotection Venotonic

(Kızılbey 2019)

AUR

Anti-inflammatory

(Daneshmand et al., 2018)

RES

Anti-oxidant Anti-inflammatory Anti-acne

(Sun et al., 2014)

QUE

Anti-inflammatory

(Bose et al., 2013)

SLNs

LT SILYM NLCs

Anti-oxidant Cellular protection Photoprotection Anti-oxidant Photoprotection Immunomodulatory

(Jeong et al., 2016) (Iqbal et al., 2018)

UA

Anti-inflammatory

(Ahmad et al., 2018)

Carbon Nanotubes

CUR

Anti-oxidant Anti-cancer

(Li et al., 2014a)

Fullerenes

AA

Photoprotection

(Ito et al., 2010 )

Dendrimers

SILIB and EGCG

Anti-inflammatory Wound healing

(Shetty et al., 2017)

Abbreviations: AA, Ascorbic acid; AUR, Auraptene; BAI, Baicalin; BE, Betulin; CAP, Capsain; CUR, Curcumin; EA, Ellagic acid; EGCG, Epigallocatechin-3-gallate; LT, Luteolin; NLC, Nanostructured lipid carrier; PHYTOC, Phytocompound; QUE, Quercetin; RES, Resveratrol; RU, Rutin; SILIB, Silibinin; SILYM, Silymarin; SLN, Solid lipid nanoparticle; UA, Ursolic acid.

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Table 2 – Examples of PHYTOC-based nanocosmeceuticals currently marketed. Name Primordiale Optimum Lip Revitalift Double Lifting Hydra Flash Bronzer Daily Face moisturizer Vital Nanoemulsion ΑVC C-Vit Liposomal Serum VITACOS VITAHERB Whitening

Brand

PHYTOC(s)

Nanocarrier

Function

Lancôme

Vitamin E

Nanocapsule

Lip treatment

L’Oreal

Pro-Retinol A

Nanosome

Anti-wrinkle

Lancôme

Vitamin E

Nanocapsule

Moisturizer

(Singh and Sharma, 2016)

Marie Louise

Vitamin A and vitamin C

Nanoemulsion

Anti-wrinkle

(Kaul et al., 2018)

Sesderma

Vitamin C

Liposome

Hydration, collagen synthesis

(Sesderma)

Vitacos Cosmetics

Extracts of 10 herbs (Aloe Vera, Glycyrrhiza gabra and others)

Nanoemulsion

Skin whitening and anti-wrinkle

(VITACOS)

(Kaul et al., 2018)

Phyto NLC Active Night Repair Serum

Sireh Emas

CUR

NLC

Moisturizer, skinwhitening and anti-wrinkle

Lyphazomeand Celazome

Dermazone Solutions

Vitamin E

Nanocapsule

Moisturizer

Nano Vita C

Eccos

Vitamin C

Nanocapsule

Anti-aging

Ref. (Singh and Sharma, 2016) (Singh and Sharma, 2016)

(The Project on Emerging Nanotechnologies) (Eccos)

Abbreviations: CUR, Curcumin; NLC, Nanostructured lipid carrier; PHYTOC, Phytocompound.

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Graphical abstract

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