Retinoids: new use by innovative drug-delivery systems

Effects of Anionic Liposome Delivery of All-Trans-Retinoic Acid on Neuroblastoma Cell Differentiation

All-trans-retinoic acid (ATRA) has long been known to affect cell growth and differentiation. To improve ATRA's therapeutic efficacy and pharmacodynamics, several delivery systems have been used. In this study, free ATRA and anionic-liposome-encapsulated ATRA were compared for their effects on SK-N-SH human neuroblastoma cell growth and differentiation. Anionic liposomes made of L-α-phosphatidylcholine (PC) and L-α-phosphatidic acid (PA), empty (PC-PA) and loaded with ATRA (PC-PA-ATRA), were characterized by dynamic light scattering (DLS) and electrophoretic mobility measurements, and drug entrapment efficiency (EE%) was measured to evaluate the applicability of the new colloidal formulation. The results of brightfield microscopy and cell growth curves indicated that ATRA, whether free or encapsulated, reduced growth and induced differentiation, resulting in SK-N-SH cells changing from epithelioid to neuronal-like morphologies, and producing a significant increase in neurite growth. To further characterize the neuro-differentiation of SK-N-SH cells, the expression of βIII-Tubulin and synaptophysin and mitochondria localization were analyzed via immunofluorescence. Increased expression of neuronal markers and a peculiar localization of mitochondria in the neuritic extensions were apparent both in ATRA- and PC-PA-ATRA-differentiated cells. As a whole, our results strongly indicate that ATRA treatment, by any means, can induce the differentiation of parent SK-N-SH, and they highlight that its encapsulation in anionic liposomes increases its differentiation ability in terms of the percentage of neurite-bearing cells. Interestingly, our data also suggest an unexpected differentiation capability of anionic liposomes per se. This work highlights the importance of developing and carefully testing novel delivery nanocarriers, which are a necessary first "step" in the development of new therapeutic settings.

pH-sensitive niosomes for ATRA delivery: A promising approach to inhibit Pin1 in high-grade serous ovarian cancer

The peptidyl-prolyl cis/trans isomerase Pin1 positively regulates numerous cancer-driving pathways, and it is overexpressed in several malignancies, including high-grade serous ovarian cancer (HGSOC). The findings that all-trans retinoic acid (ATRA) induces Pin1 degradation strongly support that ATRA treatment might be a promising approach for HGSOC targeted therapy. Nevertheless, repurposing ATRA into the clinics for the treatment of solid tumors remains an unmet need mainly due to the insurgence of resistance and its ineffective delivery. In the present study, niosomes have been employed for improving ATRA delivery in HGSOC cell lines. Characterization of niosomes including hydrodynamic diameter, ζ-potential, morphology, entrapment efficiency and stability over time and in culture media was performed. Furthermore, pH-sensitiveness and ATRA release profile were investigated to demonstrate the capability of these vesicles to release ATRA in a stimuli-responsive manner. Obtained results documented a nanometric and monodispersed samples with negative ζ-potential. ATRA was efficiently entrapped, and a substantial release was observed in the presence of acidic pH (pH 5.5). Finally, unloaded niosomes showed good biocompatibility while ATRA-loaded niosomes significantly increased ATRA Pin1 inhibitory activity, which was consistent with cell growth inhibition. Taken together, ATRA-loaded niosomes might represent an appealing therapeutic strategy for HGSOC therapy.

Phasor-FLIM-guided unraveling of ATRA supramolecular organization in liposomal nanoformulations

Here we use fluorescence lifetime imaging microscopy (FLIM) to study the supramolecular organization of nanoencapsulated liposomal all-trans retinoic acid (ATRA), exploiting ATRA's intrinsic fluorescence as a source of signal and phasor transformation as a fit-free analytical approach to lifetime data. Our non-invasive method is suitable for checking for the presence of a fraction of ATRA molecules interacting with liposomal membranes. The results are validated by independent small-angle X-ray scattering (SAXS) and nano-differential scanning calorimetry (NanoDSC) measurements, probing ATRA's putative position on the membrane and effect on membrane organization. Besides the insights on the specific case-study proposed, the present results confirm the effectiveness of Phasor-FLIM analysis in elucidating the nanoscale supramolecular organization of fluorescent drugs in pharmaceutical formulations. This underscores the importance of leveraging advanced imaging techniques to deepen our understanding and optimize drugs' performance in delivery applications.

Localized topical drug delivery systems for skin cancer: Current approaches and future prospects

Topical drug delivery presents a novel substitute to the conventional drug-distribution routes of oral delivery and injection. Apart from the simplicity and non-invasiveness, the skin also serves as a “reservoir” that sustains administration over a period of days. Nanocarriers provide new potential for the treatment of skin disease. The skin’s barrier function offers a considerable obstacle for the potential nanocarriers to infiltrate into the tissue. However, the barrier is partially weakened in case of damage or inflammation, as in the case of skin cancer. Nanoparticles may promote the penetration of the skin. Extensive research has been done into producing nanoparticles for topical distribution; nevertheless, relatively little progress has been achieved in transferring them to the clinic for treating skin malignancies. The prior art features the critical concepts of skin malignancies and techniques in current clinical care. The present review gives a complete viewpoint of the numerous nanoparticle technologies studied for the topical treatment of skin malignancies and outlines the hurdles that hamper its advancement from the bench to the bedside. The review also intends to give knowledge of the routes that control nanoparticle penetration into the skin and their interactions inside the tissue.

All-Trans Retinoic Acid and Doxorubicin Delivery by Folic Acid Modified Polymeric Micelles for the Modulation of Pin1-Mediated DOX-Induced Breast Cancer Stemness and Metastasis

Stemness and metastasis are the two main challenges in cancer therapy and are related to disease relapse post-treatment. They both have a strong correlation with chemoresistance and poor prognosis, ultimately leading to treatment failure. It has been reported that chemotherapy can induce stemness and metastasis in many cancer types, especially treatment with the chemotherapeutic agent doxorubicin (DOX) in breast cancer. A combination treatment is an efficient and elegant approach in cancer therapy through simultaneous delivery of two or more drugs with a delivery system for its synergistic effect, which is not an additive of two individual drugs. Herein, we report a combinatorial system with DOX and all-trans retinoic acid (ATRA) to address both of the above issues. As a common critical regulatory factor for oncogenic signal transduction pathways, Pin1 is a specific isomerase highly expressed within various tumor cells. ATRA, a newly identified Pin1 inhibitor, can abolish several oncogenic pathways by effectively inhibiting and degrading overexpressed Pin1. We successfully developed a folic acid (FA)-modified chitosan (CSO)-derived polymer (FA-CSOSA) and obtained FA-CSOSA/DOX and FA-CSOSA/ATRA drug-loaded micelles. FA modification can improve the uptake of the nanoparticles in tumor cells and tumor sites via folate receptor-mediated cell internalization. Compared to treatment with DOX alone, the combined treatment induced 4T1 cell apoptosis in a synergistic manner. Reduced stemness-related protein expression and inhibited metastasis were observed during treatment with FA-CSOSA/DOX and FA-CSOSA/ATRA and were found to be associated with Pin1. Further in vivo experiments showed that treatment with FA-CSOSA/DOX and FA-CSOSA/ATRA resulted in 85.5% tumor inhibition, which was 2.5-fold greater than that of cells treated with DOX·HCl alone. This work presents a new paradigm for addressing chemotherapy-induced side effects via degradation of Pin1 induced by tumor-targeted delivery of DOX and ATRA.

Retinoids Delivery Systems in Cancer: Liposomal Fenretinide for Neuroectodermal-Derived Tumors

Retinoids are a class of natural and synthetic compounds derived from vitamin A. They are involved in several biological processes like embryogenesis, reproduction, vision, growth, inflammation, differentiation, proliferation, and apoptosis. In light of their important functions, retinoids have been widely investigated for their therapeutic applications. Thus far, their use for the treatment of several types of cancer and skin disorders has been reported. However, these therapeutic agents present several limitations for their widespread clinical translatability, i.e., poor solubility and chemical instability in water, sensitivity to light, heat, and oxygen, and low bioavailability. These characteristics result in internalization into target cells and tissues only at low concentration and, consequently, at an unsatisfactory therapeutic dose. Furthermore, the administration of retinoids causes severe side-effects. Thus, in order to improve their pharmacological properties and circulating half-life, while minimizing their off-target uptake, various retinoids delivery systems have been recently developed. This review intends to provide examples of retinoids-loaded nano-delivery systems for cancer treatment. In particular, the use and the therapeutic results obtained by using fenretinide-loaded liposomes against neuroectodermal-derived tumors, such as melanoma, in adults, and neuroblastoma, the most common extra-cranial solid tumor of childhood, will be discussed.

Oral delivery of all-trans retinoic acid mediated by liposome carriers

All-trans retinoic acid (ATRA) is a molecule that finds wide applications in medicine. Connection between cancer cell proliferation and ATRA is a well-established item. Driven by the potential applications of liposomes in stabilizing and protecting therapeutic compounds thus enabling effective delivery of encapsulated compounds, recent research efforts have been directed to understanding mechanisms of oral delivery through the gastrointestinal tract. The surface charge of the liposome bilayers can modify the interactions between the aggregates and the gastrointestinal fluids. Here, we investigated the ability of cationic and anionic liposomes to encapsulate, protect and deliver ATRA in an in-vitro digestion process as a different oral administration route. Stability and encapsulation efficiency of ATRA in negatively and positively charged liposomes enriched with α-tocopherol were investigated by means of UV-vis spectroscopy, dynamic light scattering and ζ-potential. The applicability of the carriers was tested by means of an in-vitro digestion procedure allowing for the measurement of the bioavailability of ATRA. From this study evidence was provided that the water insoluble molecules, ATRA and α-tocopherol are intercalated in liposome membranes regardless of the surface charge of the vesicle bilayers. Comparisons between cationic and anionic liposomes incorporating retinoic acid show differences in bioavailability. The cationic vesicles are preferable for a larger amount of ATRA bioavailability, which can be understood from electrostatic interactions. Thus ATRA is ionized in a wide range of pHs but protonated in anionic vesicles.

Microencapsulation of amorphous solid dispersions of fenretinide enhances drug solubility and release from PLGA in vitro and in vivo

The purpose of this study was to develop solid dispersions of fenretinide(4HPR), incorporate them into poly(lactic-co-glycolic)(PLGA) millicylindrical implants, and evaluate the resulting implants in vitro and in vivo for future applications in oral cancer chemoprevention. Due to the extreme hydrophobicity of 4HPR, 4HPR-polyvinylpyrrolidone (PVP) amorphous solid dispersions(ASDs) were prepared for solubility enhancement. The optimal PVP-4HPR ratio of 9/1(w/w) provided a 50-fold solubility enhancement in aqueous media, which was sustained over 1 week. PVP-4HPR ASD particles were loaded into PLGA millicylinders and drug release was evaluated in vitro in PBST and in vivo by recovery from subcutaneous injection in rats. While initial formulations of PLGA PVP-4HPR millicylinders only released 10% 4HPR in vitro after 28 days, addition of the plasticizer triethyl-o-acetyl-citrate(TEAC) into PVP-4HPR ASDs resulted in a 5.6-fold total increase in drug release. Remarkably, the TEAC-PVP-4HPR PLGA implants demonstrated slow, continuous, and nearly complete release over 1 month in vivo compared to a 25% release for our previously reported formulation incorporating solubilizers and pore-forming agents. Hence, a combination of PLGA plasticizer and ASD formation provides an avenue for long-term controlled release in vivo for the exceptionally difficult drug to formulate, 4HPR, and a suitable formulation for future evaluation in rodent models of oral cancer.

Characterization of Retinol Stabilized in Phosphatidylcholine Vesicles with and without Antioxidants

Retinol stability has been reported to be improved by encapsulation in liposomes, both with and without cholesterol. However, this improvement is limited because of lipid peroxidation. In this study, we compare the stability of retinol in phosphatidylcholine liposomes under ultraviolet (UV) light or standard room air, with and without the addition of antioxidants. Both butylated hydroxytoluene (BHT) and a proprietary mix (StoppOx) improved the shelf stability from <10 to over 30 d. The addition of cholesterol had no effect. Fluorescence imaging showed a heterogeneous distribution of retinol within the vesicles, including within the aqueous layer. Fluorescence lifetimes were equally heterogeneous. Under UV irradiation, StoppOx protected retinol for significantly longer than BHT and via different mechanisms. This suggests that natural antioxidants work well to improve the retinol stability, but that further work to determine the optimal vesicle structure remains to be performed.

Mechanistic Analysis of Human Skin Distribution and Follicular Targeting of Adapalene-Loaded Biodegradable Nanospheres With an Insight Into Hydrogel Matrix Influence, In Vitro Skin Irritation, and In Vivo Tolerability

This work aimed at the development of a biocompatible, non-oily nanomedicine for follicular delivery of adapalene (AD) ameliorating its irritation potential for convenient localized topical treatment of acne vulgaris. AD was efficiently incorporated into poly-ε-caprolactone nanospheres (NS) with an encapsulation efficiency of 84.73% ± 1.52%, a particle size of 107.5 ± 8.19 nm, and zeta potential of -13.1 mV demonstrating a sustained-release behavior. The AD-NS were embedded in either hydroxypropyl methylcellulose (HPMC) or hyaluronate (HA) gel. The ex vivo human skin dermatokinetics of AD from each system was studied. The nanoparticles dispersion showed significantly higher AD retention in the epidermis and dermis than AD suspension. NS-HPMC decreased whereas NS-HA increased AD retained in all the skin layers. The fate of the NS and the role of the hydrogel in modulating skin distribution was evaluated by confocal laser scanning microscopy (CLSM) imaging of fluorescently labeled NS. CLSM illustrated follicular localization of the florescent NS. HPMC gel restricted the presence of NS to the stratum corneum and epidermis. HA gel enhanced the penetration of NS to all the skin layers. In vitro skin irritation using human dermal fibroblasts and in vivo animal tolerability studies were performed. Accordingly, HA gel-dispersed AD-NS presented a nonirritant compromised cosmeceutical formulation suitable for oily acneic skin.

Anticancer activity of all-trans retinoic acid-loaded liposomes on human thyroid carcinoma cells

All-trans retinoic acid (ATRA) is an anti-tumor compound, exerting different anti-cancer effects on different types of cancer cells. Unfortunately, retinoids are also characterized by certain side effects following systemic administration, such as the burning of skin and general malaise. The highly variable degree of bioavailability of ATRA plus its tendency to induce its own destruction through metabolic degradation following oral treatment necessitate the development of alternative formulations. The aim of this work is to evaluate the physico-chemical properties of unilamellar, ATRA-containing liposomes and to investigate the cytotoxic activity of this potential nanomedicine on human thyroid carcinoma cells. Liposomes made up of DPPC/Chol/DSPE-mPEG2000 (6:3:1 molar ratio), characterized by a mean diameter of ∼200nm, a polydispersity index of 0.1 and a negative surface charge, were used as ATRA-carriers and their antiproliferative efficacy was investigated in comparison with the free drug on three different human thyroid carcinoma cell lines (PTC-1, B-CPAP, and FRO) through MTT-testing. The liposomes protected the ATRA against photodegradation and increased its antiproliferative properties due to the improvement of its cellular uptake. ATRA-loaded liposomes could be a novel formulation useful for the treatment of anaplastic thyroid carcinoma.

Cationic Supramolecular Vesicular Aggregates for Pulmonary Tissue Selective Delivery in Anticancer Therapy

The biopharmaceutical properties of supramolecular vesicular aggregates (SVAs) were characterized with regard to their physicochemical features and compared with cationic liposomes (CLs). Neutral and cationic SVAs were synthesized using two different copolymers of poly(aspartyl hydrazide) by thin-layer evaporation and extrusion techniques. Both copolymers were self-assembled in pre-formulated liposomes and formed neutral and cationic SVAs. Gemcitabine hydrochloride (GEM) was used as an anticancer drug and loaded by a pH gradient remote loading procedure, which significantly increased drug loading inside the SVAs. The resulting average size of the SVAs was 100 nm. The anticancer activity of GEM-loaded neutral and cationic SVAs was tested in human alveolar basal epithelial (A549) and colorectal cancer (CaCo-2) cells. GEM-loaded cationic SVAs increased the anticancer activity in A549 and CaCo-2 cells relative to free drug, neutral SVAs, and CLs. In vivo biodistribution in Wistar rats showed that cationic SVAs accumulate at higher concentrations in lung tissue than neutral SVAs and CLs. Cationic SVAs may therefore serve as an innovative future therapy for pulmonary carcinoma.

Nitrite and nitrate-dependent generation of anti-inflammatory fatty acid nitroalkenes

A gap in our understanding of the beneficial systemic responses to dietary constituents nitrate (NO3(-)), nitrite (NO2(-)) and conjugated linoleic acid (cLA) is the identification of the downstream metabolites that mediate their actions. To examine these reactions in a clinical context, investigational drug preparations of (15)N-labeled NO3(-) and NO2(-) were orally administered to healthy humans with and without cLA. Mass spectrometry analysis of plasma and urine indicated that the nitrating species nitrogen dioxide was formed and reacted with the olefinic carbons of unsaturated fatty acids to yield the electrophilic fatty acid, nitro-cLA (NO2-cLA). These species mediate the post-translational modification (PTM) of proteins via reversible Michael addition with nucleophilic amino acids. The PTM of critical target proteins by electrophilic lipids has been described as a sensing mechanism that regulates adaptive cellular responses, but little is known about the endogenous generation of fatty acid nitroalkenes and their metabolites. We report that healthy humans consuming (15)N-labeled NO3(-) or NO2(-), with and without cLA supplementation, produce (15)NO2-cLA and corresponding metabolites that are detected in plasma and urine. These data support that the dietary constituents NO3(-), NO2(-) and cLA promote the further generation of secondary electrophilic lipid products that are absorbed into the circulation at concentrations sufficient to exert systemic effects before being catabolized or excreted.

Niosomes from 80s to present: the state of the art

Efficient and safe drug delivery has always been a challenge in medicine. The use of nanotechnology, such as the development of nanocarriers for drug delivery, has received great attention owing to the potential that nanocarriers can theoretically act as "magic bullets" and selectively target affected organs and cells while sparing normal tissues. During the last decades the formulation of surfactant vesicles, as a tool to improve drug delivery, brought an ever increasing interest among the scientists working in the area of drug delivery systems. Niosomes are self assembled vesicular nanocarriers obtained by hydration of synthetic surfactants and appropriate amounts of cholesterol or other amphiphilic molecules. Just like liposomes, niosomes can be unilamellar or multilamellar, are suitable as carriers of both hydrophilic and lipophilic drugs and are able to deliver drugs to the target site. Furthermore, niosomal vesicles, that are usually non-toxic, require less production costs and are stable over a longer period of time in different conditions, so overcoming some drawbacks of liposomes. The niosome properties are specifically dictated by size, shape, and surface chemistry which are able to modify the drug's intrinsic pharmacokinetics and eventual drug targeting to the areas of pathology. This up-to-date review deals with composition, preparation, characterization/evaluation, advantages, disadvantages and application of niosomes.

A retinyl palmitate-loaded solid lipid nanoparticle system: effect of surface modification with dicetyl phosphate on skin permeation in vitro and anti-wrinkle effect in vivo

Surface-modified solid lipid nanoparticles (SLNs) containing retinyl palmitate (Rpal) were prepared by the hot-melt method using Gelucire 50/13(®) and Precirol ATO5(®). Dicetyl phosphate (DCP) was added to negatively charge the surfaces of the SLNs and thereby enhance the skin distribution properties of Rpal. In vitro skin permeation and in vivo anti-aging studies were performed using SLNs dispersed in a hydrogel. The SLNs were under 100 nm in size with an even polydispersity index (PDI), and the high absolute zeta-potential value was sufficient to maintain the colloidal stability of the SLNs. DCP-modified negative SLNs (DCPmod-SLNs) enhanced the skin distribution of Rpal 4.8-fold and delivered Rpal to a greater depth than did neutral SLNs. The in vivo anti-wrinkle effect of the DCPmod-SLN formulation was Rpal dose-dependent. However, the anti-wrinkle effects of the DCPmod-SLN formulations were significantly different from that of the negative control and effectively prevented the reduction of elastin and superoxide dismutase by UV irradiation. In conclusion, the DCPmod-SLN system presented is a good candidate for topical Rpal delivery.

Adoptive transfer of all-trans-retinal-induced regulatory T cells ameliorates experimental autoimmune arthritis in an interferon-gamma knockout model

Maintaining an appropriate balance between subsets of CD4(+) helper T cells and T regulatory cells (Tregs) is a critical process in immune homeostasis and a protective mechanism against autoimmunity and inflammation. To identify the role of vitamin A-related compounds, we investigated the regulation of interleukin (IL)-17-producing helper T cells (Th17 cells) and Tregs treated with all-trans-retinal (retinal). CD4(+)T cells or total cells from the spleens of C57BL/6 mice were stimulated under Treg-polarizing (anti-CD3/CD28 and TGF-β) or Th17-polarizing (anti-CD3/CD28, TGF-β, and IL-6) conditions in the presence or absence of retinal. To analyze their suppressive abilities, retinal-induced Tregs or TGF-β-induced Tregs were co-cultured with responder T cells. Collagen-induced arthritis (CIA) was established in interferon (IFN)-γ knockout mice. On day 13, retinal-induced Tregs were adoptively transferred to mice with established CIA after second immunizations. Compared with TGF-β-induced Treg cells, retinal-induced Tregs showed increased Foxp3 expression and mediated stronger suppressive activity. Under Th17-polarizing conditions, retinal inhibited the production of IL-17 and increased the expression of Foxp3.Retinal-induced Tregs showed therapeutic effects in IFN-γ knockout CIA mice. Thus, we demonstrated that retinal reciprocally regulates Foxp3(+) Tregs and Th17 cells. These findings suggest that retinal, a vitamin A metabolite, can regulate the balance between pro- and anti-inflammatory immunity. A better understanding of the manipulation of Foxp3 and Tregs may enable the application of this tremendous therapeutic potential in various autoimmune diseases.

Nanocarriers for vascular delivery of antioxidants

Antioxidant enzymes (AOEs) catalase and superoxide dismutase (SOD) detoxify harmful reactive oxygen species, but the therapeutic utility of AOEs is hindered by inadequate delivery. AOE modification by poly-ethylene glycol (PEG) and encapsulation in PEG-coated liposomes increases the AOE bioavailability and enhances protective effects in animal models. Pluronic-based micelles formed with AOEs show even more potent protective effects. Furthermore, polymeric nanocarriers (PNCs) based on PEG-copolymers protect encapsulated AOEs from proteolysis and improve delivery to the target cells, such as the endothelium lining the vascular lumen. Antibodies to endothelial determinants conjugated to AOEs or AOE carriers provide targeting and intracellular delivery. Targeted liposomes, protein conjugates and magnetic nanoparticles deliver AOEs to sites of vascular oxidative stress in the cardiovascular, pulmonary and nervous systems. Further advances in nanodevices for AOE delivery will provide a basis for the translation of this approach in the clinical domain.

Are retinoids potential therapeutic agents in disorders of social cognition including autism?

Increasing evidence suggests that the nonapeptide, oxytocin (OT), helps shape social and affiliative behaviors not only in lower mammals but also in humans. Recently, an essential mediator of brain OT release has been discovered, ADP-ribosyl cyclase and/or CD38. We have subsequently shown that polymorphisms across the CD38 gene are associated with autism spectrum disorders (ASD). Notably, CD38 expression in lymphoblastoid cells (LBC) is reduced in cell lines derived from ASD subjects compared to parental cell lines. Intriguingly, a correlation was observed between CD38 expression and measures of social function in ASD. Finally, we have shown that all-trans retinoic acid (ATRA), a known inducer of CD38 transcription, can rescue low CD38 expressing LBC lines derived from ASD subjects and restore normal levels of transcription of this ectoenzyme providing 'proof of principle' in a peripheral model that retinoids are potential therapeutic agents in ASD.

Penetration enhancer containing vesicles as carriers for dermal delivery of tretinoin

The ability of a recently developed novel class of liposomes to promote dermal delivery of tretinoin (TRA) was evaluated. New penetration enhancer-containing vesicles (PEVs) were prepared adding to conventional phosphatidylcholine vesicles (control liposomes) different hydrophilic penetration enhancers: Oramix NS10 (OrNS10), Labrasol (Lab), Transcutol P (Trc), and propylene glycol (PG). Vesicles were characterized by morphology, size distribution, zeta potential, incorporation efficiency, stability, rheological behaviour, and deformability. Small, negatively charged, non-deformable, multilamellar vesicles were obtained. Rheological studies showed that PEVs had fluidity higher than conventional liposomes. The influence of the obtained PEVs on (trans)dermal delivery of tretinoin was studied by ex vivo diffusion experiments through new born pig skin using formulations having the drug both inside and outside the vesicles, having TRA only inside, in comparison with non-incorporated drug dispersions of the same composition used to produce the studied vesicles. Main result of these experiments was an improved cutaneous drug accumulation and a reduced transdermal TRA delivery (except for PG-PEVs). TRA deposition provided by PEVs was higher for dialysed than for non-dialysed vesicles. Further, the accumulation increased in the order: control liposomes<PG-PEVs<Trc-PEVs≤Or-PEVs<Lab-PEVs. SEM analysis of the skin gave evidence of PEVs' ability to strongly interact with the intercellular lipids causing an enlargement of this region.