Oleic acid: its effects on stratum corneum in relation to (trans)dermal drug delivery

Design of Ionic Liquid Formulations with Azone-Mimic Structures for Enhanced Drug Skin Permeation

Although laurocapram (Azone) significantly enhances the skin permeation of drugs, its development was hindered by its skin irritation. We then developed an Azone-mimic ionic liquid (IL-Azone), composed of less irritating cationic ε-caprolactam and anionic myristic acid. IL-Azone dissociates to the original cation and anion in the presence of water in the formulation. We tried to select a formulation suitable for IL-Azone in the present study. Each formulation contained 5 % of either Azone or IL-Azone along with the model drug antipyrine, and skin permeation experiments of the drug were conducted. The results revealed that IL-Azone did not enhance skin permeation when combined with most formulations tested. However, a notable and rapid enhancement in skin permeation was observed when combined with white petrolatum. This effect could be attributed to the minimal water content in white petrolatum, which prevented IL-Azone degradation. Furthermore, its permeation-enhancing effects from IL-Azone in white petrolatum were more pronounced and rapid than Azone. The rapid onset observed with IL-Azone can be attributed to its degradation into its original components at the interface between the stratum corneum and the living epidermis, which results in a shorter lag time before achieving a steady-state concentration in the SC compared to Azone.

Effect of Penetration Enhancer on the Structure of Stratum Corneum: On-Site Study by Confocal Polarized Raman Imaging

Keratin and lipid structures in the stratum corneum (SC) are closely related to the SC barrier function. The application of penetration enhancers (PEs) disrupts the structure of SC, thereby promoting infiltration. To quantify these PE-induced structural changes in SC, we used confocal Raman imaging (CRI) and polarized Raman imaging (PRI) to explore the integrity and continuity of keratin and lipid structures in SC. The results showed that water is the safest PE and that oleic acid (OA), sodium dodecyl sulfate (SDS), and low molecular weight protamine (LMWP) disrupted the ordered structure of keratin, while azone and liposomes had less of an effect on keratin. Azone, OA, and SDS also led to significant changes in lipid structure, while LMWP and liposomes had less of an effect. Establishing this non-invasive and efficient strategy will provide new insights into transdermal drug delivery and skin health management.

Time-Dependent Differences in the Effects of Oleic Acid and Oleyl Alcohol on the Human Skin Barrier

Oleic acid and oleyl alcohol are commonly used permeation and penetration enhancers to facilitate topical drug delivery. Here, we aimed to better understand the mechanism of their enhancing effects in terms of their interactions with the human skin barrier using diclofenac diethylamine (DIC-DEA), a nonsteroidal anti-inflammatory drug for topical pain management. Oleic acid promoted DIC-DEA permeation through ex vivo human skin more rapidly than oleyl alcohol (both applied at 0.75%) due to fluidization of stratum corneum lipids as revealed by infrared spectroscopy. After 12 h, the effect of these enhancers on DIC-DEA permeation leveled off, fluidization was no longer evident, and skin permeabilization was mainly due to the formation of fluid enhancer-rich domains. Contrary to oleyl alcohol, oleic acid adversely affected two indicators of the skin barrier integrity, transepidermal water loss and skin electrical impedance. The content of oleyl alcohol in the stratum corneum was lower than that of oleic acid (even 12 h after the enhancers were removed from the skin surface), but it caused higher DIC-DEA retention in both epidermis and dermis compared to oleic acid. The effects of oleyl alcohol and oleic acid on DIC-DEA permeation and retention in the skin were similar after a single and repeated application (4 doses every 12 h). Thus, oleyl alcohol offers several advantages over oleic acid for topical drug delivery.

Effects of Sodium Salts of Fatty Acids and Their Derivatives on Skin Permeation of Cromolyn Sodium

Atopic dermatitis is a chronic inflammatory disorder with rising prevalence. The safety concerns over usually used steroids are driving the need for developing an effective atopic dermatitis treatment. The use of therapeutic agents such as cromolyn sodium (CS) is suggested. However, due to its physicochemical properties, CS permeation across the skin is a challenge. The aim of this study was to investigate the effect of sodium salts of fatty acids or their derivatives with varied carbon chain lengths as potential enhancers on the skin permeation of CS. These included sodium caprylate, salcaprozate sodium, sodium decanoate, sodium palmitate, and sodium oleate dissolved in propylene glycol along with CS (4% w/w). In vitro permeation of the formulations across the dermatomed porcine ear skin was investigated over 24 h using Franz Diffusion cells. The amount of CS permeation from propylene glycol was 5.54 ± 1.06 µg/cm2 after 24 h. Initial screening of enhancers (enhancer: drug::1:1) showed enhancement in permeation of CS using sodium oleate and sodium caprylate, which were then investigated in higher ratio of drug: enhancer (1:2). Among all the formulations tested, sodium oleate (enhancer: drug::1:2) was observed to significantly (p < 0.05) enhance the permeation of CS with the highest total delivery of 359.79 ± 78.92 µg/cm2 across skin in 24 h and higher drug retention in the skin layers (153.0 ± 24.93 µg/cm2) as well. Overall, sodium oleate was found to be the most effective enhancer followed by sodium caprylate for improving the topical delivery of CS.

Neutral Oil-Incorporated Liposomal Nanocarrier for Increased Skin Delivery of Ascorbic Acid

In this study, a neutral oil-incorporated liposomal system (lipo-oil-some, LOS) was designed to improve the skin absorption of ascorbic acid (Vit C), and the effects of an edge activator and neutral oil on the skin absorption of Vit C were evaluated. As components of the LOS system, sodium deoxycholate, polysorbate 80, and cholesterol were screened as edge activators, and camellia oil, tricaprylin, and grapeseed oil were employed as neutral oils. The LOS systems prepared by the ethanol injection method were spherical in shape, 130-350 nm in size, and had 4-27% Vit C loading efficiency (%). In a skin absorption study using a Franz diffusion cell mounted with porcine skin, the LOS system prepared with sodium deoxycholate (10 w/w% of phospholipid) exhibited 1.2-and 2.9-fold higher absorption than those prepared with polysorbate 80 and cholesterol, respectively. Moreover, the type of neutral oil had a marked effect on the absorption of Vit C; the liposomal system containing camellia oil provided 1.3 to 1.8 times higher flux (45.4 μg/cm²∙h) than vesicles with tricaprylin or grapeseed oil, respectively. The optimized lipid nanocarrier is expected to be a promising tool for promoting the skin absorption of Vit C and improving its dermatological functions.

Development and Skin Penetration Pathway Evaluation Using Confocal Laser Scanning Microscopy of Microemulsions for Dermal Delivery Enhancement of Finasteride

This study aimed to develop microemulsions using poloxamer 124 as a surfactant to improve the skin penetration of finasteride and to investigate the skin penetration pathways of these microemulsions by colocalization techniques using confocal laser scanning microscopy (CLSM). The prepared finasteride-loaded microemulsions had average particle sizes ranging from 80.09 to 136.97 nm with particle size distributions within acceptable ranges and exhibited negative surface charges. The obtained microemulsions could significantly increase the skin penetration of finasteride compared to a finasteride solution. According to the skin penetration pathway evaluation conducted with CLSM, the microemulsions were hair follicle-targeted formulations due to penetration via the transfollicular pathway as a major skin penetration pathway. Additionally, this study found that the microemulsions also penetrated via the intercluster pathway more than via the intercellular pathway and transcellular pathway. The intercluster pathway, intercellular pathway, and transcellular pathway were considered only minor pathways.

Levonorgestrel Microneedle Array Patch for Sustained Release Contraception: Formulation, Optimization and In Vivo Characterization

Background: The goal of this work was to develop a levonorgestrel liposome-loaded microneedle array patch for contraception. Methods: Levonorgestrel-loaded liposome was formulated by a solvent injection technique, characterized, and studied. Results: The formulated liposomes were characterized for particle size (147 ± 8 nm), polydispersity index (0.207 ± 0.03), zeta potential (−23 ± 4.25 mV), drug loading (18 ± 3.22%) and entrapment efficiency (85 ± 4.34%). A cryo high-resolution transmission electron microscopy and cryo field emission gun scanning electron microscopy study showed spherical shaped particles with a smooth surface. The in vitro drug release and in vivo pharmacokinetic study showed sustained behaviour of Levonorgestrel for 28 days. Conclusion: The levonorgestrel liposome-loaded microneedle array patch showed better contraception than the drug-loaded microneedle array patch.

Thermal analysis of mammalian stratum corneum using differential scanning calorimetry for advancing skin research and drug delivery

For effective topical and transdermal drug delivery, it is necessary for most actives to penetrate and permeate through the stratum corneum (SC). Extensive investigation of the thermal behaviour of mammalian SC has been performed to understand the barrier function of the skin. However, little attention has been paid to the related experimental variables in thermal analysis of the SC using differential scanning calorimetry that may influence the results obtained from such studies. In this review, we provide a comprehensive overview of the thermal transitions of the SC of both porcine and human skin. More importantly, the selection and impact of the experimental and instrumental parameters used in thermal analysis of the SC are critically evaluated. New opportunities for the use of thermal analysis of mammalian SC in advancing skin research, particularly for elucidation of the actions of excipients employed in topical and transdermal formulations on the skin are also highlighted.

Effect of Olive Oil Acidity on Skin Delivery of Diclofenac: In Vitro Evaluation and Ex Vivo Skin Permeability Studies

Olive oil is a vegetable oil which has been successfully used as a skin penetrating agent. Acidity of olive oil is considered as one of the characteristic properties of olive oil. Olive oil acidity was selected as a parameter under investigation for evaluation of skin permeability. The acidities of the three investigated olive oils are varying from 0.75±0.16 to 2±0.17. Olive oil with acidity equals 2.0 showed the highest skin permeation for 12 h and cutaneous deposition with significant difference compared to the permeation values of 0.75 and F1.4 acidities. Results of cutaneous secretion of cytokines suggested that higher penetration was accompanied higher cytokines' secretions. Olive oil with acidity equals 2.0 also showed more prominent skin changes which suggested to be due to acidity and fatty acids' content. These results suggest that olive oil might improve the epidermal permeability, which is more pronounced in highly acidic olive oil, through weakening of skin barriers followed by acting of cytokines on re-building effective barriers. Finally, based on the current study, highly acidic olive oil is more efficient skin permeation enhancer vehicle than less acidic ones and can be efficiently used in formulation of cutaneous drug delivery systems.

In Vitro Skin Permeation of Idebenone from Lipid Nanoparticles Containing Chemical Penetration Enhancers

Lipid nanoparticles (LNPs) have been proposed as carriers for drug skin delivery and targeting. As LNPs effectiveness could be increased by the addition of chemical penetration enhancers (PE), in this work, the feasibility of incorporating PE into LNPs to improve idebenone (IDE) targeting to the skin was investigated. LNPs loading IDE 0.7% w/w were prepared using hydrophilic (propylene glycol, PG, 10% w/w or N-methylpyrrolidone, NMP, 10% w/w) and/or lipophilic PE (oleic acid, OA, 1% w/w; isopropyl myristate, IPM, 3.5% w/w; a mixture of 0.5% w/w OA and 2.5% w/w IPM). All LNPs showed small sizes (<60 nm), low polydispersity index and good stability. According to the obtained results, IDE release from LNPs was not the rate-limiting step in IDE skin penetration. No IDE permeation was observed through excised pigskin from all LNPs, while the greatest increase of IDE penetration into the different skin layers was obtained using the mixture OA/IPM. The antioxidant activity of IDE-loaded LNPs, determined by the oxygen radical absorbance capacity assay, was greater than that of free IDE. These results suggest that the use of suitable PE as LNPs components could be regarded as a promising strategy to improve drug targeting to the skin.

Current Status of Amino Acid-Based Permeation Enhancers in Transdermal Drug Delivery

Transdermal drug delivery (TDD) presents many advantages compared to other conventional routes of drug administration, yet its full potential has not been achieved. The administration of drugs through the skin is hampered by the natural barrier properties of the skin, which results in poor permeation of most drugs. Several methods have been developed to overcome this limitation. One of the approaches to increase drug permeation and thus to enable TDD for a wider range of drugs consists in the use of chemical permeation enhancers (CPEs), compounds that interact with skin to ultimately increase drug flux. Amino acid derivatives show great potential as permeation enhancers, as they exhibit high biodegradability and low toxicity. Here we present an overview of amino acid derivatives investigated so far as CPEs for the delivery of hydrophilic and lipophilic drugs across the skin, focusing on the structural features which promote their enhancement capacity.

Topical Unsaturated Fatty Acid Vesicles Improve Antioxidant Activity of Ammonium Glycyrrhizinate

Linoleic and oleic acids are natural unsaturated fatty acids involved in several biological processes and recently studied as structural components of innovative nanovesicles. The use of natural components in the pharmaceutical field is receiving growing attention from the scientific world. The aim of this research work is to design, to perform physico-chemical characterization and in vitro/in vivo studies of unsaturated fatty acids vesicles containing ammonium glycyrrhizinate, obtaining a new topical drug delivery system. The chosen active substance is well known as an anti-inflammatory compound, but its antioxidant activity is also noteworthy. In this way, the obtained nanocarriers are totally natural vesicles and they have shown to have suitable physico-chemical features for topical administration. Moreover, the proposed nanocarriers have proven their ability to improve the in vitro percutaneous permeation and antioxidant activity of ammonium glycyrrhizinate on human keratinocytes (NCTC 2544 cells). In vivo studies, carried out on human volunteers, have demonstrated the biocompatibility of unsaturated fatty acid vesicles toward skin tissue, indicating a possible clinical application of unsaturated fatty acid vesicles for the treatment of topical diseases.

Development of a highly persistent silicone-based sprayable emulsion containing essential oils for treatment of skin infections

Essential oils have known a renewed interest, particularly for their antimicrobial properties. In the field of skin delivery of essential oils, fluid oil-in-water (O/W) emulsions have been studied for several years in order to improve their stability. When dealing with infections of the upper skin layers, these vehicles, in spite of their low viscosity, must have a good skin persistence and also concentrate the essential oil components in the target skin layers. Given the well-known ability of alkylsiloxysilicate resins to induce a very substantive and non-occlusive film after cutaneous application in an appropriate preparation, it has been undertaken to use them to prepare a highly persistent O/W fluid emulsion of essential oil. Hence, after the successful development of a fluid silicone-in-water (Si/W) emulsion integrating a 100% trimethylsiloxysilicate resin, the essential oil was incorporated in this emulsion. The physical and chemical stabilities of the prepared emulsion were then studied in the final packaging under different storage conditions. In addition, the skin penetration profile of essential oil from this vehicle was investigated, ex vivo, on pig ear skin, using Franz diffusion cells and analytical techniques such as confocal Raman microscopy. As the developed vehicle was found to meet our delivery expectations, its skin tolerance has been proven by an in vivo chromametric evaluation of its irritant potential. The skin persistence of this emulsion containing an antimicrobial essential oil was then studied. Considering its properties, the developed emulsion is expected to represent a real asset in the treatment of skin infections, particularly infections of upper layers of human skin such as dermatophytosis.

Ionically Crosslinked Complex Gels Loaded with Oleic Acid-Containing Vesicles for Transdermal Drug Delivery

Skin is an attractive site for drug administration partly because of its easy accessibility and favorable properties (e.g., less invasiveness and high patient compliance) over some other common routes of administration. Despite this, the efficiency in transdermal drug delivery has been largely limited by poor skin permeation. To address this problem, this study reports the generation of oleic acid-containing vesicles, which can enhance the drug delivery efficiency while showing good stability and limited skin disruption. Upon being loaded into a complex gel, along with the incorporation of the polymer blending technique, a delivery system exhibiting tunable transdermal flux of 2,3,5,4'-tetrahydroxystilbene 2-O-β-D-glucoside is reported. Taking the good biocompatibility and tunable delivery performance into account, our system warrants further development and optimization for future applications in the treatment of skin diseases.

Distinct Influence of Saturated Fatty Acids on Malignant and Nonmalignant Human Lung Epithelial Cells

The impact of saturated fatty acids (FA) on viability and properties of malignant and nonmalignant cells has not been studied in detail so far. The present study was aimed at evaluation of the influence of saturated FA (10:0-18:0) on malignant (A459) and nonmalignant (BEAS-2B) human lung epithelial cells. FA strongly affected A549 cells, but not BEAS-2B cells. Viability of A549 cells incubated with 14:0-18:0 was decreased by 53-91% as compared to untreated cells. Cell membrane stiffness in those cells as measured by atomic force microscopy was also reduced. Median value of apparent Young's modulus of untreated A549 cell membrane was 16.9 kPa and it decreased to 8.9 kPa for cells incubated with 14:0. Viability and mechanical properties of BEAS-2B cells were not altered by presence of FA. Those surprising discrepancies can be related to the differences in FA uptake rate. A549 cells were found to incorporate higher amount of FA and this corresponded to decrease in cell membrane stiffness and reduced cell viability. The performed studies showed that saturated FA have distinct influence on various types of cells, which may be exploited in development of the advanced lipid drug delivery systems.

Permeation enhancers in transdermal drug delivery: benefits and limitations

Introduction: Transdermal drug delivery has several clinical benefits over conventional routes of drug administration. To open the transdermal route for a wider range of drugs, including macromolecules, numerous physical and chemical techniques to overcome the natural low skin permeability have been developed.Areas covered: This review focuses on permeation enhancers (penetration enhancers, percutaneous absorption promoters or accelerants), which are chemicals that increase drug flux through the skin barrier. First, skin components, drug permeation pathways, and drug properties are introduced. Next, we discuss properties of enhancers, their various classifications, structure-activity relationships, mechanisms of action, reversibility and toxicity, biodegradable enhancers, and synergistic enhancer combinations.Expert opinion: Overcoming the remarkable skin barrier properties in an efficient, temporary and safe manner remains a challenge. High permeation-enhancing potency has long been perceived to be associated with toxicity and irritation potential of such compounds, which has limited their further development. In addition, the complexity of enhancer interactions with skin, formulation and drug, along with their vast chemical diversity hampered understanding of their mechanisms of action. The recent development in the field revealed highly potent yet safe enhancers or enhancer combinations, which suggest that enhancer-aided transdermal drug delivery has yet to reach its full potential.

Permeability of frog skin to chemicals: effect of penetration enhancers

Rarely do commercial chemical products contain solely the active chemical/ingredient. It is therefore important to consider whether ingredients other than the active may: 1) alter absorption of the active chemical, or 2) be absorbed themselves, resulting in systemic effects. Frogs have highly permeable skin and are routinely exposed to commercial chemical products in the environment or therapeutically. Ethanol and propylene glycol (PG), which have known penetration-enhancing effects, are commonly included in such products. The current study has therefore investigated the in vitro absorption kinetics through Rh. marina skin of three model chemicals – caffeine, benzoic acid, and ibuprofen – formulated individually as solutions containing: 1%, 10% or 30% v/v ethanol, or 20% v/v PG. Differential scanning calorimetry and histology were used to characterise fresh frog skin, investigate the mechanism of these enhancers in frog skin, and to determine whether these enhancers significantly affected skin structure. Results showed that the extent of absorption enhancement was influenced by chemical, enhancer and skin region, and that enhancement was generally not consistent for individual enhancers or skin regions. The exception was 1% v/v ethanol, which did not significantly alter flux across the skin for any of the chemicals evaluated. Caffeine absorption was not enhanced by any of the investigated penetration enhancers, and was in fact significantly reduced by 30% v/v ethanol and PG. Ethanol caused concentration-dependant changes in skin morphology and should be avoided in concentrations ≥10% v/v. PG, however, caused minimal changes to the skin and consistently improved absorption of benzoic acid and ibuprofen through all skin regions. Owing to the significant changes in skin structure following ≥10% v/v ethanol exposure, it is recommended to avoid its use in frogs. For enhancement of penetration of moderately-to-highly lipophilic chemicals, this study has identified 20% v/v PG should to be the enhancer of choice.

Development, characterization and evaluation of topical methotrexate-entrapped deformable liposome on imiquimod-induced psoriasis in a mouse model

The aim of this study was to prepare and characterize topical methotrexate (MTX) with different percentages (0.05%, 0.1%, 0.25% and 0.5%) entrapped in deformable liposomes using phosphatidylcholine and oleic acid. The effectiveness and sub-acute toxicity of these topical formulations were investigated in imiquimod (IMQ)-induced psoriasis in a mouse model (IMQP). The particle sizes of formulations were around 100 nm with a mean zeta potential of -72.87 mV. The entrapment efficiency (EE%) of MTX in liposomal formulations were more than 85%. Franz cell permeability studies indicated that permeation of MTX through the healthy BALB/c mice skin is very low; however, in the inflammatory skin, which was induced by IMQ it was significant (50%). Liposomal MTX (LM 0.05 and 0.1%) caused significant reduction of thickness score dose-dependently in IMQP compared to the injected MTX. Moreover, investigation of the inflammatory factor and pathological examinations of skin proved the superiority of the LM treating group. Pathological examinations also showed there are no toxicity in organs of the mice that received the LM. Blood cell count test didn't show any abnormality. MTX-entrapped deformable liposomes could be a topical option in future for the treatment of human psoriasis with a less toxicity and merit further investigations.

Effect of permeation enhancers on in vitro release and transdermal delivery of lamotrigine from Eudragit®RS100 polymer matrix-type drug in adhesive patches

The drug-in-adhesive (DIA)-type matrix patches of lamotrigine are developed using variable permeation enhancers (oleic acid, PG, lemon oil and aloe vera), and drug in vitro release and its permeation are evaluated. Lamotrigine has been long used as an anti-epileptic, mood stabilizer, to treat bipolar disorder in adults and off label as an antidepressant. lamotrigine matrix patches comprising of Eudragit®RS100 (rate-controlling polymer) and DuroTak® 387-2510 (adhesive) were prepared by pouring the solution on backing membrane (3M-9720). The thickness of 120 µm was adjusted through micrometer film applicator. USP Apparatus V was used for the evaluation of release profile, which was fitted into various mathematical models. Quality characteristics of patches were determined through weight variation, moisture content, moisture uptake and drug content evaluation. FTIR studies were performed for drug-excipient compatibility; Franz diffusion cell was employed for studying in vitro permeation parameters such as flux, lag time, and ER. Skin sensitivity study of optimized patch was also performed. The release from patches comprising of PG and oleic acid was maximum, i.e., 96.24 ± 1.15% and 91.12 ± 1.11%, respectively. Formulations (A1-A5) exhibited Makoid-Banakar release profile. Formulation A3 consisting of oleic acid was optimized due to enhanced permeation of drug across skin compared to other enhancers with enhancement ratio of 3.55. Skin sensitivity study revealed patch as safe and non-allergenic. The study demonstrates that oleic acid can be used as a suitable permeation enhancer for transdermal delivery of lamotrigine from matrix-type patches.

Microemulsion and Microporation Effects on the Genistein Permeation Across Dermatomed Human Skin

This study reports the microemulsion (ME) effects on the permeation of genistein across normal (intact) and microporated human skin. The genistein formulation was optimized to know the stable ME region in the pseudo-ternary phase diagrams and to maximize the skin permeation and retention of genistein. The phase diagrams were constructed with different oil phases, surfactants, and their combinations. The influence of formulation factors on the permeation through intact and microporated human skin was determined. Based on its wide ME region, as well as permeation enhancement effects, oleic acid was used as an oil phase with various surfactants and co-surfactants to further maximize the ME region and skin permeation. The water content in the formulation played an important role in the ME stability, droplet size, and flux of genistein. For example, the ME with 20% water exhibited 4- and 9-fold higher flux as compared to the ME base (no water) and aqueous suspension, respectively. Likewise, this formulation had demonstrated 2- and 4-fold higher skin retention as compared to the ME base (no water) and aqueous suspension, respectively. The skin microporation did not significantly increase the skin permeation of genistein from ME formulations. The ME composition, water content, and to a lesser extent the ME particle size played a role in improving the skin permeation and retention of genistein.

State of the art in Stratum Corneum research: The biophysical properties of ceramides

This review is summarizing an important part of the state of the art in stratum corneum research. A complete overview on discoveries about the general biophysical and physicochemical properties of the known ceramide species' is provided. The ceramides are one of the three major components of the lipid matrix and mainly govern its properties and structure. They are shown to exhibit very little redundancy, despite the minor differences in their chemical structure. The results are discussed, compared to each other as well as the current base of knowledge. New interesting aspects and concepts are concluded or suggested. A novel interpretation of the 3-dimensional structure of the lipid matrix and its influence on the barrier function will be discussed. The most important conclusion is the presentation of a new and up to date theoretical model of the nanostructure of the short periodicity phase. The model suggests three perpendicular layers: The rigid head group region, the rigid chain region and, a liquid-like overlapping middle layer. The general principle of the skin barrier function is highlighted in regard to this structure and the ceramides biophysical and physicochemical properties. As a result of these considerations, the entropy vs. enthalpy principle is introduced, shedding light on the function as well as the effectiveness of the skin barrier. Additionally, general ideas to effectively overcome this barrier principle for dermal and transdermal delivery of actives or how to use it for specific targeting of the stratum corneum are proposed.

Elucidation of penetration enhancement mechanism of Emu oil using FTIR microspectroscopy at EMIRA laboratory of SESAME synchrotron

It has been proposed that Emu oil possesses skin permeation-enhancing effect. This study aimed to address its possible penetration enhancement mechanism(s) using IR microscopy, in accordance with LPP theory. The penetration of Emu oil through the layers of human skin was accomplished by monitoring oil-IR characteristic feature at 3006cm^-1. The unsaturated components of Emu oil accumulated at about 270μm depth of skin surface. The interaction of Emu oil with lipid and protein constituents of SC was investigated in comparison with a commonly used enhancer, IPM. Inter-sample spectral differences were identified using PCA and linked with possible enhancement mechanisms. Emu oil treatment caused a change in the slope of the right contour of amide I band of the protein spectral range. This was also clear in the second derivative spectra where the emergence of a new shoulder at higher frequency was evident, suggesting disorganization of keratin α-helix structure. This effect could be a result of disruption of some hydrogen bonds in which amide CO and NH groups of keratin are involved. The low intensity of the emerged shoulder is also in agreement with formation of weaker hydrogen bonds. IPM did not affect the protein component. No conclusions regarding the effect of penetration enhancers on the SC lipids were obtained. This was due to the overlap of the endogenous (skin) and exogenous (oil) CH stretching and scissoring frequencies. The SC carbonyl stretching peak disappeared as a result of IPM treatment which may reflect some degree of lipid extraction.

Overview and Future Potential of Buccal Mucoadhesive Films as Drug Delivery Systems for Biologics

The main route of administration for drug products is the oral route, yet biologics are initially developed as injectables due to their limited stability through the gastrointestinal tract and solubility issues. In order to avoid injections, a myriad of investigations on alternative administration routes that can bypass enzymatic degradation and the first-pass effect are found in the literature. As an alternative site for biologics absorption, the buccal route presents with a number of advantages. The buccal mucosa is a barrier, providing protection to underlying tissue, but is more permeable than other alternative routes such as the skin. Buccal films are polymeric matrices designed to be mucoadhesive properties and usually formulated with permeability enhancers to improve bioavailability. Conventionally, buccal films for biologics are manufactured by solvent casting, yet recent developments have shown the potential of hot melt extrusion, and most recently ink jet printing as promising strategies. This review aims at depicting the field of biologics-loaded mucoadhesive films as buccal drug delivery systems. In light of the literature available, the buccal epithelium is a promising route for biologics administration, which is reflected in clinical trials currently in progress, looking forward to register and commercialize the first biologic product formulated as a buccal film.

Oral transmucosal delivery of naratriptan

Naratriptan (NAR) is currently used as the hydrochloride salt (NAR.HCl) for the treatment of migraine and is available in tablet dosage forms for oral administration. Buccal drug delivery offers a number of advantages compared with conventional oral delivery including rapid absorption, avoidance of first pass metabolism and improved patient compliance. We have previously prepared and characterised the base form of NAR and shown that it has more favourable properties for buccal delivery compared with NAR.HCl. This study describes the design and evaluation of a range of formulations for oral transmucosal delivery of NAR base. Permeation studies were conducted using excised porcine buccal tissue mounted in Franz cells. Of the neat solvents examined, Transcutol^® P (TC) showed the greatest enhancement effects and was the vehicle in which NAR was most soluble. The mechanisms by which TC might promote permeation were further probed using binary systems containing TC with either buffer or Miglyol 812^® (MG). Mass balance studies were also conducted for these systems. The permeation of TC as well as NAR was also monitored for TC:MG formulations. Overall, TC appears to promote enhanced membrane permeation of NAR because of its rapid uptake into the buccal tissue. Synergistic enhancement of buccal permeation was observed when TC was combined with MG and this is attributed to the increased thermodynamic activity of NAR in these formulations. Significantly enhanced permeation of NAR was achieved for TC:MG and this was also associated with less TC remaining on the tissue or in the tissue at the end of the experiment. To our knowledge this is the first report where both enhancer and active have been monitored in buccal permeation studies. The findings underline the importance of understanding the fate of vehicle components for rational formulation design of buccal delivery systems.

Lipid-based nanocarriers for oral peptide delivery

This article is aimed to overview the lipid-based nanostructures designed so far for the oral administration of peptides and proteins, and to analyze the influence of their composition and physicochemical (particle size, zeta potential) and pharmaceutical (drug loading and release) properties, on their interaction with the gastro-intestinal environment, and the subsequent PK/PD profile of the associated drugs. The ultimate goal has been to highlight and comparatively analyze the key factors that may be determinant of the success of these nanocarriers for oral peptide delivery. The article ends with some prospects on the challenges to be addressed for the intended commercial success of these delivery vehicles.

Chemical penetration enhancers in stratum corneum - Relation between molecular effects and barrier function

Skin is attractive for drug therapy because it offers an easily accessible route without first-pass metabolism. Transdermal drug delivery is also associated with high patient compliance and through the site of application, the drug delivery can be locally directed. However, to succeed with transdermal drug delivery it is often required to overcome the low permeability of the upper layer of the skin, the stratum corneum (SC). One common strategy is to employ so-called penetration enhancers that supposedly act to increase the drug passage across SC. Still, there is a lack of understanding of the molecular effects of so-called penetration enhancers on the skin barrier membrane, the SC. In this study, we provide a molecular characterization of how different classes of compounds, suggested as penetration enhancers, influence lipid and protein components in SC. The compounds investigated include monoterpenes, fatty acids, osmolytes, surfactant, and Azone. We employ natural abundance (13)C polarization transfer solid-state nuclear magnetic resonance (NMR) on intact porcine SC. With this method it is possible to detect small changes in the mobility of the minor fluid lipid and protein SC components, and simultaneously obtain information on the major fraction of solid SC components. The balance between fluid and solid components in the SC is essential to determine macroscopic material properties of the SC, including barrier and mechanical properties. We study SC at different hydration levels corresponding to SC in ambient air and under occlusion. The NMR studies are complemented with diffusion cell experiments that provide quantitative data on skin permeability when treated with different compounds. By correlating the effects on SC molecular components and SC barrier function, we aim at deepened understanding of diffusional transport in SC, and how this can be controlled, which can be utilized for optimal design of transdermal drug delivery formulations.

Localized Epidermal Drug Delivery Induced by Supramolecular Solvent Structuring

The preferential localization of drug molecules in the epidermis of human skin is considered advantageous for a number of agents, but achieving such a delivery profile can be problematic. The aim of the present study was to assess if the manipulation of solvent supramolecular structuring in the skin could be used to promote drug residence in the epidermal tissue. Skin deposition studies showed that a 175-fold increase in the epidermal loading of a model drug diclofenac (138.65 ± 11.67 μg·cm(-2)), compared to a control (0.81 ± 0.13 μg·cm(-2)), could be achieved by colocalizing the drug with a high concentration of propylene glycol (PG) in the tissue. For such a system at 1 h postdose application, the PG flux into the skin was 9.3 mg·cm(2)·h(-1) and the PG-water ratio in the epidermis was 76:24 (v/v). At this solvent ratio infrared spectroscopy indicated that PG rich supramolecular structures, which displayed a relatively strong physical affinity for the drug, were formed. Encouraging the production of the PG-rich supermolecular structures in the epidermis by applying diclofenac to the skin using a high PG loading dose (240 μg·cm(-2)) produced an epidermal-transdermal drug distribution of 6.8:1. However, generating water-rich solvent supermolecular structures in the epidermis by applying diclofenac using a low PG loading dose (2.2 μg·cm(-2)) led to a loss of preferential epidermal localization of diclofenac in the tissue (0.7:1 epidermal-transdermal drug distribution). This change in diclofenac skin deposition profile in response to PG variations and the accompanying FTIR data supported the notion that supramolecular solvent structures could control drug accumulation in the human epidermis.

Nanovesicles of nitrendipine with lipid complex for transdermal delivery: pharmacokinetic and pharmacodynamic studies

CONTEXT

Vesicular transdermal delivery can enhance the bioavailability of a drug especially affected by first-pass metabolism, e.g. nitrendipine. However effective transdermal delivery employs permeation enhancer, e.g oleic acid (OA) with ceramide 2, stearic acid, behenic acid, and cholesteryl sulfate lipid complex.

OBJECTIVE

This study investigated the preparation, characterization of physicochemical properties, ex vivo permeation using human skin, pharmacokinetic parameters and antihypertensive potential in rats, of nitrendipine-loaded nanovesicles of ceramide 2, stearic acid, behenic acid and cholesteryl sulfate containing oleic acid gel (NOVG).

MATERIALS AND METHODS

The nanovesicles were made using film hydration method and characterized for physicochemical properties, ex vivo permeation using human skin, pharmacokinetic parameters and antihypertensive potential.

RESULTS

Nitrendipine-loaded nanovesicles of ceramide-2 containing oleic acid (NOV-5) have shown fluxes in the range of 4.88-24.72 μg/cm(2)/h nitrendipine oral suspension (NOS) at equal dose. NOVG-5 has shown almost 33% reduction in blood pressure in the first hour and a further decrease of 25% in the second hour to restore the normal pressure.

DISCUSSION

The permeation increases with increase in OA content. OA gets integrated in vesicle wall and enhances its permeability, whereas ceramide content makes sure that skin does not become damaged even after permeation.

CONCLUSION

NOVG-5 has shown the most favorable physicochemical properties and good permeation through skin providing good management of hypertension during crucial initial hours.

Molecular interactions of plant oil components with stratum corneum lipids correlate with clinical measures of skin barrier function

Plant-derived oils consisting of triglycerides and small amounts of free fatty acids (FFAs) are commonly used in skincare regimens. FFAs are known to disrupt skin barrier function. The objective of this study was to mechanistically study the effects of FFAs, triglycerides and their mixtures on skin barrier function. The effects of oleic acid (OA), glyceryl trioleate (GT) and OA/GT mixtures on skin barrier were assessed in vivo through measurement of transepidermal water loss (TEWL) and fluorescein dye penetration before and after a single application. OA's effects on stratum corneum (SC) lipid order in vivo were measured with infrared spectroscopy through application of perdeuterated OA (OA-d34 ). Studies of the interaction of OA and GT with skin lipids included imaging the distribution of OA-d34 and GT ex vivo with IR microspectroscopy and thermodynamic analysis of mixtures in aqueous monolayers. The oil mixtures increased both TEWL and fluorescein penetration 24 h after a single application in an OA dose-dependent manner, with the highest increase from treatment with pure OA. OA-d34 penetrated into skin and disordered SC lipids. Furthermore, the ex vivo IR imaging studies showed that OA-d34 permeated to the dermal/epidermal junction while GT remained in the SC. The monolayer experiments showed preferential interspecies interactions between OA and SC lipids, while the mixing between GT and SC lipids was not thermodynamically preferred. The FFA component of plant oils may disrupt skin barrier function. The affinity between plant oil components and SC lipids likely determines the extent of their penetration and clinically measurable effects on skin barrier functions.

Dermic diffusion and stratum corneum: a state of the art review of mathematical models

Transdermal biotechnologies are an ever increasing field of interest, due to the medical and pharmaceutical applications that they underlie. There are several mathematical models at use that permit a more inclusive vision of pure experimental data and even allow practical extrapolation for new dermal diffusion methodologies. However, they grasp a complex variety of theories and assumptions that allocate their use for specific situations. Models based on Fick's First Law found better use in contexts where scaled particle theory Models would be extensive in time-span but the reciprocal is also true, as context of transdermal diffusion of particular active compounds changes. This article reviews extensively the various theoretical methodologies for studying dermic diffusion in the rate limiting dermic barrier, the stratum corneum, and systematizes its characteristics, their proper context of application, advantages and limitations, as well as future perspectives.

Determination of tolerable fatty acids and cholera toxin concentrations using human intestinal epithelial cells and BALB/c mouse macrophages

The positive role of fatty acids in the prevention and alleviation of non-human and human diseases have been and continue to be extensively documented. These roles include influences on infectious and non-infectious diseases including prevention of inflammation as well as mucosal immunity to infectious diseases. Cholera is an acute intestinal illness caused by the bacterium Vibrio cholerae. It occurs in developing nations and if left untreated, can result in death. While vaccines for cholera exist, they are not always effective and other preventative methods are needed. We set out to determine tolerable concentrations of three fatty acids (oleic, linoleic and linolenic acids) and cholera toxin using mouse BALB/C macrophages and human intestinal epithelial cells, respectively. We solubilized the above fatty acids and used cell proliferation assays to determine the concentration ranges and specific concentrations of the fatty acids that are not detrimental to human intestinal epithelial cell viability. We solubilized cholera toxin and used it in an assay to determine the concentration ranges and specific concentrations of cholera toxin that do not statistically decrease cell viability in BALB/C macrophages. We found the optimum fatty acid concentrations to be between 1-5 ng/μl, and that for cholera toxin to be < 30 ng per treatment. This data may aid future studies that aim to find a protective mucosal role for fatty acids in prevention or alleviation of cholera infections.

Oleic acid disorders stratum corneum lipids in Langmuir monolayers

Oleic acid (OA) is well-known to affect the function of the skin barrier. In this study, the molecular interactions between OA and model stratum corneum (SC) lipids consisting of ceramide, cholesterol, and palmitic acid (PA) were investigated with Langmuir monolayer and associated techniques. Mixtures with different OA/SC lipid compositions were spread at the air/water interface, and the phase behavior was tracked with surface pressure-molecular area (π-A) isotherms. With increasing OA levels in the monolayer, the films became more fluid and more compressible. The thermodynamic parameters derived from π-A isotherms indicated that there are preferential interactions between OA and SC lipids and that films of their mixtures were thermodynamically stable. The domain structure and lipid conformational order of the monolayers were studied through Brewster angle microscopy (BAM) and infrared reflection absorption spectroscopy (IRRAS), respectively. Results indicate that lower concentrations of OA preferentially mix with and disorder the ceramide-enriched domains, followed by perturbation of the PA-enriched domains and disruption of SC lipid domain separation at higher OA levels.

Preparation and characterization of lipid based nanosystems for topical delivery of quercetin

The main objective of this study was to evaluate the potential of lipid nanosystems for topical delivery of the naturally occurring flavonoid quercetin. These lipid based nanosystems were manufactured using a solvent free probe ultrasonication process. Formulation factors such as the nature of the lipid (solid/combination of solid and liquid) in solid lipid nanoparticle (SLN) and nanostructured lipid carrier (NLC) systems and drug loading were evaluated to produce an optimum formulation with adequate physical stability for up to 14 weeks at 2-8°C. The mean particle size of the optimized formulation was around 282 nm, with a zeta potential value of -36.57 ± 2.67 mV, indicating the formation of a stable system. Release studies showed a biphasic release profile, characterized by an initial burst release followed by a more controlled release pattern from both SLN and NLC systems. The NLC system showed the highest improvement in topical delivery of quercetin manifested by the amount of quercetin retained in full thickness human skin, compared to a control formulation with similar composition and particle size in the micrometer range. This study demonstrated the feasibility of nanostructured lipid carrier systems for improved topical delivery of quercetin.

Assessment of the potential irritancy of oleic acid on human skin: Evaluation in vitro and in vivo

As skin barrier modulating compounds, fatty acids are frequently used in formulations for transdermal or topical delivery. In this study the effects of oleic acid on keratinocytes in vitro was compared with its in vivo skin irritancy in humans. Dose- and time-dependent effects of oleic acid were examined in submerged human keratinocyte cultures, in reconstructed human epidermis (RE-DED), and in excised human skin, using alterations in morphology and changes in interleukin-1alpha mRNA levels as endpoints. In vitro results were compared with responses of living human skin after topical application of oleic acid, using non-invasive bioengineering methods. Direct interaction of oleic acid and submerged keratinocyte cultures resulted in cell toxicity at very low concentrations of the fatty acid. By contrast, when oleic acid was applied topically on RE-DED or on excised skin, no alterations in morphology were observed. Modulation of stratum corneum thickness indicated a key role of the stratum corneum barrier in the control of oleic acid-induced toxicity. In agreement with these findings, no epidermal tissue damage was seen in vivo, whereas oleic acid induced a mild but clearly visible skin irritation and inflammatory cells were present in the upper dermal blood vessels. Small amounts of oleic acid induced IL-1alpha mRNA expression in submerged keratinocyte cultures, whereas in RE-DED and in excised skin, IL-1alpha mRNA levels were increased only when the concentration applied topically was at least two orders of magnitude higher. It is concluded that minute amounts of oleic acid are sufficient to cause local (i.e. inside the viable epidermis) modulation of cytokine production. These concentrations do not affect morphology but induce skin irritation in vivo. To achieve comparable effects in the skin, much higher topical doses are needed than expected according to the locally required levels, owing to the rate-limiting transport of the fatty acid across the stratum corneum barrier.

Self-assembled nanostructures of fully hydrated monoelaidin-elaidic acid and monoelaidin-oleic acid systems

In recent years, there has been a surge of interest in exploring the effect of trans-fatty acids (TFAs) on biological membrane properties. The research studies are motivated by an increasing body of evidence suggesting that the consumption of TFAs increases the risk of developing negative health effects such as coronary heart disease and cancer. The ultimate goal of studying the lipid-fatty acid interactions at the molecular level is to predict the biological role of fatty acids in cells. In this regard, it is interesting to elucidate the effect of loading TFAs and their counterpart cis-fatty acids (CFAs) on the physical properties of lipid model membranes. Here, the present study focuses on discussing the following: (1) the effect of mixing monoelaidin (ME, TFA-containing lipid) with its counterpart monoolein (MO, CFA-containing lipid) on modulating the fully hydrated self-assembled structure, and (2) the influence of solubilizing oleic acid (OA) and its trans counterpart elaidic acid (EA) on the fully hydrated ME system. The ME model membrane was selected due to its sensitivity to variations in lipid composition and temperature. Synchrotron small-angle X-ray scattering (SAXS) was applied for studying the temperature-dependent structural behavior of the fully hydrated ME/MO-based system prepared with an equal ME/MO weight ratio and also for characterizing the fully hydrated OA- and EA-loaded ME systems. Wide-angle X-ray (WAXS) experiments were also performed for characterizing the formed crystalline lamellar phases at ambient temperatures. The results demonstrate the significant influence of the partial replacement of ME by MO on the phase behavior. The addition of MO induces the lamellar-nonlamellar phase transitions at ambient temperatures and promotes the formation of the inverted type hexagonal (H(2)) phase above 72 °C. The fully hydrated ME/EA and ME/OA systems with their rich polymorphism exhibit an interesting temperature-dependent complex behavior. The experimental findings show that the temperature-induced phase transitions are dictated by the solubilized fatty acid concentration and its configuration. Both EA and OA have a significant impact on the fully hydrated ME system. Similar to previous published studies, OA induces a significantly stronger mean negative membrane curvature as compared to EA. The two phase diagrams are discussed in terms of water-lipid and lipid-fatty acid interactions, membrane bending, and lipid packing concepts. A newly observed interesting epitaxial relationship for the lamellar-hexagonal phase transition in the EA-loaded ME system is illustrated and discussed in detail.

Physico-chemical characteristics of methotrexate-entrapped oleic acid-containing deformable liposomes for in vitro transepidermal delivery targeting psoriasis treatment

This study aimed to investigate the physico-chemical characteristics and in vitro permeability of methotrexate (MTX)-entrapped deformable liposomes prepared from phosphatidylcholine (PC) and oleic acid (OA), comparing with those of MTX-entrapped conventional liposomes prepared from PC and cholesterol (CH). Two formulations of MTX-entrapped PC2:CH1 and PC9:CH1 liposomes and one formulation of MTX-entrapped PC2.5:OA1 liposomes were prepared. The size, size distribution, zeta potential, thermal properties, entrapment efficiency, stability, and in vitro permeability across a porcine skin of the MTX-entrapped liposomes were evaluated. All liposome formulations showed a narrow size distribution with the size range of 80-140 nm which is appropriate for the skin permeability. The percentage of MTX loading, entrapment efficiency and the stability of MTX-entrapped PC2:CH1 and PC9:CH1 liposomes were slightly higher than those of MTX-entrapped PC2.5:OA1 liposomes. However, the MTX-entrapped PC2.5:OA1 liposomes enhanced the skin permeability characterized by the higher concentration and flux of MTX diffused across or accumulated in the epidermis and dermis layers of porcine skin. The enhanced permeability of MTX-entrapped PC2.5:OA1 liposomes was explained by 2 mechanisms: (1) the deformable and elasticity characteristics of OA-containing liposomes and (2) a property as a skin penetration enhancer of OA. This suggested that the PC2.5:OA1 deformable liposome was one of promising candidates to enhance the permeability of MTX for the treatment of psoriasis.

Oleic acid peroxidation in the presence of metallo-porphyrins

The influence of free bases of meso-tetrakis(3,5-di-tert-butyl-4-hydroxy-phenyl)porphyrins and meso-tetraphenylporphyrins and their complexes of Co , Ni , Cu , Pt upon the radical chain oxidation of oleic acid as model substrates for lipid peroxidation has been studied. It was shown that the introduction of the antioxidative phenolic fragment into the porphyrin ring leads to the dual activity of phenolic porphyrins when compared with their tetraphenyl substituted analogues in substrate oxidation. Free base phenolic porphyrins and their nickel, copper, platinum complexes demonstrate acute inhibitory effect upon oleic acid peroxidation due to the key role of 2,6-di-tert-butylphenol moities, whereas cobalt porphyrin exhibits dual activity associated with the presence of both the redox active metal center and phenolic group.

Absorption enhancers: applications and advances

Absorption enhancers are functional excipients included in formulations to improve the absorption of a pharmacologically active drug. The term absorption enhancer usually refers to an agent whose function is to increase absorption by enhancing membrane permeation, rather than increasing solubility, so such agents are sometimes more specifically termed permeation enhancers. Absorption enhancers have been investigated for at least two decades, particularly in efforts to develop non-injection formulations for peptides, proteins, and other pharmacologically active compounds that have poor membrane permeability. While at least one product utilizing an absorption enhancer for transdermal use has reached the market, quite a few more appear to be at the threshold of becoming products, and these include oral and transmucosal applications. This paper will review some of the most advanced absorption enhancers currently in development and the formulation technologies employed that have led to their success. In addition, a more basic review of the barriers to absorption and the mechanisms by which those barriers can be surmounted is presented. Factors influencing the success of absorption-enhancing formulations are discussed. If ultimately successful, the products now in development should offer non-injection alternatives for several peptide or protein drugs currently only administered by injection. The introduction of new absorption enhancers as accepted pharmaceutical excipients, and the development of formulation technologies that afford the greatest benefit/risk ratio for their use, may create opportunities to apply these enabling technologies more broadly to existing drugs with non-optimal delivery properties.

Effect of oleic acid modified polymeric bilayered nanoparticles on percutaneous delivery of spantide II and ketoprofen

The objective of the present study was to evaluate the effect of oleic acid modified polymeric bilayered nanoparticles (NPS) on combined delivery of two anti-inflammatory drugs, spantide II (SP) and ketoprofen (KP) on the skin permeation. NPS were prepared using poly(lactic-co-glycolic acid) (PLGA) and chitosan. SP and KP were encapsulated in different layers alone or/and in combination (KP-NPS, SP-NPS and SP+KP-NPS). The surface of NPS was modified with oleic acid (OA) ('Nanoease' technology) using an established procedure in the laboratory (KP-NPS-OA, SP-NPS-OA and SP+KP-NPS-OA). Fluorescent dyes (DiO and DID) containing surface modified (DiO-NPS-OA and DID-NPS-OA) and unmodified NPS (DiO-NPS and DID-NPS) were visualized in lateral rat skin sections using confocal microscopy and Raman confocal spectroscopy after skin permeation. In vitro skin permeation was performed in dermatomed human skin and HPLC was used to analyze the drug levels in different skin layers. Further, allergic contact dermatitis (ACD) model was used to evaluate the response of KP-NPS, SP-NPS, SP+KP-NPS, KP-NPS-OA, SP-NPS-OA and SP+KP-NPS-OA treatment in C57BL/6 mice. The fluorescence from OA modified NPS was observed up to a depth of 240μm and was significantly higher as compared to non-modified NPS. The amount of SP and KP retained in skin layers from OA modified NPS increased by several folds compared to unmodified NPS and control solution. In addition, the combination index value calculated from ACD response for solution suggested an additive effect and moderate synergism for NPS-OA. Our results strongly suggest that surface modification of bilayered nanoparticles with oleic acid improved drug delivery to the deeper skin layers.