Stratum Corneum Intercellular Lipids Research Articles

Changes in the composition of molecular species of covalently bound and free ceramides [EOS], and their correlation with disease severity in atopic dermatitis.

Ceramides are major constituents of stratum corneum (SC) intercellular lipids involved in skin barrier function. The ratio of molecular species of ceramides and their correlation with disease severity was examined in patients with atopic dermatitis (AD). Thirty-eight patients with AD and 32 healthy controls (HCs) were assessed for transepidermal water loss, SC collection and clinical assessment. The ceramide content of different molecular species in the samples was quantified using high-performance liquid chromatography coupled with tandem mass spectrometry. Unsaturated acyl chains of both covalently bound and free ceramides [EOS] were higher in AD lesional skin than those in AD non-lesional or normal HC skin. The proportion of unsaturated acyl chains (C30:1, C32:1 and C34:1) was higher than other ceramide molecular species among covalently bound and free ceramides [EOS] in patients with AD. The proportion of unsaturated acyl chains in covalently bound ceramides was positively correlated with transepidermal water loss (r = 0.600) when considering the total number of non-lesional and lesional skin. Additionally, thymus and activation-regulated chemokine (TARC) showed a positive correlation with unsaturated acyl chains proportion in AD non-lesional (r = 0.676) and lesional (r = 0.503) skin. Our study is the first to show the increase in unsaturated acyl chains of both covalently bound and free ceramides [EOS] in lesional and non-lesional skin in AD for each molecular species. This increase is associated with dryness and impaired barrier function, which correlates with TARC levels, a marker for the degree of type 2 inflammation. We speculate that type 2 inflammation exacerbation leads to abnormal epidermal lipid metabolism in the skin of patients with AD.

The effects of size and surface functionalization of polystyrene nanoplastics on stratum corneum model membranes: An experimental and computational study

Nanoplastics are mainly generated from the decomposition of plastic waste and artificial production and have attracted much attention due to their wide distribution in the environment and the potential risk for humans. As the largest organ of the human body, the skin is inevitably in contact with nanoplastics. Stratum corneum is the first barrier when the skin is exposed to nanoplastics. However, little is known about the interactions between nanoplastics and stratum corneum. Here, the effects of particle size and surface functionalization (amino-modified and carboxy-modified) of polystyrene nanoplastics on the stratum corneum models were studied by Langmuir monolayer and molecular dynamics simulations. An equimolar mixture of ceramide/cholesterol/free fatty acid was used to mimic stratum corneum intercellular lipids. The Langmuir monolayer studies demonstrated that the larger size and surface functionalization of polystyrene nanoplastics significantly reduced the stability of stratum corneum lipid monolayer in a concentration-dependent fashion. Simulation results elucidated that functionalized polystyrene oligomers had a stronger interaction with lipid components of the stratum corneum model membrane. The cell experiments also indicated that functionalized polystyrene nanoplastics, especially for amino-modified polystyrene nanoplastics, had significant cytotoxicity on normal human dermal fibroblast cells. Our results provide fundamental information and the basis for a deeper understanding of the health risks of nanoplastics to humans.

A thermodynamic and kinetic analysis of human epidermal penetration of phenolic compounds: II. Maximum flux and solute diffusion through stratum corneum lipids

Warming the skin is a key means of promoting solute permeation through the skin. Changes in solute permeation associated with variations in skin temperature also assist in understanding the mechanism by which solutes permeate the skin. However, few studies have considered the relative impact of temperature on the main determinants of the maximum flux for a solute across the skin, the solubility of a solute and its diffusivity in the stratum corneum. In this study, we quantified for the first time the thermodynamics associated with the maximum skin fluxes for a series of phenolic compounds of similar size but with varying lipophilicity (defined by the logarithms of their octanol/water partition coefficient, logP). These studies were undertaken using aqueous donor solutions (along with testosterone as a reference solute) across human epidermal membranes in vertical Franz diffusion cells at 4 °C, 24 °C and 37 °C with intermittent receptor sampling and volume replacement over 24 h. Kinetic and thermodynamic analyses included the estimation of the stratum corneum (SC) apparent SC diffusivity from the SC maximum fluxes and SC solubilities and the associated activation energies, enthalpies and entropies for diffusion. The key findings were that the differences in the maximum flux of phenolic compounds varying in lipophilicity mainly arose from differences in SC solubility at the various temperatures and that, at the highest temperature, SC permeability and SC diffusion were affected by SC lipid fluidisation and that variations in SC - water partitioning enthalpies explain some of the previously low activation energies for permeation of the more lipophilic phenols. Higher enthalpies for diffusion were seen for solutes with addition hydrogen bonding capacity and the highest negative entropy was observed with the more compact solutes. Various relationships between the derived thermodynamic parameters were explored and interpreted in a proposed model for solute partitioning into and permeation through the SC intercellular lipid lamellae.

Thermodynamic and kinetic analysis of human epidermal penetration of phenolic compounds: I. Stratum corneum solubility and partitioning

Warming of the skin is now an accepted means of promoting skin permeation. Accordingly, the usually quite onerous thermodynamic studies on solute transport through the skin have practical applications. Phenolic compounds permeate through the skin by partitioning into and diffusing through the stratum corneum (SC) intercellular lipids, with their size being the main determinant of their maximal solute flux through skin. This paper sought to characterise the enthalpic and entropic changes associated with the solubility and equilibrium partitioning into the human SC of a series of phenols similar in size but with differing log P from aqueous vehicles.The solubilities of 9 phenolic compounds, covering a range of polarities, were determined in water and SC following 72 h at 4, 24, 32 and 37 °C which allowed the estimation of the SC-water partition coefficients. Van’t Hoff plots were then used to estimate the enthalpies and entropies for the SC solubility, water solubility and SC partitioning of phenols. In addition, partition coefficients of 3 of the 9 phenols from mineral oil into hydrated and dehydrated SC were measured at the same temperatures. Van’t Hoff plots were then used to estimate the enthalpies and entropies for the SC solubility, water solubility and SC partitioning of phenols from the oil.The SC solubility for the polar phenols increased more with temperature than the non-polar phenols, with the SC-water partition coefficients increasing with temperature for the polar phenols but decreasing with temperature for the non-polar phenols. Thermodynamic analyses suggest that, while enthalpy and entropy effects are involved in the SC partitioning of the non-polar solutes, the SC partitioning of the polar phenols were almost entirely entropy driven. The resultant thermodynamic parameters are consistent with the polar phenols being mainly associated with the SC polar head groups whereas the nonpolar phenols were more likely to be located in the interior interface SC lipid region adjacent to the polar head groups. Further, hydrating the SC led to an increase in the enthalpy of partitioning for both the polar and non-polar phenols studied. The estimated entropy of the partitioning for solutes from dehydrated SC suggests this is not only a hydrophobic effect in water but that the partitioning arises from the nature of phenolic compound - SC intercellular lipid interactions and SC intercellular lipid entropy. This partitioning process is dominated more by the extent of interaction between the SC and solute than the hydrophobic effect in water and is likely to be even greater above the SC lipid phase transition at around 36 °C for hydrated epidermal membranes.

Effect of the oat, horse chestnut, cowherb, soy, quinoa and soapwort extracts on skin‐mimicking monolayers and cell lines

AbstractThe main goal of the study was to compare the effect of aqueous extracts of oat (Avena sativa L.), horse chestnut (Aesculus hippocastanum L.), quinoa (Chenopodium quinoa Willd.), soapwort (Saponaria officinalis L.), cowherb (Vaccaria hispanica [P. Mill.] Rauschert) and soy (Glycine max L.) on model lipid monolayers mimicking the lipid membrane of keratinocytes and intercellular lipids of stratum corneum, and on human skin‐related cell lines. Two lipid monolayers, consisting of a dipalmitoylphosphatidylcholine (DPPC) and cholesterol mixture in a molar ratio of 7:3 and Ceramide VI, stearic acid and cholesterol in a molar ratio of 1:1:0.7, and two cell lines (human keratinocyte HaCaT and human skin malignant melanoma A375) were employed. None of the extracts reduced surface pressure below the level achieved for bare monolayers. The strength of the effect on the lipid monolayers (horse chestnut > cowherb > soapwort > soy) points to the existence of some specific interactions responsible for the observed affinity of biosurfactants from the extracts to the lipids in the monolayers. The cytotoxicity tests performed with two model skin cell lines showed that all six plants extracts significantly reduced the cells' viability in a concentration‐dependent way. The model lipid monolayers were not solubilized by the investigated surface‐active extracts. The latter thus proved interesting candidates for application in mild cleansing cosmetic formulations. Penetration of the monolayers by surface‐active components of some extracts, especially horse chestnut, cowherb and soapwort, opens new possibilities for topical delivery of active components.

Effect of galactosylceramide on stratum corneum intercellular lipid synthesis in a three-dimensional cultured human epidermis model

Intercellular lipids in the stratum corneum (SC), such as ceramide (CER), free fatty acid (FFA), and cholesterol (CHOL), contribute to the formation of stable lamellar structures in the SC, making them important for skin barrier function. β-Galactosylceramide (GalCer) is a glycosphingolipid that is used in some cosmetics and quasi-drugs in anticipation of a moisturizing effect. GalCer promotes keratinocyte differentiation and increases CER production by increasing β-glucocerebrosidase (β-GCase) activity. However, few reports have described the mechanism of these effects, and detailed studies on the role of GalCer in intercellular lipid production in the SC have not been conducted. This study investigated the effect of GalCer on the metabolism and production of intercellular lipids in the SC in a three-dimensional cultured epidermis model. After reacting GalCer with a homogenate solution of three-dimensional cultured epidermis, GalCer was hardly metabolized. Treatment of the three-dimensional cultured epidermis with GalCer increased the expression of genes involved in the β-GCase metabolic pathway and promoted CER production. In addition, GalCer treatment reduced the expression of FFA metabolism-related genes as well as palmitic acid levels. In addition, transepidermal water loss, which is a barrier index, was reduced by GalCer treatment. These findings suggested that GalCer, which is hardly metabolized, affects the production of intercellular lipids in the SC and improves skin barrier function.

Increased Levels of Short-Chain Ceramides Modify the Lipid Organization and Reduce the Lipid Barrier of Skin Model Membranes

The skin barrier function is attributed to the stratum corneum (SC) intercellular lipid matrix, which is composed primarily of ceramides (CERs), free fatty acids, and cholesterol. These lipids are organized in two lamellar phases: the short and long periodicity phases (SPP and LPP), respectively. The LPP is considered important for the skin barrier function. High levels of short-chain CERs are observed in various inflammatory skin diseases and have been correlated with barrier dysfunction. In this research, we investigated how the increase in the fraction of the short-chain CER with a nonhydroxy C16 acyl chain linked to a C18 sphingosine base CER NS(C16) at the expense of the physiological chain length CER NS with a C24 acyl chain (CER NS(C24)) impacts the microstructure and barrier function of a lipid model that mimicked certain characteristics of the SC lipid organization. The permeability and lipid organization of the model membranes were compared with that of a control model without CER NS(C16). The permeability increased significantly when ≥50% of CER NS(C24) was substituted with CER NS(C16). Employing biophysical techniques, we showed that the lipid packing density reduced with an increasing proportion of CER NS(C16). Substitution of 75% of CER NS(C24) by CER NS(C16) resulted in the formation of phase-separated lipid domains and alteration of the LPP structure. Using deuterium-labeled lipids enabled simultaneous characterization of the C24 and C16 acyl chains in the lipid models, providing insight into the mechanisms underlying the reduced skin barrier function in diseased skin.

A Lipid Mixture Enriched by Ceramide NP with Fatty Acids of Diverse Chain Lengths Contributes to Restore the Skin Barrier Function Impaired by Topical Corticosteroid

Introduction: The stratum corneum (SC) is a skin barrier that consists of corneocytes, intercellular lipids, and corneodesmosomes. Ceramides are composed of sphingoid bases linked with various types of fatty acids (FAs), and they are an essential constituent of SC intercellular lipids. Among their subtypes, ceramide NP with a phytosphingosine base is especially important. Most of the previous studies on barrier recovery have focused on a specific ceramide with a single chain FA, not with diverse chain lengths. Skin barrier function is impaired by various factors, including topical corticosteroid. Objective: We evaluated whether a lipid mixture enriched by ceramide NP with FAs of diverse chain lengths (CER [NP]*) can restore the skin barrier function impaired by topical corticosteroid. Methods: Twenty-seven healthy adult male volunteers were recruited. Topical corticosteroid was applied on both volar forearms of volunteers. Then, the test cream containing a lipid mixture with CER (NP)* was applied on the left forearm, and a vehicle cream without a lipid mixture was applied on the right forearm of each subject. The functional parameters of the skin barrier were compared before and after the treatment. Epidermal differentiation markers, hyaluronic acid synthase 3 (HAS3), cytokine levels, and the lipid profiles in the SC were analyzed. Results: The functional parameters of the skin barrier, such as barrier recovery rate, SC integrity, and SC hydration were significantly improved in the test cream-applied site compared to the vehicle cream-applied sites. Filaggrin and HAS3 levels were significantly higher in the sites applied with the test cream. Interleukin (IL)-1α levels were also significantly increased in these sites. IL-2, IL-6, IL-10, and IL-13 levels were significantly decreased in the test cream-applied sites. Lipid analyses showed that C18, C20, and total ceramide NP levels significantly increased in the sites where the test cream was applied. Also, C16, C18, C20, C24, and total ceramide NP levels were significantly elevated in the test cream-applied sites after acute barrier disruption. Conclusion: Our results demonstrate that a lipid mixture enriched by CER (NP)* could recover the barrier function impaired by topical corticosteroid.

Formulation of bicelles with cholesterol using a semi-spontaneous method

Stratum corneum intercellular lipids play an important role in skin barrier function and are therefore considered useful in pharmaceutical and cosmetics products. In this study, we formulated cholesterol (Cho), the main component of intercellular lipids, into bicelles using a semi-spontaneous method, with the ultimate aim of extending the utility of bicelles in cosmetics. Bicelles are disk-shaped structures in which the planar part comprises long-chain phospholipids and the rims comprise short-chain phospholipids. We used soybean lecithin (SL) and nonionic surfactants (NS) to formulate Cho into bicelles using a semi-spontaneous method. Cho was successfully formulated into bicelles using poly(oxyethylene) cholesteryl ether (with an average of 10 ethylene oxide units, ChEO10) as the NS. We identified the boundaries of the bicelle region in the SL-Cho-ChEO10 system by measuring particle sizes. A bicelle region was formed up to around a maximum mixing ratio of 10wt% Cho, representing a mole fraction (mol%) of approximately 33. Phase changes in the system were observed. Comparison of poly(oxyethylene) cholesteryl ethers containing an average of 10 or 20 (ChEO20) ethylene oxide units revealed that the size of the hydrophilic group affects both the bicelle formation region and the mixing ratio of Cho. We analyzed the state of the SL-Cho-ChEO10 bicelles by differential scanning calorimetry and found that samples containing only phospholipid (SL/Ch/ChEO10 = 1/0/0) provided an endothermic peak between 50 and 55 °C, corresponding to the gel-liquid crystal transition point of the phospholipid. In contrast, the bicelle regions (SL/Cho/ChEO10 = 0.4/0/0.6 and 0.37/0.05/0.58) lacked a gel liquid crystal transition point and a liquid-ordered state was induced by Cho or ChEO10. This indicates that these bicelles are highly stable towards thermal changes.

The Effect of a Ceramide-Containing Product on Stratum Corneum Lipid Levels in Dry Legs.

Roughly equimolar concentrations of ceramides, cholesterol, and free fatty acids arranged in lamellar sheets form the intercellular lipid barrier in the stratum corneum (SC). Intercellular lipid deficiencies, specifically ceramides, and barrier disruption are associated with many dermatologic conditions, including dry skin. This study explored the relationship between the improvement in the signs of dry skin and the amounts of ceramides in the SC by combining clinical observations with a biochemical analysis to quantify the level of SC intercellular lipids. The efficacy of a multilamellar vesicular emulsion (MVE), ceramide-containing moisturizing cream was evaluated in a randomized, investigator-blinded, split-leg study on female subjects with dry, itchy skin. The cream increased skin hydration and demonstrated an immediate and sustained reduction in the visible signs of dry skin and subject perceived sensory discomfort. Additionally, ceramide, cholesterol and free fatty acid levels in the SC significantly increased after 4 weeks of moisturizer application. Thus, the clinical effect of the ceramide-containing moisturizing cream on dry, itchy skin was accompanied by an increase in SC intercellular lipid levels. J Drugs Dermatol. 2020;19(4):372-376. doi:10.36849/JDD.2020.4796.

Increased 1-Deoxysphingolipids and Skin Barrier Dysfunction in the Skin of X-ray or Ultraviolet B Irradiation and Atopic Dermatitis Lesion Could Be Prevented by Moisturizer with Physiological Lipid Mixture.

BackgroundSkin diseases characterized by epithelial barrier dysfunction show altered sphingolipid metabolism, which results in changes in the stratum corneum intercellular lipid components and structure. Under pathological conditions, 1-deoxysphingolipids form as atypical sphingolipids from de novo sphingolipid biosynthesis.ObjectiveThis study investigated the potential role of 1-deoxysphingolipids in skin barrier dysfunction secondary to X-ray and ultraviolet B (UVB) irradiation in vitro and in vivo. It was also evaluated changes in the expression of 1-deoxysphingolipids in lesional human skin of atopic dermatitis.MethodsIn this study, the changes in these 1-deoxysphingolipids levels of skin and serum samples were investigated in skin barrier dysfunction associated with X-ray and UVB irradiation in vitro and in vivo.ResultsIncreased 1-deoxysphingolipids were observed in cultured normal human epidermal keratinocytes after X-ray irradiation. X-ray or UVB irradiation increased the production of 1-deoxysphingosine in a reconstituted 3-dimensional (3D) skin model. Interestingly, treatment with a physiological lipid mixture (multi-lamellar emulsion contained pseudoceramide), which can strengthen the epidermal permeability barrier function, resulted in decreased 1-deoxysphingosine formation in a reconstituted 3D skin model. Further investigation using a hairless mouse model showed similar preventive effects of physiological lipid mixture against 1-deoxysphingosine formation after X-ray irradiation. An increased level of 1-dexoysphingosine in the stratum corneum was also observed in lesional skin of atopic dermatitis.Conclusion1-deoxysphingosine might be a novel biomarker of skin barrier dysfunction and a physiological lipid mixture treatment could prevent 1-deoxysphingosine production and consequent skin barrier dysfunction.

Thermotropic Behavior of Intercellular Lipids in Stratum Corneum and Application of Structure Analysis of Intercellular Lipids into Development of Transdermal/Topical Formulation

Thermotropic Behavior of Intercellular Lipids in Stratum Corneum and Application of Structure Analysis of Intercellular Lipids into Development of Transdermal/Topical Formulation

Physicochemical characterization and thermal behavior of hexosomes containing ketoconazole as potential topical antifungal delivery system

Objective: The main purpose of this article is to show the valuable characteristics that liotropic liquid crystal systems possess to be employed as new drug delivery systems.Significance: Colloidal aqueous dispersions of lyotropic liquid crystal mesophases such as the identified as cubosomes and hexosomes, and so on, have received considerable attention due to their unique nanostructures and their thermodynamic properties, which provide the potential as a sustained drug release matrix. Additionally, their large surface area and similarity with the liquid crystal structures of intercellular lipids of stratum corneum enhances the interaction with the skin and mucous, increasing the potential for topical drug delivery efficiency of biopharmaceutical class II drugs as the antifungal ketoconazole.Methods: This article presents the results in morphological characteristics, particle size, ζ potential, flow, thermal behavior and drug release studies of hexosomes containing ketoconazole (LHLC-K) obtained with glycerol monooleate, propylene glycol monolaurate, poloxamer, and water mixtures.Results: This colloidal system exhibits a Newtonian-type flow and a hexagonal nanostructure with a median particle size of 107 ± 20 nm and ζ potential of +4.45 ± 0.50 mV. Through differential scanning calorimetry studies, the LHLC-K demonstrated physical and chemical stability for more than six months and mesophasic thermal reversibility between 10 and 50 °C. Finally, LHLC-K releases ketoconazole following a kinetics described by the first order model.Conclusions: Physicochemical properties of the hexosomes containing ketoconazole are important for topical mycosis treatment administration, conditions of storage, and for its incorporation into the formulation of semi-solid dosage forms.

Investigation of the enhancement effect of the natural transdermal permeation enhancers from Ledum palustre L. var. angustum N. Busch: Mechanistic insight based on interaction among drug, enhancers and skin

It has been reported that natural transdermal permeation enhancers (TPEs) are superior in safety compared with synthetic TPEs. The essential oil (EO) of Ledum palustre L. var. angustum N. Busch had a strong enhancement effect on drug skin permeation based on previous studies. However, their enhancement mechanisms and safety were still unclear. The composition of the EO was determined using GC–MS. By using donepezil (DNP) as a model drug, the enhancement effect of the constituents of the EO and the EO were evaluated by in vitro skin permeation test. Confocal laser scanning microscopy (CLSM), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and molecular docking were used to investigate the interaction among drug, enhancers and skin. Skin retention amount, apparent partition coefficient (K′) and molecular simulation were used to reflect the effect of the enhancers on drug partition into skin. The skin irritation potential was evaluated using in vivo skin erythema analysis. The results showed that the main constituents of the EO were sabinene (SA), 4-terpineol (TE), p-cymene (CY) and cuminaldehyde (CU). CU was the main active constituent of the EO, which facilitated skin permeation of DNP. CU improved the skin permeation of DNP by increasing the mobility of the stratum corneum (SC) intercellular lipids, decreasing the interaction between DNP and the SC intercellular lipids, and improving the partition of DNP into the SC layer. Besides the superior enhancement effect, CU also showed a lower skin irritation potential compared with the EO. This work gave us some enlightenment that the effectiveness and safety of the natural transdermal permeation enhancers could be improved by understanding their composition and the enhancement mechanisms.

673 11β-hydroxysteroid dehydrogenase type 1 activation induced by UVB might be a possible mechanism of skin barrier dysfunction due to UV exposure

Ultraviolet light (UV) radiation to the skin causes dose- and wavelength- dependent reactions, including skin barrier dysfunction. Long-term exposure to even low dose UV induces the alteration of skin barrier presenting prominent ceramide decrease in the stratum corneum (SC) intercellular lipids. 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1), which converts inactive cortisone to active cortisol in peripheral tissues and inhibits keratinocytes and fibroblasts proliferation, is known to be induced by UVB. We performed in vitro, in vivo, ex-vivo studies to elucidate whether skin barrier dysfunction induced by UV could be resulted from 11β-HSD1 activation after UV irradiation. We observed that 11β-HSD1 expression was increased by cortisol treatment itself and UV irradiation, thereby rapidly converting cortisone into cortisol. UVB irradiation increases 11β-HSD1 expression as well as inflammatory cytokines using HSD11B1 siRNA transfected normal human epidermal keratinocytes. 11β-HSD1 mRNA was prominently higher in UVB irradiated primary human keratinocytes compared with control. Keratinocytes transfected with HSD11B1 siRNA decreased the expression of 11β-HSD1 mRNA and did not increase cortisol even when the keratinocytes were irradiated by UVB. In vitro, increased cortisol converted by 11β-HSD1 inhibits keratinocyte differentiation. Cortisone decreased the mRNA and protein expression of keratinocyte differentiation markers in UVB-exposed keratinocytes. 11β-HSD1 expression remarkably increased in UV exposed skin and intrinsic aged skin. Skin barrier function presented by transpidermal water loss, SC hydration and SC integrity was impaired in long term UV exposed skin and intrinsic aged skin. Therefore, 11β-HSD1 activation by UVB might suggest another possible mechanism on skin barrier dysfunction due to UV exposure.

625 Role of eutectic mixture of ceramides for reconstruction of stratum corneum intercellular lipid model

625 Role of eutectic mixture of ceramides for reconstruction of stratum corneum intercellular lipid model

In vivo confocal Raman microscopic determination of depth profiles of the stratum corneum lipid organization influenced by application of various oils

BackgroundThe intercellular lipids (ICL) of stratum corneum (SC) play an important role in maintaining the skin barrier function. The lateral and lamellar packing order of ICL in SC is not homogenous, but rather depth-dependent. ObjectiveThis study aimed to analyze the influence of the topically applied mineral-derived (paraffin and petrolatum) and plant-derived (almond oil and jojoba oil) oils on the depth-dependent ICL profile ordering of the SC in vivo. MethodConfocal Raman microscopy (CRM), a unique tool to analyze the depth profile of the ICL structure non-invasively, is employed to investigate the interaction between oils and human SC in vivo. ResultsThe results show that the response of SC to oils’ permeation varies in the depths. All oils remain in the upper layers of the SC (0–20% of SC thickness) and show predominated differences of ICL ordering from intact skin. In these depths, skin treated with plant-derived oils shows more disordered lateral and lamellar packing order of ICL than intact skin (p<0.05). In the intermediate layers of SC (30–50% of SC thickness), the oils do not influence the lateral packing order of SC ICL (p>0.1), except plant-derived oils at the depth 30% of SC thickness. In the deeper layers of the SC (60–100% of SC thickness), no difference between ICL lateral packing order of the oil-treated and intact skin can be observed, except that at the depths of 70–90% of the SC thickness, where slight changes with more disorder states are measured for plant-derived oil treated skin (p<0.1), which could be explained by the penetration of free fatty acid fractions in the deep-located SC areas. ConclusionBoth oil types remain in the superficial layers of the SC (0–20% of the SC thickness). Skin treated with mineral- and plant-derived oils shows significantly higher disordered lateral and lamellar packing order of ICL in these layers of the SC compared to intact skin. Plant-derived oils significantly changed the ICL ordering in the depths of 30% and 70–90% of the SC thickness, which is likely due to the penetration of free fatty acids in the deeper layers of the SC.

440 Functional relationship between anti-oxidant barrier and permeability barrier of skin is mediated by stratum corneum intercellular lipid

440 Functional relationship between anti-oxidant barrier and permeability barrier of skin is mediated by stratum corneum intercellular lipid

Disrupted constitution of stratum corneum intercellular lipids contribute to barrier disruption in glycated epidermis

Disrupted constitution of stratum corneum intercellular lipids contribute to barrier disruption in glycated epidermis

Time dependence of the enhancement effect of chemical enhancers: Molecular mechanisms of enhancing kinetics

Chemical enhancers are widely used for facilitating drug penetration in transdermal drug delivery system (TDDS). However, there is a lack of knowledge about how the enhancement effect changes over time. In this study, on the basis of kinetic parameters of enhancement effect, molecular details of the dynamic enhancement process was described and a new hypothesis of the recovery mechanism of the skin barrier function was proposed. Using pretreated skin and flurbiprofen patch, the effects of Azone (AZ) and menthyl decanoate (MT-10) were evaluated with in vitro permeation experiment and further confirmed by confocal laser scanning microscopy (CLSM) and TEWL. The results showed that the enhancement ratio (ER) increased firstly, then reached a plateau and finally decreased. The enhancement effect of MT-10 was slower (Tonset, MT-10>Tonset, AZ), weaker (ERmax, MT-10<ERmax, AZ) and shorter (Teff, MT-10<Teff, AZ) than that of AZ. According to the results of CLSM, ATR-FTIR and molecular dynamic simulation, the dynamic enhancement effect was caused by the variation of the diffusion coefficient of intercellular lipid in the stratum corneum (SC), which was dependent on the affinity between enhancers and lipid. Moreover, the skin barrier function recovered although a large amount of enhancers still existed in the SC. Additionally, according to the results of ATR-FTIR, molecular docking and skin retention study, the dynamic effect of AZ on the skin protein only induced skin irritation but showed no influence on drug penetration, so did the amount of the enhancer. In conclusion, dynamic enhancement effect was caused by the dynamic effect of the enhancer on the SC intercellular lipid, and the skin barrier function recovered by accepting the enhancer as a new component of the lipid bilayer.