特应性皮炎动物模型表皮脂合成的研究

目的:探讨特应性皮炎(AD)皮肤生理改变(包括表皮水分丢失量和角质层水分含量)是否与表皮脂的代谢有关。方法:在小鼠的背部和躯干外涂2,4-二硝基氟苯(DNFB),建立小鼠特应性皮炎模型,利用14[C]乙酸对AD模型表皮脂的代谢进行研究,并用电子显微镜对AD皮肤的超微结构进行观察。结果:AD表皮的胆固醇和脂肪酸的合成速度明显低于对照组,正常对照组的角质细胞间均为正常的复层板层膜结构。而皮炎组的深层角质细胞间虽可见正常的复层板层结构,但有许多没有加工完全的膜结构存在。结论:推测AD皮肤生理的异常改变可能是由于表皮脂的合成减少和角质细胞间膜异常所致。     

The pretreatment effect of chemical skin penetration enhancers in transdermal drug delivery using iontophoresis.

The transdermal drug delivery (TDD) system has largely been divided into physical, biochemical and chemical methods. Recently, combinations of these methods were introduced for more effective delivery with less side effects. We performed this study to identify the effectiveness and mechanism of TDD using the physical method, 'iontophoresis', plus the chemical method, 'pretreatment with chemical enhancer'. The action sites of chemical enhancers in the stratum corneum (SC) were observed by electron microscope. We also studied whether this combined method synergistically impaired the skin barrier. To confirm the synergistic effect on skin penetration by this combined method, we measured the blood glucose level after insulin iontophoresis following a chemical enhancer pretreatment in rabbits. The results were that (1) dilatation of the intercellular lipid layers of the SC and lacunae was prominent in pretreatment with chemical enhancers inducing high transepidermal water loss (TEWL); (2) the skin barrier impairment, with repeated treatments showing an increased TEWL and also epidermal proliferation, was increased with the chemical enhancers that showed a high TEWL immediately after treatment; (3) the combination of chemical enhancer pretreatment and iontophoresis showed no synergistic impairment of the skin barrier, and (4) the chemical enhancer pretreatment with greater impairment of the skin barrier could increase the delivery of insulin by iontophoresis. The results showed that a combination of chemical enhancer pretreatment and iontophoresis could deliver drugs more effectively than iontophoresis alone. Our proposed theory is that iontophoretic drug delivery may be easier through the dilated intercellular spaces of the SC which have a lower electrical impedance following the chemical enhancer pretreatment. Because the effect and the side effects in the combination are decided by the chemical enhancer rather than iontophoresis, the development of proper chemical enhancers is important in future plans.     

Biophysical and morphological changes in the stratum corneum lipids induced by UVB irradiation

BACKGROUND: UV irradiation induces a variety of responses in the epidermis, including sunburn cell formation, epidermal hyperplasia, and epidermal permeability barrier disruption. OBJECTIVE: The aim of present study was to assess the effects of UVB irradiation in the intercellular lipids in murine stratum corneum. METHODS: Adult hairless mice were exposed to a single UVB dose (0.15 J/cm(2)), the Fourier transform infrared (FT-IR) spectroscopic study was performed to investigate the effect on the biophysical changes in the stratum corneum lipids, barrier function was monitored by transepidermal water loss (TEWL) measurement, and the morphological alterations of stratum corneum was examined by electron microscopy using ruthenium tetroxide postfixation. RESULTS: The FT-IR spectroscopic study revealed that there was the shift to higher wavenumbers of the symmetric and asymmetric stretching peaks near 2850 and 2920 cm(-1) respectively at days 3-4 after a single UVB irradiation, reflecting to the increase in motional freedom of lipids hydrocarbon chains, call as disordering of lipids. Moreover, A single UVB irradiation also caused a significant increase in TEWL, the increase in TEWL began after 2 days and peaked at day 4. Electron microscopic observations revealed that marked morphological abnormalities in the intercellular domains, including abnormal profile of lamellar granules and its contents at the interface between stratum corneum and stratum granulosum and the persistence of the nuclei in the stratum corneum. Moreover, the separated fragmentary lipid lamellae, excessive numbers of lamellae in stacks, both the elongated and enlarged lacuna as well as the extracellular whorls were present within the widen space of the stratum corneum. CONCLUSION: The both of biophysical and morphological changes of the stratum corneum lipids may reflect to the mechanisms of perturbation of the epidermal permeability barrier induced by UVB irradiation.     

Impaired cutaneous permeability barrier function, skin hydration, and sphingomyelinase activity in keratin 10 deficient mice

Point mutations in the suprabasal cytokeratins 1 (K1) or 10 (K10) in humans have been shown to be the cause of the congenital ichthyosis epidermolytic hyperkeratosis. Recently, a K10 deficient mouse model was established serving as a model for epidermolytic hyperkeratosis. Homozygotes suffered from severe skin fragility and died shortly after birth. Heterozygotes developed hyperkeratosis with age. To see whether phenotypic abnormalities in the mouse model were associated with changes in skin barrier function and skin water content we studied basal transepidermal water loss and capacity for barrier repair after experimental barrier disruption as well as stratum corneum hydration. Also, we determined the activities of acid and neutral sphingomyelinase key enzymes of the tumor necrosis factor and interleukin-1 signal transduction pathways generating the ceramides most important for epidermal permeability barrier homeostasis. Neonatal homozygotes showed an 8-fold increase in basal transepidermal water loss compared with wild type controls. Adult heterozygotes exhibited delayed barrier repair after experimental barrier disruption. Stratum corneum hydration was reduced in homozygous and heterozygous mice. Acid sphingomyelinase activity, which is localized in the epidermal lamellar bodies and generates ceramides for extracellular lipid lamellae in the stratum corneum permeability barrier, was reduced in homozygous as well as heterozygous animals. Neutral sphingomyelinase activity, which has a different location and generates ceramides involved in cell signaling, was increased. The reduction in acid sphingomyelinase activity may explain the recently described decreased ratio of ceramides to total lipids in K10 deficient mice. In summary, our results demonstrate the crucial role of the keratin filament for permeability barrier function and stratum corneum hydration.     

Hydration disrupts human stratum corneum ultrastructure

Using transmission and cryo-scanning electron microscopy, we confirm that extended water exposure leads to extensive disruption of stratum corneum intercellular lipid lamellae. We define the in vivo swelling behavior of the stratum corneum: exposure to water for 4 or 24 h results in a 3- or 4-fold expansion of the stratum corneum thickness, respectively. Corneocytes swell uniformly with the exception of the outermost and inner two to four corneocyte layers, which swell less. We show that hydration induces large pools of water in the intercellular space, pools that can exceed the size of water-swollen corneocytes. By 4 h of water exposure there are numerous small and large intercellular pools of water ("cisternae") present throughout the stratum corneum, and at 24 h these cisternae substantially increase in size. Within cisternae the lipid structure is disrupted by lamellar delamination ("roll-up"). Cisternae appear to be disk-shaped structures that do not obviously communicate. Cisternae appear to contain considerable lipidic and other material and to contain a substantial fluid volume that can rival the volume of the dry stratum corneum. Similar results are obtained following urine exposure. With urine exposure, cisternae communicate with salts in the external solution. This study illustrates the disruptive effect of overhydration on the stratum corneum intercellular space, identifies large and numerous unanticipated intercellular cisternal structures, defines the magnitude of stratum corneum swelling, and identifies stratum corneum cell layers that swell less. The study suggests the stratum corneum is a more chaotic structure than previously envisioned, and provides a framework for better understanding desquamation, irritancy, and percutaneous transport.     

Depletion of stratum corneum intercellular lipid lamellae and barrier function abnormalities after long-term topical corticosteroids

The intercellular lipid lamellae of the stratum corneum (SC) is believed to provide the permeability barrier of the epidermis. Previous functional studies have demonstrated an increase in the transepidermal water loss (TEWL) after long-term use of topical corticosteroids (TCS); however, direct morphological confirmation of this barrier abnormality is still lacking. The aim of this study was to determine whether any abnormality could be detected in the structure of the SC intercellular lipid lamellae in patients after long-term TCS. Atrophic skin and untreated normal skin of 10 patients after long-term TCS were examined by transmission electron microscopy using ruthenium tetroxide- fixed tissue for the multilamellar lipid sheets of SC, and oil red O stain for neutral lipids of the SC. Layers of the SC were evaluated by 0·1% methylene blue stain after alkaline expansion, and TEWL was measured by Evaporimeter EPI. The TCS-treated atrophic skin had fewer layers of horny cells, mean 9–4 layers, than the normal control skin, 18 layers (P<0·001) and increased TEWL of 21·3g/m² compared with the control skin TEWL of 6·7 g/m²(P<0·01). The mean neutral lipid content of the SC was also significantly lower (P<0·001). Moreover, ultrastructural studies revealed a marked decrease in both the numbers of intercellular lipid lamellae of SC and membrane-coating granules of stratum granulosum in the atrophic skin. These results suggest that the diminution in the SC intercellular lipid lamellae and SC cell layers play an important part in the pathogenesis of barrier dysfunction after long-term use of TCS.     

A new computer-based evaporimeter system for rapid and precise measurements of water diffusion through stratum corneum in vitro.

It is important to have reliable methods for evaluation of skin barrier function when questions such as barrier perturbing effects of different agents and occlusive effects of different formulations are to be elucidated. A wealth of clinical work relates to measurements of transepidermal water loss in vivo, a method much affected by ambient air relative humidity, temperature, skin irritation processes, psychologic status of the subject, etc., factors that cause the method to suffer from low precision (i.e., high random error). Relating to these obstacles, we have developed a closed in vitro system for measurements of water diffusion rate through pieces of isolated stratum corneum at steady-state conditions, where the relative humidity and temperature is held constant and data can be collected continuously. Our evaporimeter-based in vitro system has a more than 3-fold higher precision (lower random error) ( approximately 10%) than measurements of transepidermal water loss in vivo ( approximately 35%). The results of our study show that: (i) the corneocyte envelopes contribute to the barrier capacity of stratum corneum; (ii) removal of the lipid intercellular matrix results in approximately a 3-fold increase in the water diffusion rate through the isolated stratum corneum (n = 20; p < 0.05), not a 100-fold as has previously been suggested; (iii) exposure to sodium dodecyl sulfate in water does neither alter the water diffusion rate (n = 10; p > 0.05) nor the water holding capacity (n = 10; p > 0.05) of stratum corneum; (iv) exposure to 1 M CaCl2 in water yields an increased water diffusion rate through stratum corneum (n = 10; p < 0.05); and (v) when applied to the stratum corneum in excess concentrations, the penetration enhancer Azone has occlusive effects on water diffusion through the stratum corneum (n = 6; p < 0.05).     

Molecular models of the intercellular lipid lamellae in mammalian stratum corneum

Intercellular lipid lamellae in the stratum corneum constitute the barrier to water diffusion and may also play a role in cohesion between corneocytes. The lamellae arise from stacks of lamellar disks that are extruded from the granular cells and then fuse edge-to-edge to form sheets. It has been proposed that each lamellar disk is formed from a flattened vesicle, and therefore consists of two lipid bilayers in close apposition. In the present study, electron microscopic examination of ruthenium-tetroxide-fixed stratum corneum from mouse, pig, and human skin revealed that the double bilayer pattern persists in the intercellular lamellae. In addition, distinctive patterning of the intercellular lamellae has led us to propose novel molecular arrangements of the intercellular lipids. These include interlamellar sharing of lipid chains to produce lipid monolayers between pairs of bilayers. The pattern reflects the provenance of the intercellular lamellae from lamellar granule disks and the nonrandom orientation of the lamellar lipids.     

Comparative ultrastructure and cytochemistry of epidermal responses to tape stripping, ethanol and vitamin A acid in hairless mice.

The responses of hairless mouse epidermis to tape stripping, ethanol and vitamin A acid were compared using electron microscopy and cytochemistry. Stripping the skin 4 times with cellophane tape removed most of the stratum corneum and caused the development of enlarged intercellular spaces and dense intramitochondrial inclusions. These changes began within an hour, reached a maximum by 24 hr, and subsided by about 4 days. There was also some accumulation of glycogen and the development of occasional basal lamina breaks and a few intracellular lipid droplets by 24 hr. Topically applied ethanol (95%) produced a similar response, though less damaging. In addition, ethanol induced the formation of numerous lipid droplets in the cytoplasm of keratinocytes by 24 hr and often caused sloughing of the stratum corneum. Vitamin A acid (3%) was dissolved in propylene glycol for application to the skin. We found the application of propylene glycol alone to produce no epidermal changes. Vitamin A acid produced mild damaging effects with small intercellular spaces and intramitochondrial inclusions, but no lipid droplets or glycogen were detected. Vitamin A acid also caused dramatic inhibition of keratinization by 24 hr. Intramitochondrial inclusions were digested by protease, indicating a protein component and they also stained with silver methenamine, indicating the presence of glycogen or glycoprotein.     

Stratum corneum lipid morphology and transepidermal water loss in normal skin and surfactant-induced scaly skin

Stratum corneum lipid morphology was evaluated using attenuated total reflectance infrared spectroscopy (ATR-IR) in normal skin and surfactant-induced scaly skin to evaluate skin barrier function. To evaluate the degree of order of the intercellular lipid alkyl chain conformation, we measured the wavenumbers (frequency shifts) of the symmetrical and asymmetrical C-H stretching vibrations observed at approximately 2850 cm^–1 and 2920 cm^–1, respectively. There was a correlation between the wave-number and transepidermal water loss in normal skin. However, no difference was observed in surfactant-induced scaly skin from the baseline value in the wavenumbers of the C-H vibrations. These results suggest that in normal skin, lipid morphology plays an important role in the barrier function of the stratum corneum. However, the decline in barrier function in scaly skin is not due to conformational disorder of the lipid alkyl chain.     

Electrical impedance and other physical parameters as related to lipid content of human stratum corneum

Background/aims: In previous studies we have shown that variations in the properties of the stratum corneum are reflected by alterations in electrical impedance. The aim of this study was to explore the ability of the electrical impedance technique to detect changes in the lipid content of the stratum corneum, and to compare It with the other non-invasive methods, measurement of transepidermal water loss and of skin moisture. Methods: Twenty-two healthy test subjects were recruited. Transepidermal water loss was measured at standard sites on the forearms and wrists, followed by skin moisture estimation by electrical capacitance, and finally by the recording of electrical impedance spectra in the frequency range 1 kHz to 1 MHz. Readings by all three methods were taken before the start of each series of test procedures, as well as after cyclohexane swabbing, a skin stripping procedure and lipid extraction, and also during the recovery process. A mixture of hexane:isopro-panol was used for lipid extraction of the skin, and the extracts were evaluated using HPLC/LSD and GC/MS/FID analysis. Biopsy samples for light and electron microscopy were obtained after lipid extraction. Results: Electrical impedance results showed greater changes after lipid extraction than either transepidermal water loss or skin moisture content. Baseline values varied from the cubital fossa to the wrist, both for the non-invasive methods and for lipid composition. Conclusions: The electrial impedance is dependent on the lipid content of the stratum corneum, as studied by lipid extraction experiments.     

Omega-hydroxyceramides are required for corneocyte lipid envelope (CLE) formation and normal epidermal permeability barrier function

Omega-hydroxyceramides (omega-OHCer) are the predominant lipid species of the corneocyte lipid envelope in the epidermis. Moreover, their omega-esterified-derivatives (acylCer) are major components of the stratum corneum extracellular lamellae, which regulate cutaneous permeability barrier function. Because epidermal omega-OHCer appear to be generated by a cytochrome P450-dependent process, we determined the effects of a mechanism-based inhibitor of omega-hydroxylation, aminobenzotriazole (ABT), on epidermal omega-OH Cer formation and barrier function. We first ascertained that ABT, but not hydroxybenzotriazole (OHBT), a chemical relative with no P450 inhibitory activity, inhibited the incorporation of [14C]-acetate into the omega-OH-containing Cer species in cultured human keratinocytes (68.1% +/- 6.9% inhibition versus vehicle-treated controls; p < 0.001), without altering the synthesis of other Cer and fatty acid species. In addition, ABT significantly inhibited the omega-hydroxylation of very long-chain fatty acids in cultured human keratinocytes. Topical application of ABT, but not OHBT, when applied to the skin of hairless mice following acute barrier disruption by tape-stripping, resulted in a significant delay in barrier recovery (e.g., 38.3% delay at 6 h versus vehicle-treated animals), assessed as increased transepidermal water loss. The ABT-induced barrier abnormality was associated with: (i) a significant decrease in the quantities of omega-OHCer in both the unbound and the covalently bound Cer pools; (ii) marked alterations of lamellar body structure and contents; and (iii) abnormal stratum corneum extracellular lamellar membrane structures, with no signs of cellular toxicity. Furthermore, pyridine-extraction of ABT- versus vehicle-treated skin, which removes all of the extracellular lamellae, leaving the covalently attached lipids, showed numerous foci with absent corneocyte lipid envelope in ABT- versus vehicle-treated stratum corneum. These results provide the first direct evidence for the importance of omega-OHCer for epidermal permeability function, and suggest further that acylCer and/or corneocyte lipid envelope are required elements in permeability barrier homeostasis.     

Aberrant lipid organization in stratum corneum of patients with atopic dermatitis and lamellar ichthyosis

There are several skin diseases in which the lipid composition in the intercellular matrix of the stratum corneum is different from that of healthy human skin. It has been shown that patients suffering from atopic dermatitis have a reduced ceramide content in the stratum corneum, whereas in the stratum corneum of lamellar ichthyosis patients, the amount of free fatty acids is decreased and the ceramide profile is altered. Both patient groups also show elevated levels of transepidermal water loss indicative of an impaired barrier function. As ceramides and free fatty acids are essential for a proper barrier function, we hypothesized that changes in the composition of these lipids would be reflected in the lipid organization in stratum corneum of atopic dermatitis and lamellar ichthyosis patients. We investigated the lateral lipid packing using electron diffraction and the lamellar organization using freeze fracture electron microscopy. In atopic dermatitis stratum corneum, we found that, in comparison with healthy stratum corneum, the presence of the hexagonal lattice (gel phase) is increased with respect to the orthorhombic packing (crystalline phase). In lamellar ichthyosis stratum corneum, the hexagonal packing was predominantly present, whereas the orthorhombic packing was observed only occasionally. This is in good agreement with studies on stratum corneum lipid models that show that the presence of long-chain free fatty acids is involved in the formation of the orthorhombic packing. The results of this study also suggest that the ceramide composition is important for the lateral lipid packing. Finally, using freeze fracture electron microscopy, changes in the lamellar organization in stratum corneum of both patient groups could be observed.     

Iontophoresis of nickel elicits a delayed cutaneous response in sensitized individuals that is similar to an allergic patch test reaction

Wearing of patch test chambers for 1-2 days is uncomfortable for patients. Allergen application by iontophoresis avoids this, but it is unknown so far whether iontophoresis itself interferes with the delayed immune response. We compared the effects occurring 48 h after iontophoresis with distilled water, 0.9% NaCl, and 0.01 M NiSO4 in normal volunteers and in nickel-sensitized patients (total n=36). Visual assessment was performed and transepidermal water loss (TEWL), stratum corneum hydration, cutaneous blood flow, and immunohistopathology were determined. After iontophoresis with nickel sulfate, only individuals sensitized to nickel reacted with a positive clinical response, increase in cutaneous blood flow, decline in epidermal CD-1a-positive cells, increase in epidermal proliferation (Ki-67-positive cells), pronounced infiltration of cells positive for CD4, CD11, or CLA, and cellular activation (expression of ICAM1, HLA-DR). Iontophoresis with distilled water or saline did not result in such reactions in volunteers with or without nickel sensitization, and the latter also tolerated nickel iontophoresis without significant skin reactions. We conclude that the delayed cutaneous response to nickel induced via iontophoresis is specific and similar to a positive patch test reaction. Iontophoresis may therefore be considered as an alternative to patch testing.     

Mode of action of glycolic acid on human stratum corneum: ultrastructural and functional evaluation of the epidermal barrier

Alpha-hydroxy acids (AHA) such as glycolic acid have recently been used extensively in cosmetic and dermatological formulas. In low concentration (2– 5%) glycolic acid is believed to facilitate progressive weakening of cohesion of the intercellular material of the stratum corneum (SC), resulting in uniform exfoliation of its outermost layers (the stratum disjunctum). Since thinning of the SC as well as changes of intercellular lipids could theoretically compromise the barrier functions of the skin, we investigated the mode of AHA action on the SC to determine whether enhanced desquamation compromises the barrier structures of the SC and changes transepidermal water loss (TEWL) values. Electron microscopy of the epidermis biopsied from the volar forearm of human volunteers after 3 weeks of treatment with a 4% glycolic acid formulation twice daily was employed to evaluate 1) epidermal morphology and thickness of the SC, (2) the lamellar body and SC lipid bilayer organization, and (3) desquamative events based on degradation of desmosomes. TEWL values and SC hydration were recorded prior to and at the end of the study. Electron microscopy revealed no ultrastructural changes in the nucleated layers of the epidermis. The lamellar body (LB) secretory system in the stratum granulosum (SG), and intercellular lipid lamellae in the SC in both vehicle- and glycolic acid-treated samples were comparable to normal human SC. Within the SC, enhanced desmosomal breakdown, promoting loss of cohesion and desquamation, was restricted to the stratum disjunctum while desmosomes of the stratum compactum were unaffected. Treated areas displayed histologically, a more compact appearing SC. TEWL values remained unchanged in glycolic acid- and vehicle-treated skin. Our findings indicate that the barrier structures of the SC are not disrupted by glycolic acid formulations at the concentration used. One of the mechanism of action of AHA on the SC seemed to be a „targeted“ desmosomal (corneosomal) action without compromising the barrier structures of the skin. Received: 20 November 1996     

Influence of the stratum corneum on transepidermal water loss and Bioavailability of a new topical steroid, difluprednate: clinical implications (author's transl)]

Comparative study of experimental and theoretical curves obtained by plotting transepidermal water loss against stratum corneum thickness in man, shows that every layer in the stratum corneum acts as part of the epidermal barrier to water loss. Another function of the stratum corneum is to decrease the cutaneous penetration of topical corticosteroids like difluprednate and to modify their bioavailability ('corticosteroid reservoir'). Our data suggest that variations in stratum corneum thickness between subjects explain variation of transepidermal water loss and sensitivity difluprednate, as there is a close relationship between these two parameters. It is then conceivable than the phototype has clinical implications is there really exists a relationship between phototype, stratum corneum thickness and sensitivity to steroids.     

Abrupt decreases in environmental humidity induce abnormalities in permeability barrier homeostasis

Previous reports demonstrated that long-term exposure to extremes in humidity influence permeability barrier homeostasis. Here the effects of a sudden shift from a high humidity to a dry environment were studied. Mice were initially maintained in either a humid (> 80% relative humidity) or normal environment (relative humidity = 40-70%), and then transferred to a dry environment (< 10% relative humidity). Within 2 d of transfer from a humid to a dry environment a 6-7-fold increase in transepidermal water loss occurred that returned to normal within 7 d. No increase in transepidermal water loss occurred in response to a switch from a normal to a dry environment. At a time when barrier function was abnormal, both stratum corneum hydration and pH were normal, indicating that the mechanisms that regulate these functions differ. Following transfer from a humid to dry environment, electron microscopy revealed a marked decrease in: (i) lamellar bodies in the outermost stratum granulosum; (ii) deposition of lamellar body contents at the stratum granulosum-stratum corneum interface; and (iii) the quantity of intercellular lamellae in the stratum corneum, which together could account for the barrier abnormality. Transfer of mice from a normal to a dry environment rapidly stimulated epidermal proliferation, whereas animals switched from a humid to a dry environment displayed a delayed increase in proliferation that might also contribute to the barrier abnormality. The present study demonstrates that sudden changes from a high to a low humidity environment results in abnormal barrier function, which could adversely influence the incidence and/or severity of skin disorders.     

Permeability Barrier Abnormality of Hairless Mouse Epidermis after Topical Corticosteroid: Characterization of Stratum Corneum Lipids by Ruthenium Tetroxide Staining and High-Performance Thin-Layer Chromatography

Topical corticosteroids (TCS) are among the most frequently used topical therapeutics. Recently, it has been shown that TCS not only has antiproliferative actions, but also inhibits the differentiation of the epidermis and finally perturbates stratum corneum (SC) barrier function. It is well established that epidermal barrier function resides within the intercellular lipids of the SC. However, to date, little is known about the effects of TCS on the structure and composition of SC lipids. We therefore used hairless mouse skin to study the sequential changes of the SC permeability barrier and their intercellular lipids by ruthenium tetroxide staining and high-performance thin-layer chromatography (HPTLC) during topical use of corticosteroids. The results demonstrated a progressive increase in transepidermal water loss accompanied by a diminution in the SC intercellular lipid lamellae, which showed a normal structure of individual lamella. Analysis of lipid composition by HPTLC after a 6-week application of TCS also showed an obvious decrease in all the main components of SC lipids, which are known to constitute the permeability barrier of the skin. In light of these results, our work provides direct morphological evidence that TCS deteriorates the permeability barrier of epidermis when applied to normal skin.     

Importance of intercellular lipids in water-retention properties of the stratum corneum: induction and recovery study of surfactant dry skin

Summary In order to further clarify the role of intercellular lipids in the water-retention properties of the stratum corneum, forearm skin of six healthy male volunteers was treated with 5% sodium dodecyl sulfate (SDS) for 1, 10, and 30 min. All treatment periods induced chapping and scaling of the stratum corneum without any inflammatory reaction, accompanied by a significant decrease in its water-retention function. Electron-microscopic analysis of SDS-treated stratum corneum revealed selective depletion of the lipids from the intercellular spaces, accompanied by marked disruption of multiple lamellae structures. Lipid analysis also showed a considerable and selective loss of intercellular lipids such as cholesterol, cholesterol ester, free fatty acid, and sphingolipids. To evaluate the recovery potential for intercellular lipids, lipids which were separated as sebaceous-rich lipids (SLs) and stratum corneum lipids (SCLs) wer applied daily on SDS-treated forearm skin. Two daily applications of the SCLs which were emulsified at 10% concentration in W/O (water in oil) cream caused a significant increase in conductance, accompanied by a definite improvement in the level of scaling over no application or W/O emulsion base only, whereas SLs in the W/O emulsion base led to no significant recovery in either conductance value or scaling. When two daily topical applications of four chromatographically separated lipid fractions (cholesterol ester, free fatty acid, cholesterol, and sphingolipid) from the SCL were carried out at 1% concentration in the same system, the cholesterol ester and sphingolipid fractions were found to induce a significant increase in the conductance value over no application. In contrast, the free fatty acid and cholesterol fractions showed no significant increase in conductance value. Similarly, the scaling which occurred after SDS treatment had a tendency to decrease after the two daily applications with the fractions of cholesterol ester, sphingolipids, and free fatty acid as compared with that of the base emulsion. These findings strongly suggest that sphingolipids, possibly in combination with other neutral lipids, play an essential role in the establishment or maintenance of water-retention capacity in the stratum corneum.