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PubMed1978

Benzocaine diffusion from polyethylene glycol through human stratum corneum.

The diffusion, penetration, and surface effects of benzocaine incorporated in various polyethylene glycol ointment bases through human stratum corneum were studied. Benzocaine diffusion was measured by following the benzocaine concentration in the receiving compartment of a diffusion cell. The ointment was placed in the other cell compartment and was separated from the receiving compartment by sheets of human stratum corneum. Surface effects were monitored by scanning electron micrographs of the stratum corneum. Results showed a decrease in drug diffusion in the presence of relatively high amounts of the lower molecular weight portions of polyethylene glycol. Scanning electron microscope studies showed that both benzocaine and polyethylene glycol affect the surface structure of the stratum corneum. Thermal analysis indicated that benzocaine dissolves in polyethylene glycol.

Adult↗
PubMed2002

Photomechanical delivery of 100-nm microspheres through the stratum corneum: implications for transdermal drug delivery.

BACKGROUND AND OBJECTIVES: Photomechanical waves (PWs) render the stratum corneum permeable and allow molecules to diffuse into the epidermis. The aim of this study was to investigate the probe size that could be delivered through the stratum corneum and into the epidermis. STUDY DESIGN/MATERIALS AND METHODS: A single PW was applied onto the rat skin in vivo. Aqueous suspensions of fluorescent microspheres, 100 nm in diameter, were used as probes for transdermal delivery. The presence of the microspheres in the epidermis was measured by a fiber-based spectrofluorimeter after the stratum corneum was removed by tape-stripping (TS). RESULTS: Exposure of the rat skin to a PW permeabilized the stratum corneum and allowed the fluorescent microspheres to diffuse into the epidermis. CONCLUSIONS: The experiments show that PWs can facilitate the delivery of very large molecules and probes into the epidermis.

Administration, Cutaneous↗
PubMed1990

In vivo percutaneous absorption: a key role for stratum corneum/vehicle partitioning.

Percutaneous absorption of five compounds was studied in the hairless rat in vivo: benzoic acid, caffeine, hydrocortisone, inulin and thiourea. The results clearly demonstrate that, as with in vitro experiments, a steady-state flux can be achieved in vivo. This steady-state flux is strongly molecule dependent. Thus, the values for inulin and benzoic acid differ by a factor of about 40. In contrast, although the physicochemical properties of the studied compounds vary widely, their lag times were not significantly different. The mean lag time was 11 +/- 2 min. Different compounds could be considered to have approximately the same apparent diffusion coefficient with regard to their percutaneous absorption in vivo. Thus, for a given thickness of stratum corneum and a given anatomical site, the penetration flux value of a substance depends only on its stratum corneum/vehicle partition coefficient. Using a classical model, we have demonstrated that the amount of substance present in the stratum corneum (Qsc) at equilibrium (30 min) is related to this partition coefficient. There is also a linear relationship between steady-state flux and Qsc. In practice, the in vivo steady-state flux of penetration of a compound can be predicted from the simple measurement of the amount present in the stratum corneum after a contact time of 30 min.

Animals↗
PubMed1995

The effect of glycerol and humidity on desmosome degradation in stratum corneum.

Moisturizers are known to have occlusive, emollient and humectant properties, all of which help to alleviate the symptoms of skin xerosis. Although the biological mode of action of moisturizers is poorly understood, the recent observation that skin xerosis is associated with incomplete desmosome digestion suggests that moisturizers improve the desquamation process in such conditions. To examine the possibility that certain moisturizers act by facilitating desmosomal digestion, we investigated the ability of glycerol, a common humectant, to influence this process in stratum corneum in vitro. Examining desmosome morphology in isolated stratum corneum by electron microscopy, it was observed that the desmosomes were in more advanced stages of degradation in glycerol-treated tissue compared with control tissue. This enhanced desmosomal degradation in glycerol-treated tissue was confirmed by significant decreases in the levels of immunoreactive desmoglein 1, a marker of desmosome integrity. Desmosomal degradation was also shown to be a humidity-dependent event, being significantly reduced at low relative humidity. The effect of glycerol on desmosome digestion was emphasized further in two in vitro model systems. Firstly, glycerol increased the rate of corneocyte loss from the superficial surface of human skin biopsies in a simple desquamation assay. Secondly, measurement of the mechanical strength of sheets of stratum corneum, using an extensiometer, indicated a dramatic reduction in the intercorneocyte forces following glycerol treatment. These studies demonstrated the ability of glycerol to facilitate desmosome digestion in vitro. Extrapolating from these results, we believe that one of the major actions of moisturizers in vivo is to aid the digestion of desmosomes which are abnormally retained in the superficial layers of xerotic stratum corneum.

Cytoskeletal Proteins↗
PubMed1993

In vivo differences between Asian, black and white in the stratum corneum barrier function.

The stratum corneum barrier function of Blacks, Caucasians and Asians were compared in vivo. A noninvasive technic, laser doppler velocimetry (LDV), was used to evaluate the cutaneous penetration of nicotinates by the determination of the lag time before vasodilatation induced by the application of those local vasodilator drugs. The study was performed on untreated skin and after removal of the stratum corneum by 12 strips. The influence of molecular weight and solubility of different nicotinates (methyl, ethyl, hexyl and vitamin E) were also studied on Japanese skin. Vasodilatation lag times assessed by LDV, with methyl nicotinate (MN), showed that skin permeability was more important in Asians (P < 0.01) and in Caucasians (P < 0.05) than in Blacks. Moreover Asian skin was significantly more sensitive to stripping (P < 0.05) than Black skin. A significant shorter lag time was obtained with small and hydrophilic nicotinates (methyl and ethyl) (P < 0.01) compared to a lipophilic one (hexyl). The alteration of the stratum corneum barrier function by stripping showed a more important modification with MN (P < 0.05) than with hexyl nicotinate. Consequently, this noninvasive method can evaluate the modifications of the stratum corneum barrier function and racial origin has to be taken into account in the determination of skin absorption.

Adult↗
PubMed1983

Non identity of non ionic detergent soluble (NIDS) protein and stratum corneum autoantigens.

The relationship between naturally occurring circulating stratum corneum autoantibodies and experimentally produced antibodies to a non ionic detergent soluble (NIDS) protein fraction from human stratum corneum has been investigated. Using indirect immunofluorescence and indirect haemagglutination techniques, anti NIDS protein serum was shown not to inhibit the autoantibody-antigen reaction. Furthermore no direct interaction could be demonstrated between sheep red blood cells coated with stratum corneum autoantigen and anti NIDS protein serum. The NIDS protein antigens therefore represent a separate and distinct class of stratum corneum antigens.

Antibodies↗
PubMed1989

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

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) were 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

A noninvasive, in vivo technique to quantitatively measure water concentration of the stratum corneum using attenuated total-reflectance infrared spectroscopy.

In order to noninvasively measure water concentration in the stratum corneum, infrared spectra were obtained using an attenuated total-reflectance technique in conjunction with Fourier transform spectroscopy. A weak water-absorbance band near 2,100 cm-1 was detected in both in vivo and in vitro spectra. The significance of this band is that it occurs in a region of the mid-infrared where the stratum corneum and most topically applied substances show no absorbance. In vitro spectra obtained as a function of ambient relative humidity showed an increase in the absorbance near 2,100 cm-1 with increasing water concentration in the stratum corneum. The combined in vivo and in vitro results lead to a quantitative assessment of water concentration in the uppermost layers of the stratum corneum.

Animals↗
PubMed1991

Stratum corneum lipid abnormalities in atopic dermatitis.

Patients with atopic dermatitis (AD) often present with a dry skin. To clarify the relationship between dry skin and lipid abnormalities within stratum corneum, stratum corneum lipids were collected from six AD patients aged 15 to 25 years and from sex- and age-matched controls. All major stratum corneum lipid classes were separated and quantitated by high-performance thin-layer chromatography/photodensitometry. Six ceramide fractions were also isolated and quantitated by thin-layer chromatography/photodensitometry. Esterified fatty acids of both ceramide 1 (acylceramides) and wax esters were analysed by capillary gas chromatography. The relative amounts of all the stratum corneum lipid classes including squalene, cholesterol esters, wax esters, triglycerides, free fatty acids, cholesterol, ceramides, cholesterol sulphate and phospholipids did not differ statistically between AD patients and controls. However, a significant decrease in proportion of ceramide 1, which is believed to be a carrier of linoleate responsible for a water-barrier function, and increased levels of esterified C18:1 fatty acids (oleate) of ceramide 1 were observed in AD patients. On the other hand, the fatty acid compositions as well as the proportions of C16:1 straight-chain component in sebum wax esters of AD patients were very similar to those of controls. These results suggest that a significantly reduced amount and/or structural alterations of ceramide 1 deriving from epidermal keratinocytes may be responsible for the impaired water-barrier function of the skin in AD.

Adolescent↗
PubMed1996

Stratum corneum lipids: the effect of ageing and the seasons.

Stratum corneum lipids play a predominant role in maintaining the water barrier of the skin. In order to understand the biological variation in the levels and composition of ceramides, ceramide 1 subtypes, cholesterol and fatty acids, stratum corneum lipids collected from tape strippings from three body sites (face, hand, leg) of female Caucasians of different age groups were analysed. In addition, we studied the influence of seasonal variation on the lipid composition of stratum corneum from the same body sites. The main lipid species were quantified using high-performance thin-layer chromatography and individual fatty acids using gas chromatography. Our findings demonstrated significantly decreased levels of all major lipid species, in particular ceramides, with increasing age. Similarly, the stratum corneum lipid levels of all the body sites examined were dramatically depleted in winter compared with spring and summer. The relative levels of ceramide 1 linoleate were also depleted in winter and in aged skin whereas ceramide 1 oleate levels increased. The other fatty acid levels remained fairly constant with both season and age, apart from lignoceric and heptadecanoic acid which showed a decrease in winter compared with summer. The decrease in the mass levels of intercellular lipids and the altered ratios of fatty acids esterified to ceramide 1, are likely to contribute to the increased susceptibility of aged skin to perturbation of barrier function and xerosis, particularly during the winter months.

Adult↗
PubMed1997

Urocanic acid isomers: relation to body site, pigmentation, stratum corneum thickness and photosensitivity.

Urocanic acid (UCA), present in the stratum corneum as trans-UCA, absorbs ultraviolet (UV) radiation and isomerizes to cis-UCA. Cis-UCA has been demonstrated to initiate suppression of selected immune responses in several experimental systems. Topical application of UCA-containing products reduces UV-induced erythema, but a role for endogenous UCA in photoprotection has not been reported. In this study the relationship between UCA isomers, pigmentation, minimal erythema dose (MED), and stratum corneum thickness was investigated. Pigmentation, concentration of total UCA, and the percentage present as the cis-isomer was measured in 36 healthy subjects, skin type I-IV, at six UV-exposed and nonexposed body sites: forehead, chest, back, outer upper arm, inner upper arm, and buttock. The MED was determined by phototesting on buttock skin, and a punch biopsy for measurement of stratum corneum thickness was taken adjacent to the site of the phototest. The percentage of cis-UCA was significantly higher in UV-exposed than on nonexposed areas. A small intraindividual variation in total UCA was found, being high on the buttock and the arm, lowest on the forehead. The subject to subject variation of total UCA was considerable at all body sites. No correlation was found between total UCA and MED, skin type, pigmentation, or stratum corneum thickness.

Adolescent↗
PubMed1997

Stratum corneum swelling. Biophysical and computer assisted quantitative assessments.

The aim of this study was to characterize the swelling behaviour of the stratum corneum. Stratum corneum pieces isolated from the breast region of 20 different females were incubated in distilled water at two different temperatures (20 degrees C and 45 degrees C) for 90 min and 24 h, respectively. Half of the stratum corneum pieces were previously extracted with chloroform-methanol (2:1). The area-enlargement was photographically recorded. The thickness enlargement was determined using a confocal laser scanning microscope. The average swelling (99% confidence interval) in the area dimension at 20 degrees C was 8.4% +/- 1.4% (n = 20), which corresponded to an average swelling in the length (lateral) dimension of approximately 4.1%. The swelling in the thickness dimension was 26.3% +/- 16.3% (n = 8). The swelling was most pronounced in the thickness dimension and was complete after 90 min of water immersion (P < 0.01, n = 5). In addition, the removal of the intercellular lipids with chloroform/methanol (2:1) induced a decreased swelling in the samples (P < 0.01, n = 20). An increase in temperature of the water from 20 degrees C to 45 degrees C resulted in an increase in swelling (P < 0.01, n = 20). Taken together our results support the idea that the mechanism of stratum corneum swelling is linked to the intercellular lipid structure and hence to skin barrier function.

Adolescent↗
PubMed1997

Tape stripping of human stratum corneum yields cell layers that originate from various depths because of furrows in the skin.

Tape stripping of human stratum corneum is widely used as a method for studying the kinetics and penetration depth of drugs. Several factors can influence the quantity of stratum corneum that is removed by a piece of tape, such as the manner of tape stripping, the hydration of the skin, cohesion between cells, body site and interindividual differences. However, few data are available about the influence of furrows in the human epidermis on the tape-stripping technique. In this study, we investigated the efficacy of tape stripping in removing complete cell layers from the superficial part of the human stratum corneum. A histological section of skin that was tape-stripped 20 times clearly showed nonstripped skin in the furrows, indicating persistent incomplete tape stripping. Replicas of tape-stripped skin surface demonstrated that even after removing 40 tape strips the furrows were still present. We validated the tape-stripping method further with X-ray microanalysis in the mapping mode by scanning electron microscopy, using a TiO2-containing compound as a marker. TiO2 applied to the skin before the tape-stripping procedures was still present after the tenth tape strip, and was specifically located on the rims of the furrows. We emphasize that results from studies using the tape-stripping method have to be viewed from the perspective that cells on one tape strip of the stratum corneum may be derived from different layers, depending on the position of the tape strip in relation to the slope of the furrow, and such results should be interpreted with considerable caution.

Adhesives↗
PubMed1998

A new HPLC-based method for the quantitative analysis of inner stratum corneum lipids with special reference to the free fatty acid fraction.

The inner stratum corneum is likely to represent the location of the intact skin barrier, unperturbed by degradation processes. In our studies of the physical skin barrier a new high-performance liquid chromatography (HPLC)-based method was developed for the quantitative analysis of lipids of the inner stratum corneum. All main lipid classes were separated and quantitated by HPLC/light scattering detection (LSD) and the free fatty acid fraction was further analysed by gas-liquid chromatography (GLC). Mass spectrometry (MS) was used for peak identification and flame ionization detection (FID) for quantitation. Special attention was paid to the free fatty acid fraction since unsaturated free fatty acids may exert a key function in the regulation of the skin barrier properties by shifting the physical equilibrium of the multilamellar lipid bilayer system towards a noncrystalline state. Our results indicated that the endogenous free fatty acid fraction of the stratum corneum barrier lipids in essence exclusively consisted of saturated long-chain free fatty acids. This fraction was characterized as a very stable population (low interindividual peak variation) dominated by saturated lignoceric acid (C24:0, 39 molar%) and hexacosanoic acid (C26:0, 23 molar%). In addition, trace amounts of very long-chain (C32-C36) saturated and monounsaturated free fatty acids were detected in human forearm inner stratum corneum. Our analysis method gives highly accurate and precise quantitative information on the relative composition of all major lipid species present in the skin barrier. Such data will eventually permit skin barrier model systems to be created which will allow a more detailed analysis of the physical nature of the human skin barrier.

2-Propanol↗
PubMed1991

Deuterium NMR investigation of polymorphism in stratum corneum lipids.

The intercellular lipid lamellae of stratum corneum constitute the major barrier to percutaneous penetration. Deuterium magnetic resonance and freeze-fracture electron microscopic investigation of hydrated lipid mixtures consisting of ceramides, cholesterol, palmitic acid and cholesteryl sulfate and approximating the stratum corneum intercellular lipid composition, revealed thermally induced polymorphism. The transition temperature of bilayer to hexagonal transition decreased as the ratio of cholesterol to ceramides in these mixtures was lowered. Lipid mixtures in which the stratum corneum ceramides were replaced by synthetic dipalmitoylphosphatidylcholine did not show any polymorphism throughout the temperature range used in the present study. The ability of the ceramide-containing samples to form hexagonal structures establishes a plausible mechanism for the assembly of the stratum corneum intercellular lamellae during the final stages of epidermal differentiation. Also, the bilayer to hexagonal phase transition of these nonpolar lipid mixtures could be used to enhance the penetration of drugs through skin.

Animals↗
PubMed1992

Ethanol effects on the stratum corneum lipid phase behavior.

The stratum corneum is considered to be the diffusional barrier of mammalian skin for water and most solutes. The intercellular lipid multilayer domains of the stratum corneum are believed to be the diffusional pathway for most lipophilic solutes. Fluidization of the lipid multilayers in the presence of ethanol is frequently conceived to result in enhanced permeation. Current investigations address the effect of ethanol on the phase behavior in terms of stratum corneum lipid alkyl chain packing, mobility and conformational order as measured by Fourier transform infrared (FTIR) spectroscopy. Phospholipid multilamellar vesicles were also studied as model systems. There appeared to be no effect of ethanol on either the solid-solid phase transition or the gel phase interchain coupling of the stratum corneum lipids. However, there was a reduction in the mobility of the alkyl chains in the presence of ethanol. Possible mechanistic relationships between the current FTIR spectroscopic results with available literature data of ethanol induced lipophilic solute penetration enhancement through the skin are discussed.

Animals↗
PubMed1987

Covalently bound omega-hydroxyacylsphingosine in the stratum corneum.

Pig epidermis was heat separated, and the stratum corneum was isolated after trypsinization. Exhaustive extraction of the stratum corneum fraction with chloroform/methanol mixtures yielded 14.7% lipid on a dry weight basis. After mild saponification of the extracted residue, additional lipid could be extracted which accounted for 2.1% of the stratum corneum weight. This bound lipid proved to consist mainly (91.9%) of N-(omega-hydroxyacyl)sphingosines in which the amide-linked omega-hydroxyacids were 28 to 34 carbon atoms in length. The release of this lipid by mild alkaline hydrolysis indicates that it is bound through an ester linkage. Half of the hydroxyceramide molecules reacted in situ with acidic acetone, suggesting that half of these molecules are attached to the stratum corneum through the omega-hydroxyl function, while the other half may be linked through one of the hydroxyl groups of the sphingosine.

Animals↗
PubMed1977

Purification and characterization of a basic protein from the stratum corneum of mammalian epidermis.

A basic protein has been isolated and purified from the stratum corneum of newborn rat epidermis. This protein is referred to as stratum corneum basic protein. It was purified by ion-exchange chromatography on DE-52 and CM-52 cellulose. The protein has a molecular weight of 50 000 on sodium dodecyl sulfate-polyacrylamide gels. It is composed of one polypeptide chain and contains no detectable carbohydrate. The protein has an isoelectric point in the range of pH 9-10, but decomposes during isoelectric focusing giving rise to a polypeptide of less than 10 000 daltons. Amino acid analysis reveals high quantities of glutamic acid, glycine, serine, arginine and relatively high levels of histidine, with these five amino acids composing 74% of the total residues. The amino acid analysis is very similar to histidine-containing keratohyalin proteins isolated from the granular layer of epidermis by several investigators. The stratum corneum basic protein differs from fibrous proteins isolated from the same cell layer with respect to net charge, amino acid composition, and molecular weight. The protein does not react with antibody to the fibrous protein. The basic protein has properties which are consistent with its possible function as a stratum corneum interfilamentous matrix protein.

Amino Acids↗