Pseudo-acylceramide with linoleic acid produces selective recovery of diminished cutaneous barrier function in essential fatty acid-deficient rats and has an inhibitory effect on epidermal hyperplasia

Horse-Derived Ceramide Accentuates Glucosylceramide Synthase and Ceramide Synthase 3 by Activating PPARβ/δ and/or PPARγ to Stimulate Ceramide Synthesis

Horse-derived ceramide (HC), which contains galactosylceramides as its main component, significantly improves skin symptoms when applied topically to patients with atopic dermatitis. We speculated that efficacy resulted from the amelioration of epidermal ceramide metabolism, and we characterized those effects using reconstructed human epidermal equivalents. Lipid analysis, RT-PCR and Western blotting revealed that HC significantly increased the total ceramide content of the stratum corneum (SC), accompanied by significantly increased gene and/or protein expression levels of ceramide synthase (CERS) 3, fatty acid elongase (ELOVL) 4, glucosylceramide synthase (GCS), β-glucocerebrosidase, sphingomyelin synthase and acid sphingomyelinase. Mechanistic analyses using cultures of primary human keratinocytes revealed the marked stimulatory effects of HC on the mRNA expression levels of CERS3, ELOVL4 and GCS under high calcium-derived differentiation conditions. Signaling analyses demonstrated that an antagonist of PPARβ/δ significantly abrogated the HC-stimulated mRNA expression levels of GCS, CERS3 and ELOVL4. GW9662, an antagonist of PPARγ, significantly abolished the HC-up-regulated mRNA expression levels of GCS and ELOVL4, but not of CERS3. These findings suggest that HC has the distinct potential to accentuate the expression of GCS, CERS3 and ELOVL4 via the activation of PPARβ/δ and/or PPARγ to accelerate ceramide synthesis in the SC.

A Nano-Emulsion Containing Ceramide-like Lipo-Amino Acid Cholesteryl Derivatives Improves Skin Symptoms in Patients with Atopic Dermatitis by Ameliorating the Water-Holding Function

Because ceramide-like lipo-amino acid cholesteryl derivatives can exert a bound water-holding function due to their lamellae-forming properties, in this study, we determined if topical application of those derivatives to atopic dry skin would elicit an ameliorative effect on skin symptoms, at least on its water-holding function. In this clinical study, daily treatment with a nano-emulsion containing 10% phytosteryl/octyldodecyl lauroyl glutamate (POLG) significantly (p < 0.0001) improved skin symptoms, including dryness/scaling, itchiness and stimulus sensations, in the non-lesional skin of patients with atopic dermatitis (AD) at 3 and at 6 weeks compared with week 0. Those significant improvements in skin symptoms were accompanied by a significantly enhanced water content (conductance) and a significant improvement of roughness (SESC) and smoothness (SESM) values measured using a Visioscan at 3 and 6 weeks. Those effects appeared concomitant with a significantly increased corneocyte size, a significantly down-regulated degree of thick abrasions, and a significant impairment of the corneocyte lipid envelope at 6 weeks. Thus, our clinical study suggests, for the first time, that topical application of the POLG nano-emulsion has the distinct potential to ameliorate atopic dry skin symptoms, particularly scaling and itchiness, in the skin of patients with AD. Those effects result from alleviation of the disrupted water-holding function probably due to the increased supply of lamellae structures into the stratum corneum despite the failure to improve barrier function.

Group IVE cytosolic phospholipase A2 limits psoriatic inflammation by mobilizing the anti-inflammatory lipid N-acylethanolamine

Psoriasis is an inflammatory disorder characterized by keratinocyte hyper-proliferation and Th17-type immune responses. However, the roles of bioactive lipids and the regulation of their biosynthesis in this chronic skin disease are not fully understood. Herein, we show that group IVE cytosolic phospholipase A₂ (cPLA₂ ε/PLA2G4E) plays a counterregulatory role against psoriatic inflammation by producing the anti-inflammatory lipid N-acylethanolamine (NAE). Lipidomics analysis of mouse skin revealed that NAE species and their precursors (N-acyl-phosphatidylethanolamine and glycerophospho-N-acylethanolamine) were robustly increased in parallel with the ongoing process of imiquimod (IMQ)-induced psoriasis, accompanied by a marked upregulation of cPLA₂ ε in epidermal keratinocytes. Genetic deletion of cPLA₂ ε exacerbated IMQ-induced ear swelling and psoriatic marker expression, with a dramatic reduction of NAE-related lipids in IMQ-treated, and even normal, skin. Stimulation of cultured human keratinocytes with psoriatic cytokines concomitantly increased PLA2G4E expression and NAE production, and supplementation with NAEs significantly attenuated the cytokine-induced upregulation of the psoriatic marker S100A9. Increased expression of cPLA₂ ε was also evident in the epidermis of psoriatic patients. These findings reveal for the first time the in vivo role of cPLA₂ ε, which is highly induced in the keratinocytes of the psoriatic skin, promotes the biosynthesis of NAE-related lipids, and contributes to limiting psoriatic inflammation.

β-Sitosterol 3-O-D-glucoside increases ceramide levels in the stratum corneum via the up-regulated expression of ceramide synthase-3 and glucosylceramide synthase in a reconstructed human epidermal keratinization model

β-Sitosterol 3-O-d-glucoside (BSG) is known to act as an agonist by binding to estrogen receptors, and estrogen has been reported to enhance the activity of β-glucocerebrosidase, an epidermal ceramide metabolizing enzyme. In this study, we determined whether BSG up-regulates ceramide levels in the stratum corneum (SC) of a reconstructed human epidermal keratinization (RHEK) model. Treatment with BSG significantly increased the total ceramide content by 1.2-fold compared to that in the control in the SC of the RHEK model, accompanied by a significant increase of the ceramide species, Cer[EOS] by 2.1-fold compared to that in the control. RT-PCR analysis demonstrated that BSG significantly up-regulated the mRNA expression levels of serine palmitoyltransferase (SPT)2, ceramide synthase (CerS)3, glucosylceramide synthase (GCS) and acid sphingomyelinase by 1.41-1.89, 1.35-1.44, 1.19 and 2.06-fold, respectively, compared to that in the control in the RHEK model. Meanwhile, BSG significantly down-regulated the mRNA expression levels of sphingomyelin synthase (SMS)2 by 0.87-0.89-fold. RT-PCR analysis also demonstrated that BSG significantly up-regulated the mRNA expression levels of CerS3 and GCS by 1.19-1.55 and 1.20-fold, respectively, but not of SPT2 and significantly down-regulated that of SMS2 by 0.74-fold in HaCaT keratinocytes. Western blotting analysis revealed that BSG significantly increased the protein expression levels of CerS3 and GCS by 1.78 and 1.28-1.32-fold, respectively, compared to that in the control in HaCaT cells. These findings indicate that BSG stimulates ceramide synthesis via the up-regulated expression levels of CerS3 and GCS in the glucosylceramide pathway, which results in a significantly increased level of total ceramides in the SC accompanied by significantly increased levels of acylceramide species such as Cer[EOS].

Cutting Edge of the Pathogenesis of Atopic Dermatitis: Sphingomyelin Deacylase, the Enzyme Involved in Its Ceramide Deficiency, Plays a Pivotal Role

Atopic dermatitis (AD) is characterized clinically by severe dry skin and functionally by both a cutaneous barrier disruption and an impaired water-holding capacity in the stratum corneum (SC) even in the nonlesional skin. The combination of the disrupted barrier and water-holding functions in nonlesional skin is closely linked to the disease severity of AD, which suggests that the barrier abnormality as well as the water deficiency are elicited as a result of the induced dermatitis and subsequently trigger the recurrence of dermatitis. These functional abnormalities of the SC are mainly attributable to significantly decreased levels of total ceramides and the altered ceramide profile in the SC. Clinical studies using a synthetic pseudo-ceramide (pCer) that can function as a natural ceramide have indicated the superior clinical efficacy of pCer and, more importantly, have shown that the ceramide deficiency rather than changes in the ceramide profile in the SC of AD patients plays a central role in the pathogenesis of AD. Clinical studies of infants with AD have shown that the barrier disruption due to the ceramide deficiency is not inherent and is essentially dependent on postinflammatory events in those infants. Consistently, the recovery of trans-epidermal water loss after tape-stripping occurs at a significantly slower rate only at 1 day post-tape-stripping in AD skin compared with healthy control (HC) skin. This resembles the recovery pattern observed in Niemann-Pick disease, which is caused by an acid sphingomyelinase (aSMase) deficiency. Further, comparison of ceramide levels in the SC between before and after tape-stripping revealed that whereas ceramide levels in HC skin are significantly upregulated at 4 days post-tape-stripping, their ceramide levels remain substantially unchanged at 4 days post-tape-stripping. Taken together, the sum of these findings strongly suggests that an impaired homeostasis of a ceramide-generating process may be associated with these abnormalities. We have discovered a novel enzyme, sphingomyelin (SM) deacylase, which cleaves the N-acyl linkage of SM and glucosylceramide (GCer). The activity of SM deacylase is significantly increased in AD lesional epidermis as well as in the involved and uninvolved SC of AD skin, but not in the skin of patients with contact dermatitis or chronic eczema, compared with HC skin. SM deacylase competes with aSMase and β-glucocerebrosidase (BGCase) to hydrolyze their common substrates, SM and GCer, to yield their lysoforms sphingosylphosphorylcholine (SPC) and glucosylsphingosine (GSP), respectively, instead of ceramide. Consistently, those reaction products (SPC and GSP) accumulate to a greater extent in the involved and uninvolved SC of AD skin compared with chronic eczema or contact dermatitis skin as well as HC skin. Successive chromatographies were used to purify SM deacylase to homogeneity with a single band of ≈43 kDa and with an enrichment of >14,000-fold. Analysis of a protein spot with SM deacylase activity separated by 2D-SDS-PAGE using MALDI-TOF MS/MS allowed its amino acid sequence to be determined and to identify it as the β-subunit of acid ceramidase (aCDase), an enzyme consisting of α- and β-subunits linked by amino-bonds and a single S-S bond. Western blotting of samples treated with 2-mercaptoethanol revealed that whereas recombinant human aCDase was recognized by antibodies to the α-subunit at ≈56 and ≈13 kDa and the β-subunit at ≈43 kDa, the purified SM deacylase was detectable only by the antibody to the β-subunit at ≈43 kDa. Breaking the S-S bond of recombinant human aCDase with dithiothreitol elicited the activity of SM deacylase with an apparent size of ≈40 kDa upon gel chromatography in contrast to aCDase activity with an apparent size of ≈50 kDa in untreated recombinant human aCDase. These results provide new insights into the essential role of SM deacylase as the β-subunit aCDase that causes the ceramide deficiency in AD skin.

Treatment with Synthetic Pseudoceramide Improves Atopic Skin, Switching the Ceramide Profile to a Healthy Skin Phenotype

Little is known about the pathophysiological linkages between altered ceramide profiles in the stratum corneum (SC) of patients with atopic dermatitis and their impaired skin barrier and water-holding functions. We studied those characteristics following topical treatment with a designed synthetic pseudoceramide (pCer) and analyzed that pathophysiological linkage by microanalyzing ceramides using normal phase liquid chromatography-electrospray ionization mass spectrometry. Four weeks of treatment with pCer significantly reduced skin symptoms, accompanied by significant decreases in transepidermal water loss and increases in water content. In the SC ceramide profiles, ceramides containing nonhydroxy fatty acids and 6-hydroxysphingosines (Cer[NH]) and ceramides containing nonhydroxy fatty acids and phytosphingosines (Cer[NP]) increased, whereas ceramides containing nonhydroxy fatty acids and sphingosines (Cer[NS]) and ceramides containing a-hydroxy fatty acids and sphingosines (Cer[AS]) decreased, with larger alkyl chain lengths in Cer[NS], distinctly representing a switch from an atopic dermatitis to a healthy skin phenotype. The level of pCer that penetrated into the SC was significantly correlated with the SC water content but not with transepidermal water loss. The level and the average carbon chain length of Cer[NS] were closely correlated with the pCer level in the SC. These findings indicate that the penetrated pCer contributes to shift the ceramide profile from an atopic dermatitis to a healthy skin phenotype. Taken together, the observed clinical efficacy of treatment with pCer provides a deep insight into the pathogenesis of atopic dermatitis as a ceramide-deficient disease.

Linoleate-enriched diet increases both linoleic acid esterified to omega hydroxy very long chain fatty acids and free ceramides of canine stratum corneum without effect on protein-bound ceramides and skin barrier function

Few studies have investigated the influence of increased amounts of dietary linoleic acid on the epidermal lipid biochemistry and TEWL in healthy subject. The influence of dietary linoleic acid on canine stratum corneum (SC) lipids was studied by feeding two groups of five dogs differential amounts of linoleic acid (LA) for three months. SC was harvested by tape stripping and lipids were analyzed by thin-layer chromatography and mass spectrometry. The dogs that were fed the higher concentration of LA showed high increases in the contents of both linoleic acid and free ceramides in the SC, whereas the protein-bound ceramide content was unchanged. Acylacids that represent the esterified form of linoleic acid in omega hydroxy very long chain fatty acids (ω-OH VLCFA) accounted for most of the elevation of LA, whereas the concentration of the free form was not significantly changed. Corroborating the absence of change in the protein-bound ceramides content of healthy dogs SC, TEWL was nearly unaffected by the linoleic acid-enriched diet.

Fractionated aliphatic alcohols as synthetic precursors of ultra long-chain monoacylglycerols for cosmetic applications

BACKGROUND

Xerosis is an abnormally dry and flaky skin condition that is associated with a change in the packing behaviour of the lipid matrix in the stratum corneum (SC), the outermost layer of the skin. This skin condition can lead to an increase in transepidermal water loss (TEWL). As ultralong-chain fatty acids have a positive effect on maintaining the packing behaviour of the SC lipid matrix, a moisturizer which contains glycerides of ultralong-chain fatty acids could act as a semi-occlusive layer on the surface of the skin. This will lower the rate of water evaporation through the epidermis and consequently help prevent or improve skin xerosis.

OBJECTIVE

To identify a novel source of ultralong-chain lipids and develop monoacylglycerols with mixed fatty acyl chain lengths that have occlusive properties superior to petrolatum.

METHODS

Initially, Performacol 425, a mixture of very long-chain fatty alcohols, was fractionated using short path distillation to yield a fraction enriched with C22:0-C26:0 fatty alcohols. The fatty alcohol fraction was then oxidized using Jones reagent, and the resulting fatty acids were esterified with glycerol to yield the corresponding monoglycerides using Novozym 435. These were then evaluated using Fourier transform infrared spectroscopy, differential scanning calorimetry and water vapour transmission rate measurements.

RESULTS

The monoacylglycerols enriched with C22:0-C26:0 displayed a melting point of 80°C and orthorhombic packing; packing behaviour mainly present in healthy SC. In addition, a phospholipid-structured emulsion containing 3% of the monoglycerides displayed occlusive properties superior to the vehicle containing 3% petrolatum jelly.

CONCLUSIONS

Performacol 425 can be a potential source of fatty alcohols to synthesize monoacylglycerols that can improve the occlusive behaviour of phospholipid-structured emulsions.

Subclinical cutaneous inflammation remained after permeability barrier disruption enhances UV sensitivity by altering ER stress responses and topical pseudoceramide prevents them

Stratum corneum forms the UV barrier. The effect of ultraviolet B (UVB) on normal skin was extensively studied; however, its effect on barrier perturbed skin remains undefined. Both barrier perturbation and UVB irradiation induce endoplasmic reticulum (ER) stress and unfolded protein response (UPR) in keratinocytes. Mild ER stress activates homeostatic UPR, while severe ER stress leads to abnormal UPR, promoting apoptosis and inflammation. Here, we investigated UV sensitivity and UVB-induced UPR in barrier-disrupted human skin and the effects of pseudoceramide-dominant emollient on UVB-induced skin responses. Tape-stripped skin of healthy volunteers showed enhanced susceptibility to erythema and augmented proinflammatory cytokines induction following suberythemal UVB irradiation. Suberythemal UVB activated XBP1 in normal skin, while increased CHOP transcription in barrier perturbed skin. After tape stripping, pseudoceramide-dominant emollient was applied for 3 days, and then, the areas were irradiated with suberythemal UVB. Pretreatment with topical pseudoceramide protected against UVB-induced upregulation of IL-1β, IL-6, and TNF-α transcription and reduced susceptibility to erythema following UVB. Topical pseudoceramide also suppressed suberythemal UVB-induced CHOP transcription in barrier-disrupted skin. Taken together, these data indicate that permeability barrier disruption increases UV sensitivity in human skin, partly via switch the UVB-induced UPR, from homeostatic signals to pro-apoptotic and proinflammatory signals. In addition, we conclude that pseudoceramide-dominant emollient suppresses excessive ER stress induction and CHOP activation following UVB in barrier damaged skin, providing evidence that pseudoceramide-dominant emollients can be promising strategies for photoprotection of the barrier damaged skin.

PNPLA1 has a crucial role in skin barrier function by directing acylceramide biosynthesis

Mutations in patatin-like phospholipase domain-containing 1 (PNPLA1) cause autosomal recessive congenital ichthyosis, but the mechanism involved remains unclear. Here we show that PNPLA1, an enzyme expressed in differentiated keratinocytes, plays a crucial role in the biosynthesis of ω-O-acylceramide, a lipid component essential for skin barrier. Global or keratinocyte-specific Pnpla1-deficient neonates die due to epidermal permeability barrier defects with severe transepidermal water loss, decreased intercellular lipid lamellae in the stratum corneum, and aberrant keratinocyte differentiation. In Pnpla1^−/− epidermis, unique linoleate-containing lipids including acylceramides, acylglucosylceramides and (O-acyl)-ω-hydroxy fatty acids are almost absent with reciprocal increases in their putative precursors, indicating that PNPLA1 catalyses the ω-O-esterification with linoleic acid to form acylceramides. Moreover, acylceramide supplementation partially rescues the altered differentiation of Pnpla1^−/− keratinocytes. Our findings provide valuable insight into the skin barrier formation and ichthyosis development, and may contribute to novel therapeutic strategies for treatment of epidermal barrier defects.

Loss-of-function mutations in PNPLA1, a gene encoding an enzyme with unknown function, cause dry and scaling skin in humans. Using mouse models with PNPLA1 deficiency, the authors show that PNPLA1 participates in the biosynthesis of acylceramide, a lipid component essential for skin barrier function.

Pseudoceramide stimulates peroxisome proliferator-activated receptor-α expression in a murine model of atopic dermatitis: molecular basis underlying the anti-inflammatory effect and the preventive effect against steroid-induced barrier impairment

Topical pseudoceramides are successfully used in skin barrier repair therapy for atopic dermatitis (AD) and demonstrated to reduce the adverse effects of topical glucocorticoids (GC). However, the molecular mechanisms involved are not fully understood. We investigated whether PC-9S (myristoyl/palmitoyloxostearamide/arachamide MEA, Neopharm, Daejeon, Korea), one of the synthetic pseudoceramides, could stimulate peroxisome proliferator-activated receptor (PPAR)α expression in a hapten [oxazolone (oxa)]-induced AD murine model (oxa-AD mice) and subsequently improved permeability barrier, reduced inflammation, and increased antimicrobial peptides (AMPs) expression. Normal hairless mice and oxa-AD mice were topically treated twice daily with either PC-9S-containing physiologic lipid mixture (PLM), vehicle (PLM), or PPARα agonist for 4 days. Topical PC-9S significantly increased PPARα expression in mouse epidermis in vivo and in oxa-AD mice skin comparable with PPARα agonist. Topical PC-9S-containing PLM significantly reduced basal trans-epidermal water loss (TEWL), surface pH, and mast cell infiltrates and prevented the decline of AMPs expression in oxa-AD mice, which were abrogated by PPARα antagonist. Then, oxa-AD mice were treated with super-potent topical GC twice daily for 4 days with or without PC-9S co-applications. Co-treatment with PC-9S-containing PLM suppressed GC-induced increase in basal TEWL, epidermal thinning, reduced loricrin expression, and impaired barrier recovery and these effects were attenuated by PPARα antagonist. Collectively, our findings suggest that pseudoceramide PC-9S-induced stimulation of PPARα expression provides a new mechanism by which pseudoceramides show anti-inflammatory property, improve the permeability and antimicrobial barrier function, and prevent the negative effects of topical GC.

Skin hydration in postmenopausal women: argan oil benefit with oral and/or topical use

The aim of this study

The aim of this study was to evaluate the effect of daily consumption and/or application of argan oil on skin hydration in postmenopausal women.

Material and methods

Sixty postmenopausal women consumed butter during the stabilization period and were randomly divided into two groups for the intervention period: the treatment group absorbed alimentary argan oil (n = 30) and the control group olive oil (n = 30). Both groups applied cosmetic argan oil in the left volar forearm during a sixty days’ period. Evaluation of skin hydration, i.e. transepidermal water loss (TEWL) and water content of the epidermis (WCE) on both volar forearms of the two groups, were performed during three visits at D0, D30 and after sixty days (D60) of oils treatment.

Results

The consumption of argan oil has led to a significant decrease in TEWL (p = 0.023) and a significant increase in WCE (p = 0.001). The application of argan oil has led to a significant decrease in TEWL (p = 0.01) and a significant increase in WCE (p < 0.001).

Conclusions

Our findings suggest that the daily consumption and application of argan oil have improved the skin hydration by restoring the barrier function and maintaining the water-holding capacity.

The structure, function, and importance of ceramides in skin and their use as therapeutic agents in skin-care products

Ceramides (CERs) are epidermal lipids that are important for skin barrier function. Much research has been devoted to identifying the numerous CERs found in human skin and their function. Alterations in CER content are associated with a number of skin diseases such as atopic dermatitis. Newer formulations of skin-care products have incorporated CERs into their formulations with the goal of exogenously applying CERs to help skin barrier function. CERs are a complex class of molecules and because of their growing ubiquity in skin-care products, a clear understanding of their role in skin and use in skin-care products is essential for clinicians treating patients with skin diseases. This review provides an overview of the structure, function, and importance of skin CERs in diseased skin and how CERs are being used in skin-care products to improve or restore skin barrier function.

Regulation of energy metabolism by long-chain fatty acids

In mammals, excess energy is stored primarily as triglycerides, which are mobilized when energy demands arise. This review mainly focuses on the role of long chain fatty acids (LCFAs) in regulating energy metabolism as ligands of peroxisome proliferator-activated receptors (PPARs). PPAR-alpha expressed primarily in liver is essential for metabolic adaptation to starvation by inducing genes for beta-oxidation and ketogenesis and by downregulating energy expenditure through fibroblast growth factor 21. PPAR-delta is highly expressed in skeletal muscle and induces genes for LCFA oxidation during fasting and endurance exercise. PPAR-delta also regulates glucose metabolism and mitochondrial biogenesis by inducing FOXO1 and PGC1-alpha. Genes targeted by PPAR-gamma in adipocytes suggest that PPAR-gamma senses incoming non-esterified LCFAs and induces the pathways to store LCFAs as triglycerides. Adiponectin, another important target of PPAR-gamma may act as a spacer between adipocytes to maintain their metabolic activity and insulin sensitivity. Another topic of this review is effects of skin LCFAs on energy metabolism. Specific LCFAs are required for the synthesis of skin lipids, which are essential for water barrier and thermal insulation functions of the skin. Disturbance of skin lipid metabolism often causes apparent resistance to developing obesity at the expense of normal skin function.

Reevaluation of the non-lesional dry skin in atopic dermatitis by acute barrier disruption: an abnormal permeability barrier homeostasis with defective processing to generate ceramide

Atopic dermatitis is characterized by disruption of the cutaneous barrier due to reduced ceramide levels even in non-lesional dry skin. Following further acute barrier disruption by repeated tape strippings, we re-characterized the non-lesional dry skin of subjects with atopic dermatitis, which shows significantly reduced levels of barrier function and ceramide but not of beta-glucocerebrosidase activity. For the first time, we report an abnormal trans-epidermal water loss homeostasis in which delayed recovery kinetics of trans-epidermal water loss occurred on the first day during the 4 days after acute barrier disruption compared with healthy control skin. Interestingly, whereas the higher ceramide level in the stratum corneum of healthy control skin was further significantly up-regulated at 4 days post-tape stripping, the lower ceramide level in the stratum corneum of subjects with atopic dermatitis was not significantly changed. In a parallel study, whereas beta-glucocerebrosidase activity at 4 days post-tape stripping was significantly up-regulated in healthy control skin compared with before tape stripping, the level of that activity remained substantially unchanged in atopic dermatitis. These findings indicate that subjects with atopic dermatitis have a defect in sphingolipid-metabolic processing that generates ceramide in the interface between the stratum corneum and the epidermis. The results also support the notion that the continued disruption of barrier function in atopic dermatitis non-lesional skin is associated with the impaired homeostasis of a ceramide-generating process, which underscores an atopy-specific inflammation-triggered ceramide deficiency that is distinct from other types of dermatitis.

Synthesis of fluorescent C24-ceramide: evidence for acyl chain length dependent differences in penetration of exogenous NBD-ceramides into human skin

Topical skin lipid supplementation may provide opportunities for controlling ceramide (Cer) deficiency in skin diseases such as atopic dermatitis or psoriasis. Here we describe the synthesis of a long-chain 7-nitrobenzo[c][1,2,5]oxadiazol-4-yl (NBD)-labeled Cer and its different penetration through human skin compared to widely used short-chain fluorescent Cer tools.

Leukotriene B(4) mediates sphingosylphosphorylcholine-induced itch-associated responses in mouse skin

In atopic dermatitis, the concentration in the skin of sphingosylphosphorylcholine (SPC), which is produced from sphingomyelin by sphingomyelin deacylase, is increased. In the present study, we investigated the itch-eliciting activity of SPC and related substances and the mechanisms of SPC action in mice. An intradermal injection of SPC, but not sphingomyelin and sphingosine, induced scratching, an itch-associated response, which was not suppressed by a deficiency in mast cells or the H(1) histamine receptor antagonist terfenadine. The action of SPC was inhibited by the mu-opioid receptor antagonist naltrexone. SPC action also was inhibited by the 5-lipoxygenase inhibitor zileuton and the leukotriene B(4) antagonist ONO-4057, but not by the cyclooxygenase inhibitor indomethacin. Moreover, SPC action was inhibited by the antiallergic agent azelastine, which suppresses the action and production of leukotriene B(4). Administration of SPC to the skin and to primary cultures of keratinocytes increased leukotriene B(4) production. SPC increased intracellular Ca(2+) ion concentration in primary cultures of dorsal root ganglion neurons and keratinocytes. These results suggest that SPC induces itching through a direct action on primary afferents and leukotriene B(4) production of keratinocytes. Sphingomyelin deacylase and SPC receptors may be previously unreported targets for antipruritic drugs.

On the effects of topical synthetic pseudoceramides: comparison of possible keratinocyte toxicities provoked by the pseudoceramides, PC104 and BIO391, and natural ceramides

BACKGROUND

Ceramides (Cer) in the stratum corneum are essential for epidermal permeability barrier function. Thus, topical Cer replacement therapy has been employed to improve barrier function in clinical situations associated with Cer deficiency, e.g., atopic dermatitis. Because of the disadvantages of both natural- and skin identical-Cer (central nervous system origins and cost, respectively), synthetic chemical mimics, or pseudoceramides (pseudo-Cer), have been utilized as Cer substitutes. Whereas increased levels of intracellular Cer trigger cell growth inhibition and apoptosis, Cer levels are maintained by metabolic/catabolic pathways protecting cells from Cer-induced apoptosis. However, since the metabolic fates of each pseudo-Cer remain unknown, their widespread deployment in topical agents has raised concern about potential toxicities.

OBJECTIVE

We compared the effects of two chemically unrelated commercially available pseudo-Cer to exogenous cell-permeant (C2)- or natural (C18)-Cer on cell growth and apoptosis thresholds in cultured human keratinocytes (CHK).

METHODS

Cell growth and cell toxicity of CHK exposed to either C2-Cer or pseudo-Cer were assessed by MTT and lactate dehydrogenase release assays. Mitochondrial membrane potential, an indicator of apoptosis, was measured using membrane permeabilized semi-intact keratinocytes exposed C2-Cer, natural-Cer or pseudo-Cer.

RESULTS

While the cell-permeant-Cer inhibits keratinocyte growth and increases cell toxicity, neither of the pseudo-Cer showed these effects. Decreased mitochondrial membrane potential occurred in CHK incubated with cell-permeant- and natural-Cer, but not pseudo-Cer.

CONCLUSIONS

Taken together with preclinical safety studies of these pseudo-Cer and their widespread use over the counter without evidence of toxicity, these studies provide further assurance about the safety of these pseudo-Cer for topical use.

Ceramide analogue 14S24 selectively recovers perturbed human skin barrier

BACKGROUND

Topical ceramide application is an effective therapeutic approach in skin disorders with disturbed barrier function, including atopic dermatitis and psoriasis.

OBJECTIVES

To evaluate ceramide analogue N-tetracosanoyl-(l)-serine tetradecyl ester (14S24) using a novel ex vivo model.

METHODS

Freshly excised human skin was disrupted by lipid extraction, tape stripping and sodium lauryl sulphate (SLS) treatment. Barrier perturbation was evaluated by the measurement of transepidermal water loss (TEWL), skin hydration and the penetration of model compound, theophylline (TH), assessed by microdialysis. The effect of topical 5% 14S24 was compared with a commercial formulation containing a skin lipid mixture (LR) and control formulation with no skin lipids (L).

RESULTS

Both LR and 14S24 produced significant recovery of TEWL and TH penetration in extracted and tape-stripped skin with 14S24 being significantly more effective. In SLS-treated skin, 14S24 decreased TEWL but not TH penetration; LR was inactive. L improved skin hydration but not barrier characteristics. Weak correlation between TEWL and TH penetration was observed in extracted and tape-stripped skin but not in SLS-treated skin.

CONCLUSIONS

Cutaneous microdialysis can serve as a useful tool for the evaluation of skin barrier recovery by topical formulations ex vivo whereas TEWL may not be an appropriate measure of skin barrier function in such studies. The excellent barrier repair activity of 14S24 could be beneficial in skin disorders with ceramide deficiency.

Novel synthetic ceramide derivatives increase intracellular calcium levels and promote epidermal keratinocyte differentiation

Ceramide is an important constituent of stratum corneum lipids, which act as both physical barriers and signal modulators. We synthesized several ceramide derivatives and investigated their effects on keratinocyte differentiation. RT-PCR and Western blotting showed that the novel synthetic ceramide derivatives K6PC-4 [N-(2,3-dihydroxypropyl)-2-hexyl-3-oxo-decanamide], K6PC-5, [N-(1,3-dihydroxypropyl-2-hexyl-3-oxo-decanamide] and K6PC-9 (N-ethanol-2-hexyl-3-oxo-decanamide) [corrected] These ceramide derivatives elicited a rapid transient increase in intracellular calcium levels, which were measured using laser scanning confocal microscopy. In addition, K6PC-4, K6PC-5, and K6PC-9 stimulated the phosphorylation of p42/44 extracellular signal-regulated kinase and c-Jun N-terminal kinase. In a reconstituted epidermis model, K6PC-4, K6PC-5, and K6PC-9 significantly increased keratin 1 expression in the suprabasal layer. These results indicate that these novel synthetic ceramide derivatives have the potential to promote keratinocyte differentiation, suggesting that the lipid molecules are applicable for treating skin diseases involving abnormal keratinocyte differentiation.

Characterization of Surfactant-Induced Skin Damage through Barrier Recovery Induced by Pseudoacylceramides

BACKGROUND AND OBJECTIVE

To determine how much barrier-reinforcing effects of ceramides contribute to prevent the surfactant-induced cutaneous deterioration.

METHODS

We compared the effects of topical application of two types of pseudoceramides on cutaneous deterioration induced by sodium dodecyl sulfate (SDS) treatment for 10 days in association with alterations of barrier function.

RESULTS

Daily application of pseudoacylceramide immediately after each SDS treatment significantly prevented the marked elevation of transepidermal water loss, which was accompanied by a marked abrogation of the increased expression in intercellular adhesion molecule 1 by epidermal cells as well as by suppressed epidermal hyperplasia. In contrast, topical application of a nonacylated pseudoceramide with poor barrier-reinforcing potential showed less preventive effects on cutaneous deterioration.

CONCLUSION

These results strongly suggest that perturbation of the skin barrier is a causative factor in surfactant-induced cutaneous changes and that reinforcing the barrier function by ceramide application is effective in preventing the surfactant-induced skin deterioration.

An accumulation of glucosylceramide in the stratum corneum due to attenuated activity of beta-glucocerebrosidase is associated with the early phase of UVB-induced alteration in cutaneous barrier function

Epidermal glucosylceramide (GlcCer) metabolism is essential to the maintenance of skin homeostasis. Although exposure of the skin to ultraviolet (UV) radiation elicits dramatic physiological and biological changes in the epidermis attributable to barrier perturbation, wrinkle formation and inflammation, little is known about UV-induced changes in GlcCer metabolism. In this study, we have assessed beta-glucocerebrosidase (GlcCer'ase) activity in murine epidermis before and after a single UVB irradiation and have compared it with GlcCer and ceramide (Cer) levels. GlcCer'ase enzymatic activity was significantly suppressed in a dose-dependent manner one day after UVB (70 mJ/cm(2)) irradiation despite a significant increase in GlcCer'ase mRNA. The marked decrease in enzyme activity was followed by an accumulation of GlcCer in the stratum corneum, which peaked at day 2. This decreased level of GlcCer'ase activity returned to 80% of the control level by day 3 followed by a return of GlcCer level to the control level by day 4. In the whole epidermis, significant increases in Cer and GlcCer levels occurred on day 3 and on day 2, respectively. These results suggest that UVB irradiation dramatically affects the metabolism of GlcCer to Cer in the epidermis (including the stratum corneum) and that this may be closely associated with the early and minor phase of UVB-induced alteration in cutaneous barrier function.

Structure, function, and dietary regulation of delta6, delta5, and delta9 desaturases

Fatty acid desaturases introduce a double bond in a specific position of long-chain fatty acids, and are conserved across kingdoms. Degree of unsaturation of fatty acids affects physical properties of membrane phospholipids and stored triglycerides. In addition, metabolites of polyunsaturated fatty acids are used as signaling molecules in many organisms. Three desaturases, Delta9, Delta6, and Delta5, are present in humans. Delta-9 catalyzes synthesis of monounsaturated fatty acids. Oleic acid, a main product of Delta9 desaturase, is the major fatty acid in mammalian adipose triglycerides, and is also used for phospholipid and cholesteryl ester synthesis. Delta-6 and Delta5 desaturases are required for the synthesis of highly unsaturated fatty acids (HUFAs), which are mainly esterified into phospholipids and contribute to maintaining membrane fluidity. While HUFAs may be required for cold tolerance in plants and fish, the primary role of HUFAs in mammals is cell signaling. Arachidonic acid is required as substrates for eicosanoid synthesis, while docosahexaenoic acid is required in visual and neuronal functions. Desaturases in mammals are regulated at the transcriptional level. Reflecting overlapping functions, three desaturases share a common mechanism of a feedback regulation to maintain products in membrane phospholipids. At the same time, regulation of Delta9 desaturase differs from Delta6 and Delta5 desaturases because its products are incorporated into more diverse lipid groups. Combinations of multiple transcription factors achieve this sophisticated differential regulation.

Biosynthesis of acylceramide in murine epidermis: characterization by inhibition of glucosylation and deglucosylation, and by substrate specificity

We have investigated the physiological significance of the glucosylation of ceramides and the subsequent deglucosylation of glucosylceramide in the synthetic pathway of acylceramide. In this metabolic pathway using [14C]-serine in organ culture, newborn murine (BALB/c) epidermis synthesizes several types of ceramides, including acylceramide, as analyzed by thin-layer chromatography. When conduritol-B-epoxide, a specific inhibitor of beta-glucocerebrosidase, was added to the culture medium, the synthesis of acylceramide was significantly suppressed in concert with a significant increase in acylglucosylceramide. Furthermore, addition of d-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol, an inhibitor of glucosyltransferase, also specifically abolished the synthesis of acylceramide whereas non-acylated ceramides were relatively less affected. We further determined whether the physiological substrate of glucosyltransferase is omega-hydroxyceramide (C30) or non-omega-hydroxylated ceramides. Of those, only non-omega-hydroxylated ceramides proved to be good substrates for glucosyltransferase in vitro. Our parallel in vitro study also demonstrated that murine epidermis contains enzymatic activity by which omega-hydroxyglucosylceramide or omega-hydroxyceramide can be converted to acylglucosylceramide or acylceramide. Collectively, these findings indicate that the majority of acylceramides found in the stratum corneum may be synthesized through a distinct sequence of enzymatic reactions consisting of the glucosylation of ceramides by glucosyltransferase, omega-hydroxylation of glucosylceramide, the acylation of omega-hydroxyglucosylceramide (possibly by an omega-acyltransferase), and the deglucosylation of acylglucosylceramide by beta-glucocerebrosidase.

Ceramide analogue 14S24 ((S)-2-tetracosanoylamino-3-hydroxypropionic acid tetradecyl ester) is effective in skin barrier repair in vitro

Stratum corneum ceramides are fundamental for maintaining the skin barrier properties. Their content is decreased in some skin diseases, e.g. atopic dermatitis, and ceramide supplementation is one of the therapeutic approaches. In the present study we have designed novel ceramide analogue 14S24 ((S)-2-tetracosanoylamino-3-hydroxypropionic acid tetradecyl ester) as a potential barrier-repairing agent. We report a convenient two-step synthesis of this analogue with high yields. The ability of 14S24 to repair the disturbed skin barrier was evaluated in vitro on the porcine skin. After 2h application of 14S24 on the skin disrupted by lipid extraction, the permeability decreased significantly almost to the values of the native skin. The compound is effective in 0.1% aqueous suspension and its effect is comparable with physiological skin lipids under the same condition. The comparison of 14S24 and skin ceramides was made via computer modelling and the in silico physico-chemical parameters are reported. We suggest that allylic hydroxyl, that is essential for the apoptogenic activity of ceramides, is not a necessary component of the skin barrier-forming ceramides. The main result of this study is to demonstrate that simpler and easier-to-synthesise ceramide analogues could be effective in the skin barrier repair.

Abnormal expression of the novel epidermal enzyme, glucosylceramide deacylase, and the accumulation of its enzymatic reaction product, glucosylsphingosine, in the skin of patients with atopic dermatitis

To clarify mechanisms underlying acylceramide deficiency as an causative factor of the permeability barrier disruption seen in the skin of patients with atopic dermatitis (AD), we hypothesized and then demonstrated the presence of a novel epidermal enzyme, termed glucosylceramide (GC) deacylase. This enzyme hydrolyzes (acyl)GC at the N-acyl site to yield its lysoform, glucosylsphingosine (GS), instead of the formation of (acyl)ceramides by beta-glucocerebrosidase. Assays of enzymatic activity using [palmitic acid-(14)C] GC as a substrate revealed that extracts from the stratum corneum and from the epidermis (but not from the dermis) of patients with AD have the significantly higher potential to hydrolyze GC at the N-acyl site to release (14)C-labeled free fatty acid than of healthy controls. To determine the in vivo physiologic function of this novel enzyme, we measured the metabolic product GS in the upper stratum corneum. In both the involved and the uninvolved stratum corneum from patients with AD, there were significant increases in the amounts of GS compared with healthy controls and there was a significant inverse correlation with the decreased content of ceramides or ceramide-1 (acylceramide). Thus, collectively these results strongly suggest the physiologic relevance of GC deacylase to the acylceramide deficiency seen in the stratum corneum of patients with AD.

Sphingosylphosphorylcholine is upregulated in the stratum corneum of patients with atopic dermatitis

To clarify the functional relevance of sphingomyelin (SM) deacylase to the ceramide deficiency seen in atopic dermatitis (AD), we developed a new highly sensitive method and measured the metabolic intermediate sphingosylphosphorylcholine (SPC) that accumulates in the stratum corneum. SPC in intercellular lipids extracted from stratum corneum was reacted with [(14)C]acetic anhydride to yield [(14)C-C(2)]SM, which was then analyzed by TLC. In both the lesional and non-lesional stratum corneum obtained from patients with AD, there was a significant increase in the content of SPC over that of healthy control subjects. There was a reciprocal relationship between increases in SPC and decreases in ceramide levels of stratum corneum obtained from healthy controls, and from lesional and non-lesional skin from patients with AD. Comparison with other sphingolipids present in the stratum corneum demonstrated that there is a significant positive correlation between SPC and glucosylsphingosine, another lysosphingolipid derived from glucosylceramide by another novel epidermal enzyme, termed glucosylceramide deacylase. In contrast, there was no correlation between SPC and sphingosine, a degradative product generated from ceramide by ceramidase. These findings strongly suggest the physiological relevance of SM deacylase function in vivo to the ceramide deficiency found in the skin of patients with AD.

Detergent-induced epidermal barrier dysfunction and its prevention

Various detergents are used as skin cleansing products. In some cases, skin cleanser removes not only dirt but also valuable skin lipids. Therefore, detergents may disrupt epidermal barrier function despite that using of detergents are required for good skin hygiene. Lipid supplements can reverse detergent-induced dysfunction of the skin barrier. Elevated transepidermal water loss (TEWL) and riboflavin penetration in 5% SLS-treated rat and human skin were reversed by supplementation of monoglyceride (MG), squalene (SQ), cholesterol ester (CE) and pseudo-ceramide (Cer2). MG and Cer2 achieved the best results. MG appears to inhibit elution of intercellular ceramides, since more ceramides remained when the detergent was supplemented with MG. Topical application of Cer2 is not effective for recovery from artificially induced barrier disruption, but supplemented Cer2 into skin cleanser has a beneficial effect for prevention of detergent-induced barrier disruption. In conclusion, the prevention of barrier disruption is most important matter for maintaining skin health and barrier function. Therefore, we think that Cer2-supplemented skin cleanser is useful for conservation of skin barrier function.

Assessment of epidermal barrier function by photoacoustic spectrometry in relation to its importance in the pathogenesis of atopic dermatitis

With the use of the photoacoustic spectrometry system, in which a mixture of lipid- and water-soluble dyes is applied to the skin and then irradiated with light from a xenon lamp (425 nm and 550 nm), we measured photoacoustic signals of both dyes within the stratum corneum and their disappearance rate through the stratum corneum. The signal intensity was higher and dyes penetrated faster in clinically normal skin of patients with atopic dermatitis (AD) compared with healthy subjects, indicating an impairment of the in vivo cutaneous permeability barrier function against both lipophilic and hydrophilic chemicals. Furthermore, penetration rates of the hydrophilic dyes tended to increase in proportion to the severity of AD and significantly correlated with serum IgE levels in the severe AD group. Thus, abnormal barrier functions of clinically normal skin in AD may predispose inflammatory processes evoked by irritants and allergens, especially their water-soluble elements.

The skin of atopic dermatitis patients contains a novel enzyme, glucosylceramide sphingomyelin deacylase, which cleaves the N-acyl linkage of sphingomyelin and glucosylceramide

We have demonstrated previously that there is an abnormal expression of sphingomyelin (SM) deacylase in the epidermis of patients with atopic dermatitis (ADe). In the present study, we have prepared N-[palmitic acid-1-(14)C]SM and N-[palmitic acid-1-(14)C]glucosylceramide (GCer) to use as substrates and have quantified SM deacylase activity by detecting the release of [(14)C]palmitic acid in extracts of the stratum corneum or the epidermis of ADe patients. In studies using [palmitic acid-1-(14)C]SM as a substrate, a pH dependency of catalytic activity with a peak at pH 5.0 was found. Preparative SDS/PAGE using an extract of ADe epidermis revealed that the molecular mass of SM deacylase is 40000 Da, which is consistent with its apparent molecular mass of 42000 Da estimated by gel-filtration analysis of stratum corneum extracts. Analytical isoelectric focusing (IEF) chromatography demonstrated that the pI values of SM deacylase, beta-glucocerebrosidase (GlcCDase), sphingomyelinase (SMase) and acid ceramidase were 4.2, 7.4, 7.0 and 5.7, respectively. In enzymic analysis using pI-4.2 SM deacylase partially purified by IEF, which had no detectable contamination with acid ceramidase, GlcCDase or SMase, radio-TLC analysis revealed that radiolabelled sphingosylphosphocholine or [1-(14)C]palmitic acid was enzymically liberated from [choline-methyl-(14)C]SM or N-[palmitoyl-1-(14)C]GCer, respectively, used as substrates. Further the pI-4.2 protein purified from extracts of the stratum corneum of ADe patients was able to hydrolyse N-[palmitoyl-1-(14)C]SM and GCer, but not N-[palmitoyl-1-(14)C]ceramide. These results indicate that a hitherto undiscovered epidermal enzyme, termed here glucosylceramide sphingomyelin deacylase, is expressed in the skin of ADe patients, which plays an important role in ceramide deficiency (including acylceramides) in the stratum corneum.

High-expression of sphingomyelin deacylase is an important determinant of ceramide deficiency leading to barrier disruption in atopic dermatitis

We have previously demonstrated that there is abnormal expression of sphingomyelin (SM) deacylase-like enzyme in the epidermis of patients with atopic dermatitis (AD), which results in decreased levels of ceramides in their involved and uninvolved stratum corneum. For quantitation of the expression of SM deacylase in AD, we synthesized 16-(9-anthroyloxy) hexadecanoylsphingosylphosphorylcholine or [palmitic acid-14C] SM and used them as substrates to directly measure the activity of SM deacylase by detecting the release of labeled free fatty acid. Direct enzymatic measurements demonstrated that stratum corneum from lesional forearm skin (volar side) of AD patients has an extremely high SM deacylase activity that is at least five times higher than in the stratum corneum from healthy controls. In stratum corneum from nonlesional skin of AD patients, SM deacylase activity is still at least three times higher than in healthy controls. In contrast, stratum corneum from contact dermatitis patients shows levels of SM deacylase similar to healthy controls. In extracts of whole epidermis biopsies from AD patients, SM deacylase activities are significantly (3-fold) increased over healthy controls in the particulate fraction, whereas there is no significant difference in the activity of sphingomyelinase between AD and healthy control. In peripheral blood lymphocytes of AD patients, there is no increase in activity compared with healthy controls, indicating a possibility that the high expression of SM deacylase is highly associated with the skin of AD patients. These findings suggest that, in contrast to changes in sphingolipid metabolism due to aging, the hitherto undiscovered enzyme SM deacylase, is highly expressed in the epidermis of AD patients, and competes with sphingomyelinase or beta-glucocerebrosidase for the common substrate SM or glucosylceramide, which leads to the ceramide deficiency of the stratum corneum in AD.

Malnutrition-associated rash of cystic fibrosis

Rash is a rare presenting sign of cystic fibrosis (CF) complicated by protein-calorie malnutrition. We measured essential fatty acid (EFA) levels in the serum of a 4-month-old girl with an erythematous, desquamating, periorificially accentuated rash in association with malnutrition and her 2-year-old sister who was diagnosed concurrently with CF but had no rash or signs of malnutrition. Both patients had biochemical evidence of EFA deficiency, suggesting that development of the rash is multifactorial. Clinical presentation, management, and possible modes of pathogenesis of the rash are reviewed. Pathogenesis of the rash appears to involve a complex interaction among deficiencies of EFAs, zinc, protein, and possibly copper, leading to disordered prostaglandin metabolism or cytokine production, or free radical-induced damage to cellular membranes due to a lack of nutrient-derived protective antioxidants.

Chemical enhancement of percutaneous absorption in relation to stratum corneum structural alterations

The outermost layer of the skin, stratum corneum (SC), provides an outstanding barrier against the external environment and is also responsible for skin impermeability toward most solutes. The barrier function is related to the unique composition of the SC lipids and their complex structural arrangement. The lipoidal matrix of the SC, therefore, is a target of penetration enhancer action. The literature on the skin barrier structure and function and on the mechanisms of action of some well established permeation promoters, with a focus on their impact on SC structural alterations, is reviewed. Data obtained from infrared, thermal, and fluorescence spectroscopic examinations of the SC and its components imply enhancer improved permeation of solutes through the SC is associated with alterations involving the hydrocarbon chains of the SC lipid components. Data obtained from electron microscopy and X-ray diffraction reveals that the disordering of the lamellar packing is also an important mechanism for increased permeation of drugs induced by penetration enhancers.

Localization of sphingomyelinase in lesional skin of atopic dermatitis patients

Because it has been suggested that the majority of the activity hydrolysing [N-methyl-14C] sphingomyelin is due to sphingomyelin acylase in the lesional skins of atopic dermatitis (AD), in this study we used immunologic techniques to localize and quantitate sphingomyelinase in AD lesional and normal skin. A polyclonal antibody raised against a synthetic polypeptide corresponding to a portion of the amino acid sequence deduced from the cDNA of human acid sphingomyelinase, cross-reacted with a 58 kDa, pI 5.8 human epidermal protein in an immunoblot analysis. The 58 kDa protein-rich fraction, partially purified by immunoprecipitation, converted [N-methyl-14C]-sphingomyelin to 14C-phosphorylcholine and ceramides. The reaction products were immunohistochemically observed in the intercellular domain from the upper spinous cell layer to the upper stratum corneum cell layers in the lesional skin of AD patients. Immunoelectron-microscopically, gold particles appeared to be concentrated in the intercellular domains of the granular-upper stratum corneum cells in the lesional skin of AD patients. The total amount of the 58 kDa protein in a 7 mm2 area of the skin was measured by quantitative immunoblot analysis; and was slightly increased in the lesional skin samples [3.5 +/- 0.3 microg per 7 mm2 (n = 7)], as compared with the nonlesional skin samples of AD patients [2.8 +/- 0.19 microg per 7 mm2 (n = 10)] and with the normal skin samples [2.7 +/- 0.22 microg per 7 mm2 (n = 10)]. This difference (between the lesional skin of AD and the nonlesional skin of AD or the normal control) was significant (nonpaired student's t test, p < 0.05).

High transepidermal water loss induces fatty acid synthesis and cutaneous fatty acid-binding protein expression in rat skin

Stratum corneum lipids (SCLs) are responsible for the water barrier function (WBF) of the skin in mammals. Recent studies have indicated that epidermal lipid synthesis might be regulated by WBF of stratum corneum and that cutaneous fatty acid-binding protein (C-FABP) plays an important role in fatty acid metabolism in epidermis. To clarify the regulatory mechanism of lipid synthesis, we assessed the effects of barrier disruption induced by either acetone treatment or linoleic acid deficiency on epidermal lipid synthesis in rat. Transepidermal water loss (TEWL) was measured with an evaporimeter before and after treatment. The time course of re-establishing SCLs was examined biochemically and histochemically and the expression of C-FABP in the epidermis was immunohistochemically examined. When the rat skin was covered with a vapor-impermeable membrane after the acetone treatment removing SCLs and inducing WBF disruption, the usual recovery of SCLs was blocked and TEWL was kept high by 24 h. In the uncovered area, rapid redeposition of SCLs within 24 h was found and associated with normal compositions of epidermal lipids including sphingolipids, free fatty acids and sterol and, immunohistochemically, C-FABP was very weakly expressed in epidermis at 0.5 and 2 h, and then strongly in the whole layers at 4 h, and returned to a normal pattern by 8 h. The epidermis of the covered rat skin was kept weak in C-FABP expression by 24 h. In the linoleic acid-deficient rats, TEWL did not increase and the expression pattern of C-FABP showed no notable change until 28 weeks after initiation of the diets, indicating that C-FABP expression may not be affected by altered essential fatty acid metabolism. These results suggest that increase of TEWL itself stimulates C-FABP expression, leading to activation of fatty acid metabolism.