Stratum corneum lipid abnormalities in atopic dermatitis

Fatty acid 2-hydroxylase, encoded by FA2H, accounts for differentiation-associated increase in 2-OH ceramides during keratinocyte differentiation

Ceramides in mammalian stratum corneum comprise a heterogeneous mixture of molecular species that subserve the epidermal permeability barrier, an essential function for survival in a terrestrial environment. In addition to a variation of sphingol species, hydroxylation of the amide-linked fatty acids contributes to the diversity of epidermal ceramides. Fatty acid 2-hydroxylase, encoded by the gene FA2H, the mammalian homologue of FAH1 in yeast, catalyzes the synthesis of 2-hydroxy fatty acid-containing sphingolipids. We assessed here whether FA2H accounts for 2-hydroxyceramide/2-hydroxyglucosylceramide synthesis in epidermis. Reverse transcription-PCR and Western immunoblots demonstrated that FA2H is expressed in cultured human keratinocytes and human epidermis, with FA2H expression and fatty acid 2-hydroxylase activity increased with differentiation. FA2H-siRNA suppressed 2-hydroxylase activity and decreased 2-hydroxyceramide/2-hydroxyglucosylceramide levels, demonstrating that FA2H accounts for synthesis of these sphingolipids in keratinocytes. Whereas FA2H expression and 2-hydroxy free fatty acid production increased early in keratinocyte differentiation, production of 2-hydroxyceramides/2-hydroxyglucosylceramides with longer chain amide-linked fatty acids (> or =C24) increased later. Keratinocytes transduced with FA2H-siRNA contained abnormal epidermal lamellar bodies and did not form the normal extracellular lamellar membranes required for the epidermal permeability barrier. These results reveal that 1) differentiation-dependent up-regulation of ceramide synthesis and fatty acid elongation is accompanied by up-regulation of FA2H; 2) 2-hydroxylation of fatty acid by FA2H occurs prior to generation of ceramides/glucosylceramides; and 3) 2-hydroxyceramides/2-hydroxyglucosylceramides are required for epidermal lamellar membrane formation. Thus, late differentiation-linked increases in FA2H expression are essential for epidermal permeability barrier homeostasis.

Altered Penetration of Polyethylene Glycols into Uninvolved Skin of Atopic Dermatitis Patients

Involved regions of the skin in atopic dermatitis (AD) patients have an altered barrier function. Whether uninvolved skin also has a diminished barrier is controversial. To assess the barrier function of uninvolved skin in AD patients, the percutaneous penetration of polyethylene glycols (PEGs) of various molecular sizes was determined in vivo in AD patients and control subjects using tape stripping of the stratum corneum (SC). The diffusion and partition coefficients were determined using Fick's second law of diffusion. The SC thickness was similar in both groups; however, the trans-epidermal water loss was higher in atopic skin. The apparent diffusion coefficient of PEGs through atopic skin was twice as high as through normal skin, and decreased with increasing molecular weight (MW) in both groups. The partition coefficient in the skin of AD patients was half of that for normal skin but as for normal skin, there was no MW dependency. Although atopic skin exhibited altered barrier with respect to diffusion and partitioning, the permeability coefficients were nearly the same for atopic and normal skin. The results support the assumption of altered skin barrier of AD patients even in the skin that is visibly unaffected by disease.

Epidermal sphingolipids: Metabolism, function, and roles in skin disorders

Mammalian epidermis produces and delivers large quantities of glucosylceramide and sphingomyelin precursors to stratum corneum extracellular domains, where they are hydrolyzed to corresponding ceramide species. This cycle of lipid precursor formation and subsequent hydrolysis represents a mechanism that protects the epidermis against potentially harmful effects of ceramide accumulation within nucleated cell layers. Prominent skin disorders, such as psoriasis and atopic dermatitis, have diminished epidermal ceramide levels, reflecting altered sphingolipid metabolism, that may contribute to disease severity/progression. Enzymatic processes in the hydrolysis of glucosylceramide and sphingomyelin, and the roles of sphingolipids in skin diseases, are the focus of this review.

Skin barrier function, epidermal proliferation and differentiation in eczema

Skin permeability barrier function is impaired in eczema, particularly in contact and atopic dermatitis (AD). In contact dermatitis disruption of the barrier by irritants and allergens is the primary event, followed by sensitization, inflammation, increased epidermal proliferation and changes in differentiation. Genetically impaired skin barrier function is already present in non-lesional and more pronounced in lesional skin in AD. Increased epidermal proliferation and disturbed differentiation, including changes in lipid composition, cause impaired barrier function in AD. Defective permeability barrier function enables the enhanced penetration of environmental allergens into the skin and initiates immunological reactions and inflammation. Barrier dysfunction is therefore crucially involved in the pathogenesis of AD. The atopic syndrome represents a genetically impaired skin barrier function as well as impaired nasal, bronchial, and intestinal mucous membranes leading to AD, allergic rhinitis, bronchial asthma or aggravation of AD. Common treatment strategies for eczema include the application of lipid-based creams and ointments, which aim toward the restoration of the defective permeability barrier, thus helping to normalize proliferation and differentiation.

An update of the defensive barrier function of skin

Skin, as the outermost organ in the human body, continuously confronts the external environment and serves as a primary defense system. The protective functions of skin include UV-protection, anti-oxidant and antimicrobial functions. In addition to these protections, skin also acts as a sensory organ and the primary regulator of body temperature. Within these important functions, the epidermal permeability barrier, which controls the transcutaneous movement of water and other electrolytes, is probably the most important. This permeability barrier resides in the stratum corneum, a resilient layer composed of corneocytes and stratum corneum intercellular lipids. Since the first realization of the structural and biochemical diversities involved in the stratum corneum, a tremendous amount of work has been performed to elucidate its roles and functions in the skin, and in humans in general. The perturbation of the epidermal permeability barrier, previously speculated to be just a symptom involved in skin diseases, is currently considered to be a primary pathophysiologic factor for many skin diseases. In addition, much of the evidence provides support for the idea that various protective functions in the skin are closely related or even co-regulated. In this review, the recent achievements of skin researchers focusing on the functions of the epidermal permeability barrier and their importance in skin disease, such as atopic dermatitis and psoriasis, are introduced.

Atopic xerosis: employment of noninvasive biophysical instrumentation for the functional analyses of the mildly abnormal stratum corneum and for the efficacy assessment of skin care products

The subtle dryness of the skin surrounding the lesions of atopic dermatitis (AD) is called atopic dry skin or atopic xerosis (AX). AX is more susceptible to the development of AD skin lesions under various environmental stimuli than the clinically normal skin of the people who have or have had or will have AD, which might be called normal atopic skin (NAS) that shows no functional differences as compared to the skin of normal individuals. Routine histopathologic studies of AX that involve the invasive procedures of biopsy are not so helpful in clarifying the underlying pathogenesis. Modern, noninvasive biophysical instrumentation provides rich and quantitative information about various functional aspects of skin. The stratum corneum (SC) of AX reveals not only decreased hydration but also mildly impaired barrier function demonstrable as an increase in transepidermal water loss, elevated pH values, and an increased turnover rate of the SC consisting of thick layers of smaller-sized corneocytes. These data suggest that AX is related to mildly increased epidermal proliferation as a result of the presence of subclinical cutaneous inflammation. Although AX skin does not display any impairment in the recovery of barrier function after physical skin irritation by tape-stripping, it produces a much more severe, long-lasting inflammatory response together with a delay in barrier repair after chemical irritation such as that induced by sodium lauryl sulphate. The SC of AX is biochemically characterized by reduction in the amounts of ceramides, especially ceramide I, sebum lipids, and water-soluble amino acids. None of these changes in SC functions are seen in NAS, which includes not only the normal-looking skin of AD patients long after regression of all active lesions but also of latent atopic skin such as neonates who later develop AD. This suggests that all of the observed functional as well as biochemical abnormalities of AX are a reflection of subclinical inflammation. The presence of the underlying inflammation in AX also differentiates it from senile xerosis. The mildly impaired SC functions of AX can be improved by daily repeated applications of effective moisturizers, i.e., corneotherapy, which is effective in preventing the exacerbating progression of AX to AD resulting from inadvertent scratching of the skin that facilitates the penetration of environmental allergens into the skin. The biophysical confirmation of such efficacy of moisturizers, including cosmetic bases on the mildly impaired barrier function and decreased water-holding capacity of the SC of AX, definitely substantiates the importance of skin care for the cosmetic skin problems that affect every individual in the cold and dry season ranging from late autumn to early spring.

Percutaneous penetration of sodium lauryl sulphate is increased in uninvolved skin of patients with atopic dermatitis compared with control subjects

BACKGROUND

Involved regions of the skin in patients with atopic dermatitis (AD) have been shown to have higher transepidermal water loss (TEWL), indicating a compromised skin barrier. Whether uninvolved skin also has diminished barrier characteristics is controversial.

OBJECTIVES

To study the penetration of sodium lauryl sulphate (SLS) into uninvolved skin of patients with AD compared with the skin of control subjects.

METHODS

Percutaneous penetration was assessed using the tape stripping technique on the stratum corneum (SC). Twenty patients with AD and 20 healthy subjects were exposed to 1% SLS for 4 h on the mid-volar forearm. After the end of exposure the SC was removed by adhesive tape. The amount of SLS was determined in each consecutive strip. Fick's second law of diffusion was used to deduce the diffusivity and the partition coefficient of SLS between water and the SC.

RESULTS

The SC thickness was similar in both groups; however, the TEWL was higher in patients with AD compared with that of the control group (mean+/-SD 8.4+/-4.3 and 6.3+/-2.0 g m-2 h-1, respectively). There was a correlation between SC thickness and TEWL in control subjects but no correlation was found in patients with AD. The diffusivity of SLS through uninvolved AD skin was higher compared with normal skin (mean+/-SD 12.7+/-5.8x10(-9) and 6.2+/-3.0x10(-9) cm-2 h-1, respectively), while the partition coefficient between SC and water was lower (mean+/-SD 137+/-64 and 196+/-107, respectively).

CONCLUSIONS

The results show a different penetration profile of SLS into the SC of patients with AD compared with control subjects. This indicates that even noninvolved skin in patients with AD has altered barrier characteristics, emphasizing the importance of skin protection and prevention of skin contact with chemicals.

A novel in vitro percutaneous penetration model: evaluation of barrier properties with p-aminobenzoic acid and two of its derivatives

PURPOSE

The objective of this study was to evaluate the utility of a stratum corneum substitute (SCS) as a novel in vitro percutaneous penetration model. The SCS consists of synthetic stratum corneum (SC) lipids (cholesterol, free fatty acids, and specific ceramides) applied onto a porous substrate. The composition, organization, and orientation of lipids in the SCS bear high resemblance to that of the intercellular barrier lipids in SC.

METHODS

The barrier integrity of the SCS was evaluated by means of passive diffusion studies, using three model compounds with different lipophilicities. The effects of lipid layer thickness, permeant lipophilicity, and altered lipid composition on the barrier properties were investigated, using isolated human SC as a control sample.

RESULTS

For all three model compounds, the permeability characteristics of the SCS with a 12-mum-thick lipid layer closely resemble those of human SC. Modification of the lipid composition, generating an SCS that lacks the characteristic long periodicity phase as present in SC, was accompanied by a 2-fold increased permeability.

CONCLUSIONS

The SCS offers an attractive tool to predict solute permeation through human skin. Moreover, as its lipid composition can be modified, they may also serve as a suitable screening model for diseased skin.

Preparation and characterization of a stratum corneum substitute for in vitro percutaneous penetration studies

The intercellular stratum corneum (SC) lipids form the main barrier for diffusion of substances through the skin. A porous substrate covered with synthetic SC lipids would be an attractive model to study percutaneous penetration, hereby replacing native human SC. Prerequisite is that this stratum corneum substitute (SCS) is prepared with a uniform lipid composition and layer thickness. Furthermore, the lipid organization and orientation should resemble that in SC. The objective of this study was to investigate the utility of an airbrush spraying device to prepare a SCS composed of cholesterol, ceramides and free fatty acids on a polycarbonate filter. The results demonstrate that a proper choice of solvent mixture and lipid concentration is crucial to achieve a uniform distribution of the applied lipids over the filter surface. A smooth and tightly packed lipid layer is only obtained when the equilibration conditions are appropriately chosen. The SCS possesses two crystalline lamellar phases with periodicities similar to those present in native SC. The orientation of these lamellae is mainly parallel to the surface of the polycarbonate filter, which resembles the orientation of the intercellular SC lipids. In conclusion, the airbrush technique enables generation of a homogeneous SCS, which ultimately may function as a predictive in vitro percutaneous penetration model.

[Disturbances of antimicrobial lipids in atopic dermatitis]

Patients with atopic dermatitis exhibit an increased susceptibility to cutaneous infections, especially to pathological colonization with superantigen-secreting Staphylococcus aureus. Recent attention has been focused on antimicrobial peptides, especially on cathelicidin and human beta-defensin-2, which are under-expressed in atopic skin. Antimicrobial lipids from the stratum corneum are also major contributors to cutaneous antimicrobial defense. Current aspects of biochemistry and function of antimicrobial lipids in atopic dermatitis are reviewed in detail. The major classes of stratum corneum lipids with antimicrobial activity are free fatty acids, glucosylceramides, and free sphingosines. Diminished levels of free sphingosines in the stratum corneum have recently been detected in atopic dermatitis and have been associated with the pathological colonization of atopic skin with Staphylococcus aureus. The superantigen staphylococcal enterotoxin B has been shown to reduce the suppressive effect of regulatory T cells on T-cell proliferation, thus augmenting T-cell activation in patients with atopic dermatitis. The killing of superantigen-secreting bacterial strains with topically applied antimicrobial lipids offers new antiseptic and immunomodulatory options for the treatment and secondary prevention of atopic dermatitis.

A study to determine the effect of tacrolimus on ceramide levels in the stratum corneum of patients with atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is characterized both by inflammation and by abnormally low ceramide levels in the stratum corneum. Tacrolimus, effective in the treatment of AD, inhibits transcription and release of inflammatory cytokines operative in AD, but it is unknown if tacrolimus normalizes ceramide levels.

METHODS

Stratum corneum ceramides of seven subjects with lesional AD were measured before and after treatment with tacrolimus ointment.

RESULTS

Treatment with tacrolimus ointment did not increase the ceramide fractions toward or to normal.

CONCLUSION

These findings suggest that tacrolimus ointment is effective in the treatment of atopic dermatitis due to its anti-inflammatory actions rather than to any restorative effect on stratum corneum ceramides.

Microanalytical systems for separations of stratum corneum ceramides

The small amount of lipids from human skin obtained with noninvasive sampling method led us to investigate microanalytical separation techniques. The lipid class analysis was performed with a micro polyvinyl alcohol-silica (PVA-Sil) column. The gradient elution was from heptane to acetone/butanol 90:10 v/v in 4%/min at 78 microL/min. In addition an evaporative light scattering detector (ELSD) was modified for micro-LC. All solvents contained 0.1% of triethylamine and formic acid in stoichiometric amount, which increased the ELSD response. In these conditions, the cholesterol eluted before free fatty acid, and squalene and triglycerides close to the dead volume. The various ceramide classes eluted following the order of the increased number of hydroxyl groups. The LOD for ceramides was 2.2 ng. The advantages of this method are the use of a normal stationary phase more reliable due to its chemical stability, its surface homogeneity and its development in microchromatography without chlorinated solvents which offers small LOD and the whole profile of lipids present in stratum corneum (SC). A method using a narrow-bore PVA-Sil column was used to collect ceramide fraction. Then the molecular species were analysed with a porous graphitic carbon column in capillary LC using a gradient from CH3OH/CHCl3 70:30 v/v to CHCl3 at 2%/min with a flow rate at 5 microL/min. The LOD obtained for ceramide was 1 ng. Both methods were assessed with SC samples obtained by rinsing a 5.7 cm2 area of the forearm with 25 mL of ethanol.

Deficient production of hexadecenoic acid in the skin is associated in part with the vulnerability of atopic dermatitis patients to colonization by Staphylococcus aureus

BACKGROUND AND OBJECTIVES

As one of the major skin fatty acids, cis-6-hexadecenoic acid (C16:1Delta6) exhibits a specific antibacterial activity and might play a specific role in the defense mechanism against Staphylococcus aureus, in healthy subjects whereas S. aureus frequently colonizes the skin of patients with atopic dermatitis (AD).

METHODS

Fatty acid composition of sebum at the recovery level was analyzed by gas chromatography and S. aureus colonizing the skin was assessed by the 'cup-scrub' method (9 patients and 10 healthy controls). To evaluate in vivo effect of C16:1Delta6 on colonization, C16:1Delta6 was applied for 2 weeks on the upper arm skin of another group of AD patients (11 patients).

RESULTS

Analysis of sebum lipids revealed that there is a significant lower free C16:1Delta6 content in nonlesional skin from AD patients compared with healthy controls. This lower content is also accompanied by a significantly lower level of C16:1Delta6 in the total fatty acid composition of sebum (analyzed following hydrolysis). The lower level of free C16:1Delta6 correlated significantly (R(2) = 0.41, p < 0.01) with the numbers of S. aureus colonizing nonlesional skin. Topical application of free C16:1Delta6 on the skin of AD patients for 2 weeks abolished the markedly increased bacterial count in 6 out of the 8 AD patients tested.

CONCLUSIONS

Free C16:1Delta6 may be involved in the defense mechanism against S. aureus in healthy skin and this deficit triggers the susceptibility of the skin to colonization by S. aureus in AD.

Role of ceramides in barrier function of healthy and diseased skin

Stratum corneum intercellular lipids play an important role in the regulation of skin water barrier homeostasis and water-holding capacity. Modification of intercellular lipid organization and composition may impair these properties. Patients with skin diseases such as atopic dermatitis, psoriasis, contact dermatitis, and some genetic disorders have diminished skin barrier function. Lipid composition in diseased skin is characterized by decreased levels of ceramide and altered ceramide profiles. To clarify mechanisms underlying ceramides as a causative factor of skin disease, investigators have examined the activity of enzymes in the stratum corneum on ceramide production and degradation. The activities of ceramidase, sphingomyelin deacylase, and glucosylceramide deacylase are increased in epidermal atopic dermatitis. Investigators have also compared the expression levels of sphingolipid activator protein in the epidermis of normal and diseased skin. A decreased level of prosaposin has been identified in both atopic dermatitis and psoriasis. These results indicate that decreased ceramide level is a major etiologic factor in skin diseases. Hence, topical skin lipid supplementation may provide opportunities for controlling ceramide deficiency and improving skin condition.

Antifungal activities of tacrolimus and azole agents against the eleven currently accepted Malassezia species

The lipophilic yeast Malassezia is an exacerbating factor in atopic dermatitis (AD) and colonizes the skin surface of patients with AD. With the goal of reducing the number of Malassezia cells, we investigated the antifungal activities of a therapeutic agent for AD, tacrolimus, and the azole agents itraconazole and ketoconazole against Malassezia species in vitro. We examined 125 strains of the 11 currently accepted Malassezia species by using the agar dilution method. All strains of the 11 Malassezia species were very susceptible to both azole agents, with MICs ranging from 0.016 to 0.25 mug/ml. Tacrolimus had antifungal activities against half of the strains, with MICs ranging from 16 to 32 mug/ml. Two of the major cutaneous floras, Malassezia globosa and Malassezia restricta, have several genotypes in the intergenic spacer region of the rRNA gene; the azole agents had slightly higher MICs for specific genotype strains of both microorganisms. A combination of azole agents and tacrolimus had a synergistic effect against Malassezia isolates, based on a fractional inhibitory index of 0.245 to 0.378. Our results provide the basis for testing these agents in future clinical trials to reduce the number of Malassezia cells colonizing the skin surface in patients with AD.

Induction of a Hardening Phenomenon by Repeated Application of SLS: Analysis of Lipid Changes in the Stratum Corneum

Adaptation of the skin to repeated influence of exogenous irritants is called the hardening phenomenon. We investigated the stratum corneum lipid composition before and after induction of a hardening phenomenon. Irritant contact dermatitis was induced in 23 non-atopic volunteers by repeated occlusive application of 0.5% sodium lauryl sulfate (SLS) over 3 weeks. At 3, 6 and 9 weeks after irritation, the SLS responses of pre-irritated skin and normal skin were compared. The horny layer lipid composition (ceramides 1-7, cholesterol and free fatty acids) was assessed before irritation and 3, 6 and 9 weeks after irritation. During the first 2 weeks of irritation the transepidermal water loss increased continuously and seemed to decrease during the third week (effect of adaptation). The barrier function of pre-irritated sites was more stable to SLS challenge. Three weeks after irritation, there was a significant increase of ceramide 1 (p<0.001). The only volunteer without hardening phenomenon showed no increase of ceramide 1. Ceramide 1 seems to play a key role as a protection mechanism against repeated irritation.

Ceramide profiles of the uninvolved skin in atopic dermatitis and psoriasis are comparable to those of healthy skin

Ceramides are sphingolipids consisting of sphingoidbases, which are amide-linked to fatty acids. In the stratum corneum, they represent the major constituent of the free extractable intercellular lipids and play a significant role in maintaining and structuring the water permeability barrier of the skin. Using thin layer chromatography, which represents the method of the first choice in analyzing the stratum corneum ceramides, at least seven classes can be distinguished. Each ceramide class contains various species, which have the same head group and different chain lengths. As in many other skin disorders, atopic dermatitis and psoriasis show derangements in content and profile of the ceramides. Such derangements were reported for both the lesional involved as well as for the normal-appearing uninvolved skin. In this study, we focused on investigating the stratum corneum ceramides of the uninvolved skin in atopic dermatitis and psoriasis patients compared to healthy skin. The aim of the investigations was to explore possible significant and specific differences which can be accomplished for purposes of early diagnostics. The skin lipids were collected by means of an in vivo topical extraction procedure using an extraction mixture consisting of n-hexane and ethanol, (2:1). An automated multiple development-high performance thin layer chromatography (AMD-HPTLC) method with photodensitometric detection were applied to separate the ceramides and to estimate their contents. For studying their molecular profile within each ceramide class, a new method of normal phase HPLC with atmospheric pressure chemical ionization mass spectrometry were used. The results obtained by AMD-HPTLC exposed no significant alterations regarding the relative composition of the major stratum corneum lipids and primarily the ceramides. In addition, the mass spectrometric profiles within each ceramide class were similar in the patients and the healthy control subjects. In conclusion, this study revealed that the normal-appearing uninvolved skin of atopic dermatitis and psoriasis patients does not prove significant or specific deficiencies with respect to the free extractable major stratum corneum lipids and mainly the ceramides, when compared to healthy skin. Thus, they cannot be used for diagnostic purposes. Furthermore, our data are not consistent with the concept that impairments in the ceramide composition represent an obligate etiologic factor for both diseases.

Keratinocytes in atopic dermatitis: inflammatory signals

Atopic dermatitis (AD) is a chronic inflammatory skin disorder that usually predates the development of allergic airway disease. In most cases, this is thought to be an allergen-driven disease with prominent roles played by antigen presenting cells and effector Th2 cells. But keratinocytes, by virtue of their location, provide an important window to the environment and are also thought to contribute to the development of AD. In this review, we discuss several biologic attributes of keratinocytes that are relevant for AD: 1) intrinsic defects in barrier function, 2) production of inflammatory mediators that promote or maintain allergic inflammation, 3) keratinocyte apoptosis, 4) effects of staphylococcal toxins on keratinocytes, and 5) potential consequences of the expression of cosignaling molecules (eg, B7 family members) and receptors important for innate immune responses (eg, Toll receptors). Clearly, these findings have highlighted a more active role played by the epithelium than was previously recognized.

Stratum corneum pH in atopic dermatitis: impact on skin barrier function and colonization with Staphylococcus Aureus

Recent studies have provided new insights into the occurrence, causes, and pathogenetic consequences of changes in the skin pH in atopic dermatitis, particularly with respect to skin barrier function and colonization with Staphylococcus aureus. Growing evidence suggests an impaired release of proton donors, such as amino acids, urocanic acid, and lactic acid, to the stratum corneum in atopic dermatitis, as a result of reductions in filaggrin proteolysis and sweat secretion. In addition, an impaired formation of free fatty acids from sebaceous lipids and epidermal phospholipids seems to be involved. Because both lipid organization and lipid metabolism in the stratum corneum requires an acidic pH, these alterations might contribute to the disturbance of skin barrier function observed in atopic dermatitis. Furthermore, bacterial growth and virulence of S. aureus, as well as defensive host mechanisms, have increasingly been delineated as pH dependent, giving rise to a new understanding of the pathophysiology underlying increased skin colonization seen in atopic dermatitis.

Acylceramide Head Group Architecture Affects Lipid Organization in Synthetic Ceramide Mixtures

The lipid organization in the upper layer of the skin, the stratum corneum (SC), is important for the skin barrier function. This lipid organization, including the characteristic 13 nm lamellar phase, can be reproduced in vitro with mixtures based on cholesterol, free fatty acids and natural as well as synthetic ceramides (CER). In human SC, nine CER classes have been identified (CER1-CER9). Detailed studies on the effect of molecular structure of individual ceramides on the SC lipid organization are only possible with synthetic lipid mixtures, as their composition can be accurately chosen and systematically modified. In the present study, small-angle X-ray diffraction was used to examine the organization in synthetic lipid mixtures of which the synthetic ceramide fraction was prepared with sphingosine-based CER1 or phytosphingosine-based CER9. The latter acylceramide contains an additional hydroxyl group at the sphingoid backbone. The results show that a gradual increase in CER1 level consistently promotes the formation of the 13 nm lamellar phase and that partial replacement of CER1 by CER9 does not affect the phase behavior. Interestingly, complete substitution of CER1 with CER9 reduces the formation of the long periodicity phase and results in phase separation of CER9.

Analysis of epidermal lipids of the healthy human skin: factors affecting the design of a control population

The intervariability of studies on the lipids of human epidermis and stratum corneum is high because of the different origin of the skin samples and the variety of extraction methods used. In the present work, a high-performance thin-layer chromatographic technique has been used to study the parameters age, sex, and anatomical site for their effects on the lipid profiles recovered from healthy epidermal skin biopsy specimens. It was found that sex-related differences were seen at the level of the total ceramide concentration. Observed decreases in lipid concentration, due to ageing, depended on the anatomical site. Therefore, these variables should be controlled in a reproducible and standardized way in order to be able to study the direct relationship between skin condition and barrier lipid composition. Only when this relation is established, results of topical treatment can be scientifically evaluated.

Impaired sphingomyelinase activity and epidermal differentiation in atopic dermatitis

A defective permeability barrier leads to the penetration of environmental allergens into the skin and initiates immunological reactions and inflammation crucially involved in the pathogenesis of atopic dermatitis (AD). Decreased stratum corneum ceramide content may cause the defect in permeability barrier function consistently found in AD. Acid and neutral sphingomyelinase (A- and N-SMase) generate ceramides with structural and signal transduction functions in epidermal proliferation and differentiation. We determined epidermal SMase activities, DNA synthesis, involucrin, loricrin, filaggrin, and keratin expression in lesional and non-lesional skin of AD patients. We found decreased epidermal A-SMase activity in lesional and non-lesional skin, correlating with reduced stratum corneum ceramide content and disturbed barrier function. N-SMase activity was reduced in non-lesional skin and more significantly reduced in lesional skin, correlating with impaired expression of cornified envelope proteins and keratins, important for skin barrier function. Changes in involucrin, loricrin, filaggrin, keratin K 5 (basal) and K 16 (proliferation associated) were noticed in non-lesional and lesional skin, whereas changes in K 10 (suprabasal), K 6 (proliferation associated), and K 17 (inflammation associated) were found only in lesional skin. In summary, reduction in SMase-generating ceramides and impaired differentiation are involved in the defective barrier function found in AD.

Ratio of immature cornified envelopes does not correlate with parakeratosis in inflammatory skin disorders

We have previously established a non-invasive method to evaluate the maturity of cornified envelopes (CEs), and have reported the appearance of immature CEs in the stratum corneum (SC) with poor barrier function, such as the SC of the face. The purpose of the present study was to evaluate CEs in inflammatory skin disorders, and to clarify the relationship between the appearance of the immature CEs and parakeratosis, which is often used as a marker for defective keratinization in inflammatory skin disorders. Cornified envelopes in the outermost SC of involved areas of psoriasis vulgaris (PV) and atopic dermatitis (AD) were strikingly heterogeneous, and consisted of immature CEs stained with anti-involucrin and mature CEs stained with Nile red, whereas CEs of the uninvolved areas were relatively homogeneous, exhibiting mature phenotype. The ratio of immature CEs was significantly higher in the involved areas of PV and AD than that in the corresponding uninvolved areas, suggesting that defective CE maturation may, at least in part, account for the inflammatory disorders. Simultaneous evaluation of CE maturity and parakeratosis was carried out by a combination of involucrin immunostaining and nuclear staining of detergent-dissociated corneocytes. In the involved area of PV, four types of corneocytes in regard to the combination of involucrin staining and nuclear remnant were observed, while both immature CEs and parakeratosis were more often detected in the involved areas of PV than in the uninvolved areas or the upper arm of healthy subjects as a normal control. Thus, corneocytes with involucrin-positive immature CEs were not always associated with parakeratosis at the cellular level. In the involved areas of PV, the ratio of immature CEs and that of parakeratosis were heterogeneous, depending on the cases, and no correlation between the ratios was observed. Inter-individual and intraindividual variations in CE maturity were also suggested by the heterogeneous localization of involucrin in the psoriatic epidermis as examined by immunohistochemistry. In addition, in the face of healthy subjects, four types of corneocytes were similarly detected, and the ratio of immature CEs was significantly higher than that of parakeratosis. These results obviously suggest that the maturation of CEs and disappearance of nuclei are differentially regulated in the epidermis.

Effect of the lactic acid bacterium Streptococcus thermophilus on stratum corneum ceramide levels and signs and symptoms of atopic dermatitis patients

A reduced amount of total ceramides could be responsible for functional abnormalities of the skin of atopic dermatitis (AD) patients. The ability of an experimental cream containing sonicated Streptococcus thermophilus to increase skin ceramide levels in healthy subjects has been previously reported. The aim of the present work was to investigate the effects of the topical administration of a S. thermophilus-containing cream on ceramide levels of stratum corneum from AD patients. A 2-week application of the cream, containing a sonicated preparation of the lactic acid bacterium S. thermophilus, in the forearm skin of 11 patients led to a significant and relevant increase of skin ceramide amounts, which could have resulted from the sphingomyelin hydrolysis through the bacterial sphingomyelinase. Moreover, in all patients the topical application of our experimental cream also resulted in the improvement of the signs and symptoms characteristic of AD skin (i.e. erythema, scaling, pruritus).

Nicotinic acid/niacinamide and the skin

Nicotinic acid (also generally known as niacin) and niacinamide (also known as nicotinamide) are similarly effective as a vitamin because they can be converted into each other within the organism. The blanket term vitamin B(3) is used for both. Niacinamide is a component of important coenzymes involved in hydrogen transfer. Here, the two codehydrogenases, nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are of central importance. Topical application of niacinamide has a stabilizing effect on epidermal barrier function, seen as a reduction in transepidermal water loss and an improvement in the moisture content of the horny layer. Niacinamide leads to an increase in protein synthesis (e.g. keratin), has a stimulating effect on ceramide synthesis, speeds up the differentiation of keratinocytes, and raises intracellular NADP levels. In ageing skin, topical application of niacinamide improves the surface structure, smoothes out wrinkles and inhibits photocarcinogenesis. It is possible to demonstrate anti-inflammatory effects in acne, rosacea and nitrogen mustard-induced irritation. Because of its verifiable beneficial effects, niacinamide would be a suitable component in cosmetic products for use in disorders of epidermal barrier function, for ageing skin, for improving pigmentary disorders and for use on skin prone to acne.

The stratum corneum: structure and function in health and disease

Our understanding of the formation, structure, composition, and maturation of the stratum corneum (SC) has progressed enormously over the past 30 years. Today, there is a growing realization that this structure, while faithfully providing a truly magnificent barrier to water loss, is a unique, intricate biosensor that responds to environmental challenges and surface trauma by initiating a series of biologic processes which rapidly seek to repair the damage and restore barrier homeostasis. The detailed ultrastructural, biochemical, and molecular dissection of the classic "bricks and mortar" model of the SC has provided insights into the basis of dry, scaly skin disorders that range from the cosmetic problems of winter xerosis to severe conditions such as psoriasis. With this knowledge comes the promise of increasingly functional topical therapies.

The characterization of molecular organization of multilamellar emulsions containing pseudoceramide and type III synthetic ceramide

To investigate the molecular organization and phase behavior of physiologic lipid mixtures that contain either newly synthesized pseudoceramide or type III synthetic ceramide, various analytical techniques were used. The phase transition temperatures detected in differential scanning calorimetry analysis were 51.19 and 50.52 for the pseudoceramide-containing physiologic lipid mixture and synthetic type III ceramide-containing lipid mixture, respectively. From the small angle XRD patterns, the multilamellar emulsion-pseudoceramide showed 11.5 nm and 7.61 nm lamellar phases, while the multilamellar emulsion-synthetic ceramide showed only a 7.61 nm lamellar phase. The nonceramide containing lipid mixture did not show any distinct repeat pattern. Lateral packing distances of multilamellar emulsion-pseudoceramide and multilamellar emulsion-synthetic ceramide were measured as 0.4119 and 0.4110 nm at 30, respectively, which indicated the presence of hexagonal lattice. On the contrary, non-multilamellar emulsion did not show any definite repeat pattern. Transmission electron microscopy observation showed nearly comparable lamellar structures in all of the tested emulsions compared to the structure of human stratum corneum intercellular lipid. Decrease of water contents resulted in phase transition into liquid phase for all the tested emulsions, whereas phase transition into orthorhombic phase was observed only in multilamellar emulsion-pseudoceramide. From these results, we concluded that the molecular organization of multilamellar emulsion-pseudoceramide was characterized as the lateral hexagonal phase and both the long and short periodicity lamellar phases, which showed structural similarity with the native human stratum corneum intercellular lipid.

Stratum corneum lipid profile and maturation pattern of corneocytes in the outermost layer of fresh scars: the presence of immature corneocytes plays a much more important role in the barrier dysfunction than do changes in intercellular lipids

BACKGROUND

The functional characteristics of the stratum corneum (SC) of fresh scars as well as keloids and hypertrophic scars are characterized by elevated transepidermal water loss (TEWL) and increased SC hydration.

OBJECTIVES

To study the composition of the intercellular lipids and maturation properties of the cornified envelope (CE) of the SC, as these are the most important components for the SC barrier function in fresh scars.

METHODS

SC lipids were extracted from the donor site for split-thickness skin grafting soon after re-epithelialization using a cup method, and were analysed with high-performance thin-layer chromatography. CEs, which were prepared from superficial layers of the SC, were double stained with Nile red and anti-involucrin.

RESULTS

We found a significant decrease in the proportion of ceramide (CER) in the SC lipids of fresh scars. We also observed changes in the SC CER profile that consisted of an increase in CER 4 and CER 7 and a decrease in CER 3, without any significant change in the proportion of CER 1. These changes were insufficient to explain the remarkably high TEWL recorded in the early stage of fresh scars. In contrast, with double staining of CE with Nile red and anti-involucrin, we detected the presence of numerous immature and less hydrophobic corneocytes in the outermost layer of the SC of fresh scars. Scanning electron microscopy of such corneocytes revealed numerous fine wrinkles on their enlarged surface area. Most of all, we found a closely similar, time-dependent, exponential decrease in the ratio of immature corneocytes with a poorly hydrophobic CE and in the recorded TEWL values in fresh scars. There was a highly significant positive correlation between the proportion of immature corneocytes in the outermost layer of the SC and TEWL values.

CONCLUSIONS

These results suggest that the SC barrier dysfunction of the fresh scars is attributable to the presence of immature corneocytes with a less hydrophobic CE, rather than to the changes in SC lipid composition.

Isolation of ceramide fractions from skin sample by subcritical chromatography with packed silica and evaporative light scattering detection

Separative method of lipid classes from the stratum corneum was developed with packed silica and supercritical CO2 containing 10% of methanol at 15 degrees C, 15 MPa and 3 ml min(-1). The elution order of lipid classes was first esterified cholesterol, triglycerides, squalene co-eluted in a single peak, then free fatty acids, free cholesterol, ceramides and finally glycosylceramides. The ceramides were eluted in several fractions which depended on the number of hydroxyl groups in the molecule, i.e. more hydroxyl groups were contained in ceramides, more important was the retention. Moreover, the retention was not altered by the presence of carbon double bond and variation of the alkyl chain length. The ceramide response with the evaporative light scattering detector was improved by turning the influence of the solvent nature on the response to advantage. Therefore, addition of various solvents with or without triethylamine and formic acid were tested in post-column due to the incompatibility of such modifiers with silica stationary phase. Thereby the solvent conditions for the separation and the detection can be adjusted almost independently. The response was greatly increased by post-column addition of 1% (v/v) triethylamine and its equivalent amount of formic acid in dichloromethane introduced at 0.1 ml min(-1) into the mobile phase. This device had allowed the detection of 400 ng of ceramide with a S/N = 21, whereas no peak was observed in absence of the post-column addition. Finally, the method was applied to the treatment of skin sample which led to highly enriched ceramide fraction.

Sequence diversity of the intergenic spacer region of the rRNA gene of Malassezia globosa colonizing the skin of patients with atopic dermatitis and healthy individuals

The lipophilic yeast Malassezia globosa is one of the major constituents of the mycoflora of the skin of patients with atopic dermatitis (AD). We compared the genotypes of M. globosa colonizing the skin surface of 32 AD patients and 20 healthy individuals for polymorphism of the intergenic spacer (IGS) 1 region of the rRNA gene. Sequence analysis demonstrated that M. globosa was divided into four major groups, which corresponded to the sources of the samples, on the phylogenetic tree. Of the four groups, two were from AD patients and one was from healthy subjects. The remaining group included samples from both AD patients and healthy subjects. In addition, the IGS 1 region of M. globosa contained short sequence repeats: (CT)(n), and (GT)(n). The number of sequence repeats also differed between the IGS 1 of M. globosa from AD patients and that from healthy subjects. These findings suggest that a specific genotype of M. globosa may play a significant role in AD, although M. globosa commonly colonizes both AD patients and healthy subjects.

Conséquences fonctionnelles des perturbations des lipides cutanés

Epidermal lipids constitute an ultimate frontier between the organism and its environment. Their essential role consists of providing a barrier limiting both transepidermal water loss and penetration of external factors, such as irritants. Efficacy of the barrier depends on the physicochemical properties of the substance applied to the skin surface and the increase in transepidermal water loss, which may be quantified, is proportional to the provoked perturbation in the barrier function. In atopic dermatitis epidermis, a significant decrease in the ceramide content and abnormally low levels of omega-6 fatty acids correlate with an increased rate of water loss at the skin surface--a sign of an impaired barrier. However, similar signs are observed in the atrophic epidermis provoked by long term local corticotherapy. Epidermal lipid profiles are also seriously modified in various ichthyoses, and are partially responsible for the hyperkeratosis observed clinically, e.g.: the recessive X-linked form is provoked by a mutation of the steroid sulphatase gene and the resulting accumulation of unconverted precursor of cholesterol. Modification of the lipid composition in acne contributes to comedo formation, whereas UV improves barrier function (and may provoke hyperkeratosis) through an increase in the stratum corneum lipid content. Another source of lipids at the epidermal surface is sebaceous glands. Waxes present in the sebum increase friction coefficient of the skin surface. Sebum also influences (decreases) the rate of penetration of lipophilic substances applied on the skin. Its role in the skin biology appears to be less vital than that of the lipids constituting the permeability barrier of the stratum corneum.

Ceramides and skin function

Ceramides are the major lipid constituent of lamellar sheets present in the intercellular spaces of the stratum corneum. These lamellar sheets are thought to provide the barrier property of the epidermis. It is generally accepted that the intercellular lipid domain is composed of approximately equimolar concentrations of free fatty acids, cholesterol, and ceramides. Ceramides are a structurally heterogeneous and complex group of sphingolipids containing derivatives of sphingosine bases in amide linkage with a variety of fatty acids. Differences in chain length, type and extent of hydroxylation, saturation etc. are responsible for the heterogeneity of the epidermal sphingolipids. It is well known that ceramides play an essential role in structuring and maintaining the water permeability barrier function of the skin. In conjunction with the other stratum corneum lipids, they form ordered structures. An essential factor is the physical state of the lipid chains in the nonpolar regions of the bilayers. The stratum corneum intercellular lipid lamellae, the aliphatic chains in the ceramides and the fatty acids are mostly straight long-chain saturated compounds with a high melting point and a small polar head group. This means that at physiological temperatures, the lipid chains are mostly in a solid crystalline or gel state, which exhibits low lateral diffusional properties and is less permeable than the state of liquid crystalline membranes, which are present at higher temperatures. The link between skin disorders and changes in barrier lipid composition, especially in ceramides, is difficult to prove because of the many variables involved. However, most skin disorders that have a diminished barrier function present a decrease in total ceramide content with some differences in the ceramide pattern. Formulations containing lipids identical to those in skin and, in particular, some ceramide supplementation could improve disturbed skin conditions. Incomplete lipid mixtures yield abnormal lamellar body contents, and disorder intercellular lamellae, whereas complete lipid mixtures result in normal lamellar bodies and intercellular bilayers. The utilization of physiological lipids according to these parameters have potential as new forms of topical therapy for dermatoses. An alternative strategy to improving barrier function by topical application of the various mature lipid species is to enhance the natural lipid-synthetic capability of the epidermis through the topical delivery of lipid precursors.

Effects of prednisolone on the cutaneous reaction and skin barrier function in mice treated with a hapten

Glucocorticoids are effective drugs for the treatment of allergic skin diseases. In the present study, we observed the effects of prednisolone on the cutaneous reaction and skin barrier function in mice treated with a hapten, 2,4-dinitrofluorobenzene. Repeated hapten application onto the mouse ear resulted in a potent ear swelling with an elevation of specific serum IgE. The ear swelling appeared following the second application of the hapten and peaked at 24 h after each application. Specific serum IgE was detected first after the fourth hapten application. Topical treatment with prednisolone apparently suppressed the swelling, whereas it failed to affect the serum specific IgE level. The hapten application caused an increase in transepidermal water loss, which was potently inhibited by prednisolone, although the water content was not affected. Amounts of triglyceride and cholesterol in the ear skin increased after repeated hapten applications, whereas the relative amount of free fatty acid and ceramide diminished. Prednisolone exhibited an inhibitory effect on the changes in lipid content. Thus prednisolone apparently inhibits the alteration of skin barrier function caused by hapten application as well as the cutaneous reaction.

New acylceramide in native and reconstructed epidermis

Culturing of normal human keratinocytes at the air-liquid interface results in the formation of fully differentiated epidermis under in vitro conditions. Although the reconstructed epidermis shows a close resemblance to native tissue, there are still some differences in the stratum corneum lipid profile and intercellular lipid organization. As ceramides belong to one of the major stratum corneum lipid classes, the aim of this study was to characterize this fraction in more detail. For this purpose, individual ceramide fractions were isolated by column chromatography and characterized by a combination of nuclear magnetic resonance spectroscopy, high-performance thin-layer chromatography, and gas chromatography. The results of this study show that in both the native and reconstructed human epidermis the extractable ceramide fraction contains, in addition to the well known acylceramides (EOS, EOH), a new acylceramide in which the omega-O-acylhydroxyacid is amide-linked to phytosphingosine (EOP). The same three sphingoid base moieties (S, P, H) are also found in ceramides with amide-linked nonhydroxy and alpha-hydroxyacids. Whereas the same types of ceramides were present in both tissues, some differences in their fatty acid profiles have been found. In reconstructed epidermis the content of linoleic acid in all three acylceramides fraction was significantly lower; the ceramide(NS) fraction was enriched in short fatty acids and the ceramide(AS) fraction was enriched in long chain alpha-hydroxyacids. These differences together with a lower content of free fatty acids may explain the differences between native and reconstructed tissue in stratum corneum lipid organization observed earlier by X-ray diffraction.

[Effects of emulsions on the stratum corneum barrier and hydration]

The appearance of the skin depends greatly on the hydration of the stratum corneum which is regulated by water binding substances of the corneocytes and also by the quality of the stratum corneum lipids. Furthermore these lipids are responsible for the barrier function. In patients with atopic dermatitis, the water binding capacity and the barrier function of the stratum corneum are reduced even in clinically healthy skin areas. Emollients can damage the stratum corneum and lead to desiccation and a disturbance of the barrier. This effect is a result of an increased permeability of the barrier lipids and direct damage to the keratinocytes and corneocytes. The degree of damage of the barrier caused by emollients in dermatological vehicles has not been sufficiently investigated. As suggested by hypothetical considerations, such an effect is not expected and cannot be demonstrated in water-in-oil-emulsions. Oil-in-water-emulsions without glycerol as well as lipophilic and hydrophilic microemulsions do damage the barrier function. Both types of microemulsions additionally lead to a dehydration of the stratum corneum. The damaging effect of oil-in-water-emulsions can be reduced by the addition of glycerol and urea.

Gamma-linolenic acid in borage oil reverses epidermal hyperproliferation in guinea pigs

As dietary sources of gamma-linolenic acid [GLA; 18:3(n-6)], borage oil (BO; 24-25 g/100 g GLA) and evening primrose oil (PO; 8-10 g/100 g GLA) are efficacious in treating skin disorders. The triglycerol stereospecificity of these oils is distinct, with GLA being concentrated in the sn-2 position of BO and in the sn-3 position of PO. To determine whether the absolute level and/or the triglycerol stereospecificity of GLA in oils affect biological efficacy, epidermal hyperproliferation was induced in guinea pigs by a hydrogenated coconut oil (HCO) diet for 8 wk. Subsequently, guinea pigs were fed diets of PO, BO or a mixture of BO and safflower oil (SO) for 2 wk. The mixture of BO and SO (BS) diet had a similar level of GLA as PO but with sn-2 stereospecificity. As controls, two groups were fed SO and HCO for 10 wk. Epidermal hyperproliferation was reversed by all three oils in the order of BO > BS > PO. However, proliferation scores of group PO were higher than of the normal control group, SO. The accumulations of dihomo-gamma-linolenic acid [DGLA; 20:3(n-6)], an elongase product of GLA, into phospholipids and ceramides, of 15-hydroxyeicosatrienoic acid (15-HETrE), the potent antiproliferative metabolite of DGLA, and of ceramides, the major lipid maintaining epidermal barrier, in the epidermis of group BO were greater than of groups BS and PO. Group BS had higher levels of DGLA, 15-HETrE and ceramides than group PO. With primary dependence on absolute levels, our data demonstrate that the antiproliferative efficacy of GLA in the epidermis is preferably exerted from sn-2 stereospecificity of GLA in BO.

Implementation of fatty acid carriers to skin irritation and the epidermal barrier

Acute perturbations are followed by barrier repair and enhanced lipid synthesis, as well as cellular fatty acid trafficking, yet irritation of the skin may be induced by repeat disturbance of barrier function. Recently, new insights in cellular fatty acid transport and metabolism have evolved with respect to skin irritation and barrier disturbances: (1) Employing sodium dodecyl sulfate, skin irritation is accompanied by the induction of an epidermal (E) cytosolic fatty acid binding protein (FABP) associated with enhanced barrier repair. Whether E-FABP contributes to the water barrier function in normal skin remains to be elucidated; (2) Cutaneous inflammation, as it occurs in irritant contact dermatitis, can be reduced by peroxisome proliferating activated receptor (PPAR) agonists, such as linoleic acid, with clinical effects comparable to that of glucocorticoids; (3) PPARalpha agonists accelerate barrier recovery and enhance lamellar body synthesis, neutral lipid synthesis, in particular that of ceramides and cholesterol; (4) PPARalpha agonists increase the minimal erythema dose in UVB-irradiated human skin. This review provides a brief overview of the current understanding of mammalian fatty acid (FA) metabolism with respect to epidermal barrier abrogation and repair, including new insights into cellular FA transport and metabolism.

Efficacy of stratum corneum lipid supplementation on human skin

Recent studies suggest that supplementing intercellular lipids of the stratum corneum in ageing populations or in people with dry skin can stimulate the functioning of the skin. This work lends support to the reinforcement capacity of two different stratum corneum lipid mixtures (synthetic stratum corneum lipid mixtures, SSCL, and internal wool lipid extracts, IWL) formulated as liposomes on healthy skin of two differently aged groups of individuals. Protection of healthy skin against detergent-induced dermatitis was evaluated. Transepidermal water loss and capacitance were used to evaluate the effect of these formulations in in vivo long-term studies. Increase in water-holding capacity is obtained only when the formulations applied are structured as liposomes. This is slightly more pronounced for aged skin. Subsequent SLS exposure reflected the protection of healthy human skin against detergent-induced dermatitis. Slightly better results were obtained with IWL containing a mixture of natural ceramides than with SSCL with only one ceramide present in the formulation. All these results support the beneficial effects of skin lipid supplementation given their resemblance to the lipids in the stratum corneum both in composition and in the structuring of the formulation.

Cutaneous late phase reaction in adult atopic dermatitis patients with high serum IgE antibody to Dermatophagoides farinae: correlation with IL-5 production by allergen-stimulated peripheral blood mononuclear cells

It is known that, in patients of allergic asthma and rhinitis, the late-phase reaction (LPR) occurs 6-12 h after allergen challenge, but there are few reports concerning cytokine production in the cutaneous LPR in atopic dermatitis (AD). We report here the results of our study on the relationship between the cutaneous LPR and the production of cytokines such as IL-4, IL-5, IL-2 and IFN-gamma by peripheral blood mononuclear cells (PBMC) of AD patients. We selected 29 pure AD patients with no history of atopic airway diseases who showed high serum IgE antibody against Dermatophagoides farinae and performed skin prick testing with three different antigens and observed the resultant cutaneous reactions in 23 of the AD patients. Furthermore, we measured the cytokine production by the cultured PBMC under the stimulation of the antigens and compared it with the results of the skin tests. 13 (57%) of these 23 AD patients demonstrated positive LPR in response to D. farinae, and the mean concentration of IL-5 produced by PBMC was higher in these LPR-positive AD patients compared to the LPR-negative ones. Additionally, we noticed that there was a positive correlation between the mean diameter of the erythema of LPR and the level of IL-5 production by PBMC in the LPR-positive patients. We suggest that there are at least two groups in AD patients, i.e. LPR-positive and LPR-negative ones. The observation of LPR can be an important and practical way to classify AD patients into subgroups, which may enable us to regard IL-5 or eosinophils as a target for treatment.

Human epidermal glucosylceramides are major precursors of stratum corneum ceramides

Ceramides are the major component of the stratum corneum, accounting for 30%-40% of stratum corneum lipids by weight, and are composed of at least seven molecular groups (designated ceramides 1-7). Stratum corneum ceramides, together with cholesterol and fatty acids, form extracellular lamellae that are responsible for the epidermal permeability barrier. Previous studies indicated that beta-glucocerebrosidase- and sphingomyelinase-dependent ceramide production from glucosylceramides and sphingomyelins, respectively, is important for epidermal permeability barrier homeostasis. A recent study indicated that sphingomyelins are precursors of two stratum corneum ceramide molecular groups (ceramides 2 and 5). In this study, we have examined the role of glucosylceramides in the generation of each of the seven stratum corneum ceramide molecular groups. First, the structures of various glucosylceramide species in human epidermis were determined by gas chromatography-mass spectrometry, fast atom bombardment-mass spectrometry, and nuclear magnetic resonance. The results indicate that total epidermal glucosylceramides are composed of six distinct molecular groups, glucosylceramides 1-6. Glucosylceramide 1 contains sphingenine and nonhydroxy fatty acids, glucosylceramide 2, phytosphingosine and nonhydroxy fatty acids, glucosylceramide 3, phytosphingosine with one double bond and nonhydroxy fatty acids, glucosylceramide 4, sphingenine and alpha-hydroxy fatty acids, glucosylceramide 5, phytosphingosine and alpha-hydroxy fatty acids, and glucosylceramide 6, phytosphingosine with one double bond and alpha-hydroxy fatty acids. The nonhydroxy fatty acids typically have 16-24-carbon-length chains, whereas alpha-hydroxy fatty acids are limited to 24-, 25-, and 26-carbon chains. The sphingosine bases are C18 or C20 chains. Next, acylglucosylceramides and glucosylceramides were treated with beta-glucocerebrosidase and the ceramides released were compared with stratum corneum ceramides. Ceramide moieties of acylglucosylceramides and glucosylceramides 1, 2, 4-6 correspond to stratum corneum ceramides 1-7. These results, together with those of our previous reports characterizing epidermal sphingomyelins, indicate that all ceramide species, including omega-hydroxy fatty-acid-containing ceramides, are derived from glucosylceramides, and fractions of ceramides 2 and 5 are from sphingomyelins. Furthermore, structural analysis of glucosylceramides revealed that human epidermal glycosphingolipids display a unique lipid profile that is rich in very long chain hydroxylated (alpha- and omega-hydroxy) fatty acids and phytosphingosine.

Ceramide-dominant barrier repair lipids alleviate childhood atopic dermatitis: changes in barrier function provide a sensitive indicator of disease activity

BACKGROUND

It is currently fashionable to consider atopic dermatitis (AD), like other inflammatory dermatoses, as immunologic in pathogenesis ("inside-outside" hypothesis). Accordingly, topical glucocorticoids and other immunosuppressive agents are mainstays of therapy, but the risk of toxicity from these agents is not insignificant, particularly in children. Alternatively, because stratum corneum (SC) permeability barrier function is also abnormal in AD, it has been hypothesized that the barrier abnormality could drive disease activity. Yet commonly used emollients and moisturizers do not correct the SC ceramide deficiency, the putative cause of the barrier abnormality.

OBJECTIVES

We assessed the efficacy of a newly developed, ceramide-dominant, physiologic lipid-based emollient, when substituted for currently used moisturizers, in 24 children who were also receiving standard therapy for stubborn-to-recalcitrant AD.

METHODS

All subjects continued prior therapy (eg, topical tacrolimus or corticosteroids), only substituting the barrier repair emollient for their prior moisturizer. Follow-up evaluations, which included severity scoring of atopic dermatitis (SCORAD) values and several biophysical measures of SC function, were performed every 3 weeks for 20 to 21 weeks.

RESULTS

SCORAD values improved significantly in 22 of 24 patients by 3 weeks, with further progressive improvement in all patients between 6 and 20 or 21 weeks. Transepidermal water loss levels (TEWL), which were elevated over involved and uninvolved areas at entry, decreased in parallel with SCORAD scores and continued to decline even after SCORAD scores plateaued. Both SC integrity (cohesion) and hydration also improved slowly but significantly during therapy. Finally, the ultrastructure of the SC, treated with ceramide-dominant emollient, revealed extracellular lamellar membranes, which were largely absent in baseline SC samples.

CONCLUSION

These studies suggest that (1) a ceramide-dominant, barrier repair emollient represents a safe, useful adjunct to the treatment of childhood AD and (2) TEWL is at least as sensitive an indicator of fluctuations in AD disease activity as are SCORAD values. These studies support the outside-inside hypothesis as a component of pathogenesis in AD and other inflammatory dermatoses that are accompanied by a barrier abnormality.