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

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

皮肤屏障功能研究进展

皮肤屏障主要由角化包膜和脂质膜、中间丝聚合蛋白、角蛋白、角化桥粒、板层小体和角质层角质形成细胞问质、紧密连接等组成,防止水分的丢失及阻止外界的侵害,维持机体内稳态.基因突变、变应原、微生物、紫外线等因素共同作用下,能导致皮肤屏障结构、代谢及功能的异常,引起鱼鳞病、特应性皮炎等皮肤病.阐明皮肤病与屏障结构及功能异常联系,指导开发有效的诊疗和预防措施.     

特应性皮炎动物模型表皮脂合成的研究

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

Efficacy of crisis intervention treatment with topical corticosteroid prednicarbat with and without partial wet-wrap dressing in atopic dermatitis

BACKGROUND: The wet-wrap treatment has been reported to be beneficial in acute episodes of atopic dermatitis (AD) skin lesions. OBJECTIVE: The efficacy of topical corticosteroid prednicarbat with and without additional wet-wrap dressing was investigated in a prospective, randomized and controlled study. METHODS: In the left-right comparison study, 24 adults and children with an acute episode of AD were included. One arm or leg was randomly treated with the topical corticosteroid prednicarbat plus wet-wrap dressing; only prednicarbat was applied on the leg or arm of the other side. RESULTS: After 48-72 h of treatment, in both groups an improvement of the local SCORAD was observed. In comparison to the side of the body treated with corticosteroid alone, the decrease of the local SCORAD in the corticosteroid plus wet-wrap dressing group was significantly better. The severity of AD improved in the wet-wrap group at an average of 4.4 points, in the corticosteroid group 3.0 (p<0.011). CONCLUSIONS: Wet-wrap therapy with a topical corticosteroid is an effective treatment option in patients with exacerbated AD. The treatment is helpful in improving skin conditions, shortening the time of corticosteroid application.     

The water content of the stratum corneum in patients with atopic dermatitis. Measurement with the Corneometer CM 420

The dry looking skin seen in many patients with atopic dermatitis reflects a defect in the epidermal barrier, the stratum corneum, as demonstrated by an increased transepidermal water loss (TEWL) and a decreased ability of the stratum corneum to bind water. The absolute amount of water within the stratum corneum is of importance both for barrier properties and for the clinical appearance of the skin. This water content was measured with a new instrument, the Corneometer CM 420, which takes advantage of the high dielectric constant of water. Forty patients with atopic dermatitis were studied--20 with dry skin and 20 with clinically normal skin on non-eczematous areas. The stratum corneum in dry skin was found to have a lower content of water than that in the clinically normal skin (p less than 0.01). Clinically normal skin in patients with atopic dermatitis did not differ significantly from normal control skin. An experiment was performed in vitro in an attempt to correlate the values obtained with the Corneometer to the absolute amount of water within the corneum.     

Pathogenesis of the permeability barrier abnormality in epidermolytic hyperkeratosis

Epidermolytic hyperkeratosis is a dominantly inherited ichthyosis, frequently associated with mutations in keratin 1 or 10 that result in disruption of the keratin filament cytoskeleton leading to keratinocyte fragility. In addition to blistering and a severe disorder of cornification, patients typically display an abnormality in permeability barrier function. The nature and pathogenesis of the barrier abnormality in epidermolytic hyperkeratosis are unknown, however. We assessed here, first, baseline transepidermal water loss and barrier recovery kinetics in patients with epidermolytic hyperkeratosis. Whereas baseline transepidermal water loss rates were elevated by approximately 3-fold, recovery rates were faster in epidermolytic hyperkeratosis than in age-matched controls. Electron microscopy showed no defect in either the cornified envelope or the adjacent cornified-bound lipid envelope, i.e., a corneocyte scaffold abnormality does not explain the barrier abnormality. Using the water-soluble tracer, colloidal lanthanum, there was no evidence of tracer accumulation in corneocytes, despite the fragility of nucleated keratinocytes. Instead, tracer, which was excluded in normal skin, moved through the extracellular stratum corneum domains. Increasing intercellular permeability correlated with decreased quantities and defective organization of extracellular lamellar bilayers. The decreased lamellar material, in turn, could be attributed to incompletely secreted lamellar bodies within granular cells, demonstrable not only by several morphologic findings, but also by decreased delivery of a lamellar body content marker, acid lipase, to the stratum corneum interstices. Yet, after acute barrier disruption a rapid release of preformed lamellar body contents was observed together with increased organelle contents in the extracellular spaces, accounting for the accelerated recovery kinetics in epidermolytic hyperkeratosis. Accelerated recovery, in turn, correlated with a restoration in calcium in outer stratum granulosum cells in epidermolytic hyperkeratosis after barrier disruption. Thus, the baseline permeability barrier abnormality in epidermolytic hyperkeratosis can be attributed to abnormal lamellar body secretion, rather than to corneocyte fragility or an abnormal cornified envelope/cornified-bound lipid envelope scaffold, a defect that can be overcome by external applications of stimuli for barrier repair.     

Stratum corneum and nail lipids in patients with atopic dermatitis. Decrease in ceramides--a pathogenetic factor in atopic xerosis?

Dry skin is seen in many patients with atopic dermatitis and correlates with a disturbed epidermal barrier function demonstrated by such features as increased transepidermal water loss and diminished stratum corneum hydration. With regard to the importance of stratum corneum lipids for the permeability barrier, we have analysed plantar (n = 8) and lumbar (n = 20) stratum corneum and nail lipids (n = 15) of atopic subjects by high-performance thin-layer chromatography (HPTLC). Compared with controls our investigations show a decrease in the ceramide fraction as a percentage of total lipid and a diminished ratio of ceramides and free sterols in atopic subjects. This implies that impaired ceramide synthesis may be a factor in the pathogenesis of atopic xerosis.     

Dietary constituents are able to play a beneficial role in canine epidermal barrier function

Epidermal barrier function is a critical attribute of mammalian skin. The barrier is responsible for preventing skin-associated pathologies through controlling egress of water and preventing ingress of environmental agents. Maintaining the quality and integrity of the epidermal barrier is therefore of considerable importance. Structurally, the barrier is composed of two main parts, the corneocytes and the intercellular lamellar lipid. The epidermal lamellar lipid comprises mainly ceramides, sterols and fatty acids. Twenty-seven nutritional components were screened for their ability to upregulate epidermal lipid synthesis. Seven of the 27 nutritional components (pantothenate, choline, nicotinamide, histidine, proline, pyridoxine and inositol) were subsequently retested using an in vitro transepidermal diffusion experimental model, providing a functional assessment of barrier properties. Ultimately, the best performing five nutrients were fed to dogs at supplemented concentrations in a 12-week feeding study. Barrier function was measured using transepidermal water loss (TEWL). It was found that a combination of pantothenate, choline, nicotinamide, histidine and inositol, when fed at supplemented concentrations, was able to significantly reduce TEWL in dogs after 9 weeks.     

Skin barrier function in patients with completely healed atopic dermatitis

Although it has been well established that the dry skin often seen in patients with atopic dermatitis shows a deranged barrier function, there is no unanimity of opinion as to whether the barrier in normal-appearing skin of patients with the disease is deranged or not. Hence, it remains unclear whether individuals with atopic dermatitis constitution have an intrinsic derangement of skin barrier function or not. To settle this problem, in the present study we examined transepidermal water loss and stratum corneum water content in normal appearing skin of the upper back of 16 patients with completely healed atopic dermatitis who had been free from skin symptoms for 5 years or more, 30 patients with active atopic dermatitis, and 39 healthy subjects. The transepidermal water loss values and the stratum corneum water content values in normal-appearing skin of the completely healed patients were not different from the values in normal controls. These findings indicate that skin barrier function is not disturbed in patients with completely healed atopic dermatitis.     

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.     

Role of the epidermal barrier in atopic dermatitis

The skin's permeability barrier protects against extensive water loss and prevents the entry into the skin of harmful substances like irritants, allergens and microorganisms. The permeability barrier is mainly located in the stratum corneum and consists of corneocytes and a lipid‐enriched intercellular domain. The barrier is formed during epidermal differentiation. In atopic dermatitis the skin barrier is disturbed already in non‐lesional skin. The disturbed skin barrier allows the entry of environmental allergens from house dust mites, animal dander and grass pollen into the skin. In predisposed individuals these allergens may trigger via immunologic pathways the inflammation of atopy. The causes for the disturbed epidermal skin barrier are changes in skin lipids and in epidermal differentiation, in particular filaggrin mutations. Filaggrin mutations lead to a disturbed skin barrier and dry skin which are hallmarks in atopic dermatitis. Therapeutic agents influence the skin barrier differently; topical therapy with potent corticosteroids does not lead to the repair of the barrier in atopic dermatitis, whereas therapy with the calcineurin inhibitors and lipid‐containing emulsions support barrier repair.     

Ultraviolet B-induced alterations of the skin barrier and epidermal calcium gradient

Ultraviolet irradiation induces a variety of cutaneous changes, including epidermal permeability barrier disruption. In the present study, we assessed the effects of ultraviolet B (UVB) irradiation in epidermal barrier function and calcium distribution in murine epidermis. Adult hairless mice were exposed to a single dose of UVB (0.15 J/cm(2)). Barrier function was evaluated by transepidermal water loss (TEWL), lanthanum perfusion. The morphological alterations were examined by histology, immunohistochemistry and electron microscopy using ruthenium tetroxide (RuO(4)) postfixation. For evaluation of the effect on epidermal calcium distribution, the ion-capture cytochemistry was employed. UVB irradiation caused a significant increase in TEWL, which peaked at day 4. In parallel, the increased number of sunburn cells and the changes in epidermal hyperplasia and proliferation were observed. Electron microscopic observation demonstrated that the water-soluble lanthanum tracer was present in the extracellular stratum corneum domains, and the increased intercellular permeability was correlated with defective organization of the extracellular lipid lamellar bilayers of the stratum corneum. Moreover, UVB irradiation also caused an appearance of calcium precipitates in the stratum corneum and transitional cell layers as well as the increased cytosolic calcium in the lower epidermis, reflecting the alterations of the epidermal calcium gradient. These results suggest that the changes of the epidermal calcium distribution pattern may correlate with the perturbation of the epidermal barrier induced by UVB irradiation.     

Transepidermal water loss in dry and clinically normal skin in patients with atopic dermatitis

To obtain data on the function of the epidermal barrier in patients with atopic dermatitis (AD) the transepidermal water loss (TEWL) was studied. Measurements were made on three body locations in two clinically well defined groups of patients with AD and in a control group. The TEWL was found to be increased both in dry non-eczematous skin and in clinically normal skin in patients with AD. The TEWL was highest in patients with dry skin. The result of the study may indicate a primary defect in the epidermal barrier: the stratum corneum.     

Development of atopic dermatitis in mice transgenic for human apolipoprotein C1

Mice with transgenic expression of human apolipoprotein C1 (APOC1) in liver and skin have strongly increased serum levels of cholesterol, triglycerides, and free fatty acids, indicative of a disturbed lipid metabolism. Importantly, these mice display a disturbed skin barrier function, evident from increased transepidermal water loss, and spontaneously develop symptoms of dermatitis including scaling, lichenification, excoriations, and pruritus. Histological analysis shows increased epidermal thickening and spongiosis in conjunction with elevated numbers of inflammatory cells (eosinophils, neutrophils, mast cells, macrophages, and CD4+ T cells) in the dermis. In addition, affected mice have increased serum levels of IgE and show abundant IgE(+) mast cells in the dermis. Partial inhibition of disease could be achieved by restoration of the skin barrier function with topical application of a lipophilic ointment. Furthermore, the development of atopic dermatitis in these mice was suppressed by corticosteroid treatment. These findings in APOC1(+/+) mice underscore the role of skin barrier integrity in the pathogenesis of atopic dermatitis.     

Topical steroids under wet-wrap dressings in atopic dermatitis--a vehicle-controlled trial

BACKGROUND: The wet-wrap dressing technique has proved to be beneficial in cases of exacerbated atopic dermatitis (AD) skin lesions. OBJECTIVE: The effect of wet-wrap dressings was investigated in a controlled trial comparing a steroid (mometasone furoate 0.1%)-containing and a steroid-free (vehicle) preparation in an in-patient comparison study. METHODS: 20 children aged 2-17 years with exacerbated AD were treated twice daily with wet-wrap dressings over a 5-day period. RESULTS: AD in treated areas significantly improved in both study arms; however, the effect was significantly better in the mometasone-treated group (p < 0.01). Transepidermal water loss improved in both arms without any significant differences. Staphylococcus aureus colonization decreased during the first 3 days of active treatment independently of the therapeutic modalities chosen. At day 5, colony counts further dropped on the steroid-treated lesions. CONCLUSION: Application of the wet-wrap dressing technique for exacerbated AD lesions is effective, combination with a topical steroid being superior to a steroid-free application without bearing the risk of a bacterial superinfection.     

Structural and functional effects of oleic acid and iontophoresis on hairless mouse stratum corneum

The aim of this study was to assess the effects of chemical and electrical modes of percutaneous penetration enhancement on the intercellular lipid lamellae of the stratum corneum. Hairless mice were treated with either oleic acid/propylene glycol and iontophoresis separately or together. Permeability barrier function was evaluated by measuring transepidermal water loss and correlated with the structure of stratum corneum intercellular lamellae, as evaluated by electron microscopy, using ruthenium tetroxide postfixation. Transepidermal water loss levels did not change following 1 h iontophoresis alone. In contrast, topical applications of 0.3 M oleic acid in propylene glycol for 1 h increased transepidermal water loss significantly. Moreover, the combined use of iontophoresis plus 0.3 M oleic acid for 1 h further increased transepidermal water loss at equivalent time points. Ultrastructural observations demonstrated both marked disorganization of the intercellular lipid lamellae, as well as the presence of distended lacunae within the stratum corneum in oleic acid/propylene glycol plus or minus iontophoresis-treated stratum corneum. This study provides direct evidence that the oleic acid/propylene glycol system can disrupt the stratum corneum lipid lamellar structures, and that coapplications of oleic acid with iontophoresis further enhance the effects of oleic acid. The synergy between chemical and physical enhancement may afford a new approach to promote transdermal drug delivery.     

Impairment of skin barrier function is not inherent in atopic dermatitis patients: a prospective study conducted in newborns

We conducted a cohort study to determine whether the barrier dysfunction of the stratum corneum that facilitates the penetration of various exacerbating agents from the environment is inherent in atopic dermatitis patients as suggested by some dermatologists. Clinical observation and biophysical measurements of the skin were performed on the cheek and on the flexor forearm of 24 newborn infants once between 2 and 14 days postnatally and 1, 3, and 6 months later. Nineteen had atopic family histories. Most of the infants had physiologic neonatal xerosis that was observed as a reduced high-frequency conductance without any impairment in the stratum corneum barrier function assessed by transepidermal water loss. Four of the 24 neonates developed atopic dermatitis around 2 to 3 months after birth. In all of them, barrier impairment noted as increased transepidermal water loss was observed only after the development of skin lesions. During their neonatal period, their transepidermal water loss and skin surface hydration state were indistinguishable from those of the neonates whose skin remained lesion-free during the observation period. Therefore, we concluded that the barrier impairment found in atopic dermatitis is not inherent but represents a phenomenon secondary to dermatitic skin changes.     

The skin: an indispensable barrier

Abstract: The skin forms an effective barrier between the organism and the environment preventing invasion of pathogens and fending off chemical and physical assaults, as well as the unregulated loss of water and solutes. In this review we provide an overview of several components of the physical barrier, explaining how barrier function is regulated and altered in dermatoses. The physical barrier is mainly localized in the stratum corneum (SC) and consists of protein‐enriched cells (corneocytes with cornified envelope and cytoskeletal elements, as well as corneodesmosomes) and lipid‐enriched intercellular domains. The nucleated epidermis also contributes to the barrier through tight, gap and adherens junctions, as well as through desmosomes and cytoskeletal elements. During epidermal differentiation lipids are synthesized in the keratinocytes and extruded into the extracellular domains, where they form extracellular lipid‐enriched layers. The cornified cell envelope, a tough protein/lipid polymer structure, resides below the cytoplasmic membrane on the exterior of the corneocytes. Ceramides A and B are covalently bound to cornified envelope proteins and form the backbone for the subsequent addition of free ceramides, free fatty acids and cholesterol in the SC. Filaggrin is cross‐linked to the cornified envelope and aggregates keratin filaments into macrofibrils. Formation and maintenance of barrier function is influenced by cytokines, 3′,5′‐cyclic adenosine monophosphate and calcium. Changes in epidermal differentiation and lipid composition lead to a disturbed skin barrier, which allows the entry of environmental allergens, immunological reaction and inflammation in atopic dermatitis. A disturbed skin barrier is important for the pathogenesis of contact dermatitis, ichthyosis, psoriasis and atopic dermatitis.     

Dry skin, barrier function, and irritant contact dermatitis in the elderly

Dry skin is characterized by a decreased lipid content and a delayed reconstitution of the epidermal barrier after skin irritation. These are problems of high relevance in the aged population, especially in the development of irritant contact dermatitis. Asteatotic and perineal irritant dermatitis are the most important subtypes of irritant contact dermatitis in the elderly. This contribution presents a compressed survey on these subtypes and elucidates their relation to an impaired barrier function. Typical irritants affecting aged individuals are explained and compared with irritants that seem to be more significant in younger people. Results of biophysical investigations, such as measurement of transepidermal water loss, are discussed regarding their age-dependence. Transepidermal water loss decreases with age, which was formerly interpreted as an indication of a decreased sensitivity. Today, we know that reconstitution of the epidermal barrier after irritation is delayed once it has been impaired. Reasons are decreased activities of enzymes involved in lipid synthesis and processing, a changed cytokine profile, a reduced acidification of aged skin, and alterations in the function of epidermal stem cells. Owing to these new insights, a reevaluation of the sensitivity of aged skin has to be initiated, especially with regard to occupational dermatology.     

Stimulation of epidermal calcium gradient loss and increase in TNF-alpha and IL-1alpha expressions by glycolic acid in murine epidermis

In a previous study, we reported that alpha-hydroxy acids (AHA), such as glycolic acid and lactic acid, did not induce any significant changes in transepidermal water loss for normal murine skin. The ultrastructural observations, however, showed that the extent of lamellar body exocytosis significantly increased. Because AHA can theoretically decrease the calcium ion concentration by chelation, topical AHA may induce the loss of epidermal calcium gradient by lowering the calcium ion concentration in the granulocytes and, subsequently, induce lamellar body secretion. The aim of this study is to verify that glycolic acid could modulate the epidermal calcium gradient and increase lamellar body exocytosis. Seventy per cent of glycolic acid aqueous solution was applied to the normal skin of hairless mice and biochemical and morphological studies were performed. The loss of epidermal calcium gradient was observed in glycolic-acid-applied skin of hairless mice and subsequent barrier function recovery processes, such as an increase in lamellar body secretion, were observed. The extracellular glycolic acid was found to inhibit the change in intracellular calcium ion concentration in response to extracellular calcium ion concentration changes in the cultured mouse keratinocyte in vitro. The protein and mRNA expressions of tumour necrosis factor-alpha and interleukin-1alpha in the murine epidermis were significantly increased after glycolic acid application. An in vitro study using cultured keratinocytes suggested that glycolic acid could lower the calcium ion concentration, at least in part, through the chelating effects of the glycolic acid on the cationic ions.