Cutaneous barrier repair and pathophysiology following barrier disruption in IL-1 and TNF type I receptor deficient mice

Isosorbide Fatty Acid Diesters Have Synergistic Anti-Inflammatory Effects in Cytokine-Induced Tissue Culture Models of Atopic Dermatitis

Atopic dermatitis (AD) is a chronic disease in which epidermal barrier disruption triggers Th2-mediated eruption of eczematous lesions. Topical emollients are a cornerstone of chronic management. This study evaluated efficacy of two plant-derived oil derivatives, isosorbide di-(linoleate/oleate) (IDL) and isosorbide dicaprylate (IDC), using AD-like tissue culture models. Treatment of reconstituted human epidermis with cytokine cocktail (IL-4 + IL-13 + TNF-α + IL-31) compromised the epidermal barrier, but this was prevented by co-treatment with IDL and IDC. Cytokine stimulation also dysregulated expression of keratinocyte (KC) differentiation genes whereas treatment with IDC or IDL + IDC up-regulated genes associated with early (but not late) KC differentiation. Although neither IDL nor IDC inhibited Th2 cytokine responses, both compounds repressed TNF-α-induced genes and IDL + IDC led to synergistic down-regulation of inflammatory (IL1B, ITGA5) and neurogenic pruritus (TRPA1) mediators. Treatment of cytokine-stimulated skin explants with IDC decreased lactate dehydrogenase (LDH) secretion by more than 50% (more than observed with cyclosporine) and in vitro LDH activity was inhibited by IDL and IDC. These results demonstrate anti-inflammatory mechanisms of isosorbide fatty acid diesters in AD-like skin models. Our findings highlight the multifunctional potential of plant oil derivatives as topical ingredients and support studies of IDL and IDC as therapeutic candidates.

In vivo imaging demonstrates ATP release from murine keratinocytes and its involvement in cutaneous inflammation after tape stripping

Adenosine 5'-triphosphate (ATP) release from keratinocytes has been observed in various stress models in vitro, but studies demonstrating epidermal ATP release in vivo are limited. To visualize extracellular ATP (eATP) in vivo, we developed enhanced green-emitting luciferase immobilized on agarose beads (Eluc-agarose). Subcutaneous injection of Eluc-agarose together with ATP into the dorsal skin of BALB/c mice following intraperitoneal luciferin injection produced detectable and measurable bioluminescence using an in vivo imaging system. Using Eluc-agarose, we demonstrated in vivo that bright bioluminescence was observed from 1 to 20 minutes after repeated tape stripping of murine skin. This bioluminescence was suppressed by the local administration of apyrase. Eluc-agarose bioluminescence was observed only in tape-stripped skin with transepidermal water loss (TEWL) between 100 and 140 g m(2) h(-1), indicating a loss of bioluminescence with excessive tape stripping (TEWL>140 g m(-2) h(-1)). Histologically, tape-stripped skin with detectable eATP had a viable epidermis and a subepidermal neutrophil infiltrate, and administration of apyrase reduced the inflammatory infiltrate. Neither a viable epidermis nor an upper dermal neutrophil infiltrate was observed after excessive tape stripping. These results suggest that tape stripping prompts ATP release from viable keratinocytes, which facilitates inflammatory cell migration. Eluc-agarose may be useful in the in vivo detection of eATP in murine models of skin diseases.

The role of the epidermis and the mechanism of action of occlusive dressings in scarring

The problem of cutaneous scarring has conventionally been approached as a pathology of the dermis. Multiple lines of evidence from the clinic, in vitro experiments, and in vivo animal and human studies, however, increasingly suggest that the epidermis plays a major role in the control of underlying dermal scar. Building on the demonstrated efficacy of silicone gel occlusion, in this paper we review the evidence for epidermal regulation of scar, and propose the novel hypothesis that dermal fibrosis is exquisitely linked to the inflammatory state of the epidermis, which in turn is linked to hydration state as a function of epidermal barrier function. In the spectrum of factors contributing to dermal scar, the epidermis and its downstream effectors offer promising new targets for the development of antiscar therapies.

The role of CD44 in cutaneous inflammation

CD44 is a transmembrane glycoprotein expressed in various tissues including the skin. Previous studies indicated that CD44 is required for epidermal permeability barrier homeostasis and keratinocyte differentiation. Yet, while some studies have demonstrated that CD44 is critical for the development of inflammation, others have shown that CD44 is not essential for the development of cutaneous inflammation. In this study, we evaluated the changes in epidermal CD44 expression in a variety of skin inflammatory models and determined whether CD44 is required for the development of cutaneous inflammation. Inflammatory responses were compared in CD44 KO versus wild-type mice in acute models of irritant and allergic contact dermatitis, as well as in a subacute allergic contact dermatitis induced by repeated hapten treatment. Inflammatory responses were assessed by measuring ear thickness and epidermal hyperplasia in haematoxylin & eosin-stained sections. Our results demonstrate that: (i) epidermal CD44 expression increases in both acute and subacute cutaneous inflammatory models; and (ii) acute disruption of the epidermal permeability barrier function increases epidermal CD44 expression. Whereas inflammatory responses did not differ between CD44 KO and wild-type mice in acute models of irritant and allergic contact dermatitis, both inflammatory responses and epidermal hyperplasia increased in CD44 KO mice following repeated hapten challenges. These results show first, that permeability barrier disruption and inflammation stimulate epidermal CD44 expression, and second, that CD44 modulates epidermal proliferation and inflammatory responses in a subacute murine allergic contact dermatitis model.

Epidermal vascular endothelial growth factor production is required for permeability barrier homeostasis, dermal angiogenesis, and the development of epidermal hyperplasia: implications for the pathogenesis of psoriasis

Primary abnormalities in permeability barrier function appear to underlie atopic dermatitis and epidermal trauma; a concomitant barrier dysfunction could also drive other inflammatory dermatoses, including psoriasis. Central to this outside-inside view of disease pathogenesis is the epidermal generation of cytokines/growth factors, which in turn signal downstream epidermal repair mechanisms. Yet, this cascade, if sustained, signals downstream epidermal hyperplasia and inflammation. We found here that acute barrier disruption rapidly stimulates mRNA and protein expression of epidermal vascular endothelial growth factor-A (VEGF-A) in normal hairless mice, a specific response to permeability barrier requirements because up-regulation is blocked by application of a vapor-impermeable membrane. Moreover, epidermal vegf(-/-) mice display abnormal permeability barrier homeostasis, attributable to decreased VEGF signaling of epidermal lamellar body production; a paucity of dermal capillaries with reduced vascular permeability; and neither angiogenesis nor epidermal hyperplasia in response to repeated tape stripping (a model of psoriasiform hyperplasia). These results support a central role for epidermal VEGF in the maintenance of epidermal permeability barrier homeostasis and a link between epidermal VEGF production and both dermal angiogenesis and the development of epidermal hyperplasia. Because psoriasis is commonly induced by external trauma [isomorphic (Koebner) phenomenon] and is associated with a prominent permeability barrier abnormality, excess VEGF production, prominent angiogenesis, and epidermal hyperplasia, these results could provide a potential outside-inside mechanistic basis for the development of psoriasis.

Thematic review series: skin lipids. The role of epidermal lipids in cutaneous permeability barrier homeostasis

The permeability barrier is required for terrestrial life and is localized to the stratum corneum, where extracellular lipid membranes inhibit water movement. The lipids that constitute the extracellular matrix have a unique composition and are 50% ceramides, 25% cholesterol, and 15% free fatty acids. Essential fatty acid deficiency results in abnormalities in stratum corneum structure function. The lipids are delivered to the extracellular space by the secretion of lamellar bodies, which contain phospholipids, glucosylceramides, sphingomyelin, cholesterol, and enzymes. In the extracellular space, the lamellar body lipids are metabolized by enzymes to the lipids that form the lamellar membranes. The lipids contained in the lamellar bodies are derived from both epidermal lipid synthesis and extracutaneous sources. Inhibition of cholesterol, fatty acid, ceramide, or glucosylceramide synthesis adversely affects lamellar body formation, thereby impairing barrier homeostasis. Studies have further shown that the elongation and desaturation of fatty acids is also required for barrier homeostasis. The mechanisms that mediate the uptake of extracutaneous lipids by the epidermis are unknown, but keratinocytes express LDL and scavenger receptor class B type 1, fatty acid transport proteins, and CD36. Topical application of physiologic lipids can improve permeability barrier homeostasis and has been useful in the treatment of cutaneous disorders.

The regulation of permeability barrier homeostasis

Disruption of the permeability barrier stimulates a repair response that leads to the restoration of barrier function. Previous studies demonstrated that changes in ions, particularly calcium, and cytokines are positive signals, whereas serine protease activation of proteinase-activated receptor 2 is a negative signal regulating barrier recovery. Ikeyama and colleagues provide data that the nitric oxide signaling pathway also regulates barrier homeostasis.

Interdigital lesions and frequency of acute dermatolymphangioadenitis in lymphoedema in a filariasis-endemic area

BACKGROUND

Lymphatic filariasis (LF) is a mosquito-borne nematode infection that causes permanent lymphatic dysfunction in virtually all infected individuals and clinical disease in a subset of these. One major sequel of infection is lymphoedema of the limbs. Lymphoedema of the leg affects an estimated 15 million persons in LF-endemic areas worldwide. Acute dermatolymphangioadenitis (ADLA) in people with filarial lymphoedema causes acute morbidity and increasingly severe lymphoedema. Episodes of ADLA are believed to be caused by bacteria, and it has been shown that entry lesions in the skin play a causative role. Clinical observations suggest that interdigital skin lesions of the feet, often assumed to be fungal, may be of particular importance.

OBJECTIVES

To investigate the epidemiology and aetiology of interdigital lesions (IDL) of the feet in filarial lymphoedema.

METHODS

The frequency and mycological aetiology of IDL in 73 patients with filarial lymphoedema were compared with 74 individuals without lymphoedema in a region of Guyana highly endemic for Wuchereria bancrofti.

RESULTS

More than 50% of patients with lymphoedema had one or more IDL (odds ratio 2.69; 95% confidence interval 1.31-5.66; P<0.005 compared with controls). The number of lesions was the strongest predictor of frequency of ADLA. Only 18% of the lesions had positive microscopy or culture for fungi (dermatophytes and Scytalidium).

CONCLUSIONS

These findings highlight the importance of interdigital entry lesions as risk factors for episodes of ADLA and have implications for the control of morbidity from filarial lymphoedema.

Common denominators for the low-cost management of leg conditions

Diseases of blood supply and drainage of the leg are common, and they frequently contribute to poverty. Management must include self-help low-cost therapy. The phlebologist, lymphologist, angiologist, or dermatologist must seek to distill their knowledge for the health worker in the general health services. Such knowledge should focus on the venous system, which is amenable to simple maneuvers such as breathing, elevation, and movement. However, the mechanisms underlying the functions of the blood vessels and lymphatics and the organ they supply or drain are inextricably interwoven. Care of the veins, the lymphatics, and the epidermis depends on attention to each together and at the same time. New knowledge of cytokines produced by the epidermis and their effects on angiogenesis and permeability suggest that care of the epidermis by washing and emollients has equal value as elevation and movement. Such maneuvers cost little and are usually available.

Acute cutaneous barrier disruption activates epidermal p44/42 and p38 mitogen-activated protein kinases in human and hairless guinea pig skin

Acute cutaneous barrier disruption of the skin elicits various homeostatic repair responses in the epidermis. Although several candidates for the signaling mechanisms that induce these responses have been reported, e.g. the calcium and ion concentration, peroxisome proliferator-activated receptor-alpha, and TNF-alpha signaling mediated by sphingomyelinases, the exact nature of the signals remains undertermined. Therefore, assuming that an important group of serine/threonine-signaling kinases, mitogen- and SAPK/JNK, might link the barrier disruption to the subsequent homeostatic responses, the activation of three MAPKs in hairless guinea pig or in human skin after barrier disruption was investigated. The epidermal barrier was insulated with tape stripping or organic solvents, and Western blotting, and immune complex kinase assay. In the skin of hairless guinea pigs, p44/42 MAPK and p38 MAPK, but nor SAPK/JNK, were continued to be activated for at least 180 min. The activation of p44/42 which positively correlated with the number of tape strippings, whereas K+ sucrose solution suppressed its activation. The activation of p44/42 MAPK was also induced by treatment of the skin with organic solvents. In similar fashion, p44/42 and p38 MAPKs were found to be activated in human skin after tape stripping. These results for strongly suggest that the activation of p44/42 and p38 MAPKs links the stimuli of barrier disruption to the subsequent homeostatic responses to repair the barrier defect.

Imiquimod-Induced Interleukin-1α Stimulation Improves Barrier Homeostasis in Aged Murine Epidermis

In response to acute disruption of the permeability barrier of aged mammals there is a diminished capacity for barrier recovery, analogous to other aged organs when stressed. Acute barrier disruption increases levels of epidermal cytokines, and cytokines are known regulators of keratinocyte mitogenesis, as well as lipid synthesis in extracutaneous tissues. Underlying the sluggish barrier recovery in aged skin are diminished mRNA and protein levels for the interleukin-1 cytokine family, and its receptors. To further elucidate the role of the interleukin-1 family of cytokines in the barrier repair response, cytokine production was stimulated in aged murine skin with topical imiquimod application. Imiquimod accelerated barrier recovery after acute insults to aged and young skin. These functional results correlated temporally with increased interleukin-1 alpha production in the epidermis following topical imiquimod administration to murine skin. Furthermore, intracutaneous injections of interleukin-1 alpha accelerated barrier recovery in aged mice. Finally, we showed that interleukin-1 alpha added to cultured human keratinocytes stimulates epidermal lipid synthesis. These studies provide further evidence for the role of reduced interleukin-1 alpha signaling in the decline of permeability barrier function in aged skin, and point to the potential use of cytokine augmentation in barrier dysfunction of the aged.

The effect of the PDE-4 inhibitor (cipamfylline) in two human models of irritant contact dermatitis

BACKGROUND

New therapeutic approaches have to be considered in the treatment of irritant contact dermatitis (ICD). Recently, phosphodiesterase 4 (PDE-4) inhibitors have been introduced as nonsteroidal, antiinflammatory agents. These agents inhibit the secretion of the cytokines thought to be involved in the pathogenesis of ICD. We investigated the effect of a new selective PDE-4 inhibitor (cipamfylline) in human models using single and repeated exposures to an irritant in a blind, randomized pilot study with healthy volunteers. We compared the effect of cipamfylline ointment with a strong corticosteroid (betamethasone-17-valerate) and with a placebo ointment.

METHODS

Ten volunteers were patch tested at four investigation sites with sodium dodecyl sulphate (1%) for 24 h. In a model that simulates chronic damage, 11 volunteers were patch tested with sodium dodecyl sulphate (0.2%) for 4 h daily for four consecutive days. The investigation sites were treated once a day with the above-mentioned agents. One site was left untreated. We used erythema scoring, measurements of transepidermal water loss (TEWL) and several immunohistochemical markers for epidermal proliferation and differentiation.

RESULTS

Repeated application revealed that betamethasone-17-valerate caused a statistically significant reduction in erythema and TEWL compared to cipamfylline and placebo. We also observed a significant suppression of proliferating cells and cytokeratin 16 expression at sites treated with betamethasone compared to the other sites. In the model for acute ICD, no significant differences were seen between the investigated sites.

CONCLUSIONS

Our results show that betamethasone-17-valerate may modulate the response in ICD. In this human model of ICD we could not confirm the efficacy of cipamfylline. Clinical studies are needed before the effect of PDE-4 inhibitors in ICD can be refuted with certainty.

Alterations in cytokine regulation in aged epidermis: implications for permeability barrier homeostasis and inflammation. I. IL-1 gene family

Acute disruption of the cutaneous permeability barrier with either solvents or tape-stripping stimulates a homeostatic metabolic response in the subjacent nucleated layers of the epidermis that results in a rapid restoration of normal permeability barrier function. When the aged epidermal permeability barrier is stressed, it reveals a diminished capacity for recovery, in comparison to young epidermis, analogous to other organs in the aged when stressed. Although the signals that regulate this homeostatic response by the epidermis have not yet been resolved, acute permeability barrier disruption stimulates release of prestored IL-1alpha, and increased production of potentially regulatory cytokines, including IL-1alpha and TNFalpha in the epidermis. In these studies, we addressed the hypothesis that cytokine dysregulation explains the permeability barrier abnormality in aged epidermis, assessing the regulation of IL-1 and TNF signaling in aged vs young mice. To determine whether the IL-1 family of cytokines plays a key role in the permeability barrier abnormality of the aged, permeability barrier recovery rates were compared in transgenic mice lacking the functional IL-1 type 1 receptor vs wild-type mice at various ages. Knockout of the IL-1 type 1 receptor exacerbates the defect in permeability barrier homeostasis that is seen in age-matched, wild-type counterparts. Furthermore, the sluggish permeability barrier recovery in aged epidermis is associated with, and at least in part attributable to, altered expression of the IL-1 family of cytokines and receptors both under basal conditions and after acute barrier perturbations. Whereas modulations in cytokine expression with epidermal permeability barrier perturbation are qualitatively similar in aged epidermis, they greatly differ quantitatively. In contrast, examination of TNFalpha mRNA and protein basally, and following barrier perturbation revealed no alterations in aged epidermis. Together, these results show that selective alterations in the IL-1 family of cytokines occur with aging and that defects in IL-1 signaling may contribute to the epidermal permeability barrier abnormality of aged skin.