Mona Man

Sphingolipids are required for mammalian epidermal barrier function. Inhibition of sphingolipid synthesis delays barrier recovery after acute perturbation.

Stratum corneum lipids comprise an approximately equimolar mixture of sphingolipids, cholesterol, and free fatty acids, arranged as intercellular membrane bilayers that are presumed to mediate the epidermal permeability barrier. Prior studies have shown that alterations in epidermal barrier function lead to a rapid increase in cholesterol and fatty acid synthesis which parallels the early stages of the repair process. Despite an abundance of indirect evidence for their role in the barrier, the importance of sphingolipids has yet to be demonstrated directly. Whereas sphingolipid synthesis also increases during barrier repair, this response is delayed in comparison to cholesterol and fatty acid synthesis (Holleran, W.M., et al. 1991. J. Lipid Res. 32:1151-1158). To further delineate the role of sphingolipids in barrier homeostasis, we assessed the impact of inhibition of sphingolipid synthesis on epidermal barrier recovery. A single topical application of beta-chloro-L-alanine (beta-CA), an irreversible inhibitor of serine-palmitoyl transferase (SPT), applied to acetone-treated skin of hairless mice resulted in: (a) greater than 75% inhibition of SPT activity at 30 min (P less than 0.001); (b) a global decrease in sphingolipid synthesis between 1 and 3 h (P less than 0.02); (c) reduction of epidermal sphingolipid content at 18 h (P less than 0.01); (d) delayed reaccumulation of histochemical staining for sphingolipids in the stratum corneum; and (e) reduced numbers and contents of lamellar bodies in the stratum granulosum. Finally, despite its immediate, marked diminution of sphingolipid synthesis, beta-CA slowed barrier recovery only at late time points (greater than 6 h) after acetone treatment. This inhibition was overridden by coapplications of ceramides (the distal SPT product), indicating that the delay in repair was not due to non-specific toxicity. These studies demonstrate a distinctive role for epidermal sphingolipids in permeability barrier homeostasis.

Cholesterol synthesis is required for cutaneous barrier function in mice.

Previous studies have shown that topical acetone treatment results in the removal of stratum corneum lipids and disruption of the permeability barrier. This disruption stimulates epidermal lipid synthesis which is associated with the rapid restoration of stratum corneum lipids and barrier function. The aim of this study was to determine the role of cutaneous cholesterol synthesis in the barrier recovery. Here we show that topical lovastatin, a competitive inhibitor of HMG CoA reductase, inhibits cholesterol synthesis. After acetone disruption of the barrier, the normal rapid return of cholesterol to the stratum corneum and recovery of barrier function is impaired in animals treated topically with lovastatin. When lovastatin animals are simultaneously treated topically with either mevalonate, the immediate product of HMG CoA reductase, or cholesterol, the final end product of the pathway, the recovery of the barrier is normalized. Lovastatin resulted in the delayed secretion and abnormal appearance of lamellar bodies. These results provide the first evidence demonstrating that cholesterol synthesis is required for the maintenance of barrier structure and function and suggests a crucial role for cholesterol synthesis in allowing for terrestrial existence.

Mice lacking 25OHD 1α-hydroxylase demonstrate decreased epidermal differentiation and barrier function ☆

Keratinocytes express high levels of 25OHD 1alpha-hydroxylase (1OHase). The product of this enzyme, 1,25(OH)(2)D, promotes the differentiation of keratinocytes in vitro. To test whether 1OHase activity is essential for keratinocyte differentiation in vivo we examined the differentiation process in mice null for the expression of the 1alphaOHase gene (1alphaOHase(-/-)) by light and electron microscopy, by immunocytochemistry for markers of differentiation, by ion capture cytochemistry for calcium localization, and by function using transepidermal water loss (TEWL) to assess barrier integrity. Levels of involucrin, filaggrin, and loricrin-markers of differentiation in the keratinocyte and critical for the formation of the cornified envelope-were reduced in the epidermis of 1alphaOHase(-/-) mice. Calcium in the outer epidermis was reduced with loss of the calcium gradient from stratum basale to stratum granulosum. TEWL was normal in the resting state, but following disruption of the barrier, 1alphaOHase(-/-) mice had a markedly prolonged recovery of barrier function associated with a reduction in lamellar body secretion and a failure to reform the calcium gradient. Thus 1,25(OH)(2)D is essential for normal epidermal differentiation, most likely by inducing the proteins and mediating the calcium signaling in the epidermis required for the generation and maintenance of the barrier.

Topical hesperidin improves epidermal permeability barrier function and epidermal differentiation in normal murine skin

Abstract:  Orange peel extract appears to exhibit beneficial effects on skin whitening, inflammation, UVB protection, as well as keratinocyte proliferation. In the present study, we determine whether topical hesperidin influences epidermal permeability barrier function and its underlying mechanisms. Hairless mice were treated topically with 2% hesperidin or 70% ethanol alone twice daily for 6 days. At the end of treatment, basal transepidermal water loss (TEWL) was measured 2 and 4 h post barrier disruption. Epidermal proliferation and differentiation were evaluated by immunohistochemical staining and Western blot analysis. Additionally, lamellar body density and secretion were assessed by electron microscopy. Although there were no significant differences in basal barrier function, in comparison with control animals, topical hesperidin significantly accelerated barrier recovery at both 2 and 4 h after acute barrier abrogation. Enhanced barrier function in hesperidin‐treated skin correlated with stimulation of both epidermal proliferation and differentiation, as well as enhanced lamellar body secretion. These results indicate that topical hesperidin enhances epidermal permeability barrier homeostasis at least in part due to stimulation of epidermal proliferation, differentiation, as well as lamellar body secretion.

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

Disruption of the permeability barrier elicits a homeostatic repair response which rapidly restores barrier function while repeated barrier perturbation results in cutaneous pathology. In response to barrier disruption there is a marked increase in epidermal TNF‐α and IL‐1 production. To determine the potential role of TNF and IL‐1 in mediating the cutaneous changes that occur following barrier disruption we compared the kinetics of barrier recovery and the degree of epidermal hyperplasia and cutaneous inflammation in TNF type I (p55) receptor and IL‐1 receptor type I (p80) deficient mice. No abnormalities in epidermal morphology were observed with light or electron microscopy in receptor deficient mice. Under baseline conditions epidermal barrier function was unchanged in receptor deficient mice. Following barrier disruption the kinetics of barrier recovery were similar in control vs TNF receptor deficient mice regardless if the barrier was disrupted by acetone treatment, SDS treatment, or tape stripping. In contrast, barrier recovery was slightly but significantly accelerated regardless of the method of barrier disruption in IL‐1 receptor deficient mice. The degree of epidermal hyperplasia and cutaneous inflammation following repeated barrier disruption was similar in control, TNF receptor, and IL‐1 receptor deficient mice. The present study demonstrates that barrier recovery is not delayed and the degree of epidermal hyperplasia and inflammation are not altered in either TNF receptor or IL‐1 receptor deficient mice, indicating that neither TNF nor IL‐1 alone are essential for either barrier repair or the cutaneous pathology induced by barrier perturbation. Whereas the increase in IL‐1 following barrier disruption may delay components of the repair response, whether either TNF‐α or IL‐1 regulate aspects of the homeostatic response remains unresolved.

Characterization of Skin Friction Coefficient, and Relationship to Stratum Corneum Hydration in a Normal Chinese Population

Background and Objectives: Studies have demonstrated that some cutaneous biophysical properties vary with age, gender and body sites. However, the characteristics of the skin friction coefficient in different genders and age groups have not yet been well established. In the present study, we assess the skin friction coefficient in a larger Chinese population. Methods: A total of 633 subjects (300 males and 333 females) aged 0.15–79 years were enrolled. A Frictiometer® FR 770 and Corneometer® CM 825 (C&K MPA 5) were used to measure the skin friction coefficient and stratum corneum hydration, respectively, on the dorsal surface of the hand, the forehead and the canthus. Results: In the females, the maximum skin friction coefficients on both the canthus and the dorsal hand skin were observed around the age of 40 years. In the males, the skin friction coefficient on the dorsal hand skin gradually increased from 0 to 40 years of age, and changed little afterward. Skin friction coefficients on some body sites were higher in females than in age-matched males in some age groups. On the canthus and the dorsal hand skin of females, a positive correlation was found between skin friction coefficient and stratum corneum hydration (p < 0.001 and p < 0.0001, respectively). In contrast, in males, the skin friction coefficient was positively correlated with stratum corneum hydration on the forehead and the dorsal hand skin (p < 0.05 and p < 0.0001, respectively). Conclusion: The skin friction coefficient varies with age, gender and body site, and positively correlates with stratum corneum hydration on some body sites.

Chinese herbal medicine (Tuhuai extract) exhibits topical anti-proliferative and anti-inflammatory activity in murine disease models

Abstract:  While psoriasis is one of the most common skin disorders in humans, effective, safe and inexpensive treatments are still largely unavailable. Chinese herbal medicine (CHM) has been used for centuries for treating psoriasis and several reports claim that systemic administration of one such CHM, Tuhuai, mainly composed of flos sophorae, smilax glabra roxb and licorice, is effective in psoriasis. However, the mechanisms by which this CHM improves psoriasis are not yet clear. Two universal features of psoriasis are epidermal hyperplasia and inflammation. Moreover, drugs that specifically inhibit epidermal hyperplasia and/or inflammation are widely used to treat psoriasis. Here, we investigated whether topical applications of Tuhuai extract exhibit anti‐proliferative and anti‐inflammatory activities in two murine models of inflammatory dermatoses. To assess Tuhuai’s potential anti‐proliferative effect, we disrupted epidermal barrier function twice‐daily for 4 days in normal hairless mice followed by topical applications of either 1% Tuhuai extract or Vehicle to both flanks immediately after each barrier perturbation. Changes in epidermal proliferation and apoptosis were evaluated by immunohistochemistry and TUNEL staining. To assess the anti‐inflammatory effects of Tuhuai, both irritant (phorbol ester) and acute allergic contact dermatitis (oxazolone) models were used. Whereas topical Tuhuai extract did not alter epidermal proliferation or induce irritation in normal skin, it both reduced epidermal hyperplasia in the epidermal hyperproliferative model, and reduced inflammation in both irritant and allergic contact dermatitis models. As topical Tuhuai extract exhibits anti‐proliferative and anti‐inflammatory properties in a variety of human models of inflammatory dermatoses, Tuhuai could provide an effective, relatively safe and inexpensive therapeutic alternative for the treatment of inflammatory dermatoses, including psoriasis.

Epidermal permeability barrier recovery is delayed in vitiligo-involved sites.

Background/Objectives: Prior studies have demonstrated that both the skin surface pH and epidermal permeability barrier function vary with skin pigmentation types. Although melanin deficiency is the main feature of vitiligo, alterations in cutaneous biophysical properties in vitiligo have not yet been well defined. In the present study, stratum corneum (SC) hydration, the skin surface pH and epidermal permeability barrier function in vitiligo were evaluated. Methods: A total of 30 volunteers with vitiligo comprising 19 males and 11 females aged 13–51 years (mean age: 27.91 ± 2.06 years) were enrolled in this study. The skin surface pH, SC hydration, melanin/erythema index and transepidermal water loss (TEWL) were measured by respective probes connected to a Courage-Khazaka MPA5. SC integrity was determined by measuring the TEWL following each D-Squame application. The barrier recovery rate was assessed at 5 h following barrier disruption by repeated tape stripping. Results: In addition to SC hydration, both melanin and erythema index were significantly lower in vitiligo lesions than in contralateral, nonlesional sites, while no difference in skin surface pH between vitiligo-involved and uninvolved areas was observed. In addition, neither the basal TEWL nor SC integrity in the involved areas differed significantly from that in the uninvolved areas. However, barrier recovery in vitiligo-involved sites was significantly delayed in comparison with uninvolved sites (40.83 ± 5.39% vs. 58.30 ± 4.71%; t = 2.441; p < 0.02). Conclusion: Barrier recovery following tape stripping of the SC is delayed in vitiligo. Therefore, improvement in epidermal permeability barrier function may be an important unrecognized factor to be considered in treating patients with vitiligo.

A topical Chinese herbal mixture improves epidermal permeability barrier function in normal murine skin

Abstract:  Chinese herbal medicine (CHM) has been shown to have beneficial effects for both skin disorders with barrier abnormality and as skin care ingredients. Yet, how CHM exerts their benefits is unclear. As most, if not all, inflammatory dermatoses are accompanied by abnormal permeability barrier function, we assessed the effects of topical CHM extracts on epidermal permeability barrier function and their potential mechanisms. Topical CHM accelerated barrier recovery following acute barrier disruption. Epidermal lipid content and mRNA expression of fatty acid and ceramide synthetic enzymes increased following topical CHM treatment in addition to mRNA levels for the epidermal glucosylceramide transport protein, ATP‐binding cassette A12. Likewise, CHM extract increased mRNA expression of antimicrobial peptides both in vivo and in vitro. These results demonstrate that the topical CHM extract enhances epidermal permeability barrier function, suggesting that topical CHM could provide an alternative regimen for the prevention/treatment of inflammatory dermatoses accompanied by barrier abnormalities.

The role of CD44 in cutaneous inflammation.

Abstract:  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.