In vivo prevention of corticosteroid-induced skin atrophy by tretinoin in the hairless mouse is accompanied by modulation of collagen, glycosaminoglycans, and fibronectin

Glucocorticoid-Induced Skin Atrophy: The Old and the New

Glucocorticoids are major therapeutic agents highly used in the medical field. Topical glucocorticoids have biologic activities which make them useful in dermatology – anti-inflammatory, vasoconstrictive, immune suppressive and antiproliferative, in treating inflammatory skin disorders (allergic contact eczema, atopic hand eczema, nummular eczema, psoriasis vulgaris or toxic-irritative eczema). Unfortunately, the beneficial effects of topical glucocorticoids are shadowed by their potential for adverse effects – muscle or skin atrophy, striae distensae, rubeosis or acne. Skin atrophy is one of the most prevalent side-effects, with changes found in all skin compartments – marked hypoplasia, elasticity loss with tearing, increased fragility, telangiectasia, bruising, cutaneous transparency, or a dysfunctional skin barrier. The structure and function of the epidermis is altered even in the short-term topical glucocorticoid treatment; it affects stratum corneum components, subsequently affecting skin barrier integrity. The dermis is altered by directly inhibiting fibroblast proliferation, reducing mast cell numbers, and loss of support; there is depletion of mucopolysaccharides, elastin fibers, matrix metalloproteases and inhibition of collagen synthesis. Atrophogenic changes can be found also in hair follicles, sebaceous glands or dermal adipose tissue. Attention should be paid to topical glucocorticoid treatment prescription, to the beneficial/adverse effects ratio of the chosen agent, and studies should be oriented on the development of newer, innovative targeted (gene or receptor) therapies.

Efficacy, safety, and cost-effectiveness of all-trans retinoic acid/Clobetasol Propionate Compound Ointment in the treatment of mild to moderate psoriasis vulgaris: A randomized, single-blind, multicenter clinical trial

To assess the efficacy, safety, and cost-effectiveness of all-trans retinoic acid/Clobetasol Propionate Compound Ointment and calcipotriol/betamethasone dipropionate ointment in the treatment of mild-to-moderate patients with psoriasis vulgaris. This was a randomized, single-blind, multicenter clinical trial. A total of 240 patients were randomized to receive twice-daily all-trans retinoic acid/Clobetasol Propionate Compound Ointment (treatment group) or once-daily calcipotriol/betamethasone dipropionate ointment (control group) for 4 weeks. The efficacy, safety, and cost-effectiveness were assessed at Weeks 2 and 4. After 4 weeks, both groups showed a significant clinical improvement compared to baseline (88.33% vs. 89.83%, respectively, p = .7112). But PASI 75 response in the treatment group was superior to the control group (44.12% vs. 28.57%, respectively, p = .0200), at Week 4. SSRI improvement rate in the treatment group was also superior to control group (67.11% vs. 59.43%, respectively, p = .0119) at Week 4. All-trans retinoic acid/Clobetasol Propionate Compound Ointment showed a significant clinical improvement in erythema, infiltration, and scales of skin lesions and PASI score compared to baseline. 1.67% of patients (treatment group) reported adverse reactions compared to 2.50% (control group) with no statistical significance. In addition, the cost-effectiveness assessment showed a higher cost-effectiveness of the treatment group compared to the control group in 4 weeks (199.25 vs. 801.51). All-trans retinoic acid/Clobetasol Propionate Compound Ointment was effective and safe in the treatment of psoriasis vulgaris with similar efficacy as calcipotriol/betamethasone dipropionate ointment and lower treatment costs.

The Treatment of Cushing's Disease

Cushing's disease (CD), or pituitary-dependent Cushing's syndrome, is a severe endocrine disease caused by a corticotroph pituitary tumor and associated with increased morbidity and mortality. The first-line treatment for CD is pituitary surgery, which is followed by disease remission in around 78% and relapse in around 13% of patients during the 10-year period after surgery, so that nearly one third of patients experience in the long-term a failure of surgery and require an additional second-line treatment. Patients with persistent or recurrent CD require additional treatments, including pituitary radiotherapy, adrenal surgery, and/or medical therapy. Pituitary radiotherapy is effective in controlling cortisol excess in a large percentage of patients, but it is associated with a considerable risk of hypopituitarism. Adrenal surgery is followed by a rapid and definitive control of cortisol excess in nearly all patients, but it induces adrenal insufficiency. Medical therapy has recently acquired a more important role compared to the past, due to the recent employment of novel compounds able to control cortisol secretion or action. Currently, medical therapy is used as a presurgical treatment, particularly for severe disease; or as postsurgical treatment, in cases of failure or incomplete surgical tumor resection; or as bridging therapy before, during, and after radiotherapy while waiting for disease control; or, in selected cases, as primary therapy, mainly when surgery is not an option. The adrenal-directed drug ketoconazole is the most commonly used drug, mainly because of its rapid action, whereas the glucocorticoid receptor antagonist, mifepristone, is highly effective in controlling clinical comorbidities, mainly glucose intolerance, thus being a useful treatment for CD when it is associated with diabetes mellitus. Pituitary-directed drugs have the advantage of acting at the site responsible for CD, the pituitary tumor. Among this group of drugs, the dopamine agonist cabergoline and the somatostatin analog pasireotide result in disease remission in a consistent subgroup of patients with CD. Recently, pasireotide has been approved for the treatment of CD when surgery has failed or when surgery is not an option, and mifepristone has been approved for the treatment of Cushing's syndrome when associated with impairment of glucose metabolism in case of the lack of a surgical indication. Recent experience suggests that the combination of different drugs may be able to control cortisol excess in a great majority of patients with CD.

Hyalinization of the pyloric stomach in CD-1 mice following oral (dietary) administration of the corticosteroid agonists mometasone furoate, budesonide, and flunisolide

The purpose of this study was to compare the toxicity of three marketed corticosteroid receptor agonists (mometasone furoate, budesonide, or flunisolide) to the stomach of female CD-1 mice following oral administration via the diet for up to 52 weeks, with a 16-week recovery period (budesonide and flunisolide). A range of tissues was examined by light microscopy, accompanied by clinical pathology measurements to assess anticipated corticosteroid effects as a surrogate marker of systemic drug exposure. Microscopic changes seen in the stomach with each corticosteroid included pyloric hyalinization. This previously unreported finding was investigated using histochemical and immunohistochemical techniques and was found to consist of hyalinized collagen, in association with increased immunohistochemical signal for transglutaminase-2 and osteopontin. The significance of the osteopontin finding is unclear; however, the ability of transglutaminase-2 to facilitate the formation of degradation resistant protein bonds implies this protein may be involved in the pathogenesis of this change. Furthermore, published evidence that transglutaminase-2 may be induced by a corticosteroid agonist raises the possibility that pyloric stomach hyalinization may be a class effect of corticosteroids via the action of this enzyme.

Test systems for the determination of glucocorticoid receptor ligand induced skin atrophy

Topical glucocorticoids are highly anti-inflammatory effective but limited by their side effect potential, with skin atrophy being the most prominent one. Thus, determining the atrophogenic potential of novel compounds targeting the glucocorticoid receptor is important. Significant progress in the understanding of glucocorticoid receptor mediated molecular action has been made providing the basis for novel glucocorticoid receptor ligands with a potentially superior effect/side effect profile. Such compounds, however, need to be tested. The present gold standard for the reliable prediction of glucocorticoid induced skin atrophy are still in vivo models, however, in vitro models may replace them to some extent in the future. Indeed, advances in technologies to determine the atrophogenic potential of compounds in vitro has been made recently and promising novel test models like the human full thickness skin models are emerging. Their full predictive value, however, needs to be further evaluated. Currently, a screening approach starting with a combination of several in vitro test systems followed by subsequent testing of the most promising compounds in rodent models is recommended prior entering clinical studies with selected development compounds.

Pituitary-targeted medical therapy of Cushing's disease

BACKGROUND

The goals of ideal medical therapy for Cushing's disease should be to target the aetiology of the disorder, as is the case for surgery, which is the current 'gold standard' treatment. However, no effective drug that directly and reliably targets the adrenocorticotropin-secreting pituitary adenoma has yet been found.

OBJECTIVE

To summarise pituitary-targeted medical treatment of Cushing's disease.

METHODS

Compounds with neuromodulatory properties and ligands of different nuclear hormone receptors involved in hypothalamo-pituitary regulation have been investigated.

RESULTS

The somatostatin analogue pasireotide and the dopamine agonist cabergoline, as well as their combination, show some therapeutic promise in the medical therapy of Cushing's disease. Other treatments such as retinoic acid analogues look promising and may be a possible option for further investigation. No other medical therapies seem to be reliably effective currently.

CONCLUSION

Since a percentage of patients treated with surgery are not cured, or improve and subsequently relapse, there is an urgent need for effective medical therapies for this disorder. At present, only cabergoline and pasireotide are under active investigation.

Retinoid receptors

"Retinoid" refers to the naturally occurring compounds with vitamin A activity and to synthetic analogues of retinol. Retinoids are key regulators of differentiation, proliferation, and inflammation. Their successful use in the treatment of various skin diseases and neoplasias has revolutionized the practice of dermatology as well as oncology. This article focuses on the retinoid receptors to elucidate our understanding of their complex biologic activity that is reflected in their therapeutic clinical effects as well as in their adverse reactions.

Action of topical thyroid hormone analogue, triiodothyroacetic acid in reversing glucocorticoid-induced skin atrophy in humans

The present study concerns the effect of topical treatment with a cream formulation of triiodothyroacetic acid (TRIAC) in comparison with a placebo preparation in producing a reversal of skin atrophy induced by long-term employment of topical glucocorticoid therapy in humans. A total of 39 patients with clinically verified skin atrophy due to long-term use of topical potent glucocorticoids were randomized. The changes in skin thickness, elastic fibers, and hyaluronic acid were evaluated by means of sonography and histology. After 8 weeks' treatment, the skin thickness measured by sonography increased by 16% in the epidermis, 8% in the dermis, and epidermis + dermis in the placebo group. In the TRIAC 0.1% group, the corresponding values were 24% ( p=0.063) in the epidermis, 28% ( p=0.042) in the dermis, and 25% ( p=0.039) in the epidermis + dermis. After 8 weeks, in the placebo group, the skin thickness measured by biopsy increased by 5% in the epidermis, epidermis + dermis, and 6% in the dermis. In the TRIAC 0.1% group, the corresponding values were 31% ( p=0.041) in the epidermis, 46% ( p=0.041) in the dermis and 44% ( p=0.043) in the epidermis + dermis. After 8 weeks, the elastic fibers of moderately irregular and thickened fibers increased by 56% in the placebo group and 100% ( p=0.043) in the TRIAC 0.1 group. This study indicates that topical treatment with TRIAC appears to reverse glucocorticoid-induced skin atrophy under the narrow conditions tested.

Glucocorticoid therapy-induced skin atrophy

Glucocorticoids (GCs) are highly effective for the topical treatment of inflammatory skin diseases. Their long-term use, however, is often accompanied by severe and partially irreversible adverse effects, with atrophy being the most prominent limitation. Progress in the understanding of GC-mediated molecular action as well as some advances in technologies to determine the atrophogenic potential of compounds has been made recently. It is likely that the detailed mechanisms of GC-induced skin atrophy will be discovered and in vitro models for the reliable prediction of atrophy will be established in the foreseeable future. This knowledge will not only facilitate safety profiling of established drugs but will also foster further drug discovery by improving compound characterization processes. New insights into GC modes of action will guide optimization strategies aiming at novel GC receptor ligands with improved effect/side effect profile.

Action of topical thyroid hormone analogues on glucocorticoid-induced skin atrophy in mice

Previously we demonstrated the stimulation of collagen synthesis in triiodothyroacetic acid (TRIAC)-topically treated human and mice. In the present study, we have evaluated the dose response effect of thyroid hormone (TH) analogues and tretinoin on glucocorticoid-induced skin atrophy in a haired mouse model. For this investigation, we treated haired mice twice daily for 7 days with various topically administered doses of TRIAC, triiodothyronine-sodium salt (T(3)-Na), diiodothyroacetic acid (DIAC), 3,5-diiodothyropropionic acid (DITPA), and tretinoin with 0.2 mM betamethasone17-valerate (BM), or with the vehicle as a control group. We also investigated a combination of commercial betamethasone dipropionate (BD) 0.05% cream and various doses of TRIAC on mouse skin. TRIAC was able to reverse the skin atrophy by 25% in a daily dose of 1 nmol/cm(2) in the presence of 0.2 mM BM (p < 0.05). Neither other TH analogues nor TRIAC in lower and higher concentrations had a significant inhibitory effect on dermal atrophy (p > 0.05). A combination of 0.2 mM BM and 10 nmol/cm(2) TRIAC was able to prevent dermal atrophy by 18%. The addition of TRIAC to 0.05% BD cream in a final concentration of 0.1% was able partially to reverse the dermal atrophy by 15% (p < 0.05). TRIAC alone in a concentration of 1,000 nmol/cm(2) stimulated dermal proliferation by 34% (p < 0.05). Other TH analogues alone had no stimulatory effect on dermal proliferation. Tretinoin 0.8 mM was able to inhibit dermal atrophy by 20% (p < 0.05) and had an effect on dermal thickness of 85% (p < 0.05). However, severe side effects with edema, erythema, and scaling were commonly observed in all tretinoin-treated mouse skin, which could partly explain the increase in dermal thickness. In contrast, no skin side effects were observed after treatment with TRIAC. This study indicates that TRIAC may have a therapeutic effect on BM-induced dermal atrophy in mouse skin and a direct stimulatory effect on dermal proliferation when given alone.

Glucocorticoids for Human Skin: New Aspects of the Mechanism of Action

Topical glucocorticoids have always been considered first-line drugs for inflammatory diseases of the skin and bronchial system. Applied systemically, glucocorticoids are used for severe inflammatory and immunological diseases and the inhibition of transplant rejection. Owing to the progress in molecular pharmacology, the knowledge of the mechanism of action has increased during the last years. Besides distinct genomic targets, which are due to the activation of specific cytoplasmatic receptors resulting in the (trans-) activation or (trans-) repression of target genes, there are non-genomic effects on the basis of the interference with membrane-associated receptors as well as with membrane lipids. In fact, various glucocorticoids appear to differ with respect to the relative influence on these targets. Thus, the extended knowledge of glucocorticoid-induced cellular signalling should allow the design and development of even more specifically acting drugs - as it has been obtained with other steroids, e.g. estrogens for osteoporosis prevention.

Skin morphology of the mutant hairless USP mouse

The morphology of the skin of the mutant hairless USP mouse was studied by histological, histochemical and immunohistochemical methods and compared to the skin of BALB/c mice. Representative sections of the dorsal skin from mice of both strains aged 18 days, and 1, 3, 6, and 8 months were studied. Sections stained with hematoxylin and eosin showed cystic formations called utricles and dermal cysts in the dermis that increased in size and number during growth. Skin thickness increased significantly at 8 months. Sections stained with picrosirius and examined with polarized light, displayed different colors, suggesting different thicknesses of dermal collagen fibers (probably types I and III). Weigert, Verhoeff and resorcin-fuchsin stains revealed fibers of the elastic system. The PAS and Alcian blue methods revealed neutral and acid glycosaminoglycans in the skin ground substance of both mouse strains. Immunohistochemical staining for fibronectin and laminin did not show differences between the mutant and BALB/c mice. Mast cells stained by the Gomori method and macrophages positive for HAM 56 antibodies were observed in both mouse strains. Except for the presence of enlarged cysts in the hairless strain, no qualitative differences were found during development of the skin of BALB/c and the mutant hairless mice.

A thyroid hormone analogue, triiodothyroacetic acid, corrects corticosteroid-downregulated collagen synthesis

The aim of this study was to compare the change in collagen synthesis between topical treatments with two doses of triiodothyroacetic acid (TRIAC), a thyroid hormone analogue, and placebo, after pretreatment with topical betamethasone 17-valerate (BM). Eighteen healthy volunteers were pretreated with BM on abdominal skin for 3 days, and were then treated for 14 days with a cream containing TRIAC (0.03% or 0.1%) or a placebo cream. Collagen production was assessed by quantifying the amino terminal propeptides of human type I and type III procollagen (PINP and PIIINP) in fluids from suction-induced blisters on the treated skin. Three days of treatment with BM led to an average reduction of PINP of 70% and of PIIINP of 50%. Seven days after treatment, the median increase in PINP was 230% (p = 0.03) in the Triac 0.03% group, 148% (p = 0.2) in the TRIAC 0.1% and 5% in the placebo group. The median increase in PINP in the skin area from the start of treatment to the end of treatment was 521% (p = 0.06) in the TRIAC 0.03% group, 339% (p = 0.2) in the TRIAC 0.1% group, and 55% in the placebo group (the p values are related to baseline). Seven days after treatment, the median increase in PIIINP was 24% (p = 0.6) in the Triac 0.03% group, 23% (p = 0.6) in the TRIAC 0.1% group, and -12% in the placebo group. The median increase in PIIINP in the skin area from the start of treatment to the end of treatment was 137% (p = 0.7) in the TRIAC 0.03% group, 230% (p = 0.9) in the TRIAC 0.1% group and 58% in the placebo group (the p values are related to baseline). Histologic examinations of sections from punch biopsies taken at the end of the treatment showed more thickened collagen fibers and increased density of PINP-producing dermal fibroblasts in the TRIAC groups compared to the placebo group. The result suggests a potential role for TRIAC-containing cream concomitant with anti-inflammatory topical treatment with potent glucocorticoids to prevent their suppressive activity on dermal collagen production.

Nipple connective tissue and its development: insights from the K14-PTHrP mouse

Parathyroid hormone-related protein (PTHrP) regulates a wide variety of developmental processes. Keratin 14 (K14) promoter-mediated overexpression of PTHrP in the epidermis during development converts the entire murine ventral skin to hairless nipple-like skin. In this report, we characterize the morphology and processes that influence the development of nipple connective tissue. The connective tissue of the nipple displayed increased levels of proteoglycans, and collagen bundles with atypical morphology, as well as increased numbers of mast cells, capillaries, nerve fibers and dermal melanocytes. The unique characteristics of nipple connective tissue were not present until mice reach 3-4 weeks of age. The adult male K14-PTHrP mouse has a less dramatic ventral skin phenotype, and does not manifest a nipple-like dermis. Ovariectomy or orchiedectomy prior to sexual maturity had no impact on the ventral skin of the male or female K14-PTHrP mice, but exposure to androgens in utero repressed many of the nipple-like characteristics in the ventral skin of the female K14-PTHrP mice.

Retinoic acid prevents experimental Cushing syndrome

Cushing syndrome is caused by an excess of adrenocorticotropic hormone (ACTH) production by neuroendocrine tumors, which subsequently results in chronic glucocorticoid excess. We found that retinoic acid inhibits the transcriptional activity of AP-1 and the orphan receptors Nur77 and Nurr1 in ACTH-secreting tumor cells. Retinoic acid treatment resulted in reduced pro-opiomelanocortin transcription and ACTH production. ACTH inhibition was also observed in human pituitary ACTH-secreting tumor cells and a small-cell lung cancer cell line, but not in normal cells. This correlated with the expression of the orphan receptor COUP-TFI, which was found in normal corticotrophs but not in pituitary Cushing tumors. COUP-TFI expression in ACTH-secreting tumor cells blocked retinoic acid action. Retinoic acid also inhibited cell proliferation and, after prolonged treatment, increased caspase-3 activity and induced cell death in ACTH-secreting cells. In adrenal cortex cells, retinoic acid inhibited corticosterone production and cell proliferation. The antiproliferative action and the inhibition of ACTH and corticosterone produced by retinoic acid were confirmed in vivo in experimental ACTH-secreting tumors in nude mice. Thus, we conclude that the effects of retinoic acid combine in vivo to reverse the endocrine alterations and symptoms observed in experimental Cushing syndrome.

Inhibition by glucocorticoids of the mast cell-dependent weal and flare response in human skin in vivo

1. This study examines the relative contributions made by inhibition of mast cell degranulation, reduction of mast cell recruitment and maturation, and lowering the responsiveness of the vasculature to histamine, in the inhibition by glucocorticoids of the weal and flare in human skin. 2. One forearm of healthy human volunteers was treated for 24 h (n=6) or daily for 21 days (n=10) with 0.05% clobetasol propionate. The other arm served as control. Weal and flare responses were elicited by intradermal injection of 20 microl of 0.3 mM codeine. The areas of the responses were measured using scanning laser Doppler imaging. Microdialysis was used to assess histamine release. Mast cell numbers and tissue histamine content were assessed in 4-mm punch biopsies. Histamine (20 microl of 1 microM i.d.) was used to assess the status of the vasculature. 3. No significant effects were seen at 24 h. At 21 days, clobetasol reduced the areas of the codeine-induced weal and flare responses by 59 and 58% respectively (both P=0.006). Mast cell numbers were reduced by 47%, (P=0.014) and total tissue histamine content by 52% (P=0.006). Codeine-induced histamine release was reduced by 44% (P=0.022). The weal, but not the flare, induced by histamine was significantly inhibited (P=0.019). Echography revealed a 15% thinning of the skin by clobetasol. 4. These results demonstrate that reduction of the weal and flare responses to codeine following clobetasol treatment, results primarily from reduced mast cell numbers and tissue histamine content rather than inhibition by corticosteroids of mast cell degranulation.

Epidermal maturation arrest

BACKGROUND

Cutaneous wound repair involves a complex and temporal integration of cytokines, formed blood components, extracellular matrix, and parenchymal cells. The normal healing process can be impeded at any step along its path by a variety of factors.

OBJECTIVE

We present four cases of abnormal wound repair in patients whose defects were left to heal by second intention following Mohs micrographic surgery. In particular, these patients experienced an unusual delay in healing with an apparent arrest of epidermal maturation.

RESULTS

Each appeared to respond to a topical steroid and/or ibuprofen. The intent of this therapy was to inhibit products of the arachadonic acid cascade or other cytokines that may have been hindering normal epidermal differentiation.

CONCLUSION

We present four case reports, a brief review of epidermal reconstitution in wounds, and a possible explanation for why our therapy may have hastened wound repair in our patients.

Topical tretinoin enhances corticosteroid-induced inhibition of tumorigenesis in hairless mice previously exposed to solar simulating radiation

The role of retinoids in hairless mouse photocarcinogenesis has been studied extensively but remains controversial. By contrast, the role of corticosteroids has hardly been investigated. Many findings indicate an antagonism between the action of these two drugs. To examine these issues, we irradiated hairless mice thrice weekly for 10 weeks with 1.5 minimal erythema doses of solar simulating radiation (UVB + UVA). In the post-UV period, groups of mice were treated topically for 30 weeks with tretinoin, corticosteroid or emollient vehicle alone or with a sequential combination of corticosteroid and tretinoin. A control group remained topically untreated. All three agents, when used alone, significantly inhibited tumorigenesis. The sequential combination produced the greatest inhibition.

Peeling agents and irritants, unlike tretinoin, do not stimulate collagen synthesis in the photoaged hairless mouse

Tretinoin has been shown to stimulate the synthesis of collagen in photo-aged human and hairless mouse skin. It has been suggested that this partial reversal of photodamage by tretinoin is a consequence of low-grade inflammation. The purpose of this study was to compare the effect of tretinoin with a number of irritants and peeling agents on collagen synthesis. Hairless mice were irradiated thrice weekly for 10 weeks with UVB. In the 10-week postirradiation period, the mice were treated topically five times per week with tretinoin (0.05%), glycolic acid (10%), benzalkonium chloride (1.0%), sodium lauryl sulfate (5%), croton oil (5%) and the water - propylene glycol vehicle. Microscopic measurements showed that the tretinoin-induced zone of new collagen was twice the depth of that induced by irritants or vehicle. The salt-soluble collagen content was determined by HPLC analysis of hydroxyproline levels. Type III procollagen was quantified by radioimmunoassay. Tretinoin-treated skin had increased amounts of collagen and type III procollagen whereas irritant- and peeling agent-treated skins were similar to vehicle-treated controls. Immunofluorescence studies were confirmatory. These results demonstrate that these agents, unlike tretinoin, do not have the capacity to enhance collagen synthesis. Therefore, it is likely that the effect of tretinoin does not depend upon irritation.

Topical tretinoin increases dermal mast cells, induces epidermal mast cell growth factor (c-kit ligand) and modulates its distribution in hairless mice

In previous studies we have noted that mast cells are increased in tretinoin-treated photoaged hairless mouse skin. Because UV radiation is known to increase mast cell numbers, we were interested in whether tretinoin alone would modulate the mast cell population in unirradiated mice. Animals were treated topically with 0.05% tretinoin, 5 days a week, for 2, 4, 6, 8 and 10 weeks. Untreated and vehicle controls were included. Biopsies were processed for light microscopy and stained with toluidine blue. Mast cells in the upper and lower dermis were scored separately under high magnification. After 2 weeks of tretinoin, mast cells in the upper dermis were significantly increased, as indicated by the appearance of small, moderately metachromatically granulated cells near the dermal-epidermal junction. Mast cells in the lower dermis, the site of a granulomatous reaction, were large, densely granular and significantly increased after 6 weeks of treatment. Immunohistochemical evaluation for mast cell growth factor (MGF) revealed a marked increase in keratinocyte cytoplasmic staining by week 2. After 4-6 weeks, membrane-associated or intercellular staining was evident. Cells in the upper dermis also showed membrane reactivity for MGF. By 8-10 weeks, epidermal MGF reactivity had dissipated in the more basal keratinocytes. These findings show that topical tretinoin can induce epidermal MGF along with an associated mast cell hyperplasia. It is suggested that the two populations of dermal mast cells may have different functions.

Cutaneous lymphangiectases associated with severe photoaging and topical corticosteroid application

We report an elderly patient with lymphangiectases arising within skin affected by photoaging, steroid atrophy, and inflammation. Bullous lesions appeared in several sites following a year of topical corticosteroid applications for neurodermatitis. Light and electron microscopy showed that the bullae consisted of dilated lymphatic vessels within the dermis. There was also marked nodular elastosis and attenuation of dermal collagen. We suggest that this patient's lymphangiectases resulted from abnormal structure and function of the dermis due to photoaging and steroid atrophy.

Evaluation of topical retinoids for cutaneous pharmacological activity in Yucatan microswine

The pharmacological effects of retinoids on skin have been studied primarily in test systems using small animals, such as mice and rabbits. Because of potentially significant differences in skin permeation and metabolism between small animals and humans, we have used Yucatan microswine as an alternative model for testing topical retinoids. Microswine skin resembles human skin, functionally and anatomically, more closely than most other species. In these studies, microswine skin was treated topically with retinoids for 5 consecutive days per week for 5 weeks. We found microswine epidermis to be functionally responsive to retinoids in that it undergoes hyperplasia and shows an increase in transepidermal water loss (TEWL). All-trans-retinoic acid, and its analogs, 13-cis-retinoic acid, 4-hydroxy-retinoic acid and 4-oxo-retinoic acid all caused epidermal thickening and increased TEWL. The three analogs were less potent than all-trans-retinoic acid. A synthetic retinoid, TTNPB, potently induced epidermal hyperplasia and increased TEWL, but a close structural analog, m-carboxy-TTNPB, which is also inactive on nuclear retinoic acid receptors, was without effects on microswine epidermis. These findings show that microswine are useful for evaluating the cutaneous effects of topical retinoids. This model could be of value in identifying retinoids with potential clinical activity.

Topical tretinoin increases the tropoelastin and fibronectin content of photoaged hairless mouse skin

Topical tretinoin treatment of photoaged hairless mice has been shown in previous studies to stimulate formation of a subepidermal zone of new connective tissue characterized by enhanced collagen synthesis. The aims of this study were to localize and/or quantify elastin, fibronectin, and glycosaminoglycans in the same model. Hairless mice (Skh-1) were irradiated thrice weekly for 10 weeks with gradually increasing doses of ultraviolet (up to 4.5 minimal erythema doses per exposure) from Westinghouse FS-40 bulbs. Mice were then treated five times a week with either 0.05% tretinoin, the ethanol:propylene glycol vehicle, or nothing for another 10 weeks. Controls included mice sacrificed after 10 weeks of ultraviolet treatment and age-matched untreated animals. The distribution of elastin and fibronectin was examined by immunofluorescence microscopy, which revealed fine fibrils in the subepidermal zone in tretinoin-treated skin. A quantitative slot-blot immunobinding assay showed that tretinoin induced a threefold higher amount of tropoelastin compared with controls. Insoluble elastin content (desmosine levels) was similar in all groups. Although fibronectin content was increased by ultraviolet radiation, tretinoin treatment induced the largest increase. In contrast, the amount of glycosaminoglycans, although increased by UVB radiation, was reduced by tretinoin treatment.

Inhibition of glucocorticoid-induced epidermal and dermal atrophy with KH 1060--a potent 20-epi analogue of 1,25-dihydroxyvitamin D3

1. The possibility of preventing and treating glucocorticoid-induced skin atrophy with KH 1060 (the potent 20-epi-22-oxa-24a-homo-26,27-dimethyl analogue of 1,25-dihydroxyvitamin D3) was examined in a hairless mouse model. 2. KH 1060 (0.625-6.25 pmol cm-2 of skin) applied topically for 7 days together with 2.5 nmol cm-2 betamethasone-17-valerate prevented, in a concentration-dependent manner, the development of epidermal, dermal and total skin thinning caused by the glucocorticoid. The effect of KH 1060 on the epidermis occurred at a lower dose than on the dermis, and at doses above 1.25 pmol cm-2 KH 1060 caused epidermal hyperplasia. 3. KH 1060 (2.5 pmol cm-2) prevented the development of betamethasone-associated skin atrophy in mice during a long-term (4 weeks) treatment, and reversed established cutaneous glucocorticoid atrophy. 4. Radiolabelling experiments with [35S]-sulphate and [3H]-proline in vivo revealed that KH 1060 stimulated the synthesis of sulphated glycosaminoglycans and hydroxyproline in skin treated with betamethasone. 5. These findings strongly suggest that KH 1060 prevents and reverses glucocorticoid-induced skin atrophy by stimulating epidermal proliferation and enhancing synthesis of extracellular matrix in the dermis.