A histological examination for skin atrophy after 6 months of treatment with fluocinolone acetonide 0.01%, hydroquinone 4%, and tretinoin 0.05% cream.

Melasma is a common disorder affecting a significant percentage of the population, particularly those with skin of color. Therapy with hydroquinone, a depigmenting agent, as a single agent or in combination with other agents has been used with variable success. A triple-combination (TC) cream combining hydroquinone 4% with tretinoin 0.05% and fluocinolone acetonide 0.01% was developed for the treatment of melasma. We studied the use of TC cream for 24 weeks and had tissue samples for all time points in 62 patients with moderate to severe melasma. The atrophogenic potential of TC cream was evaluated through serial histopathologic examination of skin biopsies. No statistically significant histopathologic signs of atrophy of the epidermis or dermis were noted at any time point throughout the study. There was a marked reduction in epidermal melanin in treated subjects; however, we did not observe any significant difference in baseline and treated samples in the amount of perivascular inflammatory infiltrate, dermal mucin, keratinocyte and melanocyte atypia, or mast cells, consistent with findings of previous studies where topical retinoids were used. An increase in the mean number of blood vessels per square millimeter of tissue was observed in 2 study cohorts between baseline and week 24. These results suggest that the risk of skin atrophy with 24-week use of TC cream for the treatment of melasma is very low.

Intracellular degradation of elastin by cathepsin K in skin fibroblasts--a possible role in photoaging.

Solar elastosis is observed in the dermis of photoaged skin and is characterized by an accumulation of abnormal elastin in the extracellular space. Several proteases that degrade elastin in the extracellular space have been implicated in its formation. The lysosomal protease cathepsin K (catK) has recently been described to be highly expressed in skin fibroblasts under certain pathologic conditions. As cat K is one of the most potent mammalian elastases, we hypothesized that catK-mediated intracellular elastin degradation may play a role in the formation of solar elastosis. Immunostaining of cultured skin fibroblasts incubated with labeled elastin demonstrated internalization of extracellular elastin to lysosomes and its degradation by catK. Induction of catK expression in fibroblasts was observed both in vitro and in vivo after exposure to longwave UVA. In contrast to fibroblasts from young donors, cells from old donors failed to activate catK in response to UVA. These data suggest a role of intracellular elastin degradation by catK in the formation of solar elastosis. We propose that an age-related decline in catK activity, in particular after UV exposure, may promote the formation of actinic elastosis through a decline of orderly intracellular elastin degradation and subsequent accumulation of elastin in the extracellular space.

Morphometric analyses of elastic tissue fibers in dermatofibroma: clues to etiopathogenesis?

BACKGROUND: The etiopathogenesis of dermatofibroma (DF), a common benign fibrohistiocytic tumor, is debatable. The goal of this study was to ascertain the density of elastic tissue fibers in DF in an effort to investigate whether this provides an insight into its etiopathogenesis. METHOD: Three groups comprising eight cellular DFs, eight paucicellular DFs and eight scars (control group) were stained with a modified Verhoeffs-van Gieson (without counterstain), and elastic fibers in three randomly selected fields within the lesional area/case semiquantitatively analyzed and examined in a blinded fashion. RESULT: The mean density of elastic tissue fibers in cellular DF was 6.81 (1.38-15.89); in paucicellular DF, 2.46 (0.14-5.79) and in scar, 2.95 (0.97-10.69). Overall, significant differences in density of elastic tissue fibers were observed only between cellular DF and the other two groups (vs. paucicellular variant, p = 0.03 and vs. scar, p = 0.05). Morphological changes observed included thickness, clumping, elongation and waviness (cellular DF) and margination of elastic tissue fibers (paucicellular variant). CONCLUSION: While the jury still appears to be out regarding the etiopathogenesis of DF, the reduction in density of elastic tissue fibers in the paucicellular variant compared with its cellular counterpart lends credence to the concept of evolutionary stages of DF.

Differential expression of the antioxidant repair enzyme methionine sulfoxide reductase (MSRA and MSRB) in human skin.

Recently, the antioxidant repair enzymes methionine-S-sulfoxide reductase A (MSRA) and methionine-R-sulfoxide reductase B (MSRB) were described in human epidermal keratinocytes and melanocytes. Methionine sulfoxide reductases (MSRs) are thought to protect against reactive oxygen species-induced oxidative damage in many organs, including the most environmentally exposed organ, human skin. We sought to examine the expression and distribution of this enzyme family (MSRA, MSRB1, MSRB2, and MSRB3) within the various compartments of healthy and diseased human skin. Expression was assessed using polyclonal MSR antibodies and immunohistochemical staining of human skin biopsies from various anatomical sites. Remarkably, MSRA expression was not only found in the epidermis as previously described but also in hair follicles and eccrine glands and was most pronounced in sebaceous glands. Furthermore, MSRB2 expression was found in melanocytes while MSRB1 and MSRB3 were both expressed within vascular endothelial cells. In conclusion, MSR enzymes are differentially expressed in human skin. Thus, modulation of MSR repair antioxidants may have implications for cutaneous aging and carcinogenesis.

Expression and regulation of cathepsin K in skin fibroblasts.

Cathepsin K (catK) is a lysosomal cysteine protease with strong collagenolytic activity well known to mediate bone resorption in osteoclasts. Recently, catK has also been reported to be expressed in other tissues. In the dermis, it is expressed only under certain circumstances such as scarring or inflammation. We therefore investigated the expression and regulation of this protease in dermal fibroblasts using immunoblotting and immunostaining. Cultured skin fibroblasts were found to strongly express catK in lysosomes. Internalization of collagen I and IV to lysosomes of fibroblasts indicates a role of catK in intracellular collagen degradation after endocytosis, a process that is different from the metalloproteinase-mediated collagen degradation in the extracellular space. In fibroblasts, interleukin-1alpha and cellular confluence upregulate catK expression and transforming growth factor-beta1 inhibits confluence-induced catK upregulation in skin fibroblasts. RANKL (ligand of receptor activator of NF-kappaB) did not alter catK expression. These regulators of catK expression are likely to play a role in the as-needed upregulation in certain skin conditions, where the prominent matrix-degrading properties of catK are thought to require tight regulation to maintain the homeostasis of the extracellular matrix.

Cathepsin K in melanoma invasion.

Cathepsin K (catK) is a lysosomal cysteine protease with strong collagenolytic activity that mediates bone resorption in osteoclasts. Recently, catK expression has been reported in skin and lung fibroblasts, which suggests a role in maintaining homeostasis of the extracellular matrix outside of bone. Matrix degradation is a pivotal step in tumor invasion and metastasis. As other proteases, in particular matrix metalloproteinases and some cathepsins, but not catK, have been described to mediate melanoma invasion, we studied catK in melanoma. Immunostaining revealed strong catK expression in most primary melanomas and all cutaneous melanoma metastases. Melanocytic nevi also demonstrated catK expression, but it was less intense than in melanomas. Melanoma lines express both the pro- and the active form of catK and internalize extracellular collagen into lysosomes. Inhibition of catK greatly reduced melanoma cell invasion through Matrigel basement membrane matrix and increased detection of internalized collagen. We suggest that catK may play an important role in melanoma invasion and metastasis by mediating intracellular degradation of matrix proteins after phagocytosis. Clinical use of catK inhibitors, a class of medication currently in clinical trials for the treatment of osteoporosis, may be a promising avenue for the treatment of melanoma.