Protective effects of glutamine on human melanocyte oxidative stress model.

BACKGROUND: Vitiligo is a disorder caused by the loss of the melanocyte activity on melanin pigment generation. Studies show that oxidative-stress induced apoptosis in melanocytes is closely related to the pathogenesis of vitiligo. Glutamine is a well known antioxidant with anti-apoptotic effects, and is used in a variety of diseases. However, it is unclear whether glutamine has an antioxidant or anti-apoptotic effect on melanocytes. AIMS: The aim of this study was to investigate the protective effects of glutamine on a human melanocyte oxidative stress model. METHODS: The oxidative stress model was established on human melanocytes using hydrogen peroxide. The morphology and viability of melanocytes, levels of oxidants [reactive oxygen species and malondialdehyde], levels of antioxidants [superoxide dismutase and glutathione-S-transferase], and apoptosis-related indicators (caspase-3, bax and bcl-2) were examined after glutamine exposure at various concentrations. Expressions of nuclear factor-E2-related factor 2, heme oxygenase-1, and heat shock protein 70 were detected using western blot technique after glutamine exposure at various concentrations. RESULTS: Our results demonstrate that pre-treatment and post-treatment with glutamine promoted melanocyte viability, increased levels of superoxide dismutase, glutathione-S-transferase and bcl-2, decreased levels of reactive oxygen species, malondialdehyde, bax and caspase-3, and enhanced nuclear factor-E2-related factor 2, heme oxygenase-1, and heat shock protein 70 expression in a dose dependent manner. The effect of pre-treatment was more significant than post-treatment, at the same concentration. LIMITATIONS: The mechanisms of glutamine activated nuclear factor-E2-related factor 2 antioxidant responsive element signaling pathway need further investigation. CONCLUSIONS: Glutamine enhances the antioxidant and anti-apoptotic capabilities of melanocytes and protects them against oxidative stress.

The immunology and inflammatory responses of human melanocytes in infectious diseases.

Melanin is a canonical and major defense molecule in invertebrates but its role in mammalian immunity remains unexplored. In contrast, several recent studies have highlighted the emerging innate immune activities of human melanin-producing cells which can sense and respond to bacterial and viral infections. Indeed, the skin is a major portal of entry for pathogens such as arboviruses (Chikungunya, Dengue) and bacteria (mycobacterium leprae, Leptospira spirochetes). Melanocytes of the epidermis could contribute to the phagocytosis of these invading pathogens and to present antigens to competent immune cells. Melanocytes are known to produce key cytokines such as IL-1ß, IL6 and TNF-α as well as chemokines. These molecules will subsequently alert macrophages, neutrophils, fibroblasts and keratinocytes through unique crosstalk mechanisms. The infection and the inflammatory responses will control melanocyte's immune and metabolic functions and could contribute to skin manifestations (rash, hyper or de-pigmentation, epidermolysis and psoriasis-like lesions). This review will address the potential role of melanocytes in immunity, inflammation and infection of the skin in health and diseases.

The role of vitamin D in melanogenesis with an emphasis on vitiligo.

Vitiligo is a common pigmentary disorder caused by the destruction of functional melanocytes. Vitamin D is an essential hormone synthesized in the skin and is responsible for skin pigmentation. Low levels of vitamin D have been observed in vitiligo patients and in patients with other autoimmune diseases. Therefore, the relationship between vitamin D and vitiligo needs to be investigated more thoroughly. We reviewed the literature to date regarding the role of vitamin D in skin pigmentation. Our review revealed that vitamin D deficiency has been identified in many conditions, including premature and dysmature birth, pigmented skin, obesity, advanced age, and malabsorption. Vitamin D increases melanogenesis and the tyrosinase content of cultured human melanocytes by its antiapoptotic effect. However, a few growth-inhibitory effects on melanocytes were also reported. Vitamin D regulates calcium and bone metabolism, controls cell proliferation and differentiation, and exerts immunoregulatory activities. Vitamin D exerts its effect via a nuclear hormone receptor for vitamin D. The topical application of vitamin D increased the number of L-3,4-dihydroxyphenylalanine-positive melanocytes. The topical application of vitamin D yields significant results when used in combination with phototherapy and ultraviolet exposure to treat vitiligo in humans. Vitamin D decreases the expression of various cytokines that cause vitiligo. In conclusion, application of vitamin D might help in preventing destruction of melanocytes thus causing vitiligo and other autoimmune disorders. The association between low vitamin D levels and the occurrence of vitiligo and other forms of autoimmunity is to be further evaluated.

Development of melanocye-keratinocyte co-culture model for controls and vitiligo to assess regulators of pigmentation and melanocytes.

BACKGROUND: There is a need to develop an in vitro skin models which can be used as alternative system for research and testing pharmacological products in place of laboratory animals. Therefore to study the biology and pathophysiology of pigmentation and vitiligo, reliable in vitro skin pigmentation models are required. AIM: In this study, we used primary cultured melanocytes and keratinocytes to prepare the skin co-culture model in control and vitiligo patients. METHODS: The skin grafts were taken from control and patients of vitiligo. In vitro co-culture was prepared after culturing primary melanocytes and keratinocytes. Co- cultures were treated with melanogenic stimulators and inhibitors and after that tyrosinase assay, MTT assay and melanin content assay were performed. RESULTS: Melanocytes and keratinocytes were successfully cultured from control and vitiligo patients and after that co-culture models were prepared. After treatment of co-culture model with melanogenic stimulator we found that tyrosinase activity, cell proliferation and melanin content increased whereas after treatment with melanogenic inhibitor, tyrosinase activity, cell proliferation and melanin content decreased. We also found some differences in the control co-culture model and vitiligo co-culture model. CONCLUSION: We successfully constructed in vitro co-culture pigmentation model for control and vitiligo patients using primary cultured melanocytes and keratinocytes. The use of primary melanocytes and keratinocytes is more appropriate over the use of transformed cells. The only limitation of these models is that these can be used for screening small numbers of compounds.

The effect of H1 and H2 receptor antagonists on melanogenesis.

BACKGROUND: Histamine was found to stimulate melanogenesis in cultured human melanocytes specifically mediated by histamine H 2 receptors via protein kinase A activation. Based on this finding, the effect of topically applied H 2 antagonist on UVB-irradiated Guinea pigs' skin was examined and found to be suppressive on the post-irradiation melanogenesis. AIMS: In this study, we tried to explore the role of topically applied H 1 and H 2 receptor antagonists, in inhibition of UVB-induced melanization. METHODS: The effect of topically applied H 1 and H 2 receptor antagonists in inhibition of melanization was done clinically and histochemically using Fontana Masson and DOPA reactions compared with placebo. RESULTS: The post-irradiation pigmentation was found to be brownish/black instead of the original light brown color. This color change occurred below the shaved orange-red fur suggesting a switch of melanogenesis from pheomelanin to eumelanin. The induced pigmentation was suppressed by topically applied H 2 antagonist while both H 1 antagonist and vehicle had no effect. The microscopic examination showed that the keratinocytes in the H 2 antagonist-treated areas contained few melanosomes while the nearby dendrites are full of them. CONCLUSION: H 2 antagonists' inhibition of UVB-induced pigmentation is not only due to suppression of melanization but also due to a specific action on melanosomes' transfer.

[Creole dyschromia or idiopathic macular hypomelanosis of the melanodermic halfcast of Guillet-Hélénon]. / Dyschromie créole ou hypomélanose maculeuse idiopathique du métis mélanoderme de Guillet-Hélénon.

Melanodermic halfcasts may develop an original cutaneous dyschromia known as "progressive and extensive hypomelanosis" (Guillet-Helenon 1988). This disease is characterized by hypochromic and coalescent macules on the back and abdomen with possible spontaneous improvement within five years, favoured by UV exposure. The disease is not restricted to a limited geographic group: eight observations were collected in melanodermic patients leaving in temperate area. The pathogenesis of the disorder involves a variation in melanosome size and distribution with decrease in production of type IV melanosomes featuring a change of ultrastructural phenotype of melanogenesis. Since it may be misdiagnosed as fungal disease, leprosy or achromic eczema leading to useless laboratory examinations, this specific and frequent disease deserves to be known and recognized.

Uptake of radioactive DOPA by Mycobacterium leprae in vitro.

Our previous studies demonstrated that Mycobacterium leprae contains a characteristic o-diphenoloxidase which converts a variety of phenolic compounds to quinones in vitro. This enzyme was not present in any other mycobacteria tested. The results reported here deal with the uptake and binding of radioactive DOPA by M. leprae. The leprosy bacilli incubated with tritium-labelled DOPA, readily took up the substrate. The binding of DOPA by the bacilli was markedly inhibited by diethyldithiocarbamate. The organisms also bound tritiated norepinephrine. Mycobacterium phlei which does not oxidize phenolic substrates failed to bind DOPA. Cultures of melanocytes which contain o-diphenoloxidase took up tritiated DOPA. Catecholamine metabolism is known to be important in myocardial cells. Cultures of turtle-heart cells did not oxidize DOPA to quinone; however, these cells bound the labelled substrate. A cell line of fibroblasts derived from armadillo skin neither oxidized nor took up DOPA. The results indicate that, like melanocytes and turtle-heart cells, M. leprae probably possesses specific receptor sites for the binding and subsequent metabolism of phenolic substrates.