The Effect Of Tacalcitol On Cultured Human Melanocytes

Background and ObjectivesVitiligo is is a common idiopathic hypomelanotic disorder, affecting 0.5–1% of the worldwide population, with no sexual predilection. Precise pathogenesis of the disease remains unknown , Theories include autoimmune, cytotoxic, biochemical, oxidant-antioxidant, neural, and viral mechanisms for destruction of epidermal melanocytes. Several treatment modalities have been used for this disease: topical corticosteroids,immunomodulators,psoralen, ultraviolet A therapy, narrowband ultraviolet B radiation, excimer laser, autologous thin thiersch grafting, traditional chinese medicine. however, no ideal drug has been found thus far, present therapies require many months to years of treatment and sometimes result in disappointing outcomes.Recently, tacalcitol have been reported to be effective in the treatment of vitiligo. Tacalcitol is a synthetic vitamin D3 analogue. Besides these well-known calcium-related actions, 1,25-(OH)2D3 and its synthetic analogs have potent immunomodulatory, anti-proliferative and pro-differentiation activities, Vitamin D compounds are first considered the main topical treatment for the mild and moderate forms of psoriasis.The first clinical observations about the topical effect of vitamin D analogs on human skin was reported in patients with psoriasis receiving treatment with calcipotriol; hyperpigmentation at the skin sites where vitamin D compounds were applied occurred as a secondary effect. This observation motivated clinicians to investigate the topical effect of the vitamin D synthetic analogs in vitiligo. Two low calcemic synthetic analogs, calcipotriol and tacalcitol, have been used for vitiligo treatment as monotherapy or in association with ultraviolet light or corticotherapy. Although some studies reported modest results, more an more trails acquired encouraging results. As this treatment is new, the causal relationship at the cellular and molecular level has been little discussed. Ranson reported Human melanocytes responded with a 50% increase in tyrosinase activity when they were incubated for 48 h with 1,25-(OH)2D3. Experiments performed on murine NCC-/melb4 line have shown that 1,25-(OH)2D3 stimulates the differentiation of immature melanocyte precursors. The mechanisms involved in the action of Vitamin D analogs targeting vitiligo depigmentation is also poor, Katayama study showed tacalcitol upregulated the expression of c-Kit mRNA by melanocytes irradiated with linear polarized infrared, UVA or short period solar irradiation, there is no domestic In vitro experiments regarding the actions of tacalcitol on pigmentation so far.The objectives is to study the effects of tacalcitol on cell proliferation, melanin synthesis, tyrosinase activity and the exppression of mRNA for tyrosinase(TYR), tyrosinase-related protein 1(TRP-1) in vitro and to explore the mechanism of tacalcitol in the treatment of vitiligo.Methods and Results1. Melanocytes of foreskins of healthy men were cultured and treated with various concentration of tacalcitol. Cell proliferation was detected by MTT assay, The synthesis of melanin by NaOH assay, and the tyrosinase activity by Dopa oxidase assay. Result: Tacalcitol could promote the proliferation of cultured melanocytes at concentration of 10-8mol/L, and it also enhanced the melanin synthesis(10-8mol/L and 10-9 mol/L) and the tyrosinase activity(10-9～10-6mol/L).2. The expression of mRNA for TYR, TRP-1 was tested by semiquantitative reverse transcription PCR. Result: The expression of mRNA for both TYR and TRP-1 was upregulated by tacalcitol at the concentrations 10-9～10-6mol/L.ConclusionThese experiments revealed that Tacalcitol could promote the proliferation of melanocytes, upregulate the expression of TYR mRNA and TRP-1 mRNA. These results may partially account for the therapeutic mechanisms of tacalcitol in the treatment of vitiligo.