Melanin synthesis is stimulated by various effectors, including α-melanocyte stimulating hormone (α-MSH), cyclic AMP (cAMP)-elevating agents (forskolin, isobutylmethylxantine, glycyrrhizin) and ultraviolet light. Our investigation focused on the identification of the melanogenic efficacy of mangosteen (Garcinia mangostana) leaf extract with regard to its effects on melanogenesis in B16F1 melanoma cells, since it has been known to possess strong anti-oxidant activities. The mangosteen leaf extract was found to stimulate melanin synthesis and tyrosinase activity in a dose-dependent manner without any significant effects on cell proliferation. Cytotoxicity of the extract was measured using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay; the highest concentration of the extract that did not affect cell viability was 32 µg/ml. Formation of melanin from cultured B16F1 melanoma induced by extract treatment was estimated using spectrophotometry. In order to clarify the subsequent mechanism of tyrosinase activation by the extract, the levels of tyrosinase expression in B16F1 melanoma were examined using an intracellular tyrosinase assay and tyrosinase zymography. Up-regulation of intracellular tyrosinase expression seemed to correlate with an increase in microphtalmia-associated transcription factor (MITF) protein levels since MITF is the key factor for genes involved in melanogenesis. Both of the results showed that tyrosinase activity was markedly enhanced from extract-treated cells. The overall results suggest that mangosteen leaf extract may be a promising candidate for the treatment of hypopigmentation disorder and useful for self-tanning cosmetic products.

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