Effect of xanthoxylin on melanogenesis

Abstract

This study intended to investigate the effect of xanthoxylin, a phenolic compound found in many plants as well as Zanthoxylum piperitum, on melanin production in mouse melanoma B16F10 cells. Xanthoxylin at the concentrations 6.25, 12.5 and 25 µg/ml significantly induced melanin production in B16F10 cells in a concentration dependent manner without any effect on cell viability. It also increased number of dendrites per cell and induced the elongation of dendrites of these melanoma cells. The mechanisms of action of xanthoxylin on melanogenesis in B16F10 cells were also investigated. MITF is a critical transcription factor that regulates the expression of tyrosinase-related protein 1 (TRP-1), tyrosinase-related protein 2 (TRP-2) and tyrosinase which are proteins or enzymes associated with melanin synthesis in melanosome of melanocytes. Xanthoxylin at the concentrations 6.25, 12.5 and 25 µg/ml significantly induced the mRNA expression of MITF as well as tyrosinase. However it did not change the mRNA expression of TRP-1 and TRP-2. Cyclic AMP-mediated protein kinase A (PKA) activation is the major signaling pathway for MITF and tyrosinase expression. Phosphatidylinositol-3-Kinase (PI3K)-mediated (PKB), PKC, and MAP kinase (MAPK) signaling pathways are the other pathways that also regulate the expression of MITF and tyrosinase. By treating B16F10 cells with 25 µg/ml xanthoxylin and 5 µM specific inhibitors of these protein kinases, these inhibitors significantly decreased xanthoxylin-induced melanin production in the following order of potency; inhibitors of PKA > PKC > MAPK (MEK1) = PKB. The inhibitors of PKA and PKC also significantly decreased xanthoxylin-stimulated MITF and tyrosinase mRNA expression while PKB and MAPK did not have any effect on this xanthoxylin activity. The inhibitory activity of the PKA inhibitor was higher than the PKC one. The results from this study suggest that xanthoxylin stimulated melanogenesis in B16F10 cells by up-regulating MITF and tyrosinase expression. It is possible that xanthoxylin may activate melanin production mainly via cAMP-mediated PKA activation. Other signaling pathways may also play role in xanthoxylin-induced melanogenesis.