8-Methoxycoumarin enhances melanogenesis via the MAPKase signaling pathway.

8-Methoxycoumarin (8-methoxy-chromen-2-one), isolated from R. graveolens L., is able to alleviate arthritis by inhibition of proinflammatory cytokines. However, its effects on melanogenesis have largely remained unreported. The present study examined the effects of 8-methoxycoumarin on melanogenesis in B16F10 murine cells, together with its effect on the mechanism of melanin synthesis. The cells were treated with different concentrations of 8-methoxycoumarin; α-MSH was used as the positive control. We found 8-methoxycoumarin to significantly increase the melanin content of the cells without exerting any cytotoxicity. In addition, it significantly upregulated the expression of tyrosinase and tyrosinase-related protein-1 and 2 via inducing the expression of microphthalmia-associated transcription factor. Furthermore, we demonstrated the involvement of mitogen-activated protein kinase (MAPK) pathway-mediated phosphorylation of p38 and c-Jun N-terminal kinase (JNK), and inhibition of phosphorylation of extracellular signal-regulated kinase (ERK) to be responsible for enhanced melanin production. Use of SB203580 (p38 inhibitor) and SP600125 (p-JNK inhibitor) corroborated these findings. Additionally, we investigated the effects of 8-methoxycoumarin on protein kinase B (AKT) phosphorylation and protein kinase A (PKA) signaling pathway (using H89, a PKA inhibitor). These results suggested that 8-methoxycoumarin increases melanogenesis via the MAPK signaling pathway. Based on these findings, we conclude that 8-methoxycoumarin could serve as a potential compound for treating hypopigmentation disorders. It could also serve as a promising chemical for hair depigmentation treatment in the cosmetic industry.