Involvement of p38 MAPK signaling pathway in the anti-melanogenic effect of San-bai-tang, a Chinese herbal formula, in B16 cells

Aim of the study: San-bai-tang (SBT), a Chinese herbal formula, is traditionally used as a skin whitener in China. In our previous screening assays, SBT was identified as an effective tyrosinase inhibitor. In this study, we aim to investigate the anti-melanogenic effect and mechanisms of SBT in B16 cells. Materials and methods: Cell viability was examined by the MTT assay. Cellular tyrosinase activity and melanin content were determined using spectrophotographic methods. Protein expression was analyzed by immunoblotting. Results: SBT inhibited tyrosinase activity with an IC₅₀ of 215.6±10.3μg/ml, and decreased cellular melanin content with an IC₅₀ of 254.8±14.5μg/ml at 48h. MTT assay demonstrated that 48-h SBT (50-400μg/ml) treatment did not show obvious cytotoxicity. Immunoblot analysis showed that SBT (100, 200 or 400μg/ml) treatment for 48h down-regulated the expression levels of phosphorylated-p38, MITF, tyrosinase, TRP-1 and TRP-2 in a dose-dependent manner. Conclusions: SBT inhibited melanogenesis in B16 cells, and suppression of p38 MAPK signaling pathway contributed to the anti-melanogenic effect of SBT by down-regulating the expression of MITF and melanogenic enzymes. These novel findings demonstrated the anti-melanogenic effect and mechanisms of SBT, and provide pharmacological basis for the traditional use of SBT.