Inhibition of the p38 and PKA signaling pathways is associated with the anti-melanogenic activity of Qian-wang-hong-bai-san, a Chinese herbal formula, in B16 cells

Ethnopharmacological relevance: Qian-wang-hong-bai-san (QW), a Chinese herbal formula, is traditionally used as a skin whitening agent in China. Aim of study: In our previous screening assays, QW was identified as an effective tyrosinase inhibitor. In this study, we aim to investigate the underlying mechanism of the anti-melanogenic effect of QW in B16 cells. Materials and methods: Cytotoxicity of QW in B16 cell line was examined by MTT assay. Cellular tyrosinase activity was determined based on the melanin content measured at 475 nm with a microplate spectrophotometer. Protein expression was analyzed by Western blotting and quantified by Quantity One. Results: QW dose-dependently inhibited tyrosinase activity and decreased melanin content at 48 h without significant cytotoxicity in B16 cells. Western blot analysis showed that QW treatment down-regulated the expression levels of phospho-p38, phospho-CREB, MITF, tyrosinase, TRP-1 and TRP-2 in a dose-dependent manner. At the same time, QW treatment for 48 h inhibited IBMX-induced elevation of cellular melanin content and tyrosinase activity. However, the attenuation of IBMX-mediated up-regulations of phospho-CREB and phospho-PKA was readily observed with 60 min of QW treatment. Conclusions: The anti-melanogenic activity of QW in B16 melanoma cells can be attributed, at least in part, to the inhibition of the p38 MAPK and PKA signaling pathways. These findings shed new light on the molecular mechanisms of the skin-whitening property of QW.