Inhibition of Melanogenesis by Xanthium strumarium L.

Abstract

Xanthium strumarium L. (Asteraceae) is traditionally used in Korea to treat skin diseases. In this study, we investigated the effects of a X. strumarium stem extract on melanin synthesis. It inhibited melanin synthesis in a concentration-dependent manner, but it did not directly inhibit tyrosinase, the rate-limiting melanogenic enzyme, and instead downregulated microphthalmia-associated transcription factor (MITF) and tyrosinase expression. MITF, the master regulator of pigmentation, is a target of the Wnt signaling pathway, which includes glycogen synthase kinase 3 beta (GSK3 beta) and beta-catenin. Hence, the influence of X. strumarium stem extract on GSK3 beta and beta-catenin was further investigated. X. strumarium induced GSK3 beta phosphorylation (inactivation), but the level of beta-catenin did not change. Moreover, a specific GSK3 beta inhibitor restored X. strumarium-induced melanin reduction. Hence, we suggest that X. strumarium inhibits melanin synthesis through downregulation of tyrosinase via GSK3 beta phosphorylation.