Baicalin-induced Akt activation decreases melanogenesis through downregulation of microphthalmia-associated transcription factor and tyrosinase

Abstract

Scutellaria baicalensis has been used topically to treat inflammatory skin diseases in traditional East Asian medicine. Because post-inflammatory hyperpigmentation of the skin is difficult to manage, we investigated the effects of baicalin, a major component of S. baicalensis, on melanin synthesis in Mel-Ab cells. Our data showed that baicalin significantly inhibited melanin production and tyrosinase activity in a dose-dependent fashion, but it did not directly influence tyrosinase activity. Moreover, baicalin treatment triggered decreases in both mRNA and protein levels of microphthalmia-associated transcription factor (MITF) and tyrosinase. Although AMP-activated protein kinase (AMPK) and extracellular signal-regulated kinase (ERK) activation were induced in baicalin-treated Mel-Ab cells, they were not responsible for baicalin-induced hypopigmentation. Because the Akt pathway is also known to be involved in regulation of melanogenic protein expression and melanin synthesis, we examined the effects of baicalin on the Akt pathway. Our results showed that baicalin treatment stimulated Akt activation. Treatment with LY294002, a specific Akt inhibitor, restored baicalin-induced melanogenesis inhibition and abolished MITF and tyrosinase downregulation by baicalin. Taken together, our data suggest that Akt activation by baicalin inhibits melanin production via downregulation of MITF and tyrosinase in Mel-Ab cells.