Isoorientin derived from Gentiana veitchiorum Hemsl. flowers inhibits melanogenesis by down-regulating MITF-induced tyrosinase expression

Gentiana is a genus of flowering plants in Gentianaceae family, which comprises of 1,600 species. The roots of few species of Gentiana, also known as Long Dan Cao in Chinese, are traditionally used in herbal remedies for a wide variety of liver-associated diseases. The medicinal part of Gentiana is root; however, the trumpet-shaped flowers are seldom being used. We investigated the anti-melanogenesis effect of water extract of Gentiana veitchiorum Hemsl. flowers, and isoorientin was identified to be the active compound. We tested the anti-melanogenesis effects of extracts deriving from different parts of G. veitchiorum, followed by identification of active ingredients within the extracts. The mechanism of inhibitory effect on melanogenesis, triggered by isoorientin, was elucidated by in vitro analyses. HPLC was applied to identify the components in water extracts from different parts of G. veitchiorum. The cytotoxicity of extracts and pure compounds in cultured B16F10 murine melanoma cells was determined by MTT and trypan blue assays. Melanin assay, tyrosinase assay, RT-PCR, luciferase assay and western blot were used to analyze the effect of isoorientin in melanin content, tyrosinase activity, as well as the expressions of those related genes and proteins. We identified an inhibitory effect on melanogenesis from water extract of G. veitchiorum flowers in B16F10 cells. Isoorientin, a major flavone in the extract, was identified to be an active ingredient causing reduction in melanin content in a dose-dependent manner. Such reduction was suggested to be a result of suppressed expression of tyrosinase (TYR), tyrosinase related protein-1 (TRP1) and DOPA-chrome tautomerase (DCT). Isoorientin also suppressed the expression of microphthalmia- associated transcription factor (MITF) through the phosphorylation of cAMP response element-binding protein (CREB). These findings indicate that isoorientin derived from G. veitchiorum flowers may be a potential skin lightening agent for the treatment of skin pigmentary disorders. [Display omitted]