Inhibitory effect of Cinnamomum osmophloeum Kanehira ethanol extracts on melanin synthesis via repression of tyrosinase expression

Melanin contributes to skin color, and tyrosinase is the enzyme that catalyzes the initial steps of melanin formation. Therefore, tyrosinase inhibitors may contribute to the control of skin hyperpigmentation. The inhibition of tyrosinase activity by Cinnamomum zeylanicum extracts was previously reported. In this report, we test the hypothesis that Cinnamomum osmophloeum Kanehira, an endemic plant to Taiwan, contains compounds that inhibit tyrosinase activity, similar to C. zeylanicum. The cytotoxicity of three sources of C. osmophloeum Kanehira ethanol extracts was measured in B16-F10 cells using a methyl thiazolyl tetrazolium bromide (MTT) assay. At concentrations greater than 21.25 μg/mL, the ethanol extracts were toxic to the cells; therefore, 21.25 μg/mL was selected to test the tyrosinase activities. At this concentration, all three ethanol extracts decreased the melanin content by 50% in IBMX-induced B16-F10 cells. In addition to the melanin content, greater than 20% of the tyrosinase activity was inhibited by these ethanol extracts. The RT-PCR results showed that tyrosinase and transcription factor MITF mRNAs expression were down-regulated. Consistent with the mRNA results, greater than 40% of the human tyrosinase promoter activity was inhibited based on the reporter assay. Furthermore, our results demonstrate that the ethanol extracts protect cells from UV exposure. C. osmophloeum Kanehira neutralized the IBMX-induced increase in melanin content in B16-F10 cells by inhibiting tyrosinase gene expression at the level of transcription. Moreover, the ethanol extracts also partially inhibited UV-induced cell damage and prevented cell death. Taken together, we conclude that C. osmophloeum Kanehira is a potential skin-whitening and protective agent.