Synopsis

To develop an active agent for skin whitening, the inhibitory effects of 285 plant extracts on tyrosinase activity were examined, and one plant extract having tyrosinase inhibition activity was chosen. Ramulus mori (young twigs of Moru • alba L.) extracts howed inhibition activity in tyrosinase and melanin synthesis in B-16 melanoma cells. To clarify the mechanism of its inhibition on melanogenesis, the effect of R. mori extracts on tyrosinase activity, synthesis, and gene expression was evaluated. R. mori extracts howed tyrosinase inhibition activity by competitive method, and there was no suppression of tyrosinase synthesis and gene expression. Further, to evaluate the inhibitory activity of R. mori n vivo, its effect on melanin production in UV-induced brown guinea pigs was examined, where a decrease ofmelanin production in the guinea pig model was observed. Also, R. mori extracts showed no toxicity in animal tests such as the acute toxicity test, the skin irritation test, the eye irritation test, the skin sensitization test, and the acute oral toxicity test, and no toxicity in the human skin irritation test. A single compound from R. mori extracts was purified using various column chromatography and recrys-tallization, and its chemical structure was identifed using mass chromatography, IR spectroscopy, and NMR analysis. The chemical structure was that of 2,3',4,5'-tetrahydroxystilbene(2-oxyresveratrol) and showed inhibition activity on tyrosinase (IC5o = 0.23 pg/ml). Also, R. mori extracts inhibited tyrosinase activity in a competitive manner (Ki = 1.5 x 10 6 M) when L-tyrosine was used as a substrate