Inhibitory Effect of Cucumis sativus on Melanin Production in Melanoma B16 Cells by Downregulation of Tyrosinase Expression

We compared the inhibitory effects on melanogenesis of six plant parts (leaves, stems, roots, whole fruits, calyxes, and fruits Without calyxes) of Cucumis sativus. MeOH extracts of leaves and stems inhibited melanin production in B16 cells. These extracts did not affect the activity Of mushroom tyrosinase or crude enzyme lysate from B16 cells. However, the extracts decreased tyrosinase expression at the protein level. These results suggest that the depigmenting mechanism of extracts from leaves and stems of C. sativus involves the expression of tyrosinase. Of eight Compounds isolated from the leaves, lutein (1) (IC50 = 170.7 mu M) and (+)-(1R,2S,5R,6S)-2,6-di-(4'-hydroxyphenyl)-3,7-dioxabicyclo[3.3.0]octane (2) (IC50 = 270.8 mu M) were found to suppress melanogenesis. Whereas 1 was found to markedly decrease the expression levels of tyrosinase, 2 only weakly reduced tyrosinase expression. This suggests that 1 is an active component in the leaves of C. sativus and is a potentially useful skin-whitening agent.