Melanogenesis-Inhibitory Activity of Aromatic Glycosides from the Stem Bark of Acer buergerianum

A new benzyl glucoside, 3-O-demethylnikoenoside (1), along with eleven known compounds, including seven aromatic glycosides, 28, three lignans, 911, and one cyclitol, 12, were isolated from the BuOH-soluble fraction of a MeOH extract of Acer buergerianum stem bark. The structures of the new compound were elucidated on the basis of extensive spectroscopic analyses and comparison with literature. Upon evaluation of compounds 112 on melanogenesis in B16 melanoma cells induced with -melanocyte-stimulating hormone (-MSH), three compounds, i.e., hovetrichoside B (8), pinoresinol 4-O--D-glucopyranoside (9), and pinoresinol 4-O--D-apiofuranosyl-(12)--D-glucopyranoside (10), have been found to exhibit inhibitory effects with 4149% melanin content compared to the control at 100M and low cytotoxicity to the cells (8192% cell viability at 100M). Western blot analysis showed that compound 8 reduced the protein levels of MITF (=microphtalmia-associated transcription factor) and tyrosinase, in a concentration-dependent manner, suggesting that 8 inhibits melanogenesis in -MSH-stimulated B16 melanoma cells by, at least in part, inhibiting the expression of MITF, followed by decreasing the expression of tyrosinase. On the other hand, upon Western blotting, compound 9 was found to reduce the protein levels of tyrosinase and TRP-2, while it increased MITF and TRP-1 (=tyrosine-related protein 1), in a concentration-dependent manner, indicating that 9 inhibits melanogenesis in -MSH-stimulated B16 melanoma cells by, at least in part, inhibiting the expression of tyrosinase and TRP-2.