Melanogenesis inhibition by gallotannins from Chinese galls in B16 mouse melanoma cells

Nowadays herbal medicines of skin-whitening cosmetics are popular with women. We attempted to find the whitening activity compounds present in many herbal medicines used for this purpose and discuss their mechanisms in melanin biosynthesis. The 70% acetone extracts of 10 kinds of herbs were investigated for their mushroom tyrosinase activity inhibition. Among these 10 extracts, Chinese galls showed inhibitory activity against tyrosinase, with a 50% inhibitory concentration (IC₅₀) value of 22 μg/ml. In a B16 mouse melanoma cell culture assay, Chinese galls dose-dependently inhibited melanin biosynthesis. Using ultraviolet A (UVA) or α-melanocyte-stimulating hormone (α-MSH) to stimulate B16 cells after Chinese gall treatment, the melanin biosynthesis of B16 cells was inhibited in a dose-dependent manner. The active compounds of Chinese galls were isolated by column chromatography, and the melanin biosynthesis inhibition in B16 melanoma cells was measured. Three gallotannins, 2,3,4,6-tetra-O-galloyl-D-glucopyranose, 1,2,3,6-tetra-O-galloyl- β-D-glucopyranose, and 1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose, were isolated from Chinese gall extract, and their IC₅₀ values of tyrosinase inhibition activity were 54, 30, and 15 μM, respectively. By the mushroom tyrosinase inhibition kinetics assay, the three gallotannins were all determined to be non-competitive inhibitors. These results indicated that Chinese galls inhibit melanin biosynthesis, associated with hyperpigmentation and can be used as skin-whitening cosmetics for skin care.