The correlation of in vitro mushroom tyrosinase activity with cellular tyrosinase activity and melanin formation in melanoma cells A2058

The inhibition of mushroom tyrosinase activity in vitro has commonly been employed for evaluation of the whitening effects of various drugs and cosmetic products because tyrosinase is the limiting enzyme in melanin formation in skin. However, questions remain as to whether the in vitro inhibition of tyrosinase activity adequately represents the whiting effects since it does not account for cellular uptake of test samples. We therefore evaluated the correlations of the inhibition of cell-free mushroom tyrosinase activity with that of cellular tyrosinase activity and melanin formation in A2058 melanoma cell line using kojic acid, ascorbic acid and water extracts of seven Chinese herbs and seven mixtures of these herbs extracted with water, ethanol or ethyl acetate at different temperatures. No significant correlation was found for the inhibition of: (1) mushroom tyrosinase activity vs. cellular tyrosinase activity (r = 0.37, p = 0.25, n = 16) or vs. cellular melanin formation (r = 0.32, p = 0.28); and (2) cellular tyrosinase activity vs. cellular melanin formation (r = 0.18, p = 0.43). Ultraviolet A irradiation of melanoma cells A2058 markedly improved the correlation between the inhibition of cellular tyrosinase and of melanin formation of these samples (r = 0.97, p < 0.001). The results suggest that UVA irradiation of melanoma A2058 cells be a useful screening method for evaluating the potential whitening effect of Chinese herbs.