In vitro and in vivo evaluation of ellagic acid on melanogenesis inhibition

The efficacy of ellagic acid (EA), one of the naturally occurring polyphenols, in inhibiting melanogenesis was examined in vitro and in vivo. When mushroom-derived tyrosinase, a metaloprotein containing copper, was incubated with EA, enzymatic activity tended to decrease with decreasing copper concentration. Enzyme activity partially recovered when copper was added to the inactivated enzyme. Tyrosinase activity in the B16 melanoma cells was observed to recover in a dose-dependent manner when copper ions were added to the medium containing EA. Based on these results, EA is thought to react specifically with the copper located at the active centre of the tyrosinase molecule. Furthermore, when EA was applied for 6 weeks to brownish guinea-pigs, which have melanocytes in their skin, at the same time as irradiating for 2 weeks with ultra-violet light, skin pigmentation was clearly suppressed and the skin to which EA had been applied showed features similar to that of non-irradiated skin. These areas were irradiated again when the application of EA had been completed, and skin pigmentation occurred at the former site of EA application. In similar studies with hydroquinone, re-pigmentation did not occur on the sites at which hydroquinone (1%) had been applied. Based on the results reported here, EA is thought to suppress melanogenesis by reacting with activated melanocytes and without injuring cells.