Biol. Pharm. Bull. 30(6) 1052—1055 (2007)

color and plays a significant role in protection the skin from UV light; while overproduction and accumulation of melanin result in various skin dermatological disorders including melasma, freckles, age spots, and sites of actinic damage or other hyperpigmentations. Thus, melanogenic inhibitors have become increasingly important ingredients in medication and cosmetics for the prevention of hyperpigmentation. Tyrosinase (polyphenol oxidase), a copper-containing monooxygenase, is a key enzyme involved in melanogenesis. Tyrosinase catalyzes two different reactions: hydroxylation of tyrosine and oxidation of the o-diphenol product, L-DOPA. DOPA oxidation generates a highly reactive intermediate, which is oxidized to form melanin through a radical-coupling pathway. In fact, the melanocyte is under continuous lowgrade oxidative stress, as melanogenesis leads to the production of hydrogen peroxide that, if inappropriately processed, can cause the generation of hydroxyl radicals and other reactive species (RS). UV light and oxidative stress caused by excessive RS are casually linked to skin disorders, indicating that antioxidants may have a beneficial effect on skin health. It is also known that RS are considered to play significant roles in the regulation of the melanocytes proliferation and melanogenesis, while RS scavengers and inhibitors of RS generation may down-regulate hyperpigmentation or thwart new UV-induced melanogenesis. The inhibition of melanogenesis may be related to GA’s antioxidant activity in scavenging reactive oxygen species. Antioxidants such as ascorbic acid derivatives are used as melanogenesis inhibitory agents, and reduced glutathione (GSH) is a well known biological antioxidant that acts as a quencher of oxidative insults, thereby playing a significant role in the inhibition of melanogenesis. Recently, we reported that the antimelanogenic action of 4,4 -dihydroxybiphenyl is likely carried out by a combined effect of its antioxidant properties and its ability to increase GSH levels. Many phenolic compounds are known to show potent antioxidant activity, and a number of naturally occurring melanogenic inhibitors contain a phenol structure. Gallic acid (GA, 3,4,5-trihydroxybenzoic acid) is a naturally occurring polyphenol antioxidant that was recently shown to have potentially healthy effects; however, the inhibitory action of GA on skin melanogenesis has not been fully explored. In this present work, I attempted to investigate the effect of GA on the mushroom tyrosinase activity, tyrosinase activity, and melanin content in B16 melanoma cells (B16 cells). Furthermore, I looked into the melanogenesis inhibitory effect of GA associated with its antioxidant property by assessing its effect on RS suppression and the GSH/GSSG (oxidized glutathione) ratio.