Biol. Pharm. Bull. 30(4) 677—681 (2007)

protects the skin from harmful effects of sunlight, but unwanted hyperpigmentation can also produce a significant psychologic stress. Therefore, many trials to induce hypopigmentation using melanin synthesis inhibitors, chemical peels and lasers have been conducted. Melanin is synthesized in the melanosomes of melanoma cells, which produce melanin by a process that involves the transformation of tyrosine into 3,4-dihydroxyphenylalanine (L-DOPA) by the enzyme tyrosinase and the subsequent transformation of L-DOPA into melanin. Tyrosinase is the key enzyme in the pathway of melanogenesis, and plays a regulatory role in the production of melanin. Accordingly, the regulation of tyrosinase may not only control melanin production but also provide a strategy for hypopigmentation. A number of compounds have been screened for their effectiveness in reducing melanogenesis, such as hydroquinone and kojic acid, which have been reported as tyrosinase inhibitors. However, these agents have various side effects, such as the adverse cutaneous toxicity of hydroquinone and tumor-promoting effect of kojic acid. Thus, there has been increasing impetus to find alternative hypopigmenting agents. Amino acids are important as they participate in multiple biochemical processes in mammals. In human, alanine and glycine are not considered essential amino acids, since they can be synthesized de novo from a non-amino acid source of nitrogen (e.g., ammonium ions) and an appropriate carbon source. On the other hand, branched-chain amino acids, such as isoleucine and leucine, are considered essential amino acids in mammals, and supplemental dietary values of these amino acids have been established from nitrogen balance studies, and are the basis of the current FAO/WHO/UNU 1985 recommendation for amino acid intake. It has been reported that dietary intake of these amino acids may have beneficial effects, since L-alanine improves the survival rate of rats in a model of acute liver failure induced by administration of D-galactosamine, glycine prevents increases in hepatocyte replication caused by potent peroxisome proliferators and tumor promoter, and isoleucine and leucine are utilized in various metabolic situations ranging from fatigue to liver cirrhosis and encephalopathy. However, no experimental data is available on the effects of amino acids on melanogenesis. Thus, we examined whether amino acids, in particular alanine, glycine, isoleucine and leucine, influence melanogenesis in B16F0 melanoma cells.