Biol. Pharm. Bull. 30(11) 2031—2036 (2007)

melanin protects the skin from the harmful effects of sunlight, but unwanted hyperpigmentation can also produce significant psychological stress. Melanin is synthesized in the melanosomes in melanocytes, which produce melanin by a process that involves the transformation of tyrosine into 3,4dihydroxyphenylalanine (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 modulation of unwanted hyperpigmentation. Various agents have been screened for their effectiveness in reducing melanogenesis, such as hydroquinone and kojic acid, which have been reported as tyrosinase inhibitors. However, these compounds have side effects, such as the adverse cutaneous toxicity of hydroquinone and tumor-promoting effect of kojic acid. Thus there has been increasing impetus to develop alternative hypopigmenting agents. Amino acids are important molecules that participate in multiple biochemical processes in mammals. Glycine is the simplest of the nonessential amino acids, and dietary glycine intake may have beneficial effects. We previously demonstrated that glycine inhibits spontaneous melanogenesis in B16F0 melanoma cells, similar to kojic acid, which is a typical tyrosinase inhibitor. However, in that study, glycine did not affect crude tyrosinase activity, therefore the mechanisms of the inhibitory effect of glycine on melanogenesis are unclear. a-Melanocyte stimulating hormone (a-MSH) is one of the major propigmentation hormones, and synthesis of a-MSH is an important determinant of constitutive pigmentation and the cutaneous response to UV. Following UV-exposure, a-MSH is produced and secreted by both keratinocytes and melanocytes in the skin. Therefore, a-MSH-induced melanogenesis in melanoma cells is thought to be a good in vitro model for UV-induced pigmentation. On the other hand, the number of in vivo experimental models of pigmentation is limited. C57BL/6J mice have been used, as they have depilation-induced hair follicle cycling and show hair pigmentation. The hair follicle passes through three key cyclic regeneration stages, telogen, anagen and catagen. Plucking of hair initiates the anagen phase of the hair cycle, followed by activation of follicular melanocytes and high tyrosinase activity. Treatment with phenolic derivatives, a substrate for tyrosinase, causes hypopigmentation of newly grown hair in C57BL/6J mice. Therefore, the melanogenesis of hair follicles in C57BL/6J mice has been recognized as a useful model for researching pigmentation in vivo. The present study was performed to investigate the mechanisms of the inhibitory effect of glycine on melanogenesis using a-MSH-induced melanogenesis in B16F0 melanoma cells and hair follicle melanogenesis in C57BL/6J mice.