JOURNAL OF COSMETIC SCIENCE 356 (DHICA). TRP-2 catalyzes the tautomerization of dopachrome to DHICA, and the fu- ture oxidation of DHICA by DHICA oxidase (TRP-1) gives rise to the DHICA-eumelanin (26,27). As is shown in Figure 3, treatment with 500 μM of geranic acid for 3 days resulted in a signifi cant reduction in the generation of intracellular tyrosinase. However, the level of intracellular TRP-2 was not altered by geranic acid treatment. Therefore, geranic acid acts specifi cally to reduce the expression of tyrosinase. DISCUSSION Based on previous reports of the tyrosinase-inhibitory effects of geranic acid (11), the inhibitory activity of geranic acid and three geranic acid derivatives on the biosyn- thesis of melanin pigment in Melan-a cells was evaluated. According to our results, geranic acid inhibited relative melanin contents by 25.6% as compared to the cell viability level at 500 μM. Additionally, geranic acid evidenced inhibitory effects on tyrosinase activity and intracellular expression. However, the inhibitory activities of geranic acid derivatives on melanin formation were found to be weaker than that of geranic acid. Geraniol, an alcohol analog of geranic acid, evidenced more profound cell toxicity than was observed with geranic acid. Citronellol and citronellic acid evidenced no signifi cant melanin synthesis-inhibitory activity at any tested concentration. Geranic acid is a colorless to pale yellow clear oily liquid, with a typical fl avor. It is fre- quently used as a perfuming agent in the cosmetics industry. Although the tyrosinase- inhibitory activity of geranic acid has been recently reported, its depigmenting properties in melanocytes were fi rst reported, to the best of our knowledge, in this study. Overall, these results indicated that geranic acid may prove useful not only as a perfuming agent but also as a skin depigmentation agent. Although Melan-a cells are commonly used in such studies, experiments using normal human melanocytes would be an appropriate next step. Figure 3. Effects of geranic acid on tyrosinase and dopachrome tautomerase expression in Melan-a cells. The Melan-a cells were treated with geranic acid for 3 days. TRP-2 (tyrosinase-related protein-2) dopachrome tautomerase.

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