RESUMO
CONTEXT: Coumarin derivatives have been reported to inhibit melanin biosynthesis. OBJECTIVE: The melanogenesis inhibitory activity of osthol, a major coumarin of the fruits of Cnidium monnieri Cusson (Umbelliferae), and optimized extraction conditions for the maximum yield from the isolation of osthol from C. monnieri fruits were investigated. MATERIALS AND METHODS: B16F10 melanomas were treated with osthol at concentration of 1, 3, and 10 µM for 72 h. The expression of melanogenesis genes, such as tyrosinase, TRP-1, and TRP-2 was also assessed. For optimization, extraction factors such as extraction solvent, extraction time, and sample/solvent ratio were tested and optimized for maximum yield of osthol using response surface methodology with the Box-Behnken design (BBD). RESULTS: Osthol inhibits melanin content in B16F10 melanoma cells with an IC50 value of 4.9 µM. The melanogenesis inhibitory activity of osthol was achieved not by direct inhibition of tyrosinase activity but by inhibiting melanogenic enzyme expressions, such as tyrosinase, TRP-1, and TRP-2. The optimal condition was obtained as a sample/solvent ratio, 1500 mg/10 ml; an extraction time 30.3 min; and a methanol concentration of 97.7%. The osthol yield under optimal conditions was found to be 15.0 mg/g dried samples, which were well matched with the predicted value of 14.9 mg/g dried samples. CONCLUSION: These results will provide useful information about optimized extraction conditions for the development of osthol as cosmetic therapeutics to reduce skin hyperpigmentation.