OBJECTIVE Synthetic compounds that are used in the clinic to regulate skin hyperpigmentation,such as arbutin,and kojic acid,are only moderately effective.But their use is limited by side effects.As part of an effort to overcome the limitations,there is a pressing need for developing effective natural product for whitening.Each of black soybean has been reported to produce anti-melanogenic effects.Especially,antioxidant and anti-aging compounds are richer in testa than the rest part of black soybean.Therefore,we hypothesized that testa of Rhynchosia nulubilis(TR)would show more anti-melanogenic effects than whole black soybean.METHODS Anti-melanogenic effect of TR was done by using mouse B16F10 melanoma.The depigmenting efficacy was then observed following topical application of the TR to UVB-stimulated hyperpigmented dorsal skin of guinea pigs.RESULTS Treatment with TR extract resulted a 27.67% decrease in melanogenesis while whole black soybean showed 5.3% decrease at mouse melanoma cell line.Colorimetric analysis showed a significantly lower depigmenting value by day 14 following treatment with TR in UVB-irradiated guinea pigs the dorsal skin,indicating that TR produced a depigmentation effect.By staining with Hematoxylin-Eosin staing and Fontana-Masson stain,we found that the TR-treated group had more effect histopathologically in epidermal melanin production than resveratrol or rice alone-treated group.TR was associated with reduction in the levels of microphthalmia-associated transcription factor(MITF),and downregulation of tyrosinase and tyrosinase-related protein(TRP-1)expression,leading to inhibit epidermal melanin production by Western blotting analysis.CONCLUSION This study suggests that the testa of R.nulubilis may be a promising candidate in regulating skin pigmentation with UVB exposure. OBJECTIVE Synthetic compounds that are used in the clinic to regulate skin hyperpigmentation, such as arbutin, and kojic acid, are only moderately effective. .But their use is limited by side effects. As part of an effort to overcome the limitations, there is a pressing need for developing effective natural product for whitening.Each of black soybean has been reported to produce anti-melanogenic effects.Especially, antioxidant and anti-aging compounds are richer in testa than the rest part of black soybean.Therefore, we hypothesized that testa of Rhynchosia nulubilis (TR) would show more anti-melanogenic effects than whole black soybean. METHODS Anti-melanogenic effect of TR was done by using mouse B16F10 melanoma. The depigmenting efficacy was then observed following topical application of the TR to UVB-stimulated hyperpigmented dorsal skin of guinea pigs.RESULTS Treatment with TR extract resulted in 27.67% decrease in melanogenesis while whole black soybean showed 5.3% decrease at mouse melanoma c ell line. Colorimetric analysis showed a significant lower depigmenting value by day 14 following treatment with TR in UVB-irradiated guinea pigs the dorsal skin, indicating that TR produced a depigmentation effect. By staining with Hematoxylin-Eosin staing and Fontana-Masson stain, we found that the TR-treated group had more effect histopathologically in epidermal melanin production than resveratrol or rice alone-treated group. TR was associated with reduction in the levels of microphthalmia-associated transcription factor (MITF), and downregulation of tyrosinase and tyrosinase-related protein (TRP-1) expression, leading to inhibit epidermal melanin production by Western blotting analysis. CONCLUSION This study suggests that the testa of R. nulubilis may be a promising candidate in regulating skin pigmentation with UVB exposure.