Resveratrol-Enriched Rice Down-Regulates Melanin Synthesis in UVB-Induced Guinea Pigs Epidermal Skin Tissue

Abstract

Synthetic compounds that are used in the clinic to regulate skin hyperpigmentation, such as arbutin, hydroquinone, and kojic acid, are only moderately effective. But, their use is limited by side effects. As part of an effort to overcome the limitations, we developed resveratrol-enriched rice (RR) using genetic engineering technique. Each of resveratrol and rice has been reported to produce anti-melanogenic effects. Therefore, we hypothesized that RR would show more anti-melanogenic effects than those of resveratrol or rice alone. Anti-melanogenic effect of RR was done by using melan-a mouse melanocytes. The depigmenting efficacy was then observed following topical application of the RR to UVB-stimulated hyperpigmented dorsal skin of guinea pigs. Treatment with RR extract resulted a 21.4 +/- 0.7% decrease in tyrosinase expression at melan-a cells. Colorimetric analysis showed a significantly lower depigmenting value by day 9 following treatment with RR in UVB-irradiated guinea pigs the dorsal skin (p<0.01), indicating that RR produced a depigmentation effect. By staining with Fontana-Masson stain, we found that the RR-treated group had more effect histopathologically in epidermal melanin production than resveratrol or rice alone-treated group. RR was associated with reduction in the levels of microphthalmia-associated transcription factor (MITF), and downregulation of tyrosinase and tyrosinase-related protein (TRP-2) expression, leading to inhibit epidermal melanin production by western blot analysis. This study suggests that the resveratrol-enriched rice may be a promising candidate in regulating skin pigmentation with UVB exposure.