Anti-tyrosinase and Anti-oxidative Activities by Asana: the Heartwood ofPterocarpusmarsupium

Abstract

Asana (the heartwood of Pterocarpus marsupium) has been utilized as an agent for diabetes mellitus in Ayurveda traditional medicine. In our research program to explore novel functions of asana extract, we focused on its skin-whitening effect because asana has been used as a remedy for chronic skin diseases. In addition, the authors have already reported an improvement in blood fluidity that brightens dull facial skin. Based on these effects, asana is a promising candidate agent that possesses both blood fluidity and anti-tyrosinase activities. We focused on the anti-tyrosinase activity and anti-oxidative activities of asana and the results are summarized in this report. We found that a 50% ethanolic extract obtained from asana (PM-ext) showed 23%, 53%, and 71% inhibition against mushroom tyrosinase at 12.5, 50, and 200 µg/mL. Oxyresveratrol and isoliquiritigenin were identified as the active compounds by activity-guided purification. Oxyresveratrol has higher potency than isoliquiritigenin and the IC50of oxyresveratrol was estimated to be 2.1 µM. On the other hand, isoliquiritigenin showed 21%, 28%, and 38% inhibition at 10, 50, and 100 µM, respectively. The inhibitory activity of oxyresveratrol was compared with 3 stilbenes, pterostilbene, resveratrol, and piceatannol. Although oxyresveratrol showed 72.8%, 81.0%, and 85.4% inhibition at 2, 5, and 10 µM, respectively, pterostilbene, resveratrol, and piceatannol showed no effects at the same concentration; these compounds also demonstrated anti-melanogenesis activity on B16 murine melanoma cells. As a result, oxyresveratrol showed the most potent activity, without cytotoxicity, with 38%, 74%, and 84% inhibition at 2, 10, and 20 µM, respectively, while pterostilbene showed 26%, 71%, and 79% inhibition at the same concentration with cytotoxicity at 10 and 20 µM. Resveratrol showed 20%, 41%, and 57% inhibition without cytotoxicity at 2, 10, and 20 µM, respectively. Auto-oxidation is one of the major factors in melanin biosynthesis and anti-oxidative activity is suitable for an anti-melanogenesis agent. We investigated the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity by PM-ext. As a result, PM-ext showed 16%, 33%, and 73% DPPH radical-scavenging activity at 10, 20, and 50 µg/mL, respectively. Oxyresveratrol showed 19%, 31%, and 59% scavenging activity at 10, 20, and 50 µM, respectively, similar to piceatannol. In addition, PM-ext showed 29%, 48%, and 80% suppressive activity on AGEs production at 3.1, 12.5, and 50 µg/mL, respectively. Oxyresveratrol showed 32%, 47%, and 55% activity at 10, 50, and 100 µM, respectively, and this was the most potent among the stilbenes tested. These results suggest that PM-ext could be a promising candidate as skin-whitening agent.