Anti-melanin and tyrosinase inhibition mechanism of polydatin and 6″-O-lauryl polydatin synthesized by microwave-assisted enzymatic catalysis

Abstract

Exploiting efficient tyrosinase inhibitors and utilizing the inhibition mechanism are of great significance to avoid enzymatic browning in food and skin melanogenesis. Polydatin had excellent tyrosinase inhibitory activity in vitro with IC50 value of 24.90 μM; however, it exhibited unsatisfactory inhibitory activity intracellularly, which was associated with poor cellular uptake. Fortunately, 6″-O-lauryl polydatin was green-efficiently synthesized by lipase-catalyzed acylation under microwave irradiation. 6″-O-lauryl polydatin exhibited superior mono-/diphenolase inhibitory activity within 100 μM than kojic acid, which had IC50 of 221 μM. Neither polydatin nor 6″-O-lauryl polydatin bound to the catalytic site, but rather bound noncovalently to the allosteric site 2 of tyrosinase through hydrogen bonds and hydrophobic interactions according to molecular simulations, thereby inducing secondary structure unfolding and reducing tyrosinase activity. 6″-O-lauryl polydatin showed stronger anti-browning effects than polydatin in the natural storage of potato and apple pieces. Polydatin and kojic acid did not induce apoptosis, but 6″-O-lauryl polydatin inhibited human melanin A375 cell proliferation by stimulating ROS overproduction and regulating cell cycle and apoptotic pathways. In addition, lipophilic 6″-O-lauryl polydatin had greater cellular uptake though suffered from intracellular hydrolysis, and exerted better tyrosinase and melanogenesis inhibitory activity than polydatin and kojic acid based on mouse B16F10 melanoma cell model. The results suggested polydatin and 6″-O-lauryl polydatin were promising tyrosinase inhibitors for anti-browning in foods or cosmetics fields.