Evaluation of Tyrosinase Inhibitory and Antioxidant Activity of Bis(carboxymethoxy) Curcumin Derivatives

Hyperpigmentation disorders are associated with various psychological health concerns and increased risk of skin cancer. Among potential therapeutic approaches, tyrosinase inhibitors represent promising candidates for treating these concerns. This study investigated the tyrosinase inhibitory activity and mechanisms of bis(carboxymethoxy) bismethoxycurcumin (4x), bis(carboxymethoxy) demethoxycurcumin (5v), and bis(carboxymethoxy) bisdemethoxycurcumin (6d). The results showed that 4x exhibited superior tyrosinase inhibitory activity across the tested concentrations (75 - 600 µM), decreasing enzyme activity to 78.52% - 36.72%, relative to 100% of the control, with an IC50 value of 272.85 µM. This compound also demonstrated the highest antioxidant activity, with values of 1.61 µM Trolox equivalent per µM 4x against the ABTS radical. The modification with a carboxymethoxy (-OCH2COOH) group enhanced the tyrosinase inhibitory and ABTS radical scavenging activities, while the absence of a methoxy group reduced these inhibitory activities. Molecular docking analysis indicated that these compounds interacted directly with the tyrosinase active site. Stronger interactions with copper atoms at the active site led to increased tyrosinase inhibitory activity, while the methoxy group proved significant for the tyrosinase inhibitory activity of 4x. Based on its superior inhibitory activity, 4x was selected for further kinetic and melanin inhibition studies, which revealed it to be a competitive inhibitor of tyrosinase with a Ki of 42.38 µM. Moreover, this compound, at concentrations of 75 - 150 µM, reduced melanin content in B16F10 cells to 88.02% - 70.57% compared to 100% of the control, without inducing cytotoxicity. These results suggest that 4x represents a promising candidate for development as an anti-hyperpigmentation agent in both cosmetic and medical applications. HIGHLIGHTS Modification with the carboxymethoxy group significantly enhances the tyrosinase inhibitory activity of curcumin, with 4x exhibiting superior tyrosinase inhibitory and ABTS radical scavenging activities among the three modified curcuminoids, namely 4x, 5v, and 6d. The presence of the methoxy group is essential for the improved anti-tyrosinase and ABTS radical scavenging activities of 4x. 4x, functioning as a competitive inhibitor of tyrosinase and decreasing melanin production in B16F10 cells, emerges as a promising candidate for further research and development as an anti-hyperpigmentation agent.