Experimental and theoretical studies on inhibition against tyrosinase activity and melanin biosynthesis by antioxidant ergothioneine

Ergothioneine, a natural derivative of histidine with a thiol/thine tautomeric structure, exhibits exceptional antioxidant properties and inhibition activities on tyrosinase. In this study, enzyme kinetics experiments and chromatographic spectral analysis revealed that ergothioneine inhibited tyrosinase in a reversible and non-competitive manner, with an inhibition constant of 0.554 mg/mL (2.41 mM). As the concentration of ergothioneine increased, the extremely flexible loop structure of tyrosinase extended from 40.1 % to 41.0 %, effectively covering the active center or binding site. Theoretical molecular docking simulation results show that ergothioneine forms complexes with tyrosinase through hydrogen bonding and salt bridges in the active center of Cu ions. Additionally, it was observed that ergothioneine's antioxidant had a stronger reducing impact on dopaquinone, an intermediate in melanin production, than the effect of ascorbic acid at an equivalent concentration (0.5 mg/mL). Ergothioneine reduced the intracellular reactive oxygen species to lower levels than the control group without UVA radiation and regulated the proliferation and differentiation in B16–F10 melanocytes. Clinical trials have shown that a 0.1 % concentration of ergothioneine can effectively suppress melanin production in irradiated skin. The significant reduction in melanin index and an increase in the individual type angle (ITA°) degree were measured after 4 weeks. These results collectively suggest that ergothioneine may be a promising inhibitor of natural antioxidant tyrosinase. Furthermore, due to its safety and efficacy, ergothioneine could be considered one of the bioactive substances for further study on diseases related to melanin production and tyrosinase activity which is of great significance for the cosmetics, medicine and food industries.