Quick screening of true tyrosinase inhibitors from natural products using tyrosinase-immobilized magnetic nanoparticles and a magnetic microplate

Tyrosinase inhibitors from natural products have applications in the pharmaceutical, food, and cosmetic industries because of the functions of tyrosinase in skin disorders and in the enzymatic browning of fruits. Current in vitro inhibitor screening assays are based on the inhibition of the oxidation of l-3,4-dihydroxyphenylalanine (l-DOPA) mediated by a mushroom tyrosinase. However, in these assays, a tyrosinase inhibitor or an antioxidant could inhibit dopaquinone formation. In this study, we aimed to eliminate this ambiguity by using a microplate assay integrating tyrosinase-immobilized magnetic nanoparticles (TYR-MNPs) and a homemade magnetic microplate for high-throughput screening. After incubating extracts of natural products with TYR-MNPs, the magnetic nanoparticles are attracted to the bottoms of wells, the extracts are rinsed, and TYR-MNPs react with l-DOPA. This method can be used to screen compounds that interact with the active sites of the enzyme, or copper chelators that bind more strongly than tyrosinase to copper ions, distinguishing them from antioxidants or tyrosinase substrates. Integration with the homemade magnetic microplate enables high-throughput inhibitor screening. Aloe vera flowers are crop by-products, and litchi flowers fall after the blossom. Our work demonstrated that these flowers have tyrosinase inhibitory effects, thus increasing their value.