Discovery of xanthine oxidase inhibitors from Olea europaea L. fruit with antioxidant activity by affinity ultrafiltration guided by molecular docking assay

Olea europaea L. (OEL) fruits play a significant role in the Mediterranean diet. OEL fruits contain abundant bioactive components and have been reported to possess potential antioxidant and xanthine oxidase (XOD) inhibition effects. However, the active components for XOD inhibition effects and related mechanisms are still unclear. In this study, the antioxidant activity of OEL fruits was assessed and showed a good effect on antioxidants. After that, the XOD inhibition effects of OEL fruits were investigated. The results indicated that OEL fruits also have a good impact on inhibiting XOD, with IC₅₀ values of 208.2 ± 1.58 μg/mL. Under the optimal experimental conditions, six potential XOD ligands in OEL fruits were screened out and three phenylethanol analogues were identified (hydroxytyrosol, 3,4-dihydroxy phenyl ethyl acetate, oleuropein). Compared to the inactivated group, 3,4-dihydroxy phenyl ethyl acetate had the highest affinity, indicating it might be the main component of the OEL fruits that inhibit XOD. Molecular docking results elucidated that the potential active components mainly form hydrogen bonds with XOD. The results showed that OEL fruits possessed potential antioxidant and XOD inhibitory effects and that the affinity ultrafiltration (UF) method is an effective method to screen potential ligands for XOD from natural products.