Screening and Mechanistic Investigation of Synergistic Xanthine Oxidase Inhibitors Based on Structure–Activity Relationships

In order to screen the synergistic inhibitors of xanthine oxidase (XOD), the inhibitory activities of 16 flavonoids in Coreopsis tinctoria were evaluated by structure–activity relationship in this study. Eight flavonoids were screened and were observed to have XOD inhibition and antioxidant capacity, and the zero-interaction potential (ZIP) score was used to determine the synergistic effect with allopurinol. Among them, butein and coreopsin showed good synergistic activity (average ZIP > 15). Subsequently, the inhibitory mechanism of butein and coreopsin alone and in combination with allopurinol on XOD was investigated using in vitro experiments. The inhibitory ability of both on XOD was relatively strong. After combination with two chalcones, the enzyme-inhibition effect of allopurinol was significantly improved. Butein and coreopsin can enhance the binding ability of allopurinol to XOD, induce the conformational change of the enzyme, and achieve synergistic inhibition. The binding mode and key amino-acid binding contribution of the complex were analyzed by computer simulation. In summary, the two chalcones might serve as potential XOD inhibitors and synergistic adjuvants for allopurinol.