Structure–Activity Relationships and Changes in the Inhibition of Xanthine Oxidase by Polyphenols: A Review

Hyperuricemia (HUA), or elevated uric acid in the blood, has become more prevalent in recent years. Polyphenols, which are known to have good inhibitory activity on xanthine oxidoreductase (XOR), are effective in uric acid reduction. In this review, we address the structure-activity relationship of flavonoids that inhibit XOR activity from two perspectives: the key residues of XOR and the structural properties of flavonoids. Flavonoids' inhibitory effect is enhanced by their hydroxyl, methoxy, and planar structures, whereas glycosylation dramatically reduces their activity. The flavonoid structure-activity relationship informed subsequent discussions of the changes that occur in polyphenols' XOR inhibitory activity during their extraction, processing, gastrointestinal digestion, absorption, and interactions. Furthermore, gastrointestinal digestion and heat treatment during processing can boost the inhibition of XOR. Polyphenols with comparable structures may have a synergistic effect, and their synergy with allopurinol thus provides a promising future research direction.