Abstract Xanthine oxidase (XO) catalyzes the oxidation of hypoxanthine to xanthine and then to uric acid. Excessive production of uric acid leads to hyperuricaemia. Due to the serious side effects of allopurinol, it is an urgent need to explore new XO inhibitors. Herein, the effects of theaflavin (TF1) on XO and anti-hyperuricaemia effect in hyperuricemic mice were investigated. Kinetic analysis indicate that TF1 is a reversible competitive inhibitor and has a significant inhibitory effect on XO with an IC50 value of 63.17 ± 0.13 μmol/L. Analysis of fluorescence spectra suggests that TF1 causes the obvious fluorescence quenching of XO, which is mainly driven by hydrophobic interactions and hydrogen bonds. Docking studies demonstrate that TF1 interacts with dozens of amino acid residues surrounded in the active cavity of XO, including Glu-879, Pro-1012, Thr-1010, Val-1011, Lys-771, Glu-802, Pro-1076, Leu-873, Leu-1014, Asn-768, Leu-648 and Phe-649. The inhibitory mechanism may be the insertion of TF1 into the active site of XO, which hinders the substrate xanthine to enter into the site. Furthermore, the results from animal experiments demonstrate that TF1 is effective in reducing serum uric acid in mice. These findings suggest that TF1 may be a potential drug candidate for the treatment of hyperuricaemia.

中文翻译：

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茶黄素对黄嘌呤氧化酶的抑制作用：小鼠抗高尿酸血症作用的可能机制

摘要 黄嘌呤氧化酶（XO）催化次黄嘌呤氧化为黄嘌呤，再氧化为尿酸。尿酸生成过多会导致高尿酸血症。由于别嘌呤醇的严重副作用，迫切需要探索新的XO抑制剂。在此，研究了茶黄素（TF1）对高尿酸血症小鼠 XO 和抗高尿酸血症的影响。动力学分析表明，TF1是一种可逆的竞争性抑制剂，对XO有显着的抑制作用，IC50值为63.17±0.13 μmol/L。荧光光谱分析表明，TF1引起XO明显的荧光猝灭，主要受疏水相互作用和氢键驱动。对接研究表明，TF1 与 XO 活性腔中包围的数十个氨基酸残基相互作用，包括 Glu-879、Pro-1012、Thr-1010、Val-1011、Lys-771、Glu-802、Pro-1076、Leu-873、Leu-1014、Asn-768、Leu-648 和 Phe-649。抑制机制可能是TF1插入XO的活性位点，阻碍底物黄嘌呤进入该位点。此外，动物实验结果表明TF1可有效降低小鼠血清尿酸。这些发现表明 TF1 可能是治疗高尿酸血症的潜在候选药物。