PDF(Pubmed)
Abstract：
Xanthine oxidoreductase is a metalloenzyme that catalyzes the final steps in purine metabolism by converting hypoxanthine to xanthine and then uric acid. Allopurinol, an analog of hypoxanthine, is widely used as an antigout drug, as xanthine oxidoreductase-mediated metabolism of allopurinol to oxypurinol leads to oxypurinol rotation in the enzyme active site and reduction of the molybdenum Mo(VI) active center to Mo(IV), inhibiting subsequent urate production. However, when oxypurinol is administered directly to a mouse model of hyperuricemia, it yields a weaker urate-lowering effect than allopurinol. To better understand its mechanism of inhibition and inform patient dosing strategies, we performed kinetic and structural analyses of the inhibitory activity of oxypurinol. Our results demonstrated that oxypurinol was less effective than allopurinol both in vivo and in vitro. We show that upon reoxidation to Mo(VI), oxypurinol binding is greatly weakened, and reduction by xanthine, hypoxanthine, or allopurinol is required for reformation of the inhibitor-enzyme complex. In addition, we show oxypurinol only weakly inhibits the conversion of hypoxanthine to xanthine and is therefore unlikely to affect the feedback inhibition of de novo purine synthesis. Furthermore, we observed weak allosteric inhibition of purine nucleoside phosphorylase by oxypurinol which has potentially adverse effects for patients. Considering these results, we propose the single-dose method currently used to treat hyperuricemia can result in unnecessarily high levels of allopurinol. While the short half-life of allopurinol in blood suggests that oxypurinol is responsible for enzyme inhibition, we anticipate multiple, smaller doses of allopurinol would reduce the total allopurinol patient load.
摘要：
黄嘌呤氧化还原酶（XOR）是一种金属酶，通过将次黄嘌呤转化为黄嘌呤，然后转化为尿酸来催化嘌呤代谢的最后步骤。别嘌呤醇,次黄嘌呤的类似物,被广泛用作抗痛风药物，由于异或介导的别嘌醇向氧嘌呤醇的代谢导致酶活性位点的氧嘌呤醇旋转和钼Mo（VI）活性中心还原为Mo（IV），抑制随后的尿酸盐产生。然而,当直接给高尿酸血症的小鼠模型服用氧普urinol时，它产生比别嘌醇更弱的尿酸盐降低作用。为了更好地了解其抑制机制并告知患者给药策略，在这里，我们进行了动力学和结构分析的抑制活性的氧嘌呤醇。我们的结果表明，在体内和体外，氧嘌呤醇的有效性均低于别嘌呤醇。我们证明，在再氧化为Mo(VI)时，氧普urinol结合被大大削弱，和黄嘌呤减少，次黄嘌呤,或别嘌呤醇是抑制剂-酶复合物的重整所必需的。此外,我们的研究表明，氧嘌呤醇仅微弱地抑制次黄嘌呤向黄嘌呤的转化，因此不可能影响从头嘌呤合成的反馈抑制。此外，我们观察到嘌呤核苷磷酸化酶的弱变构抑制，对患者有潜在的不良影响。考虑到这些结果,我们提出,目前用于治疗高尿酸血症的单剂量方法可导致别嘌呤醇的不必要的高水平.尽管别嘌呤醇在血液中的半衰期较短，但这表明氧嘌呤醇是酶抑制的原因，我们预计会有多个，较小剂量的别嘌醇会降低患者的总别嘌醇负荷.
