University of Aga Khan Medical School, Karachi, Pakistan.
Free Radic Biol Med. 2011 Jul 1;51(1):179-84. doi: 10.1016/j.freeradbiomed.2011.04.004. Epub 2011 Apr 15.
Xanthine oxidase (XO) is a critical source of reactive oxygen species (ROS) that contribute to vascular inflammation. Binding of XO to vascular endothelial cell glycosaminoglycans (GAGs) results in significant resistance to inhibition by traditional pyrazolopyrimidine-based inhibitors such as allopurinol. Therefore, we compared the extent of XO inhibition (free and GAG-bound) by allopurinol to that by febuxostat, a newly approved nonpurine XO-specific inhibitor. In solution, febuxostat was 1000-fold more potent than allopurinol at inhibiting XO-dependent uric acid formation (IC₅₀= 1.8 nM vs 2.9 μM). Association of XO with heparin-Sepharose 6B (HS6B-XO) had minimal effect on the inhibition of uric acid formation by febuxostat (IC₅₀= 4.4 nM) while further limiting the effect of allopurinol (IC₅₀= 64 μM). Kinetic analysis of febuxostat inhibition revealed K(i) values of 0.96 (free) and 0.92 nM (HS6B-XO), confirming equivalent inhibition for both free and GAG-immobilized enzyme. When XO was bound to endothelial cell GAGs, complete enzyme inhibition was observed with 25 nM febuxostat, whereas no more than 80% inhibition was seen with either allopurinol or oxypurinol, even at concentrations above those tolerated clinically. The superior potency for inhibition of endothelium-associated XO is predictive of a significant role for febuxostat in investigating pathological states in which XO-derived ROS are contributive and traditional XO inhibitors are only slightly effective.
黄嘌呤氧化酶（XO）是活性氧（ROS）的重要来源，可导致血管炎症。XO 与血管内皮细胞糖胺聚糖（GAG）结合，导致其对传统的吡唑并嘧啶类抑制剂（如别嘌呤醇）的抑制作用显著增强。因此，我们比较了别嘌呤醇和非嘌呤类 XO 特异性抑制剂非布司他对 XO 的抑制程度（游离型和与 GAG 结合型）。在溶液中，非布司他抑制 XO 依赖性尿酸生成的效力比别嘌呤醇高 1000 倍（IC₅₀=1.8 nM 比 2.9 μM）。与肝素-琼脂糖 6B（HS6B-XO）结合的 XO 对非布司他抑制尿酸生成的作用影响最小（IC₅₀=4.4 nM），同时进一步限制了别嘌呤醇的作用（IC₅₀=64 μM）。非布司他抑制作用的动力学分析显示 K(i)值分别为 0.96（游离型）和 0.92 nM（HS6B-XO），证实游离型和 GAG 固定型酶的抑制作用相当。当 XO 与内皮细胞 GAG 结合时，用 25 nM 的非布司他可观察到完全抑制酶的活性，而用别嘌呤醇或氧嘌呤醇观察到的抑制率不超过 80%，即使在浓度高于临床耐受的水平。对内皮细胞相关 XO 抑制作用的强大效力表明，非布司他在研究 XO 衍生的 ROS 有贡献而传统 XO 抑制剂作用有限的病理状态方面具有重要作用。
