Febuxostat inhibition of endothelial-bound XO: Implications for targeting vascular ROS production

• Published in: Free radical biology & medicine Vol. 51; no. 1; pp. 179 - 184
• Main Authors: Malik, Umair Z., Hundley, Nicholas J., Romero, Guillermo, Radi, Rafael, Freeman, Bruce A., Tarpey, Margaret M., Kelley, Eric E.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.07.2011
• Subjects: Allopurinol; Allopurinol - pharmacology; Animals; Cattle; Cells, Cultured; Endothelial cells; Endothelial Cells - metabolism; enzyme inhibition; Enzyme Inhibitors - pharmacology; Febuxostat; Free radicals; glycosaminoglycans; Glycosaminoglycans - metabolism; Inflammation; Kinetics; Oxypurinol; Oxypurinol - pharmacology; Reactive oxygen species; Reactive Oxygen Species - metabolism; Thiazoles - pharmacology; Uloric; uric acid; Xanthine oxidase; Xanthine Oxidase - antagonists & inhibitors; Xanthine Oxidase - metabolism; Xanthine oxidase inhibitors; Reactive oxygen species; Xanthine oxidase inhibitors; Free radicals; Febuxostat; Allopurinol; Uloric; Inflammation; GAG; Endothelial cells; ROS; XO; Xanthine oxidase; XOR; Oxypurinol; XDH
• ISSN: 0891-5849; 1873-4596
• DOI: 10.1016/j.freeradbiomed.2011.04.004

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=1.8nM vs 2.9μM). Association of XO with heparin–Sepharose 6B (HS6B-XO) had minimal effect on the inhibition of uric acid formation by febuxostat (IC50=4.4nM) while further limiting the effect of allopurinol (IC50=64μM). Kinetic analysis of febuxostat inhibition revealed Ki values of 0.96 (free) and 0.92nM (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 25nM 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.