The Role of Oxidative Stress in Hyperuricemia and Xanthine Oxidoreductase (XOR) Inhibitors

Figure 4

Chemical structure of xanthine oxidoreductase (XOR) and XOR inhibitors. Xanthine oxidase (XOR) is the enzyme that catalyzes the oxidation of hypoxanthine to xanthine and xanthine to uric acid. XOR contains two forms: xanthine dehydrogenase (XDH) and xanthine oxidase (XO). XDH prefers NAD⁺ as the substrate, and XO prefers O₂. XOR has 2 flavin molecules (FAD), 2 molybdenum atoms, and 8 iron atoms bound per enzymatic unit. The molybdenum atoms are the active sites of the enzyme, and the iron atoms are part of the [2Fe-2S] ferredoxin iron-sulfur clusters and participate in electron transfer reactions. XOR is a critical target of drug action in the treatment of hyperuricemia. XOR inhibitors are potentially effective drugs to control the related diseases and dysfunctions and include allopurinol, oxypurinol, febuxostat, and topiroxostat.