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There is substantial evidence that oxidative stress participates in the pathophysiology of cardiovascular disease. Biochemical, molecular and pharmacological studies further implicate xanthine oxidoreductase (XOR) as a source of reactive oxygen species in the cardiovascular system. XOR is a member of the molybdoenzyme family and is best known for its catalytic role in purine degradation, metabolizing hypoxanthine and xanthine to uric acid with concomitant generation of superoxide. Gene expression of XOR is regulated by oxygen tension, cytokines and glucocorticoids. XOR requires molybdopterin, iron–sulphur centres, and FAD as cofactors and has two interconvertible forms, xanthine oxidase and xanthine dehydrogenase, which transfer electrons from xanthine to oxygen and NAD⁺, respectively, yielding superoxide, hydrogen peroxide and NADH. Additionally, XOR can generate superoxide via NADH …