Oxygen free radicals are generated by the xanthine oxidase system and the generated free radicals provide the pathophysiological link of uric acid with a variety of deleterious effects, including increased cytokine production, apoptosis, and endothelial dysfunction. They suggested that the effects of xanthine oxidase, which was expressed only in the myocardium, were local and not systemic [16]. Here, XDH is linked to endothelial dysfunction.