Hyperuricemia and endothelial function: From molecular background to clinical perspectives

Uric acid is the end product of purine metabolism catalyzed by xanthine oxidase in humans. In the process of purine metabolism, reactive oxygen species, including superoxide, are generated concomitantly with uric acid production, which may deteriorate endothelial function through the reaction of superoxide with nitric oxide (NO), leading to decreased NO bioavailability and increased production of peroxynitrite, a reactive oxidant. Therefore, xanthine oxidase may be a therapeutic target in the treatment of endothelial dysfunction. Indeed, clinical studies have shown that endothelial dysfunction is restored by treatment with a xanthine oxidase inhibitor in patients with cardiovascular risk factors. However, it has not been fully determined whether uric acid per se is an independent causal risk factor of endothelial dysfunction in humans. Although experimental studies have indicated that uric acid absorbed into endothelial cells via the activation of uric acid transporters expressed in endothelial cells causes endothelial dysfunction through increased oxidative stress and inflammation, an actual biological effect of uric acid on endothelial function in vivo has not been fully elucidated, in part, because of the difficulty in investigating the effect of uric acid alone on endothelial function due to the close associations of uric acid with other conventional cardiovascular risk factors and the complicated relationship between uric acid and endothelial function attributed to the potent antioxidant properties of uric acid. In this review, we focus on the relationship between uric acid and endothelial function from molecular to clinical perspectives.