Xanthine Oxidase - Clinical Significance

Clinical Significance

Xanthine oxidase is a superoxide-producing enzyme found normally in serum and the lungs, and its activity is increased during influenza A infection.

During severe liver damage, xanthine oxidase is released into the blood, so a blood assay for XO is a way to determine if liver damage has happened.

As well, because xanthine oxidase is a metabolic pathway for uric acid formation, the xanthine oxidase inhibitor allopurinol is used in the treatment of gout. Since xanthine oxidase is involved in the metabolism of 6-mercaptopurine, caution should be taken before administering allopurinol and 6-mercaptopurine, or its prodrug azathioprine, in conjunction.

Xanthinuria is a rare genetic disorder where the lack of xanthine oxidase leads to high concentration of xanthine in blood and can cause health problems such as renal failure. There is no specific treatment, sufferers are advised by doctors to avoid foods high in purine and to maintain a high fluid intake. Type I xanthinuria has been traced directly to mutations of the XDH gene which mediates xanthine oxidase activity. Type II xanthinuria may result from a failure of the mechanism which inserts sulfur into the active sites of xanthine oxidase and aldehyde oxidase, a related enzyme with some overlapping activities (such as conversion of allopurinol to oxypurinol.

Inhibition of xanthine oxidase has been proposed as a mechanism for improving cardiovascular health.

Both xanthine oxidase and xanthine oxidoreductase are also present in corneal epithelium and endothelium and may be involved in oxidative eye injury.