Plasma xanthine oxidase activity in patients with adult respiratory distress syndrome

Abstract

Oxygen metabolites have been implicated in the pathogenesis of various types of acute tissue injury. One biologic source of oxygen metabolites is the reaction catalyzed by the enzyme xanthine oxidase. Because we previously demonstrated that the substrates for xanthine oxidase (hypoxanthine and xanthine) are elevated in the plasma of critically ill patients, we questioned whether the enzyme itself might also be present. We therefore measured hypoxanthine concentration and xanthine oxidase activity in the plasma of 15 patients with ARDS and in 13 non-ARDS critically ill patients. Plasma xanthine oxidase activity in our ARDS group (1,514 +/- 975 mlU/L, mean +/- SE) was higher than that seen in the non-ARDS group (17 +/- 4 mlU/L, P [pre] .05). Plasma hypoxanthine was elevated in both groups, and there was no difference between the ARDS and non-ARDS groups (22.0 +/- 9.2 [mu]mol/L and 11.8 +/- 4.3 [mu]mol/L, respectively). The presence of both circulating xanthine oxidase and its substrate demonstrates the potential for intravascular oxygen metabolite production. These toxic products may then cause tissue injury in ARDS.