Antioxidant defences in rat, pig, guinea pig, and human hearts: comparison with xanthine oxidoreductase activity

Abstract

Objective: Cardiac injury, related to ischaemia and reperfusion, may be caused by the action of oxygen free radicals. Xanthine oxidoreductase activity may be an important free radical source. During cardiac ischaemia, the native dehydrogenase form may be converted to the oxidase form, which uses molecular oxygen to form superoxide radicals. Superoxide dismutase converts the radicals to H2O2, which is detoxified by catalase and glutathione peroxidase. In view of the large differences in xanthine oxidoreductase in various species, the activity of these antioxidant enzymes was investigated.

Methods: Normal rodent and porcine as well as explanted human hearts were perfused according to Langendorff. After a 30 minute stabilisation period, hypoxanthine was added to the perfusion buffer to estimate xanthine oxidoreductase. Hearts or biopsies were freeze clamped after 90 minutes. Effluent xanthine and urate were assayed with high performance liquid chromatography; tissue reduced glutathione content and the activity of superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase were determined spectrophotometrically. Apparent xanthine oxidoreductase was calculated as xanthine +2 x urate production.

Results: Xanthine oxidoreductase was (mU.g-1 protein, mean(SEM), n = 5-7): rat, 470(40); guinea pig, 270(41); pig < 1.5; and human, 5.4(1.0). Superoxide dismutase activities were (U.g-1 protein): rat, 13,370(1030); guinea pig, 10,100(1110); pig, 12,800(450); and human, 7400(450). Catalase activity (k < or = 10.g-1 protein) was low in all species studied. Glutathione peroxidase activity was 93(7) U.g-1 protein in rat heart, and 10 x lower in the other species. Glutathione reductase activity was (U.g-1 protein): rat, 15.0(1.6); guinea pig, 10.4(1.3); pig, 16.0(1.5); and human, 26.6(2.0). Tissue reduced glutathione concentrations were (mumol.g-1 protein): rat, 13.5(0.8); guinea pig, 18.5(0.9); pig, 11.1(2.9); and human 17.2(1.7).

Conclusions: Considerable species differences in xanthine oxidoreductase activity exist, contrasting with the smaller variations in antioxidant enzyme activities. In the species examined catalase activities were very low. Rat hearts are far better protected against H2O2 than the other three species. Xanthine oxidoreductase induced free-radical damage probably plays a minor role in pig and human hearts. Human myocardium seems less protected against superoxide radicals.