Superoxide radical and xanthine oxidoreductase activity in the human heart during cardiac operations

Background. The results of clinical trials of xanthine oxidoreductase inhibition in cardiac surgery are encouraging, although studies have failed to localize the enzyme to the human heart and to localize free radical activity to fresh human heart. Methods. We adapted a histochemical staining technique based on the reduction of nitro blue tetrazolium to formazan by superoxide radical. In six samples of right atrium graded blindly on a scale of 0 through 4, strong staining (median grade, 3) of the microvasculature was seen. This was blocked by allopurinol in paired sections (median grade, 1; p < 0.01). Chemiluminescence can be used as an index of superoxide radical activity. Atrial samples were taken from 13 patients at five time points during coronary bypass grafting and placed in buffered luminol. Then chemiluminescence was measured. Results. A 15-fold rise in chemiluminescence (295.93 ± 39.47 mV) was demonstrated during reperfusion compared with the control value (19.06 ± 0.47 mV). Chemiluminescence at 1 minute after release of the cross-clamp was significantly higher (p < 0.05) by analysis of variance versus values obtained before bypass and 1 minute before and 30 minutes after reperfusion. Conclusions. In this study we have identified superoxide radical activity and a possible generating system (xanthine oxidoreductase) in the human heart.