Myocardial release of malondialdehyde and purine compounds during coronary bypass surgery

Free radicals and lipid peroxidation have been suggested to play an important role in the pathophysiology of myocardial reperfusion injury. The purpose of the present study was to monitor myocardial malondialdehyde (MDA) production as an index of lipid peroxidation during ischemia-reperfusion sequences in patients undergoing elective coronary bypass grafting. There has been a lot of debate on the role of xanthine oxidase as a potential superoxide anion generator and thus lipid peroxidation in human myocardium. To evaluate the activity of xanthine oxidase pathway, we measured the changes in the transcardiac concentration differences in adenosine, inosine, hypoxanthine, xanthine, and uric acid.

The coronary sinus-aortic root differences (CS-Ao) of MDA, oxypurines, and nucleosides were measured by a recently developed ion-pairing high-performance liquid chromatographic (HPLC) method. Fifteen patients were included in the study, and 13 of them demonstrated a more than 10-fold increase in net myocardial production of MDA on intermittent reperfusion during the aortic cross-clamp period. In 2 patients, MDA was not detectable in any of the CS or Ao samples. Before aortic cross-clamping, the CS-Ao concentration differences in adenosine, inosine, hypoxanthine, xanthine, and uric acid were 0.59 +/- 0.19, 0.23 +/- 0.05, 0.89 +/- 0.36, 0.58 +/- 0.32, and 11.4 +/- 4.9 mumol/L, respectively. After aortic cross-clamping, the sum of the transcardiac differences of these compounds increased up to 2.8-fold and then gradually decreased after declamping of the aorta. There was a weak positive correlation between transcardiac concentration differences of MDA and xanthine plus uric acid (r = .48, P < .01). The postoperative functional recovery or leakage of cardiac enzymes was not affected by the level of MDA net release during the aortic cross-clamp period, however.

We conclude that myocardial lipid peroxidation, estimated as MDA formation, is common during intermittent ischemia-reperfusion sequences in coronary bypass surgery, although some patients may be better protected. Xanthine oxidase appears to be operative in human myocardium, and free radicals generated in this reaction might also be involved in the observed lipid peroxidation process. Increased degradation of myocardial adenine nucleotides and concomitant lipid peroxidation may play a specific role in the development of reperfusion injury. In this study, however, more extensive lipid peroxidation was not associated with impaired functional recovery.