Oxyradical-induced antioxidant and lipid changes in cultured human cardiomyocytes

Because the chronically cyanotic myocardium is thought to be more susceptible to oxyradical injury than the noncyanotic myocardium during cardiovascular surgery, we studied the oxyradical susceptibility of human ventricular cardiomyocytes cultured at high and low oxygen tension (PO2) levels. Passage 4 tetralogy of Fallot cardiomyocytes were cultured at PO2 levels of 150 and 40 mmHg for 14 days and then exposed for 10 min to superoxide radicals. The cellular levels of ATP, phospholipid fatty acids, phospholipid conjugated dienes, alpha-tocopherol, and activities of superoxide dismutase, catalase, and glutathione peroxidase were measured. ATP levels decreased more markedly in the low-PO2 group. Although the decrease in alpha-tocopherol levels was similar for both groups, phospholipid conjugated diene formation and phospholipid unsaturated fatty acid loss was greater in the low-PO2 cells. Glutathione peroxidase activity was rapidly inhibited. Superoxide dismutase activity was unaffected, and catalase activity was inhibited by no more than 50%. Although extracellular superoxide dismutase with catalase did not inhibit phospholipid conjugated diene formation and phospholipid breakdown, extracellular glutathione peroxidase with reduced glutathione did limit phospholipid damage. With the occurrence of membrane lipid peroxidation, the decreased glutathione peroxidase activity in the cyanotic tetralogy of Fallot myocardium determines cardiomyocyte membrane susceptibility to oxidant injury.