Oxidative stress reversibly inactivates myocardial enzymes during cardiac arrest

Oxidative stress during cardiac arrest may inactivate myocardial enzymes and thereby exacerbate ischemic derangements of myocardial metabolism. This study examined the impact of cardiac arrest on left ventricular enzymes. Beagles were subjected to 5 min of cardiac arrest and 5 min of open-chest cardiac compressions (OCCC) before epicardial direct current countershocks were applied to restore sinus rhythm. Glutathione/glutathione disulfide redox state (GSH/GSSG) and a panel of enzyme activities were measured in snap-frozen left ventricle. To test whether oxidative stress during arrest inactivated the enzymes, metabolic (pyruvate) or pharmacological (N-acetyl-l-cysteine) antioxidants were infused intravenously for 30 min before arrest. During cardiac arrest, activities of phosphofructokinase, citrate synthase, aconitase, malate dehydrogenase, creatine kinase, glucose-6-phosphate dehydrogenase, and glutathione reductase fell by 56, 81, 55, 34, 42, 55, and 45%, respectively, coincident with 50% decline in GSH/GSSG. OCCC effected full recovery of glutathione reductase and partial recovery of citrate synthase and aconitase, in parallel with GSH/GSSG. Phosphofructokinase, malate dehydrogenase, creatine kinase, and glucose-6-phosphate dehydrogenase recovered only after cardioversion. Antioxidant pretreatments augmented phosphofructokinase, aconitase, and malate dehydrogenase activities before arrest and enhanced these activities, as well as those of citrate synthase and glucose-6-phosphate dehydrogenase, during arrest. In conclusion, cardiac arrest reversibly inactivates several important myocardial metabolic enzymes. Antioxidant protection of these enzymes implicates oxidative stress as a principal mechanism of enzyme inactivation during arrest.