DO NITROXIDES PROTECT CARDIOMYOCYTES FROM HYDROGEN-PEROXIDE OR SUPEROXIDE

The aim of the research was to study the role played by extracellular O-2(.-) radicals, which are implicated in cardiac cell damage and the protective effect by cell-permeable, nitroxide, superoxide dismutase-m imics. Cardiomyocytes cultures from 1-day-old rats served as the test- system. Experiments were performed since 5th day in culture when >80% of the cells were beating myocardial cells. Oxidative damage was induc ed by 0.5 mM hypoxanthine and 0.06 U/ml xanthine oxidase or by 10 mM g lucose and 0.15 U/ml glucose oxidase. The parameters used to evaluate damages were spontaneous beating, lactate dehydrogenase release and AT P level. The rhythmic pulsation was followed microscopically. To deter mine the kinetics of cytosolic enzyme release from the cells, media sa mples were collected at various points of time and assayed for enzyme activity. To determine the cellular ATP, cells were washed with sodium phosphate buffer, scraped off and boiled for 3 min with sodium phosph ate buffer. Following centrifugation the supernatant was collected and ATP was determined by the chemiluminogenic assay using firefly tails. The present results indicate that nitroxide stable free radicals, in the millimolar concentration range, provide full protection without to xic side-effect. Unlike exogenously added SOD that failed to protect, exogenous catalase provided almost full protection. In addition, the m etal-chelating agent dipyridyl, but not diethylene-triamine-pentaaceta te or desferrioxamine, protected the cultured cells. The present resul ts suggest that H2O2 is the predominant toxic species mediating the ox idative damage whereas extracellular superoxide radical does not contr ibute to cultured cardiomyocyte damage. Since nitroxides do not remove H2O2 they can protect the cells possibly by oxidizing the metal ions and inhibiting the Fenton reaction. The superoxide dismutase-mimic act ivity of nitroxides does not seem to underlie their protective effect, however, the involvement of intracellular O-2(.-) cannot be excluded.