EFFICACY OF LIPID-SOLUBLE, MEMBRANE-PROTECTIVE AGENTS AGAINST HYDROGEN-PEROXIDE CYTOTOXICITY IN CARDIAC MYOCYTES

We examined the efficacy of a group of drugs that stabilize the cell m embrane and can potentially prevent cytotoxicity in cultured fetal chi ck cardiac myocytes exposed to hydrogen peroxide (H2O2). The effects o f various membrane-protective agents were determined by analysis of th e kinetics of lactic dehydrogenase (LDH) release. The kinetic paramete rs calculated from the data include a rate constant fbr release of LDH (k(b)) and the fraction of total LDH that is released from the cells (CIIMax). The CII(Max)s derived from a range of H2O2 concentrations re veal that the mean toxic concentration of H2O2 is 1.1 mM and that the pattern of toxicity is consistent with the damage being directly propo rtional to the concentration of the free radicals generated from the H 2O2. Maximum nontoxic concentrations of three amphiphilic membrane pro tective agents had no effect upon cytotoxicity from H2O2 The slightly polar lipophilic agent, Trolox C, a vitamin E derivative, was also wit hout protective effect at a maximum nontoxic concentration. The highly lipophilic agent, probucol, had a small protective effect at 50 mu M, the maximum concentration we succeeded in solubilizing in the culture medium. However, the lipophilic 21-aminosteroid U74500, delivered to the cells in an emulsion, markedly reduced cytotoxicity from H2O2 The CII Max was significantly reduced and the protection was concentration dependent over a range of concentrations from 50-400 nmol/ml. Further more, the inhibition by U74500 was fully consistent with a mechanism o f scavenging of free radicals formed during lipid peroxidation. In sup port of this hypothesis, a dose of 400 nmoles/ml completely prevented an increase in lipid peroxides due to H2O2 exposure, whereas there was a sixfold increase during exposure to H2O2 in untreated myocytes. Thu s, a lipid soluble 21-aminosteroid prevented lipid peroxidation and re duced cardiac myocyte injury during exposure to H2O2, probably by scav enging of free radicals formed during lipid peroxidation in the cell m embrane, whereas amphiphilic agents, which probably altered the physic ochemical structure of the cell membrane but did not scavenge free rad icals, were not protective.