PROTECTION OF MYOCYTES AGAINST FREE RADICAL-INDUCED DAMAGE BY ACCELERATED TURNOVER OF THE GLUTATHIONE REDOX CYCLE

The primary defence mechanism of myocytes against peroxides and peroxi de-derived peroxyl and alkoxyl radicals is the glutathione redox cycle . The purpose of the present study was to increase the turnover rate o f this cycle by stimulating the glutathione peroxidase catalysed react ion (2GSH-->GSSG), the glutathione reductase catalysed reaction (GSSG- ->2GSH), or both. Neonatal rat heart cell cultures were subjected to a standardized protocol of oxidative stress using 80 mu mol.l(-1) cumen e hydroperoxide (CHPO) for 0-90 min. The consequences of this protocol were described in terms of cellular concentrations of GSH, GSSG, NADP H and ATP, formation of malondialdelhyde (MDA), release of GSSG and of ATP catabolites, depression of contraction frequency, cellular calciu m overload and enzyme release Trolox-C, an analogue of vitamin E, acce lerated the glutathione peroxidase reaction leading to lowering of GSH concentration and the GSH/GSSG ratio, less MDA formation, diminished negative chronotropy, delayed calcium overload, and less enzyme releas e. Glucose was used to accelerate the glutathione reductase reaction b y supplying NADPH, leading to higher GSH concentration and a higher GS H/GSSG ratio, less MDA formation, diminished negative chronotropy, unc hanged development of calcium overload, and less enzyme release. As a full turn of the glutathione redox cycle involves both the peroxidase and the reductase reactions, the combination of Trolox-C and glucose w as superior to either of the two alone: 90 min following addition of C HPO together with Trolox-C and glucose, the GSH concentration and the GSH/GSSG ratio were almost normal MDA formation was extremely low, cal cium overload was markedly delayed, and enzyme release hardly occurred at all. Cells remained beating in the observation period of 30 min. W e conclude that the capacity of the glutathione redox cycle to withsta nd oxidative stress can be increased by stimulation of either the pero xidase reaction or the reductase reaction, and that optimal redox cycl ing is achieved by stimulation of both reactions.