MITOCHONDRIAL METABOLISM OF A HYDROPEROXIDE TO FREE-RADICALS IN HUMANENDOTHELIAL-CELLS - AN ELECTRON-SPIN-RESONANCE SPIN-TRAPPING INVESTIGATION

Oxidative damage to the vascular endothelium may be an important event in the promotion of atherosclerosis. Several lines of evidence sugges t that lipid hydroperoxides may be responsible for the induction of su ch damage. Hydroperoxides cause loss of endothelial cell integrity, in crease the permeability of the endothelium to macromolecules, and comp romise its ability to control vascular tone via the secretion of vasoa ctive molecules in response to receptor stimulation. The molecular mec hanisms responsible for these effects are, however, poorly understood. In this paper, we describe an e.s.r. spin-trapping investigation into the metabolism of the model hydroperoxide compound tert-butylhydroper oxide to reactive free radicals in intact human endothelial cells. The hydroperoxide is shown to undergo a single electron reduction to form free radicals. Experiments with metabolic poisons indicate that the m itochondrial electron-transport chain is the source of electrons for t his reduction. The metal-ion-chelating agent desferrioxamine was found to prevent cell killing by tert-butylhydroperoxide, but did not affec t free radical formation, suggesting that free metal ions may serve to promote free-radical chain reactions involved in cell killing followi ng the initial conversion of the hydroperoxide to free radicals by mit ochondria. These processes may well be responsible for many of the rep orted effects of hydroperoxides on endothelial cell integrity and func tion.