Mitochondrial metabolism of a hydroperoxide to free radicals in human endothelial 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 suggest that lipid hydroperoxides may be responsible for the induction of such damage. Hydroperoxides cause loss of endothelial cell integrity, increase the permeability of the endothelium to macromolecules, and compromise its ability to control vascular tone via the secretion of vasoactive molecules in response to receptor stimulation. The molecular mechanisms 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-butylhydroperoxide 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 mitochondrial electron-transport chain is the source of electrons for this reduction. The metal-ion-chelating agent desferrioxamine was found to prevent cell killing by tert-butylhydroperoxide, but did not affect free radical formation, suggesting that free metal ions may serve to promote free-radical chain reactions involved in cell killing following the initial conversion of the hydroperoxide to free radicals by mitochondria. These processes may well be responsible for many of the reported effects of hydroperoxides on endothelial cell integrity and function.