INHIBITION OF NADH-LINKED MITOCHONDRIAL RESPIRATION BY 4-HYDROXY-2-NONENAL

During the progression of certain degenerative conditional including m yocardial ischemia-reperfusion injury, mitochondria are a source of in creased free-radical generation and exhibit declines in respiratory fu nction(s). It has therefore been suggested that oxidative damage to mi tochondrial components plays a critical role in the pathology of these processes. Polyunsaturated fatty acids of membrane lipids are prime m olecular targets of free-radical damage. A major product of lipid pero xidation, 4-hydroxy-2-nonenal (WNE), is highly cytotoxic and can readi ly react with and damage protein. In this study, the effects of HNE on intact cardiac mitochondria were investigated to gain insight into po tential mechanisms by which free radicals mediate mitochondrial dysfun ction. Exposure of mitochondria to micromolar concentrations of HNE ca used rapid declines in NADH-linked but not succinate-linked state 3 an d uncoupled respiration. The activity of complex I was unaffected by H NE under the conditions of our experiments. Loss of respiratory activi ty reflected the inability of HNE-treated mitochondria to meet NADH de mand during maximum rates of O-2 consumption. HNE exerted its effects on intact mitochondria by inactivating alpha-ketoglutarate dehydrogena se. These results therefore identify a potentially important mechanism by which free radicals bring about declines in mitochondrial respirat ion.