Short-term impairment of energy production in isolated rat liver mitochondria by hypoxia/reoxygenation: involvement of oxidative protein modification

The aim of the present study was to elucidate the role of mitochondria in liver impairment after ischaemia/reperfusion. It is commonly assumed that mitochondria are in part responsible for tissue damage by impaired oxidative phosphorylation as a consequence of the attack of radicals generated within the mitochondria. The principal support for this hypothesis was found by exposing isolated mitochondria to temporary hypoxia in combination with alterations of substrate supply. Rat liver mitochondria treated in this way responded with impaired ADP-stimulated respiration after reoxygenation, which decreased with time of hypoxia and reoxygenation. The decline of the activity of the NADH-cytochrome c-oxidoreductase complex found under these conditions is likely to cause the drop in active respiration. No changes in the content of respiratory chain complexes, determined by Blue Native PAGE, could be demonstrated. However, oxidative modifications of mitochondrial proteins, indicated by carbonyl formation, were found. Likewise, products of lipid peroxidation, such as lipid peroxides and malondialdehyde, were formed. Mitochondria were still able to build up a transmembrane potential and did not show drastic changes in membrane conductivity after hypoxia/reoxygenation stress. The presence of water-soluble antioxidants exhibited a beneficial effect, diminishing the decline of active respiration after 5 min of hypoxia and 10 min of reoxygenation. These observations strongly suggest that mitochondria play a pathogenic role in ischaemia/reperfusion injury, which is at least in part mediated by an oxygen-derived free-radical-linked mechanism.