Role of oxygen in oxidation of lipid and protein during ischemia/reperfusion in isolated perfused rat lung

Abstract

Considerable evidence has accumulated that oxygen free radicals play a major role in ischemic injury, particularly when followed by reperfusion. Few reports have demonstrated the occurrence of oxidative damage during the ischemic period, itself. Our laboratory has demonstrated that events occurring during an ischemic period with adequate oxygen supply can mimic the "oxygen paradox," using lipid peroxidation as an index of oxidative stress and lung edema as an index of tissue injury. The present study compares lipid peroxidation and oxidation of soluble (100,000g supernatant) protein during ischemia and reperfusion in isolated rat lung model perfused with artificial medium and ventilated with varying alveolar oxygen tension. Protein oxidation was determined by a modified dinitrophenylhydrazine (DNPH) method using Sephadex G-25 column chromatography to isolate the DNPH bound proteins. Global ischemia was produced by discontinuing perfusion while ventilation continued with gas mixtures containing 5% CO2 and a fixed oxygen concentration between 0 and 95%. After 1 h ischemia in the isolated rat lung ventilated with 20% oxygen, protein carbonyls and thiobarbituric acid reactive substances (TBARS) increased significantly compared with controls. These changes were more pronounced after 60 min of reperfusion with 95% oxygen in the ventilation gas. With 0% oxygen (95% nitrogen and 5% CO2) content of the ventilating gas during ischemia, TBARS and protein carbonyls remained at the control level. The wet/dry weight ratio showed changes parallel to the indices of tissue oxidation. The presence of 5,8,11,14-eicosatetraynoic, an inhibitor of cyclooxygenase and lipoxygenase pathways, in the perfusate had no effect on the generation of protein carbonyls although inhibition of lipid peroxidation was demonstrated. This implies that the oxidation of soluble protein is not mediated by the eicosanoid metabolic cascade. These data indicate that oxidative processes occur during ischemia and are dependent on the alveolar oxygen concentration. Oxidation of soluble protein can be used as an index of oxidative damage during lung ischemia and reperfusion.