Date of Award
Doctor of Philosophy (PhD)
Said H. Audi
Anne V. Clough
David L. Roerig, Elizabeth Jacobs, John F. LaDisa
A common initial treatment of hypoxemia in patients with lung failure secondary to acute lung injury (e.g., adult respiratory distress syndrome) is oxygen (O2) therapy (hyperoxia). However, prolonged O2 therapy causes lung O2 toxicity, which can further impair lung functions. The rat model of lung O2 toxicity replicates key features of human lung O2 toxicity. In addition, rats develop tolerance or susceptibility to 100% O2 by pre-exposing them to 85% O2 (hyper-85) or 60% O2 (hyper-60) for 7 days, respectively. Therefore, the long-term objectives of this study are to elucidate mechanisms involved in rat tolerance of 100% O2, and to further understanding of the mechanisms involved in lung O2 toxicity. In this work, the effects of rat exposure to hyperoxia on targeted lung cytosolic/mitochondrial redox enzymes with pro- or anti-oxidant properties were evaluated using indicator dilution methods. The effect of hyperoxia on mitochondrial membrane potential in cultured endothelial cells was also evaluated using an approach developed in this study. Computational modeling was used for quantitative analysis data from intact lungs or cultured endothelial cells, and for estimation of parameters descriptive of the activities of targeted enzymes and mitochondrial membrane potential. The results revealed an increase in the lung activity of NAD(P)H:quinone oxidoreductase 1 (NQO1) in hyper-85 and hyper-60 rats, a decrease in the lung activity of NADH:ubiquinone reductase (complex I) in rats exposed to 85% O2 for >24 hours and an increase in the lung activity of Q-cytochrome c reductase (complex III) in hyper-85 rats. Exposure of endothelial cells to 95% O2 for 48 hours did not alter mitochondrial membrane potential but increased its sensitivity to mitochondrial uncouplers. These results suggest that the decrease in the activity of complex I might be an early manifestation of an adaptive response to 100% O2; and the increase in the activity of complex III might be important to this adaptive response. Thus, complexes I and III could serve as non-invasive indices of lung O2 toxicity or tolerance using clinical imaging methods, or as therapeutic targets for protecting against lung O2 toxicity.