Hyperoxia-Induced Lung Injury in Gamma-Glutamyl Transferase Deficiency Is Associated with Alterations in Nitrosative and Nitrative Stress

Elizabeth S. Klings^*, Matthew H. Lowry^*, Guihua Li^*, Jyh-Chang Jean^*, Bernadette O. Fernandez, Maria F. Garcia-Saura, Martin Feelisch and Martin Joyce-Brady^*

From the Pulmonary Center,^* and the Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, Massachusetts

${gamma}$ -Glutamyl transferase (GGT) regulates glutathione metabolismand cysteine supply. GGT inactivation in GGT^enu1 mice limitscysteine availability causing cellular glutathione deficiency.In lung, the resultant oxidant burden is associated with increasednitric oxide (NO) production, yet GGT^enu1 mice still exhibithigher mortality in hyperoxia. We hypothesized that NO metabolismis altered under severe oxidant stress and contributes to lungcellular injury and death. We compared lung injury, NO synthase(NOS) expression, nitrate/nitrite production, nitroso productformation, peroxynitrite accumulation, and cell death in wild-typeand GGT^enu1 mice in normoxia and hyperoxia. The role of NOSactivity in cell death was determined by NOS inhibition. Exposureof wild-type mice to hyperoxia caused increased lung injury,altered NO metabolism, and induction of cell death comparedwith normoxia, which was attenuated by NOS inhibition. Eachof these lung injury indices were magnified in hyperoxia-exposedGGT^enu1 mice except nitrosation, which showed a diminished decreasecompared with wild-type mice. NOS inhibition attenuated celldeath only slightly, likely due to further exacerbation of oxidantstress. Taken together, these data suggest that apoptosis inhyperoxia is partially NO-dependent and reiterate the importanceof cellular glutathione in lung antioxidant defense. Therefore,reduced denitrosylation of proteins, possibly resulting in impairedcellular repair, and excessive apoptotic cell death likely contributeto increased lung injury and mortality of GGT^enu1 mice in hyperoxia.