Abstract 198: The Extracellular Superoxide Dismutase is Essential for Preventing Acute Lung Injury at Ambient Oxygen Tension
The extracellular superoxide dismutase (ecSOD) is highly expressed in vessels, lung and heart. Mice with traditional deletion of ecSOD have normal hemodynamics at baseline, but develop augmented hypertension and endothelial dysfunction in resistance vessels in response to angiotensin II. In addition, when given 100% oxygen, ecSOD−/ − mice develop severe lung injury. Traditional deletion of ecSOD throughout the lifetime of the mouse could allow compensatory mechanisms that would mask the true function of this protein. We sought to determine if acute deletion of ecSOD would alter hemodynamics in adult animals. Mice were generated with loxP sites flanking the ecSOD coding region and were backcrossed to the C57Blk/6 background. These mice were crossed with mice transgenic for Tamoxifen (Tam)-inducible Cre (Tgcre/tam) and then bred to homozygosity for the loxP flanked ecSOD. These ecSODloxP x Tgcre/tam mice were then treated with Tam (3 mg/20g) IP for 5 days. Western blot confirmed >70% decrease in ecSOD protein in aorta and lungs of ecSODloxP x Tgcre/tam mice after Tam injection and lung ecSOD enzyme activity was similarly diminished. Tam injection had no effect on these parameters in C57Blk/6 mice. These results were confirmed by immunostaining. Strikingly, acute deletion of ecSOD caused death in >90% of ecSODloxP x Tgcre/tam mice within 15 days, while injection of Tam in C57Blk/6 was without effect. IP injection of vehicle (corn oil) had no effect in either C57Blk/6 or ecSODloxP x Tgcre/tam mice. Histology revealed severe lung damage following acute deletion of ecSOD, with marked thickening of the alveolar septa, obliteration of alveolar spaces and massive inflammatory infiltrate. Using ESR, we found acute deletion of ecSOD increased lung superoxide by 6 fold. Before demise, blood pressure and heart rate did not change significantly. Cardiac function, as determined by echocardiogram was not altered by ecSOD deletion. These results indicate that while acute deletion of ecSOD has no effects on cardiovascular parameters, ecSOD is essential for survival in the presence of ambient levels of oxygen. Acute inactivation of ecSOD, as can occur upon exposure to peroxynitrite or peroxides, could lead to the adult respiratory distress syndrome.