Inhaled nitric oxide prevents 3-nitrotyrosine formation in the lungs of neonatal mice exposed to > 95% oxygen

Inhaled nitric oxide is being evaluated as a preventative therapy for patients at risk for bronchopulmonary dysplasia (BPD). Nitric oxide (NO), in the presence of superoxide, forms peroxynitrite, which reacts with tyrosine residues on proteins to form 3-nitrotyrosine (3-NT). However, NO can also act as an antioxidant and was recently found to improve the oxidative balance in preterm infants. Thus, we tested the hypothesis that the addition of a therapeutically relevant concentration (10 ppm) of NO to a hyperoxic exposure would lead to decreased 3-NT formation in the lung. FVB mouse pups were exposed to either room air (21% [O.sub.2]) or >95% [O.sub.2] with or without 10 ppm NO within 24 h of birth. In the first set of studies, body weights and survival were monitored for 7 days, and exposure to >95% [O.sub.2] resulted in impaired weight gain and near 100% mortality by 7 days. However, the mortality occurred earlier in pups exposed to >95% [O.sub.2] + NO than in pups exposed to > 95% [O.sub.2] alone. In a second set of studies, lungs were harvested at 72 h. Immunohistochemistry of the lungs at 72 h revealed that the addition of NO decreased alveolar, bronchial, and vascular 3-NT staining in pups exposed to both room air and hyperoxia. The lung nitrite levels were higher in animals exposed to > 95% oxygen + NO than in animals exposed to >95% oxygen alone. The protein levels of myeloperoxidase, monocyte chemotactic protein-1, and intracellular adhesion molecule-1 were assessed after 72 h of exposure and found to be greatest in the lungs of pups exposed to > 95% [O.sub.2].This hyperoxia-induced protein expression was significantly attenuated by the addition of 10 ppm NO. We propose that in the presence of> 95% [O.sub.2], peroxynitrite formation results in protein nitration; however, adding excess NO to the > 95% [O.sub.2] exposure prevents 3-NT formation by NO reacting with peroxynitrite to produce nitrite and N [O.sub.2].We speculate that the decreased protein nitration observed with the addition of NO may be a potential mechanism limiting hyperoxic lung injury. Keywords Protein nitration * Peroxynitrite * Lung injury * Oxygen toxicity
Introduction Inhaled nitric oxide (iNO) is a selective pulmonary vasodilator approved for the treatment of term and near-term neonates with hypoxic respiratory failure associated with evidence of pulmonary hypertension. The [...]