Plasma 3-nitrotyrosine is elevated in premature infants who develop bronchopulmonary dysplasia

Premature infants are susceptible to bronchopulmonary dysplasia (BPD), a chronic lung disease of infancy that appears to be caused in part by oxidative stress from hyperoxia. To investigate the possible role of nitric oxide-derived oxidants such as peroxynitrite in the etiology of BPD, we measured levels of plasma 3-nitrotyrosine, which is produced by the reaction of peroxynitrite with proteins.

Ten premature infants who developed BPD, defined as requiring supplemental oxygen beyond 36 weeks' postmenstrual age, were identified retrospectively from a group of subjects enrolled in a clinical trial of antenatal therapy. Serial plasma samples had been collected on these infants during the first month of life as part of the trial. Sixteen comparison premature infants were identified from the same population: 5 had no lung disease, 6 had respiratory distress syndrome that resolved, and 5 had residual lung disease at 28 days of life that resolved by 36 weeks' postmenstrual age. Plasma 3-nitrotyrosine levels were measured using a solid phase immunoradiochemical method.

All 3-nitrotyrosine values in infants without BPD were <0.25 ng/mg protein, and levels did not change with postnatal age. Plasma 3-nitrotyrosine concentrations were significantly higher in infants with BPD, increasing approximately fourfold during the first month of life. For the 20 infants who had blood samples available at 28 days of life, plasma 3-nitrotyrosine levels correlated with the fraction of inspired oxygen that the infant was receiving (r = 0.7).

Plasma 3-nitrotyrosine content is increased during the first month of life in infants who develop BPD. This suggests that peroxynitrite-mediated oxidant stress may contribute to the development of this disease in premature infants and that 3-nitrotyrosine may be useful as an early plasma indicator of infants at risk for developing BPD.