OXIDATION OF PROTEINS IN NEONATAL LUNGS

Objective. To develop a method capable of quantifying the oxidative modification of proteins in pulmonary fluid obtained during routine suctioning of neonates receiving ventilation, thus providing an integrated assessment of antioxidant defenses. Design. Consecutive sample of neonates receiving ventilation. Setting. Neonatal intensive care unit. Patients. Twenty-six neonates receiving ventilation with a gestational age of 24 to 42 weeks, from whom 246 samples were collected and analyzed. Measurements and results. The carbonyl content in the lavage samples was measured by reaction with 2,4-dinitrophenylhydrazine followed by high-pressure liquid chromatography. Oxidation of proteins caused introduction of carbonyl groups into the side chains of the protein, providing a convenient and relatively specific marker of oxidative damage. On the first day of life, the initial protein-bound carbonyl for each neonate was usually low and consequently was not significantly related to birth weight, gestational age, or initial ventilatory requirements. Examination of the changes in pulmonary protein carbonyl in the first days of life revealed correlations of interest. In the first day of life, four neonates whose average inspired oxygen were < 40% showed no increase in carbonyl content, whereas four neonates whose inspired oxygen was > 40% showed an average increase in carbonyl of 51% (P < .001). Also, the need for ventilation > 3 days was correlated with elevated carbonyl in those first 3 days. The carbonyl content averaged over the first 3 days was 0.13 +/- 0.02 mol carbonyl/mol protein for the eight neonates receiving ventilation < 72 hours, whereas the nine needing longer ventilation had a carbonyl content of 0.28 +/- 0.03 mol carbonyl/mol protein (P < .05). Seven neonates were treated with dexamethasone because of ventilator dependence at 14 days of age. In these neonates, treatment was associated with a 50% reduction in carbonyl content within 48 hours (P < .02). Conclusions. Oxidative damage to pulmonary proteins can be quantitated in samples obtained during routine suctioning of neonates receiving ventilation. The amount of oxidatively modified protein may provide a quantitative assessment of oxygen toxicity and of pulmonary antioxidant defenses.