Myeloperoxidase activity as a lung injury marker in the lamb model of congenital diaphragmatic hernia

Purpose: The antioxidant system is the primary intracellular defense system of the lung against oxygen toxicity (neutrophil sequestration). The CDH la mb model antioxidant system is deficient. It is hypothesized that pulmonary neutrophil sequestration may play a part in the acute lung injury of CDH p atients. Myeloperoxidase (MPO) is a major constituent of neutrophil cytopla smic granules and its activity therefore is a direct measure of neutrophil presence and an indirect indicator of lung injury. Methods: Eight lambs had left-sided diaphragmatic hernias surgically create d at 80 days' gestation and were delivered by cesarean section at 140 to 14 5 days. Eight littermate lambs served as controls. Lambs were either killed before ventilation or were ventilated conventionally for 4 hours with 100% O-2 and then killed. The lungs were dissected en bloc and snap frozen. The samples were homogenized, sonicated, freeze-thawed, and separated by densi ty centrifugation. Supernatants were analyzed for myeloperoxidase (MPO) act ivity by spectrophotometry with o-dianisidine dihydrochloride and hydrogen peroxide at 460 nm. The MPO activity was normalized to the protein content of the supernatant and expressed as units of MPO activity per milligram of protein. Results: There was significantly more MPO activity in the CDH-ventilated lu ngs than controls similarly ventilated (3,203 +/- 665 versus 1,220 +/- 194, P = .001). There was no difference in MPO activity between the CDH and con trol lungs (318 +/- 57 v 348 +/- 61; P = .5), There was no difference betwe en right and left lungs in any group. Conclusions: Ventilation and hyperoxia leads to neutrophil accumulation in lung tissue, which is most pronounced in the CDH lung tissue. This is a fur ther clue to the pathophysiology of iatrogenic lung injury in CDH. The myel operoxidase assay may now be used to evaluate antenatal or postnatal antiox idant therapies for iatrogenic lung injury in CDH. Copyright (C) 2001 by W. B. Saunders Company.