Phospholipase A2 is present in meconium and inhibits the activity of pulmonary surfactant: an in vitro study.

UNLABELLED: Atelectasis, a major contributor to pulmonary dysfunction in meconium aspiration syndrome (MAS), is produced by bronchiolar obstruction and surfactant inactivation. It has been shown that substances in meconium, e.g. fatty acids, inhibit surfactant activity. However, the role of the enzyme phospholipase A2 (PLA2), which hydrolyses surfactant in adult respiratory distress syndrome (ARDS), has not yet been studied. Our objective was to investigate whether PLA2 is present in meconium and inhibits pulmonary surfactant activity in vitro. Therefore, the presence of PLA2 activity in meconium, collected from 10 newborns, was measured by the formation of lysophosphatidylcholine after incubation of meconium with radioactively labelled dipalmitoylphosphatidylcholine. Meconium was fractionated by Sephadex G-100 column chromatography and the fractions were assayed for PLA2 activity. Also, their effect on the surface tension of surfactant (Curosurf) was measured using a pulsating bubble surfactometer (PBS). PLA2 activity was present in all meconium samples. Addition of meconium to surfactant significantly increased surface tension (mean +/- SD: 1.7 +/- 1.6 mN/m to 24.3 +/- 6.7 mN/m, p = 0.0001) and only the addition of the PLA2 containing fraction from meconium to surfactant also significantly increased surface tension (mean 1.7 +/- 1.6 mN/m to 19.0 +/- 3.58 mN/m, p < 0.0001).

CONCLUSION: PLA2 is present in meconium and inhibits the activity of pulmonary surfactant in vitro. Therefore, PLA2 in meconium may contribute to surfactant inactivation and alveolar atelectasis in MAS.