Our results demonstrate that captopril pretreatment significantly inhibits meconium-induced lung cell death, cytokine, and ANGEN expression in newborn lungs.

Background. We previously showed that meconium cuases lung cell death by apoptosis and inflammatory cytokine expression. Whether this is due to meconium exposure itself, or meconium related hypoxia remains unclear. Objectives. To elucidate the effects of meconium, saline, milk, hypoxia and hyperoxia induced lung injury. Design/Methods. We studied 5 groups of rabbit pups: (I) normal saline; (II) Milk; (III) 10% solution of meconium; (IV) only to 15 minutes of hypoxia (10% O2), and (V) 5 minutes of hypoxia (95% O2). After exposure lung lavage cells were used for apoptotic cell count and cytokine expression. In vitro response of human A 549 epithelial cells to meconium-and milk exposure was also studied. Results. There was no difference in cell death between saline and milk groups. However, meconium caused a significant cell loss compared to saline and milk—Inflammatory cytokines increased significantly in meconium group compared to saline or milk group. Although hypoxic and hyperoxic lungs showed increased inflammatory reaction compared to saline-treated lungs, this injury was not significant compared to meconium group. Studies with A549 cells also showed similar results. Conclusions. We conclude that lung cell injury in meconium aspiration is maily from meconium itself.

We have recently purified from meconium-instilled rabbit lungs a novel serine proteinase inhibitor, with an apparent molecular mass of 50 kDa, which we assign to be alpha1-antitripsin. We hypothesize that serpin may attenuate pulmonary inflammation and improve surfactant function after meconium aspiration. Alpha1-antitripsin is a member of the proteinase inhibitor (serpin) superfamily and inhibitor of neutrophil elastase, and it can be identified as a member of the family by its amino acid sequence due to the high degree of conserved residues. Alpha1-antitripsin is synthesized by epithelial cells, macrophages, monocytes, and neutrophils. Deficiency in alpha1-antitripsin leads to exposure of lungs to uncontrolled proteolytic attack from neutrophil elastase or other damaging factors culminating in lung destruction and cell apoptosis. We hypothesize that accumulation of alpha1-antitripsin in the lungs serves as a predisposed protection against meconium-induced lung injury. In this paper, we show how this knowledge can lead to the development of novel therapeutic approaches for treatment of MAS.

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