ABSTRACT:We hypothesized that fetal pancreatic digestive enzymes play a role in the lung damage after meconium aspiration. We studied the effect of meconium on the A549 alveolar epithelial cell line. The exposure of the cells to 0.5 to 5% meconium resulted in significant disruption of connections between A549 cells and caused dose-dependent cell detachment, without signs of cell death. A protease inhibitor cocktail prevented the A549 cell detachment induced by meconium. After the exposure to 2.5% meconium, a protective effect was quantified by measuring light absorbance by gentian violet stain of still attached cells. The protease inhibitor cocktail and chymostatin showed significant protective effects, increasing the number of attached cells by 135 and 123%, respectively (p Ͻ 0.05). Other individual protease inhibitors tested in the detachment assay (AEBSF, leupeptin, E-64, aprotinin, benzamidine, phosphamidon, and aminohexanoic acid) did not offer statistically significant protection. These results afford a new perspective on the pathophysiology of meconium aspiration syndrome (MAS). We speculate that disruption of intercellular connections and cell detachment from the basement membrane are key events in the pathology associated with MAS. The observed protective effects of protease inhibitors suggest that they may be useful in the treatment and/or prophylaxis of MAS. (Pediatr Res 68: 221-224, 2010) M econium aspiration syndrome (MAS) is a persistent problem in neonatal medicine. Despite a relatively low incidence, it is responsible for as many as 1000 deaths annually in the United States alone (1). Severely affected babies require highly skilled care and complicated technologies to survive. These skills and technologies are not widely available even in the developed world. The broad view on MAS pathophysiology, incidence, impact, prophylaxis, and treatment modalities is well described in the series of recent reviews (1-4).Currently used MAS treatment measures are all supportive in nature and do not directly affect the injurious actions of meconium on the lung. Thus, there is still no effective and safe treatment or prophylactic measure for MAS once the meconium has passed below the vocal cords into the lungs.Research on the mechanisms of MAS-induced injury remains focused on events after the initial injury. Moreover, there is a paucity of ideas and research on how meconium actually damages lungs, apart from mechanical obstruction of the airways. Despite the fact that the pathogenicity of meconium is attributed to its chemical composition (which makes it thick, viscous, sticky, and in some way damaging to pulmonary tissues) and a wealth of studies on its particular constituents, there is little literature on attempts to use this knowledge to explain mechanisms of meconium effects on the tracheobronchial tree.In a recent article, we hypothesized that fetal pancreatic enzymes that are present in meconium might play a direct role in the pathogenesis of MAS through digestion of pulmonary tissues (5). Although the p...