Meconium Stimulates Production of Thromboxanes From Human Alveolar Epithelial Cell A549 ♦ 1687

Abstract

Meconium Aspiration Syndrome (MAS) is an important cause of morbidity and mortality in the perinatal period. Despite the clinical relevance of MAS, its pathogenesis is poorly understood. In addition, cells and cell products involved in meconium-induced alterations of lung functions are not well defined. We have recently shown that meconium increases the release of cyclo-oxigenase products of arachidonic acid metabolism from murine alveolar macrophages in a cell culture system (Ped Res 39:349A, 1996). These findings assume significant importance since prostanoids appear to be involved in the regulation of several cellular functions: constriction of airway smooth muscle, control of vascular smooth muscle tone and reactivity, modulation of inflammatory/immune cell responses. As a result, they have been invoked in the pathogenesis of several inflammatory lung diseases. To extend our in vitro observations, we investigated whether exposure to meconium leads to changes in thromboxane release from airway epithelial cells in culture. A549 cells were incubated at 37°C in 5% CO2. Under these conditions, cells were approximately 90% confluent on the day after seeding. After preliminary concentration- and time-response experiments, monolayers of A549 cells were incubated with either 1% meconium or serum free medium alone for 6 hours and then washed. After incubation for 24 hours, samples were removed and assayed. Cell viability was determined by the trypan blue exclusion method. The production of a putative mediator of airway dysfunction, thromboxane A2(TXA2), was determined by measuring its immediate and stable metabolite TXB2. This was accomplished by determining the release of TXB2 in the supernatant fluids by enzyme immunoassay. Results were expressed in terms of pg/mg protein (mean±SE). We found meconium produced a significant increase in TXB2 release as demonstrated by the following values: 238.3±37.2 vs 1142.3±218.2 (p=0.0005, paired t-test) for control and meconium-stimulated cells respectively. These findings suggest that exposure to meconium may disrupt the cyclo-oxigenase pathway within airway epithelial cells thus leading to production of substances capable of altering airway function. Further studies are needed to define the role played by epithelial derived prostanoids in the pathogenesis of MAS-induced lung injury.