Protective role of glucocorticosteroid prior to endotoxin exposure in cultured neonatal type II alveolar epithelial cells

Background: Dexamethasone (DEX) is widely used for antenatal lung maturation and has been investigated to prevent premature lung injury by inhibiting postnatal inflammation. Its pharmacological mechanisms in the treatment of bacterial infection-induced injury of neonatal lung parenchymal cells remain to be clarified. We hypothesized that DEX pretreatment may attenuate endotoxin-induced growth suppression and regulate cytokine mRNA expression in cultured neonatal type II alveolar epithelial cells (AEC-II). Methods: AEC-II of newborn piglets were freshly isolated and cultured. After pretreatment of 0.01, 0.1, 1.0 and 10 moll DEX (E0.01, E0.1, E1.0 and E10 group, respectively) for 24 h, the cells were cultured with 1 mu g/ml lipopolysaccharides (LPS) for 7 days with medium replacement every 24 h. Messenger RNA expression of surfactant proteins (SPs), pro-inflammatory cytokines and multiple growth factors (GF) were determined by RTPCR, along with the cell growth and apoptosis measurements. Results: LPS without DEX pretreatment suppressed cell proliferation, enhanced expression of pro-inflammatory cytokine mRNA and apoptosis, which was ameliorated in all DEX-pretreated groups on day 3. On day 3 and 5, only cells pretreated by E1.0 and E10 showed a 20-fold increase in insulin-like GF-1 mRNA expression whereas the expression of other GFs was down-regulated. LPS exposure reduced the expression of SP-A, B, C and Aquaporin-5 mRNA on day 3-7. However, the expression of SP-C mRNA was increased in E1.0 on day 3, which was supported by in situ expression of pro-SP-C with immunocytochemical assay. Conclusion: LPS-induced in vitro AEC-II injury was partially prevented by DEX pretreatment, with 1.0 mu mol/l being the potentially optimal concentration. (253 words).