Reoxygenation results in cell death of human alveolar epithelial cells

Abstract

Background The functional response of isolated alveolar epithelial cells (AECs) to ischemia/reperfusion injury (I/R) is incompletely understood. Using a cell culture model, we investigated the tolerance of human type II alveolar cells (ATII) to hypoxia and subsequent reoxygenation. Methods Cell cultures of A549 cells (human lung adenocarcinoma) and primary ATII were incubated in 95% N 2/5% CO 2 saturated medium at 37°C for 48 hours or 72 hours. The hypoxic medium was subsequently exchanged to normoxic medium at 37°C. Lactate dehydrogenase (LDH) release and mitochondrial viability, as assessed by WST-1 metabolism, were determined during both hypoxia and reoxygenation. A549 cells and ATII maintained under normoxic conditions served as controls. Results Before reoxygenation, after 48 or 72 hours of hypoxia, WST-1 metabolism in A549 cells was significantly reduced ( p < 0.05), but LDH release remained low in both cell types. Reoxygenation after 48 h of hypoxia was associated with recovery of WST-1 metabolism and an only minimal increase in LDH release. Reoxygenation after 72 hours of hypoxia, in contrast, induced marked injury in both A549 cells and primary ATII as indicated by significantly reduced WST-1 metabolism and a dramatic increase of LDH release compared with normoxic controls ( p < 0.05). Conclusions Viability of alveolar cell lines and primary ATII is maintained during hypoxia for up to 72 hours. Reoxygenation after 72 hours of hypoxia results in rapid development of injury and cell death in both cell types.