Intestinal epithelial cells mediate lung injury after ethanol exposure and hypoxic insult

Alcohol (EtOH) use may potentiate acute lung injury and development of acute respiratory distress syndrome in patients with shock or sepsis. Gut ischemia/reperfusion (I/R) episodes are common in these settings and may have systemic effects. Human pulmonary microvascular endothelial cells (HMVEC) and Caco-2 intestinal epithelial cells were used to study gut-lung interactions after EtOH exposure in vitro.

Confluent HMVEC monolayers were established and transepithelial electrical resistance measured (T = 0 minutes.). Polarized Caco-2 monolayers were challenged with 0.1% EtOH under normoxia (21% O2) or with hypoxia (5% O2), followed by reoxygenation. Basal chamber supernatants were obtained and incubated with the HMVEC monolayers. Direct exposure of HMVEC to 0.1% EtOH was used in some experiments and media served as control. Monolayer integrity was assessed by permeability to fluorescein isothiocyanate albumin and changes in transepithelial electrical resistance (T = 90 minutes). HMVEC apoptosis and necrosis were determined by staining with Hoechst 33258 and propidium iodide. HMVEC intracellular redox balance was determined by the ratio of disulfide and reduced forms of glutathione.

HMVEC monolayer integrity was severely compromised after exposure to culture supernatants obtained from Caco-2 cells exposed to both EtOH and H/R, but not either alone. This was associated with a significantly higher HMVEC apoptotic rate and alterations in the disulfide and reduced forms of glutathione ratio.

Gut-lung interactions after EtOH exposure and ischemia/reperfusion insults lead to lung injury and may potentiate the clinical evolution of acute respiratory distress syndrome. These in vitro findings confirm clinical experience and provide a model to further elucidate the pathogenic mechanisms.