Smoke/burn injury-induced respiratory failure elicits apoptosis in ovine lungs and cultured lung cells, ameliorated with arteriovenous CO₂ removal

Study objectives: The purpose of this study was to examine the effects of two supportive therapies, conventional mechanical ventilation (CMV) and arteriovenous CO₂ removal (AVCO₂R), during treatment of severe smoke/burn injury-induced ARDS. Design: Sheep were exposed to a smoke/burn injury (lethal dose causing death in 40% of animals); lung tissue and blood was collected prior to injury (control), when an ARDS criterion was met (Pao₂/fraction of inspired oxygen ratio < 200), then after 72 h of either CMV (group 1) or AVCO₂R (group 2). Lung tissue was studied by standard histopathologic techniques; cultured lung cells were studied in media supplemented with serum from all four groups. Measurements and results: In vivo assays demonstrate less apoptotic cell death, and in vitro assays show significantly greater (p < 0.05) cell survival in group 2 (AVCO₂R) than in group 1 (CMV) or baseline. Differential gene expression demonstrates significantly higher messenger RNA levels of proapoptotic and tumor necrosis factor (TNF)-α in cells incubated in baseline media. After exposure of cultured lung cells to conditioned media, protein expression assay of the culture medium revealed no TNF-α, TNF receptor (TNFR)-1, or TNFR-2, however, cultured cell lysate reveals elevated levels of TNF-α, TNFR-1 and caspase-3 in all groups; most occurred in cells incubated in baseline media (p < 0.05). HOECHST stain, DNA fragmentation, and caspase-3 cleavage show that AVCO₂R ameliorates apoptosis in this model. Conclusions: This in vitro work specifically examines cell death in lung cells as a result of smoke/burn injury and effects of therapeutic interventions. Our in vivo studies temporally correlate the clinical pathology to that studied in these lung cells and show that both in vivo and in vitro cell death is predominantly apoptotic and is significantly reduced by AVCO₂R.