Acute hypoxia increases alveolar macrophage tumor necrosis factor activity and alters NF-κB expression

Alterations in alveolar macrophage (AM) function during sepsis-induced hypoxia may influence tumor necrosis factor (TNF) secretion and the progression of acute lung injury. Nuclear factor (NF)-kappa B is thought to regulate the expression of endotoxin [lipopolysaccharide (LPS)]-induced inflammatory cytokines such as TNF, and NF-kappa B may also be influenced by changes in O-2 tension. It is thus proposed that acute changes in O-2 tension surrounding AMs alter NF-kappa B activation and TNF secretion in these lung cells. AM-derived TNF secretion and NF-kappa B expression were determined after acute hypoxic exposure of isolated Sprague-Dawley rat AMs. Adhered AMs (10(6)/ml) were incubated (37 degrees C at 5% CO2) for 2 h with LPS (Pseudomonas aeruginosa, 1 mu g/ml) in normoxia (21% O-2-5% CO2) or hypoxia (1.8% O-2-5% CO2). AM-derived TNF activity was measured with a TNF-specific cytotoxicity assay. Electrophoretic mobility shift and supershift assays were used to determine NF-kappa B activation and to identify NF-kappa B isoforms in AM extracts. In addition, mRNAs for selected AM proteins were determined with RNase protection assays. LPS-exposed AMs in hypoxia had higher levels of TNF (P < 0.05) and enhanced expression of NF-kappa B (P < 0.05); the predominant isoforms were p65 and c-Rel. Increased mRNA bands for TNF-alpha, interleukin-1 alpha, and interleukin-lp were also observed in the hypoxic AMs. These results suggest that acute hypoxia in the lung may induce enhanced NF-kappa B activation in AMs, which may result in increased production and release of inflammatory cytokines such as TNF.