Acute hypoxia decreases E. coli LPS-induced cytokine production and NF-κB activation in alveolar macrophages

Reductions in alveolar oxygenation during lung hypoxia/reoxygenation (H/R) injury are common after gram-negative endotoxemia. However, the effects of H/R on endotoxin-stimulated cytokine production by alveolar macrophages are unclear and may depend upon thresholds for hypoxic oxyradical generation in situ. Here TNF-α and IL-1β production were determined in rat alveolar macrophages stimulated with Escherichia coli lipopolysaccharide (LPS, serotype O55:B5) while exposed to either normoxia for up to 24 h, to brief normocarbic hypoxia (1.5 h at an atmospheric PO2 = 10 ± 2 mm Hg), or to combined H/R. LPS-induced TNF-α and IL-1β were reduced at the peak of hypoxia and by reoxygenation in LPS + H/R cells (P < 0.01) compared with normoxic controls despite no changes in reduced glutathione (GSH) or in PGE2 production. Both TNF-α mRNA and NF-κB activation were reduced by hypoxia that suppressed superoxide anion generation. Thus, dynamic reductions in the ambient PO2 of alveolar macrophages that do not deplete GSH suppress LPS-induced TNF-α expression, IL-1β production, and NF-κB activation even as oxyradical production is decreased.