Relative hyperoxia augments lipopolysaccharide-stimulated cytokine secretion by murine macrophages.

BACKGROUND: Increased systemic levels of inflammatory mediators are seen after open abdominal operations. Macrophages that are exposed to lipopolysaccharide secrete cytokines. Peritoneal macrophages normally reside in a pO(2) of 40 mm Hg. We hypothesize that exposure of lipopolysaccharide-stimulated macrophages to "non-physiologic" pO(2) augments cytokine secretion. METHOD: Murine macrophages were preconditioned to a pO(2) of 40 mm Hg for 24 hours. The medium then was discarded and exchanged for a medium containing a pO(2) of 40, 150, or 440 mm Hg. Macrophages were incubated in the desired pO(2) for 6 and 24 hours while stimulated with lipopolysaccharide (0 to 100 ng/mL). The effect of pO(2) was compared. Supernatant tumor necrosis factor (TNF) and interleukin-6 were measured with enzyme-linked immunosorbent assay. Statistics were performed with analysis of variance. RESULTS: We found dose-dependent lipopolysaccharide-stimulated TNF and interleukin-6 production with macrophages incubated at physiologic pO(2). Higher pO(2) did not stimulate TNF and interleukin-6 in the absence of lipopolysaccharide. However, a pO(2) of 150 and 440 mm Hg significantly (P <.05) increased lipopolysaccharide-stimulated TNF and interleukin-6 production versus 45 mm Hg. CONCLUSION: Our data suggest synergy between increased pO(2) and lipopolysaccharide for macrophage TNF and interleukin-6 production. Similar pO(2) elevations may occur with an open peritoneum or high supplemental O(2). Cytokines from peritoneal macrophages may contribute to the increased systemic inflammation after open operations.