Relative hyperoxia augments lipopolysaccharide-stimulated cytokine secretion by murine macrophages

Abstract

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 pO2 of 40 mm Hg. We hypothesize that exposure of lipopolysaccharide-stimulated macrophages to “non-physiologic” pO2 augments cytokine secretion. Method. Murine macrophages were preconditioned to a pO2 of 40 mm Hg for 24 hours. The medium then was discarded and exchanged for a medium containing a pO2 of 40, 150, or 440 mm Hg. Macrophages were incubated in the desired pO2 for 6 and 24 hours while stimulated with lipopolysaccharide (0 to 100 ng/mL). The effect of pO2 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 pO2. Higher pO2 did not stimulate TNF and interleukin-6 in the absence of lipopolysaccharide. However, a pO2 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 pO2 and lipopolysaccharide for macrophage TNF and interleukin-6 production. Similar pO2 elevations may occur with an open peritoneum or high supplemental O2. Cytokines from peritoneal macrophages may contribute to the increased systemic inflammation after open operations. (Surgery 2003;133:538-46.)