Polymyxin B prevents lipopolysaccharide-induced release of tumor necrosis factor-alpha from alveolar macrophages.

Polymyxin B (PmB) blocks many of the toxic effects of lipopolysaccharide by mechanisms that are not yet understood. The production of tumor necrosis factor-alpha (TNF-alpha) by isolated rat alveolar macrophages in response to lipopolysaccharide and macrophage-activating factor was blocked by PmB at concentrations of 100, 10, and 1 micrograms/ml. Gentamicin enhanced rather than inhibited TNF production at the 100-micrograms/ml concentrations and had no effect at low concentration. Similar inhibitory effects were induced by PmB in an in vivo model in which rat macrophage TNF production was stimulated by intratracheally injected lipopolysaccharide. Because many of the effects of lipopolysaccharide are mediated by TNF, this inhibition provides a mechanism to explain the protection afforded by PmB against lipopolysaccharide-induced toxicity.