Mechanisms of reprogrammed macrophage endotoxin signal transduction after lipopolysaccharide pretreatment.

BACKGROUND

Dysregulation of macrophage tumor necrosis factor (TNF) and interleukin-(IL-1) release results from repetitive lipopolysacharride (LPS) stimulation. In this study we investigated the mechanisms of LPS pretreatment (LPSp) signal transduction producing altered LPS-activated (LPSa) cytokine release.

METHODS

Murine macrophages were treated with medium alone, actinomycin D, cycloheximide, a protein kinase C inhibitor (H7), or the nitric oxide synthase inhibitor L-NMA. Macrophages were then pretreated with 100 ng/ml LPSp and cultured in medium alone, a nitric oxide donor (sodium nitroprusside), or a cyclic adenosine monophosphate donor (8 bromoadenosine) for 20 hours. Cultures were then washed, and fresh medium containing 1 microgram/ml LPSa was added. TNF and IL-1 release in 24-hour supernatant was measured by bioassays.

RESULTS

LPSp inhibited TNF and enhanced IL-1 release. The results with actinomycin D and cycloheximide suggested that LPSp effects did not require transcription, but IL-1 enhancement required protein synthesis. Addition of 8-bromo-cyclic adenosine monophosphate, H7, or nitroprusside prevented LPSp-induced augmentation of IL-1 but had no effect on inhibition of TNF release. Inhibition of LPSp-induced nitric oxide production with L-NMA had no effect on TNF or IL-1.

CONCLUSIONS

Complex, independent, but incompletely understood signal transduction pathways for LPSp-induced alterations in LPSa-stimulated macrophage TNF and IL-1 release were shown. Understanding altered signal transduction from prior LPS stimulation may suggest new therapies to control dysregulated macrophage cytokine release in sepsis.