MECHANISMS OF REPROGRAMMED MACROPHAGE ENDOTOXIN SIGNAL-TRANSDUCTION AFTER LIPOPOLYSACCHARIDE PRETREATMENT

Background. Dysregulation of macrophage tumor necrosis factor (TNF) and interleukin-1 (IL-1) release results from repetitive lipopolysacharride (LPS) stimulation. In this study we investigated the mechanisms of LPS pretreatment (LPS(p)) signal transduction producing altered LPS-activated (LPS(a)) cytokine release. Methods. Murine macrophages were treated with medium alone, actinomycin D, cyclohesimide, a protein kinase C inhibitor (H7), or the nitric oxide synthase inhibitor L-NMA. Macrophages were then pretreated with 100 ng/ml LPS(p) 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 mu g/ml LPS(a) 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 cyclohesimide 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 nitric oxide production with L-NMA had no effect on TNF or IL-1. Conclusions. Complex, independent, but incompletely understood signal transduction pathways for LPS(p)-induced alterations in LPSa-stimulated macrophage TNF and IL-1 release were shown. Understanding altered signal transduction form prior LPS stimulation may suggest new therapies to control dysregulated macrophage cytokine release in sepsis.