MECHANISMS OF REPROGRAMMED MACROPHAGE ENDOTOXIN SIGNAL-TRANSDUCTION AFTER LIPOPOLYSACCHARIDE PRETREATMENT

Background. Dysregulation of macrophage tumor necrosis factor (TNF) an d interleukin-1 (IL-1) release results from repetitive lipopolysacharr ide (LPS) stimulation. In this study we investigated the mechanisms of LPS pretreatment (LPS(p)) signal transduction producing altered LPS-a ctivated (LPS(a)) cytokine release. Methods. Murine macrophages were t reated with medium alone, actinomycin D, cyclohesimide, a protein kina se C inhibitor (H7), or the nitric oxide synthase inhibitor L-NMA. Mac rophages were then pretreated with 100 ng/ml LPS(p) and cultured in me dium alone, a nitric oxide donor (sodium nitroprusside), or a cyclic a denosine monophosphate donor (8-bromoadenosine) for 20 hours. Cultures were then washed, and fresh medium containing 1 mu g/ml LPS(a) was ad ded. TNF and IL-1 release in 24-hour supernatant was measured by bioas says. Results. LPSp inhibited TNF and enhanced IL-1 release. The resul ts with actinomycin D and cyclohesimide suggested that LPSp effects di d not require transcription, but Il-1 enhancement required protein syn thesis. Addition of 8-bromo=cyclic adenosine monophosphate, H7, or nit roprusside prevented LPSp-induced nitric oxide production with L-NMA h ad no effect on TNF or IL-1. Conclusions. Complex, independent, but in completely understood signal transduction pathways for LPS(p)-induced alterations in LPSa-stimulated macrophage TNF and IL-1 release were sh own. Understanding altered signal transduction form prior LPS stimulat ion may suggest new therapies to control dysregulated macrophage cytok ine release in sepsis.