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.
West
M A
MA
Department of Surgery, Hennepin County Medical Center, University of Minnesota, Minneapolis 55415, USA.
Seatter
S C
SC
Bellingham
J
J
Clair
L
L
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D004731:Endotoxins / Q000494:pharmacology*; D007375:Interleukin-1 / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008264:Macrophages / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D009569:Nitric Oxide / Q000502:physiology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D015398:Signal Transduction / Q000187:drug effects*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D004731:Endotoxins; D007375:Interleukin-1; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; D003609:Dactinomycin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D009569:Nitric Oxide; D003513:Cycloheximide; D011493:Protein Kinase C