Endotoxin tolerance is associated with altered GTP-binding protein function

Abstract

Previous studies have suggested that guanine nucleotide regulatory (G) proteins modulate endotoxin-stimulated peritoneal macrophage arachidonic acid (AA) metabolism. Endotoxin-stimulated metabolism of AA by peritoneal macrophages is decreased in endotoxin tolerance (Rogers et al. Prostaglandins 31: 639-650, 1986). These observations led to a study of G protein function and AA metabolism by peritoneal macrophages in endotoxin tolerance. Endotoxin tolerance was induced by the administration of sublethal doses of endotoxin. AA metabolism was assessed by measurement of thromboxane B2 (TxB2), a cyclooxygenase metabolite. NaF (5 mM), an activator of G proteins, significantly stimulated TxB2 synthesis in control macrophages from 7.7 +/- 0.2 to 19.1 +/- 0.6 (SE) ng/ml (P less than 0.05) at 2 h and was partially inhibited by pertussis toxin, suggesting a G protein-dependent mechanism. Salmonella enteritidis endotoxin (50 micrograms/ml) stimulated a similar increase in TxB2 levels (23 +/- 0.4 ng/ml, P less than 0.05). In contrast to control macrophages, macrophages from endotoxin-tolerant rats stimulated with either NaF or S. enteritidis endotoxin had TxB2 levels that were only 30 and 2% of the respective stimulated control cells. Basal guanosine-triphosphatase (GTPase) activity (33 +/- 6 pmol.mg-1.min-1) in endotoxin-tolerant macrophage membranes was significantly lower (P less than 0.05) than control basal activity (158 +/- 5 pmol.mg-1.min-1). This suppression of macrophage GTPase activity was apparent 48 h after the first in vivo sublethal endotoxin injection (100 micrograms/kg ip). The reduced GTPase activity paralleled in vitro cellular hyporesponsiveness to endotoxin-stimulated TxB2 production.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of Cross-Tolerance by Lipopolysaccharide and Highly Purified Lipoteichoic Acid Via Different Toll-Like Receptors Independent of Paracrine Mediators

“…Expression of CD14 is unaffected or even increased after LPS stimulation, thus it is highly unlikely that tolerance is mediated via expression of this LPS receptor (45,46). Refractoriness in response to LPS preexposure has been shown to be associated with altered G protein content (47,48), phospholipase D and phosphatidylinositol-3 kinase expression (49), and compromised protein kinase C activation (50). Others described suppressed signal transduction via both the mitogen-activated protein kinase cascade (30,(51)(52)(53) and I-B kinases, resulting in impaired transcription of NF-B-and AP-1-regulated genes (30,54).…”

Different Modes of IL-10 and TGF-β to Inhibit Cytokine-Dependent IFN-γ Production: Consequences for Reversal of Lipopolysaccharide Desensitization

“…Apart from endogenous IL-10, other intrinsic mechanisms are likely to be involved in LPS desensitization. Described potential mechanisms include alteration of G protein binding (46,47), impaired mitogen-activated protein kinase (48), or Toll-like receptor 4 signaling involving the induction of IL-1R-associated kinase M (49) and suppressor of cytokine signaling 1/3 (50 -52), as well as increased expression of the p50 subunit of NF-B (53, 54). These intrinsic mechanisms might explain why the restoration of TNF-␣ production did not completely correlate to the restored IFN-␥ levels in our experiments.…”

Biomonitoring for assessment of organic dust-induced lung inflammation

“…Endotoxin tolerance was induced in half of the mice from each exposure group, as previously described [27,32] Swine CAFO dust extract Dust samples were obtained from an Eastern Iowa swine CAFO by vacuuming vertical surfaces with a sampling vacuum. An extract of the dust was prepared at a concentration of 100 mg?mL -1 in sterile, physiological saline.…”