ENDOTOXIN TOLERANCE IMPAIRS A PERTUSSIS-TOXIN-SENSITIVE G-PROTEIN REGULATING TUMOUR NECROSIS FACTOR RELEASE BY MACROPHAGES FROM TUMOUR-BEARING RATS

Abstract The aim of this work was to study whether a G-protein regulates lipopolysaccharide (LPS) induced TNF-α production in tumour-bearing rat peritoneal macrophages differently to in normal rats. We also investigated whether a state of `early endotoxin tolerance' affects LPS induced TNF-α release via a G-protein-mediated phenomenon. LPS-stimulated (50μgml −1 of Salmonella enteritidis LPS) TNF-α release was investigated in peritoneal macrophages harvested from both normal rats and tumour-bearing rats. Cholera toxin (10, 100 and 1000ngml −1 ) did not significantly modify LPS-induced TNF-α release. In contrast pertussis toxin (0.1, 1.0 and 10ngml −1 ) significantly increased LPS-induced TNF-α release and inhibited LPS-stimulated prostaglandin E 2 (PGE 2 ) production in both normal rat macrophages and tumour-bearing rat macrophages. Pertussis toxin effects on these LPS responses were correlated with a pertussis-toxin-mediated ADP-ribosylation of a 41kDa protein(s). The LPS-mediated responses were significantly greater in macrophages from tumour-bearing rats than in macrophages from normal rats. PGE 2 (10 −9 , 10 −8 and 10 −7 M ) suppressed LPS-induced TNF-α production in a dose-dependent fashion. A state of `early endotoxin tolerance' was then induced in tumour-bearing rats by a single intravenous injection of 125μgrat −1 of LPS, and experiments were performed on peritoneal macrophages harvested 24h after LPS injection. In tolerant macrophages pertussis toxin induced an increase in LPS-stimulated TNF-α release and an inhibition in LPS-stimulated PGE 2 release significantly lower than in macrophages harvested from non-tolerant tumour bearing rats. Our results suggest that a pertussis-toxin-sensitive G-protein may serve to regulate the synthesis of TNF-α in rat peritoneal macrophages and that the activity of this pertussis-sensitive G-protein is increased in macrophages from tumour-bearing rats. Furthermore, our experiments would indicate that a `state of endotoxin tolerance', caused by altering the function of presumably a G i -protein, may exert beneficial effects on the functions of macrophages in tumour-bearing rats.