Endotoxin tolerance impairs a pertussis-toxin-sensitive G- protein regulating tumour necrosis factor release by macrophages from tumour-bearing rats

The aim of this work was to study whether a G-protein regulates lipopolysaccharide (LPS) induced TNF-alpha 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-alpha release via a G-protein-mediated phenomenon. LPS-stimulated (50 micrograms ml-1 of Salmonella enteritidis LPS) TNF-alpha release was investigated in peritoneal macrophages harvested from both normal rats and tumour-bearing rats. Cholera toxin (10, 100 and 1000 ng ml-1) did not significantly modify LPS-induced TNF-alpha release. In contrast pertussis toxin (0.1, 1.0 and 10 ng ml-1) significantly increased LPS-induced TNF-alpha release and inhibited LPS-stimulated prostaglandin E2 (PGE2) 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 41 kDa protein(s). The LPS-mediated responses were significantly greater in macrophages from tumour-bearing rats than in macrophages from normal rats. PGE2 (10(-9), 10(-8) and 10(-7) M) suppressed LPS-induced TNF-alpha 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 125 micrograms rat-1 of LPS, and experiments were performed on peritoneal macrophages harvested 24 h after LPS injection. In tolerant macrophages pertussis toxin induced an increase in LPS-stimulated TNF-alpha release and an inhibition in LPS-stimulated PGE2 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-alpha 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 Gi-protein, may exert beneficial effects on the functions of macrophages in tumour-bearing rats.