TNF tolerance and cytotoxicity in the liver:: the role of interleukin-1β, inducible nitric oxide-synthase and heme oxygenase-1 in D-galactosamine-sensitized mice

Objective and design: Pretreatment with tumor necrosis factor (TNF)-alpha induces tolerance towards itself in experimental liver injury. Material and treatment: To study mechanisms of TNF tolerance we used knockout mice for either TNF-receptor-2 (TNFR-2), inducible nitric oxide (NO)-synthase (iNOS) or caspase-1 (ICE) or inhibited heme oxygenase-1 (HO-1) by treatment with zinc-protoporphyrin 9. Liver damage was induced by administration of TNF to mice sensitized with D-galactosamine (GalN). Tolerance was induced by pretreatment with low doses of TNF. Methods: Severity of liver injury was assessed by determination of plasma transaminases and apoptosis. Time courses of intra-hepatic NOS, interleukin-1beta (IL-1beta) and HO-1 expression after TNF treatment were measured by reverse transcription polymerase chain reaction (RT-PCR). TNF-receptor- 1 (TNFR-1) expression was determined by immunofluorescent staining. Results: TNF-pretreatment did not affect TNFR-1 expression in the liver and resulted in time dependent up-regulation of NOS, IL- 1beta and HO-1. TNF- pretreated TNFR-2, NOS or ICE knockout mice were as sensitive towards GalN/TNF as the wild type, while mice with impaired HO-1 activity were even more sensitive, but tolerance was inducible in all TNF-pretreated mice. Conclusions: TNF tolerance towards GalN/TNF treatment is mediated by TNFR-1. IL- 1beta, NOS and HO-1 neither mediated TNF-tolerance nor TNF cytotoxicity.