Tumor necrosis factor induced oxidative stress in isolated mouse hepatocytes

Tumor necrosis factor alpha (TNF alpha) is a macrophage-derived cytokine which participates in homeostatic tissue repair. It is also a potentially useful antitumor agent. Liver toxicity, however, limits TNF alpha's clinical utility and suggests that it may play a role in liver toxicity of various etiologies. To determine the direct effects of TNF alpha on hepatocytes, in the absence of infiltrating leukocytes and other inflammatory mediators, an isolated mouse hepatocyte model has been used in the present study. Hepatocytes exposed to recombinant human TNF alpha (1-10 micrograms/ml) exhibited intracellular GSH depletion and GSSG efflux during the first 2 hr of exposure, but no cytotoxicity was observed. However, TNF alpha was toxic to hepatocytes pretreated with 1,3-bis(chloroethyl)-1-nitrosourea to inhibit GSSG-reductase activity. Furthermore, these cells exhibited a greater efflux of GSSG upon exposure to TNF alpha. TNF alpha also caused a marked decrease in cellular ATP concentrations, which occurred after initiation of effects on the glutathione pool. These findings indicate that high concentrations of TNF alpha induce an oxidant stress in isolated hepatocytes. The antioxidants mannitol and benzoate, as well as the iron chelator deferoxamine, reduced the extent of TNF alpha-induced oxidant effects in hepatocytes, which indicates that the oxidant stress may involve hydroxyl radical generation. Hepatocytes treated with ruthenium red or fructose were less susceptible to TNF alpha-induced ATP depletion, which suggests that mitochondrial calcium cycling may be involved in disruption to energy metabolism.