Relation of biological activity of mutant forms of recombinant human tumor necrosis factor alpha and accumulation of sphingosine in murine liver.

TNF-alpha induced sphingomyelin hydrolysis by sphingomyelinase and both sphingosine and ceramide generation have been reported to be implicated in a number of TNF-alpha responses, including cytotoxicity and apoptosis. We found that sphingosine, a highly cytotoxic product of enzymatic degradation of sphingomyelin, is accumulated in liver of mice treated with TNF-alpha. To determine the role of sphingosine in TNF-alpha toxicity, TNF-alpha mutants differing in their cytotoxicity to L929 cells as well as haemorrhagic tumor necrosis, tumor regression and lethal toxicity in mice were used in our experiments. The mutants with highest toxicity and tumor-necrotizing activity caused accumulation of sphingosine exceeded its control level 5,5 times in murine liver cells. TNF-alpha variants which caused moderate increase in sphingosine content were significantly less toxic. The observed relationship between toxicity of TNF-alpha mutants, the toxicity of sphingosine, and the extent of its accumulation in murine liver provides evidence to suggest that this sphingomyelin metabolite may be mediator of TNF-alpha-induced cell damage and death.