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 bot h sphingosine and ceramide generation have been reported to be implica ted in a number of TNF-alpha responses, including cytotoxicity and apo ptosis. We found that sphingosine, a highly cytotoxic product of enzym atic degradation of sphingomyelin, is accumulated in liver of mice tre ated with TNF-alpha. To determine the role of sphingosine in TNF-alpha toxicity, TNF-alpha mutants differing in their cytotoxicity to L929 c ells as well as haemorrhagic tumor necrosis, tumor regression and leth al toxicity in mice were used in our experiments. The mutants with hig hest toxicity and tumor-necrotizing activity caused accumulation of sp hingosine exceeded its control level 5,5 times in murine liver cells. TNF-alpha variants which caused moderate increase in sphingosine conte nt were significantly less toxic. The observed relationship between to xicity of TNF-alpha mutants, the toxicity of sphingosine, and the exte nt of its accumulation in murine liver provides evidence to suggest th at this sphingomyelin metabolite may be mediator of TNF-alpha - induce d cell damage and death.