TUMOR-NECROSIS-FACTOR-ALPHA INCREASES ATP CONTENT IN METABOLICALLY INHIBITED L929 CELLS PRECEDING CELL-DEATH

The effects of tumor necrosis factor-alpha (TNF) on ATP levels were st udied in metabolically inhibited L929 cells. Treatment of these cells with TNF in the presence of actinomycin D or cycloheximide induces cyc lic changes in the intracellular ATP content preceding cell death. Aft er 3 h of incubation, the intracellular ATP content increased by 48 +/ - 6% (p < 0.001), but at 4 h, it decreased to the control level. Two h ours later, it increased again by 23 +/- 5% over the control level (p < 0.001). Coinciding with cell death, ATP content decreased progressiv ely until almost complete depletion. These changes in ATP content were associated with parallel alterations in the respiratory coupling and with increased generation of reactive oxygen species. The mechanism by which TNF/ actinomycin D or TNF/cycloheximide increased cellular ATP seemed to be dependent on the mitochondrial ATP synthesis and related to the cytotoxic effect of TNF, since blockade of mitochondrial electr on transport prevented the increase in cellular ATP, the formation of reactive oxygen species, and the apoptotic cell death caused by TNF. W e suggest that the TNF/actinomycin Dor TNF/cycloheximide-induced chang es in intracellular ATP levels may be involved in the cytotoxic effect of TNF in metabolically inhibited L929 cells.