Failure of tumor necrosis factor and interleukin-1 to elicit superoxide production in the mitochondrial matrices of mammalian cells.

Subversion of mitochondrial electron transport to the production of O2.- has been proposed as a mechanism of tumor necrosis factor (TNF)-mediated cell killing and to a lesser extent interleukin-1 (IL-1) and lipopolysaccharide (LPS) cytotoxicity. We utilized the O2.- -sensitive aconitases to measure changes in steady-state 02.- levels in the mitochondrial matrix and cytoplasm of cultured mammalian cells in response to these inflammatory mediators. TNF alpha did not measurably affect aconitase activity, and thus mitochondrial 02.- production, in either cultured human A549 cells or murine L929 cells while TNF alpha clearly caused cytotoxicity as revealed by impaired mitochondrial respiration. IL-1 alpha and Escherichia coli LPS also failed to affect the aconitase activity in A549 cells. Neither the O2.- scavenger Mn(III) TMPyP nor the H2O2 scavenger catalase protected L929 cells against the cytotoxicity of TNF alpha. In conclusion, TNF, IL-1, and LPS do not appear to exert cytotoxicity, or MnSOD gene induction effects, by eliciting mitochondrial O2.- production.