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 O•−2has 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 O•−2-sensitive aconitases to measure changes in steady-state O•−2levels in the mitochondrial matrix and cytoplasm of cultured mammalian cells in response to these inflammatory mediators. TNFα did not measurably affect aconitase activity, and thus mitochondrial O•−2production, in either cultured human A549 cells or murine L929 cells while TNFα clearly caused cytotoxicity as revealed by impaired mitochondrial respiration. IL-1α andEscherichia coliLPS also failed to affect the aconitase activity in A549 cells. Neither the O•−2scavenger Mn(III)TMPyP nor the H2O2scavenger catalase protected L929 cells against the cytotoxicity of TNFα. In conclusion, TNF, IL-1, and LPS do not appear to exert cytotoxicity, or MnSOD gene induction effects, by eliciting mitochondrial O•−2production.