Possible Involvement of Free Radical Scavenging Properties in the Action of Tumor Necrosis Factor-α

Constitutive production of hydroxyl radicals from four established cancer cell lines was detected as spin adducts of 5,5-dimethyl-1-pyroline-N-oxide (DMPO), using an electron spin resonance spectrometer. The generated hydroxyl radicals was decreased in three out of four cancer cell lines when incubated in vitro for 3 h with TNF-α No direct scavenging effect of TNF-α on hydroxyl radicals or superoxide anions was observed in the in vitro radical generation system. The modulation of intracellular reactive oxygen species of these cancer cells by adding menadione or CuDIPS to the culture medium changed the antiproliferative effect of TNF-α on the cells. The ultrastructural localization of the radical-generating sites in cancer cells was visualized using the diaminobenzidine/horseradish peroxide histochemical system at the electron microscopic level. The hydrogen peroxide-dependent formation of electron-dense materials localized at the mitochondrial membranes was decreased after the treatment of the cancer cells with TNF-α. These data indicate that the reduction of radical generation in cancer cells by TNF-α may be an early mechanism that contributes to the antiproliferative effect of this cytokine on some cancer cells. Copyright © 1997 Elsevier Science Inc.