POSSIBLE INVOLVEMENT OF FREE-RADICAL SCAVENGING PROPERTIES IN THE ACTION OF TUMOR-NECROSIS-FACTOR-ALPHA

Constitutive production of hydroxyl radicals from four established can cer cell lines was detected as spin adducts of 5,5-dimethyl-1-pyroline -N-oxide (DMPO), using an electron spin resonance spectrometer. The ge nerated hydroxyl radicals was decreased in three out of four cancer ce ll lines when incubated in vitro for 3 h with TNF-alpha No direct scav enging effect of TNF-alpha on hydroxyl radicals or superoxide anions w as observed in the in vitro radical generation system. The modulation of intracellular reactive oxygen species of these cancer cells by addi ng menadione or CuDIPS to the culture medium changed the antiprolifera tive effect of TNF-alpha on the cells. The ultrastructural localizatio n 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-alpha. These data indicate that the reduction of radical generation in cancer cells by TNF-alpha may be an early mechanism that contributes to the antiproliferative effect of this cytokine on some cancer cells. Copyri ght (C) 1997 Elsevier Science Inc.