REDUCTION OF MTT BY GLUTATHIONE-S-TRANSFERASE

The reduction of the tetrazolium salt 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromine (MTT) to a blue formazan product is wi dely used for assaying cell survival and proliferation. The reduction reaction is catalyzed by dehydrogenases localized in the mitochondria of viable cells. As part of an analysis of the ability of glutathione S-transferase (GST) enzymes to protect cells from electrophilic compou nds, we found extremely high background levels of the formazan product produced by cells that over overexpressed the mouse GST P1-1 enzyme. Further analysis with purified GST enzymes confirmed the ability of th ese en zymes ro reduce MTT in vitro. These data suggest that cytotoxic ity assays using MTT should be interpreted with caution, especially wh en studying the effects of compounds that cart influence GST expressio n.