Myeloperoxidase-catalyzed phenoxyl radicals of vitamin E homologue, 2,2,5,7,8-pentamethyl-6-hydroxychromane, do not induce oxidative stress in live HL-60 cells

We used myeloperoxidase-containing HL-60 cells to generate phenoxyl radical s from nontoxic concentrations of a vitamin E homologue, 2,2,5,7,8-pentamet hy-6-hydroxychromane (PMC) to test whether these radicals can induce oxidat ive stress in a physiological intracellular environment. In the presence of H2O2, we were able to generate steady-state concentrations of PMC phenoxyl radicals readily detectable by EPR in viable HL-60 cells. In HL-60 cells p retreated with succinylacetone, an inhibitor of heme synthesis, a greater t han 4-fold decrease in myeloperoxidase activity resulted in a dramatically decreased steady-state concentrations of PMC phenoxyl radicals hardly detec table in EPR spectra. We further conducted sensitive measurements of GSH ox idation and protein sulfhydryl oxidation as well as peroxidation in differe nt classes of membrane phospholipids in HL-60 cells. We found that conditio ns compatible with the generation and detection of PMC phenoxyl radicals we re not associated with either oxidation of GSH, protein SH-groups or phosph olipid peroxidation. We conclude that PMC phenoxyl radicals do not induce o xidative stress under physiological conditions in contrast to their ability to cause lipid peroxidation in isolated lipoproteins in vitro. (C) 2000 Ac ademic Press.