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 radicals from nontoxic concentrations of a vitamin E homologue, 2,2,5,7,8-pentamethyl-6-hydroxychromane (PMC) to test whether these radicals can induce oxidative stress in a physiological intracellular environment. In the presence of H 2 O 2, 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 pretreated with succinylacetone, an inhibitor of heme synthesis, a greater than 4-fold decrease in myeloperoxidase activity resulted in a dramatically decreased steady-state concentrations of PMC phenoxyl radicals hardly detectable in EPR spectra. We further conducted sensitive measurements of GSH oxidation and protein sulfhydryl oxidation as well as peroxidation in different classes of membrane phospholipids in HL-60 cells. We found that conditions compatible with the generation and detection of PMC phenoxyl radicals were not associated with either oxidation of GSH, protein SH-groups or phospholipid peroxidation. We conclude that PMC phenoxyl radicals do not induce oxidative stress under physiological conditions in contrast to their ability to cause lipid peroxidation in isolated lipoproteins in vitro.