Vitamin E slows the rate of free radical-mediated lipid peroxidation in cells

Much of what is known about the antioxidant mechanism of vitamin E has been learned from studies of lipid dispersions, solutions, or subcellular organelles. We have investigated the effect of vitamin E supplementation on intact live eucaryotic cells. L1210 murine leukemia cells were exposed to an oxidative stress induced by 20 microM Fe2+ and 100 microM ascorbic acid introduced immediately before oxidative measurements were begun, and the kinetics of the generation of lipid-derived free radicals, as measured by EPR spin trapping (a product) and O2 consumption (a reactant) were measured. Cells grown for 24 h with supplemental (5-100 microM) vitamin E in their media had a slower rate of lipid radical generation compared to cells grown without vitamin E supplementation; this inhibition in the rate of oxidation was generally dependent upon the amount of vitamin E supplementation. In complementary studies measuring O2 consumption, 5-100 microM vitamin E slowed the rate of oxidation (10-fold with 100 microM supplemental vitamin E) consistent with the EPR studies. The membrane active drug edelfosine accentuated the vitamin E effects; vitamin E introduced a discernible lag phase (time delay) in both lipid radical generation and O2 consumption that was not seen in the absence of edelfosine. Vitamin E supplementation of cells also altered the kinetics of ascorbate free radical formation. We conclude that vitamin E inhibits lipid peroxidation in cells by slowing the rate of lipid peroxidation; but with iron/ascorbate as the initiating system, vitamin E does not delay the onset of peroxidation. Of special interest is that these free radical peroxidation events parallel cell membrane damage as detected using trypan blue exclusion. These observations are consistent with the free radical events preceding and causing the observed membrane damage.