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 subcell ular organelles. We have investigated the effect of vitamin E suppleme ntation on intact live eucaryotic cells. L1210 murine leukemia cells w ere exposed to an oxidative stress induced by 20 mu M Fe2+ and 100 mu M ascorbic acid introduced immediately before oxidative measurements w ere begun, and the kinetics of the generation of lipid-derived free ra dicals, as measured by EPR spin trapping (a product) and O-2 consumpti on (a reactant) were measured. Cells grown for 24 h with supplemental (5-100 mu M) vitamin E in their media had a slower rate of lipid radic al generation compared to cells grown without vitamin E supplementatio n; this inhibition in the rate of oxidation was generally dependent up on the amount of vitamin E supplementation, In complementary studies m easuring O-2 consumption, 5-100 mu M vitamin E slowed the rate of oxid ation (10-fold with 100 mu M supplemental vitamin E) consistent with t he EPR studies. The membrane active drug edelfosine accentuated the vi tamin E effects; vitamin E introduced a discernible lag phase (time de lay) in both lipid radical generation and O-2 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 con clude that vita:min E inhibits lipid peroxidation in cells by slowing the rate of lipid peroxidation; but with iron/ascorbate as the initiat ing system, vitamin E does not delay the onset of peroxidation, Of spe cial interest is that these free radical peroxidation events parallel cell membrane damage as detected using trypan blue exclusion. These ob servations are consistent with the free radical events preceding and c ausing the observed membrane damage. (C) 1996 Academic Press, Inc.