In vitro inhibition by estrogens of the oxidative modifications of human lipoproteins

Estrogens exert protective actions against atherosclerosis, part of these effects having been ascribed to their antioxidant properties. The aim of this work was to assess the ability of estrogens to prevent the oxidative modifications of low density lipoproteins (LDL) and other plasma lipoprotein fractions whose relationship with atherosclerosis has been less studied. For this purpose, different estrogen compounds were used: natural and synthetic estrogens, and catecholestrogens. The molecules were added in vitro to human LDL and very low density lipoproteins (VLDL) in the presence of Cu2+. The lipoprotein oxidative modifications were determined by measuring the formation of thiobarbituric acid reactive substances, the appearance of conjugated dienes and the degradation of tryptophan groups from the apoproteins. In VLDL, 2-hydroxyestradiol and diethylstilbestrol exerted potent antioxidant effects similar to those found for alpha-tocopherol and probucol. 17beta-Estradiol and 4-hydroxyestradiol also prevented VLDL oxidation, but to a lesser extent. When LDL were used, estrogens similarly exerted antioxidant actions, 2-hydroxyestradiol being the most potent inhibitor. These results show that estrogens, whose antioxidant actions have been demonstrated in other experimental models, also possess the ability to prevent in vitro the oxidative modifications of human plasma LDL and VLDL.