Tamoxifen, esterified estradiol, and physiologic concentrations of estradiol inhibit oxidation of low-density lipoprotein by endothelial cells

Objective: We investigated the antioxidant effect of tamoxifen, esterified estradiol, and physiologic concentrations of 17β-estradiol on endothelial cell–mediated oxidation of low-density lipoprotein. Study Design: Human umbilical vein endothelial cells were preincubated with nanomolar concentrations of estradiol, estradiol stearate, and tamoxifen. Low-density lipoprotein was isolated and incubated with cells in serum-free medium. Oxidation of low-density lipoprotein was quantified after 8, 16, and 24 hours of incubation as the formation of thiobarbituric acid–reactive substances. Results: Compared with control, preincubation of human umbilical vein endothelial cells with 1- or 10-nmol/L estradiol resulted in a 12% reduction in the formation of thiobarbituric acid–reactive substances at 24 hours. Preincubation of human umbilical vein endothelial cells with either 10-nmol/L estradiol 17-stearate or 10-nmol/L tamoxifen resulted in 26% and 20% decreases, respectively, in formation of thiobarbituric acid–reactive substances at 24 hours. The difference in the reduction in thiobarbituric acid–reactive substances between control and treatment wells became more pronounced over time. Conclusion: Under these experimental conditions, tamoxifen, esterified estradiol, and physiologic concentrations of exogenous estradiol inhibit oxidation of low-density lipoprotein by human umbilical vein endothelial cells. (Am J Obstet Gynecol 2001;184:1060-3.)