Increase of intracellular reactive oxygen species (ROS) has been proposed to cause endothelial injury, and oxidized LDL (oxLDL) actions are associated with an early increase of ROS. Estrogen protects vascular cells partly via its antioxidant effects and by preventing lipid peroxidation. However, whether it can inhibit oxLDL-induced stimulation of ROS generation in endothelial cells is unknown. We utilized the fluorescent dye (DCFH-DA) to measure ROS generation and compared the stimulant effect of tert-butylhydroperoxide (TBH) and oxLDL in human umbilical vein endothelial cells (HUVECs). We found that TBH, H2O2, and oxLDL rapidly stimulated ROS generation, and in a dose-dependent manner with TBH. A concentration of estrogen effective in preventing lipid peroxidation was employed either by pretreatment of cells 18h prior to or by direct co-incubation (30 min) with HUVEC and oxLDL. Estrogen (54 μM) pretreatment significantly suppressed both TBH- and oxLDL- induced stimulation of ROS generation. Both 1 and 54 μM concentration of estrogen could directly inhibit oxLDL-induced ROS production in HUVECs. Thus, either 18h pretreatment or 30 min co-incubation with estrogen reduced stimulated ROS generation, suggesting that both cellular and direct actions of estrogen may be involved.
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