Abstract: ObjectiveTo study the effect of equol(Eq),a metabolite of soybean isoflavones,on apoptosis and proliferation of vascular endothelial cells.MethodsVascular endothelial cells(ECV-304)were cultured in vitro and treated with different concentrations of Eq (0, 6.25,12.5,25,50,and 100 μmol/L) for 24 hours and then the cells were collected.Reactive oxygen species(ROS),apoptosis and cell cycle were determined with flow cytometry.Apoptosis-related proteins(Bax,Bcl-2,and caspase-3)were detected with immunohistochemical method.Eq-related cell proliferation inhibition rate(IR)was measured with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT)reduction assay.ResultsCompared with that of the control group,lower concentration of Eq(6.25 and 12.5 μmol/L)reduced intracellular ROS,whereas the higher concentration(100 μmol/L)of Eq increased intracellular ROS.The apoptosis rates of the cells treated with Eq of higher concentration(25,50 and 100 μmol/L)were increased(9.67%,12.17%,and 12.87%).Lower concentration of Ep did not affect the cell cycle also,while higher concentration of Ep caused G1 arrest.The IR of the ECV-304 cells treated with different concentrations of Eq(6.25,12.5,25,50,and 100 μmol/L) were -8.23±2.21%,-3.29±1.07%,6.75±1.73%,25.46.23±4.82%,and 36.93±4.66%,respectively.Lower concentration of Eq promoted but the higher concentration inhibited the proliferation of the cells.Compared with the control group,the expression of Bax and caspase-3 in the cells treated with Eq(25 μmol/L)for 24 hours increased,while the expression of Bcl-2 decreased.ConclusionLower concentration of Eq could reduce intracellular ROS,promote cell proliferation,while higher concentration of Eq could induce cell apoptosis and cell cycle arrest.