Effects of siSIRT transfection on the inhibitory effect of oxymatrine on oxidative stress in ox-LDL-treated HUVECs. HUVECs transfected with siSIRT1 or siCon were treated with oxymatrine (4 µM) for 2 h prior to treatment with ox-LDL (100 µg/ml) for 24 h. (A) DCFH-DA staining for ROS. Scale bar, 200 µm. (B) Quantitative analysis for ROS generation by flow cytometry. (C) Cell MDA assay kit for measuring MDA content. (D) JC-1 kit for measuring mitochondrial membrane potential. (E) SOD assay kit for measuring SOD activity. (F) CAT assay kit for measuring CAT activity. (G) GSH-Px assay kit for measuring GSH-Px activity. Data are expressed as the mean ± SD, n=3. *P<0.05 and **P<0.01 vs. the control group; #P<0.05 and ##P<0.01 vs. the ox-LDL group; NSP>0.05 vs. the OMT + ox-LDL group; $P<0.05 and $$P<0.01 vs. the OMT + ox-LDL + siCon group. OMT, oxymatrine; ox-LDL, oxidized low-density lipoprotein; NS, no statistical significance; siSIRT1, siRNAs for SIRT1; siCon, siRNAs for negative control; HUVECs, human umbilical vein endothelial cells; SIRT, sirtuin; MDA, malondialdehyde; SOD, superoxide dismutase; CAT, catalase; GSH-Px, glutathione peroxidase; ROS, reactive oxygen species; DCFH-DA, 2′,7′-dichlorofluorescein diacetate.