Lp(a) and LDL induce apoptosis in human endothelial cells and in rabbit aorta: Role of oxidative stress

Abstract

Background. Atherogenic lipoproteins cause injury to the vascular wall in the early phase of atherogenesis. We assessed the effects of native (nLDL) and oxidized (oxLDL) low-density lipoprotein (LDL) and lipoprotein (a) [Lp(a)] on O2- formation and cell death in cultured human umbilical vein endothelial cells (HUVECs) and rabbit aorta (RA). Methods and Results. O2- formation of HUVECs and RA segments was not influenced by nLDL, but was dose dependently increased by oxLDL and was moderately increased by nLp(a). oxLp(a) was the most potent stimulus for O2- formation, increasing it in HUVECs by 356% at 5 μg/ml and in RA by 294% at 100 μg/ml. Apoptosis was detected by DNA fragmentation and Annexin assay in HUVECs and by TUNEL staining in RA. Incubation of HUVECs and RA with oxLDL, but not nLDL, dose and time dependently induced apoptosis with only a minimal effect on necrosis. nLp(a) elicited a small but significant effect on apoptosis, whereas oxLp(a) induced apoptosis more potently than oxLDL in HUVECs and RA and caused necrotic cell death in HUVECs. Induction of apoptosis by oxLDL and oxLp(a) in RA was enhanced by the superoxide dismutase (SOD) inhibitor, diethyl-dithio-carbamate, and was blunted by SOD and catalase in HUVECs and RA, suggesting that O2- formation was involved. The concentration of lysophosphatidylcholine, a lipoprotein oxidation product and stimulus for O2- formation, was significantly enhanced by factor 5 in oxLDL and by factor 7 in oxLp(a) compared with native lipoproteins. Conclusion. Atherogenic lipoproteins stimulate O2- formation and induction of apoptosis in HUVECs and RA, and may thereby influence the pathogenesis of atherosclerosis.