Oxidized low density lipoprotein induces apoptosis via generation of reactive oxygen species in vascular smooth muscle cells

Objective: Death of vascular smooth muscle cell (VSMC) induced by oxidized LDL (oxLDL) can occur by both necrosis and apoptosis which may contribute t o plaque instability and rupture. Reactive oxygen species (ROS) induces apo ptosis in VSMC and is involved in oxLDL action, we tested the hypothesis he re that a coupling exists between ROS generation and apoptosis of oxLDL-tre ated VSMC. Methods: Cultured VSMC from rat aorta were treated with oxLDL, a poptosis and necrosis were distinguished by using FITC-annexin V label and propidium iodide stain, analyzed by flow cytometry. ROS generation of VSMCs was detected by the fluorescence intensity of DCF. Apoptosis was also dete rmined by cleavage of procaspase-3. Results: OxLDL induced apoptosis (3 h) in a dose-dependent manner and reached maximum (with near-basal necrosis) a t a concentration of 300 mug/ml. At this and lower (100 mug/ml) concentrati on, oxLDL, but not native LDL, stimulated ROS production rapidly (less than or equal to5 min) and ROS level remained elevated for at least 45 min. Cat alase and deferoxamine reduced both oxLDL-induced apoptosis and ROS generat ion. Superoxide dismutase and benzoic acid neither reduced the oxLDL-induce d ROS generation nor inhibited apoptosis. Since oxLDL-induced ROS generatio n were inhibited by nordihydroguaiaretic acid and rotenone, lipoxygenase an d mitochondrial pathways could be involved. In addition, catalase, deferoxa mine, and N-acetylcysteine inhibited oxLDL-induced cleavage of procaspase-3 as well. Conclusions: ROS generation and apoptosis are tightly coupled in oxLDL-treated VSMCs. Antioxidants that reduced ROS level inhibited apoptosi s, those that did not reduce ROS level were ineffective. Both mitochondrial and lipoxygenase activities may be involved. (C) 2001 Elsevier Science B.V . All rights reserved.