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(Arteriosclerosis, Thrombosis, and Vascular Biology. 1999;19:2387-2394.)
© 1999 American Heart Association, Inc.

Atherosclerosis and Lipoproteins

Vitamin C Protects Human Vascular Smooth Muscle Cells Against Apoptosis Induced by Moderately Oxidized LDL Containing High Levels of Lipid Hydroperoxides

Richard C. M. Siow; Justin P. Richards; Kevin C. Pedley; David S. Leake; Giovanni E. Mann

From the Centre for Cardiovascular Biology and Medicine, GKT School of Biomedical Sciences, King's College, London (R.C.M.S., K.C.P., G.E.M.), and Cell and Molecular Biology Research Division, School of Animal and Microbial Sciences, University of Reading, Reading (J.P.R., D.S.L.), UK.

Correspondence to Dr Richard Siow, Division of Cardiovascular Medicine, Department of Medicine, School of Clinical Medicine, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge, CB2 2QQ, UK. E-mail rcms2{at}cam.ac.uk

Abstract—Vascular cell death is a key feature of atherosclerotic lesions and may contribute to the plaque "necrotic" core, cap rupture, and thrombosis. Oxidatively modified low-density lipoproteins (LDLs) are implicated in the pathogenesis of atherosclerosis, and dietary antioxidants are thought to protect the vasculature against LDL-induced cytotoxicity. Because LDL oxidative modification may vary within atherosclerotic lesions, we examined the effects of defined, oxidatively modified LDL species on human arterial smooth muscle cell apoptosis and the cytoprotective effects of vitamin C. Moderately oxidized LDL (0 to 300 µg protein/mL), which has the highest content of lipid hydroperoxides, induced smooth muscle cell apoptosis within 6 hours, whereas native LDL and mildly and highly oxidized LDL had no effect. Moderately oxidized LDL increased cellular DNA fragmentation, release of fragmented DNA into the culture medium, and annexin V binding and decreased mitochondrial dehydrogenase activity and expression of the antiapoptotic mediator Bcl-x_L. Treatment of cells with native LDL together with the lipid hydroperoxide 13(S)-hydroperoxyoctadeca-9Z,11E-dienoic acid (HPODE, 200 µmol/L, 6 to 24 hours) also induced apoptotic cell death. Pretreatment of smooth muscle cells with vitamin C (0 to 100 µmol/L, 24 hours) attenuated the cytotoxicity and apoptosis induced by both moderately oxidized LDL and HPODE. Our findings suggest that moderately oxidized LDL, with its high lipid hydroperoxide content, rather than mildly or highly oxidized LDL, causes apoptosis of human smooth muscle cells and that vitamin C supplementation may provide protection against plaque instability in advanced atherosclerosis.

Key Words: smooth muscle, vascular • low-density lipoprotein, oxidized • apoptosis • ascorbic acid • Bcl-x_L • atherosclerosis

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