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(Arteriosclerosis, Thrombosis, and Vascular Biology. 1997;17:3338-3346.)
© 1997 American Heart Association, Inc.

Articles

Copper Ions Promote Peroxidation of Low Density Lipoprotein Lipid by Binding to Histidine Residues of Apolipoprotein B100, But They Are Reduced at Other Sites on LDL

Peter Wagner; ; Jay W. Heinecke

From the Departments of Internal Medicine (P.W., J.W.H.) and Molecular Biology and Pharmacology (J.W.H.), Washington University School of Medicine, St Louis, Mo.

Correspondence to Dr Jay W. Heinecke, Division of Atherosclerosis, Nutrition and Lipid Research, Box 8046, 660 South Euclid Ave, St. Louis, MO 63110. E-mail heinecke{at}im.wustl.edu

Abstract Oxidized LDL is implicated in the pathogenesis of atherosclerosis. A widely studied model for oxidation of the lipid in LDL involves Cu²⁺. Recent studies suggest that Cu²⁺ may be reduced to Cu¹⁺ by -tocopherol to initiate LDL lipid peroxidation. LDL demonstrates binding sites for Cu²⁺, but the nature of these binding sites, as well their role in promoting Cu²⁺ reduction and lipid peroxidation, has not been established. In the current studies, we used diethylpyrocarbonate (DEPC) to modify the histidine residues of apolipoprotein B100, the major protein in LDL. First, we demonstrated that histidine residues were preferentially modified by DEPC under our experimental conditions. Then we monitored the kinetics of Cu²⁺-promoted oxidation of LDL and DEPC-modified LDL. In both cases, the progress curve of lipid peroxidation exhibited a lag phase and a propagation phase. However, when LDL was modified with DEPC, the length of the lag phase was prolonged whereas the rate of lipid peroxidation during the propagation phase was lower. Studies with LDL oxidized by 2,2'-azobis (2-amidinopropane) hydrochloride and phosphatidylcholine liposomes oxidized with hydroxyl radical established that DEPC was not acting simply as a nonspecific inhibitor of lipid peroxidation. DEPC treatment of LDL almost completely inhibited its ability to bind Cu²⁺. These observations suggest that peroxidation of the lipids in LDL can proceed with normal kinetics only when Cu²⁺ binds preferentially to sites on apolipoprotein B100 that contain histidine residues. We also compared the kinetics of Cu²⁺ reduction in the absence and presence of DEPC. There was no effect of DEPC modification on either the rate or extent of Cu²⁺ reduction by LDL. Therefore LDL is likely to contain a second class of binding sites for Cu²⁺ that does not involve histidine residues. Thus, LDL appears to contain at least two classes of Cu²⁺-binding sites: histidine containing sites, which are responsible in part for promoting lipid peroxidation during the propagation phase, and sites at which Cu²⁺ is reduced without binding to histidine.

Key Words: LDL oxidation • atherosclerosis • lipid peroxidation • metal binding • vitamin E

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				A. Roland, R. A. Patterson, and D. S. Leake Measurement of Copper-Binding Sites on Low Density Lipoprotein Arterioscler. Thromb. Vasc. Biol., April 1, 2001; 21(4): 594 - 602. [Abstract] [Full Text] [PDF]