LDL Modified by Hypochlorous Acid Is a Potent Inhibitor of Lecithin-Cholesterol Acyltransferase Activity

• Published in: Arteriosclerosis, thrombosis, and vascular biology Vol. 21; no. 6; pp. 1040 - 1045
• Main Authors: McCall, Mark R, Carr, Anitra C, Forte, Trudy M, Frei, Balz
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA American Heart Association, Inc 01.06.2001; Hagerstown, MD Lippincott
• Subjects: Atherosclerosis (general aspects, experimental research); Biological and medical sciences; Blood and lymphatic vessels; Cardiology. Vascular system; Chloramines - chemistry; Cysteine - chemistry; Humans; Hypochlorous Acid - chemistry; Lipid Peroxidation; Lipid Peroxides - physiology; Lipoproteins, LDL - chemistry; Lipoproteins, LDL - pharmacology; Medical sciences; Phosphatidylcholine-Sterol O-Acyltransferase - antagonists & inhibitors; Vascular disease; Human; Lipoprotein LDL; Acyltransferases; Hypochlorous acid; Enzyme; Pathogenesis; Transferases; Atherosclerosis; Cardiovascular disease; Phosphatidylcholine-sterol O-acyltransferase
• ISSN: 1079-5642; 1524-4636
• DOI: 10.1161/01.ATV.21.6.1040

ABSTRACT—Modification of low density lipoprotein (LDL) by myeloperoxidase-generated HOCl has been implicated in human atherosclerosis. Incubation of LDL with HOCl generates several reactive intermediates, primarily N-chloramines, which may react with other biomolecules. In this study, we investigated the effects of HOCl-modified LDL on the activity of lecithin-cholesterol acyltransferase (LCAT), an enzyme essential for high density lipoprotein maturation and the antiatherogenic reverse cholesterol transport pathway. We exposed human LDL (0.5 mg protein/mL) to physiological concentrations of HOCl (25 to 200 μmol/L) and characterized the resulting LDL modifications to apolipoprotein B and lipids; the modified LDL was subsequently incubated with apolipoprotein B–depleted plasma (density >1.063 g/mL fraction), which contains functional LCAT. Increasing concentrations of HOCl caused various modifications to LDL, primarily, loss of lysine residues and increases in N-chloramines and electrophoretic mobility, whereas lipid hydroperoxides were only minor products. LCAT activity was extremely sensitive to HOCl-modified LDL and was reduced by 23% and 93% by LDL preincubated with 25 and 100 μmol/L HOCl, respectively. Addition of 200 μmol/L ascorbate or N-acetyl derivatives of cysteine or methionine completely prevented LCAT inactivation by LDL preincubated with ≤200 μmol/L HOCl. Protecting the free thiol groups of LCAT with 5,5′-dithio-bis-(2-nitrobenzoic acid) before exposure to HOCl-modified LDL, which inhibits lipid hydroperoxide–mediated inactivation of LCAT, failed to prevent the loss of enzyme activity. Our data indicate that N-chloramines from HOCl-modified LDL mediate the loss of plasma LCAT activity and provide a novel mechanism by which myeloperoxidase-generated HOCl may promote atherogenesis.