Ldl modified by hypochlorous acid is a potent inhibitor of lecithin-cholesterol acyltransferase activity.
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 micromol/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 micromol/L HOCl, respectively. Addition of 200 micromol/L ascorbate or N-acetyl derivatives of cysteine or methionine completely prevented LCAT inactivation by LDL preincubated with </=200 micromol/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.
McCall
M R
MR
Linus Pauling Institute, Oregon State University, Corvallis 97331-6512, USA.
Carr
A C
AC
Forte
T M
TM
Frei
B
B
D002700:Chloramines / Q000737:chemistry; D003545:Cysteine / Q000737:chemistry; D006801:Humans; D006997:Hypochlorous Acid / Q000737:chemistry*; D015227:Lipid Peroxidation; D008054:Lipid Peroxides / Q000502:physiology; D008077:Lipoproteins, LDL / Q000737:chemistry / Q000494:pharmacology*; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000037:antagonists & inhibitors*
D002700:Chloramines; D008054:Lipid Peroxides; D008077:Lipoproteins, LDL; D006997:Hypochlorous Acid; D007862:Phosphatidylcholine-Sterol O-Acyltransferase; D003545:Cysteine