Correlation of Antiphospholipid Antibody Recognition with the Structure of Synthetic Oxidized Phospholipids

doi:10.1074/jbc.M108860200

Correlation of Antiphospholipid Antibody Recognition with the Structure of Synthetic Oxidized Phospholipids

IMPORTANCE OF SCHIFF BASE FORMATION AND ALDOL CONDENSATION*

From the Departments of ^‡Chemistry and Biochemistry and ^¶Medicine, University of California San Diego, La Jolla, California 92093-0601

Abstract

The oxidation of low density lipoproteins (LDL) has been correlated with atherogenesis through a variety of pathways. The process involves nonspecific fragmentation, oxidative breakdown, and modification of the lipids and protein of LDL. The process yields a variety of bioactive products, including aldehyde-containing phospholipids, which can cross-react with primary amines (i.e. peptides or phospholipid head groups) to yield Schiff base products. We also demonstrate that such oxidized phospholipid products may further react through a post-oxidation chemical pathway involving aldol condensation. EO6, an IgM monoclonal autoantibody to oxidized phospholipids, blocks the uptake of oxidized LDL (OxLDL) by macrophages. Because the epitope(s) of EO6 also blocks the uptake of OxLDL, a series of oxidized phospholipids, their peptide complexes, and their aldol condensates have been synthesized and characterized, and their antigenicity has been determined. This study defines structural motifs of oxidized phospholipids responsible for antigenicity for EO6. Certain monomeric phospholipids containing short chain fatty acids were antigenic whether oxidized or not in the sn-2 position. However, oxidized phospholipids containing sn-1 long chain fatty acids were not antigenic unless the sn-2 oxidized fatty acid contained an aldehyde that first reacted with a peptide yielding a Schiff base or the sn-2 oxidized fatty acid underwent an aldol type self-condensation. Our data indicate that the phosphorylcholine head group is essential for antigenicity, but its availability depends on the oxidized phospholipid conformation. We suggest that upon oxidation, similar reactions occur in phospholipids on the surface of LDL, generating ligands for macrophage recognition. Synthetic imine adducts of oxidized phospholipids of this type are capable of blocking the uptake of OxLDL.

Footnotes

↵* This work was supported by National Institutes of Health Grants HL57505 (to J. L. W.), HL56989 (to La Jolla Specialized Center of Research in Molecular Medicine and Atherosclerosis), and GM20501 (to E. A. D), Tobacco Related Disease Research Program Grant 0KT-0220 (to P. F.), and an American Heart Association Western States Affiliates postdoctoral fellowship (to P. F.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵§ These authors contributed equally to this work, as did the laboratories of Drs. Witztum and Dennis.
↵‖ To whom correspondence and reprint requests should be addressed. Fax: 858-534-7390; E-mail: edennis@ucsd.edu.
Published, JBC Papers in Press, December 14, 2001, DOI 10.1074/jbc.M108860200
Abbreviations:

LDL

low density lipoprotein

OxLDL

oxidized LDL

PC

phosphorylcholine

PAPC

1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine

POVPC

1-palmitoyl-2-(5′-oxo)valeroyl-sn-glycero-3-phosphorylcholine

BSA

bovine serum albumin

KLH

keyhole limpet hemocyanin

PBS

phosphate-buffered saline

HPLC

high performance liquid chromatography

PONPC

1-palmitoyl-2-(9′-oxo)nonanoyl-sn-glycero-3-phosphorylcholine

C₆OVPC

1-caproyl-2-(5′-oxo)valeroyl-sn-glycero-3-phosphorylcholine

PAF

platelet-activating factor

PAPE

1-palmitoyl-2-arachidonoyl phosphatidylethanolamine

PLPS

1-palmitoyl-2-linoleoyl phosphatidylserine
- Received September 13, 2001.
- Revision received December 13, 2001.
The American Society for Biochemistry and Molecular Biology, Inc.