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Open Access Research

Time course-changes in phosphatidylcholine profile during oxidative modification of low-density lipoprotein

Naoko Sasabe1, Yuka Keyamura12, Takashi Obama1, Nozomi Inoue1, Yukihiro Masuko1, Yu Igarashi1, Toshihiro Aiuchi1, Rina Kato1, Tomohiro Yamaguchi1, Hiroshi Kuwata3, Sanju Iwamoto4, Akira Miyazaki4, Shuntaro Hara3, Tomohiro Yoshikawa2 and Hiroyuki Itabe1*

Author Affiliations

1 Division of Biological Chemistry, Department of Molecular Biology, Showa University School of Pharmacy, Tokyo, Japan

2 Free Radical Research Project, Otsuka Pharmaceutical Co. Ltd., Tokushima, Japan

3 Division of Health Chemistry, Department of Healthcare and Regulatory Sciences, Showa University School of Pharmacy, Tokyo, Japan

4 Department of Biochemistry, Showa University School of Medicine, Tokyo, Japan

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Lipids in Health and Disease 2014, 13:48  doi:10.1186/1476-511X-13-48

Published: 14 March 2014

Abstract

Background

Oxidized phosphatidylcholines (oxPC) and lysophosphatidylcholine (lysoPC) generated during the formation of oxidized low-density lipoprotein (oxLDL) are involved in atherosclerotic lesion development. We investigated the time course-changes in phosphatidylcholine (PC) molecular species during oxidation of LDL to determine how those atherogenic PCs are produced.

Methods

Human and rabbit LDLs were pretreated with or without a selective platelet-activating factor acetylhydrolase (PAF-AH) inhibitor. LDL was oxidized by incubation with copper sulfate, and PC profiles were analyzed by liquid chromatography-tandem mass spectrometry.

Results

When human LDL was oxidized, the peak areas for polyunsaturated fatty acid (PUFA)-containing PC species dramatically decreased after a short lag period, concomitantly lysoPC species increased sharply. Although a variety of oxPC species containing oxidized fatty acyl groups or cleaved acyl chains are formed during LDL oxidation, only a few oxPC products accumulated in oxLDL: 1-palmitoyl-2-(9-oxo-nonanoyl) PC and long-chain oxPC with two double bonds. Pretreatment of LDL with the PAF-AH inhibitor greatly reduced lysoPC production while it had no effect on lipid peroxidation reactions and oxPC profiles. Rabbit LDL, which has a different composition of PC molecular species and needs a longer time to reach achieve full oxidation than human LDL, also accumulated lysoPC during oxidation. The increase in lysoPC in rabbit oxLDL was suppressed by pretreatment with the PAF-AH inhibitor. The major oxPC species formed in rabbit oxLDL were almost the same as human oxLDL.

Conclusions

These results suggest that lysoPC species are the major products and PAF-AH activity is crucial for lysoPC generation during oxidation of LDL. The oxPC species accumulated are limited when LDL is oxidized with copper ion in vitro.

Keywords:
Oxidized LDL; PC molecular species; LC-MS/MS; Oxidized PC; PAF-AH; Pefabloc; lysoPC; PONPC; Rabbit LDL