Electrospray ionization mass spectrometry identifies substrates and products of lipoprotein-associated phospholipase A2 in oxidized human low density lipoprotein

Davis, Bill, Koster, Grielof, Douet, Lisa J., Scigelova, Michaela, Woffendin, Gary, Ward, Joanna M., Smith, Alberto, Humphries, Julia, Burnand, Kevin G., Macphee, Colin H. and Postle, Anthony D. (2008) Electrospray ionization mass spectrometry identifies substrates and products of lipoprotein-associated phospholipase A2 in oxidized human low density lipoprotein. The Journal of Biological Chemistry, 283 (10), 6428-6437. (doi:10.1074/jbc.M709970200). (PMID:18165686)

Abstract

There is increasing evidence that modified phospholipid products of low density lipoprotein (LDL) oxidation mediate inflammatory processes within vulnerable atherosclerotic lesions. Lipoprotein-associated phospholipase A2 (Lp-PLA2) is present in vulnerable plaque regions where it acts on phospholipid oxidation products to generate the pro-inflammatory lysophsopholipids and oxidized non-esterified fatty acids. This association together with identification of circulating Lp-PLA2 levels as an independent predictor of cardiovascular disease provides a rationale for development of Lp-PLA2 inhibitors as therapy for atherosclerosis. Here we report a systematic analysis of the effects of in vitro oxidation in the absence and presence of an Lp-PLA2 inhibitor on the phosphatidylcholine (PC) composition of human LDL. Mass spectrometry identifies three classes of PC whose concentration is significantly enhanced during LDL oxidation. Of these, a series of molecules, represented by peaks in the m/z range 594-666 and identified as truncated PC oxidation products by accurate mass measurements using an LTQ Orbitrap mass spectrometer, are the predominant substrates for Lp-PLA2. A second series of oxidation products, represented by peaks in the m/z range 746-830 and identified by LTQ Orbitrap analysis as non-truncated oxidized PCs, are quantitatively more abundant but are less efficient Lp-PLA2 substrates. The major PC products of Lp-PLA2, saturated and mono-unsaturated lyso-PC, constitute the third class. Mass spectrometric analysis confirms the presence of many of these PCs within human atherosclerotic lesions, suggesting that they could potentially be used as in vivo markers of atherosclerotic disease progression and response to Lp-PLA2 inhibitor therapy.

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Contributors

Author: Lisa J. Douet

Author: Anthony D. Postle

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