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Journal of Lipid Research, Vol. 48, 1533-1538, July 2007
Copyright © 2007 by American Society for Biochemistry and Molecular Biology

The transfer of VLDL-associated phospholipids to activated platelets depends upon cytosolic phospholipase A₂ activity

Salam Ibrahim^*,,,**,,, Catherine Calzada^*,,,**,,, Valérie Pruneta-Deloche^*,,,**,,, Michel Lagarde^*,,,**,, and Gabriel Ponsin^1,*,,,**,,

^* Université de Lyon, Lyon, F-69003 France
Institut National de la Santé et de la Recherche Médicale, U870, Institut Fédératif de Recherche 62, Lyon, F-69008 France
Institut National de la Recherche Agronomique, Unité Mixte de Recherche 1235, Lyon, F-69008 France
^** Institut National des Sciences Appliquées-Lyon, Régulations Métaboliques, Nutrition et Diabètes, Villeurbanne, F-69621 France
Université Lyon 1, Lyon, F-69003 France
Hospices Civils de Lyon, Lyon, F-69008 France

Published, JLR Papers in Press, April 24, 2007.

¹ To whom correspondence should be addressed. e-mail: gabriel.ponsin{at}insa-lyon.fr

We previously reported that VLDL could transfer phospholipids (PLs) to activated platelets. To identify the metabolic pathway involved in this process, the transfer of radiolabeled PLs from VLDL (200 µM PL) to platelets (2 x 10⁸/ml) was measured after incubations of 1 h at 37°C, with or without thrombin (0.1 U/ml) or LPL (500 ng/ml), in the presence of various inhibitors, including aspirin, a cyclooxygenase inhibitor (300 µM); esculetin, a 12-lipoxygenase inhibitor (20 µM); methyl-arachidonyl-fluorophosphonate (MAFP), a phospholipase A₂ (PLA₂) inhibitor (100 µM); 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis (acetoxymethyl) ester (BAPTA-AM), a Ca²⁺ chelator (20 µM); bromoenol lactone (BEL), a Ca²⁺- independent phospholipase A₂ (iPLA₂) inhibitor (100 nM); and 1-[6-[[17ß-3-methoxyestra-1,3,5(10)-trien-17-yl-]amino]hexyl]1H-pyrrole-2,5-dione (U73122), a phospholipase C (PLC) inhibitor (20 µM). Aspirin and esculetin had no effect, showing that PL transfer was not dependent upon cyclooxygenase or lipoxygenase pathways. The transfer of PL was inhibited by MAFP, U73122, and BAPTA-AM. Although MAFP inhibited both cytosolic phospholipase A₂ (cPLA₂) and iPLA₂, only cPLA₂ is a calcium-dependent enzyme. Because calcium mobilization is favored by PLC and inhibited by BAPTA-AM, the transfer of PL from VLDL to platelets appeared to result from a cPLA₂-dependent process. The inhibition of iPLA₂ by BEL had no effect on PL transfers.

Supplementary key words thrombin • lipoprotein lipase • metabolic inhibitors • Ca²⁺- independent phospholipase A₂ • very low density lipoprotein

Abbreviations: BAPTA-AM, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis (acetoxymethyl) ester; BEL, bromoenol lactone; cPLA₂, cytosolic phospholipase A₂; iPLA₂, Ca²⁺-independent phospholipase A₂; MAFP, methyl arachidonyl fluorophosphonate; [¹⁴C]PAPC, 1-palmitoyl-2-[1-¹⁴C]arachidonyl-phosphatidylcholine; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PL, phospholipid; PLA₂, phospholipase A₂; PLC, phospholipase C; PLTP, phospholipid transfer protein; TXB₂, thromboxane B₂; U73122, 1-[6-[[17ß-3-methoxyestra-1,3,5(10)-trien-17-yl-]amino]hexyl]-1H-pyrrole-2,5-dione

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