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Abstract
LDL-associated phospholipids (PLs) may be transferred into platelets. In this work, we characterized the role of VLDLs as PL donors. VLDL transferred radiolabeled PLs to platelets in a temperature- and concentration-dependent manner. LPL stimulated this process through its action on VLDL lipolysis, because it was abolished by tetrahydrolipstatin. LPL also stimulated the platelet production of thromboxane B2 (TXB2). Both LPL actions were inhibited in the presence of fatty acid-free albumin, suggesting that they were attributable to fatty acids generated during VLDL lipolysis. To study the relationship between PL transfers and platelet activation, we performed incubations in the presence of HDL, a physiological acceptor of PL released from VLDL. HDL antagonized the transfer of PL from VLDL to platelets but had no effect on the production of TXB2, suggesting that PL transfers were driven by platelet activation. Confirming this idea, thrombin stimulated both the production of TXB2 and the transfers of PL. In conclusion, VLDL can transfer PL to platelets. These transfers are stimulated by LPL and thrombin through their action on platelet activation. They might be enhanced in pathologies characterized by increased VLDL concentrations.
Highlights
LDL-associated phospholipids (PLs) may be transferred into platelets
LDL and HDL transport the major part of lipoprotein PL, they do not necessarily represent the sole source of PL for Abbreviations: [3H]DPPC, 1,2-dipalmitoyl-([3H]methyl-choline)phosphatidylcholine; FAF, fatty acid-free; [14C]PAPC, 1-palmitoyl-2-[114C]arachidonyl-phosphatidylcholine; [14C]PAPE, 1-palmitoyl-2-[114C]arachidonyl-phosphatidylethanolamine; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PL, phospholipid; PLA2, phospholipase A2; TG, triglyceride; THL, tetrahydrolipstatin; TXB2, thromboxane B2
Platelets were incubated with [14C]PAPC-labeled VLDL (200 nmol phospholipid/ml) for 1 h at 37jC in a total volume of 1.5 ml in the presence or absence of LPL (100 ng/ml). Their intracellular contents in intact [14C]PAPC, [14C]TXB2, and [14C]arachidonic acid were determined after thin-layer chromatography, as described in Materials and Methods
Summary
LDL-associated phospholipids (PLs) may be transferred into platelets. In this work, we characterized the role of VLDLs as PL donors. These transfers are stimulated by LPL and thrombin through their action on platelet activation They might be enhanced in pathologies characterized by increased VLDL concentrations.—Ibrahim, S., A. The transfer of LDL- or HDL-derived PE into platelets, but not that of PC or sphingomyelin, was stimulated by platelet activators, including thrombin, collagen, and ADP, and was dependent on the secretion of an unidentified cellular protein factor [11]. VLDLs are lipoproteins secreted by the liver in the circulation, where they undergo hydrolysis of their core triglyceride (TG) content through the successive actions of LPL and hepatic lipase, which results in the formation of LDL [12, 13] During this process, the excess VLDL surface components, including apolipoproteins, cholesterol, and PL, are released from the particles. We present in vitro evidence showing that this transfer may occur under physiological conditions, that it is facilitated by the action of LPL, and that it is dependent on the activation of platelets
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