Triglyceride-rich lipoprotein metabolism in unique VLDL receptor, LDL receptor, and LRP triple-deficient mice

The very low density lipoprotein receptor (VLDLR), low density lipoprotein receptor (LDLR), and low density lipoprotein receptor-related protein (LRP) are the three main apolipoprotein E-recognizing endocytic receptors involved in the clearance of triglyceride (TG)-rich lipoproteins from plasma. Whereas LDLR deficiency in mice results in the accumulation of plasma LDL-sized lipoproteins, VLDLR or LRP deficiency alone only minimally affects plasma lipoproteins. To investigate the combined effect of the absence of these receptors on TG-rich lipoprotein levels, we have generated unique VLDLR, LDLR, and LRP triple-deficient mice. Compared with wild-type mice, these mice markedly accumulated plasma lipids and lipases. These mice did not show aggravated hyperlipidemia compared with LDLR and LRP double-deficient mice, but plasma TG was increased after high-fat diet feeding. In addition, these mice showed a severely decreased postprandial TG clearance typical of VLDLR-deficient (VLDLR-/-) mice. Collectively, although VLDLR deficiency in LRP- and LDLR-/- mice does not aggravate hyperlipidemia, these triple-deficient mice represent a unique model of markedly delayed TG clearance on a hyperlipidemic background.     

Bone marrow-derived HL mitigates bone marrow-derived CETP-mediated decreases in HDL in mice globally deficient in HL and the LDLr

The objective of this study was to determine the combined effects of HL and cholesteryl ester transfer protein (CETP), derived exclusively from bone marrow (BM), on plasma lipids and atherosclerosis in high-fat-fed, atherosclerosis-prone mice. We transferred BM expressing these proteins into male and female double-knockout HL-deficient, LDL receptor-deficient mice (HL^−/−LDLr^−/−). Four BM chimeras were generated, where BM-derived cells expressed 1) HL but not CETP, 2) CETP and HL, 3) CETP but not HL, or 4) neither CETP nor HL. After high-fat feeding, plasma HDL-cholesterol (HDL-C) was decreased in mice with BM expressing CETP but not HL (17 ± 4 and 19 ± 3 mg/dl, female and male mice, respectively) compared with mice with BM expressing neither CETP nor HL (87 ± 3 and 95 ± 4 mg/dl, female and male mice, respectively, P < 0.001 for both sexes). In female mice, the presence of BM-derived HL mitigated this CETP-mediated decrease in HDL-C. BM-derived CETP decreased the cholesterol component of HDL particles and increased plasma cholesterol. BM-derived HL mitigated these effects of CETP. Atherosclerosis was not significantly different between BM chimeras. These results suggest that BM-derived HL mitigates the HDL-lowering, HDL-modulating, and cholesterol-raising effects of BM-derived CETP and warrant further studies to characterize the functional properties of these protein interactions.     

Upregulation of liver VLDL receptor and FAT/CD36 expression in LDLR-/- apoB100/100 mice fed trans-10,cis-12 conjugated linoleic acid

This study explores the mechanisms responsible for the fatty liver setup in mice fed trans-10,cis-12 conjugated linoleic acid (t10c12 CLA), hypothesizing that an induction of low density lipoprotein receptor (LDLR) expression is associated with lipid accumulation. To this end, the effects of t10c12 CLA treatment on lipid parameters, serum lipoproteins, and expression of liver lipid receptors were measured in LDLR(-/-) apoB(100/100) mice as a model of human familial hypercholesterolemia itself depleted of LDLR. Mice were fed t10c12 CLA over 2 or 4 weeks. We first observed that the treatment induced liver steatosis, even in the absence of LDLR. Mice treated for 2 weeks exhibited hypertriglyceridemia with high levels of VLDL and HDL, whereas a 4 week treatment inversely induced a reduction of serum triglycerides (TGs), essentially through a decrease in VLDL levels. In the absence of LDLR, the mRNA levels of other proteins, such as VLDL receptor, lipoprotein lipase, and fatty acid translocase, usually not expressed in the liver, were upregulated, suggesting their involvement in the steatosis setup and lipoprotein clearance. The data also suggest that the TG-lowering effect induced by t10c12 CLA treatment was attributable to both the reduction of circulating free fatty acids in response to the severe lipoatrophy and the high capacity of liver to clear off plasma lipids.     

Lipolytic and ligand-binding functions of hepatic lipase protect against atherosclerosis in LDL receptor-deficient mice

To elucidate the separate contributions of the lipolytic versus ligand-binding functions of hepatic lipase (HL) to lipoprotein metabolism and atherosclerosis, and to investigate the role of the low density lipoprotein receptor (LDLr) in these processes, we compared mice expressing catalytically active HL (HL-WT) with mice expressing inactive HL (HL-S145G) in a background lacking endogenous HL and the LDLr (LDLr-KOxHL-KO). HL-WT and HL-S145G reduced (P < 0.05 for all) cholesterol (55% vs. 20%), non-HDL-cholesterol (63% vs. 22%), and apolipoprotein B (apoB; 34% vs. 16%) by enhancing the catabolism of autologous (125)I-apoB-intermediate density lipoprotein (IDL)/LDL (fractional catabolic rate in day(-1): 6.07 +/- 0.25, LDLr-KOxHL-WT; 4.76 +/- 0.30, LDLr-KOxHL-S145G; 3.70 +/- 0.13, LDLr-KOxHL-KO); HL-WT had a greater impact on the concentration, composition, particle size, and catabolism of apoB-containing lipoproteins (apoB-Lps) and HDL. Importantly, consistent with the changes in apoB-Lps, atherosclerosis in LDLr-KOxHL-KO mice fed a regular chow diet (RCD) was reduced by both HL-WT and HL-S145G (by 71% and 51% in cross-sectional analysis, and by 85% and 67% in en face analysis; P < 0.05 for all). These data identify physiologically relevant but distinct roles for the lipolytic versus ligand-binding functions of HL in apoB-Lp metabolism and atherosclerosis and demonstrate that their differential effects on these processes are mediated by changes in catabolism via non-LDLr pathways. These changes, evident even in the presence of apoE, establish an antiatherogenic role of the ligand-binding function of HL in LDLr-deficient mice.     

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

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 microM PL) to platelets (2 x 10(8)/ml) was measured after incubations of 1 h at 37 degrees 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 microM); esculetin, a 12-lipoxygenase inhibitor (20 microM); methyl-arachidonyl-fluorophosphonate (MAFP), a phospholipase A(2) (PLA(2)) inhibitor (100 microM); 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis (acetoxymethyl) ester (BAPTA-AM), a Ca(2+) chelator (20 microM); bromoenol lactone (BEL), a Ca(2+)- independent phospholipase A(2) (iPLA(2)) inhibitor (100 nM); and 1-[6-[[17beta-3-methoxyestra-1,3,5(10)-trien-17-yl-]amino]hexyl]1H-pyrrole-2,5-dione (U73122), a phospholipase C (PLC) inhibitor (20 microM). 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 A(2) (cPLA(2)) and iPLA(2), only cPLA(2) 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 cPLA(2)-dependent process. The inhibition of iPLA(2) by BEL had no effect on PL transfers.     

Atorvastatin increases human serum levels of proprotein convertase subtilisin/kexin type 9

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has gained attention as a key regulator of serum low density lipoprotein cholesterol (LDL-C) levels. This novel protease causes the degradation of hepatic low density lipoprotein receptors. In humans, gain-of-function mutations in PCSK9 cause a form of familial hypercholesterolemia, whereas loss-of-function mutations result in significantly decreased LDL-C levels and cardiovascular risk. Previous studies have demonstrated that statins upregulate PCSK9 mRNA expression in cultured cells and animal models. In light of these observations, we studied the effect of atorvastatin on circulating PCSK9 protein levels in humans using a sandwich ELISA to quantitate serum PCSK9 levels in patients treated with atorvastatin or placebo for 16 weeks. We observed that atorvastatin (40 mg/day) significantly increased circulating PCSK9 levels by 34% compared with baseline and placebo and decreased LDL-C levels by 42%. These results suggest that the addition of a PCSK9 inhibitor to statin therapy may result in even further LDL-C decreases.     

The hepatic uptake of VLDL in lrp-ldlr-/-vldlr-/- mice is regulated by LPL activity and involves proteoglycans and SR-BI

LPL activity plays an important role in preceding the VLDL remnant clearance via the three major apolipoprotein E (apoE)-recognizing receptors: the LDL receptor (LDLr), LDL receptor-related protein (LRP), and VLDL receptor (VLDLr). The aim of this study was to determine whether LPL activity is also important for VLDL remnant clearance irrespective of these receptors and to determine the mechanisms involved in the hepatic remnant uptake. Administration of an adenovirus expressing LPL (AdLPL) into lrp(-)ldlr(-/-)vldlr(-/-) mice reduced both VLDL-triglyceride (TG) and VLDL-total cholesterol (TC) levels. Conversely, inhibition of LPL by AdAPOC1 increased plasma VLDL-TG and VLDL-TC levels. Metabolic studies with radiolabeled VLDL-like emulsion particles showed that the clearance and hepatic association of their remnants positively correlated with LPL activity. This hepatic association was independent of the bridging function of LPL and HL, since heparin did not reduce the liver association. In vitro studies demonstrated that VLDL-like emulsion particles avidly bound to the cell surface of primary hepatocytes from lrp(-)ldlr(-/-)vldlr(-/-) mice, followed by slow internalization, and involved heparin-releaseable cell surface proteins as well as scavenger receptor class B type I (SR-BI). Collectively, we conclude that hepatic VLDL remnant uptake in the absence of the three classical apoE-recognizing receptors is regulated by LPL activity and involves heparan sulfate proteoglycans and SR-BI.     

Atherosclerosis is enhanced by testosterone deficiency and attenuated by CETP expression in transgenic mice

In this work, we investigated the impact of testosterone deficiency and cholesteryl ester transfer protein (CETP) expression on lipoprotein metabolism and diet-induced atherosclerosis. CETP transgenic mice and nontransgenic (nTg) littermates were studied 4 weeks after bilateral orchidectomy or sham operation. Castrated mice had an increase in the LDL fraction (+36% for CETP and +79% for nTg mice), whereas the HDL fraction was reduced (-30% for CETP and -11% for nTg mice). Castrated mice presented 1.7-fold higher titers of anti-oxidized LDL (Ox-LDL) antibodies than sham-operated controls. Plasma levels of CETP, lipoprotein lipase, and hepatic lipase were not changed by castration. Kinetic studies showed no differences in VLDL secretion rate, VLDL-LDL conversion rate, or number of LDL and HDL receptors. Competition experiments showed lower affinity of LDL from castrated mice for tissue receptors. Diet-induced atherosclerosis studies showed that testosterone deficiency increased by 100%, and CETP expression reduced by 44%, the size of aortic lesion area in castrated mice. In summary, testosterone deficiency increased plasma levels of apolipoprotein B-containing lipoproteins (apoB-LPs) and anti-OxLDL antibodies, decreased LDL receptor affinity, and doubled the size of diet-induced atherosclerotic lesions. The expression of CETP led to a milder increase of apoB-LPs and reduced atherosclerotic lesion size in testosterone-deficient mice.     

Inactivation of ANGPTL3 reduces hepatic VLDL-triglyceride secretion

Humans and mice lacking angiopoietin-like protein 3 (ANGPTL3) have pan-hypolipidemia. ANGPTL3 inhibits two intravascular lipases, LPL and endothelial lipase, and the low plasma TG and HDL-cholesterol levels in ANGPTL3 deficiency reflect increased activity of these enzymes. The mechanism responsible for the low LDL-cholesterol levels associated with ANGPTL3 deficiency is not known. Here we used an anti-ANGPTL3 monoclonal antibody (REGN1500) to inactivate ANGPTL3 in mice with genetic deficiencies in key proteins involved in clearance of ApoB-containing lipoproteins. REGN1500 treatment consistently reduced plasma cholesterol levels in mice in which Apoe, Ldlr, Lrp1, and Sdc1 were inactivated singly or in combination, but did not alter clearance of rabbit ¹²⁵I-βVLDL or mouse ¹²⁵I-LDL. Despite a 61% reduction in VLDL-TG production, VLDL-ApoB-100 production was unchanged in REGN1500-treated animals. Hepatic TG content, fatty acid synthesis, and fatty acid oxidation were similar in REGN1500 and control antibody-treated animals. Taken together, our findings indicate that inactivation of ANGPTL3 does not affect the number of ApoB-containing lipoproteins secreted by the liver but alters the particles that are made such that they are cleared more rapidly from the circulation via a noncanonical pathway(s). The increased clearance of lipolytic remnants results in decreased production of LDL in ANGPTL3-deficient animals.     

The apoE isoform binding properties of the VLDL receptor reveal marked differences from LRP and the LDL receptor

Apolipoprotein E (apoE) associates with lipoproteins and mediates their interaction with members of the LDL receptor family. ApoE exists as three common isoforms that have important distinct functional and biological properties. Two apoE isoforms, apoE3 and apoE4, are recognized by the LDL receptor, whereas apoE2 binds poorly to this receptor and is associated with type III hyperlipidemia. In addition, the apoE4 isoform is associated with the common late-onset familial and sporadic forms of Alzheimer's disease. Although the interaction of apoE with the LDL receptor is well characterized, the specificity of other members of this receptor family for apoE is poorly understood. In the current investigation, we have characterized the binding of apoE to the VLDL receptor and the LDL receptor-related protein (LRP). Our results indicate that like the LDL receptor, LRP prefers lipid-bound forms of apoE, but in contrast to the LDL receptor, both LRP and the VLDL receptor recognize all apoE isoforms. Interestingly, the VLDL receptor does not require the association of apoE with lipid for optimal recognition and avidly binds lipid-free apoE. It is likely that this receptor-dependent specificity for various apoE isoforms and for lipid-free versus lipid-bound forms of apoE is physiologically significant and is connected to distinct functions for these receptors.     

Reproducibility of stable isotope-labeled tracer measures of VLDL-triglyceride and VLDL-apolipoprotein B-100 kinetics

To gain insight into the mechanisms regulating plasma lipid homeostasis, FFA, VLDL-triglyceride (TG), and VLDL-apolipoprotein B-100 (apoB-100) kinetics are commonly assessed using stable isotope-labeled tracer methods. The reproducibility of these measurements, which is critical for the experimental design, is unknown. Therefore, we investigated the repeatability of plasma FFA, VLDL-TG, and VLDL-apoB-100 kinetics in eight healthy men using stable isotope-labeled tracer techniques. There were no systematic differences in plasma FFA, VLDL-TG, and VLDL-apoB-100 concentrations and kinetics between the two studies. Intraindividual day-to-day variability for various outcome variables ranged from 15% to 25%, and almost all of this was of biological origin. The most robust outcome variables were FFA rate of appearance and hepatic VLDL-TG and VLDL-apoB-100 secretion rates; the least robust were VLDL-TG and VLDL-apoB-100 plasma clearance rates and mean residence times. Overall, physiologically meaningful differences in mean values (i.e., 25-30% in magnitude) can be obtained with a sample size of 6-10 subjects for paired studies and 12-20 subjects per group for cross-sectional studies, assuming a type I error rate of 0.05 and a type II error rate of 0.20 (i.e., 80% power). These findings will be useful for future studies investigating FFA, VLDL-TG, and VLDL-apoB-100 kinetics with the methods described.     

The glycosylation-dependent interaction of perlecan core protein with LDL: implications for atherosclerosis

Perlecan is a major heparan sulfate (HS) proteoglycan in the arterial wall. Previous studies have linked it to atherosclerosis. Perlecan contains a core protein and three HS side chains. Its core protein has five domains (DI–DV) with disparate structures and DII is highly homologous to the ligand-binding portion of LDL receptor (LDLR). The functional significance of this domain has been unknown. Here, we show that perlecan DII interacts with LDL. Importantly, the interaction largely relies on O-linked glycans that are only present in the secreted DII. Among the five repeat units of DII, most of the glycosylation sites are from the second unit, which is highly divergent and rich in serine and threonine, but has no cysteine residues. Interestingly, most of the glycans are capped by the negatively charged sialic acids, which are critical for LDL binding. We further demonstrate an additive effect of HS and DII on LDL binding. Unlike LDLR, which directs LDL uptake through endocytosis, this study uncovers a novel feature of the perlecan LDLR-like DII in receptor-mediated lipoprotein retention, which depends on its glycosylation. Thus, perlecan glycosylation may play a role in the early LDL retention during the development of atherosclerosis.     

Relation between insulin resistance and fast-migrating LDL subfraction as characterized by capillary isotachophoresis

The proportion of the electronegative low density lipoprotein [LDL(-)] subfraction, which is atherogenic, is increased in type 2 diabetes but is not reduced by glycemic control. Therefore, we evaluated the ability of a new technique, capillary isotachophoresis (cITP), to quantify charge-based LDL subfractions and examined the relation between insulin resistance and the cITP fast-migrating (f) LDL levels. Seventy-five 10-year-old boys were included. The two cITP LDL subfractions, fLDL and major LDL subfractions, were proportional to the LDL protein content within the range of 0.1-0.8 mg/ml LDL protein. Levels of cITP fLDL were positively correlated with triglyceride (TG) levels and negatively correlated with LDL size. Insulin resistance as assessed by the homeostasis model assessment (HOMA-IR) was positively correlated (P < 0.01) with cITP fLDL levels (r = 0.41). The relation between HOMA-IR and cITP fLDL levels depended on TG levels but was independent of body mass index and LDL size. cITP lipoprotein analysis is an accurate and sensitive method for quantifying charge-based LDL subfractions in human plasma, and insulin resistance is related to cITP fLDL independent of LDL size.     

Severe hypertriglyceridemia in human APOC1 transgenic mice is caused by apoC-I-induced inhibition of LPL

Studies in humans and mice have shown that increased expression of apolipoprotein C-I (apoC-I) results in combined hyperlipidemia with a more pronounced effect on triglycerides (TGs) compared with total cholesterol (TC). The aim of this study was to elucidate the main reason for this effect using human apoC-I-expressing (APOC1) mice. Moderate plasma human apoC-I levels (i.e., 4-fold higher than human levels) caused a 12-fold increase in TG, along with a 2-fold increase in TC, mainly confined to VLDL. Cross-breeding of APOC1 mice on an apoE-deficient background resulted in a marked 55-fold increase in TG, confirming that the apoC-I-induced hyperlipidemia cannot merely be attributed to blockade of apoE-recognizing hepatic lipoprotein receptors. The plasma half-life of [3H]TG-VLDL-mimicking particles was 2-fold increased in APOC1 mice, suggesting that apoC-I reduces the lipolytic conversion of VLDL. Although total postheparin plasma LPL activity was not lower in APOC1 mice compared with controls, apoC-I was able to dose-dependently inhibit the LPL-mediated lipolysis of [3H]TG-VLDL-mimicking particles in vitro with a 60% efficiency compared with the main endogenous LPL inhibitor apoC-III. Finally, purified apoC-I impaired the clearance of [3H]TG-VLDL-mimicking particles independent of apoE-mediated hepatic uptake in lactoferrin-treated mice. Therefore, we conclude that apoC-I is a potent inhibitor of LPL-mediated TG-lipolysis.     

LDL and HDL transfer rates across peripheral microvascular endothelium agree with those predicted for passive ultrafiltration in humans

The mechanisms by which LDLs and HDLs cross the vascular endothelium from plasma into interstitial fluid are not understood, and have never been studied in humans in vivo. We determined whether the plasma-to-lymph clearance rates of LDL and HDL conform with those predicted by passive ultrafiltration through intercellular pores, or if it is necessary to invoke an active process such as receptor-mediated transcytosis. Plasma and afferent peripheral lymph were collected under steady-state conditions from 30 healthy men, and assayed for seven globular proteins of molecular radii 2.89–8.95 nm, complement C3, and apo AI, apo AII, and apo B. Plasma-to-lymph clearance rates of the seven proteins fitted the relation expected for molecules of their size when transported through two populations of pores of radius 4.95 and 20.1 nm. The same model parameters were then found to accurately predict the clearance rates of both HDL and LDL. The apparent clearance of complement C3, previously shown to be secreted by cultured endothelium, exceeded that predicted by the model. We conclude that the transport of HDL and LDL from plasma into interstitial fluid across the peripheral vascular endothelium in healthy humans can be explained by ultrafiltration without invoking an additional active process such as transcytosis.     

Electronegative LDLs from familial hypercholesterolemic patients are physicochemically heterogeneous but uniformly proapoptotic

A highly electronegative fraction of human plasma LDLs, designated L5, has distinctive biological activity that includes induction of apoptosis in bovine aortic endothelial cells (BAECs). This study was performed to identify a relationship between LDL density, electronegativity, and biological activity, namely, the induction of apoptosis in BAECs. Plasma LDLs from normolipidemic subjects and homozygotic familial hypercholesterolemia subjects were separated into five subfractions, with increasing electronegativity from L1 to L5, and into seven subfractions according to increasing density, D1 to D7. L1 to L5 were also separated according to density, and D1 to D7 were separated according to charge. The density profiles of L1 to L5 were similar (maximum density = 1.030 +/- 0.002 g/ml). Induction of apoptosis by all seven density subfractions was confined to the highly electronegative fraction, L5, and within each density subfraction the magnitude of apoptosis correlated with the L5 content. Electronegative LDL is heterogeneous with respect to density and composition, and induction of apoptosis is more strongly associated with LDL electronegativity than with LDL size or density.     

Endogenous apoC-I increases hyperlipidemia in apoE-knockout mice by stimulating VLDL production and inhibiting LPL

Previous studies have shown that overexpression of human apolipoprotein C-I (apoC-I) results in moderate hypercholesterolemia and severe hypertriglyceridemia in mice in the presence and absence of apoE. We assessed whether physiological endogenous apoC-I levels are sufficient to modulate plasma lipid levels independently of effects of apoE on lipid metabolism by comparing apolipoprotein E gene-deficient/apolipoprotein C-I gene-deficient (apoe-/-apoc1-/-), apoe-/-apoc1+/-, and apoe-/-apoc1+/+ mice. The presence of the apoC-I gene-dose-dependently increased plasma cholesterol (+45%; P < 0.001) and triglycerides (TGs) (+137%; P < 0.001), both specific for VLDL. Whereas apoC-I did not affect intestinal [3H]TG absorption, it increased the production rate of hepatic VLDL-TG (+35%; P < 0.05) and VLDL-[35S]apoB (+39%; P < 0.01). In addition, apoC-I increased the postprandial TG response to an intragastric olive oil load (+120%; P < 0.05) and decreased the uptake of [3H]TG-derived FFAs from intravenously administered VLDL-like emulsion particles by gonadal and perirenal white adipose tissue (WAT) (-34% and -25%, respectively; P < 0.05). As LPL is the main enzyme involved in the clearance of TG-derived FFAs by WAT, and total postheparin plasma LPL levels were unaffected, these data demonstrate that endogenous apoC-I suffices to attenuate the lipolytic activity of LPL. Thus, we conclude that endogenous plasma apoC-I increases VLDL-total cholesterol and VLDL-TG dose-dependently in apoe-/- mice, resulting from increased VLDL particle production and LPL inhibition.     

Transfer of very low density lipoprotein-associated phospholipids to activated human platelets

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.