Effects of VLDL, chylomicrons, and chylomicron remnants on platelet aggregability

Effects of remnant cholesterol on the efficacy of genotype-guided dual antiplatelet in CYP2C19 loss-of -function carriers with minor stroke or transient ischaemic attack: a post-hoc analysis of the CHANCE-2 trial

Background

The atherogenicity of remnant cholesterol (RC), a contributor to residual risk of cardiovascular events, has been underlined by recent guidelines. We aimed to evaluate the relationship between RC levels and the efficacy and safety of genotype-guided dual antiplatelet therapy in the CHANCE-2 trial.

Methods

This post-hoc study used data from the CHANCE-2 trial, which was a randomised, double-blind, placebo-controlled trial of 6412 patients (aged >40 years) enrolled from 202 hospitals in China, between Sept 23, 2019, and March 22, 2021, who carried CYP2C19 loss-of-function alleles and had either an acute minor stroke or high-risk transient ischaemic attack (TIA), and could start treatment within 24 h of symptom onset. Participants received either (1:1) ticagrelor plus aspirin (control) or clopidogrel plus aspirin (intervention) and the effect of reducing the 3-month risk of any new stroke was assessed (ischemic or haemorrhagic, primary outcome). From the CHANCE-2 study population, we enrolled 5890 patients with complete data on RC. The cutoff point of RC for distinguishing patients with greater benefit from ticagrelor-aspirin versus clopidogrel-aspirin was determined with subpopulation treatment effect pattern plot. The primary efficacy and safety outcome was recurrent stroke and severe or moderate bleeding within 90 days, respectively. CHANCE-2 is registered with ClinicalTrials.gov, NCT04078737.

Findings

The cutoff to define elevated RC was 0.91 mmol/L. Ticagrelor-aspirin versus clopidogrel-aspirin was associated with a reduced risk of recurrent stroke in patients with non-elevated RC levels (122 [5.3%] versus 179 [7.8%]; hazard ratio [HR], 0.68; 95% confidence interval [CI], 0.54-0.85), but this benefit was absent in those with elevated RC levels (58 [8.4%] versus 48 [7.3%]; HR, 1.10; 95% CI, 0.73-1.65; P-interaction = 0.03). When analyzed as a continuous variable, the benefit of ticagrelor-aspirin on recurrent stroke decreased as RC levels increased. The rates of severe or moderate bleeding between treatment groups were similar across RC categories (0.3% versus 0.3%, P-interaction = 0.95).

Interpretation

Our post-hoc findings suggest that RC could be a potential biomarker to discriminate patients who received more benefits from ticagrelor-aspirin versus clopidogrel-aspirin therapy in CYP2C19 loss-of-function carriers with minor stroke or TIA. These findings need to be validated in an independent study.

Funding

The National Key Research and Development Program of China, Beijing Natural Science Foundation Haidian original innovation joint fund, Fund for Young Talents of Beijing Medical Management Center, the high-level public health talents, Training Fund for Open Projects at Clinical Institutes and Departments of Capital Medical University; and Salubris.

Mild hyperlipidemia in mice aggravates platelet responsiveness in thrombus formation and exploration of platelet proteome and lipidome

Hyperlipidemia is a well-established risk factor for cardiovascular diseases. Millions of people worldwide display mildly elevated levels of plasma lipids and cholesterol linked to diet and life-style. While the prothrombotic risk of severe hyperlipidemia has been established, the effects of moderate hyperlipidemia are less clear. Here, we studied platelet activation and arterial thrombus formation in Apoe^-/- and Ldlr^-/- mice fed a normal chow diet, resulting in mildly increased plasma cholesterol. In blood from both knockout mice, collagen-dependent thrombus and fibrin formation under flow were enhanced. These effects did not increase in severe hyperlipidemic blood from aged mice and upon feeding a high-fat diet (Apoe^-/- mice). Bone marrow from wild-type or Ldlr^-/- mice was transplanted into irradiated Ldlr^-/- recipients. Markedly, thrombus formation was enhanced in blood from chimeric mice, suggesting that the hyperlipidemic environment altered the wild-type platelets, rather than the genetic modification. The platelet proteome revealed high similarity between the three genotypes, without clear indication for a common protein-based gain-of-function. The platelet lipidome revealed an altered lipid profile in mildly hyperlipidemic mice. In conclusion, in Apoe^-/- and Ldlr^-/- mice, modest elevation in plasma and platelet cholesterol increased platelet responsiveness in thrombus formation and ensuing fibrin formation, resulting in a prothrombotic phenotype.

Large triglyceride-rich lipoproteins from fasting patients with type 2 diabetes activate platelets

AIMS

Type 2 diabetes (T2D) patients present with risk factors for atherothrombosis such as fasting hypertriglyceridaemia and platelet hyperactivity. Our study objective was to determine the effect of large triglyceride-rich lipoproteins (TGRL) from fasting T2D patients on platelet aggregation and, if any, to identify the signaling pathway involved.

METHODS

Large TGRL were isolated from the plasma of 25 T2D patients by ultracentrifugation (density < 1.000 g/mL). Platelets were isolated from healthy blood donors (HBD) and suspended in buffer, then preincubated in the presence or absence of TGRL and stimulated with either collagen or thrombin. Platelet aggregation and the arachidonic acid (AA) signaling pathway were studied.

RESULTS

Fasting T2D large TGRL were mostly of hepatic origin (apoB100/apoB48 ratio: 42 ± 7) and rich in triglycerides (TG/total apoB ratio: 4.2 ± 0.5), and able to potentiate agonist-stimulated platelet aggregation (collagen: +68%, P < 0.05; thrombin: +771%, P < 0.05). It should also be mentioned that TGRL from the plasma of HBD (n = 7) had no effect on platelet aggregation. In addition, T2D large TGRL increased thromboxane B₂ (TxB₂) concentration in platelets stimulated with either collagen (+34%, P < 0.05) or thrombin (+37%, P < 0.05) compared with platelets stimulated with either of these agonists without TGRL. Phosphorylation of p38 MAPK and cytosolic phospholipase A₂ (cPLA₂) was enhanced after incubation of platelets with T2D TGRL and thrombin (+87% and +32%, respectively, P < 0.05) compared with platelets incubated with thrombin only.

CONCLUSION

Large TGRL from fasting T2D patients may play a role in the development of atherothrombosis by increasing platelet aggregation and activating the platelet AA signaling pathway.

Exploring the potential of the platelet membrane proteome as a source of peripheral biomarkers for Alzheimer's disease

Introduction

Peripheral biomarkers to diagnose Alzheimer's disease (AD) have not been established. Given parallels between neuron and platelet biology, we hypothesized platelet membrane-associated protein changes may differentiate patients clinically defined with probable AD from noncognitive impaired controls.

Methods

Purified platelets, confirmed by flow cytometry were obtained from individuals before fractionation by ultracentrifugation. Following a comparison of individual membrane fractions by SDS-PAGE for general proteome uniformity, equal protein weight from the membrane fractions for five representative samples from AD and five samples from controls were pooled. AD and control protein pools were further divided into molecular weight regions by one-dimensional SDS-PAGE, prior to digestion in gel. Tryptic peptides were analyzed by reverse-phase liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Ionized peptide intensities were averaged for each identified protein in the two pools, thereby measuring relative protein abundance between the two membrane protein pools. Log₂-transformed ratio (AD/control) of protein abundances fit a normal distribution, thereby permitting determination of significantly changed protein abundances in the AD pool.

Results

We report a comparative analysis of the membrane-enriched platelet proteome between patients with mild to moderate AD and cognitively normal, healthy subjects. A total of 144 proteins were determined significantly altered in the platelet membrane proteome from patients with probable AD. In particular, secretory (alpha) granule proteins were dramatically reduced in AD. Of these, we confirmed significant reduction of thrombospondin-1 (THBS1) in the AD platelet membrane proteome by immunoblotting. There was a high protein-protein connectivity of proteins in other pathways implicated by proteomic changes to the proteins that define secretory granules.

Conclusions

Depletion of secretory granule proteins is consistent with a preponderance of post-activated platelets in circulation in AD. Significantly changed pathways implicate additional AD-related defects in platelet glycoprotein synthesis, lipid homeostasis, amyloidogenic proteins, and regulators of protease activity, many of which may be useful plasma membrane-expressed markers for AD. This study highlights the utility of LC-MS/MS to quantify human platelet membrane proteins and suggests that platelets may serve as a source of blood-based biomarkers in neurodegenerative disease.

Effect of remnant-like particle on shear-induced platelet activation and its inhibition by antiplatelet agents

Remnant-like particles (RLPs) have been reported to promote atherosclerosis and to have effects on platelet function. We studied the effects of RLP on shear-induced platelet activation and their inhibition by antiplatelet agents in vitro. RLP were separated using two monoclonal antibodies, anti apo B-100 and anti apo A-I. These RLP fractions were added to whole blood (WB) or platelet-rich plasma (PRP) in serial dilution of 1, 10 or 100 microg RLP triglyceride (TG) per ml of total sample volume. These samples were incubated, and then stimulated with a high shear stress of 108 dyn/cm(2). Shear-induced platelet aggregation (SIPA) was calculated from the percentage of single platelet loss. P-selectin expression on platelet surface and platelet-derived microparticle (PMP) generation were measured before and after stimulation with shear stress using flow cytometer. SIPA was significantly enhanced by RLP in WB but not in PRP. This enhancing effect was not dose-dependent and was greatest at 10 microg TG/ml. P-selectin expression induced by shear stress was only enhanced by RLP at a concentration of 100 microg TG/ml in both WB and PRP, while generation of PMP induced by shear stress was only enhanced by RLP at a concentration of 100 microg TG/ml in WB. Aspirin inhibited only the enhancement of SIPA by RLPs, while cilostazol inhibited the enhancement of not only SIPA but also p-selectin expression and PMP generation by RLPs.

Induction of Atherosclerosis by Human Chylomicron Remnants: A Hypothesis

Epidemiologic studies have provided support for the association between delayed remnant removal and premature atherosclerosis. Triglyceride-rich particles such as chylomicrons and chylomicron remnants that carry dietary derived fats, may play a role in the early stages of developing arteriosclerosis. Currently research focuses on these lipoprotein classes seeking distinguishing factors that causes some lipoproteins to be atherogenic while others are not. Such lipoproteins could be involved in atherogenesis directly or indirectly. Direct involvement occurs by interaction of triglyceride-rich particles with the arterial wall, possibly affecting the artery wall by oxidative stress, direct endothelial toxicity by constituents such as lysophosphatidylcholine or oxysterols, induction of prothrombotic changes, stimulation of endothelial expression of cell adhesion molecules and direct interaction with circulating blood cells. Indirect involvement refers to the influence of triglyceride-rich lipoproteins on other lipoproteins on the composition of low density lipoprotein (LDL) and high density lipoprotein (HDL) particles. We propose that in individuals with delayed removal of chylomicron remnants, the prolonged exposure of areas of endothelium that have been partially activated by turbulent flow, to specific components of the remnants, results in the endothelial cells becoming further activated and able to bind monocytes. During or shortly after the transcytosis to the intima and transformation of monocytes to macrophages, the macrophages become engorged with remnant derived lipids and form the nidus of a fatty streak.

EPA, but not DHA, decreases mean platelet volume in normal subjects

The first indication of platelet activation is an increase in mean platelet volume (MPV). n-3 FA are known to inhibit platelet function and to reduce the risk for coronary heart disease. The purpose of this study was to determine the effects of EPA and DHA on MPV. Healthy subjects received olive oil placebo for 4 wk and then were randomly assigned to receive 4 g of ethyl esters of either safflower oil (n = 11), EPA (n = 10), or DHA (n = 12) for 4 wk. At the end of placebo run-in and treatment periods, MPV (fL; mean +/- SEM) and platelet count (PLT-CT; 10(3)/microL blood) were measured in the basal state and after ex vivo stimulation with collagen (10 microg/mL), cold (4 degrees C), and heat (37 degrees C). Unlike DHA, EPA lowered MPV as compared with safflower oil (7.2 +/- 0.1 vs. 7.5 +/- 0.1 fL; P < 0.05) and raised PLT-CT (211 +/- 18 vs.192 +/- 18 10(3)/microL; P < 0.05) in the fasting state. Collagen and cold significantly increased MPV whereas heat lowered MPV regardless of treatment. All stimuli decreased PLT-CT. EPA significantly increased platelet EPA (0.2 +/- 0.1 vs. 3.3 +/- 0.4%) and docosapentaenoic acid (DPA; 2.2 +/- 0.3 vs. 2.9 +/- 0.3%) concentrations, but not DHA. DHA treatment significantly increased DHA (1.4 +/- 0.2 vs. 4.1 +/- 0.5%) and DPA (2.0 +/- 0.4 vs. 3.0 +/- 0.4%) concentrations, but not EPA. In conclusion, EPA, but not DHA, reduces platelet activation, an early step in platelet aggregation.

Postprandial lipemia is associated with platelet and monocyte activation and increased monocyte cytokine expression in normolipemic men

The activation of platelets and monocytes has been implicated in the development of cardiovascular diseases. We asked the question if postprandial lipemia following a fat- containing meal is associated with platelet and monocyte activation and increased platelet-monocyte interaction. Thirteen healthy, normal weight, normolipemic males, 20 to 49 years, consumed a 40% fat meal of whole foods. Blood samples were obtained at fasting and 3 1/2 and 6 hours after ingestion. Triglyceride levels increased to 48% over baseline at 3 1/2 hours postconsumption and returned to fasting levels by 6 hours. Multiparameter flow cytometry using monoclonal antibodies showed that the percentage of platelets expressing surface P-selectin and the activated conformation the GPIIb-IIa receptor was significantly higher at 3 1/2 hours compared to fasting. The percentage of platelet-monocyte aggregates increased by 36% at 3 1/2 hours and 43% at 6 hours postconsumption. The percentage of monocytes expressing intracellular tumor necrosis factor-alpha (TNF-alpha) increased seven and eightfold at 3 1/2 and 6 hours, respectively. The expression of interleukin-1beta (IL-1beta increased in a similar manner. These data suggest activation of platelets and monocytes after a moderate fat meal. Repetitive activation of platelets and monocytes could be an early event in the initiation and development of atherosclerosis.

Standardized ultrasound as a new method to induce platelet aggregation: evaluation, influence of lipoproteins and of glycoprotein IIb/IIIa antagonist tirofiban

Most of the published studies concerning platelet aggregation were performed with chemical stimulation procedures, however, mechanical stimulation might be a better simulation of physiological activation of platelets. In order to evaluate the influence of ultrasound on platelet aggregation in vitro, we developed an ultrasound device in a standardized set-up, and we evaluated the influence of lipoproteins and the glycoprotein IIb/IIIa inhibitor tirofiban on ultrasound induced platelet aggregation. A cylindrical shaped plastic test tube with 1 ml of platelet-rich plasma was placed in an ultrasound bath (35 kHz) for 5 s. The ultrasound energy transfer into the sample (Delta W=3.77 J) was calculated using the average temperature increase (averaged by 0.935 degrees C) of the sample. Platelet aggregation was quantified immediately after stimulation with ultrasound or adenosine diphosphate (ADP 2.1 and 4.2 microM) by the Myrenne Aggregometer PA2 at low (40 s(-1)) and afterwards at high (2500 s(-1)) shear. To evaluate the influence of lipoproteins, seven healthy male volunteers were investigated before and after a fat load (50 g fat per m(2) body surface), and 11 patients suffering from hypercholesterolemia and atherosclerotic disease before and after a single low-density lipoprotein (LDL) apheresis. Platelet aggregation after ultrasound stimulation was well correlated with platelet aggregation after ADP (r between 0.50 and 0.95). However, when exposed to high shear, the low shear-induced platelet aggregates were more stable after ultrasound stimulation compared with ADP stimulation either with or without tirofiban. After the fat load triglyceride concentration increased from 0.86+/-0.39 to 2.10+/-1.10 mmol l(-1) (P<0.05) resulting in a reduced formation of platelet aggregates after weak (ADP 2.1 microM) but not after strong (ADP 4.2 microM or ultrasound) stimuli. After a single LDL apheresis LDL cholesterol dropped from 3.99+/-0.90 to 1.06+/-0.55 mmol l(-1) (P<0.005). No changes in platelet aggregation were observed with the exception of a lower aggregation when exposed to high shear after stimulation with 2.1 microM ADP. In conclusion, we found the ultrasound stimulation of platelet-rich plasma easy to perform. The platelet aggregation after ultrasound stimulation correlated well with stimulation after ADP. While a reduction in LDL cholesterol concentration had only slight effects on platelet aggregation, an increase in triglyceride concentration resulted in a reduced formation of platelet aggregates after weak stimulation.

Adenosine 5'-diphosphate as a factor in platelet aggregation induced by human plasma remnant lipoproteins

The action of lipoprotein lipase on chylomicrons (CM) and very low density lipoproteins (VLDL) produces remnant lipoproteins (RLP) which are rich in triglycerides, cholesterol and apolipoprotein E (apo E). Apo E serves as a ligand for uptake of RLP by macrophages, platelets, endothelial cells and other cells expressing the LDL-receptor or the remnant receptor, thus having a major role in the clearance of plasma cholesterol and triglycerides, but at the same time, uptake of apo E-bearing RLP can profoundly alter the physiology of these cells and promote atherosclerosis. Like RLP, blood platelets also have roles in atherosclerosis and thrombosis, hence it is likely that RLP influence platelet activity as well. RLP derived from normal human plasma VLDL and CM were prepared using two monoclonal antibodies, anti-apo B-100 (JI-H) and anti-apo A-I (H-12) coupled to Sepharose 4B gel to form an immunoaffinity column. Lipoproteins containing apo B-100 including VLDL and LDL adsorb to (JI-H)-gel, while CM and HDL with apo A-I adsorb to (H-12)-gel. The particles in the unbound fraction (RLP) are rich in apo B-48, apo E and apo B-100 containing particles with multiple molecules of apo E. The RLP fraction with a total triglyceride of 14+/-3.2 mg/ml; cholesterol, 0.39+/-0.1 mg/ml and protein, 0.78+/-0.24 mg/ml (n=19) was added to aliquots of blood of man, rabbits, guinea pigs, mice, and rats at protein equivalents of 0.98 to 78 microg/ml blood and agitated gently at 37 degrees C for 40 sec. Platelet aggregation was measured as a fall in single platelet count. RLP induced aggregation of platelets in man (p<0.005) rabbit (p<0.0005), guinea pig (p<0.002) and mouse (p<0.0001), but no RLP induced platelet aggregation was observed in the rat blood. Scanning electron microscopy revealed that in the presence of RLP, platelets had adhered to and formed aggregates on red cells. The platelet response to RLP was inhibited by apyrase known to scavenge ADP, by 5 microM 2-chloroadenosine, a platelet ADP receptor antagonist and by 3.4 microM cilostazol, a phosphodiesterase type III inhibitor known to raise cyclic AMP level in platelets. It is thought that RLP cause leakage of ADP from red cells which then mediates platelet aggregation.

The in vitro effects of chylomicron remnant and very low density lipoprotein remnant on platelet aggregation in blood obtained from healthy persons

We investigated the in vitro influence of chylomicron (CM) remnant and very low density lipoprotein (VLDL) remnant on platelet aggregation in healthy persons. The separation of CM and VLDL remnants from serum was performed using an immunoaffinity gel mixture containing anti apo B-100 and anti apo A-1 antibodies coupled to Sepharose 4B. The preincubation with CM and VLDL remnants significantly enhanced the platelet aggregation in whole blood and in platelet rich plasma (PRP) induced by collagen. This effect was observed in whole blood with the addition of VLDL remnant at the concentration of 5 mu g/ml, and in PRP with the addition of CM remnant at the concentration of 1 and 5 mu g/ml, and with the addition of VLDL remnant at the concentration of 5 and 10 mu g/ml. These results may indicate that increase in remnant lipoproteins may be a part of the reasons for atherosclerotic and thrombotic complications.