Shear stress-dependent platelet function after LDL cholesterol apheresis

Antithrombotic therapy and bleeding risk in the era of aggressive lipid-lowering: current evidence, clinical implications, and future perspectives

ABSTRACT

The clinical efficacy of proprotein convertase subtilisin/kexin type 9 inhibitors (PCSK9i) in reducing major cardiovascular adverse events related to atherosclerotic cardiovascular disease (ASCVD) has been well established in recent large randomized outcome trials. Although the cardiovascular and all-cause mortality benefit of PCSK9i remains inconclusive, current cholesterol management guidelines have been modified toward more aggressive goals for lowering low-density lipoprotein cholesterol (LDL-C). Consequently, the emerging concept of "the lower the better" has become the paradigm of ASCVD prevention. However, there is evidence from observational studies of a U-shaped association between baseline LDL-C levels and all-cause mortality in population-based cohorts. Among East Asian populations, low LDL-C was associated with an increased risk for hemorrhagic stroke in patients not on antithrombotic therapy. Accumulating evidence showed that low LDL-C was associated with an enhanced bleeding risk in patients on dual antiplatelet therapy following percutaneous coronary intervention. Additionally, low LDL-C was associated with a higher risk for incident atrial fibrillation and thereby, a possible increase in the risk for intracranial hemorrhage after initiation of anticoagulation therapy. The mechanism of low-LDL-C-related bleeding risk has not been fully elucidated. This review summarizes recent evidence of low-LDL-C-related bleeding risk in patients on antithrombotic therapy and discusses potential measures for reducing this risk, underscoring the importance of carefully weighing the pros and cons of aggressive LDL-C lowering in patients on antithrombotic therapy.

LDL cholesterol levels and in-hospital bleeding in patients on high-intensity antithrombotic therapy: findings from the CCC-ACS project

AIMS 

Emerging evidence has linked cholesterol metabolism with platelet responsiveness. We sought to examine the dose-response relationship between low-density lipoprotein cholesterol (LDL-C) and major in-hospital bleeds in acute coronary syndrome (ACS) patients.

METHODS AND RESULTS 

Among 42 378 ACS patients treated with percutaneous coronary intervention (PCI) enrolled in 240 hospitals in the Improving Care for Cardiovascular Disease in China-ACS project from 2014 to 2019, a total of 615 major bleeds, 218 ischaemic events, and 337 deaths were recorded. After controlling for baseline variables, a non-linear relationship was observed for major bleeds, with the higher risk at lower LDL-C levels. No dose-response relationship was identified for ischaemic events and mortality. A threshold value of LDL-C <70 mg/dL was associated with an increased risk for major bleeds (adjusted odds ratio: 1.49; 95% confidence interval: 1.21-1.84) in multivariable-adjusted logistic regression models and in propensity score-matched cohorts. The results were consistent in multiple sensitivity analyses. Among ticagrelor-treated patients, the LDL-C threshold for increased bleeding risk was observed at <88 mg/dL, whereas for clopidogrel-treated patients, the threshold was <54 mg/dL. Across a full spectrum of LDL-C levels, the treatment effect size associated with ticagrelor vs. clopidogrel on major bleeds favoured clopidogrel at lower LDL-C levels, but no difference at higher LDL-C levels.

CONCLUSIONS 

In a nationwide ACS registry, a non-linear association was identified between LDL-C levels and major in-hospital bleeds following PCI, with the higher risk at lower levels. As the potential for confounding may exist, further studies are warranted.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02306616.

Platelet-Activation Mechanisms and Vascular Remodeling

This overview article for the Comprehensive Physiology collection is focused on detailing platelets, how platelets respond to various stimuli, how platelets interact with their external biochemical environment, and the role of platelets in physiological and pathological processes. Specifically, we will discuss the four major functions of platelets: activation, adhesion, aggregation, and inflammation. We will extend this discussion to include various mechanisms that can induce these functional changes and a discussion of some of the salient receptors that are responsible for platelets interacting with their external environment. We will finish with a discussion of how platelets interact with their vascular environment, with a special focus on interactions with the extracellular matrix and endothelial cells, and finally how platelets can aid and possibly initiate the progression of various vascular diseases. Throughout this overview, we will highlight both the historical investigations into the role of platelets in health and disease as well as some of the more current work. Overall, the authors aim for the readers to gain an appreciation for the complexity of platelet functions and the multifaceted role of platelets in the vascular system. © 2017 American Physiological Society. Compr Physiol 8:1117-1156, 2018.

Lipoprotein Apheresis

Patients with familial hypercholesterolemia (FH) have early development of atherosclerosis and cardiovascular disease (CVD). Lipid level-lowering medications are not always successful in reducing increased low-density lipoprotein C (LDL-C) levels. Lipoprotein apheresis (LA) therapy has proven its clinical benefit in reducing CVD events for patients with FH with hypercholesterolemia. LA reduces LDL-C levels by more than 60% in patients with FH and reduces CVD events. LA also reduces Lp(a) levels and CVD events. LA reduces inflammatory markers and blood viscosity.

DMSO inhibits human platelet activation through cyclooxygenase-1 inhibition. A novel agent for drug eluting stents?

BACKGROUND

DMSO is routinely infused together with hematopoietic cells in patients undergoing myeloablative therapy and was recently found to inhibit smooth muscle cells proliferation and arterial thrombus formation in the mouse by preventing tissue factor (TF), a key activator of the coagulation cascade. This study was designed to investigate whether DMSO prevents platelet activation and thus, whether it may represent an interesting agent to be used on drug eluting stents.

METHODS AND RESULTS

Human venous blood from healthy volunteers was collected in citrated tubes and platelet activation was studied by cone and platelet analyzer (CPA) and rapid-platelet-function-assay (RPFA). CPA analysis showed that DMSO-treated platelets exhibit a lower adherence in response to shear stress (-15.54+/-0.9427%, n=5, P<0.0001 versus control). Additionally, aggregometry studies revealed that DMSO-treated, arachidonate-stimulated platelets had an increased lag phase (18.0%+/-4.031, n=9, P=0.0004 versus control) as well as a decreased maximal aggregation (-6.388+/-2.212%, n=6, P=0.0162 versus control). Inhibitory action of DMSO could be rescued by exogenous thromboxane A2 and was mediated, at least in part, by COX-1 inhibition.

CONCLUSIONS

Clinically relevant concentrations of DMSO impair platelet activation by a thromboxane A2-dependent, COX-1-mediated effect. This finding may be crucial for the previously reported anti-thrombotic property displayed by DMSO. Our findings support a role for DMSO as a novel drug to prevent not only proliferation, but also thrombotic complications of drug eluting stents.

Modelling thrombosis using dissipative particle dynamics method

AIM

Arterial occlusion is a leading cause of cardiovascular disease. The main mechanism causing vessel occlusion is thrombus formation, which may be initiated by the activation of platelets. The focus of this study is on the mechanical aspects of platelet-mediated thrombosis which includes the motion, collision, adhesion and aggregation of activated platelets in the blood. A review of the existing continuum-based models is given. A mechanical model of platelet accumulation onto the vessel wall is developed using the dissipative particle dynamics (DPD) method in which the blood (i.e. colloidal-composed medium) is treated as a group of mesoscale particles interacting through conservative, dissipative, attractive and random forces.

METHODS

Colloidal fluid components (plasma and platelets) are discretized by mesoscopic (micrometre-size) particles that move according to Newton's law. The size of each mesoscopic particle is small enough to allow tracking of each constituent of the colloidal fluid, but significantly larger than the size of atoms such that, in contrast to the molecular dynamics approach, detailed atomic level analysis is not required.

RESULTS

To test this model, we simulated the deposition of platelets onto the wall of an expanded tube and compared our computed results with the experimental data of Karino et al. (Miscrovasc. Res. 17, 238-269, 1977). By matching our simulations to the experimental results, the platelet aggregation/adhesion binding force (characterized by an effective spring constant) was determined and found to be within a physiologically reasonable range.

CONCLUSION

Our results suggest that the DPD method offers a promising new approach to the modelling of platelet-mediated thrombosis. The DPD model includes interaction forces between platelets both when they are in the resting state (non-activated) and when they are activated, and therefore it can be extended to the analysis of kinetics of binding and other phenomena relevant to thrombosis.

Low HDL cholesterol, smoking and IL-13 R130Q polymorphism are associated with myocardial infarction in Greek Cypriot males. A pilot study

This study was carried out in Greek Cypriot males to identify risk factors that predispose to myocardial infarction (MI). Genetic and lipid risk factors were investigated for the first time in a Greek Cypriot male case-control study.Contrary to other studies, mean low density lipoprotein cholesterol did not differ between cases and controls. High density lipoprotein cholesterol on the other hand, although within normal range in cases and controls, was significantly higher in the control population. In agreement with many other studies, smoking was significantly more prevalent in cases compared with controls. In pooled cases and controls, smokers had a significantly lower HDL-C level compared with non-smokers. The frequency of the IL-13 R130Q homozygotes for the mutation (QQ), as well as the mutant allele were significantly higher in cases compared with controls. The IL-13 R130Q variant, or another locus, linked to it, may increase the risk of MI.

Dark Chocolate Improves Coronary Vasomotion and Reduces Platelet Reactivity

Background— Dark chocolate has potent antioxidant properties. Coronary atherosclerosis is promoted by impaired endothelial function and increased platelet activation. Traditional risk factors, high oxidative stress, and reduced antioxidant defenses play a crucial role in the pathogenesis of atherosclerosis, particularly in transplanted hearts. Thus, flavonoid-rich dark chocolate holds the potential to have a beneficial impact on graft atherosclerosis.

Methods and Results— We assessed the effect of flavonoid-rich dark chocolate compared with cocoa-free control chocolate on coronary vascular and platelet function in 22 heart transplant recipients in a double-blind, randomized study. Coronary vasomotion was assessed with quantitative coronary angiography and cold pressor testing before and 2 hours after ingestion of 40 g of dark (70% cocoa) chocolate or control chocolate, respectively. Two hours after ingestion of flavonoid-rich dark chocolate, coronary artery diameter was increased significantly (from 2.36±0.51 to 2.51±0.59 mm, P <0.01), whereas it remained unchanged after control chocolate. Endothelium-dependent coronary vasomotion improved significantly after dark chocolate (4.5±11.4% versus −4.3±11.7% in the placebo group, P =0.01). Platelet adhesion decreased from 4.9±1.1% to 3.8±0.8% ( P =0.04) in the dark chocolate group but remained unchanged in the control group.

Conclusions— Dark chocolate induces coronary vasodilation, improves coronary vascular function, and decreases platelet adhesion 2 hours after consumption. These immediate beneficial effects were paralleled by a significant reduction of serum oxidative stress and were positively correlated with changes in serum epicatechin concentration.