Thrombus formation on apex of arterial stenoses: the need for a fluid high shear stenosis diagnostic device

Platelet Adhesion Mediated by von Willebrand Factor at High Shear Rates Is Associated with Premature Coronary Artery Disease

This study investigated von Willebrand factor (VWF)-mediated platelet adhesion at high shear rates in patients with premature coronary artery disease (CAD). The study included 84 patients with stable premature CAD and 64 patients without CAD. Whole blood samples were perfused through a microfluidic cell over a collagen-coated surface at a shear rate of 1300 s^-1. Measurements were performed before and after the inhibition of VWF-specific platelet GPIb receptors with an anti-GPIb monoclonal antibody (mAb). Platelet adhesion decreased by 77.0% (55.9; 84.7) in patients with premature CAD and by 29.6% (0.0; 59.7) in control patients after the inhibition of VWF-platelet interaction with anti-GPIb mAb (p < 0.001). After adjusting for traditional risk factors, the odds ratio for premature CAD per 1% decrease in GPIb-mediated platelet adhesion was 1.03 (95% CI, 1.02-1.05; p < 0.001). The optimal cut-off level value of GPIb-mediated platelet adhesion was 62.8%, with 70.2% sensitivity and 81.2% specificity for CAD. The plasma levels of VWF or antiplatelet therapy did not affect the GPIb-mediated component of platelet adhesion. Thus, the GPIb-mediated component of platelet adhesion was more pronounced in patients with premature CAD. This may indicate the possible role of excessive VWF-platelet interactions in the development of premature CAD.

Determinants of Endogenous Fibrinolysis in Whole Blood Under High Shear in Patients With Myocardial Infarction

Hypofibrinolysis is a recently-recognized risk factor for recurrent cardiovascular events in patients with ST-segment elevation myocardial infarction (STEMI), but the mechanistic determinants of this are not well understood. In patients with STEMI, we show that the effectiveness of endogenous fibrinolysis in whole blood is determined in part by fibrinogen level, high sensitivity C-reactive protein, and shear-induced platelet reactivity, the latter directly related to the speed of thrombin generation. Our findings strengthen the evidence for the role of cellular components and bidirectional crosstalk between coagulatory and inflammatory pathways as determinants of hypofibrinolysis.

Are all wines made from various grape varieties beneficial in the prevention of myocardial infarction and stroke?

Aim:

Epidemiologic studies support the assumption (French paradox hypothesis) that drinking red wine is beneficial in the prevention of cardiovascular diseases. Our recent works however cast doubt on such claim. Earlier we have shown that the antithrombotic activity of various fruits and vegetables mainly depends on their varieties. For this reason, several varieties of red and white grapes were tested for antithrombotic effect in animal experiments.

Results:

Antithrombotic effect of 45 red and white grape varieties were assessed in the present study. Out of the 45, one red grape variety showed antithrombotic effect, while the majority of red and white grape varieties enhanced thrombosis.

Conclusion:

Most red and white grape varieties enhanced thrombotic activity of blood.

Red wine is widely believed to prevent heart attack and stroke as claimed by a French Paradox hypothesis. Antithrombotic effect of 45 grape varieties was measured in the present study. Only very few red and white varieties inhibited the experimentally induced thrombosis while the majority of the tested varieties enhanced thrombotic activity of blood. Thus, our findings challenge the prevailing claims of the French Paradox.

Shear-Dependent Platelet Aggregation: Mechanisms and Therapeutic Opportunities

Cardiovascular diseases (CVD) are the number one cause of morbidity and death worldwide. As estimated by the WHO, the global death rate from CVD is 31% wherein, a staggering 85% results from stroke and myocardial infarction. Platelets, one of the key components of thrombi, have been well-investigated over decades for their pivotal role in thrombus development in healthy as well as diseased blood vessels. In hemostasis, when a vascular injury occurs, circulating platelets are arrested at the site of damage, where they are activated and aggregate to form hemostatic thrombi, thus preventing further bleeding. However, in thrombosis, pathological activation of platelets occurs, leading to uncontrolled growth of a thrombus, which in turn can occlude the blood vessel or embolize, causing downstream ischemic events. The molecular processes causing pathological thrombus development are in large similar to the processes controlling physiological thrombus formation. The biggest challenge of anti-thrombotics and anti-platelet therapeutics has been to decouple the pathological platelet response from the physiological one. Currently, marketed anti-platelet drugs are associated with major bleeding complications for this exact reason; they are not effective in targeting pathological thrombi without interfering with normal hemostasis. Recent studies have emphasized the importance of shear forces generated from blood flow, that primarily drive platelet activation and aggregation in thrombosis. Local shear stresses in obstructed blood vessels can be higher by up to two orders of magnitude as compared to healthy vessels. Leveraging abnormal shear forces in the thrombus microenvironment may allow to differentiate between thrombosis and hemostasis and develop shear-selective anti-platelet therapies. In this review, we discuss the influence of shear forces on thrombosis and the underlying mechanisms of shear-induced platelet activation. Later, we summarize the therapeutic approaches to target shear-sensitive platelet activation and pathological thrombus growth, with a particular focus on the shear-sensitive protein von Willebrand Factor (VWF). Inhibition of shear-specific platelet aggregation and targeted drug delivery may prove to be much safer and efficacious approaches over current state-of-the-art antithrombotic drugs in the treatment of cardiovascular diseases.

Prevention of thrombotic disorders by antithrombotic diet and exercise: evidence by using global thrombosis tests

Prevention of thrombotic disorders has priority over treatment. There are only two pathologically relevant tests which are suitable for measuring the overall thrombotic status both in experimental conditions and in humans. The Global Thrombosis Test (GTT) and the Global Parallel-Plate Thrombosis Test can detect the pathologically relevant global thrombotic status. These tests have been successfully used for monitoring the effect of antithrombotic drugs and for developing novel antithrombotic agents. By using GTT, varieties of fruits, vegetables, and regular physical exercise have been tested for the effect on global thrombotic status. This review discusses the published evidence for the benefit of diet of selected fruit and vegetable varieties and doing regular physical exercise on improving thrombotic status. Future clinical trials monitored by GTT or Global Parallel-Plate Thrombosis Test could decide on the effectiveness of an experimentally proven antithrombotic diet with regular physical exercise in the prevention of thrombotic diseases.

The impact of blood shear rate on arterial thrombus formation

The shear rate and corresponding shear stress have impacts on arterial thrombus formation. In particular, the effects of increasing concentration of platelets at the vessel wall and activation of platelets at this site increase the growth and stability of the thrombi which may result in a fatal narrowing of the arterial lumen. The efficacy of many antithrombotic agents is shear dependent as well. It is apparent that there is a need for a point-of-care device to rapidly monitor the risk for arterial thrombosis and to optimize antithrombotic therapy in vitro. The present review focuses on the essential role of shear rate on arterial thrombus formation in native human blood drawn directly from an antecubital vein.

A Combined Optical Coherence Tomography and Intravascular Ultrasound Study on Plaque Rupture, Plaque Erosion, and Calcified Nodule in Patients With ST-Segment Elevation Myocardial Infarction: Incidence, Morphologic Characteristics, and Outcomes After Percutaneous Coronary Intervention

OBJECTIVES

This study sought to evaluate the incidence of plaque rupture (PR), plaque erosion (PE), and calcified nodule (CN) using optical coherence tomography (OCT) in patients with ST-segment elevation myocardial infarction (STEMI); to compare detailed morphologic plaque characteristics of PR, PE, and CN with optical coherence tomography and intravascular ultrasound; and to compare the post-procedure outcomes among PR, PE, and CN.

BACKGROUND

The incidence and detailed morphologic characteristics of PR, PE, and CN in STEMI patients and their outcome after percutaneous coronary intervention (PCI) are unknown.

METHODS

A total of 112 STEMI patients who underwent PCI within 24 h [corrected] from symptom onset were included. Both optical coherence tomography and intravascular ultrasound were performed following aspiration thrombectomy.

RESULTS

The incidence of PR, PE, and CN was 64.3%, 26.8%, and 8.0%, respectively. PE and CN, compared with PR, had more fibrous plaque (p < 0.001 and p < 0.001) and less thin-cap fibroatheroma (p < 0.001 and p < 0.001) as well as smaller plaque burden (p = 0.003 and p = 0.001) and remodeling index (p = 0.003 and p < 0.001). PE had greater plaque eccentricity index than PR and CN (p < 0.001 and p < 0.001). CN had greater calcified arc and shallower calcium than PR (p < 0.001 and p < 0.001) or PE (p < 0.001 and p < 0.001). More than one-half of CN had negative remodeling. PE had a lower incidence of no-reflow phenomenon after PCI than PR (p = 0.011).

CONCLUSIONS

PE was the underlying mechanism in one-fourth of STEMI. PE was characterized by eccentric fibrous plaque. CN was characterized by superficial large calcium and negative remodeling. PE was associated with less microvascular damage after PCI.

Nanodiagnostics, nanopharmacology and nanotoxicology of platelet–vessel wall interactions

In physiological conditions, the interactions between blood platelets and endothelial cells play a major role in vascular reactivity and hemostasis. By contrast, increased platelet activation contributes to the pathogenesis of vascular pathology such as atherosclerosis, thrombosis, diabetes mellitus, hypertension and carcinogenesis. Nanomedicine, including nanodiagnostics and nanotherapeutics is poised to be used in the management of vascular diseases. However, the inherent risk and potential toxicity resultant from the use of nanosized (<100 nm) materials need to be carefully considered. This review, basing on a systematic search of literature provides state-of-the-art and focuses on new discoveries, as well as the potential benefits and threats in the field of nanodiagnostics, nanopharmacology and nanotoxicology of platelet–vessel wall interactions.

Computational Modeling of Thrombotic Microparticle Deposition in Nonparallel Flow Regimes

Thrombotic microparticles (MPs) released from cells and platelets in response to various stimuli are present in elevated numbers in various disease states that increase the risk for thrombotic events. In order to understand how particles of this size may localize in nonparallel flow regimes and increase thrombotic risk, a computational analysis of flow and MP deposition was performed for 3 deg of stenosis at moderate Reynolds number (20 < Re < 80) and for recirculation zones at low Reynolds (∼1) number. The results indicate that MP deposition results primarily from impaction and not by diffusive flux.

Microvascular platforms for the study of platelet-vessel wall interactions

Platelets interact with the endothelium to regulate vascular integrity and barrier function, mediate inflammation and immune response, and prevent and arrest hemorrhage. In this review, we describe existing tools to study the flow-dependent interactions of platelets with the vessel wall. We also discuss our work on building engineered microvessels to study the roles of platelets on endothelial barrier function, endothelial sprouting, and thrombus formation on both quiescent and stimulated endothelium. In particular, we will show the advantage of using a cell-remodelable system in the studies of platelet-vessel wall interactions.

The effects of arterial flow on platelet activation, thrombus growth, and stabilization

Injury of an arterial vessel wall acutely triggers a multifaceted process of thrombus formation, which is dictated by the high-shear flow conditions in the artery. In this overview, we describe how the classical concept of arterial thrombus formation and vascular occlusion, driven by platelet activation and fibrin formation, can be extended and fine-tuned. This has become possible because of recent insight into the mechanisms of: (i) platelet-vessel wall and platelet-platelet communication, (ii) autocrine platelet activation, and (iii) platelet-coagulation interactions, in relation to blood flow dynamics. We list over 40 studies with genetically modified mice showing a role of platelet and plasma proteins in the control of thrombus stability after vascular injury. These include multiple platelet adhesive receptors and other junctional molecules, components of the ADP receptor signalling cascade to integrin activation, proteins controlling platelet shape, and autocrine activation processes, as well as multiple plasma proteins binding to platelets and proteins of the intrinsic coagulation cascade. Regulatory roles herein of the endothelium and other blood cells are recapitulated as well. Patient studies support the contribution of platelet- and coagulation activation in the regulation of thrombus stability. Analysis of the factors determining flow-dependent thrombus stabilization and embolus formation in mice will help to understand the regulation of this process in human arterial disease.

Validation of the human tissue factor/FVIIa complex as an antithrombotic target and the discovery of a synthetic peptide

This review focuses on the validation of the principal initiator of human coagulation, the tissue factor (TF)/coagulation factor (F)VIIa complex, as an antithrombotic target, as well as on the discovery of a cyclic pentapeptide (PN7051), which dose-dependently inhibits TF/FVIIa-induced coagulation and thrombus formation. Target validation and studies of antithrombotic efficacy were performed with a human thrombosis model employing non-anticoagulated blood from severe homozygous FVII-deficient patients and healthy individuals at blood-flow conditions mimicking those in healthy and diseased vessels. Additional validation included an anti-TF monoclonal antibody, recombinant TF pathway inhibitor, recombinant inactivated-active site FVIIa and all-trans retinoic acid. Structural and biological characterization of PN7051 and other peptides from the same FVII domain indicate that PN7051 interferes with an essential interaction between the epidermal growth factor domain-2-like and the catalytic domains of FVIIa. A peptidomimetics approach is suggested to further improve the antithrombotic potency of PN7051.