Advances in the monitoring of anti-P2Y12therapy

Monitoring of Antiplatelet Therapy

In the late 1990s, the antithrombotic antiplatelet agent, clopidogrel, a P2Y12 inhibitor, was introduced. Around the same time, there was an increase in a number of new methods to measure platelet function (e.g., PFA-100 in 1995), and this has continued. It became evident that not all patients responded to clopidogrel in the same way and that some patients had a relative "resistance" to therapy, termed "high on-treatment platelet reactivity." This then led to some publications to advocate platelet function testing being used for patients on antiplatelet therapy. Platelet function testing was also suggested for use in patients awaiting cardiac surgery after stopping their antiplatelet therapy as a way of balancing thrombotic risk pre-surgery and bleeding risk perioperatively. This chapter will discuss some of the commonly used platelet function tests used in these settings, particularly those that are sometimes referred to as point-of-care tests or that require minimal laboratory sample manipulation. The latest guidance and recommendations for platelet function testing will be discussed following several clinical trials looking at the usefulness of platelet function testing in these clinical settings.

[Integral tests of the hemostasis system in assessing the efficiency of acetylsalicylic acid in patients with ischemic heart disease]

Despite the fact that acetylsalicylic acid (ASA) is the "gold" standard for the prevention of cardiovascular complications in patients with coronary heart disease (CAD), a number of patients still have risks of atherothrombosis. In the present study, the antithrombotic effect of ASA in patients with CAD was assessed in platelet-rich plasma (PRP) using integral tests of the hemostasis study: the T-TAS system (Total Thrombus-formation Analysis System) and the thrombin generation test (TGT). The study involved 34 patients with stable CAD (11 women, 23 men) and people (15 women, 18 men) in the control group. As a result of assessing the activity of thrombus formation using the T-TAS system, a significant decrease in the area under the curve (AUC10) was found in the group with CAD patients compared with the control (135.6 [88.0-222.3] and 260.5 [217.3-301.9], respectively, p.

Clinical validation of AggreGuide A-100 ADP, a novel assay for assessing the antiplatelet effect of oral P2Y12 antagonists

In this prospective, 3-arm, repeated-measure multicenter investigation in 280 patients with cardiovascular risk factors, platelet aggregation was measured with the novel AggreGuide A-100 ADP (A-100 ADP) and VerifyNow (VN)-PRU assays at baseline, and after United States Food and Drug Administration approved loading and 7 days maintenance doses of clopidogrel (n = 94), prasugrel (n = 43) or ticagrelor, (n = 143). Based on the predetermined cutoff values of < 4.7 platelet activity index with A-100 ADP assay to indicate antiplatelet response, more than 91% of patients met the criteria following loading and maintenance doses of prasugrel and more than 84% patients met the criteria following loading and maintenance doses of ticagrelor whereas only 32% and 51% of patients met the criteria following loading and maintenance doses of clopidogrel, respectively. The total percent agreement between the A-100 ADP and VN-PRU assays was 89%. The A-100 ADP assay, which includes whole blood in motion, performs comparably to the VN-PRU assay in a study of patients with cardiovascular risk factors treated with P2Y₁₂ inhibitors possessing known differences in antiplatelet potencies. Trial registration ClinicalTrials.gov Identifier: NCT3111420.

Efficacy of Monitoring Platelet Function by an Automated PL-12 Analyzer During the Treatment of Acute Cerebral Infarction With Antiplatelet Medicine

Numerous methods can be used to investigate the function of platelets; however, technical issues limit tends to limit the applicability of such methods in the clinic.

Comparison of four methods to assess high-on platelet reactivity under P2Y12 receptor inhibitor

P2Y12 receptor inhibitors are antiplatelet agents commonly prescribed in the treatment of coronary artery disease. Their efficacy can be limited by high on-treatment platelet reactivity (HPR), which can be evaluated by different biological assays. Most commonly, HPR is evaluated by flow cytometric vasodilator-stimulated phosphoprotein-phosphorylation (VASP-P) assay, which can be time consuming. To evaluate the potential interest of novel technologies, we compared four different assays. Ninety patients receiving P2Y12 inhibitors were included. Four technologies were evaluated: the current standard test measuring VASP-P by flow cytometry, the historical reference test based on light transmittance aggregation (LTA), and two relatively novel techniques: whole blood multiple electrode aggregometry (MEA) and platelet function analyzer (PFA), which are less time consuming. The three latter tests were compared with the VASP-P assay as a reference using receiver operating characteristics (ROC) analysis: LTA has an excellent comparability with the VASP test (ROC AUC > 0.9); the other two tests (multiplate and PFA) have only satisfactory comparability (ROC AUC around 0.7) and therefore may not replace the VASP "gold standard" test, if importance is attached to a quantitative assessment of the substitution parameter of VASP. Nevertheless, if a binary approach of the anti-aggregation result is sought, then one can conclude that the three tests are equivalent since Cohen's kappa coefficients are very close for the three tests (k = 0.548 for LTA; k = 0.554 for MEA; k = 0.570 for PFA/P2Y), and a similar proportion of patients are misclassified (15% for LTA, 14% for MEA, and 13.6% for PFA). Discriminant factor analysis using all the parameters provided by each test did not improve the diagnostic performance of MEA or PFA. In conclusion, only LTA shows a good comparability to the VASP assay using ROC curve analysis, probably because misclassified patients have results close to the cutoff values. All three tests have moderate agreement regarding the classification of patients as responders to P2Y12 inhibition.

Atherothrombosis and Thromboembolism: Position Paper from the Second Maastricht Consensus Conference on Thrombosis

Atherothrombosis is a leading cause of cardiovascular mortality and long-term morbidity. Platelets and coagulation proteases, interacting with circulating cells and in different vascular beds, modify several complex pathologies including atherosclerosis. In the second Maastricht Consensus Conference on Thrombosis, this theme was addressed by diverse scientists from bench to bedside. All presentations were discussed with audience members and the results of these discussions were incorporated in the final document that presents a state-of-the-art reflection of expert opinions and consensus recommendations regarding the following five topics: 1. Risk factors, biomarkers and plaque instability: In atherothrombosis research, more focus on the contribution of specific risk factors like ectopic fat needs to be considered; definitions of atherothrombosis are important distinguishing different phases of disease, including plaque (in)stability; proteomic and metabolomics data are to be added to genetic information. 2. Circulating cells including platelets and atherothrombosis: Mechanisms of leukocyte and macrophage plasticity, migration, and transformation in murine atherosclerosis need to be considered; disease mechanism-based biomarkers need to be identified; experimental systems are needed that incorporate whole-blood flow to understand how red blood cells influence thrombus formation and stability; knowledge on platelet heterogeneity and priming conditions needs to be translated toward the in vivo situation. 3. Coagulation proteases, fibrin(ogen) and thrombus formation: The role of factor (F) XI in thrombosis including the lower margins of this factor related to safe and effective antithrombotic therapy needs to be established; FXI is a key regulator in linking platelets, thrombin generation, and inflammatory mechanisms in a renin-angiotensin dependent manner; however, the impact on thrombin-dependent PAR signaling needs further study; the fundamental mechanisms in FXIII biology and biochemistry and its impact on thrombus biophysical characteristics need to be explored; the interactions of red cells and fibrin formation and its consequences for thrombus formation and lysis need to be addressed. Platelet-fibrin interactions are pivotal determinants of clot formation and stability with potential therapeutic consequences. 4. Preventive and acute treatment of atherothrombosis and arterial embolism; novel ways and tailoring? The role of protease-activated receptor (PAR)-4 vis à vis PAR-1 as target for antithrombotic therapy merits study; ongoing trials on platelet function test-based antiplatelet therapy adjustment support development of practically feasible tests; risk scores for patients with atrial fibrillation need refinement, taking new biomarkers including coagulation into account; risk scores that consider organ system differences in bleeding may have added value; all forms of oral anticoagulant treatment require better organization, including education and emergency access; laboratory testing still needs rapidly available sensitive tests with short turnaround time. 5. Pleiotropy of coagulation proteases, thrombus resolution and ischaemia-reperfusion: Biobanks specifically for thrombus storage and analysis are needed; further studies on novel modified activated protein C-based agents are required including its cytoprotective properties; new avenues for optimizing treatment of patients with ischaemic stroke are needed, also including novel agents that modify fibrinolytic activity (aimed at plasminogen activator inhibitor-1 and thrombin activatable fibrinolysis inhibitor.

Assessment of bleeding risk in patients with coronary artery disease on dual antiplatelet therapy

Patients with coronary artery disease are usually treated with dual antiplatelet therapy (DAPT) after percutaneous coronary intervention. Patients on DAPT are at risk of both ischaemic and bleeding events. Although side-lined for a long time, real-life studies have shown that both the incidence and the associated morbidity and mortality of outof-hospital bleeding are high. This indicates that prevention of (postinterventional) bleeding is as important as prevention of ischaemia. For this purpose it is crucial to reliably identify patients with a high bleeding risk. In order to postulate an algorithm, which could help identifying these patients, we performed a systematic review to determine the value of previously proposed prognostic modalities for bleeding. We searched and appraised the following tools: platelet function tests, genetic tests, bleeding scores and questionnaires and haemostatic tests. Most studies indicated that low on-treatment platelet reactivity (LTPR), as measured by several platelet function tests, and the carriage of CYP2C19*17 allele were independent risk factors for bleeding. A bleeding score also proved to be helpful in identifying patients at risk. No studies on haemostatic tests were retrieved. Several patient characteristics were also identified as independent predictors of bleeding, such as older age, female sex and renal failure. Combining these risk factors we propose an algorithm that would hypothetically facilitate identification of those patients at highest risk, warranting prevention measures for bleeding. This could be a starting point for further research concerning the topic.

Application of a strain rate gradient microfluidic device to von Willebrand's disease screening

Von Willebrand's disease (VWD) is the most common inherited bleeding disorder caused by either quantitative or qualitative defects of von Willebrand factor (VWF). Current tests for VWD require relatively large blood volumes, have low throughput, are time-consuming, and do not incorporate the physiologically relevant effects of haemodynamic forces. We developed a microfluidic device incorporating micro-contractions that harnesses well-defined haemodynamic strain gradients to initiate platelet aggregation in citrated whole blood. The microchannel architecture has been specifically designed to allow for continuous real-time imaging of platelet aggregation dynamics. Subjects aged ≥18 years with previously diagnosed VWD or who presented for evaluation of a bleeding disorder, where the possible diagnosis included VWD, were tested. Samples were obtained for device characterization as well as for pathology-based testing. Platelet aggregation in the microfluidic device is independent of platelet amplification loops but dependent on low-level platelet activation, GPIb/IX/V and integrin α_IIbβ₃ engagement. Microfluidic output directly correlates with VWF antigen levels and is able to sensitively detect aggregation defects associated with VWD subtypes. Testing demonstrated a strong correlation with standard clinical laboratory-based tests. Head-to-head comparison with PFA100® demonstrated equivalent, if not improved, sensitivity for screening aggregation defects associated with VWD. This strain rate gradient microfluidic prototype has the potential to be a clinically useful, rapid and high throughput-screening tool for VWD as well as other strain-dependent platelet disorders. In addition, the microfluidic device represents a novel approach to examine the effects of high magnitude/short duration (ms) strain rate gradients on platelet function.

Novel strategies for assessing platelet reactivity

There are many approaches to assessing platelet reactivity and many uses for such measurements. Initially, measurements were based on the ability of platelets separated from other blood cells to aggregate together following activation with an appropriate 'aggregating agent'. Later, measurements of platelet aggregation in blood itself were performed, and this led to a point-of-care approach to platelet function testing. Measurement of secretory activity through the appearance of the activation marker P-selectin on platelets now provides an alternative approach, which enables remote testing. Measurement of vasodilator-stimulated phosphoprotein phosphorylation is also moving toward application in situations remote from the testing laboratory. Here we provide an overview of the various approaches that are now available, assess their advantages and disadvantages, and describe some of the clinical situations in which they are being used.

Platelet function testing as a biomarker for efficacy of antiplatelet drugs

Despite the overwhelming evidence in support of the efficacy of dual antiplatelet therapy with aspirin and clopidogrel, it is also obvious that not all patients benefit from these drugs to the same extent. This interindividual variability in platelet responses may underlie clinical differences in drug efficacy, with potential for optimization of antiplatelet therapy to prevent ischemic events without excessively increasing bleeding risk. This review presents the current evidence regarding platelet function testing for monitoring of antiplatelet therapy, with emphasis on the prognostic value of platelet function testing to predict ischemic and bleeding events. The potential of platelet function testing to provide personalized antiplatelet therapy is also discussed, with an outlook toward the future of platelet function testing in high-risk individuals.

Impact of platelet phenotype on myocardial infarction

In acute myocardial infarction patients the injured vascular wall triggers thrombus formation in the damage site. Fibrin fibers and blood cellular elements are the major components of thrombus formed in acute occlusion of coronary arteries. It has been established that the initial thrombus is primarily composed of activated platelets rapidly stabilized by fibrin fibers. This review highlights the role of platelet membrane phenotype in pathophysiology of myocardial infarction. Here, we regard platelet phenotype as quantitative and qualitative parameters of the plasma membrane outer surface, which are crucial for platelet participation in blood coagulation, development of local inflammation and tissue repair.

Comparison of the antiplatelet effect of two clopidogrel bisulfate formulations: Plavix and generic-Egitromb

Due to expansion of the pharmaceutical market it seems necessary to prove the efficacy of the generic drugs. The aim of this study is to compare the effects of two clopidogrel formulations: brand-name-Plavix and generic drug - Egitromb. This is a prospective, randomized study comparing two groups of patients treated with two clopidogrel: brand-name Plavix and generic drug- Egitromb. The 53 consecutive patients with stable coronary artery disease qualifying for coronary angiography and PCI were enrolled in this trial. They were randomized into two groups. In the group A (n = 28) patients received Egitromb 300 mg at admission followed by 8 days of 75 mg Egitromb daily. In the group B (n = 25) patients received Plavix 300 mg on the admission followed by 8 days of 75 mg Plavix maintenance therapy. Blood samples for multiple electrode aggregometry testing were drawn at baseline, 5 hours and 8 days after taking the loading dose. Median values of platelet aggregation inhibition did not differ between the Plavix and Egitromb groups when assessed at baseline: 239AU/min (IQR:329) vs. 209 (IQR:406; p = 0.894), 5 hours after loading: 183 AU/min (IQR:107) vs. 165 (IQR:171; p = 0.831) or at day 8: 174 AU/min (IQR:133) vs. 211 (IQR:133; p = 0.332. The study showed no difference in the therapeutic effect of two clopidogrel formulations (Egitromb and Plavix).

Reversal strategy in antagonizing the P2Y12 -inhibitor ticagrelor

BACKGROUND

Patients on antiplatelet therapy have a higher incidence of bleeding complications. Reversal of antiplatelet drug effects is an important issue at trauma or emergency departments. For old and conventional anticoagulants, reversal strategies are established. While the effects of ticagrelor are reversible, developing a method to restore platelet function in patients is of importance due to its longer half-life (approximately 8 h), compared with other P2Y12 -inhibitors.

MATERIALS AND METHODS

We report an ex vivo model to reverse the effects of the novel and highly effective P2Y12 -inhibitor ticagrelor in 20 healthy volunteers. To normalize platelet reactivity, we added increasing amounts of autologous platelet-rich plasma (PRP) to whole blood which was obtained 3 h after the intake of 180 mg of ticagrelor. Platelet aggregation was assessed by whole blood multiple electrode aggregometry (MEA), which is based on impedance aggregometry.

RESULTS

The basal ADP-induced platelet aggregation averaged 71 ± 16 U (Units). Ticagrelor decreased ADP-induced platelet aggregation to 16 ± 8 U. A clear dose-response was obtained after spiking whole blood with increasing amounts of PRP. It is estimated that ≥2 units of apheresis platelet concentrates will be necessary to completely restore baseline platelet aggregation in the majority of patients after ticagrelor.

CONCLUSIONS

Platelets dose dependently improve ex vivo platelet aggregation of subjects after a loading dose of 180 mg of ticagrelor, making transfusion of platelet concentrates potentially useful in bleeding patients and those who need to undergo emergency surgery.