Standardization of light transmittance aggregometry for monitoring antiplatelet therapy: an adjustment for platelet count is not necessary

Convolutional neuronal network for identifying single-cell-platelet-platelet-aggregates in human whole blood using imaging flow cytometry

Imaging flow cytometry is an attractive method to investigate individual cells by optical properties. However, imaging flow cytometry applications with clinical relevance are scarce so far. Platelet aggregation naturally occurs during blood coagulation to form a clot. However, aberrant platelet aggregation is associated with cardiovascular disease under steady-state conditions in the blood. Several types of so-called antiplatelet drugs are frequently described to reduce the risk of stroke or cardiovascular diseases. However, an efficient monitoring method is missing to identify the presence and frequency of platelet-platelet aggregates in whole blood on a single cell level. In this work, we employed imaging flow cytometry to identify fluorescently labeled platelets in whole blood with a conditional gating strategy. Images were post-processed and aligned. A convolutional neural network was designed to identify platelet-platelet aggregates of two, three, and more than three platelets, and results were validated against various data set properties. In addition, the neural network excluded erythrocyte-platelet aggregates from the results. Based on the results, a parameter for detecting platelet-platelet aggregates, the weighted platelet aggregation, was developed. If employed on a broad scale with proband and patient samples, our method could aid in building a future diagnostic marker for cardiovascular disease and monitoring parameters to optimize drug prescriptions in such patient groups.

Discordance in tests used to detect inhibition of the P2Y12 receptor in patients undergoing interventional neuroradiology procedures

BACKGROUND

Clopidogrel is an inhibitor of the P2Y12 platelet receptor but testing to demonstrate a drug effect is controversial since there are often discordant results between different tests methods.

METHODS

Samples from patients taking clopidogrel prior to intracranial flow-diversion procedures were tested using light transmission aggregometry (LTA), whole blood impedance aggregometry (WBIA) and the VerifyNow device (VND). Samples were classified as concordant if all test results were either responsive (inhibition) or resistant. Discordant results were separated using the VND into those with a responsive versus a resistant test result.

RESULTS

Samples from 96 patients were studied. Concordance for all three tests was seen in 53/96 (55%) of samples, of which 41 (43%) were responsive and 12 (12%) were resistant. Discordance was observed in 43 samples (45%), 37 (28%) of which were caused by responsive VND and either a resistant WBIA or LTA and 6 (7%) of which were caused by a resistant VND but a responsive test result using either WBIA or LTA. These two discordant groups differed in both platelet count and hematocrit, but no such difference was present between the two concordant groups.

CONCLUSION

Discordance in P2Y12 inhibition testing may be partly explained by sample platelet count and hematocrit.

Studying the efficacy of antiplatelet drugs on atherosclerosis by optofluidic imaging on a chip

Vascular stenosis caused by atherosclerosis instigates activation and aggregation of platelets, eventually resulting in thrombus formation. Although antiplatelet drugs are commonly used to inhibit platelet activation and aggregation, they unfortunately cannot prevent recurrent thrombotic events in patients with atherosclerosis. This is partially due to the limited understanding of the efficacy of antiplatelet drugs in the complex hemodynamic environment of vascular stenosis. Conventional methods for evaluating the efficacy of antiplatelet drugs under stenosis either fail to simulate the hemodynamic environment of vascular stenosis characterized by high shear stress and recirculatory flow or lack spatial resolution in their analytical techniques to statistically identify and characterize platelet aggregates. Here we propose and experimentally demonstrate a method comprising an in vitro 3D stenosis microfluidic chip and an optical time-stretch quantitative phase imaging system for studying the efficacy of antiplatelet drugs under stenosis. Our method simulates the atherogenic flow environment of vascular stenosis while enabling high-resolution and statistical analysis of platelet aggregates. Using our method, we distinguished the efficacy of three antiplatelet drugs, acetylsalicylic acid (ASA), cangrelor, and eptifibatide, for inhibiting platelet aggregation induced by stenosis. Specifically, ASA failed to inhibit stenosis-induced platelet aggregation, while eptifibatide and cangrelor showed high and moderate efficacy, respectively. Furthermore, we demonstrated that the drugs tested also differed in their efficacy for inhibiting platelet aggregation synergistically induced by stenosis and agonists (e.g., adenosine diphosphate, and collagen). Taken together, our method is an effective tool for investigating the efficacy of antiplatelet drugs under vascular stenosis, which could assist the development of optimal pharmacologic strategies for patients with atherosclerosis.

Relationship between the Responsiveness of Amyloid β Protein to Platelet Activation by TRAP Stimulation and Brain Atrophy in Patients with Diabetes Mellitus

Type 2 DM is a risk factor for dementia, including Alzheimer's disease (AD), and is associated with brain atrophy. Amyloid β protein (Aβ) deposition in the brain parenchyma is implicated in the neurodegeneration that occurs in AD. Platelets, known as abundant storage of Aβ, are recognized to play important roles in the onset and progression of AD. We recently showed that Aβ negatively regulates platelet activation induced by thrombin receptor-activating protein (TRAP) in healthy people. In the present study, we investigated the effects of Aβ on the TRAP-stimulated platelet activation in DM patients, and the relationship between the individual responsiveness to Aβ and quantitative findings of MRI, the volume of white matter hyperintensity (WMH)/intracranial volume (IC) and the volume of parenchyma (PAR)/IC. In some DM patients, Aβ reduced platelet aggregation induced by TRAP, while in others it was unchanged or rather enhanced. The TRAP-induced levels of phosphorylated-Akt and phosphorylated-HSP27, the levels of PDGF-AB and the released phosphorylated-HSP27 correlated with the degree of platelet aggregability. The individual levels of not WMH/IC but PAR/IC was correlated with those of TRAP-stimulated PDGF-AB release. Collectively, our results suggest that the reactivity of TRAP-stimulated platelet activation to Aβ differs in DM patients from healthy people. The anti-suppressive feature of platelet activation to Aβ might be protective for brain atrophy in DM patients.

Platelet Aggregation Before Aspirin Initiation in Pediatric Patients With Congenital Heart Disease at High Risk of Thrombosis

Background

Aspirin following unfractionated heparin is the most common anticoagulation strategy for pediatric patients who experienced cardiac surgery at high risk of thrombosis. The platelet aggregation test is the golden method to evaluate the aspirin effect on platelet function. However, the platelet aggregation basal status before postoperative aspirin initiation and the related clinical influencing factors hasn't been investigated systemically in this population.

Methods

In a prospective cohort of 247 children, arachidonic acid-induced platelet aggregation (PAG-AA) was measured by means of light transmission aggregometry (LTA) before the first dose of aspirin after cardiac surgical procedure and the perioperative variables were also collected. Distribution of this population's PAG-AA basal status was described. Univariate and multivariate logistic regression analysis were performed to identify the main influencing factors of PAG-AA.

Results

The median time of aspirin administration was 2 (1–27) days after surgery and the corresponding median value of basal PAG-AA was 20.70% (1.28–86.49%), with 67.6% population under 55% and 47.8% population under 20%. Patients undergoing cardiopulmonary bypass (CPB) had a significantly lower basal PAG-AA than those without (30.63 ± 27.35 vs. 57.91 ± 27.58, p = 0.013). While patients whose test done within 3 days after CPB had a significantly lower PAG-AA than those out of 3 days (25.61 ± 25.59 vs. 48.59 ± 26.45, p = 0.001). Univariate analysis implied that the influencing factors of the basal PAG-AA including CPB use, test time point, cyanosis, and platelet count. Multivariate regression analysis indicated that only CPB use, test time point, and platelet count were the main independent influencing factors for the basal PAG-AA.

Conclusion

The majority of children have impaired basal platelet aggregometry responses before postoperative aspirin initiation. The main influencing factors are CPB use, test time point, and platelet count. To establish the platelet aggregometry baseline prior to commencement of aspirin therapy, testing should be performed 3 days later following the procedure when effect of CPB is basically over.

Pharmacological Difference Between Platelet Aggregations in Cardioembolic Stroke Patients with Direct Oral Anticoagulants: A Pilot Study

Background Selecting the appropriate direct oral anticoagulants (DOACs) for embolic ischemic stroke patients, especially on concurrent antiplatelet therapy, is important. However, a limited number of studies have reported on the pharmacological differences in platelet aggregation of each DOAC. We aimed to evaluate the antiplatelet effects of selected DOACs, by comparing dabigatran (a direct oral thrombin inhibitor) and factor Xa (FXa) inhibitors (apixaban and rivaroxaban) in patients who had suffered a cardioembolic stroke. Methods We retrospectively evaluated 12 patients diagnosed with a cardioembolic stroke who took any DOAC without an antiplatelet drug and underwent platelet aggregation tests within 60 days from the onset of symptoms. The platelet aggregation tests were analyzed by both light transmission aggregometry and VerifyNow®. Results Six patients (50%) took dabigatran, while the other six (50%) took an FXa inhibitor (n = 4 for apixaban and n = 2 for rivaroxaban). From the light transmission aggregometry analysis, it was found that the maximal extent of aggregation for adenosine diphosphate (ADP) was significantly higher with dabigatran than with FXa inhibitors, and the ED₅₀ value of ADP on platelet aggregation was significantly lower with dabigatran than with FXa inhibitors. Moreover, the VerifyNow® analyses revealed that P2Y₁₂ reaction units were significantly higher with dabigatran than with FXa inhibitors. Conclusions Dabigatran had little impact on platelet aggregation compared to FXa inhibitors in patients who had suffered a cardioembolic stroke with atrial fibrillation, and who took DOACs for secondary prevention within 60 days from the onset.

Influencing factors and differences in Born aggregometry in specialized hemostaseological centers – results of a multi-center laboratory comparison

Introduction  Light transmission aggregometry (LTA) is regarded as the gold standard in platelet function diagnostics. However, there is a relevant degree of interlaboratory variability in practical applications.

Objective  The aim of the present study was to develop a practicable laboratory comparison on LTA and to analyze differences and influencing factors in regard to standardization in five specialized hemostaseological centers.

Methods  The study was performed on 30 patients in total. Each center performed LTA on blood samples from six healthy volunteers (three men and three women) using the inductors collagen (Col), adenosine diphosphate (ADP), arachidonic acid (ARA), and ristocetin. The LTA was performed three times using different methods as follows: (1) International Society on Thrombosis and Haemostasis recommendations with identical reagents, (2) in-house protocols and the identical reagents; and (3) in-house protocols and in-house reagents.

Results  A total of 396 measurements of 30 probands were performed. Even after standardization of the protocol and using identical reagents, there were significant differences between the centers regarding the final and maximum aggregation ( p  = 0.002 and <0.001) and further significant differences in the maximum and final aggregation according to the wavelength of the device used to measure the LTA (PAP-8: 430 nm, APACT 4004: 740 nm [ p  < 0.001 each]). Using identical reagents but individual inductor concentrations and laboratory protocols also resulted in different maximum and final aggregation. The largest differences were seen with Col and ristocetin; there were significant influences from the reagents' manufacturers in the results of aggregometry for the inductor Col ( p  < 0.01) but not for ADP, ARA, and ristocetin.

Conclusion  In this study, we proved that there are significant influences from the used aggregometers, inductors concentrations, and manufacturers. These results illustrate the challenges and importance of standardization of LTA.

Screening and diagnosis of inherited platelet disorders

Inherited platelet disorders are important conditions that often manifest with bleeding. These disorders have heterogeneous underlying pathologies. Some are syndromic disorders with non-blood phenotypic features, and others are associated with an increased predisposition to developing myelodysplasia and leukemia. Platelet disorders can present with thrombocytopenia, defects in platelet function, or both. As the underlying pathogenesis of inherited thrombocytopenias and platelet function disorders are quite diverse, their evaluation requires a thorough clinical assessment and specialized diagnostic tests, that often challenge diagnostic laboratories. At present, many of the commonly encountered, non-syndromic platelet disorders do not have a defined molecular cause. Nonetheless, significant progress has been made over the past few decades to improve the diagnostic evaluation of inherited platelet disorders, from the assessment of the bleeding history to improved standardization of light transmission aggregometry, which remains a "gold standard" test of platelet function. Some platelet disorder test findings are highly predictive of a bleeding disorder and some show association to symptoms of prolonged bleeding, surgical bleeding, and wound healing problems. Multiple assays can be required to diagnose common and rare platelet disorders, each requiring control of preanalytical, analytical, and post-analytical variables. The laboratory investigations of platelet disorders include evaluations of platelet counts, size, and morphology by light microscopy; assessments for aggregation defects; tests for dense granule deficiency; analyses of granule constituents and their release; platelet protein analysis by immunofluorescent staining or flow cytometry; tests of platelet procoagulant function; evaluations of platelet ultrastructure; high-throughput sequencing and other molecular diagnostic tests. The focus of this article is to review current methods for the diagnostic assessment of platelet function, with a focus on contemporary, best diagnostic laboratory practices, and relationships between clinical and laboratory findings.

The porcine abattoir blood model-Evaluation of platelet function for in-vitro hemocompatibility investigations

BACKGROUND

The major obstacle of blood-contacting medical devices is insufficient hemocompatibility, particularly thrombogenicity and platelet activation. Pre-clinical in-vitro testing allows for the evaluation of adverse thrombogenicity-related events, but is limited, among others, by the availability and quantity of human blood donations. The use of animal blood is an accepted alternative for several tests; however, animal and particularly abattoir blood might present species-specific differences to human blood as well as elevated blood values, and pre-activated platelets due to stressed animals and non-standardized blood collection.

MATERIAL & METHODS

To this end, we investigated porcine abattoir blood in comparison to human donor blood with the focus on platelet pre-activation and remaining activation potential. By means of light transmission aggregometry, aggregation kinetics of platelet rich plasma after stimulation with three different concentrations of each adenosine diphosphate (ADP) (5 µM, 10 µM, 20 µM) and collagen (2.5 µg/ml, 5 µg/ml, 10 µg/ml) were monitored.

RESULTS

The activation with collagen revealed no significant differences in platelet behavior of the two species. In contrast, stimulation with ADP resulted in a lower maximum aggregation and a high disaggregation for porcine abattoir blood. The latter is a species-specific phenomenon of porcine platelets. Variations within each study cohort were comparable for human and abattoir pig.

CONCLUSION

The similarities in platelet activation following collagen stimulation and the preservation of the porcine-specific reaction to ADP prove a general functionality of the abattoir blood. This finding provides a first step towards the complete validation of the porcine abattoir blood model.

Amyloid β protein negatively regulates human platelet activation induced by thrombin receptor-activating protein

Amyloid β protein deposition in cerebral vessels, a characteristic of Alzheimer's disease, is a risk factor for intracerebral hemorrhage. Amyloid β protein directly modulates human platelet function; however, the exact mechanism of action is unclear. Therefore, we investigated the effects of amyloid β protein on human platelet activation using an aggregometer with laser scattering. Amyloid β protein decreased platelet aggregation induced by thrombin receptor-activating protein, but not by collagen and ADP. Amyloid β protein also suppressed platelet aggregation induced by SCP0237 and A3227. Platelet-derived growth factor-AB secretion and phosphorylated-heat shock protein 27 release by thrombin receptor-activating protein were inhibited by amyloid β protein. Additionally, thrombin receptor-activating protein-induced phosphorylation of JNK and p38 MAP kinase was reduced by amyloid β protein. Collectively, our results strongly suggest that amyloid β protein negatively regulates protease-activated receptor-elicited human platelet activation. These findings may indicate a cause of intracerebral hemorrhage due to amyloid β protein.

Effects of pentoxifylline on canine platelet aggregation

BACKGROUND

Pentoxifylline can decrease platelet function in humans, but the anti-platelet effects of pentoxifylline in dogs is unknown. The addition of a luciferin-luciferase reagent during platelet aggregometry can induce a dose-dependent potentiation of platelet aggregation.

OBJECTIVE

To determine if exposure to pentoxifylline, without the addition of a luciferin-luciferase reagent during aggregometry, causes canine platelet dysfunction. Our hypotheses were that pentoxifylline would inhibit platelet function, and that the addition of a luciferin-luciferase reagent would obscure detection of pentoxifylline-induced platelet dysfunction as measured via aggregometry.

METHODS

Seven healthy Walker hound dogs. Platelet-rich plasma (PRP) and whole blood were treated for 30 minutes with pentoxifylline: 0 (control), 1 and 2 μg/mL. The platelet aggregation was determined using optical (maximum amplitude) and impedance (ohms) aggregometry using collagen as the agonists, with and without a luciferin-luciferase reagent. Four samples were analysed per concentration and the results were averaged.

RESULTS

Based on optical aggregometry, there was no difference (p = 0.964) in the mean maximum amplitude at any pentoxifylline concentration, with and without the luciferin-luciferase reagent. During impedance aggregometry, the addition of a luciferin-luciferase reagent was associated with significantly (p < 0.001) greater platelet aggregation in response to a collagen agonist, regardless of the presence or absence of pentoxifylline.

CONCLUSIONS

Pentoxifylline does not exert an in vitro anti-platelet effect on canine platelet aggregation when collagen is used as an agonist, but it is unknown if long-term oral drug administration will inhibit platelet aggregation. The addition of a luciferin-luciferase reagent during platelet aggregometry can artificially enhance canine platelet aggregation.

Is monitoring of antiplatelet therapy by light transmission aggregometry dependent on instrument and reagent used?

INTRODUCTION

Light transmission aggregometry (LTA), used to detect clopidogrel resistance in patients under antiplatelet therapy, is prone to multiple variables potentially influencing results and interpretation. Currently, no attention is given to type of aggregometer or reagent used. The aim of this study was to evaluate the interassay variability between two aggregometers (Chronolog700 and TA-8V), using two different ADP reagents (Chrono-Par^® and Agro-Bio ADP) in patients under clopidogrel therapy. Additionally, LTA results were correlated to CYP2C19-polymorphism.

METHODS

Light transmission aggregometry was performed in 20 healthy individuals and 30 patients using both aggregometers, and applying two different reagents (2.5 and 5 µmol/L). The maximum platelet aggregation (ADP_max ), the platelet aggregation at 6 minutes (ADP_6min ), and the percentage of disaggregation at 6 min (ADP_%disaggr ) were compared between four applied combinations. Additionally, 23 clopidogrel-resistant patients according to Chronolog700-Chrono-par^® ADP reagent analysis were tested for CYP2C19*2 polymorphism.

RESULTS

Comparison of the LTA of healthy individuals revealed a significant lower ADP_max , lower ADP_6min , and higher ADP_%disaggr with the TA-8V aggregometer compared to Chronolog700, regardless of the reagent. In contrast, LTA results in patients are depending on the reagent, with significant higher ADP_max and ADP_6min and lower ADP_%disaggr using Chrono-Par^® compared to Agro-Bio ADP reagent. All intermediate clopidogrel metabolizers (CYP2C19*2 carriers) were correctly classified as clopidogrel resistant using Chrono-Par^® , in contrast to the Agro-Bio ADP reagent.

CONCLUSION

Light transmission aggregometry in clopidogrel-treated patients is mainly depending on the type of ADP reagent. Comparison of LTA with genotype reveals that the choice of instrument seems less influencing. In contrast, in the healthy individuals, differences could be attributed to the instrument.

Clinical effectiveness and safety of salvia miltiorrhiza depside salt combined with aspirin in patients with stable angina pectoris: A multicenter, pragmatic, randomized controlled trial

BACKGROUND

Salvia Miltiorrhiza Depside Salt (SMDS) was extracted from Salvia miltiorrhiza with high-quality control of active principles. In 2005, China's FDA approved the use of SMDS for stable angina pectoris (SAP), but the evidence of SMDS combined with aspirin remains unclear.

PURPOSE

The aim of this study was to assess the clinical effectiveness and safety of SMDS combined with aspirin in patients with SAP.

METHODS

A multicenter, pragmatic, three-armed parallel group and an individually randomized controlled superiority trial was designed. Participants aged 35 to 75 years old with SAP were recruited from four "Class Ⅲ Grade A" hospitals in China. Participants who were randomized into the SMDS group were treated with SMDS by intravenous drip. Participants in the control group received aspirin enteric-coated tablets (aspirin). Participants who were randomly assigned to the combination group received SMDS combined with aspirin. All participants received standard care from clinicians, without any restrictions. The primary outcome measure was thromboelastography (TEG). Secondary outcome measures included symptom score of the Seattle Angina Questionnaire (SAQ), visual analogue scale (VAS) score of traditional Chinese medicine (TCM) symptoms, platelet aggregation measured by light transmittance aggregometry (LTA), and fasting blood glucose. Effectiveness evaluation data were collected at baseline and ten days after treatment. Researchers followed up with participants for one month after treatment to determine whether adverse events (AEs) or adverse drug reactions (ADRs) such as bleeding tendency occurred. All statistical calculations were carried out with R 3.5.3 statistical analysis software.

RESULTS

A total of 135 participants completed follow-up data on the primary outcome after ten days of treatment. Participants in the SMDS combined aspirin group had the highest improvement rate of sensitivity in AA% [p < 0.001, 95% CI (0.00-0.00)], from 30.6% before treatment to 81.6% after treatment. Participants with drug resistance (AA% < 20%) in the SMDS combined with aspirin group also had the highest sensitivity rate [p < 0.001, 95% CI (0.00-0.00)] after treatment (accounting for 81.0% of the combination group and 60.7% of the sensitive participants). The improvement of TCM symptoms in participants treated with SMDS combined with aspirin was significantly better than that of the aspirin group [MD = 1.71, 95% CI (0.15-3.27), p = 0.032]. There were no significant differences in other indexes (R, TPI, MA, K, CI, α value) of TEG, SAQ, platelet aggregation and fasting blood glucose among the three groups. No bleeding tendency or ADRs occurred in all participants.

CONCLUSION

SMDS combined with aspirin is a clinically effective and safe intervention to treat adults aged 35 and older with SAP. This trial shows that SMDS combined with aspirin can significantly improve the sensitivity rate of AA% in TEG and the VAS score of TCM symptoms. Further large samples and high-quality research are needed to determine if certain participants might benefit more from SMDS combined with aspirin. The study protocol was registered in the Clinical Trials USA registry (registration No. NCT02694848).

Anti-Platelet Aggregation and Anti-Cyclooxygenase Activities for a Range of Coffee Extracts (Coffea arabica)

Coffee is rich in caffeine (CF), chlorogenic acid (CGA) and phenolics. Differing types of coffee beverages and brewing procedures may result in differences in total phenolic contents (TPC) and biological activities. Inflammation and increases of platelet activation and aggregation can lead to thrombosis. We focused on determining the chemical composition, antioxidant activity and inhibitory effects on agonist-induced platelet aggregation and cyclooxygenase (COX) of coffee beverages in relation to their preparation method. We prepared instant coffee and brewed coffee beverages using drip, espresso, and boiling techniques. Coffee extracts were assayed for their CF and CGA contents using HPLC, TPC using colorimetry, platelet aggregation with an aggregometer, and COX activity using ELISA. The findings have shown all coffee extracts, except the decaffeinated types, contained nearly equal amounts of CF, CGA, and TPC. Inhibitory effects of coffee extracts on platelet aggregation differed depending on the activation pathways induced by different agonists. All espresso, drip and boiled coffee extracts caused dose dependent inhibition of platelet aggregation induced by ADP, collagen, epinephrine, and arachidonic acid (ARA). The most marked inhibition was seen at low doses of collagen or ARA. Espresso and drip extracts inhibited collagen-induced platelet aggregation more than purified caffeine or CGA. Espresso, boiled and drip coffee extracts were also a more potent inhibitors of COX-1 and COX-2 than purified caffeine or CGA. We conclude that inhibition of platelet aggregation and COX-1 and COX-2 may contribute to anti-platelet and anti-inflammatory effects of espresso and drip coffee extracts.

Pharmacokinetic, pharmacodynamic, and pharmacogenetic assays to monitor clopidogrel therapy

Clopidogrel is the most common and widely used antiplatelet agent for patients with coronary artery disease following confirmation by electrocardiographic studies. The nonresponsiveness of patients to clopidogrel and the possibility of testing for clopidogrel resistance by platelet function assays (PFA) are contentious issues. Light transmission aggregometry (LTA) is considered as the gold standard test among all PFA. In this review, the most commonly used PFA used for monitoring the effect of clopidogrel, LTA, vasodilator-stimulated phosphoprotein assay phosphorylation, rotational thromboelastometry (ROTEM) delta and ROTEM platelet, thromboelastography, PFA-100, VerifyNow P2Y12 assay, Multiplate analyzer, Plateletworks assay and pharmacogenetic studies, are comparatively discussed including their principles of action, advantages, and disadvantages. VerifyNow P2Y12 assay can be accepted as the ideal point of care test out of the discussed assays. However, modified assays are required which could overcome the limitations associated with currently available assays.

GPR56/ADGRG1 is a platelet collagen-responsive GPCR and hemostatic sensor of shear force

We identified the known collagen receptor GPR56/ADGRG1 on platelets. GPR56 is an adhesion G protein-coupled receptor that becomes activated following forced dissociation of its N-terminal fragment and C-terminal fragment or seven-transmembrane spanning domain (7TM). Fragment dissociation reveals the cryptic stalk of the 7TM, which acts as a tethered peptide agonist, and for GPR56, this activates platelet G13 signaling. GPR56 pharmacological probes activated platelets to undergo shape change and aggregation, which are critical for the formation of hemostatic plugs. Gpr56^−/− mice exhibit prolonged bleeding, defective platelet plug formation in vessel injury assays, and delayed thrombotic vessel occlusion. Shear-force dependency of platelet adhesion to immobilized collagen was found to be GPR56 dependent.

Circulating platelets roll along exposed collagen at vessel injury sites and respond with filipodia protrusion, shape change, and surface area expansion to facilitate platelet adhesion and plug formation. Various glycoproteins were considered to be both collagen responders and mediators of platelet adhesion, yet the signaling kinetics emanating from these receptors do not fully account for the rapid platelet cytoskeletal changes that occur in blood flow. We found the free N-terminal fragment of the adhesion G protein-coupled receptor (GPCR) GPR56 in human plasma and report that GPR56 is the platelet receptor that transduces signals from collagen and blood flow-induced shear force to activate G protein 13 signaling for platelet shape change. Gpr56^−/− mice have prolonged bleeding, defective platelet plug formation, and delayed thrombotic occlusion. Human and mouse blood perfusion studies demonstrated GPR56 and shear-force dependence of platelet adhesion to immobilized collagen. Our work places GPR56 as an initial collagen responder and shear-force transducer that is essential for platelet shape change during hemostasis.

Ticagrelor Inhibits Toll-Like and Protease-Activated Receptor Mediated Platelet Activation in Acute Coronary Syndromes

Purpose

Since ticagrelor inhibits the cellular uptake of adenosine, thereby increasing extracellular adenosine concentration and biological activity, we hypothesized that ticagrelor has adenosine-dependent antiplatelet properties. In the current study, we compared the effects of ticagrelor and prasugrel on platelet activation in acute coronary syndrome (ACS).

Methods

Platelet surface expression of P-selectin and activated glycoprotein (GP) IIb/IIIa in response to adenosine diphosphate (ADP), the toll-like receptor (TLR)-1/2 agonist Pam3CSK4, the TLR-4 agonist lipopolysaccharide (LPS), the protease-activated receptor (PAR)-1 agonist SFLLRN, and the PAR-4 agonist AYPGKF were measured by flow cytometry in blood from 80 ticagrelor- and 80 prasugrel-treated ACS patients on day 3 after percutaneous coronary intervention. Residual platelet aggregation to arachidonic acid (AA) and ADP were assessed by multiple electrode aggregometry and light transmission aggregometry.

Results

ADP-induced platelet activation and aggregation, and AA-induced platelet aggregation were similar in patients on ticagrelor and prasugrel, respectively (all p ≥ 0.3). Further, LPS-induced platelet surface expression of P-selectin and activated GPIIb/IIIa did not differ significantly between ticagrelor- and prasugrel-treated patients (both p > 0.4). In contrast, Pam3CSK4-induced platelet surface expression of P-selectin and activated GPIIb/IIIa were significantly lower in ticagrelor-treated patients (both p ≤ 0.005). Moreover, SFLLRN-induced platelet surface expression of P-selectin and activated GPIIb/IIIa were significantly less pronounced in patients on ticagrelor therapy compared to prasugrel-treated patients (both p < 0.03). Finally, PAR-4 mediated platelet activation as assessed by platelet surface expression of activated GPIIb/IIIa following stimulation with AYPGKF was significantly lower in patients receiving ticagrelor (p = 0.02).

Conclusion

Ticagrelor inhibits TLR-1/2 and PAR mediated platelet activation in ACS patients more strongly than prasugrel.

Laboratory Techniques Used to Diagnose Constitutional Platelet Dysfunction

Platelets play a major role in primary hemostasis, where activated platelets form plugs to stop hemorrhaging in response to vessel injuries. Defects in any step of the platelet activation process can cause a variety of platelet dysfunction conditions associated with bleeding. To make an accurate diagnosis, constitutional platelet dysfunction (CPDF) should be considered once von Willebrand disease and drug intake are ruled out. CPDF may be associated with thrombocytopenia or a genetic syndrome. CPDF diagnosis is complex, as no single test enables the analysis of all aspects of platelet function. Furthermore, the available tests lack standardization, and repeat tests must be performed in specialized laboratories especially for mild and moderate forms of the disease. In this review, we provide an overview of the laboratory tests used to diagnose CPDF, with a focus on light transmission platelet aggregation (LTA), flow cytometry (FC), and granules assessment. Global tests, mainly represented by LTA, are often initially performed to investigate the consequences of platelet activation on platelet aggregation in a single step. Global test results should be confirmed by additional analytical tests. FC represents an accurate, simple, and reliable test to analyze abnormalities in platelet receptors, and granule content and release. This technique may also be used to investigate platelet function by comparing resting- and activated-state platelet populations. Assessment of granule content and release also requires additional specialized analytical tests. High-throughput sequencing has become increasingly useful to diagnose CPDF. Advanced tests or external research laboratory techniques may also be beneficial in some cases.

Microfluidics in Haemostasis: A Review

Haemostatic disorders are both complex and costly in relation to both their treatment and subsequent management. As leading causes of mortality worldwide, there is an ever-increasing drive to improve the diagnosis and prevention of haemostatic disorders. The field of microfluidic and Lab on a Chip (LOC) technologies is rapidly advancing and the important role of miniaturised diagnostics is becoming more evident in the healthcare system, with particular importance in near patient testing (NPT) and point of care (POC) settings. Microfluidic technologies present innovative solutions to diagnostic and clinical challenges which have the knock-on effect of improving health care and quality of life. In this review, both advanced microfluidic devices (R&D) and commercially available devices for the diagnosis and monitoring of haemostasis-related disorders and antithrombotic therapies, respectively, are discussed. Innovative design specifications, fabrication techniques, and modes of detection in addition to the materials used in developing micro-channels are reviewed in the context of application to the field of haemostasis.

High Prevalence of Sticky Platelet Syndrome in Patients with Infertility and Pregnancy Loss

Platelet hyperaggregability, known as sticky platelet syndrome (SPS), is a prothrombotic disorder that has been increasingly associated with pregnancy loss. In this retrospective study, we aimed to investigate the clinical and diagnostic relevance of SPS in 208 patients with infertility and unexplained pregnancy loss history. We studied 208 patients that had been referred to undergo a dose-dependent platelet aggregation response to adenosine diphosphate and epinephrine using light transmission aggregometry modified by Mammen during an 11-year period. Patients’ platelet aggregation response was compared with platelet function in 29 female healthy controls of fertile age with no previous history of pregnancy loss. We found a prevalence of SPS type II (33.2%) in 208 female patients with infertility and pregnancy loss. ∆-epinephrine-induced platelet aggregation in patients with SPS was significantly decreased (median 7% and range −21 to 43%) compared to patients without SPS (median 59%, range 7–88% and p < 0.0001) and healthy controls (median 57%, range 8–106% and p < 0.0001). The optimum SPS-diagnostic cutoff value for ∆-epinephrine aggregation was ≤32% (sensitivity 95.7%, specificity 95.2%). SPS patients with low-dose acetylsalicylic acid (ASA) therapy (n = 56) showed improved pregnancy outcome (32 pregnancies; live births n = 18 (56%)) compared to SPS patients without low-dose ASA (n = 13) (3 pregnancies; live births n = 1 (33%)). Our study demonstrates the clinical and diagnostic relevance of platelet hyperaggregation in women with infertility and pregnancy loss history. Further studies should investigate the potential of SPS as a novel decisional tool with both diagnostic and clinical implications in infertility and pregnancy loss.

Individual variations in platelet reactivity towards ADP, epinephrine, collagen and nitric oxide, and the association to arterial function in young, healthy adults

INTRODUCTION

Platelet aggregation and secretion can be induced by a large number of endogenous activators, such as collagen, adenosine diphosphate (ADP) and epinephrine. Conversely, the blood vessel endothelium constitutively release platelet inhibitors including nitric oxide (NO) and prostacyclin. NO and prostacyclin are also well-known vasodilators and contribute to alterations in local blood flow and systemic blood pressure.

MATERIALS AND METHODS

In this study we investigated individual variations in platelet reactivity and arterial functions including blood pressure and flow-mediated vasodilation (FMD) in 43 young, healthy individuals participating in the Lifestyle, Biomarkers and Atherosclerosis (LBA) study. Platelet aggregation and dense granule secretion were measured simultaneously by light transmission and luminescence. FMD was measured with ultrasound.

RESULTS

The platelet function assay showed inter-individual differences in platelet reactivity. Specifically, a sub-group of individuals had platelets with an increased response to low concentrations of ADP and epinephrine, but not collagen. When the NO-donor S-nitroso-N-acetyl-DL-penicillamine (SNAP) was combined with high doses of these platelet activators, the results indicated for sub-groups of NO-sensitive and NO-insensitive platelets. The individuals with NO-sensitive platelets in response to SNAP in combination with collagen had a higher capacity of FMD of the arteria brachialis.

CONCLUSIONS

Platelet reactivity towards ADP, epinephrine and NO differs between young, healthy individuals. Some individuals have a more effective response towards NO, both in the aspect of platelet inhibition ex vivo, as well as vasodilation in vivo.

The Effects of Andrographis paniculata on Platelet Activity in Healthy Thai Volunteers

Background. Andrographis paniculata (AP) has been used in Thai traditional medicine to treat various infections, including the common cold and fever. Its bioactive compound, andrographolide, has shown antiplatelet activities in an in vitro study model. Since clinical studies of the effects of AP on the human platelet function have never been reported, we investigated its effect on platelet activity in ten healthy volunteers. Methods. Two grams of AP was taken 3 times within one day. The blood was withdrawn by venipuncture before and 2 and 24 hours after the AP administration to analyze the effects of AP on platelet aggregation, the expression of enzyme cyclooxygenase (COX) mRNA and protein, and TXB₂, including P-selectin. Result. Even though there was no significant change in the studied parameters, this study exhibited patient-to-patient variability in platelet function. It was found that ADP-induced platelet aggregation tended to decrease after AP administration, while epinephrine-induced platelet aggregation in females tended to be higher than that in males for the entire study period. Moreover, COX-1 mRNA levels tended to decrease while P-selectin levels tended to rise after AP administration. Conclusion. These controversial results are possibly due to the multifactorial mechanisms of platelet aggregation as well as the multichemical composition of AP. Further study, probably at the molecular level, is needed to unveil the underlying mechanisms of action of AP.

Effects of immunosuppressive agents on the hemostatic system in normal dogs

Background

In dogs, the effects of immunosuppressive medications on hemostasis are not well known.

Hypothesis/Objectives

The objective was to determine the effects of immunosuppressive medications on primary and secondary hemostasis. Our hypothesis was that cyclosporine and prednisone would increase markers of hypercoagulability and thromboxane synthesis, while azathioprine, mycophenolate mofetil, and leflunomide would have minimal effects on hemostasis.

Animals

Eight healthy dogs.

Methods

A randomized, cross‐over study used aggregometry, the PFA‐100 platelet function analyzer, viscoelastometry, platelet count, and prothrombin and activated partial thromboplastin times to evaluate hemostasis during the administration of prednisone, azathioprine, cyclosporine, mycophenolate mofetil, and leflunomide for 1 week each at standard oral doses. Urine 11‐dehydro‐thromboxane‐B₂ (11‐dTXB₂) and 6‐keto‐prostaglandin‐F_1α (6‐keto‐PGF_1α) concentrations, normalized to urine creatinine concentration, were measured.

Results

The aggregometry amplitude decreased from 51 ± 21 to 27 ± 14 (P = .002) during leflunomide treatment (ADP activation), but there were no differences in amplitude (P = .240) for any medications when platelets were activated with collagen. For all medications, there were no significant differences in viscoelastometry indices (ACT, P = .666; ClotRate, P = .340; and platelet function, P = .411) and platelet count (P = .552). Compared with pretreatment values, urinary 11‐dTXB₂‐to‐creatinine ratio increased (P = .001) after drug administration (from 3.7 ± 0.6 to 5.6 ± 1.1). Cyclosporine was associated with an increase (P < .001) in the 6‐keto‐PGF_1α‐to‐creatinine ratio (from 10.3 ± 4.6 to 22.1 ± 5.3).

Conclusions and Clinical Importance

Most immunosuppressive drugs do not enhance platelet function or coagulation in healthy dogs, suggesting that these medications might not predispose hypercoagulable dogs to thromboembolism. The results of our study need to be correlated with the clinical outcomes of hypercoagulable dogs.

Pneumatic tube system transport does not alter platelet function in optical and whole blood aggregometry, prothrombin time, activated partial thromboplastin time, platelet count and fibrinogen in patients on anti-platelet drug therapy

Introduction

The aim of this study was to assess pneumatic tube system (PTS) alteration on platelet function by the light transmission aggregometry (LTA) and whole blood aggregometry (WBA) method, and on the results of platelet count, prothrombin time (PT), activated partial thromboplastin time (APTT), and fibrinogen.

Materials and methods

Venous blood was collected into six 4.5 mL VACUETTE® 9NC coagulation sodium citrate 3.8% tubes (Greiner Bio-One International GmbH, Kremsmünster, Austria) from 49 intensive care unit (ICU) patients on dual anti-platelet therapy and immediately hand carried to the central laboratory. Blood samples were divided into 2 Groups: Group 1 samples (N = 49) underwent PTS (4 m/s) transport from the central laboratory to the distant laboratory and back to the central laboratory, whereas Group 2 samples (N = 49) were excluded from PTS forces. In both groups, LTA and WBA stimulated with collagen, adenosine-5’-diphosphate (ADP), arachidonic acid (AA) and thrombin-receptor-activated-peptide 6 (TRAP-6) as well as platelet count, PT, APTT, and fibrinogen were performed.

Results

No statistically significant differences were observed between blood samples with (Group 1) and without (Group 2) PTS transport (P values from 0.064 – 0.968). The AA-induced LTA (bias: 68.57%) exceeded the bias acceptance limit of ≤ 25%.

Conclusions

Blood sample transportation with computer controlled PTS in our hospital had no statistically significant effects on platelet aggregation determined in patients with anti-platelet therapy. Although AA induced LTA showed a significant bias, the diagnostic accuracy was not influenced.

Implementation of buffy-coat-derived pooled platelet concentrates for internal quality control of light transmission aggregometry: a proof of concept study

Essentials In platelet function testing, standardized internal controls (IQC) are not commercially provided. Platelet function testing was performed daily on aliquoted pooled platelet concentrates. Pooled platelet concentrates showed stability for control purposes from Monday to Friday. Pooled platelet concentrates provide the necessary steadiness to serve as IQC material.

SUMMARY

Background Standardized commercially available control material for internal quality control (IQC) of light transmission aggregometry (LTA) is still lacking. Moreover, the availability of normal blood donors to provide fresh platelets is difficult in small laboratories, where 'volunteers' may be in short supply. Objectives To evaluate the implementation of buffy-coat-derived pooled platelet concentrates (PCs) for IQC material for LTA. Methods We used buffy-coat-derived pooled PCs from the blood bank as IQC material for LTA. On each weekend one PC was prepared (> 200 mL) and aliquoted from the original storage bag on a daily basis in four baby bags (40-50 mL), which were delivered from Monday to Friday to our laboratory. The IQC measurements of at least 85 work-weeks (from Monday to Friday) were evaluated with this new IQC material. LTA was performed on a four-channel Chronolog 700 Aggregometer (Chronolog Corporation, Havertown, PA, USA) (agonists: collagen, adenosine diphosphate [ADP], arachidonic acid [AA] and thrombin receptor activator peptide-6 [TRAP-6]). Results The medians of platelet aggregation from IQC measurements with collagen, ADP and AA from Monday to Friday were 68.0-59.5, 3.0-2.0 and 51.0-50.0%, respectively, and the mean of platelet aggregation with TRAP-6 was 71.2-66.4%. Conclusions Buffy-coat-derived pooled PCs serve as a reliable and robust IQC material for LTA measurements and would be beneficial for the whole laboratory procedure and employees' safety.

In vivo and protease-activated receptor-1-mediated platelet activation but not response to antiplatelet therapy predict two-year outcomes after peripheral angioplasty with stent implantation

Data linking the response to antiplatelet therapy with clinical outcomes after angioplasty and stenting for lower extremity artery disease (LEAD) are scarce. Moreover, associations of in vivo and thrombin-inducible platelet activation with the occurrence of adverse events have not been investigated in these patients, so far. We therefore assessed clinical outcomes and on-treatment platelet reactivity by four test systems in 108 patients receiving dual antiplatelet therapy after infrainguinal angioplasty and stenting for LEAD. Further, in vivo and thrombin receptor-activating peptide (TRAP)-6-inducible glycoprotein (GP) IIb/IIIa activation and P-selectin expression were measured as sensitive parameters of platelet activation. The primary endpoint was defined as the composite of atherothrombotic events and target vessel restenosis or reocclusion. Residual platelet reactivity to adenosine diphosphate and arachidonic acid was similar between patients without and with adverse outcomes within two-year follow-up (all p>0.05). Further, the occurrence of clinical endpoints did not differ significantly between patients without and with high on-treatment residual platelet reactivity by all test systems (all p>0.05). In contrast, in vivo and TRAP-6-inducible platelet activation were significantly more pronounced in patients with subsequent adverse events (all p<0.05), and high levels of platelet activation were independent predictors of the primary endpoint (adjusted hazard ratios: 3.5 for high in vivo activated GPIIb/IIIa, 2.9 for high TRAP-6-inducible activated GPIIb/IIIa, 2.3 for high in vivo P-selectin, and 3 for high TRAP-6-inducible P-selectin; all p<0.05). In conclusion, in vivo and protease-activated receptor-1-mediated platelet activation predict two-year clinical outcomes in stable patients undergoing angioplasty and stenting for LEAD.

Comparison of current platelet functional tests for the assessment of aspirin and clopidogrel response

The two most widely used antiplatelet drugs in the world are aspirin and clopidogrel. However, some patients on aspirin and/or clopidogrel therapy do not respond appropriately to either aspirin or clopidogrel. This phenomenon is usually called “aspirin/clopidogrel resistance”. Several platelet function tests have been used in various studies for the assessment of aspirin and clopidogrel resistance in healthy individuals and patients admitted in cardiology departments. An accurate assessment of platelet response to aspirin/clopidogrel could benefit patients by proposing tailored-antiplatelet therapy based on test results. However, there is a clear lack of standardisation of such techniques and their analytical variability may induce misinterpretation. After a quick report of the mechanisms responsible for aspirin/clopidogrel resistance, we describe the pre-analytical aspects and the analytical performances of current platelet function tests (Light-transmission aggregometry, whole-blood aggregometry, VerifyNow®, Platelet Function Analyzer®, thromboelastography, VASP assay) that are used for the assessment of aspirin/clopidogrel resistance in clinical studies. Considering the different variables that have to be taken into account with each of the platelet function tests, a particular attention should be paid when interpreting results.

Perioperative changes in platelet count and function in patients undergoing cardiac surgery

Background: Patients undergoing cardiac surgery are at increased risk of bleeding due to multifactorial coagulopathies. In the present study, we aimed at investigating the changes in platelet count and function during and after surgery as well as determining the association of the platelet dysfunction with bleeding and transfusion requirements in these patients.

Methods: A total of 40 adult patients scheduled for elective valve coronary cardiac surgery were included in this prospective observational study. Changes in platelet count and function with ADP, acid arachidonic, and collagen (light transmission aggregometry) were analyzed at three time points: before CPB, after CPB, and 24 hours after end of surgery. Postoperative bleeding and intraoperative transfusion requirements were recorded.

Results: There were a significant reverse correlation between CPB time and ADP-induced aggregation, particularly after CPB and postoperative AA-induced aggregation. There was not any significant correlation between platelet count and function at all-time points. Both platelet count and platelet aggregation significantly reduced during CPB. While platelet aggregation increased on postoperative Day 1, platelet count reduced by about 40% after CPB, and remained at this level postoperatively. Patients with abnormal ADP-induced aggregation had significant increased postoperative bleeding and transfusion requirements.

Conclusion: The results of this study demonstrate that platelet count and platelet aggregation are reduced during CPB. Our results emphasized the effect of platelet dysfunction on increased postoperative bleeding and transfusion requirements. Perioperative monitoring of platelet function can be considered as a bleeding management strategy for implantation of PBM programs.

Effects of pH and concentration of sodium citrate anticoagulant on platelet aggregation measured by light transmission aggregometry induced by adenosine diphosphate

The 2013 ISTH-SSC guidelines for the standardization of light transmission aggregometry (LTA) were largely based on expert consensus, as studies directly comparing LTA methodologies were lacking. We experimentally tested the cogency of ISTH-SSC recommendations pertaining to use of anticoagulant, in particular whether: (1) buffered citrate (BC) is preferable to unbuffered citrate (C); (2) the two recommended concentrations of sodium citrate (109 and 129 mM) are equivalent in terms of platelet aggregation (PA). Blood from 16 healthy volunteers was collected into BC and C (109 and 129 mM). PA was measured by LTA in platelet-rich plasma (PRP) stimulated by adenosine diphosphate (ADP) (2 μM) immediately after PRP preparation and up to 4 hr after blood collection; pH and platelet counts in PRP were measured in parallel. pH in PRP increased with time up to about 8 for all anticoagulants, although it was lower in BC than in C at all times. In BC, PA was lower at 45 min, but equivalent at all other times. PA was higher and more stable in sodium citrate 109 mM than in 129 mM at all times. The extent of PA did not change for up to 2 hr after blood collection, and subsequently dramatically decreased. In contrast with ISTH-SSC recommendations, (1) BC does not show advantages compared to C; (2) 109 mM citrate is preferable to 129 mM, because it better supports PA; and (3) LTA studies should be completed within 2 hr of blood collection, instead of the recommended 4 hr.

Claimed effects, outcome variables and methods of measurement for health claims proposed under European Community Regulation 1924/2006 in the framework of protection against oxidative damage and cardiovascular health

BACKGROUND AND AIMS

The high number of negative opinions from the European Food Safety Authority (EFSA) to the requests for authorization of health claims is largely due to the design of human intervention studies, including the inappropriate choice of outcome variables (OVs) and of their methods of measurement (MMs). The present manuscript reports the results of an investigation aimed to collect, collate and critically analyse the information in relation to claimed effects, OVs and MMs, in the context of protection against oxidative damage and cardiovascular health compliant with Regulation 1924/2006.

METHODS AND RESULTS

Claimed effects, OVs and the related MMs were collected from EFSA Guidance documents and applications for authorization of health claims under Articles 13.5 and 14. The OVs and their MMs were evaluated only if the claimed effect was sufficiently defined and was considered beneficial by EFSA. The collection, collation and critical analysis of the relevant scientific literature consisted in the definition of the keywords, the PubMed search strategies and the creation of databases of references. The critical analysis of the OVs and their MMs was performed on the basis of the literature review and was aimed at defining the appropriateness of OVs and MMs in the context of the specific claimed effects.

CONCLUSIONS

The information provided in this document could serve to EFSA for the development of further guidance on the scientific requirements for health claims, as well as to the stakeholders for the proper design of human intervention studies aimed to substantiate such health claims.

Comparison of Platelet Reactivity in Black Versus White Patients With Acute Coronary Syndromes After Treatment With Ticagrelor

Ticagrelor, a potent platelet inhibitor, has primarily been studied in white patients. Platelet reactivity among black patients with acute coronary syndrome (ACS) on ticagrelor, however, is unknown. Our objective was to compare platelet reactivity in black versus white patients with ACS treated with ticagrelor. We conducted a prospective, pharmacodynamic study of 29 black patients with ACS treated with ticagrelor. Platelet reactivity was assessed at 1, 4, and 8 hours after a loading dose of ticagrelor 180 mg and at 30 days on a maintenance dose of ticagrelor 90 mg twice daily. Assays included light transmission aggregometry, VerifyNow P2Y12, and vasodilator-stimulated phosphoprotein. We provided comparison with a historical white cohort. Platelet reactivity among blacks with ACS on ticagrelor was similar to that in whites, except that blacks had lower values at 4 hours, 8 hours, and on maintenance therapy for light transmission aggregometry with 20 μmol/L adenosine diphosphate. Among blacks, high-on-treatment platelet reactivity for all 3 assays was uncommon at 1 hour and nonexistent at 4 hours, 8 hours, and while on maintenance therapy. Blacks preloaded with clopidogrel (n = 17) had significantly lower results of VerifyNow (64 ± 65 vs 198 ± 86, p <0.001) and vasodilator-stimulated phosphoprotein (12.8 ± 21.6 vs 58.9 ± 19.9, p <0.001) at 1 hour compared with those with no clopidogrel preload. In conclusion, among patients with ACS receiving ticagrelor, levels of platelet reactivity in blacks are similar to that in whites. This suggests that the cardiovascular benefits of ticagrelor observed in the platelet inhibition and patient outcomes (PLATO) trial are likely to be observed in blacks and whites.

Decreased platelet responsiveness to clopidogrel correlates with CYP2C19 and PON1 polymorphisms in atherosclerotic patients

Clopidogrel and aspirin are the most commonly used medications worldwide for dual antiplatelet therapy after percutaneous coronary intervention. However, clopidogrel hyporesponsiveness related to gene polymorphisms is a concern. Populations with higher degrees of genetic admixture may have increased prevalence of clopidogrel hyporesponsiveness. To assess this, we genotyped CYP2C19, ABCB1, and PON1 in 187 patients who underwent percutaneous coronary intervention. Race was self-defined by patients. We also performed light transmission aggregometry with adenosine diphosphate (ADP) and arachidonic acid during dual antiplatelet therapy. We found a significant difference for presence of the CYP2C19*2 polymorphism between white and non-white patients. Although 7% of patients had platelet resistance to clopidogrel, this did not correlate with any of the tested genetic polymorphisms. We did not find platelet resistance to aspirin in this cohort. Multivariate analysis showed that patients with PON1 and CYP2C19 polymorphisms had higher light transmission after ADP aggregometry than patients with native alleles. There was no preponderance of any race in patients with higher light transmission aggregometry. In brief, PON1 and CYP2C19 polymorphisms were associated with lower clopidogrel responsiveness in this sample. Despite differences in CYP2C19 polymorphisms across white and non-white patients, genetic admixture by itself was not able to identify clopidogrel hyporesponsiveness.

Platelet Function Analyzed by Light Transmission Aggregometry

Analysis of platelet function is widely used for diagnostic work-up in patients with increased bleeding tendency. During the last decades, platelet function testing has also been introduced for evaluation of antiplatelet therapy, but this is still recommended for research purposes only. Platelet function can also be assessed for hyper-aggregability, but this is less often evaluated. Light transmission aggregometry (LTA) was introduced in the early 1960s and has since been considered the gold standard. This optical detection system is based on changes in turbidity measured as a change in light transmission, which is proportional to the extent of platelet aggregation induced by addition of an agonist. LTA is a flexible method, as different agonists can be used in varying concentrations, but performance of the test requires large blood volumes and experienced laboratory technicians as well as specialized personal to interpret results. In the present chapter, a protocol for LTA is described including all steps from pre-analytical preparation to interpretation of results.

Effects of Firocoxib, Flunixin Meglumine, and Phenylbutazone on Platelet Function and Thromboxane Synthesis in Healthy Horses

OBJECTIVE

Determine the effects of nonsteroidal anti-inflammatory drugs (NSAID) on platelet function and thromboxane synthesis immediately after drug administration and following 5 days of NSAID administration in healthy horses.

STUDY DESIGN

Randomized cross-over study.

ANIMALS

Healthy adult horses (n=9; 6 geldings and 3 mares).

METHODS

Horses received either flunixin meglumine (1.1 mg/kg IV every 12 hours), phenylbutazone (2.2 mg/kg IV every 12 hours), or firocoxib (loading dose of 0.27 mg/kg IV on day 1, then 0.09 mg/kg IV every 24 hours for 4 days) for a total of 5 days. Blood samples were collected prior to drug administration (day 0), 1 hour after initial NSAID administration (day 1), and then 1 hour post-NSAID administration on day 5. Platelet function was assessed using turbidimetric aggregometry and a platelet function analyzer. Serum thromboxane B₂ concentrations were determined by commercial ELISA kit. A minimum 14 day washout period occurred between trials.

RESULTS

At 1 hour and 5 days postadministration of firocoxib, flunixin meglumine, or phenylbutazone, there was no significant effect on platelet aggregation or function using turbidimetric aggregometry or a platelet function analyzer. There was, however, a significant decrease in thromboxane synthesis at 1 hour and 5 days postadministration of flunixin meglumine and phenylbutazone that was not seen with firocoxib.

CONCLUSION

Preoperative administration of flunixin meglumine, phenylbutazone, or firocoxib should not inhibit platelet function based on our model. The clinical implications of decreased thromboxane B₂ synthesis following flunixin meglumine and phenylbutazone administration are undetermined.

The effects of clopidogrel and omeprazole on platelet function in normal dogs

Omeprazole is used concurrently with clopidogrel to reduce gastrointestinal adverse effects. In humans, the concurrent use of these two drugs can reduce the antiplatelet efficacy of clopidogrel. Our objective was to determine the effects of omeprazole and clopidogrel on platelet function in healthy dogs. A crossover study utilized turbidimetric aggregometry (ADP and collagen) and the PFA-100^® with the collagen/ADP cartridge to evaluate platelet function in eight healthy dogs during the administration of clopidogrel (1 mg/kg/24 h p.o.), omeprazole (1 mg/kg/24 h p.o.), and a combination of clopidogrel and omeprazole. Drug metabolite concentrations were also measured. Compared to pretreatment, on Days 3 and 5, with ADP as the agonist, there was a significant decrease in maximum amplitude on aggregometry for both clopidogrel and clopidogrel/omeprazole groups. The following revealed no significant differences between clopidogrel and clopidogrel/omeprazole groups when compared on Days 3 and 5: maximum amplitude on aggregometry with ADP or collagen agonists, and PFA-100^® closure times. When compared to the clopidogrel group, clopidogrel metabolite concentrations in the clopidogrel/omeprazole group were significantly higher on Days 3 and 5. The concurrent administration of omeprazole and clopidogrel in healthy dogs was associated with an increase in the plasma concentration of an inactive metabolite of clopidogrel, but does not significantly alter the antiplatelet effects of clopidogrel.

The Effects of Cyclosporine and Aspirin on Platelet Function in Normal Dogs

Background

Cyclosporine increases thromboxane synthesis in dogs, potentially increasing the thrombogenic properties of platelets.

Hypothesis/Objectives

Our hypothesis was that the concurrent administration of low‐dose aspirin and cyclosporine would inhibit cyclosporine‐associated thromboxane synthesis without altering the antiplatelet effects of aspirin. The objective was to determine the effects of cyclosporine and aspirin on primary hemostasis.

Animals

Seven healthy dogs.

Methods

A randomized, crossover study utilized turbidimetric aggregometry and a platelet function analyzer to evaluate platelet function during the administration of low‐dose aspirin (1 mg/kg PO q24h), high‐dose aspirin (10 mg/kg PO q12h), cyclosporine (10 mg/kg PO q12h), and combined low‐dose aspirin and cyclosporine. The urine 11‐dehydro‐thromboxane‐B₂ (11‐dTXB₂)‐to‐creatinine ratio also was determined.

Results

On days 3 and 7 of administration, there was no difference in the aggregometry amplitude or the platelet function analyzer closure time between the low‐dose aspirin group and the combined low‐dose aspirin and cyclosporine group. On day 7, there was a significant difference in amplitude and closure time between the cyclosporine group and the combined low‐dose aspirin and cyclosporine group. High‐dose aspirin consistently inhibited platelet function. On both days, there was a significant difference in the urinary 11‐dTXB₂‐to‐creatinine ratio between the cyclosporine group and the combined low‐dose aspirin and cyclosporine group. There was no difference in the urinary 11‐dTXB₂‐to‐creatinine ratio among the low‐dose aspirin, high‐dose aspirin, and combined low‐dose aspirin and cyclosporine groups.

Conclusions and Clinical Importance

Low‐dose aspirin inhibits cyclosporine‐induced thromboxane synthesis, and concurrent use of these medications does not alter the antiplatelet effects of aspirin.

Effects of thermosensitive poly(N-isopropylacrylamide) on blood coagulation

Thermosensitive poly(N-isopropylacrylamide) (PNIPAM), hydrophilic below its lower critical solution temperature (LCST) of 32 °C and hydrophobic above it, has been widely used as a drug and gene delivery system with intelligent temperature-responsivity. In this work, we studied the in vitro and in vivo effects of PNIPAM on blood coagulation function, and further investigated the interactions of PNIPAM with coagulation-related blood components at cellular and molecular levels. Overall, PNIPAM demonstrated anti-coagulant activity in vitro and in vivo. Specifically, PNIPAM displayed cell membrane activity and caused red blood cell (RBC) aggregation at higher concentrations, but did not impair the membrane integrity of RBCs. PNIPAM inhibited platelet aggregation selectively through the arachidonic acid pathway. PNIPAM also disturbed the structure and conformation of fibrinogen. By contrast, PNIPAM did not affect the activity of the clotting factors in vitro but inhibited the activity of the clotting factors in vivo. The interaction of PNIPAM with plasma proteins was confirmed by a plasma protein absorption study with proteomics analysis. These findings provide key information on the hemocompatibility evaluation and antithrombotic applications of PNIPAM.

Current status and future prospects for platelet function testing in the diagnosis of inherited bleeding disorders

Platelets play a crucial role in haemostasis by preventing bleeding at the site of vascular injury. Several defects in platelet morphology and function have been identified and described over the years. Although a range of methodologies is available to assess platelet function, a significant proportion of subjects with bleeding symptoms and normal coagulation parameters still appear to have normal results on platelet function testing. This might suggest that the reason for bleeding is multifactorial and is due to a combination of several minor defects in platelet function and/or other parts of the haemostatic system or might indicate that the currently available platelet function tests do not provide optimal diagnostic power. This review will summarize the established platelet function tests used for diagnosing inherited platelet abnormalities in adults and children, and discuss the newly developed methodologies as well as unmet challenges and potential areas for further improvement in this field.

High on-treatment platelet reactivity in patients with ischemic cerebrovascular disease: assessment of prevalence and stability over time using four platelet function tests

High on-treatment platelet reactivity (HTPR), referred to as a higher than expected platelet reactivity in patients under antiplatelet therapy, could influence outcome in cerebrovascular disease (CVD), but its prevalence and its stability over time is uncertain. Platelet reactivity was assessed in 18 patients with ischemic stroke/transient ischemic attack (TIA) 7 days (D7) and 90 days (D90) after prescription of clopidogrel, using four methods: light transmission aggregometry with 5 μmol/l ADP (LTA-ADP), vasodilator-stimulated phosphoprotein (VASP), Verify Now P2Y12 and platelet function analyzer (PFA) P2Y. HTPR was defined as LTA-ADP more than 46%; PFA-100-P2Y closure time less than 106 s; VerifyNow P2Y12, PRU greater than 235, VASP, PRI greater than 50%. Patients displayed, both at D7 and D90, a marked inhibition of platelet reactivity towards ADP in all tests as compared with reference levels. Correlations between the results obtained with all the tests at D7 and D90 and between measurements on each day in each test were low-to-moderate. The prevalence of HTPR for all the tests was 40% at D7 and 42% at D90. There was a moderate degree of agreement (k statistic < 0.5) between tests with regard to categorizing patients as HTPR/No-HTPR (D7 and D90). The on-clopidogrel platelet reactivity phenotype, HTPR/No-HTPR, remained stable in 55-72% of patients, depending on the test. A high prevalence of HTPR is found among CVD patients treated with clopidogrel and this platelet reactivity phenotype remains over time. There is poor agreement between the different platelet function tests for categorizing the platelet reactivity phenotype in these patients. The new PFA-100 P2Y equals other platelet function assays for evaluating HTPR in CVD.

Sex differences of leukocyte-platelet interactions and on-treatment platelet reactivity in patients with atherosclerosis

OBJECTIVE

To investigate differences of platelet activation and on-treatment residual platelet reactivity between female and male patients with atherosclerotic cardiovascular disease.

METHODS

We compared P-selectin expression, activated glycoprotein (GP) IIb/IIIa and leukocyte-platelet aggregates (LPA) by flow cytometry between 110 female and 206 male patients undergoing angioplasty and stenting. On-treatment residual platelet reactivity was determined by two test systems.

RESULTS

The expression of P-selectin and GPIIb/IIIa did not differ significantly between female and male patients. In contrast, females showed a significantly more pronounced formation of LPA in vivo, in response to thrombin receptor-activating peptide-6 and in response to adenosine diphosphate. Further, high LPA were seen more frequently in female patients. Finally, protease-activated receptor (PAR)-1 mediated platelet reactivity by both assays was significantly higher in females.

CONCLUSION

Female sex is associated with a more pronounced formation of LPA and increased PAR-1 mediated platelet reactivity in atherosclerotic cardiovascular disease.