Residual Platelet Aggregation Research Articles

Towards a greater understanding of reduced response to aspirin in children with congenital heart disease post-cardiac surgery using immature platelet fraction

ObjectiveA high platelet turnover rate may produce a population of platelets that confers an inadequate response to aspirin. We aimed to investigate the relationship between residual platelet aggregation and platelet turnover in paediatric cardiology patients on aspirin monotherapy by evaluating the fraction of immature platelets as a marker for turnover and secondly to test the predictive value of the immature platelet fraction (IPF) to classify patients as responsive or non-responsive to aspirin. MethodsSixty patients divided into two age categories (≤90 days, >90 days of age) were included in this prospective observational study. Patients were then stratified into tertiles using their IPF level. Platelet studies included thromboelastography with platelet mapping (TEGPM). ResultsThe overall incidence of ‘inadequate response to aspirin’ was 38 % in our patient cohort recently post-cardiac surgery a consequence that warrants further study. The frequency of inadequate response to aspirin was higher in the upper tertile of IPF when compared to the lower tertile, (88 %) versus (4 %) respectively (p < 0.05). The ‘cut off’ for IPF was determined to be 3.9 % with a sensitivity of 95.7 %, and a specificity of 92.9 % (area under the curve of 0.955 [CI 0.896–1.014, p < 0.05]). ConclusionThis study demonstrates that inadequate response to aspirin occurs in approximately 38 % of patients undergoing specific high-risk congenital cardiac procedures using the dosing practice of a national centre. This study supports the hypothesis that an elevated platelet turnover may result in aspirin being less effective in patients who are recently post cardiac surgery. These data are of direct translational relevance.

Pharmacokinetic and pharmacodynamic profiles of a novel phospholipid-aspirin complex liquid formulation and low dose enteric-coated aspirin: results from a prospective, randomized, crossover study

Low dose enteric-coated aspirin (EC-ASA) is routinely used for secondary cardiovascular event prevention. However, absorption of EC tablets is poor, which can result in subtherapeutic antiplatelet effects. Phospholipid-aspirin liquid filled capsules (PL-ASA) are a novel FDA-approved immediate-release formulation designed to reduce gastrointestinal (GI) injury by limiting direct contact with the stomach lining. We compared the pharmacokinetic (PK) and pharmacodynamic (PD) profiles of PL-ASA versus EC-ASA at a low dose. This randomized, open-label, crossover study assessed PK and PD following a single 81-mg dose of PL-ASA versus EC-ASA under fasting conditions in 36 volunteers without cardiovascular disease between 18 and 75 years of age. Volunteers were randomly assigned 1:1 to either PL-ASA then EC-ASA or vice versa with a minimum 14-day washout. Assessments included PK parameters for acetylsalicylic acid and salicylic acid, platelet aggregation in response to arachidonic acid (AA), and serum thromboxane B2 (TxB2) assessments over 24 h. PL-ASA was rapidly absorbed. PL-ASA reached Tmax 3 h earlier (1.01 vs. 4.00 h, p < 0.0001), with almost double the Cmax (720 vs. 368 ng/mL, p < 0.0001) and overall 44% higher exposure of acetylsalicylic acid (AUC0-t: 601 vs. 416 h*ng/mL, p = 0.0013) compared with EC-ASA. Within 1 h of dosing, PL-ASA achieved significantly lower residual platelet aggregation, which persisted for the full 24 h (median AA-LTA was 47% with PL-ASA vs. 80.5% with EC-ASA; p = 0.0022 at hour-24). Treatment with PL-ASA also resulted in significantly lower serum TxB2 concentrations at each time point compared with EC-ASA (all p-values < 0.05). PL-ASA resulted in faster and more complete aspirin absorption paralleled by more prompt and potent platelet inhibition compared with EC-ASA after a single 81 mg dose. PL-ASA represents an attractive novel aspirin formulation for the secondary prevention of cardiovascular events.Clinical Trial Registration ClinicalTrials.gov identifier: NCT04811625.

Impact of body size on platelet function in patients with acute coronary syndrome on dual antiplatelet therapy

IntroductionPatients undergoing acute percutaneous coronary intervention receive dual antiplatelet therapy for secondary prevention. Recurrent myocardial infarction or bleedings are possibly due to under- or overdosing of antiplatelet therapy in relation to body size. MethodsWe correlated residual platelet aggregation with body mass index, body surface area, lean body mass and blood volume in 220 patients on prasugrel (n = 121) or ticagrelor (n = 99). ResultsPlatelet aggregation outside the recommended window was recorded in 85 patients, but not correlated with any of the body indices. ConclusionBody size does not affect platelet response to prasugrel or ticagrelor at the guideline-recommended fixed dosages.

Prognostic implication of systemic inflammatory state on antiplatelet effect in patients after percutaneous coronary intervention for ST-elevation myocardial infarction: A retrospective cohort study.

Patients with ST-elevation myocardial infarction (STEMI) show an inflammatory response. The level of systemic inflammation is known to affect platelet aggregation function and antiplatelet therapy, which leads to different clinical prognosis. This study aims to evaluate the prognostic implication of systemic inflammatory state in patients with STEMI undergoing percutaneous coronary intervention.In this study, 203 patients with STEMI who underwent primary percutaneous coronary intervention were included. The patients were divided into 3 groups based on the inflammation levels assessed by tertiles of high-sensitivity C-reactive protein (hs-CRP) level on admission. Platelet aggregation evaluation was performed by residual platelet reactivity, which was assessed by the value of residual ADP-induced light transmittance aggregometry after clopidogrel maintenance dose therapy and in follow-up. Major adverse cardiac events (MACEs) were defined to include all-cause mortality, cardiovascular mortality, reinfarction, target vessel revascularization (TVR), cardiopulmonary resuscitation, advanced heart failure, ventricular fibrillation or ventricular tachycardia, and atrioventricular block.Levels of white blood cell was observed to be significantly higher at high tertile levels. Residual ADP-induced platelet aggregation was significantly higher at high tertile levels after clopidogrel maintenance dose therapy and in follow-up. Multivariate analysis identified that reperfusion time, alanine aminotransferase, platelet count, ADP-induced light transmittance aggregometry in follow-up and hs-CRP was independent predictors of MACEs. Platelet inhibition function of clopidogrel decreases progressively at different inflammation levels. The different levels of hs-CRP were demonstrated to be associated with MACEs at follow-up assessments.The presence of hs-CRP was not only significantly associated with platelet inhibition function, but was also a prognostic marker in STEMI.

High residual platelet aggregation in patients with coronary artery disease: a new methodological approach to detection

Aim. To develop a new methodological approach to assessment of collagen-induced platelet aggregation in patients with coronary artery disease (CAD) and to determine the quality of various methods for detecting high residual platelet reactivity (HRPR) to predict the risk of myocardial perfusion disturbance. Materials and methods. 36 patients (10 men and 26 women) aged 41–83 years and having stable CAD were examined. All patients had been undergoing continuous antiaggregation therapy for 6 months. We evaluated platelet aggregation using a laser analyzer with collagen as an aggregation inducer by the standard method 1 and our own patented method 2. The degree of platelet aggregation (%) and the size of aggregates in relative units (r.u.) in platelet-rich plasma were estimated. Myocardial perfusion scintigraphy with 99mTc-methoxy-isobutylisonitrile was performed according to a two-day stress-rest protocol. The summed stress score (SSS) values were used for analysis. SSS &lt; 4 was regarded as normal myocardial perfusion. Results . The degree of platelet aggregation according to method 1 was 12 (5; 64)%, the aggregate size was 3 (2; 7) r.u. The degree of platelet aggregation according to method 2 was 44 (13; 78)%, and the aggregate size was 5 (4; 8) r.u. Method 2 allowed to diagnose the presence of myocardial ischemia with an aggregation degree ≥ 44.9% with sensitivity of 84% and specificity of 92% (area under the curve (AUC) = 0.89; p &lt; 0.0001; odds ratio (OR) 2.18; 95% confidence interval (CI) 0.57–0.98) and an increase in aggregate size ≥ 4.80 r.u. with sensitivity of 84% and specificity of 84% (AUC = 0.95; p &lt; 0.00001; OR 5.83; 95% CI 0.72–0.99). Conclusion. In patients with CAD, detection of high rates of collagen- induced platelet aggregation using the patented technique is associated with the risk of impaired myocardial perfusion. The developed new methodological approach to detection of HRPR allowed to determine high risk of atherothrombotic complications in additional 22% of the examined patients.

Persistent long-term platelet activation and endothelial perturbation in women with Takotsubo syndrome

BackgroundTakotsubo (TTS) syndrome is an acute cardiac condition characterized by transient and reversible left ventricle dysfunction that mainly affects postmenopausal women. Catecholamine burst is the most accredited mechanism underpinning TTS onset and leading to endothelial dysfunction and platelet activation. Even if the use of low dose acetylsalycilic acid (ASA) in this clinical setting is based on both clinical presentation and unfavorable long-term prognosis, its efficacy has been recently challenged. AimThis study was designed to assess endothelial function, residual thromboxane formation and platelet aggregation in TTS women on low-dose ASA treatment at long-term follow-up. MethodsTwenty-eight females with previously diagnosis of TTS syndrome were enrolled. Data were compared to those obtained from 23 coronary artery disease (CAD) women with a history of acute myocardial infarction, and 26 control subjects with no TTS or clinically evident CAD. Psychological and clinical profile were assessed in all study groups at the enrollment. Main metabolites involved in L-arginine/nitric oxide pathway, urinary prostacyclin, serum and urine thromboxane metabolites were measured by LCMS/MS methods. Thrombomodulin levels were quantified using an ELISA kit, and platelet aggregation, carried out on platelet rich-plasma, was induced by ADP or by epinephrine (EPI), norepinephrine (NORE) and TRAP-6, alone or in association with ADP and evaluated by Born’s method. ResultsIn TTS women an endothelial derangement, characterized by reduced citrulline production and increased thrombomodulin concentration, with no perturbation in prostacyclin levels, was evidenced. In addition, despite ASA treatment, TTS displayed a higher residual thromboxane formation, in parallel with an enhanced platelet response to compared to CAD. ConclusionsOur study highlighted the presence of endothelial perturbation in TTS patients even at long-term from the index event. The residual thromboxane production and platelet aggregation still leave open the question about the use of low dose ASA in this clinical setting.

Residual platelet reactivity in low-dose aspirin-treated patients with class 1 obesity

BackgroundRecent data suggest a decreased clinical efficacy of low-dose aspirin in patients weighing ≥70 kg. We therefore investigated the impact of body weight and class 1 obesity on thromboxane generation and platelet reactivity to arachidonic acid (AA) in 316 patients on dual antiplatelet therapy following angioplasty and stenting. MethodsPlatelet surface expression of P-selectin and activated glycoprotein (GP) IIb/IIIa in response to AA were determined by flow cytometry as sensitive markers of platelet activation. Urinary 11-dehydro-thromboxane B2 (11-dehydro-TXB2) and serum TXB2 were measured by commercially-available immunoassays. On-treatment residual AA-inducible platelet aggregation was assessed by light transmission aggregometry (LTA), the VerifyNow aspirin assay and multiple electrode aggregometry (MEA). ResultsClass 1 obesity was independently associated with increased platelet surface expression of P-selectin and activated GPIIb/IIIa, but not with urinary 11-dehydro-TXB2, serum TXB2, and on-treatment platelet aggregation by all assays. Of all measured parameters, only MEA showed a positive albeit very weak correlation with body weight (r = 0.13, p = 0.02). Furthermore, the results of all tests did not differ significantly between patients without and with a body weight ≥ 70 kg. After adjustment for age and diabetes by multivariate logistic regression analysis, the frequency of high-on treatment residual TXB2 generation and high on-treatment residual AA-inducible platelet reactivity (HRTG/HRPR) did not differ significantly between obese and non-obese patients. ConclusionClass 1 obesity is associated with enhanced platelet activation in response to AA in patients on dual antiplatelet therapy. This seems to be independent of cyclooxygenase-1 inhibition and does not translate into HRTG/HRPR.

Resistance to Antiplatelet Therapy Is Associated With Symptoms of Cerebral Ischemia in Carotid Artery Disease.

Background:Platelet inhibitory therapy is prescribed to prevent arterial thromboembolism in patients with atherosclerotic disease. Although taken by millions of people, around 30% are resistant to the treatment they are being prescribed.Aims:To determine whether symptoms of cerebral ischemia, or pre-operative cerebral emboli, in patients admitted for a carotid endarterectomy were associated with resistance to aspirin or clopidogrel.Methods:Venous blood from 133 patients immediately before carotid endarterectomy (CEA) was analyzed for resistance to aspirin and clopidogrel by multiplate impedance aggregometry. The number of emboli/hour entering the ipsilateral middle cerebral artery was counted by transcranial Doppler (TCD) on the day before surgery in 33 of these patients.Results:Resistance was found in 21 (26.3%) of 100 patients taking aspirin and 14 (42%) of 33 taking clopidogrel. Mean (sd) residual platelet aggregation was significantly higher at 41.9(32) Au in patients who had suffered recent symptoms of cerebral ischemia compared with 30.8(16) Au in asymptomatic patients (p = 0.012). Residual platelet aggregation also correlated significantly with the number of emboli/hour counted by TCD in the ipsilateral middle cerebral artery (r = 0.45, p = 0.009).Conclusion:Antiplatelet resistance was associated with the frequency of cerebral emboli and recent symptoms of cerebral ischemia in patients with carotid disease. Definitive clinical studies are needed to explore whether testing for antiplatelet resistance should be undertaken routinely in patients starting platelet inhibitory therapy for cardiovascular disease.

MRP4 over-expression has a role on both reducing nitric oxide-dependent antiplatelet effect and enhancing ADP induced platelet activation

The impact of inhibition of multidrug resistance protein 4 (MRP4) on nitric oxide (NO) resistance and on ADP-induced platelet aggregation is unknown. The aim of this investigation was to verify whether platelet NO resistance correlates with MRP4 expression and evaluate whether this can be reduced by in vitro MRP4 inhibition mediated by cilostazol. Moreover, we assessed if inhibition of MRP4-mediated transport reduces ADP-induced platelet reactivity. The inhibitory effect of sodium nitroprusside (SNP), a NO-donor that enhances cyclic guanosine monophosphate (cGMP) cytosolic concentration, was assessed in platelets obtained from aspirin treated patients and in a control population. The inhibitory effect of SNP was evaluated by ADP-induced aggregation in SNP-treated platelets. The impact of MRP4 on ADP-induced platelet aggregation was performed in high on aspirin residual platelet reactivity (HARPR) patients and compared to healthy volunteers (HV), and a control cohort (CTR). In aspirin-treated patients with high levels of MRP4, reduced SNP inhibition was found compared to those with low levels of MRP4. MRP4 inhibition by cilostazol significantly reduced ADP-induced platelet aggregation in HARPR population, and to a lesser extent in HV and CTR populations. In conclusion, cilostazol can mitigate the hyper-reactive platelet phenotype of HARPR patients by reducing residual ADP-induced platelet aggregation and increasing NO-dependent endothelial antiplatelet effects.

Serum uric acid level negatively correlated with the prevalence of clopidogrel low response in patients undergoing antiplatelet treatment with aspirin and clopidogrel

Background and aimsIt has been reported that elevated serum uric acid (SUA) is related to inflammation and potentially to platelet hyper-reactivity. However, the relationship between elevated SUA and residual platelet reactivity is uncertain in patients on dual antiplatelet treatment (DAPT) with aspirin and clopidogrel. Methods and resultsA cross-sectional cohort study was conducted on 2569 patients undergoing DAPT with aspirin and clopidogrel. Patients' SUA levels, residual platelet aggregation, routine blood tests and clinical characteristics were recorded. The relationship between SUA level and residual platelet aggregation was assessed by correlation analysis, and the relationship between SUA level and the prevalence of clopidogrel low response (CLR) was assessed by multivariate logistic regression analysis. Adenosine diphosphate (ADP) induced platelet aggregation (PLADP) was higher in normal-SUA group than that in hyperuricemia group [30(21, 40) % vs. 27(19, 39) %, p = 0.032]. No significant difference was found for arachidonic acid (AA) induced platelet aggregation (PLAA) between the two groups [4(2, 5) % vs. 3(2, 5) %, p = 0.557]. The correlation between SUA and PLADP was statistically significant(r = −0.115, p < 0.001), while that between SUA and PLAA was non-significant (r = −0.012, p = 0.643). Using the multivariate logistic regression analysis, higher SUA concentration was associated with a decreased risk of clopidogrel low response (CLR) (OR [95%CI] = 0.997 [0.995–0.999], p = 0.001). ConclusionThis is the largest study to date showing that in patients receiving DAPT with aspirin and clopidogrel, SUA is independently and negatively associated with the prevalence of clopidogrel low response. Clinical trial registrationURL: http://www.clinicaltrials.gov Unique Identifier: NCT01955200.

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

PurposeSince 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).MethodsPlatelet 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.ResultsADP-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).ConclusionTicagrelor inhibits TLR-1/2 and PAR mediated platelet activation in ACS patients more strongly than prasugrel.

Effects of the rs2244613 polymorphism of the CES1 gene on the antiplatelet effect of the receptor P2Y12 blocker clopidogrel.

Background The aim of this study was to evaluate the association of the carriage of the rs2244613 polymorphism of the CES1 gene with clopidogrel resistance as well as to evaluate the effectiveness of antiplatelet therapy in the carriers of this marker who have had acute coronary syndrome (ACS). This study also analyzes the procedure of percutaneous coronary intervention and compares the rs2244613 carrier rate between patients with ACS and healthy participants. Methods The study involved 81 patients diagnosed with ACS and 136 conditionally healthy participants. The optical detection of platelet agglutination by VerifyNow was employed to measure residual platelet reactivity in patients with ACS. The rs2244613 polymorphism was determined using real-time polymerase chain reaction. Results According to the results, the AA genotype of the rs2244613 polymorphism of the CES1 gene was detected in 37 patients (45.6%), the CA genotype in 42 patients (51.8%) and the CC genotype in 2 patients (2.6%). The level of residual platelet reactivity in rs2244613 carriers was higher compared with patients who did not have this allelic variant: 183.23 PRU ± 37.24 vs. 154.3 PRU ± 60.36 (p = 0.01). The frequencies of the minor allele C were 28.4% and 28.3% in patients with ACS and healthy participants, respectively. The results of the linear statistical model PRU due to CES1 genotype were as follows: df = 1, F = 6.96, p = 0.01). The standardized beta was 0.285 (p = 0.01) and R2 was 0.081. However, we also added CYP2C19*2 and *17 into the linear regression model. The results of the model were as follows: df = 3, F = 5.1, p = 0.003) and R2 was 0.166. Conclusions We identified a statistically significant correlation between the carriage of the rs2244613 polymorphism of the CES1 gene and the level of residual platelet aggregation among patients with ACS and the procedure of percutaneous coronary intervention.

ASSOCIATION OF PLATELET-DERIVED MICROVESICLES WITH HIGH ON-TREATMENT PLATELET REACTIVITY IN CONVALESCENT ISCHEMIC STROKE PATIENTS TREATED WITH ACETYLSALICYLIC ACID

Elevated concentrations of platelet-derived microvesicles are found in cerebrovascular diseases. The impact of acetylsalicylic acid on these microvesicles remains inconsistent, despite its well-established effect on platelet aggregation. High residual platelet aggregation is defined as high on-treatment platelet reactivity, while “treatment failure” is the occurrence of vascular events despite antiplatelet treatment. The aim of this study was to determine whether the antiaggregatory effect of acetylsalicylic acid correlates with platelet-derived microvesicles in convalescent ischaemic stroke patients and cardiovascular risk factor controls as well as to evaluate the association between high on-treatment platelet reactivity and recurrent vascular events with the studied platelet-derived microvesicle parameters. The study groups consisted of 76 convalescent stroke patients and 74 controls. Total platelet-derived microvesicles, annexino-positive microvesicles number, and platelet-derived microvesicles with surface expression of proinflammatory (CD40L, CD62P, CD31) and procoagulant (PS, GPIIb/IIIa) markers were characterized and quantified using flow cytometry. Cyclooxygenase-1-specific platelet responsiveness, with whole blood impedance platelet aggregation under arachidonic acid stimulation and the serum concentration of thromboxane B2, were evaluated. Neither acetylsalicylic acid intake nor modification of its daily dose caused statistically significant differences in the studied microvesicle parameters. Additionally, no statistically significant differences in the studied microvesicle parameters were revealed between high on-treatment platelet reactivity and non-high on-treatment platelet reactivity subjects in either study subgroup. However, elevated concentrations of PAC-1+/CD61+, CD62P+/CD61+ and CD31+/CD61+ microvesicles were found in stroke patients with treatment failure, defined in this study as a recurrent vascular events in a one-year follow-up period. This study revealed no relationship between circulating microvesicle number and platelet aggregation. The procoagulant and proinflammatory phenotype of circulating platelet-derived microvesicles might contribute to acetylsalicylic acid treatment failure.

Impact of CYP2C19 Polymorphism on Antiplatelet Potency of Prasugrel 5 and 10 mg Daily Maintenance

Background: Whether genetic polymorphisms (GP) impact residual platelet aggregation (RPA) following prasugrel is unclear, especially during maintenance phase. We assessed the influence of CYP2C19 GP carriers on RPA in the prospective observational cohort study. Methods and Results: All post-stent patients (n = 206) received prasugrel 60 mg loading and either 5 or 10 mg daily maintenance with aspirin100 mg. RPA levels by light transmission aggregometry (LTA), multiplate electrode aggregometry (MEA), and VerifyNow (P2Y12 reaction units, PRU) with CYP2C19 GP were measured simultaneously. Demographics and clinical characteristics were not useful for predicting response after prasugrel. GP carriers exhibited higher RPA (PRU: p = 0.001, LTA: p = 0.001, MEA: p = 0.023) than noncarriers. CYP2C19 carriers had higher RPA for 5 mg (n = 35; LTA: p = 0.043, MEA: p = 0.023) and reached significance for 10 mg (n = 27; LTA: p = 0.001, PRU: p = 0.001) prasugrel. When divided into extensive, intermediate, and poor metabolizers, all exhibited statistical differences among the 3 groups (LTA: 14.9 ± 12.3%, 22.6 ± 14.9%, 22.9 ± 15.6%, p = 0.002; PRU: 104.1 ± 70.8%, 141.8 ± 78.0%, 151.0 ± 84.8%, p = 0.003; MEA: 19.7 ± 8.9%, 24.4 ± 12.2%, 28.1 ± 14.7%, p = 0.002). Conclusion: CYP2C19 GP impacts RPA during maintenance phase prasugrel in Korean outpatients. This effect is consistent for both of the approved prasugrel doses potentially affecting long-term outcomes including bleeding risks. However, the clinical utility of these findings is still uncertain, and requires more evidence from larger randomized trials beyond East Asians.

Response to aspirin therapy in patients with myeloproliferative neoplasms depends on the platelet count

Patients with myeloproliferative neoplasms (MPN) are at an increased risk of thrombotic events even during antiplatelet therapy with aspirin. In the current study, we sought to investigate the association of the platelet count with the inhibitory potential of antiplatelet therapy in MPN. We determined arachidonic acid (AA)- and adenosine diphosphate (ADP)-inducible platelet reactivity by multiple electrode aggregometry in 93 patients with essential thrombocythemia, polycythemia vera or primary myelofibrosis. In patients without aspirin therapy (n = 44), the platelet count did not correlate with platelet aggregation. In aspirin-treated patients (n = 49), we observed a moderate correlation of residual AA-inducible platelet aggregation with the platelet count (r = 0.49; P < 0.001). Further, patients with high on-treatment residual platelet reactivity to AA (HRPR AA) had a significantly higher platelet count than patients without HRPR AA (547 × 109/L [340 - 644 × 109/L] vs 358 × 109/L [242 - 501 × 109/L], P = 0.01). Receiver-operating characteristic curve analysis revealed a platelet count of ≥317 × 109/L as best threshold to distinguish between patients without and with HRPR AA (area under the curve: 0.73). After adding the direct ADP P2Y12 inhibitor cangrelor to blood samples from all 93 patients in vitro, residual ADP-inducible platelet reactivity correlated weakly with the platelet count (r = 0.26, P = 0.01), but the platelet count did not differ significantly between patients with and without HRPR ADP (396 × 109/L [316 - 644 × 109/L] vs 340 × 109/L [241 - 489 × 109/L]; P = 0.2). In conclusion, our findings suggest that the extent of platelet inhibition by aspirin in patients with MPN at least in part depends on their individual platelet count.

How does measurement of platelet P-selectin compare with other methods of measuring platelet function as a means of determining the effectiveness of antiplatelet therapy?

Measurement of P-selectin on activated platelets as a means of measuring platelet function utilizing the technology described here has the advantage of not requiring immediate access to specialist equipment and expertise. Blood samples are activated, fixed, stored, and transported to a central laboratory for flow cytometric analysis. Here we have compared P-selectin with other more traditional approaches to measuring platelet function in blood and/or platelet-rich plasma (PRP) from patients with acute coronary syndromes on treatment for at least 1 month with either aspirin and clopidogrel or aspirin with prasugrel. The comparators were light transmission aggregometry (LTA), VerifyNow and Multiplate aggregometry (for determining the effects of aspirin) and LTA, VerifyNow and Multiplate together with the BioCytex VASP phosphorylation assay (for the P2Y12 antagonists). The P-selectin Aspirin Test revealed substantial inhibition of platelet function in all but three of 96 patients receiving aspirin with clopidogrel and in none of 51 patients receiving aspirin and prasugrel. The results were very similar to those obtained using LTA. There was only one patient with high residual platelet aggregation and low P-selectin expression. The same patients identified as “non-responders” to aspirin also presented with the highest residual platelet activity as measured using the VerifyNow system, although not quite as well separated from the other values. With the Multiplate test only one of these patients clearly stood out from the others. The results obtained using the P-selectin P2Y12 Test in 102 patients taking aspirin and clopidogrel were similar to the more traditional approaches in that a wide scatter of results was obtained. Generally, high values seen with the P-selectin P2Y12 Test were also high with the LTA, VerifyNow, Multiplate, and BioCytex VASP P2Y12 Tests. Similarly, low residual platelet function using the P2Y12 test was seen irrespective of the testing procedure used. However, there were differences in some patients. Prasugrel was always more effective than clopidogrel in inhibiting platelet function with none of 56 patients (P-selectin and VerifyNow), only 2 of 56 patients (Multiplate) and only 3 of 56 patients (Biocytex VASP) demonstrating high on-treatment residual platelet reactivity (HRPR) defined using previously published cut-off values. The exception was LTA where there were 11 of 56 patients with HRPR. It remains to be seen which experimental approach provides the most useful information regarding outcomes after adjusting therapies in treated patients.

Direct factor IXa inhibition with the RNA-aptamer pegnivacogin reduces platelet reactivity in vitro and residual platelet aggregation in patients with acute coronary syndromes.

Residual platelet reactivity is a predictor of poor prognosis in patients with acute coronary syndromes (ACSs) undergoing percutaneous coronary intervention. Thrombin is a major platelet activator and upon initiation of the coagulation cascade, it is subsequently produced downstream of factor IXa, which itself is known to be increased in ACS. Pegnivacogin is a novel RNA-aptamer based factor IXa inhibitor featuring a reversal agent, anivamersen. We hypothesized that pegnivacogin could reduce platelet reactivity. Whole blood samples from healthy volunteers were incubated in vitro in the presence and absence of pegnivacogin and platelet reactivity was analysed. In addition, platelet aggregometry was performed in blood samples from ACS patients in the RADAR trial featuring the intravenous administration of pegnivacogin as well as reversal by anivamersen. In vitro, pegnivacogin significantly reduced adenosine diphosphate-induced CD62P-expression (100% vs. 89.79±4.04%, p=0.027, n=9) and PAC-1 binding (100% vs. 83.02±4.08%, p=0.010, n=11). Platelet aggregation was reduced (97.71±5.30% vs. 66.53±9.92%, p=0.013, n=10) as evaluated by light transmission aggregometry. In the presence of the RNA-aptamer reversal agent anivamersen, neither CD62P-expression nor platelet aggregation was attenuated. In patients with ACS treated with aspirin and clopidogrel, residual platelet aggregation was significantly reduced 20 min after intravenous bolus of 1 mg/kg pegnivacogin (100% versus 43.21±8.23%, p=0.020). Inhibition of factor IXa by pegnivacogin decreases platelet activation and aggregation in vitro. This effect was negated by anivamersen. In ACS patients, platelet aggregation was significantly reduced after intravenous pegnivacogin. An aptamer-based anticoagulant inhibiting factor IXa therefore might be a promising antithrombotic strategy in ACS patients.

Platelet reactivity in human immunodeficiency virus infected patients on dual antiplatelet therapy for an acute coronary syndrome: the EVERE2ST-HIV study.

To explore platelet reactivity on dual antiplatelet therapy (DAPT) of acute coronary syndrome (ACS) patients infected with HIV. Acute coronary syndrome patients infected with HIV (n = 80) were matched to ACS patients without HIV (n = 160) on age, sex, diabetes, and DAPT (aspirin 100%, clopidogrel 68%, prasugrel 31%, ticagrelor 1%). Platelet reactivity was evaluated after ACS (>30 days) by measuring residual platelet aggregation (RPA) to aspirin and to P2Y12 inhibitors with light transmission aggregometry (LTA), VerifyNow aspirin assay (ARU), and P2Y12 assay (PRU) and with the VASP platelet reactivity index (VASP-PRI). Proportion of patients with high residual platelet reactivity (HPR) was evaluated. HIV-infected ACS patients had higher levels of platelet reactivity in response to P2Y12 inhibitors (RPA: 23.8 ± 2.7% vs. 15.3 ± 1.3%; P = 0.001; PRU: 132 ± 10 vs. 107.4 ± 6.6; P = 0.04; and VASP-PRI: 45.2 ± 2.6% vs. 32.0 ± 2.0%; P < 0.001) and to aspirin (RPA: 3.6 ± 1.5% vs. 0.4 ± 0.1%; P = 0.004 and ARU: 442 ± 11 vs. 407 ± 5; P = 0.002) compared with non-HIV. HIV-infection was independently associated with increased platelet reactivity regardless of the test used (RPA: P = 0.005; PRU: P < 0.001 and VASP-PRI: P < 0.001) and a higher proportion of HPR (OR = 7.6; P < 0.001; OR = 2.06; P = 0.06; OR = 2.91; P = 0.004, respectively) in response to P2Y12 inhibitors. Similar results were found with aspirin. Protease inhibitors use was associated with increased platelet reactivity and higher rate of HPR. Acute coronary syndrome patients infected with HIV have increased levels of platelet reactivity and higher prevalence of HPR to P2Y12 inhibitors and aspirin than non-HIV patients. These results could provide potential explanations for the observed increase risk of recurrent ischemic events in the HIV-infected population.

Perioperative management and monitoring of antiplatelet agents: a focused review on aspirin and P2Y12 inhibitors.

Platelets play pivotal roles in hemostasis as well as pathological arterial thrombosis. The combination of aspirin and a P2Y12 inhibitor has become the mainstay therapy in the ageing population with cardiovascular conditions, particularly during and after percutaneous coronary intervention. A number of novel P2Y12 inhibitors has become available in the recent years, and they markedly vary in pharmacokinetic and pharmacodynamic properties. Perioperative physicians today face a challenge of preventing hemorrhage due to platelet inhibitors, while minimizing thrombotic risks. There are several point-of-care platelet function tests available in the peri-procedural assessment of residual platelet aggregation. However, these platelet function tests are not standardized in terms of sample processing, agonist type and potency as well as methods of detecting platelet activity. Understanding the differences in pharmacological properties of antiplatelet agents, principles of platelet function tests, and pertinent hemostatic strategies may be useful to anesthesiologists and intensivists who manage perioperative issues associated with antiplatelet agents. The objectives of this review are: 1) to discuss clinical data on aspirin and P2Y12 inhibitors relating to perioperative bleeding, 2) to outline different features of point-of-care platelet function tests, and 3) to discuss therapeutic options for the prevention and treatment of bleeding associated with antiplatelet agents.

Impact of CYP2C19 Variants on Clinical Efficacy of Clopidogrel and 1-Year Clinical Outcomes in Coronary Heart Patients Undergoing Percutaneous Coronary Intervention

The impact of pharmacogenetic variants of cytochrome P450 2C19 (CYP2C19) on clopidogrel-mediated effects on platelet inhibition, inflammatory response and endothelial function, as well as risk of major adverse cardiovascular events (MACE), in coronary heart patients undergoing percutaneous coronary intervention (PCI) was investigated. To this end, we assessed the residual platelet aggregation rate (RPA), maximal aggregation rate (MAR) and plasma levels of sCD40L, sP-selectin, MMP-9, sVCAM-1 and sE-selectin after 24 h of PCI in 559 patients treated with clopidogrel and followed up for 1 year for evidence of MACE. CYP2C19 *2 and *3 variants were identified using a clopidogrel-sensitive gene detection kit. Our results showed higher RPA and MAR as well as increased sE-selectin, sCD40L, sP-selectin, MMP-9, and sVCAM-1 levels in CYP2C19 intermediate metabolizer (IM, CYP2C19*1/*2, or *1/*3), poor metabolizer (PM, CYP2C19*2/*2, *2/*3, or *3/*3) and combined IM+PM groups, relative to those in extensive metabolizers (EM, CYP2C19*1/*1). In total, 519 patients completed 1 year of follow-up, among which 69 (13.3%) experienced MACE. The risk of MACE in CYP2C19 IM+PM patients was 2.664 times higher than that in CYP2C19 EM patients (OR = 2.664 (1.397–5.193), P = 0.004). The data suggest that CYP2C19*2 and *3 variants modulate the drug efficacy of clopidogrel in coronary heart patients undergoing PCI and further enhance the risk of MACE. Accordingly, CYP2C19 pharmacogenetic profiling may be beneficial for coronary heart patients undergoing PCI to predict the efficacy of treatment with clopidogrel. We propose that IM and PM patients should benefit from treatment with higher clopidogrel doses to improve efficacy and reduce the incidence of MACE.