Multi-institutional patterns of clopidogrel response among patients undergoing transcarotid artery revascularization

OBJECTIVE

Current guidelines recommend dual antiplatelet therapy (DAPT) in patients undergoing carotid artery stenting. The most common DAPT regimen is aspirin and clopidogrel, a P2Y12 receptor antagonist; however, the prevalence of clopidogrel resistance (CR) in patients undergoing percutaneous coronary interventions may exceed 60%. Few studies have investigated the prevalence and impact of CR in patients undergoing extracranial carotid artery stenting, particularly transcarotid artery revascularization (TCAR).

METHODS

Consecutive high-risk patients ≥ 18 years who underwent TCAR for high grade (≥70%) and/or symptomatic (≥50%) carotid stenosis with preoperative P2Y12 testing between August 2019 and December 2021 were identified across five institutions. Preoperative platelet reactivity was measured with the VerifyNow P2Y12 Reaction Unit (PRU) Test (Instrumentation Laboratory, Bedford, MA), with CR defined as PRU ≥ 194 and hyper-response as PRU <70. Patients without preoperative P2Y12 testing within 30 days prior to TCAR or those on a non-clopidogrel P2Y12 inhibitor preoperatively were excluded. The primary outcome of interest was prevalence of CR. Secondary outcomes of interest included the incidence of ischemic and hemorrhagic complications.

RESULTS

Of 92 patients identified, the majority were male (59%) and Caucasian (75%) with a mean age of 75 years (±8, range 56-92). Preoperatively, 93% of patients were on aspirin, 100% on clopidogrel, and 13% on therapeutic anticoagulation. At presentation, 36% were symptomatic. The mean preoperative P2Y12 was 156 PRU (±76, range 6-349). In total, 30 (33%) patients met criteria for CR (mean PRU 240 ± 37; range 197-349), and 15 (16%) met criteria for hyper-responder (mean PRU 38 ± 20; range 6-68). There was no significant difference by clopidogrel response phenotype in terms of sex (p = 0.246), race (p = 0.384), or symptomatic presentation (p = 0.956). Postoperatively, the cumulative incidence of stroke and MI was 2.1%, with no statistically significant difference in the incidence of in-hospital stroke (PRU 238, p = 0.489) or MI (PRU 168, p = 1) between clopidogrel phenotypes. Three (3.3%) patients, one CR (PRU 240) and two responders (PRU 119 and PRU 189), experienced postoperative access site hematomas that required no subsequent intervention. No other index hospitalization hemorrhagic complications occurred.

CONCLUSIONS

Using preoperative P2Y12 testing with a threshold PRU ≥ 194 to define CR, we identified a high prevalence of CR in patients undergoing TCAR similar to that in the pre-existing coronary literature. We found no significant differences in postoperative ischemic or hemorrhagic complications by clopidogrel response phenotype, although complication rates in the overall study cohort were low. CR may be a spectrum from responder to partial responder to complete non-responder, and this may account for the differences in our CR cohort compared to the ROADSTER 2 protocol deviation cohort. Further investigation is warranted to determine if a quantitative assessment of CR is sufficient to identify patients at risk of developing secondary cerebrovascular ischemic events in this patient population.

Preprocedural P2Y12 inhibition and decrease in platelet count following transcatheter aortic valve replacement

BACKGROUND

Thrombocytopenia after transcatheter aortic valve replacement (TAVR) is associated with adverse clinical outcomes. Whether preprocedural P2Y₁₂ inhibition prevents postprocedural thrombocytopenia is uncertain.

METHODS

This retrospective analysis identified consecutive patients (n = 266) undergoing TAVR between November 2016 and July 2017. Preprocedure clopidogrel load ≥300 mg or maintenance P2Y₁₂ inhibitor therapy defined preprocedural P2Y₁₂ inhibition. Patients who did not consent for the registry (n = 8), with baseline severe thrombocytopenia (<90 × 10³  platelets/μL; n = 14), or without baseline platelet count (n = 4) were excluded. The primary outcome was proportion of patients who developed >20% decrease in platelet count from baseline to day 1 post-TAVR.

RESULTS

Patients with (n = 134) versus without (n = 106) preprocedural P2Y₁₂ inhibition had no differences in platelet count at baseline. Patients with preprocedural P2Y₁₂ inhibition had a significantly lower proportion of the primary outcome (34.3% vs. 57.5%, p = .001) and a lower absolute decrease in platelet count (32.8 × 10³ vs. 45.8 × 10³  platelet/μL, p = .01). Of patients without baseline thrombocytopenia (n = 198), a numerically lower rate of patients with versus without preprocedural P2Y₁₂ inhibition developed thrombocytopenia on day 1 post-TAVR (25.5% vs. 36.4%, p = .1).

CONCLUSION

Patients who received preprocedural P2Y₁₂ inhibition prior to TAVR were less likely to demonstrate a decrease in platelet count after TAVR. Prospective studies to further understand the clinical implication of these findings are warranted.

Impact of Point-of-Care Platelet Function Testing Among Patients With and Without Acute Coronary Syndromes Undergoing Percutaneous Coronary Intervention With Drug-Eluting Stents (from the ADAPT-DES Study)

We sought to examine if the risk conferred by high on-treatment platelet reactivity (HPR) varies based upon clinical presentation. We examined the relation between HPR (P2Y12 reaction units >208) and adverse ischemic and bleeding events among patients with and without acute coronary syndromes (ACS) from ADAPT-DES; 51.7% of patients had ACS. After clopidogrel loading, ACS patients had higher P2Y12 reaction units and a greater prevalence of HPR based on VerifyNow P2Y12 assay. Of 92 definite or probable stent thrombosis (ST) events at 2 years, 65.2% occurred among patients with ACS. HPR was independently associated with ST in ACS patients (adjusted hazard ratio 2.29, 95% confidence interval 1.32 to 3.98) but not with clinically relevant bleeding. Although no statistical interactions between ACS status and these associations were observed, non-ACS patients exhibited an attenuated association between HPR and ST, and an inverse association between HPR and clinically relevant bleeding. HPR was similarly associated with myocardial infarction, but not with overall mortality in ACS and non-ACS patients. In conclusion, the majority of ST events in the 2 years after drug-eluting stent placement occurred in ACS patients; HPR was strongly associated with ST in these patients. These data support current recommendations for using more potent antiplatelet therapies in ACS patients.

Reversibility of platelet P2Y12 inhibition by platelet supplementation: ex vivo and in vitro comparisons of prasugrel, clopidogrel and ticagrelor

Essentials Successful outcome of platelet transfusion depends on specific antiplatelet therapy in use. We assessed if ticagrelor, clopidogrel or prasugrel impacts on donor platelet activity ex vivo. Ticagrelor and/or its active metabolite in plasma or bound to platelets can inhibit donor platelets. This might compromise the effectiveness of platelet transfusion therapy.

SUMMARY

Background Platelet transfusion is the conventional approach to restore platelet function during acute bleeds or surgery, but successful outcome depends on the specific antiplatelet therapy. Notably ticagrelor is associated with inadequate recovery of platelet function after platelet transfusion. We examined whether plasma and/or platelets from ticagrelor-treated patients influence donor platelet function, in comparison with clopidogrel and prasugrel. Methods Platelet transfusion was mimicked ex vivo by mixing naïve donor platelet-rich plasma (PRP) or gel-filtered platelets (GFP) in defined proportions with PRP, plasma or GFP from cardiovascular patients receiving standard care including medication with prasugrel, clopidogrel or ticagrelor (n = 20 each). Blood was taken 4 h after the previous dose. HLA2/HLA28 haplotyping let us distinguish net (all platelet) and individual patient/donor platelet reactivity in mixtures of patient/donor platelets, measured by flow cytometry analysis of ADP-induced fibrinogen binding and CD62P expression. Results ADP responsiveness of donor platelets was dramatically reduced by even low (10%) concentrations of PRP or plasma from ticagrelor-treated patients. Clopidogrel and prasugrel were associated with more modest donor platelet inhibition. GFP from ticagrelor-treated patients but not patients receiving clopidogrel or prasugrel also suppressed donor GFP function upon mixing, suggesting the transfer of ticagrelor from patient platelets to donor platelets. This transfer did not lead to recovery of ADP responsiveness of patient's platelets. Conclusion Collectively, these observations support the concept that ticagrelor and/or its active metabolite in plasma or bound to platelets can inhibit donor platelets, which might compromise the effectiveness of platelet transfusion therapy.

A complementary role for tetraspanin superfamily member TSSC6 and ADP purinergic P2Y12 receptor in platelets

Tumor-suppressing subchromosomal transferable fragment cDNA 6 (TSSC6) expression is restricted to hematopoietic organs and tissues where it plays a role in hematopoietic-cell function. The ADP purinergic receptor P2Y12 is mainly expressed by platelets with important clinical significance as a target for several clinically approved antithrombotic agents. We have previously shown a physical association between P2Y12 and TSSC6 in platelets. Hence our aim was to investigate whether this physical association is translated to functional effects. To investigate this possibility, we used wild-type or TSSC6 knockout (KO) mice treated with either PBS or 50mg/kg clopidogrel. TSSC6 KO mice treated with clopidogrel exhibited synergy in delayed kinetics of clot retraction, reduced collagen-mediated platelet aggregation, and platelet spreading on fibrinogen. Platelets derived from TSSC6 mice with P2Y12 blockade form smaller thrombi when perfused over a collagen matrix under arterial flow. Clopidogrel treated TSSC6 KO arterioles showed smaller and less stable thrombi with increased tendency to embolise in vivo. These studies demonstrate a complementary role between TSSC6 and P2Y12 receptor in platelets in regulating 'outside in' integrin αIIbβ3 signalling thrombus growth and stability.

Receptor homodimerization plays a critical role in a novel dominant negative P2RY12 variant identified in a family with severe bleeding

Essentials Three dominant variants for the autosomal recessive bleeding disorder type-8 have been described. To date, there has been no phenotype/genotype correlation explaining their dominant transmission. Proline plays an important role in P2Y12R ligand binding and signaling defects. P2Y12R homodimer formation is critical for the receptor function and signaling.

SUMMARY

Background Although inherited platelet disorders are still underdiagnosed worldwide, advances in molecular techniques are improving disease diagnosis and patient management. Objective To identify and characterize the mechanism underlying the bleeding phenotype in a Caucasian family with an autosomal dominant P2RY12 variant. Methods Full blood counts, platelet aggregometry, flow cytometry and western blotting were performed before next-generation sequencing (NGS). Detailed molecular analysis of the identified variant of the P2Y12 receptor (P2Y12R) was subsequently performed in mammalian cells overexpressing receptor constructs. Results All three referred individuals had markedly impaired ADP-induced platelet aggregation with primary wave only, despite normal total and surface P2Y12R expression. By NGS, a single P2RY12:c.G794C substitution (p.R265P) was identified in all affected individuals, and this was confirmed by Sanger sequencing. Mammalian cell experiments with the R265P-P2Y12R variant showed normal receptor surface expression versus wild-type (WT) P2Y12R. Agonist-stimulated R265P-P2Y12R function (both signaling and surface receptor loss) was reduced versus WT P2Y12R. Critically, R265P-P2Y12R acted in a dominant negative manner, with agonist-stimulated WT P2Y12R activity being reduced by variant coexpression, suggesting dramatic loss of WT homodimers. Importantly, platelet P2RY12 cDNA cloning and sequencing in two affected individuals also revealed three-fold mutant mRNA overexpression, decreasing even further the likelihood of WT homodimer formation. R265 located within extracellular loop 3 (EL3) is one of four residues that are important for receptor functional integrity, maintaining the binding pocket conformation and allowing rotation following ligand binding. Conclusion This novel dominant negative variant confirms the important role of R265 in EL3 in the functional integrity of P2Y12R, and suggests that pathologic heterodimer formation may underlie this family bleeding phenotype.

Differential proteomic analysis of platelets suggested target-related proteins in rabbit platelets treated with Rhizoma Corydalis

CONTEXT

Corydalis yanhusuo W.T. Wang (Papaveraceae) (Rhizoma Corydalis) showed inhibitory effects on rabbit platelet aggregation induced by ADP, thrombin (THR) or arachidonic acid (AA).

OBJECTIVE

This study separates and identifies the possible target-related platelet proteins and suggests possible signal cascades of RC antiplatelet aggregation.

MATERIALS AND METHODS

Based on comparative proteomics, the differentially expressed platelet proteins treated before and after with 50 mg/mL RC 90% ethanol extract (for 15 min at 37 °C) were analyzed and identified by two dimensional gel electrophoresis (2-DE) and MALDI-TOF-MS/MS. To further verify the possible signalling pathways of RC antiplatelet aggregation function, the concentration of calcium (Ca²⁺) was measured by Fura-2/AM fluorescence (Ex 340/380 nm, Em 500 nm) (RC final concentrations of 0.0156-0.1563 mg/mL), the levels of P-selectin and cyclic guanosine monophosphate (cGMP) were quantified by ELISA (OD. 450 nm) (RC final concentrations of 0.0156-1.5625 mg/mL), and the 5-hydroxytryptamine (5-HT) level was measured using ortho-phthalaldehyde (OPT) fluorescence (Ex 340 nm, Em 470 nm) (RC final concentrations of 0.3125-1.5625 mg/mL).

RESULTS

The expression of 52 proteins were altered in rabbit platelets after the treatment and the MALDI-TOF-MS analysis indicated that those proteins include 12 cytoskeleton proteins, 7 cell signalling proteins, 3 molecular chaperone proteins, 6 proteins related to platelet function, 16 enzymes and 7 other related proteins. Furthermore, RC extract could decrease the levels of 5-HT [inhibition rate of 96.80% (p < 0.05, vs. THR-activated group) treated with 0.7813 mg/mL of RC], Ca²⁺[172.73 ± 5.07 to 113.56 ± 5.46 nM (p < 0.001, vs. THR-activated group) treated with 0.0313 mg/mL of RC] and P-selectin [13.48 ± 0.96 ng/3 × 10⁸ to 11.64 ± 0.17 ng/3 × 10⁸ (p < 0.05, vs. THR-activated group) treated with 0.0156 mg/mL of RC], and increase in cGMP level [38.93 ± 0.57 to 50.26 ± 4.05 ng/3 × 10⁸ (p < 0.05, vs. THR-activated group) treated with 1.5165 mg/mL of RC] in ADP (10 μmol/L), THR (0.25 u/mL) or AA-(0.205 mmol/L) activated rabbit platelets.

DISCUSSION AND CONCLUSION

The present study indicated that P2Y12 receptor might be one of the direct target proteins of RC in platelets. The signal cascades network of RC after binding with P2Y12 receptor is mediating Gαi proteins to activate downstream signalling pathways (AC and/or PI3K signalling pathways) for the inhibition of platelet aggregation.

Incomplete reversibility of platelet inhibition following prolonged exposure to ticagrelor

Essentials Irreversible platelet inhibition persists after reversibly-binding ticagrelor is discontinued. Reversibility of platelet inhibition by ticagrelor and its active metabolite was assessed. Incomplete recovery was observed after prolonged exposure to ticagrelor. Activated GPIIb-IIIa and P-selectin, not platelet reactivity index, showed irreversibility.

SUMMARY

Introduction Ticagrelor is described as a reversible P2Y12 antagonist. However, residual platelet inhibition persists after discontinuation of ticagrelor when plasma levels are undetectable. We assessed the reversibility of platelet inhibition by ticagrelor and its active metabolite (T-AM) in comparison with cangrelor and prasugrel's active metabolite (P-AM). Methods Whole blood was treated in vitro with ~ 50% inhibitory concentrations of ticagrelor, T-AM, cangrelor, P-AM and assessed for ADP-stimulated activated GPIIb-IIIa and P-selectin and vasodilator-stimulated phosphoprotein (VASP) platelet reactivity index (PRI) before and after 100-fold dilution. Results Platelets exposed for 30 min to ticagrelor, T-AM or cangrelor showed full recovery of activated GPIIb-IIIa but only partial recovery of P-selectin. Longer exposure (24 h) to the drug decreased reversibility of activated GPIIb-IIIa by ticagrelor (65.1% [49.5-80.6], % of vehicle with 95% confidence interval [CI]) and T-AM (88.8% [79.2-98.3]), but not by cangrelor (101.4% [96.4-106.4]). Compared with 30 min exposure, the reversibility of P-selectin further decreased after 24 h exposure to ticagrelor (from 91.8% [82.1-101.5] to 51.8% [45.5-85.0]), but not T-AM (from 79.0% [67.8-90.3] to 77.4% [61.8-93.1]) or cangrelor (from 76.0% [67.6-84.4] to 76.2% [70.6-81.8]). In contrast, 24 h exposure to ticagrelor, T-AM and cangrelor resulted in full recovery of platelet reactivity as measured by PRI. Platelets exposed to P-AM showed no recovery of ADP reactivity. Conclusions Incomplete recovery after prolonged exposure to ticagrelor, observed by activated GPIIb-IIIa and P-selectin but not upstream VASP signaling, suggests that P2Y12 regains functionality and irreversible changes occur independent of VASP signaling.

Duration of dual antiplatelet therapy in acute coronary syndrome

Despite a large volume of evidence supporting the use of dual antiplatelet therapy in patients with acute coronary syndrome, there remains major uncertainty regarding the optimal duration of therapy. Clinical trials have varied markedly in the duration of therapy, both across and within trials. Recent systematic reviews and meta-analyses suggest that shorter durations of dual antiplatelet therapy are superior because the avoidance of atherothrombotic events is counterbalanced by the greater risks of excess major bleeding with apparent increases in all-cause mortality with longer durations. These findings did not show significant heterogeneity according to whether patients had stable or unstable coronary heart disease. Moreover, the potential hazards and benefits may differ when applied to the general broad population of patients encountered in everyday clinical practice who have markedly higher bleeding and atherothrombotic event rates. Clinicians lack definitive information regarding the duration of therapy in patients with acute coronary syndrome and risk scores do not appear to be sufficiently robust to address these concerns. We believe that there is a pressing need to undertake a broad inclusive safety trial of shorter durations of therapy in real world populations of patients with acute coronary syndrome. The clinical evidence would further inform future research into strategies for personalised medicine.

Synergistic Inhibition of Both P2Y1 and P2Y12 Adenosine Diphosphate Receptors As Novel Approach to Rapidly Attenuate Platelet-Mediated Thrombosis

OBJECTIVE

Unlike currently approved adenosine diphosphate receptor antagonists, the new diadenosine tetraphosphate derivative GLS-409 targets not only P2Y12 but also the second human platelet adenosine diphosphate receptor P2Y1 and may, therefore, be a promising antiplatelet drug candidate. The current study is the first to investigate the in vivo antithrombotic effects of GLS-409.

APPROACH AND RESULTS

We studied (1) the in vivo effects of GLS-409 on agonist-stimulated platelet aggregation in anesthetized rats, (2) the antithrombotic activity of GLS-409 and the associated effect on the bleeding time in a canine model of platelet-mediated coronary artery thrombosis, and (3) the inhibition of agonist-stimulated platelet aggregation by GLS-409 versus selective P2Y1 and P2Y12 inhibition in vitro in samples from healthy human subjects before and 2 hours after aspirin intake. In vivo treatment with GLS-409 significantly inhibited adenosine diphosphate- and collagen-stimulated platelet aggregation in rats. Further, GLS-409 attenuated cyclic flow variation, that is, platelet-mediated thrombosis, in vivo in our canine model of unstable angina. The improvement in coronary patency was accompanied by a nonsignificant 30% increase in bleeding time. Of note, GLS-409 exerted its effects without affecting rat and canine hemodynamics. Finally, in vitro treatment with GLS-409 showed effects similar to that of cangrelor and the combination of cangrelor with the selective P2Y1 inhibitor MRS 2179 on agonist-stimulated platelet aggregation in human platelet-rich plasma and whole blood before and 2 hours after aspirin intake.

CONCLUSIONS

Synergistic inhibition of both P2Y1 and P2Y12 adenosine diphosphate receptors by GLS-409 immediately attenuates platelet-mediated thrombosis and effectively blocks agonist-stimulated platelet aggregation irrespective of concomitant aspirin therapy.

Type 2 Diabetes and ADP Receptor Blocker Therapy

Type 2 diabetes (T2D) is associated with several abnormalities in haemostasis predisposing to thrombosis. Moreover, T2D was recently connected with a failure in antiplatelet response to clopidogrel, the most commonly used ADP receptor blocker in clinical practice. Clopidogrel high on-treatment platelet reactivity (HTPR) was repeatedly associated with the risk of ischemic adverse events. Patients with T2D show significantly higher residual platelet reactivity on ADP receptor blocker therapy and are more frequently represented in the group of patients with HTPR. This paper reviews the current knowledge about possible interactions between T2D and ADP receptor blocker therapy.

The STIB score: a simple clinical test to predict clopidogrel resistance

BACKGROUND

High platelet reactivity (HPR) to clopidogrel is associated with an increased risk of ischaemic complications during and after coronary interventions and concerns up to 50% of patients undergoing PCI.

AIM OF THE STUDY

The aim of the study was to identify patients with HPR to clopidogrel using bedside clinical information obtained in the Stent Thrombosis In Belgium (STIB) trial.

METHODS

Data on platelet reactivity using the VerifyNow® point-of-care assay were obtained in 844 patients undergoing PCI for stable coronary artery disease 12 to 24 hours after a 600-mg loading dose of clopidogrel was given. Demographic, clinical and baseline routine biological tests were obtained and compared with P2Y12 reaction units (PRU). Patients with PRU>230 (HPR) were considered as non-responders to clopidogrel.

RESULTS

HPR was observed in 424/844 pts. Age, weight, body mass index (BMI), HPR to aspirin, diabetes, renal failure (MDRD<60 ml/min), haemoglobin (Hb), haematocrit, fibrinogen, glycaemia and glycated haemoglobin were associated with HPR to clopidogrel. In multivariate analysis, only Hb (OR: 0.77), BMI (OR: 1.06) and diabetes (OR: 1.62) emerged as independent risk factors. Hb<13.9 g/dl, BMI>28 kg/m2 and presence of diabetes were equally associated to predict HPR and can be added to derive a simple score to predict clopidogrel resistance. Although 38.5% of patients without a single clinical predictor still have HPR, 2/3 patients with 2 or 3 risk factors are resistant to clopidogrel.

CONCLUSIONS

STIB HPR score allows identification of patients with a high probability of resistance to clopidogrel based on diabetes, Hb<13.9 g/dl and BMI>28 kg/m2. This bedside clinical test could be useful for the identification of patients in whom another P2Y12 inhibitor should be recommended before and after PCI.

Platelet P2Y12 Inhibitors Reduce Systemic Inflammation and Its Prothrombotic Effects in an Experimental Human Model

OBJECTIVE

Clinical studies suggest that platelet P2Y12 inhibitors reduce mortality from sepsis, although the underlying mechanisms have not been clearly defined in vivo. We hypothesized that P2Y12 inhibitors may improve survival from sepsis by suppressing systemic inflammation and its prothrombotic effects. We therefore determined whether clopidogrel and the novel, more potent P2Y12 inhibitor, ticagrelor, modify these responses in an experimental human model.

APPROACH AND RESULTS

We randomized 30 healthy volunteers to ticagrelor (n=10), clopidogrel (n=10), or no antiplatelet medication (controls; n=10). We examined the effect of P2Y12 inhibition on systemic inflammation, which was induced by intravenous injection of Escherichia coli endotoxin. Both P2Y12 inhibitors significantly reduced platelet-monocyte aggregate formation and peak levels of major proinflammatory cytokines, including tumor necrosis factor α, interleukin-6, and chemokine (C-C motif) ligand 2. In contrast to clopidogrel, ticagrelor also significantly reduced peak levels of IL-8 and growth colony-stimulating factor and increased peak levels of the anti-inflammatory cytokine IL-10. In addition, ticagrelor altered leukocyte trafficking. Both P2Y12 inhibitors suppressed D-dimer generation and scanning electron microscopy revealed that ticagrelor also suppressed prothrombotic changes in fibrin clot ultrastructure.

CONCLUSIONS

Potent inhibition of multiple inflammatory and prothrombotic mechanisms by P2Y12 inhibitors demonstrates critical importance of platelets as central orchestrators of systemic inflammation induced by bacterial endotoxin. This provides novel mechanistic insight into the lower mortality associated with P2Y12 inhibitors in patients with sepsis in clinical studies.

A pharmacodynamic study of the optimal P2Y12 inhibitor regimen for East Asian patients with acute coronary syndrome

BACKGROUND/AIMS

Newer P2Y12 inhibitors, such as prasugrel and ticagrelor, have greater antiplatelet efficacy but may increase the risk of bleeding. In this study, we compared the pharmacodynamic efficacy of prasugrel and ticagrelor in East Asian patients with acute coronary syndrome (ACS).

METHODS

We selected 83 ACS patients undergoing percutaneous coronary intervention who were discharged with 90 mg ticagrelor twice daily (n = 24), 10 mg prasugrel daily (n = 39) or 5 mg prasugrel daily (n = 20). After 2 to 4 weeks, on-treatment platelet reactivity (OPR) was assessed in terms of P2Y12 reaction units (PRUs) using the VerifyNow P2Y12 assay (Accumetrics). We compared East Asian (85 < PRU ≤ 275) and Caucasian (85 < PRU ≤ 208) criteria for assessing the therapeutic window of OPR.

RESULTS

OPR was lowest in the ticagrelor group, followed by the 10 mg prasugrel and 5 mg prasugrel groups (49.1 ± 29.9 vs. 83.7 ± 57.1 vs. 168.5 ± 60.8, respectively; p < 0.001). The 5 mg prasugrel group had the highest proportion of patients with OPR values within the therapeutic window, followed by the 10 mg prasugrel and ticagrelor groups (90.0% vs. 46.2% vs. 12.5%, respectively; p < 0.001 for East Asian criteria; 60.0% vs. 43.6% vs. 12.5%, respectively; p < 0.001 for Caucasian criteria).

CONCLUSIONS

Short-term administration of 5 mg prasugrel facilitated maintenance within the therapeutic window of OPR compared with the 10 mg prasugrel and ticagrelor groups. Thus, 5 mg prasugrel daily may be the optimal antiplatelet regimen for stabilized East Asian ACS patients.

Exploration of efficacy and bleeding with combined phosphoinositide 3-kinase β inhibition and aspirin in man

BACKGROUND

Based on animal and human data, phosphoinositide 3-kinase (PI3K)β is a promising antithrombotic target. However, the relation between efficacy and bleeding when combined with current antiplatelet therapies is unclear.

OBJECTIVE

To strengthen the PI3Kβ target validation using the short-acting inhibitor AZD6482 alone and in different combinations with P2Y12 and cyclooxygenase (COX)-1 inhibition in vitro (human platelets), in vivo (dog), and in healthy subjects.

METHODS AND RESULTS

Evaluation of complete target inhibition of PI3Kβ (by AZD6482), P2Y12 (by ticagrelor), and COX-1 (by aspirin) alone and in the different combinations vs. concentration responses for a panel of platelet agonists in vitro (adenosine diphosphate, collagen, thrombin receptor activating peptide) indicates that the rank order of antiplatelet efficacy is P2Y12  > PI3Kβ > COX-1 as monotherapy and P2Y12 plus PI3Kβ > P2Y12 plus COX-1 > PI3Kβ plus COX-1 as dual therapy, with little additional effect with triple therapy. Use of a conscious dog model to assess ex vivo antiplatelet effect in parallel with bleeding time prolongation (standard incision in the ear) confirms the wide separation of efficacy vs. bleeding for PI3Kβ inhibition and that this separation is reduced when combined with aspirin and more reduced when combined with clopidogrel. In healthy subjects, AZD6482, in combination with aspirin, shows a potential for greater antiplatelet potency but less bleeding potential compared with clopidogrel plus aspirin.

CONCLUSIONS

PI3Kβ inhibition, in comparison with P2Y12 and COX-1, delivers medium antiplatelet effect but with minimal bleeding. PI3Kβ inhibition, in combination with aspirin, in healthy subjects, provides a potential for greater overall antiplatelet effect compared with clopidogrel plus aspirin, but with significantly less bleeding potential.

Does the response to aspirin and clopidogrel vary over 6 months in patients with ischemic heart disease?

BACKGROUND

Dual-antiplatelet therapy (DAPT) with aspirin and a P2Y12 inhibitor, mostly clopidogrel, is the default therapy in both acute coronary syndrome (ACS) and after intracoronary stents. It is well established that responses to antiplatelet therapy (APT), particularly clopidogrel, are subject to considerable interindividual variability.

OBJECTIVES

We investigated whether responses to APT in individuals vary significantly over time.

METHODS

Simultaneous assay with VerifyNow(™) and short thrombelastography (s-TEG) was performed before and at four time points over 6 months after hospital discharge in 40 patients receiving DAPT. Serum thromboxane B2 levels were also measured.

RESULTS

While aspirin response units (ARU) by VerifyNow(™) and serum thromboxane B2 levels remained stable over time, arachidonic acid (AA)-mediated platelet aggregation with s-TEG (i.e. area under the curve at 15 min in AA channel, AUC15AA ) increased at 1 week compared with predischarge (P < 0.008). In addition, platelet reactivity units (PRU) by VerifyNow(™) (P = 0.046) and adenosine diphosphate (ADP)-mediated platelet aggregation with s-TEG (i.e. AUC15ADP ) also increased at 1 week compared with predischarge (P = 0.026). There were no significant changes in either platelet reactivity or rates of high on-treatment platelet reactivity while receiving clopidogrel beyond 1 week.

CONCLUSIONS

This study demonstrates important variability in responses to APT within individuals between predischarge and 1 week but not thereafter. The use of a single early (predischarge) platelet function assay as an indicator of future response may therefore be flawed. The design of future strategies to assess individual responses for tailored therapy needs to take this into account.

The role of perioperative antiplatelet therapy and platelet reactivity testing in carotid revascularization: overview of the evidence

Antiplatelet therapy has reduced the incidence of thromboembolic events for patients undergoing carotid revascularization. However, the platelet inhibitory effect of aspirin and clopidogrel, the most commonly used P2Y12 receptor inhibitors, is variable among patients. Patients displaying high platelet reactivity despite aspirin or clopidogrel treatment are at higher risk for thromboembolic events during and after carotid revascularization. In order to reduce the incidence of high platelet reactivity, more potent P2Y12 receptor inhibitors as prasugrel are used. However, this strategy increases the risk of bleeding. As there is evidence of a therapeutic window for platelet inhibition, platelet function tests could be helpful for tailoring antiplatelet therapy based on the patient's thrombotic and bleeding risk. This evidence overview describes the most commonly used platelet inhibitors, platelet function tests and the current evidence for tailoring of antiplatelet therapy to patients undergoing carotid revascularization.

Point-of-care platelet reactivity determination with VerifyNow-P2Y12 following administration of clopidogrel or prasugrel: data from a real-world, clinical care inpatient setting

OBJECTIVES

To describe VerifyNow-P2Y12 (VN-P2Y12, Accumetrics, San Diego, CA) results from patients treated with either clopidogrel or prasugrel who were seeking care in a hospital setting.

BACKGROUND

VN-P2Y12 is a point-of-care device that measures platelet reactivity to adenosine diphosphate. Past assessments of thienopyridine therapy utilizing VN-P2Y12 have largely come from clinical trial settings. There are limited data from real-world settings.

METHODS

Electronic medical record data from Huntsville Hospital (Huntsville, AL) for those who underwent VN-P2Y12 testing for clopidogrel or prasugrel between January 1, 2009 and October 31, 2010 were analyzed. The VN-P2Y12 data included P2Y12 reaction units (PRUs) and device-reported percentage of inhibition. Descriptive analyses were conducted with t tests, and a logistic regression model was estimated to assess the association between patient characteristics and the likelihood of platelet nonresponse.

RESULTS

In total, 2882 tests (2476 with clopidogrel and 406 with prasugrel) were analyzed. For clopidogrel and prasugrel, respectively, mean PRU standard deviation (SD) was 206 (90) and 107 (93; P < 0.0001) and mean % inhibition (SD) was 31% (26%) and 63% (31%; P < 0.0001). Treatment with clopidogrel alone (odds ratio [OR] = 5.25; P < 0.0001), being non-Caucasian (OR = 1.48; P = 0.0440), obese (OR = 1.49; P = 0.0010), anemic (OR = 3.29; P < 0.0001), diabetic (OR = 1.75; P < 0.0001), and having a history of myocardial infarction (OR = 1.57; P < 0.0001) were significant predictors of having PRU ≥ 235.

CONCLUSION

This real-world data analysis shows results that are consistent with clinical trial results, namely that compared with clopidogrel, prasugrel is associated with significantly lower PRU and greater percentage of inhibition, regardless of age, race, gender, diabetes, obesity, or proton pump inhibitor use.

Impact of mild hypothermia on platelet responsiveness to aspirin and clopidogrel: an in vitro pharmacodynamic investigation

The combination of percutaneous coronary intervention (PCI) and therapeutic hypothermia in comatose patients after cardiac arrest due to an acute coronary syndrome has been reported to be safe and effective. However, recent investigations suggest that hypothermia may be associated with impaired response to clopidogrel and greater risk of thrombotic complications after PCI. This investigation aimed to evaluate the effect of hypothermia on the pharmacodynamic response of aspirin and clopidogrel in patients (n = 20) with ST elevation myocardial infarction undergoing primary PCI. Higher platelet reactivity (ADP stimulus) was observed in samples incubated at 33 °C compared with those at 37 °C (multiple electrode aggregometry, 235.2 ± 31.4 AU×min vs. 181.9 ± 30.2 AU×min, p < 0.001; VerifyNow P2Y12, 172.9 ± 20.3 PRU vs. 151.0 ± 19.3 PRU, p = 0.004). Numerically greater rates of clopidogrel poor responsiveness were also observed at 33 °C. No differences were seen in aspirin responsiveness. In conclusion, mild hypothermia was associated with reduced clopidogrel-mediated platelet inhibition with no impact on aspirin effects.

CLINICAL RELEVANCE

Mild therapeutic hypothermia is associated with impaired response to clopidogrel therapy, which might contribute to increase the risk of thrombotic events in ACS comatose patients undergoing PCI.

Hematocrit alters VerifyNow P2Y12 assay results independently of intrinsic platelet reactivity and clopidogrel responsiveness

BACKGROUND

The VerifyNow P2Y12 assay assesses the adequacy of clopidogrel therapy by measuring ADP-induced platelet activation in whole blood. Low hematocrit is associated with high clopidogrel on-treatment platelet reactivity (HTPR) defined by this assay.

OBJECTIVES

To characterize the effect of hematocrit on VerifyNow values and determine if it is due to hematocrit-dependent changes in intrinsic platelet reactivity or an in vitro assay phenomenon.

PATIENTS/METHODS

Adenosine diphosphate-induced platelet activation was measured using the VerifyNow P2Y12 assay, whole blood impedance and light transmission platelet aggregometry (LTA) before and after clopidogrel loading in 113 patients undergoing elective cardiac catheterization. Iso-TRAP-induced platelet activation was additionally measured using the VerifyNow device. Multivariate modeling employing clinical and laboratory variables was used to investigate the association between hematocrit and VerifyNow values.

RESULTS

VerifyNow P2Y12 reaction units (PRU) and iso-TRAP Base units before and after clopidogrel loading, but not their relative change, exhibited strong negative correlation with hematocrit (P ≤ 0.0005 for both). While hematocrit remained a strong predictor of post-clopidogrel PRU (P = 0.001) in multivariate modeling, it was independent of post-clopidogrel ADP-induced platelet reactivity as measured by LTA (P = 0.001). Correcting for the effects of hematocrit resulted in a 15-39% reduction in the prevalence of HTPR defined by thresholds of 208-236 PRU.

CONCLUSIONS

The effect of hematocrit on VerifyNow PRU values is an in vitro phenomenon that is independent of intrinsic change in ADP-induced platelet reactivity and clopidogrel responsiveness. Correcting for hematocrit when using this assay may more accurately identify patients with HTPR that may benefit from alternative antiplatelet therapy.

Cost-effectiveness of universal and platelet reactivity assay-driven antiplatelet therapy in acute coronary syndrome

Assays monitoring P2Y12 platelet reactivity can accurately predict which patients will have a poor response to clopidogrel. We sought to determine the cost-effectiveness of using platelet reactivity assays (PRAs) to select a dual-antiplatelet regimen for patients with acute coronary syndrome. A hybrid decision tree Markov model was developed to determine the cost-effectiveness of universal clopidogrel, ticagrelor, or prasugrel (given to all patients) or PRA-driven ticagrelor or prasugrel (given to patients with high platelet reactivity, defined as >230 on the VerifyNow P2Y12 assay; the others received generic clopidogrel). We assumed a cohort of 65-year-old patients with acute coronary syndrome and an incidence of high platelet reactivity of 32% and 13% at ~24 to 48 hours after revascularization and 1 month, respectively. The 5-year costs, quality-adjusted life-years, and incremental cost-effectiveness ratios were calculated for PRA-driven ticagrelor and prasugrel compared with universal clopidogrel, ticagrelor, or prasugrel. PRA-driven ticagrelor and prasugrel were cost-effective compared with universal clopidogrel (incremental cost-effectiveness ratio $40,100 and $49,143/quality-adjusted life-year, respectively); however, universal ticagrelor and prasugrel were not (incremental cost-effectiveness ratio $61,651 and $96,261/quality-adjusted life-year, respectively). Monte Carlo simulation suggested PRA-driven ticagrelor, PRA-driven prasugrel, universal ticagrelor, and universal prasugrel would have an incremental cost-effectiveness ratio <$50,000/quality-adjusted life-year in 52%, 40%, 23%, and 2% of the iterations compared with universal clopidogrel, respectively. Universal ticagrelor and prasugrel were not cost-effective compared with their respective PRA-driven regimens (incremental cost-effectiveness ratio $68,182; $116,875/quality-adjusted life-year, respectively). Monte Carlo simulation suggested universal ticagrelor and prasugrel would have an incremental cost-effectiveness ratio <$50,000/quality-adjusted life-year in 26% and 4% of iterations compared with their respective PRA-driven regimens. The results were most sensitive to differences in agent costs and drug-specific relative risks of death. In conclusion, even with generic clopidogrel, PRA-driven selection of antiplatelet therapy appeared to be a cost-effective strategy with the potential to decrease the overall acute coronary syndrome-associated healthcare costs.

Human platelet protease-activated receptor-1 responsiveness to thrombin related to P2Y12 inhibition

Dual antiplatelet therapy with aspirin and adenosine diphosphate (ADP) receptor inhibitors significantly improves the outcome of patients with stable coronary heart disease. However, abundant thrombin generation, which is not influenced by this dual antiplatelet therapy, is a major reason for recurrent thromboembolic disease in these patients. We, therefore, assessed in a hypothesis generating study in patients with stable coronary artery disease specifically the relation of responsiveness of the platelet thrombin receptor protease-activated receptor (PAR)-1 to the magnitude of the inhibition of the ADP receptor. PAR-1 regulation was studied prospectively in 86 consecutive patients with stable coronary artery disease treated with aspirin and clopidogrel (67 patients) or prasugrel (19 patients) and correlated the data to ADP inducible platelet reactivity by impedance aggregometry. PAR-1 expression did not differ between patients on aspirin and clopidogrel vs patients on aspirin and prasugrel (P > 0.5). PAR-1 levels were correlated to P-selectin expression (P < 0.0001). The higher the PAR-1 expression the more profound was the in vitro thrombin-inducible platelet activation. However, neither ex vivo PAR-1 expression nor in vitro thrombin-inducible PAR-1 were correlated to ADP-inducible platelet aggregation (P > 0.5). Thus, like in a real life scenario, patients with stable ischemic heart disease on dual antiplatelet therapy may express high levels of PAR-1, which are associated with profound thrombin-inducible platelet activation. This responsiveness cannot be predicted by the magnitude of ADP responsiveness.

Pharmacodynamic impacts of proton pump inhibitors on the efficacy of clopidogrel in vivo--a systematic review

BACKGROUND

There is considerable debate about whether concomitant use of proton pump inhibitors (PPIs) should be recommended for patients who are prescribed clopidogrel after acute coronary syndrome. Most pharmacokinetic and pharmacodynamic studies in vivo were conducted using small sample sizes and were single centered, resulting in conflicting data.

HYPOTHESIS

PPIs may attenuate the antiplatelet effect of clopidogrel in vivo and lead to an increased risk of cardiovascular events.

METHODS

PubMed, the Cochrane Library, Embase, Web of Science, and China Biology Medicine Disc were searched. Randomized controlled trials that compared pharmacodynamic impacts of a PPI on the efficacy of clopidogrel in vivo were included. Two independent reviewers evaluated study quality and extracted data for meta-analysis.

RESULTS

We identified 8 eligible studies. Compared to clopidogrel treatment alone, patients who received both a PPI and clopidogrel had less of a decrease in the platelet reactivity index (weighted mean difference [WMD]: 8.18; 95% confidence interval [CI]: 6.81-9.56; P<0.00001), less adenosine 5'-diphosphate-induced platelet aggregation inhibition (WMD: 7.28; 95% CI: 2.44-12.11; P=0.003), higher P2Y12 reaction units (WMD: 40.58; 95% CI: 19.31-61.86; P=0.0002), and higher risks of clopidogrel resistance (odds ratio [OR]: 2.49; 95% CI: 1.49-4.14; P=0.0005). There were no significant differences, however, for the incidences of major adverse cardiovascular events between the 2 groups (OR: 1.07; 95% CI: 0.44-2.59; P=0.88), and treatment with a PPI and clopidogrel significantly reduced the risk of adverse gastrointestinal events (OR: 0.16; 95% CI: 0.04-0.62; P=0.008).

CONCLUSIONS

Concomitant use of a PPI with clopidogrel attenuated the antiplatelet effect of clopidogrel, but may be clinically unimportant because there were no clinical differences in the risk for major adverse cardiovascular events.

P2Y12 protects platelets from apoptosis via PI3k-dependent Bak/Bax inactivation

BACKGROUND

Platelet ADP receptor P2Y(12) is well studied and recognized as a key player in platelet activation, hemostasis and thrombosis. However, the role of P2Y(12) in platelet apoptosis remains unknown.

OBJECTIVES

To evaluate the role of the P2Y(12) receptor in platelet apoptosis.

METHODS

We used flow cytometry and Western blotting to assess apoptotic events in platelets treated with ABT-737 or ABT-263, and stored at 37°C, combined with P2Y(12) receptor antagonists or P2Y(12) -deficient mice.

RESULTS

 P2Y(12) activation attenuated apoptosis induced by ABT-737 in human and mouse platelets in vitro, evidenced by reduced phosphatidylserine (PS) exposure, diminished depolarization of mitochondrial inner transmembrane potential (ΔΨm) and decreased caspase-3 activation. Through increasing the phosphorylation level of Akt and Bad, and changing the interaction between different Bcl-2 family proteins, P2Y(12) activation inactivated Bak/Bax. This antiapoptotic effect could be abolished by P2Y(12) antagonism or PI3K inhibition. We also observed the antiapoptotic effect of P2Y(12) activation in platelets stored at 37°C. P2Y(12) activation improved the impaired activation responses of apoptotic platelets stressed by ABT-737. In platelets from mice dosed with ABT-263 in vivo, clopidogrel or deficiency of P2Y(12) receptor enhanced apoptosis along with increased Bak/Bax activation.

CONCLUSIONS

This study demonstrates that P2Y(12) activation protects platelets from apoptosis via PI3k-dependent Bak/Bax inactivation, which may be physiologically important to counter the proapoptotic challenge. Our findings that P2Y(12) blockade exaggerates platelet apoptosis induced by ABT-263 (Navitoclax) also imply a novel drug interaction of ABT-263 and P2Y(12) antagonists.

Relationship between post-treatment platelet reactivity and ischemic and bleeding events at 1-year follow-up in patients receiving prasugrel

BACKGROUND

Post-treatment platelet reactivity (PR) is associated with ischemic and bleeding events in patients receiving P2Y12 receptor antagonists.

OBJECTIVES

We aimed to study the relationship between post-treatment PR after a 60-mg loading dose (LD) of prasugrel and 1-year thrombotic and bleeding events.

METHOD

Patients were prospectively included in this multicenter study if they had a successful percutaneous coronary intervention (PCI) for acute coronary syndrome (ACS) and received prasugrel. The platelet reactivity index (PRI) was measured using the Vasodilator-Stimulated Phosphoprotein index (VASP) after a prasugrel LD. Endpoints included the rate of thrombotic events and bleeding events at 1 year.

RESULTS

Among the 301 patients enrolled, 9 (3%) were lost to follow-up at 1 year. The rates of thrombotic and bleeding events at 1 year were of 7.5% and 6.8%, respectively. Receiver-operating curve (ROC) analysis demonstrated an optimal cut-off value of 53.5% of PRI to predict thrombotic events at 1 year. Using this cut-off value we observed that patients exhibiting high on-treatment platelet reactivity (HTPR) had a higher rate of thrombotic events (22.4% vs. 2.9%; P < 0.001). In parallel the optimal cut-off value of PRI to predict bleeding was 16%. Patients with a PRI ≤ 16% had a higher rate of bleeding events compared with those with a PRI > 16% (15.6% vs. 3.3%; P < 0.001). In multivariate analysis, the PRI predicted both thrombotic and bleeding events (OR: 1.44, 95% confidence interval [CI]: 1.2-1.72; P < 0.001 and OR: 0.75, 95% CI: 0.59-0.96; P = 0.024 [respectively, per 10% increase]).

CONCLUSION

Platelet reactivity measurement after a prasugrel LD predicts both ischemic and bleeding events at 1 year follow-up for ACS patients undergoing PCI.

P2Y(12) receptors in platelets and other hematopoietic and non-hematopoietic cells

The P2Y(12) receptor is a Gi-coupled ADP receptor first described in blood platelets where it plays a central role in the complex processes of activation and aggregation. Platelet granules store important amounts of ADP which are released upon stimulation by interaction of platelets with the damaged vessel wall. Therefore, the P2Y(12) receptor is a key player in primary hemostasis and in arterial thrombosis and is an established target of antithrombotic drugs like the thienopyridine compounds ticlopidine, clopidogrel, and prasugrel or the direct, reversible antagonists ticagrelor and cangrelor. Beyond the platelet physiology and pharmacology, recent studies have revealed the expression of the P2Y(12) receptor in other hematopoietic cells including leukocyte subtypes and microglia in the central nervous system as well as in vascular smooth muscle cells. These studies indicate putative roles of the P2Y(12) receptor in inflammatory states and diseases of the brain, lung, and blood vessels. The selective role of P2Y(12) among other P2 receptors as well as the possible impact of P2Y(12) targeting drugs in these processes remain to be evaluated.

Response variability to clopidogrel: is tailored treatment, based on laboratory testing, the right solution?

Clopidogrel is an antithrombotic prodrug, whose active metabolite inhibits platelet function by irreversibly binding to the platelet receptor for adenosine diphosphate, P2Y(12). Wide inter-individual variability of response to clopidogrel has been reported in several studies: a significant proportion of treated patients (about one-third) exhibit a suboptimal inhibition of platelet function. Genetic and environmental factors that influence the absorption and/or the extent of metabolism of clopidogrel to its active metabolite account for the observed variability of response. Tailored treatment based on the results of laboratory tests of platelet function has been proposed as a solution to this problem, which has important clinical implications. Although it is often considered a desirable evolution of modern medicine, tailored treatment based on laboratory tests is actually an old remedy (of yet unproven efficacy, in the case of antiplatelet therapy) for the problem of response variability to antithrombotic drugs with unpredictable bioavailability. When possible, the use of alternative drugs with more uniform and predictable bioavailability, and with favourable profiles in terms of risk/benefit and cost-benefit ratios should be preferred. Moreover, tailored treatment with laboratory tests must be validated in randomized clinical trials before its implementation can be recommended. We still need to identify and standardize the laboratory test for this purpose, as well as answer basic questions on its clinical utility and cost-effectiveness, before tailoring clopidogrel therapy based on laboratory tests can be recommended in clinical practise.

Relationship between clopidogrel-induced platelet P2Y12 inhibition and stent thrombosis or myocardial infarction after percutaneous coronary intervention-a case-control study

BACKGROUND

Insufficient platelet inhibition is a major determinant of stent thrombosis (STh), although the etiology is multifactorial. On-clopidogrel platelet reactivity was investigated in patients with previous angiographically confirmed STh, myocardial infarction (MI), and controls.

METHODS

Using the Swedish Coronary Angiography and Angioplasty Registry, we identified patients with angiographically confirmed STh (n = 48) or MI (n = 30) while on dual antiplatelet therapy within 6 months of percutaneous coronary intervention (PCI) and matched control patients (n = 78). On-clopidogrel platelet reactivity was measured with VerifyNow P2Y12 and vasodilator-stimulated phosphoprotein (VASP) phosphorylation assay.

RESULTS

The mean P2Y12 reaction units (PRU) was higher (246.8 ± 75.9 vs 200.0 ± 82.7, P = .001) in STh patients compared with controls. The optimal cutoff for STh was 222 PRU or higher (area under the curve 0.69, P < .0001) in a receiver operating characteristics (ROC) analysis. The cutoff level resulted in 70.2% sensitivity and 67.3% specificity. There was no significant difference in mean PRU but a higher device-reported percent inhibition (45.1 ± 23.8 vs 32.1 ± 23.2, P = .04) in patients with MI compared with controls. Results with the VASP phosphorylation assay were not related to the occurrence of STh or MI.

CONCLUSIONS

STh was associated with high on-clopidogrel platelet reactivity measured with VerifyNow (cutoff level of PRU ≥222) but spontaneous MI in stented patients on clopidogrel treatment was not. There was, however, a substantial overlap in on-clopidogrel platelet reactivity between patients with and without on-treatment STh questioning the clinical use of platelet function testing to identify patients at high risk for STh.

In the presence of strong P2Y12 receptor blockade, aspirin provides little additional inhibition of platelet aggregation

BACKGROUND

Aspirin and antagonists of platelet ADP P2Y(12) receptors are often coprescribed for protection against thrombotic events. However, blockade of platelet P2Y(12) receptors can inhibit thromboxane A(2) (TXA(2))-dependent pathways of platelet activation independently of aspirin.

OBJECTIVES

To assess in vitro whether aspirin adds additional antiaggregatory effects to strong P2Y(12) receptor blockade.

METHODS

With the use of platelet-rich plasma from healthy volunteers, determinations were made in 96-well plates of platelet aggregation, TXA(2) production and ADP/ATP release caused by ADP, arachidonic acid, collagen, epinephrine, TRAP-6 amide and U46619 (six concentrations of each) in the presence of prasugrel active metabolite (PAM; 0.1-10 μmol L(-1)), aspirin (30 μmol L(-1)), PAM + aspirin or vehicle. results: PAM concentration-dependently inhibited aggregation; for example, aggregation in response to all concentrations of ADP and U46619 was inhibited by ≥ 95% by PAM at > 3 μmol L(-1) . In further tests of PAM (3 μmol L(-1)), aspirin (30 μmol L(-1)) and PAM + aspirin, aspirin generally failed to produce more inhibition than PAM or additional inhibition to that caused by PAM. The antiaggregatory effects of PAM were associated with reductions in the platelet release of both TXA(2) and ATP + ADP. Similar effects were found when either citrate or lepirudin were used as anticoagulants, and when traditional light transmission aggregometry was conducted at low stirring speeds.

CONCLUSIONS

P2Y(12) receptors are critical to the generation of irreversible aggregation through the TXA(2) -dependent pathway. As a result, strong P2Y(12) receptor blockade alone causes inhibition of platelet aggregation that is little enhanced by aspirin. The clinical relevance of these observations remains to be determined.

Platelet function testing in practice: a case study

Dual antiplatelet therapy with aspirin and a thienopyridine reduces ischemic cardiovascular events following percutaneous coronary intervention. However, despite this treatment, residual risk of ischemic events persists. Among other factors, enhanced platelet reactivity after thienopyridine therapy is associated with an increased risk of ischemic cardiovascular events. A heterogeneous and variable patient response to the thienopyridine clopidogrel exists and has been attributed to a number of genetic, pharmacologic, and clinical factors. Developments in point-of-care platelet function testing allow for the assessment of on-treatment platelet reactivity after thienopyridine therapy and thus identify poor responders. We report two cases of stent thrombosis in which the bedside rapid platelet function VerifyNow P2Y12 Assay® (Accumetrics, San Diego, CA) was used to determine on-treatment platelet reactivity and identify potential etiologies of the thrombotic events.