High platelet reactivity and clinical outcome – Fact and fiction

Combined Antiplatelet Therapy Reduces the Proinflammatory Properties of Activated Platelets

The cause of atherothrombosis is rupture or erosion of atherosclerotic lesions, leading to an increased risk of myocardial infarction or stroke. Here, platelet activation plays a major role, leading to the release of bioactive molecules, for example, chemokines and coagulation factors, and to platelet clot formation. Several antiplatelet therapies have been developed for secondary prevention of cardiovascular events, in which anticoagulant drugs are often combined. Besides playing a role in hemostasis, platelets are also involved in inflammation. However, it is unclear whether current antiplatelet therapies also affect platelet immune functions. In this study, the possible anti-inflammatory effects of antiplatelet medications on chemokine release were investigated using enzyme-linked immunosorbent assay and on the chemotaxis of THP-1 cells toward platelet releasates. We found that antiplatelet medication acetylsalicylic acid (ASA) led to reduced chemokine (CC motif) ligand 5 (CCL5) and chemokine (CXC motif) ligand 4 (CXCL4) release from platelets, while leukocyte chemotaxis was not affected. Depending on the agonist, α _IIb β ₃ and P2Y ₁₂ inhibitors also affected CCL5 or CXCL4 release. The combination of ASA with a P2Y ₁₂ inhibitor or a phosphodiesterase (PDE) inhibitor did not lead to an additive reduction in CCL5 or CXCL4 release. Interestingly, these combinations did reduce leukocyte chemotaxis. This study provides evidence that combined therapy of ASA and a P2Y ₁₂ or PDE3 inhibitor can decrease the inflammatory leukocyte recruiting potential of the releasate of activated platelets.

Assessment of Platelet Reactivity and Inflammatory Markers in Coronary Artery Bypass Graft Patients Treated with Acetylsalicylic Acid with Flavonoid Supplementation

The recommended pharmacological therapy for patients with coronary artery disease (CAD) treated by coronary artery bypass grafting (CABG) is acetylsalicylic acid (ASA). To improve the antiplatelet effect, supplementation with flavonoids is also recommended. The aim of this study was to estimate anti-aggregation properties of diosmin, in combination with ASA, pre- and postoperatively and assess the relationship of this therapy with inflammatory processes in CAD patients undergoing CABG. The study patients (n = 26) took diosmin (1000 mg/day); the control patients (n = 27) took a placebo. The therapeutic period for taking diosmin was from at least 30 days before to 30 days after CABG. All patients also took 75 mg/day ASA. Platelet aggregation and IL-6, CRP, and fibrinogen concentrations were determined before and 30 days after surgery. Results showed that diosmin did not enhance the anti-aggregation effect of ASA at any assessment time. However, there was a stronger anti-aggregation effect 30 days after surgery that was diosmin independent and was associated with acute-phase markers in the postoperative period. Increased levels of inflammatory markers in the late phase of the postoperative period may provide an unfavorable prognostic factor in long-term follow-up, which should prompt the use of stronger antiplatelet therapy in patients after CABG.

[Evaluation of treatment adaptation for low response to ASA in vascular surgery]

Hintergrund

Eine verminderte antithrombozytäre Prophylaxe („Low-Response [LR]“/„high on-treatment platelet reactivity [HPR]“) mit Acetylsalicylsäure (ASS) ist mit einem erhöhten Risiko für thrombembolische Ereignisse assoziiert. Die Prävalenz einer Low-Response ist mit ca. 20 % häufig und ein Therapieregime wurde bisher noch nicht etabliert. Das Ziel dieser prospektiven Studie war es, die Effektivität eines Therapieschemas zur Therapieanpassung bei detektierter LR/HPR bei gefäßchirurgischen Patienten zu evaluieren.

Methodik

Insgesamt wurden 36 gefäßchirurgischen Patienten mit einer antithrombozytären Dauermedikation mit ASS 100 mg/Tag und einer nachgewiesenen ASS-Low-Response (ALR) in die Studie eingeschlossen. Entsprechend dem festgelegten Therapieplan wurde bei diesen Patienten eine Therapieanpassung durchgeführt und eine Kontrollaggregometrie zur Erfolgskontrolle durchgeführt. Das verwendete Therapieschema folgte dem Test-and-treat-Prinzip. Zur Beurteilung der Wirkung von ASS diente die Impedanzaggregometrie mittels Mehrelektrodenaggregometer (Multiplate).

Ergebnisse

Insgesamt konnten alle 36 Patienten erfolgreich in eine Response überführt werden. Bei 32 (88,89 %) Patienten erfolgte eine Dosiserhöhung auf 300 mg ASS, 2 (5,56 %) Patienten wurden von ASS auf Clopidogrel umgestellt. Bei weiteren 2 (5,56 %) Patienten wurde auf eine orale Antikoagulation mit Phenprocoumon aufgrund anderer Indikationen umgestellt. Blutungskomplikationen oder Nebenwirkungen traten nicht auf.

Schlussfolgerung

Das gewählte Therapieschema zur Behandlung einer Low-Response erwies sich als effektiv und sicher bei gefäßchirurgischen Patienten. Überwiegend führte eine leitliniengerechte Dosiserhöhung der Prophylaxe von 100 mg auf 300 mg ASS zu einer effektiven Thrombozytenaggregationshemmung in der Aggregometrie.

Perioperative changes of response to antiplatelet medication in vascular surgery patients

Introduction

Reduced antiplatelet activity of aspirin (ALR) or clopidogrel (CLR) is associated with an increased risk of thromboembolic events. The reported prevalence data for low-responders vary widely and there have been few investigations in vascular surgery patients even though they are at high risk for thromb-embolic complications. The aim of this prospective observational monocentric study was to elucidate possible changes in ALR or CLR after common vascular procedures.

Methods

Activity of aspirin and clopidogrel was measured by impedance aggregometry using a multiple electrode aggregometer (Multiplate®). Possible risk factors for ALR or CLR were identified by demographical, clinical data and laboratory parameters. In addition, a follow-up aggregometry was performed after completion of the vascular procedure to identify changes in antiplatelet response.

Results

A total of 176 patients taking antiplatelet medications aspirin and/or clopidogrel with peripheral artery disease (PAD) and/or carotid stenosis (CS) were included in the study. The prevalence of ALR was 13.1% and the prevalence of CLR was 32% in the aggregometry before vascular treatment. Potential risk factors identified in the aspirin group were concomitant insulin medication (p = 0.0006) and elevated C-reactive protein (CRP) (p = 0.0021). The overall ALR increased significantly postoperatively to 27.5% (p = 0.0006); however, there was no significant change in CLR that was detected. In a subgroup analysis elevation of the platelet count was associated with a post-procedure increase of ALR incidence.

Conclusion

The incidence of ALR in vascular surgery patients increases after vascular procedures. An elevated platelet count was detected as a risk factor. Further studies are necessary to analyse this potential influence on patency rates of vascular reconstructions.

Platelet aggregation is not altered among men with diabetes mellitus

AIMS

Platelets are pivotal in arterial thrombosis, and platelet hyperresponsiveness may contribute to the increased incidence of cardiovascular events in diabetes mellitus. Consequently, we hypothesized that increased in vitro platelet aggregation responses exist in men with diabetes mellitus.

METHODS

The Danish Cardiovascular Screening Trial (DANCAVAS) is a community-based cardiovascular screening trial including men aged 65-74 years. Platelet aggregation was tested using 96-well light transmission aggregometry with thrombin receptor-activating peptide (TRAP), adenosine diphosphate, collagen type 1, arachidonic acid and protease-activated receptor-4 in three concentrations. Further, cardiovascular risk factors and coronary artery calcification (CAC), estimated by CT scans and ankle-brachial index, were obtained.

RESULTS

Included were 720 men aged 65-74 years, 110 with diabetes mellitus. Overall, there was no difference in platelet aggregation among men with versus without diabetes mellitus when adjusting for or excluding platelet inhibitor treatment and men with established cardiovascular disease (CVD). This was true for all agonists, e.g., 10 µM TRAP-induced platelet aggregation of median 69% (IQR 53-75) versus 70% (IQR 60-76) in men with versus without diabetes mellitus. Platelet aggregation did not correlate with HbA_1c or CAC. Men with diabetes mellitus displayed higher CAC, median 257 Agatston units (IQR 74-1141) versus median 111 Agatston units (IQR 6-420) in the remaining individuals, p < 0.0001.

CONCLUSIONS

Among outpatients with diabetes mellitus, but no CVD and no platelet inhibitor treatment, neither are platelets hyperresponsive in diabetes mellitus, nor is platelet aggregation associated with glycemic status or with the degree of coronary atherosclerosis.

TRIAL REGISTRATION

ISRCTN12157806.

[Clinical and prognostic value of the residual activity of platelets in patients with acute coronary syndrome without st segment elevation]

AIM

To study clinical prognostic value of residual platelet activity in patients with acute coronary syndrome without ST segment elevation.

MATERIAL AND METHODS

The study included 120 patients with acute coronary syndrome without ST segment elevation (NSTE ACS) with coronary artery stenting. Testing of residual reactivity of platelets in the subjects was carried out after loading doses of  aspirin and P2Y12-inhibitors.Patients were divided into two groups comparable in gender and age: with low residual reactivity of platelets (LRR), n=90 and with high residual reactivity of platelets (HRR), n=30. Between the groups a comparative assessment of clinical-laboratory and instrumental indicators, development of a combined end point (ischemic events) and bleeding during follow-up (16 ± 6 months).

RESULTS

The group with HRR was initially heavier: patients with angina pectoris of functional class III, atrial fibrillation, myocardial infarction, was a higher risk on the GRACE (202,6±11 vs. 148,6±7, р=0,03),increased levels of Troponin T (70,0 vs. 45,5%, р=0,02), acute occlusion in the coronary arteries (66,6 vs. 42,4%, р=0,02).The combined endpoint was more often reported in patients with HRR (40 vs. 20,7%, р=0,04). Patients with ADP-aggregation of platelets in the range 0-1 Om had a greater risk of developing hemorrhagic events (17,1 vs. 2,1%, RR 8,05 CI: 1,1-59,9, р=0,01).

CONCLUSION

In patients with NSTE ACSHRR after loading doses of aspirin and P2Y12-inhibitor was associated with the development of repeated atherothrombotic events. Very low LRR was associated with the development of bleeding.

Management of antiplatelet therapy in patients undergoing neuroendovascular procedures

Neuroendovascular techniques for treating cerebral aneurysms and other cerebrovascular pathology are increasingly becoming the standard of care. Intraluminal stents, aneurysm coils, and other flow diversion devices typically require concomitant antiplatelet therapy to reduce thromboembolic complications. The variability inherent with the pharmacodynamic response to common antiplatelet agents such as aspirin and clopidogrel complicates optimal selection of antiplatelet agents by clinicians. This review serves to discuss the literature related to antiplatelet use in neuroendovascular procedures and provides recommendations for clinicians on how to approach patients with variable response to antiplatelet agents, particularly clopidogrel.

[Prevalence of acetylsalicylic acid (ASA) - low response in vascular surgery]

BACKGROUND

Research has revealed that a decreased antiplatelet effect (low response [LR]/high on-treatment platelet reactivity [HPR]) of acetylsalicylic acid (ASA) and clopidogrel is associated with an increased risk of thromboembolic events. There are extensive ASA low response (ALR) and clopidogrel low response (CLR) prevalence data in the literature, but there are only a few studies concerning vascular surgical patients. The aim of this study was to examine the prevalence and risk factors of ALR and CLR in vascular surgical patients.

MATERIALS AND METHODS

We examined n = 154 patients with an antiplatelet long-term therapy, who were treated due to peripheral artery occlusive disease (PAD) and/or arteria carotis interna stenosis (CVD). To detect an ALR or CLR, we examined full blood probes with impedance aggregometry (ChronoLog® Aggregometer model 590). Risk factors were examined by acquisition of concomitant disease, severity of vascular disease, laboratory test results and medication.

RESULTS

We found a prevalence of 19.3 % in the ALR group and of 21.1 % in the CLR group. Risk factors for ALR were an increased platelet and leucocyte count and co-medication with pantoprazole. We found no significant risk factors for a decreased antiplatelet effect of clopidogrel treatment.

CONCLUSION

The investigated prevalence for ALR and CLR are in the range of other studies, particularly based on cardiological patients. More investigations are needed to gain a better evaluation of the risk factors for HPR and to develop an effective antiplatelet therapy regime to prevent cardiovascular complications.

Haemodialysis impairs clopidogrel but not aspirin responsiveness in patients with end-stage renal disease

Dual antiplatelet therapy (DAPT) with aspirin (ASA) and clopidogrel (Clp) is the standard treatment to reduce ischaemic coronary events, but in patients with end-stage renal disease (ESRD) the efficacy of Clp remains unclear. Patients with ESRD are at higher risk for coronary artery disease (CAD) and also their post-interventional outcome is worse compared to patients with normal renal function. Little is known about the influence of haemodialysis (HD) on ASA and Clp responsiveness. To assess the effect of HD on ASA- and Clp-responsiveness in patients with documented CAD and ESRD, 31 patients with ESRD (mean age 66.5 ± 1.8 years, 23 male ) on DAPT were evaluated for their ASA and Clp responsiveness with the Verify Now System (Accumetrics Inc.) We measured the antiplatelet effect in all ESRD patients at three time points: T1: just before HD; T2: directly after HD; T3: steady state on a HD free day one week after T1. In our study at baseline 10 (32.3%) patients were ASA-low responder (ASA-LR) and 14 (45.2%) patients Clp-low responder (Clp-LR). There was a significant difference in the PRU values before ( T1) and immediately after HD (T2) [PRU T1=234 (169; 274) vs PRUT2= 247 (199; 278); pT1,2=0.036; ]. Results were shown as median ARU T1 (25th, 75th percentile) or median PRU T1 (25th, 75th percentile). Hence HD seems to impair responsiveness to Clp, resulting in an increase of 6.5 % Clp-LR. No significant differences in the ARU values at the different time-points were found.

A randomised trial on platelet function-guided de-escalation of antiplatelet treatment in ACS patients undergoing PCI

Outcomes of acute coronary syndrome (ACS) patients undergoing percutaneous coronary intervention (PCI) have been significantly improved with the use of potent P2Y12 receptor inhibitors like prasugrel. While most of the ischaemic risk reduction for prasugrel versus clopidogrel was demonstrated in the early treatment period, the risk of bleeding became particularly prominent during the chronic course of therapy. It may therefore be a valid approach to substitute prasugrel for clopidogrel in the early phase of chronic antiplatelet treatment after PCI. In the Testing Responsiveness To Platelet Inhibition On Chronic Antiplatelet Treatment For Acute Coronary Syndromes (TROPICAL-ACS) trial, we aim to compare standard prasugrel therapy with a de-escalating antiplatelet treatment approach guided by platelet function testing (PFT). The study is an investigator-initiated European multicentre, randomised clinical trial in biomarker-positive ACS patients after successful PCI. Two thousand six hundred patients will be randomised prior to hospital discharge in a 1:1 fashion to either receive standard prasugrel therapy (control group) or de-escalating therapy (one-week prasugrel followed by one-week clopidogrel and PFT-guided maintenance therapy from day 14 after hospital discharge, monitoring group). Patients of the monitoring group with high on-clopidogrel platelet reactivity (HPR) based on Multiplate analyzer testing (HPR: ≥ 46U per consensus definition) will be switched back to prasugrel, whereas those without HPR (<46 U) will continue clopidogrel treatment. The overall study treatment duration will be one year in both groups. The primary endpoint of the study is net clinical benefit (combined incidence of cardiovascular death, myocardial infarction, stroke and bleeding ≥ grade 2 according to BARC criteria) one-year after randomisation. TROPICAL-ACS is the first large-scale, randomised controlled trial assessing the clinical value of a PFT-guided de-escalation of antiplatelet treatment in biomarker positive ACS patients undergoing PCI.

ClinicalTrials.gov Identifier: NCT01959451

Circulating miRNAs: messengers on the move in cardiovascular disease

Note: The review process for this paper was fully handled by G. Y. H. Lip, Editor in Chief.

High platelet reactivity – the challenge of prolonged anticoagulation therapy after ACSI

Despite dual antiplatelet therapy (DAPT), one-year event rates after acute coronary syndrome (ACS) vary from 9–12%. The development of novel oral anticoagulants (NOAC) without a need for monitoring has initiated renewed interest for prolonged adjunctive anticoagulation. Importantly, the cornerstone of treatment after ACS consists of long-term DAPT. In that context, the NOACs have only been tested as adjunctive therapy. Of all new agents, only rivaroxaban –in a substantially lower dose than used for atrial fibrillation– has been demonstrated to improve outcome, albeit at the cost of bleeding. In selected cases, adjunctive therapy with dose-adjusted vitamin-K antagonists (international normalized ratio [INR] 2.0–3.0) can be considered as well. These two strategies of prolonged anticoagulation can be considered in case of ‘high platelet reactivity’, i.e. in patients at high risk of recurrent thrombotic events despite DAPT. Both during admission and after discharge for ACS, the use of NOACs in doses indicated for atrial fibrillation is strictly contra-indicated in patients on DAPT. In case of post-discharge anticoagulation therapy for atrial fibrillation, patients should preferably receive vitamin-K antagonists (INR 2.0–3.0), with discontinuation of one antiplatelet agent as soon as clinically justifiable. Importantly, the impact of prolonged anticoagulation (low-dose rivaroxaban, vitamin-K antagonists) as adjunctive to DAPT after ACS has not been addressed with the most potent antiplatelet agents (prasugrel, ticagrelor) and merits further study. Despite the potential indication of prolonged oral anticoagulation as adjunctive treatment, it remains to be established whether anticoagulation therapy could also be an alternative for either aspirin or thienopyridine treatment in selected ACS patients on DAPT.

Cost–effectiveness analysis of personalized antiplatelet therapy in patients with acute coronary syndrome

Aim: This study aimed to compare the clinical and economic outcomes of pharmacogenetic-guided (PG-guided) and platelet reactivity testing-guided antiplatelet therapy for patients with acute coronary syndrome undergoing percutaneous coronary intervention. Methods: A decision-analytic model was simulated including four antiplatelet strategies: universal clopidogrel 75 mg daily, universal alternative P2Y12 inhibitor (prasugrel or ticagrelor), PG-guided therapy, and platelet reactivity testing-guided therapy. Results: PG-guided therapy was the preferred option with lowest cost (US$75,208) and highest quality-adjusted life years gained (7.6249 quality-adjusted life years). The base-case results were robust in sensitivity analysis. Conclusion: PG-guided antiplatelet therapy showed the highest probability to be preferred antiplatelet strategy for acute coronary syndrome patients with percutaneous coronary intervention.

Comparing of light transmittance aggregometry and modified thrombelastograph in predicting clinical outcomes in Chinese patients undergoing coronary stenting with clopidogrel

BACKGROUND

Several platelet function tests are currently used to measure responsiveness to antiplatelet therapy. This study was to compare two tests, light transmittance aggregometry (LTA) and modified thrombelastography (mTEG), for predicting clinical outcomes in Chinese patients after percutaneous coronary intervention (PCI).

METHODS

Prospective, observational, single-center study of 789 Chinese patients undergoing PCI was enrolled. This study was investigated the correlations between the two tests and performed receiver operating characteristic curve (ROC) analysis for major adverse cardiovascular events (MACEs) at 1-year follow-up.

RESULTS

MACEs occurred in 32 patients (4.1%). Correlations were well between the two tests in the adenosine diphosphate induced platelet reactivity (Spearman r = 0.733, P < 0.001). ROC-curve analysis demonstrated that LTA (area under the curve [AUC]: 0.677; 95% confidence interval [CI]: 0.643-0.710; P = 0.0009), and mTEG (AUC: 0.684; 95% CI: 0.650-0.716; P = 0.0001) had moderate ability to discriminate between patients with and without MACE. MACE occurred more frequently in patients with high on-treatment platelet reactivity (HPR) when assessed by LTA (7.4% vs. 2.7%; P < 0.001), and by TEG (6.7% vs. 2.6%; P < 0.001). Kaplan-Meier analysis demonstrated that HPR based on the LTA and mTEG was associated with almost 3-fold increased risk of MACE at 1-year follow-up.

CONCLUSIONS

The correlation between LTA and mTEG is relatively high in Chinese patients. HPR measured by LTA and mTEG were significantly associated with MACE in Chinese patients undergoing PCI.

Clinical pharmacokinetics and pharmacodynamics of clopidogrel

Acute coronary syndromes (ACS) remain life-threatening disorders, which are associated with high morbidity and mortality. Dual antiplatelet therapy with aspirin and clopidogrel has been shown to reduce cardiovascular events in patients with ACS. However, there is substantial inter-individual variability in the response to clopidogrel treatment, in addition to prolonged recovery of platelet reactivity as a result of irreversible binding to P2Y12 receptors. This high inter-individual variability in treatment response has primarily been associated with genetic polymorphisms in the genes encoding for cytochrome (CYP) 2C19, which affect the pharmacokinetics of clopidogrel. While the US Food and Drug Administration has issued a boxed warning for CYP2C19 poor metabolizers because of potentially reduced efficacy in these patients, results from multivariate analyses suggest that additional factors, including age, sex, obesity, concurrent diseases and drug-drug interactions, may all contribute to the overall between-subject variability in treatment response. However, the extent to which each of these factors contributes to the overall variability, and how they are interrelated, is currently unclear. The objective of this review article is to provide a comprehensive update on the different factors that influence the pharmacokinetics and pharmacodynamics of clopidogrel and how they mechanistically contribute to inter-individual differences in the response to clopidogrel treatment.

An Assay of Measuring Platelet Reactivity Using Monoclonal Antibody against Activated Platelet Glycoprotein IIb/IIIa in Patients Taking Clopidogrel

Background and Objectives

Residual platelet reactivity in patients who are taking clopidogrel is commonly measured with VerifyNow assay, which is based on the principle of light transmission aggregometry. However, to evaluate the residual platelet reactivity, it would be more accurate if the reactivity of platelet glycoprotein (GP) IIb/IIIa is directly monitored. In this study, PAC1, a monoclonal antibody against activated platelet GP IIb/IIIa, was used to measure the residual platelet reactivity.

Subjects and Methods

Twenty seven patients with coronary artery disease taking clopidogrel were enrolled. Platelets in whole blood were stained with fluorescein isothiocyanate (FITC)-conjugated PAC1. Mean fluorescence intensity (MFI) and % positive platelets (PP) were measured with flow cytometry, and the binding index (BI; MFI × %PP/100) was calculated. P2Y12 reaction unit (PRU) and % inhibition of VerifyNow assay were also measured in the usual manner.

Results

PRU of VerifyNow assay correlated significantly with MFI, %PP, and BI at 10 µM (r=0.59, 0.73, and 0.60, respectively, all p<0.005) and 20 µM of adenosine diphosphate (ADP; r=0.61, 0.75, and 0.63, respectively, all p<0.005). The % inhibition also correlated significantly with MFI, %PP, and BI at 10 µM (r=-0.60, -0.69, and -0.59, respectively, all p<0.005) and 20 µM of ADP (r=-0.63, -0.71, and -0.62, respectively, all p<0.005).

Conclusion

Direct measurements of the reactivity of platelet GP IIb/IIIa were feasible using PAC1 and flow cytometry in patients taking clopidogrel. Further clinical studies are required to determine the cut-off values which would define high residual platelet reactivity in patients on this treatment protocol.

High On-Treatment Platelet Reactivity Associated With Prasugrel

Objective: To report a case of high on-treatment platelet reactivity (HTPR) with prasugrel maintenance therapy despite adequate initial platelet response to a loading dose. Case Summary: A 51-year-old woman presented to the emergency department complaining of chest pain. She was diagnosed with acute-on-chronic systolic heart failure and non-ST-elevated myocardial infarction (MI). She had a previous MI with bare metal stent placement and was taking aspirin and prasugrel 10 mg daily. Once admitted, a P2Y12 assay revealed HTPR (331 PRU); therefore, prasugrel was reloaded (60 mg). The next day a P2Y12 assay showed adequate platelet reactivity inhibition (118 PRU), so prasugrel 10 mg daily was continued in the hospital and on discharge. Seventeen days after discharge she was readmitted for possible ischemia. On day 3 of admission, a P2Y12 assay revealed HTPR (278 PRU); subsequently, prasugrel was discontinued and ticagrelor started. After 3 doses of ticagrelor, a P2Y12 assay was 97 PRU, so ticagrelor was continued. Five months have passed since discharge. The patient continues to take ticagrelor and has had no further cardiac events. Discussion: HTPR indicates hypo- or nonresponsiveness for antiplatelet agents and may result in serious adverse events. HTPR has rarely been reported with prasugrel or ticagrelor. An objective causality assessment of our case revealed a probable association between HTPR and prasugrel. Conclusion: Patient education and recognition of signs and symptoms associated with prasugrel HTPR may prevent morbidity and mortality from treatment failure. Additional research may determine incidence, risk factors, and optimal management of HTPR with prasugrel.

Association between platelet reactivity and circulating platelet-derived microvesicles in patients with acute coronary syndrome

High on-treatment platelet reactivity (HPR) to clopidogrel has been shown to increase the risk of cardiovascular events. Platelet-derived microvesicles (PMVs) may be prothrombotic and contribute to the risk of recurrent events observed in patients with HPR. However, PMVs may also serve as biomarkers and be used to assess platelet function. We investigated the association between platelet responses to clopidogrel (measured by whole blood impedance aggregometry) and circulating PMVs in patients with acute coronary syndrome (ACS). Blood samples were obtained at discharge from 200 patients with ACS who had undergone percutaneous coronary intervention (PCI). All patients were loaded with aspirin and clopidogrel before PCI. ADP-induced whole blood impedance aggregometry and measurement of PMVs were performed. Cut-off values for HPR and other reactivity (i.e. normal on-treatment reactivity, NPR and low on-treatment reactivity, LPR) to clopidogrel were set according to data from large prospective studies. We measured PMVs as phosphatidylserine and CD42a positive vesicles, together with CD62P or CD40L, using flow cytometry. ADP-induced platelet aggregation revealed that approximately 20% of patients had HPR. Levels of PMVs were almost two-fold higher in the HPR group compared with patients without HPR (for both CD42a- and CD62P-positive PMVs, p < 0.01). Furthermore, patients with LPR to clopidogrel had significantly fewer PMVs exposing CD62P than patients with HPR or those with NPR to clopidogrel. Patients with HPR during clopidogrel treatment have elevated levels of circulating PMVs, indicating ongoing platelet activation despite clopidogrel treatment. Moreover, in patients with LPR to clopidogrel, circulating PMV numbers are decreased. Taken together, our data suggest that PMVs are potential biomarkers of antiplatelet responses to clopidogrel. If PMVs also have prognostic value after, ACS should be tested in future studies.

Pharmacodynamic effects of cilostazol versus clopidogrel in stented patients under proton pump inhibitor co-administration: the ACCEL-PARAZOL study

AIM

Proton pump inhibitor (PPI) therapy has been shown to attenuate the antiplatelet effects of clopidogrel. The aim of this study was to compare the antiplatelet effects of cilostazol versus clopidogrel in patients co-administered a PPI.

METHODS

We enrolled PPI-naïve stented patients treated with standard clopidogrel and aspirin therapy for at least six months (n=100). The patients were randomly assigned to receive either cilostazol at a dose of 100mg twice daily (CILO group) or clopidogrel at a dose of 75mg daily (CLPD group) in addition to lansoprazole (30mg daily). The platelet aggregation (PA) determined using light transmittance aggregometry and the platelet reactivity index (PRI) obtained using a vasodilator-stimulated phosphoprotein phosphorylation assay were measured before randomization and at the 14-day follow-up visit. The primary endpoint was the PRI value at follow-up.

RESULTS

At follow-up, the CLPD group showed similar values of PRI as the CILO group (66.9±14.0% vs. 63.1±14.1%; mean difference: 3.9%; 95% confidence interval of difference: -1.7% to 9.4%; p=0.174). However, the 6μg/mL collagen- and 0.5mg/mL arachidonic acid-induced PA values in the CLPD group were higher than those observed in the CILO group (mean differences: 9.8% to 11.1%; all p values ＜0.001). CYP2C19 loss-of-function allele carriage was the major contributing factor associated with the PRI level in the absence of lansoprazole treatment (with a gene-dose effect); this association was not observed in the subjects receiving lansoprazole co-administration in the CLPD group.

CONCLUSIONS

During lansoprazole co-administration, cilostazol treatment achieves a more favorable platelet function profile than clopidogrel therapy. The use of combination treatment with cilostazol and aspirin deserves further attention with respect to the management of stable stented patients requiring PPI co-administration.

Risk of stroke in patients with high on-clopidogrel platelet reactivity to adenosine diphosphate after percutaneous coronary intervention

Several prospective studies have shown that high on-clopidogrel platelet reactivity (HPR) in patients undergoing percutaneous coronary intervention (PCI) is a risk factor for ischemic events. All studies were insufficiently powered to detect differences in stroke between patients with HPR and those without. Therefore, we performed a systematic review and meta-analysis of available publications aimed at determining whether patients undergoing PCI with HPR are also at increased risk of stroke. We searched for prospective studies enrolling patients undergoing PCI and treated with aspirin and clopidogrel that reported on clinical relevance of HPR to adenosine diphosphate. Study end point was the rate of stroke. We also investigated whether there was an interaction on the relative risk of stroke between HPR, clinical presentation, duration of follow-up, or laboratory methods. Fourteen studies including 11,959 patients were deemed eligible. On pooled analysis, the risk of stroke was higher in patients with HPR compared with patients with no HPR (1.2% vs 0.7%, relative risk on fixed effect 1.84, 95% confidence interval 1.21 to 2.80). There was no heterogeneity among the studies (I(2) = 0%, p = 0.5). Clinical presentation (p = 0.39 for interaction), duration of follow-up (p = 0.87 for interaction), and laboratory method for detection of HPR (p = 0.99 for interaction) did not affect the relative increase in the risk of stroke in patients with HPR compared with patients with no HPR. In conclusion, in patients with coronary artery disease undergoing PCI, the presence of HPR to adenosine diphosphate is a risk factor for stroke.

Impact of obesity and the metabolic syndrome on response to clopidogrel or prasugrel and bleeding risk in patients treated after coronary stenting

This study aimed to analyze the impact of body mass index (BMI) and the metabolic syndrome (MS) on responses to clopidogrel or prasugrel and bleeding risk after acute coronary syndrome. The study included 1,542 consecutive patients who underwent coronary stenting (287 clopidogrel 75 mg, 868 clopidogrel 150 mg, and 387 prasugrel 10 mg). Platelet reactivity was assessed 1 month after discharge using platelet reactivity index vasodilator stimulated phosphoprotein (PRI VASP). Three hundred thirty-six patients (21.8%) were obese (BMI ≥30), and we observed higher platelet reactivity associated with higher BMI across thienopyridine regimens. Incidence of high on-treatment platelet reactivity (PRI VASP >50%) was higher in obese than nonobese patients (p <0.05 for all regimens). Conversely, incidence of low on-treatment platelet reactivity with prasugrel therapy (PRI VASP <20%) was lower in obese than nonobese patients: 13% (12 of 93) versus 33% (97 of 294); odds ratio 0.30, 95% confidence interval 0.16 to 0.58; p <0.001. Accordingly, incidence of Bleeding Academic Research Consortium bleeding complications was higher in nonobese than in obese patients: 10% (119 of 1,206) versus 6% (20 of 336); odds ratio 1.7, 95% confidence interval 1.1 to 2.8; p = 0.03. This impaired response was only observed in obese patients with the MS, and obese with the MS had significantly higher platelet reactivity than other obese patients with all regimens (p <0.01). Obese patients without the MS had no significant difference in platelet reactivity compared with nonobese patients. In conclusion, the present study confirmed that BMI has a strong impact on response to clopidogrel and prasugrel with higher incidence of high on-treatment platelet reactivity, lower incidence of low on-treatment platelet reactivity, and lower bleeding complication in obese patients. However, among obese patients, the presence of the MS strongly affects response to antiplatelet agents, indicating that the metabolic status might be a better predictor of platelet inhibition than BMI.

Discrepant coagulation profile in HIV infection: elevated D-dimer but impaired platelet aggregation and clot initiation

OBJECTIVES

In HIV infection, cardiovascular disease (CVD) has emerged as a clinical problem, and elevated D-dimer has been reported. The pathophysiologic mechanisms underlying this remain unclear. We aimed to investigate whether untreated HIV-infected individuals display evidence of functional coagulopathy and whether this was associated with microbial translocation.

DESIGN

The study population consisted of 50 HIV-infected untreated individuals and 50 HIV-infected individuals on combination antiretroviral therapy (cART). Groups were matched for age, sex and current CD4cell count.

METHODS

Coagulation analyses included D-dimer and the functional haemostatic whole blood tests, thromboelastography (TEG) and platelet aggregation (Multiplate, impedance aggregometry). Microbial translocation was assessed by plasma levels of lipopolysaccharide (LPS).

RESULTS

A larger proportion of untreated individuals compared with treated individuals had D-dimer above normal reference range (27.7 vs. 2.2%, P = 0.001). In both treated and untreated individuals, delayed clot initiation with TEG R-time above upper reference range (18 and 28%, respectively, both P < 0.001) and TEG angle below lower reference range [14% (P = 0.004) and 24% (P < 0.001), respectively] was found. In untreated individuals, 64.6% had aggregation response below threshold in at least two of four tests compared with 36.7% in treated individuals (P = 0.010). Untreated individuals with increased D-dimer levels were relatively hypercoagulable by thromboelastography. Furthermore, in untreated patients, a negative association between microbial translocation and platelet aggregation was found.

CONCLUSION

Elevated D-dimer in untreated HIV-infected individuals was confirmed. However, in both untreated and treated individuals, reduced platelet aggregation and clot initiation was found. The impact of reduced platelet function in HIV infection and a potential role of microbial translocation warrant further investigation.

Relation between the vasodilator-stimulated phosphoprotein phosphorylation assay and light transmittance aggregometry in East Asian patients after high-dose clopidogrel loading

OBJECTIVES

We analyzed the relation between platelet aggregation measured by light transmittance aggregometry (LTA) and platelet reactivity index (PRI) measured by vasodilator-stimulated phosphoprotein phosphorylation (VASP-P) assay.

BACKGROUND

It has been suggested that LTA and VASP-P assay correlate differently according to the level of P2Y12 receptor blockade by thienopyridines.

METHODS

We simultaneously measured platelet function by LTA and VASP-P assay in 466 East Asians undergoing elective percutaneous coronary intervention after a 600-mg clopidogrel loading. High on-clopidogrel platelet reactivity (HPR) was defined by published consensus criteria.

RESULTS

The degree of correlation between LTA and the VASP-P assay was different according to PRI levels. The correlation was lower in patients with poor responsiveness (PRI >60%) (n = 216) (0.035 ≤ r(2) ≤ 0.047), which was greater in responsive patients (PRI ≤60%) (n = 250) (0.315 ≤ r(2) ≤ 0.526). Despite a 600-mg loading, East Asians had a high prevalence of HPR (40.1%-63.5%), and the prevalence of HPR also differed between LTA and VASP-P assay. A PRI cutoff of >58% (area under curve, 0.829; 95% confidence intervals, 0.792-0.862; P < .001) corresponded to the published HPR cutoff by 5-μM adenosine diphosphate-induced maximal platelet aggregation >46%.

CONCLUSIONS

This is the largest study correlating platelet reactivity measured by LTA and VASP-P assay in a percutaneous coronary intervention-treated cohort. The correlation is dependent on the level of responsiveness. Future investigations are needed to better define the optimal cutoffs of HPR measured by LTA and VASP-P assay for personalized antiplatelet therapy.

Glucose intolerance and insulin resistance as predictors of low platelet response to clopidogrel in patients with minor ischemic stroke or TIA

The relation between high on-treatment platelet reactivity (HPR), and the level of glucose intolerance and insulin resistance (IR) was studied in clopidogrel-treated patients with minor ischemic stroke or TIA. The cohort consisted of 66 patients, 11 of which had known type 2 diabetes mellitus (DM). Platelet aggregation in whole blood (Multiplate™) and metabolic variables were measured 1 month after acute onset of neurological symptoms. Glucose tolerance was measured by Oral Glucose Tolerance Test (OGTT). IR was estimated by homeostasis model assessment HOMA-IR. Patients were categorized as "responders" (R) or "non-responders" (NR) to clopidogrel according to an established cut-off in platelet aggregation induced by adenosine diphosphate (ADP). In total, 14/66 (21%) patients were NR. Impaired glucose tolerance (IGT), impaired fasting glucose (IFG) or DM was seen in 13/14 NR (93%), while for R this was the case in 25/52 (48%), p = 0.001. The percentage of NR was 33% in patients with DM and 35% in patients with IGT or IFG. In the group with normal glucose tolerance (NGT) the percentage of NR was low, 4% (1/28). Fasting plasma glucose (f-PG) was higher for NR than for R, 6.0 (5.5-6.7) mM vs. 5.3 (5.0-6.0) mM, p = 0.023. Glycated hemoglobin (HbA1c) did not differ between NR and R. NR also had higher arachidonic acid-induced platelet aggregation than R, and a tendency towards higher aggregation induced by thrombin receptor agonist peptide (TRAP), indicating that HPR reflects a global platelet hyper-reactivity. HOMA-IR was calculated for 52 of the patients above without known diabetes, 9 of which were NR (17%). NR were significantly more insulin resistant than R, with median HOMA-IR 4.5 (3.0-7.4) compared to 2.1 (1.5-3.2) for R, p = 0.001. HOMA-IR and fasting plasma insulin were the only metabolic variables with significant relationships to ADP-induced platelet aggregation. The results suggest that HPR develops in the pre-diabetic phase. A metabolic disturbance with glucose intolerance and/or high level of IR was a pre-requisite for HPR in the tested cohort. Conversely, normal glucose tolerance combined with normal or mildly elevated HOMA-IR excluded HPR. NR are likely to constitute a high-risk group among patients with ischemic cerebrovascular disease. Measurement of f-PG or HbA1c is insufficient to identify NR, while OGTT and HOMA-IR are more predictive.

Platelet function in health and disease: from molecular mechanisms, redox considerations to novel therapeutic opportunities

Increased oxidative stress appears to be of fundamental importance in the pathogenesis and development of several disease processes. Indeed, it is well known that reactive oxygen species (ROS) exert critical regulatory functions within the vascular wall, and it is, therefore, plausible that platelets represent a relevant target for their action. Platelet activation cascade (including receptor-mediated tethering to the endothelium, rolling, firm adhesion, aggregation, and thrombus formation) is tightly regulated. In addition to already well-defined platelet regulatory factors, ROS may participate in the regulation of platelet activation. It is already established that enhanced ROS release from the vascular wall can indirectly affect platelet activity by scavenging nitric oxide (NO), thereby decreasing the antiplatelet properties of endothelium. On the other hand, recent data suggest that platelets themselves generate ROS, which may evoke pro-thrombotic responses, triggering many biological processes participating in atherosclerosis initiation, progression, and complication. That oxidative stress may alter platelet function is conceivable when considering that antioxidants play a role in the prevention of cardiovascular disease, although the precise mechanism accounting for changes attributable to antioxidants in atherosclerosis remains unknown. It is possible that the effects of antioxidants may be a consequence of their enhancing or promoting the antiplatelet effects of NO derived from both endothelial cells and platelets. This review focuses on current knowledge regarding ROS-dependent regulation of platelet function in health and disease, and summarizes in vitro and in vivo evidence for their physiological and potential therapeutic relevance.

Translational platelet research in patients with coronary artery disease: what are the major knowledge gaps?

Translational platelet function investigations performed in the percutaneous coronary intervention (PCI)-treated population receiving clopidogrel have identified high platelet reactivity to ADP (HPR) as a major risk factor for both acute as well as long-term ischaemic event occurrence, including stent thrombosis. Recent studies have highlighted the relation of single nucleotide polymorphisms of genes involved in clopidogrel absorption and metabolism to reduced pharmacokinetic and pharmacodynamic responses to clopidogrel. CYP 2C19 loss-of-function (LoF) allele carriage has been associated with increased thrombotic risk in the PCI population. However, there is no information regarding the utility of platelet function testing to predict outcomes in patients with stable coronary artery disease and in medically managed patients with acute coronary syndromes. Additionally, few studies have included longitudinal assessment of platelet function to assess a potential time-dependent relation to ischaemic event occurrence and no phase-III antiplatelet-therapy trial has included a large enough platelet function sub-study to examine the relation between on-treatment platelet reactivity, bleeding, and ischaemic event occurrence. Therefore, futher studies are needed to delineate the role of platelet function testing across the spectrum of symptomatic coronary artery disease.

Network meta-analysis of prasugrel, ticagrelor, high- and standard-dose clopidogrel in patients scheduled for percutaneous coronary interventions

Since novel antiplatelet treatments (prasugrel, ticagrelor, high-dose clopidogrel) have been predominantly tested against standard-dose clopidogrel, data on direct comparisons between these therapies are scarce. We therefore indirectly compared their efficacy and safety in patients undergoing percutaneous coronary intervention. Electronic databases were searched systematically to identify head-to-head randomised controlled trials (RCTs). Network meta-analysis was performed using generalised linear mixed models with adjustment for length of follow-up. Findings were corroborated by mixed treatment comparison through Bayesian methods. Fourteen RCTs were identified and included in the analysis (high- vs. standard-dose clopidogrel: 9 trials, prasugrel vs. high-dose clopidogrel: 2 trials, prasugrel vs. standard-dose clopidogrel: 2 trials, ticagrelor vs. standard-dose clopidogrel: 1 trial). No significant differences were found for efficacy outcomes except for stent thrombosis favouring prasugrel (vs. ticagrelor: odds ratio [OR] 0.63, 95% confidence interval [CI]: 0.42, 0.94; vs. high-dose clopidogrel: OR 0.70, 95%CI: 0.48, 1.01). Prasugrel exhibited a similar bleeding risk as high-dose clopidogrel, but more major (OR 1.43, 95%CI 1.07, 1.90) and major or minor bleeding (OR 1.36, 95%CI 1.09, 1.69) compared to ticagrelor. Ticagrelor was also associated with less major or minor bleeding compared to high-dose clopidogrel (OR 0.81, 95%CI 0.69, 0.96). No differences were seen for non CABG-related major bleeding between the three strategies. Results were corroborated in a subgroup analysis comprising only patients with acute coronary syndromes. In the absence of head-to-head clinical trials, network meta-analysis suggests potentially relevant differences in efficacy and bleeding risk among novel antiplatelet treatments and may thereby advance understanding of their differential therapeutic properties.

Genetics of ischemic stroke, stroke-related risk factors, stroke precursors and treatments

Stroke remains a leading cause of death worldwide and the first cause of disability in the western world. Ischemic stroke (IS) accounts for almost 80% of the total cases of strokes and is a complex and multifactorial disease caused by the combination of vascular risk factors, environment and genetic factors. Investigations of the genetics of atherosclerosis and IS has greatly enhanced our knowledge of this complex multifactorial disease. In this article we sought to review common single-gene disorders relevant to IS, summarize candidate gene and genome-wide studies aimed at discovering genetic stroke risk factors and subclinical phenotypes, and to briefly discuss pharmacogenetics related to stroke treatments. Genetics of IS is, in fact, one of the most promising research frontiers and genetic testing may be helpful for novel drug discoveries as well as for appropriate drug and dose selection for treatment of patients with cerebrovascular disease.

Description of response to aspirin and clopidogrel in outpatients with coronary artery disease using multiple electrode impedance aggregometry

Identification of outpatients with high platelet reactivity (HPR) on antiplatelet treatment is an unmet need. The present study was conducted in healthy individuals (n = 50) and in outpatients with coronary artery disease (CAD) at a distance from the acute ischemic episode (aspirin group, n = 71; aspirin/clopidogrel group, n = 106). We studied the feasibility and the precision of whole blood multiple electrode aggregometry (MEA) after triggering platelet aggregation by arachidonic acid or adenosine diphospate (ADP). The MEA can be performed on whole blood within 2 hours after sample venipuncture. The threshold for the diagnosis of HPR is situated at 55 and 50 U for the arachidonic acid and ADP test, respectively. Frequency of HPR was 7% and 20% in aspirin and aspirin/clopidogrel groups, respectively. In 3.8% of patients in aspirin/clopidogrel group, combined HPR on aspirin and clopidogrel was found. In outpatients with CAD, use of MEA is feasible for the diagnosis of HPR.

Thrombotic microangiopathy: a role for magnesium?

Despite advances in more recent years, the pathophysiology and especially treatment modalities of thrombotic microangiopathy (TMA) largely remain enigmatic. Disruption of endothelial homeostasis plays an essential role in TMA. Considering the proven causal association between magnesium and both endothelial function and platelet aggregability, we speculate that a magnesium deficit could influence the course of TMA and the related haemolytic uraemic syndrome and thrombotic thrombocytopenic purpura. A predisposition towards TMA is seen in many conditions with both extracellular and intracellular magnesium deficiency. We propose a rationale for magnesium supplementation in TMA, in analogy with its evidence-based therapeutic application in pre-eclampsia and suggest, based on theoretical grounds, that it might attenuate the development of TMA, minimise its severity and prevent its recurrence. This is based on several lines of evidence from both in vitro and in vivo data showing dose-dependent effects of magnesium supplementation on nitric oxide production, platelet aggregability and inflammation. Our hypothesis, which is further amenable to assessment in animal models before therapeutic applications in humans are implemented, could be explored both in vitro and in vivo to decipher the potential role of magnesium deficit in TMA and of the effects of its supplementation.