Antiplatelet drug 'resistance'. Part 2: laboratory resistance to antiplatelet drugs—fact or artifact?

Insights into platelet pharmacology from a cryo-EM structure of the ABCC4 transporter

Structural determination of the ABCC4 transporter is a major first step in providing crucial molecular insights into the transport of platelet substrates into granules, as well as drug transport from platelets. The findings provide a framework for understanding platelet interactions and potential design of specific platelet antagonists.

Pharmacokinetic, pharmacodynamic, and pharmacogenetic assays to monitor clopidogrel therapy

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

Point-of-care platelet function tests: relevance to arterial thrombosis and opportunities for improvement

Studies using whole blood platelet aggregometry as a laboratory research tool, provided important insights into the mechanism and modulators of platelet aggregation. Subsequently, a number of point-of-care (POC) platelet function tests (PFTs) were developed for clinical use, based on the concept that an individual’s thrombotic profile could be assessed in vitro by assessing the response to stimulation of platelet aggregation by specific, usually solo agonists such as adenosine diphosphate (ADP), collagen and thrombin. However, adjusting antiplatelet medication in order to improve the results of such POC PFTs has not translated into a meaningful reduction in cardiovascular events, which may be attributable to important differences between the POC PFT techniques and in vivo conditions, including patient-to-patient variability. Important limitations of most tests include the use of citrate-anticoagulated blood. Citrate directly and irreversibly diminishes platelet function and even after recalcification, it may result in altered platelet aggregation in response to ADP, epinephrine or collagen, and interfere with thrombin generation from activated platelets. Furthermore, most tests do not employ flowing blood and therefore do not assess the effect of high shear forces on platelets that initiate, propagate and stabilize arterial thrombi. Finally, the effect of endogenous thrombolysis, due to fibrinolysis and dislodgement, which ultimately determines the outcome of a thrombotic stimulus, is mostly not assessed. In order to accurately reflect an individual’s predisposition to arterial thrombosis, future tests of thrombotic status which overcome these limitations should be used, to improve cardiovascular risk prediction and to guide pharmacotherapy.

Anticoagulation and Spine Surgery

STUDY DESIGN

Literature review.

OBJECTIVE

Preoperative management of therapeutic anticoagulation in spine surgery is critical to minimize risk of thromboembolic events yet prevent postsurgical complications. Limited research is available, and most guidelines are based on drug half-lives. We aim to clarify current guidelines and available evidence for safe practice of spine surgery in this patient population.

METHODS

A literature search in PubMed was done encompassing comprehensive search terms to locate published literature on anticoagulation and spine surgery. Predefined inclusion and exclusion criteria were applied and data extraction was performed.

RESULTS

A total of 17 articles met the final inclusion criteria. Of these, 12 articles were retrospective chart reviews, 3 were prospective observational studies, and 2 were systematic reviews. Current practice suggests holding warfarin until international normalized ratio <1.4, anti-Xa drugs for 48 to 72 hours, 12 to 24 hours for low-molecular-weight heparin, and 4 to 24 hours for heparin, before surgery. Antiplatelet agents can be stopped for 1 to 3 days prior to operation (81-500 mg) but must be stopped for 1 week for doses >1 g/d. For Plavix, 5 to 7 days of discontinuation advised to prevent complications.

CONCLUSIONS

This review provides an overview of main anticoagulation agents seen in preoperative setting for spine patients. Although data is mixed and no true randomized control trials are available, there is growing evidence suggesting the aforementioned guidelines are needed to optimize anticoagulation in setting of spine surgery. Further studies are needed to elucidate risk of complications while operating under therapeutic levels of anticoagulation for a variety of comorbid conditions.

Clinical utility of mean platelet volume and immature platelet fraction in acute coronary syndrome

Background

Platelets play an important role in the pathogenesis of acute coronary syndrome (ACS). Patients with ACS have an increased mean platelet volume (MPV) and immature platelet fraction (IPF) resulting in elevation of thrombotic ability. In this study, we evaluated the diagnostic performance of MPV and IPF in identifying suspected ACS patients at emergency department. Moreover, we investigated the correlation between MPV or IPF with initial troponin I (TnI), one of the current ACS biomarkers.

Methods

This was a single-center study recruiting suspected ACS patients who had acute chest pain at the emergency department. Whole blood samples were obtained from all participants and MPV and IPF were measured by Sysmex XE-5000 hematology analyzer within 20 min of blood sampling. The diagnostic values of MPV and IPF in identifying ACS were analyzed retrospectively.

Result

In this study, 63 in 104 suspected ACS patients were diagnosed as ACS (65.3%). MPV and IPF were higher in ACS patients compared to non-ACS patients (MPV: 10.7 ± 0.80 fL vs 10.0 ± 0.64 fL, p < 0.001; IPF: 3.7 ± 2.64% vs 3.1 ± 2.69%, p = 0.030). MPV and IPF were similar in unstable angina and acute myocardial infarction patients. We showed that elevation of MPV could be an independent predictive factor of ACS (odds ratio: 5.038). At the optimal cut-off value of 10.55 fL (AUC 95% CI: 0.637–0.836), the diagnostic performance of MPV in predicting ACS had an area under a receiver operating characteristic curve (AUC) of 0.736 with sensitivity and specificity of 54.2% and 82.8%, respectively. Patients with both of initial TnI and MPV higher than the established cut-off value had increased incidence (3.792 fold) for ACS development compared to patients with TnI below the cut-off value. Furthermore, diagnosing ACS with both MPV and initial TnI increased the positive predictive value from 84.2% to 86.7%. No correlation was observed between MPV or IPF and the mortality rate of ACS patients (MPV: 3.8% vs 11.1%, p = 0.300; IPF: 12.0% vs 37.5%, p = 0.054).

Conclusion

Here we show that ACS patients have higher MPV and IPF compared to non-ACS patients. We further demonstrate that MPV can be utilized as an independent predictor for early diagnosis of low-risk ACS patients who have acute chest pain.

Whole blood platelet aggregation determined by the ROTEM platelet equipment; reference intervals and stability

Point of care testing of residual effect of antiplatelet therapy in trauma patients or during major surgery may result in improved clinical management of significant bleeding. We included 121 healthy individuals (57 females and 64 males, aged 22-65 years) in order to establish reference intervals for platelet aggregation induced by adenosine diphosphate (ADPTEM, 10 µM), arachidonic acid (ARATEM, 0.42 mM) and thrombin activating peptide (TRAPTEM, 36 µM) employing the ROTEM platelet module. Further, the impact of citrate (3.2%) and hirudin (>15 µg/ml) as anticoagulants was evaluated. Finally, we investigated assay stability (15, 30, 60, and 120 min after blood sampling) (n = 8) and between-day variation (n = 5). We report reference intervals for 121 healthy individuals and reference intervals by gender. We observed significantly higher platelet aggregation in females than in males (all P-values < 0.05). No correlation between age and platelet aggregation was observed, except for the parameter TRAPTEM amplitude (A6), in which a decline in A6 was observed with increasing age (P = 0.03). We observed significantly lower levels of platelet aggregation in citrate tubes than in hirudin tubes (all P-values < 0.05), except from TRAPTEM maximum slope, where no significant difference was observed (P = 0.40).The stability was acceptable (≤20% deviation) for up to 120 min for ARATEM in citrate tubes, and up to 60 min for the ADPTEM and TRAPTEM assays in citrate tubes. In hirudin tubes we found ADPTEM and ARATEM assays to be stable for 60 min, while the stability of TRAPTEM in hirudin tubes was found to be stable for 30 min. Using citrate tubes, the between-day variation (mean coefficient of variation, CV) was 19-20% for ADPTEM, 19-26% for TRAPTEM, and 10% for ARATEM, whereas the mean CV was 11-13% for all three assays in hirudin tubes.In conclusion, we established combined and gender-specific reference intervals for three platelet aggregation assays in both citrate- and hirudin tubes. In citrate tubes, the stability of the ROTEM platelet assays was 60-120 min, while the stability in hirudin tubes was 30-60 min. The between-day variation was lowest for samples obtained in hirudin tubes.

Secondary Stroke Prophylaxis with Clopidogrel Produces Sufficient Antiplatelet Response

BACKGROUND

Antiplatelet therapy is a cornerstone prevention strategy for secondary ischemic stroke (IS) and transient ischemic attack (TIA). Yet, a proportion of patients who receive antiplatelet therapy experience recurrent ischemic cerebrovascular events. A recent meta-analysis found an increased risk of recurrent stroke in clopidogrel- or aspirin-treated patients with ischemic stroke who had high on-treatment platelet reactivity (HTPR). Few studies have focused specifically on clopidogrel HTPR. Therefore, the aim of this study was to examine the relationship between clopidogrel HTPR and recurrent ischemic events in a population of Danish patients with IS.

METHODS

We performed a prospective observational study to evaluate the relationship between HTPR defined as platelet reaction units >208 and a composite primary endpoint of recurrent stroke, TIA, acute myocardial infarction (AMI), or vascular death over a 2-year follow-up period.

RESULTS

A total of 142 patients were included in the final statistical analysis, but only 3 patients (2.1%) demonstrated clopidogrel HTPR. The median time of on-treatment platelet testing was 75 days. Recurrent IS, TIA, AMI, or vascular death occurred in 14 patients (10%). Of these, 1 new ischemic event (AMI) occurred in a HTPR patient. There was no difference in the frequency of new ischemic events between the HTPR and non-HTPR groups (P = .27); moreover, the number of patients with HTPR was too small for statistical analysis.

CONCLUSIONS

Clopidogrel HTPR does not seem to be a major contributor to recurrent ischemic events in Danish ischemic stroke patients.

Medication History versus Point-of-Care Platelet Activity Testing in Patients with Intracerebral Hemorrhage

OBJECTIVE

We evaluated whether reduced platelet activity detected by point-of-care (POC) testing is a better predictor of hematoma expansion and poor functional outcomes in patients with intracerebral hemorrhage (ICH) than a history of antiplatelet medication exposure.

METHODS

Patients presenting with spontaneous ICH were enrolled in a prospective observational cohort study that collected demographic, clinical, laboratory, and radiographic data. We measured platelet activity using the PFA-100 (Siemens AG, Germany) and VerifyNow-ASA (Accumetrics, CA) systems on admission. We performed univariate and adjusted multivariate analyses to assess the strength of association between those measures and (1) hematoma growth at 24 hours and (2) functional outcomes measured by the modified Rankin Scale (mRS) at 3 months.

RESULTS

We identified 278 patients for analysis (mean age 65 ± 15, median ICH score 1 [interquartile range 0-2]), among whom 164 underwent initial neuroimaging within 6 hours of symptom onset. Univariate association with hematoma growth was stronger for antiplatelet medication history than POC measures, which was confirmed in multivariable models (β 3.64 [95% confidence interval [CI] 1.02-6.26], P = .007), with a larger effect size measured in the under 6-hour subgroup (β 7.20 [95% CI 3.35-11.1], P < .001). Moreover, antiplatelet medication history, but not POC measures of platelet activity, was independently associated with poor outcome at 3 months (mRS 4-6) in the under 6-hour subgroup (adjusted OR 3.6 [95% CI 1.2-11], P = .023).

CONCLUSION

A history of antiplatelet medication use better identifies patients at risk for hematoma growth and poor functional outcomes than POC measures of platelet activity after spontaneous ICH.

Impaired thrombolytic status predicts adverse cardiac events in patients undergoing primary percutaneous coronary intervention

Antithrombotic medications reduce thrombosis but increase bleeding. Identification of ST-elevation myocardial infarction (STEMI) patients at risk of recurrent thrombosis could allow targeted treatment with potent antithrombotic medications, with less potent agents in others, to reduce bleeding. Conventional platelet function tests assess platelet reactivity only, yet there is increasing evidence that endogenous thrombolytic potential determines outcome following thrombus initiation. We investigated whether assessing both platelet reactivity and endogenous thrombolysis, could identify STEMI patients at high-risk of recurrent thrombotic events. Thrombotic status was assessed in STEMI patients, before and after primary percutaneous coronary intervention (PPCI), at discharge and at 30 days; with 12 months’ followup. The time to form an occlusive thrombus under high shear (occlusion time, OT), and time to restore flow by endogenous thrombolysis (lysis time, LT) was measured using the point-of-care Global Thrombosis Test (GTT) in the cardiac catheterisation laboratory. Impaired endogenous thrombolysis (prolonged LT ≥ 3000 s), seen in 13 % patients pre-PPCI, was related to major adverse cardiac events, MACE (HR: 3.31, 95 %CI: 1.02–10.78, p = 0.045), driven by cardiovascular death (HR: 4.17, 95 %CI: 0.99–17.51, p = 0.05). Enhanced (rapid) endogenous thrombolysis (LT < 1000 s) was associated with spontaneous reperfusion, ST-segment resolution and Thrombolysis In Myocardial Infarction 3 flow pre-PPCI. Baseline OT was shorter in those with MACE (especially recurrent myocardial infarction and stroke) than those without (253 ± 150 s vs 354 ± 134 s, p=0.017). Endogenous thrombolysis, when impaired, is associated with increased cardiovascular risk, and when enhanced, with spontaneous reperfusion. Endogenous thrombolysis may be a novel target for pharmacological intervention, and allow targeting of potent antithrombotic medications to high-risk patients.

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

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

PEAR1 is not a major susceptibility gene for cardiovascular disease in a Flemish population

Background

Platelet Endothelial Aggregation Receptor 1 (PEAR1), a membrane protein highly expressed in platelets and endothelial cells, plays a role in platelet contact-induced activation, sustained platelet aggregation and endothelial function. Previous reports implicate PEAR1 rs12041331 as a variant influencing risk in patients with coronary heart disease. We investigated whether genetic variation in PEAR1 predicts cardiovascular outcome in a white population.

Methods

In 1938 participants enrolled in the Flemish Study on Environment, Genes and Health Outcomes (51.3% women; mean age 43.6 years), we genotyped 9 tagging SNPs in PEAR1, measured baseline cardiovascular risk factors, and recorded Cardiovascular disease incidence. For SNPs, we contrasted cardiovascular disease incidence of minor-allele heterozygotes and homozygotes (variant) vs. major-allele homozygotes (reference) and for haplotypes carriers vs. non-carriers. In adjusted analyses, we accounted for family clusters and baseline covariables, including sex, age, body mass index, mean arterial pressure, the total-to-HDL cholesterol ratio, smoking and drinking, antihypertensive drug treatment, and history of cardiovascular disease and diabetes mellitus.

Results

Over a median follow-up of 15.3 years, 238 died and 181 experienced a major cardiovascular endpoint. The multivariable-adjusted hazard ratios of eight PEAR1 SNPs, including rs12566888, ranged from 0.87 to 1.07 (P ≥0.35) and from 0.78 to 1.30 (P ≥0.15), respectively. The hazard ratios of three haplotypes with frequency ≥10% ranged from 0.93 to 1.11 (P ≥0.49) for mortality and from 0.84 to 1.03 (P ≥0.29) for a cardiovascular complications. These results were not influenced by intake of antiplatelet drugs, nonsteroidal anti-inflammatory drugs, or both (P-values for interaction ≥ 0.056).

Conclusions

In a White population, we could not replicate previous reports from experimental studies or obtained in patients suggesting that PEAR1 might be a susceptibility gene for cardiovascular complications.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-017-0411-x) contains supplementary material, which is available to authorized users.

The application of thromboelastogram in detection of indexes of antiplatelet therapy for coronary heart disease

BACKGROUND

This study aims to explore the application value of thromboelastogram (TEG) in antiplatelet therapy in coronary artery intervention.

METHODS

A retrospective analysis of 90 cases of coronary interventional treatment was conducted in our hospital from January 2010 to January 2012. Cases were divided into three groups, according to the kind of coronary heart disease: angina pectoris (AP) group (30 cases), unstable angina pectoris (UAP) group (30 cases) and acute myocardial infarction (AMI) group (30 cases). TEG changes in patients between the three groups were analyzed.

RESULTS

The differences in international normalized ratio (INR) and activated partial thromboplastin time (APTT) indexes among the three groups of patients were statistically significant (P<0.05), but these indexes significantly decreased in the AMI group. Furthermore, D-D, Fgb, Angle and MA indexes significantly increased in the UAP and AMI groups, compared with the AP group; while TEG regular parameter K and R values were markedly reduced. Coagulation graphics were higher in the UAP and AMI groups than in the AP group (χ²=4.261, 3.908; P<0.05), suggesting that the difference was statistically significant. In 11 cases of ischemic events, arachidonic acid (AA)-induced platelet inhibition rate was 63.63%, while adenosine diphosphate (ADP)-induced platelet inhibition rate was 36.37% (χ²=5.026; P<0.05); suggesting that ADP-induced platelet inhibition rate was markedly reduced. This is the main risk of ischemic events within three months after percutaneous coronary intervention.

CONCLUSIONS

The detection of indexes of antiplatelet therapy in coronary artery intervention is helpful for antiplatelet medication, thus can effectively reduce the incidence of ischemic events.

Proteomic signatures of antiplatelet drugs: new approaches to exploring drug effects

Antiplatelet agents represent the mainstay of acute coronary syndrome (ACS) therapy to prevent ischemic events and to improve safety in patients undergoing percutaneous coronary intervention. However, despite the availability of several drugs and the use of dual antiplatelet therapy, the pharmacological response is highly variable with a subset of patients continuing to experience recurrent thrombotic events, revealing a wide variability in platelet response to antiplatelet drugs. Several factors may explain this, including genetic variation and environmental factors. Here we look at the application of proteomic analysis, an approach that provides an integrated readout of these diverse influences.

Enhanced pre-operative thrombolytic status is associated with the incidence of deep venous thrombosis in patients undergoing total knee arthroplasty

Background

Deep venous thrombosis (DVT), which is often associated with pulmonary embolism (PE), is a serious complication after total knee arthroplasty (TKA). In the present study, we examined the overall thrombotic and thrombolytic status using Global Thrombosis Test (GTT) in non-anticoagulated blood of patients undergoing TKA to develop the predictable marker for the incidence of DVT.

Methods

DVT was diagnosed using doppler ultrasonography a day after the surgery in 31 patients with osteoarthritis (n = 24), rheumatoid arthritis (n = 6) and ankylosing spondylitis (n = 1) by the well-trained operator. We measured overall thrombotic and thrombolytic status using GTT and other biomarkers, which is associated with blood coagulation and fibrinolysis, before and immediately after the surgery.

Results

Newly-generated DVT during the operation was detected in 11 of 31 patients (35.4%) 1 day after TKA. There were no differences in markers of coagulation (PT and APTT), platelet activity (platelet aggregation-induced by ADP and collagen) and fibrinolysis (FDP and D-dimer) between non-DVT and DVT group both before and after the surgery. Both Pre- and Post-operative GTT-occlusion times (OT), an index of platelet reactivity, were tended to be shorter, but not significant, in DVT group compared with non-DVT group. Pre-operative GTT-lysis time (LT), an index of thrombolytic activity, was significantly shorter in DVT group compared with non-DVT group, while there were no differences in post-operative value of this index between DVT group and non-DVT group, suggesting overall thrombolytic activity was enhanced in DVT group before surgery.

Conclusions

Our data suggest that enhancement of pre-operative thrombolytic activity assessed by GTT may be a predictable marker for the incidence of DVT after TKA.

Evaluation of laboratory methods routinely used to detect the effect of aspirin against new reference methods

BACKGROUND

Aspirin, a commonly used antiplatelet agent, blocks platelet thromboxane A₂ (TXA₂) formation from arachidonic acid (AA) by acetylating platelet cyclooxygenase-1 (COX-1). Laboratory methods currently used to detect this antiplatelet effect of aspirin provide variable results. We have reported three methods that assess platelet COX-1 acetylation (inactivation) by aspirin and its direct consequences. The first and second assays use monoclonal anti-human-COX-1 antibodies that only detect acetylated (inactivated) COX-1 and active (non-acetylated) COX-1, respectively. The third method measures platelet production of TXB₂ (the stable metabolite of TXA₂) in vitro in response to AA. We compared the results of these three reference methods with other routinely used methods for assessing the functional consequences aspirin treatment.

METHODS

108 healthy volunteers were treated with low-dose aspirin for 7 days. On day 7 following aspirin treatment COX-1 in the platelets was fully acetylated whereas only non-acetylated COX-1 was present in the day 0 platelets. Further, TXB2 production by day 7 platelets was completely blocked. The following tests were performed on the samples obtained from study participants before and after seven days of aspirin treatment: PFA-100 closure time with collagen/epinephrine cartridge, VerifyNow (VN) Aspirin Assay, platelet aggregation and ATP secretion using AA, ADP, epinephrine and collagen as agonists.

RESULTS

Comparing the pre-treatment and day 7 values, methods that use AA as platelet agonist (AA-induced platelet aggregation/secretion and VN Aspirin Assay) showed high discriminative power. In contrast, results of the other tests showed considerable overlap between day 7 and day 0 values.

CONCLUSIONS

Only assays that clearly distinguish between acetylated and non-acetylated platelet COX-1 are useful for establishing the antiplatelet effect of aspirin. The other tests are not suitable for this purpose.

Platelet function tests in clinical cardiology: unfulfilled expectations

This review is a critical evaluation of publications in the past decade on the usefulness of platelet function tests (PFTs) in clinical cardiology, in aiding diagnosis, predicting risk, and monitoring therapy. The ideal PFT should: 1) detect baseline platelet hyperreactivity; 2) allow individualization of antiplatelet medication; 3) predict thrombotic risk; and 4) predict bleeding risk. The practicalities of clinical cardiology demand rapid, accurate, and reliable tests that are simple to operate at the bedside and available 24 h a day, 7 days a week. Point-of-care PFTs most widely evaluated clinically include PFA-100 and VerifyNow. None of these tests can reliably detect platelet hyperreactivity and thus identify a prothrombotic state. Identification of antiplatelet nonresponsiveness or hyporesponsiveness is highly test specific, and does not allow individualization of therapy. The power of PFTs in predicting thrombotic events for a given individual is variable and often modest, and alteration of antithrombotic treatment on the basis of the results of PFTs has not been shown to alter clinical outcome. PFTs in current mainstream use cannot reliably assess bleeding risk. These tests have been in use for over a decade, but the hopes raised by PFTs in clinical practice remain unfulfilled. Although physiologically relevant measurement of platelet function now is more important than ever, a critical reappraisal of available techniques in light of clinical requirements is needed. The use of native blood, global stimulus instead of individual agonists, contribution of thrombin generation by activated platelets to the test results, and establishment of a PFT therapeutic range for each antiplatelet drug should be considered and is discussed.

Impaired thrombolysis: a novel cardiovascular risk factor in end-stage renal disease

AIMS

End-stage renal disease (ESRD) patients have an excess cardiovascular risk, above that predicted by traditional risk factor models. Prothrombotic status may contribute to this increased risk. Global thrombotic status assessment, including measurement of occlusion time (OT) and thrombolytic status, may identify vulnerable patients. Our aim was to assess overall thrombotic status in ESRD and relate this to cardiovascular risk.

METHODS AND RESULTS

Thrombotic and thrombolytic status of ESRD patients (n = 216) on haemodialysis was assessed using the Global Thrombosis Test. This novel, near-patient test measures the time required to form (OT) and time required to lyse (lysis time, LT) an occlusive platelet thrombus. Patients were followed-up for 276 ± 166 days for major adverse cardiovascular events (MACE, composite of cardiovascular death, non-fatal MI, or stroke). Peripheral arterial or arterio-venous fistula thrombosis was a secondary endpoint. Occlusion time was reduced (491 ± 177 vs. 378 ± 96 s, P < 0.001) and endogenous thrombolysis was impaired (LT median 1820 vs.1053 s, P < 0.001) in ESRD compared with normal subjects. LT ≥ 3000 s occurred in 42% of ESRD patients, and none of the controls. Impaired endogenous thrombolysis (LT ≥ 3000 s) was strongly associated MACE (HR = 4.25, 95% CI = 1.58-11.46, P = 0.004), non-fatal MI and stroke (HR = 14.28, 95% CI = 1.86-109.90, P = 0.01), and peripheral thrombosis (HR = 9.08, 95% CI = 2.08-39.75, P = 0.003). No association was found between OT and MACE.

CONCLUSION

Impaired endogenous thrombolysis is a novel risk factor in ESRD, strongly associated with cardiovascular events.

The first comprehensive and quantitative analysis of human platelet protein composition allows the comparative analysis of structural and functional pathways

Antiplatelet treatment is of fundamental importance in combatting functions/dysfunction of platelets in the pathogenesis of cardiovascular and inflammatory diseases. Dysfunction of anucleate platelets is likely to be completely attributable to alterations in posttranslational modifications and protein expression. We therefore examined the proteome of platelets highly purified from fresh blood donations, using elaborate protocols to ensure negligible contamination by leukocytes, erythrocytes, and plasma. Using quantitative mass spectrometry, we created the first comprehensive and quantitative human platelet proteome, comprising almost 4000 unique proteins, estimated copy numbers for ∼ 3700 of those, and assessed intersubject (4 donors) as well as intrasubject (3 different blood samples from 1 donor) variations of the proteome. For the first time, our data allow for a systematic and weighted appraisal of protein networks and pathways in human platelets, and indicate the feasibility of differential and comprehensive proteome analyses from small blood donations. Because 85% of the platelet proteome shows no variation between healthy donors, this study represents the starting point for disease-oriented platelet proteomics. In the near future, comprehensive and quantitative comparisons between normal and well-defined dysfunctional platelets, or between platelets obtained from donors at various stages of chronic cardiovascular and inflammatory diseases will be feasible.

The influence of aspirin dose and glycemic control on platelet inhibition in patients with type 2 diabetes mellitus

BACKGROUND

Low-dose aspirin seems to offer no benefit in the primary prevention of cardiovascular disease in type 2 diabetes mellitus (DM2). The anti-platelet effect may be diminished by poor glycemic control or inadequate dosing of aspirin.

OBJECTIVES

To study the effects of both glycemic control and increasing aspirin dose on platelet response to aspirin in DM2 patients and matched controls.

PATIENTS/METHODS

Platelet effects of increasing doses of aspirin (30, 100 and 300 mg daily) were prospectively assessed in 94 DM2 patients and 25 matched controls by measuring thromboxane levels in urine (11-dhTxB2) and platelet aggregation using VerifyNow(®) and light transmission aggregometry (LTA). DM2 patients were stratified for glycemic control (hemoglobin-A1c [HbA1c] ≤ 53, 53-69, ≥ 69 mmol mol(-1)).

RESULTS

At baseline, median 11-dhTxB2 excretion was higher in the poorly controlled patients (77 ng mmol(-1)), and the moderately controlled (84 ng mmol(-1)) compared with the well-controlled patients (64 ng mmol(-1)) and controls (53 ng mmol(-1)), P < 0.01. Next, 30 mg of aspirin reduced 11-dhTxB2 excretion to 31, 29 and 24 ng mmol(-1) in the poorly, moderately and well-controlled patients, respectively, and to 19 ng mmol(-1) in controls, P < 0.001. VerifyNow(®) and LTA were also incompletely suppressed in DM2 patients using 30 mg of aspirin, but 100 mg resulted in similar platelet suppression in all groups, with no additional effect of 300 mg.

CONCLUSIONS

DM2 patients with inadequate glycemic control (HbA1c > 53 mmol mol(-1)) have higher baseline platelet activity and incomplete suppression of platelet activity with 30 mg of aspirin. However, 100 mg of aspirin leads to optimal inhibition irrespective of glycemic control, and 300 mg does not further improve platelet suppression.

Chinese herb and formulas for promoting blood circulation and removing blood stasis and antiplatelet therapies

Atherothrombosis, which directly threatens people's health and lives, is the main cause of morbidity and mortality all over the world. Platelets play a key role in the development of acute coronary syndromes (ACSs) and contribute to cardiovascular events. Oral antiplatelet drugs are a milestone in the therapy of cardiovascular atherothrombotic diseases. In recent years, many reports have shown the possibility that “resistance” to oral anti-platelet drugs and many adverse reactions, such as serious bleeding risk, which provides an impetus for developing new anti-platelet drugs possesses highly efficiency and fewer adverse effects. Study on the blood stasis syndrome and promoting blood circulation and removing blood stasis is the most active field of research of integration of traditional and western medicine in China. Blood-stasis syndrome and platelet activation have close relationship, many Chinese herb and formulas for promoting blood circulation and removing blood stasis possess definite anti-platelet effect. This paper covers the progress of anti-platelet mechanism of Chinese herb and formulas for promoting blood circulation and removing blood stasis and is to be deeply discussed in further research.

Variability in the responsiveness to low-dose aspirin: pharmacological and disease-related mechanisms

The main pharmacological aspects of pharmacodynamics (PD) and pharmacokinetics (PK) of aspirin as antiplatelet agent were unravelled between the late sixties and the eighties, and low-dose aspirin given once daily has been shown to be a mainstay in the current treatment and prevention of cardiovascular disorders. Nevertheless, several PD and PK aspects of aspirin in selected clinical conditions have recently emerged and deserve future clinical attention. In 1994, the term "aspirin resistance" was used for the first time, but, until now, no consensus exists on definition, standardized assay, underlying mechanisms, clinical impact, and possible efficacy of alternative therapeutic interventions. At variance with an undefined aspirin-resistant status, in the last 5 years, the concept of variability in response to aspirin due to specific pathophysiological mechanisms and based on PK and/or PD of the drug has emerged. This growing evidence highlights the existence and possible clinical relevance of an interindividual variability of pharmacological aspirin response and calls for new, large studies to test new low-dose aspirin-based regimens which may ameliorate platelet acetylation, reduce variability in drug responsiveness, and improve clinical efficacy on selected populations.

Antiplatelet therapy in elderly patients

With remarkable advances of medical care, the aging population is growing rapidly. Cardiovascular disease remains the leading cause of morbidity and mortality in elderly people and therefore antiplatelet therapy has been a mainstay of cardiovascular medicines for reducing and preventing cardiovascular risk in these populations. The benefits of several antiplatelet drugs in the elderly are well documented. However, there are limited data regarding the optimal use of antiplatelet agents considering the risk:benefit ratio in elderly patients, who are more vulnerable to safety issues owing to different pharmacokinetics and pharmacodynamics as compared with young patients. In this article, we review currently available evidence regarding the efficacy and safety of antiplatelet therapy (i.e., aspirin, old and new P2Y12 inhibitors and glycoprotein IIb/IIIa inhibitors) in the elderly for primary and secondary prevention strategies in cardiovascular care.

Impact of genetic polymorphisms on clinical response to antithrombotics

Antithrombotic therapy, including anticoagulants as well as antiplatelet drugs, is an important component in the treatment of cardiovascular disease. Variability in response to such medications, of which pharmacogenetic response is a major source, can decrease or enhance the benefits expected. This review is a comprehensive assessment of the literature published to date on the effects of genetic polymorphisms on the actions of a variety of antithrombotic medications, including warfarin, clopidogrel, prasugrel, and aspirin. Literature evaluating surrogate markers in addition to the impact of pharmacogenetics on clinical outcomes has been reviewed. The results of the studies are conflicting as to what degree pharmacogenetics will affect medication management in cardiovascular disease. Additional research is necessary to discover, characterize, and prospectively evaluate genetic and non-genetic factors that impact antithrombotic treatment in order to maximize the effectiveness and limit the harmful effects of these valuable agents.

Selective and rapid monitoring of dual platelet inhibition by aspirin and P2Y12 antagonists by using multiple electrode aggregometry

Background

Poor platelet inhibition by aspirin or clopidogrel has been associated with adverse outcomes in patients with cardiovascular diseases. A reliable and facile assay to measure platelet inhibition after treatment with aspirin and a P2Y₁₂ antagonist is lacking. Multiple electrode aggregometry (MEA), which is being increasingly used in clinical studies, is sensitive to platelet inhibition by aspirin and clopidogrel, but a critical evaluation of MEA monitoring of dual anti-platelet therapy with aspirin and P2Y₁₂ antagonists is missing.

Design and Methods

By performing in vitro and ex vivo experiments, we evaluated in healthy subjects the feasibility of using MEA to monitor platelet inhibition of P2Y₁₂ antagonists (clopidogrel in vivo, cangrelor in vitro) and aspirin (100 mg per day in vivo, and 1 mM or 5.4 mM in vitro) alone, and in combination. Statistical analyses were performed by the Mann-Whitney rank sum test, student' t-test, analysis of variance followed by the Holm-Sidak test, where appropriate.

Results

ADP-induced platelet aggregation in hirudin-anticoagulated blood was inhibited by 99.3 ± 1.4% by in vitro addition of cangrelor (100 nM; p < 0.001) and by 64 ± 35% by oral clopidogrel (600 mg) intake (p < 0.05; values are means ± SD). Pre-incubation of blood with aspirin (1 mM) or oral aspirin intake (100 mg/day for 1 week) inhibited arachidonic acid (AA)-stimulated aggregation >95% and 100 ± 3.2%, respectively (p < 0.01). Aspirin did not influence ADP-induced platelet aggregation, either in vitro or ex vivo. Oral intake of clopidogrel did not significantly reduce AA-induced aggregation, but P2Y₁₂ blockade by cangrelor (100 nM) in vitro diminished AA-stimulated aggregation by 53 ± 26% (p < 0.01). A feasibility study in healthy volunteers showed that dual anti-platelet drug intake (aspirin and clopidogrel) could be selectively monitored by MEA.

Conclusions

Selective platelet inhibition by aspirin and P2Y₁₂ antagonists alone and in combination can be rapidly measured by MEA. We suggest that dual anti-platelet therapy with these two types of anti-platelet drugs can be optimized individually by measuring platelet responsiveness to ADP and AA with MEA before and after drug intake.

[Perioperative management of patients with coronary stents in non-cardiac surgery]

In patients with coronary stents scheduled for surgery the question arises whether and how antiplatelet therapy should be continued. Risks of perioperative bleeding and of acute stent thrombosis have to be considered simultaneously. The bleeding risk depends primarily on the kind of surgery and on patient comorbidity. The risk of stent thrombosis is increased in these patients due to the thrombogenic surface of the stents. The main determinants are hereby the time duration after stent implantation, the kind of the stent [uncoated (bare-metal stent, BMS) or coated (drug-eluting stent, DES)], as well as angiographic and clinical patient factors. Therefore, perioperative antiplatelet therapy has to be individually adapted for each patient. Bridging with heparin is ineffective. Bridging with intravenous antiplatelet drugs during the perioperative interruption of oral antiplatelet therapy might be a potential procedure in high-risk patients. Whether bedside monitoring of antiplatelet therapy improves the perioperative management of these patients and reduces adverse outcome is object of current studies.

Clinical management of clopidogrel inefficiency by point of care platelet function testing and individual adjustment of anti-platelet therapy--initial experiences

Insufficient inhibition of ADP dependent platelet aggregation by clopidogrel is associated with an increased risk for adverse coronary events, such as stent thrombosis, after percutaneous coronary intervention. Here, we describe an approach to the clinical management of patients with insufficient inhibition of ADP dependent platelet aggregation by clopidogrel involving dose adjustment or switching of the thienoyridine. We put special emphasize on a patient who experienced recurrent acute myocardial infarction due to stent thrombosis associated with severe clopidogrel non response following elective coronary drug eluting stent implantation. In this patient, an inadequate clopidogrel effect at maintenance doses was confirmed by repeated platelet function assessment with a multiple electrode impedance point of care platelet function test. Subsequent dose adjustments still did not result in sufficient inhibition of ADP dependent platelet aggregation. Only after switching to the then shortly available new thienopyridine prasugrel could a sufficient platelet inhibition be obtained. However, our data from further patients show that although this may overcome inadequate clopidogrel efficiency in many cases, even under prasugrel suboptimal platelet inhibition may occur.

Predicting and preventing stroke after transient ischemic attack

The prognosis of transient ischemic attacks (TIAs) is not as favorable as previously thought. Given a risk of stroke of approximately 10% in the first week following a TIA, urgent evaluation and initiation of treatment are required. Recently developed scores to predict the early risk of subsequent stroke in individual patients may guide treatment decisions in the acute phase. Lately it has become clear that transient attacks with nonfocal symptoms are not benign either, as these were found to be associated with an increased risk of vascular disease. The significance of this finding and its implications for treatment are not yet clear. There is substantial evidence from a number of clinical trials that adequate secondary prevention therapies can reduce the risk of stroke after TIA. In addition to the conventional vascular risk factors, interest has grown in less strong but more prevalent lifestyle factors, but trials evaluating the effect of modifying these factors are as yet lacking.