Evaluation of platelet function and pharmacological platelet inhibition in patients with myeloproliferative disorders using multiple electrode aggregometry

Platelet thromboxane inhibition by low-dose aspirin in polycythemia vera: Ex vivo and in vivo measurements and in silico simulation

Low-dose aspirin is currently recommended for patients with polycythemia vera (PV), a myeloproliferative neoplasm with increased risk of arterial and venous thromboses. Based on aspirin pharmacodynamics in essential thrombocythemia, a twice-daily regimen is recommended for patients with PV deemed at particularly high thrombotic risk. We investigated the effects of low-dose aspirin on platelet cyclooxygenase activity and in vivo platelet activation in 49 patients with PV, as assessed by serum thromboxane (TX) B2 and urinary TXA2 /TXB2 metabolite (TXM) measurements, respectively. A previously described pharmacokinetic-pharmacodynamic in silico model was used to simulate the degree of platelet TXA2 inhibition by once-daily (q.d.) and twice-daily (b.i.d.) aspirin, and to predict the effect of missing an aspirin dose during q.d. and b.i.d. regimens. Serum TXB2 averaged 8.2 (1.6-54.7) ng/ml and significantly correlated with the platelet count (γ = 0.39) and urinary TXM (γ = 0.52) in multivariable analysis. One-third of aspirin-treated patients with PV displayed less-than-maximal platelet TXB2 inhibition, and were characterized by significantly higher platelet counts and platelet-count corrected serum TXB2 than those with adequate inhibition. Eight patients with PV were sampled again after 12 ± 4 months, and had reproducible serum TXB2 and urinary TXM values. The in silico model predicted complete inhibition of platelet-derived TXB2 by b.i.d. aspirin, a prediction verified in a patient with PV with the highest TXB2 value while on aspirin q.d. and treated short-term with a b.i.d. regimen. In conclusion, one in three patients with PV on low-dose aspirin display less-than-maximal inhibition of platelet TXA2 production. Serum TXB2 measurement can be a valuable option to guide precision dosing of antiplatelet therapy in patients with PV.

Platelet Reactivity and Response to Aspirin and Clopidogrel in Patients with Platelet Count Disorders

Background

Platelet reactivity and response to antiplatelet drugs, acetylsalicylic acid (ASA) and clopidogrel, in patients with thrombocytopenia and thrombocythemia can have a potentially important effect on the outcome. The effectiveness and safety of antiplatelet drugs in such patients has not been well examined. Measuring the effect of ASA and clopidogrel on platelets could help guide the therapy. Nevertheless, platelet response to antiplatelet drugs is not routinely measured in platelet count disorders and relevant evidence is scarce.

Aims

The study aimed to measure platelet reactivity and response to ASA and clopidogrel in patients with platelet count disorders.

Materials and Methods

This was a cross-sectional study of consecutive patients hospitalized in cardiology and hematology departments in the years 2018–2019. The study included patients with thrombocytopenia (PLT < 150 G/L) and thrombocythemia (PLT > 450 G/L) on ASA or dual antiplatelet therapy (DAPT; ASA plus clopidogrel). Controls included patients on antiplatelet drugs with normal platelet count. Platelet reactivity was measured in whole blood (Multiplate aggregometer, Roche, Switzerland) using arachidonic acid (AA), adenosine-5′-diphosphate (ADP), and thrombin receptor agonist peptide-6 (TRAP) as agonists. Platelet aggregation was expressed in arbitrary units (AU). AA-induced aggregation was used as a measure of response to ASA with a cut-off above 30 AU showing high on-treatment platelet reactivity to ASA (HTPR-A). ADP-induced aggregation measured response to clopidogrel with a cut-off above 48 AU for high on-treatment platelet reactivity to clopidogrel (HTPR-C). TRAP-induced aggregation measured baseline platelet reactivity not affected by oral antiplatelet drugs.

Results

The study included 174 patients. There were 64 patients with thrombocytopenia, 30 patients with chronic thrombocythemia, and 80 controls. All patients were on 75 mg of ASA and 32% of them additionally on 75 mg of clopidogrel due to a history of recent coronary artery angioplasty. AA- and ADP-induced aggregation was comparable between thrombocytopenic patients and controls (median (IQR) 19 (7–28) vs. 23 (15–38) for AA AU and 32 (16–44) vs. 50 (32–71) for ADP AU, respectively), while it was significantly higher in thrombocythemic patients (median (IQR) 80 (79–118) for AA AU and 124 (89–139) for ADP AU). TRAP-induced aggregation showed significantly lowest aggregation in thrombocytopenic (median (IQR) 41 (34–60) for TRAP AU) and highest in thrombocythemic patients (median (IQR) 137 (120–180) for TRAP AU). HTPR-A was frequent in thrombocythemic patients in comparison with thrombocytopenic patients and controls (60% vs. 4% vs. 15%, respectively; p < 0.0002). HTPR-C was highly common in thrombocythemic patients and least common in thrombocytopenic ones in comparison with controls (80% vs. 8% vs. 40%, respectively; p < 0.001).

Conclusion

Chronic thrombocytopenia does not significantly affect platelet reactivity and response to ASA and clopidogrel in comparison with controls. Thrombocytosis significantly increases platelet reactivity and attenuates response to both ASA and clopidogrel.

Acquired platelet function disorders

The possibility of an acquired platelet function disorder should be considered in patients who present with recent onset muco-cutaneous bleeding. Despite the availability of newer and faster platelet function assays, light transmission aggregometry (LTA) remains the preferred diagnostic test. This review examines and discusses the causes of acquired platelet dysfunction; most commonly drugs, dietary factors, medical disorders and procedures. In addition to well-known antiplatelet therapies, clinicians should be alert for newer drugs which can affect platelets, such as ibrutinib. There is little clinical trial evidence to guide the management of acquired platelet function defects, but we summarise commonly employed strategies, which include addressing the underlying cause, antifibrinolytic agents, desmopressin infusions, and in selected patients, platelet transfusions.

Platelet characteristics in patients with essential thrombocytosis

BACKGROUND

Essential thrombocytosis (ET) is a myeloproliferative disorder characterized by an increased platelet count. ET is associated with an increased risk of thrombosis, and procoagulant features of the disease may include an increased number of reactive reticulated platelets and an increased aggregation potential. We aimed to explore the association between platelet count, platelet turnover, and platelet aggregation in patients with ET.

METHODS

We included 24 ET patients who discontinued antiplatelet therapy prior to blood sampling. Reticulated platelets were assessed as immature platelet count (IPC) and immature platelet fraction by automated flow cytometry (Sysmex XE-5000). Platelet aggregation was investigated by impedance aggregometry (Multiplate^® Analyzer) and aggregation potential by flow cytometry (NAVIOS).

RESULTS

Our results showed that ET patients had increased IPC compared to healthy individuals (median 12.3 vs. median 6.9, P < 0.0001). Furthermore, a positive correlation between platelet count and impedance aggregation was demonstrated using arachidonic acid (r = 0.48, P = 0.02), thrombin-receptor-activating-peptide (r = 0.46, P = 0.03) and adenosine diphosphate (r = 0.56, P = 0.007) as agonists. Finally, an increased aggregation potential was demonstrated in ET patients compared to healthy individuals.

CONCLUSIONS

The study showed that ET patients compared to healthy individuals have an increased amount of reticulated platelets and increased aggregation potential. These findings might in part explain the increased thromboembolic risk in patients with ET. © 2018 International Clinical Cytometry Society.

Recurrent Cardiovascular Events Despite Antiplatelet Therapy in a Patient with Polycythemia Vera and Accelerated Platelet Turnover

Patient: Male, 58

Final Diagnosis: STEMI

Symptoms: Angina pectoris

Medication:—

Clinical Procedure: —

Specialty: Hematology

Whole Blood Platelet Aggregation Test and Prediction of Hemostatic Difficulty After Tooth Extraction in Patients Receiving Antiplatelet Therapy

When patients on antiplatelet therapy (APT) require minor invasive surgery, APT is usually continued to limit the risk of thrombosis. However, the possibility of hemostatic difficulties necessitates the monitoring of platelet aggregation to prevent unexpected bleeding. We examined whether whole blood aggregometry as a point-of-care testing (POCT) could be useful as a tool for predicting hemostatic difficulties. Sixty-five patients receiving APT and 15 patients who were not receiving APT were enrolled in the present study; all patients were scheduled to undergo a tooth extraction. Whole blood samples were obtained and were examined using multiple electrode aggregometry. The aggregometry was performed using arachidonic acid (AA), adenosine diphosphate (ADP), and thrombin receptor activating peptide. Hemostatic difficulty was defined as a need for more than 10 minutes of compression to achieve hemostasis. The AA test results were significantly lower in patients treated with aspirin (control: 97.7 [29.0] U, aspirin: 14.5 [7.2] U, P < .001). The ADP test results were also significantly lower in patients treated with a P2Y₁₂ inhibitor (control: 77.7 [21.7] U, P2Y₁₂ inhibitor: 37.3 [20.4] U, P < .01). Six of the examined cases exhibited hemostatic difficulties. The cutoff values for the prediction of hemostatic difficulty were 16.5 U for the AA test (sensitivity, 0.833; specificity, 0.508) and 21 U for the ADP test (sensitivity, 0.847; specificity, 0.500). Our study showed that whole blood aggregometry was useful as a POCT for the prediction of hemostatic difficulties after tooth extraction in patients receiving APT.

Changes in response to antiaggregatory treatment in patients with myeloproliferative neoplasms: a sequential study using multiple electrode aggregometry

In the present study, we used multiple electrode aggregometry (MEA) to investigate the response to aspirin and clopidogrel treatment, and its potential changes over a long-time disease course in patients with myeloproliferative neoplasms (MPNs). arachidonic acid (ASPI), ADP, and thrombin receptor activating peptide (TRAP) tests were performed at two timepoints between 32-50 months in 21 patients with MPN and 1-46 months in 29 controls. We further checked the medical records of the participants to identify a potential correlation of changes in the treatment response with clinical events. In MPN, four out of 13 patients treated with 100 mg of aspirin, no patients receiving 50 mg of aspirin, and one out of five clopidogrel-treated patients showed a therapeutic antiplatelet effect. In the subsequent examinations, five patients changed from response to nonresponse or vice versa. Initial nonresponse and changes from an initial response to nonresponse were observed in six patients with thrombotic events. In the controls, 25 out of 26 aspirin-treated patients and two out of three clopidogrel-treated patients showed an initially adequate in-vitro response. Except from one patient changing from initial aspirin nonresponse to response, all controls showed a stable response state. One control with two ischemic strokes showed a nonresponse to clopidogrel. In conclusion, MEA detects the response to antiaggregatory treatment, as well as its changes during the disease course in patients with MPN. An initial or subsequent nonresponse was observed in patients with thrombotic events.

Assessment of the response to acetylsalicylic acid in patients with myeloproliferative neoplasms by whole blood assays: a comparison of the PFA-100 with multiple electrode aggregometry

Since thrombotic and haemorrhagic complications are the most important causes of morbidity and mortality in myeloproliferative neoplasms (MPN), establishing valid techniques for the monitoring of antiaggregatory treatment would be beneficial. The aim of this study was to assess the aspirin responsiveness in patients with MPN by multiple electrode aggregometry (MEA) and the PFA-100, to determine the concordance rate between the two techniques and to examine a potential clinical impact. Twenty-two consecutive outpatients with polycythaemia vera and essential thrombocythaemia receiving long-time treatment with 100 mg of aspirin were included and clinically re-evaluated within six months after study entry. All subjects were identified as aspirin responders using the PFA-100, whereas only nine (41%) study participants were detected as responders by MEA. The difference in the response rates was statistically highly significant (p < 0.0001). The median aggregation result was 55.5 U (8-123) in the ASPI test, and the median PFA-100 closure time (CT) was 300 sec (221 to 300) in the COL-EPI test. Within the clinical observation period no thrombotic or haemorrhagic events occurred in the study population. In this study we concluded that MEA and the PFA-100 are suitable devices for the detection of a response to aspirin treatment in patients with MPN, but differ significantly in the response rates and thus show a low concordance rate.

Effects of pantoprazole on dual antiplatelet therapy in stable angina pectoris patients after percutaneous coronary intervention

BACKGROUND

Our aim was to prospectively assess the potential influence of pantoprazole therapy on the antiplatelet effects of acetylsalicylic acid (ASA) and clopidogrel (CLO) in stable angina pectoris (SAP) patients after percutaneous coronary intervention (PCI).

METHODS

Forty-four patients with SAP (CCS I-III) and successful PCI with stent implantation were enrolled into the study. The patients were divided into group proton pump inhibitors (PPI): 23 patients with indications for PPI (F/M = 9/14; age = 64 ± 9; standard therapy + 20 mg pantoprazole) and the control group (group C): 21 patients (F/M = 6/15; age = 64 ± 8; standard therapy). The platelet function analysis in whole blood based on impedance aggregometry (ASPI, COL, ADP, TRAP tests) using Multiplate--V2.02.11 was performed 18-24 h after the PCI + CLO loading dose (600 mg) and 30 days after PCI.

RESULTS

Both baseline patient characteristics and clinical outcomes were comparable between the study groups. There were no differences in the mean values of the platelets (PTL) tests measured at the 30(th) day after PCI between both groups (PPI vs. C: ASPI: 24.6 ± 10.0 vs. 42.1 ± 14.8 U, COL: 32.9 ± 8.6 vs. 34.0 ± 7.7 U, ADP: 26.8 ± 12.4 vs. 30.4 ± 8.1 U, TRAP: 78.7 ± 16.6 vs. 78.1 ± 22.6 U, p = ns). The mean delta values of the PTL tests (18-24 h post-PCI/30 days post-PCI) were also comparable between the groups. The PTL aggregometry results were related to time (ADP, ASPI, TRAP vs. time, p = 0.001; COL vs. time, p = 0.03)--the baseline values of ADP, ASPI, COL and TRAP tests were smaller than those measured after the one-month observation.

CONCLUSION

Pantoprazole treatment does not impair the efficacy of dual antiplatelet therapy in patients with SAP after PCI.

Do blood collection methods influence whole-blood platelet function analysis?

Pre-analytical variables interact with standard coagulation parameters. How these variables affect the platelet function analysis is not completely known. How collection site and puncture method affect multiple electrode aggregometry (MEA) and platelet function analyzer (PFA-100®) was compared regarding contact activation. First, volunteers scheduled for elective cardiac surgery had blood collected from four lines: venous, arterial, central venous and by venipuncture. MEA and PFA-100® were analysed blinded for site origin. Second, two samples (citrate, Corn Trypsin Inhibitor, CTI) were collected in syringe or vacuum tubes. Thrombin generation (TG) was determined. MEA was triggered by adenosine diphosphate (ADP, 6.4 µM), arachidonic acid (ASPI, 0.5 mM), collagen (Col, 3.2 µg/ml), ristocetin (Risto, 0.2 mg/ml) and thrombin receptor-activating peptide (TRAP, 32 µM). PFA-100® was triggered by collagen/epinephrine and collagen/ADP. TG was assessed in platelet-poor plasma with 1 pM tissue factor and 4 µM phospholipids and without trigger. Data were analysed using a two-way mixed-effects model for the intraclass correlation (ICC) and by the Mann-Whitney U-test. MEA and PFA-100® revealed good correlation (ICC) between the sites. CTI inhibited TG significantly more effective than citrate. Contact activation was independent of the collection method. Only the MEA ASPI test revealed significant differences between the two collection methods. Blood sampling from all lines for MEA and PFA-100® assays is justified. Contact activation is always present. Apparently this does not influence platelet function test results. Collection methods do not seem relevant, although, one should always consider using a standardized method.