Antiplatelet drugs in patients with enhanced platelet turnover: biomarkers versus platelet function testing

Bleeding in acute coronary syndrome: from definitions, incidence, and prognosis to prevention and management

INTRODUCTION

In patients with acute coronary syndrome (ACS), the ischemic benefit of antithrombotic treatment is counterbalanced by the risk of bleeding. The recognition that bleeding events have prognostic implications (i.e. mortality) similar to recurrent ischemic events led to the development of treatment regimens aimed at balancing both ischemic and bleeding risks.

AREAS COVERED

This review aims at describing definitions, incidence, and prognosis related to bleeding events in ACS patients as well as bleeding-avoidance strategies for their prevention and management of bleeding complications.

EXPERT OPINION

Management of ACS patients has witnessed remarkable progress after the shift in focusing on the trade-off between ischemia and bleeding. Efforts in standardizing bleeding definitions will allow for better defining the prognostic impact of different types of bleeding events and enable to identify the high-bleeding risk patient. Such efforts will allow to balance the trade-off between the thrombotic and bleeding risk of the individual patient translating into better downward diagnostic and therapeutic decision-making. Novel strategies aiming at maximizing the safety and efficacy of antithrombotic regimens as well as the development of novel antithrombotic drugs and reversal agents and technological advances will allow for optimization of bleeding-avoidance strategies and management of bleeding complications.

Immature Platelet Fraction Predicts Adverse Events in Patients With Acute Coronary Syndrome: the ISAR-REACT 5 Reticulated Platelet Substudy

BACKGROUND

Immature or reticulated platelets are associated with impaired efficacy of antiplatelet drugs and adverse events in cardiovascular patients. Their role as a predictive biomarker in patients with acute coronary syndrome treated with potent P2Y₁₂ receptor inhibitors is not fully understood. We aimed to prospectively evaluate reticulated platelets as a predictor of the primary end point of the ISAR-REACT 5 trial consisting of death, myocardial infarction, or stroke at 1 year in patients with acute coronary syndrome randomized to prasugrel or ticagrelor.

METHODS

Immature platelet fraction (IPF) was assessed within 48 hours after randomization. Patients were divided based on the IPF median values: the IPF^high group included patients with IPF>median and the IPF^low group included patients with IPF≤median. Platelet aggregation was assessed using the Multiplate Analyzer and was correlated to IPF.

RESULTS

Five hundred seventy-seven patients were included in the study. IPF values in % (median [interquartile range]) within the first 48 hours did not differ between the two study groups: 3.6 (2.5-5.2)% in the prasugrel group and 3.6 (2.5-5.4)% in the ticagrelor group (P=0.882). The incidence of the primary end point was significantly higher in the IPF^high (IPF>3.6%) group compared with the IPF^low (IPF≤3.6%) group: 13.0% versus 7.2% (HR_adj, 1.74 [1.02-3.00]; P=0.044), independently from the assigned drug (P_int=0.159). No significant association between IPF and BARC 3 to 5 bleeding was observed. ADP-induced platelet aggregation correlated significantly with IPF in patients treated with prasugrel (r=0.22; P=0.005) while no correlation was detected in patients treated with ticagrelor (r=0.09; P=0.257).

CONCLUSIONS

Independently from drug treatment, IPF was associated with the primary end point and therefore is a promising biomarker for the prediction of adverse cardiovascular events in patients with acute coronary syndrome treated with prasugrel or ticagrelor.

REGISTRATION

https://www.

CLINICALTRIALS

gov; Unique identifier: NCT01944800.

Advanced Flow Cytometry Using the SYTO-13 Dye for the Assessment of Platelet Reactivity and Maturity in Whole Blood

Newly produced immature platelets are larger, contain higher amounts of residual RNA, and are more reactive than mature platelets. Flow cytometry using the SYTO-13 dye is a method for the subdivision of immature platelets from mature platelets based on the labelling of intracellular platelet RNA, enabling the simultaneous investigation of the reactivity of each platelet population. This method provides detailed information on several aspects of platelet physiology using a combination of platelet surface markers and agonists. Currently, no standardized protocol exists across laboratories. Here, we describe a flow cytometry protocol in detail to investigate platelet reactivity and its relation to platelet maturity. We analyzed 20 healthy individuals with the protocol and compared the platelet subpopulation with the highest SYTO-13 labelling (in the first quintile, "SYTO-high") corresponding to the most immature platelets (highest RNA content) with the platelet subpopulation with the lowest SYTO-13 labelling (in the fifth quintile, "SYTO-low") corresponding to the mature platelets with the lowest RNA content. SYTO-high platelets had overall significantly increased platelet reactivity compared with that of SYTO-low platelets. The presented method may be a valuable research tool for the analysis of platelet reactivity and its relation to platelet maturity.

Laboratory Markers of Platelet Production and Turnover

Platelets are formed from bone marrow megakaryocytes, circulate in blood for 7-10 days, and then are destroyed in the spleen and/or liver. Platelet production depends on the megakaryocyte population state in the bone marrow: number and size of the cells. The platelet turnover, i.e., the number of platelets passing through the bloodstream in a certain time, is determined by both the rate of their production and the rate of their destruction. The review considers laboratory markers, which are used to assess platelet production and turnover in the patients with hematologic and cardiovascular pathologies. These markers include some characteristics of platelets themselves: (i) content of reticulated ("young") forms in the blood detected by their staining with RNA dyes; (ii) indicators of the platelet size determined in hematology analyzers (mean volume, percentage of large forms) and in flow cytometers (light scattering level). Alterations of platelet production and turnover lead to the changes in blood plasma concentrations of such molecules as thrombopoietin (TPO, main mediator of megakaryocyte maturation and platelet formation in the bone marrow) and glycocalicin (soluble fragment of the membrane glycoprotein Ib detached from the surface of platelets during their destruction). Specific changes in the markers of platelet production and turnover have been observed in: (i) hypoproductive thrombocytopenias caused by suppression of megakaryocytes in the bone marrow; (ii) immune thrombocytopenias caused by accelerated clearance of the autoantibody-sensitized platelets; and (iii) thrombocytosis (both primary and reactive). The paper presents the data indicating that in patients with cardiovascular diseases an increased platelet turnover and changes in the corresponding markers (platelet size indexes and content of reticulated forms) are associated with the decreased efficacy of antiplatelet drugs and increased risk of thrombotic events, myocardial infarction, and unstable angina (acute coronary syndrome).

Immature platelets in patients with Covid-19: association with disease severity

Coronavirus disease 2019 (Covid-19) is associated with a high incidence of venous and arterial thromboembolic events. Currently, there are no clinical or laboratory markers that predict thrombotic risk. Circulating immature platelets are hyper-reactive platelets, which are associated with arterial thrombotic events. The aim of this study was to assess whether the proportion of circulating immature platelets is associated with disease severity in Covid-19 patients. Patients admitted with Covid-19 disease were prospectively assessed. Immature platelet count (IPC) and immature platelet fraction (IPF) were measured at admission and at additional time points during the hospital course using the Sysmex XN-3000 auto-analyzer. A total of 136 consecutive patients with Covid-19 were recruited [mean age 60 ± 19 years, 49% woman, 56 (41%) had mild-moderate disease and 80 (59%) had severe disease at presentation]. The median IPF% was higher in patients with severe compared to mild-moderate disease [5.8 (3.9-8.7) vs. 4.2 (2.73-6.45), respectively, p = 0.01]. The maximal IPC value was also higher in patients with severe disease [15 (10.03-21.56), vs 10.9 (IQR 6.79-15.62), respectively, p = 0.001]. Increased IPC was associated with increased length of hospital stay. Patients with severe Covid-19 have higher levels of IPF than patients with mild-moderate disease. IPF may serve as a prognostic marker for disease severity in Covid-19 patients.

Lower Antiplatelet Effect of Aspirin in Essential Thrombocythemia than in Coronary Artery Disease

Background  Patients with essential thrombocythemia (ET) and coronary artery disease (CAD) have increased risk of thromboembolic complications. In addition, a reduced antiplatelet effect of aspirin has been demonstrated in both patient groups. As ET is a platelet disorder, platelets may be more important for the thromboembolic risk in ET than in CAD. We aimed to investigate the antiplatelet effect of aspirin and platelet turnover in ET versus CAD patients.

Methods  We included 48 ET patients and an age-matched group of 48 CAD patients. The effect of aspirin was evaluated by thromboxane B ₂ (TXB ₂ ) levels and platelet aggregation. Platelet turnover was assessed by immature platelet count (IPC) and immature platelet fraction (IPF).

Results  ET patients had reduced effect of aspirin compared with CAD patients, demonstrated by significantly higher TXB ₂ levels (median of differences = 22.3 ng/mL, p  < 0.0001) and platelet aggregation (median of differences = 131.0 AU*min, p  = 0.0003). Furthermore, ET patients had significantly higher IPC ( p  < 0.0001) and IPF ( p  = 0.0004) than CAD patients.

Conclusion  ET patients have lower 24-hour antiplatelet effect of aspirin than CAD patients. This may be explained by an increased platelet production and turnover counteracting the antiplatelet effect of aspirin. These findings strengthen the rationale for exploring novel antiplatelet regimens in ET patients to reduce the risk of cardiovascular events.

Platelet reticulated forms, size indexes, and functional activity. Interactions in healthy volunteers

Reticulated platelets (RP) are young, functionally active platelet forms which are detected by RNA staining. Their content in the circulation reflects the intensity of bone marrow thrombocytopoesis. The aim of this study was to assess in healthy volunteers the relationship between RP percentage and platelet size and activity. RP were quantitated by thiazole orange staining using flow cytometry. Platelet size indexes included mean platelet volume (MPV), platelet large cell ratio (P-LCR) measured in a Coulter type hematological analyzer and forward scattering (FSC) measured in a flow cytometer. Platelet functional activity was evaluated by expression of activated glycoprotein (GP) IIb-IIIa (PAC-1 antibody binding) and P-selectin with the use of flow cytometry. Platelets were activated by thrombin receptor activating peptide (TRAP) (10 and 1 µM) and ADP (20 and 2.5 µM). The percentage of RP in healthy volunteers varied from 2.9% to 23.8% (mean ± SD ‒ 11.7 ± 4.7%, n = 99) and correlated with all platelet size indexes: MPV, P-LCR and FCS (r from 0.452 to 0.529, p < .001, n = 87-99). On average, RP were distributed at a ratio of 9:1 between 50% subpopulations of large and small platelets according to their FSC index. Expression of GP IIb-IIIa activated form correlated with RP percentage and platelet size indexes when platelets were activated by TRAP and ADP at both applied concentrations (r from 0.309 to 0.560, p from 0.014 to < 0.001, n = 50-62). P-selectin expression correlated with RP percentage and platelet size indexes when platelets were activated by 10 µM TRAP inducing maximum expression of this activation marker (r from 0.332 to 0.556, p from 0.008 to < 0.001, n = 65), but not by weaker agonists: 1 µM TRAP, 20 and 2.5 µM ADP (r < 0.3, n = 54-66). Thus, high RP content in healthy volunteers is associated with increased platelet size and activity in the whole platelet population.

Maternal and offspring high-fat diet leads to platelet hyperactivation in male mice offspring

Maternal over-nutrition increases the risk of diabetes and cardiovascular events in offspring. While prominent effects on cardiovascular health are observed, the impact on platelet physiology has not been studied. Here, we examined whether maternal high-fat diet (HF) ingestion affects the platelet function in lean and obese offspring. C57BL6/N mice dams were given a HF or control (C) diet for 8 weeks before and during pregnancy. Male and female offspring received C or HF diets for 26 weeks. Experimental groups were: C/C, dam and offspring fed standard laboratory diet; C/HF dam fed standard laboratory diet and offspring fed HF diet; HF/C and HF/HF. Phenotypic and metabolic tests were performed and blood collected for platelet studies. Compared to C/C, offspring HF groups were obese, with fat accumulation, hyperglycaemia and insulin resistance. Female offspring did not present platelet hyperactivity, hence we focused on male offspring. Platelets from HF/HF mice were larger, hyperactive and presented oxidative stress when compared to C/C. Maternal and offspring HF diet results in platelet hyperactivation in male mouse offspring, suggesting a novel ‘double-hit’ effect.

Once- versus Twice-Daily Aspirin in Patients at High Risk of Thrombotic Events: Systematic Review and Meta-Analysis

BACKGROUND

Acetylsalicylic acid (ASA) is a frequently used antiplatelet agent, although some individuals have reduced antiplatelet responses on ASA, with recurrent ischemic events. It has been proposed that shortening the ASA dosing interval may overcome the time-dependent renewal of the drug target, leading to a greater antiplatelet effect. We conducted a systematic review of randomized controlled trials (RCTs) to determine the efficacy of once- versus twice-daily ASA in conditions with increased platelet turnover.

METHODS

We conducted a systematic review and meta-analysis by searching the CENTRAL, MEDLINE, and Embase databases for RCTs assessing once- versus twice-daily ASA. Data were screened, extracted, and appraised by two independent reviewers, and were pooled using a random-effects model. The primary outcomes were major adverse cardiovascular events (MACEs) and serum thromboxane B2 (TxB2). Other pharmacodynamic measures were retrieved as secondary outcomes. Results were reported as mean differences with corresponding 95% confidence intervals (CIs). We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.

RESULTS

Seven RCTs were included, enrolling 379 participants overall. None of the studies reported clinical outcomes. Pooled results showed that compared with once-daily ASA, twice-daily ASA was associated with a decrease in mean TxB2 of 1.42 ng/mL (95% CI - 2.71 to - 0.13; I² = 66%). We found no differences in subgroup analyses based on disease subtype, trial blinding, or trial design. A greater antiplatelet activity of the twice-daily regimen was also found when using PFA-100-ADP methods, although not when using the VerifyNow, LTA-AA, and multiplate methods.

CONCLUSIONS

Twice-daily ASA was associated with a greater antiplatelet effect compared with standard once-daily ASA.

Immature platelets in patients hospitalized with Covid-19

Coronavirus disease 2019 (Covid-19) is associated with high incidence of venous and arterial thromboembolic events. Currently, there are no markers to guide antithrombotic therapy in Covid-19. Immature platelets represent a population of hyper-reactive platelets associated with arterial events. This prospective study compared consecutive Covid-19 patients (n = 47, median age = 56 years) to patients with acute myocardial infarction (AMI, n = 100, median age = 59 years) and a group of stable patients with cardiovascular risk factors (n = 64, median age = 68 years). Immature platelet fraction (IPF) and immature platelet count (IPC) were determined by the Sysmex XN-3000 auto-analyzer on admission and at subsequent time-points. IPF% on admission was higher in Covid-19 than the stable group and similar to the AMI group (4.8% [IQR 3.4-6.9], 3.5% [2.7-5.1], 4.55% [3.0-6.75], respectively, p = 0.0053). IPC on admission was also higher in Covid-19 than the stable group and similar to the AMI group (10.8 × 10⁹/L [8.3-18.1], 7.35 × 10⁹/L [5.3-10.5], 10.7 × 10⁹/L [7.7-16.8], respectively, P < 0.0001). The maximal IPF% among the Covid-19 group was higher than the stable group and similar to the AMI group. The maximal IPC in Covid-19 was higher than the maximal IPC in both the stable and AMI groups (COVID-19: 14.4 × 10⁹/L [9.4-20.9], AMI: 10.9 × 10⁹/L [7.6-15.2], P = 0.0035, Stable: 7.55 × 10⁹/L [5.55-10.5], P < 0.0001). Patients with Covid-19 have increased immature platelets indices compared to stable patients with cardiovascular risk factors, and as the disease progresses also compared to AMI patients. The enhanced platelet turnover and reactivity may have a role in the development of thrombotic events in Covid-19 patients.

Immature cell fractions after cessation of chronic P2Y12-inhibition in patients with coronary artery diseases

Changes in circulating cell populations may promote ischemic events that occur soon after discontinuation of P2Y₁₂-inhibition. The aim of the study was to track the course of thrombopoietic and erythropoietic cells in patients with coronary artery diseases (CAD) after planned and physician-driven cessation of chronic P2Y₁₂-inhibition (clopidogrel 75 mg OD, or prasugrel 10 mg OD, or ticagrelor 90 mg BID). Cell fractions were determined in 62 patients at baseline (the last day of P2Y₁₂-inhibitor intake), on day-10, day-30, and day-180 thereafter. Immature platelet fraction (IPF), immature reticulocyte fraction (IRF), reticulocyte hemoglobin content (Ret-Hb) and red blood cell count (RBC) significantly increased from baseline to day-180 (IPF: p = .003; IRF: p = .013; Ret-Hb: p < .001; RBC: p = .044). Platelet count, leucocyte count and immature granulocyte fraction did not change over time (p = .561, p = .869, and p = .161, respectively). Fibrinogen levels significantly declined over time (p = .011), thrombopoietin levels increased in a non-significant manner (p = .379). We did not observe any significant interaction with choice of P2Y₁₂-inhibitor, therefore suggesting a drug class-effect. Our data shows, that discontinuation of dual antiplatelet therapy is associated with raised thrombopoietic and erythropoietic activity in the bone marrow, without significant upregulation of thrombopoietin. This provides further evidence for a direct stimulation of precursor cells by P2Y_12-inhibitors.

Platelet Functions During Extracorporeal Membrane Oxygenation. Platelet-Leukocyte Aggregates Analyzed by Flow Cytometry as a Promising Tool to Monitor Platelet Activation

Extracorporeal membrane oxygenation (ECMO) is an extracorporeal circulation used to manage patients with severe circulatory or respiratory failure. It is associated with both high bleeding and thrombosis risks, mainly as a result of biomaterial/blood interface phenomena, high shear stress, and complex inflammatory response involving the activation of coagulation and complement systems, endothelial cells, leukocytes, and platelets. Besides their critical role in hemostasis, platelets are important players in inflammatory reactions, especially due to their ability to bind and activate leukocytes. Hence, we reviewed studies on platelet function of ECMO patients. Moreover, we addressed the issue of platelet–leukocyte aggregates (PLAs), which is a key step in both platelet and leukocyte activation, and deserves to be investigated in these patients. A reduced expression of GPIb and GPVI was found under ECMO therapy, due to the shedding processes. However, defective platelet aggregation is inconsistently reported and is still not clearly defined. Due to the high susceptibility of PLAs to pre-analytical conditions, defining and strictly adhering to a rigorous laboratory methodology is essential for reliable and reproducible results, especially in the setting of complex inflammatory situations like ECMO. We provide results on sample preparation and flow cytometric whole blood evaluation of circulating PLAs.

Antiplatelet effects of citalopram in patients with ischaemic stroke: A randomized, placebo-controlled, double-blind study

We evaluated the effect of SSRI treatment on platelet aggregation in patients with ischaemic stroke and included patients from the randomized double-blind controlled study of citalopram in acute ischaemic stroke (TALOS). Patients on clopidogrel were included 6 months after acute ischaemic stroke. Platelet parameters, including P2Y12 platelet reactivity using the VerifyNow System, were measured at the last day of study treatment and repeated after a 14-day wash-out period. A total of 60 patients were included (n = 32 randomized to citalopram). Platelet aggregation levels did not differ between the citalopram group (mean 116, 95% CI 89 to 143) and the placebo group (mean 136, 95% CI 109 to 163) (On-treatment, p = 0.14). Similarly, there was no significant change in platelet aggregation in the citalopram group from on-treatment to post-treatment (mean difference 2.0; 95% CI -18 to 14). Platelet count, size and turnover were not affected by SSRI treatment. In conclusion, SSRI therapy did not lead to statistically significant inhibition of platelet aggregation in ischaemic stroke patients treated with clopidogrel.

Aspirin antiplatelet effects are associated with body weight

BACKGROUND

Aspirin is indispensable in secondary prevention of ischemic events. Recently, it was reported that clinical aspirin effects are hampered in patients above 70 kg body weight. It is well known that a plethora of reasons beside obesity is associated with increased platelet reactivity and insufficient aspirin effects (HTPR). However, data regarding an association between pharmacodynamic response to aspirin and body weight are missing.

METHODS

In this pilot study, we included 59 patients from University Hospital Duesseldorf. Impedance aggregometry was used to assess pharmacodynamic response to aspirin.

RESULTS

AA-induced platelet reactivity was significantly higher in patients above 70 kg (<70 kg: 28.27 ± 26.33 vs. >70 kg: 45.93 ± 27.1, p = .035) and correlated well with the bodyweight of patients in this study (r = 0.33, R² = 0.09, p = .016). According to this, insufficient pharmacodynamic response (HTPR) to aspirin was significantly more frequent in patients over 70 kg (<70 kg: 25% vs. >70 kg: 43%, p = .035).

CONCLUSION

Insufficient pharmacodynamic response to aspirin is associated with body weight. This finding may play a role in the impaired clinical efficacy of aspirin in patients >70 kg. An optimal aspirin regime in these patients needs to be evaluated in large scale trials.

Reticulated Platelets as Predictor of Myocardial Injury and 30 Day Mortality After Non-cardiac Surgery

OBJECTIVE

A pre-operative marker for identification of patients at risk of peri-operative adverse events and 30 day mortality might be the percentage of young, reticulated platelets (pRP). This study aimed to determine the predictive value of pre-operative pRP on post-operative myocardial injury (PMI) and 30 day mortality, in patients aged ≥ 60 years undergoing moderate to high risk non-cardiac surgery.

METHODS

The incidence of PMI (troponin I > 0.06 μg/L) and 30 day mortality was compared for patients with normal and high pRP (≥2.82%) obtained from The Utrecht Patient Orientated Database. The predictive pRP value was assessed using logistic regression. A prediction model for PMI or 30 day mortality with known risk factors was compared with a model including increased pRP using the area under the receiving operator characteristics curve (AUROC).

RESULTS

In total, 26.5% (607/2289) patients showed pre-operative increased pRP. Increased pRP was associated with more PMI and 30 day mortality compared with normal pRP (36.1% vs. 28.3%, p < .001 and 8.6% vs. 3.6%, p < .001). The median pRP was higher in patients suffering PMI and 30 day mortality compared with not (2.21 [IQR: 1.57-3.11] vs. 2.07 [IQR: 1.52-1.78], p = .002, and 2.63 [IQR: 1.76-4.15] vs. 2.09 [IQR: 1.52-3.98], p < .001). pRP was independently related to PMI (OR: 1.28 [95% CI: 1.04-1.59], p = .02) and 30 day mortality (OR: 2.35 [95% CI: 1.56-3.55], p < .001). Adding increased pRP to the predictive model of PMI or 30 day mortality did not increase the AUROC 0.71 vs. 0.72, and 0.80 vs. 0.81.

CONCLUSION

In patients undergoing major non-cardiac surgery, increased pre-operative pRP is related to 30 day mortality and PMI.

The Influence of Inflammation on Fibrinogen Turnover and Redistribution of the Hemostatic Balance to a Prothrombotic State in High On-Treatment Platelet Reactivity-Dual Poor Responder (HTPR-DPR) Patients

Knowledge about the influence of inflammation on platelet function and relocation of hemostatic balance to hypercoagulable state is still unclear. We compared two groups of patients who suffer from acute vs. chronic inflammatory process and additionally present high on-treatment platelet reactivity-dual platelet resistance. We did not found any differences in platelet aggregation between both investigated groups, but patients who suffer from chronic inflammation presented stronger relocation of the hemostatic balance to the hypercoagulability. A high concentration of prothrombin fragment F1+2 together with higher activity of von Willebrand factor in critical limb ischemia shows more exaggerated fibrinogen turnover although the blood concentration of this factor was in normal range. We concluded that high on-treatment platelet reactivity-dual platelet resistance and intensified inflammation are linked with elevated platelet and fibrinogen turnover to counteract proper hemostatic balance in favor of a prothrombotic state.

Aspirin in childhood acute ischemic stroke: The evidence for treatment and efficacy testing

Aspirin is the most commonly prescribed antiplatelet agent worldwide, but evidence supporting its use varies by age and disease process. Despite its frequent use in childhood acute ischemic stroke prevention and management, major knowledge gaps exist about optimal pediatric aspirin use, particularly in this setting, where high-quality clinical trials are urgently needed. This review focuses upon the evidence for aspirin use in childhood acute ischemic stroke, includes a summary of aspirin pharmacology to highlight misconceptions and common clinical situations which may limit its efficacy, and discusses the techniques and potential role of laboratory monitoring of aspirin efficacy in children.

Reference interval for immature platelet fraction on Sysmex XN haematology analyser in adult population

Introduction

The Sysmex XN-series haematology analyser has newly adopted a fluorescent channel to measure immature platelet fraction (IPF). To promote the clinical utility of this promising parameter, establishing a reliable reference interval is mandatory. According to previous studies, IPF values may be affected by the employed analyser and the ethnic background of the individual, but no differences seem to be found between individuals’ genders. Therefore, this study aimed to define the reference interval for IPF in a Spanish population following Clinical and Laboratory Standard Institute (CLSI) guidelines.

Materials and methods

A total of 153 healthy Caucasian adults from Spain met the inclusion criteria. IPF measurement was performed by means of a Sysmex XN-2000 haematology analyser. A non-parametric percentile method was used to calculate the reference intervals in accordance with CLSI guidelines.

Results

The obtained reference interval for IPF on the Sysmex XN-2000 was 1.6–9.6% (90% confidence intervals (CIs) were 1.5–1.8 and 9.3–11.5, respectively). No significant gender difference in IPF reference intervals was observed (P = 0.101).

Conclusions

This study provides, for the first time, a reference interval for IPF using a Sysmex XN-2000 in a Spanish population, ranging from 1.6 to 9.6%. These data are needed to evaluate platelet production in several conditions such as thrombocytopenia, inflammatory states and cardiovascular diseases, as well as for future research.

Understanding Platelets in Infectious and Allergic Lung Diseases

Emerging evidence suggests that platelets, cytoplasmic fragments derived from megakaryocytes, can no longer be considered just as mediators in hemostasis and coagulation processes, but as key modulators of immunity. Platelets have received increasing attention as the emergence of new methodologies has allowed the characterization of their components and functions in the immune continuum. Platelet activation in infectious and allergic lung diseases has been well documented and associated with bacterial infections reproduced in several animal models of pulmonary bacterial infections. Direct interactions between platelets and bacteria have been associated with increased pulmonary platelet accumulation, whereas bacterial-derived toxins have also been reported to modulate platelet function. Recently, platelets have been found extravascular in the lungs of patients with asthma, and in animal models of allergic lung inflammation. Their ability to interact with immune and endothelial cells and secrete immune mediators makes them one attractive target for biomarker identification that will help characterize their contribution to lung diseases. Here, we present an original review of the last advances in the platelet field with a focus on the contribution of platelets to respiratory infections and allergic-mediated diseases.

Increased platelet reactivity in dyslipidemic patients with coronary artery disease on dual anti-platelet therapy

INTRODUCTION

The optimal duration of dual anti-platelet therapy (DAPT) following percutaneous coronary intervention (PCI) is still a matter of debate. Biomarkers may help to identify patients who will benefit from extended DAPT. The aim of the study was to test the interaction between lipid parameters and platelet function in patients with coronary artery disease (CAD) on DAPT.

MATERIAL AND METHODS

Overall, 58 patients on DAPT were prospectively included following PCI in stable CAD. Platelet markers, i.e. mean platelet volume (MPV), platelet distribution width (PDW), fraction of reticulated thrombocytes (RT) and ADP-induced multiple electrode aggregometry (MEA), as well as serum lipids, i.e. high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC), triglycerides (TG) and remnant cholesterol (RC), were assessed after intake of a maintenance dose of ASA and P2Y12 inhibitor.

RESULTS

A significant inverse correlation was found for HDL-C levels and markers of platelet activation: MPV (r = -0.351, p = 0.009), PDW (r = -0.391, p = 0.003), fraction of RT (r = -0.402, p = 0.003) and ADP-induced MEA (r = -0.345, p = 0.011). Only a weak or no association was found between other lipid parameters and platelet markers. After multivariable adjustment, HDL-C levels served as a strong and significant predictor of MPV (95% CI: -0.039 to -0.009; p = 0.002), PDW (95% CI: -0.094 to -0.034; p < 0.0001), RT (95% CI: -0.107 to -0.031; p = 0.001) and MEA (95% CI: -0.540 to -0.170; p < 0.0001), while TG, LDL-C, RC and TC were not significantly associated with platelet function.

CONCLUSIONS

Within lipid parameters, only HDL-C levels are strongly associated with markers of platelet activation in CAD patients on DAPT. Accordingly, detection of dyslipidemia might indicate the need for prolongation of DAPT.

Effect of remote ischaemic conditioning on platelet aggregation and platelet turnover

Remote ischaemic conditioning (RIC) is a new beneficial treatment for patients with ST-elevation myocardial infarction. RIC may inhibit thrombus formation and, therefore, we investigated whether RIC affects platelet aggregation and turnover. 30 healthy male volunteers were subjected to intervention on day 1 (sham intervention, no aspirin), day 2 (RIC, no aspirin), and day 16 (RIC, treated 7 days with aspirin 75 mg/day). RIC was performed as four cycles of 5 min interchangeable inflation and deflation using an automated cuff. Blood samples were collected 5 min before, as well as 5 and 45 min after RIC. Platelet aggregation was measured by Multiplate® using collagen (COLtest), adenosine diphosphate (ADPtest), and arachidonic acid (ASPItest) as agonists. Platelet turnover was evaluated by flow cytometry. Serum thromboxane B₂ was determined by ELISA to confirm aspirin compliance. We found no significant change in platelet aggregation at visit 1 (COLtest: p = 0.32; ADPtest: p = 0.24; ASPItest: p = 0.07), visit 2, except for ADP-induced platelet aggregation evaluated 5 min after RIC (COLtest: p = 0.39; ADPtest: p = 0.02; ASPItest: p = 0.39), or visit 3 (COLtest: p = 0.48; ADPtest: p = 0.61; ASPItest: p = 0.90). Platelet turnover was not influenced by RIC, neither on nor off aspirin (all p-values > 0.07). (1) RIC did not affect platelet aggregation in healthy young men. (2) RIC did not affect platelet turnover in healthy young men. (3) Aspirin did not influence the effect of RIC on platelet aggregation and turnover. (4) Future studies exploring the effect of RIC on platelet aggregation and turnover in patients with ischaemic heart disease are warranted.

Endothelial dysfunction and platelet hyperactivity in type 2 diabetes mellitus: molecular insights and therapeutic strategies

The incidence and prevalence of diabetes mellitus is rapidly increasing worldwide at an alarming rate. Type 2 diabetes mellitus (T2DM) is the most prevalent form of diabetes, accounting for approximately 90-95% of the total diabetes cases worldwide. Besides affecting the ability of body to use glucose, it is associated with micro-vascular and macro-vascular complications. Augmented atherosclerosis is documented to be the key factor leading to vascular complications in T2DM patients. The metabolic milieu of T2DM, including insulin resistance, hyperglycemia and release of excess free fatty acids, along with other metabolic abnormalities affects vascular wall by a series of events including endothelial dysfunction, platelet hyperactivity, oxidative stress and low-grade inflammation. Activation of these events further enhances vasoconstriction and promotes thrombus formation, ultimately resulting in the development of atherosclerosis. All these evidences are supported by the clinical trials reporting the importance of endothelial dysfunction and platelet hyperactivity in the pathogenesis of atherosclerotic vascular complications. In this review, an attempt has been made to comprehensively compile updated information available in context of endothelial and platelet dysfunction in T2DM.

Twenty-four-hour time dependency of clopidogrel effects in patients with acute coronary syndromes: The CiCAD-Study

Long-term evidence shows an increased risk of cardiovascular events in the morning hours and recent studies in aspirin-treated patients have shown increased platelet reactivity at the end of the dosing interval. Similar pharmacodynamic analyses of adenosine-diphosphate (ADP) receptor inhibitors are scarce. We therefore investigated changes in clopidogrel-dependent platelet function and activation over 24 h and whether enhanced platelet turnover might explain diurnal variability of platelet function and activation. Twenty-one patients after acute coronary syndromes (ACS) on maintenance doses of clopidogrel (75 mg) and aspirin (100 mg) Once per day (OD) were included. Blood was collected at five time points in 24 h. Platelet function and activation was analyzed by vasodilator-stimulated phosphoprotein-phosphorylation (VASP-P), Verify Now, multiple electrode aggregometry (MEA), and platelet PAC-1 and P-selectin (P-sel) expression. Additionally, platelet count, mean platelet volume (MPV), and reticulated platelet fraction (RPF) were analyzed. There was significant diurnal variability of clopidogrel effects as documented with VASP-P, Verify Now, and PAC-1 and P-sel (all p < 0.05), whereas MEA did not differ over 24 h. Neither MPV nor RPF varied significantly over 24 h. In patients with high RPF, platelet function and activation was significantly higher in all assays, compared to patients with low RPF (all p < 0.05). However, the changes over time in low versus high RPF groups were similar. ADP-dependent platelet function and activation recovers significantly at the end of the 24-h dosing interval in patients with ACS on a maintenance dose of clopidogrel and aspirin. Although platelet function and activation is increased in patients with higher RPF, platelet turnover might not explain the observed diurnal variability.

Effects of Aspirin on Endothelial Function and Hypertension

Purpose of review

Endothelial dysfunction is intimately related to the development of various cardiovascular diseases, including hypertension, and is often used as a target for pharmacological treatment. The scope of this review is to assess effects of aspirin on endothelial function and their clinical implication in arterial hypertension.

Recent findings

Emerging data indicate the role of platelets in the development of vascular inflammation due to the release of proinflammatory mediators, for example, triggered largely by thromboxane. Vascular inflammation further promotes oxidative stress, diminished synthesis of vasodilators, proaggregatory and procoagulant state. These changes translate into vasoconstriction, impaired circulation and thrombotic complications. Aspirin inhibits thromboxane synthesis, abolishes platelets activation and acetylates enzymes switching them to the synthesis of anti-inflammatory substances.

Summary

Aspirin pleiotropic effects have not been fully elucidated yet. In secondary prevention studies, the decrease in cardiovascular events with aspirin outweighs bleeding risks, but this is not the case in primary prevention settings. Ongoing trials will provide more evidence on whether to expand the use of aspirin or stay within current recommendations.

Toward the Relevance of Platelet Subpopulations for Transfusion Medicine

Circulating platelets consist of subpopulations with different age, maturation state and size. In this review, we address the association between platelet size and platelet function and summarize the current knowledge on platelet subpopulations including reticulated platelets, procoagulant platelets and platelets exposing signals to mediate their clearance. Thereby, we emphasize the impact of platelet turnover as an important condition for platelet production in vivo. Understanding of the features that characterize platelet subpopulations is very relevant for the methods of platelet concentrate production, which may enrich or deplete particular platelet subpopulations. Moreover, the concept of platelet size being associated with platelet function may be attractive for transfusion medicine as it holds the perspective to separate platelet subpopulations with specific functional capabilities.

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

Acetylsalicylic acid in critically ill patients: a cross-sectional and a randomized trial

BACKGROUND

Despite decades of clinical use, the pharmacokinetics and the effects of acetylsalicylic acid (ASA) in critically ill patients remain ill-defined. We aimed to investigate the pharmacokinetics and the effects of different ASA formulations during critical illness.

DESIGN

A cross-sectional study and a randomized, parallel-group trial were performed. Critically ill patients under chronic oral ASA treatment (100 mg enteric-coated) were screened for high 'on-treatment' platelet reactivity (HTPR) according to arachidonic acid-induced whole-blood aggregometry. Thirty patients with HTPR were randomized to receive 100 mg ASA intravenously, 100 mg enteric-coated ASA bid (bis in die) or 81 mg chewable ASA (n = 10 per group). Serum thromboxane B2 (TXB2) levels, ASA and salicylic acid levels were quantified.

RESULTS

Of 66 patients, 85% (95% confidence intervals 74-93%) had HTPR. Compared to baseline infusion of 100 mg, ASA significantly reduced platelet aggregation after 24 h to median 80% (Quartiles: 66-84%). Intake of 81 mg chewable ASA significantly reduced platelet aggregation to 75% (54-86%) after four hours, but increased it to 117% after 24 h (81-163%). Treatment with 100 mg enteric-coated ASA bid decreased platelet aggregation after 24 h to median 56% (52-113%). Baseline TXB2 levels were median 0·35 ng/mL (0·07-0·94). Infusion of ASA or intake of 100 mg ASA bid reduced TXB2 levels to 0·07-0·18 ng/mL after 24 h, respectively. Chewable ASA reduced TXB2 levels only transiently. Pharmacokinetic analysis revealed highly variable absorption patterns of oral ASA formulations.

CONCLUSION

There is a very high prevalence of HTPR in critically ill patients on peroral ASA therapy, caused by an incomplete suppression of TXB2 and/or by impaired absorption of ASA.

Platelet turnover predicts outcome after coronary intervention

Elevated platelet turnover contributes to high platelet reactivity. High platelet reactivity after percutaneous coronary intervention (PCI) is associated with major adverse cardiovascular events (MACE). The purpose of this study was to determine the prognostic value of platelet turnover and function with regard to MACE after PCI with stent implantation. In this prospective observational study, 486 consecutive patients after PCI on aspirin and clopidogrel were included to determine platelet turnover (mean platelet volume (MPV), reticulated platelet fraction (RPF)) and platelet function (multiple electrode aggregometry (MEA), vasodilator-stimulated phosphoprotein-phosphorylation (VASP-P) assay). At six-months follow-up, MACE occurred in 10.7 % of patients. RPF (odds ratio [OR]=1.173 (95% confidence interval [CI 95 %] 1.040-1.324), p=0.009) and MPV (OR=1.459 (CI 95 % 1.059-2.008), p=0.021) were univariable predictors of MACE, whereas VASP-P (OR=1.016 (CI 95 % 1.000-1.032), p=0.052) and MEA (OR=0.999 (CI 95 % 0.980-1.017), p=0.895) failed to predict MACE. RPF remained the only platelet variable independently associated with MACE. The best model to predict MACE included: troponin I (OR=1.007 (CI 95 % 1.002-1.012), p=0.009), RPF (OR=1.136 (CI 95 % 1.001-1.288), p=0.048), CRP (OR=1.008 (CI 95 % 1.001-1.014), p=0.023) and history of myocardial infarction (OR=2.039 (CI 95 % 1.093-3.806), p=0.025). RPF (OR=1.211 (CI 95 % 1.042-1.406), p=0.012) was also independently associated with in-hospital bleedings. In conclusion, RPF as index of platelet turnover is an independent predictor of MACE and bleeding events in PCI patients on dual antiplatelet therapy. Since RPF can reliably be quantified along with routine haemograms, RPF might easily be applied in the setting of cardiovascular risk prediction.

Platelet Activation: The Mechanisms and Potential Biomarkers

Beyond hemostasis and thrombosis, an increasing number of studies indicate that platelets play an integral role in intercellular communication, mediating inflammatory and immunomodulatory activities. Our knowledge about how platelets modulate inflammatory and immunity has greatly improved in recent years. In this review, we discuss recent advances in the pathways of platelet activation and potential application of platelet activation biomarkers to diagnosis and prediction of disease states.

Cardiovascular events occur independently of high on-aspirin platelet reactivity and residual COX-1 activity in stable cardiovascular patients

Several studies have indicated that approximately 25 % of patients treated with aspirin exhibit high on-treatment platelet reactivity (HTPR), which is potentially associated with cardiovascular events (CVEs). However, this association is still controversial, since the mechanisms by which HTPR contributes to CVEs remain unclear and a no standardised definition of HTPR has been established. To determine whether HTPR is associated with CVE recurrence and what type of assay would best predict CVE recurrence, we conducted a multicentre prospective cohort study of 592 stable cardiovascular outpatients treated with aspirin monotherapy for secondary prevention. Their HTPR was determined by arachidonic acid- or collagen-induced aggregation assays using two different agonist concentrations. Residual cyclooxygenase (COX)-1 activity was assessed by measuring serum thromboxane (TX)B2 or urinary 11-dehydro TXB2. Shear-induced platelet thrombus formation was also examined. We followed all patients for two years to evaluate how these seven indexes were related to the recurrence of CVEs (cerebral infarction, transient ischaemic attack, myocardial infarction, unstable angina, revascularisation, other arterial thrombosis, or cardiovascular death). Of 583 patients eligible for the analysis, CVEs occurred in 69 (11.8 %). A Cox regression model identified several classical risk factors associated with CVEs. However, neither HTPR nor high residual COX-1 activity was significantly associated with CVEs, even by applying cut-off values suggested in previous reports or a receiver-operating characteristic analysis. In conclusion, recurrence of CVEs occurred independently of HTPR and residual COX-1 activity. Thus, our findings do not support the use of platelet or COX-1 functional testing for predicting clinical outcomes in stable cardiovascular patients.