High-on-treatment platelet reactivity predicts adverse outcome after carotid artery stenting: A prospective study.

BACKGROUND AND PURPOSE: High-on-treatment platelet reactivity (HTPR) has been established as a predictor of major adverse cardiovascular events (MACE) in patients undergoing percutaneous coronary interventions on dual antiplatelet therapy (DAPT), but no data are available on its predictive value in patients on DAPT after carotid artery stenting (CAS). We aimed to evaluate the possible association between HTPR in patients on aspirin plus clopidogrel therapy after CAS and subsequent MACE. METHODS: All consecutive patients treated with CAS in a single institution were enrolled in a prospective clinical study. HTPR was evaluated with 5 different laboratory assays carried out just before CAS. MACE incidence (cerebral ischemia, myocardial infarction, stent thrombosis, acute limb ischemia and vascular death) was evaluated at 30 days and thereafter at yearly visits. RESULTS: A total of 300 patients were enrolled in the study, and eight were then excluded because blood samples resulted unsuitable for the laboratory testing or CAS aborted for technical problems. Median follow-up was 5.8 years and during this period 47 MACE occurred. HTPR detected by multiplate electronic aggregometry (MEA) and the VASP phosphorylation assay (VASP) were associated with a significantly enhanced risk of MACE (p = 0.048 and p = 0.038, respectively). However, HTPR to three tests (HTPR3) was more strongly predictive of increased risk of a vascular event at follow up (p = 0.005) at bivariate analysis and also at Cox regression multivariate analysis (p = 0.002). CONCLUSIONS: HTPR to three different assays (mainly to VASP + PFA P2Y+ VerifyNow) in patients on DAPT after CAS has predictive value for subsequent MACE. Prospective studies to assess whether platelet function testing-guided antiplatelet therapy is superior to standard DAPT in patient undergoing CAS should be considered.

The role of platelets, neutrophils and endothelium in COVID-19 infection.

INTRODUCTION: COVID-19 is associated to an increased risk of thrombosis, as a result of a complex process that involves the activation of vascular and circulating cells, the release of soluble inflammatory and thrombotic mediators and blood clotting activation. AREAS COVERED: This article reviews the pathophysiological role of platelets, neutrophils, and the endothelium, and of their interactions, in the thrombotic complications of COVID-19 patients, and the current and future therapeutic approaches targeting these cell types. EXPERT OPINION: Virus-induced platelet, neutrophil, and endothelial cell changes are crucial triggers of the thrombotic complications and of the adverse evolution of COVID-19. Both the direct interaction with the virus and the associated cytokine storm concur to trigger cell activation in a classical thromboinflammatory vicious circle. Although heparin has proven to be an effective prophylactic and therapeutic weapon for the prevention and treatment of COVID-19-associated thrombosis, it acts downstream of the cascade of events triggered by SARS-CoV-2. The identification of specific molecular targets interrupting the thromboinflammatory cascade upstream, and more specifically acting either on the interaction of SARS-CoV-2 with blood and vascular cells or on the specific signaling mechanisms associated with their COVID-19-associated activation, might theoretically offer greater protection with potentially lesser side effects.

Platelets and Matrix Metalloproteinases: A Bidirectional Interaction with Multiple Pathophysiologic Implications.

Platelets contain and release several matrix metalloproteinases (MMPs), a highly conserved protein family with multiple functions in organism defense and repair. Platelet-released MMPs as well as MMPs generated by other cells within the cardiovascular system modulate platelet function in health and disease. In particular, a normal hemostatic platelet response to vessel wall injury may be transformed into pathological thrombus formation by platelet-released and/or by locally generated MMPs. However, it is becoming increasingly clear that platelets play a role not only in hemostasis but also in immune response, inflammation and allergy, atherosclerosis, and cancer development, and MMPs seem to contribute importantly to this role. A deeper understanding of these mechanisms may open the way to novel therapeutic approaches to the inhibition of their pathogenic effects and lead to significant advances in the treatment of cardiovascular, inflammatory, and neoplastic disorders.

Laboratory diagnosis of clinically relevant platelet function disorders.

Inherited platelet function disorders (IPFDs) represent a significant fraction of congenital hemorrhagic disorders, and may be associated with bleeding of considerable severity. IPFDs may be difficult to diagnose and a preliminary accurate clinical examination and an objective evaluation of the severity of the bleeding history are mandatory. The laboratory investigation of IPFDs should follow a rational algorithm based on a streamlined panel of laboratory tests with subsequent steps of increasing levels of complexity. First screening tests include platelet count, peripheral blood smear, light transmission aggregometry, measurement of platelet granule content and release, and the expression of glycoproteins by flow cytometry. Several of these tests have been largely employed, and a few validated, for the diagnosis of IPFDs and some recent developments are discussed. Point-of-care tests may provide the advantage of rapidity and the possibility to study platelet function in whole blood, but further studies are required to clarify their potential diagnostic application. Genotyping is recommended for some conditions (genotype/phenotype correlations, forms associated with a high risk of developing hematologic malignancies) but, especially when carried out by next-generation sequencing (NGS) techniques, needs to be critically evaluated taking into account clinical and laboratory phenotypes.

Neuromedin U potentiates ADP- and epinephrine-induced human platelet activation.

Neuromedin U (NmU) is a pleiotropic hypothalamic neuropeptide involved in the gut-brain axis. It acts via both a Gαq/11-coupled receptor (NMUR1) and a Gαi-coupled receptor (NMUR2) in different cell types. Expression of both receptors was reported in platelets, but their significance for NmU signaling remains elusive. We studied the potential effects of NmU on human platelet activation. In platelet-rich plasma (PRP), NmU alone (up to 10µM) did not induce any measurable aggregation, but at nanomolar concentrations, it potentiated platelet aggregation by low (mean 0.47µM) ADP concentrations (from 25.9±3.6% to 74.8±2.7% maximal aggregation for ADP vs. ADP+NmU, 100nM, mean±SEM, n=13), accompanied by platelet P-selectin expression and intracellular calcium mobilization. Accordingly, platelet preincubation with NmU for 2min sensitized platelets for subsequent activation by ADP. When P2Y1 was inactivated by 50µM MRS2179, NmU comparably potentiated ADP-induced PRP aggregation, suggestive of cooperative activation with Gαi-coupled P2Y12. Likewise, NmU potentiated platelet aggregation by Gαi-operated epinephrine at subthreshold concentrations (99ng/ml, mean), but not that by Gαq-dependent serotonin (20µM). Platelet aggregation by NmU/epinephrine combination was fully inhibited by the Gαq inhibitor YM-254890 (1µM). qPCR detection and western blot analysis substantiated platelet expression of NMUR1 in different donors, a finding collectively complying with functionally relevant Gαq/11-mediated activation of platelet NMUR1 by NmU. Our findings advocate further studies on platelet sensitization by NmU, released during vascular activation and injury, to define its role as a modifier of platelet responsiveness to the physiological activation signals, operational in cardiovascular health and disease.

Diagnosis of suspected inherited platelet function disorders: results of a worldwide survey.

BACKGROUND: Diagnosis of inherited platelet function disorders (IPFDs) is important for appropriate management and to improve epidemiologic and clinical knowledge. However, there remains a lack of consensus on the diagnostic approach. OBJECTIVES: To gain knowledge on the current practices for the diagnosis of IPFD worldwide. METHODS: A 67-item questionnaire was distributed to the ISTH members and to the members of several national hemostasis and thrombosis societies. RESULTS: A total of 202 laboratories from 37 countries participated in the survey. The most frequent criterion to define patients with a suspected IPFD was a history of mucocutaneous bleeding and no acquired cause, but heterogeneity on the identification criteria was evident. Only 64.5% of respondents performed a direct clinical interview. On average, each laboratory studied 72 patients per year. The most commonly used laboratory equipment were the light-transmission aggregometer, the Platelet Function Analyzer-100, and the flow cytometer. Screening tests were platelet count, peripheral blood smear, light-transmission aggregometry, and Platelet Function Analyzer-100. Second-step tests were flow cytometry, molecular genetic analysis, and electron microscopy. Methodologies varied widely. In total, ~ 14,000 patients were investigated yearly and 60% turned out to not have a defect. Of the remaining 40%, only 8.7% received a diagnosis at a molecular level. CONCLUSIONS: Many laboratories worldwide are involved in the diagnosis of IPFD. A large fraction of the patients studied remain without a diagnosis. A high variability in the diagnostic approaches is evident.

Platelet and endothelial activation in catastrophic and quiescent antiphospholipid syndrome.

Antiphospholipid antibodies (aPL) seem to induce a prothrombotic state by activating endothelium and platelets, but no studies have evaluated systematically the effects of aPL from patients with the antiphospholipid syndrome (APS) in quiescent versus catastrophic phase. Our aims were to evaluate the in vitro effects on platelet activation of anti-ß2 glycoprotein I (anti-ß2GPI) antibodiesisolated from APS patientin either quiescent or catastrophic phase and to investigate ex vivo platelet and endothelial activation in patients with quiescent or catastrophic APS. Anti-ß2GPI antibodies were isolated from plasma of a pregnant woman in two different stages of APS (quiescent and catastrophic, respectively). They were co-incubated with washed platelets from healthy controls that were then challenged with TRAP-6 (thrombin receptor activating peptide 6) and the expression of P- selectin (P-sel) on platelets was assessed by flow cytometry. Moreover, plasma samples from six patients with quiescent, four with catastrophic APS and 10 controls were assessed for several markers of platelet and endothelial activation. The results showed that purified anti-ß2GPI antibodies co-incubated with platelets enhanced TRAP-6- induced platelet P-sel expression. Notably, anti-ß2GPI antibodies isolated during the catastrophic phase enhanced platelet P-sel expression more than antibodies isolated from the same patient in the quiescent stage of disease. Moreover, APS patients had significantly higher plasma levels of soluble (s) Psel, sCD40 ligand, soluble vascular cell adhesion molecule 1 and monocyte chemoattractant protein 1 than control subjects. In addition, sP-sel and von Willebrand factor activity were significantly higher during catastrophic than in quiescent phase.

In vitro effect of anti-ß2 glycoprotein I antibodies on P-selectin expression, a marker of platelet activation.

OBJECTIVE: Antiphospholipid antibodies (aPL) associated with thrombembolic events and/or pregnancy morbidity characterize the so-called antiphospholipid syndrome (APS). Beta2glycoprotein I (ß2GPI) represents the major target antigen for aPL, but the pathogenic role of anti-ß2GPI antibodies (aß2GPI) is still unclear. Some authors assume they play a role in activating platelets. The effects of aß2GPI antibodies on platelet P-selectin expression were evaluated in this study. METHODS: Aß2GPI antibodies in the plasma of a pregnant APS patient were isolated by affinity chromatography during two different stages (catastrophic and quiescent) of the disease. Gel filtered platelets (100,000/µl) from healthy volunteers were incubated with ß2-GPI (20 µg/ml) and with different concentrations (5, 25 e 50 µg/ml) of aß2GPI antibodies. P-selectin surface expression on platelets was assessed by flow cytometry using a specific fluorescent antibody directed against P-selectin. RESULTS: Aß2GPI antibodies induced platelet activation only in the presence of thrombin receptor activator for peptide 6 (TRAP-6), a platelet agonist, at a subthreshold concentration. Aß2GPI antibody enhancement on platelet surface P-selectin expression was stronger in the catastrophic than in the quiescent phase of the disease (47% versus 15%). CONCLUSIONS: TRAP-6 dependent platelet activation by aß2GPI antibodies is consistent with the "two hit" pathogenetic hypothesis for thrombosis. Aß2GPI antibodies induce higher platelet P-selectin expression during the active rather than in the acute phases.

Endothelial and platelet function alterations in HIV-infected patients.

The HIV epidemic has huge dimensions: in 2009, 33.3million people worldwide, including 2.5million children, were affected by human immunodeficiency virus (HIV) infection. The introduction of Highly Active Anti-Retroviral Therapy (HAART) has significantly modified the course of HIV disease, with longer survival and improved quality of life, but it has simultaneously lead to the appearance of previously unrecognized complications, such as ischemic cardiovascular events. Many studies have shown a higher rate of premature atherosclerosis in patients with HIV infection, leading to coronary, cerebrovascular, or peripheral arterial disease. However, it is still debated whether cardiovascular complications are a consequence of HIV infection itself or of the long-term use of HAART. In particular, myocardial infarction has been suggested to be associated with the use of abacavir. Endothelial dysfunction and platelet activation are markers of atherosclerosis and of increased cardiovascular risk. Here we review the evidence that endothelial dysfunction and platelet alterations are associated with chronic HIV infection, the possible role of different HAARTs, and the possible pathophysiologic mechanisms. Potential therapeutic implications are also discussed.

A new case of acquired Glanzmann's thrombasthenia: diagnostic value of flow cytometry.

BACKGROUND: Acquired Glanzmann's thrombasthenia (aGT) is a rare hemorrhagic disorder caused by autoantibodies, alloantibodies, or paraproteins directed against platelet GPIIb/IIIa. Its diagnosis requires several laboratory assays and mixing tests, which are complex and time consuming. We describe here a new case of aGT and compare different tests for the detection of GPIIb/IIIa-blocking autoantibodies. METHODS: A previously healthy 27-year-old male developed severe mucocutaneous bleeding, despite a normal platelet count, associated with non Hodgkin lymphoma. RESULTS: Blood clotting tests were normal. Bleeding time and PFA-100 were unmeasurable. Platelet aggregation was absent in response to all agonists except ristocetin. Platelet adhesion to collagen at high shear was impaired. Platelet granular content and release was normal. Flow cytometry showed normal binding of some anti-GPIIb/IIIa antibodies (SZ21 and SAP), and decreased binding of others (P2, SZ22, A2A 9/6). Binding of PAC-1, against activated GPIIb/IIIa, and of fibrinogen, was absent. In mixing tests, patient's serum inhibited aggregation, adhesion, and PAC-1 and A2A9/6 binding to control platelets. The patient's antibody, purified by affinity chromatography, recognized purified GPIIb by western blotting. Isolated patient's IgG inhibited platelet aggregation and A2A 9/6 binding by flow cytometry. CONCLUSIONS: Flow cytometry is especially useful for the diagnosis of aGT, being the only test able to characterize both the functional effect and the molecular target of the patient's autoantibody.

Intraplatelet signaling mechanisms of the priming effect of matrix metalloproteinase-2 on platelet aggregation.

OBJECTIVE: Platelets contain and release some matrix metalloproteinases (MMPs), enzymes involved in the degradation of extracellular matrix, and one of these (MMP-2) exerts a proaggregatory effect. We explored the signal transduction mechanisms activated by MMP-2 in human blood platelets. METHODS AND RESULTS: Recombinant, human MMP-2, added before stimulation with subthreshold doses of different agonists, potentiated platelet activation, calcium influx, IP3 formation, and pleckstrin phosphorylation. Wortmannin and LY29400, two PI3-K inhibitors, suppressed the potentiating effects of MMP-2 and preincubation with MMP-2 enhanced the thrombin-induced association of the p85alpha PI3-K subunit with the cytoskeleton and increased the phosphorylation of PKB. Protein tyrosine kinase inhibitors, MAP kinase inhibitors, PLA2 inhibitors, cyclooxygenase inhibitors and antagonists of the P2Y1 and P2Y12 receptors did not affect the potentiating activity of MMP-2 on platelets. CONCLUSION: Our data show that MMP-2, at a concentration released by activated platelets, facilitates platelet activation acting at the level of a second messenger system common to different agonists and related to the activation of PI3-K. Platelet-released MMP-2 may contribute to platelet activation in vivo.