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1.
Platelet extracellular vesicles in COVID-19: Potential markers and makers.
Puhm, F, Flamand, L, Boilard, E
Journal of leukocyte biology. 2022;(1):63-74
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Abstract
Platelets and platelet extracellular vesicles (pEV) are at the crossroads of coagulation and immunity. Extracellular vesicles are messengers that not only transmit signals between cells, but also provide information about the status of their cell of origin. Thus, pEVs have potential as both biomarkers of platelet activation and contributors to pathology. Coronavirus Disease-19 (COVID-19), caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a complex disease affecting multiple organs and is characterized by a high degree of inflammation and risk of thrombosis in some patients. In this review, we introduce pEVs as valuable biomarkers in disease with a special focus on their potential as predictors of and contributors to COVID-19.
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Emerging Role of Platelet-Endothelium Interactions in the Pathogenesis of Severe SARS-CoV-2 Infection-Associated Myocardial Injury.
Rossouw, TM, Anderson, R, Manga, P, Feldman, C
Frontiers in immunology. 2022;:776861
Abstract
Cardiovascular dysfunction and disease are common and frequently fatal complications of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Indeed, from early on during the SARS-CoV-2 virus pandemic it was recognized that cardiac complications may occur, even in patients with no underlying cardiac disorders, as part of the acute infection, and that these were associated with more severe disease and increased morbidity and mortality. The most common cardiac complication is acute cardiac injury, defined by significant elevation of cardiac troponins. The potential mechanisms of cardiovascular complications include direct viral myocardial injury, systemic inflammation induced by the virus, sepsis, arrhythmia, myocardial oxygen supply-demand mismatch, electrolyte abnormalities, and hypercoagulability. This review is focused on the prevalence, risk factors and clinical course of COVID-19-related myocardial injury, as well as on current data with regard to disease pathogenesis, specifically the interaction of platelets with the vascular endothelium. The latter section includes consideration of the role of SARS-CoV-2 proteins in triggering development of a generalized endotheliitis that, in turn, drives intense activation of platelets. Most prominently, SARS-CoV-2-induced endotheliitis involves interaction of the viral spike protein with endothelial angiotensin-converting enzyme 2 (ACE2) together with alternative mechanisms that involve the nucleocapsid and viroporin. In addition, the mechanisms by which activated platelets intensify endothelial activation and dysfunction, seemingly driven by release of the platelet-derived calcium-binding proteins, SA100A8 and SA100A9, are described. These events create a SARS-CoV-2-driven cycle of intravascular inflammation and coagulation, which contributes significantly to a poor clinical outcome in patients with severe disease.
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PON1 Q192R is associated with high platelet reactivity with clopidogrel in patients undergoing elective neurointervention: A prospective single-center cohort study.
Tanaka, K, Matsumoto, S, Ainiding, G, Nakahara, I, Nishi, H, Hashimoto, T, Ohta, T, Sadamasa, N, Ishibashi, R, Gomi, M, et al
PloS one. 2021;(8):e0254067
Abstract
BACKGROUND AND PURPOSE The impact of the paraoxonase-1 (PON1) polymorphism, Q192R, on platelet inhibition in response to clopidogrel remains controversial. We aimed to investigate the association between carrier status of PON1 Q192R and high platelet reactivity (HPR) with clopidogrel in patients undergoing elective neurointervention. METHODS Post-clopidogrel platelet reactivity was measured using a VerifyNow® P2Y12 assay in P2Y12 reaction units (PRU) for consecutive patients before the treatment. Genotype testing was performed for PON1 Q192R and CYP2C19*2 and *3 (no function alleles), and *17. PRU was corrected on the basis of hematocrit. We investigated associations between factors including carrying ≥1 PON1 192R allele and HPR defined as original and corrected PRU ≥208. RESULTS Of 475 patients (232 men, median age, 68 years), HPR by original and corrected PRU was observed in 259 and 199 patients (54.5% and 41.9%), respectively. Carriers of ≥1 PON1 192R allele more frequently had HPR by original and corrected PRU compared with non-carriers (91.5% vs 85.2%, P = 0.031 and 92.5% vs 85.9%, P = 0.026, respectively). In multivariate analyses, carrying ≥1 PON1 192R allele was associated with HPR by original (odds ratio [OR] 1.96, 95% confidence interval [CI] 1.03-3.76) and corrected PRU (OR 2.34, 95% CI 1.21-4.74) after adjustment for age, sex, treatment with antihypertensive medications, hematocrit, platelet count, total cholesterol, and carrying ≥1 CYP2C19 no function allele. CONCLUSIONS Carrying ≥1 PON1 192R allele is associated with HPR by original and corrected PRU with clopidogrel in patients undergoing elective neurointervention, although alternative results related to other genetic polymorphisms cannot be excluded.
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Platelet calcium signaling by G-protein coupled and ITAM-linked receptors regulating anoctamin-6 and procoagulant activity.
Fernández, DI, Kuijpers, MJE, Heemskerk, JWM
Platelets. 2021;(7):863-871
Abstract
Most agonists stimulate platelet Ca2+ rises via G-protein coupled receptors (GPCRs) or ITAM-linked receptors (ILRs). Well studied are the GPCRs stimulated by the soluble agonists thrombin (PAR1, PAR4), ADP (P2Y1, P2Y12), and thromboxane A2 (TP), signaling via phospholipase (PLC)β isoforms. The platelet ILRs glycoprotein VI (GPVI), C-type lectin-like receptor 2 (CLEC2), and FcγRIIa are stimulated by adhesive ligands or antibody complexes and signal via tyrosine protein kinases and PLCγ isoforms. Marked differences exist between the GPCR- and ILR-induced Ca2+ signaling in: (i) dependency of tyrosine phosphorylation; (ii) oscillatory versus continued Ca2+ rises by mobilization from the endoplasmic reticulum; and (iii) smaller or larger role of extracellular Ca2+ entry via STIM1/ORAI1. Co-stimulation of both types of receptors, especially by thrombin (PAR1/4) and collagen (GPVI), leads to a highly enforced Ca2+ rise, involving mitochondrial Ca2+ release, which activates the ion and phospholipid channel, anoctamin-6. This highly Ca2+-dependent process causes swelling, ballooning, and phosphatidylserine expression, establishing a unique platelet population swinging between vital and necrotic (procoagulant 'zombie' platelets). Additionally, the high Ca2+ status of procoagulant platelets induces a set of additional events: (i) Ca2+ dependent cleavage of signaling proteins and receptors via calpain and ADAM isoforms; (ii) microvesiculation; (iii) enhanced coagulation factor binding; and (iv) fibrin-coat formation involving transglutaminases. Given the additive roles of GPCR and ILR in Ca2+ signal generation, high-throughput screening of biomolecules or small molecules based on Ca2+ flux measurements provides a promising way to find new inhibitors interfering with prolonged high Ca2+, phosphatidylserine expression, and hence platelet procoagulant activity.
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5.
Effects of Nutrients on Platelet Function: A Modifiable Link between Metabolic Syndrome and Neurodegeneration?
Arnoldussen, IAC, Witkamp, RF
Biomolecules. 2021;(10)
Abstract
Metabolic syndrome increases the risk of vascular dementia and other neurodegenerative disorders. Recent studies underline that platelets play an important role in linking peripheral with central metabolic and inflammatory mechanisms. In this narrative review, we address the activation of platelets in metabolic syndrome, their effects on neuronal processes and the role of the mediators (e.g., serotonin, platelet-derived growth factor). Emerging evidence shows that nutritional compounds and their metabolites modulate these interactions-specifically, long chain fatty acids, endocannabinoids and phenolic compounds. We reviewed the role of activated platelets in neurovascular processes and nutritional compounds in platelet activation.
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A review of in vitro studies of the anti-platelet potential of citrus fruit flavonoids.
Olas, B
Food and chemical toxicology : an international journal published for the British Industrial Biological Research Association. 2021;:112090
Abstract
The citrus plants of the Rutaceae, such as oranges, grapefruits and mandarins, are cultivated worldwide. Their fruits and their juices are rich sources of flavonoids: for example, hesperidin and narirutin in oranges, and narirutin and naringin in grapefruits. Although these flavonoids have been found to potentially modulate blood platelet activity, most studies have been performed in vitro; in addition, the body of evidence regarding antiplatelet activity is relatively weak and the exact mechanisms remain poorly understood. More importantly, the concentrations of flavonoids studied in vitro (i.e. 3.125-300 μM) with washed blood platelets did not always correspond with their physiological concentrations in vivo, i.e. in whole blood after oral administration, and citrus fruit flavonoids are also characterized by low bioavailability. Therefore, more detailed studies on the antiplatelet potential of citrus flavonoids are needed, especially in in vivo models.
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7.
The thrombopoietin receptor: revisiting the master regulator of platelet production.
Hitchcock, IS, Hafer, M, Sangkhae, V, Tucker, JA
Platelets. 2021;(6):770-778
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Abstract
Thrombopoietin (TPO) and its receptor, MPL, are the primary regulators of platelet production and critical for hematopoietic stem cell (HSC) maintenance. Since TPO was first cloned in 1994, the physiological and pathological roles of TPO and MPL have been well characterized, culminating in the first MPL agonists being approved for the treatment of chronic immune thrombocytopenia in 2008. Dysregulation of the TPO-MPL signaling axis contributes to the pathogenesis of hematological disorders: decreased expression or function results in severe thrombocytopenia progressing to bone marrow failure, while hyperactivation of MPL signaling, either by mutations in the receptor or associated Janus kinase 2 (JAK2), results in pathological myeloproliferation. Despite its importance, it was only recently that the long-running debate over the mechanism by which TPO binding activates MPL has been resolved. This review will cover key aspects of TPO and MPL structure and function and their importance in receptor activation, discuss how these are altered in hematological disorders and consider how a greater understanding could lead to the development of better-targeted and more efficacious therapies.
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8.
Iron and platelets: A subtle, under-recognized relationship.
Brissot, E, Troadec, MB, Loréal, O, Brissot, P
American journal of hematology. 2021;(8):1008-1016
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Abstract
The role of iron in the formation and functioning of erythrocytes, and to a lesser degree of white blood cells, is well established, but the relationship between iron and platelets is less documented. Physiologically, iron plays an important role in hematopoiesis, including thrombopoiesis; iron levels direct, together with genetic factors, the lineage commitment of megakaryocytic/erythroid progenitors toward either megakaryocyte or erythroid progenitors. Megakaryocytic iron contributes to cellular machinery, especially energy production in platelet mitochondria. Thrombocytosis, possibly favoring vascular thrombosis, is a classical feature observed with abnormally low total body iron stores (mainly due to blood losses or decreased duodenal iron intake), but thrombocytopenia can also occur in severe iron deficiency anemia. Iron sequestration, as seen in inflammatory conditions, can be associated with early thrombocytopenia due to platelet consumption and followed by reactive replenishment of the platelet pool with possibility of thrombocytosis. Iron overload of genetic origin (hemochromatosis), despite expected mitochondrial damage related to ferroptosis, has not been reported to cause thrombocytopenia (except in case of high degree of hepatic fibrosis), and iron-related alteration of platelet function is still a matter of debate. In acquired iron overload (of transfusional and/or dyserythropoiesis origin), quantitative or qualitative platelet changes are difficult to attribute to iron alone due to the interference of the underlying hematological conditions; likewise, hematological improvement, including increased blood platelet counts, observed under iron oral chelation is likely to reflect mechanisms other than the sole beneficial impact of iron depletion.
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An epitope-based approach of HLA-matched platelets for transfusion: a noninferiority crossover randomized trial.
Marsh, JC, Stanworth, SJ, Pankhurst, LA, Kallon, D, Gilbertson, AZ, Pigden, C, Deary, AJ, Mora, AS, Brown, J, Laing, ES, et al
Blood. 2021;(3):310-322
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Abstract
Platelet transfusion refractoriness results in adverse outcomes and increased health care costs. Managing refractoriness resulting from HLA alloimmunization necessitates the use of HLA antigen-matched platelets but requires a large platelet donor pool and does not guarantee full matching. We report the first randomized, double-blind, noninferiority, crossover trial comparing HLA epitope-matched (HEM) platelets with HLA standard antigen-matched (HSM) platelet transfusions. Alloimmunized, platelet-refractory, thrombocytopenic patients with aplastic anemia, myelodysplastic syndrome, or acute myeloid leukemia were eligible. HEM platelets were selected using HLAMatchMaker epitope (specifically eplet) matching. Patients received up to 8 prophylactic HEM and HSM transfusions provided in random order. The primary outcome was 1-hour posttransfusion platelet count increment (PCI). Forty-nine patients were randomized at 14 UK hospitals. For intention to treat, numbers of evaluable transfusions were 107 and 112 for HEM and HSM methods, respectively. Unadjusted mean PCIs for HEM and HSM methods were 23.9 (standard deviation [SD], 15) and 23.5 (SD, 14.1), respectively (adjusted mean difference, -0.1; 95% confidence interval [CI], -2.9 to 2.8). Because the lower limit of the 95% CI was not greater than the predefined noninferiority limit, the HEM approach was declared noninferior to the HSM approach. There were no differences in secondary outcomes of platelet counts, transfusion requirements, and bleeding events. Adequate 1-hour PCI was more frequently observed, with a mean number of 3.2 epitope mismatches, compared with 5.5 epitope mismatches for inadequate 1-hour increments. For every additional epitope mismatch, the likelihood of an adequate PCI decreased by 15%. Epitope-matched platelets should be considered to support HLA alloimmunized patients. This trial was registered at www.isrctn.com as #ISRCTN23996532.
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Zinc: an endogenous and exogenous regulator of platelet function during hemostasis and thrombosis.
Ahmed, NS, Lopes-Pires, M, Pugh, N
Platelets. 2021;(7):880-887
Abstract
Zinc (Zn2+) is an essential micronutrient and the second most abundant trace metal in the human body. The important role that Zn2+ plays in hemostasis is exemplified by platelet-related bleeding phenotypes coinciding with dietary Zn2+ deficiency. These phenotypes are rectified upon Zn2+ supplementation. Labile (unbound) Zn2+ is present in the plasma at micromolar levels, but is also detected in atherosclerotic plaques, and released from platelet α granules. Therefore, it is likely that localized Zn2+ concentrations are higher at sites of thrombosis and hemostasis. Exogenous Zn2+ is a regulator of the hemostatic responses, with roles during coagulation and platelet activation. Extracellular Zn2+ gains access to the platelet cytosol and induces full platelet activation at high concentrations, and potentiates platelets to activation by conventional agonists at lower concentrations. Zn2+-induced platelet activation is dependent on PKC and integrin αIIbβ3, and is associated with tyrosine phosphorylation of platelet proteins. Agonist evoked platelet activation results in intracellular Zn2+ ([Zn2+]i) fluctuations that are sensitive to the platelet redox state. Increases in [Zn2+]i correlate with activation responses, including shape change, granule release, αIIbβ3 activation and phosphatidyl-serine exposure, consistent with a role as a second messenger. This review provides insight into the numerous demonstrated and potential roles for Zn2+ in platelet function during thrombosis and hemostasis, highlighting its increasing acceptance as an intracellular and extracellular platelet regulatory agent.