Studies of Fibrinogen Binding to Platelets by Flow Cytometry: An Improved Method for Studies of Platelet Activation

1992 ◽  
Vol 68 (02) ◽  
pp. 221-225 ◽  
Author(s):  
Tomas L Lindahl ◽  
Roger Festin ◽  
Anders Larsson
Keyword(s):  
Flow Cytometry ◽  
Platelet Activation ◽  
Whole Blood ◽  
Platelet Rich Plasma ◽  
Fluorescein Isothiocyanate ◽  
Human Platelets ◽  
Membrane Receptors ◽  
Human Fibrinogen ◽  
Fibrinogen Binding ◽  
Cell Data

SummaryPlatelet function is dependent upon membrane receptors and their interaction with other proteins. Platelet activation appears to cause a structural change of the glycoprotein IIb/IIIa complex that exposes the fibrinogen binding site, which subsequently binds fibrinogen. Fluorescence-activated flow cytometry (FACS) is an efficient method for studying membrane proteins. Flow cytometry gives single-cell data, allowing the detection of only a small proportion of labelled platelets in whole blood without any washing steps. One problem with this method is that the labelled antibodies and the antigen, if present in plasma, form an immune complex, which may cause false positive reactions due to interaction between mammalian IgG and Fcγ receptors on the platelets.We show that immune complexes with chicken IgG do not activate human platelets. We have developed a method for measuring platelet-bound fibrinogen in whole blood and platelet-rich plasma utilising fluorescein isothiocyanate (FITC)-conjugated chicken antibodies directed towards human fibrinogen. As low as 1% activated platelets could be detected without interference from Fc-interactions.

scholarly journals Platelet activation via PAR4 is involved in the initiation of thrombin generation and in clot elasticity development

2007 ◽  
Vol 97 (03) ◽  
pp. 417-424 ◽  
Author(s):  
Sofia Ramström ◽  
Maria Bjerke ◽  
Tomas Lindahl ◽  
Karin Vretenbrant
Keyword(s):  
Platelet Activation ◽  
Thrombin Generation ◽  
Platelet Rich Plasma ◽  
Physiological Role ◽  
Human Platelets ◽  
Coagulation Cascade ◽  
Fluorescent Intensity ◽  
Fibrinogen Binding ◽  
Low Concentrations ◽  
Physiological Relevance

SummaryThrombin is a pivotal enzyme formed in the coagulation cascade and an important and potent platelet activator. The two pro-tease-activated thrombin receptors on human platelets are denoted PARI and PAR4. The physiological relevance of PAR4 is still unclear, as both aggregation and secretion can be accomplished by PARI activation alone. In the present study we have investigated the role of PARs in platelet activation, blood coagulation, clot elasticity and fibrinolysis. Flow cytometry, free oscillation rheometry and thrombin generation measurements were used to analyze blood or platelet-rich plasma from healthy individuals. Maximum PARI activation with the peptide SFLLRN gave fewer fibrinogen-binding platelets with lower mean fluorescent intensity than maximum PAR4 activation with AYPGKF. Inhibition of any of the receptors prolonged clotting times. However, PARI is more important for fibrinolysis; inhibition of this receptor prolonged all the steps in the fibrinolytic process. Clot elasticity decreased significantly when the PAR4 receptor was inhibited. In the thrombin generation measurements, PAR4 inhibition delayed the thrombin generation start and peak, but did not affect the total amount of thrombin generated. PAR I inhibition had no significant impact on thrombin generation. We found that PAR4 is most likely activated by low concentrations of thrombin during the initial phase of thrombin generation and is of importance to the clotting time. Furthermore, we suggest that the PAR4 receptor may have a physiological role in the stabilisation of the coagulum.

Thrombin-Mediated Platelet Activation of Lysed Whole Blood and Platelet-Rich Plasma: A Comparison Between Platelet Activation Markers and Ultrastructural Alterations

2016 ◽  
Vol 22 (3) ◽  
pp. 630-639 ◽  
Author(s):  
Tanya N. Augustine ◽  
Wendy J. van der Spuy ◽  
Lindsay L. Kaberry ◽  
Millicent Shayi
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Flow Cytometry ◽  
Platelet Activation ◽  
Diagnostic Tool ◽  
Whole Blood ◽  
Platelet Rich Plasma ◽  
Ultrastructural Changes ◽  
Ultrastructural Alterations ◽  
Scanning Electron

AbstractPlatelet ultrastructural alterations representing spurious activation have been identified in pathological conditions. A limitation of platelet studies is that sample preparation may lead to artifactual activation processes which may confound results, impacting the use of scanning electron microscopy as a supplemental diagnostic tool. We used scanning electron microscopy and flow cytometry to analyze platelet activation in platelet-rich plasma (PRP) and whole blood (WB) samples. PRP generated using a single high g force centrifugation, and WB samples treated with a red blood cell lysis buffer, were exposed to increasing concentrations of the agonist thrombin. Platelets in lysed WB samples responded to thrombin by elevating the activation marker CD62p definitively, with corresponding ultrastructural changes indicating activation. Conversely, CD62p expression in PRP preparations remained static. Ultrastructural analysis revealed fully activated platelets even under low concentration thrombin stimulation, with considerable fibrin deposition. It is proposed that the method for PRP production induced premature platelet activation, preventable by using an inhibitor of platelet aggregation and fibrin polymerization. Nevertheless, our results show a definitive correspondence between flow cytometry and scanning electron microscopy in platelet activation studies, highlighting the potential of the latter technique as a supplemental diagnostic tool.

Flow Cytometry Analysis of Intracellular VASP Phosphorylation for the Assessment of Activating and Inhibitory Signal Transduction Pathways in Human Platelets

1999 ◽  
Vol 82 (09) ◽  
pp. 1145-1152 ◽  
Author(s):  
Ulrike Schwarz ◽  
Jörg Geiger ◽  
Ulrich Walter ◽  
Martin Eigenthaler
Keyword(s):  
Flow Cytometry ◽  
Platelet Activation ◽  
Intracellular Signaling ◽  
Platelet Rich Plasma ◽  
Umbilical Vein ◽  
Cardiovascular Complications ◽  
Human Platelets ◽  
Mitogen Activated Protein Kinase ◽  
Therapeutic Interventions ◽  
Platelet Protein

SummaryIncreased platelet adhesion or aggregation are key events in the pathogenesis of cardiovascular diseases. Exact determination of the platelet activation state is essential to recognize, prevent, and treat cardiovascular complications due to platelet dysfunction. Initial phases of platelet activation and inhibition are characterized by phosphorylation of specific intracellular proteins. However, methodological problems often prevent analysis of platelet protein phosphorylation under clinical conditions. A novel flow cytometry-based method using a phosphorylation-specific antibody was developed for fast and easy quantification of the phosphorylation state of a specific intracellular platelet protein. This method was used to analyze various platelet receptors and their intracellular signaling which may be impaired in genetic or acquired disorders or altered due to therapeutic interventions. In a first clinical application, the inhibitory effects of ticlopidine and clopidogrel on the platelet P2YAC ADP receptor were monitored.Abbreviations: ADP: adenosine 5’-diphosphate; cAMP: cyclic adenosine-3’,5’-monophosphate; cGMP: cyclic guanosine-3’,5’-monophosphate; HUVECs: human umbilical vein endothelial cells; MAPK: mitogen-activated protein kinase; PG-E1: prostaglandin E1; PRP: platelet-rich plasma; SNP: sodium nitroprusside; VASP: vasodilator-stimulated phosphoprotein

A Flow Cytometry Method for Characterizing Platelet Activation

2020 ◽  
Author(s):  
Brian Alzua ◽  
Mark Smith ◽  
Yan Chen
Keyword(s):  
Flow Cytometry ◽  
Medical Device ◽  
Platelet Activation ◽  
Medical Devices ◽  
Whole Blood ◽  
Platelet Rich Plasma ◽  
Thrombus Formation ◽  
Standard Regimen ◽  
Activated Platelets ◽  
Wide Range

Abstract Hemocompatibility testing is critical for assessing the safety of blood-contacting medical devices. Comprehensive hemocompatibility testing requires examining a wide range of possible adverse effects cause by direct or indirect blood contact, such as hemolysis, complement activation, and thrombus formation [1]. Moreover, these domains each encompass complex intercellular processes with many potential targets for analysis. For example, the current testing paradigm of platelet function may involve exposing the device to human whole blood and performing simple blood counts and/or macroscopic evaluation to determine the extent of platelet activation and clot formation as described in ASTM F2888-19. However, this approach does not capture any observations for device-mediated initiation of any steps in the platelet activation pathway prior to aggregation. We have validated a method to evaluate platelet activation by quantifying surface p-selectin expression after exposure to various materials. This method will provide an additional level of detail about potential platelet activating properties of a medical device. Flow cytometry has been used previously to measure platelet activation for clinical and research purposes. We sought to adapt this method to test for platelet activation induced by exposure of blood to medical devices or materials. We determined that processing fresh whole blood to platelet-rich plasma (PRP) by gentle centrifugation enhanced the signal compared to fresh blood itself. In each experiment, devices were exposed to PRP according to an extraction ratio of 6 cm2/mL for 1 hour. A blank control consisting of untreated PRP, and a positive control consisting of ADP, a potent agonist, were also used. After the exposure, excess plasma was removed from the articles and combined with anti-CD61 (to stain for platelets) and anti-CD62P (to stain for activated platelets) antibodies. Flow cytometry was then performed to quantify the percentage of CD62P+ over the total CD61+ cells to measure the percentage of activated platelets. In order to optimize the method, we investigated the effect of several experimental factors, including anticoagulant usage, donor variability, and selection of reference materials to serve as controls. Our results indicate that the flow cytometry-based method is consistent and reproducible, quick and easy to perform, and is well-correlated with results from the standard platelet and leukocyte count assay. The flow cytometry-based platelet activation method is a powerful supplement to the standard regimen of medical device hemocompatibility testing.

Serotonergic mechanisms enhance platelet-mediated thrombogenicity

2009 ◽  
Vol 102 (09) ◽  
pp. 511-519 ◽  
Author(s):  
Irene Lopez-Vilchez ◽  
Maribel Diaz-Ricart ◽  
Fulgencio Navalon ◽  
Esther Gomez ◽  
Cristobal Gasto ◽  
...  
Keyword(s):  
Platelet Activation ◽  
Whole Blood ◽  
Thrombin Generation ◽  
Platelet Rich Plasma ◽  
Thrombus Formation ◽  
Selective Inhibition ◽  
Human Platelets ◽  
Experimental Conditions ◽  
Perfusion Studies

SummaryAlthough it is generally acknowledged that serotonin (5-HT) is a weak agonist for human platelets, recent information suggests an association between serotonergic mechanisms and cardiovascular risk. We investigated the action of 5-HT on adhesive, cohesive and procoagulant properties of human platelets. Impact of 5-HT on whole blood coagulation and thrombin generation was measured by modified thromboelastometry (TEM) and specific fluorogenic assays. We evaluated the effects of 5-HT on thrombus formation in an in-vitro model of thrombosis using human flowing blood. In platelet-rich plasma (PRP), 5-HT favoured the expression of CD62-P, and procoagulant molecules on platelet membranes. These effects were potentiated in the presence of Ca++ and/or ADP. Incubation with 5-HT accelerated clotting times and augmented clot strength in whole blood TEM, and enhanced thrombin generation in PRP. In perfusion studies, 5-HT significantly increased fibrin deposition at low shear (300s-1) and enhanced platelet thrombus formation on the damaged vascular surface at high shear (1,200s-1). Selective inhibition of serotonin reuptake (SSRI) attenuated effects of 5-HT on platelet activation and downregulated the prothrombotic tendencies observed in the previous experimental conditions. In general, reductions of thrombogenic patterns observed with SSRI were more evident under shear conditions (aggregation and perfusion systems) and less evident under steady conditions (TEM and thrombin generation assays). In conclusion, 5-HT is not a weak agonist for human platelets; instead it accentuates platelet activation, potentiates procoagulant responses on human blood and increases thrombogenesis on damaged vascular surfaces. The remarkable antithrombotic actions achieved through SSRI deserve further mechanistic and clinical investigations.

Effects of a Monoclonal Antibody to Glycoprotein IIb/IIIa (P256) and of Enzymically Derived Fragments of P256 on Human Platelets

1991 ◽  
Vol 65 (04) ◽  
pp. 432-437 ◽  
Author(s):  
A W J Stuttle ◽  
M J Powling ◽  
J M Ritter ◽  
R M Hardisty
Keyword(s):  
Monoclonal Antibody ◽  
Flow Cytometry ◽  
Platelet Aggregation ◽  
Calcium Ions ◽  
Human Platelet ◽  
Human Platelets ◽  
In Vivo Detection ◽  
Fibrinogen Binding ◽  
Specific Antagonist

SummaryThe anti-platelet monoclonal antibody P256 is currently undergoing development for in vivo detection of thrombus. We have examined the actions of P256 and two fragments on human platelet function. P256, and its divalent fragment, caused aggregation at concentrations of 10−9−3 × 10−8 M. A monovalent fragment of P256 did not cause aggregation at concentrations up to 10−7 M. P256–induced platelet aggregation was dependent upon extracellular calcium ions as assessed by quin2 fluorescence. Indomethacin partially inhibited platelet aggregation and completely inhibited intracellular calcium mobilisation. Apyrase caused partial inhibition of aggregation. Aggregation induced by the divalent fragment was dependent upon fibrinogen and was inhibited by prostacyclin. Aggregation induced by the whole antibody was only partially dependent upon fibrinogen, but was also inhibited by prostacyclin. P256 whole antibody was shown, by flow cytometry, to induce fibrinogen binding to indomethacin treated platelets. Monovalent P256 was shown to be a specific antagonist for aggregation induced by the divalent forms. In–111–labelled monovalent fragment bound to gel-filtered platelets in a saturable and displaceable manner. Monovalent P256 represents a safer form for in vivo applications

A Simple and Rapid Method to Determine GPIIb/IIIa-Receptor Inhibitor Activity in Whole Blood

1999 ◽  
Vol 19 (03) ◽  
pp. 134-138
Author(s):  
Gitta Kühnel ◽  
A. C. Matzdorff
Keyword(s):  
Flow Cytometry ◽  
Platelet Count ◽  
Blood Sample ◽  
Platelet Activation ◽  
Whole Blood ◽  
Receptor Occupancy ◽  
Aggregate Formation ◽  
Inhibitor Activity ◽  
Receptor Inhibitor

SummaryWe studied the effect of GPIIb/IIIa-inhibitors on platelet activation with flow cytometry in vitro. Citrated whole blood was incubated with increasing concentrations of three different GPIIb/IIIa-inhibitors (c7E3, DMP728, XJ757), then thrombin or ADP were added and after 1 min the sample was fixed. Samples without c7E3 but with 0.1 U/ml thrombin had a decrease in platelet count. Samples with increasing concentrations of c7E3 had a lesser or no decrease in platelet count. The two other inhibitors (DMP 725, XJ757) gave similar results. GPIIb/IIIa-inhibitors prevent aggregate formation and more single platelets remain in the blood sample. The agonist-induced decrease in platelet count correlates closely with the concentration of the GPIIb/IIIa inhibitor and receptor occupancy. This correlation may be used as a simple measure for inhibitor activity in whole blood.

scholarly journals The Serine/Threonine Protein Phosphatase 2A (PP2A) Regulates Syk Activity in Human Platelets

2020 ◽  
Vol 21 (23) ◽  
pp. 8939
Author(s):  
Stephanie Makhoul ◽  
Elena Kumm ◽  
Pengyu Zhang ◽  
Ulrich Walter ◽  
Kerstin Jurk
Keyword(s):  
Protein Kinase ◽  
Platelet Activation ◽  
Protein Phosphatase ◽  
Feedback Inhibition ◽  
Protein Phosphatase 2A ◽  
Human Platelets ◽  
Membrane Receptors ◽  
Functional Link ◽  
S Protein ◽  
Phosphatase 2A

Distinct membrane receptors activate platelets by Src-family-kinase (SFK)-, immunoreceptor-tyrosine-based-activation-motif (ITAM)-dependent stimulation of spleen tyrosine kinase (Syk). Recently, we reported that platelet activation via glycoprotein (GP) VI or GPIbα stimulated the well-established Syk tyrosine (Y)-phosphorylation, but also stoichiometric, transient protein kinase C (PKC)-mediated Syk serine(S)297 phosphorylation in the regulatory interdomain-B, suggesting possible feedback inhibition. The transient nature of Syk S297 phosphorylation indicated the presence of an unknown Syk pS297 protein phosphatase. In this study, we hypothesize that the S-protein phosphatase 2A (PP2A) is responsible for Syk pS297 dephosphorylation, thereby affecting Syk Y-phosphorylation and activity in human washed platelets. Using immunoblotting, we show that specific inhibition of PP2A by okadaic acid (OA) alone leads to stoichiometric Syk S297 phosphorylation, as analyzed by Zn2+-Phos-tag gels, without affecting Syk Y-phosphorylation. Pharmacological inhibition of Syk by PRT060318 or PKC by GF109203X only minimally reduced OA-induced Syk S297 phosphorylation. PP2A inhibition by OA preceding GPVI-mediated platelet activation induced by convulxin extended Syk S297 phosphorylation but inhibited Syk Y-phosphorylation. Our data demonstrate a novel biochemical and functional link between the S-protein phosphatase PP2A and the Y-protein kinase Syk in human platelets, and suggest that PP2A represents a potential enhancer of GPVI-mediated Syk activity caused by Syk pS297 dephosphorylation.

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