Ultrastructural Studies of Platelet Aggregates From Human Subjects Receiving Clopidogrel and From a Patient With an Inherited Defect of an ADP-Dependent Pathway of Platelet Activation

Our study investigated the effect of the antithrombotic drug clopidogrel (75 mg/d for 7 days) on the ultrastructure of platelet aggregates induced by ADP or 2-methylthio-ADP (2-MeS-ADP) in citrated platelet-rich plasma and examined the activation state of the GP IIb/IIIa complexes. Results were compared with those obtained for patient M.L., who has a congenital disorder characterized by a reduced and reversible platelet response to ADP. When untreated normal platelets were stimulated with high-dose ADP, electron microscopy revealed large and stable aggregates often surrounded by a layer of what appeared to be degranulated platelets. The reversible aggregates of platelets from subjects receiving clopidogrel or from patient M.L. did not show this layer. Electron microscopy showed that in both situations, the aggregates were composed of loosely bound platelets with few contact points. Immunogold labeling of ultrathin sections of Lowicryl-embedded aggregates formed by ADP or 2-MeS-ADP showed a much decreased platelet surface staining by (1) a polyclonal anti-fibrinogen antibody and (2) AP-6, a murine anti–ligand-induced binding site monoclonal antibody specific for GP IIb/IIIa complexes occupied with fibrinogen. Similar findings were seen after disaggregation, when many single platelets were present that showed no signs of secretion. Flow cytometry confirmed that the number of ligand-occupied GP IIb/IIIa complexes was much lower on platelets stimulated with ADP or 2-MeS-ADP after clopidogrel treatment. As expected from previous studies, ADP-induced platelet shape change and Ca 2+ influx were unaffected by clopidogrel. These results agree with the hypothesis that platelet activation by ADP is biphasic and highlight a receptor-induced activation pathway affected by clopidogrel (or congenitally impaired in patient M.L.) that is necessary for the full activation of GP IIb/IIIa and the formation of stable macroaggregates.

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The active metabolite of prasugrel inhibits ADP-stimulated thrombo-inflammatory markers of platelet activation: Influence of other blood cells, calcium, and aspirin

Thrombosis and Haemostasis ◽

10.1160/th07-01-0010 ◽

2007 ◽

Vol 98 (07) ◽

pp. 192-200 ◽

Cited By ~ 33

Author(s):

Joseph Jakubowski ◽

You FuLi ◽

Marc Barnard ◽

Marsha Fox ◽

Matthew Linden ◽

...

Keyword(s):

Platelet Aggregation ◽

Platelet Activation ◽

Whole Blood ◽

Blood Cells ◽

Inflammatory Markers ◽

Active Metabolite ◽

Platelet Rich Plasma ◽

Shape Change ◽

Flow Cytometric Analysis ◽

Platelet Surface

SummaryThe novel thienopyridine prodrug prasugrel, a platelet P2Y12 ADP receptor antagonist, requires in vivo metabolism for activity. Although pharmacological data have been collected on the effects of prasugrel on platelet aggregation,there are few data on the direct effects of the prasugrel’s active metabolite, R-138727, on other aspects of platelet function. Here we examined the effects of R-138727 on thrombo-inflammatory markers of platelet activation, and the possible modulatory effects of other blood cells, calcium, and aspirin. Blood (PPACK or citrate anticoagulated) from healthy donors pre- and post-aspirin was incubated with R-138727 and the response to ADP assessed in whole blood or platelet-rich plasma (PRP) by aggregometry and flow cytometric analysis of leukocyte-platelet aggregates,platelet surface P-selectin, and GPIIb-IIIa activation. Low-micromolar concentrations of R-138727 resulted in a rapid and consistent in-hibition of these ADP-stimulated thrombo-inflammatory markers.These rapid kinetics required physiological calcium levels, but were largely unaffected by aspirin. Lower IC50 values in whole blood relative to PRP suggested that other blood cells affect ADP-induced platelet activation and hence the net inhibition by R-138727. R-138727 did not inhibit P2Y12-mediated ADP-induced shape change, even at concentrations that completely inhibited platelet aggregation, confirming the specificity of R-138727 for P2Y12. In conclusion, R-138727, the active metabolite of prasugrel, results in rapid, potent, consistent, and selective inhibition of P2Y12-mediated up-regulation of thromboinflammatory markers of platelet activation.This inhibition is enhanced in the presence other blood cells and calcium,but not aspirin.

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Abstract 39: Platelet Reactivity to Prostaglandin E2 is a Novel Modifiable Risk Factor for St-Elevation Myocardial Infarction

Arteriosclerosis Thrombosis and Vascular Biology ◽

10.1161/atvb.36.suppl_1.39 ◽

2016 ◽

Vol 36 (suppl_1) ◽

Author(s):

Eitan A Friedman ◽

Elias V Haddad ◽

Valentinas Joksas ◽

Shi Huang ◽

Meng Xu ◽

...

Keyword(s):

Myocardial Infarction ◽

Cardiovascular Risk ◽

Platelet Activation ◽

Platelet Reactivity ◽

Platelet Rich Plasma ◽

Coronary Intervention ◽

Prostaglandin E ◽

Platelet Response ◽

Increased Risk ◽

St Elevation

Background: Patients with lower thresholds for platelet activation are at increased risk for primary and recurrent myocardial infarction (MI) and overall cardiovascular (CV) mortality. We have demonstrated that there are two phenotypes of platelet response to Prostaglandin E 2 (PGE 2 ), such that it increases threshold for aggregation in 45% of individuals (inhibitory) and lowers threshold for aggregation in 55% (potentiating). As PGE 2 is present in atherosclerotic plaques, and its receptors are present on platelets, biologic variability in PGE 2 responses may have clinical implications. We hypothesized that patients with higher thresholds for platelet activation would have a lower risk of thrombotic CV events, specifically ST-Elevation MI (STEMI). Methods: 85 patients undergoing percutaneous coronary intervention for stable or unstable coronary disease were phenotyped for PGE 2 response. Platelet rich plasma was treated with various concentrations of U46,619 (thromboxane agonist) with or without PGE 2 100 nM, and phenotype determined by light aggregometry. Analysis of the maximum PGE 2 effect (maximum aggregation with PGE 2 minus maximum aggregation without it) was performed using linear and non-linear statistical methods. Results: Traditional cardiovascular risk factors were similar between groups. A higher percentage of patients with the potentiating phenotype had a history of STEMI than those with the inhibitory phenotype. Logistic regression using restricted cubic spline showed that the predicted probabilities of STEMI increased from 0.04 (at the strongest inhibitory phenotype) to 0.43 (at the median phenotype). The OR of phenotype at the median relative to that at the 10th quantile was 7.4 (95 % CI=1.6, 34.8). Conclusions: PGE 2 inhibitory phenotype confers a decreased lifetime risk of STEMI in individuals at high risk for CV events. We have previously shown that an EP3 receptor antagonist converts the potentiating to the inhibitory phenotype. Thus, the PGE2 phenotype may be a novel marker of cardiovascular risk that may also identify patients who would benefit from an EP3 antagonist.

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Inhibition of collagen-induced platelet activation by 5'-p- fluorosulfonylbenzoyl adenosine: evidence for an adenosine diphosphate requirement and synergistic influence of prostaglandin endoperoxides

Blood ◽

10.1182/blood.v68.2.565.565 ◽

1986 ◽

Vol 68 (2) ◽

pp. 565-570 ◽

Cited By ~ 16

Author(s):

RW Colman ◽

WR Figures ◽

LM Scearce ◽

AM Strimpler ◽

FX Zhou ◽

...

Keyword(s):

Platelet Activation ◽

Shape Change ◽

Thromboxane A2 ◽

Adenosine Diphosphate ◽

Platelet Surface ◽

Prostaglandin Endoperoxide ◽

Fibrinogen Binding ◽

Low Concentrations ◽

Absolute Requirement

Abstract The relative roles of platelet autacoids such as adenosine diphosphate (ADP), prostaglandin endoperoxides, and thromboxane A2 (TXA2) in collagen-induced platelet activation are not fully understood. We reexamined this relationship using the ADP affinity analogue, 5'-p- fluorosulfonylbenzoyl adenosine (FSBA), which covalently modifies a receptor for ADP on the platelet surface, thereby inhibiting ADP- induced platelet activation. Collagen-induced shape change, aggregation, and fibrinogen binding were each fully inhibited under conditions in which FSBA is covalently incorporated and could not be overcome by raising the collagen used to supramaximal concentrations. In contrast, TXA2 synthesis stimulated by collagen under conditions that produced maximum aggregation was only minimally inhibited by FSBA. Since covalent incorporation of FSBA has been previously shown to specifically inhibit ADP-induced activation of platelets, the present study supports the contention that ADP is required for collagen-induced platelet activation. Under similar conditions, indomethacin, an inhibitor of cyclooxygenase, inhibited collagen-induced shape change, indicating that endoperoxides and/or TXA2 also play a role in this response. Shape change induced by low concentrations (10 nmol/L) of the stable prostaglandin endoperoxide, azo-PGH2, was also inhibited by FSBA. These observations indicate a role for ADP in responses elicited by low concentrations of endoperoxides. However, at higher concentrations of azo-PGH2 (100 nmol/L), inhibition by FSBA could be overcome. Thus, the effect of collagen apparently has an absolute requirement for ADP for aggregation and fibrinogen binding and for both ADP and prostaglandins for shape change. Aggregation and fibrinogen binding induced by prostaglandin endoperoxides also required ADP as a mediator, but ADP is not absolutely required at high endoperoxide concentration to induce shape change.

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von Willebrand factor bound to glycoprotein Ib is cleared from the platelet surface after platelet activation by thrombin

Blood ◽

10.1182/blood.v79.8.2011.2011 ◽

1992 ◽

Vol 79 (8) ◽

pp. 2011-2021 ◽

Cited By ~ 30

Author(s):

P Hourdille ◽

HR Gralnick ◽

E Heilmann ◽

A Derlon ◽

AM Ferrer ◽

...

Keyword(s):

Flow Cytometry ◽

Platelet Activation ◽

Von Willebrand Factor ◽

Platelet Rich Plasma ◽

Surface Expression ◽

Von Willebrand Disease ◽

Platelet Surface ◽

Immunogold Staining ◽

Von Willebrand ◽

Willebrand Factor

Abstract We recently reported that after activation of human platelets by thrombin, glycoprotein (GP) Ib-IX complexes are translocated to the surface-connected canalicular system (SCCS) (Blood 76:1503, 1990). As GPIb is a major receptor for von Willebrand factor (vWF) in platelet adhesion, we have now examined the consequences of thrombin activation on the organization of vWF bound to GPIb on the platelet surface. Studies were performed using monoclonal or polyclonal antibodies in either immunogold staining and electron microscopy (Au-EM) or in flow cytometry. When unstirred platelet-rich plasma was incubated with ristocetin, bound vWF was located by Au-EM as discrete masses regularly distributed over the cell surface. Platelets from a patient with Glanzmann's thrombasthenia, lacking GPIIb-IIIa complexes, gave a similar pattern, confirming that this represented binding to GPIb. That ristocetin was not precipitating vWF before their binding to the platelets was shown by the detection of similar masses on the surface of platelets of a patient with type IIB von Willebrand disease. Experiments were continued using washed normal platelets incubated in Tyrode-EDTA, the purpose of the EDTA being to limit the surface expression of endogenous vWF after platelet stimulation. Under these conditions, platelets were treated with ristocetin for 5 minutes at 37 degrees C in the presence of increasing amounts of purified vWF. This was followed by incubation with thrombin (0.5 U/mL) for periods of up to 10 minutes. Flow cytometry showed a time-dependent loss in the surface expression of vWF bound to GPIb and these changes were confirmed by Au-EM. In particular, immunogold staining performed on ultrathin sections showed that the bulk of the vWF was being cleared to internal membrane systems. Surface clearance of vWF during thrombin- induced platelet activation is a potential mechanism for regulating platelet adhesivity.

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Fucosyltransferase VI Induces Platelet Activation: A Novel Property of a Plasma Glycosyltransferase.

Blood ◽

10.1182/blood.v114.22.4016.4016 ◽

2009 ◽

Vol 114 (22) ◽

pp. 4016-4016

Author(s):

José-Tomás Navarro ◽

Shwan Tawfiq ◽

Roland Wohlgemuth ◽

Karin M. Hoffmeister ◽

Robert Sackstein

Keyword(s):

Flow Cytometry ◽

Platelet Aggregation ◽

Platelet Activation ◽

Light Transmission ◽

Conflicts Of Interest ◽

Platelet Rich Plasma ◽

Surface Protein ◽

Surface Flow ◽

Platelet Surface ◽

Biochemical Studies

Abstract Abstract 4016 Poster Board III-952 A number of glycosyltransferases are present in human plasma with the α(1→3) fucosyltransferase, Fucosyltransferase VI (FTVI), having the highest plasma concentration. Notably, elevated plasma levels of FTVI are associated with a variety of cancers and correlate with tumor load/progression. The well-known association of neoplasia with thromboembolic complications prompted us to examine whether FTVI has direct effect(s) on platelet function. We obtained human platelets from blood of healthy donors and separated from platelet-rich plasma by differential centrifugation. Freshly isolated platelets (x108/ml) were stirred and exposed at 37°C to varying concentrations (20, 40, 60 and 80 mU/mL) of glycosyltransferases FTVI, β-1-4-galactosyltransferase-I (βGalT-I), or α,2-3-N-sialyltransferase (α2,3-N-ST), or to 1 U/mL thrombin. Platelet aggregation and activation was assessed by aggregometry (light transmission) or by flow cytometry of FSC/SSC characteristics and of surface expression of P-Selectin, respectively. FT-VI reproducibly induced platelet aggregation and activation, whereas other glycosyltransferases (β4GalT-I and α2,3-N-ST) had no effect on platelets. FTVI activation of platelets was concentration-dependent, and the aggregation curve for FTVI was one wave, similar to that for thrombin. FTVI-induced platelet activation was independent of catalytic conversion of surface glycans, but was inhibited by FTVI denaturation, indicating that FTVI-induced platelet activation is a lectin-mediated process. To determine the membrane target(s) mediating FTVI-induced platelet activation, biochemical studies were performed after catalytic exofucosylation of the platelet surface. Flow cytometry after platelet exofucosylation showed formation of the carbohydrate structure sLex, detected by the mAb Heca452, but no formation of Lex (CD15). Western blot showed that enforced fucosylation induced sLex on a single platelet surface protein, and further biochemical studies revealed that this protein is GPIbα. These findings unveil a previously unrecognized property of FTVI as an activator of platelets, mediated via a specific lectin/carbohydrate interaction on GP1ba, and offer novel perspectives on the pathobiology of tumor-associated thrombogenesis. Disclosures: No relevant conflicts of interest to declare.

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In vivo effects of eltrombopag on platelet function in immune thrombocytopenia: no evidence of platelet activation

Blood ◽

10.1182/blood-2011-11-393900 ◽

2012 ◽

Vol 119 (17) ◽

pp. 4066-4072 ◽

Cited By ~ 55

Author(s):

Bethan Psaila ◽

James B. Bussel ◽

Matthew D. Linden ◽

Bracken Babula ◽

Youfu Li ◽

...

Keyword(s):

Platelet Activation ◽

Platelet Function ◽

Whole Blood ◽

Immune Thrombocytopenia ◽

Ex Vivo ◽

Platelet Reactivity ◽

Adenosine Diphosphate ◽

High Dose ◽

Platelet Surface

Abstract The effects of eltrombopag, a thrombopoietin-receptor agonist, on platelet function in immune thrombocytopenia (ITP) are not fully characterized. This study used whole blood flow cytometry to examine platelet function in 20 patients receiving eltrombopag treatment at days 0, 7, and 28. Platelet surface expression of activated GPIIb/IIIa, P-selectin, and GPIb was measured with and without low and high adenosine diphosphate (ADP) and thrombin receptor activating peptide (TRAP) concentrations. Before eltrombopag treatment with no ex vivo agonist, platelet activation was higher in ITP patients than controls. Platelet GPIb and activated GPIIb/IIIa expression without added agonist was unchanged following eltrombopag treatment, whereas a slight increase in P-selectin was observed. Expression of P-selectin and activated GPIIb/IIIa in response to high-dose ADP was lower during eltrombopag treatment than at baseline. Eltrombopag led to a slight increase in platelet reactivity to TRAP only in responders to eltrombopag but not to levels above those in controls; whole blood experiments demonstrated that this increase was probably because of higher platelet counts rather than higher platelet reactivity. In conclusion, although thrombocytopenic ITP patients have higher baseline platelet activation than controls, eltrombopag did not cause platelet activation or hyper-reactivity, irrespective of whether the platelet count increased.

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TLT-1 Regulates Thrombus Growth Under Non-Inflammatory Conditions

Blood ◽

10.1182/blood-2021-152975 ◽

2021 ◽

Vol 138 (Supplement 1) ◽

pp. 1050-1050

Author(s):

Angela Doerr ◽

Denise Pedrosa ◽

Maria Schander ◽

Yotis A. Senis ◽

Alexandra Mazharian ◽

...

Keyword(s):

Platelet Activation ◽

Type I Collagen ◽

Platelet Rich Plasma ◽

Thrombus Formation ◽

Type I ◽

Wild Type ◽

Platelet Surface ◽

Knock Out ◽

Integrin Αiibβ3

Abstract Background Thrombus formation is a complex, dynamic and multistep process, based on two crucial steps: platelet adhesion and platelet aggregation that both involve the large multimeric plasma glycoprotein Von Willebrand Factor (VWF). VWF binding to the GPIb/X/V complex initiates platelet adhesion to the vessel wall at high shear stress and triggers platelet activation resulting in the generation of thrombin and activation of integrin αIIbβ3 on the platelet surface. This activation of αIIbβ3 in turn leads to outside-in signalling and promotes binding of αIIbβ3 to fibrinogen and VWF, mediating thrombus growth. Trigging receptor expressed on myeloid cells like transcript-1 (TLT-1) is a transmembrane receptor, which is targeted to α-granules of platelets and megakaryocytes. Thrombin-induced platelet activation rapidly presents TLT-1 on the platelet surface and releases a soluble form (sTLT-1) into the circulation. To date the only known ligand for TLT-1 is fibrinogen and TLT-1 has been implicated in the regulation of inflammation-associated thrombosis. Interestingly, a putative interaction of VWF with TLT-1 was indicated by a screen with known platelet receptors. Aim We aimed to evaluate the effect of TLT-1/VWF interaction on platelet aggregation and thrombus formation. Methods Recombinant TLT-1 and VWF were purified and the interaction between TLT-1 and VWF was analyzed by surface plasmon resonance. Static interaction was confirmed by an ELISA based binding assay. Flow assays assessed TLT-1 dependent thrombus formation in vitro. The effects of TLT-1 knockout on thrombus formation in vivo were examined via intravital microscopy of the flow restricted inferior vena cava (IVC) and imaging of platelet attachment and fibrin formation over 6 hours. Furthermore, thrombus formation and resolution was followed by high resolution ultrasound imaging after stenosis induction for 28 days. Integrin aIIbb3 activation was analysed by flow cytometry using the JonA antibody in murine platelet rich plasma. Results VWF bound to soluble TLT-1 with high affinity in a calcium dependent manner (K D = 1.9 nM). The binding site on VWF was mapped to the A3D4 domains and high molecular weight VWF multimers had the greatest affinity for TLT-1. Moreover, HEK293 cells transfected with TLT-1 bound to VWF and VWF strings formed specifically on TLT-1 expressing cells, confirming the interaction between the two proteins. VWF inhibited the binding of fibrinogen to TLT-1, suggesting that VWF is a preferred binding partner of TLT-1. Human platelets exhibited increased TLT-1 surface expression after TRAP-6 induced platelet activation and TLT-1 was detected throughout thrombi formed under flow. Furthermore, a TLT-1 blocking antibody inhibited the interaction of TLT-1 with VWF and reduced platelet capture to type I collagen under shear stress. Ex vivo perfusion of blood from TLT-1 knock out mice over type I collagen also resulted in reduced thrombus formation compared to blood from wild-type mice. TLT-1 knock-out platelets were activated by thrombin similar to wild-type controls, based on P-selectin expression in platelet rich plasma. However, activation of integrin αIIbβ3 determined by JonA staining was reduced in the absence of TLT-1. This phenotype of reduced integrin αIIbβ3 activation on P-selectin positive platelets was phenocopied by the thrombin platelet response in platelet rich plasma from VWF -/- mice, but not GPIbα-deficient mice, indicating that the TLT-1-VWF interaction on platelets directly influences integrin αIIbβ3 activation. Significantly, thrombus formation was markedly reduced in TLT-1 knockout mice in the IVC model in vivo in comparison to wild-type mice. Conclusions This study demonstrates that TLT-1 is a novel platelet ligand for VWF, and that TLT-1 may preferentially bind VWF over fibrinogen. We propose a TLT-1/VWF dependent integrin αIIbβ3 activation mechanism which plays a pivotal role in thrombus formation under non-inflammatory and potentially inflammatory conditions. Disclosures Ruf: ICONIC Therapeutics: Consultancy; MeruVasimmune: Current holder of individual stocks in a privately-held company; ARCA bioscience: Consultancy, Patents & Royalties.

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Changes in G-Actin after Platelet Activation in Platelet Rich Plasma

Thrombosis and Haemostasis ◽

10.1055/s-0038-1646351 ◽

1992 ◽

Vol 68 (06) ◽

pp. 727-730 ◽

Cited By ~ 6

Author(s):

S Heptinstall ◽

J Glenn ◽

P Spangenberg

Keyword(s):

Platelet Aggregation ◽

Platelet Activation ◽

Actin Polymerization ◽

Platelet Rich Plasma ◽

Shape Change ◽

Inhibition Assay ◽

Activated Platelets ◽

Lysis Buffer ◽

Two Phases ◽

Rapid Conversion

SummaryWe have used the DNase I inhibition assay to study changes in G-actin after platelet activation in platelet-rich plasma (PRP) induced by ADP. Because of problems associated with depolymerization of F-actin after lysis of ADP-activated platelets in the presence of plasma, G-actin was measured using a lysis buffer that contained formaldehyde to prevent any depolymerization of F-actin.Different patterns of response were seen depending on the concentration of ADP used, and these were modified by avoiding aggregation by either not stirring the sample or by adding EDTA. The results show rapid conversion of G-actin to F-actin in association with shape change, and there is a further decrease in G-actin associated with irreversible platelet aggregation. Thus evidence is presented that actin polymerization occurs in two phases after ADP stimulation.

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Influence of Fibrinogen Split Products on Platelets

Thrombosis and Haemostasis ◽

10.1055/s-0038-1654084 ◽

1967 ◽

Vol 17 (01/02) ◽

pp. 078-098 ◽

Cited By ~ 13

Author(s):

M. I Barnhart ◽

D. C Cress ◽

R. L Henry ◽

J. M Riddle

Keyword(s):

Platelet Aggregation ◽

Plasma Concentration ◽

Whole Blood ◽

Platelet Rich Plasma ◽

Platelet Response ◽

Transient Nature ◽

Platelet Morphology ◽

Platelet Aggregates

SummaryBreakdown products of fibrinogen and fibrin can play a role in hemostasis and also may be of consequence in thrombosis. β2 fibrinogen derivative D is an electropositive terminal proteolysis product of fibrinolysis which has the ability to aggregate platelets. The normal plasma concentration of such nonclottable fibrinogen relatives is 0.2 mg/ml. During fibrinolysis this concentration may reach 5 mg/ml plasma. Addition of β 2 fibrinogen D (raising the plasma concentration 0.1 to 5 mg/ml) either in vivo or in vitro induced platelet aggregations. Moreover, alterations in platelet morphology occurred which were obvious by electron microscopy.Platelet depletion was a consistent response to the infusion of purified β2 fibrinogen D (8 to 55 mg/kg body weight) into dogs. Circulating platelets decreased as much as 85% but were only temporarily aggregated and reappeared in the circulation within 1 to 5 hrs. Small platelet aggregates circulated while large aggregates were trapped in the microcirculation. Thrombin was not responsible for the platelet aggregations as neither prothrombin nor clottable fibrinogen were changed significantly. The transient nature and morphological features of the platelet response according to microscopic criteria were prominent during and after infusion of β2 fibrinogen D.In vitro studies included 3 systems; washed platelets, platelet rich plasma and whole blood. Positive results were obtained with all, but platelets in whole blood were most responsive. The magnitude of platelet aggregation and morphology correlated with the concentration of β2 fibrinogen D. Platelet aggregation induced by ADP (10~5 mg/ml) was compared with that induced by β2 fibrinogen D (0.09 to 0.72 mg/ml). With either reagent aggregates were of dendritic forms. Combination of the 2 reagents was additive but did not further change the morphology. Additional factors seem necessary for development of viscous metamorphosis.

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Different Effects of Aspirin, Dipyridamole and UD-CG 115 on Platelet Activation in a Model of Vascular Injury: Studies with Extracellular Matrix Covered with Endothelial Cells

Thrombosis and Haemostasis ◽

10.1055/s-0038-1661678 ◽

1986 ◽

Vol 56 (03) ◽

pp. 333-339 ◽

Cited By ~ 21

Author(s):

A Eldor ◽

I Vlodavsky ◽

Z Fuks ◽

T H Muller ◽

W G Eisert

Keyword(s):

Extracellular Matrix ◽

Endothelial Cells ◽

Platelet Aggregation ◽

Cyclic Amp ◽

Platelet Activation ◽

Platelet Rich Plasma ◽

Thromboxane A2 ◽

Phase Microscopy ◽

Large Platelet ◽

Platelet Aggregates

SummaryCultured endothelial cells produce an extracellular matrix (ECM) which activates platelets, similarly to deendothelialized vascular segments. Platelet-rich plasma (PRP) was incubated with endothelial cells cultures seeded in various densities on ECM. The interaction of the platelets with this artifical intima was evaluated by phase microscopy and by thromboxane A2 (TXA2) and prostacyclin (PGI2) measurement. Large platelet aggregates were formed on exposed ECM. Platelets aggregation but not adhesion on the ECM was markedly inhibited by the presence of endothelial cells. Pretreatment of the endothelial cells with 0.1 mM aspirin reduced their PGI2 synthesis and was associated with platelet aggregation on the ECM. 10 μM dipyridamole markedly inhibited platelet activation by ECM when the drug was added to citrated whole blood before PRP preparation. UD-CG 115 which elevates cyclic AMP in cardiac muscle, inhibited platelet aggregation and TXA2 production induced by ECM, in the presence as well as in the absence of endothelial cells, without any effect on endothelial PGI2 production.

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