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Fibrinogen Binding (fibrinogen + binding)

Distribution by Scientific Domains

Medical Sciences	85%
3 Other Domains	15%

Selected Abstracts

Platelet activation, myocardial ischemic events and postoperative non-response to aspirin in patients undergoing major vascular surgery

JOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 10 2007
S. RAJAGOPALAN
Summary.,Objectives:,Myocardial ischemia is the leading cause of postoperative mortality and morbidity in patients undergoing major vascular surgery. Platelets have been implicated in the pathogenesis of acute thrombotic events. We hypothesized that platelet activity is increased following major vascular surgery and that this may predispose patients to myocardial ischemia.Methods:,Platelet function in 136 patients undergoing elective surgery for subcritical limb ischemia or infrarenal abdominal aortic aneurysm repair was assessed by P-selectin expression and fibrinogen binding with and without adenosine diphosphate (ADP) stimulation, and aggregation mediated by thrombin receptor-activating peptide and arachidonic acid (AA). Cardiac troponin-I (cTnI) was performed.Results:,P-selectin expression increased from days 1 to 3 after surgery [median increase from baseline on day 3: 53% (range: ,28% to 212%, P < 0.01) for unstimulated and 12% (range: ,9% to 45%, P < 0.01) for stimulated]. Fibrinogen binding increased in the immediate postoperative period [median increase from baseline: 34% (range: ,46% to 155%, P < 0.05)] and decreased on postoperative day 3 (P < 0.05). ADP-stimulated fibrinogen binding increased on day1 (P < 0.05) and thereafter decreased. Platelet aggregation increased on days 1,5 (P < 0.05). Twenty-eight (21%) patients had a postoperative elevation (> 0.1 ng mL,1) of cTnI. They had significantly increased AA-stimulated platelet aggregation in the immediate postoperative period and on day 2 (P < 0.05), and non-response to aspirin (48% vs. 26%, P = 0.036).Conclusions:,This study has shown increased platelet activity and the existence of non-response to aspirin following major vascular surgery. Patients with elevated postoperative cTnI had significantly increased AA-mediated platelet aggregation and a higher incidence of non-response to aspirin compared with patients who did not. [source]

Endothelin attenuates endothelium-dependent platelet inhibition in man

ACTA PHYSIOLOGICA, Issue 4 2010
R. E. Malmström
Abstract Aim:, The vascular endothelium produces several substances, including nitric oxide (NO) and endothelin-1 (ET-1), which participate in the regulation of vascular tone in humans. Both these substances may exert other actions of importance for cardiovascular disease, e.g. effects on vascular smooth muscle cell proliferation and inflammation, and NO inhibits platelet function. Experiments were designed to investigate the effect of ET-1 on endothelium-dependent vasodilatation and attenuation of platelet activation. Methods:, In 25 healthy male subjects (25 ± 1 years), forearm blood flow was measured by venous occlusion plethysmography, and platelet activity was assessed by whole blood flow cytometry (platelet fibrinogen binding and P-selectin expression) in unstimulated and adenosine diphosphate (ADP)-stimulated samples during administration of ET-1, the endothelium-dependent vasodilator acetylcholine and the NO synthase inhibitor l -NMMA. Results:, Acetylcholine increased forearm blood flow and significantly inhibited platelet activation in both unstimulated and ADP-stimulated samples. In samples stimulated with 0.3 ,m ADP, fibrinogen binding decreased from 41 ± 4% to 31 ± 3% (P < 0.01, n = 11) after acetylcholine administration. The vasodilator response to acetylcholine was significantly impaired during infusions of ET-1 and l -NMMA. ET-1 did not affect platelet activity per se, whereas l -NMMA increased platelet P-selectin expression. Both ET-1 and l -NMMA attenuated the acetylcholine-induced inhibition of platelet activity. Conclusions:, Our study indicates that, further to inhibiting endothelium-dependent vasodilatation, ET-1 may also attenuate endothelium-dependent inhibition of platelet activation induced by acetylcholine. An enhanced ET-1 activity, as suggested in endothelial dysfunction, may affect endothelium-dependent platelet modulation and thereby have pathophysiological implications. [source]

Pharmacodynamics and pharmacokinetics of YM128, a GPIIb/IIIa antagonist prodrug

DRUG DEVELOPMENT RESEARCH, Issue 3 2002
Ken-ichi Suzuki
Abstract We examined the biochemical properties of YM-57029 ({4-[4-(4-Carbamimidoylphenyl)-3-oxopiperazin-1-yl]piperidino}acetic acid monohydrochloride trihydrate) and the pharmacodynamics and pharmacokinetics of its prodrug, YM128 (Ethyl (Z)-(4-{4-[4-(N2 -hydroxycarbamimidoyl)phenyl]-3-oxopiperazin-1-yl}piperidino)acetate), an orally-active glycoprotein IIb/IIIa (GPIIb/IIIa) antagonist. YM-57029 strongly inhibited aggregation of human platelets induced by various agonists, with IC50 values ranging from 3.6 to 51 nM. YM-57029 specifically inhibited fibrinogen binding to purified GPIIb/IIIa about 1,000-fold more potently than Arg-Gly-Asp-Ser (RGDS). Moreover, YM-57029 effectively inhibited an Arg-Gly-Asp (RGD) peptide binding to platelets, suggesting that YM-57029 competed with the RGD sequence of ligand. YM-57029 or YM128 dose-dependently inhibited ex vivo platelet aggregation after iv bolus injection or oral administration to beagle dogs and cynomolgus monkeys. However, YM128 exerted more potent and prolonged inhibitory effects on platelet aggregation than YM-57029 after oral administration to cynomolgus monkeys. Furthermore, YM-57029 prolonged template bleeding time at a dose that inhibited ex vivo platelet aggregation during cumulative iv infusion to cynomolgus monkeys. Metabolic and pharmacokinetic studies showed that YM128 effectively converted into YM-57029 in liver microsomes from humans as well as dogs and monkeys, and that bioavailabilities of YM128 in dogs and monkeys were 32.3 and 22.2%, respectively. These results suggest that YM128, a prodrug of YM-57029, may be a valuable GPIIb/IIIa antagonist with good bioavailability in humans. Drug Dev. Res. 55:149,161, 2002. © 2002 Wiley-Liss, Inc. [source]

What is vinculin needed for in platelets?

JOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 10 2010
J. V. MITSIOS
Summary.,Background: Vinculin links integrins to the cell cytoskeleton by virtue of its binding to proteins such as talin and F-actin. It has been implicated in the transmission of mechanical forces from the extracellular matrix to the cytoskeleton of migrating cells. Vinculin's function in platelets is unknown. Objective: To determine whether vinculin is required for the functions of platelets and their major integrin, ,IIb,3. Methods: The murine vinculin gene (Vcl) was deleted in the megakaryocyte/platelet lineage by breeding Vcl fl/fl mice with Pf4,Cre mice. Platelet and integrin functions were studied in vivo and ex vivo. Results: Vinculin was undetectable in platelets from Vcl fl/fl Cre+ mice, as determined by immunoblotting and fluorescence microscopy. Vinculin-deficient megakaryocytes exhibited increased membrane tethers in response to mechanical pulling on ,IIb,3 with laser tweezers, suggesting that vinculin helps to maintain membrane cytoskeleton integrity. Surprisingly, vinculin-deficient platelets displayed normal agonist-induced fibrinogen binding to ,IIb,3, aggregation, spreading, actin polymerization/organization, clot retraction and the ability to form a procoagulant surface. Furthermore, vinculin-deficient platelets adhered to immobilized fibrinogen or collagen normally, under both static and flow conditions. Tail bleeding times were prolonged in 59% of vinculin-deficient mice. However, these mice exhibited no spontaneous bleeding and they formed occlusive platelet thrombi comparable to those in wild-type littermates in response to carotid artery injury with FeCl3. Conclusion: Despite promoting membrane cytoskeleton integrity when mechanical force is applied to ,IIb,3, vinculin is not required for the traditional functions of ,IIb,3 or the platelet actin cytoskeleton. [source]

Platelet activation, myocardial ischemic events and postoperative non-response to aspirin in patients undergoing major vascular surgery

A novel functional role for the highly conserved , -subunit KVGFFKR motif distinct from integrin ,IIb,3 activation processes

JOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 8 2006
K. AYLWARD
Summary.,Background: The highly conserved integrin , -subunit membrane-proximal motif KVGFFKR plays a decisive role in modulating the activation of integrin ,IIb,3. Previously, we have shown that a platelet permeable palmityl (pal)-peptide with this seven amino acid sequence can directly activate ,IIb,3 leading to platelet aggregation. Objectives: To investigate further the role of the KVGFFKR motif in integrin ,IIb,3 function. Methods: We used two sequence-specific complementary model systems, palmityl pal-peptides in platelets, and mutant ,IIb,3 -expressing Chinese Hamster Ovary (CHO) cell lines. Results: In platelets we show that the two phenylalanine amino acids in pal-KVGFFKR (pal-FF) peptide are critical for stimulating platelet aggregation. Pal-FF peptide treatment of platelets also gives rise to a tyrosine phosphorylation signal despite the presence of inhibitors of fibrinogen binding. In CHO cells, a double alanine substitution, ,IIb(F992A, F993A),3, induces constitutive integrin activation but prevents actin stress fiber formation upon adhesion to fibrinogen, suggesting that ,IIb,3 -mediated cytoskeletal reorganization is also dependent on F992 and F993. This further highlights a critical role for the two phenylalanine residues in both of these ,IIb,3 -mediated processes. Conclusion: In addition to regulating integrin ,IIb,3 activation state, the KVGFFKR motif also influences cytoskeletal reorganization. This activity is critically determined by F992 and F993 within the seven amino acid sequence. [source]

Megakaryocytes derived from human embryonic stem cells: a genetically tractable system to study megakaryocytopoiesis and integrin function

JOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 2 2006
M. GAUR
Summary.,Background:,The platelet fibrinogen receptor, a heterodimer consisting of integrin subunits ,IIb and ,3, is required for platelet aggregation, spreading, and hemostasis. Platelet agonists such as thrombin and adenosine diphosphate (ADP) lead to the activation of ,IIb,3, thereby enhancing its affinity and avidity for binding fibrinogen (inside-out signaling). Furthermore, fibrinogen binding to ,IIb,3 triggers cytoskeletal changes and granule release (outside-in signaling).Aim:,Genetic approaches to characterize the molecular pathways involved in ,IIb,3 signaling are not possible with anucleate blood platelets. Therefore, we have established an OP9 stromal cell co-culture system to generate megakaryocytes from human embryonic stem cells (hESCs).Results:,,IIb,3 activation, measured by soluble fibrinogen binding to hESC-derived megakaryocytes, /GPIb,+ cells, is readily detectable following stimulation with known platelet agonists. Dose,response curves for peptide agonists specific for the two platelet thrombin receptors, protease-activated receptor 1 (PAR1) and PAR4, show a relative responsiveness that mirrors that of human platelets, and sub-maximal ADP responses are augmented by epinephrine. Moreover, hESC-derived megakaryocytes undergo lamellipodia formation, actin filament assembly, and vinculin localization at focal adhesions when plated on a fibrinogen-coated surface, characteristic of ,IIb,3 outside-in signaling. Undifferentiated hESCs genetically modified by lentiviral infection can be cloned and maintained in an undifferentiated state and then differentiated into megakaryocytes capable of ,IIb,3 activation.Conclusion:,Using hESCs, we have developed a renewable source of human megakaryocytes, and a genetically tractable system for studying megakaryocytopoiesis and ,IIb,3 signaling in the native cellular environment. [source]

A 13-bp deletion in ,IIb gene is a founder mutation that predominates in Palestinian-Arab patients with Glanzmann thrombasthenia

JOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 12 2005
N. ROSENBERG
Summary. Glanzmann thrombasthenia (GT) is a rare autosomal recessive bleeding disorder caused by lack or dysfunction of ,IIb,3 in platelets. GT is relatively frequent in highly inbred populations. We previously identified a 13-bp deletion in the ,IIb gene that causes in-frame deletion of six amino acids in three Palestinian GT patients. In this study, we determined the molecular basis of GT in all known Palestinian patients, examined whether Jordanian patients harbor the same mutations, analyzed whether there is a founder effect for the 13-bp deletion, and determined the mechanism by which the 13-bp deletion abolishes ,IIb,3 surface expression. Of 11 unrelated Palestinian patients, eight were homozygous for the 13-bp deletion that displayed common ancestry by haplotype analysis, and was estimated to have occurred 300,600 years ago. Expression studies in baby hamster kidney cells showed that substitution of Cys107 or Trp110 located within the deletion caused defective ,IIb,3 maturation. Substitution of Trp110, but not of Cys107, prevented fibrinogen binding. The other Palestinian patients harbored three novel mutations: G2374 deletion in ,IIb gene, TT1616-7 deletion in ,3 gene, and IVS14: ,3C , G in ,3 gene. The latter mutation caused cryptic splicing predicting an extended cytoplasmic tail of ,3 and was expressed as dysfunctional ,IIb,3. None of 15 unrelated Jordanian patients carried any of the described mutations. [source]

Association of the antagonism of von Willebrand factor but not fibrinogen by platelet ,IIb,3 antagonists with prolongation of bleeding time

JOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 10 2005
T. AOKI
Summary.,Background:,The ,IIb,3 antagonists inhibit platelet aggregation and are used as antithrombotic agents for cardiothrombotic disease. The present study investigates the correlation of inhibition of fibrinogen and von Willebrand factor (VWF) binding by ,IIb,3 antagonists with the inhibition of platelet aggregation and prolongation of bleeding time (BT). Methods:,Inhibition of fibrinogen and VWF binding were assessed in a purified ,IIb,3 -binding assay. As an in vitro cell-based assay, platelet aggregation and VWF-mediated adhesion studies were performed using human platelets. In vivo effects on BT were measured using a template device in dogs at the same time as an ex vivo aggregation study was performed. Results:,In vitro studies demonstrated that the antiaggregatory effects of ,IIb,3 antagonists correlate with their inhibition of fibrinogen binding, but not VWF. Interestingly, the effects of ,IIb,3 antagonists on BT could be differentiated from the inhibition of platelet aggregation. Furthermore, this differentiation was strongly correlated with the different inhibitory potencies between fibrinogen and VWF binding, as well as that between VWF-mediated adhesion and aggregation. Conclusions:,Our study provides novel evidence showing that the inhibitory effect of ,IIb,3 antagonists on VWF, but not fibrinogen binding, correlates with their ability to prolong BT. [source]

Differential response of platelets to chemokines: RANTES non-competitively inhibits stimulatory effect of SDF-1,

JOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 1 2004
B. Shenkman
Summary.,Background:,Among the chemokines related to CXC and CC receptor groups and released from platelets, leukocytes and endothelial cells, SDF-1, TARC and MDC have been found to be platelet agonists. Platelets do not contain SDF-1,. In contrast, RANTES is constitutively present in platelet ,-granules and released upon platelet activation. Objectives:,To study a possible role of RANTES as a modulator of SDF-1, effect on platelets, in relation to CXCR4 and various CC receptors. Methods:,CXCR-4 (CXCL12) receptor expression and platelet activation were evaluated by flow cytometry, platelet deposition was studied by cone and plate(let) analyzer, and platelet aggregation by turbidometric aggregometry. Results:,Flow cytometry studies revealed similar expression of CXCR-4, the specific receptor of SDF-1, on intact, inactivated, and activated platelets. Preincubation of platelets with RANTES affected neither CXCR-4 expression, nor SDF-1, binding to the platelet membrane. In the presence of fibrinogen, SDF-1, activated gel-filtered platelets. RANTES did not activate platelets, but substantially (by 70%) inhibited SDF-1,-induced fibrinogen binding. Similarly, RANTES abrogated the promoting effect of SDF-1, on whole blood platelet adhesion to endothelial cell monolayer under venous flow conditions. In platelet-rich plasma, RANTES moderately inhibited SDF-1,-induced platelet aggregation, while it did not affect aggregation induced by thrombin-receptor activation peptide, adenosine diphosphate, or phorbol 12-myristate 13-acetate. A synergistic inhibitory effect of RANTES and prostaglandin E1 used at subthreshold concentrations, on SDF-1,-induced aggregation and SDF-1,-induced fibrinogen binding to platelets was observed, which may suggest involvement of RANTES in a cAMP-dependent signal transduction pathway. Conclusions:,RANTES non-competitively inhibits activation of platelets by SDF-1,, and thus may play a regulatory role in platelet response to inflammation. [source]

Involvement of the ,3 E749ATSTFTN756 region in stabilizing integrin ,IIb,3 -ligand interaction

JOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 10 2003
P. E. M. H. Litjens
Summary., Platelet integrin ,IIb,3 must be activated via intracellular mechanisms before it binds soluble ligands, and it is thought to be activated at its extracellular site by surface-bound ligands. Integrin activation is associated with rearrangement of the cytoskeleton and phosphorylation of proteins that become localized in focal contacts. In these processes, the cytoplasmic tail of the ,-subunit plays a central role. We introduced peptides homologous to the E749ATSTFTN756 domain (E,N peptide) and the T755NITYRGT762 domain (T,T peptide) of ,3 in streptolysin O-permeabilized platelets and analyzed the initial interaction with soluble fibronectin, fibrinogen and PAC-1 after stimulation with thrombin. E,N peptide left the initial binding of fibronectin intact but interfered with stable receptor occupancy. E,N peptide also inhibited fibrinogen binding, thereby reducing the formation of large aggregates. Strikingly, E,N peptide did not disturb the binding of PAC-1, which is known to reflect activation of the integrin. E,N peptide also inhibited tyrosine phosphorylation of focal adhesion kinase, a response known to be dependent on ,IIb,3. T,T peptide did not affect these processes. In a model for outside-in integrin activation, E,N peptide disrupted the binding of CHO cells expressing ,IIb,3 to surface-bound ligand. Again, T,T peptide had no effect. We conclude that the E749ATSTFTN756 region of the ,3 -tail stabilizes the binding of soluble and surface-bound ligand to integrin ,IIb,3 via a mechanism that involves the phosphorylation of FAK. [source]

Glycoprotein Ib,IX-mediated activation of integrin ,IIb,3: effects of receptor clustering and von Willebrand factor adhesion

JOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 6 2003
M. Arya
Summary., The interaction between the platelet glycoprotein (GP) Ib,IX complex and von Willebrand factor (VWF) initiates both hemostasis and pathological thrombosis. This interaction is not only the first adhesive event of platelets at sites of vessel injury, but also facilitates fibrinogen binding to ,IIb,3, which subsequently results in platelet aggregation. Since it has been suggested that GP Ib,IX clustering may promote platelet activation, we investigated the effect of such clustering on both VWF,GP Ib,IX and fibrinogen,,IIb,3 bonds using optical tweezers. In our system, fusion of tandem repeats of FK506-binding protein (FKBP) to the cytoplasmic tail of the GP IX subunit of the GP Ib,IX complex allowed subsequent receptor clustering within the plasma membrane by the bivalent, cell-permeant small molecule ligand AP20187. We measured binding forces between polystyrene beads coated with either plasma-derived VWF or the VWF A1 domain and GP Ib,IX(FKBP)2, and those between fibrinogen-coated beads and ,IIb,3 expressed on Chinese hamster ovary cells. The minimal detachment force between GP Ib,IX(FKBP)2 and A1 or plasma-derived VWF doubled after AP20187 was added. The binding force between immobilized fibrinogen and ,IIb,3 was not changed by the clustering agent; however, the strength of single fibrinogen,,IIb,3 bonds increased significantly after ligation of GP Ib,IX(FKBP)2 by A1. These results demonstrate that GP Ib,IX clustering increases the overall strength of its interaction with VWF. Furthermore, signals from GP Ib,IX can activate ,IIb,3, thereby increasing the strength of its interaction with fibrinogen. [source]

Orbofiban: An orally active GPIIb/IIIa platelet receptor antagonist

MEDICINAL RESEARCH REVIEWS, Issue 3 2001
Nancy S. Nicholson
Abstract A key role has been established for platelet activation and thrombus formation in the pathogenesis of acute coronary syndromes, and restenosis after percutaneous interventions. Antiplatelet agents that have a wider spectrum of activity than aspirin, and clopidogrel would be expected to provide improved antithrombotic protection. Preclinical studies were used to predict clinical efficacy of orally active GPIIb/IIIa antagonists such as xemilofiban, sibrafiban, lefradafiban, and orbofiban. While clinical trials have shown potent and sustained platelet inhibition, outcomes of trials with these first generation GPIIb/IIIa compounds have been disappointing. The active moiety of orbofiban is a potent and specific inhibitor of fibrinogen binding to GPIIb/IIIa, leading to inhibition of platelet aggregation to a wide variety of agonists. Studies comparing inhibition of aggregation and bleeding suggest that chronic inhibition of platelet aggregation can be achieved without major bleeding side effects. Thrombus formation is prevented in canine models of thrombosis. Orbofiban is approximately 28% bioavailable with a t1/2 of 18,hr. The high bioavailability, long half-life, and potential safety suggest orbofiban would be suitable for chronic oral administration. Clinical data demonstrate that orally administered orbofiban has the desired pharmacodynamic effect of inhibiting platelet aggregation but does not demonstrate clinical benefit when examined in large-scale trials. © 2001 John Wiley & Sons, Inc. Med Res Rev, 21, No. 3, 211,226, 2001 [source]

Interaction of Plasma Deposited HMDSO-Based Coatings with Fibrinogen and Human Blood Plasma: The Correlation between Bulk Plasma, Surface Characteristics and Biomolecule Interaction

PLASMA PROCESSES AND POLYMERS, Issue 5 2010
Ram P. Gandhiraman
Abstract The success of a biomaterial depends on the nature of interaction and the progressive reaction between the biological components and the surface of the biomaterial. In order to control the interaction between the biomaterial and biological component, it is necessary to understand the factors that influence the protein adsorption and cell proliferation. Surface chemistry plays a crucial role in the success of any blood contacting biomaterial. Plasma enhanced chemical vapour deposition (PECVD) is an interesting commonly used technique for tailoring surface characteristics while retaining bulk material properties. Two different films, namely polymer-like and silica-like coatings, with varying surface characteristics have been deposited from hexamethyldisiloxane, by PECVD, on 316L stainless steel. A correlation between the bulk plasma, interfacial adhesion of the coating to 316L steel, surface characteristics and biomolecule interaction is presented in this work. The interfacial adhesion strength analysis demonstrated that silica-like coatings have higher adhesion strength to 316L stainless steel than polymer-like coatings, caused due to the formation of a strong FeOSi and CrOSi bonds. It was observed that the effect of nanoscale surface roughness (close to 6,nm) was less significant, and that the surface chemistry played a significant role in governing the fibrinogen adsorption. Highest fibrinogen adsorption on plain steel was due to the electrostatic interaction of the metal oxide layer with the protein. Hydrophobicity of the polymer-like film resulted in a higher fibrinogen binding than the silica-like films. [source]

Platelet CD62 expression and PDGFAB secretion in patients undergoing PTCA and treatment with abciximab

BRITISH JOURNAL OF CLINICAL PHARMACOLOGY, Issue 6 2001
J. Graff
Aims, To investigate a correlation of the platelet activation marker CD62 and secretion of the growth factor PDGF from platelets in coronary patients under therapy with the GPIIb/IIIa-inhibitor abciximab. Methods, Flow cytometric assessment of fibrinogen binding (GPIIb/IIIa-binding site) and CD62 expression, as well as PDGF release of human platelets (immunoassay) and platelet aggregation with 20 µm ADP and 2 µg ml,1 collagen were evaluated in nine patients with stable coronary artery disease. Patients were undergoing elective balloon angioplasty and were treated with aspirin (100 mg day,1), heparin (ACT < 220 s) and abciximab (bolus and infusion over 12 h). Blood samples were obtained before initiation of abciximab therapy (under aspirin and heparin) (I), 3 h after angioplasty under abciximab (II) and 12 h after termination of abciximab infusion (III). Results, Compared with sample I before abciximab therapy, fibrinogen binding was reduced to 37% (± 34 s.d., P < 0.05) (II) and 55% (± 40 s.d., P < 0.05) (III). Reduced fibrinogen binding also led to a significant reduction of the aggregation response to ADP (down to 37% ± 20) and collagen (down to 0%). Mean fluorescence intensity of CD62-expression was 78 units (± 20 s.d.) (I), 72 units (± 14 s.d.) (II) and 64 units (± 12 s.d., P < 0.05) (III). PDGF release from isolated, washed platelets was 99 (± 33 s.d.) ng/109 platelets at (I), 82 (± 31 s.d.) ng/109 platelets and 96 (± 30 s.d.) ng/109 platelets. Conclusions, The results indicate that despite a strong reduction of GPIIb/IIIa-binding and platelet aggregation, CD62 as a marker of platelet secretion and the secretion product PDGF were only slightly reduced under abciximab treatment. No direct correlation between CD62 expression and PDGF release could be demonstrated. [source]

High glucose levels enhance platelet activation: involvement of multiple mechanisms

BRITISH JOURNAL OF HAEMATOLOGY, Issue 3 2006
Dzana Sudic
Summary Diabetes mellitus (DM) and hyperglycaemia are associated with platelet activation. The present study was designed to investigate how high glucose levels influence platelet function. Fasting human blood was incubated with different concentrations of d -glucose (5, 15 and 30 mmol/l) and other sugars without or with in vitro stimuli. Platelet activation was monitored by whole blood flow cytometry. High glucose levels enhanced adenosine diphosphate (ADP)- and thrombin receptor-activating peptide (TRAP)-induced platelet P-selectin expression, and TRAP-induced platelet fibrinogen binding. Similar effects were seen with 30 mmol/l l -glucose, sucrose and galactose. Hyperglycaemia also increased TRAP-induced platelet-leucocyte aggregation. Protein kinase C (PKC) blockade did not counteract the enhancement of platelet P-selectin expression, but abolished the enhancement of TRAP-induced platelet fibrinogen binding by hyperglycaemia. Superoxide anion scavenging by superoxide dismutase (SOD) attenuated the hyperglycaemic enhancement of platelet P-selectin expression, but did not counteract the enhancement of TRAP-induced platelet fibrinogen binding. Hyperglycaemia did not alter platelet intracellular calcium responses to agonist stimulation. Blockade of cyclo-oxygenase (COX), phosphotidylinositol-3 (PI3) kinase, or nitric oxide synthase, or the addition of insulin did not influence the effect of hyperglycaemia. In conclusion, high glucose levels enhanced platelet reactivity to agonist stimulation through elevated osmolality. This occurred via superoxide anion production, which enhanced platelet P-selectin expression (secretion), and PKC signalling, which enhanced TRAP-induced fibrinogen binding (aggregablity). [source]

A Val193Met mutation in GPIIIa results in a GPIIb/IIIa receptor with a constitutively high affinity for a small ligand

BRITISH JOURNAL OF HAEMATOLOGY, Issue 1 2001
John Fullard
We have identified a patient designated as (GTa) with Glanzmann's Thrombasthenia (GT) diagnosed on the basis of a prolonged bleeding time and failure of the patient's platelets to aggregate. The number of glycoprotein (GP)IIb/IIIa receptors on the platelet surface was 37% of normal and those receptors displayed a defect in soluble fibrinogen binding. Nevertheless, GTa platelets showed increased adhesion to solid-phase fibrinogen and binding affinity for the RGD-mimetic 3H-SC52012, a non-peptide GPIIb/IIIa antagonist. Dithiothreitol (DTT) and ADP enhanced the affinity for [3H]-SC52012 in normal platelets, but had little effect in GTa platelets. These findings suggested that GTa platelets were locked in an altered affinity state. Genetic analysis showed that GTa was a compound heterozygote for the GPIIIa gene. One allele showed a deletion at the 3, end of exon 3 resulting in a premature stop codon. The second GPIIIa allele had a G to A transition at nucleotide 577, resulting in a Val193Met substitution. HEK 293T cells transfected with mutant GPIIb/IIIaV193M bound [3H]-SC52012 with a higher affinity than wild-type GPIIb/IIIa, and this was not increased by DTT. The mutant receptor distinguishes between platelet adhesion and aggregation, and demonstrates the phenotype that may be expected when platelet aggregation alone is inhibited. [source]

Effects of warm-up on exercise capacity, platelet activation and platelet,leucocyte aggregation in patients with claudication ,

BRITISH JOURNAL OF SURGERY (NOW INCLUDES EUROPEAN JOURNAL OF SURGERY), Issue 1 2005
S. Pasupathy
Background: The effects of exercise and warm-up were investigated in patients with claudication. Methods: This case,control crossover study involved two treadmill exercise tests, one preceded by a warm-up. Exercise continued until maximal leg pain (patients with claudication) or exhaustion (controls). Blood was taken before, and 5 and 60 min after exercise for flow cytometric analysis of platelet activation and platelet,leucocyte aggregation. Results: Both cohorts (eight patients with claudication of median age 63 years and eight healthy controls of median age 63·5 years) demonstrated improvement in exercise capacity after warm-up (13·1 per cent, P = 0·012 and 15·6 per cent, P = 0·008 respectively). Platelet activation increased after exercise in patients with claudication (fibrinogen binding: 1·11 per cent before exercise versus 2·63 per cent after exercise, P = 0·008; P-selectin: 0·68 versus 1·11 per cent, P = 0·028). Neither agonist stimulation nor warm-up altered this trend. Platelet,leucocyte (PLA) and platelet,neutrophil (PNA) aggregation were similarly increased immediately after exercise in patients with claudication (PLA: 7·6 versus 13·0 per cent, P = 0·004; PNA: 6·8 versus 10·2 per cent, P = 0·012). These remained high 60 min after exercise only in patients with claudication, but recovered to baseline levels when preceded by warm-up. Warm-up significantly desensitized PNA after stimulation with 10 µmol/l adenosine 5,-diphosphate at all time points. Conclusion: Warm-up increased the exercise capacity of patients with claudication. Exercise induced a thromboinflammatory response, with PLA and PNA persistently increased after 60 min in patients with claudication, an effect diminished after warm-up. Copyright © 2004 British Journal of Surgery Society Ltd. Published by John Wiley & Sons, Ltd. [source]

Thromboembolic events after carotid endarterectomy are not prevented by aspirin, but are due to the platelet response to adenosine 5,-diphosphate

BRITISH JOURNAL OF SURGERY (NOW INCLUDES EUROPEAN JOURNAL OF SURGERY), Issue 4 2000
P. D. Hayes
Background: Aspirin therapy fails to prevent a number of postprocedural thrombotic events, yet it still remains the standard antiplatelet regimen in most vascular surgical centres. After carotid endarterectomy (CEA), thrombosis of the endarterectomized vessel is preceded by increasing numbers of microemboli that can be detected with transcranial Doppler (TCD). The number and rate of emboli is highly predictive of thrombotic stroke. It was hypothesized that a preoperative test of platelet function might identify the mechanism(s) underlying post-CEA thrombosis. Methods: Blood was taken from 120 patients using a standardized phlebotomy technique. Platelet fibrinogen binding was measured by whole blood flow cytometry, in unstimulated samples, and in response to adenosine 5,-diphosphate (ADP) (10,5,10,7 mol l,1) and thrombin (0·02,0·16 units ml,1). Platelet aggregation was measured using ADP (4,20 × 10,7 mol l,1). The ability of aspirin to inhibit platelets was assessed by the aggregation induced by arachidonic acid. For the first 3 h after operation, the number of emboli occurring was quantified using TCD. Results: Of the 120 patients studied, 110 were monitored by TCD. These were divided into patients with more than 25 postoperative emboli (n = 22) and those with fewer than 25 emboli (n = 88). The degree of platelet inhibition induced by aspirin was not significantly different between the two groups (P = 0·89). However, platelets from the group with high rates of embolization bound 58 per cent more fibrinogen on flow cytometry in response to stimulation with a physiological dose of ADP (10,7 mol l,1) (P = 0·006). Aggregation of platelets from this group was also increased in response to ADP (35 per cent) relative to the group with few emboli (P = 0·001). ADP also induced more rapid aggregation in the patients with more than 25 emboli (P = 0·04). There was no difference in the activity of resting platelets (P = 0·4) or platelets stimulated by thrombin (P = 0·43), between the two groups of patients. Conclusion: These data suggest that it is the platelet response to ADP which is important in arterial thrombotic complications rather than products of the cyclo-oxygenase pathway. This observation could have significant therapeutic implications for other vascular or interventional procedures in which the endothelium is disrupted. © 2000 British Journal of Surgery Society Ltd [source]