Association of fibrinogen-bound glycoprotein IIb-IIIa complexes on the activated platelet surface.
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Animals↗
Biomedical subjects
A T Nurden
Publications and source records attributed to A T Nurden.
Visualization of activation-dependent epitopes on glycoprotein IIb-IIIa complexes of platelets stimulated by thrombin: immunogold staining of ultrathin sections.
An immunoglobulin M monoclonal antibody (IgM MAb; AP-6) recognizing the sequence 211-221 of glycoprotein (GP) IIIa enabled a study of the distribution of this epitope on unstimulated or thrombin-activated platelets. Flow cytometry was used to evaluate the expression of this epitope on platelets and immunogold staining on ultrathin sections to analyze its distribution within the cell. There was little or no binding of AP-6 to unstimulated platelets, but immunogold staining showed labeling associated with the membranes of alpha-granules. The binding of AP-6 to thrombin-stimulated platelets was compared with that of anti-RIBS MAbs and antifibrinogen polyclonal antibodies. An increased expression of the AP6 epitope was observed on membranes of the surface-connected canalicular system and at the periphery of the cell as early as 10 to 15 seconds after platelet activation by thrombin. At the same time, binding of anti-RIBS MAbs confirmed that at least part of the endogenous fibrinogen had left the alpha-granules and was bound to platelet membranes. Staining with polyclonal antifibrinogen antibody also revealed fibrinogen in vesicles resulting from granule fusion. Rapidly, the pool of internal membranes with bound fibrinogen became exposed to the outside of the platelet, a process involving the unfolding of membranes and pseudopod formation. Our results provide evidence that activation of GP IIb-IIIa and binding of fibrinogen to platelet membranes can occur before their expression at the platelet surface. They also suggest the presence of an alpha-granule pool of GP IIb-IIIa linked to fibrinogen in unstimulated platelets.
Antigens, Human Platelet↗
Polymorphisms of platelet receptors as risk factors in coronary thrombosis.
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Animals↗
ADP-induced P-selectin expression on platelets as a predictor of successful thrombolysis.
Unlike coronary thrombolysis, the role of platelet activity in the outcome of local thrombolytic therapy for peripheral ischaemia is not well understood. In the present study ten patients undergoing local pulse spray thrombolysis (PST) with recombinant tissue-type plasminogen activator (rt-PA), six patients undergoing conventional infusion thrombolysis (CT) with rt-PA and another six patients undergoing arteriography with iopamidol were studied. Venous blood samples obtained before and after the procedure were analysed using a flow cytometric technique for detection of platelet activation after labelling platelets with VH10, a monoclonal antibody against P-selectin. In the present study no significant differences were observed in P-selectin expression before and after any of the procedures, except that P-selectin expression following ADP stimulation was reduced in patients who had received conventional thrombolysis. Unexpectedly, we observed relatively greater P-selectin expression, particularly after ADP stimulation, both before and following thrombolysis in ten patients in whom thrombolysis was successful compared with six patients in whom thrombolysis was unsuccessful. ADP-induced P-selectin expression on platelets may therefore be a useful predictor of outcome of peripheral intra-arterial thrombolysis.
Adenosine Diphosphate↗
New thoughts on strategies for modulating platelet function through the inhibition of surface receptors.
Platelets play a key role in arterial thrombosis. Inhibition of platelet function forms an essential part of anti-thrombotic therapy. Although aspirin is a cost-effective drug which offers considerable scope in the prevention of arterial thrombosis, it only inhibits part of the platelet activation process. Much recent progress has concerned the inhibition of surface receptors of platelets. Ticlopidine and clopidogrel specifically interfere with the ADP-induced activation pathway. Inhibitors of GP IIb-IIIa complexes, including c7E3, block the final step of the platelet aggregation process as used by all physiologic agonists and are proving powerful therapeutic agents. This review looks at these and future advances in the construction of therapeutic strategies aimed at combatting arterial thrombosis.
Animals↗
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 Ca2+ 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.
Adenosine Diphosphate↗
[A study of platelet activation following coronary angioplasty. Effect on acute occlusion and restenosis].
The development of monoclonal anti-platelet antibodies to activation-dependent epitopes has made possible the study of the appearance of activated platelets in the blood by cytometry. This was undertaken in 35 patients undergoing coronary angioplasty. Blood was sampled through the femoral venous catheter introducer before the procedure, at 3 minutes and 3, 24 and 48 hours after angioplasty. Systematic coronary angiography was performed at about 6 months and vessel diameters were quantified by a digitised technique. In general, platelet activation was not observed before angioplasty or in the first hours following the procedure. On the other hand, a significant number of activated platelets was observed secondarily : 7 +/- 7.3% at the 24th hour and 6.8 +/- 5.9% at the 48th hour. There was a significant correlation between the level of platelet activation before angioplasty and that at the 24th hour (r = 0.52, p = 0.01). There was a tendency to more activated circulating platelets before and 24 hours after angioplasty in patients with acute occlusion. The correlation coefficient between the level of activated platelets 24 hours after angioplasty and progression of stenosis at 6 months was not statistically significant (r = 0.29). Therefore, the authors demonstrated platelet activation, which was sometimes considerable, inconstantly in circulating venous blood of patients with angina 24 hours after coronary angioplasty despite treatment with aspirin. Activated platelets may play a role in constituting acute occlusion by thrombosis but their detection was not predictive of restenosis.
Adult↗
PAICA: a method for characterizing platelet-associated antibodies--its application to the study of idiopathic thrombocytopenic purpura and to the detection of platelet-bound c7E3.
In idiopathic thrombocytopenic purpura (ITP), autoantibodies reacting with antigens on the platelet membrane bring about accelerated platelet destruction. We now report PAICA ("Platelet-Associated IgG Characterization Assay"), a method for detecting autoantibodies bound to specific membrane glycoproteins in total platelet lysates. This monoclonal antibody (MAb) capture assay takes into account the fact that antibodies on circulating platelets may be translocated to internal pools as well as being on the surface. A total of twenty ITP patients were examined by PAICA, and the results compared with those obtained by measuring (i) serum antibodies bound to paraformaldehyde-fixed control platelets by ELISA, (ii) IgG bound to the surface of the patient's own platelets by flow cytometry (PSIgG), (iii) total platelet-associated IgG (PAIgG) by ELISA and (iv) serum antibodies reacting with control platelets by MAIPA ("Monoclonal Antibody-specific Immobilization of Platelet Antigens"). Of twelve patients with elevated PAIgG, nine had increased PSIgG yet eleven reacted positively in PAICA. Of these, eight possessed antibodies directed against GP IIb-IIIa, two against GP Ib-IX and one patient possessed antibodies directed against GP IIb-IIIa and GP Ia-IIa respectively. Only seven of the patients possessed serum antibodies detectable by MAIPA. PAICA was also able to detect platelet-associated c7E3 (the chimeric form of Fab fragments of the MAb 7E3) following its infusion during antithrombotic therapy, when it proved more sensitive over a seven-day period than a MAIPA assay adapted for assessing surface-bound antibody. We propose that PAICA provides added sensitivity to the detection of platelet-associated antibodies in immune thrombocytopenias or following therapy with humanized MAbs.
Adult↗
Calcium involvement in aminophospholipid exposure and microparticle formation during platelet activation: a study using Ca2+-ATPase inhibitors.
The development of procoagulant activity and microparticle formation during platelet activation is known to depend on an increase in cytosolic Ca2+ levels. We have studied the mechanisms leading to these events using FITC-labeled recombinant annexin V, a protein which binds with a high affinity to aminophospholipids, in flow cytometry. In particular, we show that the Ca(2+)-ATPase inhibitors thapsigargin and cyclopiazonic acid are as potent inducers of aminophospholipid exposure and microparticle formation as the ionophore A23187. In contrast, 2,5-di-tert-butyl-1, 4-benzohydroquinone induced negligible microparticle formation, although platelets abundantly bound annexin V-FITC. That platelet activation had occurred was confirmed by binding studies with VH10, a monoclonal antibody specific for the alpha-granule membrane glycoprotein GMP-140, and by prothrombinase activity measurements. These results demonstrate that microvesiculation is not an automatic response to aminophospholipid exposure. The Ca(2+)-ATPase inhibitors induced different intracellular Ca2+ levels as measured using fluo-3 as a calcium dye. These were 10 +/- 4 microM (n = 11) for thapsigargin (3 microM), 19.6 +/- 2.2 microM (n = 8) for cyclopiazonic acid (100 microM), and 0.619 +/- 0.137 microM (n = 8) for 2,5-di-tert-butyl-1,4-benzohydroquinone (100 microM). Calpain activity, as assessed in platelets by analyzing the degradation of cytoskeletal proteins, was only observed with agents that stimulated microparticle formation. Phospholipid transbilayer movement was studied by measuring annexin V binding during platelet activation. Results showed that aminophospholipid exposure induced by ionophore A23187 (t1/2 = 133 +/- 14 s) was more rapid than that induced by TG (t1/2 = 280 +/- 30 s), although the rate-limiting step in the assay was the binding of annexin V to activated platelets (t1/2 = 70-80 s). Interestingly, the presence of annexin V itself during the activation inhibited microparticle formation, although degradation of platelet proteins by calpain continued to occur. Our results clearly show (i) that aminophospholipid exposure and platelet microvesiculation are independent but closely regulated events and (ii) that while both processes are associated with an increase in intracellular Ca2+, microvesiculation additionally requires Ca(2+)-induced calpain activation and a fusion process inhibited by annexin V.
Annexin A5↗
Flow cytometry reveals activated GP IIb-IIIa complexes on platelets from patients undergoing thrombolytic therapy after acute myocardial infarction.
We report the detection of activated GP IIb-IIIa complexes on platelets of patients undergoing thrombolytic therapy after acute myocardial infarction. Protocols were established for the monoclonal antibodies (mAbs): VH10, anti-P-selectin, a marker of platelet secretion; 9F9 and F26, two anti-RIBS (receptor-induced binding sites) mAbs specific for fibrinogen (Fg) bound to the GP IIb-IIIa receptor. Of ten patients studied: two were treated with streptokinase, four with APSAC (anisoylated plasminogen-streptokinase activator complex), and three with rt-PA. Platelets were tested on at least five occasions in the week following therapy. The percentage of platelets positive with 9F9 was often high, and reached a maximum within three days. By this time, plasma Fg levels, which fell during fibrinolysis, had begun to return to normal. Levels of activated platelets had fallen to baseline after 7 days. PAC-1, a mAb which binds directly to the activated GP IIb-IIIa complex, confirmed the results with 9F9, but F26 was a less sensitive probe. Binding of the anti-P-selectin mAb (VH10) was low, showing that little secretion had occurred. A concentration-dependent inhibition of 9F9 binding by RGDW peptide, a competitive inhibitor for Fg on GP IIb-IIIa, confirmed that Fg (or epitope-containing degradation products) were being located by the antibody. The activation of GP IIb-IIIa occurred despite the patients receiving aspirin and heparin. Thus platelets of some fibrinolytic patients have an increased tendency for surface activation within the first 72 h after treatment, a finding which would be compatible with an increased thrombotic tendency.
Adult↗
A human monoclonal antibody obtained from EBV-transformed B cells with specificity for myosin.
We describe the preparation of a stable human lymphoblastoid cell line obtained during ex vivo studies in which peripheral blood lymphocytes of a Glanzmann's thrombasthenia patient were transformed with Epstein-Barr virus. Somatic hybrids secreted an IgM monoclonal antibody (B7) that reacted with the myosin heavy chain of human platelets by immunoblotting. Flow cytometry showed that B7 barely recognized unstimulated intact platelets, but bound abundantly after permeabilization of fixed cells with Triton X-100. The reactivity of the antibody on thin sections of human myocardium and aorta was studied by immunohistochemistry. B7 specifically stained myosin of myocytes, but there was no labelling of aortic smooth muscle cells. The epitope was conserved in cardiac or skeletal myosin prepared from pig or rabbit. Measurement of the dissociation constant in a competitive ELISA showed that B7 bound with high affinity (10(-8) M). Purified Fab fragments retained their ability to bind to myosin, suggesting that B7 may be useful in the imaging of myocardial necrosis after myocardial infarction, myocarditis, cardiac drug toxicosis or graft rejection. This work also shows that EBV transformation of B cells may uncover naturally occurring autoantibodies which under normal circumstances are inhibited by the immune surveillance system.
Adult↗
Polymorphisms of human platelet membrane glycoproteins: structure and clinical significance.
The haemostatic response of platelets of any one individual will be influenced by the genetic profile of the total population of receptors expressed on the platelet surface. Among the parameters to consider will be (i) the density of each receptor, (ii) the rate at which genes are transcribed and receptors produced and (iii) the presence or not of structural polymorphisms. Already, consideration of the known polymorphisms on GP IIb and GP IIIa raises most interesting questions on the structure/function relationship for this receptor. For example, there is often no obvious pattern as to which polymorphisms will influence platelet function and which will risk giving rise to a diallelic alloantigen system. Thus, mutation at Arg214 results in a loss in the ability of the complex to support platelet aggregation, whereas a mutation at Arg143 has resulted in the production of an immune response (see above). As I have pointed out earlier, examples from inherited platelet disorders show that even a single mutated allele can influence receptor function. Others have shown that polymorphisms of plasma proteins (see 52) or membrane glycoproteins such as E-selectin of endothelial cells (see 53) can give rise to risk factors for thrombosis and/or atherosclerosis. It would be interesting to know whether polymorphisms of platelet glycoprotein receptors (and those shared with other vascular cells) also represent risk factors in cardiovascular disease.
Amino Acid Sequence↗
Two human antibodies reacting with different epitopes on integrin beta 3 of platelets and endothelial cells.
Glanzmann's thrombasthenia is an inherited bleeding disorder that results from a deficit of glycoprotein (GP) IIb-IIIa complexes in platelets. Patient (EBV) is an adult male with GP IIb-IIIa levels < 5% of normal values and a history of blood transfusions. Western-blot analysis revealed a strong IgG antibody to GP IIIa in his plasma. The determinants were localized to the minimum-sized fragment of GP IIIa (50 kDa) retained on chymotrypsin-treated platelets and were lost on reduction of disulphides. A female patient (AF), previously described by us [Jallu, V., Pico, M., Chevaleyre, J., Vezon, G., Kunicki, T.J. & Nurden, A.T. (1992) Hum. Antibod. Hybridomas 3, 93-106] developed her anti-GP-IIIa antibody during pregnancy. This antibody was poorly reactive with the 50-kDa proteolytic fragment, yet bound to 115-kDa and 60-kDa hydrolytic products of GP IIIa. Antibodies from both patients recognized the GP-IIIa-like protein of endothelial cells, thus confirming that they were directed against the integrin beta 3-subunit. The (EBV) antibody reacted strongly with GP IIb-IIIa in an antigen capture assay performed with each of a panel of four murine monoclonal antibodies (mAbs) recognizing different epitopes on GP IIb-IIIa. In contrast, that from (AF) was specifically inhibited by AP-3, a murine mAb whose epitope is thought to be localized between amino acids 324-422 of GP IIIa. The residual GP IIb and GP IIIa contents of platelets from each patient were assessed in Western blotting using chemiluminescence detection. SZ-22, a murine mAb to the GP IIb heavy chain (140 kDa), located small amounts of a 130-kDa protein in (EBV) platelets. The anti-GP IIIa mAbs XII F9, P 37 and P 97 revealed trace amounts of protein with a relative mobility identical to that of GP IIIa in both (AF) and (EBV) platelets. This residual GP IIIa represented less than 0.5% of the amount in normal platelets. When, for each patient, plasma was tested in Western blotting against their own platelets, autoantibody activity to the residual GP IIIa was detected in both cases. Thus, patients (AF) and (EBV) have developed anti-GP-IIIa antibodies with restricted and distinct epitopes but recognizing self antigens.
Antigen-Antibody Reactions↗
Markers of platelet activation in coronary heart disease patients.
We have applied flow cytometry to the detection of activated platelets in patients with coronary heart disease. Paraformaldehyde-fixed platelets were incubated with one of the following monoclonal antibodies (MAbs): Bx-1 (anti-GP Ib), AP-2 (anti-GP IIb-IIIa complex), VH10 (anti-GMP-140, a glycoprotein of the alpha-granule membrane), or PAC-1 (directed against an activation-dependent determinant on GP IIb-IIIa complexes). Bound antibody was quantitated after the addition of FITC-conjugated anti-immunoglobulin. This report highlights studies on 16 unstable angina patients undergoing transluminal angioplasty. Blood samples were taken at different periods before and after the angioplasty. Levels of activated platelets were variable, remaining in the 2-4% range of control donors for some, but increasing to 10-30% post-angioplasty for others (despite all patients receiving heparin and aspirin). Maximum numbers of activated platelets were detected at 24 or 48 h. Nonetheless, the amount of antibody bound to individual platelets rarely reached the levels seen when control platelets were stimulated with thrombin in vitro. Results with VH10 and PAC-1 often, but not always, correlated suggesting different pathways of platelet activation.
Angina, Unstable↗
The ex vivo production of human monoclonal antibodies to glycoprotein IIb-IIIa complexes of blood platelets.
The integrin alpha IIb beta 3 (GPIIb-IIIa complex) of blood platelets mediates platelet aggregation by binding adhesive proteins which form bridges between activated cells. This same process is implicated in arterial thrombosis. The goal of our research is to take B-lymphocytes from patients possessing inhibitory antibodies to GPIIb-IIIa and develop technology permitting their production ex vivo. Starting point is the peripheral blood from two patients with Glanzmann's thrombasthenia, an inherited disorder in which platelets lack these complexes, and where high titre antibodies to GPIIb-IIIa have formed following contact with normal platelets after transfusion and/or pregnancy. We describe a strategy of in vitro stimulation to overcome the following constraints: (i) peripheral blood contains a low concentration of antigen-reactive specific B-cells, and (ii) the circulating B-cells are arrested in a phase in which additional stimuli are required to induce antigen-specific clonal activation. Optimal conditions involve the use of a combination of growth factors, polyclonal activators and soluble GPIIb-IIIa prior to the fusion of activated B-cells with either (a) the murine myeloma cell line X63 Ag 8,653 or (b) the heteromyeloma cell line SPM4-0. In this way, we have obtained several cell lines secreting antibodies specific for the GPIIb-IIIa complex. Our next aim is to rescue the relevant human immunoglobulin genes from these hybridoma cells.
Aged↗
Glycoprotein Ia-IIa (VLA-2) and glycoprotein Ib-IX complexes are processed independently during thrombin-induced platelet activation.
We have previously shown that when human platelets are stimulated by thrombin, glycoprotein Ib-IX (GP Ib-IX) complexes are cleared to the surface-connected canalicular system (Blood 1990;76:1503). The question arose as to whether GP Ia-IIa complexes (VLA-2), another adhesion receptor thought to be linked to the membrane cytoskeleton, behaved similarly. Monoclonal antibodies to GP Ia-IIa were used in either (1) immunofluorescence procedures and flow cytometry or (2) immunogold staining and electron microscopy. In flow cytometry, VLA-2 was shown to have a low but variable expression in the platelets of different donors. Immunogold staining showed that the complexes were regularly distributed over the platelet surface. This was best seen after staining of paraformaldehyde-fixed whole mounts, where bound antibodies were often visualized in small clusters. The surface expression of VLA-2 receptors increased somewhat after thrombin stimulation, the receptors coming from a small intracellular pool revealed by flow cytometric analysis of Triton X-100-permeabilized cells. Immunogold staining showed that after activation the receptors were equally as present on pseudopods as on the peripheral zone of the platelet. Down-regulation, as seen with GP Ib-IX complexes, was not observed. Our results therefore show that two-way trafficking of adhesion receptors can occur during platelet activation. This would imply that GP Ib-IX and VLA-2 are attached to different elements within the membrane cytoskeleton.
Blood Platelets↗
Annexin V as a probe of aminophospholipid exposure and platelet membrane vesiculation: a flow cytometry study showing a role for free sulfhydryl groups.
Annexin V, a protein with a high affinity and a strict specificity for aminophospholipids at physiologic calcium concentrations, was used to probe platelet activation and the development of procoagulant activity. Platelet secretion was studied in parallel using VH10, a murine monoclonal antibody specific for GMP-140, an alpha-granule membrane glycoprotein. Both proteins were labeled with fluorescein isothiocyanate and platelet activation was assessed by flow cytometry. Microparticles, which are shed from the platelet surface and also support procoagulant activity, were distinguished from platelets according to their associated light scattering signal. The relative ability of different inducers to trigger exposure of the procoagulant surface and microparticle formation was: ionophore A23187 > thrombin plus collagen > collagen > thrombin. The density of aminophospholipid on microparticles was higher than on remnant platelets. Platelet activation by these agonists was accompanied by GMP-140 exposure, both on platelets and microparticles. Here, thrombin was the most efficient agonist. The mechanisms responsible for the above processes were investigated using E-64-d, a specific membrane-permeable inhibitor of Ca(2+)-activated protease (calpain); tetracaine, an activator of calpain; and N-ethylmaleimide and diamide, two sulfhydryl-reactive agents. These agents were added to platelets alone or before stimulation by agonists. Calpain activity was assessed by the hydrolysis of cytoskeletal proteins as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Results showed that calpain activity is not essential for aminophospholipid translocation or for secretion. In contrast, although sulfhydryl-reactive agents alone can trigger procoagulant activity, they inhibit microvesicle formation and platelet secretion induced by the above agonists, suggesting that different mechanisms account for these phenomena. The use of annexin V in flow cytometry is a rapid method to assess procoagulant activity in platelets and the loss of phospholipid asymmetry in cell membranes.
Annexin A5↗
A review of the role of platelet membrane glycoproteins in the platelet-vessel wall interaction.
This review concerns our understanding of the molecular basis of platelet function in haemostasis. In particular, we indicate how research into platelet membrane glycoprotein (GP) receptors is yielding vital information on the mechanisms of platelet adhesion and aggregation. These receptors, nearly always complexes of two or more subunits, are now known to belong to distinct gene families, some of which are unique to platelets while others are widely distributed in mammalian tissues. GP Ib-IX complexes are responsible for the high-shear-rate-dependent adhesion of platelets to von Willebrand factor (vWF) exposed within the subendothelium of damaged vessels. Other adhesion receptors include members of the VLA subclass of the integrin family: VLA-2, VLA-5 and VLA-6, which mediate platelet adhesion to collagen, fibronectin and laminin, respectively. Platelet aggregation is initiated by distinct populations of receptors specific for each physiological agonist. Many of these receptors, including the highly important and recently cloned thrombin receptor, have seven transmembrane domains and possess highly selective agonist-binding determinants. Finally, we highlight platelet aggregation and the role of GP IIb-IIIa complexes which, following platelet activation, bind fibrinogen and other adhesive proteins. The latter, through being polyvalent for GP IIb-IIIa, then form the bridges linking adjoining platelets. The 'ligand-binding pocket' of GP IIb-IIIa contains at least three sequences essential for ligand binding; fibrinogen also binds to the activated complex through identified domains, one of which, the Arg-Gly-Asp (RGD) sequence, is also found in vWF and the other adhesive proteins able to support platelet aggregation. Finally, we further describe how these, and other glycoproteins in both surface and internal membrane systems, constitute a complex receptor network capable of translocation and reorganization after platelet activation. In cardiovascular disease, platelets accumulate within arteries whose luminal surface has been modified through atherosclerosis. Recent molecular advances are yielding exciting opportunities for the development of new, and more powerful, drugs acting as specific inhibitors of thrombotic processes.
Amino Acid Sequence↗