Effect of heparin removal filter.
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Filtration↗
Biomedical subjects
L K Jennings
Publications and source records attributed to L K Jennings.
A flow cytometric assay using mepacrine for study of uptake and release of platelet dense granule contents.
Diagnosis of platelet dense granule storage pool disease and release defects at present requires a combination of studies including lumiaggregometry, conventional platelet aggregation, radioactive serotonin uptake and release, and electron microscopy. Flow cytometric methods have been developed to study platelet activation, aggregation, and alpha-granule protein release. Here, we have investigated the use of flow cytometry for analysis of platelet dense granule content uptake and release using mepacrine as a fluorescent marker. Mepacrine (quinacrine) is rapidly taken up and localized in dense granules of platelets. For the assay, as little as 20 microliters of blood from a fingerstick collected without anticoagulant or venous blood collected in 3.8% sodium citrate were diluted 1:40 with 2 ml Hanks balanced salt solution (BSS). 300 microliters of this cell suspension were incubated with mepacrine alone, or simultaneously with a mouse monoclonal antibody to human platelet glycoprotein IIb (Tab), used as a platelet-specific marker. The bound monoclonal antibody was then indirectly labelled with the fluorochrome, RED670. 100 microliters of the sample were further diluted with Hanks BSS for one- or two-colour flow cytometric analysis. To verify that mepacrine uptake was related to platelet dense granule content, platelets of beige mice, a strain with dense granule deficiency, were examined. Their mepacrine uptake was substantially decreased compared to that of normal mice. Decreased mepacrine uptake also was demonstrated in platelets of a patient with Hermansky-Pudlak syndrome in which a deficiency of platelet dense granules is characteristic. In both human and mouse platelets, mepacrine uptake was proportional to platelet size. Thrombin induced mepacrine release in a dose-dependent manner from 0.003 to 0.4 U/ml. Therefore both platelet uptake and release of mepacrine can be readily detected by flow cytometry. Flow cytometry provides an attractive alternative to aggregation and radioactive serotonin as methods to study defects in platelet dense granule function.
Animals↗
Interspecies comparison of platelet aggregation, LIBS expression and clot retraction: observed differences in GPIIb-IIIa functional activity.
We examined interspecies differences in the function of the platelet fibrinogen receptor, GPIIb-IIIa, by comparing platelet aggregation responses to adenosine diphosphate (ADP) added alone or in combination with a GPIIIa specific monoclonal antibody (mAb), D3. D3 can activate the GPIIb-IIIa receptor in the absence of platelet activation, and it preferentially binds to a region on the GPIIIa subunit after the GPIIb-IIIa complex is occupied by ligand. Using human, monkey, dog, rabbit and pig platelets, we examined whether all species' platelets bound the D3 mAb similarly, and if the binding of Arg-Gly-Asp-Ser (RGDS) peptides induced the exposure of the anti-LIBS (D3) epitope as previously described for human platelets. We also evaluated how blocking of this neoantigenic region by the D3 mAb affected clot retraction, a process that requires linkage of GPIIb-IIIa with fibrin(ogen) and the platelet cytoskeleton. We found that all species tested bound the D3 mAb. Only in human and monkey platelets did D3 cause aggregation as well as inhibit clot retraction. However, in all species tested, except for pig, D3 prevented disaggregation of platelets typically observed when platelets are treated with low dose ADP. With the exception of pig platelets, there was increased D3 binding to platelets in the presence of RGDS peptides. We propose that this region of GPIIIa is important in the conformational changes that GPIIb-IIIa undergoes during the binding of ligand in most species tested. Our studies suggest 1) there are measurable inter-species differences in GPIIb-IIIa mediated platelet aggregation and clot retraction, 2) LIBS expression due to receptor occupancy is a common but not all-inclusive response and 3) interspecies comparisons may be useful in understanding structural and functional aspects of platelet GPIIb-IIIa.
Adenosine Diphosphate↗
Activation of the fibrinogen binding site on platelets isolated from a patient with the Strasbourg I variant of Glanzmann's thrombasthenia.
One proposed ligand binding site on platelet integrin alpha IIb beta 3 is the region of the beta 3 subunit encompassing amino acids 211-221. However, we recently showed that synthetic peptides corresponding to amino acids 211-221 inhibit fibrinogen binding to alpha IIb beta 3 by binding to alpha IIb beta 3 and not to fibrinogen. In this study, we show that AP6, a monoclonal antibody (MoAb) directed against amino acids 214-221 of beta 3, bound to immobilized active alpha IIb beta 3 but did not inhibit fibrinogen binding to the complex. We then determined whether nonfunctional alpha IIb beta 3 on platelets with a beta 3 Arg-214-->Trp mutation (Strasbourg I variant of Glanzmann's thrombasthenia or GTV) could be induced to aggregate after treatment with dithiothreitol (DTT). DTT has been shown to expose the fibrinogen receptor on normal platelets. DTT treatment of GTV platelets did result in the formation of the fibrinogen binding site as indicated by the binding of pI-55, an MoAb that only binds to the activated form of alpha IIb beta 3. Furthermore, DTT-treated GTV platelets aggregated in the presence of fibrinogen and divalent cations. This aggregation was inhibited by EDTA, RGDS, and the selective alpha IIb beta 3 antagonist, Ro 43-5054. These data show that Arg-214 of beta 3 is not required for fibrinogen binding or for platelet aggregation. However, this amino acid appears to be critical for the formation and for the maintenance of the correct tertiary structure of the fibrinogen binding site on alpha IIb beta 3.
Amino Acid Sequence↗
Platelet p24/CD9, a member of the tetraspanin family of proteins.
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Animals↗
A GP IIIa ligand-induced binding site antibody detects multiple GP IIb-IIIa conformations, and its binding is modulated by various ligands.
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Antibodies, Monoclonal↗
Cocaine-induced platelet defects.
BACKGROUND AND PURPOSE: Numerous studies have demonstrated an association between acute cardiac events, cerebrovascular accidents, and cocaine use. The underlying mechanisms leading to these complications have not been well defined. Using various in vitro model systems, it has been reported that cocaine, up to or greater than an order of magnitude of the lethal dose, causes either inhibitory or proaggregatory effects on platelet function. METHODS: To address these reported discrepancies, we examined the effect of cocaine and its carrier on the activation and aggregation of human platelets in vitro. RESULTS: We found that cocaine inhibited platelet aggregation when platelets were challenged with ADP, collagen, or arachidonic acid. This inhibition was due to a direct effect on fibrinogen binding to the activated platelet. Cocaine also caused the dissociation of preformed platelet aggregates. At these same concentrations, cocaine did not inhibit agonist-mediated increases in cytosolic calcium or inhibit platelet shape change, suggesting that its effect on platelet aggregation was a selective process and not due to a total destruction of platelet function. Interestingly, the organization of the cytoskeleton of activated platelets, a secondary event critical to cell receptor clustering and clot retraction, was disrupted by cocaine treatment. In addition, alterations in platelet protein electrophoretic patterns were observed on preincubation of platelets with cocaine. CONCLUSIONS: We conclude that cocaine may have a direct inhibitory effect on the ability of platelets to participate in thrombus formation. The contribution of this effect as an underlying mechanism of sudden death in cocaine abusers is unknown.
Adenosine Diphosphate↗
Reversible conformational changes induced in glycoprotein IIb-IIIa by a potent and selective peptidomimetic inhibitor.
Platelet glycoprotein (GP) IIb-IIIa inhibitors may become useful antithrombotic agents. Ro 43-5054 is a low molecular weight, noncyclic, peptidomimetic inhibitor that is three orders of magnitude more potent than RGDS in inhibiting fibrinogen binding to purified GPIIb-IIIa and in preventing platelet aggregation. Comparisons of RGDS and Ro 43-5054 in cell adhesion assays showed that, in contrast to RGDS, Ro 43-5054 was highly selective GPIIb-IIIa inhibitor. Effects of RGDV and Ro 43-5054 on the conformation and activation state of GPIIb-IIIa were also examined. RGDV and Ro 43-5054 induced conformational changes in purified inactive GPIIb-IIIa as determined by binding of the monoclonal antibody D3GP3 (D3). These conformational alterations were not reversed after inhibitor removal, as indicated by the continued exposure of the D3 epitope and a newly acquired ability to bind fibrinogen. Similarly, RGDV and Ro 43-5054 induced conformational changes in GPIIb-IIIa on the intact platelet. However, after removal of the inhibitors, exposure of the D3 epitope was fully reversed and the platelets did not aggregate in the absence of agonist. Thus, while RGD(X) peptides and Ro 43-5054 transformed purified inactive GPIIb-IIIa into an irreversibly activated conformer, the effects of these inhibitors were reversible on the intact platelet. This suggests that factors present in the platelet membrane or cytoplasm may regulate in part the ability of the complex to shift between active and inactive conformers.
Antibodies, Monoclonal↗
The effect of residual heparin on the interpretation of heparin-induced platelet aggregation in the diagnosis of heparin-associated thrombocytopenia.
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Heparin↗
Assessment of lumiaggregometry for research and clinical laboratories.
Platelet aggregometry is often used to help diagnose storage pool disease (SPD-reduced amounts of granule nucleotides) and release defects (abnormal release of granule nucleotides). The general assumption that normal aggregation patterns are sufficient to rule out the diagnosis of one of these disorders has been invalidated by the recent publication of two papers describing patients with clinical bleeding, prolonged bleeding times and normal aggregation patterns in spite of defective release. The lumiaggregometer provides a tool for measuring platelet release and aggregation simultaneously. This paper presents a standardized, reproducible method for the use of the lumiaggregometer based on a "standard curve". Data obtained during the development of the procedure are presented including normal ranges of release at different concentrations of agonists, release measured in intrinsic disorders as well as in patients on aspirin, and values for release relative to varying platelet counts. A monoclonal antibody (anti-p24/CD9; MAb7) which activates platelets similarly to thrombin and may be a useful reagent for distinguishing SPD and release defects is also introduced.
Adenosine Triphosphate↗
Further characterization of the loop structure of platelet glycoprotein IIIa: partial mapping of functionally significant glycoprotein IIIa epitopes.
Glycoprotein (GP) IIb-IIIa serves as the platelet fibrinogen receptor. Studies of the tertiary structure of GPIIIa have shown that the protein has a large loop structure of at least 325 amino acids in length. To further characterize this loop structure, intact platelets were digested with alpha-chymotrypsin. Digestion products were examined using the anti-GPIIIa monoclonal antibodies (MoAbs) AP3, D3GP3, and C5GP3, as well as the human alloantibody, anti-PLA1. AP3 recognized GPIIIa digestion products of 109, 95, and 68 Kd. D3GP3 and C5GP3 recognized an additional band of 51 Kd. Time course digestions demonstrated that the 51-Kd fragment was generated by proteolysis of the 68-Kd peptide. Sequence analysis of the reduced 51-Kd peptide showed that this fragment began at amino acid 422. The nonreduced 51-Kd peptide was reactive with antibodies directed against the first 13 amino acids of GPIIIa, demonstrating the presence of a covalently attached N-terminal peptide. These data suggest that: (1) the minimum length of the loop structure is at least 384 amino acids; (2) the AP3 epitope is formed at least in part by a determinant contained within residues 348 to 421; and (3) the D3GP3 and C5GP3 epitopes are contained within amino acids 422 to 692 of GPIIIa, a region that may be flexible and involved in conformational changes that occur after ligand binding.
Amino Acid Sequence↗
Activation-independent exposure of the GPIIb-IIIa fibrinogen receptor.
Following platelet activation, surface receptors for fibrinogen are exposed. On the activated platelet, glycoprotein IIb-IIIa (GPIIb-IIIa) serves as the receptor for fibrinogen. However, the molecular mechanisms which regulate GPIIb-IIIa fibrinogen receptor exposure are unknown. D3GP3 is an IgG1, kappa monoclonal antibody which is specific for glycoprotein IIIa (GPIIIa). The binding of D3GP3 to GPIIIa, in intact GPIIb-IIIa complexes, induces fibrinogen binding and platelet aggregation. To determine if D3GP3 binding to GPIIIa directly caused the exposure of fibrinogen receptors or, secondarily, due to stimulus response coupling, platelet activation parameters were monitored following the addition of D3GP3 to platelets suspensions. D3GP3 binding did not induce detectable Ca++ mobilization, protein phosphorylation or activation of the pertussis toxin sensitive G-protein subunit alpha-41. Further, D3GP3-induced aggregation was not blocked by PGE1, aspirin, apyrase or the combination of all three reagents. Scanning electron microscopy of D3GP3-induced aggregates demonstrated that the aggregates were composed of discoid platelets. These data suggest that the binding of D3GP3 to GPIIIa induced a conformational change in GPIIb-IIIa such that the fibrinogen receptor was exposed in an activation-independent fashion. This provides evidence that conformational changes in the GPIIb-IIIa complex can result in the transformation of the complex to the high affinity binding competent state.
Antibodies, Monoclonal↗
The effect of glycoprotein IIb-IIIa receptor occupancy on the cytoskeleton of resting and activated platelets.
The platelet integrin, glycoprotein IIb-IIIa (GPIIb-IIIa), serves as the receptor for fibrinogen. This study examined what effect GPIIb-IIIa receptor occupancy had on the cytoskeleton of resting and activated platelets. Triton X-100-insoluble residues (cytoskeletons) were isolated from resting washed platelets incubated with either 500 microM RGDS or 500 microM RGES and examined for protein content. RGDS did not increase the amount of GPIIb-IIIa associated with the cytoskeletal residues which sedimented at either 15,800 x g or 100,000 x g. To determine the effect of receptor occupancy on the formation of the activated platelet cytoskeleton, stirred and nonstirred RGDS-treated platelets in plasma were activated with ADP. Triton X-100-insoluble residues were isolated and examined for both protein content and retention of GPIIb-IIIa. Further, morphological studies were performed on the RGDS-ADP-stimulated platelets. The results of this study suggest that 1) RGDS peptide receptor occupancy does not lead to GPIIb-IIIa linkage to the cytoskeleton, 2) ADP-stimulated platelet shape change, polymerization of actin, and association of myosin with the cytoskeleton are unaffected by RGDS peptide receptor occupancy. 3) RGDS inhibits an aggregation-dependent incorporation of ABP, alpha-actinin, talin, and GPIIb-IIIa into the Triton-insoluble residue.
Actinin↗
cDNA cloning and expression of platelet p24/CD9. Evidence for a new family of multiple membrane-spanning proteins.
This study was designed to clone, sequence, and express the full-length cDNA for the human platelet p24/CD9 antigen. A 1.3-kilobase cDNA clone was identified that has an open reading frame encoding a mature protein of 228 amino acids (approximately 25,400 Da) containing 10 cysteine residues and four putative transmembrane domains. The identity of the clone was confirmed by: (i) its predicted size, (ii) identity to four peptide sequences from the isolated protein including the NH2 terminus, and (iii) expression of the isolated clone in Xenopus oocytes and Chinese hamster ovary cells. p24/CD9 has sequence identity (24-34%) to four other cell-surface proteins: ME491, a melanoma antigen; CO-029, a carcinoma antigen; CD37, a leukocyte antigen; and SM23, an antigen of the parasitic helminth Schistosoma mansoni. The five proteins have a similar number of amino acids and are characterized by the presence of four putative transmembrane domains. These data indicate the presence of a new family of surface antigens that may function in cellular activation and differentiation.
Amino Acid Sequence↗
Interaction of two GPIIb/IIIa monoclonal antibodies with platelet Fc receptor (Fc gamma RII).
We have previously used the IV-3 monoclonal antibody specific for Fc gamma RII to demonstrate that platelet activation by CD9 monoclonal antibodies such as ALB-6 is mediated by the Fc gamma RII. Here, we show that platelet activation following addition of a monoclonal antibody directed against GPIIb/IIIa, P256 is completely blocked by IV-3, as monitored by serotonin release, calcium and pH modifications. However, aggregation was only partially inhibited. D3GP3 is another monoclonal antibody directed against GPIIIa which has been shown to induce platelet aggregation by exposure of the fibrinogen binding site. The present study demonstrates that this phenomenon is not accompanied by calcium flux or pH modification, nor is it blocked by pretreatment of platelet by IV-3. Despite its apparent independence from the Fc gamma RII activation pathway, D3GP3, but not its Fab fragment, was able to inhibit ALB-6 induced activation, including serotonin release, calcium flux and pH modifications. Binding studies demonstrated that D3GP3 (20 micrograms/ml, 0.13 microM) does not block ALB-6 binding to CD9 antigen but completely blocks IV-3 binding to the Fc receptor for concentrations of IV-3 ranging from 0 to 15 nM. Together, these results suggest an interaction between GPIIb/IIIa, Fc gamma RII and GPIIb/IIIa monoclonal antibodies which in some cases can result in activation of platelets through Fc gamma RII.
Antibodies, Monoclonal↗
Hemostasis in Glanzmann's thrombasthenia (GT): GT platelets interfere with the aggregation of normal platelets.
The transfusion requirements for a 6-year-old Glanzmann's thrombasthenia (GT) patient undergoing tonsillectomy and adenoidectomy were studied. Transfusion of pheresed platelets from a single normal donor increased the platelet count by 63 x 10(9)/L but did not correct the bleeding time. Since the ratio of normal:GT platelets in vivo was approximately 1:5, it was possible that GT platelets interfered with the function of normal platelets. To test this hypothesis, mixtures of platelet-rich plasma (PRP) from a normal donor and the patient were studied to determine a ratio of normal:GT platelets that would yield acceptable in vitro aggregation. Normal:GT ratios of 1:4 and 3:2 resulted in 25% and 59% aggregation, respectively. Mixtures of normal and nonfunctional ethylene glycol tetra-acetic acid-treated platelets gave similar results. Aggregates from mixtures of normal and patient platelets were also examined morphologically by light microscopy and were proportional in size to the normal:GT platelet ratio. Transfusion of platelets from the pheresis of four donors increased the patient's platelet count by greater than 300 x 10(9)/L (normal:GT ratio 1:1), produced 53% aggregation, and resulted in satisfactory postoperative hemostasis. The platelet transfusion requirement for this GT patient was much greater than would have been expected in the absence of aggregation-defective platelets.
Antibodies, Monoclonal↗
A conformation-dependent epitope of human platelet glycoprotein IIIa.
This study explores conformational states of human platelet glycoprotein IIIa (GP IIIa) and possible mechanisms of fibrinogen receptor exposure. D3GP3 is an IgG1, kappa monoclonal antibody generated against purified GP IIIa and found to be specific for GP IIIa by immunoprecipitation and Western blot analysis. The binding of D3GP3 to resting platelets caused fibrinogen binding (approximately 5,000 molecules/platelet) and platelet aggregation but not secretion. Platelets express 40,000-50,000 GP IIb-IIIa molecules in their surface membranes. However, resting platelets only bound approximately 5,000 D3GP3 molecules/platelet. D3GP3 binding to platelets could be increased 2-3-fold by dissociation of the GP IIb-IIIa complex with 5 mM EDTA or by occupying the fibrinogen receptor with either RGDS peptides or fibrinogen. Platelet stimulation with ADP in the absence of fibrinogen did not cause increased D3GP3 binding above control levels. These data suggest that 1) GP IIb-IIIa can exist in multiple conformations in the platelet membrane, 2) D3GP3 binding to GP IIIa can expose the fibrinogen receptor, 3) the binding of either RGDS peptides or fibrinogen causes exposure of the D3GP3 epitope, and 4) platelet activation in the absence of ligand does not induce the same conformational changes in GP IIb-IIIa as does receptor occupancy by RGDS peptides or fibrinogen.
Antibodies, Monoclonal↗
The activation of human platelets mediated by anti-human platelet p24/CD9 monoclonal antibodies.
Anti-human platelet p24/CD9 (p24/monoclonal antibody 7) causes the activation of platelets and in the presence of calcium induces platelet aggregation. Our studies suggest that platelet response to this antibody is mediated at least in part by the pertussis toxin-sensitive guanine nucleotide-binding proteins (G proteins) that stimulate phosphoinositide hydrolysis and inhibit adenylate cyclase. Prior exposure of saponin-treated platelets to anti-p24/CD9 inhibited the [32P] ADP-ribosylation of the alpha 41 protein by pertussis toxin. Platelet aggregation induced by this antibody is preceded by and/or accompanied by accelerated phosphatidylinositol turnover, the generation of inositol phosphates and diacylglycerol (DAG), calcium mobilization, and protein phosphorylation. The production of inositol phosphate(s) was measurable within 15 s of either anti-p24/CD9 or thrombin addition. Within 10 s of antibody addition (10 micrograms/ml), the level of DAG was 200% over that of the control and similar to that observed with 2 units/ml thrombin (201% over that of the control). Therefore, as it appears to be true for thrombin, platelet response upon binding of anti-p24/CD9 is primarily mediated by the activation of phospholipase C. When platelets pretreated with aspirin (200 microM) and apyrase (1 mg/ml) were subsequently exposed to anti-p24/CD9, aggregation still occurred. This indicates that neither secreted ADP nor thromboxane generation is required for this aggregation response. Using indo-1 and ratio cytofluorometry, we observed that an increase in platelet cytosolic calcium is a relatively early event and occurs in either the presence or absence of calcium in the external media. Phosphorylation studies of platelet proteins showed that anti-p24/CD9 binding to platelets caused increased phosphorylation of four proteins with apparent molecular masses of 50,000, 47,000, 36,000, and 20,000 daltons. These studies suggest that platelet activation mediated by the surface protein p24/CD9 is mainly through the stimulation of a phospholipase C, the activation of which is responsible for the generation of second messengers inositol trisphosphate and DAG.
Adenylate Cyclase Toxin↗