Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.6 (thromboplastin)
 13,278 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Lipid peroxidation and the accompanying translocation of phosphatidylserine (PS) from the inner to the outer leaflet of the lipid bilayer have recently been identified as key components of a signaling pathway for phagocytosis of apoptotic cells by macrophages. Drug-induced hemolytic anemia has long been known to be caused by an accelerated uptake of damaged (but intact) erythrocytes by macrophages in the spleen, and this process has been associated with enhanced formation of reactive oxygen species (ROS). However, the role of lipid peroxidation in hemolytic injury has remained unclear, and the effect of hemolytic agents on the distribution of PS in the erythrocyte membrane is unknown. The present studies were undertaken to determine whether lipid peroxidation and PS translocation could be detected in rat and human erythrocytes by three types of direct-acting hemolytic agents--dapsone hydroxylamine, divicine hydroquinone, and phenylhydrazine. 2',7'-Dichlorodihydrofluorescein diacetate was employed as a probe for intracellular ROS formation; lipid peroxidation was assessed by GC/MS analysis of F2-isoprostanes; and PS externalization was measured by annexin V labeling and the prothrombinase assay. The data confirmed that all three hemolytic agents generate ROS within erythrocytes under hemolytic conditions; however, no evidence for lipid peroxidation or PS translocation was detected. Instead, ROS production by these hemolytic agents was associated with extensive binding of oxidized and denatured hemoglobin to the membrane cytoskeleton. The data suggest that the transmembrane signal for macrophage recognition of hemolytic injury may be derived from oxidative alterations to erythrocyte proteins rather than to membrane lipids.
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PMID:Lipids versus proteins as major targets of pro-oxidant, direct-acting hemolytic agents. 1610 47

Activated platelets provide a procoagulant surface for the assembly and expression of prothrombinase complex. Expression of activity is associated with the binding of the protease factor Xa (FXa) and the co-factor Va (FVa) to the procoagulant surface. A flow cytometric methodology to measure annexin V-FITC as well as FVa and FXa binding to ionophore A 23187 activated platelets is described. Annexin V-FITC was used to determine platelet exposure of phosphatidylserine. The binding was calcium-dependent and excess of unlabelled annexin V (10-fold) prevented the binding of the labelled protein. The binding of FVa and FXa to platelets was measured using specific FITC-labelled monoclonal antibodies. The FITC labelled antibodies were displaced by 10-to 20-fold excess of unlabelled antibodies. Binding was strictly Ca2+-dependent. Fixation of platelets by formaldehyde caused artificial binding of annexin V, FVa and FXa as well, irrespective of the platelet activation status. Using gel-filtered platelets, the binding of FVa increased with alpha -granule secretion but the amount of stored FVa was not sufficient to saturate the available platelet binding sites. Exogenous FVa was needed for maximal FVa binding to occur. No binding of FXa from internal platelet stores was observed. Addition of exogenous FVa and FXa resulted in FXa binding to the platelet surface. The methodology might be of use for the study of platelets from patients with bleeding disorders.
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PMID:Flow cytometric analysis of agonist-induced annexin V, factor Va and factor Xa binding to human platelets. 1679 97

Non-apoptotic externalization of phosphatidylserine (PS) can act as a reactive surface for the efficient assembly of the prothrombinase complex leading to thrombin generation and coagulation. Here we show that extracellular ATP, acting at the macrophage P2X(7) receptor, drives the rapid Ca(2+)-dependent formation and release of PS-rich microvesicles that enhance the assembly of the prothrombinase complex and subsequent formation of thrombin. Incubation with P2X(7) receptor antagonists (KN-62 and Brilliant Blue G) attenuates ATP induced prothrombotic responses. Consistent with the hypothesis that exposed PS enhances prothrombinase activity; pre-incubation with annexin V blocks the increase in thrombin formation. The rapid translocation of PS and formation of pro-thrombotic microvesicles occurs in the absence of cell lysis. These data demonstrate that the pro-inflammatory P2X(7) receptor can also support and propagate rapid increases in thrombin formation.
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PMID:Murine macrophage P2X7 receptors support rapid prothrombotic responses. 1717 37

Tumstatin, a 28-kDa C-terminal fragment of collagen IV, is a potent anti-angiogenic protein and inhibitor of tumour growth. Recombinant tumstatin was prepared from Escherichia coli deposited as insoluble, inactive inclusion bodies. In the present study, we produced soluble and biologically active recombinant human tumstatin in E. coli by the coding region of tumstatin being linked to the 3'-end of the maltose-binding protein (MBP) gene. The fusion protein was expressed as the soluble form after induction by isopropylthio-beta-D-galactoside (IPTG). MBP-tumstatin was purified by amylose affinity chromatography. MBP can be removed by digestion with factor Xa. Expression could represent 20% of the total soluble protein in E. coli, allowing approximately 8.6 mg of highly purified protein to be obtained per litre of bacterial culture. The purified tumstatin specifically inhibited the proliferation of endothelial cells in a dose-dependent manner. Annexin V-FITC apoptotic assay showed that recombinant tumstatin induced significant increase of apoptotic endothelial cells after 20 h of exposure to 20 microg/ml tumstatin, and when tumstatin was incubated on the chicken embryo, chorioallantoic membrane at doses of 1-15 microg, there was a dramatic decrease in the microvasculature allantoids of chicken embryos neovascular vessel test in vivo demonstrated that tumstatin treatment at doses of 1-15 microg gives rise to dramatically decrease the number of neovascular vessel. Our study provides a feasible and convenient approach to produce soluble and biologically active tumstatin.
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PMID:Expression of soluble, biologically active recombinant human tumstatin in Escherichia coli. 1838 39

Recent studies suggest the impact of apoptosis on the mechanisms leading to hypercoagulability. We aimed to clarify the potential role of neutrophil apoptosis in neutropenia and hypercoagulable state encountered in chronic liver disease patients. This study was conducted on 15 normal controls and 45 patients with chronic liver disease classified according to modified Child Pugh classification into, Child A, B and C groups (15 cases each). Haemostatic parameters studied include, prothrombin time, partial thromboplastin time, tissue factor, protein C antigen, protein S antigen, and markers of haemostatic activation [prothrombin fragment 1+2 (F1+2), thrombus precursor protein (TpP) and D-dimer]. Flowcytometric study was done for quantitative assay of neutrophil apoptotic subpopulations to detect the percentage of early and late apoptotic, and necrotic neutrophils using Annexin V-FITC/propidium iodide dye. Semiquantitative assay of apoptotic neutrophils showing DNA fragmentation was performed on neutrophil culture using terminal deoxynucleotidyl transferase mediated deoxyuridine triphosphate nick end labelling test. In addition to enzyme-linked immunosorbent assay for soluble Fas (APO-1/CD95) in culture supernatant. The results revealed a rise in the neutrophil apoptotic and necrotic markers with progression of the disease, and they were inversely correlated with the absolute neutrophil count. The apoptotic neutrophil cells showed a significant positive correlation with several haemostatic parameters (tissue factor, prothrombin fragment 1+2, thrombus precursor protein and D-dimer). Regression analysis proved that apoptotic parameters are independent determinants of prothrombotic markers, which further incriminate the apoptotic mechanisms in the hypercoagulable state encountered in this clinical setting.
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PMID:Impact of neutrophil apoptosis on haemostatic activation in chronic liver disease patients. 1868 37

One of the mechanisms by which platelet-derived microparticles elicit procoagulant activity is by an increased exposure of phosphatidylserine on their surface. We have previously demonstrated the utility of an activated factor X-based assay for the detection of procoagulant phospholipid activity [Xa clotting time (XACT)]. The objective of this study was to further characterize the specificity of the XACT to detect microparticle-associated procoagulant phospholipid activity. XACT testing for procoagulant phospholipid was measured using an ST4 machine and microparticle counting was performed using flow cytometry for Annexin V binding. Plasma microparticle counts were significantly correlated to XACT times (P = 0.0001). The XACT assay was insensitive to tissue factor, whereas the addition of microparticles to a whole blood sample shortened XACT times. Procoagulant phospholipid activity could be detected in both citrate and EDTA anticoagulated samples; however, XACT times and microparticle counts were more stable in EDTA anticoagulated samples over a 60 min period. The procoagulant phospholipid activity of microparticles generated by collagen stimulation was significantly impaired in EDTA anticoagulated samples when compared with citrate. Microparticles were capable of higher degrees of thrombin generation than equivalent concentrations of phosphatidylserine (as assessed by XACT times), suggesting that other factors bound to the microparticle surface enhance the procoagulant response. In conclusion, the XACT assay is a specific method for the detection of procoagulant phospholipid activity arising from phosphatidylserine on the microparticle surface; however, other factors presumably bound to the surface of the microparticle may also contribute to enhanced thrombin generation detectable by prothrombinase assays.
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PMID:Detection of the procoagulant activity of microparticle-associated phosphatidylserine using XACT. 1959 14

HDL has anti-atherogenic properties, and plasma levels of HDL cholesterol correlate inversely with risk of coronary artery disease. HDL reportedly functions as a cofactor to the anticoagulant activated protein C (APC) in the degradation of factor Va (FVa). The aim of the present study was to elucidate the mechanism by which HDL functions as cofactor to APC. Consistent with a previous report, HDL isolated from human plasma by ultracentrifugation was found to stimulate APC-mediated degradation of FVa. However, further purification of HDL by gel filtration revealed that the stimulating activity was not a property of HDL. Instead, the stimulating activity eluted completely separately from HDL in the high-molecular-weight void volume fractions. The active portion of these fractions stimulated FVa degradation by APC and supported the assembly of factor Xa and FVa into a functional prothrombinase complex. Both the procoagulant and anticoagulant activities were blocked by addition of annexin V, suggesting that the active portion was negatively charged phospholipid membranes. These results demonstrate that HDL does not stimulate the APC/protein S effect and that the activity previously reported to be a property of HDL is instead caused by contaminating negatively charged phospholipid membranes.
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PMID:Reevaluation of the role of HDL in the anticoagulant activated protein C system in humans. 2044 51

Tissue factor (TF) is the cellular receptor for plasma protease factor VIIa (FVIIa), and the TF-FVIIa complex initiates coagulation in both hemostasis and thrombosis. Cell surface-exposed TF is mainly cryptic and requires activation to fully exhibit the procoagulant potential. Recently, the protein disulfide isomerase (PDI) has been hypothesized to regulate TF decryption through the redox switch of an exposed disulfide in TF extracellular domain. In this study, we analyzed PDI contribution to coagulation using an in vitro endothelial cell model. In this model, extracellular PDI is detected by imaging and flow cytometry. Inhibition of cell surface PDI induces a marked increase in TF procoagulant function, whereas exogenous addition of PDI inhibits TF decryption. The coagulant effects of PDI inhibition were sensitive to annexin V treatment, suggesting exposure of phosphatidylserine (PS), which was confirmed by prothrombinase assays and direct labeling. In contrast, exogenous PDI addition enhanced PS internalization. Analysis of fluorescent PS revealed that PDI affects both the apparent flippase and floppase activities on endothelial cells. In conclusion, we identified a new mechanism for PDI contribution to coagulation on endothelial cells, namely, the regulation of PS exposure, where PDI acts as a negative regulator of coagulation.
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PMID:Extracellular protein disulfide isomerase regulates coagulation on endothelial cells through modulation of phosphatidylserine exposure. 2044 8

Accumulating evidence indicates that microparticles (MPs) are important mediators of the interaction between cancer and the hemostatic system. We conducted a large prospective cohort study to determine whether the number of circulating procoagulant MPs is elevated in cancer patients and whether the elevated MP levels are predictive of occurrence of venous thrombembolism (VTE). We analyzed plasma samples of 728 cancer patients from the ongoing prospective observational Vienna Cancer and Thrombosis Study. Study endpoint was the occurrence of symptomatic VTE. Sixty-five age- and sex-matched healthy controls were recruited for defining the cut-off point for elevated MPs (4.62 nanomolar phosphatidylserine [nM PS]), which was set at the 95th percentile of MP levels in healthy controls. The measurement of MPs was performed after capture onto immobilized annexin V, and determination of their procoagulant activity was quantified with a prothrombinase assay. During a median observation period of 710 days, 53 patients developed VTE. MP levels (nM PS) were significantly higher in cancer patients than in healthy controls (median [25th-75th percentile], 3.95 [1.74-7.96] vs. 1.19 [0.81-1.67], p<0.001). Multivariate analysis including age, sex, surgery, chemo- and radiotherapy showed no statistically significant association of the hazard ratio of elevated MPs with VTE (0.95 [95% CI, 0.55-1.64], p=0.856). In conclusion, MP levels were elevated in cancer patients compared to healthy individuals in this study. However, elevated MP levels were not predictive of VTE.
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PMID:Circulating procoagulant microparticles in cancer patients. 2098 26

Thrombosis in paroxysmal nocturnal haemoglobinuria (PNH) has been suggested to be due to several pathophysiological states: a suppressed fibrinolytic system, increased leucocyte-derived tissue factor, complement (C')-mediated damage to platelets and endothelia, or increased platelet- and endothelium-derived microparticles (MPs). Because haemolytic attack is often accompanied by thrombosis in PNH, we studied the role of C'-induced release of MPs in the thrombogenesis of PNH. C' activation induced procoagulant alteration in PNH red blood cells (RBC), when assessed by thrombin generation in the presence of C'-activated PNH RBC, which was abolished by their subsequent treatment with annexin V. Significant amounts of procoagulant MPs, measured by phosphatidylserine-binding prothrombinase activity, were released from PNH RBC in association with the formation of C5b-9, but not significantly before C5b-8. Generation of procoagulant, annexin V-binding, MPs from C'-activated RBC was studied also by flow cytometry. While phorbol 12-myristate 13-acetate, an activator of protein kinase C (PKC), induced the release of MPs from normal RBC as well as PNH RBC, C'-induced release of MPs from PNH RBC was Ca(2+) -independent and not associated with the activation of PKC, calpain or caspase. Procoagulant properties of MPs released from PNH RBC could contribute to the thrombogenesis of PNH.
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PMID:Procoagulant properties of microparticles released from red blood cells in paroxysmal nocturnal haemoglobinuria. 2124 Dec 75


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