bluuebunny/crossref_metadata_2025_split huggingface dataset:
Congenital Resistance to Activated Protein C in Patients with Lupus Anticoagulants: Evaluation of Two Functional Assays
Authors: Duca Francesca , Ruggeri Luisa , Finazzi Guido , Negri Barbara , Moia Marco , Galli Monica 
Published: March 2018

SummaryThe R506Q mutation (“Factor V Leiden”) is responsible for the resistance to activated Protein C (aPCR), that is evaluated by coagulation tests. Such tests cannot be used in patients with lupus anticoagulants (LAs), due to the interfering effect exerted by these antibodies on “in vitro” phospholipid-dependent coagulation tests. For this reason, assays have been developed to evaluate aPCR that are insensitive to the presence of LA antibodies. We evaluated two such coagulation tests in the plasma of 82 consecutive patients with LAs. By polymerase chain reaction 3 patients (3.6%) were found heterozygous for the R506Q mutation. aPCR was evaluated by two clotting assays, proposed to be “insensitive” to the presence of LAs: 1. aPCR-tissue factor-based assay, using Factor V deficient plasma and 1:40 diluted test plasma; 2. aPCR-dRVVT-based assay with highly concentrated phospholipids. Their interassay coefficient of variation was 28% and 6.2%, respectively. Compared to the polymerase chain reaction analysis, the 2 tests displayed the following characteristics: sensitivity 67% vs 100%, specificity 92% vs 96%, positive predictive value 25% vs 50%, negative predictive value 99% vs 100%, respectively. Among LA patients without the R506Q mutation, 5 scored positive in the aPCR-tissue factor-based assay, 2 in the aPCR-dRVVT-based assay and another one in both assays. Our findings suggest that the aPCRdRVVT-based test is more reliable and sensitive than the aPCR-tissue factor-based one to the R506Q mutation in patients with LAs. Both assays, when negative, make unlikely the presence of the R506Q mutation. Polymerase chain reaction analysis remains, however, to be performed when either test is positive.
Assessment of the Influence of Citrate Concentration on the International Normalized Ratio (INR) Determined with Twelve Reagent-instrument Combinations
Authors: Chantarangkul Veena , Clerici Marigrazia , Negri Barbara , Mannucci Pier Mannuccio , Tripodi Armando 
Published: March 2018

SummaryCitrate concentration is one of the variables that can affect coagulation tests. However, few studies have so far been performed to assess the magnitude of this effect on coagulation tests in general and PT in particular. The aim of this study was to assess the extent of influence of citrate concentration on the PT test with results expressed as INR. Twelve reagent-instrument combinations (systems) were calibrated vs. the Reference Preparation BCT/441 using plasmas collected in either 105 mM or 129 mM citrate from normals and anticoagulated patients (OAT). PTs for plasmas collected in 129 mM citrate were longer than those collected in 105 mM both for normals and patients on OAT, but the ratios (patient-to-normal clotting times) for the two citrate concentrations were significantly different in many instances, implying that the International Sensitivity Index (ISI) is also different. ISIs for calibrations with plasmas collected in 105 mM were greater (up to 10%) than those with plasmas collected in 129 mM citrate. When PT ratios were transformed into INR using crossover ISIs (i.e., plasmas collected in 105 mM and ISI determined with plasmas collected in 129 mM citrate, or vice versa) we found that an INR of 4.5 could be up to 20% apart from the value that would have been obtained if the appropriate ISI was used. Moreover, if the ISI determined with the manual technique was used to convert PTs obtained with a particular instrument into INR, the effect of citrate concentration was even greater (INR difference up to 64%). Should these observations be valid for other systems, they might provide additional explanations for the frequent reports which document discrepancies in the INR determined with different systems to which incorrect ISI might have been applied. World-wide consensus on a single citrate concentration to collect patients’ as well as lyophilized plasmas to be used in External Quality Assessment Schemes and for local system calibration is therefore urgently needed.
Effects of Radiographic Contrast Agents on Thrombin Formation and Activity
Authors: Parker Andrew , Fay William 
Published: March 2018

SummaryClinical trials suggest that the risk of thrombosis during coronary angioplasty is lower with ionic contrast agents than with nonionic contrast agents. However, the molecular mechanisms underlying this effect are unknown. This study examined the effects of contrast agents on thrombin formation and its interaction with substrates, inhibitors, and ligands to define potential mechanisms by which contrast agents affect thrombus formation. Two ionic agents, diatrizoate and ioxaglate, and one nonionic agent, ioversol, were studied. Ionic agents inhibited factor X activation by the tissue factor-factor VIIa complex more potently than ioversol (53 ± 3.7, 43.0 ± 1.9, and 26.5 ± 2.4% inhibition by diatrizoate, ioxaglate, and ioversol, respectively, at concentrations of 5%). Ionic contrast agents were potent inhibitors of prothrombinase function, inhibiting thrombin formation by >75% at contrast concentrations of 0.6% (p <0.005). Ioversol inhibited prothrombinase to a significantly lesser extent than ionic agents. Clotting assays suggested that ioxaglate was the most potent inhibitor of thrombin generation in plasma despite having the least effect on fibrin polymerization. Contrast agents inhibited binding of thrombin to fibrin, with ionic agents producing a more potent effect than ioversol (p <0.02). However, contrast agents did not inhibit thrombin-mediated platelet activation, had only a minor effect on inhibition of thrombin by antithrombin III, and did not affect thrombin-hirudin interactions. In summary, these studies identify specific mechanisms by which radiographic contrast agents inhibit thrombin formation and function – i.e. inhibition of tissue factor-dependent factor Xa generation, inhibition of the prothrombinase complex, and inhibition of thrombin binding to fibrin. These findings may help to explain the reduced risk of thrombosis during coronary angioplasty associated with ionic contrast agents.
Modulation of Plasminogen Activator Inhibitor 1 by Triton X-100 – Identification of Two Consecutive Conformational Transitions
Authors: Gils Ann , Declerck Paul 
Published: March 2018

SummaryPlasminogen activator inhibitor-1 (PAI-1) is a unique member of the serpin superfamily because of its conformational and functional flexibility. In the present study, we have evaluated the influence of the nonionic detergent Triton X-100 (TX-100) on the functional stability and conformational transitions of PAI-1.At 37° C, TX-100 induced a concentration-dependent decrease of the functional half-life of PAI-1 resulting in half-lives of 177 ± 54 min (mean ± SD, n = 3), 19 ± 2 min, 1.7 ± 0.3 min and 0.53 ± 0.03 min in the presence of 0.005, 0.010, 0.020 and 0.2% TX-100, respectively, compared to a half-life of 270 ± 146 min in the absence of TX-100. Conformational analysis at various time points and at different temperatures (0° C, 25° C, 37° C) revealed that this inactivation proceeds through the formation of a substrate-like intermediate followed by the formation of the latent form. Kinetic evaluation demonstrated that this conversion fits to two consecutive first-order transitions, i.e. active substrate latent. The k1 value was strongly dependent on the concentration of TX-100 (e.g. 0.002 ± 0.0006 s -1 and 0.029 ± 0.003 s -1 for 0.01% and 0.2% TX-100 at 37° C) whereas the conversion of substrate to latent (k2) was virtually independent of the TX-100 concentration (i.e. 0.012 ± 0.002 s -1 and 0.011 ± 0.001 s -1 for 0.01 and 0.2% TX-100 at 37° C).Experiments with a variety of other non-ionic amphiphilic compounds revealed that the amphiphilic character of the compound is, at least in part, responsible for the observed effects and strongly indicate that the currently reported mechanism of inactivation is of general importance for the conformational transitions in PAI-1.In conclusion, TX-100 changes the initial conformation of PAI-1 resulting in altered functional properties. This observation allows us to develop a new model for the mechanism involved in the conformational flexibility of PAI-1 and may provide new insights for the development of strategies for interference with PAI-1 activity.
Purification of the Porcine Platelet GP IIb-IIIa Complex and the Propolypeptide of von Willebrand Factor
Authors: Royo Teresa , Vidal Matilde , Badimon Lina 
Published: March 2018

SummaryPlatelet membrane glycoproteins (GP) are involved in platelet adhesion and aggregation. The glycoprotein IIb-IIIa complex (GP IIbIIIa) is a Ca2+-dependent heterodimer that binds fibrinogen and other adhesive proteins, thereby mediating platelet aggregation and adhesion. We have purified two major glycoproteins from pig platelets by Concanavalin A-Sepharose, Heparin-Sepharose and Sephacryl S-300 HR chromatography (Fitzgerald et al. Anal Biochem, 1985): i) the GP IIb-IIIa complex, GP IIb Mr = 140,000 and GP IIIa a single chain of Mr = 95,000-100,000; and ii) a predominant glycoprotein of high molecular weight, the propolypeptide of von Willebrand factor (Mr = 80,000-100,000). Western-blot analysis of the purified GP IIb-IIIa showed that only certain monoclonal antibodies against the human receptor specifically recognize the porcine complex. Differences between the porcine and human GP IIb-IIIa glycoproteins could partially explain the decreased inhibitory effects of GP IIb/IIIa-antagonists (against the human receptor) in porcine platelets.
Characteristics of the Interaction between Thrombin Exosite1 and the Sequence 269-297 of Platelet Glycoprotein Ibα
Authors: Bouton Marie-Christine , Thurieau Christophe , Guillin Marie-Claude , Jandrot-Perrus Martine 
Published: March 2018

SummaryThe interaction between GPIb and thrombin promotes platelet activation elicited via the hydrolysis of the thrombin receptor and involves structures located on the segment 238-290 within the N-terminal domain of GPIbα and the positively charged exosite 1 on thrombin. We have investigated the ability of peptides derived from the 269-287 sequence of GPIbα to interact with thrombin. Three peptides were synthesized, including Ibα 269-287 and two scrambled peptides R1 and R2 which are comparable to Ibα 269-287 with regards to their content and distribution of anionic residues. However, R2 differs from both Ibα 269-287 and R1 by the shifting of one proline from a central position to the N-terminus. By chemical cross-linking, we observed the formation of a complex between 125I-Ibα 269-287 and α-thrombin that was inhibited by hirudin, the C-terminal peptide of hirudin, sodium pyrophosphate but not by heparin. The complex did not form when γ-thrombin was substituted for α-thrombin. Ibα 269-287 produced only slight changes in thrombin amidolytic activity and inhibited thrombin binding to fibrin. R1 and R2 also formed complexes with α-thrombin, modified slightly its catalytic activity and inhibited its binding to fibrin. Peptides Ibα 269-287 and R1 inhibited platelet aggregation and secretion induced by low thrombin concentrations whereas R2 was without effect. Our results indicate that Ibα 269-287 interacts with thrombin exosite 1 via mainly electrostatic interactions, which explains why the scrambled peptides also interact with exosite 1. Nevertheless, the lack of effect of R2 on thrombin-induced platelet activation suggests that proline 280 is important for thrombin interaction with GPIb.
Reconstituted High Density Lipoprotein (rHDL) Modulates Platelet Activity In Vitro and Ex Vivo
Authors: Spycher Martin , Doran Jan , Lerch Peter 
Published: March 2018

SummaryA reconstituted high density lipoprotein (rHDL) prepared for clinical use was tested for its influence on platelet activity modulated by various stimuli. In a first series of in vitro experiments, rHDL was added to blood in a concentration series, and platelet rich plasma (PRP) was isolated. Platelets were stimulated with arachidonic acid, collagen, epinephrine or ADP, and platelet aggregation was assessed. rHDL mediated a dose dependent inhibition of the platelet activity. With purified platelets rHDL inhibited the release reaction induced by collagen, but not by thrombin, as measured by CD62P (P-Selectin) expression on the plasma membrane. Ex vivo experiments were performed with PRP from volunteers, previously infused with 25 mg rHDL/kg body weight and 40 mg rHDL/kg body weight, respectively. Platelet activity in PRP was assessed before, and up to 30 h after the end of the rHDL infusion. A transient inhibition of the platelet aggregation induced by arachidonic acid and collagen was observed which was more pronounced in the group receiving 40 mg rHDL/kg body weight. In both groups of experiments, in vitro and ex vivo, the inhibition of the platelet activity was also dependent on the stimulus used.
A Mutation in Plasma Platelet-activating Factor Acetylhydrolase (Val279Phe) Is a Genetic Risk Factor for Cerebral Hemorrhage but not for Hypertension
Authors: Yoshida Hidemi , Imaizumi Tadaatsu , Fujimoto Koji , Itaya Hiroyuki , Hiramoto Makoto , Yoshimizu Nobuhiro , Fukushi Kazue , Satoh Kei 
Published: March 2018

SummaryPlatelet-activating factor (PAF) acetylhydrolase is an enzyme that inactivates PAF. Deficiency of this enzyme is caused by a missense mutation in the gene. We previously found a higher prevalence of this mutation in patients with ischemic stroke. This fact suggests that the mutation might enhance the risk for stroke through its association with hypertension. We have addressed this hypothesis by analyzing the prevalence of the mutation in hypertension. We studied 138 patients with essential hypertension, 99 patients with brain hemorrhage, and 270 healthy controls. Genomic DNA was analyzed for the mutant allele by the polymerase-chain reaction. The prevalence of the mutation was 29.3% (27.4% heterozygotes and 1.9% homozygotes) in controls and 36.2% in hypertensives and the difference was not significant. The prevalence in patients with brain hemorrhage was significantly higher than the control: 32.6% heterozygotes and 6.1% homozygotes (p <0.05). PAF acetylhydrolase deficiency may be a genetic risk factor for vascular diseases.
Prothrombin and Its Derivatives Stimulate Motility of Melanoma Cells
Authors: Zhou Hong , Gabazza Esteban , Takeya Hiroyuki , Deguchi Hiroshi , Urano Hajime , Adachi Yukihiko , Suzuki Koji 
Published: March 2018

SummarySeveral studies indicated that activation of the clotting system may promote the growth and the invasive behavior of tumor cells. In the present study, we evaluated the migratory response of various melanoma cell lines to several clotting factors and prothrombin derivatives (thrombin, fragment 1, fragment 2 and kringle 1 fragment). Prothrombin, thrombin and fragment 1 stimulated chemotaxis of the murine (K-1735 M2, X21) and human A375 (SM) melanoma cell lines. Prothrombin and prothrombin fragment 1 showed their maximal chemo-tactic activity at 0.5~1 μM. Chemotaxis induced by thrombin was inhibited by hirudin, but not that induced by prothrombin or fragment 1. Other clotting proteins and the fragment 2 and kringle 1 fragment of prothrombin did not elicit chemotactic activity. Checkerboard analysis indicated that motility was directional with a significant chemokinetic component. The K-1735 M2 cells also migrated in a concentration-dependent manner to substratum-bound insoluble prothrombin, thrombin or fragment 1. Ligand binding assays showed that both prothrombin and fragment 1 bound to K-1735 M2 cells with apparent Kds of 0.5 μM. This binding was inhibited by an excess concentration of unlabeled prothrombin and fragment 1 but not by similar concentrations of other prothrombin fragments. These findings suggest that prothrombin and its fragment 1 exert chemotactic activity on melanoma cells by different mechanisms and different binding sites from that induced by thrombin.
Interaction of the A1 Subunit of Factor VIIIa and the Serine Protease Domain of Factor X Identified by Zero-length Cross-linking
Authors: Lapan Kirsty , Fay Philip 
Published: March 2018

SummaryWe have previously used a solid phase binding assay to localize a Factor X (FX) interactive site to the acidic C-terminus of the A1 subunit of FVIIIa (Lapan KA, Fay PJ. J Biol Chem 1997; 272: 2082-2088). The complex of FVIII-FX was made covalent following reaction with the zero-length cross-linking reagent 1-ethyl-3-(3-dimethylaminopropyl-)carbodiimide hydrochloride (EDC). Western blotting of the thrombin-cleaved complex showed that the A1 subunit of FVIIIa associated with FX heavy chain. The FX-A1 product was also detected following cross-linking to the A1/A3-C1-C2 dimer, but not the activated protein C-cleaved A1336/A3-C1-C2 form, indicating that a residue(s) in the region spanning Met337-Arg372 contributed to the intermolecular ion pair(s). A synthetic peptide to this acidic region (FVIII337-372) cross-linked to FX and the product was alkaline resistant indicating that amide linkage(s) were formed. Sequence analysis of the FX-FVIII337-372 adduct suggested that the first 12 NH2-terminal residues of the FX and peptide do not participate in cross-link formation. Conversion of the cross-linked product to FXa by RVV-X showed that the peptide was associated with the serine protease-forming domain of the heavy chain. These results indicate that the association of FVIIIa and FX occurs from a salt linkage(s) formed between residues of the A1 acidic C-terminus of the cofactor (within residues 349-372) and the serine protease-forming domain of the substrate.
Platelet Associated Fibrinogen and ICAM-2 Induce Firm Adhesion of Neutrophils under Flow Conditions
Authors: Kuijper P. H. M. , Torres H. I. Gallardo , Lammers J.-W. J. , Sixma J. J. , Koenderman L. , Zwaginga J. J. 
Published: March 2018

SummarySurface-bound platelets support selectin-mediated rolling and β2-integrin-mediated firm adhesion of neutrophils (PMN) under flow conditions. We examined which ligands on platelets mediate this firm adhesion. Surface-bound platelets express ICAM-2 and GPIIbIIIa-bound fibrinogen, which are ligands for LFA-1 and MAC-1. In a well defined model for vessel wall injury, blood from an afibrinogenemic patient was perfused over ECM-coated coverslips to obtain fibrinogen-free platelet surfaces. At high shear rates, PMN-adhesion to fibrinogen-free platelet surfaces decreased compared to fibrinogen-containing controls. Under these conditions, firm adhesion and not rolling was blocked demonstrating the importance of fibrinogen in this process. In addition, MAC-1 and LFA-1 on PMN and ICAM-2 on platelets played a role in firm adhesion; the effect of blocking antibodies was most evident at high shear. The effects of fibrinogen depletion and ICAM-2 blocking were additive. In conclusion, multiple redundant ligands, like ICAM-2 and fibrinogen, induce firm and shear resistant PMN adhesion to platelets under flow conditions. Individually these ligands become critical at higher shear. Blocking of two or more interactions also interferes with low shear adhesion.
Two Repressor Elements Inhibit Expression of the von Willebrand Factor Gene Promoter In Vitro
Authors: Ardekani Ali , Greenberger Joel , Jahroudi Nadia 
Published: March 2018

SummaryA fragment of the human von Willebrand factor (VWF) gene promoter corresponding to sequences –487 to +247 bp functions as an endothelial specific promoter in cell culture. We have previously reported that a GATA transcription factor functions as an activator and an NF1 like protein functions as a repressor of this promoter fragment. We have now identified a second negative regulatory element in the VWF promoter that interacts with nuclear factor(s) (designated R) in both bovine aortic endothelial and smooth muscle cells. Inhibition of either the NF1 or the R repressor alone is not sufficient to activate the VWF promoter in smooth muscle cells. The present studies reveal that simultaneous inhibition of both repressors activates the VWF promoter in smooth muscle cells. The data support a model of selective derepression to explain the endothelial cell specific activity of the –487 to +247 fragment of the VWF promoter in vitro.
Purification and Characterization of Kaouthiagin, a von Willebrand Factor-Binding and -Cleaving Metalloproteinase from Naja kaouthia Cobra Venom
Authors: Hamako Jiharu , Nishida Sachiyo , Nomura Shosaku , Fujimura Yoshihiro , Ito Masayuki , Ozeki Yasuhiro , Titani Koiti , Matsui Taei 
Published: March 2018

SummaryA von Willebrand factor (vWF)-binding and -cleaving metalloproteinase, termed “kaouthiagin”, was purified from the venom of cobra snake Naja kaouthia. Kaouthiagin is a monomer with a molecular mass of about 46 kDa and 51 kDa under non-reducing and reducing conditions, respectively, and the N-terminal amino acid sequence is homologous to high molecular mass snake venom metalloproteinases. Kaouthiagin bound to vWF in a divalent ion-independent manner, but the reduced kaouthiagin failed to interact with vWF, suggesting that the protein conformation maintained by intrachaindisulfide linkages of the molecule is essential for the binding to vWF. Neither botrocetin nor bitiscetin, vWF-binding modulators from another snake venom, interfered with the binding between kaouthiagin and vWF, but a monoclonal antibody VW92-3 specific to the N-terminal region of vWF (residues 1-910) inhibited the binding. Without affecting platelet GPIb/IX and GPIIb/IIIa, kaouthiagin specifically cleaved vWF between residues Pro-708 and Asp-709 in a divalent ion-dependent manner to diminish the multimeric structure of vWF in plasma, resulting in the loss of ristocetin-induced platelet aggregability and the collagen-binding activity of vWF. These results indicate that kaouthiagin is a unique metalloproteinase which specifically binds to and cleaves vWF at a specific site and that it will be a useful tool for functional dissection of vWF.
Plaque Rupture and Plaque Erosion
Authors: Burke Allen P. , Farb Andrew , Virmani Renu 
Published: March 2018

SummaryThere are multiple substrates for coronary thrombosis overlying an atherosclerotic plaque. The most common, plaque rupture, consists of an interruption of a thin fibrous cap overlying a lipid rich core. Plaque rupture is a result of macrophage infiltration and matrix degradation, is often seen in calcified plaques, and is highly associated with hypercholesterolemia. A less common substrate, plaque erosion, is not associated with elevated cholesterol and is the prime cause of coronary thrombosis in premenopausal women. The characteristic histologic features are abundant surface smooth muscle cells and proteoglycans, and a small or absent lipid rich core. The mechanisms of plaque erosion are unclear, and there are no consistent risk factors, although patients are often smokers.
TNK-tPA for Acute Myocardial Infarction: The Clinical Experience
Authors: Pislaru Sorin V. , Van de Werf Frans 
Published: March 2018

SummaryThrombolytic therapy has become the mainstay of treatment for acute transmural myocardial infarction. Present fibrinolytic regimens have a number of shortcomings, including the failure to induce early and sustained reperfusion in as many as 40-50% of the patients, and to prevent reocclusion in another 10-20% of the patients. The efforts for improving thrombolysis are focused on the development of new agents (fibrinolytics, anticoagulants, and antiplatelet agents). TNK-tPA is a triple combination mutant of wild-type tissue plasminogen activator that exhibits a longer plasma half-life, an enhanced fibrin-specificity, and an increased resistance to the plasminogen activator inhibitor-1. This paper summarizes the results of clinical trials with TNK-tPA in acute myocardial infarction.