| 1. |
- Boknäs, Niklas, et al.
(författare)
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Thrombin-induced platelet activation via PAR4 : pivotal role for exosite II
- 2014
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Ingår i: Thrombosis and Haemostasis. - Stuttgart, Germany : Schattauer Gmbh. - 0340-6245 .- 2567-689X. ; 112:3, s. 558-565
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Tidskriftsartikel (refereegranskat)abstract
- Thrombin-induced platelet activation via PAR1 and PAR4 is an important event in haemostasis. Although the underlying mechanisms responsible for ensuring efficient PAR1 activation by thrombin have been extensively studied, the potential involvement of recognitions sites outside the active site of the protease in thrombin-induced PAR4 activation is largely unknown. In this study, we developed a new assay to assess the importance of exosite I and II for PAR4 activation with alpha- and gamma-thrombin. Surprisingly, we found that exosite II is critical for activation of PAR4. We also show that this dependency on exosite II likely represents a new mechanism, as it is unaffected by blockage of the previously known interaction between thrombin and glycoprotein Ib alpha.
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| 2. |
- Lindahl, Tomas, et al.
(författare)
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A novel prothrombin time method to measure all non-vitamin K-dependent oral anticoagulants (NOACs)
- 2017
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Ingår i: Upsala Journal of Medical Sciences. - : Taylor & Francis Group. - 0300-9734 .- 2000-1967. ; 122:3, s. 171-176
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Tidskriftsartikel (refereegranskat)abstract
- Background: There is a clinical need for point-of-care (POC) methods for non-vitamin K-dependent oral anticoagulants (NOACs). We modified a routine POC procedure: Zafena’s Simple Simon™ PT-INR, a room-temperature, wet-chemistry prothrombin time method of the Owren-type.Methods: To either increase or decrease NOAC interference, two assay variants were devised by replacing the standard 10 µL end-to-end capillary used to add the citrated plasma sample to 200 µL of prothrombin time (PT) reagent by either a 20 µL or a 5 µL capillary. All assay variants were calibrated to show correct PT results in plasma samples from healthy and warfarin-treated persons.Results: For plasmas spiked with dabigatran, apixaban, or rivaroxaban, the 20 µL variant showed markedly higher PT results than the 5 µL. The effects were even more pronounced at room temperature than at +37 °C. In plasmas from patients treated with NOACs (n = 30 for each) there was a strong correlation between the PT results and the concentration of NOACs as determined by the central hospital laboratory. For the 20 µL variant the PT response of linear correlation coefficient averaged 0.90. The PT range was INR 1.1–2.1 for dabigatran and apixaban, and INR 1.1–5.0 for rivaroxaban. Using an INR ratio between the 20 µL and 5 µL variants (PTr20/5) made the NOAC assay more robust and independent of the patient sample INR value in the absence of NOAC. Detection limits were 80 µg/L for apixaban, 60 µg/L for dabigatran, and 20 µg/L for rivaroxaban.Conclusions: A wet-chemistry POC PT procedure was modified to measure the concentrations of three NOACs using a single reagent.
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| 3. |
- Lindahl, Tomas, et al.
(författare)
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More efficient reversal of dabigatran inhibition of coagulation by activated prothrombin complex concentrate or recombinant factor VIIa than by four-factor prothrombin complex concentrate
- 2015
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Ingår i: Thrombosis Research. - : Elsevier. - 0049-3848 .- 1879-2472. ; 135:3, s. 544-547
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Tidskriftsartikel (refereegranskat)abstract
- The number of patients on antithrombotic treatment due to atrial fibrillation and venous thromboembolism is increasing fast due to an aging population. A growing proportion will be treated with novel oral anticoagulants, the first in clinical use was the direct oral thrombin inhibitor dabigatran (Pradaxa (R)). A small percentage of the patients on dabigatran will experience serious bleeding or be in need of urgent surgery. The aim of this study was to test the effects of different hemostatic agents in potentially reversing the anticoagulant effects in vitro in blood or platelet-rich plasma (PRP) spiked with dabigatran. Whole blood or PRP was spiked with the active substance dabigatran, 200 mu g/L. We measured clotting time being induced by 1.4 pmol/L tissue factor using the instrument ReoRox2 (TM) and initial clot growth velocity from a tissue factor covered surface using the instrument Thrombodynamics Analyzer T-2 (TM). Dabigatran prolonged clotting time 5-fold but reduced clot growth velocity only slightly. The reversing effects of prothrombin complex concentrates (PCC), activated PCC (APCC) and recombinant activated factor VII (rFVIIa) were then tested. APCC (1.8 U/mL) reduced the prolonged clotting time by 1/3, rFVIIa (2 mu g/L) only slightly (n = 10-20). The reduction was not significant using Mann-Whitney test but significant using t-test with Bonferronis correction for multiple comparisons, whereas PCC (0.56 U/mL) had no effect on clotting time. APCC doubled initial clot growth velocity, although even more in the absence of dabigatran. In conclusion, APCC and rFVIIa, but not PCC, seem to reverse, at least partially, some effects of dabigatran on coagulation parameters. Systematic evaluation of case reports, registries and, ultimately, randomized clinical trials are needed to elucidate potential benefit for patients. (C) 2014 Elsevier Ltd. All rights reserved.
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| 4. |
- Tynngård, Nahreen, et al.
(författare)
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Platelet adhesion changes during storage studied with a novel method using flow cytometry and protein-coated beads
- 2015
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Ingår i: Platelets. - : Taylor & Francis. - 0953-7104 .- 1369-1635. ; 26:2, s. 177-185
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present study was to set up and evaluate a novel method for studies of platelet adhesion and activation in blood and platelet suspensions such as platelet concentrate (PC) samples using protein-coated polystyrene beads and flow cytometry. To demonstrate its usefulness, we studied PCs during storage. PCs were prepared by aphaeresis technique (n = 7). Metabolic variables and platelet function was measured on day 1, 5, 7 and 12 of storage. Spontaneous and TRAP-6-induced adhesion to fibrinogen-and collagen-coated beads was analyzed by flow cytometry. P-selectin and phosphatidyl serine (PS) expression was assessed on platelets bound to beads as well as on non-adherent platelets. Platelet adhesion to fibrinogen beads had increased by day 12 and adhesion to collagen beads at day 7 of storage (p<0.05). TRAP-6 stimulation significantly increased the platelet adhesion to fibrinogen beads (p<0.05) as well as the P-selectin and PS exposure on platelets bound to beads (p<0.01) during the first 7 days of storage, but by day 12, significant changes were no longer induced by TRAP-6 stimulation. We demonstrate that our adhesion assay using protein-coated polystyrene beads can be used to assess the adhesion properties of platelets during storage without the addition of red blood cells. Therefore it may offer a useful tool for future studies of platelet adhesive capacity in transfusion medicine and other settings.
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