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- Nylander, Sven, et al.
(author)
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Thrombin-induced platelet activation and its inhibition by anticoagulants with different modes of action
- 2003
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In: Blood Coagulation and Fibrinolysis. - : Ovid Technologies (Wolters Kluwer Health). - 0957-5235 .- 1473-5733. ; 14:2, s. 159-167
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Journal article (peer-reviewed)abstract
- Thrombin-induced platelet activation involves cleavage of protease-activated receptors (PARs) 1 and 4, and interaction, via glycoprotein (Gp)Ibα, with the platelet GpIb/IX/V complex. This study investigated inhibition of platelet activation by thrombin inhibitors with different modes of action: two reversible direct thrombin inhibitors, melagatran and inogatran; hirudin, a tightly binding direct thrombin inhibitor; and two indirect thrombin inhibitors, heparin and dalteparin. Up-regulation of P-selectin (CD62P) and PAR-1 cleavage was measured in human whole blood, by flow cytometry. The thrombin concentration that induced 50% of maximum (EC50) PAR-1 cleavage was 0.028 nmol/l, while that of platelet activation (CD62P) was over two-fold higher (0.64 nmol/l). The EC50 of a PAR-1-independent component, defined as a further activating effect of thrombin on top of the maximum PAR-1-activating peptide (AP) effect, was 3.2 nmol/l. All anticoagulants were concentration-dependent inhibitors of thrombin-induced platelet activation and PAR-1 cleavage, but none inhibited PAR-1-AP or PAR-4-AP induced activation. Melagatran and inogatran were more potent inhibitors of CD62P up-regulation than of PAR-1 cleavage; conversely, hirudin, heparin and dalteparin were more potent inhibitors of PAR-1 cleavage.Thus, reversible direct thrombin inhibitors, such as melagatran, are potent inhibitors of thrombin-induced platelet activation, acting mainly by inhibition of a PAR-1-independent component.
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| 3. |
- Whiss, Per A, 1966-, et al.
(author)
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Divalent cations and the protein surface co-ordinate the intensity of human platelet adhesion and P-selectin surface expression
- 2002
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In: Blood Coagulation and Fibrinolysis. - : Ovid Technologies (Wolters Kluwer Health). - 0957-5235 .- 1473-5733. ; 13:5, s. 407-416
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Journal article (peer-reviewed)abstract
- At sites of blood vessel injury, platelets adhere to exposed vessel components, such as collagen, or immobilized fibrinogen derived from plasma or activated platelets. The divalent cations Mg2+ and Ca2+ are essential for platelet adhesion and activation, but Mg2+ can also inhibit platelet activation. The present study evaluates, by an enzymatic method, the effects of various divalent cations on the adhesion of isolated human platelets to collagen, fibrinogen, albumin or plastic in vitro. By enzyme-linked immunosorbent assay, platelet surface expression of P-selectin was measured to estimate the state of activation on adherence. Mg2+ increased platelet adhesion exclusively to collagen and fibrinogen at physiologically relevant concentrations. At higher concentrations, the adhesion declined. Ca2+ induced a weak adhesion only to fibrinogen at physiological doses and a peak of increased adhesion to all protein-coated surfaces at 10 mmol/l. Mn2+ elicited dose-dependent adhesion only to collagen and fibrinogen. Zn2+, Ni2+ and Cu2+ increased the adhesion of platelets independently of the surface. Ca2+ dose-dependently inhibited adhesion elicited by Mg2+ to collagen and fibrinogen. No other combination of divalent cations elicited such an effect. Mg2+-dependent platelet adhesion to collagen and Ca2+-dependent adhesion to fibrinogen increased P-selectin expression. Thus, the present study shows that the outcome of the platelet adhesion depends on the surface and the access of divalent cations, which co-ordinate the intensity of platelet adhesion and P-selectin surface expression.
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| 5. |
- Alikhan, R, et al.
(author)
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Prevention of venous thromboembolism in medical patients with enoxaparin: a subgroup analysis of the MEDENOX study
- 2003
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In: Blood Coagulation and Fibrinolysis. - 1473-5733. ; 14:4, s. 341-346
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Journal article (peer-reviewed)abstract
- The Medical Patients with Enoxaparin (MEDENOX) trial was a randomized, placebo-controlled study that defined the risk of venous thromboembolism (VTE) in acutely ill, immobilized, general medical patients and the efficacy of the low-molecular-weight heparin, enoxaparin, in preventing thrombosis. We performed a post-hoc analysis to evaluate the effect of 40 mg enoxaparin once daily on MEDENOX patient outcome in different types of acute medical illness (heart failure, respiratory failure, infection, rheumatic disorder and inflammatory bowel disease) and pre-defined risk factors (chronic heart and chronic respiratory failure, age, immobility, previous VTE and cancer). The primary outcome was the occurrence of documented VTE between days 1 and 14. The relative risk reduction [95% confidence intervals (CI)] for VTE comparing 40 mg enoxaparin with placebo in the subgroups were: acute heart failure, 0.29 (95% CI, 0.10-0.84); acute respiratory failure, 0.25 (95% CI, 0.10-0.65); acute infectious disease, 0.28 (95% CI, 0.09-0.81); and acute rheumatic disorder, 0.48 (95% CI, 0.11-2.16). The relative risk reduction for VTE in the pre-defined risk factor subgroups were: chronic heart failure, 0.26 (95% Cl, 0.08-0.92); chronic respiratory failure, 0.26 (95% CI, 0.10-0.68); age, 0.22 (95% CI, 0.09-0.51); immobility, 0.53 (95% CI, 0.14-1.72); previous VTE, 0.49 (95% CI, 0.15-1.68); and cancer, 0.50 (95% CI, 0.14-1.72). The beneficial effects of enoxaparin extend to a wide range of acutely ill medical patients. (C) 2003 Lippincott Williams Wilkins.
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| 8. |
- Berntorp, Erik, et al.
(author)
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NovoSeven in warfarin-treated patients
- 2000
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In: Blood Coagulation and Fibrinolysis. - 1473-5733. ; 11:Suppl 1, s. 113-115
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Journal article (peer-reviewed)abstract
- Haemorrhages represent a major complication of treatment with vitamin K antagonists. In cases of severe bleeding, a prompt effect on the increased International Normalized Ratio value is vital to achieve haemostasis. As conventional treatment, that is plasma or plasma-derived concentrates, carries the risk of blood-borne virus transmission, new treatments are needed. An open, multicentre pilot trial is currently under way to determine the effect of recombinant activated factor VII (rFVIIa; NovoSeven) administered to patients experiencing a bleeding episode after receiving vitamin K antagonists. When rFVIIa was given to a patient with a warfarin-induced nosebleed, it had an immediate haemostatic effect and the International Normalized Ratio value virtually normalized.
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