| 1. |
- Bäck, Jennie, et al.
(författare)
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Activated human platelets induce factor XIIa-mediated contact activation
- 2010
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Ingår i: Biochemical and Biophysical Research Communications - BBRC. - : Elsevier BV. - 0006-291X .- 1090-2104. ; 391:1, s. 11-17
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Tidskriftsartikel (refereegranskat)abstract
- Earlier studies have shown that isolated platelets in buffer systems can promote activation of FXII or amplify contact activation, in the presence of a negatively charge substance or material. Still proof is lacking that FXII is activated by platelets in a more physiological environment. In this study we investigate if activated platelets can induce FXII-mediated contact activation and whether this activation affects clot formation in human blood. Human platelets were activated with a thrombin receptor-activating peptide, SFLLRN-amide, in platelet-rich plasma or in whole blood. FXIIa and FXIa in complex with preferentially antithrombin (AT) and to some extent C1-inhibitor (C1INH) were generated in response to TRAP stimulation. This contact activation was independent of surface-mediated contact activation, tissue factor pathway or thrombin. In clotting whole blood FXIIa-AT and FXIa-AT complexes were specifically formed, demonstrating that AT is a potent inhibitor of FXIIa and FXIa generated by platelet activation. Contact activation proteins were analyzed by flow cytometry and FXII, FXI, high-molecular weight kininogen, and prekallikrein were detected on activated platelets. Using chromogenic assays, enzymatic activity of platelet-associated FXIIa, FXIa, and kallikrein were demonstrated. Inhibition of FXIIa in non-anticoagulated blood also prolonged the clotting time. We conclude that platelet activation triggers FXII-mediated contact activation on the surface and in the vicinity of activated platelets. This leads specifically to generation of FXIIa-AT and FXIa-AT complexes, and contributes to clot formation. Activated platelets may thereby constitute an intravascular locus for contact activation, which may explain the recently reported importance of FXII in thrombus formation.
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| 2. |
- Bäck, Jennie, et al.
(författare)
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Contact activation products are new potential biomarkers to evaluate the risk of thrombotic events in systemic lupus erythematosus
- 2013
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Ingår i: Arthritis Research & Therapy. - : Springer Science and Business Media LLC. - 1478-6362 .- 1478-6354. ; 15:6
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: Patients with systemic lupus erythematosus (SLE) have persistent platelet activation and an increased risk of thrombotic events, which cannot be accounted for by traditional cardiovascular risk factors. Factor (F)XII has a potentially important role in thrombus formation and is triggered by activated platelets. We therefore asked whether the contact system is involved in inflammation and vascular disease (VD) in SLE. Methods: Fibrin clots were incubated with purified FXII or whole blood, and the activation and regulation of FXII were studied. Plasma from SLE patients with (n = 31) or without (n = 38) previous VD and from matched healthy controls (n = 68) were analyzed for the presence of complexes formed between contact system enzymes and antithrombin (AT) or C1 inhibitor (C1INH) and evaluated with regard to clinical data and laboratory parameters. Results: Fibrin clots elicited FXII activation and acted as co-factors for AT. In clotting plasma, the levels of FXIIa-AT increased, and FXIIa-C1INH decreased. A similar reciprocal relationship existed in SLE patients. FXIIa-AT was elevated in the SLE patients with a history of VD, while the corresponding levels of factor FXIIa-C1INH were significantly decreased. FXIIa-AT correlated strongly with platelet parameters. The odds ratio for VD among the SLE patients was 8.9 if they had low levels of FXIIa-C1INH, 6.1 for those with high levels of FXIIa-AT, and increased to 23.4 for those with both decreased levels of FXIIa-C1INH and increased levels of FXIIa-AT. Conclusions: Activation of FXII is elicited by fibrin during thrombotic reactions in vitro and in vivo, and fibrin acts as a heparin-like co-factor and regulates AT. Patients with SLE had altered levels of FXIIa-serpin complexes, supporting that the contact system is involved in this disease. FXIIa-serpin complexes are strongly associated with previous VD in SLE patients, suggesting that these complexes are potential biomarkers for monitoring and assessing the risk of thrombotic events in SLE.
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| 3. |
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| 4. |
- Bäck, Jennie, et al.
(författare)
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Distinctive regulation of contact activation by antithrombin and C1-inhibitor on activated platelets and material surfaces
- 2009
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Ingår i: Biomaterials. - : Elsevier BV. - 0142-9612 .- 1878-5905. ; 30:34, s. 6573-6580
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Tidskriftsartikel (refereegranskat)abstract
- Activated human plate lets trigger FXII-mediated contact activation, which leads to the generation of FXIIa-antithrombin (AT) and FXIa-AT complexes. This suggests that contact activation takes place at different sites, on activated platelets and material surfaces, during therapeutic procedures involving biomaterials in contact with blood and is differentially regulated. Here we show that activation in platelet-poor plasma, platelet-rich plasma (PRP), and whole blood induced by glass, kaolin, and polyphosphate elicited high levels of FXIIa-C1-inhibitor (C1INH), low levels of FXIa-C1INH and KK-C1INH, and almost no AT complexes. Platelet activation, in both PRP and blood, led to the formation of FXIIa-AT, FXIa-AT, and kallikrein (KK)-AT but almost no C1INH complexes. In severe trauma patients, FXIIa-AT and FXIa-AT were correlated with the release of thrombospondin-1 (TSP-1) from activated platelets. In contrast, FXIIa-C1INH complexes were detected when the FXIIa-AT levels were low. No correlations were found between FXIIa-C1INH and FXIIa-AT or TSP-1. Inhibition of FXIIa on material surfaces was also shown to affect the function of aggregating platelets. In conclusion, formation of FXIIa-AT and FXIIa-C1INH complexes can help to distinguish between contact activation triggered by biomaterial surfaces and by activated platelets. Platelet aggregation studies also demonstrated that platelet function is influenced by material surface-mediated contact activation and that generation of FXIIa-AT complexes may serve as a new biomarker for thrombotic reactions during therapeutic procedures employing biomaterial devices.
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| 5. |
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| 6. |
- Bäck, Jennie, 1981-
(författare)
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The Plasma Contact System : New Functional Insights from a Hemostatic and Thrombotic Perspective
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The physiological role of the plasma contact system still remains a partial enigma. The aim of the presented work was to expand our understanding of the plasma contact system, focusing on its physiological activation and function, principally from a hemostatic perspective. It also explored contact system activation under pathological conditions. We found that when human platelets become activated in blood, plasma proteins of the contact system bind to platelets and initiate contact activation. The platelet-triggered contact activation contributed to clot formation by shortening the clotting time and enhancing clot stability. We demonstrated that the regulation of contact activation elicited by activated platelets differed from the previously described contact activation elicited by negatively charged material surfaces. Platelet-triggered contact activation and activation propelled by clotting blood were found to be regulated by antithrombin, whereas material-induced activation was regulated by C1 inhibitor. We also showed that the fibrin fibers that are formed during the clot process further enhance and propagate the contact activation initially induced by activated platelets. Fibrin not only activated factor XII but also seemed to increase the affinity of antithrombin for the proteases of the contact system, leading to the generation of contact enzyme-antithrombin complexes during clot formation. To determine whether the contact system might be involved in the inflammation and vascular disease associated with systemic lupus erythematosus (SLE), we analyzed plasma samples from SLE patients. These patients were found to have altered levels of contact enzyme-serpin complexes, supporting the concept that the contact system may be involved in the pathophysiology of SLE. The contact enzyme-antithrombin complexes were clearly linked to platelet activation in vivo. Altered levels of both FXIIa-antithrombin and FXIIa-C1 inhibitor were found to be correlated with previous vascular disease and may therefore be potential biomarkers for assessing the risk of thrombotic events in SLE patients. These findings add to our knowledge of how the plasma contact system is activated and functions in vivo and will help us to understand the role of the contact system, not only in hemostasis but also in vascular disease and thrombotic conditions.
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| 7. |
- Hamad, Osama A, et al.
(författare)
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Platelets, Complement, and Contact Activation : Partners in inflammation and thrombosis
- 2012
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Ingår i: Current Topics in Innate Immunity II. - New York, NY : Springer. - 9781461401056 - 9781461401063 ; , s. 185-205
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Konferensbidrag (refereegranskat)abstract
- Platelet activation during thrombotic events is closely associated with complement and contact system activation, which in turn leads to inflammation . Here we review the interactions between activated platelets and the complement and contact activation systems in clotting blood. Chondroitin sulfate A (CS-A), released from alpha granules during platelet activation, is a potent mediator of crosstalk between platelets and the complement system. CS-A activates complement in the fluid phase, generating anaphylatoxins that mediate leukocyte activation. No complement activation seems to occur on the activated platelet surface, but C3 in the form of C3(H2O) is bound to the surfaces of activated platelets . This finding is consistent with the strong expression of membrane-bound complement regulators present at the platelet surface. CS-A exposed on the activated platelets is to a certain amount responsible for recruiting soluble regulators to the surface. Platelet-bound C3(H2O) acts as a ligand for leukocyte CR1 (CD35), potentially enabling platelet–leukocyte interactions. In addition, platelet activation leads to the activation of contact system enzymes, which are specifically inhibited by antithrombin, rather than by C1INH, as is the case when contact activation is induced by material surfaces. Thus, in addition to their traditional role as initiators of secondary hemostasis, platelets also act as mediators and regulators of inflammation in thrombotic events.
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| 8. |
- Nilsson, Per H., et al.
(författare)
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The creation of an antithrombotic surface by apyrase immobilization
- 2010
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Ingår i: Biomaterials. - : Elsevier BV. - 0142-9612 .- 1878-5905. ; 31:16, s. 4484-4491
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Tidskriftsartikel (refereegranskat)abstract
- Blood incompatibility reactions caused by surfaces often involve platelet activation and subsequent platelet-initiated activation of the coagulation and complement cascades. The goal of this study was to immobilize apyrase on a biomaterial surface in order to develop an enzymatically active surface that would have the capacity to inhibit platelet activation by degrading ADP. We were able to immobilize apyrase on a polystyrene surface with preservation of the enzymatic activity. We then analyzed the hemocompatibility of the apyrase surface and of control surfaces by incubation with platelet-rich plasma (PRP) or whole blood. Monitoring of markers of platelet, coagulation, and complement activation and staining of the surfaces revealed decreased levels of platelet and coagulation activation parameters on the apyrase surface. The formation of antithrombin-thrombin and antithrombin-factor XIa complexes and the extent of platelet consumption were significantly lower on the apyrase surface than on any of the control surfaces. No significant differences were seen in complement activation (C3a levels). Staining of the apyrase surface revealed low platelet adherence and no formation of granulocyte platelet complexes. These results demonstrate that it is possible to create an antithrombotic surface targeting the ADP amplification of platelet activation by immobilizing apyrase.
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| 9. |
- Nilsson, Per, et al.
(författare)
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IMMOBILIZATION OF APYRASE CREATES AN ANTITHROMBOTIC BIOMATERIAL SURFACE
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Blood incompatibility reactions caused by surfaces often involve platelet activation and subsequent platelet-initiated activation of the coagulation and complement cascades. The goal of this proof-of-principle study was to immobilize apyrase on a biomaterial surface in order to develop an enzymatically active surface that would have the capacity to inhibit platelet activation by degradating ADP. We were able to immobilize apyrase on a polystyrene surface with preservation of the enzymatic activity. We then analyzed the hemocompatibility of the apyrase surface and of control surfaces (serum albumin, avidin, polystyrene, and glass) by incubation with platelet-rich plasma (PRP) or whole blood. Monitoring of markers of platelet, coagulation, and complement activation and staining of the surfaces revealed decreased levels of platelet and coagulation activation parameters on the apyrase surface. The level of complex formation between antithrombin and thrombin or factor XIa and the extent of the platelet loss were significantly lower on the apyrase surface than on any of the control surfaces. No significant differences were seen in complement activation (C3a levels). Staining of the apyrase surface revealed low platelet adherence and no formation of granulocyte-platelet complexes. These results demonstrate that it is possible to create an anti-thrombotic surface targeting the ADP amplification of platelet activation by immobilizing apyrase.
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