The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Andras Gruber - One of the best experts on this subject based on the ideXlab platform.
-
Role of platelets in regulating activated Coagulation Factor XI activity.
American journal of physiology. Cell physiology, 2021Co-Authors: Stephanie E Reitsma, Andras Gruber, David Gailani, Erik I. Tucker, Owen J. T. Mccarty, Jiaqing Pang, Vikram Raghunathan, Joseph J. Shatzel, Christina U. Lorentz, Cristina PuyAbstract:Factor XI (FXI) has been shown to bind platelets, but the functional significance of this observation remains unknown. Platelets are essential for hemostasis and play a critical role in thrombosis, whereas FXI is not essential for hemostasis but promotes thrombosis. An apparent functional contradiction, platelets are known to support thrombin generation, yet platelet granules release protease inhibitors, including those of activated FXI (FXIa). We aim to investigate the secretory and binding mechanisms by which platelets could support or inhibit FXIa activity. The presence of platelets enhanced FXIa activity in a purified system and increased Coagulation Factor IX (FIX) activation by FXIa and fibrin generation in human plasma. In contrast, platelets reduced the activation of FXI by activated Coagulation Factor XII (FXIIa) and the activation of FXII by kallikrein (PKa). Incubation of FXIa with the platelet secretome, which contains FXIa inhibitors, such as protease neXIn-II, abolished FXIa activity, yet in the presence of activated platelets, the secretome was not able to block the activity of FXIa. FXIa variants lacking the anion-binding sites did not alter the effect of platelets on FXIa activity or interaction. Western blot analysis of bound FXIa [by FXIa-platelet membrane immunoprecipitation] showed that the interaction with platelets is zinc dependent and, unlike FXI binding to platelets, not dependent on glycoprotein Ib. FXIa binding to the platelet membrane increases its capacity to activate FIX in plasma likely by protecting it from inhibition by inhibitors secreted by activated platelets. Our findings suggest that an interaction of FXIa with the platelet surface may induce an allosteric modulation of FXIa.
-
abstract 661 role of Coagulation Factor XI in regulating endothelial cell barrier function
Arteriosclerosis Thrombosis and Vascular Biology, 2019Co-Authors: Anh T P Ngo, Andras Gruber, Erik I. Tucker, Cristina Puy, Jiaqing Pang, Christina U. Lorentz, Norah G Verbout, Courtney Howard, Hagai Tavori, Owen J. T. MccartyAbstract:Background: Atherosclerosis is characterized by subendothelial lipid deposition, leukocyte infiltration, and smooth muscle proliferation that may lead to plaque rupture and atherothrombosis, a majo...
-
Removal of the C-terminal domains of ADAMTS13 by activated Coagulation Factor XI induces platelet adhesion on endothelial cells under flow conditions
Frontiers in medicine, 2017Co-Authors: Kathleen S. Garland, Andras Gruber, Jevgenia Zilberman-rudenko, David Gailani, Erik I. Tucker, Owen J. T. Mccarty, Stephanie E Reitsma, Toshiaki Shirai, Cristina PuyAbstract:Platelet recruitment to sites of vascular injury is mediated by von Willebrand Factor (VWF). The shear-induced unraveling of ultra-large VWF multimers causes the formation of a "stringlike" conformation, which rapidly recruits platelets from the bloodstream. A disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) regulates this process by cleaving VWF to prevent aberrant platelet adhesion; it is unclear whether the activity of ADAMTS13 itself is regulated. The serine proteases α-thrombin and plasmin have been shown to cleave ADAMTS13. Based on sequence homology, we hypothesized that activated Coagulation Factor XI (FXIa) would likewise cleave ADAMTS13. Our results show that FXIa cleaves ADAMTS13 at the C-terminal domains, generating a truncated ADAMTS13 with a deletion of part of the thrombospondin type-1 domain and the CUB1-2 domains, while α-thrombin cleaves ADAMTS13 near the CUB1-2 domains and plasmin cleaves ADAMTS13 at the metalloprotease domain and at the C-terminal domain. Using a cell surface immunoassay, we observed that FXIa induced the deletion of the CUB1-2 domains from ADAMTS13 on the surface of endothelial cells. Removal of the C-terminal domain of ADAMTS13 by FXIa or α-thrombin caused an increase in ADAMTS13 activity as measured by a fluorogenic substrate (FRETS) and blocked the ability of ADAMTS13 to cleave VWF on the endothelial cell surface, resulting in persistence of VWF strands and causing an increase in platelet adhesion under flow conditions. We have demonstrated a novel mechanism for Coagulation proteinases including FXIa in regulating ADAMTS13 activity and function. This may represent an additional hemostatic function by which FXIa promotes local platelet deposition at sites of vessel injury.
-
platelet derived short chain polyphosphates enhance the inactivation of tissue Factor pathway inhibitor by activated Coagulation Factor XI
PLOS ONE, 2016Co-Authors: Cristina Puy, Andras Gruber, David Gailani, Erik I. Tucker, Stephanie A. Smith, James H. Morrissey, Ivan Ivanov, Owen J. T. MccartyAbstract:INTRODUCTION Factor (F) XI supports both normal human hemostasis and pathological thrombosis. Activated FXI (FXIa) promotes thrombin generation by enzymatic activation of FXI, FIX, FX, and FV, and inactivation of alpha tissue Factor pathway inhibitor (TFPIα), in vitro. Some of these reactions are now known to be enhanced by short-chain polyphosphates (SCP) derived from activated platelets. These SCPs act as a coFactor for the activation of FXI and FV by thrombin and FXIa, respectively. Since SCPs have been shown to inhibit the anticoagulant function of TFPIα, we herein investigated whether SCPs could serve as coFactors for the proteolytic inactivation of TFPIα by FXIa, further promoting the efficiency of the extrinsic pathway of Coagulation to generate thrombin. METHODS AND RESULTS Purified soluble SCP was prepared by size-fractionation of sodium polyphosphate. TFPIα proteolysis was analyzed by western blot. TFPIα activity was measured as inhibition of FX activation and activity in Coagulation and chromogenic assays. SCPs significantly accelerated the rate of inactivation of TFPIα by FXIa in both purified systems and in recalcified plasma. Moreover, platelet-derived SCP accelerated the rate of inactivation of platelet-derived TFPIα by FXIa. TFPIα activity was not affected by SCP in recalcified FXI-depleted plasma. CONCLUSIONS Our data suggest that SCP is a coFactor for TFPIα inactivation by FXIa, thus, expanding the range of hemostatic FXIa substrates that may be affected by the coFactor functions of platelet-derived SCP.
-
the formation of microthrombi in parenchymal microvessels after traumatic brain injury is independent of Coagulation Factor XI
Journal of Neurotrauma, 2016Co-Authors: Susanne M. Schwarzmaier, Ciaran De Chaumont, Matilde Balbi, Nicole A. Terpolilli, Christoph Kleinschnitz, Andras Gruber, Nikolaus PlesnilaAbstract:Abstract Microthrombus formation and bleeding worsen the outcome after traumatic brain injury (TBI). The aim of the current study was to characterize these processes in the brain parenchyma after experimental TBI and to determine the involvement of Coagulation Factor XI (FXI). C57BL/6 mice (n = 101) and FXI-deficient mice (n = 15) were subjected to controlled cortical impact (CCI). Wild-type mice received an inhibitory antibody against FXI (14E11) or control immunoglobulin G 24 h before or 30 or 120 min after CCI. Cerebral microcirculation was visualized in vivo by 2-photon microscopy 2-3 h post-trauma and histopathological outcome was assessed after 24 h. TBI induced hemorrhage and microthrombus formation in the brain parenchyma (p < 0.001). Inhibition of FXI activation or FXI deficiency did not reduce cerebral thrombogenesis, lesion volume, or hemispheric swelling. However, it also did not increase intracranial hemorrhage. Formation of microthrombosis in the brain parenchyma after TBI is independent of ...
Owen J. T. Mccarty - One of the best experts on this subject based on the ideXlab platform.
-
Role of platelets in regulating activated Coagulation Factor XI activity.
American journal of physiology. Cell physiology, 2021Co-Authors: Stephanie E Reitsma, Andras Gruber, David Gailani, Erik I. Tucker, Owen J. T. Mccarty, Jiaqing Pang, Vikram Raghunathan, Joseph J. Shatzel, Christina U. Lorentz, Cristina PuyAbstract:Factor XI (FXI) has been shown to bind platelets, but the functional significance of this observation remains unknown. Platelets are essential for hemostasis and play a critical role in thrombosis, whereas FXI is not essential for hemostasis but promotes thrombosis. An apparent functional contradiction, platelets are known to support thrombin generation, yet platelet granules release protease inhibitors, including those of activated FXI (FXIa). We aim to investigate the secretory and binding mechanisms by which platelets could support or inhibit FXIa activity. The presence of platelets enhanced FXIa activity in a purified system and increased Coagulation Factor IX (FIX) activation by FXIa and fibrin generation in human plasma. In contrast, platelets reduced the activation of FXI by activated Coagulation Factor XII (FXIIa) and the activation of FXII by kallikrein (PKa). Incubation of FXIa with the platelet secretome, which contains FXIa inhibitors, such as protease neXIn-II, abolished FXIa activity, yet in the presence of activated platelets, the secretome was not able to block the activity of FXIa. FXIa variants lacking the anion-binding sites did not alter the effect of platelets on FXIa activity or interaction. Western blot analysis of bound FXIa [by FXIa-platelet membrane immunoprecipitation] showed that the interaction with platelets is zinc dependent and, unlike FXI binding to platelets, not dependent on glycoprotein Ib. FXIa binding to the platelet membrane increases its capacity to activate FIX in plasma likely by protecting it from inhibition by inhibitors secreted by activated platelets. Our findings suggest that an interaction of FXIa with the platelet surface may induce an allosteric modulation of FXIa.
-
abstract 661 role of Coagulation Factor XI in regulating endothelial cell barrier function
Arteriosclerosis Thrombosis and Vascular Biology, 2019Co-Authors: Anh T P Ngo, Andras Gruber, Erik I. Tucker, Cristina Puy, Jiaqing Pang, Christina U. Lorentz, Norah G Verbout, Courtney Howard, Hagai Tavori, Owen J. T. MccartyAbstract:Background: Atherosclerosis is characterized by subendothelial lipid deposition, leukocyte infiltration, and smooth muscle proliferation that may lead to plaque rupture and atherothrombosis, a majo...
-
Removal of the C-terminal domains of ADAMTS13 by activated Coagulation Factor XI induces platelet adhesion on endothelial cells under flow conditions
Frontiers in medicine, 2017Co-Authors: Kathleen S. Garland, Andras Gruber, Jevgenia Zilberman-rudenko, David Gailani, Erik I. Tucker, Owen J. T. Mccarty, Stephanie E Reitsma, Toshiaki Shirai, Cristina PuyAbstract:Platelet recruitment to sites of vascular injury is mediated by von Willebrand Factor (VWF). The shear-induced unraveling of ultra-large VWF multimers causes the formation of a "stringlike" conformation, which rapidly recruits platelets from the bloodstream. A disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) regulates this process by cleaving VWF to prevent aberrant platelet adhesion; it is unclear whether the activity of ADAMTS13 itself is regulated. The serine proteases α-thrombin and plasmin have been shown to cleave ADAMTS13. Based on sequence homology, we hypothesized that activated Coagulation Factor XI (FXIa) would likewise cleave ADAMTS13. Our results show that FXIa cleaves ADAMTS13 at the C-terminal domains, generating a truncated ADAMTS13 with a deletion of part of the thrombospondin type-1 domain and the CUB1-2 domains, while α-thrombin cleaves ADAMTS13 near the CUB1-2 domains and plasmin cleaves ADAMTS13 at the metalloprotease domain and at the C-terminal domain. Using a cell surface immunoassay, we observed that FXIa induced the deletion of the CUB1-2 domains from ADAMTS13 on the surface of endothelial cells. Removal of the C-terminal domain of ADAMTS13 by FXIa or α-thrombin caused an increase in ADAMTS13 activity as measured by a fluorogenic substrate (FRETS) and blocked the ability of ADAMTS13 to cleave VWF on the endothelial cell surface, resulting in persistence of VWF strands and causing an increase in platelet adhesion under flow conditions. We have demonstrated a novel mechanism for Coagulation proteinases including FXIa in regulating ADAMTS13 activity and function. This may represent an additional hemostatic function by which FXIa promotes local platelet deposition at sites of vessel injury.
-
platelet derived short chain polyphosphates enhance the inactivation of tissue Factor pathway inhibitor by activated Coagulation Factor XI
PLOS ONE, 2016Co-Authors: Cristina Puy, Andras Gruber, David Gailani, Erik I. Tucker, Stephanie A. Smith, James H. Morrissey, Ivan Ivanov, Owen J. T. MccartyAbstract:INTRODUCTION Factor (F) XI supports both normal human hemostasis and pathological thrombosis. Activated FXI (FXIa) promotes thrombin generation by enzymatic activation of FXI, FIX, FX, and FV, and inactivation of alpha tissue Factor pathway inhibitor (TFPIα), in vitro. Some of these reactions are now known to be enhanced by short-chain polyphosphates (SCP) derived from activated platelets. These SCPs act as a coFactor for the activation of FXI and FV by thrombin and FXIa, respectively. Since SCPs have been shown to inhibit the anticoagulant function of TFPIα, we herein investigated whether SCPs could serve as coFactors for the proteolytic inactivation of TFPIα by FXIa, further promoting the efficiency of the extrinsic pathway of Coagulation to generate thrombin. METHODS AND RESULTS Purified soluble SCP was prepared by size-fractionation of sodium polyphosphate. TFPIα proteolysis was analyzed by western blot. TFPIα activity was measured as inhibition of FX activation and activity in Coagulation and chromogenic assays. SCPs significantly accelerated the rate of inactivation of TFPIα by FXIa in both purified systems and in recalcified plasma. Moreover, platelet-derived SCP accelerated the rate of inactivation of platelet-derived TFPIα by FXIa. TFPIα activity was not affected by SCP in recalcified FXI-depleted plasma. CONCLUSIONS Our data suggest that SCP is a coFactor for TFPIα inactivation by FXIa, thus, expanding the range of hemostatic FXIa substrates that may be affected by the coFactor functions of platelet-derived SCP.
-
Abstract 56: Coagulation Factor XI Promotes Distal Platelet Activation and Single Platelet Consumption in the Bloodstream Under Shear Flow
Arteriosclerosis Thrombosis and Vascular Biology, 2016Co-Authors: Jevgenia Zilberman-rudenko, Asako Itakura, Chantal P Wiesenekker, Owen J. T. MccartyAbstract:Objective: Coagulation Factor XI (FXI) has been shown to contribute to thrombus formation on collagen or tissue Factor (TF)-coated surfaces in vitro and in vivo by enhancing thrombin generation. Whether the role of the intrinsic pathway of Coagulation is restricted to the local site of thrombus formation is unknown. This study was designed to determine whether FXI could promote both proXImal and distal platelet activation and aggregate formation in the bloodstream. Approach and Results: Pharmacological blockade of FXI activation or thrombin activity in blood did not affect local platelet adhesion, yet reduced local platelet aggregation, thrombin localization and fibrin formation on immobilized collagen and TF under shear flow, ex vivo. Downstream of the thrombus formed on immobilized collagen or collagen and 10 pM TF, platelet CD62P expression and microaggregate formation and progressive platelet consumption were significantly reduced in the presence of FXI-function blocking antibodies or a thrombin inhib...
Elaine Gray - One of the best experts on this subject based on the ideXlab platform.
-
Establishment of the World Health Organization First International Standard for Factor XII, Plasma, Human.
Frontiers in medicine, 2017Co-Authors: Helen V. Wilmot, Peter Rigsby, Jason Hockley, Elaine GrayAbstract:The 1st International Standard (IS) for Blood Coagulation Factor XI, Plasma, has been successfully used for potency labelling of Factor XI (FXI) therapeutics and for diagnosis of FXI deficiency in patients. With stocks of the 1st IS near depletion, a replacement is required. In addition to the functional activity value, assignment of an antigen value to the 2nd IS would allow harmonization of antigen assay methods and differentiation of patients who have low functional activity but normal antigen FXI levels from patients who have both low functional and antigen FXI levels. The aims of this study were therefore to assign FXI functional activity to the 2nd IS for Factor XI, Plasma, and to additionally assign a new analyte, FXI antigen, to the same International Standard. The candidate material was prepared from double-spun, virology negative, normal plasma which was pooled and filled into siliconized glass ampoules and subsequently freeze-dried. Assignment of the functional activity (FXI:C) value in International Units (IU) was performed by one-stage clotting assay by 29 laboratories, relative to the 1st IS. The overall geometric mean was 0.71 IU/ampoule with extremely low inter-laboratory variability (expressed as geometric coefficient of variation) of 1.8%. The antigen value assignment was performed by 11 laboratories and was calculated relative to normal plasma pools, as is customary with new Coagulation Factor analytes. The amount of antigen present in 1 ml of normal plasma was taken to be 1 unit. The overall geometric mean for the antigen assays was 0.78 IU/ampoule with an inter-laboratory variation of 10%. The candidate (15/180) was established by the World Health Organization (WHO) Expert Committee on Biological Standardization (ECBS) in 2016 as the WHO 2nd IS for Blood Coagulation Factor XI, Plasma, with a functional activity value (FXI:C) of 0.71 IU/ampoule and an antigen value (FXI:Ag) of 0.78 IU/ampoule.
-
ASSIGNMENT OF POTENCY TO THE WHO 1 ST INTERNATIONAL STANDARD FOR BLOOD Coagulation Factor XI IN PLASMA, HUMAN (04/102) AND CALIBRATION OF BLOOD Coagulation Factor XI IN SSC SECONDARY PLASMA STANDARD LOT #3
2017Co-Authors: Only, Elaine Gray, Stephen Thomas, Peter RigsbyAbstract:INTERNATIONAL STANDARD FOR BLOOD Coagulation Factor XI IN PLASMA, HUMAN (04/102) AND CALIBRATION OF BLOOD Coagulation Factor XI IN SSC SECONDARY PLASMA STANDARD LOT #3 Elaine Gray, Stephen Thomas and Peter Rigsby* Division of Haematology and *Biostatistics Section National Institute for Biological Standards and Control Potters Bar, Hertfordshire, UK. SUMMARY
-
assignment of potency to the who 1 st international standard for blood Coagulation Factor XI in plasma human 04 102 and calibration of blood Coagulation Factor XI in ssc secondary plasma standard lot 3
2017Co-Authors: English Only, Elaine Gray, Stephen Thomas, Peter RigsbyAbstract:INTERNATIONAL STANDARD FOR BLOOD Coagulation Factor XI IN PLASMA, HUMAN (04/102) AND CALIBRATION OF BLOOD Coagulation Factor XI IN SSC SECONDARY PLASMA STANDARD LOT #3 Elaine Gray, Stephen Thomas and Peter Rigsby* Division of Haematology and *Biostatistics Section National Institute for Biological Standards and Control Potters Bar, Hertfordshire, UK. SUMMARY
Erik I. Tucker - One of the best experts on this subject based on the ideXlab platform.
-
Role of platelets in regulating activated Coagulation Factor XI activity.
American journal of physiology. Cell physiology, 2021Co-Authors: Stephanie E Reitsma, Andras Gruber, David Gailani, Erik I. Tucker, Owen J. T. Mccarty, Jiaqing Pang, Vikram Raghunathan, Joseph J. Shatzel, Christina U. Lorentz, Cristina PuyAbstract:Factor XI (FXI) has been shown to bind platelets, but the functional significance of this observation remains unknown. Platelets are essential for hemostasis and play a critical role in thrombosis, whereas FXI is not essential for hemostasis but promotes thrombosis. An apparent functional contradiction, platelets are known to support thrombin generation, yet platelet granules release protease inhibitors, including those of activated FXI (FXIa). We aim to investigate the secretory and binding mechanisms by which platelets could support or inhibit FXIa activity. The presence of platelets enhanced FXIa activity in a purified system and increased Coagulation Factor IX (FIX) activation by FXIa and fibrin generation in human plasma. In contrast, platelets reduced the activation of FXI by activated Coagulation Factor XII (FXIIa) and the activation of FXII by kallikrein (PKa). Incubation of FXIa with the platelet secretome, which contains FXIa inhibitors, such as protease neXIn-II, abolished FXIa activity, yet in the presence of activated platelets, the secretome was not able to block the activity of FXIa. FXIa variants lacking the anion-binding sites did not alter the effect of platelets on FXIa activity or interaction. Western blot analysis of bound FXIa [by FXIa-platelet membrane immunoprecipitation] showed that the interaction with platelets is zinc dependent and, unlike FXI binding to platelets, not dependent on glycoprotein Ib. FXIa binding to the platelet membrane increases its capacity to activate FIX in plasma likely by protecting it from inhibition by inhibitors secreted by activated platelets. Our findings suggest that an interaction of FXIa with the platelet surface may induce an allosteric modulation of FXIa.
-
abstract 661 role of Coagulation Factor XI in regulating endothelial cell barrier function
Arteriosclerosis Thrombosis and Vascular Biology, 2019Co-Authors: Anh T P Ngo, Andras Gruber, Erik I. Tucker, Cristina Puy, Jiaqing Pang, Christina U. Lorentz, Norah G Verbout, Courtney Howard, Hagai Tavori, Owen J. T. MccartyAbstract:Background: Atherosclerosis is characterized by subendothelial lipid deposition, leukocyte infiltration, and smooth muscle proliferation that may lead to plaque rupture and atherothrombosis, a majo...
-
Removal of the C-terminal domains of ADAMTS13 by activated Coagulation Factor XI induces platelet adhesion on endothelial cells under flow conditions
Frontiers in medicine, 2017Co-Authors: Kathleen S. Garland, Andras Gruber, Jevgenia Zilberman-rudenko, David Gailani, Erik I. Tucker, Owen J. T. Mccarty, Stephanie E Reitsma, Toshiaki Shirai, Cristina PuyAbstract:Platelet recruitment to sites of vascular injury is mediated by von Willebrand Factor (VWF). The shear-induced unraveling of ultra-large VWF multimers causes the formation of a "stringlike" conformation, which rapidly recruits platelets from the bloodstream. A disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) regulates this process by cleaving VWF to prevent aberrant platelet adhesion; it is unclear whether the activity of ADAMTS13 itself is regulated. The serine proteases α-thrombin and plasmin have been shown to cleave ADAMTS13. Based on sequence homology, we hypothesized that activated Coagulation Factor XI (FXIa) would likewise cleave ADAMTS13. Our results show that FXIa cleaves ADAMTS13 at the C-terminal domains, generating a truncated ADAMTS13 with a deletion of part of the thrombospondin type-1 domain and the CUB1-2 domains, while α-thrombin cleaves ADAMTS13 near the CUB1-2 domains and plasmin cleaves ADAMTS13 at the metalloprotease domain and at the C-terminal domain. Using a cell surface immunoassay, we observed that FXIa induced the deletion of the CUB1-2 domains from ADAMTS13 on the surface of endothelial cells. Removal of the C-terminal domain of ADAMTS13 by FXIa or α-thrombin caused an increase in ADAMTS13 activity as measured by a fluorogenic substrate (FRETS) and blocked the ability of ADAMTS13 to cleave VWF on the endothelial cell surface, resulting in persistence of VWF strands and causing an increase in platelet adhesion under flow conditions. We have demonstrated a novel mechanism for Coagulation proteinases including FXIa in regulating ADAMTS13 activity and function. This may represent an additional hemostatic function by which FXIa promotes local platelet deposition at sites of vessel injury.
-
platelet derived short chain polyphosphates enhance the inactivation of tissue Factor pathway inhibitor by activated Coagulation Factor XI
PLOS ONE, 2016Co-Authors: Cristina Puy, Andras Gruber, David Gailani, Erik I. Tucker, Stephanie A. Smith, James H. Morrissey, Ivan Ivanov, Owen J. T. MccartyAbstract:INTRODUCTION Factor (F) XI supports both normal human hemostasis and pathological thrombosis. Activated FXI (FXIa) promotes thrombin generation by enzymatic activation of FXI, FIX, FX, and FV, and inactivation of alpha tissue Factor pathway inhibitor (TFPIα), in vitro. Some of these reactions are now known to be enhanced by short-chain polyphosphates (SCP) derived from activated platelets. These SCPs act as a coFactor for the activation of FXI and FV by thrombin and FXIa, respectively. Since SCPs have been shown to inhibit the anticoagulant function of TFPIα, we herein investigated whether SCPs could serve as coFactors for the proteolytic inactivation of TFPIα by FXIa, further promoting the efficiency of the extrinsic pathway of Coagulation to generate thrombin. METHODS AND RESULTS Purified soluble SCP was prepared by size-fractionation of sodium polyphosphate. TFPIα proteolysis was analyzed by western blot. TFPIα activity was measured as inhibition of FX activation and activity in Coagulation and chromogenic assays. SCPs significantly accelerated the rate of inactivation of TFPIα by FXIa in both purified systems and in recalcified plasma. Moreover, platelet-derived SCP accelerated the rate of inactivation of platelet-derived TFPIα by FXIa. TFPIα activity was not affected by SCP in recalcified FXI-depleted plasma. CONCLUSIONS Our data suggest that SCP is a coFactor for TFPIα inactivation by FXIa, thus, expanding the range of hemostatic FXIa substrates that may be affected by the coFactor functions of platelet-derived SCP.
-
Coagulation Factor XI Promotes Distal Platelet Activation and Single Platelet Consumption in the Bloodstream Under Shear Flow
Arteriosclerosis thrombosis and vascular biology, 2016Co-Authors: Jevgenia Zilberman-rudenko, Andras Gruber, Asako Itakura, Chantal P Wiesenekker, Ralf Vetter, Coen Maas, David Gailani, Erik I. Tucker, Christoph Gerdes, Owen J. T. MccartyAbstract:Objective—Coagulation Factor XI (FXI) has been shown to contribute to thrombus formation on collagen or tissue Factor–coated surfaces in vitro and in vivo by enhancing thrombin generation. Whether the role of the intrinsic pathway of Coagulation is restricted to the local site of thrombus formation is unknown. This study was aimed to determine whether FXI could promote both proXImal and distal platelet activation and aggregate formation in the bloodstream. Approach and Results—Pharmacological blockade of FXI activation or thrombin activity in blood did not affect local platelet adhesion, yet reduced local platelet aggregation, thrombin localization, and fibrin formation on immobilized collagen and tissue Factor under shear flow, ex vivo. Downstream of the thrombus formed on immobilized collagen or collagen and 10 pmol/L tissue Factor, platelet CD62P expression, microaggregate formation, and progressive platelet consumption were significantly reduced in the presence of FXI function-blocking antibodies or a...
Peter Rigsby - One of the best experts on this subject based on the ideXlab platform.
-
Establishment of the World Health Organization First International Standard for Factor XII, Plasma, Human.
Frontiers in medicine, 2017Co-Authors: Helen V. Wilmot, Peter Rigsby, Jason Hockley, Elaine GrayAbstract:The 1st International Standard (IS) for Blood Coagulation Factor XI, Plasma, has been successfully used for potency labelling of Factor XI (FXI) therapeutics and for diagnosis of FXI deficiency in patients. With stocks of the 1st IS near depletion, a replacement is required. In addition to the functional activity value, assignment of an antigen value to the 2nd IS would allow harmonization of antigen assay methods and differentiation of patients who have low functional activity but normal antigen FXI levels from patients who have both low functional and antigen FXI levels. The aims of this study were therefore to assign FXI functional activity to the 2nd IS for Factor XI, Plasma, and to additionally assign a new analyte, FXI antigen, to the same International Standard. The candidate material was prepared from double-spun, virology negative, normal plasma which was pooled and filled into siliconized glass ampoules and subsequently freeze-dried. Assignment of the functional activity (FXI:C) value in International Units (IU) was performed by one-stage clotting assay by 29 laboratories, relative to the 1st IS. The overall geometric mean was 0.71 IU/ampoule with extremely low inter-laboratory variability (expressed as geometric coefficient of variation) of 1.8%. The antigen value assignment was performed by 11 laboratories and was calculated relative to normal plasma pools, as is customary with new Coagulation Factor analytes. The amount of antigen present in 1 ml of normal plasma was taken to be 1 unit. The overall geometric mean for the antigen assays was 0.78 IU/ampoule with an inter-laboratory variation of 10%. The candidate (15/180) was established by the World Health Organization (WHO) Expert Committee on Biological Standardization (ECBS) in 2016 as the WHO 2nd IS for Blood Coagulation Factor XI, Plasma, with a functional activity value (FXI:C) of 0.71 IU/ampoule and an antigen value (FXI:Ag) of 0.78 IU/ampoule.
-
ASSIGNMENT OF POTENCY TO THE WHO 1 ST INTERNATIONAL STANDARD FOR BLOOD Coagulation Factor XI IN PLASMA, HUMAN (04/102) AND CALIBRATION OF BLOOD Coagulation Factor XI IN SSC SECONDARY PLASMA STANDARD LOT #3
2017Co-Authors: Only, Elaine Gray, Stephen Thomas, Peter RigsbyAbstract:INTERNATIONAL STANDARD FOR BLOOD Coagulation Factor XI IN PLASMA, HUMAN (04/102) AND CALIBRATION OF BLOOD Coagulation Factor XI IN SSC SECONDARY PLASMA STANDARD LOT #3 Elaine Gray, Stephen Thomas and Peter Rigsby* Division of Haematology and *Biostatistics Section National Institute for Biological Standards and Control Potters Bar, Hertfordshire, UK. SUMMARY
-
assignment of potency to the who 1 st international standard for blood Coagulation Factor XI in plasma human 04 102 and calibration of blood Coagulation Factor XI in ssc secondary plasma standard lot 3
2017Co-Authors: English Only, Elaine Gray, Stephen Thomas, Peter RigsbyAbstract:INTERNATIONAL STANDARD FOR BLOOD Coagulation Factor XI IN PLASMA, HUMAN (04/102) AND CALIBRATION OF BLOOD Coagulation Factor XI IN SSC SECONDARY PLASMA STANDARD LOT #3 Elaine Gray, Stephen Thomas and Peter Rigsby* Division of Haematology and *Biostatistics Section National Institute for Biological Standards and Control Potters Bar, Hertfordshire, UK. SUMMARY