Corn Trypsin Inhibitor Research Articles

Assessment of the protein interaction between coagulation factor XII and corn trypsin inhibitor by molecular docking and biochemical validation

Essentials Corn Trypsin Inhibitor (CTI) is a selective inhibitor of coagulation Factor XII (FXII).Molecular modelling of the CTI‐FXIIa complex suggested a canonical inhibitor binding mode.Mutagenesis revealed the CTI inhibitory loop and helices α1 and α2 mediate the interaction.This confirms that CTI inhibits FXII in canonical fashion and validates the molecular model. SummaryBackgroundCorn trypsin inhibitor (CTI) has selectivity for the serine proteases coagulation factor XII and trypsin. CTI is in widespread use as a reagent that specifically inhibits the intrinsic pathway of blood coagulation but not the extrinsic pathway.ObjectivesTo investigate the molecular basis of FXII inhibition by CTI.MethodsWe performed molecular docking of CTI, using its known crystal structure, with a model of the activated FXII (FXIIa) protease domain. The interaction model was verified by use of a panel of recombinant CTI variants tested for their ability to inhibit FXIIa enzymatic activity in a substrate cleavage assay.ResultsThe docking predicted that: (i) the CTI central inhibitory loop P1 Arg34 side chain forms a salt bridge with the FXIIa S1 pocket Asp189 side chain; (ii) Trp22 from CTI helix α1 interacts with the FXIIa S3 pocket; and (iii) Arg43 from CTI helix α2 forms a salt bridge with FXIIa H1 pocket Asp60A. CTI amino acid substitution R34A negated all inhibitory activity, whereas the G32W, L35A, W22A and R42A/R43A substitutions reduced activity by large degrees of 108‐fold, 41‐fold, 158‐fold, and 100‐fold, respectively; the R27A, W37A, W39A and R42A substitutions had no effect. Synthetic peptides spanning CTI residues 20–44 had inhibitory activity that was three‐fold to 4000‐fold less than that of full‐length CTI.ConclusionsThe data confirm the validity of a canonical model of the FXIIa–CTI interaction, with helix α1 (Trp22), central inhibitory loop (Arg34) and helix α2 (Arg43) of CTI being required for effective binding by contacting the S1, S3 and H1 pockets of FXIIa, respectively.

The pharmacokinetics and pharmacodynamics of single-dose and multiple-dose recombinant activated factor VII in patients with haemophilia A or B.

To compare the pharmacokinetics (PK) of rFVIIa after 3×90μgkg-1 doses vs a single dose (270μgkg-1 ) in haemophilia patients and to evaluate TEG/TGA results postdosing to determine how these assays relate to PK findings. Patients in this open-label, single-centre, randomized, crossover trial received one injection of 270μgkg-1 rFVIIa crossed over with three injections of 90μgkg-1 rFVIIa in a non-bleeding state. For TEG, kaolin and tissue factor were used as activators; TGA was performed on frozen platelet-rich and platelet-poor plasma, with and without corn trypsin inhibitor. FVIIa activity was evaluated using in vivo samples. TGA showed a dose-dependent effect of rFVIIa on thrombin generation; TEG revealed lower dose-dependent effects. Both showed some differences between single-/multiple-dose rFVIIa; both supported the PK findings. While TEG and TGA are not yet clinically predictive, both supported the PK results. Data suggest that, while a single dose of 270μgkg-1 rFVIIa provides slightly higher haemostatic potential than the multiple-dose regimen of 3×90μgkg-1 , the latter results in prolonged activity levels compared with a higher single dose.

Alginate microbeads are coagulation compatible, while alginate microcapsules activate coagulation secondary to complement or directly through FXII.

Alginate microcapsules are prospective candidate materials for cell encapsulation therapy. The material surface must be free of host cell adhesion to ensure free diffusion of nutrition and oxygen to the encapsulated cells. Coagulation activation is one gateway to cellular overgrowth through deposition of fibrin. Herein we used a physiologically relevant whole blood model to investigate the coagulation potential of alginate microcapsules and microbeads. The coagulation potentials and the pathways of activation were depending on the surface properties of the materials. Activation of the complement system could also be involved, thus emphasizing a complement-coagulation cross-talk. Our findings points to complement and coagulation inhibition as intervention point for preventing host reactions, and enhance functional cell-encapsulation devices.

Recombinant factor VIIa addition to haemophilic blood perfused over collagen/tissue factor can sufficiently bypass the factor IXa/VIIIa defect to rescue fibrin generation.

Factor VIII (FVIII) or factor IX (FIX)-deficient haemophilic patients display deficits in platelet and fibrin deposition under flow detectable in microfluidics. Compared to fibrin generation, decreased platelet deposition in haemophilic blood flow is more easily rescued with recombinant factor VIIa (rFVIIa), whereas rFVIIa requires FXIIa participation to generate fibrin when tissue factor (TF) is absent. Perfusion of haemophilic whole blood (WB) over collagen/TF surfaces was used to determine whether rFVIIa/TF was sufficient to bypass poor FIXa/FVIIIa function in blood from patients with haemophilia A and B. Whole blood treated with high-dose corn trypsin inhibitor (40 μg mL-1 ) from seven healthy donors and 10 patients was perfused over fibrillar collagen presenting low or high TF (TFlow or TFhigh ) at wall shear rate of 100 s-1 . With WB from healthy controls, platelet deposition and fibrin accumulation increased as TF increased. Factor-deficient WB (1-3% of normal) displayed striking deficits in platelet deposition and fibrin formation at either TFlow or TFhigh . In contrast, mildly factor-deficient WB (14-32%) supported fibrin formation under flow on TFhigh /collagen. With either TFlow or TFhigh , exogenously added rFVIIa (20 nm) increased platelet deposition and fibrin accumulation in WB from factor-deficient patients (1-3% of normal) to levels commensurate with untreated healthy WB. The absence of FIXa/FVIIIa in patients with severe haemophilia results in deficits in fibrin formation that cannot be rescued by wall-derived TF ex vivo. The effects of rFVIIa on platelet adhesion and rFVIIa/TF can act together to reinforce thrombin generation, platelet deposition and fibrin formation under flow.

A Microfluidic Flow Chamber Model for Platelet Transfusion and Hemostasis Measures Platelet Deposition and Fibrin Formation in Real-time

Microfluidic models of hemostasis assess platelet function under conditions of hydrodynamic shear, but in the presence of anticoagulants, this analysis is restricted to platelet deposition only. The intricate relationship between Ca2+-dependent coagulation and platelet function requires careful and controlled recalcification of blood prior to analysis. Our setup uses a Y-shaped mixing channel, which supplies concentrated Ca2+/Mg2+ buffer to flowing blood just prior to perfusion, enabling rapid recalcification without sample stasis. A ten-fold difference in flow velocity between both reservoirs minimizes dilution. The recalcified blood is then perfused in a collagen-coated analysis chamber, and differential labeling permits real-time imaging of both platelet and fibrin deposition using fluorescence video microscopy. The system uses only commercially available tools, increasing the chances of standardization. Reconstitution of thrombocytopenic blood with platelets from banked concentrates furthermore models platelet transfusion, proving its use in this research domain. Exemplary data demonstrated that coagulation onset and fibrin deposition were linearly dependent on the platelet concentration, confirming the relationship between primary and secondary hemostasis in our model. In a timeframe of 16 perfusion min, contact activation did not take place, despite recalcification to normal Ca2+ and Mg2+ levels. When coagulation factor XIIa was inhibited by corn trypsin inhibitor, this time frame was even longer, indicating a considerable dynamic range in which the changes in the procoagulant nature of the platelets can be assessed. Co-immobilization of tissue factor with collagen significantly reduced the time to onset of coagulation, but not its rate. The option to study the tissue factor and/or the contact pathway increases the versatility and utility of the assay.

A Microfluidic Flow Chamber Model for Platelet Transfusion and Hemostasis Measures Platelet Deposition and Fibrin Formation in Real-time.

Microfluidic models of hemostasis assess platelet function under conditions of hydrodynamic shear, but in the presence of anticoagulants, this analysis is restricted to platelet deposition only. The intricate relationship between Ca2+-dependent coagulation and platelet function requires careful and controlled recalcification of blood prior to analysis. Our setup uses a Y-shaped mixing channel, which supplies concentrated Ca2+/Mg2+ buffer to flowing blood just prior to perfusion, enabling rapid recalcification without sample stasis. A ten-fold difference in flow velocity between both reservoirs minimizes dilution. The recalcified blood is then perfused in a collagen-coated analysis chamber, and differential labeling permits real-time imaging of both platelet and fibrin deposition using fluorescence video microscopy. The system uses only commercially available tools, increasing the chances of standardization. Reconstitution of thrombocytopenic blood with platelets from banked concentrates furthermore models platelet transfusion, proving its use in this research domain. Exemplary data demonstrated that coagulation onset and fibrin deposition were linearly dependent on the platelet concentration, confirming the relationship between primary and secondary hemostasis in our model. In a timeframe of 16 perfusion min, contact activation did not take place, despite recalcification to normal Ca2+ and Mg2+ levels. When coagulation factor XIIa was inhibited by corn trypsin inhibitor, this time frame was even longer, indicating a considerable dynamic range in which the changes in the procoagulant nature of the platelets can be assessed. Co-immobilization of tissue factor with collagen significantly reduced the time to onset of coagulation, but not its rate. The option to study the tissue factor and/or the contact pathway increases the versatility and utility of the assay.

Elevated plasma TFPI activity causes attenuated TF-dependent thrombin generation in early onset preeclampsia.

Early onset preeclampsia (EOP) is a pregnancy-specific proinflammatory disorder that is characterised by competing thrombotic and bleeding risks. It was the aim of this study to characterise thrombin generation, a major determinant of thrombotic and bleeding risk, in order to better understand the haemostatic balance in patients with EOP. Patients with EOP were recruited at the Rotunda Hospital, Dublin. Twenty-six cases of EOP were recruited over a 21-month period, out of 15,299 deliveries at the Rotunda. Blood samples were collected into sodium citrate plus corn trypsin inhibitor anticoagulated vacutainers, platelet-poor plasma was prepared, and calibrated automated thrombography was used to assess thrombin generation. Results were compared to age and sex-matched non-pregnant controls (n=13) and age- and gestation-matched pregnant controls (n=20). The rate and extent of thrombin generation triggered by low-dose tissue factor (TF) was significantly reduced in patients with EOP compared to pregnant controls, most significantly in cases of severe EOP. EOP patients displayed a trend towards an increased response to endogenous activated protein C and thrombomodulin relative to pregnant controls. Plasma tissue factor pathway inhibitor (TFPI) activity was increased in EOP patients. Inhibition of TFPI abolished the attenuation of thrombin generation stimulated by low-dose TF. In conclusion, patients with EOP are characterised by an attenuated coagulation response characterised by reduced thrombin generation stimulated by low-dose TF and elevated plasma TFPI activity. These changes in coagulation may modulate thrombotic risk and bleeding risk in patients with EOP.

Analysis of the substrate specificity of Factor VII activating protease (FSAP) and design of specific and sensitive peptide substrates.

Factor VII (FVII) activating protease (FSAP) is a circulating serine protease that is likely to be involved in a number of disease conditions such as stroke, atherosclerosis, liver fibrosis, thrombosis and cancer. To date, no systematic information is available about the substrate specificity of FSAP. Applying phage display and positional scanning substrate combinatorial library (PS-SCL) approaches we have characterised the specificity of FSAP towards small peptides. Results were evaluated in the context of known protein substrates as well as molecular modelling of the peptides in the active site of FSAP. The representative FSAP-cleaved sequence obtained from the phage display method was Val-Leu-Lys-Arg-Ser (P4-P1'). The sequence X-Lys/Arg-Nle-Lys/Arg (P4-P1) was derived from the PS-SCL method. These results show a predilection for cleavage at a cluster of basic amino acids on the nonprime side. Quenched fluorescent substrate (Ala-Lys-Nle-Arg-AMC) (amino methyl coumarin) and (Ala-Leu-Lys-Arg-AMC) had a higher selectivity for FSAP compared to other proteases from the hemostasis system. These substrates could be used to measure FSAP activity in a complex biological system such as plasma. In histone-treated plasma there was a specific activation of pro-FSAP as validated by the use of an FSAP inhibitory antibody, corn trypsin inhibitor to inhibit Factor XIIa and hirudin to inhibit thrombin, which may account for some of the haemostasis-related effects of histones. These results will aid the development of further selective FSAP activity probes as well as specific inhibitors that will help to increase the understanding of the functions of FSAP in vivo.

Continuous Thrombin Generation in Whole Blood: New Applications

Background.Hemostatic tests have been utilized to clarify the blood coagulation potential of both healthy and diseased individuals. They include tests for whole blood and plasma clotting times, coagulation and fibrinolytic factors and, recently, thrombin generation (TG). TG assays provide explicit information and remain the most physiologically-relevant hemostatic tests ex vivo. We have currently been using a TG assay in whole blood, described by Ninivaggi et al. (2012), for the evaluation of several hemostatic agents and disorders of blood coagulation.Methods.Whole blood from either healthy donors or trauma patients was drawn into 3.2% sodium citrate [± 0.1 mg/mL corn trypsin inhibitor (CTI) prior to the assay; prevents contact pathway activation] or into 3.2% sodium citrate/0.1 mg/mL CTI. Selected agents were added to blood prior to recalcification and TG was monitored in a fluorogenic assay.Packed red blood cells (pRBC) from healthy donors were reconstituted with platelet-poor plasma (PPP) and treated with 0.1 mg/mL CTI. TG was monitored in the absence of any exogenous initiation, in the presence of 5 pM TF initiation and also in the presence of synthetic phospholipids.Results.Whole BloodA. Blood from 10 healthy donors was collected into both citrate (with CTI added prior to the assay) and CTI/citrate and TG was monitored ± 5 pM relipidated tissue factor (TF) initiation. In the absence of TF, blood collected into citrate led to a lag phase ~3-fold longer than that in the presence of TF and peak thrombin ~1.4-fold lower. Blood collected into CTI/citrate, in the absence of TF, led to a lag phase ~6.4-fold longer than that in the presence of TF and peak thrombin ~4.3-fold lower.B. Titrations of relipidated TF and FXIa into citrated blood containing CTI led to concentration-dependent changes in the duration of the lag phase.C. Several TG antagonists were evaluated in citrated blood containing CTI triggered with 5 pM TF.a. 0.5 U/mL unfractionated heparin prolonged the lag phase ~2-fold and suppressed the peak thrombin ~3-fold.b. Hemophilia A and B were "induced" via the addition of inhibitory antibodies to FVIII and FIX, respectively, and although the lag phase was not altered both additions led to significant TG suppression with peak thrombin dropping ~3-fold.c. Several thrombin and FXa inhibitors were evaluated at their pharmacologic concentrations. Fondaparinux slightly prolonged the lag phase, whereas dabigatran increased it by 2.6-fold. Rivaroxaban doubled the lag phase while bivalirudin was slightly less efficient. None of these inhibitors had a pronounced effect on the rate and peak value of TG.d. Activated protein C (APC) at 10 nM slightly prolonged the lag phase and suppressed the peak thrombin.D. Citrate blood from a trauma patient was tested for endogenous activity. In the presence of CTI and absence of an initiator, α-TF antibody did not alter TG, indicating the absence of functional TF. α-FXIa antibody prolonged the lag phase and suppressed TG and α-FIXa antibody completely abolished TG, indicating the presence of active FXIa and FIXa.Packed Red Blood Cells (pRBC)In the absence of an initiator, no TG was observed in pRBC/CTI reconstituted with PPP. The addition of 5 pM TF led to TG after ~8 min with a peak value slightly lower than in blood (described in A).The addition of phospholipids did not change the TG profile.Conclusions.This continuous whole blood TG assay requires 15 µL of blood for a triplicate analysis of a single condition and has the potential for the evaluation of TG in disorders relevant to blood coagulation and for the monitoring of treatments administered in response to these disorders. DisclosuresMann:Haematologic Technologies, Inc.: Employment, Equity Ownership; Baxter: Consultancy; Bayer: Consultancy; Biogen IDEC: Consultancy; CSL Behring: Consultancy; Merck: Consultancy; Pfizer: Consultancy; The Medicines Company: Consultancy; XO1: Consultancy; Vascular Solutions: Consultancy; Stago: Consultancy.

Neutrophil Extracelluar Traps Contributes to the Hypercoagulable State and Liver Damage in Liver Cirrhosis

Background: We recently reported that phosphatidylserine on blood and endothelial cells played an important role in the hypercoagulable state of liver cirrhosis (Wu et al, Liver Int 2016). Recent studies showed that enoxaparin could reduce the incidence of portal vein thrombosis and alleviate liver decompensation. Thus, we speculate that there may be other mechanisms involved in the hypercoagulability of cirrhosis. Neutrophil extracelluar traps (NETs) play an important role in thrombosis and organ dysfunction. Whether the benefit of enoxaparin is due to inhibiting NETs in cirrhotic patients remains unknown. Our objectives were to study the formation of NETs and their role in the hypercoagulable state and liver damage in cirrhotic patients.Methods:Cirrhotic patients (n = 36), healthy controls (n = 10), and mice treated with CCl4 (n = 50) were studied. Immunofluorescence confocal microscope was used to analyze and quantify NETs formation in neutrophil cells from human and mice. TAT and fibrin formation assays in normal and cirrhotic plasma were performed to analyze the procoagulant activity of NETs. Calibrated automated thrombography (CAT) was performed with and without 6 nM thrombomodulin I to analyze TM resistance changes induced by NETs. Liver injury was assessed by plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activity, determined spectrophotometrically, and by morphometric evaluation of left lateral liver lobes. DNase I and activated protein C (APC) were used to abolish NETs.Results: We observed that cirrhotic platelets induced 1.9 fold higher NETs formation in neutrophil cells (p = 0.021). Increased NETs promoted higher TAT (Fig 1A, B) and fibrin formation in normal and cirrhotic plasma (p < 0.05). DNase I abolished the procoagulant activity of NETs in corn trypsin inhibitor (CTI ) or anti-TF pre-treated plasma (p < 0.001) (Fig 1C). TM pre-induced with NETs for 24 h showed a higher endogenous thrombin potential (ETP) than no treatment in normal plasma using CAT (p = 0.032). APC and de-N-sulfated heparin (de-N-Hep), but not DNase I, can decrease the ETP ratio (with/without TM) in cirrhotic plasma (p < 0.05) (Fig 1D). Mice treated with CCl4 showed a higher ALT, AST, necrotic area (Fig 2), and NETs formation than control (p < 0.05). DNase I and enoxaparin decreased ALT, AST, necrotic area (Fig 2) and NETs formation (p < 0.05).Conclusions:Cirrhotic patients have enhanced NETs formation compared to healthy controls. NETs initiated intrinsic and extrinsic coagulation pathway and impaired anticoagulant function of TM. Additionally, NETs partly contributed to tissue injury in the liver of cirrhotic mice. DNase I and enoxaparin can disconnect NETs and decreased the toxin to liver. [Display omitted] [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

A Novel Beneficial Role for Macitentan in Patients at High Thrombosis Risk: Attenuation of Platelet-Mediated Derangements of Blood Coagulation in Eisenmenger Syndrome

IntroductionEisenmenger syndrome is a rare manifestation of congenital cardiac disease with pulmonary hypertension. Potentially dangerous thrombotic and haemorrhagic complications frequently occur in patients with ES and raise significant clinical dilemmas. Underlying mechanisms are unknown but are thought to be linked to the underlying pulmonary vascular disease. Endothelin-1 (ET-1) signalling in the pulmonary vasculature is implicated in the pathogenesis of ES and Macitentan (a novel dual ET-1 receptor antagonist) has been shown to improve clinical outcomes. However the effect of Macitentan on reversing abnormal blood coagulation is unknown.We aimed to characterise derangements in physiological procoagulant and anticoagulant pathways in ES and to assess the effect of Macitentan therapy in modulating haemostasis in this disorder. We hypothesized that an enhanced understanding of pro-and anticoagulant mechanisms in these patients has the potential to improve risk stratification and targeting of antithrombotic therapy to patients at high risk of thrombosis.MethodsBlood was collected from subjects with ES and age/gender-matched healthy controls into citrated tubes, some containing corn trypsin inhibitor (CTI, a contact pathway inhibitor; final concentration 50µg/mL).Parameters of plasma thrombin generation in platelet-rich and platelet-poor plasma were assessed by calibrated automated thrombography (CAT) in the presence or absence of exogenous tissue factor (TF), anionic phospholipid (PL) and activated protein C (APC).ResultsPlatelet-dependent blood coagulation measured by CAT was enhanced in ES platelet-rich plasma (PRP) relative to healthy volunteers despite lower platelet counts: peak thrombin generation (TG) was significantly higher in ES subjects v controls in PRP (230.6±10.9 vs 188.3±13.1 nM; p=0.025) and lagtime to TG (6.1±0.3 vs 7.8±0.5 mins, p=0.005), time to peak TG (11.5±0.5 vs 15.2±0.6 mins, p=0.0003) and TG velocity index (43.9±3.7 vs 26.3±2.4 nM/min, p=0.001) were significantly accelerated. No significant differences in TG parameters in PPP were observed between groups suggesting a critical mechanistic role for platelet activity in supporting hypercoagulability in ES. TG in PRP was also found to be significantly enhanced in ES in the presence of CTI, suggesting that in vitro or in vivocontact pathway activation does not contribute to the enhanced coagulation activation observed in this disorder.The anticoagulant activity of APC is PL dependent and in healthy PPP incubated with exogenous PL (as a substitute for platelet PL), TG was potently inhibited. Conversely, in healthy PRP (in the absence of exogenous PL), APC activity was attenuated. Remarkably, this effect was not observed among the ES subjects, where APC anticoagulant activity was significantly increased in PRP, with significantly lower residual peak plasma thrombin generation and endogenous thrombin potential relative to that observed in healthy volunteer PRP. APC anticoagulant activity in PPP (both in the presence and absence of exogenous PL) was similar between groups. These findings suggest that platelets also modulate the activity of the APC pathway in ES, but in a manner which could promote bleeding.Among the 7 subjects who commenced macitentan therapy, at 6 months peak TG in PRP was significantly lower (234.5±9.8 vs 204.6±14.1 nM, p=0.002) and the enhanced sensitivity to APC in PRP was also attenuated. No significant difference in any parameter of TG was observed in PPP following macitentan therapy.ConclusionPlatelet activity appears to contribute significantly to hypercoagulability in ES but also appears to modulate the activity of endogenous anticoagulant pathways reflecting the clinical phenotype where bleeding and thrombotic risks frequently co-exist. Our findings suggest that targeted pharmacological agents such as the dual endothelin-1 antagonists (which crucially do not confer a bleeding risk) may attenuate platelet-mediated derangements in blood coagulation. Given the significant clinical dilemmas posed by the presence of competing thrombotic and haemorrhagic tendencies in ES, these finding are likely to be of significant translational relevance. DisclosuresWalsh:Actelion UK: Research Funding. Maguire:Actelion UK: Research Funding. Ní Áinle:Actelion UK: Research Funding.

Tissue Factor Pathway Inhibitor Mediates Attenuation of Tissue Factor-Stimulated Thrombin Generation in Early Onset Preeclampsia

IntroductionPregnancy increases the risk of venous thromboembolism (VTE) in women. Interestingly, preeclampsia, an extremely pro-inflammatory disorder specific to pregnancy is associated with a lower than expected increase in thrombotic risk compared to other proinflammatory disorders. The mechanism underling this lower thrombotic risk is unknown. The aim of this study was to investigate the coagulation balance, a major determinant of VTE risk, in early onset preeclampsia (EOP) patients. EOP is the most inflammatory form of preeclampsia, characterised by the development of hypertension and proteinuria prior to 34 weeks gestation.MethodsPlatelet-poor plasma was collected from patients with early onset preeclampsia (EOP n=26), matched pregnant (n=20) and non pregnant controls (n=16). Calibrated automated thrombography, an assay of thrombin generation and TFPI assays were performed. Data are expressed as mean ± standard deviation.ResultsDuring the study period, 15,299 women delivered and 40 patients developed EOP, of whom 26 were successfully recruited with consent. For comparison, 16 non pregnant controls and 20 pregnant controls were also recruited. When artefactual contact activation was inhibited by using corn trypsin inhibitor as anticoagulant, EOP patients were characterised by a decrease in the rate and extent of Tissue Factor (TF) thrombin generation compared to pregnant controls. There was a prolongation of the time to peak thrombin generation (16 ± 4 minutes vs. 13 ± 2 minutes, p < 0.05), a decrease in the velocity index (25 ± 17nM/minute vs. 41 ± 27nM/minute, p < 0.05), and a decrease in peak thrombin generation (150 ± 80 nM IIa vs. 210 ± 70 nM IIa, p < 0.05 ) in EOP compared to pregnant controls. This reduction in the rate and extent of thrombin generation was most amplified in patients with severe EOP (multi-organ involvement) compared with moderate EOP. This lower overall procoagulant state seen was further emphasised by the increase in sensitivity to the anticoagulant activity of exogenously added activated protein C and thrombomodulin observed in EOP. Again, the increased sensitivity to APC and thrombomodulin was most apparent in severe EOP cases. Previous studies have shown that preeclampsia is characterised by a increase in plasma TFPI activity. As such, we investigated whether increases in plasma TFPI activity explained the reduction in TF-dependent thrombin generation. Consistent with previous studies, plasma tissue factor pathway inhibitor (TFPI) levels and plasma TFPI activity significantly increased in EOP, most notably in severe EOP cases. There was a significant inverse correlation between total TFPI levels and peak thrombin generation (r2 = -0.64, p < 0.05) and TFPI activity and peak thrombin generation (r2= -0.52, p < 0.05). The inhibition of TFPI with a polyclonal anti-TFPI antibody abolished the attenuation in thrombin generation seen in severe EOP.ConclusionIn conclusion, TF-dependent thrombin generation is reduced in patients with early onset preeclampsia due to increases in plasma TFPI activity. These findings may partially explain the lower thrombosis risk observed in patients with early onset preeclampsia relative to comparable systemic proinflammatory conditions. These data also have future potential in helping clinicians to manage competing bleeding and thrombotic risks in these very high-risk patients. DisclosuresMaguire:Actelion UK: Research Funding. Ní Áinle:Actelion UK: Research Funding.

Nephrotic Syndrome Clots Are Resistant to Fibrinolysis Despite Elevated Plasmin Generation

IntroductionNephrotic syndrome (NS) is characterized by massive proteinuria (secondary to podocyte injury), hypoalbuminemia, and edema. Importantly, NS is associated with a complex acquired hypercoagulopathy and a high prevalence (~25%) of life-threatening thrombotic complications. We have recently demonstrated that NS disease severity is directly proportional to hypercoagulability,in two well-established animal models of NS (puromycin aminonucleoside (PAN) and Adriamycin (ADR) rats). Furthermore, thromboelastometry studies by our group and others have suggested a resistance to fibrinolysis in both rats and humans with NS. Increasing evidence suggests that myriad abnormalities of the hemostatic system may be implicated in the pathogenesis of altered fibrin clot formation during NS; however the relationship between hypofibrinolysis and NS disease severity requires further validation and the mechanisms underlying the hypofibrinolytic defect remain unknown. Thus, the aim of the present study was to delineate the relationship between disease severity (proteinuria and hypoalbuminemia) and hypofibrinolysis using two rodent models of NS: a transgenic rat expressing the human diphtheria toxin receptor (hDTR) in a podocyte-specific manner and the well-established PAN rat model. We hypothesized that hypofibrinolysis is directly proportional to NS disease severity.MethodsUsing the hDTR rat, we compared markers of global hemostasis (ROTEM) and fibrinolysis to disease severity. A range of severity was induced by a single I.P. injection of diphtheria toxin (0, 25, 50 & 75 ng/kg; n= 7-8/group). On day 10 post-injection, morning spot urines were collected and analyzed for protein:creatinine ratio. Rats were then anesthetized and venous blood (IVC) was collected into 0.32% NaCitrate/1.45 µM Corn Trypsin Inhibitor [final concentrations] and immediately analyzed with ROTEM (whole blood; intem) before being spun down to platelet poor plasma (PPP). Plasma clot lysis assay (CLA) was performed using urokinase (50 IU). Plasmin generation was measured using a fluorogenic substrate in plasma with addition of 10 nM tissue plasminogen activator (tPA).ResultsHypercoagulopathy in the hDTR NS model: Disease severity (proteinuria and hypoalbuminemia) was significantly correlated with endogenous thrombin potential, peak thrombin, and hypercoagulopathic ROTEM parameters (clot formation time, intermediate firmness (amplitude at 10 & 20 min), and maximum clot firmness).Hypofibrinolysis: The amount of lysis at 60 min (LI60) on ROTEM was significantly correlated with proteinuria in both the DTR and PAN models (R2=0.167; P=0.015 & R2=0.740; P<0.001, respectively), suggesting that NS thrombi are resistant to fibrinolysis in a manner that is proportional to disease severity. These findings were confirmed with the CLA, such that plasma clot lysis was significantly negatively correlated with proteinuria (R2=0.196; P=0.007 & R2=0.214; P=0.010) and significantly positively correlated with hypoalbuminemia (R2=0.310; P<0.001 & R2=0.240; P=0.006), in the DTR & PAN models, respectively.Plasmin Generation Assay: Plasmin generation increased with disease severity, such that it was highly correlated with proteinuria and hypoalbuminemia in both models (P<0.001; Figure). Interestingly, there was no correlation between plasmin generation and plasma clot lysis. (P=0.101 & P=0.126 in DTR & PAN rats, respectively).ConclusionsNS disease severity is directly proportional to hypercoagulability in a podocyte-specific rodent model of NS; thus confirming our previously published findings in a podocyte-specific experimental model of NS. Moreover, this hypercoagulopathy leads to formation of a clot that is resistant to fibrinolysis. Paradoxically, the increased plasmin generation implies that the fibrinolytic system is also hyperactive in NS. Thus, it must be concluded that the clot is resistant, even to this increased plasmin that is generated. Future studies will explore the mechanisms underlying and in vivo significance of this fibrinolytic resistance. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Thrombin Generation and Bleeding Phenotype during Personalized Prophylaxis with Recombinant Human FVIII in Previously Treated Patients with Severe Hemophilia A

Background and objectivesIn apharmacokinetic (PK)-guided personalized prophylaxis study with human-cl rhFVIII(Nuwiq®), a factor VIII (FVIII) concentrate from a human cell line,58% of the previously treated adult patients (PTPs) with severe hemophilia A received 2 or fewer prophylactic infusions per weekwith a median dosing interval of3.5 days. Seventy-three percent (73%) of patients did not experience any bleeding and 83% had no spontaneous bleeding episodes during the 6-month personalized prophylaxis period. The objective of this analysis was to evaluate the relationship between endogenous thrombin generation (TG) as well as FVIII plasma concentrations with the bleeding phenotype.Study design and methodsThis prospective, open-label, multicenter study included 66 adult PTPs with severe hemophilia A. After the previously given FVIII concentrate was washed out, patients received human-cl rhFVIII(60 IU/kg) for PK evaluation. Individual PK data were analyzed to determine doses and injection intervals that would theoretically result in a trough FVIII plasma level of ≥1%. Individualized prophylaxis lasted 6 months. TG and FVIII:C plasma concentrations were measured before and during the PK assessment, and trough TG and FVIII:C levels were measured 2, 4 and 6 months after the start of personalized prophylaxis. For TG, blood was drawn in trisodium citrate tubes (0.106 M) containing 1.45 µM corn trypsin inhibitor, centrifuged twice to obtain platelet poor plasma, and stored frozen until central analysis. TG was initiated by adding tissue factor (1 pM), and endogenous thrombin potential (ETP) was measured using the calibrated, automated TG assay.FVIII:C was measured using one-stage (automated APTT, Trinity Biotech, Siemens BCX-XP) and chromogenic assays (Coatest SP FVIII Kit, Chromogenix, Siemes BCS-XP).ResultsData on both baseline ETP and bleeding rate during PK-guided individualized prophylaxis were available for 32 patients. Twenty-one patients did not experience any bleeding episode, and 25 patients had no spontaneous bleeding episodes. The mean baseline ETP did not differ between patients with and without any bleeding (373 ± 334 vs 367 ± 168 nmol*min), but was considerably lower in patients who had spontaneous bleeding episodes compared with those without spontaneous bleeding episodes (164 ± 66 vs 426 ± 231 nmol*min). Data on trough ETPs and FVIII:C during personalized prophylaxis were available for 34 patients.Patients with low TG potential tended to experience more frequent spontaneous bleeding episodes during this phase of the protocol (Figure 1), while low FVIII:C levels seemed to be less related to spontaneous bleeding episodes.ConclusionsLow TG capacity seems to be correlated with increased frequency of spontaneous bleeding episodes, irrespective of trough FVIII plasma levels. Further prospective studies should be carried out to evaluate the value of this global coagulation parameter in the personalization prophylactic treatment in patients with hemophilia A in comparison with trough FVIII coagulant activity. [Display omitted] DisclosuresKlamroth:Biogen Idec: Other: honoraria for advisory boards and speaker fees; Baxalta: Other: honoraria for advisory boards and speaker fees ; Bayer: Other: honoraria for advisory boards and speaker fees; CSL Behring: Other: honoraria for advisory boards and speaker fees; NovoNordisk: Other: honoraria for advisory boards and speaker fees; SOBI: Other: honoraria for advisory boards and speaker fees; pfizer: Other: honoraria for advisory boards and speaker fees; Octapharma: Other: honoraria for advisory boards and speaker fees; uniqure: Other: honoraria for advisory boards and speaker fees. Windyga:Biogen: Consultancy, Equity Ownership, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Patents & Royalties, Research Funding, Speakers Bureau; Aspen: Consultancy, Equity Ownership, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Patents & Royalties, Research Funding, Speakers Bureau; Nordisk: Consultancy, Equity Ownership, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Patents & Royalties, Research Funding, Speakers Bureau; Alexion: Other: Speaker’s honorarium; Sanofi: Consultancy, Equity Ownership, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Patents & Royalties, Research Funding, Speakers Bureau; Octapharma: Consultancy, Equity Ownership, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Patents & Royalties, Research Funding, Speakers Bureau; Baxalta, now part of Shire: Consultancy, Equity Ownership, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Other: Investigator Clinical Studies, Patents & Royalties, Research Funding, Speakers Bureau; CSL Behring: Consultancy, Equity Ownership, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Patents & Royalties, Research Funding, Speakers Bureau. Bichler:Octapharma: Employment. Knaub:Octapharma: Employment. Negrier:NovoNordisk: Membership on an entity’s Board of Directors or advisory committees, Other: Travel support, Research Funding; LFB: Membership on an entity’s Board of Directors or advisory committees; Alnylam: Research Funding; Bayer: Membership on an entity’s Board of Directors or advisory committees, Other: Travel support; CSL Behring: Membership on an entity’s Board of Directors or advisory committees, Research Funding; Octapharma: Membership on an entity’s Board of Directors or advisory committees, Other: Travel support, Research Funding; Pfizer: Research Funding; SOBI: Membership on an entity’s Board of Directors or advisory committees; Baxter: Membership on an entity’s Board of Directors or advisory committees.

New Tools to Study Contact Activation.

The recent availability of a sensitive chromogenic method approach for determination of FXIa activity has been explored for designing sensitive methods for FXIIa and kallikrein, both using FXa formation as the read-out. For both enzymes the assay range 1–10 nmol/L provides a resolution of about 0.8 absorbance units with a total assay time of about 20 min. For studies on activation kinetics, subsampling and extensive dilution can be performed in MES–bovine serum albumin (BSA) buffer pH 5.7 for quenching of enzyme activity and with ensuing determination of FXa generation in a chromogenic FXIa method. Optionally, suitable inhibitors such as aprotinin and/or corn trypsin inhibitor may be included. The stability of FXIa, FXIIa, and kallikrein in MES–BSA buffer was shown to be at least 5 h on ice. In conclusion, the use of a sensitive chromogenic FXIa method either per se or in combination with MES–BSA buffer pH 5.7 are new and potentially valuable tools for the study of contact factor enzymes and their inhibitors. So far, dose–response studies of FXIIa and kallikrein have been limited to purified systems, and hence more data are required to learn whether these new methods might or might not be applicable to the determination of FXIIa and kallikrein activities in plasma.

Role of tissue factor expression in thrombin generation by canine tumor cells.

To measure thrombin generation by high and low tissue factor (TF)-expressing canine cancer cell lines. Canine cell lines CMT25 (high TF-expressing mammary gland tumor cell line) and HMPOS (low TF-expressing osteosarcoma cell line). Thrombin generation by cancer cells was measured in pooled normal canine plasma by use of calibrated automated thrombography without added trigger reagents. Results were expressed as lag time, time to peak thrombin concentration, peak thrombin concentration, and total thrombin concentration or thrombin generation potential. Corn trypsin inhibitor, hirudin, and annexin V were used to inhibit contact activation, thrombin formation, and phosphatidylserine activity, respectively. Pooled normal human plasma deficient in coagulation factors VII, VIII, IX, X, XI, or XII was used to assess the role of individual coagulation factors on thrombin generation. CMT25 generated significantly more thrombin than did HMPOS (mean ± SD, 3,555 ± 604 nM thrombin•min and 636 ± 440 nM thrombin•min, respectively). Thrombin generation of CMT25 was dependent on factor VII and phosphatidylserine and was independent of contact activation. In contrast, thrombin generation of HMPOS was attributed to contact activation. High TF-expressing canine mammary cancer cells generated thrombin in a plasma milieu in vitro in a factor VII- and phosphatidylserine-dependent manner. These findings support a role for TF in hypercoagulability detected in dogs with mammary gland tumors and potentially for other tumors that strongly express TF.

Purified DNA, but Not Neutrophil Extracellular Traps (NETs), Promotes Contact Activation of Coagulation

IntroductionNetosis refers to the extracellular release of nuclear material from neutrophils (PMNs) in the form of a meshwork called neutrophil extracellular traps (NETs). NETs are composed of a scaffold of DNA decorated with histones and specific cytoplasmic granules of neutrophils. Beside their ability to trap bacteria, NETs have been shown to promote thrombosis in animal models. Purified NET components have been suggested to enhance coagulation. However, the exact mechanisms by which intact NETs affect coagulation remain unclear.ObjectiveTo assess the effect of intact NETs on the activation of the contact system of coagulation.MethodsHuman PMNs were isolated from whole blood collected in 3.2% citrate (1 vol citrate / 9 vol blood) from normal volunteers using a negative selection by magnetic beads coated with antibodies directed against specific antigens of other blood cell types. Purity of PMN isolates was ≥ 96% while viability (assessed using trypan blue staining) was ≥ 98%. Isolated PMNs were re-suspended in RPMI + 0.5% bovine serum albumin or in normal pooled platelet-poor plasma (PPP) at 10-15,000 cells/µl final concentration. Re-suspended PMNs were stimulated to form NETs using phorbol myristate acetate (PMA: 600 nM) or ionophore (A23187: 5µM) and incubated at 37ᵒC in 5% CO2 for 3 hours. The effect of NETs was assessed on a synthetic construct of the contact system in-vitro using purified proteins (FXII, FXI, Prekallikrein and High Molecular Weight Kininogen) at physiologic concentrations in Hepes buffered saline containing 2mM Ca2+ and 0.1% polyethylene glycol (8000MW). The reaction was quenched with an equal volume of antithrombin (7uM), corn trypsin inhibitor (CTI, 0.2mg/mL) and heparin (1U/mL) at time points up to 1 hour after mixing with NETs. FXIa-antithrombin complexes were then detected using an in-house sandwich ELISA method. Thrombin generation (TG) was also monitored during 1 hour in re-calcified PPP containing stimulated PMNs with added 4µM synthetic phospholipid vesicles (PC:PE:PS). Finally, DNA was purified from neutrophils and its effect on contact activation was assessed in both the synthetic contact and plasma systems. Kaolin was used as positive control in both test systems; buffer without surface was used as the negative control in the synthetic contact system, and re-calcified PPP without added neutrophils was used as negative control in the TG assay.ResultsMassive amounts of NETs were released from stimulated PMNs as seen on fluorescence microscopy after staining for DNA using sytox green (Fig. I A&C). Extracellular release of NETs was confirmed by digestion following treatment with DNAse 1 (Fig. I B&D).Extracted DNA triggered contact activation (measured as XIa-antithrombin complexes) in buffer and enhanced TF-independent TG in PPP in a concentration dependent manner (Fig. I E&G). The latter was attenuated by corn trypsin inhibitor (0.1mg/mL) and abolished in FXII- or FXI-deficient plasma (Figure IE) indicating the dependency on the contact pathway activation.In contrast, intact NETs did not trigger contact activation in buffer and failed to enhance TG in re-calcified PPP in the absence of TF (Fig. I E&H).ConclusionsUnlike purified DNA, intact NETs failed to activate coagulation via contact activation. These findings need to be confirmed using other readouts of contact system activation. These results do not exclude an effect of intact Nets on contact system amplification. [Display omitted] DisclosuresMonroe:Novo Nordisk: Honoraria, Research Funding.

Engineering a Valve-Regulated Endothelialized Microfluidic Device As an "in Vitro" Bleeding Time for Assessing Global Hemostasis

Introduction: Hemostasis encompasses an ensemble of regulated and balanced interactions among platelets (and other blood cells), coagulation factors, the endothelium, and the hemodynamic forces of the circulation. Unfortunately, current bleeding assays assess only isolated aspects of this complex process. A single assay that incorporates all of the major components of hemostasis would be of significant value in the research and clinical settings. To that end, we leveraged our laboratory's expertise in microfluidic systems to construct an "in vitro" bleeding time. Specifically, we developed a perfusable "endothelialized" microvasculature model that, via a pressure-controlled microscale valve, sustains a controlled, localized vascular "injury" after which bleeding and hemostatic plug formation ensues. This system incorporates recalcified human whole blood with minimal anticoagulation with corn trypsin inhibitor (CTI), controlled perfusion at physiologic flow conditions, and a confluent monolayer of any endothelial cell type. When used in conjunction with fluorescently tagged antibodies or cellular dyes, the entire hemostatic process can be tracked in real time with single cell resolution. As human blood and cells can be used exclusively, this microfluidic system is ideal for studying healthy as well as patient samples. Here, we describe proof of concept experiments utilizing healthy human blood samples and a high-titer antibody that completely inhibits Factor VIII activity.Materials and Methods: The polydimethysiloxane (PDMS)-based microfluidic bleeding time device is comprised of a fluidic, membrane valve, and channel layer (Figure 1A). The fluidic channel was pre-coated with collagen type 1 and fibronectin. Human umbilical cord vein or aortic endothelial cells were seeded in the main fluidic channel with membrane valve in the closed position (Figure 1B, valve closed), then cultured under flow to reach confluence. The "vascular injury" was introduced by providing negative pressure to pull down membrane valve at the middle of the device, where the endothelium is disrupted and an opening (i.e., the "bleed") is created (Figure 1B, valve opened). Human blood was collected in citrated buffer with CTI. Immediately after the injury, recalcified blood was perfused into the device at a shear rate of 500 s-1 and time-lapse images were taken by a confocal microscope. Wound width, bleeding time, and fluorescent intensity were measured and analyzed.Results and Discussion: Here we demonstrate that our microfluidic system enables us to directly analyze microvascular injury, bleeding, and then hemostasis using human cells and blood. After the wound was introduced, blood flow in fluidic channel divided into main channel (Figure 2, horizontal flow) and into the collagen I-coated wound channel, i.e. "bleeding" (vertical flow). The wound width was varied depending on the valve size and pressure given, and ranged from 73.22 to 231.86 µm (n=55, average 132.67 ± 5.48 µm). The average time to cessation of blood flow into the wound channel (i.e. the "bleeding time") was 546.02 ± 38.26 seconds. Interestingly, individual wound width and bleeding time did not correlate (R2 = 0.087), suggesting that the time course of hemostasis was not affected by wound size. Immediately after the injury, platelet adhesion and aggregation led to the formation of hemostatic plug at the wound area followed by fibrin formation, which were visually confirmed via immunofluorescence (CD41) and fluorescent-tagged fibrinogen (Figure 2). In addition, fluorescently-tagged CD15, CD45, and Annexin V binding enabled us to visualize other cellular and molecular components pertinent in hemostasis. Finally, treating healthy blood with an antibody against A2 domain of Factor VIII (anti-A2 MAb 2-76) effectively induced a severe Hemophilia A phenotype. While platelet plug formation was unchanged, the antibody caused instability of clot and repeated re-bleeding. In fact, none of the MAb 2-76-treated conditions exhibited hemsostasis (n=5, the longest recording period 4865 sec), compared to the vehicle control. Also reduced fibrinogen/fibrin accumulation was observed in MAb 2-76-treated blood (Figure 3). Our ongoing studies will provide spatiotemporal insights into how different cellular and molecular components interact during hemostatic process and with use of patient samples, how they go awry in diseased conditions. [Display omitted] [Display omitted] [Display omitted] DisclosuresJobe:Bayer: Membership on an entity's Board of Directors or advisory committees; Biogen: Membership on an entity's Board of Directors or advisory committees; CSL-Behring: Membership on an entity's Board of Directors or advisory committees.

Histone H4-Induced Thrombin Generation in Fresh and "Reconstituted" Blood

Background. Histones are components of nucleosomes and can be released from activated immune cells as well as from necrotic and apoptotic cells. The release of histones is associated with an increased prothrombotic activity. It has been suggested that this activity is caused by the stimulation of platelets, interference with the protein C pathway, changes in red blood cell (RBC) function, etc. Studies published so far were done in plasma or using purified cells and proteins. We extended these studies by evaluating thrombin (FIIa) generation in fresh and "reconstituted" blood triggered with histone H4 and examined contribution of several proteins on this process.Methods. Blood from 8 healthy donors (4 male and 4 female, none of them on oral contraceptives; one male and one female donor were drawn twice) was drawn into 3.2% sodium citrate, 0.1 mg/mL corn trypsin inhibitor (CTI; prevents contact pathway activation) and 20 µg/mL H4 were added followed by recalcification. FIIa generation (TG) was monitored in a fluorogenic assay derived from the CAT method. When desired, either monoclonal inhibitory antibodies to factor (F)XIa, FIXa and tissue factor (TF) (αFXIa-2, αFIX-91 and αTF-5, respectively; all at 0.1 mg/mL) or kallikrein inhibitor aprotinin (10 µM) were added to blood. In parallel, TG in washed RBC reconstituted (50/50) either with platelet poor (PPP) or platelet rich (PRP) plasma ("reconstituted blood") was analyzed at the same conditions. FIIa generation in an autologous plasma was also analyzed.Results.A. Whole blood. In the absence of any exogenous activator, the lag phase and peak value of TG in CTI blood varied in a wide range (see the table). An addition of H4 to the blood shortened the lag phase and increased peak FIIa concentration for all donors. An addition of αFXIa-2 slightly prolonged the lag phase and slightly suppressed other parameters of FIIa generation. Aprotinin had a somewhat more pronounced effect on the lag phase but only marginally affected other parameters of FIIa generation. αFIX-91 almost completely suppressed H4-initiated FIIa generation, whereas αTF-5 had almost no effect on the process. Table 1ConditionsLag (min)Max FIIa (nM)Max Rate (nM/min)AUC (nM*min)RangeAverage ± SDRangeAverage ± SDRangeAverage ± SDRangeAverage ± SDCTI(n=10)9 - 2313.4 ± 4.236.6 - 109.563.7 ± 25.114.5 - 92.648.9 ± 26.6309.3 - 687.8487.6 ± 130.1CTI + H4(n=10)2.6 - 7.44.7 ± 1.466.3 - 134.799.4 ± 22.436.8 - 83.357.9 ± 15.4417.5 - 865.8571.1 ± 145CTI + H4 + αFXIa-2(n=9)2.4 - 8.55.2 ± 1.956.6 - 103.983.6 ± 13.222.9 - 69. 444.9 ± 13.2409.9 - 680.3522 ± 90.4CTI + H4 + aprotinin(n=9)3.3 - 8.15.5 ± 1.662.3 - 144.295.1 ± 25.736 - 94.458.1 ± 19.4409.2 - 1056.2599.5 ± 203.6CTI + H4 + αFIXa-91(n=6)NQNQNQNQNQNQNQNQCTI + H4 + αTF-2(n=6)3.2 - 7.44.9 ± 1.765.1 - 128.490.1 ± 21.843.4 - 16973.9 ± 47.6434.1 - 867.7543.1 ± 166*NQ = Not Quantifiable (in 4 of 6 experiments no FIIa generation was observed and in 2 experiments it was negligible).B. RBC. In the absence of any exogenous activator, no FIIa generation was observed in 50 min. in RBC reconstituted with PPP. An addition of H4 led to FIIa generation after a lag phase of 17.7±4.3 min with the maximum active FIIa concentration (66.5±12.4 nM) lower than that observed in whole blood. Additions of either αFXIa-2 or aprotinin had no pronounced effect on FIIa generation, whereas no FIIa was observed in the presence of αFIX-91. When RBC were reconstituted with PRP, H4-induced FIIa generation parameters became similar to those observed in whole blood.C. Autologous PPP. No FIIa generation was observed in CTI PPP in the absence of any exogenous activator. An addition of H4 led to a delayed (25-30 min lag phase) and inefficient FIIa generation (maximum 10-15 nM). αFXIa-2 had no effect on FIIa generation, αFIX-91 completely suppressed it and aprotinin had an intermediate effect.Conclusions. 1). H4 has a pronounced effect in enhancing FIIa generation in fresh blood and washed RBC reconstituted with PPP and PRP; 2). Inhibition of contact pathway proteins has minor effect on H4-induced FIIa generation; 3). Inhibition of FIXa almost completely abolishes H4-induced FIIa generation; 4). RBC reconstituted with PPP can support H4-induced FIIa generation and platelets enhance this process; 5). H4-induced FIIa generation in PPP is negligible. DisclosuresMann:Haematologic Technologies, Inc; Baxter, Diagnostica Stago, Bayer, CSL Behring, Alnylam.: Consultancy, Equity Ownership.

One-Stage FVIII Activity Is Inversely Correlated with Heavy Menstrual Bleeding in Hemophilia a Carriers

IntroductionThe majority of carriers of hemophilia A have historically been considered to have normal hemostasis (FVIII:C >50%) and thus not have an increased bleeding tendency. However, our research group has demonstrated that some hemophilia A carriers can experience increased bleeding compared to normal women despite this normal FVIII activity. In our recently published study in adult hemophilia A carriers there was no correlation between FVIII:C, as measured by a one-stage coagulation assay, and bleeding phenotype, as measured by the MCMDM-1 VWD bleeding score. In this follow up study we sought to determine which of these hemophilia A carriers with normal FVIII:C are at risk for bleeding. The goal of this study is to determine the relationship between FVIII assays (one-stage and chromogenic) and thrombin generation with both menstrual bleeding and an overall bleeding tendency. MethodsWe recruited mothers of children with hemophilia A in the Emory University pediatric bleeding disorders clinic. We included only adult (>18 year of age) obligate hemophilia A carriers that did not have a concomitant bleeding disorder or chronic disease that would increase their bleeding tendency. We gathered basic demographic information and evaluated the overall bleeding tendency using the ISTH Bleeding Assessment Tool (ISTH BAT), a semi-quantitative assessment of bleeding scored from 0 to 56. We considered a score of 6 or higher consistent with pathologic bleeding. In addition, we inventoried menstrual bleeding with the Pictorial Bleeding Assessment Chart (PBAC), a visual representation of menstrual blood loss. We considered a PBAC greater than 100 consistent with heavy menstrual bleeding. Plasma samples were collected from each subject at the time of the survey in sodium citrate tubes without corn trypsin inhibitor. Samples were double spun at 2,500 rpm for 15 minutes and stored at -80°C.Laboratory evaluation for each subject included FVIII:C, measured by one-stage coagulation assay (aPTT reagent with micronized silica) and chromogenic assay (COATEST SP4 FVIII kit, Chromogenix), as well as thrombin generation (Calibrated Automated Thrombogram, PPP-Reagent Low, FluCa Kit) to evaluate endogenous thrombin potential (ETP, nM*min), peak thrombin (nM) and lag time (min). We performed linear regression using GraphPad Prism; p<0.05 was considered significant. ResultsOver a three-month period, we approached 32 adult obligate hemophilia A carriers; 23 agreed to participate in the survey, 16 consented to blood draw. One carrier was excluded in extreme outlier analysis and due to an autoimmune disorder, leaving 15 evaluable subjects. Our cohort is relatively young with a median age of 41 years (range 23-51), predominantly Caucasian (53%, 8/15) and the majority carry a severe mutation (10/15 severe, 2/15 moderate, 3/15 mild).Reproductive bleeding (post-partum hemorrhage and/or menstrual bleeding) was commonly reported (93%, 14/15). The median ISTH BAT bleeding score for subjects was 2 (range 1-8). The median PBAC score was 148 (range 10-608). The carriers had a relatively normal FVIII:C by one-stage assay with a median of 0.78 U/mL (range 0.30 - 1.06) and by chromogenic assay with a median of 1.15 U/mL (range 0.66 - 1.9). FVIIIC by one-stage assay was inversely correlated to PBAC (r2 =0.4; p=0.01, figure 1A). Conversely, FVIII:C by chromogenic assay did not correlate with PBAC, however trended toward significance (r2 = 0.19; p=0.10, figure 1A). Additionally, there was no correlation found between FVIII:C (one-stage or chromogenic assay) and ISTH BAT bleeding score (figure 1B). There was also no correlation found between bleeding score or PBAC and the parameters of the thrombin generation assay or between severity of the closest male relative's hemophilia and any of the assays performed. ConclusionsIn our cohort of adult obligate hemophilia A carriers, as the FVIII:C (one-stage assay) decreased, the menstrual bleeding tendency increased as measured by the PBAC. We were unable to find a correlation between other measures of hemostasis, including the chromogenic assay and thrombin generation, and commonly used bleeding assessment tools. Further larger studies are warranted to help determine which hemophilia A carriers would be at risk for bleeding. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.