Increased Peak Thrombin Generation Research Articles

Low molecular weight heparin decreases pro-coagulant activity in clinical MSC products

Background aimsMesenchymal stromal cells (MSCs) are multipotent adult cells that can be isolated from tissues including bone marrow [MSC(BM)], adipose [MSC(AT)] and umbilical cord [MSC(CT)]. Previous studies have linked expression of tissue factor (TF) on MSC surfaces to a procoagulant effect. Venous thromboembolism (VTE), immediate blood-mediated inflammatory reaction (IBMIR) and microvascular thrombosis remain a risk with intravascular MSC therapy. We examined the effect of low molecular weight heparin (LMWH) on clinical-grade MSCs using calibrated automated thrombography (CAT). MethodsClinical grade MSC(BM)s, MSC(AT)s and MSC(CT)s harvested at passage 4 were added to normal pooled plasma (NPP) to a final concentration of either 400 000 or 50 000 cells/mL. LMWH was added to plasma in increments of 0.1 U/mL. Thrombin generation (TG) was measured using CAT. Flow cytometry was conducted on the cells to measure MSC phenotype and TF load. ResultsPresence of MSCs decreased lag time and increased peak TG. All cell lines demonstrated a dose response to LMWH, with MSC(AT) demonstrating the least thrombogenicity and most sensitivity to LMWH. TG was significantly reduced in all cell lines at doses of 0.2 U/mL LMWH and higher. DiscussionAll MSC types and concentrations had a decrease in peak thrombin and TG with increasing amounts of LMWH. While this in vitro study cannot determine optimal dosing, it suggests that LMWH can be effectively used to lower the risk of VTE associated with intravascular administration of MSCs. Future in vivo work can be done to determine optimal dosing and effect on IBMIR and VTE.

Effects of regional citrate anticoagulation on thrombin generation, fibrinolysis and platelet function in critically ill patients receiving continuous renal replacement therapy for acute kidney injury: a prospective study

BackgroundRegional citrate anticoagulation (RCA) is recommended for continuous renal replacement therapy (CRRT). However, filter life varies and premature filter clotting can occur. The aims of this explorative prospective study were to investigate the effects of RCA on thrombin generation, fibrinolysis and platelet function in critically ill patients receiving CRRT, to compare clotting parameters between systemic and intra-circuit blood samples, and to screen participants for coagulation disorders. We recruited critically ill adult patients admitted to a 30-bedded Intensive care unit in a tertiary care hospital who required CRRT with RCA for acute kidney injury (AKI). Patients with pre-existing thrombotic, bleeding tendencies or a CRRT duration less than 48 h were excluded. We measured coagulation and thrombophilia parameters at baseline. Thrombin generation, D-dimer and platelet function were measured pre-CRRT and at 12, 24, 36, 48 and 72 h after commencing CRRT using blood samples taken from the arterial line and the circuit.ResultsAt baseline, all eleven patients (mean age 62.4 years, 82% male) had Factor VIII and von Willebrand Factor concentrations above reference range and significantly increased peak thrombin generation. During CRRT, there were no significant changes in systemic maximum peak thrombin generation, time to peak thrombin generation, fibrinogen, D-dimer and platelet function analysis. We observed no significant difference between paired samples taken from the patient's arterial line and the circuit.ConclusionsCritically ill patients with AKI requiring CRRT are hypercoagulable. Citrate used for anticoagulation during CRRT does not affect thrombin generation, D-dimer or platelet function. Systemic clotting parameters reflect intra-circuit results.Trial registration: ClinicalTrials.gov Identifier: NCT02486614.Registered 01 July 2015—Registered after recruitment of first patient. https://clinicaltrials.gov/ct2/show/NCT02486614

A modified thrombin generation assay to evaluate the plasma coagulation potential in the presence of emicizumab, the bispecific antibody to factors IXa/X

Emicizumab shortens activated partial thromboplastin time (aPTT) greater than Factor (F)VIII. Clot waveform analysis triggered by ellagic acid and tissue factor trigger (Elg/TF) provided a useful means of assessing emicizumab activity. Thrombin generation assays (TGA) using this trigger reagent might also overcome the difficulties associated with aPTT by emicizumab. To compare TGA triggered by Elg/TF and other reagents (FXIa, TF) for evaluating emicizumab activity. Emicizumab, FVIII, or FVIII-bypassing agents (BPAs) were incubated with FVIII-deficient plasmas prior to TGA initiated by Elg/TF (0.2μM/0.5pM), FXIa (5.21pM), or TF (PPP-Reagent LOW®). Emicizumab, FVIII, or BPAs increased peak thrombin generation (peak-Th) dose-dependently using Elg/TF-trigger and the other triggers. Low responses were evident with FXIa-trigger and the enhanced effects remained below normal levels with Elg/TF-trigger. Experiments using FVIII with emicizumab demonstrated an additive effect on peak-Th using Elg/TF-trigger, and this effect appeared to be less at FVIII ≥ 40IU/dl. BPAs with emicizumab appeared to mediate additive effects, although its effects were variable. Parameters of thrombin generation from BPAs and emicizumab with Elg/TF-trigger were improved to normal level compared to low TF-trigger. Elg/TF-TGA could evaluate global coagulation potential during emicizumab prophylaxis including concomitant therapy with FVIII or BPAs.

Hemostatic potential of cold-stored non-leukoreduced whole blood over time: An assessment of platelet function and thrombin generation for optimal shelf life.

Cold-stored low-titer whole blood (WB) is becoming increasingly used as the preferred product for initial hemorrhagic shock resuscitation. The purpose of this study was to identify whether the current 21-day shelf life is the optimal duration for storage of WB, maintaining hemostatic efficacy. Five units of fresh low-titer group O WB (non-leukoreduced) were acquired from our regional blood center. These units were stored at 4°C for up to 21 days as per current clinical storage guidelines in our emergency department. Hemostatic parameters were measured in vitro at 0 days, 7 days, 14 days, and 21 days. Assessments of hemostatic potential included cell count, rapid thrombelastography (r-TEG) and kaolin thrombelastography (TEG), multiplate impedance aggregometry, and calibrated automated thrombogram (CAT). Univariate analysis, including one-way analysis of variance with repeated measures, was performed (STATA 12.1). Compared with baseline product (0 days), both platelet count and platelet function of WB showed sharp decreases at 7 days and again at 14 days. Platelet function deterioration was noted by r-TEG c (MA), TEG-MA, and multiplate arachidonic acid and adenosine diphosphate (all p < 0.001). With respect to clot initiation, r-TEG ACT and TEG R-time were similar over the 21-day shelf life (p = 0.058 and p = 0.620, respectively). Thrombin generation assessed by CAT demonstrated stable endogenous thrombin potential over the course of storage (p = 0.162), but increased peak thrombin generation and quicker time to peak generation after 7 days. While the platelet function of WB degrades significantly at 7 days (and again at 14 days), clot initiation remains stable over time, and thrombin generation appears to be improved at 7 days. This study supports a current storage limit for cold-stored, low-titer WB of 14 days.

Thrombin Generation Assay in Plasma from Hemophilia a Patients with or without Inhibitors on Concizumab Prophylaxis: Spiking with rFVIIa or aPCC

Introduction: Concizumab is a humanized monoclonal antibody that inhibits tissue factor pathway inhibitor (TFPI). Concizumab is currently in clinical development as a subcutaneous prophylactic therapy for hemophilia A and B patients with and without inhibitors. Breakthrough bleeding episodes experienced by inhibitor patients while on concizumab prophylaxis may be treated with the bypassing agents recombinant activated factor VII (rFVIIa; NovoSeven®) or activated prothrombin complex concentrate (aPCC; FEIBA®). Aim: To investigate the in vitro effect of rFVIIa and aPCC on hemophilia A plasma containing concizumab using a thrombin generation assay and pooled plasma spiked with concizumab or samples from patients treated prophylactically with concizumab. Methods: Pooled hemophilia A plasma was spiked with concizumab at 1, 3 and 10 nM and patient plasma samples from explorer4 (n=16; hemophilia with inhibitors; NCT03196284) and explorer5 (n=30; hemophilia A; NCT03196297) before and during concizumab prophylaxis at steady state exposure levels were assessed. Samples were spiked with rFVIIa (25 or 75 nM) or aPCC (0.25, 0.5 or 1 U/mL), and analyzed using a thrombin generation assay initiated with tissue factor (PPP-Low, Thrombinoscope). The effects of rFVIIa or aPCC in the absence or presence of concizumab were compared using ANOVA methodology. Results: Addition of rFVIIa or aPCC to hemophilia A plasma with or without inhibitors increased peak thrombin generation both in the absence and presence of concizumab. A significant additional effect of rFVIIa and aPCC was observed for all concizumab concentrations spiked to the plasma pool. Overall, the effects of the combination of concizumab and rFVIIa or aPCC were mainly additive; however, a small but statistically significant drug-drug interaction was observed for rFVIIa (25 nM or 75 nM) and aPCC (0.5 U/ml or 1 U/mL) in the presence of 10 nM concizumab. At this concizumab concentration, the additive effect of aPCC corresponded to 68% of the total observed effect and the additive effect of rFVIIa to 85% of the total observed effect. At lower concizumab concentrations (1 and 3 nM), statistically significant drug-drug effects were only observed in combination with aPCC. No excessive thrombin generation above the level obtained with 1 IU/mL recombinant factor VIII (rFVIII) was observed at 1 nM concizumab combined with either rFVIIa (25 and 75 nM) or aPCC 0.5 U/mL. However, addition of 1 U/mL aPCC to 1 nM concizumab resulted in a thrombin peak modestly above the upper 95% confidence interval of the rFVIII range. In the experiments using plasma from patients treated with concizumab, the increase in thrombin peak upon addition of rFVIIa was within or below the range observed by spiking with 1 IU/mL rFVIII. The increase in thrombin peak upon addition of aPCC was within or above the rFVIII range. The effects of concizumab and rFVIIa or aPCC were mainly additive; however, a small, statistically significant contribution caused by drug-drug interaction was observed for concizumab and rFVIIa (75 nM) in both plasma from patients with and without inhibitors, and for 1 U/mL aPCC in plasma from patients with inhibitors. The additive effects of concizumab and rFVIIa corresponded to between 60% (25 nM rFVIIa, plasma without inhibitors) and 75% (75 nM rFVIIa, inhibitor plasma), and the additive effects of concizumab and 1 U/mL aPCC corresponded to 77% of the total observed effects. Conclusions: Addition of rFVIIa or aPCC to hemophilia A plasma with or without inhibitors increased peak thrombin generation as expected both in the absence and presence of concizumab. Thus, the bypassing agents function as expected in plasma containing concizumab. The effects of concizumab and rFVIIa or aPCC were mainly additive. A small but statistically significant contribution was synergistic in accordance with the concizumab mechanism of action (Hilden I et al, Blood, 2012). These in vitro results support the concomitant use of bypassing agents to treat breakthrough bleeding episodes in hemophilia with inhibitor patients on concizumab prophylactic treatment. Disclosures Kjalke: Novo Nordisk A/S: Employment, Honoraria. Kjelgaard-Hansen:Novo Nordisk A/S: Employment, Equity Ownership. Andersen:Novo Nordisk A/S: Employment, Equity Ownership, Honoraria. Hilden:Novo Nordisk A/S: Employment, Equity Ownership, Patents &amp; Royalties.

The Combination of Marzeptacog Alfa (Activated) or Eptacog Alfa (Activated) with Emicizumab Appears Comparable As Assessed By the Thrombin Generation Test in Hemophilia a Plasma

Background: Hemophilia patients treated prophylactically with emicizumab (Hemlibra®) may experience break-through bleeds or require additional hemostatic coverage for procedures or surgery. Currently available therapies including rFVIIa (Eptacog Alfa (Activated); NovoSeven®) and aPCC (FEIBA®) have been used with Hemlibra to treat bleeding or when additional coverage is required. While NovoSeven appears safe in combination with Hemlibra (HAVEN 1 to 4 clinical trials), thrombotic events have been observed with concurrent use of FEIBA and Hemlibra. While safe and efficacious when used as directed, NovoSeven must be infused intravenously. Ideally, for patients on subcutaneous (SC) prophylaxis with Hemlibra adjunct rFVIIa could be dosed SC too. Marzeptacog alfa (activated) (MarzAA) is a novel rFVIIa differentiated by increased potency and the ability to be administered SC to achieve pharmacologically relevant plasma concentrations. Thus, MarzAA provides a potential solution to address this unmet need in hemophilia therapy. Objective: Demonstrate the procoagulant potential of MarzAA, NovoSeven or FEIBA alone or in combination with Hemlibra using the thrombin generation assay in platelet poor hemophilia A (HA) plasma. The thrombin generation potential will therefore provide a surrogate marker to assess the potential safety and efficacy of SC MarzAA in combination with Hemlibra. Methods: A thrombin generation assay was performed using the PPP-Low Tissue Factor and phospholipid containing thrombin generation assay reagent (#TS31.00, Thrombinoscope, Stago). Citrated hemophilia A plasma was spiked with increasing concentrations (0, 25, 50, and 100 µg/mL) of Hemlibra together with various concentrations of each bypassing agent: MarzAA at 0, 0.1, 0.5, 1, 2.5, 5, and 10 µg/mL, NovoSeven at 1, 2.5, 5, 10, and 50 µg/mL or FEIBA at 0.25, and 0.50 IU/ml. Statistical significance was set at α = 0.05. Results: We assessed the relative potencies of MarzAA and NovoSeven in HA plasma. As expected, MarzAA demonstrated an approximate ten-fold increased potency vs NovoSeven. Both rFVIIa compounds increased peak thrombin generation in the HA plasma to the level of normal plasma and beyond. The effect of adding normalizing levels of MarzAA (1 µg/mL), NovoSeven (10 µg/mL) or FEIBA (0.5 IU/mL) to HA plasma containing clinically relevant concentrations of Hemlibra was evaluated (Fig 1). When correcting for the effect of Hemlibra alone, the increase in peak thrombin generation induced by FEIBA was significantly greater than that observed for both MarzAA and NovoSeven (P&lt;0.002). In contrast, the observed increases in thrombin generation for MarzAA and NovoSeven in combination with Hemlibra were statistically indistinguishable. FEIBA was not tested at the highest clinically relevant concentration (2.0 IU/mL) as assay limitations were already approached at 0.5 IU/ml, corresponding to ~25% of the plasma concentration expected for a clinical FEIBA dose of 100 IU/kg. Furthermore, concentrations of MarzAA (5 µg/mL) or NovoSeven (50 µg/mL) 50-fold higher than expected after standard doses were required before peak thrombin generation became statistically indistinguishable from FEIBA at 0.5 IU/mL when all three compounds were evaluated in the presence of Hemlibra. Conclusion: As assessed by in vitro thrombin generation, equipotent concentrations of MarzAA and NovoSeven exhibit comparable characteristics when spiked into HA plasma containing Hemlibra at clinically relevant concentrations. Based on these data, MarzAA and NovoSeven are expected to behave similarly in combination with Hemlibra when dosed to achieve equipotent plasma concentrations. Figure 1 Disclosures Knudsen: Catalyst Biosciences: Employment, Equity Ownership. Kumar:Catalyst Biosciences: Employment, Equity Ownership. Del Greco:Catalyst Biosciences: Consultancy, Equity Ownership. Neuman:Catalyst Biosciences: Employment, Equity Ownership. Levy:Catalyst Biosciences: Employment, Equity Ownership. Blouse:Catalyst Biosciences: Employment, Equity Ownership.

Coagulation Factor Levels and Underlying Thrombin Generation Patterns in Adult Extracorporeal Membrane Oxygenation Patients.

There is a paucity of data on the underlying procoagulant-anticoagulant balance during extracorporeal membrane oxygenation (ECMO). We hypothesized that adult ECMO patients would have an imbalance between procoagulant and anticoagulant factors, leading to an abnormal underlying thrombin generation (TG) pattern. Twenty adult venoarterial (VA) ECMO patients had procoagulant and anticoagulant factor levels measured temporally on ECMO day 1 or 2, day 3, and day 5. In heparin-neutralized plasma, underlying TG patterns, and sensitivity to activated protein C were assessed using calibrated automated thrombogram. TG parameters including lag time, peak TG, and endogenous thrombin potential (ETP) were compared against 5 normal plasma controls (3 males and 2 females) obtained from a commercial supplier. Thrombomodulin (TM) was added to some samples to evaluate for activated protein C resistance. Procoagulant factors (factor [F] II, FV, and FX) were mostly in normal reference ranges and gradually increased during the first 5 ECMO days (P = .022, <.001, <.001). FVIII levels were elevated at all time points and did not change (P = .766). In contrast, FXI was in the low-normal range but did not increase during ECMO (P = .093). Antithrombin (AT) and protein C levels were below normal but increased during the first 5 ECMO days (P = .002 and P = .014). Heparinase-treated samples showed prolonged lag time, increased peak TG, and increased ETP compared to controls; mean difference in lag time on ECMO day 1 or 2 = 6.0 minutes (99% confidence interval [CI], 2.8-9.2), peak TG = 193.4 (99% CI, 122.5-264.3), and ETP = 1170.4 (99% CI, 723.2-1617.6). After in vitro TM treatment, differences in TG parameters were accentuated and ECMO samples appeared insensitive to TM treatment; mean difference in lag time on ECMO day 1 or 2 = 9.3 minutes (99% CI, 6.2-12.4), peak TG = 233.0 (99% CI, 140.9-325.1), and ETP = 1322.5 (99% CI, 764.8-1880.2). Similar differences in TG parameters were observed on ECMO days 3 and 5. Contact activation occurs during ECMO, but procoagulant factor levels are generally preserved. Although heparin-neutralized TG is delayed, peak TG and ETP are supranormal in the setting of high FVIII and low AT and protein C levels. Resistance to TM is also apparent. These changes demonstrate a possible mechanism for hypercoagulability during adult VA ECMO.

Factor IX from prothrombin complex concentrate augments low dose tissue factor-triggered thrombin generation in vitro

BackgroundProthrombin complex concentrate (PCC) is increasingly used to correct acquired coagulopathy in trauma and surgery. Dosing of PCC is guided by the prothrombin time, which only reflects the onset of thrombin generation, but does not account for variations in intrinsic pathway coagulation factors, including factor IX (FIX). We hypothesised that FIX contained in PCC could strongly influence thrombin generation patterns. MethodsPooled normal, FIX-deficient, and warfarinised plasma were used to analyse the effects of FIX contained in PCC. PCC was evaluated at final concentrations of 0.2 and 0.4 IU ml−1 in FIX-deficient and normal plasma, and at 0.6 IU ml−1 in warfarinised plasma with elevated FVIII (1.5 IU ml−1), 40% dilution with saline, or both. The effects on thrombin generation were assessed by measuring both procoagulant and inhibitory segments. ResultsFIX-deficient plasma had lower peak thrombin generation [30.6 (20.5–35.8) nM vs 130.2 (107–168) nM] and endogenous thrombin potential [472 (391–532) nM vs 1096 (958–1190) nM] than normal plasma. PCC addition resulted in significant increases of peak thrombin generation [81.8 (37.3–98.3) nM] and endogenous thrombin potential [808 (472–842) nM] in FIX-deficient plasma. The combination of FVIII and PCC resulted in greater increases relative to each agent alone, restoring normal thrombin generation. After 40% dilution, adding PCC, FVIII, or both, to FIX-deficient plasma increased peak thrombin generation, and prolonged the inhibitory phase of the endogenous thrombin potential. ConclusionsFIX derived from PCC strongly enhances tissue factor-triggered thrombin generation in the presence of elevated FVIII activity. Haemodilution further enhances procoagulant effects of FIX and FVIII by slowing down inhibition of procoagulant enzymes. Dosing of PCC per prothrombin time may underestimate PCC's procoagulant potential because it does not account for intrinsic tenase or antithrombin activity.

Evaluation of thrombin generation in classical Philadelphianegative myeloproliferative neoplasms / Evaluarea generării trombinei în neoplasmele mieloproliferative Philadelphia- negative

Abstract Introduction: Patients with Philadelphia-negative chronic myeloproliferative neoplasms (Ph-MPN), polycytemia vera (PV), essential thrombocythaemia (ET) and primary myelofibrosis (PMF), are prone to develop thrombotic events. We aimed to investigate the coagulation status in their plasma using thrombin generation assay (TGA), a functional global assay, on Ceveron® Alpha. Materials and methods: The samples were collected from 89 consecutive Ph-negative MPN patients and from 78 controls into K2EDTA and CTAD tubes for blood cell counts, TGA and coagulation screening tests. Thrombin generation was analysed in platelet-poor plasma using Technothrombin® TGA assay kit. Results: We found a significantly increased peak thrombin generation (p=0.049) and velocity index (VI) (p=0.012) in patients in comparison with controls, especially in ET patients, and a significantly higher values for peak thrombin (p=0.043) and VI (p=0.042) in patients receiving anagrelide in comparison with those treated with hydroxyurea. We also noticed an inverse correlation between the length of cytoreductive therapy and TGA parameters, (peak thrombin R=-0.25, p=0.018, AUC R=-0.257, p=0.015, and VI R=-0.21, p=0.048). Conclusion: Our results suggest that Ph-MPN patients, and especially those with ET, are predisposed to thrombotic events due to their higher peak thrombin and VI values and their risk may decreases as treatment is longer. Patients treated with hydroxyurea generate less thrombin and could be less prone to develop thrombotic events in comparison with those treated with anagrelide.

Analysis of Racial Disparity in Plasma of Healthy Volunteers Using Rotational Thromboelastometry Reveals Higher Prothrombotic Profile in African Americans

Racial differences in the incidence of arterial and venous thrombotic events are well established in literature, with a higher incidence noted in African Americans compared to Caucasians. Several studies have tried to explain this difference, by looking separately at chemical biomarkers, socioeconomic and clinical risk factors. Yet the exact reason behind this disparity remains unclear. At least one study of thrombin generation suggested that African ethnicity was associated with increased peak thrombin generation when compared to Caucasians. Rotational thromboelastometry is a visco-elastic methodology that offers a global assessment of hemostasis using either whole blood or plasma. We explored the racial differences in rotational thromboelastometry findings using plasma samples from healthy volunteers. We studied a cohort of 9 otherwise healthy adult volunteers with no history of cardiovascular nor thromboembolic events, 5 African Americans and 4 Caucasians. After informed consent, we collected citrated whole blood samples and processed them within 3 hours of phlebotomy. Platelet free plasma, obtained after centrifugation of whole blood for 20 minutes, was kept frozen at -70°C, and then thawed at 37°C for 5 minutes prior to testing. Samples were re-calcified with star-tem® reagent, and then the in-tem® reagent was added. The latter contains an optimized concentration of ellagic acid and partial thromboplastin phospholipid from rabbit brain. Thromboelastometry parameters including Clot Formation Time, Alpha Angle, and Maximum Clot Firmness were determined. We then compared the data between the two study populations using parametric unpaired Student’s t-test. Our results showed that the Clot Formation Time was higher in the plasma of Caucasians when compared to African Americans with a difference between means of 40.1 ± 4.4 seconds (p &lt;.0001); the Alpha Angle was lower in Caucasians with a difference between means of 3.45 ± 0.3 degrees (p &lt;.0001); and the Maximum Clot Firmness was lower in Caucasians with a difference between means of 9.75 ± 2 mm (p &lt;.01). These findings demonstrated that the plasma of Caucasians took longer to reach the maximum firmness, and this maximum firmness was less than that reached in the plasma of African Americans. This reveals a significantly increased prothrombotic profile in the plasma of African Americans compared to Caucasians. Despite the limited number of participants, the striking observed differences in the thromboelastometry parameters suggest that global assays may offer benefit in assessing thrombotic risks in disparate patient populations, as they incorporate multiple components of the hemostatic system. Higher numbers of subjects and assessment of both whole blood and plasma are indicated. We are currently in the process of expanding our cohort to confirm these preliminary results. Disclosures No relevant conflicts of interest to declare.

Coagulation Factor XI and Factor XII in DNA-Induced Thrombin Generation

Components of the blood coagulation mechanism are activated during infections as part of the innate immune response to invading microorganisms. This process is crucial for limiting spread of infection; however, excessive activation of coagulation can contribute to thrombotic tissue ischemia and systemic inflammation. During a variety of conditions associated with leukocyte activation and tissue damage, including sepsis, levels of cell free DNA rise in plasma. Neutrophils are one source of free DNA, releasing chromatin upon activation to form neutrophil extracellular traps (NETs). DNA in NETs form a physical barrier that contains microorganisms, while histones and antimicrobial proteins associated with DNA have bactericidal properties. NETs trigger platelet activation and coagulation, and likely contribute to inflammation, thrombosis and disseminated intravascular coagulation in sepsis. In a murine venous thrombosis model, neutrophils and NETs appear to contribute to thrombus formation through a process involving factor XII (fXII) (von Bruhl et al. J Exp Med 2012;209:819). When plasma fXII binds to anionic surfaces it is converted to the protease fXIIa. The results with the mouse model suggest that DNA, an anionic polymer, contributes to thrombosis by enhancing fXII activation.FXIIa contributes to thrombin generation and thrombosis by converting zymogen factor XI (fXI), to the protease factor XIa (fXIa). FXI has been implicated in the pathology of sepsis and thrombosis in animal models. Mice lacking fXI have better survival than wild type mice after ligation and puncture of the cecum, and are more resistant to Listeria infection. Inhibition or deficiency of fXI/fXIa confers an antithrombotic phenotype in rodents, rabbits and primates. Furthermore, epidemiologic data support a role for fXI in arterial and venous thrombosis in humans. FXI is activated in plasma by fXIIa or thrombin; however, the reactions proceed slowly in the absence of anionic substances. This suggests that a cofactor with anionic properties is required for fXI activation in vivo. For example, polymers of inorganic phosphate (polyphosphate or polyP) released by platelets enhance fXI activation by thrombin 3000-fold and by fXIIa 30-fold. PolyP also induces fXI and fXII autoactivation. The backbone of DNA is a type of phosphate polymer. We examined the capacity of DNA to enhance fXI and fXII activation and to contribute to fXI/fXII-dependent plasma coagulation.We isolated DNA from human peripheral blood leukocytes. Like polyP, DNA induced fXII autoactivation. Similarly, fXI underwent autoactivated in the presence of DNA, with the rate of activation increasing as DNA concentration increased. For reactions with either fXII or fXI, the enhancing effect of DNA was neutralized by treatment with DNAse. DNA, but not DNAse treated DNA, enhanced fXI activation by fXIIa 4-fold and by thrombin 30-fold compared to reactions without DNA. FXI is a dimeric protein composed of two identical subunits. PolyP binds to each fXI subunit through two anion binding sites (ABS), one on the fXI apple 3 domain (ABS1) and the other on the fXI catalytic domain (ABS2). These interactions are required for polyP-mediated enhancement of fXI activation by thrombin and fXIIa. Using DNA as a cofactor, the rate of activation of fXI lacking ABS1 by thrombin or fXIIa was 4-fold slower than for wild type fXI, while DNA failed to enhance activation of fXI lacking ABS2. This indicates that binding of fXI to DNA through the ABSs is required for expression of the DNA cofactor effect. Addition of DNA (50 ug/ml) induced thrombin generation in normal plasma (Endogenous Thrombin Potential 356 nM.min) through a process that was blocked by a fXIIa inhibitor (corn trypsin inhibitor) or a monoclonal antibody to fXI. Thrombin generation is dependent on fXI in normal plasma triggered to clot with a low (0.2 pM) concentration of tissue factor. Addition of DNA (50 ug/ml) to this system increased peak thrombin generation and endogenous thrombin potential by ~50%, while shortening time to peak thrombin potential. This effect was completely neutralized by an antibody to fXI. In conclusion, fXII and fXI have a propensity to bind to, and become activated on, anionic polymers and surfaces. Our results suggest that DNA released from leukocytes or damaged tissues could enhance activation of these protease zymogens, facilitating their contribution to hypercoagulability and inflammation. DisclosuresGailani:Aronora: Consultancy, Membership on an entity’s Board of Directors or advisory committees; Bayer: Consultancy, Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding; Dyax: Consultancy, Research Funding; Instrument Laboratory: Consultancy, Research Funding; Isis: Consultancy; Merck: Consultancy; Novartis: Consultancy.

The Anticoagulant Effect of Protamine Sulfate Is Attenuated in the Presence of Platelets or Elevated Factor VIII Concentrations

Protamine sulfate is the antidote for heparin, but in excess it exerts weak anticoagulation. We evaluated the effects of increasing protamine concentrations (0 to 24 microg/mL) on prothrombin time and diluted Russell's viper venom time measurements on thrombin generation in platelet-poor and platelet-rich plasma after activation by tissue factor or actin, and on thromboelastometry in platelet-poor plasma and whole blood from 6 healthy volunteers. The reversibility of excess protamine (24 microg/mL) by recombinant factor VIIa or factor VIII/von Willebrand factor concentrate was also tested. Protamine prolonged prothrombin time and Russell's viper venom time, concentration dependently. Protamine also increased lag time and decreased peak of thrombin generation in platelet-poor plasma after tissue factor and actin activation. In platelet-rich plasma with platelets at 50 to 200 x 10(3)/microL, protamine (24 microg/mL) prolonged the lag time, but had no effect on peak thrombin generation. The addition of factor VIII/von Willebrand factor (1.5-3.0 U/mL) to platelet-poor plasma with protamine (24 microg/mL) decreased lag time and increased peak thrombin generation with actin activation. A therapeutic concentration of recombinant factor VIIa (60 nM) only affected the lag time of thrombin generation triggered with actin. In agreement, protamine increased coagulation time evaluated by thromboelastometry significantly more in platelet-poor plasma than in whole blood. We demonstrated that protamine affects the propagation of thrombin generation, which is partially reversed by platelets or increased factor VIII/von Willebrand factor concentrations. The present data suggest that excess protamine might potentially increase bleeding in the case of severe thrombocytopenia or low factor VIII.

Patients with the Antiphospholipid Syndrome (APLS) Show Hypercoagulability Due to Hypofibrinolysis and Increased Fibrin Generation, but Thrombin Generation Is Variable

We have previously demonstrated hypercoagulability utilizing a global haemostatic assay, the Overall Haemostatic Potential (OHP) in a heterogenous population of patients with a demonstrable lupus anticoagulant. Our aim in this study was to determine whether the OHP assay demonstrated a persistent hypercoagulable state in a well-defined prospective population with APLS and whether global assays were able to predict the occurrence of thrombotic complications. Informed consent was obtained and blood was collected on three occasions, three months apart from 54 patients with APLS, recruited from Haematology clinics at Royal North Shore Hospital, Sydney, Australia between May 2005 and November 2007. Clinical data was collected including history of prior and subsequent thrombotic events. Two control groups consisted of 200 healthy blood donors and 20 patients with autoimmune disorders, but no history of thrombosis. Assays performed were PT, INR, APTT, FVIIIc, lupus anticoagulant assay (LAC), anticardiolipin antibodies (ACLA), b2-glycoprotein1 antibodies (B2GP1), a thrombin generation assay (Calibrated Automated Thrombogram, CAT) and the OHP assay which utilizes thrombin (0.03 IU/ml) and rt-PA (350 ng/ml) to trigger fibrin generation and fibrinolysis, respectively, in platelet poor plasma. Change in optical density in microtitre wells is measured over 60 minutes. Statistical analysis involved calculation of means, SD, T-tests and paired T-tests utilizing SPSS v16.0. Fifty percent of APLS patients were male, compared with 10% of the autoimmune control group. APLS had been diagnosed on the basis of persistent antiphospholipid antibodies and at least one thrombotic event: VTE (n=46), ATE (n=6) or recurrent late miscarriage (n=2). Number of thrombotic events prior to study entry ranged form 1 to 6 per patient, with 49/66 events unprovoked. Samples from APLS patients on anticoagulation (OAC, n=35) were analysed separately from those not anticoagulated (n=19). Global assay results for samples collected at different time points were stable, with no significant differences on paired T-test. APLS patients had significantly shorter PT, higher fibrinogen, increased fibrin generation and reduced fibrinolysis parameters (p<0.001), compared with healthy donors. The autoimmune control group also showed hypercoagulable OHP parameters compared with healthy donors (p<0.001), with assay results comparable to those in APLS patients, not on OAC. The only thrombin generation assay parameter significantly increased in APLS patients, not on OAC, compared with controls was peak thrombin (266 vs 298 nM, p=0.016). However thrombin generation was significantly suppressed in those on OAC (p<0.001). Only one patient had recurrent DVT during the study. The OHP assay identifies a hypercoagulable state in APLS patients with reduced fibrinolysis and increased fibrin generation, even when anticoagulated. The calibrated automated thrombogram (CAT) showed increased peak thrombin generation in APLS patients not on OAC but endogenous thrombin potential (ETP) was not significantly elevated. Thrombin generation was suppressed by OAC therapy. These global assays show differential results in patients with APLS. More prolonged follow up will be necessary to determine whether the assays predict recurrent thrombotic events and are useful in risk stratification of APLS patients.

Improved Clot Formation by Combined Administration of Activated Factor VII (NovoSeven®) and Fibrinogen (Haemocomplettan® P)

Recombinant activated factor VII (rFVIIa) is increasingly used for treating refractory bleeding after cardiac surgery. However, hemostasis also depends on coagulation factors, including fibrinogen, which stabilizes platelet plugs at sites of vascular injury. We compared the hemostatic effects of rFVIIa, fibrinogen, or their combination. Blood samples were obtained from 12 volunteers and from 7 patients after cardiopulmonary bypass (CPB). The in vitro effects of rFVIIa (1.5 microg/mL), fibrinogen (100 mg/dL), and the combination were evaluated under simulated coagulopathy in volunteer plasma using heparin (0.1 U/mL) or tissue plasminogen activator (0.1 microg/mL). Hemostatic interventions were compared using thromboelastometry, which measures clotting time (CT, s), angle of thrombus formation, and maximal clot firmness (MCF, mm). The Thrombinoscope was used to quantitate thrombin generation after addition of fibrinogen and/or rFVIIa. In heparinized volunteer plasma, rFVIIa shortened CT (1st and 3rd quartiles) from 663 (522-736) to 435 (397-531) s, but it did not affect MCF. Fibrinogen increased MCF from 26.0 (24.4-26.7) to 30.5 (26.3-31.5) mm without affecting CT. The combination of rFVIIa and fibrinogen in heparinized samples was most effective in improving CT to 359 (324-522) s and MCF to 29 (27.8-31.0) mm. In tissue plasminogen activator-treated volunteer plasma, fibrinolysis increased by more than 45% by the addition of rFVIIa. After CPB, both CT and MCF were most improved with coadministration of rFVIIa and fibrinogen. Thrombinoscope evaluation demonstrated that rFVIIa decreased the lag time and increased peak thrombin generation, whereas fibrinogen had no effect. The onset of fibrin formation and thrombin generation were shortened after rFVIIa addition, but fibrin clot strength was only increased after fibrinogen supplementation. In vitro clot formation was most improved by using both rFVIIa and fibrinogen in whole blood after CPB.