Peak Thrombin Levels Research Articles

In vitro studies show synergistic effects of a procoagulant bispecific antibody and bypassing agents

Background Investigational non-factor products such as emicizumab offer a treatment option for patients with hemophilia and inhibitors. However, their mechanism of action raises questions regarding safety when they are combined with treatments for breakthrough bleeding. Objectives To evaluate in vitro thrombin generation (TG) and clot formation for combinations of activated prothrombin complex concentrate (aPCC), recombinant activated factor VII (rFVIIa), and a sequence-identical analog of emicizumab (SIA). Methods Therapeutic concentrations of SIA (20-600 nm) alone or with aPCC (0.05-1 U mL-1 ), isolated aPCC components or rFVIIa (0.88-5.25 μg mL-1 ) were tested for TG and compared with reference ranges for healthy donor plasma. Coagulation of FVIII-inhibited blood was determined with a widely established method, i.e. rotational thromboelastometry (ROTEM), and confirmed with the Total Thrombus-formation Analysis System. Results and conclusions SIA (600 nm) or aPCC (0.5 U mL-1 ) alone resulted in peak thrombin levels of 21.4 nm and 38.6 nm, respectively, both of which are lower than normal (83.7 ± 29.8 nm). SIA plus aPCC (0.5 U mL-1 ) increased the peak thrombin level 17-fold over SIA alone, exceeding the reference plasma value by 4.2-fold. This hypercoagulable effect occurred with 600 nmSIA combined with as little as 0.25 U mL-1 aPCC, confirmed by ROTEM. FIX was the main driver for enhanced TG. SIA plus rFVIIa (1.75 μg mL-1 ) induced a 1.8-fold increase in the peak thrombin level in platelet-rich plasma, but it did not reach the normal range. These in vitro experiments demonstrate excessive TG after administration of a combination of aPCC and SIA at clinically relevant doses. Careful judgement may be required when breakthrough bleeding is treated in patients receiving emicizumab.

An increased tendency in fibrinogen activity and its association with a hypo-fibrinolytic state in early stages after injury in patients without acute traumatic coagulopathy (ATC)

Acute traumatic coagulopathy (ATC) diagnosed by prolongation of APTT and/or PT/INR involves alterations in platelet activity, coagulation and fibrinolysis. However, data showing the haemostatic situation in injured patients without ATC are scarce. To assess whether haemostatic impairment is also present in injured patients without ATC, ten injured patients without ATC and ten normal individuals were examined. The patients were sampled on arrival at the emergency department 0, 2, 12 h after surgical or other intervention. Thrombin generation, fibrin formation and fibrin proteolysis were determined via several laboratory methods, using tissue factor as the coagulation trigger. Thrombograms demonstrated that trauma accelerated both thrombin generation and decay. In the presence of unaffected peak thrombin levels, these two contradictory effects cancelled each other out, leading to the global endogenous thrombin potential (ETP) remaining normal. Under the mediation of normal ETP, fibrin network permeability (Ks) kept the reference levels in the two groups of subjects. Fibrinogen (FBG) activity (Clauss) rose with time from 0 to 2 h and 12 h, which significantly slowed down Clot Lysis Potential as determined by an in vitro method with exogenous t-PA. Summary: the main haemostatic impairment in the present patients concerned an increased tendency in FBG activity. Since an increase in FBG is a biomarker of acute inflammation and also predicts greater fibrin production which down-regulates fibrinolysis, we suggest that during early stages after injury, patients without ATC may suffer from worsening inflammation and confront enhancement of thrombosis risk due to dysfunction of fibrinolysis.

Assessment of the procoagulant potential after laparoscopic sleeve gastrectomy: a potential role for extended thromboprophylaxis

BackgroundBariatric surgery is associated with increased thromboembolic risk, which may extend well beyond hospital stay. The hemostatic mechanisms implicated in this risk are not well established. ObjectivesWe aimed to determine the dynamics of hemostatic changes and procoagulant potential among patients undergoing laparoscopic sleeve gastrectomy, during both the early and late postoperative periods. SettingA university hospital. MethodsPatients who underwent laparoscopic sleeve gastrectomy were recruited consecutively to this study. Blood samples were taken preoperatively, before discharge (postoperative day [POD] 3), and at the first follow-up visit (POD10). All samples were tested for complete blood count, C-reactive protein, von Willebrand factor, factor VIII, fibrinogen, and thrombin generation. ResultsThe median preoperative body mass index of the 26 participants was 41.3 (38.7–43.3) kg/m2. Compared with preoperative evaluation, fibrinogen, von Willebrand factor antigen and activity, and factor VIII levels were significantly higher at POD3 and POD10 (P<.0001 for all comparisons). Peak thrombin levels and endogenous thrombin potential (ETP) were higher at POD3 (P = .005 for both comparisons) and POD10 (P = .0009 and<.0001) compared with baseline. ETP and peak thrombin, as well as fibrinogen, von Willebrand factor, and factor VIII levels, were comparable between POD3 and POD10. Multivariate analysis showed that the only predictor of postoperative ETP was the preoperative ETP level (β = .55, P = .007). ConclusionsAs determined by thrombin generation, laparoscopic sleeve gastrectomy was associated with hypercoagulability, which persisted during POD10. This finding suggests a possible benefit of extended thromboprophylaxis. Nevertheless, our results should be interpreted with caution due to the lack of a control group.

Low thrombin generation predicts poor prognosis in ischemic stroke patients after thrombolysis.

Thrombolysis by intravenous recombinant tissue plasminogen activator (rt-PA) is an effective therapy in acute ischemic stroke (AIS). Thrombin generation test (TGT) is a global hemostasis test providing information about the speed and amount of generated thrombin in plasma. Here we aimed to find out whether results of this test before the initiation of thrombolysis might predict outcomes. Study population included 120 consecutive AIS patients, all within 4.5 hours of their symptom onset, who underwent thrombolysis by rt-PA. Blood samples were collected from all patients upon admission and TGT was performed using platelet poor plasma. Clinical data of patients including the NIHSS were registered at admission, day 1 and 7 after therapy. The ASPECT score was assessed using CT images taken before and 24 hours after thrombolysis. Long-term functional outcome was defined 3 months after the event by the modified Rankin Scale. Endogenous Thrombin Potential (ETP) and Peak Thrombin were significantly lower in patients with cardioembolic IS. Symptomatic intracranial hemorrhage (SICH) was found in 6 patients and was significantly associated with low ETP and Peak Thrombin levels. A multiple logistic regression model revealed that an ETP result in the lower quartile is an independent predictor of mortality within the first two weeks (OR: 6.03; 95%CI: 1.2–30.16, p<0.05) and three months after the event (OR: 5.28; 95%CI: 1.27–21.86, p<0.05). Low levels of ETP and Peak Thrombin parameters increase the risk of therapy associated SICH. A low ETP result is an independent predictor of short- and long-term mortality following thrombolysis.

An Antibody to Tissue Factor Pathway Inhibitor (PF-06741086) in Combination with Recombinant Factor VIIa Increases Hemostasis in Hemophilia Plasma without Excessive Thrombin Generation

Hemophilia is a hereditary bleeding disorder caused by intrinsic coagulation pathway deficiencies of Factor VIII (hemophilia A) or Factor IX (hemophilia B). Tissue factor pathway inhibitor (TFPI) is a Kunitz-type serine protease inhibitor that negatively regulates thrombin generation within the extrinsic pathway of coagulation. In hemophilia patients the extrinsic pathway remains intact and thus augmentation of this pathway may circumvent the clotting deficiency in hemophilia. PF-06741086, a monoclonal antibody that binds to and neutralizes the inhibitory activity of TFPI is being developed as a potential treatment for bleeding disorders including hemophilia A and hemophilia B with and without inhibitors.Currently, treatment of inhibitor patients is managed by bypass treatments, such as recombinant Factor VIIa (rFVIIa). The effect of PF-06741086 on thrombin generation in the presence of increasing concentrations of rFVIIa (0.0002 to 20 µg/mL) was studied in severe hemophilia A plasma. A dose-dependent increase in thrombin generation was observed over vehicle control with the addition of rFVIIa to the hemophilia plasma. Addition of a fixed concentration of PF-06741086 (16 µg/mL) in combination with rFVIIa resulted in an increase in thrombin generation including higher peak thrombin and shortening of lag time compared to rFVIIa alone. The TGA profiles with the combination of PF-06741086 and rFVIIa at 0.2, 2, and 20 µg/mL were similar suggesting a saturation of mechanism at these concentrations. The combination of PF-06741086 and rFVIIa restored thrombin generation to normal plasma levels at all rFVIIa concentrations examined.The TFPI inhibitory activity of PF-06741086 on thrombin generation in the presence and absence of rFVIIa was further studied in additional hemophilia A plasmas, including hemophilia A plasmas with inhibitors and hemophilia B plasma. All donors had less than 1% coagulation factor activity. A rFVIIa concentration of 2 µg/mL was selected because it corresponded to plasma levels that could be observed following dosing of FVIIa and because the thrombin generation response in hemophilia plasma was similar with FVIIa added to hemophilia A plasma at 0.2, 2 and 20 µg/mL. The concentration of PF-06741086 was 16 µg/mL in these studies. The effect of PF-06741086 on thrombin generation was also measured in non-hemophilic plasma which would have the full complement of coagulation factors. The addition of PF-06741086 alone or in combination with rFVIIa to hemophilia A and B plasma resulted in an increase in thrombin generation including higher peak thrombin concentration and shortening of lag time compared to addition of rFVIIa alone. In hemophilic plasma samples with inhibitors (3 - 1261 Bethesda Units), PF-06741086 alone also restored thrombin generation. A minimal additive effect in peak thrombin generation was observed with the combination of PF-06741086 (16 µg/mL) and 2 µg/mL rFVIII. The midpoint peak thrombin levels achieved with PF-06741086 alone or in combination with rFVIIa were similar to those observed in non-hemophilic plasma and did not exceed the level observed in non-hemophilic plasma dosed with PF-06741086. To summarize, use of rFVIIa in combination with PF-06741086 results in increased thrombin generation in hemophilia A, hemophilia B and inhibitor plasmas without inducing excessive coagulation. DisclosuresRakhe:Pfizer: Employment. Hett:Pfizer: Employment. Murphy:Pfizer: Employment. Pittman:Pfizer: Employment.

Synergistic Effects of a Procoagulant Bispecific Antibody and Rescue Therapies on Thrombin Generation- a Potential Safety Risk

Background: Investigational non-factor products, such as ACE 910 (Emicizumab), offer potential new treatment options for hemophilia patients with inhibitors. However, their uncertain and unregulated mechanisms of action raise multiple concerns around safety and efficacy in specific clinical contexts. As an antibody to FIXa and FX, ACE 910 lacks the inherent regulatory characteristics that are present in replacement factor and bypassing agents in the context of hemostasis.FEIBA is a plasma-derived, activated prothrombin complex concentrate developed to prevent and treat bleeding episodes in hemophilia A and B patients with inhibitors. There are more than 40 years of clinical experience with FEIBA. Extensive prospective clinical study data, as well as post-approval pharmacovigilance data demonstrated the product to be safe and highly effective. In an ongoing phase III study (NCT02622321), hemophilia A patients with inhibitors are treated with Emicizumab. To evaluate the treatment options for ACE910-treated patients experiencing breakthrough bleeding, we studied, in-vitro, the thrombin generation profile of various combinations of FEIBA with a biosimilar version of ACE910.Methods: A biosimilar antibody to Emicizumab (BS-Em) was expressed in mammalian cells, purified and extensively biochemically characterized. Therapeutic doses of BS-Em (200-600nM) in combination with several concentrations of FEIBA (0.1-1IU/ml) were analyzed in standard in-vitro thrombin generation (TG) experiments (1pM TF trigger) using 3 inhibitor patient plasma. A normal range of TG for the experimental conditions used was established using plasma from 34 healthy individuals.Results: The combination of FEIBA and BS-Em resulted in peak thrombin values of >500nM (600nM BS-Em/1IU/ml FEIBA) while the normal range was established to span peak thrombin levels of ~50-120nM thrombin. Titration experiments established that at 600nM BS-Em, FEIBA concentrations of >0.2IU/ml led to peak thrombin values 4- 10-fold higher than the normal range.Conclusions: Our in-vitro experiments demonstrate an excessive thrombin generation potential for the combination of BS-Em and FEIBA at concentrations expected to be generated in patients participating in this study. Caution and clinical judgement will be required when considering the use of ACE910 in hemophilia A patients with inhibitors as options to treat breakthrough bleeds if they occur might be reduced or lead to potential AE. DisclosuresKnappe:Shire: Employment. Hartmann:Shire: Employment. Goldstein:Shire: Employment. Ewenstein:Shire: Employment. Valentino:Shire: Employment. Scheiflinger:Shire: Employment.

Evidence of Thrombin-Independent Generation of Activated Protein C

Introduction: In a recent study, we performed autologous serum infusions to evaluate the elimination kinetics of hemostasis-related biomarkers in healthy human subjects. In order to monitor a serum-induced activation of coagulation, we measured free thrombin in the infused serum and in plasma samples taken during and after infusion, but did not detect any de novo thrombin formation [PLoS One. 2015; 10(12): e0145012]. To study if the low levels of free thrombin in the infused serum induce generation of activated protein C (APC) we additionally measured APC in samples drawn after autologous serum infusion and in vitro in a purified system.Methods: Autologous serum was infused (50 mL/30 min) into 19 healthy volunteers. Four of them were simultaneously receiving infusions of the thrombin inhibitor argatroban (1 µg/kg/min), initiated 1 h before and ceased 1 h after starting the infusion of serum. Thrombin and APC were measured in serum and in plasma samples drawn before and in 15-min intervals during the infusion of serum, using a highly-sensitive oligonucleotide-based enzyme capture assay (OECA) platform. In in vitro experiments, APC formation was induced by addition of purified thrombin or serum to buffer containing protein C and thrombomodulin in excess, and CaCl2 at physiological concentrations. The formation of APC was subsequently measured by OECA.Results: In the autologous serum median (interquartile range) concentrations of thrombin and APC were 6.68 (4.63 - 8.73) ng/mL and 9.17 (7.63 - 13.91) ng/mL, thus doses of 0.12 (0.07 - 0.15) ng/mL of thrombin and 0.16 (0.14 - 0.22) ng/mL of APC were infused per mL of the subjects' plasma volume. In the plasma of probands, that did not receive argatroban, peak thrombin levels of 0.04 (0.00 - 0.08) ng/mL were measured, indicating a rapid inactivation of thrombin by endogenous inhibitors present in the plasma. However, with 1.41 (0.76 - 2.97) ng/mL peak APC levels exceeded the infused APC doses by a multiple. This was also true for the plasma samples from the probands that received argatroban, in which peak levels of APC of 0.94 (0.79 - 1.22) ng/mL were measured despite thrombin inhibition indicated by prolongation of the aPTT of 42.9 (40.1 - 44.4) s and thrombin time of 78.3 (69.3 - 87.2) s. In the in vitro experiments addition of argatroban at the concentrations achieved in the probands completely abolished APC generation up to a thrombin concentration of 5 ng/ml. Addition of human serum as a source for thrombin in the same purified system consistently induced generation of greater amounts of APC than expected on the basis of the amount of thrombin present in the serum samples.Conclusions: The data obtained provide evidence for a thrombin-independent mechanism of APC formation. Further in vitro studies with endothelial cells are required to identify the components that are involved in this alternative way of APC generation. DisclosuresRühl:CSL Behring: Research Funding; Bayer: Consultancy, Honoraria. Müller:Novo Nordisk: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees.

A combined approach using global coagulation assays quickly differentiates coagulation disorders with prolonged aPTT and low levels of FVIII activity.

Patients with mild/moderate hemophilia (H)A, acquired HA (AHA) and lupus anticoagulants (LA), have prolonged aPTTs with low levels of factor (F)VIII activity, but the differentiation of these disorders is complex and time consuming. We established an approach to quickly differentiate these disorders using comprehensive coagulation tests. Patients' plasmas with mild/moderate HA, AHA, LA without anti-phospholipid syndrome [LA-APS(-)], and LA with APS [LA-APS(+)] were examined using clot waveform analysis (CWA) and thrombin generation test (TGT). Activated protein C (APC) sensitivity was assessed by TGT. CWA revealed similarly prolonged clot times in all groups [NP/mild/moderate HA/AHA/LA-APS(-)/LA-APS(+); 33±1/82±12/116±44/90±29/96±15s] but significantly different decreased maximal coagulation velocity (3.1±0.1/1.3±0.3/0.9±0.5/1.6±0.3/2.2±0.5). In TGT, AHA group demonstrated severely reduced peak-thrombin levels (362±23/170±27/49±21/158±75/158±99nM), whilst both LA groups markedly prolonged lag times (4.5±0.3/5.0±0.4/4.7±0.8/12.5±7.7/28.8±11.8min), suggesting that AHA could be readily identified, but the different LA sub-types failed to be classified. An APC sensitivity demonstrated that 'normalized' APC-induced levels of peak thrombin in LA-APS(+) were significantly lower relative to LA-APS(-) (normalized %inhibition; 5±7/42±39%). Our studies confirmed that %inhibition by APC was significantly decreased in NP preincubated with purified IgGs from LA-APS(+) compared to LA-APS(-), facilitating differentiation between LA groups. A combined approach using CWA and TGT could be a useful means of differentiating coagulation disorders with prolonged aPTT.

Is one-size-fits-all strategy adequate for platelet storage?

BackgroundPlatelet suspensions (PSs) are stored at room temperature. However, recent reports show that PSs stored at 4 °C possess superior hemostatic properties. We compared the viabilities and thrombin generation capacities of PSs stored either at 4 °C or 22 °C hours. Materials and MethodsTwenty units of apheresis derived platelets (ADPs) from 20 male donors and 20 units of random platelet suspensions (RPSs) from another 20 male donors were obtained. Half of the ADPs and half of the RPSs (10 units/per group) were stored at 4 °C, the other halves of ADPs and RPSs (10 units/per group) were stored in agitators at 22 °C for 48 hours. The flow cytometric viability tests and thrombin generation tests of the PSs were assessed. ResultsThe viabilities of both ADPs and RPSs group platelets, stored either at 4 °C or 22 °C for 48 hours, were not statistically significantly different. The ADPs and RPSs stored at 4 °C generated significantly higher peak thrombin levels than the platelets stored at 22 °C. Moreover, the ADPs group stored at 4 °C showed significantly shorter time to thrombin generation and reach peak levels. ConclusionThe PSs stored at 4 °C showed higher and faster thrombin generation capacities than the room temperature PSs. Given the superior hemostatic properties of refrigerated platelets, creating different storage temperature capabilities for specific transfusion purposes may be a prudent approach, especially for improving the outcome of bleeding trauma casualties.

Computational simulation and comparison of prothrombin complex concentrate dosing schemes for warfarin reversal in cardiac surgery

Prothrombin complex concentrate (PCC) is increasingly used for acute warfarin reversal. We hypothesized that computational modeling of thrombin generation (TG) could be used to optimize the timing and dose of PCC during hemodilution induced by cardiopulmonary bypass (CPB). Thrombin generation patterns were modeled in anticoagulated patients (n=59) using a published computational model. Four dosing schemes were evaluated including single full dose (median, 41.2IU/kg) of PCC before or after CPB, ½-dose before and after CPB, or 1/3-dose before CPB plus 2/3-dose after CPB. Hemodilution was modeled as 40 or 60% dilution of factors from baseline. The lag time (s) of TG, and peak thrombin level (nM) were evaluated. Prolonged lag time, and reduced peak TG were due to low vitamin K-dependent (VKD) factors, and pre-CPB PCC dose-dependently restored TG to near-normal or normal range. After 40% dilution, TG parameters were similar among 4 regimens at the end of therapy. The recovery of VKD factors was less when PCC was given before CPBafter 60 % dilution, but TG parameters were considered hemostatically effective (>200nM) with any regimen. Withholding the full dose of PCC until post-CPB resulted in severely depressed TG peak (median, 47nM) after 60 % dilution, and some supra-normal TG peaks after treatment. Pre-CPB administration of full or divided doses of PCC prevents extremely low TG peak during surgery, and maintains hemostatic TG peaks in both 40 and 60% hemodilution models. Although PCC's hemostatic activity appears to be highest using the full dose after CPB, hypercoagulability may develop in some cases.

Clinical Course and Management of Surgical Emergency in a Severe Hemophilia a Patient Under Weekly Subcutaneous Administration of a Bispecific Antibody to Factors IXa and X (ACE910)

Clinical Course and Management of Surgical Emergency in a Severe Hemophilia a Patient Under Weekly Subcutaneous Administration of a Bispecific Antibody to Factors IXa and X (ACE910)

A New Look into Childhood Acute ITP: The Relationship Between Thrombin Generation and Thrombocytopenia

Introduction: Immune thrombocytopenic purpura (ITP) is the most common cause of primary isolated thrombocytopenia of childhood. Although ITP results in profound thrombocytopenia, the severity of bleeding in this disease does not correlate well with the platelet count suggesting a compensatory procoagulant state. The primary aim of this study is to evaluate thrombin generation in childhood acute ITP patients compared to age-matched controls and examine procoagulant activity in relation to bleeding severity in childhood acute ITP.Methods: After IRB consent was approved, platelet poor plasma was isolated from acute ITP patients at the time of initial diagnosis and serially for up to 6 months post-diagnosis. A single sample was obtained from age-matched controls. Thrombin generation assays were run via the Calibrated Automated Thrombogram (CAT) using reagent containing 1pM tissue factor and 4uM phospholipid. Peak thrombin levels were measured and compared to control samples using paired t-test analysis. Clinical bleeding severity was assessed using a modified overall Buchanan bleeding score at each time point (0=no bleeding, 1=minor, 2=mild, 3=moderate, 4=severe, 5=life threatening bleeding).Results: Samples from 19 childhood acute ITP patients, mean age 7 years, and 8 controls, mean age 5 years, were assessed. The figure below demonstrates that despite profound thrombocytopenia, the peak thrombin values of acute ITP patients were higher than controls throughout the first 3-4 months following diagnosis. ITP assays were significantly different from controls at the following time-points: 1-2 weeks (p =0.001), 3-4 weeks (p =0.022), 5-8 weeks (p =0.0009), 9-12 weeks (p =0.004), and 13-16 weeks (p =0.006) post-diagnosis. Peak thrombin values returned to values similar to controls 17 weeks from diagnosis. With the onset of acute ITP, higher bleeding scores were related to more severe thrombocytopenia. In ITP patients, thrombin peak values remained elevated regardless of resolving thrombocytopenia and improved bleeding scores (see figure).Conclusion: To our knowledge, this is the first study to assess longitudinal thrombin generation using the CAT in childhood ITP patients. In a highly significant pattern, acute ITP patients demonstrated sustained elevated peak thrombin levels compared to controls, even at acute onset of disease. Certainly, thrombin release, and subsequent thrombin generation play a compensatory role to decrease bleeding among childhood ITP patients when the platelet count remains in the 10-50,000 range. But, based on bleeding scores, this elevated thrombin may not be able to overcome the bleeding phenotype at presentation when platelets are most profoundly decreased or absent. Greater understanding of the etiology of this thrombin potential in childhood acute ITP is critical, as the thrombocytopenia in this disorder may be triggered or linked to a larger post infectious or inflammatory coagulopathy. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Reversal of dabigatran effects in models of thrombin generation and hemostasis by factor VIIa and prothrombin complex concentrate.

The oral thrombin inhibitor dabigatran has the drawbacks that it does not have a validated antidote. Data from animal studies and plasma coagulation assays suggest that prothrombin complex concentrate (PCC) or recombinant factor VIIa (FVIIa) might reverse dabigatran anticoagulation. Cellular elements make a significant contribution to hemostasis. Our goals were to (1) test the hypothesis that both FVIIa and a 4-factor PCC improve parameters of thrombin generation in the presence of dabigatran in a cell-based model; and (2) determine whether results in a cell-based model correlate with hemostasis in vivo. PCC reversed dabigatran effects on the rate, peak, and total amount of thrombin but did not shorten the lag (n = 6 experiments in triplicate). By contrast, FVIIa shortened the lag, increased the rate and peak, but did not improve total thrombin (n = 6). Effects of PCC were seen at both therapeutic and markedly supratherapeutic dabigatran levels, whereas beneficial effects of FVIIa decreased as the dabigatran level increased. The PCC effect was reproduced by adding prothrombin, factor X, and factor IX. At therapeutic dabigatran levels, both PCC and FVIIa normalized hemostasis time in a mouse saphenous vein bleeding model. A cell-based model reflects the effects on thrombin generation of clinically relevant levels of FVIIa and PCC in the presence of dabigatran. Enhancing the rate of thrombin generation and peak thrombin level appear to correlate best with hemostasis in vivo. The ineffectiveness of FVIIa at supratherapeutic dabigatran levels may explain conflicting reports of its efficacy in dabigatran reversal.

Activation of the Intrinsic Coagulation Pathway in Patients With Chronic Urticaria.

PurposeAlthough coagulation activation has been reported in chronic urticaria, data pertaining to detailed changes in coagulation factors and global coagulation status are lacking. The current study evaluated global coagulation status in patients with chronic urticaria using thrombin generation assay (TGA) and the levels of individual coagulation factors.MethodsPatients with chronic urticaria (n=57) and 20 healthy controls were enrolled. TGA was performed under stimulation with 2 concentrations of tissue factor (TF). Coagulation factors and conventional coagulation assays were also analyzed.ResultsAlthough patients with chronic urticaria showed prolonged activated partial thromboplastin time, prothrombin time did not differ significantly between patients and controls. In both 1 pM and 5 pM TF-stimulated TGA, peak thrombin and endogenous thrombin potential (ETP) levels were markedly decreased in patients with chronic urticaria. As expected, intrinsic coagulation factors (VIII, IX, and XII), as well as coagulation factors of the common pathway (II, V, and X), were consistently decreased. Additionally, D-dimer was significantly increased in patients as compared to controls. In multivariate regression analysis, the presence of chronic urticaria was the only significant independent contributor to the low ETP value.ConclusionsChronic urticaria is characterized by in vivo coagulation activation through the intrinsic coagulation pathway, which can be measured with sensitivity using TGA.

Influence of ABO type on global coagulation assay results: effect of coagulation factor VIII.

As ABO blood type influences the plasma level of coagulation factor VIII (FVIII), it likely also affects activated partial thromboplastin time (aPTT) and thrombin generation assay (TGA) values. Here, we aimed to investigate the effect of ABO type on the normal values of three global coagulation assays: prothrombin time (PT), aPTT, and TGA. PT, aPTT, TGA [1 or 5 pmol/L tissue factor (TF)], coagulation factors, anticoagulation factors, and ABO type were measured in 200 healthy adults. aPTT was significantly prolonged in those with type O compared with those with type non-O, whereas PT was not significantly different between those with type O and type non-O. The time to peak induced by 5 pmol/L TF was significantly prolonged, and the peak thrombin level was decreased in those with type O compared with those with type non-O. FVIII was a major contributor to the ABO-specific reference range of aPTT, 5 pmol/L TF-induced time to peak, and peak thrombin level. The reference ranges of aPTT and TGA (time to peak and peak thrombin level) differed by ABO type. FVIII level is considered a major contributor to ABO type-specific differences with respect to aPTT and TGA.

A TFPI Inhibitory Half Life Extended Fusion Peptide Proves Efficacy in FVIII Knock out Mice and Marmoset Monkeys

IntroductionTissue factor pathway inhibitor (TFPI) is an important inhibitor of the extrinsic coagulation pathway as it inhibits factor Xa (FXa) and the tissue factor (TF) – FVIIa complex. Inhibition of TFPI with blocking antibodies, aptamers, or peptide inhibitors improves hemostasis and may become an option to treat patients with hemophilia including those with inhibitors. We developed a TFPI-antagonistic fusion peptide (FP) consisting of a linear and a cyclic peptide connected by a linker. The two peptide entities bind to different epitopes on TFPI and together synergistically inhibit TFPI. The FP was further improved by half-life extending (HL) non-covalent albumin binding. HL-FP was characterized for in vitroinhibition of TFPI, pharmacokinetics, and improvement of coagulation in animal models of hemophilia.MethodsHL-FP was characterized in a set of in vitro assays for binding to and inhibition of TFPI. Interaction with immobilized TFPI was studied by BiaCore. Functional inhibition was analyzed in model assay systems such as inhibition of FXa and FX activation by TF/FVIIa and plasma assays according to the calibrated automated thrombography (CAT) protocol at low TF in hemophilia plasma. Addition of TFPI simulated conditions of potentially elevated TFPI plasma concentrations. In a single dose PK study, mice (n=6 per time point) received 400 nmol/kg of the HL-FP intravenously (i.v.) or subcutaneously (s.c.). Plasma was sampled up to 38 h after dosing and HL-FP level quantified by a compound specific LC-MS protocol. To provide an ex vivo activity measure, FVIII inhibitory antibodies were added to mouse plasma to mimic a hemophilic condition and then analyzed by calibrated automated thrombography (CAT). A 2-week repeated i.v. dose study in mice investigated TFPI accumulation due to HL-FP. HL-FP was dosed at 40, 400, and 2000 nmol/kg and mouse plasma TFPI levels determined by ELISA. The efficacy of the HL-FP was studied in a hemophilia A mouse tail cut model and in a marmoset monkey model of ex vivoimprovement of coagulation. FVIII knockout mice (n=16 per group) were dosed i.v. with 12-400 nmol/kg HL-FP in the presence of a sub-therapeutic level of recombinant FVIII (10 U/kg) and blood loss (mg) was assessed. Marmoset monkeys (N=4) received 400 nmol/kg HL-FP i.v. and plasma samples obtained 1 h after dosing were analyzed by CAT in the presence of FVIII inhibitory antibodies.ResultsHL-FP bound to and efficiently inhibited TFPI as demonstrated in several in vitro test systems. Binding affinity of < 1nM correlated well with functional inhibition of TFPI in model assays, resulting in IC50s of ~0.7nM. The HL-fusion peptide (HL-FP) efficiently inhibited plasma TFPI, which resulted in an improvement of all thrombin generation parameters in plasma of hemophilia A and B patients, with EC50s ranging from 6 to 20nM. HL-FP increased peak thrombin levels of hemophilia plasma to or slightly above a range established for individual normal plasma. Non-covalent binding to albumin substantially increased the half-life to ~4 h with ~ 50% s.c. bioavailability in mice. The ex vivo procoagulant activity determined by CAT correlated well with HL-FP plasma concentrations. In the repeated dose study, the HL-FP was well tolerated and did not accumulate TFPI, which strongly indicates that HL-FP did not interfere with TFPI clearance receptor interactions. HL-FP significantly reduced bleeding in the hemophilia mouse tail cut bleeding model at a dose as low as 40 nmol/kg. In marmoset monkeys, HL-FP efficiently improved ex vivo plasma thrombin generation, even at low peptide plasma concentrations (25- 55 nM).SummaryWe developed a TFPI inhibitor composed of two TFPI antagonistic peptides that completely inhibits TFPI. Introduction of an entity non-covalently bound to albumin provides intermediate half-life extension and s.c. bioavailability. This HL-FP improved coagulation and hemostasis in animal models of hemophilia and did not interfere with TFPI clearance receptor interactions. TFPI-antagonistic peptides with a prolonged half-life, resistance to elevated TFPI, and minimal interference with TFPI clearance. Our HL-FP appears to be useful in preventing bleeding in hemophilia and provides a FVIII and FIX independent approach for non-i.v. treatment. DisclosuresDockal:Baxter Innovations GmbH, Vienna, Austria: Employment. Hartmann:Baxter Innovations GmbH, Vienna, Austria: Employment. Polakowski:3B Pharmaceuticals GmbH, Berlin, Germany: Employment. Panholzer:Baxter Innovations GmbH, Vienna, Austria: Employment. Kammlander:Baxter Innovations GmbH, Vienna, Austria: Employment. Osterkamp:3B Pharmaceuticals, Berlin, Germany: Employment. Reineke:3B Pharmaceuticals GmbH, Berlin, Germany: Employment. Schiviz:Baxter Innovations GmbH, Vienna, Austria: Employment. Hoellriegl:Baxter Innovations GmbH, Vienna, Austria: Employment. Scheiflinger:Baxter Innovations GmbH, Vienna, Austria: Employment.

Reduced Polyethylene Glycol-Conjugated B-Domain–Deleted Factor VIII (PEG-BDD-FVIII) Clearance: Selective Peg Steric Modulation without Affecting Potency

Prophylactic factor VIII (FVIII) replacement therapy in hemophilia A requires intravenous administration up to every other day due to the short half-life of FVIII in plasma. Plasma half-life extension of FVIII by polyethylene glycol (PEG) conjugation is thought to be mediated by decreasing hepatic clearance of FVIII. BAY 94-9027 is a rationally designed B-domain–deleted (BDD) FVIII molecule, in which a single 60-kDa PEG molecule was attached to a specific amino acid (1804) to increase its circulating half-life and reduce the exposure to epitopes reported to cause immunogenicity in the A3 domain while preserving full biological function. BAY 94-9027 is currently in clinical trials and has prolonged half-life and improved efficacy in animal models and humans.As a first step in determining whether the half-life extension with BAY 94-9027 is related to steric hindrance exerted by PEG, we investigated whether PEG impacts BAY 94-9027 binding interactions. Direct binding of HKB11-derived FVIII, BAY 94-9027 or BDD-FVIII, was assessed by measuring the ability of a panel of immobilized monoclonal antibodies directed toward different FVIII domains to capture FVIII. Interactions with more physiologic partners were indirectly assessed by thrombin generation assay (TGA) and by an in vitro hepatocyte clearance assay. TGA monitored FVIII-dependent thrombin generation, while the hepatocyte clearance assay assessed the ability of primary human hepatocytes to remove FVIII from the incubation medium.Our results indicate that the presence of the A3-directed PEG reduced BAY 94-9027 capture by immobilized antibodies directed toward the FVIII regions at or near the site of conjugation. Capture by antibodies directed toward the A3 and C2 domains were most impacted, while those directed toward A1 and A2 still bound BAY 94-9027. The A3-specific C7F7 antibody showed ~50% lower capture of BAY 94-9027 vs BDD-FVIII at 20 ng/mL of FVIII. C7F7 capture of PEG-BDD-FVIII was further reduced when a di-PEG conjugate of BDD-FVIII was subjected to the same assay, again confirming that PEG sterically modulates PEG-BDD-FVIII reactivity to the antibody. To determine whether the steric effects observed with PEG may impact FVIII function globally, TGA was performed with BAY 94-9027 spiked into FVIII-deficient plasma and subjected to 1 pM tissue factor initiation. By TGA, both BDD-FVIII and BAY 94-9027 generated comparable peak thrombin levels, with EC50 values of 3.9 and 3.2 nM for BDD-FVIII and BAY 94-9027, respectively. As thrombin generation is a consequence of activated FVIII amplification of factor X activation by activated factor IX, these results indicate that the PEG did not disrupt activated PEG-BDD-FVIII interactions with its partners in the factor Xase enzyme complex, consistent with published PEG-BDD-FVIII efficacy. By hepatocyte clearance assay, PEG-BDD-FVIII clearance was reduced ~30-40% compared with BDD-FVIII, regardless of whether von Willebrand factor was present. This reduction in hepatocyte clearance is likely to contribute to the prolonged plasma half-life reported for BAY 94-9027 (Mei B, et al. Blood. 2010;116(2):270-279; Coyle TE, et al. Journal of Thrombosis and Haemostasis. 2014;12(4):488-496). DisclosuresBlasko:Bayer Healthcare: Employment. Leong:Bayer Healthcare: Employment. Sim:Bayer Healthcare: Employment. Tang:Bayer Healthcare: Employment. Ho:Bayer Healthcare: Employment. Wu:Bayer Healthcare: Employment. Kauser:Bayer Healthcare: Employment. Subramanyam:Bayer Healthcare: Employment.

Altered plasma fibrin clot properties and fibrinolysis in patients with multiple myeloma

Multiple myeloma (MM) is associated with increased risk of venous and arterial thromboembolism. Formation of denser and poorly lysable fibrin clots is observed in patients with arterial and venous thromboembolism. We investigated fibrin clot properties and their determinants in MM patients. Ex vivo plasma fibrin clot permeability, turbidity and susceptibility to lysis were evaluated in 106 MM patients at the time of diagnosis vs. 100 age- and sex-matched controls. MM patients had lower clot permeability (Ks ), compaction, indicating denser fibrin clots, impaired fibrin polymerization with longer lag phase and lower final turbidity (D-Dmax ), combined with hypofibrinolysis reflected by longer lysis time and slower rate of D-dimer release from fibrin clots (D-Drate ) compared with controls (all P<0·001). Patients with IgG MM had lower Ks compared with IgA MM [5·9 (5·1-6·4) vs. 6·3 (5·9-7·2) 10(-9) cm(2) ; P=0·007] and longer lysis time compared with light-chain-disease patients [11·4 (10·9-12·3) vs. 10·7 (9·8-11·9) min; P=0·022]. Of the fibrin variables, only Ks was significantly lower in patients with International Staging System (ISS) grade III than in those with ISS grade I and II [5·9 (4·9-6·6) vs. 6·2 (5·7-6·8) 10(-9) cm(2) ; P=0·015]. Multivariate analysis adjusted for age and fibrinogen showed that in MM patients elevated peak thrombin levels determine Ks and D-Dmax , while thrombin-activatable fibrinolysis inhibitor (TAFI) activity predicts Ks , t50% , D-Drate and lag phase. Our study demonstrates prothrombotic fibrin clot phenotype in patients with MM, with a significant impact of increased thrombin formation and TAFI activity.

Weight-adjusted LMWH Prophylaxis Provides More Effective Thrombin Inhibition in Morbidly Obese Pregnant Women

IntroductionLow molecular weight heparin (LMWH) prophylaxis has been recommended for morbidly obese pregnant women (>40kg/m2). There is very little data on the anticoagulant effects of LMWH in this group. We investigated two different dosing regimens; fixed dose and weight-adjusted dose on the anticoagulant effects of the LMWH tinzaparin used for thromboprophylaxis in obese pregnant women. Materials and MethodsTwenty morbidly obese pregnant women were started on a fixed dose of tinzaparin (4,500 iu/day) at 32weeks gestation and then changed to a weight-adjusted dose (75iu/kg/day) for the remainder of their pregnancy. Four-hour post LMWH, venous bloods were taken after each initial dose and repeated every two weeks until delivery. Twenty normal weight women who did not receive LMWH at the same gestation were used as controls. ResultsPrior to LMWH prophylaxis, tissue factor pathway inhibitor (TFPI) levels in the obese group at 32weeks were significantly lower (p<0.001) and endogenous thrombin potential (ETP) and peak thrombin levels in obese group were significantly higher, compared with controls (p<0.0001; p<0.001).There was no significant difference between ETP levels before and after fixed LMWH. However, ETP levels were significantly lower post weight-adjusted dose compared with post fixed dose. There was a significant effect of LMWH on TFPI levels, (p<0.0001). ETP correlated positively with total body weight prior to LMWH (r=0.631) (p<0.05) and at fixed dose (r=0.578) (p<0.05). ConclusionMorbidly obese pregnant women have increased thrombin generation and reduced natural anticoagulant in third trimester. This prothrombotic state was more effectively attenuated by weight-adjusted than fixed LMWH doses.

Individuals with coronary artery disease at a young age and features of the metabolic syndrome have an increased prothrombotic potential

The relation between coagulation and atherosclerosis has been extensively described, pointing towards a hypercoagulable state in patients with atherosclerosis, especially in young individuals. However, not all studies were conclusive. It is known that the metabolic syndrome (MetS), a risk factor for coronary artery disease (CAD), is related to a higher incidence of thrombo-embolic events. We hypothesised that individuals with CAD at a young age and MetS have an increased prothrombotic potential. It was the study objective to analyse the endogenous thrombin potential (ETP) and related thrombin generation parameters in patients with CAD before the age of 51 in men and 56 in women with and without MetS features and their healthy first-degree relatives. In this case-control study we included 118 CAD patients and 50 first-degree relatives (controls). Parameters of thrombin generation were obtained with calibrated automated thrombinography. An adjusted general linear model (GLM) showed a positive association between the peak thrombin levels and the presence of CAD at a young age. Based on the NCEP criteria we divided our patient group in CAD patients with and without MetS, and compared them to the controls without MetS. We showed that CAD patients with MetS have increased ETP levels, both in comparison with healthy first-degree relatives and with CAD patients without MetS. There were no differences in ETP between patients without MetS and healthy controls. In conclusion, this study shows that individuals with CAD at a young age and MetS features have an increased prothrombotic potential, compared to CAD patients without MetS.