Comparison of the effect of edoxaban,a direct factor Xa inhibitor,with a direct thrombin inhibitor,melagatran, and heparin on intracerebral hemorrhage induced by collagenase in rats

Introduction

Intracerebral hemorrhage (ICH) is a major clinical concern with anticoagulation therapy. The effect of a new oral direct FXa inhibitor, edoxaban, was determined in a rat model of ICH and compared with a direct thrombin inhibitor, melagatran, and heparin.

Methods

To induce ICH, 0.1 U collagenase type VII was injected into the striatum of male Wistar rats under anesthesia with thiopental or halothane. Immediately after ICH induction, edoxaban, melagatran, or heparin were infused intravenously. Five hours after ICH induction, the brain was removed and ICH size was measured. To estimate the margin of safety, antithrombotic effects were evaluated in a rat venous thrombosis model.

Results

Edoxaban at 6 mg/kg/h significantly increased ICH volume (1.8-fold) and prolonged prothrombin time (PT) 2.8-fold compared to the vehicle group. No deaths were observed with edoxaban. Melagatran at 1 mg/kg/h increased ICH volume at 1 mg/kg/h (2.8-fold) with 6.1-fold PT prolongation. At 3 mg/kg/h, all rats died due to severe ICH (3.9-fold). Heparin at both 100 and 500 U/kg/h significantly increased ICH. At 500 U/kg/h, 5 out of 8 rats died. The doses required for 50% inhibition of thrombosis of edoxaban, melagatran, and heparin were 0.045 mg/kg/h, 0.14 mg/kg/h, and 55 U/kg/h, respectively. The safety margins between antithrombotic and ICH exacerbation effects of these anticoagulants were 133, 7.1, and 1.8, respectively.

Conclusion

The safety margin of edoxaban was wider than that of melagatran or heparin. These results suggest that edoxaban may be preferable from the perspective of ICH exacerbation risk.     

Target-mediated clearance and bio-distribution of a monoclonal antibody against the Kunitz–type protease inhibitor 2 domain of Tissue Factor Pathway Inhibitor

Introduction

A humanised monoclonal antibody, concizumab, that binds with high affinity to the Kunitz-type protease inhibitor (KPI) 2 domain of human tissue factor pathway inhibitor (TFPI) is in clinical development. It promotes coagulation by neutralising the inhibitory function of TFPI and may provide a subcutaneous prophylaxis option for patients with haemophilia. We aimed to study biodistribution and pharmacokinetics (PK) of concizumab.

Materials and Methods

Blockage of cellular TFPI by concizumab was measured by tissue factor/Factor VIIa-mediated Factor X activation on human EA.hy926 cells. Biodistribution of concizumab was analysed in rabbits by immunohistology, and the PK was measured in rabbits and rats.

Results and Conclusions

Concizumab bound to cell surface TFPI on EA.hy926 cells and neutralised TFPI inhibition of Factor X activation. The antibody cross-reacted with rabbit TFPI, but not with rat TFPI, allowing for comparative PK studies. PK data in rats described a log-linear profile typical for a non-binding antibody, whereas PK data in rabbits revealed a non-linear, dose-dependent profile, consistent with a target-mediated clearance mechanism. Immunohistology in rabbits during target-saturation showed localisation of the antibody on the endothelium of the microvasculature in several organs. We observed a marked co-localisation with endogenous rabbit TFPI, but a negligible sub-endothelial build-up. Concizumab binds and neutralises the inhibitory effect of cell surface-bound TFPI. The PK profile observed in rabbits is consistent with a TFPI-mediated drug disposition. Double immunofluorescence shows co-localisation of the antibody with TFPI on the endothelium of the microvasculature and points to this TFPI as a putative target involved in the clearance mechanism.     

Gla-domainless factor Xa: molecular bait to bypass a blocked tenase complex

Background

Hemophilia is caused by deficiencies in coagulation factor VIII or IX, resulting in direct blockade of the intrinsic tenase complex and indirect blockade of the extrinsic tenase complex which is rapidly inhibited upon binding of factor Xa to tissue factor pathway inhibitor. We evaluated the ability of Gla-domainless factor Xa, a truncated form of factor Xa devoid of procoagulant properties, to bind to tissue factor pathway inhibitor and to alleviate the physiological inhibition of the extrinsic tenase.

Design and Methods

Using a thrombin generation assay triggered by a low concentration of tissue factor, we evaluated the ability of Gla-domainless factor Xa to restore blood coagulation in plasma from hemophilia A and B patients without and with inhibitors. We then compared its efficacy to generate thrombin to depletion of antithrombin or tissue factor pathway inhibitor by specific antibodies. Finally, we compared the kinetics of neutralization of factor Xa and Gla-domainless factor Xa by antithrombin and tissue factor pathway inhibitor.

Results

Gla-domainless factor Xa was able to restore thrombin generation in plasma samples from hemophiliacs. This effect was observed for plasma from hemophilia A patients without or with inhibitors and for plasma from hemophilia B patients. Gla-domainless factor Xa had a lower affinity than factor Xa for tissue factor pathway inhibitor whereas the affinities of both proteins for antithrombin were similar. Finally, despite a short half-life in plasma, the effect of Gla-domainless factor Xa on thrombin generation was sustained for at least 1 hour.

Conclusions

As Gla-domainless factor Xa was able to restore thrombin generation in plasma from hemophilia patients, our results suggest that it may be an effective alternative to current treatments for hemophilia with or without an inhibitor.     

苏灵局部止血及体外抑制FXa+t-PA诱导纤溶酶原激活作用

目的探讨苏灵(SL)体外对人血浆凝固时间的影响、局部给药对小鼠剪尾后出血的促凝作用及体外对纤溶系统的影响。方法将磷酸钠缓冲液、SL溶液和人凝血酶溶液与人血浆混合,血凝仪测定其凝固时间;将分别浸有磷酸钠缓冲液(溶媒组)、SL溶液和人凝血酶溶液的纱布敷于小鼠剪尾后的伤口上,计算出血时间和出血量,评价各组的止血效果;采用SDS-PAGE方法检测SL对人纤溶酶原的降解作用,吸光度法测定SL体外对FXa+t-PA诱导的纤溶酶原激活作用的影响。结果 SL和人凝血酶能明显缩短人血浆凝固时间,并能明显缩短小鼠剪尾的止血时间及减少出血量,与溶媒组比较差异有统计学意义(P0.05);SL对人纤溶酶原没有直接的裂解作用,不激活人纤溶酶原;SL可抑制FXa+t-PA诱导的人纤溶酶原体外激活。结论 SL具有良好的局部止血效果,其部分作用机制可能与抑制FXa激活纤溶系统有关。     

A Computational Analysis of FXa Generation by TF:FVIIa on the Surface of Rat Vascular Smooth Muscle Cells

A computational model was developed to investigate the contribution of classical mass transport and flow parameters to factor X (FX) activation by the tissue factor–factor VIIa complex (TF:VIIa) on one wall of a parallel-plate flow chamber. The computational results were compared to previously obtained experimental data for the generation of factor Xa (FXa) by TF:VIIa on the surface of cultured rat vascular smooth muscle cells. In this study, the complete steady-state convection–diffusion equation was solved using the commercial software package, FLUENT (Fluent Inc., Lebanon, New Hampshire). A user-defined subroutine interfaced with FLUENT implemented the surface reaction which was modeled using classical Michaelis–Menten reaction kinetics. The numerical solutions were obtained for 12 cases which used combinations of three wall shear rates and four reaction rates. The numerically obtained fluxes for a given reaction rate displayed a wall shear rate dependence which ranged from classical kinetic reaction control (no dependence) to pure diffusional control (maximum dependence). The experimental data, however, were not represented by numerical data generated using a single reaction rate. The three numerically obtained fluxes which corresponded most closely to the experimental fluxes were determined using three different V _max values. This finding supports the hypothesis that there may be a direct effect of flow on the TF:VIIa complex or the cell membrane. © 1998 Biomedical Engineering Society. PAC98: 8722-q, 8710+e     

利伐沙班的合成

 目的：合成高效、直接的FXa抑制剂利伐沙班。方法：以2-(2-氯乙氧基)乙酰氯、对硝基苯胺为原料,合成利伐沙班。结果：合成了利伐沙班,总收率为42.46%,纯度95.19%(HPLC)。结论：通过优化反应条件,缩短了反应时间。     

Results of a systematic evaluation of treatment outcomes for heparin-induced thrombocytopenia in patients receiving danaparoid, ancrod, and/or coumarin explain the rapid shift in clinical practice during the 1990s

INTRODUCTION: Randomized controlled trials evaluating treatment of acute, transient, but uncommon diseases are difficult to perform. The prothrombotic adverse drug reaction, heparin-induced thrombocytopenia (HIT), is such an example. During the mid-1980s, the defibrinogenating snake venom, ancrod (+/-warfarin, Canada), or coumarin (warfarin, Canada; phenprocoumon, Germany) alone, were often used to treat HIT. During the 1990s, danaparoid+/-coumarin began to replace ancrod (+/-coumarin), or coumarin alone, for treating HIT, despite danaparoid not being approved for treatment of HIT. METHODS: We performed a retrospective evaluation of treatment outcomes from 1986 to 1999, comparing danaparoid+/-coumarin (n=62) versus ancrod+/-coumarin or coumarin alone (controls, n=56). RESULTS: The predefined composite endpoint of adjudicated new, progressive, or recurrent thrombosis (including thrombotic death), or limb amputation, at day 7 (maximum, one event per patient) was significantly lower in danaparoid-treated patients, compared with controls: 8/62=12.9% (95% CI, 4.3-21.5) vs. 22/56=39.3% (95% CI, 26.1-52.5); p=0.0014. We also found a lower frequency of the composite endpoint at end of study (day 35) in danaparoid-treated patients: 12/62=19.4% vs. 24/56=42.9% (p=0.0088). Major bleeding (by day 7) occurred in 7/62 (11.3%) and 16/56 (28.6%) of danaparoid-treated and control patients, respectively (p=0.0211). CONCLUSIONS: The replacement of ancrod+/-coumarin, or coumarin alone, by danaparoid (+/-coumarin) in the mid-1990s for the treatment of HIT was justified by improved efficacy and safety.     

利伐沙班合成工艺改进

目的优化利伐沙班的合成工艺。方法以N-苯基乙醇胺为起始原料,与氯乙酰氯环合、然后经硝化、还原、酰胺化、再经环合、脱保护、最后经酰胺化制得利伐沙班。结果合成的利伐沙班的总收率为41.7%。其结构经IR、1H-NMR和MS确证。结论工艺经改进后,操作简化,成本降低,收率提高,适合工业化生产。     

Antithrombin deficiency in three Japanese families: One novel and two reported point mutations in the antithrombin gene

Introduction

Inherited antithrombin (AT) deficiency is associated with a predisposition to familial venous thromboembolic disease. We analyzed the AT gene in three unrelated patients with an AT deficiency who developed thrombosis.

Materials and Methods

We analyzed the SERPINC1 gene in three patients. Additionally, we expressed the three mutants in the COS-1 cells and compared their secretion rates and levels of AT activity with those of the wild-type (WT).

Results

We identified three distinct heterozygous mutations of c.2534C>T: p.56Arginine → Cysteine (R56C), c.13398C>A: p.459Alanine → Aspartic acid (A459D) and c.2703C>G: p.112 Proline → Arginine (P112R). In the in vitro expression experiments, the AT antigen levels in the conditioned media (CM) of the R56C mutant were nearly equal to those of WT. In contrast, the AT antigen levels in the CM of the A459D and P112R mutants were significantly decreased. The AT activity of R56C was decreased in association with a shorter incubation time in a FXa inhibition assay and a thrombin inhibition-based activity test. However, the AT activity of R56C was comparable to that of WT when the incubation time was increased.

Conclusions

We concluded that the R56C mutant is responsible for type II HBS deficiency. We considered that the A459D and P112R mutants can be classified as belonging to the type I AT deficiency.     

Inhibitors of Factor Xa

The development of directly acting, orally-active anticoagulants is an important drug discovery target. Many companies are involved in this area and the most popular target is Factor Xa (FXa). Inhibitors of FXa prevent the generation of thrombin which is the active enzyme in clot formation as well as platelet activation. Patents for FXa inhibitors from Aventis and AstraZeneca are reviewed here. The AstraZeneca patent is a continuation of a previous patent and contains virtually no biological data. The Aventis patent covers a large number of compounds. The compounds described have two amidino groups, which are important in many different protease inhibitors. However, this can lead to problems including lack of oral activity as well as lack of specificity. The only biological data presented are the K_ivalues for a number of compounds in an in vitro FXa assay.