Synergistic effect of a factor Xa inhibitor, TAK-442, and antiplatelet agents on whole blood coagulation and arterial thrombosis in rats

Efficacy and safety of next-generation tick transcriptome-derived direct thrombin inhibitors

Despite their limitations, unfractionated heparin (UFH) and bivalirudin remain standard-of-care parenteral anticoagulants for percutaneous coronary intervention (PCI). We discovered novel direct thrombin inhibitors (DTIs) from tick salivary transcriptomes and optimised their pharmacologic activity. The most potent, ultravariegin, inhibits thrombin with a K_i of 4.0 pM, 445-fold better than bivalirudin. Unexpectedly, despite their greater antithrombotic effect, variegin/ultravariegin demonstrated less bleeding, achieving a 3-to-7-fold wider therapeutic index in rodent thrombosis and bleeding models. When used in combination with aspirin and ticagrelor in a porcine model, variegin/ultravariegin reduced stent thrombosis compared with antiplatelet therapy alone but achieved a 5-to-7-fold lower bleeding time than UFH/bivalirudin. Moreover, two antibodies screened from a naïve human antibody library effectively reversed the anticoagulant activity of ultravariegin, demonstrating proof-of-principle for antidote reversal. Variegin and ultravariegin are promising translational candidates for next-generation DTIs that may reduce peri-PCI bleeding in the presence of antiplatelet therapy.

Suppressive Effects of Aspirin for Postthoracotomy Pleural Adhesion in Rats

BACKGROUND

Postoperative adhesion is one of major concerns at re-thoracotomy. Aspirin has both the anti-platelet and anti-inflammatory effects, and decreases several cytokines production.

OBJECTIVE

We investigated that aspirin could reduce postoperative adhesion formation in a rat model.

METHODS

We cauterised the lung visceral pleural to make postoperative adhesion in rats. The animals were allocated to a control group and an aspirin administration group (100 mg/kg/day for 14 days). We performed re-thoracotomy and evaluated the adhesion lengths on day 14. We also investigated the cytokine expression in the adhesion region and the peripheral tissue with platelet-derived growth factor (PDGF), platelet-derived growth factor receptor (PDGFR), alpha smooth muscle actin (α-SMA), transforming growth factor beta 1 (TGF-β1), and vascular endothelial growth factor-A (VEGF-A), sequentially.

RESULTS

The adhesion lengths were significantly shorter in the aspirin group than that in the control group (8.7±2.0 mm vs 11.2±1.1 mm, p=0.024). The expressions of PDGF and PDGFR were lower in the aspirin group than that in the control group on day 3. The expression of α-SMA on fibroblasts decreased in the aspirin group on day 3. There was no significant difference in the expressions of TGF-β1 and VEGF-A with administration of aspirin.

CONCLUSIONS

Aspirin could reduce postoperative pleural adhesion by inhibiting the expression of PDGF.

Anti-thrombotic effect of a factor Xa inhibitor TAK-442 in a rabbit model of arteriovenous shunt thrombosis stimulated with tissue factor

Objective

Arterial thrombosis is triggered by tissue factor, which is a transmembrane glycoprotein can be released into the blood circulation after plaque rupture. Animal models with reflecting ruptured plaque lesions will be useful to understand efficacy of anticoagulant. In this study, we sought to improve a common arteriovenous shunt model in rabbits, aiming for a model of thrombosis stimulated with tissue factor, and to investigate the anti-thrombotic effect of a direct factor Xa inhibitor TAK-442 in the model.

Results

In the model where thrombus was stimulated with a thrombogenic silk thread soaked with recombinant human tissue factor, thrombus formation was significantly reduced by TAK-442 at more than 37.5 µg/kg, accompanied with prolonged plasma hemostatic parameters. Although efficacious doses of anti-coagulants in ordinary arteriovenous thrombosis models are widely reported to be higher than those in venous thrombosis models, TAK-442 showed its efficacy in the present arteriovenous shunt thrombosis model, with equivalent sensitivity in a previously reported venous model. TAK-442 might be effective under conditions thrombus formed is more influenced by tissue factor pathway.

Immediate laser-induced hemostasis in anticoagulated rats subjected to oral soft tissue surgery: a double-blind study

Given the growing trend towards medical indications for continuous use of anticoagulants, the number of patients on these medications continues to rise. The management of patients on oral anticoagulants requiring oral surgical procedures has aroused much controversy. Changes in an anticoagulation regimen are associated with an increased risk of thromboembolism. However, it seems logical and advantageous for the patients' health if surgery could be performed without any change to the anticoagulation therapy. In dentistry, high-power lasers have been poorly explored in this field. The hemostatic properties of high-power lasers could be helpful during oral soft tissue surgeries in anticoagulated patients. The aim of this study was to compare bleeding time in anticoagulated rats after lingual frenectomy performed with a scalpel or diode laser with bleeding time in healthy animals. Twenty-four male Wistar rats were assigned to four groups (n = 6): (CS) Control-Scalpel Surgery; (AS) Anticoagulated-Scalpel Surgery; (CL) Control-Laser (diode laser 810 nm/1.5 W) Surgery; and (AL) Anticoagulated-Laser Surgery (diode laser 810 nm/1.5 W). Warfarin administration was used to induce anticoagulation. Blood was blotted every 30 seconds with filter paper until bleeding stopped to verify bleeding time. Two blinded researchers performed the surgeries and collected the bleeding time data. Diode laser surgery led to complete hemostasis in rats during and after lingual frenectomy. Zero bleeding was assessed during surgeries and after diode laser surgeries in anticoagulated rats. Laser-induced hemostasis offered an alternative solution to the controversial issue of intraoperative and postoperative bleeding control in patients on anticoagulation therapy.

Phase 2 study of TAK-442, an oral factor Xa inhibitor, in patients following acute coronary syndrome

TAK-442 is an oral direct factor Xa inhibitor. We sought to determine the dose-dependent effect of TAK-442 on major bleeding when added to standard treatment in stabilised patients with acute coronary syndrome (ACS). In this phase II double-blind study, 2,753 ACS patients were randomised to TAK-442 or placebo in addition to usual care using a three-stage adaptive design. Patients were randomised to placebo in all stages, but doses of TAK-442 escalated from 10 mg BID, 20 mg twice-daily (BID), or 40 mg once-daily (QD) in stage 1; to 40 mg BID, 80 mg QD, or 80 mg BID in stage 2; and to 160 mg QD or 120 mg BID in stage 3. Study drug was started 36 hours after emergent treatment of ACS and within seven days of admission, and continued for 24 weeks. The primary endpoint was incidence of TIMI (thrombolysis in myocardial infarction) major bleeding. TIMI major bleeding incidence was low, but higher with the pooled TAK-442 doses than with placebo (17 [0.9%] vs 4 [0.5%]; p=0.47), although the difference was neither significant nor dose-dependent. However, a dose response was evident when using the modified ISTH scale. The incidence of cardiovascular events was similar among TAK-442 dose groups and placebo. When administered over a wide range of doses after an ACS event, TAK-442 treatment did not result in a dose-dependent increase in TIMI major bleeding, but increased bleeding was observed when a more sensitive bleeding scale was used. There was no evidence for efficacy.

A Novel Direct Factor Xa Inhibitory Peptide with Anti-Platelet Aggregation Activity from Agkistrodon acutus Venom Hydrolysates

Snake venom is a natural substance that contains numerous bioactive proteins and peptides, nearly all of which have been identified over the last several decades. In this study, we subjected snake venom to enzymatic hydrolysis to identify previously unreported bioactive peptides. The novel peptide ACH-11 with the sequence LTFPRIVFVLG was identified with both FXa inhibition and anti-platelet aggregation activities. ACH-11 inhibited the catalytic function of FXa towards its substrate S-2222 via a mixed model with a K_i value of 9.02 μM and inhibited platelet aggregation induced by ADP and U46619 in a dose-dependent manner. Furthermore, ACH-11 exhibited potent antithrombotic activity in vivo. It reduced paralysis and death in an acute pulmonary thrombosis model by 90% and attenuated thrombosis weight in an arterio-venous shunt thrombosis model by 57.91%, both at a dose of 3 mg/kg. Additionally, a tail cutting bleeding time assay revealed that ACH-11 did not prolong bleeding time in mice at a dose of 3 mg/kg. Together, our results reveal that ACH-11 is a novel antithrombotic peptide exhibiting both FXa inhibition and anti-platelet aggregation activities, with a low bleeding risk. We believe that it could be a candidate or lead compound for new antithrombotic drug development.

Influence of chronic administration of anabolic androgenic steroids and taurine on haemostasis profile in rats: a thrombelastographic study

Anabolic androgenic steroids (AAS) are synthetic derivatives of testosterone with thrombogenic potential in high doses and long-term administration. Taurine, a widely distributed amino-sulfonic acid, is known for its beneficial effects in hypercoagulable states. In order to assess the impact of chronic administration of high doses of AAS and taurine upon haemostasis process in rats, 40 male Wistar rats were divided into four equal groups: control group (group C) - no treatment; androgen group (group A) - received 10 mg/kg per week of nandrolone decanoate (DECA); taurine (group T) - received oral supplementation of 2% taurine in drinking water; androgen and taurine group (group AT) - concomitant administration of DECA and taurine. After 12 weeks, blood samples were collected and haemostasis parameters were assessed with the thrombelastographic (TEG) analysis system: reaction time, clot kinetics (K, α), final clot strength, coagulation index and the clot lysis (Ly30). Nandrolone significantly decreased reaction time in group A compared with control (P<0.001), whereas taurine significantly increase reaction time (P=0.01), and this effect was maintained in group AT compared with group A (P=0.009). Similar differences between groups have been recorded for the clot kinetics parameters K, α. The final clot strength and coagulation index were significantly increased in group A versus group C (P=0.04, respectively P<0.001), but not in group AT versus group C (P>0.05). There were no differences in clot lysis, as shown by Ly30. Nandrolone produces an accelerated clot development and an increased clot firmness in Wistar rats. Taurine association ensures a protective effect against this hypercoagulable state, partially restoring the altered parameters of the coagulation profile.

Arterial antithrombotic activity of rivaroxaban, an orally active factor Xa inhibitor, in a rat electrolytic carotid artery injury model of thrombosis

Rivaroxaban, an oral, direct factor Xa inhibitor, has been approved in several countries for thromboprophylaxis after elective hip or knee arthroplasty based on favorable benefit-risk profile and improved efficacy compared to enoxaparin in reducing the composite of symptomatic and asymptomatic deep vein thrombosis, nonfatal pulmonary embolism, and all-cause mortality. Given the potential therapeutic utility of factor Xa inhibition in arterial thrombosis, we evaluated the antithrombotic activity of rivaroxaban in a model of arterial thrombosis in anesthetized rats in which thrombotic occlusion was induced by electrolytic injury of the carotid artery. Rivaroxaban, 0.3, 1 or 3 mg/kg, enoxaparin, 10 mg/kg, or vehicle were infused intravenously to anesthetized rats and time to occlusion as well as coagulation parameters monitored following carotid electrolytic injury. Although the lowest dose of rivaroxaban (0.3 mg/kg) did not prolong occlusion time compared to vehicle, rivaroxaban at 1 or 3 mg/kg prevented occlusion in all vessels during the 30-min observation period (median occlusion time >30 min), which was greater than that following a single dose of enoxaparin infused at a dose of 10 mg/kg (median time to occlusion = 21.6 min). Rivaroxaban was also effective following oral dosing at 3 mg/kg. Rivaroxaban's antithrombotic activity was paralleled by dose-dependent increases in prothrombin time (PT) and activated clotting time (ACT) without significant changes in activated partial thromboplastin time. Rivaroxaban also markedly increased Russell's viper venom time (RVVT) and decreased thrombin-antithrombin complex concentrations at all doses. These findings support the potential utility of rivaroxaban in arterial thrombotic disorders such as acute coronary syndrome, stroke and peripheral arterial disease.

New and emerging anticoagulant therapy for atrial fibrillation and acute coronary syndrome

Abstract Thrombosis is an underlying cause of many cardiovascular disorders, and generation of thrombi in the arterial circulation can lead to unstable angina, myocardial infarction, or ischemic stroke. Antithrombotic therapy is widely used, with proven benefit to prevent ischemic stroke and thromboembolic events in patients with atrial fibrillation (AF) or to prevent further ischemic complications in patients with acute coronary syndrome (ACS). Traditional anticoagulants (including unfractionated heparin, low-molecular-weight heparin, and warfarin) and antiplatelet agents (including aspirin, clopidogrel, and prasugrel) are typically used for these indications. Limitations to their use include variable pharmacokinetic and pharmacodynamic profiles, inability to inhibit fibrin-bound thrombin, risk of heparin-induced thrombocytopenia, delayed onset of action, numerous drug interactions, need for substantial laboratory monitoring and dosage titrations, hyporesponsiveness or resistance, hypersensitivity, adverse events, and bleeding. To overcome some of the limitations of traditional agents, new antithrombotic agents under development are highly selective for specific coagulation factors blocking the synthesis of thrombin. Clinicians must have an understanding of the new anticoagulants to aid in the selection of appropriate therapies for patients. We describe the most relevant phases II and III clinical trials that evaluated several recent emerging anticoagulant drugs for use in patients with AF or ACS. The advantages of many new agents include predictable pharmaco-dynamic response and pharmacokinetic parameters, allowing for fixed oral dosing with no need for laboratory monitoring. For patients with AF, dabigatran is already approved for the prevention of stroke and systemic embolism, rivaroxaban appears to be an effective alternative to warfarin in high-risk patients, and apixaban may also be an effective alternative to aspirin in patients unable to take warfarin. Otamixaban shows promise as an intravenous alternative for patients with ACS in the acute care setting. Likewise, rivaroxaban, dabigatran, and darexaban with or without dual antiplatelet therapy may be beneficial for secondary prevention of ischemic events in patients with ACS.

Inhibitors of propagation of coagulation: factors V and X

Cardiovascular diseases are still the most important cause of morbidity and mortality in western countries and antithrombotic treatment is nowadays widely used. Drugs able to reduce coagulation activation are the treatment of choice for a number of arterial and/or venous thromboembolic conditions. Some of the drugs currently used for this purpose, such as heparins (UFH or LMWH) and VKA, have limitations consisting of a narrow therapeutic window and an unpredictable response with the need of laboratory monitoring in order to assess their efficacy and safety. These drawbacks have stimulated an active research aimed to develop new drugs able to act on single factors involved in the coagulation network, with predictable response. Intense experimental and clinical work on new drugs has focused on synthetic agents, which could preferably be administered orally and at fixed doses. The most advanced clinical development with new anticoagulants has been achieved for those inhibiting FXa and some of them, like fondaparinux, are already currently used in clinical practice. Other agents, such as rivaroxaban, apixaban, otamixaban and edoxaban are under development and have already been studied or are currently under investigation in large scale phase III clinical trials for prevention and treatment of venous thromboembolism, atrial fibrillation and acute coronary syndromes. Some of them have proved to be more effective than conventional therapy. Data on some agents inhibiting FVa are still preliminary and some of these drugs have so far been considered only in patients with disseminated intravascular coagulation secondary to sepsis.

Heparin-associated anti-Xa activity and platelet-derived prothrombotic and proinflammatory biomarkers in moderate to high-risk patients with acute coronary syndrome

Heparin compounds, to include fractionated and unfractionated preparations, exert both antithrombotic and antiinflammatory effects through combined inhibition of factor Xa and thrombin. The contribution of modulated platelet activity in vivo is less clearly defined. The SYNERGY library was a prospectively designed repository for candidate clinical, hemostatic, platelet, and molecular biomarkers from patients participating in SYNERGY--a large-scale, randomized clinical trial evaluating the comparative benefits of unfractionated heparin (UFH) and enoxaparin in high-risk patients with acute coronary syndrome (ACS). Samples were collected from 201 patients enrolled at 26 experienced, participating sites and shipped to established core laboratories for analysis of platelet, endothelium-derived, inflammatory and coagulation activity biomarkers. Tissue factor pathway inhibitor (TFPI)--a vascular endothelial cell-derived factor Xa regulatory protein-correlated directly with plasma anti-Xa activity (unadjusted: r = 0.23, P < 0.0001; adjusted: β = 0.10; P = 0.001), as did TFPI-fXa complexes (unadjusted: r = 0.34, P < 0.0001; adjusted: β = 0.38; P = < 0.0001). In contrast, there was a direct and inverse relationship between anti-Xa activity and two platelet-derived biomarkers-plasminogen activator inhibitor-1 (unadjusted: r = -0.18, P = 0.0012; adjusted: β = -0.10; P = 0.021) and soluble CD40 ligand (unadjusted: r = -0.11, P = 0.05; adjusted: β = -0.13; P = 0.049). All measured analyte relationships persisted after adjustment for age, creatinine clearance, weight, sex, and duration of treatment. Differences in biomarkers between patients receiving UFH and those randomized to enoxaparin were not observed. The ability of heparin compounds to affect the prothrombotic and proinflammatory states which characterize ACS may involve factor Xa-related modulation of platelet activation and expression. Whether this potentially beneficial effect is direct or indirect and achieved, at least in part, through the release of endothelial cell-derived coagulation regulatory proteins will require further investigation.