Bioequivalence and pharmacodynamics of a generic dabigatran etexilate capsule in healthy Chinese subjects under fasting and fed conditions.

To assess bioequivalence of a generic dabigatran etexilate capsule in healthy Chinese subjects under fasting and fed conditions. This was an open-label, single-center, randomized four-period crossover study with a 7-day washout period. A single oral dose of 150 mg generic dabigatran etexilate capsule (test drug) or a commercial dabigatran etexilate capsule (Pradaxa® , reference drug) was given to healthy volunteers under the fasting and fed conditions. Plasma concentrations of total and free dabigatran were detected using a validated HPLC-MS/MS method. A noncompartmental method was used for pharmacokinetic analysis and established coagulation assays were applied for pharmacodynamic analysis. The 90% CIs of the test/reference ratios of Cmax , AUC0-t , and AUC0-∞ for the total dabigatran concentration were 92.57%-106.58%, 91.63%-106.32%, and 92.54%-106.17%, respectively, under fasting condition, and 99.30%-110.74%, 98.58%-105.37%, and 97.75%-103.99%, respectively, under fed conditions. The 90% CIs of the ratios of the parameters for the free dabigatran were 93.18%-106.98%, 92.13%-107.10%, 92.89%-106.48%, respectively, under fasting condition, and 100.05%-110.89%, 99.37%-106.23%, 97.59%-103.98%, respectively, under the fed condition. Additionally, the upper limit of the 90% CIs for σWT/σWR was below 2.5. There were no significant differences in the coagulation parameters including thrombin clotting time, activated partial thromboplastin time, and anti-IIa activity between the two preparations. The generic dabigatran etexilate capsule is bioequivalent to the brand-named product in healthy Chinese volunteers under fasting and fed conditions. The two products have comparable pharmacodynamic parameters, with a good safety profile. In addition, food intake influences absorption of both products in a similar way.

Differential effects of direct factor IIa and factor Xa inhibitors in protein C-deficient plasma detected using thrombin generation and viscoelastometry assays.

INTRODUCTION: Protein C (PC) deficiency results in dysregulated thrombin generation and increases thrombosis risk. METHODS: In order to investigate the potential effects of anticoagulant drugs in PC deficiency, we evaluated the pharmacodynamic effect of selective direct factor (F) IIa inhibitors (dabigatran and argatroban), selective direct FXa inhibitors (rivaroxaban and apixaban) and an indirect FXa/FIIa inhibitor (enoxaparin) in commercial PC-deficient plasma using thrombin generation and viscoelastometry assays modified to reflect PC anticoagulant activity. RESULTS: Endogenous thrombin potential (ETP) and peak thrombin concentration (PTC) were increased in PC-deficient plasma but this corrected completely with PC concentrate. Inhibition of FIIa and FXa with the selective inhibitors also corrected the increased ETP and PTC but required high drug concentrations. There was sustained low-level thrombin generation in PC-deficient plasma with FXa inhibitors but not with FIIa inhibitors. Adding PC concentrate to PC-deficient plasma anticoagulated with dabigatran had little additional effect on ETP or PTC. In contrast, addition of even small quantities of PC concentrate to PC-deficient plasma anticoagulated with rivaroxaban further diminished ETP, primarily by abolishing sustained thrombin generation. In the viscoelastometry assay, the coagulation time was shortened and α-angle increased in PC-deficient plasma. These abnormalities reversed with both dabigatran and rivaroxaban. CONCLUSION: The selective direct FXa and FIIa inhibitors at high concentrations both counteracted the abnormal thrombin generation and clot formation observed in PC-deficient plasma, but with qualitative differences in their effects.

A Study for the Access to a Semi-synthetic Regioisomer of Natural Fucosylated Chondroitin Sulfate with Fucosyl Branches on N-acetyl-Galactosamine Units.

Fucosylated chondroitin sulfate (fCS) is a glycosaminoglycan found up to now exclusively in the body wall of sea cucumbers. It shows several interesting activities, with the anticoagulant and antithrombotic as the most attractive ones. Its different mechanism of action on the blood coagulation cascade with respect to heparin and the retention of its activity by oral administration make fCS a very promising anticoagulant drug candidate for heparin replacement. Nonetheless, its typically heterogeneous structure, the detection of some adverse effects and the preference for new drugs not sourced from animal tissues, explain how mandatory is to open an access to safer and less heterogeneous non-natural fCS species. Here we contribute to this aim by investigating a suitable chemical strategy to obtain a regioisomer of the natural fCS polysaccharide, with sulfated l-fucosyl branches placed at position O-6 of N-acetyl-d-galactosamine (GalNAc) units instead of O-3 of d-glucuronic acid (GlcA) ones, as in natural fCSs. This strategy is based on the structural modification of a microbial sourced chondroitin polysaccharide by regioselective insertion of fucosyl branches and sulfate groups on its polymeric structure. A preliminary in vitro evaluation of the anticoagulant activity of three of such semi-synthetic fCS analogues is also reported.

A paradoxical thrombogenic mutation in factor II at the target site of arthropod bleeding toxin.

Loss-of-function mutations in coagulation cascade proteins lead to bleeding diasthesis. In contrast, gain-of-function mutations in these proteins, which are exceptionally rare, lead to hereditary thrombosis. This is best exemplified by Factor V (i.e., Factor V Leiden) and Factor II (i.e., p.Arg596Leu). Here, we report a family with hereditary thrombosis. The proposita presented with cerebral venous thrombosis accompanied by infarction at the age of 12 years. Despite anticoagulation therapy with oral warfarin, she later developed deep venous thrombosis in her hepatic portal veins at the age of 27 years. A medical exome analysis identified a de novo heterozygous mutation p.Tyr434His in Factor II, which was segregated within the family. A retrospective molecular diagnosis was made using a preserved surgical specimen from the proposita's mother, who had died 10 years earlier. The p.Tyr434 residue, which was substituted in the presently reported family, was located in "exosite I" of thrombin, a critical recognition site for fibrinogen, protein C, and thrombin aptamer. Therefore, the mutant thrombin likely exerted its thrombophilic effect by altering the affinity of thrombin to downstream substrates. Furthermore, the "exosite I" domain of thrombin was inhibited by the arthropod bleeding toxin Triabin (a protein discovered from the saliva of the blood-sucking triatomine bug Triatoma pallidipennis). Our observation that patients with a p.Tyr434His mutation exhibited recurrent thrombosis provides the first proof-of-concept in humans that a pharmacologic agent targeting "exosite I" could be an effective means of specifically modulating the thrombogenic-side of the coagulation system via the inhibition of factor II.

Non-vitamin K oral anticoagulants (NOAC) and the risk of myocardial infarction: Differences between factor IIa and factor Xa inhibition?

Guidelines already recommend non-vitamin K oral anticoagulants (NOAC) over vitamin-K antagonists (VKA) for stroke prevention in patients with atrial fibrillation. However, recommendations are lacking with respect to which NOAC to use. At the moment, NOACs may employ two different molecular mechanisms: Factor IIa inhibition (dabigatran) and factor Xa inhibition (apixaban, edoxaban, rivaroxaban). The focus of this review is to compare and contrast potential differences between factor IIa- and factor Xa inhibition with respect to risk of myocardial infarction and to detail underlying mechanisms.

Anti-IIa activity and antitumor properties of a hybrid heparin/heparan sulfate-like compound from Litopenaeus vannamei shrimp.

In this present study, the anti-IIa activity and the antitumor properties of a hybrid heparin/heparan sulfate-like compound (sH/HS) from Litopenaeus vannamei shrimp heads are related. In addition to inhibiting 90.7% of thrombin activity at the lowest tested concentration (0.5 µg/mL), sH/HS compound stimulated the synthesis of antithrombotic heparan sulfate by endothelial cells in a dose-dependent manner. In vitro experiments demonstrated that the molecule from shrimp displayed a potent anti-angiogenic effect, reducing over 80% of the tubular structures formation at 50 and 100 µg/mL. In addition, sH/HS compound was able to inhibit the migration of B16F10 cells at all tested concentrations without affecting the cell viability. Although the studied compound had no effect on the proliferation of such cells during a period of 24 h, it had a significant long-term anti-proliferative effect, reducing about 80% of colony formation and anchorage-independent growth at 50 and 100 µg/mL concentrations. When its effectiveness was tested in vivo, it was demonstrated that sH/HS promoted a reduction of more than 90% of tumor growth. In the context of thromboembolic disorders associated with cancer, such findings make the sH/HS compound an excellent target for studies on inhibiting of development and tumor progression, and the prevention of coagulopathies.

Anticoagulation in atrial fibrillation : Current evidence and guideline recommendations.

Atrial fibrillation (AF) is the most frequently encountered sustained arrhythmia with a prevalence of 0.5-10%, depending predominantly on age. The arrhythmia is associated with significant morbidity and mortality, mainly due to thromboembolic events including stroke and systemic embolisms. These complications can be effectively prevented with anticoagulation therapy either with vitamin K antagonists (VKA) or with non-vitamin K antagonists (NOAC). VKA therapy is effective in preventing strokes but these medications are difficult to use, are associated with significant bleeding risk, and have pharmacokinetic/dynamic properties that make their use cumbersome. NOACs-either factor II or factor Xa inhibitors-have been developed over the past two decades and have been tested against VKA in large randomized controlled trials. This trial evidence was complemented more recently by increasing real-world data comprising several 100,000 patients. Finally, NOACs have been examined for their use in specific clinical situations, for example, in patients undergoing cardioversion, catheter ablation, or coronary interventions. In all of these clinical scenarios, NOACs have been similarly effective or-in many instances-even superior to treatment with VKA. Recent guidelines, therefore, recommend NOAC therapy for stroke prevention in AF as first-line therapy.

Structural analysis and biological activity of a highly regular glycosaminoglycan from Achatina fulica.

Edible snails have been widely used as a health food and medicine in many countries. A unique glycosaminoglycan (AF-GAG) was purified from Achatina fulica. Its structure was analyzed and characterized by chemical and instrumental methods, such as Fourier transform infrared spectroscopy, analysis of monosaccharide composition, and 1D/2D nuclear magnetic resonance spectroscopy. Chemical composition analysis indicated that AF-GAG is composed of iduronic acid (IdoA) and N-acetyl-glucosamine (GlcNAc) and its average molecular weight is 118kDa. Structural analysis clarified that the uronic acid unit in glycosaminoglycan (GAG) is the fully epimerized and the sequence of AF-GAG is →4)-α-GlcNAc (1→4)-α-IdoA2S (1→. Although its structure with a uniform repeating disaccharide is similar to those of heparin and heparan sulfate, this GAG is structurally highly regular and homogeneous. Anticoagulant activity assays indicated that AF-GAG exhibits no anticoagulant activities, but considering its structural characteristic, other bioactivities such as heparanase inhibition may be worthy of further study.

Design, synthesis, and evaluation of heparan sulfate mimicking glycopolymers for inhibiting heparanase activity.

Heparanase is an enzyme which cleaves heparan sulfate (HS) polysaccharides of the extracellular matrix. It is a regulator of tumor behavior, plays a key role in kidney related diseases and autoimmune diabetes. We report herein the use of computational studies to extract the natural HS-heparanase interactions as a template for the design of HS mimicking glycopolymers. Upon evaluation, a glycopolymer with 12 repeating units was determined to be the most potent inhibitor and to have tight-binding characteristics. This glycopolymer also lacks anticoagulant activity.

The Antithrombotic Potential of Tinzaparin and Enoxaparin Upon Thrombin Generation Triggered In Vitro by Human Ovarian Cancer Cells IGROV1.

BACKGROUND: A documented relationship between ovarian cancer and thrombosis does exist. Low-molecular-weight heparins (LMWHs) are cornerstone drugs in the primary prevention and treatment of venous thromboembolic events in patients with cancer. However, cancer cells may alter the efficiency of these antithrombotic agents. OBJECTIVE: We aimed to characterize the procoagulant phenotype of human epithelial ovarian adenocarcinoma cells, IGROV1, and to compare the capacity of tinzaparin and enoxaparin to inhibit thrombin generation triggered by these cells. METHODS: Thrombin generation induced by different concentrations of IGROV1 cells on platelet poor plasma (PPP) was assessed by the calibrated automated thrombogram assay. Tissue factor (TF) expression was studied using Western blot analysis. Then, the experimental model of thrombin generation was used to compare the inhibitory effect of clinically relevant concentrations of both tinzaparin and enoxaparin. The inhibitory concentration 50 (IC50) of the mean rate index and the endogenous thrombin potential and the 2-fold increase in lag time were analyzed on the basis of the anti-Xa and anti-IIa activities of the LMWHs. RESULTS: IGROV1 cells suspended into PPP resulted in a significant increase in thrombin generation in the absence of any exogenous source of TF and phospholipids. Tissue factor was expressed by IGROV1 cells. Tinzaparin was a more potent inhibitor of thrombin generation than enoxaparin. The inhibition of thrombin generation induced by IGROV1 cancer cells depended mainly on the anti-Xa activity of the LMWHs. CONCLUSION: This experimental study in ovarian cancer cells demonstrates that the antithrombotic activity of LMWHs is not completely predicted by the anti-Xa or anti-IIa activities measured in PPP.

[PROCURING OF ІNTRAOPERATIVE HEMOSTASIS IN REVASCULARIZATION INTERVENTIONS].

Results of the hemostasis conduction in conditions of revascularization in 106 patients, оperated on for atherosclerotic affection of aorta and the main arteries of the lower extremities, were adduced. Syndrome of hypercoagulation of traumatic stage of surgical intervention in early postoperative period is developing due to thrombinemia on background of a fibrinolytic system depression. There was proved a necessity to impact on thrombin-fibrinous factor (factor ІІа) of hemocoagulant cascade by application of nonfractionized heparins immediately after conclusion of operative intervention with thromboprophylaxis prolongation, using low-molecular heparins (impact on Ха factor) in accordance to the branch standards.

[Reversal strategies for non-vitamin K antagonist oral anticoagulants].

Non-vitamin K oral anticoagulants (NOACs) are alternatives to vitamin K antagonists and provide consistent anticoagulation with equal or better clinical outcome and no need for routine monitoring. Bleeding is a feared complication of anticoagulants. Until recently, no specific agent has been available for reversal of NOACs. Idarucizumab binds dabigatran for rapid reversal of its activity without procoagulant effects. Andexanet alpha (expected release in 2016) and PER977 are antidotes under clinical development. This article summarizes current and potential future options to antagonize NOACs.

Inhibition of coagulation proteases Xa and IIa decreases ischemia-reperfusion injuries in a preclinical renal transplantation model.

Coagulation is an important pathway in the pathophysiology of ischemia-reperfusion injuries. In particular, deceased after circulatory death (DCD) donors undergo a no-flow period, a strong activator of coagulation. Hence, therapies influencing the coagulation cascade must be developed. We evaluated the effect of a new highly specific and effective anti-Xa/IIa molecule, with an integrated innovative antidote site (EP217609), in a porcine preclinical model mimicking injuries observed in DCD donor kidney transplantation. Kidneys were clamped for 60 minutes (warm ischemia), then flushed and preserved for 24 hours at 4°C in University of Wisconsin (UW) solution (supplemented or not). EP217609-supplemented UW solution (UW-EP), compared with unfractionated heparin-supplemented UW solution (UW-UFH) or UW alone (UW). A mechanistic investigation was conducted in vitro: addition of EP217609 to endothelial cells during hypoxia at 4°C in the UW solution inhibited thrombin generation during reoxygenation at 37°C in human plasma and reduced tumor necrosis factor alpha, intercellular adhesion molecule 1, and vascular cell adhesion molecule 1 messenger RNA cell expressions. In vivo, function recovery was markedly improved in the UW-EP group. Interestingly, levels of thrombin-antithrombin complexes (reflecting thrombin generation) were reduced 60 minutes after reperfusion in the UW-EP group. In addition, 3 months after transplantation, lower fibrosis, epithelial-mesenchymal transition, inflammation, and leukocyte infiltration were observed. Using this new dual anticoagulant, anti-Xa/IIa activity during kidney flush and preservation is protected by reducing thrombin generation at revascularization, improving early function recovery, and decreasing chronic lesions. Such an easy-to-deploy clinical strategy could improve marginal graft outcome.

Exploiting the antithrombotic effect of the (pro)thrombin inhibitor bothrojaracin.

Bothrojaracin is a 27 kDa C-type lectin-like protein from Bothrops jararaca snake venom. It behaves as a potent thrombin inhibitor upon high-affinity binding to thrombin exosites. Bothrojaracin also forms a stable complex with prothrombin that can be detected in human plasma. Formation of the zymogen-inhibitor complex severely decreases prothrombin activation and contributes to the anticoagulant activity of bothrojaracin. In the present study, we employed two rodent models to evaluate the antithrombotic effect of bothrojaracin in vivo: stasis-induced thrombosis and thrombin-induced pulmonary thromboembolism. It was observed that bothrojaracin interacts with rat prothrombin in plasma. Ex-vivo assays showed stable complex formation even after 24 h of a single bothrojaracin dose. As a result, bothrojaracin showed significant antithrombotic activity in a rat venous thrombosis model elicited by thromboplastin combined with stasis. The antithrombotic activity of bothrojaracin (1 mg/kg) persisted for up to 24 h and it was associated with moderate bleeding as assessed by a tail transection method. Formation of bothrojaracin-prothrombin complex has been also observed following intravenous administration of the inhibitor into mice. As a result, bothrojaracin effectively protected mice from thrombin-induced fatal thromboembolism. We conclude that bothrojaracin is a potent antithrombotic agent in vivo and may serve as a prototype for the development of new zymogen-directed drugs that could result in prolonged half-life and possible decreased hemorrhagic risk.

Regulation of expression of venom toxins: silencing of prothrombin activator trocarin D by AG-rich motifs.

Trocarin D (TroD), a venom prothrombin activator from Tropidechis carinatus, shares similar structure and function with blood coagulation factor Xa [Tropidechis carinatus FX (TrFX) a]. Their distinct physiologic roles are due to their distinct expression patterns. The genes of TroD and TrFX are highly similar, except for promoter and intron 1, indicating that TroD has probably evolved by duplication of FX, the plasma counterpart. The promoter insertion in TroD accounts for the elevated but not venom gland-specific expression. Here we examined the roles of 3 insertions and 2 deletions in intron 1 of TroD in the regulation of expression using luciferase as a reporter. By systematic deletions, we showed that a 209 bp region within the second insertion silences expression in mammalian and unmilked venom gland cells. Through bioinformatics analysis, we identified 5 AG-rich motifs in this region. All except the 5th motif are important for silencing function. YY1, Sp3 and HMGB2 were identified to bind these AG-rich motifs and silence gene expression in mammalian cells. Similar AG-rich motif clusters are also found in other toxin genes but not in their physiologic counterparts. Thus, AG-rich motifs contribute to regulation of expression of TroD, and probably other toxin genes.-Han, S. X., Kwong, S., Ge, R., Kolatkar, P. R., Woods, A. E., Blanchet, G., Kini, R. M. Regulation of expression of venom toxins: silencing of prothrombin activator trocarin D by AG-rich motifs.

Meta-Analysis of Efficacy and Safety of New Oral Anticoagulants Compared With Uninterrupted Vitamin K Antagonists in Patients Undergoing Catheter Ablation for Atrial Fibrillation.

Anticoagulation in catheter ablation (CA) of atrial fibrillation (AF) is of paramount importance for prevention of thromboembolic events, and recent studies favor uninterrupted vitamin K antagonists (VKAs). We aimed to compare the efficacy and safety of new oral anticoagulants (NOACs) to uninterrupted VKAs for anticoagulation in CA by performing a meta-analysis. PubMed, EMBASE, the Cochrane Library, and Clinicaltrials.gov databases were searched for studies comparing NOACs with uninterrupted VKAs in patients who underwent CA for AF from January 1, 2000, to August 31, 2015. Odds ratio (OR) and Peto's OR (POR) were used to report for event rates >1% and <1%, respectively. A total of 11,686 patients with AF who underwent CA in 25 studies were included in this analysis. There was no significant difference between NOACs and uninterrupted VKAs in occurrence of stroke or transient ischemic attacks (POR 1.35, 95% CI 0.62 to 2.94) and major bleeding (POR 0.87, 95% CI 0.58 to 1.31), which were consistent in subgroup analysis of interrupted and uninterrupted NOACs. A lower risk of minor bleeding was observed with NOACs (OR 0.80, 95% CI 0.65 to 1.00), and no major differences were observed for the risk of thromboembolic events, cardiac tamponade or pericardial effusion requiring drainage, and groin hematoma. NOACs, whether interrupted preprocedure or not, were associated with equal rates of stroke or TIA and major bleeding complications and less risk of minor bleeding compared with uninterrupted VKAs in CA for AF.

The treatment of cancer-associated venous thromboembolism in the era of the novel oral anticoagulants.

INTRODUCTION: The initial and long-term administration of low-molecular-weight heparin (LMWH) is now regarded as the treatment of choice for the therapy of patients with cancer-associated venous thromboembolism (CAT). However, LMWH requires daily subcutaneous injections and can induce thrombocytopenia. In recent years, novel direct oral anticoagulants (DOAC) have emerged to potentially replace conventional treatments. AREAS COVERED: The advantages and limitations of conventional approaches for the treatment of CAT are presented and analyzed based on available findings and on recommendations from international guidelines, as is the potential for the DOAC. EXPERT OPINION: LMWH still remains the mainstay of initial and long-term treatment of CAT. Vitamin K antagonists may have a role in patients with inactive cancer and in those with severe renal failure. Whether there is a potential for the DOAC is uncertain. Indeed, most patients with advanced cancer were excluded from the trials addressing their value. Although available findings are encouraging, before implementing them in the routine clinical practice there is the need for dedicated studies in which cancer patients, whichever their severity and prognosis, are allocated to either DOAC or LMWH, which represent the standard of treatment for patients with CAT.