Inhibitors of propagation of coagulation: factors V and X

A review of drugs that contribute to bleeding risk in general dental practice

The risk of postoperative bleeding is a daily concern for many general dental practitioners. A thorough medical and medication history must be taken to consider all risk factors, particularly drugs, that contribute to bleeding risk. While the risk from drugs such as aspirin, warfarin and clopidogrel are well known, the extent to which new antiplatelet agents and direct oral anticoagulants affect bleeding risk is less well understood. In addition, there are drugs other than antithrombotics, such as antidepressants and complementary medicines that also impair haemostasis. The aim of this paper is to provide dentists with an updated overview of the drugs commonly encountered in general dental practice that can contribute to a patient's postoperative bleeding risk.

Edoxaban in atrial fibrillation patients with established coronary artery disease: Insights from ENGAGE AF–TIMI 48

Background:

The relative efficacy and safety profile of the oral Factor Xa inhibitor edoxaban compared with warfarin in patients with atrial fibrillation and established coronary artery disease (CAD) has not been analyzed.

Materials and methods:

In the ENGAGE AF–TIMI 48 trial, two edoxaban regimens were compared with warfarin in 21,105 patients with atrial fibrillation and CHADS2 ⩾2. We analyzed the primary trial endpoints (efficacy: stroke or systemic embolic event, safety: International Society on Thrombosis and Haemostasis major bleeding) in patients with versus without CAD, and used interaction testing to assess for treatment effect modification.

Results:

The 4510 patients (21.4%) with known CAD were older, more likely male, on aspirin, with lower creatinine clearance and higher CHADS2 and HAS-BLED scores ( p <0.001 for each). Treatment with the higher-dose edoxaban regimen (versus warfarin) in patients with known CAD tended to have a greater reduction in stroke/systemic embolic event compared with patients without CAD (CAD: hazard ratio 0.65 (0.46–0.92) versus no CAD: hazard ratio 0.94 (0.79–1.12), p-INT 0.062) and also in myocardial infarction (CAD: hazard ratio 0.69 (0.49–0.98) versus no CAD: hazard ratio 1.24 (0.89–1.72), p-INT 0.017), while there was a similar reduction in bleeding irrespective of CAD status (hazard ratio 0.81 and 0.80, p-INT 0.97). Presence or absence of CAD did not modify the efficacy or safety profile of the lower-dose edoxaban regimen (versus warfarin).

Conclusion:

The reduction in ischemic events with the higher-dose edoxaban regimen versus warfarin was greater in patients with CAD, while bleeding was significantly reduced with edoxaban regardless of CAD status. The efficacy and safety profile of the lower-dose edoxaban regimen relative to warfarin was unaffected by CAD status.

The Development of New Factor Xa Inhibitors Based on Amide Synthesis

BACKGROUND

Factor Xa (FXa) is known to play a central role in blood coagulation cascade and considered to be one of the most attractive targets for oral anticoagulants of new generation.

OBJECTIVE

Our approach for the development of directly acting oral anticoagulants (DOAC), FXa inhibitors was demonstrated in this work.

METHOD

Chemical synthesis is the base of our approach for the development of potential inhibitors. In this work, the substances like R1-(CONH)-R2-(CONH)-R3 are being developed, using previously described docking and screening methods, where R1, R2 and R3 are some chemical groups and (CONH) are amide bonds connecting R1, R2 and R3. The direction of amide bond (CONH) could be arbitrary for R1, R2 and R2, R3.

RESULTS

Chemical modifications were made in the frame of the results, taking into account the structure of FXa, chemical synthesis capabilities, as well as patentability of the target compounds. Subnanomolar potency of several developed compounds was achieved. Several analyzers and various testing-suites have been used to measure the concentration that doubled the prothrombin time (PTx2). Moreover, in human plasma the PTx2 concentration of the compound 217 (DD217) turned out to be 80±20 nM. The compound efficacy has proved by in vivo assays including oral administrations in rats, rabbits and monkeys.

CONCLUSION

The pharmacodynamic profile of DD217 for oral administration in cynomolgus monkeys proves the efficacy of the compound, which makes it promising for the future preclinical trials.

Popular naturally occurring antioxidants as potential anticoagulant drugs

Blood coagulation is a physiological process whose main task is prevention of blood loss from injured vessels. This process consists of a series of zymogens proteolytic activation leading to the generation of the main coagulation enzyme - thrombin. Besides its important role in blood coagulation process, thrombin is involved in many cardiovascular diseases, which are responsible for almost half of fatalities in economically developed countries. The evidence for the increased generation and in vivo activity of thrombin was observed in the plasma of individuals at high risk for clinically significant venous and arterial thromboembolic complications. Antioxidants activity of plants extracts has been well known for many years and was confirmed by many publications. However, during the last decade many research centers presented results suggesting anticoagulant potential of various plant extracts. Many researchers have also provided evidence that polyphenol compounds are able to inhibit the activity of many enzymes, including serine proteases. All research described in this review clearly indicate that polyphenols and polyphenol-rich extracts possess not only antioxidative but also anticoagulant properties and may be useful in creation of new therapeutic agents or dietary supplements. Based on described properties polyphenols would be very helpful with both prevention and treatment of thromboembolic complications associated with multiple failures of haemostasis, because the available therapeutic agents do not offer such double-effects (antioxidant and anticoagulant).

Novel anticoagulants - an update on the latest developments and management for clinicians treating patients on these drugs

There are several novel anticoagulant agents that are being increasingly used as an alternative to warfarin, with these drugs being reported to be at least as effective if not better. Their increased use means that oral care clinicians should have a sound understanding of the mechanism of action, pharmacology, reversal strategies and management of bleeding in patients taking these drugs. Surprisingly, there is little published in the current literature specific to professionals involved in oral health care. In this review, we provide an overview of these drugs and discuss the management of patients who need an oral procedure based on currently available literature and clinical trials.

Theoretical Study of Molecular Structure and Physicochemical Properties of Novel Factor Xa Inhibitors and Dual Factor Xa and Factor IIa Inhibitors

The geometries and energies of factor Xa inhibitors edoxaban, eribaxaban, fidexaban, darexaban, letaxaban, and the dual factor Xa and thrombin inhibitors tanogitran and SAR107375 in both the gas-phase and aqueous solution were studied using the Becke3LYP/6-31++G(d,p) or Grimme’s B97D/6-31++G(d,p) method. The fully optimized conformers of these anticoagulants show a characteristic l-shape structure, and the water had a remarkable effect on the equilibrium geometry. According to the calculated pKa values eribaxaban and letaxaban are in neutral undissociated form at pH 7.4, while fidexaban and tanogitran exist as zwitterionic structures. The lipophilicity of the inhibitors studied lies within a large range of log P between 1 and 4. The dual inhibitor SAR107375 represents an improvement in structural, physicochemical and pharmacokinetic characteristics over tanogitran. At blood pH, SAR107375 predominantly exists in neutral form. In contrast with tanogitran, it is better absorbed and more lipophilic and active after oral application.

Update on Edoxaban for the Prevention and Treatment of Thromboembolism: Clinical Applications Based on Current Evidence

Vitamin K antagonists (VKA) and heparins have been utilized for the prevention and treatment of thromboembolism (arterial and venous) for decades. Targeting and inhibiting specific coagulation factors have led to new discoveries in the pharmacotherapy of thromboembolism management. These targeted anticoagulants are known as direct oral anticoagulants (DOACs). Two pharmacologically distinct classes of targeted agents are dabigatran etexilate (Direct Thrombin Inhibitor (DTI)) and rivaroxaban, apixaban, and edoxaban (direct oral factor Xa inhibitors (OFXaIs)). Emerging evidence from the clinical trials has shown that DOACs are noninferior to VKA or low-molecular-weight heparins in the prevention and treatment of thromboembolism. This review examines the role of edoxaban, a recently approved OFXaI, in the prevention and treatment of thromboembolism based on the available published literature. The management of edoxaban in the perioperative setting, reversibility in bleeding cases, its role in cancer patients, the relevance of drug-drug interactions, patient satisfaction, financial impacts, and patient education will be discussed.

Latest developments in anticoagulant drug discovery

Thromboembolic diseases have increased in number over the past years. Oral anticoagulants impair the formation and progression of thrombotic processes and are therefore of great importance in the treatment of these diseases. Until recently, vitamin K antagonists were used to block the coagulation system. But these agents display a lot of interactions besides their narrow therapeutic range and have potential risk of hemorrhage complications. Therefore, other factors of the coagulation cascade are currently being explored as therapeutic targets for the development of novel anticoagulants. This review will provide an overview of new drugs promising more effectiveness in the treatment of arterial and venous embolism. Furthermore, pharmacodynamics and drug interactions regarding new anticoagulants will be reported.

Polyphenol compounds belonging to flavonoids inhibit activity of coagulation factor X

Blood coagulation consists of series of zymogens which can be converted by limited proteolysis to active enzymes leading to the generation of thrombin and conversion of fibrinogen into fibrin by this enzyme. The activated factor X (FXa) forms prothrombinase complex on phosphatidylserine containing surface which is responsible for conversion of prothrombin to thrombin. One molecule of FXa generates more than 1000 thrombin molecules. Therefore FXa is a novel target for modern anticoagulant therapy. The aim of our present study is to examine the effects of the well-known plant polyphenolic compounds on factor Xa amidolytic activity and characterization of these interactions using bioinformatic ligand docking method. We observed that only four polyphenols belonging to flavonoids group: procyanidin B2, cyanidin, quercetin and silybin, had inhibitory effect on FXa activity. Bioinformatic analyses revealed that procyanidin B2, cyanidin, quercetin and silybin bound in the S1-S4 pockets located in vicinity of the FXa active site and blocked access of substrates to Ser195. The results presented here showed that flavonoids might be potential structural bases for design of new nature-based, safe, orally bioavailable direct FXa inhibitors.

Antithrombotic effect of chikusetsusaponin IVa isolated from Ilex paraguariensis (Maté)

The triterpene chikusetsusaponin IVa was isolated from the fruit of Ilex paraguariensis. Using biochemical and pharmacological methods, we demonstrated that chikusetsusaponin IVa (1) prolongs the recalcification time, prothrombin time, activated partial thromboplastin time, and thrombin time of normal human plasma in a dose-dependent manner, (2) inhibits the amidolytic activity of thrombin and factor Xa upon synthetic substrates S2238 and S2222, (3) inhibits thrombin-induced fibrinogen clotting (50% inhibition concentration, 199.4 ± 9.1 μM), and (4) inhibits thrombin- and collagen-induced platelet aggregation. The results also indicate that chikusetsusaponin IVa preferentially inhibits thrombin in a competitive manner (K(i)=219.6 μM). Furthermore, when administered intravenously to rats, chikusetsusaponin IVa inhibited thrombus formation in a stasis model of venous thrombosis, although it did not induce a significant bleeding effect. Chikusetsusaponin IVa also prolonged the ex vivo activated partial thromboplastin time. Altogether, these data suggest that chikusetsusaponin IVa exerts antithrombotic effects, including minor hemorrhagic events. This appears to be important for the development of new therapeutic agents.

Test of the month: The chromogenic antifactor Xa assay

As the number of anticoagulant drugs increases and new ones are brought to market, the utility of the routine screening coagulation tests of today--namely the prothrombin time and activated partial thromboplastin time--will be significantly reduced in many clinical situations. Although the new anticoagulants are designed to require less frequent monitoring, it is imperative that the proper test is selected in situations where monitoring is needed. In addition, tests that are designed for the new generation of drugs may be informative in certain situations for monitoring the anticoagulants that have been in use for many years. Here, we present the chromogenic antifactor Xa assay and demonstrate its utility and its limitations in monitoring three anticoagulant drugs (unfractionated heparin, low molecular weight heparin, and fondaparinux) as well as one emerging anticoagulant, rivaroxaban.