Novel anticoagulants in atrial fibrillation stroke prevention

Studies on in vivo antithrombotic activity of quercetin, a natural flavonoid isolated from a traditional medicinal plant, African eggplant (Solanum indicum)

ETHNOPHARMACOLOGICAL RELEVANCE

Every year, cardiovascular diseases (CVDs) account for about 17.9 million deaths, making them the primary cause of both morbidity and mortality. Conventional drugs, which are often prescribed to treat cardiovascular diseases, are costly and have adverse effects. Consequently, dietary modifications and other medications are needed. Traditional use of Solanum indicum as cardiotonic to treat hypertension and anticoagulant potency has been reported but poorly evaluated scientifically.

AIM OF THE STUDY

This study investigated the in vivo anticoagulant activity and mechanism of anticoagulation of quercetin (QC), a bioactive compound isolated from S. indicum (SI) hydroethanolic fruit extract.

MATERIALS AND METHODS

Bioassay-guided fractionation (anticoagulant activity) extracted QC from hydroethanolic SI extract. QC was extensively characterized biochemically and pharmacologically. The interaction between QC and thrombin was investigated using spectrofluorometric and isothermal calorimetric methods. Cytotoxicity, antiplatelet, and thrombolytic studies were carried out in vitro. The Swiss albino mice were used to assess the in vivo, anticoagulant, and antithrombotic activities of QC.

RESULTS

QC exhibits anticoagulant activity via (i) uncompetitive inhibition of thrombin but not FXa with a Ki value of 33.11 ± 4.2 μM and (ii) a partial inhibition of thrombin-catalyzed platelet aggregation with an IC50 value of 13.2 ± 1.2 μM. The experimental validation of the in silico study's prediction of QC's binding to thrombin was confirmed by spectrofluorometric and isothermal calorimetric analyses. QC was nontoxic to mammalian, non-hemolytic cells and demonstrated thrombolytic activity by activating plasminogen. QC demonstrated in vivo anticoagulant efficacy, preventing k-carrageen-induced thrombus formation in mice's tails. In the acute circulatory stasis paradigm in mice, QC reduces thromboxane B2 (TXB2) and endothelin-1 (ET-1) while increasing nitric oxide synthase (eNOS) and 6-keto prostaglandin F1α (6-keto-PGF1 α).

CONCLUSION

Effective in vivo anticoagulant and antithrombotic properties of S. indicum's bioactive component QC point to the plant's potential use as a herbal anticoagulant medication for preventing and treating cardiovascular diseases linked to thrombosis.

How Good is Jarzynski's Equality for Computer-Aided Drug Design?

Accurate determination of the binding affinity of the ligand to the receptor remains a difficult problem in computer-aided drug design. Here, we study and compare the efficiency of Jarzynski’s equality (JE) combined with steered molecular dynamics and the linear interaction energy (LIE) method by assessing the binding affinity of 23 small compounds to six receptors, including β-lactamase, thrombin, factor Xa, HIV-1 protease (HIV), myeloid cell leukemia-1, and cyclin-dependent kinase 2 proteins. It was shown that Jarzynski’s nonequilibrium binding free energy ΔG_neq^Jar correlates with the available experimental data with the correlation levels R = 0.89, 0.86, 0.83, 0.80, 0.83, and 0.81 for six data sets, while for the binding free energy ΔG_LIE obtained by the LIE method, we have R = 0.73, 0.80, 0.42, 0.23, 0.85, and 0.01. Therefore, JE is recommended to be used for ranking binding affinities as it provides accurate and robust results. In contrast, LIE is not as reliable as JE, and it should be used with caution, especially when it comes to new systems.

Characterization of a novel selective factor Xa inhibitor, DJT06001, which reduces thrombus formation with low risk of bleeding

Factor Xa (FXa) is a serine protease that plays key roles in linking the intrinsic and extrinsic coagulation pathways to the final common pathway. DJT06001 is an oral, highly specific and direct FXa inhibitor for the prevention and treatment of thromboembolic diseases. We characterized the compound in vitro and studied its in vivo activity in rat thrombosis models, as well as bleeding risk and Pharmacokinetics and Pharmacodynamics (PK/PD) relationship. DJT06001 inhibited free FXa with an inhibitory constant (Ki) of 0.99 nM, and exhibited >10000-fold selectivity for FXa than for other related serine proteases. DJT06001 concentration-dependently inhibited FXa activity in the prothrombinase complex with an IC₅₀ of 2.53 nM. The concentrations for DJT06001 to double the prothrombin time (PT) and activated partial thromboplastin time (APTT) were 0.74 and 0.57 μM, respectively. Importantly, DJT06001 did not impair platelet aggregation induced by ADP, platelet activating factor (PAF) and collagen. Furthermore, DJT06001 inhibited thrombus formation in rat thrombosis models in a dose dependent manner. And in rat tail bleeding risk test, it caused less bleeding than rivaroxaban at doses that achieve the same antithrombotic effect. PK/PD studies further demonstrated that there was a good correlation between the plasma concentrations of DJT06001and its inhibition of plasma FXa activity and prolongation of PT. In conclusion, DJT06001 was shown to be a potent and specific FXa inhibitor with excellent PK/PD profiles and it could be developed as a new anticoagulant for the management of thromboembolic diseases.

Inhibitory Effect of Triterpenoids from Panax ginseng on Coagulation Factor X

Enzymes involved in the coagulation process have received great attention as potential targets for the development of oral anti-coagulants. Among these enzymes, coagulation factor Xa (FXa) has remained the center of attention in the last decade. In this study, 16 ginsenosides and two sapogenins were isolated, identified and quantified. To determine the inhibitory potential on FXa, the chromogenic substrates method was used. The assay suggested that compounds 5, 13 and 18 were mainly responsible for the anti-coagulant effect. Furthermore, these three compounds also possessed high thrombin selectivity in the thrombin inhibition assay. Furthermore, Glide XP from Schrödinger was employed for molecular docking to clarify the interaction between the bioactive compounds and FXa. Therefore, the chemical and biological results indicate that compounds 5 (ginsenoside Rg2), 13 (ginsenoside Rg3) and 18 (protopanaxtriol, PPT) are potential natural inhibitors against FXa.

Generation of an anti-Dabigatran Monoclonal Antibody and Its Use in a Highly Sensitive and Specific Enzyme-Linked Immunosorbent Assay for Serum Dabigatran

BACKGROUND

Dabigatran (DT) is a direct thrombin inhibitor used to prevent venous and arterial thromboembolism due to atrial fibrillation. DT is the active form of the commercially available prodrug DT etexilate. Although DT has many clinical advantages over warfarin, it increases the incidence of bleeding in patients with renal dysfunction. Circulating levels of DT are increased in such patients because it is mainly eliminated by renal excretion. Therapeutic drug monitoring may therefore help to prevent adverse DT effects, but no method for measuring circulating DT levels has been reported, except for an analysis by liquid chromatography-tandem mass spectrometry. This study sought to develop a novel enzyme-linked immunosorbent assay (ELISA) to measure DT concentrations.

METHODS

Mice were immunized with a DT-keyhole limpet hemocyanin conjugate to generate an anti-DT antibody. Immunized mouse splenocytes and myeloma cells (SP2/0) were fused to obtain an anti-DT monoclonal antibody (DT-mAb). DT-mAb and DT solutions were added to microplate wells coated with a DT-human serum albumin conjugate. DT concentrations were determined based on the principles of ELISA.

RESULTS

DT-mAb was successfully purified from a hybridoma, and the competitive ELISA developed using this DT-mAb could evaluate DT concentrations ranging from 7.8 to 125 ng/mL. The ELISA signal was not linear using DT-spiked serum; however, it was linear when serum ultrafiltrate was used. Weak cross-reactivity with DT etexilate was detected, but no cross-reactivity was observed with other structurally related drugs or drugs commonly used for the treatment of atrial fibrillation.

CONCLUSIONS

The developed competitive ELISA is a valuable and specific tool to analyze free DT in serum ultrafiltrate for therapeutic drug monitoring and pharmacokinetic studies.

Suboptimal Use of Oral Anticoagulants in Atrial Fibrillation: Has the Introduction of Direct Oral Anticoagulants Improved Prescribing Practices?

BACKGROUND AND OBJECTIVES

Atrial fibrillation (AF) and the associated risk of stroke are emerging epidemics throughout the world. Suboptimal use of oral anticoagulants for stroke prevention has been widely reported from observational studies. In recent years, direct oral anticoagulants (DOACs) have been introduced for thromboprophylaxis. We conducted a systematic literature review to evaluate current practices of anticoagulation in AF, pharmacologic features and adoption patterns of DOACs, their impacts on proportion of eligible patients with AF who receive oral anticoagulants, persisting challenges and future prospects for optimal anticoagulation.

LITERATURE SOURCE AND SELECTION CRITERIA

In conducting this review, we considered the results of relevant prospective and retrospective observational studies from real-world practice settings. PubMed (MEDLINE), Scopus (RIS), Google Scholar, EMBASE and Web of Science were used to source relevant literature. There were no date limitations, while language was limited to English. Selection was limited to articles from peer reviewed journals and related to our topic.

RESULTS

Most studies identified in this review indicated suboptimal use of anticoagulants is a persisting challenge despite the availability of DOACs. Underuse of oral anticoagulants is apparent particularly in patients with a high risk of stroke. DOAC adoption trends are quite variable, with slow integration into clinical practice reported in most countries; there has been limited impact to date on prescribing practice.

CONCLUSION

Available data from clinical practice suggest that suboptimal oral anticoagulant use in patients with AF and poor compliance with guidelines still remain commonplace despite transition to a new era of anticoagulation featuring DOACs.

Contemporary developments in the discovery of selective factor Xa inhibitors: A review

Thrombosis is a leading cause of death in cardiovascular diseases such as myocardial infarction (MI), unstable angina and acute coronary syndrome (ACS) in the industrialized world. Venous thromboembolism is observed in about 1 million people every year in United States causing significant morbidity and mortality. Conventional antithrombotic therapy has been reported to have several disadvantages and limitations like inconvenience in oral administration, bleeding risks (heparin analogs), narrow therapeutic window and undesirable interactions with food and drugs (vitamin K antagonist-warfarin). The unmet medical demand for orally active safe anticoagulants has generated widespread interest among the medicinal chemists engaged in this field. To modulate blood coagulation, various enzymes involved in the coagulation process have received great attention as potential targets by various research groups for the development of oral anticoagulants. Among these enzymes, factor Xa (FXa) has remained the centre of attention in the last decade. Intensive research efforts have been made by various research groups for the development of small, safe and orally bioavailable FXa inhibitors. This review is an attempt to compile the research work of various researchers in the direction of development of FXa inhibitors reported since 2010 onward.

Design, synthesis and antithrombotic evaluation of novel dabigatran etexilate analogs, a new series of non-peptides thrombin inhibitors

Thrombin is a serine protease that plays a key role in blood clotting, which makes it a promising target for the treatment of thrombotic diseases. Dabigatran is direct potent thrombin inhibitor. Based on bioisosteric and scaffold hopping principle, two dabigatran mimics (I-1 and II-1) in which the benzamidine moiety of dabigatran was replaced by a tricyclic fused scaffold were designed, synthesized and evaluated for their in vitro activities for inhibiting thrombin. The results reveal that compounds I-1 (IC50=9.20nM) and II-1 (IC50=7.48nM) are potent direct thrombin inhibitors and the activity is in the range of reference drug. On this basis, twenty-two ester and carbamate derivatives of I-1 or II-1 were prepared and evaluated for their anticoagulant activity. Prodrugs I-4a (IC50=0.73μM), I-4b (IC50=0.75μM), II-2a (IC50=1.44μM) and II-2b (IC50=0.91μM) display excellent effects of inhibiting thrombin induced-platelet aggregation. Moreover, compounds I-9 and II-4, which contain a cleavable moiety with anti-platelet activity, show the best anticoagulant efficacy among the tested compounds in the rat venous thrombosis model. The compounds which have better in vitro and in vivo activity were subjected to rat tail bleeding test, and the result demonstrates that compound I-9 is less likely to have bleeding risk than dabigatran etexilate.

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.

New oral anticoagulants for atrial fibrillation: are they worth the risk?

Atrial fibrillation (AF) is the most common cardiac arrhythmia in the U.S. Anticoagulation is recommended for stroke prevention in AF patients with intermediate-to-high stroke risk (i.e., patients with a CHADS2 score of 1 or greater). Warfarin was previously the only option for oral anticoagulation in these patients, but three new oral anticoagulants have become available as alternatives for warfarin in patients with nonvalvular AF. The advantages of the newer agents include a rapid onset, predictable pharmacokinetics, and no need for routine anticoagulation monitoring. Dabigatran (Pradaxa) and apixaban (Eliquis) have demonstrated improved efficacy compared with warfarin. Rivaroxaban (Xarelto) was non-inferior to warfarin for stroke prevention in AF. Apixaban demonstrated a reduced incidence of major bleeding compared with warfarin and a reduction in all-cause mortality. Limitations to the use of the new oral anticoagulants include the lack of a reversal agent; an inability to use the therapies in specific patient populations (such as those with severe renal or hepatic impairment); limited experience with drug-drug and drug-disease interactions; and a lack of available coagulation tests to quantify their effects. Although the newer agents have higher acquisition costs, the benefits of cost savings may be derived from the potential for decreasing the incidence of hemorrhagic stroke and intracranial bleeding and reducing the need for anticoagulation monitoring. Benefits and risks should be carefully weighed before these agents are prescribed for patients presenting with new-onset AF.

Clinical diseases with thrombotic risk and their pharmacologycal treatment: how they change the therapeutic attitude in dental treatments

The new antiplatelets and anticoagulant drugs have been recently introduced in the daily medical practices for the control of thromboembolism associated with different diseases. The dental assistance of these patients forces us to know these drugs, understand their action mechanisms and try to decrease the risks that entail ours actions in these patients, making a thorough analysis of the risk of bleeding that is going to be related to our medical intervention, as well as the use of all the control measures of the hemorrhage from our knowledge with these patients, and to be prudent. The communication with the medical specialist that supervises these patients must be maxim, being necessary to make clinic trials for establishing protocols or guides of the handling with these patients during the odontological treatment.

Key words:Antiplatelet drugs, anticoagulants drugs, new/classic, thrombotic risk, hemorrhagic risk, dental treatment, caution.

Oral Anticoagulation Therapy for Elderly Patients With Atrial Fibrillation

Elderly individuals are prone to nonvalvular atrial fibrillation (AF) with associated risks of arterial thromboembolic disease. Despite definitive guidelines, oral anticoagulant therapy (OAC) is notoriously underutilized in patients with AF. Physicians cite excessive bleeding risk as one reason they omit OAC for their older patients with AF. Improved understanding of the pathophysiology of age-related bleeding may improve risk–benefit assessments for warfarin and newer antithrombotic agents. We reviewed the literature to identify age-related pathophysiological elements that can exacerbate the likelihood of bleeding. In the context of the Hypertension, Abnormal renal/liver function, Stroke, Bleeding history or predisposition, Labile international normalized ratio, Elderly, Drugs/alcohol concomitantly (HAS-BLED) bleeding risk framework, we highlight age-related physiological dynamics that predispose to hemorrhage. The combination of increased age (>65 years) with the other elements of the risk factor stratification model identifies patients with AF who are especially susceptible to OAC-related bleeding, irrespective of the agent used. Empirically adjusting OAC dose relative to these common bleeding risks may help to achieve an improved risk–benefit therapeutic ratio.