Magnetic nanoparticles immobilized thrombin ligand fishing to screen thrombin inhibitors in natural products

In this study, thrombin was immobilized with magnetic particles modified by glutaraldehyde. The changes in secondary structures of immobilized enzyme revealed an increment in conformational rigidity and stability, which can be reflected in temperature and pH stability as well as the tolerance of organic reagents. The optimal reutilization times of magnetic particle immobilized thrombin were 7 times, and the half-life of enzyme activity preserved at room temperature was 5 days, which was 2.5 times higher than that of free enzyme. Ligusticum chuanxiong and Anemarrhenae Rhizoma with high enzyme inhibitory activity were selected for primary screening, and six potential inhibitors of thrombin were identified by HPLC/MS. The results showed that three compounds in Anemarrhenae Rhizoma had better predictive thrombin inhibitory activity. Through the in vitro thrombin activity inhibition experiment, it was also verified that mangiferin and neo-mangiferin had an ideal thrombin activity inhibition effect, which was consistent with the results of molecular docking.

MXene-sensitized electrochemiluminescence sensor for thrombin activity detection and inhibitor screening

Thrombin, a crucial enzyme involved in blood coagulation and associated diseases, requires accurate detection of its activity and screening of inhibitors for clinical diagnosis and drug discovery. To address this, an electrochemiluminescence (ECL) method was developed to detect thrombin activity based on the sensitization of Ti₃C₂T_x MXene, which could sensitize the Ru(bpy)₃²⁺ ECL system greatly. The thrombin-cleavable substrate bio-S-G-R-P-V-L-G-C was used as recognizer to evaluate the activity of thrombin. Under the optimal conditions, the limit of detection for thrombin in serum was 83 pU/mL (S/N = 3) with a linear range from 0.1 nU/mL to 1 µU/mL. Moreover, the developed ECL biosensor was employed to screen for thrombin inhibitors from Artemisiae argyi Folium. Four potential thrombin inhibitors (isoquercitrin, nepetin, L-camphor, L-borneol) were screened out with inhibition rates beyond 50%, among which isoquercitrin had the best inhibition rate of 90.26%. Isoquercitrin and nepetin were found to be competitive inhibitors of thrombin, with [Formula: see text] values of 0.91 μM and 2.18 μM, respectively. Molecular docking results showed that these compounds could interact with the active sites of thrombin through hydrogen bonds including ASP189, SER195, GLY216, and GLY219. The electrochemical biosensor constructed provides a new idea for the detection of thrombin activity and screening of its inhibitors.

Ecarin-Based Methods for Measuring Thrombin Inhibitors

Ecarin is a venom from the saw-scaled viper, Echis carinatus, which catalyzes prothrombin into meizothrombin. This venom is used in several hemostasis laboratory assays, including ecarin clotting time (ECT) and ecarin chromogenic assays (ECA). The use of these ecarin-based assays was first implemented as a tool for monitoring the infusion of a direct thrombin inhibitor, hirudin. Subsequently, this method has been more recently employed for measuring either the pharmacodynamic or pharmacokinetic properties of the oral direct thrombin inhibitor, dabigatran. In this chapter, the procedure for performing manual ECT and automated and manual ECA for measuring thrombin inhibitors is described.

[Management of bleeding in patients on antithrombotic therapy]

BACKGROUND

Severe bleeding under antithrombotic therapy is common and challenging in intensive care medicine; on the one hand, rapid bleeding control must be achieved and, on the other hand, thromboembolic complications must be avoided.

AIMS

The paper will provide a brief overview of direct oral anticoagulants, therapeutic options and precise instructions for dealing with severe bleeding.

RESULTS

In addition to general measures in direct oral anticoagulant (DOAC)-associated major bleeding, prothrombin complex concentrate (PCC), idarucizumab and andexanet alfa are available as specific antidote therapy. In case of bleeding under heparin therapy, protamine sulfate is available as a possible antidote.

CONCLUSIONS

In particular, the importance of andexanet alfa in the treatment of factor Xa inhibitor-associated bleeding requires further investigation.

In silico Prediction of Inhibitory Constant of Thrombin Inhibitors Using Machine Learning

BACKGROUND

Thrombin is the central protease of the vertebrate blood coagulation cascade, which is closely related to cardiovascular diseases. The inhibitory constant Ki is the most significant property of thrombin inhibitors.

METHOD

This study was carried out to predict Ki values of thrombin inhibitors based on a large data set by using machine learning methods. Taking advantage of finding non-intuitive regularities on high-dimensional datasets, machine learning can be used to build effective predictive models. A total of 6554 descriptors for each compound were collected and an efficient descriptor selection method was chosen to find the appropriate descriptors. Four different methods including multiple linear regression (MLR), K Nearest Neighbors (KNN), Gradient Boosting Regression Tree (GBRT) and Support Vector Machine (SVM) were implemented to build prediction models with these selected descriptors.

RESULTS

The SVM model was the best one among these methods with R2=0.84, MSE=0.55 for the training set and R2=0.83, MSE=0.56 for the test set. Several validation methods such as yrandomization test and applicability domain evaluation, were adopted to assess the robustness and generalization ability of the model. The final model shows excellent stability and predictive ability and can be employed for rapid estimation of the inhibitory constant, which is full of help for designing novel thrombin inhibitors.

New Oral Anticoagulants and Their Reversal Agents

OPINION STATEMENT

Direct oral anticoagulants (DOAC) are an attractive therapeutic option for anticoagulant treatment in the setting of venous thromboembolism or non-valvular atrial fibrillation. These drugs overall appear to have a lower risk of life-threatening hemorrhage than the vitamin K antagonists. In addition, they demonstrate more predictable and stable pharmacokinetics. Measurement of the degree of anticoagulation is desirable in patients with DOAC-associated hemorrhage, but commonly available coagulation assays show poor sensitivity for degree of DOAC effect. DOAC-specific tests are time consuming and not widely available. All coagulation tests should be interpreted considering the timing of last intake and renal function. When life-threatening bleeding occurs, hemostasis should be restored as rapidly as possible. Non-specific prohemostatic drugs may have a role in DOAC reversal, and specific antidotes are at different stages of development. In this review, we provide a summary of DOAC characteristics and an overview of the different therapeutic options available for DOAC reversal.

Molecular modeling studies, synthesis and biological evaluation of dabigatran analogues as thrombin inhibitors

In this work, 48 thrombin inhibitors based on the structural scaffold of dabigatran were analyzed using a combination of molecular modeling techniques. We generated three-dimensional quantitative structure-activity relationship (3D-QSAR) models based on three alignments for both comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA) to highlight the structural requirements for thrombin protein inhibition. In addition to the 3D-QSAR study, Topomer CoMFA model also was established with a higher leave-one-out cross-validation q(2) and a non-cross-validation r(2), which suggest that the three models have good predictive ability. The results indicated that the steric, hydrophobic and electrostatic fields play key roles in QSAR model. Furthermore, we employed molecular docking and re-docking simulation explored the binding relationship of the ligand and the receptor protein in detail. Molecular docking simulations identified several key interactions that were also indicated through 3D-QSAR analysis. On the basis of the obtained results, two compounds were designed and predicted by three models, the biological evaluation in vitro (IC50) demonstrated that these molecular models were effective for the development of novel potent thrombin inhibitors.

Effective inhibition of thrombin by Rhipicephalus microplus serpin-15 (RmS-15) obtained in the yeast Pichia pastoris

The cattle tick (Rhipicephalus microplus) affects cattle industries in tropical and subtropical countries because it is the vector of babesiosis and anaplasmosis which constitutes a threat to the health of cattle. During blooding feeding, ticks secrete saliva containing a complex of bioactive molecules into the injured site to evade host's defensive responses. Serine protease inhibitors (serpins) are important anti-haemostatic molecules present in tick saliva that are necessary for a successful blood feeding. Several serpin sequences have been reported in R. microplus but there is a gap of information about their functions during host-parasite interactions. In this study, the RmS-15 expressed in the yeast Pichia pastoris was characterised using kinetic assays and in vitro analysis. The inhibitory enzymatic assays conducted showed that RmS-15 is a physiological inhibitor of thrombin with a stoichiometric inhibition (SI) of 1.5 and high inhibition affinity with ka=9.3±0.5×104M(-1)s(-1). RmS-15 delayed the clotting of plasma in a dose-dependent manner as determined in a recalcification time assay. Significant elevated ELISA titres were observed in tick resistant and susceptible cattle on day 28 after the tick infestation (p<0.001). This data suggests direct contact of RmS-15 with the immune system of the host at the tick-feeding site. The present study contributed to the understanding of the biological functions of R. microplus serpins during host-parasite interactions which contributes to the design of future innovative methods for tick control.

Newer Pharmaceutical Agents for STEMI Interventions

ST-elevation myocardial infarction (STEMI) causes 12.6% of deaths worldwide. Treatment strategies involve early revascularization by percutaneous coronary intervention and/or fibrinolytics, with adjunctive pharmacologic therapy. While antiplatelet therapy remains the cornerstone of pharmacologic management, newer antithrombotic therapies are showing benefit in the reduction of long-term thrombotic events following acute vessel occlusion. Future directions in adjunctive STEMI management include the use of hematopoietic stem cell therapy or growth factors to induce proliferation and differentiation of cardiac myocytes.