Effects of dabigatran in vitro on thrombin biomarkers by Calibrated Automated Thrombography in patients after ischemic stroke

DOAC-associated bleeding, hemostatic strategies, and thrombin generation assays - a review of the literature

Direct oral anticoagulants (DOACs) account for most oral anticoagulant use. DOAC-associated bleeding events are commonly encountered in clinical practice and are associated with substantial morbidity and mortality. Both specific reversal agents and nonspecific hemostatic therapies, such as prothrombin complex concentrates, are used in the management of DOAC-associated bleeding. Measuring hemostatic efficacy and demonstrating a clinical impact from these therapies among studies of bleeding patients is challenging. Thrombin generation assays provide information on the total hemostatic potential of plasma, and have emerged as a promising modality to both measure the impact of DOACs on coagulation and to evaluate the effects of hemostatic therapies among patients with DOAC-associated bleeding. The mechanisms by which nonspecific hemostatic agents impact coagulation and thrombin generation in the context of DOAC therapy are unclear. As a result, we undertook a review of the literature using a systematic search strategy with the goal of summarizing the effects of DOACs on thrombin generation and the effects of both specific reversal agents and nonspecific hemostatic therapies on DOAC-altered thrombin generation parameters. We sought to identify clinical studies focusing on whether altered thrombin generation is associated with clinical bleeding and whether correction of altered thrombin generation parameters predicts improvements in clinical hemostasis. Lastly, we sought to outline future directions for the application of thrombin generation assays toward anticoagulation therapies and the question of anticoagulation reversal.

Stepper-Based Training Improves Monocyte-Platelet Aggregation and Thrombin Generation in Nonambulatory Hemiplegic Patients

PURPOSE

Nonambulatory stroke patients are extremely sedentary, but most available data concerning exercise training in stroke patients are related to ambulatory patients. This study aimed to investigate the efficacy of stepper-based exercise training on cardiopulmonary fitness, monocyte subtypes, and associated monocyte-platelet aggregates (MPA) and thrombin generation (TrG) in nonambulatory hemiplegic patients with ischemic stroke.

METHOD

Thirty-eight patients were randomized into exercise training (ET, n = 20) and usual care (UC, n = 18) groups. The ET underwent supervised exercise training (60% peak work rate) using a recumbent stepper for two to four sessions per week and 36 sessions in total. In addition, 12 healthy participants were enrolled as healthy controls. Monocyte characteristics, MPA, and plasma TrG kinetics were determined before and after intervention by flow cytometry and calibrated automated thrombogram® (CAT).

RESULTS

Seventeen and 15 patients completed the protocol in the ET and UC groups. Peak V̇O2 improved in ET (15.7 ± 4.8 vs 18.9 ± 5.3 mL·min-1·kg-1, +20%), so did the phase angle of the hemiplegic limbs. The counts of total MPA and MPA associated with three monocyte subtypes, alongside CD42b expression all declined in ET with subtypes 2 and 1 being the most prominent. Macrophage inflammatory protein 1β (MIP-1 β) level also declined. The TrG kinetics was attenuated after ET by delaying initiation and reducing the rising slope and peak of thrombin production. In UC, no difference was revealed in the pre-post comparison.

CONCLUSIONS

Stepper-based ET is feasible in nonambulatory hemiplegic patients and is effective in improving aerobic fitness. Moreover, it decreases heteroaggregation of monocytes with platelets, especially in monocyte subtypes 2 and 1. Thrombin generation was also attenuated. Hence, stepper-based ET may be incorporated in the rehabilitation of nonambulatory hemiplegic patients.

The role of thrombin in central nervous system activity and stroke

Background

Thrombin is a key factor of hemostasis, mediating the conversion of fibrinogen into fibrin. Along with prothrombin, of which thrombin is the active derivative, it has been found locally expressed in the central nervous system. This article aims to describe the role of thrombin in the normal functioning of the central nervous system and stroke.

Methods

In this mini-review, the specialized databases Medscape, PubMed, and Web of Science, from the years 2003–2018, were used to find relevant documents by using MeSH terms: “thrombin” and “stroke”.

Results

Prothrombin and thrombin influence neural development, protection and regeneration, thrombin being a relatively strong regulating factor of brain function. However, high levels of thrombin are detrimental to neuronal health, and cause atherosclerotic plaque development and instability - a leading cause of cerebral infarction. In stroke, thrombin promotes direct cellular toxicity, vascular disruption, oxidative stress and inflammatory response. There is a direct correlation between thrombin activity in the affected brain hemisphere and the infarction volume. Direct acting thrombin inhibitors, like dabigatran, significantly decrease the risk of ischemic stroke.

Conclusion

Further studies on the correlation between thrombin levels, generation and activity and the risk and recurrence of ischemic cerebral stroke should give new insight on this association, resulting in an optimized practical therapeutic approach.

How the direct oral anticoagulant apixaban affects thrombin generation parameters

BACKGROUND AND OBJECTIVES

Apixaban is a direct oral anticoagulant (DOAC) targeting factor Xa and thus quenching thrombin generation and clot formation. However, little information is available on the influence that apixaban may have on the parameters of thrombin generation.

METHODS

Aliquots of a pooled normal plasma have been added with increased concentrations of purified apixaban and were used to assess the degree of modification brought about by the drug on the basic tests of coagulation prothrombin and activated partial thromboplastin time (PT and APTT) and on thrombin generation parameters.

RESULTS

The study shows that while apixaban has little effect on PT or APTT it does affect all the parameters of thrombin generation, including the lag-time (which is increased), the endogenous thrombin potential (ETP) and thrombin-peak (both decreased although to a different extent), and the velocity index (decreased). Interestingly, the above effects were more pronounced when the measurements were recorded in the presence of thrombomodulin, thus making the ratio (with/without thrombomodulin) to decrease consistently as a function of the apixaban concentrations.

CONCLUSIONS

These findings support the antithrombotic properties of apixaban and can help to understand the mechanism(s) of action of this drug. Thrombin generation could be used as a convenient laboratory tool to assess the anticoagulant activity of other drugs and to make between-DOAC comparison.

Measurement of dabigatran in standardly used clinical assays, whole blood viscoelastic coagulation, and thrombin generation assays

Dabigatran, a direct thrombin inhibitor, is increasingly used clinically as one of the new oral anticoagulants. This review summarizes the assays available to measure its activity and includes the relative sensitivity of the different assays for this agent. In addition to plasma-based clotting tests, assays commonly used in surgical/emergency settings, such as activated clotting time and thromboelastometry/thromboelastography, are reviewed. In addition, the thrombin generation assay is discussed as an important method to determine the potential risk of thrombosis or bleeding and its relevance to the measurement of direct thrombin inhibitors.

Impact of moderate blast exposures on thrombin biomarkers assessed by calibrated automated thrombography in rats

Severe blast exposures are frequently complicated with fatal intracranial hemorrhages. However, many more sustain low level blasts without tissue damage detectable by brain imaging. To investigate effects of nonlethal blast on thrombin-related biomarkers, rats were subjected to two different types of head-directed blast: 1) moderate "composite" blast with strong head acceleration or 2) moderate primary blast, without head acceleration. Thrombin generation (TG) ex vivo after blast was studied by calibrated automated thrombography (CAT). In the same blood samples, we assessed maximal concentration of TG (TGmax), start time, peak time, mean time, and concentrations of protein markers for vascular/hemostatic dysfunctions: integrin α/β, soluble endothelial selectin (sE-selectin), soluble intercellular cell adhesion molecule-1 (sICAM-1), and matrix metalloproteinases (MMP)-2, MMP-8, and MMP-13. Blast remarkably affected all TG indices. In animals exposed to "composite" blast, TGmax peaked at 6 h (∼4.5-fold vs. control), sustained at day 1 (∼3.8-fold increase), and declined to a 2-fold increase over control at day 7 post-blast. After primary blast, TGmax also rose to ∼4.2-fold of control at 6 h, dropped to ∼1.7-fold of control at day 1, and then exhibited a slight secondary increase at 2-fold of control at day 7. Other TG indices did not differ significantly between two types of blast exposure. The changes were also observed in other microvascular/inflammatory/hemostatic biomarkers. Integrin α/β and sICAM-1 levels were elevated after both "composite" and primary blast at 6 h, 1 day, and 7 days. sE-selectin exhibited near normal levels after "composite" blast, but increased significantly at 7 days after primary blast; MMP-2, MMP-8, and MMP-13 slightly rose after "composite" blast and significantly increased (∼2-4-fold) after primary blast. In summary, CAT may have a clinical diagnostic utility in combination with selected set of microvascular/inflammatory biomarkers in patients subjected to low/moderate level blast exposures.