Thrombin Receptor Agonist Peptide-Induced Platelet Aggregation Is Reduced in Patients Receiving Dabigatran

Ex Vivo Antiplatelet Effects of Oral Anticoagulants

BACKGROUND

The impact of non-vitamin K antagonist oral anticoagulants (NOACs) on platelet function is still unclear. We conducted a comprehensive ex vivo study aimed at assessing the effect of the four currently marketed NOACs on platelet function.

METHODS

We incubated blood samples from healthy donors with concentrations of NOACs (50, 150 and 250 ng/mL), in the range of those achieved in the plasma of patients during therapy. We evaluated generation of thrombin; light transmittance platelet aggregation (LTA) in response to adenosine diphosphate (ADP), thrombin receptor-activating peptide (TRAP), human γ-thrombin (THR) and tissue factor (TF); generation of thromboxane (TX)B2; and expression of protease-activated receptor (PAR)-1 and P-selectin on the platelet surface.

RESULTS

All NOACs concentration-dependently reduced thrombin generation compared with control. THR-induced LTA was suppressed by the addition of dabigatran at any concentration, while TF-induced LTA was reduced by factor-Xa inhibitors. ADP- and TRAP-induced LTA was not modified by NOACs. TXB2 generation was reduced by all NOACs, particularly at the highest concentrations. We found a concentration-dependent increase in PAR-1 expression after incubation with dabigatran, mainly at the highest concentrations, but not with FXa inhibitors; P-selectin expression was not changed by any drugs.

CONCLUSIONS

Treatment with the NOACs is associated with measurable ex vivo changes in platelet function, arguing for antiplatelet effects beyond the well-known anticoagulant activities of these drugs. There are differences, however, among the NOACs, especially between dabigatran and the FXa inhibitors.

Influence of PAR-1 in patients with non-valvular atrial fibrillation: The antiplatelet effect of dabigatran

INTRODUCTION

Dabigatran, a direct thrombin inhibitor, has been widely used in patients with non-valvular atrial fibrillation (NVAF) and is considered to have an antiplatelet effect. However, the mechanisms remain unclear. We evaluated protease-activated receptor-1 (PAR-1) expression and activation by thrombin on platelets from NVAF patients, before and after dabigatran treatment, in addition to the expression of platelet activation marker CD62P.

MATERIALS AND METHODS

The study included 18 NVAF patients. We used flow cytometry to measure the binding of PAR-1 monoclonal antibodies (SPAN12 and WEDE15) and the expression of CD62P with and without thrombin stimulation, before, 14 days after, and 28 days after treatment with dabigatran. Coagulation fibrinolysis markers were also measured.

RESULTS

PAR-1 expression was significantly lower in NVAF patients than in healthy controls (HC); it was further reduced by thrombin stimulation. CD62P expression was almost absent on the platelets in NVAF patients, but was significantly increased by thrombin stimulation. PAR-1 expression was not significantly different before and after treatment; CD62P expression was inhibited by dabigatran. The levels of coagulation markers were significantly higher in NVAF patients than in HC, and decreased after treatment.

CONCLUSIONS

Lower expression of PAR-1 in NVAF patients resulted from the cleavage of PAR-1 on some platelets, by exposure to small amounts of thrombin in vivo. The therapeutic effect of dabigatran in NVAF patients was demonstrated by inhibition of CD62P expression on the platelet upon thrombin stimulation in vitro. Our results indicate that dabigatran may reveal antithrombotic activity with antiplatelet and anticoagulant effects.

Impact of Dabigatran Treatment on Rotation Thromboelastometry

A rapid and reliable assessment of the dabigatran effect is desirable in dabigatran treated patients with uncontrolled bleeding or before acute surgery. The aim of this study was to study the anticoagulant effects of dabigatran in patients with atrial fibrillation (AF) as assessed by the whole blood assays ROTEM, and how data from these methods correlate to plasma dabigatran concentrations measured by Hemoclot. ROTEM was performed with ROTEM Gamma (Pentapharm GmbH, Munich, Germany). The assays used in our study were Ex-tem and In-tem assay. Plasma dabigatran concentrations were determined by hemoclot thrombin inhibitor assay (Hyphen BioMed, France) at trough and post-dose in 27 patients on dabigatran 150 mg BID. Median plasma dabigatran concentrations at trough were 74 ng/mL (11.2–250) and post-dose (2 h after ingestion) 120 ng/mL (31–282). The ROTEM clotting time (CT) and maximum clot firmnes (MCF) correlated strongly with dabigatran concentrations when activated with the reagents Ex-tem (p < 0.0001) and In-tem (p < 0.0001). In summary, in our study, we have found that the ROTEM variable CT and MCF, when activated with triggers Ex-tem and In-tem, has a strong and highly significant correlation with the plasma dabigatran concentration in a real-life population of AF-patients and could thereby be an alternative to estimate dabigatran concentration in emergency situations. However, additional studies are needed to further validate these findings.

Different DOACs Control Inflammation in Cardiac Ischemia-Reperfusion Differently

RATIONALE

While thrombin is the key protease in thrombus formation, other coagulation proteases, such as fXa (factor Xa) or aPC (activated protein C), independently modulate intracellular signaling via partially distinct receptors.

OBJECTIVES

To study the differential effects of fXa or fIIa (factor IIa) inhibition on gene expression and inflammation in myocardial ischemia-reperfusion injury.

METHODS AND RESULTS

Mice were treated with a direct fIIa inhibitor (fIIai) or direct fXa inhibitor (fXai) at doses that induced comparable anticoagulant effects ex vivo and in vivo (tail-bleeding assay and FeCl₃-induced thrombosis). Myocardial ischemia-reperfusion injury was induced via left anterior descending ligation. We determined infarct size and in vivo aPC generation, analyzed gene expression by RNA sequencing, and performed immunoblotting and ELISA. The signaling-only 3K3A-aPC variant and inhibitory antibodies that blocked all or only the anticoagulant function of aPC were used to determine the role of aPC. Doses of fIIai and fXai that induced comparable anticoagulant effects resulted in a comparable reduction in infarct size. However, unbiased gene expression analyses revealed marked differences, including pathways related to sterile inflammation and inflammasome regulation. fXai but not fIIai inhibited sterile inflammation by reducing the expression of proinflammatory cytokines (IL [interleukin]-1β, IL-6, and TNFα [tumor necrosis factor alpha]), as well as NF-κB (nuclear factor kappa B) and inflammasome activation. This anti-inflammatory effect was associated with reduced myocardial fibrosis 28 days post-myocardial ischemia-reperfusion injury. Mechanistically, in vivo aPC generation was higher with fXai than with fIIai. Inhibition of the anticoagulant and signaling properties of aPC abolished the anti-inflammatory effect associated with fXai, while inhibiting only the anticoagulant function of aPC had no effect. Combining 3K3A-aPC with fIIai reduced the inflammatory response, mimicking the fXai-associated effect.

CONCLUSIONS

We showed that specific inhibition of coagulation via direct oral anticoagulants had differential effects on gene expression and inflammation, despite comparable anticoagulant effects and infarct sizes. Targeting individual coagulation proteases induces specific cellular responses unrelated to their anticoagulant effect.

Impact of Edoxaban on Thrombin-Dependent Platelet Aggregation

Edoxaban, a direct factor Xa inhibitor (FXa), is the fourth direct oral anticoagulant (DOAC) approved for clinical use. As the main adverse event is bleeding, it is relevant whether edoxaban has additional effects on platelet function. We aimed to assess in vitro aggregation in patients with atrial fibrillation (AF) receiving edoxaban. We evaluated 20 AF patients treated with edoxaban. We assessed light transmittance platelet aggregation (LTA) with 100 nmol/L γ-thrombin. The LTA was performed at 2 time-points. The thrombin-induced platelet aggregation was significantly lower 2 hours after edoxaban was taken compared to baseline measurement (27.25% ± 30.8% vs. 60.35% ± 33.3%). In addition, we also performed 16 subanalyses in order to identify the differences in the outcome of different comorbidities, age, dosage, liver and kidney function tests, and concomitant treatment. Results of the subgroup analyses were consistent with the findings of the main analysis; there was no apparent heterogeneity across the prespecified subgroups. The thrombin-induced platelet aggregation is reduced in non-valvular AF patients receiving edoxaban.

First evidence: rivaroxaban and apixaban reduce thrombin-dependent platelet aggregation

Rivaroxaban and apixaban are direct oral anticoagulants whose target specificity is to activate factor X (FXa). It is still not fully understood how xabans impact platelet function. This single-center observational study aimed to assess in vitro platelet function in patients with atrial fibrillation receiving rivaroxaban or apixaban. It examined quantification of platelet aggregation assessed by light transmission aggregometry in thirty-four patients treated with apixaban or rivaroxaban. The thrombin-induced platelet aggregation was significantly lower 2 h after taking selected xabans compared to baseline value (69.55 ± 32.15% vs. 44.79 ± 34.97.9%; p < 0.0001). This effect was only observed in patients who received rivaroxaban or apixaban for more than 1 week. The thrombin-induced platelet aggregation is reduced in cardiovascular patients receiving rivaroxaban or apixaban. This reduction is likely to depend on the duration of the treatment. Duration of treatment should be considered in future studies focusing on DOACs and platelet aggregation.

Dabigatran affects thrombin-dependent platelet aggregation after a week-long therapy

OBJECTIVE

Dabigatran is a direct thrombin inhibitor. As the main adverse event is bleeding, it is relevant whether dabigatran has additional effects on platelet function. If so, it could affect the bleeding risk. We aimed to assess in vitro aggregation in patients with atrial fibrillation (AF) receiving dabigatran.

DESIGN

We evaluated 32 AF patients treated with dabigatran (study group) and 18 non-anticoagulated non-AF blood donors (control group). We assessed light transmittance platelet aggregation (LTA) with 100 nmol/L γ-thrombin in both groups. The LTA was performed at two time-points in our dabigatran group of patients.

RESULTS

The thrombin-induced platelet aggregation was significantly lower two hours after dabigatran was taken compared to baseline measurement (9% ± 6% vs. 29% ± 21%) in our study group. Moreover, we observed that the baseline value of platelet aggregation in patients on dabigatran treatment was significantly lower compared to healthy volunteers (29% ± 21% vs. 89 ± 8). However, one subanalysis showed that this significant reduction in platelet aggregation at baseline was only observed in patients who received dabigatran for over a week.

CONCLUSION

The thrombin-induced platelet aggregation is reduced in non-valvular AF patients receiving dabigatran after a week-long therapy.