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.

Inhibitory Effects of P2Y12 Receptor Antagonist on PAR1- and PAR4-AP-Induced Platelet Aggregation in Patients with Stroke or TIA.

OBJECTIVES: The inhibitory effects of P2Y12 receptor antagonist on PAR1- and PAR4-activating peptide (AP)-induced platelet aggregation have not been fully elucidated. The present study aimed to investigate the inhibitory effects of P2Y12 receptor antagonist on PAR1- and PAR4-AP-induced platelet aggregation using platelet-rich plasma (PRP) from individuals including patients with stroke or transient ischemic attack (TIA). MATERIALS AND METHODS: PRP was given to 10 healthy individuals pretreated in vitro with cangrelor, then stimulated with adenosine diphosphate (ADP), PAR4-AP, or PAR1-AP. Moreover, 20 patients were enrolled from 148 consecutive patients with acute ischemic stroke or TIA admitted to our institute between December 2017 and April 2019. PRP obtained from each patient before and >7 days after initiation of clopidogrel was similarly stimulated with these agonists. Platelet aggregation was measured using an automatic coagulation analyzer in all participants. RESULTS: In healthy individuals, ADP- and PAR4-AP-induced platelet aggregations were significantly inhibited depending on the cangrelor concentration in vitro, while PAR1-AP-induced platelet aggregation was slightly inhibited. In patients with stroke or TIA, clopidogrel inhibited ADP-induced platelet aggregation at all concentrations, and significantly inhibited PAR4-AP-induced platelet aggregation at 50 µmol/L of PAR4-AP (p<0.05), especially in 5 patients who showed high reactivity to PAR4-AP. PAR1-AP-induced platelet aggregation was also slightly inhibited. CONCLUSIONS: We showed significant inhibitory effects on PAR4-AP-induced platelet aggregation by clopidogrel in patients with stroke or TIA who had high reactivity to PAR4-AP.

Evaluating recanalization of relevant lenticulostriate arteries in acute ischemic stroke using high-resolution MRA at 7T.

BACKGROUND: Occluded major intracranial arteries can spontaneously recanalize in patients with acute ischemic stroke mainly due to embolic mechanisms. However, it remains unknown whether recanalization can occur in perforating arteries, such as lenticulostriate arteries. Therefore, in the present study, we assessed changes suggesting recanalization of the lenticulostriate arteries in patients with acute ischemic stroke of the lenticulostriate artery territory using high-resolution magnetic resonance angiography (HR-MRA) at 7T. METHODS: We prospectively examined 39 consecutive patients with acute infarcts confined within the lenticulostriate artery territory. Using a 7T scanner during the acute period and one month thereafter, we evaluated imaging findings indicating the recanalization of the relevant lenticulostriate arteries, following which we examined differences in other imaging findings and clinical characteristics between patients with/without recanalization. RESULTS: HR-MRA findings suggestive of recanalization (i.e. patent lenticulostriate arteries within acute infarct lesions with/without hemorrhagic changes) were observed in 8 (25%) of 32 patients who were eligible for analyses. These findings were detected in three and five patients on the baseline and follow-up images, respectively. The lengths of relevant lenticulostriate arteries on the follow-up MRA were significantly larger in patients with recanalization than in those without (P = 0.01). However, there were no significant differences in the infarct volume or clinical outcomes between the recanalization and non-recanalization groups. CONCLUSION: HR-MRA at 7T revealed that recanalization of the relevant lenticulostriate arteries can occur in patients with acute ischemic stroke confined to the lenticulostriate artery territory.

Thrombin-induced platelet aggregation -effect of dabigatran using automated platelet aggregometry.

Dabigatran, a direct oral thrombin inhibitor, has two therapeutic effects: anticoagulation; and antiplatelet activity. In the clinical field, evaluation of the effect of dabigatran on thrombin-induced platelet aggregation is difficult because of fibrin clot formation and platelet aggregation. The aim of this study was to establish a new platelet aggregation method and to investigate the effects of dabigatran on thrombin-induced platelet aggregation. Platelet aggregation with thrombin was performed with automated light transmission aggregometry (CS2400; Sysmex, Kobe, Japan) in 40 healthy subjects. Thrombin-induced platelet aggregation was performed using thrombin and platelet-rich plasma (PRP), and thrombin-induced fibrin polymerization was inhibited by adding the peptide Gly-Pro-Arg-Pro (GPRP). The effect of dabigatran was then evaluated using the above method. Thrombin at < 0.2 U/mL did not induce platelet aggregation in most normal subjects. Median maximum aggregation percent (MA%) (25th-75th percentile) with 0.5 and 1.0 U/mL of thrombin was 87.0% (79.3-90.8%), and 90.2% (86.5-92.2%), respectively. The anti-platelet effects of dabigatran were then evaluated with these concentrations of thrombin. Dabigatran (final concentration, 2.5-1000 nM) inhibited platelet aggregation by 0.2-1.0 U/mL of thrombin in a concentration-dependent manner in vitro. Dabigatran showed potent inhibitory effects against platelet aggregation induced by 0.5 and 1.0 U/mL thrombin with half maximal inhibitory concentrations of 10.5 and 40.4 nM, respectively. A standard for thrombin-induced platelet aggregation was developed using the CS2400 in healthy subjects, and dabigatran was confirmed to inhibit thrombin-induced platelet aggregation in vitro with PRP.

An Anatomical Variation in the Cervical Carotid Artery of a Young Stroke Patient.

The cervical carotid artery has been reported to show anatomical variations. We report the case of a young stroke patient with a small right-parietal-lobe infarction whose cervical carotid artery showed anatomical variation. The right internal carotid artery (ICA) originated at the C2 level of the external carotid artery with protrusion at the right carotid bifurcation. The vessel wall of the protrusion showed a high signal intensity on T1-weighted magnetic resonance carotid plaque imaging. The protrusion, considered a remnant of the ICA, possibly caused the stroke due to the formation of thrombi as a result of changes in blood flow and viscosity.