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.

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.

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.

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.

Computational Fluid Dynamics Analysis of Lateral Striate Arteries in Acute Ischemic Stroke Using 7T High-resolution Magnetic Resonance Angiography.

BACKGROUND: Infarcts in the lateral striate artery (LSA) territory can be caused by several pathological changes, including lipohyalinosis and microatheroma. However, fluid dynamic effects on these changes remain unknown. Thus, we investigated whether the fluid dynamic metrics of the LSAs were altered in patients with acute ischemic stroke using computational fluid dynamics (CFD) analysis. METHODS: Fifty-one patients with acute ischemic stroke confined in the basal ganglia and/or corona radiata underwent high-resolution magnetic resonance angiography (HR-MRA) at 7T. We performed CFD analyses to obtain indices including the wall shear stress (WSS), WSS gradient (WSSG), and flow velocity (FV) and compared these values between the ipsilesional and contralesional sides in the patients with infarcts in the LSA or non-LSA territories. RESULTS: In patients with LSA-territory infarcts, the WSS, WSSG, and FV values were significantly lower in the ipsilesional LSAs than in the contralesional LSAs (P = .01-.03), while these values in the proximal middle cerebral arteries showed no significant lateralities. In contrast, in patients with non-LSA-territory infarcts, there were no significant lateralities in the metrics between the ipsilesional and contralesional sides. CONCLUSIONS: The CFD analyses using HR-MRA revealed significantly low WSS and WSSG values of the ipsilesional LSAs compared with that of the contralesional side in patients with LSA-territory infarcts, suggesting that fluid dynamic factors of LSAs can be one of the risk factors for LSA-territory infarctions.

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.

Detecting lenticulostriate artery lesions in patients with acute ischemic stroke using high-resolution MRA at 7 T.

BACKGROUND: Recent advances in high-resolution (HR) magnetic resonance angiography (MRA) using ultrahigh-field systems enable direct visualization of the lenticulostriate arteries (LSAs), which had been hardly achieved by conventional MRA. Hence, by using HR-MRA at 7 T, we attempted to assess occlusive changes in the LSAs in patients with LSA territorial infarcts. METHODS: We prospectively examined 34 consecutive patients with acute ischemic stroke in the LSA territory using a 7 T scanner. We measured the lengths of the relevant LSAs on HR-MRA and the diameters/volume of the infarcts and compared these between the patients with/without occlusive changes in the LSAs. RESULTS: On HR-MRA, occlusion of the LSAs was observed in 19 (59%) of 32 patients who were eligible for the analyses. The curved/straight lengths of the LSAs in the patients with LSA occlusion (23.1-31.1/17.8-24.3 mm) were significantly shorter than in those without apparent LSA occlusion (25.8-39.5/24.0-30.4 mm) ( P = 0.027/0.003). The anteroposterior/superoinferior diameters of the infarcts were significantly larger in the occluded-LSA group (14.5-21.4/14.9-22.2 mm) than in the intact-LSA group (10.9-16.8/10.8-16.2 mm) ( P = 0.041/0.011). In addition, the curved lengths of the relevant LSAs showed significant correlations with the superoinferior diameters of the infarcts ( r = 0.38, P = 0.034). CONCLUSION: Occlusive changes in the LSAs were frequently found in patients with acute ischemic stroke within the LSA territory when using HR-MRA at 7 T and were substantially related to superoinferior extension of the infarcts.

T1-Weighted Magnetic Resonance Carotid Plaque Imaging: a Comparison between Conventional and Fast Spin-Echo Techniques.

BACKGROUND: Magnetic resonance imaging is widely used to evaluate the intraplaque components of the cervical carotid artery. The non-gated T1-weighted spin-echo (SE) technique has been reported to have an excellent ability for discriminating stable and unstable plaques. However, the diagnostic performance of various SE-based techniques remains unclear. Hence, we compared plaque signals obtained by 3 kinds of SE-based methods with histological findings. METHODS: We prospectively examined 40 patients who underwent carotid endarterectomy by using 1.5-T scanners and obtained 2-dimensional (2D) conventional spin-echo (CSE), 2D fast spin-echo (FSE), and 3-dimensional (3D)-FSE images with identical repetition times. We calculated contrast ratios (CRs) of the plaques against adjacent muscles and compared these values with the pathological classification of the specimens. RESULTS: The CRs of type VII-VIII (calcific/fibrous), IV-V (lipid-rich/necrotic), and VI (complex/hemorrhagic) plaques were significantly different between all the methods (P <.001) and were discriminated from each other at sensitivities of 83%-100% and specificities of 94%-100%. The CRs of type IV-V plaques significantly differed between the methods (low to high, 2D-FSE, 2D-CSE, and 3D-FSE; P <.05); those of the type VI plaques were significantly lower with the 2D-FSE method than with the other methods (P <.01). CONCLUSIONS: The SE-based T1-weighted images can readily discriminate plaque characteristics with high sensitivities and specificities, although the signal intensity of unstable plaques was significantly high on the 3D-FSE images and significantly low on the 2D-FSE images.

Intracranial Plaque Characterization in Patients with Acute Ischemic Stroke Using Pre- and Post-Contrast Three-Dimensional Magnetic Resonance Vessel Wall Imaging.

BACKGROUND: Magnetic resonance vessel wall imaging (VWI) techniques have been developed to assess atherosclerotic plaques in intracranial arteries, which are a cardinal cause of ischemic stroke. However, the clinical roles of plaque-related vulnerability and inflammation remain unclear. Hence, we evaluated plaque characteristics using VWI of the proximal middle cerebral artery (M1) in patients with acute ischemic stroke. METHODS: We prospectively examined 30 consecutive patients with acute noncardioembolic stroke in the M1 territory using pre-/postcontrast T1-weighted (T1W) three-dimensional (3D) VWI with a 3-Tesla scanner. The contrast ratio (CR) and contrast enhancement of the plaques were measured bilaterally at M1. RESULTS: Plaques were identified in the bilateral M1s of all patients, and no substantial stenosis existed. The M1 plaque CRs ipsilateral to the infarct (46.7%-67.9%) were significantly higher than the plaque CRs on the contralateral side (34.3%-69.4%), particularly in patients with lacunar infarcts (P <.01). In contrast, the occurrence of plaque enhancement was not different between the ipsilateral (20.0%) and contralateral (16.7%) sides. Further, the CRs in the nonlacunar group were significantly higher than the CRs in the lacunar group (P <.05), whereas enhanced plaques tended to be more frequent in the nonlacunar group, but this difference was not significant (P = .09). CONCLUSIONS: T1W 3D-VWI revealed that the signal intensity of M1 plaques was significantly higher in the affected side and in nonlacunar-type infarcts of patients with acute stroke, suggesting that unstable plaques in the M1 can cause stroke events presumably due to atherothrombotic mechanisms.

Detection of vessel wall lesions in spontaneous symptomatic vertebrobasilar artery dissection using T1-weighted 3-dimensional imaging.

BACKGROUND: Spontaneous intracranial vertebrobasilar artery dissection (iVBD) is a cause of ischemic stroke and subarachnoid hemorrhage in young adults that can be detected noninvasively by using multisequence magnetic resonance imaging (MRI). However, MRI findings are sometimes difficult to interpret, and its accuracy tends to be suboptimal, especially during the acute period. Therefore, we investigated whether 3-dimensional (3D) vessel wall imaging (VWI) technique could readily detect iVBD lesions in acute phase patients. METHODS: Sixteen consecutive patients with acute ischemic stroke caused by iVBD were prospectively examined with a 1.5-T magnetic resonance scanner. T1-weighted (T1W) 3D-VWI was obtained using a flow-sensitized 3D fast spin-echo technique. In addition, multisequence MRI comprising magnetic resonance angiography (MRA), basiparallel anatomical scanning (BPAS), and axial T1W imaging (T1WI) were also examined. Presence of luminal stenosis, aneurysmal dilatation, intramural high signal, and intimal flap/double lumen of the vertebral and basilar arteries were visually assessed using each technique. RESULTS: On 3D-VWI, luminal stenosis, aneurysmal dilatation, intramural high signal, and intimal flap were observed in 16 (100%), 11 (68.8%), 16 (100%), and 1 (6.3%) patients, respectively. In contrast, on conventional techniques, these findings were observed in 15 (93.8%, MRA with BPAS), 12 (75.0%, MRA with BPAS), 12 (75.0%, T1WI), and 12 (75.0%, MRA) patients, respectively. CONCLUSIONS: The T1W 3D-VWI can directly visualize vessel wall iVBD lesions during the acute period of stroke compared with multisequence MRI.

Evaluating middle cerebral artery atherosclerotic lesions in acute ischemic stroke using magnetic resonance T1-weighted 3-dimensional vessel wall imaging.

BACKGROUND: Atherosclerotic lesions in intracranial arteries are a leading cause of ischemic stroke. Magnetic resonance angiography (MRA) is often used to assess atherosclerotic changes by detecting luminal narrowing, whereas it cannot directly visualize atherosclerotic lesions. Here, we used a 3-dimensional vessel wall imaging (3D-VWI) technique to evaluate intracranial arterial wall changes in acute stroke. METHODS: Eighteen consecutive patients with acute noncardioembolic stroke in the middle cerebral artery (MCA) territory who were prospectively examined with a 1.5-T magnetic resonance scanner were studied. T1-weighted (T1-W) 3D-VWI was obtained using a flow-sensitized 3D fast-spin echo technique. Wall thickening of MCA that suggests atherosclerotic plaques was visually evaluated and the contrast ratio (CR) of signal intensity of the lesions to that of the corpus callosum was calculated and compared with stenotic changes by MRA. RESULTS: Wall thickenings of the MCA ipsilateral and contralateral to the lesion were observed in almost all patients on 3D-VWI (94.4% and 94.4%, respectively), whereas MRA showed stenotic changes of 50% only in 1 patient (5.9%; P < .001). The CR of the thickened wall in the ipsilateral MCA was significantly higher than that in the contralateral MCA (median, .53 and .45, respectively; P = .028), suggesting of unstable plaques consisting of hemorrhage or lipid. CONCLUSIONS: The T1-W 3D-VWI can provide direct visualization of atherosclerotic lesions of the intracranial arteries in stroke patients, and it can detect signal change suggestive of unstable plaque.

Voxel-based morphometry of disproportionate cerebrospinal fluid space distribution for the differential diagnosis of idiopathic normal pressure hydrocephalus.

OBJECTIVE: To determine whether voxel-based morphometry of the cerebrospinal fluid (CSF) space can accurately differentiate iNPH from other related neurological disorders. METHODS: Nineteen patients with surgically proven iNPH and 24 patients with Alzheimer's disease (AD), 18 patients with Parkinson's disease (PD), and 14 healthy elderlies were examined. Regions of interest (ROIs) in the ventricular/sylvian (VS) and high convexity/midline (HCM) areas were used in VBM, and differences in CSF volume within these ROIs among the 4 groups were examined. RESULTS: The relative CSF volume in the VS-ROI in the iNPH group (.64) was significantly higher than that in the AD, PD, and healthy control groups (.26, .29, and .17, respectively; P < .001), whereas the relative CSF volume in the HCM-ROI was significantly reduced in the iNPH (.10) than in the other (.17, .16, and .16, respectively) groups (P < .001). Furthermore, the ratio of the 2 areas (VS/HCM) was markedly higher in the iNPH (6.87) than in the other (1.65, 1.74, .97, respectively) groups (P < .001), with sensitivity and specificity of .89 and 1.00, respectively. CONCLUSIONS: The VBM-based CSF space analysis can detect disproportionate changes in CSF space and differentiate iNPH patients from those with AD or PD and healthy elderlies accurately.

Noninvasive evaluation of collateral blood flow through circle of Willis in cervical carotid stenosis using selective magnetic resonance angiography.

BACKGROUND: Preoperative assessment of intracranial collateral circulation is helpful in predicting cerebral ischemia during surgical procedures for cervical internal carotid artery (ICA) stenosis. However, magnetic resonance angiography (MRA) and other less-invasive techniques cannot evaluate collateral blood flow because these techniques are nonselective. Hence, by using a newly developed selective MRA technique, we attempted to visualize collaterals via the circle of Willis in patients with ICA stenosis. METHODS: Twelve patients who underwent carotid endarterectomy were prospectively examined with a 1.5-T MR scanner. Both selective and nonselective MRA were obtained using a 3-dimensional time-of-flight technique, with or without a cylindrical saturation pulse that suppresses the flow signal from the region of the target ICA. Maximum intensity projection MRA images were generated and compared with digital subtraction angiography (DSA) images. RESULTS: In all patients, the distal flow signal of the ipsilateral ICA was completely suppressed on selective MRA compared with nonselective MRA. In addition, collateral blood flow through the anterior and posterior communicating arteries was visualized in 5 and 2 patients, respectively. These findings corresponded well with the DSA imaging. CONCLUSIONS: Selective MRA techniques can readily suppress signals from the distal blood flow of the target artery and visualize the presence of collateral flows through the circle of Willis in patients with cervical ICA stenosis.