Search

The thrombotic microangiopathy observed in malignant hypertension is similar to that of thrombotic thrombocytopenic purpura, which is associated with a deficiency of ADAMTS13, a von Willebrand factor (VWF)-cleaving protease that cleaves large prothrombogenic multimers. We hypothesized that ADAMTS13 is deficient in malignant hypertension and that the severity of thrombotic microangiopathy is associated with decreased ADAMTS13 activity. We included 20 patients with malignant and 20 patients with severe hypertension, and 20 matched normotensive individuals served as control subjects. VWF, active VWF, and free hemoglobin were assessed to explore predictors of ADAMTS13 activity. Patients with malignant hypertension had lower ADAMTS13 activity (80%; interquartile range: 53% to 130%) compared with control subjects (99% interquartile range: 82% to 129%; P<0.01) but not compared with patients with severe hypertension (P=0.14). ADAMTS13 activity negatively correlated with lactic dehydrogenase levels after logarithmic transformation (r=-0.65; P<0.001) and was associated with platelet count (r=0.34; P=0.04) and the presence of schistocytes (r=-0.37; P=0.02). Apart from the association with thrombotic microangiopathy, ADAMTS13 was inversely associated with creatinine (r=-0.42; P=0.008). Increasing levels of VWF were associated with a decrease in ADAMTS13 activity (r=-0.34; P=0.03). There was no significant association between ADAMTS13 activity and other parameters, including blood pressure. In conclusion, ADAMTS13 is decreased in malignant hypertension and associated with the severity of thrombotic microangiopathy, likely because of the release of VWF after endothelium stimulation. A severe deficiency could not be demonstrated. More studies are needed to identify the role of ADAMTS13 in the thrombotic microangiopathy and ischemic complications of malignant hypertension. [ABSTRACT FROM AUTHOR]

Background: Cerebral microbleeds (CMBs) have been observed in healthy elderly people undergoing systematic brain magnetic resonance imaging. The potential role of acute triggers on the appearance of CMBs remains unknown. We aimed to describe the incidence of new CMBs after transcatheter aortic valve replacement (TAVR) and to identify clinical and procedural factors associated with new CMBs including hemostatic measures and anticoagulation management., Methods: We evaluated a prospective cohort of patients with symptomatic aortic stenosis referred for TAVR for CMBs (METHYSTROKE [Identification of Epigenetic Risk Factors for Ischemic Complication During the TAVR Procedure in the Elderly]). Standardized neurologic assessment, brain magnetic resonance imaging, and analysis of hemostatic measures including von Willebrand factor were performed before and after TAVR. Numbers and location of microbleeds on preprocedural magnetic resonance imaging and of new microbleeds on postprocedural magnetic resonance imaging were reported by 2 independent neuroradiologists blinded to clinical data. Measures associated with new microbleeds and postprocedural outcome including neurologic functional outcome at 6 months were also examined., Results: A total of 84 patients (47% men, 80.9±5.7 years of age) were included. On preprocedural magnetic resonance imaging, 22 patients (26% [95% CI, 17%-37%]) had at least 1 microbleed. After TAVR, new microbleeds were observed in 19 (23% [95% CI, 14%-33%]) patients. The occurrence of new microbleeds was independent of the presence of microbleeds at baseline and of diffusion-weighted imaging hypersignals. In univariable analysis, a previous history of bleeding ( P =0.01), a higher total dose of heparin ( P =0.02), a prolonged procedure ( P =0.03), absence of protamine reversion ( P =0.04), higher final activated partial thromboplastin time ( P =0.05), lower final von Willebrand factor high-molecular-weight:multimer ratio ( P =0.007), and lower final closure time with adenosine-diphosphate ( P =0.02) were associated with the occurrence of new postprocedural microbleeds. In multivariable analysis, a prolonged procedure (odds ratio, 1.22 [95% CI, 1.03-1.73] for every 5 minutes of fluoroscopy time; P =0.02) and postprocedural acquired von Willebrand factor defect (odds ratio, 1.42 [95% CI, 1.08-1.89] for every lower 0.1 unit of high-molecular-weight:multimer ratio; P =0.004) were independently associated with the occurrence of new postprocedural microbleeds. New CMBs were not associated with changes in neurologic functional outcome or quality of life at 6 months., Conclusions: One out of 4 patients undergoing TAVR has CMBs before the procedure and 1 out of 4 patients develops new CMBs. Procedural or antithrombotic management and persistence of acquired von Willebrand factor defect were associated with the occurrence of new CMBs., Registration: URL: https://www., Clinicaltrials: gov; Unique identifier: NCT02972008.

Background: Platelet cross-linking during arterial thrombosis involves von Willebrand Factor (VWF) multimers. Therefore, proteolysis of VWF appears promising to disaggregate platelet-rich thrombi and restore vessel patency in acute thrombotic disorders such as ischemic stroke, acute coronary syndrome, or acute limb ischemia. N -Acetylcysteine (NAC, a clinically approved mucolytic drug) can reduce intrachain disulfide bonds in large polymeric proteins. In the present study, we postulated that NAC might cleave the VWF multimers inside occlusive thrombi, thereby leading to their dissolution and arterial recanalization., Methods: Experimental models of thrombotic stroke induced by either intra-arterial thrombin injection or ferric chloride application followed by measurement of cerebral blood flow using a combination of laser Doppler flowmetry and MRI were performed to uncover the effects of NAC on arterial thrombi. To investigate the effect of NAC on larger vessels, we also performed ferric chloride-induced carotid artery thrombosis. In vitro experiments were performed to study the molecular bases of NAC thrombolytic effect, including platelet aggregometry, platelet-rich thrombi lysis assays, thromboelastography (ROTEM), and high-shear VWF string formation using microfluidic devices. We also investigated the putative prohemorrhagic effect of NAC in a mouse model of intracranial hemorrhage induced by in situ collagenase type VII injection., Results: We demonstrated that intravenous NAC administration promotes lysis of arterial thrombi that are resistant to conventional approaches such as recombinant tissue-type plasminogen activator, direct thrombin inhibitors, and antiplatelet treatments. Through in vitro and in vivo experiments, we provide evidence that the molecular target underlying the thrombolytic effects of NAC is principally the VWF that cross-link platelets in arterial thrombi. Coadministration of NAC and a nonpeptidic GpIIb/IIIa inhibitor further improved its thrombolytic efficacy, essentially by accelerating thrombus dissolution and preventing rethrombosis. Thus, in a new large-vessel thromboembolic stroke model in mice, this cotreatment significantly improved ischemic lesion size and neurological outcome. It is important to note that NAC did not worsen hemorrhagic stroke outcome, suggesting that it exerts thrombolytic effects without significantly impairing normal hemostasis., Conclusions: We provide evidence that NAC is an effective and safe alternative to currently available antithrombotic agents to restore vessel patency after arterial occlusion., (© 2017 American Heart Association, Inc.)

Rationale: Percutaneous aortic valve procedures are a major breakthrough in the management of patients with aortic stenosis. Residual gradient and residual aortic regurgitation are major predictors of midterm and long-term outcome after percutaneous aortic valve procedures. We hypothesized that (1) induction/recovery of high molecular weight (HMW) multimers of von Willebrand factor defect could be instantaneous after acute changes in blood flow, (2) a bedside point-of-care assay (platelet function analyzer-closure time adenine DI-phosphate [PFA-CADP]), reflecting HMW multimers changes, could be used to monitor in real-time percutaneous aortic valve procedures., Objective: To investigate the time course of HMW multimers changes in models and patients with instantaneous induction/reversal of pathological high shear and its related bedside assessment., Methods and Results: We investigated the time course of the induction/recovery of HMW multimers defects under instantaneous changes in shear stress in an aortic stenosis rabbit model and in patients undergoing implantation of a continuous flow left ventricular assist device. We further investigated the recovery of HMW multimers and monitored these changes with PFA-CADP in aortic stenosis patients undergoing transcatheter aortic valve implantation or balloon valvuloplasty. Experiments in the aortic stenosis rabbit model and in left ventricular assist device patients demonstrated that induction/recovery of HMW multimers occurs within 5 minutes. Transcatheter aortic valve implantation patients experienced an acute decrease in shear stress and a recovery of HMW multimers within minutes of implantation which was sustained overtime. In patients with residual high shear or with residual aortic regurgitation, no recovery of HMW multimers was observed. PFA-CADP profiles mimicked HMW multimers recovery both in transcatheter aortic valve implantation patients without aortic regurgitation (correction) and transcatheter aortic valve implantation patients with aortic regurgitation or balloon valvuloplasty patients (no correction)., Conclusions: These results demonstrate that variations in von Willebrand factor multimeric pattern are highly dynamic, occurring within minutes after changes in blood flow. It also demonstrates that PFA-CADP can evaluate in real time the results of transcatheter aortic valve procedures., (© 2015 American Heart Association, Inc.)

Objective: Gene therapy for severe von Willebrand disease (vWD) seems an interesting treatment alternative with long-term therapeutic potential. We investigated the feasibility of targeting the liver for ectopic expression of physiologically active von Willebrand factor (vWF)., Methods and Results: The capacity of transgene-encoded murine vWF to restore vWF function was studied in a mouse model of severe vWD after liver-specific gene transfer by hydrodynamic injection. By using a hepatocyte-specific alpha1 antitrypsin promoter, a considerably higher and longer-lasting vWF expression was obtained when compared with a cytomegalovirus promoter, reaching maximum vWF plasma levels that are 10+/-1 times higher than the wild-type level. Liver-expressed vWF showed the full range of multimers, including the high molecular weight multimers, and restored factor VIII plasma levels, consistent with correction of the bleeding time 3 but not 7 days after gene transfer. Importantly, transgene encoded plasma vWF restored proper platelet adhesion and aggregation in a FeCl(3) induced thrombosis model., Conclusions: High ectopic expression of transgene encoded plasma vWF can be obtained after gene transfer to the liver. Liver-expressed vWF was fully multimerized and able to restore proper platelet plug formation in severe vWD. The liver therefore seems an attractive target for gene therapy for severe vWD.

Objective: von Willebrand Factor (vWF) structure-function relationship has been studied only in vitro. To investigate the physiological importance of particular vWF domains, we have introduced mutations into murine vWF (mvWF) cDNA inhibiting vWF binding to glycoprotein (Gp) Ib, GpIIbIIIa, and to fibrillar collagen., Methods and Results: We delivered wild-type (WT) or mutant mvWF cDNA into vWF-deficient (Vwf-/-) mice using hydrodynamic injection and assessed whether hemorrhagic symptoms could be corrected. Hydrodynamic gene transfer resulted in high expression of plasma mvWF 24 hours after injection (438+/-63% for 50 microg of cDNA). Factor VIII activity was normalized in Vwf-/- mice injected with mvWF cDNA and multimerization was achieved. Bleeding time was corrected after injection of WT mvWF cDNA in Vwf-/- mice whereas noninjected mice did not stop bleeding. Injection of the GpIIbIIIa and the collagen binding mutants in Vwf-/- mice also resulted in a correction of bleeding time whereas mice injected with the GpIb binding mutant were bleeding for as long they were observed, although blood loss was decreased compared with noninjected mice (61+/-21 microL versus 232+/-63 microL)., Conclusions: Our model allows the rapid in vivo evaluation of specific mutations on plasma vWF function.

Objective: The interaction of platelets with low density lipoprotein (LDL) contributes to the development of cardiovascular disease. Platelets are activated by native LDL (nLDL) through apoE Receptor 2' (apoER2')-mediated signaling to p38(MAPK) and by oxidized LDL (oxLDL) through lysophosphatidic acid (LPA) signaling to Rho A and Ca2+. Here we report a new mechanism for platelet activation by oxLDL., Methods and Results: Oxidation of nLDL increases p38(MAPK) activation through a mechanism that is (1) independent of LPA, and (2) unlike nLDL-signaling not desensitized by prolonged platelet-LDL contact or inhibited by receptor-associated protein or chondroitinase ABC. Antibodies against scavenger receptors CD36 and SR-A alone fail to block p38(MAPK) activation by oxLDL but combined blockade inhibits p38(MAPK) by >40% and platelet adhesion to fibrinogen under flow by >60%. Mouse platelets deficient in either CD36 or SR-A show normal p38(MAPK) activation by oxLDL but combined deficiency of CD36 and SR-A disrupts oxLDL-induced activation of p38(MAPK) by >70%., Conclusion: These findings reveal a novel platelet-activating pathway stimulated by oxLDL that is initiated by the combined action of CD36 and SR-A.

Objective: To explore the effect of the Heerlen polymorphism and C4b-binding protein (C4BP) on protein S catabolism in vitro and in vivo., Methods and Results: Radiolabeled protein S was efficiently bound and intracellularly degraded by THP-1 macrophages, and both processes were strongly reduced in the presence of the protein S-carrier protein C4BP. To test whether C4BP displays a similar protective effect in vivo, survival experiments were performed in mice. In the absence of C4BP, radiolabeled human protein S disappeared in a biphasic manner (mean residence time [MRT] 2 hours). However, the presence of C4BP resulted in a 4-fold prolonged survival of protein S (MRT 8 hours; P<0.0001). We also applied this experimental model to recombinant protein S-Heerlen, a naturally occurring variant that contains a Ser460Pro substitution. These clearance experiments revealed a strongly decreased survival of recombinant protein S-S460P (MRT 0.6 hours; P=0.021), which could be compensated partially by C4BP (MRT 1.4 hours; P=0.012 compared with protein S-S460P)., Conclusions: Protein S-S460P has a reduced survival in vivo, which may explain the low levels of free protein S in individuals carrying this polymorphism. Furthermore, C4BP prevents premature clearance of protein S and uses this ability to compensate the increased clearance of protein S-S460P.