MRI-based microthrombi detection in stroke with polydopamine iron oxide.

In acute ischemic stroke, even when successful recanalization is obtained, downstream microcirculation may still be obstructed by microvascular thrombosis, which is associated with compromised brain reperfusion and cognitive decline. Identifying these microthrombi through non-invasive methods remains challenging. We developed the PHySIOMIC (Polydopamine Hybridized Self-assembled Iron Oxide Mussel Inspired Clusters), a MRI-based contrast agent that unmasks these microthrombi. In a mouse model of thromboembolic ischemic stroke, our findings demonstrate that the PHySIOMIC generate a distinct hypointense signal on T2*-weighted MRI in the presence of microthrombi, that correlates with the lesion areas observed 24 hours post-stroke. Our microfluidic studies reveal the role of fibrinogen in the protein corona for the thrombosis targeting properties. Finally, we observe the biodegradation and biocompatibility of these particles. This work demonstrates that the PHySIOMIC particles offer an innovative and valuable tool for non-invasive in vivo diagnosis and monitoring of microthrombi, using MRI during ischemic stroke.

N-Acetylcysteine to Reduce Mortality for Patients Requiring Cardiac Catheterization or Cardiac Surgery: A Systematic Review and Meta-analysis.

ABSTRACT: Multimers of von Willebrand factor play a critical role in various processes inducing morbidity and mortality in cardiovascular-risk patients. With the ability to reduce von Willebrand factor multimers, N-acetylcysteine (NAC) could reduce mortality in patients undergoing coronary catheterization or cardiac surgery. However, its impact in perioperative period has never been studied so far in regard of its potential cardiovascular benefits. Then, 4 databases were searched for randomized controlled trials that compared in-hospital mortality between an experimental group, with NAC, and a control group without NAC, in patients undergoing coronary catheterization or cardiac surgery. The primary efficacy outcome was in-hospital mortality. Secondary outcomes were the occurrence of thrombotic events, major cardiovascular events, myocardial infarction, and contrast-induced nephropathy. The safety outcome was occurrence of hemorrhagic events. Nineteen studies totaling 3718 patients were included. Pooled analysis demonstrated a reduction of in-hospital mortality associated with NAC: odds ratio, 0.60; 95% confidence interval, 0.39-0.92; P = 0.02. The occurrence of secondary outcomes was not significantly reduced with NAC except for contrast-induced nephropathy. No difference was reported for hemorrhagic events. Subgroup analyses revealed a life-saving effect of NAC in a dose-dependent manner with reduction of in-hospital mortality for the NAC high-dose group, but not for the NAC standard-dose (<3500-mg) group. In conclusion, without being able to conclude on the nature of the mechanism involved, our review suggests a benefit of NAC in cardiovascular-risk patients in perioperative period in terms of mortality and supports prospective confirmatory studies.

Factor XII protects neurons from apoptosis by epidermal and hepatocyte growth factor receptor-dependent mechanisms.

BACKGROUND: Factor XII (FXII) is a serine protease that participates in the intrinsic coagulation pathway. Several studies have shown that plasma FXII exerts a deleterious role in cerebral ischemia and traumatic brain injury by promoting thrombo-inflammation. Nevertheless, the impact of FXII on neuronal cell fate remains unknown. OBJECTIVES: We investigated the role of FXII and FXIIa in neuronal injury and apoptotic cell death. METHODS: We tested the neuroprotective roles of FXII and FXIIa in an experimental model of neuronal injury induced by stereotaxic intracerebral injection of N-methyl-D-aspartic acid (NMDA) in vivo and in a model of apoptotic death of murine primary neuronal cultures through serum deprivation in vitro. RESULTS: Here, we found that exogenous FXII and FXIIa reduce brain lesions induced by NMDA injection in vivo. Furthermore, FXII protects cultured neurons from apoptosis through a growth factor--like effect. This mechanism was triggered by direct interaction with epidermal growth factor (EGF) receptor and subsequent activation of this receptor. Interestingly, the "proteolytically" active and two-chain form of FXII, FXIIa, exerts its protective effects by an alternative signaling pathway. FXIIa activates the pro-form of hepatocyte growth factor (HGF) into HGF, which in turn activated the HGF receptor (HGFR) pathway. CONCLUSION: This study describes two novel mechanisms of action of FXII and identifies neurons as target cells for the protective effects of single and two-chain forms of FXII. Therefore, inhibition of FXII in neurological disorders may have deleterious effects by preventing its beneficial effects on neuronal survival.

Molecular Magnetic Resonance Imaging of Endothelial Activation in the Central Nervous System.

Endothelial cells of the central nervous system over-express surface proteins during neurological disorders, either as a cause, or a consequence, of the disease. Since the cerebral vasculature is easily accessible by large contrast-carrying particles, it constitutes a target of choice for molecular magnetic resonance imaging (MRI). In this review, we highlight the most recent advances in molecular MRI of brain endothelial activation and focus on the development of micro-sized particles of iron oxide (MPIO) targeting adhesion molecules including intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), P-Selectin and E-Selectin. We also discuss the perspectives and challenges for the clinical application of this technology in neurovascular disorders (ischemic stroke, intracranial hemorrhage, subarachnoid hemorrhage, diabetes mellitus), neuroinflammatory disorders (multiple sclerosis, brain infectious diseases, sepsis), neurodegenerative disorders (Alzheimer's disease, vascular dementia, aging) and brain cancers (primitive neoplasms, metastasis).

Potent Thrombolytic Effect of N-Acetylcysteine on Arterial Thrombi.

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.

Hyperfibrinolysis increases blood-brain barrier permeability by a plasmin- and bradykinin-dependent mechanism.

Hyperfibrinolysis is a systemic condition occurring in various clinical disorders such as trauma, liver cirrhosis, and leukemia. Apart from increased bleeding tendency, the pathophysiological consequences of hyperfibrinolysis remain largely unknown. Our aim was to develop an experimental model of hyperfibrinolysis and to study its effects on the homeostasis of the blood-brain barrier (BBB). We induced a sustained hyperfibrinolytic state in mice by hydrodynamic transfection of a plasmid encoding for tissue-type plasminogen activator (tPA). As revealed by near-infrared fluorescence imaging, hyperfibrinolytic mice presented a significant increase in BBB permeability. Using a set of deletion variants of tPA and pharmacological approaches, we demonstrated that this effect was independent of N-methyl-D-aspartate receptor, low-density lipoprotein-related protein, protease-activated receptor-1, or matrix metalloproteinases. In contrast, we provide evidence that hyperfibrinolysis-induced BBB leakage is dependent on plasmin-mediated generation of bradykinin and subsequent activation of bradykinin B2 receptors. Accordingly, this effect was prevented by icatibant, a clinically available B2 receptor antagonist. In agreement with these preclinical data, bradykinin generation was also observed in humans in a context of acute pharmacological hyperfibrinolysis. Altogether, these results suggest that B2 receptor blockade may be a promising strategy to prevent the deleterious effects of hyperfibrinolysis on the homeostasis of the BBB.

Synergistic effect of thrombin and CD40 ligand on endothelial matrix metalloproteinase-10 expression and microparticle generation in vitro and in vivo.

OBJECTIVE: Thrombin induces CD40 ligand (CD40L) and matrix metalloproteinases (MMPs) under inflammatory/prothrombotic conditions. Thrombin and CD40L could modulate endothelial MMP-10 expression in vitro and in vivo. METHODS AND RESULTS: Human endothelial cells were stimulated with thrombin (0.1-10 U/mL), CD40L (0.25-1 µg/mL), or their combination (thrombin/CD40L) to assess MMP-10 expression and microparticle generation. Thrombin/CD40L elicited higher MMP-10 mRNA (5-fold; P<0.001) and protein levels (4.5-fold; P<0.001) than either stimulus alone. This effect was mimicked by a protease-activated receptor-1 agonist and antagonized by hirudin, a-protease-activated receptor-1, α-CD40L, and α-CD40 antibodies. The synergistic effect was dependent on p38 mitogen-activated protein kinase and c-Jun N-terminal kinase-1 pathways. Thrombin also upregulated the expression of CD40 in endothelial cell surface increasing its availability, thereby favoring its synergistic effects with CD40L. In mice, thrombin/CD40L further increased the aortic MMP-10 expression. Septic patients with systemic inflammation and enhanced thrombin generation (n=60) exhibited increased MMP-10 and soluble CD40L levels associated with adverse clinical outcome. Endothelial and systemic activation by thrombin/CD40L and lipopolysaccharide also increased microparticles harboring MMP-10 and CD40L. CONCLUSIONS: Thrombin/CD40L elicited a strong synergistic effect on endothelial MMP-10 expression and microparticles containing MMP-10 in vitro and in vivo, which may represent a new link between inflammation/thrombosis with prognostic implications.