Subarachnoid Hemorrhage Severely Impairs Brain Parenchymal Cerebrospinal Fluid Circulation in Nonhuman Primate.

BACKGROUND AND PURPOSE: Subarachnoid hemorrhage (SAH) is a devastating form of stroke with neurological outcomes dependent on the occurrence of delayed cerebral ischemia. It has been shown in rodents that some of the mechanisms leading to delayed cerebral ischemia are related to a decreased circulation of the cerebrospinal fluid (CSF) within the brain parenchyma. Here, we evaluated the cerebral circulation of the CSF in a nonhuman primate in physiological condition and after SAH. METHODS: We first evaluated in physiological condition the circulation of the brain CSF in Macacafacicularis, using magnetic resonance imaging of the temporal DOTA-Gd distribution after its injection into the CSF. Then, animals were subjected to a minimally invasive SAH before an MRI evaluation of the impact of SAH on the brain parenchymal CSF circulation. RESULTS: We first demonstrate that the CSF actively penetrates the brain parenchyma. Two hours after injection, almost the entire brain is labeled by DOTA-Gd. We also show that our model of SAH in nonhuman primate displays the characteristics of SAH in humans and leads to a dramatic impairment of the brain parenchymal circulation of the CSF. CONCLUSIONS: The CSF actively penetrates within the brain parenchyma in the gyrencephalic brain, as described for the glymphatic system in rodent. This parenchymal CSF circulation is severely impaired by SAH.

Vascular Tissue-Type Plasminogen Activator Promotes Intracranial Aneurysm Formation.

BACKGROUND AND PURPOSE: Although the mechanisms that contribute to intracranial aneurysm (IA) formation and rupture are not totally elucidated, inflammation and matrix remodeling are incriminated. Because tPA (tissue-type plasminogen activator) controls both inflammatory and matrix remodeling processes, we hypothesized that tPA could be involved in the pathophysiology of IA. METHODS: Immunofluorescence analyses of tPA and its main substrate within the aneurysmal wall of murine and human samples were performed. We then compared the formation and rupture of IAs in wild-type, tPA-deficient and type 1 plasminogen activator inhibitor-deficient mice subjected to a model of elastase-induced IA. The specific contribution of vascular versus global tPA was investigated by performing hepatic hydrodynamic transfection of a cDNA encoding for tPA in tPA-deficient mice. The formation and rupture of IAs were monitored by magnetic resonance imaging tracking for 28 days. RESULTS: Immunofluorescence revealed increased expression of tPA within the aneurysmal wall. The number of aneurysms and their symptomatic ruptures were significantly lower in tPA-deficient than in wild-type mice. Conversely, they were higher in plasminogen activator inhibitor-deficient mice. The wild-type phenotype could be restored in tPA-deficient mice by selectively increasing circulating levels of tPA via hepatic hydrodynamic transfection of a cDNA encoding for tPA. CONCLUSIONS: Altogether, this preclinical study demonstrates that the tPA present in the blood stream is a key player of the formation of IAs. Thus, tPA should be considered as a possible new target for the prevention of IAs formation and rupture.

Impaired glymphatic perfusion after strokes revealed by contrast-enhanced MRI: a new target for fibrinolysis?

BACKGROUND AND PURPOSE: The aim of the present study was to investigate the impact of different stroke subtypes on the glymphatic system using MRI. METHODS: We first improved and characterized an in vivo protocol to measure the perfusion of the glymphatic system using MRI after minimally invasive injection of a gadolinium chelate within the cisterna magna. Then, the integrity of the glymphatic system was evaluated in 4 stroke models in mice including subarachnoid hemorrhage (SAH), intracerebral hemorrhage, carotid ligature, and embolic ischemic stroke. RESULTS: We were able to reliably evaluate the glymphatic system function using MRI. Moreover, we provided evidence that the glymphatic system was severely impaired after SAH and in the acute phase of ischemic stroke, but was not altered after carotid ligature or in case of intracerebral hemorrhage. Notably, this alteration in glymphatic perfusion reduced brain clearance rate of low-molecular-weight compounds. Interestingly, glymphatic perfusion after SAH can be improved by intracerebroventricular injection of tissue-type plasminogen activator. Moreover, spontaneous arterial recanalization was associated with restoration of the glymphatic function after embolic ischemic stroke. CONCLUSIONS: SAH and acute ischemic stroke significantly impair the glymphatic system perfusion. In these contexts, injection of tissue-type plasminogen activator either intracerebroventricularly to clear perivascular spaces (for SAH) or intravenously to restore arterial patency (for ischemic stroke) may improve glymphatic function.

From Stroke to Dementia: a Comprehensive Review Exposing Tight Interactions Between Stroke and Amyloid-ß Formation.

Stroke and Alzheimer's disease (AD) are cerebral pathologies with high socioeconomic impact that can occur together and mutually interact. Vascular factors predisposing to cerebrovascular disease have also been specifically associated with development of AD, and acute stroke is known to increase the risk to develop dementia.Despite the apparent association, it remains unknown how acute cerebrovascular disease and development of AD are precisely linked and act on each other. It has been suggested that this interaction is strongly related to vascular deposition of amyloid-ß (Aß), i.e., cerebral amyloid angiopathy (CAA). Furthermore, the blood-brain barrier (BBB), perivascular space, and the glymphatic system, the latter proposedly responsible for the drainage of solutes from the brain parenchyma, may represent key pathophysiological pathways linking stroke, Aß deposition, and dementia.In this review, we propose a hypothetic connection between CAA, stroke, perivascular space integrity, and dementia. Based on relevant pre-clinical research and a few clinical case reports, we speculate that impaired perivascular space integrity, inflammation, hypoxia, and BBB breakdown after stroke can lead to accelerated deposition of Aß within brain parenchyma and cerebral vessel walls or exacerbation of CAA. The deposition of Aß in the parenchyma would then be the initiating event leading to synaptic dysfunction, inducing cognitive decline and dementia. Maintaining the clearance of Aß after stroke could offer a new therapeutic approach to prevent post-stroke cognitive impairment and development into dementia.

Cranioplasty Reverses Dysfunction of the Solutes Distribution in the Brain Parenchyma After Decompressive Craniectomy.

BACKGROUND: Solutes distribution by the intracranial cerebrospinal fluid (CSF) fluxes along perivascular spaces and through interstitial fluid (ISF) play a key role in the clearance of brain metabolites, with essential functions in maintaining brain homeostasis. OBJECTIVE: To investigate the impact of decompressive craniectomy (DC) and cranioplasty (CP) on the efficacy of solutes distribution by the intracranial CSF and ISF flux. METHODS: Mice were allocated in 3 groups: sham surgery, DC, and DC followed by CP. The solutes distribution in the brain parenchyma was assessed using T1 magnetic resonance imaging after injection of DOTA-Gadolinium in the cisterna magna. This evaluation was performed at an early time point following DC (after 2 d) and at a later time point (after 15 d). We evaluated the solutes distribution in the whole brain and in the region underneath the DC area. RESULTS: Our results demonstrate that the global solutes distribution in the brain parenchyma is impaired after DC in mice, both at early and late time-points. However, there was no impact of DC on the solutes distribution just under the craniectomy. We then provide evidence that this impairment was reversed by CP. CONCLUSION: The solute distribution in the brain parenchyma by the CSF and ISF is impaired by DC, a phenomenon reversed by CP.

Optimized tPA: A non-neurotoxic fibrinolytic agent for the drainage of intracerebral hemorrhages.

Intracerebral hemorrhage (ICH) is the most severe form of stroke. Catheter-delivered thrombolysis with recombinant tissue-type plasminogen activator (rtPA) for the drainage of ICH is currently under evaluation in a phase III clinical trial (MISTIE III). However, in a pig model of ICH, in situ fibrinolysis with rtPA was reported to increase peri-lesional edema by promoting N-methyl-D-aspartate (NMDA)-dependent excitotoxicity. In the present study, we engineered a non-neurotoxic tPA variant, OptPA, and investigated its safety and efficacy for in situ fibrinolysis in a rat model of ICH. Magnetic resonance imaging analyses of hematoma and edema volumes, behavioral tasks and histological analyses were performed to measure the effects of treatments. In vitro, OptPA was equally fibrinolytic as rtPA without promoting NMDA-dependent neurotoxicity. In vivo, in situ fibrinolysis using OptPA reduced hematoma volume, like rtPA, but it also reduced the evolution of peri-hematomal neuronal death and subsequent edema progression. Overall, this preclinical study demonstrates beneficial effects of OptPA compared to rtPA for the drainage of ICH.

Modification of apparent intracerebral hematoma volume on T2∗-weighted images during normobaric oxygen therapy may contribute to false diagnosis.

It was previously reported that normobaric oxygen therapy (NBO) significantly affected T2∗-weighted imaging in a mouse model of intracerebral hemorrhage (ICH). However, it is unclear whether a similar phenomenon exists in large volume ICH as seen in human pathology. We investigated the effects of NBO on T2∗-weighted images in a pig model of ICH. Our data show that NBO makes disappear a peripheral crown of the hematoma, which in turn decreases the apparent volume of ICH by 18%. We hypothesized that this result could be translated to ICH in human, and subsequently could lead to inaccurate diagnostic.

Cerebrospinal fluid flow increases from newborn to adult stages.

Solute transport through the brain is of major importance for the clearance of toxic molecules and metabolites, and it plays key roles in the pathophysiology of the central nervous system. This solute transport notably depends on the cerebrospinal fluid (CSF) flow, which circulates in the subarachnoid spaces, the ventricles and the perivascular spaces. We hypothesized that the CSF flow may be different in the perinatal period compared to the adult period. Using in vivo magnetic resonance imaging (MRI) and near-infrared fluorescence imaging (NIRF), we assessed the dynamic of the CSF flow in rodents at different ages. By injecting a contrast agent into the CSF, we first used MRI to demonstrate that CSF flow gradually increases with age, with the adult pattern observed at P90. This observation was confirmed by NIRF, which revealed an increased CSF flow in P90 rats when compared with P4 rats not only at the surface of the brain but also deep in the brain structures. Lastly, we evaluated the exit routes of the CSF from the brain. We demonstrated that indocyanine green injected directly into the striatum spread throughout the parenchyma in adult rats, whereas it stayed at the injection point in P4 rats. Moreover, the ability of CSF to exit through the nasal mucosa was increased in the adult rodents. Our results provide evidence that the perinatal brain has nonoptimal CSF flow and exit and, thus, may have impaired clean-up capacity. © 2018 Wiley Periodicals, Inc. Develop Neurobiol, 2018.

Cervical artery tortuosity is associated with intracranial aneurysm.

Background Intracranial aneurysms may be associated with an underlying arteriopathy, leading to arterial wall fragility. Arterial tortuosity is a major characteristic of some connective tissue disease. Aim To determine whether intracranial aneurysm is associated with an underlying arteriopathy. Methods Using a case-control design, from May 2012 to May 2013, we selected intracranial aneurysm cases and controls from consecutive patients who had conventional cerebral angiography in our center. Cases were patients with newly diagnosed intracranial aneurysm. Controls were patients who had diagnostic cerebral angiography and free of aneurysm. The prevalence of tortuosity, retrospectively assessed according to standard definitions, was compared between cases and controls and, association between tortuosity and some aneurysm characteristics was examined, in cases only. Results About 659 arteries from 233 patients (112 cases and 121 controls) were examined. Tortuosity was found in 57 (51%) cases and 31 (26%) controls (adjusted OR = 2.71; 95%CI, 1.53-4.80). The same trend was found when looking at each tortuosity subtype (simple tortuosity, coil, kink) or at carotid or vertebral territory separately. In contrast, no association between tortuosity and rupture status, aneurysm number or neck size was found. Conclusions Cervical artery tortuosity is significantly associated with intracranial aneurysm, although not related to main aneurysm characteristics. Our results support the presence of an underlying diffuse arteriopathy in intracranial aneurysm patients.

Urokinase versus Alteplase for intraventricular hemorrhage fibrinolysis.

Intraventricular hemorrhage (IVH) is the most severe form of stroke with intraventricular fibrinolysis (IVF) as a hopeful treatment. Urokinase (uPA) and tissue-type plasminogen activator (tPA) are used for IVF in Human. No clinical trial has evaluated the differential impact of these two fibrinolytics for IVF. Thus, we decided here to compare the use of these two fibrinolytics in a pre-clinical study. IVH was induced in rats by injection of collagenase type VII within the brain parenchyma followed by an IVF. Rats were randomized to receive uPA, tPA or saline within the ventricle, and cerebrospinal fluid was aspirated. Hematoma and ventricular volumes, brain water contents, inflammation and neurological deficits were measured at day three post-treatments. We also performed in vitro studies, in which neuronal cultures were subjected to an excitotoxic paradigm in the presence of either uPA or tPA. In the IVH model, we showed that although both uPA and tPA led to reduced ventricular volumes, only uPA significantly improved functional recovery. These results could be explained by the fact that uPA, in contrast of tPA, fails to promote inflammatory processes and neurotoxicity. Our study provides evidence supporting the use of uPA for fibrinolysis of IVH. A clinical trial could be warranted if tPA failed to improve outcomes in human IVH.