A murine model of subarachnoid hemorrhage

Establishment of a novel protocol for assessing the severity of subarachnoid hemorrhage in circle Willis perforation mouse model

The Circle of Willis perforation (cWp) mouse model is a key tool in subarachnoid hemorrhage (SAH) research; however, inconsistent bleeding volumes can challenge experimental reliability. To address this issue, we introduced the ROB Scoring System, a novel protocol integrating Rotarod Tests (RT), Open-field Tests (OT) video analysis, and daily Body Weight Loss (BWL) monitoring to precisely categorize SAH severity. Forty C57BL/6 mice underwent cWp SAH induction, categorized by ROB into severity subgroups (severe, moderate, mild). Validation compared ROB trends in subgroups, and ROB outcomes with autopsy results on postoperative days three and seven for acute and sub-acute evaluations. Mortality rates were analyzed via the survival log-rank test, revealing a significant difference among SAH subgroups (P < 0.05). Strong correlations between ROB grades and autopsy findings underscored its precision. Notably, the severe group exhibited 100% mortality within 4 days post SAH onset. Single parameters (RT, OT, BWL) were insufficient for distinguishing SAH severity levels. The ROB score represents a significant advancement, offering an objective method for precise categorization and addressing inherent bleeding variations in the cWp SAH model. This standardized protocol enhances the reliability and effectiveness of the SAH translational research, providing a valuable tool for future investigations into this critical area.

Neutrophils and Neutrophil Extracellular Traps Cause Vascular Occlusion and Delayed Cerebral Ischemia After Subarachnoid Hemorrhage in Mice

BACKGROUND

After subarachnoid hemorrhage (SAH), neutrophils are deleterious and contribute to poor outcomes. Neutrophils can produce neutrophil extracellular traps (NETs) after ischemic stroke. Our hypothesis was that, after SAH, neutrophils contribute to delayed cerebral ischemia (DCI) and worse outcomes via cerebrovascular occlusion by NETs.

METHODS

SAH was induced via endovascular perforation, and SAH mice were given either a neutrophil-depleting antibody, a PAD4 (peptidylarginine deiminase 4) inhibitor (to prevent NETosis), DNAse-I (to degrade NETs), or a vehicle control. Mice underwent daily neurological assessment until day 7 and then euthanized for quantification of intravascular brain NETs (iNETs). Subsets of mice were used to quantify neutrophil infiltration, NETosis potential, iNETs, cerebral perfusion, and infarction. In addition, NET markers were assessed in the blood of aneurysmal SAH patients.

RESULTS

In mice, SAH led to brain neutrophil infiltration within 24 hours, induced a pro-NETosis phenotype selectively in skull neutrophils, and caused a significant increase in iNETs by day 1, which persisted until at least day 7. Neutrophil depletion significantly reduced iNETs, improving cerebral perfusion, leading to less neurological deficits and less incidence of DCI (16% versus 51.9%). Similarly, PAD4 inhibition reduced iNETs, improved neurological outcome, and reduced incidence of DCI (5% versus 30%), whereas degrading NETs marginally improved outcomes. Patients with aneurysmal SAH who developed DCI had elevated markers of NETs compared with non-DCI patients.

CONCLUSIONS

After SAH, skull-derived neutrophils are primed for NETosis, and there are persistent brain iNETs, which correlated with delayed deficits. The findings from this study suggest that, after SAH, neutrophils and NETosis are therapeutic targets, which can prevent vascular occlusion by NETs in the brain, thereby lessening the risk of DCI. Finally, NET markers may be biomarkers, which can predict which patients with aneurysmal SAH are at risk for developing DCI.

Continued P2X7 activation leads to mitochondrial fission and compromising microglial phagocytosis after subarachnoid haemorrhage

Subarachnoid haemorrhage (SAH) has a high rate of disability and mortality. Extremely damaging molecules, including adenosine triphosphate (ATP), are released from extravasated red blood cells and nerve cells, which activate microglia and induce sterile tissue injury and organ dysfunction. P2X purinoceptor 7 (P2X7) is one of the most important purine receptors on the microglial surface and is involved in the proinflammatory activation of microglia. While P2X7 can also affect microglial phagocytosis, the mechanism is not clear. Here, we demonstrated that microglial phagocytosis is progressively impaired under continued BzATP exposure and P2X7 activation. Furthermore, we found that P2X7 activation leads to increased intracellular Ca²⁺ levels and activates Calcineurin, which dephosphorylates dynamin-related protein 1 (DRP1) S637. The dephosphorylation of DRP1 at S637 leads to increased mitochondrial fission and decreased mitochondrial function, which may be responsible for the decreased microglial phagocytosis. Finally, we pharmacologically inhibited P2X7 activation in mice, which resulted in rescue of mitochondrial function and decreased microglial proliferation, but improved phagocytosis after SAH. Our study confirmed that P2X7 activation after SAH leads to the impairment of microglial phagocytosis through mitochondrial fission and verified that P2X7 inhibition restores microglial phagocytosis both in vitro and in vivo.

Influence of neurovascular anatomy on perforation site in different mouse strains using the filament perforation model for induction of subarachnoid hemorrhage

BACKGROUND

Filament perforation is a widely-used method to induce subarachnoid hemorrhage (SAH) in mice. Whereas the perforation site has been assumed to be in the branching of middle cerebral artery (MCA) and anterior cerebral artery (ACA), we recently observed more proximal perforations.

METHODS

Filament perforation was performed in CD1- (n = 10) and C57Bl/6N-mice (n = 9) ex vivo. The filament was left in place and the perforation site was microscopically assessed. Digital subtraction angiography (DSA) was performed in CD1- (n = 9) and C57Bl/6J-mice (n = 29) and anatomical differences of the internal carotid artery (ICA) were determined.

RESULTS

Whereas in C57Bl/6N-mice perforation occurred in the proximal intracranial ICA in 89% (n = 8), in CD1-mice the perforation site was in the proximal ICA in 50% (n = 5), in the branching between MCA and ACA in 40% (n = 4), and in the proximal ACA in 10% (n = 1). DSA revealed a stronger angulation (p<0.001) of the ICA in CD1-mice (163.5±2.81°) compared to C57Bl/6J-mice (124.5±5.49°). Body weight and ICA-angle showed no significant correlation in C57Bl/6J- (r = -0.06, pweight/angle = 0.757) and CD1-mice (r = -0.468, pweight/angle = 0.242).

CONCLUSION

Filament perforation in mice occurs not only at the hitherto presumed branching between MCA and ACA, but seems to depend on mouse strain and anatomy as the proximal intracranial ICA may also be perforated frequently.

Quantification of Capillary Perfusion in an Animal Model of Acute Intracranial Hypertension

Intracranial hypertension (IH) is a common feature of many pathologies, including brain edema. In the brain, the extended network of capillaries ensures blood flow to meet local metabolic demands. Capillary circulation may be severely affected by IH, but no studies have quantified the effect of intracranial pressure (ICP) and cerebral perfusion pressure (CPP) on capillary perfusion during the development of brain edema. We used optical coherence tomography angiography to quantify relative changes of fractional perfused volume (FPV) in cortical capillaries and simultaneously monitored ICP and blood pressure (BP) in anesthetized male C57Bl/6NTac mice during development of brain edema induced by water intoxication (WI) within 30 min. WI induced severe IH and brain herniation. ICP and CPP reached 90.2 mm Hg and 38.4 mm Hg, respectively. FPV was significantly affected already at normal ICP (ICP <15 mm Hg, slope ≈ -1.46, p < 0.001) and, at the onset of IH (ICP = 20-22 mm Hg), FPV was 17.9 ± 13.3% lower than baseline. A decreasing trend was observed until the ICP peak (Δ%FPV = -43.6 ± 19.2%). In the ICP range of 7-42 mm Hg, relative changes in FPV were significantly correlated with ICP, BP, and CPP (p < 0.001), with ICP and CPP being the best predictors. In conclusion, elevated ICP induces a gradual collapse of the cerebral microvasculature, which is initiated before the clinical threshold of IH. In summary, the estimate of capillary perfusion might be essential in patients with IH to assess the state of the brain microcirculation and to improve the availability of oxygen and nutrients to the brain.

Translational Genomics in Neurocritical Care: a Review

Translational genomics represents a broad field of study that combines genome and transcriptome-wide studies in humans and model systems to refine our understanding of human biology and ultimately identify new ways to treat and prevent disease. The approaches to translational genomics can be broadly grouped into two methodologies, forward and reverse genomic translation. Traditional (forward) genomic translation begins with model systems and aims at using unbiased genetic associations in these models to derive insight into biological mechanisms that may also be relevant in human disease. Reverse genomic translation begins with observations made through human genomic studies and refines these observations through follow-up studies using model systems. The ultimate goal of these approaches is to clarify intervenable processes as targets for therapeutic development. In this review, we describe some of the approaches being taken to apply translational genomics to the study of diseases commonly encountered in the neurocritical care setting, including hemorrhagic and ischemic stroke, traumatic brain injury, subarachnoid hemorrhage, and status epilepticus, utilizing both forward and reverse genomic translational techniques. Further, we highlight approaches in the field that could be applied in neurocritical care to improve our ability to identify new treatment modalities as well as to provide important information to patients about risk and prognosis.

DHEA Attenuates Microglial Activation via Induction of JMJD3 in Experimental Subarachnoid Haemorrhage

Background

Microglia are resident immune cells in the central nervous system and central to the innate immune system. Excessive activation of microglia after subarachnoid haemorrhage (SAH) contributes greatly to early brain injury, which is responsible for poor outcomes. Dehydroepiandrosterone (DHEA), a steroid hormone enriched in the brain, has recently been found to regulate microglial activation. The purpose of this study was to address the role of DHEA in SAH.

Methods

We used in vivo models of endovascular perforation and in vitro models of haemoglobin exposure to illustrate the effects of DHEA on microglia in SAH.

Results

In experimental SAH mice, exogenous DHEA administration increased DHEA levels in the brain and modulated microglial activation. Ameliorated neuronal damage and improved neurological outcomes were also observed in the SAH mice pretreated with DHEA, suggesting neuronal protective effects of DHEA. In cultured microglia, DHEA elevated the mRNA and protein levels of Jumonji d3 (JMJD3, histone 3 demethylase) after haemoglobin exposure, downregulated the H3K27me3 level, and inhibited the transcription of proinflammatory genes. The devastating proinflammatory microglia-mediated effects on primary neurons were also attenuated by DHEA; however, specific inhibition of JMJD3 abolished the protective effects of DHEA. We next verified that DHEA-induced JMJD3 expression, at least in part, through the tropomyosin-related kinase A (TrkA)/Akt signalling pathway.

Conclusions

DHEA has a neuroprotective effect after SAH. Moreover, DHEA increases microglial JMJD3 expression to regulate proinflammatory/anti-inflammatory microglial activation after haemoglobin exposure, thereby suppressing inflammation.

Carbon monoxide attenuates vasospasm and improves neurobehavioral function after subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is a devastating form of hemorrhagic stroke and is a serious medical condition caused by bleeding usually due to a ruptured aneurysm. Oxidative stress and inflammation from hemoglobin and heme released from lysed red blood cells are some postulated causes of vasospasm during SAH, which could lead to delayed cerebral ischemia. At low amounts, carbon monoxide (CO) gas may be neuroprotective through anti-inflammation, anti-cell death, and restoration of normal blood flow. Hence, this study focuses on a noninvasive strategy to treat SAH by using CO as a therapeutic medical gas. Mice were treated with 250 ppm CO or air for 1h started at 2h after SAH. Various anatomical and functional outcomes were monitored at 1 and 7d after SAH. CO decreased neurological deficit score (47.4 ± 10.5%) and increased activity (30.0 ± 9.1%) and stereotypic counts (261.5 ± 62.1%) at 7d. There was a significant increase in lumen area/wall thickness ratio in the middle cerebral artery (173.5 ± 19.3%), which tended to increase in the anterior cerebral artery (25.5 ± 4.3%) at 7d. This is the first report to demonstrate that CO minimizes delayed SAH-induced neurobehavioral deficits, which suggests that post-treatment with CO gas or CO-donors can be further tested as a potential therapy against SAH.

A Volumetric Method for Quantification of Cerebral Vasospasm in a Murine Model of Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is a subtype of hemorrhagic stroke. Cerebral vasospasm that occurs in the aftermath of the bleeding is an important factor determining patient outcome and is therefore frequently taken as a study endpoint. However, in small animal studies on SAH, quantification of cerebral vasospasm is a major challenge. Here, an ex vivo method is presented that allows quantification of volumes of entire vessel segments, which can be used as an objective measure to quantify cerebral vasospasm. In a first step, endovascular casting of the cerebral vasculature is performed using a radiopaque casting agent. Then, cross-sectional imaging data are acquired by micro computed tomography. The final step involves 3-dimensional reconstruction of the virtual vascular tree, followed by an algorithm to calculate center lines and volumes of the selected vessel segments. The method resulted in a highly accurate virtual reconstruction of the cerebrovascular tree shown by a diameter-based comparison of anatomical samples with their virtual reconstructions. Compared with vessel diameters alone, the vessel volumes highlight the differences between vasospastic and non-vasospastic vessels shown in a series of SAH and sham-operated mice.

Xenon Reduces Neuronal Hippocampal Damage and Alters the Pattern of Microglial Activation after Experimental Subarachnoid Hemorrhage: A Randomized Controlled Animal Trial

Objective

The neuroprotective properties of the noble gas xenon have already been demonstrated using a variety of injury models. Here, we examine for the first time xenon’s possible effect in attenuating early brain injury (EBI) and its influence on posthemorrhagic microglial neuroinflammation in an in vivo rat model of subarachnoid hemorrhage (SAH).

Methods

Sprague-Dawley rats (n = 22) were randomly assigned to receive either Sham surgery (n = 9; divided into two groups) or SAH induction via endovascular perforation (n = 13, divided into two groups). Of those randomized for SAH, 7 animals were postoperatively ventilated with 50 vol% oxygen/50 vol% xenon for 1 h and 6 received 50 vol% oxygen/50 vol% nitrogen (control). The animals were sacrificed 24 h after SAH. Of each animal, a cerebral coronal section (−3.60 mm from bregma) was selected for assessment of histological damage 24 h after SAH. A 5-point neurohistopathological severity score was applied to assess neuronal cell damage in H&E and NeuN stained sections in a total of four predefined anatomical regions of interest. Microglial activation was evaluated by a software-assisted cell count of Iba-1 stained slices in three cortical regions of interest.

Results

A diffuse cellular damage was apparent in all regions of the ipsilateral hippocampus 24 h after SAH. Xenon-treated animals presented with a milder damage after SAH. This effect was found to be particularly pronounced in the medial regions of the hippocampus, CA3 (p = 0.040), and dentate gyrus (DG p = 0.040). However, for the CA1 and CA2 regions, there were no statistical differences in neuronal damage according to our histological scoring. A cell count of activated microglia was lower in the cortex of xenon-treated animals. This difference was especially apparent in the left piriform cortex (p = 0.017).

Conclusion

In animals treated with 50 vol% xenon (for 1 h) after SAH, a less pronounced neuronal damage was observed for the ipsilateral hippocampal regions CA3 and DG, when compared to the control group. In xenon-treated animals, a lower microglial cell count was observed suggesting an immunomodulatory effect generated by xenon. As for now, these results cannot be generalized as only some hippocampal regions are affected. Future studies should assess the time and localization dependency of xenon’s beneficial properties after SAH.

Baicalin Attenuates Subarachnoid Hemorrhagic Brain Injury by Modulating Blood-Brain Barrier Disruption, Inflammation, and Oxidative Damage in Mice

In subarachnoid hemorrhagic brain injury, the early crucial events are edema formation due to inflammatory responses and blood-brain barrier disruption. Baicalin, a flavone glycoside, has antineuroinflammatory and antioxidant properties. We examined the effect of baicalin in subarachnoid hemorrhagic brain injury. Subarachnoid hemorrhage was induced through filament perforation and either baicalin or vehicle was administered 30 min prior to surgery. Brain tissues were collected 24 hours after surgery after evaluation of neurological scores. Brain tissues were processed for water content, real-time PCR, and immunoblot analyses. Baicalin improved neurological score and brain water content. Decreased levels of tight junction proteins (occludin, claudin-5, ZO-1, and collagen IV) required for blood-brain barrier function were restored to normal level by baicalin. Real-time PCR data demonstrated that baicalin attenuated increased proinflammatory cytokine (IL-1β, IL-6, and CXCL-3) production in subarachnoid hemorrhage mice. In addition to that, baicalin attenuated microglial cell secretion of IL-1β and IL-6 induced by lipopolysaccharide (100 ng/ml) dose dependently. Finally, baicalin attenuated induction of NOS-2 and NOX-2 in SAH mice at the mRNA and protein level. Thus, we demonstrated that baicalin inhibited microglial cell activation and reduced inflammation, oxidative damage, and brain edema.

Value of Three-Dimensional Maximum Intensity Projection Display to Assist in Magnetic Resonance Imaging (MRI)-Based Grading in a Mouse Model of Subarachnoid Hemorrhage

Background

Subarachnoid hemorrhage (SAH) is one of the most devastating cerebrovascular disorders. We report on the diagnostic value of three-dimensional (3-D) maximum intensity projection (MIP) reconstruction of T2*-weighted magnetic resonance images (MRI), processed using graphical user interface-based software, to aid in the accurate grading of endovascular-perforation-induced SAH in a mouse model.

Material/Methods

A total of 30 mice were subjected to SAH by endovascular perforation; three (10%) were scored as grade 0, six (20%) as grade 1, six (20%) as grade 2, eight (27%) as grade 3, and seven (23%) as grade 4 according to T2*-weighted coronal slices. In comparison, none of mice were scored as grade 0, eight (27%) as grade 1, five (17%) as grade 2, nine (30%) as grade 3, and eight (27%) as grade 4 based on subsequent evaluation using reconstructed 3-D MIP images.

Results

Mice scored as grade 0 (10%; no visible SAH) on T2*-coronal images were categorized as grades 1 (thin/localized SAH) and 3 (thick/diffuse SAH) according to 3-D MIP images. Grades based on T2* 3-D MIP images were more closely correlated with conventional SAH score (r²=0.59; P<0.0001) and neurological score (r²=0.25; P=0.005) than those based on T2*-coronal slices (r²=0.46; P<0.0001 for conventional score and r²=0.15; P=0.035 for neurological score).

Conclusions

These results suggest that 3-D MIP images generated from T2*-weighted MRI data may be useful for the simple and precise grading of SAH severity in mice to overcome the weakness of the current MRI-based SAH grading system.

Endovascular Perforation Murine Model of Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is a subtype of stroke with disastrous outcomes of high disability and mortality. A variety of endeavors have been developed to explore a SAH animal model for investigation of the disease. Among these models, the endovascular perforation SAH model was considered to be the most simulative to the clinical human SAH because it reproduces several pathophysiology procedures and presents some of the most important post-hemorrhage features. An applicable SAH animal model should have the characteristics of low mortality rate, limited surgical manipulation, and adaptation to many species, which permits reproducibility and standardization. An intensive discussion of how to improve the techniques and refine the procedure has taken place in the last decade. This report describes our experiences with a murine model of SAH. We aim to standardize and optimize the procedures to establish a relatively stable animal model for SAH research.

Protocol for the induction of subarachnoid hemorrhage in mice by perforation of the Circle of Willis with an endovascular filament

Genetically engineered mice are a valuable tool to investigate the molecular and cellular mechanisms leading to brain damage following subarachnoid hemorrhage (SAH). Therefore, several murine SAH models were developed during the last 15 years. Among those models, the perforation of the Circle of Willis by an endovascular filament or “filament model” turned out to become the most popular one, since it is believed to reproduce some of the most prominent pathophysiological features observed after human SAH. Despite the importance of the endovascular filament model for SAH research, relatively few studies were published using this technique during the past years and a number of laboratories reported problems establishing the technique. This triggered discussions about the standardization, reproducibility, and the reliability of the model. In order to improve this situation, the current paper aims to provide a comprehensive hands-on protocol of the murine endovascular filament model. The protocol proved to result in induction of SAH in mice with high intrapersonal and interpersonal reproducibility and is based on our experience with this technique for more than 10 years. By sharing our experience with this valuable model, we aim to initiate a constantly ongoing discussion process on the improvement of standards and techniques in the field of experimental SAH research.