The Acute Phase of Experimental Subarachnoid Hemorrhage: Intracranial Pressure Dynamics and Their Effect on Cerebral Blood Flow and Autoregulation

A novel method for detecting intracranial pressure changes by monitoring cerebral perfusion via electrical impedance tomography

BACKGROUND

Acute and critical neurological diseases are often accompanied with elevated intracranial pressure (ICP), leading to insufficient cerebral perfusion, which may cause severe secondary lesion. Existing ICP monitoring techniques often fail to effectively meet the demand for real-time noninvasive ICP monitoring and warning. This study aimed to explore the use of electrical impedance tomography (EIT) to provide real-time early warning of elevated ICP by observing cerebral perfusion.

METHODS

An intracranial hypertension model was prepared by injecting autologous un-anticoagulated blood into the brain parenchyma of twelve Landrace swine. Invasive ICP monitoring was used as a control method, and a high-precision EIT system was used to acquire and analyze the changing patterns of cerebral perfusion EIT image parameters with respect to ICP. Four EIT parameters related to cerebral perfusion were extracted from the images, and their potential application in detecting ICP elevation was analyzed.

RESULTS

When ICP increased, all EIT perfusion parameters decreased significantly (P < 0.05). When the subjects were in a state of intracranial hypertension (ICP > 22 mmHg), the correlation between EIT perfusion parameters and ICP was more significant (P < 0.01), with correlation coefficients ranging from -0.72 to -0.83. We tested the objects when they were in baseline ICP and in ICP of 15-40 mmHg. Under both circumstances, ROC curve analysis showed that the comprehensive model of perfusion parameters based on the random forest algorithm had a sensitivity and specificity of more than 90% and an area under the curve (AUC) of more than 0.9 for detecting ICP increments of both 5 and 10 mmHg.

CONCLUSION

This study demonstrates the feasibility of using perfusion EIT to detect ICP increases in real time, which may provide a new method for real-time non-invasive monitoring of patients with increased ICP.

Multifaceted role of thrombin in subarachnoid hemorrhage: Focusing on cerebrospinal fluid circulation disorder

Subarachnoid hemorrhage (SAH) is a severe neurological condition characterized by high morbidity and mortality. The unfavorable prognosis of SAH is closely associated with early brain injury (EBI) and delayed cerebral ischemia (DCI), wherein thrombin plays a role as part of the secondary injury components following hemorrhage in these two pathological processes. Additionally, thrombin contributes to disruptions in the circulation of cerebrospinal fluid (CSF), thereby giving rise to a spectrum of sequelae following SAH, including cerebral edema, hydrocephalus, cognitive impairments, and depressive symptoms. This review aims to provide a comprehensive understanding of the pathological role of thrombin in EBI, DCI, and CSF circulation following SAH, with a specific focus on its impact on the glymphatic-meningeal lymphatic system-a crucial mechanism for waste clearance and neurohomeostatic regulation. Additionally, this review offers an overview of current pharmacological interventions and treatment modalities targeting pathogenic mechanisms, aiming to mitigate brain injury and promote neurological recovery post-SAH.

Neuritin attenuates neuroinflammation and apoptosis in early brain injury after subarachnoid hemorrhage via endoplasmic reticulum stress-related inflammatory pathways

Neuroinflammation is a key destructive pathophysiological process in early brain injury (EBI) following subarachnoid hemorrhage (SAH). Recent studies have discovered that endoplasmic reticulum stress-related inflammatory pathways include the IRE1α-TRAF2-NF-κB pathway, PERK-eIF2α-NF-κB pathway, and ATF6-AKT -NF-κB pathway leading to neuroinflammatory response. Neuritin is a neurotrophin that is involved in neuronal plasticity and regeneration. Studies have suggested that Neuritin has a vital role in reducing neuroinflammation, and can also decrease the expression of proteins related to endoplasmic reticulum stress following SAH. This suggests that Neuritin could be a potential therapeutic target for SAH and other neurological conditions. However, the regulatory mechanisms of Neuritin in ER stress-related inflammatory pathways after SAH are not yet fully understood. In this work, we discovered that the activation of ER stress-related inflammatory pathways leads to neuroinflammation, which further aggravates neuronal apoptosis after SAH. Our findings indicate that Neuritin overexpression play a neuroprotective role by inhibiting IRE1α-TRAF2-NF-κB pathway, PERK-eIF2α-NF-κB pathway, and ATF6-AKT-NF-κB pathway associated with endoplasmic reticulum stress. These inhibitory effects on neuroinflammation ultimately reduce nerve cell apoptosis.

The potential of disulfiram as a drug to improve the prognosis after the onset of subarachnoid hemorrhage

Subarachnoid hemorrhage due to rupture of intracranial aneurysms has a poor outcome, making this disease being the social problem. Inflammation evoked by the increase in intracranial pressure and the clot in the subarachnoid space after the onset of SAH exacerbates neuronal death and vasospasm, resulting in the poor outcome and severe aftereffects. Here, FROUNT mediates CCR2 and CCR5 signaling as an intracellular molecule binding to these chemoattractant receptors which facilitate the migration of inflammatory cells, such as macrophages, in situ to trigger inflammation there. Animal model of subarachnoid hemorrhage was established in rats through intrathecal injection of autologous blood. The effect of the FROUNT inhibitor, disulfiram, on survival rate, neuronal death in hippocampus or vasospasm was then examined. The intrathecal administration of disulfiram significantly suppressed the infiltration of CD68-positive macrophages and myeloperoxidase-positive neutrophils toward the clot in the cistern in situ. In this condition, disulfiram ameliorated the death of animals after the onset of subarachnoid hemorrhage in rats. In addition, disulfiram suppressed both the two major events after subarachnoid hemorrhage, the neuronal death in hippocampus and vasospasm. The pharmacological inhibition of CCR2 and CCR5 signaling by disulfiram could thus be the therapeutic strategy to improve the outcome of subarachnoid hemorrhage.

Impact of Carotid Siphon Calcification on the Course and Outcome of Patients With Aneurysmal Subarachnoid Hemorrhage

BACKGROUND

Carotid siphon calcification (CSC) serves as a marker of atherosclerosis and therefore may influence the outcome after subarachnoid hemorrhage (aSAH). We aimed to analyze the impact of CSC on neurological outcomes, ischemia, and vasospasm.

METHODS

A total of 716 patients with aSAH were treated between December 2004 and June 2016 in our central European tertiary neurovascular care center in Essen, Germany. CSC was recorded using the Woodcock scale (grades 0-3) on a computed tomography scan. Study end points included an unfavorable outcome at 6 months post-aSAH (modified Rankin Scale score ≥4), vasospasm, and early cerebral ischemia (72 hours) and delayed cerebral ischemia (delayed cerebral ischemia; >72 hours) in the follow-up computed tomography scans. The associations were adjusted for patients' baseline characteristics and secondary complications. Finally, within a subgroup analysis, patients with and without daily aspirin intake after endovascular aneurysm occlusion were compared.

RESULTS

Increasing grades of CSC were associated with lower rates of vasospasm in the anterior circulation. Severe CSC (grade 3) was independently related to the risk of an unfavorable outcome (adjusted odds ratio [aOR], 4.06 [95% CI, 1.98-8.33]; P<0.001) and early cerebral ischemia (aOR, 1.58 [95% CI, 1.03-2.43]; P=0.035) but not delayed cerebral ischemia (aOR, 1.08 [95% CI, 0.67-1.73]; P=0.763). In the aspirin subgroup analysis, the negative effect of severe CSC on functional outcome remained significant only in aSAH cases without aspirin (aOR, 5.47 [95% CI, 2.38-12.54]; P<0.001). In contrast, there was no association between severe CSC and unfavorable outcomes among individuals with daily aspirin intake (aOR, 0.84 [95% CI, 0.59-4.21]; P=0.603).

CONCLUSIONS

Our data suggest CSC as a cerebrovascular risk factor resulting in higher rates of early cerebral ischemia and unfavorable outcomes after aSAH. However, by increasing arterial stiffness, CSC might lower the probability of vasospasm, which could explain the missing link between CSC and delayed cerebral ischemia. Additionally, aspirin intake seems to potentially mitigate the negative impact of CSC on aSAH outcome. Further investigations are needed to confirm the observations from the present study.

Ferroptosis in early brain injury after subarachnoid hemorrhage: review of literature

Spontaneous subarachnoid hemorrhage (SAH), mainly caused by ruptured intracranial aneurysms, is a serious acute cerebrovascular disease. Early brain injury (EBI) is all brain injury occurring within 72 h after SAH, mainly including increased intracranial pressure, decreased cerebral blood flow, disruption of the blood-brain barrier, brain edema, oxidative stress, and neuroinflammation. It activates cell death pathways, leading to neuronal and glial cell death, and is significantly associated with poor prognosis. Ferroptosis is characterized by iron-dependent accumulation of lipid peroxides and is involved in the process of neuron and glial cell death in early brain injury. This paper reviews the research progress of ferroptosis in early brain injury after subarachnoid hemorrhage and provides new ideas for future research.

Animal Welfare Aspects in Planning and Conducting Experiments on Rodent Models of Subarachnoid Hemorrhage

Subarachnoid hemorrhage is an acute life-threatening cerebrovascular disease with high socio-economic impact. The most frequent cause, the rupture of an intracerebral aneurysm, is accompanied by abrupt changes in intracerebral pressure, cerebral perfusion pressure and, consequently, cerebral blood flow. As aneurysms rupture spontaneously, monitoring of these parameters in patients is only possible with a time delay, upon hospitalization. To study alterations in cerebral perfusion immediately upon ictus, animal models are mandatory. This article addresses the points necessarily to be included in an animal project proposal according to EU directive 2010/63/EU for the protection of animals used for scientific purposes and herewith offers an insight into animal welfare aspects of using rodent models for the investigation of cerebral perfusion after subarachnoid hemorrhage. It compares surgeries, model characteristics, advantages, and drawbacks of the most-frequently used rodent models-the endovascular perforation model and the prechiasmatic and single or double cisterna magna injection model. The topics of discussing anesthesia, advice on peri- and postanesthetic handling of animals, assessing the severity of suffering the animals undergo during the procedure according to EU directive 2010/63/EU and weighing the use of these in vivo models for experimental research ethically are also presented. In conclusion, rodent models of subarachnoid hemorrhage display pathophysiological characteristics, including changes of cerebral perfusion similar to the clinical situation, rendering the models suited to study the sequelae of the bleeding. A current problem is low standardization of the models, wherefore reporting according to the ARRIVE guidelines is highly recommended. Animal welfare aspects of rodent models of subarachnoid hemorrhage. Rodent models for investigation of cerebral perfusion after subarachnoid hemorrhage are compared regarding surgeries and model characteristics, and 3R measures are suggested. Anesthesia is discussed, and advice given on peri- and postanesthetic handling. Severity of suffering according to 2010/63/EU is assessed and use of these in vivo models weighed ethically.

Effect of isolated intracranial hypertension on cerebral perfusion within the phase of primary disturbances after subarachnoid hemorrhage in rats

Introduction

Elevated intracranial pressure (ICP) and blood components are the main trigger factors starting the complex pathophysiological cascade following subarachnoid hemorrhage (SAH). It is not clear whether they independently contribute to tissue damage or whether their impact cannot be differentiated from each other. We here aimed to establish a rat intracranial hypertension model that allows distinguishing the effects of these two factors and investigating the relationship between elevated ICP and hypoperfusion very early after SAH.

Methods

Blood or four different types of fluids [gelofusine, silicone oil, artificial cerebrospinal fluid (aCSF), aCSF plus xanthan (CX)] were injected into the cisterna magna in anesthetized rats, respectively. Arterial blood pressure, ICP and cerebral blood flow (CBF) were continuously measured up to 6 h after injection. Enzyme-linked immunosorbent assays were performed to measure the pro-inflammatory cytokines interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α) in brain cortex and peripheral blood.

Results

Silicone oil injection caused deaths of almost all animals. Compared to blood, gelofusine resulted in lower peak ICP and lower plateau phase. Artificial CSF reached a comparable ICP peak value but failed to reach the ICP plateau of blood injection. Injection of CX with comparable viscosity as blood reproduced the ICP course of the blood injection group. Compared with the CBF course after blood injection, CX induced a comparable early global ischemia within the first minutes which was followed by a prompt return to baseline level with no further hypoperfusion despite an equal ICP course. The inflammatory response within the tissue did not differ between blood or blood-substitute injection. The systemic inflammation was significantly more pronounced in the CX injection group compared with the other fluids including blood.

Discussion

By cisterna magna injection of blood substitution fluids, we established a subarachnoid space occupying rat model that exactly mimicked the course of ICP in the first 6 h following blood injection. Fluids lacking blood components did not induce the typical prolonged hypoperfusion occurring after blood-injection in this very early phase. Our study strongly suggests that blood components rather than elevated ICP play an important role for early hypoperfusion events in SAH.

The Critical Role of Sirt1 in Subarachnoid Hemorrhages: Mechanism and Therapeutic Considerations

The subarachnoid hemorrhage (SAH) is an important cause of death and long-term disability worldwide. As a nicotinamide adenine dinucleotide-dependent deacetylase, silent information regulator 1 (Sirt1) is a multipotent molecule involved in many pathophysiological processes. A growing number of studies have demonstrated that Sirt1 activation may exert positive effects on SAHs by regulating inflammation, oxidative stress, apoptosis, autophagy, and ferroptosis. Thus, Sirt1 agonists may serve as potential therapeutic drugs for SAHs. In this review, we summarized the current state of our knowledge on the relationship between Sirt1 and SAHs and provided an updated overview of the downstream molecules of Sirt1 in SAHs.

Application of Quantitative Computed Tomographic Perfusion in the Prognostic Assessment of Patients with Aneurysmal Subarachnoid Hemorrhage Coexistent Intracranial Atherosclerotic Stenosis

The comorbidity of aneurysmal subarachnoid hemorrhage (aSAH) with intracranial atherosclerotic stenosis (ICAS) has been suggested to increase the risk of postoperative ischemic stroke. Logistic regression models were established to explore the association between computed tomography perfusion (CTP) parameters and 3-month neurological outcomes and delayed cerebral ischemia (DCI). Prognostic-related perfusion parameters were added to the existing prognostic prediction models to evaluate model performance improvement. Tmax > 4.0 s volume > 0 mL was significantly associated with 3-month unfavorable neurological outcomes after adjusting for potential confounders (OR 3.90, 95% CI 1.11–13.73), whereas the stenosis degree of ICAS was not. Although the cross-validated area under the curve (AUC) was similar after the addition of the Tmax > 4.0 s volume > 0 mL (SAHIT: p = 0.591; TAPS: p = 0.379), the continuous net reclassification index (cNRI) and integrated discrimination index (IDI) showed that the perfusion parameters significantly improved the performance of the two models (p < 0.001 for all comparisons). Patients with coexistent aSAH and ICAS, Tmax > 4.0 s volume > 0 mL is an independent factor of 3-month neurological outcomes. A quantitative assessment of cerebral perfusion may help accurately screen patients with poor outcomes due to the coexistence of aSAH and ICAS.

A novel method for repeated cerebrospinal fluid sampling and long-term monitoring of intracranial pressure in rats

Cannulation implantation into the cisterna magna is an important procedure in cerebrospinal fluid (CSF) sampling and intracranial pressure (ICP) monitoring. The disadvantages of existing techniques include the risk of brain damage, compromised muscle mobility, and the complexity of the procedures. In the present study, the authors describe a modified, simple, and reliable procedure for long-term cannulation implantation into the cisterna magna in rats. The device consists of four parts: the puncture segment, the connection segment, the fixing segment, and the external segment. Intraoperative ICP monitoring and post-operative computed tomography (CT) scans were performed, which confirmed the accuracy and safety of this method. There were no limitations on the daily activities of the rats when long-term drainage was carried out for 1 week. This new technique offers an improved method of cannulation and will be a potentially useful method for CSF sampling and ICP monitoring in neuroscience research.

Opening a window to the acutely injured brain: Simultaneous retinal and cerebral vascular monitoring in rats

Many recent research projects have described typical chronic changes in the retinal vasculature for diverse neurovascular and neurodegenerative disorders such as stroke or Alzheimer's disease. Unlike cerebral vasculature, retinal blood vessels can be assessed non-invasively by retinal vessel analysis. To date, there is only a little information about potential simultaneous reactions of retinal and cerebral vessels in acute neurovascular diseases. The field of applications of retinal assessment could significantly be widened if more information about potential correlations between those two vascular beds and the feasibility of non-invasive retinal vessel analysis in acute neurovascular disease were available. Here, we present our protocol for the simultaneous assessment of retinal and cerebral vessels in an acute setting in anesthetized rats using a non-invasive retinal vessel analyzer and a superficial tissue imaging system for laser speckle contrast analysis via a closed bone window. We describe the experimental set-up in detail, outline the pitfalls of repeated retinal vessel analyses in an experimental set-up of several hours, and address issues that arise from the simultaneous use of two different assessment tools. Finally, we demonstrate the robustness and variability of the reactivity of retinal vessels to hypercapnia at baseline as well as their reproducibility over time using two anesthetic protocols common for neurovascular research. In summary, the procedures described in this protocol allow us to directly compare retinal and cerebral vascular beds and help to substantiate the role of the retina as a "window to the brain."

The mechanism and relevant mediators associated with neuronal apoptosis and potential therapeutic targets in subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is a dominant cause of death and disability worldwide. A sharp increase in intracranial pressure after SAH leads to a reduction in cerebral perfusion and insufficient blood supply for neurons, which subsequently promotes a series of pathophysiological responses leading to neuronal death. Many previous experimental studies have reported that excitotoxicity, mitochondrial death pathways, the release of free radicals, protein misfolding, apoptosis, necrosis, autophagy, and inflammation are involved solely or in combination in this disorder. Among them, irreversible neuronal apoptosis plays a key role in both short- and long-term prognoses after SAH. Neuronal apoptosis occurs through multiple pathways including extrinsic, mitochondrial, endoplasmic reticulum, p53 and oxidative stress. Meanwhile, a large number of blood contents enter the subarachnoid space after SAH, and the secondary metabolites, including oxygenated hemoglobin and heme, further aggravate the destruction of the blood-brain barrier and vasogenic and cytotoxic brain edema, causing early brain injury and delayed cerebral ischemia, and ultimately increasing neuronal apoptosis. Even there is no clear and effective therapeutic strategy for SAH thus far, but by understanding apoptosis, we might excavate new ideas and approaches, as targeting the upstream and downstream molecules of apoptosis-related pathways shows promise in the treatment of SAH. In this review, we summarize the existing evidence on molecules and related drugs or molecules involved in the apoptotic pathway after SAH, which provides a possible target or new strategy for the treatment of SAH.

New Insights of Early Brain Injury after Subarachnoid Hemorrhage: A Focus on the Caspase Family

Spontaneous subarachnoid hemorrhage (SAH), primarily caused by ruptured intracranial aneurysms, remains a prominent clinical challenge with a high rate of mortality and morbidity worldwide. Accumulating clinical trials aiming at the prevention of cerebral vasospasm (CVS) have failed to improve the clinical outcome of patients with SAH. Therefore, a growing number of studies have shifted focus to the pathophysiological changes that occur during the periods of early brain injury (EBI). New pharmacological agents aiming to alleviate EBI have become a promising direction to improve outcomes after SAH. Caspases belong to a family of cysteine proteases with diverse functions involved in maintaining metabolism, autophagy, tissue differentiation, regeneration, and neural development. Increasing evidence shows that caspases play a critical role in brain pathology after SAH. Therefore, caspase regulation could be a potential target for SAH treatment. Herein, we provide an overview pertaining to the current knowledge on the role of caspases in EBI after SAH, and we discuss the promising therapeutic value of caspase-related agents after SAH.

New Mechanisms and Targets of Subarachnoid Hemorrhage: A Focus on Mitochondria

Spontaneous subarachnoid hemorrhage (SAH) accounts for 5-10% of all strokes and is a subtype of hemorrhagic stroke that places a heavy burden on health care. Despite great progress in surgical clipping and endovascular treatment for ruptured aneurysms, cerebral vasospasm (CVS) and delayed cerebral ischemia (DCI) threaten the long-term outcomes of patients with SAH. Moreover, there are limited drugs available to reduce the risk of DCI and adverse outcomes in SAH patients. New insight suggests that early brain injury (EBI), which occurs within 72 h after the onset of SAH, may lay the foundation for further DCI development and poor outcomes. The mechanisms of EBI mainly include excitotoxicity, oxidative stress, neuroinflammation, blood-brain barrier (BBB) destruction, and cellular death. Mitochondria are a double-membrane organelle, and they play an important role in energy production, cell growth, differentiation, apoptosis, and survival. Mitochondrial dysfunction, which can lead to mitochondrial membrane potential (Δψm) collapse, overproduction of reactive oxygen species (ROS), release of apoptogenic proteins, disorders of mitochondrial dynamics, and activation of mitochondria-related inflammation, is considered a novel mechanism of EBI related to DCI as well as post-SAH outcomes. In addition, mitophagy is activated after SAH. In this review, we discuss the latest perspectives on the role of mitochondria in EBI and DCI after SAH. We emphasize the potential of mitochondria as therapeutic targets and summarize the promising therapeutic strategies targeting mitochondria for SAH.

Dynamic Measurements of Cerebral Blood Flow Responses to Cortical Spreading Depolarization in the Murine Endovascular Perforation Subarachnoid Hemorrhage Model

Delayed cerebral ischemia (DCI) is the most severe complication after subarachnoid hemorrhage (SAH), and cortical spreading depolarization (CSD) is believed to play a vital role in it. However, the dynamic changes in cerebral blood flow (CBF) in response to CSD in typical SAH models have not been well investigated. Here, SAH was established in mice with endovascular perforation. Subsequently, the spontaneous CBF dropped instantly and then returned to baseline rapidly. After KCl application to the cortex, subsequent hypoperfusion waves occurred across the groups, while a lower average perfusion level was found in the SAH groups (days 1-7). Moreover, in the SAH groups, the number of CSD decreased within day 7, and the duration and spreading velocity of the CSD increased within day 3 and day 14, respectively. Next, we continuously monitored the local field potential (LFP) in the prefrontal cortex. The results showed that the decrease in the percentage of gamma oscillations lasted throughout the whole process in the SAH group. In the chronic phase after SAH, we found that the mice still had cognitive deficits but experienced no obvious tissue damage. In summary, SAH negatively affects the CBF responses to CSD and the spontaneous LFP activity and causes long-term cognitive deficits in mice. Based on these findings, in the specific phase after SAH, DCI is induced or exacerbated more easily by potential causers of CSD in clinical practice (edema, erythrocytolysis, inflammation), which may lead to neurological deterioration.

Depolarization time and extracellular glutamate levels aggravate ultraearly brain injury after subarachnoid hemorrhage

Early brain injury after aneurysmal subarachnoid hemorrhage (SAH) worsens the neurological outcome. We hypothesize that a longer duration of depolarization and excessive release of glutamate aggravate neurological outcomes after SAH, and that brain hypothermia can accelerate repolarization and inhibit the excessive release of extracellular glutamate and subsequent neuronal damage. So, we investigated the influence of depolarization time and extracellular glutamate levels on the neurological outcome in the ultra-early phase of SAH using a rat injection model as Experiment 1 and then evaluated the efficacy of brain hypothermia targeting ultra-early brain injury as Experiment 2. Dynamic changes in membrane potentials, intracranial pressure, cerebral perfusion pressure, cerebral blood flow, and extracellular glutamate levels were observed within 30 min after SAH. A prolonged duration of depolarization correlated with peak extracellular glutamate levels, and these two factors worsened the neuronal injury. Under brain hypothermia using pharyngeal cooling after SAH, cerebral perfusion pressure in the hypothermia group recovered earlier than that in the normothermia group. Extracellular glutamate levels in the hypothermia group were significantly lower than those in the normothermia group. The early induction of brain hypothermia could facilitate faster recovery of cerebral perfusion pressure, repolarization, and the inhibition of excessive glutamate release, which would prevent ultra-early brain injury following SAH.

A Narrative Review on Translational Research in Acute Brain Injury

There has been a constant endeavor to reduce the mortality and morbidity associated with acute brain injury. The associated complex mechanisms involving biomechanics, markers, and neuroprotective drugs/measures have been extensively studied in preclinical studies with an ultimate aim to improve the patients' outcomes. Despite such efforts, only few have been successfully translated into clinical practice. In this review, we shall be discussing the major hurdles in the translation of preclinical results into clinical practice. The need is to choose an appropriate animal model, keeping in mind the species, age, and gender of the animal, choosing suitable outcome measures, ensuring quality of animal trials, and carrying out systematic review and meta-analysis of experimental studies before proceeding to human trials. The interdisciplinary collaboration between the preclinical and clinical scientists will help to design better, meaningful trials which might help a long way in successful translation. Although challenging at this stage, the advent of translational precision medicine will help the integration of mechanism-centric translational medicine and patient-centric precision medicine.

The blood-brain barrier and the neurovascular unit in subarachnoid hemorrhage: molecular events and potential treatments

The response of the blood-brain barrier (BBB) following a stroke, including subarachnoid hemorrhage (SAH), has been studied extensively. The main components of this reaction are endothelial cells, pericytes, and astrocytes that affect microglia, neurons, and vascular smooth muscle cells. SAH induces alterations in individual BBB cells, leading to brain homeostasis disruption. Recent experiments have uncovered many pathophysiological cascades affecting the BBB following SAH. Targeting some of these pathways is important for restoring brain function following SAH. BBB injury occurs immediately after SAH and has long-lasting consequences, but most changes in the pathophysiological cascades occur in the first few days following SAH. These changes determine the development of early brain injury as well as delayed cerebral ischemia. SAH-induced neuroprotection also plays an important role and weakens the negative impact of SAH. Supporting some of these beneficial cascades while attenuating the major pathophysiological pathways might be decisive in inhibiting the negative impact of bleeding in the subarachnoid space. In this review, we attempt a comprehensive overview of the current knowledge on the molecular and cellular changes in the BBB following SAH and their possible modulation by various drugs and substances.

Impact of Cerebral Autoregulation Monitoring in Cerebrovascular Disease: A Systematic Review

Cerebral autoregulation (CA) prevents brain injury by maintaining a relatively constant cerebral blood flow despite fluctuations in cerebral perfusion pressure. This process is disrupted consequent to various neurologic pathologic processes, which may result in worsening neurologic outcomes. Herein, we aim to highlight evidence describing CA changes and the impact of CA monitoring in patients with cerebrovascular disease, including ischemic stroke, intracerebral hemorrhage (ICH), and aneurysmal subarachnoid hemorrhage (aSAH). The study was preformed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines. English language publications were identified through a systematic literature conducted in Ovid Medline, PubMed, and Embase databases. The search spanned the dates of each database's inception through January 2021. We selected case-control studies, cohort observational studies, and randomized clinical trials for adult patients (≥ 18 years) who were monitored with continuous metrics using transcranial Doppler, near-infrared spectroscopy, and intracranial pressure monitors. Of 2799 records screened, 48 studies met the inclusion criteria. There were 23 studies on ischemic stroke, 18 studies on aSAH, 5 studies on ICH, and 2 studies on systemic hypertension. CA impairment was reported after ischemic stroke but generally improved after tissue plasminogen activator administration and successful mechanical thrombectomy. Persistent impairment in CA was associated with hemorrhagic transformation, malignant cerebral edema, and need for hemicraniectomy. Studies that investigated large ICHs described bilateral CA impairment up to 12 days from the ictus, especially in the presence of small vessel disease. In aSAH, impairment of CA was associated with angiographic vasospasm, delayed cerebral ischemia, and poor functional outcomes at 6 months. This systematic review highlights the available evidence for CA disruption during cerebrovascular diseases and its possible association with long-term neurological outcome. CA may be disrupted even before acute stroke in patients with untreated chronic hypertension. Monitoring CA may help in establishing individualized management targets in patients with cerebrovascular disease.

Individualized cerebral perfusion pressure in acute neurological injury: are we ready for clinical use?

PURPOSE OF REVIEW

Individualizing cerebral perfusion pressure based on cerebrovascular autoregulation assessment is a promising concept for neurological injuries where autoregulation is typically impaired. The purpose of this review is to describe the status quo of autoregulation-guided protocols and discuss steps towards clinical use.

RECENT FINDINGS

Retrospective studies have indicated an association of impaired autoregulation and poor clinical outcome in traumatic brain injury (TBI), hypoxic-ischemic brain injury (HIBI) and aneurysmal subarachnoid hemorrhage (aSAH). The feasibility and safety to target a cerebral perfusion pressure optimal for cerebral autoregulation (CPPopt) after TBI was recently assessed by the COGITATE trial. Similarly, the feasibility to calculate a MAP target (MAPopt) based on near-infrared spectroscopy was demonstrated for HIBI. Failure to meet CPPopt is associated with the occurrence of delayed cerebral ischemia in aSAH but interventional trials in this population are lacking. No level I evidence is available on potential effects of autoregulation-guided protocols on clinical outcomes.

SUMMARY

The effect of autoregulation-guided management on patient outcomes must still be demonstrated in prospective, randomized, controlled trials. Selection of disease-specific protocols and endpoints may serve to evaluate the overall benefit from such approaches.

Subarachnoid Hemorrhage Induces Sub-acute and Early Chronic Impairment in Learning and Memory in Mice

Subarachnoid hemorrhage (SAH) leads to significant long-term cognitive deficits, so-called the post-SAH syndrome. Existing neurological scales used to assess outcomes of SAH are focused on sensory-motor functions. To better evaluate short-term and chronic consequences of SAH, we explored and validated a battery of neurobehavioral tests to gauge the functional outcomes in mice after the circle of Willis perforation-induced SAH. The 18-point Garcia scale, applied up to 4 days, detected impairment only at 24-h time point and showed no significant difference between the Sham and SAH group. A decrease in locomotion was detected at 4-days post-surgery in the open field test but recovered at 30 days in Sham and SAH groups. However, an anxiety-like behavior undetected at 4 days developed at 30 days in SAH mice. At 4-days post-surgery, Y-maze revealed an impairment in working spatial memory in SAH mice, and dyadic social interactions showed a decrease in the sociability in SAH mice, which spent less time interacting with the stimulus mouse. At 30 days after ictus, SAH mice displayed mild spatial learning and memory deficits in the Barnes maze as they committed significantly more errors and used more time to find the escape box but still were able to learn the task. We also observed cognitive dysfunction in the SAH mice in the novel object recognition test. Taken together, these data suggest dysfunction of the limbic system and hippocampus in particular. We suggest a battery of 5 basic behavioral tests allowing to detect neurocognitive deficits in a sub-acute and chronic phase following the SAH.

Apelin-13 attenuates early brain injury through inhibiting inflammation and apoptosis in rats after experimental subarachnoid hemorrhage

BACKGROUND

Early brain injury (EBI) has been considered as the major contributor to the neurological dysfunction and poor clinical outcomes of subarachnoid hemorrhage (SAH). Studies showed that apelin-13 exhibits a neuroprotective effect in brain damage induced by cerebral ischemia. However, it remains unclear whether apelin-13 could exhibit the protective functions following SAH. The present study aimed to validate the neuroprotective role of apelin-13 in SAH, and further investigated the underlying mechanisms.

METHODS AND RESULTS

We constructed SAH rat model and we found that apelin-13 significantly alleviated neurological disorder and brain edema, improved memory deficits in SAH rats. Apelin-13 treatment decreased contents of TNF-α and IL-1β in cerebral spinal fluid of SAH rat by using ELISA. Apelin-13 treatment promoted the expression of APJ and Bcl-2, and decreased the level of active caspase-3 and Bax in the temporal cortex after SAH by using western blot. Also, apelin-13 attenuated the cortical cell death and neuronal degeneration as shown by TUNEL, FJB and Nissl staining. However, ML221, an inhibitor of APJ, significantly reversed all the above neuroprotective effects of apelin-13. Moreover, a neuron-microglia co-culture system, which mimic SAH in vitro, confirmed the protective effect of apelin-13 on neurons and the inhibitory effect on inflammation through apoptosis-related proteins.

CONCLUSIONS

These data demonstrated that apelin-13 exhibit a neuroprotective role after SAH through inhibition of apoptosis in an APJ dependent manner.

Burrowing behaviour of rats: Strain differences and applicability as well-being parameter after intracranial surgery

In mice, burrowing is considered a species-typical parameter for assessing well-being, while this is less clear in rats. This exploratory study evaluated burrowing behaviour in three rat strains during training and in the direct postoperative phase after complex intracranial surgery in different neuroscience rat models established at Hannover Medical School or Aachen University Hospital. Male Crl:CD (SD; n = 18), BDIX/UlmHanZtm (BDIX; n = 8) and RjHan:WI (Wistar; n = 35) rats were individually trained to burrow gravel out of a tube on four consecutive days. Thereafter, BDIX rats were subjected to intracranial injection of BT4Ca cells and tumour resection (rat glioma model), SD rats to injection of 6-hydroxydopamine (6-OHDA) or vehicle (rat Parkinson's disease model) and Wistar rats to endovascular perforation or sham surgery (rat subarachnoid haemorrhage (SAH) model). Burrowing was retested on the day after surgery. During training, BDIX rats burrowed large amounts (mean of 2370 g on the fourth day), while SD and Wistar rats burrowed less gravel (means of 846 and 520 g, respectively). Burrowing increased significantly during training only in Wistar rats. Complex surgery, that is, tumour resection (BDIX), 6-OHDA injection (SD) and endovascular perforation or sham surgery for SAH (Wistar) significantly reduced burrowing and body weight, while simple stereotactic injection of tumour cells or vehicle did not affect burrowing. Despite the training, burrowing differed between the strains. In the direct postoperative phase, burrowing was reduced after complex surgery, indicating reduced well-being. Reduced burrowing was accompanied with postoperative weight loss, a validated and recognised quantitative measure for severity assessment.

Vascular Reactivity to Hypercapnia Is Impaired in the Cerebral and Retinal Vasculature in the Acute Phase After Experimental Subarachnoid Hemorrhage

Objective: Impaired cerebral blood flow (CBF) regulation, such as reduced reactivity to hypercapnia, contributes to the pathophysiology after aneurysmal subarachnoid hemorrhage (SAH), but temporal dynamics in the acute phase are unknown. Featuring comparable molecular regulation mechanisms, the retinal vessels participate in chronic and subacute stroke- and SAH-associated vessel alterations in patients and can be studied non-invasively. This study is aimed to characterize the temporal course of the cerebral and retinal vascular reactivity to hypercapnia in the acute phase after experimental SAH and compare the potential degree of impairment.

Methods: Subarachnoid hemorrhage was induced by injecting 0.5 ml of heparinized autologous blood into the cisterna magna of male Wistar rats using two anesthesia protocols [isoflurane/fentanyl n = 25 (Sham + SAH): Iso—Group, ketamine/xylazine n = 32 (Sham + SAH): K/X—Group]. CBF (laser speckle contrast analysis) and physiological parameters were measured continuously for 6 h. At six predefined time points, hypercapnia was induced by hypoventilation controlled via blood gas analysis, and retinal vessel diameter (RVD) was determined non-invasively.

Results: Cerebral reactivity and retinal reactivity in Sham groups were stable with only a slight attenuation after 2 h in RVD of the K/X—Group. In the SAH Iso—Group, cerebral and retinal CO2 reactivity compared to baseline was immediately impaired starting at 30 min after SAH (CBF p = 0.0090, RVD p = 0.0135) and lasting up to 4 h (p = 0.0136, resp. p = 0.0263). Similarly, in the K/X—Group, cerebral CO2 reactivity was disturbed early after SAH (30 min, p = 0.003) albeit showing a recovery to baseline after 2 h while retinal CO2 reactivity was impaired over the whole observation period (360 min, p = 0.0001) in the K/X—Group. After normalization to baseline, both vascular beds showed a parallel behavior regarding the temporal course and extent of impairment.

Conclusion: This study provides a detailed temporal analysis of impaired cerebral vascular CO2 reactivity starting immediately after SAH and lasting up to 6 h. Importantly, the retinal vessels participate in these acute changes underscoring the promising role of the retina as a potential non-invasive screening tool after SAH. Further studies will be required to determine the correlation with functional outcomes.

COG133 Attenuates the Early Brain Injury Induced by Blood-Brain Barrier Disruption in Experimental Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is a kind of severe hemorrhagic stroke, and early brain injury acted as one of the main causes of death and delayed neurological deficit in patients with subarachnoid hemorrhage. In this process, the function and structural integrity of the blood-brain barrier play an important role. In this study, we have observed whether the apolipoprotein E (apoE) mimetic peptide, COG133, can alleviate early brain injury after subarachnoid hemorrhage. For this purpose, an experimental subarachnoid hemorrhage model was constructed in mice and treated by intravenous injection of COG133 at a dosage of 1 mg/kg. Then, the function and integrity of the blood-brain barrier were detected, and the pyroptosis level of the neuron was determined. The results showed that COG133 could protect blood-brain barrier function and structure integrity, reduce early brain injury, and ameliorate neurological function after subarachnoid hemorrhage. In terms of molecular mechanism, COG133 inhibits blood-brain barrier destruction through the proinflammatory CypA-NF-κB-MMP9 pathway and reduces neuronal pyroptosis by inhibiting NLRP3 inflammasome activation. In conclusion, this study demonstrated that apoE-mimetic peptide, COG133, can play a neuroprotective role by protecting blood-brain barrier function and inhibiting brain cell pyroptosis to reduce early brain injury after subarachnoid hemorrhage.

Sirtuin 5-Mediated Lysine Desuccinylation Protects Mitochondrial Metabolism Following Subarachnoid Hemorrhage in Mice

BACKGROUND AND PURPOSE

Sirt5 (Sirtuin 5) desuccinylates multiple metabolic enzymes and plays an important role in maintaining energy homeostasis. The goal of this study was to determine whether Sirt5-mediated desuccinylation restores the energy metabolism and protects brain against subarachnoid hemorrhage (SAH).

METHODS

Male C57BL/6 or Sirt5^-/- mice were used. The endovascular perforation SAH model was applied. Protein lysine succinylation in the brain cortex was examined using liquid chromatography-tandem mass spectrometry analysis. The brain metabolism was evaluated by measurement of brain pH as well as ATP and reactive oxygen species level. Neuronal cell death and neurobehavioral deficits were assessed 24 hours after SAH. The expression and desuccinylation activity of Sirt5, lysine succinylation of citrate synthase and ATP synthase subunits were investigated by Western blot, immunohistochemistry, and ELISA in SAH mice and patients. Furthermore, the benefits of resveratrol-mediated Sirt5 activation were investigated.

RESULTS

A total of 211 lysine succinylation sites were differentially expressed on 170 proteins in mice brain after SAH. Thirty-nine percent of these succinylated proteins were localized in mitochondria and they are related to energy metabolism. SAH caused a decrease of Sirt5 expression and succinylated citrate synthase as well as the subunits of ATP synthase, subsequently lowered brain pH, reduced ATP and increased reactive oxygen species production, leading to neuronal cell death, and neurological deficits. Knockdown of Sirt5 aggravated SAH-induced effects, mentioned above. Administration of resveratrol resulted in activation of Sirt5. The activation was accompanied both with restoration of the mitochondrial metabolism and alleviation of early brain injury as well as with desuccinylating citrate synthase and ATP synthase.

CONCLUSIONS

Protein lysine succinylation is a biochemical hallmark of metabolic crisis after SAH, and disruption of lysine succinylation through activation of Sirt5 might be a promising therapeutic strategy for the treatment of SAH.

Baseline characteristics and outcome for aneurysmal versus non-aneurysmal subarachnoid hemorrhage: a prospective cohort study

This study aims to investigate the characteristics of patients with mild aneurysmal and non-aneurysmal perimesencephalic and non-perimesencephalic subarachnoid hemorrhage (aSAH, pmSAH, npmSAH) with emphasis on admission biomarkers, clinical course, and outcome. A prospective cohort of 115 patients with aSAH (Hunt and Hess 1–3) and of 35 patients without aneurysms (16 pmSAH and 19 npmSAH) admitted between January 2014 and January 2020 was included. Demographic data, blood samples on admission, complications (hydrocephalus, shunt dependency, delayed cerebral ischemia DCI, DCI-related infarction, and mortality), and outcome after 6 months were analyzed. Demographic data was comparable between all groups except for age (aSAH 55 [48–65] vs. npmSAH 60 [56–68] vs. pmSAH 52 [42–60], p = 0.032) and loss of consciousness (33% vs. 0% vs. 0%, p = 0.0004). Admission biomarkers showed poorer renal function and highest glucose levels for npmSAH patients. Complication rate in npmSAH was high and comparable to that of aSAH patients (hydrocephalus, shunt dependency, DCI, DCI-related infarction, mortality), but nearly absent in patients with pmSAH. Favorable outcome after 6 months was seen in 92.9% of pmSAH, 83.3% of npmSAH, and 62.7% of aSAH (p = 0.0264). In this prospective cohort of SAH patients, npmSAH was associated with a complicated clinical course, comparable to that of patients with aSAH. In contrast, such complications were nearly absent in pmSAH patients, suggesting fundamental differences in the pathophysiology of patients with different types of non-aneurysmal hemorrhage. Our findings underline the importance for a precise terminology according the hemorrhage etiology as a basis for more vigilant management of npmSAH patients. NCT02142166, 05/20/2014, retrospectively registered.

Cerebral Autoregulation in Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is a devastating stroke subtype with a high rate of mortality and morbidity. The poor clinical outcome can be attributed to the biphasic course of the disease: even if the patient survives the initial bleeding emergency, delayed cerebral ischemia (DCI) frequently follows within 2 weeks time and levies additional serious brain injury. Current therapeutic interventions do not specifically target the microvascular dysfunction underlying the ischemic event and as a consequence, provide only modest improvement in clinical outcome. SAH perturbs an extensive number of microvascular processes, including the “automated” control of cerebral perfusion, termed “cerebral autoregulation.” Recent evidence suggests that disrupted cerebral autoregulation is an important aspect of SAH-induced brain injury. This review presents the key clinical aspects of cerebral autoregulation and its disruption in SAH: it provides a mechanistic overview of cerebral autoregulation, describes current clinical methods for measuring autoregulation in SAH patients and reviews current and emerging therapeutic options for SAH patients. Recent advancements should fuel optimism that microvascular dysfunction and cerebral autoregulation can be rectified in SAH patients.

Monitoring and Prognostic Analysis of Severe Cerebrovascular Diseases Based on Multi-Scale Dynamic Brain Imaging

Severe cerebrovascular disease is an acute cerebrovascular event that causes severe neurological damage in patients, and is often accompanied by severe dysfunction of multiple systems such as breathing and circulation. Patients with severe cerebrovascular disease are in critical condition, have many complications, and are prone to deterioration of neurological function. Therefore, they need closer monitoring and treatment. The treatment strategy in the acute phase directly determines the prognosis of the patient. The case of this article selected 90 patients with severe cerebrovascular disease who were hospitalized in four wards of the Department of Neurology and the Department of Critical Care Medicine in a university hospital. The included cases were in accordance with the guidelines for the prevention and treatment of cerebrovascular diseases. Patients with cerebral infarction are given routine treatments such as improving cerebral circulation, protecting nutrient brain cells, dehydration, and anti-platelet; patients with cerebral hemorrhage are treated within the corresponding safe time window. We use Statistical Product and Service Solutions (SPSS) Statistics21 software to perform statistical analysis on the results. Based on the study of the feature extraction process of convolutional neural network, according to the hierarchical principle of convolutional neural network, a backbone neural network MF (Multi-Features)—Dense Net that can realize the fusion, and extraction of multi-scale features is designed. The network combines the characteristics of densely connected network and feature pyramid network structure, and combines strong feature extraction ability, high robustness and relatively small parameter amount. An end-to-end monitoring algorithm for severe cerebrovascular diseases based on MF-Dense Net is proposed. In the experiment, the algorithm showed high monitoring accuracy, and at the same time reached the speed of real-time monitoring on the experimental platform. An improved spatial pyramid pooling structure is designed to strengthen the network’s ability to merge and extract local features at the same level and at multiple scales, which can further improve the accuracy of algorithm monitoring by paying a small amount of additional computational cost. At the same time, a method is designed to strengthen the use of low-level features by improving the network structure, which improves the algorithm’s monitoring performance on small-scale severe cerebrovascular diseases. For patients with severe cerebrovascular disease in general, APACHEII1, APACHEII2, APACHEII3 and the trend of APACHEII score change are divided into high-risk group and low-risk group. The overall severe cerebrovascular disease, severe cerebral hemorrhage and severe cerebral infarction are analyzed, respectively. The differences are statistically significant.

Noninvasive real-time assessment of intracranial pressure after traumatic brain injury based on electromagnetic coupling phase sensing technology

Background

To investigate the feasibility of intracranial pressure (ICP) monitoring after traumatic brain injury (TBI) by electromagnetic coupling phase sensing, we established a portable electromagnetic coupling phase shift (ECPS) test system and conducted a comparison with invasive ICP.

Methods

TBI rabbits’ model were all synchronously monitored for 24 h by ECPS testing and invasive ICP. We investigated the abilities of the ECPS to detect targeted ICP by feature extraction and traditional classification decision algorithms.

Results

The ECPS showed an overall downward trend with a variation range of − 13.370 ± 2.245° as ICP rose from 11.450 ± 0.510 mmHg to 38.750 ± 4.064 mmHg, but its change rate gradually declined. It was greater than 1.5°/h during the first 6 h, then decreased to 0.5°/h and finally reached the minimum of 0.14°/h. Nonlinear regression analysis results illustrated that both the ECPS and its change rate decrease with increasing ICP post-TBI. When used as a recognition feature, the ability (area under the receiver operating characteristic curve, AUCs) of the ECPS to detect ICP ≥ 20 mmHg was 0.88 ± 0.01 based on the optimized adaptive boosting model, reaching the advanced level of current noninvasive ICP assessment methods.

Conclusions

The ECPS has the potential to be used for noninvasive continuous monitoring of elevated ICP post-TBI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-021-02049-3.

INT-777 attenuates NLRP3-ASC inflammasome-mediated neuroinflammation via TGR5/cAMP/PKA signaling pathway after subarachnoid hemorrhage in rats

BACKGROUND

Inflammasome-mediated neuroinflammation plays an important role in the pathogenesis of early brain injury (EBI) following subarachnoid hemorrhage (SAH). The activation of the TGR5 receptor has been shown to be neuroprotective in a variety of neurological diseases. This study aimed to investigate the effects of the specific synthetic TGR5 agonist, INT-777, in attenuating NLRP3-ASC inflammasome activation and reducing neuroinflammation after SAH.

METHODS

One hundred and eighty-four male Sprague Dawley rats were used. SAH was induced by the endovascular perforation. INT-777 was administered intranasally at 1 h after SAH induction. To elucidate the signaling pathway involved in the effect of INT-777 on inflammasome activation during EBI, TGR5 knockout CRISPR and PKA inhibitor H89 were administered intracerebroventricularly and intraperitoneally at 48 h and 1 h before SAH. The SAH grade, short- and long-term neurobehavioral assessments, brain water content, western blot, immunofluorescence staining, and Nissl staining were performed.

RESULTS

The expressions of endogenous TGR5, p-PKA, and NLRP3-ASC inflammasome were increased after SAH. INT-777 administration significantly decreased NLRP3-ASC inflammasome activation in microglia, reduced brain edema and neuroinflammation, leading to improved short-term neurobehavioral functions at 24 h after SAH. The administration of TGR5 CRISPR or PKA inhibitor (H89) abolished the anti-inflammation effects of INT-777, on NLRP3-ASC inflammasome, pro-inflammatory cytokines (IL-6, IL-1β, and TNF-a), and neutrophil infiltration at 24 h after SAH. Moreover, early administration of INT-777 attenuated neuronal degeneration in hippocampus on 28 d after SAH.

CONCLUSIONS

INT-777 attenuated NLRP3-ASC inflammasome-dependent neuroinflammation in the EBI after SAH, partially via TGR5/cAMP/PKA signaling pathway. Early administration of INT-777 may serve as a potential therapeutic strategy for EBI management in the setting of SAH.

Subarachnoid Hemorrhage Increases Level of Heme Oxygenase-1 and Biliverdin Reductase in the Choroid Plexus

Subarachnoid hemorrhage is a specific, life-threatening form of hemorrhagic stroke linked to high morbidity and mortality. It has been found that the choroid plexus of the brain ventricles forming the blood-cerebrospinal fluid barrier plays an important role in subarachnoid hemorrhage pathophysiology. Heme oxygenase-1 and biliverdin reductase are two of the key enzymes of the hemoglobin degradation cascade. Therefore, the aim of present study was to investigate changes in protein levels of heme oxygenase-1 and biliverdin reductase in the rat choroid plexus after experimental subarachnoid hemorrhage induced by injection of non-heparinized autologous blood to the cisterna magna. Artificial cerebrospinal fluid of the same volume as autologous blood was injected to mimic increased intracranial pressure in control rats. Immunohistochemical and Western blot analyses were used to monitor changes in the of heme oxygenase-1 and biliverdin reductase levels in the rat choroid plexus after induction of subarachnoid hemorrhage or artificial cerebrospinal fluid application for 1, 3, and 7 days. We found increased levels of heme oxygenase-1 and biliverdin reductase protein in the choroid plexus over the entire period following subarachnoid hemorrhage induction. The level of heme oxygenase-1 was the highest early (1 and 3 days) after subarachnoid hemorrhage indicating its importance in hemoglobin degradation. Increased levels of heme oxygenase-1 were also observed in the choroid plexus epithelial cells at all time points after application of artificial cerebrospinal fluid. Biliverdin reductase protein was detected mainly in the choroid plexus epithelial cells, with levels gradually increasing during subarachnoid hemorrhage. Our results suggest that heme oxygenase-1 and biliverdin reductase are involved not only in hemoglobin degradation but probably also in protecting choroid plexus epithelial cells and the blood-cerebrospinal fluid barrier from the negative effects of subarachnoid hemorrhage.

Acyl-CoA synthetase long chain family member 4 plays detrimental role in early brain injury after subarachnoid hemorrhage in rats by inducing ferroptosis

Aims

Acyl‐CoA synthetase long chain family member 4 (ACSL4) is closely related to tumor genesis and development in certain tissues. However, the function of ACSL4 in early brain injury (EBI) caused by subarachnoid hemorrhage (SAH) is unclear. In this study, we investigated the expression patterns and role of ACSL4 in SAH and post‐SAH EBI using a rat model of SAH.

Methods

The rat model of SAH was induced by autologous blood injection into the prechiasmatic cistern of rats. We also used two specific inhibitors of ferroptosis (Ferrostatin‐1 and Liproxstatin‐1) to investigate the role of ferroptosis in EBI.

Results

We found that ACSL4 levels in brain tissue increased significantly in post‐SAH EBI. Inhibiting the expression of ACSL4 using small interfering RNAs alleviated inflammation, blood‐brain barrier (BBB) impairment, oxidative stress, brain edema, and behavioral and cognitive deficits, and increased the number of surviving neurons, after SAH. Similar effects were obtained by suppressing ferroptosis.

Conclusions

ACSL4 exacerbated SAH‐induced EBI by mediating ferroptosis. These findings may provide a theoretical basis for potential therapy aimed at alleviating post‐SAH EBI.

The role of immune inflammation in aneurysmal subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is a devastating disease, which mainly caused by the rupture of an intracranial aneurysm. Clinical trials have demonstrated that cerebral vasospasm (CVS) is not the sole contributor to delayed cerebral ischemia (DCI) and poor outcomes in patients with aSAH. Currently, accumulating evidence suggests that early brain injury (EBI), which occurs within 72 h after the onset of aSAH, lays the foundation for subsequent pathophysiological changes and poor outcomes of patients. The pathological mechanisms of EBI mainly include increased intracranial pressure, oxidative stress, neuroinflammation, blood-brain barrier (BBB) disruption, cerebral edema and cell death. Among them, the brain immune inflammatory responses involve a variety of immune cells and active substances, which play an important role in EBI after aSAH and may be related to DCI and long-term outcomes. Thus, attention should be paid to strategies targeting cerebral immune inflammatory responses. In this review, we discuss the role of immune inflammatory responses in the occurrence and development of aSAH, as well as some inflammatory biomarkers related to CVS, DCI, and aSAH outcomes. In addition, we also summarize the potential therapeutic drugs that target cerebral immune inflammatory responses for patients with aSAH in current research.

Subarachnoid Hemorrhage Induces Dynamic Immune Cell Reactions in the Choroid Plexus

Subarachnoid hemorrhage (SAH) is a specific form of hemorrhagic stroke that frequently causes intracranial hypertension. The choroid plexus (CP) of the brain ventricles is responsible for producing cerebrospinal fluid and forms the blood - cerebrospinal fluid barrier. The aim of the current study was to determine whether SAH induces an immune cell reaction in the CP and whether the resulting increase in intracranial pressure (ICP) itself can lead to cellular changes in the CP. SAH was induced by injecting non-heparinized autologous blood to the cisterna magna. Artificial cerebrospinal fluid (ACSF) instead of blood was used to assess influence of increased ICP alone. SAH and ACSF animals were left to survive for 1, 3, and 7 days. SAH induced significantly increased numbers of M1 (ED1+, CCR7+) and M2 (ED2+, CD206+) macrophages as well as MHC-II+ antigen presenting cells (APC) compared to naïve and ACSF animals. Increased numbers of ED1+ macrophages and APC were found in the CP only 3 and 7 days after ACSF injection, while ED2+ macrophage number did not increase. CD3+ T cells were not found in any of the animals. Following SAH, proliferation activity in the CP gradually increased over time while ACSF application induced higher cellular proliferation only 1 and 3 days after injection. Our results show that SAH induces an immune reaction in the CP resulting in an increase in the number of several macrophage types in the epiplexus position. Moreover, we also found that increased ICP due to ACSF application induced both an immune reaction and increased proliferation of epiplexus cells in the CP. These findings indicate that increased ICP, and not just blood, contributes to cellular changes in the CP following SAH.

Mfsd2a Attenuates Blood-Brain Barrier Disruption After Sub-arachnoid Hemorrhage by Inhibiting Caveolae-Mediated Transcellular Transport in Rats

Blood-brain barrier (BBB) disruption is one of the critical mechanisms of brain injury induced by subarachnoid hemorrhage (SAH). Past studies have often focused on the tight junctions of endothelial cells. However, low transcellular transport levels also play an important role in the normal functioning of the BBB. Major facilitator superfamily domain-containing 2a (Mfsd2a) has been demonstrated to be essential for the maintenance of the normal BBB. Our present study aimed to explore the roles and mechanisms of Mfsd2a in BBB disruption after SAH. In this study, a prechiasmatic cistern single-injection model was used to produce experimental SAH in Sprague-Dawley rats. Specific small-interfering RNA and plasmids were used to downregulate and upregulate the expression of Mfsd2a prior to assessments in our SAH model. Omega-3 fatty acid deficiency diet was used to reduce DHA in rat brain. The expression level of Mfsd2a decreased significantly after SAH and reached its lowest level at 72 h post-SAH, which then gradually recovered. At 72 h after SAH, BBB function was disrupted; upregulation of Mfsd2a reversed this damage, whereas downregulation of Mfsd2a exacerbated this damage. These effects were primarily mediated through transcellular transport, especially for changes in caveolae compared to those of tight junctions. After stopping the supply of omega-3 fatty acids, the effect of Mfsd2a on inhibition of caveolae and protection of the blood-brain barrier was eliminated. Taken together, Mfsd2a inhibits caveolae-based transcellular transport by transporting omega-3 fatty acids to protect the BBB after SAH.

Activation of TGR5 with INT-777 attenuates oxidative stress and neuronal apoptosis via cAMP/PKCε/ALDH2 pathway after subarachnoid hemorrhage in rats

BACKGROUND

Oxidative stress and neuronal apoptosis play important roles in the pathogenesis of early brain injury (EBI) after subarachnoid hemorrhage (SAH). The activation of TGR5, a novel membrane-bound bile acid receptor, possesses anti-oxidative stress and anti-apoptotic effects in hepatobiliary disease and kidney disease. The present study aimed to explore the neuroprotective effect of TGR5 activation against EBI after SAH and the potential underlying mechanisms.

METHODS

The endovascular perforation model of SAH was performed on 199 Sprague Dawley rats to investigate the beneficial effects of TGR5 activation after SAH. INT-777, a specific synthetic TGR5 agonist, was administered intranasally at 1 h after SAH induction. TGR5 CRISPR and ALDH2 CRISPR were administered intracerebroventricularly at 48 h before SAH to illuminate potential mechanisms. The SAH grade, short-term and long-term neurobehavioral tests, TUNEL staining, Fluoro-Jade C staining, Nissl staining, immunofluorescence staining, and western blots were performed at 24 h after SAH.

RESULTS

The expressions of endogenous TGR5 and ALDH2 gradually increased and peaked at 24 h after SAH. TGR5 was expressed primarily in neurons, as well as in astrocytes and microglia. The activation of TGR5 with INT-777 significantly improved the short-term and long-term neurological deficits, accompanied by reduced the oxidative stress and neuronal apoptosis at 24 h after SAH. Moreover, INT-777 treatment significantly increased the expressions of TGR5, cAMP, phosphorylated PKCε, ALDH2, HO-1, and Bcl-2, while downregulated the expressions of 4-HNE, Bax, and Cleaved Caspase-3. TGR5 CRISPR and ALDH2 CRISPR abolished the neuroprotective effects of TGR5 activation after SAH.

CONCLUSIONS

In summary, the activation of TGR5 with INT-777 attenuated oxidative stress and neuronal apoptosis via the cAMP/PKCε/ALDH2 signaling pathway after SAH in rats. Furthermore, TGR5 may serve as a novel therapeutic target to ameliorate EBI after SAH.

The role and therapeutic potential of heat shock proteins in haemorrhagic stroke

Heat shock proteins (HSPs) are induced after haemorrhagic stroke, which includes subarachnoid haemorrhage (SAH) and intracerebral haemorrhage (ICH). Most of these proteins function as neuroprotective molecules to protect cerebral neurons from haemorrhagic stroke and as markers to indicate cellular stress or damage. The most widely studied HSPs in SAH are HSP70, haeme oxygenase-1 (HO-1), HSP20 and HSP27. The subsequent pathophysiological changes following SAH can be divided into two stages: early brain injury and delayed cerebral ischaemia, both of which determine the outcome for patients. Because the mechanisms of HSPs in SAH are being revealed and experimental models in animals are continually maturing, new agents targeting HSPs with limited side effects have been suggested to provide therapeutic potential. For instance, some pharmaceutical agents can block neuronal apoptosis signals or dilate cerebral vessels by modulating HSPs. HO-1 and HSP70 are also critical topics for ICH research, which can be attributed to their involvement in pathophysiological mechanisms and therapeutic potential. However, the process of HO-1 metabolism can be toxic owing to iron overload and the activation of succedent pathways, for example, the Fenton reaction and oxidative damage; the overall effect of HO-1 in SAH and ICH tends to be protective and harmful, respectively, given the different pathophysiological changes in these two types of haemorrhagic stroke. In the present study, we focus on the current understanding of the role and therapeutic potential of HSPs involved in haemorrhagic stroke. Therefore, HSPs may be potential therapeutic targets, and new agents targeting HSPs are warranted.

Neutrophils mediate early cerebral cortical hypoperfusion in a murine model of subarachnoid haemorrhage

Cerebral hypoperfusion in the first hours after subarachnoid haemorrhage (SAH) is a major determinant of poor neurological outcome. However, the underlying pathophysiology is only partly understood. Here we induced neutropenia in C57BL/6N mice by anti-Ly6G antibody injection, induced SAH by endovascular filament perforation, and analysed cerebral cortical perfusion with laser SPECKLE contrast imaging to investigate the role of neutrophils in mediating cerebral hypoperfusion during the first 24 h post-SAH. SAH induction significantly increased the intracranial pressure (ICP), and significantly reduced the cerebral perfusion pressure (CPP). At 3 h after SAH, ICP had returned to baseline and CPP was similar between SAH and sham mice. However, in SAH mice with normal neutrophil counts cortical hypoperfusion persisted. Conversely, despite similar CPP, cortical perfusion was significantly higher at 3 h after SAH in mice with neutropenia. The levels of 8-iso-prostaglandin-F2α in the subarachnoid haematoma increased significantly at 3 h after SAH in animals with normal neutrophil counts indicating oxidative stress, which was not the case in neutropenic SAH animals. These results suggest that neutrophils are important mediators of cortical hypoperfusion and oxidative stress early after SAH. Targeting neutrophil function and neutrophil-induced oxidative stress could be a promising new approach to mitigate cerebral hypoperfusion early after SAH.

Thromboelastography with Platelet Mapping Detects Platelet Dysfunction in Patients with Aneurysmal Subarachnoid Hemorrhage with Rebleeding

BACKGROUND

Aneurysmal subarachnoid hemorrhage (aSAH) has high rates of disability and mortality, and aneurysm rebleeding is associated with poor functional outcomes. Thrombelastography with platelet mapping (TEG-PM) measures platelet function; however, it has not yet been researched in aSAH. We aimed to use TEG-PM to detect changes in platelet function in patients with aSAH and the difference in patients with and without rebleeding.

METHODS

We retrospectively included patients with aSAH who underwent a TEG-PM test on admission. Rebleeding was diagnosed according to clinical and imaging data. TEG-PM data of patients with unruptured intracranial aneurysms (UIA) were also obtained as controls. Univariate and multivariate logistic regression models were performed to investigate the relationship between the platelet function and rebleeding.

RESULTS

A total of 245 aSAH patients and 32 UIA patients were included in our study. Compared with controls, patients with aSAH demonstrated higher arachidonic acid (AA) and adenosine diphosphate (ADP) inhibition of platelet function (P<0.05). Among them, 27 patients with Hunt-Hess grade IV or V were classified as the severe SAH group. There was a significant correlation between the severe SAH group and the degree of pathway inhibition (P<0.05). Furthermore, AA (Spearman's r=0.264, P<0.001) and ADP (Spearman's r=0.183, P=0.004) inhibition were elevated in Hunt-Hess grade-dependent manners. The AA (Spearman's r=0.169, P=0.008) and ADP (Spearman's r=0.233, P<0.001) inhibition were also significantly correlated with Fisher grade. Thirty-five patients (14.3%) suffered rebleeding. Rebleeding was significantly correlated with systolic blood pressure (P=0.011), diastolic blood pressure (P=0.008), Hunt-Hess grade (P=0.034), Fisher grade (P=0.015), AA inhibition (P<0.001), and ADP inhibition (P<0.001). Multivariate logistic regression analysis model revealed that both AA (P=0.037) and ADP inhibition (P=0.008) were independent determinants for rebleeding.

CONCLUSION

TEG-PM may assess platelet dysfunction in patients with aSAH, and the diminished platelet response to ADP and AA may be associated with rebleeding. These findings deserve further investigation.

Neuroprotection mediated by the Wnt/Frizzled signaling pathway in early brain injury induced by subarachnoid hemorrhage

The Wnt/Frizzled signaling pathway participates in many inflammation-linked diseases. However, the inflammatory response mediated by the Wnt/Frizzled signaling pathway in experimental subarachnoid hemorrhage has not been thoroughly investigated. Consequently, in this study, we examined the potential role of the Wnt/Frizzled signaling pathway in early brain injury in rat models of subarachnoid hemorrhage. Simultaneously, possible neuroprotective mechanisms were also investigated. Experimental subarachnoid hemorrhage rat models were induced by injecting autologous blood into the prechiasmatic cistern. Experiment 1 was designed to examine expression of the Wnt/Frizzled signaling pathway in early brain injury induced by subarachnoid hemorrhage. In total, 42 adult rats were divided into sham (injection of equivalent volume of saline), 6-, 12-, 24-, 48-, 72-hour, and 1-week subarachnoid hemorrhage groups. Experiment 2 was designed to examine neuroprotective mechanisms of the Wnt/Frizzled signaling pathway in early brain injury induced by subarachnoid hemorrhage. Rats were treated with recombinant human Wnt1 (rhwnt1), small interfering Wnt1 (siwnt1) RNA, and monoclonal antibody of Frizzled1 (anti-Frizzled1) at 48 hours after subarachnoid hemorrhage. Expression levels of Wnt1, Frizzled1, β-catenin, peroxisome proliferator-activated receptor-γ, CD36, and active nuclear factor-κB were examined by western blot assay and immunofluorescence staining. Microglia type conversion and inflammatory cytokine levels in brain tissue were examined by immunofluorescence staining and enzyme-linked immunosorbent assay. Our results show that compared with the sham group, expression levels of Wnt1, Frizzled1, and β-catenin were low and reduced to a minimum at 48 hours, gradually returning to baseline at 1 week after subarachnoid hemorrhage. rhwnt1 treatment markedly increased Wnt1 expression and alleviated subarachnoid hemorrhage-induced early brain injury (within 72 hours), including cortical cell apoptosis, brain edema, and neurobehavioral deficits, accompanied by increasing protein levels of β-catenin, CD36, and peroxisome proliferator-activated receptor-γ and decreasing protein levels of nuclear factor-κB. Of note, rhwnt1 promoted M2-type microglia conversion and inhibited release of inflammatory cytokines (interleukin-1β, interleukin-6, and tumor necrosis factor-α). In contrast, siwnt1 RNA and anti-Frizzled1 treatment both resulted in an opposite effect. In conclusion, the Wnt/Frizzled1 signaling pathway may participate in subarachnoid hemorrhage-induced early brain injury via inhibiting the inflammatory response, including regulating microglia type conversion and decreasing inflammatory cytokine release. The study was approved by the Animal Ethics Committee of Anhui Medical University and First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China (approval No. LLSC-20180202) in May 2017.