CSF neutrophils are implicated in the development of vasospasm in subarachnoid hemorrhage

The urotensin II receptor triggers an early meningeal response and a delayed macrophage-dependent vasospasm after subarachnoid hemorrhage in male mice

Subarachnoid hemorrhage (SAH) can be associated with neurological deficits and has profound consequences for mortality and morbidity. Cerebral vasospasm (CVS) and delayed cerebral ischemia affect neurological outcomes in SAH patients, but their mechanisms are not fully understood, and effective treatments are limited. Here, we report that urotensin II receptor UT plays a pivotal role in both early events and delayed mechanisms following SAH in male mice. Few days post-SAH, UT expression is triggered by blood or hemoglobin in the leptomeningeal compartment. UT contributes to perimeningeal glia limitans astrocyte reactivity, microvascular alterations and neuroinflammation independent of CNS-associated macrophages (CAMs). Later, CAM-dependent vascular inflammation and subsequent CVS develop, leading to cognitive dysfunction. In an SAH model using humanized UTh+/h+ male mice, we show that post-SAH CVS and behavioral deficits, mediated by UT through Gq/PLC/Ca2+ signaling, are prevented by UT antagonists. These results highlight the potential of targeting UT pathways to reduce early meningeal response and delayed cerebral ischemia in SAH patients.

Targeting NETosis in Acute Brain Injury: A Systematic Review of Preclinical and Clinical Evidence

Acute brain injury (ABI) remains one of the leading causes of death and disability world-wide. Its treatment is challenging due to the heterogeneity of the mechanisms involved and the variability among individuals. This systematic review aims at evaluating the impact of anti-histone treatments on outcomes in ABI patients and experimental animals and defining the trend of nucleosome levels in biological samples post injury. We performed a search in Pubmed/Medline and Embase databases for randomized controlled trials and cohort studies involving humans or experimental settings with various causes of ABI. We formulated the search using the PICO method, considering ABI patients or animal models as population (P), comparing pharmacological and non-pharmacological therapy targeting the nucleosome as Intervention (I) to standard of care or no treatment as Control (C). The outcome (O) was mortality or functional outcome in experimental animals and patients affected by ABI undergoing anti-NET treatments. We identified 28 studies from 1246 articles, of which 7 were experimental studies and 21 were human clinical studies. Among these studies, only four assessed the effect of anti-NET therapy on circulating markers. Three of them were preclinical and reported better outcome in the interventional arm compared to the control arm. All the studies observed a significant reduction in circulating NET-derived products. NETosis could be a target for new treatments. Monitoring NET markers in blood and cerebrospinal fluid might predict mortality and long-term outcomes. However, longitudinal studies and randomized controlled trials are warranted to fully evaluate their potential, as current evidence is limited.

Targeting brain-peripheral immune responses for secondary brain injury after ischemic and hemorrhagic stroke

The notion that the central nervous system is an immunologically immune-exempt organ has changed over the past two decades, with increasing evidence of strong links and interactions between the central nervous system and the peripheral immune system, both in the healthy state and after ischemic and hemorrhagic stroke. Although primary injury after stroke is certainly important, the limited therapeutic efficacy, poor neurological prognosis and high mortality have led researchers to realize that secondary injury and damage may also play important roles in influencing long-term neurological prognosis and mortality and that the neuroinflammatory process in secondary injury is one of the most important influences on disease progression. Here, we summarize the interactions of the central nervous system with the peripheral immune system after ischemic and hemorrhagic stroke, in particular, how the central nervous system activates and recruits peripheral immune components, and we review recent advances in corresponding therapeutic approaches and clinical studies, emphasizing the importance of the role of the peripheral immune system in ischemic and hemorrhagic stroke.

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.

Immunological Profile of Vasospasm after Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) carries high mortality and disability rates, which are substantially driven by complications. Early brain injury and vasospasm can happen after SAH and are crucial events to prevent and treat to improve prognosis. In recent decades, immunological mechanisms have been implicated in SAH complications, with both innate and adaptive immunity involved in mechanisms of damage after SAH. The purpose of this review is to summarize the immunological profile of vasospasm, highlighting the potential implementation of biomarkers for its prediction and management. Overall, the kinetics of central nervous system (CNS) immune invasion and soluble factors' production critically differs between patients developing vasospasm compared to those not experiencing this complication. In particular, in people developing vasospasm, a neutrophil increase develops in the first minutes to days and pairs with a mild depletion of CD45+ lymphocytes. Cytokine production is boosted early on after SAH, and a steep increase in interleukin-6, metalloproteinase-9 and vascular endothelial growth factor (VEGF) anticipates the development of vasospasm after SAH. We also highlight the role of microglia and the potential influence of genetic polymorphism in the development of vasospasm and SAH-related complications.

Systemic innate myeloid responses to acute ischaemic and haemorrhagic stroke

Acute ischaemic and haemorrhagic stroke account for significant disability and morbidity burdens worldwide. The myeloid arm of the peripheral innate immune system is critical in the immunological response to acute ischaemic and haemorrhagic stroke. Neutrophils, monocytes, and dendritic cells (DC) contribute to the evolution of pathogenic local and systemic inflammation, whilst maintaining a critical role in ongoing immunity protecting against secondary infections. This review aims to summarise the key alterations to myeloid immunity in acute ischaemic stroke, intracerebral haemorrhage (ICH), and subarachnoid haemorrhage (SAH). By integrating clinical and preclinical research, we discover how myeloid immunity is affected across multiple organ systems including the brain, blood, bone marrow, spleen, and lung, and evaluate how these perturbations associate with real-world outcomes including infection. These findings are placed in the context of the rapidly developing field of human immunology, which offers a wealth of opportunity for further research.

Compartmental Cerebrospinal Fluid Events Occurring after Subarachnoid Hemorrhage: An "Heparin Oriented" Systematic Review

Subarachnoid hemorrhage (SAH) represents a severe acute event with high morbidity and mortality due to the development of early brain injury (EBI), secondary delayed cerebral ischemia (DCI), and shunt-related hydrocephalus. Secondary events (SSE) such as neuroinflammation, vasospasm, excitotoxicity, blood-brain barrier disruption, oxidative cascade, and neuronal apoptosis are related to DCI. Despite improvement in management strategies and therapeutic protocols, surviving patients frequently present neurological deficits with neurocognitive impairment. The aim of this paper is to offer to clinicians a practical review of the actually documented pathophysiological events following subarachnoid hemorrhage. To reach our goal we performed a literature review analyzing reported studies regarding the mediators involved in the pathophysiological events following SAH occurring in the cerebrospinal fluid (CSF) (hemoglobin degradation products, platelets, complement, cytokines, chemokines, leucocytes, endothelin-1, NO-synthase, osteopontin, matricellular proteins, blood-brain barrier disruption, microglia polarization). The cascade of pathophysiological events secondary to SAH is very complex and involves several interconnected, but also distinct pathways. The identification of single therapeutical targets or specific pharmacological agents may be a limited strategy able to block only selective pathophysiological paths, but not the global evolution of SAH-related events. We report furthermore on the role of heparin in SAH management and discuss the rationale for use of intrathecal heparin as a pleiotropic therapeutical agent. The combination of the anticoagulant effect and the ability to interfere with SSE theoretically make heparin a very interesting molecule for SAH management.

Identification of the key immune-related genes in aneurysmal subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is a major cause of death and morbidity worldwide, often due to rupture of intracranial aneurysms (IAs). Immune infiltration and inflammatory activation play key roles in the process of aneurysmal SAH (aSAH). This study aimed to elaborate the immune infiltration and identify related biomarkers both in blood and tissue samples from patients with aSAH. Expression data of aSAH and healthy control samples were obtained from gene expression omnibus (GEO) database. Overall, a blood sample dataset GSE36791 and a tissue sample dataset GSE122897 were included. Differentially expressed genes (DEGs) between aSAH and healthy samples were explored. We applied GO biological and Gene Set Enrichment Analyses (GSEA) processes to access the functional enrichment. Then feature elimination algorithms based on random forest were used to screen and verify the biomarkers of aSAH. We performed three computational algorithms including Cell type Identification by Estimating Relative Subsets of RNA Transcripts (CIBERSORT), Microenvironment Cell Populations-counter (MCPcounter), and xcell to evaluate the immune cell infiltration landscape to identify the unique infiltration characteristics associated with rupturing. We found 2,220 DEGs (856 upregulated and 1,364 downregulated) in the original dataset. Functional analysis revealed most of these genes are enriched in immunological process, especially related with neutrophil response. Similar signaling pathway enrichment patterns were observed in tissue sample dataset and ClueGo. Analysis of immune microenvironment infiltration suggested neutrophils were abnormally upregulated in aSAH compared with those in the control group. Key gene SRPK1 was then filtered based on feature elimination algorithms, and transcription factor (TF) ZNF281 is assumed to participate in immunomodulation by regulating expression of SRPK1. Several immunomodulators such as CXCR1 and CXCR2 also appear to be involved in the progression of aSAH. In the present study, we performed a comprehensive stratification and quantification of the immune infiltration status of aSAH. By exploring the potential mechanism for aSAH based on several computational algorithms, key genes including SRPK1 and ZNF281 were filtered. This study may be of benefit to patients who are at high risk of suffering aSAH which allows for early diagnosis and potential therapy.

Neutrophil to lymphocyte ratio predicting poor outcome after aneurysmal subarachnoid hemorrhage: A retrospective study and updated meta-analysis

Background

The relationship between neutrophil to lymphocyte ratio (NLR) and poor outcome of aneurysmal subarachnoid hemorrhage (aSAH) is controversial. We aim to evaluate the relationship between NLR on admission and the poor outcome after aSAH.

Method

Part I: Retrospective analysis of aSAH patients in our center. Baseline characteristics of patients were collected and compared. Multivariate analysis was used to evaluate parameters independently related to poor outcome. Receiver operating characteristic (ROC) curve analysis was used to determine the best cut-off value of NLR. Part II: Systematic review and meta-analysis of relevant literature. Related literature was selected through the database. The pooled odds ratio (OR) and corresponding 95% confidence interval (CI) were calculated to evaluate the correlation between NLR and outcome measures.

Results

Part I: A total of 240 patients with aSAH were enrolled, and 52 patients had a poor outcome. Patients with poor outcome at 3 months had a higher admission NLR, Hunt & Hess score, Barrow Neurological Institute (BNI) scale score, Subarachnoid Hemorrhage Early Brain Edema Score (SEBES), and proportion of hypertension history. After adjustment, NLR at admission remained an independent predictor of poor outcome in aSAH patients (OR 0.76, 95% CI 0.69-0.83; P < 0.001). The best cut-off value of NLR in ROC analysis is 12.03 (area under the curve 0.805, 95% CI 0.735 - 0.875; P < 0.001). Part II: A total of 16 literature were included. Pooled results showed that elevated NLR was significantly associated with poor outcome (OR 1.31, 95% CI 1.14-1.49; P < 0.0001) and delayed cerebral ischemia (DCI) occurrence (OR 1.32, 95% CI 1.11-1.56; P = 0.002). The results are more reliable in large sample sizes, low NLR cut-off value, multicenter, or prospective studies.

Conclusion

Elevated NLR is an independent predictor of poor outcome and DCI occurrence in aSAH.

Longitudinal ventricular cerebrospinal fluid profile in patients with spontaneous subarachnoid hemorrhage

Background

Spontaneous subarachnoid hemorrhage (SAH) is a severe neurological disease that frequently requires placement of external ventricular drainage (EVD). Cerebrospinal fluid (CSF) obtained via the drain is used to detect potential complications of SAH.

Objective

This study aimed to describe the longitudinal profile of routine CSF parameters in patients with SAH and to identify associations with neurological complications.

Methods

A total of thirty-three patients with spontaneous SAH who required an EVD and had at least three consecutive CSF samples collected over a period of more than 7 days were included in this study.

Results

A median of 6 longitudinally collected CSF samples per patient were available within 1–22 days after SAH onset. Overall, red blood cells (RBC) steadily decreased over time, whereas white blood cells (WBC) and total protein (TP) increased until days 6 and 13, respectively, and decreased thereafter. The estimated decay rates of RBC, WBC, and TP were 28, 22, and 6% per day. Distinct CSF patterns over time were linked to known complications after SAH. Patients with rebleeding showed increased RBC, TP, and phagocytosing cells compared to patients without re-bleeding. For ventriculitis, an elevated cell index with a higher proportion of granulocytes was characteristic. CSF of patients with delayed cerebral ischemia showed increased RBC and WBC compared to patients without DCI. Early CSF WBC and cell index were predictive for the occurrence of DCI and ventriculitis later during the disease course. The amount of daily CSF drainage via EVD had no impact on routine CSF parameters.

Conclusion

Longitudinal CSF characteristics are associated with SAH-related complications.

Minocycline decreases blood-brain barrier permeability following aneurysmal subarachnoid hemorrhage: a randomized, double-blind, controlled trial

OBJECTIVE

Aneurysmal subarachnoid hemorrhage (aSAH)-induced vasospasm is linked to increased inflammatory cell trafficking across a permeable blood-brain barrier (BBB). Elevations in serum levels of matrix metalloprotease 9 (MMP9), a BBB structural protein, have been implicated in the pathogenesis of vasospasm onset. Minocycline is a potent inhibitor of MMP9. The authors sought to detect an effect of minocycline on BBB permeability following aSAH.

METHODS

Patients presenting within 24 hours of symptom onset with imaging confirmed aSAH (Fisher grade 3 or 4) were randomized to high-dose (10 mg/kg) minocycline or placebo. The primary outcome of interest was BBB permeability as quantitated by contrast signal intensity ratios in vascular regions of interest on postbleed day (PBD) 5 magnetic resonance permeability imaging. Secondary outcomes included serum MMP9 levels and radiographic and clinical evidence of vasospasm.

RESULTS

A total of 11 patients were randomized to minocycline (n = 6) or control (n = 5) groups. No adverse events or complications attributable to minocycline were reported. High-dose minocycline administration was associated with significantly lower permeability indices on imaging analysis (p < 0.01). There was no significant difference with respect to serum MMP9 levels between groups, although concentrations trended upward in both cohorts. Radiographic vasospasm was noted in 6 patients (minocycline = 3, control = 3), with only 1 patient developing symptoms of clinical vasospasm in the minocycline cohort. There was no difference between cohorts with respect to Lindegaard ratios, transcranial Doppler values, or onset of vasospasm.

CONCLUSIONS

Minocycline at high doses is well tolerated in the ruptured cerebral aneurysm population. Minocycline curtails breakdown of the BBB following aSAH as evidenced by lower permeability indices, though minocycline did not significantly alter serum MMP9 levels. Larger randomized clinical trials are needed to assess minocycline as a neuroprotectant against aSAH-induced vasospasm. Clinical trial registration no.: NCT04876638 (clinicaltrials.gov).

Early Fevers and Elevated Neutrophil-to-Lymphocyte Ratio are Associated with Repeat Endovascular Interventions for Cerebral Vasospasm in Patients with Aneurysmal Subarachnoid Hemorrhage

BACKGROUND

Patients with aneurysmal subarachnoid hemorrhage (aSAH) may develop refractory arterial cerebral vasospasm requiring multiple endovascular interventions. The aim of our study is to evaluate variables associated with need for repeat endovascular treatments in refractory vasospasm and to identify differences in outcomes following one versus multiple treatments.

METHODS

We retrospectively reviewed patients treated for aSAH between 2017 and 2020 at two tertiary care centers. We included patients who underwent treatment (intraarterial infusion of vasodilatory agents or mechanical angioplasty) for radiographically diagnosed vasospasm in our analysis. Patients were divided into those who underwent single treatment versus those who underwent multiple endovascular treatments for vasospasm.

RESULTS

Of the total 418 patients with aSAH, 151 (45.9%) underwent endovascular intervention for vasospasm. Of 151 patients, 95 (62.9%) underwent a single treatment and 56 (37.1%) underwent two or more treatments. Patients were more likely to undergo multiple endovascular treatments if they had a Hunt-Hess score > 2 (odds ratio [OR] 5.10 [95% confidence interval (CI) 1.82-15.84]; p = 0.003), a neutrophil-to-lymphocyte ratio > 8.0 (OR 3.19 [95% CI 1.40-7.62]; p = 0.028), and more than two fevers within the first 5 days of admission (OR 7.03 [95% CI 2.68-20.94]; p < 0.001). Patients with multiple treatments had poorer outcomes, including increased length of stay, delayed cerebral ischemia, in-hospital complications, and higher modified Rankin scores at discharge.

CONCLUSIONS

A Hunt-Hess score > 2, a neutrophil-to-lymphocyte ratio > 8.0, and early fevers may be predictive of need for multiple endovascular interventions in refractory cerebral vasospasm after aSAH. These patients have poorer functional outcomes at discharge and higher rates of in-hospital complications.

RNase A Inhibits Formation of Neutrophil Extracellular Traps in Subarachnoid Hemorrhage

Background: Subarachnoid hemorrhage (SAH) caused by rupture of an intracranial aneurysm, is a life-threatening emergency that is associated with substantial morbidity and mortality. Emerging evidence suggests involvement of the innate immune response in secondary brain injury, and a potential role of neutrophil extracellular traps (NETs) for SAH-associated neuroinflammation. In this study, we investigated the spatiotemporal patterns of NETs in SAH and the potential role of the RNase A (the bovine equivalent to human RNase 1) application on NET burden. Methods: A total number of n=81 male C57Bl/6 mice were operated utilizing a filament perforation model to induce SAH, and Sham operation was performed for the corresponding control groups. To confirm the bleeding and exclude stroke and intracerebral hemorrhage, the animals received MRI after 24h. Mice were treated with intravenous injection of RNase A (42μg/kg body weight) or saline solution for the control groups, respectively. Quadruple-immunofluorescence (IF) staining for cell nuclei (DAPI), F-actin (phalloidin), citrullinated H3, and neurons (NeuN) was analyzed by confocal imaging and used to quantify NET abundance in the subarachnoid space (SAS) and brain parenchyma. To quantify NETs in human SAH patients, cerebrospinal spinal fluid (CSF) and blood samples from day 1, 2, 7, and 14 after bleeding onset were analyzed for double-stranded DNA (dsDNA) via Sytox Green. Results: Neutrophil extracellular traps are released upon subarachnoid hemorrhage in the SAS on the ipsilateral bleeding site 24h after ictus. Over time, NETs showed progressive increase in the parenchyma on both ipsi- and contralateral site, peaking on day 14 in periventricular localization. In CSF and blood samples of patients with aneurysmal SAH, NETs also increased gradually over time with a peak on day 7. RNase application significantly reduced NET accumulation in basal, cortical, and periventricular areas. Conclusion: Neutrophil extracellular trap formation following SAH originates in the ipsilateral SAS of the bleeding site and spreads gradually over time to basal, cortical, and periventricular areas in the parenchyma within 14days. Intravenous RNase application abrogates NET burden significantly in the brain parenchyma, underpinning a potential role in modulation of the innate immune activation after SAH.

Clinical significance of platelet to neutrophil ratio and platelet to lymphocyte ratio in patients with aneurysmal subarachnoid hemorrhage

The aim of study was aimed to investigate associations of platelet-to-neutrophil ratio (PNR) and platelet-to-lymphocyte ratio (PLR) on admission with clinical outcomes of patients with aneurysmal subarachnoid hemorrhage (aSAH). A retrospective analysis was performed on patients who were treated for aSAH. Unfavorable clinical outcome was defined as Modified Rankin Scale (mRS) score of 3-6 at 90-days. Receiver operating characteristic curve analysis was performed to detect optimal cutoff values of PNR and PLR for predicting clinical outcomes. Logistic regression was used to explore associations of PNR and PLR with clinical outcomes. A total of 544 patients with aSAH were enrolled. Of them, 152 (29.9%) had unfavorable clinical outcome. Optimal cutoff values of PNR and PLR to predict clinical outcomes at 90 days after aSAH were 25 and 130, respectively (P < 0.001 and <0.001, respectively). In multivariate logistic regression analysis, PNR <25 and PLR ≥ 130 were associated with unfavorable clinical outcome at 90 days after aSAH (odds ratio [OR]: 1.81; 95% confidence interval [CI]: 1.23-3.69; P = 0.018 and OR: 1.56; 95% CI: 1.18-2.62; P = 0.031, respectively). PNR and PLR as novel inflammatory biomarkers could predict the clinical outcome after aSAH. PNR <22 and PLR ≥ 130 were associated with unfavorable clinical outcome at 90 days after aSAH.

RAR-Related Orphan Receptor Gamma T (RoRγt)-Related Cytokines Play a Role in Neutrophil Infiltration of the Central Nervous System After Subarachnoid Hemorrhage

BACKGROUND

How inflammatory cells are recruited into the central nervous system is a topic of interest in a number of neurological injuries. In aneurysmal subarachnoid hemorrhage (SAH), neutrophil accumulation in the central nervous system 3 days after the hemorrhage is a critical step in the development of delayed cerebral injury (DCI). The mechanism by which neutrophils enter the central nervous system is still unclear.

METHODS AND RESULTS

To identify human effectors of neutrophil recruitment, cerebrospinal fluid (CSF) samples were taken from a small, selected sample of SAH patients with external ventricular drainage devices (10 patients). Among a battery of CSF cytokines tested 3 days after SAH, five cytokines were associated with poor 90-day outcome (modified Rankin Score 3-6). A parallel study in a mouse model of mild SAH showed elevation in three cytokines in the CNS compared to sham. IL-17 and IL-2 were increased in both patients and the mouse model. IL-17 was investigated further because of its known role in neutrophil recruitment. Inhibition of RAR-Related Orphan Receptor Gamma T, the master transcription factor of IL-17, with the inverse agonist GSK805 suppressed neutrophils entry into the CNS after SAH compared to control. Using an IL-17 reporter mouse, we investigated the source of IL-17 and found that myeloid cells were a common IL-17-producing cell type in the meninges after SAH, suggesting an autocrine role for neutrophil recruitment.

CONCLUSIONS

Taken together, IL-17 appears to be in important factor in the recruitment of neutrophils into the meninges after SAH and could be an important target for therapies to ameliorate DCI.

Cerebrovascular Anomalies: Perspectives From Immunology and Cerebrospinal Fluid Flow

Appropriate vascular function is essential for the maintenance of central nervous system homeostasis and is achieved through virtue of the blood-brain barrier; a specialized structure consisting of endothelial, mural, and astrocytic interactions. While appropriate blood-brain barrier function is typically achieved, the central nervous system vasculature is not infallible and cerebrovascular anomalies, a collective terminology for diverse vascular lesions, are present in meningeal and cerebral vasculature supplying and draining the brain. These conditions, including aneurysmal formation and rupture, arteriovenous malformations, dural arteriovenous fistulas, and cerebral cavernous malformations, and their associated neurological sequelae, are typically managed with neurosurgical or pharmacological approaches. However, increasing evidence implicates interacting roles for inflammatory responses and disrupted central nervous system fluid flow with respect to vascular perturbations. Here, we discuss cerebrovascular anomalies from an immunologic angle and fluid flow perspective. We describe immune contributions, both common and distinct, to the formation and progression of diverse cerebrovascular anomalies. Next, we summarize how cerebrovascular anomalies precipitate diverse neurological sequelae, including seizures, hydrocephalus, and cognitive effects and possible contributions through the recently identified lymphatic and glymphatic systems. Finally, we speculate on and provide testable hypotheses for novel nonsurgical therapeutic approaches for alleviating neurological impairments arising from cerebrovascular anomalies, with a particular emphasis on the normalization of fluid flow and alleviation of inflammation through manipulations of the lymphatic and glymphatic central nervous system clearance pathways.

Admission Neutrophil to Lymphocyte Ratio for Predicting Outcome in Subarachnoid Hemorrhage

PURPOSE

We sought to evaluate the relationship between admission neutrophil-to-lymphocyte ratio (NLR) and functional outcome in aneurysmal subarachnoid hemorrhage (aSAH) patients.

MATERIAL AND METHODS

Consecutive patients with aSAH were treated at two tertiary stroke centers during a five-year period. Functional outcome was defined as discharge modified Rankin score dichotomized at scores 0-2 (good) vs. 3-6 (poor).

RESULTS

474 aSAH patients were evaluated with a mean NLR 8.6 (SD 8.3). In multivariable logistic regression analysis, poor functional outcome was independently associated with higher NLR, older age, poorer clinical status on admission, prehospital statin use, and vasospasm. Increasing NLR analyzed as a continuous variable was independently associated with higher odds of poor functional outcome (OR 1.03, 95%CI 1.00-1.07, p=0.05) after adjustment for potential confounders. When dichotomized using ROC curve analysis, a threshold NLR value of greater than 6.48 was independently associated with higher odds of poor functional outcome (OR 1.71, 95%CI 1.07-2.74, p=0.03) after adjustment for potential confounders.

CONCLUSIONS

Higher admission NLR is an independent predictor for poor functional outcome at discharge in aSAH patients. The evaluation of anti-inflammatory targets in the future may allow for improved functional outcome after aSAH.

Neuroprotective Strategies in Aneurysmal Subarachnoid Hemorrhage (aSAH)

Aneurysmal subarachnoid hemorrhage (aSAH) remains a disease with high mortality and morbidity. Since treating vasospasm has not inevitably led to an improvement in outcome, the actual emphasis is on finding neuroprotective therapies in the early phase following aSAH to prevent secondary brain injury in the later phase of disease. Within the early phase, neuroinflammation, thromboinflammation, disturbances in brain metabolism and early neuroprotective therapies directed against delayed cerebral ischemia (DCI) came into focus. Herein, the role of neuroinflammation, thromboinflammation and metabolism in aSAH is depicted. Potential neuroprotective strategies regarding neuroinflammation target microglia activation, metalloproteases, autophagy and the pathway via Toll-like receptor 4 (TLR4), high mobility group box 1 (HMGB1), NF-κB and finally the release of cytokines like TNFα or IL-1. Following the link to thromboinflammation, potential neuroprotective therapies try to target microthrombus formation, platelets and platelet receptors as well as clot clearance and immune cell infiltration. Potential neuroprotective strategies regarding metabolism try to re-balance the mismatch of energy need and supply following aSAH, for example, in restoring fuel to the TCA cycle or bypassing distinct energy pathways. Overall, this review addresses current neuroprotective strategies in aSAH, hopefully leading to future translational therapy options to prevent secondary brain injury.

Sequential expression of neutrophil chemoattractants in cerebrospinal fluid after subarachnoid hemorrhage

OBJECTIVE

Neutrophils induce inflammation through the exocytosis of cytotoxic granule proteins. Recently, neutrophils have been reported to be an independent parameter associated with unfavorable outcomes after subarachnoid hemorrhage (SAH). However, the mechanism by which neutrophils accumulate within the CSF after SAH remains undetermined.

METHODS

Concentrations of C5a, epithelial neutrophil activating peptide 78 (ENA-78), interleukin-8 (IL-8), growth-regulated oncogene-α (GRO-α), neutrophil gelatinase-associated lipocalin (NGAL) and myeloperoxidase (MPO) were measured serially until day 14 in the CSF of 10 patients with SAH. CSF samples obtained from patients suffering from unruptured aneurysms were used as controls.

RESULTS

The concentrations of C5a and ENA-78 were significantly increased on day 1, while those of IL-8 and GRO-α significantly increased during days 3-7 compared with those of the control samples. The levels of NGAL and MPO, components of neutrophil granules, significantly increased during days 1-5 and days 1-3, respectively, after SAH and gradually decreased thereafter. The correlations between ENA-78 and C5a on day 1, IL-8 and GRO-α on days 3-7, and NGAL and MPO on days 1-3 were significant.

CONCLUSION

These neutrophil chemoattractants might be serially involved in the infiltration of neutrophils into the CSF after SAH. Migrated neutrophils play an important role in inflammatory reactions in the central nervous system after SAH.

PD-1+ Monocytes Mediate Cerebral Vasospasm Following Subarachnoid Hemorrhage

BACKGROUND

Cerebral vasospasm is a major source of morbidity and mortality following aneurysm rupture and has limited treatment options.

OBJECTIVE

To evaluate the role of programmed death-1 (PD-1) in cerebral vasospasm.

METHODS

Endovascular internal carotid artery perforation (ICAp) was used to induce cerebral vasospasm in mice. To evaluate the therapeutic potential of targeting PD-1, programmed death ligand-1 (PD-L1) was administered 1 h after ICAp and vasospasm was measured histologically at the level of the ICA bifurcation bilaterally. PD-1 expressing immune cell populations were evaluated by flow cytometry. To correlate these findings to patients and evaluate the potential of PD-1 as a biomarker, monocytes were isolated from the peripheral blood and analyzed by flow cytometry in a cohort of patients with ruptured cerebral aneurysms. The daily frequency of PD-1+ monocytes in the peripheral blood was correlated to transcranial Doppler velocities as well as clinical and radiographic vasospasm.

RESULTS

We found that PD-L1 administration prevented cerebral vasospasm by inhibiting ingress of activated Ly6c+ and CCR2+ monocytes into the brain. Human correlative studies confirmed the presence of PD-1+ monocytes in the peripheral blood of patients with ruptured aneurysms and the frequency of these cells corresponded with cerebral blood flow velocities and clinical vasospasm.

CONCLUSION

Our results identify PD-1+ monocytes as mediators of cerebral vasospasm and support PD-1 agonism as a novel therapeutic strategy.

Vitamin D-A New Perspective in Treatment of Cerebral Vasospasm

BACKGROUND

Cerebral vasospasm (CVS) is a frequent complication after subarachnoid hemorrhage (SAH), with no sufficient therapy and a complex pathophysiology.

OBJECTIVE

To explore the vitamin D system as a potential treatment for CVS.

METHODS

25-vitamin D3 levels tested between 2007 and 2015 and data of SAH patients admitted during the months with a peak vs nadir of VitD3 values were analyzed, retrospectively. We prospectively correlated VitD3 and vasospasm/outcome data in SAH patients admitted in 2017. An experimental mice SAH model and cell culture model were used to investigate the effect of 1,25-dihydroxyvitamin D3 (1,25-VitD3). Additionally, the mediators acting in the VitD mechanism were researched and detected.

RESULTS

Based on the retrospective analysis demonstrating an increased frequency of vasospasm in SAH patients during the low vitamin D period in winter, we started basic research experiments. Active 1,25-VitD3 hormone attenuated CVS, neurological deficit, and inflammation after intrathecal blood injection in mice. Deletion of the vitamin D receptor in the endothelium or in myeloid cells decreased the protective 1,25-VitD3 effect. Co-culture experiments of myeloid and endothelial cells with blood confirmed the anti-inflammatory 1,25-VitD3 effect but also revealed an induction of stroma-cell-derived factor 1α (SDF1α), vascular endothelial growth factor, and endothelial nitric oxide synthase by 1,25-VitD3. In mice, SDF1α mimicked the protective effect of 1,25-VitD3 against CVS. From bench to bedside, CVS severity was inversely correlated with vitamin D plasma level, prospectively. Patients with more severe CVS exhibited attenuated expression of SDF1α and 1,25-VitD3-responsive genes on circulating myeloid cells.

CONCLUSION

1,25-VitD3 attenuates CVS after SAH by inducing SDF1α. However, VitD administration should be tested as optional treatment to prevent CVS.

Alpha power decrease in quantitative EEG detects development of cerebral infarction after subarachnoid hemorrhage early

OBJECTIVE

In subarachnoid hemorrhage (SAH), transcranial Doppler/color-coded-duplex sonography (TCD/TCCS) is used to detect delayed cerebral ischemia (DCI). In previous studies, quantitative electroencephalography (qEEG) also predicted imminent DCI. This study aimed to compare and analyse the ability of qEEG and TCD/TCCS to early identify patients who will develop later manifest cerebral infarction.

METHODS

We analysed cohorts of two previous qEEG studies. Continuous six-channel-EEG with artefact rejection and a detrending procedure was applied. Alpha power decline of ≥ 40% for ≥ 5 hours compared to a 6-hour-baseline was defined as significant EEG event. Median reduction and duration of alpha power decrease in each channel was determined. Vasospasm was diagnosed by TCD/TCCS, identifying the maximum frequency and days of vasospasm in each territory.

RESULTS

34 patients were included (17 male, mean age 56 ± 11 years, Hunt and Hess grade: I-V, cerebral infarction: 9). Maximum frequencies in TCD/TCCS and alpha power reduction in qEEG were correlated (r = 0.43; p = 0.015). Patients with and without infarction significantly differed in qEEG parameters (maximum alpha power decrease: 78% vs 64%, p = 0.019; summed hours of alpha power decline: 236 hours vs 39 hours, p = 0.006) but showed no significant differences in TCD/TCCS parameters.

CONCLUSIONS

There was a moderate correlation of TCD/TCCS frequencies and qEEG alpha power reduction but only qEEG differentiated between patients with and without cerebral infarction.

SIGNIFICANCE

qEEG represents a non-invasive, continuous tool to identify patients at risk of cerebral infarction.

Development of the Cerebrospinal Fluid in Early Stage after Hemorrhage in the Central Nervous System

Extravasation of blood in the central nervous system (CNS) represents a very strong damaged associated molecular patterns (DAMP) which is followed by rapid inflammation and can participate in worse outcome of patients. We analyzed cerebrospinal fluid (CSF) from 139 patients after the CNS hemorrhage. We compared 109 survivors (Glasgow Outcome Score (GOS) 5-3) and 30 patients with poor outcomes (GOS 2-1). Statistical evaluations were performed using the Wilcoxon signed-rank test and the Mann–Whitney U test. Almost the same numbers of erythrocytes in both subgroups appeared in days 0–3 (p = 0.927) and a significant increase in patients with GOS 2-1 in days 7–10 after the hemorrhage (p = 0.004) revealed persistence of extravascular blood in the CNS as an adverse factor. We assess 43.3% of patients with GOS 2-1 and only 27.5% of patients with GOS 5-3 with low values of the coefficient of energy balance (KEB < 15.0) in days 0–3 after the hemorrhage as a trend to immediate intensive inflammation in the CNS of patients with poor outcomes. We consider significantly higher concentration of total protein of patients with GOS 2-1 in days 0–3 after hemorrhage (p = 0.008) as the evidence of immediate simultaneously manifested intensive inflammation, swelling of the brain and elevation of intracranial pressure.

Evaluation of the Effectiveness of Lumbar Punctures in Aneurysmal Subarachnoid Hemorrhage Patient with External Ventricular Drainage

BACKGROUND

For aSAH patients with external ventricular drainage (EVD) because of hydrocephalus, the consensus on application of CSF drainage from the lumbar cistern is mixed owing to concerns about its safety and questionable effectiveness. This study evaluated the additional effectiveness of CSF drainage from the lumbar cistern in aSAH patients with EVD.

METHODS

This was a retrospective and observational study of adult patients with aSAH who were admitted to the intensive care unit at the Wuhan Union Hospital between June 2018 and June 2019. Three aSAH patients with EVD and serial lumbar punctures (LPs) were selected for comparison of CSF components. Four more aSAH patients who underwent divergent CSF drainage were selected to profile the additional effectiveness of lumbar cistern drainage in aSAH patients with EVD.

RESULTS

Cases 1-3 with EVD and serial LPs showed dramatically higher red blood cell (RBC) and leukocyte counts with steeper changing curve in the lumbar cistern CSF than in the ventricle CSF. Case 5 had EVD alone and showed a slower clearing rate of blood clot in subarachnoid space compared with case 1. Case 4, with serial LPs alone, showed a steep changing curve of both RBC and leukocyte counts in the lumbar cistern CSF. Cases 6 and 7, with EVD and follow-up LPs, showed dramatically higher RBC and leukocyte counts in the lumbar cistern CSF than in the ventricle CSF after almost 2 weeks of EVD.

CONCLUSIONS

For aSAH patients with EVD, serial LPs can accelerate clearance of toxic products from the subarachnoid space.

Predictive Relevance of Early Temperature Elevation on the Risk of Delayed Cerebral Ischemia Development Following Aneurysmal Subarachnoid Hemorrhage

BACKGROUND

Fever in aneurysmal subarachnoid hemorrhage (aSAH) has been associated with delayed cerebral ischemia (DCI), but its relevance in risk stratification has not been explored. This study investigated whether early temperature elevation following aSAH predicts impending clinical deterioration caused by DCI.

METHODS

Relevant cases were identified from a prospectively maintained database for consecutive patients with aSAH treated at our center between July 2015 and January 2020. Temperature readings obtained every 2 hours for individual patients from admission through day 14 were recorded and analyzed. Demographic, clinical, treatment, and angiographic data were extracted from the electronic medical record. The primary end point was the occurrence of DCI (clinical and radiographic vasospasm). Multivariate logistic regression analyses were performed to account for patient age, smoking status, and VASOGRADE classification.

RESULTS

The study included 175 patients (124 women) with aSAH. The median age at diagnosis was 55.4 years (range, 20.5-87.2 years). Clinical DCI occurred in 58 patients; 2 (1.1%) responded to hemodynamic augmentation, and 56 (32.0%) required intra-arterial therapy. Temperature graphs showed a marked divergence on day 4 between clinical DCI and non-DCI groups (1.12°C ± 0.15°C and 0.76°C ± 0.08°C, respectively, P = 0.007). Patients with temperature elevation ≥2.5°C on day 4 or 5 compared with their admission temperature were more likely to clinically deteriorate owing to DCI (odds ratio 4.55, 95% confidence interval 1.31-15.77, P = 0.017).

CONCLUSIONS

Temperature elevation of ≥2.5°C on day 4 or 5 compared with baseline suggests a greater risk of clinical deterioration owing to DCI.

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.

Impact of Ventilator-associated Pneumonia on Cerebrospinal Fluid Inflammation During Immunosuppression After Subarachnoid Hemorrhage: A Pilot Study

INTRODUCTION

Brain injuries can cause systemic immunosuppression, which in turn can lead to infections that adversely affect the injured brain and worsen clinical outcomes. This study aimed to investigate whether systemic infection, such as ventilator-associated pneumonia (VAP), induce intracranial inflammation in patients with subarachnoid hemorrhage (SAH).

METHODS

This prospective, observational study included 16 adults with SAH treated in the neuro-intensive care unit. Three paired cerebrospinal fluid samples (obtained from an external ventricular drain) and peripheral blood samples were obtained on days 1 to 3, 4 to 5, and 6 to 7 after SAH onset. Cell counts, cell phenotypes (monocyte HLA-DR, T regulatory cells, lymphocytes, and neutrophils), and inflammatory mediator levels were monitored.

RESULTS

Six patients developed VAP in the context of systemic immunosuppression demonstrated by a reduction in monocyte HLA-DR expression, lymphopenia, increased percentages of circulating T regulatory cells, and increased proportions of immature and immunosuppressive neutrophil subsets. During VAP, there was de novo recruitment of leukocytes into the cerebrospinal fluid, preferentially neutrophils, which exacerbated intracranial inflammation.

CONCLUSIONS

VAP increased intracranial inflammatory responses in patients with SAH despite the occurrence of systemic immunosuppression. A better understanding of cell trafficking and their pleiotropic functions in brain injury is needed to define the optimal strategies for preventing infections in patients with SAH.

Can Aspartate Aminotransferase in the Cerebrospinal Fluid Be a Reliable Predictive Parameter?

Brain ischemia after central nervous system (CNS) bleeding significantly influences the final outcome of patients. Catalytic activities of aspartate aminotransferase (AST) in the cerebrospinal fluid (CSF) to detect brain ischemia were determined in this study. The principal aim of our study was to compare the dynamics of AST in 1956 CSF samples collected from 215 patients within a 3-week period after CNS hemorrhage. We compared concentrations of the AST catalytic activities in the CSF of two patient groups: survivors (Glasgow Outcome Score (GOS) 5–3) and patients in a vegetative state or dead (GOS 2–1). All statistical evaluations were performed using mixed models and the F-test adjusted by Kenward and Roger and the Bonferroni adjustment for multiple tests. The significantly higher catalytic activities of AST in the CSF from patients with the GOS of 2–1 when compared to those who survived (GOS 5–3, p = 0.001) were found immediately after CNS haemorrhage. In the further course of time, the difference even increased (p < 0.001). This study confirmed the key association between early signs of brain damage evidenced as an elevated AST activity and the prediction of the final patient’s clinical outcome. The study showed that the level of AST in the CSF could be the relevant diagnostic biomarker of the presence and intensity of brain tissue damage.

Preliminary results in the analysis of the immune response after aneurysmal subarachnoid hemorrhage

Cerebral vasospasm (VSP) is a common phenomenon after aneurysmal subarachnoid hemorrhage (aSAH) and contributes to neurocognitive decline. The natural history of the pro-inflammatory immune response after aSAH has not been prospectively studied in human cerebrospinal fluid (CSF). In this pilot study, we aimed to identify specific immune mediators of VSP after aSAH. Peripheral blood (PB) and CSF samples from patients with aSAH were prospectively collected at different time-points after hemorrhage: days 0–1 (acute); days 2–4 (pre-VSP); days 5–9 (VSP) and days 10 + (post-VSP peak). Presence and severity of VSP was assessed with computed tomography angiography/perfusion imaging and clinical examination. Cytokine and immune mediators’ levels were quantified using ELISA. Innate and adaptive immune cells were characterized by flow cytometry, and cell counts at different time-points were compared with ANOVA. Confocal immunostaining was used to determine the presence of specific immune cell populations detected in flow cytometry. Thirteen patients/aneurysms were included. Five (38.5%) patients developed VSP after a mean of 6.8 days from hemorrhage. Flow cytometry demonstrated decreased numbers of CD45+ cells during the acute phase in PB of aSAH patients compared with healthy controls. In CSF of VSP patients, NK cells (CD3-CD161 +) were increased during the acute phase and progressively declined, whereas CD8+CD161+ lymphocytes significantly increased at days 5–9. Microglia cells (CD45dimCD11b +) increased over time after SAH. This increase was particularly significant in patients with VSP. Levels of VEGF and MMP-9 were consistently higher in VSP patients, with the highest difference occurring at the acute phase. Confocal immunostaining demonstrated the presence of CD8+CD161+ lymphocytes in the arterial wall of two unruptured intracranial aneurysms. In this preliminary study, human CSF showed active presence of innate and adaptive immune cells after aSAH. CD8+CD161+ lymphocytes may have an important role in the inflammatory response after aneurysmal rupture and were identified in the aneurysmal wall of unruptured brain aneurysms. Microglia activation occurs 6 + days after aSAH.

Serum Alkaline Phosphatase Level is Associated with Angiographic Vasospasm, Delayed Cerebral Ischemia-Caused Clinical Deterioration, and Functional Outcome After Aneurysmal Subarachnoid Hemorrhage

BACKGROUND

Alkaline phosphatase (ALP) has been implicated to be associated with poor outcome in ischemic stroke patients, yet its role in aneurysmal subarachnoid hemorrhage (aSAH) patients is unknown. The current study aimed to investigate the on-admission and short-term variation trend of ALP levels in aSAH patients as well as its associations with vasospasm, delayed cerebral ischemia (DCI), and outcome after aSAH.

METHODS

Between January 2014 and May 2018, all consecutive aSAH patients were prospectively enrolled. Blood samples from patients and 78 healthy individuals were obtained. Baseline information, clinical data, and radiologic data were collected, and serum ALP levels during hospitalization were measured. Patients were followed up for 6 months.

RESULTS

One hundred and ninety-six aSAH patients were included. The serum ALP levels in aSAH patients were significantly higher compared to controls (71 vs. 61 U/L, p = 0.0002), yet did not differ significantly between patients with severe (WFNS 4-5) and mild clinical condition (72 vs. 63 U/L, p = 0.3362). However, ALP was significantly higher in patients with severe radiologic status (modified Fisher 3-4) compared to those with mild radiologic status (77 vs. 61.5 U/L, p = 0.0005). A significant correlation emerged between modified Fisher score and ALP level (r = 0.246, p = 0.001). Multivariable analysis found that higher ALP level was associated with angiographic vasospasm (OR 1.019, 95% CI 1.002-1.036, p = 0.026) and DCI-caused clinical deterioration (OR 1.019, 95% CI 1.001-1.037, p = 0.037), while higher WFNS score, modified Fisher score, and ALP level were independently associated with unfavorable outcome (serum ALP level, OR 1.083, 95% CI 1.041-1.127, p < 0.001). Trend analysis of ALP level based on 103 patients' data revealed a significant decrease in ALP level on post-admission day 7-9 (median; on-admission day vs. post-admission day 7-9, 72 vs. 60 U/L, p = 0.0012; post-admission day 3-5 vs. day 7-9, 70 vs. 60 U/L, p = 0.0052) and subsequent increase in ALP level on post-admission day 12-14 (median, 84 U/L, p < 0.0001). Higher ALP levels were observed in patients with unfavorable outcome on on-admission day, post-admission day 3-5, and 12-14 (median; unfavorable vs. favorable; on-admission day, 86 vs. 67 U/L, p = 0.0122; post-admission day 3-5, 80 vs. 64 U/L, p = 0.0044; post-admission day 7-9, 75 vs. 53.5 U/L, p < 0.0001) but not on post-admission day 12-14.

CONCLUSIONS

Elevated serum ALP level is associated with vasospasm, DCI-caused clinical deterioration, and functional outcome after aSAH. Further studies are required to examine the potential role of serum ALP as an outcome predictor for aSAH patients.

Druggable Sphingolipid Pathways: Experimental Models and Clinical Opportunities

Intensive research in the field of sphingolipids has revealed diverse roles in cell biological responses and human health and disease. This immense molecular family is primarily represented by the bioactive molecules ceramide, sphingosine, and sphingosine 1-phosphate (S1P). The flux of sphingolipid metabolism at both the subcellular and extracellular levels provides multiple opportunities for pharmacological intervention. The caveat is that perturbation of any single node of this highly regulated flux may have effects that propagate throughout the metabolic network in a dramatic and sometimes unexpected manner. Beginning with S1P, the receptors for which have thus far been the most clinically tractable pharmacological targets, this review will describe recent advances in therapeutic modulators targeting sphingolipids, their chaperones, transporters, and metabolic enzymes.

White Blood Cell Count Improves Prediction of Delayed Cerebral Ischemia Following Aneurysmal Subarachnoid Hemorrhage

BACKGROUND

Immune dysregulation has long been implicated in the development of delayed cerebral ischemia (DCI) following aneurysmal subarachnoid hemorrhage (aSAH).

OBJECTIVE

To determine the relationship of inflammatory cell biomarkers with DCI.

METHODS

We evaluated 849 aSAH patients who were enrolled into a prospective observational cohort study and had a white blood cell (WBC) differential obtained within 72 h of bleed onset.

RESULTS

WBC count > 12.1 × 109/L (odds ratio 4.6; 95% confidence interval [CI]: 1.9-11, P < 0.001) was the strongest Complete Blood Count (CBC) predictor of DCI after controlling for clinical grade (P < .001), thickness of SAH blood on admission computed tomography (P = .002), and clipping aneurysm repair (P < .001). A significant interaction between clinical grade and WBC count (odds ratio 0.8, 95% CI: 0.6-1.0, P = .02) revealed that good-grade patients with elevated WBC counts (49%: 273/558) had increased odds for DCI indistinguishable from poor-grade patients. Multivariable Cox regression also showed that elevated WBC counts in good-grade patients increased the hazard for DCI to that of poor-grade patients (hazard ratio 2.1, 95% CI 1.3-3.2, P < .001). Receiver operating characteristic curve analysis of good-grade patients revealed that WBC count (area under the curve [AUC]: 0.63) is a stronger DCI predictor than the modified Fisher score (AUC: 0.57) and significantly improves multivariable DCI prediction models (Z = 2.0, P = .02, AUC: 0.73; PPV: 34%; NPV: 92%).

CONCLUSION

Good-grade patients with early elevations in WBC count have a similar risk and hazard for DCI as poor-grade patients. Good-grade patients without elevated WBC may be candidates to be safely downgraded from the intensive care unit, leading to cost savings for both patient families and hospitals.

Immune Characterization in Aneurysmal Subarachnoid Hemorrhage Reveals Distinct Monocytic Activation and Chemokine Patterns

The pathophysiology of delayed cerebral ischemia (DCI) after aneurysmal subarachnoid hemorrhage (aSAH) is incompletely understood. Intrathecal activation of inflammatory immune cells is suspected to play a major role for the induction of DCI. The aim of this study is to identify immune cell subsets and mediators involved in the pathogenesis of DCI. We prospectively collected blood and CSF from 25 patients with aSAH at early and late time points. We performed multicolor flow cytometry of peripheral blood and CSF, analyzing immune cell activation and pro-inflammatory cyto- and chemokines. In addition to the primary immune analysis, we retrospectively analyzed immune cell dynamics in the CSF of all our SAH patients. Our results show an increased monocyte infiltration secondary to aneurysm rupture in patients with DCI. Infiltrating monocytes are defined by a non-classical (CD14^dim CD16⁺) phenotype at early stages. The infiltration is most likely triggered by the intrathecal immune activation. Here, high levels of pro-inflammatory chemokines, such as CXCL1, CXCL9, CXCL10, and CXCL11, are detected. The intrathecal cellular activation profile of monocytes was defined by upregulation of CD163 and CD86 on monocytes and a presumable later differentiation into antigen-presenting plasmacytoid dendritic cells (pDCs) and hemosiderophages. Peripheral immune activation was reflected by CD69 upregulation on T cells. Analysis of DCI prevalence, Hunt and Hess grade, and clinical outcome correlated with the degree of immune activation. We demonstrate that monocytes and T cells are activated intrathecally after aSAH and mediate a local inflammatory response which is presumably driven by chemokines. Our data shows that the distinct pattern of immune activation correlates with the prevalence of DCI, indicating a pathophysiological connection to the incidence of vasospasm.

Blood-Related Toxicity after Traumatic Brain Injury: Potential Targets for Neuroprotection

Emergency visits, hospitalizations, and deaths due to traumatic brain injury (TBI) have increased significantly over the past few decades. While the primary early brain trauma is highly deleterious to the brain, the secondary injury post-TBI is postulated to significantly impact mortality. The presence of blood, particularly hemoglobin, and its breakdown products and key binding proteins and receptors modulating their clearance may contribute significantly to toxicity. Heme, hemin, and iron, for example, cause membrane lipid peroxidation, generate reactive oxygen species, and sensitize cells to noxious stimuli resulting in edema, cell death, and increased morbidity and mortality. A wide range of other mechanisms such as the immune system play pivotal roles in mediating secondary injury. Effective scavenging of all of these pro-oxidant and pro-inflammatory metabolites as well as controlling maladaptive immune responses is essential for limiting toxicity and secondary injury. Hemoglobin metabolism is mediated by key molecules such as haptoglobin, heme oxygenase, hemopexin, and ferritin. Genetic variability and dysfunction affecting these pathways (e.g., haptoglobin and heme oxygenase expression) have been implicated in the difference in susceptibility of individual patients to toxicity and may be target pathways for potential therapeutic interventions in TBI. Ongoing collaborative efforts are required to decipher the complexities of blood-related toxicity in TBI with an overarching goal of providing effective treatment options to all patients with TBI.

Neuroinflammation and Microvascular Dysfunction After Experimental Subarachnoid Hemorrhage: Emerging Components of Early Brain Injury Related to Outcome

Aneurysmal subarachnoid hemorrhage has a high mortality rate and, for those who survive this devastating injury, can lead to lifelong impairment. Clinical trials have demonstrated that cerebral vasospasm of larger extraparenchymal vessels is not the sole contributor to neurological outcome. Recently, the focus of intense investigation has turned to mechanisms of early brain injury that may play a larger role in outcome, including neuroinflammation and microvascular dysfunction. Extravasated blood after aneurysm rupture results in a robust inflammatory response characterized by activation of microglia, upregulation of cellular adhesion molecules, recruitment of peripheral immune cells, as well as impaired neurovascular coupling, disruption of the blood-brain barrier, and imbalances in endogenous vasodilators and vasoconstrictors. Each of these phenomena is either directly or indirectly associated with neuronal death and brain injury. Here, we review recent studies investigating these various mechanisms in experimental models of subarachnoid hemorrhage with special emphasis on neuroinflammation and its effect on microvascular dysfunction. We discuss the various therapeutic targets that have risen from these mechanistic studies and suggest the utility of a multi-targeted approach to preventing delayed injury and improving outcome after subarachnoid hemorrhage.

The role of endogenous bromotyrosine in health and disease

Bromotyrosine is a stable by-product of eosinophil peroxidase activity, a result of eosinophil activation during an inflammatory immune response. The elevated presence of bromotyrosine in tissue, blood, and urine in medical conditions involving eosinophil activation has highlighted the potential role of bromotyrosine as a medical biomarker. This is highly beneficial in a paediatric setting as a urinary noninvasive biomarker. However, bromotyrosine and its derivatives may exert biological effects, such as protective effects in the brain and pathogenic effects in the thyroid. Understanding these pathways may yield therapeutic advancements in medicine. In this review, we summarize the existing evidence present in literature relating to bromotyrosine formation and metabolism, identify the biological actions of bromotyrosine and evaluate the feasibility of bromotyrosine as a medical biomarker.

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.

Continuous infusion of low-dose unfractionated heparin after aneurysmal subarachnoid hemorrhage: a preliminary study of cognitive outcomes

OBJECTIVE

Cognitive dysfunction occurs in up to 70% of aneurysmal subarachnoid hemorrhage (aSAH) survivors. Low-dose intravenous heparin (LDIVH) infusion using the Maryland protocol was recently shown to reduce clinical vasospasm and vasospasm-related infarction. In this study, the Montreal Cognitive Assessment (MoCA) was used to evaluate cognitive changes in aSAH patients treated with the Maryland LDIVH protocol compared with controls.

METHODS

A retrospective analysis of all patients treated for aSAH between July 2009 and April 2014 was conducted. Beginning in 2012, aSAH patients were treated with LDIVH in the postprocedural period. The MoCA was administered to all aSAH survivors prospectively during routine follow-up visits, at least 3 months after aSAH, by trained staff blinded to treatment status. Mean MoCA scores were compared between groups, and regression analyses were performed for relevant factors.

RESULTS

No significant differences in baseline characteristics were observed between groups. The mean MoCA score for the LDIVH group (n = 25) was 26.4 compared with 22.7 in controls (n = 22) (p = 0.013). Serious cognitive impairment (MoCA ≤ 20) was observed in 32% of controls compared with 0% in the LDIVH group (p = 0.008). Linear regression analysis demonstrated that only LDIVH was associated with a positive influence on MoCA scores (β = 3.68, p =0.019), whereas anterior communicating artery aneurysms and fevers were negatively associated with MoCA scores. Multivariable linear regression analysis resulted in all 3 factors maintaining significance. There were no treatment complications.

CONCLUSIONS

This preliminary study suggests that the Maryland LDIVH protocol may improve cognitive outcomes in aSAH patients. A randomized controlled trial is needed to determine the safety and potential benefit of unfractionated heparin in aSAH patients.

Admission neutrophil–lymphocyte ratio predicts delayed cerebral ischemia following aneurysmal subarachnoid hemorrhage

Background

Delayed cerebral ischemia (DCI) following aneurysmal subarachnoid hemorrhage (aSAH) has a multifactorial pathophysiology, with immune dysregulation being an important component. The neutrophil–lymphocyte ratio (NLR) is an established prognostic marker in patients with cancer, cardiac disease, and sepsis.

Objective

To determine whether there is a relationship between NLR and DCI in patients with aSAH.

Methods

We evaluated 1067 patients with aSAH between 2006 and 2015 enrolled in a single-center, prospective, observational cohort study. Admission white blood cell differentials (NLR) were analyzed using a cut-off point of ≥5.9. DCI from cerebral vasospasm was defined as the occurrence of focal neurological impairment, or a decrease in at least two points on the Glasgow Coma Scale, which was not apparent immediately after aneurysm occlusion, and could not be attributed to other causes. Cerebral infarct was defined as a new infarct on CT that was not visible on the admission or immediate postoperative scan, when the cause was thought to be vasospasm by the research team. Logistic regression models were generated.

Results

We found that 768 (72%) patients had an admission NLR ≥5.9. In a multivariable model, elevated NLR was associated with poor admission Hunt-Hess grade (OR=1.6, 95% CI 1.2 to 2.6, p=0.005), Caucasian ethnicity (OR=2.6, 95% CI 1.9 to 3.7, p<0.001), anterior aneurysm location (OR=1.7, 95% CI 1.2 to 2.4, p=0.004), loss of consciousness at ictus (OR=1.4, 95% CI 1.0 to 2.0, p=0.055), and thick SAH (modified Fisher grade ≥3) (OR=1.8, 95% CI 1.3 to 2.4, p<0.001). Admission NLR predicted development of delayed cerebral ischemia (DCI) (OR=1.7; 95% CI 1.1 to 2.5, p=0.008) after controlling for known predictors such as age, poor admission clinical grade, thick SAH blood, and elevated admission mean arterial pressure.

Conclusions

This study provides further evidence of the association between inflammation and DCI. Admission NLR is a readily available and convenient biomarker that may be a clinically useful tool for prognostication when evaluating aSAH.

Quantitative EEG After Subarachnoid Hemorrhage Predicts Long-Term Functional Outcome

PURPOSE

Delayed cerebral ischemia is a major complication after subarachnoid hemorrhage. Our previous study showed that alpha power reduction in continuous quantitative EEG predicts delayed cerebral ischemia. In this prospective cohort, we aimed to determine the prognostic value of alpha power in quantitative EEG for the long-term outcome of patients with subarachnoid hemorrhage.

METHODS

Adult patients with nontraumatic subarachnoid hemorrhage were included if admitted early enough for EEG to start within 72 hours after symptom onset. Continuous six-channel EEG was applied. Unselected EEG signals underwent automated artifact rejection, power spectral analysis, and detrending. Alpha power decline of ≥40% for ≥5 hours was defined as critical EEG event based on previous findings. Six-month outcome was obtained using the modified Rankin scale.

RESULTS

Twenty-two patients were included (14 male; mean age, 59 years; Hunt and Hess grade I-IV; duration of EEG monitoring, median 14 days). Poor outcome (modified Rankin scale, 2-5) was noted in 11 of 16 patients (69%) with critical EEG events. All six patients (100%) without EEG events achieved an excellent outcome (modified Rankin scale 0, 1) (P = 0.0062; sensitivity 100%, specificity 54.5%). Vasospasm detected with transcranial Doppler/Duplex sonography appeared 1.5 days after EEG events and showed weaker association with outcome (P = 0.035; sensitivity 100%, specificity 45.5%). There was no significant association between EEG events and ischemic lesions on imaging (P = 0.1). Also, no association between ischemic lesions and outcome was seen (P = 0.64).

CONCLUSIONS

Stable alpha power in quantitative EEG reflects successful therapy and predicts good functional outcome after subarachnoid hemorrhage. Critical alpha power reduction indicates an increased risk of poor functional outcome.

Ischemia-reperfusion injury in stroke: impact of the brain barriers and brain immune privilege on neutrophil function

Reperfusion injury following ischemic stroke is a complex pathophysiological process involving numerous mechanisms ranging from the release of excitatory amino acids and ion disequilibrium to the induction of apoptosis and necrosis, to oxidative stress and inflammation. The migration of neutrophils into the brain parenchyma and release of their abundant proteases are generally considered the main cause of neuronal cell death and acute reperfusion injury following ischemic stroke. Recent findings in experimental and human stroke have challenged this view, as the majority of neutrophils were rather found to accumulate within the neurovascular unit (NVU) and the subarachnoid space (SAS) where they remain separated from the brain parenchyma by the glia limitans. The brain parenchyma is an immune-privileged site that is not readily accessible to immune cells and does not elicit stereotypic adaptive or innate immune responses. Understanding brain immune privilege requires intimate knowledge of its unique anatomy in which the brain barriers, that include the glia limitans, establish compartments that differ remarkably with regard to their accessibility to the immune system. We here propose that the brain immune privilege also extends to an ischemic insult, where the brain parenchyma does not evoke a rapid infiltration of neutrophils as observed in ischemic events in peripheral organs. Rather, neutrophil accumulation in the NVU and SAS could have a potential impact on cerebrospinal fluid (CSF) drainage from the central nervous system (CNS) and thus on edema formation and reperfusion injury after ischemic stroke. Integrating the anatomical and functional implications of the brain immune privilege with the unquestionable role of neutrophils in reperfusion injury is a prerequisite to exploit appropriate strategies for therapeutic interventions aiming to reduce neuronal cell death after ischemic stroke.

Large Vessel Vasospasm Is Not Associated with Cerebral Cortical Hypoperfusion in a Murine Model of Subarachnoid Hemorrhage

Clinical studies on subarachnoid hemorrhage (SAH) have shown discrepancies between large vessel vasospasm, cerebral perfusion, and clinical outcome. We set out to analyze the contribution of large vessel vasospasm to impaired cerebral perfusion and neurological impairment in a murine model of SAH. SAH was induced in C57BL/6 mice by endovascular filament perforation. Vasospasm was analyzed with microcomputed tomography, cortical perfusion by laser SPECKLE contrast imaging, and functional impairment with a quantitative neuroscore. SAH animals developed large vessel vasospasm, as shown by significantly lower vessel volumes of a 2.5-mm segment of the left middle cerebral artery (MCA) (SAH 5.6 ± 0.6 nL, sham 8.3 ± 0.5 nL, p < 0.01). Induction of SAH significantly reduced cerebral perfusion of the corresponding left MCA territory compared to values before SAH, which only recovered partly (SAH vs. sham, 15 min 35.7 ± 3.1 vs. 101.4 ± 10.2%, p < 0.01; 3 h, 85.0 ± 8.6 vs. 121.9 ± 13.4, p < 0.05; 24 h, 75.3 ± 4.6 vs. 110.6 ± 11.4%, p < 0.01; 72 h, 81.8 ± 4.8 vs. 108.5 ± 14.5%, n.s.). MCA vessel volume did not correlate significantly with MCA perfusion after 72 h (r = 0.34, p = 0.25). Perfusion correlated moderately with neuroscore (24 h: r = - 0.58, p < 0.05; 72 h: r = - 0.44, p = 0.14). There was no significant correlation between vessel volume and neuroscore after 72 h (r = - 0.21, p = 0.50). In the murine SAH model, cerebral hypoperfusion occurs independently of large vessel vasospasm. Neurological outcome is associated with cortical hypoperfusion rather than large vessel vasospasm.

Aneurysmal Subarachnoid Hemorrhage and Vasospasm

Aneurysmal subarachnoid hemorrhage is potentially fatal and is associated with poor outcomes in many patients. Advances in neurosurgical and medical management of ruptured aneurysms have improved mortality rates in patients with aneurysmal subarachnoid hemorrhage. Surgical and endovascular interventions, such as external ventricular drain placement, aneurysm clipping, and endovascular coiling, have been developed over the past few decades. Patients with aneurysmal subarachnoid hemorrhage are also at risk for cerebral vasospasm and delayed cerebral ischemia. This article describes the diagnosis and treatment of aneurysmal subarachnoid hemorrhage, vasospasm, and cerebral ischemia. Concurrent medical considerations and ideas for future neuroinflammatory vasospasm research are also discussed.

Permeability imaging as a predictor of delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage

Blood-brain barrier (BBB) dysfunction has been implicated in ischemic risk following aneurysmal subarachnoid hemorrhage (aSAH), but never directly imaged. We prospectively examined whether post-bleed day 4 dynamic contrast-enhanced magnetic resonance (DCE-MR) BBB permeability imaging could predict development of delayed cerebral ischemia (DCI). Global MR-derived BBB permeability ( K_trans) was significantly higher in aSAH patients who subsequently developed DCI (five patients; 2.28 ± 0.09 × 10^-3 min^-1) compared to those who experienced radiographic vasospasm only (three patients; 1.85 ± 0.12 × 10^-3 min^-1; p < 0.05), or no vasospasm/ischemia (eight patients; 1.74 ± 0.07 × 10^-3 min^-1; p < 0.01). K_trans > 2 × 10^-3 min^-1 predicted development of DCI (AUC = 0.98, 95% CI: 0.93-1). Global BBB dysfunction following aSAH is detectable with DCE-MR and predictive of ischemic risk.

Unique Contribution of Haptoglobin and Haptoglobin Genotype in Aneurysmal Subarachnoid Hemorrhage

Survivors of cerebral aneurysm rupture are at risk for significant morbidity and neurological deficits. Much of this is related to the effects of blood in the subarachnoid space which induces an inflammatory cascade with numerous downstream consequences. Recent clinical trials have not been able to reduce the toxic effects of free hemoglobin or improve clinical outcome. One reason for this may be the inability to identify patients at high risk for neurologic decline. Recently, haptoglobin genotype has been identified as a pertinent factor in diabetes, sickle cell, and cardiovascular disease, with the Hp 2-2 genotype contributing to increased complications. Haptoglobin is a protein synthesized by the liver that binds free hemoglobin following red blood cell lysis, and in doing so, prevents hemoglobin induced toxicity and facilitates clearance. Clinical studies in patients with subarachnoid hemorrhage indicate that Hp 2-2 patients may be a high-risk group for hemorrhage related complications and poor outcome. We review the relevance of haptoglobin in subarachnoid hemorrhage and discuss the effects of genotype and expression levels on the known mechanisms of early brain injury (EBI) and cerebral ischemia after aneurysm rupture. A better understanding of haptoglobin and its role in preventing hemoglobin related toxicity should lead to novel therapeutic avenues.

Higher leukocyte count predicts 3-month poor outcome of ruptured cerebral aneurysms

It is not fully established whether leukocyte can predict the poor outcome for ruptured cerebral aneurysms (CA) or not. Here, we retrospectively analyzed the clinical data of 428 patients with ruptured CA between 2010 and 2015. Patients’ demographic data, including gender, age, history of smoking, alcohol, hypertension, diabetes and hypercholesterolemia, Hunt-Hess and Fisher grade, occurrence of hydrocephalus, aneurysm location, time to surgery, delayed ischemic neurological deficit (DIND) and peak leukocyte of blood test from day 1 to 3 after aneurysmal rupture were recorded and analyzed. In the multivariable analysis model, gender, Fisher grade, time to surgery and hydrocephalus were not relevant to poor outcome. However, Hunt-Hess grade, DIND and preoperative leukocyte count (>13.84 × 10⁹/L) were significantly associated with adverse outcome. The respective increased risks were 5.2- (OR 5.24, 95% CI 1.67–16.50, p = 0.005), 6.2-(OR 6.24, 95% CI 3.55–10.99, p < 0.001) and 10.9-fold (OR 10.93, 95% CI 5.98–19.97, p < 0.001). The study revealed that Hunt-Hess grade, DIND and preoperative leukocyte count (>13.84 × 10⁹/L) were independent risk factors for poor outcome of ruptured CA at 3 months. Higher leukocyte count is a convenient and useful marker to predict 3-month poor outcome for ruptured CA.

[Prognostic significance of leukocyte count in the venous blood in the acute stage of cerebral aneurism rupture]

AIM

To determine a prognostic role of leukocyte count in the venous blood in the acute stage of cerebral aneurysm (CA) rupture.

MATERIAL AND METHODS

Fifty-one patients with CA rupture, aged from 20 to 65 years, hospitalized in the first 72 h over the period from 01.10.12 to 01.02.16 were examined. The severity of disease and anatomical form of hemorrhage was corresponded to III-IV degree on the W. Hunt - R. Hess scale and Fisher scale. All patients underwent surgery. Outcomes after open and endovascular surgeries were similar.

RESULTS

Normal leukocyte number in the venous blood at admission was identified in 12 (24%) of patients (on average 7.3±1.4·109/L), leukocytosis in 39 (76%) (14.3±3.1·109/L) (p<0.0001). Leukocyte number in the acute stage of CA rupture was correlated with the frequency and severity of the vessel spasm. In 28 (55%) of patients with ischemic lesions of the brain matter, mean leukocyte number in the first 72 h after hemorrhage was higher by 2-24% (3±4.8·109/L) compared to patients without ischemia (11.9±2.5·109/L) (p=0.06). The level of leukocytes in survivors was lower by 3 - 28% (122±3.4·109/L) compared to patients with fatal outcome and patients with severe neurological deficit after the surgery (14.5±3.9·109/L) (p>0.05).

CONCLUSION

The increase in leukocyte number in the venous blood in the first 72 h after CA rupture ≥10,1·109/L is a reliable risk factor of marked vessel spasm. The level of leukocytes in patients with cerebral ischemia and poor prognosis in the first 72h after aneurysmal hemorrhage was higher by 2-28% compared to survivors without neurological impairment or mild neurological deficit.

ICAM-1null C57BL/6 Mice Are Not Protected from Experimental Ischemic Stroke

Accumulation of neutrophils in the brain is a hallmark of cerebral ischemia and considered central in exacerbating tissue injury. Intercellular adhesion molecule (ICAM)-1 is upregulated on brain endothelial cells after ischemic stroke and considered pivotal in neutrophil recruitment as ICAM-1-deficient mouse lines were found protected from experimental stroke. Translation of therapeutic inhibition of ICAM-1 into the clinic however failed. This prompted us to investigate stroke pathogenesis in Icam1^tm1Alb C57BL/6 mutants, a true ICAM-1^null mouse line. Performing transient middle cerebral artery occlusion, we found that absence of ICAM-1 did not ameliorate stroke pathology at acute time points after reperfusion. Near-infrared imaging showed comparable accumulation of neutrophils in the ischemic hemispheres of ICAM-1^null and wild type C57BL/6 mice. We also isolated equal numbers of neutrophils from the ischemic brains of ICAM-1^null and wild type C57BL/6 mice. Immunostaining of the brains showed neutrophils to equally accumulate in the leptomeninges and brain parenchymal vessels of ICAM-1^null and wild type C57BL/6 mice. In addition, the lesion size was comparable in ICAM-1^null and wild type mice. Our study demonstrates that absence of ICAM-1 neither inhibits cerebral ischemia-induced accumulation of neutrophils in the brain nor provides protection from ischemic stroke.