Targeting chronic inflammation in cerebral aneurysms: focusing on NF-κB as a putative target of medical therapy

The preliminary study suggests an association between NF-ĸB pathway activation and increased plasma 20S proteasome activity in intracranial aneurysm patients

The significant role of increased activation of 20S proteasomes in the development of abdominal aortic aneurysms has been well-established in a mouse model. The available literature lacks similar studies concerning brain aneurysms. The aim of the study was to verify the hypothesis that patients with unruptured intracranial aneurysms (UIA) have increased 20S proteasome ChT-L activity compared to the control group of individuals without vascular lesions in the brain. In the next step, the relationship between the activity of 20S proteasomes ChT-L and precursor proteins from the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) family, namely NF-κB1 (p105), NF-κB2 (p100), NF-κB p65, and the inflammatory chemokine MCP-1, was examined. Patients with UIA had significantly higher 20S ChT-L proteasome activity compared to the control group. Patients with multiple aneurysms had significantly higher 20S proteasome ChT-L activity compared to those with single aneurysms. In patients with UIA, the activity of the 20S proteasome ChT-L negatively correlated with the concentration of NF-κB1 (p105) and NF-κB p65 precursor proteins and positively correlated with the concentration of the cerebrospinal fluid chemokine MCP-1. Our results may suggest that increased 20S proteasome ChT-L activity in UIA patients modulates inflammation in the cerebral arterial vessel via the MCP-1 chemokine as a result of activation of the canonical NF-κB pathway.

Molecular biomarkers for vascular cognitive impairment and dementia

As disease-specific interventions for dementia are being developed, the ability to identify the underlying pathology and dementia subtypes is increasingly important. Vascular cognitive impairment and dementia (VCID) is the second most common cause of dementia after Alzheimer disease, but progress in identifying molecular biomarkers for accurate diagnosis of VCID has been relatively limited. In this Review, we examine the roles of large and small vessel disease in VCID, considering the underlying pathophysiological processes that lead to vascular brain injury, including atherosclerosis, arteriolosclerosis, ischaemic injury, haemorrhage, hypoperfusion, endothelial dysfunction, blood-brain barrier breakdown, inflammation, oxidative stress, hypoxia, and neuronal and glial degeneration. We consider the key molecules in these processes, including proteins and peptides, metabolites, lipids and circulating RNA, and consider their potential as molecular biomarkers alone and in combination. We also discuss the challenges in translating the promise of these biomarkers into clinical application.

Vessel Wall Imaging of Intracranial Arteries: Fundamentals and Clinical Applications

With the increasing use of 3-tesla MRI scanners and the development of applicable sequences, it has become possible to achieve high-resolution, good contrast imaging, which has enabled the imaging of the walls of small-diameter intracranial arteries. In recent years, the usefulness of vessel wall imaging has been reported for numerous intracranial arterial diseases, such as for the detection of vulnerable plaque in atherosclerosis, diagnosis of cerebral arterial dissection, prediction of the rupture of cerebral aneurysms, and status of moyamoya disease and cerebral vasculitis. In this review, we introduce the histological characteristics of the intracranial artery, discuss intracranial vessel wall imaging methods, and review the findings of vessel wall imaging for various major intracranial arterial diseases.

Prevalence and risk factors of unruptured intracranial aneurysms in ischemic stroke patients - A global meta-analysis

Background

Unruptured intracranial aneurysms (UIAs) have an estimated global prevalence of 2.8% in the adult population; however, UIA was identified among more than 10% of ischemic stroke patients. Many epidemiological studies and reviews have pointed to the presence of UIA among patients with ischemic stroke; yet, the extent of this association is not fully known. We performed a systematic review and meta-analysis to determine the prevalence of UIA in patients admitted to hospitals with ischemic stroke and transient ischemic attack (TIA) at both global and continental levels and evaluate factors associated with UIA in this population.

Methods

We identified, in five databases, all studies describing UIA in ischemic stroke and TIA patients between January 1, 2000, and December 20, 2021. Included studies were of observational and experimental design.

Results

Our search yielded 3581 articles of which 23 were included, with a total of 25,420 patients. The pooled prevalence of UIA was 5% (95% confidence interval [CI] = 4-6%) with stratified results showing 6% (95% CI = 4-9%), 6% (95% CI = 5-7%), and 4% (95% CI = 2-5%) in North America, Asia, and Europe, respectively. Significant risk factors were large vessel occlusion (odds ratios [OR] = 1.22, 95% CI = 1.01-1.47) and hypertension (OR = 1.45, 95% CI = 1.24-1.69), while protective factors were male sex (OR = 0.60, 95% CI = 0.53-0.68) and diabetes (OR = 0.82, 95% CI = 0.72-0.95).

Conclusion

The prevalence of UIA is notably higher in ischemic stroke patients than the general population. Physicians should be aware of common risk factors in stroke and aneurysm formation for appropriate prevention.

Methylprednisolone is related to lower incidence of postoperative bleeding after flow diverter treatment for unruptured intracranial aneurysm

Background and objectives

Regarding the anti-inflammatory effect, methylprednisolone is a candidate to prevent patients with unruptured intracranial aneurysms (UIAs) from postoperative bleeding (PB) after flow diverter (FD) treatment. This study aimed to investigate whether methylprednisolone is related to a lower incidence of PB after FD treatment for UIAs.

Methods

This study retrospectively reviewed UIA patients receiving FD treatment between October 2015 and July 2021. All patients were observed until 72  h after FD treatment. The patients receiving methylprednisolone (80  mg, bid, for at least 24 h) were considered as standard methylprednisolone treatment (SMT) users, otherwise as non-SMT users. The primary endpoint indicated the occurrence of PB, including subarachnoid hemorrhage, intracerebral hemorrhage, and ventricular bleeding, within 72 h after FD treatment. This study compared the incidence of PB between SMT users and non-SMT users and investigated the protective effect of SMT on PB after FD treatment using the Cox regression model. Finally, after controlling the potential factors related to PB, we performed subgroup analysis to further confirm the protective effect of SMT on PB.

Results

This study finally included 262 UIA patients receiving FD treatment. PB occurred in 11 patients (4.2%), and 116 patients (44.3%) received SMT postoperatively. The median time from the end of surgery to PB was 12.3 h (range: 0.5-48.0 h). SMT users had a lower incidence of PB comparing with non-SMT users (1/116, 0.9% vs. 10/146, 6.8%, respectively; p = 0.017). The multivariate Cox analysis demonstrated that SMT users (HR, 0.12 [95%CI, 0.02-0.94], p = 0.044) had a lower risk of PB postoperatively. After controlling the potential factors related to PB (i.e., gender, irregular shape, surgical methods [FD and FD + coil] and UIA sizes), the patients receiving SMT still had a lower cumulative incidence of PB, comparing with patients receiving non-SMT (all p < 0.05).

Conclusion

SMT was correlated with the lower incidence of PB for patients receiving FD treatment and may be a potential method to prevent PB after the FD treatment.

Canonical NF-κB signaling pathway and GRO-α/CXCR2 axis are activated in unruptured intracranial aneurysm patients

Activation of the nuclear factor kappa-B (NF-κB) stimulates the production of pro-inflammatory molecules involved in the formation of intracranial aneurysms (IA). The study aimed to assess the NF-κB p65 subunit and the GRO-α chemokine and its receptor CXCR2 concentrations in unruptured intracranial aneurysm patients (UIA, n = 25) compared to individuals without vascular changes in the brain (n = 10). It was also analyzed whether tested proteins are related to the size and number of aneurysms. Cerebrospinal fluid (CSF) and serum protein levels were measured using the ELISA method. Median CSF and serum NF-κB p65 concentrations were significantly lower, while median CSF GRO-α and CXCR2 concentrations were significantly higher in UIA patients compared to the control group. CSF and serum NF-κB p65 concentrations negatively correlated with the number of aneurysms. In UIA patients the median GRO-α concentration was two-fold and CXCR2 almost four-fold higher in CSF compared to the serum value. CSF GRO-α concentration positively correlated with the size of aneurysms.Significantly decreased CSF NF-κB p65 and significantly increased CSF GRO-α and its CXCR2 receptor concentrations in UIA patients compared to the control group may altogether suggest that the canonical NF-κB signaling pathway is activated and its target pro-inflammatory genes are highly expressed in UIA patients. However, to unequivocally assess the involvement of the classical NF-κB pathway with the participation of the NF-κB p65 subunit and the GRO-α/CXCR2 axis in the formation of IA, further in vivo model studies are needed.

Why Are Women Predisposed to Intracranial Aneurysm?

Intracranial aneurysm (IA) is a frequent and generally asymptomatic cerebrovascular abnormality characterized as a localized dilation and wall thinning of intracranial arteries that preferentially arises at the arterial bifurcations of the circle of Willis. The devastating complication of IA is its rupture, which results in subarachnoid hemorrhage that can lead to severe disability and death. IA affects about 3% of the general population with an average age for detection of rupture around 50 years. IAs, whether ruptured or unruptured, are more common in women than in men by about 60% overall, and more especially after the menopause where the risk is double-compared to men. Although these data support a protective role of estrogen, differences in the location and number of IAs observed in women and men under the age of 50 suggest that other underlying mechanisms participate to the greater IA prevalence in women. The aim of this review is to provide a comprehensive overview of the current data from both clinical and basic research and a synthesis of the proposed mechanisms that may explain why women are more prone to develop IA.

IL-6 Quotient (The Ratio of Cerebrospinal Fluid IL-6 to Serum IL-6) as a Biomarker of an Unruptured Intracranial Aneurysm

Background

Studies conducted so far have focused mainly on the assessment of IL-6 levels in patients with ruptured brain aneurysms. Carrying out detailed studies in patients with un-ruptured brain aneurysms (UIA) would be extremely important, as it would answer the question of whether IL-6 plays also a role in primary aneurysm formation and growth.

Methods

IL-6, S100, NSE, and albumin concentrations in 67 UIA patients and 17 individuals without vascular lesions in the brain were tested using in vitro diagnostic immunoassays according to the manufacturers' instructions. IL-6 Quotient was calculated by dividing cerebrospinal fluid (CSF) IL-6 by serum IL-6.

Results

We showed that IL-6 Quotient was significantly higher in UIA patients (1.78) compared to the control group (0.87; p<0.001). Multivariate logistic regression analysis demonstrated that a growth in IL-6 Quotient increases the probability of UIA diagnosis. In UIA patients CSF IL-6 concentration was significantly higher (4.55 pg/ml) compared to the serum concentration (2.39 pg/ml; p<0.001). In both the study and control group, the blood-brain barrier was intact, thus the CSF-blood gradient of the IL-6 concentration in UIA patients was likely to be the expression of local synthesis of the cytokine within the central nervous system. Patients with multiple brain aneurysms had significantly higher CSF IL-6 levels (5.08 pg/ml) compared to individuals with a single aneurysm (4.14 pg/ml; p=0.0227).

Conclusion

This totality of the may suggest IL-6 as a biomarker for UIA formation; however, further studies are needed to unequivocally confirm clinical application of IL-6 concentration evaluation.

Protective effects of BP-1-102 against intracranial aneurysms-induced impairments in mice

The development of non-invasive pharmacological therapies to prevent the progression and rupture of intracranial aneurysms (IAs) is an important field of research. This study attempts to reveal the role of BP-1-102, an oral bioavailable signal transducer and activator of transcription 3 (STAT3) inhibitor, in IA. We first constructed an IA mouse model by injecting elastase into the cerebrospinal fluid with simultaneous induction of hypertension by deoxycorticosterone acetate (DOCA) implantation. The results showed that the proportion of IA rupture in mice after BP-1-102 administration was significantly reduced, and the survival time was significantly extended. Further research showed that compared with the vehicle group, the proportion of macrophages infiltrated at the aneurysm and the expression of pro-inflammatory cytokines in the BP-1-102 administration group were significantly reduced. The contractile phenotype vascular smooth muscle cell (VSMC) specific markers, SM22α and αSMA, were significantly upregulated in the BP-1-102 group. Furthermore, we found that BP-1-102 inhibited the expression of critical proteins in the nuclear factor kappa-B and Janus kinase 2/STAT3 signalling pathways. Our study shows that BP-1-102 significantly decreases the rupture of IA, reduces the inflammatory responses and modulates the phenotype of VSMCs, suggesting that BP-1-102 could be utilised as a potential intervention drug for IA.

Internal modulation of proteolysis in vascular extracellular matrix remodeling: role of ADAM metallopeptidase with thrombospondin type 1 motif 5 in the development of intracranial aneurysm rupture

Intracranial aneurysms (IAs) are common cerebrovascular diseases that carry a high mortality rate, and the mechanisms that contribute to IA formation and rupture have not been elucidated. ADAMTS-5 (ADAM Metallopeptidase with Thrombospondin Type 1 Motif 5) is a secreted proteinase involved in matrix degradation and ECM (extracellular matrix) remodeling processes, and we hypothesized that the dysregulation of ADAMTS-5 could play a role in the pathophysiology of IA. Immunofluorescence revealed that the ADAMTS-5 levels were decreased in human and murine IA samples. The administration of recombinant protein ADAMTS-5 significantly reduced the incidence of aneurysm rupture in the experimental model of IA. IA artery tissue was collected and utilized for histology, immunostaining, and specific gene expression analysis. Additionally, the IA arteries in ADAMTS-5-administered mice showed reduced elastic fiber destruction, proteoglycan accumulation, macrophage infiltration, inflammatory response, and apoptosis. To further verify the role of ADAMTS-5 in cerebral vessels, a specific ADAMTS-5 inhibitor was used on another model animal, zebrafish, and intracranial hemorrhage was observed in zebrafish embryos. In conclusion, our findings indicate that ADAMTS-5 is downregulated in human IA, and compensatory ADAMTS-5 administration inhibits IA development and rupture with potentially important implications for treating this cerebrovascular disease.

MSK1 downregulation is involved in inflammatory responses following subarachnoid hemorrhage in rats

Subarachnoid hemorrhage (SAH) is a life-threatening neurological disease. Recently, inflammatory factors have been confirmed to be responsible for the brain damage associated with SAH. Therefore, studying the post-SAH inflammatory reaction may clarify the mechanism of SAH. Mitogen and stress-activated protein kinase 1 (MSK1) causes the phosphorylation of NF-κB and regulates the activity of pro-inflammatory transcription factors. The present study aimed to identify the potential role of MSK1 in inflammation and brain damage development following SAH. A cisterna magna blood injection model was established in Sprague-Dawley rats. Hematoxylin and eosin staining, reverse transcription-quantitative polymerase chain reaction assays and double immunofluorescence staining were used to analyze the role of MSK1, IL-1β and TNF-α in the inflammatory process after SAH. In a model of lipopolysaccharide-induced astrocyte inflammation, the effect of overexpressing MSK1 overexpression was analyzed by western blot analysis. The results demonstrated that MSK1 expression were negatively correlated with TNF-α and IL-1β expression levels, and reached peak levels 2 days after TNF-α and IL-1β. The double immunofluorescence staining results showed that the expression of MSK1 was in the same plane of view as TNF-α and IL-1β in the brain cortex. Furthermore, the in vitro studies indicated that the overexpression of MSK1 inhibited the expression of TNF-α and IL-1β following LPS challenge. These results imply that MSK1 may be involved in the inflammatory reaction following SAH, and may potentially serve as a negative regulator of inflammation.

Pharmacological inhibition of STAT3 by BP-1-102 inhibits intracranial aneurysm formation and rupture in mice through modulating inflammatory response

As an inhibitor of STAT3, BP-1-102 can regulate the inflammation response caused by vascular smooth muscle cells (VSMCs) by inhibiting the JAK/STAT3/NF-κB pathway, thereby attenuating the symptoms of intracranial aneurysm (IA). IA mouse model was established by stereotactic injection of elastase to evaluate the effect of BP-1-102. The expression levels of smooth muscle markers and matrix metalloproteinases (MMPs) were detected by qRT-PCR, and the levels of inflammatory factors were detected by ELISA and qRT-PCR. The protein levels of the NF-κB signaling pathway factors were examined by Western blot. BP-1-102 reduced blood pressure in aneurysm mice, up-regulated smooth muscle cell markers MHC, SMA, and SM22, and down-regulated the expression of MMP2 and MMP9 in vascular tissues. At the same time, BP-1-102 also down-regulated the expression levels of inflammatory response factors and the NF-κB pathway proteins. In the IA model, BP-1-102 can reduce the expression of inflammatory factors and MMPs bound to NF-κB by inhibiting the activation of the JAK/STAT3/NF-κB pathway proteins, and then restore the vascular wall elastin to reduce blood pressure, thereby treating aneurysm.

Ratio of IL-8 in CSF versus Serum Is Elevated in Patients with Unruptured Brain Aneurysm

Only scarce data pertaining to interleukin 8 (IL-8) and monocyte chemoattractant protein-1 (MCP-1) chemokines in human aneurysm can be found in the current literature. Therefore, the aim of this study was the evaluation of cerebrospinal fluid (CSF) and serum IL-8 and MCP-1 concentration in unruptured intracranial aneurysm (UIA) patients (n = 25) compared to the control group (n = 20). IL-8 and MCP-1 concentrations were measured with ELISA method. We demonstrated that CSF IL-8 concentration of UIA patients is significantly higher (p < 0.001) than that presented in the serum, which can indicate its local synthesis within central nervous system. CSF IL-8 concentration was also significantly related to aneurysm size, which may reflect the participation of IL-8 in the formation and development of brain aneurysms. IL-8 Quotient (CSF IL-8 divided by serum IL-8) in UIA patients was statistically higher compared to control individuals (p = 0.045). However, the diagnostic utility analysis did not equivocally indicate the diagnostic usefulness of the IL-8 Quotient evaluation in brain aneurysm patients. Nevertheless, this aspect requires further study.

RNA sequencing analysis revealed the induction of CCL3 expression in human intracranial aneurysms

Intracranial aneurysm (IA) is a socially important disease as a major cause of subarachnoid hemorrhage. Recent experimental studies mainly using animal models have revealed a crucial role of macrophage-mediated chronic inflammatory responses in its pathogenesis. However, as findings from comprehensive analysis of unruptured human IAs are limited, factors regulating progression and rupture of IAs in humans remain unclear. Using surgically dissected human unruptured IA lesions and control arterial walls, gene expression profiles were obtained by RNA sequence analysis. RNA sequencing analysis was done with read count about 60~100 million which yielded 6~10 billion bases per sample. 79 over-expressed and 329 under-expressed genes in IA lesions were identified. Through Gene Ontology analysis, ‘chemokine activity’, ‘defense response’ and ‘extracellular region’ were picked up as over-represented terms which included CCL3 and CCL4 in common. Among these genes, quantitative RT-PCR analysis using another set of samples reproduced the above result. Finally, increase of CCL3 protein compared with that in control arterial walls was clarified in IA lesions. Findings of the present study again highlight importance of macrophage recruitment via CCL3 in the pathogenesis of IA progression.

Real-time Imaging of an Experimental Intracranial Aneurysm in Rats

Subarachnoid hemorrhage due to rupture of a pre-existing intracranial aneurysm has quite a poor outcome in spite of intensive medical care. Hemodynamic stress loaded on intracranial arterial walls is considered as a trigger and a regulator of formation and progression of the disease, but how intracranial arterial walls or intracranial aneurysm walls behave under hemodynamic stress loading remains unclear. The purpose of this study was to visualize and analyze the wall motion of intracranial aneurysms to detect a pathological flow condition. We subjected a transgenic rat line, in which endothelial cells are specifically visualized by expression of a green fluorescent protein, to an intracranial aneurysm model and observed a real-time motion of intracranial arterial walls or intracranial aneurysm walls by a multiphoton laser confocal microscopy. The anterior cerebral artery–olfactory artery bifurcation was surgically exposed for the monitoring. First, we observed the proper flow-dependent physiological dilatation of a contralateral intracranial artery in response to increase of blood flow by one side of carotid ligation. Next, we observed intracranial aneurysm lesions induced in a rat model and confirmed that a wall motion of the dome was static, whereas that of the neck was more dynamic in response to pulsation of blood flow. We successfully monitored a real-time motion of intracranial aneurysm walls. Findings obtained from such a real-time imaging will provide us many insights especially about the correlation of mechanical force and the pathogenesis of the disease and greatly promote our understanding of the disease.

New Pathophysiological Considerations on Cerebral Aneurysms

Cerebral aneurysm is a common cerebrovascular disease that is sometimes complicated by rupture or an enlarged mass. We are now aggressively evaluating and managing unruptured cerebral aneurysms based on a significant concern for the high morbidity and mortality related to its associated complications. However, the actual rupture rate is very low and the diagnostic and treatment modalities are expensive and invasive, which may lead to unnecessary costs and potential medical complications. This disproportionate situation is related to a poor understanding of the natural course and pathophysiology of cerebral aneurysms. In consideration of the concept that not all cerebral aneurysms must be removed, we need to examine their course and progression more accurately. Cerebral aneurysms may follow a variety of pathophysiological scenarios over their lifetime, from formation to growth and rupture. The disease course and the final outcome can differ depending on the timing and intensity of the pathological signals acting on the cerebral vessel wall. We should delineate a method of predicting the stability and risk of rupture of the lesion based on a comprehensive knowledge of the vessel wall integrity. This review deals with the basic knowledge and advanced concepts underlying the pathophysiology of cerebral aneurysms.

Quantitative proteomics analysis of differentially expressed proteins in ruptured and unruptured cerebral aneurysms by iTRAQ

The underlying pathophysiological mechanisms involved in cerebral aneurysms rupture remain unclear. This study was performed to investigate the differentially expressed proteins between ruptured and unruptured aneurysms using quantitative proteomics. The aneurysmal walls of six ruptured aneurysms and six unruptured aneurysms were collected during the surgical operation. The isobaric tags for relative and absolute quantification (iTRAQ) were used to identify the differentially expressed proteins and western blotting was performed to validate the expression of the proteins of interest. Bioinformatics analysis of the differentially expressed proteins was also performed using the KEGG database and GO database. Between ruptured and unruptured aneurysms, 169 proteins were found differently expressed, including 74 up-regulated proteins and 95 down-regulated proteins with a fold change ≥ 2 and p value ≤ .05. KEGG pathway analysis revealed that phagosome, focal adhesion and ECM-receptor interaction were the most common pathways involved in aneurysm rupture. In addition, the differential expressions of ITGB3, CRABP1 and S100A9 were validated by western blotting. Through the iTRAQ method, we found that inflammatory responses and cell-matrix interactions may play a significant role in the rupture of cerebral aneurysms. These findings provide a basis for better understanding of pathophysiological mechanisms associated with aneurysm rupture.

BIOLOGICAL SIGNIFICANCE

Intracranial aneurysm is the leading cause of life-threating subarachnoid hemorrhage which can cause 45% patients die within 30 days and severe morbidity in long-term survivors. With a high prevalence ranging from 1% to 5% in general population, cerebral aneurysm has become a widespread health hazard over past decades. Though great advances have been achieved in the diagnosis and treatment of this disease, the underlying pathophysiological mechanisms of aneurysm rupture remains undetermined and a lot of uncertainty still exists surrounding the treatment of unruptured cerebral aneurysms. Clarifying the mechanism associated with aneurysm rupture is important for estimating the rupture risk, as well as the development of new treatment strategy. Some previous studies have analyzed the molecular differences between ruptured and unruptured IAs at gene and mRNA levels, but further comprehensive proteomic studies are relatively rare. Here we performed a comparative proteomics study to investigate the differentially expressed proteins between ruptured IAs (RIAs) and unruptured IAs (UIAs). Results of our present study will provide more insights into the pathogenesis of aneurysm rupture at protein level. With a better understanding of pathophysiological mechanisms associated with aneurysm rupture, some noninvasive treatment strategies may be developed in the future.

Association of renin-angiotensin system genetic polymorphisms and aneurysmal subarachnoid hemorrhage

OBJECTIVE

Renin-angiotensin system (RAS) genetic polymorphisms are thought to play a role in cerebral aneurysm formation and rupture. The Cerebral Aneurysm Renin-Angiotensin System (CARAS) study prospectively evaluated common RAS polymorphisms and their relation to aneurysmal subarachnoid hemorrhage (aSAH).

METHODS

The CARAS study prospectively enrolled aSAH patients and controls at 2 academic centers in the United States. A blood sample was obtained from all patients for genetic evaluation and measurement of plasma angiotensin-converting enzyme (ACE) concentration. Common RAS polymorphisms were detected using 5′ exonuclease (TaqMan) genotyping assays and restriction fragment length polymorphism analysis.

RESULTS

Two hundred forty-eight patients were screened, and 149 aSAH patients and 50 controls were available for analysis. There was a recessive effect of the C allele of the angiotensinogen (AGT) C/T single-nucleotide polymorphism (SNP) (OR 1.94, 95% CI 0.912–4.12, p = 0.0853) and a dominant effect of the G allele of the angiotensin II receptor Type 2 (AT2) G/A SNP (OR 2.11, 95% CI 0.972–4.57, p = 0.0590) on aSAH that did not reach statistical significance after adjustment for potential confounders. The ACE level was significantly lower in aSAH patients with the II genotype (17.6 ± 8.0 U/L) as compared with the ID (22.5 ± 12.1 U/L) and DD genotypes (26.6 ± 14.2 U/L) (p = 0.0195).

CONCLUSIONS

The AGT C/T and AT2 G/A polymorphisms were not significantly associated with aSAH after controlling for potential confounders. However, a strong trend was identified for a dominant effect of the G allele of the AT2 G/A SNP. Downregulation of the local RAS may contribute to the formation of cerebral aneurysms and subsequent presentation with aSAH. Further studies are required to elucidate the relevant pathophysiology and its potential implication in treatment of patients with aSAH.

A sphingosine-1-phosphate receptor type 1 agonist, ASP4058, suppresses intracranial aneurysm through promoting endothelial integrity and blocking macrophage transmigration

Background and Purpose

Intracranial aneurysm (IA), common in the general public, causes lethal subarachnoid haemorrhage on rupture. It is, therefore, of utmost importance to prevent the IA from rupturing. However, there is currently no medical treatment. Recent studies suggest that IA is the result of chronic inflammation in the arterial wall caused by endothelial dysfunction and infiltrating macrophages. The sphingosine‐1‐phosphate receptor type 1 (S1P₁ receptor) is present on the endothelium and promotes its barrier function. Here we have tested the potential of an S1P₁ agonist, ASP4058, to prevent IA in an animal model.

Experimental Approach

The effects of a selective S1P₁ agonist, ASP4058, on endothelial permeability and migration of macrophages across an endothelial cell monolayer were tested in vitro using a Transwell system, and its effects on the size of IAs were evaluated in a rat model of IA.

Key Results

S1P₁ receptor was expressed in endothelial cells of human IA lesions and control arterial walls. ASP4058 significantly reduced FITC‐dextran leakage through an endothelial monolayer and suppressed the migration of macrophages across the monolayer in vitro. Oral administration of ASP4058 reduced the vascular permeability, macrophage infiltration and size of the IAs by acting as an S1P₁ agonist in the rat model. This effect was mimicked by another two structurally‐unrelated S1P₁ agonists.

Conclusion and Implications

A selective S1P₁ agonist is a strong drug candidate for IA treatment as it promotes the endothelial cell barrier and suppresses the trans‐endothelial migration of macrophages in IA lesions.

Prostaglandin E2-EP2-NF-κB signaling in macrophages as a potential therapeutic target for intracranial aneurysms

Intracranial aneurysms are common but are generally untreated, and their rupture can lead to subarachnoid hemorrhage. Because of the poor prognosis associated with subarachnoid hemorrhage, preventing the progression of intracranial aneurysms is critically important. Intracranial aneurysms are caused by chronic inflammation of the arterial wall due to macrophage infiltration triggered by monocyte chemoattractant protein-1 (MCP-1), macrophage activation mediated by the transcription factor nuclear factor κB (NF-κB), and inflammatory signaling involving prostaglandin E₂ (PGE₂) and prostaglandin E receptor subtype 2 (EP2). We correlated EP2 and cyclooxygenase-2 (COX-2) with macrophage infiltration in human intracranial aneurysm lesions. Monitoring the spatiotemporal pattern of NF-κB activation during intracranial aneurysm development in mice showed that NF-κB was first activated in macrophages in the adventitia and in endothelial cells and, subsequently, in the entire arterial wall. Mice with a macrophage-specific deletion of Ptger2 (which encodes EP2) or macrophage-specific expression of an IκBα mutant that restricts NF-κB activation had fewer intracranial aneurysms with reduced macrophage infiltration and NF-κB activation. In cultured cells, EP2 signaling cooperated with tumor necrosis factor-α (TNF-α) to activate NF-κB and synergistically induce the expression of proinflammatory genes, including Ptgs2 (encoding COX-2). EP2 signaling also stabilized Ccl2 (encoding MCP-1) by activating the RNA-stabilizing protein HuR. Rats administered an EP2 antagonist had reduced macrophage infiltration and intracranial aneurysm formation and progression. This signaling pathway in macrophages thus facilitates intracranial aneurysm development by amplifying inflammation in intracranial arteries. These results indicate that EP2 antagonists may therefore be a therapeutic alternative to surgery.

Sustained expression of MCP-1 by low wall shear stress loading concomitant with turbulent flow on endothelial cells of intracranial aneurysm

INTRODUCTION

Enlargement of a pre-existing intracranial aneurysm is a well-established risk factor of rupture. Excessive low wall shear stress concomitant with turbulent flow in the dome of an aneurysm may contribute to progression and rupture. However, how stress conditions regulate enlargement of a pre-existing aneurysm remains to be elucidated.

RESULTS

Wall shear stress was calculated with 3D-computational fluid dynamics simulation using three cases of unruptured intracranial aneurysm. The resulting value, 0.017 Pa at the dome, was much lower than that in the parent artery. We loaded wall shear stress corresponding to the value and also turbulent flow to the primary culture of endothelial cells. We then obtained gene expression profiles by RNA sequence analysis. RNA sequence analysis detected hundreds of differentially expressed genes among groups. Gene ontology and pathway analysis identified signaling related with cell division/proliferation as overrepresented in the low wall shear stress-loaded group, which was further augmented by the addition of turbulent flow. Moreover, expression of some chemoattractants for inflammatory cells, including MCP-1, was upregulated under low wall shear stress with concomitant turbulent flow. We further examined the temporal sequence of expressions of factors identified in an in vitro study using a rat model. No proliferative cells were detected, but MCP-1 expression was induced and sustained in the endothelial cell layer.

CONCLUSIONS

Low wall shear stress concomitant with turbulent flow contributes to sustained expression of MCP-1 in endothelial cells and presumably plays a role in facilitating macrophage infiltration and exacerbating inflammation, which leads to enlargement or rupture.

Molecular basis for intracranial aneurysm formation

Intracranial aneurysm (IA) is a socially important disease both because it has a high prevalence and because of the severity of resultant subarachnoid hemorrhages after IA rupture. The major concern of current IA treatment is the lack medical therapies that are less invasive than surgical procedures for many patients. The current situation is mostly caused by a lack of knowledge regarding the regulating mechanisms of IA formation. Hemodynamic stress, especially high wall shear stress, loaded on arterial bifurcation sites is recognized as a trigger of IA formation from studies performed in the field of fluid dynamics. On the other hand, many studies using human specimens have also revealed the presence of active inflammatory responses, such as the infiltration of macrophages, in the pathogenesis of IA. Because of these findings, recent experimental studies, mainly using animal models of IA, have revealed some of the molecular mechanisms linking hemodynamic stress and long-lasting inflammation in IA walls. Currently, we propose that IA is a chronic inflammatory disease regulated by a positive feedback loop consisting of the cyclooxygenase (COX)-2 - prostaglandin (PG) E2 - prostaglandin E receptor 2 (EP2) - nuclear factor (NF)-κB signaling pathway triggered under hemodynamic stress and macrophage infiltration via NF-κB-mediated monocyte chemoattractant protein (MCP)-1 induction. These findings indicate future directions for the development of therapeutic drugs for IAs.

Exacerbation of intracranial aneurysm and aortic dissection in hypertensive rat treated with the prostaglandin F-receptor antagonist AS604872

Intracranial aneurysm (IA) and aortic dissection are both complications of hypertension and characterized by degeneration of the media. Given the involvement of prostaglandin F2α and its receptor, FP, in extracellular matrix remodeling in a mouse model of pulmonary fibrosis, here we induced hypertension and IA in rats by salt loading and hemi-lateral ligation of renal and carotid arteries and examined effects of a selective FP antagonist, AS604872, on these vascular events. AS604872 significantly accelerated degeneration of the media in both cerebral artery and aorta as evidenced by thinning of the media and disruption of the elastic lamina and promoted IA and aortic dissection. Notably, AS604872 induced expression of pro-inflammatory genes such as E-selectin in lesions and significantly enhanced macrophage infiltration. Suppression of surface expression of E-selectin with cimetidine prevented macrophage infiltration and aortic dissection. Thus, AS604872 exacerbates vascular inflammation in hypertensive rats and facilitates IA and aortic dissection. These results demonstrate that both IA and aortic dissection are caused by chronic inflammation of the arterial wall, which is worsened by AS604872, cautioning that other FP antagonists may share such deleterious actions in vascular homeostasis and suggesting that AS604872 can be used to make models of these vascular diseases with extensive degeneration.

Inflammation, vasospasm, and brain injury after subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) can lead to devastating neurological outcomes, and there are few pharmacologic treatments available for treating this condition. Both animal and human studies provide evidence of inflammation being a driving force behind the pathology of SAH, leading to both direct brain injury and vasospasm, which in turn leads to ischemic brain injury. Several inflammatory mediators that are elevated after SAH have been studied in detail. While there is promising data indicating that blocking these factors might benefit patients after SAH, there has been little success in clinical trials. One of the key factors that complicates clinical trials of SAH is the variability of the initial injury and subsequent inflammatory response. It is likely that both genetic and environmental factors contribute to the variability of patients' post-SAH inflammatory response and that this confounds trials of anti-inflammatory therapies. Additionally, systemic inflammation from other conditions that affect patients with SAH could contribute to brain injury and vasospasm after SAH. Continuing work on biomarkers of inflammation after SAH may lead to development of patient-specific anti-inflammatory therapies to improve outcome after SAH.

Critical role of TNF-alpha-TNFR1 signaling in intracranial aneurysm formation

Background

Intracranial aneurysm (IA) is a socially important disease due to its high incidence in the general public and the severity of resultant subarachnoid hemorrhage that follows rupture. Despite the social importance of IA as a cause of subarachnoid hemorrhage, there is no medical treatment to prevent rupture, except for surgical procedures, because the mechanisms regulating IA formation are poorly understood. Therefore, these mechanisms should be elucidated to identify a therapeutic target for IA treatment. In human IAs, the presence of inflammatory responses, such as an increase of tumor necrosis factor (TNF)-alpha, have been observed, suggesting a role for inflammation in IA formation. Recent investigations using rodent models of IAs have revealed the crucial role of inflammatory responses in IA formation, supporting the results of human studies. Thus, we identified nuclear factor (NF)-kappaB as a critical mediator of inflammation regulating IA formation, by inducing downstream pro-inflammatory genes such as MCP-1, a chemoattractant for macrophages, and COX-2. In this study, we focused on TNF-alpha signaling as a potential cascade that regulates NF-kappaB-mediated IA formation.

Results

We first confirmed an increase in TNF-alpha content in IA walls during IA formation, as expected based on human studies. Consistently, the activity of TNF-alpha converting enzyme (TACE), an enzyme responsible for TNF-alpha release, was induced in the arterial walls after aneurysm induction in a rat model. Next, we subjected tumor necrosis factor receptor superfamily member 1a (TNFR1)-deficient mice to the IA model to clarify the contribution of TNF-alpha-TNFR1 signaling to pathogenesis, and confirmed significant suppression of IA formation in TNFR1-deficient mice. Furthermore, in the IA walls of TNFR1-deficient mice, inflammatory responses, including NF-kappaB activation, subsequent expression of MCP-1 and COX-2, and infiltration of macrophages into the IA lesion, were greatly suppressed compared with those in wild-type mice.

Conclusions

In this study, using rodent models of IAs, we clarified the crucial role of TNF-alpha-TNFR1 signaling in the pathogenesis of IAs by inducing inflammatory responses, and propose this signaling as a potential therapeutic target for IA treatment.

Higher levels of coated-platelets are observed in patients with subarachnoid hemorrhage but lower levels are associated with increased mortality at 30 days

BACKGROUND

Coated-platelets are procoagulant platelets observed upon dual agonist stimulation with collagen and thrombin. Coated-platelet levels are elevated in non-lacunar ischemic stroke compared to either lacunar stroke or controls. In contrast, coated-platelet levels are decreased in spontaneous intracerebral hemorrhage (ICH) and inversely correlated with bleed size. We now report the first investigation of coated-platelets in patients with subarachnoid hemorrhage (SAH).

METHODS

Coated-platelet levels were determined in 40 consecutive patients with spontaneous SAH and in 40 controls. Results are reported as percent of cells converted to coated-platelets. Mortality at one month was recorded for all patients.

RESULTS

Coated-platelet levels (mean ± SD) were significantly higher in SAH patients compared to controls (41.8 ± 11.4% vs. 30.7 ± 12.2%, p<0.0001). Among all patients, mortality at 1 month was 20% (8 deaths). Patients were analyzed according to tertiles of coated-platelet levels (split at <36.7%, 36.7-46.2%, >46.2%). The 1-month mortality differed significantly between the coated-platelet tertiles (p=0.01) with 46% mortality (6/13) among patients in the lowest tertile (lowest levels) compared to 14.3% (2/14) among those in the middle tertile and 0% in the highest tertile.

CONCLUSIONS

Coated-platelet levels are higher in SAH patients compared to controls. However, lower coated-platelet levels are associated with increased 1-month mortality in SAH patients, a finding compatible with prior observations of an inverse relationship between coated-platelet levels and bleed volume in ICH. The current data support the role played by these prothrombotic platelets in thrombosis or hemorrhage and suggest a potential place for coated-platelet levels in predicting prognosis after SAH.

Association between NFKB1 -94 insertion/deletion ATTG polymorphism and risk of intracranial aneurysm

OBJECTIVE

Growing evidence indicates that vascular inflammation is a common phenomenon in the pathogenesis of intracranial aneurysms (IAs). Nuclear factor kappa B is a key molecule that is involved in the vascular inflammation of IA. We hypothesized that an insertion/deletion (ins/del) ATTG polymorphism located between two putative key promoter regulatory elements in the NFKB1 gene may be related to the risk of IA.

METHODS

We performed a case-control study, including 164 patients with IA and 525 healthy controls in a Chinese population using a polymerase chain reaction-polyacrylamide gel electrophoresis assay.

RESULTS

A significantly decreased risk of IA was observed in the ATTG1/ATTG2 and ATTG2/ATTG2 genotypes compared with the ATTG1/ATTG1 genotype (ATTG1/ATTG2 vs. ATTG1/ATTG1: odds ratio [OR]=0.58, 95% confidence interval [95% CI]=0.39-0.87, p=0.007; ATTG2/ATTG2 vs. ATTG1/ATTG1: OR=0.12, 95% CI=0.06-0.23, p<0.001), and also the ATTG2 allele (ATTG2 vs. ATTG1: OR=0.41, 95% CI=0.32-0.54, p<0.001).

CONCLUSION

These findings suggest that the NFKB1 -94ins/del ATTG polymorphism may contribute to the risk of IA.

"Sit back, observe, and wait." Or is there a pharmacologic preventive treatment for cerebral aneurysms?

Intracranial aneurysms (IA) are a relatively frequent vascular abnormality. The prevailing opinion is that cerebral aneurysmal disease is related to hemodynamic and genetic factors, associated with structural weakness in the arterial wall which was acquired by a specific, often unknown, event. Possibly the trigger moment of aneurysm formation may depend on the dynamic arterial growth, which is closely related to aging/atherosclerosis. In most individuals, an endovascular/microsurgical approach is possible in order to obliterate the IA. However, in a number of patients with an unruptured IA (UIA), the neurosurgeon's decision is to just "sit back, observe, and wait", based on the favorable natural history of some of the UIAs. Furthermore, some individuals need to be kept under close observation since they have a higher chance of developing IA, especially those with at least two affected first-degree relatives with an IA, subjects with polycystic kidney disease, and patients who have undergone an aneurysm intervention. In these examples prophylactic strategies should be adopted, if it is at all possible. The main question is deciding the best option of clinical treatment for these cases, when surgical approach is contraindicated, or for those subjects who are more prone to develop an IA. In the present article, we hypothetically suggest a pharmacologic form of treatment with statins, beta-adrenergic blocker agents, and/or angiotensin-converting-enzyme inhibitor/angiotensin II receptor blockers to inhibit or slow down IA formation, taking into consideration some pathophysiological aspects related to aneurysmal development, such as: hemodynamic stress, arterial wall inflammation, nitric oxide formation, and atheromatous disease.

Guidelines for the management of aneurysmal subarachnoid hemorrhage: a guideline for healthcare professionals from the American Heart Association/american Stroke Association

PURPOSE

The aim of this guideline is to present current and comprehensive recommendations for the diagnosis and treatment of aneurysmal subarachnoid hemorrhage (aSAH).

METHODS

A formal literature search of MEDLINE (November 1, 2006, through May 1, 2010) was performed. Data were synthesized with the use of evidence tables. Writing group members met by teleconference to discuss data-derived recommendations. The American Heart Association Stroke Council's Levels of Evidence grading algorithm was used to grade each recommendation. The guideline draft was reviewed by 7 expert peer reviewers and by the members of the Stroke Council Leadership and Manuscript Oversight Committees. It is intended that this guideline be fully updated every 3 years.

RESULTS

Evidence-based guidelines are presented for the care of patients presenting with aSAH. The focus of the guideline was subdivided into incidence, risk factors, prevention, natural history and outcome, diagnosis, prevention of rebleeding, surgical and endovascular repair of ruptured aneurysms, systems of care, anesthetic management during repair, management of vasospasm and delayed cerebral ischemia, management of hydrocephalus, management of seizures, and management of medical complications.

CONCLUSIONS

aSAH is a serious medical condition in which outcome can be dramatically impacted by early, aggressive, expert care. The guidelines offer a framework for goal-directed treatment of the patient with aSAH.

PGE(2) -EP(2) signalling in endothelium is activated by haemodynamic stress and induces cerebral aneurysm through an amplifying loop via NF-κB

BACKGROUND AND PURPOSE

Cerebral aneurysm is a frequent cerebrovascular event and a major cause of fatal subarachnoid haemorrhage, but there is no medical treatment for this condition. Haemodynamic stress and, recently, chronic inflammation have been proposed as major causes of cerebral aneurysm. Nevertheless, links between haemodynamic stress and chronic inflammation remain ill-defined, and to clarify such links, we evaluated the effects of prostaglandin E(2) (PGE(2) ), a mediator of inflammation, on the formation of cerebral aneurysms.

EXPERIMENTAL APPROACH

Expression of COX and prostaglandin E synthase (PGES) and PGE receptors were examined in human and rodent cerebral aneurysm. The incidence, size and inflammation of cerebral aneurysms were evaluated in rats treated with COX-2 inhibitors and mice lacking each prostaglandin receptor. Effects of shear stress and PGE receptor signalling on expression of pro-inflammatory molecules were studied in primary cultures of human endothelial cells (ECs).

KEY RESULTS

COX-2, microsomal PGES-1 and prostaglandin E receptor 2 (EP(2) ) were induced in ECs in the walls of cerebral aneurysms. Shear stress applied to primary ECs induced COX-2 and EP(2) . Inhibition or loss of COX-2 or EP(2) in vivo attenuated each other's expression, suppressed nuclear factor κB (NF-κB)-mediated chronic inflammation and reduced incidence of cerebral aneurysm. EP(2) stimulation in primary ECs induced NF-κB activation and expression of the chemokine (C-C motif) ligand 2, essential for cerebral aneurysm.

CONCLUSIONS AND IMPLICATIONS

These results suggest that shear stress activated PGE(2) -EP(2) pathway in ECs and amplified chronic inflammation via NF-κB. We propose EP(2) as a therapeutic target in cerebral aneurysm.

Statins promote the growth of experimentally induced cerebral aneurysms in estrogen-deficient rats

BACKGROUND AND PURPOSE

The pathogenesis of cerebral aneurysms is linked to inflammation, degradation of the extracellular matrix, and vascular wall apoptosis. Statins exert pleiotropic effects on the vasculature, independent of their cholesterol-lowering properties. To explore the detailed pathogenesis of cerebral aneurysms, we examined their progression in a rat model and studied whether statins prevent their initiation and growth.

METHODS

Cerebral aneurysms were induced in female rats subjected to hypertension, increased hemodynamic stress, and estrogen deficiency. The development of aneurysm was assessed morphologically on corrosion casts. The effects of pravastatin (5, 25, or 50 mg/kg per day) and of simvastatin (5 mg/kg per day) on their aneurysms were studied. Human brain endothelial cells were also used to determine the effects of pravastatin.

RESULTS

Pravastatin (5 mg/kg per day) reduced endothelial damage and inhibited aneurysm formation; there was an association with increased endothelial nitric oxide synthase (eNOS) levels and a decrease in human brain endothelial cell adhesion molecules. Unexpectedly, 25 mg/kg per day and 50 mg/kg per day pravastatin and 5 mg/kg per day simvastatin promoted aneurysmal growth, and high-dose pravastatin induced aneurysmal rupture. The deleterious effects exerted by these statins were associated with an increase in apoptotic caspase-3 levels and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive cells, suggesting that statins exert bidirectional effects.

CONCLUSIONS

Our results provide the first evidence that cerebral aneurysm growth is partly associated with apoptosis and issue a warning that statins exert bidirectional effects on cerebral aneurysms. Additional intensive research is necessary to understand better their mechanisms and to identify patients in whom the administration of statins may elicit deleterious effects.

Cellular and molecular responses of the basilar terminus to hemodynamics during intracranial aneurysm initiation in a rabbit model

BACKGROUND/AIMS

Hemodynamics constitute a critical factor in the formation of intracranial aneurysms. However, little is known about how intracranial arteries respond to hemodynamic insult and how that response contributes to aneurysm formation. We examined early cellular responses at rabbit basilar termini exposed to hemodynamic insult that initiates aneurysmal remodeling.

METHODS

Flow in the basilar artery was increased by bilateral carotid artery ligation. After 2 and 5 days, basilar terminus tissue was examined by immunohistochemistry and quantitative PCR.

RESULTS

Within 2 days of flow increase, internal elastic lamina (IEL) was lost in the periapical region of the bifurcation, which experienced high wall shear stress and positive wall shear stress gradient. Overlying endothelium was still largely present in this region. IEL loss was associated with localized apoptosis and elevated expression of matrix metalloproteinases (MMPs) 2 and 9. A small number of inflammatory cells were sporadically scattered in the bifurcation adventitia and were not concentrated in regions of IEL loss and MMP elevation. Elevated MMP expression colocalized with smooth muscle α-actin in the media.

CONCLUSION

The initial vascular response to aneurysm-initiating hemodynamic insult includes localized matrix degradation and cell apoptosis. Such destructive remodeling arises from intrinsic mural cells, rather than through inflammatory cell infiltration.

The role of the renin—angiotensin system in the pathogenesis of intracranial aneurysms

Introduction: Recent work has begun to elucidate the pathogenesis of intracranial aneurysms (IA) and has shown that many genes are involved in the risk for this condition. There has also been increasing research interest in the renin—angiotensin system (RAS) in the brain and its involvement in a range of cardiovascular and neurological disorders. The possibility that the RAS is implicated in the pathogenesis of IA merits further investigation. The aim of this article is to review the literature on the pathogenesis of IA and the pathophysiological significance of the brain RAS, and to identify directions for research into their association.

Methods and results : A survey of the literature in these fields shows that although factors contributing to systemic hypertension predispose to IA, a large number of genes involved in endothelial cell adhesion, smooth muscle activity, extracellular matrix dynamics and the inflammatory and immune responses are also implicated. The brain RAS has a significant role in regulating blood pressure and in maintaining cerebrovascular autoregulation, but angiotensin II receptors are also involved in the maintenance of endothelial cell and vascular smooth muscle function and in the inflammatory response in the brain.

Conclusions: There is strong, albeit largely circumstantial, evidence in the literature for a relationship between the brain RAS and the formation of IA. Research on the association between polymorphisms in RAS-related genes and the incidence of unruptured and ruptured IA is indicated.

The development and the use of experimental animal models to study the underlying mechanisms of CA formation

Cerebral aneurysms (CAs) have a high prevalence and can cause a lethal subarachnoid hemorrhage. Currently, CAs can only be treated with invasive surgical procedures. To unravel the underlying mechanisms of CA formation and to develop new therapeutic drugs for CAs, animal models of CA have been established, modified, and analyzed. Experimental findings from these models have clarified some of the potential mechanisms of CA formation, especially the relationship between hemodynamic stress and chronic inflammation. Increased hemodynamic stress acting at the site of bifurcation of cerebral arteries triggers an inflammatory response mediated by various proinflammatory molecules in arterial walls, inducing pathological changes in the models similar to those observed in the walls of human CAs. Findings from animal studies have provided new insights into CA formation and may contribute to the development of new therapeutic drugs for CAs.