Inflammation and intracranial aneurysms

Classification models using circulating neutrophil transcripts can detect unruptured intracranial aneurysm

Background

Intracranial aneurysms (IAs) are dangerous because of their potential to rupture. We previously found significant RNA expression differences in circulating neutrophils between patients with and without unruptured IAs and trained machine learning models to predict presence of IA using 40 neutrophil transcriptomes. Here, we aim to develop a predictive model for unruptured IA using neutrophil transcriptomes from a larger population and more robust machine learning methods.

Methods

Neutrophil RNA extracted from the blood of 134 patients (55 with IA, 79 IA-free controls) was subjected to next-generation RNA sequencing. In a randomly-selected training cohort (n = 94), the Least Absolute Shrinkage and Selection Operator (LASSO) selected transcripts, from which we constructed prediction models via 4 well-established supervised machine-learning algorithms (K-Nearest Neighbors, Random Forest, and Support Vector Machines with Gaussian and cubic kernels). We tested the models in the remaining samples (n = 40) and assessed model performance by receiver-operating-characteristic (ROC) curves. Real-time quantitative polymerase chain reaction (RT-qPCR) of 9 IA-associated genes was used to verify gene expression in a subset of 49 neutrophil RNA samples. We also examined the potential influence of demographics and comorbidities on model prediction.

Results

Feature selection using LASSO in the training cohort identified 37 IA-associated transcripts. Models trained using these transcripts had a maximum accuracy of 90% in the testing cohort. The testing performance across all methods had an average area under ROC curve (AUC) = 0.97, an improvement over our previous models. The Random Forest model performed best across both training and testing cohorts. RT-qPCR confirmed expression differences in 7 of 9 genes tested. Gene ontology and IPA network analyses performed on the 37 model genes reflected dysregulated inflammation, cell signaling, and apoptosis processes. In our data, demographics and comorbidities did not affect model performance.

Conclusions

We improved upon our previous IA prediction models based on circulating neutrophil transcriptomes by increasing sample size and by implementing LASSO and more robust machine learning methods. Future studies are needed to validate these models in larger cohorts and further investigate effect of covariates.

Role of matrix metalloproteinases in the pathogenesis of intracranial aneurysms

Intracranial aneurysms (IAs) are a result of complex interactions between biochemical and mechanical forces and can lead to significant morbidity if they rupture and cause subarachnoid hemorrhage. This review explores the role of matrix metalloproteinases (MMPs) in the pathogenesis and progression of IAs. In addition to providing a review of the normal function of MMPs, it is intended to explore the interaction between inflammation and abnormal blood flow and the resultant pathological vascular remodeling processes seen in the development and rupture of IAs. Also reviewed is the potential for the use of MMPs as a diagnostic tool for assessment of aneurysm development and progression.

Is smoking a risk factor for bleeding in adult men with cerebral arteriovenous malformations? A single-center regression study from China

OBJECTIVE

To assess whether smoking increases the risk of bleeding in patients with cerebral arteriovenous malformations (CAVM).

MATERIAL AND METHODS

According to our research plan, 385 CAVM patients admitted to Beijing Tiantan Hospital from December 2015 to January 2018 were included in this study, including 210 bleeding patients and 175 non-bleeding patients. We divided patients into three subgroups of current smokers, ex-smokers (those who quit smoking for one year or more) and non-smokers. The relationship between smoking and the risk of CAVM rupture was assessed by univariate and multivariate regression analysis.

RESULTS

Multivariate regression analysis showed that there was a statistically significant difference between current smoker and non-smoker (OR = 1.87, p = 0.019). Among the covariates of the multivariate regression analysis, the location, combined with blood flow-related intracranial aneurysms and size were related to the risk of CAVM bleeding.

CONCLUSION

Current smoking may increase the risk of CAVM bleeding; however, there was no significant correlation between ex-smoking and CAVM bleeding.

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.

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.

Novel in vivo Assessment of Unruptured Intracranial Aneurysm Inflammatory Factors

Background and Purpose: The growth and eventual rupture of intracranial aneurysms may be due to an underlying inflammatory process as evidenced by pathological examination of aneurysm walls. We hypothesize that unruptured aneurysms have an increased inflammatory milieu within their lumen in comparison to the rest of the cerebral arterial vascular system.

Methods: Blood was sampled from unruptured aneurysms in patients presenting for aneurysm coil embolization and C3 and C4 complement values from this serum were compared with complement values in the parent artery.

Results: Ten patients were enrolled over 32 months with a mean aneurysm size of 9.1 mm. Compared to control samples drawn from peripheral circulation, there were significant decreases of both C3 (p = 0.0003) and C4 (p = 0.0063) levels in aneurysmal blood samples.

Conclusions: A state of decreased complement indicative of classic pathway activation was found in all tested aneurysms, thus providing evidence of an ongoing process of complement activation in the blood of live, unruptured aneurysm sacs.

Potential Therapeutic Strategies for Intracranial Aneurysms Targeting Aneurysm Pathogenesis

Subarachnoid hemorrhage resulting from intracranial aneurysms (IAs) is associated with high rates of morbidity and mortality. Although trigger mechanisms in the pathogenesis of IAs have not been fully elucidated, accumulating evidence has demonstrated that inflammation acts as a critical contributor to aneurysm pathogenesis. IAs is initiated by disruption and dysfunction of endothelial cells (ECs) caused by abnormal wall shear stress (WSS). Subsequently, vascular inflammation can trigger a series of biochemical reactions resulting in vascular smooth muscle cell (VSMC) apoptosis and migration, accompanied by inflammatory cell infiltration, secretion of various cytokines, and inflammatory factors. These changes result in degradation of vascular wall, leading to the progression and eventual rupture of IAs. Increasing our knowledge of the pathogenesis of these lesions will offer physicians new options for prevention and treatment. In this study, we review aneurysmal pathogenesis to seek for safe, effective, and non-invasive therapeutic strategies.

Flow Diversion for Treatment of Partially Thrombosed Aneurysms: A Multicenter Cohort

BACKGROUND

Partially thrombosed intracranial aneurysms (PTIA) represent a unique subset of intracranial aneurysms with an ill-defined natural history, posing challenges to standard management strategies. This study aims to assess the efficacy of flow diversion in the treatment of this pathology.

METHODS

A retrospective review of patients with flow-diverted PTIA at 6 cerebrovascular centers was performed. Clinical and radiographic data were collected from the medical records, with the primary outcome of aneurysmal occlusion and secondary outcomes of clinical status and complications.

RESULTS

Fifty patients with 51 PTIA treated with flow diversion were included. Median age was 56.5 years. Thirty-three (64.7%) aneurysms were saccular and 16 (31.4%) were fusiform/dolichoectatic. The most common location was the internal carotid artery (54.9%) followed by the vertebral and basilar arteries (17.7% and 17.7%, respectively). Last imaging follow-up was performed at a median of 25.1 (interquartile range, 12.8-43) months. Complete occlusion at last radiographic follow-up was achieved in 37 (77.1%) aneurysms. Pretreatment aneurysm thrombosis of >50% was associated with a significantly lower rate of complete aneurysm occlusion (58.8 vs. 87.1%, P = 0.026) with a trend toward better functional outcome (modified Rankin scale <2) at last follow-up in patients with <50% pretreatment aneurysm thrombosis (96.8 vs. 82.4; P = 0.08). Ischemic complications occurred in 5 (9.8%) patients, producing symptoms in 4 (7.8%) and resultant mortality in 2 (4.2%) patients.

CONCLUSIONS

Flow diversion treatment of PTIA has adequate efficacy along with a reasonable safety profile. Aneurysms harboring large amounts of pretreatment thrombus were associated with lower rates of complete occlusion.

Characteristics of circulating monocytes at baseline and after activation in patients with intracranial aneurysm

Intracranial aneurysm (IA) is a bulging of blood vessels around the brain that is often asymptomatic but may cause severe complications and death if ruptured. Macrophage-mediated immune responses can contribute to the development of IA. During homeostasis and inflammation, circulating monocytes can infiltrate the vasculature, where they develop into macrophages, and modulate immune responses. Based on the expression of CD14 and CD16, total circulating monocytes can be distinguished into three main subsets, including the CD14⁺CD16^- classical monocytes, the CD14⁺CD16⁺ intermediate monocytes, and the CD14^loCD16⁺⁺ non-classical monocytes. In this study, we found that frequencies of CD14⁺CD16^- classical monocytes were significantly lower in IA patients than in healthy controls, while the frequencies of CD14⁺CD16⁺ intermediate monocytes and CD14^loCD16⁺⁺ non-classical monocytes were significantly higher in IA patients than in healthy controls. The frequencies of CD14⁺CD16⁺ intermediate monocytes were further elevated in IA-ruptured patients compared to those in IA-unruptured patients. Compared to classical monocytes, intermediate monocytes and non-classical monocytes presented higher TNF-α and IL-1β expression. When cocultured with autologous naive CD4 T cells, intermediate and non-classical monocytes preferentially promoted the expression of TBX21 and RORC over the expression of FOXP3 in CD4 T cells. Inhibition of TNF-α and IL-1β slightly reduced TBX21 expression and markedly reduced RORC expression, and at the same time significantly increased FOXP3 expression in CD4 T cells. Overall, this study demonstrated that the monocytes were dysregulated in IA patients in a manner that favored the development of proinflammatory responses.

Inflammation promotes progression of thrombi in intracranial thrombotic aneurysms

Advances in the understanding of the pathogenesis of arteriosclerosis, abdominal aorta aneurysms and dissections, and carotid artery plaques have focused on chronic inflammation. In this study, we report that inflammatory changes of thrombi contribute to the enlargement and growth of giant intracranial thrombotic aneurysms. Surgical and postmortem samples were collected from 12 cases of large or giant intracranial thrombotic aneurysms diagnosed via pathological investigations. Degeneration of the aneurysmal wall and the infiltration of inflammatory cells in the thrombi were assessed. The number of blood cells and immunohistochemical stain-positive cells was enumerated, and the inflammation and neovascularization in the thrombi were assessed. In all cases, the appearance of inflammatory cells (CD68⁺ cells, CD206⁺ cells, lymphocytes, and neutrophils) was apparent in the thrombi. The number of CD34⁺ cells was moderately correlated with the number of CD68⁺ cells, and CD34⁺ cells significantly and strongly correlated with the number of CD206⁺ cells. Based on the number of neutrophils per CD68⁺ cells, we classified the cases into 2 groups: a macrophage inflammation-dominant group and a neutrophilic inflammation-dominant group. The neutrophilic inflammation-dominant group had significantly more cases with previous treatments and neurological symptoms due to mass effect than the macrophage inflammation-dominant group. Chronic inflammation due to macrophages in thrombi is a fundamental mechanism in the enlargement of an intracranial thrombotic aneurysm, and neutrophilic inflammation can accelerate this process. Microvascularization in thrombi is linked to inflammation and might promote thickening of the intima and repeated intimal microbleeds.

Epigenetic landscapes suggest that genetic risk for intracranial aneurysm operates on the endothelium

BACKGROUND

Genetics play an important role in intracranial aneurysm (IA) pathophysiology. Genome-wide association studies have identified several single nucleotide polymorphisms (SNPs) that are linked to IA but how they affect disease pathobiology remains poorly understood. We used Encyclopedia of DNA Elements (ENCODE) data to investigate the epigenetic landscapes surrounding genetic risk loci to determine if IA-associated SNPs affect functional elements that regulate gene expression and if those SNPs are most likely to impact a specific type of cells.

METHODS

We mapped 16 highly significant IA-associated SNPs to linkage disequilibrium (LD) blocks within the human genome. Within these regions, we examined the presence of H3K4me1 and H3K27ac histone marks and CCCTC-binding factor (CTCF) and transcription-factor binding sites using chromatin immunoprecipitation-sequencing (ChIP-Seq) data. This analysis was conducted in several cell types relevant to endothelial (human umbilical vein endothelial cells [HUVECs]) and inflammatory (monocytes, neutrophils, and peripheral blood mononuclear cells [PBMCs]) biology. Gene ontology analysis was performed on genes within extended IA-risk regions to understand which biological processes could be affected by IA-risk SNPs. We also evaluated recently published data that showed differential methylation and differential ribonucleic acid (RNA) expression in IA to investigate the correlation between differentially regulated elements and the IA-risk LD blocks.

RESULTS

The IA-associated LD blocks were statistically significantly enriched for H3K4me1 and/or H3K27ac marks (markers of enhancer function) in endothelial cells but not in immune cells. The IA-associated LD blocks also contained more binding sites for CTCF in endothelial cells than monocytes, although not statistically significant. Differentially methylated regions of DNA identified in IA tissue were also present in several IA-risk LD blocks, suggesting SNPs could affect this epigenetic machinery. Gene ontology analysis supports that genes affected by IA-risk SNPs are associated with extracellular matrix reorganization and endopeptidase activity.

CONCLUSION

These findings suggest that known genetic alterations linked to IA risk act on endothelial cell function. These alterations do not correlate with IA-associated gene expression signatures of circulating blood cells, which suggests that such signatures are a secondary response reflecting the presence of IA rather than indicating risk for IA.

Roles of Nicotine in the Development of Intracranial Aneurysm Rupture

Background and Purpose- Tobacco cigarette smoking is considered to be a strong risk factor for intracranial aneurysmal rupture. Nicotine is a major biologically active constituent of tobacco products. Nicotine's interactions with vascular cell nicotinic acetylcholine receptors containing α7 subunits (α7*-nAChR) are thought to promote local inflammation and sustained angiogenesis. In this study, using a mouse intracranial aneurysm model, we assessed potential contributions of nicotine exposure and activation of α7*-nAChR to the development of aneurysmal rupture. Methods- Intracranial aneurysms were induced by a combination of deoxycorticosterone-salt induced hypertension and a single-dose elastase injection into cerebrospinal fluid in mice. Results- Exposure to nicotine or an α7*-nAChR-selective agonist significantly increased aneurysm rupture rate. Coexposure to an α7*-nAChR antagonist abolished nicotine's deleterious effect. In addition, nicotine's promotion of aneurysm rupture was absent in smooth muscle cell-specific α7*-nAChR subunit knockout mice but not in mice lacking α7*-nAChR on endothelial cells or macrophages. Nicotine treatment increased the mRNA levels of vascular endothelial growth factor, platelet-derived growth factor-B, and inflammatory cytokines. α7*-nAChR antagonist reversed nicotine-induced upregulation of these growth factors and cytokines. Conclusions- Our findings indicate that nicotine exposure promotes aneurysmal rupture through actions on vascular smooth muscle cell α7*-nAChR.

Vessel wall imaging in intracranial aneurysms

High-resolution vessel wall imaging (HR-VWI) is becoming a useful tool in the characterization and identification of unstable unruptured brain aneurysms. However, it has not been validated for clinical use. The current evidence on HR-VWI techniques for characterization of brain aneurysms is described in this review. Specific imaging approaches such as aneurysm wall contrast enhancement, MRI-quantitative susceptibility mapping, and 7T MRI are described in detail.

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.

Myeloperoxidase Associates With Degenerative Remodeling and Rupture of the Saccular Intracranial Aneurysm Wall

Rupture of a saccular intracranial aneurysm (sIA) is often fatal. Thus, early detection of rupture-prone sIAs is vital. Myeloperoxidase (MPO), derived mainly from neutrophils, associates with sIA rupture, and therefore its role in sIA pathogenesis warrants further studies. We analyzed MPO and its association with other histological markers in 36 (16 unruptured and 20 ruptured) sIA samples by immunohistochemistry. MPO was present in all studied sIAs, and its expression associated with wall inflammatory cell infiltrations (r = 0.50, 0.63, and 0.75, all p ≤ 0.002), degenerative remodeling (p = 0.002) and rupture (p = 0.003). MPO associated strongly with the presence of organized luminal thrombi (p < 0.001), which also stained positive for MPO. Polymorphonuclear MPO+ cells were detected in the sIA walls, indicating neutrophils as MPO-source. MPO correlated strongly with accumulation of oxidized lipids (r = 0.67, p < 0.001) and loss of smooth muscle cells (r = -0.68, p < 0.001), suggesting that MPO is a relevant source of oxidative stress leading to cell death in the sIA wall. Furthermore, MPO associated with erythrocyte fragmentation (r = 0.74, p < 0.001) and iron deposition (p = 0.041), 2 outcomes known to amplify MPO-dependent oxidative stress. Taken together, these results suggest that MPO associates with degenerative remodeling predisposing to sIA wall rupture and may serve as a biomarker of a rupture-prone sIA wall.

Histological analysis of infiltrating macrophages in the cerebral aneurysm walls

A series of recent evidences suggested activated macrophages have broadly two distinct forms that possess opposite functions for the process of inflammation: classically activated macrophages (M1/kill macrophages) and alternatively activated macrophages (M2/repair macrophages) according to their functions and expression markers. To elucidate what roles those two phenotypes of macrophages play in the evolution of cerebral aneurysm, the presence of macrophages inside the aneurysm walls was assessed with an immunohistochemical approach. The portions of the aneurysm domes deflated after neck clipping were utilized for the further histological examinations, including immunostainings with five antibodies to identify macrophage subpopulations. In this study, contrary to the previous reports, the following various ratios of subtypes were observed in the aneurysm walls: M1 > M2 (2 cases), M1 < M2 (2 cases), M1 = M2 (3 cases). While M1-like macrophages have been typically regarded as a main driver of the degenerating process, these surprisingly richer presences of M2-like macrophages in the aneurysm walls suggests that an unrecognized biological process might be in play in aneurysm development.

Analysis of Peripheral Blood Cells' Transcriptome in Patients With Subarachnoid Hemorrhage From Ruptured Aneurysm Reveals Potential Biomarkers

BACKGROUND

Subarachnoid hemorrhage (SAH) is an uncommon disease. Considering ruptured intracranial aneurysms as the main cause of this disease and only a minority of the intracranial aneurysms will rupture sooner or later, to understand the underlying pathology or a specific gene expression profile of an impending ruptured intracranial aneurysm is of great importance.

METHODS

The transcriptome in peripheral blood cells of patients with SAH from ruptured aneurysm was compared with that of control patients suffering from headaches. The microarray dataset GSE36791 comprised 43 patients with SAH from ruptured aneurysms and 18 control patients. Differential expression analysis was performed with the R language packages to identify differentially expressed genes (DEGs). Gene Ontology enrichment analysis and Kyoto Encyclopedia of Genes and Genomes pathway database analysis were performed to identify significantly altered biological functions and pathways, respectively. The protein-protein interaction networks were constructed with information from the STRING database.

RESULTS

A total of 528 DEGs were identified, of which 311 were upregulated and 217 downregulated. Clustering analysis confirmed that these genes can distinguish ruptured aneurysm SAH patients from the control patients. The DEGs were mainly enriched for immune/inflammation response and related pathways. Among the DEGs, 8 genes (ARG1, MAPK14, RPS2, SPI1, FYN, CEBPB, FLOT1, and CD4) were identified as the key regulators in the Protein-Protein Interaction network. MAPK14, CEBPB, FLOT1, and CD4 might be potential biomarkers of SAH.

CONCLUSION

This study identified a range of DEGs SAH patients with ruptured aneurysms, which may enhance our current knowledge on this disease and may provide potential biomarkers of this disease.

Intracranial Aneurysm as a Macrophage-mediated Inflammatory Disease

Subarachnoid hemorrhage (SAH) is mainly attributable to the rupture of intracranial aneurysms (IAs). Although the outcome of SAH is considerably poor in spite of the recent intensive medical care, mechanisms regulating the progression of IAs or triggering rupture remain to be clarified, making the development of effective preemptive medicine to prevent SAH difficult. However, a series of recent studies have been expanding our understanding of the pathogenesis of IAs. These studies have suggested the crucial role of macrophage-mediated chronic inflammation in the pathogenesis of IAs. In histopathological analyses of IA lesions in humans and induced in animal models, the number of macrophages infiltrating in lesions is positively correlated with enlargement or rupture of IAs. In animal models, a genetic deletion or an inhibition of monocyte chemotactic protein-1, a major chemoattractant for macrophages, or a pharmacological depletion of macrophages consistently suppresses the development and progression of IAs. Furthermore, a macrophage-specific deletion of Ptger2 (gene for prostaglandin E receptor subtype 2) or a macrophage-specific expression of a mutated form of IκBα which inhibits nuclear translocation of nuclear factor κB significantly suppress the development of IAs, supporting the role of macrophages and the inflammatory signaling functioning there in the pathogenesis of IAs. The development of drug therapies suppressing macrophage-mediated inflammatory responses in situ can thus be a potential strategy in the pre-emptive medicine targeting SAH. In this manuscript, we summarize the experimental evidences about the pathogenesis of IAs focused on inflammatory responses and propose the definition of IAs as a macrophage-mediated inflammatory disease.

Prostaglandin-cytokine crosstalk in chronic inflammation

Chronic inflammation underlies various debilitating disorders including autoimmune, neurodegenerative, vascular and metabolic diseases as well as cancer, where aberrant activation of the innate and acquired immune systems is frequently seen. Since non-steroidal anti-inflammatory drugs exert their effects by inhibiting COX and suppressing PG biosynthesis, PGs have been traditionally thought to function mostly as mediators of acute inflammation. However, an inducible COX isoform, COX-2, is often highly expressed in tissues of the chronic disorders, suggesting an as yet unidentified role of PGs in chronic inflammation. Recent studies have shown that in addition to their short-lived actions in acute inflammation, PGs crosstalk with cytokines and amplify the cytokine actions on various types of inflammatory cells and drive pathogenic conversion of these cells by critically regulating their gene expression. One mode of such PG-mediated amplification is to induce the expression of relevant cytokine receptors, which is typically observed in Th1 cell differentiation and Th17 cell expansion, events leading to chronic immune inflammation. Another mode of amplification is cooperation of PGs with cytokines at the transcription level. Typically, PGs and cytokines synergistically activate NF-κB to induce the expression of inflammation-related genes, one being COX-2 itself, which makes PG-mediated positive feedback loops. This signalling consequently enhances the expression of various NF-κB-induced genes including chemokines to macrophages and neutrophils, which enables sustained infiltration of these cells and further amplifies chronic inflammation. In addition, PGs are also involved in tissue remodelling such as fibrosis and angiogenesis. In this article, we review these findings and discuss their relevance to human diseases.

Biomarkers from circulating neutrophil transcriptomes have potential to detect unruptured intracranial aneurysms

BACKGROUND

Intracranial aneurysms (IAs) are dangerous because of their potential to rupture and cause deadly subarachnoid hemorrhages. Previously, we found significant RNA expression differences in circulating neutrophils between patients with unruptured IAs and aneurysm-free controls. Searching for circulating biomarkers for unruptured IAs, we tested the feasibility of developing classification algorithms that use neutrophil RNA expression levels from blood samples to predict the presence of an IA.

METHODS

Neutrophil RNA extracted from blood samples from 40 patients (20 with angiography-confirmed unruptured IA, 20 angiography-confirmed IA-free controls) was subjected to next-generation RNA sequencing to obtain neutrophil transcriptomes. In a randomly-selected training cohort of 30 of the 40 samples (15 with IA, 15 controls), we performed differential expression analysis. Significantly differentially expressed transcripts (false discovery rate < 0.05, fold change ≥ 1.5) were used to construct prediction models for IA using four well-known supervised machine-learning approaches (diagonal linear discriminant analysis, cosine nearest neighbors, nearest shrunken centroids, and support vector machines). These models were tested in a testing cohort of the remaining 10 neutrophil samples from the 40 patients (5 with IA, 5 controls), and model performance was assessed by receiver-operating-characteristic (ROC) curves. Real-time quantitative polymerase chain reaction (PCR) was used to corroborate expression differences of a subset of model transcripts in neutrophil samples from a new, separate validation cohort of 10 patients (5 with IA, 5 controls).

RESULTS

The training cohort yielded 26 highly significantly differentially expressed neutrophil transcripts. Models using these transcripts identified IA patients in the testing cohort with accuracy ranging from 0.60 to 0.90. The best performing model was the diagonal linear discriminant analysis classifier (area under the ROC curve = 0.80 and accuracy = 0.90). Six of seven differentially expressed genes we tested were confirmed by quantitative PCR using isolated neutrophils from the separate validation cohort.

CONCLUSIONS

Our findings demonstrate the potential of machine-learning methods to classify IA cases and create predictive models for unruptured IAs using circulating neutrophil transcriptome data. Future studies are needed to replicate these findings in larger cohorts.

Antithrombotic therapy and intracranial bleeding in subjects with sporadic brain arteriovenous malformations: preliminary results from a retrospective study

Whether antithrombotic treatment is safe and/or affects the risk of intracranial bleeding in subjects with sporadic brain arteriovenous malformations (AVMs) is unknown. We conducted a retrospective analysis on the use of antithrombotics among patients affected by brain AVMs in follow-up at our institution. Attention was paid to the type of antithrombotic drug (either antiplatelets or anticoagulants), current or past use, dosage, and duration of treatment. Several clinical and angioarchitectural features of brain AVMs were also taken into consideration. The association between the use of antithrombotics and haemorrhagic onset was analyzed. A total of 77 patients were included in this study. Among them, ten patients were taking antithrombotic drugs at the time of AVM diagnosis. The rate of haemorrhagic onset was not significantly different between subjects who were and were not taking antithrombotic drugs (40 vs 55.2%, p = ns). Among the many clinical and angioarchitectural features analyzed, the only parameter that showed a statistically significant association with haemorrhagic onset was the size of the nidus. Patients who took antithrombotic treatments after being diagnosed with a brain AVM did not show an increased rate of intracranial haemorrhage over time considering a mean follow-up 4 years. In our study, antithrombotic treatment was not associated with increased intracranial bleeding among subjects with brain AVMs. In the presence of a strong clinical indication, antiplatelet and anticoagulant medications should not be denied a priori to patients with brain AVMs. Studies on larger populations are necessary to confirm these data.

Dilating Vascular Diseases: Pathophysiology and Clinical Aspects

Atherosclerotic disease of the vessels is a significant problem affecting mortality and morbidity all over the world. However, dilatation of the vessels either in the arterial system or in the venous territory is another vessel disease. Varicocele, pelvic, and peripheral varicose veins and hemorrhoids are aneurysms of the venous vascular regions and have been defined as dilating venous disease, recently. Coronary artery ectasia, intracranial aneurysm, and abdominal aortic aneurysm are examples of arterial dilating vascular diseases. Mostly, they have been defined as variants of atherosclerosis. Although there are some similarities in terms of pathogenesis, they are distinct from atherosclerotic disease of the vessels. In addition, pathophysiological and histological similarities and clinical coexistence of these diseases have been demonstrated both in the arterial and in the venous system. This situation underlies the thought that dilatation of the vessels in any vascular territory should be considered as a systemic vessel wall disease rather than being a local disease of any vessel. These patients should be evaluated for other dilating vascular diseases in a systematic manner.

The role of inflammation and potential use of sex steroids in intracranial aneurysms and subarachnoid hemorrhage

Background

Aneurysmal subarachnoid hemorrhage (aSAH) continues to be a devastating neurological condition with a high risk of associated morbidity and mortality. Inflammation has been shown to increase the risk of complications associated with aSAH such as vasospasm and brain injury in animal models and humans. The goal of this review is to discuss the inflammatory mechanisms of aneurysm formation, rupture and vasospasm and explore the role of sex hormones in the inflammatory response to aSAH.

Methods

A literature review was performed using PubMed using the following search terms: "intracranial aneurysm," "cerebral aneurysm," "dihydroepiandrosterone sulfate" "estrogen," "hormone replacement therapy," "inflammation," "oral contraceptive," "progesterone," "sex steroids," "sex hormones" "subarachnoid hemorrhage," "testosterone." Only studies published in English language were included in the review.

Results

Studies have shown that administration of sex hormones such as progesterone and estrogen at early stages in the inflammatory cascade can lower the risk and magnitude of subsequent complications. The exact mechanism by which these hormones act on the brain, as well as their role in the inflammatory cascade is not fully understood. Moreover, conflicting results have been published on the effect of hormone replacement therapy in humans. This review will scrutinize the variations in these studies to provide a more detailed understanding of sex hormones as potential therapeutic agents for intracranial aneurysms and aSAH.

Conclusion

Inflammation may play a role in the pathogenesis of intracranial aneurysm formation and subarachnoid hemorrhage, and administration of sex hormones as anti-inflammatory agents has been associated with improved functional outcome in experimental models. Further studies are needed to determine the therapeutic role of these hormones in the intracranial aneurysms and aSAH.

Inflammatory changes in the aneurysm wall: a review

Rupture of a saccular intracranial artery aneurysm (IA) causes subarachnoid hemorrhage, a significant cause of stroke and death. The current treatment options, endovascular coiling and clipping, are invasive and somewhat risky. Since only some IAs rupture, those IAs at risk for rupture should be identified. However, to improve the imaging of rupture-prone IAs and improve IA treatment, IA wall pathobiology requires more thorough knowledge. Chronic inflammation has become understood as an important phenomenon in IA wall pathobiology, featuring inflammatory cell infiltration as well as proliferative and fibrotic remodulatory responses. We review the literature on what is known about inflammation in the IA wall and also review the probable mechanisms of how inflammation would result in the degenerative changes that ultimately lead to IA wall rupture. We also discuss current options in imaging inflammation and how knowledge of inflammation in IA walls may improve IA treatment.

High Serum Level of Matrix Metalloproteinase-7 Is Associated With Increased Risk of Spontaneous Subarachnoid Hemorrhage

BACKGROUND AND PURPOSE

Increased degradation of the extracellular matrix in the arterial wall by matrix metalloproteinases (MMPs) may be an important mechanism in the pathogenesis of intracranial aneurysms and subarachnoid hemorrhage (SAH). MMP-2 and MMP-9 have been suggested to be involved in matrix degradation preceding SAH. We studied serum levels of MMP-1, -2, -3, -7, -9, -10, and -12 and the risk of incident SAH.

METHODS

A nested case-control study within the population-based cohort, Malmö Diet and Cancer study, was performed including incident cases of spontaneous SAH (n=79) and controls matched by age, sex, and follow-up time (n=232). MMPs were measured in serum from the baseline examination in 1991 to 1996. MMPs were compared between cases and controls, using conditional logistic regression adjusting for risk factors.

RESULTS

Baseline levels of MMP-7, MMP-10, and MMP-12 were significantly higher in incident SAH cases compared with controls. Odds ratios (95% confidence interval) for SAH per 1 SD increase of MMP-7, MMP-10, and MMP-12 were 1.78 (1.31-2.41), 1.45 (1.11-1.91), and 1.53 (1.17-2.01), respectively. After adjustment for SAH risk factors, MMP-7 was still significantly associated with SAH (odds ratio: 1.64; 95% confidence interval: 1.19-2.27; P=0.0026), whereas associations for MMP-10 and MMP-12 were attenuated and nonsignificant. We did not find any association between high serum levels of MMP-2 or MMP-9 and SAH risk.

CONCLUSIONS

High serum level of MMP-7 was associated with increased risk of incident spontaneous SAH, independently of the main risk factors for SAH. High serum levels of MMP-2 and MMP-9 did not predict SAH risk.

High-resolution Imaging of Myeloperoxidase Activity Sensors in Human Cerebrovascular Disease

Progress in clinical development of magnetic resonance imaging (MRI) substrate-sensors of enzymatic activity has been slow partly due to the lack of human efficacy data. We report here a strategy that may serve as a shortcut from bench to bedside. We tested ultra high-resolution 7T MRI (µMRI) of human surgical histology sections in a 3-year IRB approved, HIPAA compliant study of surgically clipped brain aneurysms. µMRI was used for assessing the efficacy of MRI substrate-sensors that detect myeloperoxidase activity in inflammation. The efficacy of Gd-5HT-DOTAGA, a novel myeloperoxidase (MPO) imaging agent synthesized by using a highly stable gadolinium (III) chelate was tested both in tissue-like phantoms and in human samples. After treating histology sections with paramagnetic MPO substrate-sensors we observed relaxation time shortening and MPO activity-dependent MR signal enhancement. An increase of normalized MR signal generated by ultra-short echo time MR sequences was corroborated by MPO activity visualization by using a fluorescent MPO substrate. The results of µMRI of MPO activity associated with aneurysmal pathology and immunohistochemistry demonstrated active involvement of neutrophils and neutrophil NETs as a result of pro-inflammatory signalling in the vascular wall and in the perivascular space of brain 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.

NF-κB-Mediated Inflammation in the Pathogenesis of Intracranial Aneurysm and Subarachnoid Hemorrhage. Does Autophagy Play a Role?

The rupture of saccular intracranial aneurysms (IA) is the commonest cause of non-traumatic subarachnoid hemorrhage (SAH)—the most serious form of stroke with a high mortality rate. Aneurysm walls are usually characterized by an active inflammatory response, and NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) has been identified as the main transcription factor regulating the induction of inflammation-related genes in IA lesions. This transcription factor has also been related to IA rupture and resulting SAH. We and others have shown that autophagy interacts with inflammation in many diseases, but there is no information of such interplay in IA. Moreover, NF-κB, which is a pivotal factor controlling inflammation, is regulated by autophagy-related proteins, and autophagy is regulated by NF-κB signaling. It was also shown that autophagy mediates the normal functioning of vessels, so its disturbance can be associated with vessel-related disorders. Early brain injury, delayed brain injury, and associated cerebral vasospasm are among the most serious consequences of IA rupture and are associated with impaired function of the autophagy⁻lysosomal system. Further studies on the role of the interplay between autophagy and NF-κB-mediated inflammation in IA can help to better understand IA pathogenesis and to identify IA patients with an increased SAH risk.

Current Perspectives in Imaging Modalities for the Assessment of Unruptured Intracranial Aneurysms: A Comparative Analysis and Review

BACKGROUND

Intracranial aneurysms (IAs) are pathologic dilatations of cerebral arteries. This systematic review summarizes and compares imaging techniques for assessing unruptured IAs (UIAs). This review also addresses their uses in different scopes of practice. Pathophysiologic mechanisms are reviewed to better understand the clinical usefulness of each imaging modality.

METHODS

A literature review was performed using PubMed with these search terms: "intracranial aneurysm," "cerebral aneurysm," "magnetic resonance angiography (MRA)," computed tomography angiography (CTA)," "catheter angiography," "digital subtraction angiography," "molecular imaging," "ferumoxytol," and "myeloperoxidase". Only studies in English were cited.

RESULTS

Since the development and improvement of noninvasive diagnostic imaging (computed tomography angiography and magnetic resonance angiography), many prospective studies and meta-analyses have compared these tests with gold standard digital subtraction angiography (DSA). Although computed tomography angiography and magnetic resonance angiography have lower detection rates for UIAs, they are vital in the treatment and follow-up of UIAs. The reduction in ionizing radiation and lack of endovascular instrumentation with these modalities provide benefits compared with DSA. Novel molecular imaging techniques to detect inflammation within the aneurysmal wall with the goal of stratifying risk based on level of inflammation are under investigation.

CONCLUSIONS

DSA remains the gold standard for preoperative planning and follow-up for patients with IA. Newer imaging modalities such as ferumoxytol-enhanced magnetic resonance imaging are emerging techniques that provide critical in vivo information about the inflammatory milieu within aneurysm walls. With further study, these techniques may provide aneurysm rupture risk and prediction models for individualized patient care.

A comparison of 4D flow MRI-derived wall shear stress with computational fluid dynamics methods for intracranial aneurysms and carotid bifurcations - A review

BACKGROUND

4D flow MRI is a relatively quick method for obtaining wall shear stress (WSS) in vivo, a hemodynamic parameter which has shown promise in risk stratification for rupture of cerebrovascular diseases such as intracranial aneurysms and atherosclerotic plaques. The accuracy of such measurements is still largely unknown.

OBJECTIVE

To quantify the accuracy of 4D flow MRI-derived wall shear stress values for intracranial aneurysms and carotid bifurcations.

METHOD

We performed a review of all original research articles which compared the magnitudes of WSS derived from 4D flow MRI with corresponding values derived from computational fluid dynamics (CFD) within both intracranial aneurysms and carotid bifurcations.

RESULT

For intracranial aneurysms and carotid bifurcations, 4D flow MRI-derived WSS estimations are generally lower in magnitude compared to WSS derived by CFD methods. These differences are more pronounced in regions of higher WSS. However, the relative distributions of WSS derived from both methods are reasonably similar.

CONCLUSION

Pooled analysis suggests that WSS magnitudes obtained by 4D flow MRI are underestimated, while the relative distribution is reasonably accurate, the latter being an important factor for determining the natural history of intracranial aneurysms and other cerebrovascular diseases. 4D flow MRI shows enormous potential in providing new risk stratification parameters which could have significant impact on individualized treatment decisions and improved patient outcomes.

Plasma miR-124 Is a Promising Candidate Biomarker for Human Intracerebral Hemorrhage Stroke

Stroke causes death or long-term disabilities and threatens the general health of the population worldwide. Recent studies have suggested that miRNAs are dysregulated and can be used as biomarkers for diagnosis and prognosis in stroke. The intracerebral hemorrhage (ICH) accounts for 15% of all the stroke cases. However, at present, little is known regarding the functions and clinical implications of miRNAs in ICH. In the present study, we established the collagenase-induced rat ICH model to mimic human ICH syndrome. We profiled the expression of 728 rat miRNAs at different time points in rat brain tissues and plasma post-ICH and identified a set human brain-enriched miRNAs that had changed expression level in the plasma of rat ICH. Among them, the expression levels of miR-124 displayed significantly synchronous alterations in rat plasma and brain tissue during ICH progression. They were significantly elevated at the acute injury phase (day 1 and 2), gradually decreased during the delayed recovery phase (day 7, 14 and 30), and finally restored to normal levels at late recovery phase (day 60). We further determined the plasma expression profile of miR-124 from human ICH patients. Similar to the pattern observed in rat ICH model, our results indicated that immediately after patients reached the hospital, the average plasma concentrations of miR-124 increased more than 100-fold in 24 h, then decreased gradually on day 2, 7, 14 and to near normal level on day 30. Taken together, these results strongly suggested that plasma concentration of miR-124 is a promising candidate biomarker for the early detection and predictive prognosis of human ICH.

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.

Identification of six polymorphisms as novel susceptibility loci for ischemic or hemorrhagic stroke by exome-wide association studies

In this study, we performed exome-wide association studies (EWASs) to identify genetic variants that confer susceptibility to ischemic stroke, intracerebral hemorrhage (ICH), or subarachnoid hemorrhage (SAH). EWAS for ischemic stroke was performed using 1,575 patients with this condition and 9,210 controls, and EWASs for ICH and SAH were performed using 673 patients with ICH, 265 patients with SAH and 9,158 controls. Analyses were performed with Illumina HumanExome-12 DNA Analysis BeadChip or Infinium Exome-24 BeadChip arrays. The relation of allele frequencies for 41,339 or 41,332 single nucleotide polymorphisms (SNPs) that passed quality control to ischemic or hemorrhagic stroke, respectively, was examined with Fisher's exact test. Based on Bonferroni's correction, a P-value of <1.21x10-6 was considered statistically significant. EWAS for ischemic stroke revealed that 77 SNPs were significantly associated with this condition. Multivariable logistic regression analysis with adjustment for age, sex and the prevalence of hypertension and diabetes mellitus revealed that 4 of these SNPs [rs3212335 of GABRB3 (P=0.0036; odds ratio, 1.29), rs147783135 of TMPRSS7 (P=0.0024; odds ratio, 0.37), rs2292661 of PDIA5 (P=0.0054; odds ratio, 0.35) and rs191885206 of CYP4F12 (P=0.0082; odds ratio, 2.60)] were related (P<0.01) to ischemic stroke. EWASs for ICH or SAH revealed that 48 and 12 SNPs, respectively, were significantly associated with these conditions. Multivariable logistic regression analysis with adjustment for age, sex and the prevalence of hypertension revealed that rs138533962 of STYK1 (P<1.0x10-23; odds ratio, 111.3) was significantly (P<2.60x10-4) associated with ICH and that rs117564807 of COL17A1 (P=0.0009; odds ratio, 2.23x10-8) was significantly (P<0.0010) associated with SAH. GABRB3, TMPRSS7, PDIA5 and CYP4F12 may thus be novel susceptibility loci for ischemic stroke, whereas STYK1 and COL17A1 may be such loci for ICH and SAH, respectively.

T cell function is dispensable for intracranial aneurysm formation and progression

Given the social importance of intracranial aneurysm as a major cause of a lethal subarachnoid hemorrhage, clarification of mechanisms underlying the pathogenesis of this disease is essential for improving poor prognosis once after rupture. Previous histopathological analyses of human aneurysm walls have revealed the presence of T cells in lesions suggesting involvement of this type of cell in the pathogenesis. However, it remains unclear whether T cell actively participates in intracranial aneurysm progression. To examine whether T cell is involved in aneurysm progression, intracranial aneurysm model of rat was used. In this model, aneurysm is induced by increase in hemodynamic force loaded on bifurcation site of intracranial arteries where aneurysms are developed. Deficiency in T cells and pharmacological inhibition of T cell function were applied to this model. CD3-positive T cells were present in human aneurysm walls, whose number was significantly larger compared with that in control arterial walls. Deficiency in T cells in rats and pharmacological inhibition of T cell function by oral administration of Cyclosporine A both failed to affect intracranial aneurysm progression, degenerative changes of arterial walls and macrophage infiltration in lesions. Although T cells are detectable in intracranial aneurysm walls, their function is dispensable for macrophage-mediated inflammation and degenerative changes in arterial walls, which presumably leads to intracranial aneurysm progression.

Effect of Headache on the Pathologic Findings of Unruptured Cerebral Saccular Aneurysms

BACKGROUND

Some patients with aneurysm exhibit warning headaches without minor bleeding, and this could be caused by stretching of the aneurysm wall. Recently, our pathologic study observed subintimal fibrin deposition in a majority of the ruptured aneurysms. However, these findings also were observed in some unruptured aneurysms. In this report, 2 unruptured aneurysms exhibited subintimal fibrin, and interestingly, one of the patients experienced severe headache within 1 month before neuroimaging.

OBJECTIVE

We performed pathologic analysis of unruptured aneurysms and collected their various clinical variables, including severe headache, to clarify the clinical characteristics of "dangerous" unruptured aneurysms.

METHODS

This study included unruptured saccular aneurysm samples (n = 17) that were resected after clipping. We compared the differences in clinical variables, including warning headache, between aneurysms with and without fibrin deposition.

RESULTS

Fibrin deposition was present in the subintimal layer in 4 patients and in the periouter membrane in 4 patients. Three of the 4 former patients experienced warning headaches, and one presented aneurysm growth. Of the latter 4 patients, one exhibited aneurysm growth, whereas the others presented with relatively large aneurysms. In the remaining 9 aneurysms without fibrin deposition, monocyte infiltration was observed in one, all aneurysms were small, and no patients experienced warning headaches or aneurysm growth.

CONCLUSIONS

Subintimal fibrin deposition is observed frequently in patients with aneurysm with warning headaches. These pathologic findings are clinically inspiring and may suggest that these aneurysms exhibit rapid stretching by newly formed aneurysms, which can result in rupture at an early stage.

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.

The impact of aspirin and anticoagulant usage on outcomes after aneurysmal subarachnoid hemorrhage: a Nationwide Inpatient Sample analysis

OBJECTIVE

Although aspirin usage may be associated with a decreased risk of rupture of cerebral aneurysms, any potential therapeutic benefit from aspirin must be weighed against the theoretical risk of greater hemorrhage volume if subarachnoid hemorrhage (SAH) occurs. However, few studies have evaluated the association between prehemorrhage aspirin use and outcomes. This is the first nationwide analysis to evaluate the impact of long-term aspirin and anticoagulant use on outcomes after SAH.

METHODS

Data from the Nationwide Inpatient Sample (NIS; 2006–2011) were extracted. Patients with a primary diagnosis of SAH who underwent microsurgical or endovascular aneurysm repair were included; those with a diagnosis of an arteriovenous malformation were excluded. Multivariable logistic regression was performed to calculate the adjusted odds of in-hospital mortality, a nonroutine discharge (any discharge other than to home), or a poor outcome (death, discharge to institutional care, tracheostomy, or gastrostomy) for patients with long-term aspirin or anticoagulant use. Multivariable linear regression was used to evaluate length of hospital stay. Covariates included patient age, sex, comorbidities, primary payer, NIS-SAH severity scale, intracerebral hemorrhage, cerebral edema, herniation, modality of aneurysm repair, hospital bed size, and whether the hospital was a teaching hospital. Subgroup analyses exclusively evaluated patients treated surgically or endovascularly.

RESULTS

The study examined 11,549 hospital admissions. Both aspirin (2.1%, n = 245) and anticoagulant users (0.9%, n = 108) were significantly older and had a greater burden of comorbid disease (p < 0.001); severity of SAH was slightly lower in those with long-term aspirin use (p = 0.03). Neither in-hospital mortality (13.5% vs 12.6%) nor total complication rates (79.6% vs 80.0%) differed significantly by long-term aspirin use. Additionally, aspirin use was associated with decreased odds of a cardiac complication (OR 0.57, 95% CI 0.36%–0.91%, p = 0.02) or of venous thromboembolic events (OR 0.53, 95% CI 0.30%–0.94%, p = 0.03). Length of stay was significantly shorter (15 days vs 17 days [12.73%], 95% CI 5.22%–20.24%, p = 0.001), and the odds of a nonroutine discharge were lower (OR 0.63, 95% CI 0.48%–0.83%, p = 0.001) for aspirin users. In subgroup analyses, the benefits of aspirin were primarily noted in patients who underwent coil embolization; likewise, among patients treated endovascularly, the adjusted odds of a poor outcome were lower among long-term aspirin users (31.8% vs 37.4%, OR 0.63, 95% CI 0.42%–0.94%, p = 0.03). Although the crude rates of in-hospital mortality (19.4% vs 12.6%) and poor outcome (53.6% vs 37.6%) were higher for long-term anticoagulant users, in multivariable logistic regression models these variations were not significantly different (mortality: OR 1.36, 95% CI 0.89%–2.07%, p = 0.16; poor outcome: OR 1.09, 95% CI 0.69%–1.73%, p = 0.72).

CONCLUSIONS

In this nationwide study, neither long-term aspirin nor anticoagulant use were associated with differential mortality or complication rates after SAH. Aspirin use was associated with a shorter hospital stay and lower rates of nonroutine discharge, with these benefits primarily observed in patients treated endovascularly.

Global Gene Expression Patterns and Somatic Mutations in Sporadic Intracranial Aneurysms

BACKGROUND

High-throughput sequencing technologies can expand our understanding of the pathologic basis of intracranial aneurysms (IAs). Our study was aimed to decipher the gene expression signature and genetic factors associated with IAs.

METHODS

We determined the gene expression levels of 3 cases of IAs by RNA sequencing. Bioinformatics analysis was conducted to identify the differentially expressed genes (DEGs) and uncover their biological function. In addition, whole genome sequencing was performed on an additional 6 cases of IAs to detect the potential somatic alterations in DEGs.

RESULTS

Compared with the normal arterial tissue, 1709 genes were differentially expressed in IAs arterial tissue. The most significantly up-regulated gene and down-regulated gene, H19 and HIST1H3J, may be essential for tumorigenesis of IAs. Hub protein of IKBKG in protein-protein interaction network was probably involved in the inflammation process in aneurysms. Another 2 hub proteins, ACTB and MKI67IP, as well as up-regulated genes, might be abnormally activated in aneurysms and involved in the pathogenesis of IAs. Further whole genome sequencing and filtering yielded 4 candidate somatic single nucleotide variants including MUC3B, and BLM may be involved in the pathogenesis of IAs. Even though, our results do not support the hypothesis of somatic mutations occurred in the DEGs.

CONCLUSIONS

Two-dimensional genomic data from transcriptome and whole genome sequencing indicated that no somatic mutations occurred in DEGs. In addition, 3 DEGs (IKBKG, ACTB, and MKI67IP) and 2 mutant genes (MUC3B and BLM) were essential in IAs.

Expression profile of long noncoding RNAs in human cerebral aneurysms: a microarray analysis

OBJECTIVE The pathogenesis of cerebral aneurysms (CAs) remains largely unknown. Long noncoding RNAs (lncRNAs) were reported recently to play crucial roles in many physiological and biological processes. Here, the authors compared the gene-expression profiles of CAs and their control arteries to investigate the potential functions of lncRNAs in the formation of CAs. METHODS A prospective case-control study was designed to identify the changes in expression of lncRNAs and mRNAs between 12 saccular CA samples (case group) and 12 paired superficial temporal artery samples (control group). Microarray analysis was performed to investigate the expression of lncRNAs and messenger RNAs (mRNAs), and reverse-transcription quantitative polymerase chain reaction was used to validate the microarray analysis findings. Then, an lncRNA target-prediction program and gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were applied to explore potential lncRNA functions. RESULTS A comparison between the case and control groups revealed that 1518 lncRNAs and 2545 mRNAs were expressed differentially. By using target-prediction program analysis, the authors constructed a complex network consisting of 2786 matched lncRNA-mRNA pairs, in which ine1 mRNA was potentially targeted by one to tens of lncRNAs, and vice versa. The results of further gene ontology and KEGG pathway analyses indicated that lncRNAs were involved mainly in regulating immune/inflammatory processes/pathways and vascular smooth muscle contraction, both of which are known to have crucial pathobiological relevance in terms of CA formation. CONCLUSIONS By comparing CAs with their control arteries, the authors created an expression profile of lncRNAs in CAs and propose here their possible roles in the pathogenesis of CAs. The results of this study provide novel insight into the mechanisms of CA pathogenesis and shed light on developing new therapeutic intervention for CAs in the future.

Association of promoter polymorphism -857C/T (rs1799724) in tumor necrosis factor gene with intracerebral hemorrhage in Korean males

BACKGROUND AND PURPOSE

Tumor necrosis factor (TNF) has been shown to be involved in the pathogenesis of hemorrhagic stroke, having deleterious effects on cerebral arteries by promoting inflammation and apoptosis in vascular and immune cells. In this study, we investigated genetic association between TNF gene and intracerebral hemorrhage (ICH) in a Korean population.

METHODS

Single nucleotide polymorphisms (SNPs) of TNF gene [-857C/T (rs1799724) and -308G/A (rs1800629)] were selected and genotyped using direct sequencing in 144 ICH patients and 455 control subjects. Genotype distribution and allele frequency were compared between cases and controls using logistic regression.

RESULTS

-857C/T was significantly associated with ICH in log-additive [odds ratio (OR) = 1.60, 95% confidence interval (CI) = 1.14-2.24, p = 0.0081], and recessive models (OR = 3.25, 95% CI = 1.28-8.27, p = 0.016). The frequency of the -857TT genotype increased in ICH patients. Allele frequency analysis also showed that the -857T allele was associated with an increased risk of ICH (OR = 1.62, 95% CI = 1.15-2.30, p = 0.006). In the analysis according to the gender, we found that the association of -857C/T was gender-different. The -857C/T was significantly associated with ICH only in males (OR = 1.99, 95% CI = 1.24-3.19, p = 0.0043 in males; OR = 1.30, 95% CI = 0.76-2.22, p = 0.34 in females).

CONCLUSION

These results suggest that promoter polymorphism of TNF gene, -857C/T, may be involved in the susceptibility of ICH in males.

Hemodynamic modeling of leukocyte and erythrocyte transport and interactions in intracranial aneurysms by a multiphase approach

Hemodynamics has been recognized as an important factor in the development, growth, and rupture of cerebral aneurysms, and investigated by computational fluid dynamics techniques using a single phase approach. However, flow-dependent cell transport and interactions are usually ignored in single phase models, in which blood is usually treated as a single phase Newtonian fluid. For getting better insight into the underlying pathology of intracranial aneurysm, cell transport and interactions should be covered in hemodynamic studies. In the present study, a multiphase hemodynamic model incorporating cell transport and interactions was developed, in which blood was modeled as multiphase fluid having a continuous phase (plasma) and two particulate phases (erythrocytes and leukocytes). The model showed good agreement with experimental data and observations in the literature, and was applied to four patient-specific aneurysms in a pulsatile manner. Leukocyte accumulations were predicted at locations with flow disturbance and low wall shear stress. The concentrations of leukocyte at accumulation sites were found to exceed 200 to 500% of normal physiological level on three unstable aneurysms, including two ruptured aneurysms and a growing aneurysm where accumulation was observed near a daughter sac and a secondary aneurysm. This suggested that aneurysms with complex secondary flow patterns could be prone to leukocyte accumulation on the wall. As this is the first study to characterize cell transport and interactions in aneurysm hemodynamics, our model can serve as a foundation for future intracranial aneurysm models.

Biology of Saccular Cerebral Aneurysms: A Review of Current Understanding and Future Directions

Understanding the biology of intracranial aneurysms is a clinical quandary. How these aneurysms form, progress, and rupture is poorly understood. Evidence indicates that well-established risk factors play a critical role, along with immunologic factors, in their development and clinical outcomes. Much of the expanding knowledge of the inception, progression, and rupture of intracranial aneurysms implicates inflammation as a critical mediator of aneurysm pathogenesis. Thus, therapeutic targets exploiting this arm of aneurysm pathogenesis have been implemented, often with promising outcomes.

Lymphocytes influence intracranial aneurysm formation and rupture: role of extracellular matrix remodeling and phenotypic modulation of vascular smooth muscle cells

BACKGROUND

Intracranial aneurysms (IA) are increasingly recognized as a disease driven by chronic inflammation. Recent research has identified key mediators and processes underlying IA pathogenesis, but mechanistic understanding remains incomplete. Lymphocytic infiltrates have been demonstrated in patient IA tissue specimens and have also been shown to play an important role in abdominal aortic aneurysms (AAA) and related diseases such as atherosclerosis. However, no study has systematically examined the contribution of lymphocytes in a model of IA.

METHODS

Lymphocyte-deficient (Rag1) and wild-type (WT; C57BL/6 strain) mice were subjected to a robust IA induction protocol. Rates of IA formation and rupture were measured, and cerebral artery tissue was collected and utilized for histology and gene expression analysis.

RESULTS

At 2 weeks, the Rag1 group had significantly fewer IA formations and ruptures than the WT group. Histological analysis of unruptured IA tissue showed robust B and T lymphocyte infiltration in the WT group, while there were no differences in macrophage infiltration, IA diameter, and wall thickness. Significant differences in interleukin-6 (IL-6), matrix metalloproteinases 2 (MMP2) and 9 (MMP9), and smooth muscle myosin heavy chain (MHC) were observed between the groups.

CONCLUSIONS

Lymphocytes are key contributors to IA pathogenesis and provide a novel target for the prevention of IA progression and rupture in patients.