Intracranial Aneurysm Formation Research Articles

Intracranial aneurysm circulating exosome-derived LncRNA ATP1A1-AS1 promotes smooth muscle cells phenotype switching and apoptosis.

Exosomal long non-coding RNAs (LncRNAs) play a crucial role in the pathogenesis of cerebrovascular diseases. However, the expression profiles and functional significance of exosomal LncRNAs in intracranial aneurysms (IAs) remain poorly understood. Through high-throughput sequencing, we identified 1303 differentially expressed LncRNAs in the plasma exosomes of patients with IAs and healthy controls. Quantitative real-time polymerase chain reaction (qRT-PCR) verification confirmed the differential expression of LncRNAs, the majority of which aligned with the sequencing results. ATP1A1-AS1 showed the most significant upregulation in the disease group. Importantly, subsequent in vitro experiments validated that ATP1A1-AS1 overexpression induced a phenotype switching in vascular smooth muscle cells, along with promoting apoptosis and upregulating MMP-9 expression, potentially contributing to IAs formation. Furthermore, expanded-sample validation affirmed the high diagnostic value of ATP1A1-AS1. These findings suggest that ATP1A1-AS1 is a potential therapeutic target for inhibiting IAs progression and serves as a valuable clinical diagnostic marker.

Molecular Basis of Cerebral Vasospasm: What Can We Learn from Transcriptome and Temporal Gene Expression Profiling in Intracranial Aneurysm?

Cerebral vasospasm (CV) is a significant complication following aneurysmal subarachnoid hemorrhage (aSAH), and lacks a comprehensive molecular understanding. Given the temporal trajectory of intracranial aneurysm (IA) formation, its rupture, and development of CV, altered gene expression might be a molecular substrate that runs through these clinical events, influencing both disease inception and progression. Utilizing RNA-Seq, we analyzed tissue samples from ruptured IAs with and without vasospasm to identify the dysregulated genes. In addition, temporal gene expression analysis was conducted. We identified seven dysregulated genes in patients with ruptured IA with vasospasm when compared with those without vasospasm. We found 192 common genes when the samples of each clinical subset of patients with IA, that is, unruptured aneurysm, ruptured aneurysm without vasospasm, and ruptured aneurysm with vasospasm, were compared with control samples. Among these common genes, TNFSF13B, PLAUR, OSM, and LAMB3 displayed temporal expression (progressive increase) with the pathological progression of disease that is formation of aneurysm, its rupture, and consequently the development of vasospasm. We validated the temporal gene expression pattern of OSM at both the transcript and protein levels and OSM emerges as a crucial gene implicated in the pathological progression of disease. In addition, RSAD2 and ATP1A2 appear to be pivotal genes for CV development. To the best of our knowledge, this is the first study to compare the transcriptome of aneurysmal tissue samples of aSAH patients with and without CV. The findings collectively provide new insights on the molecular basis of IA and CV and new leads for translational research.

Impinging flow mediates vascular endothelial cell injury through the PKCα/ERK/PPARγ pathway in vitro.

This study aims to elucidate the mechanisms underlying endothelial injury in the context of intracranial aneurysm formation and development, which are associated with vascular endothelial injury caused by hemodynamic abnormalities. Specifically, we focus on the involvement of PKCα, an intracellular signaling transmitter closely linked to vascular diseases, and its role in activating MAPK. Additionally, we investigate the protective effects of PPARγ, a vasculoprotective factor known to attenuate vascular injury by mitigating the inflammatory response in the vessel wall. The study employs a modified T chamber to replicate fluid flow conditions at the artery bifurcation, allowing us to assess wall shear stress effects on human umbilical vein endothelial cells (HUVECs) in vitro. Through experimental manipulations involving PKCα knockdown and Ca2+ and MAPK inhibitors, we evaluate the phosphorylation status of PKCα, NF-κB, ERK5, ERK1/2, JNK1/2/3, and P38, as well as the expression levels of PPARγ, NF-κB, and MMP2 via western blot analysis. The cellular localization of phosphorylated NF-κB was determined using immunofluorescence. Our results showed that impinging flow resulted in the activation of PKCα, followed by the phosphorylation of ERK5, ERK1/2, and JNK1/2/3, leading to a decrease in PPARγ expression, an increase in the expression of NF-κB and MMP2, and the induction of apoptotic injury. Inhibition of PKCα activation or knockdown of PKCα using shRNA leads to a suppression of ERK5, ERK1/2, JNK1/2/3, and P38 phosphorylation, an elevation in PPARγ expression, and a reduction in NF-κB and MMP2 expression, alleviated apoptotic injury. Furthermore, we observe that the regulation of PPARγ, NF-κB, and MMP2 expression is influenced by ERK5 and ERK1/2 phosphorylation, and activation of PPARγ effectively counteracts the elevated expression of NF-κB and MMP2. Our findings suggest that the PKCα/ERK/PPARγ pathway plays a crucial role in mediating endothelial injury under conditions of impinging flow, with potential implications for vascular diseases and intracranial aneurysm development.

Transition of intracranial aneurysmal wall enhancement from high to low wall shear stress mediation with size increase: A hemodynamic study based on 7T magnetic resonance imaging

BackgroundWall shear stress (WSS) has been proved to be related to the formation, development and rupture of intracranial aneurysms. Aneurysm wall enhancement (AWE) on magnetic resonance imaging (MRI) can be caused by inflammation and have confirmed its relationship with low WSS. High WSS can also result in inflammation but the research of its correlation with AWE is lack because of the focus on large aneurysms limited by 3T MRI in most previous studies.This study aimed to assess the potential association between high or low WSS and AWE in different aneuryms. Especially the relationship between high WSS and AWE in small aneurysm. MethodsForty-three unruptured intracranial aneurysms in 42 patients were prospectively included for analysis. 7.0 T MRI was used for imaging. Aneurysm size was measured on three-dimensional time-of-flight (TOF) images. Aneurysm-to-pituitary stalk contrast ratio (CRstalk) was calculated on post-contrast black-blood T1-weighted fast spin echo sequence images. Hemodynamics were assessed by four-dimensional flow MRI. ResultsThe small aneurysms group had more positive WSS–CRstalk correlation coefficient distribution (dome: 78.6 %, p = 0.009; body: 50.0 %, p = 0.025), and large group had more negative coefficient distribution (dome: 44.8 %, p = 0.001; body: 69.0 %, p = 0.002). Aneurysm size was positively correlated with the significant OSI–CRstalk correlation coefficient at the dome (p = 0.012) and body (p = 0.010) but negatively correlated with the significant WSS–CRstalk correlation coefficient at the dome (p < 0.001) and body (p = 0.017). ConclusionAWE can be mediated by both high and low WSS, and translate from high WSS- to low WSS-mediated pathways as size increase. Additionally, AWE may serve as an indicator of the stage of aneurysm development via different correlations with hemodynamic factors.

Causal relationship between telomere length and risk of intracranial aneurysm: a bidirectional Mendelian randomization study.

Telomere length is closely linked to the aging phenotype, where cellular aging results in the production of a cascade of cell factors and the senescence-associated secretory phenotype (SASP), leading to an inflammatory response. The presence of inflammation plays a crucial role in the formation of intracranial aneurysms. Nevertheless, the relationship between telomere length and intracranial aneurysms remains unclear. This study aims to explore the causal connection between telomere length and intracranial aneurysms through the utilization of Mendelian randomization (MR) analysis. Data on telomere length were obtained from the genome-wide association studies conducted on the UK Biobank, comprising a total of 472,174 participants. Data on intracranial aneurysms were obtained from the summary dataset of the Global Genome-wide Association Study (GWAS) conducted by the International Stroke Genetics Consortium. The dataset consisted of 7,495 cases and 71,934 controls, all of European descent. Initially, the linkage disequilibrium score was used to investigate the connection between telomere length and intracranial aneurysms. Subsequently, a bidirectional MR was conducted using two-sample analysis to assess whether there is a causal connection between telomere length and intracranial aneurysm risk. The results were analyzed utilizing five MR methods, with the inverse variance weighted method serving as the main methodology. In addition, we did various analyses to evaluate the presence of heterogeneity, pleiotropy, and sensitivity in the study results. A reverse MR analysis was conducted to investigate potential reverse causal links. In the forward MR analysis, it was observed that both the inverse variance-weighted and weighted median analyses implied a potential causal relationship between longer telomere length and a decreased incidence of intracranial aneurysms (IVW: OR = 0.66, 95% CI: 0.47-0.92, p = 1.49 × 10-2). There was no heterogeneity or horizontal pleiotropy. The findings were verified to be robust through the utilization of leave-one-out analysis. The use of reverse MR analysis did not establish a potential causal link between the occurrence of intracranial aneurysms and telomere length. There may exist a potential correlation between longer telomere length and a decreased likelihood of intracranial aneurysms within the European population. The present study offers novel insights into the correlation between telomere length and intracranial aneurysms. Additional research is required to clarify the underlying mechanisms and validate our discoveries in diverse populations.

Decoding the biology and clinical implication of neutrophils in intracranial aneurysm.

Abundant neutrophils have been identified in both ruptured and unruptured intracranial aneurysm (IA) domes, with their function and clinical implication being poorly characterized. We employed single-cell RNA sequencing (scRNA-Seq) datasets of both human and murine model, and external bulk mRNA sequencing datasets to thoroughly explore the features and functional heterogeneous of neutrophils infiltrating the IA dome. We found that both unruptured and ruptured IA dome contain a substantial population of neutrophils, characterized by FCGR3B, G0S2, CSF3R, and CXCR2. These cells exhibited heterogeneity in terms of function and differentiation. Despite similar transcriptional activation, neutrophils in IA dome expressed a repertoire of gene programs that mimicked transcriptomic alterations observed from bone marrow to peripheral blood, showing self-similarity. In addition, the recruitment of neutrophils in unruptured IA was primarily mediated by monocytes/macrophages, and once ruptured, both neutrophils, and a specific subset of inflammatory smooth muscle cells (SMCs) were involved in the process. The receiver operator characteristic curve (ROC) analysis indicated that distinct neutrophil subclusters were associated with IA formation and rupture, respectively. By reviewing current studies, we found that neutrophils play a detrimental role to IA wall integrity through secreting specific ligands, ferroptosis driven by ALOX5AP and PTGS2, and the formation of neutrophil extracellular traps (NETs) mediated by PADI4. This study delineated the biology and potential clinical implications of neutrophils in IA dome and provided a reliable basis for future researches.

Homocysteine serum levels in patients with ruptured and unruptured intracranial aneurysms: a case-control study.

There is very few data regarding homocysteine's influence on the formation and rupture of intracranial aneurysms. To compare homocysteine levels between patients with ruptured and unruptured intracranial aneurysms, and to evaluate possible influences of this molecule on vasospasm and functional outcomes. This is a retrospective, case-control study. We evaluated homocysteinemia differences between patients with ruptured and unruptured aneurysms; and the association of homocysteine levels with vasospasm and functional outcomes. Logistic regressions were performed. A total of 348 participants were included: 114 (32.8%) with previous aneurysm rupture and 234 (67.2%) with unruptured aneurysms. Median homocysteine was 10.75µmol/L (IQR = 4.59) in patients with ruptured aneurysms and 11.5µmol/L (IQR = 5.84) in patients with unruptured aneurysms. No significant association was detected between homocysteine levels and rupture status (OR = 0.99, 95% CI = 0.96-1.04). Neither mild (>15µmol/L; OR = 1.25, 95% CI 0.32-4.12) nor moderate (>30µmol/L; OR = 1.0, 95% CI = 0.54-1.81) hyperhomocysteinemia demonstrated significant correlations with ruptured aneurysms. Neither univariate (OR = 0.86; 95% CI 0.71-1.0) nor multivariable age-adjusted (OR = 0.91; 95% CI = 0.75-1.05) models evidenced an association between homocysteine levels and vasospasm. Homocysteinemia did not influence excellent functional outcomes at 6 months (mRS≤1) (OR = 1.04; 95% CI = 0.94-1.16). There were no differences regarding homocysteinemia between patients with ruptured and unruptured intracranial aneurysms. In patients with ruptured aneurysms, homocysteinemia was not associated with vasospasm or functional outcomes.

Metabolic alterations of peripheral blood immune cells and heterogeneity of neutrophil in intracranial aneurysms patients.

Intracranial aneurysms (IAs) represent a severe cerebrovascular disease that can potentially lead to subarachnoid haemorrhage. Previous studies have demonstrated the involvement of peripheral immune cells in the formation and progression of IAs. Nevertheless, the impact of metabolic alterations in peripheral immune cells and changes in neutrophil heterogeneity on the occurrence and progression of IAs remains uncertain. Single-cell Cytometry by Time-of-Flight (CyTOF) technology was employed to profile the single-cell atlas of peripheral blood mononuclear cells (PBMCs) and polymorphonuclear cells (PMNs) in 72 patients with IAs. In a matched cohort, metabolic shifts in PBMC subsets of IA patients were investigated by contrasting the expression levels of key metabolic enzymes with their respective counterparts in the healthy control group. Simultaneously, compositional differences in peripheral blood PMNs subsets between the two groups were analysed to explore the impact of altered heterogeneity in neutrophils on the initiation and progression of IAs. Furthermore, integrating immune features based on CyTOF analysis and clinical characteristics, we constructed an aneurysm occurrence model and an aneurysm growth model using the random forest method in conjunction with LASSO regression. Different subsets exhibited distinct metabolic characteristics. Overall, PBMCs from patients elevated CD98 expression and increased proliferation. Conversely, CD36 was up-regulated in T cells, B cells and monocytes from the controls but down-regulated in NK and NKT cells. The comparison also revealed differences in the metabolism and function of specific subsets between the two groups. In terms of PMNs, the neutrophil landscape within patients group revealed a pronounced shift towards heightened complexity. Various neutrophil subsets from the IA group generally exhibited lower expression levels of anti-inflammatory functional molecules (IL-4 and IL-10). By integrating clinical and immune features, the constructed aneurysm occurrence model could precisely identify patients with IAs with high prediction accuracy (AUC=0.987). Furthermore, the aneurysm growth model also exhibited superiority over ELAPSS scores in predicting aneurysm growth (lower prediction errors and out-of-bag errors). These findings enhanced our understanding of peripheral immune cell participation in aneurysm formation and growth from the perspectives of immune metabolism and neutrophil heterogeneity. Moreover, the predictive model based on CyTOF features holds the potential to aid in diagnosing and monitoring the progression of human IAs.

Current Mouse Models of Intracranial Aneurysms: Analysis of Pharmacological Agents Used to Induce Aneurysms and Their Impact on Translational Research.

Intracranial aneurysms (IAs) are rare vascular lesions that are more frequently found in women. The pathophysiology behind the formation and growth of IAs is complex. Hence, to date, no single pharmacological option exists to treat them. Animal models, especially mouse models, represent a valuable tool to explore such complex scientific questions. Genetic modification in a mouse model of IAs, including deletion or overexpression of a particular gene, provides an excellent means for examining basic mechanisms behind disease pathophysiology and developing novel pharmacological approaches. All existing animal models need some pharmacological treatments, surgical interventions, or both to develop IAs, which is different from the spontaneous and natural development of aneurysms under the influence of the classical risk factors. The benefit of such animal models is the development of IAs in a limited time. However, clinical translation of the results is often challenging because of the artificialcourse of IA development and growth. Here, we summarize the continuous improvement in mouse models of IAs. Moreover, we discuss the pros and cons of existing mouse models of IAs and highlight the main translational roadblocks and how to improve them to increase the success of translational IA research.

Elucidating key immunological biomarkers and immune microenvironment dynamics in aging-related intracranial aneurysm through integrated multi-omics analysis.

The exact cause of intracranial aneurysms (IA) is still unclear. However, pro-inflammatory factors are known to contribute to IA progression. The specific changes in the immune microenvironment of IAs remain largely unexplored. This study analyzed single-cell sequencing data from a male mouse model of brain aneurysm, focusing on samples before and after elastase-induced Willis aneurysms. The data helped identify eight distinct cell subpopulations: fibroblasts, macrophages, NK cells, endothelial cells, B cells, granulocytes, and monocytes. The study also involved bulk RNA sequencing of 97 IA samples, utilizing ssGSEA and CIBERSORT algorithms for analysis. Intercellular communication among these cells was inferred to understand the immune dynamics in IA. The study found that fibroblasts and macrophages are predominant in various disease states of IA. Notably, the onset of IA was marked by a significant increase in fibroblasts and a decrease in macrophages. There was a marked increase in cellular interactions, especially involving macrophages, at the onset of the disease. Through enrichment analysis, 12 potential immunogenic biomarkers were identified. Of these, Rgs1 emerged as a critical molecule in IA formation, confirmed through secondary validation in a single-cell sequencing dataset. This comprehensive analysis of immune cell composition and intercellular communication in IA tissues highlights the significant roles of macrophages and the molecule Rgs1. These findings shed light on the physiological and pathological conditions of IA, offering new insights into its immune microenvironment.

Is Oral Streptococcus mutans with Collagen-Binding Protein a Risk Factor for Intracranial Aneurysm Rupture or Formation?

Introduction: Streptococcus mutans (SM) with the collagen-binding protein Cnm is a unique member of the oral resident flora because it causes hemorrhagic vascular disorders. In the multicenter study, we examined the relationship between Cnm-positive SM (CP-SM) and intracranial aneurysm (IA) rupture, which remains unknown. Methods: Between May 2013 and June 2018, we collected whole saliva samples from 431 patients with ruptured IAs (RIAs) and 470 patients with unruptured IAs (UIAs). Data were collected on age, sex, smoking and drinking habits, family history of subarachnoid hemorrhage, aneurysm size, number of teeth, and comorbidities of lifestyle disease. Results: There was no difference in the positivity rate of patients with CP-SM between the patients with RIAs (17.2%) and those with UIAs (19.4%). In subanalysis, the rate of positivity for CP-SM was significantly higher in all IAs p = 0.0304). In the entire cohort, the rate of positivity for CP-SM was lower in larger aneurysms than in smaller aneurysms (p = 0.0393). Conclusions: CP-SM was not involved in the rupture of UIAs. In the subanalysis, the possibility of its involvement in the formation of vulnerable aneurysms remained.

Current understanding of macrophages in intracranial aneurysm: relevant etiological manifestations, signaling modulation and therapeutic strategies.

Macrophages activation and inflammatory response play crucial roles in intracranial aneurysm (IA) formation and progression. The outcome of ruptured IA is considerably poor, and the mechanisms that trigger IA progression and rupture remain to be clarified, thereby developing effective therapy to prevent subarachnoid hemorrhage (SAH) become difficult. Recently, climbing evidences have been expanding our understanding of the macrophages relevant IA pathogenesis, such as immune cells population, inflammatory activation, intra-/inter-cellular signaling transductions and drug administration responses. Crosstalk between macrophages disorder, inflammation and cellular signaling transduction aggravates the devastating consequences of IA. Illustrating the pros and cons mechanisms of macrophages in IA progression are expected to achieve more efficient treatment interventions. In this review, we summarized the current advanced knowledge of macrophages activation, infiltration, polarization and inflammatory responses in IA occurrence and development, as well as the most relevant NF-κB, signal transducer and activator of transcription 1 (STAT1) and Toll-Like Receptor 4 (TLR4) regulatory signaling modulation. The understanding of macrophages regulatory mechanisms is important for IA patients' clinical outcomes. Gaining insight into the macrophages regulation potentially contributes to more precise IA interventions and will also greatly facilitate the development of novel medical therapy.

Plasma levels of CD36 and glutathione as biomarkers for ruptured intracranial aneurysm.

Evidence has proved that intracranial aneurysm (IA) formation and rupture might be closely related to inflammatory response and oxidative stress. Our objective was to evaluate the potential of CD36 and glutathione (GSH) as biomarkers for IA. In this study, the enzyme-linked immunosorbent assay was used to measure the plasma levels of CD36 and GSH in 30 IA patients and 30 healthy controls. Then, correlation analysis, receiver operating characteristic (ROC) curve, and logistic regression analysis were performed. The results showed that the plasma level of CD36 in IA patients was significantly higher than that in the control group (P < 0.0001), and plasma GSH was significantly lower compared with that in the control group (P < 0.0001). ROC analysis showed that CD36 and GSH had high sensitivity (90.0 and 96.6%) and specificity (96.6 and 86.6%) for IA diagnosis. The combined sensitivity and specificity achieved were 100 and 100%, respectively. The plasma levels of CD36 and GSH did not show a significant correlation with age, the Glasgow Coma Scale, Hunter-Hess score, aneurysm size, aneurysm height, aneurysm neck, and aspect ratio. The AUC of the logistic regression model based on CD36 and GSH was 0.505. Our results suggested that the combination of plasma CD36 and GSH could serve as potential biomarkers for IA rupture.

The Role of Gut and Oral Microbiota in the Formation and Rupture of Intracranial Aneurysms: A Literature Review.

In recent years, there has been a growing interest in the role of the microbiome in cardiovascular and cerebrovascular diseases. Emerging research highlights the potential role of the microbiome in intracranial aneurysm (IA) formation and rupture, particularly in relation to inflammation. In this review, we aim to explore the existing literature regarding the influence of the gut and oral microbiome on IA formation and rupture. In the first section, we provide background information, elucidating the connection between inflammation and aneurysm formation and presenting potential mechanisms of gut-brain interaction. Additionally, we explain the methods for microbiome analysis. The second section reviews existing studies that investigate the relationship between the gut and oral microbiome and IAs. We conclude with a prospective overview, highlighting the extent to which the microbiome is already therapeutically utilized in other fields. Furthermore, we address the challenges associated with the context of IAs that still need to be overcome.

The SNHG12/microRNA-15b-5p/MYLK axis regulates vascular smooth muscle cell phenotype to affect intracranial aneurysm formation

ObjectiveThis research was dedicated to investigating the impact of the SNHG12/microRNA (miR)-15b-5p/MYLK axis on the modulation of vascular smooth muscle cell (VSMC) phenotype and the formation of intracranial aneurysm (IA). MethodsSNHG12, miR-15b-5p and MYLK expression in IA tissue samples from IA patients were tested by RT-qPCR and western blot. Human aortic vascular smooth muscle cells (VSMCs) were cultivated with H2O2 to mimic IA-like conditions in vitro, and the cell proliferation and apoptosis were measured by MTT assay and Annexin V/PI staining. IA mouse models were established by induction with systemic hypertension combined with elastase injection. The blood pressure in the tail artery of mice in each group was assessed and the pathological changes in arterial tissues were observed by HE staining and TUNEL staining. The expression of TNF-α and IL-1β, MCP-1, iNOS, caspase-3, and caspase-9 in the arterial tissues were tested by RT-qPCR and ELISA. The relationship among SNHG12, miR-15b-5p and MYLK was verified by bioinformatics, RIP, RNA pull-down, and luciferase reporter assays. ResultsThe expression levels of MYLK and SNHG12 were down-regulated and that of miR-15b-5p was up-regulated in IA tissues and H2O2-treated human aortic VSMCs. Overexpressed MYLK or SNHG12 mitigated the decrease in proliferation and increase in apoptosis of VSMCs caused by H2O2 induction, and overexpression of miR-15b-5p exacerbated the decrease in proliferation and increase in apoptosis of VSMCs caused by H2O2 induction. Overexpression of miR-15b-5p reversed the H2O2-treated VSMC phenotypic changes caused by SNHG12 up-regulation, and overexpression of MYLK reversed the H2O2-treated VSMC phenotypic changes caused by up-regulation of miR-15b-5p. Overexpression of SNHG12 reduced blood pressure and ameliorated arterial histopathological damage and VSMC apoptosis in IA mice. The mechanical analysis uncovered that SNHG12 acted as an endogenous RNA that competed with miR-15b-5p, thus modulating the suppression of its endogenous target, MYLK. ConclusionDecreased expression of SNHG12 in IA may contribute to the increasing VSMC apoptosis via increasing miR-15b-5p expression and subsequently decreasing MYLK expression. These findings provide potential new strategies for the clinical treatment of IA.

The Role of the NF-kB Pathway in Intracranial Aneurysms.

The pathophysiology of intracranial aneurysms (IA) has been proven to be closely linked to hemodynamic stress and inflammatory pathways, most notably the NF-kB pathway. Therefore, it is a potential target for therapeutic intervention. In the present review, we investigated alterations in the vascular smooth muscle cells (VSMCs), extracellular matrix, and endothelial cells by the mediators implicated in the NF-kB pathway that lead to the formation, growth, and rupture of IAs. We also present an overview of the NF-kB pathway, focusing on stimuli and transcriptional targets specific to IAs, as well as a summary of the current strategies for inhibiting NF-kB activation in IAs. Our report adds to previously reported data and future research directions for treating IAs using compounds that can suppress inflammation in the vascular wall.

Neutrophils: Novel Contributors to Estrogen-Dependent Intracranial Aneurysm Rupture Via Neutrophil Extracellular Traps.

Background Intracranial aneurysms (IAs) are more prevalent in women than men, and aneurysmal subarachnoid hemorrhage disproportionately affects postmenopausal women. These sex differences suggest estrogen protects against IA progression that can lead to rupture, but the underlying mechanisms are not fully understood. Although studies have demonstrated estrogen regulates inflammatory processes that contribute to IA pathogenesis, the role of neutrophils remains to be characterized. Using a murine model, we tested our hypothesis that neutrophils contribute to IA pathophysiology in an estrogen-dependent manner. Methods and Results We compared neutrophil infiltration in C57BL/6 female mice that develop IAs to those with a normal circle of Willis. Next, we investigated the estrogen-dependent role of neutrophils in IA formation, rupture, and symptom-free survival using a neutrophil depletion antibody. Finally, we studied the role of neutrophil extracellular trap formation (NETosis) as an underlying mechanism of aneurysm progression. Mice that developed aneurysms had increased neutrophil infiltration compared with those with a normal circle of Willis. In estrogen-deficient female mice, both neutrophil depletion and NETosis inhibition decreased aneurysm rupture. In estrogen-deficient female mice treated with estrogen rescue and estrogen-intact female mice, neither neutrophil depletion nor NETosis inhibition affected IA formation, rupture, or symptom-free survival. Conclusions Neutrophils contribute to aneurysm rupture in an estrogen-dependent manner. NETosis appears to be an underlying mechanism for neutrophil-mediated IA rupture in estrogen deficiency. Targeting NETosis may lead to the development of novel therapeutics to protect against IA rupture in the setting of estrogen deficiency.

Intraluminal assessment of inflammatory factors in patients with intracranial aneurysms.

The formation, growth, and rupture of intracranial aneurysms (IA) are due to several pathophysiological mechanisms, including focal hemodynamic injury and inflammation of the arterial wall. We investigated the differences between venous, parent artery, and intra-aneurysmal blood by measuring inflammatory factors and antibodies in patients with ruptured (rIA) or unruptured intracranial aneurysms (uIA). A prospective study was performed in patients who presented with IA and required endovascular treatment. Blood was drawn from the lumen of the aneurysm sac, the parent artery, and the peripheral veins, to determine the serum concentrations of complement factors C3, C4, IgG, IgM, IgA antibodies, and C-reactive protein (CRP). Thirty-six patients (15 with uIA and 21 with rIA) were enrolled in the study. In both groups, C3, C4, IgM, IgG, and IgA showed a gradual decrease from venous to intra-aneurysmal samples, but only IgG in the parent artery and intra-aneurysmal samples reached a significant decrease in uIA compared with venous samples. Accordingly, C3 and IgG concentrations in the intra-aneurysmal samples showed a significant decrease in rIA compared with venous samples. A significant increase in CRP concentrations was observed in parent artery and intra-aneurysmal samples from patients with rIA compared with patients with uIA; a significant increase in C3 concentrations was observed in parent artery samples from patients with rIA compared with patients with uIA, and a significant decrease in IgM concentrations was observed in venous, parent artery, and intra-aneurysmal samples from patients with rIA compared with patients with uIA. A decrease in C3 and IgG in the aneurysm sac indicates activation of the complement system in the arterial wall. CRP in the aneurysm sac and lumen of the parent artery was significantly increased in ruptured compared with unruptured aneurysms, whereas venous, parent artery, and intra-aneurysmal IgM were decreased in ruptured compared with unruptured aneurysms. These results argue for the role of an ongoing inflammatory process in aneurysms leading to their growth and rupture.

Gut microbiome in intracranial aneurysm growth, subarachnoid hemorrhage, and cerebral vasospasm: a systematic review with a narrative synthesis.

Intracranial aneurysms (IA) are the most common cerebral vascular pathologies. Their rupture leads to the most dangerous subtype of stroke-aneurysmal subarachnoid hemorrhage (aSAH), which may be followed by cerebral vasospasm and ischemic sequelae. Recently, an imbalance within the intestinal microbiota, referred to as dysbiosis, was suggested to play a role in the formation, progression, and rupture of IA. As no systematic review on this topic exists, considering the significance of this matter and a lack of effective prophylaxis against IA or cerebral vasospasm, we aim to sum up the current knowledge regarding their associations with intestinal microbiome, identify the gaps, and determine future prospects. Scientific databases were systematically and independently searched by two authors from inception to 1st May 2023 for original articles regarding the role of intestinal microbiota in intracranial aneurysmal growth, aSAH occurrence, as well as in cerebral vasospasm following aSAH. The PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) checklist was followed in an abstraction process. The STROBE tool was applied to assess the risk of bias. This research was funded by the National Science Centre, Poland (grant number 2021/41/N/NZ2/00844). Of 302 records, four studies were included that fully met eligibility criteria. Studies reported (1) that the relative abundance of Hungatella hathewayi is a protective factor against aneurysm growth and rupture, resulting from the reduced inflammation and extracellular matrix remodeling in the cerebral arterial wall and from reduced metalloproteinase-mediated degradation of smooth muscle cells in cerebral vessels. (2) Relative abundance of Campylobacter ureolyticus is associated with aSAH. (3) No article has evaluated microbiota in relation to cerebral vasospasm following aSAH although there is an ongoing study. We concluded that intestinal microbiota might be a potential target for diagnostic and therapeutic tools to improve the management of cerebral aneurysms. However, more studies of prospective design are needed.

Greater hemodynamic stresses initiate aneurysms on major cerebral arterial bifurcations.

To retrospectively investigate the hemodynamic stresses in initiating aneurysm formation on major cerebral arterial bifurcations with computational fluid dynamics (CFD) analysis. The cerebral 3D angiographic data of major cerebral arterial bifurcations of the internal carotid, middle cerebral, anterior cerebral, and basilar arteries in 80 patients harboring bifurcation aneurysms and 80 control subjects with no aneurysms were retrospectively collected for the CFD analysis of hemodynamic stresses associated with aneurysm formation. Bifurcation angles at major bifurcations in all patients were significantly positively (P < 0.001) correlated with the age. At the center of direct flow impingement (CDFI) on the bifurcation wall, total pressure was the highest but dropped rapidly toward the branches. Wall shear stress, dynamic pressure, strain rate, and vorticity were lowest at the CDFI but they increased quickly toward the branches. The bifurcation angle was significantly (P < 0.001) enlarged in patients with bifurcation aneurysms than those without them, for all major arterial bifurcations. Most aneurysms leaned toward the smaller arterial branch or the arterial branch that formed a smaller angle with the parent artery, where the hemodynamic stresses increased significantly (P < 0.05), compared with those on the contralateral arterial branch forming a larger angle with the parent artery. Following the aneurysm development, all the hemodynamic stresses on the aneurysm dome decreased significantly (P < 0.001) compared with those at the initiation site on the bifurcation wall after virtual aneurysm removal. With the decrease of bifurcation angles, all the hemodynamic stresses decreased. The formation of intracranial aneurysms on major intracranial arterial bifurcations is significantly associated with locally abnormally augmented hemodynamic stresses, which must be reduced.