Estrogen protects against intracranial aneurysm rupture in ovariectomized mice

Gender-specific prognosis models reveal differences in subarachnoid hemorrhage patients between sexes

BACKGROUND

Subarachnoid hemorrhage (SAH) represents a severe stroke subtype. Our study aims to develop gender-specific prognostic prediction models derived from distinct prognostic factors observed among different-gender patients.

METHODS

Inclusion comprised SAH-diagnosed patients from January 2014 to March 2016 in our institution. Collected data encompassed patients' demographics, admission severity, treatments, imaging findings, and complications. Three-month post-discharge prognoses were obtained via follow-ups. Analyses assessed gender-based differences in patient information. Key factors underwent subgroup analysis, followed by univariate and multivariate analyses to identify gender-specific prognostic factors and establish/validate gender-specific prognostic models.

RESULTS

A total of 929 patients, with a median age of 57 (16) years, were analyzed; 372 (40%) were male, and 557 (60%) were female. Differences in age, smoking history, hypertension, aneurysm presence, and treatment interventions existed between genders (p < 0.01), yet no disparity in prognosis was noted. Subgroup analysis explored hypertension history, aneurysm presence, and treatment impact, revealing gender-specific variations in these factors' influence on the disease. Screening identified independent prognostic factors: age, SEBES score, admission GCS score, and complications for males; and age, admission GCS score, intraventricular hemorrhage, treatment interventions, symptomatic vasospasm, hydrocephalus, delayed cerebral ischemia, and seizures for females. Evaluation and validation of gender-specific models yielded an AUC of 0.916 (95% CI: 0.878-0.954) for males and 0.914 (95% CI: 0.885-0.944) for females in the ROC curve. Gender-specific prognostic models didn't significantly differ from the overall population-based model (model 3) but exhibited robust discriminative ability and clinical utility.

CONCLUSION

Variations in baseline and treatment-related factors among genders contribute partly to gender-based prognosis differences. Independent prognostic factors vary by gender. Gender-specific prognostic models exhibit favorable prognostic performance.

Animal Models of Intracranial Aneurysms: History, Advances, and Future Perspectives

Intracranial aneurysms (IA) are a disease process with potentially devastating outcomes, particularly when rupture occurs leading to subarachnoid hemorrhage. While some candidates exist, there is currently no established pharmacological prevention of growth and rupture. The development of prophylactic treatments is a critical area of research, and preclinical models using animals play a pivotal role. These models, which utilize various species and induction methods, each possess unique characteristics that can be leveraged depending on the specific aim of the study. A comprehensive understanding of these models, including their historical development, is crucial for appreciating the advantages and limitations of aneurysm research in animal models.We summarize the significant roles of animal models in IA research, with a particular focus on rats, mice, and large animals. We discuss the pros and cons of each model, providing insights into their unique characteristics and contributions to our understanding of IA. These models have been instrumental in elucidating the pathophysiology of IA and in the development of potential therapeutic strategies.A deep understanding of these models is essential for advancing research on preventive treatments for IA. By leveraging the unique strengths of each model and acknowledging their limitations, researchers can conduct more effective and targeted studies. This, in turn, can accelerate the development of novel therapeutic strategies, bringing us closer to the goal of establishing an effective prophylactic treatment for IA. This review aims to provide a comprehensive view of the current state of animal models in IA research.

Vitamin D deficiency promotes intracranial aneurysm rupture

Intracranial aneurysm rupture causes severe disability and high mortality. Epidemiological studies show a strong association between decreased vitamin D levels and an increase in aneurysm rupture. However, the causality and mechanism remain largely unknown. In this study, we tested whether vitamin D deficiency promotes aneurysm rupture and examined the underlying mechanism for the protective role of vitamin D against the development of aneurysm rupture utilizing a mouse model of intracranial aneurysm. Mice consuming a vitamin D-deficient diet had a higher rupture rate than mice with a regular diet. Vitamin D deficiency increased proinflammatory cytokines in the cerebral arteries. Concurrently, vitamin D receptor knockout mice had a higher rupture rate than the corresponding wild-type littermates. The vitamin D receptors on endothelial and vascular smooth muscle cells, but not on hematopoietic cells, mediated the effect of aneurysm rupture. Our results establish that vitamin D protects against the development of aneurysmal rupture through the vitamin D receptors on vascular endothelial and smooth muscle cells. Vitamin D supplementation may be a viable pharmacologic therapy for preventing aneurysm rupture.

Role of inflammatory mediators in intracranial aneurysms: A review

The formation, growth, and rupture of intracranial aneurysms (IAs) involve hemodynamics, blood pressure, external stimuli, and a series of hormonal changes. In addition, inflammatory response causes the release of a series of inflammatory mediators, such as IL, TNF-α, MCP-1, and MMPs, which directly or indirectly promote the development process of IA. However, the specific role of these inflammatory mediators in the pathophysiological process of IA remains unclear. Recently, several anti-inflammatory, lipid-lowering, hormone-regulating drugs have been found to have a potentially protective effect on reducing IA formation and rupture in the population. These therapeutic mechanisms have not been fully elucidated, but we can look for potential therapeutic targets that may interfere with the formation and breakdown of IA by studying the relevant inflammatory response and the mechanism of IA formation and rupture involved in inflammatory mediators.

Sex differences in patients with and without high-risk factors associated with aneurysmal subarachnoid hemorrhage

BACKGROUND

Controversy remains regarding the appropriate screening for intracranial aneurysms or for the treatment of aneurysmal subarachnoid hemorrhage (aSAH) for patients without known high-risk factors for rupture. This study aimed to assess how sex affects both aSAH presentation and outcomes for aSAH treatment.

METHOD

A retrospective cohort study was conducted of all patients treated at a single institution for an aSAH during a 12-year period (August 1, 2007-July 31, 2019). An analysis of women with and without high-risk factors was performed, including a propensity adjustment for a poor neurologic outcome (modified Rankin Scale [mRS] score > 2) at follow-up.

RESULTS

Data from 1014 patients were analyzed (69% [n = 703] women). Women were significantly older than men (mean ± SD, 56.6 ± 14.1 years vs 53.4 ± 14.2 years, p < 0.001). A significantly lower percentage of women than men had a history of tobacco use (36.6% [n = 257] vs 46% [n = 143], p = 0.005). A significantly higher percentage of women than men had no high-risk factors for aSAH (10% [n = 70] vs 5% [n = 16], p = 0.01). The percentage of women with an mRS score > 2 at the last follow-up was significantly lower among those without high-risk factors (34%, 24/70) versus those with high-risk factors (53%, 334/633) (p = 0.004). Subsequent propensity-adjusted analysis (adjusted for age, Hunt and Hess grade, and Fisher grade) found no statistically significant difference in the odds of a poor outcome for women with or without high-risk factors for aSAH (OR = 0.7, 95% CI = 0.4-1.2, p = 0.18).

CONCLUSIONS

A higher percentage of women versus men with aSAH had no known high-risk factors for rupture, supporting more aggressive screening and management of women with unruptured aneurysms.

Pharmacological Inhibition of Epidermal Growth Factor Receptor Prevents Intracranial Aneurysm Rupture by Reducing Endoplasmic Reticulum Stress

BACKGROUND

Multiple pathways and factors are involved in the rupture of intracranial aneurysms. The EGFR (epidermal growth factor receptor) has been shown to mediate inflammatory vascular diseases, including atherosclerosis and aortic aneurysm. However, the role of EGFR in mediating intracranial aneurysm rupture and its underlying mechanisms have yet to be determined. Emerging evidence indicates that endoplasmic reticulum (ER) stress might be the link between EGFR activation and the resultant inflammation. ER stress is strongly implicated in inflammation and apoptosis of vascular smooth muscle cells, both of which are key components of the pathophysiology of aneurysm rupture. Therefore, we hypothesized that EGFR activation promotes aneurysmal rupture by inducing ER stress.

METHODS

Using a preclinical mouse model of intracranial aneurysm, we examined the potential roles of EGFR and ER stress in developing aneurysmal rupture.

RESULTS

Pharmacological inhibition of EGFR markedly decreased the rupture rate of intracranial aneurysms without altering the formation rate. EGFR inhibition also significantly reduced the mRNA (messenger RNA) expression levels of ER-stress markers and inflammatory cytokines in cerebral arteries. Similarly, ER-stress inhibition also significantly decreased the rupture rate. In contrast, ER-stress induction nullified the protective effect of EGFR inhibition on aneurysm rupture.

CONCLUSIONS

Our data suggest that EGFR activation is an upstream event that contributes to aneurysm rupture via the induction of ER stress. Pharmacological inhibition of EGFR or downstream ER stress may be a promising therapeutic strategy for preventing aneurysm rupture and subarachnoid hemorrhage.

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 artificial course 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.

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.

Oestrogen ameliorates blood-brain barrier damage after experimental subarachnoid haemorrhage via the SHH pathway in male rats

BACKGROUND

Sex differences affect the occurrence, progression and regression of subarachnoid haemorrhage (SAH). Oestrogen plays a protective role in alleviating the vasospasm and neuronal apoptosis induced by SAH. However, whether oestrogen affects blood‒brain barrier (BBB) integrity has not been fully studied. Oestrogen has been found to regulate the sonic hedgehog (SHH) signalling pathway through the oestrogen receptor in gastric cancer and adrenal glands, and the SHH signalling pathway has an important role in maintaining the BBB by upregulating the expression of tight junction proteins. In this study, we investigated the relationship between oestrogen and the SHH signalling pathway using clinical data and established an experimental SAH model to explore whether oestrogen could ameliorate BBB damage after SAH through the SHH pathway.

METHODS

Correlations between oestrogen and the SHH pathway were analysed by patients' cerebrospinal fluid (CSF) samples and the Genotype-Tissue Expression database (GTEx). Then, an experimental rat SAH model was established using the endovascular perforation method and treated with oestrogen, oestrogen inhibitors and SHH signalling pathway inhibitors. Then, the effects of oestrogen on BBB damage were analysed by western blot, immunofluorescence and neurobehavioural experiments.

RESULTS

ESLIA detection and correlation analysis showed that oestrogen levels in patients' CSF were positively correlated with the SHH pathway, which was further verified by GTEx gene-correlation analysis. SHH was found to be mainly expressed in neurons and astrocytes in rats under physiological conditions and was upregulated by oestrogen pretreatment. In the SAH model, oestrogen pretreatment was found to reverse SAH-induced decreases in the SHH pathway, which were counteracted by oestrogen receptor inhibitors. Furthermore, oestrogen pretreatment reduced SAH-induced BBB damage, brain oedema and neurological dysfunction, which were eliminated by SHH pathway inhibitors.

CONCLUSION

In conclusion, we demonstrate here that oestrogen pretreatment ameliorates brain injury after SAH, at least in part through SHH pathway-mediated BBB protection.

Animal model contributes to the development of intracranial aneurysm: A bibliometric analysis

Introduction

Studies on intracranial aneurysms (IAs) using animal models have evolved for decades. This study aimed to analyze major contributors and trends in IA-related animal research using bibliometric analysis.

Methods

IA-related animal studies were retrieved from the Web of Science database. Microsoft Excel 2010, GraphPad Prism 6, VOSviewer, and CiteSpace were used to collect and analyze the characteristics of this field.

Results

A total of 273 publications were retrieved. All publications were published between 1976 and 2021, and the peak publication year is 2019. Rat model were used in most of the publications, followed by mice and rabbits. Japan (35.5%), the United States (30.0%), and China (20.1%) were the top three most prolific countries. Although China ranks third in the number of publications, it still lacks high-quality articles and influential institutions. Stroke was the most prolific journal that accepted publications related to IA research using animal models. Circulation has the highest impact factor with IA-related animal studies. Hashimoto N contributed the largest number of articles. Meng hui journal published the first and second highest cited publications. The keywords “subarachnoid hemorrhage,” “macrophage,” “rupture,” “mice,” “elastase,” “gene,” “protein,” “proliferation,” and “risk factors” might be a new trend for studying IA-related animal research.

Conclusions

Japan and the Unites States contributed the most to IA–related animal studies, in terms of both researchers and institutions. Although China ranks third in terms of the number of publications, it should strengthen the quality of its publications. Researchers should pay attention to the latest progress of Stroke, Journal of Neurosurgery, Neurosurgery, and Circulation for their high-quality IA-related animal studies. Using animal IA models, especially mice, to investigate the molecular mechanisms of IA may be the frontier topic now and in future.

Association of Reproductive Life Span and Age at Menopause With the Risk of Aneurysmal Subarachnoid Hemorrhage

BACKGROUND AND OBJECTIVES

Subarachnoid hemorrhage from cerebral aneurysm remains a devastating disease with high mortality and morbidity. Cerebral aneurysm and its rupture are more prevalent in postmenopausal women and have been postulated to be hormonally influenced. The goal of this study was to investigate the associations of female-specific factors, including reproductive life span, age at menarche, and age at menopause, with the incidence of aneurysmal subarachnoid hemorrhage (aSAH) in women.

METHODS

Participants in the Nurses' Health Study were followed up from 1980 or the time of reaching menopause until 2018. Only women with natural menopause or surgical menopause due to bilateral oophorectomy were included. Reproductive life span was defined by subtracting the age at menarche from the age at menopause. Multivariable-stratified proportional hazards models were used to study reproductive life span, age at menarche, and age at menopause with the incidence of aSAH. Multivariable models were adjusted for age, race, smoking, hysterectomy, hypertension, hyperlipidemia, body mass index, hormone therapy use, oral contraceptive use, and parity.

RESULTS

A total of 97,398 postmenopausal women with reproductive life span data were included; 138 participants developed aSAH, which was confirmed on medical record review by a physician. A shorter reproductive life span (≤35 years) was associated with a 2-fold higher incidence of aSAH after multivariable adjustment (hazard ratio [HR] 2.0 [95% CI 1.4-2.8]). Early age at menopause (age <45 years) was similarly associated with a higher risk of aSAH (HR 2.1 [95% CI 1.4-3.1]), but age at menarche was not. Use of oral contraceptives and postmenopausal hormone therapy was not associated with the incidence of aSAH.

DISCUSSION

An earlier age at menopause and a shorter reproductive life span duration (≤35 years) were associated with a higher risk of incident aSAH in women. No associations were noted for age at menarche, parity, oral contraceptive use, or postmenopausal therapy use.

Intracranial aneurysm wall (in)stability-current state of knowledge and clinical perspectives

Intracranial aneurysm (IA), a local outpouching of cerebral arteries, is present in 3 to 5% of the population. Once formed, an IA can remain stable, grow, or rupture. Determining the evolution of IAs is almost impossible. Rupture of an IA leads to subarachnoid hemorrhage and affects mostly young people with heavy consequences in terms of death, disabilities, and socioeconomic burden. Even if the large majority of IAs will never rupture, it is critical to determine which IA might be at risk of rupture. IA (in)stability is dependent on the composition of its wall and on its ability to repair. The biology of the IA wall is complex and not completely understood. Nowadays, the risk of rupture of an IA is estimated in clinics by using scores based on the characteristics of the IA itself and on the anamnesis of the patient. Classification and prediction using these scores are not satisfying and decisions whether a patient should be observed or treated need to be better informed by more reliable biomarkers. In the present review, the effects of known risk factors for rupture, as well as the effects of biomechanical forces on the IA wall composition, will be summarized. Moreover, recent advances in high-resolution vessel wall magnetic resonance imaging, which are promising tools to discriminate between stable and unstable IAs, will be described. Common data elements recently defined to improve IA disease knowledge and disease management will be presented. Finally, recent findings in genetics will be introduced and future directions in the field of IA will be exposed.

Sex Differences in Cerebral Aneurysms and Subarachnoid Hemorrhage

Sex differences in cerebral aneurysm occurrence and characteristics have been well described. Although sex differences in outcomes following ischemic stroke have been identified, the effect of sex on outcomes following hemorrhagic stroke, and in particular, aneurysm treatment has been less studied. We describe the current state of knowledge regarding the impact of sex on treatment and outcomes of cerebral aneurysms. Although prior studies suggest that aneurysm prevalence and progression may be related to sex, we did not find clear evidence that outcomes following subarachnoid hemorrhage vary based on sex. Last, we identify areas for future research that could enhance understanding of the role sex plays in this context.

Formation, Growth, or Rupture of De Novo Intracranial Aneurysms: Long-Term Follow-up Study of Subarachnoid Hemorrhage Survivors

BACKGROUND

The survival rate of aneurysmal subarachnoid hemorrhage (aSAH) has gradually increased, leading to more clinical cases of de novo intracranial aneurysms (DNIAs).

OBJECTIVE

To identify the characteristics of patients with DNIA growth or rupture.

METHODS

We included 1601 patients with aSAH treated by clipping from January 1993 to May 2010. According to the inclusion and exclusion criteria, 233 patients had no DNIAs, and 63 patients had 77 DNIAs. We assessed the incidence rate of DNIAs and risk factors for DNIA formation. After dichotomizing the DNIA group into the heed (patients with DNIA rupture or growth) and stable groups (patients without DNIA growth), we assessed the risk factors for DNIA growth or rupture.

RESULTS

The total follow-up period was 4427.9 patient-years. The incidence rate per patient-year was 1.42%. Age ≤50 yr, family history of aneurysm, and multiplicity at initial aSAH were significant risk factors for DNIA formation. Multivariate regression analysis revealed that female sex (odds ratio [OR], 5.566; 95% confidence interval [CI], 1.241-24.952), duration from initial aSAH to DNIA detection <120 mo (OR, 5.043; 95% CI, 1.362-18.668), multiplicity at initial aSAH (OR, 4.859; 95% CI, 1.207-19.563), and maximum DNIA diameter ≥4 mm (OR, 11.104; 95% CI, 2.337-52.772) were significant risk factors for DNIA growth or rupture.

CONCLUSION

DNIAs had a higher incidence rate than expected. Taking into account the presented incidence rate and risk factors, long-term surveillance in aSAH survivors for more than a decade may be worth considering, at least on a case-by-case basis.

Roles of Phytoestrogen in the Pathophysiology of Intracranial Aneurysm

[Figure: see text].

Neutrophil Extracellular Traps Promote the Development of Intracranial Aneurysm Rupture

[Figure: see text].

Tobacco Use: A Major Risk Factor of Intracerebral Hemorrhage

Spontaneous intracerebral hemorrhage (sICH) is one of the deadliest subtypes of stroke, and no treatment is currently available. One of the major risk factors is tobacco use. In this article, we review literature on how tobacco use affects the risk of sICH and also summarize the known effects of tobacco use on outcomes following sICH. Several studies demonstrate that the risk of sICH is higher in current cigarette smokers compared to non-smokers. The literature also establishes that cigarette smoking not only increases the risk of sICH but also increases hematoma growth, results in worse outcomes, and increases the risk of death from sICH. This review also discusses potential mechanisms activated by tobacco use which result in an increase in risk and severity of sICH. Exploring the underlying mechanisms may help alleviate the risk of sICH in tobacco users as well as may help better manage tobacco user sICH patients.

Endogenous animal models of intracranial aneurysm development: a review

The pathogenesis and natural history of intracranial aneurysm (IA) remains poorly understood. To this end, animal models with induced cerebral vessel lesions mimicking human aneurysms have provided the ability to greatly expand our understanding. In this review, we comprehensively searched the published literature to identify studies that endogenously induced IA formation in animals. Studies that constructed aneurysms (i.e., by surgically creating a sac) were excluded. From the eligible studies, we reported information including the animal species, method for aneurysm induction, aneurysm definitions, evaluation methods, aneurysm characteristics, formation rate, rupture rate, and time course. Between 1960 and 2019, 174 articles reported endogenous animal models of IA. The majority used flow modification, hypertension, and vessel wall weakening (i.e., elastase treatment) to induce IAs, primarily in rats and mice. Most studies utilized subjective or qualitative descriptions to define experimental aneurysms and histology to study them. In general, experimental IAs resembled the pathobiology of the human disease in terms of internal elastic lamina loss, medial layer degradation, and inflammatory cell infiltration. After the early 2000s, many endogenous animal models of IA began to incorporate state-of-the-art technology, such as gene expression profiling and 9.4-T magnetic resonance imaging (MRI) in vivo imaging, to quantitatively analyze the biological mechanisms of IA. Future studies aimed at longitudinally assessing IA pathobiology in models that incorporate aneurysm growth will likely have the largest impact on our understanding of the disease. We believe this will be aided by high-resolution, small animal, survival imaging, in situ live-cell imaging, and next-generation omics technology.

Sex-related differences in wall remodeling and intraluminal thrombus resolution in a rat saccular aneurysm model

OBJECTIVE

Intracranial aneurysms (IAs) are more often diagnosed in women. Hormones and vessel geometry, which influences wall shear stress, may affect pathophysiological processes of the arterial wall. Here, the authors investigated sex-related differences in the remodeling of the aneurysm wall and in intraluminal thrombus resolution.

METHODS

A well-characterized surgical side-wall aneurysm model was used in female, male, and ovariectomized rats. Decellularized grafts were used to model highly degenerated and decellularized IA walls and native grafts to model healthy IA walls. Aneurysm growth and thrombus composition were analyzed at 1, 7, 14, and 28 days. Sex-related differences in vessel wall remodeling were compared with human IA dome samples of men and pre- and postmenopausal women.

RESULTS

At 28 days, more aneurysm growth was observed in ovariectomized rats than in males or non-ovariectomized female rats. The parent artery size was larger in male rats than in female or ovariectomized rats, as expected. Wall inflammation increased over time in all groups and was most severe in the decellularized female and ovariectomized groups at 28 days compared with the male group. Likewise, in these groups the most elastin fragmentation was seen at 28 days. In female rats, on days 1, 7, and 14, the intraluminal thrombus was mainly composed of red blood cells and fibrin. On days 14 and 28, macrophage and smooth muscle cell invasion inside the thrombus was shown, leading to the removal of red blood cells and deposition of collagen and elastin. On days 14 and 28, similar profiles of thrombus reorganization were observed in male and ovariectomized female rats. However, collagen content in thrombi and vessel wall macrophage content were higher in aneurysms of male rats at 28 days than in those of female rats. On day 28, thrombus coverage by endothelial cells was lower in ovariectomized than in female or male rats. Finally, analysis of human IA domes showed that endothelial cell coverage was lower in men and postmenopausal women than in younger women.

CONCLUSIONS

Aneurysm growth and intraluminal thrombus resolution show sex-dependent differences. While certain processes (endothelial cell coverage and collagen deposition) point to a strong hormonal dependence, others (wall inflammation and aneurysm growth) seem to be influenced by both hormones and parent artery size.

Multiple and mirror intracranial aneurysms: study of prevalence and associated risk factors

OBJECTIVE

Multiple intracranial aneurysms (MIA) account for 30% of all intracranial aneurysms, while mirror aneurysms, a subgroup of MIA, are present in 5% of all patients with cerebral aneurysms. We investigated the risk factors associated with the presence of multiple and mirror intracranial aneurysms.

METHODS

1404 patients, 314 males (22.4%) and 1090 female (77.6%) were enrolled for this study. Diagnosis was performed with a digital subtraction angiography (DSA). Multiplicity was defined as the presence of two or more aneurysms and mirror aneurysms as one pair of aneurysms involving bilateral corresponding arteries. Patients were followed-up from September 2009 till August 2018. Individuals' characteristics such as sex, age, smoking, hypertension and use of contraceptives were evaluated.

RESULTS

Five hundred and twelve patients (36.4%) were diagnosed with MIA, approximately 4%/year. We observed 203 pairs of mirror aneurysms, accounting for 406 aneurysms (13% of the population). There was an increased frequency of females with multiple (p < 0.001, OR = 1.883, 95% CI = 1.386-2.560) and mirror aneurysms (p < 0.001, OR = 2.828, 95% CI = 1.725-4.636). Smoking was associated with multiplicity (p< 0.001, OR = 1.458, 95% CI = 1.160-1.833), as well as advanced age (p < 0.001, OR = 1.938, 95% CI = 1.438-2.611), but there was no significant relation with presence of mirror aneurysms. We observed higher frequency of baby aneurysms (<3mm) in the group of patients with MIA, while giant aneurysms (>25 mm) were most found in patients with only one aneurysm (p < 0.001). No differences between patients who used contraceptives against patients who did not use were found (p = 0.600).

CONCLUSIONS

Gender and smoking, known risk factors to the development of a single intracranial aneurysm, are proportionally increased in patients with MIA. Hypertension and oral contraceptives were not associated with multiplicity.

Interleukin-6 Promotes Murine Estrogen Deficiency-Associated Cerebral Aneurysm Rupture

BACKGROUND

Estrogen deficiency is associated with cerebral aneurysm rupture, but the precise mechanism is unknown.

OBJECTIVE

To test the hypothesis that IL-6 is required for the increase in aneurysm rupture rate observed in estrogen-deficient mice.

METHODS

We analyzed IL-6 expression in human cerebral aneurysms. We induced cerebral aneurysms in estrogen-deficient female C57BL/6 mice that had undergone 4-vinylcyclohexene diepoxide (VCD) treatment or bilateral ovariectomy (OVE). Mice were blindly randomized to selective IL-6 inhibition (IL-6 receptor [IL-6R] neutralizing antibody, n = 25) or control (isotype-matched IgG, n = 28). Murine cerebral arteries at the circle of Willis were assessed for aneurysm rupture and macrophage infiltration.

RESULTS

IL-6 is expressed in human cerebral aneurysms, but not in control arteries. Serum IL-6 is elevated in ovariectomized female mice compared to sham control (14.3 ± 1.7 pg/mL vs 7.4 ± 1.5 pg/mL, P = .008). Selective IL-6R inhibition suppressed cerebral aneurysm rupture in estrogen-deficient mice compared with control (VCD: 31.6% vs 70.0%, P = .026; OVE: 28.6% vs 65.2%, P = .019). IL-6R inhibition had no effect on formation or rupture rate in wild-type mice. IL-6R neutralizing antibody significantly reduced macrophage infiltration at the circle of Willis (1.9 ± 0.2 vs 5.7 ± 0.6 cells/2500 μm2; n = 8 vs n = 15; P < .001).

CONCLUSION

IL-6 is increased in the serum of estrogen-deficient mice and appears to play a role in promoting murine estrogen deficiency-associated cerebral aneurysm rupture via enhanced macrophage infiltration at the circle of Willis. Inhibition of IL-6 signaling via IL-6 receptor neutralizing antibody inhibits aneurysm rupture in estrogen-deficient mice. IL-6 receptor inhibition had no effect on aneurysm formation or rupture in wild-type animals.

Mast Cell Promotes the Development of Intracranial Aneurysm Rupture

BACKGROUND AND PURPOSE

Inflammation has emerged as a key component of the pathophysiology of intracranial aneurysms. Mast cells have been detected in human intracranial aneurysm tissues, and their presence was associated with intramural microhemorrhage and wall degeneration. We hypothesized that mast cells play a critical role in the development of aneurysmal rupture, and that mast cells can be used as a therapeutic target for the prevention of aneurysm rupture.

METHODS

Intracranial aneurysms were induced in adult mice using a combination of induced systemic hypertension and a single injection of elastase into the cerebrospinal fluid. Aneurysm formation and rupture were assessed over 3 weeks. Roles of mast cells were assessed using a mast cell stabilizer (cromolyn), a mast cell activator (C48/80), and mice that are genetically lacking mature mast cells (Kit^W-sh/W-sh mice).

RESULTS

Pharmacological stabilization of mast cells with cromolyn markedly decreased the rupture rate of aneurysms (80% versus 19%, n=10 versus n =16) without affecting the aneurysm formation. The activation of mast cells with C48/80 significantly increased the rupture rate of aneurysms (25% versus 100%, n=4 versus n=5) without affecting the overall rate of aneurysm formation. Furthermore, the genetic deficiency of mast cells significantly prevented aneurysm rupture (80% versus 25%, n=10 versus n=8, wild-type versus Kit^W-sh/W-sh mice).

CONCLUSIONS

These results suggest that mast cells play a key role in promoting aneurysm rupture but not formation. Stabilizers of mast cells may have a potential therapeutic value in preventing intracranial aneurysm rupture in patients.

Sex and Genetic Background Effects on the Outcome of Experimental Intracranial Aneurysms

BACKGROUND AND PURPOSE

Intracranial aneurysm formation and rupture risk are, in part, determined by genetic factors and sex. To examine their role, we compared 3 mouse strains commonly used in cerebrovascular studies in a model of intracranial aneurysm formation and rupture.

METHODS

Intracranial aneurysms were induced in male CD1 (Crl:CD1[ICR]), male and female C57 (C57BL/6NCrl), and male 129Sv (129S2/SvPasCrl or 129S1/SvImJ) mice by stereotaxic injection of elastase at the skull base, combined with systemic deoxycorticosterone acetate-salt hypertension. Neurological deficits and mortality were recorded. Aneurysms and subarachnoid hemorrhage grades were quantified postmortem, either after spontaneous mortality or at 7 to 21 days if the animals survived. In separate cohorts, we examined proinflammatory mediators by quantitative reverse transcriptase-polymerase chain reaction, arterial blood pressure via the femoral artery, and the circle of Willis by intravascular latex casting.

RESULTS

We found striking differences in aneurysm formation, rupture, and postrupture survival rates among the groups. 129Sv mice showed the highest rates of aneurysm rupture (80%), followed by C57 female (36%), C57 male (27%), and CD1 (21%). The risk of aneurysm rupture and the presence of unruptured aneurysms significantly differed among all 3 strains, as well as between male and female C57. The same hierarchy was observed upon Kaplan-Meier analysis of both overall survival and deficit-free survival. Subarachnoid hemorrhage grades were also more severe in 129Sv. CD1 mice showed the highest resistance to aneurysm rupture and the mildest outcomes. Higher mean blood pressures and the major phenotypic difference in the circle of Willis anatomy in 129Sv provided an explanation for the higher incidence of and more severe aneurysm ruptures. TNFα (tumor necrosis factor-alpha), IL-1β (interleukin-1-beta), and CCL2 (chemokine C-C motif ligand 2) expressions did not differ among the groups.

CONCLUSIONS

The outcome of elastase-induced intracranial aneurysm formation and rupture in mice depends on genetic background and shows sexual dimorphism.

The Bilateral Ovariectomy in a Female Animal Exacerbates the Pathogenesis of an Intracranial Aneurysm

Considering the poor outcome of subarachnoid hemorrhage (SAH) due to the rupture of intracranial aneurysms (IA), mechanisms underlying the pathogenesis of IAs, especially the rupture of lesions, should be clarified. In the present study, a rat model of IAs in which induced lesions spontaneously ruptured resulting in SAH was used. In this model, the combination of the female sex and the bilateral ovariectomy increased the incidence of SAH, similar to epidemiological evidence in human cases. Importantly, unruptured IA lesions induced in female animals with bilateral ovariectomy were histopathologically similar to ruptured ones in the presence of vasa vasorum and the accumulation of abundant inflammatory cells, suggesting the exacerbation of the disease. The post-stenotic dilatation of the carotid artery was disturbed by the bilateral ovariectomy in female rats, which was restored by hormone replacement therapy. The in vivo study thus suggested the protective effect of estrogen from the ovary on endothelial cells loaded by wall shear stress. β-estradiol or dihydrotestosterone also suppressed the lipopolysaccharide-induced expression of pro-inflammatory genes in cultured macrophages and neutrophils. The results of the present study have thus provided new insights about the process regulating the progression of the disease.

Preclinical Intracranial Aneurysm Models: A Systematic Review

Intracranial aneurysms (IA) are characterized by weakened cerebral vessel walls that may lead to rupture and subarachnoid hemorrhage. The mechanisms behind their formation and progression are yet unclear and warrant preclinical studies. This systematic review aims to provide a comprehensive, systematic overview of available animal models for the study of IA pathobiology. We conducted a systematic literature search using the PubMed database to identify preclinical studies employing IA animal models. Suitable articles were selected based on predefined eligibility criteria following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Included studies were reviewed and categorized according to the experimental animal and aneurysm model. Of 4266 returned results, 3930 articles were excluded based on the title and/or abstract and further articles after screening the full text, leaving 123 studies for detailed analysis. A total of 20 different models were found in rats (nine), mice (five), rabbits (four), and dogs (two). Rat models constituted the most frequently employed intracranial experimental aneurysm model (79 studies), followed by mice (31 studies), rabbits (12 studies), and two studies in dogs. The most common techniques to induce cerebral aneurysms were surgical ligation of the common carotid artery with subsequent induction of hypertension by ligation of the renal arteries, followed by elastase-induced creation of IAs in combination with corticosterone- or angiotensin-induced hypertension. This review provides a comprehensive summary of the multitude of available IA models to study various aspects of aneurysm formation, growth, and rupture. It will serve as a useful reference for researchers by facilitating the selection of the most appropriate model and technique to answer their scientific question.

Potential Influences of Gut Microbiota on the Formation of Intracranial Aneurysm

Gut microbiota modulates metabolic and immunoregulatory axes and contributes to the pathophysiology of diseases with inflammatory components, such as atherosclerosis, diabetes mellitus, and ischemic stroke. Inflammation is emerging as a critical player in the pathophysiology of an intracranial aneurysm. Therefore, we hypothesized that the gut microbiota affects aneurysm formation by modulating inflammation. We induced intracranial aneurysms in mice by combining systemic hypertension and a single injection of elastase into the cerebrospinal fluid. Depletion of the gut microbiota was achieved via an oral antibiotic cocktail of vancomycin, metronidazole, ampicillin, and neomycin. Antibiotics were given 3 weeks before aneurysm induction and either continued until the end of the experiment or stopped 1 day before aneurysm induction. We also assessed the effects of the gut microbiota depletion on macrophage infiltration and mRNA levels of inflammatory cytokines. Gut microbiota depletion by antibiotics reduced the incidence when antibiotics were started 3 weeks before aneurysm induction and continued until the end of the experiment (83% versus 6%, P<0.001). Even when antibiotics were stopped 1 day before aneurysm induction, the gut microbiota depletion significantly reduced the incidence of aneurysms (86% versus 28%, P<0.05). Both macrophage infiltration and mRNA levels of inflammatory cytokines were reduced with gut microbiota depletion. These findings suggest that the gut microbiota contributes to the pathophysiology of aneurysms by modulating inflammation. Human studies are needed to determine the exact contribution of the gut microbiota to the pathophysiology of aneurysm formation and disease course in humans.

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.

Association of Bone Mineral Density With the Risk of Intracranial Aneurysm

Importance

Disruption of extracellular matrix integrity is critically involved in both intracranial aneurysm and bone fragility. Furthermore, both intracranial aneurysm and osteoporosis have a female predominance, and sex hormones are considered to affect this discrepancy.

Objective

To evaluate the association between bone mineral density and intracranial aneurysm.

Design, Setting, and Participants

A cross-sectional study conducted with 14 328 patients who underwent brain magnetic resonance angiography and bone mineral densitometry as a part of a health examination at a specialized center for comprehensive health examination in Seoul, the largest metropolitan area in the Republic of Korea, between December 2004 and November 2015. After excluding patients with insufficient clinical information (n = 1102) and with ambiguous intracranial arterial lesion (n = 441), 12 785 were included in the analysis.

Exposures

Bone mineral density was measured at the lumbar vertebrae (L1 to L4), femur neck, and total hip using dual-energy x-ray absorptiometry.

Main Outcomes and Measures

Multiple logistic regression or linear regression was used to examine the association between tertiles of bone mineral density and the presence, size, and multiplicity of intracranial aneurysms. In secondary analyses, we analyzed postmenopausal women and men 50 years and older (n = 8722) because they are particularly at risk of decreased bone mineral density.

Results

Among 12 785 patients in the study (7242 women [56.6%]; mean [SD] age, 54.8 [10.1] years) intracranial aneurysms were found in 472 patients (3.7%). Lower bone mineral density was associated with an increased risk of harboring intracranial aneurysm. In multivariable logistic regression analyses, odds ratios for the highest compared with the lowest bone mineral density tertile were 1.30 (95% CI, 1.03-1.64) in the lumbar spine, 1.30 (95% CI, 1.03-1.64) in the femoral neck, and 1.27 (95% CI, 1.01-1.60) in the total hip after adjusting for age, sex, and vascular risk factors. In a linear regression model adjusted for age, sex, and vascular risk factors, the lowest tertile of bone mineral density in the lumbar spine was associated with an increased log-transformed size of aneurysm (β, 0.196; SE, 0.047). In secondary analyses, these associations were more definite and a low T score (<-1 SD) was additionally associated with multiple aneurysms (OR, 1.84; 95% CI, 1.05-3.30) after adjusting for age, sex, and vascular risk factors.

Conclusions and Relevance

Bone mineral density may be associated with the presence, size, and multiplicity of intracranial aneurysm. The study findings provide evidence for shared pathophysiology between intracranial aneurysm and bone fragility.

In vivo cerebral aneurysm models

Cerebral aneurysm rupture is a devastating event resulting in subarachnoid hemorrhage and is associated with significant morbidity and death. Up to 50% of individuals do not survive aneurysm rupture, with the majority of survivors suffering some degree of neurological deficit. Therefore, prior to aneurysm rupture, a large number of diagnosed patients are treated either microsurgically via clipping or endovascularly to prevent aneurysm filling. With the advancement of endovascular surgical techniques and devices, endovascular treatment of cerebral aneurysms is becoming the first-line therapy at many hospitals. Despite this fact, a large number of endovascularly treated patients will have aneurysm recanalization and progression and will require retreatment. The lack of approved pharmacological interventions for cerebral aneurysms and the need for retreatment have led to a growing interest in understanding the molecular, cellular, and physiological determinants of cerebral aneurysm pathogenesis, maturation, and rupture. To this end, the use of animal cerebral aneurysm models has contributed significantly to our current understanding of cerebral aneurysm biology and to the development of and training in endovascular devices. This review summarizes the small and large animal models of cerebral aneurysm that are being used to explore the pathophysiology of cerebral aneurysms, as well as the development of novel endovascular devices for aneurysm treatment.

Endothelial dysfunction in cerebral aneurysms

Endothelial cell (EC) dysfunction is known to contribute to cerebral aneurysm (CA) pathogenesis. Evidence shows that damage or injury to the EC layer is the first event in CA formation. The mechanisms behind EC dysfunction in CA disease are interrelated and include hemodynamic stress, hazardous nitric oxide synthase (NOS) activity, oxidative stress, estrogen imbalance, and endothelial cell-to-cell junction compromise. Abnormal variations in hemodynamic stress incite pathological EC transformation and inflammatory zone formation, ultimately leading to destruction of the vascular wall and aneurysm dilation. Hemodynamic stress activates key molecular pathways that result in the upregulation of chemotactic cytokines and adhesion molecules, leading to inflammatory cell recruitment and infiltration. Concurrently, oxidative stress damages EC-to-EC junction proteins, resulting in interendothelial gap formation. This further promotes leukocyte traffic into the vessel wall and the release of matrix metalloproteinases, which propagates vascular remodeling and breakdown. Abnormal hemodynamic stress and inflammation also trigger adverse changes in NOS activity, altering proper EC mediation of vascular tone and the local inflammatory environment. Additionally, the vasoprotective hormone estrogen modulates gene expression that often suppresses these harmful processes. Crosstalk between these sophisticated pathways contributes to CA initiation, progression, and rupture. This review aims to outline the complex mechanisms of EC dysfunction in CA pathogenesis.

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.

The role of inflammation and potential pharmacological therapy in intracranial aneurysms

Intracranial aneurysms remain important clinical concern. There is relatively low risk of rupture of symptomless aneurysms incidentally found in MRA or CTA performed due to other indications. Not all of the intracranial aneurysms should or can be treated with neurosurgery intervention or endovascular embolization. Clinical strategy for small, symptomless, unruptured aneurysms is still questionable. Mechanisms underlying aneurysms formation, progression and rupture are poorly understood. Inflammation is one of the factors suspected to participate in these processes. Therefore the aim of this manuscript is to present current state of knowledge about the role of inflammation in the formation and progression of intracranial aneurysms and in their rupture process. Current knowledge about possible pharmacological treatment of intracranial aneurysms will also be presented. Macrophages infiltration seems to participate in the formation of intracranial aneurysms. Inhibition of signals sent by macrophages may prevent the aneurysms formation. Inflammation present in the wall of the aneurysm seems to be also related to the aneurysm's rupture risk. However it does not seem to be the only cause of the degeneration, but it can be a possible target of drug therapy. Some preliminary studies in humans indicate the potential role of aspirin as a factor that decrease the level of inflammation and lower the risk of rupture of intracranial aneurysms. However further research including a greater number of subjects and a prospective randomized design are necessary to assess the role of aspirin in preventing strategy for small, symptomless, unruptured intracranial aneurysms.

Vasospasm-related complications after subarachnoid hemorrhage: the role of patients' age and sex

BACKGROUND

Outcome of aneurysmal subarachnoid hemorrhage (SAH) depends strongly on occurrence of symptomatic vasospasm (SV) leading to delayed cerebral ischemia (DCI). Various demographic, radiographic, and clinical predictors of SV have been reported so far, partially with conflicting results. The aim of this study was to analyze the role of patients' age and sex on SV/DCI risk, especially to identify age and sex-specific risk groups.

METHODS

All patients admitted with acute SAH during a 14-year-period ending in 2016 were eligible for this study. The study endpoints were the following: SV requiring spasmolysis, occurrence of DCI in follow-up computed tomography scans and unfavorable outcome at 6 months (modified Rankin scale > 2).

RESULTS

Nine hundred ninety-four patients were included in this study. The majority was female (666; 67%). SV, DCI, and unfavorable outcomes were observed in 21.5, 21.8, and 43.6% of the patients, respectively. Younger age (p < 0.001; OR = 1.03 per year decrease) and female sex (p = 0.025; OR = 1.510) were confirmed as independent predictors of SV. Regarding the sex differences, there were three age groups for SV/DCI risk ≤ 54, 55-74, and ≥ 75 years. Male patients showed earlier decrease in SV risk (at ≥ 55 vs. ≥ 75 years in females). Therefore, SAH females aged between 55 and 74 years were at the highest risk for DCI and unfavorable outcome, as compared to younger/older females (p = 0.001, OR = 1.77/p = 0.001, OR = 1.80). In contrast, their male counterparts did not show these risk alterations (p = 0.445/p = 0.822).

CONCLUSION

After acute SAH, female and male patients seem to show different age patterns for the risk of SV and DCI. Females aged between 55 and 74 years are at particular risk of vasospasm-related SAH complications, possibly due to onset of menopause.

CLINICAL TRIAL REGISTRATION NUMBER

DRKS, Unique identifier: DRKS00008749.

Protective Effect of Mesenchymal Stem Cells Against the Development of Intracranial Aneurysm Rupture in Mice

BACKGROUND

Mesenchymal stem cells (MSCs) are multipotent stem or stromal cells found in multiple tissues. Intravenous MSC injections have been used to treat various diseases with an inflammatory component in animals and humans. Inflammation is emerging as a key component of pathophysiology of intracranial aneurysms. Modulation of inflammation by MSCs may affect sustained inflammatory processes that lead to aneurysmal rupture.

OBJECTIVE

To assess the effect of MSCs on the development of aneurysm rupture using a mouse model.

METHODS

Intracranial aneurysms were induced with a combination of a single elastase injection into the cerebrospinal fluid and deoxycorticosterone acetate salt-induced hypertension in mice. We administered allogeneic bone marrow-derived MSCs or vehicle, 6 and 9 d after aneurysm induction.

RESULTS

MSC administration significantly reduced rupture rate (vehicle control vs MSCs, 90% vs 36%; P < .05). In cell culture experiments with an MSC and mast cell coculture, MSCs stabilized mast cells through cyclooxygenase-2 (COX-2)-dependent production of prostaglandin E2, thereby reducing the release of proinflammatory cytokines from mast cells. Pretreatment of MSCs with COX-2 inhibitor, NS-398, abolished the protective effect of MSCs against the development of aneurysm rupture.

CONCLUSION

Intravenous administration of MSCs after aneurysm formation prevented aneurysmal rupture in mice. The protective effect of MSCs against the development of aneurysm rupture appears to be mediated in part by the stabilization of mast cells by MSCs.

Estrogen Deficiency Promotes Cerebral Aneurysm Rupture by Upregulation of Th17 Cells and Interleukin-17A Which Downregulates E-Cadherin

BACKGROUND

Estrogen deficiency is associated with the development of cerebral aneurysms; however, the mechanism remains unknown. We explored the pathway of cerebral aneurysm development by investigating the potential link between estrogen deficiency and inflammatory factors.

METHODS AND RESULTS

First, we established the role of interleukin-17 (IL-17)A. We performed a cytokine screen demonstrating that IL-17A is significantly expressed in mouse and human aneurysms (P=0.03). Likewise, IL-17A inhibition was shown to prevent aneurysm formation by 42% (P=0.02) and rupture by 34% (P<0.05). Second, we found that estrogen deficiency upregulates T helper 17 cells and IL-17A and promotes aneurysm rupture. Estrogen-deficient mice had more ruptures than control mice (47% versus 7%; P=0.04). Estradiol supplementation or IL-17A inhibition decreased the number of ruptures in estrogen-deficient mice (estradiol 6% versus 37%; P=0.04; IL-17A inhibition 18% versus 47%; P=0.018). Third, we found that IL-17A-blockade protects against aneurysm formation and rupture by increased E-cadherin expression. IL-17-inhibited mice had increased E-cadherin expression (P=0.003). E-cadherin inhibition reversed the protective effect of IL-17A inhibition and increased the rate of aneurysm formation (65% versus 28%; P=0.04) and rupture (12% versus 0%; P=0.22). However, E-cadherin inhibition alone does not significantly increase aneurysm formation in normal mice or in estrogen-deficient mice. In cell migration assays, E-cadherin inhibition promoted macrophage infiltration across endothelial cells (P<0.05), which may be the mechanism for the estrogen deficiency/IL-17/E-cadherin aneurysm pathway.

CONCLUSIONS

Our data suggest that estrogen deficiency promotes cerebral aneurysm rupture by upregulating IL-17A, which downregulates E-cadherin, encouraging macrophage infiltration in the aneurysm vessel wall.

Is fetal-type posterior cerebral artery a risk factor for intracranial aneurysm as analyzed by multislice CT angiography?

Fetal-type posterior cerebral artery (FTP) is a common anatomic variation that is closely associated with intracranial aneurysm. In the present study, multislice computed tomography angiography (CTA) was performed to assess whether FTP is a risk factor for intracranial aneurysm. CTA data of 364 consecutive cases of patients who were suspected with cerebrovascular disease or intracranial aneurysm of intracranial artery from 2013 to 2016 were reviewed and the incidence rates of FTP, other variations of the circle of Willis, intracranial aneurysm and FTP with intracranial aneurysm were evaluated. The χ² test was used to assess the influence of FTP and gender on the incidence rates of other variations of the circle of Willis, intracranial aneurysm and internal carotid artery-posterior communicating artery (ICA-PComA) aneurysm. Binary logistic regression analysis was performed to assess the associations of FTP and gender with intracranial aneurysm and ICA-PComA aneurysm. Compared with non-FTP patients, FTP cases exhibited significantly higher rates of other variations of the circle of Willis (χ²=80.173, P<0.001) and ICA-PComA aneurysm (χ²=4.437, P=0.035). Among patients with FTP and bilateral FTP, more female than male patients with intracranial aneurysm were identified. However, among all patients with intracranial aneurysm, no statistically significant differences in the prevalence of FTP (χ²=2.577, P=0.108) and bilateral FTP (χ²=2.199, P=0.159) between males and females were identified. Binary logistic regression analysis revealed that FTP and gender were risk factors for intracranial aneurysm and ICA-PComA aneurysm. A moderate association between FTP and ICA-PComA aneurysm (OR=2.762) were identified, although there was a weak association between FTP and intracranial aneurysm [odds ratio (OR)=1.365]. Furthermore, a strong association was identified between gender and intracranial aneurysm (OR=0.328), and a moderate association existed between gender and ICA-PComA aneurysm (OR=0.357). In conclusion, female gender is an independent risk factor for intracranial aneurysm, and FTP and female gender are independent risk factors for ICA-PComA aneurysm.

Bazedoxifene, a selective estrogen receptor modulator, reduces cerebral aneurysm rupture in Ovariectomized rats

Background

Estrogen deficiency is thought to be responsible for the higher frequency of aneurysmal subarachnoid hemorrhage in post- than premenopausal women. Estrogen replacement therapy appears to reduce this risk but is associated with significant side effects. We tested our hypothesis that bazedoxifene, a clinically used selective estrogen receptor (ER) modulator with fewer estrogenic side effects, reduces cerebral aneurysm rupture in a new model of ovariectomized rats.

Methods

Ten-week-old female Sprague-Dawley rats were subjected to ovariectomy, hemodynamic changes, and hypertension to induce aneurysms (ovariectomized aneurysm rats) and treated with vehicle or with 0.3 or 1.0 mg/kg/day bazedoxifene. They were compared with sham-ovariectomized rats subjected to hypertension and hemodynamic changes (HT rats). The vasoprotective effects of bazedoxifene and the mechanisms underlying its efficacy were analyzed.

Results

During 12 weeks of observation, the incidence of aneurysm rupture was 52% in ovariectomized rats. With no effect on the blood pressure, treatment with 0.3 or 1.0 mg/kg/day bazedoxifene lowered this rate to 11 and 17%, almost the same as in HT rats (17%). In ovariectomized rats, the mRNA level of ERα, ERβ, and the tissue inhibitor of metalloproteinase-2 was downregulated in the cerebral artery prone to rupture at 5 weeks after aneurysm induction; the mRNA level of interleukin-1β and the matrix metalloproteinase-9 was upregulated. In HT rats, bazedoxifene restored the mRNA level of ERα and ERβ and decreased the level of interleukin-1β and matrix metalloproteinase-9. These findings suggest that bazedoxifene was protective against aneurysmal rupture by alleviating the vascular inflammation and degradation exacerbated by the decrease in ERα and ERβ.

Conclusions

Our observation that bazedoxifene decreased the incidence of aneurysmal rupture in ovariectomized rats warrants further studies to validate this response in humans.

Electronic supplementary material

The online version of this article (10.1186/s12974-017-0966-7) contains supplementary material, which is available to authorized users.

Sex differences in vascular physiology and pathophysiology: estrogen and androgen signaling in health and disease

Sex differences between women and men are often overlooked and underappreciated when studying the cardiovascular system. It has been long assumed that men and women are physiologically similar, and this notion has resulted in women being clinically evaluated and treated for cardiovascular pathophysiological complications as men. Currently, there is increased recognition of fundamental sex differences in cardiovascular function, anatomy, cell signaling, and pathophysiology. The National Institutes of Health have enacted guidelines expressly to gain knowledge about ways the sexes differ in both normal function and diseases at the various research levels (molecular, cellular, tissue, and organ system). Greater understanding of these sex differences will be used to steer future directions in the biomedical sciences and translational and clinical research. This review describes sex-based differences in the physiology and pathophysiology of the vasculature, with a special emphasis on sex steroid receptor (estrogen and androgen receptor) signaling and their potential impact on vascular function in health and diseases (e.g., atherosclerosis, hypertension, peripheral artery disease, abdominal aortic aneurysms, cerebral aneurysms, and stroke).

MRI Characterization in the Acute Phase of Experimental Subarachnoid Hemorrhage

A number of mechanisms have been proposed for the early brain injury after subarachnoid hemorrhage (SAH). In this study, we investigated the radiographic characteristics and influence of gender on early brain injury after experimental SAH. SAH was induced by endovascular perforation in male and female rats. Magnetic resonance imaging was performed in a 7.0-T Varian MR scanner at 24 h after SAH. The occurrence and size of T2 lesions, ventricular dilation, and white matter injury (WMI) were determined on T2-weighted images (T2WI). The effects of SAH on heme oxygenase-1 and fibrin/fibrinogen were examined by Western blotting and immunohistochemistry. SAH severity was assessed using a MRI grading system, and neurological function was evaluated according to a modified Garcia's scoring system. T2 hyperintensity areas and enlarged ventricles were observed in T2WI coronal sections 24 h after SAH. The overall incidence of T2 lesions, WMI, and hydrocephalus was 54, 20, and 63%, respectively. Female rats had a higher incidence of T2 hyperintensity lesions and hydrocephalus, as well as larger T2 lesion volumes and higher average ventricular volume. SAH rats graded at 3-4 (our previously validated MRI grading scale) had larger T2 lesion volumes, more hydrocephalus, and worse neurological function compared with those graded at 0-2. In conclusion, T2 lesion, WMI, and hydrocephalus were the most prevalent MRI characteristics 24 h after experimental SAH. The T2 lesion area matched with fibrinogen/fibrin positive staining in the acute phase of SAH. SAH induced more severe brain injury in females compared to males in the acute phase of SAH.

Treatment of unruptured intracranial aneurysms: a review

INTRODUCTION

Unruptured brain aneurysms (UIAs) present a challenge due to the lack of definitive understanding of their natural history and treatment outcomes. As the treatment of UIAs is aimed at preventing the possibility of rupture, the immediate risk of treatment must be weighed against the risk of rupture in the future. As such, treatment for a large proportion of UIAs is currently individualized.

AREAS COVERED

In this article, we discuss the important natural history studies of UIAs and discuss the existing scientific evidence and recent advances that help identify the rupture risk guide management of UIAs. We also address the recent advances in pharmacological therapy of UIAs. Expert commentary: In the recent years, there have been great advances in understanding the pathophysiology of UIAs and determining the rupture risk going beyond the traditional parameter of aneurysm size. Aneurysm morphology and hemodynamics play a pivotal role in growth and rupture. A true randomized trial for the management of UIAs is the need of the hour.

A higher aneurysmal subarachnoid hemorrhage incidence in women prior to menopause: a retrospective analysis of 4,895 cases from eight hospitals in China

BACKGROUND

Subarachnoid hemorrhage (SAH) from a ruptured cerebral aneurysm is a devastating disease. Despite the risk factors, including hypertension, cigarette smoking and alcohol use, are more common in men, aneurysmal SAH belongs to a few diseases which the incidence is higher in women than in men. Sex hormones, especially estrogen, might be protective against this condition. Hormone replacement therapy (HRT) seems to be associated with a reduced risk for aneurysmal SAH. This study aims to know the prevalence of aneurysmal SAH of men and women at different ages.

METHODS

The age and gender information of 4,895 case of aneurysmal SAH (3,016 females, 1,879 males) were collected retrospectively from eight institutions in mainland China. The prevalence of aneurysmal SAH of men and women at different ages was analyzed.

RESULTS

The data showed women had a higher incidence of aneurysmal SAH than men starting at late thirties, and men might have a higher incidence of aneurysmal SAH than women only before 37-year-old.

CONCLUSIONS

Menopause may not be the only dominant factor causing higher incidence of aneurysmal SAH in women than in men.

Preemptive Medicine for Cerebral Aneurysms

Most of cerebral aneurysms (CAs) are incidentally discovered without any neurological symptoms and the risk of rupture of CAs is relatively higher in Japanese population. The goal of treatments for patients with CAs is complete exclusion of the aneurysmal rupture risk for their lives. Since two currently available major treatments, microsurgical clipping and endovascular coiling, have inherent incompleteness to achieve cure of CAs with some considerable treatment risks, and there is no effective surgical or medical intervention to inhibit the formation of CAs in patients with ruptured and unruptured CAs, new treatment strategies with lower risk and higher efficacy should be developed to prevent the formation, growth, and rupture of CAs. Preemptive medicine for CAs should be designed to prevent or delay the onset of symptoms from CAs found in an asymptomatic state or inhibit the de novo formation of CAs, but we have no definite methods to distinguish rupture-prone aneurysms from rupture-resistant ones. Recent advancements in the research of CAs have provided us with some clues, and one of the new treatment strategies for CAs will be developed based on the findings that several inflammatory pathways may be involved in the formation, growth, and rupture of CAs. Preemptive medicine for CAs will be established with specific biomarkers and imaging modalities which can sensor the development of CAs.

Sex Differences in the Formation of Intracranial Aneurysms and Incidence and Outcome of Subarachnoid Hemorrhage: Review of Experimental and Human Studies

Intracranial aneurysms are defined as pathological dilatations of cerebral arteries and rupture of intracranial aneurysms leads to subarachnoid hemorrhage (SAH). The goal of this review was to outline the sex differences in the formation and progression of intracranial aneurysms as well as sex-related differences in incidence and outcome of SAH. The literature review was performed using PubMed with a combination of these search terms: "subarachnoid hemorrhage," "incidence," "outcome," "sex," "gender," "male," "female," "experimental," "mice," and "rats." Studies written in English were used. Female sex is thought to be a risk factor for aneurysm formation, especially in postmenopausal age populations, suggesting the potential protective involvement of sex steroids. Female sex is also considered a risk factor for SAH occurrence. Although incidence and mortality are confirmed to be higher in females in most studies, they elucidated no clear differences in the functional outcome among SAH survivors. The effect of gender on the pathophysiology of SAH is not very well understood; nevertheless, the majority of pre-clinical studies suggest a beneficial effect of sex steroids in experimental SAH. Moreover, conflicting results exist on the role and effect of hormone replacement therapies and oral contraceptive pills on the incidence and outcome of human SAH. Sex differences exist in the formation of aneurysms as well as the incidence and mortality of SAH. Potential therapeutic effects of sex steroids have been replicated in many animal studies, but their potential use in the treatment of acute SAH in human populations needs more future study.