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

Genetic associations of sex hormones with cerebral aneurysm formation and subarachnoid hemorrhage: A two-sample Mendelian randomization analysis

BACKGROUND AND AIM

Women are more likely than men to develop aneurysmal subarachnoid hemorrhage, and this difference is more pronounced in women after menopause, suggesting a possible correlation between sex hormone levels and cerebral aneurysm formation and rupture.

METHODS AND RESULTS

We selected genetic variants closely related to estrogen (estradiol), bioavailable testosterone (Bio T), and sex hormone-binding globulin (SHBG) as instrumental variables from the pooled data of the IEU Open GWAS project and cerebral aneurysm (CA) and subarachnoid hemorrhage (SAH) data from two independent datasets from the same study. Two-sample Mendelian randomization was subsequently performed to determine whether the relevant sex hormones and SHBG are causally associated with the formation and rupture of CA. We identified 14 causal associations of related sex hormones and their binding proteins with cerebral aneurysm formation and rupture. Inverse-variance weighting revealed that genetically predicted increased BioT levels reduced the risk of SAH development and genetically predicted increased levels of SHBG in females influenced reduced the risk of cerebral aneurysm formation. After excluding sex differences, weighted mode revealed opposite results, but there was no difference in the IVW, MR-Egger regression, weighted median, or simple mode analyses. No significant effects of the concentrations of other relevant sex hormones or SHBG on the risk of cerebral aneurysm formation or rupture were found.

CONCLUSIONS

Our study may explain the mechanisms underlying the increased incidence of cerebral aneurysms in menopausal women and provide new directions for intervention in cerebral aneurysm formation and rupture, but further studies are needed.

Genetic determinants of insufficiency of the collateral circulation

It has been estimated that approximately two million neurons, sixteen billion synapses and twelve kilometers of axons are lost each minute following anterior large-vessel stroke. The level of collateral blood flow has become recognized as a primary determinant of the pace of this loss and an important factor in clinical decision-making. Many of the topics in this review cover recent developments that have not been reviewed elsewhere. These include that: the number and diameter of collaterals and collateral blood flow vary greatly in the brain and other tissues of healthy individuals; a large percentage of individuals are deficient in collaterals; the underlying mechanism arises primarily from naturally occurring polymorphisms in genes/genetic loci within the pathway that drives collateral formation during development; evidence indicates collateral abundance does not exhibit sexual dimorphism; and that collaterals-besides their function as endogenous bypass vessels-may have a physiological role in optimizing oxygen delivery. Animal and human studies in brain and other tissues, where available, are reviewed. Details of many of the studies are provided so that the strength of the findings and conclusions can be assessed without consulting the original literature. Key questions that remain unanswered and strategies to address them are also discussed.

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.

Female mice display sex-specific differences in cerebrovascular function and subarachnoid haemorrhage-induced injury

BACKGROUND

In male mice, a circadian rhythm in myogenic reactivity influences the extent of brain injury following subarachnoid haemorrhage (SAH). We hypothesized that female mice have a different cerebrovascular phenotype and consequently, a distinct SAH-induced injury phenotype.

METHODS

SAH was modelled by pre-chiasmatic blood injection. Olfactory cerebral resistance arteries were functionally assessed by pressure myography; these functional assessments were related to brain histology and neurobehavioral assessments. Cystic fibrosis transmembrane conductance regulator (CFTR) expression was assessed by PCR and Western blot. We compared non-ovariectomized and ovariectomized mice.

FINDINGS

Cerebrovascular myogenic reactivity is not rhythmic in females and no diurnal differences in SAH-induced injury are observed; ovariectomy does not unmask a rhythmic phenotype for any endpoint. CFTR expression is rhythmic, with similar expression levels compared to male mice. CFTR inhibition studies, however, indicate that CFTR activity is lower in female arteries. Pharmacologically increasing CFTR expression in vivo (3 mg/kg lumacaftor for 2 days) reduces myogenic tone at Zeitgeber time 11, but not Zeitgeber time 23. Myogenic tone is not markedly augmented following SAH in female mice and lumacaftor loses its ability to reduce myogenic tone; nevertheless, lumacaftor confers at least some injury benefit in females with SAH.

INTERPRETATION

Female mice possess a distinct cerebrovascular phenotype compared to males, putatively due to functional differences in CFTR regulation. This sex difference eliminates the CFTR-dependent cerebrovascular effects of SAH and may alter the therapeutic efficacy of lumacaftor compared to males.

FUNDING

Brain Aneurysm Foundation, Heart and Stroke Foundation and Ted Rogers Centre for Heart Research.

Secondary Ischemia Assessment in Murine and Rat Preclinical Subarachnoid Hemorrhage Models: A Systematic Review

BACKGROUND

Delayed cerebral ischemia represents a significant contributor to death and disability following aneurysmal subarachnoid hemorrhage. Although preclinical models have shown promising results, clinical trials have consistently failed to replicate the success of therapeutic strategies. The lack of standardized experimental setups and outcome assessments, particularly regarding secondary vasospastic/ischemic events, may be partly responsible for the translational failure. The study aims to delineate the procedural characteristics and assessment modalities of secondary vasospastic and ischemic events, serving as surrogates for clinically relevant delayed cerebral ischemia, in recent rat and murine subarachnoid hemorrhage models.

METHODS AND RESULTS

We conducted a systematic review of rat and murine in vivo subarachnoid hemorrhage studies (published: 2016-2020) using delayed cerebral ischemia/vasospasm as outcome parameters. Our analysis included 102 eligible studies. In murine studies (n=30), the endovascular perforation model was predominantly used, while rat studies primarily employed intracisternal blood injection to mimic subarachnoid hemorrhage. Particularly, the injection models exhibited considerable variation in injection volume, rate, and cerebrospinal fluid withdrawal. Peri-interventional monitoring was generally inadequately reported across all models, with body temperature and blood pressure being the most frequently documented parameters (62% and 34%, respectively). Vasospastic events were mainly assessed through microscopy of large cerebral arteries. In 90% of the rat and 86% of the murine studies, only male animals were used.

CONCLUSIONS

Our study underscores the substantial heterogeneity in procedural characteristics and outcome assessments of experimental subarachnoid hemorrhage research. To address these challenges, drafting guidelines for standardization and ensuring rigorous control of methodological and experimental quality by funders and journals are essential.

REGISTRATION

URL: https://www.crd.york.ac.uk/prospero/; Unique identifier: CRD42022337279.

Gender Differences in Procedural Clinical Complications and Outcomes of Intracranial Aneurysms: Analysis of the Stroke Thrombectomy and Aneurysm Registry

BACKGROUND AND OBJECTIVES

Some studies have shown that female patients had a poorer prognosis after endovascular treatment for ruptured intracranial aneurysm than male patients. However, data have been sparse regarding differences in the periprocedural and perioperative complication rate with ruptured and unruptured intracranial aneurysms.

METHODS

This retrospective cohort study used data from the Stroke Thrombectomy and Aneurysm Registry, a database of 9 institutions in the United States, Europe, and Asia. The study presented intracranial aneurysms after microsurgical and/or endovascular treatment from January 1, 2013, to December 31, 2022. The primary outcome was incidence of periprocedural cerebral infarction. Secondary outcomes were periprocedural intracranial hemorrhage, periprocedural mortality, perioperative vasospasm, and functional outcome at 90 days after procedure.

RESULTS

Among 3342 patients with aneurysm, 2447 were female and 857 were male, and the mean age of female and male patients was 59.6 and 57.1 years, respectively. Current smoker, family history of aneurysm, and ruptured aneurysm were observed in 23.5% vs 35.7 %, 10.8 % vs 5.7%, and 28.2% vs 40.5% of female and male patients, respectively. In female patients, internal carotid artery aneurysms were more commonly observed (31.1% vs 17.3%); however, anterior cerebral artery aneurysms were less commonly observed (18.5% vs 33.8%) compared with male patients. Periprocedural cerebral infarction rate was lower in female than male patients (2.4% vs 4.4%; P = .002). The adjusted odds ratio of primary outcome of female to male patients was 0.72 (95% CI, 0.46-1.12). Incidence of periprocedural intracranial hemorrhage and periprocedural mortality and perioperative symptomatic vasospasm and functional outcome was similar in both groups. In subgroup analysis, periprocedural cerebral infarction due to microsurgical treatment occurred frequently in male patients while incidence in endovascular treatment was similar in both groups (interaction P = .005).

CONCLUSION

This large multicenter registry of patients undergoing intracranial aneurysm treatment found that female patients were not at increased risk of perioperative complications.

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.

Kunming mouse strain is less susceptible to elastase-induced abdominal aortic aneurysms

BACKGROUND

Porcine pancreatic elastase (PPE) is successfully used to induce abdominal aortic aneurysm (AAA) in mice. However, differences between mouse strains in susceptibility to PPE induction have been reported. Kunming mouse is one of the most frequently used strains in China but whether it is suitable for induction of AAA by PPE application remains unclear.

METHODS

PPE infusion (1.5 units/ml) in temporary controlled aorta was performed to induce AAAs in both C57BL/6J and Kunming mice. Phosphate-buffered saline (PBS) application was used as vehicle control. The aorta diameters of all mice were measured at days 0 and 14 after surgery to evaluate the AAA formation.

RESULTS

After 14 days of PPE or PBS infusion, all mice were sacrificed and aorta tissues were collected for histological staining analysis. At the 14th day after infusion, PPE successfully induced aortic dilation in Kunming mice and typical AAA in C57BL/6J mice. The aorta diameter increased by 0.23 mm in Kunming mice after PPE infusion, while it was 0.72 mm in the C57BL/6J strain. PPE induced mild elastin degradation, smooth muscle cell (SMC) depletion and mural leucocyte infiltration in Kunming mice, but in PPE-sensitive C57BL/6J mice, it induced total loss of SMCs, elastin disappearance and diffused infiltrated leucocytes in aortic aneurysmal segments. The effects of PPE in inducing angiogenesis and upregulating matrix metalloproteinase 2 and 9 expression in Kunming mice were also weaker than that in C57BL/6J mice.

CONCLUSION

At the reported dose of PPE, Kunming mouse is not as susceptible to AAA formation as C57BL/6J mice. The failure of PPE to induce AAA formation in Kunming mice may be associated to its inability to boost a strong inflammatory response.

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.

Tobacco Smoking Increases Methylation of Polypyrimidine Tract Binding Protein 1 Promoter in Intracranial Aneurysms

DNA methylation at the gene promoter region is reportedly involved in the development of intracranial aneurysm (IA). This study aims to investigate the methylation levels of polypyrimidine tract-binding protein 1 (PTBP1) in IA, as well as its potential to predict IA. Forty-eight patients with IA and 48 age- and sex-matched healthy controls were recruited into this study. Methylation levels of CpG sites were determined via bisulfite pyrosequencing. The PTBP1 levels in the blood were determined using a real-time quantitative reverse transcription-polymerase chain reaction test. Significant differences were found between IAs and controls in CpG1 (p = 0.001), CpG2 (p < 0.001), CpG3 (p = 0.037), CpG4 (p = 0.003), CpG5 (p = 0.006), CpG6 (p = 0.02), and mean methylation (p < 0.001). The mRNA level of PTBP1 in the blood was much lower in IAs compared with controls (p = 0.002), and the PTBP1 expression was significantly associated with DNA methylation promoter levels in individuals (r = −0.73, p < 0.0001). In addition, stratification analysis comparing smokers and non-smokers revealed that tobacco smokers had significantly higher levels of DNA methylation in PTBP1 than non-smokers (p = 0.002). However, no statistical difference in PTBP1 methylation was found between ruptured and unruptured IA groups (p > 0.05). The ROC analyses of curves revealed that PTBP1 methylation may be a predictor of IA regardless of sex (both sexes, area under curve (AUC) = 0.78, p < 0.0001; male, AUC = 0.76, p = 0.002; female, AUC = 0.79, p < 0.0001). These findings suggest that long-term tobacco smoke exposure led to DNA methylation in the promoter region of the PTBP1 gene, which further decreased PTBP1 gene expression and participated in the pathogenesis of IA. The methylation of PTBP1 may be a potential predictive marker for the occurrence of IA.

Integrated Transcriptional Profiling Analysis and Immune-Related Risk Model Construction for Intracranial Aneurysm Rupture

Intracranial aneurysms (IAs) may cause lethal subarachnoid hemorrhage upon rupture, but the molecular mechanisms are poorly understood. The aims of this study were to analyze the transcriptional profiles to explore the functions and regulatory networks of differentially expressed genes (DEGs) in IA rupture by bioinformatics methods and to identify the underlying mechanisms. In this study, 1,471 DEGs were obtained, of which 619 were upregulated and 852 were downregulated. Gene enrichment analysis showed that the DEGs were mainly enriched in the inflammatory response, immune response, neutrophil chemotaxis, and macrophage differentiation. Related pathways include the regulation of actin cytoskeleton, leukocyte transendothelial migration, nuclear factor κB signaling pathway, Toll-like receptor signaling pathway, tumor necrosis factor signaling pathway, and chemokine signaling pathway. The enrichment analysis of 20 hub genes, subnetworks, and significant enrichment modules of weighted gene coexpression network analysis showed that the inflammatory response and immune response had a causal relationship with the rupture of unruptured IAs (UIAs). Next, the CIBERSORT method was used to analyze immune cell infiltration into ruptured IAs (RIAs) and UIAs. Macrophage infiltration into RIAs increased significantly compared with that into UIAs. The result of principal component analysis revealed that there was a difference between RIAs and UIAs in immune cell infiltration. A 4-gene immune-related risk model for IA rupture (IRMIR), containing CXCR4, CXCL3, CX3CL1, and CXCL16, was established using the glmnet package in R software. The receiver operating characteristic value revealed that the model represented an excellent clinical situation for potential application. Enzyme-linked immunosorbent assay was performed and showed that the concentrations of CXCR4 and CXCL3 in serum from RIA patients were significantly higher than those in serum from UIA patients. Finally, a competing endogenous RNA network was constructed to provide a potential explanation for the mechanism of immune cell infiltration into IAs. Our findings highlighted the importance of immune cell infiltration into RIAs, providing a direction for further research.