Inflammation and intracranial aneurysms

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

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Increased Oxidative Stress and Xanthine Oxidase Activity in Human Ruptured Cerebral Aneurysms

Recent studies have suggested that oxidative stress may be involved in the development of arterial aneurysms. Xanthine oxidase is implicated in the generation of reactive oxygen species under pathological conditions in the cardiovascular system, and increased xanthine oxidase activity has been reported in human aortic aneurysms. We, therefore, studied the changes of xanthine oxidase activity and oxidative stress in human ruptured cerebral aneurysms. Six cerebral aneurysmal samples were obtained during surgery. Normal arteries of the similar size (one superficial temporal artery, four uterine arteries and three right gastroepiploic arteries) were used as controls. The xanthine oxidase activity was measured with a commercial assay kit, and its expression was localized by immunohistochemistry. The xanthine oxidase activity was significantly increased in aneurysms by 4.1 fold (P<0.05) compared to control arteries. This was accompanied by an elevated malondialdehyde (MDA) level (8.3±5.1 versus 2.9±0.7 nmol/g protein, mean ±SD, P<0.05), a marker of oxidative stress. Immunohistochemistry established that xanthine oxidase was mainly expressed in infiltrating inflammatory cells. Our study indicates that xanthine oxidase may have an important role in the increased oxidative stress in ruptured cerebral aneurysms. Further studies are needed to clarify the role of XO-derived reactive oxygen species in the development and rupture of cerebral aneurysms.

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

INTRODUCTION

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

RESULTS

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

CONCLUSIONS

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

Aneurysmal Subarachnoid Hemorrhage and Neuroinflammation: A Comprehensive Review

Aneurysmal subarachnoid hemorrhage (SAH) can lead to devastating outcomes including vasospasm, cognitive decline, and even death. Currently, treatment options are limited for this potentially life threatening injury. Recent evidence suggests that neuroinflammation plays a critical role in injury expansion and brain damage. Red blood cell breakdown products can lead to the release of inflammatory cytokines that trigger vasospasm and tissue injury. Preclinical models have been used successfully to improve understanding about neuroinflammation following aneurysmal rupture. The focus of this review is to provide an overview of how neuroinflammation relates to secondary outcomes such as vasospasm after aneurysmal rupture and to critically discuss pharmaceutical agents that warrant further investigation for the treatment of subarachnoid hemorrhage. We provide a concise overview of the neuroinflammatory pathways that are upregulated following aneurysmal rupture and how these pathways correlate to long-term outcomes. Treatment of aneurysm rupture is limited and few pharmaceutical drugs are available. Through improved understanding of biochemical mechanisms of injury, novel treatment solutions are being developed that target neuroinflammation. In the final sections of this review, we highlight a few of these novel treatment approaches and emphasize why targeting neuroinflammation following aneurysmal subarachnoid hemorrhage may improve patient care. We encourage ongoing research into the pathophysiology of aneurysmal subarachnoid hemorrhage, especially in regards to neuroinflammatory cascades and the translation to randomized clinical trials.

RNA Sequencing Analysis of Intracranial Aneurysm Walls Reveals Involvement of Lysosomes and Immunoglobulins in Rupture

BACKGROUND AND PURPOSE

Analyzing genes involved in development and rupture of intracranial aneurysms can enhance knowledge about the pathogenesis of aneurysms, and identify new treatment strategies. We compared gene expression between ruptured and unruptured aneurysms and control intracranial arteries.

METHODS

We determined expression levels with RNA sequencing. Applying a multivariate negative binomial model, we identified genes that were differentially expressed between 44 aneurysms and 16 control arteries, and between 22 ruptured and 21 unruptured aneurysms. The differential expression of 8 relevant and highly significant genes was validated using digital polymerase chain reaction. Pathway analysis was used to identify enriched pathways. We also analyzed genes with an extreme pattern of differential expression: only expressed in 1 condition without any expression in the other.

RESULTS

We found 229 differentially expressed genes in aneurysms versus controls and 1489 in ruptured versus unruptured aneurysms. The differential expression of all 8 genes selected for digital polymerase chain reaction validation was confirmed. Extracellular matrix pathways were enriched in aneurysms versus controls, whereas pathways involved in immune response and the lysosome pathway were enriched in ruptured versus unruptured aneurysms. Immunoglobulin genes were expressed in aneurysms, but showed no expression in controls.

CONCLUSIONS

For rupture of intracranial aneurysms, we identified the lysosome pathway as a new pathway and found further evidence for the role of the immune response. Our results also point toward a role for immunoglobulins in the pathogenesis of aneurysms. Immune-modifying drugs are, therefore, interesting candidate treatment strategies in the prevention of aneurysm development and rupture.

ADAMTS genes and the risk of cerebral aneurysm

OBJECTIVE Cerebral aneurysms (CAs) affect 2%-5% of the population, and familial predisposition plays a significant role in CA pathogenesis. Several lines of evidence suggest that genetic variations in matrix metalloproteinase genes (MMP) are involved in the etiopathology of CAs. The authors performed a case-control study to investigate the effect of 4 MMP variants from the ADAMTS family on the pathogenesis of CAs. METHODS To identify susceptible genetic variants, the authors investigated 8 single nucleotide polymorphisms (SNPs) in 4 genes from the ADAMTS family (ADAMTS2, -7, -12, and -13) known to be associated with vascular diseases. The study included 353 patients with CAs and 1055 healthy adults. RESULTS The authors found significant associations between CA susceptibility and genetic variations in 3 members of the ADAMTS family. The largest risk for CA (OR 1.32, p = 0.006) was observed in carriers of the ADAMTS2 variant rs11750568, which has been previously associated with pediatric stroke. Three SNPs under investigation are associated with a protective effect in CA pathogenesis (ADAMTS12 variant rs1364044: OR 0.65, p = 0.0001; and ADAMTS13 variants rs739469 and rs4962153: OR 0.77 and 0.63, p = 0.02 and 0.0006, respectively), while 2 other ADAMTS13 variants may confer a significant risk (rs2301612: OR 1.26, p = 0.011; rs2285489: OR 1.24, p = 0.02). CONCLUSIONS These results suggest that reduced integrity of the endothelial wall, as conferred by ADAMTS variants, together with inflammatory processes and defective vascular remodeling plays an important role in CA pathogenesis, although the mechanism of action remains unknown. The authors' findings may lead to specific screening of at-risk populations in the future.

Experimental animal models and inflammatory cellular changes in cerebral ischemic and hemorrhagic stroke

Stroke, including cerebral ischemia, intracerebral hemorrhage, and subarachnoid hemorrhage, is the leading cause of long-term disability and death worldwide. Animal models have greatly contributed to our understanding of the risk factors and the pathophysiology of stroke, as well as the development of therapeutic strategies for its treatment. Further development and investigation of experimental models, however, are needed to elucidate the pathogenesis of stroke and to enhance and expand novel therapeutic targets. In this article, we provide an overview of the characteristics of commonly-used animal models of stroke and focus on the inflammatory responses to cerebral stroke, which may provide insights into a framework for developing effective therapies for stroke in humans.

Onyx Embolization of a Ruptured Rotundum Foreman Artery Aneurysm in a Patient with Moyamoya Disease: A Case Report

BACKGROUND

Hemorrhage caused by the rupture of a rotundum foreman artery pseudoaneurysm in Moyamoya disease (MMD) is rarely reported.

CASE DESCRIPTION

We report a case of 46-year-old man with MMD presenting with left temporal lobe hemorrhage. Cerebral angiogram showed a pseudoaneurysm located on the rotundum branch of the left internal maxillary artery, which anastomosed with a pial vessel. Using onyx 18, we successfully embolized the pseudoaneurysm. The patient was discharged neurologically intact.

CONCLUSION

Given the difficulties and risks of surgery, onyx embolization of rotundum foreman artery aneurysm accompanied with MMD is feasible and effective.

Intracranial Aneurysms: Wall Motion Analysis for Prediction of Rupture

Intracranial aneurysms are a common pathologic condition with a potential severe complication: rupture. Effective treatment options exist, neurosurgical clipping and endovascular techniques, but guidelines for treatment are unclear and focus mainly on patient age, aneurysm size, and localization. New criteria to define the risk of rupture are needed to refine these guidelines. One potential candidate is aneurysm wall motion, known to be associated with rupture but difficult to detect and quantify. We review what is known about the association between aneurysm wall motion and rupture, which structural changes may explain wall motion patterns, and available imaging techniques able to analyze wall motion.

Imaging Inflammation in Cerebrovascular Disease

Imaging inflammation in large intracranial artery pathology may play an important role in the diagnosis of and risk stratification for a variety of cerebrovascular diseases. Looking beyond the lumen has already generated widespread excitement in the stroke community, and the potential to unveil molecular processes in the vessel wall is a natural evolution to develop a more comprehensive understanding of the pathogenesis of diseases, such as ICAD and brain aneurysms.

Pathogenesis of intracranial aneurysm is mediated by proinflammatory cytokine TNFA and IFNG and through stochastic regulation of IL10 and TGFB1 by comorbid factors

BACKGROUND

Intracranial aneurysm (IA) is often asymptomatic until the time of rupture resulting in subarachnoid hemorrhage (SAH).There is no precise biochemical or phenotype marker for diagnosis of aneurysm. Environmental risk factors that associate with IA can result in modifying the effect of inherited genetic factors and thereby increase the susceptibility to SAH. In addition subsequent to aneurismal rupture, the nature and quantum of inflammatory response might be critical for repair. Therefore, genetic liability to inflammatory response caused by polymorphisms in cytokine genes might be the common denominator for gene and environment in the development of aneurysm and complications associated with rupture.

METHODS

Functionally relevant polymorphisms in the pro- and anti-inflammatory cytokine genes IL-1 complex (IL1A, IL1B, and IL1RN), TNFA, IFNG, IL3, IL6, IL12B, IL1RN, TGFB1, IL4, and IL10] were screened in radiologically confirmed 220 IA patients and 250 controls from genetically stratified Malayalam-speaking Dravidian ethnic population of south India. Subgroup analyses with genetic and environmental variables were also carried out.

RESULTS

Pro-inflammatory cytokines TNFA rs361525, IFNG rs2069718, and anti-inflammatory cytokine IL10 rs1800871 and rs1800872 were found to be significantly associated with IA, independent of epidemiological factors. TGFB1 rs1800469 polymorphism was observed to be associated with IA through co-modifying factors such as hypertension and gender. Functional prediction of all the associated SNPs of TNFA, IL10, and TGFB1 indicates their potential role in transcriptional regulation. Meta-analysis further reiterates that IL1 gene cluster and IL6 were not associated with IA.

CONCLUSIONS

The study suggests that chronic exposure to inflammatory response mediated by genetic variants in pro-inflammatory cytokines TNFA and IFNG could be a primary event, while stochastic regulation of IL10 and TGFB1 response mediated by comorbid factors such as hypertension may augment the pathogenesis of IA through vascular matrix degradation. The implication and interaction of these genetic variants under a specific environmental background will help us identify the resultant phenotypic variation in the pathogenesis of intracranial aneurysm. Identifying genetic risk factors for inflammation might also help in understanding and addressing the posttraumatic complications following the aneurismal rupture.

Statins and subarachnoid hemorrhage in Medicare patients with unruptured cerebral aneurysms

BACKGROUND

Statins have been shown to decrease aneurysm progression and rupture in two experimental settings: animals with cerebral aneurysm and humans with abdominal aortic aneurysms.

AIMS

To investigate statin use and outcomes in humans with unruptured cerebral aneurysms through Medicare administrative data.

METHODS

We used a 40% random sample Medicare denominator file and corresponding inpatient, outpatient (2003-2011), and prescription (2006-2011) claims to conduct a retrospective cohort study of patients diagnosed with unruptured cerebral aneurysms, between 2003 and 2011. We used propensity score-adjusted models to investigate the association between statin use and risk of subarachnoid hemorrhage. Secondary analyses repeated the main models stratified on tobacco use status and separately assessed other composite outcomes.

RESULTS

We identified 28 931 patients with unruptured cerebral aneurysms (average age 72·0 years, 72·6% female); mean follow-up was 30·0 months; 41·3% used statins. Overall, 593 patients developed subarachnoid hemorrhage, and 703 underwent treatment before subarachnoid hemorrhage. Current or recent statin use was not associated with a difference in subarachnoid hemorrhage risk (odds ratio, 1·03; 95% conflict of interest 0·86-1·23); models stratified on tobacco use status were nearly identical. No association was observed between statin use and the composite outcome of subarachnoid hemorrhage or aneurysm treatment (odds ratio, 0·94; 95% conflict of interest, 0·84-1·06). The risk of subarachnoid hemorrhage or out-of-hospital death was lower among statin users (odds ratio, 0·69; 95% conflict of interest, 0·64-0·74).

CONCLUSIONS

Statin use by patients with unruptured cerebral aneurysms was not associated with subarachnoid hemorrhage risk. Given the prior animal experimental studies demonstrating a protective effect, further prospective studies are needed to investigate the potential relationship.

Aspirin Inhibits Degenerative Changes of Aneurysmal Wall in a Rat Model

Aneurysmal subarachnoid hemorrhage still has a high mortality and morbidity despite notable advances in surgical approaches to cerebral aneurysm (CA). We examined the role of aspirin in vascular inflammation and degeneration. CA was induced in male Sprague-Dawley rats by ligating left common carotid artery and bilateral posterior renal arteries with or without aspirin treatment. The right anterior cerebral artery/olfactory artery (ACA/OA) bifurcations were stripped and assessed morphologically after Verhoeff's Van Gieson staining. Blood sample was obtained to examine circulating CD34(+) CD133(+) endothelial progenitor cells (EPCs), platelet aggregation and platelet counts. Macrophages infiltration in aneurysmal wall was evaluated by immunohistochemistry. Expression of matrix metalloproteinase-2 and 9 (MMP-2 and 9), nuclear factor kappa B (NF-κB), macrophage chemoattractant protein-1 (MCP-1) and vascular cell adhesion molecule-1 (VCAM-1) was examined by RT-PCR. 2 months after CA induction, surgically treated rats manifested aneurysmal degeneration in ACA/OA bifurcations. Aspirin-treated rats exhibited a significant decrease in degradation of internal elastic lamina (IEL), medial layer thinning, CA size and macrophages infiltration with reduced expression of MMP-2 and 9 compared with rats in the CA group. RT-PCR demonstrated that the upregulation of NF-κB, MCP-1 and VCAM-1 after CA induction was reversed by aspirin treatment. Aspirin treatment following CA induction increased circulating EPCs to near control levels and reduced platelet aggregation without changing platelet counts. The evidence suggested that aspirin significantly reduced degeneration of aneurysm walls by inhibiting macrophages-mediated chronic inflammation and mobilizing EPCs.

Mouse models of intracranial aneurysm

Subarachnoid hemorrhage secondary to rupture of an intracranial aneurysm is a highly lethal medical condition. Current management strategies for unruptured intracranial aneurysms involve radiological surveillance and neurosurgical or endovascular interventions. There is no pharmacological treatment available to decrease the risk of aneurysm rupture and subsequent subarachnoid hemorrhage. There is growing interest in the pathogenesis of intracranial aneurysm focused on the development of drug therapies to decrease the incidence of aneurysm rupture. The study of rodent models of intracranial aneurysms has the potential to improve our understanding of intracranial aneurysm development and progression. This review summarizes current mouse models of intact and ruptured intracranial aneurysms and discusses the relevance of these models to human intracranial aneurysms. The article also reviews the importance of these models in investigating the molecular mechanisms involved in the disease. Finally, potential pharmaceutical targets for intracranial aneurysm suggested by previous studies are discussed. Examples of potential drug targets include matrix metalloproteinases, stromal cell-derived factor-1, tumor necrosis factor-α, the renin-angiotensin system and the β-estrogen receptor. An agreed clear, precise and reproducible definition of what constitutes an aneurysm in the models would assist in their use to better understand the pathology of intracranial aneurysm and applying findings to patients.

Immune cells subpopulations in cerebrospinal fluid and peripheral blood of patients with Aneurysmal Subarachnoid Hemorrhage

Background

There is growing evidence supporting the role of inflammation in aneurysmal subarachnoid hemorrhage (aSAH) pathophysiology and it is of great interest to elucidate which immune mechanisms are involved.

Methods

12 aSAH patients and 28 healthy controls were enrolled prospectively. We assessed leukocytes subpopulations and their activation status by flow cytometry in cerebrospinal fluid (CSF) and peripheral blood (PB) of SAH patients at the same time and in PB of controls.

Results

Monocytes and neutrophils were activated in CSF of aSAH patients. The percentage of CD14⁺⁺CD16⁺ monocytes were higher in CSF than in PB of aSAH patients, and were also increased in PB of aSAH patients compared with controls. An enhanced expression of CD69 was shown in CSF neutrophils compared with PB in aSAH patients. PB of aSAH patients showed lower percentage of total lymphocytes compared with controls PB. Additionally, lymphocytes were activated in CSF and PB of aSAH patients. CD4⁺ and CD8⁺ T cells had a decreased expression on CD3 and higher levels of CD69 in CSF compared with PB in aSAH patients. Moreover, PB CD4⁺ and CD8⁺ T cells of aSAH patients were activated compared with controls. Additionally, CD28 expression was decreased on CSF T lymphocytes.

Conclusions

Our data suggest an important recruitment of leukocytes to the site of injury in aSAH as well as an increased activation at this level. Overall, these results indicate that aSAH probably stimulates both the innate and adaptive immune responses.

Pathological findings of saccular cerebral aneurysms-impact of subintimal fibrin deposition on aneurysm rupture

Although several studies have suggested that aneurysmal wall inflammation and laminar thrombus are associated with the rupture of saccular aneurysms, the mechanisms leading to the rupture remain obscure. We performed full exposure of aneurysms before clip application and attempted to keep the fibrin cap on the rupture point. Using these specimens in a nearly original state before surgery, we conducted a pathological analysis and studied the differences between ruptured and unruptured aneurysms to clarify the mechanism of aneurysmal wall degeneration. This study included ruptured (n = 28) and unruptured (n = 12) saccular aneurysms resected after clipping. All of the ruptured aneurysms were obtained within 24 h of onset. Immunostainings for markers of inflammatory cells (CD68) and classical histological staining techniques were performed. Clinical variables and pathological findings from ruptured and unruptured aneurysms were compared. Patients with ruptured or unruptured aneurysms did not differ by age, gender, size, location, and risk factors, such as hypertension, smoking, and hyperlipidemia. The absence or fragmentation of the internal elastica lamina, the myointimal hyperplasia, and the thinning of the aneurysmal wall were generally observed in both aneurysms. The existence of subintimal fibrin deposition, organized laminar thrombus, intramural hemorrhage, neovascularization, and monocyte infiltration are more frequently observed in ruptured aneurysms. Multivariate logistic regression analysis showed that ruptured aneurysm was associated with presence of subintimal fibrin deposition and monocyte infiltration. These findings suggest that subintimal fibrin deposition and chronic inflammation have a strong impact on degeneration of the aneurysmal wall leading to their rupture, and this finding may be caused by endothelial dysfunction.

Inflammatory mediators in vascular disease: identifying promising targets for intracranial aneurysm research

Inflammatory processes are implicated in many diseases of the vasculature and have been shown to play a key role in the formation of intracranial aneurysms (IAs). Although the specific mechanisms underlying these processes have been thoroughly investigated in related pathologies, such as atherosclerosis, there remains a paucity of information regarding the immunopathology of IA. Cells such as macrophages and lymphocytes and their effector molecules have been suggested to be players in IA, but their specific interactions and the role of other components of the inflammatory response have yet to be determined. Drawing parallels between the pathogenesis of IA and other vascular disorders could provide a roadmap for developing a mechanistic understanding of the immunopathology of IA and uncovering useful targets for therapeutic intervention. Future research should address the presence and function of leukocyte subsets, mechanisms of leukocyte recruitment and activation, and the role of damage-associated molecular patterns in IA.

Molecular mechanisms of the formation and progression of intracranial aneurysms

Until recently, only a little was understood about molecular mechanisms of the development of an intracranial aneurysm (IA). Recent advancements over the last decade in the field of genetics and molecular biology have provided us a wide variety of evidences supporting the notion that chronic inflammation is closely associated with the pathogenesis of IA development. In the field of genetics, large-scale Genome-wide association studies (GWAS) has identified some IA susceptible loci and genes related to cell cycle and endothelial function. Researches in molecular biology using human samples and animal models have revealed the common pathway of the initiation, progression, and rupture of IAs. IA formation begins with endothelial dysfunction followed by pathological remodeling with degenerative changes of vascular walls. Medical treatments inhibiting inflammatory cascades in IA development are likely to prevent IA progression and rupture. Statins and aspirin are expected to suppress IA progression by their anti-inflammatory effects. Decoy oligodeoxynucleotides (ODNs) inhibiting inflammatory transcription factors such as nuclear factor kappa-B (NF-κB) and Ets-1 are the other promising choice of the prevention of IA development. Further clarification of molecular mechanisms of the formation and progression of IAs will shed light to the pathogenesis of IA development and provide insight into novel diagnostic and therapeutic strategies for IAs.

Rho kinase as a target for cerebral vascular disorders

The development of novel pharmaceutical treatments for disorders of the cerebral vasculature is a serious unmet medical need. These vascular disorders are typified by a disruption in the delicate Rho signaling equilibrium within the blood vessel wall. In particular, Rho kinase overactivation in the smooth muscle and endothelial layers of the vessel wall results in cytoskeletal modifications that lead to reduced vascular integrity and abnormal vascular growth. Rho kinase is thus a promising target for the treatment of cerebral vascular disorders. Indeed, preclinical studies indicate that Rho kinase inhibition may reduce the formation/growth/rupture of both intracranial aneurysms and cerebral cavernous malformations.

E-Selectin Expression Increased in Human Ruptured Cerebral Aneurysm Tissues

Objectives:

The purpose of the present study is to investigate the expression of inflammation factor endothelial-leukocyte adhesion molecule (E-selectin, CD62E) in cerebral aneurysm walls and its relationship with aneurysm rupture.

Methods:

Cerebral aneurysm tissue samples were collected at the time of surgical clipping of nine patients with history of subarachnoid hemorrhage, and then compared with control artery tissues from the superficial temporal arteries (STA) of five patients with intracranial tumors. Immunohistochemistry (IHC) was performed to reveal and localize E-selectin expression in the aneurysms and artery tissues. Western blot analysis was used to relatively quantify the level of E-selectine protein expression in cerebral aneurysms when compared with normal arteries.

Results:

E-selectin was detected in the wall of all the aneurysm tissue samples and was rarely found in normal control arteries by IHC, and it was concentrated in proliferating and disorganized epithelia cells. Moreover, with the Western blot method, the E-selectin protein level increased significantly in aneurysm tissues compared to normal STA.

Conclusions:

E-selectin might be an important factor involved in the process of cerebral aneurysm formation and rupture, by promoting inflammation and weakening cerebral artery walls.

Does Aneurysmal Wall Enhancement on Vessel Wall MRI Help to Distinguish Stable From Unstable Intracranial Aneurysms?

Background and Purpose—

Arterial wall enhancement on vessel wall MRI was described in intracranial inflammatory arterial disease. We hypothesized that circumferential aneurysmal wall enhancement (CAWE) could be an indirect marker of aneurysmal wall inflammation and, therefore, would be more frequent in unstable (ruptured, symptomatic, or undergoing morphological modification) than in stable (incidental and nonevolving) intracranial aneurysms.

Methods—

We prospectively performed vessel wall MRI in patients with stable or unstable intracranial aneurysms. Two readers independently had to determine whether a CAWE was present.

Results—

We included 87 patients harboring 108 aneurysms. Interreader and intrareader agreement for CAWE was excellent (κ=0.85; 95% confidence interval, 0.75–0.95 and κ=0.90; 95% confidence interval, 0.83–0.98, respectively). A CAWE was significantly more frequently seen in unstable than in stable aneurysms (27/31, 87% versus 22/77, 28.5%, respectively; P <0.0001). Multivariate logistic regression, including CAWE, size, location, multiplicity of aneurysms, and daily aspirin intake, revealed that CAWE was the only independent factor associated with unstable status (odds ratio, 9.20; 95% confidence interval, 2.92–29.0; P =0.0002).

Conclusions—

CAWE was more frequently observed in unstable intracranial aneurysms and may be used as a surrogate of inflammatory activity in the aneurysmal wall.

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

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

Brain arteriovenous malformation modeling, pathogenesis, and novel therapeutic targets

Patients harboring brain arteriovenous malformation (bAVM) are at life-threatening risk of rupture and intracranial hemorrhage (ICH). The pathogenesis of bAVM has not been completely understood. Current treatment options are invasive, and ≈ 20 % of patients are not offered interventional therapy because of excessive treatment risk. There are no specific medical therapies to treat bAVMs. The lack of validated animal models has been an obstacle for testing hypotheses of bAVM pathogenesis and testing new therapies. In this review, we summarize bAVM model development and bAVM pathogenesis and potential therapeutic targets that have been identified during model development.

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

Background

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

Results

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

Conclusions

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

Suppression of cerebral aneurysm formation in rats by a tumor necrosis factor-α inhibitor

OBJECT

Although cerebral aneurysmal subarachnoid hemorrhage is a devastating disease for humans, effective medical treatments have not yet been established. Recent reports have shown that regression of some inflammatory-related mediators has protective effects in experimental cerebral aneurysm models. This study corroborated the effectiveness of tumor necrosis factor-α (TNF-α) inhibitor for experimentally induced cerebral aneurysms in rats.

METHODS

Five-week-old male rats were prepared for induction of cerebral aneurysms and divided into 3 groups, 2 groups administered different concentrations of a TNF-α inhibitor (etanercept), and 1 control group. One month after aneurysm induction, 7-T MRI was performed. The TNF-α inhibitor groups received subcutaneous injection of 25 μg or 2.5 μg of etanercept, and the control group received subcutaneous injection of normal saline every week. The TNF-α inhibitor administrations were started at 1 month after aneurysm induction to evaluate its suppressive effects on preexisting cerebral aneurysms. Arterial circles of Willis were obtained and evaluated 3 months after aneurysm induction.

RESULTS

Rats administered a TNF-α inhibitor experienced significant increases in media thickness and reductions in aneurysmal size compared with the control group. Immunohistochemical staining showed that treatment with a TNF-α inhibitor suppressed matrix metalloproteinase (MMP)-9 and inducible nitric oxide synthase (iNOS) expression through the luminal surface of the endothelial cell layer, the media and the adventitia at the site of aneurysmal formation, and the anterior cerebral artery-olfactory artery bifurcation. Quantitative polymerase chain reaction also showed suppression of MMP-9 and iNOS by TNF-α inhibitor administration.

CONCLUSIONS

Therapeutic administration of a TNF-α inhibitor significantly reduced the formation of aneurysms in rats. These data also suggest that TNF-α suppression reduced some inflammatory-related mediators that are in the downstream pathway of nuclear factor-κB.

Gene expression profiles in intracranial aneurysms

In this study, we extracted total RNA from 15 intracranial aneurysms and 17 superficial temporal artery samples, then performed genome-wide expression profiling using the Affymetrix U133 Plus 2.0 GeneChip. Genes that were differentially expressed between intracranial aneurysms and arterial samples were identified using significance analysis for microarrays, and the expression patterns of three randomly-selected genes were verified by real-time polymerase chain reaction analysis. We identified 3 736 differentially-expressed genes out of the 47,000 assayed transcripts. A total of 179 genes showed a >10-fold change in expression between the aneurysms and the arterial samples. Genes involved in the proliferation, migration, and apoptosis of vascular muscle cells, atherosclerosis, extracellular matrix disruption, and inflammatory reactions were associated with the formation of intracranial aneurysms. There were no significant differences in gene expression profile between unruptured and ruptured aneurysms.

Current management of delayed cerebral ischemia: update from results of recent clinical trials

Subarachnoid hemorrhage (SAH) accounts for 5-7% of all strokes worldwide and is associated with high mortality and morbidity. Even after surgical intervention, approximately 30% of patients develop long-term cognitive and neurological deficits that significantly affect their capacity to return to work or daily life unassisted. Much of this stems from a secondary ischemic phenomenon referred to as delayed cerebral ischemia (DCI). While DCI has been historically attributed to the narrowing of the large basal cerebral arteries, it is now recognized that numerous pathways contribute to its pathogenesis, including microcirculatory dysfunction, microthrombosis, cortical spreading depression, and early brain injury. This paper seeks to summarize some of the key pathophysiological events that are associated with poor outcome after SAH, provide a general overview of current methods of treating SAH patients, and review the results of recent clinical trials directed at improving outcome after SAH. The scientific basis of these studies will be discussed, in addition to the available results and recommendations for effective patient management. Therapeutic methods under current clinical investigation will also be addressed. In particular, the mechanisms by which they are expected to elicit improved outcome will be investigated, as well as the specific study designs and anticipated time lines for completion.

Inflammation and cerebral aneurysms

Cerebral aneurysms (CAs) occur in up to 5% of the population in the US, and up to 7% of all strokes are caused by CA rupture. Little is known about the pathophysiology of cerebral aneurysm formation, though inflammatory cells such as macrophages and neutrophils have been found in the walls of CAs. After many studies of both human specimens and experimentally induced animal models of aneurysms, the predominant model for CA formation and progression is as follows: (1) endothelial damage and degeneration of the elastic lamina, (2) inflammatory cell recruitment and infiltration, (3) and chronic remodeling of vascular wall. Endothelial damage can be caused by changes in hemodynamic stress, which results in the upregulation of proinflammatory cytokine secretion followed by the recruitment of various inflammatory cells. This recruitment and subsequent infiltration induces smooth muscle cell proliferation, apoptosis, and remodeling of the artery wall. These complex events are thought to lead to aneurysm rupture. This review will focus on the role of the immune system in the formation and progression of saccular CA and the ways in which the immune response may be modulated to treat aneurysms and prevent rupture.

Factors affecting formation and rupture of intracranial saccular aneurysms

Unruptured intracranial aneurysms represent a decisional challenge. Treatment risks have to be balanced against an unknown probability of rupture. A better understanding of the physiopathology is the basis for a better prediction of the natural history of an individual patient. Knowledge about the possible determining factors arises from a careful comparison between ruptured versus unruptured aneurysms and from the prospective observation and analysis of unbiased series with untreated, unruptured aneurysms. The key point is the correct identification of the determining variables for the fate of a specific aneurysm in a given individual. Thus, the increased knowledge of mechanisms of formation and eventual rupture of aneurysms should provide significant clues to the identification of rupture-prone aneurysms. Factors like structural vessel wall defects, local hemodynamic stress determined also by peculiar geometric configurations, and inflammation as trigger of a wall remodeling are crucial. In this sense the study of genetic modifiers of inflammatory responses together with the computational study of the vessel tree might contribute to identify aneurysms prone to rupture. The aim of this article is to underline the value of a unifying hypothesis that merges the role of geometry, with that of hemodynamics and of genetics as concerns vessel wall structure and inflammatory pathways.

Ruptured mycotic cerebral aneurysm development from pseudoocclusion due to septic embolism

Background:

Cerebral mycotic aneurysms are rare sequelae of systemic infections that can cause profound morbidity and mortality with rupture. Direct bacterial extension and vessel integrity compromise from septic emboli have been implicated as mechanisms for formation of these lesions. We report the 5-day development of a ruptured mycotic aneurysm arising from a septic embolism that caused a focal M1 pseudoocclusion.

Case Description:

A 14-year-old girl developed acute left-sided hemiparesis while hospitalized for subacute bacterial endocarditis that was found after she presented with a 2-week history of fever, myalgia, shortness of breath, and lethargy. Mitral valve vegetations were confirmed in the setting of hemophilus bacteremia. Brain magnetic resonance (MR) imaging and angiography confirmed middle cerebral artery infarct with focal pseudoocclusion of the distal M1 segment. Given that further middle cerebral artery territory was at risk, a trial of heparin was attempted for revascularization but required discontinuation owing to hemorrhagic conversion. Decline of the patient's mental status necessitated craniectomy for decompression. Postoperatively, her mental status improved with residual left hemiparesis. On the third postoperative day (5 days after MR angiography), the patient's neurologic condition acutely declined, with development of right-sided mydriasis. Computed tomography (CT) angiography revealed a ruptured 19 × 16 mm pseudoaneurysm arising from the M1 site of the previous occlusion. Emergent coiling of aneurysm and parent vessel followed by hematoma evacuation ensued. At discharge, the patient had residual left hemiparesis but intact speech and cognition.

Conclusion:

Focal occlusions due to septic emboli should be considered high-risk for mycotic aneurysm formation, prompting aggressive monitoring with neuroimaging and treatment when indicated.

Inflammation and human cerebral aneurysms: current and future treatment prospects

The formation of cerebral aneurysms and their rupture propensity is of immediate clinical importance. Current management includes observation with expectant management, microsurgical clipping and/or endovascular coiling. The surgical options are invasive and are not without increased risk despite the technological advances. Recent human and animal studies have shown that inflammation plays a critical role in aneurysm formation and progression to rupture. Modulating this inflammatory process may prove to be clinically significant. This review will discuss cerebral aneurysm pathogenesis with a focus on current and future research of potential use of pharmaceutical agents that attenuate inflammation in the aneurysm wall leading to decreased risk of aneurysm rupture.

Modified murine intracranial aneurysm model: aneurysm formation and rupture by elastase and hypertension

Introduction

Cerebral aneurysms occur in up to 5% of the population. There are several murine models of aneurysms; however, all have limitations and none reproducibly model aneurysm rupture. To fulfill this need, we modified two current rodent aneurysm models to create a murine model which reproducibly produces intracranial aneurysms and rupture.

Methods

The left common carotid arteries and the right renal arteries were ligated in C57BL/6 female mice with a hypertensive diet. One week later, small burr holes were created with a stereotactic frame using the following stereotactic measurements: 1.2 mm rostral and 0.7 mm lateral to the right of the bregma. A 26 G needle was gradually advanced via the burr hole until contact with the skull base, upon which the needle was pulled back 0.3 mm. Five, 10 and 20 μL of 10 U/mL elastase solution and 10 μL of 1 U/mL elastase solution were stereotactically injected into the basal cisterns. Angiotensin II was then continually infused at a dose of 1000 ng/kg/min via an osmotic pump placed subcutaneously. In the control mice, 20 μL bromophenol blue solution was injected. Three weeks later, or earlier if mice expired prior to 3 weeks, the circle of Willis was inspected by microscopy for aneurysm formation and/or signs of rupture. Histological analyses were then performed to evaluate elastic lamina destruction, inflammatory cell and macrophage infiltration, absence of intimal endothelial cells and thickening of the smooth muscle layer within the aneurysm wall. To compare with human aneurysms, human aneurysm specimens (n=35; 34 unruptured and 1 ruptured) and normal control superficial temporal arteries (STAs) (n=9) were examined.

Results

All mice given 5, 10 and 20 μL of 10 U/mL elastase solution developed intracranial aneurysms within the circle of Willis; 40%, 60% and 50% of mice had ruptured aneurysms, respectively. In mice given 10 μL of 1.0 U/mL elastase solution, 90% developed intracranial aneurysms and 20% had ruptured aneurysms. Aneurysms were confirmed by examining the destruction of the elastic lamina. Aneurysms consistently demonstrated CD45 positive inflammatory cell and F4/80 positive macrophage infiltration within the aneurysm wall which was not present in the circle of Willis of normal sham-operated mice. These results were similar to those in human aneurysms and STA control arteries.

Conclusions

We modified two current rodent aneurysm models to create a murine model that produces consistent aneurysms and rupture and can be used for studying cerebral aneurysm formation, rupture and treatment.

Localized increase of chemokines in the lumen of human cerebral aneurysms

BACKGROUND AND PURPOSE

Inflammation may play an important role in the formation and rupture of cerebral aneurysms. Chemokines act as chemoattractants for leukocytes directing them toward sites of tissue inflammation. The purpose of this study was to determine whether chemokines and chemoattractant cytokines were increased in the lumen of human cerebral aneurysms.

METHODS

The concentrations of chemokines and other inflammatory molecules in blood samples drawn from the lumen of human cerebral aneurysms of 16 consecutive patients (harboring 18 aneurysms) were compared with blood samples from the femoral arteries of the same patients. Three aneurysms had ruptured.

RESULTS

The mean plasma concentration of regulated on activation, normal T cell expressed and secreted (RANTES), monokine-induced-by-γ-interferon (MIG), interferon-γ-induced protein-10 (IP-10), eotaxin, interleukin (IL) 8, and IL17 was significantly higher in samples taken from cerebral aneurysms compared with femoral arteries. In contrast, plasma concentrations of all remaining inflammatory molecules (except IL6) that were tested did not differ between cerebral aneurysms and femoral arteries. For unruptured aneurysms, there was a significantly higher mean plasma concentration of monocyte chemoattractant protein-1 as well as RANTES, MIG, IP-10, eotaxin, IL8, and IL17 in samples obtained from cerebral aneurysms.

CONCLUSIONS

High plasma concentrations of chemokines (monocyte chemoattractant protein-1, RANTES, MIG, IP-10, and eotaxin) and chemoattractant cytokines (IL8 and IL17) were found in the lumen of human cerebral aneurysms. These findings suggest that there may be an active recruitment of inflammatory cells into the aneurysm wall that may be exploited therapeutically.

A combination of genetic, molecular and haemodynamic risk factors contributes to the formation, enlargement and rupture of brain aneurysms

Many people carry cerebral aneurysms but are generally unaware of their presence until they rupture, resulting in high morbidity or mortality. The pathogenesis and aetiology of aneurysms are largely unknown; however, a greater understanding, by analysing the genetic, molecular and haemodynamic risk factors involved in the initiation, enlargement, and rupture of aneurysms, could lead to effective prevention, early diagnosis and more effective treatment. The risk of aneurysm is increased by a family history of aneurysms, and amongst certain populations, namely in Japan and Finland. Several other risk factors are documented, including hypertension, smoking, alcohol consumption, and female sex. Studies indicate a higher occurrence of cerebral aneurysms in females compared to males. Oestrogen protects several components within the artery wall, and inhibits some of the inflammatory molecules that could cause aneurysms. At menopause, the oestrogen level decreases and the incidence of aneurysm increases. Haemodynamic stresses have been shown to be involved in the formation, growth and rupture of aneurysms. This is often associated with hypertension, which also increases the risk of aneurysm rupture. When an unruptured aneurysm is detected the decision to treat can be complicated, since only 1-2% of aneurysms eventually rupture. Haemodynamic simulation software offers an effective tool for the consideration of treatment options for patients who carry unruptured aneurysms. The assessment must consider the risks of interventional treatments versus non-interventional management options, such as controlling blood pressure.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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