Pathogenesis Of Intracranial Aneurysms Research Articles

Abstract TP85: Impact of Periodontal Disease and -Bacteria on Intracranial Aneurysms

Introduction: Periodontal Gram-negative bacteria and their products can initiate inflammatory responses in periodontal tissues with systemic consequences. They are associated with the pathogenesis of atherosclerosis and ischemic stroke. Local inflammation and oxidative stress play a crucial role in the pathophysiology of intracranial aneurysms (IAs). Under the hypothesis that the severity of periodontal disease is associated with the formation and rupture of IAs we assessed which periodontal pathogens contribute to the pathogenesis of IAs. Methods: We enrolled patients with ruptured- (n=5, age 60±11.9) and unruptured IAs (n=13, age 67±6.1) and controls without IAs (n=7, age 58±8.5); their prior informed consent was obtained. The severity of periodontitis was recorded using the community periodontal index (CPI) of the Treatment Needs code. Subgingival plaques (n=23) were evaluated with the quantitative real-time PCR assay to check for the Gram-negative bacteria Aggregatibacter actinomycetemcomitans (Aa), Fusobacterium nucleatum, Treponema denticola, Prevotella intermedia (Pi), Tannerella forsythia, and Porphyromonas gingivalis (Pg). Plasma IgG titers of antibody against Pg, Pi, Aa, and Eikenella corrodens were evaluated by ELISA. Results: The CPI was significantly higher in patients with IAs than the controls (2.7 vs 1.9, p<0.05) and their DNA level of subgingival plaques and their plasma IgG titers of Pg were also higher. Periodontal disease was more severe and the plasma IgG titers of Pg were higher in patients with ruptured- than unruptured IAs, suggesting that Pg is associated not only with the formation but also the rupture of IAs. Conclusions: We present evidence that severe periodontal disease and Pg infection may be involved in the pathophysiology of IAs. The management of periodontal diseases may help to prevent the formation and rupture of IAs.

Dysregulation of CD4+T Cell Subsets in Intracranial Aneurysm

Intracranial aneurysms (IAs) and potential IA rupture are one of the direct causes of permanent brain damage and mortality. Interestingly, the major risk factors of IA development, including hemodynamic stress, hypertension, smoking, and genetic predispositions, are closely associated with a proinflammatory immune status. Therefore, we examined the roles of CD4(+) T cells in IA pathogenesis. IA patients exhibited peripheral CD4(+) T-cell imbalance, with overrepresented T helper 1 (Th1) and Th17 activities and underrepresented Th2 and regulatory T (Treg) activities, including increased IFN-γ, TNF-α, and IL-17 production and decreased IL-10 production from total CD4(+) T cells. Chemokine receptors CXCR3 and CCR6 were used to identify Th1, Th2, and Th17 cell subsets, and CD4(+)CD25(hi) was used to identify Treg cells. Based on these markers, the data then showed altered cytokine production by each cell type and shifted subpopulation frequency. Moreover, this shift in frequency was directly correlated with IA severity. To examine the underlying mechanism of CD4(+) T cell skewing, we cocultured CD4(+) T cells with autologous monocytes and found that coculture with monocytes could significantly increase IFN-γ and IL-17 production through contact-independent mechanisms, demonstrating that monocytes could potentially contribute to the altered CD4(+) T cell composition in IA. Analyzing mRNA transcripts revealed significantly upregulated IL-1β and TNF-α expression by monocytes from IA patients. We found a loss of CD4(+) T cell subset balance that was likely to promote a higher state of inflammation in IA, which may exacerbate the disease through a positive feedback loop.

Whole Blood Gene Expression Profiles of Patients with a Past Aneurysmal Subarachnoid Hemorrhage.

BackgroundThe pathogenesis of development and rupture of intracranial aneurysms (IA) is largely unknown. Also, screening for IA to prevent aneurysmal subarachnoid hemorrhage (aSAH) is inefficient, as disease markers are lacking. We investigated gene expression profiles in blood of previous aSAH patients, who are still at risk for future IA, aiming to gain insight into the pathogenesis of IA and aSAH, and to make a first step towards improvement of aSAH risk prediction.Methods and ResultsWe collected peripheral blood of 119 patients with aSAH at least two years prior, and 118 controls. We determined gene expression profiles using Illumina HumanHT-12v4 BeadChips. After quality control, we divided the dataset in a discovery (2/3) and replication set (1/3), identified differentially expressed genes, and applied (co-)differential co-expression to identify disease-related gene networks. No genes with a significant (false-discovery rate <5%) differential expression were observed. We detected one gene network with significant differential co-expression, but did not find biologically meaningful gene networks related to a history of aSAH. Next, we applied prediction analysis of microarrays to find a gene set that optimally predicts absence or presence of a history of aSAH. We found no gene sets with a correct disease state prediction higher than 40%.ConclusionsNo gene expression differences were present in blood of previous aSAH patients compared to controls, besides one differentially co-expressed gene network without a clear relevant biological function. Our findings suggest that gene expression profiles, as detected in blood of previous aSAH patients, do not reveal the pathogenesis of IA and aSAH, and cannot be used for aSAH risk prediction.

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

BackgroundIntracranial 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.MethodsFunctionally 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.ResultsPro-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.ConclusionsThe 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12974-015-0354-0) contains supplementary material, which is available to authorized users.

Abstract 111: A Novel Role for Endogenous HGF in the Pathogenesis of Intracranial Aneurysms

Background and Purpose: Inflammation plays a key role in formation and rupture of intracranial aneurysms. Because hepatocyte growth factor (HGF) modulates vascular inflammation, we sought to assess the role of endogenous HGF in the pathogenesis of intracranial aneurysms. Methods: Circulating HGF concentrations in blood samples drawn from the lumen of human intracranial aneurysms or femoral arteries were compared in 16 patients. Intracranial aneurysm and superficial temporal artery tissue samples from patients undergoing clipping (n=10) were immunostained with antibodies to HGF and its receptor c-Met. Intracranial aneurysms were induced in mice treated with PF-04217903 (a c-Met antagonist) or vehicle. Expression of inflammatory molecules was also measured in cultured endothelial, smooth muscle cells and monocytes treated with LPS in presence or absence of HGF and PF-04217903. Results: HGF concentrations were significantly higher in blood collected from human intracranial aneurysm (1076 ± 656 pg/ml) than in femoral arteries (196 ± 436 pg/ml, p0.05), but significantly increased the prevalence of subarachnoid hemorrhage and decreased survival in mice (P&lt;0.05). HGF attenuated expression of markers of inflammation in human aortic endothelial cells (P&lt;0.05), but not in human aortic smooth muscle cells or monocytes. Conclusion: Plasma HGF concentrations are higher in intracranial aneurysms. HGF and c-Met are expressed in intracranial aneurysms. HGF signaling through c-Met may decrease inflammation in endothelium and protect from intracranial aneurysm rupture. The findings of this study may have significant therapeutic implications for prevention of intracranial aneurysm formation and rupture.

Deficiency of endothelium-specific transcription factor Sox17 induces intracranial aneurysm.

Intracranial aneurysm (IA) is a common vascular disorder that frequently leads to fatal vascular rupture. Although various acquired risk factors associated with IA have been identified, the hereditary basis of IA remains poorly understood. As a result, genetically modified animals accurately modeling IA and related pathogenesis have been lacking, and subsequent drug development has been delayed. The transcription factor Sox17 is robustly expressed in endothelial cells of normal intracerebral arteries. The combination of Sox17 deficiency and angiotensin II infusion in mice induces vascular abnormalities closely resembling the cardinal features of IA such as luminal dilation, wall thinning, tortuosity, and subarachnoid hemorrhages. This combination impairs junctional assembly, cell-matrix adhesion, regeneration capacity, and paracrine secretion in endothelial cells of intracerebral arteries, highlighting key endothelial dysfunctions that lead to IA pathogenesis. Moreover, human IA samples showed reduced Sox17 expression and impaired endothelial integrity, further strengthening the applicability of this animal model to clinical settings. Our findings demonstrate that Sox17 deficiency in mouse can induce IA under hypertensive conditions, suggesting Sox17 deficiency as a potential genetic factor for IA formation. The Sox17-deficient mouse model provides a novel platform to develop therapeutics for incurable IA.

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.

Association between the hsa-miR-146a rs2910164 functional polymorphism with susceptibility to intracranial aneurysm

Vascular inflammation has been shown to be involved in the pathogenesis of intracranial aneurysms (IA). MiRNAs are key molecules that participate in the regulation of many important biological processes including inflammation. Studies on the hsa-miR-146a rs2910164 polymorphism and its association with different inflammatory related diseases have engendered inconsistent results, and until now, there have been no reports on the association between this polymorphism and the susceptibility to IA. In this study, we aimed to investigate whether the rs2910164 polymorphism is involved in the process of IA. We genotyped 164 patients with IA and 478 healthy controls using a polymerase chain reaction-restriction fragment length polymorphism assay. All subjects were Chinese. The distributions of rs2910164 genotypes and alleles between patients with IA and healthy controls were similar [CG vs CC: odds ratio (OR) = 0.701, 95% confidence interval (CI) = 0.456-1.080; GG vs CC: OR = 0.920, 95%CI = 0.524-1.617; G vs C: OR = 0.939, 95%CI = 0.731-1.208, respectively]. No association was found between the hsa-miR-146a rs2910164 polymorphism and the risk of IA in the analyzed population.

The role of leukocytes in the formation and rupture of intracranial aneurysms

Ruptured intracranial aneurysms (IAs) affect a small proportion of the population; however, the morbidity and mortality is disproportionally high. Although little is known about IA formation, progression, and rupture, mounting evidence suggests that inflammation may play an important role in IA pathogenesis. There is emerging evidence to suggest that leukocytes play a key role in generating and maintaining a pathologic inflammatory response that leads to aneurysm formation and rupture. We present the current literature pertaining to the role of leukocytes in aneurysm formation, progression, and rupture. The contributions of individual cell types are detailed, with special attention paid to the cytokine and molecular profiles. The role of magnetic resonance imaging as a means by which to evaluate aneurysm-associated inflammation is reviewed. Finally, we discuss leukocytes as potential targets of pharmacologic intervention.

Novel role for endogenous hepatocyte growth factor in the pathogenesis of intracranial aneurysms.

Inflammation plays a key role in formation and rupture of intracranial aneurysms. Because hepatocyte growth factor (HGF) protects against vascular inflammation, we sought to assess the role of endogenous HGF in the pathogenesis of intracranial aneurysms. Circulating HGF concentrations in blood samples drawn from the lumen of human intracranial aneurysms or femoral arteries were compared in 16 patients. Tissue from superficial temporal arteries and ruptured or unruptured intracranial aneurysms collected from patients undergoing clipping (n=10) were immunostained with antibodies to HGF and its receptor c-Met. Intracranial aneurysms were induced in mice treated with PF-04217903 (a c-Met antagonist) or vehicle. Expression of inflammatory molecules was also measured in cultured human endothelial, smooth muscle cells and monocytes treated with lipopolysaccharides in presence or absence of HGF and PF-04217903. We found that HGF concentrations were significantly higher in blood collected from human intracranial aneurysms (1076±656 pg/mL) than in femoral arteries (196±436 pg/mL; P<0.001). HGF and c-Met were detected by immunostaining in superficial temporal arteries and in both ruptured and unruptured human intracranial aneurysms. A c-Met antagonist did not alter the formation of intracranial aneurysms (P>0.05), but significantly increased the prevalence of subarachnoid hemorrhage and decreased survival in mice (P<0.05). HGF attenuated expression of vascular cell adhesion molecule-1 (P<0.05) and E-Selectin (P<0.05) in human aortic endothelial cells. In conclusion, plasma HGF concentrations are elevated in intracranial aneurysms. HGF and c-Met are expressed in superficial temporal arteries and in intracranial aneurysms. HGF signaling through c-Met may decrease inflammation in endothelial cells and protect against intracranial aneurysm rupture.

Downregulation of T cell immunoglobulin and mucin protein 3 in the pathogenesis of intracranial aneurysm.

Evidence has shown that inflammation acts as a critical contributor to the pathogenesis of intracranial aneurysm (IA), a potentially devastating clinical problem. T cell immunoglobulin and mucin protein 3 (Tim-3) is a negative regulatory molecule and plays important roles in the inflammation process. In the current study, we investigated the expression of Tim-3 and its correlation with tumor necrosis factor alpha (TNF-α) in IA patients. Data showed that both messenger RNA (mRNA) level and protein level of Tim-3 were significantly decreased in CD4+ T cells and CD8+ T cells from IA patients than from healthy controls (P < 0.001). However, expression of Tim-3 was not altered in monocytes between patients and healthy donors. Further analyses revealed that patients with ruptured aneurysm had significantly lower level of Tim-3 in CD8+ T cells than those with un-ruptured aneurysm. In addition, a negative correlation between serum level of TNF-α and the expression of Tim-3 in CD4+ T cells was observed in IA patients. Similar correlation was also identified in CD8+ T cells from IA patients. Our study suggests that Tim-3 may participate in the development and progression of IA by probably its negative regulation on TNF-α.

Effect of vascular anatomy on the formation of basilar tip aneurysms.

The pathogenesis of intracranial aneurysms is multifactorial and includes genetic, environmental, and anatomic influences. Hemodynamic stress plays a particular role in the formation of intracranial aneurysms, which is conditioned by the geometry and morphology of the vessel trees. To identify image-based morphological parameters that correlated with the formation of basilar artery tip aneurysms (BTAs) in a location-specific manner. Morphological parameters obtained from computed tomographic angiographies of 33 patients with BTAs and 33 patients with aneurysms at other locations were evaluated with Slicer, an open-source image analysis software, to generate 3-dimensional models of the aneurysms and surrounding vascular architecture. We examined the diameters and vessel-to-vessel angles of the main vessels at the basilar bifurcation in patients with and without BTAs. To control for genetic and other risk factors, only patients with at least 1 aneurysm were included. Univariate and multivariate analyses were performed to determine statistical significance. Sixty-six patients (33 with BTAs, 33 with other aneurysms) who were evaluated from 2008 to 2013 were analyzed. Multivariate logistic regression revealed that a larger angle between the posterior cerebral arteries (odds ratio, 1.04; P = 1.42 × 10(-3)) and a smaller basilar artery diameter (odds ratio, 0.23; P = .02) were most strongly associated with BTA formation after adjustment for other morphological and clinical variables. Larger posterior cerebral artery angles and smaller basilar artery diameters are associated with the formation of basilar tip aneurysms. These parameters are easily measurable by the clinician and will aid in screening strategies in high-risk patients.

Association of Versican (VCAN) gene polymorphisms rs251124 and rs2287926 (G428D), with intracranial aneurysm

Intracranial aneurysm (IA) accounts for 85% of Subarachnoid Hemorrhage (SAH) and is mainly caused due to the weakening of arterial wall. The structural integrity of the intracranial arteries is mainly influenced by the extracellular matrix (ECM) remodeling. The Proteoglycan Versican plays an important role in extracellular matrix assembly and plays a major role in the pathogenesis of IA. The linkage studies also indicated VCAN as a putative candidate gene for IA in the 5q22–31 region. Using a case–control study design, we tested the hypothesis whether the variants in VCAN gene, nonsynonymous variants in the coding region of Glycosaminoglycan α (GAG-α) and GAG-β and two reported SNPs involved in splicing rs251124 and rs173686 can increase the risk of aSAH among South Indian patients, either independently, or by interacting with other risk factors of the disease. We selected 200 radiologically confirmed aneurysmal cases and 250 ethnically, age and sex matched controls from the Dravidian Malayalam speaking population of South India. The present study reiterated the earlier association of rs251124 with intracranial aneurysm (P=0.0002) and also found a novel association with rs2287926 (G428D) in exon 7 coding for GAG-α with intracranial aneurysm (P=0.0015). Interestingly, both these SNPs contributed to higher risk for aneurysm in males. In-silico analysis predicted this SNP to have the highest functional relevance in the gene which might have a potentially altered regulatory role in transcription and splicing. Using meta-analysis with available literature rs251124 was found to be the strongest intracranial aneurysm marker for global ethnicities. This study with a novel functional SNP rs2287926 (G428D) further substantiates the potential role of VCAN in the pathogenesis of IA.

Molecular basis for intracranial aneurysm formation.

Intracranial aneurysm (IA) is a socially important disease both because it has a high prevalence and because of the severity of resultant subarachnoid hemorrhages after IA rupture. The major concern of current IA treatment is the lack medical therapies that are less invasive than surgical procedures for many patients. The current situation is mostly caused by a lack of knowledge regarding the regulating mechanisms of IA formation. Hemodynamic stress, especially high wall shear stress, loaded on arterial bifurcation sites is recognized as a trigger of IA formation from studies performed in the field of fluid dynamics. On the other hand, many studies using human specimens have also revealed the presence of active inflammatory responses, such as the infiltration of macrophages, in the pathogenesis of IA. Because of these findings, recent experimental studies, mainly using animal models of IA, have revealed some of the molecular mechanisms linking hemodynamic stress and long-lasting inflammation in IA walls. Currently, we propose that IA is a chronic inflammatory disease regulated by a positive feedback loop consisting of the cyclooxygenase (COX)-2 - prostaglandin (PG) E2 - prostaglandin E receptor 2 (EP2) - nuclear factor (NF)-κB signaling pathway triggered under hemodynamic stress and macrophage infiltration via NF-κB-mediated monocyte chemoattractant protein (MCP)-1 induction. These findings indicate future directions for the development of therapeutic drugs for IAs.

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

BackgroundIntracranial 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.ResultsWe 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.ConclusionsIn 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.

Abstract W P365: Critical Role of Smooth Muscle Cell Phenotypic Modulation in Cerebral Aneurysm Formation and Rupture

Objective: Little is known about smooth muscle cell (SMC) phenotypic modulation in the cerebral circulation or pathogenesis of intracranial aneurysms. TNF-α has been associated with aneurysms, but a direct role has not been established. Methods: Cultured cerebral SMC were treated with TNF-α for PCR, western blot, chromatin immune-precipitation (CHIP), and adenovirus promoter transfection. In vivo experiments were carried out in the following models: application of TNF-α to the surface of carotid arteries, cerebral model of hypertension and hemodynamic stress, and cerebral model of aneurysm formation and rupture. The TNF-α inhibitor 3,6’dithiothalidomide (DTH) was synthesized. Results: Cultured cerebral SMC over-expressing myocardin induced expression of key SMC contractile genes (SM-α-actin, SM-22α, SM-MHC), while dominant negative suppressed expression. TNF-α treatment inhibited this contractile phenotype and induced pro-inflammatory genes (MCP-1, MMPs, VCAM-1, IL-1β). TNF-α increased expression of KLF4 and KLF4 siRNA abrogated TNF-α induced phentotypic modulation. These mechanisms were confirmed in vivo following exposure of rat carotid arteries to TNF-α and early in a model of cerebral hypertension and hemodynamic stress prior to cerebral aneurysm formation. Treatment with DTH reversed these pathological vessel wall alterations. TNF-α knock-out mice and DTH pre-treatment decreased the incidence of aneurysm formation and rupture. As compared with sham mice, TNF-α expression was not significantly different in TNF-α knock-out mice or those pre-treated with DTH, but was elevated in unruptured and ruptured aneurysms. Initiation of DTH 7 days after aneurysm induction did not alter aneurysm incidence, but resulted in stabilization and decreased rupture. CHIP assays in vivo and in vitro demonstrated that TNF-α promotes epigenetic changes through KLF4 dependent alterations in promoter regions of myocardin, SMC’s, and inflammatory genes. Conclusion: TNF-α induces phenotypic modulation of cerebral SMC through myocardin and KLF4 regulated pathways. These results demonstrate a novel role for TNF-α in promoting a pro-inflammatory phenotype. These data suggests a critical role of TNF-α in the formation and rupture of aneurysms.

Statins as a Candidate of Drugs for Intracranial Aneurysm Treatment

The treatment for intracranial aneurysm (IA) is socially important because of poor outcome posed by subarachnoid hemorrhage after rupture. Further, the incidence of IAs in general public is high and, indeed, in developed countries many IAs are incidentally found through brain check. However, to date, options for treatment of IAs to prevent rupture are quite limited only to surgical procedures such as microsurgical clipping and endovascular coiling. Taking into account unavoidable risks of complication from surgical interventions and numerous aneurysm careers without treatment, less invasive medical therapies should be established. In human IA lesions, the presence of inflammatory responses, such as expressions of pro-inflammatory mediators and infiltration of inflammatory cells, have been reported, which suggests the involvement of inflammatory responses in the pathogenesis of IA. Recent experimental studies using rodent models have revealed the crucial role of inflammatory responses mediated by NF-κB activation in IA formation and progression and supported the notion that IA is an inflammatory disease affected intracranial arteries. To find out a candidate drug for IA treatments, the effect of several drugs with anti-inflammatory and anti-NF-κB actions on IA progression has been examined using rodent models and revealed the excellent inhibitory effect of statins (HMG-CoA reductase inhibitors) on IA progression. Based on these findings, the case-control study was recently carried out enrolling patients with unruptured or ruptured IAs to examine the effect of statin usage on rupture. This study revealed the significant differences in the ratio of statin usage between two groups and notably the remarkable reduction of risk of rupture of pre-existing IAs under statin usage at the adjusted odds ratio of 0.30. Recent laboratory and clinical studies make considerable achievement toward the future development of drugs for IA treatment and especially suggest the potential of statins as a candidate.

TNF-α Induces Phenotypic Modulation in Cerebral Vascular Smooth Muscle Cells: Implications for Cerebral Aneurysm Pathology

Little is known about vascular smooth muscle cell (SMC) phenotypic modulation in the cerebral circulation or pathogenesis of intracranial aneurysms. Tumor necrosis factor-alpha (TNF-α) has been associated with aneurysms, but potential mechanisms are unclear. Cultured rat cerebral SMCs overexpressing myocardin induced expression of key SMC contractile genes (SM-α-actin, SM-22α, smooth muscle myosin heavy chain), while dominant-negative cells suppressed expression. Tumor necrosis factor-alpha treatment inhibited this contractile phenotype and induced pro-inflammatory/matrix-remodeling genes (monocyte chemoattractant protein-1, matrix metalloproteinase-3, matrix metalloproteinase-9, vascular cell adhesion molecule-1, interleukin-1 beta). Tumor necrosis factor-alpha increased expression of KLF4, a known regulator of SMC differentiation. Kruppel-like transcription factor 4 (KLF4) small interfering RNA abrogated TNF-α activation of inflammatory genes and suppression of contractile genes. These mechanisms were confirmed in vivo after exposure of rat carotid arteries to TNF-α and early on in a model of cerebral aneurysm formation. Treatment with the synthesized TNF-α inhibitor 3,6-dithiothalidomide reversed pathologic vessel wall alterations after induced hypertension and hemodynamic stress. Chromatin immunoprecipitation assays in vivo and in vitro demonstrated that TNF-α promotes epigenetic changes through KLF4-dependent alterations in promoter regions of myocardin, SMCs, and inflammatory genes. In conclusion, TNF-α induces phenotypic modulation of cerebral SMCs through myocardin and KLF4-regulated pathways. These results demonstrate a novel role for TNF-α in promoting a pro-inflammatory/matrix-remodeling phenotype, which has important implications for the mechanisms behind intracranial aneurysm formation.

Association Between NFKB1 −94 Insertion/Deletion ATTG Polymorphism and Risk of Intracranial Aneurysm

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

High Wall Shear Stress and Spatial Gradients in Vascular Pathology: A Review

Cardiovascular pathologies such as intracranial aneurysms (IAs) and atherosclerosis preferentially localize to bifurcations and curvatures where hemodynamics are complex. While extensive knowledge about low wall shear stress (WSS) has been generated in the past, due to its strong relevance to atherogenesis, high WSS (typically >3Pa) has emerged as a key regulator of vascular biology and pathology as well, receiving renewed interests. As reviewed here, chronic high WSS not only stimulates adaptive outward remodeling, but also contributes to saccular IA formation (at bifurcation apices or outer curves) and atherosclerotic plaque destabilization (in stenosed vessels). Recent advances in understanding IA pathogenesis have shed new light on the role of high WSS in pathological vascular remodeling. In complex geometries, high WSS can couple with significant spatial WSS gradient (WSSG). A combination of high WSS and positive WSSG has been shown to trigger aneurysm initiation. Since endothelial cells (ECs) are sensors of WSS, we have begun to elucidate EC responses to high WSS alone and in combination with WSSG. Understanding such responses will provide insight into not only aneurysm formation, but also plaque destabilization and other vascular pathologies and potentially lead to improved strategies for disease management and novel targets for pharmacological intervention.