Critical roles of macrophages in the formation of intracranial aneurysm

Tumor necrosis factor-α modulates cerebral aneurysm formation and rupture

Inflammation is a critical process behind cerebral aneurysm formation and rupture. Tumor necrosis factor alpha (TNF-α) is a key immune modulator that has been implicated in cerebral aneurysm pathophysiology. This may occur through TNF-α-mediated endothelial injury, smooth muscle cell phenotypic modulation, recruitment of macrophages, activation of chemotactic cytokines, upregulation of matrix remodeling genes, production of free radicals leading to oxidative stress, and ultimately cellular apoptosis. Recent studies have indicated that TNF-α may be a potential target for the development of novel medical therapies, but additional experimental data is needed to clarify the intricacies of TNF-α activation and its critical downstream targets in cerebral aneurysms. This review provides an update on the mechanisms underlying TNF-α-induced molecular modulation in cerebral aneurysms.

A critical role for proinflammatory behavior of smooth muscle cells in hemodynamic initiation of intracranial aneurysm

Background

Intracranial aneurysm initiation is poorly understood, although hemodynamic insult is believed to play an important role in triggering the pathology. It has recently been found in a rabbit model that while macrophages are absent during hemodynamic aneurysm initiation, matrix metalloproteinases (MMPs) are elevated and co-localize with smooth muscle cells (SMCs). This study investigates whether SMCs play a mechanistic role in aneurysm initiation triggered by hemodynamics.

Methods

Aneurysmal damage was induced at the basilar terminus via bilateral common carotid artery ligation in rabbits (n = 45, plus 7 sham controls). 16 ligated rabbits were treated with doxycycline to inhibit MMPs, 7 received clodronate liposomes to deplete circulating monocytes, and the rest received no drug. Effects of the treatments on aneurysm development were assessed histologically 5 days and 6 months after ligation. MMP production and expression of inflammatory markers by SMCs was monitored by immunohistochemistry and in situ hybridization.

Results

Treatment with doxycycline attenuated aneurysmal development examined at 5 days and 6 months, suggesting that MMPs contribute to aneurysm initiation. However, systemic depletion of macrophages did not decrease MMPs or suppress aneurysmal development. Immunofluorescence showed that during aneurysm initiation MMP-2 and MMP-9 were distributed in SMCs, and in situ hybridization indicated that they were transcribed by SMCs. In regions of early aneurysmal lesion, SMCs exhibited decreased expression of smooth muscle actin and increased NF-κB and MCP-1 expressions.

Conclusions

During aneurysm initiation triggered by hemodynamics, SMCs rather than macrophages are responsible for MMP production that is critical for aneurysmal lesion development. These SMCs exhibit proinflammatory behavior.

The emerging role of ferumoxytol-enhanced MRI in the management of cerebrovascular lesions

Inflammation is increasingly being understood to be a key component to the pathophysiology of cerebrovascular lesions. Ferumoxytol, an iron oxide nanoparticle coated by a carbohydrate shell, has been used in MRI studies as an inflammatory marker because it is cleared by macrophages. Ferumoxytol-enhanced MRI has emerged as an important tool for noninvasive assessment of the inflammatory status of cerebrovascular lesions, namely aneurysms and arteriovenous malformations. Moreover, preliminary evidence suggests that ferumoxytol-enhanced MRI could be applied as a non-invasive tool to differentiate “unstable” lesions that require early intervention from “stable” lesions in which observation may be safe. Assessment of the effects of anti-inflammatory pharmacological interventions on cerebrovascular lesions is also a potentially crucial application of the technique. Future improvements in technique and MRI signal quantification will certainly pave the way for widespread and efficient use of ferumoxytol-enhanced MRI in clinical practice. In this paper, we review current data regarding ferumoxytol-enhanced MRI and discuss its current/potential applications and future perspectives.

The role of oxidative stress in cerebral aneurysm formation and rupture

Oxidative stress is known to contribute to the progression of cerebrovascular disease. Additionally, oxidative stress may be increased by, but also augment inflammation, a key contributor to cerebral aneurysm development and rupture. Oxidative stress can induce important processes leading to cerebral aneurysm formation including direct endothelial injury as well as smooth muscle cell phenotypic switching to an inflammatory phenotype and ultimately apoptosis. Oxidative stress leads to recruitment and invasion of inflammatory cells through upregulation of chemotactic cytokines and adhesion molecules. Matrix metalloproteinases can be activated by free radicals leading to vessel wall remodeling and breakdown. Free radicals mediate lipid peroxidation leading to atherosclerosis and contribute to hemodynamic stress and hypertensive pathology, all integral elements of cerebral aneurysm development. Preliminary studies suggest that therapies targeted at oxidative stress may provide a future beneficial treatment for cerebral aneurysms, but further studies are indicated to define the role of free radicals in cerebral aneurysm formation and rupture. The goal of this review is to assess the role of oxidative stress in cerebral aneurysm pathogenesis.

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.

Intracranial aneurysm formation in type-one diabetes rats

BACKGROUND & OBJECTIVE

Diabetes mellitus (DM) plays an important role in the pathogenesis of vascular complications including arteriosclerosis and ischemic stroke. Whether DM impacts intracranial aneurysm (IA) formation has not been extensively investigated. In this study, we tested the underlying mechanism of type one DM (T1DM) induced IA formation in rats.

EXPERIMENTAL APPROACHES

T1DM was induced by streptozotocin injection. Rats were euthanized at 0, 4 and 10 weeks after T1DM induction. To evaluate cerebral vascular perfusion, Fluorescein isothiocyanate - dye was injected at 5 min prior to euthanasia. Vascular perfusion was measured by laser scanning confocal microscopy. Trichrome, Elastica van Gieson, alpha-smooth muscle actin (a-SMA) and receptor of advanced glycation end-products (RAGE), toll-like receptor 4 (TLR4) and matrix metalloproteinase 9 (MMP9) immunostaining were performed. The IA formation was classified by 0-3 stages: 0: Normal; 1: Endothelial damage; 2: Moderate protrusion; and 3: Saccular aneurysm formation.

RESULTS

T1DM significantly increased IA formation identified by the classification of aneurysmal changes compared with non-DM rats (p<0.05). However, T1DM induced IA formations were classified as stage 1 and stage 2, but not stage 3. Cerebral vascular perfusion was significantly decreased in T1DM rats compared to non-DM rats (p<0.01). DM10W rats exhibited a significant decrease of cerebral vascular perfusion compared to DM4W rats (p<0.05). T1DM rats also significantly increased the internal carotid artery (ICA) intimae and media thickness, and decreased the internal carotid artery diameter compared to non-DM rats. RAGE, MMP9 and TLR4 expression were significantly increased in T1DM rats compared to non-DM rats. The increased RAGE, TLR4 and MMP9 significantly correlated with IA formation (p<0.05).

CONCLUSION

T1DM increases IA formation. The increased RAGE, MMP9 and TLR4 expressions might contribute to IA formation in T1DM rats.

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.

Investigating the influence of haemodynamic stimuli on intracranial aneurysm inception

We propose a novel method to reconstruct the hypothetical geometry of the healthy vasculature prior to intracranial aneurysm (IA) formation: a Frenet frame is calculated along the skeletonization of the arterial geometry; upstream and downstream boundaries of the aneurysmal segment are expressed in terms of the local Frenet frame basis vectors; the hypothetical healthy geometry is then reconstructed by propagating a closed curve along the skeleton using the local Frenet frames so that the upstream boundary is smoothly morphed into the downstream boundary. This methodology takes into account the tortuosity of the arterial vasculature and requires minimal user subjectivity. The method is applied to 22 clinical cases depicting IAs. Computational fluid dynamic simulations of the vasculature without IA are performed and the haemodynamic stimuli in the location of IA formation are examined. We observe that locally elevated wall shear stress (WSS) and gradient oscillatory number (GON) are highly correlated (20/22 for WSS and 19/22 for GON) with regions susceptible to sidewall IA formation whilst haemodynamic indices associated with the oscillation of the WSS vectors have much lower correlations.

Dysregulated Expression Profiles of MicroRNAs of Experimentally Induced Cerebral Aneurysms in Rats

OBJECTIVE

Cerebral aneurysm (CA) is an important acquired cerebrovascular disease that can cause catastrophic results. MicroRNAs (miRNAs) are small non-coding RNAs, playing essential roles in modulating basic physiologic and pathological processes. Currently, evidences have been established about biologic relationship between miRNAs and abdominal aortic aneurysms. However, biologic roles of miRNAs in CA formation have not been explained yet. We employed microarray analysis to detect and compare miRNA expression profiles in late stage of CA in rat model.

METHODS

Twenty-six, 7-week-old male Sprague-Dawley rats underwent a CA induction procedure. The control animals (n=11) were fed a normal diet, and the experimental animals (n=26) were fed a normal diet with 1% normal saline for 3 months. Then, the rats were sacrificed, their cerebral arteries were dissected, and the five regions of aneurysmal dilation on the left posterior communicating artery were cut for miRNA microarrays analysis. Six miRNAs (miRNA-1, miRNA-223, miRNA-24-1-5p, miRNA-551b, miRNA-433, and miRNA-489) were randomly chosen for validation using real-time quantitative PCR.

RESULTS

Among a set of differentially expressed miRNAs, 14 miRNAs were over-expressed more than 200% and 6 miRNAs were down-expressed lower than 50% in the CA tissues.

CONCLUSION

The results show that miRNAs might take part in CA formation probably by affecting multiple target genes and signaling pathways. Further investigations to identify the exact roles of these miRNAs in CA formation are required.

Evidence that acetylsalicylic acid attenuates inflammation in the walls of human cerebral aneurysms: preliminary results

Background

Inflammatory cells and molecules may play a critical role in formation and rupture of cerebral aneurysms. Recently, an epidemiologic study reported that acetylsalicylic acid (ASA) decreases the risk of aneurysm rupture. The goal of this study was to determine the effects of ASA on inflammatory cells and molecules in the walls of human cerebral aneurysms, using radiographic and histological techniques.

Methods and Results

Eleven prospectively enrolled patients harboring unruptured intracranial aneurysms were randomized into an ASA‐treated (81 mg daily) group (n=6) and an untreated (control) group (n=5). Aneurysms were imaged at baseline using ferumoxytol‐enhanced MRI to estimate uptake by macrophages. After 3 months, patients were reimaged before undergoing microsurgical clipping. Aneurysm tissues were collected for immunostaining with monoclonal antibodies for cyclooxygenase‐1 (COX‐1), cyclooxygenase‐2 (COX‐2), microsomal prostaglandin E2 synthase‐1 (mPGES‐1), and macrophages. A decrease in signal intensity on ferumoxytol‐enhanced MRI was observed after 3 months of ASA treatment. Expression of COX‐2 (but not COX‐1), mPGES‐1, and macrophages was lower in the ASA group than in the control group.

Conclusions

This study provides preliminary radiographical and histological evidence that ASA may attenuate the inflammatory process in the walls of human cerebral aneurysms.

Clinical Trial Registration

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01710072.

Imaging aspirin effect on macrophages in the wall of human cerebral aneurysms using ferumoxytol-enhanced MRI: preliminary results

BACKGROUND AND PURPOSE

Daily intake of aspirin was shown to decrease human cerebral aneurysm rupture by 60%. The feasibility of imaging macrophages in human cerebral aneurysm walls using ferumoxytol-enhanced MRI has been demonstrated. The goal of the present study is to image aspirin effect on macrophages in the wall of human cerebral aneurysm using ferumoxytol-enhanced MRI.

MATERIAL AND METHODS

Five patients with known intracranial aneurysms underwent baseline imaging using T2(*) gradient-echo and T1 MRI sequences using ferumoxytol-enhanced MRI 72-hour post-ferumoxytol infusion. Patients then received 81 mg aspirin per os daily. After 3 months, imaging studies were repeated and analyzed by co-registration using a histogram and subtraction of follow-up images from baseline.

RESULTS

In all five patients, after 3 months of treatment with aspirin, the signal intensity corresponding to the uptake of ferumoxytol by macrophages in the aneurysm wall was less intense than in the baseline images. This was confirmed by co-registration of images using histogram and subtraction of follow-up images from baseline.

CONCLUSION

These preliminary results suggest the feasibility of imaging aspirin effect on macrophages localized in the wall of human cerebral aneurysm using ferumoxytol-enhanced MRI. The findings provide radiographic evidence of decreased inflammation in human cerebral aneurysms with daily intake of aspirin using macrophages as a surrogate marker for inflammation.

Meningeal and choroid plexus cells--novel drug targets for CNS disorders

The meninges and choroid plexus perform many functions in the developing and adult human central nervous system (CNS) and are composed of a number of different cell types. In this article I focus on meningeal and choroid plexus cells as targets for the development of drugs to treat a range of traumatic, ischemic and chronic brain disorders. Meningeal cells are involved in cortical development (and their dysfunction may be involved in cortical dysplasia), fibrotic scar formation after traumatic brain injuries (TBI), brain inflammation following infections, and neurodegenerative disorders such as Multiple Sclerosis (MS) and Alzheimer's disease (AD) and other brain disorders. The choroid plexus regulates the composition of the cerebrospinal fluid (CSF) as well as brain entry of inflammatory cells under basal conditions and after injuries. The meninges and choroid plexus also link peripheral inflammation (occurring in the metabolic syndrome and after infections) to CNS inflammation which may contribute to the development and progression of a range of CNS neurological and psychiatric disorders. They respond to cytokines generated systemically and secrete cytokines and chemokines that have powerful effects on the brain. The meninges may also provide a stem cell niche in the adult brain which could be harnessed for brain repair. Targeting meningeal and choroid plexus cells with therapeutic agents may provide novel therapies for a range of human brain disorders.

Cigarette smoke and inflammation: role in cerebral aneurysm formation and rupture

Smoking is an established risk factor for subarachnoid hemorrhage yet the underlying mechanisms are largely unknown. Recent data has implicated a role of inflammation in the development of cerebral aneurysms. Inflammation accompanying cigarette smoke exposure may thus be a critical pathway underlying the development, progression, and rupture of cerebral aneurysms. Various constituents of the inflammatory response appear to be involved including adhesion molecules, cytokines, reactive oxygen species, leukocytes, matrix metalloproteinases, and vascular smooth muscle cells. Characterization of the molecular basis of the inflammatory response accompanying cigarette smoke exposure will provide a rational approach for future targeted therapy. In this paper, we review the current body of knowledge implicating cigarette smoke-induced inflammation in cerebral aneurysm formation/rupture and attempt to highlight important avenues for future investigation.

Thrombosis heralding aneurysmal rupture: an exploration of potential mechanisms in a novel giant swine aneurysm model

BACKGROUND AND PURPOSE

The relationship between aneurysm dimensions, flow, thrombosis, and rupture remains poorly understood. We attempted to clarify this relationship by exploring various swine aneurysm models.

MATERIALS AND METHODS

Bilateral carotid aneurysms were constructed according to 3 protocols in 24 animals: small aneurysms with wide necks (group 1; n = 6 animals); small aneurysms with small necks (group 2; n = 4 animals), and giant aneurysms with large necks (group 3; n = 14 animals). Group 3 included 3 subgroups, related to testing the model in various experimental conditions: The neck was clipped in 3 animals; venous pouches lacked an endothelial lining in 4 animals; and 7 were control animals. Animals were followed until rupture, or for 1-4 weeks. Angiography was performed postoperatively and before euthanasia. We studied lesion pathology, paying attention to thrombosis, recanalization, wall composition, and perianeurysmal hemorrhage.

RESULTS

Groups differed significantly in aneurysm dimensions and aspect ratio (P = .002). Ruptures occurred more frequently in animals with untreated giant aneurysms (7/7) than in animals with small wide-neck (0/6) or small-neck (2/4) aneurysms (P = .002). Ruptures occurred only in animals with thrombosed aneurysms. Lesions lacking an endothelial lining and 5 of 6 clipped venous pouches thrombosed but did not rupture. One giant lesion ruptured despite complete clipping. The wall was deficient in α-actin and was infiltrated with inflammatory cells and erythrocytes in all thrombosed cases, ruptured or not. Ruptures were associated with recanalizing channels in 9 of 10 cases.

CONCLUSIONS

Thrombosis, inflammation, and recanalization may precipitate aneurysmal ruptures in a swine model.

Early change in ferumoxytol-enhanced magnetic resonance imaging signal suggests unstable human cerebral aneurysm: a pilot study

BACKGROUND AND PURPOSE

The clinical significance of early (ie, within the first 24 hours) uptake of ferumoxytol by macrophages in the wall of human cerebral aneurysms is not clear. The purpose of this study was to determine whether early uptake of ferumoxytol suggests unstable cerebral aneurysm.

METHODS

Thirty unruptured aneurysms in 22 patients were imaged with magnetic resonance imaging 24 hours after infusion of ferumoxytol. Eighteen aneurysms were also imaged 72 hours after infusion of ferumoxytol. Aneurysm dome tissue was collected from 4 patients with early magnetic resonance imaging signal changes, 5 patients with late signal changes, and 5 other patients with ruptured aneurysms. The tissue was immunostained for expression of cyclooxygenase-1, cyclooxygenase-2, microsomal prostaglandin E2 synthase-1, and macrophages.

RESULTS

In 23% (7/30) of aneurysms, there was pronounced early uptake of ferumoxytol. Four aneurysms were clipped. The remaining 3 aneurysms were managed conservatively; all 3 ruptured within 6 months. In 53% (16 of 30) of aneurysms, there was pronounced uptake of ferumoxytol at 72 hours. Eight aneurysms were surgically clipped, and 8 were managed conservatively; none ruptured or increased in size after 6 months. Expression of cyclooxygenase-2, microsomal prostaglandin E2 synthase-1, and macrophages was similar in unruptured aneurysms with early uptake of ferumoxytol and ruptured aneurysms. Expression of these inflammatory molecules was significantly higher in aneurysms with early uptake of ferumoxytol versus aneurysms with late uptake.

CONCLUSIONS

Uptake of ferumoxytol in aneurysm walls within the first 24 hours strongly suggests aneurysm instability and probability of rupture within 6 months, and may warrant urgent intervention.

Paneth cell-mediated multiorgan dysfunction after acute kidney injury

Acute kidney injury (AKI) is frequently complicated by extrarenal multiorgan injury, including intestinal and hepatic dysfunction. In this study, we hypothesized that a discrete intestinal source of proinflammatory mediators drives multiorgan injury in response to AKI. After induction of AKI in mice by renal ischemia-reperfusion or bilateral nephrectomy, small intestinal Paneth cells increased the synthesis and release of IL-17A in conjunction with severe intestinal apoptosis and inflammation. We also detected significantly increased IL-17A in portal and systemic circulation after AKI. Intestinal macrophages appear to transport released Paneth cell granule constituents induced by AKI, away from the base of the crypts into the liver. Genetic or pharmacologic depletion of Paneth cells decreased small intestinal IL-17A secretion and plasma IL-17A levels significantly and attenuated intestinal, hepatic, and renal injury after AKI. Similarly, portal delivery of IL-17A in macrophage-depleted mice decreased markedly. In addition, intestinal, hepatic, and renal injury following AKI was attenuated without affecting intestinal IL-17A generation. In conclusion, AKI induces IL-17A synthesis and secretion by Paneth cells to initiate intestinal and hepatic injury by hepatic and systemic delivery of IL-17A by macrophages. Modulation of Paneth cell dysregulation may have therapeutic implications by reducing systemic complications arising from AKI.

Macrophage imbalance (M1 vs. M2) and upregulation of mast cells in wall of ruptured human cerebral aneurysms: preliminary results

BACKGROUND

M1 and M2 cells are two major subsets of human macrophages that exert opposite effects on the inflammatory response. This study aims to investigate the role of macrophage M1/M2 imbalance and mast cells in the progression of human cerebral aneurysms to rupture.

METHODS

Ten patients with cerebral aneurysms (five ruptured and five unruptured) underwent microsurgical clipping. During the procedure, a segment of the aneurysm dome was resected and immunostained with monoclonal antibodies for M1 cells (anti-HLA DR), M2 cells (anti-CD 163), and mast cells (anti-tryptase clone AA). A segment of the superficial temporal artery (STA) was also removed and immunostained with monoclonal antibodies for M1, M2, and mast cells.

RESULTS

All ten aneurysm tissues stained positive for M1, M2, and mast cells. M1 and M2 cells were present in equal proportions in unruptured aneurysms. This contrasted with a marked predominance of M1 over M2 cells in ruptured aneurysms (p = 0.045). Mast cells were also prominently upregulated in ruptured aneurysms (p = 0.001). Few M1 and M2 cells were present in STA samples.

CONCLUSIONS

M1/M2 macrophages and mast cells are found in human cerebral aneurysms; however, M1 and mast cell expression seems to markedly increase in ruptured aneurysms. These findings suggest that macrophage M1/M2 imbalance and upregulation of mast cells may have a role in the progression of cerebral aneurysms to rupture.

Regression of intracranial aneurysms by simultaneous inhibition of nuclear factor-κB and Ets with chimeric decoy oligodeoxynucleotide treatment

BACKGROUND

Despite a high mortality and morbidity of subarachnoid hemorrhage due to an intracranial aneurysm (IA), there is no effective medical treatment to prevent the rupture of IAs. Recent studies have revealed the involvement of the transactivation of proinflammatory genes by nuclear factor-κB (NF-κB) and Ets-1 in the pathogenesis of IA formation and enlargement.

OBJECTIVE

To examine the regressive effect of chimeric decoy oligodeoxynucleotides (ODNs), which simultaneously inhibit NF-κB and Ets-1, on IA development in the rat model.

METHODS

One month after IA induction, rats were treated with NF-κB decoy ODNs or chimeric decoy ODNs. Size, media thickness, macrophage infiltration, and collagen biosynthesis in IA walls were analyzed in both groups.

RESULTS

The treatment with chimeric decoy ODNs decreased IA size and thickened IA walls of preexisting IAs induced in the rat model, although the treatment with NF-κB decoy ODNs failed to regress preexisting IAs. Chimeric decoy ODN-treated rats exhibited decreased expression of monocyte chemotactic protein-1 and macrophage infiltration in IA walls. In addition, decreased collagen biosynthesis in IA walls was ameliorated in the chimeric decoy ODN-treated group.

CONCLUSION

The results suggest the possibility of a minimally invasive molecular therapy targeting the inhibition of NF-κB and ets-1 for IAs in humans.

Biology of intracranial aneurysms: role of inflammation

Intracranial aneurysms (IAs) linger as a potentially devastating clinical problem. Despite intense investigation, our understanding of the mechanisms leading to aneurysm development, progression and rupture remain incompletely defined. An accumulating body of evidence implicates inflammation as a critical contributor to aneurysm pathogenesis. Intracranial aneurysm formation and progression appear to result from endothelial dysfunction, a mounting inflammatory response, and vascular smooth muscle cell phenotypic modulation producing a pro-inflammatory phenotype. A later final common pathway appears to involve apoptosis of cellular constituents of the vessel wall. These changes result in degradation of the integrity of the vascular wall leading to aneurysmal dilation, progression and eventual rupture in certain aneurysms. Various aspects of the inflammatory response have been investigated as contributors to IA pathogenesis including leukocytes, complement, immunoglobulins, cytokines, and other humoral mediators. Furthermore, gene expression profiling of IA compared with control arteries has prominently featured differential expression of genes involved with immune response/inflammation. Preliminary data suggest that therapies targeting the inflammatory response may have efficacy in the future treatment of IA. Further investigation, however, is necessary to elucidate the precise role of inflammation in IA pathogenesis, which can be exploited to improve the prognosis of patients harboring IA.

Pharmacological stabilization of intracranial aneurysms in mice: a feasibility study

BACKGROUND AND PURPOSE

An increasing number of unruptured intracranial aneurysms are being detected, partly due to the increased use of brain imaging techniques. Pharmacological stabilization of aneurysms for the prevention of aneurysmal rupture could potentially be an attractive alternative approach to clipping or coiling in patients with unruptured intracranial aneurysms. We have developed a mouse model of intracranial aneurysm that recapitulates key features of intracranial aneurysms. In this model, subarachnoid hemorrhage from aneurysmal rupture causes neurological symptoms that can be easily detected by a simple neurological examination. Using this model, we tested whether anti-inflammatory agents such as tetracycline derivatives, or a selective inhibitor of matrix metalloproteinases-2 and -9 (SB-3CT), can prevent the rupture of intracranial aneurysms.

METHODS

Aneurysms were induced by a combination of induced hypertension and a single injection of elastase into the cerebrospinal fluid in mice. Treatment with minocycline, doxycycline, or SB-3CT was started 6 days after aneurysm induction. Aneurysmal rupture was detected by neurological symptoms and confirmed by the presence of intracranial aneurysms with subarachnoid hemorrhage.

RESULTS

Minocycline and doxycycline significantly reduced rupture rates (vehicle versus doxycycline=80% versus 35%, P<0.05; vehicle versus minocycline=73% versus 24%, P<0.05) without affecting the overall incidence of aneurysms. However, SB-3CT did not affect the rupture rate (62% versus 55%, P=0.53).

CONCLUSIONS

Our data established the feasibility of using a mouse model of intracranial aneurysm to test pharmacological stabilization of aneurysms. Tetracycline derivatives could be potentially effective in preventing aneurysmal rupture.

Upregulation of cyclooxygenase-2 (COX-2) and microsomal prostaglandin E2 synthase-1 (mPGES-1) in wall of ruptured human cerebral aneurysms: preliminary results

BACKGROUND AND PURPOSE

Cyclooxygenase-2 (COX-2) and Microsomal Prostaglandin E2 Synthase-1 (mPGES-1) catalyze isomerization of the cyclooxygenase product PGH2 into PGE2. Deletion of COX-2/mPGES-1 suppresses carotid artery atherogenesis and angiotensin II-induced aortic aneurysms formation, and attenuates neointimal hyperplasia after vascular injury in mice. The upregulation of COX-2/mPGES-1 in the wall of ruptured human cerebral aneurysms is not known.

METHODS

Ten patients with intracranial aneurysms (5 ruptured and 5 nonruptured) underwent microsurgical clipping. During the procedure, a segment of the aneurysm dome was resected and immunostained with monoclonal antibodies for COX-1, COX-2, and mPGES-1. A segment of the superficial temporal artery was also removed and immunostained with monoclonal antibodies for COX-1, COX-2, and mPGES-1.

RESULTS

All 10 aneurysm tissues stained positive for mPGES-1 monoclonal antibody. Expression of mPGES-1 was more abundant in ruptured aneurysm tissue than in nonruptured aneurysms, based on a semiquantitative grading. None of the superficial temporal artery specimens expressed mPGES-1. COX-2 was upregulated in the same distribution as was mPGES-1. COX-1 was present constitutively in all tissues.

CONCLUSIONS

COX-2/mPGES-1 are expressed in the wall of human cerebral aneurysms and more abundantly so in ruptured aneurysms than in nonruptured. We speculate that the protective effect of aspirin against rupture of cerebral aneurysms may be mediated in part by inhibition of COX-2/mPGES-1.

Prostaglandins and chronic inflammation

Chronic inflammation is the basis of various chronic illnesses including cancer and vascular diseases. However, much has yet to be learned how inflammation becomes chronic. Prostaglandins (PGs) are well established as mediators of acute inflammation, and recent studies in experimental animals have provided evidence that they also function in transition to and maintenance of chronic inflammation. One role PGs play in such processes is amplification of cytokine signaling. As such, PGs can facilitate acquired immunity and induce long-lasting immune inflammation. PGs also contribute to chronic inflammation by making a positive feedback loop and/or by inducing chemokines and recruiting inflammatory cells to alternate active cell populations at affected sites. PGs also contribute to tissue remodeling as seen in angiogenesis and fibrosis. Although such roles of PGs should be verified in human diseases, these findings suggest that PG signaling is a promising therapeutic target of chronic inflammatory diseases.

Inflammation, endoplasmic reticulum stress, autophagy, and the monocyte chemoattractant protein-1/CCR2 pathway

Numerous inflammatory cytokines have been implicated in the pathogenesis of cardiovascular diseases. Monocyte chemoattractant protein (MCP)-1/CCL2 is expressed by mainly inflammatory cells and stromal cells such as endothelial cells, and its expression is upregulated after proinflammatory stimuli and tissue injury. MCP-1 can function as a traditional chemotactic cytokine and also regulates gene transcription. The recently discovered novel zinc-finger protein, called MCPIP (MCP-1-induced protein), initiates a series of signaling events that causes oxidative and endoplasmic reticulum (ER) stress, leading to autophagy that can result in cell death or differentiation, depending on the cellular context. After a brief review of the basic processes involved in inflammation, ER stress, and autophagy, the recently elucidated role of MCP-1 and MCPIP in inflammatory diseases is reviewed. MCPIP was found to be able to control inflammatory response by inhibition of nuclear factor-κB activation through its deubiquitinase activity or by degradation of mRNA encoding a set of inflammatory cytokines through its RNase activity. The potential inclusion of such a novel deubiquitinase in the emerging anti-inflammatory strategies for the treatment of inflammation-related diseases such as cardiovascular diseases and type 2 diabetes is briefly discussed.

Macrophage imaging within human cerebral aneurysms wall using ferumoxytol-enhanced MRI: a pilot study

OBJECTIVE

Macrophages play a critical role in cerebral aneurysm formation and rupture. The purpose of this study is to demonstrate the feasibility and optimal parameters of imaging macrophages within human cerebral aneurysm wall using ferumoxytol-enhanced MRI.

METHODS AND RESULTS

Nineteen unruptured aneurysms in 11 patients were imaged using T2*-GE-MRI sequence. Two protocols were used. Protocol A was an infusion of 2.5 mg/kg of ferumoxytol and imaging at day 0 and 1. Protocol B was an infusion of 5 mg/kg of ferumoxytol and imaging at day 0 and 3. All images were reviewed independently by 2 neuroradiologists to assess for ferumoxytol-associated loss of MRI signal intensity within aneurysm wall. Aneurysm tissue was harvested for histological analysis. Fifty percent (5/10) of aneurysms in protocol A showed ferumoxytol-associated signal changes in aneurysm walls compared to 78% (7/9) of aneurysms in protocol B. Aneurysm tissue harvested from patients infused with ferumoxytol stained positive for both CD68+, demonstrating macrophage infiltration, and Prussian blue, demonstrating uptake of iron particles. Tissue harvested from controls stained positive for CD68 but not Prussian blue.

CONCLUSIONS

Imaging with T2*-GE-MRI at 72 hours postinfusion of 5 mg/kg of ferumoxytol establishes a valid and useful approximation of optimal dose and timing parameters for macrophages imaging within aneurysm wall. Further studies are needed to correlate these imaging findings with risk of intracranial aneurysm rupture.

Gene expression changes: five years after creation of elastase-induced aneurysms

PURPOSE

Intracranial saccular aneurysms are associated with chronic remodeling of the arterial wall. The pathobiology of aneurysm growth and rupture is poorly understood. The present study was performed to study the gene expression patterns in elastase-induced saccular aneurysms in rabbits 5 years after aneurysm creation, compared with unoperated control arteries.

MATERIALS AND METHODS

Elastase-induced saccular aneurysms were created in 25 rabbits and followed up for 5 years. Thirteen rabbits died during follow-up for reasons unrelated to the aneurysms. RNA was isolated from aneurysm tissue and the control contralateral common carotid artery in five of the 12 surviving animals, and analyzed for gene expression by using human gene microarrays. Genes with statistical differences between groups (P < .05 and fold change ≥ 1.5 and ≤ 0.75) were considered differentially expressed. Real-time polymerase chain reaction (RT-PCR) was used for confirmation of gene microarray findings for selected genes.

RESULTS

Fifty-three of 13,353 genes (0.4%) were differentially expressed in the aneurysms compared with the unoperated control arteries. Molecular and functional pathway analysis revealed that immunoregulatory molecules, growth factors, cell adhesion molecules, and structural molecules were differentially expressed in the aneurysms compared with controls. RT-PCR results of selected genes confirmed the differential expression identified by using the gene chip microarray.

CONCLUSIONS

Significant modulation in a variety of biochemical and cellular functions in chronic aneurysms provides molecular insights into the pathophysiology of saccular aneurysms.