Background and Purpose-Recent studies have suggested that chronic inflammation actively participates in cerebral aneurysm (CA) formation. Macrophages accumulate in CA walls and express proinflammatory genes promoting CA progression, but the molecular mechanisms of monocyte/macrophage recruitment into CA walls remain to be elucidated. Methods-Monocyte chemoattractant protein-1 (MCP-1) expression in experimentally induced CAs was assessed by immunohistochemistry and Western blotting. The role of MCP-1 in CA formation was examined by MCP-1 -/-mice and a plasmid DNA encoding a dominant negative mutant of MCP-1 (7ND). MCP-1 expression in human CAs was examined by immunohistochemistry. Results-MCP-1 expression was upregulated in aneurysmal walls at the early stage of CA formation. MCP-1 -/-mice exhibited a significant decrease of CA formation and macrophage accumulation with decreased expression of matrix metalloproteinase-2, -9, and inducible nitric oxide synthase. Immunohistochemistry for the DNA binding form of nuclear factor-kappa B showed nuclear factor-kappa B activation in MCP-1-expressing cells. Blockade of MCP-1 activity by 7ND resulted in the inhibition of CA progression in rats. In human CAs, MCP-1 was also expressed in CA walls. Conclusions-These data suggest that MCP-1 plays a crucial role in CA formation as a major chemoattractant for monocyte/macrophage. MCP-1 expression in CA walls is induced through nuclear factor-kappa B activation. MCP-1 may be a novel therapeutic target of medical treatment preventing CA progression.

Background-Subarachnoid hemorrhage caused by the rupture of cerebral aneurysm (CA) remains a life-threatening disease despite recent diagnostic and therapeutic advancements. Recent studies strongly suggest the active participation of macrophage-mediated chronic inflammatory response in the pathogenesis of CA. We examined the role of nuclear factor-B (NF-B) in the pathogenesis of CA formation in this study. Methods and Results-In experimentally induced CAs in rats, NF-B was activated in cerebral arterial walls in the early stage of aneurysm formation with upregulated expression of downstream genes. NF-B p50 subunitdeficient mice showed a decreased incidence of CA formation with less macrophage infiltration into the arterial wall. NF-B decoy oligodeoxynucleotide also prevented CA formation when it was administered at the early stage of aneurysm formation in rats. Macrophage infiltration and expression of downstream genes were dramatically inhibited by NF-B decoy oligodeoxynucleotide. In human CA walls, NF-B also was activated, especially in the intima. Conclusions-Our data indicate that NF-B plays a crucial role as a key regulator in the initiation of CA development by inducing some inflammatory genes related to macrophage recruitment and activation. NF-B may represent a therapeutic target of a novel medical treatment for CA.

BACKGROUND AND PURPOSECerebral aneurysm is a frequent cerebrovascular event and a major cause of fatal subarachnoid haemorrhage, but there is no medical treatment for this condition. Haemodynamic stress and, recently, chronic inflammation have been proposed as major causes of cerebral aneurysm. Nevertheless, links between haemodynamic stress and chronic inflammation remain ill-defined, and to clarify such links, we evaluated the effects of prostaglandin E2 (PGE2), a mediator of inflammation, on the formation of cerebral aneurysms. EXPERIMENTAL APPROACHExpression of COX and prostaglandin E synthase (PGES) and PGE receptors were examined in human and rodent cerebral aneurysm. The incidence, size and inflammation of cerebral aneurysms were evaluated in rats treated with COX-2 inhibitors and mice lacking each prostaglandin receptor. Effects of shear stress and PGE receptor signalling on expression of pro-inflammatory molecules were studied in primary cultures of human endothelial cells (ECs). KEY RESULTSCOX-2, microsomal PGES-1 and prostaglandin E receptor 2 (EP2) were induced in ECs in the walls of cerebral aneurysms. Shear stress applied to primary ECs induced COX-2 and EP2. Inhibition or loss of COX-2 or EP2 in vivo attenuated each other's expression, suppressed nuclear factor kB (NF-kB)-mediated chronic inflammation and reduced incidence of cerebral aneurysm. EP2 stimulation in primary ECs induced NF-kB activation and expression of the chemokine (C-C motif) ligand 2, essential for cerebral aneurysm. CONCLUSIONS AND IMPLICATIONSThese results suggest that shear stress activated PGE2-EP2 pathway in ECs and amplified chronic inflammation via NF-kB. We propose EP2 as a therapeutic target in cerebral aneurysm. BJPBritish Journal of Pharmacology DOI:10.1111DOI:10. /j.1476DOI:10. -5381.2011 British Journal of Pharmacology (2011) IntroductionSubarachnoid haemorrhage is a serious cardiovascular event.It is fatal in 45% of patients within 30 days of onset, whereas 30% suffer from moderate to severe morbidity (van Gijn et al., 2007). The main cause of subarachnoid haemorrhage is a rupture of a pre-existing cerebral aneurysm, which is seen in 1-5% of the general public (Wiebers et al., 2003). Given this high prevalence and susceptibility to subarachnoid haemorrhage, treatment of cerebral aneurysm before rupture is important. Currently, there is no medical treatment that would directly interfere with cerebral aneurysm formation because the pathogenesis of these aneurysms remains unknown. In addition, surgical procedures for cerebral aneurysm have a risk of complication, even though it is low. Therefore, most patients are only given treatments to control some risk factors such as hypertension, rather than any direct treatment for the aneurysm itself.To elucidate the molecular mechanisms of cerebral aneurysm formation, we established a rodent model of cerebral aneurysm (Hashimoto et al., 1978;Morimoto et al., 2002) through inducing haemodynamic stress at bifurcation sites of cerebral arteries. Haemodynamic force is considered ...

Background and Purpose-The pathophysiology of cerebral aneurysms (CAs) is linked to chronic inflammation and degradation of extracellular matrix in vascular walls. Because statins have protective effects on various vascular diseases independent of their lipid-lowering effects, we investigated the effect of simvastatin on CA progression. Methods-CAs were induced in Sprague-Dawley rats with or without oral administration of simvastatin. The size and media thickness of CAs was evaluated 3 months after aneurysm induction. Expression of macrophage chemoattractant protein-1, vascular cell adhesion molecule-1, endothelial nitric oxide synthase, interleukin-1␤, inducible nitric oxide synthase, matrix metalloproteinase-2, and matrix metalloproteinase-9 in aneurysmal walls was examined by reverse transcriptase-polymerase chain reaction and immunohistochemistry. To examine whether simvastatin has a suppressive effect on preexisting CAs, simvastatin administration started at 1 month after aneurysm induction. Results-Rats treated with simvastatin exhibited a significant increase in media thickness and a significant reduction in aneurysmal size compared with control rats. Treatment with simvastatin resulted in reduced expression of macrophage chemoattractant protein-1 and vascular cell adhesion molecule-1, increased expression of endothelial nitric oxide synthase, and reduced the number of macrophage infiltration. In quantitative polymerase chain reaction and immunohistochemistry, simvastatin significantly inhibited upregulated expression of interleukin-1␤, inducible nitric oxide synthase, matrix metalloproteinase-2, and matrix metalloproteinase-9 associated with CA progression. Gelatin zymography revealed decreased activity of matrix metalloproteinase-2 and matrix metalloproteinase-9 in aneurysmal walls by simvastatin treatment. Simvastatin also effectively inhibited aneurysm enlargement and thinning of the media of preexisting CAs. Conclusions-Treatment with simvastatin suppresses the development of CAs by inhibiting inflammatory reactions in aneurysmal walls. Simvastatin also has a preventive effect on the progression of preexisting CAs. Simvastatin is a promising candidate of a novel medical treatment for the prevention of CA progression.

Cerebral aneurysm (CA) is a relatively common disease and can cause a catastrophic subarachnoid hemorrhage with a high mortality and morbidity rate. Despite its clinical and social importance, the detailed mechanism of CA formation remains to be elucidated, resulting in the absence of effective medical treatment against CAs. Recent studies revealed that chronic inflammation in arterial walls by hemodynamic force is implicated in CA formation. Reactive oxygen species (ROS) are a major mediator of inflammation and actively participate in the pathogenesis of various vascular diseases. In the present study, we first assessed the expression of ROS-producing and -eliminating genes in CA walls by immunohistochemistry and RT-PCR analysis. The ROS-producing gene, p47phox, was upregulated in infiltrating macrophages and medial smooth muscle cells in arterial walls. Upregulated ROS-producing genes and suppressed ROS-eliminating genes suggested that ROS overproduction occurred in aneurysmal walls. In situ superoxide imaging by dihydroethidium, which showed ROS overproduction in aneurysmal walls, confirmed this hypothesis. Edaravone, a powerful free radical scavenger, effectively inhibited CA formation by suppressing inflammation-related gene expression in aneurysmal walls. Furthermore, CA formation was markedly inhibited by p47phox deletion in mice and was accompanied by decreased inflammation in aneurysmal walls. These data suggested the active participation of ROS and p47phox in CA formation and the therapeutic potential of an ROS-eliminating agent against CA formation.

Data obtained by using NC-2300 revealed an important role of cysteine cathepsins in the progression of CAs. Our findings strongly suggest that an imbalance between cysteine cathepsins and their inhibitor may cause the excessive breakdown of extracellular matrix in the arterial walls leading to the progression and rupture of CAs.

Cerebral aneurysm (CA) has a high prevalence and causes a fatal subarachnoid hemorrhage. Although CA is a socially important disease, there are currently no medical treatments for CA, except for surgical procedures, because the detailed mechanisms of CA formation remain unclear. From recent studies, we propose that CA is a chronic inflammatory disease of the arterial walls and various inflammation-related factors participate in its pathogenesis. Mast cells are well recognized as major inflammatory cells related to allergic inflammation. Mast cells have numerous cytoplasmic granules that contain various cytokines. Recent studies have revealed that mast cells contribute to various vascular diseases through degranulation and release of cytokines. In the present study, we examined the role of mast cells in the pathogenesis of CA using an experimental rat model. The number of mast cells was significantly increased in CA walls during CA formation. Inhibitors of mast cell degranulation effectively inhibited the size and medial thinning of induced CA through the inhibition of chronic inflammation, as evaluated by nuclear factor-kappa B activation, macrophage infiltration, and the expression of monocyte chemoattractant protein-1, matrix metalloproteinases (MMPs), and interleukin-1beta. Furthermore, an in vitro study revealed that the degranulation of mast cells induced the expression and activation of MMP-2, -9, and inducible nitric oxide synthase in primary cultured smooth muscle cells from rat intracranial arteries. These results suggest that mast cells contribute to the pathogenesis of CA through the induction of inflammation and that inhibitors of mast cell degranulation can be therapeutic drugs for CA.

Pitavastatin has a suppressive effect on CA progression through the inhibition of NF-kappaB activation in aneurysmal walls. Moreover, pitavastatin treatment can cause the regression of degenerative changes in preexisting CA walls. Pitavastatin is a promising candidate for a novel preventive agent against subarachnoid hemorrhage.