Background and Purpose— Mechanisms of initiation, progression and rupture of cerebral aneurysms have not yet been fully understood despite its clinical significance. Matrix metalloproteinases (MMPs) are a family of proteinases which are involved in the remodeling of vascular walls. In the present study, we investigated the significance of MMPs in the progression of cerebral aneurysms. Methods— Cerebral aneurysms were experimentally induced in 7-week-old male Sprague-Dawley rats. MMP-2 and MMP-9 expression was examined by immunohistochemistry and RT-PCR. Gelatinase activity in aneurysmal walls was assessed by in situ zymography. A selective inhibitor for MMP-2, -9 and -12, tolylsam, was used to examine the effect of inhibition of MMP-2 and MMP-9. Results— Macrophages infiltrated in arterial walls of experimentally induced rat cerebral aneurysms and expressed MMP-2 and -9. Macrophage infiltration and MMP expression was increased with the progression of aneurysms. Gelatinase activity attributable to MMP-2 and MMP-9 increased in arterial walls of rat cerebral aneurysms. Furthermore, tolylsam reduced the ratio of advanced aneurysms in our rat model. Conclusions— These data suggest that macrophage-derived MMP-2 and -9 may play an important role in the progression of cerebral aneurysms. The findings of this study will shed a new light into the pathogenesis of cerebral aneurysms and highlight the importance of inflammatory response causing the degeneration of extracellular matrix in the process of this disease.

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-κB (NF-κB) in the pathogenesis of CA formation in this study. Methods and Results— In experimentally induced CAs in rats, NF-κB was activated in cerebral arterial walls in the early stage of aneurysm formation with upregulated expression of downstream genes. NF-κB p50 subunit–deficient mice showed a decreased incidence of CA formation with less macrophage infiltration into the arterial wall. NF-κB 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-κB decoy oligodeoxynucleotide. In human CA walls, NF-κB also was activated, especially in the intima. Conclusions— Our data indicate that NF-κB 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-κB may represent a therapeutic target of a novel medical treatment for CA.

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 AND PURPOSE Cerebral 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 APPROACH Expression 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 RESULTS COX‐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 EP₂in vivo attenuated each other's expression, suppressed nuclear factor κB (NF‐κB)‐mediated chronic inflammation and reduced incidence of cerebral aneurysm. EP₂ stimulation in primary ECs induced NF‐κB activation and expression of the chemokine (C‐C motif) ligand 2, essential for cerebral aneurysm.CONCLUSIONS AND IMPLICATIONS These results suggest that shear stress activated PGE₂‐EP₂ pathway in ECs and amplified chronic inflammation via NF‐κB. We propose EP₂ as a therapeutic target in cerebral aneurysm.

Inhibition of prostaglandin E ₂ signaling in macrophages may be a pharmacological option for treating intracranial aneurysms.

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-1β, 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-1β, 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.