Molecular Indices of Apoptosis Activation in Elastase-Induced Aneurysms After Embolization With Platinum Coils

Enigma of what is Known about Intracranial Aneurysm Occlusion with Endovascular Devices

Aneurysmal subarachnoid Hemorrhage is a major cause of neurological morbidity and mortality. Over the years vascular neurosurgery has witnessed technological advances aimed to reduce the morbidity and mortality. Several endovascular devices have been used in clinical practice to achieve this goal in the management of ruptured and unruptured cerebral aneurysms. Recurrence due to recanalization is encountered in all of these endovascular devices as well as illustrated by Barrow Ruptured Aneurysm Trial. Histological and molecular characterization of the aneurysms treated with endovascular devices is an area of active animal and human research studies. Yet, the pathobiology illustrating the mechanisms of aneurysmal occlusion and healing lacks evidence. The enigma of aneurysmal healing following treatment with endovascular devices needs to be de-mystified to understand the biological interaction of endovascular device and aneurysm and thereby guide the future development of endovascular devices aimed at better aneurysm occlusion. We performed a comprehensive and detailed literature review to bring all the known facts of the pathobiology of intracranial aneurysm healing, the knowledge of which is of paramount importance to neurosurgeons, an interventional neuroradiologist, molecular biologist, geneticists, and experts in animal studies. This review serves as a benchmark of what is known and platform for future studies basic science research related to intracranial aneurysms.

Mechanisms of Healing in Coiled Intracranial Aneurysms: A Review of the Literature

Recanalization of intracranial aneurysms following endovascular coiling remains a frustratingly common occurrence. An understanding of the molecular and histopathologic mechanisms of aneurysm healing following coil embolization is essential to improving aneurysm occlusion rates. Histopathologic studies in coiled human and experimental aneurysms suggest that during the first month postcoiling, thrombus formation and active inflammation occur within the aneurysm dome. Several months following embolization, the aneurysm is excluded from the parent vessel by formation of a neointimal layer, which is often thin and discontinuous, across the aneurysm neck. Numerous coil modifications and systemic therapies have been tested in animals and humans in an attempt to improve the aneurysm-healing process; these modifications have met with variable levels of success. In this review, we summarize the histopathologic and molecular biology of aneurysm healing and discuss how these findings have been applied in an attempt to improve angiographic outcomes in patients with intracranial aneurysms.

Bone morphogenetic protein-7 ameliorates cerebral ischemia and reperfusion injury via inhibiting oxidative stress and neuronal apoptosis

Previous studies have indicated that bone morphogenetic protein-7 (BMP-7) is neuroprotective against cerebral ischemia/reperfusion (IR) injury. The present study was undertaken to determine the molecular mechanisms involved in this effect. Adult male Wistar rats were subjected to 2 h of transient middle cerebral artery occlusion (MCAO), followed by 24 h of reperfusion. BMP-7 (10⁻⁴ g/kg) or vehicle was infused into rats at the onset of reperfusion via the tail vein. Neurological deficits, infarct volume, histopathological changes, oxidative stress-related biochemical parameters, neuronal apoptosis, and apoptosis-related proteins were assessed. BMP-7 significantly improved neurological and histological deficits, reduced the infarct volume, and decreased apoptotic cells after cerebral ischemia. BMP-7 also markedly enhanced the activities of antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX), and reduced the level of malondialdehyde (MDA) in IR rats. In addition, Western blot analysis indicated that BMP-7 prevented cytochrome c release, inhibited activation of caspase-3, caspase-9 and caspase-8. Our data suggested that BMP-7 has protective effects against cerebral IR injury in rats, and the neuroprotective effects may be attributed to attenuating oxidative stress and inhibiting neuronal apoptosis.

Intracellular signaling pathways and size, shape, and rupture history of human intracranial aneurysms

BACKGROUND

Size and morphological features are associated with intracranial aneurysm (IA) rupture. The cellular mechanisms of IA development and rupture are poorly known.

OBJECTIVE

We studied the expression and phosphorylation of different intracellular signaling molecules in the IA wall compared with IA morphological features to understand better the cellular pathways involved in IA development and wall degeneration.

METHODS

Nine ruptured and 17 unruptured human IA samples were collected intraoperatively. The expression levels and phosphorylation state of 3 mitogen-activated protein kinases (c-Jun N-terminal kinase [JNK], p38, extracellular signal-regulated kinase [ERK]), Bcl-2 antagonist of cell death (Bad), mammalian target of rapamycin (mTOR), cyclic AMP response element binding protein (CREB), and Akt were determined by Western blotting. The localization of signaling proteins was determined by immunofluorescence. From 3-dimensional segmentation of computed tomography angiographic data, size and shape indexes were calculated.

RESULTS

We found a 5-fold difference in phospho-Bad levels between ruptured and unruptured IAs. Phospho-mTOR was downregulated 2.5-fold in ruptured IAs. Phospho-p54 JNK, phospho-p38, and phospho-Akt levels correlated positively with IA size. Phospho-CREB levels were significantly associated with nonsphericity and ellipticity indexes. Phospho-Akt and phospho-p38 correlated negatively with undulation index.

CONCLUSION

The signaling pathway profile (apoptosis, cell proliferation, stress signaling) differs between ruptured and unruptured IAs and is associated with IA geometry. Our results increase the knowledge of IA development and wall degeneration.

Proteomic analysis of aneurysm healing mechanism after coil embolization: comparison of dense packing with loose packing

BACKGROUND AND PURPOSE

In clinical practice, durability of occlusion following coil embolization is superior in densely packed, compared with loosely packed, aneurysms. In a rabbit model, we probed, by using proteomics tools, the biologic mechanisms associated with densely packed and completely occluded aneurysms, compared with loosely packed and incompletely occluded aneurysms, to explore the biologic mechanisms of intra-aneurysmal healing following embolization.

MATERIALS AND METHODS

Elastase-induced, saccular aneurysms were created in 24 rabbits. Aneurysms were allowed to mature, after which aneurysms were either densely (packing attenuation >25%) or loosely (packing attenuation <20%) packed with platinum coils by endovascular means. After 2 weeks (n = 6 for both groups) and 4 weeks (n = 6 for both groups) of implantation, aneurysm samples harboring coils were harvested. Soluble proteins were extracted from the necks and domes of aneurysms, and proteins were studied using proteomics and bioinformatics tools.

RESULTS

In dome tissue, 128 proteins at 2 weeks, and 8 proteins at 4 weeks, were differentially expressed in densely packed, compared with loosely packed, aneurysms. In the neck tissue, 2 proteins at 4 weeks were differentially expressed in densely packed aneurysms. Specific pathway analysis revealed that compared with loosely packed aneurysms, densely packed aneurysms were associated with up-regulation of cell-to-cell signaling and cell adhesion at 2 weeks. Conversely, at 4 weeks, densely packed aneurysms showed a decrease in the expression of structural proteins compared with loosely packed aneurysms.

CONCLUSIONS

These findings may focus efforts on specific targets aimed at improving the long-term healing of intracranial, saccular aneurysms.

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.

Intrinsic pathway-mediated apoptosis in elastase-induced aneurysms in rabbits

BACKGROUND AND OBJECTIVES

The pathophysiology of saccular aneurysms is complex and multifactorial. The aim of the present study was to understand the mechanism of apoptosis in an elastase-induced aneurysm model in rabbits.

MATERIALS AND METHODS

Elastase-induced saccular aneurysms were created at the origin of the right common carotid artery in 20 rabbits. Aneurysm samples were harvested at 2 and 12 weeks after creation. Expression of apoptosis-associated proteins, including caspases and bcl-2 proteins, were assessed by Western blot analysis (n = 5 at both time points). Terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling (TUNEL) staining, which indicates the presence of apoptosis, was performed in tissue sections (n = 5 at both time points). The unoperated contralateral common carotid artery was used as a control.

RESULTS

Expression of active caspase-3, the final executioner of apoptosis, and caspase-9, the mediator of the intrinsic mitochondrial pathway, was observed in aneurysms at 2 weeks, whereas the expression of activated caspase-8, the mediator of the extrinsic death receptor pathway, was absent at both time points. Expression of antiapoptotic proteins, Bcl-2 and phospho-Bad, was down-regulated in aneurysms compared with controls at 2 weeks. None of these proteins were differentially expressed at 12 weeks. These results were confirmed by the presence of TUNEL-positive cells in some aneurysms at the early time point.

CONCLUSIONS

In this study of elastase-induced aneurysms in a rabbit model, activation of apoptosis is mediated predominantly by the Bcl-2-mediated intrinsic pathway through the activation of caspase-9.

Gene expression profiling of experimental saccular aneurysms using deoxyribonucleic acid microarrays

BACKGROUND AND PURPOSE

The molecular characteristics of the pathophysiology of saccular aneurysms remain poorly understood. The purpose of the current study was to investigate the expression of various groups of genes at different stages of aneurysm age in elastase-induced saccular aneurysms in rabbits through the use of deoxyribonucleic acid (DNA) microarrays.

MATERIALS AND METHODS

A microarray consisting of genes related to cell adhesion, apoptosis, cell signaling, growth, inflammation, vascular remodeling, and oxidative stress was constructed by using rabbit nucleotide sequences. Elastase-induced saccular aneurysms were created at the origin of the right common carotid artery (CCA) in 12 rabbits. Two weeks (n=6) and 12 weeks (n=6) after aneurysm creation, ribonucleic acid (RNA) was isolated from the aneurysm and the control unoperated left CCA and was used for microarray experiments. Real-time polymerase chain reaction (RT-PCR) was performed for validation of microarray results.

RESULTS

Of 209 genes, 157 (75%) at 2 weeks and 88 (42%) at 12 weeks demonstrated statistically significant differential expression between aneurysm tissue and the control left CCA tissue (P < .05). Multiple genes implicated in vessel wall remodeling were found to be elevated at 2 weeks and at 12 weeks. Expression of cell adhesion molecules and antioxidant enzymes was down-regulated at 2 weeks but was not significantly different from that of controls at 12 weeks. Most transcription factors, inflammatory genes, and structural genes showed underexpression at both time points. The expression profiles of selected genes were confirmed by RT-PCR.

CONCLUSION

Multiple genes in diverse pathways have been differentially expressed in the rabbit aneurysm model.