Ex vivo gene therapy with adenovirus-mediated transforming growth factor beta1 expression for endovascular treatment of aneurysm: results in a canine bilateral aneurysm model

Inflammatory changes in the aneurysm wall: a review

Rupture of a saccular intracranial artery aneurysm (IA) causes subarachnoid hemorrhage, a significant cause of stroke and death. The current treatment options, endovascular coiling and clipping, are invasive and somewhat risky. Since only some IAs rupture, those IAs at risk for rupture should be identified. However, to improve the imaging of rupture-prone IAs and improve IA treatment, IA wall pathobiology requires more thorough knowledge. Chronic inflammation has become understood as an important phenomenon in IA wall pathobiology, featuring inflammatory cell infiltration as well as proliferative and fibrotic remodulatory responses. We review the literature on what is known about inflammation in the IA wall and also review the probable mechanisms of how inflammation would result in the degenerative changes that ultimately lead to IA wall rupture. We also discuss current options in imaging inflammation and how knowledge of inflammation in IA walls may improve IA treatment.

Perspectives on stem cell-based elastic matrix regenerative therapies for abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) are potentially fatal conditions that are characterized by decreased flexibility of the aortic wall due to proteolytic loss of the structural matrix. This leads to their gradual weakening and ultimate rupture. Drug-based inhibition of proteolytic enzymes may provide a nonsurgical treatment alternative for growing AAAs, although it might at best be sufficient to slow their growth. Regenerative repair of disrupted elastic matrix is required if regression of AAAs to a healthy state is to be achieved. Terminally differentiated adult and diseased vascular cells are poorly capable of affecting such regenerative repair. In this context, stem cells and their smooth muscle cell-like derivatives may represent alternate cell sources for regenerative AAA cell therapies. This article examines the pros and cons of using different autologous stem cell sources for AAA therapy, the requirements they must fulfill to provide therapeutic benefit, and the current progress toward characterizing the cells' ability to synthesize elastin, assemble elastic matrix structures, and influence the regenerative potential of diseased vascular cell types. The article also provides a detailed perspective on the limitations, uncertainties, and challenges that will need to be overcome or circumvented to translate current strategies for stem cell use into clinically viable AAA therapies. These therapies will provide a much needed nonsurgical treatment option for the rapidly growing, high-risk, and vulnerable elderly demographic.

Differential gene expression in well-healed and poorly healed experimental aneurysms after coil treatment

PURPOSE

To compare gene expression patterns between well-healed and poorly healed aneurysms following coil embolization in a rabbit model.

MATERIALS AND METHODS

The Institutional Animal Care and Use Committee approved all procedures before initiation of the study. Elastase-induced, saccular aneurysms were created in rabbits and embolized by using platinum microcoils. Group 1 aneurysms were densely packed (volumetric packing density, >30%) to achieve good healing, whereas group 2 aneurysms were loosely packed (volumetric packing density, <20%), which yields poor healing. At 2 or 4 weeks after implantation, samples were harvested. RNA was isolated separately from the necks and domes of the aneurysms and analyzed by using a microarray containing 294 rabbit genes. Genes with significant differences between groups (P < .05; false discovery rate, <0.1; fold change, ≥1.2 and ≤0.8) were considered differentially expressed.

RESULTS

At 2 weeks, of 294 genes, 22 (7.5%) genes in the neck and 14 (4.8%) genes in the dome were differentially expressed between groups; at 4 weeks, of 294 genes, 25 (8.5%) genes in the neck and 17 (5.8%) genes in the dome were differentially expressed between groups. Genes overexpressed in group 1 as compared with group 2 aneurysms included those encoding proteases, adhesion molecules, and chemoattractant molecules. Conversely, group 2 aneurysms had increased expression of genes encoding structural molecules, including collagens, as compared with expression in group 1 aneurysms.

CONCLUSION

Robust healing after coil embolization is associated with substantial biological activity, as evidenced by overexpression of proteases, adhesion molecules, and chemoattractants. However, contrary to prior hypotheses, structural molecules such as collagen were not associated with the healing response in the rabbit model.

Long-Term toxicity studies in Canine of E10A, an adenoviral vector for human endostatin gene

E10A, a recombinant adenovirus type 5 vector carrying the human endostatin gene, may be a promising gene therapy drug in the treatment of solid tumors by antiangiogenesis, but a preclinical safety evaluation of E10A has not yet been performed. With high and low doses equivalent to 30 and 7.5 times the human curative dose, respectively, intramuscular injections of E10A were given once daily, 6 days/week, for 3 months, followed by a 1-month recovery period. As of 4 months, all experimental animals appeared generally healthy: normal behavior and eating habits, no nausea, vomiting, or salivation, no abnormal changes in urination or defecation, and increased body weight with the time of experiment. Urinalysis, hemogram, blood biochemistry, electrocardiogram, macroscopic and microscopic studies of organs and tissues were done before treatment, at month 3 of treatment, and 1 month posttreatment. At all time points, no significant abnormal toxic effects were noted. Preliminary investigation of E10A immunotoxicity in dogs indicated that anti-adenoviral antibodies were generated, in a dose- and time-independent manner, after E10A injection. Our data demonstrated that, long term, high-dose intramuscular administration of recombinant human endostatin-carrying adenovirus (E10A) was not notably toxic and might be safe for clinical therapeutic use, although additional long-term toxicity studies by other administration routes are still necessary.

Proteinase systems and thoracic aortic aneurysm progression

Thoracic aortic aneurysms (TAAs) are a rare but potentially devastating condition. Current surgical treatment of TAAs usually involves a major operation, which conveys many risks to the patient. Better knowledge of the cellular events that lead to aneurysm formation may elucidate less morbid treatment options for this condition. A number of recent studies have identified that the relative abundance and activity of extracellular matrix (ECM) proteolytic systems are increased with TAAs. Specifically, the matrix metalloproteinases (MMPs) have been linked through numerous studies to TAA formation. MMPs comprise a family of ECM-degrading proteinases. Endogenous tissue inhibitors (TIMPs) normally regulate MMP activity, and the activation of MMPs is complex and tightly controlled. Aneurysm formation may be related to relative changes in the balance between MMP/TIMP abundance favoring proteolysis. Through ECM degradation, the medial layer will undergo structural remodeling and a loss of structural integrity, leading to TAA formation. The goals of this review are to examine the structure of the normal and aneurysmal thoracic aorta and to place the new findings regarding ECM proteolysis in perspective with regard to TAA formation and progression. Through an integration of basic and clinical studies regarding the underlying molecular basis for proteolysis of the thoracic aorta, improved diagnostic, prognostic, and therapeutic strategies for this disease process are likely to be realized.

Growth factor receptor expression and remodeling of saccular cerebral artery aneurysm walls: implications for biological therapy preventing rupture

OBJECTIVE

Remodeling of the saccular cerebral artery aneurysm (SCAA) wall, known to be associated with rupture, might be modified with bioactive endovascular implants or systemic drug therapy targeted at growth factor receptors to prevent rupture. The receptors regulating SCAA wall remodeling are, however, unknown.

MATERIALS AND METHODS

Immunostaining for 12 growth factor receptors, and markers for matrix synthesis, proliferation, and inflammatory cell infiltration, were analyzed in 21 unruptured and 35 ruptured aneurysm fundi resected after microsurgical clipping of the aneurysm neck. The results were compared with clinical and radiological data.

RESULTS

Eleven of the 12 receptors studied were expressed at varying intensities in the 56 SCAA walls. Only transforming growth factor (TGF)beta-R2 and vascular endothelial growth factor (VEGF)-R1 were associated with rupture and basic fibroblast growth factor-R1 with minor leaks (P = 0.018). TGFbeta-R3 and VEGF-R1 was associated with wall remodeling (P = 0.043 and 0.027), and VEGF-R1 was associated with T-cell and macrophage infiltration as well as organization of luminal thrombosis (P = 0.019). VEGF-R2 was associated with myointimal hyperplasia (P = 0.017) and proliferation (P < 0.001).

CONCLUSION

VEGF, TGFbeta, and basic fibroblast growth factor receptors were associated with SCAA wall remodeling, making them potential targets for bioactive endovascular implants or drug therapy aiming to reinforce the SCAA wall.

Overexpression of transforming growth factor-beta1 stabilizes already-formed aortic aneurysms: a first approach to induction of functional healing by endovascular gene therapy

BACKGROUND

The cell response to transforming growth factor-beta1 (TGF-beta1), a multipotent cytokine with healing potential, varies according to tissue context. We have evaluated the ability of TGF-beta1 overexpression by endovascular gene therapy to stabilize abdominal aortic aneurysms (AAAs) already injured by inflammation and proteolysis.

METHODS AND RESULTS

Active TGF-beta1 overexpression was obtained in already-developed experimental AAAs in rats after endovascular delivery of an adenoviral construct encoding for a mutated form of active simian TGF-beta1 and in an explant model using human atherosclerotic AAA fragments incubated with recombinant active TGF-beta1. Transient exogenous TGF-beta1 overexpression by endovascular gene delivery was followed by induction of endogenous rat TGF-beta1. Overexpression of active TGF-beta1 in experimental AAAs was associated with diameter stabilization, preservation of medial elastin, decreased infiltration of monocyte-macrophages and T lymphocytes, and a decrease in matrix metalloproteinase-2 and -9, which was also observed in the explant model, in both thrombus and wall. In parallel with downregulation of the destructive process, active TGF-beta1 overexpression triggered endoluminal reconstruction, replacing the thrombus by a vascular smooth muscle cell-, collagen-, and elastin-rich intima.

CONCLUSIONS

Local TGF-beta1 self-induction after transient exogenous overexpression reprograms dilated aortas altered by inflammation and proteolysis and restores their ability to withstand arterial pressure without further dilation. This first demonstration of stabilization of expanding AAAs by delivery of a single multipotent self-promoting gene supports the view that endovascular gene therapy should be considered for treatment of aneurysms.

Gene Therapy and Endovascular Treatment of Intracranial Aneurysms

Background— Endovascular treatment of intracranial aneurysms is safe and effective but too often is followed by recurrences. Gene therapy may improve healing after embolization, and endovascular approaches may offer future in situ delivery systems designed to prevent aneurysm rupture.

Summary of Review— Advances in coil technology have focused on coating strategies designed to modify the biological reaction to the embolic agent. Gene therapy in cardiovascular applications is limited by low efficiency and transient gene expression. Current advances include the potential use of circulating progenitor cells for ex vivo genetic manipulations followed by in vivo delivery. Direct gene transfer may also be enhanced in situ by coils carrying antibody-tethered adenovirus or through the use of cell-specific or radiation-inducible promoters. Candidate genes that may be of value in promoting healing after endovascular treatment include growth factors and metalloproteinase inhibitors. A better understanding of the biology of aneurysm is necessary to conceive strategies designed to control the development of these lesions before their rupture.

Conclusions— Many technical difficulties remain to be solved, but the combination of gene therapy and endovascular techniques offers multiple therapeutic possibilities in the future control of intracranial aneurysms.