Growth factors stimulate neointimal cells in vitro and increase the thickness of the neointima formed at the neck of porcine aneurysms treated by embolization

Fucoidan-coated coils improve healing in a rabbit elastase aneurysm model

BACKGROUND

Recanalization of coiled aneurysms remains unresolved. To limit aneurysm recanalization after embolization with coils, we propose an innovative approach to optimize aneurysm healing using fucoidan-coated coils.

OBJECTIVE

To evaluate the short-term efficacy and long-term safety of the new coil system with conventional angiography, histology, and multiphoton microscopy for follow-up of fibrosis and neointima formation.

METHODS

We conducted a feasibility study on rabbit elastase-induced aneurysms. Embolization was carried out with bare platinum coils, fucoidan-coated coils, or dextran-coated coils. Aneurysms were controlled after 1 month by digital subtraction angiography (DSA). Aneurysm samples were collected and processed for histological analysis. Aneurysm healing and fibrosis were measured by quantifying collagen according to the histological healing score by combining standard light microscopy and multiphoton imaging. We divided 27 rabbits into three groups: bare platinum group, fucoidan group, and dextran group as controls.

RESULTS

Angiographic grading showed a trend toward less recanalization in the fucoidan group, although there were no significant differences among the three groups (P=0.21). Histological healing was significantly different according to the presence of more collagen in the neck area of aneurysms in the fucoidan group versus the bare platinum group (P=0.011), but not in the dextran group. Histological index was significantly better at the aneurysm neck in the fucoidan group than in the bare platinum group (P=0.004). Collagen organization index was also significantly better in the fucoidan group than in the bare platinum group (P=0.007).

CONCLUSION

This proof-of-concept study demonstrated the feasibility and efficacy of treatment with fucoidan-coated coils to improve aneurysm healing. The results in this rabbit in vivo model showed that fucoidan-coated coils have the potential to improve healing following endovascular treatment.

The potential for resident lung mesenchymal stem cells to promote functional tissue regeneration: understanding microenvironmental cues

Tissue resident mesenchymal stem cells (MSCs) are important regulators of tissue repair or regeneration, fibrosis, inflammation, angiogenesis and tumor formation. Bone marrow derived mesenchymal stem cells (BM-MSCs) and endothelial progenitor cells (EPC) are currently being considered and tested in clinical trials as a potential therapy in patients with such inflammatory lung diseases including, but not limited to, chronic lung disease, pulmonary arterial hypertension (PAH), pulmonary fibrosis (PF), chronic obstructive pulmonary disease (COPD)/emphysema and asthma. However, our current understanding of tissue resident lung MSCs remains limited. This review addresses how environmental cues impact on the phenotype and function of this endogenous stem cell pool. In addition, it examines how these local factors influence the efficacy of cell-based treatments for lung diseases.

In vivo embolization of lateral wall aneurysms in canines using the liquid-to-solid gelling PPODA-QT polymer system: 6-month pilot study

OBJECT

Over the past 20 years, endovascular embolization has become the preferred method of treating cerebral aneurysms. While there are many embolic devices on the market, none is ideal. In this study the authors investigated the use of a liquid-to-solid gelling polymer system-that is, poly(propylene glycol) diacrylate and pentaerythritol tetrakis (3-mercaptopropionate) (PPODA-QT)-to embolize in vivo aneurysms over a 6-month period.

METHODS

Experimental aneurysms were created in the carotid arteries of 9 canines. Aneurysms were embolized with the polymer only (PPODA-QT, 3 dogs), filled with PPODA-QT after placement of a "framing" platinum coil (coil+PPODA-QT, 3 dogs), or packed with platinum coils (coils only, 3 dogs). Aneurysm occlusion was angiographically monitored immediately and 6 months after embolization. After 6 months, the ostial regions of explanted aneurysms were assessed macroscopically and histologically.

RESULTS

All aneurysms showed 100% angiographic occlusion at 6 months, but turbulent blood flow was observed in 1 coils-only sample. Ostial regions of explanted coils-only aneurysms showed neointimal tissue surrounding individual coils but no continuous tissue layer over the aneurysm neck. All PPODA-QT aneurysms displayed smooth ostial surfaces, but 2 of 3 coil+PPODA-QT aneurysms showed polymer (unassociated with the coil) protruding into the vessel lumen, contributing to rough ostial surfaces. Neointimal tissue was present in PPODA-QT and coil+PPODA-QT aneurysms and covered smooth ostial surfaces more completely than in coils-only aneurysms.

CONCLUSIONS

This study compared neointimal tissue overgrowth in the ostium of experimental aneurysms embolized with PPODA-QT, PPODA-QT plus a framing coil, or coils alone. The coils-only and coil+PPODA-QT groups showed rough and discontinuous ostial surfaces, which hindered neointimal tissue coverage. The PPODA-QT aneurysms consistently produced smooth ostial surfaces that facilitated more complete neointimal tissue coverage over aneurysm necks.

Stent-assisted coiling of bifurcation aneurysms may improve endovascular treatment: a critical evaluation in an experimental model

BACKGROUND AND PURPOSE

Endovascular treatment of wide-neck bifurcation aneurysms often results in incomplete occlusion or aneurysm recurrence. The goals of this study were to compare results of coil embolization with or without the assistance of self-expandable stents and to examine how stents may influence neointima formation.

MATERIALS AND METHODS

Wide-neck bifurcation aneurysms were constructed in 24 animals and, after 4-6 weeks, were randomly allocated to 1 of 5 groups: 1) coil embolization using the assistance of 1 braided stent (n = 5); 2) coil embolization using the assistance of 2 braided stents in a Y configuration (n = 5); 3) coil embolization without stent assistance (n = 6); 4) Y-stenting alone (n = 4); and 5) untreated controls (n = 4). Angiographic results were compared at baseline and at 12 weeks, by using an ordinal scale. Neointima formation at the neck at 12 weeks was compared among groups by using a semiquantitative grading scale. Bench studies were performed to assess stent porosities.

RESULTS

Initial angiographic results were improved with single stent-assisted coiling compared with simple coiling (P = .013). Angiographic results at 12 weeks were improved with any stent assistance (P = .014). Neointimal closure of the aneurysm neck was similar with or without stent assistance (P = .908), with neointima covering coil loops but rarely stent struts. Y-stent placement alone had no therapeutic effect. Bench studies showed that porosities can be decreased with stent compaction, but a relatively stable porous transition zone was a limiting factor.

CONCLUSIONS

Stent-assisted coiling may improve results of embolization by allowing more complete initial coiling, but these high-porosity stents did not provide a scaffold for more complete neointimal closure of aneurysms.

Isolated progressive visual loss after coiling of paraclinoid aneurysms

BACKGROUND AND PURPOSE

The proximity of the paraclinoid segment of the internal carotid artery to the visual pathways may result in visual deficits when patients present with aneurysms in this segment. Although surgical clip ligation of these aneurysms has been the standard of care for decades, the advent of coil embolization has permitted endovascular therapy in those aneurysms with favorable dome-to-neck ratios. Although immediate nonprogressive visual loss after coil embolization of paraclinoid aneurysms has been well described, isolated progressive visual loss immediately or shortly following coil embolization, to our knowledge, has not. We have identified 8 patients who experienced progressive loss of vision, unassociated with any other neurologic deficits, developing immediately or shortly after apparently uncomplicated coil embolization of a paraclinoid aneurysm.

MATERIALS AND METHODS

This study is a retrospective case series of 8 patients seen at 4 separate academic institutions. Inpatient and outpatient records were examined to determine patient demographics, previous ocular and medical history, and ophthalmic status before endovascular embolization. In addition, details of the primary endovascular therapy and subsequent surgical and nonsurgical interventions were recorded. Follow-up data, including most recent best-corrected visual acuity, postoperative course, and duration of follow-up were documented.

RESULTS

Eight patients developed progressive visual loss in 1 or both eyes immediately or shortly after apparently uncomplicated coiling of a paraclinoid aneurysm. MR imaging findings suggested that the visual loss was most likely caused by perianeurysmal inflammation related to the coils used to embolize the aneurysm, enlargement or persistence of the aneurysm despite coiling, or a combination of these mechanisms. Most patients experienced improvement in vision, 2 apparently related to treatment with systemic corticosteroids.

CONCLUSION

Patients in whom endovascular treatment of a paraclinoid aneurysm is contemplated should be warned about the potential for both isolated nonprogressive and progressive visual loss in 1 or both eyes. Patients in whom progressive visual loss occurs may benefit from treatment with systemic corticosteroids.

Mechanisms of occlusion and recanalization in canine carotid bifurcation aneurysms embolized with platinum coils: an alternative concept

BACKGROUND AND PURPOSE

Endovascular treatment of aneurysms may result in complete or incomplete occlusions or may be followed by recurrences. The goal of the present study was to better define pathologic features associated with so-called healing or recurrences after coiling and to propose an alternative concept to the currently accepted view.

MATERIALS AND METHODS

Experimental canine venous pouch aneurysms were created by using a T-type (group A, N = 29) or a Y-type constructed bifurcation (group B, N = 37) between the carotid arteries. Coil embolization was performed 2 weeks later; and angiography, immediately after and at 12 weeks. Angiographic results, neointima formation at the neck, endothelialization, and organization of thrombus were compared between groups by using qualitative scores and immunohistochemistry.

RESULTS

Angiographic results at 3 months were significantly better in group A than in group B (P = .001). Macroscopic neointimal scores were also better (P = .012). Only 10/32 aneurysms with satisfactory results at angiography were completely sealed by neointima formation. Animals with residual or recurrent aneurysms had significantly worse neointimal scores than those with completely occluded ones (P = .0003). On histologic sections, the neointima was constantly present in "healed" and in recurrent aneurysms. This neointima was a multicellular layer of alpha-actin+ cells in a collagenous matrix, covered with a single layer of nitric oxide synthetase (NOS+) endothelial cells, whether it completely occluded the neck of the aneurysm or dived into the recurring or residual space between the aneurysm wall and the coil mass embedded in organizing thrombus.

CONCLUSION

Complete angiographic occlusions at 3 months can be associated with incomplete neointimal closure of the neck at pathology. Thrombus organization, endothelialization, and neointima formation can occur concurrently with recurrences.

The cell cycle: a critical therapeutic target to prevent vascular proliferative disease

Percutaneous coronary intervention is the preferred revascularization approach for most patients with coronary artery disease. However, this strategy is limited by renarrowing of the vessel by neointimal hyperplasia within the stent lumen (in-stent restenosis). Vascular smooth muscle cell proliferation is a major component in this healing process. This process is mediated by multiple cytokines and growth factors, which share a common pathway in inducing cell proliferation: the cell cycle. The cell cycle is highly regulated by numerous mechanisms ensuring orderly and coordinated cell division. The present review discusses current concepts related to regulation of the cell cycle and new therapeutic options that target aspects of the cell cycle.

Type I and Collateral Flow in Experimental Aneurysm Models Treated with Stent-Grafts

PURPOSE

To evaluate the influence of a collateral branch on the evolution of type I leaks after endovascular aneurysm repair in an experimental model.

MATERIALS AND METHODS

Bilateral aneurysms were constructed in the common iliac arteries of 12 dogs by using venous patches. A collateral branch was added on one aneurysm on one side by implantation of the sacroiliac trunk on the sac. Balloon-expandable stent-grafts were implanted 2 months later. In six dogs, type I endoleaks were created on the side with the collateral branch by using plastic deformation of the stent-graft (group 1). Stent-grafts were fully expanded on the contralateral side in the same dogs (group 2, control group). In the remaining six dogs, type I endoleaks were created on the side without the collateral branch (group 3), and stent-grafts were fully expanded on the side with the collateral branch, creating a type II endoleak (group 4). Follow-up imaging was performed with Doppler ultrasonography and angiography until the animals were sacrificed at 3 months. Leaks were classified as major, moderate, or absent with use of findings at imaging and pathologic examinations.

RESULTS

No endoleaks were observed in group 2 (control group). Endoleaks were persistent in 83% of aneurysms in groups 1 (5/6 type I), 3 (5/6 type I), and 4 (5/6 type II). Type I leaks were major in three of six cases when associated with a collateral branch (group 1) and moderate when they were not (group 3; P < .05). Before sacrifice, larger aneurysmal diameters were observed only in group 1 (110% +/- 18) as compared with control group 2 (85% +/- 12) (P < .05).

CONCLUSION

More prominent leaks and larger aneurysms are observed when a collateral branch is associated with a type I endoleak.

Effects of stenting the parent artery on aneurysm filling and gene expression of various potential factors involved in healing of experimental aneurysms

SUMMARY

Intracranial stents are increasingly used in the endovascular treatment of aneurysms, but very little is known regarding their effect on the cellular and molecular evolution of aneurysms. Bilateral venous pouch lateral wall carotid aneurysms were created in 20 dogs. All dogs then underwent angiography and balloon-expandable stenting of one aneurysm four to six weeks later. Fifteen dogs underwent aneurysm harvesting at one day (n=3), four days (n=4), seven days (n=3), and 14 days (n=5) for mRNA expression analysis, using axial sections taken from the aneurysm neck and fundus for RTPCR amplification of four cytokines or growth factors: TNF-a, TGF-b1, MCP-1, and PDGFBB; two adhesion molecules: VCAM-1 and PECAM-1; five matrix modifying agents; MMP- 2, 9, TIMPs 1, 3, 4, and two cellular markers: CD34 and a-SMA. Five other dogs, sacrificed at 12 weeks, were examined for extent of filling of the aneurysm neck with organized tissue and for neointima formation at the aneurysm ostium. Angiography was performed prior to sacrifice in all animals, and compared with initial studies. Eleven out of 20 stented aneurysms showed a favorable angiographic evolution, while none of the 20 nonstented aneurysms improved (p=0.001). Pathology showed partially occluded aneurysms, with neointima formation around the stent struts.Observed trends in mRNA expression, that stenting increased expression of genes involved in organization and neointima formation, agreed with experimental hypotheses, but differences between stented and non-stented aneurysms did not reach statistical significance. Parent vessel stenting was associated with angiographic improvement of aneurysm appearance. Modifications in mRNA expression patterns following stenting deserve further study to better establish potential molecular targets to promote aneurysm healing.

Effect of radioactivity on stent-graft incorporation after endovascular treatment of aneurysms: An animal study

Poor stent-graft (SG) incorporation into the vessel wall, following endovascular repair of abdominal aortic aneurysms (EVAR), can lead to endoleaks and SG migration. Low-dose radiation can prevent aneurysm recurrence after coil embolization, and has been associated with a "paradoxical" increase in neointima formation after stenting in a few studies. It was hypothesized that in situ beta radiation emitted from SG could improve its incorporation by preventing the persistence of circulating channels between the implant and the vessel wall and increasing neointima formation around the SG. Phosphorus 32 ((32)P, 200 or 400 kBq per SG (n = 6 each)) was ion implanted on the external surface of balloon-expandable SGs. Twelve radioactive and six non-radioactive SGs were deployed in iliac arteries of nine Mongrel dogs. Neointima formation inside the graft and the persistence of circulating flow through an artificial groove created during the endovascular procedure were assessed by follow-up imaging and by blinded, computerized histomorphometric analysis after animal sacrifice at 3 months. Occlusion occurred in four radioactive SGs. A lesser number of patent grooves was observed along high-activity SGs than along control SGs (1/3 versus 4/4). No difference in neointima formation was observed in radioactive and non-radioactive SGs. Alteration of external graft surface was observed after ion implantation. Ion implantation of (32)P on SGs does not seem to be a viable strategy to improve incorporation and prevent type-I endoleak after EVAR.

Drug-Eluting Coronary Stents

The introduction and widespread use of coronary stents have been the most important advancement in the percutaneous treatment of coronary artery disease since the introduction of balloon angioplasty. Coronary artery stents reduce the rate of angiographic and clinical restenosis compared to balloon angioplasty. This angiographic restenosis was further reduced with the introduction of drug-eluting stents and hence further reduction in the frequency of major adverse cardiac events. Herein we present a comprehensive and up-to-date review about the use of drug-eluting stents in the treatment of coronary artery disease.

Endovascular Treatment of Aneurysms: Gene Expression of Neointimal Cells Recruited on the Embolic Agent and Evolution with Recurrence in an Experimental Model

PURPOSE

The authors attempted to identify genes associated with healing or recurrence after embolization in an aneurysm model in which neointima formation at the neck varies according to flow zones. A better understanding of the relationship between blood flow, molecular events, and healing or recurrence may provide future avenues to improve results of endovascular treatment of aneurysms.

METHODS

Bilateral carotid venous pouch aneurysms were constructed in 36 dogs and embolized with gelatin sponges. Angiography and pathological studies were performed at T0 and/or 3 weeks (n=22). Angiographic results and neointima formation were scored using a qualitative index applied to the distal (inflow) and proximal (outflow) zones of the neck. In 14 animals, mRNA expression 1 to 14 days after embolization at the proximal or distal segment of the sponge was analyzed by RT-PCR, attempting to correlate flow zones, gene expression, and neointima formation.

RESULTS

Aneurysms recurred at 3 weeks, as shown by significantly worse angiographic scores as compared to T0 (P<.01). Neointimal scores differed at pathology, with a more complete neointima at the proximal as compared to the distal aspect of the sponge at 3 weeks (P=.027). Embolization was followed by migration of CD31+, CD14+, smooth muscle alpha-actin+ (SMA+) cells that progressively expressed metalloproteinases (MMP-9,-12,-14), but stable or lesser, retarded expression of inhibitors (TIMP1-4). Growth factors (PDGF-BB, TGF-beta1, TNF-alpha, MCP-1 and Ang-1) were expressed at increasing levels, maximal at 7 to 14 days. Differences between distal and proximal zones were limited to increased expression of MMP-2 proximally (P<.035).

CONCLUSION

Gene expression after embolization is compatible with patterns associated with neointima formation. The authors have not identified key factors involved in recurrence.

Healing of Intracranial Aneurysms with Bioactive Coils

Inadequate healing is an important mechanism for aneurysm development and recanalization after embolization. Matrix coils have been shown by experimental studies to enhance vascular repair and fibrosis, thus reducing the risk of recanalization. The clinical application of Matrix coils represents the transition from pure mechanical occlusion to adjunct biologic healing of aneurysms. Our preliminary clinical experience reveals evidence of a healing response in aneurysms treated with Matrix coils. This technology can be further improved through the incorporation of new knowledge on the molecular pathogenesis of aneurysms and the cellular and molecular mechanisms of healing.

Forkhead transcription factors inhibit vascular smooth muscle cell proliferation and neointimal hyperplasia

Vascular smooth muscle cell (VSMC) proliferation and migration contribute significantly to atherosclerosis, postangioplasty restenosis, and transplant vasculopathy. Forkhead transcription factors belonging to the FoxO subfamily have been shown to inhibit growth and cell cycle progression in a variety of cell types. We hypothesized that forkhead proteins may play a role in VSMC biology. Under in vitro conditions, platelet-derived growth factor (PDGF)-BB, tumor necrosis factor-alpha, and insulin-like growth factor 1 stimulated phosphorylation of FoxO in human coronary artery smooth muscle cells via MEK1/2 and/or phosphatidylinositol 3-kinase-dependent signaling pathways. PDGF-BB, tumor necrosis factor-alpha, and insulin-like growth factor 1 treatment resulted in the nuclear exclusion of FoxO, whereas PDGF-BB alone down-regulated the FoxO target gene, p27(kip1), and enhanced cell survival and progression through the cell cycle. These effects were abrogated by overexpression of a constitutively active, phosphorylation-resistant mutant of the FoxO family member, TM-FKHRL1. The anti-proliferative effect of TM-FKHRL1 was partially reversed by small interfering RNA against p27(kip1). In a rat balloon carotid arterial injury model, adenovirus-mediated gene transfer of FKHRL1 caused an increase in the expression of p27(kip1) in the VSMC and inhibition of neointimal hyperplasia. These data suggest that FoxO activity inhibits VSMC proliferation and activation and that this signaling axis may represent a therapeutic target in vasculopathic disease states.

New Devices Designed to Improve the Long-Term Results of Endovascular Treatment of Intracranial Aneurysms. A Proposition for a Randomized Clinical Trial to Assess their Safety and Efficacy

SUMMARY

Endovascular coiling can improve the outcome of patients with ruptured intracranial aneurysms, but angiographic recurrences are frequent compared to surgical clipping. New coils or devices have been introduced to improve long-term results of endovascular treatment but none have been the object of a valid clinical trial. We have proposed a multicentric randomized double-blind study comparing radioactive and standard coil occlusion of aneurysms. The purpose of this article is to review issues that are specific to the design of clinical trials to assess embolic agents that could improve the long-term efficacy of endovascular treatment of intracranial aneurysms. The proposed trial is a randomized, multi-center, prospective, controlled trial comparing the new generation coils to standard platinum coils. Blinding, if at all possible, is preferable to minimize bias, at least for follow-up angiographic studies that should cover a period of 18 months. All patients with an intracranial aneurysm eligible for endovascular treatment would be proposed to participate. The study would enrol approximately 500 patients equally divided between the two groups, recruited within two years, to demonstrate a decrease in the recurrence rate, the primary outcome measure, from 20% to 10%. Secondary outcome measures should assure that complications, initial clinical and angiographic results remain unchanged. Independent data safety and monitoring committees are crucial to the credibility of trials and to ensure scientific rigor and objectivity. The scientific demonstration of an improved long-term efficacy, without significant compromise regarding safety, is mandatory before considering the widespread use of a new embolic device for the endovascular treatment of aneurysms.

Endovascular Aortic Aneurysm Repair with Stent-Grafts: Experimental Models Can Reproduce Endoleaks

PURPOSE

To develop canine aneurysm models that can reproduce type II endoleaks after endovascular aneurysm repair (EVAR) with stent-grafts.

MATERIALS AND METHODS

A fusiform infrarenal abdominal aortic aneurysm model (AAA) was surgically created with a jugular vein patch, while preserving collateral vessels (n = 3). To allow comparative studies within the same animal, a bilateral iliac aneurysm model was also constructed with venous patches and surgical re-implantation of the sacroiliac trunk (n = 3). Stent-grafts were implanted by femoral approach at least 2 months later in both aortic and iliac models. Follow-up imaging was performed by Doppler ultrasound (US) and angiography until animals were killed 3 months after EVAR.

RESULTS

Angiography revealed immediate type II leaks in all cases. Leaks were still present at autopsy 3 months after EVAR in all cases, and were revealed at pre-death angiography in all but one case. At autopsy, leaks were characterized by the presence of large endothelialized channels that formed within the thrombus between the stent-graft and the aneurysmal wall.

CONCLUSION

As shown in this pilot study, persistent type II leaks after EVAR can be reproduced in aortic and iliac animal models. The iliac model can be created bilaterally in the same animal, thus allowing for comparative evaluation of different therapies. These models could be used to better understand the mechanisms of endoleak, and to assess future developments aimed to improve the outcomes after EVAR.

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

OBJECTIVE

Endovascular treatment of cerebral aneurysm is safe and effective, but recurrence of disease is frequent compared with results with surgery. The purpose of this study was to determine the effects of recombinant transforming growth factor beta(1) (rTGFbeta(1)) secreted by transplanted autologous vascular smooth muscle cells (VSMC) on results of endovascular treatment.

METHODS

VSMC from canine femoral arteries were infected with adenovirus vector encoding rTGFbeta(1)/green fluorescent protein (rTGFbeta(1)/GFP) or GFP only. rTGFbeta(1) production was measured with an enzyme-linked immunosorbent assay, and autocrine and paracrine effects of rTGFbeta(1) on cell functions were quantified with a proliferation assay and collagen synthesis. A bilateral carotid aneurysm model was used to compare angiographic and pathologic results after embolization with sponges seeded (n = 14) or not seeded (n = 34) with VSMC expressing TGFbeta(1) or GFP (n = 7 each). Transgene retention was confirmed with Western blot analysis.

RESULTS

In vitro, TGFbeta(1) production varied from 0.9 to 180 ng/mL/d with increasing multiplicity of infection (MOI). Collagen synthesis was doubled at low (<300) MOI and increased by one and a half times at high (>or=300) MOI. rTGFbeta(1) was biologically active, as shown with the mink lung epithelial cell proliferation assay. VSMC grafts showed effective GFP expression up to 3 weeks after transplantation. Angiographic results were improved and neointima thickness was increased with cellular grafts, as compared with controls, but there was no significant difference between aneurysms treated with VSMC encoding rTGFbeta(1)/GFP or GFP vectors.

CONCLUSION

Cellular grafts can promote healing of aneurysms, but overexpression of rTGFbeta(1)/GFP did not demonstrate added benefits in this model.

Cold hibernated elastic memory foams for endovascular interventions

Cold hibernated elastic memory (CHEM) polyurethane-based foam is a new shape memory polymeric self-deployable structure. Standard cytotoxicity and mutagenicity tests were conducted on CHEM in vitro, to ensure biocompatibility before studying potential medical applications. In vivo, lateral wall aneurysms were constructed on both carotid arteries of eight dogs. Aneurysms were occluded per-operatively with CHEM blocks. In two dogs, CHEM embolization was compared with gelatin sponge fragment embolization. Internal maxillary arteries (Imax) were also occluded with CHEM using a 6F transcatheter technique. Angiography and pathology were used to study the evolution of aneurysms and Imax at 3 and 12 weeks. Imax embolized with CHEM foam remained occluded at 3 weeks. Most aneurysms embolized with CHEM showed a small residual crescent of opacification at initial angiography, but angiographic scores were significantly better at 3 weeks. Thick neointima formation over the CHEM at the neck of aneurysms was demonstrated at pathology. The foamy nature of CHEM favours the ingrowth of cells involved in neointima formation. New devices for endovascular interventions could be designed using CHEM's unique physical properties.

Enhanced formation of fibrosis in a rabbit aneurysm by gelatin hydrogel incorporating basic fibroblast growth factor

OBJECTIVE

This study was undertaken to analyze whether the controlled release of basic fibroblast growth factor (bFGF) can promote intrasaccular thrombosis in an experimental aneurysmal model.

METHODS

Carotid aneurysms were constructed in 80 rabbits with venous pouches and treated by placing gelatin hydrogels into each aneurysm incorporating 0, 25, 50, or 100 microg of bFGF or incorporating 100 microg of bFGF with different water contents. In the controls, the venous pouches either were not treated or were treated with gauze alone. Gelatin hydrogel was used for the controlled release of bFGF into the aneurysms. The formation of fibrosis in the aneurysms was histologically viewed to assess the area occupied by the fibrous tissues at 3 and 6 weeks after the hydrogel application. The effect of the bFGF dose and water content on obliterating the aneurysm by the hydrogels incorporating bFGF was also investigated.

RESULTS

Six weeks after the application of gelatin hydrogels with a water content of 95 wt% incorporating 100 microg of bFGF, the lateral pouch orifice was completely closed, obliterating the aneurysm at the level of tissue appearance, in contrast to hydrogels incorporating lower doses of bFGF and other control agents. The venous pouch aneurysm was histologically occupied with the newly formed fibrous tissue, and the fibrous tissue area and percentage of the aneurysmal lumen occupied by the fibrosis-gauze complex were significantly larger than those of other hydrogel applications (P < 0.05). The neointima tissue was homogeneously covered with a monolayer of Factor VIII-positive cells. The fact that there was no difference in the water content in the fibrosis formation induced by the bFGF-incorporated gelatin hydrogels indicated that the hydrogel biodegradability did not affect the obliteration of the aneurysm.

CONCLUSION

Local controlled release of bFGF stimulated the formation of in vivo fibrosis, resulting in obliteration of the aneurysm. The long-term results of the fibrous organization remain speculative.