Acceleration of aneurysm healing by controlled release of basic fibroblast growth factor with the use of polyethylene terephthalate fiber coils coated with gelatin hydrogel

Lumen-oriented versus wall-oriented treatment strategies for intracranial aneurysms - A systematic review of suggested therapeutic concepts

The development of new treatment strategies for intracranial aneurysms (IAs) has been and continues to be a major interest in neurovascular research. Initial treatment concepts were mainly based on a physical-mechanistic disease understanding for IA occlusion (lumen-oriented therapies). However, a growing body of literature indicates the important role of aneurysm wall biology (wall-oriented therapies) for complete IA obliteration. This systematic literature review identified studies that explored endovascular treatment strategies for aneurysm treatment in a preclinical setting. Of 5278 publications screened, 641 studies were included, categorized, and screened for eventual translation in a clinical trial. Lumen-oriented strategies included (1) enhanced intraluminal thrombus organization, (2) enhanced intraluminal packing, (3) bridging of the intraluminal space, and (4) other, alternative concepts. Wall-oriented strategies included (1) stimulation of proliferative response, (2) prevention of aneurysm wall cell injury, (3) inhibition of inflammation and oxidative stress, and (4) inhibition of extracellular matrix degradation. Overall, lumen-oriented strategies numerically still dominate over wall-oriented strategies. Among the plethora of suggested preclinical treatment strategies, only a small minority were translated into clinically applicable concepts (36 of 400 lumen-oriented and 6 of 241 wall-oriented). This systematic review provides a comprehensive overview that may provide a starting point for the development of new treatment strategies.

The choice of biopolymer is crucial to trigger angiogenesis with vascular endothelial growth factor releasing coatings

Bio-based coatings and release systems for pro-angiogenic growth factors are of interest to overcome insufficient vascularization and bio-integration of implants. This study compares different biopolymer-based coatings on polyethylene terephthalate (PET) membranes in terms of coating homogeneity and stability, coating thickness in the swollen state, endothelial cell adhesion, vascular endothelial growth factor (VEGF) release and pro-angiogenic properties. Coatings consisted of carbodiimide cross-linked gelatin type A (GelA), type B (GelB) or albumin (Alb), and heparin (Hep), or they consisted of radically cross-linked gelatin methacryloyl-acetyl (GM5A5) and heparin methacrylate (HepM5). We prepared films with thicknesses of 8-10 µm and found that all coatings were homogeneous after washing. All gelatin-based coatings enhanced the adhesion of primary human endothelial cells compared to the uncoated membrane. The VEGF release was tunable with the loading concentration and dependent on the isoelectric points and hydrophilicities of the biopolymers used for coating: GelA-Hep showed the highest releases, while releases were indistinguishable for GelB-Hep and Alb-Hep, and lowest for GM5A5-HepM5. Interestingly, not only the amount of VEGF released from the coatings determined whether angiogenesis was induced, but a combination of VEGF release, metabolic activity and adhesion of endothelial cells. VEGF releasing GelA-Hep and GelB-Hep coatings induced angiogenesis in a chorioallantoic membrane assay, so that these coatings should be considered for further in vivo testing.

Development of a stent capable of the controlled release of basic fibroblast growth factor and argatroban to treat cerebral aneurysms: In vitro experiment and evaluation in a rabbit aneurysm model

An ideal stent to treat cerebral aneurysms should have an antithrombotic effect on the inner stent blood-facing side and a tissue organization effect on the outer aneurysmal side of the stent. The objective of this study is to evaluate the feasibility of a drug containing stent in the in vivo treatment of cerebral aneurysms. Argatroban, an antithrombotic drug, is encapsulated in biodegradable poly (d,l-lactide-co-glycolide) (PLGA) microspheres for the controlled release with an in vitro study conducted to evaluate the drug release and anticoagulation behavior of released drug. Basic fibroblast growth factor (bFGF), an organization drug, is released from gelatin hydrogels. The stents are coated with gelatin hydrogels incorporating bFGF and PLGA microspheres containing argatroban, and applied to the carotid artery aneurysm of an elastase-induced rabbit model. Most of the aneurysm cavity is occupied by loose connective tissues in the group treated with drug-coated stents, whereas extensive massive hematomas are observed in the group treated with drug-free stents. The occurrence rate of in-stent thrombus is small in the drug-coated stents. The stent incorporating bFGF and PLGA microspheres containing argatroban is an effective device for cerebral aneurysm treatment. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2185-2194, 2019.

Controlled Release of Vascular Endothelial Growth Factor from Heparin-Functionalized Gelatin Type A and Albumin Hydrogels

Bio-based release systems for pro-angiogenic growth factors are of interest, to overcome insufficient vascularization and bio-integration of implants. In this study, we investigated heparin-functionalized hydrogels based on gelatin type A or albumin as storage and release systems for vascular endothelial growth factor (VEGF). The hydrogels were crosslinked using carbodiimide chemistry in presence of heparin. Heparin-functionalization of the hydrogels was monitored by critical electrolyte concentration (CEC) staining. The hydrogels were characterized in terms of swelling in buffer solution and VEGF-containing solutions, and their loading with and release of VEGF was monitored. The equilibrium degree of swelling (EDS) was lower for albumin-based gels compared to gelatin-based gels. EDS was adjustable with the used carbodiimide concentration for both biopolymers. Furthermore, VEGF-loading and release were dependent on the carbodiimide concentration and loading conditions for both biopolymers. Loading of albumin-based gels was higher compared to gelatin-based gels, and its burst release was lower. Finally, elevated cumulative VEGF release after 21 days was determined for albumin-based hydrogels compared to gelatin A-based hydrogels. We consider the characteristic net charges of the proteins and degradation of albumin during release time as reasons for the observed effects. Both heparin-functionalized biomaterial systems, chemically crosslinked gelatin type A or albumin, had tunable physicochemical properties, and can be considered for controlled delivery of the pro-angiogenic growth factor VEGF.

A novel tissue engineering approach using an endothelial progenitor cell–seeded biopolymer to treat intracranial saccular aneurysms

Object

Recurrence after endovascular coiling of intracranial aneurysms is reported in up to 42% of cases and is attributed to the lack of endothelialization across the neck. In this study the authors used a novel tissue engineering approach to promote endothelialization by seeding endothelial progenitor cells (EPCs) within a fibrin polymer injected endovascularly into the aneurysm.

Methods

Experimental aneurysms were created in New Zealand White rabbits and were left untreated, surgically clipped, or embolized with platinum coils, fibrin biopolymer alone, or fibrin combined with autologous cultured EPCs.

Results

In aneurysms treated with EPCs, a confluent monolayer of endothelial cells with underlying neointima was demonstrated across the neck at 16 weeks posttreatment, which was not observed with aneurysms treated using the other methods.

Conclusions

This novel technique may address reasons for the limited durability of standard coil embolization and provides further avenues for the development of improved devices for the care of patients with aneurysms.

Embolization of a common carotid aneurysm with rhVEGF coupled to a pH-responsive chitosan in a rat model

Object

Treatment of cerebral aneurysms by endovascular deployment of liquid embolic agents has been proposed as an alternative strategy to conventional coiling, and new materials are being developed for embolization. In this study, the authors used a single-injection, biocompatible, biodegradable and pH-responsive acrylated chitosan (aCHN) with conjugated vascular endothelial growth factor (rhVEGF) in a rat aneurysm model.

Methods

The efficacy of the aCHN formulation with rhVEGF was tested using a common carotid artery occlusion model in rats, and the extent of embolization was evaluated using quantitative, qualitative, and histopathological techniques after 14 days of implantation.

Results

The mean occlusion was significantly greater for the rhVEGF/aCHN-treated group (96.8 ± 3.0%) than for the group receiving aCHN (74.7 ± 5.6%) (p < 0.01). Through qualitative evaluation, intimal and medial proliferation were significantly greater with rhVEGF/aCHN than with aCHN and controls (p < 0.001). Degradation of the aCHN filler was monitored in concert with the production of extracellular matrix components. Macrophages migrated in and proliferated inside the occluded carotid artery lumens were identified by histological and immunostainings. Results showed resorption of chitosan with concurrent development of collagen and elastin into the vessel lumen, suggesting clot maturation into fibrosis.

Conclusions

Chitosan with a bioactive agent such as rhVEGF showed excellent results in occluding aneurysms in a rat model.

Endovascular embolization of intracranial aneurysms

Intracranial aneurysm (ICA) is a common condition but with a high mortality rate when rupture occurs. The treatment of ruptured or unruptured ICA, especially with an endovascular approach, has been evolving rapidly. The current generally accepted opinion suggests that endovascular embolization is an effective technique for preventing the recurrence of aneurysm rupture, but the rebleeding rate after endovascular embolization is found to be higher than that after surgical clipping. In addition, long-term follow-up data are required for the evaluation of the effectiveness of endovascular treatment in unruptured ICA. This review presents the current understanding of ICA, the selection of optimal treatment approaches, and in particular, the advances in endovascular embolization in the treatment of ICA, including embolic materials, therapeutic and assisting techniques, long-term effectiveness, and limitations.

A Polyvinyl Alcohol Core Coil Containing Basic Fibroblast Growth Factor Evaluated in Rabbits with Aneurysms Induced by Elastase

OBJECTIVE

The present study evaluates the effect of a novel coil with a polyvinyl alcohol (PVA) core that delivered basic fibroblast growth factor (bFGF) to aneurysms in rabbits induced by elastase.

METHODS

PVA was processed to form small threads and inserted into the central core of a primary coil (PVA-core coil). After immersion in saline or bFGF (500 or 2000 mug/ml), PVA-core coils were implanted into elastase-induced aneurysms in rabbits in vivo. Follow-up angiography was performed 4 and 8 weeks after embolization, and the effects were histologically semiquantified according to a grading scale.

RESULTS

Follow-up angiography showed that the coils did not compact or protrude and that clots did not form in any group. The score of gross neck healing was significantly higher in the 8-week 2000 bFGF group than in the 8-week PVA coil group (2.7 +/- 0.6 versus 0.0 +/- 0.0, P < 0.05). The dome healing score was significantly higher in the 4-week 2000 bFGF group than that of the 4-week PVA coil group (4.0 +/- 0.0 versus 2.7 +/- 0.6, P < 0.05). Cells positive for alpha-smooth muscle actin densely accumulated in the dome of the aneurysm embolized with PVA-core coils containing bFGF.

CONCLUSION

Implantation of the PVA-core coil containing bFGF accelerated tissue growth at the neck as well as in the dome of aneurysms induced by elastase in rabbits. These results suggested that PVA-core coils could prevent the recanalization of embolized aneurysms.

[Development of functional drug carriers to realize advanced medical therapy]

Drug delivery systems (DDS) have customarily been developed as part of the technology and methodology used to enhance the in vivo efficacy of therapeutic drugs. However, the DDS concept can also be used for prophylactic and diagnostic drugs to enhance their respective medical efficacy. When applied to biological signaling factors, such as growth factors and genes, which can regulate the proliferation and differentiation of cells, DDS are expected to realize cell-based tissue regeneration therapy. Basic research on biology and medicine which scientifically supports the advanced medical therapies currently available will be advanced by making use of DDS techniques. This paper overviews functional drug carriers indispensable for DDS which are part of the fundamental technology and methodology to achieve such advances.

Regenerative inductive therapy based on DDS technology of protein and gene

Recent development of biomedical engineering including biomaterials and drug delivery system (DDS) as well as basic biology and medicine has enabled cells to induce regeneration repairing of defective tissues as well as substitute the biological functions of damaged organs. For successful tissue regeneration, it is undoubtedly indispensable to give cells a local environment which allows cells to efficiently promote their proliferation and differentiation and consequently induce cell-based tissue regeneration. Tissue engineering is one of the biomedical forms to create this regeneration environment of cells. The tissue and organ repairing based on their regeneration induction has been realized by combining cells with the tissue engineering technology or methodology in a surgical or internally medical manner. This paper overviews the present status and future direction of tissue engineering for regenerative inductive therapy, briefly explaining the key technology of tissue engineering, especially DDS of growth factor and gene.

Drug delivery systems for the treatment of sensorineural hearing loss

Sensorineural hearing loss is one of the most common disabilities in our society. Experimentally, many candidates for therapeutic molecules have been discovered. However, the lack of safe and effective methods for drug delivery to the cochlea has been a considerable obstacle to clinical application. Local application of therapeutic molecules into the cochlea has been used in clinic and in animal experiments. Advances in pharmacological technology provide various drug delivery systems via biomaterials, which can be utilized for local drug delivery to the cochlea. Recent studies in the field of otology have demonstrated the potential of synthetic and natural biomaterials for local drug delivery to the cochlea. Although problems still remain to be resolved for clinical application, introduction into clinical practice of these controlled-release systems may be reasonable because of their certain advantages over previous methods.

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.

Acceleration of Aneurysm Healing by Hollow Fiber Enabling the Controlled Release of Basic Fibroblast Growth Factor

OBJECTIVE

The objective of this study was to develop an embolization material of hollow fiber combined with gelatin hydrogel for the controlled release of basic fibroblast growth factor (bFGF). We examined feasibility of the material in embolization healing aneurysm by bFGF-induced tissue organization.

METHODS

An aneurysm was prepared at the common carotid artery of 60 rabbits by the end-to-side anastomosis of jugular venous pouch. The hollow fibers combined with or without 100 microg free bFGF or gelatin hydrogel incorporating 0, 10, 50, or 100 microg bFGF were applied to the aneurysm. Tissue appearance or histological observation was performed 1, 2, 3, and 6 weeks after application to evaluate the area embolized by fibrous organization in the aneurysm and the neointima formation at the aneurysm orifice.

RESULTS

When applied with the hollow fibers combined with gelatin hydrogel containing 100 microg bFGF, the aneurysm was histologically occupied by fibrous tissue newly formed 3 weeks later, whereas neointima was formed at the aneurysm orifice. The histological area occupied by fibrous tissue was significantly larger than that of hollow fibers combined with 100 microg bFGF. No influence of bFGF dose on the aneurysm healing by the fibers combined with hydrogels incorporating bFGF was observed.

CONCLUSION

Local, controlled release of bFGF from the hollow fibers combined with gelatin hydrogel incorporating bFGF accelerated the aneurysm healing by tissue organization.

A triple bifurcation aneurysm model for evaluating complex endovascular therapies in dogs

OBJECT

Animal aneurysm models are required for the study of the hemodynamics and pathophysiology of intracranial aneurysms in humans and so that experimental treatments can be tested prior to clinical trials. The authors developed a canine model that consistently produces up to three bifurcation aneurysms similar in morphological features and hemodynamics to human intracranial aneurysms.

METHODS

In 10 mongrel dogs, a harvested segment of the external jugular vein was anastamosed to an external carotid artery (CA)-lingual artery bifurcation arteriotomy site to create a lateral bifurcation aneurysm. The surgery was repeated on the contralateral side in each animal to form a second lateral bifurcation aneurysm and, in five dogs, a CA-CA crossover anastomosis was also performed to create a terminal bifurcation aneurysm. Nineteen of 20 lateral bifurcation aneurysms were confirmed in 10 dogs by diagnostic angiography 7 to 14 days after surgery. Aneurysm fundus-to-neck ratios ranged from 1 to 2, depending on the size of the arteriotomy. The terminal bifurcation aneurysms were confirmed in all five dogs by diagnostic angiography 7 to 14 days after the procedure. The authors later tested endovascular techniques for embolizing the aneurysms.

CONCLUSIONS

Three bifurcation aneurysms of sufficient size for endovascular access can be created in a reproducible fashion in the same animal. This model is useful for studying complex endovascular procedures in aneurysms that mimic the human condition and for testing new devices and techniques.

Emerging Concepts in the Treatment of Intracranial Aneurysms: Stents, Coated Coils, and Liquid Embolic Agents

ENDOVASCULAR TECHNIQUES FOR the treatment of intracranial aneurysms are rapidly evolving. Modifications of more traditional coils have been introduced. Such modifications include newer coils coated with various polymers to increase both coil thrombogenicity and degree of aneurysm packing. In addition, newer coil designs aimed at improving the conformability of the coil to the aneurysm have been used with promising preliminary results. The availability of a newer generation of stents specifically designed for intracranial navigation allows for more effective treatment of aneurysms with wide necks, which usually have been considered unsuitable for optimal endovascular treatment. Endovascular alternatives to coil embolization, such as liquid embolic materials, also have been explored for the treatment of intracranial aneurysms, with varying results. We summarize the rationale for use of these newer devices and early clinical experiences. Areas of current research and future directions of endovascular aneurysm treatment also are discussed.

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.

Biomaterials Used in Injectable Implants (Liquid Embolics) for Percutaneous Filling of Vascular Spaces

The biomaterials currently used in injectable implants (liquid embolics) for minimally invasive image-guided treatment of vascular lesions undergo, once injected in situ, a phase transition based on a variety of physicochemical principles. The mechanisms leading to the formation of a solid implant include polymerization, precipitation and cross-linking through ionic or thermal process. The biomaterial characteristics have to meet the requirements of a variety of treatment conditions. The viscosity of the liquid is adapted to the access instrument, which can range from 0.2 mm to 3 mm in diameter and from a few centimeters up to 200 cm in length. Once such liquid embolics reach the vascular space, they are designed to become occlusive by inducing thrombosis or directly blocking the lesion when hardening of the embolics occurs. The safe delivery of such implants critically depends on their visibility and their hardening mechanism. Once delivered, the safety and effectiveness issues are related to implant functions such as biocompatibility, biodegradability or biomechanical properties. We review here the available and the experimental products with respect to the nature of the polymer, the mechanism of gel cast formation and the key characteristics that govern the choice of effective injectable implants.

Genetic loci that control the angiogenic response to basic fibroblast growth factor

Angiogenesis is controlled by a balance between stimulatory growth factors and endogenous inhibitors. We propose that the balance of stimulators and inhibitors, as well as the general sensitivity of the endothelium to these factors, varies from individual to individual. Indeed, we have found that individual mouse strains have dramatically different responses to growth factor-induced neovascularization. Quantitative trait loci (QTLs), which influence the extent of angiogenesis induced by vascular endothelial growth factor (VEGF), were previously identified by our laboratory. Since genetic susceptibility may vary according to the angiogenic stimulator, we have undertaken a similar mapping approach to identify QTLs that influence basic fibroblast growth factor (FGF2) induced neovascularization in the BXD series of recombinant inbred mouse strains. Composite and multiple interval mapping identified areas of chromosomes 4, 13, 15, and 18. These new angiogenesis QTLs, named AngFq1 through AngFq4 (for angiogenesis due to FGF2), are different from previously identified VEGF QTLs. The mapped regions contain several genes involved in the angiogenic process including matrix metalloproteinase 16, eph receptor A7, angiopoetin 1, endothelial lipase, and autotaxin. Differences in these regions may influence individual susceptibility to angiogenesis related diseases such as cancer, macular degeneration, atherosclerosis, and arthritis.

Endovascular treatment of intracranial aneurysms: comparative evaluation in a terminal bifurcation aneurysm model in dogs

Object. The authors investigated whether HydroCoils decreased coil compaction and aneurysm recanalization in a canine model of a large, wide-necked, high-flow bifurcation aneurysm.

Methods. Eleven experimental aneurysms were created. Two aneurysms were untreated (Group 1); three were treated with standard platinum coils (Guglielmi Detachable Coils; Group 2); and six were treated with platinum framing coils and filling HydroCoils (Group 3). Comparative angiographic and histopathological data were analyzed at 2 weeks and again at 3 months.

At 3 months, the Group 1 aneurysms remained patent without spontaneous thrombosis. After coil placement the percentage of aneurysm filling by volume ranged from 59 to 90% (mean 75.4%) for Group 3 (HydroCoil-treated) and 34.3 to 48.9% (mean 39.6%) for Group 2 (GDC-treated) (p < 0.05). At 14 days, two of the three Group 2 aneurysms exhibited coil compaction and aneurysm recanalization at the neck; in both cases the condition worsened at 3 months. At 14 days and 3 months, five of the six Group 3 aneurysms were 100%, and one of six was 90% occluded and remained stable. At 3 months, the neointima of the aneurysm neck was significantly thicker in the Group 3 lesions, which had been treated by HydroCoils (0.329 ± 0.191 mm), than in Group 2 lesions, which had been treated with GDCs (0.026 ± 0.018 mm) (p , 0.001). No thrombus formation occurred in Group 2; however, in two of the six aneurysms in Group 3, thrombus formed at the coil—neck interface.

Conclusions. The experimental canine bifurcation aneurysm model overcomes the limitations of side-wall aneurysm models. In this model, HydroCoils resulted in significantly denser coil packing, less follow-up coil compaction, and thicker neointimal tissue at the neck of the lesion. HydroCoils also appeared more thrombogenic at the aneurysm neck—parent artery interface.

Remodeling of Saccular Cerebral Artery Aneurysm Wall Is Associated With Rupture

Background and Purpose— The cellular mechanisms of degeneration and repair preceding rupture of the saccular cerebral artery aneurysm wall need to be elucidated for rational design of growth factor or drug-releasing endovascular devices.

Methods— Patient records, preoperative vascular imaging studies, and the snap-frozen fundi resected after microsurgical clipping from 66 aneurysms were studied. Immunostainings for markers of smooth muscle cell (SMC) phenotype, proliferation, and inflammatory cell subtypes and TUNEL reaction were performed.

Results— Unruptured (24) and ruptured (42) aneurysms had similar dimensions (median diameter in unruptured 6 mm; median in ruptured 7 mm; P =0.308). We identified 4 basic types of aneurysm wall that associated with rupture: (1) endothelialized wall with linearly organized SMCs (17/66; 42% ruptured), (2) thickened wall with disorganized SMCs (20/66; 55% ruptured), (3) hypocellular wall with either myointimal hyperplasia or organizing luminal thrombosis (14/66; 64% ruptured), and (4) an extremely thin thrombosis-lined hypocellular wall (15/66; 100% ruptured). Apoptosis, de-endothelialization, luminal thrombosis, SMC proliferation, and T-cell and macrophage infiltration associated with rupture. Furthermore, macrophage infiltration associated with SMC proliferation, and both were increased in ruptured aneurysms resected <12 hours from rupture, suggesting that these were not just reactive changes.

Conclusions— Before rupture, the wall of saccular cerebral artery aneurysm undergoes morphological changes associated with remodeling of the aneurysm wall. Some of these changes, like SMC proliferation and macrophage infiltration, likely reflect ongoing repair attempts that could be enhanced with pharmacological therapy.