Intramyocardial sustained delivery of basic fibroblast growth factor improves angiogenesis and ventricular function in a rat infarct model

The inhibition of postinfarct ventricle remodeling without polycythaemia following local sustained intramyocardial delivery of erythropoietin within a supramolecular hydrogel

Erythropoietin (EPO) can protect myocardium from ischemic injury, but it also plays an important role in promoting polycythaemia, the potential for thrombo-embolic complications. Local sustained delivery of bioactive agents directly to impaired tissues using biomaterials is an approach to limit systemic toxicity and improve the efficacy of therapies. The present study was performed to investigate whether local intramyocardial injection of EPO with hydrogel could enhance cardioprotective effect without causing polycythaemia after myocardial infarction (MI). To test the hypothesis, phosphate buffered solution (PBS), alpha-cyclodextrin/MPEG-PCL-MPEG hydrogel, recombined human erythropoietin (rhEPO) in PBS, or rhEPO in hydrogel were injected into the infarcted area immediately after MI in rats. The hydrogel allowed a sustained release of EPO, which inhibited cell apoptosis and increased neovasculature formation, and subsequently reduced infarct size and improved cardiac function compared with other groups. Notably, there was no evidence of polycythaemia from this therapy, with no differences in erythrocyte count and hematocrit compared with the animals received PBS or hydrogel blank injection. In conclusion, intramyocardial delivery of rhEPO with alpha-cyclodextrin/MPEG-PCL-MPEG hydrogel may lead to cardiac performance improvement after MI without apparent adverse effect.

Biomaterial technology for tissue engineering applications

Tissue engineering is a newly emerging biomedical technology and methodology to assist and accelerate the regeneration and repairing of defective and damaged tissues based on the natural healing potentials of patients themselves. For the new therapeutic strategy, it is indispensable to provide cells with a local environment that enhances and regulates their proliferation and differentiation for cell-based tissue regeneration. Biomaterial technology plays an important role in the creation of this cell environment. For example, the biomaterial scaffolds and the drug delivery system (DDS) of biosignalling molecules have been investigated to enhance the proliferation and differentiation of cell potential for tissue regeneration. In addition, the scaffold and DDS technologies contribute to develop the basic research of stem cell biology and medicine as well as obtain a large number of cells with a high quality for cell transplantation therapy. A technology to genetically engineer cells for their functional manipulation is also useful for cell research and therapy. Several examples of tissue engineering applications with the cell scaffold and DDS of growth factors and genes are introduced to emphasize the significance of biomaterial technology in new therapeutic and research fields.

Reconstruction of emphysematous lung tissue using slowly released basic fibroblast growth factor from gelatin microspheres

Basic fibroblast growth factor (bFGF) has a variety of activities including regeneration and neovascularization. This study was an attempt to reconstruct emphysematous lung tissue employing slow release of bFGF. Twenty beagle dogs were randomly split into four groups: a) control group (n = 5), b) porcine pancreatic elastase (PPE)-induced emphysema group (n = 5), c) FGF-MS group [n = 5, a suspension of bFGF-incorporated gelatin microspheres (MS) was injected via the pulmonary artery of emphysema model animals], and d) MS group (n = 5, MS without bFGF were injected). Four weeks after injection, the treated lungs were observed histologically, and the mean linear intercept (Lm) was calculated in each group. Lm in the FGF-MS and MS groups was significantly smaller than that in the emphysema group (p < 0.0001), and the size of the dilated alveoli was similar to that in the control group. These changes were more evident in the FGF-MS group, where almost normal alveoli and dense microvascularization were observed around the small pulmonary arteries. Reconstruction of emphysematous lungs was achieved by intrapulmonary arterial administration of MS with or without bFGF. This method may allow trans-pulmonary arterial therapy for pulmonary emphysema.

Transfection efficiency of TDL compound in HUVEC enhanced by ultrasound-targeted microbubble destruction

The aim of the present study was to explore the gene transfection efficiency of Tat peptide/plasmid DNA/ liposome (TDL) compound combined with ultrasound-targeted microbubble destruction (UTMD) in human umbilical vein endothelial cell (HUVEC). Tat peptide, plasmid DNA (pIRES2-EGFP-HGF) and Lipofectamine 2000 were used to prepare the TDL compound. Microbubbles were prepared using mechanic vibration. The expression of the report gene enhanced green fluorescent protein (EGFP) was observed using fluorescent microscopy and flow cytometry. The viability of HUVEC was measured by MTT assay. mRNA and protein of HGF was analyzed by reverse transcription-polymerase chain reaction and Western Blot. The intensity of green fluorescence and the gene transfection efficiency of TDL compound + microbubbles + ultrasound group were higher than those of other groups, and no significantly different viability was found between TDL compound + microbubbles + ultrasound group and the other groups. The HGF mRNA and HGF protein of TDL compound + microbubbles + ultrasound group were higher than those of other groups. Our finding demonstrated that UTMD could enhance the transfection efficiency of TDL compound without obvious effects on the cell viability of HUVEC, suggesting that the combination of UTMD and TDL compound might be a useful tool for the gene therapy of ischemic heart disease.

Myocardial repair: from salvage to tissue reconstruction

Cardiac tissue reconstruction following myocardial infarction represents a major challenge in cardiovascular therapy, as current clinical approaches are limited in their ability to regenerate or replace damaged myocardium. Thus, different novel treatments have been introduced aimed at myocardial salvage and repair. Here, we present a review of recent advancements in cardiac cell, gene-based and tissue engineering therapies. Selected strategies in cell therapy and new tools for myocardial gene transfer are summarized. Finally, we consider novel approaches to myocardial tissue engineering as a platform for the integration of various modalities in an attempt to rejuvenate infarcted tissue in vivo.

Microvascular transplantation after acute myocardial infarction

The primary objective of this study was to evaluate epicardial transplantation of an intact microvascular network for treatment of myocardial ischemia in a murine model of acute myocardial infarction. We describe transplantation of an intact microvascular network constructed from isolated microvascular segments stabilized in a 3-dimensional matrix to the epicardial surface after acute myocardial infarction. This microvascular graft was implanted as a patch on the epicardium of mice after left coronary artery ligation. After 14 and 28 days of implantation, left ventricular (LV) function was assessed and grafts evaluated via histology and cytochemistry. Inosculation of microvessels within the graft with host coronary microcirculation occurred as early as 7 days after initial tissue grafting. Morphologic evaluation of the grafts revealed arterioles, venules, capillaries, and erythrocytes within vascular lumina. Control grafts of collagen alone remained avascular. LV infarct size was smaller, and LV function improved in treated animals. Engraftment of whole microvascular units can be achieved to support cell-assisted vascular remodeling. Microvascular grafts may provide therapeutic benefit as a primary treatment or serve as a microvascular platform for cardiac repair and regeneration.

Myocardial tissue engineering

INTRODUCTION

Regeneration of the infarcted myocardium after a heart attack is one of the most challenging aspects in tissue engineering. Suitable cell sources and optimized biocompatible materials must be identified.

SOURCES OF DATA

In this review, we briefly discuss the current therapeutic options available to patients with heart failure post-myocardial infarction. We describe the various strategies currently proposed to encourage myocardial regeneration, with focus on the achievements in myocardial tissue engineering (MTE). We report on the current cell types, materials and methods being investigated for developing a tissue-engineered myocardial construct.

AREAS OF AGREEMENT

Generally, there is agreement that a 'vehicle' is required to transport cells to the infarcted heart to help myocardial repair and regeneration.

AREAS OF CONTROVERSY

Suitable cell source, biomaterials, cell environment and implantation time post-infarction remain obstacles in the field of MTE.

GROWING POINTS

Research is being focused on optimizing natural and synthetic biomaterials for tissue engineering. The type of cell and its origin (autologous or derived from embryonic stem cells), cell density and method of cell delivery are also being explored.

AREAS TIMELY FOR DEVELOPING RESEARCH

The possibility is being explored that materials may not only act as a support for the delivered cell implants, but may also add value by changing cell survival, maturation or integration, or by prevention of mechanical and electrical remodelling of the failing heart.

Intra-thoracic fibrous tissue induction by polylactic acid and epsilon-caprolactone copolymer cubes, with or without slow release of basic fibroblast growth factor

OBJECTIVE

We investigated whether implantation of polylactic acid and epsilon-caprolactone copolymer (PLAC) cubes with or without basic fibroblast growth factor (b-FGF) released slowly from gelatin microspheres was able to induce fibrous tissue in the dead space remaining after pneumonectomy in the thoracic cavity.

METHODS

Left pneumonectomy was performed in Japanese white rabbits. In the control group (n=6), the left thoracic cavity was closed without any treatment. In the FGF group (n=6), gelatin microspheres that released 100 microg of b-FGF were implanted into the left thoracic cavity. In the PLAC group (n=6), PLAC cubes were implanted into the left thoracic cavity. In the PLAC/FGF group (n=6), both PLAC cubes and gelatin microspheres releasing 100 microg of b-FGF were implanted into the left thoracic cavity.

RESULTS

In the control and FGF groups, herniation of the heart, mediastinal shift, and overinflation of the right lung were observed. No granular tissue formation was observed. In the PLAC and PLAC/FGF groups, a dense area of newly formed soft tissue was observed, and only a mild mediastinal shift was observed during the 3-month follow-up period. Pathological examination revealed induction of fibrous and granular tissue in the left thoracic cavity. The foreign-body reaction induced by PLAC was very mild.

CONCLUSIONS

Implantation of PLAC cubes with or without gelatin microspheres releasing 100 microg of b-FGF is able to induce fibrous tissue in the post-pneumonectomy dead space.

Experimental tissue regeneration by DDS technology of bio-signaling molecules

The medical therapy of tissue regeneration achieved by biomaterial-based tissue engineering has been currently expected as the third option following reconstructive surgery and organ transplantation. The basic idea of this regenerative therapy is to assist the self-healing potentials of body to induce the natural regeneration and repairing of defective or injured tissue. To this end, it is practically important to create a local environment which enables cells to promote their proliferation and differentiation, resulting in the induction of cell-based tissue regeneration. Tissue engineering is a biomedical technology or methodology to build up this regeneration environment by making use of biomaterials. Drug delivery system (DDS) is a biomaterial technology to enhance the in vivo biological functions of bio-signaling molecules (growth factors and genes) for promoted tissue regeneration. This paper overviews the recent status of tissue regeneration therapy based on the DDS technology of bio-signaling molecules.

Myocardial tissue engineering: a review

Myocardial tissue engineering, a concept that intends to overcome the obstacles to prolonging patients' life after myocardial infarction, is continuously improving. It comprises a biomaterial based 'vehicle', either a porous scaffold or dense patch, made of either natural or synthetic polymeric materials, to aid transportation of cells into the diseased region in the heart. Many different cell types have been suggested for cell therapy and myocardial tissue engineering. These include both autologous and embryonic stem cells, both having their advantages and disadvantages. Biomaterials suggested for this specific tissue-engineering application need to be biocompatible with the cardiac cells and have particular mechanical properties matching those of native myocardium, so that the delivered donor cells integrate and remain intact in vivo. Although much research is being carried out, many questions still remain unanswered requiring further research efforts. In this review, we discuss the various approaches reported in the field of myocardial tissue engineering, focusing on the achievements of combining biomaterials and cells by various techniques to repair the infarcted region, also providing an insight on clinical trials and possible cell sources in cell therapy. Alternative suggestions to myocardial tissue engineering, in situ engineering and left ventricular devices are also discussed.

Combined therapy with human cord blood cell transplantation and basic fibroblast growth factor delivery for treatment of myocardial infarction

BACKGROUND

Transplanting cord blood-derived cells has been shown to augment neovascularization in ischaemic tissue.

AIM

To test whether sustained delivery of basic fibroblast growth factor (bFGF) enhances the efficacy of angiogenic cord blood mononuclear cell (CBMNC) transplantation therapy in treating myocardial infarction.

METHODS

Three weeks after myocardial infarction, Sprague-Dawley rats were randomised to either injection of medium only (control), CBMNC transplantation, sustained bFGF delivery, or combined CBMNC transplantation and sustained bFGF delivery. Six weeks after treatment, tissue formation, neovascularization, and apoptotic activity in the infarct regions were evaluated by histology and immunohistochemistry. Left ventricular (LV) dimensions and function were evaluated by magnetic resonance imaging.

RESULTS

Combined bFGF delivery and CBMNC transplantation significantly enhanced neovascularization in the ischaemic myocardium, as compared with either therapy alone. The enhanced neovascularization was likely due to increased VEGF and bFGF expression. The combined therapy also exhibited a reduced infarct area and apoptosis in the ischaemic myocardium, as compared with either individual therapy. The combined therapy did not attenuate LV dilation or increase ejection fraction significantly over either individual therapy.

CONCLUSION

This study demonstrates that sustained bFGF delivery enhances the angiogenic efficacy of CBMNC transplantation in rat myocardial infarction models.

Gelatin microspheres encapsulated with a nonpeptide angiogenic agent, ginsenoside Rg1, for intramyocardial injection in a rat model with infarcted myocardium

Angiogenic therapies may need to select a stable agent to be delivered. In the study, a nonpeptide angiogenic agent, ginsenoside Rg(1) (Rg(1)), was encapsulated in the gelatin microspheres (MSs) crosslinked with genipin and intramuscularly injected into a rat model with infarcted myocardium. bFGF was used as a control. After swelling in an aqueous environment, the MSs without crosslinking became collapsed and stuck together. For those crosslinked, the swollen MSs appeared to be more stable with an increasing the degree of crosslinking. After it was released from MSs in vitro, the remaining activity of bFGF on HUVEC proliferation reduced significantly, while that of Rg(1) remained constant. An inspection of the retrieved hearts revealed a large aneurysmal left ventricle (LV) with a thinned myocardium and a significant myocardial fibrosis for that treated with the Empty MSs (without drug encapsulation). However, those receiving the MSs encapsulated with bFGF or Rg(1) attenuated the enlargement of the LV cavity and the development of myocardial fibrosis. The densities of microvessels found in the border zones of the infarct treated with the bFGF or Rg(1) MSs were significantly greater than that treated with the Empty MSs. These results indicated that Rg(1), a stable angiogenic agent, successfully enhanced the myocardial perfusion and preserved the infarcted LV function.

Activin A as a critical mediator of capillary formation: interaction with the fibroblast growth factor action

The present study was conducted to elucidate the role of activin A in capillary formation. When bovine aortic endothelial cells (BAEC) were cultured in a collagen gel, basic fibroblast growth factor (FGF-2) induced tube formation. Activin A also induced tube formation and the addition of two factors together was more effective. BAEC produced both FGF-2 and activin A as autocrine factors. Exogenous FGF-2 did not affect the production of activin A but instead upregulated the type II activin receptor. On the other hand, activin A increased the expression of FGF-2 as well as the FGF receptor. Most importantly, when the action of endogenous activin A was blocked by adding follistatin, the tubulogenic action of FGF-2 was nearly completely inhibited. Activin-induced tubulogenesis was markedly inhibited by overexpression of Smad7, an inhibitory Smad. Similarly, an inhibitor of p44/42 mitogen-activated protein (MAP) kinase attenuated the activin-mediated tubulogenesis, whereas an inhibitor of p38 MAP kinase had no effect. These results indicate that FGF-2 and activin A enhance their signals each other in BAEC, and endogenous activin A is critical for FGF-2-induced capillary formation.

Enhanced angiogenesis by gelatin hydrogels incorporating basic fibroblast growth factor in rabbit model of hind limb ischemia

Recently we have developed new sustained release system of basic fibroblast growth factor (bFGF) using gelatin hydrogel as a carrier. Using this system, we examined the effect of topical sustained release of bFGF on angiogenesis and tissue blood perfusion in a rabbit model of hind limb ischemia. Thirty-two rabbits underwent excision of right femoral artery under general anesthesia. Two weeks later the rabbits were randomized into four groups (n = 8 each): no treatment, intramuscular injection of gelatin hydrogel alone, and intramuscular injection of gelatin hydrogel incorporating 30 microg and 100 microg of bFGF. Four weeks after each treatment, selective angiography, tissue blood flowmetry using laser Doppler perfusion imaging, and histological examination of thigh muscle were performed. In groups treated with bFGF incorporating gelatin hydrogel, tissue blood flow, number of arterioles, and vascular density were significantly increased in a dose-dependent manner 4 weeks after the treatment. Serum concentrations of bFGF and vascular endothelial growth factor were not elevated 4 weeks after the treatment. In conclusion, sustained release of bFGF using gelatin hydrogel augmented angiogenesis and improved tissue blood flow after excision of the femoral artery.

Sustained-release erythropoietin ameliorates cardiac function in infarcted rat-heart without inducing polycythemia

BACKGROUND

The usefulness of sustained-release erythropoietin for improving left ventricular (LV) function without polycythemia was evaluated in a rat chronic myocardial infarction model.

METHODS AND RESULTS

Four weeks after left coronary artery ligation, 50 Sprague-Dawley rats were assigned to 5 groups (n=10, each). Control group had a gelatin sheet (20x20 mm) containing saline applied to the infarct area, whereas the 4 treatment groups had gelatin sheets incorporating erythropoietin 0.1 U, 1 U, 10 U and 100 U, respectively. Endpoint measurements performed at 8 weeks after the coronary ligation revealed that the fractional area change was larger for erythropoietin 1 U and 10 U than in the other 3 groups. The LV end-systolic elastance and the time constant of isovolumic relaxation were better for erythropoietin 1 U and 10 U than in the other 3 groups. The density of vessels larger than 50 microm in diameter was the highest in the erythropoietin 1 U group. The number of red blood cells was significantly increased in groups receiving erythropoietin 10 U and 100 U.

CONCLUSIONS

Gelatin hydrogel sheets incorporating 1 U erythropoietin improved LV function without inducing polycythemia in a rat chronic myocardial infarction model.

Combined Treatment With Sustained-Release Basic Fibroblast Growth Factor and Heparin Enhances Neovascularization in Hypercholesterolemic Mouse Hindlimb Ischemia

BACKGROUND

Whether the combined treatment with sustained-release basic fibroblast growth factor (bFGF) and heparin enhances neovascularization in hypercholesterolemic mouse hindlimb ischemia was investigated.

METHODS AND RESULTS

Wild-type C57BL/6 and low density lipoprotein receptor-deficient mice were assigned to 1 of the following 4 experimental groups and treated for 2 weeks after femoral artery extraction: group N, no treatment; group H, daily subcutaneous injection of heparin calcium; group F, single intramuscular injection of the sustained-release bFGF microspheres; and group FH, combined treatment with sustained-release bFGF and heparin. Among the wild-type mice at 4 weeks after femoral artery extraction, the laser Doppler perfusion image index (LDPII) in groups H, F, and FH was significantly higher than that in group N. The vascular density in group FH was the highest among the 4 groups. The maturation index in the 3 treated groups was significantly higher than that in group N. Among the hypercholesterolemic mice, the LDPII in group FH was significantly higher than that in the other 3 groups. The vascular density and maturation index in group FH were the highest among the 4 groups.

CONCLUSIONS

Combined treatment with sustained-release bFGF and heparin enhanced neovascularization in the hypercholesterolemic hindlimb ischemia model.

Application of bFGF and BDNF to Improve Angiogenesis and Cardiac Function

BACKGROUND

Brain-derived neurotrophic factor (BDNF) is a survival factor for endothelial cells and expresses in the ischemic myocytes. The purpose of this study was to assess whether the simultaneous application of basic fibroblast growth factor (bFGF) and BDNF incorporating gelatin hydrogels improves angiogenesis and cardiac function in ischemic myocardium compared with bFGF applied alone.

MATERIALS AND METHODS

Direct intramyocardial injection of 100 microg of bFGF plus 25 microg of BDNF, 100 microg of bFGF, or saline were performed in canine infarct model. Colored microspheres were injected to assess the regional myocardial blood flow. Cardiac function was evaluated by cine magnetic resonance imaging (MRI). Immunohistochemical staining and enzyme linked immunosorbent assay (ELISA) were used to observe the localization and expression of bFGF and BDNF protein, and myocardial microvessel density was assessed by von Willebrand factor staining.

RESULTS

Left ventricular ejection fraction (LVEF) was higher in bFGF plus BDNF group than in saline or bFGF group. Blood flow of the peri-infarct region was increased by bFGF plus BDNF treatment. The distribution of bFGF and BDNF-positive cardiomyocytes was similar in three groups. The expression of bFGF and BDNF protein and microvessel density in bFGF plus BDNF group was higher than in the other two groups.

CONCLUSIONS

This study indicates that the sustained dual release of bFGF and BDNF incorporating gelatin hydrogels can improve angiogenesis and left ventricular function in the ischemic myocardium compared with bFGF applied alone. bFGF plus BDNF administration may be a promising therapeutic strategy for the treatment of ischemic myocardium.

Periurethral injection of sustained release basic fibroblast growth factor improves sphincteric contractility of the rat urethra denervated by botulinum-a toxin

PURPOSE

We evaluated the effects of sustained release basic fibroblast growth factor injection in rat urethra denervated by botulinum-A toxin (Wako Life Science, Osaka, Japan).

MATERIALS AND METHODS

A total of 30 female Sprague-Dawley rats underwent periurethral injection of 10 U botulinum-A toxin to induce chemical denervation of the urethral sphincter. Leak point pressure in the waking state was determined and a significant decrease in leak point pressure vs that in control rats was confirmed (mean +/- SD 58.7 +/- 6.2 vs 120.7 +/- 13.0 cm H(2)O, p <0.0001). Two weeks later 0, 50 and 200 microg basic fibroblast growth factor incorporating 200 microl gelatin hydrogels in 10 rats each were injected into the urethral sphincter, enabling sustained release of basic fibroblast growth factor for 2 weeks. Four weeks later injection leak point pressure measurement and histological evaluation of the urethra were performed.

RESULTS

Leak point pressure in rats with 50 and 200 microg basic fibroblast growth factor injection was significantly higher than in rats with the 0 microg injection (82.7 +/- 9.0 vs 95.1 +/- 6.2 and 119.3 +/- 8.1 cm H(2)O, p = 0.0021 and <0.0001, respectively). Maximum cross-sectional area of the urethral smooth muscle layer in the 50 and 200 microg groups significantly increased compared with that in the urethra in the 0 micro group, which was considered 100% (114.1% +/- 15.8% and 132.5% +/- 13.4%, p = 0.029 and <0.0001, respectively). Similarly the cross-sectional area of the striated sphincter in the 50 and 200 microg groups was greater than the 100% in the 0 microg group (112.3% +/- 15.6% and 124.3% +/- 14.1%, p = 0.069 and 0.0007, respectively). Vascular density in the urethral peri-atrophic zone in the 50 and 200 microg groups was significantly higher than in the 0 microg group (p = 0.027 and <0.0001, respectively).

CONCLUSIONS

Sustained release basic fibroblast growth factor injection in the chemically denervated urethral sphincter facilitates regeneration of the urethral muscles and improves sphincteric contractility. Endoscopic periurethral injection of basic fibroblast growth factor incorporating gelatin hydrogels may be an attractive therapy for stress urinary incontinence.

Biomaterials for the treatment of myocardial infarction

For nearly a decade, researchers have investigated the possibility of cell transplantation for cardiac repair. More recently, the emerging fields of tissue engineering and biomaterials have begun to provide potential treatments. Tissue engineering approaches are designed to repair lost or damaged tissue through the use of growth factors, cellular transplantation, and biomaterial scaffolds. There are currently 3 biomaterial approaches for the treatment of myocardial infarction (MI). The first involves polymeric left ventricular restraints in the prevention of heart failure. The second utilizes in vitro engineered cardiac tissue, which is subsequently implanted in vivo. The final approach entails injecting cells and/or a scaffold into the myocardium to create in situ engineered cardiac tissue. This review gives an overview of the current progress in the growing field of biomaterials for the treatment of MI.

Autoperipheral blood mononuclear cell transplantation improved giant ulcers due to chronic arteriosclerosis obliterans

We report the case of a 74-year-old man with Fontaine stage IV chronic arteriosclerosis obliterans who had been suffering from inveterate giant skin ulcers on the dorsum and heel of the right foot. As conventional medical treatments had not improved these ulcers and surgical treatment was considered unfeasible, amputation of the right lower limb below the knee appeared to represent the only option. The patient was admitted to Tottori University Hospital to attempt a new angiogenic therapy using auto-mononuclear cell transplantation to avoid amputation. On admission, neither right ankle blood pressure nor transcutaneous partial pressure of oxygen at the right toe were detectable. The patient had a history of multiple cerebral infarctions, and collection of mononuclear cells from bone marrow was considered too difficult, so collection of peripheral blood mononuclear cells was selected. Transcutaneous partial pressure of oxygen and skin temperature in the treated limb started to improve from 2 weeks after implantation. Ulcer size was recognizably reduced by 1 month after treatment. Partial auto-skin implantation on the right heel was performed 2 months after treatment, and the giant skin ulcer was finally completely covered. No adverse effects were noted during follow-up lasting 1 year. These results suggest that peripheral blood mononuclear cell implantation may offer a suitable alternative rescue therapy for patients with critical limb ischemia whose general condition is not good.

Cochlear Protection by Local Insulin-Like Growth Factor-1 Application Using Biodegradable Hydrogel

OBJECTIVE

The aim of this experimental study was to examine the potential of local recombinant human insulin-like growth factor-1 (rhIGF-1) application through a biodegradable hydrogel for the treatment of cochleae.

METHODS

A hydrogel immersed with rhIGF-1 was placed on the round window membrane of Sprague-Dawley rats while a hydrogel immersed with physiological saline was applied to control animals. On day 3 after drug application, the animals were exposed to white noise at 120 dB sound pressure level (SPL) for 2 hours. Cochlear function was monitored using measurements of auditory brain stem responses (ABRs) at frequencies of 8, 16, and 32 kHz. The temporal bones were collected 7 or 30 days after noise exposure and the loss of hair cells was quantitatively analyzed.

RESULTS

Local rhIGF-1 treatment significantly reduced the elevation of ABR thresholds on days 7 and 30 after noise exposure. Histologic analysis revealed that local rhIGF-1 treatment significantly prohibited the loss of outer hair cells.

CONCLUSIONS

These findings demonstrate that local IGF-1 application through the biodegradable hydrogel has the potential for protection of cochleae from noise trauma.

The wrapping method using biodegradable felt strips has a preventive effect on the thinning of the aortic wall: Experimental study in the canine aorta

OBJECTIVES

Wrapping methods have been widely used to reinforce the anastomotic site in vascular surgery; however, postoperative changes in the aortic wall wrapped by nonbiodegradable felt have not been well characterized. The purposes of this investigation are to elucidate the sequelae of wrapping with nonbiodegradable felt on the aortic wall and to modify those changes by using biodegradable felt with or without basic fibroblast growth factor (bFGF).

METHODS

The descending thoracic aortas of 15 beagles were wrapped with three different materials: nonbiodegradable polytetrafluoroethylene (PTFE) felt, biodegradable polyglycol acid (PGA) material, and PGA with 100 microg bFGF (n = 5 in each group). The descending thoracic aorta was resected after 3 months. The thickness of the aortic wall, vessel density in the media and the adventitia, and the wall strength were assessed. Untreated native aortic wall served as a normal control.

RESULTS

The thickness of the media of the PTFE group was lower than that of the PGA + bFGF group (66% +/- 5% vs 85% +/- 6% of control, P < .05). The adventitia-media ratio in the PTFE group decreased compared with controls (59.1% of normal, P < 0.05), whereas those in the PGA and PGA + bFGF groups increased (172.1% and 189.6% of normal, respectively, P < .01). The collagen-smooth muscle ratio in the media was higher in the PTFE group than in the controls (0.14 +/- 0.02 vs 0.07 +/- 0.01, P < .01). The number of vessels in the adventitia was higher in the PGA + bFGF group than those in PTFE or PGA groups (29.6 +/- 2.5/mm2 vs 6.4 +/- 0.8/mm2, 19.0 +/- 1.1/mm2, P < .01). The PGA + bFGF group demonstrated larger failure force than the PTFE group (4.0 +/- 0.3 kgf vs 1.6 +/- 0.3 kgf, P < .01). The failure stress in the PGA and PGA + bFGF groups was larger than that in PTFE group (PTFE:PGA + bFGF = 5.3 +/- 0.9 x10(2) kPa:11.7 +/- 1.7 x 10(2) kPa, P < .01; PTFE:PGA = 5.3 +/- 0.9 x 10(2) kPa:11.2 +/- 1.2 x 10(2) kPa, P < .05).

CONCLUSION

The aortic wall wrapped with nonbiodegradable PTFE felt showed a reduced thickness and diminished vessels in the adventitia. Biodegradable felt (PGA), with or without bFGF, modified these histologic changes. The vessel-rich thickened adventitia, after wrapping by PGA with bFGF, was associated with increased aortic wall strength.

CLINICAL RELEVANCE

This investigation was conducted in an attempt to elucidate mechanisms underlying the occurrence of late postoperative false aneurysm after aortic surgery. We hypothesized that sustaining compression of the aorta by the felt strip may cause structural derangement and local ischemia on the aortic wall. We used a simple wrapping of the aorta with a felt strip rather than a felt strip at anastomotic sites to simplify the experimental model and to exclude confounding factors brought by technical inconsistency on the surgical anastomosis. We further attempted to find a clue for preventing adverse effects of wrapping with a conventional felt strip. Practically, we pursued a possible application of a biodegradable felt strip to aortic wrapping in our experimental model before we proceed in a clinical application of the new material.

Novel strategy for treatment of inner ears using a biodegradable gel

OBJECTIVE

The present study aimed to evaluate the efficacy of a biodegradable hydrogel as a drug-delivery medium for the inner ear. Brain-derived neurotrophic factor (BDNF) was chosen as the agent to be administered.

METHOD

First, we used an enzyme-linked immunosorbent assay to measure BDNF concentrations in the cochlear fluid after placing a hydrogel containing this agent onto the round-window membrane of the ear. Second, the functional and histologic protection of the auditory primary neurons (spiral ganglion neurons [SGNs]) by BDNF applied through the hydrogel was examined using an animal model of SGN degeneration.

RESULTS

The results revealed sustained delivery of BDNF into the cochlear fluid by way of the hydrogel. Second, the functional and histologic protection of the auditory primary neurons (SGNs) by BDNF applied through the hydrogel was examined using an animal model of SGN degeneration. The measurement of electrically evoked auditory-brainstem responses demonstrated that BDNF delivered by way of the hydrogel significantly reduced the threshold elevation. Immunohistochemistry for neurofilament 200 kD demonstrated increased survival of SGNs because of BDNF application through the hydrogel.

CONCLUSION

These findings indicate that biodegradable hydrogels can be used for drug delivery to the inner ear.

Effects of Intramyocardial Administration of Slow-Release Basic Fibroblast Growth Factor on Angiogenesis and Ventricular Remodeling in a Rat Infarct Model

BACKGROUND

Basic fibroblast growth factor (bFGF) stimulates neoangiogenesis. Incorporation into biodegradable gelatin hydrogels provides the sustained release of bFGF. The effects of intramyocardial injections of slow-release bFGF on neoangiogenesis in a rat model of infarction were investigated.

METHODS AND RESULTS

Myocardial infarction was induced in rats using coronary artery ligation. A total of 124 rats received an intramyocardial injection of 20 microg of bFGF, the same amount of bFGF incorporated into gelatin hydrogel (bFGF + gel), gelatin hydrogel (gel) or saline. Ventricular function was evaluated by echocardiography 2 or 4 weeks later. Morphometric and histological analyses were used to evaluate infarct size, vascular density and myocardial apoptosis. Capillary density in the infarct border zone was higher in the bFGF and bFGF + gel groups than in the saline and gel groups at 4 weeks (p<0.001). Arteriolar density was higher in the bFGF + gel group than in the other 3 groups (p<0.05). The bFGF and bFGF + gel groups contained fewer apoptotic cardiomyocytes in the border zone than the saline and gel groups (p<0.01). The bFGF+gel group had thicker (p<0.05) and less expanded infarcts (p<0.01) compared with the saline group at 4 weeks.

CONCLUSIONS

Incorporation of bFGF in gelatin hydrogels enhanced the effects of bFGF on arteriogenesis, ventricular remodeling and cardiac function.

Significance of release technology in tissue engineering

Regenerative medical therapy has been expected to compensate for the therapeutic disadvantages of reconstructive surgery and organ transplantation, as well as offering a new therapeutic strategy. The objective of regenerative medical therapy is to induce the repair of defective tissues based on the natural healing potential of patients. For successful tissue regeneration, it is indispensable to provide cells with a local environment of artificial extracellular matrix where they can proliferate and differentiate efficiently. Tissue engineering is the key to this regeneration environment; release technology often enhances the in vivo stability of growth factors and related genes and prolongs the maintenance of biological functions for tissue regeneration.

Aortic elastic properties and left ventricular diastolic dysfunction in patients with obstructive sleep apnea

Although the responsible mechanisms are not yet fully known, obstructive sleep apnea is associated with an increased risk for cardiovascular disease and events. The aorta is not only a conduit delivering blood to the tissues but is also an important modulator of the entire cardiovascular system, its elastic properties also affecting left ventricular function and coronary blood flow. The aim of this study was to determine left ventricular diastolic function and aortic elastic properties in patients with obstructive sleep apnea syndrome. Fourteen male patients with obstructive sleep apnea and 14 age- and body mass index-matched healthy male controls took part in the study as a control group. All subjects underwent echocardiographic examination; left ventricular cavity dimension, standard and tissue Doppler parameters, and aortic diameter (3 cm above aortic valve) at systole and diastole were measured. While the aortic stiffness index in patients with obstructive sleep apnea was significantly higher than that of the control group (4.5 +/- 0.3 vs 2.1 +/- 0.1, P = 0.001), the aortic distensibility index was found to be lower in this group compared with controls (2.4 +/- 1.2 vs 3.9 +/- 1.5 cm2 dynes(-1) 10(-6), P = 0.009). Furthermore, peak velocity of myocardial systolic wave and peak velocities of myocardial diastolic waves in sleep apnea patients were lower than in controls. There was an association between aortic stiffness and the apnea hypopnea index (coefficient = 0.49, P = 0.002). We also found an inverse correlation between peak velocity of myocardial diastolic wave and aortic stiffness (coefficient = -0.43, P = 0.003), using multiple linear regression. Increased aortic stiffness that is associated with the severity of disease in patients with obstructive sleep apnea may lead to diastolic dysfunction of the left ventricle.

Custom design of the cardiac microenvironment with biomaterials

Many strategies for repairing injured myocardium are under active investigation, with some early encouraging results. These strategies include cell therapies, despite little evidence of long-term survival of exogenous cells, and gene or protein therapies, often with incomplete control of locally-delivered dose of the factor. We propose that, ultimately, successful repair and regeneration strategies will require quantitative control of the myocardial microenvironment. This precision control can be engineered through designed biomaterials that provide quantitative adhesion, growth, or migration signals. Quantitative timed release of factors can be regulated by chemical design to direct cellular differentiation pathways such as angiogenesis and vascular maturation. Smart biomaterials respond to the local environment, such as protease activity or mechanical forces, with controlled release or activation. Most of these new biomaterials provide much greater flexibility for regenerating tissues ex vivo, but emerging technologies like self-assembling nanofibers can now establish intramyocardial cellular microenvironments by injection. This may allow percutaneous cardiac regeneration and repair approaches, or injectable-tissue engineering. Finally, materials can be made to multifunction by providing sequential signals with custom design of differential release kinetics for individual factors. Thus, new rationally-designed biomaterials no longer simply coexist with tissues, but can provide precision bioactive control of the microenvironment that may be required for cardiac regeneration and repair.

Angiogenesis with biomaterial-based drug- and cell-delivery systems

Angiogenesis, the formation of new blood vessels from existing ones, is an important event in several biological processes, including wound healing. It plays a key role in determining the final functionality and integration of any implanted medical device. In addition, angiogenesis is a required event for organ development and has been accepted as a rate-limiting step in engineering tissue replacements. Besides these regenerative processes, uncontrolled angiogenesis is also involved in a number of pathologies, including tumor growth and metastases. Like angiogenesis, biomaterials also play a role in wound healing after medical device implantation and in tissue engineering. Interactions between the device biomaterials and host tissue will factor into the final device integration. Additionally, tissue-engineering strategies utilize biomaterials to a great extent because the paradigm of tissue engineering involves the use of cells, growth factors and scaffolding matrices in order to regenerate or replace tissue. Since almost all tissues are three-dimensional, the biomaterial scaffold plays an integral role in the paradigm. This review will emphasize the influence of biomaterials on angiogenesis as it applies to medical device implantation, tissue engineering and therapies for pathological angiogenesis.

Site-specific delivery of acidic fibroblast growth factor stimulates angiogenic and osteogenic responsesin vivo

A major clinical problem in orthopedics is the healing of nonunion fractures. Limitations of this bone repair process include insufficient angiogenesis and mineralization. Integrating appropriate biomaterials with site-specific neovascularization and osteogenesis at the wound site has been the focus of several clinically relevant therapeutic strategies. As an extracellular protein, acidic fibroblast growth factor (FGF-1) induces, coordinates, and sustains site-specific molecular responses associated with angiogenesis and osteogenesis. To establish the ability of this growth factor to coordinate bone regenerative process in vivo, site-specific delivery of FGF-1, entrapped in a fibrin/hydroxyapatite composite, was evaluated. Kinetic analysis in vivo revealed the biocomposite was capable of delivering biologically active FGF-1. Release kinetics revealed an initial delivery of 87.5 ng/h of active FGF-1 in the first 20 h, followed by a reduced delivery of 28 ng/h during the next 20 h. In situ immunohistological analyses demonstrated that FGF-1-containing implants induced increased angiogenesis and infiltration of cells expressing osteogenic related markers (i.e., osteopontin, osteocalcin). Collectively, these efforts support that site-specific delivery of active FGF-1 in a fibrin/hydroxyapatite composite is competent to induce not only angiogenesis but also osteogenic cellular responses.

Protein-based signaling systems in tissue engineering

Tissue engineering aims to replace damaged tissues or organs using either transplanted cells or host cells recruited to the target site. Protein signaling is crucial to regulate cell phenotype and thus engineered tissue structure and function. Biomaterial vehicles are being designed to incorporate and locally deliver various molecules involved in this signaling, including both growth factors and peptides that mimick whole proteins. Controlling the concentration, local duration and spatial distribution of these factors is key to their utility and efficacy. Recent advances have been made in the development of polymeric delivery systems intended to achieve this control.