Combination of in vivo angiopoietin-1 gene transfer and autologous bone marrow cell implantation for functional therapeutic angiogenesis

Transmembrane stem factor nanodiscs enhanced revascularization in a hind limb ischemia model in diabetic, hyperlipidemic rabbits

Therapies to revascularize ischemic tissue have long been a goal for the treatment of vascular disease and other disorders. Therapies using stem cell factor (SCF), also known as a c-Kit ligand, had great promise for treating ischemia for myocardial infarct and stroke, however clinical development for SCF was stopped due to toxic side effects including mast cell activation in patients. We recently developed a novel therapy using a transmembrane form of SCF (tmSCF) delivered in lipid nanodiscs. In previous studies, we demonstrated tmSCF nanodiscs were able to induce revascularization of ischemia limbs in mice and did not activate mast cells. To advance this therapeutic towards clinical application, we tested this therapy in an advanced model of hindlimb ischemia in rabbits with hyperlipidemia and diabetes. This model has therapeutic resistance to angiogenic therapies and maintains long term deficits in recovery from ischemic injury. We treated rabbits with local treatment with tmSCF nanodiscs or control solution delivered locally from an alginate gel delivered into the ischemic limb of the rabbits. After eight weeks, we found significantly higher vascularity in the tmSCF nanodisc-treated group in comparison to alginate treated control as quantified through angiography. Histological analysis also showed a significantly higher number of small and large blood vessels in the ischemic muscles of the tmSCF nanodisc treated group. Importantly, we did not observe inflammation or mast cell activation in the rabbits. Overall, this study supports the therapeutic potential of tmSCF nanodiscs for treating peripheral ischemia.

Exploring the Effects of Human Bone Marrow-Derived Mononuclear Cells on Angiogenesis In Vitro

Cell therapies involving the administration of bone marrow-derived mononuclear cells (BM-MNCs) for patients with chronic limb-threatening ischemia (CLTI) have shown promise; however, their overall effectiveness lacks evidence, and the exact mechanism of action remains unclear. In this study, we examined the angiogenic effects of well-controlled human bone marrow cell isolates on endothelial cells. The responses of endothelial cell proliferation, migration, tube formation, and aortic ring sprouting were analyzed in vitro, considering both the direct and paracrine effects of BM cell isolates. Furthermore, we conducted these investigations under both normoxic and hypoxic conditions to simulate the ischemic environment. Interestingly, no significant effect on the angiogenic response of human umbilical vein endothelial cells (HUVECs) following treatment with BM-MNCs was observed. This study fails to provide significant evidence for angiogenic effects from human bone marrow cell isolates on human endothelial cells. These in vitro experiments suggest that the potential benefits of BM-MNC therapy for CLTI patients may not involve endothelial cell angiogenesis.

Transmembrane Stem Factor Nanodiscs Enhanced Revascularization in a Hind Limb Ischemia Model in Diabetic, Hyperlipidemic Rabbits

Therapies to revascularize ischemic tissue have long been a goal for the treatment of vascular disease and other disorders. Therapies using stem cell factor (SCF), also known as a c-Kit ligand, had great promise for treating ischemia for myocardial infarct and stroke, however clinical development for SCF was stopped due to toxic side effects including mast cell activation in patients. We recently developed a novel therapy using a transmembrane form of SCF (tmSCF) delivered in lipid nanodiscs. In previous studies, we demonstrated tmSCF nanodiscs were able to induce revascularization of ischemia limbs in mice and did not activate mast cells. To advance this therapeutic towards clinical application, we tested this therapy in an advanced model of hindlimb ischemia in rabbits with hyperlipidemia and diabetes. This model has therapeutic resistance to angiogenic therapies and maintains long term deficits in recovery from ischemic injury. We treated rabbits with local treatment with tmSCF nanodiscs or control solution delivered locally from an alginate gel delivered into the ischemic limb of the rabbits. After eight weeks, we found significantly higher vascularity in the tmSCF nanodisc-treated group in comparison to alginate treated control as quantified through angiography. Histological analysis also showed a significantly higher number of small and large blood vessels in the ischemic muscles of the tmSCF nanodisc treated group. Importantly, we did not observe inflammation or mast cell activation in the rabbits. Overall, this study supports the therapeutic potential of tmSCF nanodiscs for treating peripheral ischemia.

Syndecan-4 Proteoliposomes Enhance Revascularization in a Rabbit Hind Limb Ischemia Model of Peripheral Ischemia

Regenerative therapeutics for treating peripheral arterial disease are an appealing strategy for creating more durable solutions for limb ischemia. In this work, we performed preclinical testing of an injectable formulation of syndecan-4 proteoliposomes combined with growth factors as treatment for peripheral ischemia delivered in an alginate hydrogel. We tested this therapy in an advanced model of hindlimb ischemia in rabbits with diabetes and hyperlipidemia. Our studies demonstrate enhancement in vascularity and new blood vessel growth with treatment with syndecan-4 proteoliposomes in combination with FGF-2 or FGF-2/PDGF-BB. The effects of the treatments were particularly effective in enhancing vascularity in the lower limb with a 2-4 increase in blood vessels in the treatment group in comparison to the control group. In addition, we demonstrate that the syndecan-4 proteoliposomes have stability for at least 28 days when stored at 4°C to allow transport and use in the hospital environment. In addition, we performed toxicity studies in the mice and found no toxic effects even when injected at high concentration. Overall, our studies support that syndecan-4 proteoliposomes markedly enhance the therapeutic potential of growth factors in the context of disease and may be promising therapeutics for inducing vascular regeneration in peripheral ischemia. STATEMENT OF SIGNIFICANCE: Peripheral ischemia is a common condition in which there is a lack of blood flow to the lower limbs. This condition can lead to pain while walking and, in severe cases, critical limb ischemia and limb loss. In this study, we demonstrate the safety and efficacy of a novel injectable therapy for enhancing revascularization in peripheral ischemia using an advanced large animal model of peripheral vascular disease using rabbits with hyperlipidemia and diabetes.

Transmembrane Stem Factor Nanodiscs Enhanced Revascularization in a Hind Limb Ischemia Model in Diabetic, Hyperlipidemic Rabbits

Therapies to revascularize ischemic tissue have long been a goal for the treatment of vascular disease and other disorders. Therapies using stem cell factor (SCF), also known as a c-Kit ligand, had great promise for treating ischemia for myocardial infarct and stroke, however clinical development for SCF was stopped due to toxic side effects including mast cell activation in patients. We recently developed a novel therapy using a transmembrane form of SCF (tmSCF) delivered in lipid nanodiscs. In previous studies, we demonstrated tmSCF nanodiscs were able to induce revascularization of ischemia limbs in mice and did not activate mast cells. To advance this therapeutic towards clinical application, we tested this therapy in an advanced model of hindlimb ischemia in rabbits with hyperlipidemia and diabetes. This model has therapeutic resistance to angiogenic therapies and maintains long term deficits in recovery from ischemic injury. We treated rabbits with local treatment with tmSCF nanodiscs or control solution delivered locally from an alginate gel delivered into the ischemic limb of the rabbits. After eight weeks, we found significantly higher vascularity in the tmSCF nanodisc-treated group in comparison to alginate treated control as quantified through angiography. Histological analysis also showed a significantly higher number of small and large blood vessels in the ischemic muscles of the tmSCF nanodisc treated group. Importantly, we did not observe inflammation or mast cell activation in the rabbits. Overall, this study supports the therapeutic potential of tmSCF nanodiscs for treating peripheral ischemia.

Peripheral artery disease: the new frontiers of imaging techniques to evaluate the evolution of regenerative medicine

Introduction: Stem cells (ESC, iPSC, MSC) are known to have intrinsic regenerative properties. In the last decades numerous findings have favored the development of innovative therapeutic protocols based on the use of stem cells (Regenerative Medicine/Cell Therapy) for the treatment of numerous diseases including PAD, with promising results in preclinical studies. So far, several clinical studies have shown a general improvement of the patient's clinical outcome, however they possess many critical issues caused by the non-randomized design of the limited number of patients examined, the type cells to be used, their dosage, the short duration of treatment and also their delivery strategy. Areas covered: In this context, the use of the most advanced molecular imaging techniques will allow the visualization of very important physio-pathological processes otherwise invisible with conventional techniques, such as angiogenesis, also providing important structural and functional data. Expert opinion: The new frontier of cell therapy applied to PAD, potentially able to stop or even the process that causes the disease, with particular emphasis on the clinical aspects that different types of cells involve and on the use of more innovative molecular imaging techniques now available.

Tissue Engineering of the Microvasculature

The ability to generate new microvessels in desired numbers and at desired locations has been a long-sought goal in vascular medicine, engineering, and biology. Historically, the need to revascularize ischemic tissues nonsurgically (so-called therapeutic vascularization) served as the main driving force for the development of new methods of vascular growth. More recently, vascularization of engineered tissues and the generation of vascularized microphysiological systems have provided additional targets for these methods, and have required adaptation of therapeutic vascularization to biomaterial scaffolds and to microscale devices. Three complementary strategies have been investigated to engineer microvasculature: angiogenesis (the sprouting of existing vessels), vasculogenesis (the coalescence of adult or progenitor cells into vessels), and microfluidics (the vascularization of scaffolds that possess the open geometry of microvascular networks). Over the past several decades, vascularization techniques have grown tremendously in sophistication, from the crude implantation of arteries into myocardial tunnels by Vineberg in the 1940s, to the current use of micropatterning techniques to control the exact shape and placement of vessels within a scaffold. This review provides a broad historical view of methods to engineer the microvasculature, and offers a common framework for organizing and analyzing the numerous studies in this area of tissue engineering and regenerative medicine. © 2019 American Physiological Society. Compr Physiol 9:1155-1212, 2019.

Therapeutic strategies for cell-based neovascularization in critical limb ischemia

Critical limb ischemia (CLI) causes severe ischemic rest pain, ulcer, and gangrene in the lower limbs. In spite of angioplasty and surgery, CLI patients without suitable artery inflow or enough vascular bed in the lesions are often forced to undergo amputation of a major limb. Cell-based therapeutic angiogenesis has the potential to treat ischemic lesions by promoting the formation of collateral vessel networks and the vascular bed. Peripheral blood mononuclear cells and bone marrow-derived mononuclear cells are the most frequently employed cell types in CLI clinical trials. However, the clinical outcomes of cell-based therapeutic angiogenesis using these cells have not provided the promised benefits for CLI patients, reinforcing the need for novel cell-based therapeutic angiogenesis strategies to cure untreatable CLI patients. Recent studies have demonstrated the possible enhancement of therapeutic efficacy in ischemic diseases by preconditioned graft cells. Moreover, judging from past clinical trials, the identification of adequate transplant timing and responders to cell-based therapy is important for improving therapeutic outcomes in CLI patients in clinical settings. Thus, to establish cell-based therapeutic angiogenesis as one of the most promising therapeutic strategies for CLI patients, its advantages and limitations should be taken into account.

Combinatorial Treatment with Apelin-13 Enhances the Therapeutic Efficacy of a Preconditioned Cell-Based Therapy for Peripheral Ischemia

Hypoxic pretreatment of peripheral blood mononuclear cells (PBMNCs) enhances therapeutic angiogenesis in ischemic tissues after cell transplantation. However, newly formed vessels generated using this approach are immature and insufficient for promoting functional recovery from severe ischemia. In this study, we examined whether apelin-13, a regulator of vessel maturation, could be an effective promoter of therapeutic angiogenesis, following severe limb ischemia. Combinatorial treatment of hypoxic preconditioned PBMNCs with apelin-13 resulted in increased blood perfusion and vascular reactivity in ischemic mouse hindlimbs compared with a monotherapy comprising each factor. Apelin-13 upregulated expression of PDGF-BB and TGF-β1 in hypoxic PBMNCs, as well as that of PDGFR-β in vascular smooth muscle cells (VSMCs). Proliferation and migration of VSMCs treated with apelin-13 was accelerated in the presence of PDGF-BB. Interestingly, expression of an apelin receptor, APJ, in PBMNC was increased under hypoxia but not under normoxia. In addition, an in vitro angiogenesis assay using a co-culture model comprising mouse thoracic aorta, hypoxic PBMNCs, and apelin-13 demonstrated that combinatorial treatment recruited mural cells to sprouted vessel outgrowths from the aortic ring, thereby promoting neovessel maturation. Thus, combinatorial injection of hypoxic PBMNCs and apelin-13 could be an effective therapeutic strategy for patients with severe ischemic diseases.

Stem cell-based therapies to promote angiogenesis in ischemic cardiovascular disease

Stem cell therapy is a promising approach for the treatment of tissue ischemia associated with myocardial infarction and peripheral arterial disease. Stem and progenitor cells derived from bone marrow or from pluripotent stem cells have shown therapeutic benefit in boosting angiogenesis as well as restoring tissue function. Notably, adult stem and progenitor cells including mononuclear cells, endothelial progenitor cells, and mesenchymal stem cells have progressed into clinical trials and have shown positive benefits. In this review, we overview the major classes of stem and progenitor cells, including pluripotent stem cells, and summarize the state of the art in applying these cell types for treating myocardial infarction and peripheral arterial disease.

Coadministration of adipose-derived stem cells and control-released basic fibroblast growth factor facilitates angiogenesis in a murine ischemic hind limb model

OBJECTIVE

Adipose-derived stem cells (ASCs) have angiogenic potential owing to their differentiation into endothelial cells and their release of angiogenic growth factors to elicit paracrine effects. In addition, control-released basic fibroblast growth factor (bFGF) sustained with a gelatin hydrogel also supports effective angiogenesis. We sought to determine if coadministration of ASCs and control-released bFGF into murine ischemic limbs facilitates angiogenesis.

METHODS

Levels of growth factors in the conditioned media of ASCs cultured with or without control-released bFGF were measured by enzyme-linked immunosorbent assays. A murine ischemic hind limb model was generated and intramuscularly injected with the following: gelatin hydrogel (group 1), a high number of ASCs (group 2), control-released bFGF (group 3), a small number of ASCs and control-released bFGF (group 4), and a high number of ASCs and control-released bFGF (group 5). Macroscopic and microscopic vascular changes were evaluated until day 7 by laser Doppler perfusion imaging and histologic analyses, respectively.

RESULTS

Secretion of hepatocyte growth factor, vascular endothelial growth factor, and transforming growth factor-β1 was enhanced by control-released bFGF. Vascular improvement was achieved in groups 4 and 5 according to laser Doppler perfusion imaging. Hematoxylin and eosin staining and CD31 immunohistochemical staining demonstrated an increase in the vascular density, vessel diameter, and thickness of vessel walls in groups 4 and 5. Cells positively stained for CD146, α-smooth muscle actin, and transforming growth factor-β1 were observed around vessel walls in groups 4 and 5.

CONCLUSIONS

These findings suggest that coadministration of ASCs and control-released bFGF facilitates angiogenesis in terms of vessel maturation in a murine ischemic hind limb model.

Gene therapy for peripheral arterial disease

INTRODUCTION

Gene therapy has emerged as a novel therapy to promote angiogenesis in patients with critical limb ischemia (CLI) caused by peripheral artery disease. Researchers working in this area have focused on pro-angiogenic factors, such as VEGF, fibroblast growth factor (FGF) and hepatocyte growth factor (HGF). Based on the elaborate studies and favorable results of basic research using naked plasmid DNA (pDNA) encoding these growth factors, some clinical Phase I and Phase II trials have been performed. The results of these studies demonstrate the safety of these approaches and their potential for symptomatic improvement in CLI patients. However, the Phase III clinical trials have so far been limited to HGF gene therapy. Because one pitfall of the Phase III trials has been the limited transgene expression achieved using naked pDNA alone, the development of more efficient gene transfer systems, such as ultrasound microbubbles and the needleless injector, as well as the addition of other genes will make these novel therapies more effective and ease the symptoms of CLI.

AREAS COVERED

This study reviews the previously published basic research and clinical trials that have studied VEGF, FGF and HGF gene therapies for the treatment of CLI. Adjunctive therapies, such as the addition of prostacyclin synthase genes and the development of more efficient gene transfer techniques for pDNA, are also reviewed.

EXPERT OPINION

To date, clinical studies have demonstrated the safety of gene therapy in limb ischemia but the effectiveness of this treatment has not been determined. Larger clinical studies, as well as the development of more effective gene therapy, are needed to achieve and confirm beneficial effects.

Controlled release strategies for bone, cartilage, and osteochondral engineering--Part I: recapitulation of native tissue healing and variables for the design of delivery systems

The potential of growth factors to stimulate tissue healing through the enhancement of cell proliferation, migration, and differentiation is undeniable. However, critical parameters on the design of adequate carriers, such as uncontrolled spatiotemporal presence of bioactive factors, inadequate release profiles, and supraphysiological dosages of growth factors, have impaired the translation of these systems onto clinical practice. This review describes the healing cascades for bone, cartilage, and osteochondral interface, highlighting the role of specific growth factors for triggering the reactions leading to tissue regeneration. Critical criteria on the design of carriers for controlled release of bioactive factors are also reported, focusing on the need to provide a spatiotemporal control over the delivery and presentation of these molecules.

Nonviral gene therapy targeting cardiovascular system

The goal of gene therapy is either to introduce a therapeutic gene into or replace a defective gene in an individual's cells and tissues. Gene therapy has been urged as a potential method to induce therapeutic angiogenesis in ischemic myocardium and peripheral tissues after extensive investigation in recent preclinical and clinical studies. A successful gene therapy mainly relies on the development of the gene delivery vector. Developments in viral and nonviral vector technology including cell-based gene transfer will further improve transgene delivery and expression efficiency. Nonviral approaches as alternative gene delivery vehicles to viral vectors have received significant attention. Recently, a simple and safe approach of gene delivery into target cells using naked DNA has been improved by combining several techniques. Among the physical approaches, ultrasonic microbubble gene delivery, with its high safety profile, low costs, and repeatable applicability, can increase the permeability of cell membrane to macromolecules such as plasmid DNA by its bioeffects and can provide as a feasible tool in gene delivery. On the other hand, among the promising areas for gene therapy in acquired diseases, ischemic cardiovascular diseases have been widely studied. As a result, gene therapy using advanced technology may play an important role in this regard. The aims of this review focus on understanding the cellular and in vivo barriers in gene transfer and provide an overview of currently used chemical vectors and physical tools that are applied in nonviral cardiovascular gene transfer.

Imaging stem cell therapy for the treatment of peripheral arterial disease

Arteriosclerotic cardiovascular diseases are among the leading causes of morbidity and mortality worldwide. Therapeutic angiogenesis aims to treat ischemic myocardial and peripheral tissues by delivery of recombinant proteins, genes, or cells to promote neoangiogenesis. Concerns regarding the safety, side effects, and efficacy of protein and gene transfer studies have led to the development of cell-based therapies as alternative approaches to induce vascular regeneration and to improve function of damaged tissue. Cell-based therapies may be improved by the application of imaging technologies that allow investigators to track the location, engraftment, and survival of the administered cell population. The past decade of investigations has produced promising clinical data regarding cell therapy, but design of trials and evaluation of treatments stand to be improved by emerging insight from imaging studies. Here, we provide an overview of pre-clinical and clinical experience using cell-based therapies to promote vascular regeneration in the treatment of peripheral arterial disease. We also review four major imaging modalities and underscore the importance of in vivo analysis of cell fate for a full understanding of functional outcomes.

The number and function of circulating CD34(+)CD133(+) progenitor cells decreased in stable coronary artery disease but not in acute myocardial infarction

OBJECTIVE

Circulating CD34(+)CD133(+) cells are one of the main sources of circulating endothelial progenitor cells (EPCs). Age is inversely related to the number and function of CD34(+)CD133(+) progenitor cells in stable coronary artery disease (CAD), but the relationship remains unclear in acute myocardial infarction (AMI). The authors aimed to clarify how ageing affects the number and function of mobilised CD34(+)CD133(+) progenitor cells in AMI.

DESIGN AND RESULTS

Circulating CD34(+)CD133(+) progenitor cells were measured by flow cytometry. Measurements were made at admission for CAD, or on day 7 after the onset of AMI. In stable CAD (n=131), circulating CD34(+)CD133(+) cells decreased with age (r=-0.344, p<0.0001). In AMI, circulating CD34(+)CD133(+) cells did not correlate with age (n=50), and multivariate analysis revealed that the decreased number of circulating CD34(+)CD133(+) cells was associated with male sex and higher peak creatinine kinase. The ability to give rise to functional EPCs, which show good migratory and tube-forming capabilities, deteriorated among stable CAD subjects (n=10) compared with AMI subjects (N=6).

CONCLUSIONS

In stable CAD, the number and function of circulating CD34(+)CD133(+) progenitor cells decreased with age, whereas those mobilised and circulating in AMI did not.

Nanoparticle-mediated endothelial cell-selective delivery of pitavastatin induces functional collateral arteries (therapeutic arteriogenesis) in a rabbit model of chronic hind limb ischemia

OBJECTIVES

We recently demonstrated in a murine model that nanoparticle-mediated delivery of pitavastatin into vascular endothelial cells effectively increased therapeutic neovascularization. For the development of a clinically applicable approach, further investigations are necessary to assess whether this novel system can induce the development of collateral arteries (arteriogenesis) in a chronic ischemia setting in larger animals.

METHODS

Chronic hind limb ischemia was induced in rabbits. They were administered single injections of nanoparticles loaded with pitavastatin (0.05, 0.15, and 0.5 mg/kg) into ischemic muscle.

RESULTS

Treatment with pitavastatin nanoparticles (0.5 mg/kg), but not other nanoparticles, induced angiographically visible arteriogenesis. The effects of intramuscular injections of phosphate-buffered saline, fluorescein isothiocyanate (FITC)-loaded nanoparticles, pitavastatin (0.5 mg/kg), or pitavastatin (0.5 mg/kg) nanoparticles were examined. FITC nanoparticles were detected mainly in endothelial cells of the ischemic muscles for up to 4 weeks. Treatment with pitavastatin nanoparticles, but not other treatments, induced therapeutic arteriogenesis and ameliorated exercise-induced ischemia, suggesting the development of functional collateral arteries. Pretreatment with nanoparticles loaded with vatalanib, a vascular endothelial growth factor receptor (VEGF) tyrosine kinase inhibitor, abrogated the therapeutic effects of pitavastatin nanoparticles. Separate experiments with mice deficient for VEGF receptor tyrosine kinase demonstrated a crucial role of VEGF receptor signals in the therapeutic angiogenic effects.

CONCLUSIONS

The nanotechnology platform assessed in this study (nanoparticle-mediated endothelial cell-selective delivery of pitavastatin) may be developed as a clinically feasible and promising strategy for therapeutic arteriogenesis in patients.

Gene transfer into human cord blood-derived CD34(+) cells by adeno-associated viral vectors

OBJECTIVE

Bone marrow-derived CD34(+) cells are currently used in clinical trials in patients with ischemic heart disease. An option to enhance activity of injected progenitors may be offered by genetic engineering of progenitor cells with angiogenic growth factors. Recombinant adeno-associated viral vectors (rAAV) have emerged as a leading gene transfer systems. In contrast to other vector systems in use for genetic engineering of CD34(+) cells, rAAV-mediated gene expression does not depend on vector integration. This is relevant for application in regenerative medicine of ischemic tissues, where transient transgene expression is likely sufficient to achieve therapeutic benefits.

MATERIALS AND METHODS

We compared three different human AAV serotypes, packaged as pseudotypes by a helper virus-free production method, for their transduction efficiency in human cord blood-derived CD34(+) cells. We further assessed the impact of vector genome conformation, of alpha(v)beta(5) and alpha(5)beta(1) integrin availability and of the transcription-modulating drugs retinoic acid and Trichostatin A on rAAV-mediated human CD34(+) cell transduction.

RESULTS

We provide, for the first time, evidence that hCD34(+) cells can be reproducibly transduced with high efficiency by self-complementary rAAV2 without inducing cytotoxicity or interfering with their differentiation potential. We further show the involvement of alpha(5)beta(1) integrin as a crucial AAV2 internalization receptor and a function for transcription-modulating drugs in enhancing rAAV-mediated transgene expression.

CONCLUSION

This study represents a first step toward translation of a combined cellular/rAAV-based therapy of ischemic disease.

Regenerative medicine in the treatment of peripheral arterial disease

The last decade has witnessed a dramatic increase in the mechanistic understanding of angiogenesis and arteriogenesis, the two processes by which the body responds to obstruction of large conduit arteries. This knowledge has been translated into novel therapeutic approaches to the treatment of peripheral arterial disease, a condition characterized by progressive narrowing of lower extremity arteries and heretofore solely amenable to surgical revascularization. Clinical trials of molecular, genetic, and cell-based treatments for peripheral artery obstruction have generally provided encouraging results.

Regenerative therapy in peripheral artery disease

Patients with peripheral artery disease (PAD) and critical limb ischemia are the main candidates for limb amputations and have a poor life expectancy. Frequently, these patients are not eligible for either surgical or percutaneous interventions aimed at mechanical revascularization. Therefore, new strategies need to be identified to offer these patients a viable therapeutic option. Gene and cell therapy hold great promise for the treatment of peripheral vascular diseases because, in animal models, local delivery of growth factors and endothelial progenitor cells result in new blood vessel formation and regeneration of ischemic tissues. In this article, are reviewed phase I and phase II gene, and cell therapy clinical trials in patients with PAD.

Locally delivered growth factor enhances the angiogenic efficacy of adipose-derived stromal cells transplanted to ischemic limbs

Ischemia is a potentially fatal medical event that is associated with as many as 30% of all deaths. Stem cell therapy offers significant therapeutic promise, but poor survival following transplantation to ischemic tissue limits its efficacy. Here we demonstrate that nanosphere-mediated growth factor delivery can enhance the survival of transplanted human adipose-derived stromal cells (hADSCs) and secretion of human angiogenic growth factors per cell, and substantially improve therapeutic efficacy of hADSCs. In vitro, in hypoxic (1% oxygen) and serum-deprived conditions that simulate in vivo ischemia, fibroblast growth factor-2 (FGF2) significantly reduced hADSC apoptosis and enhanced angiogenic growth factor secretion. In vivo, hADSCs delivered intramuscularly into ischemic hind limbs in combination with FGF2 resulted in significant improvements in limb survival and blood perfusion, as well as survival of the transplanted hADSCs and secretion of human angiogenic growth factors (i.e., vascular endothelial growth factor, hepatocyte growth factor, and FGF2). Interestingly, the majority of transplanted hADSCs were localized adjacent to the microvessels rather than being incorporated into them, suggesting that their major contribution to angiogenesis might be to increase paracrine secretion of angiogenic growth factors. This study demonstrates the potential of hADSCs in combination with growth factors for use in the treatment of ischemia.

Synergistic effects of autologous cell and hepatocyte growth factor gene therapy for neovascularization in a murine model of hindlimb ischemia

Autologous cell implantation and angiogenic gene therapy have been evaluated in critical limb ischemic patients. Here, we compared the features of these strategies individually and in combination. C57BL/6J mice with ischemic hindlimbs were injected with adherent mononuclear cells (aMNCs) from bone marrow or adenovirus encoding the hepatocyte growth factor (HGF) gene (Ad-HGF). Under comparable angiogenic conditions, 10 × 105 aMNCs produced significantly higher amounts of VEGF and FGF-2 and stimulated the number of arterioles in ischemic muscle compared with 1 × 108 plaque-forming units (pfu) of Ad-HGF. Ad-HGF produced 10 times more HGF in ischemic muscle compared with aMNCs. Injection of 0.3 × 105 aMNCs previously transfected with Ad-HGF (aMNC/Ad-HGF) increased blood flow and elevated the numbers of capillaries and arterioles to levels comparable with that seen with 10 × 105 aMNCs or 1 × 108 pfu of Ad-HGF. Hypoxic conditions induced the apoptotic death of aMNCs. However, coincubation with HGF or aMNC/Ad-HGF protected cells against apoptosis. HGF stimulated the migration of aMNCs, and the migration capacity of the aMNC/Ad-HGF group was significantly higher than that in the aMNC/Ad-LacZ group. In conclusion, cell-based HGF gene therapy decreased the number of cells required for neovascularization. This strategy can be an effective angiogenic therapy.

Erythropoietin augments the efficacy of therapeutic angiogenesis induced by allogenic bone marrow stromal cells in a rat model of limb ischemia

Transplantation of adult marrow stromal cells (MSCs) has been developed as a new method of treating severe ischemia diseases by therapeutic angiogenesis. Erythropoietin (EPO) is capable of inducing angiogenesis and inhibiting MSCs apoptosis. The effect of EPO on the therapeutic potency of MSCs transplantation in a rat model of limb ischemia was investigated in the current study. The results indicate that the combined treatment with MSC transplantation and EPO infusion is superior to MSC transplantation alone in the treatment of limb ischemia. MSCs transplantation and EPO infusion could enhance the angiogenic effect of each other to achieve a better therapeutic effect. This combination therapy may become a more effective approach for ischemia diseases of the limbs.

Coadministration of endothelial and smooth muscle progenitor cells enhances the efficiency of proangiogenic cell-based therapy

Cell-based therapy is a promising approach designed to enhance neovascularization and function of ischemic tissues. Interaction between endothelial and smooth muscle cells regulates vessels development and remodeling and is required for the formation of a mature and functional vascular network. Therefore, we assessed whether coadministration of endothelial progenitor cells (EPCs) and smooth muscle progenitor cells (SMPCs) can increase the efficiency of cell therapy. Unilateral hindlimb ischemia was surgically induced in athymic nude mice treated with or without intravenous injection of EPCs (0.5 x 10(6)), SMPCs (0.5 x 10(6)) and EPCs+SMPCs (0.25 x 10(6)+0.25 x 10(6)). Vessel density and foot perfusion were increased in mice treated with EPCs+SMPCs compared to animals receiving EPCs alone or SMPCs alone (P<0.001). In addition, capillary and arteriolar densities were enhanced in EPC+SMPC-treated mice compared to SMPC and EPC groups (P<0.01). We next examined the role of Ang-1/Tie2 signaling in the beneficial effect of EPC and SMPC coadministration. Small interfering RNA directed against Ang-1-producing SMPCs or Tie2-expressing EPCs blocked vascular network formation in Matrigel coculture assays, reduced the rate of incorporated EPCs within vascular structure, and abrogated the efficiency of cell therapy. Production of Ang-1 by SMPCs activates Tie2-expressing EPCs, resulting in increase of EPC survival and formation of a stable vascular network. Subsequently, the efficiency of EPC- and SMPC-based cotherapy is markedly increased. Therefore, coadministration of different types of vascular progenitor cells may constitute a novel therapeutic strategy for improving the treatment of ischemic diseases.

Emerging hurdles in stem cell therapy for peripheral vascular disease

Peripheral vascular disease (PVD) is a growing medical problem in Western societies and presents itself mainly in two different clinical forms. Intermittent claudication is an early moderate manifestation, while patients with critical limb ischemia suffer from severe muscle tissue loss or ulcers and are at high risk for limb amputation. Unfortunately, many patients cannot be helped with currently available surgical or endovascular revascularization procedures because of the complex anatomy of the vascular occlusion and/or the presence of other risk factors. Noninvasive stem cell therapy has been proposed as an alternative for such patients. Although pioneering clinical experience with stem cell-related therapy seems promising, it is too early for general clinical use of this technique, since many questions remain unanswered. Indeed, while questions about safety, dose, and administration route/timing/frequency are the first ones to be addressed when designing a stem cell-based clinical approach, there is accumulating evidence from recent (pre-)clinical studies that other issues may also be at stake. For instance, the choice of stem cells to be used and its precise mechanism of action, the need/possibility for concurrent tissue regeneration in case of irreversible tissue loss, the differentiation degree and specific vascular identity of the transplanted cells, and the long-term survival of engrafted cells in the absence of a normal supportive tissue environment should be well considered. Here, rather than presenting a comprehensive and extensive overview on the current literature on stem/progenitor cells and revascularization, we highlight some of the outstanding issues emerging from the recent (pre-)clinical literature that may codetermine the successful application of stem cells in a wide range of PVD patients in the future.

PlGF-MMP-9-expressing cells restore microcirculation and efficacy of cell therapy in aged dystrophic muscle

Sclerosis and reduced microvessel density characterize advanced stages of muscular dystrophy and hamper cell or gene delivery, precluding treatment of most individuals with Duchenne muscular dystrophy. Modified tendon fibroblasts expressing an angiogenic factor (placenta growth factor, PlGF) and a metalloproteinase (matrix metalloproteinase-9, MMP-9) are able to restore a vascular network and reduce collagen deposition, allowing efficient cell therapy in aged dystrophic mice. These data open the possibility of extending new therapies to currently untreatable individuals.

Dramatic regulation of heparanase activity and angiogenesis gene expression in synovium from patients with rheumatoid arthritis

OBJECTIVE

Although heparanase is recognized as a proangiogenic factor, the involvement of heparanase in rheumatoid arthritis (RA) is unclear. In this study, we assessed heparanase activity in synovial fluid (SF) and synovial tissue (ST) from patients with RA or osteoarthritis (OA), and analyzed the expression of angiogenic pathway-focused genes in ST from RA and OA patients.

METHODS

SF and ST were obtained from the knees of patients with either RA or OA and from asymptomatic donors with no documented history of degenerative or inflammatory joint diseases. Heparanase activity was determined by an enzymatic assay using a radiolabeled substrate, and the presence of heparanase in ST was demonstrated by Western blotting. The expression of angiogenesis genes, including heparanase, in ST was analyzed by real-time quantitative polymerase chain reaction.

RESULTS

Heparanase activity was dramatically higher (>100-fold) in SF and ST from RA patients than in SF and ST from OA patients and asymptomatic donors. Active heparanase enzyme was detected and heparanase messenger RNA was up-regulated in ST from RA patients. We also found that angiogenesis gene expression was significantly regulated in RA synovium, and was correlated with heparanase activity.

CONCLUSION

These findings are novel and contribute to our understanding of joint destruction in RA, suggesting that heparanase may be a reliable prognostic factor for RA progression and an attractive target for the treatment of RA.

Improvement of Postnatal Neovascularization by Human Embryonic Stem Cell–Derived Endothelial-Like Cell Transplantation in a Mouse Model of Hindlimb Ischemia

Background— We established an efficient preparation method to obtain endothelial-like cells (ECs) from human embryonic stem cells (hESCs) and tested whether these hESC-ECs would show therapeutic potential for treatment of hindlimb ischemia.

Methods and Results— ECs differentiated from hESCs were obtained by mechanical isolation and cell sorting for von Willebrand factor. The isolated hESC-ECs maintained endothelial cell–specific characteristics such as endothelial marker expression and capillary formation. One day after surgical induction of hindlimb ischemia in athymic mice, hESC-ECs were injected intramuscularly into ischemic limbs. Four weeks after treatment, hESC-EC treatment significantly increased limb salvage (36%) compared with treatment with medium (0%). In addition, laser Doppler imaging showed that the ratio of blood perfusion (ischemic to normal limb) was increased significantly ( P <0.01) by hESC-EC treatment (0.511±0.167) compared with medium injection (0.073±0.061). Capillary and arteriole densities were 658±190/mm 2 and 30±11/mm 2 in the hESC-EC group, respectively, whereas those in the medium group were 392±118/mm 2 and 16±8/mm 2 , respectively ( P <0.01). Reverse-transcription polymerase chain reaction with human-specific primers revealed mRNA expression of human endothelial markers and human angiogenic factors in ischemic mouse tissues. The transplanted hESC-ECs were localized as capillaries near muscle tissues in ischemic regions or incorporated in the vessels between muscle tissues, as confirmed by human nuclear antigen staining with platelet/endothelial cell adhesion molecule or von Willebrand factor.

Conclusions— This study demonstrates that hESC-EC transplantation improves blood perfusion and limb salvage by facilitating postnatal neovascularization in a mouse model of hindlimb ischemia. Thus, hESC-ECs might be useful as an alternative cell source for angiogenic therapy.

Engineering blood vessels by gene and cell therapy

Cardiovascular-related syndromes are the leading cause of morbidity and mortality worldwide. Arterial narrowing and blockage due to atherosclerosis cause reduced blood flow to the brain, heart and legs. Bypass surgery to improve blood flow to the heart and legs in these patients is performed in hundreds of thousands of patients every year. Autologous grafts, such as the internal thoracic artery and saphenous vein, are used in most patients, but in a significant number of patients such grafts are not available and synthetic grafts are used. Synthetic grafts have higher failure rates than autologous grafts due to thrombosis and scar formation within graft lumen. Cell and gene therapy combined with tissue engineering hold a great promise to provide grafts that will be biocompatible and durable. This review describes the field of vascular grafts in the context of tissue engineering using cell and gene therapies.

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.

Bone marrow cell-mediated cardiovascular repair: potential of combined therapies

Recent evidence indicates that bone-marrow cells (BMCs) can contribute to the healing process of the injured cardiovascular system via the chemokine receptor CXCR4/SDF-1, thymosin beta(4) and integrin alpha(4)beta(1) molecular pathways. During tissue ischemia overwhelming numbers of detrimental oxygen radicals are generated, and therefore treatment with antioxidants and L-arginine, the precursor of nitric oxide (NO), could induce beneficial effects beyond those achieved by BMC transplantation alone. Recent studies have reported that BMCs have enhanced neovascularization capacity in cotreatment with alpha-tocopherol (vitamin E), ascorbic acid (vitamin C) and L-arginine. Moreover, BMC therapy can be combined with gene therapy. Clinical trials employing BMCs in the treatment of cardiovascular diseases have been completed with mixed or positive results, and several trials are ongoing. Here, we discuss the clinical potential of BMC transplantation alone and in combined therapy that aims to restore organ vascularization and function. We also consider the mechanisms of mobilization, differentiation and incorporation of BMCs.

A role for the aryl hydrocarbon receptor in regulation of ischemia-induced angiogenesis

OBJECTIVE

The aryl hydrocarbon receptor (AHR) is a transcription factor that binds to DNA as a heterodimer with the AHR nuclear translocator (ARNT) after interaction with ligands such as polycyclic and halogenated aromatic hydrocarbons found in tobacco smoke and the environment. We have investigated the interaction between AHR and hypoxia signaling pathways in regulation of angiogenesis with the use of a surgical model of ischemia.

METHODS AND RESULTS

Ischemia was induced by femoral artery occlusion in wild-type and AHR-null mice. Ischemia-induced angiogenesis was markedly enhanced in AHR-null mice compared with that in wild-type animals. Ischemia-induced upregulation of the expression of hypoxia-inducible factor-1alpha (HIF-1alpha) and ARNT as well as that of target genes for these transcription factors, such as that for vascular endothelial growth factor (VEGF), were also enhanced in AHR-null mice. Furthermore, the DNA binding activity of the HIF-1alpha-ARNT complex as well as the association of HIF-1alpha and ARNT with the VEGF gene promoter were increased by ischemia to a greater extent in AHR-null mice than in wild-type animals.

CONCLUSIONS

Ablation of AHR resulted in enhancement of ischemia-induced angiogenesis. This effect was likely attributable in part to the associated enhancement of ischemia-induced VEGF expression, which in turn may be caused by an increased abundance and activity of the HIF-1alpha-ARNT heterodimer.

New vectors and strategies for cardiovascular gene therapy

Cardiovascular diseases are the major cause of morbidity and mortality in both men and women in industrially developed countries. These disorders may result from impaired angiogenesis, particularly in response to hypoxia. Despite many limitations, gene therapy is still emerging as a potential alternative for patients who are not candidates for traditional revascularization procedures, like angioplasty or vein grafts. This review focuses on recent approaches in the development of new gene delivery vectors, with great respect to newly discovered AAV serotypes and their modified forms. Moreover, some new cardiovascular gene therapy strategies have been highlighted, such as combination of different angiogenic growth factors or simultaneous application of genes and progenitor cells in order to obtain stable and functional blood vessels in ischemic tissue.