Polymeric gene delivery of ischemia-inducible VEGF significantly attenuates infarct size and apoptosis following myocardial infarct

Gene Therapy for Cardiovascular Disease: Clinical Perspectives

Cardiovascular disease (CVD) stands as one of the leading causes of death in the United States, with its prevalence steadily on the rise. Traditional therapeutic approaches, such as pharmacological treatment, cardiovascular intervention, and surgery, have inherent limitations. In response to these challenges, cardiac gene therapy has emerged as a promising alternative for treating CVD patients. However, several obstacles persist, including the low efficiency of gene transduction, immune reactions to vectors or transduced cells, and the occurrence of off-target effects. While preclinical research has demonstrated significant success in various CVD model in both small and large animals, the translation of these findings to clinical applications has, for the most part, yielded disappointing results, except for some early, albeit small, trials. This review aims to provide a comprehensive summary of recent preclinical and clinical studies on gene therapy for various CVDs. Additionally, we discuss the existing limitations and challenges that hinder the widespread clinical application of cardiac gene therapy.

Do platelets protect the heart against ischemia/reperfusion injury or exacerbate cardiac ischemia/reperfusion injury? The role of PDGF, VEGF, and PAF

BACKGROUND

Acute myocardial infarction (AMI) is one of the main causes of death. It is quite obvious that there is an urgent need to develop new approaches for treatment of AMI.

OBJECTIVE

This review analyzes data on the role of platelets in the regulation of cardiac tolerance to ischemia/reperfusion (I/R).

METHODS

It was performed a search of topical articles using PubMed databases.

FINDINGS

Platelets activated by a cholesterol-enriched diet, thrombin, and myocardial ischemia exacerbate I/R injury of the heart. The P2Y12 receptor antagonists, remote ischemic postconditioning and conditioning alter the properties of platelets. Platelets acquire the ability to increase cardiac tolerance to I/R. Platelet-derived growth factors (PDGFs) increase tolerance of cardiomyocytes and endothelial cells to I/R. PDGF receptors (PDGFRs) were found in cardiomyocytes and endothelial cells. PDGFs decrease infarct size and partially abrogate adverse postinfarction remodeling. Protein kinase C, phosphoinositide 3-kinase, and Akt involved in the cytoprotective effect of PDGFs. Vascular endothelial growth factor increased cardiac tolerance to I/R and alleviated adverse postinfarction remodeling. The platelet-activating factor (PAF) receptor inhibitors increase cardiac tolerance to I/R in vivo. PAF enhances cardiac tolerance to I/R in vitro. It is possible that PAF receptor inhibitors could protect the heart by blocking PAF receptor localized outside the heart. PAF protects the heart through activation of PAF receptor localized in cardiomyocytes or endothelial cells. Reactive oxygen species and kinases are involved in the cardioprotective effect of PAF.

CONCLUSION

Platelets play an important role in the regulation of cardiac tolerance to I/R.

Polyethylenimine (PEI) in gene therapy: Current status and clinical applications

Polyethlyenimine (PEI) was introduced 1995 as a cationic polymer for nucleic acid delivery. PEI and its derivatives are extensively used in basic research and as reference formulations in the field of polymer-based gene delivery. Despite its widespread use, the number of clinical applications to date is limited. Thus, this review aims to consolidate the past applications of PEI in DNA delivery, elucidate the obstacles that hinder its transition to clinical use, and highlight potential prospects for novel iterations of PEI derivatives. The present review article is divided into three sections. The first section examines the mechanism of action employed by PEI, examining fundamental aspects of cellular delivery including uptake mechanisms, release from endosomes, and transport into the cell nucleus, along with potential strategies for enhancing these delivery phases. Moreover, an in-depth analysis is conducted concerning the mechanism underlying cellular toxicity, accompanied with approaches to overcome this major challenge. The second part is devoted to the in vivo performance of PEI and its application in various therapeutic indications. While systemic administration has proven to be challenging, alternative localized delivery routes hold promise, such as treatment of solid tumors, application as a vaccine, or serving as a therapeutic agent for pulmonary delivery. In the last section, the outcome of completed and ongoing clinical trials is summarized. Finally, an expert opinion is provided on the potential of PEI and its future applications. PEI-based formulations for nucleic acid delivery have a promising potential, it will be an important task for the years to come to introduce innovations that address PEI-associated shortcomings by introducing well-designed PEI formulations in combination with an appropriate route of administration.

Cardiac aorta-derived extracellular matrix scaffold enhances critical mediators of angiogenesis in isoproterenol-induced myocardial infarction mice

An incapability to improve lost cardiac muscle caused by acute ischemic injury remains the most important deficiency of current treatments to prevent heart failure. We investigated whether cardiomyocytes culturing on cardiac aorta-derived extracellular matrix scaffold has advantageous effects on cardiomyocytes survival and angiogenesis biomarkers' expression. Ten male NMRI mice were randomly divided into two groups: (1) control (healthy mice) and (2) myocardial infarction (MI)-induced model group (Isoproterenol/subcutaneously injection/single dose of 85 mg/kg). Two days after isoproterenol injection, all animals were sacrificed to isolate cardiomyocytes from myocardium tissues. The fresh thoracic aorta was obtained from male NMRI mice and decellularized using 4% sodium deoxycholate and 2000 kU DNase-I treatments. Control and MI-derived cardiomyocytes were seeded on decellularized cardiac aorta (DCA) considered three-dimensional (3D) cultures. To compare, the isolated cardiomyocytes from control and MI groups were also cultured as a two-dimensional (2D) culture system for 14 days. The cell viability was examined by MTT assay. The expression levels of Hif-1α and VEGF genes and VEGFR1 protein were tested by real-time PCR and western blotting, respectively. Moreover, the amount of VEGF protein was evaluated in the conditional media of the 2D and 3D systems. The oxidative stress was assessed via MDA assay. Hif-1α and VEGF genes were downregulated in MI groups compared to controls. However, the resulting data showed that decellularized cardiac aorta matrices positively affect the expression of Hif-1α and VEGF genes. The expression level of VEGFR1 protein was significantly (p ≤ 0.01) upregulated in both MI and healthy cell groups cultured on decellularized cardiac aorta matrices as a 3D system compared to the MI cell group cultured in the 2D systems. Furthermore, MDA concentration significantly decreased in 3D-cultured cells (MI and healthy cell groups) rather than the 2D-cultured MI group (p ≤ 0.015). The findings suggest that cardiac aorta-derived extracellular scaffold by preserving VEGF, improving the cell viability, and stimulating angiogenesis via upregulating Hif-1α, VEGF, and VEGFR1 in cardiomyocytes could be considered as a potential approach along with another therapeutic method to reduce the complications of myocardial infarction and control the progressive pathological conditions related to MI.

Dual-Functional Dendrimer Micelles with Glycyrrhizic Acid for Anti-Inflammatory Therapy of Acute Lung Injury

Dendrimer micelles with glycyrrhizic acid (GA) were developed for anti-inflammatory therapy of acute lung injury (ALI). Cholesterol was conjugated to histidine- and arginine-grafted polyamidoamine (PamHR) for micelle formation. The cholesterol-conjugated PamHR (PamHRchol) was mixed with amphiphilic GA to produce PamHRchol/GA mixed micelles. The GA integrated into the micelles had two functions: it acted as an anti-inflammatory drug and facilitated intracellular gene delivery. The PamHRchol/GA micelles formed stable complexes with plasmid DNA. Integrating GA into the micelles increased their transfection efficiency. Confocal microscopy and flow-cytometry studies confirmed that the PamHRchol/GA micelles improved cellular uptake compared with PamHRchol. A competition assay with free GA suggested that the enhanced transfection efficiency of the micelles might be due to the interaction between GA and its receptor. In addition, GA has a membrane-destabilizing effect, and a chloroquine pretreatment assay confirmed that GA increased endosomal escape. Furthermore, the PamHRchol/GA micelles reduced tumor necrosis factor-α in lipopolysaccharide-activated Raw264.7 cells, suggesting a mechanism for its anti-inflammatory effects. To evaluate the therapeutic potential of the PamHRchol/GA micelles, the heme oxygenase-1 (HO-1) gene was delivered into the lungs of mice with ALI. The PamHRchol/GA micelles had higher gene delivery efficiency into the lungs than polyethylenimine (25 kDa, PEI25k) and the PamHRchol micelles. The combined effects of the HO-1 gene and GA produced effective anti-inflammation response in the lungs of the ALI animals. Therefore, the dual-function PamHRchol/GA micelles, which acted as an anti-inflammatory drug and a gene carrier, could be a useful therapy for inflammatory lung diseases.

Long noncoding RNA C2dat1 protects H9c2 cells against hypoxia injury by downregulating miR-22

Myocardial ischemia is accompanied with hypoxia injury in myocardial cells. Long noncoding RNAs (lncRNA) CAMK2D-associated transcript 1 (C2dat1) C2dat1) has been linked with several ischemic diseases. However, the investigation regarding its role in myocardial ischemia is relatively rare. The aim of this study was to examine the role of C2dat1 in hypoxia response in H9c2 cells. H9c2 cells were subjected to hypoxia to evoke cell damage. Expressions of C2dat1, miR-22, and VEGF in H9c2 cells were altered by transfection, and then cell survival, migration, and invasion were respectively assessed posttransfection. Regulatory relationship between C2dat1, miR-22, and VEGF, as well as the involvement of PI3K/AKT/mTOR and JAK/STAT3 pathways in H9c2 cells injury was then studied. C2dat1 upregulation ameliorated hypoxia injury in H9c2 cells due to the increased viability, migration, and invasion, as well as the decreased apoptosis. miR-22 was negatively regulated by C2dat1. The effects of C2dat1 on H9c2 cells injured by hypoxia were attenuated when miR-22 was overexpressed. VEGF was a target gene of miR-22, and VEGF exerted similar protective effects to C2dat1. Finally, we found that silence of C2dat1 deactivated PI3K/AKT/mTOR and JAK/STAT3 pathways via regulating miR-22 and its downstream gene VEGF. C2dat1-miR-22-VEGF axis could regulate hypoxia injury in H9c2 cells. C2dat1 alleviated hypoxia injury possibly via downregulating miR-22, then upregulating VEGF, which further enhancing the activation of PI3K/AKT/mTOR and JAK/STAT3 pathways.

Vascular endothelial growth factor gene polymorphisms and coronary heart disease: a systematic review and meta-analysis

We performed this study to better elucidate the relationship between vascular endothelial growth factor (VEGF) polymorphisms and coronary heart disease (CHD). Eligible articles were searched in PubMed, Medline, Embase, Scopus and CNKI. A total of 24 studies containing 6489 CHD patients and 5664 control subjects were analyzed. Our overall and subgroup analyses suggested that rs699947 polymorphism was significantly associated with CHD susceptibility in both Caucasians and Asians, rs1570360 polymorphism was significantly associated with CHD susceptibility in Caucasians, and rs3025039 polymorphism was significantly associated with CHD susceptibility in Asians. Besides, rs3025039 polymorphism was significantly correlated with the number of affected coronary arteries, while rs699947 and rs2010963 polymorphisms were significantly correlated with poor collateral circulation in CHD patients. Overall, our findings indicate that VEGF rs699947, rs1570360, and rs3025039 polymorphisms may affect CHD susceptibility. Moreover, VEGF rs699947 and rs2010963 polymorphisms may serve as genetic biomarkers of poor collateral circulation after myocardial ischemia.

Water-Soluble Polymer Assists N-Methyl-D-Aspartic Acid Receptor 2B siRNA Delivery to Relieve Chronic Inflammatory Pain In Vitro and In Vivo

We constructed a water-soluble lipopolymer (WSLP) as a nonviral gene carrier to deliver siRNA targeting NR2B. The cytotoxicity and serum stability of WSLP loaded with siRNA were evaluated, and the knockdown efficiency of WSLP/NR2B-siRNA in PC12 cells was examined. The results showed that WSLP could protect the loading siRNAs from enzymatic degradation in serum and exhibit low cytotoxicity to cells. After transfection, WSLP/NR2B-siRNA complexes reduced the NR2B transcriptional level by 50% and protein level by 55% compared to control siRNA. Moreover, 3 days after intrathecal injection of WSLP/NR2B-siRNA complexes into rats, the NR2B protein expression decreased significantly to 58%, compared to control treatment (p < 0.01). Injection of WSLP with scrambled siRNA or of polyethylenimine (PEI) with NR2B-siRNA did not show this inhibitory effect. Additionally, injection of WSLP/NR2B-siRNA complexes significantly relieved inflammatory pain in rats at 3, 4, and 5 days with reduced MWT and decreased TWL scores, while injection of WSLP with scrambled siRNA or of PEI with NR2B-siRNA did not. These results demonstrated that WSLP can efficiently deliver siRNA targeting NR2B to PC12 cells and relieve pain in rats with chronic inflammatory pain.

Gene delivery of hypoxia-inducible VEGF targeting collagen effectively improves cardiac function after myocardial infarction

Vascular endothelial growth factor (VEGF) plays important roles in improvement of cardiac function following myocardial infarction (MI). However, the lack of a steerable delivery system of VEGF targeting the infarcted myocardium reduces the therapeutic efficacy and safety. Here, we constructed a series of lentiviral vector systems which could express a fusion protein consisted of a collagen-binding domain (CBD) and hVEGF (CBDhVEGF), under the control of 5HRE-hCMVmp (5HRE), the hypoxia-inducible promoter consists of five copies of the hypoxia-responsive element (HRE) and a human cytomegalovirus minimal promoter (hCMVmp). We demonstrated that 5HRE has the comparable ability to strongly drive CBDhVEGF under hypoxic condition as the ubiquitous CMV promoter, but it can hardly drive target gene under normoxic condition. 5HRE-drived CBDhVEGF specifically bound to type I collagen and significantly promoted the viability of HUVEC cells. Moreover, after injection of lentivirus into heart of mouse with MI, CBDhVEGF was mainly retained in infarcted myocardium where containing rich collagen and significantly improved angiogenesis and cardiac function when compared with hVEGF. Moreover, CBDhVEGF mediated by lentivirus has little leakage from infarcted zone into blood than hVEGF. Taken together, our results indicate that 5HRE-CBDhVEGF lentiviral vector system could improve cardiac function in the collagen-targeting and hypoxia-inducible manners.

Gene delivery nanoparticles to modulate angiogenesis

Angiogenesis is naturally balanced by many pro- and anti-angiogenic factors while an imbalance of these factors leads to aberrant angiogenesis, which is closely associated with many diseases. Gene therapy has become a promising strategy for the treatment of such a disordered state through the introduction of exogenous nucleic acids that express or silence the target agents, thereby engineering neovascularization in both directions. Numerous non-viral gene delivery nanoparticles have been investigated towards this goal, but their clinical translation has been hampered by issues associated with safety, delivery efficiency, and therapeutic effect. This review summarizes key factors targeted for therapeutic angiogenesis and anti-angiogenesis gene therapy, non-viral nanoparticle-mediated approaches to gene delivery, and recent gene therapy applications in pre-clinical and clinical trials for ischemia, tissue regeneration, cancer, and wet age-related macular degeneration. Enhanced nanoparticle design strategies are also proposed to further improve the efficacy of gene delivery nanoparticles to modulate angiogenesis.

Hypoxia-inducible tumour-specific promoters as a dual-targeting transcriptional regulation system for cancer gene therapy

Transcriptional targeting is the best approach for specific gene therapy. Hypoxia is a common feature of the tumour microenvironment. Therefore, targeting gene expression in hypoxic cells by placing transgene under the control of a hypoxia-responsive promoter can be a good strategy for cancer-specific gene therapy. The hypoxia-inducible gene expression system has been investigated more in suicide gene therapy and it can also be of great help in knocking down cancer gene therapy with siRNAs. However, this system needs to be optimised to have maximum efficacy with minimum side effects in normal tissues. The combination of tissue-/tumour-specific promoters with HRE core sequences has been found to enhance the specificity and efficacy of this system. In this review, hypoxia-inducible gene expression system as well as gene therapy strategies targeting tumour hypoxia will be discussed. This review will also focus on hypoxia-inducible tumour-specific promoters as a dual-targeting transcriptional regulation systems developed for cancer-specific gene therapy.

Leukemia Inhibitory Factor and Fibroblast Growth Factor 2 Critically and Mutually Sustain Pluripotency of Rabbit Embryonic Stem Cells

Effects of leukemia inhibitory factor (LIF) and fibroblast growth factor 2 (FGF2) on establishment and maintenance of rabbit embryonic stem cell (rESC) lines were assessed. When grown on MEF feeders, rESC lines derived from fertilized embryos were established and maintained in medium containing paracrine factors LIF (via STAT3) and/or FGF2 (via MEK-ERK1/2 and PI3K-AKT). However, high levels of ERK1/2 and AKT activities in rESCs were crucial for maintaining their undifferentiated proliferation. Although rESCs under the influence of either LIF (500, 1,000, and 2,000 U/ml) or FGF2 (5, 10, and 20 ng/ml) alone had enhanced expression of pluripotency markers, peak expression occurred when both LIF (1,000 U/ml) and FGF2 (10 ng/ml) were applied. Induced dephosphorylation of STAT3, ERK1/2, and AKT by specific inhibitors limited growth of rESCs and caused remarkable losses of self-renewal capacity; therefore, we inferred that STAT3, ERK, and AKT had essential roles in maintaining rESC proliferation and self-renewal. We concluded that LIF and FGF2 jointly maintained the undifferentiated state and self-renewal of rESCs through an integrative signaling module.

VEGF-A promotes cardiac stem cell engraftment and myocardial repair in the infarcted heart

BACKGROUND

The objective of this study was to determine whether vascular endothelial growth factor (VEGF)-A subtypes improve cardiac stem cell (CSC) engraftment and promote CSC-mediated myocardial repair in the infarcted heart.

METHODS

CSCs were treated with VEGF receptor (VEGFR) inhibitors, VCAM-1 antibody (VCAM-1-Ab), or PKC-α inhibitor followed by the treatment with VEGF-A. CSC adhesion assays were performed in vitro. In vivo, the PKH26-labeled and VCAM-1-Ab or PKC-α inhibitor pre-treated CSCs were treated with VEGF-A followed by implantation into infarcted rat hearts. The hearts were then collected for measuring CSC engraftment and evaluating cardiac fibrosis and function 3 or 28days after the CSC transplantation.

RESULTS

All three VEGF-A subtypes promoted CSC adhesion to extracellular matrix and endothelial cells. VEGF-A-mediated CSC adhesion required VEGFR and PKCα signaling. Importantly, VEGF-A induced VCAM-1, but not ICAM-1 expression in CSCs through PKCα signaling. In vivo, VEGF-A promoted the engraftment of CSCs in infarcted hearts, which was attenuated by PKCα inhibitor or VCAM-1-Ab. Moreover, VEGF-A-mediated CSC engraftment resulted in a reduction in infarct size and fibrosis. Functional studies showed that the transplantation of the VEGF-A-treated CSCs stimulated extensive angiomyogenesis in infarcted hearts as indicated by the expression of cardiac troponin T and von Willebrand factor, leading to an improved performance of left ventricle. Blockade of PKCα signaling or VCAM-1 significantly diminished the beneficial effects of CSCs treated with VEGF-A.

CONCLUSION

VEGF-A promotes myocardial repair through, at least in part, enhancing the engraftment of CSCs mediated by PKCα/VCAM-1 pathway.

Functional polymers of gene delivery for treatment of myocardial infarct

Ischemic heart disease is rapidly growing as the common cause of death in the world. It is a disease that occurs as a result of coronary artery stenosis and is caused by the lack of oxygen within cardiac muscles due to an imbalance between oxygen supply and demand. The conventional medical therapy is focused on the use of drug eluting stents, coronary-artery bypass graft surgery and anti-thrombosis. Gene therapy provides great opportunities for treatment of cardiovascular disease. In order for gene therapy to be successful, the development of proper gene delivery systems and hypoxia-regulated gene expression vectors is the most important factors. Several non-viral gene transfer methods have been developed to overcome the safety problems of viral transduction. Some of which include plasmids that regulate gene expression that is controlled by environment specific promoters in the transcriptional or the translational level. This review explores polymeric gene carriers that target the myocardium and hypoxia-inducible vectors, which regulate gene expression in response to hypoxia, and their application in animal myocardial infarction models.

Role of biomaterials in prevention of in-stent restenosis

Coronary balloon angioplasty and coronary stenting are the procedures used in healing coronary artery disease. However, injury of arteries during angioplasty and stenting causes cell stimulations in tissue. Cell movement and thrombosis lead to re-narrowing of widened vessel called restenosis. Several new types of carriers and technology have been developed to suppress and/or prevent restenosis. Authors review the polymeric materials featured in drug/gene carrier systems, nanovehicles, and stent coating materials against restenosis.

MSC-based VEGF gene therapy in rat myocardial infarction model using facial amphipathic bile acid-conjugated polyethyleneimine

Mesenchymal stem cells (MSCs) have attracted much attention in regenerative medicine owing to their apparent usefulness as multi-potent replacement cells. The potential of MSC therapy can be further improved by transforming MSCs with therapeutic genes that maximize the efficacy of gene therapy and their own therapeutic ability. Since most conventional transfection methodologies have shown marginal success in delivering exogenous genes into primary cultured cells, efficient gene transfer into primary MSCs is a prerequisite for the development of MSC-based gene therapy strategies to achieve repair and regeneration of damaged tissues. Herein, facially amphipathic bile acid-modified polyethyleneimine (BA-PEI) conjugates were synthesized and used to transfer hypoxia-inducible vascular endothelial growth factor gene (pHI-VEGF) in MSCs for the treatment of rat myocardial infarction. Under the optimized transfection conditions, the BA-PEI conjugates significantly increased the VEGF protein expression levels in rat MSCs, compared with traditional transfection methods such as Lipofectamine™ and branched-PEI (25 kDa). Furthermore, the prepared pHI-VEGF-engineered MSCs (VEGF-MSCs) resulted in improved cell viability, particularly during severe hypoxic exposure in vitro. The transplantation of MSCs genetically modified to overexpress VEGF by BA-PEI enhanced the capillary formation in the infarction region and eventually attenuated left ventricular remodeling after myocardial infarction in rats. This study demonstrates the applicability of the BA-PEI conjugates for the efficient transfection of therapeutic genes into MSCs and the feasibility of using the genetically engineered MSCs in regenerative medicine for myocardial infarction.

Emulsion electrospun nanofibers as substrates for cardiomyogenic differentiation of mesenchymal stem cells

The potential of cardiomyogenic differentiation of human mesenchymal stem cells (hMSCs) on emulsion electrospun scaffold containing poly(L-lactic acid)-co-poly-(ε-caprolactone), gelatin and vascular endothelial growth factor (PLCL/GV) was investigated in this study. The characterizations of the scaffold were carried out using scanning electron microscope (SEM), transmission electron microscope, water contact angle and porometer. The proliferation of hMSCs showed that 73.4% higher cell proliferation on PLCL/GV scaffolds than that on PLCL scaffold after 20 days of cell culture. Results of 5-chloromethylfluorescein diacetate staining and SEM morphology analysis indicated that hMSCs differentiated on PLCL/GV scaffolds showed irregular morphology of cardiomyocyte phenotype compared to the typical long and thin hMSC phenotype. Immunostaining results showed the expression of alpha actinin and myosin heavy chain. Our studies identified emulsion electrospinning as a method for fabrication of core-shell fibers suitable for the differentiation of stem cells to cardiac cells, with potential application in cardiac regeneration.

Hypoxia-based strategies for angiogenic induction: the dawn of a new era for ischemia therapy and tissue regeneration

Therapeutic angiogenesis promises to aid the healing and regeneration of tissues suffering from a compromised vascular supply. Ischaemia therapy has so far primarily focused on delivering isolated angiogenic growth factors. The limited success of these strategies in clinical trials, however, is increasingly forcing researchers to recognize the difficulties associated with trying to mimic the angiogenic process, due to its natural complexity. Instead, a new school of thought is gradually emerging, focusing on how to induce angiogenesis at its onset, by utilizing hypoxia, the primary angiogenic stimulus in physiological, as well pathological states. This shift in therapeutic approach is underlined by the realization of the importance of depressed HIF-1 α-mediated gene programming in non-healing ischemic tissues, which could explain their apparent habituation to chronic hypoxic stress and the limited capacity to generate adaptive angiogenesis. Hypoxia-based strategies, then effectively aim to override the habituated angiogenic cellular response, re-start the regenerative process and drive it to completion. Here we make a distinction between those strategies that utilize hypoxia in vitro as a preconditioning tool to optimize the angiogenic potential of tissue/cells before transplantation, vs. strategies that aim to induce hypoxia-induced signaling in vivo, directly, through pharmacological means or gene transfer. We then discuss possible future directions for the field, as it moves into the phase of clinical trials.

Post-translational regulation of a hypoxia-responsive VEGF plasmid for the treatment of myocardial ischemia

Vascular endothelial growth factor (VEGF) gene therapy to promote therapeutic angiogenesis has been advanced as an alternative treatment for myocardial ischemia. The unregulated expression of VEGF and the use of viral vectors, however, have slowed the clinical development of angiogenic gene therapy. The development of clinically beneficial angiogenic gene therapy requires a disease-specific gene expression system and an efficient non-viral gene carrier. To address these requirements, we developed a new post-translationally regulated hypoxia-responsible VEGF plasmid, pβ-SP-ODD-VEGF, and a dendrimer-type bio-reducible polymer, PAM-ABP. The efficacy of VEGF gene therapy with the PAM-ABP/pβ-SP-ODD-VEGF was evaluated and compared to the RTP-VEGF plasmid, a previously constructed hypoxia-inducible plasmid, in an ischemia/reperfusion (I/R) rat model. Cine magnetic resonance imaging was used to analyze the ischemia/reperfusion rats treated with either the PAM-ABP/pβ-SP-ODD-VEGF or the PAM-ABP/RTP-VEGF. The PAM-ABP/pβ-SP-ODD-VEGF treatment more effectively protected cardiomyocytes against apoptosis, preserved left ventricular (LV) function, and prevented LV remodeling compared to the PAM-ABP/RTP-VEGF-treated rats. These results suggest that the pβ-SP-ODD-VEGF with PAM-ABP may be efficacious in the treatment of acute ischemic heart disease.

Irbesartan administration therapeutically influences circulating endothelial progenitor cell and microparticle mobilization by involvement of pro-inflammatory cytokines

Circulating microparticles (MPs) and endothelial progenitor cells (EPCs) correlate with endothelial dysfunction and contribute to the pathogenesis of atherosclerosis. In this context, we explored whether the angiotensin II type I receptor antagonist, irbesartan, exerts a pharmacological control in the atherosclerotic process by the improvement of EPC mobilization and inhibitory effects on MP release and VEGF and SDF-1α levels in the hypertensive-hypercholesterolemic (HH) hamster model. The HH hamsters were treated with irbesartan (50mg/kg b.w/day administered by gavage) for 4 month (HHI). We analyzed MP/EPC infiltration in vascular wall before and after irbesartan administration as well as the endothelial function and expression of VEGF/SDF-1α in plasma and tissue and of molecular pathways activated by them. The results showed that treatment with irbesartan significantly increased EPC infiltration and decreased MP infiltration. The mechanisms underlying this response include the reduction/increase of a number of specific membrane receptors exposed by MPs (TF, P-Selectin, E-Selectin, PSGL-1, Rantes), respectively, by EPCs (β2-Integrins, α4β1-integrin), the augmentation of endothelium-mediated vasodilation and the reduction of protein expression of VEGF/SDF-1α followed by: (1) the diminishment of pro-inflammatory endothelial cytokines: VEGFR1, VEGFR2, CXCR4, Tie2, PIGF with role in EPC homing to sites of damaged endothelium; and (2) the increase of protein expression of COX-2, PGI2 synthase molecules with role in the improvement of arterial wall vasodilatation. In conclusion, the study underlines that irbesartan administration therapeutically improves/reduces EPC, respectively, MP mobilization and this action may be of salutary relevance contributing to its beneficial cardiovascular effects.

Targeted gene delivery to ischemic myocardium by homing peptide-guided polymeric carrier

Myocardial ischemia needs an alternative treatment such as gene therapy for the direct protection of cardiomyocytes against necrosis or apoptosis and to prevent the development of myocardial fibrosis and cardiac dysfunction. Despite the utility of gene therapy, its therapeutic use is limited due to inadequate transfection in cardiomyocytes and difficulty in directing to ischemic myocardium. Here, we present a polymeric gene carrier that is capable of targeting ischemic myocardium, resulting in high localization within the ischemic zone of the left ventricle (LV) of an ischemia/reperfusion (I/R) rat model upon systemic administration. Cystamine bisacrylamide-diamino hexane (CD) polymer was modified with the ischemic myocardium-targeted peptide (IMTP) and D-9-arginine (9R) for dual effects of the homing to ischemic myocardium and enhanced transfection efficiency with minimized polymer use. Conjugation of IMTP and 9R to CD led to an increase in transfection under hypoxia and significantly reduced the amount of polymer required for high transfection. Finally, we confirmed targeting of IMTP-CD-9R/DNA polyplex to ischemic myocardium and enhanced gene expression in LV of the I/R rat after tail vein injection. This study provides a clue that gene therapy for the treatment of myocardial ischemia can be achieved by using homing peptide-guided gene delivery systems.

Post-translational regulated and hypoxia-responsible VEGF plasmid for efficient secretion

Gene therapy using angiogenic genes has emerged as a potentially viable alternative treatment strategy for myocardial ischemia. Non-specific expression of angiogenic genes, however, may result in side effects, including the growth of occult tumors. Regulation of gene expression may help to avoid the occurrence of these side effects. In this study, a plasmid expressing vascular endothelial growth factor (VEGF) was constructed with an oxygen dependent degradation (ODD) domain and a secretion signal peptide (SP) in order to stabilize the VEGF protein and facilitate the secretion of VEGF protein, specifically under hypoxic conditions. We found that this plasmid, pβ-SP-ODD-VEGF, expresses the SP-ODD-VEGF protein at increased levels under hypoxic conditions compared to normoxic conditions. Since the size of the ODD domain is almost the same as that of VEGF, the ODD-VEGF fusion protein may have lower secretion efficiency. To address this issue, a furin recognition site was located between the ODD domain and the VEGF site to facilitate elimination of the SP-ODD domain from the fusion protein before its secretion. This optimizes the likelihood that the VEGF secreted from the target cells will be wild-type VEGF. Treatment with a furin inhibitor reduced the secretion efficiency of the VEGF, indicating that furin digestion increases the secretion of VEGF. The secreted wild-type VEGF facilitated the growth of endothelial cells more efficiently under hypoxic conditions than normoxic conditions. These results suggest that this plasmid, pβ-SP-ODD-VEGF, warrants further study as a more efficient form of hypoxia-inducible gene therapy for the treatment of myocardial ischemia.

Nonviral delivery of genetic medicine for therapeutic angiogenesis

Genetic medicines that induce angiogenesis represent a promising strategy for the treatment of ischemic diseases. Many types of nonviral delivery systems have been tested as therapeutic angiogenesis agents. However, their delivery efficiency, and consequently therapeutic efficacy, remains to be further improved, as few of these technologies are being used in clinical applications. This article reviews the diverse nonviral gene delivery approaches that have been applied to the field of therapeutic angiogenesis, including plasmids, cationic polymers/lipids, scaffolds, and stem cells. This article also reviews clinical trials employing nonviral gene therapy and discusses the limitations of current technologies. Finally, this article proposes a future strategy to efficiently develop delivery vehicles that might be feasible for clinically relevant nonviral gene therapy, such as high-throughput screening of combinatorial libraries of biomaterials.

Nanoparticles targeting the infarcted heart

We report a nanoparticulate system capable of targeting the heart after myocardial infarction (MI). Targeting is based on overexpression of angiotensin II type 1 (AT1) receptor in the infarcted heart. Liposomes 142 nm in diameter were conjugated with a ligand specific to AT1. The nanoparticles were able to specifically target cardiac cells in vitro, and in the infarcted heart after intravenous injection in vivo. This system may be useful for delivering therapeutic agents specifically to the infarcted heart.

Biomaterials to Enhance Stem Cell Function in the Heart

Transplantation of stem cells into the heart can improve cardiac function after myocardial infarction and in chronic heart failure, but the extent of benefit and of reproducibility of this approach are insufficient. Survival of transplanted cells into myocardium is poor, and new strategies are needed to enhance stem cell differentiation and survival in vivo. In this review, we describe how biomaterials can enhance stem cell function in the heart. Biomaterials can mimic or include naturally occurring extracellular matrix and also instruct stem cell function in different ways. Biomaterials can promote angiogenesis, enhance engraftment and differentiation of stem cells, and accelerate electromechanical integration of transplanted stem cells. Biomaterials can also be used to deliver proteins, genes, or small RNAs together with stem cells. Furthermore, recent evidence indicates that the biophysical environment of stem cells is crucial for their proliferation and differentiation, as well as their electromechanical integration. Many approaches in regenerative medicine will likely ultimately require integration of molecularly designed biomaterials and stem cell biology to develop stable tissue regeneration.

Regulatory systems for hypoxia-inducible gene expression in ischemic heart disease gene therapy

Ischemic heart diseases are caused by narrowed coronary arteries that decrease the blood supply to the myocardium. In the ischemic myocardium, hypoxia-responsive genes are up-regulated by hypoxia-inducible factor-1 (HIF-1). Gene therapy for ischemic heart diseases uses genes encoding angiogenic growth factors and anti-apoptotic proteins as therapeutic genes. These genes increase blood supply into the myocardium by angiogenesis and protect cardiomyocytes from cell death. However, non-specific expression of these genes in normal tissues may be harmful, since growth factors and anti-apoptotic proteins may induce tumor growth. Therefore, tight gene regulation is required to limit gene expression to ischemic tissues, to avoid unwanted side effects. For this purpose, various gene expression strategies have been developed for ischemic-specific gene expression. Transcriptional, post-transcriptional, and post-translational regulatory strategies have been developed and evaluated in ischemic heart disease animal models. The regulatory systems can limit therapeutic gene expression to ischemic tissues and increase the efficiency of gene therapy. In this review, recent progresses in ischemic-specific gene expression systems are presented, and their applications to ischemic heart diseases are discussed.

Stem cells and growth factor delivery systems for cardiovascular disease

Coronary (CAD) and peripheral (PAD) artery diseases are major causes of morbidity and mortality, and millions of CAD and PAD patients are treated by various medications, bypass surgery or angioplasty around the world. Such patients might benefit from novel stem cells and tissue engineering strategies aimed at accelerating natural processes of postnatal collateral vessel formation and repairing damaged tissues. By combining three fundamental "tools", namely stem cells, biomaterials and growth factors (GFs), such strategies may enhance the efficacy of cell therapy in several ways: (a) by supplying exogenous stem cells or GFs that stimulate resident cardiac stem cell (CSC) migration, engraftment and commitment to cardiomyocytes, and that induce and modulate arterial response to ischemia; (b) by supporting the maintenance of GFs and transplanted stem cells in the damaged tissues through the use of biocompatible and biodegradable polymers for a period of time sufficient to allow histological and anatomical restoration of the damaged tissue. This review will discuss the potential of combining stem cells and new delivery systems for growth factors, such as vehicle-based delivery strategies or cell-based gene therapy, to facilitate regeneration of ischemic tissues. These approaches would promote the ability of resident CSCs or of exogenous multipotent stem cells such as adipose tissue-derived mesenchymal stem cells (AT-MSCs) to induce the healing of damaged tissue, by recruiting and directing these cells into the damage area and by improving angiogenesis and reperfusion of ischemic tissues.

Biomaterials to gene delivery

It has been over 40 years since I started biomaterials research. This article is a short summary of past research in my laboratory.

VEGF/SDF-1 promotes cardiac stem cell mobilization and myocardial repair in the infarcted heart

AIMS

The objective of this study was to investigate whether vascular endothelial growth factor (VEGF) secreted by mesenchymal stem cells (MSC) improves myocardial survival and the engraftment of implanted MSC in infarcted hearts and promotes recruitment of stem cells through paracrine release of myocardial stromal cell-derived factor-1α (SDF-1α).

METHODS AND RESULTS

VEGF-expressing MSC ((VEGF)MSC)-conditioned medium enhanced SDF-1α expression in heart slices and H9C2 cardiomyoblast cells via VEGF and the vascular endothelial growth factor receptor (VEGFR). The (VEGF)MSC-conditioned medium markedly promoted cardiac stem cell (CSC) migration at least in part via the SDF-1α/CXCR4 pathway and involved binding to VEGFR-1 and VEGFR-3. In vivo, (VEGF)MSC-stimulated SDF-1α expression in infarcted hearts resulted in massive mobilization and homing of bone marrow stem cells and CSC. Moreover, VEGF-induced SDF-1α guided the exogenously introduced CSC in the atrioventricular groove to migrate to the infarcted area, leading to a reduction in infarct size. Functional studies showed that (VEGF)MSC transplantation stimulated extensive angiomyogenesis in infarcted hearts as indicated by the expression of cardiac troponin T, CD31, and von Willebrand factor and improved the left ventricular performance, whereas blockade of SDF-1α or its receptor by RNAi or antagonist significantly diminished the beneficial effects of (VEGF)MSC.

CONCLUSION

Exogenously expressed VEGF promotes myocardial repair at least in part through SDF-1α/CXCR4-mediated recruitment of CSC.

Hypoxia-inducible vascular endothelial growth factor-engineered mesenchymal stem cells prevent myocardial ischemic injury

In the absence of repair mechanisms involving angiogenesis and cardiomyogenesis, loss of cardiomyocytes after myocardial injury is a primary causative factor in the progression toward heart failure. In an effort to reduce ischemic myocardial damage, we investigated the effects on infarcted myocardium of transplantation of genetically modified mesenchymal stem cells (MSCs) that specifically expressed vascular endothelial growth factor (VEGF) under hypoxic conditions. A hypoxia-inducible VEGF expression vector was introduced into MSCs (HI-VEGF-MSCs) using a nonviral delivery method, which were then used for the treatment of ischemic myocardial injury in rats. In HI-VEGF-MSCs, VEGF expression was significantly increased by hypoxia in vitro as compared to normoxia. Likewise, in vivo administration of HI-VEGF-MSCs induced ischemia-responsive VEGF production, leading to a significant increase in myocardial neovascularization after myocardial infarction. When compared with unmodified-MSCs, HI-VEGF-MSCs were retained in infarcted myocardium in greater numbers and remarkably reduced the number of apoptotic cells the infarcted area. Transplantation of HI-VEGF-MSCs resulted in a substantial attenuation of left ventricular remodeling in rat myocardial infarction. This study demonstrates that cell-based gene therapy using genetically engineered MSCs to express VEGF in response to hypoxic stress can be a promising therapeutic strategy for the treatment of ischemic heart disease.

Combined gene therapy with hypoxia-inducible factor-1α and heme oxygenase-1 for therapeutic angiogenesis

Transfection with either hypoxia-inducible factor-1α (HIF-1α) or heme oxygenase-1 (HO-1) gene can induce neovascularization in ischemic tissues. Although expression of transfected HIF-1α gene occurs rapidly, the expressed HIF-1α protein degrades quickly, limiting its therapeutic efficacy. Meanwhile, expressed HO-1 protein does not rapidly undergo degradation, but gene expression occurs a couple of days after transfection, resulting in apoptosis and a delay in angiogenesis in ischemic tissues at the incipient period of HO-1 gene transfection. We hypothesize that combined delivery of HIF-1α and HO-1 gene will enhance antiapoptosis and neovascularization in ischemic tissue compared with HIF-1α or HO-1 single-gene therapy. To test this hypothesis, ischemic mouse hindlimbs were treated with HIF-1α and/or HO-1 gene therapy. The combined gene therapy proved superior to both single-gene therapies, resulting in rapid expression of HIF-1α gene and long-term maintenance of expressed HO-1 protein. The apoptosis in the ischemic region was significantly less, and angiogenic growth factor secretion and angiogenesis were greater in the combined gene therapy than in either of the single-gene therapies. Our results suggest that a combined gene therapy of HIF-1α and HO-1 enhances the transfection of both genes and improves angiogenesis compared with either single-gene therapy.

Effect of hypoxia-inducible VEGF gene expression on revascularization and graft function in mouse islet transplantation

For gene transfer strategies to improve islet engraftment, vascular endothelial growth factor (VEGF) expression should be regulated in a way that matches the transient nature of revascularization with simultaneously avoiding undesirable effects of overexpression. The aim of this study was to investigate the effects of hypoxia-inducible VEGF gene transfer using the RTP801 promoter on islet grafts. We implanted pSV-hVEGF transfected, pRTP801-hVEGF transfected or nontransfected mouse islets under the kidney capsule of streptozotocin-induced diabetic syngeneic mice. Human VEGF immunostaining of day 3 grafts revealed that the pRTP801-hVEGF transfected group had higher hVEGF expression compared with the pSV-hVEGF transfected group. BS-1 staining of day 3 grafts from the pRTP801-hVEGF transfected group showed the highest vascular density, which was comparable with day 6 grafts from the nontransfected group. In 360 islet equivalent (IEQ)-transplantation which reverted hyperglycemia in all mice, the area under the curve of glucose levels during intraperitoneal glucose tolerance test 7 weeks post-transplant was lower in mice transplanted with pRTP801-hVEGF transfected grafts compared with mice transplanted with nontransfected grafts. In 220 IEQ-transplantations, diabetic mice transplanted with pRTP801-hVEGF islets became normoglycemic more rapidly compared with mice transplanted with pSV-hVEGF or nontransfected islets, and diabetes reversal rate after 50 days was 90%, 68%, and 50%, respectively. In conclusion, our results indicate that regulated overexpression of hVEGF in a hypoxia-inducible manner enhances islet vascular engraftment and preserves islet function overtime in transplants.

Bioreducible polymer-transfected skeletal myoblasts for VEGF delivery to acutely ischemic myocardium

Implantation of skeletal myoblasts to the heart has been investigated as a means to regenerate and protect the myocardium from damage after myocardial infarction. While several animal studies utilizing skeletal myoblasts have reported positive findings, results from clinical studies have been mixed. In this study we utilize a newly developed bioreducible polymer system to transfect skeletal myoblasts with a plasmid encoding vascular endothelial growth factor (VEGF) prior to implantation into acutely ischemic myocardium. VEGF has been demonstrated to promote revascularization of the myocardium following myocardial infarction. We report that implanting VEGF expressing skeletal myoblasts into acutely ischemic myocardium produces superior results compared to implantation of untransfected skeletal myoblasts. Skeletal myoblasts expressing secreted VEGF were able to restore cardiac function to non-diseased levels as measured by ejection fraction, to limit remodeling of the heart chamber as measured by end systolic and diastolic volumes, and to prevent myocardial wall thinning. Additionally, arteriole and capillary formation, retention of viable cardiomyocytes, and prevention of apoptosis was significantly improved by VEGF expressing skeletal myoblasts compared to untransfected myoblasts. This work demonstrates the feasibility of using bioreducible cationic polymers to create engineered skeletal myoblasts to treat acutely ischemic myocardium.

Gene therapy for ischemic heart disease

Current pharmacologic therapy for ischemic heart disease suffers multiple limitations such as compliance issues and side effects of medications. Revascularization procedures often end with need for repeat procedures. Patients remain symptomatic despite maximal medical therapy. Gene therapy offers an attractive alternative to current pharmacologic therapies and may be beneficial in refractory disease. Gene therapy with isoforms of growth factors such as VEGF, FGF and HGF induces angiogenesis, decreases apoptosis and leads to protection in the ischemic heart. Stem cell therapy augmented with gene therapy used for myogenesis has proven to be beneficial in numerous animal models of myocardial ischemia. Gene therapy coding for antioxidants, eNOS, HSP, mitogen-activated protein kinase and numerous other anti apoptotic proteins have demonstrated significant cardioprotection in animal models. Clinical trials have demonstrated safety in humans apart from symptomatic and objective improvements in cardiac function. Current research efforts are aimed at refining various gene transfection techniques and regulation of gene expression in vivo in the heart and circulation to improve clinical outcomes in patients that suffer from ischemic heart disease. In this review article we will attempt to summarize the current state of both preclinical and clinical studies of gene therapy to combat myocardial ischemic disease. This article is part of a Special Section entitled "Special Section: Cardiovascular Gene Therapy".

Women and heart disease--physiologic regulation of gene delivery and expression: bioreducible polymers and ischemia-inducible gene therapies for the treatment of ischemic heart disease

Ischemic heart disease (IHD) is the leading cause of death in the United States today. This year over 750,000 women will have a new or recurrent myocardial infarction. Currently, the mainstay of therapy for IHD is revascularization. Increasing evidence, however, suggests that revascularization alone is insufficient for the longer-term management of many patients with IHD. To address these issues, innovative therapies that extend beyond revascularization to protection of the myocyte and preservation of ventricular function are required. The emergence of gene therapy and proteomics offers the potential for innovative prophylactic and treatment strategies for IHD. The goal of our research is to develop therapeutic gene constructs for the treatment of myocardial ischemia that are clinically safe and effective. Toward this end, we describe the development of physiologic regulation of gene delivery and expression using bioreducible polymers and ischemia-inducible gene therapies for the potential treatment of ischemic heart disease in women.

Hypoxia-specific gene expression for ischemic disease gene therapy

Gene therapy for ischemic diseases has been developed with various growth factors and anti-apoptotic genes. However, non-specific expression of therapeutic genes may induce deleterious side effects such as tumor formation. Hypoxia-specific regulatory systems can be used to regulate transgene expression in hypoxic tissues, in which gene expression is induced in ischemic tissues, but reduced in normal tissues by transcriptional, translational or post-translational regulation. Since hypoxia-inducible factor 1 (HIF-1) activates transcription of genes in hypoxic tissues, it can play an important role in the prevention of myocardial and cerebral ischemia. Hypoxia-specific promoters including HIF-1 binding sites have been used for transcriptional regulation of therapeutic genes. Also, hypoxia-specific untranslated regions (UTRs) and oxygen dependent degradation (ODD) domains have been investigated for translational and post-translational regulations, respectively. Hypoxia-specific gene expression systems have been applied to various ischemic disease models, including ischemic myocardium, stroke, and injured spinal cord. This review examines the current status and future challenges of hypoxia-specific systems for safe and effective gene therapy of ischemic diseases.

Novel polymer carriers and gene constructs for treatment of myocardial ischemia and infarction

The number one cause of mortality in the US is cardiovascular related disease. Future predictions do not see a reduction in this rate especially with the continued rise in obesity [P. Poirier, et al., Obesity and cardiovascular disease: pathophysiology, evaluation, and effect of weight loss, Arterioscler Thromb Vasc Biol. 26(5), (2006) 968-976.; K. Obunai, S. Jani, G.D. Dangas, Cardiovascular morbidity and mortality of the metabolic syndrome, Med.Clin. North Am., 91(6), (2007) 1169-1184]. Even so, potential molecular therapeutic targets for cardiac gene delivery are in no short supply thanks to continuing advances in molecular cardiology. However, efficient and safe delivery remains a bottleneck in clinical gene therapy [O.J. Muller, H.A. Katus, R. Bekeredjian, Targeting the heart with gene therapy-optimized gene delivery methods, Cardiovasc Res, 73(3), (2007) 453-462]. Viral vectors are looked upon favorably for their high transduction efficiency, although their ability to elicit toxic immune responses remains [C.F. McTiernan, et al., Myocarditis following adeno-associated viral gene expression of human soluble TNF receptor (TNFRII-Fc) in baboon hearts, Gene Ther, 14(23), (2007) 1613-1622]. However, this high transduction does not necessarily translate into improved efficacy [X. Hao, et al., Myocardial angiogenesis after plasmid or adenoviral VEGF-A(165) gene transfer in rat myocardial infarction model, Cardiovasc Res., 73(3), (2007) 481-487]. Naked DNA remains the preferred method of DNA delivery to cardiac myocardium and has been explored extensively in clinical trials. The results from these trials have demonstrated efficacy in regard to secondary end-points of reduced symptomatology and perfusion, but have failed to establish significant angiogenesis or an increase in myocardial function [P.B. Shah, D.W. Losordo, Non-viral vectors for gene therapy: clinical trials in cardiovascular disease, Adv Genet, 54, (2005) 339-361]. This may be due in part to reduced transfection efficiency but can also be attributed to use of suboptimal candidate genes. Currently, polymeric non-viral gene delivery to cardiac myocardium remains underrepresented. In the past decade several advances in non-viral vector development has demonstrated increased transfection efficiency [O.J. Muller, H.A. Katus, R. Bekeredjian, Targeting the heart with gene therapy-optimized gene delivery methods, Cardiovasc Res, 73(3), (2007) 453-462]. Of these polymers, those that employ lipid modifications to improve transfection or target cardiovascular tissues have proven themselves to be extremely beneficial. Water-soluble lipopolymer (WSLP) consists of a low molecular weight branched PEI (1800) and cholesterol. The cholesterol moiety adds extra condensation by forming stable micellular complexes and was later employed for myocardial gene therapy to exploit the high expression of lipoprotein lipase found within cardiac tissue. Use of WSLP to deliver hypoxia-responsive driven expression of hVEGF to ischemic rabbit myocardium has proven to provide for even better expression in cardiovascular cells than Terplex and has demonstrated a significant reduction in infarct size (13+/-4%, p<0.001) over constitutive VEGF expression (32+/-7%, p=0.007) and sham-injected controls (48+/-7%). A significant reduction in apoptotic values and an increase in capillary growth were also seen in surrounding tissue. Recently, investigations have begun using bioreducible polymers made of poly(amido polyethylenimines) (SS-PAEI). SS-PAEIs breakdown within the cytoplasm through inherent redox mechanisms and provide for high transfection efficiencies (upwards to 60% in cardiovascular cell types) with little to no demonstrable toxicity. In vivo transfections in normoxic and hypoxic rabbit myocardium have proven to exceed those results of WSLP transfections by 2-5 fold [L.V. Christensen, et al., Reducible poly(amido ethylenediamine) for hypoxia-inducible VEGF delivery, J Control Release, 118(2), (2007) 254-261]. This new breed of polymer(s) may allow for decreased doses and use of new molecular mechanisms not previously available due to low transfection efficiencies. Little development has been seen in the use of new gene agents for treatment of myocardial ischemia and infarction. Current treatment consists of using mitogenic factors, described decades earlier, alone or in combination to spur angiogenesis or modulating intracellular Ca2+ homeostasis through SERCA2a but to date, failed to demonstrate clinical efficacy. Recent data suggests that axonal guidance cues also act on vasculature neo-genesis and provide a new means of investigation for treatment.