Percutaneous arterial gene transfer in a rabbit model. Efficiency in normal and balloon-dilated atherosclerotic arteries

Vascular Nanomedicine: Current Status, Opportunities, and Challenges

The term "nanotechnology" was coined by Norio Taniguchi in the 1970s to describe the manipulation of materials at the nano (10-9) scale, and the term "nanomedicine" was put forward by Eric Drexler and Robert Freitas Jr. in the 1990s to signify the application of nanotechnology in medicine. Nanomedicine encompasses a variety of systems including nanoparticles, nanofibers, surface nano-patterning, nanoporous matrices, and nanoscale coatings. Of these, nanoparticle-based applications in drug formulations and delivery have emerged as the most utilized nanomedicine system. This review aims to present a comprehensive assessment of nanomedicine approaches in vascular diseases, emphasizing particle designs, therapeutic effects, and current state-of-the-art. The expected advantages of utilizing nanoparticles for drug delivery stem from the particle's ability to (1) protect the drug from plasma-induced deactivation; (2) optimize drug pharmacokinetics and biodistribution; (3) enhance drug delivery to the disease site via passive and active mechanisms; (4) modulate drug release mechanisms via diffusion, degradation, and other unique stimuli-triggered processes; and (5) biodegrade or get eliminated safely from the body. Several nanoparticle systems encapsulating a variety of payloads have shown these advantages in vascular drug delivery applications in preclinical evaluation. At the same time, new challenges have emerged regarding discrepancy between expected and actual fate of nanoparticles in vivo, manufacturing barriers of complex nanoparticle designs, and issues of toxicity and immune response, which have limited successful clinical translation of vascular nanomedicine systems. In this context, this review will discuss challenges and opportunities to advance the field of vascular nanomedicine.

Efficient transgene expression from naked DNA delivered into an arterio-venous fistula model for kidney dialysis

BACKGROUND

Patients with kidney failure frequently require the formation of an arterio-venous fistula (AVF) in which a vein is connected to an artery resulting in arterialization of the vein to allow adequate blood flow into an external 'artificial kidney'. In most patients, neo-intimal hyperplasia (NIH) ensues, causing narrowing and subsequent occlusion of the vein, leading to significant morbidity. The cellular events causing venous NIH may serve as ideal targets for molecular-based therapies. However, therapeutic gene delivery into the vascular system is seriously impeded by problems related to the low efficacy and toxicity of targeted viral vector delivery.

MATERIALS AND METHODS

To explore the feasibility of a plasmid-based vascular gene delivery system, we established a rat AVF model that develops NIH. Plasmids encoding for reporter or therapeutic genes were delivered into the blood vessels at the time or after AVF formation.

RESULTS

Intra-luminal injection of plasmid into the AVF resulted in extensive and long-term reporter gene expression at the venous limb mainly at the site of NIH formation. Transgene expression was confined to endothelial cells and myofibroblasts that migrate inwards from the adventitia and form the NIH lesion. There was no detrimental tissue reaction to plasmid delivery, contrasting with the severe inflammatory response observed after adenovirus infection. Intra-vascular delivery of a plasmid carrying the endothelial nitric oxide synthase gene resulted in sustained production of nitric oxide, previously shown to mitigate NIH formation.

CONCLUSIONS

These findings open the possibility of vascular transduction with naked DNA bearing therapeutic genes in areas prone to NIH to ameliorate vein graft pathologies using simple and clinically applicable vector delivery methods.

Nanomedicine approaches in vascular disease: a review

Nanomedicine approaches have revolutionized the treatment of cancer and vascular diseases, where the limitations of rapid nonspecific clearance, poor biodistribution and harmful side effects associated with direct systemic drug administration can be overcome by packaging the agents within sterically stabilized, long-circulating nanovehicles that can be further surface-modified with ligands to actively target cellular/molecular components of the disease. With significant advancements in genetics, proteomics, cellular and molecular biology and biomaterials engineering, the nanomedicine strategies have become progressively refined regarding the modulation of surface and bulk chemistry of the nanovehicles, control of drug release kinetics, manipulation of nanoconstruct geometry and integration of multiple functionalities on single nanoplatforms. The current review aims to capture the various nanomedicine approaches directed specifically toward vascular diseases during the past two decades. Analysis of the promises and limitations of these approaches will help identify and optimize vascular nanomedicine systems to enhance their efficacy and clinical translation in the future.

FROM THE CLINICAL EDITOR

Nanomedicine-based approaches have had a major impact on the treatment and diagnosis of malignancies and vascular diseases. This review discusses various nanomedicine approaches directed specifically toward vascular diseases during the past two decades, highlighting their advantages, limitations and offering new perspectives on future applications.

Intramuscular gene transfer of fibroblast growth factor-1 using improved pCOR plasmid design stimulates collateral formation in a rabbit ischemic hindlimb model

Fibroblast growth factor 1 (FGF1) is an angiogenic factor known to play a role in the growth of arteries. The purpose of this study was to evaluate the usefulness of direct intramuscular injection of an optimized expression plasmid encoding FGF1 to augment collateral formation and tissue perfusion in a rabbit ischemic hindlimb model. Truncated FGF1 fused to the human fibroblast interferon (FIN) signal peptide was expressed from a newly designed plasmid backbone with an improved safety profile for gene therapy applications. In vitro, optimization of plasmid design yielded in a dramatic increase in expression efficiency for FGF1, independent of the presence of a signal peptide, as analyzed by Western Blotting. In vivo, successful transgene expression could be demonstrated by FGF1 immunostaining after gene application. FGF1 plasmid containing FIN signal peptide (100, 500, and 1,000 mug), when injected into ischemic muscle areas of rabbits 10 days after ligation of the external iliac artery, exhibited a pronounced therapeutic effect on collateral formation to the ischemic hindlimb in a dose-depending manner, as assessed by physiological (blood pressure ratio, maximal intra-arterial Doppler flow) and anatomical (angiographic score, histologic evaluation of capillary density) measurements 30 days after therapy, compared to saline or lacZ control plasmid. FGF1 plasmid without a signal peptide sequence resulted in a comparable therapeutic effect on collateral formation at comparable doses (500 and 1,000 mug). Our results indicate that intramuscular FGF1 gene application could be useful to stimulate collateral formation in a situation of chronic peripheral ischemia. The presence of a signal peptide does not seem to be obligatory to achieve bioactivity of intramuscular transfected FGF1. An optimized vector design improved both biosafety of gene transfer and expression efficiency of the transgene, rendering this vector highly suitable for human gene therapy. Therefore, this new generation vector encoding FGF1 might be useful as an alternative treatment for patients with chronic ischemic disorders not amenable to conventional therapy.

Long-term tracing of adenoviral expression in rat and rabbit using luciferase imaging

BACKGROUND

Luciferase optical imaging provides a novel method to monitor transgene expression in small living animals. As the genetic and immunological heritages of particular animals significantly affect the expression of adenovirus-delivered transgenes, it is essential to know the expression patterns specific to athymic nude and Sprague-Dawley rats, two strains commonly used in rodent models. In this study we set out to determine these patterns. At the same time, we tested luciferase optical imaging in a larger animal, the rabbit.

METHODS

A recombinant luciferase adenoviral vector was injected subcutaneously or intramuscularly into athymic nude rats, Sprague-Dawley rats, and Dutch Belted rabbits. The luciferase expression was assessed using a cooled charge-coupled device.

RESULTS

The luminescent signal was capable of passing through at least 1.3 cm of muscle tissue and proved to be much stronger when luciferin was delivered via a local injection than by an intraperitoneal injection. Although the types of immune cells differed between immunodeficient and immunocompetent rats, similar amounts and patterns of luciferase expression were observed in the musculature in two rat strains during the 1st month after a viral intramuscular injection. The duration of luciferase expression was longer than 15 months in athymic nude rats, 9 months in Sprague-Dawley rats, and 6 months in rabbits following a direct viral injection.

CONCLUSIONS

Luciferase expression after adenoviral gene delivery can persist for longer than 6 months, even in immunocompetent animals. Live imaging of luciferase expression can be performed not only in small animals, but also in larger animals such as rabbits.

Expression of coxsackievirus and adenovirus receptor in neointima of the rat carotid artery

Our previous study revealed that the coxsackievirus and adenovirus receptor (CAR) is a homophilic cell adhesion molecule and may function as a sensor of cell-cell interactions in the brain and damaged heart. In this study, we investigated if CAR expression is involved in the formation of neointimal hyperplasia using a balloon injury model of rat carotid artery. Cultured vascular smooth muscle cells (SMCs) from rat aorta were also studied. CAR antigen was constitutively detected in the endothelial cells (ECs) but not in SMCs before injury. On Day 5 after balloon injury, CAR was expressed strongly in the first layer of medial SMCs. Neointimal hyperplasia was observed on Day 7, and strong expressions of CAR concomitantly with proliferating cell nuclear antigen (PCNA) were obvious in the neointimal SMCs, while CAR in medial SMCs disappeared. The expression of CAR mRNA reached a peak on Day 7 and declined gradually to the basal levels. When the ECs regenerated on Day 14, CAR antigen was observed in the ECs but disappeared in the neointima. CAR together with PCNA was expressed abundantly in the proliferating SMCs in vitro and diminished in cells grown to a confluent state. The abundant expression of CAR in the neointima may facilitate an adenoviral gene therapy.

Preventing saphenous vein graft failure: does gene therapy have a role?

Gene therapy potentially allows local delivery and expression of cytokines, growth factors, and other mediators. In spite of increasing knowledge of the human genome, applications in clinical practice are only just beginning. The main limitations of effective clinical gene therapy are safety and low transfection efficiency. Saphenous vein grafts permit the transfection of the conduit ex vivo. This allows a variety of transfection techniques to be used, enhancing the transfection efficiency while limiting the risk of systemic complications. This review examines the potential mechanisms of gene delivery and genetic targets that may be applied to saphenous vein graft failure.

Gene transfer strategies to inhibit neointima formation

Vascular smooth muscle cell (VSMC) proliferation after arterial injury results in neointima formation and plays an important role in the pathogenesis of restenosis after angioplasty, in-stent restenosis, vascular bypass graft occlusion, and allograft vasculopathy. Major progress has been made recently in elucidating the cellular and molecular mechanisms underlying neointima formation. However, no known curative treatment currently exists. In cases in which pharmacologic and surgical interventions have had limited success, gene therapy remains a potential strategy for the treatment of such vascular proliferative diseases. To date, recombinant adenoviral vectors continue to be the most efficient methods of gene transfer into the arterial wall. However, concerns over the safety of using viral vectors in a clinical situation have inspired the considerable progress that has been made in improving both viral and nonviral modes of gene transfer. This review discusses some of the recent insights and outstanding progress in vascular gene therapeutic approaches to inhibit neointima both from a biologic and therapeutic perspective.

Biochemical and biophysical characteristics of lipoplexes pertinent to solid tumour gene therapy

Cationic liposomes have become the reagent of choice for transfer of nucleic acids such as plasmids and oligodeoxynucleotides to cells in culture and in vivo. Whilst these reagents have several advantages over other forms of nucleic acid transfer methods, toxicity remains a significant problem, especially in vivo. Recent studies have also highlighted the immunostimulatory nature of these cationic vesicles when complexed to plasmid DNA, a phenomenon that may be harnessed for efficacious usage against tumours. Current research in this dynamic technological field is aimed at the development of cationic lipids that have negligible toxic effects and enhanced transfection capabilities.

Vehicles for oligonucleotide delivery to tumours

The vasculature of a tumour provides the most effective route by which neoplastic cells may be reached and eradicated by drugs. The fact that a tumour's vasculature is relatively more permeable than healthy host tissue should enable selective delivery of drugs to tumour tissue. Such delivery is relevant to carrier-mediated delivery of genetic medicine to tumours. This review discusses the potential of delivering therapeutic oligonucleotides (ONs) to tumours using cationic liposomes and cyclodextrins (CyDs), and the major hindrances posed by the tumour itself on such delivery. Cationic liposomes are generally 100-200 nm in diameter, whereas CyDs typically span 1.5 nm across. Cationic liposomes have been used for the introduction of nucleic acids into mammalian cells for more than a decade. CyD molecules are routinely used as agents that engender cholesterol efflux from lipid-laden cells, thus having an efficacious potential in the management of atherosclerosis. A recent trend is to employ these oligosaccharide molecules for delivering nucleic acids in cells both in-vitro and in-vivo. Comparisons are made with other ON delivery agents, such as porphyrin derivatives (< 1 nm), branched chain dendrimers (approximately 10 nm), polyethylenimine polymers (approximately 10 nm), nanoparticles (20-1,000 nm) and microspheres (> 1 microm), in the context of delivery to solid tumours. A discourse on how the chemical and physical properties of these carriers may affect the uptake of ONs into cells, particularly in-vivo, forms a major basis of this review.

Gene therapy in vascular surgery comes of age

In the last decade, gene therapy for cardiovascular diseases has been becoming a reality. However, although numerous successful experimental studies have suggested possible strategies of gene therapy for cardiovascular disorders, the clinical outcome remains limited. Because cardiovascular diseases are the result of complex causes, there is no exact answer to the following question: Which is the best gene to treat vascular diseases? In addition, current limitations include less clinically relevant vectors regarding both gene-transfer efficiency and safety, and at present, most efforts are focused on identifying more effective therapeutic genes, as well as developing more effective vectors. Furthermore, greater pathophysiologic understanding of these diseases, including vein-graft remodeling and ischemic limbs, is required. Regarding the relevant vector, we recently developed a novel mononegavirus-based gene-transfer vector, namely recombinant Sendai virus, which has shown dramatically superior gene-transfer efficiency to other vectors, including adenovirus, in several organs (eg, the vessel wall and skeletal muscles). These efforts now offer new possibilities to get more fruits in the field of gene therapy for vascular surgery.

Imaging of light emission from the expression of luciferases in living cells and organisms: a review

Luciferases are enzymes that emit light in the presence of oxygen and a substrate (luciferin) and which have been used for real-time, low-light imaging of gene expression in cell cultures, individual cells, whole organisms, and transgenic organisms. Such luciferin-luciferase systems include, among others, the bacterial lux genes of terrestrial Photorhabdus luminescens and marine Vibrio harveyi bacteria, as well as eukaryotic luciferase luc and ruc genes from firefly species (Photinus) and the sea pansy (Renilla reniformis), respectively. In various vectors and in fusion constructs with other gene products such as green fluorescence protein (GFP; from the jellyfish Aequorea), luciferases have served as reporters in a number of promoter search and targeted gene expression experiments over the last two decades. Luciferase imaging has also been used to trace bacterial and viral infection in vivo and to visualize the proliferation of tumour cells in animal models.

Local gene delivery to the vessel wall

This review will provide an overview of delivery strategies that are being evaluated for vascular gene therapy. We will limit our discussion to those studies that have been demonstrated, utilizing in vivo model systems, to limit post-interventional restenosis. We also discuss the efficacy of the vectors and methods currently being used to transfer genetic material to the vessel wall. The efficiency of these techniques is a critical issue for the successful application of gene therapy.

Somatic gene therapy in the cardiovascular system

This review surveys a range of approaches using plasmid DNA encoding the 165-amino-acid isoform of vascular endothelial growth factor (phVEGF165) to therapeutically modulate micro- or macrovascular endothelial cells, focusing on strategies to augment postnatal collateral circulation in arterial insufficiency or to accelerate re-endothelialization after balloon angioplasty to prevent restenosis. We focus on intra-arterial and intramuscular/intramyocardial gene transfer of the VEGF165 gene, the options that have been most thoroughly studied to date in patients. We review developmental and postnatal significance of the endothelial-cell-specific mitogen VEGF that has stimulated these studies and present limitations of current knowledge as well as challenges for the future.

Gene Therapy for Cardiovascular Disease

During the past decade, gene therapy for the treatment of many inherited and acquired medical problems has become the subject of increasing focus in both the scientific litera ture and the lay press. This review examines the history and current status of gene therapy for advanced chronic periph eral and myocardial ischemia.

Delivery of lipoplexes for genotherapy of solid tumours: role of vascular endothelial cells

The cells constituting a solid tumour may vary considerably due to biological disparities, but for a solid tumour to pose as a threat to its host, an adequate blood supply has to be established. Although neovascularisation may have dire consequences for the host, it provides a common route by which tumours in general may be reached and eradicated by drugs. The fact that a tumour's vasculature is relatively more permeable than healthy host tissue means that selective delivery of drugs may be achieved. A closer examination of the role played by the cells making up the tumour vascular bed, vascular endothelial cells (VECs), is required to facilitate design of ways for enhancing drug delivery to solid tumours via the vascular route. VECs have two major roles in the body, barrier and transport, both of which are highly pertinent to drug delivery. This review discusses the factors regulating VEC function, and how these cells may be manipulated in-vivo to improve the selective delivery of lipoplexes, carriers for gene therapy constructs, to solid tumours. It also discusses how genotherapeutic drugs may be targeted against tumour VECs on the premise that by killing these cells, the tumour itself will perish.

Current, new and future treatments in dyslipidaemia and atherosclerosis

The new therapeutic options available to clinicians treating dyslipidaemia in the last decade have enabled effective treatment for many patients. The development of the HMG-CoA reductase inhibitors (statins) have been a major advance in that they possess multiple pharmacological effects (pleiotropic effects) resulting in potent reductions of low density lipoproteins (LDL) and prevention of the atherosclerotic process. More recently, the newer fibric acid derivatives have also reduced LDL to levels comparable to those achieved with statins, have reduced triglycerides, and gemfibrozil has been shown to increase high density lipoprotein (HDL) levels. Nicotinic acid has been made tolerable with sustained-release formulations, and is still considered an excellent choice in elevating HDL cholesterol and is potentially effective in reducing lipoprotein(a) [Lp(a)] levels, an emerging risk factor for coronary heart disease (CHD). Furthermore, recent studies have reported positive lipid-lowering effects from estrogen and/or progestogen in postmenopausal women but there are still conflicting reports on the use of these agents in dyslipidaemia and in females at risk for CHD. In addition to lowering lipid levels, these antihyperlipidaemic agents may have directly or indirectly targeted thrombogenic, fibrinolytic and atherosclerotic processes which may have been unaccounted for in their overall success in clinical trials. Although LDL cholesterol is still the major target for therapy, it is likely that over the next several years other lipid/lipoprotein and nonlipid parameters will become more generally accepted targets for specific therapeutic interventions. Some important emerging lipid/lipoprotein parameters that have been associated with CHD include elevated triglyceride, oxidised LDL cholesterol and Lp(a) levels, and low HDL levels. The nonlipid parameters include elevated homocysteine and fibrinogen, and decreased endothelial-derived nitric oxide production. Among the new investigational agents are inhibitors of squalene synthetase, acylCoA: cholesterol acyltransferase, cholesteryl ester transfer protein, monocyte-macrophages and LDL cholesterol oxidation. Future applications may include thyromimetic therapy, cholesterol vaccination, somatic gene therapy, and recombinant proteins, in particular, apolipoproteins A-I and E. Non-LDL-related targets such as peroxisome proliferator-activating receptors, matrix metalloproteinases and scavenger receptor class B type I may also have clinical significance in the treatment of atherosclerosis in the near future. Before lipid-lowering therapy, dietary and lifestyle modification is and should be the first therapeutic intervention in the management of dyslipidaemia. Although current recommendations from the US and Europe are slightly different, adherence to these recommendations is essential to lower the risk of atherosclerotic vascular disease, more specifically CHD. New guidelines that are expected in the near future will encompass global opinions from the expert scientific community addressing the issue of target LDL goal (aggressive versus moderate lowering) and the application of therapy for newer emerging CHD risk factors.

Photodynamic therapy with local photosensitizer delivery inhibits experimental intimal hyperplasia

BACKGROUND

Photodynamic therapy (PDT), the light activation of photosensitizer dyes for the production of free radicals, effectively inhibits experimental intimal hyperplasia with systemic administration of the photosensitizer. The local application of the photosensitizer directly into a vascular lesion to avoid systemic side effects and tightly control dose administration has theoretical appeal. The aim of this study was to quantify serum and arterial tissue uptake after site-specific photosensitizer delivery and, following PDT, determine its effectiveness at inhibiting intimal hyperplasia.

STUDY DESIGN/MATERIALS AND METHODS

The rat common carotid artery was balloon-injured, pressurized at 400 mm Hg for 2 minutes with the photosensitizer dye benzoporphyrin-derivative (BPD), and irradiated with 690 nm laser light at a fluence of 100 J/cm2. Control animals were pressurized with saline only, or received no additional treatment than balloon-injury.

RESULTS

Pressurization with BPD resulted in complete penetration of the intima and media and was associated with relatively high tissue, but almost no detectable serum BPD concentrations. No skin photosensitization or other systemic side effects were observed with photosensitizer administration. After 9 days, PDT-treated arteries displayed a significantly lower number of smooth muscle cells in the arterial wall than balloon-injured (P < 0.001) or saline-pressurized arteries (P < 0.0002), and no intimal hyperplasia. At 21 days, IH after PDT was significantly reduced as compared with balloon-injured (P < 0.0004), or saline-pressurized arteries (P < 0.003) with no arterial dilatation.

CONCLUSIONS

Site-specific delivery of liposomal BPD followed by PDT represents a safe method to treat arteries, and may be effectively used in vivo to inhibit the development of intimal hyperplasia.

Optimization of nonviral gene transfer of vascular smooth muscle cells in vitro and in vivo

Gene therapy strategies for the prevention of restenosis postangioplasty are promising. Nonviral gene transfer to the arterial wall in vivo has so far been limited by poor efficiency. This study aimed to optimize transfection of primary vascular smooth muscle cells using cationic nonviral formulations based on cholesterol derivates (DC-, DAC-, DCQ-, and Sp-Chol), double-chained amphiphils (LipofectAMINE, DOTMA, DOSGA, DOSPER, and DOCSPER), or heterogeneous reagents (Superfect, Effectene, and Tfx-50). Estimation of transfection efficiencies was performed using galactosidase assays at different ratios of transfection reagent to plasmid DNA with reporter gene. Toxicity was monitored by analyzing cell metabolism. Transfer efficiency and safety were determined in a porcine restenosis model for local gene therapy using morphometry, histology, galactosidase assays, and reverse-transcriptase polymerase chain reaction. The highest in vitro transfection efficiency was achieved using the recently developed DOCSPER liposomes, with transfer rates of at least 20% in vascular smooth muscle cells. Transfer efficiency was further enhanced up to 20% by complexing with poly-L-lysine. Transfection efficiency in vivo in a porcine restenosis model was up to 15% of adventitial cells using DOCSPER versus 0.1% using LipofectAMINE. Toxicity in vivo and in vitro was lowest using DOCSPER. Increased biological effects were demonstrated following optimization of transfer conditions.

Vascular Applications of Human Gene Therapy

Complexing recombinant DNA with cationic liposomes is a convenient means of introducing foreign genes into cells (lipofection) and could potentially form the basis for genetically modifying diseased blood vessels in patients. The mechanism of lipofection is incompletely understood, but it is recognized that the degree of successful gene transfer is highly dependent on cell type. We have transfected primary cultures of human vascular smooth muscle cells with a plasmid expressing either firefly luciferase (Luc) or nuclear-localized beta-galactosidase (NL-beta-gal). Cells were derived from either normal human internal mammary arteries, fragments of primary atherosclerotic plaque, or fragments of restenotic lesion. Concurrent lipofection of rabbit vascular smooth muscle cells and NIH 3T3 cells was performed as well. Compared with NIH 3T3 cells, expression in human vascular smooth muscle cells was markedly reduced: In cells derived from internal mammary artery, Luc expression, normalized for protein content, was 123-fold lower than in NIH 3T3 cells, while the proportion of cells expressing NL-beta-gal was 30-fold lower. Luc expression in cells derived from restenotic tissue was significantly greater than from cells derived from primary plaque. Within a given population of cells, the mitotic index of cells expressing the recombinant gene was significantly higher than the mitotic index for the total population of cells (p < 0.05). Finally, cotransfection experiments, in which lipofection of smooth muscle cells was performed using genes for NL-beta-gal and for human growth hormone, showed that among positive transfectants a high proportion of cells (23-36%) coexpressed both genes. Thus, the efficiency of successful lipofection in human vascular smooth muscle cells in vitro is low. Transfection appears to be preferentially facilitated in cells derived from restenotic tissue and specific properties of smooth muscle cells, including growth rates, appear to be critical for successful transfection. Further elucidation of cell properties that promote transfection is required to augment the efficiency of liposome-mediated gene transfer in human vascular cells.

A pressure-mediated nonviral method for efficient arterial gene and oligonucleotide transfer

In this study, we report a method of controlled pressure-mediated delivery of "naked" DNA that achieves efficient and safe arterial gene and oligonucleotide transfer. We demonstrated a pressure-dependent uptake of fluorescein-labeled (FITC) oligonucleotide (ODN) in rabbit carotid arteries with preexisting neointimal hyperplasia, using nondistending intravascular delivery pressures ranging from 0 to 760 mm Hg. At an infusion pressure of 50 mm Hg, 10.5+/-5% of neointimal cell nuclei were positive for nuclear uptake of FITC-ODN 4 days after transfection. With an infusion pressure of 760 mm Hg, the transfection efficiency increased to 84.2+/-5.3% of neointimal cells, and to 64.5+/-11.6 and 92.4+/-5.5% of medial and adventitial cells, respectively. Similar patterns of FITC-ODN uptake were seen in atherosclerotic injured arteries. We also investigated the pressure-mediated delivery of plasmid DNA. Transfection of a luciferase expression plasmid, using an infusion pressure of 760 mm Hg, yielded luciferase expression of 816.6+/-108.6 fg/mg protein in normal rabbit carotid arteries, as compared with 38.9+/-23.7 fg/mg protein at 100 mm Hg. Luciferase expression was significantly higher in pressure-transfected injured atherosclerotic arteries (5467.3+/-1047.6 fg/mg protein at 760 mm Hg). Transfection of beta-galactosidase indicated that significant transgene expression occurred in the neointima and media. These data indicate that this pressure-mediated transfection method yields efficient oligonucleotide delivery and enhances transduction with plasmid DNA in normal as well as injured nonatherosclerotic or atherosclerotic arteries.

Characterization of vascular gene transfer using a novel cationic lipid

INTRODUCTION

Cationic liposomes are an alternative non-viral vector for gene therapy, but several factors affect transfection efficiency. A novel cationic lipid, o-ethyldioleoylphosphatidylcholinium (EDOPC), was studied for characterization of the time course and effects of lipid composition, concentration, charge ratio, mixing techniques, passage number, and stimulated state on transfection of human vascular cells, represented by human umbilical vein endothelial cells (HUVEC).

METHODS

HUVEC cultures were seeded at a density of 45,000 cells/well in 24-well plates and incubated overnight. Triplicate wells were transfected with samples of EDOPC/reporter plasmid for 2 h, followed by a 24-h expression time, which was the peak expression time point in an initial time-course experiment. Measuring luciferase in cell lysates quantitated gene expression.

RESULTS

Transfection of HUVEC with EDOPC was optimal with a concentration of 100 microgram lipid/well, ratio of 3:1 EDOPC:plasmid, fractional mixing of lipid and plasmid, centrifugation, and incubation in serum-free media. Transfections in sequential passages showed striking decreases in gene expression and regression analysis revealed the relationship: RLU = 120,000 - (10, 400 x passage number), r(2) = 0.947. HUVEC activated by cytokine stimulation remain susceptible to gene transfer specifically with EDOPC.

SUMMARY

During transfection of HUVEC with cationic lipid species, an increase in passage number is associated with linear reduction in luciferase expression, and hence passage number must be controlled in comparative experiments. Characteristics of EDOPC may permit site-specific efficient transfection of activated human vascular cells that can be isolated from serum by mechanical methods.

Gene therapy as a therapeutic intervention for vascular disease

Gene therapy for the treatment of many medical problems, including vascular disease, has become the subject of increasing discussion in both the scientific literature and the national press over the past decade. This review will examine the history and current status of gene therapy for vascular proliferative disorders and advanced chronic peripheral and cardiac ischemia.

Lipoplexes and tumours. A review

The need for genotherapy to refocus its attention on to laboratory evaluation of better methods rather than proceeding to the clinic with semi-apt tools for genetic transfer has been highlighted in clinical study reports documented to date. Quintessential for tumour genotherapy is the ability to target abnormal cells, hence reducing exposure of normal cells to genetic material whilst maximizing gene dosage to tumour cells. This becomes increasingly important as genotherapy establishes itself in the clinic alongside the older modes of treatment. This review has discussed the applicability of lipoplexes for genotherapy of solid tumours. Lipoplexes have been used extensively for gene transfer into cells, such as cancerous cells, deficient for a certain gene product. While cationic liposomes have many advantages over other forms of delivery mechanisms, several problems hinder their use in-vivo. A closer examination of the physical limitations of current lipoplex preparations, the development and testing of novel formulations, combined with more attention to the cellular processes of cell membrane breaching and nuclear entry, may enhance gene delivery. Essential for tumour genotherapy is the ability to target these lipoplexes into tumour sites whilst reducing gene dosage to other normal tissues. Development of a better lipofection agent may indeed require a collaboration of the fields of physiology, cell biology, molecular biology, biochemistry, chemistry and membrane physics.

Gene therapy for cerebrovascular disease

OBJECTIVE

To review the principles of and the experimental and clinical results of gene therapy for cerebrovascular disease.

METHODS

Literature review.

RESULTS

Vectors for gene transfer into the brain or into the cerebral vasculature include naked plasmid deoxyribonucleic acid, cationic liposomes, and viruses such as adenovirus, retrovirus, adeno-associated virus, and herpes simplex virus. Experiments using these vectors showed that intra- or perivascular application to systemic arteries can lead to transfection and expression of a foreign transgene in the adventitia and the endothelium. Intrathecal administration can lead to transfection and foreign transgene expression in leptomeningeal cells as well as in fibroblasts of blood vessel adventitia. Biological effects demonstrated thus far include increased nitric oxide production by transfection of cerebral arterial adventitia with adenovirus expressing nitric oxide synthase. Adenoviruses carrying foreign genes have been used to decrease neuronal damage in cerebral ischemia and to decrease blood pressure in spontaneously hypertensive rats. Vectors and therapeutic applications for gene therapy are evolving rapidly.

CONCLUSION

Gene therapy for cerebrovascular disease is likely to have clinical application in the near future and will have a major impact on neurosurgery. Neurosurgeons will need to be aware of the literature in this area.

Adenovirus-mediated gene transfer is augmented in basilar and carotid arteries of heritable hyperlipidemic rabbits

BACKGROUND AND PURPOSE

There are major differences in susceptibility of intracranial and extracranial arteries to atherosclerosis. The goal of this study was to examine adenovirus-mediated gene transfer to basilar and carotid arteries of Watanabe heritable hyperlipidemic (WHHL) rabbits, which have spontaneous hypercholesterolemia and atherosclerosis, and normal New Zealand White (NZW) rabbits. We used 2 different adenoviral vectors, driven by either cytomegalovirus (CMV) or Rous sarcoma virus (RSV) promoters.

METHODS

Basilar and carotid arteries were removed from WHHL and NZW rabbits and cut into rings. The arteries were incubated with an adenoviral vector that expresses beta-galactosidase and is driven by either a cytomegalovirus (CMV) or Rous sarcoma virus (RSV) promoter (AdCMVbetagal or AdRSVbetagal). Arteries were incubated with virus for 2 hours, and then incubated in medium for 24 hours to allow expression of transgene. Transgene expression was assessed by enzyme activity (Galacto-Light assay) and by a histochemical method after X-Gal staining.

RESULTS

After gene transfer, beta-galactosidase was expressed in endothelium and adventitia but not media. There were moderately severe atherosclerotic lesions in carotid arteries and early lesions in basilar arteries. Enzyme activity after gene transfer with AdCMVbetagal (3x10(11) particles/mL) was greater in the basilar artery of WHHL than NZW (137+/-40 versus 25+/-10 mU/mg protein, P<0.05) (mean+/-SE) and in the carotid artery (133+/-27 versus 34+/-11 mU/mg protein, P<0.05). After gene transfer with AdRSVbetagal, transgene expression was similar in arteries from WHHL and normal NZW rabbits.

CONCLUSIONS

This is the first study to examine gene transfer to intracranial and extracranial arteries from atherosclerotic animals. The findings suggest that an adenoviral vector with a CMV, but not RSV, promoter provides greater transgene expression in the basilar and carotid arteries from spontaneously atherosclerotic rabbits than from normal rabbits.

Ex vivo gene transfer of endothelial nitric oxide synthase to atherosclerotic rabbit aortic rings improves relaxations to acetylcholine

Cholesterol feeding results in impaired endothelium dependent vasorelaxation. The role of nitric oxide in this process is unclear. The aim of this study was to evaluate the role of nitric oxide in cholesterol-induced vasomotor dysfunction by examining the effect of overexpression of eNOS in the hypercholesterolemic rabbit aorta on vascular reactivity. Vascular rings from the thoracic aorta of hypercholesterolemic rabbits were exposed ex vivo either to an adenoviral vector encoding endothelial nitric oxide synthase (AdeNOS) or Escherichia coli beta Galactosidase (AdbetaGal). Transgene expression was examined by histochemistry for beta galactosidase, immunohistochemistry for eNOS and cyclic GMP measurements and vasomotor studies were performed. Transgene expression was found to localize to the endothelium and adventitia. cGMP levels were significantly greater in AdeNOS compared to AdbetaGal transduced rings. Acetylcholine mediated relaxation was significantly impaired in cholesterol fed rabbits and was markedly improved by overexpression of eNOS. These results suggest that reduced NO bioavailability observed in cholesterol-induced vascular dysfunction can be partially overcome by eNOS gene transfer.

Requirements for enhanced transgene expression by untranslated sequences from the human cytomegalovirus immediate-early gene

BACKGROUND

The cytomegalovirus immediate early (CMV IE) promoter has been widely used for heterologous expression. Further enhancements of gene expression from this potent promoter may allow for the development of improved gene transfer strategies. We aimed to determine whether inclusion of the first exon (5' untranslated) and first intron of the CMV IE gene would increase heterologous transgene expression in primary target cells and to determine the sequences required for any observed increases.

MATERIALS AND METHODS

Comparisons of reporter gene expression were made following transient transfection of vascular smooth muscle cells (VSMCs) with plasmids containing the first exon and intron from the CMV IE gene or deletional mutations. Comparisons were also made using a heterologous promoter (RSV).

RESULTS

Gene expression from the CMV IE promoter was increased 5.7-fold in VSMC with the inclusion of the first exon and intron. Similar increases were seen with other target cells and from the heterologous RSV promoter. This increase was associated with an increase in steady-state mRNA. Deletion analyses demonstrated that the enhancement was dependent on the presence of the 5' portion of the first exon while deletion of large segments within the intron was associated with similar levels of expression compared with the parental plasmid.

CONCLUSIONS

Inclusion of the first exon and intron from the CMV IE gene increases expression from the CMV IE promoter. This enhancement is seen with the heterologous RSV promoter and is associated with an increase in steady-state mRNA. Deletion analyses suggest that this enhancement is associated with inclusion of sequences within the 5' portion of the first exon and inclusion of an intron.

Gene therapy for tissue repair and regeneration

This review presents a current overview of the discipline of human gene therapy. In addition, a gene therapy method is described in which plasmid genes are transferred from a structural matrix carrier into fresh wound sites so as to enhance tissue repair and regeneration. The potential to develop a gene therapy for bone regeneration is discussed in detail.

Gene therapy for restenosis: are we ready?

The application of gene therapy techniques to the clinical problem of coronary restenosis has generated tremendous attention and enthusiasm. Use of gene transfer technology to prevent a common intractable illness would represent a watershed event for human gene therapy. However, the time is not yet right to initiate gene therapy trials for restenosis. The biology of restenosis is incompletely understood, catheter-based gene delivery is poorly adapted to the coronary circulation, and current gene transfer vectors are ill-suited for safe and effective gene delivery to the coronary artery wall. Basic research designed to overcome these obstacles is currently more appropriate than the initiation of clinical trials.

Gene therapy for restenosis: getting nearer the heart of the matter

Intensive work over the past decade has been directed to the study of vascular gene transfer as an approach to the unresolved problem of restenosis. This effort has resulted in a significant foundation of knowledge relative to the activities of potentially therapeutic gene products as well as the capabilities and limitations of vector systems and mechanical delivery modalities available for effecting the vascular expression of these gene products. In several instances, significant progress has been made by experiments highlighting unexpected difficulties and the need for more comprehensive understanding. It is thus now possible to clearly define and address specific challenges that must be overcome in order to make feasible progress from the preclinical to the clinical arena. The key challenges at present appear to include the evolution of clinically practical delivery methods that meet the kinetic requirements of achieving efficient gene transduction and the availability of vectors that maximize efficiency while minimizing undesirable host responses. Emerging data suggest that approaches to solving each of these issues may have recently been developed. Basic research evaluating these new delivery mechanisms and molecular vectors is essential to establish their true potential for use in the clinical arena.

Augmented adenovirus-mediated gene transfer to atherosclerotic vessels

Vascular endothelium is an important target for gene transfer in atherosclerosis. In this study, we examined gene transfer to normal and atherosclerotic blood vessels from two species, using an organ culture method. Using normal aorta, we determined optimal dose, duration of exposure to adenovirus, and duration of incubation of vessels in tissue culture. Aortas from normal and atherosclerotic monkeys were cut into rings and incubated for 2 hours with a recombinant adenovirus, carrying the reporter gene for beta-galactosidase driven by a cytomegalovirus (CMV) promoter. After 20 hours of incubation, transgene expression was assessed with a morphometric method after histochemical staining and a chemiluminescent assay of enzyme activity. Expression of beta-galactosidase after histochemical staining, expressed as percentage of total cells, was similar in adventitial cells of normal monkeys (21 +/- 4%, mean +/- SE%) and atherosclerotic monkeys (25 +/- 12%). Transgene expression in endothelium was higher in atherosclerotic than in normal vessel (53 +/- 3% versus 27 +/- 7%, P < .05). Chemiluminescent assay indicated greater beta-galactosidase activity (2.5 +/- 0.6 mU/mg of protein) in the intima and media of atherosclerotic than normal vessels (0.6 +/- 0.2 mU/mg of protein, P < .05). Aortas from normal (n = 6) and atherosclerotic (n = 5) rabbits also were examined. Transgene expression (after histochemical staining) in endothelium was much greater in atherosclerotic than normal rabbits (39 +/- 3% versus 9 +/- 2%, P < .05) and expression in adventitial cells was similar (normal 23 +/- 2%, atherosclerotic 24 +/- 4%). Chemiluminescent assay indicated greater beta-galactosidase activity (1.2 +/- 0.4 mU/mg of protein) in the intima and media of atherosclerotic than normal vessels (0.2 +/- 0.1 mU/mg protein, P < .05). These findings suggest that an adenoviral vector with a CMV promoter provides similar transgene expression in adventitia of both normal and atherosclerotic vessels. Gene transfer to the endothelium was much more effective in atherosclerotic than in normal vessels. Thus it may be possible to achieve greater transgene expression in atherosclerotic than in normal arteries.

Novel methods for adenovirus-mediated gene transfer to blood vessels in vivo

Adenovirus-mediated gene transfer is a promising method for studies of vascular biology and potentially for gene therapy. Intravascular approaches for gene transfer to blood vessels in vivo generally require interruption of blood flow and have several limitations. We have used two alternative approaches for gene transfer to blood vessels in vivo using perivascular application of vectors. First, replication-deficient adenovirus expressing nuclear-targeted bacterial beta-galactosidase was injected into cerebrospinal fluid via the cisterna magna of rats. Leptomeningeal cells over the major arteries were efficiently transfected, and adventitial cells of large vessels and smooth muscle cells of small vessels were occasionally stained. When viral suspension was injected with the rat in a lateral position, the reporter gene was expressed extensively on the ipsilateral surface of the brain. Thus, adenovirus injected into cerebrospinal fluid provides gene transfer in vivo to cerebral blood vessels and, with greater efficiency, to perivascular tissue. Furthermore, positioning of the head may 'target' specific regions of the brain. Second, vascular gene delivery was accomplished by perivascular injection of virus in peripheral vessels. Injection of the adenoviral vector within the periarterial sheath of monkeys resulted in gene transfer to the vessel wall that was substantial in magnitude although limited to cells in the adventitia. Approximately 20% of adventitial cells expressed the transgene, with no gene transfer to cells in the intima or media. These approaches may provide alternative approaches for gene transfer to blood vessels, and may be useful for studies of vascular biology and perhaps vascular gene therapy.

Sustained local drug delivery to the arterial wall via biodegradable microspheres

This study was designed to evaluate the feasibility of applying locally delivered polylactic acid microspheres for drug delivery to the arterial wall. To study drug persistence, rhodamine-loaded microspheres were infused into one carotid artery of 14 rabbits and plain rhodamine solution into the other by using a porous balloon. To study tissue response, plain microspheres and dexamethasone-loaded microspheres were infused into the carotid arteries of another group of rabbits. To study the antiproliferative effects of locally delivered drug, 20 rabbits were subjected to overstretch balloon injury to both carotid arteries and divided into 4 groups: injury alone, plain microspheres, dexamethasone-loaded microspheres, and microspheres containing colchicine and dexamethasone. Fluorescent microspheres persisted in the vessel wall for 4 wk, whereas rhodamine without microspheres disappeared at 72 h. Histopathologic studies in arteries infused with unloaded microspheres showed inflammatory cell infiltrate with polymorphonuclear cells at 1 wk and macrophages and giant cells at 4 wk. Arteries infused with dexamethasone-loaded microspheres did not show any inflammatory cell infiltrate. Local delivery of dexamethasone or dexamethasone plus colchicine did not result in significant change in the intima-to-media ratio or in residual lumen following balloon injury. Polylactic acid microspheres may be used for prolonged delivery of drugs or other bioactive agents locally to the arterial wall. They induce an inflammatory reaction that is suppressable by dexamethasone in the microspheres. Dexamethasone or dexamethasone and colchicine delivered via this system, however, failed to reduce the degree of intimal hyperplasia after overstretch balloon injury to the rabbit carotid arteries.

Gene therapy for vascular disease

Atherosclerosis is a degenerative process characterized by endothelial cell dysfunction, inflammatory cell adhesion and infiltration, and the accumulation of cellular and matrix elements leading to the formation of fibrocellular plaques. In the end stages, advanced occlusive plaques limit blood flow and oxygen delivery resulting in the well-known ischemic syndromes of the coronary, skeletal muscle, mesenteric, and cerebrovascular circulation. Moreover, sudden critical ischemic events may be precipitated by plaque disturbance, rupture, hemorrhage, and/or thrombosis. Traditional pharmacologic approaches have been effective in reducing serum cholesterol and controlling thrombosis but, in the main, have had little impact on the treatment of advanced lesions. The purpose of this review is to examine the current status of gene therapy for vascular proliferation, aberrant endothelial function, thrombosis, peripheral ischemia, and modification of the blood/biomaterial interface.

Gene therapy and vascular disease: potential applications in vascular surgery

Advances in molecular biology have generated methods that are used to enhance diagnosis and treatment of a variety of human diseases. More recently modification of gene expression in cells by gene transfer has been introduced as a new therapeutic modality. The targeting of vascular cells with this method is appealing not only for anatomical reasons, but also because endovascular techniques provide access to the vasculature and makes site-specific delivery possible. Over the past few years, gene transfer has been widely used to explore the pathophysiology of vascular diseases in experimental models and available data suggests that this method may eventually become a therapeutic alternative for vascular disorders such as restenosis, graft failure, and critical ischaemia. In the following we discuss the methodology of gene transfer, its tentative use in vascular diseases related to vascular surgery, and the problems associated with this new technology.

Established immunity precludes adenovirus-mediated gene transfer in rat carotid arteries. Potential for immunosuppression and vector engineering to overcome barriers of immunity

Preclinical arterial gene transfer studies with adenoviral vectors are typically performed in laboratory animals that lack immunity to adenovirus. However, human patients are likely to have prior exposures to adenovirus that might affect: (a) the success of arterial gene transfer; (b) the duration of recombinant gene expression; and (c) the likelihood of a destructive immune response to transduced cells. We confirmed a high prevalence (57%) in adult humans of neutralizing antibodies to adenovirus type 5. We then used a rat model to establish a central role for the immune system in determining the success as well as the duration of recombinant gene expression after adenovirus-mediated gene transfer into isolated arterial segments. Vector-mediated recombinant gene expression, which was successful in naive rats and prolonged by immunosuppression, was unsuccessful in the presence of established immunity to adenovirus. 4 d of immunosuppressive therapy permitted arterial gene transfer and expression in immune rats, but at decreased levels. Ultraviolet-irradiated adenoviral vectors, which mimic advanced-generation vectors (reduced viral gene expression and relatively preserved capsid function), were less immunogenic than were nonirradiated vectors. A primary exposure to ultraviolet-irradiated (but not nonirradiated) vectors permitted expression of a recombinant gene after redelivery of the same vector. In conclusion, arterial gene transfer with current type 5 adenoviral vectors is unlikely to result in significant levels of gene expression in the majority of humans. Both immunosuppression and further engineering of the vector genome to decrease expression of viral genes show promise in circumventing barriers to adenovirus-mediated arterial gene transfer.

Incorporation of β-Galactosidase-Expressing Endothelial Cells into the Skeletal Muscle Microvascular Bed of Mice

Cloned murine endothelial cells (cEC) were used as a carrier system for introducing a foreign gene into the microvascular bed of the hind limb of inbred mice. cEC were transfected with a β-galactosidase-neo fusion construct, which enables both selection for DNA uptake in the presence of G 418 and the staining of cells for β-galactosidase activity. Transfected cEC adhered and integrated readily into confluent monolayers of nontransfected cEC (up to 26% of total cell number). Seeding lacZ-transfected cEC on explanted arteries revealed rapid adhesion of the cells (within minutes) to the intact endothelium. After injection of 106transfected EC via the femoral artery into the microvascular bed of the hind limb their presence was documented by β-galactosidase staining after various time periods (1 h to 4 wk). Implanted cEC were detected in numerous elements of the microcirculation both in frozen sections and in squash preparations of the hind limb muscle and in the femoral bone up to 4 wk after the injection. The microvascular bed of skeletal muscle of the mouse as a recipient site for transduced syngeneic endothelial cells is, thus, a suitable experimental model to study various strategies for somatic gene therapy. Copyright © 1997 Elsevier Science Inc.