Local adenoviral-mediated inducible nitric oxide synthase gene transfer inhibits neointimal formation in the porcine coronary stented model

Pharmacological prevention of intimal hyperplasia: A state-of-the-art review

Intimal hyperplasia (IH) occurs in a considerable number of cases of blood vessel reconstruction by stenting or balloon angioplasty, venous bypass grafting, and arteriovenous dialysis accesses. It is triggered by endothelial injury during the vascular intervention and leads to vessel restenosis with life-threatening consequences for patients. To date, the drugs used for IH prevention in clinics-paclitaxel and rapalog drugs-have been focusing primarily on the vascular smooth muscle cell (VSMC) proliferation pathway of IH development. Limitations, such as endothelial toxicity and inappropriate drug administration timing, have spurred the search for new and efficient pharmacological approaches to control IH. In this state-of-the-art review, we present the pathways of IH development, focusing on the key events and actors involved in IH. Subsequently, we discuss different drugs and drug combinations interfering with these pathways based on their effect on peripheral circulation IH models in animal studies, or on clinical reports. The reports were obtained through an extensive search of peer-reviewed publications in Pubmed, Embase, and Google Scholar, with search equations composed based on five concepts around IH and their various combinations. To improve vascular intervention outcomes, rethinking of conventional therapeutic approaches to IH prevention is needed. Exploring local application of drugs and drug combinations acting on different pathophysiological pathways of IH development has the potential to provide effective and safe restenosis prevention.

Delivery of viral vectors for gene therapy in intimal hyperplasia and restenosis in atherosclerotic swine

Cardiovascular diseases including atherosclerosis are a major financial and health burden globally. Inflammation associated with atherosclerosis results in the development of plaques that can rupture causing thrombosis, stroke, or death. The most widely used treatment for the removal of atherosclerotic plaques is percutaneous transluminal coronary angioplasty (PTCA) with or without stenting. Although this is a safer and minimally invasive method, restenosis and intimal hyperplasia after interventional procedure remains a major hurdle and more refined approaches are needed. Studies in large animal models such as pigs have facilitated a greater understanding of the underlying mechanisms of the disease and provided novel targets for therapeutic intervention. In pre-clinical studies, viral vector gene therapy has emerged as a promising option for the reduction and/or prevention of restenosis and intimal hyperplasia. Although studies in animal models have generated promising results, clinical trials have yet to prove the clinical efficacy of gene therapy in coronary artery diseases. In this review, we examined and critically reviewed the most recent advances in viral vector gene therapy obtained from studies using porcine model of atherosclerosis.

Drug- and Gene-eluting Stents for Preventing Coronary Restenosis

Coronary artery disease (CAD) has been reported to be a major cause of death worldwide. Current treatment methods include atherectomy, coronary angioplasty (as a percutaneous coronary intervention), and coronary artery bypass. Among them, the insertion of stents into the coronary artery is one of the commonly used methods for CAD, although the formation of in-stent restenosis (ISR) is a major drawback, demanding improvement in stent technology. Stents can be improved using the delivery of DNA, siRNA, and miRNA rather than anti-inflammatory/anti-thrombotic drugs. In particular, genes that could interfere with the development of plaque around infected regions are conjugated on the stent surface to inhibit neointimal formation. Despite their potential benefits, it is necessary to explore the various properties of gene-eluting stents. Furthermore, multifunctional electronic stents that can be used as a biosensor and deliver drug- or gene-based on physiological condition will be a very promising way to the successful treatment of ISR. In this review, we have discussed the molecular mechanism of restenosis, the use of drug- and gene-eluting stents, and the possible roles that these stents have in the prevention and treatment of coronary restenosis. Further, we have explained how multifunctional electronic stents could be used as a biosensor and deliver drugs based on physiological conditions.

Surface modification of coronary stents with SiCOH plasma nanocoatings for improving endothelialization and anticoagulation

The surface properties of intravascular stent play a crucial role in preventing in-stent restenosis (ISR). In this study, SiCOH plasma nanocoatings were used to modify the surfaces of intravascular stents to improve their endothelialization and anticoagulation properties. SiCOH plasma nanocoatings with thickness of 30-40 nm were deposited by low-temperature plasmas from a gas mixture of trimethysilane (TMS) and oxygen at different TMS:O2 ratios. Water contact angle measurements showed that the SiCOH plasma nanocoating surfaces prepared from TMS:O2  = 1:4 are hydrophilic with contact angle of 29.5 ± 1.9°. The SiCOH plasma nanocoated 316L stainless steel (316L SS) wafers were first characterized by in vitro adhesion tests for blood platelets and human umbilical vein endothelial cells. The in vitro test results showed that the SiCOH plasma nanocoatings prepared from TMS:O2  = 1:4 had excellent hemo- and cytocompatibility. With uncoated 316L SS stents as the control, the SiCOH plasma nanocoated 316L SS stents were implanted into rabbit abdominal artery model for in vivo evaluation of re-endothelialization and ISR inhibition. After implantation for 12 weeks, the animals testing results showed that the SiCOH plasma nanocoatings accelerated re-endothelialization and inhibited ISR with lumen reduction of 26.3 ± 10.1%, which were considerably less than the 41.9 ± 11.6% lumen reduction from the uncoated control group.

Nanoparticle drug- and gene-eluting stents for the prevention and treatment of coronary restenosis

Percutaneous coronary intervention (PCI) has become the most common revascularization procedure for coronary artery disease. The use of stents has reduced the rate of restenosis by preventing elastic recoil and negative remodeling. However, in-stent restenosis remains one of the major drawbacks of this procedure. Drug-eluting stents (DESs) have proven to be effective in reducing the risk of late restenosis, but the use of currently marketed DESs presents safety concerns, including the non-specificity of therapeutics, incomplete endothelialization leading to late thrombosis, the need for long-term anti-platelet agents, and local hypersensitivity to polymer delivery matrices. In addition, the current DESs lack the capacity for adjustment of the drug dose and release kinetics appropriate to the disease status of the treated vessel. The development of efficacious therapeutic strategies to prevent and inhibit restenosis after PCI is critical for the treatment of coronary artery disease. The administration of drugs using biodegradable polymer nanoparticles as carriers has generated immense interest due to their excellent biocompatibility and ability to facilitate prolonged drug release. Despite the potential benefits of nanoparticles as smart drug delivery and diagnostic systems, much research is still required to evaluate potential toxicity issues related to the chemical properties of nanoparticle materials, as well as to their size and shape. This review describes the molecular mechanism of coronary restenosis, the use of DESs, and progress in nanoparticle drug- or gene-eluting stents for the prevention and treatment of coronary restenosis.

Efficient transduction of vascular smooth muscle cells with a translational AAV2.5 vector: a new perspective for in-stent restenosis gene therapy

Coronary artery disease represents the leading cause of mortality in the developed world. Percutaneous coronary intervention (PCI) involving stent placement remains disadvantaged by restenosis or thrombosis. Vascular gene-therapy-based methods may be approached, but lack a vascular gene delivery vector.

We report a safe and efficient long-term transduction of rat carotid vessels after balloon-injury intervention with a translational optimized AAV2.5 vector. Compared to other known AAV serotypes, AAV2.5 demonstrated the highest transduction efficiency of human coronary artery vascular smooth muscle cells (VSMC) in vitro. Local delivery of AAV2.5-driven transgenes in injured carotid arteries resulted in transduction as soon as day 2 after surgery and persisted for at least 30 days. In contrast to adenovirus 5 vector, inflammation was not detected in AAV2.5-transduced vessels. The functional effects of AAV2.5-mediated gene transfer on neointimal thickening were assessed using the sarco/endoplasmic reticulum Ca²⁺ ATPase (SERCA2a) human gene, known to inhibit VSMC proliferation. At 30 days, human SERCA2a mRNA was detected in transduced arteries. Morphometric analysis revealed a significant decrease of neointimal hyperplasia in AAV2.5-SERCA2a transduced arteries: 28.36±11.30 (n=8) vs 77.96±24.60 (n=10) μm², in AAV2.5-GFP-infected, p<0.05.

In conclusion, AAV2.5 vector can be considered as a promising safe and effective vector for vascular gene therapy.

Endovascular Gene Delivery from a Stent Platform: Gene- Eluting Stents

A synergistic impact of research in the fields of post-angioplasty restenosis, drug-eluting stents and vascular gene therapy over the past 15 years has shaped the concept of gene-eluting stents. Gene-eluting stents hold promise of overcoming some biological and technical problems inherent to drug-eluting stent technology. As the field of gene-eluting stents matures it becomes evident that all three main design modules of a gene-eluting stent: a therapeutic transgene, a vector and a delivery system are equally important for accomplishing sustained inhibition of neointimal formation in arteries treated with gene delivery stents. This review summarizes prior work on stent-based gene delivery and discusses the main optimization strategies required to move the field of gene-eluting stents to clinical translation.

Nitric oxide and nitrite-based therapeutic opportunities in intimal hyperplasia

Vascular intimal hyperplasia (IH) limits the long term efficacy of current surgical and percutaneous therapies for atherosclerotic disease. There are extensive changes in gene expression and cell signaling in response to vascular therapies, including changes in nitric oxide (NO) signaling. NO is well recognized for its vasoregulatory properties and has been investigated as a therapeutic treatment for its vasoprotective abilities. The circulating molecules nitrite (NO(2)(-)) and nitrate (NO(3)(-)), once thought to be stable products of NO metabolism, are now recognized as important circulating reservoirs of NO and represent a complementary source of NO in contrast to the classic L-arginine-NO-synthase pathway. Here we review the background of IH, its relationship with the NO and nitrite/nitrate pathways, and current and future therapeutic opportunities for these molecules.

Early hypercholesterolemia contributes to vasomotor dysfunction and injury associated atherogenesis that can be inhibited by nitric oxide

OBJECTIVE

Atherosclerosis results in vasomotor dysfunction, in part, through impairment of nitric oxide (NO) dependent vasodilation. It is unclear whether blood vessels are dysfunctional in an early environment of hypercholesterolemia alone and if this contributes to the vascular injury response. We hypothesize that early hypercholesterolemia, prior to gross vascular changes, contributes to vasomotor dysfunction and the vascular injury response. The efficacy of NO therapy to protect against the injury response in this setting was also assessed.

METHODS

The effect of oxidized low density lipoprotein (oxLDL) and inducible NO synthase (iNOS) gene transfer on rat aortic smooth muscle cell (SMC) proliferation was measured with (3)H-thymidine incorporation. Common carotid arteries (CCA) from wild-type C57BL6 (WT or C57) and apolipoprotein E deficient (ApoE KO) mice fed normal or Western diets for 6 to 8 weeks were tested for vasomotor function using an arteriograph system. Studies were repeated after CCA injury. The effect of iNOS gene transfer on morphometry by histology and vasomotor responses in injured CCAs in ApoE KO was examined.

RESULTS

OxLDL increased SMC proliferation by >50%. In SMC expressing iNOS, NO production was unaffected by oxLDL and reduced oxLDL and still inhibited SMC proliferation. Endothelium dependent vasorelaxation was reduced in uninjured CCAs from ApoE KO and C57 mice on the Western vs normal diet (ApoE 39% ± 2% vs 55% ± 13%; C57 50% ± 13% vs 76% ± 5%, P < .001) and was increased with longer durations of hypercholesterolemia. Endothelium-dependent and independent vasodilator responses were severely disrupted in C57 and ApoE KO mice 2 weeks following CCA injury but both recovered by 4 weeks. CCA injury in ApoE KO mice resulted in the formation of atheromatous lesions while C57 mice showed no change (intima 27,795 ± 1829 vs 237 ± 28 μm(2); media 46,306 ± 2448 vs 11,714 ± 392 μm(2), respectively; P < .001). This structural change in the ApoE KO reduced distensibility and increased stiffness. Finally, iNOS gene transfer to injured CCA in ApoE KO mice dramatically reduced atheromatous neointimal lesion formation.

CONCLUSIONS

Early hypercholesterolemia impairs endothelial function, with severity being related to duration and magnitude of hypercholesterolemia. Severe hypercholesterolemia leads to atheromatous lesion formation following injury and stresses the role of vascular injury in atherogenesis and suggests different mechanisms are involved in endothelial dysfunction and the injury response. Despite these changes, iNOS gene transfer still effectively inhibits atheroma formation. These findings support early correction of hypercholesterolemia and emphasize the potential role for NO based therapies in disease states.

Non-viral eNOS gene delivery and transfection with stents for the treatment of restenosis

BACKGROUND

In this study, we have examined local non-viral gene delivery, transfection, and therapeutic efficacy of endothelial nitric oxide synthase (eNOS) encoding plasmid DNA administered using coated stents in a rabbit iliac artery restenosis model.

METHODS

Lipopolyplexes (LPPs) with eNOS expressing plasmid DNA were immobilized on stainless steel stents using poly(D,L-lactide-co-glycolide) (PLGA) and type B gelatin coatings. The gene-eluting stents were implanted bilaterally in the denuded iliac arteries and eNOS transfection and therapeutic efficacy were examined 14 days after implantation.

RESULTS

The results show that non-viral lipopolyplex-coated stents can efficiently tranfect eNOS locally in the arterial lumen assessed by PCR and ELISA. Human eNOS ELISA levels were significantly raised 24 hours after transfection compared to controls (125 pg eNOS compared to <50 pg for all controls including naked DNA). Local eNOS production suppressed smooth muscle cell proliferation and promoted re-endothelialization of the artery showing a significant reduction in restenosis of 1.75 neointima/media ratio for stents with lipoplexes encoding eNOS compared with 2.3 neointima/media ratio for stents with lipoplexes encosing an empty vector.

CONCLUSIONS

These results support the hypothesis that a potent non-viral gene vector encoding for eNOS coated onto a stent can inhibit restenosis through inhibition of smooth muscle cell growth and promotion of a healthy endothelium.

Factors that affect mass transport from drug eluting stents into the artery wall

Coronary artery disease can be treated by implanting a stent into the blocked region of an artery, thus enabling blood perfusion to distal vessels. Minimally invasive procedures of this nature often result in damage to the arterial tissue culminating in the re-blocking of the vessel. In an effort to alleviate this phenomenon, known as restenosis, drug eluting stents were developed. They are similar in composition to a bare metal stent but encompass a coating with therapeutic agents designed to reduce the overly aggressive healing response that contributes to restenosis. There are many variables that can influence the effectiveness of these therapeutic drugs being transported from the stent coating to and within the artery wall, many of which have been analysed and documented by researchers. However, the physical deformation of the artery substructure due to stent expansion, and its influence on a drugs ability to diffuse evenly within the artery wall have been lacking in published work to date. The paper highlights previous approaches adopted by researchers and proposes the addition of porous artery wall deformation to increase model accuracy.

Nitric oxide synthase gene therapy: progress and prospects

NOS gene therapy has been the focus of extensive research as dysfunction of this enzyme has been implicated in several cardiovascular diseases. Research has concentrated on comparing the effect of gene delivery of NOS isoforms (eNOS, iNOS and nNOS) in healthy and diseased animal models on intimal hyperplasia, restenosis, vascular tone and ischemia-reperfusion injury. Most results demonstrate therapeutic benefits following vascular gene delivery of all NOS in pre-clinical models of cardiovascular disease. eNOS has been shown to have particular promise as it promotes re-endothelialisation and inhibits intimal hyperplasia in injured blood vessels. The ultimate goal is to translate the benefit of NOS gene therapy in animal models into clinical practise. To develop NOS gene therapy for clinical use further work needs to be undertaken to improve delivery systems and vectors to minimise detrimental side-effects and enhance positive treatment outcomes. This review focuses on current research on NOS gene therapy in cardiovascular disease and identifies the next steps that would be necessary to lead to clinical trials.

Immobilization of plasmid DNA on an anti-DNA antibody modified coronary stent for intravascular site-specific gene therapy

BACKGROUND

The aim of the present study was to investigate the incorporation of plasmid DNA (pDNA) onto a coronary stent by chemo-immunoconjugation for achieving site-specific gene delivery.

METHODS

Anti-DNA immunoglobulin M antibody was chemically linked onto collagen-coated stent by using N-succinimidyl-3-(2-pyridyldithiol)-propionate as cross-linker. pDNA was tethered on the antibody-immobilized stent by highly specific antigen-antibody affinity interaction. Radioactive-labeled antibody and pDNA were used to evaluate binding capacity and stability. A reporter plasmid pEGFP was tethered on the antibody-immobilized stents that was assessed in cell culture and in rabbit carotid model.

RESULTS

The amount of antibody chemically linked on the stents was 15-fold higher than that of the control and its retention time was also significantly longer. The pEGFP-tethered stents had no detrimental effects on cell growth. In cell culture studies, numerous green fluorescent protein (GFP)-transfected cells were only found on the stent, which demonstrated high localization and efficiency of gene delivery. The overall GFP transfection efficiency in treated rabbit carotid arteries was 2.8 +/- 0.7% of the total cells. However, the rate of neointima transfection was 7.0 +/- 0.8% of total cells in this region. Importantly, no distal spreading of the vector was detected by polymerase chain reaction, either in distal organs or in the downstream segments of the stented arteries.

CONCLUSIONS

For the first time, our group reports the successful use of anti-DNA antibody-immobilized metal stent as plasmid gene delivery system that possess high efficiency and site-specificity in vitro and in vivo.

Local delivery of gene vectors from bare-metal stents by use of a biodegradable synthetic complex inhibits in-stent restenosis in rat carotid arteries

BACKGROUND

Local drug delivery from polymer-coated stents has demonstrated efficacy for preventing in-stent restenosis; however, both the inflammatory effects of polymer coatings and concerns about late outcomes of drug-eluting stent use indicate the need to investigate innovative approaches, such as combining localized gene therapy with stent angioplasty. Thus, we investigated the hypothesis that adenoviral vectors (Ad) could be delivered from the bare-metal surfaces of stents with a synthetic complex for reversible vector binding.

METHODS AND RESULTS

We synthesized the 3 components of a gene vector binding complex: (1) A polyallylamine bisphosphonate with latent thiol groups (PABT), (2) a polyethyleneimine (PEI) with pyridyldithio groups for amplification of attachment sites [PEI(PDT)], and (3) a bifunctional (amine- and thiol-reactive) cross-linker with a labile ester bond (HL). HL-modified Ad attached to PABT/PEI(PDT)-treated steel surfaces demonstrated both sustained release in vitro over 30 days and localized green fluorescent protein expression in rat arterial smooth muscle cell cultures, which were not sensitive to either inhibition by neutralizing anti-Ad antibodies or inactivation after storage at 37 degrees C. In rat carotid studies, deployment of steel stents configured with PABT/PEI(PDT)/HL-tethered adenoviral vectors demonstrated both site-specific arterial Ad(GFP) expression and adenovirus-luciferase transgene activity per optical imaging. Rat carotid stent delivery of adenovirus encoding inducible nitric oxide synthase resulted in significant inhibition of restenosis.

CONCLUSIONS

Reversible immobilization of adenovirus vectors on the bare-metal surfaces of endovascular stents via a synthetic complex represents an efficient, tunable method for sustained release of gene vectors to the vasculature.

Beneficial effect of a short-acting NO donor for the prevention of neointimal hyperplasia

Nitric oxide (NO)-based therapies effectively inhibit neointimal hyperplasia in animal models of arterial injury and bypass grafting, but are not available clinically. We created a simple, effective, locally applied NO-eluting therapy to prevent restenosis after vascular procedures. We investigated the efficacy of perivascular delivery of two distinctly different diazeniumdiolate NO donors, 1-[2-(carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate (PROLI/NO) (short half-life) and diazeniumdiolated poly(acrylonitrile) (PAN/NO) (long half-life), in powder or gel form (30% poloxamer 407), at inhibiting neointimal hyperplasia using the rat carotid artery injury model. Two weeks postinjury, all of the NO-eluting therapies successfully reduced neointimal hyperplasia. However, most dramatically, PROLI/NO powder reduced intimal area by 91.2% (p<0.05) versus injury alone. PROLI/NO powder was noted to reduce the medial area (40.2% vs injury alone, p<0.05), whereas other groups showed no such effect. Three days postinjury, each NO treatment group significantly reduced cellular proliferation. However, inflammatory markers revealed a distinct pattern: PAN/NO groups displayed increased leukocyte infiltration (p<0.05), whereas PROLI/NO groups displayed less macrophage infiltration (p<0.05). In conclusion, perivascular delivery of diazeniumdiolate NO donors in powder or gel form effectively inhibits neointimal hyperplasia. Application of short-acting PROLI/NO powder most effectively inhibited neointimal hyperplasia and inflammation and may represent a simple, clinically applicable NO-eluting therapy to prevent neointimal hyperplasia and restenosis after open vascular interventions.

Delivery of large biopharmaceuticals from cardiovascular stents: a review

This review focuses on new and emerging large-molecule bioactive agents delivered from stent surfaces in drug-eluting stents (DESs) to inhibit vascular restenosis in the context of interventional cardiology. New therapeutic agents representing proteins, nucleic acids (small interfering RNAs and large DNA plasmids), viral delivery vectors, and even engineered cell therapies require specific delivery designs distinct from traditional smaller-molecule approaches on DESs. While small molecules are currently the clinical standard for coronary stenting, extension of the DESs to other lesion types, peripheral vasculature, and nonvasculature therapies will seek to deliver an increasingly sophisticated armada of drug types. This review describes many of the larger-molecule and biopharmaceutical approaches reported recently for stent-based delivery with the challenges associated with formulating and delivering these drug classes compared to the current small-molecule drugs. It also includes perspectives on possible future applications that may improve safety and efficacy and facilitate diversification of the DESs to other clinical applications.

Cardiovascular gene therapy: current status and therapeutic potential

Gene therapy is emerging as a potential treatment option in patients suffering from a wide spectrum of cardiovascular diseases including coronary artery disease, peripheral vascular disease, vein graft failure and in-stent restenosis. Thus far preclinical studies have shown promise for a wide variety of genes, in particular the delivery of genes encoding growth factors such as vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) to treat ischaemic vascular disease both peripherally and in coronary artery disease. VEGF as well as other genes such as TIMPs have been used to target the development of neointimal hyperplasia to successfully prevent vein graft failure and in-stent restenosis in animal models. Subsequent phase I trials to examine safety of these therapies have been successful with low levels of serious adverse effects, and albeit in the absence of a placebo group some suggestion of efficacy. Phase 2 studies, which have incorporated a placebo group, have not confirmed this early promise of efficacy. In the next generation of clinical gene therapy trials for cardiovascular disease, many parameters will need to be adjusted in the search for an effective therapy, including the identification of a suitable vector, appropriate gene or genes and an effective vector delivery system for a specific disease target. Here we review the current status of cardiovascular gene therapy and the potential for this approach to become a viable treatment option.

Dimethylarginine dimethylaminohydrolase promotes endothelial repair after vascular injury

OBJECTIVES

We sought to determine if a reduction in asymmetric dimethylarginine (ADMA) enhances endothelial regeneration.

BACKGROUND

Asymmetric dimethylarginine is an endogenous inhibitor of nitric oxide synthase (NOS). Increased plasma levels of ADMA are associated with endothelial vasodilator dysfunction in patients with vascular disease or risk factors. Asymmetric dimethylarginine is eliminated largely by the action of dimethylarginine dimethylaminohydrolase (DDAH), which exists in 2 isoforms. Dimethylarginine dimethylaminohydrolase-1 transgenic (TG) mice manifest increased DDAH activity, reduced plasma and tissue ADMA levels, increased nitric oxide synthesis, and reduced systemic vascular resistance.

METHODS

The left femoral arteries of DDAH1 TG mice and wild-type (WT) mice were injured by a straight spring wire, and regeneration of the endothelial cell (EC) monolayer was assessed. Endothelial sprouting was assayed with growth factor-reduced Matrigel.

RESULTS

Regeneration of the EC monolayer was more complete 1 week after injury in TG mice (WT vs. TG: 40.0 +/- 6.5% vs. 61.2 +/- 6.4%, p < 0.05). The number of CD45 positive cells at the injured sites was reduced by 62% in DDAH TG mice (p < 0.05). Four weeks after injury, the neointima area and intima/media ratio were attenuated in DDAH TG mice (WT vs. TG: 0.049 +/- 0.050 mm2 vs. 0.031 +/- 0.060 mm2, 3.1 +/- 0.5 vs. 1.7 +/- 0.2, respectively, p < 0.05). Endothelial cell sprouting from vascular segments increased in TG mice (WT vs. TG: 24.3 +/- 3.9 vs. 39.0 +/- 2.2, p < 0.05).

CONCLUSIONS

We find for the first time an important role for DDAH in EC regeneration and in neointima formation. Strategies to enhance DDAH expression or activity might be useful in restoring the endothelial monolayer and in treating vascular disease.

Lipoplex gene transfer of inducible nitric oxide synthase inhibits the reactive intimal hyperplasia after expanded polytetrafluoroethylene bypass grafting

OBJECTIVE

Intimal hyperplasia (IH) is most commonly the cause of graft occlusion in infrainguinal bypass grafting for arterial occlusive disease. We investigated the influence of nitric oxide on the IH of the arterial vessel wall at the region of prosthetic bypass anastomoses.

METHODS

Experiments were performed in 10 Foxhound dogs. We used a technique of inducible nitric oxide synthase (iNOS) overexpression by a non-virus-mediated, liposome-based iNOS gene transfer. The plasmid pSCMV-iNOS, which drives the expression of iNOS under control of the cytomegalovirus promoter, was complexed with cationic liposomes (lipoplexes). Segments of both carotid arteries were pretreated by intramural injection of a lipoplex solution by using an infiltrator balloon catheter (Infiltrator Drug Delivery Balloon System). In each dog, iNOS was administered at one side, and a control vector (pSCMV2) was administered at the contralateral side. Carotid arteries were ligated, and bypass grafts (expanded polytetrafluoroethylene, 6-mm, ring enforced) were implanted on both sides. The proximal and distal anastomoses (end-to-side fashion; running nonabsorbable sutures) were placed in the pretreated regions. After 6 months, the prostheses were excised, and the intimal thicknesses of 50 cross sections (orcein staining) of each anastomosis were measured planimetrically.

RESULTS

The average reduction of the neointima thickness of the iNOS side in proximal anastomoses at the prosthetic wall, suture region, and arterial wall was 43%, 52%, and 81%, respectively. In distal anastomoses, the average reduction was 40%, 47%, and 52%, respectively. All differences of neointima thickness between the iNOS and control sides were statistically significant (Wilcoxon test; P < or = .05).

CONCLUSIONS

Inducible NOS expression is an efficient approach for inhibition of IH. In contrast to earlier studies, which investigated the efficacy of gene therapeutic NOS expression at 3 to 4 weeks after intervention, the novelty of our findings is that a single local lipoplex-mediated transfection of the vascular wall with iNOS-expressing plasmids leads to a reduction of IH in a prosthetic in vivo model even after 6 months. Because all components can be manufactured under Good Manufacturing Practice conditions (the quality-management system of the European pharmaceutical industry based on ISO 9000), this approach is also amenable to human therapy.

Bisphosphonate-mediated gene vector delivery from the metal surfaces of stents

The clinical use of metallic expandable intravascular stents has resulted in improved therapeutic outcomes for coronary artery disease. However, arterial reobstruction after stenting, in-stent restenosis, remains an important problem. Gene therapy to treat in-stent restenosis by using gene vector delivery from the metallic stent surfaces has never been demonstrated. The present studies investigated the hypothesis that metal-bisphosphonate binding can enable site-specific gene vector delivery from metal surfaces. Polyallylamine bisphosphonate (PAA-BP) was synthesized by using Michael addition methodology. Exposure to aqueous solutions of PAA-BP resulted in the formation of a monomolecular bisphosphonate layer on metal alloy surfaces (steel, nitinol, and cobalt-chromium), as demonstrated by x-ray photoelectron spectroscopy. Surface-bound PAA-BP enabled adenoviral (Ad) tethering due to covalent thiol-binding of either anti-Ad antibody or a recombinant Ad-receptor protein, D1. In arterial smooth muscle cell cultures, alloy samples configured with surface-tethered Ad were demonstrated to achieve site-specific transduction with a reporter gene, (GFP). Rat carotid stent angioplasties using metal stents exposed to aqueous PAA-BP and derivatized with anti-knob antibody or D1 resulted in extensive localized Ad-GFP expression in the arterial wall. In a separate study with a model therapeutic vector, Ad-inducible nitric oxide synthase (iNOS) attached to the bisphosphonate-treated metal stent surface via D1, significant inhibition of restenosis was demonstrated (neointimal/media ratio 1.68 +/- 0.27 and 3.4 +/- 0.35; Ad-iNOS vs. control, P < 0.01). It is concluded that effective gene vector delivery from metallic stent surfaces can be achieved by using this approach.

Local gene transduction of cyclooxygenase-1 increases blood flow in injured atherosclerotic rabbit arteries

BACKGROUND

Cyclooxygenase-1 (COX-1) is the rate-limiting component in the synthesis of prostacyclin (PGI2), an important vasodilator and antithrombotic molecule. In balloon-injured, atherosclerosis-free porcine arteries, COX-1 gene transduction increases PGI2 production, induces durable vasodilation, and reduces thrombus formation. We tested the effectiveness of COX-1 local gene transduction for the prevention of postangioplasty restenosis in atherosclerotic arteries in a hypercholesterolemic rabbit model.

METHODS AND RESULTS

We injured 1 carotid artery in 43 Watanabe heritable hyperlipidemic rabbits and performed local gene transduction using a viral vector containing the COX-1 gene (AdCOX-1, n=22) or no genes (Adnull, n=21). Three days later, AdCOX-1-treated arteries stimulated with arachidonic acid produced 100% more PGI2 (P<0.01), 400% more prostaglandin E2 (PGE2) (P<0.01), 400% more prostaglandin E1 (PGE1) (P<0.01), and 250% more cAMP (P<0.05) than Adnull-treated arteries. Twenty-eight days after treatment, Doppler sonography showed that blood flow velocity was preserved in AdCOX-1-treated arteries (ratio 0.92, injured compared with contralateral uninjured carotid artery) but reduced in Adnull-treated arteries (ratio 0.39), suggesting that AdCOX-1 prevented restenosis after injury. COX-1-transduced arteries also showed 80% greater lumen area 28 days after injury (P<0.01).

CONCLUSIONS

The effectiveness of COX-1 in preventing restenosis and preserving normal blood flow 28 days after injury results from increased lumen area caused by durable vasodilation. COX-1 efficacy correlates with an early increase in the production of PGI2, PGE2, PGE1 (known to cause vasodilation), and cAMP. These results demonstrate for the first time that COX-1 gene transduction is an effective treatment for the prevention of postangioplasty restenosis of atherosclerotic arteries under clinically relevant conditions.

Efficient transduction of vascular endothelial cells with recombinant adeno-associated virus serotype 1 and 5 vectors

Recombinant adeno-associated virus (rAAV) has become an attractive tool for gene therapy because of its ability to transduce both dividing and nondividing cells, elicit a limited immune response, and the capacity for imparting long-term transgene expression. Previous studies have utilized rAAV serotype 2 predominantly and found that transduction of vascular cells is relatively inefficient. The purpose of the present study was to evaluate the transduction efficiency of rAAV serotypes 1 through 5 in human and rat aortic endothelial cells (HAEC and RAEC). rAAV vectors with AAV2 inverted terminal repeats containing the human alpha1-antitrypsin (hAAT) gene were transcapsidated using helper plasmids to provide viral capsids for the AAV1 through 5 serotypes. True type rAAV2 and 5 vectors encoding beta-galactosidase or green fluorescence protein were also studied. Infection with rAAV1 resulted in the most efficient transduction in both HAEC and RAEC compared to other serotypes (p < 0.001) at 7 days posttransduction. Interestingly, expression was increased in cells transduced with rAAV5 to levels surpassing rAAV1 by day 14 and 21. Transduction with rAAV1 was completely inhibited by removal of sialic acid with sialidase, while heparin had no effect. These studies are the first demonstration that sialic acid residues are required for rAAV1 transduction in endothelial cells. Transduction of rat aortic segments ex vivo and in vivo demonstrated significant transgene expression in endothelial and smooth muscle cells with rAAV1 and 5 serotype vectors, in comparison to rAAV2. These results suggest the unique potential of rAAV1 and rAAV5-based vectors for vascular-targeted gene-based therapeutic strategies.

iNOS Gene Transfer for Graft Disease

Vascular bypass surgery involves the use of a vascular conduit to circumvent a site of vascular compromise. Vascular graft failure continues to plague both the patients receiving and the surgeons performing these interventions. Demand for the development of a therapy to reduce intimal hyperplasia--the most common cause of bypass graft failure--is significant and has been the goal of many biotechnology groups. The development of gene therapy as a feasible clinical intervention has allowed for novel methods of inhibiting intimal hyperplasia to be conceived. This review describes the evolution of gene transfer of the inducible nitric oxide synthase (iNOS) gene, one of the most successful preclinical interventions to date for vascular disease.

Nitric oxide and arterial disease

Nitric oxide (NO) is a molecule that has gained recognition as a crucial modulator of vascular disease. NO has a number of intracellular effects that lead to vasorelaxation, endothelial regeneration, inhibition of leukocyte chemotaxis, and platelet adhesion. Its role in vascular disease has been intensively investigated and further elucidated over the past two decades. It is important in the pathogenesis of many cardiovascular diseases, including atherosclerosis, intimal hyperplasia, and aneurysmal disease. In addition, NO has been used as a therapeutic tool to treat diseases that range from recurrent stenosis to inhibiting thrombotic events. Many commonly used medications have their therapeutic actions through the production of NO. This review highlights the vascular biologic characteristics of NO, its role in the pathogenesis of cardiovascular disease processes, and its potential therapeutic applications.