Overexpression of p53 Increases Lumen Size and Blocks Neointima Formation in Porcine Interposition Vein Grafts

The role of transcription factors in the pathogenesis and therapeutic targeting of vascular diseases

Transcription factors (TFs) constitute an essential component of epigenetic regulation. They contribute to the progression of vascular diseases by regulating epigenetic gene expression in several vascular diseases. Recently, numerous regulatory mechanisms related to vascular pathology, ranging from general TFs that are continuously activated to histiocyte-specific TFs that are activated under specific circumstances, have been studied. TFs participate in the progression of vascular-related diseases by epigenetically regulating vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs). The Krüppel-like family (KLF) TF family is widely recognized as the foremost regulator of vascular diseases. KLF11 prevents aneurysm progression by inhibiting the apoptosis of VSMCs and enhancing their contractile function. The presence of KLF4, another crucial member, suppresses the progression of atherosclerosis (AS) and pulmonary hypertension by attenuating the formation of VSMCs-derived foam cells, ameliorating endothelial dysfunction, and inducing vasodilatory effects. However, the mechanism underlying the regulation of the progression of vascular-related diseases by TFs has remained elusive. The present study categorized the TFs involved in vascular diseases and their regulatory mechanisms to shed light on the potential pathogenesis of vascular diseases, and provide novel insights into their diagnosis and treatment.

Large animal model of vein grafts intimal hyperplasia: A systematic review

Coronary artery bypass grafting remains the treatment of choice for a large cohort of patients with significant coronary disease. Despite the increased use of arterial grafts, the long saphenous vein remains the most commonly used conduit. Long-term graft patency continues to be the Achilles heel of saphenous vein grafts. This is due to the development of intimal hyperplasia, a chronic inflammatory disease that results in the narrowing and occlusion of a significant number of vein grafts. Research models for intimal hyperplasia are essential for a better understanding of pathophysiological processes of this condition. Large animal models resemble human anatomical structures and have been used as a surrogate to study disease development and prevention over the years. In this paper, we systematically review all published studies that utilized large animal models of vein graft disease with a focus on the type of model and any therapeutic intervention, specifically the use of external stents/mesh.

The p53 pathway in vasculature revisited: A therapeutic target for pathological vascular remodeling?

Pathological vascular remodeling contributes to the development of restenosis following intraluminal interventions, transplant vasculopathy, and pulmonary arterial hypertension. Activation of the tumor suppressor p53 may counteract vascular remodeling by inhibiting aberrant proliferation of vascular smooth muscle cells and repressing vascular inflammation. In particular, the development of different lines of small-molecule p53 activators ignites the hope of treating remodeling-associated vascular diseases by targeting p53 pharmacologically. In this review, we discuss the relationships between p53 and pathological vascular remodeling, and summarize current experimental data suggesting that drugging the p53 pathway may represent a novel strategy to prevent the development of vascular remodeling.

Development of gene therapy with a cyclic adenosine monophosphate response element decoy oligodeoxynucleotide to prevent vascular intimal hyperplasia

OBJECTIVE

Intimal hyperplasia (IH) is the main cause of therapeutic failure after vascular and endovascular surgery. However, there is currently no targeted therapy for the treatment of IH. We recently reported that the inhibition of cyclic adenosine monophosphate response element (CRE) binding protein (CREB) activation is important in vein graft IH. We focused on a decoy oligodeoxynucleotide (ODN) therapeutic strategy for suppressing IH as a clinical application. The objective of this study was to confirm the therapeutic effect of a CRE decoy ODN in an animal model as a novel therapy for preventing intimal hyperplasia as the first step of the preclinical study of our strategy.

METHODS

We designed two phosphorothioate CREs and two scramble decoy ODNs and screened them using a CREB transcription assay to check their ability to bind to a CRE sequence. We chose a CRE decoy ODN with high first-binding ability and transfected it into vascular smooth muscle cells (VSMCs) in vitro. Proliferation and migration were assessed using MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assays and modified Boyden chamber assays. We examined CRE activity using a luciferase reporter gene assay. We assessed the expression of messenger RNAs by quantitative real-time polymerase chain reaction. In a wire-injury mouse model (C57BL6, n = 6), CRE decoy ODN was transfected into the injured vessel wall using an ultrasound-sonoporation method in vivo. Mitogen-activated protein kinase-activated protein kinase 3 (MAPKAPK3) and four and a half LIM domains 5 (FHL5) expression of pregrafting vein remnants were assessed by immunohistologic analyses.

RESULTS

Compared with scramble decoy ODN, the selected CRE decoy ODN could significantly decrease CRE activity (mean ± standard error of the mean: 0.20 ± 0.03 vs 1.00 ± 0.16, n = 6; P < .05) as shown by a luciferase reporter gene assay, VSMC proliferation (0.73 ± 0.04 vs 0.89 ± 0.02, n = 6; P < .05) and migration (96.4 ± 6.1 vs 311.4 ± 19.1 migrated VSMCs/well, n = 6; P < .05) after 24-hour transfection. The CRE decoy ODN significantly suppressed the formation of IH at injured vessel walls in an animal model, as analyzed by pathologic staining (0.20 ± 0.02 vs 0.56 ± 0.08, area of the intima/area of the artery vs the control after 21 days' transfection, n = 6; P < .05). Furthermore, MAPKAPK3 and FHL5, which are CREB activators, were significantly expressed in pregrafting vein remnants in diabetes mellitus patients.

CONCLUSIONS

CREB-CRE signaling is an important mechanism of IH formation, and CRE decoy therapy can help preventing IH. This study is the first part of the preclinical study of our strategy.

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.

Inhibition of neddylation by MLN4924 improves neointimal hyperplasia and promotes apoptosis of vascular smooth muscle cells through p53 and p62

Targeting apoptosis of vascular smooth muscle cells (VSMCs) represents an attractive approach to diminish the occurrence of restenosis. Neddylation is a highly conserved post-translational modification process and inhibition of neddylation has been shown to regulate apoptosis of other cells. However, the impacts of neddylation inhibition on VSMCs and neointimal hyperplasia have not been studied. In our present study, we have shown that MLN4924, a selective inhibitor of NEDD8-activating enzyme (NAE), markedly inhibited neointimal hyperplasia and accumulation of VSMCs, whereas increased apoptosis in the vascular wall. In vitro studies revealed that MLN4924 induced G2/M arrest and apoptosis of human VSMCs. Knockdown of NAE1 had similar effects. MLN4924 upregulated p53 and p62 in human VSMCs. Knockdown of either p53 or p62 mitigated the impacts of MLN4924 on G2/M arrest and apoptosis. Moreover, p53 knockdown abolished MLN4924-induced upregulation of p62. Finally, smooth muscle p53 knockout mice were generated and subjected to femoral artery injury and MLN4924 treatment. Deficiency of p53 in smooth muscle blocked the effects of MLN4924 on neointimal hyperplasia and apoptosis. Together, our results revealed that neddylation inhibition induces apoptosis through p53 and p62 in VSMCs and improves neointimal hyperplasia mainly by promoting apoptosis through smooth muscle p53 in mice. These pre-clinical data provide strong translational implications for targeting restenosis by perturbation of neddylation using MLN4924.

Inhibition of Smooth Muscle β-Catenin Hinders Neointima Formation After Vascular Injury

OBJECTIVE

Smooth muscle cells (SMCs) contribute to neointima formation after vascular injury. Although β-catenin expression is induced after injury, whether its function is essential in SMCs for neointimal growth is unknown. Moreover, although inhibitors of β-catenin have been developed, their effects on SMC growth have not been tested. We assessed the requirement for SMC β-catenin in short-term vascular homeostasis and in response to arterial injury and investigated the effects of β-catenin inhibitors on vascular SMC growth.

APPROACH AND RESULTS

We used an inducible, conditional genetic deletion of β-catenin in SMCs of adult mice. Uninjured arteries from adult mice lacking SMC β-catenin were indistinguishable from controls in terms of structure and SMC marker gene expression. After carotid artery ligation, however, vessels from mice lacking SMC β-catenin developed smaller neointimas, with lower neointimal cell proliferation and increased apoptosis. SMCs lacking β-catenin showed decreased mRNA expression of Mmp2, Mmp9, Sphk1, and S1pr1 (genes that promote neointima formation), higher levels of Jag1 and Gja1 (genes that inhibit neointima formation), decreased Mmp2 protein expression and secretion, and reduced cell invasion in vitro. Moreover, β-catenin inhibitors PKF118-310 and ICG-001 limited growth of mouse and human vascular SMCs in a dose-dependent manner.

CONCLUSIONS

SMC β-catenin is dispensable for maintenance of the structure and state of differentiation of uninjured adult arteries, but is required for neointima formation after vascular injury. Pharmacological β-catenin inhibitors hinder growth of human vascular SMCs. Thus, inhibiting β-catenin has potential as a therapy to limit SMC accumulation and vascular obstruction.

High expression of ubiquitin-specific peptidase 39 is associated with the development of vascular remodeling

Vascular remodeling is the primary cause underlying the failure of angioplasty surgeries, including vascular stenting, transplant vasculopathy and vein grafts. Multiple restenosis‑associated proteins and genes have been identified to account for this. In the present study, the functions of ubiquitin‑specific peptidase 39 (USP39) were investigated in the context of two vascular remodeling models (a mouse common carotid artery ligation and a pig bilateral saphenous vein‑carotid artery interposition graft). USP39 has previously been observed to be upregulated in ligated arteries, and this result was confirmed in the pig vein graft model. In addition, Transwell assay results demonstrated that vascular smooth muscle cell (VSMC) migration was suppressed by lentiviral vector‑mediated downregulation of USP39 and enhanced by upregulation of USP39. Furthermore, knockdown of USP39 inhibited VSMC cell proliferation and the expression of cyclin D1 and cyclin‑dependent kinase 4, as analyzed via cell counting, MTT assay and western blotting. These results suggest that USP39 may represent a novel therapeutic target for treating vascular injury and preventing vein-graft failure.

Administration of perivascular cyanoacrylate for the prevention of cellular damage in saphenous vein grafts: an experimental model

Objective:

The saphenous vein is the most commonly used graft in coronary artery bypass surgery, since no suitable arterial graft is available. However, the frequency of late graft failure is a cause for research into graft protection. The objective of this study was to investigate the effect of synthetic adhesive cyanoacrylate administration on the saphenous vein graft for preventing vascular damage due to internal pressure on the graft.

Methods:

In this study we enrolled 20 volunteer subjects who had undergone coronary artery bypass surgery and who had excess saphenous vein grafts. Perivascular cyanoacrylate was administered to one of two saphenous vein grafts explanted from each patient. The other saphenous vein graft from each patient was not treated and was used as the control. A model of the arterial system was created using a saphenous vein cardiopulmonary bypass system. Circulation was maintained at 120 mmHg for 45 minutes. Afterwards, the grafts were subjected to histopathological examination.

Results:

The cyanoacrylate group of grafts did not develop severe vascular damage compared with many instances of moderate and severe damage due to compression in the control group of grafts (p = 0.003).

Conclusion

Perivascular administration of cyanoacrylate appeared to be successful in the prevention of early saphenous vein graft injury. No in vivo study has been performed to date to assess endothelial damage in the saphenous vein, in order to demonstrate the long-term effect of cyanoacrylate. Further investigations are needed in this regard.

Efficient gene transfer and durable transgene expression in grafted rabbit veins

Venous bypass grafts are useful treatments for obstructive coronary artery disease. However, their usefulness is limited by accelerated atherosclerosis. Genetic engineering of venous bypass grafts that prevented atherosclerosis could improve long-term graft patency and clinical outcomes. We used a rabbit model of jugular vein-to-carotid interposition grafting to develop gene therapy for vein-graft atherosclerosis. Rabbit veins were easily transduced in situ with a first-generation adenoviral vector; however, most transgene expression (∼80%) was lost within 3 days after arterial grafting. This rapid loss of transgene expression was not prevented by transducing veins after grafting or by prolonged ex vivo transduction. However, delaying vein-graft transduction for 28 days (after the vein had adapted to the arterial circulation) prevented this early loss of transgene expression. We used the delayed transduction approach to test the durability of expression of a therapeutic transgene (apolipoprotein A-I) expressed from a helper-dependent adenoviral (HDAd) vector. HDAd DNA and apolipoprotein A-I mRNA were easily detectable in transduced vein grafts. Vector DNA and mRNA declined by 4 weeks, and then persisted stably for at least 6 months. Delaying transduction for 28 days after grafting permitted initiation of vein-graft neointimal growth and medial thickening before gene transfer. However, vein-graft lumen diameter was not compromised, because of gradual outward remodeling of grafted veins. Our data highlight the promise of HDAd-mediated gene therapy, delivered to arterialized vein grafts, for preventing vein-graft atherosclerosis.

Gene therapy for heart disease: molecular targets, vectors and modes of delivery to myocardium

Despite the numerous hurdles that gene therapy has encountered along the way, clinical trials over the last few years are showing promising results in many fields of medicine, including cardiology, where many targets are moving toward clinical development. In this review, the authors discuss the current state of the art in terms of clinical and preclinical development. They also examine vector technology and available vector-delivery strategies.

Pseudotyping the adenovirus serotype 5 capsid with both the fibre and penton of serotype 35 enhances vascular smooth muscle cell transduction

Ex vivo gene therapy during coronary artery bypass grafting (CABG) holds great potential to prevent excessive smooth muscle cell (SMC) proliferation, neointima formation and graft failure. The most successful preclinical strategies to date have utilised vectors based on the species C adenovirus, Ad5, which engages the Coxsackie and Adenovirus receptor (CAR) as its primary attachment receptor. Profiling receptors on human SMCs demonstrated the absence of CAR but substantial expression of the species B receptor CD46. We performed transduction experiments using Ad5 and the CD46-utilising adenovirus Ad35, and found Ad35 significantly more efficient at transducing SMCs. To evaluate whether transduction could be further augmented, we evaluated chimeric CD46-utilising Ad5/Ad35 vectors comprising the Ad5 capsid pseudotyped with the Ad35 fibre alone (Ad5/F35) or in combination with the Ad35 penton (Ad5/F35/P35). In human smooth muscle cells (hSMCs), Ad5/F35/P35 mediated significantly higher levels of transduction than either parental vector or Ad5/F35. Ex vivo transduction experiments using mouse aortas from CD46 transgenics demonstrated that Ad5/F35/P35 was significantly more efficient at transducing SMCs than the other vectors tested. Finally, ex vivo transduction and immunofluorescent colocalisation experiments using human tissue from CABG procedures confirmed the preclinical potential of Ad5/F35/P35 as an efficient vector for vascular transduction during CABG.

'No-touch' saphenous vein harvesting improves graft performance in patients undergoing coronary artery bypass surgery: a journey from bedside to bench

The saphenous vein is the most commonly used conduit in patients undergoing coronary artery bypass surgery yet its patency is inferior to the internal thoracic artery. Vascular damage inflicted to the vein when using conventional harvesting techniques affects its structure. Endothelial denudation is associated with early vein graft failure while damage of the outermost vessel layers has adverse long-term effects on graft performance. While many in vitro and in vivo experimental studies aimed at improving vein graft patency have been performed to date no significant 'bench to bedside' advances have been made. Among experimental strategies employed is the use of pharmacological agents, gene targeting and external stents. A 'no-touch' technique, where the saphenous vein is removed with minimal trauma and normal architecture preserved, produces a superior graft with long term patency comparable to the internal thoracic artery. Interestingly, many experimental studies are aimed at repairing or replacing those regions of the saphenous vein damaged when harvesting conventionally. 'No-touch' harvesting is superior in coronary artery bypass patients with long-term data published 5years ago. Here we describe a 'bedside to bench' situation where the mechanisms underlying the improved performance of 'no touch' saphenous vein grafts in patients have been studied in the laboratory.

Prevention of coronary in-stent restenosis and vein graft failure: does vascular gene therapy have a role?

Coronary artery bypass grafting (CABG) and percutaneous coronary intervention (PCI), including stent insertion, are established therapies in both acute coronary syndromes (ACS) and symptomatic chronic coronary artery disease refractory to pharmacological therapy. These continually advancing treatments remain limited by failure of conduit grafts in CABG and by restenosis or thrombosis of stented vessel segments in PCI caused by neointimal hyperplasia, impaired endothelialisation and accelerated atherosclerosis. While pharmacological and technological advancements have improved patient outcomes following both procedures, when grafts or stents fail these result in significant health burdens. In this review we discuss the pathophysiology of vein graft disease and in-stent restenosis, gene therapy vector development and design, and translation from pre-clinical animal models through human clinical trials. We identify the key issues that are currently preventing vascular gene therapy from interfacing with clinical use and introduce the areas of research attempting to overcome these.

Cardiac gene therapy in large animals: bridge from bench to bedside

Several clinical trials are evaluating gene transfer as a therapeutic approach to treat cardiac diseases. Although it has just started on the path to clinical application, recent advances in gene delivery technologies with increasing knowledge of underlying mechanisms raise great expectations for the cardiac gene therapy. Although in vivo experiments using small animals provide the therapeutic potential of gene transfer, there exist many fundamental differences between the small animal and the human hearts. Before applying the therapy to clinical patients, large animal studies are a prerequisite to validate the efficacy in an animal model more relevant to the human heart. Several key factors including vector type, injected dose, delivery method and targeted cardiac disease are all important factors that determine the therapeutic efficacy. Selecting the most optimal combination of these factors is essential for successful gene therapy. In addition to the efficacy, safety profiles need to be addressed as well. In this regard, large animal studies are best suited for comprehensive evaluation at the preclinical stages of therapeutic development to ensure safe and effective gene transfer. As the cardiac gene therapy expands its potential, large animal studies will become more important to bridge the bench side knowledge to the clinical arena.

Sustained reduction of vein graft neointima formation by ex vivo TIMP-3 gene therapy

BACKGROUND

Coronary artery vein graft failure, resulting from thrombosis, intimal thickening, and atherosclerosis, is a significant clinical problem, with approximately 50% of vein grafts failing within 10 years. Intimal thickening is caused by migration of vascular smooth muscle cells from the media to the intima, where they proliferate. Interventions using gene transfer to inhibit vascular smooth muscle cells proliferation and migration are attractive because ex vivo access to the graft is possible. The involvement of matrix-degrading metalloproteinases in intimal thickening is well established, and we previously showed that adenoviral-delivered overexpression of an endogenous inhibitor, the tissue inhibitor of metalloproteinases-3 (TIMP-3), significantly retarded intimal thickening in short-term autologous porcine arteriovenous interposition grafts (28 days). However, it is essential to determine whether this approach will provide longer-term benefits.

METHODS AND RESULTS

We assessed whether a recombinant adenovirus that overexpresses TIMP-3 (RAdTIMP-3) affects vein graft intimal thickening in the longer term (at 3 months). Porcine saphenous veins were subjected to luminal infection with 2.5×10(10) pfu/mL RAdTIMP-3 or RAd60 (control virus) or vehicle control, for 30 minutes before implantation into the carotid artery. Analysis of grafts harvested 3 months after delivery revealed that RAdTIMP-3-infected grafts had significantly reduced intimal areas compared with both controls (3.2 ± 0.4 mm(2) versus 5.6 ± 0.7 mm(2) and 5.9 ± 0.5 mm(2), RAdTIMP-3, RAd60, and vehicle, respectively). Medial areas were also significantly decreased by TIMP-3 (3.8 ± 0.3 mm(2) versus 6.7 ± 1.0 mm(2) and 5.2 ± 0.4 mm(2), RAdTIMP-3, RAd60, and vehicle, respectively).

CONCLUSIONS

Overexpression of TIMP-3 provides a sustained retardation of vein graft intimal thickening and highlights the translational potential for ex vivo TIMP-3 gene therapy.

Inhibition of MDM2 attenuates neointimal hyperplasia via suppression of vascular proliferation and inflammation

AIMS

Tumour protein p53 plays an important role in the vascular remodelling process as well as in oncogenesis. p53 is negatively regulated by murine double minute 2 (MDM2). A recently developed MDM2 inhibitor, nutlin-3, is a non-genotoxic activator of the p53 pathway. So far, the effect of MDM2 inhibition on vascular remodelling has not been elucidated. We therefore investigated the effect of nutlin-3 on neointima formation.

METHODS AND RESULTS

Nutlin-3 up-regulated p53 and its downstream target p21 in vascular smooth muscle cells (VSMCs). DNA synthesis assay and flow cytometric analysis revealed that nutlin-3 inhibited platelet-derived growth factor (PDGF)-induced VSMC proliferation by cell cycle arrest. This inhibitory effect was abrogated in p53-siRNA-transfected VSMCs. Furthermore, nutlin-3 inhibited PDGF-stimulated VSMC migration. Treatment with nutlin-3 attenuated neointimal hyperplasia at 28 days after vascular injury in mice, associated with up-regulation of p53 and p21. BrdU incorporation was decreased at 14 days after injury in nutlin-3-treated mice. TUNEL assay showed that nutlin-3 did not exaggerate apoptosis of the injured vessels. Infiltration of macrophages and T-lymphocytes and mRNA expression of chemokine (C-C motif) ligand-5, interleukin-6, and intercellular adhesion molecule-1 were decreased in the injured vessels of nutlin-3-treated mice. Nutlin-3 suppressed NF-κB activation in VSMCs, but not in p53-siRNA-transfected VSMCs.

CONCLUSIONS

The MDM2 antagonist nutlin-3 inhibits VSMC proliferation, migration, and NF-κB activation, and also attenuates neointimal hyperplasia after vascular injury in mice, which is associated with suppression of vascular cell proliferation and an inflammatory response. Targeting MDM2 might be a potential therapeutic strategy for the treatment of vascular proliferative diseases.

Mechanisms of vein graft adaptation to the arterial circulation: insights into the neointimal algorithm and management strategies

For patients with coronary artery disease or limb ischemia, placement of a vein graft as a conduit for a bypass is an important and generally durable strategy among the options for arterial reconstructive surgery. Vein grafts adapt to the arterial environment, and the limited formation of intimal hyperplasia in the vein graft wall is thought to be an important component of successful vein graft adaptation. However, it is also known that abnormal, or uncontrolled, adaptation may lead to abnormal vessel wall remodeling with excessive neointimal hyperplasia, and ultimately vein graft failure and clinical complications. Therefore, understanding the venous-specific pathophysiological and molecular mechanisms of vein graft adaptation are important for clinical vein graft management. Of particular importance, it is currently unknown whether there exist several specific distinct molecular differences in the venous mechanisms of adaptation that are distinct from arterial post-injury responses; in particular, the participation of the venous determinant Eph-B4 and the vascular protective molecule Nogo-B may be involved in mechanisms of vessel remodeling specific to the vein. This review describes (1) venous biology from embryonic development to the mature quiescent state, (2) sequential pathologies of vein graft neointima formation, and (3) novel candidates for strategies of vein graft management. Scientific inquiry into venous-specific adaptation mechanisms will ultimately provide improvements in vein graft clinical outcomes.

Control of cell proliferation in atherosclerosis: insights from animal models and human studies

Excessive hyperplastic cell growth within occlusive vascular lesions has been recognized as a key component of the inflammatory response associated with atherosclerosis, restenosis post-angioplasty, and graft atherosclerosis after coronary artery bypass. Understanding the molecular mechanisms that regulate arterial cell proliferation is therefore essential for the development of new tools for the treatment of these diseases. Mammalian cell proliferation is controlled by a large number of proteins that modulate the mitotic cell cycle, including cyclin-dependent kinases, cyclins, and tumour suppressors. The purpose of this review is to summarize current knowledge about the role of these cell cycle regulators in the development of native and graft atherosclerosis that has arisen from animal studies, histological examination of specimens from human patients, and genetic studies.

In vivo modulation of Nogo-B attenuates neointima formation

Nogo-B was recently identified as a novel vascular marker; the normally high vascular expression of Nogo-B is rapidly lost following vascular injury. Here we assess the potential therapeutic effects of Ad-Nogo-B delivery to injured vessels in vivo. Nogo-B overexpression following Ad-Ng-B infection of vascular smooth muscle cells (VSMCs) was shown to block proliferation and migration in a dose-dependent manner in vitro. We next assessed the effects of Ad-Ng-B treatment on neointima formation in two in vivo models of acute vascular injury. Adventitial delivery of Ad-Ng-B to wire-injured murine femoral arteries led to a significant decrease in the intimal area [0.014 mm(2) versus 0.030 mm(2) (P = 0.049)] and the intima:media ratio [0.78 versus 1.67 (P = 0.038)] as compared to the effects of Ad-beta-Gal control virus at 21 days after injury. Similarly, lumenal delivery of Ad-Ng-B to porcine saphenous veins prior to carotid artery grafting significantly reduced the intimal area [2.87 mm(2) versus 7.44 mm(2) (P = 0.0007)] and the intima:media ratio [0.32 versus 0.55 (P = 0.0044)] as compared to the effects following the delivery of Ad- beta-Gal, at 28 days after grafting. Intimal VSMC proliferation was significantly reduced in both the murine and porcine disease models. Gene delivery of Nogo-B exerts a positive effect on vascular injury-induced remodeling and reduces neointimal development in two arterial and venous models of vascular injury.

Comparison of anticoagulant effects on vein grafts between human TFPI gene transfection and aspirin oral administration

To develop a more efficient antithrombotic way after coronary artery bypass grafting (CABG), the anticoagulant effects were compared of human tissue factor pathway inhibitor (TFPI) gene transfection and aspirin oral administration (traditional method) on vein grafts. An eukaryotic expression plasmid pCMV-(Kozak) TFPI was prepared. Animal model of carotid artery bypass grafting was constructed. In operation, endothelial cells of vein grafts in TFPI group and empty plasmid control group were transfected with pCMV-(Kozak) TFPI and empty plasmid pCMV respectively, while no transfection was conducted in aspirin control group. After operation, aspirin (2 mg.kg(-1).(-1)) was administered (i.g.) in aspirin control group. Three days later, grafts (n=10) were harvested for RT-PCR, Western blotting and immunohistochemical analyses of exogenous gene expression and for pathological, scanning electron microscopic observation of thrombus. Thirty days later, the patency rates of remnant grafts (n=10) were recorded by vessel Doppler ultrasonography. Human TFPI gene products were detected in gene transferred vein grafts. Three days later, thrombi were found in 7 animals of aspirin control group and in 8 animals of empty plasmid control group, but in only 1 of TFPI group (P<0.01). Thirty days later, 5 grafts were occluded in empty plasmid control group, but none of grafts was occluded in the other groups (P<0.05). The endothelial surfaces of grafts in both of the control groups were covered with aggregated erythrocytes and platelets, and it were not seen in TFPI group. It was suggested that the anticoagulant effects on vein grafts of human TFPI gene transfection are better than those of aspirin.

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.

Mechanism of dipyridamole's action in inhibition of venous and arterial smooth muscle cell proliferation

Dipyridamole is a potential pharmacological agent to prevent vascular stenosis because of its antiproliferative properties. The mechanisms by which dipyridamole inhibits the growth of vascular smooth muscle cells, especially venous smooth muscle cells, are unclear. In the present study, dipyridamole transiently but significantly increased cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) levels in human venous and arterial smooth muscle cells in a time- and dose-dependent manner. Peak concentrations of both cyclic nucleotides were achieved at 15-30 min. and correlated with inhibition of proliferation in both cell types. The antiproliferative effects of dipyridamole observed at 48 hr were similar whether drug exposure was only 15 min. or sustained for 48 hr. Specific competitive inhibitors of protein kinases A and G attenuated the antiproliferative effects of subsaturating concentrations of dipyridamole, with the effects of protein kinase inhibition being particularly pronounced in venous smooth muscle cells. Flow cytometry analysis showed that dipyridamole caused an enrichment of cells in G(0)/G(1) and a corresponding reduction of cells in S phase. These data indicate that a transient increase in cGMP and cAMP is sufficient to induce downstream kinase activation and subsequent cell cycle arrest, and that protein kinase G may be more important than protein kinase A in mediating the growth inhibitory effect of dipyridamole in venous protein kinase.

Estrogen accelerates G1 to S phase transition and induces a G2/M phase-predominant apoptosis in synthetic vascular smooth muscle cells

OBJECTIVE

To investigate the mechanisms underlying the vascular-protective effects of estrogen.

METHODS

The synthetic (subcultured for 3-4 passages) rat vascular smooth muscle cells were exposed to gradient concentrations (10(-10)-10(-5) M) of 17beta-estradiol. The growth, cell cycle progression and apoptosis of the cells, and the related proteins including Cyclin D1, Cdk4, p38, Bax and Bcl-2 were analyzed in MTT, flow cytometry, ELISA or Western blot.

RESULTS

17beta-estradiol in the physiological concentrations (10(-10)-10(-8) M) promoted the smooth muscle cell growth in a concentration-dependent manner, accelerated transition of the cells from G1 to S phases, and up-regulated expressions of Cyclin D1 and Cdk4. Meanwhile, the hormone (10(-9)-10(-7) M) triggered a G2/M phase-predominant apoptosis of the cells in a concentration- and time-dependent manner, which was accompanied by increased phosphorylation of p38 and expression of Bax.

CONCLUSIONS

The effect of estrogen on the synthetic vascular smooth muscle cell is dual. It promotes proliferation of the cells by accelerating their G1/S phase transition via up-regulating Cyclin D1 and Cdk4; and on the other hand, it induces apoptosis of the proliferating cells by up-regulating Bax through p38-MAPK pathway.

Opportunities for gene therapy in preventing vein graft failure after coronary artery bypass surgery

The poor patency rates for coronary artery bypass grafting (CABG) using autologous saphenous vein necessitate the need for continued research into the potential clinical utility of gene therapy. Bypass grafting is ideally suited for gene therapy, as graft can be genetically modified ex vivo prior to grafting in the coronary vasculature. Research to date has demonstrated effective blockade of late vein graft failure through overexpression of a variety of transgenes that modulate the proliferative, migratory and/or apoptotic indexes of cells in the graft wall. This has resulted in a substantial wealth of preclinical data that support advancement to clinical trials. Future translation into clinical trials will ensure that this exciting and highly relevant area of gene therapy is fully evaluated for potential routine clinical practice to improve patency rates of bypass graft procedures involving saphenous vein.

Ultrasound-mediated delivery of TIMP-3 plasmid DNA into saphenous vein leads to increased lumen size in a porcine interposition graft model

Progressive saphenous vein graft (SVG) narrowing and occlusion remains a major limitation of coronary artery bypass grafting and is an important target for gene therapy. Ex vivo adenoviral gene transfer of tissue inhibitor of metalloproteinase 3 (TIMP-3) reduces adverse SVG remodelling postarterialization, but concerns remain over the use of viral vectors in patients. Ultrasound exposure (USE) in the presence of echocontrast microbubbles (ECM) substantially enhances nonviral gene delivery. We investigated the effects of ultrasound-enhanced gene delivery (UEGD) of TIMP-3 plasmid on vascular remodelling in porcine SVG. Maximal luciferase activity (3000-fold versus naked plasmid alone) and TIMP-3 transgene expression in porcine vascular smooth muscle cells in vitro was achieved using USE at 1 MHz, 1.8 mechanical index (MI), 6% duty cycle (DC) in the presence of 50% (v/v) BR14 ECM (Bracco). These conditions were therefore utilized for subsequent studies in vivo. Yorkshire White pigs received carotid interposition SVG that were untransfected or had undergone ex vivo UEGD of lacZ (control) or TIMP-3 plasmids. At 28 d postgrafting, lumen and total vessel area were significantly greater in the TIMP-3 group (10.1+/-1.2 and 25.5+/-2.2 mm2, respectively) compared to untransfected (6.34+/-0.5 and 20.8+/-1.9 mm2) or lacZ-transfected (6.1+/-0.7 and 19.7+/-1.2 mm2) controls (P<0.01). These data indicate that nonviral TIMP-3 plasmid delivery by USE achieves significant biological effects in a clinically relevant model of SV grafting, and is the first study to demonstrate the potential for therapeutic UEGD to prevent SVG failure.

Improved gene delivery to human saphenous vein cells and tissue using a peptide-modified adenoviral vector

The establishment of efficient gene delivery to target human tissue is a major obstacle for transition of gene therapy from the pre-clinical phases to the clinic. The poor long-term patency rates for coronary artery bypass grafting (CABG) is a major clinical problem that lacks an effective and proven pharmacological intervention. Late vein graft failure occurs due to neointima formation and accelerated atherosclerosis. Since CABG allows a clinical window of opportunity to genetically modify vein ex vivo prior to grafting it represents an ideal opportunity to develop gene-based therapies. Adenoviral vectors have been frequently used for gene delivery to vein ex vivo and pre-clinical studies have shown effective blockade in neointima development by overexpression of candidate therapeutic genes. However, high titers of adenovirus are required to achieve sufficient gene delivery to provide therapeutic benefit. Improvement in the uptake of adenovirus into the vessel wall would therefore be of benefit. Here we determined the ability of an adenovirus serotype 5 vector genetically-engineered with the RGD-4C integrin targeting peptide inserted into the HI loop (Ad-RGD) to improve the transduction of human saphenous vein smooth muscle cells (HSVSMC), endothelial cells (HSVEC) and intact saphenous vein compared to a non-modified virus (Ad-CTL). We exposed each cell type to virus for 10, 30 or 60 mins and measured transgene at 24 h post infection. For both HSVSMC and HSVEC Ad-RGD mediated increased transduction, with the largest increases observed in HSVSMC. When the experiments were repeated with intact human saphenous vein (the ultimate clinical target for gene therapy), again Ad-RGD mediated higher levels of transduction, at all clinically relevant exposures times (10, 30 and 60 mins tissue:virus exposure). Our study demonstrates the ability of peptide-modified Ad vectors to improve transduction to human vein graft cells and tissue and has important implications for gene therapy for CABG.