Expansive remodeling in venous bypass grafts: novel implications for vein graft disease

Platelet Membrane-Encapsulated Poly(lactic-co-glycolic acid) Nanoparticles Loaded with Sildenafil for Targeted Therapy of Vein Graft Intimal Hyperplasia

Autologous vein grafts have attracted widespread attention for their high transplantation success rate and low risk of immune rejection. However, this technique is limited by the postoperative neointimal hyperplasia, recurrent stenosis and vein graft occlusion. Hence, we propose the platelet membrane-coated Poly(lactic-co-glycolic acid) (PLGA) containing sildenafil (PPS). Platelet membrane (PM) is characterised by actively targeting damaged blood vessels. The PPS can effectively target the vein grafts and then slowly release sildenafil to treat intimal hyperplasia in the vein grafts, thereby preventing the progression of vein graft restenosis. PPS effectively inhibits the proliferation and migration of vascular smooth muscle cell (VSMCs) and promotes the migration and vascularisation of human umbilical vein endothelial cells (HUVECs). In a New Zealand rabbit model of intimal hyperplasia in vein grafts, the PPS significantly suppressed vascular stenosis and intimal hyperplasia at 14 and 28 days after surgery. Thus, PPS represents a nanomedicine with therapeutic potential for treating intimal hyperplasia of vein grafts.

External Support of Autologous Internal Jugular Vein Grafts with FRAME Mesh in a Porcine Carotid Artery Model

BACKGROUND

Autologous vein grafts are widely used for bypass procedures in cardiovascular surgery. However, these grafts are susceptible to failure due to vein graft disease. Our study aimed to evaluate the impact of the latest-generation FRAME external support on vein graft remodeling in a preclinical model.

METHODS

We performed autologous internal jugular vein interposition grafting in porcine carotid arteries for one month. Four grafts were supported with a FRAME mesh, while seven unsupported grafts served as controls. The conduits were examined through flowmetry, angiography, macroscopy, and microscopy.

RESULTS

The one-month patency rate of FRAME-supported grafts was 100% (4/4), whereas that of unsupported controls was 43% (3/7, Log-rank p = 0.071). On explant angiography, FRAME grafts exhibited significantly more areas with no or mild stenosis (9/12) compared to control grafts (3/21, p = 0.0009). Blood flow at explantation was higher in the FRAME grafts (145 ± 51 mL/min) than in the controls (46 ± 85 mL/min, p = 0.066). Area and thickness of neo-intimal hyperplasia (NIH) at proximal anastomoses were similar for the FRAME and the control groups: 5.79 ± 1.38 versus 6.94 ± 1.10 mm2, respectively (p = 0.558) and 480 ± 95 vs. 587 ± 52 μm2/μm, respectively (p = 0.401). However, in the midgraft portions, the NIH area and thickness were significantly lower in the FRAME group than in the control group: 3.73 ± 0.64 vs. 6.27 ± 0.64 mm2, respectively (p = 0.022) and 258 ± 49 vs. 518 ± 36 μm2/μm, respectively (p = 0.0002).

CONCLUSIONS

In our porcine model, the external mesh FRAME improved the patency of vein-to-carotid artery grafts and protected them from stenosis, particularly in the mid regions. The midgraft neo-intimal hyperplasia was two-fold thinner in the meshed grafts than in the controls.

A novel biodegradable external stent regulates vein graft remodeling via the Hippo-YAP and mTOR signaling pathways

Coronary artery bypass graft (CABG) has been confirmed to effectively improve the prognosis of coronary artery disease, which is a major public health concern worldwide. As the most frequently used conduits in CABG, saphenous vein grafts have the disadvantage of being susceptible to restenosis due to intimal hyperplasia. To meet the urgent clinical demand, adopting external stents (eStents) and illuminating the potential mechanisms underlying their function are important for preventing vein graft failure. Here, using 4-axis printing technology, we fabricated a novel biodegradable and flexible braided eStent, which exerts excellent inhibitory effect on intimal hyperplasia. The stented grafts downregulate Yes-associated protein (YAP), indicating that the eStent regulates vein graft remodeling via the Hippo-YAP signaling pathway. Further, as a drug-delivery vehicle, a rapamycin (RM)-coated eStent was designed to amplify the inhibitory effect of eStent on intimal hyperplasia through the synergistic effects of the Hippo and mammalian target of rapamycin (mTOR) signaling pathways. Overall, this study uncovers the underlying mechanisms of eStent function and identifies a new therapeutic target for the prevention of vein graft restenosis.

Identification and Analysis of Differentially Expressed Genes in Human Saphenous Vein Endothelial Cells Overexpressing Domain-Containing mTOR-Interacting Protein (DEPTOR) by RNA-Seq

Background

Autologous saphenous vein is the most common choice for coronary artery bypass grafting. This study was conducted to identify and characterize differentially expressed genes (DEGs) induced by overexpressing DEPTOR in human saphenous vein endothelial cells (hsVECs) that might play roles in restenosis.

Material/Methods

hsVECs isolated from the saphenous veins were transfected with DEPTOR overexpression vector and analyzed for mTOR expression. RNA was prepared from the cells and sequenced using high-throughput sequencing technology (RNA-Seq). The DEGs were analyzed based on enrichment scores in GO terms and KEGG pathways.

Results

The cells had typical hsVEC morphology and characteristics based on the HE staining and immunohistochemical and immunofluorescence assays. The expression of mTOR increased, and 102 genes were upregulated, and 409 genes were downregulated after DEPTOR overexpression. KEGG analysis showed that the DEGs were mainly enriched in 20 signal pathways, such as Focal adhesion and ECM-receptor interaction pathways. The DEGs were enriched in GO terms such as integrin binding and glycosaminoglycan binding. For cellular components, GO analysis revealed that the DEGs were enriched in main axon, plasma membrane part, cell junction, and proteinaceous extracellular matrix. DEGs included many cytokines, such as bone morphogenetic protein-7, interleukin-8, interleukin-1β, and inhibin, which have important effects on vascular growth and inflammation.

Conclusions

The overexpression of DEPTOR in hsVECs results in DEGs that are involved in cell proliferation and differentiation, intercellular junction, and extracellular matrix receptor. These findings may provide valuable molecular information for improving venous permeability through manipulation of DEPTOR and related mTOR pathways.

Autologous endothelialized vein allografts in coronary artery bypass surgery - Long term results

BACKGROUND

Lack of autologous graft material restricts the ability to treat patients requiring coronary artery bypass surgery (CABG). An off the shelf tissue engineered small diameter vascular graft is the holy grail of cardiovascular surgery.

METHODS

Allograft saphenous veins were harvested from organ donors, cryopreserved, deendothelialized and then seeded with autologous endothelial cells prior to implantation during coronary artery bypass surgery. All patients treated were followed-up until death and angiographic results were collected. Grafts were explanted during autopsy and immunohistochemistry was performed.

RESULTS

Twelve patients received 15 engineered grafts. Mean patient survival was 9.1 ± 1.8 years. Six month graft patency was 80 (95% CI: 59-100) and 9 month graft patency was 50 (95% CI: 27-93) - graft patency detected up to 32 months after surgery. Immunohistochemistry in grafts explanted showed a presence of CD31 and CD68 positive cells in the luminal region of the vessel walls and layers of Collagen Type I in the abluminal vessel walls.

CONCLUSIONS

Our small diameter tissue engineered vascular graft shows openness up to 32 months after implantation. Immunohistochemistry suggests that monocyte activation may lead to vessel remodeling with thickening of the vessel wall. Research should concentrate on a manipulation of remodeling processes.

Vein graft failure: from pathophysiology to clinical outcomes

Occlusive arterial disease is a leading cause of morbidity and mortality worldwide. Aside from balloon angioplasty, bypass graft surgery is the most commonly performed revascularization technique for occlusive arterial disease. Coronary artery bypass graft surgery is performed in patients with left main coronary artery disease and three-vessel coronary disease, whereas peripheral artery bypass graft surgery is used to treat patients with late-stage peripheral artery occlusive disease. The great saphenous veins are commonly used conduits for surgical revascularization; however, they are associated with a high failure rate. Therefore, preservation of vein graft patency is essential for long-term surgical success. With the exception of 'no-touch' techniques and lipid-lowering and antiplatelet (aspirin) therapy, no intervention has hitherto unequivocally proven to be clinically effective in preventing vein graft failure. In this Review, we describe both preclinical and clinical studies evaluating the pathophysiology underlying vein graft failure, and the latest therapeutic options to improve patency for both coronary and peripheral grafts.

Adventitial vessel growth and progenitor cells activation in an ex vivo culture system mimicking human saphenous vein wall strain after coronary artery bypass grafting

Saphenous vein graft disease is a timely problem in coronary artery bypass grafting. Indeed, after exposure of the vein to arterial blood flow, a progressive modification in the wall begins, due to proliferation of smooth muscle cells in the intima. As a consequence, the graft progressively occludes and this leads to recurrent ischemia. In the present study we employed a novel ex vivo culture system to assess the biological effects of arterial-like pressure on the human saphenous vein structure and physiology, and to compare the results to those achieved in the presence of a constant low pressure and flow mimicking the physiologic vein perfusion. While under both conditions we found an activation of Matrix Metallo-Proteases 2/9 and of microRNAs-21/146a/221, a specific effect of the arterial-like pressure was observed. This consisted in a marked geometrical remodeling, in the suppression of Tissue Inhibitor of Metallo-Protease-1, in the enhanced expression of TGF-β₁ and BMP-2 mRNAs and, finally, in the upregulation of microRNAs-138/200b/200c. In addition, the veins exposed to arterial-like pressure showed an increase in the density of the adventitial vasa vasorum and of cells co-expressing NG2, CD44 and SM22α markers in the adventitia. Cells with nuclear expression of Sox-10, a transcription factor characterizing multipotent vascular stem cells, were finally found in adventitial vessels. Our findings suggest, for the first time, a role of arterial-like wall strain in the activation of pro-pathologic pathways resulting in adventitial vessels growth, activation of vasa vasorum cells, and upregulation of specific gene products associated to vascular remodeling and inflammation.

Elevated expression levels of miR-143/5 in saphenous vein smooth muscle cells from patients with Type 2 diabetes drive persistent changes in phenotype and function

Type 2 diabetes (T2DM) promotes premature atherosclerosis and inferior prognosis after arterial reconstruction. Vascular smooth muscle cells (SMC) respond to patho/physiological stimuli, switching between quiescent contractile and activated synthetic phenotypes under the control of microRNAs (miRs) that regulate multiple genes critical to SMC plasticity. The importance of miRs to SMC function specifically in T2DM is unknown. This study was performed to evaluate phenotype and function in SMC cultured from non-diabetic and T2DM patients, to explore any aberrancies and investigate underlying mechanisms. Saphenous vein SMC cultured from T2DM patients (T2DM-SMC) exhibited increased spread cell area, disorganised cytoskeleton and impaired proliferation relative to cells from non-diabetic patients (ND-SMC), accompanied by a persistent, selective up-regulation of miR-143 and miR-145. Transfection of premiR-143/145 into ND-SMC induced morphological and functional characteristics similar to native T2DM-SMC; modulating miR-143/145 targets Kruppel-like factor 4, alpha smooth muscle actin and myosin VI. Conversely, transfection of antimiR-143/145 into T2DM-SMC conferred characteristics of the ND phenotype. Exposure of ND-SMC to transforming growth factor beta (TGFβ) induced a diabetes-like phenotype; elevated miR-143/145, increased cell area and reduced proliferation. Furthermore, these effects were dependent on miR-143/145. In conclusion, aberrant expression of miR-143/145 induces a distinct saphenous vein SMC phenotype that may contribute to vascular complications in patients with T2DM, and is potentially amenable to therapeutic manipulation.

Inhibition of vein graft stenosis with a c-jun targeting DNAzyme in a cationic liposomal formulation containing 1,2-dioleoyl-3-trimethylammonium propane (DOTAP)/1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE)

BACKGROUND/OBJECTIVES

Coronary artery bypass grafting (CABG) is among the most commonly performed heart surgical procedures. Saphenous vein graft failure due to stenosis impedes the longer-term success of CABG. A key cellular event in the process of vein graft stenosis is smooth muscle cell hyperplasia. In this study, we evaluated the effect of a DNAzyme (Dz13) targeting the transcription factor c-Jun in a rabbit model of vein graft stenosis in a cationic liposomal formulation containing 1,2-dioleoyl-3-trimethylammonium propane (DOTAP)/1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE). Dz13 in DOTAP/DOPE has undergone preclinical toxicological testing, and a Phase I clinical trial we recently conducted in basal cell carcinoma cancer patients demonstrates that it is safe and well tolerated after local administration.

METHODS

Effects of Dz13 in a formulation containing DOTAP/DOPE on smooth muscle cell (SMC) growth and c-Jun expression were assessed. Dz13 transfection was determined by cellular uptake of carboxyfluorescein-labeled Dz13. Autologous jugular vein to carotid artery transplantation was performed in New Zealand White rabbits to investigate the effect of the Dz13 in DOTAP/DOPE formulation on intimal hyperplasia.

RESULTS

Dz13/DOTAP/DOPE reduced SMC proliferation and c-Jun protein expression in vitro compared with an impotent form of Dz13 bearing a point mutation in its catalytic domain (Dz13.G>C). The Dz13(500 μg)/DOTAP/DOPE formed lipoplexes that were colloidally stable for up to 1h on ice (0°C) and 30 min at 37°C, allowing sufficient uptake by the veins. Dz13 (500 μg) inhibited neointima formation 28 d after end-to-side transplantation.

CONCLUSIONS

This formulation applied to veins prior to transplantation may potentially be useful in efforts to reduce graft failure.

Vein graft failure

After the creation of an autogenous lower extremity bypass graft, the vein must undergo a series of dynamic structural changes to stabilize the arterial hemodynamic forces. These changes, which are commonly referred to as remodeling, include an inflammatory response, the development of a neointima, matrix turnover, and cellular proliferation and apoptosis. The sum total of these processes results in dramatic alterations in the physical and biomechanical attributes of the arterialized vein. The most clinically obvious and easily measured of these is lumen remodeling of the graft. However, although somewhat less precise, wall thickness, matrix composition, and endothelial changes can be measured in vivo within the healing vein graft. Recent translational work has demonstrated the clinical relevance of remodeling as it relates to vein graft patency and the systemic factors influencing it. By correlating histologic and molecular changes in the vein, insights into potential therapeutic strategies to prevent bypass failure and areas for future investigation are explored.

Diet-induced obesity drives negative mouse vein graft wall remodeling

INTRODUCTION

The heightened inflammatory phenotype associated with obesity has been linked to the development of cardiovascular diseases. Short-term high-fat feeding induces a proinflammatory state that may impact the blood vessel wall. CD11c, a significantly increased dendritic cell biomarker during diet-induced obesity (DIO), may have a mechanistic role in this high-fat feeding effect. We hypothesized that the proinflammatory effect of short-term DIO accelerates vein bypass graft failure via CD11c-dependent mechanisms.

METHODS

Male 9-week-old DIO mice (n = 13, C57BL/6J recipients; n = 6, CD11c(-/-) recipients) and normal chow controls (n = 15, C57BL/6J recipients; n = 6, CD11c(-/-) recipients) underwent unilateral carotid interposition vein isografting (inferior vena cava from the same diet and genetic background donor), with a midgraft or outflow focal stenosis. Vein grafts were harvested at either 1 week (immunohistochemical staining for early CD11c expression) or 4 weeks later (morphometric analyses and CD11c evaluation).

RESULTS

Despite a 40% larger body size, C57BL/6J DIO mice had 44% smaller poststenosis vein graft lumens (P = .03) than their controls via an acceleration of overall negative vein graft wall remodeling in the day-28 midgraft focal stenosis model but not in the outflow stenosis model. Higher CD11c expression occurred in DIO midgraft-stenosis vein graft walls, both at postoperative days 7 and 28. In contrast, with in vivo CD11c deficiency, DIO did not elicit this poststenotic negative remodeling but attenuated intimal hyperplasia.

CONCLUSIONS

These findings highlight negative wall remodeling as a potential factor leading to vein graft failure and provide direct evidence that short-term dietary alterations in the mammalian metabolic milieu can have lasting implications related to acute vascular interventions. DIO induces negative mouse vein graft wall remodeling via CD11c-depedent pathways.

Apolipoprotein(a) acts as a chemorepellent to human vascular smooth muscle cells via integrin αVβ3 and RhoA/ROCK-mediated mechanisms

Lipoprotein(a) (Lp(a)) is an independent risk factor for the development of cardiovascular disease. Vascular smooth muscle cell (SMC) motility and plasticity, functions that are influenced by environmental cues, are vital to adaptation and remodelling in vascular physiology and pathophysiology. Lp(a) is reportedly damaging to SMC function via unknown molecular mechanisms. Apolipoprotein(a) (apo(a)), a unique glycoprotein moiety of Lp(a), has been demonstrated as its active component. The aims of this study were to determine functional effects of recombinant apo(a) on human vascular SMC motility and explore the underlying mechanism(s). Exposure of SMC to apo(a) in migration assays induced a potent, concentration-dependent chemorepulsion that was RhoA and integrin αVβ3-dependent, but transforming growth factor β-independent. SMC manipulation through RhoA gene silencing, Rho kinase inhibition, statin pre-treatment, αVβ3 neutralising antibody and tyrosine kinase inhibition all markedly inhibited apo(a)-mediated SMC migration. Our data reveal unique and potent activities of apo(a) that may negatively influence SMC remodelling in cardiovascular disease. Circulating levels of Lp(a) are resistant to lipid-lowering strategies and hence a greater understanding of the mechanisms underlying its functional effects on SMC may provide alternative therapeutic targets.

Expandable external support device to improve Saphenous Vein Graft Patency after CABG

Objectives

Low patency rates of saphenous vein grafts remain a major predicament in surgical revascularization. We examined a novel expandable external support device designed to mitigate causative factors for early and late graft failure.

Methods

For this study, fourteen adult sheep underwent cardiac revascularization using two vein grafts for each; one to the LAD and the other to the obtuse marginal artery. One graft was supported with the device while the other served as a control. Target vessel was alternated between consecutive cases. The animals underwent immediate and late angiography and were then sacrificed for histopathologic evaluation.

Results

Of the fourteen animals studied, three died peri-operatively (unrelated to device implanted), and ten survived the follow-up period. Among surviving animals, three grafts were thrombosed and one was occluded, all in the control group (p = 0.043). Quantitative angiographic evaluation revealed no difference between groups in immediate level of graft uniformity, with a coefficient-of-variance (CV%) of 7.39 in control versus 5.07 in the supported grafts, p = 0.082. At 12 weeks, there was a significant non-uniformity in the control grafts versus the supported grafts (CV = 22.12 versus 3.01, p < 0.002). In histopathologic evaluation, mean intimal area of the supported grafts was significantly lower than in the control grafts (11.2 mm^² versus 23.1 mm^² p < 0.02).

Conclusions

The expandable SVG external support system was found to be efficacious in reducing SVG’s non-uniform dilatation and neointimal formation in an animal model early after CABG. This novel technology may have the potential to improve SVG patency rates after surgical myocardial revascularization.

Role of hemodynamic forces in the ex vivo arterialization of human saphenous veins

BACKGROUND

Human saphenous vein grafts are one of the salvage bypass conduits when endovascular procedures are not feasible or fail. Understanding the remodeling process that venous grafts undergo during exposure to arterial conditions is crucial to improve their patency, which is often compromised by intimal hyperplasia. The precise role of hemodynamic forces such as shear stress and arterial pressure in this remodeling is not fully characterized. The aim of this study was to determine the involvement of arterial shear stress and pressure on vein wall remodeling and to unravel the underlying molecular mechanisms.

METHODS

An ex vivo vein support system was modified for chronic (up to 1 week), pulsatile perfusion of human saphenous veins under controlled conditions that permitted the separate control of arterial shear stress and different arterial pressure (7 mm Hg or 70 mm Hg).

RESULTS

Veins perfused for 7 days under high pressure (70 mm Hg) underwent significant development of a neointima compared with veins exposed to low pressure (7 mm Hg). These structural changes were associated with altered expression of several molecular markers. Exposure to an arterial shear stress under low pressure increased the expression of matrix metalloproteinase (MMP)-2 and MMP-9 and tissue inhibitor of metalloproteinase (TIMP)-1 at the transcript, protein, and activity levels. This increase was enhanced by high pressure, which also increased TIMP-2 protein expression despite decreased levels of the cognate transcript. In contrast, the expression of plasminogen activator inhibitor-1 increased with shear stress but was not modified by pressure. Levels of the venous marker Eph-B4 were decreased under arterial shear stress, and levels of the arterial marker Ephrin-B2 were downregulated under high-pressure conditions.

CONCLUSIONS

This model is a valuable tool to identify the role of hemodynamic forces and to decipher the molecular mechanisms leading to failure of human saphenous vein grafts. Under ex vivo conditions, arterial perfusion is sufficient to activate the remodeling of human veins, a change that is associated with the loss of specific vein markers. Elevation of pressure generates intimal hyperplasia, even though veins do not acquire arterial markers.

CLINICAL RELEVANCE

The pathological remodeling of the venous wall, which leads to stenosis and ultimately graft failure, is the main limiting factor of human saphenous vein graft bypass. This remodeling is due to the hemodynamic adaptation of the vein to the arterial environment and cannot be prevented by conventional therapy. To develop a more targeted therapy, a better understanding of the molecular mechanisms involved in intimal hyperplasia is essential, which requires the development of ex vivo models of chronic perfusion of human veins.

Extraluminal atherosclerosis: an under-recognised finding in human aortocoronary venous bypass grafts

BACKGROUND

Coronary artery bypass grafting (CABG) is commonly compromised by graft atherosclerosis. Histopathologic studies confirm various forms of atherosclerosis, including positively remodelled lesions in native coronary arteries but there are no histopathologic reports of extraluminal atherosclerosis in vein grafts.

METHODS

We prospectively investigated the histopathologic presence and pattern of extraluminal atherosclerosis in human old vein grafts in a two-year interval among patients undergoing redo-CABG at three university hospitals in Tehran. We separately documented clinical and angiographic findings.

RESULTS

We evaluated 100 segments from 20 human old vein grafts obtained during the redo CABG. All but four segments demonstrated some degrees of luminal narrowing. Luminal atherosclerotic plaques were detectable in 61 segments. We detected extraluminal atheroscleoris in seven segments. Mean vessel wall thickness was greater in segments containing extraluminal plaques (1.41±0.26 mm versus 0.91±0.04 mm, P=0.008). Angiographic findings had a modest correlation with presence or absence of luminal atheromatous lesions (Spearman's rho: 0.331, P=0.007). Angiographic degree of stenosis could not predict the presence of positively remodelled atherosclerotic plaques (Spearman's rho: -2.21, P=0.073).

CONCLUSION

Previous studies suggested positive remodelling in vein grafts. Out study provides histopathologic evidence on extraluminal atherosclerosis in human aortocoronary vein grafts.

The effects of PPARγ agonist rosiglitazone on neointimal hyperplasia in rabbit carotid anastomosis model

Background

Neointimal hyperplasia involving smooth muscle cell (SMC) proliferation, migration and extracellular matrix (ECM) degradation is an important component of atherosclerosis. It develops as a response to vascular injury after balloon angioplasty and vascular graft placement. Matrix metalloproteinases (MMPs) induce SMC proliferation, migration and contribute to intimal hyperplasia by degrading ECM. PPARγ agonists inhibit SMC proliferation, migration and lesion formation. In this study, we aimed to investigate the effects of PPARγ agonist rosiglitazone on neointimal hyperplasia and gelatinase (MMP-2 and MMP-9) expressions in rabbit carotid anastomosis model.

Methods

New Zealand white rabbits (n = 13, 2.7–3.2 kg) were divided into placebo and treatment groups. Right carotid artery (CA) was transected and both ends were anastomosed. Treatment group (n = 6) received rosiglitazone (3 mg/kg/day/p.o.) and placebo group (n = 7) received PBS (phosphate buffered saline, 2.5 ml/kg/day/p.o.) for 4 weeks postoperatively. After the sacrification, right and left CAs were isolated. Morphometric analyses and immunohistochemical examinations for gelatinases were performed.

Results

Intimal area (0.055 ± 0.005 control vs 0.291 ± 0.020 μm² anastomosed, p < 0,05) and index (0.117 ± 0.002 control vs 0.574 ± 0.013 anastomosed, p < 0,01) significantly increased in anastomosed arteries compared to control arteries from placebo group. However, in rosiglitazone-treated group, intimal area (0.291 ± 0.020 PBS vs 0.143 ± 0.027 rosiglitazone, p < 0,05) and index (0.574 ± 0.013 PBS vs 0.263 ± 0.0078 rosiglitazone, p < 0,01) significantly decreased. Furthermore, gelatinase immunopositivity was found to have significantly increased in anastomosed arteries from placebo group and decreased with rosiglitazone treatment.

Conclusions

These results suggest that rosiglitazone may prevent neointimal hyperplasia, which is the most important factor involved in late graft failure, by inhibiting gelatinase enzyme expression.

Animal models for studying vein graft failure and therapeutic interventions

Vein grafts have been extensively used to bypass blockages in arteries, but are themselves subject to early closure by thrombosis or later obstruction by vein graft disease (neointimal hyperplasia and remodelling). Animal models are a crucial means of testing potential therapeutic and surgical interventions to prevent graft stenosis and occlusion. This review outlines many of the animal models of vein grafting. Recent studies include targeted gene therapy to prevent acute vein graft thrombosis and the use of folic acid to limit graft failure in diabetic pigs.

Inhibitory effects of calcitonin gene-related peptides on experimental vein graft disease

BACKGROUND

Vein graft disease is a chronic inflammatory disease and limits the long-term clinical outcome of coronary revascularization. Because calcitonin gene-related peptide (CGRP) inhibits macrophage infiltration and inflammatory mediators, we hypothesized that transfected CGRP gene would inhibit macrophage infiltration and expression of inflammatory mediators in vein graft disease.

METHODS

Autologous rabbit jugular vein grafts were incubated ex vivo in a solution of mosaic adeno-associated virus vectors containing CGRP gene (AAV2/1.CGRP) or Escherichia coli B-galactosidase gene (LacZ) or a saline solution and then interposed in the carotid artery. Expression of CGRP gene was identified by reverse transcription-polymerase chain reaction, and E. coli LacZ gene expression was identified by X-gal staining. Intima to media ratios were evaluated at postoperative 4 weeks. Macrophages were identified with CD68 antibody by immunocytochemistry. Inflammatory mediators were measured with real-time polymerase chain reaction.

RESULTS

The CGRP and LacZ gene expression were positive at postoperative 4 weeks. The intima to media ratio was significantly inhibited in the AAV2/1.CGRP group. Macrophage infiltration and expression of inflammatory mediators including monocyte chemoattractant protein-1, tumor necrosis factor-alpha, inducible nitric oxide synthase, and matrix metalloproteinase-9 were also significantly inhibited in the AAV2/1.CGRP group.

CONCLUSIONS

Transfection of AAV2/1.CGRP inhibited inflammatory mediator expression, macrophage infiltration, and neointimal hyperplasia in experimental vein graft disease.

Inhibition of neointimal formation and hyperplasia in vein grafts by external stent/sheath

Synthetic and to a lesser extent vein graft failure is still a major problem in the treatment of peripheral arterial disease, with neointimal hyperplasia being the main cause for graft occlusion in the medium and long term. This review aims to establish the current status of external stents or sheaths in the prevention of intimal hyperplasia in small diameter (< 6 mm) vein grafts.

Mechanical buckling of veins under internal pressure

Venous tortuosity is associated with multiple disease states and is often thought to be a consequence of venous hypertension and chronic venous disease. However, the underlying mechanisms of vein tortuosity are unclear. We hypothesized that increased pressure causes vein buckling that leads to a tortuous appearance. The specific aim of this study was to determine the critical buckling pressure of veins. We determined the buckling pressure of porcine jugular veins and measured the mechanical properties of these veins. Our results showed that the veins buckle when the transmural pressure exceeds a critical pressure that is strongly related to the axial stretch ratio in the veins. The critical pressures of the eight veins tested were 14.2 +/- 5.4 and 26.4 +/- 9.0 mmHg at axial stretch ratio 1.5 and 1.7, respectively. In conclusion, veins buckle into a tortuous shape at high lumen pressures or reduced axial stretch ratios. Our results are useful in understanding the development of venous tortuosity associated with varicose veins, venous valvular insufficiency, diabetic retinopathy, and vein grafts.

Effect of matrix metalloproteinase-9 knockout on vein graft remodelling in mice

Long-term success in vein grafting for bypassing arteries blocked by atherosclerosis is limited by migration and proliferation of smooth muscle cells to form a neointima. Matrix metalloproteinases (MMPs), in particular MMP-2 and MMP-9, are implicated in neointimal formation by freeing smooth muscle cells from the cell-matrix contacts that normally restrict migration. We investigated the role of MMP-9 in vein grafts directly, using knockout mice. Vein grafts in MMP-9(-/-) and wild-type mice had similar luminal and graft areas at 1, 4 and 8 weeks after engraftment, increasing with time. There was a relationship between the perimeter of the external elastic lamina and graft thickness (indicating graft remodelling) in MMP-9(-/-) mice at 1 week after surgery not apparent in control mice until later (r(2) = 0.933 for MMP-9(-/-) mice, r(2) = 0.040 for wild-type mice). Grafts in MMP-9(-/-) mice had 6-fold more pro- and active MMP-2 (p = 0.013, p = 0.026) than grafts in wild-type mice. Grafts from MMP-9(-/-) mice also had more collagen (p = 0.046 at 8 weeks), without any difference in cell number. Thus, while a lack of MMP-9 did not alter vein graft wall area or cellularity, grafts from MMP-9(-/-)mice accumulated more collagen and had earlier linear expansive remodelling, possibly due to an early compensatory increase in MMP-2.

Adaptive changes in autogenous vein grafts for arterial reconstruction: clinical implications

For patients with the most severe manifestations of lower extremity arterial occlusive disease, bypass surgery using autogenous vein has been the most durable reconstruction. However, the incidence of bypass graft stenosis and graft failure remains substantial and wholesale improvements in patency are lacking. One potential explanation is that stenosis arises not only from over exuberant intimal hyperplasia, but also due to insufficient adaptation or remodeling of the vein to the arterial environment. Although in vivo human studies are difficult to conduct, recent advances in imaging technology have made possible a more comprehensive structural examination of vein bypass maturation. This review summarizes recent translational efforts to understand the structural and functional properties of human vein grafts and places it within the context of the rich existing literature of vein graft failure.

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.

Established neointimal hyperplasia in vein grafts expands via TGF-beta-mediated progressive fibrosis

In weeks to months following implantation, neointimal hyperplasia (NIH) in vein grafts (VGs) transitions from a cellularized to a decellularized phenotype. The inhibition of early cellular proliferation failed to improve long-term VG patency. We have previously demonstrated that transforming growth factor-beta(1) (TGF-beta(1))/connective tissue growth factor (CTGF) pathways mediate a conversion of fibroblasts to myofibroblasts in the early VG (<2 wk). We hypothesize that these similar pathways drive fibrosis observed in the late VG lesion. Within rabbit VGs, real-time RT-PCR, Western blot analysis, ELISA, and immunohistochemistry were used to examine TGF-beta/CTGF pathways in late (1-6 mo) NIH. All VGs exhibited a steady NIH growth (P = 0.006) with significant reduction in cellularity (P = 0.01) over time. Substantial TGF-beta profibrotic activities, as evidenced by enhanced TGF-beta(1) activation, TGF-beta receptor types I (activin receptor-like kinase 5)-to-II receptor ratio, SMAD2/3 phosphorylation, and CTGF production, persisted throughout the observation period. An increased matrix synthesis was accompanied by a temporal reduction of matrix metalloproteinase-2 (P = 0.001) and -9 (P < 0.001) activity. VG NIH is characterized by a conversion from a proproliferative to a profibrotic morphology. An enhanced signaling via TGF-beta/CTGF coupled with reduced matrix metalloproteinase activities promotes progressive fibrotic NIH expansion. The modulation of late TGF-beta/CTGF signaling may offer a novel therapeutic strategy to improve the long-term VG durability.