Nitric oxide synthase and adenylyl and guanylyl cyclase activity in porcine interposition vein grafts

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.

Vasa vasorum inside out/outside in communication: a potential role in the patency of saphenous vein coronary artery bypass grafts

The saphenous vein (SV) is the most commonly used conduit for revascularization in patients undergoing coronary artery bypass surgery (CABG). The patency rate of this vessel is inferior to the internal thoracic artery (ITA). In the majority of CABG procedures the ITA is removed with its outer pedicle intact whereas the (human) SV (hSV) is harvested with pedicle removed. The vasa vasorum, a microvessel network providing the adventitia and media with oxygen and nutrients, is more pronounced and penetrates deeper towards the lumen in veins than in arteries. When prepared in conventional CABG the vascular trauma caused when removing the hSV pedicle damages the vasa vasorum, a situation affecting transmural flow potentially impacting on graft performance. In patients, where the hSV is harvested with pedicle intact, the vasa vasorum is preserved and transmural blood flow restored at graft insertion and completion of CABG. By maintaining blood supply to the hSV wall, apart from oxygen and nutrients, the vasa vasorum may also transport factors potentially beneficial to graft performance. Studies, using either corrosion casts or India ink, have shown the course of vasa vasorum in animal SV as well as in hSV. In addition, there is some evidence that vasa vasorum of hSV terminate in the vessel lumen based on ex vivo perfusion, histological and ultrastructural studies. This review describes the preparation of the hSV as a bypass conduit in CABG and its performance compared with the ITA as well as how and why its patency might be improved by harvesting with minimal trauma in a way that preserves an intact vasa vasorum.

Dual Role of CREB in The Regulation of VSMC Proliferation: Mode of Activation Determines Pro- or Anti-Mitogenic Function

Vascular smooth muscle cell (VSMC) proliferation has been implicated in the development of restenosis after angioplasty, vein graft intimal thickening and atherogenesis. We investigated the mechanisms underlying positive and negative regulation of VSMC proliferation by the transcription factor cyclic AMP response element binding protein (CREB). Incubation with the cAMP elevating stimuli, adenosine, prostacyclin mimetics or low levels of forksolin activated CREB without changing CREB phosphorylation on serine-133 but induced nuclear translocation of the CREB co-factors CRTC-2 and CRTC-3. Overexpression of CRTC-2 or -3 significantly increased CREB activity and inhibited VSMC proliferation, whereas CRTC-2/3 silencing inhibited CREB activity and reversed the anti-mitogenic effects of adenosine A2B receptor agonists. By contrast, stimulation with serum or PDGF_BB significantly increased CREB activity, dependent on increased CREB phosphorylation at serine-133 but not on CRTC-2/3 activation. CREB silencing significantly inhibited basal and PDGF induced proliferation. These data demonstrate that cAMP activation of CREB, which is CRTC2/3 dependent and serine-133 independent, is anti-mitogenic. Growth factor activation of CREB, which is serine-133-dependent and CRTC2/3 independent, is pro-mitogenic. Hence, CREB plays a dual role in the regulation of VSMC proliferation with the mode of activation determining its pro- or anti-mitogenic function.

The Hippo pathway mediates inhibition of vascular smooth muscle cell proliferation by cAMP

AIMS

Inhibition of vascular smooth muscle cell (VSMC) proliferation by intracellular cAMP prevents excessive neointima formation and hence angioplasty restenosis and vein-graft failure. These protective effects are mediated via actin-cytoskeleton remodelling and subsequent regulation of gene expression by mechanisms that are incompletely understood. Here we investigated the role of components of the growth-regulatory Hippo pathway, specifically the transcription factor TEAD and its co-factors YAP and TAZ in VSMC.

METHODS AND RESULTS

Elevation of cAMP using forskolin, dibutyryl-cAMP or the physiological agonists, Cicaprost or adenosine, significantly increased phosphorylation and nuclear export YAP and TAZ and inhibited TEAD-luciferase report gene activity. Similar effects were obtained by inhibiting RhoA activity with C3-transferase, its downstream kinase, ROCK, with Y27632, or actin-polymerisation with Latrunculin-B. Conversely, expression of constitutively-active RhoA reversed the inhibitory effects of forskolin on TEAD-luciferase. Forskolin significantly inhibited the mRNA expression of the pro-mitogenic genes, CCN1, CTGF, c-MYC and TGFB2 and this was reversed by expression of constitutively-active YAP or TAZ phospho-mutants. Inhibition of YAP and TAZ function with RNAi or Verteporfin significantly reduced VSMC proliferation. Furthermore, the anti-mitogenic effects of forskolin were reversed by overexpression of constitutively-active YAP or TAZ.

CONCLUSION

Taken together, these data demonstrate that cAMP-induced actin-cytoskeleton remodelling inhibits YAP/TAZ-TEAD dependent expression of pro-mitogenic genes in VSMC. This mechanism contributes novel insight into the anti-mitogenic effects of cAMP in VSMC and suggests a new target for intervention.

cAMP-induced actin cytoskeleton remodelling inhibits MKL1-dependent expression of the chemotactic and pro-proliferative factor, CCN1

Elevation of intracellular cAMP concentration has numerous vascular protective effects that are in part mediated via actin cytoskeleton-remodelling and subsequent regulation of gene expression. However, the mechanisms are incompletely understood. Here we investigated whether cAMP-induced actin-cytoskeleton remodelling modulates VSMC behaviour by inhibiting expression of CCN1. In cultured rat VSMC, CCN1-silencing significantly inhibited BrdU incorporation and migration in a wound healing assay. Recombinant CCN1 enhanced chemotaxis in a Boyden chamber. Adding db-cAMP, or elevating cAMP using forskolin, significantly inhibited CCN1 mRNA and protein expression in vitro; transcriptional regulation was demonstrated by measuring pre-spliced CCN1 mRNA and CCN1-promoter activity. Forskolin also inhibited CCN1 expression in balloon injured rat carotid arteries in vivo. Inhibiting RhoA activity, which regulates actin-polymerisation, by cAMP-elevation or pharmacologically with C3-transferase, or inhibiting its downstream kinase, ROCK, with Y27632, significantly inhibited CCN1 expression. Conversely, expression of constitutively active RhoA reversed the inhibitory effects of forskolin on CCN1 mRNA. Furthermore, CCN1 mRNA levels were significantly decreased by inhibiting actin-polymerisation with latrunculin B or increased by stimulating actin-polymerisation with Jasplakinolide. We next tested the role of the actin-dependent SRF co-factor, MKL1, in CCN1 expression. Forskolin inhibited nuclear translocation of MKL1 and binding of MKL1 to the CCN1 promoter. Constitutively-active MKL1 enhanced basal promoter activity of wild-type but not SRE-mutated CCN1; and prevented forskolin inhibition. Furthermore, pharmacological MKL-inhibition with CCG-1423 significantly inhibited CCN1 promoter activity as well as mRNA and protein expression. Our data demonstrates that cAMP-induced actin-cytoskeleton remodelling regulates expression of CCN1 through MKL1: it highlights a novel cAMP-dependent mechanism controlling VSMC behaviour.

Coronary artery bypass graft: why is the saphenous vein prone to intimal hyperplasia?

Proliferation and migration of smooth muscle cells and the resultant intimal hyperplasia cause coronary artery bypass graft failure. Both internal mammary artery and saphenous vein are the most commonly used bypass conduits. Although an internal mammary artery graft is immune to restenosis, a saphenous vein graft is prone to develop restenosis. We found significantly higher activity of phosphatase and tensin homolog (PTEN) in the smooth muscle cells of the internal mammary artery than in the saphenous vein. In this article, we critically review the pathophysiology of vein-graft failure with detailed discussion of the involvement of various factors, including PTEN, matrix metalloproteinases, and tissue inhibitor of metalloproteinases, in uncontrolled proliferation and migration of smooth muscle cells towards the lumen, and invasion of the graft conduit. We identified potential target sites that could be useful in preventing and (or) reversing unwanted consequences following coronary artery bypass graft using saphenous vein.

Saphenous vein graft disease: review of pathophysiology, prevention, and treatment

Saphenous vein graft (SVG) disease after coronary artery bypass grafting (CABG) occurs in three phases: thrombosis, intimal hyperplasia, and atherosclerosis. Within the first month, thrombosis plays a major role. From month 1 to month 12, intimal hyperplasia occurs. Beyond 12 months, atherosclerosis becomes the primary cause for late graft failure. Endothelial damage has been shown to be the major underlying pathophysiology of SVG disease. Many factors contribute to endothelial damage from the moment the vein is harvested to when the vein is grafted into an arterial environment. To address this disease process, various therapeutic modalities, from surgical methods to medical treatment, have been evaluated. Surgically, the technical method of harvesting the vein has been shown to affect SVG patency. From a pharmacologic perspective, only two guideline class I recommended medications, aspirin and statins, have been shown to improve short- and long-term SVG patency after CABG. Despite these surgical and medical advances, SVG disease remains a significant problem with 1-year patency rates of 89% dropping to 61% after 10 years. This review discusses the pathogenesis of SVG disease, predictors of SVG failure, and current surgical and pharmacologic therapies to address SVG disease, including possible future treatment.

'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.

Angiotensin-(1–7) Inhibits Vascular Remodelling in Rat Jugular Vein Grafts via Reduced ERK1/2 and p38 MAPK Activity

This study evaluated the effect of angiotensin (Ang)-(1–7) on vascular remodelling in a rat autologous jugular vein graft model in which rats underwent autologous jugular vein graft transplantation (Ang-[1–7] and control groups) or sham surgery (sham group). The animals received continuous jugular infusion of Ang-(1–7) at 25 μg/kg per h (Ang-[1–7] group) or normal saline (control and sham groups) starting 3 days after surgery. Ang-(1–7) infusion reduced venous graft hyperplasia, vascular remodelling, extracellular signal-regulated kinase 1/2 (ERK1/2) activation, p38 mitogen-activated protein kinase (MAPK) activation and levels of proliferating cell nuclear antigen and α-smooth muscle actin compared with control animals. The vascular tissue Ang II level was higher in Ang-(1–7) and control rats than in sham animals. These findings suggest that Ang-(1–7) acts by inhibiting the activation of ERK1/2 and p38 MAPK in vascular tissue. The use of exogenous Ang-(1–7) could improve the outcome of vein grafting through the attenuation of vascular remodelling.

Pharmacologic relaxation of vein grafts is beneficial compared with pressure distention caused by upregulation of endothelial nitric oxide synthase and nitric oxide production

OBJECTIVE

Pressure distention of veins during preparation for bypass surgery is believed to impair vascular integrity and reduce graft patency. We previously suggested a combination of pharmacologic vasodilatators as an alternative to distention. Vascular homeostasis is largely regulated by nitric oxide. We investigated the role of distention in comparison with pharmacologic vasorelaxation in the regulation of nitric oxide synthases, nitric oxide bioavailability, and vascular reactivity in vein grafts.

METHODS

In a porcine model the internal jugular vein from either side received pressure distention or the combination of vasodilators (alpha-adrenergic antagonist, phenoxybenzamine, 10 micromol/L; Rho-kinase inhibitor, HA-1077 [fasudil], 50 mumol/L; calcium blocker, nicardipine, 1 micromol/L) and then was grafted into the carotid artery. Regulation of nitric oxide synthase, as well as nitrate and nitrite levels, were examined in vein grafts after 2 weeks of implantation.

RESULTS

Distention of jugular veins resulted in reduction of vasoconstriction in response to depolarization and agonist stimulation. Arterial grafting doubled inducible nitric oxide synthase expression in both grafts but caused a pronounced upregulation of endothelial nitric oxide synthase protein (by 57.3% +/- 5%) only in drug-treated grafts, whereas in distended grafts the endothelial nitric oxide synthase level was decreased by 27.5% +/- 2.7%. The downregulated endothelial nitric oxide synthase level in the distended grafts was accompanied by a 45.2% +/- 3.1% reduction of phospho-endothelial nitric oxide synthase Ser1177 levels and by a significant reduction in nitric oxide synthase activity (12.1% +/- 1.2%) and nitrate production (48.9% +/- 5.6%) in comparison with that seen in drug-treated grafts.

CONCLUSIONS

Pharmacologic preparation of the vein grafts results in upregulation of endothelial nitric oxide synthase and increased nitric oxide production in the vein grafts after arterial implantation. This might provide greater clinical benefit than conventional pressure-distention methods.

Pharmacologic inhibition of vein graft neointimal hyperplasia

Although arterial conduits are widely used and have improved the long-term results of coronary artery bypass grafting, vein grafts remain important additional conduits in coronary surgery. Newer studies show a saphenous vein graft patency of 60% or more at 10 years postoperatively. The pathology of vein graft disease consists of thrombosis, neointimal hyperplasia, and vein graft atherosclerosis, which limit graft longevity. Therapeutic strategies to prevent vein graft disease include external stenting, pharmacotherapy, and gene therapy. The potential benefits of a pharmacologic approach are as follows: (1) Drugs with a broad clinical experience can be used; (2) side effects of systemic application can be minimized by local therapy; and (3) no vascular injury, such as pressurizing the vein for a viral transfection approach, is necessary. The different sites for pharmacotherapy in vein graft disease are reviewed in this article.

Altered S-phase kinase-associated protein-2 levels are a major mediator of cyclic nucleotide-induced inhibition of vascular smooth muscle cell proliferation

Cyclic nucleotides inhibit vascular smooth muscle cell (VSMC) proliferation but the underlying molecular mechanisms are incompletely understood. We studied the role of S-phase kinase-associated protein-2 (Skp2), an F-box protein of SCFSkp2 ubiquitin ligase responsible for polyubiquitylation of and subsequent proteolysis of p27Kip1, a key step leading to cell cycle progression. Skp2 mRNA and protein were upregulated in mitogen-stimulated VSMCs and after balloon injury in rat carotid arteries, where the time course and location of Skp2 expression closely paralleled that of proliferating cell nuclear antigen. Skp2 small interference RNA (siRNA) reduced Skp2 expression, increased p27Kip1 levels, and inhibited VSMC proliferation in vitro. cAMP-elevating agents prominently inhibited VSMC proliferation and Skp2 expression through inhibiting Skp2 transcription as well as decreasing Skp2 protein stability. Consistent with this, activation of protein kinase A, a downstream target of cAMP, was shown to negatively regulate focal adhesion kinase (FAK) phosphorylation and Skp2 expression. Adenovirus-mediated Skp2 expression reversed cAMP-induced p27Kip1 upregulation and rescued cAMP-related S-phase entry inhibition up to 50%. 8-bromo-cGMP also moderately reduced Skp2 and cell proliferation when VSMCs were incubated with low serum concentration. Interestingly, we showed that 8-bromo-cGMP inhibited Skp2 expression also through activation of protein kinase A, not protein kinase G, which conversely enhanced FAKY397 phosphorylation and Skp2 expression. After balloon injury of rat carotid arteries, local forskolin treatment significantly reduced FAKY397 phosphorylation, Skp2 expression, VSMC proliferation, and subsequent neointimal thickening. These data demonstrate for the first time that Skp2 is an important factor in VSMC proliferation and its inhibition by cyclic nucleotides.

Influence of ischemic injury on vein graft remodeling: role of cyclic adenosine monophosphate second messenger pathway in enhanced vein graft preservation

OBJECTIVE

Endothelial injury during the harvest of saphenous vein grafts might play an important role in the development of vein graft disease after coronary artery bypass grafting. Using a murine autologous arterialized vein patch model, we tested whether the initial ischemic insult of vein grafts was linked to the later development of graft neointimal hyperplasia and whether the restoration of the cyclic adenosine monophosphate second messenger pathway would attenuate the development of neointimal hyperplasia.

METHODS

A segment of the external jugular vein of a mouse was grafted onto its abdominal aorta. Three weeks after the operation, the degree of neointimal hyperplasia of the implanted graft was compared among (1) grafts without preservation, (2) grafts with 2 hours of preservation (25 degrees C) in heparinized saline, and (3) grafts with 2 hours of preservation in heparinized saline in the presence of a cyclic adenosine monophosphate analog. In addition, cyclic adenosine monophosphate contents of vein grafts and leukocyte adherence to the graft endothelium were assessed.

RESULTS

Cyclic adenosine monophosphate contents were significantly decreased after 2 hours of preservation (212 +/- 8 vs 156 +/- 5 pmol/L, P < .01). The grafts preserved for 2 hours showed greater neointimal hyperplasia compared with the grafts without preservation (neointimal expansion, 68.7% +/- 9.6% vs 46.1% +/- 4.8%; P < .01). The addition of a cyclic adenosine monophosphate analog to the preservation solution significantly suppressed neointimal hyperplasia of grafts preserved for 2 hours (44.3% +/- 5.0%). Inhibiting the cyclic adenosine monophosphate-dependent protein kinase by adding Rp-cAMPS abrogated the beneficial effects. Furthermore, grafts preserved for 2 hours had significantly more leukocytes adhering to the graft endothelium 24 hours after the operation compared with nonpreserved grafts, which was significantly reduced by the cyclic adenosine monophosphate treatment.

CONCLUSIONS

Ischemic insult during vein graft harvest and preservation is a key factor in the development of vein graft neointimal hyperplasia at least in part caused by the depletion of cyclic adenosine monophosphate. We conclude that stimulation of the cyclic adenosine monophosphate second messenger pathway might be a potential strategy for the prevention of vein graft disease.

Saphenous Vein Grafts: To Use or Not to Use?

The choice of the graft conduit is crucial to the success of coronary artery bypass grafting (CABG) because the patency of a coronary conduit is closely associated with an uneventful postoperative course and better long-term patient survival. From the beginning of coronary bypass surgery venous conduits particularly the great saphenous veins (GSV) have been the most frequently used coronary conduit from the beginning of the coronary bypass surgery. However, over the last decade or so, coronary bypass graft surgery with arterial revascularization of all diseased coronaries has shown to be efficient because arterial grafts have better long-term patency, especially left internal mammary artery (LIMA), compared with venous grafts. Early vein graft failure coupled with occlusion is the most important limitation of saphenous vein grafts. Nevertheless, vein grafting is still an integral part of cardiac surgical practice. This review provides a summary of the patency rates, technical features and certain characteristics of the venous conduits. It also examines the current understanding and knowledge of venous histology, vein graft pathology and the associated endothelial and smooth muscle cell physiology and pharmacology. In addition, the existing and the emerging strategies to combat and control vein graft intimal hyperplasia and accelerated atherosclerosis are reviewed in detail.

The influence of hemodynamics and wall biomechanics on the thrombogenicity of vein segments perfused in vitro1

This study addresses the hypothesis that exposure to peripheral arterial (ART) or coronary (COR) hemodynamics and wall biomechanics affect platelet deposition on vein segments. Intact human saphenous vein (HSV) and porcine internal jugular vein (PIJV) segments were studied under venous (VEN), ART, and COR environments using in vitro perfusion systems. Wall shear stress (tau) and circumferential wall stress (sigma(theta)) were calculated for PIJV segments. Platelet deposition was measured using a radioactive assay. PIJV ART segments exhibited a 14% increase in inner diameter over time (P < 0.05). tau, acting on PIJV ART specimens, was less at 6 h compared with time 0 (P < 0.05). sigma(theta) was lower in the VEN specimens compared with ART and COR groups (P < 0.01). Platelet deposition decreased by 40% on PIJV ART segments (P < 0.05) but increased 3.2-fold on PIJV COR segments (P < 0.05) versus VEN control segments. Platelet deposition was increased 1.75-fold in COR HSV cases versus VEN segments. These data indicate that short-term exposure to COR conditions lead to enhanced platelet deposition, whereas ART conditions decrease platelet deposition.

Saphenous Vein Grafts: to Use or Not to Use?

The choice of the graft conduit is crucial to the success of coronary artery bypass grafting (CABG) because the patency of a coronary conduit is closely associated with an uneventful postoperative course and better long-term patient survival. From the beginning of coronary bypass surgery venous conduits particularly the great saphenous vein (GSV) has been the most frequently used coronary conduit. However, over the last decade or so, coronary bypass graft surgery with arterial revascularization of all diseased coronaries has shown to be efficient because arterial grafts have better long-term patency, especially left internal mammary artery (LIMA), compared with venous grafts. Early vein graft failure coupled with occlusion is the most important limitation of saphenous vein grafts. Nevertheless, vein grafting is still an integral part of cardiac surgical practice. This review provides a summary of the patency rates, technical features and certain characteristics of the venous conduits. It also examines the current understanding and knowledge of venous histology, vein graft pathology and the associated endothelial and smooth muscle cell physiology and pharmacology. In addition, the existing and the emerging strategies to combat and control vein graft intimal hyperplasia and accelerated atherosclerosis are reviewed in detail.

Immunocytochemical Study on Endothelial Integrity of Saphenous Vein Grafts Harvested by Minimally Invasive Surgery with the Use of Vascular Mayo Stripers. A Randomized Controlled Trial

OBJECTIVES

The aim of this study is to compare the endothelial integrity of saphenous vein grafts harvested by minimally invasive surgery and veins harvested conventionally for coronary artery bypass surgery in 200 participants who were assigned to interventions by using random allocation.

DESIGN

Randomized controlled trial. Methods. Immunocytochemistry with anti-CD 31 antibodies and anti-nitric oxide synthase (NOS) antibodies were employed to identify the endothelial integrity.

RESULTS

The CD 31 immunostaining showed that the endothelial cell integrity of the minimally invasive harvested veins was preserved in 82+/-13% of the circumference of luminal endothelium, while in conventionally harvested grafts it was reduced to 64+/-15% (p=0.05).> This was associated with the lack of CD 31 expression in vasa vasorum (10 and 18%) in both groups, respectively, (p=0.02). The NOS immunostaining revealed that the endothelial integrity of the minimally invasive harvested grafts was preserved in 96+/-4% of the luminal endothelium circumference as compared to 74+/-10% in conventionally harvested grafts (p=0.05). The percentage of cases with the lack of NOS expression in all vasa vasorum was 12 and 21%, in G1 and G2, respectively, (p=0.02).

CONCLUSION

The endothelial integrity of saphenous vein grafts harvested by minimally invasive surgery is better preserved than with the grafts obtained by the conventional manner. This could play an important role in improving vein graft patency rates.

Understanding and treating vein graft atherosclerosis

BACKGROUND

Vein grafts have been used as bypass conduits for coronary artery disease since the 1960s. This widely used treatment, however, is complicated by the development of changes in the vein graft, which resemble atherosclerosis and are often termed as such. They occur at about 10 years, which leads to the need for reoperation in some patients. The purpose of this review is to summarize the knowledge regarding the pathophysiology of vein graft "atherosclerosis," as well as promising new treatments for this disease.

METHODS

The relevant literature relating to the epidemiology, histology, cell and molecular pathophysiology and treatment of vein graft atherosclerosis is reviewed.

RESULTS

The development of vein graft atherosclerosis differs from arterial atherosclerosis. Studies have examined the role of trauma, lipids, vasoactive mediators, smooth muscle cell mitogens, smooth muscle cells apoptosis, adhesion molecules and proteases. Therapies have been developed to prevent vein graft atherosclerosis based on these studies and have been tested using animal models and in patients.

DISCUSSION

Promising new therapies have been developed based on current knowledge and further applications of genomics will allow for the further identification of risk factors and mechanistic insights. The use of arterial grafts such as the internal mammary artery, which have higher patency rates at 10 years compared with vein grafts as well as approaches to revascularize infarcted myocardium may one day replace the use of vascular conduits.

Accelerated reendothelialization with suppressed thrombogenic property and neointimal hyperplasia of rabbit jugular vein grafts by adenovirus-mediated gene transfer of C-type natriuretic peptide

BACKGROUND

Vein graft disease limits the late results of coronary revascularization. C-type natriuretic peptide (CNP) inhibits the growth of vascular smooth muscle cells. Given the effects of CNP on cGMP cascade, we hypothesized that transfected CNP genes modulate endothelial repair and thrombogenicity in the vein graft.

METHODS AND RESULTS

Autologous rabbit jugular vein grafts were incubated ex vivo in a solution of adenovirus vectors containing CNP gene (Ad.CNP) or Escherichia coli lac Z gene (Ad.LacZ) and then interposed in the carotid artery. Reendothelialization, mural thrombi formation, and intima/media ratio were evaluated on the 14th and 28th postoperative days. More reendothelialization was seen in Ad.CNP-infected grafts than in Ad.LacZ-infected grafts both at 14 days (0.81+/-0.05 versus 0.30+/-0.14, P<0.01) and at 28 days (0.96+/-0.01 versus 0.45+/-0.08, P<0.001). The mural thrombus area was smaller in Ad.CNP-infected grafts than in Ad.LacZ-infected grafts. Neointimal thickening was significantly suppressed in the Ad.CNP group. The in vitro wound assay with human coronary artery endothelial cells revealed significant potentiation of the wound repair process by CNP and atrial natriuretic peptide administration.

CONCLUSIONS

Infected Ad.CNP accelerated reendothelialization and suppressed thrombosis and neointimal hyperplasia. The method may potentially prevent vein graft disease in patients undergoing coronary artery revascularization.

Preserved endothelial integrity and nitric oxide synthase in saphenous vein grafts harvested by a 'no-touch' technique

BACKGROUND

The saphenous vein is the most commonly used conduit for coronary artery bypass surgery, but 1-year occlusion rates as high as 30 per cent have been reported. In conventional surgery, considerable damage to the vein occurs during harvesting. The aim of this study was to compare endothelial integrity and nitric oxide synthase (NOS) in saphenous veins harvested by a novel 'no-touch' technique and veins harvested conventionally.

METHODS

Immunohistochemistry was used to study endothelial integrity, and a combination of histochemistry and autoradiography was employed to identify NOS in human saphenous veins harvested by conventional and no-touch techniques.

RESULTS

The endothelial lining of conventional grafts was reduced compared with that of no-touch grafts (52 versus 73 per cent; P = 0.04). This was associated with a concomitant reduction of NOS availability; NOS was also present in the adventitial vasa vasorum of no-touch vessels.

CONCLUSION

Some of the sites with potential for nitric oxide release in vivo are removed during conventional saphenous vein harvesting. These sites were preserved after no-touch harvesting, suggesting the potential to improve coronary artery bypass graft patency.

Adventitial versus intimal liposome-mediated ex vivo transfection of canine saphenous vein grafts with endothelial nitric oxide synthase gene

PURPOSE

Experiments were designed (1) to evaluate liposome-mediated endothelial constitutive nitric oxide synthase (ecNOS) transfection in vein grafts and (2) to compare intimal and adventitial routes of transfection.

METHODS

Male mongrel dogs (N = 36) underwent bilateral femoral artery bypass grafting with the lateral saphenous vein. In each animal one vein was transfected with plasmid (pVR1012) containing the ecNOS gene, and another vein was transfected with plasmid alone (control). Gene transfer was performed from either the intimal surface (Group I, n = 18) or the adventitial surface (Group II, n = 18). In each group there were three transfection subgroups (n = 6 each): (a ) 10 microg/mL naked plasmid DNA, (b ) 10 microg/mL plasmid DNA + liposome (LipofectAMINE PLUS), and (c ) 100 microg/mL plasmid DNA + LipofectAMINE PLUS. Grafts were harvested on the third postoperative day, and the transfection was assessed with molecular techniques and enzyme assay for activity of NOS by conversion of tritiated l-arginine to tritiated l-citrulline. Proliferating cells were quantified with a digital analysis of histologic sections after nuclear antigen Ki-67 (MIB1) immunohistochemistry.

RESULTS

Transgene was identified with polymerase chain reaction in all ecNOS-transfected grafts, regardless of transfection modality. However, significant transcription of the ecNOS transgene was observed only in Group IIc (mean ecNOS messenger RNA, 8.7+/-1.7 vs. 3.1+/-0.7 x 10(-2) attomole/microL, in transfected compared with control grafts, respectively, P =.01). NOS activity increased approximately twofold in this group (11.58+/-2.1 and 6.3+/-1.0 pmol tritiated l-citrulline per milligram protein per hour in transfected and control grafts, respectively, P = .05). Numbers of proliferating cells did not differ among ecNOS-transfected and control grafts in any transfection group.

CONCLUSION

These results suggest that ecNOS transfection of vein grafts is feasible through intimal and adventitial routes with naked DNA or a liposomal vector. However, efficient transcription of the transgene is evident at postoperative day 3 only after adventitial transfection of 100 microg/mL of the gene.

Inhibition of intracellular Ca2+ mobilisation by low antiproliferative concentrations of thapsigargin in human vascular smooth-muscle cells

Low nanomolar concentrations of thapsigargin, a modulator of intracellular Ca2+ ([Ca2+]i) pools, inhibit vascular smooth-muscle cell (VSMC) proliferation. Because the mechanisms underlying this effect have not been defined, the effect of antiproliferative concentrations of thapsigargin on [Ca2+]i in fura-2-loaded VSMCs was studied by using dynamic video imaging of [Ca2+]i. After seeding on coverslips, human VSMCs were incubated for 1-48 h with thapsigargin before loading with fura-2 or during imaging. Mobilisation of [Ca2+]i was stimulated with 1 microM ionomycin in Ca2+-free medium and the increase in [Ca2+]i detected by using Ca2+ imaging techniques. Continuous exposure of cells to low concentrations of thapsigargin (which failed measurably to increase in [Ca2+]i) reduced the ionomycin response in a time- and dose-dependent manner (100% inhibition at 10 nM thapsigargin after 1 h exposure). After exposure of cells to 10 nM thapsigargin for 1 h followed by washing and further incubation for < or = 72 h, there was a time-dependent recovery of the ionomycin response. Because the concentrations of thapsigargin and exposure times are identical to those that inhibit replication in VSMCs, it is proposed that depletion of [Ca2+]i pools mediates the inhibitory effect of thapsigargin on VSMC proliferation.

Nitric oxide, prostacyclin and cyclic nucleotide formation in externally stented porcine vein grafts

Non-restrictive, porous, external stents inhibit neointima formation in porcine vein grafts. Since the mechanisms underlying these effects are unknown we investigated the impact of this external stent on factors known to inhibit vascular smooth muscle cell proliferation: prostacyclin (PGI2), nitric oxide (NO), cAMP and cGMP formation in different regions of stented and unstented porcine vein grafts. Paired stented and unstented saphenous vein-carotid artery interposition grafting was carried out in Landrace pigs. One month after surgery, the vessels were excised and the formation of PGI2, cAMP and cGMP determined using radioimmunoassay and nitric oxide synthase (NOS) distribution studied using autoradiography and histochemistry. There were no significant differences between PGI2, cAMP and cGMP (nitroprusside-stimulated) formation in the medial/intimal regions of grafts of stented vein graft and ungrafted saphenous vein whereas all were significantly reduced in unstented vein graft. A23187-stimulated cGMP formation (mediated by NO release) and NOS content was significantly greater in the medial/intimal region of stented and unstented vein graft compared to ungrafted saphenous vein, indicating induction of endothelial NOS (eNOS) in both types of graft. This normalisation of the PGI2-cAMP axis and guanylyl cyclase activity in the medial/intimal region may contribute to the beneficial impact of the external stent on vein graft thickening. The increase in eNOS in both stented and unstented vein grafts mitigates against this isoform as playing a role in mediating the inhibitory effect of the stent on neointima formation. In the adventitia of both stented and unstented grafts there was an increase in PGI2, cAMP and cGMP formation compared to ungrafted saphenous vein, the production being greater in the stented compared to the unstented graft. In the adventitia of stented veini grafts, NOS, detected with NAPDH diaphorase staining, was associated with microvessels as well as with inflammatory cells. Taken together, these data are suggestive of a role for PGI2 and NO in promoting microangiogenesis in the adventitia of stented vein grafts which may in turn minimize graft hypoxia, an established contributory factor to neointima formation.

Towards the prevention of vein graft failure

Improved outcome after coronary bypass surgery over the last decade has been attributed largely to the increasing use of arterial conduits and their superior patency rates over that of saphenous vein grafts. In spite of this trend, autologous saphenous vein has remained an important and convenient conduit for a variety of operative scenarios, and is still used for more than 70% of grafts. As a result, vein graft failure continues to represent a significant clinical and economic burden upon the health care service. Between 15 to 30% of saphenous vein grafts occlude within the first year of surgery, increasing to over 50% after 10 years. By this time, more than 10% of patients will require further intervention to alleviate symptoms arising from occluded grafts and progression of native disease. Graft occlusion arises either from early thrombosis or the later onset of 'vein graft disease' and subsequent atherosclerotic changes.