Pharmacologic inhibition of vein graft neointimal hyperplasia

Molecular differences between arterial and venous grafts in the first year after coronary artery bypass grafting

Despite commonly used for coronary artery bypass surgery, saphenous vein (SV) grafts have significantly lower patency rates in comparison to internal thoracic artery (ITA) grafts, which might be due to the structural characteristics of the vessel wall but also due to differences in oxidative stress adaptation and molecular signaling and regulation. This human post mortem study included a total of 150 human bypass grafts (75 SV grafts and 75 ITA grafts) obtained from 60 patients divided into five groups due to the time period of implantation: group 1: baseline group without grafting; group 2: 1 day; group 3: > 1 day-1 week; group 4: > 1 week-1 month; group 5: > 1 month-1 year. Pieces of 3 mm length were fixed with formaldehyde, dehydrated, wax embedded, cut into sections of 3 µm thickness, and histologically and immunohistochemically examined. Over the whole time period, we observed a lower neointima formation and a better preserved media in ITA grafts with a higher percentage of TNF-α, PDGFR-α, and VEGF-A in nearly all vessel wall layers, a higher amount of MMP-7, MMP-9, EGFR, and bFGF positive cells in SV grafts and a timely different peak not only between ITA and SV grafts but also within the various vessel wall layers of both graft types. Since most of the examined growth factors, growth factor receptors and cytokines are regulated by MAPKs, our results suggest an activation of different pathways in both vessel graft types immediately after bypass grafting.

Do storage solutions protect endothelial function of arterialized vein graft in an experimental rat model?

BACKGROUND

This study aims to compare the effects of storage solutions commonly used in coronary artery bypass grafting on the vascular reactivity in vein graft interposed in arterial position in syngeneic rats.

METHODS

Twenty-seven male Lewis rats were sacrified to sample a vein graft implanted 6 weeks ago into abdominal aorta position. The vein grafts were inferior venae cavae initially pretreated with heparinized saline solution (HS) or autologous heparinized blood (AHB) or our referent solution, GALA. The endothelial functionality, the in situ Reactive Oxygen Species (ROS) levels and the histological characteristics were conducted from segments of arterialized vein graft.

RESULTS

At 6 weeks, graft thrombosis occurred respectively in 22% of AHB group, 62.5% in the HS group and 82.5% in the GALA group. In each group, significative intimal hyperplasia was observed. After 6 weeks, an endothelium-remodeling layer associated with an increase of wall thickness was observed in each group. Endothelium-dependent tone was reduced in the vein graft regardless of the group. No difference was observed concerning the ROS in vein graft between the different groups. In distal aortic sections, ROS levels were increased in HS and GALA groups.

CONCLUSIONS

Storage solutions used in this experimental model of vein graft implanted in arterial position cause graft injury and a complete disappearance of vascular reactivity. GALA solution did not reduce intimal risk hyperplasia when the vein graft was exposed to arterial flow in a rat model.

The effect of storage solutions on endothelial function and saphenous vein graft patency

Vein graft failure is a complex mechanism that can be triggered immediately after surgical harvesting. Storage solutions have a major role in preventing endothelial cell damage during harvesting. While normal saline is still widely used, buffered solutions seem to better preserve endothelial integrity and function. This review aims to summarize the current literature surrounding vein graft storage solutions.

Linking gene dynamics to vascular hyperplasia - Toward a predictive model of vein graft adaptation

Reductionist approaches, where individual pieces of a process are examined in isolation, have been the mainstay of biomedical research. While these methods are effective in highly compartmentalized systems, they fail to account for the inherent plasticity and non-linearity within the signaling structure. In the current manuscript, we present the computational architecture for tracking an acute perturbation in a biologic system through a multiscale model that links gene dynamics to cell kinetics, with the overall goal of predicting tissue adaptation. Given the complexity of the genome, the problem is made tractable by clustering temporal changes in gene expression into unique patterns. These cluster elements form the core of an integrated network that serves as the driving force for the response of the biologic system. This modeling approach is illustrated using the clinical scenario of vein bypass graft adaptation. Vein segments placed in the arterial circulation for treatment of advanced occlusive disease can develop an aggressive hyperplastic response that narrows the lumen, reduces blood flow, and induces in situ thrombosis. Reducing this hyperplastic response has been a long-standing but unrealized goal of biologic researchers in the field. With repeated failures of single target therapies, the redundant response pathways are thought to be a fundamental issue preventing progress towards a solution. Using the current framework, we demonstrate how theoretical genomic manipulations can be introduced into the system to shift the adaptation to a more beneficial phenotype, where the hyperplastic response is mitigated and the risk of thrombosis reduced. Utilizing our previously published rabbit vein graft genomic data, where grafts were harvested at time points ranging from 2 hours to 28 days and under differential flow conditions, and a customized clustering algorithm, five gene clusters that differentiated the low flow (i.e., pro-hyperplastic) from high flow (i.e., anti-hyperplastic) response were identified. The current analysis advances these general associations to create a model that identifies those genes sets most likely to be of therapeutic benefit. Using this approach, we examine the range of potential opportunities for intervention via gene cluster over-expression or inhibition, delivered in isolation or combination, at the time of vein graft implantation.

Perivascular medical devices and drug delivery systems: Making the right choices

Perivascular medical devices and perivascular drug delivery systems are conceived for local application around a blood vessel during open vascular surgery. These systems provide mechanical support and/or pharmacological activity for the prevention of intimal hyperplasia following vessel injury. Despite abundant reports in the literature and numerous clinical trials, no efficient perivascular treatment is available. In this review, the existing perivascular medical devices and perivascular drug delivery systems, such as polymeric gels, meshes, sheaths, wraps, matrices, and metal meshes, are jointly evaluated. The key criteria for the design of an ideal perivascular system are identified. Perivascular treatments should have mechanical specifications that ensure system localization, prolonged retention and adequate vascular constriction. From the data gathered, it appears that a drug is necessary to increase the efficacy of these systems. As such, the release kinetics of pharmacological agents should match the development of the pathology. A successful perivascular system must combine these optimized pharmacological and mechanical properties to be efficient.

Arterial levels of oxygen stimulate intimal hyperplasia in human saphenous veins via a ROS-dependent mechanism

Saphenous veins used as arterial grafts are exposed to arterial levels of oxygen partial pressure (pO₂), which are much greater than what they experience in their native environment. The object of this study is to determine the impact of exposing human saphenous veins to arterial pO₂. Saphenous veins and left internal mammary arteries from consenting patients undergoing coronary artery bypass grafting were cultured ex vivo for 2 weeks in the presence of arterial or venous pO₂ using an established organ culture model. Saphenous veins cultured with arterial pO₂ developed intimal hyperplasia as evidenced by 2.8-fold greater intimal area and 5.8-fold increase in cell proliferation compared to those freshly isolated. Saphenous veins cultured at venous pO₂ or internal mammary arteries cultured at arterial pO₂ did not develop intimal hyperplasia. Intimal hyperplasia was accompanied by two markers of elevated reactive oxygen species (ROS): increased dihydroethidium associated fluorescence (4-fold, p<0.05) and increased levels of the lipid peroxidation product, 4-hydroxynonenal (10-fold, p<0.05). A functional role of the increased ROS saphenous veins exposed to arterial pO₂ is suggested by the observation that chronic exposure to tiron, a ROS scavenger, during the two-week culture period, blocked intimal hyperplasia. Electron paramagnetic resonance based oximetry revealed that the pO₂ in the wall of the vessel tracked that of the atmosphere with a ~30 mmHg offset, thus the cells in the vessel wall were directly exposed to variations in pO₂. Monolayer cultures of smooth muscle cells isolated from saphenous veins exhibited increased proliferation when exposed to arterial pO₂ relative to those cultured at venous pO₂. This increased proliferation was blocked by tiron. Taken together, these data suggest that exposure of human SV to arterial pO₂ stimulates IH via a ROS-dependent pathway.

The effect of resveratrol on intimal hyperplasia and endothelial proliferation of rabbit carotid artery anastomosis

OBJECTIVES

We assessed the effect of resveratrol on intimal hyperplasia and endothelial proliferation after its use for carotid artery anastomosis in rabbits.

METHODS

Fourteen New Zealand-type male rabbits, weighing a mean of 2-3 kg were selected randomly. Their right carotid arteries were transected and anastomosed side by side using 8/0 polypropylene. The rabbits were divided into two groups with seven in each group. While the rabbits in the first group were accepted as the Control group, the rabbits in the second group were given resveratrol (1 mg/kg/day) for 14 days intravenously. At the end of the 28th day, all the carotid artery segments that were transected and anastomosed and the left carotid arteries that did not undergo surgery were removed and evaluated histologically.

RESULTS

The results of histological evaluation were as follows: lumen diameter (P <0.001) and lumen area (P <0.05) of the Resveratrol group were larger than those of the Control group, intimal thickness (P <0.05) and media thickness of the Resveratrol group (P = 0.04) were thinner than those of the Control group, and intima/media ratio of the Control group was found to be greater than that of the Resveratrol group (P = 0.002).

CONCLUSIONS

Resveratrol can prevent intimal hyperplasia and endothelial proliferation following surgical anastomosis.

Targeting Wnt-Frizzled signaling in cardiovascular diseases

Wnts are secreted glycoproteins implicated in biological processes ranging from embryonic cardiac development to uncontrolled cell proliferation in diseased conditions. Cardiovascular disease is a major cause of morbidity and mortality worldwide. Phenotypic modulation of vascular smooth muscle cells, migration and proliferation in intimal layer and increased extracellular matrix production are some of the known hallmarks of cardiovascular pathologies. Heterogeneity associated with the binding of Wnts to their transmembrane receptors, Frizzled, and coreceptors low density lipoprotein-receptor-related protein is indeed intriguing. Nuclear-cytoplasmic shuttling of beta-catenin and activation of transcriptional factors, lymphoid enhancer factor and T cell activation factor leading to target gene activation has remained elusive. Our review highlights the emerging role of Wnt-Frizzled signaling in cardiovascular diseases. Overall, the pathway appears to be an attractive therapeutic target in identifying susceptible individuals at risk of developing restenosis/other vascular pathologies in the near future.

Suramin inhibits PDGF-stimulated receptor phosphorylation, proteoglycan synthesis and glycosaminoglycan hyperelongation in human vascular smooth muscle cells

Objectives

Suramin is a polysulfonated naphthylurea with antiparasitic and potential antineoplastic activity. Suramin's pharmacological actions, which have not yet been fully elucidated, include antagonism of the action of platelet-derived growth factor (PDGF) at its receptor. We investigated the effects of suramin on PDGF-stimulated proteoglycan synthesis.

Methods

Human vascular smooth muscle cells (VSMCs) were incubated in the presence and absence of PDGF and suramin with [3H]thymidine or 35SO4 as radiolabels. Mitogenic response was determined by [3H]thymidine incorporation. PDGFβ receptor phosphorylation was assessed by western blotting. Proteoglycan size and glycosaminoglycan chain synthesis and size were determined by sodium dodecyl sulfate–polyacrylamide gel electrophoresis. The Alphascreen phosphotyrosine assay kit was used to investigate PDGFβ receptor tyrosine kinase inhibition by suramin.

Key findings

Suramin decreased PDGF-stimulated proliferation, proteoglycan synthesis and GAG chain hyperelongation. Suramin also directly inhibited PDGFβ receptor kinase activity as well as PDGFβ receptor phosphorylation in intact VSMCs.

Conclusions

These data show that inhibition of PDGFβ receptor phosphorylation in intact cells is necessary to define a fully active PDGF antagonist. They also confirm that PDGFβ receptor kinase activity is necessary for PDGF-mediated atherogenic changes in proteoglycan synthesis and support efforts to develop PDGFβ receptor antagonists as potential anti-atherosclerotic agents.

The use of antithrombotic therapies in reducing synthetic small-diameter vascular graft thrombosis

BACKGROUND

Thrombosis of synthetic small-diameter bypass grafts remains a major problem. The aim of this article is to review the antithrombotic strategies that have been used in an attempt to reduce graft thrombogenicity.

METHODS

A PubMed/MEDLINE search was performed using the search terms "vascular graft thrombosis," "small-diameter graft thrombosis," "synthetic graft thrombosis" combined with "antithrombotic," "antiplatelet," "anticoagulant," "Dacron," "PTFE," and "polyurethane."

RESULTS

The majority of studies on antithrombotic therapies have used either in vitro models or in vivo animal experiments. Many of the therapies used in these settings do show antithrombotic efficacy against synthetic graft materials. There is however, a distinct lack of human in vivo studies to further delineate the performance and limitations of therapies displaying good antithrombotic characteristics.

CONCLUSION

Very few antithrombotic therapies have translated into clinical use. More human in vivo studies are required to assess the efficacy and safety of such therapies.

Effects of alcohol on pericardial adhesion formation in hypercholesterolemic swine

OBJECTIVE

Reoperative cardiac surgery is complicated in part because of extensive adhesions encountered during the second operation. The purpose of this study was to examine the effects of alcohol with and without resveratrol (red wine vs vodka) on postoperative pericardial adhesion formation in a porcine model of hypercholesterolemia and chronic myocardial ischemia.

METHODS

Male Yorkshire swine were fed a high-cholesterol diet to simulate conditions of coronary artery disease followed by surgical placement of an ameroid constrictor to induce chronic ischemia. Postoperatively, control pigs continued their high-cholesterol diet alone, whereas the 2 experimental groups had diets supplemented with red wine or vodka. Seven weeks after ameroid placement, all animals underwent reoperative sternotomy.

RESULTS

Compared with controls, pericardial adhesion grade was markedly reduced in the vodka group, whereas there was no difference in the wine group. Intramyocardial fibrosis was significantly reduced in the vodka group compared with controls. There was no difference in expression of proteins involved in focal adhesion formation between any groups (focal adhesion kinase, integrin alpha-5, integrin beta-1, paxillin, vinculin, protein tyrosine kinase 2, protein kinase C ε, and phosphorylated protein kinase C ε). The wine group exhibited elevated C-reactive protein levels versus the control and vodka groups.

CONCLUSIONS

Postoperative vodka consumption markedly reduced the formation of pericardial adhesions and intramyocardial fibrosis, whereas red wine had no effect. Analysis of protein expression did not reveal any obvious explanation for this phenomenon, suggesting a post-translational effect of alcohol on fibrous tissue deposition. The difference in adhesion formation in the vodka versus wine groups may be due to increased inflammation in the wine group.

Effective silencing of adhesion molecules on venous endothelial cells for protection of venous bypass grafts

OBJECTIVE

The patency of venous conduits after aortocoronary bypass grafting is still not satisfactory and needs to be improved. Atherosclerotic alterations mediated by adhesion molecules triggering the transmigration of leukocytes are regarded as one of the major causes for venous graft failure. This study deals with short interfering RNA (siRNA)-mediated silencing of adhesion molecule expression on venous endothelial cells, which could lead to a new therapeutic strategy, resulting in improved patency rates by inhibiting early graft alterations.

METHODS

Primary human venous endothelial cells (HVECs) were cultured in a newly developed perfusion model and subsequently transfected with specific siRNAs targeting three different adhesion molecules (the E-selectin (ESELE), the intercellular adhesion molecule 1 (ICAM-1), and the vascular adhesion molecule (VCAM-1)), followed by stimulation with tumor necrosis factor-alpha (TNF-α). Isolated leukocytes were perfused under physiological shear stress conditions, and their attachment to HVEC after single and triple transfection was quantified.

RESULTS

siRNA transfection effectively knocks down adhesion molecule expression on venous endothelial cells, which subsequently reduces leukocyte attachment. Leukocyte adhesion to activated HVEC was significantly reduced after transfection by specific siRNAs in each case compared to the controls (p<0.05). Transfection with a mixture of all three siRNA sequences improved this effect even more (p<0.05).

CONCLUSION

For the first time, a functional protection of HUEC in a model simulating physiologic vascular conditions by using nonviral transfection of the cells in a setup with high relevance for clinical applicability was demonstrated. Therefore, siRNA transfection of bypass material may develop into a new therapeutic option to improve the quality of venous graft material in the future.

Protandim attenuates intimal hyperplasia in human saphenous veins cultured ex vivo via a catalase-dependent pathway

Human saphenous veins (HSVs) are widely used for bypass grafts despite their relatively low long-term patency. To evaluate the role of reactive oxygen species (ROS) signaling in intima hyperplasia (IH), an early stage pathology of vein-graft disease, and to explore the potential therapeutic effects of up-regulating endogenous antioxidant enzymes, we studied segments of HSV cultured ex vivo in an established ex vivo model of HSV IH. Results showed that HSV cultured ex vivo exhibit an ~3-fold increase in proliferation and ~3.6-fold increase in intimal area relative to freshly isolated HSV. Treatment of HSV during culture with Protandim, a nutritional supplement known to activate Nrf2 and increase the expression of antioxidant enzymes in several in vitro and in vivo models, blocks IH and reduces cellular proliferation to that of freshly isolated HSV. Protandim treatment increased the activity of SOD, HO-1, and catalase 3-, 7-, and 12-fold, respectively, and decreased the levels of superoxide (O(2)(•-)) and the lipid peroxidation product 4-HNE. Blocking catalase activity by cotreating with 3-amino-1,2,4-triazole abrogated the protective effect of Protandim on IH and proliferation. In conclusion, these results suggest that ROS-sensitive signaling mediates the observed IH in cultured HSV and that up-regulation of endogenous antioxidant enzymes can have a protective effect.

Pretreatment with intraluminal rapamycin nanoparticle perfusion inhibits neointimal hyperplasia in a rabbit vein graft model

PURPOSE

Poly lactic-co-glycolic acid nanoparticles (PLGA-NP) are widely used as a biodegradable biomaterial in medicine. Rapamycin-eluting stents have been used for prevention of restenosis during surgery. This study investigated the effect of pretreatment with intraluminal perfusion of carbopol-encapsulated rapamycin-loaded PLGA nanoparticles (RAP-PLGA-NP) on neointimal hyperplasia in a rabbit vein graft model.

METHODS

A segment of common carotid artery was replaced with a segment of external jugular vein in 60 rabbits which were then separated into four treatment groups, ie, Group 1, in which vein grafts were pretreated with intraluminal RAP-PLGA-NP perfusion, Group 2 in which vein grafts underwent equivalent empty vehicle (PLGA-NP) perfusion, Group 3, in which vein grafts received no treatment, and Group 4, which served as a sham operation group receiving normal vein contrast. On postoperative day 28, the grafts and normal veins were harvested for histologic examination, flow cytometry analysis, and high-performance liquid chromatography measurement.

RESULTS

Compared with Group 1, the intima of the grafts were thickened, the ratio of intimal area to vessel area increased, and the collagen volume index of the vein grafts increased significantly in Groups 2 and 3. The cell proliferation index in Group 1 (21.11 ± 3.15%) was much lower than that in Group 2 (30.35 ± 2.69%) and in Group 3 (33.86 ± 8.72%). By high-performance liquid chromatography measurement, retention of rapamycin was detected in Group 1 (11.2 ± 0.37 μg/10 mg) 28 days after single drug perfusion.

CONCLUSION

Pretreatment with intraluminal RAP-PLGA-NP perfusion may inhibit neointimal hyperplasia in vein grafts by penetrating into local tissue and limiting cell proliferation.

The role of ex-vivo gene therapy of vein grafts with Egr-1 decoy in the suppression of intimal hyperplasia

OBJECTIVES

To test the hypothesis that vein graft intimal hyperplasia can be significantly suppressed by a single intra-operative transfection of the graft with a decoy oligonucleotide (ODN) binding the transcription factor Egr-1.

DESIGN

Experimental study.

MATERIALS AND METHODS

Jugular vein to carotid artery interposition grafts in rabbits were treated with Egr-1 decoy, mutant decoy ODN, vehicle alone, using a non-distending pressure of 300 mm Hg for 20 min, or were left untreated. All animals were fed a 2% cholesterol diet. The animals were sacrificed after 48h, 6 weeks and 12 weeks. Paraffin-embedded vein sections were subjected to angiometric analysis.

RESULTS

Successful delivery of the ODN was confirmed by DAPI staining. Quantitative real-time PCR revealed a 60% decrease of the Egr-1 gene expression in the animals in which the Egr-1 decoy ODN was delivered. Cellular proliferation was also significantly decreased as indicated by the Ki-67 labelling index. An increase in intimal and medial thickness was found in all vein grafts. However, intimal thickness was significantly reduced in the grafts treated with Egr-1 decoy ODN, whereas luminal area was significantly increased.

CONCLUSION

A single intra-operative pressure-mediated transfection of vein grafts with Egr-1 decoy ODN significantly suppresses intimal hyperplasia in a rabbit hypercholesterolaemic model.

Differential expression of pancreatitis-associated protein and thrombospondins in arterial versus venous tissues

BACKGROUND/AIMS

Arteries and veins modulate cardiovascular homeostasis and contribute to hypertension pathogenesis. Functional differences between arteries and veins are based upon differences in gene expression. To better characterize these expression patterns, and to identify candidate genes that could be manipulated selectively in the venous system, we performed whole genome expression profiling of arteries and veins.

METHODS

We used the CodeLink platform and the major artery (thoracic aorta) and vein (caudal vena cava) of the rat.

RESULTS

The most prominent difference was pancreatitis-associated protein (PAP1), expressed 64-fold higher in vena cava versus aorta. Expression of mRNA for thrombospondins (TSP-1, TSP-4) was greater than 5-fold higher in veins versus arteries. Higher mRNA expression of TSP-1, TSP-2, TSP-4 and PAP1 in vena cava versus aorta was confirmed by PCR. Immunohistochemical analysis of tissue sections qualitatively confirmed a higher expression of these proteins in vena cava versus aorta.

CONCLUSION

This is the first gene array study of adult rat arterial and venous tissues, and also the first study to report differences in inflammatory genes between arteries and veins. Data from these studies may provide novel insights into the genetic basis for functional differences between arteries and veins in health and disease.

Inhibition of adhesion molecule expression on human venous endothelial cells by non-viral siRNA transfection

Objective: Expression of adhesion molecule receptors on venous endothelial cells crucially influences the fate of venous grafts by mediating leukocyte-endothelium interactions. These interactions include adhesion of leukocytes to the endothelium, followed by transendothelial migration, leading to neointimal hyperplasia and finally graft occlusion. Therefore, inhibition of adhesion molecule expression may be a promising strategy to improve the quality of venous grafts. We tested the efficiency of non-viral transfection of human venous endothelial cells with short interfering RNA (siRNA) to specificially down-regulate adhesion molecule expression. Methods: Primary cultures of human venous endothelial cells (HVEC) were examined for expression of the adhesion molecules ICAM1, VCAM1 and E-selectin (SELE) after non viral siRNA transfection. Adhesion molecule expression was measured by flow cytometry, real-time PCR and immunoblotting after stimulation with TNF-alpha, an inflammatory cytokine. Results: Non-transfected cells showed a strong increase of adhesion molecule expression following cytokine stimulation (p<0.01). Upon transfection with specific siRNAs a six fold decrease in ICAM1 (p<0.001) and SELE expression and cell positivity (p<0.05) and a twofold decrease in VCAM1 expression and cell positivity (p<0.01) could be observed. SiRNA-mediated gene suppression of adhesion molecules was also reflected by corresponding decreases in adhesion protein and transcript levels. Conclusions: The expression of adhesion molecules on HVECs can be effectively inhibited by specific siRNAs using a safe, non-viral transfection approach. This is a promising tool to precondition venous bypass grafts in order to interfere with endothelium-leukocyte interactions and to prohibit neointima thickening or atherosclerosis, which are regarded to be the most important causes of venous graft failure.

Arterialization of a vein graft promotes cell cycle progression through Akt and p38 mitogen-activated protein kinase pathways: impact of the preparation procedure

BACKGROUND

Vein arterialization following bypass surgery often leads to graft occlusion, but the underlying cellular mechanisms have been poorly studied.

OBJECTIVES

Cell cycle progression and the activation of proliferation signalling were compared in arterialized grafts prepared either according to the conventional procedure or using pharmacological relaxation with the native vein.

METHODS

Using the porcine carotid-jugular bilateral interposition graft model on one side, a segment of porcine jugular vein was prepared for grafting using the conventional procedure, with pressure distention at 300 mmHg; the segment grafted on the other side was treated with a combination of pharmacological vasodilators. Both veins were grafted into the carotid artery for two weeks.

RESULTS

On the immunolabelling of proliferation cell nuclear antigen, a greater number of proliferating cells was found in the conventionally prepared grafts compared with pharmacologically prepared grafts. Cyclin D1 expression and phosphorylation of retinoblastoma increased after implantation, coinciding with nuclear accumulation of beta-catenin, activation of the Akt and mitogen-activated protein kinase cascades, and upregulated phosphatase and tensin homologue phosphorylation. Replacement of distention with pharmacological relaxation reduced the increase in cyclin D1 expression, phosphorylation of retinoblastoma, Akt-Thr(308), glycogen synthase kinase 3 beta and p38, but not extracellular signal-regulated kinases. This technique preserved the active phosphatase and tensin homologue, as well as the expression of cyclin-dependent kinase inhibitor p21(Cip1), while elevating the expression of p27(Kip1).

CONCLUSIONS

It was concluded that two-week arterial implantation stimulates proliferation signalling and promotes the cell cycle in vein grafts. Replacement of the conventional preparation procedures with pharmacological vasorelaxation restricts the activation of proliferation and cell cycle progression, and can be beneficial for improving vein graft patency.

Diagnostic Performance of 64-Slice Computed Tomography in Evaluation of Coronary Artery Bypass Grafts

OBJECTIVE

The purpose of this study was to compare the diagnostic accuracy of 64-slice CT with that of invasive angiography in the detection of greater than 50% graft stenosis within 2 weeks of coronary artery bypass grafting and to investigate the clinical value of 64-slice CT.

SUBJECTS AND METHODS

Forty-one patients (70 grafts, 46 arterial and 24 venous) underwent 64-slice CT a mean of 2.6 years after minimally invasive or conventional coronary artery bypass surgery.

RESULTS

All 70 grafts were assessable, and none of the grafts was excluded from analysis. For the detection of 50-90% graft stenosis, the sensitivity of CT was 75%, the specificity was 95%, the positive predictive value was 67%, and the negative predictive value was 97% (true disease prevalence, 8/70 grafts; 11%). Greater than 50% graft stenosis and occlusion pooled together (prevalence, 14/70; 20%) were detected with a sensitivity of 85%, specificity of 95%, positive predictive value of 80%, and negative predictive value of 96%. Vein graft disease was found in eight (42%) of 19 patent vein grafts (graft age, 15.6 +/- 2.3 years). The disease was nonobstructive in three (16%) of the 19 grafts. The course of the left internal mammary artery was median retrosternal (< 1 cm deep) in 33.3% of conventionally sutured grafts.

CONCLUSION

Sixty-four-slice CT angiography can be used for accurate exclusion of greater than 50% graft stenosis, but detection of distal anastomotic stenosis is limited, and the degree of stenosis can be overestimated. The advantages of CT, however, are that it is noninvasive, vein graft disease can be diagnosed at an early stage, and complementary evaluation of extracardiac anatomic features provides useful information before coronary artery bypass grafting is redone.

Inhibition of adhesion molecule expression on human venous endothelial cells by non-viral siRNA transfection

Objective:

Expression of adhesion molecule receptors on venous endothelial cells crucially influences the fate of venous grafts by mediating leukocyte-endothelium interactions. These interactions include adhesion of leuko-cytes to the endothelium, followed by transendothelial migration, leading to neointimal hyperplasia (NIH) and finally graft occlusion. Therefore, inhibition of adhesion molecule expression may be a promising strategy to improve the quality of venous grafts.We tested the efficiency of non-viral transfection of human venous endothe-lial cells (HVEC) with short interfering RNA (siRNA) to specifically down-regulate adhesion molecule expression.

Methods:

Primary cultures of HVEC were examined for expression of the adhesion molecules ICAM1, VCAM1 and E-selectin (SELE) after non viral siRNA transfection. Adhesion molecule expression was measured by flow cytom-etry, real-time polymerase chain reaction and immunoblotting after stimulation with TNF-α, an inflammatory cytokine.

Results:

Non-transfected cells showed a strong increase of adhesion molecule expression following cytokine stimulation (P < 0.01). Upon transfection with specific siRNAs a sixfold decrease in ICAM1 (P < 0.001) and SELE expression and cell positivity (P < 0.05) and a twofold decrease in VCAM1 expression and cell positiv-ity (P < 0.01) Pcould be observed. SiRNA-mediated gene suppression of adhesion molecules was also reflected by corresponding decreases in adhesion protein and transcript levels.

Conclusions:

The expression of adhesion molecules on HVECs can be effectively inhibited by specific siRNAs using a safe, non-viral transfection approach. This is a promising tool to pre-condition venous bypass grafts in order to interfere with endothelium-leukocyte interactions and to prohibit neointima thickening or ath-erosclerosis, which are regarded to be the most important causes of venous graft failure.