Thrombosis and Neointima Formation in Vein Grafts Are Inhibited by Locally Applied Aspirin Through Endothelial Protection

Early thrombus formation is required for eccentric and heterogeneous neointimal hyperplasia under disturbed flow

BACKGROUND

Anticoagulation and antiplatelet therapy effectively inhibit neointimal hyperplasia (NIH) in both arterial and venous systems but not in arteriovenous fistulae (AVF). The main site of AVF failure is the juxta-anastomotic area that is characterized by disturbed flow compared with laminar flow in the arterial inflow and the venous outflow.

OBJECTIVES

We hypothesized that early thrombus formation is required for eccentric and heterogeneous NIH in the presence of disturbed flow.

METHODS

Needle puncture and sutured AVF were created in C57BL/6 mice, in PF4-Cre × mT/mG reporter mice, and in Wistar rats. Human AVF samples were second-stage basilic vein transpositions. The tissues were examined by histology, immunofluorescence, immunohistochemistry, and en face staining.

RESULTS

In the presence of disturbed flow, both mouse and human AVF showed eccentric and heterogeneous NIH. Maladapted vein wall was characterized by eccentric and heterogeneous neointima that was composed of a different abundance of thrombus and smooth muscle cells. PF4-cre × mT/mG reporter mice AVF showed that green fluorescent protein-labeled platelets deposit on the wall directly facing the fistula exit with endothelial cell loss and continue to accumulate in the presence of disturbed flow. Neither disturbed flow with limited endothelial cell loss nor nondisturbed flow induced heterogeneous neointima in different animal models.

CONCLUSION

Early thrombus contributes to late heterogeneous NIH in the presence of disturbed flow. Disturbed flow, large area of endothelial cell loss, and thrombus formation are critical to form eccentric and heterogeneous NIH. Categorization of adapted or maladapted walls may be helpful for therapy targeting heterogeneous NIH.

Ang-1 and VEGF: central regulators of angiogenesis

Angiopoietin-1 (Ang-1) and Vascular Endothelial Growth Factor (VEGF) are central regulators of angiogenesis and are often inactivated in various cardiovascular diseases. VEGF forms complexes with ETS transcription factor family and exerts its action by downregulating multiple genes. Among the target genes of the VEGF-ETS complex, there are a significant number encoding key angiogenic regulators. Phosphorylation of the VEGF-ETS complex releases transcriptional repression on these angiogenic regulators, thereby promoting their expression. Ang-1 interacts with TEK, and this phosphorylation release can be modulated by the Ang-1-TEK signaling pathway. The Ang-1-TEK pathway participates in the transcriptional activation of VEGF genes. In summary, these elements constitute the Ang-1-TEK-VEGF signaling pathway. Additionally, Ang-1 is activated under hypoxic and inflammatory conditions, leading to an upregulation in the expression of TEK. Elevated TEK levels result in the formation of the VEGF-ETS complex, which, in turn, downregulates the expression of numerous angiogenic genes. Hence, the Ang-1-dependent transcriptional repression is indirect. Reduced expression of many target genes can lead to aberrant angiogenesis. A significant overlap exists between the target genes regulated by Ang-1-TEK-VEGF and those under the control of the Ang-1-TEK-TSP-1 signaling pathway. Mechanistically, this can be explained by the replacement of the VEGF-ETS complex with the TSP-1 transcriptional repression complex at the ETS sites on target gene promoters. Furthermore, VEGF possesses non-classical functions unrelated to ETS and DNA binding. Its supportive role in TSP-1 formation may be exerted through the VEGF-CRL5-VHL-HIF-1α-VH032-TGF-β-TSP-1 axis. This review assesses the regulatory mechanisms of the Ang-1-TEK-VEGF signaling pathway and explores its significant overlap with the Ang-1-TEK-TSP-1 signaling pathway.

Digital light 4D printing of bioresorbable shape memory elastomers for personalized biomedical implantation

Four-dimensional (4D) printing unlocks new potentials for personalized biomedical implantation, but still with hurdles of lacking suitable materials. Herein, we demonstrate a bioresorbable shape memory elastomer (SME) with high elasticity at both below and above its phase transition temperature (Ttrans). This SME can be digital light 3D printed by co-polymerizing glycerol dodecanoate acrylate prepolymer (pre-PGDA) with acrylic acid monomer to form crosslinked Poly(glycerol dodecanoate acrylate) (PGDA)-Polyacrylic acid (PAA), or PGDA-PAA network. The printed complex, free-standing 3D structures with high-resolution features exhibit shape programming properties at a physiological temperature. By tuning the pre-PGDA weight ratios between 55 wt% and 70 wt%, Ttrans varies between 39.2 and 47.2 ℃ while Young's moduli (E) range 40-170 MPa below Ttrans with fractural strain (εf) of 170 %-200 %. Above Ttrans, E drops to 1-1.82 MPa which is close to those of soft tissue. Strikingly, εf of 130-180 % is still maintained. In vitro biocompatibility test on the material shows > 90 % cell proliferation and great cell attachment. In vivo vascular grafting trials underline the geometrical and mechanical adaptability of these 4D printed constructs in regenerating the aorta tissue. Biodegradation of the implants shows the possibility of their full replacement by natural tissue over time. To highlight its potential for personalized medicine, a patient-specific left atrial appendage (LAA) occluder was printed and implanted endovascularly into an in vitro heart model. STATEMENT OF SIGNIFICANCE: 4D printed shape-memory elastomer (SME) implants particularly designed and manufactured for a patient are greatly sought-after in minimally invasive surgery (MIS). Traditional shape-memory polymers used in these implants often suffer from issues like unsuitable transition temperatures, poor biocompatibility, limited 3D design complexity, and low toughness, making them unsuitable for MIS. Our new SME, with an adjustable transition temperature and enhanced toughness, is both biocompatible and naturally degradable, particularly in cardiovascular contexts. This allows implants, like biomedical scaffolds, to be programmed at room temperature and then adapt to the body's physiological conditions post-implantation. Our studies, including in vivo vascular grafts and in vitro device implantation, highlight the SME's effectiveness in aortic tissue regeneration and its promising applications in MIS.

Anti-Inflammatory and Anti-Thrombogenic Properties of Arterial Elastic Laminae

Elastic laminae, an elastin-based, layered extracellular matrix structure in the media of arteries, can inhibit leukocyte adhesion and vascular smooth muscle cell proliferation and migration, exhibiting anti-inflammatory and anti-thrombogenic properties. These properties prevent inflammatory and thrombogenic activities in the arterial media, constituting a mechanism for the maintenance of the structural integrity of the arterial wall in vascular disorders. The biological basis for these properties is the elastin-induced activation of inhibitory signaling pathways, involving the inhibitory cell receptor signal regulatory protein α (SIRPα) and Src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP1). The activation of these molecules causes deactivation of cell adhesion- and proliferation-regulatory signaling mechanisms. Given such anti-inflammatory and anti-thrombogenic properties, elastic laminae and elastin-based materials have potential for use in vascular reconstruction.

Titanium(IV) Oxo-Complex with Acetylsalicylic Acid Ligand and Its Polymer Composites: Synthesis, Structure, Spectroscopic Characterization, and Photocatalytic Activity

The titanium oxo complexes are widely studied, due to their potential applications in photocatalytic processes, environmental protection, and also in the biomedical field. The presented results concern the oxo complex synthesized in the reaction of titanium(IV) isobutoxide and acetylsalicylic acid (Hasp), in a 4:1 molar ratio. The structure of isolated crystals was solved using the single-crystal X-ray diffraction method. The analysis of these data proves that [Ti₄O₂(OⁱBu)₁₀(asp)₂]·H₂O (1) complex is formed. Moreover, the molecular structure of (1) was characterized using vibrational spectroscopic techniques (IR and Raman), ¹³C NMR, and UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS). The photocatalytic activity of the synthesized complex was determined with the use of composite foils produced by the dispersion of (1) micrograins, as the inorganic blocks, in a polycaprolactone (PCL) matrix (PCL + (1)). The introduction of (1) micrograins to the PCL matrix caused the absorption maximum shift up to 425–450 nm. The studied PCL + (1) composite samples reveal good activity toward photodecolorization of methylene blue after visible light irradiation.

Aspirin ameliorates pulmonary vascular remodeling in pulmonary hypertension by dampening endothelial-to-mesenchymal transition

Pulmonary vascular remodeling (PVR) is the pathological basis of pulmonary hypertension (PH). Incomplete understanding of PVR etiology has hindered drug development for this devastating disease, which exhibits poor prognosis despite the currently available therapies. Endothelial-to-mesenchymal transition (EndMT), a process of cell transdifferentiation, has been recently implicated in cardiovascular diseases, including PH. But the questions of how EndMT occurs and how to pharmacologically target EndMT in vivo have yet to be further answered. Herein, by performing hematoxylin-eosin and immunofluorescence staining, transmission electron microscopy and Western blotting, we found that EndMT plays a key role in the pathogenesis of PH, and importantly that aspirin, a FDA-approved widely used drug, was capable of ameliorating PVR in a preclinical rat model of hypoxia-induced PH. Moreover, aspirin exerted its inhibitory effects on EndMT in vitro and in vivo by suppressing HIF-1α/TGF-β1/Smads/Snail signaling pathway. Our data suggest that EndMT represents an intriguing drug target for the prevention and treatment of hypoxic PH and that aspirin may be repurposed to meet the urgent therapeutic needs of hypoxic PH patients.

Recent advances in nanomaterials for therapy and diagnosis for atherosclerosis

Atherosclerosis is a chronic inflammatory disease driven by lipid accumulation in arteries, leading to narrowing and thrombosis. It affects the heart, brain, and peripheral vessels and is the leading cause of mortality in the United States. Researchers have strived to design nanomaterials of various functions, ranging from non-invasive imaging contrast agents, targeted therapeutic delivery systems to multifunctional nanoagents able to target, diagnose, and treat atherosclerosis. Therefore, this review aims to summarize recent progress (2017-now) in the development of nanomaterials and their applications to improve atherosclerosis diagnosis and therapy during the preclinical and clinical stages of the disease.

Aspirin restores endothelial function by mitigating 17β-estradiol-induced α-SMA accumulation and autophagy inhibition via Vps15 scaffold regulation of Beclin-1 phosphorylation

AIMS

Previous studies have shown that the widespread use of estrogen preparations can cause adverse outcomes such as thrombosis and cardiovascular disease. Autophagy is a biochemical process necessary to maintain cell homeostasis. The present study investigated whether E-2 mediates autophagy-induced endothelial cell dysfunction. The role of aspirin in this process was then studied.

MAIN METHODS

Western blot, fluorescence microscopy, electron transmission microscopy, plasma construction and transfection, vasoreactivity study in wire myograph are all used in this study.

KEY FINDINGS

We found that E-2 activated the PI3K/mTOR signaling pathway and inhibited the formation of the Atg14L-Beclin1-Vps34-Vps15 complex, thereby inhibiting autophagy. Aspirin promoted Beclin1 phosphorylation in autophagy initiation complexes and enhanced autophagy. Furthermore, E-2 treatment of HAECs resulted in endothelial dysfunction by inhibiting autophagy and leading to accumulation of α-smooth muscle actin (α-SMA). E-2 inhibited the activation of eNOS and reduced the expression of eNOS protein. In the mouse aortic vascular function test, E-2 disrupted endothelium-dependent vasodilation. An α-SMA-shRNA lentivirus eliminated the disruption to endothelium-dependent vasodilation by E-2. Aspirin inhibited α-SMA accumulation by enhancing autophagy, reversed endothelial functional impairment caused by E-2, and promoted endothelium-dependent vasodilation.

SIGNIFICANCE

This study provides new evidence that E-2 inhibits autophagy and induces abnormal accumulation of α-SMA, resulting in endothelial cell dysfunction and affecting vasodilation. Aspirin can effectively restore the endothelial cell function disrupted E-2.

Drug-eluting Vein Graft with Acetylsalicylic Acid-Ticagrelor-Unfractionated Heparin Complex Inhibits Early Graft Thrombosis

Background

Bypass graft surgery remains to be an important treatment option for left main and multivessel coronary artery disease. Approximately 2% of saphenous vein grafts are lost immediately after the coronary artery bypass graft operations and 12% in the first month due to thrombosis.

Aims

To administer one anticoagulant and two antiplatelet agents in a way that locally affects the vein graft before the bypass operation and to thereby analyse their effects on early graft thrombosis.

Study Design

Animal experimentation.

Methods

Since ticagrelor was used locally for the first time in this study, its efficacy in combination with other drugs (acetylsalicylic acid, acetylsalicylic acid and ticagrelor, and acetylsalicylic acid + ticagrelor + unfractionated heparin) was examined on rats including control (untreated) and sham (pluronic gel) group (n=14 for each group). Before the tunica adventitia layer of the femoral veins was bypassed to the femoral artery, it was coated with the drug-eluting pluronic F-127 gel. The presence or absence of thrombus in the vein graft samples was recorded under light microscopy. In vein graft preparations where thrombus was detected, the thrombus area (μm2) was calculated using the Axiovision software. Immunohistochemical staining was performed with the anti-rat von Willebrand factor polyclonal antibody kit.

Results

The number of preparations containing thrombus was significantly lower in the acetylsalicylic acid + ticagrelor + unfractionated heparin group than in the acetylsalicylic acid, control, and sham groups, according to the comparisons made on the 1st and 3rd days (p=0.001 and 0.02, respectively). von Willebrand factor staining was significantly lower in the acetylsalicylic acid + ticagrelor + unfractionated heparin group than in the other groups on the 3rd day (p=0.005).

Conclusion

Locally effective acetylsalicylic acid-ticagrelor-unfractionated heparin complex has been shown to significantly reduce thrombus formation in vein grafts in this experimental model. Local administration of these drugs, which are routinely administered orally just before stent implantations, on the vein graft before the bypass is performed can prevent the loss of vein grafts due to thrombus, thereby reducing the mortality and morbidity of these patients.

Antiplatelet agents maintain arteriovenous fistula and graft function in patients receiving hemodialysis: A nationwide case-control study

Background

In this study, we evaluated the effects of various medications on the patency of vascular access (VA) for hemodialysis.

Methods

We analyzed data from the Longitudinal Health Insurance Database of Taiwan. We adopted a case–control study design within a cohort of patients who had received regular hemodialysis between 2002 and 2012; 34,354 patients with first VA failure were identified, and the duration from VA creation date to the first VA failure date was calculated. We then classified these patients into two groups, namely arteriovenous fistula (AVF, n = 25,933) and arteriovenous graft (AVG, n = 8,421). Each group was further divided into two subgroups, namely short-term (<1 year) and long-term (≥1 year) patency.

Results

The risk factors for early VA failure were age ≥65 years, diabetes mellitus, hyperlipidemia, cerebral vascular disease, congestive heart failure, peripheral artery disease, and sepsis. Male sex, hypertension, cancer, and peptic ulcer were associated with early AVF failure. Antiplatelet therapy increased the AVF and AVG patency times with adjusted odds ratios of 0.748 (95% confidence interval [CI]: 0.703–0.796, p < 0.0001) and 0.810 (95% CI: 0.728–0.901, p = 0.0001), respectively. A significant decrease in the VA failure risk was observed with an increase in the cumulative defined daily dose of antiplatelet agents.

Conclusion

This nationwide study demonstrated that some risk factors were associated with early VA failure and that the use of antiplatelet agents prevented the loss of VA patency in a dose–response manner. Thus, antiplatelet drugs should be routinely administered to high-risk patients receiving dialysis.

Perioperative urinary thromboxane metabolites and outcome of coronary artery bypass grafting: a nested case-control study

OBJECTIVE

As a marker of in vivo thromboxane generation, high-level urinary thromboxane metabolites (TXA-M) increase the occurrence of cardiovascular events in high-risk patients. To investigate whether perioperative urinary TXA-M level is associated with major adverse cardiac and cerebrovascular events (MACCE) after coronary artery bypass graft (CABG) surgery, we designed a nested case-control study.

DESIGN

Observational, nested case-control study.

SETTING

Single-centre outcomes research in Fuwai Hospital, Beijing, China.

PARTICIPANTS

One thousand six hundred and seventy Chinese patients undergoing CABG surgery from September 2011 to October 2013.

METHODS

We obtained urinary samples from 1670 Chinese patients undergoing CABG 1 hour before surgery (pre-CABG), and 6 hours (post-CABG 6 hours) and 24 hours after surgery (post-CABG 24 hours). Patients were followed up for 1 year, and we observed 56 patients had MACCE. For each patient with MACCE, we matched three control subjects. Perioperative urinary TXA-M of the three time spots was detected in these 224 patients.

RESULTS

Post-CABG 24 hours TXA-M is significantly higher than that of patients without MACCE (11 101vs8849 pg/mg creatine, P=0.007). In addition, patients in the intermediate tertile and upper tertile of post-CABG 24 hours urinary TXA-M have a 2.2 times higher (HR 2.22, 95% CI 1.04 to 4.71, P=0.038) and a 2.8 times higher (HR 2.81, 95% CI 1.35 to 5.85, P=0.006) risk of 1 year MACCE than those in the lower tertile, respectively.

CONCLUSIONS

In conclusion, post-CABG 24 hours urinary TXA-M elevation is associated with an increase of 1 year adverse events after CABG, indicating that the induction of cyclo-oxygenase-2 by surgery-related inflammatory stimuli or platelet turnover may be responsible for the high levels of post-CABG urinary TXA-M.

TRIAL REGISTRATION NUMBER

NCT01573143.

A Cytokine-Like Protein Dickkopf-Related Protein 3 Is Atheroprotective

Supplemental Digital Content is available in the text.

Background:

Dickkopf-related protein 3 (DKK3) is a secreted protein that is involved in the regulation of cardiac remodeling and vascular smooth muscle cell differentiation, but little is known about its role in atherosclerosis.

Methods:

We tested the hypothesis that DKK3 is atheroprotective using both epidemiological and experimental approaches. Blood DKK3 levels were measured in the Bruneck Study in 2000 (n=684) and then in 2005 (n=574). DKK3-deficient mice were crossed with apolipoprotein E^-/- mice to evaluate atherosclerosis development and vessel injury-induced neointimal formation. Endothelial cell migration and the underlying mechanisms were studied using in vitro cell culture models.

Results:

In the prospective population-based Bruneck Study, the level of plasma DKK3 was inversely related to carotid artery intima-media thickness and 5-year progression of carotid atherosclerosis independently from standard risk factors for atherosclerosis. Experimentally, we analyzed the area of atherosclerotic lesions, femoral artery injury-induced reendothelialization, and neointima formation in both DKK3^-/-/apolipoprotein E^-/- and DKK3^+/+/apolipoprotein E^-/- mice. It was demonstrated that DKK3 deficiency accelerated atherosclerosis and delayed reendothelialization with consequently exacerbated neointima formation. To explore the underlying mechanisms, we performed transwell and scratch migration assays using cultured human endothelial cells, which exhibited a significant induction in cell migration in response to DKK3 stimulation. This DKK3-induced migration activated ROR2 and DVL1, activated Rac1 GTPases, and upregulated JNK and c-jun phosphorylation in endothelial cells. Knockdown of the ROR2 receptor using specific siRNA or transfection of a dominant-negative form of Rac1 in endothelial cells markedly inhibited cell migration and downstream JNK and c-jun phosphorylation.

Conclusions:

This study provides the evidence for a role of DKK3 in the protection against atherosclerosis involving endothelial migration and repair, with great therapeutic potential implications against atherosclerosis.

Initiation of antiplatelet medication after surgical thrombectomy jeopardized arteriovenous graft longevity

INTRODUCTION

The efficacy of antiplatelet agents in preventing thrombosis in newly formed arteriovenous graft (AVG) in hemodialysis (HD) patients has been extensively examined. The aim of this study was to investigate the possible effect of initiation of antiplatelet medications on preventing AVG thrombosis recurrence after surgical thrombectomy for acute occlusion in HD patients. Whether post-operatively antiplatelet medications have protective effects on the patency or longevity of AVG after surgical thrombectomy in HD patients has not been investigated.

METHODS

We conducted a 4-year quasi-randomized study of the unassisted patency and AVG longevity for 213 HD patients with or without initiating antiplatelet drugs after receiving surgical thrombectomy for first episode of acute AVG thrombosis.

RESULTS

From the propensity-score-matched quasi-randomized study, initiation of antiplatelet drugs after first surgical thrombectomy in HD patients did not prevent the recurrence of surgical thrombectomy (log-rank p = 0.81), but significantly decreased the longevity of the access (log-rank p = 0.034). Multivariate Cox model demonstrated that prescription of antiplatelet drugs significantly increased the risk of graft failure (adjusted hazard ratio 2.13, p = 0.025).

CONCLUSIONS

Adjunctive prescription with antiplatelet medications in HD patients after surgical thrombectomy did not prevent recurrent thrombosis of AV access, but significantly jeopardized the longevity of AVG after surgical thrombectomy.

Vein graft disease in a knockout mouse model of hyperhomocysteinaemia

A major reason for vein graft failure after coronary artery bypass grafting is neointimal hyperplasia and thrombosis. Elevated serum levels of homocysteine (Hcy) are associated with higher incidence of cardiovascular disease, but homocysteine levels also tend to increase during the first weeks or months after cardiac surgery. To investigate this further, C57BL/6J mice (WT) and cystathionine-beta-synthase heterozygous knockout mice (CBS+/-), a mouse model for hyperhomocysteinaemia, underwent interposition of the vena cava of donor mice into the carotid artery of recipient mice. Two experimental groups were examined: 20 mice of each group underwent bypass surgery (group 1: WT donor and WT recipient; group 2: CBS+/- donor and CBS+/- recipient). After 4 weeks, the veins were harvested, dehydrated, paraffin-embedded, stained and analysed by histomorphology and immunohistochemistry. Additionally, serum Hcy levels in CBS knockout animals and in WT animals before and after bypass surgery were measured. At 4 weeks postoperatively, group 2 mice showed a higher percentage of thrombosis compared to controls, a threefold increase in neointima formation, higher general vascularization, a lower percentage of elastic fibres with shortage and fragmentation in the neointima, a lower percentage of acid mucopolysaccharides in the neointima and a more intense fibrosis in the neointima and media. In conclusion, hyperhomocysteinaemic cystathionine-beta-synthase knockout mice can play an important role in the study of mechanisms of vein graft failure. But further in vitro and in vivo studies are necessary to answer the question whether or not homocysteine itself or a related metabolic factor is the key aetiologic agent for accelerated vein graft disease.

Cilostazol, Not Aspirin, Prevents Stenosis of Bioresorbable Vascular Grafts in a Venous Model

OBJECTIVE

Despite successful translation of bioresorbable vascular grafts for the repair of congenital heart disease, stenosis remains the primary cause of graft failure. In this study, we investigated the efficacy of long-term treatment with the antiplatelet drugs, aspirin and cilostazol, in preventing stenosis and evaluated the effect of these drugs on the acute phase of inflammation and tissue remodeling.

APPROACH AND RESULTS

C57BL/6 mice were fed a drug-mixed diet of aspirin, cilostazol, or normal chow during the course of follow-up. Bioresorbable vascular grafts, composed of poly(glycolic acid) mesh sealed with poly(l-lactide-co-ε-caprolactone), were implanted as inferior vena cava interposition conduits and followed up for 2 weeks (n=10 per group) or 24 weeks (n=15 per group). Both aspirin and cilostazol suppressed platelet activation and attachment onto the grafts. On explant at 24 weeks, well-organized neotissue had developed, and cilostazol treatment resulted in 100% graft patency followed by the aspirin (67%) and no-treatment (60%) groups (P<0.05). Wall thickness and smooth muscle cell proliferation in the neotissue of the cilostazol group were decreased when compared with that of the no-treatment group at 24 weeks. In addition, cilostazol was shown to have an anti-inflammatory effect on neotissue at 2 weeks by regulating the recruitment and activation of monocytes.

CONCLUSIONS

Cilostazol prevents stenosis of bioresorbable vascular graft in a mouse inferior vena cava implantation model up to 24 weeks and is accompanied by reduction of smooth muscle cell proliferation and acute inflammation.

Topical cilostazol inhibits neointimal hyperplasia in a rat interposition vein graft model

BACKGROUND

Neointimal hyperplasia is a common cause of vein graft failure resulting from luminal narrowing and occlusion. Cilostazol is a U.S. Food and Drug Administration-approved phosphodiesterase III and platelet aggregation inhibitor commonly used in peripheral vascular disease. The authors studied whether topical cilostazol treatment at the time of vein grafting helps limit the development of neointimal hyperplasia in a rat model.

METHODS

Six experimental rats and six control rats underwent interposition vein grafting into the femoral artery, followed by a single topical dose of cilostazol applied around the vein graft in the experimental animals. After 4 weeks, grafts were harvested and underwent histologic staining of axial sections to visualize intima thickness and elastin/myocyte content. Quantification was performed to assess total intima area. The intima-to-media and the intima-to-sum of intima and media ratios were determined to control for discrepancies in overall graft size.

RESULTS

Cilostazol-treated grafts had a thinner intima layer with less myocyte content compared with control grafts, amounting to an 82 percent decrease in total intima area compared with controls. A similar trend was seen even after controlling for overall graft size, with 85 and 76 percent reductions seen in intima-to-media and intima-to-sum of intima and media ratios, respectively.

CONCLUSIONS

A single intraoperative dose of cilostazol applied locally significantly reduced intima size and smooth muscle content in rat interposition vein grafts examined 4 weeks postoperatively. A topical dose of cilostazol at surgery may therefore be helpful in controlling neointimal hyperplasia and reducing the need for systemic medications to prolong vein graft patency.

Gene therapy for the prevention of vein graft disease

Ischemic cardiovascular disease remains the leading cause of death worldwide. Despite advances in the medical management of atherosclerosis over the past several decades, many patients require arterial revascularization to reduce mortality and alleviate ischemic symptoms. Technological advancements have led to dramatic increases in the use of percutaneous and endovascular approaches, yet surgical revascularization (bypass surgery) with autologous vein grafts remains a mainstay of therapy for both coronary and peripheral artery disease. Although bypass surgery is highly efficacious in the short term, long-term outcomes are limited by relatively high failure rates as a result of intimal hyperplasia, which is a common feature of vein graft disease. The supply of native veins is limited, and many individuals require multiple grafts and repeat procedures. The need to prevent vein graft failure has led to great interest in gene therapy approaches to this problem. Bypass grafting presents an ideal opportunity for gene therapy, as surgically harvested vein grafts can be treated with gene delivery vectors ex vivo, thereby maximizing gene delivery while minimizing the potential for systemic toxicity and targeting the pathogenesis of vein graft disease at its onset. Here we will review the pathogenesis of vein graft disease and discuss vector delivery strategies and potential molecular targets for its prevention. We will summarize the preclinical and clinical literature on gene therapy in vein grafting and discuss additional considerations for future therapies to prevent vein graft disease.

Contribution of stem cells to neointimal formation of decellularized vessel grafts in a novel mouse model

Artificial vessel grafts are often used for the treatment of occluded blood vessels, but neointimal lesions commonly occur. To both elucidate and quantify which cell types contribute to the developing neointima, we established a novel mouse model of restenosis by grafting a decellularized vessel to the carotid artery. Typically, the graft developed neointimal lesions after 2 weeks, resulting in lumen closure within 4 weeks. Immunohistochemical staining revealed the presence of endothelial and smooth muscle cells, monocytes, and stem/progenitor cells at 2 weeks after implantation. Explanted cultures of neointimal tissues displayed heterogeneous outgrowth in stem cell medium. These lesional cells expressed a panel of stem/progenitor markers, including c-kit, stem cell antigen-1 (Sca-1), and CD34. Furthermore, these cells showed clonogenic and multilineage differentiation capacities. Isolated Sca-1(+) cells were able to differentiate into endothelial and smooth muscle cells in response to vascular endothelial growth factor (VEGF) or platelet-derived growth factor (PDGF)-BB stimulation in vitro. In vivo, local application of VEGF to the adventitial side of the decellularized vessel increased re-endothelialization and reduced neointimal formation in samples at 4 weeks after implantation. A population of stem/progenitor cells exists within developing neointima, which displays the ability to differentiate into both endothelial and smooth muscle cells and can contribute to restenosis. Our findings also indicate that drugs or cytokines that direct cell differentiation toward an endothelial lineage may be effective tools in the prevention or delay of restenosis.

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.

Aspirin and immune system

The time-tested gradual exploration of aspirin's diverse pharmacological properties has made it the most reliable therapeutic agent worldwide. In addition to its well-argued anti-inflammatory effects, many new and exciting data have emerged regarding the role of aspirin in cells of the immune system and certain immunopathological states. For instance, aspirin induces tolerogenic activity in dendritic cells and determines the fate of naive T cells to regulatory phenotypes, which suggests its immunoregulatory potential in relevance to immune tolerance. It also displays some intriguing traits to modulate the innate and adaptive immune responses. In this article, the immunomodulatory relation of aspirin to different immune cells, such as neutrophils, macrophages, dendritic cells (DCs), natural killer (NK) cells, and the T and B lymphocytes has been highlighted. Moreover, the clinical prospects of aspirin in terms of autoimmunity, allograft rejection and immune tolerance have also been outlined.

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

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

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.

Apoptosis, cell proliferation and modulation of cyclin-dependent kinase inhibitor p21(cip1) in vascular remodelling during vein arterialization in the rat

Neo-intima development and atherosclerosis limit long-term vein graft use for revascularization of ischaemic tissues. Using a rat model, which is technically less challenging than smaller rodents, we provide evidence that the temporal morphological, cellular, and key molecular events during vein arterialization resemble the human vein graft adaptation. Right jugular vein was surgically connected to carotid artery and observed up to 90 days. Morphometry demonstrated gradual thickening of the medial layer and important formation of neo-intima with deposition of smooth muscle cells (SMC) in the subendothelial layer from day 7 onwards. Transmission electron microscopy showed that SMCs switch from the contractile to synthetic phenotype on day 3 and new elastic lamellae formation occurs from day 7 onwards. Apoptosis markedly increased on day 1, while alpha-actin immunostaining for SMC almost disappeared by day 3. On day 7, cell proliferation reached the highest level and cellular density gradually increased until day 90. The relative magnitude of cellular changes was higher in the intima vs. the media layer (100 vs. 2 times respectively). Cyclin-dependent kinase inhibitors (CDKIs) p27(Kip1) and p16(INKA) remained unchanged, whereas p21(Cip1) was gradually downregulated, reaching the lowest levels by day 7 until day 90. Taken together, these data indicate for the first time that p21(Cip1) is the main CDKI protein modulated during the arterialization process the rat model of vein arterialization that may be useful to identify and validate new targets and interventions to improve the long-term patency of vein grafts.

Adventitial delivery of platelet-derived endothelial cell growth factor gene prevented intimal hyperplasia of vein graft

BACKGROUND

Platelet-derived endothelial cell growth factor (PD-ECGF), also known as thymidine phosphorylase (TP) reportedly inhibits vascular smooth muscle cells (VSMCs) migration and proliferation. We hypothesized that adventitial administration of the PD-ECGF/TP gene will suppress intimal hyperplasia and prevent vein graft failure.

METHODS

The study used 68 female rabbits. Rabbit jugular vein was autogenously transplanted into carotid artery with a cuff anastomotic technique. To define vascular wall gene transfer efficiency, poloxamer hydrogel (20%) containing plasmid vector encoding the LacZ gene and different concentrations of trypsin (0%, 0.1%, 0.25%, and 0.5%, n = 5 for each group) was applied to the adventitia of the vein graft. Gene transfer efficiency was evaluated 7 days later by X-gal staining. An additional 48 rabbits received poloxamer hydrogel (20%) containing 0.25% trypsin and the human PD-ECGF/TP gene, LacZ gene, or saline. Intima thickness was evaluated at 2 and 8 weeks after grafting (n = 8 for each group at each time point). Transgene expression was examined by reverse transcriptase-polymerase chain reaction, immunoblotting assay, and immunohistochemical staining. Immunohistochemical staining was also used to determine VSMC proliferation, heme oxygenase-1 expression, and macrophage infiltration.

RESULTS

Incorporation of trypsin into the poloxamer hydrogel significantly increased vessel wall gene transfer. Trypsin at 0.25% and 0.5% resulted in higher gene transfer at the same level without effecting intimal hyperplasia and inflammation; thus, trypsin at 0.25% concentration was used for subsequent experiments. Compared with the LacZ and saline groups, grafts receiving the PD-ECGF/TP gene significantly reduced intimal thickness at 2 and 8 weeks after treatment. The ratio of proliferative VSMC was lower in PD-ECGF/TP treated grafts. Histologic examination of the PD-ECGF/TP transgene grafts demonstrated high expression of heme oxygenase-1, which has been reported to inhibit VSMC proliferation, suggesting that heme oxygenase-1 may be important in the inhibition effect of PD-ECGF/TP on VSMC. No neoplastic or morphologic changes were found in the remote organs.

CONCLUSIONS

A safe and highly efficient gene transfer method was developed by using poloxamer hydrogel and a low concentration of trypsin. Neointimal hyperplasia was significantly reduced by adventitial application of the PD-ECGF/TP gene to the vein graft. Our data suggest that adventitial delivery of the PD-ECGF/TP gene after grafting may be promising method for preventing vein graft failure.

Burn wound angiogenesis is increased by exogenously administered recombinant leptin in rats

BACKGROUND: Leptin is a potent direct angiogenic factor that stimulates endothelial cell migration and activation in vitro and angiogenesis in vivo. In addition, leptin has been discussed to play an important role in angiogenesis, as it promotes the formation of new blood vessels. PURPOSE: The effect of exogenously administered leptin on the healing process of a full tissue burn wound model. METHODS: Sixty-three Sprague-Dawley male rats were used. Full tissue burn wound was created by electrocautery. The width of the pin was 0.3 cm; its length was 2 cm and was used at the "cut" modulation. Rats were divided into seven groups of nine animals each. Burn wounds were injected with murine recombinant leptin and the rats were sacrificed 3, 7 and 9 days after surgery. Every group had obtained three animals for the three different days of sacrifice. Three different leptin doses of 250 pg/ml, 500 pg/ml and 1000 pg/ml were used in different animal groups (A, B and C). For every one of the three leptin doses used, another animal group was evaluated by using the combined injection of leptin and antileptin (A1, B1, and C1), in order to study the inhibitory effect to the leptin factor. Nine rats were served as controls. These were injected with 0.3 ml water for injection solution and sacrificed at the same time intervals. After sacrifice of the animals, the skin was grossly determined by its appearance, colour and texture. Full thickness burn wounds were dissected for histological examination. A qualitative analysis of angiogenesis in the burn wound was conducted following a standard hematoxylin and eosin stain. The wound tissue samples from each experimental group underwent immunohistochemical evaluation of microvessel density by endothelial cell staining with mouse anti-rat CD 34 monoclonal antibody. RESULTS: The most impressive growth of new blood vessels appeared seven and nine days after treatment with the highest leptin doses. There were no significant differences in microvessel density between the seventh and the ninth postoperative day among different groups treated with leptin. All wounds from the control group, as well as those from animal groups treated with the combined injection of leptin and antileptin did not develop any new vessels. CONCLUSION: Exogenous administration of recombinant leptin increases early tissue angiogenesis in the burn wound level of an experimental animal model.

Tumor necrosis factor receptor-2 signaling attenuates vein graft neointima formation by promoting endothelial recovery

OBJECTIVE

Inflammation appears intricately linked to vein graft arterialization. We have previously shown that tumor necrosis factor (TNF) receptor-1 (TNFR1, p55) signaling augments vein graft neointimal hyperplasia (NH) and remodeling through its effects on vascular smooth muscle cells (SMCs). In this study we examined the role of TNFR2 (p75) signaling in vein graft arterialization.

METHODS AND RESULTS

Inferior vena cava-to-carotid artery interposition grafting was performed between p75-/- and congenic (C57B1/6J) wild-type (WT) mice. Six weeks postoperatively, neointimal and medial dimensions were greater in p75-/- grafts placed into p75-/- recipients (by 42% or 60%, respectively; P<0.05), when compared with WT veins grafted into WT recipients. Relative to WT vein grafts, p75 deficiency augmented early (2-week-old) graft vascular cell adhesion molecule (VCAM)-1 expression (by 2.4-fold, P<0.05), increased endothelial cell apoptosis (2-fold), and delayed graft re-endothelialization. Both cellular proliferation in early, and collagen I content of mature (6-week-old) vein grafts were increased (by 70% and 50%, respectively) in p75-/- grafts. P75 deficiency augmented TNF-induced apoptosis of cultured endothelial cells, but did not affect TNF-stimulated SMC proliferation or migration induced by co-cultured macrophages.

CONCLUSIONS

TNF signaling via p75 reduces vein graft neointimal hyperplasia through mechanisms involving reduction of adhesion molecule expression and endothelial cell apoptosis.

Progress in clinical neurosciences: The 'antiplatelet' agents and the role of the endothelium

The antiplatelet drugs, commonly used in the prevention and treatment of cerebrovascular disease, possess a number of effects that are independent of direct antiplatelet actions. Beneficial and detrimental effects both occur. The endothelium is an important mediator of these non-antiplatelet effects. We performed a literature search to locate articles related to acetylsalicylic acid (aspirin), clopidogrel, ticlopidine, and dipyridamole and the interactions of these medications with the endothelium. The role of each of the above medications is explored in relation to vasodilation, inflammation, oxidation, platelet-leukocyte interactions, and thrombogenic tendency via platelet-vessel wall interactions.

Therapeutics of vein graft intimal hyperplasia: 100 years on

Intimal hyperplasia is central to the pathology of vein graft re-stenosis, and despite considerable advances in our understanding of vascular biology since it was first described 100 years ago, it is still a significant clinical problem. Recent decades have seen the development of many new therapeutic agents aimed at treating this condition, but the successes of laboratory studies have not been replicated in the clinic yet. This review discusses these therapeutic agents, how their modes of action relate to the pathogenesis of vein graft intimal hyperplasia, and considerations of ways in which such therapy may be improved in the future.

Inhibition of the ubiquitin-proteasome system: a new avenue for atherosclerosis

BACKGROUND

The ubiquitin-proteasome system (UPS) is thought to be functionally active in atherosclerosis (AS) lesions. Aspirin was found to be a potent inhibitor of the UPS in some tumour studies; however, its effect on AS remains to be demonstrated in vivo.

METHODS

New Zealand rabbits were placed on a normal diet (N) or on a normal diet with aspirin (NI) or on an atherogenic diet without (H) or with aspirin (HI) for 12 weeks. Proteasome activity, concentrations of plasma lipids and levels of peroxidation were determined. Ubiquitin/ubiquitin-conjugates (Ub), IkappaBalpha, phosphorylated IkappaB (pIkappaBalpha) and p65 were investigated by Western blotting or immunochemistry.

RESULTS

Concentrations of plasma lipids and peroxidation levels were higher in H or HI vs. N or NI. Histological analysis showed that atheroma was increased in H. Ub and IkappaBalpha were mainly localised in subendothelium and media vascular smooth muscle cells. Western blots revealed that Ub, IkappaBalpha, and pIkappaBalpha were increased, whereas p65 was lower in HI vs. H. The activity of the 20S proteasome was functionally active in H vs. N, NI or HI, while the 26S proteasome was not affected in any of the groups.

CONCLUSIONS

Aspirin can attenuate the pathogenesis of atheroma formation, the degradation of IkappaBalpha and pIkappaBalpha, and lower the expression of p65, indicating that its therapeutic effects on AS may be via inhibition of the UPS.

Vascular Access Outcomes and Medication Use: A USRDS Study

Several medications have been proposed to improve hemodialysis (HD) vascular access outcomes based on potentially favorable anticoagulant, antiplatelet, or pleiotropic properties. The purpose of this study was to evaluate the relationship between medication use and vascular access patency in a group of HD patients. We conducted a historical cohort study of the US Renal Data System Dialysis Mortality and Morbidity Wave II study to identify patients with an arteriovenous fistula (AVF), polytetrafluoroethylene (PTFE) graft, or a permanent catheter for vascular access. Cox regression analysis, adjusted for age, gender, race, history of coronary artery disease, peripheral vascular disease, or coronary artery bypass graft, was used to model the hazard ratio (HR) of permanent vascular access failure. Of the 2001 HD patients in the Wave II study, 901 (45%) were included in the analysis. PTFE graft patency was greater for males (HR, 0.73; 95% CI 0.53-1.00, p = 0.05) and for older individuals (HR, 0.99; 95% CI 0.98-1.00, p = 0.02). Treatment with antiplatelet medications, ticlopidine and dipyridamole (HR, 3.54; 95% CI 1.07-11.76; p = 0.04), or aspirin (HR, 2.49; 95% CI 1.31-4.73; p = 0.005) was associated with significantly worse AVF patency. Antiplatelet agents had a significant negative association with access patency in this cohort. In contrast to other published data, it was difficult to identify any beneficial effect of specific medications on access patency.

Murine models of myocardial and limb ischemia: Diagnostic end-points and relevance to clinical problems

Ischemic disease represents the new epidemic worldwide. Animal models of ischemic disease are useful because they can help us to understand the underlying pathogenetic mechanisms and develop new therapies. The present review article summarizes the results of a consensus conference on the status and future development of experimentation in the field of cardiovascular medicine using murine models of peripheral and myocardial ischemia. The starting point was to recognize the limits of the approach, which mainly derive from species- and disease-related differences in cardiovascular physiology. For instance, the mouse heart beats at a rate 10 times faster than the human heart. Furthermore, healing processes are more rapid in animals, as they rely on mechanisms that may have lost relevance in man. The main objective of the authors was to propose general guidelines, diagnostic end points and relevance to clinical problems.

Controlled release of small interfering RNA targeting midkine attenuates intimal hyperplasia in vein grafts

OBJECTIVE

Intimal hyperplasia is a major obstacle to patency after vein grafting. Despite of a diverse array of trials to prevent it, a satisfactory therapeutic strategy for clinical use has not been established. However, sufficient inhibition of early stages of intimal hyperplasia may prevent this long-term progressive disease. Midkine (MK) is a heparin-binding growth factor that was originally discovered as the product of a retinoic acid-responsive gene. We previously demonstrated that MK-deficient mice exhibit a striking reduction of neointima formation in a restenosis model, which is reversed on systemic MK administration. In this study, we evaluated a strategy of using small interfering RNA (siRNA) targeting MK as a therapy for vein graft failure.

METHODS

We first made a highly effective siRNA to rabbit MK. Jugular vein-to-carotid artery interposition vein grafts, which are applied to a low flow condition, were made in Japanese white rabbits. Small interfering RNA mixed with atelocollagen was administrated to the external wall of grafted veins. Cy3-conjugated stabilized siRNA was used to confirm its stability and successful transfer into the vein graft wall. Neointimal hyperplasia was evaluated 4 weeks after the operation. The proliferation index and leukocyte infiltration were determined.

RESULTS

MK expression was induced and reached the maximum level 7 days after operation. Fluorescence of Cy3-labeled siRNA could be detected in the graft wall even 7 days after operation. Knockdown of the gradually increasing expression was achieved by perivascular application of siRNA using atelocollagen. The intima-media ratio and the intima thickness at 28 days after grafting were both reduced >90% by this treatment compared with controls. This phenomenon was preceded by significant reductions of inflammatory cell recruitment to the vessel walls and subsequent cell proliferation in MK siRNA-treated grafts.

CONCLUSIONS

These results suggest that midkine is a candidate molecular target for preventing vein graft failure. Furthermore, for clinical applications of siRNA, a single intraoperative atelocollagen-based nonviral delivery method could be a reliable approach to achieve maximal function of siRNA in vivo. This strategy may be a useful and practical form of gene therapy against human vein graft failure.

The potassium channel opener levcromakalim causes expansive remodelling of experimental vein grafts

BACKGROUND

Maintenance of luminal area is essential for the optimal performance of venous bypass grafts. However, injury and response to the arterial circulation evoke vascular remodelling that favors intimal hyperplasia, with luminal encroachment and inward remodelling. Potassium channel-opening drugs reduce tissue workload and peripheral vascular resistance and through these mechanisms could favor outward or expansive remodelling of vein grafts. We tested the hypothesis that levcromakalim, a potassium channel opener, would enhance expansive remodelling in vein grafts.

METHODS

A randomized, double-blind, placebo-controlled trial was conducted in 33 rats with vena cava-to-aorta bypass grafts. Drugs were administered via osmotic pump for 7 days after surgery. Half the cohort had bromodeoxyuridine (BrdU) infused at day 6. Morphometric analysis was conducted of pressure perfusion-fixed grafts harvested at 1 week and 4 weeks.

RESULTS

At 1 week, lumen area was similar in both groups (1.82 +/- 0.39 mm(2) placebo vs 1.85 +/- 0.36 mm(2) levcromakalim), although medial cell density and BrdU staining were significantly increased in the placebo group. At 4 weeks, lumen area was unchanged in the placebo group (1.88 +/- 0.51 mm(2)) but had increased to 2.32 +/- 0.46 mm(2) in the levcromakalim group (P = .039 vs 1 week), with a very significant reduction in the intimal area (levcromakalim, 0.06 +/- 0.02 mm(2) vs placebo, 0.33 +/- 0.17 mm(2); P = .001).

CONCLUSIONS

Early, short-term treatment with levcromakalim favors expansive remodelling of experimental vein grafts to mimic the effect of external stenting. This expansive remodelling was associated with a reduction in medial cell proliferation at 1 week.

CLINICAL RELEVANCE

Critical limb ischemia can be treated by bypass surgery or angioplasty, but inward remodelling with restenosis is a common problem. There has been little previous experimental work to identify treatments associated with expansive remodelling, which would increase the chances of vessel patency. Here, in a randomized trial, we show that short-term treatment with a potassium channel opener (a class of drug that can be used to treat hypertension) results in strong, expansive remodelling, with increases the lumen area and graft size of experimental vein grafts by >25%.

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.

Experimental study of tissue-type plasminogen activator gene to prevent vein grafts stenosis

The effects of in vivo local expression of recombined human tissue-type plasminogen activator (t-PA) gene on the thrombosis and neointima formation of vein grafts were explored. Jugular vein-to-artery bypass grafting was performed on 72 New Zealand white rabbits. The rabbits were divided into 3 groups according to the different processing methods: transfected t-PA gene group (n = 24), vector group (n = 24) and blank control group (n = 24). Samples of vein grafts were harvested at different time points after surgery. The expression of t-PA gene in vein graft was detected by RT-PCR and the synthesis of t-PA protein by Western-Blot assay. The t-PA activity was measured by chromogenic substrate assay. The Cr51 labeled platelets accumulation in vein grafts was counted. The histopathological changes were compared in intima hyperplasia index among the three groups after operation. The results showed that at the 2nd, 5th, 14th and 28th day after operation, RT-PCR and Western-blot confirmed the expression of t-PA mRNA and protein at the site of gene transfer. The t-PA activity detected on the 2nd, 5th, 14th and 28th day in experimental group was 370.63 +/- 59.44, 344.13 +/- 48.47, 252.87 +/- 51.80 and 161.75 +/- 68.94 U/g respectively, and disappeared on the 60th day and undetected in the control groups. The number of platelets accumulated in the vein grafts in gene group, vector group and blank control group was (85.04 +/- 21.58) 10(6), (225.87 +/- 85.13) 10(6) and (211.7 +/- 78.02) 10(6) respectively. The number of platelets accumulated in gene group was significantly fewer than that in the control groups. Morphometric analysis revealed that intimal hyperplasia was markedly reduced in the t-PA gene group as compared with that in the control groups. It was suggested that the local expression of t-PA gene in vein graft significantly inhibited the accumulation of platelets, thrombosis and concomitant intimal hyperplasia, by which stenosis of bypass graft could be prevented effectively.

Accelerated arteriosclerosis of vein grafts in inducible NO synthase(-/-) mice is related to decreased endothelial progenitor cell repair

Inducible NO synthase (iNOS) is expressed by macrophages and smooth muscle cells in atherosclerotic lesions. Previously, we have established a mouse model for vein graft arteriosclerosis by grafting autologous jugular veins or vena cava to carotid arteries. Using this model, we studied the role of iNOS in the development of vein graft arteriosclerosis in iNOS(-/-) mice. Four weeks after grafting, neointimal hyperplasia of vein grafts in iNOS(-/-) mice was increased 2-fold compared with that of wild-type controls. Neointimal lesions contained mainly MAC-1+ macrophages and alpha-actin+ smooth muscle cells (SMCs) in both vein grafts of iNOS(-/-) and iNOS(+/+) mice. Immunofluorescence analysis revealed that increased iNOS expression in neointimal macrophages and SMCs of wild-type, but not iNOS(-/-), mice coincided with increased vascular endothelial growth factor (VEGF) expression in vein grafts. When vein grafts were performed in iNOS(-/-)/TIE2-LacZ transgenic mice expressing LacZ gene only in endothelial cells, the number of beta-galactosidase+ cells in iNOS(-/-) vein grafts were significantly decreased. Furthermore, treatment with the NOS inhibitor NG-nitro-L-arginine methyl ester resulted in delayed endothelial progenitor cell attachment, whereas L-arginine intake through drinking water enhanced endothelial repair. Interestingly, local application of VEGF to iNOS(-/-) vein grafts restored endothelial progenitor homing and reduced neointimal lesions, whereas the VEGF receptor inhibitor SU1498 increased the lesion formation. Additionally, iNOS-deficient SMCs showed a low level of VEGF production in response to interleukin 1beta stimulation. Thus, iNOS deficiency accelerates neointima formation by abrogating VEGF production and endothelial progenitor cell attachment and differentiation.

Progenitor cells in vascular disease

Stem cell research has the potential to provide solutions to many chronic diseases via the field of regeneration therapy. In vascular biology, endothelial progenitor cells (EPCs) have been identified as contributing to angiogenesis and hence have therapeutic potential to revascularise ischaemic tissues. EPCs have also been shown to endothelialise vascular grafts and therefore may contribute to endothelial maintenance. EPC number has been shown to be reduced in patients with cardiovascular disease, leading to speculation that atherosclerosis may be caused by a consumptive loss of endothelial repair capacity. Animal experiments have shown that EPCs reendothelialise injured vessels and that this reduces neointimal formation, confirming that EPCs have an atheroprotective effect. Smooth muscle cell accumulation in the neointimal space is characteristic of many forms of atherosclerosis, however the source of these cells is now thought to be from smooth muscle progenitor cells (SMPCs) rather than the adjacent media. There is evidence for the presence of SMPCs in the adventitia of animals and that SMPCs circulate in human blood. There is also data to support SMPCs contributing to neointimal formation but their origin remains unknown. This article will review the roles of EPCs and SMPCs in the development of vascular disease by examining experimental data from in vitro studies, animal models of atherosclerosis and clinical studies.

Altered vascular remodeling in fibulin-5-deficient mice reveals a role of fibulin-5 in smooth muscle cell proliferation and migration

Fibulin (fbln)-5 is an elastin-binding protein required for assembly and organization of elastic fibers. To examine the potential role of fbln-5 in vascular remodeling and neointima formation, we induced vascular injury by carotid artery ligation in fbln-5(-/-) mice. Mutant mice displayed an exaggerated vascular remodeling response that was accompanied by severe neointima formation with thickened adventitia. These abnormalities were not observed in elastin(+/-) mice that exhibited a comparable reduction of vessel extensibility to fbln-5(-/-) mice. Thus, the severe remodeling response could not be attributed to altered extensibility of the vessel wall alone. Vascular smooth muscle cells cultured from fbln-5(-/-) mice displayed enhanced proliferative and migratory responses to mitogenic stimulation relative to wild-type cells, and these responses were inhibited by overexpression of fbln-5. These findings demonstrate the importance of the elastic laminae in vascular injury, and reveal an unexpected role of fbln-5 as an inhibitor of vascular smooth muscle cell proliferation and migration.

The Contegra conduit in the right ventricular outflow tract induces supravalvular stenosis

OBJECTIVE

We sought to evaluate the incidence and nature of pulmonary stenosis after implantation of the bovine jugular vein graft (Contegra; Medtronic, Inc, Minneapolis, Minn) in the right ventricular outflow tract.

METHODS

Between May 2000 and September 2002, 58 Contegra conduits (8-22 mm) were implanted during primary (n = 27) or redo operations (n = 31) in 57 patients, with ages ranging from 2 days to 48 years (mean, 9 years). Indications were truncus arteriosus (n = 16), tetralogy of Fallot (n = 28), pulmonary replacement in the Ross operation (n = 10), and Rastelli-type repair for double-outlet right ventricle (n = 4). Echocardiography was prospectively performed by a fixed team of investigators during follow-up (mean, 22.7 +/- 10 months). A peak gradient of greater than 50 mm Hg was considered severe stenosis.

RESULTS

Two patients died from Staphylococcus aureus -induced septicemia and enterococcal endocarditis after 12 days and 12 weeks, respectively. One patient died of heart failure caused by endocardial fibroelastosis after 1 year. Freedom from severe stenosis at the distal anastomosis was 91% +/- 3% at 3 months, 68% +/- 6% at 12 months, and 49% +/- 8% at 24 months. The risk of development of stenosis does not change over time. Younger age and its derivatives (graft size and indication) are significantly related to the occurrence of severe stenosis ( P < .0001). Seventeen (29%) conduits required an endovascular intervention (balloon dilatation or stent). Seven (12%) conduits were explanted (endocarditis, 2; stenosis, 5). Histologic analysis of the explanted conduits showed excessive proliferation of neointima at the level of the distal anastomosis. Valve regurgitation was observed in 9 (16%) conduits and was always secondary to dilatation in the presence of severe distal stenosis.

CONCLUSION

The Contegra conduit induces a neointimal proliferation at the level of the pulmonary anastomosis. This leads to a high incidence of severe stenosis at intermediate-term follow-up.