Adventitial myofibroblasts contribute to neointimal formation in injured porcine coronary arteries

Association of atherosclerotic risk factors with carotid adventitial thickness assessed by ultrasonography

PURPOSE

There is increasing evidence that adventitial inflammation may participate in atherosclerosis development. The aim of this study was to investigate which atherosclerotic risk factors correlated with carotid adventitial thickness (AT) and to compare them with those associated with carotid intima-media thickness (IMT). We also set out to test the hypothesis that there is a significant correlation between IMT and AT in the carotid arteries.

METHODS

The far carotid artery wall IMT and AT were measured by high-resolution B-mode ultrasound in 128 persons (mean, 65 +/- 8 years). A number of conventional and novel, clinically and laboratory-derived risk factors were assessed.

RESULTS

Significant correlation (r = 0.35, p < 0.0001) was demonstrated between the IMT and AT. The stepwise forward multiple regression analysis revealed correlations between IMT and leukocyte count, C-reactive protein level, and hypertension, whereas the Chlamydia (C.) pneumoniae IgA antibodies and fibrinogen levels, gender, and smoking correlated merely with AT. The homocysteine/methionine ratio correlated with both IMT and AT.

CONCLUSION

The association between IMT and AT may reflect an interaction between intimal, medial, and adventitial pathology. Different risk factors are associated with the increased AT or IMT. It is possible that inflammation and some chronic infections, such as those induced by C. pneumoniae, could have a marked influence on adventitial cell proliferation.

Exercise training decreases the size and alters the composition of the neointima in a porcine model of percutaneous transluminal coronary angioplasty (PTCA)

Exercise training (EX) following percutaneous transluminal coronary angiography (PTCA) reduces progression to restenosis and increases event-free survival rates. Our aim was to determine whether EX inhibits lesion development and/or alters the extracellular matrix (ECM) composition of the neointima (NI) in a porcine PTCA model. Miniature Yucatan swine were assigned to cage confinement (SED) or EX for 20 wk. After 16 wk, all animals underwent a PTCA procedure of the left anterior descending artery (LAD) and left circumflex artery (LCX), with subsequent placement of an externalized jugular catheter. Animals recovered for 2 days and then resumed the previous protocol of SED or EX. Twelve days following PTCA, all animals received an intravenous bromodeoxyuridine (BrdU) injection to label proliferating cells. At 28 days following PTCA, the animals were euthanized, the LAD and LCX excised, and underwent standard histological processing for total collagen, type I collagen, fibronectin, BrdU, and Verhoeff-van Gieson stain. Our results demonstrate that EX significantly decreased lesion size and NI proliferation (-48%) in the LAD (P < 0.05) but not the LCX. Furthermore, EX attenuated type I collagen expression only in LAD, whereas total collagen was increased (5.9%) and fibronectin was decreased (-7.9%) in the NI of both vessels (P < 0.05). In conclusion, EX following PTCA may increase event-free survival rates following PTCA by decreasing lesion size and altering ECM composition.

AGEs increased migration and inflammatory responses of adventitial fibroblasts via RAGE, MAPK and NF-kappaB pathways

OBJECTIVE

Advanced glycation end products (AGEs) and vascular adventitial fibroblasts (AFs) are involved in diabetes-related vascular complications. However, the effect of AGEs on AFs remains unclear. The aim of this study was to observe the impact of AGEs on cell migration capacity and associated inflammatory responses of AFs.

METHODS AND RESULTS

Isolated vascular AFs of Sprague-Dawley rats were cultured, harvested after 24h synchronization and challenged with AGE-HSA. AGE-HSA upregulated the expression of receptor for advanced glycation end products (RAGE), significantly increased the migration capacity and inflammatory mediators MCP-1, IL-6, VCAM-1 expressions on AFs. These effects could be significantly attenuated by anti-RAGE neutralizing antibody, p38, ERK1/2 and JNK MAPK inhibitors as well as by candesartan. AGE-HAS also upregulated NF-kappaB transcriptional activity and I-kappaB-alpha phosphorylation, effect that was significantly inhibited by candesartan.

CONCLUSIONS

AGE-HSA increased the migration capacity and inflammatory responses of rat AFs via RAGE-MAPK-NF-kappaB pathways. Candesartan effectively inhibited these effects which might be a novel vascular protection mechanism of candesartan.

Nitric oxide regulates the 26S proteasome in vascular smooth muscle cells

It is well established that nitric oxide (NO) inhibits vascular smooth muscle cell (VSMC) proliferation by modulating cell cycle proteins. The 26S proteasome is integral to protein degradation and tightly regulates cell cycle proteins. Therefore, we hypothesized that NO directly inhibits the activity of the 26S proteasome. The three enzymatic activities (chymotrypsin-like, trypsin-like and caspase-like) of the 26S proteasome were examined in VSMC. At baseline, caspase-like activity was approximately 3.5-fold greater than chymotrypsin- and trypsin-like activities. The NO donor S-nitroso-N-acetylpenicillamine (SNAP) significantly inhibited all three catalytically active sites in a time- and concentration-dependent manner (P<0.05). Caspase-like activity was inhibited to a greater degree (77.2% P<0.05). cGMP and cAMP analogs and inhibitors had no statistically significant effect on basal or NO-mediated inhibition of proteasome activity. Dithiothreitol, a reducing agent, prevented and reversed the NO-mediated inhibition of the 26S proteasome. Nitroso-cysteine analysis following S-nitrosoglutathione exposure revealed that the 20S catalytic core of the 26S proteasome contains 10 cysteines which were S-nitrosylated by NO. Evaluation of 26S proteasome subunit protein expression revealed differential regulation of the alpha and beta subunits in VSMC following exposure to NO. Finally, immunohistochemical analysis of subunit expression revealed distinct intracellular localization of the 26S proteasomal subunits at baseline and confirmed upregulation of distinct subunits following NO exposure. In conclusion, NO reversibly inhibits the catalytic activity of the 26S proteasome through S-nitrosylation and differentially regulates proteasomal subunit expression. This may be one mechanism by which NO exerts its effects on the cell cycle and inhibits cellular proliferation in the vasculature.

Interstitial flow promotes vascular fibroblast, myofibroblast, and smooth muscle cell motility in 3-D collagen I via upregulation of MMP-1

Neointima formation often occurs in regions where the endothelium has been damaged and the transmural interstitial flow is elevated. Vascular smooth muscle cells (SMCs) and fibroblasts/myofibroblasts (FBs/MFBs) contribute to intimal thickening by migrating from the media and adventitia into the site of injury. In this study, for the first time, the direct effects of interstitial flow on SMC and FB/MFB migration were investigated in an in vitro three-dimensional system. Collagen I gels were used to mimic three-dimensional extracellular matrix (ECM) for rat aortic SMCs and FBs/MFBs. Exposure to interstitial flow induced by 1 cmH(2)O pressure differential (shear stress, approximately 0.05 dyn/cm(2); flow velocity, approximately 0.5 microm/s; and Darcy permeability, approximately 10(-11) cm(2)) substantially enhanced cell motility. Matrix metalloproteinase (MMP) inhibitor (GM-6001) abolished flow-induced migration augmentation, which suggested that the enhanced motility was MMP dependent. The upregulation of MMP-1 played a critical role for the flow-enhanced motility, which was further confirmed by silencing MMP-1 gene expression. Longer exposures to higher flows suppressed the number of migrated cells, although MMP-1 gene expression remained high. This suppression was a result of both flow-induced tissue inhibitor of metalloproteinase-1 upregulation and increased apoptotic and necrotic cell death. Interstitial flow did not affect MMP-2 gene expression or activity in the collagen I gel for any cell type. Our findings shed light on the mechanism by which vascular SMCs and FBs/MFBs contribute to intimal thickening in regions of vascular injury where interstitial flow is elevated.

Cellular phenotypes in human stenotic lesions from haemodialysis vascular access

BACKGROUND

Haemodialysis vascular access dysfunction (due to venous stenosis and thrombosis) is a leading cause of hospitalization and morbidity. The aim of the current study was to identify the specific cell types present within stenotic tissue samples from patients with AV fistula and graft failure.

METHODS

Discarded tissue segments were collected from the stenotic portions (usually near the graft-vein anastomosis or the AV anastomosis) of 23 dialysis grafts and 20 AV fistulae, and examined for expression of smooth muscle alpha actin, desmin, vimentin and a macrophage marker.

RESULTS

The majority of cells within the venous neointima (both grafts and fistulae) were myofibroblasts, with a smaller number of desmin positive smooth muscle cells. The graft neointima had a similar cellular phenotype, albeit without any desmin positive contractile smooth muscle cells. The majority of cells within the PTFE graft material were macrophages. Analysis of sequential sections revealed the presence of fibroblasts within the venous neointima and intragraft region.

CONCLUSIONS

Our results demonstrate that contractile smooth muscle cells, myofibroblasts, fibroblasts and macrophages all play a role in the pathogenesis of dialysis access dysfunction (grafts and fistulae). Targeting these specific cell types might result in the development of novel therapeutic paradigms for haemodialysis vascular access dysfunction.

Regulation of arterial remodeling and angiogenesis by urokinase-type plasminogen activatorThis article is one of a selection of papers from the NATO Advanced Research Workshop on Translational Knowledge for Heart Health (published in part 2 of a 2-part Special Issue)

A wide variety of disorders are associated with an imbalance in the plasminogen activator system, including inflammatory diseases, atherosclerosis, intimal hyperplasia, the response mechanism to vascular injury, and restenosis. Urokinase-type plasminogen activator (uPA) is a multifunctional protein that in addition to its fibrinolytic and matrix degradation capabilities also affects growth factor bioavailability, cytokine modulation, receptor shedding, cell migration and proliferation, phenotypic modulation, protein expression, and cascade activation of proteases, inhibitors, receptors, and modulators. uPA is the crucial protein for neointimal growth and vascular remodeling. Moreover, it was recently shown to be implicated in the stimulation of angiogenesis, which makes it a promising multipurpose therapeutic target. This review is focused on the mechanisms by which uPA can regulate arterial remodeling, angiogenesis, and cell migration and proliferation after arterial injury and the means by which it modulates gene expression in vascular cells. The role of domain specificity of urokinase in these processes is also discussed.

Negligible contribution of coronary adventitial fibroblasts to neointimal formation following balloon angioplasty in swine

Adventitial fibroblasts have previously been proposed to be a major constituent of the neointima following coronary balloon angioplasty. The present study utilized the bromodeoxyuridine (BrdU) pulse-chase technique to track adventitial fibroblast migration early after balloon injury in swine. BrdU (30 mg/kg), a marker of proliferating cells, was given intravenously 1 or 2 days after balloon angioplasty. For each time point, one animal was euthanized 24 h after injection to identify the location of the proliferating cells, while a second animal was euthanized 25 days after angioplasty to determine whether the proliferating cells migrated to form the neointima. Our results demonstrate that BrdU-positive cells were located primarily in the adventitia with all three time points 24 h after balloon angioplasty. Furthermore, when BrdU was injected on day 1 or 2 only 0.65 +/- 0.17% and 1.7 +/- 0.64%, respectively, of neointimal cells were BrdU positive on day 25. In conclusion, these results demonstrate a negligible contribution of coronary adventitial fibroblasts to neointima formation following coronary balloon angioplasty, supporting the concept that the neointima is primarily of smooth muscle cell origin.

Vascular progenitor cells and translational research: the role of endothelial and smooth muscle progenitor cells in endogenous arterial remodelling in the adult

There has been much recent research into the therapeutic use of stem and progenitor cells for various diseases. Alongside this, there has also been considerable interest in the normal roles that endogenous precursor cells may play in both physiological and pathological settings. In the present review, we focus on two types of progenitor cell which are of potential relevance to vascular homoeostasis, namely the EPC (endothelial progenitor cell) and the smooth muscle progenitor cell. We discuss evidence for their existence and sources in adults, and the various techniques currently used to identify these cells. We examine data obtained from studies using different methods of progenitor identification and relate these to each other, in order to provide a framework in which to interpret the literature in this area. We review evidence for the influence of these vascular progenitor cells upon vascular function and the development and progression of atherosclerosis.

Expression profiles in surgically-induced carotid stenosis: a combined transcriptomic and proteomic investigation

Vascular injury aimed at stenosis removal induces local reactions often leading to restenosis. The aim of this study was a concerted transcriptomic-proteomics analysis of molecular variations in a model of rat carotid arteriotomy, to dissect the molecular pathways triggered by vascular surgical injury and to identify new potential anti-restenosis targets. RNA and proteins extracted from inbred Wistar Kyoro (WKY) rat carotids harvested 4 hrs, 48 hrs and 7 days after arteriotomy were analysed by Affymetrix rat microarrays and by bidimensional electrophoresis followed by liquid chromatography and tandem mass spectrometry, using as reference the RNA and the proteins extracted from uninjured rat carotids. Results were classified according to their biological function, and the most significant Kyoro Encyclopedia of Genes and Genomes (KEGG) pathways were identified. A total of 1163 mRNAs were differentially regulated in arteriotomy-injured carotids 4 hrs, 48 hrs and 7 days after injury (P < 0.0001, fold-change > or =2), while 48 spots exhibited significant changes after carotid arteriotomy (P < 0.05, fold-change > or =2). Among them, 16 spots were successfully identified and resulted to correspond to a set of 19 proteins. mRNAs were mainly involved in signal transduction, oxidative stress/inflammation and remodelling, including many new potential targets for limitation of surgically induced (re)stenosis (e.g. Arginase I, Kruppel like factors). Proteome analysis confirmed and extended the microrarray data, revealing time-dependent post-translational modifications of Hsp27, haptoglobin and contrapsin-like protease inhibitor 6, and the differential expression of proteins mainly involved in contractility. Transcriptomic and proteomic methods revealed functional categories with different preferences, related to the experimental sensitivity and to mechanisms of regulation. The comparative analysis revealed correlation between transcriptional and translational expression for 47% of identified proteins. Exceptions from this correlation confirm the complementarities of these approaches.

Pathophysiology of aortocoronary saphenous vein bypass graft disease

Aortocoronary saphenous vein bypass grafting relieves anginal pain in patients with coronary artery disease. However, its effectiveness is limited due to graft failure; the 10-year patency rate is 50%-60%. Early, 1-year and late graft failure may be due to thrombosis, fibrointimal hyperplasia and atherosclerosis, respectively. There is general agreement that vein graft atherosclerosis differs from arterial lesions in terms of temporal and histological changes. Vein graft atherosclerosis is more rapid, with diffuse concentric changes and a less noticeable fibrous cap, making venous plaques more vulnerable to rupture and subsequent thrombus formation. Despite progress in understanding the pathophysiology, some aspects of vein graft atherosclerosis need to be clarified. This review focuses on the pathophysiologic aspects of this widespread, costly and disabling disease, with emphasis on late graft occlusion and distinctions between arterial and venous atherosclerosis in terms of histology, pathophysiology and risk factors.

Meta-iodobenzylguanidine, an inhibitor of arginine-dependent mono(ADP-ribosyl)ation, prevents neointimal hyperplasia

The association of ADP-ribosylation with cell proliferation and ischemia-reperfusion injury suggests that it may be a suitable target for therapeutic control of revascularization-induced injury. The purpose of this study was to investigate the inhibitory actions of ADP-ribosylation inhibitors on restenosis. In organ culture, the poly(ADP-ribose) polymerase (PARP) inhibitor 3,4-dihydro-5-methylisoquinolinone (PD128763) was unable to prevent neointimal hyperplasia, whereas the arginine-dependent mono(ADP-ribosyl)transferase (ART) inhibitor meta-iodobenzylguanidine (MIBG) was highly effective (EC(50) 21 microM). Treatment with 3-aminobenzamide (3AB), a less potent ART inhibitor, also produced a significant reduction in neointimal hyperplasia. Single doses (25 mM) of MIBG and 3AB were also applied within a fibrin coagulum directly to the adventitial surface of the porcine femoral artery after balloon catheter injury in vivo. MIBG reduced the neointimal index, measured 14 days after angioplasty, by 82%, whereas 3AB was ineffective. However, when extended to 45 days, the neointimal index was not significantly decreased by MIBG treatment relative to control. Assessment of MIBG release from the fibrin glue showed that the bulk of the compound was eluted within 3 days, suggesting that the vehicle was not suitable for long-term delivery. On the other hand, direct infusion of MIBG into vessels was able to reduce neointimal hyperplasia over 14 days in organ culture. These data support the conclusion that the cellular retention characteristics of MIBG contribute significantly to the efficacy of this compound. Based on these results, ART, but not PARP, may be a credible target for therapeutic treatment of restenosis.

Smooth muscle cells, dendritic cells and mast cells are sources of TNFalpha and nitric oxide in human carotid artery atherosclerosis

INTRODUCTION

In atherogenesis, dendritic cells, beside presenting antigens, may be sources of tumour necrosis factor (TNF)alpha and nitric oxide (NO), together with mast cells and smooth muscle cells.

MATERIAL AND METHODS

We have looked at the expression of TNFalpha and inducible NO synthase (iNOs) by these cells by affinity cytochemistry in autoptical specimens from normal carotid arteries and not ruptured, hemorrhagic or calcified atheromata.

RESULTS

Round to dendritic, major histocompatibility complex class II molecules (MHC-II+) cells and avidin-labeled mast cells were rare in normal arteries and significantly more numerous in atheromata. Many MHC-II+ cells expressed S-100 antigen; while a few were positive for phalloidin; appreciable fractions of these cells were immunoreactive for TNFalpha and iNOs, both in control specimens and atheromata. The fraction of mast cells labeled for iNOs was significantly lower in atheromata than in controls. Phalloidin positive cells were the most abundant cell type in the normal intima and atheromata; the fractions of these cells labeled for TNFalpha and iNOs were significantly higher in atheromata than in controls. Very few of these cells were also labeled for MHC-II. Computerized image analysis confirmed that the amounts of iNOs and TNFalpha were higher in atheromata than in controls. The increase in TNFalpha in atheromata was also confirmed by western blot.

CONCLUSIONS

Dendritic cells and mast cells can participate to the generation of TNFalpha and NO in the normal arterial wall and in atheromata, but myointimal cells are candidates as major sources of these molecules.

Nox4 oxidase overexpression specifically decreases endogenous Nox4 mRNA and inhibits angiotensin II-induced adventitial myofibroblast migration

The vascular adventitia is emerging as an important modulator of vessel remodeling. Adventitial myofibroblasts migrate to the neointima after balloon angioplasty, contributing to restenosis. We postulated that angiotensin II (Ang II) enhances adventitial myofibroblast migration in vitro via reduced nicotinamide-adenine dinucleotide phosphate oxidase-derived H(2)O(2) and that Nox4-based oxidase promotes migration. Ang II increased myofibroblast migration in a concentration-dependent manner, with a peak increase of 1023+/-83%. Rat adventitial myofibroblasts were cotransfected with human Nox4 and human p22-phox plasmids or an empty vector. PCR showed an 8-fold increase in human Nox4 and human p22-phox plasmid expression. Using RT-PCR with primers specifically designed for rat reduced nicotinamide-adenine dinucleotide phosphate oxidases, endogenous Nox levels were determined. Ang II decreased endogenous Nox4 and Nox1 mRNA to 41% and 27% of control, respectively, but had no effect on Nox2. Cotransfection with human Nox4 and human p22-phox plasmids combined with Ang II reduced endogenous Nox4 mRNA levels (37+/-5% of control; P<0.05), whereas it had no significant effect on Nox1 or Nox2. In empty vector-transfected cells, Ang II increased myofibroblast migration by 192+/-32% versus vehicle (P<0.01) while increasing H(2)O(2) (473+/-22% versus control; P<0.001). Cotransfection with human Nox4 and human p22-phox plasmids decreased Ang II-induced migration (46+/-6%; P<0.001) in parallel with attenuation of H(2)O(2) production (23+/-8% versus empty vector; P<0.05). Our data suggest that Nox4 promotes Ang II-induced myofibroblast migration via an H(2)O(2)-dependent pathway. The data also suggest that Nox4 causes feedback inhibition of its own expression in adventitial myofibroblasts.

Preventing restenosis after angioplasty: a multistage approach

Arterial reconstruction procedures, including balloon angioplasty, stenting and coronary artery bypass, are used to restore blood flow in atherosclerotic arteries. Restenosis of these arteries has remained a major limitation of the application of these procedures, especially in the case of balloon angioplasty. Post-angioplasty restenosis results from two major processes: neointimal formation and constrictive remodelling. Neointimal formation is initiated by arterial injury with a resultant loss of contractile phenotype in tunica media, leading to VSMC [vascular SM (smooth muscle) cell] migration from the tunica media to the intima. Migrated VSMCs contribute to the intimal thickening by the excessive synthesis of ECM (extracellular matrix) and proliferation. However, increased neointimal mass is not solely responsible for luminal narrowing. Inward constrictive remodelling is also considered as a major cause of delayed failure of angioplasty. At later stages after angioplasty, the increase in contractile forces leads to lumen narrowing. Recent studies show that SM contractile proteins are re-expressed in the neointima, concomitant with late lumen loss. Therefore one important question is whether the restoration of contractile phenotype, which can suppress VSMC migration, is favourable or detrimental. In this review, the importance of viewing restenosis as a multistage process is discussed. Different stages of restenosis occur in a sequential manner and are related to each other, but in each stage a different strategy should be taken into consideration to reduce restenosis. Defining the role of each process not only reshapes the current concept, but also helps us to target restenosis with more efficacy.

Factor Xa stimulates proinflammatory and profibrotic responses in fibroblasts via protease-activated receptor-2 activation

Coagulation proteases have been suggested to play a role in the pathogenesis of tissue remodeling and fibrosis. We therefore assessed the proinflammatory and fibroproliferative effects of coagulation protease factor (F)Xa. We show that FXa elicits a signaling response in C2C12 and NIH3T3 fibroblasts. FXa-induced ERK1/2 phosphorylation was dependent on protease-activated receptor (PAR)-2 cleavage because desensitization with a PAR-2 agonist (trypsin) but not a PAR-1 agonist (thrombin) abolished FXa-induced signal transduction and PAR-2 siRNA abolished FXa-induced ERK1/2 phosphorylation. The PAR-2-dependent cellular effects of FXa led to fibroblast proliferation, migration, and differentiation into myofibroblasts, as demonstrated by the expression of alpha-smooth muscle actin and desmin, followed by the secretion of the cytokines monocyte chemotactic protein-1 and interleukin-6 as well as the expression of the fibrogenic proteins transforming growth factor-beta and fibronectin. To assess the relevance of FXa-induced proliferation and cell migration, we examined the effect of FXa in a wound scratch assay. Indeed, FXa facilitated wound healing in a PAR-2- and ERK1/2-dependent manner. Taken together, these results support the notion that, beyond its role in coagulation, FXa-dependent PAR-2 cleavage might play a role in the progression of tissue fibrosis and remodeling.

Beneficial effect of a short-acting NO donor for the prevention of neointimal hyperplasia

Nitric oxide (NO)-based therapies effectively inhibit neointimal hyperplasia in animal models of arterial injury and bypass grafting, but are not available clinically. We created a simple, effective, locally applied NO-eluting therapy to prevent restenosis after vascular procedures. We investigated the efficacy of perivascular delivery of two distinctly different diazeniumdiolate NO donors, 1-[2-(carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate (PROLI/NO) (short half-life) and diazeniumdiolated poly(acrylonitrile) (PAN/NO) (long half-life), in powder or gel form (30% poloxamer 407), at inhibiting neointimal hyperplasia using the rat carotid artery injury model. Two weeks postinjury, all of the NO-eluting therapies successfully reduced neointimal hyperplasia. However, most dramatically, PROLI/NO powder reduced intimal area by 91.2% (p<0.05) versus injury alone. PROLI/NO powder was noted to reduce the medial area (40.2% vs injury alone, p<0.05), whereas other groups showed no such effect. Three days postinjury, each NO treatment group significantly reduced cellular proliferation. However, inflammatory markers revealed a distinct pattern: PAN/NO groups displayed increased leukocyte infiltration (p<0.05), whereas PROLI/NO groups displayed less macrophage infiltration (p<0.05). In conclusion, perivascular delivery of diazeniumdiolate NO donors in powder or gel form effectively inhibits neointimal hyperplasia. Application of short-acting PROLI/NO powder most effectively inhibited neointimal hyperplasia and inflammation and may represent a simple, clinically applicable NO-eluting therapy to prevent neointimal hyperplasia and restenosis after open vascular interventions.

A hypothesis: adiponectin mediates anti-atherosclerosis via adventitia-AMPK-iNOS pathway

Adiponectin is an adipocyte-derived protein with insulin-sensitizing, anti-inflammatory, and anti-atherogenic properties and is abundantly found in plasma. Vascular adventitia is the outermost connective and supporting tissue of vessels. Recently, increasing evidence has shown that infection in the adventitia is one of the causes of atherosclerosis and restenosis. Our previous study indicated that local transferring adenovirus expressing adiponectin gene (Ad-APN) to intima and adventitia can suppress atherosclerosis, but the exact mechanism is still obscure. We speculate that with infection in the adventitia, adiponectin can activate AMP-activated protein kinase (AMPK) through adiponectin receptors in the membranes of adventitial fibroblasts and then inhibit the expression and activity of inducible nitric oxide synthase (iNOS); secretion of adventitial infective factors; division, proliferation and translation of adventitial fibroblasts; and change of adventitial fibroblasts to myofibroblasts, finally decreasing oxidative/nitrative stress to reduce atherosclerotic plaque area and stabilize atherosclerotic plaques. The proposition may provide clues into the development of a novel treatment for atherosclerosis.

The cell cycle: a critical therapeutic target to prevent vascular proliferative disease

Percutaneous coronary intervention is the preferred revascularization approach for most patients with coronary artery disease. However, this strategy is limited by renarrowing of the vessel by neointimal hyperplasia within the stent lumen (in-stent restenosis). Vascular smooth muscle cell proliferation is a major component in this healing process. This process is mediated by multiple cytokines and growth factors, which share a common pathway in inducing cell proliferation: the cell cycle. The cell cycle is highly regulated by numerous mechanisms ensuring orderly and coordinated cell division. The present review discusses current concepts related to regulation of the cell cycle and new therapeutic options that target aspects of the cell cycle.

The role of the adventitia in vascular inflammation

Traditional concepts of vascular inflammation are considered "inside-out" responses centered on the monocyte adhesion and lipid oxidation hypotheses. These mechanisms likely operate in concert, holding the central tenet that the inflammatory response is initiated at the luminal surface. However, growing evidence supports a new paradigm of an "outside-in" hypothesis, in which vascular inflammation is initiated in the adventitia and progresses inward toward the intima. Hallmarks of the outside-in hypothesis include population of the adventitia with exogenous cell types, including monocytes, macrophages, and lymphocytes, the phenotypic switch of adventitial fibroblasts into migratory myofibroblasts, and increased vasa vasorum neovascularization. The resident and migrating cells deposit collagen and matrix components, respond to and upregulate inflammatory chemokines and/or antigens, and regulate the local redox state of the adventitia. B cells and T cells generate local humoral immune responses against local antigen presentation by foam cells and antigen presenting cells. These events result in increased local expression of cytokines and growth factors, evoking an inflammatory response that propagates inward toward the intima. Ultimately, it appears that the basic mechanisms of cellular activation and migration in vascular inflammation are highly conserved across a variety of cardiovascular disease states and that major inflammatory events begin in the adventitia.

Expression and function of vascular endothelial growth factor receptors (Flt-1 and Flk-1) in vascular adventitial fibroblasts

Vascular endothelial growth factor receptors (VEGFRs) are previously considered to exist exclusively in endothelial cells. However, little is known if the receptors are expressed in other non-endothelial cells. In this study, we measured activation of two VEGFRs, Flk-1 and Flt-1, and their biological functions in cultured adventitial fibroblasts and injured rat carotid injury arteries induced by balloon angioplasty. Our results indicated that Flt-1, but not Flk-1, existed in adventitial fibroblasts. Angiotensin II increased Flt-1 protein expression in a time- and concentration-dependent manner. Adventitial fibroblast migration stimulated by vascular endothelial growth factor (VEGF) and placental growth factor (PIGF) required Flt-1 expression. The Flt-1-induced adventitial fibroblast migration was blocked by anti-Flt-1 neutralizing antibody and soluble VEGFR1 protein (sFlt-1). However, Flt-1 activation did not enhance cell proliferation. In addition, Flt-1 expression was significantly increased in the neointima and adventitia in injured rat carotid arteries. We concluded that functional expression of Flt-1 in adventitial fibroblasts might be an important mediator in the pathogenesis of vascular remodeling after arterial injury.

Applying elastic fibre biology in vascular tissue engineering

For the treatment of vascular disease, the major cause of death in Western society, there is an urgent need for tissue-engineered, biocompatible, small calibre artery substitutes that restore biological function. Vascular tissue engineering of such grafts involves the development of compliant synthetic or biomaterial scaffolds that incorporate vascular cells and extracellular matrix. Elastic fibres are major structural elements of arterial walls that can enhance vascular graft design and patency. In blood vessels, they endow vessels with the critical property of elastic recoil. They also influence vascular cell behaviour through direct interactions and by regulating growth factor activation. This review addresses physiological elastic fibre assembly and contributions to vessel structure and function, and how elastic fibre biology is now being exploited in small diameter vascular graft design.

The role of vascular stem cells in atherogenesis and post-angioplasty restenosis

It is well known that atherosclerosis prevails in elderly populations as ageing acts as a recognized risk factor for this disease. Although the pathogenic factors leading to atherosclerosis are highly heterogeneous, traditionally speaking, the causative risk factors include hyperlipidemia, hypertension, diabetes mellitus and smoking, which can damage to endothelial function, and subsequently promote lipid penetration and inflammatory cell infiltration. Damaged endothelial cells (ECs) may be replaced by neighboring cell division, while damaged smooth muscle cells (SMCs) may be replaced by medial SMCs emigrating into the intima during atherogenesis. However, this standpoint is challenged by recent findings that vascular progenitor/stem cells (VPCs) may contribute to atherogenesis and post-angioplasty restenosis. VPCs are a group of primitive cells that have the potential to produce mature, functional cells in the vascular wall. VPCs residing in bone marrow, vascular wall or circulating in the peripheral blood may be stimulated by a variety of pathogenic factors. These stem cells then participate in regeneration, repair and remodeling of the injured arterial wall. This new concept may bring about a great breakthrough in understanding the pathogenesis of atherosclerosis and develop novel therapeutic strategies for coronary heart disease. This article will mainly review the role of VPCs in atherogenesis, thus providing a novel understanding about the pathophysiology of atherosclerosis.

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.

The role of periadventitial fat in atherosclerosis

CONTEXT

It has become increasingly evident that adipose tissue is a multifunctional organ that produces and secretes multiple paracrine and endocrine factors. Research into obesity, insulin resistance, and diabetes has identified a proinflammatory state associated with obesity. Substantial differences between subcutaneous and omental fat have been noted, including the fact that omental fat produces relatively more inflammatory cytokines. Periadventitial fat, as a specific adipose tissue subset, has been overlooked in the field of atherosclerosis despite its potential diagnostic and therapeutic implications.

OBJECTIVE

To review (1) evidence for the role of adventitial and periadventitial fat in vessel remodeling after injury, (2) the relationship between adventitial inflammation and atherosclerosis, (3) the association between periadventitial fat and plaque inflammation, and (4) the diagnostic and therapeutic implications of these roles and relationships for the progression of atherosclerosis.

DATA SOURCES

We present new data showing greater uptake of iron, administered in the form of superparamagnetic iron oxide, in the periadventitial fat of atherosclerotic mice than in control mice. In addition, macrophage density in the periadventitial fat of lipid-rich plaques is increased compared with fibrocalcific plaques.

CONCLUSIONS

There is a striking paucity of data on the relationship between the periadventitial fat of coronary arteries and atherosclerosis. Greater insight into this relationship might be instrumental in making strides into the pathophysiology, diagnosis, and treatment of coronary artery disease.

Smooth muscle cell signal transduction: implications of vascular biology for vascular surgeons

Vascular smooth muscle cells exhibit varied responses after vessel injury and surgical interventions, including phenotypic switching, migration, proliferation, protein synthesis, and apoptosis. Although the source of the smooth muscle cells that accumulate in the vascular wall is controversial, possibly reflecting migration from the adventitia, from the circulating blood, or in situ differentiation, the intracellular signal transduction pathways that control these processes are being defined. Some of these pathways include the Ras-mitogen-activated protein kinase, phosphatidylinositol 3-kinase-Akt, Rho, death receptor-caspase, and nitric oxide pathways. Signal transduction pathways provide amplification, redundancy, and control points within the cell and culminate in biologic responses. We review some of the signaling pathways activated within smooth muscle cells that contribute to smooth muscle cell heterogeneity and development of pathology such as restenosis and neointimal hyperplasia.

Effects of fluid shear stress on adventitial fibroblast migration: implications for flow-mediated mechanisms of arterialization and intimal hyperplasia

The involvement of vascular fibroblasts (FBs) and smooth muscle (SM)-like cells in physiological and pathological processes in large vessels (intimal hyperplasia) and microvessels (capillary arterialization), and the realization that these cells are exposed to interstitial flow shear stress (SS), motivate this study of SS on FB migratory activity. Rat adventitial FBs were grown to either 30-50% confluence (subconfluent FBs; SFBs) or full confluence (confluent FBs; CFBs) in culture. Immunofluorescence and Western blotting assays were conducted to evaluate the expression of two phenotype markers: SM alpha-actin and SM myosin heavy chain (MHC). Both assays indicated a significant increase in SM alpha-actin expression in CFBs compared with SFBs, suggesting a phenotype difference between the two cell populations. SFBs and CFBs both expressed minimal SM MHC. Both cell populations were seeded on Matrigel-coated cell culture inserts and exposed to 4 h of either 1 or 20 dyn/cm(2) SS via a rotating disk apparatus in the presence of the chemoattractant platelet-derived growth factor-BB to quantify the effect of SS on SFB and CFB migration. Four hours of 20 dyn/cm(2) SS significantly enhanced SFB migration while it suppressed CFB migratory activity. Four hours of 1 dyn/cm(2) SS did not significantly alter either SFB or CFB migration levels. Because of the distinct migratory responses of SFBs and CFBs in response to SS, phenotype modulation appears to be one way to regulate their involvement in both physiological and pathological remodeling processes.

Gene therapy of fibroproliferative vasculopathies: current ideas in molecular mechanisms and biomedical technology

Intimal hyperplasia occurs primarily as a part of the pathogenesis of coronary artery disease or secondary to therapeutic intervention in relieving vascular occlusion. Intimal hyperplasia involving vascular smooth muscle cells is found in atherosclerosis, post-balloon angioplasty restenosis, in-stent restenosis and vein graft disease, predominantly involving the use of saphenous vein conduits in coronary artery bypass grafting procedures. One potentially exciting area is that of gene therapy. Gene and protein expression patterns at the site of vasculoproliferative lesions have been widely studied and several target areas have been identified on the basis of whether the gene has an antiproliferative, proapoptotic, matrix degrading or endothelial protective action. Blood vessels are easily accessible for the delivery of the gene product, and experimental studies using animal models have used catheter-delivered gene products at the site of vascular injury. Currently, the application of antisense technology and adenoviral vector-mediated delivery has shown significant promise, albeit in in vitro or animal model settings. In this review, we discuss the current knowledge in the application of gene therapy in fibroproliferative vasculopathies. We examine some of the cellular mechanisms and intermediaries which could be potential candidates for gene targeting. We also present some of the advances in biomedical technology that might provide useful vehicles for pinpoint delivery of the gene product. Could the future of restenosis treatment be in gene therapy or is it misplaced enthusiasm?

Urokinase-type plasminogen activator deficiency (uPA-KO) prevented carotid artery ligation-induced vascular remodeling in mice

It has been demonstrated that urokinase-type plasminogen activator (uPA) plays an important role in vascular remodeling. This study was designed to determine whether uPA deficiency (KO) affects carotid artery ligation-induced vessel remodeling and the interaction with angiotensin II (Ang II). Ligation of the left common carotid artery in 6-month-old wild-type (C57 black/6J) mice for 4 weeks induced a concentric remodeling with vessel wall thickening, characterized by cell proliferation in neointima, media, and adventitia, and with lumen narrowing without a significant enlargement of overall vessel dimension. Intima lesions were characterized by alpha-actin positive smooth muscle cell (SMC) proliferation in a matrix background. No detectable presence of MAC-3 positive macrophages existed in the vascular wall. The ligation-induced vascular neointimal formation and adventitial proliferation, but not lumen narrowing and media expansion, were completely prevented in age-matched uPA-KO mice. Chronic infusion of Ang II (1.44 mg/kg per day) via a subcutaneously implanted osmotic minipump did not significantly affect the gross morphology of the nonligated carotid artery from both wild-type and uPA-KO mice, but it enhanced ligation-induced vascular remodeling. However, in the presence of Ang II, uPA deficiency had no effects on ligation-induced mophermetric change, but it partially and significantly reduced cell proliferation. These data indicate that uPA may play a critical role in ligation-induced vessel remodeling. Ang II may activate other mechanisms independent of uPA to exacerbate ligation-induced vascular remodeling.

Activation of adventitial fibroblasts contributes to the early development of atherosclerosis: A novel hypothesis that complements the “Response-to-Injury Hypothesis” and the “Inflammation Hypothesis”

The role of the adventitia in vascular function and vascular lesion formation has been largely ignored. This article introduces the hypothesis that the activation of the adventitia, specifically the fibroblasts, contributes to the formation of intimal atherosclerotic lesions. The evidence for this hypothesis includes: (a) the early proliferative changes seen in fibroblasts found in the adventitia; (b) the increase and the alteration of extracellular matrix deposition in the adventitia; (c) fibroblast differentiation into myofibroblasts and migration into the intima; and (d) fibroblast synthesis and release of cytokines that have potent effects on neighboring smooth muscle and endothelial cells prior to intimal lesion formation. In conclusion, the activation of adventitial fibroblasts is a key regulator of vascular function and structure from the "outside-in" and contributes to the development of atherosclerotic lesions. The outer location of the adventitia makes it a suitable location for drug delivery and gene therapy aimed at preventing and treating atherosclerosis.

Gingival fibroblasts inhibit MMP-1 and MMP-3 activities in an ex-vivo artery model

The main arterial pathologies can be associated with a deregulation of remodeling involving matrix metalloproteinases (MMPs), whereas gingival healing is characterized by an absence of fibrosis or irreversible elastin/collagen degradation. The aim of our study was to evaluate the effect of gingival fibroblasts on MMP-1 and MMP-3 secretion in an organotypic artery culture. MMP-1 and MMP-3 secretions and activities (dot blots, zymography, ELISA) were evaluated in coculture of rabbit artery in the presence or not of gingival fibroblasts. MMP-1/TIMP-1 and MMP-3/TIMP-1 complexes forms were measured by ELISA. Complementary studies were performed using human aortic smooth muscle cells cocultured with adventitial, dermal, or gingival fibroblasts. Our results indicated that MMP-1 and MMP-3 free-forms activities were significantly reduced in coculture. This inhibition was linked to a significant increase of TIMP-1 leading to formation of TIMP-1/MMPs complexes. Due to the presence of gingival fibroblasts, the decrease in MMP-1 and MMP-3 efficiency thus contributes to diminish the degradation of artery. This cellular therapy strategy could be promising in artery pathologies treatment.

Evidence supporting changes in Nogo-B levels as a marker of neointimal expansion but not adaptive arterial remodeling

Both neointimal hyperplasia and inward remodeling contribute to restenosis and lumen loss. Nogo-B has been recently described as an inhibitor of vascular injury and neointimal hyperplasia. To determine whether Nogo-B expression may be a mediator of inward remodeling, we examine the localization of expression of Nogo-B in an in vivo model that examines both neointimal hyperplasia and inward remodeling. The rabbit carotid artery was subjected to balloon injury, outflow branch ligation to reduce flow, or both balloon injury and reduction in flow. In balloon injury-induced neointimal hyperplasia Nogo-B expression was reduced in the intima and media but stimulated in the adventitia. In low flow-induced inward remodeling medial Nogo-B expression was not reduced and adventitial Nogo-B expression was not stimulated. Low flow significantly augmented balloon injury-induced neointimal hyperplasia and was accompanied by reduced intimal and medial Nogo-B expression, and increased adventitial Nogo-B expression in both smooth muscle cells and macrophages. Low flow-induced inward remodeling is not associated with changes in medial Nogo-B expression and is distinct from injury-induced neointimal hyperplasia. Pharmacological strategies to inhibit neointimal hyperplasia and restenosis using normal flow models may only partially account for lumen loss and therefore may not accurately predict responses in patients with extensive outflow disease.

Paclitaxel Delivered to Adventitia Attenuates Neointima Formation Without Compromising Re-Endothelialization After Angioplasty in a Porcine Restenosis Model

PURPOSE

To investigate the effect of paclitaxel delivered into the adventitia of pig femoral arteries on neointima formation and hyperplasia as well as re-endothelialization.

METHODS

Paclitaxel or vehicle was delivered into the adventitia of pig femoral arteries using a needle injection catheter following balloon overstretch. Arteries were then serially examined by angiography, Evan's blue staining, morphometry, and immunohistochemistry for up to 12 weeks.

RESULTS

Local adventitial delivery of paclitaxel significantly attenuated neointima formation. The area of neointima (0.41+/-0.17 versus 2.75+/-0.81 mm(2), p<0.01), the ratio of intima to media (0.12+/-0.05 versus 0.86+/-0.35, p<0.05), and the degree of stenosis (12.80%+/-3.13% versus 47.06%+/-7.25%, p<0.01) were significantly lower in the paclitaxel-treated group compared to controls. Furthermore, cell proliferation was significantly diminished following adventitial delivery of paclitaxel from day 3 to 21 compared to controls. Complete re-endothelialization was observed 3 weeks after intervention in both groups of arteries treated with paclitaxel or vehicle alone.

CONCLUSION

Paclitaxel delivered into the adventitia of pig femoral arteries effectively attenuates neointima formation after angioplasty without compromising re-endothelialization. Adventitial drug delivery may therefore be an alternative to drug-eluting stents for the prevention of restenosis.

Controversies in the Use of Intraluminal Shunts During Off-Pump Coronary Artery Bypass Grafting Surgery

Technical advances have made the performance of multivessel off-pump coronary artery bypass feasible. Snaring and intraluminal shunts are the techniques used for vascular control. Snaring provides a bloodless surgical field, is usually well tolerated by the patient, and is supported by years of clinical experience. Intraluminal shunts aim to achieve hemostasis at the arteriotomy site and to allow antegrade flow to provide myocardial protection. There are unresolved issues regarding whether shunts have a clinical benefit, do provide adequate flow to provide myocardial protection, and whether they cause significant endothelial damage. In this article, we have reviewed the literature to lend perspective to these issues.

Hemodialysis vascular access dysfunction: a cellular and molecular viewpoint

Hemodialysis vascular access dysfunction is a major cause of morbidity and hospitalization in the hemodialysis population. The major cause of hemodialysis vascular access dysfunction is venous stenosis as a result of neointimal hyperplasia. Despite the magnitude of the clinical problem, however, there has been a paucity of novel therapeutic interventions in this field. This is in marked contrast to a recent plethora of targeted interventions for the treatment of arterial neointimal hyperplasia after coronary angioplasty. The reasons for this are two-fold. First there has been a relative lack of cellular and molecular research that focuses on venous neointimal hyperplasia in the specific setting of hemodialysis vascular access. Second, there have been inadequate efforts by the nephrology community to translate the recent advances in molecular and interventional cardiology into therapies for hemodialysis vascular access. This review therefore (1) briefly examines the different forms of hemodialysis vascular access that are available, (2) describes the pathology and pathogenesis of hemodialysis vascular access dysfunction in both polytetrafluoroethylene grafts and native arteriovenous fistulae, (3) reviews recent concepts about the pathogenesis of vascular stenosis that could potentially be applied in the setting of hemodialysis vascular access dysfunction, (4) summarizes novel experimental and clinical therapies that could potentially be used in the setting of hemodialysis vascular access dysfunction, and, finally, (5) offers some broad guidelines for future innovative translational and clinical research in this area that hopefully will reduce the huge clinical morbidity and economic costs that are associated with this condition.

C-type natriuretic peptide for reduction of restenosis: gene transfer is superior over single peptide administration

BACKGROUND

Restenosis is still a significant clinical problem limiting the long-term therapeutic success following balloon dilation or stent implantation. New approaches are necessary inhibiting neointima formation and simultaneously promoting re-endothelialization. Therefore, long-term therapeutic effects of adventitial liposome-mediated C-type natriuretic protein (CNP) gene and CNP peptide applications in a porcine model for restenosis post-angioplasty were investigated.

METHODS

For in vitro applications, primary cultures of porcine vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) were used. Gene transfer was performed with cationic lipid DOCSPER [1,3-dioleoyloxy-2-(N5-carbamoylspermine)propane]. In vivo treatment of pig femoral arteries was adventitial using a needle injection catheter following balloon angioplasty. Arteries were investigated by angiography, Evan's blue staining, histomorphometry, immunohistochemistry, PCR and RT-PCR.

RESULTS

Using CNP gene transfer in vitro, 29.4+/-7.2% reduction of cell proliferation in VSMCs was observed. In ECs, the CNP gene did not compromise cellular growth. For the CNP peptide the optimal concentration was 1 mM with 50.7+/-11.3% reduction of VSMC proliferation and 12.1+/-5.3% enhancement of growth of ECs. Three weeks following application in vivo complete re-endothelialization was observed in all treated groups. At 3 months significant reduction of neointima formation was observed using CNP gene vs. CNP peptide (85.9+/-7.8% vs. 63.3+/-27.6% reduction, P<0.05) compared to control treatment.

CONCLUSION

Periadventitial liposome-mediated CNP gene transfer in vivo resulted in a significant long-term reduction of neointima formation without compromising endothelial repair and was superior over single CNP peptide administration. Advantages of CNP are its physiological origin and simultaneous inhibition of VSMC proliferation and promotion of EC growth.

Role of the adventitia in pulmonary vascular remodeling

An increasing volume of experimental data indicates that the adventitial fibroblast, in both the pulmonary and systemic circulations, is a critical regulator of vascular wall function in health and disease. A rapidly emerging concept is that the vascular adventitia acts as biological processing center for the retrieval, integration, storage, and release of key regulators of vessel wall function. In response to stress or injury, resident adventitial cells can be activated and reprogrammed to exhibit different functional and structural behaviors. In fact, under certain conditions, the adventitial compartment may be considered the principal injury-sensing tissue of the vessel wall. In response to vascular stresses such as overdistension and hypoxia, the adventitial fibroblast is activated and undergoes phenotypic changes, which include proliferation, differentiation, upregulation of contractile and extracellular matrix proteins, and release of factors that directly affect medial smooth muscle cell tone and growth and that stimulate recruitment of inflammatory and progenitor cells to the vessel wall. Each of these changes in fibroblast phenotype modulates either directly or indirectly changes in overall vascular function and structure. The purpose of this review is to present the current evidence demonstrating that the adventitial fibroblast acts as a key regulator of pulmonary vascular function and structure from the "outside-in."

Urokinase plasminogen activator in injured adventitia increases the number of myofibroblasts and augments early proliferation

Myofibroblasts are involved in vessel remodeling during the development of hypertension as well as after angioplasty and aortocoronary grafting, but the mechanisms of myofibroblastic phenotypic modulation are not fully elucidated. We assessed the role of urokinase plasminogen activator (uPA) and its proteolytic activity in myofibroblast differentiation and the early proliferation following mechanical injury of the rat carotid adventitia. The effects of perivascular application of recombinant uPA (r-uPA), proteolytically inactive r-uPA(H/Q) and uPA neutralizing antibody were evaluated 4 days after surgical injury to the adventitia. The phenotype of adventitial cells was assessed using anti-alpha-smooth muscle actin (alpha-SM actin) antibody, anti-SM heavy chain myosin, anti-high-molecular-weight caldesmon, anti-smoothelin and anti-ED-1 antibodies, proliferation by the expression of proliferating cell nuclear antigen, and the size of the adventitia by quantitative morphometry. Four days after injury, the intensive immunostaining for urokinase appeared in the rat carotid artery adventitia. At the same time, the frequency of alpha-SM actin-positive adventitial cells was 1.8+/-1.1% in uninjured arteries and 25.2+/-5.4% in injured arteries (p<0.05), and the respective frequency of ED-1-positive cells 1.5+/-1.1 and 25.0+/-5.2%. The application of exogenous r-uPA doubled the numbers of alpha-SM actin-positive adventitial cells to 55.7+/-6.8% (p<0.05). ED-1-positive cells and proliferating cell nuclear antigen-positive cells as well as the size of the adventitia were also significantly increased after r-uPA compared with injury alone. In contrast, the proteolytically inactive r-uPA(H/Q) did not affect any parameters. The application of uPA neutralizing antibody attenuated the frequency of alpha-SM actin-positive cells to 12.6+/-3.5% (p<0.05), the frequency of ED-1-positive cells, and the numbers of adventitial cells. r-uPA stimulation of cultured human skin fibroblasts significantly increased the alpha-SM actin content in a concentration-dependent manner. In contrast, r-uPAH/Q did not induce changes in alpha-SM actin content. We conclude that uPA, which is upregulated in the injured adventitia, can augment adventitial cell accumulation, including myofibroblasts, and adventitia growth early after injury of the rat carotid artery adventitia by mechanisms involving proteolysis.

Perivascular paclitaxel wraps block arteriovenous graft stenosis in a pig model

BACKGROUND

Haemodialysis vascular access dysfunction is currently a huge clinical problem. In an attempt to reduce the morbidity associated with haemodialysis vascular access dysfunction, we have previously developed and validated a local perivascular paclitaxel release system that has been shown to release paclitaxel for at least 3 weeks. The aim of the current study was to evaluate the in vivo use of these perivascular wraps (for both safety and efficacy) at different time points in our pig model of arteriovenous graft stenosis.

METHODS

Paclitaxel-loaded ethylene vinyl acetate wraps were placed around the graft-vein anastomosis on one side, with control polymers being placed on the contralateral side in our pig model of arteriovenous graft stenosis. Animals were sacrificed at early (10-11 days), middle (23-24 days) and late (32-38 days) time points. The entire graft-vein anastomosis was removed at the time of sacrifice and assessed for the extent of luminal stenosis using histomorphometric techniques.

RESULT

Graft-vein anastomoses treated with the paclitaxel-loaded polymers had an almost complete absence of luminal stenosis at the middle (23-24 days) and late (32-38 days) time points (when one would expect the development of neointimal hyperplasia) as compared with the contralateral control graft-vein anastomoses (37.90% luminal stenosis in the controls vs 0.10% in the paclitaxel group). There were minimal local side effects from this procedure.

CONCLUSIONS

Our results demonstrate the safety and efficacy of paclitaxel-loaded perivascular wraps in the setting of a pig model of arteriovenous graft stenosis. We believe that such a local approach which could be easily applied at the time of surgery is ideally suited for use in the clinical setting of haemodialysis vascular access dysfunction. It is likely that this novel approach could result in a significant reduction in the huge economic and health morbidity costs currently associated with this recalcitrant clinical problem.

Intramural Stress Increases Exponentially with Stent Diameter: A Stress Threshold for Neointimal Hyperplasia

PURPOSE

Techniques designed to increase initial luminal diameter during stent implantation may ultimately lead to early restenosis by causing substantial vessel wall trauma and promoting neointimal hyperplasia. The purpose of this study was to evaluate the impact of stent oversizing on resultant arterial wall stress concentrations and examine the concept of a "stress threshold" for neointimal hyperplasia development.

MATERIALS AND METHODS

A previously described three-dimensional large-strain hyperelastic numeric model was used to examine the nonlinear isotropic behavior of a 6-mm-diameter artery during stent deployment. An in situ axial prestretch of 10% and a mean arterial pressure of 100 mm Hg (13.3 kPa) were applied before stepwise expansion of a simulated Palmaz-Schatz stent to a diameter 30% greater than that of the native artery. The variation of arterial wall von Mises stresses with percentage diameter inflation was then compared with the known distribution of stent-induced neointimal hyperplasia.

RESULTS

The order in which location-specific peak stresses exceeded a predetermined stress threshold was constant: the stent ends surpassed the threshold first, followed by the stent cross-links, then the stent struts, and finally the bare area between the stent struts. These locations corresponded in order to the most common locations of intimal proliferation after stent deployment. An exponential relationship between peak stress concentration and percent stent inflation was formulated.

CONCLUSIONS

Stent-induced intramural stress injury beyond a certain threshold may cause early restenosis by triggering neointimal hyperplasia. Maximum stress concentrations increase exponentially with stent deployment diameter, highlighting the importance of minimal stent overexpansion and novel stent designs that specifically address peak stress reduction.

Application to Vascular Adventitia of a Nonviral Vector for TIMP-1 Gene Therapy to Prevent Intimal Hyperplasia

Somatic gene transfer continues to have potential for the study and therapy of cardiovascular disease. We have developed a modular, self-assembling, nonviral system consisting of Lipofectin, integrin-targeting peptides, and plasmid DNA (LID) and we have applied this to a model of vascular injury, rat carotid angioplasty. Marker gene studies identified transfection of adventitial cells after vector delivery to that layer. Human tissue inhibitor of metalloproteinase-1 (hTIMP-1) was tested as a therapeutic gene product after direct application to the exposed adventitial layer. Vascular LID.hTIMP-1 transfection was confirmed by polymerase chain reaction and gene expression by immunohistochemistry at 7 days. Neointimal areas were 0.160 +/- 0.078 and 0.225 +/- 0.052 mm(2) for LID.hTIMP-1-transfected (n = 14) and LID.pCI-transfected (n = 12) vessels, respectively, at 14 days, and 0.116 +/- 0.068 mm(2) (n = 14) and 0.194 +/- 0.095 mm(2) (n = 14), respectively, at 28 days, representing a 29 and 40% reduction in neointimal hyperplasia at 14 and 28 days, respectively, after balloon dilatation. Neointima-to-media ratios were similarly reduced. In addition, expansile remodeling after balloon injury was inhibited at 14 days, the area within the external elastic lamina being 0.50 +/- 0.02 and 0.61 +/- 0.02 mm(2) in LID.hTIMP-1- and LID.pCI-transfected arteries, respectively (p < 0.0005). We have demonstrated an effective system of therapeutic gene transfer, particularly targeting the arterial adventitia, where transfer of genes involved in matrix remodeling and cell migration may be useful.

Adventitial delivery of dominant-negative p67phox attenuates neointimal hyperplasia of the rat carotid artery

Several essential components of NADPH oxidase, including p22phox, gp91phox (nox2) and its homologs nox1 and nox4, p47phox, p67phox, and rac1, are present in the vasculature. We previously reported that p67phox is essential for adventitial fibroblast NADPH oxidase O2- production. Thus we postulated that inhibition of adventitial p67phox activity would attenuate angioplasty-induced hyperplasia. To test this hypothesis, we treated the adventitia of carotid arteries with a control adenovirus (Ad-control), a virus expressing dominant-negative p67phox (Ad-p67dn), or a virus expressing a competitive peptide (gp91ds) targeting the p47phox-gp91phox interaction (Ad-gp91ds). Common carotid arteries (CCAs) from male Sprague-Dawley rats were transfected with Ad-control, Ad-p67dn, or Ad-gp91ds in pluronic gel. After 2 days, a 2-F (Fogarty) catheter was used to injure CCAs in vivo. After 14 days, CCAs were perfusion-fixed and analyzed. In 13 experiments, digital morphometry suggested a reduction of neointimal hyperplasia with Ad-p67dn compared with Ad-control; however, the reduction did not reach statistical significance (P = 0.058). In contrast, a significant reduction was achieved with Ad-gp91ds (P = 0.006). No changes in medial area or remodeling were observed with either treatment. Moreover, adventitial fibroblast proliferation in vitro was inhibited by Ad-gp91ds but not by Ad-p67dn, despite confirmation that Ad-p67dn inhibits NADPH oxidase in fibroblasts. These data appear to suggest that a multicomponent vascular NADPH oxidase plays a role in neointimal hyperplasia. However, inhibition of p47phox may be more effective than inhibition of p67phox at attenuating neointimal growth.