Histopathology of in-stent restenosis in patients with peripheral artery disease

Disappearance of a small intracranial aneurysm as a result of vessel straightening and in-stent stenosis following use of an Enterprise vascular reconstruction device

In-stent stenosis after stent-assisted coil embolization is a rare but well-known complication. A 32-year-old woman with an unruptured wide-necked left internal carotid artery (ICA) terminus aneurysm and an ipsilateral very small anterior choroidal artery aneurysm underwent stent-assisted coil embolization for the ICA terminus aneurysm. The 4-month follow-up angiography revealed diffuse in-stent stenosis and disappearance of the untreated anterior choroidal artery aneurysm, retaining the patency of the anterior choroidal artery. To our knowledge, this is the first report to demonstrate the course of in-stent stenosis and disappearance of an untreated small intracranial aneurysm as a result. We report this unique case and discuss the interesting mechanism underlying this phenomenon, and also provide a review of the relevant literature.

Muscle-derived stem cells promote angiogenesis and attenuate intimal hyperplasia in different murine vascular disease models

Muscle-derived stem cells (MDSCs) are known to promote angiogenesis, but have never been studied in vascular diseases. We differentiated MDSCs into endothelial lineage cells in vitro by stimulation with shear stress and vascular endothelial growth factor. Such differentiated MDSCs (diff-MDSC) showed strong angiogenic potential in vitro. When tested in ischemic hindlimbs of mice, diff-MDSCs increased perfusion and decreased necrosis of the ischemic limbs, by promoting new vessel formation and by upregulating genes involved in endothelial expression. Such effects were not observed with native MDSCs (without endothelial stimulation in vitro). Diff-MDSCs were also injected into carotid arteries of rats after balloon denudation of the intima layer to induce intimal hyperplasia. The cell-treated group had significantly reduced intima-to-media thickness ratio compared to control, thus attenuating intimal hyperplasia by early re-endothelialization of the intima layer. Our findings suggest that MDSCs are a potential source of stem cell therapy for treatment of various vascular diseases, by inducing angiogenesis to improve perfusion in sites of ischemia, and by preventing intimal hyperplasia in sites of vessel injury.

Macrophage proliferation and apoptosis in atherosclerosis

PURPOSE OF REVIEW

Atherosclerosis is driven by cardiovascular risk factors that cause the recruitment of circulating immune cells beneath the vascular endothelium. Infiltrated monocytes differentiate into different macrophage subtypes with protective or pathogenic activities in vascular lesions. We discuss current knowledge about the molecular mechanisms that regulate lesional macrophage proliferation and apoptosis, two processes that occur during atherosclerosis development and regulate the number and function of macrophages within the atherosclerotic plaque.

RECENT FINDINGS

Lesional macrophages in early phases of atherosclerosis limit disease progression by phagocytizing modified lipoproteins, cellular debris and dead cells that accumulate in the plaque. However, macrophages in advanced lesions contribute to a maladaptive, nonresolving inflammatory response that can lead to life-threatening acute thrombotic diseases (myocardial infarction or stroke). Macrophage-specific manipulation of genes involved in cell proliferation and apoptosis modulates lesional macrophage accumulation and atherosclerosis burden in mouse models, and studies are beginning to elucidate the underlying mechanisms.

SUMMARY

Despite recent advances in our understanding of macrophage proliferation and apoptosis in atherosclerotic plaques, it remains unclear whether manipulating these processes will be beneficial or harmful. Advances in these areas may translate into more efficient therapies for the prevention and treatment of atherothrombosis.

In-stent stenosis of stent-assisted coil embolization of the supraclinoid internal carotid artery aneurysm

The intracranial stent functions primarily to prevent protrusion of coils into the parent vessel during the embolization of wide-necked cerebral aneurysms and might also reduce aneurysm recanalization rate. In spite of these advantages, little is known about the long-term interaction of the stent with the parent vessel wall. We present a rare case of severe in-stent stenosis occurring as a delayed complication of Neuroform stent-assisted coil embolization of an unruptured intracranial aneurysm.

Vinpocetine suppresses pathological vascular remodeling by inhibiting vascular smooth muscle cell proliferation and migration

Abnormal vascular smooth muscle cell (SMC) activation is associated with various vascular disorders such as atherosclerosis, in-stent restenosis, vein graft disease, and transplantation-associated vasculopathy. Vinpocetine, a derivative of the alkaloid vincamine, has long been used as a cerebral blood flow enhancer for treating cognitive impairment. However, its role in pathological vascular remodeling remains unexplored. Herein, we show that systemic administration of vinpocetine significantly reduced neointimal formation in carotid arteries after ligation injury. Vinpocetine also markedly decreased spontaneous remodeling of human saphenous vein explants in ex vivo culture. In cultured SMCs, vinpocetine dose-dependently suppressed cell proliferation and caused G1-phase cell cycle arrest, which is associated with a decrease in cyclin D1 and an increase in p27Kip1 levels. In addition, vinpocetine dose-dependently inhibited platelet-derived growth factor (PDGF)-stimulated SMC migration as determined by the two-dimensional migration assays and three-dimensional aortic medial explant invasive assay. Moreover, vinpocetine significantly reduced PDGF-induced type I collagen and fibronectin expression. It is noteworthy that PDGF-stimulated phosphorylation of extracellular signal-regulated kinases 1/2 (ERK1/2), but not protein kinase B, was specifically inhibited by vinpocetine. Vinpocetine powerfully attenuated intracellular reactive oxidative species (ROS) production, which largely mediates the inhibitory effects of vinpocetine on ERK1/2 activation and SMC growth. Taken together, our results reveal a novel function of vinpocetine in attenuating neointimal hyperplasia and pathological vascular remodeling, at least partially through suppressing ROS production and ERK1/2 activation in SMCs. Given the safety profile of vinpocetine, this study provides insight into the therapeutic potential of vinpocetine in proliferative vascular disorders.

In vitro study of role of trace amount of Cu release from Cu-bearing stainless steel targeting for reduction of in-stent restenosis

A novel 316L type Cu-bearing stainless steel was developed in present work, aiming at reducing the occurrence of the in-stent restenosis after implantations of coronary stents, through trace amount of Cu release from surface of the steel in body fluid. It was found that there was a trace amount of Cu released from the Cu-bearing steel in a simulated body fluid, with no cytotoxicity. All the in vitro experimental results proved that this Cu-bearing steel could not only inhibit the proliferation of vascular smooth muscle cells, reducing the formation of thrombosis, which are the main reasons for happening of the in-stent restenosis, but also promote the proliferation of vascular endothelial cells needed for the revascularization, showing that this novel steel is prospective to be a new material for manufacturing coronary stents with function of reducing the in-stent restenosis.

Dual roles of hyaluronic acids in multilayer films capturing nanocarriers for drug-eluting coatings

We developed hyaluronic acid (HA)-based multilayer films capturing polymeric nanocarriers (NCs) for drug delivery. The electrostatic interactions between positively charged linear polyethylene imines (LPEI) and negatively charged HAs are the main driving forces to form multilayers based on the layer-by-layer (LbL) deposition. NCs were easily incorporated within the multilayer film due to intra- and/or inter-hydrogen bonding among HA chains. The amount of NCs captured by the HA chains was varied by the ratio between HAs and NCs as well as the length (i.e., molecular weight) and absolute number density of HAs in solution. Biocompatibility of the NC-capturing HA multilayer films was tested with the human dermal fibroblast (HDF) culture. In addition, the controlled release of paclitaxel (PTX) from the HA multilayer films successfully led to the apoptosis of human aortic smooth muscle cells (hSMC) in vitro, implying that the NC-capturing HA multilayer films would be quite useful as drug-eluting stent systems to prevent the restenosis after surgery.

Histological examination of vascular lesions caused by stent implantation in humans and in comparative experimental animal model

A comparative analysis of human and experimental animal (canine) tissues was performed to characterize and describe cellular and histological responses during the processes of newly forming intravascular tissues after stent implantation. Routine histological and immunohistochemical evaluation of 20 human samples and 9 samples from animal models were used one day, one week and one month after the stent implantation. After one day of implantation, there was no difference between the human and canine peripheral arteries, suggesting a similar cellular and histological response in the early phase. In contrast, after one week of implantation, during the proliferative phase the repairing human tissue showed less intensive production of inflammatory cells and more intensive increase in number of vascular cells than did the canine model. In addition, cellular changes normally restituted by the end of one month in canine peripheral arteries, but vascular cells persisted in human atherosclerotic arteries. In conclusion, results of this study suggest differences in both phases of vascular repair in the post-stented period, because both proliferative and regressive phases showed histological differences in canine and human samples. In canine, the restitution of vascular wall was completed by the end of first month but persistent vascular cell proliferation was visible in the human peripheral arteries. It can be suggested that delayed cellular response might indicate restenosis but also can be considered considered as a progression of the original arterial disease.

IκBNS regulates interleukin-6 production and inhibits neointimal formation after vascular injury in mice

AIMS

IκBNS regulates a subset of Toll-like receptor (TLR)-dependent genes including interleukin-6 (IL-6) by inhibiting nuclear factor-κB (NF-κB). IL-6 is an inflammatory biomarker for cardiovascular diseases. The aim of this study was to determine whether IκBNS changes arterial inflammation and intimal hyperplasia after vascular injury.

METHODS AND RESULTS

We investigated neointimal formation in IκBNS-deficient (IκBNS(-/-); C57BL/6 background) and wild-type (IκBNS(+/+)) mice 2 weeks after cuff injury. The mean intimal area and the intima/media ratio of IκBNS(-/-) mice increased 89% (8066 ± 1141 vs. 4267 ± 1095 μm(2); P = 0.027) and 100% (0.72 ± 0.13 vs. 0.36 ± 0.09; P = 0.032) compared with IκBNS(+/+) mice. We observed significant up-regulation of TLR4 in injured arteries of IκBNS(-/-) mice. NF-κB activity in the intima of IκBNS(-/-) mice was 5.1-fold higher (P = 0.008) compared with IκBNS(+/+) mice at 7 days post-injury. IL-6 mRNA levels in injured arteries of IκBNS(-/-) mice were 1.8-fold higher (P = 0.002) compared with those of IκBNS(+/+) mice at 3 days post-injury. Vascular smooth muscle cells from IκBNS(-/-) mice showed a significant increase in cell migration compared with those from IκBNS(+/+) mice after IL-6 stimulation in the scratch-wound healing assay. Furthermore, anti-mouse IL-6 receptor antibody (MR16-1) significantly reduced intimal hyperplasia compared with control IgG injection in IκBNS(-/-) mice. These findings suggest that IL-6 participates in the development of neointimal hyperplasia after vascular injury in IκBNS(-/-) mice.

CONCLUSION

IκBNS down-regulates TLR4 expression, NF-κB activity, and IL-6 production after vascular injury. IκBNS might suppress intimal hyperplasia caused by vascular inflammation such as atherosclerosis, and restenosis after angioplasty.

Progenitor cells in pulmonary vascular remodeling

Pulmonary hypertension is characterized by cellular and structural changes in the walls of pulmonary arteries. Intimal thickening and fibrosis, medial hypertrophy and fibroproliferative changes in the adventitia are commonly observed, as is the extension of smooth muscle into the previously non-muscularized vessels. A majority of these changes are associated with the enhanced presence of α-SM-actin+ cells and inflammatory cells. Atypical abundances of functionally distinct endothelial cells, particularly in the intima (plexiform lesions), and also in the perivascular regions, are also described. At present, neither the origin(s) of these cells nor the molecular mechanisms responsible for their accumulation, in any of the three compartments of the vessel wall, have been fully elucidated. The possibility that they arise from either resident vascular progenitors or bone marrow-derived progenitor cells is now well established. Resident vascular progenitor cells have been demonstrated to exist within the vessel wall, and in response to certain stimuli, to expand and express myofibroblastic, endothelial or even hematopoietic markers. Bone marrow-derived or circulating progenitor cells have also been shown to be recruited to sites of vascular injury and to assume both endothelial and SM-like phenotypes. Here, we review the data supporting the contributory role of vascular progenitors (including endothelial progenitor cells, smooth muscle progenitor cells, pericytes, and fibrocytes) in vascular remodeling. A more complete understanding of the processes by which progenitor cells modulate pulmonary vascular remodeling will undoubtedly herald a renaissance of therapies extending beyond the control of vascular tonicity and reduction of pulmonary artery pressure.

In-stent stenosis of stent assisted endovascular treatment on intracranial complex aneurysms

OBJECTIVE

To introduce the frequency and segment analysis of in-stent stenosis for intracranial stent assisted endovascular treatment on complex aneurysms.

METHODS

A retrospective study was performed in 158 patients who had intracranial complex aneurysms and were treated by endovascular stent application with or without coil embolization. Of these, 102 patients were evaluated with catheter based angiography after 6, 12, and 18 months. Aneurysm location, using stent, time to stenosis, stenosis rate and narrowing segment were analyzed.

RESULTS

Among follow-up cerebral angiography done in 102 patients, 8 patients (7.8%) were shown an in-stent stenosis. Two patients have unruptured aneurysm and six patients have ruptured one. Number of Neuroform stents were 7 cases (7.5%) and Enterprise stent in 1 case (11.1%). Six patients demonstrated in-stent stenosis at 6 months after stent application and remaining two patients were shown at 12 months, 18 months, respectively.

CONCLUSION

In-stent stenosis can be confronted after intracranial stent deployment. In our study, no patient showed symptomatic stenosis and there were no patients who required to further treatment except continuing antiplatets medication. In-stent stenosis has been known to be very few when they are placed into the non-pathologic parent artery during the complex aneurysm treatment, but the authors found that it was apt to happen on follow up angiography. Although the related symptom was not seen in our cases, the luminal narrowing at the stented area may result the untoward hemodynamic event in the specific condition.

Electrical stimulation inhibits neointimal hyperplasia after abdominal aorta balloon injury through the PTEN/p27Kip1 pathway

Electric fields (EFs) exert biological effects on promoting wound healing by facilitating cell division, cell proliferation, and cell directional migration toward the wound. In this study, we examined the inhibitory effect of direct-current (DC) EFs on the formation of neointimal hyperplasia and the possible mechanism in an abdominal aorta balloon injury rabbit model. Sixty rabbits were divided into normal, control, and experimental groups. After establishment of the abdominal aorta balloon injury model, electrodes were implanted into the bilateral psoas major muscle in control and experimental groups. Only the experimental group received electric stimulation (EFs applied at 3 or 4 V/cm for 30 min/day) for 1, 2, and 4 weeks, respectively. Neointimal hyperplasia of the abdominal aorta and proliferation of vascular smooth muscle cells (VSMCs) were measured. Expressions of collagen, p27(Kip1), and phosphatase and tensin homolog deleted on chromosome 10 (PTEN) were detected. Results showed that the ratio of the tunica intima area to the tunica media area, the expression of type-I collagen in the neointimal, and the proliferating cell nuclear antigen index in experimental groups were significantly less than those in control groups 2 weeks post-operation (P< 0.01). Expressions of p27(Kip1) and PTEN were increased in experimental groups compared with control groups (P< 0.01). In conclusion, our results suggested that the application of DC EFs could inhibit neointimal hyperplasia and reduce collagen expression after abdominal aorta balloon injury. This was probably induced by upregulation of PTEN/p27(Kip1) expression, thereby inhibiting VSMC proliferation.

The role of endothelial cells and their progenitors in intimal hyperplasia

Intimal hyperplasia leading to restenosis is the major process that limits the success of cardiovascular intervention. The emergence of vascular progenitor cells and, in particular, endothelial progenitor cells has led to great interest in their potential therapeutic value in preventing intimal hyperplasia. We review the mechanism of intimal hyperplasia and highlight the important attenuating role played by a functional endothelium. The role of endothelial progenitor cells in maintaining endothelial function is reviewed and we describe how reduced progenitor cell number and function and reduced endothelial function lead to an increased risk of intimal hyperplasia. We review other potential sources of endothelial cells, including monocytes, mesenchymal stem cells and tissue resident stem cells. Endothelial progenitor cells have been used in clinical trials to reduce the risk of restenosis with varied success. Progenitor cells have huge therapeutic potential to prevent intimal hyperplasia but a more detailed understanding of vascular progenitor cell biology is necessary before further clinical trials are commenced.

Regulatory polymorphism in transcription factor KLF5 at the MEF2 element alters the response to angiotensin II and is associated with human hypertension

Krüppel-like factor 5 (KLF5) is a zinc-finger-type transcription factor that mediates the tissue remodeling in cardiovascular diseases, such as atherosclerosis, restenosis, and cardiac hypertrophy. Our previous studies have shown that KLF5 is induced by angiotensin II (AII), although the precise molecular mechanism is not yet known. Here we analyzed regulatory single nucleotide polymorphisms (SNPs) within the KLF5 locus to identify clinically relevant signaling pathways linking AII and KLF5. One SNP was located at -1282 bp and was associated with an increased risk of hypertension: subjects with the A/A and A/G genotypes at -1282 were at significantly higher risk for hypertension than those with the G/G genotype. Interestingly, a reporter construct corresponding to the -1282G genotype showed much weaker responses to AII than a construct corresponding to -1282A. Electrophoretic mobility shift, chromatin immunoprecipitation, and reporter assays collectively showed that the -1282 SNP is located within a functional myocyte enhancer factor 2 (MEF2) binding site, and that the -1282G genotype disrupts the site and reduces the AII responsiveness of the promoter. Moreover, MEF2 activation via reactive oxygen species and p38 mitogen-activated protein kinase induced KLF5 expression in response to AII, and KLF5 and MEF2 were coexpressed in coronary atherosclerotic plaques. These results suggest that a novel signaling and transcription network involving MEF2A and KLF5 plays an important role in the pathogenesis of cardiovascular diseases such as hypertension.

Control of cell proliferation in atherosclerosis: insights from animal models and human studies

Excessive hyperplastic cell growth within occlusive vascular lesions has been recognized as a key component of the inflammatory response associated with atherosclerosis, restenosis post-angioplasty, and graft atherosclerosis after coronary artery bypass. Understanding the molecular mechanisms that regulate arterial cell proliferation is therefore essential for the development of new tools for the treatment of these diseases. Mammalian cell proliferation is controlled by a large number of proteins that modulate the mitotic cell cycle, including cyclin-dependent kinases, cyclins, and tumour suppressors. The purpose of this review is to summarize current knowledge about the role of these cell cycle regulators in the development of native and graft atherosclerosis that has arisen from animal studies, histological examination of specimens from human patients, and genetic studies.

GLUT1-induced cFLIP expression promotes proliferation and prevents apoptosis in vascular smooth muscle cells

Enhanced expression of the facilitative glucose transporter, GLUT1, has been shown to inhibit apoptosis in several cell systems including vascular smooth muscle cells (VSMCs). A decrease in apoptosis could lead to increased VSMC numbers in neointimal and medial arterial layers under several pathologic conditions. The hypothesis underlying these studies is that GLUT1 induces expression of antiapoptotic and prosurvival genes that increase VSMC survival. Transcriptomic analysis of A7r5 VSMCs, in which GLUT1 was acutely overexpressed, showed a 2.14-fold increase in c-FLICE inhibitory protein (cFLIP), which promotes cellular growth and prevents apoptosis through caspase 8 binding. We confirmed that overexpression of GLUT1 induced mRNA and protein expression of both the long and short isoforms of cFLIP (cFLIP(L) and cFLIP(S)) in primary and stable immortalized VSMC lines as well as in aortas from GLUT1 transgenic mice. Increased GLUT1 reduced VSMC death by more than twofold after serum withdrawal, as evidenced by decreased caspase 3 activity and Trypan blue exclusion studies. GLUT1 overexpression resulted in a greater than twofold increase in proliferating cell nuclear antigen expression and live cell numbers, consistent with augmented VSMC proliferation. Lentiviral knockdown of cFLIP(L) showed that cFLIP(L) was necessary for the proproliferative and antiapoptotic effects of GLUT1 overexpression. Taken together, these data suggest that GLUT1 induction of cFLIP(L) expression augments proliferation and prevents apoptosis in VSMCs.

Characterization of primary and restenotic atherosclerotic plaque from the superficial femoral artery: Potential role of Smad3 in regulation of SMC proliferation

OBJECTIVE

To characterize and compare primary and restenotic lesions of the superficial femoral artery and analyze the contribution of TGF-beta/Smad3 signaling to the pathophysiology of peripheral artery occlusive disease.

METHODS AND RESULTS

Immunohistochemical studies were performed on specimens retrieved from the superficial femoral artery of patients undergoing either atherectomy for primary atherosclerotic or recurrent disease after stenting and/or prior angioplasty. Immunohistochemical analysis revealed a significantly higher smooth muscle cell (SMC) content (alpha-actin+) and expression of Smad3 in restenotic lesions while primary lesions contained significantly more leukocytes (CD45+) and macrophages (CD68+). Further studies demonstrated colocalization of Smad3 with alpha-actin and PCNA, suggesting a role for Smad3 in the proliferation observed in restenotic lesions. To confirm a role for Smad3 in SMC proliferation, we both upregulated Smad3 via adenoviral mediated gene transfer (AdSmad3) and inhibited Smad3 through transfection with siRNA in human aortic SMCs, then assessed cell proliferation with tritiated thymidine. Overexpression of Smad3 enhanced whereas inhibition of Smad3 decreased cell proliferation.

CONCLUSION

Differences in cellular composition and cell proliferation in conjunction with the finding that Smad3 is expressed exclusively in restenotic disease suggest that TGF-beta, through Smad3 signaling, may play an essential role in SMC proliferation and the pathophysiology of restenosis in humans.

Contribution of circulating vascular progenitors in lesion formation and vascular healing: lessons from animal models

PURPOSE OF REVIEW

It is a widely accepted view that vascular repair results from migration and proliferation of adjacent cells in animal models. On the contrary, accumulating evidence suggests that bone marrow can give rise to endothelial-like cells and smooth muscle like cells that potentially contribute to vascular healing, remodeling, and lesion formation under physiological and pathological conditions. The aim of this article is to review recent findings obtained from animal models of vascular diseases regarding bone marrow derived progenitor cells.

RECENT FINDINGS

Studies using chimeric animals revealed that bone marrow derived cells exist at the sites of vascular healing and lesion formation after injury. High-resolution histological analyses revealed that those bone marrow derived cells do express some markers for endothelial cells or smooth muscle cells. Peripheral mononuclear cells could differentiate into endothelial-like cells or smooth muscle like cells in vitro according to the culture conditions.

SUMMARY

Circulating progenitors significantly contribute to vascular repair and lesion formation. These findings provide the basis for the development of new therapeutic strategies that involve targeting the mobilization, homing, differentiation, and proliferation of bone marrow- derived vascular progenitor cells.

Negative regulation of quinone reductase 2 by resveratrol in cultured vascular smooth muscle cells

1. Resveratrol, a polyphenol in red wine, has a cardioprotective effect. Resveratrol-targeting protein (RTP) has been purified using a resveratrol affinity column (RAC) and has been identified as quinone reductase type 2 (NQO2). We hypothesize that NQO2 is the target protein of resveratrol in vascular smooth muscle cells (VSMC) and that resveratrol inhibits proliferation of VSMC through its action on NQO2. In the present study, we investigated the correlation between NQO2 regulation and cell proliferation in VSMC in response to resveratrol treatment. 2. The RTP was purified using RAC and was detected with a NQO2 polyclonal antibody. The VSMC were incubated with resveratrol (1, 10 and 50 micromol/L) for 24, 48 and 72 h. Cell proliferation was detected by cell counting and bromodeoxyuridine (BrdU) assay. A lentiviral vector incorporating NQO2 short interference (si) RNA of short hairpin design was constructed and transduced into VSMC. Real-time quantitative polymerase chain reaction was used to measure NQO2 mRNA levels; NQO2 expression was determined by western blot analysis. 3. Using RAC, we extracted a 26 kDa protein from aortic smooth muscle, which was referred to as RTP-26. Proliferation of VSMC was inhibited by resveratrol in a concentration- and time-dependent manner. The mRNA and protein expression of NQO2 was also repressed by resveratrol in a concentration- and time-dependent manner. A similar pattern of inhibition was observed for cells treated with resveratrol (25 micromol/L) as for cells transduced with a lentiviral vector containing siRNA sequences against NQO2. 4. Collectively, these data indicate that the suppression of VSMC proliferation mediated by resveratrol correlates with NQO2 downregulation.

Molecular MRI of hematopoietic stem-progenitor cells: in vivo monitoring of gene therapy and atherosclerosis

A characteristic feature of atherosclerotic cardiovascular disease is the diffuse involvement of arteries across the entire human body and the presence of multiple, simultaneous lesions. The diffuse nature of this disease creates a unique challenge for early diagnosis and effective treatment. We believe that recent progress in the field of molecular MRI has opened new avenues towards solving the problem. A new technology has been developed that uses molecular MRI to monitor the migration and homing of hematopoietic stem-progenitor cells to injured arteries and atherosclerosis. In this Review, we introduce several novel technical developments in the field of molecular MRI of atherosclerosis, including advanced techniques for magnetic labeling of stem-progenitor cells and molecular MRI of hematopoietic bone marrow cells migrating to injured arteries and homing to atherosclerotic plaques. In addition, we examine molecular MRI of vascular gene therapy mediated by stem-progenitor cells. These new techniques provide the basis for the further development of in vivo MRI techniques to monitor stem-cell-mediated vascular gene therapy for multiple and diffuse atherosclerotic cardiovascular lesions.

Characterizing the expansive deformation of a bioresorbable polymer fiber stent

Polymeric vascular stents must employ other strategies than malleable deformation, as generally practiced with metal stents, to expand and withstand compressive stresses in situ. The stent expansion strategy must further consider induced flow perturbations and wall stresses that may injure the vessel wall and promote thrombogenesis. Analyzing the stresses furled stents undergo during balloon-assisted expansion is an important first step in achieving a better understanding of stent-wall mechanical interactions, thereby to improve stent function. To this end, we performed finite element (FE) analysis of the balloon-induced unfurling of an internally coiled, bioresorbable polymeric stent employing a 3D FE solid model of a 120 degrees symmetric stent segment and a large deformation finite strain formulation. Uni-axial tensile testing of stent fiber elastic to plastic yielding provided the mechanical property information, and the von Mises criterion was employed to establish the elastic-plastic transition in the FE model. The model was validated with pressure and deformation measurements obtained during stent expansion tests. The internal coils of this inner coil-outer coil design twisted as the stent expanded, leading to plastic yielding at the point of tangency of the inner and outer coils. The remaining stent fiber portions underwent elastic bending. Cross-sections revealed only the outside surface layer of the coiled fiber underwent plastic yielding. The interior elastic fiber was supported by this plastic shell. The analysis suggests that during balloon-induced expansion, local plastic yielding in torsion "sets" the stent fibers, imparting high radial collapse resistance. The results further suggest that the stent exerts non-uniform mechanical forces on the vessel wall during expansion.

Circulating progenitor cells contribute to neointimal formation in nonirradiated chimeric mice

Recent evidence suggests that bone marrow-derived cells may contribute to repair and lesion formation following vascular injury. In most studies, bone marrow-derived cells were tracked by transplanting exogenous cells into bone marrow that had been compromised by irradiation. It remains to be determined whether endogenous circulating progenitors actually contribute to arterial remodeling under physiological conditions. Here, we established a parabiotic model in which two mice were conjoined subcutaneously without any vascular anastomosis. When wild-type mice were joined with transgenic mice that expressed green fluorescent protein (GFP) in all tissues, GFP-positive cells were detected not only in the peripheral blood but also in the bone marrow of the wild-type mice. The femoral arteries of the wild-type mice were mechanically injured by insertion of a large wire. At 4 wk, there was neointima hyperplasia that mainly consisted of alpha-smooth muscle actin-positive cells. GFP-positive cells were readily detected in the neointima (14.8+/-4.5%) and media (31.1+/-8.8%) of the injured artery. Some GFP-positive cells expressed alpha-smooth muscle actin or an endothelial cell marker. These results indicate that circulating progenitors contribute to re-endothelialization and neointimal formation after mechanical vascular injury even in nonirradiated mice.

Clinical in-stent restenosis with bare metal stents: is it truly a benign phenomenon?

OBJECTIVE

In-stent restenosis (ISR) remains an important problem following percutaneous coronary intervention (PCI). Although it is generally believed that patients with ISR present with stable angina, this has not been well characterized. The aim of this study was to define the incidence, predictors, timing and clinical presentation of patients with ISR requiring repeat catheterization.

DESIGN

Using a multiregion prospective database which captures all patients undergoing cardiac catheterization and revascularization in the Province of Alberta, Canada, consecutive bare metal stent (BMS) implantations from January 1, 1998 to December 31, 2002 were analyzed. All patients with a repeat angiogram within one year of the index PCI were reviewed for evidence of clinical-ISR (CISR), defined as ISR as the cause for clinical presentation at angiography.

RESULTS

Of the 12,492 consecutive PCI patients reviewed, 2521 had repeat angiography and 744 patients (6.0%) had CISR by study definition. The mean time to repeat angiography in CISR patients was 5.4+/-2.7 months and multivariate analysis identified female gender, diabetes mellitus, and prior PCI as predictors. The majority of patients presented with an acute coronary syndrome: 52.2% unstable angina/non-ST elevation myocardial infarction and 18.5% ST elevation myocardial infarction. Only 25.3% presented with stable exertional angina.

CONCLUSION

Although the incidence of CISR within one year after BMS was relatively low, the recurrent clinical event in the majority of cases was a high-risk coronary syndrome. Thus, careful consideration of the risks of ISR to a specific patient against the cost implications of novel and expensive means to decrease its occurrence is required.

Gene therapy for restenosis: biological solution to a biological problem

Coronary artery disease remains a significant health threat afflicting millions of individuals worldwide. Despite the development of a variety of technologies and catheter based interventions, post-procedure restenosis is still a significant concern. Gene therapy has emerged as a promising approach aimed at modification of cellular processes that give rise to restenosis. When juxtaposed alongside the failure of traditional pharmacotherapeutics to eliminate restenosis, gene therapy has engendered great expectations for cubing coronary restenosis. In this review we have discussed an overview of gene therapy approaches that hve been utilized to reduce restenosis in preclinical and clinical studies, current status of anti-restenosis gene therapy and perspectives on its future application. For brevity, we have limited our discussion on anti-restenosis gene therapy to the introduction of a nucleic acid to the cell, tissue, organ or organism in order to give rise to the expression of a protein, the function of which will confer therapeutic effect. For the purpose of this review, we have focused ou discussion on two relevant anti-restenosis strategies, anti-proliferative and pro-endothelialization.

Transfection of the DNA for the Receptor KDR/flk-1 Attenuates Neointimal Proliferation and Luminal Narrowing in a Coronary Stent Angioplasty Model

BACKGROUND

Neointimal proliferation resulting in luminal renarrowing is the major cause of restenosis limiting the long-term success of coronary angioplasty in 20 to 30% of patients. Local transfection of the DNA encoding for VEGF has been shown to enhance re-endothelialization and reduce neointimal proliferation in an experimental model. We tested the hypothesis that transfection of the DNA for the receptor of vascular endothelial growth factor VEGF, KDR-flk-1, reduces neointimal proliferation after angioplasty.

METHODS

In a minipig model, we performed coronary stent implantation, followed by injection of either KDR/flk-1 DNA (200 microg of linearized DNA in a CMV-promotor) or LacZ control in two coronary artery segments per animal in a randomized, blinded protocol (n = 22 animals). Expression of KDR/flk-1 was analyzed using in situ hybridization after 4, 7, and 14 days.

RESULTS

In KDR-transfected coronary segments, expression of KDR/flk-1 occurred earlier and to much stronger extent compared to LacZ-transfected segments. After 4 weeks (n = 10) neointimal proliferation and luminal narrowing was significantly reduced in KDR/flk-1 transfected animals. No expression of locally transfected DNA was detected in other organs.

CONCLUSION

The hypothesis is supported, that expression of the VEGF-receptor KDR/flk-1 can be rate-limiting for endothelial regeneration and that its transient overexpression at the time angioplasty can prevent excessive neointimal proliferation resulting in restenosis.

Pathological Effects of Pulmonary Vein beta-Radiation in a Swine Model

INTRODUCTION

Atrial fibrillation (AF) may be triggered by ectopic beats originating in sleeves of atrial myocardium entering the pulmonary veins (PVs). PV isolation by means of circumferential ostial or atrial radiofrequency ablation is an effective but also a difficult and long procedure, requiring extensive applications that can have serious potential complications. Our objective was to examine pathological effects of PV beta-radiation, particularly the ability to destroy PV myocardial sleeves without inducing PV stenosis and other unwanted effects, in order to establish its potential feasibility for the treatment of AF.

METHODS AND RESULTS

Ten minipigs were studied. A phosphorus-32 source wire centered within a 2.5-mm diameter balloon catheter (Galileo III Intravascular Radiotherapy System, Guidant, Santa Clara, CA, USA) was used to deliver beta-radiation to the superior wall of the right PV trunk. Pathological analysis was performed either immediately after ablation (2 pigs) or 81 +/- 27 days later (8 pigs). Acute effects of PV beta-radiation consisted of endothelial denudation covered by white thrombus, elastic lamina disruption, and PV sleeve necrosis. Late effects consisted of mild focal neointimal hyperplasia that reduced the PV luminal area by only 1.3 +/- 1.8%, elastic lamina thickening, and PV sleeve fibrosis. Four of these 8 PVs were completely re-endothelized. Lesions were transmural in 6 of 10 radiated PVs and segmental, involving 28 +/- 7% of the right PV perimeter.

CONCLUSION

Intravascular beta-radiation can induce transmural necrosis and fibrosis of PV myocardial sleeves without PV stenosis and other unwanted effects, which supports a potential usefulness of this energy source in the treatment of AF.

Cutting balloons for the treatment of vascular stenoses

The aim of this article is to review the mechanism, technical characteristics, biological response and clinical applications of cutting balloon angioplasty in peripheral vessels. The cutting balloon is a non-compliant, balloon catheter equipped with three-to-four microtome-sharp atherotomes. When used appropriately, it is safe and easy to use, with a high immediate success rate and few complications, provided oversizing is avoided. There is some evidence that pre-dilation with a standard or high-pressure balloon may also predispose to vascular rupture. The cutting balloon has proved to be beneficial in treating difficult complex lesions in the coronary arteries. Early experience in non-coronary vessels shows that cutting balloon angioplasty can be used to treat peripheral bypass anastomotic and haemodialysis fistula stenoses that are resistant to conventional high-inflation pressures. Its application in de novo peripheral arterial lesions and non-coronary in-stent restenosis is still under discussion. Theoretically, this device induces a smaller degree of vessel wall injury localised to the area of incisions and sparing the interincisional segments; however, this postulated reduction in restenosis rates has not been confirmed in clinical practice.

Inflammatory responses involving tumor necrosis factor receptor-associated factor 6 contribute to in-stent lesion formation in a stent implantation model of rabbit carotid artery

OBJECTIVE

Inflammatory responses are considered to represent a unique property after stent implantation, and we previously demonstrated that inflammatory signaling involving tumor necrosis factor receptor-associated factor 6 (TRAF6) contributes to neointimal formation in a balloon injury model of rabbit carotid artery. The purpose of this study was to examine the role of TRAF6 in in-stent lesion formation after stent implantation in the rabbit carotid artery.

METHODS

Rabbit carotid arteries were injured with a 2F Fogarty catheter, and 28 days later, the same arteries were implanted with a 3-mm-diameter Palmaz-Schatz stent. A dominant negative (DN) form of TRAF6 (pME-FLAG-T6deltaRZ5) was then transferred using a plasmid-based electroporation method. Its effects were evaluated compared with the findings in arteries treated with control plasmid (pME-FLAG).

RESULTS

Immunostaining with anti-FLAG tag antibody showed that an expression plasmid vector containing the DN-TRAF6 sequence was successfully transferred to the arterial intima and media. Morphometric analyses revealed that the increase of intimal area in in-stent lesions was significantly inhibited by DN-TRAF6 14 days after stent implantation (DN-TRAF6 group, 3.01 +/- 0.25 x 10(5) microm2 vs control group, 4.25 +/- 0.23 x 10(5) microm2, P < .01), and the cell density was increased compared with that in the control group. In the DN-TRAF6 plasmid-treated vessels, cell replication was prevented in both the intima and media, and fewer leukocytes adhered to the luminal surface. Moreover, DN-TRAF6 suppressed macrophage infiltration, activation of proteases, and proteoglycan accumulation in the in-stent intima.

CONCLUSIONS

These findings suggest that TRAF6 plays an important role in cell replication, inflammatory cell infiltration, protease activity, and extracellular matrix accumulation that contributes to in-stent lesion development.

Transluminal Stenting for Femoropopliteal Occlusive Disease: Analysis of Restenosis by Serial Arteriography

Our objective was to evaluate restenosis after stenting of femoropopliteal occlusions and the impact of percutaneous transluminal angioplasty (PTA) on recurrent stenosis. We used a retrospective analysis of contrast angiograms obtained during follow-up of stented limbs. Subjects included 27 claudicants (34 limbs) who had complete superficial femoral artery occlusion treated with PTA and Wallstents at the Veterans Adminstration Medical Center. During follow-up, 31 PTAs, three thrombolytic treatments, and one additional stenting were performed. Outcome was measured by contrast angiography. Primary patency at 1 and 3 years was 38% and 8% after stenting, and secondary patency (PTA required at least once in 21/34 limbs) was 89% and 55%, respectively. PTA performed during follow-up reduced within-stent restenosis on average from 48.3 +/- 13.6% to 22.8 +/- 18.0%. Recurrent stenosis after PTA measured 14.9 +/- 10.9 months later was 46.8 +/- 16.7%, showing little permanent impact of PTA on stenosis. Severe within-stent stenosis develops commonly after initial stenting of complete femoropopliteal occlusions. Supplemental PTA performed during follow-up provides immediate improvement in lumen diameter, but severe restenosis is still likely to recur.

The role of circulating precursors in vascular repair and lesion formation

The accumulation of smooth muscle cells (SMCs) plays a principal role in atherogenesis, post-angioplasty restenosis and transplantation-associated vasculopathy. Therefore, much effort has been expended in targeting the migration and proliferation of medial smooth muscle cells to prevent occlusive vascular remodeling. Recent evidence suggests that bone marrow-derived circulating precursors can also give rise to endothelial cells and smooth muscle cells that contribute to vascular repair, remodeling, and lesion formation under physiological and pathological conditions. This article overviews recent findings on circulating vascular progenitor cells and describes potential therapeutic strategies that target these cells to treat occlusive vascular diseases.

Stent-mediated methylprednisolone delivery reduces macrophage contents and in-stent neointimal formation

OBJECTIVE

Corticosteroids have a wide range of biological effects. Stent-based methylprednisolone delivery could effectively suppress peri-strut inflammation and neointima induced by a polymer matrix. We tested the safety and efficacy of local stent-mediated methylprednisolone delivery using a biological coating on in-stent neointimal formation in a porcine coronary stent model.

METHODS

Stainless steel coronary stents were dip-coated in a biological polymer/ methylprednisolone solution, resulting in total load of 530 mug methylprednisolone per stent. In-vitro drug release was performed. Stainless steel bare stents, polymer-only and methylprednisolone-coated stents (MP) were implanted in coronary arteries of pigs with a stent/artery ratio of 1.2 : 1. Histopathologic evaluation, morphometry and immunohistochemistic staining were analyzed at 4-week follow-up.

RESULTS

In-vitro drug release studies showed sustained release up to 10 weeks. In vivo the vascular response of polymer-only-coated stents was comparable with the bare stents. No increased peri-strut inflammation and neointimal hyperplasia were observed. The in-stent neointimal formation of methylprednisolone-coated stents was significantly reduced compared with the bare and polymer-only-coated stents (bare, 1.92+/-0.73; polymer-only, 2.14+/-1.50; MP, 1.01+/-0.47 mm, P=0.019). The macrophage content of methylprednisolone-coated stents (bare, 30.74+/-48.67; polymer-only, 19.55+/-24.60; MP, 1.16+/-3.33/mm, P=0.072) was dramatically decreased. However, there were no significant difference among the three group in terms of the proliferating cells expressed by proliferation cell nuclear antigens.

CONCLUSION

Stent-based local methylprednisolone delivery could effectively decrease both vascular macrophage infiltration and in-stent neointimal hyperplasia.

Apolipoprotein E inhibition of vascular hyperplasia and neointima formation requires inducible nitric oxide synthase

Previous studies have shown apolipoprotein E (apoE) recruitment to medial layers of carotid arteries after vascular injury in vivo and apoE activation of inducible nitric oxide synthase (iNOS) in smooth muscle cells in vitro. This investigation explored the relationship between medial apoE recruitment and iNOS activation in protection against neointimal hyperplasia. ApoE was present in both neointimal-resistant C57BL/6 mice and neointimal-susceptible FVB/N mice 24 h after carotid denudation, but iNOS expression was observed only in the neointimal-resistant C57BL/6 mice. However, iNOS was not observed in apoE-defective C57BL/6 mice. In contrast, overexpression of apoE in FVB/N mice activated iNOS expression in the injured vessels, resulting in protection against neointimal hyperplasia. ApoE and iNOS were colocalized in the medial layer of neointimal-resistant mouse strains. Endothelial denudation of carotid arteries in the iNOS-deficient NOS2(-/-) mice did not increase neointimal hyperplasia but significantly increased medial thickness and area. The iNOS-specific inhibitor also abrogated the apoE protective effects on vascular response to injury in apoE-overexpressing FVB/N mice. Thus, injury-induced activation of iNOS requires apoE recruitment. Moreover, both apoE and iNOS are necessary for the suppression of cell proliferation, and apoE recruitment without iNOS expression resulted in medial hyperplasia without cell migration to the intima.

Cutting Balloon: Review on Principles and Background of Use in Peripheral Arteries

This review describes peripheral use of cutting balloon (CB) angioplasty (CBA), its characteristics, and its distinction from conventional BA and describes the experimental and clinical background of its current use in peripheral arteries.

2005 Dr. Gary J. Becker Young Investigator Award: Periprocedural Oral Administration of the Leflunomide Analogue FK778 Inhibits Neointima Formation in a Double-injury Rat Model of Restenosis

PURPOSE

To test the efficacy of limited oral administration of the new leflunomide analogue FK778 for suppression of neointima proliferation in a double-injury restenosis model in the rat.

MATERIALS AND METHODS

For induction of aortic lesions, silicon cuffs were placed operatively around the infrarenal aortas of Lewis rats. After 21 days, the aortic cuffs were removed and the lesions were dilated with 2-F Fogarty catheters inserted via the left common carotid artery. The novel immunosuppressant FK778 was administered at a dose of 5 mg/kg body weight (group 1) or 15 mg/kg body weight (group 2) in a total of 38 animals. For both doses, three different periinterventional time periods, each with a 5-day course of oral FK778, were defined as follows: (i) days -2 to 2, (ii) days 1-5, and (iii) days 7-11, with six or seven rats in each group. After 3 weeks, intima/media ratios were assessed morphometrically and immunohistochemistry for quantification of intimal alpha-actin expression was performed.

RESULTS

In both dose groups, there was a trend toward inhibition of neointima formation when the 5-day course of FK778 was started before or 1 day after the intervention. However, in the lower-dose group, inhibition of neointima was not statistically significant regardless of the time frame of treatment (groups 1a-c). With the higher dose, suppression of intimal hyperplasia was significant when FK778 was administered between days 1 and 5 after angioplasty (group 2b; P<.01). Expression of alpha-actin in the intima of FK778-treated rats was significantly reduced when the drug was started 2 days before angioplasty in group 1a (P<.05) or 1 day after angioplasty in both dosage groups (group 1b, P<.01; group 2b, P<.05).

CONCLUSION

In the double-injury rat model presented, balloon-mediated proliferation of smooth muscle cells in the intima with consecutive intimal thickening was influenced by FK778 in a dose-dependent manner. However, long-term studies are needed to exclude a delay of vascular healing in this particular model.

Short-term rapamycin for inhibition of neointima formation after balloon-mediated aortic injury in rats: is there a window of opportunity for systemic prophylaxis of restenosis?

PURPOSE

To evaluate the efficacy of limited short-term systemic administration of rapamycin to prevent neointimal intimal hyperplasia (NIH) in a double-injury rat model of restenosis.

METHODS

Aortic lesions were induced by perivascular placement of silicone cuffs around the aorta of 36 Lewis rats. After 3 weeks, the cuffs were removed, and the vessels were subjected to secondary balloon injury. Rapamycin (sirolimus) was intravenously administered for 5 days in dosages of 0.5 or 2 mg/kg/d beginning at various time points relative to the balloon injury: (1) days -2 to +2, (2) days 1 to 5, or (3) days 7 to 11. For each treatment period, 6 rats received the 5-day course of the lower or higher dose of rapamycin. Eight rats served as controls undergoing 2-stage injury without rapamycin treatment. Morphometry and immunohistochemistry were performed at 21 days after angioplasty.

RESULTS

NIH and intimal alpha-actin expression were inhibited by both dosages when treatment started 2 days before or 1 day after angioplasty. Results were statistically significant for the lower dose when started 1 day after angioplasty (p < 0.01) and for the higher dose when initiated 2 days before the intervention (p < 0.05). Treatment commencing at 7 days did not reduce NIH in either dosage group.

CONCLUSIONS

In a double-injury rat model, NIH can be inhibited by short-term systemic rapamycin, but suppression of early cell migration and proliferation is pivotal. A limited peri-interventional antiproliferative therapy may be of value as an adjunct to control restenosis after balloon angioplasty and/or stenting.

Temporal and spatial characterization of cellular constituents during neointimal hyperplasia after vascular injury: Potential contribution of bone-marrow-derived progenitors to arterial remodeling

BACKGROUND

Exuberant smooth muscle cells (SMCs) hyperplasia is the major cause of postangioplasty restenosis. We suggested that circulating smooth muscle progenitor cells might contribute to lesion formation after vascular injury.

METHODS

We extensively investigated the cellular constituents during neointimal formation after mechanical vascular injury.

RESULTS

A large wire was inserted into the mouse femoral artery, causing complete endothelial denudation and marked enlargement of the lumen with massive apoptosis of medial SMCs. At 2 h, the injured artery remained dilated with a thin media containing very few cells. A scanning electron microscopy showed fibrin and platelet deposition at the luminal side. One week after the injury, CD45-positive hematopoietic cells accumulated at the luminal side. Those CD45-positive cells gradually disappeared, whereas neointimal hyperplasia was formed with alpha-smooth muscle actin (SMA) positive cells. Bone marrow cells and peripheral mononuclear cells differentiated into alpha-SMA-positive cells in the presence of PDGF and basic FGF. Moreover, in bone marrow chimeric mice, bone-marrow-derived cells substantially contributed to neointimal hyperplasia after wire injury.

CONCLUSION

These results suggest that early accumulation of hematopoietic cells may play a role in the pathogenesis of SMC hyperplasia under certain circumstances.