A new rat model of small vessel stenting

Treatment Outcomes of Stent-Assisted Coil Embolization for Ruptured Vertebral Artery Dissecting Aneurysms: The Preservation of Branches May Improve the Prognosis

Objective

Subarachnoid hemorrhage due to ruptured vertebral artery dissecting aneurysm (rVADA) is associated with a high frequency of acute rebleeding and requires early treatment following onset. Parent artery occlusion (PAO) or stent-assisted coiling (SAC) embolization is selected as a treatment option according to the individual patient condition. This report is a retrospective examination evaluating the treatment outcomes for rVADA.

Methods

The subjects were 20 rVADA patients (16 men and 4 women) who underwent endovascular treatment at our institution. The mean patient age was 52.9 years. Ten patients each were allocated to the PAO group and SAC group. We evaluated and compared the following parameters: presence of hemorrhagic complications, presence of ischemic complications, requirement of retreatment, and Glasgow Outcome Scale (GOS) after 90 days.

Results

The reasons for selecting SAC were contralateral occlusion or a small diameter in three patients, the posterior inferior cerebellar artery (PICA) involvement in three patients, perforating artery from dissected lesion in five patients, and anterior spinal artery in one patient. There was no rebleeding in any patient. Symptomatic ischemic complications were observed in four patients in the PAO group and in one in the SAC group. Hyper-intense lesions in the brainstem on MRI DWI were noted in five patients in PAO group and in one in the SAC group. Retreatment was required for three patients in the PAO group and for four in the SAC group. Favorable outcomes (GOS 4, 5) after 90 days were observed for three patients in the PAO group and for eight patients in the SAC group (p = 0.0257).

Conclusion

SAC that can preserve branches is a useful treatment option for rVADA. Further studies on a greater number of subjects are required to establish the optimal dose of antiplatelet agents and anticoagulants, and for stent selection.

Apolipoprotein E deficient rats generated via zinc-finger nucleases exhibit pronounced in-stent restenosis

The long-term success of coronary stent implantation is limited by in-stent restenosis (ISR). In spite of a broad variety of animal models available, an ideal high-throughput model of ISR has been lacking. Apolipoprotein E (apoE) deficient rats enable the evaluation of human-sized coronary stents while at the same time providing an atherogenic phenotype. Whereas apoE deficient rats have been proposed as animal model of atherosclerosis, to date it is unknown whether they also develop pronounced ISR. We sought to assess ISR after abdominal aorta stent implantation in apoE deficient rats. A total of 42 rats (16 wildtype, 13 homozygous apoE^−/− and 13 heterozygous apoE^+/− rats) underwent abdominal aorta stent implantation. After 28 days blood samples were analyzed to characterize lipid profiles. ISR was assessed by histomorphometric means. Homozygous apoE^−/− rats exhibited significantly higher total cholesterol and low-density cholesterol levels than wildtype apoE^+/+ and heterozygous apoE^+/− rats. ISR was significantly pronounced in homozygous apoE^−/− rats as compared to wildtype apoE^+/+ (p = <0.0001) and heterozygous apoE^+/− rats (p = 0.0102) on western diet. Abdominal aorta stenting of apoE^−/− rats is a reliable model to investigate ISR after stent implantation and thus can be used for the evaluation of novel stent concepts. Apolipoprotein E (apoE) deficient rats have been proposed as animal model of atherosclerosis. We investigated the development of restenosis 28 days after stent implantation into the abdominal aorta of wildtype apoE^+/+, homozygous apoE^−/− and heterozygous apoE^+/− rats, respectively. Homozygous apoE^−/− rats exhibited significantly higher LDL and significantly lower HDL cholesterol levels compared to wildtype apoE^+/+ and heterozygous apoE^+/− rats. Restenosis after stent implantation was significantly pronounced in western-diet-fed homozygous apoE^−/− rats, accompanied by a significantly increased neointimal thickness. Thus, apoE knockout rats exhibit elevated restenosis and might provide a novel tool for testing of innovative stent concepts.

Non-coding RNAs in vascular remodeling and restenosis

Vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) are crucial in vascular remodeling. They exert pivotal roles in the development and progression of atherosclerosis, vascular response to injury, and restenosis after transcatheter angioplasty. As a witness of their importance in the cardiovascular system, a large body of evidence has accumulated about the role played by micro RNAs (miRNA) in modulating both VSMCs and ECs. More recently, a growing number of long noncoding RNA (lncRNAs) came beneath the spotlights in this research field. Several mechanisms have been revealed by which lncRNAs are able to exert a relevant biological impact on vascular remodeling. The aim of this review is to provide an integrated summary of ncRNAs that exert a relevant biological function in VSMCs and ECs of the vascular wall, with emphasis on the available clinical evidence of the potential usefulness of these molecules as circulating biomarkers of in-stent restenosis.

The effects of stenting on coronary endothelium from a molecular biological view: Time for improvement?

Coronary artery stenting following balloon angioplasty represents the gold standard in revascularization of coronary artery stenoses. However, stent deployment as well as percutaneous transluminal coronary angioplasty (PTCA) alone causes severe injury of vascular endothelium. The damaged endothelium is intrinsically repaired by locally derived endothelial cells and by circulating endothelial progenitor cells from the blood, leading to re‐population of the denuded regions within several weeks to months. However, the process of re‐endothelialization is often incomplete or dysfunctional, promoting in‐stent thrombosis and restenosis. The molecular and biomechanical mechanisms that influence the process of re‐endothelialization in stented segments are incompletely understood. Once the endothelium is restored, endothelial function might still be impaired. Several strategies have been followed to improve endothelial function after coronary stenting. In this review, the effects of stenting on coronary endothelium are outlined and current and future strategies to improve endothelial function after stent deployment are discussed.

Biodegradable Magnesium Stent Treatment of Saccular Aneurysms in a Rat Model - Introduction of the Surgical Technique

The steady progess in the armamentarium of techniques available for endovascular treatment of intracranial aneurysms requires affordable and reproducable experimental animal models to test novel embolization materials such as stents and flow diverters. The aim of the present project was to design a safe, fast, and standardized surgical technique for stent assisted embolization of saccular aneurysms in a rat animal model. Saccular aneurysms were created from an arterial graft from the descending aorta.The aneurysms were microsurgically transplanted through end-to-side anastomosis to the infrarenal abdominal aorta of a syngenic male Wistar rat weighing >500 g. Following aneurysm anastomosis, aneurysm embolization was performed using balloon expandable magnesium stents (2.5 mm x 6 mm). The stent system was retrograde introduced from the lower abdominal aorta using a modified Seldinger technique. Following a pilot series of 6 animals, a total of 67 rats were operated according to established standard operating procedures. Mean surgery time, mean anastomosis time, and mean suturing time of the artery puncture site were 167 ± 22 min, 26 ± 6 min and 11 ± 5 min, respectively. The mortality rate was 6% (n=4). The morbidity rate was 7.5% (n=5), and in-stent thrombosis was found in 4 cases (n=2 early, n=2 late in stent thrombosis). The results demonstrate the feasibility of standardized stent occlusion of saccular sidewall aneurysms in rats - with low rates of morbidity and mortality. This stent embolization procedure combines the opportunity to study novel concepts of stent or flow diverter based devices as well as the molecular aspects of healing.

Magnetic Nanoparticle-Mediated Targeting of Cell Therapy Reduces In-Stent Stenosis in Injured Arteries

Although drug-eluting stents have dramatically reduced the recurrence of restenosis after vascular interventions, the nonselective antiproliferative drugs released from these devices significantly delay reendothelialization and vascular healing, increasing the risk of short- and long-term stent failure. Efficient repopulation of endothelial cells in the vessel wall following injury may limit complications, such as thrombosis, neoatherosclerosis, and restenosis, through reconstitution of a luminal barrier and cellular secretion of paracrine factors. We assessed the potential of magnetically mediated delivery of endothelial cells (ECs) to inhibit in-stent stenosis induced by mechanical injury in a rat carotid artery stent angioplasty model. ECs loaded with biodegradable superparamagnetic nanoparticles (MNPs) were administered at the distal end of the stented artery and localized to the stent using a brief exposure to a uniform magnetic field. After two months, magnetic localization of ECs demonstrated significant protection from stenosis at the distal part of the stent in the cell therapy group compared to both the proximal part of stent in the cell therapy group and the control (stented, nontreated) group: 1.7-fold (p < 0.001) less reduction in lumen diameter as measured by B-mode and color Doppler ultrasound, 2.3-fold (p < 0.001) less reduction in the ratios of peak systolic velocities as measured by pulsed wave Doppler ultrasound, and 2.1-fold (p < 0.001) attenuation of stenosis as determined through end point morphometric analysis. The study thus demonstrates that magnetically assisted delivery of ECs is a promising strategy for prevention of vessel lumen narrowing after stent angioplasty procedure.

Circulating soluble LR11, a novel marker of smooth muscle cell proliferation, is enhanced after coronary stenting in response to vascular injury

OBJECTIVE

Restenosis after vascular intervention remains a major clinical problem. Circulating LR11 has been shown a novel marker of intimal smooth muscle cell (SMC) proliferation in human and animal studies. The present study was performed to clarify the clinical significance of circulating LR11 in patients with stable angina pectoris after coronary stenting.

METHODS AND RESULTS

We firstly investigated the circulating sLR11 levels for 28 days after arterial injury in mice, and then assessed time-dependent change in circulating sLR11 level after coronary stenting in a clinical study. Mouse sLR11 levels rapidly increased to 4.0-fold of the control value without cuff placement at postoperative day (POD) 14, and the levels gradually declined to 3.1-fold of the control value until POD 28 in mice. The circulating soluble LR11 levels were measured (before and at 14, 60 and 240 days after coronary stenting in a clinical study of 102 consecutive patients with stable angina pectoris who were treated with percutaneous coronary intervention. Circulating sLR11 levels were significantly increased on days 14 and 60 after the procedure and positively associated with the angiographic late loss index.

CONCLUSIONS

Our study suggested that circulating sLR11 levels may be a potential marker for angiographic late loss in patients after coronary stenting. Further mechanistic studies are expected to know the clinical significance of sLR11 as a novel marker for intimal SMC.

Experimental model of rat aorta angioplasty with a Paclitaxel releasing balloon catheter

We present an original and safe experimental model of the rat aorta angioplasty with a paclitaxel-releasing balloon catheter. No toxic effects of the drug on experimental animals were detected.

The role of atherectomy in the treatment of lower extremity peripheral artery disease

Background

The incidence of lower extremity peripheral artery disease (LE-PAD) continues to increase and associated morbidity remains high. Despite the significant development of percutaneous revascularization strategies, over the past decade, LE-PAD still represents a unique challenge for interventional cardiologists and vascular surgeons.

Method

Typical features of atherosclerosis that affects peripheral vascular bed (diffuse nature, poor distal runoff, critical limb ischemia, chronic total occlusion) contribute to the disappointing results of traditional percutaneous transluminal angioplasty (PTA). New technologies have been developed in attempt to improve the safety and effectiveness of percutaneous revascularization. Among these, atherectomy, debulking and removing atherosclerotic plaque, offers the potential advantage of eliminating stretch on arterial walls and reducing rates of restenosis.

Conclusions

This review summarizes the features and the current applications of new debulking devices.

Inhibition of miR-92a increases endothelial proliferation and migration in vitro as well as reduces neointimal proliferation in vivo after vascular injury

The role of miR-92a on vascular remodelling after injury is currently unknown. Thus, the aim of the present study was to evaluate the role of miR-92a on rat endothelial and vascular smooth muscle cells proliferation and migration in vitro as well as after balloon injury or arterial stenting in vivo. MiR-92a was highly expressed in RAO-ECs and vascular endothelium, but not in RAO-SMCs or medial smooth muscle as assessed by real-time RT-PCR. Importantly, BrdU incorporation and wound healing assay provide evidence that functional inhibition of miR-92a resulted in an increased RAO-ECs proliferation and migration, but had no effect on RAO-SMCs proliferation or migration in vitro. Immunoblotting analysis revealed an increased phosphorylation of ERK1/2, JNK/SAPK as well as eNOS and phospho-eNOS increased expression level in RAO-ECs as a consequence of miR-92a inhibition. Using gain and loss of function experiments, we showed that miR-92a modulates regulation of KLF4 and MKK4 expression level in endothelial cells. Finally, in vivo administration of antagomiR-92a significantly enhanced re-endothelialization in injured carotid arteries and reduced neointimal formation after balloon injury or arterial stenting. These data provide the first evidence that inhibition of miR-92a may represent a novel strategy to improve endothelial regeneration and reduce restenosis after vascular injury.

Glycosylated hemoglobin (HbA1c) levels and clinical outcomes in diabetic patients following coronary artery stenting

Background

Diabetes has been shown to be independent predictor of restenosis after percutaneous coronary intervention (PCI). The aim of the present study was to investigate whether a pre- and post-procedural glycaemic control in diabetic patients was related to major advance cardiovascular events (MACE) during follow up.

Methods

We evaluated 2884 consecutive patients including 2181 non-diabetic patients and 703 diabetics who underwent coronary stenting. Diabetes mellitus was defined as the fasting blood sugar concentration ≥ 126 mg/dL, or the use of an oral hypoglycemic agent or insulin at the time of admission. Diabetic patients were categorized into two groups based on their mean HbA1c levels for three measurements (at 0, 1, and 6 months following procedure): 291 (41.4%) diabetics with good glycaemic control (HbA1c ≤ 7%) and 412 (58.6%) diabetics with poor glycaemic control (HbA1c > 7%).

Results

The adjusted risk of MACE in diabetic patients with poor glycaemic control (HbA1c > 7%) was 2.1 times of the risk in non-diabetics (adjusted HR = 2.1, 95% CI: 1.10 to 3.95, p = 0.02). However, the risk of MACE in diabetics with good glycaemic control (HbA1c ≤ 7%) was not significantly different from that of non-diabetics (adjusted HR = 1.33, 95% CI: 0.38 to 4.68, p = 0.66).

Conclusions

Our data suggest that there is an association between good glycaemic control to obtain HbA1c levels ≤7% (both pre-procedural glycaemic control and post-procedural) with a better clinical outcome after PCI.

Role of IN-1233 in the prevention of neointimal hyperplasia after stent placement in a rat artery model

PURPOSE

To evaluate the efficacy of an activin receptor-like kinase (ALK) 5 inhibitor, IN-1233, for the prevention of neointimal hyperplasia after bare stent placement in a rat common iliac artery (CIA) model.

MATERIALS AND METHODS

All experiments were approved by the committee of animal research. A self-expanding metallic bare stent (2 mm × 6 mm) was inserted into the left CIA of 26 Sprague-Dawley male rats (300-360 g) under fluoroscopic guidance. IN-1233 was injected via the intraperitoneal route daily in 13 rats for 8 weeks after stent placement (group A); the other 13 rats underwent stent placement only (group B). Angiography was performed immediately and 4 weeks and 8 weeks after stent placement. Rats were sacrificed at 8 weeks after stent placement, and histologic findings were obtained. The neointimal area (NA), percentage of neointimal hyperplasia (%NH), and neointimal-to-medial area ratio (N/M) were assessed and compared between the two groups.

RESULTS

Stent placement was technically successful. In 25 rats, arteries with stent placement were angiographically patent, whereas 1 rat in group B had an occlusion. The NA (0.31 mm(2) ± 0.09 vs 0.56 mm(2) ± 0.17; P < .001), the %NH (26.16% ± 8.75 vs 44.71% ± 17.75; P < .001) and the N/M (1.93 ± 0.77 vs 4.77 ± 2.26; P < .001) were significantly decreased in group A compared with group B.

CONCLUSIONS

IN-1233 was shown in this study to be effective for the prevention of neointimal hyperplasia after bare metallic stent placement in a rat CIA model.

Comparison of bare metal stent and paclitaxel-eluting stent using a novel rat aorta stent model

The purpose of our study was to create a novel rat aorta stent implantation model. Stainless steel bare metal stents (BMS) or paclitaxel-eluting stents (PES) were implanted in male Sprague-Dawley rats (BW 400 ± 20 g). Two and four weeks after stent implantation, the aorta were collected, fixed with 2% glutaraldehyde, and cut into two segments. One segment was used for scanning electron microscopy analysis to evaluate re-endothelialization, and the other segment was used to calculate the neointimal area. At 2 weeks after stenting, the appearance of neointimal hyperplasia was less in the PES group than in the BMS group. At 4 weeks after stenting, no significant difference in neointimal hyperplasia was observed between two groups. On the other hand, the PES group showed more thrombus formation and less re-endothelialization compared to the BMS group. This study demonstrated the ability of a novel rat model of aorta stenting via a common carotid artery to measure the efficacy and safety of commercially available drug-eluting stents.

Mechanisms of smooth muscle cell proliferation and endothelial regeneration after vascular injury and stenting: approach to therapy

Bare metal stents (BMS) successfully prevented abrupt artery closure and reduced the restenosis rate compared with balloon angioplasty. This review summarizes laboratory and recent clinical investigations concerning neointimal formation and endothelial regeneration after vascular injury. BMS efficacy was severely hampered by proliferating vascular smooth muscle cells (VSMCs), and the resultant neointimal hyperplasia, which is the only mechanism responsible for restenosis after metal stent placement. The advent of drug-eluting stents (DES) in 2002 have since then revolutionized interventional cardiology. By using the stent struts as a platform coated with polymers to elute drugs targeting VSMC proliferation, a substantial attenuation of in-stent restenosis is feasible. As with any medical innovation this technology still has restrictive factors, and novel approaches are promoted to improve the safety and efficacy of DES. Indeed, the antiproliferative properties of DES impair and/or delay endothelialization, hence leading to late stent thrombosis. Improvements in percutaneous coronary intervention procedures include the use of the so-called "second-generation DES", together with new coating technologies, bioabsorbable stents, and non-drug-based stent coatings. Particular emphasis will be placed on the concept that endothelial regeneration might be pursued as well as reduction of VSMC proliferation to allow stable successful revascularization after DES deployment.

Trans-iliac rat aorta stenting: a novel high throughput preclinical stent model for restenosis and thrombosis

BACKGROUND

Currently, preclinical stent development requires elaborate large animal models, which are time consuming and expensive. We herein report a high throughput rat aorta stenting model which could provide a rapid and low-cost platform for preclinical stent development.

METHODS

A total of 86 metal stents (316L stainless steel 13 mm, VasoTech, Inc.) coated with poly (D, L-lactide-co-glycolide)/amorphous calcium phosphate (PLGA/ACP) copolymer were pre-mounted on 1.5 mm × 15 mm balloon catheters and were implanted into aspirin treated Sprague-Dawley rats (500-700 g) initially using either direct placement in the abdominal aorta (group A, n = 7) or a trans-iliac approach (cut-down, group B, n = 79). The surviving rats were sacrificed at 1, 2, 4, and 12 wk post-implantation and the stented arteries were analyzed histopathologically.

RESULTS

Four rats died in group A and nine rats died in group B within 48 h post-stent implantation (mortality: 57% versus 11%, P < 0.05). All animals that died had stent thrombosis/paralysis with visible thrombus on necropsy. Histologically, neointimal growth peaked at approximately 4 wk post-implantation.

CONCLUSION

This result suggests that human-sized stents can be successfully implanted into the rat aorta via iliac artery insertion with a significantly higher survival rate than trans-aorta implantation. The model system allows rapid (4-12 wk) assessment of stent biocompatibility with mortality/paralysis used as an indicator of stent thrombosis.

A rat esophageal model to investigate stent-induced tissue hyperplasia

PURPOSE

To evaluate the feasibility of stent placement and the formation of tissue hyperplasia caused by stent placement in a rat esophageal model.

MATERIALS AND METHODS

Twenty Sprague-Dawley rats were divided into four groups to assess differing stent diameters and design (group I, 4 mm diameter and a large mesh gap; group II, 5 mm diameter and a large mesh gap; group III, 5 mm diameter and a small mesh gap; and group IV, barbs added to the group III stents). Follow-up, 1-week, and 3-week esophagograms were obtained. Rats were euthanized 3 weeks after stent placement. Microscopic findings were evaluated in groups with an incidence of less than 50% stent migration.

RESULTS

Stent placement was technically successful in all rats, and there were no procedure-related complications. No esophageal perforation occurred during follow-up. The incidence of stent migration was 100%, 60%, 40%, and 0% in groups I through IV, respectively. The esophagi with stent migration showed only a small amount of tissue hyperplasia; however, esophagi without stent migration showed gross tissue hyperplasia through the mesh. The microscopic findings were evaluated in groups III and IV. The degree of inflammatory cell infiltration, papillary projection thickness, granulation tissue area, and percentage of the granulation tissue area were higher in group IV than in group III; however, there was no statistical significance.

CONCLUSIONS

Esophageal stent placement was feasible in a rat model, and formation of tissue hyperplasia was evident in rats without stent migration. With barbed stents, there was the least incidence of stent migration without esophageal perforation.

A novel mouse model of in situ stenting

AIMS

Animal models of stenting are mostly limited to larger animals or involve substantial abdominal surgery in rodents. We aimed to develop a simple, direct model of murine stenting.

METHODS AND RESULTS

We designed a miniature, self-expanding, nitinol wire coil stent that was pre-loaded into a metal stent sheath. This was advanced into the abdominal aorta of the mouse, via femoral access, and the stent deployed. In-stent restenosis was investigated at 1, 3, 7, and 28 days post-stenting. The model was validated by investigation of neointima formation in mice deficient in signalling via the interleukin-1 receptor (IL-1R1), compared with other injury models. Ninety-two per cent of mice undergoing the procedure were successfully stented. All stented vessels were patent. Inflammatory cells were seen in the adventitia and around the stent strut up to 3 days post-stenting. At 3 days, an early neointima was present, building to a mature neointima at 28 days. In mice lacking IL-1R1, the neointima was 64% smaller than that in wild-type controls at the 28-day timepoint, in agreement with other models.

CONCLUSION

This is the first description of a successful model of murine in situ stenting, using a stent specifically tailored for use in small thin-walled arteries. The procedure can be undertaken by a single operator without the need for an advanced level of microsurgical skill and is reliable and reproducible. The utility of this model is demonstrated by a reduction in in-stent restenosis in IL-1R1-deficient mice.

Preclinical Models of Restenosis and Their Application in the Evaluation of Drug-Eluting Stent Systems

Coronary arterial disease (CAD) is the leading cause of death in the United States, the European Union, and Canada. Percutaneous coronary intervention (PCI) has revolutionized the treatment of CAD, and it is the advent of drug-eluting stent (DES) systems that has effectively allayed much of the challenge of restenosis that has plagued the success of PCI through its 30-year history. However, DES systems have not been a panacea: There yet remain the challenges associated with interventions involving bare metallic stents as well as newly arisen concerns related to the application of DES systems. To effectively address these novel and ongoing issues, animal models are relied on both to project the safety and efficacy of endovascular devices and to provide insight into the pathophysiology underlying the vascular response to injury and mechanisms of restenosis. In this review, preclinical models of restenosis are presented, and their application and limitation in the evaluation of device-based interventional technologies for the treatment of CAD are discussed.

Local delivery of gene vectors from bare-metal stents by use of a biodegradable synthetic complex inhibits in-stent restenosis in rat carotid arteries

BACKGROUND

Local drug delivery from polymer-coated stents has demonstrated efficacy for preventing in-stent restenosis; however, both the inflammatory effects of polymer coatings and concerns about late outcomes of drug-eluting stent use indicate the need to investigate innovative approaches, such as combining localized gene therapy with stent angioplasty. Thus, we investigated the hypothesis that adenoviral vectors (Ad) could be delivered from the bare-metal surfaces of stents with a synthetic complex for reversible vector binding.

METHODS AND RESULTS

We synthesized the 3 components of a gene vector binding complex: (1) A polyallylamine bisphosphonate with latent thiol groups (PABT), (2) a polyethyleneimine (PEI) with pyridyldithio groups for amplification of attachment sites [PEI(PDT)], and (3) a bifunctional (amine- and thiol-reactive) cross-linker with a labile ester bond (HL). HL-modified Ad attached to PABT/PEI(PDT)-treated steel surfaces demonstrated both sustained release in vitro over 30 days and localized green fluorescent protein expression in rat arterial smooth muscle cell cultures, which were not sensitive to either inhibition by neutralizing anti-Ad antibodies or inactivation after storage at 37 degrees C. In rat carotid studies, deployment of steel stents configured with PABT/PEI(PDT)/HL-tethered adenoviral vectors demonstrated both site-specific arterial Ad(GFP) expression and adenovirus-luciferase transgene activity per optical imaging. Rat carotid stent delivery of adenovirus encoding inducible nitric oxide synthase resulted in significant inhibition of restenosis.

CONCLUSIONS

Reversible immobilization of adenovirus vectors on the bare-metal surfaces of endovascular stents via a synthetic complex represents an efficient, tunable method for sustained release of gene vectors to the vasculature.

Biocompatibility: meeting a key functional requirement of next-generation medical devices

The array of polymeric, biologic, metallic, and ceramic biomaterials will be reviewed with respect to their biocompatibility, which has traditionally been viewed as a requirement to develop a safe medical device. With the emergence of combination products, a paradigm shift is occurring that now requires biocompatibility to be designed into the device. In fact, next-generation medical devices will require enhanced biocompatibility by using, for example, pharmacological agents, bioactive coatings, nano-textures, or hybrid systems containing cells that control biologic interactions to have desirable biologic outcomes. The concept of biocompatibility is moving from a "do no harm" mission (i.e., nontoxic, nonantigenic, nonmutagenic, etc.) to one of doing "good," that is, encouraging positive healing responses. These new devices will promote the formation of normal healthy tissue as well as the integration of the device into adjacent tissue. In some contexts, biocompatibility can become a disruptive technology that can change therapeutic paradigms (e.g., drug-coated stents). New database tools to access biocompatibility data of the materials of construction in existing medical devices will facilitate the use of existing and new biomaterials for new medical device designs.

Fludarabine prevents smooth muscle proliferation in vitro and neointimal hyperplasia in vivo through specific inhibition of STAT-1 activation

Drug-eluting stents are increasingly used to reduce in-stent restenosis and adverse cardiac events after percutaneous coronary interventions. However, the race for the ideal drug-eluting stent is still on, with special regard to the best stent-coating system and the most effective and less toxic drug. Fludarabine, a nucleoside analog, has both anti-inflammatory and antiproliferative cellular effects. The aim of the present study was to assess the cellular and molecular effects of fludarabine on vascular smooth muscle cell (VSMC) growth in vitro and in vivo and the feasibility and efficacy of a fludarabine-eluting stent. To study the biomolecular effects of fludarabine on VSMC proliferation in vitro, rat VSMCs were grown in the presence of 50 μM fludarabine or in the absence of the same. To evaluate the in vivo effect of this drug, male Wistar rats underwent balloon injury of the carotid artery, and fludarabine was locally delivered at the time of injury. Finally, fludarabine-eluting stents were in-laboratory manufactured and tested in a rabbit model of in-stent restenosis. Fludarabine markedly inhibited VSMC proliferation in cell culture. Furthermore, fludarabine reduced neointimal formation after balloon angioplasty in a dose-dependent manner, and fludarabine-eluting stents reduced neointimal hyperplasia by ∼50%. These in vitro and in vivo cellular effects were specifically associated with the molecular switch-off of signal transducer and activator of transcription (STAT)-1 activation, without affecting other STAT proteins. Fludarabine abolishes VSMC proliferation in vitro and reduces neointimal formation after balloon injury in vivo through specific inhibition of STAT-1 activation. Fludarabine-eluting stents are feasible and effective in reducing in-stent restenosis in rabbits.

Increased In-Stent Stenosis in ApoE Knockout Mice

OBJECTIVE

We aimed to develop and validate a model of angioplasty and stenting in mice that would allow investigation of the response to stent injury using genetically modified mouse strains.

METHODS AND RESULTS

Aortic segments from either C57BL/6 wild-type or atherosclerotic ApoE-KO mice underwent balloon angioplasty alone or balloon angioplasty and stenting with a 1.25x2.5 mm stainless steel stent. Vessels were carotid-interposition grafted into genetically identical littermate recipients and harvested at 1, 7, 14, or 28 days. In wild-type mice, stenting generated an inflammatory vascular injury response between days 1 to 7, leading to the development of neointimal hyperplasia by day 14, which further increased in area by day 28 leading to the development of in-stent stenosis. Uninjured vessels and vessels injured by balloon angioplasty alone developed minimal neointimal hyperplasia. In stented ApoE-KO mice, neointimal area at 28 days was 30% greater compared with wild-type mice.

CONCLUSIONS

By reproducing important features of human stenting in atherosclerotic mice, we provide the potential to investigate molecular pathways and evaluate novel therapeutic targets for stent injury and restenosis.

Vascular neointimal formation and signaling pathway activation in response to stent injury in insulin-resistant and diabetic animals

Diabetes and insulin resistance are associated with increased disease risk and poor outcomes from cardiovascular interventions. Even drug-eluting stents exhibit reduced efficacy in patients with diabetes. We now report the first study of vascular response to stent injury in insulin-resistant and diabetic animal models. Endovascular stents were expanded in the aortae of obese insulin-resistant and type 2 diabetic Zucker rats, in streptozotocin-induced type 1 diabetic Sprague-Dawley rats, and in matched controls. Insulin-resistant rats developed thicker neointima (0.46+/-0.08 versus 0.37+/-0.06 mm2, P=0.05), with decreased lumen area (2.95+/-0.26 versus 3.29+/-0.15 mm2, P=0.03) 14 days after stenting compared with controls, but without increased vascular inflammation (ED1+ tissue macrophages). Insulin-resistant and diabetic rat vessels did exhibit markedly altered signaling pathway activation 1 and 2 weeks after stenting, with up to a 98% increase in p-ERK (anti-phospho ERK) and a 54% reduction in p-Akt (anti-phospho Akt) stained cells. Western blotting confirmed a profound effect of insulin resistance and diabetes on Akt and ERK signaling in stented segments. p-ERK/p-Akt ratio in stented segments uniquely correlated with neointimal response (R2=0.888, P=0.04) in insulin-resistant and type 1 and 2 diabetic rats, but not in lean controls. Transfemoral aortic stenting in rats provides insight into vascular responses in insulin resistance and diabetes. Shifts in ERK and Akt signaling related to insulin resistance may reflect altered tissue repair in diabetes accompanied by a shift in metabolic:proliferative balance. These findings may help explain the increased vascular morbidity in diabetes and suggest specific therapies for patients with insulin resistance and diabetes.

Characterization of a New Double-Injury Restenosis Model in the Rat Aorta

PURPOSE

To characterize a new rat model of restenosis for evaluation of local or systemic drug strategies.

METHODS

Arterial lesions were induced by placement of silicone cuffs around the aorta of Lewis rats. After 21 days, the cuffs were removed, and a subgroup of rat aortas was subjected to secondary balloon injury. Remodeling of wall compartments and cell kinetics were assessed morphometrically at 3, 7, 14, 21, and 28 days after the single and double-injury approaches. Immunohistochemistry was used to assess the distribution of macrophages, smooth muscle cells, and proliferating cells within the layers of the arterial wall in the experimental groups versus sham-operated and untreated controls.

RESULTS

After cuff placement, the adventitia initially undergoes significant enlargement, while the media shows a reduction in relative thickness. Accumulation of cells within the adventitia at 3 and 7 days is followed by a marked decline in cell density at 14 days, with simultaneously increasing cell numbers in the intima. At this time, activated macrophages are detected in the adventitia, indicating chronic inflammation. Following cuff placement, mild intimal hyperplasia develops. In the double-injury model, extensive neointimal hyperplasia forms rapidly, with a peak at 14 days.

CONCLUSIONS

This new double-injury model is technically easy, and multiple experiments can be accrued in short periods of time. It provides an additional platform to identify new targets and strategies for the prophylaxis of postangioplasty restenosis.

Aging exacerbates negative remodeling and impairs endothelial regeneration after balloon injury

Many older patients, because of their high prevalence of coronary artery disease, are candidates for percutaneous coronary interventions (PCI), but the effects of vascular aging on restenosis after PCI are not yet well understood. Balloon injury to the right carotid artery was performed in adult and old rats. Vascular smooth muscle cell (VSMC) proliferation, apoptotic cell death, together with Akt induction, telomerase activity, p27kip1, and endothelial nitric oxide synthase (eNOS) expression was assessed in isolated arteries. Neointima hyperplasia and vascular remodeling along with endothelial cell regeneration were also measured after balloon injury. Arteries isolated from old rats exhibited a significant reduction of VSMC proliferation and an increase in apoptotic death after balloon injury when compared with adult rats. In the vascular wall of adult rats, balloon dilation induced Akt phosphorylation, and this was barely present in old rats. In arteries from old rats, Akt-modulated cell cycle check points like telomerase activity and p27kip1 expression were decreased and increased, respectively, compared with adults. After balloon injury, old rats showed a significant reduction of neointima formation and an increased vascular negative remodeling compared with adults. These results were coupled by a marked delay in endothelial regeneration in aged rats, partially mediated by a decreased eNOS expression and phosphorylation. Interestingly, chronic administration of l-arginine prevented negative remodeling and improved reendothelialization after balloon injury in aged animals. A decreased neointimal proliferation, an impaired endothelial regeneration, and an increase in vascular remodeling after balloon injury were observed in aged animals. The molecular mechanisms underlying these responses seem to be a reduced Akt and eNOS activity.

Rat Abdominal Aorta Stenting: A New and Reliable Small Animal Model for In-Stent Restenosis

BACKGROUND

A high throughput animal model may enhance pathophysiological studies to mechanisms of in-stent restenosis (ISR). More and appropriate antibodies and transgenic and knockout strains are available in rats. Consequently, a model for ISR in the rat would be convenient for pathobiological studies. Here we present the full characteristics of a rat ISR model suitable for high throughput stent research.

METHODS

The abdominal aorta of rats was separated from surrounding tissue and a BeStenttrade mark 2 or a Cyphertrade mark sirolimus-eluting stent was locally inserted. After 1, 3, 7, 28 and 56 days, the aortas were harvested, fixed, embedded and cut. Morphometric analysis was performed and inflammation scored.

RESULTS

The neointimal area increased to a maximum after 28 days (0.55 +/- 0.08 mm(2)). Subsequently, the neointimal area slightly decreased. The injury score and the neointimal area were linearly correlated (r = 0.85, p < 0.01). Thrombus formation was present after 1 day. Leukocyte adherence was evident after 1 day, maximal after 3 days (93 +/- 21 cells/section) and decreased thereafter. The inflammation score increased after 3 days to a maximum after 7 days (1.37 +/- 0.06) and declined thereafter. After 28 days the Cypher sirolimus-eluting stent decreased the stenosis in comparison to the BeStent 2 (10.2 +/- 0.85 vs. 18.0 +/- 2.0%, respectively, p < 0.01).

CONCLUSIONS

Stent deployment in the rat abdominal aorta results in thrombus formation, inflammation and neointimal formation. Moreover, there is a linear correlation between the injury score and the neointimal area. These responses resemble ISR events as seen in other animal models. Moreover, a known anti-restenotic stent also reduces neointimal formation in this model. Rat abdominal aorta stenting is a promising animal model for ISR, it is suitable for testing commercially manufactured stents and studying the pathophysiology of ISR.

Effect of stent coating alone on in vitro vascular smooth muscle cell proliferation and apoptosis

Synthetic polymers, like methacrylate (MA) compounds, have been clinically introduced as inert coatings to locally deliver drugs that inhibit restenosis after stent. The aim of the present study was to evaluate the effects of MA coating alone on vascular smooth muscle cell (VSMC) growth in vitro. Stainless steel stents were coated with MA at the following doses: 0.3, 1.5, and 3 ml. Uncoated/bare metal stents were used as controls. VSMCs were cultured in dishes, and a MA-coated stent or an uncoated bare metal stent was gently added to each well. VSMC proliferation was assessed by bromodeoxyuridine (BrdU) incorporation. Apoptosis was analyzed by three distinct approaches: 1) annexin V/propidium iodide fluorescence detection; 2) DNA laddering; and 3) caspase-3 activation and PARP cleavage. MA-coated stents induced a significant decrease of BrdU incorporation compared with uncoated stents at both the low and high concentrations. In VSMCs incubated with MA-coated stents, annexin V/propidium iodide fluorescence detection showed a significant increase in apoptotic cells, which was corroborated by the typical DNA laddering. Apoptosis of VSMCs after incubation with MA-coated stents was characterized by caspase-3 activation and PARP cleavage. The MA-coated stent induced VSMC growth arrest by inducing apoptosis in a dose-dependent manner. Thus MA is not an inert platform for eluting drugs because it is biologically active per se. This effect should be taken in account when evaluating an association of this coating with antiproliferative agents for in-stent restenosis prevention.

Physical training increases eNOS vascular expression and activity and reduces restenosis after balloon angioplasty or arterial stenting in rats

The effects of dynamic exercise on restenosis after vascular injury are still unknown. The consequences of balloon dilation-induced injury on neointimal hyperplasia, vascular negative remodeling, and reendothelialization were assessed in sedentary and trained rats. Ex vivo eNOS vascular expression and activity were investigated in carotid arteries isolated from sedentary and exercised rats. The in vivo effects of eNOS inhibition by L-NMMA on vessel wall after balloon dilation were evaluated in sedentary and exercised rats. We also investigated the effects of exercise on neointimal formation in a rat stent model of vascular injury. Compared with sedentary group, the arteries isolated from trained rats showed higher levels of eNOS protein expression and activity 7 days after balloon dilation. A significant reduction of both neointimal hyperplasia and negative remodeling was observed 14 days after balloon injury in trained compared with sedentary rats. Moreover, we demonstrated that exercise training produced accelerated reendothelialization of the balloon injured arterial segments compared with sedentary. L-NMMA administration eliminated the benefits of physical training on vessel wall after balloon dilation. Finally, a decrease of neointimal hyperplasia as well as of platelet aggregation was observed after stent deployment in trained rats compared with sedentary. In conclusion, physical exercise could favorably affect restenosis after balloon angioplasty and stenting. Increase in eNOS expression and activity might contribute to the potential beneficial effects of exercise on the vessel wall after vascular injury.

Rat carotid artery dilation by PTCA balloon catheter induces neointima formation in presence of IEL rupture

The best animal angioplasty model is the porcine model, which is expensive and not available in all laboratories. The aim of this study was to describe a new rat model of angioplasty. An injury was induced with the use of a standard percutaneous transluminal coronary angioplasty (PTCA) 1.5-mm balloon catheter. The neointimal tissue, arterial dimensions, and the injury index were assessed following angioplasty. Ki-67 expression was detected to evaluate cell turnover after balloon angioplasty. In contrast with the standard Clowes model, a significant neointimal formation was detected only in the presence of ruptured internal elastic lamina (IEL). A positive correlation between the percentage of ruptured IEL and the amount of neointimal tissue was also demonstrated. The percentage of IEL fracture correlates with the proliferation index by anti-Ki-67 immunolabeling 7 and 14 days after the angioplasty. Significant arterial negative remodeling was observed following PTCA balloon dilation. In conclusion, our inexpensive animal model of restenosis after angioplasty may have great relevance toward a better understanding of the mechanisms and toward assessment of new therapeutical strategies for this phenomenon.

Coronary in-stent restenosis: current status and future strategies

In-stent restenosis (ISR) is a novel pathobiologic process, histologically distinct from restenosis after balloon angioplasty and comprised largely of neointima formation. As percutaneous coronary intervention increasingly involves the use of stents, ISR is also becoming correspondingly more frequent. In this review, we examine the available studies of the histology and pathogenesis of ISR, with particular reference to porcine and other animal models. An overview of mechanical treatments is then provided, which includes PTCA, directional coronary atherectomy and high speed rotational atherectomy. Radiation-based therapies are discussed, including a summary of current problems associated with this modality of treatment. Finally, novel strategies for the prevention of ISR are addressed, including novel developments in stents and stent coatings, conventional drugs, nucleic acid-based drugs and gene transfer. Until recently, limited pharmacologic and mechanical treatment options have been available for both treatment and prevention of ISR. However, recent advances in gene modification and gene transfer therapies and, more particularly, in local stent-based drug delivery systems make it conceivable that the incidence of ISR will now be seriously challenged.