Morphologic characteristics of lesion formation and time course of smooth muscle cell proliferation in a porcine proliferative restenosis model

Integrative multiomics analysis of neointima proliferation in human saphenous vein: implications for bypass graft disease

Introduction

Human saphenous veins (SV) are widely used as grafts in coronary artery bypass (CABG) surgery but often fail due to neointima proliferation (NP). NP involves complex interplay between vascular smooth muscle cells (VSMC) and fibroblasts. Little is known, however, regarding the transcriptomic and proteomic dynamics of NP. Here, we performed multi-omics analysis in an ex vivo tissue culture model of NP in human SV procured for CABG surgery.

Methods and results

Histological examination demonstrated significant elastin degradation and NP (indicated by increased neointima area and neointima/media ratio) in SV subjected to tissue culture. Analysis of data from 73 patients suggest that the process of SV adaptation and NP may differ according to sex and body mass index. RNA sequencing confirmed upregulation of pro-inflammatory and proliferation-related genes during NP and identified novel processes, including increased cellular stress and DNA damage responses, which may reflect tissue trauma associated with SV harvesting. Proteomic analysis identified upregulated extracellular matrix-related and coagulation/thrombosis proteins and downregulated metabolic proteins. Spatial transcriptomics detected transdifferentiating VSMC in the intima on the day of harvesting and highlighted dynamic alterations in fibroblast and VSMC phenotype and behavior during NP. Specifically, we identified new cell subpopulations contributing to NP, including SPP1 + , LGALS3 + VSMC and MMP2 + , MMP14 + fibroblasts.

Conclusion

Dynamic alterations of gene and protein expression occur during NP in human SV. Identification of the human-specific molecular and cellular mechanisms may provide novel insight into SV bypass graft disease.

Heterogeneous vascular response after implantation of bare nitinol self-expanding stents in the swine femoropopliteal artery

BACKGROUND

Mechanism of femoropopliteal in-stent restenosis has been underappreciated.

AIM

The aim of this animal study was to elucidate vascular response after femoropopliteal bare nitinol self-expanding stents (SESs) implantation.

METHODS

Misago, Smart Flex, or Innova stent was randomly implanted in 36 swine femoropopliteal arteries. At week 4, quantitative vessel analysis (QVA) was performed on 36 legs, of which 18 underwent histological evaluation after angiography. The remaining 18 legs underwent QVA and histological evaluation at week 13.

RESULTS

Fibrin deposition was excessive at week 4. Internal elastic lamina (IEL) progressively enlarged over time, and vessel injury developed from mild level at week 4 to moderate level at week 13. Vessel inflammatory reaction was mild to moderate at week 4, and was moderate to severe at week 13. Increased fibrin deposition was an early-acting, IEL enlargement and increased vessel inflammation were long-acting, and increased vessel injury and giant cells infiltration were late-acting contributors to neointimal hyperplasia (NIH). Stent type altered time-dependent process of vessel injury, vessel inflammation, eosinophils and giant cells infiltration. Misago had less fibrin deposition and vessel enlargement, and less progressive vessel injury, vessel inflammation, and eosinophils and giant cells infiltration. Net lumen as assessed by percent diameter stenosis or minimum lumen diameter was preserved with Misago, but was not preserved with the other stents.

CONCLUSIONS

In the context of bare nitinol SES platform with less progressive mechanical stress and inflammatory reaction, the advantage of less NIH outweighed the disadvantage of less vessel enlargement, leading to net lumen preservation.

Native extracellular matrix orientation determines multipotent vascular stem cell proliferation in response to cyclic uniaxial tensile strain and simulated stent indentation

Cardiovascular disease is the leading cause of death worldwide, with multipotent vascular stem cells (MVSC) implicated in contributing to diseased vessels. MVSC are mechanosensitive cells which align perpendicular to cyclic uniaxial tensile strain. Within the blood vessel wall, collagen fibers constrain cells so that they are forced to align circumferentially, in the primary direction of tensile strain. In these experiments, MVSC were seeded onto the medial layer of decellularized porcine carotid arteries, then exposed to 10%, 1 Hz cyclic tensile strain for 10 days with the collagen fiber direction either parallel or perpendicular to the direction of strain. Cells aligned with the direction of the collagen fibers regardless of the orientation to strain. Cells aligned with the direction of strain showed an increased number of proliferative Ki67 positive cells, while those strained perpendicular to the direction of cell alignment showed no change in cell proliferation. A bioreactor system was designed to simulate the indentation of a single, wire stent strut. After 10 days of cyclic loading to 10% strain, MVSC showed regions of densely packed, highly proliferative cells. Therefore, MVSC may play a significant role in in-stent restenosis, and this proliferative response could potentially be controlled by controlling MVSC orientation relative to applied strain.

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ECM constrained MVSC align with collagen fibers when cells are strained parallel to collagen.

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Straining MVSC aligned parallel to the direction of strain increased cell proliferation.

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Simulated stent strut indentation showed increased cell density surrounding the indented wire.

Animal Models of Neointimal Hyperplasia and Restenosis: Species-Specific Differences and Implications for Translational Research

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Neointimal hyperplasia is the major factor contributing to restenosis after angioplasty procedures.

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Multiple animal models exist to study basic and translational aspects of restenosis formation.

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Animal models differ substantially, and species-specific differences have major impact on the pathophysiology of the model.

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Genetic, dietary, and mechanical interventions determine the translational potential of the animal model used and have to be considered when choosing the model.

The process of restenosis is based on the interplay of various mechanical and biological processes triggered by angioplasty-induced vascular trauma. Early arterial recoil, negative vascular remodeling, and neointimal formation therefore limit the long-term patency of interventional recanalization procedures. The most serious of these processes is neointimal hyperplasia, which can be traced back to 4 main mechanisms: endothelial damage and activation; monocyte accumulation in the subintimal space; fibroblast migration; and the transformation of vascular smooth muscle cells. A wide variety of animal models exists to investigate the underlying pathophysiology. Although mouse models, with their ease of genetic manipulation, enable cell- and molecular-focused fundamental research, and rats provide the opportunity to use stent and balloon models with high throughput, both rodents lack a lipid metabolism comparable to humans. Rabbits instead build a bridge to close the gap between basic and clinical research due to their human-like lipid metabolism, as well as their size being accessible for clinical angioplasty procedures. Every different combination of animal, dietary, and injury model has various advantages and disadvantages, and the decision for a proper model requires awareness of species-specific biological properties reaching from vessel morphology to distinct cellular and molecular features.

Differentially expressed miR-152, a potential biomarker for in-stent restenosis (ISR) in peripheral blood mononuclear cells (PBMCs) of coronary artery disease (CAD) patients

BACKGROUND AND AIMS

In-stent restenosis (ISR) remains the most daunting challenge of current treatments of coronary artery disease (CAD). MicroRNAs (miRNAs) are prominent regulators of key pathological processes leading to restenosis and used as diagnostic tools in different studies. miR-152 and miR-148a are implicated to contribute in the putative intracellular mechanisms of ISR. The aim of present study is to investigate the potential early-stage diagnostic role of miR-152 and miR-148a expression levels for ISR in peripheral blood mononuclear cells (PBMCs) of patients who underwent stent implantation.

METHODS AND RESULTS

The miRNAs that are supposed to be involved in the ISR were nominated by bioinformatics approach mainly using miRWalk3. Then by quantitative real-time PCR, we determined the relative expression of miR-152 and miR-148a of PBMCs from ISR patients with their age/sex-matched controls.

RESULTS

The presence of ISR significantly coincided with a decrease in the relative expression of miR-152. The area under the curve (AUC) for miR-152 receiver operating characteristic (ROC) curve was 0.717 (95% CI; 0.60-0.83) with a sensitivity of 70% and a specificity of 67%, suggesting that the miRNA expression level might be employed to identify patients at risk of ISR.

CONCLUSIONS

To the best of our knowledge, this is the first work to show that the miR-152 expression level can possibly be applied to predict CAD patients at risk of ISR. The results suggest that the expression levels of miR-152 in PBMCs may serve as a biomarker for ISR. Our finding suggests the importance of miRNA levels in PBMCs as a novel biological tool to detect diseases in their early clinical stages.

Risk prediction of in-stent restenosis among patients with coronary drug-eluting stents: current clinical approaches and challenges

Introduction: In-stent restenosis (ISR) has been one of the biggest limitations to the success of percutaneous coronary intervention for the treatment of coronary artery disease (CAD). The introduction of drug-eluting stent (DES) was a revolution in the treatment of CAD because these devices drastically reduced ISR to very low levels (<5%). Subsequently, newer generation DES treatments have overcome the drawbacks of first-generation DES, i.e. delayed endothelialization, and late stent thrombosis. However, the issue of late ISR, including neoatherosclerosis after DES implantation especially in high-risk patients and complex lesions, still exists as a challenge to be overcome.Areas covered: We discuss the mechanisms of ISR development including neoatherosclerosis, past and current clinical status of ISR, and methods to predict and overcome this issue from pathological and clinical points of view.Expert opinion: The initial drawbacks of first-generation DES, such as delayed endothelial healing and subsequent risk of late stent thrombosis, have been improved upon by the current generation DES. To achieve better long-term clinical outcomes, further titration of drug-release and polymer degradation profile, strut thickness as well as material innovation are needed.

Oversized composite braided biodegradable stents with post-dilatation for pediatric applications: mid-term results of a porcine study

Our aim was to apply a composite braided biodegradable stent (CBBS) made from poly p-dioxanone (PPDO) and polycaprolactone (PCL) as an alternative to metallic stents for the treatment of pediatric endovascular disease. CBBS properties after adjunctive post-dilatation were assessed using radial force testing. CBBS degradation was assessed using in vitro measurements. Self-expandable CBBSs (8 × 20 mm) were implanted in abdominal aortas with an oversizing ratio of 1.1-1.4 (group A, n = 12) and in common iliac arteries with an oversizing ratio >1.4 (group B, n = 12). Self-expandable metal WALLSTENTs (8 × 21 mm) were implanted in common iliac arteries with an oversizing ratio >1.4 and served as controls (group C, n = 12). Artery evaluations including angiography and histological examinations were performed at 1, 4, 6 and 12 months after stent implantation. Eight millimeter CBBSs delivered in 8Fr sheaths with adjunctive post-dilatation had properties similar to those of metallic benchmark stents and were degraded in 12 months, with mild to moderate inflammation-induced neointimal hyperplasia and vessel restenosis. Post-dilatation and oversizing are suggested when using CBBSs for polymeric strut tissue embedding and optimal wall apposition, but an overextended ratio should be avoided because of the induction of less-desirable neointimal hyperplasia. Mid-term outcomes of CBBSs with adjunctive post-dilatation were better than those of WALLSTENTs in a swine endovascular disease model.

Plasma levels of miR-143 and miR-145 are associated with coronary in-stent restenosis within 1 year of follow-up after drug-eluting stent implantation

Background

ISR remains the major adverse outcome after percutaneous coronary intervention (PCI). MicroRNAs have been demonstrated to be associated with coronary plaque and stable in the blood and can be used as biomarkers/predictors. This study aimed to investigate whether circulating microRNAs could predict in-stent restenosis (ISR).

Methods

MicroRNA array was used to detect differently expressed microRNAs between 30 ISR patients and 30 non-ISR patients in the derivation cohort. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to validate the microRNA array results and to detect levels of target microRNAs in the validation cohort. All patients were followed up for at least 1 year, and major adverse cardiac events (MACEs) were recorded. Univariate and multivariate logistic regression analysis were applied to find factors associated with ISR. Receiver operating characteristics (ROC) and Kaplan-Meier survival curves were used to analyze the predictive ability of the microRNA score for ISR.

Results

MicroRNA array and qRT-PCR showed that miR-143, 145, 425, 208, and let-7g were differently expressed between ISR patients and non-ISR patients. Multivariate analysis demonstrated that lower levels of mir-143 (OR =2.36, 95% CI: 1.43–3.67) and mir-145 (OR =2.12, 95% CI: 1.56–3.48) were associated with ISR. MicroRNA scores differed statistically between ISR patients and non-ISR patients (49.18±2.05 vs. 52.10±2.41, P<0.01) and has predictive ability for ISR with an area under the curve (AUC) of 0.8206 (95% CI: 0.7155–0.9256, P<0.01). In the validation cohort, Kaplan-Meier survival curves demonstrated that patients with higher microRNA scores have better prognosis in 1 year of follow-up.

Conclusions

A lower plasma level of mir-143/145 predicts a higher risk of ISR and a worse outcome.

The adipokine vaspin is associated with decreased coronary in-stent restenosis in vivo and inhibits migration of human coronary smooth muscle cells in vitro

BACKGROUND

Percutaneous coronary intervention represents the most important treatment modality of coronary artery stenosis. In-stent restenosis (ISR) is still a limitation for the long-term outcome despite the introduction of drug eluting stents. It has been shown that adipokines directly influence vessel wall homeostasis by influencing the function of endothelial cells and arterial smooth muscle cells. Visceral adipose tissue-derived serpin vaspin was recently identified as a member of serine protease inhibitor family and serveral studies could demonstrate a relation to metabolic diseases. The aim of this study was to investigate a role of vaspin in the development of in-stent restenosis in vivo and on migration of smooth muscle cells and endothelial cells in vitro.

METHODS

We studied 85 patients with stable coronary artery disease who underwent elective and successful PCI with implatation of drug eluting stents. Blood samples were taken directly before PCI. Vaspin plasma levels were measured by specific ELISA. ISR was evaluated eight months later by coronary angiography. Human coronary artery smooth muscle cells (HCASMC) and human umbilical vein endothelial cells (HUVEC) migration was analyzed by an in-vitro migration assay with different concentrations (0.004ng/mL up to 40ng/mL) of vaspin as well as by an scratch assay. For proliferation an impedance measurement with specialiced E-Plates was performed.

RESULTS

During the follow up period, 14 patients developed ISR. Patients with ISR had significantly lower vaspin plasma levels compared to patients without ISR (0.213 ng/ml vs 0.382 ng/ml; p = 0.001). In patients with plasma vaspin levels above 1.35 ng/ml we could not observe any restenosis. There was also a significant correlation of plasma vaspin levels and late lumen loss in the stented coronary segments. Further we could demonstrate that vaspin nearly abolishes serum induced migration of HCASMC (100% vs. 9%; p<0.001) in a biphasic manner but not migration of HUVEC. Proliferation of HCASMC and HUVEC was not modulated by vaspin treatment.

CONCLUSION

We were able to show that the adipokine vaspin selectively inhibits human coronary SMC migration in vitro and has no effect on HUVEC migration. Vaspin had no effect on proliferation of HUVEC which is an important process of the healing of the stented vessel. In addition, the occurrence of ISR after PCI with implantation of drug eluting stents was significantly associated with low vaspin plasma levels before intervention. Determination of vaspin plasma levels before PCI might be helpful in the identification of patients with high risk for development of ISR after stent implantation. In addition, the selective effects of vaspin on smooth muscle cell migration could potentially be used to reduce ISR without inhibition of re-endothelialization of the stented segment.

Histological and Mechanical Behavior of INC 01 and 02 Bare Metal Stents Against a Commercial Stent: A Preclinical Study in a Porcine Model

BACKGROUND

PCI is an expensive procedure in our population and it implies a huge cost for the institutions and National Health Service.

AIM OF THE STUDY

The main objective was to evaluate the technical and biological success of two stents designed in Mexico.

METHODS

Ten York pigs, 4-6 months of age, underwent implantation of the bare metal INC-01 (10 stents) and INC-02 (6 stents) coronary stent in addition to a conventional commercial stent (10 stents). Technical success was evaluated immediately with angiography and Intravascular Ultrasound IVUS, continued by a mean follow-up of 4 month and a final angiographic, IVUS and histological evaluation.

RESULTS

Initial technical success, angiography and IVUS between the three stents were not significant. One stent presented restenosis in follow-up (commercial stent), but all other stents presented excellent clinical outcome, satisfactory angiographic and IVUS results. Inflammation, proliferation and endothelialization between the stents had no major differences in histological analysis in a mean of 4 months follow-up.

CONCLUSIONS

In this pig model, the INC 01 and INC 02 stents showed the same delivering technical success, angiographic and IVUS features, biological and histological response compared to commercial last generation stents.

Reduced histologic neo in-stent restenosis after use of a paclitaxel-coated cutting balloon in porcine coronary arteries

The incidence of in-stent restenosis (ISR) has declined dramatically, but once it develops, no current treatment option, such as drug-eluting stents, drug-coated balloons, or cutting balloons (CBs), prevents re-narrowing of the stented atherosclerotic artery. In this preclinical study, we aimed to improve the efficacy of ISR treatment by coating CBs with paclitaxel (paclitaxel-eluting cutting balloon; PECB) and to characterize the histological features of neo-ISRs that arise after ISR treatment. ISR was induced by bare metal stent (BMS) implantation in coronary arteries in pigs. After one month of follow-up, the BMS-induced ISR was treated with either CB or PECB. After another month, we performed quantitative coronary angiography, explanted the treated arteries and assessed histopathological and histomorphometric parameters. In addition, we compared the histological features of neo-ISRs with pre-treatment ISRs. Injury, inflammation, fibrin deposition, and endothelialization scores were similar between the CB and PECB groups at one month after ISR treatment. Neointimal area (0.87±0.61 vs. 1.95±1.14 mm², p=0.02), mean neointimal thickness (0.40±0.39 vs. 0.99±0.56 mm, p=0.01), and percent area stenosis (27.3±20.4 vs. 48.3±22.9%, p=0.04) were decreased in PECB-treated coronary arteries compared to CB-treated arteries, respectively. Density of cells (predominantly smooth muscle cells; SMCs) was increased in neo-ISRs (3.51±3.05×10³ vs. 6.35±2.57×10³ cells/mm², p<0.01), but significantly more CD68⁺ and CD20⁺ cells were found in the pre-treatment ISRs. In conclusion, PECB treatment of ISRs led to better results in terms of smaller neointimal area and %area stenosis of the neo-ISR. SMC density was increased in neo-ISRs in contrast with higher percentage of CD68⁺ and CD20⁺ cells in pre-treatment ISRs.

Distal Edge Stenosis After Stent Placement for Isolated Superior Mesenteric Artery Dissection: Mechanisms and Risk Factor Analysis

PURPOSE

To analyze factors potentially associated with the occurrence of distal edge stenosis after stent placement for isolated superior mesenteric artery dissection (ISMAD).

MATERIALS AND METHODS

Cases of consecutive patients who were diagnosed with spontaneous ISMAD between February 2010 and July 2018 were retrospectively identified. Of the 123 cases identified, 45 patients (42 men; three women) underwent endovascular stent placement and were included in the study. Univariate and multivariate analyses were used to assess factors potentially associated with distal edge stenosis.

RESULTS

The technical success rate among study patients was 100%. During 26.7 ± 17.3 months of follow-up, CT angiography demonstrated good distal edge patency in 25 patients (55.6%) and evidence of distal edge stenosis in 20 patients (44.4%). In univariate analysis, stent length (odds radio [OR] 1.03; 95% confidence interval [CI] 1.01, 1.06; P = .02), stent-to-vessel (S/V) diameter ratio (OR 2.27; 95% CI 1.35, 3.82; P < .01), and angulation at the distal edge (OR 1.05; 95% CI 1.00, 1.10; P =.03) were significantly associated with distal edge stenosis; only S/V diameter ratio (OR 3.36; 95% CI 1.41, 7.99; P < .01) and angulation at the distal edge (OR 1.12; 95% CI 1.01, 1.23; P =.03) retained this significance in multivariate analysis.

CONCLUSIONS

Distal edge stenosis after stent placement for ISMAD is common. S/V diameter ratio and angulation at the distal edge are independent risk factors for distal edge stenosis in patients with ISMAD who undergo stent placement.

Swine model of in-stent stenosis in the iliac artery evaluating the serial time course

The aim of this study was to propose a new animal model evaluating the serial time course of in-stent stenosis by repeated carotid artery catheterization in the same animal. 16 bare-metal stents were implanted in the normal external and internal iliac artery of 8 miniature pigs. Repeated measurements were performed in the same animal every 2 weeks for 12 weeks through carotid artery catheterization. The time course and peak neointimal proliferation were evaluated by intravascular ultrasound. Health of all animals was assessed by clinical and hematological examinations. As a result, 7 times of carotid artery catheterization was performed per pig, but all animals remained healthy without both any complications and hematological inflammatory abnormalities. The time course of neointimal proliferation of each stent was observed from the stage of hyperplasia to partial regression. The peak neointimal proliferation varied from 6 to 12 weeks despite implantation of identical stents using the same deployment method. In conclusion, repeated carotid artery catheterization to the same animal is feasible without animal health deterioration. This model should be useful to evaluate the time course of neointimal proliferation after stent deployment in preclinical study.

Management of isolated femoropopliteal in-stent restenosis

OBJECTIVE

The optimal catheter-directed therapy for femoropopliteal in-stent restenosis (ISR) remains controversial with limited durability. The natural history of untreated ISR is not well characterized. We evaluated the midterm outcomes of patients with asymptomatic isolated femoropopliteal ISR who were observed under a surveillance program.

METHODS

Patients treated with isolated femoropopliteal stents from January 2009 to December 2013 were retrospectively investigated for the development of ISR. ISR was classified on the basis of duplex ultrasound criteria, with >50% defined as peak systolic velocity (PSV) twice that of the normal vessel and >75% as PSV >400 cm/s or four times the normal PSV. Asymptomatic patients with ISR of >50% were tracked for progression to high-grade (>75%) stenosis, occlusion, need for reintervention, and amputation.

RESULTS

Asymptomatic ISR of >50% was identified in 62 (15.3%) of 402 patients with isolated femoropopliteal stents. The mean time for development of ISR was 22.1 (±20.1) months. The mean age was 72 (±9.7) years, and 34 (55.7%) patients were female. Thirty-one (50%) patients were diabetic, 18 (29.1%) were smokers, and 8 (12.9%) had chronic kidney disease. Indications for treatment were claudication in 49 (79.0%), tissue loss in 9 (14.5%), and rest pain in 4 (6.4%) patients. TransAtlantic Inter-Society Consensus (TASC) A lesions were treated in 13 (21%) patients, TASC B lesions in 24 (38.7%), and TASC C lesions in 25 (40.3%). Three-vessel runoff was identified in 25 (40.3%) patients, two-vessel runoff in 18 (29.0%), and one-vessel runoff in 19 (30.6%). Under surveillance, ISR of >50% progressed to >75% or occlusion in 20 (32.3%) patients. The mean time to progression was 17.4 months, and the mean overall follow-up was 33.1 months. Reintervention was required in 22 (35.0%) patients, with an average of 1.95 (range, 1-4) interventions per patient. Reintervention was undertaken in 19 (86%) patients for claudication and in 3 (18%) patients for critical limb ischemia. One patient required an amputation despite previous reintervention for progression. Progression to >75% stenosis was predictive of need for reintervention (P = .004).

CONCLUSIONS

Under a surveillance program, asymptomatic patients with femoropopliteal ISR of >50% may be observed with a low risk of limb loss. Given the slow rate of progression and the poor durability of reintervention, surveillance with delayed intervention may be warranted.

Mid-term clinical outcomes after bailout drug-eluting stenting for suboptimal drug-coated balloon results: Insights from a Milan registry

BACKGROUND

Drug-coated balloon (DCB) is an alternative to drug-eluting stent (DES) for the treatment of small vessel or in-stent restenosis (ISR) lesions, with bailout stenting reserved for poor results after DCB inflation (residual stenosis or dissection). Data regarding bailout stenting with DES are limited. The aim of this study was to evaluate clinical outcomes after bailout stenting with DES for suboptimal DCB results.

METHODS

From June 2009 to December 2015, patients who underwent bailout DES implantation for suboptimal results after DCB (residual stenosis > 30% or type C-F dissection) in 2 high-volume centers in Italy were analyzed. The primary endpoint was target lesion failure (TLF) defined as composite of cardiac mortality, target vessel myocardial infarction (MI) and target lesion revascularization (TLR).

RESULTS

A total of 103 patients (125 lesions) were analyzed. Mean age was 68.8 ± 9.5 years, 21.4% were diabetic, and 92.2% underwent PCI for stable angina. The left anterior descending artery was most commonly treated (35.2%), followed by right coronary artery (17.6%) and left circumflex artery (17.6%). Lesion complexity was high (type B2/C: 88.8%) and 24.8% were ISR lesions. During the follow-up period (median: 858 days [interquartile range: 467-1665]), the TLF rate was 4.3% at 1 year and 15.4% at 2 years, and mainly driven by TLR (3.3% at 1 year, 14.5% at 2 years, respectively). There were no target vessel MI or definite/probable stent thrombosis events.

CONCLUSIONS

Bailout stenting with DES for suboptimal DCB results is a feasible and safe strategy at mid-term follow-up.

Nanoparticle-Mediated Cell Capture Enables Rapid Endothelialization of a Novel Bare Metal Stent

Incomplete endothelialization of intracoronary stents has been associated with stent thrombosis and recurrent symptoms, whereas prolonged use of dual antiplatelet therapy increases bleeding-related adverse events. Facilitated endothelialization has the potential to improve clinical outcomes in patients who are unable to tolerate dual antiplatelet therapy. The objective of this study was to demonstrate the feasibility of magnetic cell capture to rapidly endothelialize intracoronary stents in a large animal model. A novel stent was developed from a magnetizable duplex stainless steel (2205 SS). Polylactic-co-glycolic acid and magnetite (Fe₃O₄) were used to synthesize biodegradable superparamagnetic iron oxide nanoparticles, and these were used to label autologous blood outgrowth endothelial cells. Magnetic 2205 SS and nonmagnetic 316L SS control stents were implanted in the coronary arteries of pigs (n = 11), followed by intracoronary delivery of magnetically labeled cells to 2205 SS stents. In this study, we show extensive endothelialization of magnetic 2205 SS stents (median 98.4% cell coverage) within 3 days, whereas the control 316L SS stents exhibited significantly less coverage (median 48.9% cell coverage, p < 0.0001). This demonstrates the ability of intracoronary delivery of magnetic nanoparticle labeled autologous endothelial cells to improve endothelialization of magnetized coronary stents within 3 days of implantation.

Early endothelialization associated with a biolimus A9 bioresorbable polymer stent in a porcine coronary model

Although Nobori^®, with a bioresorbable polymer and biolimus A9 abluminal coating, has unique characteristics, few data exist regarding endothelialization early after implantation. Fifteen Nobori^® and 14 control bare-metal stents (S-stent™) were implanted in 12 pigs. Histopathology of stented segments, inflammation, and intimal fibrin content was evaluated on the 2nd and 14th day after implantation. On the 2nd day, endothelial cells were morphologically and immunohistologically confirmed on the surface of both stents, although some inflammatory cells might be involved. Stent surface endothelialization evaluated with a scanning electron microscope showed partial cellular coverage in both stents. On the 14th day, neointimal thickness and percentage of the neointimal area were significantly lower in Nobori^® than in S-stent™ (51.4 ± 4.5 vs. 76.4 ± 23.6 µm, p < 0.05 and 10.8 ± 2.6 vs. 14.1 ± 4.2%, p < 0.01). No significant differences were found in these parameters on the 2nd day (17.3 ± 14.9 vs. 26.7 ± 13.6 µm and 3.7 ± 3.0 vs. 6.7 ± 3.7%), in inflammatory and intimal fibrin content scores. These results demonstrate that endothelialization could occur early after Nobori^® implantation with similar inflammatory reaction to bare-metal stents, probably contributing to low frequency of in-stent thrombosis and restenosis.

Meta-Analysis-Derived Benchmarks of Patency and Target Lesion Revascularization of Percutaneous Balloon Angioplasty from Prospective Clinical Trials of Symptomatic Femoropopliteal In-Stent Restenosis

PURPOSE

To establish historic benchmarks of patency and target lesion revascularization (TLR) in a study-level meta-analysis of prospective studies of balloon angioplasty in treating femoropopliteal in-stent restenosis (ISR).

MATERIALS AND METHODS

Data from the balloon angioplasty control arms of 4 randomized multicenter trials (1 Food and Drug Administration-approved study in the United States and 3 conducted in Europe) and 1 European prospective registry were included. Trials included patients with Rutherford stage 1-5 disease or Fontaine ischemia classification states IIb, III, IV and femoropopliteal ISR lesion lengths of 4-27 cm. A two-stage meta-analysis was conducted with study-specific estimates obtained from the randomized trials at the first stage and an analysis that pooled all study-specific estimates at the second stage. The Breslow-Day test of homogeneity was performed on patency and TLR at 6 months and 1 year.

RESULTS

Analysis of the balloon-angioplasty control arms of the 5 prospective trials identified 303 patients (mean lesion length, 144.5 mm ± 88.0; vessel diameter, 4.9 mm ± 0.7). Six- and 12-month duplex ultrasound patency rates were 60.7% and 33%, respectively. Six- and 12-month TLR rates with and without "bailout" stent placement considered as TLR were 37.9% and 55.4% and 27.0% and 42.6%, respectively.

CONCLUSIONS

It is feasible to derive 6-month and 1-year patency and TLR benchmark data from existing prospective trials of balloon angioplasty in femoropopliteal ISR. However, the study is limited by the lack of data from larger prospective trials with longer-term follow-up.

Secreted Matrix Metalloproteinase-9 of Proliferating Smooth Muscle Cells as a Trigger for Drug Release from Stent Surface Polymers in Coronary Arteries

Cardiovascular diseases are the leading causes of death in industrialized countries. Atherosclerotic coronary arteries are commonly treated with percutaneous transluminal coronary intervention followed by stent deployment. This treatment has significantly improved the clinical outcome. However, triggered vascular smooth muscle cell (SMC) proliferation leads to in-stent restenosis in bare metal stents. In addition, stent thrombosis is a severe side effect of drug eluting stents due to inhibition of endothelialization. The aim of this study was to develop and test a stent surface polymer, where cytotoxic drugs are covalently conjugated to the surface and released by proteases selectively secreted by proliferating smooth muscle cells. Resting and proliferating human coronary artery smooth muscle cells (HCASMC) and endothelial cells (HCAEC) were screened to identify an enzyme exclusively released by proliferating HCASMC. Expression analyses and enzyme activity assays verified selective and exclusive activity of the matrix metalloproteinase-9 (MMP-9) in proliferating HCASMC. The principle of drug release exclusively triggered by proliferating HCASMC was tested using the biodegradable stent surface polymer poly-l-lactic acid (PLLA) and the MMP-9 cleavable peptide linkers named SRL and AVR. The specific peptide cleavage by MMP-9 was verified by attachment of the model compound fluorescein. Fluorescein release was observed in the presence of MMP-9 secreting HCASMC but not of proliferating HCAEC. Our findings suggest that cytotoxic drug conjugated polymers can be designed to selectively release the attached compound triggered by MMP-9 secreting smooth muscle cells. This novel concept may be beneficial for stent endothelialization thereby reducing the risk of restenosis and thrombosis.

Local Stent-Based Release of Transforming Growth Factor-β1 Limits Arterial In-Stent Restenosis

The long-term success of intra-arterial stenting remains limited by in-stent restenosis (ISR). Transforming growth factor-β1 (TGF-β1) can inhibit smooth muscle cell (SMC) proliferation and migration and convert SMCs into extracellular matrix (ECM)-synthesizing cells. Here, we evaluate the effects of stent-based delivery of TGF-β1 on ISR in a rabbit model. Channeled stents loaded with TGF-β1 or control microspheres were deployed in rabbit aortas. Stented aortas were harvested at 7 and 28 d and evaluated for Ki-67-positive cells, collagenous ECM production, and intima-to-media (I/M) ratio. At 7 d, the TGF-β1 group exhibited fewer Ki-67-positive cells were found for the TGF-β1 group (17.87 ± 2.18 cells per mm(2)) relative to control (25.07 ± 2.65 cells per mm(2), p = 0.04), but increased collagen content (31.4 ± 2.5 percentage area) compared with control (29.3 ± 1.2 percentage area, p = 0.019). The I/M ratio in the TGF-β1 group was reduced by 50% and 9.1% versus control at 7 d (0.13 ± 0.02 vs. 0.26 ± 0.02, p = 0.0001) and 28 d (1.80 ± 0.05 vs. 1.98 ± 0.08, p = 0.0038), respectively. Stent-based controlled release of TGF-β1 limits ISR and is associated with inhibition of SMC proliferation but an increase in ECM production.

Role of Animal Models in Coronary Stenting

Coronary angioplasty initially employed balloon dilatation only. This technique revolutionized the treatment of coronary artery disease, although outcomes were compromised by acute vessel closure, late constrictive remodeling, and restenosis due to neointimal proliferation. These processes were studied in animal models, which contributed to understanding the biology of endovascular arterial injury. Coronary stents overcome acute recoil, with improvements in the design and metallurgy since then, leading to the development of drug-eluting stents and bioresorbable scaffolds. These devices now undergo computer modeling and benchtop and animal testing before evaluation in clinical trials. Animal models, including rabbit, sheep, dog and pig are available, all with individual benefits and limitations. In smaller mammals, such as mouse and rabbit, the target for stenting is generally the aorta; whereas in larger animals, such as the pig, it is generally the coronary artery. The pig coronary stenting model is a gold-standard for evaluating safety; but insights into biomechanical properties, the biology of stenting, and efficacy in controlling neointimal proliferation can also be gained. Intra-coronary imaging modalities such as intravascular ultrasound and optical coherence tomography allow precise serial evaluation in vivo, and recent developments in genetically modified animal models of atherosclerosis provide realistic test beds for future stents and scaffolds.

Healing arterial ulcers: Endothelial lining regeneration upon vascular denudation injury

Thrombosis and restenosis are the most prevalent late complications of coronary artery stenting. Current standards of clinical care focus on prevention of smooth muscle cell proliferation by the use of drug-eluting stents able to release anti-proliferative drugs. Unfortunately, these drugs also block endothelial cell proliferation and, in this manner, prevent recovery of endothelial cell coverage. Continued lack of endothelial repair leaves the root cause of thrombosis and restenosis unchanged, creating a vicious cycle where drug-mediated prevention of restenosis simultaneously implies promotion of thrombosis. In this issue of Vascular Pharmacology, Hussner and colleagues provide in vitro evidence and a mechanistic basis for the use of atorvastatin in stents as a way to bypass this roadblock. Here we review the pathological mechanisms and therapeutic approaches to restore flow in occluded arteries. We argue that rational design of drug eluting stents should focus on specific inhibition of smooth muscle cell proliferation with concurrent stimulation of endothelial regeneration. We comment on the current poor understanding of the cellular and molecular regulation of endothelial cell proliferation in the context of a functional artery, and on the pitfalls of extrapolating from the well-studied process of neovascularization by sprouting vessel formation.

Sequential Structural and Fluid Dynamics Analysis of Balloon-Expandable Coronary Stents: A Multivariable Statistical Analysis

Several clinical studies have identified a strong correlation between neointimal hyperplasia following coronary stent deployment and both stent-induced arterial injury and altered vessel hemodynamics. As such, the sequential structural and fluid dynamics analysis of balloon-expandable stent deployment should provide a comprehensive indication of stent performance. Despite this observation, very few numerical studies of balloon-expandable coronary stents have considered both the mechanical and hemodynamic impact of stent deployment. Furthermore, in the few studies that have considered both phenomena, only a small number of stents have been considered. In this study, a sequential structural and fluid dynamics analysis methodology was employed to compare both the mechanical and hemodynamic impact of six balloon-expandable coronary stents. To investigate the relationship between stent design and performance, several common stent design properties were then identified and the dependence between these properties and both the mechanical and hemodynamic variables of interest was evaluated using statistical measures of correlation. Following the completion of the numerical analyses, stent strut thickness was identified as the only common design property that demonstrated a strong dependence with either the mean equivalent stress predicted in the artery wall or the mean relative residence time predicted on the luminal surface of the artery. These results corroborate the findings of the large-scale ISAR-STEREO clinical studies and highlight the crucial role of strut thickness in coronary stent design. The sequential structural and fluid dynamics analysis methodology and the multivariable statistical treatment of the results described in this study should prove useful in the design of future balloon-expandable coronary stents.

Multicenter randomized trial of 3-month cilostazol use in addition to dual antiplatelet therapy after biolimus-eluting stent implantation for long or multivessel coronary artery disease

BACKGROUND

There are conflicting data on the use of cilostazol as triple antiplatelet therapy (TAPT) for improving clinical outcomes after drug-eluting stent implantation. We aimed to evaluate whether 3-month use of cilostazol in addition to dual antiplatelet therapy (DAPT) improved clinical outcomes in patients with long or multivessel coronary artery disease (CAD) after biolimus-eluting stent (BES) implantation.

METHODS

Patients (n = 630) who had been successfully treated with BES implantation for lesions with ≥28 mm in stent length or ≥2 stents for different coronary arteries were enrolled in this prospective randomized multicenter trial. All patients were randomly assigned to receive either DAPT (aspirin and clopidogrel for 12 months, n = 314) or TAPT (DAPT plus 3-month cilostazol use, n = 316). The primary end point was a device-oriented composite consisting of cardiac death, myocardial infarction (not clearly attributable to a nontarget vessel), and ischemia-driven target lesion revascularization at 1-year follow-up.

RESULTS

A total of 314 patients in DAPT and 308 patients in TAPT were analyzed. Multivessel CAD was present in 65.7% of patients. Stents ≥28 mm in length were implanted in 58.1% of lesions. There were no significant differences in baseline and angiographic characteristics between the 2 groups. The primary end point was similar between the 2 groups (2.3% in DAPT vs 1.9% in TAPT, log-rank P = .799).

CONCLUSIONS

In patients treated with BES implantation for long or multivessel CAD, 3 months of cilostazol use in addition to DAPT did not improve clinical outcome at 1-year follow-up.

Perivascular delivery of neomycin inhibits the activation of NF-κB and MAPK pathways, and prevents neointimal hyperplasia and stenosis after arterial injury

The nuclear transcription factor kappaB (NF-kappaB) is a cytoplasmic dimer that, as the family of mitogen-activated protein kinase (MAPK), can directly regulate the expression of early genes and genes involved in the stress response, following a variety of physiological or pathological stimuli. Both of them stimulate the transcription of many proteins, which are considered important during inflammation. A crucial role has been assigned to these factors in cellular proliferation and in neointimal hyperplasia secondary to the endothelial lesion of arterial vessels. On the other hand, it has been described that neomycin can have an inhibitory function on tumor cell proliferation, through the inhibition of different intracellular pathways of signaling, among them the NF-kappaB and MAPK pathways. Rat common carotid artery was subjected to balloon angioplasty. Neomycin sulfate (18 mg) was applied using pluronic acid gel on the adventitial surface of the injured vessel. MAPK and NF-kappaB activation was quantified after 24 hours with immunohistochemical staining. Neointimal formation was quantified after 14 days with morphometry. Immunohistochemistry results demonstrating MAPK and NF-kappaB activation reveal that both transcription factors are activated in the media of the control vessel wall. In contrast, the immunoreactivity for MAPK and NF-kappaB in the sections obtained from arteries treated with neomycin over 24 hours was insufficient or nonexistent. Treatment with neomycin on adventitia over 14 days in arteries on which angioplasty was performed shows a neointimal index (intimal area/medial area) decrease of 71% in comparison with arteries that were not treated. The adventitial neomycin treatment over 14 days produces a very significant increase (287.5%; p<0.0001) in the arterial luminal circumference in comparison with arteries treated with vehicle. These results support the theory that neomycin plays an important role against neointimal hyperplasia through the inhibition of MAPK and NF-kappaB activation.

Xiongshao for restenosis after percutaneous coronary intervention in patients with coronary heart disease

BACKGROUND

Percutaneous coronary intervention (PCI) with stent placement is a standard treatment for coronary heart disease (CHD). In-stent restenosis after PCI remains an important clinical problem. Xiongshao capsule has been reported to be beneficial in preventing restenosis after PCI in CHD patients. However, the strength of evidence to support its use is unclear.

OBJECTIVES

To systematically assess the efficacy and safety of Chinese herbal medicine Xiongshao capsule in preventing restenosis after PCI in patients with CHD.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library (Issue 3 of 2012), MEDLINE (OVID) (1948 to week 1 March 2012), EMBASE (OVID) (1980 to week 10 2012), ISI Web of Science with Conference Proceedings (1970 to 14 March 2012), LILACS (1982 to 15 March 2012), Chinese biomedical literature database (1980 to May 2012), China National Knowledge Infrastructure (1994 to May 2012), Chinese Medical Current Contents (1994 to May 2012), VIP Database for Chinese Technical Periodicals (1989 to May 2012), Chinese Master's Theses Full-Text Database (1994 to May 2012), China Doctor Dissertation Full-Text Database (1994 to May 2012), and China Proceedings of Conference Full-Text Database (1994 to May 2012). We also searched ongoing trials and research registries.

SELECTION CRITERIA

All randomised controlled trials comparing Xiongshao capsule alone/plus conventional western medicine with the same conventional western medicine alone/plus placebo in participants with CHD who met the recognised diagnostic criteria and had successfully undergone a PCI procedure were included.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials and extracted data. Two review authors independently assessed the risk of bias of included trials using The Cochrane Collaboration tool, and any disagreements were resolved by discussion with a third review author. Data were pooled for meta-analysis using the fixed-effect model, and the results were expressed as risk ratios (RRs) with 95% confidence intervals (CIs).

MAIN RESULTS

Four trials involving 649 participants were included in this review. Two of these trials (459 participants) were designed as randomised, double-blind, placebo-controlled trials with an adequate methodological description; the other two trials (190 participants) described an inadequate methodological design. All four trials with 649 participants were included in the meta-analysis. Significant differences were noted in rates of restenosis, recurrence angina pectoris, and serious cardiovascular adverse events between Xiongshao capsule plus conventional western medicine and the same conventional western medicine alone; RR values (95% CIs) were 0.41 (0.22 to 0.75), 0.47 (0.31 to 0.72), and 0.47 (0.25 to 0.90), respectively. Xiongshao capsule plus conventional western medicine showed more significant reductions in restenosis (RR 0.52, 95% CI 0.33 to 0.80), recurrence angina pectoris (RR 0.26, 95% CI 0.18 to 0.38), and serious cardiovascular adverse events (RR 0.45, 95% CI 0.28 to 0.70) than the same conventional western medicine plus placebo. Safety outcomes and adverse events of the Xiongshao capsule were reported in two trials, which reported no adverse events.

AUTHORS' CONCLUSIONS

The summary estimates indicate a protective effect of Xiongshao on restenosis and suggest that Xiongshao capsule may be used to prevent restenosis after a PCI procedure in CHD patients. However, this evidence is derived from small randomised trials, all conducted in China, and two of the included trials showed important methodological limitations that undermine the validity of the findings. Additional high-quality research trials with sufficient sample size are required.

Drug-eluting stent restenosis: effect of drug type, release kinetics, hemodynamics and coating strategy

Restenosis following stent implantation diminishes the procedure's efficacy influencing long-term clinical outcomes. Stent-based drug delivery emerged a decade ago as an effective means of reducing neointimal hyperplasia by providing localized pharmacotherapy during the acute phase of the stent-induced injury and the ensuing pathobiological mechanisms. However, drug-eluting stent (DES) restenosis may still occur especially when stents are used in complex anatomical and clinical scenarios. A DES consists of an intravascular metallic frame and carriers which allow controlled release of active pharmaceutical agents; all these components are critical in determining drug distribution locally and thus anti-restenotic efficacy. Furthermore, dynamic flow phenomena characterizing the vascular environment, and shear stress distribution, are greatly influenced by stent implantation and play a significant role in drug deposition and bioavailability within local vascular tissue. In this review, we discuss the performance of DES and the interaction of the different DES components with the hemodynamic milieu emphasizing on the inhibition of clinical restenosis.

Oversizing and restenosis with self-expanding stents in iliofemoral arteries

PURPOSE

Uncoated self-expanding nitinol stents (NS) are commonly oversized in peripheral arteries. In current practice, 1-mm oversizing is recommended. Yet, oversizing of NS may be associated with increased restenosis. To provide further evidence, NS were implanted in porcine iliofemoral arteries with a stent-to-artery-ratio between 1.0 and 2.3. Besides conventional uncoated NS, a novel self-expanding NS with an antiproliferative titanium-nitride-oxide (TiNOX) coating was tested for safety and efficacy.

METHODS

Ten uncoated NS and six TiNOX-coated NS (5-6 mm) were implanted randomly in the iliofemoral artery of six mini-pigs. After implantation, quantitative angiography (QA) was performed for calculation of artery and minimal luminal diameter. Follow-up was performed by QA and histomorphometry after 5 months.

RESULTS

Stent migration, stent fracture, or thrombus formation were not observed. All stents were patent at follow-up. Based on the location of the stent (iliac/femoral) and the stent-to-artery-ratio, stent segments were divided into "normal-sized" (stent-to-artery-ratio < 1.4, n = 12) and "oversized" (stent-to-artery-ratio ≥ 1.4, n = 9). All stent segments expanded to their near nominal diameter during follow-up. Normal-sized stent segments increased their diameter by 6% and oversized segments by 29%. A significant correlation between oversizing and restenosis by both angiography and histomorphometry was observed. Restenosis rates were similar for uncoated NS and TiNOX-coated NS.

CONCLUSIONS

TiNOX-coated NS are as safe and effective as uncoated NS in the porcine iliofemoral artery. All stents further expand to near their nominal diameter during follow-up. Oversizing is linearly and positively correlated with neointimal proliferation and restenosis, which may not be reduced by TiNOX-coating.

Effectiveness of triptolide-coated stent on decreasing inflammation and attenuation of intimal hyperplasia in a pig after coronary angioplasty

OBJECTIVE

The study is to test the efficacy of triptolide-coated stent on anti-inflammatory and inhibiting intimal hyperplasia in preventing restenosis.

METHODS

A total of 15 triptolide-coated stents (TCSs), 12 drug-eluting stents (DESs), and 12 bare metal stents (BMSs) were deployed in porcine coronary arteries. Coronary angiography, histopathologic and inflammatory markers levels were analyzed at 4 week after stenting.

RESULTS

At 4-week follow-up, quantitative coronary angiography (QCA) showed that minimum lumen diameter was greater, and percentage stenosis and late lumen loss in TCS group and DES group were less than that of BMS group. Compared to BMS group, injury and inflammation score in TCS group and DES group were decreased, neointimal area significantly reduced and lumen area enlarged in TCS, DES group as well.

CONCLUSION

Triptolide-coated stent showed the effect of preventing restenosis via inhibition of neointimal hyperplasia and anti-inflammation acts after coronary angioplasty.

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.

Histopathologic evaluation of patent ductus arteriosus stents after hybrid stage I palliation

The aim of this study was to determine the histopathology of patent ductus arteriosus (PDA) in-stent stenosis after hybrid stage I palliation. The hybrid approach to palliation of hypoplastic left heart syndrome can be complicated by the development of in-stent stenosis of the PDA. This may obstruct retrograde aortic arch flow, decrease systemic circulation, and lead to interstage interventional procedures. Stented PDA samples removed from eight patients undergoing comprehensive stage II repair were examined by way of radiography and histochemistry (hematoxylin and eosin, Movat pentachrome, α-smooth muscle actin, and proliferating cell nuclear antigen). A retrospective chart review of the patients was also performed. PDA stents were in place in the PDA for a mean period of 169 ± 28 days in patients who had a mean age of 176 ± 30 days at the time of stent removal. Stent deployment caused chronic inflammation, caused fibrin deposition, and induced vascular smooth muscle-cell (VSMC) proliferation in the area immediately surrounding the stent struts. The neointimal region was composed largely of smooth muscle cells that appeared to be fully differentiated by the lack of PCNA staining. Neointimal thickening occurs in the PDA after stent placement for hybrid palliation of HLHS and is the result of inflammation, extracellular matrix deposition, and smooth muscle-cell proliferation in the peristrut region. This finding suggests that proliferating VSMCs in the peristrut region may provide the impetus for inward neointimal formation and therefore the manifestation of in-stent stenosis.

Polymer-free paclitaxel-coated Zilver PTX Stents--evaluation of pharmacokinetics and comparative safety in porcine arteries

PURPOSE

To evaluate the pharmacokinetics and safety of the Zilver PTX Drug-Eluting Stent (Cook Medical, Bloomington, Indiana) in a normal porcine artery model.

MATERIALS AND METHODS

Pharmacokinetic analyses were performed using 18 pigs, each implanted with four paclitaxel-coated stents. Paclitaxel remaining on the stents, delivered locally (to artery wall), regionally (to adjacent and downstream muscle), and systemically (to plasma), was determined at various times through 56 days. For safety evaluation, local, regional, and systemic responses were grossly and histologically assessed at 1 month, 3 months, and 6 months in 21 additional pigs and compared with the responses to bare metal stents in 21 separate pigs.

RESULTS

Stents delivered approximately 95% of the total paclitaxel within 24 hours after deployment. Nonetheless, there were sustained paclitaxel levels in the artery wall through 56 days, maintained at approximately 20% of the peak level through 14 days. Very little paclitaxel was distributed regionally or systemically, becoming undetectable in plasma at 10 hours. Complete necropsy, hematology, and serum chemistry revealed no adverse effects associated with the paclitaxel-coated stents. Within 3 months, vessels with both paclitaxel-coated and bare metal stents showed comparable, complete healing.

CONCLUSIONS

The Zilver PTX stent appears to be safe, achieves sustained paclitaxel levels in the artery wall, and shows complete vessel healing comparable to bare metal stents within 3 months.

The representative porcine model for human cardiovascular disease

To improve human health, scientific discoveries must be translated into practical applications. Inherent in the development of these technologies is the role of preclinical testing using animal models. Although significant insight into the molecular and cellular basis has come from small animal models, significant differences exist with regard to cardiovascular characteristics between these models and humans. Therefore, large animal models are essential to develop the discoveries from murine models into clinical therapies and interventions. This paper will provide an overview of the more frequently used large animal models, especially porcine models for preclinical studies.

Therapeutic potential for protein kinase C inhibitor in vascular restenosis

Vascular restenosis, an overreaction of biological response to injury, is initialized by thrombosis and inflammation. This response is characterized by increased smooth muscle cell migration and proliferation. Available pharmacological treatments include anticoagulants, antiplatelet agents, immunosuppressants, and antiproliferation agents. Protein kinase C (PKC), a large family of serine/threonine kinases, has been shown to participate in various pathological stages of restenosis. Consequently, PKC inhibitors are expected to exert a wide range of pharmacological activities therapeutically beneficial for restenosis. In this review, the roles of PKC isozymes in platelets, leukocytes, endothelial cells, and smooth muscle cells are discussed, with emphasis given to smooth muscle cells. We will describe cellular and animal studies assessing prevention of restenosis with PKC inhibitors, particularly targeting -α, -β, -δ, and -ζ isozymes. The delivery strategy, efficacy, and safety of such PKC regulators will also be discussed.

The pre-clinical animal model in the translational research of interventional cardiology

Scientific discoveries for improvement of human health must be translated into practical applications. Such discoveries typically begin at "the bench" with basic research, then progress to the clinical level. In particular, in the field of interventional cardiology, percutaneous cardiovascular intervention has rapidly evolved from an experimental procedure to a therapeutic clinical setting. Pre-clinical studies using animal models play a very important role in the evaluation of efficacy and safety of new medical devices before their use in human clinical studies. This review provides an overview of the emerging role, results of pre-clinical studies and development, and evaluation of animal models for percutaneous cardiovascular intervention technologies for patients with symptomatic cardiovascular disease.

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.

Stent-based release of a selective PDGF-receptor blocker from the bis-indolylmethanon class inhibits restenosis in the rabbit animal model

Long-term success of modern therapies for myocardial ischemia is limited by restenosis, with proliferation and migration of vascular smooth muscle cells (VSMC) as key events. Since findings in recent years indicate, that the Platelet Derived Growth Factor (PDGF) is an important selective factor in mitogenic and motogenic pathways of VSMC, different concepts for reducing restenosis by inhibiting PDGF signaling have been investigated, with local delivery of small receptor kinase inhibitors looking most promising. We tested the stent-based delivery of the PDGF-receptor inhibitor D-65495, a bis(1H-2-indolyl)methanone, in the rabbit iliac artery model of restenosis. New Zealand white rabbits underwent balloon dilation of iliac arteries for implantation of D-65495-coated or non-coated (solvent, either DMSO or 90%THF / 10% DMSO) coronary stents. After 4 weeks stents were removed and neointima formation in medial and proximal/ distal stent sections was histomorphometrically and immunohistochemically analyzed. Arteries with D-65495 eluting stents showed an up to 50% reduced restenosis compared to control stents. Also, the neointimal area was reduced, but there were no significant differences in injury score. Importantly, endothelialization was similar for control stents as well as for D-65495-coated stents, suggesting absence of a general cytostatic effect of the inhibitor. The impact of D-65495 on PDGF-receptor signaling in the vessel wall was indirectly assessed by immunohistochemical staining for activated protein kinase Akt, and PCNA as a proliferation marker and revealed some reduction for the inhibitor-treated vessels. In conclusion, the application of D-65495 caused a significant decrease in neointima formation, further supporting the concept of using locally released PDGF-receptor kinase inhibitors as anti-restenotic agents.

Neointimal vascularization and intimal thickening in response to self‐expanding stents: a swine model

BACKGROUND

Neovascularization has been suggested as a biological response to vessel injury and associated with restenosis. Self-expanding (SE) stents generate a lasting force on the arterial wall and may lead to an increased arterial response with time.

OBJECTIVES

To characterize the process of neovascularization with SE stents, and to correlate it with vascular injury, inflammation and intimal proliferation.

METHODS

Sixty-nine SE stents were im-planted in 37 non-atherosclerotic pigs.Detailed, multisection histological examination was performed at 15 days, 1, 3 and 6 months post-deployment. Neo-vascularization in addition to other histologic parameters where determined and scored.

RESULTS

Intravascular-ultrasound-based average vessel diameter was 3.3 +/- 0.04 mm; stent size was 3.75 +/- 0.35 mm leading to an oversizing ratio of 1.14 +/- 0.15. Intimal thickness (IT), inflammatory score (IFS) and vascularization score(VAS) reached peak values at three months (IT = 344 +/- 202 1m, IFS = 0.91 +/- 0.5, and VAS = 1.56 +/- 0.8). In contrast,the injury score (INS) continued to increase at all time-points, with maximum value at six months (INS = 1.6 +/- 0.7). Both vascularization and inflammation indices increased with an increase in the injury score (p < 0.01). When vessels were divided according to vascularization score (VAS <1.5 and >1.5) there was a significant difference in IT.

CONCLUSION

Neovascularization in response to SE stents is a time-dependent phenomenon and interacts with injury and inflammation. The remodeling of the vessel wall caused by the sustained force of the SE stent on the arterial wall enhances the formation of neovascularization. Neointimal formation is related to the degree of neovascularization.

Late stent expansion and neointimal proliferation of oversized Nitinol stents in peripheral arteries

For peripheral endovascular intervention, self-expanding (SE) stents are commonly oversized in relation to target arteries to assure optimal wall apposition and prevent migration. However, the consequences of oversizing have not been well studied. The purpose of this study was to examine the effects of SE stent oversizing (OS) with respect to the kinetics of late stent expansion and the long-term histological effects of OS. Pairs of overlapped 8 x 28-mm Nitinol SE stents were implanted into the iliofemoral arteries of 14 Yucatan swine. Due to variations in target artery size, the stent-to-artery ratio ranged from 1.2:1 to 1.9:1. Lumen and stent diameters were assessed by quantitative angiography at the time of implantation. Following angiographic assessment at 6 months, stented arteries were perfusion-fixed, sectioned, and stained for histological analysis. Immediately following implantation, the stents were found to be expanded to a range of 4.7-7.1 mm, largely conforming to the diameter of the recipient target artery. The stents continued to expand over time, however, and all stents had enlarged to nearly their 8-mm nominal diameter by 6 months. The histological effects of OS were profound, with marked increases in injury and luminal area stenosis, including a statistically significant linear correlation between stent-to-artery ratio and area stenosis. In this experimental model of peripheral endovascular intervention, oversized Nitinol SE stents are constrained by their target artery diameter upon implantation but expand to their nominal diameter within 6 months. Severe OS (stent-to-artery ratio >1.4:1) results in a profound long-term histological response including exuberant neointimal proliferation and luminal stenosis.

Treatment of in-stent restenosis with beraprost sodium: an experimental study of short- and intermediate-term effects in dogs

1. The aim of the present study was to evaluate the inhibitory effects of the short-term administration of beraprost sodium, a stable prostaglandin I(2) analogue, on neointimal thickening after stenting. 2. To examine the immediate and short-term effects, Z-stents were placed in the iliac veins of 12 dogs, which were randomly assigned to either a beraprost-treated or control (saline) group. Beraprost (0.35 microg/kg per min) or saline (1.5 mL/min) was administered 30 min before stenting and was continued for 5 h thereafter. Platelet aggregation was measured before and after drug administration. At 3, 7 and 14 days after stenting, dogs were killed and immunohistochemical staining for proliferating cell nuclear antigen was used to quantify the proliferation of vascular smooth muscle cells (SMC). To evaluate intermediate-term effects, a Z-stent was placed in the right iliac vein in 10 dogs, followed by beraprost treatment. Three days later, a second Z-stent was placed contralaterally with saline infusion as a control. After 4 weeks, dogs were killed and neointimal thickness was measured under a light microscope to calculate the intima : media area ratio. 3. Platelet aggregation was more significantly suppressed in the beraprost-treated than in the control group (P = 0.01). In addition, SMC proliferation was significantly lower in the beraprost-treated group 7 and 14 days after stenting (P < 0.05). Over the intermediate term, the intima : media area ratio was significantly lower in the beraprost-treated vein compared with control (P < 0.05). 4. In conclusion, short-term beraprost treatment during stenting suppresses in situ platelet aggregation and SMC proliferation, thus reducing neointimal thickening.

Endogenous testosterone attenuates neointima formation after moderate coronary balloon injury in male swine

AIMS

Previous studies from our laboratory have demonstrated that testosterone increases coronary smooth muscle protein kinase C delta (PKC delta) both in vivo and in vitro and inhibits coronary smooth muscle proliferation by inducing G(0)/G(1) cell cycle arrest in a PKC delta-dependent manner. The purpose of the present study was to determine whether endogenous testosterone limits coronary neointima (NI) formation in a porcine model of post-angioplasty restenosis.

METHODS AND RESULTS

Sexually mature, male Yucatan miniature swine were either left intact (IM), castrated (CM), or castrated with testosterone replacement (CMT; Androgel, 10 mg/day). Angioplasty was performed in both the left anterior descending and left circumflex coronary arteries with balloon catheter overinflation to induce either moderate (1.25-1.3 x diameter; 3 x 30 s) or severe (1.4x diameter; 3 x 30 s) injury, and animals were allowed to recover for either 10 or 28 days. Injured coronary sections were dissected, fixed, stained (Verheoff-Van Gieson, Ki67, PKC delta, p27), and analysed. Vessels without internal elastic laminal rupture were excluded. Following moderate injury, intimal area, intima-to-media ratio (I/M), and I/M normalized to rupture index (RI) were increased in CM compared with IM and CMT. RI, medial area, and intimal/medial thickness (IMT) were not different between groups. NI formation was inversely related to serum testosterone concentration. Conversely, following severe injury, there were no significant differences between the groups. Testosterone inhibited proliferation and stimulated PKC delta and p27(kip1) expression during NI formation (10 days post-injury).

CONCLUSION

These findings demonstrate that endogenous testosterone limits coronary NI formation in male swine and provides support for a protective role for testosterone in coronary vasculoproliferative diseases, such as restenosis and atherosclerosis.