The Genous™ endothelial progenitor cell capture stent accelerates stent re-endothelialization but does not affect intimal hyperplasia in porcine coronary arteries

Poly(l-lactide)/polycaprolactone based multifunctional coating to deliver paclitaxel/VEGF and control the degradation rate of magnesium alloy stent

Despite significant advancements made in cardiovascular stents, restenosis, thrombosis, biocompatibility, and clinical complications remain a matter of concern. Herein, we report a biodegradable Mg alloy stent with a dual effect of the drug (Paclitaxel) and growth factor (VEGF) release. To mitigate the fast degradation of Mg alloy, inorganic and organic coatings were formed on the alloy surface. The optimized hierarchal sequence of the coating was the first layer consisting of magnesium fluoride, followed by poly(l-lactide) and hydroxyapatite coating, and finally sealed by a polycaprolactone layer (MgC). PLLA and HAp were used to increase the adhesion strength and biocompatibility of the coating. Paclitaxel and VEGF were loaded in the final PCL layer (Mg-C/PTX-VEGF). As compared to bare Mg alloy (28 % weight loss), our MgC system showed (3.1 % weight loss) successful decrease in the degradation rate. Further, the in vitro biocompatibility illustrated the highly biocompatible nature of our drug and growth factor-loaded system. The in vivo results displayed that the drug loading decreased the inflammation and neointimal hyperplasia as indicated by the α-SMA and CD-68 antibody staining. The growth factor helped in the endothelialization which was established by the FLKI and ICAM antibody staining of the tissue.

A small-diameter vascular graft immobilized peptides for capturing endothelial colony-forming cells

Combining synthetic polymers and biomacromolecules prevents the occurrence of thrombogenicity and intimal hyperplasia in small-diameter vascular grafts (SDVGs). In the present study, an electrospinning poly (L)-lactic acid (PLLA) bilayered scaffold is developed to prevent thrombosis after implantation by promoting the capture and differentiation of endothelial colony-forming cells (ECFCs). The scaffold consists of an outer PLLA scaffold and an inner porous PLLA biomimetic membrane combined with heparin (Hep), peptide Gly-Gly-Gly-Arg-Glu-Asp-Val (GGG-REDV), and vascular endothelial growth factor (VEGF). Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and contact angle goniometry were performed to determine successful synthesis. The tensile strength of the outer layer was obtained using the recorded stress/strain curves, and hemocompatibility was evaluated using the blood clotting test. The proliferation, function, and differentiation properties of ECFCs were measured on various surfaces. Scanning electronic microscopy (SEM) was used to observe the morphology of ECFCs on the surface. The outer layer of scaffolds exhibited a similar strain and stress performance as the human saphenous vein via the tensile experiment. The contact angle decreased continuously until it reached 56° after REDV/VEGF modification, and SEM images of platelet adhesion showed a better hemocompatibility surface after modification. The ECFCs were captured using the REDV + VEGF + surface successfully under flow conditions. The expression of mature ECs was constantly increased with the culture of ECFCs on REDV + VEGF + surfaces. SEM images showed that the ECFCs captured by the REDV + VEGF + surface formed capillary-like structures after 4 weeks of culture. The SDVGs modified by REDV combined with VEGF promoted ECFC capture and rapid differentiation into ECs, forming capillary-like structures in vitro. The bilayered SDVGs could be used as vascular devices that achieved a high patency rate and rapid re-endothelialization.

Intraprocedural endothelial cell seeding of arterial stents via biotin/avidin targeting mitigates in-stent restenosis

Impaired endothelialization of endovascular stents has been established as a major cause of in-stent restenosis and late stent thrombosis. Attempts to enhance endothelialization of inner stent surfaces by pre-seeding the stents with endothelial cells in vitro prior to implantation are compromised by cell destruction during high-pressure stent deployment. Herein, we report on the novel stent endothelialization strategy of post-deployment seeding of biotin-modified endothelial cells to avidin-functionalized stents. Acquisition of an avidin monolayer on the stent surface was achieved by consecutive treatments of bare metal stents (BMS) with polyallylamine bisphosphonate, an amine-reactive biotinylation reagent and avidin. Biotin-modified endothelial cells retain growth characteristics of normal endothelium and can express reporter transgenes. Under physiological shear conditions, a 50-fold higher number of recirculating biotinylated cells attached to the avidin-modified metal surfaces compared to bare metal counterparts. Delivery of biotinylated endothelial cells to the carotid arterial segment containing the implanted avidin-modified stent in rats results in immediate cell binding to the stent struts and is associated with a 30% reduction of in-stent restenosis in comparison with BMS.

Endothelial Progenitor Cells in Coronary Artery Disease: From Bench to Bedside

Endothelial progenitor cells (EPCs) are a heterogeneous group of cells present in peripheral blood at various stages of endothelial differentiation. EPCs have been extensively investigated in patients with coronary artery disease (CAD), with controversial findings both on their role in atherosclerosis progression and in the process of neointimal growth after a percutaneous coronary intervention (PCI). Despite nearly 2 decades of experimental and clinical investigations, however, the significance of EPCs in clinical practice remains unclear and poorly understood. This review provides an update on the role of EPCs in the most common clinical scenarios that are experienced by cardiologists managing patients with CAD. We here summarize the main findings on the association of EPCs with cardiovascular risk factors, coronary atherosclerosis, and myocardial ischemia. We then discuss the potential effects of EPCs in post-PCI in-stent restenosis, as well as most recent findings with EPC-coated stents. Based on the mounting evidence of the relationship between levels of EPCs and several different adverse cardiovascular events, EPCs are emerging as novel predictive biomarkers of long-term outcomes in patients with CAD.

Applying Principles of Regenerative Medicine to Vascular Stent Development

Stents are a widely-used device to treat a variety of cardiovascular diseases. The purpose of this review is to explore the application of regenerative medicine principles into current and future stent designs. This review will cover regeneration-relevant approaches emerging in the current research landscape of stent technology. Regenerative stent technologies include surface engineering of stents with cell secretomes, cell-capture coatings, mimics of endothelial products, surface topography, endothelial growth factors or cell-adhesive peptides, as well as design of bioresorable materials for temporary stent support. These technologies are comparatively analyzed in terms of their regenerative effects, therapeutic effects and challenges faced; their benefits and risks are weighed up for suggestions about future stent developments. This review highlights two unique regenerative features of stent technologies: selective regeneration, which is to selectively grow endothelial cells on a stent but inhibit the proliferation and migration of smooth muscle cells, and stent-assisted regeneration of ischemic tissue injury.

M. P. Integrating particle tracking with computational fluid dynamics to assess haemodynamic perturbation by coronary artery stents

AIMS

Coronary artery stents have profound effects on arterial function by altering fluid flow mass transport and wall shear stress. We developed a new integrated methodology to analyse the effects of stents on mass transport and shear stress to inform the design of haemodynamically-favourable stents.

METHODS AND RESULTS

Stents were deployed in model vessels followed by tracking of fluorescent particles under flow. Parallel analyses involved high-resolution micro-computed tomography scanning followed by computational fluid dynamics simulations to assess wall shear stress distribution. Several stent designs were analysed to assess whether the workflow was robust for diverse strut geometries. Stents had striking effects on fluid flow streamlines, flow separation or funnelling, and the accumulation of particles at areas of complex geometry that were tightly coupled to stent shape. CFD analysis revealed that stents had a major influence on wall shear stress magnitude, direction and distribution and this was highly sensitive to geometry.

CONCLUSIONS

Integration of particle tracking with CFD allows assessment of fluid flow and shear stress in stented arteries in unprecedented detail. Deleterious flow perturbations, such as accumulation of particles at struts and non-physiological shear stress, were highly sensitive to individual stent geometry. Novel designs for stents should be tested for mass transport and shear stress which are important effectors of vascular health and repair.

Effects of local coronary blood flow dynamics on the predictions of a model of in-stent restenosis

Computational models are increasingly used to study cardiovascular disease. However, models of coronary vessel remodelling usually make some strong assumptions about the effects of a local narrowing on the flow through the narrowed vessel. Here, we test the effects of local flow dynamics on the predictions of an in-stent restenosis (ISR) model. A previously developed 2D model of ISR is coupled to a 1D model of coronary blood flow. Then, two different assumptions are tested. The first assumption is that the vasculature is always able to adapt, and the volumetric flow rate through the narrowed vessel is kept constant. The second, alternative, assumption is that the vasculature does not adapt at all, and the ratio of the pressure drop to the flow rate (hydrodynamic resistance) stays the same throughout the whole process for all vessels unaffected by the stenosis, and aortic or venous blood pressure does not change either. Then, the dynamics are compared for different locations in coronary tree for two different reendothelization scenarios. The assumptions of constant volumetric flow rate (absolute vascular adaptation) versus constant aortic pressure drop and no adaptation do not significantly affect the growth dynamics for most locations in the coronary tree, and the differences can only be observed at the locations where a strong alternative flow pathway is present. On the other hand, the difference between locations is significant, which is consistent with small vessel size being a risk factor for restenosis. These results suggest that the assumption of a constant flow is a good approximation for ISR models dealing with the typical progression of ISR in the most often stented locations such as the proximal parts of left anterior descending (LAD) and left circumflex (LCX) arteries.

Epigallocatechin gallate mediated sandwich-like coating for mimicking endothelium with sustained therapeutic nitric oxide generation and heparin release

In-stent restenosis after stenting is generally characterized by an inflammatory response, excessive proliferation of smooth muscle cells, and delayed healing of the endothelium layer. In this study, inspired by catechol/gallol surface chemistry, a sandwich-like layer-by-layer (LBL) coating was developed using chitosan and heparin as polyelectrolytes, along with the embedding of an epigallocatechin gallate/copper (EGCG/Cu) complex. The embedding of EGCG stabilized the coating by various intermolecular interactions in the LBL coating (e.g., π-π stacking, weak intermolecular crosslinking, and enriched hydrogen bonding) and supported the sustained release of the cargo heparin over 90 days. This design enabled a biomimetic endothelium function in terms of the sustained release of heparin and continuous in situ generation of nitric oxide, driven by the catalytic decomposition of endogenous S-nitrostothiols by copper ions. The result showed enhanced durability of anticoagulation and suppressed inflammatory response. Moreover, the "sandwich-like" coating supported the growth of endothelial cells and up-regulated the protein expression of vascular endothelial growth factor, while effectively suppressing the proliferation and migration of smooth muscle cells (SMCs) via the up-regulation of cyclic guanosine monophosphate. Ex vivo and in vivo experiments demonstrated the effectiveness of the sandwich-like coating in preventing thrombosis formation, suppressing the growth of SMCs, reducing the infiltration and activation of inflammatory cells, and ultimately achieving rapid in situ endothelialization. Hence, the EGCG-assisted sandwich-like coating might be used as a robust and versatile surface modification strategy for implantable cardiovascular devices.

Dual-Peptide-Functionalized Nanofibrous Scaffolds Recruit Host Endothelial Progenitor Cells for Vasculogenesis to Repair Calvarial Defects

Vasculogenesis (de novo formation of vessels) induced by endothelial progenitor cells (EPCs) is requisite for vascularized bone regeneration. However, there exist few available options for promoting vasculogenesis within artificial bone grafts except for exogenous EPC transplantation, which suffers from the source of EPC, safety, cost, and time concerns in clinical applications. This study aimed at endogenous EPC recruitment for vascularized bone regeneration by using a bioinspired EPC-induced graft. The EPC-induced graft was created by immobilizing two bioactive peptides, WKYMVm and YIGSR, on the surface of poly(ε-caprolactone) (PCL)/poliglecaprone (PGC) nanofibrous scaffolds via a polyglycolic acid (PGA)-binding peptide sequence. Remarkable immobilization efficacy of WKYMVm and YIGSR peptides and their sustained release (over 14 days) from scaffolds were observed. In vivo and in vitro studies showed robust recruitment of EPCs, which subsequently contributed to early vasculogenesis and ultimate bone regeneration. The dual-peptide-functionalized nanofibrous scaffolds proposed in this study provide a promising therapeutic strategy for vasculogenesis in bone defect repair.

Location-Specific Comparison Between a 3D In-Stent Restenosis Model and Micro-CT and Histology Data from Porcine In Vivo Experiments

BACKGROUND

Coronary artery restenosis is an important side effect of percutaneous coronary intervention. Computational models can be used to better understand this process. We report on an approach for validation of an in silico 3D model of in-stent restenosis in porcine coronary arteries and illustrate this approach by comparing the modelling results to in vivo data for 14 and 28 days post-stenting.

METHODS

This multiscale model includes single-scale models for stent deployment, blood flow and tissue growth in the stented vessel, including smooth muscle cell (SMC) proliferation and extracellular matrix (ECM) production. The validation procedure uses data from porcine in vivo experiments, by simulating stent deployment using stent geometry obtained from micro computed tomography (micro-CT) of the stented vessel and directly comparing the simulation results of neointimal growth to histological sections taken at the same locations.

RESULTS

Metrics for comparison are per-strut neointimal thickness and per-section neointimal area. The neointimal area predicted by the model demonstrates a good agreement with the detailed experimental data. For 14 days post-stenting the relative neointimal area, averaged over all vessel sections considered, was 20 ± 3% in vivo and 22 ± 4% in silico. For 28 days, the area was 42 ± 3% in vivo and 41 ± 3% in silico.

CONCLUSIONS

The approach presented here provides a very detailed, location-specific, validation methodology for in silico restenosis models. The model was able to closely match both histology datasets with a single set of parameters. Good agreement was obtained for both the overall amount of neointima produced and the local distribution. It should be noted that including vessel curvature and ECM production in the model was paramount to obtain a good agreement with the experimental data.

Capturing Endothelial Cells by Coronary Stents - From Histology to Clinical Outcomes

Introduction of drug-eluting stents (DES) in the therapy of patients with coronary artery disease resulted in the significant reduction of in-stent restenosis compared to bare-metal stent (BMS) treatment. However, the high incidence of late stent thrombosis with DES emerged as one of the safety concerns after their implantation. Enhancing stent endothelization by improved early healing and neointimal strut coverage emerged as possible solution for this late complication. Endothelial progenitor cells (EPC) capturing stents are designed to promote in situ endothelization with immobilized, antihuman, anti-CD34 antibodies attached to the luminal stent surface. Anti-CD34 antibodies target and capture EPC from circulation, which further differentiate into vascular endothelial cells and form functional endothelial layer on the stent surface. These cells are also capable of secreting pro-angiogenic factors that stimulate local endothelial cells to proliferate and migrate. Preclinical and clinical studies proved feasibility, efficacy and safety of EPC capturing stents in stable and high-risk patients with coronary artery disease. Rapid and extensive endothelization of EPC capturing stents translated into favorable profile of clinical outcomes, comparable to efficacy of BMSs and DESs. Therefore, we here present the most important results from the experimental and clinical studies that explored ECP capturing strategy to enhance endothelization, reduce the incidence of instent thrombosis and improve outcomes of patients with coronary artery disease, along with the future perspectives in this promising therapeutic approach.

The REMEDEE trial: 5-Year results on a novel combined sirolimus-eluting and endothelial progenitor cells capturing stent

OBJECTIVES

To evaluate the long-term safety and efficacy of the novel combined sirolimus-eluting endothelial progenitor cell capture Combo stent (OrbusNeich, Fort Lauderdale, FL) at 5 years in the REMEDEE (Randomized study to Evaluate the safety and effectiveness of an abluMinal sirolimus coated bio-Engineered stEnt) trial.

BACKGROUND

Drug-eluting stents have limited restenosis and reintervention but are complicated by late and very late thrombosis and accelerated neoatherosclerosis. Alternative or adjunctive technologies are needed to address these limitations.

METHODS

A total of 183 patients with de novo lesions in native coronary arteries were randomized 2:1 to Combo (n = 124) or Taxus Liberté (n = 59). Primary endpoint was 9 month angiographic in-stent late lumen loss and the secondary endpoint was the occurrence of major adverse events (MACE) through 5-year follow-up.

RESULTS

Compared with Taxus, after 5 years the Combo stent was associated with similar rates of MACE (18.3% vs. 16.9%, p = .89), cardiac death (0.8% vs. 5.1%, p = .07), myocardial infarction (4.1% vs. 3.4%, p = .81), target lesion (9.4% vs. 10.2%, p = .78), and target vessel revascularization (14.4% vs. 11.9%, p = .73). No cases of definite stent thrombosis were reported in the Combo group. The follow-up rate at 5 years was 97.7%.

CONCLUSION

At 5-year follow-up, the Combo stent remained clinically safe and effective with an overall low rate of MACE comparable to Taxus.

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.

Endothelial repair is dependent on CD11c+ leukocytes to establish regrowing endothelial sheets with high cellular density

Endothelial injury makes the vessel wall vulnerable to cardiovascular diseases. Injured endothelium regenerates by collective sheet migration, that is, the endothelial cells coordinate their motion and regrow as a sheet of cells with retained cell-cell contacts into the wounded area. Leukocytes appear to be involved in endothelial repair in vivo; however, little is known about their identity and role in the reparative sheet migration process. To address these questions, we developed a high-quality en face technique that enables visualizing of leukocytes and endothelial cells simultaneously following an endoluminal scratch wound injury of the mouse carotid artery. We discovered that regrowing endothelium forms a broad proliferative front accompanied by CD11c⁺ leukocytes. Functionally, the leukocytes were dispensable for the initial migratory response of the regrowing endothelial sheet, but critical for the subsequent formation and maintenance of a front zone with high cellular density. Marker expression analyses, genetic fate mapping, phagocyte targeting experiments, and mouse knock-out experiments indicate that the CD11c⁺  leukocytes were mononuclear phagocytes with an origin from both Ly6C^high and Ly6C^low monocytes. In conclusion, CD11c⁺ mononuclear phagocytes are essential for a proper endothelial regrowth following arterial endoluminal scratch injury. Promoting the endothelial-preserving function of CD11c⁺  leukocytes may be a strategy to enhance endothelial repair following surgical and endovascular procedures.

Uncertainty Quantification of a Multiscale Model for In-Stent Restenosis

Purpose

Coronary artery stenosis, or abnormal narrowing, is a widespread and potentially fatal cardiac disease. After treatment by balloon angioplasty and stenting, restenosis may occur inside the stent due to excessive neointima formation. Simulations of in-stent restenosis can provide new insight into this process. However, uncertainties due to variability in patient-specific parameters must be taken into account.

Methods

We performed an uncertainty quantification (UQ) study on a complex two-dimensional in-stent restenosis model. We used a quasi-Monte Carlo method for UQ of the neointimal area, and the Sobol sensitivity analysis (SA) to estimate the proportions of aleatory and epistemic uncertainties and to determine the most important input parameters.

Results

We observe approximately 30% uncertainty in the mean neointimal area as simulated by the model. Depending on whether a fast initial endothelium recovery occurs, the proportion of the model variance due to natural variability ranges from 15 to 35%. The endothelium regeneration time is identified as the most influential model parameter.

Conclusion

The model output contains a moderate quantity of uncertainty, and the model precision can be increased by obtaining a more certain value on the endothelium regeneration time. We conclude that the quasi-Monte Carlo UQ and the Sobol SA are reliable methods for estimating uncertainties in the response of complicated multiscale cardiovascular models.

Shear stress: An essential driver of endothelial progenitor cells

The blood flow through vessels produces a tangential, or shear, stress sensed by their innermost layer (i.e., endothelium) and representing a major hemodynamic force. In humans, endothelial repair and blood vessel formation are mainly performed by circulating endothelial progenitor cells (EPCs) characterized by a considerable expression of vascular endothelial growth factor receptor 2 (VEGFR2), CD34, and CD133, pronounced tube formation activity in vitro, and strong reendothelialization or neovascularization capacity in vivo. EPCs have been proposed as a promising agent to induce reendothelialization of injured arteries, neovascularization of ischemic tissues, and endothelialization or vascularization of bioartificial constructs. A number of preconditioning approaches have been suggested to improve the regenerative potential of EPCs, including the use of biophysical stimuli such as shear stress. However, in spite of well-defined influence of shear stress on mature endothelial cells (ECs), articles summarizing how it affects EPCs are lacking. Here we discuss the impact of shear stress on homing, paracrine effects, and differentiation of EPCs. Unidirectional laminar shear stress significantly promotes homing of circulating EPCs to endothelial injury sites, induces anti-thrombotic and anti-atherosclerotic phenotype of EPCs, increases their capability to form capillary-like tubes in vitro, and enhances differentiation of EPCs into mature ECs in a dose-dependent manner. These effects are mediated by VEGFR2, Tie2, Notch, and β1/3 integrin signaling and can be abrogated by means of complementary siRNA/shRNA or selective pharmacological inhibitors of the respective proteins. Although the testing of sheared EPCs for vascular tissue engineering or regenerative medicine applications is still an unaccomplished task, favorable effects of unidirectional laminar shear stress on EPCs suggest its usefulness for their preconditioning.

Endothelial mimetic multifunctional surfaces fabricated via polydopamine mediated copper immobilization

Nitric oxide (NO), which is continuously released from the normal healthy endodermis cell layer of the vascular system, plays a crucial role in the stability and health maintenance of blood vessels.

Preparation of Vascular Endothelial Cadherin Loaded-Amphoteric Copolymer Decorated Coronary Stents for Anticoagulation and Endothelialization

A new strategy for preparation of blood-contact materials, with their short-term anticoagulation depending on zwitterionic structure and long-term hemocompatibility based on endothelialization, was proposed, performed, and proved. The copolymer made of sulfonamide zwitterionic and acrylic acid was designed and synthesized, and grafted to the surface of the bare metal coronary stent. Then, the vascular endothelial cadherin (VE-Cad), one of the specific antibodies of endothelial progenitor cells (EPCs), was fixed onto the copolymer chain. Finally, it is proved by in vitro blood tests that the coronary stent decorated with VE-Cad loaded-amphoteric copolymer displayed good platelet anti-adhesion characteristic. This anti-adhesion characteristic was attributed to the zwitterionic structure and the biofunctionality of specifically capturing EPCs confirmed by the results that the antibody-decorated coronary stent was trapped with EPCs. Finally, the in vivo implantation experiments of the antibody-decorated coronary stent in rabbit for 4 weeks were carried out. Results indicated that the endothelium and smooth surface of the antibody-loaded stent was found to be due to the covered effect of EPCs, without obvious intimal hyperplasia. The strategy we proposed has great potential in the design and preparation of blood-contact biomedical materials and devices.

Direct surface modification of metallic biomaterials via tyrosine oxidation aiming to accelerate the re-endothelialization of vascular stents

Rapid in-situ re-endothelialization of coronary stents is one of the most effective approaches to inhibit late thrombosis and restenosis. Strut surfaces allowing excellent adhesion and migration of endothelial cells and endothelial progenitor cells may accelerate in-situ re-endothelialization. Here, a well-known endothelial cell adhesive peptide, Arg-Glu-Asp-Val (REDV), was directly immobilized onto metallic surfaces by means of single-step tyrosine oxidation with copper chloride (II) and hydrogen peroxide, which we recently reported as a new biomaterial modification technique. REDV immobilization on a 316L stainless steel plate improved endothelial cell adhesion and effectively suppressed platelet adhesion in vitro. In addition, a Co-Cr stent immobilized with Ac-Tyr-Gly-Gly-Gly-Arg-Glu-Asp-Val (Y-REDV) was implanted into a rabbit abdominal aorta. On 7 days postimplantation, 80% of the strut surface of the Y-REDV-immobilized stent was covered by a thin neointimal layer and was similar in appearance to native endothelium. Restenosis and late thrombosis were not observed in the Y-REDV-immobilized stent for 42 days. These findings suggest that direct immobilization of Y-REDV peptide onto metallic biomaterials by tyrosine oxidation is effective for promoting in-situ re-endothelialization in vascular stents. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 491-499, 2018.

Strategies to develop endogenous stem cell-recruiting bioactive materials for tissue repair and regeneration

A leading strategy in tissue engineering is the design of biomimetic scaffolds that stimulate the body's repair mechanisms through the recruitment of endogenous stem cells to sites of injury. Approaches that employ the use of chemoattractant gradients to guide tissue regeneration without external cell sources are favored over traditional cell-based therapies that have limited potential for clinical translation. Following this concept, bioactive scaffolds can be engineered to provide a temporally and spatially controlled release of biological cues, with the possibility to mimic the complex signaling patterns of endogenous tissue regeneration. Another effective way to regulate stem cell activity is to leverage the inherent chemotactic properties of extracellular matrix (ECM)-based materials to build versatile cell-instructive platforms. This review introduces the concept of endogenous stem cell recruitment, and provides a comprehensive overview of the strategies available to achieve effective cardiovascular and bone tissue regeneration.

Five-year follow-up of the endothelial progenitor cell capturing stent versus the paxlitaxel-eluting stent in de novo coronary lesions with a high risk of coronary restenosis

OBJECTIVES

To assess the long-term safety and clinical efficacy of the Genous endothelial progenitor cell capturing stent (ECS) compared with the TAXUS Liberté paclitaxel-eluting stent (PES) in lesions with a high risk of restenosis.

BACKGROUND

Instead of the use of cytotoxic or cytostatic drugs in drug-eluting stents, a "pro-healing" approach in ECS may overcome impeded healing response due to delayed functional endothelialization of the stent struts.

METHODS

In the prospective, randomized TRIAS pilot study 193 patients with coronary artery lesions carrying a high risk of restenosis were included (ECS: n = 98, PES: n = 95). The primary focus of this analysis was target vessel failure (TVF) at 5 years. Dual antiplatelet therapy was prescribed for ≥1 month after ECS and for ≥6 months after PES.

RESULTS

At 5 years follow-up, no significant differences were found in TVF (ECS 24% vs. PES 29%, risk difference 95% confidence interval (RDCI) -17.3% to 7.4%). Between 2 and 5 years after the index procedure, low numbers of TVF were observed in ECS compared with PES (ECS 4% vs. PES 16%, RDCI -20.8% to -2.3%). There was no definite stent thrombosis in ECS compared with four patients in the PES group.

CONCLUSION

This is the first randomized study providing very long-term clinical efficacy and safety of the ECS in lesions carrying a high risk of restenosis. At 5 years follow-up, TVF rates in ECS group are numerically lower compared with PES due to an increase of events between 2 and 5 years after the index procedure.

A Comparison of Fully-Coupled 3D In-Stent Restenosis Simulations to In-vivo Data

We describe our fully-coupled 3D multiscale model of in-stent restenosis, with blood flow simulations coupled to smooth muscle cell proliferation, and report results of numerical simulations performed with this model. This novel model is based on several previously reported 2D models. We study the effects of various parameters on the process of restenosis and compare with in vivo porcine data where we observe good qualitative agreement. We study the effects of stent deployment depth (and related injury score), reendothelization speed, and simulate the effect of stent width. Also we demonstrate that we are now capable to simulate restenosis in real-sized (18 mm long, 2.8 mm wide) vessel geometries.

Heparin/DNA aptamer co-assembled multifunctional catecholamine coating for EPC capture and improved hemocompatibility of vascular devices

Good hemocompatibility and rapid endothelialization are two key factors in the success of stent interventional therapy. In this study, aptamers with the ability to capture endothelial progenitors and anticoagulant molecular heparin were successfully immobilized on the surface of dopamine/polyethylenimine (PDA/PEI) copolymer coating via electrostatic interaction. The results of X-ray spectroscopy (XPS), water contact angle (WCA), and immunofluorescence staining tests confirmed the successful introduction of heparin and aptamers. Platelet adhesion and whole blood experiments demonstrated that the hemocompatibility of the co-modified surface was improved. Dynamic endothelial progenitor cell (EPC) capture experiments showed that the modified surfaces could effectively capture the endothelial progenitor in dynamic conditions. More importantly, ex vivo experiments revealed that the modified surfaces could regulate the distribution of CD34/vWF-positive cells on stent surfaces, and this was beneficial for the endothelialization of vascular stents. These results suggested that heparin and aptamer co-modified stents could capture EPCs and promote endothelialization. This surface co-modification strategy has great potential for enhancing stent development.

Anti-thrombotic technologies for medical devices

Thrombosis associated with medical devices may lead to dramatic increases in morbidity, mortality and increased health care costs. Innovative strategies are being developed to reduce this complication and provide a safe biocompatible interface between device and blood. This article aims to describe the biological phenomena underlying device-associated thrombosis, and surveys the literature describing current and developing technologies designed to overcome this challenge. To reduce thrombosis, biomaterials with varying topographical properties and incorporating anti-thrombogenic substances on their surface have demonstrated potential. Overall, there is extensive literature describing technical solutions to reduce thrombosis associated with medical devices, but clinical results are required to demonstrate significant long-term benefits.

Endothelial repair in stented arteries is accelerated by inhibition of Rho-associated protein kinase

Aims

Stent deployment causes endothelial cells (EC) denudation, which promotes in-stent restenosis and thrombosis. Thus endothelial regrowth in stented arteries is an important therapeutic goal. Stent struts modify local hemodynamics, however the effects of flow perturbation on EC injury and repair are incompletely understood. By studying the effects of stent struts on flow and EC migration, we identified an intervention that promotes endothelial repair in stented arteries.

Methods and Results

In vitro and in vivo models were developed to monitor endothelialization under flow and the influence of stent struts. A 2D parallel-plate flow chamber with 100 μm ridges arranged perpendicular to the flow was used. Live cell imaging coupled to computational fluid dynamic simulations revealed that EC migrate in the direction of flow upstream from the ridges but subsequently accumulate downstream from ridges at sites of bidirectional flow. The mechanism of EC trapping by bidirectional flow involved reduced migratory polarity associated with altered actin dynamics. Inhibition of Rho-associated protein kinase (ROCK) enhanced endothelialization of ridged surfaces by promoting migratory polarity under bidirectional flow (P < 0.01). To more closely mimic the in vivo situation, we cultured EC on the inner surface of polydimethylsiloxane tubing containing Coroflex Blue stents (65 μm struts) and monitored migration. ROCK inhibition significantly enhanced EC accumulation downstream from struts under flow (P < 0.05). We investigated the effects of ROCK inhibition on re-endothelialization in vivo using a porcine model of EC denudation and stent placement. En face staining and confocal microscopy revealed that inhibition of ROCK using fasudil (30 mg/day via osmotic minipump) significantly increased re-endothelialization of stented carotid arteries (P < 0.05).

Conclusions

Stent struts delay endothelial repair by generating localized bidirectional flow which traps migrating EC. ROCK inhibitors accelerate endothelial repair of stented arteries by enhancing EC polarity and migration through regions of bidirectional flow.

Bioresorbable Scaffolds for Atheroregression: Understanding of Transient Scaffolding

This review focuses on the clinical and biological features of the bioresorbable scaffolds in interventional cardiology highlighting scientific achievements and challenges of the transient scaffolding with Absorb BVS. Special attention is granted to the vascular biology pathways which, involved in the resorption of scaffold, artery remodeling and mechanisms of Glagovian atheroregression setting the stage for subsequent clinical applications. Twenty five years ago Glagov described the phenomenon of limited external elastic membrane enlargement in response to an increase in plaque burden. We believe this threshold becomes the target for development of strategies that reverse atherosclerosis, and particularly transient scaffolding has a potential to be a tool to ultimately conquer atherosclerosis.

In situ Endothelialization: Bioengineering Considerations to Translation

Improving patency rates of current cardiovascular implants remains a major challenge. It is widely accepted that regeneration of a healthy endothelium layer on biomaterials could yield the perfect blood-contacting surface. Earlier efforts in pre-seeding endothelial cells in vitro demonstrated success in enhancing patency, but translation to the clinic is largely hampered due to its impracticality. In situ endothelialization, which aims to create biomaterial surfaces capable of self-endothelializing upon implantation, appears to be an extremely promising solution, particularly with the utilization of endothelial progenitor cells (EPCs). Nevertheless, controlling cell behavior in situ using immobilized biomolecules or physical patterning can be complex, thus warranting careful consideration. This review aims to provide valuable insight into the rationale and recent developments in biomaterial strategies to enhance in situ endothelialization. In particular, a discussion on the important bio-/nanoengineering considerations and lessons learnt from clinical trials are presented to aid the future translation of this exciting paradigm.

Comparison of reendothelialization and neointimal formation with stents coated with antibodies against endoglin and CD34 in a porcine model

Anti-CD34 coated stents are the only commercialized antibody-coated stents currently used for coronary artery diseases with various limitations. Endoglin plays important roles in the proliferation of endothelial cells and vascular remodeling and could be an ideal target surface molecule. The objective of this study was to investigate the efficacy of stents coated with anti-endoglin antibodies (ENDs) in terms of endothelial recovery and the reduction of neointimal formation. The performance of ENDs was evaluated by comparing with stents coated with anti-CD34 antibodies (CD34s), sirolimus-eluting stents (SESs), and bare metal stents (BMSs). Stents were randomly assigned and placed in the coronary arteries of juvenile pigs. Histomorphometric analysis and scanning electron microscopy were performed after stent implantation. Our results showed at 14 days after stent implantation, the neointima area and percent area stenosis in ENDs and CD34s were remarkably decreased compared with those in BMSs and SESs (P<0.05). Moreover, the percentage of reendothelialization was significantly higher in ENDs and CD34s than that in SESs or BMSs at both 7 and 14 days (P<0.05). There was no difference in the neointima area, percent area stenosis, and percentage of reendothelialization in ENDs compared with CD34s. The artery injury and the inflammation scores were similar in all groups at both 7 and 14 days. Our results demonstrate that the performance of ENDs is similar to the commercial CD34s, without the disadvantages of CD34s, and both are better than SESs and BMSs. ENDs potentially offer an alternative approach to reduce restenotic process and enhance reendothelialization after stent implantation.

Impact of an endothelial progenitor cell capturing stent on coronary microvascular function: comparison with drug-eluting stents

BACKGROUND/AIMS

Although drug-eluting stents (DESs) effectively reduce restenosis following percutaneous coronary intervention (PCI), they also delay re-endothelialization and impair microvascular function, resulting in adverse clinical outcomes. Endothelial progenitor cell (EPC) capturing stents, by providing a functional endothelial layer on the stent, have beneficial effects on microvascular function. However, data on coronary microvascular function in patients with EPC stents versus DESs are lacking.

METHODS

Seventy-four patients who previously underwent PCI were enrolled in this study. Microvascular function was evaluated 6 months after PCI based on the index of microvascular resistance (IMR) and the coronary flow reserve (CFR). IMR was calculated as the ratio of the mean distal coronary pressure at maximal hyperemia to the inverse of the hyperemic mean transit time (hTmn). The CFR was calculated by dividing the hTmn by the baseline mean transit time.

RESULTS

Twenty-one patients (age, 67.2 ± 9.6 years; male:female, 15:6) with an EPC stent and 53 patients (age, 61.5 ± 14.7 years; male:female, 40:13) with second-generation DESs were included in the study. There were no significant differences in the baseline clinical and angiographic characteristics of the two groups. Angiography performed 6 months postoperatively did not show significant differences in their CFR values. However, patients with the EPC stent had a significantly lower IMR than patients with second-generation DESs (median, 25.5 [interquartile range, 12.85 to 28.18] vs. 29.0 [interquartile range, 15.42 to 39.23]; p = 0.043).

CONCLUSIONS

Microvascular dysfunction was significantly improved after 6 months in patients with EPC stents compared to those with DESs. The complete re-endothelialization achieved with the EPC stent may provide clinical benefits over DESs, especially in patients with microvascular dysfunction.

Elastin-like recombinamer-covered stents: Towards a fully biocompatible and non-thrombogenic device for cardiovascular diseases

We explored the use of recently developed gels obtained by the catalyst free click reaction of elastin-like recombinamers (ELRs) to fabricate a new class of covered stents. The approach consists in embedding bare metal stents in the ELR gels by injection molding, followed by endothelialization under dynamic pressure and flow conditions in a bioreactor. The mechanical properties of the gels could be easily tuned by choosing the adequate concentration of the ELR components and their biofunctionality could be tailored by inserting specific sequences (RGD and REDV). The ELR-covered stents exhibited mechanical stability under high flow conditions and could undergo crimping and deployment without damage. The presence of RGD in the ELR used to cover the stent supported full endothelialization in less than 2weeks in vitro. Minimal platelet adhesion and fibrin adsorption were detected after exposure to blood, as shown by immunostaining and scanning electron microscopy. These results prove the potential of this approach towards a new and more effective generation of covered stents which exclude the atherosclerotic plaque from the blood stream and have high biocompatibility, physiological hemocompatibility and reduced response of the immune system.

Hematopoietic stem cell capture and directional differentiation into vascular endothelial cells for metal stent-coated chitosan/hyaluronic acid loading CD133 antibody

A series of metal stents coated with chitosan/hyaluronic acid (CS/HA) loading antibodies by electrostatic self-assembled method were prepared, and the types of cells captured by antibodies and their differentiation in vascular endothelial cells (ECs) evaluated by molecular biology and scanning electron microscope. The results showed that CD133 stent can selectively capture hematopoietic stem cells (HSC),which directionally differentiate into vascular ECs in peripheral blood by (CS/HA) induction, and simultaneously inhibit migration and proliferation of immune cells and vascular smooth muscle cells (MCs). CD34 stent can capture HSC, hematopoietic progenitor cells that differentiate into vascular ECs and immune cells, promoting smooth MCs growth, leading to thrombosis, inflammation, and rejection. CD133 stent can be implanted into miniature pig heart coronary and can repair vascular damage by capturing own HSC, thus contributing to the rapid natural vascular repair, avoiding inflammation and rejection, thrombosis and restenosis. These studies demonstrated that CD133 stent of HSC capture will be an ideal coated metal stent providing a new therapeutic approach for cardiovascular and cerebrovascular disease.

Healing the injured vessel wall using microRNA-facilitated gene delivery

Drug-eluting stents have emerged as potent weapons in the treatment of patients with symptomatic coronary artery disease by reducing restenosis rates; however, a significant clinical consequence of these stents is delayed reendothelialization, which may increase the risk of late stent thrombosis. In this issue of the JCI, Santulli and colleagues generated an adenovirus that expresses the cyclin-dependent kinase inhibitor p27(Kip1) (p27) and bears four tandem copies of target sequences for the endothelial cell-enriched microRNA (miRNA) miR-126-3p (Ad-p27-126TS) in an attempt to specifically reduce proliferation of vascular smooth muscle cells, but not endothelial cells. Indeed, delivery of Ad-p27-126TS to balloon-injured arteries in rats not only induced faster and more complete reendothelialization, but also effectively improved neointimal hyperplasia, hypercoagulability, and vasoreactivity. Collectively, these findings provide a cogent foundation for the potential therapeutic use of miRNA-facilitated gene delivery strategies to heal vessel wall injury.

Modelling the effect of a functional endothelium on the development of in-stent restenosis

Treatment of stenosed coronary arteries by balloon angioplasty and stenting results in arterial injury including severe damage to the endothelium at the site of treatment and initiates a complex cascade of inflammatory processes that may lead to the development of in-stent restenosis (ISR). Many clinical and biological factors involved in the progression of restenotic lesions have been studied in detail over the past few years but the mystery behind the pathophysiological mechanisms of this disease is still unresolved. In the present work, the effects of re-endothelialization and nitric oxide release on neointimal growth are investigated in-silico using a two dimensional multi-scale model of ISR. The effect of stent deployment depths on the development of ISR is studied as a function of time after stenting. Two dimensional domains were prepared by deploying bare metal stent struts at three different deployment depths into the tissue. Shear stress distribution on endothelial cells, obtained by blood flow simulations, was translated into nitric oxide production that keeps the smooth muscle cells in quiescent state. The cellular growth trends were plotted as a function of time and the data indicate a positive correlation between the neointimal growths and strut deployment depths in the presence of a functional endothelium, in qualitative agreement with in-vivo data. Additionally, no ISR is observed if a functional endothelium appears much earlier.

The effects of stenting on shear stress: relevance to endothelial injury and repair

Stent deployment following balloon angioplasty is used routinely to treat coronary artery disease. These interventions cause damage and loss of endothelial cells (EC), and thus promote in-stent thrombosis and restenosis. Injured arteries are repaired (intrinsically) by locally derived EC and by circulating endothelial progenitor cells which migrate and proliferate to re-populate denuded regions. However, re-endothelialization is not always complete and often dysfunctional. Moreover, the molecular and biomechanical mechanisms that control EC repair and function in stented segments are poorly understood. Here, we propose that stents modify endothelial repair processes, in part, by altering fluid shear stress, a mechanical force that influences EC migration and proliferation. A more detailed understanding of the biomechanical processes that control endothelial healing would provide a platform for the development of novel therapeutic approaches to minimize damage and promote vascular repair in stented arteries.

First in vitro and in vivo results of an anti-human CD133-antibody coated coronary stent in the porcine model

BACKGROUND

Drug-eluting stents successfully reduce restenosis at the cost of delayed re-endothelialization. A novel concept to enhance re-endothelialization is the use of antibody-coated stents which capture circulating progenitor cells. A CD34-positive-cell-capturing stent was recently developed with conflicting clinical results. CD133 is a glycoprotein expressed on circulating hematopoietic and putative endothelial-regenerating cells and may be superior to CD34.

OBJECTIVE

The aim of our study was to develop a CD133-cell-capturing bare-metal stent and investigate feasibility, safety, and efficacy of CD133-stents in terms of re-endothelialization and neointima inhibition.

METHODS AND RESULTS

Anti-human CD133-antibodies were covalently attached to bare-metal stents. In vitro, binding capacity of CD133-stents was studied, revealing a significantly higher affinity of human CD133-positive cells to CD133-stents compared with mononuclear cells (MNCs). In vivo, 15 landrace pigs received BMS and CD133-stents in either RCX or LAD (n = 30 stents). Re-endothelialization was examined on day 1 (n = 4), 3 (n = 4) and day 7 (n = 4) using scanning electron microscopy. In histology, injury and inflammatory scores, as well as diameter restenosis were evaluated after day 7 (n = 3), 14 (n = 4), and 28 (n = 2). Overall no reduction in re-endothelialization, diameter stenosis or inflammatory score was seen with CD133-stents.

CONCLUSION

Stent coating with anti-human CD133-antibodies was successfully achieved with effective binding of CD133-positive cells. However, in vivo, no difference in re-endothelialization or neointima formation was evident with the use of CD133-stents compared with BMS. The low number of circulating CD133-positive cells and an increase in unspecific binding of MNCs over time may account for the observed lack of efficacy.

Coronary stents: historical development, current status and future directions

INTRODUCTION

Coronary angioplasty with stenting has revolutionized the treatment of coronary artery disease. This article describes the history of coronary angioplasty and stenting, reviews the contemporary stents and recommendations and highlights the on-going work and potential future directions.

SOURCES OF DATA

This review examined the data on coronary stents available in PubMed.

AREAS OF AGREEMENT

Coronary artery stenting is the treatment of choice for patients requiring coronary angioplasty. Stents, and particularly drug-eluting stents, reduce the risk of restenosis, but may be associated with the hazard of late stent thrombosis. Dual anti-platelet treatment is recommended for patients receiving coronary stents.

AREAS OF CONTROVERSY

The selection of stents for various lesions and patients and the duration of anti-platelet therapy remain debated areas.

AREAS TIMELY FOR DEVELOPING RESEARCH

There are on-going preclinical and clinical studies to develop better stent platforms, more biocompatible polymers, novel anti-proliferative and anti-platelet drugs, pro-healing stents and bioresorbable scaffolds.

Enhanced human endothelial progenitor cell adhesion and differentiation by a bioinspired multifunctional nanomatrix

Endothelial progenitor cell (EPC)-capturing techniques have led to revolutionary strategies that can improve the performance of cardiovascular implant devices and engineered tissues by enhancing re-endothelialization and angiogenesis. However, these strategies are limited by controversies regarding the phenotypic identities of EPCs as well as their inability to target and prevent the other afflictions associated with current therapies, namely, thrombosis and neointimal hyperplasia. Therefore, the goal of this study was to study the efficacy of a bioinspired multifunctional nanomatrix in recruiting and promoting the differentiation of EPCs toward an endothelial lineage. The bioinspired nanomatrix combines multiple components, including self-assembled peptide amphiphiles (PAs) that include cell adhesive ligands, nitric oxide (NO)-producing donors, and enzyme-mediated degradable sequences to achieve an endothelium-mimicking character. In this study, human peripheral blood mononuclear cells (PBMNCs) were isolated and cultured on the bioinspired multifunctional nanomatrix. Initial cell adhesion, lectin staining, acetylated low-density lipoprotein uptake, and expression of endothelial markers, including CD31, CD34, von Willebrand Factor, and VEGFR2, were analyzed. The results from this study indicate that the NO releasing bioinspired multifunctional nanomatrix promotes initial adhesion of EPCs when compared to control surfaces. The expression of endothelial markers is also increased on the bioinspired multifunctional nanomatrix, suggesting that it directs the differentiation of EPCs toward an endothelial phenotype. The bioinspired nanomatrix therefore provides a novel biomaterial-based platform for capturing as well as directing EPC behavior. Therefore, this study has the potential to positively impact the patency of cardiovascular devices such as stents and vascular grafts as well as enhanced angiogenesis for ischemic or engineered tissues.

The prevention of restenosis in vivo with a VEGF gene and paclitaxel co-eluting stent

Long-term clinical studies of drug-eluting stents (DES) have reported high incidence of late thrombosis. Given the growing concern over the clinical application of this technology, we have developed a stent coated with bi-layered PLGA nanoparticles (BL-PLGA NPs) containing VEGF plasmid in the outer layer and paclitaxel (PTX) in the inner core (VEGF/PTX NPs). We hypothesized that early release of VEGF gene would promote re-endothelialization, while slow release of PTX would suppress smooth muscle cell proliferation. Using Fc plasmid as a reporter gene, we observed that Fc/PTX NPs successfully expressed Fc protein, but did not show cytotoxicity or anti-proliferative effect during the first 7 days in cell culture. In contrast, PTX NPs showed strong anti-proliferative effect staring from day 1 in culture, suggesting sequential release of gene and PTX from the BL-PLGA NPs. In vivo effects of the treated stent were assessed in mini-swines. Implantation of GFP/PTX NP-coated stents revealed efficient local GFP gene transfection at day 7. VEGF/PTX NP-coated stents showed complete re-endothelialization and significantly suppressed in-stent restenosis after 1 month compared to commercial DES. In conclusion, the VEGF/PTX NP-coated stents promote early endothelium healing while inhibit smooth muscle cell proliferation through sequential release of the VEGF gene and paclitaxel.

Coronary artery stenting in a patient with chronic immune thrombocytopenic purpura: a clinical conundrum

A patient with long-standing immune thrombocytopenic purpura (ITP) would logically contradict antiplatelet use due to increased bleeding risk during coronary stenting. Coronary stenting using an endothelial progenitor cells (EPC) capture stents (Genous™) was used to successfully revascularise our patient using a transradial approach. The only complication was extensive superficial ecchymosis on the patient's forearm from antiplatelet use, which resolved spontaneously. To the best of our knowledge, this is the first case report of EPC capture stents in a chronic ITP patient.

Recent Advances in the Treatment of ST-Segment Elevation Myocardial Infarction

ST-segment elevation myocardial infarction (STEMI) represents the most urgent condition for patients with coronary artery disease. Prompt diagnosis and therapy, mainly with primary angioplasty using stents, are important in improving not only acute survival but also long-term prognosis. Recent advances in angioplasty devices, including manual aspiration catheters and drug-eluting stents, and pharmacologic therapy, such as potent antiplatelet and anticoagulant agents, have significantly enhanced the acute outcome for these patients. Continuing efforts to educate the public and to decrease the door-to-balloon time are essential to further improve the outcome for these high-risk patients. Future research to normalize the left ventricular function by autologous stem cell therapy may also contribute to the quality of life and longevity of the patients surviving STEMI.

Impact of Parallel Micro-Engineered Stent Grooves on Endothelial Cell Migration, Proliferation, and Function

Background—

Stent luminal surface characteristics influence surface endothelialization. We hypothesize that luminal stent microgrooves created in the direction of coronary flow accelerate endothelial cell migration, resulting in lower levels of neointimal formation.

Methods and Results—

Surface coverage efficiency was evaluated in vitro by allowing human aortic endothelial cells (HAEC) to migrate onto microgrooved (G) or smooth (NG) surfaces. HAEC functionality was assessed by proliferation rate, apoptosis rate, nitric oxide production, and inflammatory markers TNF-α and VCAM-1 expression. Early endothelialization and restenosis studies were performed using the porcine coronary injury model. Stainless steel stents of identical design with (GS) and without (NGS) luminal microgrooves were used. The commercially available Multi-Link Vision (MLVS) stent of identical design was used as a control. The degree of GS and NGS surface endothelialization was compared at 3 days. Biocompatibility and tissue response outcomes were evaluated at 28 days. The in vitro study demonstrated that at 7 days the presence of surface microgrooves increased HAEC migration distance >2-fold. Cell proliferation rate and nitric oxide production were increased and apoptosis rate was decreased. There was no difference in inflammatory marker expression. At 3 days, coronary artery stent endothelialization was significantly increased in GS compared with NGS (81.3% versus 67.5%, P =0.0002). At 28 days, GS exhibited lower neointimal thickness compared with either NGS (21.1%, P =0.011) or MLVS (40.8%, P =0.014).

Conclusion—

Parallel microgrooves on coronary stent luminal surfaces promote endothelial cell migration and positively influence endothelial cell function, resulting in decreased neointimal formation in the porcine coronary injury model.

Ultrasound-guided percutaneous delivery of tissue-engineered endothelial cells to the adventitia of stented arteries controls the response to vascular injury in a porcine model

OBJECTIVE

High restenosis rates are a limitation of peripheral vascular interventions. Previous studies have shown that surgical implantation of a tissue-engineered endothelium onto the adventitia surface of injured vessels regulates vascular repair. In the present study, we developed a particulate formulation of tissue-engineered endothelium and a method to deliver the formulation perivascular to injured blood vessels using a percutaneous, minimally invasive technique.

METHODS

Stainless steel stents were implanted in 18 balloon-injured femoral arteries of nine domestic swine, followed by ultrasound-guided percutaneous perivascular injection of gelatin particles containing cultured allogeneic porcine aortic endothelial cells (PAE). Controls received injections of empty particles (matrix) or no perivascular injection (sham) after stent deployment. Animals were sacrificed after 90 days.

RESULTS

Angiographic analysis revealed a significantly greater lumen diameter in the stented segments of arteries treated with PAE/matrix (4.72 ± 0.12 mm) compared with matrix (4.01 ± 0.20 mm) or sham (4.03 ± 0.16 mm) controls (P < .05). Similarly, histologic analysis revealed that PAE/matrix-treated arteries had the greatest lumen area (20.4 ± 0.7 mm(2); P < .05) compared with controls (16.1 ± 0.9 mm(2) and 17.1 ± 1.0 mm(2) for sham and matrix controls, respectively) and the smallest intimal area (3.3 ± 0.4 mm(2); P < .05) compared with controls (6.2 ± 0.5 mm(2) and 4.4 ± 0.5 mm(2) for sham and matrix controls, respectively). Overall, PAE-treated arteries had a 33% to 50% decrease in percent occlusion (P < .05) compared with controls. Histopathological analysis revealed fewer leukocytes present in the intima in the PAE/matrix group compared with control groups, suggesting that the biological effects were in part due to inhibition of the inflammatory phase of the vascular response to injury.

CONCLUSIONS

Minimally invasive, perivascular delivery of PAE/matrix to stented arteries was performed safely using ultrasound-guided percutaneous injections and significantly decreased stenosis. Application at the time of or subsequent to peripheral interventions may decrease clinical restenosis rates.