Endothelial cell repopulation after stenting determines in-stent neointima formation: effects of bare-metal vs. drug-eluting stents and genetic endothelial cell modification

UV-Triggered Hydrogel Coating of the Double Network Polyelectrolytes for Enhanced Endothelialization

The left atrial appendage (LAA) occluder is an important medical device for closing the LAA and preventing stroke. The device-related thrombus (DRT) prevents the implantation of the occluder in exerting the desired therapeutic effect, which is primarily caused by the delayed endothelialization of the occluder. Functional coatings are an effective strategy for accelerating the endothelialization of occluders. However, the occluder surface area is particularly large and structurally complex, and the device is subjected to a large shear friction in the sheath during implantation, which poses a significant challenge to the coating. Herein, a hydrogel coating by the in situ UV-triggered polymerization of double-network polyelectrolytes is reported. The findings reveal that the double network and electrostatic interactions between the networks resulted in excellent mechanical properties of the hydrogel coating. The sulfonate and Arg-Gly-Asp (RGD) groups in the coating promoted hemocompatibility and endothelial growth of the occluder, respectively. The coating significantly accelerated the endothelialization of the LAA occluder in a canine model is further demonstrated. This study has potential clinical benefits in reducing both the incidence of DRT and the postoperative anticoagulant course for LAA closure.

Field-Induced Agglomerations of Polyethylene-Glycol-Functionalized Nanoclusters: Rheological Behaviour and Optical Microscopy

This research aims to investigate the agglomeration processes of magnetoresponsive functionalized nanocluster suspensions in a magnetic field, as well as how these structures impact the behaviour of these suspensions in biomedical applications. The synthesis, shape, colloidal stability, and magnetic characteristics of PEG-functionalized nanoclusters are described in this paper. Experiments using TEM, XPS, dynamic light scattering (DLS), VSM, and optical microscopy were performed to study chain-like agglomeration production and its influence on colloidal behaviour in physiologically relevant suspensions. The applied magnetic field aligns the magnetic moments of the nanoclusters. It provides an attraction between neighbouring particles, resulting in the formation of chains, linear aggregates, or agglomerates of clusters aligned along the applied field direction. Optical microscopy has been used to observe the creation of these aligned linear formations. The design of chain-like structures can cause considerable changes in the characteristics of ferrofluids, ranging from rheological differences to colloidal stability changes.

Silk + flow-diverter stent for the treatment of intracranial aneurysms associated with balloon angioplasty: A retrospective study

Background

The silk + flow-diverter stent is increasingly used to treat complex intracranial aneurysms including wide-neck and fusiform aneurysms. Balloon angioplasty has been used to better appose the flow diverter (FD) to the vessel wall and, thus, improve aneurysm occlusion rates and decrease periprocedural complications. Sparse data are available concerning the results of this technique. We report our experience with silk + FD associated with balloon angioplasty for the treatment of intracranial aneurysms.

Methods

A retrospective study was conducted on all patients treated by the silk + FD. Clinical charts, procedural data, and angiographic results were reviewed and compared between those treated with balloon angioplasty. A multivariate analysis was conducted to identify predictors of complications, occlusion, and outcome.

Results

Between July 2014 and May 2016, we identified 209 patients with 223 intracranial aneurysms. There were 176 (84.2%) women and 33 (15.8%) men. The most common stent size used was 4.5 mm in 101 patients (46.1%), followed by 4 mm in 57 patients (26%). Univariate analysis observed that stent diameter was significantly related to aneurysm occlusion (P < 0.05). Patients with more than 1 aneurysm treated with silk + stent have a 9.07 times greater chance of having complications in the procedure than patients with only 01 aneurysm (OR = 9.07; P = 0.0008). Patients who had angioplasty without the use of a balloon have a 13.69-times-higher risk of complications (OR = 13.69; P = 0.0003). Older age, larger aneurysms, and the use of more than 1 FD device were predictors of recanalization.

Conclusion

Endovascular treatment of intracranial aneurysms with the silk + FD associated with balloon angioplasty is a safe and effective therapeutic option. Balloon angioplasty in combination with FD lowers the risk of complications. Higher complication rates and worse outcomes are associated with older age and large aneurysms.

Effects of semiquinone-rich surface on the behaviors of vascular cells

Dopamine has been widely used for surface modification of cardiovascular medical devices as it forms films on most substrates that provide functional groups for surface chemical modification. However, under oxidative stress, the phenolic hydroxyl group on dopamine can undergo reversible transformation into phenol-semiquinone-quinone, which can cause cytotoxicity and immunotoxicity. In this study, we measured the effects of semiquinone on the behavior of vascular wall cells and inflammatory cells under oxidative stress via ultraviolet irradiation with a hydrogen peroxide diluent. Na₂S₂O₃ was used as a stabilizer to obtain a semiquinone-rich poly-dopamine film, then phenol-semiquinone-quinone ratio on its surface was evaluated at three irradiation-oxidation time points. We found that the poly-dopamine film with ultraviolet irradiation in hydrogen peroxide solution for 15 min had the highest semiquinone occupancy of 19.18%. In the experimental group irradiated for 15 min, endothelial cells were cultured statically for 3 days and the number of surface adherent endothelial cells in the group with added semiquinone stabilizer was reduced to 73% of that in the group without stabilizer, indicating that semiquinone rich surface inhibits adhesion and proliferation of endothelial cells; Smooth muscle cells were cultured statically for 3 days, and the number of adherent smooth muscle on surfaces without stabilizer was reduced to 75% of that on surfaces with stabilizer added, indicating that semiquinone rich surfaces promote smooth muscle proliferation. These results demonstrate that semiquinone can adversely affect the repair effect after implantation of cardiovascular materials. Therefore, our study provides a reference for the application and optimization of dopamine in cardiovascular implant materials.

Dual-catalytic CuTPP/TiO2 nanoparticles for surface catalysis engineering of cardiovascular materials

Endowing materials with catalytic activities analogous to those of the natural endothelium to thus enhance their biological performance has become an option for constructing advanced blood-contact materials. The electron transfer between Cu2+ and Cu+ in the porphyrin center can catalyze the reaction of GSH and GSNO to generate NO, and this electron transfer can also catalyze the decomposition of ROS. Based on this, we created a dual-catalytic surface possessing NO-generating and ROS-scavenging activities to better mimic the versatile catalytic abilities of the endothelium. Copper tetraphenylporphyrin/titanium dioxide nanoparticles (CuTPP/TiO2-NPs) exhibiting excellent NO-generating and ROS-scavenging activities were synthesized and immobilized on the material surface to form a dual-catalytic film (CuTPP/TiO2-film) with the help of the catechol chemistry technique. Unlike most single catalytic surfaces, the dual-catalytic CuTPP/TiO2-film effectively regulated the microenvironment surrounding the implanted device by releasing NO signaling molecules and scavenging harmful ROS. This dual-catalytic film exhibited excellent biosafety and biocompatibility with anti-thrombosis, vascular wall cells (ECs and SMCs) modulation, and anti-inflammatory properties. We envision that this dual-catalytic endothelial bionic strategy may provide a promising solution to the clinical problems plaguing blood-contact devices and provide a novel basis for the further development of surface catalytic-engineered biomaterials.

Biofunctionalization of cardiovascular stents to induce endothelialization: Implications for in- stent thrombosis in diabetes

Stent thrombosis remains one of the main causes that lead to vascular stent failure in patients undergoing percutaneous coronary intervention (PCI). Type 2 diabetes mellitus is accompanied by endothelial dysfunction and platelet hyperactivity and is associated with suboptimal outcomes following PCI, and an increase in the incidence of late stent thrombosis. Evidence suggests that late stent thrombosis is caused by the delayed and impaired endothelialization of the lumen of the stent. The endothelium has a key role in modulating inflammation and thrombosis and maintaining homeostasis, thus restoring a functional endothelial cell layer is an important target for the prevention of stent thrombosis. Modifications using specific molecules to induce endothelial cell adhesion, proliferation and function can improve stents endothelialization and prevent thrombosis. Blood endothelial progenitor cells (EPCs) represent a potential cell source for the in situ-endothelialization of vascular conduits and stents. We aim in this review to summarize the main biofunctionalization strategies to induce the in-situ endothelialization of coronary artery stents using circulating endothelial stem cells.

Recent advance in treatment of atherosclerosis: Key targets and plaque-positioned delivery strategies

Atherosclerosis, a chronic inflammatory disease of vascular wall, is a progressive pathophysiological process with lipids oxidation/depositing initiation and innate/adaptive immune responses. The coordination of multi systems covering oxidative stress, dysfunctional endothelium, diseased lipid uptake, cell apoptosis, thrombotic and pro-inflammatory responding as well as switched SMCs contributes to plaque growth. In this circumstance, inevitably, targeting these processes is considered to be effective for treating atherosclerosis. Arriving, retention and working of payload candidates mediated by targets in lesion direct ultimate therapeutic outcomes. Accumulating a series of scientific studies and clinical practice in the past decades, lesion homing delivery strategies including stent/balloon/nanoparticle-based transportation worked as the potent promotor to ensure a therapeutic effect. The objective of this review is to achieve a very brief summary about the effective therapeutic methods cooperating specifical targets and positioning-delivery strategies in atherosclerosis for better outcomes.

Arsenic trioxide activates yes-associated protein by lysophosphatidic acid metabolism to selectively induce apoptosis of vascular smooth muscle cells

Inhibition of vascular smooth muscle cells (VSMCs) proliferation without dysregulating endothelial cells (ECs) may provide an ideal therapy for in-stent restenosis. Due to its anti-proliferation effect on VSMCs and pro-endothelium effect, arsenic trioxide (ATO) has been used in a drug-eluting stent in a recent clinical trial. However, the underlying mechanism by which ATO achieves this effect has not been determined. In the present work, we showed that ATO induced apoptosis in VSMCs but not in ECs. Mechanistically, ATO achieved this through modulation of cellular metabolism to increase lysophosphatidic acid (LPA) in VSMCs, while LPA concentration was stable in ECs. The elevated LPA facilitated the nuclear accumulation and initiated the transcriptional function of Yes-associated protein (YAP) in VSMCs. YAP regulated the transcription of N6-Methyladenosine (m⁶A) modulators (Mettl14 and Wtap) to increase the m⁶A methylation levels of apoptosis-related genes to induce their high expression and exacerbate VSMCs apoptosis. On the other hand, YAP nuclear accumulation in ECs was not observed. Collectively, our data exhibited the molecular process involved in selective apoptosis of VSMCs induced by ATO.

Exosome-eluting stents for vascular healing after ischaemic injury

Drug-eluting stents implanted after ischaemic injury reduce the proliferation of endothelial cells and vascular smooth muscle cells and thus neointimal hyperplasia. However, the eluted drug also slows down the re-endothelialization process, delays arterial healing and can increase the risk of late restenosis. Here we show that stents releasing exosomes derived from mesenchymal stem cells in the presence of reactive oxygen species enhance vascular healing in rats with renal ischaemia-reperfusion injury, promoting endothelial cell tube formation and proliferation, and impairing the migration of smooth muscle cells. Compared with drug-eluting stents and bare-metal stents, the exosome-coated stents accelerated re-endothelialization and decreased in-stent restenosis 28 days after implantation. We also show that exosome-eluting stents implanted in the abdominal aorta of rats with unilateral hindlimb ischaemia regulated macrophage polarization, reduced local vascular and systemic inflammation, and promoted muscle tissue repair.

New Technologies With Increased Precision Improve Understanding of Endothelial Cell Heterogeneity in Cardiovascular Health and Disease

Endothelial cells (ECs) are vital for blood vessel integrity and have roles in maintaining normal vascular function, healing after injury, and vascular dysfunction. Extensive phenotypic heterogeneity has been observed among ECs of different types of blood vessels in the normal and diseased vascular wall. Although ECs with different phenotypes can share common functions, each has unique features that may dictate a fine-tuned role in vascular health and disease. Recent studies performed with single-cell technology have generated powerful information that has significantly improved our understanding of EC biology. Here, we summarize a variety of EC types, states, and phenotypes recently identified by using new, increasingly precise techniques in transcriptome analysis.

A tailored extracellular matrix (ECM) - Mimetic coating for cardiovascular stents by stepwise assembly of hyaluronic acid and recombinant human type III collagen

Collagen, a central component of the extracellular matrix (ECM), has been widely applied in tissue engineering, among others, for wound healing or bone and nerve regeneration. However, the inherent thrombogenic properties of collagen hinder the application in blood-contacting devices. Herein, a brand-new recombinant human type III collagen (hCOLIII) was explored that does not present binding sites for platelets while retaining the affinity for endothelial cells. The hCOLIII together with hyaluronic acid (HA) were deposited on the substrates via layer-by-layer assembly to form an ECM-mimetic multilayer coating. In vitro platelet adhesion and ex vivo blood circulation tests demonstrated prominent thromboprotective properties for the hCOLIII-based ECM-mimetic coating. In addition, the coating effectively guided the vascular cell fate by supporting the proliferation of endothelial cells and inhibiting the proliferation of smooth muscle cells by differentiating them to a more contractile phenotype. A polylactic acid (PLA) stent coated with hCOLIII-based ECM-mimetic coating was implanted in the abdominal aorta of rabbits to investigate the healing of the neointima. The enhanced endothelialization, suppressed inflammatory response, inhibition of excessive neointimal hyperplasia, and the superior thromboprotection strongly indicated the prospect of the hCOLIII-based ECM-mimetic coating as a tailored blood-contacting material for cardiovascular stents.

Methodology for comprehensive cell-level analysis of wound healing experiments using deep learning in MATLAB

BACKGROUND

Endothelial healing after deployment of cardiovascular devices is particularly important in the context of clinical outcome. It is therefore of great interest to develop tools for a precise prediction of endothelial growth after injury in the process of implant deployment. For experimental investigation of re-endothelialization in vitro cell migration assays are routinely used. However, semi-automatic analyses of live cell images are often based on gray value distributions and are as such limited by image quality and user dependence. The rise of deep learning algorithms offers promising opportunities for application in medical image analysis. Here, we present an intelligent cell detection (iCD) approach for comprehensive assay analysis to obtain essential characteristics on cell and population scale.

RESULTS

In an in vitro wound healing assay, we compared conventional analysis methods with our iCD approach. Therefore we determined cell density and cell velocity on cell scale and the movement of the cell layer as well as the gap closure between two cell monolayers on population scale. Our data demonstrate that cell density analysis based on deep learning algorithms is superior to an adaptive threshold method regarding robustness against image distortion. In addition, results on cell scale obtained with iCD are in agreement with manually velocity detection, while conventional methods, such as Cell Image Velocimetry (CIV), underestimate cell velocity by a factor of 0.5. Further, we found that iCD analysis of the monolayer movement gave results just as well as manual freehand detection, while conventional methods again shows more frayed leading edge detection compared to manual detection. Analysis of monolayer edge protrusion by ICD also produced results, which are close to manual estimation with an relative error of 11.7%. In comparison, the conventional Canny method gave a relative error of 76.4%.

CONCLUSION

The results of our experiments indicate that deep learning algorithms such as our iCD have the ability to outperform conventional methods in the field of wound healing analysis. The combined analysis on cell and population scale using iCD is very well suited for timesaving and high quality wound healing analysis enabling the research community to gain detailed understanding of endothelial movement.

The biological responses and mechanisms of endothelial cells to magnesium alloy

Due to its good biocompatibility and degradability, magnesium alloy (Mg alloy) has shown great promise in cardiovascular stent applications. Rapid stent re-endothelialization is derived from migrated and adhered endothelial cells (ECs), which is an effective way to reduce late thrombosis and inhibit hyperplasia. However, fundamental questions regarding Mg alloy affecting migration and adhesion of ECs are not fully understood. Here, we evaluated the effects of Mg alloy on the ECs proliferation, adhesion and migration. A global gene expression profiling of ECs co-culturing with Mg alloy was conducted, and the adhesion- and migration-related genes were examined. We found that Mg alloy had no adverse effects on ECs viability but significantly affected ECs migration and adhesion. Co-cultured with Mg alloy extract, ECs showed contractive adhesion morphology and decreased motility, which was supported by the down-regulation of adhesion-related genes (Paxillin and Vinculin) and migration-related genes (RAC 1, Rho A and CDC 42). Accordingly, the re-endothelialization of Mg alloy stent was inhibited in vivo. Our results may provide new inspiration for improving the broad application of Mg alloy stents.

The Combined Contribution of Vascular Endothelial Cell Migration and Adhesion to Stent Re-endothelialization

Coronary stent placement inevitably causes mechanical damage to the endothelium, leading to endothelial denudation and in-stent restenosis (ISR). Re-endothelialization depends mainly on the migration of vascular endothelial cells (VECs) adjacent to the damaged intima, as well as the mobilization and adhesion of circulating VECs. To evaluate the combined contribution of VEC migration and adhesion to re-endothelialization under flow and the influence of stent, in vitro models were constructed to simulate various endothelial denudation scales (2 mm/5 mm/10 mm) and stent deployment depths (flat/groove/bulge). Our results showed that (1) in 2 mm flat/groove/bulge models, both VEC migration and adhesion combined completed the percentage of endothelial recovery about 27, 16, and 12%, and migration accounted for about 21, 15, and 7%, respectively. It was suggested that the flat and groove models were in favor of VEC migration. (2) With the augmentation of the injury scales (5 and 10 mm), the contribution of circulating VEC adhesion on endothelial repair increased. Taken together, endothelial restoration mainly depended on the migration of adjacent VECs when the injury scale was 2 mm. The adhered cells contributed to re-endothelialization in an injury scale-dependent way. This study is helpful to provide new enlightenment for surface modification of cardiovascular implants.

Adenosine kinase is critical for neointima formation after vascular injury by inducing aberrant DNA hypermethylation

AIMS

Adenosine receptors and extracellular adenosine have been demonstrated to modulate vascular smooth muscle cell (VSMC) proliferation and neointima formation. Adenosine kinase (ADK) is a major enzyme regulating intracellular adenosine levels but is function in VSMC remains unclear. Here, we investigated the role of ADK in vascular injury-induced smooth muscle proliferation and delineated the mechanisms underlying its action.

METHODS AND RESULTS

We found that ADK expression was higher in the neointima of injured vessels and in platelet-derived growth factor-treated VSMCs. Genetic and pharmacological inhibition of ADK was enough to attenuate arterial injury-induced neointima formation due to inhibition of VSMC proliferation. Mechanistically, using infinium methylation assays and bisulfite sequencing, we showed that ADK metabolized the intracellular adenosine and potentiated the transmethylation pathway, then induced the aberrant DNA hypermethylation. Pharmacological inhibition of aberrant DNA hypermethylation increased KLF4 expression and suppressed VSMC proliferation as well as the neointima formation. Importantly, in human femoral arteries, we observed increased ADK expression and DNA hypermethylation as well as decreased KLF4 expression in neointimal VSMCs of stenotic vessels suggesting that our findings in mice are relevant for human disease and may hold translational significance.

CONCLUSION

Our study unravels a novel mechanism by which ADK promotes VSMC proliferation via inducing aberrant DNA hypermethylation, thereby down-regulating KLF4 expression and promoting neointima formation. These findings advance the possibility of targeting ADK as an epigenetic modulator to combat vascular injury.

Vascular toxic effects of cancer therapies

Cancer therapies can lead to a broad spectrum of cardiovascular complications. Among these, cardiotoxicities remain of prime concern, but vascular toxicities have emerged as the second most common group. The range of cancer therapies with a vascular toxicity profile and the clinical spectrum of vascular toxic effects are quite broad. Historically, venous thromboembolism has received the greatest attention but, over the past decade, the arterial toxic effects, which can present as acute vasospasm, acute thrombosis and accelerated atherosclerosis, of cancer therapies have gained greater recognition. This Review focuses on these types of cancer therapy-related arterial toxicity, including their mechanisms, and provides an update on venous thromboembolism and pulmonary hypertension associated with cancer therapies. Recommendations for the screening, treatment and prevention of vascular toxic effects of cancer therapies are outlined in the context of available evidence and society guidelines and consensus statements. The shift towards greater awareness of the vascular toxic effects of cancer therapies has further unveiled the urgent needs in this area in terms of defining best clinical practices. Well-designed and well-conducted clinical studies and registries are needed to more precisely define the incidence rates, risk factors, primary and secondary modes of prevention, and best treatment modalities for vascular toxicities related to cancer therapies. These efforts should be complemented by preclinical studies to outline the pathophysiological concepts that can be translated into the clinic and to identify drugs with vascular toxicity potential even before their widespread clinical use.

Promoting endothelialization of flow-diverting stents: a review

Intracranial flow-diverting (FD) stents have revolutionized the treatment of intracranial aneurysms in recent years, but complications resulting from failed endothelialization can still occur. Approaches to promote endothelialization are understudied, but hold promise in mitigating both short- and long-term complications associated with FD stent insertion. The aim of this review is to highlight the various features of and modifications that have been made to FD stents in order to expedite endothelialization. More specifically, we focus on how endothelialization can be influenced by the stent design, wall apposition, surface modifications, and the inclusion of biological agents.

Endothelium-Mimicking Multifunctional Coating Modified Cardiovascular Stents via a Stepwise Metal-Catechol-(Amine) Surface Engineering Strategy

Stenting is currently the major therapeutic treatment for cardiovascular diseases. However, the nonbiogenic metal stents are inclined to trigger a cascade of cellular and molecular events including inflammatory response, thrombogenic reactions, smooth muscle cell hyperproliferation accompanied by the delayed arterial healing, and poor reendothelialization, thus leading to restenosis along with late stent thrombosis. To address prevalence critical problems, we present an endothelium-mimicking coating capable of rapid regeneration of a competently functioning new endothelial layer on stents through a stepwise metal (copper)-catechol-(amine) (MCA) surface chemistry strategy, leading to combinatorial endothelium-like functions with glutathione peroxidase-like catalytic activity and surface heparinization. Apart from the stable nitric oxide (NO) generating rate at the physiological level (2.2 × 10^-10 mol/cm²/min lasting for 60 days), this proposed strategy could also generate abundant amine groups for allowing a high heparin conjugation efficacy up to ∼1 μg/cm², which is considerably higher than most of the conventional heparinized surfaces. The resultant coating could create an ideal microenvironment for bringing in enhanced anti-thrombogenicity, anti-inflammation, anti-proliferation of smooth muscle cells, re-endothelialization by regulating relevant gene expressions, hence preventing restenosis in vivo. We envision that the stepwise MCA coating strategy would facilitate the surface endothelium-mimicking engineering of vascular stents and be therefore helpful in the clinic to reduce complications associated with stenosis.

A particle-based model for endothelial cell migration under flow conditions

Endothelial cells (ECs) play a major role in the healing process following angioplasty to inhibit excessive neointima. This makes the process of EC healing after injury, in particular EC migration in a stented vessel, important for recovery of normal vessel function. In that context, we present a novel particle-based model of EC migration and validate it against in vitro experimental data. We have developed a particle-based model of EC migration under flow conditions in an in vitro vessel with obstacles. Cell movement in the model is a combination of random walks and directed movement along the local flow velocity vector. For model calibration, a set of experimental data for cell migration in a similarly shaped channel has been used. We have calibrated the model for a baseline case of a channel with no obstacles and then applied it to the case of a channel with ridges on the bottom surface, representative of stent strut geometry. We were able to closely reproduce the cell migration speed and angular distribution of their movement relative to the flow direction reported in vitro. The model also reproduces qualitative aspects of EC migration, such as entrapment of cells downstream from the flow-disturbing ridge. The model has the potential, after more extensive in vitro validation, to study the effect of variation in strut spacing and shape, through modification of the local flow, on EC migration. The results of this study support the hypothesis that EC migration is strongly affected by the direction and magnitude of local wall shear stress.

Delayed Stroke after Aneurysm Treatment with Flow Diverters in Small Cerebral Vessels: A Potentially Critical Complication Caused by Subacute Vasospasm

Flow diversion (FD) is a novel endovascular technique based on the profound alteration of cerebrovascular hemodynamics, which emerged as a promising minimally invasive therapy for intracranial aneurysms. However, delayed post-procedural stroke remains an unexplained concern. A consistent follow-up-regimen has not yet been defined, but is required urgently to clarify the underlying cause of delayed ischemia. In the last two years, 223 patients were treated with six different FD devices in our center. We identified subacute, FD-induced segmental vasospasm (SV) in 36 patients as a yet unknown, delayed-type reaction potentially compromising brain perfusion to a critical level. Furthermore, 86% of all patients revealed significant SV approximately four weeks after treatment. In addition, 56% had SV with 25% stenosis, and 80% had additional neointimal hyperplasia. Only 13% exhibited SV-related high-grade stenosis. One of those suffered stroke due to prolonged SV, requiring neurocritical care and repeated intra-arterial (i.a.) biochemical angioplasty for seven days to prevent territorial infarction. Five patients suffered newly manifested, transient hemicrania accompanying a compensatorily increased ipsilateral leptomeningeal perfusion. One treated vessel obliterated permanently. Hence, FD-induced SV is a frequent vascular reaction after FD treatment, potentially causing symptomatic ischemia or even stroke, approximately one month post procedure. A specifically early follow-up-strategy must be applied to identify patients at risk for ischemia, requiring intensified monitoring and potentially anti-vasospastic treatment.

Reduction-Responsive Nucleic Acid Delivery Systems To Prevent In-Stent Restenosis in Rabbits

Cardiovascular and cerebrovascular ischemic diseases seriously affect human health. Endovascular stent placement is an effective treatment but always leads to in-stent restenosis (ISR). Gene-eluting stent, which combines gene therapy with stent implantation, is a potential method to prevent ISR. In this study, an efficient gene-eluting stent was designed on the basis of one new nucleic acid delivery system to decrease the possibility of ISR. The reduction-responsive branched nucleic acid vector (SKP) with low cytotoxicity was first synthesized via ring-opening reaction. The impressive in vitro transfection performances of SKP were proved using luciferase reporter, enhanced green fluorescent protein plasmid, and vascular endothelial growth factor plasmid (pVEGF). Subsequently, SKP/pVEGF complexes were coated on the surfaces of pretreated clinical stents to construct gene-eluting stents (S-SKP/pVEGF). Antirestenosis performance of S-SKP/pVEGF was evaluated via implanting stents into rabbit aortas. S-SKP/pVEGF could lead to the localized upregulation of VEGF proteins, improve the progress of re-endothelialization, and inhibit the development of ISR in vivo. Such efficient pVEGF-eluting stent with responsive nucleic acid delivery systems is very promising to prevent in-stent restenosis of cerebrovascular diseases.

High-Density Lipoproteins and Apolipoprotein A-I Improve Stent Biocompatibility

Revascularization because of coronary artery disease is commonly achieved by percutaneous coronary intervention with stent deployment. Refinement in interventional techniques, major improvements in stent design (particularly drug-eluting stents), and adjunctive pharmacotherapy with dual antiplatelet regimens have led to marked reductions in the overall rates of stent failure. However, even with the advancements made in the latest generation of drug-eluting stents, unresolved biological problems persist including delayed re-endothelialization and neoatherosclerosis, which can promote late expansion of the neointima and late stent thrombosis. Novel strategies are still needed beyond what is currently available to specifically address the pathobiological processes that underpin the residual risk for adverse clinical events. This review focuses on the emerging evidence that HDL (high-density lipoproteins) and its main apo (apolipoprotein), apoA-I, exhibit multiple vascular biological functions that are associated with an improvement in stent biocompatibility. HDL/apoA-I have recently been shown to inhibit in-stent restenosis in animal models of stenting and suppress smooth muscle cell proliferation in in vitro studies. Reconstituted HDL also promotes endothelial cell migration, endothelial progenitor cell mobilization, and re-endothelialization. Furthermore, reconstituted HDL decreases platelet activation and HDL cholesterol is inversely associated with the risk of thrombosis. Finally, reconstituted HDL/apoA-I suppresses key inflammatory mechanisms that initiate in-stent neoatherosclerosis and can efflux cholesterol from plaque macrophages, an important function of HDLs that prevents plaque progression. These unique multifunctional effects of HDL/apoA-I suggest that, if translated appropriately, have the potential to improve stent biocompatibility. This may provide an alternate and more efficacious therapeutic pathway for the translation of HDL.

Predictors of strut coverage of drug eluting stent implantation in diabetic patients

BACKGROUND

Incomplete re-endothelialization of drug eluting stent (DES) segments has been associated with the occurrence of major adverse cardiac events after DES implantation. It is unknown whether on-clopidogrel platelet reactivity (OPR) and/or circulating endothelial progenitor cells (EPC) levels may predict uncovered strut rate in diabetic patients treated by DES implantation.

METHODS

One-hundred and five diabetic patients undergoing elective DES implantation were included into the study. EPC levels and OPR were assessed at 24 h (baseline) and 3 months. EPC were evaluated by flow cytometric analysis and defined by the co-expression of the markers CD34 and KDR. OPR was assessed using the impedance aggregometer. The degree of DES re-endothelialization was assessed at 3 months by optical coherence tomography.

RESULTS

A direct correlation was observed between the uncovered strut rate and OPR both at baseline (r = 0.47: p < 0.001) and at the 3 months (r = 0.25: p = 0.015). On the contrary, we found no significant correlation between EPC level and uncovered strut rate either at baseline (r = -0.02; p = 0.85) or at 3 months (r = -0.06; p = 0.13). By multivariable regression analysis, independent predictors of uncovered strut rate > 5% were complex lesions (OR = 5.35; 95% confidence interval 1.32-17.57; p = 0.027) and OPR at baseline (OR = 4.73; 95% confidence interval 1.04-8.14; p = 0.039).

CONCLUSIONS

In diabetic patients treated with DES implantation OPR at baseline and complex lesions are independent predictors of uncovered strut rate at 3 months.

Coronary stents with inducible VEGF/HGF-secreting UCB-MSCs reduced restenosis and increased re-endothelialization in a swine model

Atherosclerotic plaques within the vasculature may eventually lead to heart failure. Currently, cardiac stenting is the most effective and least invasive approach to treat this disease. However, in-stent restenosis is a complex chronic side effect of stenting treatment. This study used coronary stents coated with stem cells secreting angiogenic growth factors via an inducible genome-editing system to reduce stent restenosis and induce re-endothelialization within the artery. The characteristics of the cells and their adhesion properties on the stents were confirmed, and the stents were transplanted into a swine model to evaluate restenosis and the potential therapeutic use of stents with stem cells. Restenosis was evaluated using optical coherence tomography (OCT), microcomputed tomography (mCT) and angiography, and re-endothelialization was evaluated by immunostaining after cardiac stent treatment. Compared to a bare metal stent (BMS) or a parental umbilical cord blood-derived mesenchymal stem cell (UCB-MSC)-coated stent, the stents with stem cells capable of the controlled release of hepatocyte growth factor (HGF) and vascular endothelial growth factor (VEGF) successfully reduced restenosis within the stent and induced natural re-endothelialization. Furthermore, UCB-MSCs exhibited the ability to differentiate into endothelial cells in Matrigel, and HGF and VEGF improved this differentiation. Our study indicates that stents coated with UCB-MSCs secreting VEGF/HGF reduce the restenosis side effects of cardiac stenting with improved re-endothelialization.

Magnetic targeting of smooth muscle cells in vitro using a magnetic bacterial cellulose to improve cell retention in tissue-engineering vascular grafts

Tissue-engineered vascular grafts (TEVG) use biologically-active cells with or without supporting scaffolds to achieve tissue remodeling and regrowth of injured blood vessels. However, this process may take several weeks because the high hemodynamic shear stress at the damaged site causes cellular denudation and impairs tissue regrowth. We hypothesize that a material with magnetic properties can provide the force required to speed up re-endothelization at the vascular defect by facilitating high cell density coverage, especially during the first 24 h after implantation. To test our hypothesis, we designed a magnetic bacterial cellulose (MBC) to locally target cells in vitro under a pulsatile fluid flow (0.514 dynes cm^-2). This strategy can potentially increase cell homing at TEVG, without the need of blood cessation. The MBC was synthesized by an in situ precipitation method of Fe³⁺ and Fe²⁺ iron salts into bacterial cellulose (BC) pellicles to form Fe₃O₄ nanoparticles along the BC's fibrils, followed by the application of dextran coating to protect the embedded nanoparticles from oxidation. The iron salt concentration used in the synthesis of the MBC was tuned to balance the magnetic properties and cytocompatibility of the magnetic hydrogel. Our results showed a satisfactory MBC magnetization of up to 10 emu/g, which is above the value considered relevant for tissue engineering applications (0.05 emu/g). The MBC captured magnetically-functionalized cells under dynamic flow conditions in vitro. MBC magnetic properties and cytocompatibility indicated a dependence on the initial iron oxide nanoparticle concentration.

STATEMENT OF SIGNIFICANCE

Magnetic hydrogels represent a new class of functional materials with great potential in TVEG because they offer a platform to (1) release drugs on demand, (2) speed up tissue regrowth, and (3) provide mechanical cues to cells by its deformability capabilities. Here, we showed that a magnetic hydrogel, the MBC, was able to capture and retain magnetically-functionalized smooth muscle cells under pulsatile flow conditions in vitro. A magnetic hydrogel with this feature can be used to obtain high-density cell coverage on sites that are aggressive for cell survival such as the luminal face of vascular grafts, whereas simultaneously can support the formation of a biologically-active cell layer that protects the material from restenosis and inflammation.

Roles for endothelial cell and macrophage Gch1 and tetrahydrobiopterin in atherosclerosis progression

Aims

GTP cyclohydrolase I catalyses the first and rate-limiting reaction in the synthesis of tetrahydrobiopterin (BH4), an essential cofactor for nitric oxide synthases (NOS). Both eNOS and iNOS have been implicated in the progression of atherosclerosis, with opposing effects in eNOS and iNOS knockout mice. However, the pathophysiologic requirement for BH4 in regulating both eNOS and iNOS function, and the effects of loss of BH4 on the progression of atherosclerosis remains unknown.

Methods and results

Hyperlipidemic mice deficient in Gch1 in endothelial cells and leucocytes were generated by crossing Gch1fl/flTie2cre mice with ApoE-/- mice. Deficiency of Gch1 and BH4 in endothelial cells and myeloid cells was associated with mildly increased blood pressure. High fat feeding for 6 weeks in Gch1fl/flTie2CreApoE-/- mice resulted in significantly decreased circulating BH4 levels, increased atherosclerosis burden and increased plaque macrophage content. Gch1fl/flTie2CreApoE-/- mice showed hallmarks of endothelial cell dysfunction, with increased aortic VCAM-1 expression and decreased endothelial cell dependent vasodilation. Furthermore, loss of BH4 from pro-inflammatory macrophages resulted in increased foam cell formation and altered cellular redox signalling, with decreased expression of antioxidant genes and increased reactive oxygen species. Bone marrow chimeras revealed that loss of Gch1 in both endothelial cells and leucocytes is required to accelerate atherosclerosis.

Conclusion

Both endothelial cell and macrophage BH4 play important roles in the regulation of NOS function and cellular redox signalling in atherosclerosis.

Arterial Thrombosis in Patients with Cancer

PURPOSE OF REVIEW

Cancer is a common cause of morbidity and mortality in the USA. While the association between venous thrombosis and malignancy is well established, arterial thrombosis has more recently been recognized as a serious complication of cancer and certain chemotherapeutic agents. This review aims to summarize the most recent literature regarding the incidence and risk factors for cancer-related arterial thrombosis, understand the pathophysiologic mechanisms of thrombosis, and highlight the specific diagnostic and treatment considerations relevant to cancer patients.

RECENT FINDINGS

Based on a recent study looking at the Surveillance, Epidemiology, and End Results (SEER) database, the incidence of arterial thromboembolic events (ATEs) in patients with cancer at 6 months is 4.7%; the presence of an ATE is predictive of worse outcomes. Certain drugs such as platinum-based agents, vascular endothelial growth factor inhibitors, tyrosine kinase inhibitors, and taxanes have been associated with high rates of ATEs. Increased platelet reactivity appears crucial to development of arterial thrombosis in cancer patients. Cancer patients have an increased risk of arterial thrombosis that is likely due to both a cancer-associated procoagulant state as well as the adverse effects of certain chemotherapeutic agents. Treatment of arterial thromboembolism in cancer patients typically requires a multidisciplinary approach in part due to high rates of thrombocytopenia and stent thrombosis in the setting of percutaneous interventions. More studies are needed to investigate optimal prophylaxis, surveillance strategies, and treatments of cancer-related arterial thromboembolic disease.

Neointimal fibrotic lead encapsulation - Clinical challenges and demands for implantable cardiac electronic devices

Every tenth patient with a cardiac pacemaker or implantable cardioverter-defibrillator implanted is expected to have at least one lead problem in his lifetime. However, transvenous leads are often difficult to remove due to thrombotic obstruction or extensive neointimal fibrotic ingrowth. Despite its clinical significance, knowledge on lead-induced vascular fibrosis and neointimal lead encapsulation is sparse. Although leadless pacemakers are already available, their clinical operating range is limited. Therefore, lead/tissue interactions must be further improved in order to improve lead removals in particular. The published data on the coherences and issues related to lead associated vascular fibrosis and neointimal lead encapsulation are reviewed and discussed in this paper.

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.

Optimizing endothelial cell functionalization for cell therapy of vascular proliferative disease using a direct contact co-culture system

Increased susceptibility to thrombosis, neoatherosclerosis, and restenosis due to incomplete regrowth of the protective endothelial layer remains a critical limitation of the interventional strategies currently used clinically to relieve atherosclerotic obstruction. Rapid recovery of endothelium holds promise for both preventing the thrombotic events and reducing post-angioplasty restenosis, providing the rationale for developing cell delivery strategies for accelerating arterial reendothelialization. The successful translation of experimental cell therapies into clinically viable treatment modalities for restoring vascular endothelium critically depends on identifying strategies for enhancing the functionality of endothelial cells (EC) derived from high cardiovascular risk patients, the target group for the majority of angioplasty procedures. Enhancing EC-associated nitric oxide (NO) synthesis by inducing overexpression of NO synthase (NOS) has shown promise as a way of increasing paracrine activity and restoring function of EC. In the present study, we developed a direct contact co-culture approach compatible with highly labile effectors, such as NO, and applied it for determining the effect of EC functionalization via NOS gene transfer on the growth of co-cultured arterial smooth muscle cells (A10 cell line) exhibiting the defining characteristics of neointimal cells. Bovine aortic endothelial cells magnetically transduced with inducible NOS-encoding adenovirus (Ad) formulated in zinc oleate-based magnetic nanoparticles (MNP[_iNOSAd]) strongly suppressed growth of proliferating A10 and attenuated the stimulatory effect of a potent mitogen, platelet-derived growth factor (PDGF-BB), whereas EC functionalization with free _iNOSAd or MNP formulated with a different isoform of the enzyme, endothelial NOS, was associated with lower levels of NO synthesis and less pronounced antiproliferative activity toward co-cultured A10 cells. These results show feasibility of applying magnetically facilitated gene transfer to potentiate therapeutically relevant effects of EC for targeted cell therapy of restenosis. The direct contact co-culture methodology provides a sensitive and reliable tool with potential utility for a variety of biomedical applications.

Impact of statin therapy intensity on endothelial progenitor cells after percutaneous coronary intervention in diabetic patients. The REMEDY-EPC late study

BACKGROUND

A low number (that is, ≤0.0038 per 100 peripheral mononuclear cells) of circulating endothelial progenitor cells (EPC) is common in diabetic patients. Statins increase EPC levels. It is unclear whether intensity of statin therapy has a different impact on EPC levels.

METHODS

Diabetic patients undergoing drug-eluting stent (DES) implantation were randomized to 1) High intensity statin therapy (atorvastatin 80mg/day; n=66) or 2) Moderate intensity statin therapy (atorvastatin 20mg/day; n=64). EPC levels were assessed at baseline, 24h and 3months. Endpoints assessed at 3months were 1) changes in the proportion of patients with low EPC levels, and 2) uncovered struts rate and neointima growth evaluated by optical coherence tomography.

RESULTS

Low EPC levels rate significantly decreased in the High intensity statin therapy group (from 31.7% to 12.7%; p=0.017) but not in the Moderate intensity statin therapy group (from 25.5% to 21.8%; p=0.81). Uncovered struts rate was similar in the 2 groups (2.4±2.6% vs 2.3±2.2%; p=0.82), whereas mean neointima area and volume were lower in the High intensity statin therapy group (0.68±0.69 vs 1.22±1.29mm²; p=0.001; and, respectively, 13.10±5.77 vs 20.19±24.08mm³; p=0.042).

CONCLUSIONS

In diabetic patients, a high intensity statin therapy 1) significantly increases EPC levels and decreases in-stent neointima area and volume, and 2) does not have an impact on the degree of stent re-endothelialization at 3months after DES implantation.

Continuously Grooved Stent Struts for Enhanced Endothelial Cell Seeding

Purpose

Implantation of pre-endothelialized stents could enhance cellular recovery of a damaged vessel wall provided attached cells remain viable, functional and are present in sufficient numbers after deployment. The purpose of this study was to evaluate the feasibility of grooved stainless steel (SS) stents as a primary endothelial cell (EC) carrier with potentially enhanced EC protection upon stent deployment.

Materials and Methods

Attachment and behavior of enzymatically harvested human adult venous ECs seeded onto gelatin-coated vascular stents were evaluated in an in vitro setting. Smooth and grooved SS stents and smooth nitinol stents were studied.

Results

All cells expressed EC markers vWF and CD31. Using rotational seeding for a period of 16–24 h, ECs attached firmly to the stents with sufficient coverage to form a confluent EC monolayer. The grooved SS wire design was found to enable attachment of three times the number of cells compared to smooth wires. This also resulted in an increased number of cells remaining on the stent after deployment and after pulsatile flow of 180 ml/min for 24 h, which did not result in additional EC detachment.

Conclusions

The grooved stent provides a potential percutaneous means to deliver sufficient numbers of viable and functional cells to a vessel segment during vascular intervention. The grooves were found to offer a favorable surface for EC attachment and protection during stent deployment in an in vitro setting.

Electronic supplementary material

The online version of this article (doi:10.1007/s00270-017-1659-4) contains supplementary material, which is available to authorized users.

An Atelocollagen Coating for Efficient Local Gene Silencing by Using Small Interfering RNA

In the last decades, many efforts have been made to counteract adverse effects after stenting atherosclerotic coronary arteries. A breakthrough in better vascular wall regeneration was noted in the new era of drug-eluting stents. A novel personalized approach is the development of gene-eluting stents promising an alteration in gene expression involved in regeneration. We investigated a coating system consisting of the polymer atelocollagen (ATCOL) and a specific small interfering RNA (siRNA) for intercellular adhesion molecule-1 (ICAM-1) found on the surface of defective endothelial cells (ECs). We demonstrated very high cell viability, in which EA.hy926 grew on 0.008% or 0.032% ATCOL layers. Additionally, hemocompatibility assays proved the biocompatibility of this coating. The highest transfection efficiency with EA.hy926 was achieved with 5 μg siRNA immobilized in ATCOL after 2 days. The release of fluorescent-labeled siRNA was about 9 days. Long-term knockdown of ICAM-1 was analyzed by flow cytometry, revealing that the coating with 0.008% ATCOL and 5 μg siICAM-1 provoked gene silencing up to 8 days. 5′-RNA ligase-mediated rapid amplification of cDNA ends PCR (RLM-RACE-PCR) demonstrated the specificity of our established ATCOL gene-silencing coating, meaning that our coating is well suited for further investigations in in vivo studies. Herein, we would like to demonstrate that our ATCOL is well-suited for better artery wall regeneration after stent implantation.

Impact of diabetes duration on 3-year clinical outcomes following coronary revascularization

OBJECTIVE

The aim of this study was to evaluate the impact of diabetes duration on long-term clinical outcomes after drug-eluting stent (DES) implantation or coronary artery bypass grafting (CABG).

METHODS

A total of 820 diabetic patients treated with initial DES (n=451) or CABG (n=369) were consecutively enrolled in this single-center follow-up study. The main outcomes included major adverse cardiac events and major adverse cardiac or cerebrovascular events (MACCEs). Cox regression analysis with propensity adjustment was used for data analysis.

RESULTS

Three-year risks of major adverse cardiac events were significantly higher in the DES group compared with the CABG group irrespective of whether the diabetes durations were less or more than 5 years [hazard ratio (HR) 2.27, 95% confidence interval (CI) 1.19-4.31, P=0.01; HR 3.73, 95% CI 2.72-10.12, P<0.01; P for interaction=0.28]. A similar trend was observed for repeat revascularization. However, CABG was associated with increased risk of stroke, especially in the patients with diabetes duration of at least 5 years (HR 0.02, 95% CI 0.002-0.12, P<0.01). Three-year risk of MACCEs was significantly higher in the DES group in patients with diabetes duration of at least 5 years (HR 2.13, 95% CI 1.34-3.39, P<0.01), but not for those less than 5 years (HR 1.03, 95% CI 0.65-1.63, P=0.91). A statistically significant interaction between diabetes duration and treatment strategy was found for MACCEs (P for interaction=0.04).

CONCLUSION

Short diabetes duration (<5 years) was associated with equal risk of MACCEs among stable coronary artery disease patients with DES and CABG, emphasizing the need to consider the duration of diabetes when determining the best strategy for patients undergoing coronary revascularization.

Neoatherosclerosis after Drug-Eluting Stent Implantation: Roles and Mechanisms

In-stent neoatherosclerosis (NA), characterized by a relatively thin fibrous cap and large volume of yellow-lipid accumulation after drug-eluting stents (DES) implantation, has attracted much attention owing to its close relationship with late complications, such as revascularization and late stent thrombosis (ST). Accumulating evidence has demonstrated that more than one-third of patients with first-generation DES present with NA. Even in the advent of second-generation DES, NA still occurs. It is indicated that endothelial dysfunction induced by DES plays a critical role in neoatherosclerotic development. Upregulation of reactive oxygen species (ROS) induced by DES implantation significantly affects endothelial cells healing and functioning, therefore rendering NA formation. In light of the role of ROS in suppression of endothelial healing, combining antioxidant therapies with stenting technology may facilitate reestablishing a functioning endothelium to improve clinical outcome for patients with stenting.

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.

Metabolic and structural integrity of magnetic nanoparticle-loaded primary endothelial cells for targeted cell therapy

AIM

To successfully translate magnetically mediated cell targeting from bench to bedside, there is a need to systematically assess the potential adverse effects of magnetic nanoparticles (MNPs) interacting with 'therapeutic' cells. Here, we examined in detail the effects of internalized polymeric MNPs on primary rat endothelial cells' structural intactness, metabolic integrity and proliferation potential.

MATERIALS & METHODS

The intactness of cytoskeleton and organelles was studied by fluorescent confocal microscopy, flow cytometry and high-resolution respirometry.

RESULTS

MNP-loaded primary endothelial cells preserve intact cytoskeleton and organelles, maintain normal rate of proliferation, calcium signaling and mitochondria energy metabolism.

CONCLUSION

This study provides supportive evidence that MNPs at doses necessary for targeting did not induce significant adverse effects on structural integrity and functionality of primary endothelial cells - potential cell therapy vectors.

Modelling the Impact of Atherosclerosis on Drug Release and Distribution from Coronary Stents

Although drug-eluting stents (DES) are now widely used for the treatment of coronary heart disease, there remains considerable scope for the development of enhanced designs which address some of the limitations of existing devices. The drug release profile is a key element governing the overall performance of DES. The use of in vitro, in vivo, ex vivo, in silico and mathematical models has enhanced understanding of the factors which govern drug uptake and distribution from DES. Such work has identified the physical phenomena determining the transport of drug from the stent and through tissue, and has highlighted the importance of stent coatings and drug physical properties to this process. However, there is limited information regarding the precise role that the atherosclerotic lesion has in determining the uptake and distribution of drug. In this review, we start by discussing the various models that have been used in this research area, highlighting the different types of information they can provide. We then go on to describe more recent methods that incorporate the impact of atherosclerotic lesions.

IL-10 Accelerates Re-Endothelialization and Inhibits Post-Injury Intimal Hyperplasia following Carotid Artery Denudation

The role of inflammation on atherosclerosis and restenosis is well established. Restenosis is thought to be a complex response to injury, which includes early thrombus formation, acute inflammation and neo-intimal growth. Inflammatory cells are likely contributors in the host response to vascular injury, via cytokines and chemokines secretion, including TNF-alpha (TNF). We have previously shown that IL-10 inhibits TNF and other inflammatory mediators produced in response to cardiovascular injuries. The specific effect of IL-10 on endothelial cell (ECs) biology is not well elucidated. Here we report that in a mouse model of carotid denudation, IL-10 knock-out mice (IL-10KO) displayed significantly delayed Re-endothelialization and enhanced neo-intimal growth compared to their WT counterparts. Exogenous recombinant IL-10 treatment dramatically blunted the neo-intimal thickening while significantly accelerating the recovery of the injured endothelium in WT mice. In vitro, IL-10 inhibited negative effects of TNF on ECs proliferation, ECs cell cycle, ECs-monocyte adhesion and ECs apoptosis. Furthermore, IL-10 treatment attenuated TNF-induced smooth muscle cells proliferation. Our data suggest that IL-10 differentially regulate endothelial and vascular smooth cells proliferation and function and thus inhibits neo-intimal hyperplasia. Thus, these results may provide insights necessary to develop new therapeutic strategies to limit vascular restenosis during percutaneous coronary intervention (PCI) in the clinics.

Magnetically enhanced cell delivery for accelerating recovery of the endothelium in injured arteries

Arterial injury and disruption of the endothelial layer are an inevitable consequence of interventional procedures used for treating obstructive vascular disease. The slow and often incomplete endothelium regrowth after injury is the primary cause of serious short- and long-term complications, including thrombosis, restenosis and neoatherosclerosis. Rapid endothelium restoration has the potential to prevent these sequelae, providing a rationale for developing strategies aimed at accelerating the reendothelialization process. The present studies focused on magnetically guided delivery of endothelial cells (EC) functionalized with biodegradable magnetic nanoparticles (MNP) as an experimental approach for achieving rapid and stable cell homing and expansion in stented arteries. EC laden with polylactide-based MNP exhibited strong magnetic responsiveness, capacity for cryopreservation and rapid expansion, and the ability to disintegrate internalized MNP in both proliferating and contact-inhibited states. Intracellular decomposition of BODIPY558/568-labeled MNP monitored non-invasively based on assembly state-dependent changes in the emission spectrum demonstrated cell proliferation rate-dependent kinetics (average disassembly rates: 6.6±0.8% and 3.6±0.4% per day in dividing and contact-inhibited EC, respectively). With magnetic guidance using a transient exposure to a uniform 1-kOe field, stable localization and subsequent propagation of MNP-functionalized EC, markedly enhanced in comparison to non-magnetic delivery conditions, were observed in stented rat carotid arteries. In conclusion, magnetically guided delivery is a promising experimental strategy for accelerating endothelial cell repopulation of stented blood vessels after angioplasty.

CD4(+) lymphocytes improve venous blood flow in experimental arteriovenous fistulae

BACKGROUND

The role of immune cells in arteriovenous fistulae (AVF) maturation is poorly understood and has received, until quite recently, little attention. This study examines the function of T lymphocytes in AVF vascular remodeling.

METHODS

Experimental fistulae were created in athymic rnu nude rats lacking mature T lymphocytes and euthymic control animals by anastomosing the left superior epigastric vein to the nearby femoral artery. Blood flow rates, wall morphology, and histologic changes were assessed in AVF 21 days after creation. The effect of CD4(+) lymphocytes on AVF maturation in athymic animals was analyzed by adoptive transfer of cells after fistula creation.

RESULTS

The absence of T lymphocytes compromised blood flow in experimental fistulae. Histopathologic inspection of AVF from athymic rats revealed that T-cell immunodeficiency negatively affected venous vascular remodeling, as evidenced by a reduced lumen, a thick muscular layer, and a low number of inflammatory cells compared with control animals. Adoptive transfer of CD4(+) lymphocytes from euthymic rats into athymic animals after fistula creation improved blood flow and reduced intima-media thickness.

CONCLUSION

These results point at the protective role of CD4(+) lymphocytes in the remodeling of the AVF vascular wall.

Kinetics of endothelialization of the multilayer flow modulator and single-layer arterial stents

The multilayer flow modulator (MFM; Cardiatis, Isnes, Belgium) is a self-expandable mesh of braided cobalt alloy wires, used for treatment of aortic and peripheral aneurysms. To further improve our understanding of this novel technology, the endothelialization kinetics of the MFM was investigated and compared with those of two marketed single-layer stents. Five porcine animal models were used in which a total of 19 stents were implanted in the iliac and carotid arteries between one and five weeks before sacrifice. All 19 stents were successfully delivered. For all devices, nonsignificant signs of inflammation or thrombosis were noted, and there was no evidence of local intolerance. The MFM developed a thin layer of endothelial cells earlier and was associated with less neointimal development than the two single-layer stents. A differing phenomenon of integration was also revealed and hypothesized as endothelialization from adhesion of circulating endothelial progenitor cells, as well as adhesion from the arterial wall, and also by the differences in trauma exposed to the arterial wall.

Glucagon-Like Peptide-1 Receptor Activation Does not Affect Re-Endothelialization but Reduces Intimal Hyperplasia via Direct Effects on Smooth Muscle Cells in a Nondiabetic Model of Arterial Injury

Diabetic patients have an increased risk of restenosis and late stent thrombosis after angioplasty, i.e. complications that are related to a defective re-endothelialization. Exendin-4, a stable glucagon-like peptide (GLP)-1 receptor agonist, has been suggested to influence the formation of intimal hyperplasia and to increase endothelial cell proliferation in vitro. Thus, the aim of this study was to investigate the mechanisms by which treatment with exendin-4 could influence re-endothelialization and intimal hyperplasia after vascular injury.

METHODS

Sprague-Dawley rats were subjected to balloon injury of the left common carotid artery and treated for 4 weeks with exendin-4 or vehicle. Intimal hyperplasia and vessel wall elasticity were monitored noninvasively by high-frequency ultrasound, and re-endothelialization was evaluated upon sacrifice using Evans blue dye.

RESULTS AND CONCLUSION

Exendin-4 selectively reduced the proliferation of smooth muscle cells (SMCs) and intimal hyperplasia in vivo without affecting the re-endothelialization process, but treatment with exendin-4 improved arterial wall elasticity. Our data also show that exendin-4 significantly decreased the proliferation and increased the apoptosis of SMCs in vitro, effects that appear to be mediated through cAMP signaling and endothelial nitric oxide synthase following GLP-1 receptor activation. Together, these effects of exendin-4 are highly desirable and may lead to an improved outcome for patients undergoing vascular interventions.

High-density lipoprotein: a novel target for antirestenosis therapy

Restenosis is an integral pathological process central to the recurrent vessel narrowing after interventional procedures. Although the mechanisms for restenosis are diverse in different pathological conditions, endothelial dysfunction, inflammation, vascular smooth muscle cell (SMC) proliferation, and myofibroblasts transition have been thought to play crucial role in the development of restenosis. Indeed, there is an inverse relationship between high-density lipoprotein (HDL) levels and risk for coronary heart disease (CHD). However, relatively studies on the direct assessment of HDL effect on restenosis are limited. In addition to involvement in the cholesterol reverse transport, many vascular protective effects of HDL, including protection of endothelium, antiinflammation, antithrombus actions, inhibition of SMC proliferation, and regulation by adventitial effects may contribute to the inhibition of restenosis, though the exact relationships between HDL and restenosis remain to be elucidated. This review summarizes the vascular protective effects of HDL, emphasizing the potential role of HDL in intimal hyperplasia and vascular remodeling, which may provide novel prophylactic and therapeutic strategies for antirestenosis.

Extent of flow recirculation governs expression of atherosclerotic and thrombotic biomarkers in arterial bifurcations

AIMS

Atherogenesis, evolution of plaque, and outcomes following endovascular intervention depend heavily on the unique vascular architecture of each individual. Patient-specific, multiscale models able to correlate changes in microscopic cellular responses with relevant macroscopic flow, and structural conditions may help understand the progression of occlusive arterial disease, providing insights into how to mitigate adverse responses in specific settings and individuals.

METHODS AND RESULTS

Vascular architectures mimicking coronary and carotid bifurcations were derived from clinical imaging and used to generate conjoint computational meshes for in silico analysis and biocompatible scaffolds for in vitro models. In parallel with three-dimensional flow simulations, geometrically realistic scaffolds were seeded with human smooth muscle cells (SMC) or endothelial cells and exposed to relevant, physiological flows. In vitro surrogates of endothelial health, atherosclerotic progression, and thrombosis were locally quantified and correlated best with an quantified extent of flow recirculation occurring within the bifurcation models. Oxidized low-density lipoprotein uptake, monocyte adhesion, and tissue factor expression locally rose up to three-fold, and phosphorylated endothelial nitric oxide synthase and Krüppel-like factor 2 decreased up to two-fold in recirculation areas. Isolated testing in straight-tube idealized constructs subject to static, oscillatory, and pulsatile conditions, indicative of different recirculant conditions corroborated these flow-mediated dependencies.

CONCLUSIONS

Flow drives variations in vascular reactivity and vascular beds. Endothelial health was preserved by arterial flow but jeopardized in regions of flow recirculation in a quasi-linear manner. Similarly, SMC exposed to flow were more thrombogenic in large recirculating regions. Health, thrombosis, and atherosclerosis biomarkers correlate with the extent of recirculation in vascular cells lining certain vascular geometries.

Endothelial retention and phenotype on carbonized cardiovascular implant surfaces

Heart valve disease is an increasing clinical burden for which there is no effective treatment outside of prosthetic replacement. Over the last 20 years, clinicians have increasingly preferred the use of biological prosthetics to mechanical valves despite their superior durability because of the lifelong anticoagulation therapy that is required. Mechanical valve surface engineering has largely focused on being as non-thrombogenic as possible, but despite decades of iteration has had insufficient impact on the anticoagulation burden. In this study, we systematically evaluate the potential for endothelialization of the pyrolytic carbon surface used in mechanical valves. We compared adsorbed adhesion ligand type (collagen I, fibronectin, laminin, and purified adhesion domain fragments GFOGER and FN7-10) and concentration on endothelial adhesion rates and adhesion strength on Medtronic-Hall prosthetic valve surfaces. Regardless of ligand type or concentration, endothelial adhesion strengthening was insufficient for their intended ultra-high shear stress environment. We then hypothesized that microfabricated trenches would reduce shear stress to tolerable levels while maintaining endothelial access to the flow stream, thereby promoting a confluent and anticoagulant endothelial monolayer. Computational fluid dynamics simulations predicted an empirical relationship of channel width, depth, and spacing that would maintain interior surface shear stress within tolerable levels. Endothelial cells seeded to confluence in these channels retained a confluent monolayer when exposed to 600 dyn/cm(2) shear stress for 48 h regardless of applied adhesive ligand. Furthermore, sheared EC expressed a mature anti-coagulant profile, including endothelial nitric oxide synthase (eNOS), VE-cadherin, and significantly downregulated plasminogen activator inhibitor-1 (PAI-1). As a final test, channeled pyrolytic carbon surfaces with confluent EC reduced human platelet adhesion 1000-fold over pyrolytic carbon alone. These results advance a promising biohybrid approach to enable active moderation of local coagulative response in mechanical heart valves, which could significantly extend the utility of this important treatment for heart valve disease.