Healing arterial ulcers: Endothelial lining regeneration upon vascular denudation injury

Moving away from metal: Step toward the future with bioresorbable vascular scaffolds and novel antiproliferative agents

Background

Peripheral arterial disease (PAD) is a common source of morbidity and mortality globally and is expected to raise increase in prevalence. Many endovascular techniques exist to manage PAD; however, there remains room for improvement, especially as it relates to below-the-knee vessels. Recent evidence and devices are leading to a resurgence of interest in bioresorbable vascular scaffolds and the -limus family of antiproliferative drugs in the PAD treatment space.

Methods

This nonsystematic review examines emerging technology for treatment of PAD with a specific focus on below-the-knee vessels and bioresorbable vascular scaffolds. Additional emerging and early technology such as novel delivery platforms are also briefly discussed with directions of future research highlighted.

Results

Bioresorbable vascular scaffold biomechanics and history are highlighted. Foundational knowledge of antiproliferative agents and evolving agents in peripheral vascular disease are also described.

Conclusions

Bioresorbable vascular scaffolds are an additional endovascular tool for the treatment of peripheral vascular disease. The integration with an antiproliferative agent may result in improved patency and performance; however, there is a paucity of data in the literature at present.

Kanglexin counters vascular smooth muscle cell dedifferentiation and associated arteriosclerosis through inhibiting PDGFR

BACKGROUND

Dysregulation of vascular smooth muscle cell (VSMC) function leads to a variety of diseases such as atherosclerosis and hyperplasia after injury. However, antiproliferative drug targeting VSMC exhibits poor specificity. Therefore, there is an urgent to develop highly specific antiproliferative drugs to prevention and treatment VSMC dedifferentiation associated arteriosclerosis. Kanglexin (KLX), a new anthraquinone compound designed by our team, has potential to regulate VSMC phenotype according to the physicochemical properties.

PURPOSE

This project aims to evaluate the therapeutic role of KLX in VSMC dedifferentiation and atherosclerosis, neointimal formation and illustrates the underlying molecular mechanism.

METHODS

In vivo, the ApoE-/- mice were fed with high-fat diet (HFD) for a duration of 13 weeks to establish the atherosclerotic model. And rat carotid artery injury model was performed to establish the neointimal formation model. In vitro, PDGF-BB was used to induce VSMC dedifferentiation.

RESULTS

We found that KLX ameliorated the atherosclerotic progression including atherosclerotic lesion formation, lipid deposition and collagen deposition in aorta and aortic sinus in atherosclerotic mouse model. In addition, The administration of KLX effectively ameliorated neointimal formation in the carotid artery following balloon injury in SD rats. The findings derived from molecular docking and surface plasmon resonance (SPR) experiments unequivocally demonstrate that KLX had potential to bind PDGFR-β. Mechanism research work proved that KLX prevented VSMC proliferation, migration and dedifferentiation via activating the PDGFR-β-MEK -ERK-ELK-1/KLF4 signaling pathway.

CONCLUSION

Collectively, we demonstrated that KLX effectively attenuated the progression of atherosclerosis in ApoE-/- mice and carotid arterial neointimal formation in SD rats by inhibiting VSMC phenotypic conversion via PDGFR-β-MEK-ERK-ELK-1/KLF4 signaling. KLX exhibits promising potential as a viable therapeutic agent for the treatment of VSMC phenotype conversion associated arteriosclerosis.

Myeloid-derived growth factor suppresses VSMC dedifferentiation and attenuates postinjury neointimal formation in rats by activating S1PR2 and its downstream signaling

Restenosis after angioplasty is caused usually by neointima formation characterized by aberrant vascular smooth muscle cell (VSMC) dedifferentiation. Myeloid-derived growth factor (MYDGF), secreted from bone marrow-derived monocytes and macrophages, has been found to have cardioprotective effects. In this study we investigated the effect of MYDGF to postinjury neointimal formation and the underlying mechanisms. Rat carotid arteries balloon-injured model was established. We found that plasma MYDGF content and the level of MYDGF in injured arteries were significantly decreased after balloon injury. Local application of exogenous MYDGF (50 μg/mL) around the injured vessel during balloon injury markedly ameliorated the development of neointimal formation evidenced by relieving the narrow endovascular diameter, improving hemodynamics, and reducing collagen deposition. In addition, local application of MYDGF inhibited VSMC dedifferentiation, which was proved by reversing the elevated levels of osteopontin (OPN) protein and decreased levels of α-smooth muscle actin (α-SMA) in the left carotid arteries. We showed that PDGF-BB (30 ng/mL) stimulated VSMC proliferation, migration and dedifferentiation in vitro; pretreatment with MYDGF (50-200 ng/mL) concentration-dependently eliminated PDGF-BB-induced cell proliferation, migration and dedifferentiation. Molecular docking revealed that MYDGF had the potential to bind with sphingosine-1-phosphate receptor 2 (S1PR2), which was confirmed by SPR assay and Co-IP analysis. Pretreatment with CCG-1423 (Rho signaling inhibitor), JTE-013 (S1PR2 antagonist) or Ripasudil (ROCK inhibitor) circumvented the inhibitory effects of MYDGF on VSMC phenotypic switching through inhibiting S1PR2 or its downstream RhoA-actin monomers (G-actin) /actin filaments (F-actin)-MRTF-A signaling. In summary, this study proves that MYDGF relieves neointimal formation of carotid arteries in response to balloon injury in rats, and suppresses VSMC dedifferentiation induced by PDGF-BB via S1PR2-RhoA-G/F-actin-MRTF-A signaling pathway. In addition, our results provide evidence for cross talk between bone marrow and vasculature.

Sirolimus-loaded exosomes as a promising vascular delivery system for the prevention of post-angioplasty restenosis

Restenosis remains the main reason for treatment failure of arterial disease. Sirolimus (SIR) as a potent anti-proliferative agent is believed to prevent the phenomenon. The application of exosomes provides an extended-release delivery platform for SIR intramural administration. Herein, SIR was loaded into fibroblast-derived exosomes isolated by ultracentrifugation. Different parameters affecting drug loading were optimized, and exosome samples were characterized regarding physicochemical, pharmaceutical, and biological properties. Cytotoxicity, scratch wound assays, and quantitative real-time PCR for inflammation- and migration-associated genes were performed. Restenosis was induced by carotid injury in a rat carotid model and then exosomes were locally administered. After 14 days, animals were investigated by computed tomography (CT) angiography, morphometric, and immunohistochemical analyses. Western blotting confirmed the presence of specific protein markers in exosomes. Characterization of empty and SIR-loaded exosomes verified round and nanoscale structure of vesicles. Among prepared formulations, desired entrapment efficiency (EE) of 76% was achieved by protein:drug proportion of 2:1 and simple incubation for 30 min at 37 °C. Also, the optimal formulation released about 30% of the drug content during the first 24 h, followed by a prolonged release for several days. In vitro studies revealed the uptake and functional efficacy of the optimized formulation. In vivo studies revealed that %restenosis was in the following order: saline > empty exosomes > SIR-loaded exosomes. Furthermore, Ki67, alpha smooth muscle actin (α-SMA), and matrix metalloproteinase (MMP) markers were less expressed in the SIR-exosomes-treated arteries. These findings confirmed that exosomal SIR could be a hopeful strategy for the prevention of restenosis.

Endothelial-Smooth Muscle Cell Interactions in a Shear-Exposed Intimal Hyperplasia on-a-Dish Model to Evaluate Therapeutic Strategies

Intimal hyperplasia (IH) represents a major challenge following cardiovascular interventions. While mechanisms are poorly understood, the inefficient preventive methods incentivize the search for novel therapies. A vessel-on-a-dish platform is presented, consisting of direct-contact cocultures with human primary endothelial cells (ECs) and smooth muscle cells (SMCs) exposed to both laminar pulsatile and disturbed flow on an orbital shaker. With contractile SMCs sitting below a confluent EC layer, a model that successfully replicates the architecture of a quiescent vessel wall is created. In the novel IH model, ECs are seeded on synthetic SMCs at low density, mimicking reendothelization after vascular injury. Over 3 days of coculture, ECs transition from a network conformation to confluent 2D islands, as promoted by pulsatile flow, resulting in a "defected" EC monolayer. In defected regions, SMCs incorporated plasma fibronectin into fibers, increased proliferation, and formed multilayers, similarly to IH in vivo. These phenomena are inhibited under confluent EC layers, supporting therapeutic approaches that focus on endothelial regeneration rather than inhibiting proliferation, as illustrated in a proof-of-concept experiment with Paclitaxel. Thus, this in vitro system offers a new tool to study EC-SMC communication in IH pathophysiology, while providing an easy-to-use translational disease model platform for low-cost and high-content therapeutic development.

The effect of end-ischaemic normothermic machine perfusion on donor hepatic artery endothelial integrity

BACKGROUND

Ex vivo normothermic machine liver perfusion (NMLP) involves artificial cannulation of vessels and generation of flow pressures. This could lead to shear stress-induced endothelial damage, predisposing to vascular complications, or improved preservation of donor artery quality. This study aims to assess the spatial donor hepatic artery (HA) endothelial quality downstream of the cannulation site after end-ischaemic NMLP.

METHODS

Remnant HA segments from the coeliac trunk up to the gastroduodenal artery branching were obtained after NMLP (n = 15) and after static cold storage (SCS) preservation (n = 15). Specimens were fixed in 10% neutral buffered formalin and sectioned at pre-determined anatomical sites downstream of the coeliac trunk. CD31 immunohistostaining was used to assess endothelial integrity by a 5-point ordinal scale (grade 0: intact endothelial lining, grade 5: complete denudation). Endothelial integrity after SCS was used as a control for the state of the endothelium at commencement of NMP.

RESULTS

In the SCS specimens, regardless of the anatomical site, near complete endothelial denudation was present throughout the HA (median scores 4.5-5). After NMLP, significantly less endothelial loss in the distal HA was present compared to SCS grafts (NMLP vs. SCS: median grade 3 vs. 4.5; p = 0.042). In NMLP specimens, near complete endothelial denudation was present at the cannulation site in all cases (median grade: 5), with significantly less loss of the endothelial lining the further from the cannulation site (proximal vs. distal, median grade 5 vs. 3; p = 0.005).

CONCLUSION

Loss of endothelial lining throughout the HA after SCS and at the cannulation site after NMLP suggests extensive damage related to surgical handling and preservation injury. Gradual improved endothelial lining along more distal sites of the HA after NMLP indicates potential for re-endothelialisation. The regenerative effect of NMLP on artery quality seems to occur to a greater extent further from the cannulation site. Therefore, arterial cannulation for machine perfusion of liver grafts should ideally be as proximal as possible on the coeliac trunk or aortic patch, while the site of anastomosis should preferentially be attempted distal on the common HA.

Smooth muscle cells-derived CXCL10 prevents endothelial healing through PI3Kγ-dependent T cells response

AIMS

Defects in efficient endothelial healing have been associated with complication of atherosclerosis such as post-angioplasty neoatherosclerosis and plaque erosion leading to thrombus formation. However, current preventive strategies do not consider re-endothelialization in their design. Here, we investigate mechanisms linking immune processes and defect in re-endothelialization. We especially evaluate if targeting phosphoinositide 3-kinase γ immune processes could restore endothelial healing and identify immune mediators responsible for these defects.

METHODS AND RESULTS

Using in vivo model of endovascular injury, we showed that both ubiquitous genetic inactivation of PI3Kγ and hematopoietic cell-specific PI3Kγ deletion improved re-endothelialization and that CD4+ T-cell population drives this effect. Accordingly, absence of PI3Kγ activity correlates with a decrease in local IFNγ secretion and its downstream interferon-inducible chemokine CXCL10. CXCL10 neutralization promoted re-endothelialization in vivo as the same level than those observed in absence of PI3Kγ suggesting a role of CXCL10 in re-endothelialization defect. Using a new established ex vivo model of carotid re-endothelialization, we showed that blocking CXCL10 restore the IFNγ-induced inhibition of endothelial healing and identify smooth muscle cells as the source of CXCL10 secretion in response to Th1 cytokine.

CONCLUSION

Altogether, these findings expose an unforeseen cellular cross-talk within the arterial wall whereby a PI3Kγ-dependent T-cell response leads to CXCL10 production by smooth muscle cells which in turn inhibits endothelial healing. Therefore, both PI3Kγ and the IFNγ/CXCL10 axis provide novel strategies to promote endothelial healing.

Surface Engineering of Cardiovascular Devices for Improved Hemocompatibility and Rapid Endothelialization

Cardiovascular devices have been widely applied in the clinical treatment of cardiovascular diseases. However, poor hemocompatibility and slow endothelialization on their surface still exist. Numerous surface engineering strategies have mainly sought to modify the device surface through physical, chemical, and biological approaches to improve surface hemocompatibility and endothelialization. The alteration of physical characteristics and pattern topographies brings some hopeful outcomes and plays a notable role in this respect. The chemical and biological approaches can provide potential signs of success in the endothelialization of vascular device surfaces. They usually involve therapeutic drugs, specific peptides, adhesive proteins, antibodies, growth factors and nitric oxide (NO) donors. The gene engineering can enhance the proliferation, growth, and migration of vascular cells, thus boosting the endothelialization. In this review, the surface engineering strategies are highlighted and summarized to improve hemocompatibility and rapid endothelialization on the cardiovascular devices. The potential outlook is also briefly discussed to help guide endothelialization strategies and inspire further innovations. It is hoped that this review can assist with the surface engineering of cardiovascular devices and promote future advancements in this emerging research field.

Targeted Repair of Vascular Injury by Adipose-Derived Stem Cells Modified with P-Selectin Binding Peptide

Percutaneous coronary intervention for coronary artery disease treatment often results in pathological vascular injury, characterized by P-selectin overexpression. Adipose-derived stem cells (ADSCs) therapeutic efficacy remains elusive due to poor ADSCs targeting and retention in injured vessels. Here, conjugated P-selectin binding peptide (PBP) to polyethylene glycol-conjugated phospholipid derivative (DMPE-PEG) linkers (DMPE-PEG-PBP; DPP) are used to facilitate the modification of PBP onto ADSCs cell surfaces via hydrophobic interactions between DMPE-PEG and the phospholipid bilayer. DPP modification neither has influence on ADSCs proliferation nor apoptosis/paracrine factor gene expression. A total of 5 × 10-6 m DPP-modified ADSCs (DPP-ADSCs) strongly binds to P-selectin-displaying activated platelets and endothelial cells (ECs) in vitro and to wire-injured rat femoral arteries when administered by intra-arterial injection. Targeted binding of ADSCs shields injury sites from platelet and leukocyte adhesion, thereby decreasing inflammation at injury sites. Furthermore, targeted binding of ADSCs recovers injured ECs functionality and reduces platelet-initiated vascular smooth muscle cells (VSMCs) chemotactic migration. Targeted binding of DPP-human ADSCs to balloon-injured human femoral arteries is also demonstrated in ex vivo experiments. Overall, DPP-ADSCs promote vascular repair, inhibit neointimal hyperplasia, increase endothelium functionality, and maintain normal VSMCs alignment, supporting preclinical noninvasive utilization of DPP-ADSCs for vascular injury.

Exercise-induced vasodilation is not impaired following radial artery catheterization in coronary artery disease patients

Diagnosis and treatment for coronary artery disease (CAD) often involves angiography and/or percutaneous coronary intervention. However, the radial artery catheterization required during both procedures may result in acute artery dysfunction/damage. While exercise-based rehabilitation is recommended for CAD patients following catheterization, it is not known if there is a period when exercise may be detrimental due to catheter-induced damage. Animal studies have demonstrated exercise-induced paradoxical vasoconstriction postcatheterization. This study aimed to examine arterial responses to acute exercise following catheterization. Thirty-three CAD patients (65.8 ± 7.3 yr, 31.5 ± 6.3 kg/m², 82% men) undergoing transradial catheterization were assessed before and 1 wk postcatheterization. Radial artery (RA) diameter and shear rate were assessed during handgrip exercise (HE), in both the catheterized (CATH) and control (CON) arms. Endothelial function was also assessed via simultaneous bilateral radial flow-mediated dilation (FMD) at both time points. We found that the increase in RA diameter and shear stress in response to HE (P < 0.0001) was maintained postcatheterization in both the CATH and CON arms, whereas FMD following catheterization was impaired in the CATH [6.5 ± 3.3 to 4.7 ± 3.5% (P = 0.005)] but not in the CON [6.2 ± 2.6 to 6.4 ± 3.5% (P = 0.797)] limb. While endothelial dysfunction, assessed by FMD, was apparent 1 wk postcatheterization, the ability of the RA to dilate in response to exercise was not impaired. The impact of catheterization and consequent endothelial denudation on vascular dys/function in humans may therefore be stimulus specific, and a highly level of redundancy appears to exist that preserves exercise-mediated vasodilator responses.NEW & NOTEWORTHY Despite depressed flow-mediated endothelium-dependent dilation following catheterization-induced damage, radial artery responses to handgrip exercise were preserved. This suggests that arterial responses to catheterization may be stimulus specific and that redundant mechanisms may compensate for vasodilator impairment during exercise. This has implications for exercise-based rehabilitation after catheterization.

Noninvasive in vivo Assessment of the Re-endothelialization Process Using Ultrasound Biomicroscopy in the Rat Carotid Artery Balloon Injury Model

OBJECTIVES

Ultrasound biomicroscopy (UBM), or ultra high-frequency ultrasound, is a technique used to assess the anatomy of small research animals. In this study, UBM was used to assess differences in intimal hyperplasia thickness as a surrogate measurement of the re-endothelialization process after carotid artery balloon injury in rats.

METHODS

Ultrasound biomicroscopic data from 3 different experiments and rat strains (Sprague Dawley, Wistar, and diabetic Goto-Kakizaki) were analyzed. All animals were subjected to carotid artery balloon injury and examined with UBM (30-70 MHz) 2 and 4 weeks after injury. Re-endothelialization on UBM was defined as the length from the carotid bifurcation to the most distal visible edge of the intimal hyperplasia. En face staining with Evans blue dye was performed at euthanasia 4 weeks after injury, followed by tissue harvesting for histochemical and immunohistochemical evaluations.

RESULTS

A significant correlation (Spearman r = 0.63; P < .0001) was identified when comparing all measurements of re-endothelialization obtained from UBM and en face staining. The findings revealed a similar pattern for all rat strains: Sprague Dawley (Spearman r = 0.70; P < .0001), Wistar (Spearman r = 0.36; P < .081), and Goto-Kakizaki (Spearman r = 0.70; P < .05). A Bland-Altman test showed agreement between en face staining and UBM. Immunohistochemical staining confirmed the presence of the endothelium in the areas detected as re-endothelialized by the UBM assessment.

CONCLUSIONS

Ultrasound biomicroscopy can be used for repeated in vivo assessment of re-endothelialization after carotid artery balloon injury in rats.

Leoligin-inspired synthetic lignans with selectivity for cell-type and bioactivity relevant for cardiovascular disease

Recently, a natural compound leoligin, a furan-type lignan, was discovered as an interesting hit compound with an anti-inflammatory pharmacological activity profile. We developed a modular and stereoselective approach for the synthesis of the edelweiss-derived lignan leoligin and used the synthetic route to rapidly prepare leoligin analogs even on the gram scale. Proof of concept of this approach together with cell-based bio-assays gained structural analogs with increased selectivity towards vascular smooth muscle versus endothelial cell proliferation inhibition, a major benefit in fighting vascular neointima formation. In addition, we identified the structural features of leoligin analogs that define their ability to inhibit the pro-inflammatory NF-κB pathway. Results are discussed in the context of structural modification of these novel synthetic lignans.

Effects of Catheterization on Artery Function and Health: When Should Patients Start Exercising Following Their Coronary Intervention?

Coronary artery disease (CAD) is a leading cause of death worldwide, and percutaneous transluminal coronary angiography (PTCA) and/or percutaneous coronary intervention (PCI; angioplasty) are commonly used to diagnose and/or treat the obstructed coronaries. Exercise-based rehabilitation is recommended for all CAD patients; however, most guidelines do not specify when exercise training should commence following PTCA and/or PCI. Catheterization can result in arterial dysfunction and acute injury, and given the fact that exercise, particularly at higher intensities, is associated with elevated inflammatory and oxidative stress, endothelial dysfunction and a pro-thrombotic milieu, performing exercise post-PTCA/PCI may transiently elevate the risk of cardiac events. This review aims to summarize extant literature relating to the impacts of coronary interventions on arterial function, including the time-course of recovery and the potential deleterious and/or beneficial impacts of acute versus long-term exercise. The current literature suggests that arterial dysfunction induced by catheterization recovers 4-12 weeks following catheterization. This review proposes that a period of relative arterial vulnerability may exist and exercise during this period may contribute to elevated event susceptibility. We therefore suggest that CAD patients start an exercise training programme between 2 and 4 weeks post-PCI, recognizing that the literature suggest there is a 'grey area' for functional recovery between 2 and 12 weeks post-catheterization. The timing of exercise onset should take into consideration the individual characteristics of patients (age, severity of disease, comorbidities) and the intensity, frequency and duration of the exercise prescription.

Common Injuries and Repair Mechanisms in the Endothelial Lining

Objective:

Endothelial cells (ECs) are important metabolic and endocrinal organs which play a significant role in regulating vascular function. Vascular ECs, located between the blood and vascular tissues, can not only complete the metabolism of blood and interstitial fluid but also synthesize and secrete a variety of biologically active substances to maintain vascular tension and keep a normal flow of blood and long-term patency. Therefore, this article presents a systematic review of common injuries and healing mechanisms for the vascular endothelium.

Data Sources:

An extensive search in the PubMed database was undertaken, focusing on research published after 2003 with keywords including endothelium, vascular, wounds and injuries, and wound healing.

Study Selection:

Several types of articles, including original studies and literature reviews, were identified and reviewed to summarize common injury and repair processes of the endothelial lining.

Results:

Endothelial injury is closely related to the development of multiple cardiovascular and cerebrovascular diseases. However, the mechanism of vascular endothelial injury is not fully understood. Numerous studies have shown that the mechanisms of EC injury mainly involve inflammatory reactions, physical stimulation, chemical poisons, concurrency of related diseases, and molecular changes. Endothelial progenitor cells play an important role during the process of endothelial repair after such injuries. What's more, a variety of restorative cells, changes in cytokines and molecules, chemical drugs, certain RNAs, regulation of blood pressure, and physical fitness training protect the endothelial lining by reducing the inducing factors, inhibiting inflammation and oxidative stress reactions, and delaying endothelial caducity.

Conclusions:

ECs are always in the process of being damaged. Several therapeutic targets and drugs were seeked to protect the endothelium and promote repair.

Glucose-Dependent Insulinotropic Polypeptide Suppresses Peripheral Arterial Remodeling in Male Mice

Glucose-dependent insulinotropic polypeptide (GIP) exhibits direct cardiovascular actions in addition to its well-known insulinotropic effect. However, the role of GIP in peripheral artery disease remains unclear. In this study, we evaluated the effects of GIP against peripheral arterial remodeling in mouse models. The genetic deletion of GIP receptor (GIPR) led to exaggerated neointimal hyperplasia after transluminal femoral artery wire injury. Conversely, chronic GIP infusion suppressed neointimal hyperplasia and facilitated endothelial regeneration. The beneficial effects of GIP were abrogated by inhibiting nitric oxide (NO) synthase, suggesting a possible mechanism mediated by NO. In cultured human umbilical vein endothelial cells (HUVECs), GIP elevated cytosolic calcium levels without affecting intracellular cAMP levels. Furthermore, GIP dose-dependently increased NO production, whereas this effect was abolished by inhibiting AMP-activated protein kinase (AMPK). GIP induced AMPK phosphorylation, which was abrogated by inhibiting phospholipase C and calcium-calmodulin-dependent protein kinase kinase but not by adenylate cyclase or liver kinase B1, suggesting the existence of a calcium-mediated GIPR signaling pathway. These effects of GIP were retained in severe hyperglycemic Leprdb/ Leprdb mice and in high-glucose-cultured HUVECs. Overall, we demonstrated the protective effects of GIP against peripheral arterial remodeling as well as the involvement of a calcium-mediated GIPR signaling pathway in vascular endothelial cells. Our findings imply the potential vascular benefits of multiple agonists targeting G protein-coupled receptors, including GIPR, which are under development for the treatment of type 2 diabetes.

Rapid Endothelialization of Off-the-Shelf Small Diameter Silk Vascular Grafts

Synthetic vascular grafts for small diameter revascularization are lacking. Clinically available conduits expanded polytetrafluorethylene and Dacron fail acutely due to thrombosis and in the longer term from neointimal hyperplasia. We report the bioengineering of a cell-free, silk-based vascular graft. In vitro we demonstrate strong, elastic silk conduits that support rapid endothelial cell attachment and spreading while simultaneously resisting blood clot and fibrin network formation. In vivo rat studies show complete graft patency at all time points, rapid endothelialization, and stabilization and contraction of neointimal hyperplasia. These studies show the potential of silk as an off-the-shelf small diameter vascular graft.

Direct Laser Interference Patterning of CoCr Alloy Surfaces to Control Endothelial Cell and Platelet Response for Cardiovascular Applications

The main drawbacks of cardiovascular bare-metal stents (BMS) are in-stent restenosis and stent thrombosis as a result of an incomplete endothelialization after stent implantation. Nano- and microscale modification of implant surfaces is a strategy to recover the functionality of the artery by stimulating and guiding molecular and biological processes at the implant/tissue interface. In this study, cobalt-chromium (CoCr) alloy surfaces are modified via direct laser interference patterning (DLIP) in order to create linear patterning onto CoCr surfaces with different periodicities (≈3, 10, 20, and 32 µm) and depths (≈20 and 800 nm). Changes in surface topography, chemistry, and wettability are thoroughly characterized before and after modification. Human umbilical vein endothelial cells' adhesion and spreading are similar for all patterned and plain CoCr surfaces. Moreover, high-depth series induce cell elongation, alignment, and migration along the patterned lines. Platelet adhesion and aggregation decrease in all patterned surfaces compared to CoCr control, which is associated with changes in wettability and oxide layer characteristics. Cellular studies provide evidence of the potential of DLIP topographies to foster endothelialization without enhancement of platelet adhesion, which will be of high importance when designing new BMS in the future.

Neoatherosclerosis and Late Thrombosis After Percutaneous Coronary Intervention: Translational Cardiology and Comparative Medicine from Bench to Bedside

Neoatherosclerosis is a form of accelerated atherosclerosis that occurs within stented segments of the coronary vessel late or very late after drug-eluting stent (DES) implantation via percutaneous coronary intervention (PCI). This proliferation of neointima with a formation of new atheromatous plaque within stent struts lacking re-endothelialization can provoke thrombotic occlusion and lead to catastrophic acute coronary events. Knowing that coronary artery disease is the leading single cause of mortality worldwide and that there is a constant trend of increase in PCI procedures, it is reasonable to conclude that late thrombotic events and neoatherosclerosis post-PCI remain an important therapeutic challenge. For these reasons, early identification of patients at risk through the means of advanced imaging methods or preventive solutions available through novel technological solutions in DES design that target pro-inflammatory pathways and enable optimized arterial healing are central strategies in prevention and treatment of in-stent neoatherosclerosis and thrombosis. Due to this, pre-clinical studies performed on animal models are crucial building blocks that enable the objective and scientific assessment of innovative technological and therapeutic solutions before they are introduced to early stages of human clinical trials. A comparative medicine approach allows designing and executing experiments in animal models with a high degree of similarity with human coronary anatomy possibly promising the translation of encouraging findings to human clinical studies. The aim of this review is to provide contemporary insights on the pathophysiology of neoatherosclerosis and in-stent thrombosis and emergence of novel biomedical and technological solutions used to counter them.

Regulation of Focal Adhesion Kinase through a Direct Interaction with an Endogenous Inhibitor

Focal adhesion kinase (FAK) plays a key role in integrin and growth factor signaling pathways. FAK-related non-kinase (FRNK) is an endogenous inhibitor of FAK that shares its primary structure with the C-terminal third of FAK. FAK S910 phosphorylation is known to regulate FAK protein-protein interactions, but the role of the equivalent site on FRNK (S217) is unknown. Here we determined that S217 is highly phosphorylated by ERK in cultured rat aortic smooth muscle cells. Blocking phosphorylation by mutation (S217A) greatly increased FRNK inhibitory potency, resulting in strong inhibition of FAK autophosphorylation at Y397 and induction of smooth muscle cell apoptosis. FRNK has been proposed to compete for FAK anchoring sites in focal adhesions, but we did not detect displacement of FAK by WT-FRNK or superinhibitory S217A-FRNK. Instead, we found FRNK interacted directly with FAK, and this interaction is markedly strengthened for the superinhibitory S217A-FRNK. The results suggest that FRNK limits growth and survival signaling pathways by binding directly to FAK in an inhibitory complex, and this inhibition is relieved by phosphorylation of FRNK at S217.

Reproducible Arterial Denudation Injury by Infrarenal Abdominal Aortic Clamping in a Murine Model

Percutaneous vascular interventions uniformly result in arterial denudation injuries that subsequently lead to thrombosis and restenosis. These complications can be attributed to impairments in re-endothelialization within the wound margins. Yet, the cellular and molecular mechanisms of re-endothelialization remain to be defined. While several animal models to study re-endothelialization after arterial denudation are available, few are performed in the mouse because of surgical limitations. This undermines the opportunity to exploit transgenic mouse lines and investigate the contribution of specific genes to the process of re-endothelialization. Here, we present a step-by-step protocol for creating a highly reproducible murine model of arterial denudation injury in the infrarenal abdominal aorta using external vascular clamping. Immunocytochemical staining of injured aortas for fibrinogen and β-catenin demonstrate the exposure of a pro-thrombotic surface and the border of intact endothelium, respectively. The method presented here has the advantages of speed, excellent overall survival rate, and relative technical ease, creating a uniquely practical tool for imposing arterial denudation injury in transgenic mouse models. Using this method, investigators may elucidate the mechanisms of re-endothelialization under normal or pathological conditions.

Soluble N-cadherin: A novel inhibitor of VSMC proliferation and intimal thickening

Reoccurrence of symptoms occurs in 30-50% of coronary artery disease patients receiving vein grafts or bare-metal stents due to intimal thickening (restenosis). Restenosis is caused by vascular smooth muscle cell (VSMC) migration and proliferation. New therapeutic approaches that reduce VSMC migration and proliferation while promoting endothelial cell (EC) coverage are required. We assessed the effect of a soluble form of N-cadherin (SNC-Fc, a fusion of the extracellular portion of N-Cadherin to a mutated Fc fragment of IgG), a cell-cell junction molecule, on human saphenous VSMC proliferation and migration in vitro. We also assessed its effect on intimal thickening in a validated human ex vivo organ culture model. We observed that SNC-Fc significantly inhibited VSMC proliferation and to a lesser extent migration. The anti-proliferative effect of SNC-Fc was mediated by the interaction of SNC-Fc with the FGFR, rather than through inhibition of β-catenin signalling. SNC-Fc also significantly reduced intimal thickening by ~85% in the ex vivo organ culture model. SNC-Fc treatment inhibited proliferation of the intimal cells but did not affect migration. SNC-Fc reduced EC apoptosis, without detrimental effects on EC proliferation and migration in vitro. Importantly SNC-Fc increased EC coverage in the ex vivo model of intimal thickening. In conclusion, we suggest that SNC-Fc may have potential as an anti-proliferative therapeutic agent for reducing restenosis which has no detrimental effects on endothelial cells.