Formation Of Intimal Hyperplasia Research Articles

Stenting-induced Vasa Vasorum compression and subsequent flow resistance: a finite element study.

Vascular stenting is a common intervention for the treatment for atherosclerotic plaques. However, stenting still has a significant rate of restenosis caused by intimal hyperplasia formation. In this study, we evaluate whether stent overexpansion leads to Vasa Vasorum (VV) compression, which may contribute to vascular wall hypoxia and restenosis. An idealized multilayered fibroatheroma model including Vasa Vasorum was expanded by three coronary stent designs up to a 1.3:1 stent/artery luminal diameter ratio (exp1.1, exp1.2, exp1.3) using a finite element analysis approach. Following Poiseuille's law for elliptical sections, the fold increase in flow resistance was calculated based on VV compression in the Intima (Int), Media (Med) and Adventitia (Adv). The VV beneath the plaque experiences the smallest degree of compression, while the opposite wall regions are highly affected by stent overexpansion. The highest compressions for Adv, Med and Int at exp1.1 are 60.7, 65.9, 72.3%, at exp1.2 are 62.1, 67.3, 73.5% and at expp1.3 are 63.2, 68.7, 74.8%. The consequent fold increase in resistance to flow for Adv, Med and Int at exp1.1 is 3.3, 4.4, 6.6, at exp1.2 is 3.5, 4.7, 7.2 and at exp1.3 is 3.8, 5.1, 7.9. Stent overexpansion induces significant VV compression, especially in the Intima and Media layers, in agreement with previously observed Media necrosis and loss in elasticity after stenting. The observed steep increase in flow resistance suggests the blood flow and associated oxygen delivery would drop up to five times in the Media and almost eight in the Intima, which may lead to intimal hyperplasia and restenosis.

Fucoidan functionalization on poly(vinyl alcohol) hydrogels for improved endothelialization and hemocompatibility

The performance of clinical synthetic small diameter vascular grafts remains disappointing due to the fast occlusion caused by thrombosis and intimal hyperplasia formation. Poly(vinyl alcohol) (PVA) hydrogels have tunable mechanical properties and a low thrombogenic surface, which suggests its potential value as a small diameter vascular graft material. However, PVA does not support cell adhesion and thus requires surface modification to encourage endothelialization. This study presents a modification of PVA with fucoidan. Fucoidan is a sulfated polysaccharide with anticoagulant and antithrombotic properties, which was shown to potentially increase endothelial cell adhesion and proliferation. By mixing fucoidan with PVA and co-crosslinked by sodium trimetaphosphate (STMP), the modification was achieved without sacrificing mechanical properties. Endothelial cell adhesion and monolayer function were significantly enhanced by the fucoidan modification. In vitro and ex-vivo studies showed low platelet adhesion and activation and decreased thrombin generation with fucoidan modified PVA. The modification proved to be compatible with gamma sterilization. In vivo evaluation of fucoidan modified PVA grafts in rabbits exhibited increased patency rate, endothelialization, and reduced intimal hyperplasia formation. The fucoidan modification presented here benefited the development of PVA vascular grafts and can be adapted to other blood contacting surfaces.

Inhibition of heat shock protein 90 attenuates post‑angioplasty intimal hyperplasia.

Intimal hyperplasia (IH) is a pathologic process that leads to restenosis after treatment for peripheral arterial disease. Heat shock protein 90 (HSP90) is a molecular chaperone that regulates protein maturation. Activation of HSP90 results in increased cell migration and proliferation. 17‑N‑allylamino‑17‑demethoxygeldanamycin (17‑AAG) and 17‑dimethylaminoethylamino‑17‑demethoxygeldanamycin (17‑DMAG) are low toxicity Food and Drug Association approved HSP90 inhibitors. The current study hypothesized that HSP90 inhibition was predicted to reduce vascular smooth muscle cell (VSMC) migration and proliferation. In addition, localized HSP90 inhibition may inhibit post‑angioplasty IH formation. For proliferation, VSMCs were treated with serum‑free media (SFM), 17‑DMAG or 17‑AAG. The selected proliferative agents were SFM, platelet derived growth factor (PDGF) or fibronectin. After three days, proliferation was measured. For migration, VSMCs were treated with SFM, 17‑AAG or 17‑DMAG with SFM, PDGF or fibronectin as chemoattractants. Balloon injury to the carotid artery was performed in rats. The groups included in the present study were the control, saline control, 17‑DMAG in 20% pluronic gel delivered topically to the adventitia or intraluminal delivery of 17‑DMAG. After 14days, arteries were fixed and sectioned for morphometric analysis. Data was analyzed using ANOVA or a student's t‑test. P<0.05 was considered to indicate a statistically significant difference. The results revealed that 17‑AAG and 17‑DMAG had no effect on cell viability. PDGF and fibronectin also increased VSMC proliferation and migration. Furthermore, both 17‑AAG and 17‑DMAG decreased cell migration and proliferation in all agonists. Topical adventitial treatment with 17‑DMAG after balloon arterial injury reduced IH. HSP90 inhibitors suppressed VSMC proliferation and migration without affecting cell viability. Topical treatment with a HSP90 inhibitor (DMAG) decreased IH formation after arterial injury. It was concluded that 17‑DMAG may be utilized as an effective therapy to prevent restenosis after revascularization.

Current understanding of intimal hyperplasia and effect of compliance in synthetic small diameter vascular grafts.

Despite much effort, synthetic small diameter vascular grafts still face limited success due to vascular wall thickening known as intimal hyperplasia (IH). Compliance mismatch between graft and native vessels has been proposed to be one of a key mechanical factors of synthetic vascular grafts that could contribute to the formation of IH. While many methods have been developed to determine compliance both in vivo and in vitro, the effects of compliance mismatch still remain uncertain. This review aims to explain the biomechanical factors that are responsible for the formation and development of IH and their relationship with compliance mismatch. Furthermore, this review will address the current methods used to measure compliance both in vitro and in vivo. Lastly, current limitations in understanding the connection between the compliance of vascular grafts and the role it plays in the development and progression of IH will be discussed.

The myristoylated alanine-rich C kinase substrate differentially regulates kinase interacting with stathmin in vascular smooth muscle and endothelial cells and potentiates intimal hyperplasia formation

ObjectiveRestenosis limits the durability of all cardiovascular reconstructions. Vascular smooth muscle cell (VSMC) proliferation drives this process, but an intact, functional endothelium is necessary for vessel patency. Current strategies to prevent restenosis employ antiproliferative agents that affect both VSMCs and endothelial cells (ECs). Knockdown of the myristoylated alanine-rich C kinase substrate (MARCKS) arrests VSMC proliferation and paradoxically potentiates EC proliferation. MARCKS knockdown decreases expression of the kinase interacting with stathmin (KIS), increasing p27kip1 expression, arresting VSMC proliferation. Here, we seek to determine how MARCKS influences KIS protein expression in these two cell types. MethodsPrimary human coronary artery VSMCs and ECs were used for in vitro experiments. MARCKS was depleted by transfection with small interfering RNA. Messenger RNA was quantitated with the real-time reverse transcription polymerase chain reaction. Protein expression was determined by Western blot analysis. Ubiquitination was determined with immunoprecipitation. MARCKS and KIS binding was assessed with co-immunoprecipitation. Intimal hyperplasia was induced in CL57/B6 mice with a femoral artery wire injury. MARCKS was knocked down in vivo by application of 10 μM of small interfering RNA targeting MARCKS suspended in 30% Pluronic F-127 gel. Intimal hyperplasia formation was assessed by measurement of the intimal thickness on cross sections of the injured artery. Re-endothelialization was determined by quantitating the binding of Evans blue dye to the injured artery. ResultsMARCKS knockdown did not affect KIS messenger RNA expression in either cell type. In the presence of cycloheximide, MARCKS knockdown in VSMCs decreased KIS protein stability but had no effect in ECs. The effect of MARCKS knockdown on KIS stability was abrogated by the 26s proteasome inhibitor MG-132. MARCKS binds to KIS in VSMCs but not in ECs. MARCKS knockdown significantly increased the level of ubiquitinated KIS in VSMCs but not in ECs. MARCKS knockdown in vivo resulted in decreased KIS expression. Furthermore, MARCKS knockdown in vivo resulted in decreased 5-ethynyl-2′-deoxyuridine integration and significantly reduced intimal thickening. MARCKS knockdown enhanced endothelial barrier function recovery 4 days after injury. ConclusionsMARCKS differentially regulates the KIS protein stability in VSMCs and ECs. The difference in stability is due to differential ubiquitination of KIS in these two cell types. The differential interaction of MARCKS and KIS provides a possible explanation for the observed difference in ubiquitination. The effect of MARCKS knockdown on KIS expression persists in vivo, potentiates recovery of the endothelium, and abrogates intimal hyperplasia formation.

MicroRNA-374b induces endothelial-to-mesenchymal transition and early lesion formation through the inhibition of MAPK7 signaling.

Endothelial–mesenchymal transition occurs during intimal hyperplasia and neointima formation via mechanisms that are incompletely understood. Endothelial MAPK7 signaling is a key mechanosensitive factor that protects against endothelial–mesenchymal transition, but its signaling activity is lost in vessel areas that are undergoing pathological remodeling. At sites of vascular remodeling in mice and pigs, endothelial MAPK7 signaling was lost. The TGFβ‐induced microRNA‐374b targets MAPK7 and its downstream effectors in endothelial cells, and its expression induces endothelial–mesenchymal transition. Gain‐of‐function experiments, where endothelial MAPK7 signaling was restored, precluded endothelial–mesenchymal transition. In human coronary artery disease, disease severity is associated with decreased MAPK7 expression levels and increased miR‐374b expression levels. Endothelial–mesenchymal transition occurs in intimal hyperplasia and early lesion formation and is governed in part by microRNA‐374b‐induced silencing of MAPK7 signaling. Restoration of MAPK7 signaling abrogated these pathological effects in endothelial cells expressing miR‐374b. Thus, our data suggest that the TGFβ‐miR‐374b‐MAPK7 axis plays a key role in the induction of endothelial–mesenchymal transition during intimal hyperplasia and early lesion formation and might pose an interesting target for antiatherosclerosis therapy. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Natural remodeling of the distal anastomosis of an above-knee femoropopliteal bypass depicted by CT angiography of lower limbs improves geometry of the reconstruction.

The geometry of the distal anastomosis of a femoropopliteal bypass influences local hemodynamics and formation of intimal hyperplasia. We hypothesized that the distal anastomosis of an above-knee femoropopliteal bypass undergoes remodeling that results in displacement of the original course of the popliteal artery and change in the anastomosis angle. We identified 43 CT angiography examination with proximal femoropopliteal bypass and either a preserved contralateral popliteal artery or previous CTA before construction of the bypass for comparison. In these examinations, we measured the displacement distance and angle at the level of the distal anastomosis and compared these measurements with clinical and imaging data. The displacement distance was 8.8+/-4.9 mm (P<0.0001) and the displacement angle was -1° (IQR=44°). The angle between the inflow and outflow artery was 153+/-16° (P<0.0001). There was a negative association between the displacement angle and the angle between the bypass and the outflow artery (r=-0.318, P=0.037). Patients with reversed venous grafts had a greater displacement of the anastomosis (14.7+/-3.0 mm) than patients with prosthetic grafts (8.0+/-4.5 mm, P=0.0011). We conclude that construction of a distal anastomosis of proximal femoropopliteal bypass results in displacement of the original course of the popliteal artery towards the bypass and this effect is more pronounced in reversed venous grafts.

A3185 Cathepsin L is responsible for wire injury- induced intimal hyperplasia

Objectives: Intimal hyperplasia (IH) is characterized by inflammatory cells infiltration and extensive smooth muscle cells proliferation that contributes to restenosis after percutaneous coronary intervention (PCI). Cathepsin L (CatL), a member of lysosome protease is highly expressed in mouse intimal hyperplasia lesions, but whether it contributes to the pathogenesis of IH remains unknown. Methods: Carotid artery intimal hyperplasia was induced in WT and CatL KO (CatL–/–) mice by wire injured surgery, and IH lesions were analyzed after 28 days. Expression of CatL in the carotid lesions was analyzed. CatL's activity was measured by CathepsinL Activity Assay Kit. Migration, proliferation and cytokine (MCP-1) production of bone marrow macrophages or smooth muscle cells derived from WT and CatL−/− mice were investigated. Results: We found that CatL expression and activity increased significantly in mouse IH lesions. The IH, intimal area and intimal/media ratio, in CatL–/– mice was significantly reduced than that in WT mice. CatL deficiency impaired macrophage infiltration 3 days after wire injury surgery, but did not affect smooth muscle cell or endothelial function directly. Proliferation and migration functions of smooth muscle cells derived from WT and CatL−/− aorta showed no significant difference. Aortic rings from WT and CatL−/− mice showed no significant difference in acetylcholine-induced endothelial relaxation responses. In vitro studies proved that production of inflammatory cytokine (MCP-1) and migration function of macrophages derived from CatL–/– mice, in response to LPS or HMGB1, were significantly impaired compared to WT macrophages. Conclusion: CatL plays an important role in intimal hyperplasia formation and suggest that CatL is a new therapeutic target for vessel restenosis after PCI.

Histological and Mechanical Assessment of Decellularized Porcine Biografts, and Its Biological Evaluation following Aortic Implantation during Mid-Term Follow-Up

Aims: Prosthetic graft infection frequently requires graft replacement. Among other options, a biological graft could serve as an alternative choice. Decellularization reduces tissue immunogenicity. Our aim was to determine an efficient decellularization method and to evaluate the decellularized porcine biografts’ adaptability. Methods: Four different protocols were implemented to decellularize porcine aortic segments (n = 4). Cell removal effectiveness and matrix structure preservation were histologically examined. Mechanical tests were performed. Decellularized porcine grafts were interpositioned in a porcine aorta. After a 6-month period, implanted samples were removed and evaluated using light and electron microscopy. Results: Histological results showed complete removal of cells and preserved connective tissue fiber structure following decellularization, using sodium dodecyl sulfate and sodium azide. Pressure tests demonstrated similar compliance to fresh vessels. In 9 out of 10 cases, pigs survived the follow-up period. Graft rejection, intimal hyperplasia, reocclusion and/or aneurysm formation were not observed. Presence of host cells and neoendothelialization were microscopically confirmed. Conclusions: This decellularization protocol enables a cost-effective preparation of biological grafts featuring reduced immunogenicity. The implanted grafts did not degenerate during the 6-month follow-up period, the lack of graft rejection suggests acceptable immunological tolerance, while recipient cells migrate into, proliferate and differentiate, thus creating the possibility for further use as an optional vascular graft.

Abstract 323: Hydrogen Sulfide Limits the Development of Intimal Hyperplasia in a Mouse Model of Femoral Wire Injury and in Human Veins

Objectives: Mainstays of contemporary therapies for this arterial occlusive disease include angioplasties, stents, endarterectomies and bypass surgery. However, these treatments suffer from high failure rates due to re-occlusive vascular wall adaptations, namely intimal hyperplasia (IH). IH develops in response to endothelium injury, leading to inflammation, vascular smooth muscle cells (VSMC) dedifferentiation, migration and proliferation at the site of injury. Hydrogen sulfide (H 2 S) is a ubiquitous signaling gazotransmitter, which exhibits antioxidant, anti-inflammatory, and vaso-relaxant properties. Thus, we hypothesized that H 2 S could reduce IH formation. Methods: WT male C57BL6/J mice submitted to femoral wire injury surgery to induce IH were treated with an H 2 S donor (NaHS) in the drinking water. IH was measured 28 days post-surgery by histology. In addition, segments of great saphenous vein obtained from patients undergoing bypass surgery were maintained in culture ex-vivo for 7days in presence of various H 2 S donors (NaHS, GYY4137, diacyltrisulfide). Finally, primary human umbilical vein endothelial cells (HUVEC) and primary human VSMC were treated in-vitro with the same H 2 S donors to study cellular proliferation and migration. Results: NaHS treatment significantly reduced IH development in the mouse model of femoral wire injury ( Figure 1 ). Similarly, the various H 2 S donors prevented the development of IH in vein segments ex-vivo. In vitro , the same H 2 S donors stimulated human endothelial cells (HUVEC) migration and proliferation, while inhibiting migration and proliferation of primary VSMC ( Figure 2 ). Conclusions: Exogenous H 2 S prevents IH formation in mice in-vivo and in human veins ex-vivo . Importantly, H 2 S reduces VSMCs but stimulates ECs proliferation and migration. These data suggest that exogenous H 2 S therapy could be used in human to minimize IH, thus limiting vascular reconstruction failure.

Anagliptin inhibits neointimal hyperplasia after balloon injury via endothelial cell-specific modulation of SOD-1/RhoA/JNK signaling in the arterial wall.

Intimal hyperplasia is one of the major complications after stenting, but the underlying mechanisms remain unclear. Our previous study found that the dipeptidyl peptidase IV (DPP-4) inhibitor, Anagliptin, suppresses intimal hyperplasia after balloon injury. Here, we further investigated the effects of Anagliptin on endothelial cell (EC) migration after balloon injury. The results showed that Anagliptin administration significantly reduced intimal hyperplasia by stimulating the migration of endothelial cells, but had no effect on the medial area after balloon injury. Anagliptin elevated the total plasma activity of SOD by up-regulating the level of SOD-1, but not SOD-2, after balloon injury. Meanwhile, pre-incubation with Anagliptin suppressed the hydrogen peroxide-mediated formation of oxidant species and apoptosis in HUVECs. In vitro pre-incubation with Anagliptin promoted the migration of HUVECs via the SOD-1/RhoA/JNK signaling pathway mediating the formation of F-actin. Collectively, the DPP-4 inhibitor, Anagliptin, regulates SOD-1/RhoA/ JNK-mediated HUVECs migration. The results suggest that Anagliptin could serve as a potential drug to prevent intimal hyperplasia formation after balloon injury.

Evaluating intimal hyperplasia under clinical conditions.

Open arterial revascularization using venous segments is frequently associated with the development of intimal hyperplasia (IH), leading to severe restenosis and graft failure. The lack of treatment to prevent this pathology is a major problem. Therefore, we generated a new porcine model, which closely mimics the clinical development of human IH, to test the therapeutic potential of candidate drugs. A patch of jugular vein was sutured to the right common carotid artery of pigs, to expose the vein to haemodynamic conditions of the arterial bed. Four weeks after surgery, the operated vessels which received no further treatment (the control group) were compared with (i) contralateral, non-operated vessels (the healthy group); (ii) vessels of pigs that received a perivascular application of a drug-free microparticle gel (the placebo group) and (iii) vessels of pigs that perioperatively received the same gel loaded with 10-mg atorvastatin (the atorvastatin group). When compared with non-operated vessels, all operated segments displayed a sizable IH which was thicker in the venous patch than in the host artery. These alterations were associated with a thickening of the intima layer of both vessels in the absence of inflammation. The intima/media ratio has been significantly increased by 2000-fold in the vein patches. Perivascular application of atorvastatin did not prevent IH formation. However, the drug increased the adventitial neovascularization in the operated vessels. The novel porcine model allows for monitoring IH formation under haemodynamic conditions which mimic clinical situations. It should facilitate the screening of innovative treatments to prevent restenosis.

Synergistic favorable effect of eicosapentaenoic acid and statin on atherosclerosis

Background and Aims: Combination of Eicosapentaenoic Acid (EPA) and HMG-CoA reductase inhibitor (statin) are known to be an effective therapy for cardiovascular diseases, however, their biological roles in the favorable effect on adverse event have not been studied well. In this study, we aimed to investigate the effect of EPA and statins focusing on plaque formation in a rabbit plaque model. Methods: Rabbit carotid artery was injured with a balloon followed by feeding with a normal diet for 4 w and then with a high-cholesterol diet for 4 w. The rabbits were either received pitavastatin alone, EPA alone, combination (pitavastatin+EPA) or vehicle (control) for 4 w with a high-cholesterol diet. The injured carotid arteries were harvested and analysed morphometrically and immunohistochemically. Results: In control group, smooth muscle cells were located on the luminal side of the plaque and lipidrich macrophages accumulated in the center of the plaque expressing Matrix Metalloproteinase-9 (MMP-9), Tissue Factor (TF), and NF-kB, those are characteristic of unstable plaques. In contrast, EPA reduced the expression of TF and NF-kB and increased the expression of PPAR-α in the plaque. Pitavastatin also reduced the expression of MMP-9, TF, and NF-kB, but not PPAR-α in the plaque. Combination of pitavastatin and EPA significantly reduced the expression of MMP-9, TF, and NF-kB increasing the expression of PPAR-α resulting in the inhibition of intimal hyperplasia and plaque formation in carotid arteries. Conclusions: Pitavastatin and EPA synergistically played a role for inhibitory effect on plaque formation decreasing the expression of inflammation-related molecules and increasing the expression of PPAR-α in injured artery.

Analysis of Computational Fluid Dynamics and Particle Image Velocimetry Models of Distal-End Side-to-Side and End-to-Side Anastomoses for Coronary Artery Bypass Grafting in a Pulsatile Flow.

Intimal hyperplasia (IH) is a major cause of graft failure. Hemodynamic factors such as stagnation and disturbed blood flow are involved in IH formation. The aim of this study is to perform a comparative analysis of distal-end side-to-side (deSTS) and end-to-side (ETS) anastomoses using computational fluid dynamics (CFD) after validating the results via particle image velocimetry (PIV).Methods and Results:We investigated the characteristics of our target flow fields using CFD under steady and pulsatile flows. CFD via PIV under steady flow in a 10-times-actual-size model was validated. The CFD analysis revealed a recirculation zone in the heel region in the deSTS and ETS anastomoses and at the distal end of the graft, and just distal to the toe of the host artery in the deSTS anastomoses. The recirculation zone sizes changed with the phase shift. We found regions of low wall shear stress and high oscillating shear index in the same areas. The PIV and CFD results were similar. It was demonstrated that the hemodynamic characteristics of CFD and PIV is the difference between the deSTS and ETS anastomoses; that is, the deSTS flow peripheral to the distal end of the graft, at the distal end and just distal to the toe of the host artery is involved in the IH formation.

Self-expanding nitinol stents of high versus low chronic outward force in de novo femoropopliteal occlusive arterial lesions (BIOFLEX-COF trial): study protocol for a randomized controlled trial

BackgroundSelf-expanding nitinol stents must be oversized at least by a minimal amount to ensure contact with the vessel wall and prevent migration. Once the stent is deployed it exerts a continuous force upon the vascular wall, termed chronic outward force (COF). Animal studies have found an increased neointimal hyperplasia in stents with high oversizing and thus high COF. Data about correlation between COF and neointimal hyperplasia in humans are currently lacking. The objective of the BIOFLEX-COF trial is to prospectively investigate differences in formation of intimal hyperplasia at 1 and 2 years after implantation of nitinol stents with high versus low COF in de novo femoropopliteal occlusive arterial lesions.MethodsThe BIOFLEX-COF trial is a prospective, quantitative, randomized study. Eighty subjects with symptomatic peripheral arterial lesions eligible for endovascular stent implantation will be enrolled and randomly assigned to either a high COF group (LifeStent Flexstar, Bard Peripheral Vascular Inc., Tempe, AZ, USA) or low COF group (Pulsar, Biotronik AG, Bülach, Switzerland) using an online randomization program to generate a random 1:1 group allocation (block randomization). After implantation and dilatation, COF at every 2 mm along the stent axis will be calculated from the actual stent diameter versus its nominal diameter.There will be two follow-up evaluations at 12 and 24 months. Primary endpoint is the amount of in-stent neointima at 1 year, assessed by contrast-enhanced CT angiography (CTA). In the control examinations, stent diameter and true lumen diameter will be measured on DICOM images every 2 mm along the stent axis to quantify the relative amount of in-stent restenosis.Secondary objectives are the amount of in-stent neointima at 2 years, device- and procedure-related adverse events and target lesion revascularization (TLR) rate.The scheduled time for recruitment is 2 years. Recruitment is expected to be complete in October 2017.DiscussionThis trial is the first to prospectively investigate the influence of COF on stent patency. If successful, the results will aid in a more precise selection of stent type and size in a given target vessel.The present study is challenging in that it compares two different self-expanding nitinol stents head-to-head against each other. To optimize the power of this study, traditional binary outcome parameters such as TLR and restenosis at Doppler ultrasound were dropped as primary endpoints. Instead, the amount of neointima inside the stent accessed by CTA was selected as (continuous) outcome parameter.Trial registrationClinicalTrials.gov Identifier: NCT03097679. Date of registration: 14 March 2017 (retrospectively registered).

Intimal hyperplasia induced by vascular intervention causes lipoprotein retention and accelerated atherosclerosis.

Accelerated atherosclerosis diminishes the long term patency of vascular interventions, such as percutaneous coronary intervention and implantation of saphenous vein grafts. However, the cause of this accelerated atherosclerosis is unclear. In this study, we tested the hypothesis that intimal hyperplasia formed following vascular intervention promotes retention of atherogenic lipoproteins. Intimal hyperplasia was surgically induced in the mouse common carotid artery. The surgery was combined with different mouse models of hypercholesterolemia to obtain different cholesterol levels and to control the onsets of hypercholesterolemia. Three weeks after surgery, samples were immunostained for apoB lipoproteins, smooth muscle cells and leukocytes. Already at mild hypercholesterolemia (193 mg/dL), pronounced apoB lipoprotein retention was found in the extracellular matrix in both intimal hyperplasia and the injured underlying media. In contrast, minimal retention was detected in the uninjured proximal region of the same vessel, or in vessels from mice with normal cholesterol levels (81 mg/dL). Induction of aggravated hypercholesterolemia 3 weeks after surgery, when a mature intimal hyperplasia had been formed, caused a very rapid development of atherosclerotic lesions. Mechanistically, we show that lipoprotein retention was almost exclusively dependent on electrostatic interactions to proteoglycan glycosaminoglycans, and the lipoprotein retention to intimal hyperplasia could be inhibited in vivo using glycosaminoglycan‐binding antibodies. Thus, formation of intimal hyperplasia following vascular intervention makes the vessel wall highly susceptible for lipoprotein retention and accelerated atherosclerosis. The increased lipoprotein retention in intimal hyperplasia can be targeted by blocking the interaction between apoB lipoproteins and glycosaminoglycans in the extracellular matrix.

Murine Aortic Crush Injury: An Efficient In Vivo Model of Smooth Muscle Cell Proliferation and Endothelial Function.

Arterial reconstruction, whether angioplasty or bypass surgery, involves iatrogenic trauma causing endothelial disruption and vascular smooth muscle cell (VSMC) proliferation. Common murine models study small vessels such as the carotid and femoral arteries. Herein we describe an in vivo system in which both VSMC proliferation and endothelial barrier function can be simultaneously assessed in a large vessel. We studied the infrarenal aortic response to injury in C57BL/6 mice. The aorta was injured from the left renal vein to the aortic bifurcation by 30 transmural crushes of 5-seconds duration with a cotton-tipped applicator. Morphological changes were assessed with conventional histology. Aorta wall thickness was measured from the luminal surface to the adventitia. EdU integration and counter staining with DAPI and alpha-actin was used to demonstrate VSMC proliferation. Activation of ERK1/2, a known moderator of intimal hyperplasia formation, was determined by Western Blot analysis. The effect of inflammation was determined by immunohistochemistry for B-cells, T-cells, and macrophages. En face sections of endothelium were visualized with scanning electron microscopy (SEM). Endothelial barrier function was determined with Evans Blue staining. Transmural injury resulted in aortic wall thickening. This injury induced VSMC proliferation, most prominently at 3 days after injury, and early activation of ERK1/2 and decreased p27kip1 expression. Injury did not result in increased B-cells, T-cells, or macrophages infiltration in the vessel wall. Injury caused partial endothelial cell denudation and loss of cell-cell contact. Injury resulted in a significant loss of endothelial barrier function, which returned to baseline after seven days. The murine transmural blunt aortic injury model provides an efficient system to simultaneously study both VSMC proliferation and endothelial barrier function in a large vessel.

Optimisation of a Novel Spiral-Inducing Bypass Graft Using Computational Fluid Dynamics

Graft failure is currently a major concern for medical practitioners in treating Peripheral Vascular Disease (PVD) and Coronary Artery Disease (CAD). It is now widely accepted that unfavourable haemodynamic conditions play an essential role in the formation and development of intimal hyperplasia, which is the main cause of graft failure. This paper uses Computational Fluid Dynamics (CFD) to conduct a parametric study to enhance the design and performance of a novel prosthetic graft, which utilises internal ridge(s) to induce spiral flow. This design is primarily based on the identification of the blood flow as spiral in the whole arterial system and is believed to improve the graft longevity and patency rates at distal graft anastomoses. Four different design parameters were assessed in this work and the trailing edge orientation of the ridge was identified as the most important parameter to induce physiological swirling flow, while the height of the ridge also significantly contributed to the enhanced performance of this type of graft. Building on these conclusions, an enhanced configuration of spiral graft is proposed and compared against conventional and spiral grafts to reaffirm its potential benefits.

Dynamic Autologous Reendothelialization of Small-Caliber Arterial Extracellular Matrix: A Preclinical Large Animal Study.

Effective cellularization is a key approach to prevent small-caliber (<4 mm) tissue-engineered vascular graft (TEVG) failure and maintain patency and contractility following implantation. To achieve this goal, however, improved biomimicking designs and/or relatively long production times (typically several months) are required. We previously reported on porcine carotid artery decellularization yielding biomechanically stable and cell supportive small-caliber (3–4 mm diameter, 5 cm long) arterial extracellular matrix (scaECM) vascular grafts. In this study, we aimed to study the scaECM graft patency in vivo and possibly improve that patency by graft pre-endothelialization with the recipient porcine autologous cells using our previously reported custom-designed dynamic perfusion bioreactor system. Decellularized scaECM vascular grafts were histologically characterized, their immunoreactivity studied in vitro, and their biocompatibility profile evaluated as a xenograft subcutaneous implantation in a mouse model. To study the scaECM cell support and remodeling ability, pig autologous endothelial and smooth muscle cells (SMCs) were seeded and dynamically cultivated within the scaECM lumen and externa/media, respectively. Finally, endothelialized-only scaECMs—hypothesized as a prerequisite for maintaining graft patency and controlling intimal hyperplasia—were transplanted as an interposition carotid artery graft in a porcine model. Graft patency was evaluated through angiography online and endpoint pathological assessment for up to 6 weeks. Our results demonstrate the scaECM-TEVG biocompatibility preserving a structurally and mechanically stable vascular wall not just following decellularization and recellularization but also after implantation. Using our dynamic perfusion bioreactor, we successfully demonstrated the ability of this TEVG to support in vitro recellularization and remodeling by primary autologous endothelial and SMCs, which were seeded on the lumen and the externa/media layers, respectively. Following transplantation, dynamically endothelialized scaECM-TEVGs remained patent for 6 weeks in a pig carotid interposition bypass model. When compared with nonrevitalized control grafts, reendothelialized grafts provided excellent antithrombogenic activity, inhibited intimal hyperplasia formation, and encouraged media wall infiltration and reorganization with recruited host SMCs. We thus demonstrate that readily available decellularized scaECM can be promptly revitalized with autologous cells in a 3-week period before implantation, indicating applicability as a future platform for vascular reconstructive procedures.

The ratio of diameters between the target artery and the bypass modifies hemodynamic parameters related to intimal hyperplasia in the distal end-to-side anastomosis.

Hemodynamics in the distal end-to-side anastomosis is related to early development of intimal hyperplasia and bypass failure. In this study we investigated the effect of diameter ratios between the target artery and the bypass at three different angles of the connection. The pulsatile flow field was visualized using particle image velocimetry in transparent models with three different angles of the connection (25°, 45°, 60°) and the diameter ratio between the bypass and the target artery was 4.6 mm : 6 mm, 6 mm : 6 mm, and 7.5 mm : 6 mm. Six parameters including location and oscillation of the stagnation point, local energy dissipation, wall shear stress (WSS), oscillatory shear index, spatial and temporal gradient of WSS and their distribution in the target artery were calculated from the flow field. In the wider bypass, the stagnation point oscillated in a greater range and was located more proximal to the anastomosis. Energy dissipation was minimal in a wider bypass with a more acute angle. The maximum WSS values were tree times greater in a narrow bypass and concentrated in a smaller circular region at the floor of the anastomosis. The oscillatory shear index increased with wider bypass and more acute angle. The maximum of spatial gradient of WSS concentrated around the floor and toe of the anastomosis and decreased with more acute angle and wider bypass, the temporal gradient of WSS was stretched more towards the side wall. Greater bypass to target vessel ratio and more acute anastomosis angle promote hemodynamics known to reduce formation of intimal hyperplasia.