Periadventitial rapamycin-eluting microbeads promote vein graft disease in long-term pig vein-into-artery interposition grafts

Neointima abating and endothelium preserving - An adventitia-localized nanoformulation to inhibit the epigenetic writer DOT1L

Open vascular reconstructions such as bypass are common treatments for cardiovascular disease. Unfortunately, neointimal hyperplasia (IH) follows, leading to treatment failure for which there is no approved therapy. Here we combined the strengths of tailoring nanoplatforms for open vascular reconstructions and targeting new epigenetic mechanisms. We produced adhesive nanoparticles (ahNP) that could be pen-brushed and immobilized on the adventitia to sustainably release pinometostat, an inhibitor drug selective to the epigenetic writer DOT1L that catalyzes histone-3 lysine-79 dimethylation (H3K79me2). This treatment not only reduced IH by 76.8% in injured arteries mimicking open reconstructions in obese Zucker rats with human-like diseases but also avoided the shortcoming of endothelial impairment in IH management. In mechanistic studies, chromatin immunoprecipitation (ChIP) sequencing revealed co-enrichment of the histone mark H3K27ac(acetyl) and its reader BRD4 at the gene of aurora kinase B (AURKB), where H3K79me2 was also enriched as indicated by ChIP-qPCR. Accordingly, DOT1L co-immunoprecipitated with H3K27ac. Furthermore, the known IH driver BRD4 governed the expression of DOT1L which controlled AURKB's protein level, revealing a BRD4- > DOT1L- > AURKB axis. Consistently, AURKB-selective inhibition reduced IH. Thus, this study presents a prototype nanoformulation suited for open vascular reconstructions, and the new insights into chromatin modulators may aid future translational advances.

Sirolimus-Embedded Silk Microneedle Wrap to Prevent Neointimal Hyperplasia in Vein Graft Model

We investigated the role of a sirolimus-embedded silk microneedle (MN) wrap as an external vascular device for drug delivery efficacy, inhibition of neointimal hyperplasia, and vascular remodeling. Using dogs, a vein graft model was developed to interpose the carotid or femoral artery with the jugular or femoral vein. The control group contained four dogs with only interposed grafts; the intervention group contained four dogs with vein grafts in which sirolimus-embedded silk-MN wraps were applied. After 12-weeks post-implantation, 15 vein grafts in each group were explanted and analyzed. Vein grafts applied with the rhodamine B-embedded silk-MN wrap showed far higher fluorescent signals than those without the wrap. The diameter of vein grafts in the intervention group decreased or remained stable without dilatation; however, it increased in the control group. The intervention group had femoral vein grafts with a significantly lower mean neointima-to-media ratio, and had vein grafts with an intima layer showing a significantly lower collagen density ratio than the control group. In conclusion, sirolimus-embedded silk-MN wrap in a vein graft model successfully delivered the drug to the intimal layer of the vein grafts. It prevented vein graft dilatation, avoiding shear stress and decreasing wall tension, and it inhibited neointimal hyperplasia.

Large animal model of vein grafts intimal hyperplasia: A systematic review

Coronary artery bypass grafting remains the treatment of choice for a large cohort of patients with significant coronary disease. Despite the increased use of arterial grafts, the long saphenous vein remains the most commonly used conduit. Long-term graft patency continues to be the Achilles heel of saphenous vein grafts. This is due to the development of intimal hyperplasia, a chronic inflammatory disease that results in the narrowing and occlusion of a significant number of vein grafts. Research models for intimal hyperplasia are essential for a better understanding of pathophysiological processes of this condition. Large animal models resemble human anatomical structures and have been used as a surrogate to study disease development and prevention over the years. In this paper, we systematically review all published studies that utilized large animal models of vein graft disease with a focus on the type of model and any therapeutic intervention, specifically the use of external stents/mesh.

PLCL vascular external sheath carrying prednisone for improving patency rate of the vein graft

Coronary artery bypass graft surgery (CABG) is an impactful treatment for coronary heart disease. Intimal hyperplasia is the central reason for the restenosis of vein grafts after CABG. The introduction of external vascular sheaths around VGs (VGs) can effectively inhibit intimal hyperplasia and ensure the patency of VGs. In this study, the well-known biodegradable copolymer poly (ε-caprolactone-co-L, L-lactide) (PLCL) was electrospun into high porosity external sheaths. The prednisone loaded in the PLCL sheath was slowly released during the degradation process of PLCL. Under the combined effects of sheath and prednisone, intimal hyperplasia was inhibited. For the cell experiments, all sheaths show low cytotoxicity to L929 cells at different concentrations at different time intervals. The ultrasonography and histological results showed prominent dilation and intimal hyperplasia of VG without sheath after two months of surgery. But there was no dilation in PLCL and PLCL_Prednisone groups. Notably, the prednisone-loaded sheath group exhibited efficacy in inhibiting intimal hyperplasia and ensured graft patency.

Extracellular signal-regulated kinase inhibition prevents venous adaptive remodeling via regulation of Eph-B4

OBJECTIVES

Vein graft adaptation (VGA) is a process that vein as a vascular graft conduits in arterial reconstructive surgery; VGA can lead to postoperative vein graft stenosis (VGS) and complications after coronary artery bypass graft and other peripheral artery bypass surgeries. VGA is characterized by vein graft loss the venous features without exhibiting arterial features; furthermore, the activation of ERK inhibited the maintenance of venous properties of the vein graft. We hypothesized that ERK inhibition can affect vein VGS through regulating the expression of EphB4.

METHODS

Rat vein transplantation model was established using wild-type and EphB4^+/- Sprague-Dawley rats. Hematoxylin-eosin, Masson, Verhoeff, actin staining, and immunohistochemistry were applied to observe the structure of the vein grafts. Vascular smooth muscle cells (VSMCs) were isolated from the vein and vein grafts. Western blotting was used to determine the expression of p-ERK1/2 and EphB4, and immunofluorescence was applied to detect the expression and location of EphB4. Cell wound scratch assay and CCK8 assay were used to determine the migration and proliferation of VSMCs. Real-time polymerase chain reaction was used to determine the mRNA expression of EphB4.

RESULTS

Western blotting in vein sample and vein graft sample detected p-ERK1/2 and ERK1/2 expression in both EphB4^+/+ and EphB4^+/- rats. The expression of p-ERK was increased in vein graft compared to vein. Immunofluorescence in VSMCs form EphB4^+/+ and EphB4^+/- rats detected EphB4 expression in both cells, and the expression of EphB4 was increased in VSMCs form EphB4^+/+ rats. SCH772984 reduces the proliferation and migration of VSMCs. Inhibition of ERK suppressed the increase of vein graft wall thickness, and the expression of collagen fibers, elastic fibers, and α-actin was decreased. Vein graft from EphB4^+/- rats reduces the expression of EphB4, and SCH772984 suppressed the decrease of EphB4 in vivo. Vein graft from EphB4^+/- rats increased the expression of EphB4, and SCH772984 suppressed the increase of EphB4 in vivo.

CONCLUSIONS

The inhibition of ERK1/2 suppressed the process of VGS by decreasing the proliferation of VSMCs. The ERK-inhibitor SCH772984 suppressed the level of VGS by extending the time of EphB4 expression during the process of VGA, thus maintaining the venousization of vein graft. The mechanism may be that the inhibitor SCH772984 suppresses the level of VGS by extending the time of EphB4 expression during the process of VGA. Therefore, our research provides a new target of VGS treatment by inhibiting the expression of ERK1/2 through the process of VGA.

Periadventitial Delivery of Simvastatin-Loaded Microparticles Attenuate Venous Neointimal Hyperplasia Associated With Arteriovenous Fistula

Background

Venous neointimal hyperplasia and venous stenosis (VS) formation can result in a decrease in arteriovenous fistula (AVF) patency in patients with end‐stage renal disease. There are limited therapies that prevent VNH/VS. Systemic delivery of simvastatin has been shown to reduce VNH/VS but local delivery may help decrease the side effects associated with statin use. We determined if microparticles (MP) composed of cyclodextrins loaded with simvastatin (MP‐SV) could reduce VS/VNH using a murine arteriovenous fistula model with chronic kidney disease.

Methods and Results

Male C57BL/6J mice underwent nephrectomy to induce chronic kidney disease. Four weeks later, an arteriovenous fistula was placed and animals were randomized to 3 groups: 20 μL of PBS or 20 μL of PBS with 16.6 mg/mL of either MP or MP‐SV. Animals were euthanized 3 days later and the outflow veins were harvested for quantitative reverse transcriptase–polymerase chain reaction analysis and 28 days later for immunohistochemistical staining with morphometric analysis. Doppler ultrasound was performed weekly. Gene expression of vascular endothelial growth factor‐A (Vegf‐A), matrix metalloproteinase‐9 (Mmp‐9), transforming growth factor beta 1 (Tgf‐β1), and monocyte chemoattractant protein‐1 (Mcp‐1) were significantly decreased in MP‐SV treated vessels compared with controls. There was a significant decrease in the neointimal area, cell proliferation, inflammation, and fibrosis, with an increase in apoptosis and peak velocity in MP‐SV treated outflow veins. MP‐SV treated fibroblasts when exposed to hypoxic injury had decreased gene expression of Vegf‐A and Mmp‐9.

Conclusions

In experimental arteriovenous fistulas, periadventitial delivery of MP‐SV decreased gene expression of Vegf‐A, Mmp‐9, Tgf‐β1 and Mcp‐1, VNH/VS, inflammation, and fibrosis.

Evaluating intimal hyperplasia under clinical conditions

OBJECTIVES

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.

METHODS

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).

RESULTS

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.

CONCLUSIONS

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.

Transfer-molded wrappable microneedle meshes for perivascular drug delivery

After surgical procedures such as coronary/peripheral bypass grafting or endarterectomy for the treatment of organ ischemia derived from atherosclerosis, intimal hyperplasia (IH) which leads to restenosis or occlusion at the site of graft anastomosis frequently occurs. In order to inhibit IH caused by abnormal growth of smooth muscle cells (SMCs) in tunica media, various perivascular drug delivery devices are reported for delivery of anti-proliferation drugs into vascular tissue. However, there still remain conflicting requirements such as local and unidirectional delivery vs device porosity, and conformal tight device installation vs pulsatile expansion and constriction of blood vessels. In this study, a biodegradable microneedle (MN) array is developed on a flexible woven surgical mesh using a transfer molding method. Mechanical properties of 'wrappable' MN meshes are investigated and compared to the properties of blood vessels. Ex vivo and in vivo animal studies demonstrate enhanced drug delivery efficiency, efficacy for IH reduction, and safety of MN mesh. In particular, MN mesh showed significantly reduced neointiamal formation (11.1%) compared to other competitive groups (23.7 and 22.2%) after 4-week in vivo animal study. Additionally, wrappable MN meshes effectively suppressed side effects such as IH due to mechanical constriction, loss of toxic drug to the surroundings, and cell death that were frequently observed with other previous perivascular drug delivery devices.

Unimolecular Micelle-Based Hybrid System for Perivascular Drug Delivery Produces Long-Term Efficacy for Neointima Attenuation in Rats

At present, there are no clinical options for preventing neointima-caused (re)stenosis after open surgery such as bypass surgery for treating flow-limiting vascular disease. Perivascular drug delivery is a promising strategy, but in translational research, it remains a major challenge to achieve long-term (e.g., > 3 months) anti(re)stenotic efficacy. In this study, we engineered a unique drug delivery system consisting of durable unimolecular micelles, formed by single multiarm star amphiphilic block copolymers with only covalent bonds, and a thermosensitive hydrogel formed by a poly(lactide-co-glycolide)-poly(ethylene glycol)-poly(lactide-co-glycolide) triblock copolymer (abbreviated as triblock gel) that is stable for about 4 weeks in vitro. The drug-containing unimolecular micelles (UMs) suspended in Triblock gel were able to sustain rapamycin release for over 4 months. Remarkably, even 3 months after perivascular application of the rapamycin-loaded micelles in Triblock gel in the rat model, the intimal/medial area ratio (a restenosis measure) was still 80% inhibited compared to the control treated with empty micelle/gel (no drug). This could not be achieved by applying rapamycin in Triblock gel alone, which reduced the intimal/medial ratio only by 27%. In summary, we created a new UM/Triblock gel hybrid system for perivascular drug delivery, which produced a rare feat of 3-month restenosis inhibition in animal tests. This system exhibits a real potential for further translation into an anti(re)stenotic application with open surgery.

Perivascular medical devices and drug delivery systems: Making the right choices

Perivascular medical devices and perivascular drug delivery systems are conceived for local application around a blood vessel during open vascular surgery. These systems provide mechanical support and/or pharmacological activity for the prevention of intimal hyperplasia following vessel injury. Despite abundant reports in the literature and numerous clinical trials, no efficient perivascular treatment is available. In this review, the existing perivascular medical devices and perivascular drug delivery systems, such as polymeric gels, meshes, sheaths, wraps, matrices, and metal meshes, are jointly evaluated. The key criteria for the design of an ideal perivascular system are identified. Perivascular treatments should have mechanical specifications that ensure system localization, prolonged retention and adequate vascular constriction. From the data gathered, it appears that a drug is necessary to increase the efficacy of these systems. As such, the release kinetics of pharmacological agents should match the development of the pathology. A successful perivascular system must combine these optimized pharmacological and mechanical properties to be efficient.

A Biodegradable Microneedle Cuff for Comparison of Drug Effects through Perivascular Delivery to Balloon-Injured Arteries

Restenosis at a vascular anastomosis site is a major cause of graft failure and is difficult to prevent by conventional treatment. Perivascular drug delivery has advantages as drugs can be diffused to tunica media and subintima while minimizing the direct effect on endothelium. This in vivo study investigated the comparative effectiveness of paclitaxel, sirolimus, and sunitinib using a perivascular biodegradable microneedle cuff. A total of 31 New Zealand white rabbits were used. Rhodamine was used to visualize drug distribution (n = 3). Sirolimus- (n = 7), sunitinib- (n = 7), and paclitaxel-loaded (n = 7) microneedle cuffs were placed at balloon-injured abdominal aortae and compared to drug-free cuffs (n = 7). Basic histological structures were not affected by microneedle devices, and vascular wall thickness of the device-only group was similar to that of normal artery. Quantitative analysis revealed significantly decreased neointima formation in all drug-treated groups (p < 0.001). However, the tunica media layer of the paclitaxel-treated group was significantly thinner than that of other groups and also showed the highest apoptotic ratio (p < 0.001). Proliferating cell nuclear antigen (PCNA)-positive cells were significantly reduced in all drug-treated groups. Sirolimus or sunitinib appeared to be more appropriate for microneedle devices capable of slow drug release because vascular wall thickness was minimally affected.

Tacrolimus-Eluting Suture Inhibits Neointimal Hyperplasia: An Experimental In Vivo Study in Rats

OBJECTIVE/BACKGROUND

Neointimal hyperplasia (NIH) remains one of the leading causes of graft failure after vascular anastomoses. Cytotoxic drugs, such as rapamycin and tacrolimus, have been shown to inhibit the development of NIH. In this study, the aim was to test the impact of a sustained releasing tacrolimus-chitosan-eluting suture on the development of NIH in a rat model.

METHODS

After tacrolimus-chitosan coating of a 7/0 polyvinylidene difluoride (PVDF) Trofilen^® suture, the tacrolimus concentration on the coated suture and in vitro release trials were performed spectrophotometrically. Twelve Wistar rats were included. After midline laparotomy, a 7-8 mm longitudinal aortotomy in the infrarenal aorta was made and then closed by a bare 7/0 PVDF (group C, n = 6) and a 7/0 tacrolimus-chitosan coated PVDF suture (0.65 μg/cm tacrolimus [0.9 wt%] + 1.82 μg/cm chitosan [2.28 wt%]) (group T, n = 6). After 1 month, rats were sacrificed and aortotomy sites were examined histologically by ratio of intimal area (including neointima) and immunohistochemically by α-smooth muscle actin (ASMA) and proliferating cell nuclear antigen (PCNA) immunostaining. The PCNA positive cells were indexed to total cell number and expressed as percentage.

RESULTS

In vitro tacrolimus release tests for a 7/0 tacrolimus-chitosan coated PVDF suture were confirmed for 1 month without an initial burst release. Endothelialisation over the aortotomy line occurred in both groups. The area of neointima was significantly reduced in group T compared with group C (ratio 0.22 ± 0.12 vs. 0.42 ± 0.11; p = .017) 1 month post-operatively. Likewise, the percentage of PCNA immunostaining significantly decreased in group C compared with group T (3.83 ± 2.85% vs. 11.17 ± 7.78%; p = .026). The cells constituting NIH were positive for ASMA immunostaining.

CONCLUSIONS

Tacrolimus-chitosan-eluting suture is shown to be an effective way to reduce NIH without interfering with normal endothelialisation.

Vein graft failure: from pathophysiology to clinical outcomes

Occlusive arterial disease is a leading cause of morbidity and mortality worldwide. Aside from balloon angioplasty, bypass graft surgery is the most commonly performed revascularization technique for occlusive arterial disease. Coronary artery bypass graft surgery is performed in patients with left main coronary artery disease and three-vessel coronary disease, whereas peripheral artery bypass graft surgery is used to treat patients with late-stage peripheral artery occlusive disease. The great saphenous veins are commonly used conduits for surgical revascularization; however, they are associated with a high failure rate. Therefore, preservation of vein graft patency is essential for long-term surgical success. With the exception of 'no-touch' techniques and lipid-lowering and antiplatelet (aspirin) therapy, no intervention has hitherto unequivocally proven to be clinically effective in preventing vein graft failure. In this Review, we describe both preclinical and clinical studies evaluating the pathophysiology underlying vein graft failure, and the latest therapeutic options to improve patency for both coronary and peripheral grafts.

Periadventitial drug delivery for the prevention of intimal hyperplasia following open surgery

BACKGROUND

Intimal hyperplasia (IH) remains a major cause of poor patient outcomes after surgical revascularization to treat atherosclerosis. A multitude of drugs have been shown to prevent the development of IH. Moreover, endovascular drug delivery following angioplasty and stenting has been achieved with a marked diminution in the incidence of restenosis. Despite advances in endovascular drug delivery, there is currently no clinically available method of periadventitial drug delivery suitable for open vascular reconstructions. Herein we provide an overview of the recent literature regarding innovative polymer platforms for periadventitial drug delivery in preclinical models of IH as well as insights about barriers to clinical translation.

METHODS

A comprehensive PubMed search confined to the past 15years was performed for studies of periadventitial drug delivery. Additional searches were performed for relevant clinical trials, patents, meeting abstracts, and awards of NIH funding.

RESULTS

Most of the research involving direct periadventitial delivery without a drug carrier was published prior to 2000. Over the past 15years there have been a surge of reports utilizing periadventitial drug-releasing polymer platforms, most commonly bioresorbable hydrogels and wraps. These methods proved to be effective for the inhibition of IH in various animal models (e.g. balloon angioplasty, wire injury, and vein graft), but very few have advanced to clinical trials. There are a number of barriers that may account for this lack of translation. Promising new approaches including the use of nanoparticles will be described.

CONCLUSIONS

No periadventitial drug delivery system has reached clinical application. For periadventitial delivery, polymer hydrogels, wraps, and nanoparticles exhibit overlapping and complementary properties. The ideal periadventitial delivery platform would allow for sustained drug release yet exert minimal mechanical and inflammatory stresses to the vessel wall. A clinically applicable strategy for periadventitial drug delivery would benefit thousands of patients undergoing open vascular reconstruction each year.

A rapamycin-releasing perivascular polymeric sheath produces highly effective inhibition of intimal hyperplasia

Intimal hyperplasia produces restenosis (re-narrowing) of the vessel lumen following vascular intervention. Drugs that inhibit intimal hyperplasia have been developed, however there is currently no clinical method of perivascular drug-delivery to prevent restenosis following open surgical procedures. Here we report a poly(ε-caprolactone) (PCL) sheath that is highly effective in preventing intimal hyperplasia through perivascular delivery of rapamycin. We first screened a series of bioresorbable polymers, i.e., poly(lactide-co-glycolide) (PLGA), poly(lactic acid) (PLLA), PCL, and their blends, to identify desired release kinetics and sheath physical properties. Both PLGA and PLLA sheaths produced minimal (<30%) rapamycin release within 50days in PBS buffer. In contrast, PCL sheaths exhibited more rapid and near-linear release kinetics, as well as durable integrity (>90days) as evidenced in both scanning electron microscopy and subcutaneous embedding experiments. Moreover, a PCL sheath deployed around balloon-injured rat carotid arteries was associated with a minimum rate of thrombosis compared to PLGA and PLLA. Morphometric analysis and immunohistochemistry revealed that rapamycin-loaded perivascular PCL sheaths produced pronounced (85%) inhibition of intimal hyperplasia (0.15±0.05 vs 1.01±0.16), without impairment of the luminal endothelium, the vessel's anti-thrombotic layer. Our data collectively show that a rapamycin-loaded PCL delivery system produces substantial mitigation of neointima, likely due to its favorable physical properties leading to a stable yet flexible perivascular sheath and steady and prolonged release kinetics. Thus, a PCL sheath may provide useful scaffolding for devising effective perivascular drug delivery particularly suited for preventing restenosis following open vascular surgery.

Periadventitial application of rapamycin-loaded nanoparticles produces sustained inhibition of vascular restenosis

Open vascular reconstructions frequently fail due to the development of recurrent disease or intimal hyperplasia (IH). This paper reports a novel drug delivery method using a rapamycin-loaded poly(lactide-co-glycolide) (PLGA) nanoparticles (NPs)/pluronic gel system that can be applied periadventitially around the carotid artery immediately following the open surgery. In vitro studies revealed that rapamycin dispersed in pluronic gel was rapidly released over 3 days whereas release of rapamycin from rapamycin-loaded PLGA NPs embedded in pluronic gel was more gradual over 4 weeks. In cultured rat vascular smooth muscle cells (SMCs), rapamycin-loaded NPs produced durable (14 days versus 3 days for free rapamycin) inhibition of phosphorylation of S6 kinase (S6K1), a downstream target in the mTOR pathway. In a rat balloon injury model, periadventitial delivery of rapamycin-loaded NPs produced inhibition of phospho-S6K1 14 days after balloon injury. Immunostaining revealed that rapamycin-loaded NPs reduced SMC proliferation at both 14 and 28 days whereas rapamycin alone suppressed proliferation at day 14 only. Moreover, rapamycin-loaded NPs sustainably suppressed IH for at least 28 days following treatment, whereas rapamycin alone produced suppression on day 14 with rebound of IH by day 28. Since rapamycin, PLGA, and pluronic gel have all been approved by the FDA for other human therapies, this drug delivery method could potentially be translated into human use quickly to prevent failure of open vascular reconstructions.

In vivo evaluation of the delivery and efficacy of a sirolimus-laden polymer gel for inhibition of hyperplasia in a porcine model of arteriovenous hemodialysis graft stenosis

Synthetic arteriovenous (AV) hemodialysis grafts are plagued by hyperplasia resulting in occlusion and graft failure yet there are no clinically available preventative treatments. Here the delivery and degradation of a sirolimus-laden polymer gel were monitored in vivo by magnetic resonance imaging (MRI) and its efficacy for inhibiting hyperplasia was evaluated in a porcine model of AV graft stenosis. Synthetic grafts were placed between the carotid artery and ipsilateral jugular vein of swine. A biodegradable polymer gel loaded with sirolimus (2.5mg/mL) was immediately applied perivascularly to the venous anastomosis, and reapplied by ultrasound-guided injections at one, two and three weeks. Control grafts received neither sirolimus nor polymer. The lumen cross-sectional area at the graft-vein anastomosis was assessed in vivo by non-invasive MRI. The explanted tissues also underwent histological analysis. A specifically developed MRI pulse sequence provided a high contrast-to-noise ratio (CNR) between the polymer and surrounding tissue that allowed confirmation of gel location after injection. Polymer signal decreased up to 80% at three to four weeks after injection, slightly faster than its degradation kinetics in vitro. The MR image of the polymer was confirmed by visual assessment at necropsy. On histological assessment, the mean hyperplasia surface area of the treated graft was 52% lower than that of the control grafts (0.43mm(2) vs. 0.89mm(2); p<0.003), while the minimum cross-sectional lumen area, as measured on MRI, was doubled (5.3mm(2) vs 2.5mm(2); p<0.05). In conclusion, customized MRI allowed non-invasive monitoring of the location and degradation of drug delivery polymer gels in vivo. Perivascular application of sirolimus-laden polymer yielded a significant decrease in hyperplasia development and an increase in lumen area at the venous anastomosis of AV grafts.

Reversal of anemia with allogenic RBC transfusion prevents post-cardiopulmonary bypass acute kidney injury in swine

Anemia during cardiopulmonary bypass (CPB) is strongly associated with acute kidney injury in clinical studies; however, reversal of anemia with red blood cell (RBC) transfusions is associated with further renal injury. To understand this paradox, we evaluated the effects of reversal of anemia during CPB with allogenic RBC transfusion in a novel large-animal model of post-cardiac surgery acute kidney injury with significant homology to that observed in cardiac surgery patients. Adult pigs undergoing general anesthesia were allocated to a Sham procedure, CPB alone, Sham+RBC transfusion, or CPB+RBC transfusion, with recovery and reassessment at 24 h. CPB was associated with dilutional anemia and caused acute kidney injury in swine characterized by renal endothelial dysfunction, loss of nitric oxide (NO) bioavailability, vasoconstriction, medullary hypoxia, cortical ATP depletion, glomerular sequestration of activated platelets and inflammatory cells, and proximal tubule epithelial cell stress. RBC transfusion in the absence of CPB also resulted in renal injury. This was characterized by endothelial injury, microvascular endothelial dysfunction, platelet activation, and equivalent cortical tubular epithelial phenotypic changes to those observed in CPB pigs, but occurred in the absence of severe intrarenal vasoconstriction, ATP depletion, or reductions in creatinine clearance. In contrast, reversal of anemia during CPB with RBC transfusion prevented the reductions in creatinine clearance, loss of NO bioavailability, platelet activation, inflammation, and epithelial cell injury attributable to CPB although it did not prevent the development of significant intrarenal vasoconstriction and endothelial dysfunction. In conclusion, contrary to the findings of observational studies in cardiac surgery, RBC transfusion during CPB protects pigs against acute kidney injury. Our study underlines the need for translational research into indications for transfusion and prevention strategies for acute kidney injury.

Rapamycin-loaded nanoparticles for inhibition of neointimal hyperplasia in experimental vein grafts

Background

Nanoparticles possess several advantages as a carrier system for intracellular delivery of therapeutic agents. Rapamycin is an immunosuppressive agent which also exhibits marked antiproliferative properties. We investigated whether rapamycin-loaded nanoparticles(NPs) can reduce neointima formation in a rat model of vein graft disease.

Methods

Poly(lactic-co-glycolic acid) (PLGA) NPs containing rapamycin was prepared using an oil/water solvent evaporation technique. Nanoparticle size and morphology were determined by dynamic light scattering methodology and electron microscopy. In vitro cytotoxicity of blank, rapamycin-loaded PLGA (RPLGA) NPs was studied using MTT Assay. Excised rat jugular vein was treated ex vivo with blank-NPs, or rapamycin-loaded NPs, then interposed back into the carotid artery position using a cuff technique. Grafts were harvested at 21 days and underwent morphometric analysis as well as immunohistochemical analysis.

Results

Rapamycin was efficiently loaded in PLGA nanoparticles with an encapsulation efficiency was 87.6%. The average diameter of NPs was 180.3 nm. The NPs-containing rapamycin at 1 ng/ml significantly inhibited vascular smooth muscular cells proliferation. Measurement of rapamycin levels in vein grafts shown that the concentration of rapamycin in vein grafts at 3 weeks after grafting were 0.9 ± 0.1 μg/g. In grafted veins without treatment intima-media thickness was 300.4 ±181.5 μm after grafting 21 days. Whereas, Veins treated with rapamycin-loaded NPs showed a reduction of intimal-media thickness of 150.2 ± 62.5 μm (p = 0.001). CD-31 staining was used to measure luminal endothelial coverage in grafts and indicated a high level of endothelialization in 21 days vein grafts with no significant effect of blank or rapamycin-loaded NPs group.

Conclusions

We conclude that sustained-release rapamycin from rapymycin loaded NPs inhibits vein graft thickening without affecting the reendothelialization in rat carotid vein-to-artery interposition grafts and this may be a promising therapy for the treatment of vein graft disease.

Pretreatment with intraluminal rapamycin nanoparticle perfusion inhibits neointimal hyperplasia in a rabbit vein graft model

PURPOSE

Poly lactic-co-glycolic acid nanoparticles (PLGA-NP) are widely used as a biodegradable biomaterial in medicine. Rapamycin-eluting stents have been used for prevention of restenosis during surgery. This study investigated the effect of pretreatment with intraluminal perfusion of carbopol-encapsulated rapamycin-loaded PLGA nanoparticles (RAP-PLGA-NP) on neointimal hyperplasia in a rabbit vein graft model.

METHODS

A segment of common carotid artery was replaced with a segment of external jugular vein in 60 rabbits which were then separated into four treatment groups, ie, Group 1, in which vein grafts were pretreated with intraluminal RAP-PLGA-NP perfusion, Group 2 in which vein grafts underwent equivalent empty vehicle (PLGA-NP) perfusion, Group 3, in which vein grafts received no treatment, and Group 4, which served as a sham operation group receiving normal vein contrast. On postoperative day 28, the grafts and normal veins were harvested for histologic examination, flow cytometry analysis, and high-performance liquid chromatography measurement.

RESULTS

Compared with Group 1, the intima of the grafts were thickened, the ratio of intimal area to vessel area increased, and the collagen volume index of the vein grafts increased significantly in Groups 2 and 3. The cell proliferation index in Group 1 (21.11 ± 3.15%) was much lower than that in Group 2 (30.35 ± 2.69%) and in Group 3 (33.86 ± 8.72%). By high-performance liquid chromatography measurement, retention of rapamycin was detected in Group 1 (11.2 ± 0.37 μg/10 mg) 28 days after single drug perfusion.

CONCLUSION

Pretreatment with intraluminal RAP-PLGA-NP perfusion may inhibit neointimal hyperplasia in vein grafts by penetrating into local tissue and limiting cell proliferation.