Vein Graft Intimal Hyperplasia Research Articles

The placental growth factor attenuates intimal hyperplasia in vein grafts by improving endothelial dysfunction

Saphenous vein grafts (SVG) patency is limited by intimal hyperplasia (IH) caused by endothelial dysfunction. This study aimed to explore the effect of placental growth factor (PlGF) on the endothelial function of SVG. In rat models of external jugular vein-carotid artery graft treated with PlGF or saline hydrogel, PlGF inhibited vein graft IH (day 28: 12.0 ± 1.9 vs. 61.7 ± 13.1 μm, P < 0.001), promoted microvessel proliferation (day 14: 33.3% 3+ vs. 50.0% 2+, P = 0.03), and increased nitric oxide (NO) production (P < 0.05 on days 1/3/5) and NO synthase (NOS) expression by immunohistochemistry. In human umbilical vein endothelial cells (HUVECs) cultured under hypoxia and treated or not with PlGF, PlGF restored the survival (50 ng/ml PlGF, 48 h: 91.7 ± 0.6% vs. 84.9 ± 0.5%, P < 0.01), migration (by Matrigel assay), and tube formation ability (junctions, tubules, and tubule total length; all P < 0.01) of HUVECs after hypoxia. PlGF increased NO production through increased eNOS expression (P < 0.05), without changes in iNOS expression. The mRNA expression of eNOS decreased after the addition of the PI3K inhibitor LY294002 (P < 0.05). PlGF promoted the protein expression of eNOS by up-regulating AKT, and the AKT and eNOS protein levels were decreased after adding LY294002 (all P < 0.05). In conclusion, PlGF is a candidate for the inhibition of IH in SVG after coronary artery bypass graft. The effects of PlGF are mediated by the upregulation of the eNOS mRNA and protein through the PI3K/AKT signaling pathway. PlGF promotes the secretion of NO by endothelial cells and thereby reduces the occurrence and development of IH.

Early Inhibition of P-Selectin/P-Selectin Glycoprotein Ligand-1 Reduces Intimal Hyperplasia in Murine Vein Grafts through Platelet Adhesion.

Inflammatory processes contribute to intimal hyperplasia (IH) and long-term failure of vein grafts used in bypass surgery. Leukocyte recruitment on endothelial cells of vessels during inflammation is regulated by P-selectin and P-selectin glycoprotein ligand-1 (PSGL-1), which also mediates the interaction between platelets and endothelial cells in vein grafts transferred to arteries. However, how this pathway causes IH in vein grafts is unclear. In this study, we used a murine model of vein grafting to investigate P-selectin-mediated platelet adhesion, followed by IH. On the luminal surface of the vein graft, leukocyte recruitment occurred mainly in areas with adhered platelets rather than on endothelial cells without adherent platelets 1 hour after vein grafting. Blockage of either P-selectin or PSGL-1 reduced platelet adhesion and leukocyte recruitment on the luminal surface of vein grafts. Inhibition of the P-selectin pathway in vein grafts significantly reduced platelet-mediated leukocyte recruitment and IH of vein grafts 28 days after surgery. The study demonstrates that functional blockage of the P-selectin/PSGL-1 pathway in the early inflammatory phase after vein grafting reduced leukocyte invasion in the vein graft wall and later IH development. The findings imply an attractive early time window for prevention of vein graft failure by manipulating platelet adhesion.

Effect of hydrogen sulfide on the intimal hyperplasia of vein grafts in rabbits

Objective To observe the effect of exogenous hydrogen sulfide (H2S) on the intimal hyperplasia of vein grafts in rabbits and and its possible molecular mechanism. Methods Forty New Zealand rabbits were randomly divided into 5 group, including blank control group (Ctr group); two weeks of simple transplantation; four weeks of simple transplantation; transplantation + NaHS 2 weeks group (NaHS: 30 μmol/kg. 3 days, 2 weeks of continuous administration), transplantation + NaHS 4 weeks group (NaHS: 30 μmol/kg. 3 days, 4 weeks of continuous administration). Rabbit jugular vein transplantation animal model was established. Administration by intraperitoneal injection once 3 days. Serum H2S level was detected by enzyme linked immunosorbent assay (ELISA). The structure and hyperplasia of vascular tissue were observed by hematoxylin-eosin staining (HE) staining. real-time quantitative polymerase chain reaction (Real-time PCR) was used to determine the expression levels of cystathionine-gamma-lyase (CSE) mRNA. CSE, Calmodulin (p-CaM/ CaM)and Cyclin D1 protein levels were measured by Western blotting. Results After NaHS treatment, the intimal hyperplasia of vein grafts was relieved. Compared with the corresponding group, the serum H2S level increased in the transplantation + NaHS 2 weeks group and transplantation + NaHS 4weeks group (33.65±4.10 vs. 23.56±4.82, P<0.05; 36.50±4.62 vs. 23.72±3.95, P<0.05). And the expression of CSE mRNA and protein increased significantly (mRNA: 0.54±0.04 vs. 0.15±0.05, P<0.05; 1.08±0.13 vs. 0.11±0.02, P<0.05; Protein: 0.56±0.06 vs. 0.47±0.03, P<0.05; 1.14±0.07 vs. 0.38±0.04, P<0.05). The expression of p-CaM/CaM and Cyclin D1 protein decreased significantly (p-CaM: 0.25±0.05 vs. 0.52±0.06, P<0.05; 1.21±0.09 vs. 2.39±0.15, P<0.05; CaM: 0.42±0.04 vs. 0.73±0.07, P<0.05, 0.47±0.05 vs. 1.17±0.06 P<0.05; Cyclin D1: 0.28±0.06 vs. 0.95±0.11, P<0.05; 0.29±0.04 vs. 1.02±0.10, P<0.05). Conclusion Exogenous hydrogen sulfide could inhibit the intima proliferation of vein grafts which related to the reduction of the expression of p-CaM/CaM and Cyclin D1. Key words: Hydrogen sulfide; Vein grafts; Transplantation; Intima hyperplasia

Effect of angiotensin1-7 on intimal hyperplasia in autogenous vein graft in rats

Objective Angiotensin1-7 (Ang1-7) and ITS inhibitor A779 were used to study the effect of Ang1-7 on intimal hyperplasia in autogenous vein graft. Methods The transplantation models of the external jugular vein to the abdominal aorta were established in 40 Specific Pathogen Free SD male rats. All models were randomly divided into control group, gel group, Ang1-7 group and A779 group (10 rats each). The adventitia of the transplanted veins was evenly sprayed with normal saline, Poloxamer 407, Poloxamer 407 mixed with Ang 1-7, Poloxamer 407 mixed with A779 respectively in each group forementioned. 5 rats form each group were sacrificed at 14th and 28th day respectively. The transplanted vein was intercepted and then stained with hematoxylin and eosin (HE). The thickness of the inner membrane (I) and medium membrane (M) of the vein grafts were measured by computer, and I/M ratio was calculated. The expression of proliferating cell nuclear antigen (PCNA), extracellular regulated protein kinase-1 (ERK-1) and angiotensin Ⅱ receptor 1 (AT1R) was determined by immunohistochemistry. Results (1)14th and 28th Day, the intimal hyperplasia of vein graft in Ang1-7 group [(59.26±7.51), (62.50±5.91) μm] was lighter than that in the other groups(P=0.001, respectively). (2)14th Day, the I/M ratio of vein graft in Ang1-7 group (0.67±0.05) was lower compare to that in other groups (P=0.001, 0.006, 0.001). 28th Day, the I/M ratio of vein graft in Ang1-7 group (0.71±0.14) was lower than that in the other groups(P=0.001, respectively). (3)There was statistically differences in the intimal thickness of vein graft between A779 group and control group at 14th, 28th day(P=0.007, 0.001). (4)14th Day, the expression of PCNA in the Ang1-7 group (21.80±7.05) was lower than that in other groups (P=0.011, 0.016, 0.001). 28th Day, the PCNA expression in the Ang1-7 group (12.80±5.31) was lower than that in the other groups (P=0.001, 0.002, 0.001). (5)14th Day, the express of ERK1 in vein graft Ang1-7 group (57.00±5.79) was lower than that in other groups (P=0.002, 0.003, 0.001). 28th Day, the express of ERK1 in vein graft Ang1-7 group(50.20±8.79) was lower than that in other groups (P=0.024, 0.017, 0.001). (6)14th Day, the express of AT1R in vein graft Ang1-7 group (27.20±6.87) was lower than that in other groups (P=0.001, 0.003, 0.001). 28th Day, the express of PCNA in vein graft Ang1-7 group(20.60±4.83) was lower than that in other groups (P=0.001, respectively). Conclusion The main cells resulting in intimal hyperplasia may be derived from the proliferation and migration of vascular smooth muscle cells in the medium membrane. Ang1-7 can significantly inhibit the expression of AT1R in the bridging vein, reduce its role in promoting endometrial proliferation, thereby reduce the proliferation and migration of VSMCs. Ang1-7 can also inhibit the expression of ERK in the bridging vein after vein transplantation; RAS and MAPK signal systems are involved in the intimal hyperplasia of vein graft. Key words: Angiotensin1-7; Vein graft; Intimal hyperplasia; Renin angiotensin system

The Effect of Local Application of Neutralizing Antibody to Interleukin-1B on the Development of Vein Graft Intimal Hyperplasia

Objective: Intimal hyperplasia (IH) remains one of the major obstacles to long term vein graft patency. IL-1B has been demonstrated to be one of the first inflammatory cytokines expressed in the rat vein graft model of IH and may be an important initiator of the sequence of events leading to the development of IH. This study was designed to establish the role of IL-1B by demonstrating the outcome of inhibiting its effects by the use of neutralizing antibodies on the development of IH in this model. Methods: Rat epigastric vein to femoral artery interposition grafts were treated with neutralizing antibody to IL-1B suspended in pluronic gel and harvested at the end of one week and two weeks. The amount of intimal hyperplasia was measured at the anastomotic and midgraft regions. Results: The amount of IH was less at the anastomotic and midgraft regions of the treated grafts at the end of one week (p&lt; 0.05), but did not differ significantly with the untreated group at the end of two weeks. Conclusion: Neutralizing antibody to IL-1B delivered locally retarded but did not prevent the occurrence of IH in vein grafts. The initiation of the cascade of events in the development of IH is affected in a major way, but not singularly by IL-1B. Key words: Vein graft, intimal hyperplasia, cytokines, interleukin-1B, antibodies

Gene therapy with antisense oligonucleotides silencing c-myc reduces neointima formation and vessel wall thickness in a mouse model of vein graft disease

Gene therapy for avoiding intimal hyperplasia of vein grafts after coronary artery bypass grafting is still discussed controversially. A promising application of gene therapy in vein grafts is the use of antisense oligonucleotides to block the expression of genes encoding cell cycle regulatory proteins in vascular smooth muscle cells. C-myc, either directly or by regulating the expression of other proteins, controls cell proliferation, apoptosis and cell survival, tissue remodeling, angiogenesis, cell metabolism, production of inflammatory and anti-inflammatory cytokines, and also participates in cell transformation.Forty C57BL/6J mice underwent interposition of the inferior vena cava from isogenic donor mice into the common carotid artery using a previously described cuff technique. Twenty mice received periadventitial administration of antisense oligonucleotides directed against c-myc (treatment group), the other twenty mice received no treatment (control group). All vein grafts were harvested two weeks after surgery, dehydrated, wax embedded, cut into slides of 2 μm thickness, stained and histologically and immunohistochemically examined under light microscope.In our study, we could show the promising effects of antisense oligonucleotide treatment in a mouse model of vein graft disease including the significant reduction of neointimal, media and total vessel wall thickness with a significantly lower percentage of SMA positive cells, elastic fibres and acid mucopolysaccharides in the neointima and media, a decreased vascularization, and a lower expression of PDGFR ß, MMP-9 and VEGF-A positive cells throughout the whole vein graft wall.

Abstract 692: Development of the Gene Therapy With CRE Decoy ODN to Prevent Vascular Intimal Hyperplasia

Background: Intimal hyperplasia (IH) is the main cause of vein graft stenosis or failure after bypass surgery. However, in the previous study, no therapeutic targets for the treatment of IH have been identified. Our recent research have been reported that the inhibition of Cyclic adenosine monophosphate response-element (CRE) binding protein (CREB) activation is a key role for vein graft IH. Objective: In consideration of future clinical application, we focused on decoy oligodeoxynucleotide (ODN) transfection as gene therapy strategy for suppressing IH. The goal of the present study is to identify whether the CRE decoy ODN had the therapeutic efficacy for suppressing IH. Methods: We developed phosphorothioate CRE decoy ODN and checked binding ability to a CRE sequence using CREB transcription assay . We chose a decoy ODN having high first-binding ability and transfected it to vascular smooth muscle cell(VSMC) in vitro. Proliferation was assessed using MTS assay and migration was assessed using a modified Boyden-chamber assay. We examined CRE activity using Luciferase reporter gene assay. We checked expression of mRNAs using qRT-PCR. In wire-injury mouse model(C57BL6,n=6), CRE decoy ODN was transfected to injured vessel wall using ultrasound-sonoporation method in vivo. Results: CREB transcription factor assay showed CRE decoy had about 80 folds binding ability of control decoy in IC50 value (vs.control,n=5). Transfer of CRE decoy ODN resulted in significantly downregulated CRE activity(vs.control,P&lt;.01,n=12) and inhibited VSMC proliferation (vs.control,P&lt;.01,n=12) and migration (vs.control,P&lt;.01,n=5). In a wire-injury mouse model, histopathological analysis revealed that transfer of the CRE decoy ODN significantly repressed IH whereas intensive IH was observed in the control group. In this vessel tissue, Levels of mRNA CCNA2 and Bcl2 were significantly lower in CRE decoy group than in control group(n=6,P&lt;.01,respectively). CRE-activated gene expression was strongly repressed. Conclusions: The present result suggested that CRE decoy ODN inhibiting CREB function provide an effective therapeutic approach to suppressing IH.

Recombinant soluble apyrase APT102 inhibits thrombosis and intimal hyperplasia in vein grafts without adversely affecting hemostasis or re‐endothelialization

Background Occlusion of vein grafts (VGs) after bypass surgery, owing to thrombosis and intimal hyperplasia (IH), is a major clinical problem. Apyrases are enzymes that scavenge extracellular ATP and ADP, and promote adenosine formation at sites of vascular injury, and hence have the potential to inhibit VG pathology. Objectives To examine the effects of recombinant soluble human apyrase, APT102, on platelets, smooth muscle cells (SMCs) and endothelial cells (ECs) in vitro, and on thrombosis and IH in murine VGs. Methods SMC and EC proliferation and migration were studied in vitro. Inferior vena cava segments from donor mice were grafted into carotid arteries of recipient mice. Results APT102 potently inhibited ADP-induced platelet aggregation and VG thrombosis, but it did not impair surgical hemostasis. APT102 did not directly inhibit SMC or EC proliferation, but significantly attenuated the effects of ATP on SMC and EC proliferation. APT102 significantly inhibited SMC migration, but did not inhibit EC migration, which may be mediated, at least in part, by inhibition of SMC, but not EC, migration by adenosine. At 4 weeks after surgery, there was significantly less IH in VGs of APT102-treated mice than in control VGs. APT102 significantly inhibited cell proliferation in VGs, but did not inhibit re-endothelialization. Conclusions Systemic administration of a recombinant human apyrase inhibits thrombosis and IH in VGs without increasing bleeding or compromising re-endothelialization. These results suggest that APT102 has the potential to become a novel, single-drug treatment strategy to prevent multiple pathologic processes that drive early adverse remodeling and occlusion of VGs.

Inhibition of proliferation of intima of coronary artery after coronary artery bypass grafting in rabbits by sirolimus

Objective To observe the inhibitory effect of sirolimus on the excessive proliferation of the intima of the coronary artery after coronary artery bypass grafting in rabbits. Methods Thirty big ear white rabbits were used in the control design. The coronary artery bypass graft on the any one side served as intervention group and coated with the Pluronic gel containing 0.3 mg sirolimus, and that on the other side served as the control group and coated with the Pluronic gel alone. After 4 weeks, the thickness of the coronary artery, the cell proliferation index and the number of p27kip1 positive cells were measured. Results The thickness of the coronary artery in the intervention group was (64.9±15.2) μm, which was significantly less than that in the control group (79.2±15.4) μm (t=1.639, P=0.007). Proliferation index in the intervention group was 30.8±7.5, significantly higher than that in the control group (21.2±10.3, t=0.731, P=0.044). Immunohistochemical staining revealed that the positive staining of of p27kip1 in coronary artery smooth muscle cells and endothelial cells was seen in the intervention group, and the number of p27kip1 positive cells in the single field was 3.9±2.4. But there was no positive expression of of p27kip1 in normal group and control group (t=1.157, P=0.025). Conclusion Sirolimus can inhibit the intimal hyperplasia of vein graft in rabbits, which is related to the up-regulation of p27kip1. Key words: Sirolimus; Vein graft; Restenosis

TNF-α promotes survival and migration of MSCs under oxidative stress via NF-κB pathway to attenuate intimal hyperplasia in vein grafts.

The oxidative stress caused by endothelial injury is involved in intimal hyperplasia (IH) in vein grafts. Mesenchymal stem cells (MSCs) can home to injured intima and promote endothelial repair. However, MSC apoptosis is increased accompanied by decreased functional activity under oxidative stress. Thus, we investigate whether tumour necrosis factor‐α (TNF‐α) can promote the survival and activity of MSCs under oxidative stress to reduce IH more effectively, and establish what role the NF‐κB pathway plays in this. In this study, we preconditioned MSCs with TNF‐α (TNF ‐α‐PCMSCs) for 24 hrs and measured the activation of the IKK/NF‐κB pathway. EdU and transwell assays were performed to assess proliferation and migration of TNF ‐α‐PCMSCs. Apoptosis and migration of TNF ‐α‐ PCMSCs were evaluated in conditions of oxidative stress by analysis of the expression of Bcl‐2 and CXCR4 proteins. TNF ‐α‐ PCMSCs were transplanted into a vein graft model, so that cell homing could be tracked, and endothelial apoptosis and IH of vein grafts were measured. The results demonstrated that TNF‐α promotes proliferation and migration of MSCs. Furthermore, survival and migration of TNF ‐α‐ PCMSCs under oxidative stress were both enhanced. A greater number of MSCs migrated to the intima of vein grafts after preconditioning with TNF‐α, and the formation of neointima was significantly reduced. These effects could be partially abolished by IKK XII (NF‐κB inhibitor). All these results indicate that preconditioning with TNF‐α can promote survival and migration of MSCs under oxidative stress via the NF‐κB pathway and thus attenuate IH of vein grafts.

A free radical scavenger (Tempol) and its effect on intimal hyperplasia of vein grafts in rats.

Reversed vein grafting exposes the vessel to a period of ischemia, reperfusion and subsequent reactive oxygen species, which may damage endothelial tissue, smooth muscle cell proliferation and later the development of intimal hyperplasia. Tempol is a free radical scavenger that permeates biological membranes. This study investigates the effects of a free radical scavenger (Tempol) on intimal hyperplasia of femoral vein grafts and the level of reactive oxygen species in rats. Arterial defects created in the femoral artery of rats were repaired with ipsilateral femoral vein grafts. Tempol was administered to group T and saline to group C on a daily basis for a period of 28 days. Blood samples were measured. The veins were stained with H&E and Verhoeff's elastic stains. Binary comparison revealed a statistically significant difference for intimal and medial thicknesses (p<0.01). This study found that a free radical scavenger (Tempol) prevents the early development of intimal hyperplasia, most probably by inhibiting the infiltration of polymorph nuclear monocytes (PNM), with evidence of increased levels of antioxidant products and decreased levels of free oxygen radicals.

Collagen External Scaffolds Mitigate Intimal Hyperplasia and Improve Remodeling of Vein Grafts in a Rabbit Arteriovenous Graft Model.

Objectives. The aim of this study was to test the effects of collagen external scaffold (CES) in intimal hyperplasia of vein grafts and explore its underlying mechanisms. Methods. Thirty-six New Zealand white rabbits were randomized into no-graft group, graft group, and CES group. The rabbit arteriovenous graft model was established. In CES group, the vein graft was wrapped around with CES. The hemodynamic parameters of vein grafts were measured intraoperatively and 4 weeks after operation by ultrasonic examination. Histological characteristics of vein grafts were also evaluated 4 weeks later. The mRNA and protein levels of proliferating cell nuclear antigen (PCNA), active cleaved-caspase-3 (ClvCasp-3), and smooth muscle 22 alpha (SM22α) were measured 4 weeks later by quantitative real-time PCR and western blot. Results. CES significantly improved the hemodynamic stability of vein grafts, with higher blood velocity and blood flow. Similarly, CES also markedly mitigated intimal hyperplasia and inhibited dilatation of vein grafts. In CES group, the upexpression of PCNA and ClvCasp-3 and the downexpression of SM22α were inhibited. Conclusion. CES exerts beneficial effects in mitigating intimal hyperplasia and improving remodeling of autogenous vein grafts, which may be associated with reducing the proliferation and apoptosis and preserving the phenotype of VSMCs.

Invited commentary

Ever since the first subcutaneous veins were used as arterial substitutes in 1949, surgeons have been searching for new and better ways to procure venous conduits. Technical and biochemical methods have included “no touch” harvesting, gentle inflation with heparinized saline or lactate, infusion with smooth muscle cell dilators or cellular preservatives, endoscopic excision, and/or genetic modification through vector-based gene transfer. To date, no method had conclusively been found to be superior to the combination of an olive-tipped catheter, room temperature heparinized saline, and a good surgeon. Even with superlative technique, however, vein graft narrowing still occurs at an alarming rate, as 30% to 50% of all veins will respond to arterialization by pathologic thickening resulting in hemodynamically significant stenosis. Certainly, a major impetus for the development of vein graft neointimal hyperplasia is the abrupt increase in diameter and wall tension that accompanies exposure of thin, systemic veins to the intra-arterial environment. In their in vivo animal study of vein grafting presented herein, Salinas et al sought to limit vein graft dilatation by pre-emptively cross-linking venous collagen through the process of photochemical tissue passivation (PTP). Treated vein grafts were less dilated by exposure to intra-arterial pressure at the time of grafting and, after 4 weeks, had thickened significantly less than their untreated counterparts. Although the actual flow lumens of treated and untreated grafts appeared similar, PTP produced a thinner, more pliable graft, with profoundly attenuated cellular activation and proliferation. It remains to be seen whether PTP would be similarly effective in more muscular saphenous veins and whether limitation of their “natural” expansion might lead to increased rates of thrombosis and failure. Nonetheless, the authors provide another convincing experimental example of how vein grafts pathologically respond to arterialization and how modulation of that response might prove therapeutically useful. Prevention of vein graft intimal hyperplasia with photochemical tissue passivationJournal of Vascular SurgeryVol. 65Issue 1PreviewSaphenous vein is the conduit of choice for bypass grafting. Saphenous vein grafts have poor long-term patency rates because of intimal hyperplasia (IH) and subsequent accelerated atherosclerosis. One of the primary triggers of IH is endothelial injury resulting from excessive dilation of the vein after exposure to arterial pressures. Photochemical tissue passivation (PTP) is a technology that cross-links adventitial collagen by a light-activated process, which limits dilation by improving vessel compliance. Full-Text PDF Open Archive

Prx1 promotes the proliferation and migration of vascular smooth muscle cells in a TLR4-dependent manner.

The present study aimed to examine the effect of peroxiredocin 1 (Prx1) on vascular smooth muscle cell (VSMC) proliferation, invasion and migration abilities, and to examine the effect of Toll‑like receptor 4 (TLR4) gene silencing on VSMC proliferation, invasion and migration induced by the overexpression of Prx1. The expression of Prx1 in rats with vein graft intimal hyperplasia (IH) was detected using western blot analysis. In addition, VSMCs were retrovirally transfected to establish stable cell lines overexpressing Prx1. An MTT assay was used to determine the effect of the overexpression of Prx1 on VSMC proliferation. A Transwell assay was used to detect the effect of the overexpression of Prx1 on the invasion of VSMCs and a wound‑healing assay was used to determine the effect of the overexpression of Prx1 on the migration of VSMCs. The Prx1‑overexpressed cells were then transfected with interference plasmids of TLR4, to detect the effect of silencing the TLR4 gene on the proliferation and migration of VSMCs using MTT and wound‑healing assays. The results showed that the expression of Prx1 (1.067±0.03) in the IH group was significantly higher, compared with that in the control (0.677±0.05). The number of VSMCs able penetrated the membrane in Prx1-overexpressed group (150±17/visual field) was significantly higher, compared with that in the control (40±5/visual field). The VSMCs in the Prx1‑overexpressed group possessed significantly higher migration ability, compared with those in the control group. The numbers of viable cells in the Prx1‑overexpression groups were 5.625±0.1x105, 8.9±0.737x105 and 10.635±0.065x105, respectively, on days 1, 2 and3post‑transfetion, which were significantly higher, compared with those in the control group (3.0±0.025x105, 4.1±0.035x105 and 5.06±0.023x105. The overexpression of Prx1 promoted the proliferation, invasion and migration abilities of the VSMCs. Silencing of the TLR4 gene attenuated the Prx1‑induced proliferation and migration of the VSMCs. Therefore, the promotion of VSMC proliferation and migration by Prx1 was dependent on TLR4, which may become a novel target in the diagnosis, treatment and prognosis of patients with IH.

Photochemical Tissue Passivation Reduces Vein Graft Intimal Hyperplasia in a Swine Model of Arteriovenous Bypass Grafting.

BackgroundBypass grafting remains the standard of care for coronary artery disease and severe lower extremity ischemia. Efficacy is limited by poor long‐term venous graft patency secondary to intimal hyperplasia (IH) caused by venous injury upon exposure to arterial pressure. We investigate whether photochemical tissue passivation (PTP) treatment of vein grafts modulates smooth muscle cell (SMC) proliferation and migration, and inhibits development of IH.Methods and Results PTP was performed at increasing fluences up to 120 J/cm2 on porcine veins. Tensiometry performed to assess vessel elasticity/stiffness showed increased stiffness with increasing fluence until plateauing at 90 J/cm2 (median, interquartile range [IQR]). At 90 J/cm2, PTP‐treated vessels had a 10‐fold greater Young's modulus than untreated controls (954 [IQR, 2217] vs 99 kPa [IQR, 63]; P=0.03). Each pig received a PTP‐treated and untreated carotid artery venous interposition graft. At 4‐weeks, intimal/medial areas were assessed. PTP reduced the degree of IH by 66% and medial hypertrophy by 49%. Intimal area was 3.91 (IQR, 1.2) and 1.3 mm2 (IQR, 0.97; P≤0.001) in untreated and PTP‐treated grafts, respectively. Medial area was 9.2 (IQR, 3.2) and 4.7 mm2 (IQR, 2.0; P≤0.001) in untreated and PTP‐treated grafts, respectively. Immunohistochemistry was performed to assess alpha‐smooth muscle actin (SMA) and proliferating cell nuclear antigen (PCNA). Objectively, there were less SMA‐positive cells within the intima/media of PTP‐treated vessels than controls. There was an increase in PCNA‐positive cells within control vein grafts (18% [IQR, 5.3]) versus PTP‐treated vein grafts (5% [IQR, 0.9]; P=0.02).ConclusionsBy strengthening vein grafts, PTP decreases SMC proliferation and migration, thereby reducing IH.

Vein graft thrombi, a niche for smooth muscle cell colonization – a hypothesis to explain the asymmetry of intimal hyperplasia

Essentials Vein graft failure is the most frequent late onset complication of coronary artery bypass grafting. Cuff technique-based interposition mouse model including new anticoagulation regime was conducted. Early vein graft thrombi may serve as a niche for smooth muscle cell colonization. The focal character of early thrombi may form the basis for the asymmetry of intimal hyperplasia. Background Autologous saphenous veins are widely used in coronary artery bypass grafting; however, 10years after surgery, 40% of grafts are completely occluded, and another 30% show reduced blood flow. Objective In the past, the central processes and signaling pathways responsible for this loss of patency have been identified. However, one central finding in the process of graft failure is so far not understood: the asymmetric character of intimal hyperplasia. It was the goal of the present study to address this aspect. Methods By the use of a cuff technique-based vein interposition mouse model with a new anticoagulation regime, alterations in vein grafts were analyzed 1h, 1day, 2days, 3days, 7days and 21days after reperfusion by means of immunolabeling, histochemistry, and high-resolution ultrasound. Results The novel and major finding of this study is that the vein graft thrombus may serve as a niche that is infiltrated and colonized by smooth muscle cells (SMCs). Fibroblast growth factor-1 and platelet-derived growth factor-B may be the SMC-attracting factors in the thrombus. The focal character of early thrombi may define the focal and asymmetric character of vein graft intimal hyperplasia. Conclusions Inhibiting the formation and reducing the size of early thrombi is an old concept for reducing vein graft failure. However, in light of the present new findings obtained under a clinic-like anticoagulation regime, early vein graft thrombus prevention/size reduction should be revisited in the prevention of graft failure.

Prevention of vein graft intimal hyperplasia with photochemical tissue passivation

Saphenous vein is the conduit of choice for bypass grafting. Saphenous vein grafts have poor long-term patency rates because of intimal hyperplasia (IH) and subsequent accelerated atherosclerosis. One of the primary triggers of IH is endothelial injury resulting from excessive dilation of the vein after exposure to arterial pressures. Photochemical tissue passivation (PTP) is a technology that cross-links adventitial collagen by a light-activated process, which limits dilation by improving vessel compliance. The objective of this study was to investigate whether PTP limits the development of IH in a rodent venous interposition graft model. PTP is accomplished by coating venous adventitia with a photosensitizing dye and exposing it to light. To assess the degree of collagen cross-linking after PTP treatment, a biodegradation assay was performed. Venous interposition grafts were placed in the femoral artery of Sprague-Dawley rats. Rats were euthanized after 4weeks, and intimal thickness was measured histologically. Vein dilation at the time of the initial procedure was also measured. Time to digestion was 63± 7minutes for controls, 101± 2.4minutes for rose bengal (RB), and 300± 0minutes for PTP (P< .001 PTP vs control). A total of 37 animals underwent the procedure: 12 PTP, 12 RB only, and 13 untreated controls. Dilation of the graft after clamp release was 99% for control, 65% for RB only, and 19% for PTP-treated (P< .001 PTP vs control). Intimal thickness was 77± 59μm in controls, 60± 27μm in RB only, and 33± 28μm in PTP-treated grafts. There was a statistically significant 57% reduction in intimal thickness after treatment with PTP compared with untreated controls (P= .03). PTP treatment of venous interposition grafts in a rat model resulted in significant collagen cross-linking, decreased vessel compliance, and significant reduction in IH.

Extracellular Vesicles Derived from Adipose Mesenchymal Stem Cells Regulate the Phenotype of Smooth Muscle Cells to Limit Intimal Hyperplasia.

Extracellular vesicles (EVs) derived from mesenchymal stem cells (MSCs) play important roles in the reduction of inflammation in multiple disease models. However, their role in vein graft (VG) remodeling is undefined. We aimed to investigate the effect of EVs from adipose MSCs (ADMSC-EVs) on VG intimal hyperplasia and to explore the possible mechanisms. After generation and characterization of control-EVs and ADMSC-EVs in vitro, we investigated their effect on the proliferation and migration of vascular smooth muscle cells (VSMCs) in vitro. Next, we established a mouse model of VG transplantation. Mice underwent surgery and received control-EVs or ADMSC-EVs by intraperitoneal injection every other day for 20days. VG remodeling was evaluated after 4weeks. We also assessed the effect of ADMSC-EVs on macrophage migration and inflammatory cytokine expression. Significant inhibitory effects of ADMSC-EVs on in vitro VSMC proliferation (p < 0.05) and migration (p < 0.05) were observed compared with control-EVs. The extent of intimal hyperplasia was significantly decreased in ADMSC-EV-treated mice compared with control-EV-treated mice (26 ± 8.4 vs. 45 ± 9.0μm, p < 0.05). A reduced presence of macrophages was observed in ADMSC-EV-treated mice (p < 0.05). Significantly decreased expression of inflammatory cytokines interleukin (IL)-6 and monocyte chemoattractant protein-1 (MCP-1) was also found in the ADMSC-EV-treated group (both p < 0.05). In addition, phosphorylation of Akt, Erk1/2, and p38 in VGs was decreased in the ADMSC-EV-treated group. We demonstrated that ADMSC-EVs exert an inhibitory effect on VG neointima formation by regulating VSMC proliferation and migration, macrophage migration, inflammatory cytokine expression, and the related signaling pathways.

Abstract 16197: Pedicled Vein Grafts in Coronary Surgery Exhibit Reduced Intimal Hyperplasia at 6 Months

Introduction: Less-than-optimal long-term patency of the saphenous vein is one of the main obstacles for the success of CABG. Harvesting saphenous veins including a pedicle of perivascular tissue has been proposed to improve graft patency rates and endothelial function. Hypothesis: We hypothesized that pedicled vein grafts would show less intimal hyperplasia at 6-month angiographic follow-up. Method: Sixty patients scheduled for first time elective on-pump CABG were randomized to conventional or pedicled vein harvesting. Exclusion criteria were insulin dependent diabetes mellitus, recent smoking or renal failure. Pedicled veins were harvested with perivascular tissue and conventional veins were skeletonized. All veins were distended manually to check for leakage and stored in heparinized blood and saline. At 6 months vein grafts were examined with Intravascular Ultrasound (IVUS) and Optical Coherence Tomography (OCT). Imaging analysis was performed by an external blinded Core-lab. Results: Fifty-four patients were available for follow-up. There were no significant differences in occlusion rates between the two groups. IVUS showed no significant difference in intima-media complex thickness (pedicled: n=28, mean 0.229 mm, SEM 0.011; conventional: n = 26, mean 0.235 mm, SEM 0.017). However, using OCT pedicled veins showed significantly less intimal thickness than conventional veins (pedicled: mean 0.270 mm, SEM 0.012; conventional: mean 0.358 mm, SEM 0.021; p&lt;0.001). In conventional veins higher perioperative flow was positively correlated to increased intimal thickness. Such a correlation was not found in pedicled grafts. The difference in response to flow was significant using a general linear model including an interaction term (adjusted R squared = 0.254, p&lt;0.018). Conclusion: Performing CABG using saphenous vein grafts harvested with a pedicle of perivascular tissue provides significantly less vein graft intimal hyperplasia at 6 months.

Abstract 293: Clinical Predictors of Endothelial Function in Human Saphenous Vein

BACKGROUND: Human saphenous vein (HSV) remains the most widely utilized conduit for vascular bypass procedures. Outcomes remain limited by vein graft failure and intimal hyperplasia. Endothelial function is considered an important determinant of vein graft failure. We have observed significant variability in endothelial function in freshly isolated HSV samples. We therefore evaluated clinical predictors of endothelial function in HSV. Methods: We obtained freshly isolated HSV samples from the operating room immediately following harvest from patients undergoing coronary artery bypass procedures from Vanderbilt University Hospital and the Nashville VA Hospital. We obtained HSV samples prior to any intraoperative manipulations. HSV viability, smooth muscle function, and endothelial-dependent relaxation (EDR) were measured in a muscle bath. We collected the following clinical and demographic information: age, height, weight, gender, ethnicity, medical comorbidities, laboratory values (creatinine, HbA1c, lipids), ejection fraction, preoperative medication regimen, and method of vein graft harvest. We performed a univariate and multivariate analysis of predictors of endothelial function in HSV. Results: HSV samples were obtained from 149 patients. HSV EDR varied from -11% to 63%. Open harvest was employed for 39 HSV samples, compared with endoscopic harvest in 110 HSV samples. On univariate analysis, only open harvest was a statistically significant predictor of endothelial function (p=0.02): mean HSV EDR was 21.5% in HSV samples harvested open, compared with 15.4% in HSV harvested with an endoscopic technique. HSV EDR was also improved with preoperative aspirin use: mean HSV EDR was 18% in patients with preoperative aspirin use compared with 11.6% in patients who were not administered preoperative aspirin in a multivariate model when controlling for method of vein graft harvest (p=0.05). Conclusions: Endoscopic vein graft harvest is associated with endothelial dysfunction in HSV, while preoperative aspirin use is associated with improved endothelial function. Further work will be necessary to determine whether these factors are associated with development of intimal hyperplasia and vein graft failure.