Search

Objective: The arteriovenous fistula (AVF) still suffers from a high number of failures caused by insufficient outward remodeling and intimal hyperplasia (IH) formation from which the exact mechanism is largely unknown. A suitable animal model is of vital importance in the unraveling of the underlying pathophysiology. However, current murine models of AVF failure do not incorporate the surgical configuration that is commonly used in humans. Because the hemodynamic profile is one of the key determinants that play a role in vascular remodeling in the AVF, it is preferable to use this same configuration in an animal model. Here we describe a novel murine model of AVF failure in which the configuration (end-to-side) is similar to what is most frequently performed in humans., Methods: An AVF was created in 45 C57BL/6 mice by anastomosing the end of a branch of the external jugular vein to the side of the common carotid artery with interrupted sutures. The AVFs were harvested and analyzed histologically at days 7, 14, and 28. Identical veins of unoperated-on mice served as controls. Intravenous near-infrared fluorescent fluorophores were used to assess the patency of the fistula., Results: The patency rates at days 7, 14, and 28 days were 88%, 90%, and 50%, respectively. The mean circumference increased up to day 14, with a maximum 1.4-fold increase at day 7 compared with the control group (1.82 ± 0.7 vs 1.33 ± 0.3 mm; P = .443). Between days 14 and 28, the circumference remained constant (2.36 ± 0.2 vs 2.45 ± 0.2 mm; P = .996). At 7 days after surgery, the intimal area consisted mainly of an acellular layer that was structurally analogous to a focal adherent thrombus. Starting at 14 days after surgery, venous IH increased significantly compared with the unoperated-on group (14 days: 115,090 ± 22,594 μm(2), 28 days: 234,619 ± 47,828 μm(2), unoperated group: 2368 ± 1056 μm(2); P = .001 and P < .001, respectively) and was mainly composed of cells positive for α-smooth muscle actin. We observed leukocytes in the adventitial side of the vein at all time points., Conclusions: Our novel murine AVF model, which incorporates a clinically relevant configuration of the anastomosis, displays similar features that are characteristic of failing human AVFs. Moreover, our findings suggest that coagulation and inflammation could both potentially play an important role in the formation of IH and subsequent AVF failure. Near-infrared fluoroscopy was a suitable alternative for conventional imaging techniques. This murine AVF-model is a valuable addition to the AVF animal model arsenal., (Copyright © 2014 Society for Vascular Surgery. All rights reserved.)

Background: Smooth muscle cell (SMC) migration and proliferation are important in the development of intimal hyperplasia, the major cause of vein graft failure. Proteases of the plasminogen activator (PA) system and of the matrix metalloproteinase (MMP) system are pivotal in extracellular matrix degradation and, by that, SMC migration. Previously, we demonstrated that inhibition of both protease systems simultaneously with viral gene delivery of the hybrid protein TIMP-1.ATF, consisting of the tissue inhibitor of metalloproteinase-1 (TIMP-1) and the receptor-binding amino terminal fragment (ATF) of urokinase, reduces SMC migration and neointima formation in an in vitro restenosis model using human saphenous vein cultures more efficiently than both protease systems separately. Because use of viral gene delivery is difficult in clinical application, this study used nonviral delivery of TIMP-1.ATF plasmid to reduce vein graft disease in a murine bypass model. Nonviral gene transfer by electroporation was used to avert major disadvantages of viral gene delivery, such as immune responses and short-term expression., Methods: Plasmids encoding ATF, TIMP-1, TIMP-1.ATF, or luciferase, as a control, were injected and electroporated in both calf muscles of hypercholesterolemic apolipoprotein E3-Leiden (APOE*3Leiden) mice (n = 8). One day after electroporation, a venous interposition of a donor mouse was placed into the carotid artery of a recipient mouse. In this model, vein graft thickening develops with features of accelerated atherosclerosis. Vein grafts were harvested 4 weeks after electroporation and surgery, and histologic analysis of the vessel wall was performed., Results: Electroporation-mediated overexpression of the plasmid vectors resulted in a prolonged expression of the transgenes and resulted in a significant reduction of vein graft thickening (ATF: 36% +/- 9%, TIMP-1: 49% +/- 5%, TIMP-1.ATF: 58% +/- 5%; P < .025). Although all constructs reduced vein graft thickening compared with the controls, the luminal area was best preserved in the TIMP-1.ATF-treated mice., Conclusion: Intramuscular electroporation of TIMP-1.ATF inhibits vein graft thickening in vein grafts in carotid arteries of hypercholesterolemic mice. Binding of TIMP-1.ATF hybrid protein to the u-PA receptor at the cell surface enhances the inhibitory effect of TIMP-1 on vein graft remodeling in vitro as well as in vivo and may be an effective strategy to prevent vein graft disease., (Copyright 2010 Society for Vascular Surgery. Published by Mosby, Inc. All rights reserved.)

Objective: Inflammatory responses to vascular injury are key events in vein graft disease and accelerated atherosclerosis, which may result in bypass failure. The monocyte chemoattractant protein-1 (MCP-1)/CC-chemokine receptor (CCR)-2 pathway is hypothesized to play a central role. A murine model for vein graft disease was used to study the effect of local application of lentiviral short hairpin RNA (shRNA) targeted against CCR2., Methods: A venous interposition was placed into the carotid artery of hypercholesterolemic apolipoprotein E3-Leiden (APOE*3-Leiden) mice to induce vein graft thickening with features of accelerated atherosclerosis. To demonstrate the efficacy of the lentiviral shRNA targeting murine CCR2 (shCCR2) in blocking vein graft disease in vivo, lentiviral shCCR2 or a control lentivirus was used to infect the vein graft locally (n = 8)., Results: Vascular CCR2 and MCP-1 messenger RNA expression levels were significantly upregulated during lesion progression in the vein graft. Infection of smooth muscle cells (SMCs) with a lentiviral shRNA targeting shCCR2 completely abolished MCP-1-induced SMC migration and inhibited SMC proliferation in vitro (n = 3 per group). Morphometric analysis of sections of grafts showed a significant 38% reduction in vein graft thickening in the shCCR2-treated mice 4 weeks after surgery (control, 0.42 +/- 0.05 mm(2); shCCR2, 0.26 +/- 0.03 mm(2); P = .007)., Conclusion: Vascular CCR2 contributes to vein graft disease, and local application of shRNA against CCR2 to the vessel wall prevents vein graft thickening in hypercholesterolemic mice, suggesting that local overexpressing of shRNA using organ-targeted lentiviral gene delivery may be a promising therapeutic tool to improve vein graft disease in bypassed patients., Clinical Relevance: Vein graft disease is an important clinical issue that results from an inflammatory response. The monocyte chemoattractant protein (MCP)-1/CC-chemokine receptor (CCR)-2 pathway plays a key role in the initiation and development of vein graft disease. This study demonstrates that perivascular overexpression of short hairpin RNA, targeted against CCR2, inhibits vein graft thickening. These data show that organ-targeted gene therapy against CCR2 in the vessel wall could be a promising therapeutic tool to improve vein graft patency in bypassed patients.

Objective: The aim of this study was to assess whether the anti-inflammatory agent dexamethasone can inhibit vein graft thickening without the occurrence of serious side effects., Methods: Venous interposition grafting was performed in the common carotid artery of hypercholesterolemic ApoE3Leiden transgenic mice. Mice were treated with dexamethasone (0.15 mg.kg(-1).d(-1) orally), and after 28 days, vein graft thickening was quantified., Results: Treatment with dexamethasone resulted in a significant 43% reduction in lesion area without changes in lesion composition when compared with nontreated controls. However, dexamethasone, when administered for a prolonged period of time, is known for its potentially serious side effects. To overcome these potential side effects of prolonged dexamethasone treatment, the effect of a short-term 7-day dexamethasone treatment was studied. This short dexamethasone treatment resulted in a 49% decrease of vein graft thickening at 28 days. Furthermore, it was demonstrated that dexamethasone treatment led to reduced local expression of several proinflammatory cytokines and factors in the vein grafts 24 hours after surgery. Finally, observations in mice were verified in human saphenous organ cultures. Exposure to dexamethasone for either 7 or 28 days significantly reduced intimal hyperplasia formation on cultured saphenous vein segments., Conclusions: Short-term anti-inflammatory treatment with dexamethasone leads to a significant reduction in vein graft thickening over an extended period, possibly by the reduction of early expression of proinflammatory cytokines. This 7-day treatment minimizes the risk of unwanted side effects of long-term dexamethasone treatment and may be a new approach to prevent graft failure.

Objective: Endovascular aneurysm repair is an alternative treatment of abdominal aortic aneurysm. The procedure is less invasive, and morbidity and most probably mortality are reduced. However, some problems, such as endoleakage, are yet to be resolved. Endoleakage can occur after graft migration, as a result of insufficient fixation of the stent graft. One cause is deficient healing between the aortic neck and the stent graft. We hypothesize that better healing, achieved by induction of vascular cell ingrowth into the graft material, results in better graft fixation. Previously we demonstrated ingrowth of neointima into the graft material if the stent graft is impregnated with a coat of basic fibroblast growth factor (bFGF), heparin, and collagen. In this study we evaluated healing with bFGF-heparin-collagen-coated stent grafts in vivo., Methods: In 4 pigs, 32 endovascular stent grafts, manufactured from standard Dacron and Gianturco Z-stents, were placed in the aorta. The stent grafts were impregnated with either bFGF-heparin containing collagen (n=16) or control collagen (n=16). After 4 and 8 weeks animals were killed, and ingrowth and healing of the stent grafts were macroscopically and electron microscopically evaluated., Results: After 8 weeks all bFGF-impregnated stent grafts demonstrated ingrowth of tissue and healing between the graft and the aorta, whereas the control nonimpregnated stent grafts showed no ingrowth. Microscopic evaluation demonstrated alpha-smooth muscle actin-positive cells, most probably smooth muscle cells or myofibroblasts, growing from the vascular wall through the graft material., Conclusion: A Dacron prosthesis impregnated with collagen, heparin, and bFGF induced graft healing in an in vivo pig model, in contrast to nonimpregnated stent grafts. This in vivo study confirms our previous findings in vitro. These results indicate that healing between Dacron and the aorta can be achieved, and suggest that type I endoleakage may be resolved by inducing healing between the aortic wall and the prosthesis with graft material containing growth factor.

Objective: One of the most life-threatening vascular diseases is rupture of an abdominal aneurysm. The conventional treatment is based on surgical reconstruction. An alternative treatment is endovascular aneurysm repair (EVAR). Despite many advantages, one of the problems of EVAR is endoleakage from deficient healing between the aortic neck and the fabric of the endograft. We hypothesize that better healing, achieved with induction of vascular cell ingrowth into the graft material, would lead to better graft healing., Methods: Both pig aorta and human normal and aneurysmal aortic wall were used for organ cultures. Various growth factors were evaluated for the potential to induce intimal hyperplasia (ie, platelet-derived growth factor, vascular endothelial growth factor, and basic fibroblast growth factor [bFGF]). After the most potent growth factor had been selected, a vascular prosthetic material (Dacron fabric) impregnated with collagen and heparin was incubated with this growth factor. Impregnated pieces of Dacron were fixated on top of the aortic organ cultures for study of ingrowth of the neointima formation into the graft material., Results: bFGF was the most potent growth factor to induce neointima in aortic organ cultures. The pieces of impregnated Dacron had a release of 5 ng/24 h of bFGF for a period of at least 28 days. With fixation on top of the aortic organ cultures, the impregnated Dacron was capable of inducing neointima formation and ingrowth of the neointima into the graft material after 28 days., Conclusion: We showed that a Dacron prosthesis impregnated with collagen, heparin, and bFGF is capable of inducing graft healing in our in vitro model, the aortic organ cultures of pig and human aortas. These results suggest that the problem of endoleakage with EVAR may be solved with a perfect proximal healing between the aortic wall and the prosthesis.