Construction of Small-Caliber,Polydiaxanone Cyclohexanone Vascular Stents

Objective of this article is to construct and characterize a three-layered small-caliber, artificial vascular stent. The outer layer of the stent consisted of small intestine submucosa (SIS), the middle layer was the polydioxanone (PDS) vascular stents, and the inner layer. The SIS and PDS were attached with 8-0 PDS thread. Crosslinking with a 10% collagen/chondroitin sulfate solution and 0.020% glutaraldehyde secured the structure. The stent was implanted into the muscles on both sides of the canines’ spine at 2, 4, 12, and 24 weeks. A MTT assay using L-929 cells measured the cytotoxicity of the implant. Histological and microscopy analyses were employed to examine the degradation characteristics of the PDS stent. Biomechanical properties of the stent were tested and compared to those of normal physiological blood vessels. The PDS stent burst pressure (43.5 ± 8.3) kPa, rupture intensity (19.1 ± 1.56) N, strain ratio (42.88 ± 3.16)%, and radial compliance (5.96 ± 0.87)%/100 mmHg were similar to that of physiological vessels. The cytotoxicity test showed that the PDS stent complied with specifications for biological materials for medical applications, with a cell toxicity ranging from 0 to 1. After 12 weeks, SIS and collagen sponge were completely replaced by fibrous connective tissue. Although there was some degradation of PDS, inflammatory cell infiltration subsided. After 24 weeks, the scaffold material began to absorb the new fibers and became filled with inflammatory cells and macrophages. This artificial vascular stent met the requirements of transplant experiments and should be further investigated for future clinical applications.     

炎性因子IL-1βIL-18对静脉移植血管再狭窄影响的动物实验研究

目的：通过观察炎性因子白细胞介素-1β、白细胞介素-18在小鼠静脉移植后再狭窄血管中的表达,为临床冠脉搭桥术后血管再狭窄的早期诊断和药物治疗提供潜在靶点。方法：48只雄性小鼠,其中24只小鼠取出下腔静脉作为供体,采用套管法移植至另外24只小鼠的右颈动脉。建立颈动静脉血管移植模型,成活后随机分成三组每组8只,分别在一周、四周、八周处死,取移植血管,观察移植血管的通畅情况、血管内膜、中膜的增殖情况及炎性因子IL-1β、IL-18的表达;以供体血管作为对照组。结果：24只模型小鼠均存活,移植静脉血管内膜、中膜不同程度增生,免疫组化结果显示,正常静脉无明显炎症细胞侵润,移植静脉在一周时组织中大量MAC-2阳性单核巨噬细胞侵润,细胞因子IL-1β、IL-18的表达与正常静脉相比明显增加,、IL-18的表达分别为（9.52±1.81）%VS（0.82±0.12）%;（7.51±1.31）%VS（0.69±0.06）%,均为P〈0.05）。在四周、八周仍有大量巨噬细胞侵润,细胞因子IL-1β高表达,四周、八周IL-1β表达分别为（7.01±1.21）%、（2.48±0.62）%。移植静脉管壁逐渐增厚,管腔逐渐狭窄;与对照组静脉比较（56.15μm±4.65μm）,一周、四周、八周血管内膜厚度显著增厚分别为（204.26μm±24.29μm 551.83μm±35.00μm 723.90μm±127.42μm,均为P〈0.05）。结论：炎性因子IL-1β、IL-18在静脉移植血管再狭窄中的表达增加,参与静脉移植后血管再狭窄的发生,因此可通过抑制炎性因子IL-1β、IL-18来治疗冠脉搭桥后静脉再狭窄。     

The clopidogrel after surgery for coronary artery disease (CASCADE) randomized controlled trial: clopidogrel and aspirin versus aspirin alone after coronary bypass surgery [NCT00228423]

Background

Saphenous vein graft disease remains a major limitation of coronary artery bypass graft surgery. The process of saphenous vein intimal hyperplasia begins just days after surgical revascularization, setting the stage for graft atherosclerotic disease and its sequalae. Clopidogrel improves outcomes in patients with atherosclerotic disease, and is effective at reducing intimal hyperplasia in animal models of thrombosis. Therefore, the goal of this study will be to evaluate the efficacy of clopidogrel and aspirin therapy versus aspirin alone in the prevention of saphenous vein graft intimal hyperplasia following coronary artery bypass surgery.

Methods

Patients undergoing multi-vessel coronary artery bypass grafting and in whom at least two saphenous vein grafts will be used are eligible for the study. Patients will be randomized to receive daily clopidogrel 75 mg or placebo, in addition to daily aspirin 162 mg, for a one year duration starting on the day of surgery (as soon as postoperative bleeding has been excluded). At the end of one year, all patients will undergo coronary angiography and intravascular ultrasound assessment of one saphenous vein graft as selected by randomization. The trial will be powered to test the hypothesis that clopidogrel and aspirin will reduce vein graft intimal hyperplasia by 20% compared to aspirin alone at one year following bypass surgery.

Discussion

This trial is the first prospective human study that will address the question of whether clopidogrel therapy improves outcomes and reduces saphenous vein graft intimal hyperplasia following cardiac surgery. Should the combination of clopidogrel and aspirin reduce the process of vein graft intimal hyperplasia, the results of this study will help redefine modern antiplatelet management of coronary artery bypass patients.     

Shear stress and pressure modulate saphenous vein remodeling ex vivo

Vein graft failure remains an important clinical challenge, but factors contributing to vein graft failure have not clearly been defined. We investigated the role of the mechanical environment in vein remodeling in an ex vivo perfusion system. Porcine saphenous veins were subjected to five different ex vivo hemodynamic environments, including one mimicking an arterial bypass graft, for one week in order to independently assess the effects of shear stress and pressure on vein remodeling. The extent of intimal hyperplasia decreased with culture under increasing shear stress, with veins cultured under the lowest levels of shear stress exhibiting the greatest ratio of intimal/medial area, 0.15+/-0.03, which was greater than that of fresh veins (0.06+/-0.01, p<0.05). All perfused veins displayed characteristics of both medial hypertrophy and eutrophic remodeling, with those veins cultured under elevated pressures showing greater increases in mass and area than those cultured under venous pressures. Medial area correlated with the average pressure under which veins were cultured (R2=0.95, p<0.001), with veins cultured under bypass graft conditions, which were exposed to the greatest pressure during the one week culture, exhibiting the largest medial area (1.69+/-0.15 mm2), which was significantly greater than that of fresh veins (1.08+/-0.05 mm2, p<0.05). However, pulsatility was not a necessary stimulus for medial growth, as increases in medial area were observed in culture conditions in which steady flow and pressure were present. Our results suggest that pressure and shear stress act independently to regulate vein remodeling, influencing changes in vessel size as well as the nature of the remodeling.     

大鼠颈部自体静脉移植模型两种吻合方法的比较

目的比较间断吻合和连续吻合法建立静脉桥狭窄动物模型的优劣。方法SD大鼠20只,分成两组（间断吻合组和连续吻合组）,取颈外静脉与颈总动脉行端端吻合。术后4周取下静脉桥,观察桥管通畅性,分析新生内膜与中膜的厚度、面积比。结果连续组与间断组相比手术时间更短,出血更少,但桥管通畅率低,两组内膜增生程度没有显著差异。结论连续吻合用时短,出血少,对术者要求更高,较易形成吻合口狭窄。两者造模效果一样。     

Does PGA external stenting reduce compliance mismatch in venous grafts?

Background  

Autogenous vein grafting is widely used in regular bypassing procedures. Due to its mismatch with the host artery in both mechanical property and geometry, the graft often over expands under high arterial blood pressure and forms a step-depth where eddy flow develops, thus causing restenosis, fibrous graft wall, etc. External stents, such as sheaths being used to cuff the graft, have been introduced to eliminate these mismatches and increase the patency. Although histological and immunochemical studies have shown some positive effects of the external stent, the mechanical mismatch under the protection of an external stent remains poorly analyzed.     

Predictive Factors of Late Venous Aortocoronary Graft Failure: Ultrastructural Studies

Background

Venous aortocoronary graft arterialization may precede a preterm occlusion in some coronary artery bypass grafting (CABG) patients. The aim of the present study was to identify ultrastructural variations in the saphenous vein wall that may have an impact on the development of venous graft disease in CABG patients.

Methods

The study involved 365 consecutive patients with a mean age of 62.9±9.4 years who underwent isolated CABG. The thickness and area of the whole venous wall, the tunica intima, the tunica media and the adventitia and the number and shape (length, thickness and length/thickness ratio) of the nuclei in the medial smooth muscle cells nuclei in the distal saphenous vein segments were evaluated by ultrastructural studies. Patients were followed up for 41 to 50 months (mean 45.1±5.1). Saphenous vein graft patency was assessed by follow-up coronary angiography. Logistic regression models were used to identify independent risk factors for late graft failure.

Results

In 71 patients significant lesions in the saphenous vein grafts were observed. The whole venous wall thickness (437.5 µm vs. 405.5 µm), tunica media thickness (257.2 µm vs. 211.5 µm), whole venous wall area (2.23 mm² vs. 2.02 mm²) and tunica media area (1.09 mm² vs. 0.93 mm²) were significantly larger for this group of patients than for those without graft disease. In the latter group more elongated smooth muscle cell nuclei (higher length/thickness ratio) were found in the tunica media of the saphenous vein segments. Thickening of the saphenous vein tunica media and chunky smooth muscle cell nuclei were identified as independent risk factors for graft disease development.

Conclusions

Saphenous vein tunica media hypertrophy (resulting in wall thickening) and chunky smooth muscle cell nuclei might predict the development of venous graft disease.     

<Emphasis Type="Italic">Chlamydia pneumoniae</Emphasis> aggravates vein graft intimal hyperplasia in a rat model

Background  

Along with angioplasty, autologus vein grafts are commonly used for artery bypass grafting in patients with advanced arterial stenosis and drug-resistant angina pectoris. Although initially a successful procedure, long-term functionality is limited due to proliferation and migration of smooth muscle cells. Like in atherosclerosis, common chronic infections caused by viruses and bacteria may contribute to this process of vein graft failure. Here we investigated the possible role of Chlamydia pneumoniae (Cpn) in the pathogenesis of venous graft failure in an experimental animal model. In 2 groups (n = 10 rats/group), an epigastric vein-to-common femoral artery interposition graft was placed. Immediately thereafter, rats were infected with Cpn (5*10⁸ IFU) or injected with control solutions. Rats were sacrificed three weeks after surgery and the grafts were harvested for morphometrical and immunohistochemical analysis.     

Expression of TGFβ1 in pulmonary vein stenosis after radiofrequency ablation in chronic atrial fibrillation of dogs

The development of pulmonary vein stenosis has recently been described after radiofrequency ablation (RF) to treat atrial fibrillation (AF). The purpose of this study was to examine expression of TGFβ1 in pulmonary vein stenosis after radiofrequency ablation in chronic atrial fibrillation of dogs. About 28 mongrel dogs were randomly assigned to the sham-operated group (n = 7), the AF group (n = 7), AF + RF group (n = 7), and RF group (n = 7). In AF or AF + RF groups, dogs underwent chronic pulmonary vein (PV) pacing to induce sustained AF. RF application was applied around the PVs until electrical activity was eliminated. Histological assessment of pulmonary veins was performed using hematoxylin and eosin staining; TGFβ1 gene expression in pulmonary veins was examined by RT-PCR analysis; expression of TGFβ1 protein in pulmonary veins was assessed by Western blot analysis. Rapid pacing from the left superior pulmonary vein (LSPV) induced sustained AF in AF group and AF + RF group. Pulmonary vein ablation terminated the chronic atrial fibrillation in dogs. Histological examination revealed necrotic tissues in various stages of collagen replacement, intimal thickening, and cartilaginous metaplasia with chondroblasts and chondroclasts. Compared with sham-operated and AF group, TGFβ1 gene and protein expressions was increased in AF + RF or RF groups. It was concluded that TGFβ1 might be associated with pulmonary vein stenosis after radiofrequency ablation in chronic atrial fibrillation of dogs. Shufeng Li and Hongli Li contributed equally to the work.     

Inflammatory cells induce neointimal growth in a rat arterial autograft model

Subendothelial invasion by leukocytes is a sign of intimal thickening in arteriosclerosis and in the response of a vessel to mechanical damage. Our study was designed to establish whether these cells are implicated in the formation of a neointima in an autologous arterial graft model in the rat and to evaluate the effects of cyclosporin A (CsA). Three study groups were established according to whether the animals were treated with CsA-Cp (Sandimmun), CsA-Et (ethanol vehicle) or received no treatment (control group). Both drug forms were administered (5 mg/kg/day, s.c.) from 4 days prior to surgery until the time of sacrifice. Antibodies specific for lymphocytes (CD4, CD8), monocytes/macrophages-ED1, smooth muscle alpha-actin and the von Willebrand factor (vWF) were used to identify the cells in the grafted arterial wall. In control grafts, the neointima had formed by 2 weeks post-implant. However, the cells comprising this layer generally presented no positivity whatsoever towards the antibodies employed. At 50 days, the new layer was observed to be formed by a vWF-positive endothelium and alpha-actin-positive cells. In all three groups, several polymorphonuclear (PMN) cells adhered to the denuded luminal surface from 7 days onwards. In the treated animals, neutrophils and monocytes were seen to infiltrate intimal and medial layers during the later post-implant stages. Around the third week post-implant, the neointima had reached the grafted segment from the distal portion of the recipient artery, and by 50 days it was similar to that seen in control specimens. Our findings suggest that: a) neutrophils play a role in neointimal thickening in this arterial autograft model; and b) CsA promotes the adhesion and infiltration of neutrophils in the injured arterial wall.     

Simulation of Flow through a Miller Cuff Bypass Graft

Unnatural temporal and spatial distributions of wall shear stress in the anastomosis of distal bypass grafts have been identified as possible factors in the development of anastomotic intimal hyperplasia in these grafts. Distal bypass graft anastomoses with an autologus vein cuff (a Miller cuff) interposed between the graft and artery have been shown to alleviate the effects of intimal hyperplasia. In this study, pulsatile flow through models of a standard end-to-side anastomosis and a Miller cuff anastomosis are computed and the resulting wall shear stress and pressure distributions analysed. The results are inconclusive, and could be taken to suggest that the unnatural distributions of shear stress that do occur along the anastomosis floor may not be particularly important in the development of intimal hyperplasia. However, it seems more likely that the positive effects of the biological and material properties of the vein cuff, which are not considered in this study, somehow outweigh the negative effects of the shear stress distributions predicted to occur on the floor of the Miller-cuff graft.     

A novel vein graft model: adaptation to differential flow environments

Accelerated intimal hyperplasia in response to altered flow environment is critical to the process of vein bypass graft failure. Lack of a reproducible animal model for dissecting the mechanisms of vein graft (VG) remodeling has limited progress toward solving this clinically significant problem. Combining a cuffed anastomotic technique with other surgical manipulations, we developed a well-defined, more robust method for studying hemodynamic factors in VG arterialization. VG with fistula placement, complete occlusion, or partial distal branch ligation (DBL) was performed in the carotid artery of 56 rabbits. Extensive hemodynamic and physiological analyses were performed to define the hemodynamic forces and histological adaptations of the wall at 1-28 days. Anastomotic time averaged 12 min, with 100% patency of bilateral grafts and unilateral grafts plus no adjunct or delayed fistula. Bilateral VG-DBL resulted in an immediate disparity in wall shear (0.8 +/- 0.1 vs. 12.4 +/- 1.1 dyn/cm2, ligated vs. contralateral graft). Grafts exposed to low shear stress responded primarily through enhanced intimal thickening (231 +/- 35 vs. 36 +/- 18 microm, low vs. high shear). High-shear-stress grafts adapted through enhanced outward remodeling, with a 24% increase in lumen diameter at 28 days (3.0 +/- 0.1 vs. 3.7 +/- 0.2 mm, low vs. high shear). We have taken advantage of the cuffed anastomotic technique and combined it with a bilateral VG-DBL model to dissect the impact of hemodynamic forces on VG arterialization. This novel model offers a robust, clinically relevant, statistically powerful small animal model for evaluation of high- and low-shear-regulated VG remodeling.     

Characterization of phospholipase A1, A2, C activity in Ureaplasma urealyticum membranes

Neointimal thickening following catheter injury is characterized, in part, by growth factor-induced vascular smooth muscle cell (VSMC) proliferation. It was hypothesized that a reduction in serum insulin-like growth factor-1 (IGF-1), characteristic of chemically-induced diabetes, would result in decreased VSMC proliferation and attenuate neointimal thickening. It was found that alloxan-treated New Zealand White rabbits exhibit varying degrees of glycemia. Rabbits classified as diabetic (glucose = 400 mg/dL) had significantly decreased serum concentration of IGF-1 (87.4 ± 14 nmol/L vs. 170 ± 14 nmol/L) and significantly decreased intimal/medial (I/M) ratios 2, 4, and 8 weeks after aortic injury compared to euglycemic rabbits (13.7 ± 2, 21.1 + mn; 2, 32.4 ± 3 in euglycemics and 6.6 ± 1, 14 ± 2, 19 ± 5 in diabetics, respectively). The I/M for high hyperglycemic animals (glucose 286-399 mg/dL) was comparable to diabetic animals yet their serum IGF-1 levels were normal rather than depressed. Vascular IGF-1 content similarly increased upon injury in both diabetic and euglycemic animals. In diabetic animals, proliferating cell nuclear antigen (PCNA) immunostaining was present by day 1 peaked by day 5 and returned to control by day 14. In euglycemic animals, staining by day 1 continued to increase through day 14. A similar increase in mitogen-activated protein kinase (MAPK) activity occurred from day 1 through day 5 in both diabetic and euglycemic animals. This is the first demonstration of an association between MAPK activity and VSMC proliferation following vascular injury in diabetic animals as previously reported in euglycemic animals. In conclusion, this study provides evidence against a direct effect of IGF-1 in the reduction in neointimal thickening, VSMC proliferation, and MAPK activity upon catheter injury in chemically-induced diabetic rabbits.     

Interference of IP-10 Expression Inhibits Vascular Smooth Muscle Cell Proliferation and Intimal Hyperplasia in Carotid Artery: A New Insight in the Prevention of Restenosis

After vascular angioplasty, vascular smooth muscle cell (VSMC) proliferation causes atherosclerosis and intimal hyperplasia leading to restenosis. Interferon-γ-inducible protein (IP)-10 plays a role in atherogenesis, but the mechanism remains unclear. We evaluated the role of IP-10 in intimal hyperplasia and restenosis. IP-10 expression was determined in arterial specimens from 20 arteriosclerotic obliteration patients and 6 healthy individuals. VSMCs were stimulated in vitro with IFN-γ and transfected with IP-10 siRNA. Silencing was verified with RT-PCR/Western blot; cell proliferation rate was detected by methyl-thiazol-tetrazolium. The carotid artery model of atherosclerosis injury was established with IP-10 siRNA. IP-10 expression was detected at 1 and 4 weeks using RT-PCR and immunohistochemistry. Artery morphology was assessed with hematoxylin-and-eosin staining, and intimal hyperplasia was evaluated by electron microscopy. IP-10 was overexpressed in arteriosclerotic obliteration group compared with control group (P < 0.05). IP-10 expression in transfected group was significantly lower than in untransfected group. The intima-to-media ratio of transfected group at 4 weeks was lower than that of untransfected group (P < 0.01). The transfected group exhibited more regular intimal structure and less hyperplasia under electron microscopy. We, therefore, concluded that IP-10 played an important role in intimal hyperplasia as siRNA-mediated IP-10 silencing inhibited aberrant VSMCs hyperplasia and reduced restenosis.     

A model of stress-induced geometrical remodeling of vessel segments adjacent to stents and artery/graft anastomoses

The mismatch between the elastic properties and initial geometry of a host artery and an implanted stent or graft cause significant stress concentration at the zones close to junctions. This may contribute to the often observed intimal hyperplasia, resulting in late lumen loss and eventual restenosis. This study proposes a mathematical model for stress-induced thickening of the arterial wall at the zones close to an implanted stent or graft. The host artery was considered initially as a cylindrical shell with constant thickness that was clamped to the stent or graft, which was assumed to be non-deformable in the circumferential direction. It was assumed that the abnormal circumferential and axial stresses due to the bending of the arterial wall cause wall thickening that tends to restore the stress state close to that existing far from the junction. The linear equations of a cylindrical shell with variable thickness were coupled to an evolution equation for the wall thickness. These equations were solved numerically and a parametric study was performed using finite difference method and explicit time step. The results show that the remodeling process is self-limiting and leads to local thickening that gradually decreases with distance from the edge of the stent/graft. Model predictions were tested against morphological findings existing in the literature. Recommendations on stent designs that reduce stress concentrations are discussed.     

Simulation of flow through a Miller cuff bypass graft

Unnatural temporal and spatial distributions of wall shear stress in the anastomosis of distal bypass grafts have been identified as possible factors in the development of anastomotic intimal hyperplasia in these grafts. Distal bypass graft anastomoses with an autologus vein cuff (a Miller cuff) interposed between the graft and artery have been shown to alleviate the effects of intimal hyperplasia. In this study, pulsatile flow through models of a standard end-to-side anastomosis and a Miller cuff anastomosis are computed and the resulting wall shear stress and pressure distributions analysed. The results are inconclusive, and could be taken to suggest that the unnatural distributions of shear stress that do occur along the anastomosis floor may not be particularly important in the development of intimal hyperplasia. However, it seems more likely that the positive effects of the biological and material properties of the vein cuff, which are not considered in this study, somehow outweigh the negative effects of the shear stress distributions predicted to occur on the floor of the Miller-cuff graft.     

Protective effects of thymoquinone on streptozotocin-induced diabetic nephropathy

The aim of this study was designed to investigate the possible beneficial effects of the thymoquinone (TQ) in streptozotocine (STZ)-induced diabetes in rats. The rats were randomly allotted into one of three experimental groups: A (control), B (diabetic untreated), and C (diabetic treated with TQ); each group contain ten animals. B and C groups received STZ. Diabetes was induced in two groups by a single intra-peritoneal (i.p) injection of STZ (50 mg/kg, freshly dissolved in 5 mmol/l citrate buffer, pH 4.5). Two days after STZ treatment, development of diabetes in two experimental groups was confirmed by measuring blood glucose levels in a tail vein blood samples. Rats with blood glucose levels of 250 mg/dl or higher were considered to be diabetic. The rats in TQ treated groups were given TQ (50 mg/kg body weight) once a day orally by using intra gastric intubation for 12 weeks starting 2 days after STZ injection. Treatment of TQ reduced the glomerular size, thickening of capsular, glomerular and tubular basement membranes, increased amounts of mesangial matrix and tubular dilatation and renal function as compared with diabetics untreated. We conclude that TQ therapy causes renal morphologic and functional improvement after STZ-induced diabetes in rats. We believe that further preclinical research into the utility of TQ treatment may indicate its usefulness as a potential treatment in diabetic nephropathy.