Early adaptation of human lower extremity vein grafts: wall stiffness changes accompany geometric remodeling

OBJECTIVE: To quantitatively describe the temporal changes in elastic properties and wall dimensions in lower-extremity vein grafts after implantation. DESIGN OF STUDY: This is a prospective study of patients (N = 38) undergoing lower extremity bypass grafts (N = 41) with autologous veins. Pulse wave velocity (PWV), luminal diameter, and wall thickness measurements were obtained by duplex ultrasound scan intraoperatively and at 1, 3, and 6 months postoperatively for assessment of graft dimensions and wall stiffness. RESULTS: Lower extremity vein grafts showed an increase in PWV (from 16 +/- 1 to 21 +/- 3 cm/s; mean +/- SEM; P =.08), reflecting an increase in wall stiffness (from 1.2 +/- 0.2 to 2.5 +/- 0.7 x 10(6) dynes/cm; P =.02) and wall thickness (from 0.47 +/- 0.03 to 0.61 +/- 0.004 mm; P =.04) over the first 6 months after implantation. Changes in lumen diameter were positively correlated with changes in external graft diameter (P <.01) and negatively correlated with initial lumen diameter (P <.01) but not with changes in the wall thickness. CONCLUSIONS: These results suggest complex remodeling of vein grafts during the first several months after implantation, with increased wall thickness occurring independent of variable changes in lumen diameter. Simultaneously, a marked increase in wall stiffness over this interval suggests a likely role for collagen deposition.     

Immunolocalization and temporal distribution of cytokine expression during the development of vein graft intimal hyperplasia in an experimental model

Purpose: Vein graft stenosis caused by intimal hyperplasia (IH) accounts for 30% to 50% of late bypass graft failures; however, the biochemical mediators of vein graft IH have been poorly defined. We attempted to evaluate the spatial and temporal distribution of five principal cytokines (interleukin-1 beta [IL-1β], platelet-derived growth factor AA [PDGF-AA], basic fibroblast growth factor [bFGF], interferon gamma [INFγ], and tumor necrosis factor alpha [TNF-α]) during the development of IH in a rat vein graft model.Methods: Rat epigastric vein interposition grafts in the femoral artery were harvested at 6 hours, 2 days, 1 week, 2 weeks, and 4 weeks after the grafting procedure and studied with immunohistochemical and standard histologic techniques. The cytokine expression in the endothelium and media/neointima was quantified as the percentage of immunopositive cells per high-power field.Results: Maximal hyperplasia occurred 2 weeks after the grafting procedure. Peak expression of IL-1β and bFGF occurred by 2 days. PDGF-AA expression paralleled the development of IH, peaking at 2 weeks and then declining. TNF-α expression increased at 1 week and remained elevated. INFγ was seen only in control grafts.Conclusions: The coordinated early release of IL-1β and bFGF and the down-regulation of INFγ seem to trigger an inflammatory response, thereby initiating IH. The process then is propagated by the release of PDGF-AA and TNF-α, with concomitant smooth muscle cell proliferation and production of extracellular matrix. It is likely that this complex milieu of local paracrine signaling is required to generate the hyperplastic response seen in failing vein grafts. (J Vasc Surg 1996;24:463-71.)     

Neointimal hyperplasia rapidly reaches steady state in a novel murine vein graft model

OBJECTIVE: Neointimal hyperplasia remains a principal cause of vein graft failure. Genetic contributions to vein graft neointimal hyperplasia could be well studied in the mouse; however, surgical approaches to vein bypass surgery in the mouse have yet to replicate approaches commonly employed in human patients. Consequently, the goal of this study was to develop a murine interposition vein graft model that reproduces characteristics of human vein graft disease. METHOD: Using C57BL/6J mice, we excised inferior venae cavae (IVCs) from donor mice and grafted them, with end-to-side anastomosis, into the carotid circulation of recipients. IVC grafts were harvested from 3 to 56 days postoperatively, and analyzed for the development of neointima and media. RESULTS: Thickening of both the vein graft neointima and media progressed rapidly between postoperative weeks 1 and 4, and reached steady state levels by approximately week four, with a graft-wall thickness of 91 +/- 4 microm (14 cell layers), a lumen area of 0.56 mm(2), an average neointima-media ratio of 0.4 to 0.6, and a predominance of alpha-smooth muscle actin-staining cells. Comprising predominately smooth muscle actin-expressing cells, the neointima was 50% thicker in the proximal than in the distal third of the grafts (P <.001), but proximal and distal vein graft anastomoses were widely patent. CONCLUSIONS: In syngeneic murine carotid interposition IVC grafts implanted with end-to-side anastomoses, moderate, nonocclusive neointimal hyperplasia reaches steady state after the fourth postoperative week. This neointimal hyperplasia, like that of human grafts, predominates near vein graft anastomoses. This vein graft model should facilitate genetic analyses of the pathogenesis of neointimal hyperplasia.     

An external,oversized, porous polyester stent reduces vein graft neointima formation,cholesterol concentration,and vascular cell adhesion molecule 1 expression in cholesterol-fed pigs

BACKGROUND: Reducing neointima formation and atherosclerosis are key goals in preventing late vein graft failure. Although pharmacologic and mechanical solutions have been proposed, the demonstration that these influence both aspects of vein graft pathology have been lacking. Supporting grafts externally with an oversized, highly porous polyester stent dramatically reduces neointima formation in normocholesterolemic pigs. However, its effects in the presence of hypercholesterolemia are unknown. METHODS: We compared wall thickening, cholesterol concentration, foam-cell formation, and the expression of the leukocyte adhesion molecule vascular cell adhesion molecule 1 after 3 months in stented and unstented saphenous vein interposition grafts into the carotid arteries of pigs fed cholesterol to cause modest hypercholesterolemia (11.2 +/- 1.2 mmol/L). RESULTS: Stenting reduced neointima formation from 5.6 +/- 0.4 to 1.2 +/- 0.2 mm(2) (n = 7; P <.00002, paired t test) and graft cholesterol concentration from 4.7 +/- 1.2 to 2.1 +/- 1.3 mg/g wet weight (P <.02). Foam cells were observed in unstented grafts (mean, 1.5% +/- 0.5% of all cells) but never in stented grafts. Vascular cell adhesion molecule 1 was strongly expressed in 53% +/- 8% of intimal and medial cells in unstented grafts but was weakly expressed in only 19% +/- 3% (n = 4, P <.05) of stented grafts. CONCLUSIONS: We conclude that external stenting with polyester favorably influences both neointima formation and early atherosclerosis, both of which are key aspects of vein graft disease, and that decreased expression of vascular cell adhesion molecule 1 is part of the underlying mechanism.     

Early biomechanical changes in lower extremity vein grafts--distinct temporal phases of remodeling and wall stiffness

BACKGROUND: The geometric and biomechanical changes that contribute to vein graft remodeling are not well established. We sought to measure patterns of adaptation in lower extremity vein grafts and assess their correlation with clinical outcomes. METHODS: We conducted a prospective, longitudinal study of patients undergoing infrainguinal reconstruction with autogenous conduit. In addition to standard duplex surveillance, lumen diameter (of a defined index segment of the conduit) and pulse wave velocity (PWV) were assessed by ultrasound imaging at surgery and at 1, 3, and 6 months postoperatively. Graft dimensions and wall stiffness were correlated with clinical outcomes. RESULTS: There were 92 patients and 96 limbs in this study. On average, vein graft lumen diameter increased during the first month of implantation from 0.37 +/- .01 cm to 0.45 +/- 0.02 cm (mean +/- SEM; P = .002), representing a relative change of +21.6% (median +/- 14%; range, -31 to +67%) during this period. Of the entire cohort, 72% of grafts demonstrated appreciable dilation of the index segment during the first month. Index segment lumen diameter did not change appreciably beyond 1 month, with the notable exception of arm vein conduits, which showed continued tendency to dilate. PWV increased during the first 6 months (17.2 +/- 1.2 m/s to 23.2 +/- 2.4 m/s; P = .008), reflecting a nearly 40% increase in conduit stiffness (2.0 +/- .6 Mdynes/cm to 3.3 +/- .8 Mdynes/cm, P = .01). The greatest relative increase (25%) in PWV occurred from months 1 to 3. Loss of primary patency occurred in 24 cases (19 revisions, 5 occlusions), with a mean reintervention time of 7.6 months. Grafts that demonstrated early positive remodeling (lumen dilatation) had a trend of increased primary patency (P = .08, log rank). Among the grafts that failed, a trend was noted toward greater wall stiffness at 1 month, 2.7 vs 1.5 Mdynes (P = .08). CONCLUSION: Vein graft remodeling appears to involve at least two distinct temporal phases. Outward remodeling of the lumen occurs early, and wall stiffness changes occur in a more delayed fashion. Early outward remodeling may be important for successful vein graft adaptation.     

Association of smooth muscle cell phenotypic modulation with extracellular matrix alterations during neointima formation in rabbit vein grafts.

PURPOSE: To clarify the mechanisms of structural changes underlying vein graft stenosis that limits efficacy of bypass grafting operation, we examined the accumulation and distribution of various extracellular matrix (ECM) components during neointima formation in rabbit vein grafts and analyzed their correlation with proliferation and phenotypic modulation of smooth muscle cells (SMCs). METHODS AND RESULTS: An autologous external jugular vein graft was transplanted into the carotid artery in 25 rabbits. After the restoration of blood flow, the graft was markedly dilated. Medial SMCs in the graft appeared to be injured, and they began to proliferate at day 4 and subsequently migrated and formed the neointima at day 7. The neointima observed at days 7 and 14 contained ECM components, including type I collagen, heparan sulfate, and chondroitin sulfate, and the intimal SMCs were phenotypically modulated from the differentiated-type (SM2-positive and SM embryonic-negative) to the dedifferentiated-type (SM2-negative and SM embryonic-positive) as determined with immunostainings for myosin heavy chain isoforms. The intimal SMC proliferation was maximal at 2 weeks and then decreased rapidly. However, the neointima continued to thicken thereafter throughout the 6-month period of the experiment, and ECM accumulation, such as type I collagen and decorin, a small dermatan sulfate proteoglycan, was a prominent feature observed in the hypocellular region of the deep intima from 2 months after the transplantation. The phenotype of the intimal SMCs gradually returned to the differentiated-type from the deep intima after 2 months, but a small number of the intimal SMCs remained in the dedifferentiated phenotype even at 6 months after the operation. CONCLUSION: The neointima in the vein graft was formed initially by means of migration and proliferation of the phenotypically modulated, dedifferentiated-type SMCs and continued to thicken by means of sustained ECM accumulation, including type I collagen and decorin, in association with the prolonged presence of the dedifferentiated-type SMCs. These chronologic features in cell kinetics and ECM accumulation may contribute to the frequent occurrence of graft wall thickening that occurs in the vein grafts.     

可降解壳聚糖血管外周支持与静脉移植物早期结构的变化

目的　探讨可降解壳聚糖血管外周支持 (CES)对静脉移植物 (VG)早期结构变化的影响 ,为临床提高VG通畅率提供新的治疗方法。　方法　将兔右颈内静脉端 端吻合于同侧颈总动脉建立静脉移植模型 ,以有无CES干预分为支架组与无支架组 (每组 2 4只兔 )。术后 1、2、4周分别切除移植静脉 ,计算机图像分析系统测量和计算内膜、中膜厚度和面积 ,免疫组织化学法检测增殖细胞核抗原 (PCNA)指数观察平滑肌细胞增殖程度。　结果　CES在术后 2周开始降解。支架组VG ,术后 1～ 2周内膜、中膜的厚度和面积、PCNA指数在术后 1周轻度增加 ,1～ 2周维持稳定 ,术后 2周分别为(2 6 3± 3 7) μm、(2 6 0± 1 9) μm、(0 5 6± 0 0 8)mm2 、(0 34± 0 0 5 )mm2 与 (11 5± 2 1) % ,明显低于无支架组的 (5 6 4± 9 4 ) μm、(47 6± 4 9) μm、(1 17± 0 0 8)mm2 、(1 2 0± 0 4 3)mm2 与 (36 6± 2 9) % (P <0 0 1) ;术后 4周虽然又增加 ,分别为 (31 7± 1 6 ) μm、(31 7± 1 6 ) μm、(0 72± 0 12 )mm2 、(0 4 2± 0 0 6 )mm2 与 (13 4± 1 2 ) % ,但仍低于无支架组的 (76 8± 8 0 ) μm、(5 7 4± 9 5 ) μm、(1 2 7± 0 17)mm2 、(1 2 7± 0 0 9)mm2 与 (16 8± 2 2 ) % (P <0 0 5 )。结论　CES     

32 P局部照射对移植静脉内膜平滑肌细胞增殖与凋亡的影响

目的 研究β射线局部照射对自体移植静脉内膜平滑肌细胞（VSMC）增生与凋亡的影响及可能机制。方法 建立80只大鼠自体静脉移植模型,随机分成^32P局部照射组、对照组,每组按3、7、14、28d随机分成4个亚组、每亚组10只。取材固定,弹力纤维染色,增殖细胞核抗原、p53、bcl-2、bax免疫组化测定,TUNEL法检测静脉平滑肌细胞的凋亡,计算机图象分析仪测量移植血管内膜厚度,计算细胞增殖及凋亡百分化。结果 术后2组移植静脉段的内膜平均厚度：7、14、28d,照射组明显 于对照组（t＝15．694,P＜0．05）;7、14d照射组VSMC增殖较对照组受到明显抑制（t＝60．157,P＜0．01）。凋亡指数14d照射组高于对照组（t＝56．176,P＜0．01）。p53的表达,2组间差异无显著性意义（t＝0．473,P＞0．05）,bax与bcl－2的表达,14d照射组高于对照组（t＝9．783,P＜0．05）。结论 ^32P局部照射可以抑制自体移植静脉的内膜增生及VSMC的增殖,促进VSMC的凋亡,可能是通过bax、bcl－2基因的表达实现的。     

大鼠自体静脉移植后内膜增生与细胞外基质堆积的研究

目的:研究静脉移植术后内膜增生(IH)中细胞基质(ECM)堆积的发生、发展及与平滑肌细胞(SMC)增殖的关系.方法:将大鼠一段颈外静脉桥接移植入颈总动脉,运用组织切片的特殊染色及免疫组化方法,观察术后1天至24周移植静脉的IH中,Ⅰ型胶原(ColⅠ)、Ⅱ型胶原(ColⅢ型)及SMC结蛋白(D_m)的变化.结果及结论:术后2周,IH中开始出现胶原的堆积,术后12周,IH中胶原含量达最大值并自此保持稳定不变,术后24周IH主要由细胞外基质组成;术后2周,IH中SMC的D_m开始表达,表明SMC的表型开始由收缩型向分泌型改变,术后6周,D_m达最大值,表明此时分泌型SMC最多,SMC可能是分泌细胞外基质的间质效应细胞.     

低剂量β-射线预防自体移植静脉内膜增生和狭窄的实验研究

目的 观察不同剂量^32P照射对兔自体移植静脉（AVG）内膜增生和狭窄的预防作用。方法 用苏木素-伊红（HE）染色、增殖细胞核抗原（PCNA）1免疫组织化学染色和计算机图像分析等方法观察每平方厘米25.9、51.8、103.6和207.2MBq/cm^2^32P照射30min后AVG内膜面积、平滑肌细胞（SMC）增殖和管腔相对丢失率,并与卡托普利治疗效果比较。结果 207.2MBq/cm^2和103.6MBq/cm^2组无明显新生内膜形成,但血管结构,细胞大量坏死;51.8MBq/cm^2组少量新生内膜形成,血管结构完整,内膜面积、SMC增殖和管腔丢失明显低于对照组和卡托普利治疗组;25.9MBq/cm^2组各指标与对照组及卡托普利组差异无显著性。结论 低剂量^32P照射（51.8MBq/cm^2,30min)可有效抑制AVG内膜增生和狭窄,且作用优于卡托普利。     

Controlled release of small interfering RNA targeting midkine attenuates intimal hyperplasia in vein grafts

OBJECTIVE: Intimal hyperplasia is a major obstacle to patency after vein grafting. Despite of a diverse array of trials to prevent it, a satisfactory therapeutic strategy for clinical use has not been established. However, sufficient inhibition of early stages of intimal hyperplasia may prevent this long-term progressive disease. Midkine (MK) is a heparin-binding growth factor that was originally discovered as the product of a retinoic acid-responsive gene. We previously demonstrated that MK-deficient mice exhibit a striking reduction of neointima formation in a restenosis model, which is reversed on systemic MK administration. In this study, we evaluated a strategy of using small interfering RNA (siRNA) targeting MK as a therapy for vein graft failure. METHODS: We first made a highly effective siRNA to rabbit MK. Jugular vein-to-carotid artery interposition vein grafts, which are applied to a low flow condition, were made in Japanese white rabbits. Small interfering RNA mixed with atelocollagen was administrated to the external wall of grafted veins. Cy3-conjugated stabilized siRNA was used to confirm its stability and successful transfer into the vein graft wall. Neointimal hyperplasia was evaluated 4 weeks after the operation. The proliferation index and leukocyte infiltration were determined. RESULTS: MK expression was induced and reached the maximum level 7 days after operation. Fluorescence of Cy3-labeled siRNA could be detected in the graft wall even 7 days after operation. Knockdown of the gradually increasing expression was achieved by perivascular application of siRNA using atelocollagen. The intima-media ratio and the intima thickness at 28 days after grafting were both reduced >90% by this treatment compared with controls. This phenomenon was preceded by significant reductions of inflammatory cell recruitment to the vessel walls and subsequent cell proliferation in MK siRNA-treated grafts. CONCLUSIONS: These results suggest that midkine is a candidate molecular target for preventing vein graft failure. Furthermore, for clinical applications of siRNA, a single intraoperative atelocollagen-based nonviral delivery method could be a reliable approach to achieve maximal function of siRNA in vivo. This strategy may be a useful and practical form of gene therapy against human vein graft failure.     

Transforming growth factor-beta1 antisense treatment of rat vein grafts reduces the accumulation of collagen and increases the accumulation of h-caldesmon

BACKGROUND: The main cause of occlusion and vein graft failure after peripheral and coronary arterial reconstruction is intimal hyperplasia. Transforming growth factor beta-1 (TGF-beta1) is a pleiotropic cytokine known to have powerful effects on cell growth, apoptosis, cell differentiation, and extracellular matrix synthesis. METHODS: To investigate the role of TGF-beta1 in intimal hyperplasia, we used adenovirus to deliver to superficial epigastric vein messenger RNA (mRNA) antisense to TGF-beta1 (Ad-AST) or the sequence encoding the bioactive form of TGF-beta1 (Ad-BAT). Infection with "empty" virus was used as a control (Ad-CMVpLpA). The treated vein was then used for an interposition graft into rat femoral artery. Grafts were harvested at 1, 2, 4, and 12 weeks and formalin-fixed for histologic studies or placed in liquid nitrogen for mRNA studies. RESULTS: Ad-AST treatment resulted in an overall reduction of TGF-beta1 expression (P = .001), and Ad-BAT treatment resulted in an overall increase in TGF-beta1 expression (P = .007). Histologic analysis showed Ad-AST caused reduced collagen build up in the neointima at 12 weeks (P = .0001). Immunohistochemical staining for h-caldesmon at 12 weeks indicated Ad-AST increased smooth muscle cells throughout the vessel wall compared with Ad-CMVpLpA (P = .0024) or Ad-BAT (P = .04). Ad-AST also resulted in reduced CD68-positive cells in the media/adventitia (P = .005 vs Ad-CMVpLpA, P = .01 vs Ad-BAT). To further understand how Ad-AST was influencing the build up of collagen, we performed quantitative polymerase chain reaction on complimentary DNA (cDNA) from homogenates of the vein grafts. Tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) was increased at 1 week by Ad-BAT (P = .048 vs Ad-CMVpLpA) and decreased by Ad-AST at all time points (P 相似文献   

Endothelialization of microporous polytetrafluoroethylene grafts in the infrarenal aorta and caval vein of the rat.

To study healing and endothelialization of vascular grafts, microporous polytetrafluoroethylene (PTFE) prostheses 2 mm in inner diameter and 5 mm long were implanted into the infrarenal aorta or caval vein of the rat. Patency was assessed in six rats from each group at days 3, 7, 14, 28, and 56 after implantation. Four grafts were occluded, two in the aorta (56 days) and two in the caval vein (3 and 14 days). The prostheses were examined via scanning electron and light microscopy for evaluation of endothelialization. At 3 days, the inner surface of the aortic grafts was covered by a plasma proteinaceous layer and that of the caval vein grafts by a thin mural thrombus. Endothelial cells then migrated from aorta/caval vein edges over the graft. At 14 days, the caval vein grafts were completely re-endothelialized, and, at 28 days, the mural thrombus in these grafts was replaced by neointima. In contrast, endothelialization of the aortic grafts had advanced only 1 mm at about 56 days, never forming a complete endothelial layer. We conclude that endothelialization of microporous PTFE prostheses is more rapid and complete in the caval vein than in the aorta of the rat.     

The effect of rigid external support on vein graft adaptation to the arterial circulation

In previous experiments vein graft wall thickening stopped when the ratio of lumen radius to wall thickness equaled that of a normal artery. This led us to postulate that wall stress, which this ratio determines, regulates wall structure. To test this hypothesis we studied the effect of decreasing lumen radius and acutely diminishing wall stress with a rigid, external support. Jugular vein grafts were interposed into the carotid artery of rabbits. The proximal half of the grafts was wrapped with a polytetrafluoroethylene graft. Twelve veins received a tight wrap (2.5 or 3 mm diameter) that decreased the graft diameter, and four received a loose wrap (5 mm diameter) that did not. These grafts were fixed by perfusion after 1 day, 11 days, or 12 weeks. Wall thickness was slightly less in all tight-wrap segments. Total cross-sectional wall area, smooth muscle cell volume, and matrix deposition were significantly reduced in tight-wrap segments. These differences were greatest at 11 days. The observation that narrowing and external support of these vein grafts causes reduction of wall area supports the hypothesis that increased wall stress might be an important stimulus for wall thickening.     

A bioabsorbable (polyglactin), nonrestrictive, external sheath inhibits porcine saphenous vein graft thickening

OBJECTIVE: External, nonrestrictive, macro-porous polyester stents prevent neointima formation in porcine vein grafts and have been proposed as a therapeutic approach to the prevention of late vein graft failure. These stents are nonbiodegradable and therefore may promote long-term foreign body problems including infection and inflammation. The effect of external macro-porous biodegradable (polyglactin) sheaths on neointimal and medial thickening in porcine vein grafts was therefore investigated. METHODS: Bilateral saphenous vein-carotid artery interposition grafting was performed in white Landrace pigs (n = 8) with external placement of polyglactin (Vicryl) sheaths (8 mm in diameter) on 1 side, with the contralateral side acting as a control. One month after surgery, grafts were explanted and wall dimensions measured on histological sections using computer-aided planimetry, and an immunocytochemical appraisal was carried out. RESULTS: All grafts were patent at explantation. Polyglactin sheaths significantly reduced intimal thickness, medial thickness, and the percentage of proliferating cells compared with unsheathed controls. There was a pronounced accumulation of macrophages, giant cells, endothelial cells, and microvessels within and surrounding the biodegradable sheath compared with controls. CONCLUSIONS: A nonrestrictive, biodegradable (polyglactin), external sheath reduces medial and intimal thickening in experimental saphenous vein grafts, possibly through inflammatory cell-mediated angiogenesis. If subsequent long-term studies confirm preservation of this beneficial effect, once the sheath biodegrades, this approach may have an advantage over the permanent polyester stent when applied clinically.