移植损伤对移植静脉影响的实验研究

目的探讨移植静脉再狭窄的机制,明确移植损伤对移植静脉的影响。方法健康新西兰大白兔36只,随机选取一侧将股静脉翻转后移植于同侧股动脉缺损(静-动组),另一侧将同等长度股静脉截取后行原位缝合(静-静组),另取正常股静脉作为对照组(取自静-动组移植前静脉的一部分)。均于术后4周取移植静脉段,行HE染色、弹力纤维的维多利亚蓝染色观察移植静脉管壁组织学变化;增殖细胞核抗原(proliferatingcellnuclearantigen,PCNA)免疫组织化学染色观察管壁细胞增殖情况;电镜观察管壁细胞超微结构改变。结果静-静组血管壁中膜平滑肌细胞增殖,但内膜(3.50±0.41μm)、中膜(12.23±1.59μm)厚度无明显变化;静-动组内膜、中膜细胞均增殖,内膜(25.60±3.21μm)、中膜(21.30±2.47μm)厚度较对照组、静-静组均增加,差异有统计学意义(P<0.01)。对照组未见PCNA阳性细胞,静-静组内膜(5.9%±1.3%)、中膜(23.4%±3.4%)PCNA阳性细胞百分比均小于静-动组内膜(16.4%±1.9%)、中膜(36.5%±3.7%),差异有统计学意义(P<0.01)。静-静组透射电镜下可见内皮细胞扁平,游离端有绒毛样突起,细胞排列紧密,中膜平滑肌细胞增殖;静-动组透射电镜下可见内皮细胞增殖明显,增殖的内皮细胞形态不规则,细胞间隙增宽,内膜中可见大量平滑肌细胞,基底膜不完整,中膜平滑肌细胞明显增殖;对照组内皮细胞形态及排列与静-静组相似,只是中膜平滑肌细胞未见增殖。结论静脉移植后可导致血管管壁细胞增殖,如合并血流动力学变化则会发生更严重的细胞增殖和迁移,导致管腔狭窄;减少移植损伤,改善移植静脉的微循环,成为预防移植静脉再狭窄的理论基础之一;静-静移植的动物模型,有助于探寻静脉移植后再狭窄的机制。     

Vein to artery grafts. A quantitative study of revascularization by vasa vasorum and its relationship to intimal hyperplasia.

Iliolumbar vein to iliac artery grafts were placed in 40 rats by microsurgical technique. Groups of animals were perfused with fixative at eight intervals between one and 20 weeks after operation, and sections of the graft and control arteries (the opposite iliacs) were analyzed microscopically. The revascularization of the graft by capillaries commenced within the first postoperative week. The level of vascularity (capillaries per cross-sectional mm2) increased during the first four weeks, maintained a constant level and declined after week 16. The grafts of the 17--20 week group were substantially less vascular than the earlier groups. Intimal thickening commenced at three to four weeks after operation, i.e. during the period of increasing graft vascularity. The mean intimal proportion of the graft was 14% at four to five weeks and at 17--20 weeks was 35% of the cross-sectional area of the graft wall. However, the actual thickness of the intima did not increase significantly with time, rather the whole graft wall tended to become thinner. At 17--20 weeks grafts which showed a high degree of intimal thickening had significantly fewer capillaries within their walls. Quantitative evidence is presented to suggest that the continued growth of the graft intima may not be supported by a similar increase in the number of vasa vasorum. Therefore, it is suggested that the reduced level of vascularity in grafts with hyperplastic intimae may form an ischemic basis for degenerative changes which are known to take place in some long-term grafts.     

Prevention of smooth muscle cell phenotypic modulation in vein grafts: a histomorphometric study.

This is a prospective study of the relationship between graft preparation technique and the subsequent morphologic fate of vein grafts. Paired vein grafts (optimal vs injury prepared) were placed in a canine model and removed over time. Vein grafts intentionally injured by warm saline storage demonstrated endothelial and smooth muscle cell damage. In the acute postimplantation period, platelet adhesion and white cell infiltration of the graft were present. By 7 days, the endothelium had "healed", but the underlying smooth muscle cells had modulated and were of the transitional or synthetic phenotype. This persisted at 30 days, but by 60 days the graft wall had remodeled to a contractile smooth muscle cell phenotype. Changes in the extracellular matrix were greatest at 30 days corresponding to changes in the smooth muscle cell phenotype. None of these injurious responses were noted in optimally prepared, papaverine treated vein grafts. The combined intima and media (lumen to adventitial edge) was measured at baseline and at graft excision with use of digitized graphic techniques. The intimal/medial thickness of injured vein graft walls was always greater than that of pair-matched optimally treated vein grafts (p less than 0.01 analysis of variance). Optimal preparation of vein grafts is effective in minimizing endothelial and smooth muscle cell injury at the time of arterial reconstruction. This preservation of endothelial and smooth muscle cell integrity prevents subsequent morphologic changes associated with the "arterialization response".     

Expression of vascular endothelial growth factor in aortocoronary saphenous vein bypass grafts

Neovascularisation is a prominent feature of long-term aortocoronary saphenous vein bypass grafts but mechanisms involved in the formation of neovessels have not been previously studied. Vascular Endothelial Growth Factor (VEGF) is an important angiogenic factor that induces migration and proliferation of endothelial cells, enhances permeability and modulates thrombogenecity. This study investigated the expression of VEGF in aortocoronary saphenous vein bypass grafts. Aortocoronary saphenous vein bypass grafts with angiographic luminal stenosis of >75% were explanted from 14 patients at redo coronary artery bypass grafting. The grafts demonstrated two distinct forms of graft occlusion: four out of the 14 graft occlusions (29%) resulted from severe hyperplastic transformation of the intima complicated by thrombi attached to the degenerating liminal endothelium; the remaining graft occlusions (71%) were due to the development of atherosclerotic lesions associated with mural thrombosis. Hiperplastically altered intimal segments were practically free of neovascularisation while atherosclerotic-like lesions contained neovessels irregularly distributed throughout. Intimal neovessels were located exclusively in microzones enriched with VEGF-expressing cells and, furthermore, neovascular endothelial cells themselves also displayed VEGF immunopositivity. Double-immunostaining revealed that in areas of neovascularisation, the vast majority macrophages (CD68+) expressed VEGF. Some CD68+ foam cells that surrounded branches of neovascularisation were also VEGF-positive. These findings suggest that VEGF expressed by neovascular endothelial cells and by macrophages may act as a local regulator of endothelial cells functions and may induce intimal neovascularisation in aortocoronary saphenous vein bypass grafts affected by atherosclerosis.     

Vein to artery grafts: a morphological and histochemical study of the histogenesis of intimal hyperplasia.

Failure of vein to artery grafts has been associated with intimal thickening (hyperplasia) and atherosclerosis. Current theories of intimal development, derived from arterial studies, show that smooth muscle cells migrate from the media to the intima after endothelial damage, where they proliferate and produce intimal hyperplasia. However, little is known of the histogenesis of these lesions in vein grafts. Experimental ilio-lumbar vein to iliac artery autografts were placed in 52 rats and analysed by light microscopy and histochemistry from 2 to 140 days after surgery. On day 2 the grafts and adjacent artery were severely damaged. Regeneration of damaged arterial tissue occurred by day 5, and thickening was already evident in the arterial intima. The intimal cells had histochemical characteristics of smooth muscle. By day 15, this hyperplastic intima was continuous across the anastomosis from the artery into the graft. After day 28 a wedge of densely packed cells was present in the vein graft intima for approximately 2 mm into the graft. By day 140, all the grafts were fully re-endothelialized. Intimal hyperplasia was present in all grafts and varied in thickness from 3 to 20 cells. Histochemical staining of these cells showed them to be of smooth muscle origin.     

CD40 co-stimulatory molecule expression by dendritic cells in primary atherosclerotic lesions in carotid arteries and in stenotic saphenous vein coronary artery grafts.

We have previously identified dendritic cells in the intima of human large arteries and stenotic vein coronary bypass grafts. The mechanisms by which these dendritic cells might regulate immune responses in atherosclerotic lesions and stenotic vein grafts are unknown. The aim of the present study was to investigate whether dendritic cells in carotid plaques and in stenotic aortocoronary vein grafts express an immunoregulatory molecule CD40.Segments of wall from eight carotid arteries and three stenotic aortocoronary saphenous vein grafts were obtained at operation. CD40+ cells were detected in all specimens of both occluded and stenotic grafts and carotid plaques. Although CD40+ cells of various cell types were intermingled in most areas within the plaques and stenotic grafts, there were sites where CD40+ cells were located in small groups. Consecutive sections demonstrated that a small population of CD40+ cells stained positively for S100. These CD40+/S100+ cells were clustered within the intima but were also found in the media and adventitia. This suggests that dendritic cells, which accumulate within vessels affected by atherosclerosis and graft disease, express CD40 co-stimulatory molecule. The expression of CD40 molecule on the dendritic cells may be important in regulating T cell responses within atherosclerotic plaques and stenotic vein grafts.     

VEIN TO ARTERY GRAFTS: A MORPHOLOGICAL AND HISTOCHEMICAL STUDY OF THE HISTOGENESIS OF INTIMAL HYPERPLASIA

Failure of vein to artery grafts has been associated with intimal thickening (hyperplasia) and atherosclerosis. Current theories of intimal development, derived from arterial studies, show that smooth muscle cells migrate from the media to the intima after endothelial damage, where they proliferate and produce intimal hyperplasia. However, little is known of the histogenesis of these lesions in vein grafts. Experimental ilio-lumbar vein to iliac artery autografts were placed in 52 rats and analysed by light microscopy and histochemistry from 2 to 140 days after surgery. On day 2 the grafts and adjacent artery were severely damaged. Regeneration of damaged arterial tissue occurred by day 5, and thickening was already evident in the arterial intima. The intimal cells had histochemical characteristics of smooth muscle. By day 15, this hyperplastic intima was continuous across the anastomosis from the artery into the graft. After day 28 a wedge of densely packed cells was present in the vein graft intima for approximately 2 mm into the graft. By day 140, all the grafts were fully re-endothelialized. Intimal hyperplasia was present in all grafts and varied in thickness from 3 to 20 cells. Histochemical staining of these cells showed them to be of smooth muscle origin.     

Adventitial remodeling with increased matrix metalloproteinase-2 activity in a porcine arteriovenous polytetrafluoroethylene grafts

BACKGROUND: We hypothesized the source of early proliferating cells contributing to venous stenosis formation in a porcine hemodialysis grafts is the adventitia and media, and migration of these cells is greatest within the first two weeks following graft placement, resulting in increased matrix metalloproteinase-2 (MMP-2) activity. METHODS: Polytetrafluoroethylene grafts from the iliac artery to the ipsilateral iliac vein were placed in 23 pigs and 5-Bromo-2'-deoxyuridine (BrdU) was given at 24 and 48 hours after surgery to assess cell proliferation and migration. Angiography and magnetic resonance angiography was performed. Animals were euthanized on day three (N= 6), day seven, (N= 5), day 14 (N= 6), and days 19 to 26 (N= 6) after graft placement, and stenotic tissue and unaffected contralateral iliac vein were removed for zymography and immunostaining. RESULTS: Migration of cells derived from the adventitia and media peaked at day 14. Adventitial diameter of the stenotic vein decreased, while the intima to media ratio increased. MMP-2 activity peaks at day seven in the adventitia and days 19 to 26 in the intima. CONCLUSION: These results confirm our hypothesis that the source of cells resulting in venous stenosis formation is derived from the adventitia and media, with cell migration being greatest within the first two weeks after graft placement with translocation of these cells into the intima at four weeks. MMP-2 activity peaks at day seven in the adventitia and again at days 19 to 26 in the intima. A key to limiting venous stenosis formation may lie in inhibiting MMP-2 by adventitial and medial targeting.     

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.     

Histologic, morphometric, and biochemical evolution of vein bypass grafts in a nonhuman primate model. I. Sequential changes within the first three months

The objective of this study was to define the histologic and morphometric evolution that accompanies the increase in cholesterol content of vein bypass grafts in a nonhuman primate model. Cephalic vein grafts were interposed bilaterally in the femoral arteries of 15 stump-tailed macaque monkeys (Macaca arctoides), which were fed a diet that sustains plasma cholesterol levels of approximately 225 mg/dl. Grafts were excised from five animals for analysis on each of postoperative days 3, 7, 14, 30, 60, and 90. Cholesterol content increased from 69 +/- 24 micrograms/100 mg (mean +/- standard deviation) in ungrafted vein to 473 +/- 122 micrograms/100 mg in grafts 90 days after implantation (p less than 0.05). By stepwise regression analysis, cholesterol content was best predicted by abundance of foam cells (r2 = 0.82). Intima comprised 13% +/- 5% of the total cross-sectional area of the wall in ungrafted vein and 59% +/- 11% at day 90 (p less than 0.001). With cholesterol content excluded from the stepwise regression, intimal area was best predicted by the presence of foam cells (r2 = 0.39). There was consistently an increase in the prevalence of polymorphonuclear leukocytes on the luminal surface and in both the intima and media during the first 14 days after grafting. Vasa vasorum, which were always present in ungrafted vein, were sparse at 3 days but reappeared by day 7. Medial fibrosis occurred in grafts, and in the 30- to 90-day interval it was directly correlated with the number of adventitial vasa vasorum present (r = 0.64, p less than 0.05). Immunohistochemistry revealed prominent staining for both platelet factor VIII and fibronectin during the first month, with a gradual decline in staining intensity thereafter. The evolution of changes in vein bypass grafts documented in this report are in general agreement with graft changes observed in humans and support the validity of our model in evaluating the histologic correlates of increased graft cholesterol content.     

Angiographic studies of atherosclerotic changes in coronary vein grafts after operation]

A total of 230 vein grafts were studied angiographically in 116 unselected survivors of 260 coronary bypass operations performed from May 1977 through October 1989 in order to investigate atherosclerotic changes in coronary vein grafts after operation. These patients were divided into three groups according to the interval from operation to angiography. In group A (30 patients) the interval was less than one year (mean interval 8.2 months), in group B (73 patients) from one to five years (mean interval 19.2 months) and in group C (13 patients) more than 5 years (mean interval 96.6 months). Fifty-five vein grafts were in group A, 153 vein grafts in group B and 22 vein grafts in group C. The graft patency rate of each group was 83.6%, 89.5% and 90.9% respectively (N.S.). To classify angiographic appearances we believe to be caused by atherosclerosis, we devised a grading system. Category I indicated that the graft outline was completely smooth without any irregularity; Category II indicated that less than 50% of the estimated surface area of the graft intima was irregular; Category III indicated that more than 50% of the intima was involved. Significant stenosis indicated narrowing reducing the lumen to less than 50% of the graft. Of the 203 patent grafts 181 grafts (89%) were in Category I, 22 grafts (11%) in Category II, but no graft in Category III. In group A of the 46 patent grafts 45 grafts (98%) were classified as Category I and 1 graft (2%) was classified as Category II.(ABSTRACT TRUNCATED AT 250 WORDS)     

Biologic degeneration of vein grafts after thrombotic occlusion: thrombectomy within 3 days results in better indices of viability

OBJECTIVES: To clarify the mechanism for poor patency of vein grafts after thrombectomy and the time limit for successful salvage operation, we investigated the time course of biologic degenerative changes in thrombosed vein grafts.Materials and methods The right femoral artery was replaced with a femoral vein graft in 25 mongrel dogs. After 3 months, grafts were explanted in 5 dogs (control grafts), and the remaining 20 dogs underwent femoral artery ligation to create a thrombosed graft. Of the 20 grafts, 5 were explanted at 3 days after ligation (group I-3) and 5 were explanted at 5 days after ligation (group I-5). Of the remaining 10 grafts, 5 underwent thrombectomy at 3 days after ligation (group II-3) and 5 underwent thrombectomy at 5 days after ligation, and were reimplanted into the left femoral artery, then explanted 28 days after reimplantation. The grafts were assessed with immunohistochemistry and prostaglandin (PG) I(2) assay (6-keto-PGI(1alpha)). RESULTS: Of the 25 grafts, occlusion recurred in 3 in group II-5 within 28 days after reimplantation. There were significant differences between group I-5 and group I-3 or control grafts for percentage of areas positive for alpha-actin, total number of cells per field, and proliferating cell nuclear antigen (PCNA)-positive cells in layer of thickened intima and atrophied media (I/M), and for total cell and PCNA- positive cell numbers per field in the adventitia. Mean 6-ketoPGF(1alpha) was 40 +/- 14.1 pg/mg/min in control dogs, 84 +/- 18.9 pg/mg/min in group I-3, and 15.4 +/- 7.7 pg/mg/min in group I-5, demonstrating a significant reduction in group I-5 (P =.009). CONCLUSION: Graft wall cell viability and PGI(2) production in thrombosed vein grafts are well preserved for up to 3 days. Therefore graft salvage operations no later than 3 days after thrombotic occlusion may provide acceptable long-term patency of salvaged grafts.     

Qualitative microscopy of implanted vein grafts. Effects of graft integrity on morphologic fate.

This is an investigation of the relationship between graft preparation techniques and the subsequent fate of vein grafts. Vein grafts intentionally injured by warm saline storage demonstrated endothelial and smooth muscle cell damage. In the acute postimplantation period, platelet adhesion/activation and white cell infiltration were present. By 7 days the endothelium had "healed," but the underlying smooth muscle cells had modulated and were of the synthetic phenotype. This persisted at 30 days, but by 60 days the graft wall remodeled with smooth muscle cells that were of the contractile phenotype, with an organized extracellular matrix. None of these injurious responses were noted in optimally prepared papaverine-treated vein grafts. Optimal preparation of vein grafts is effective in minimizing endothelial and smooth muscle cell injury before and after arterial reconstruction. Prevention of vein graft injury during harvesting prevents the morphologic changes characteristic of the "arterialization response."     

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.     

Development of a method to prevent degenerative changes of the vein graft for arterial reconstruction]

Autologous vein graft is frequently used for arterial reconstruction in vascular surgery. Its' long-term patency rate, however, is low because of the degenerative changes of the vein wall. Of the basis of our hypothesis that the degenerative changes are mainly caused by an over-distension of vein wall in arterial system, in this study, autologous vein grafts of rabbit (N = 56) were implanted in the carotid arteries. To prevent overdistension, some of the grafts were covered with prosthesis which was made of microporous, compliant biodegradable polyurethane and were compared with those without prosthesis. The integrity of the architecture of the vein wall covered with prosthesis was well preserved at 6 weeks after implantation, where the biodegradation of prosthesis induced an optimal arterialization of the vein grafts. The results indicate that this method may prevent the degenerative changes of vein wall such as fibrosis and intimal hyperplasia, which would cause poor long-term patency of vein graft used for arterial reconstruction.     

The evolution of morphologic and biomechanical changes in reversed and in-situ vein grafts.

A comparative study of experimental reversed (RV) and in-situ (INS) vein grafts with respect to the evolution of morphologic and compliance characteristics was done in a canine model. In addition, the compliance characteristics in a series of human INS vein grafts were recorded as a function of time after operation. At 6 months after implantation, all experimental grafts displayed well-developed intimal hyperplasia. There was no significant difference in either absolute intimal thickness (INS 0.133 +/- 0.09 mm vs. RV 0.085 +/- 0.06 mm; NS) nor in the percentage of the total wall thickness occupied by the intima when experimental INS grafts were compared with RV grafts after 6 months. Similarly, compliance values of INS and RV vein grafts were similar at all time intervals examined up to 6 months after operation. Thirty-three human INS vein grafts had a mean compliance value of 1.74 +/- 0.72 (percent radial changes per mmHg X 10(-2) at a median postoperative interval of 14 weeks. This value did not differ significantly from those measured in the INS vein grafts. Although all vein grafts examined retained their native viscoelastic properties, this study suggests that functioning human INS vein grafts are less compliant than previously suspected on the basis of prior ex-vivo and clinical studies of RV saphenous vein grafts. The purported clinical superiority of the INS vein graft cannot be explained on the basis of superior biomechanical performance or failure to develop intimal hyperplasia.     

Initial histopathology of the autovein graft in late occlusion after arterial reconstruction

Five patients developed local stenosis of autologous vein grafts implanted for femoro-popliteal arterial occlusive lesions. This stenosis occurred in the vein grafts 2 months to 5 years after the initial operation. Histopathologic study revealed that the stenotic segments had a thickened intima with a prominent proliferation of smooth muscle cells associated with fibrous extracellular matrix. There were no findings showing deposition of mural thrombi, as has heretofore been reported. The intimal thickening due to excessive fibromuscular proliferative response of the vein graft may possibly play an important role in the development of late graft occlusion.     

Ultrastructural evidence of the effects of shear stress variation on intimal thickening in dogs with arterially transplanted autologous vein grafts

Based on our findings that changes in wall shear stress, not the rate of blood flow, were the main hemodynamic factor related to intimal hyperplasia of autologous vein grafts, we further investigated the effect of wall shear stress variation on sequential ultrastructural changes in the intimal hyperplasia of arterially transplanted autovein grafts, using canine models. As noted, wall shear stress variation (tau-variation) could be defined by the variation in wall shear stress within a cardiac cycle, using a desktop flow waveform analyzer. In Group I, which had a high flow rate of 78.4 +/- 4.6 ml/min and low tau-variation of 36.1 +/- 2.2 dynes/cm2, intimal hyperplasia was significant. Ultrastructurally, there was a marked transformation of intimal smooth muscle cells to secretory cells 2 to 4 weeks after implantation. The surface of the intima was lined with modified smooth muscle cells at 2 weeks after implantation. In Group II, which had a low flow rate of 5.6 +/- 2.2 ml/min and normal tau-variation value (174.6 +/- 13.0 dynes/cm2), intimal hyperplasia was minimal, and there were several layers of contractile type smooth muscle cells, with characteristic myofibrillae. The surface of the intima was lined with endothelial cells at 2 weeks after implantation. These findings suggest that, in regions of low wall shear stress variation, intimal smooth muscle cells of autovein grafts may well become secretory cells, and enhanced platelet adherence could occur during early intimal repair, causing intimal hyperplasia to develop.     

去端肽胶原介导小干扰RNA抑制大鼠静脉移植物内膜增生

目的 评价局部应用组织因子小干扰RNA(siRNA)抑制静脉移植物内膜增生的效果.方法 SD大鼠120只,体重260～300 g,建立颈外静脉一颈总动脉移植模型后随机分成4组,每组30只.A组:去端肽胶原-TF StealthTMSelect RNAi组.B组:去端肽胶原-TF SteaLtHTM RNAi阴性对照组,C组:去端肽胶原组,D组:空白对照组.使用去端肽胶原-siRNA混合物涂抹于静脉移植物周围,免疫印迹检测术后1、3、7、14、28 d管壁组织因子蛋白表达,免疫组织化学法检测术后3 d管壁组织因子表达,同时检测术后14 d管壁增殖细胞核抗原指数,计算术后28 d新生内膜厚度.去端肽胶原-BLOCK-iTTM荧光寡核苷酸平行实验组12只,分别于术后3、7 d检测管壁BLOCK-iTTM寡核苷酸荧光确认其稳定性和转染效率.结果 平行实验组静脉移植物可观察到BLOCK-iTTM绿色荧光并持续到术后7 d.术后3 d A组siRNA有效抑制管壁TF蛋白表达,术后14 d A组与其他组比较增殖细胞核抗原指数明显减少(P＜0.05),术后28 d A组新生内膜厚度明显低于其他组(P＜0.05).结论 去端肽胶原携带siRNA可有效下调静脉移植物组织因子表达,抑制内膜增生.     

Expression of apoptosis-related proteins and structural features of cell death in explanted aortocoronary saphenous vein bypass grafts.

This study aimed to investigate the features of cell death occurring in aortocoronary saphenous vein bypass grafts. Human aortocoronary saphenous vein bypass grafts with angiographic luminal stenosis of > 75% were explanted from 14 patients at redo coronary artery bypass grafting. Proteins associated with apoptotic pathways were identified immunohistochemically using antibodies to Bcl-2, Fas, BAX, p53 and CPP32. Cells undergoing DNA fragmentation were identified by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL). DNA synthesis was investigated using the antibody to proliferating cell nuclear antigen (PCNA). Ultrastructural features of cell death were examined by electron microscopy. Anti-apoptotic (Bcl-2) and pro-apoptotic (Bax, p53, CPP32 and Fas) proteins were expressed throughout the graft wall, but marked differences in the characteristics of cell death were noted between atherosclerotic and non-atherosclerotic areas of the intima. In atherosclerotic areas, pro-apoptotic proteins were widely expressed, but ultrastructural analysis failed to identify cells showing typical features of apoptosis. In these areas, necrotic cells were frequently observed, with negative correlation of Bcl-2 expression with TUNEL. Pro-apoptotic proteins showed no correlation with TUNEL. In contrast, in non-atherosclerotic areas of vein grafts, the expression of both anti-apoptotic (Bcl-2) and pro-apoptotic proteins (p53, Bax and CPP32) correlated with TUNEL. In atherosclerotic areas, non-atherosclerotic intimal areas, and in the underlying media, the numbers of TUNEL+ cells correlated with PCNA positivity. Ultrastructurally, apoptotic bodies and features of necrosis were observed in non-atherosclerotic areas of grafts. The present observations indicate that in atherosclerotic areas, cell death occurs mainly by necrosis, while in non-atherosclerotic areas, cell death occurs by both necrosis and apoptosis. An imbalance between DNA fragmentation and DNA synthesis may contribute to graft instability and failure.