Intimal changes in the cephalic vein of renal failure patients before arterio-venous fistula (AVF) construction.

Native cephalic vein remains the superior dialysis conduit, even thirty years after it was first described. However, up to 37% of hemodialysis patients develop progressive stenosis in the venous circuit of arterio-venous fistula (AVF), which may later cause thrombosis and occlusion. To study the pre-existing morphological changes in the wall of the cephalic vein before AVF construction, we collected 23 cephalic vein specimens from 3 normal, young trauma and twenty renal failure patients. The samples were collected at the time of vascular repair in the first group and AVF construction in the second group. Sections were prepared and stained for both light and transmission electron microscopy (TEM) examination. Compared with normal cephalic vein, all pre-access cephalic veins showed thickening of the wall and intimal hyperplasia. Other changes were loss of internal elastic lamina in 9 (45%) patients, loss of endothelial cell layer in 6 (30%), inflammatory cell infiltration of the wall in 5 (25%), mural calcification in 3 (15%) and telangiectasia in 2 (10%). Other ultrastructural changes observed were intimal hypertrophy, degeneration and loss of the endothelial cells, degeneration and fraying of smooth muscle cells (SMCs) and loss of wall components into the lumen. In conclusion, most of the apparently normal cephalic veins of renal failure patients showed morphological abnormalities at the time of AVF construction, which may well influence the outcome of shunts in terms of future stenosis and failure. It seems likely that the later development of AVF stenosis may be the result of pre-existing disease rather than the direct insult of arterialization.     

Smooth muscle changes in varicose veins: an ultrastructural study.

In order to understand the pathology of varicose veins, we prospectively collected a total of 23 vein specimens both from the normal proximal thigh long saphenous vein (LSV) in 3 young trauma patients and from the unstripped proximal LSV near the sapheno-femoral junction and the distal calf blowouts in 10 primary varicose veins patients. Ultra-thin sections were examined under the transmission electron microscope (TEM). Compared with the normal control LSV, varicose vein sections showed increase in the diameter of the lumen, hypertrophy of the wall and elongation and invagination of the intima. Smooth muscle cells (SMCS) lost their normal fusiform shape and were widely separated by increased amounts of extra-cellular collagen fibers. The cells underwent marked degeneration, vacuolization and disintegration into fiber-like material and small separated fragments. SMCs were seen in the subintimal tissue and some of them were lost into tile lumen. SMCs also showed marked phagocytic activity, engulfing not only collagen and elastic fibers, but also other smooth muscle cells. Although these changes were more marked and advanced in the distal calf blowouts, they were also present in the proximal, clinically non-dilated LSV. In conclusion, SMCs of varicose veins show severe degeneration in both the distal calf blowouts and the proximal, clinically non-varicose LSV. It appears that they both form and phagocytose collagen and elastic fibers and play a major role in the pathogenesis of varicose veins.     

Ultrastructural Changes of the Smooth Muscle in Esophageal Atresia

Esophageal atresia (EA) with or without tracheo-esophageal fistula (TEF) is a relatively rare congenital anomaly. Despite the advances in the management techniques and neonatal intensive care, esophageal dysmotility remains a very common problem following EA/TEF repair. Our current study aimed to describe the most significant ultrastructural changes of the smooth muscle cells (SMCs) trying to highlight some of the underlying mechanisms of esophageal dysmotility following EA/TEF repair. Twenty-three biopsies were obtained from the tip of the lower esophageal pouch (LEP) of 23 patients during primary repair of EA/TEF. Light microscopic examination was performed with hematoxylin and eosin (HE), and Van Gieson’s stains. Ultrastructural examination was done using transmission electron microscopy (TEM). Histopathological examination showed distortion of smooth muscle layer and deposition of an abundant amount of fibrous tissue in-between smooth muscles. Using TEM, SMCs exhibited loss of the cell-to-cell adhesion, mitochondrial vacuolation, formation of myelin figures, and apoptotic fragmentation. There were also plasmalemmal projections and formation of ghost bodies. Interestingly, SMCs were found extending pseudopodia-like projections around adjacent collagen fibers. Engulfed collagen fibers by SMCs underwent degradation within autophagic vacuoles. Degeneration of SMCs and deposition of abundant extracellular collagen fibers are prominent pathological changes in LEP of EA/TEF. These changes might contribute to the pathogenesis of esophageal dysmotility in patients who have survived EA/TEF.     

Structural changes in the tunica intima of varicose veins: a histopathological and ultrastructural study

Many factors have been implicated in the aetiology of varicose veins; however, there is ample evidence implicating that the defect is in the wall of the lower limb veins. In order to know the pathological changes in the tunica intima of varicose veins, the smooth muscle cells (SMCs), collagen and elastin of varicose and control patients were studied by light and electron microscopy. The morphological changes in the SMCs, collagen and elastin point to a possible secretory or phagocytic role of the SMCs in producing abnormal immature collagen or elastin fibres or in modulation of function of SMCs due to excessive production of extracellular matrix (ECM).     

Subnormal shear stress-induced intimal thickening requires medial smooth muscle cell proliferation and migration

Arterial intimal thickening is consisted of predominately smooth muscle cells (SMC). The source of these SMCs and mechanisms response for their changes have not been well cleared. Using a model of rabbit common carotid artery (CCA) shear induced intimal thickening, we sought to identify and describe the source of SMCs in intima. The enlarged CCA 28 days after arteriovenous fistula (AVF) creation was subjected to subnormal wall shear stress (WSS) for 1, 3, and 7 days by closure of the AVF. To determine SMC proliferation, BrdU pulse labeling of SMCs was performed. BrdU-labeled SMCs were tracked over time to further confirm SMC migration. In response to subnormal WSS intimal thickening developed progressively. BrdU-labeled SMCs localized in the subendothelial area. When the BrdU-labeled medial SMCs were tracked 1 day after AVF closure, progenies of these BrdU-incorporated SMCs increased by 4.8-fold with 75% of them in the intima. They were 12-fold increased with 83% in the intima 7 days after. En face examination showed an accumulation of SMCs in internal elastic lamina gap after AVF closure, which later migrated into subendothelial area. In situ hybridization revealed increased TGF-beta1 mRNA expression in intimal SMCs. This study demonstrates that the medial SMCs are the predominant cells in subnormal WSS-induced intimal thickening. Early expression of TGF-beta1 may play an important role in the process of intimal thickening.     

Tissue engineering of small intestinal tissue using collagen sponge scaffolds seeded with smooth muscle cells

In a previously reported attempt to regenerate small intestine with autologous tissues, collagen scaffolds were used without cell seeding or with autologous mesenchymal stem cell seeding. However the regenerated intestine lacked a smooth muscle layer. To accomplish regeneration of a smooth muscle layer, this present study used collagen scaffolds seeded with the smooth muscle cells (SMC) in a canine model. Autologous SMC were isolated from stomach wall and cultured. Two types of scaffolds were fabricated: in SMC (+), cultured SMCs were mixed with collagen solution and poured into a collagen sponge; and in SMC (-), SMCs were omitted. Both scaffolds were implanted into defects of isolated ileum as a patch graft. Animals were euthanized at 4, 8, and 12 weeks; for the last time point, the ileal loop had been reanastomosed at 8 weeks. At 12 weeks, the SMC (-) group showed a luminal surface covered by a regenerated epithelial cell layer with very short villi; however only a thin smooth muscle layer was observed, representing the muscularis mucosae. In the SMC (+) group, the luminal surface was covered completely by a relatively well-developed epithelial layer with numerous villi. Implanted SMCs were seen in the lamina propria and formed a smooth muscle layer. Thus, we concluded that collagen sponge scaffolds seeded with autologous SMCs have a potential for small intestine regeneration.     

Collagen and elastin degradation by matrix metalloproteinases and tissue inhibitors of matrix metalloproteinase in aortic dissection

The degradation of collagen fibrils and elastic fibers in 21 cases of acute aortic dissection (AD) was ultrastructurally and immunohistochemically investigated; and the expression of the catabolic matrix metalloproteinases (MMPs)-1, -2, -3, and -9 and their inhibitors, the tissue inhibitors of matrix metalloproteinase (TIMPs)-1 and -2, was studied. The features of the entry site of the dissection (ES; 21 ascending aortas) were compared with those of fully remote sites (RS; 19 nondissected abdominal aortas) and the ascending aortas from 10 control cases. By electron microscopy, the medial layer at the ES and adjacent intact aortic wall demonstrated spirally thickened collagen fibrils with a typical banding pattern that were almost always colocalized with elastic lamellae, which often exhibited attenuation, fragmentation, or disruption. In addition, the basement membrane surrounding the smooth muscle cells (SMCs) comprising the media was frequently thinned or lost at the ES. These findings were rarely seen at the RS or in the aortas of controls. Immunohistochemically, the expression of MMP-1 was significantly in the cytoplasm of SMCs of both the intima and media at the ES and adjacent intact wall, and significant expression of MMP-2 and -9 was found in SMCs of the intima compared with the RS and controls. Significant expression of TIMP-1 and -2 was demonstrated in the cytoplasm of SMCs at the ES and adjacent intact wall compared with that at the RS and the control specimens. These findings suggest that the degradation of proteins associated with fibrosis and the occurrence of AD are not merely coincident, but rather that AD is induced by alterations of the extracellular matrix caused by changes of SMCs at a segment of the ascending aorta made vulnerable through hemodynamic stress, especially that caused by hypertension.     

Annulo-aortic ectasia

Summary The aortic wall of the human ascending aorta from 44 patients operated on for annulo-aortic ectasia (AAE) was studied. Light microscopy revealed significantly greater cystic change, elastic fragmentation, fibrosis and disappearance of smooth muscle cells in aortic media in AAE than in control specimens taken at autopsy. Occasional aortae, however, were morphologically almost normal. Eight of the patients had Marfan's syndrome. No significant differences were observed between them and the other 36 patients, except for a tendency to have less pronounced fibrosis. There were 9 patients who, in addition to the changes mentioned, had advanced atherosclerosis, and their aortae showed more extensive fibrosis and medial necrosis. Pooling of proteoglycan matrix, degeneration of elastic lamellae, increased amount of collagen and necrosis of smooth muscle cells characterized the electron microscopic findings of 13 patients. The collagen fibers seemed to be of normal shape. In conclusion, changes in annulo-aortic ectasia are characterized by severe cystic medial necrosis. The changes are basically similar in Marfan and non-Marfan patients.     

慢性肾功能衰竭促进小鼠动静脉瘘内膜增生

目的观察慢性肾功能衰竭对小鼠动静脉内瘘术后血管内膜增生的影响及单核细胞趋化蛋白-1(MCP-1)在内膜增生中的作用。方法将24只C57小鼠分为对照组(n=12)与实验组(n=12),实验组行左肾全切及右肾上极动脉结扎,对照组行假手术,术后6周行左侧颈总动脉-颈外静脉端吻合建立动静脉瘘(AVF)模型,AVF术后3周取瘘口静脉端血管组织。观察各组小鼠AVF内膜组织的病理改变及小鼠血液尿素氮(BUN)水平与内膜增生程度的关系;免疫组化法、RT-PCR及Western blot检测各组静脉组织α平滑肌肌动蛋白(α-SMA)、Ki-67、NF-κB及MCP-1的蛋白及mRNA的表达。结果 1)实验组较对照组小鼠血BUN水平明显上升(P0.05),静脉端内膜增生更显著,管腔更狭窄(P0.05)。2)实验组血管增生内膜α-SMA表达明显增加,血管平滑肌细胞(VSMC)增殖显著,NF-κB及MCP-1表达明显上升(均P0.05)。3)MCP-1促进体外培养VSMC增殖。结论慢性肾功能衰竭可明显增高NF-κB及MCP-1表达,从而促进动静脉瘘内膜增生及VSMC增殖。     

Significance of cytomegalovirus infection in the failure of native arteriovenous fistula

High cytomegalovirus (CMV) IgG levels have been identified as a risk factor for arteriovenous fistula (AVF) failure. None of the 68 patents in our study were CMV IgM positive, although 96% were CMV IgG positive. CMV antigens were detected in the radial artery or cephalic vein of 46% of patients who received an AVF. The presence of CMV antigens or high serum CMV IgG levels had no prognostic value for AVF failure.     

Structural identification and characterization of arteries and veins in the placental stem villi

The vascular wall structure in the human full-term placental villi of normal pregnancy was studied by means of light and electron microscopy with an improved technique of perfusion fixation and tissue preparation. We observed 81 sections of stem villi that showed cross-sectional profiles of paired vessels in their center. Both vascular walls contained a large amount of extracellular matrix and no elastic lamina between smooth muscle cells of the media, making identification of the artery and the vein quite difficult at first sight. We then noted that the density of the smooth muscle cell population was always considerably higher in one than the other, and identified the former as artery and the latter as vein on the basis of their connection with larger arteries and veins running on the chorionic plate. Between the paired vessels, the artery had a smaller caliber than the vein, and the ratio of venous to arterial caliber was distributed from 1.0 to 2.5. The thickness of media was usually thicker in the vein than in the artery. Clusters of elastic fibers were found occasionally in the media of arteries and veins, and basement membrane-like materials were associated frequently with the elastic fibers and were distributed widely in the media as well as in the adventitia. In the veins, the smooth muscle cells of the most superficial part of the media contained well-developed rough endoplasmic reticulum and Golgi apparatus, indicating differentiation to secrete extracellular matrices. The present study revealed the difference of wall structure between arteries and veins in the placental stem villi for the first time at the ultrastructural level, and suggested differentiation of venous smooth muscle cells, possibly by some influence from the luminal side.     

Viscoelasticity of the vessel wall: the role of collagen and elastic fibers.

The aortic wall contains collagen fibrils, smooth muscle cells, and elastic fibers as the primary load-bearing components. It is well known that the collagen fibrils bear loads in the circumferential direction, whereas elastic fibers provide longitudinal as well as circumferential support. Stiffening of the vessel wall is associated with loss of elastic tissue and increases in the collagen content: however, little is known about the mechanism of vessel wall stiffening with age. The purpose of this review is to attempt to relate structural changes that occur to the collagen and elastic fibers to changes in the viscoelastic behavior that are associated with aging. Analysis of the viscoelastic mechanical properties of collagen fibrils from tendon, skin, and aortic wall suggest that the collagen fibrils of aortic wall are different than those of other tissues. The elastic spring constant of the collacen fibrils in vessel walls is significantly less than that found in tendon, suggesting that the presence of type III collagen in aortic wall increases the flexibility of the collagen fibrils. Furthermore, it is hypothesized that changes in the interface between collagen fibrils, elastic fibers, and smooth muscle during aging and in connective tissue disorders leads to changes in the viscoelasticity of the vessel wall.     

人异体移植肾之闭塞性动脉病的病理学研究

目的对移植肾之闭塞性动脉病（ｏｂｌｉｔｅｒａｔｉｖｅａｒｔｅｒｉｏｐａｔｈｙ,ＯＢＡ）进行组织学观察;分析病变中细胞成分;探讨其发病机理。方法对７４例急性血管型和慢性型排斥反应的移植肾进行光镜,电镜和免疫组化ＬＳＡＢ法观察。结果ＯＢＡ病变主要累及所有７４例移植肾内叶间动脉,弓形动脉和小叶间动脉内膜。２９例（３９．２％）在肾移植术后３个月内就能形成ＯＢＡ。早期病变１９例（２５．７％）,表现为动脉内膜炎;晚期病变５５例（７４．３％）,以动脉内膜梭形平滑肌细胞增生,管壁纤维化为主。ＯＢＡ病变中的细胞成分,一方面来自宿主;另一方面来自移植肾动脉壁本身,包括Ｔ淋巴细胞、单核（巨噬）细胞、内皮细胞和不同表型———“收缩型”及“合成型”平滑肌细胞,后者分泌Ⅰ,Ⅲ型胶原。结论ＯＢＡ是发生于移植后肾内动脉壁的增殖性病变,是移植物血管壁本身的细胞成分与宿主免疫细胞间一系列相互作用的结果,是一种免疫反应。     

Effect of the shape and configuration of smooth muscle cells on the diffusion of ATP through the arterial wall

In this study, the shape and the configuration of smooth muscle cells (SMCs) within the arterial wall are altered to investigate their influence on molecular transport across the media layer of the thoracic aorta wall. In a 2D geometry of the media layer containing SMCs, the finite-element method has been employed to simulate the diffusion of solutes through the media layer. The media is modeled as a heterogeneous system composed of SMCs having elliptic or circular cross sections embedded in a homogeneous porous medium made of proteoglycan and collagen fibers with an interstitial fluid filling the void. The arrangement of SMCs is in either ordered or disordered fashion for different volume fractions of SMCs. The interstitial fluid enters the media through fenestral pores, which are assumed to be distributed uniformly over the internal elastic lamina (IEL). Results revealed that in an ordered arrangement of SMCs, the concentration of adenosine 5′-triphosphate (ATP) over the surface of SMCs with an elliptic cross section is 5–8% more than those of circular SMCs in volume fractions of 0.4–0.7. The ATP concentration at the SMC surface decreases with volume fraction in the ordered configuration of SMCs. In a disordered configuration, the local ATP concentration at the SMC surface and in the bulk are strongly dependent on the distance between neighboring SMCs, as well as the minimum distance between SMCs and fenestral pores. Moreover, the SMCs in farther distances from the IEL are as important as those just beneath the IEL in disordered configurations. The results of this study lead us to better understanding of the role of SMCs in controlling the diffusion of important species such as ATP within the arterial wall.     

Altered collagen expression in jugular veins in multiple sclerosis

IntroductionVenous abnormalities have been associated with different neurological conditions, and the presence of a vascular involvement in multiple sclerosis (MS) has long been anticipated. In view of the recent debate regarding the existence of cerebral venous outflow impairment in MS due to abnormalities of the azygos or internal jugular veins (IJVs), we have studied the morphological and biological features of IJVs in MS patients.MethodsWe examined (a) IJVs specimens from MS patients who underwent surgical reconstruction of the IJV and specimens of the great saphenous vein used for surgical reconstruction, (b) different vein specimens from an MS patient dead of an unrelated cause, and (c) autoptical and surgical IJV specimens from patients without MS. Collagen deposition was assessed by means of Sirius red staining followed by polarized light examination. The expression of collagen type I and III, cytoskeletal proteins (α-smooth muscle actin and smooth muscle myosin heavy chains), and inflammatory markers (CD3 and CD68) was investigated.ResultsThe extracranial veins of MS patients showed focal thickenings of the wall characterized by a prevailing yellow–green birefringence (corresponding to thin, loosely packed collagen fibers) correlated to a higher expression of type III collagen. No differences in cytoskeletal protein and inflammatory marker expression were observed.DiscussionThe IJVs of MS patients presenting a focal thickening of the vein wall are characterized by the prevalence of loosely packed type III collagen fibers in the adventitia. Further studies are required to determine whether the observed venous alterations play a role in MS pathogenesis.     

Engineering of an elastic large muscular vessel wall with pulsatile stimulation in bioreactor

Tissue engineering offers a new approach for the construction of vascular substitutes in vitro with proper mechanical properties. Although success has been made in the engineering of small blood vessels (<6mm in diameter), it remains a challenge to engineer large vessels (>6mm in diameter) due to their insufficient biomechanical property. In the current study, an elastic large vessel wall (6mm in diameter) was engineered by loading a polyglycolic acid (PGA) unwoven fiber scaffold seeded with smooth muscle cells (SMCs) on a vessel reactor designed with dynamic culture conditions. SMCs were isolated from canine carotid artery and expanded before seeding on a PGA fiber mesh. The cell-seeded PGA mesh was then loaded on a vessel reactor and subjected to pulsatile stimuli. Grossly, an elastic vessel wall was formed after 8 weeks of dynamic engineering. Histological examination showed well-orientated smooth muscle cells and collagenous fibers in the group with dynamic culture. In addition, the phenotype of SMCs was confirmed by positive staining of smooth muscle alpha-actin and calponin. On the contrary, disorganized smooth muscle cells and collagenous fibers were observed in the group under static culture without stimuli. Furthermore, the engineered vessels under dynamic culture exhibited significant improvements on biomechanical property over the one from static culture. Our results indicate that the approach developed in the current work is efficient for large vessel engineering. This approach may also be suitable for the engineering of other tissues with muscular tubular structure.     

The influence of RGD-bearing hydrogels on the re-expression of contractile vascular smooth muscle cell phenotype

This study reports on the ability of poly(ethylene glycol) diacrylate (PEGDA) hydrogel scaffolds with pendant integrin-binding GRGDSP peptides (RGD-gels) to support the re-differentiation of cultured vascular smooth muscle cells (SMCs) toward a contractile phenotype. Human coronary artery SMCs were seeded on RGD-gels, hydrogels with other extracellular matrix derived peptides, fibronectin (FN) and laminin (LN). Differentiation was induced on RGD-gels with low serum medium containing soluble heparin, and the differentiation status was monitored by mRNA expression, protein expression, and intracellular protein organization of the contractile smooth muscle markers, smooth muscle α-actin, calponin, and SM-22α. RGD-gels supported a rapid induction (2.7- to 25-fold up-regulation) of SMC marker gene mRNA, with expression levels that were equivalent to FN and LN controls. Marker protein levels mirrored the changes in mRNA expression, with levels on RGD-gels indistinguishable from FN and LN controls. Furthermore, these markers co-localized in stress fibers within SMCs on RGD-gels suggesting the recapitulation of a contractile apparatus within the cells. These results indicate that SMCs cultured on RGD-bearing hydrogels can re-differentiate toward a contractile phenotype suggesting this material is an excellent candidate for further development as a bioactive scaffold that regulates SMC phenotype.     

猪肝门静脉壁组织结构增龄性变化的定量分析

目的　探讨猪肝门静脉壁结构成分的增龄性变化 ,为猪 -人异种肝移植提供理论依据。方法　取正常不同月龄猪肝门静脉 ,HE染色 ,Weigert、Anilineblue及桔黄G分染弹性纤维、胶原纤维和平滑肌 ,光镜观察 ,计算机图像分析系统测量各结构成分的相对含量。结果　猪肝门静脉随月龄的增长胶原纤维的含量逐渐升高 ,弹性纤维的含量相对稳定 ,平滑肌的含量在 3月龄时最高 ,胶原纤维与弹性纤维含量的比值 (C/E)逐渐升高。结论　猪肝门静脉壁各结构成分的相对含量随增龄发生变化 ,在实施猪 -人异种肝移植时应选择与人肝门静脉壁结构成分含量相近的月龄猪作为供体。     

Changes in the Organization of the Smooth Muscle Cells in Rat Vein Grafts

Mechanical tensile stress in vein grafts increases suddenly under the influence of arterial blood pressure. In this study, we examined the influence of increased tensile stress on the organization of the smooth muscle cells (SMCs) in the neointima and media of the rat vein grafts. An autogenous jugular vein was grafted into the abdominal aorta of the rat, and changes in the organization of the vein graft SMCs were studied by observing the distribution of SMC actin filaments and nuclei at 3 min and 1, 5, 10, and 30 days after surgery. In a normal jugular vein, the average wall circumferential tensile stress was ~ 3 kPa at an internal pressure of 3 mm Hg. The SMCs, that contained long, slender actin filamentous bundles, were oriented mainly in the circumferential direction of the vessel, and constituted a 2- to 3-cell-thick medial layer underneath the endothelium. In a vein graft, the wall circumferential tensile stress suddenly increased by ~ 140 times compared with the control level. In response to this suddenly increased stress, the SMC layer was stretched into a structure with scattered pores and disrupted SMC actin filamentous bundles within 3 min. This initial change was followed by a rapid reduction in the density of the SMC nuclei and actin filaments within 1 day and progressive SMC proliferation, that was associated with medial thickening and a change in the SMC orientation from 5 to 30 days. Further studies showed that a local inflation of normal jugular veins to 120 mm Hg for 3 min induced a similar change as found in the vein grafts, whereas the organization of the SMCs was not significantly changed in vein-vein grafts, that did not experience a change in tensile stress. These results suggested that increased tensile stress contributed to the initial damage of the SMCs and played a role in the regulation of medial SMC remodeling in vein grafts. © 1998 Biomedical Engineering Society. PAC98: 8722-q, 8745-k