Structural features of cell death in atherosclerotic lesions affecting long-term aortocoronary saphenous vein bypass grafts

Aortocoronary saphenous vein bypass grafts fail because of structural pathologies (thrombosis, intimal hyperplasia and atherosclerosis) within the 'arterialized' vein leading to graft stenosis. This study examined structural characteristics of atherosclerotic alterations in long-term aortocoronary artery saphenous vein bypass grafts with particular attention to the features of cell death in atherosclerotic lesions. Stenotic vein grafts were obtained from 10 patients at redo coronary artery bypass grafting operations. All the grafts were affected by histological abnormalities, with eight out of ten grafts showing evidence of atherosclerotic alterations in the intimal hyperplastic layer. Areas containing foam cells were examined by electron microscopy. Cells with cytoplasmic lipid accumulations were characterized by varying degrees of chromatin condensation, fragmentation or dispersion, by focal areas of oedema and vacuolisation of their cytoplasm, and by plasmalemmal destruction. Some lipid-filled cells exhibiting signs of destruction contained myofilaments and basal membrane fragments, allowing them to be identified as smooth muscle cells. Macrophage foam cells were found to have undergone similar destruction. No cells showing nuclear degeneration were observed to have intact cytoplasmic organelles. Neither were apoptotic bodies identified, but necrotic remnants were frequently seen. The results suggest that cell death in atherosclerotic lesions affecting aortocoronary artery saphenous vein bypass grafts occurs through oncosis rather than by apoptosis.     

Time course of the regression of intimal hyperplasia in experimental vein grafts.

A previous study in which vein grafts were removed from the arterial circulation and reimplanted into the venous circulation of the same animal demonstrated regression of vein graft intimal hyperplasia and medial thickening within 14 days. The present study was designed to characterize the kinetics of the morphological and ultrastructural changes over this 14-day period. Twenty-one male New Zealand White rabbits received a reversed vein interposition bypass graft of the right common carotid artery. Fourteen days after the procedure, 21 vein grafts were isolated, removed, and reimplanted into the contralateral external jugular venous system as veno-venous interposition bypass grafts (reversal grafts). The grafts were harvested at 60 minutes, 1 day, 3 days, 5 days, 7 days, and 14 days after reversal. Before insertion into the venous circulation, the vein graft had a confluent endothelial cell surface with multiple layers of smooth muscle cells representing intimal hyperplasia. After 1 hour, the reversal graft retained an intact endothelial cell layer with no evidence of tissue edema or cellular disruption. By 24 hours, there were a few blood cells on the endothelial cell surface. There was no inflammatory infiltrate seen in the subendothelium, and the smooth muscle cells were unaltered. At 3 days, the endothelial cell lining remained intact with no polymorphonucleocytes in the subendothelium or within the graft wall. Underlying smooth muscle cells at this time were noted to contain cytoplasmic vacuoles. At 5 days, there were no inflammatory cells seen on the surface or within the vein graft wall, but many of the underlying smooth muscle cells within the intimal hyperplasia were noted to be fragmented and to have clumping of chromatin. After 7 days, the endothelial cells remained intact and there was widespread evidence of apoptosis beneath the subendothelium with highly fragmented smooth muscle cells, some of which were histologically in the process of breaking up. At 14 days, the grafts retained uniform endothelial cell surfaces. Most of the smooth muscle cells that composed the intimal hyperplasia seen before implantation as a reversal graft were gone. Areas of newly laid down collagen could be observed. There were no acute inflammatory cells but for some mast cells seen in the graft wall. This study demonstrates that in this model, regression of intimal hyperplasia was associated with apoptosis of the smooth muscle cells and the deposition of collagen. There was no evidence that this process is mediated by an acute inflammatory response. Regression therefore appears to be due to induction of smooth muscle cell apoptosis by either a reduction in pressure or flow or a combination of both factors. The findings will enable a systematic cellular and molecular analysis of the biology of regression, which may afford clues to better understand the biology of the developing intimal hyperplasia.     

Human atherosclerosis. II. Immunocytochemical analysis of the cellular composition of human atherosclerotic lesions.

The authors have performed immunocytochemical investigations of the distribution of various cell types in human atherosclerotic plaques using monoclonal antibodies specific to smooth muscle cells (CGA7 [Gown et al, J Cell Biol 1985, 100:807-813] and HHF35 [Tsukada et al, Am J Pathol (In press)] ); lymphocytes (T200 antigen); endothelial cells (Factor VIII and the Ulex europeus agglutinin); and macrophages, the latter with a new macrophage-specific antibody HAM56. All studies were performed on methanol-Carnoy's-fixed, paraffin-embedded tissues. In areas of grossly normal aorta, significant numbers of macrophages were noted within areas of diffuse intimal thickening. The cellular composition of the following three types of raised lesions were analyzed: fibro-fatty lesions, which, despite their gross appearance, consistent with fibrous plaques, were composed almost exclusively of macrophages and lymphocytes and almost devoid of smooth muscle cells; fibrous plaques, which were predominantly composed of smooth muscle cells displaying considerable morphologic heterogeneity and an admixture of blood-borne cells; advanced plaques, which were characterized by complex layers of smooth muscle cells and macrophages with considerable variation from region to region. Also noted were foci of medial and even intimal vascularization subjacent to the more advanced plaques. These studies demonstrate the application of monoclonal antibody technology to the study of the cellular composition of human atherosclerotic lesions.     

Long-term engraftment of bone marrow-derived cells in the intimal hyperplasia lesion of autologous vein grafts

Intimal hyperplasia of autologous vein grafts is a critical problem affecting the long-term patency of many types of vascular reconstruction. Within intimal hyperplasia lesions, smooth muscle cells are a major component, playing an essential role in the pathological process. Given that bone marrow-derived cells may differentiate into smooth muscle cells in the neointima of injured arteries, we hypothesized that the bone marrow may serve as a source for some of the smooth muscle cells within intimal hyperplasia lesions of vein grafts. To test this hypothesis, we used an established mouse model for intimal hyperplasia in wild-type mice that had been transplanted with bone marrow from a green fluorescent protein (GFP+/+) transgenic mouse. High-resolution confocal microscopy analysis performed 2 and 8 weeks after grafting demonstrated expression of GFP in 5.4 +/- 0.8% and 11.9 +/- 2.3%, respectively, of smooth muscle cells within intimal hyperplasia lesions. By 16 weeks, GFP expression in smooth muscle cells was not detected by immunohistochemistry; however, real-time PCR revealed that 20.2 +/- 1.7% of the smooth muscle cells captured from the neointima lesion by laser capture microdissection at 16 weeks contained GFP DNA. Our results suggest that bone marrow-derived cells differentiated into smooth muscle cells within the intimal lesion and may provide a novel clinical approach for decreasing intimal hyperplasia in vein grafts.     

Rapid development of vein graft atheroma in ApoE-deficient mice

Several animal models manifesting lesions resembling neointimal hyperplasia of human vein grafts have been developed, but no spontaneous atheromatous lesions in their vein grafts have been observed. We developed and here characterize a new animal model of vein graft atheroma, a maturated atherosclerotic plaque, in apoE-deficient mice. The lesion displayed classical complex morphological features and heterogeneous cellular compositions and consisted of a fibrous cap, infiltrated mononuclear cells, foam cells, cholesterol crystal structure, necrotic core with calcification, and neovasculature. Cell component analysis revealed smooth muscle cells (SMCs) localized in the cap region, macrophages which made up a large portion of the lesions, and CD4+ T cells scattered under the cap. Importantly, apoptotic/necrotic cells determined by TUNEL assay in vein grafts into apoE-/- mice were significantly higher than wild-type mice, although a similar number of proliferating cell nuclear antigen-positive cells in both types of lesions was found. Interestingly, vascular SMCs cultivated from aortas of apoE-deficient mice showed a high rate of spontaneous apoptosis/necrosis and a higher rate of cell death stimulated by a nitric oxide donor, sodium nitroprusside, H(2)O(2), and oxidized low density lipoprotein (LDL), although no difference in proliferation of both SMCs incubated with platelet-derived growth factor, angiotensin II, LDL, and oxidized LDL was seen. Thus, the pathogenic mechanisms of vein graft atheroma involve increased intimal cell death initiated by biomechanical stress and amplified by hypercholesterolemia, which leads to continuous recruitment of blood mononuclear cells to constitute atheromatous lesions. This mouse model resembling human vein graft disease has many advantages over other animal models.     

Immunohistochemical and ultrastructural detection of advanced glycation end products in atherosclerotic lesions of human aorta with a novel specific monoclonal antibody.

To elucidate the deposition of advanced glycation end products (AGEs) in aortic atherosclerosis, aortic walls were obtained from 25 autopsy cases and examined immunohistochemically and immunoelectron microscopically with a monoclonal antibody specific for AGEs, 6D12. Among the autopsy cases, atherosclerotic lesions were found in the aortas of 22 cases and were composed of diffuse intimal thickening, fatty streaks, atherosclerotic plaques, and/or complicated lesions. In these cases, intracellular AGE accumulation was demonstrated in the intimal lesions of aortic atherosclerosis in 12 cases. Compared with the diffuse intimal thickening, intracellular AGE accumulation was marked in the fatty streaks and atherosclerotic plaques. Immunohistochemical double staining with 6D12 and monoclonal antibodies for macrophages or muscle actin or a polyclonal antibody for scavenger receptors demonstrated that the AGE accumulation in macrophages or their related foam cells was marked in the diffuse intimal thickening and fatty streak lesions and that almost all macrophages and macrophage-derived foam cells possessed scavenger receptors. Immunoelectron microscopic observation revealed the localization of 6D12-positive reaction in lysosomal lipid vacuoles or electron-dense granules of the foam cells. These results indicate that AGE accumulation occurs in macrophages, smooth muscle cells, and their related foam cells.     

自体移植兔静脉细胞增殖与钙激活钾通道的变化

目的: 研究静脉移植后钙激活钾通道(K_Ca)的变化,并探讨其病理生理意义。方法: 将兔的双侧股静脉倒置移植于同侧股动脉缺损之间,采用离体血管灌流的方法,测定移植静脉环的张力。分别以图像分析和四唑盐(MTT)比色法检测移植静脉内膜增厚的程度以及K_Ca的阻断剂盐酸四乙胺(tetraethylammonium chloride, TEA)对培养的家兔股静脉血管平滑肌细胞(vascular smooth muscle cells, VSMCs)增殖的影响。进而采用膜片钳技术记录K_Ca电流。 结果: 移植后1 week, 静脉的收缩性和内膜相对厚度没有显著变化。静脉移植后2 weeks,收缩性和内膜相对厚度显著大于对照组(P＜0.05, n=8)。移植后4 weeks静脉的收缩性和内膜相对厚度进一步大于对照组(P＜0.01, n=8)。TEA(2-8 mmol/L)显著增加培养VSMCs的MTT吸光值,并且有剂量依赖性(P＜0.05, n=8)。膜片钳实验结果显示,指令电位在(30-60)mV时,移植(1-4) weeks静脉VSMCs的K_Ca 电流密度均显著低于对照组(P＜0.05, n=5),指令电位在20 mV时,只有移植4 weeks静脉VSMCs的K_Ca电流密度显著低于对照组(P＜0.05, n=5)。结论: 自体移植静脉VSMC的K_Ca受到抑制,可能是血管收缩性增强、VSMCs异常增殖的原因,从而导致自体移植静脉痉挛和狭窄。     

Foam cell replication and smooth muscle cell apoptosis in human saphenous vein grafts

Occlusion of saphenous vein grafts is a major problem after coronary artery bypass grafting. Segments of occluded and suboccluded implanted aortocoronary grafts were obtained during re-intervention bypass grafting in 47 patients yielding a total of 80 vein grafts. The grafts were studied by immunohistochemistry for smooth muscle cells (ÉL-SMC actin), macrophages (HAM56), cell replication (PCNA, Ki-67) and transmission and scanning electronmicroscopy (TEM, SEM). In 81% of the examined grafts the (sub)occlusion was due to a myo-intimal thickening and an associated luminal accumulation of foam cells and mural thrombi. The foam cells were constantly found at the luminal site of the myo-intimal thickening and within the luminal part of adherent thrombi. Transmission electronmicroscopy demonstrated phagocytosis of platelets and platelet fragments by the foam cells. A significant fraction of the foam cells demonstrated nuclear immunoreactivity for Ki-67 and PCNA. The myo-intimal thickening of the vein grafts was composed of smooth muscle cells lying in a fibrous tissue matrix. The smooth muscle cells were surrounded by prominent basal lamina and showed ultrastructural features of apoptosis. Our results support the hypothesis that phagocytosis of lipid rich platelets by monocytes set up a mechanism for foam cell formation and replication in human saphenous vein grafts. The transformation of a smooth muscle cell rich myo-intimal thickening towards a fibrous, cell poor intimal thickening could be induced by progressive smooth muscle cell loss through apoptosis.     

Role of macrophage and smooth muscle cell apoptosis in association with oxidized low-density lipoprotein in the atherosclerotic development.

To examine the role of the apoptosis of macrophages and smooth muscle cells in the development of atherosclerosis, human aortic tissues with intimal lesions were immunostained with antibodies against terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL), single-stranded DNA (clone F7-26), and active caspase-3. Apoptotic cells were detected in the intima using both TUNEL and single-stranded DNA, however, the latter method was the more sensitive one for detecting apoptotic cells in the early stages of atherosclerosis. The number of apoptotic cells increased as the disease progressed. It implies that the apoptosis of intimal cells is involved in the formation of atherosclerotic lesions. In addition, quantitative analyses of the cell types undergoing apoptosis using double-immunostaining revealed that the susceptibility of macrophages and smooth muscle cells to apoptosis was greater specifically in atheroma than in the other atherosclerotic lesions, and macrophages were more susceptible to apoptosis than smooth muscle cells. The frequency and spatial distribution of oxidized low-density lipoprotein (oxLDL) (FOH1a/DLH3)-positive cells were examined by immunohistochemistry, and the results resembled those of apoptotic cells. The number of oxLDL-positive cells in the intima significantly correlated with the susceptibility of smooth muscle cells, but not with that of macrophages, to apoptosis. These results suggest that oxLDL affects the apoptosis of smooth muscle cells during the atherosclerotic development.     

Spontaneous atherosclerosis: An ultrastructural study in the White Carneau pigeon

Summary The atherosclerotic lesions, associated with the celiac intimal smooth muscle cushions, of four and five year old White Carneau pigeons were studied with the light and electron miscroscopes. Light microscopic examination of the spontaneous lesions demonstrated large intimal cushions composed of smooth muscle, abundant collagen, clusters of foam cells and cholesterol crystal clefts.Ultrastructural examination of the intimal atheroma revealed dilatations between apposing endothelial cells which contained a flocculent material, similar to that seen in the subendothelial space. The subendothelial compartment contained abundant collagen, extracellular lipid, vesiculated material and cell processes which contained a flocculent matrix and tubular-like elements. In addition, fibroblast-like interlaminar cells were often observed. Numerous intimal smooth muscle cells were seen which displayed varied morphology. Abundant foam cells were also present within the intimal atheromas.The presence of atherosclerotic lesions in preexisting intimal smooth muscle cushions suggests that hemodynamic factors may be important in the progression of these spontaneous lesions. Endothelial cell dilatations may provide an important route of transport for circulating elements which may accumulate within the subendothelial space. Morphologically, it appears that the smooth muscle cells undergo modification and may represent the precursors of foam cells in this species.Supported by a General Reserach Support Grant from NIH and The University of Texas     

Neue Aspekte der Biochemie und Biologie der Arterienwand

Summary Early lesions of arteriosclerosis are characterized by proliferating smooth muscle cells, macrophages, and foam cells. In addition, large amounts of connective tissue components and cholesterol esters are found. These changes are primarily located in the intima of the arterial wall. The initial mechanisms responsible for lesion formation are largely unknown. In recent years progress has been made particularly in fields of research related to the biochemistry of arterial wall cells in tissue culture. The findings obtained allow us to deepen our knowledge of the pathophysiology of arteriosclerosis. Of special interest are mechanisms involved in the maintenance of the thromboresistent endothelium, the factors triggering proliferation of intimal smooth muscle cells, and the transformation of macrophages to foam cells.

Diese Arbeit wurde von der Deutschen Forschungsgemeinschaft unterstützt (Sachbeihilfe HA 1083/2-2)     

Identification of macrophages and smooth muscle cells in human atherosclerosis using monoclonal antibodies

Sections of human atherosclerotic plaques were stained by the indirect immunoperoxidase technique using three rat anti-human monoclonal antibodies: YAML 501.4 (anti-'leukocyte-common' (T200) antigen; YTH 8.18 (antimacrophage cytoplasm); and YPC 1/3 . 12 (anti-smooth muscle cell). The cells of diffuse intimal thickening were almost all smooth muscle cells but there were rare subendothelial macrophages. Focal lesions, in contrast, contained numerous macrophages as well as smooth muscle cells. Macrophage 'foam cells' were particularly numerous in fatty streaks and in advanced fibro-fatty plaques, but were less conspicuous in focal fibro-elastic lesions. The results confirm that macrophages are an important component of atherosclerotic plaques and suggest that they may have a significant role in atherogenesis in man.     

Identification of macrophages and smooth muscle cells with monoclonal antibodies in the human atherosclerotic plaque

Summary Sections of human atherosclerotic plaques, obtained from 21 autopsy cases with various degrees of atherosclerosis, were stained with the indirect immunoperoxidase technique using specific monoclonal antibodies against macrophages and smooth muscle cells. Distinctive results were found in differing stages: Single blood monocytes were observed in diffuse intimal thickening and the foam cells seen in fatty streaks were mostly identified as mature tissue macrophages, while only very few blood monocytes were present. The spindle cells observed in fibroelastic plaques showed positive reactions to antibodies against desmin, which points to their derivation from smooth muscle cells, whereas only a few macrophage-derived foam cells were seen in these lesions. In the complicated lesions the majority of foam cells were macrophage-derived, but there was also a small number of foam cells positive to antibodies against desmin, suggesting a smooth muscle cell derivation. - Our results confirm that in human atherosclerotic plaques the majority of the foam cells are obviously macrophage-derived, which emphasizes the important role of macrophages in the morphogenesis of these lesions.Supported by Landesamt für Forschung Nordrhein-Westfalen     

Expression of intercellular adhesion molecule-1 in atherosclerotic plaques.

Immunohistochemistry of human atherosclerotic arteries demonstrates expression of the intercellular adhesion molecule-1 (ICAM-1) on endothelial cells, macrophages, and smooth muscle cells of the plaques. Normal arterial endothelial cells and intimal smooth muscle outside plaques give weaker or negative reactions; these differ from the strong endothelial expression in small vessels. Quantitative color-image analysis of the endothelial layer shows increased expression of ICAM-1 in all subtypes of atherosclerotic lesions, except fibrous plaques. Endothelial expression of ICAM-1 may be involved in the recruitment of monocytes to the lesion, as suggested by its role in the entry of leukocytes, including monocytes, into foci of inflammation. Collaboration with other mechanisms, particularly chemoattractant factors, may be important for this effect. ICAM-1 enhanced monocyte recruitment is a potential mechanism for the growth of an atherosclerotic plaque.     

Early changes in fine structures of the aortic arch in hamsters fed a high cholesterol diet

Intimal changes at the prelesional stage of atherosclerotic lesions were investigated ultrastructurally using hamsters fed a high cholesterol diet for 1 day to 1 month. Observations were restricted to the lesion-prone area in the aortic arch. The endothelial cells began to show well-developed rough endoplasmic reticulum and Golgi apparatus after a few days of the cholesterol diet. After three days, macrophages which contained a few lipid droplets were observed just below the endothelium. We found that the intimal smooth muscle cell formed a gap junction with the process of the medial smooth muscle cell. After a few weeks to 1 month on the diet, the intima became markedly thickened and filled with dense extracellular matrices. The intimal smooth muscle cells showed well-developed rough endoplasmic reticulum and Golgi apparatus with immature granules, suggestive of high secretory activity. The present study showed that endothelial ultrastructural changes, macrophage invasion, and medial smooth muscle cell migration are very early events occurring within a few days after cholesterol intake commences.     

Various cell types in human atherosclerotic lesions express ICAM-1. Further immunocytochemical and immunochemical studies employing monoclonal antibody 10F3.

The specificity of monoclonal antibody 10F3, generated to smooth muscle cells isolated from fetal human aorta, has been further explored in a series of biological, biochemical, and immunocytochemical studies. In the first assay, it was found that 10F3 could inhibit aggregation of phytohemagglutinin (PHA)-induced lymphocytes in a manner comparable to that of antibody RR1/1, an anti-intercellular adhesion molecule 1 (ICAM-1) monoclonal antibody. In immunoprecipitation experiments followed by one-dimensional gel electrophoresis, both 10F3 and RR1/1 immunoprecipitated 90 kd proteins, with results suggesting that the two antibodies recognized different epitopes of the same molecule. A series of immunocytochemical studies on human atherosclerotic lesions was performed; using single-labeling techniques, 10F3-positive cells were found in the vessel wall and in lesions of virtually all specimens of fatty streaks and fibrous plaques. Using double-labeling techniques, 10F3-positive macrophages and 10F3-positive smooth muscle cells were found; however, there were also a significant number of non-smooth muscle, nonmacrophage 10F3-positive cells. These studies demonstrate that 10F3 identifies ICAM-1, and that this protein is expressed on a variety of cell types in human atherosclerotic lesions. ICAM-1 may represent a developmentally regulated protein that is expressed in fetal but not adult mesenchymal cells, but can be re-expressed in pathologic processes such as atherosclerosis.     

Inducible expression of vascular cell adhesion molecule-1 by vascular smooth muscle cells in vitro and within rabbit atheroma.

Vascular cell adhesion molecule-1 (VCAM-1), a mononuclear leukocyte adhesion molecule, is expressed in cultured vascular endothelial cells activated by cytokines and is induced in rabbit aortic endothelium in vivo within 1 week after initiation of an atherogenic diet. We now demonstrate that vascular smooth muscle cells can also express VCAM-1 in rabbit atherosclerotic lesions in vivo and in response to cytokines in vitro. Immunohistochemical staining of aortas from rabbits fed a 0.3% cholesterol-containing diet revealed that a portion of smooth muscle cells within intimal foam cell-rich lesions expressed VCAM-1. The intimal VCAM-1-expressing cells localized predominantly in regions above the internal elastic lamina. These VCAM-1-positive cells had the typical spindle shape of smooth muscle cells but had reduced alpha-actin expression in comparison to normal medial smooth muscle cells, and did not bear markers for endothelium, macrophages, and T cells. In culture, rabbit aortic smooth muscle cells expressed VCAM-1 mRNA and protein in a time- and concentration-dependent fashion when exposed to interferon-gamma or Gram-negative bacterial lipopolysaccharide. Cultured human vascular smooth muscle cells also expressed VCAM-1 mRNA and protein in response to lipopolysaccharide, interferon-gamma, and interleukin-4. The monokines interleukin-1 alpha and tumor necrosis factor-alpha did not induce VCAM-1 expression in either rabbit or human vascular smooth muscle cells. Inducible VCAM-1 expression by vascular smooth muscle cells in vivo during hypercholesterolemia and in vitro in response to certain cytokines suggests a broader range of VCAM-1 functions in vascular biology than heretofore appreciated.     

Understanding and treating vein graft atherosclerosis.

BACKGROUND: Vein grafts have been used as bypass conduits for coronary artery disease since the 1960s. This widely used treatment, however, is complicated by the development of changes in the vein graft, which resemble atherosclerosis and are often termed as such. They occur at about 10 years, which leads to the need for reoperation in some patients. The purpose of this review is to summarize the knowledge regarding the pathophysiology of vein graft "atherosclerosis," as well as promising new treatments for this disease. METHODS: The relevant literature relating to the epidemiology, histology, cell and molecular pathophysiology and treatment of vein graft atherosclerosis is reviewed. RESULTS: The development of vein graft atherosclerosis differs from arterial atherosclerosis. Studies have examined the role of trauma, lipids, vasoactive mediators, smooth muscle cell mitogens, smooth muscle cells apoptosis, adhesion molecules and proteases. Therapies have been developed to prevent vein graft atherosclerosis based on these studies and have been tested using animal models and in patients. DISCUSSION: Promising new therapies have been developed based on current knowledge and further applications of genomics will allow for the further identification of risk factors and mechanistic insights. The use of arterial grafts such as the internal mammary artery, which have higher patency rates at 10 years compared with vein grafts as well as approaches to revascularize infarcted myocardium may one day replace the use of vascular conduits.     

Reduction of smooth muscle hyperplasia in vein grafts in athymic rats

While developing an animal model of a vascular malformation, we found that two doses of cyclosporin A significantly reduced the smooth muscle cell hyperplasia observed in vein-arterial interposition grafts in Sprague-Dawley rats. Therefore, we hypothesized that T cells may either produce or augment a mitogen for vascular smooth muscle cells. To further investigate this, we quantitated the extent of smooth muscle cell hyperplasia in the vein grafts of athymic nude rats that lack mature, functioning T cells. Male Sprague-Dawley rats (275 to 350 gm) and athymic nude rats were anesthetized, and a segment of the superficial epigastric vein was placed into the transected femoral artery using microsurgical techniques. Sprague-Dawley rats (N = 9) and athymic nude rats (N = 5) undergoing vein grafting received 30 mg/kg cyclosporin A intraperitoneally, intraoperatively and 24 hours later. Sprague-Dawley rats (N = 7) and athymic nude rats (N = 6) that had vein grafts were not treated with cyclosporin A. Animals were killed at either 3 weeks or 6 weeks and histologic sections were taken from the middle of the graft to avoid clamp-induced trauma. At 3 weeks, untreated vein grafts in Sprague-Dawley rats exposed to arterial pressure exhibited a nine-fold increase in smooth muscle hyperplasia compared with the preoperative vein. Treatment of Sprague-Dawley rats with cyclosporin A resulted in a 57% reduction of smooth muscle hyperplasia (p less than 0.05). Vein grafts from athymic nude rats exhibited a 51% reduction in smooth muscle hyperplasia (p less than 0.05). Sprague-Dawley rats killed at 6 weeks revealed a recovery of smooth muscle hyperplasia equivalent to an untreated Sprague-Dawley vein graft at 3 weeks. Inhibition of smooth muscle hyperplasia persisted for 6 weeks in the athymic nude rats. Cyclosporin A administration or T cell deficiency in athymic nude rats decreases the smooth muscle hyperplasia observed in venous grafts exposed to arterial pressure. This finding provides evidence for a possible role of T cells in the regulation of cell growth in the vascular wall.     

Aortocoronary bypass graft in dogs: late histological changes.

Late histological changes occurring in aortocoronary bypass vein grafts were studied by lignt and electron microscopy in three dogs killed one, two and three years after grafting. The changes consisted of intimal thickening due to a proliferation of modified smooth muscle cells (myointimal hyperplasia) and replacement of most of the medial smooth muscle by fibrocytes. Serial angiography in the dogs did not reveal progression of the intimal thickening after one month.