Pericytes and periendothelial cells of brain parenchyma vessels co-express aminopeptidase N, aminopeptidase A, and nestin

Within the parenchyma of the CNS, the endothelium of all vessels is surrounded by a layer of cells, pericytes in capillaries and periendothelial or intima smooth muscle cells in other vessels. The origin of these cell types, their relationship, and their role are unclear. However, it has been recently shown that genetically engineered mice that lack pericytes develop microaneurysms at late gestation and die before birth (Lindahl et al. [1997] Science 277:242-245). The goal of this study was to identify in situ molecular markers that would be common to pericytes and periendothelial cells of adult mouse brain. Immunocytochemistry experiments were carried out at the optical and electron-microscopic levels on mouse brain sections with antibodies specific for aminopeptidase N, aminopeptidase A, and the intermediate filament nestin. The results of our experiments show that in all brain parenchyma vessels of all sizes, pericytes and periendothelial cells are immunoreactive for aminopeptidase N, essentially at the plasma membrane level, and are also labeled by nestin specific antibodies, which decorate typical intermediate filaments. In addition, brain pericytes and periendothelial cells are also immunoreactive to monoclonal antibodies to aminopeptidase A. In contrast, pericytes and periendothelial cells do not express microglial markers. Taken together these data show that pericytes and periendothelial intima smooth muscle cells share common markers, suggesting a common origin or function, and are distinct from microglia.

Intimal deposition of functional von Willebrand factor in atherogenesis

During the formation of intimal thickening in normocholesterolemic rabbits, von Willebrand factor (vWF) is increased in the endothelial cells (ECs) and deposited in the intima. We investigated whether this also occurs during cholesterol-induced plaque formation, whether the synthesis of vWF increases, and whether this influences platelet adhesion. Rabbits were fed a cholesterol-rich (0.3%) diet for 26 weeks. Thereafter, half of the animals received a normal diet for another 26 weeks (cholesterol withdrawal). To induce intimal thickening in normocholesterolemic rabbits, collars were positioned around the carotid artery. Arterial segments were studied using immunohistochemistry, reverse transcription-polymerase chain reaction, electron microscopy, and platelet adhesion tests. Cholesterol treatment induced plaque formation in the aorta. The ECs had a cuboidal aspect, showed a dense immunoreactivity for vWF, a pronounced rough endoplasmic reticulum, and numerous Weibel-Palade bodies. There were subendothelial vWF deposits in the plaques and vWF mRNA was significantly increased as compared with controls. Similar changes were seen after collar-induced intimal thickening. After cholesterol withdrawal, both vWF mRNA and the ultrastructural morphology of the ECs normalized, and the vWF deposits disappeared from the plaque. Perfusion studies with anticoagulated rabbit blood over cross-sections of atherosclerotic aortas revealed increased vWF-mediated platelet adhesion in the subendothelial plaque region. Whereas rabbit platelets perfused through the lumen adhered to the same extent to de-endothelialized aortas of normocholesterolemic and atherosclerotic rabbits, vWF mediated platelet adhesion to endothelium was observed in atherosclerotic but not in normal aortas. Our results show an increased synthesis and (sub)endothelial presence of vWF after vascular injury, with functional consequences for platelet deposition on the vessel wall.

Alimentary lipemia, postprandial triglyceride-rich lipoproteins, and common carotid intima-media thickness in healthy, middle-aged men

BACKGROUND

Alimentary lipemia has been associated with coronary heart disease and common carotid artery intima-media thickness (IMT). This study was designed to investigate the relations of subclasses of postprandial triglyceride-rich lipoproteins (TRLs) with IMT.

METHODS AND RESULTS

Ninety-six healthy 50-year-old men with an apolipoprotein (apo) E3/E3 genotype underwent an oral fat tolerance test and B-mode carotid ultrasound examination. The apo B-48 and apo B-100 contents of each fraction of TRLs were determined as a measure of chylomicron remnant and VLDL particle concentrations. In the fasting state, LDL cholesterol (P<0.05) and basal proinsulin (P<0. 05) were significantly related to IMT, whereas HDL cholesterol, plasma triglycerides, and insulin were not. In the postprandial state, plasma triglycerides at 1 to 4 hours (P<0.01 at 2 hours), total triglyceride area under the curve (AUC) (P<0.05), incremental triglyceride AUC (P<0.01), and the large VLDL (Sf 60 to 400 apo B-100) concentration at 3 hours (P<0.05) were significantly related to IMT. Multivariate analyses showed that plasma triglycerides at 2 hours, LDL cholesterol, and basal proinsulin were consistently and independently related to IMT when cumulative tobacco consumption, alcohol intake, waist-to-hip circumference ratio, and systolic blood pressure were included as confounders.

CONCLUSIONS

These results provide further evidence for postprandial triglyceridemia as an independent risk factor for early atherosclerosis and also suggest that the postprandial triglyceridemia is a better predictor of IMT than particle concentrations of individual TRLs.

Apoptosis and Bcl-xs in the intimal thickening of balloon-injured carotid arteries

We performed balloon injury in the rat carotid artery and identified intimal thickening after injury. Balloon-injured carotid arteries showed maximum thickness of the neointima on the 14th day before complete endothelial cell regeneration. In this lesion we identified apoptosis of vascular smooth muscle cells (VSMCs) by in situ DNA labelling and electron microscopy in the neointima on the 14th day after injury. mRNA expression levels of bcl-2, bax, bcl-x, p53 and caspase-1 were determined by the reverse transcriptase-polymerase chain reaction method both in injured and uninjured carotid arteries. Neither bcl-2 nor bcl-xl mRNA expression was detected in either injured or uninjured arteries, whereas bax and p53 mRNA expression was identified and their mRNA levels were not altered after balloon injury. In contrast, both bcl-xs and caspase-1 mRNA was detected and was markedly induced only in the injured carotid artery. Positive staining for immunoreactive Bcl-x was observed specifically in the injured arterial wall and co-localized with positive staining of nuclei identified by in situ DNA labelling. We conclude that two opposite cellular responses, VSMC proliferation and apoptosis, exist together in the neointima of the rat carotid artery after balloon injury, and selective induction of Bcl-xs expression is a key regulator of VSMC apoptosis in the process of vascular remodelling.

Short-term effects of a new intravascular nitinol stent in canine arteries

RATIONALE AND OBJECTIVES

To evaluate the short-term effects of a new nitinol stent on canine arteries.

METHODS

Eighteen nitinol mesh stents were placed in abdominal aortas, common iliac arteries, and renal arteries of six dogs. Angiography was performed to evaluate the patency rates and structural changes of arteries at 1 day, 3 weeks, 4 weeks, and 10 weeks after stent insertion. Gross and light microscopic examinations were performed after angiography.

RESULTS

On angiography, the patency rate was 100%, and no thrombosis was observed. All side branches from stented segments were patent. The mean neointimal thickness over and between stent wires was 94 and 167 microns. No difference was found between the aorta and the small vessels. Histologically, the neointima was covered with endothelium and was composed of subintimal fibrosis with mild inflammation.

CONCLUSIONS

The new type of nitinol mesh stent showed a high patency rate, with no thrombosis and relatively thin neointimal proliferation.

Ultrastructural analogies between intimal alterations in veins from diabetic patients and animals with STZ-induced diabetes

The aim of this study was to document similarities and differences between veins from human diabetic patients and an experimentally induced diabetic animal model. The saphenous vein and posterior tibial vein from diabetic patients and the femoral vein from rats were studied. An increase in the extracellular matrix with migration of smooth muscle cells and endothelial alterations were observed in the intima of all specimens. These findings demonstrate that there is a high degree of similarity between the pathological changes in the venous wall during human diabetes mellitus and streptozotocin (STZ) induced-diabetes. This finding validates STZ induced-diabetes in rats as a model for further experimental study to clarify the fate of the diabetic venous wall when used as a graft.

Ultrastructure of early lipid accumulation in ApoE-deficient mice

Apolipoprotein (apo) E-deficient mice develop severe hypercholesterolemia and have lesions that progress from fatty streaks to fibrous plaques distributed in lesion-prone areas throughout the aorta. Lesions develop in apoE-deficient mice on a regular chow diet and will occur faster on a diet higher in cholesterol. Examination of the aortas from these mice on a chow diet by high-resolution, freeze-etch electron microscopy demonstrated lipid retention in the intima by 3 weeks of age. Lipid was retained in the matrix as individual particles between 33 and 48 nm in diameter, aligned along the collagen fibrils and in aggregates consisting of lipid particles with average diameters of 33 and 68 nm. Larger particles seemed to have formed from fusion of smaller particles. Lipid retention was more widespread in 5- and 9-week-old mice. Monocyte attachment to endothelial cells was observed by electron microscopy at 5 weeks of age. The appearance of the intimal lipid was similar to that previously described in rabbit models and suggests that lipid interaction with matrix filaments and subsequent aggregation of lipid particles are critical first steps in the process of foam cell formation.

Circulating thrombomodulin and hematological alterations in type 2 diabetic patients with retinopathy

To clarify the relationship between circulating thrombomodulin (TM) and endothelial cell damage in diabetes mellitus, plasma levels of TM were quantitated by an enzyme linked immunoabsorbant assay (ELISA) in 164 type 2 diabetes mellitus and 72 normal control subjects, and these levels were compared with those of von Willebrand factor antigen (vWf: Ag), thrombin antithrombin III complexes (TAT), plasmin-alpha2-plasmin inhibitor complexes (PIC), fibrinogen, D-dimer, urinary albumin excretion rate (AER), intima-media thickness (IMT) and plaque score of the common carotid artery assessed with high resolution B-mode ultrasonography. Plasma levels of TM, vWf: Ag, TAT, PIC, AER, IMT and plaque score were significantly increased in the diabetic patients compared to the normal control subjects. Plasma TM levels showed significant correlation with vWf: Ag (r=0.350, p<0.0001), TAT (r = 0.334, p < 0.0001), PIC (r = 0.450, p < 0.0001), AER (r = 0.334, p < 0.0001), IMT (r = 0.181, P<0.01), plaque score (r=0.385, p<0.0001). Among four groups of diabetic patients, divided based on their severity of diabetic retinopathy, there were no significant differences in age, sex, systolic and diastolic blood pressure levels, HbA,1c, or plasma lipid levels, although the plasma levels of TM, vWf: Ag, TAT, PIC, AER, IMT and the plaque score in the patients with proliferative retinopathy were significantly higher than those of the healthy controls and patients with simple retinopathy. Among the 43 normoalbuminuric patients without intima-media thickness or thickened plaque (AER<30 mg/g Creatinine, IMT<1.0 mm, plaque score = 0), plasma levels of TM, vWf: Ag, TAT, PIC were significantly higher in those patients with retinopathy than in those without retinopathy. Multivariate analysis showed TM, TAT and PIC levels to be independent predictors of diabetic retinopathy. In conclusion, circulating TM reflects endothelial cell damage in patients with diabetic retinopathy, and hypercoagulability might play an important role in endothelial cell damage.

Endothelial cells lining transjugular intrahepatic portasystemic shunts originate in hepatic sinusoids: implications for pseudointimal hyperplasia

The phenotype of the endothelial cells (ECs) in the pseudointima of transjugular intrahepatic portasystemic shunts (TIPS) and the mechanisms of pseudointima formation after TIPS were unknown. We hypothesized that TIPS were lined by hepatic sinusoidal ECs, which stimulated the migration of smooth muscle cells (SMCs) into the pseudointima and their proliferation. Studies were done with the following specific aims: (1) isolation of ECs from TIPS pseudointima and comparison of their phenotype with human cirrhotic sinusoidal and vascular ECs derived from hepatic and portal veins as well as aorta, and (2) testing of the effects of TIPS ECs on TIPS-derived SMC migration and proliferation. ECs were isolated from eight TIPS retrieved from liver explants by immunomagnetic separation using monodispersed magnetizable polystyrene beads (Dynabeads M-450) coated with Ulex Europeus 1. EC phenotypes were examined by transmission electron microscopy, factor VIII-related antigen, CD31, CD14, and CD34 expression, uptake of acetylated LDL and secretion of type IV collagen. The effects of EC-conditioned media on SMC migration and proliferation were tested in multiwell chemotaxis chambers and by cell counting, respectively. ECs were obtained from TIPS pseudointima with >95% purity. The phenotype of TIPS-derived ECs matched that of cirrhotic sinusoidal endothelium (both expressed CD14) and differed from that of vascular endothelium (CD14 negative, Weibel-Palade positive). Conditioned media from both stenosed (n = 3) and nonstenosed (n = 3) TIPS-derived endothelial cells produced a marked (>100%) P <.001 increase in migration as well as (up to 88%) P <.01 proliferation of SMCs from both stenosed (n = 3) as well as nonstenosed TIPS (n = 3). These data indicate that TIPS pseudointima are lined by hepatic sinusoidal endothelial cells, which stimulate pseudointima formation by increasing SMC migration and proliferation.

Immunohistological and ultrastructural analysis of the intimal thickening in coarctation of human aorta

OBJECTIVES

The histological nature and characteristics of aortic coarctation are not clearly defined, the aim of this study is to analyse intimal thickening in aortic coarctation.

METHODS

In order to characterize the components of intimal thickening in coarctation, narrowed segments of aorta obtained after surgery from ten children were examined immunocytochemically and by electron microscopy.

RESULTS

Histological analysis of aortic coarctation demonstrated a widened subendothelial region with separation of endothelial cells from the internal elastic lamina. Masson's trichrome staining showed a marked increase in extracellular matrix and cell numbers in the intimal thickening compared with normal aorta. Cellular component analysis demonstrated invagination of the intima by smooth muscle actin-positive cells, with a fragmentation of the internal elastic lamina. No proliferating smooth muscle and inflammatory cells were identified in the intima. In order to characterize the smooth muscle cell phenotypes, various smooth muscle cell markers were sought using specific monoclonal antibodies: alpha-smooth muscle actin, smooth muscle-myosin heavy chain, heavy caldesmon, desmin. In moderate coarcted aorta, at least two distinct smooth muscle phenotypes were identified. In the juxtamedial part of the intima smooth muscle, cells were differentiated and expressed all smooth muscle markers; in the subendothelial part of the intimal thickening, the majority of smooth muscle cells expressed only alpha-smooth muscle actin and appeared dedifferentiated. In regions of marked stenosis, a strong expression of smooth muscle-myosin heavy chain, and heavy caldesmon in the intimal thickening pointed to the presence of redifferentiated smooth muscle cells, not still expressing desmin. Electron microscopic examination also revealed a variety of smooth muscle cell phenotypes in the intimal thickening. In the superficial layer, smooth muscle cells appeared to be in the synthetic state, while in the deeper part, both synthetic and contractile components were identified.

CONCLUSIONS

These observations indicated that human coarctation was characterized by intimal recruitment of non-proliferating smooth muscle cells with dedifferentiated phenotype. However, the presence of smooth muscle cells with an intermediate phenotype in the narrowest part of the coarctation suggest that the redifferentiation process could participate in the pathogenesis of aortic coarctation.

Stents covered by an autologous arterial graft in porcine coronary arteries: feasibility, vascular injury and effect on neointimal hyperplasia

OBJECTIVE

The use of stents has improved results after balloon coronary angioplasty. Several materials have been proposed for covering the metallic surface of the stent to reduce the rate of subacute thrombosis and restenosis. In our institution, an autologous arterial graft was used for covering the external surface of a conventional stent. The angiographic and histological response in a porcine coronary artery model was investigated.

METHODS

An autologous arterial graft was removed from the femoral artery and carefully prepared. Subsequently, a conventional stent was covered externally by the arterial graft. Twenty-two covered stents and 22 uncovered regular stents were implanted alternatively in the coronary arteries of 22 pigs. One animal died immediately after the procedure, due to thrombus formation in the uncovered stent. Six animals were sacrificed at seven days and the remaining animals were sacrificed at two months. Before the sacrifice, coronary angiography was performed in all animals.

RESULTS

Thrombosis was detected in two control segments and in one covered stented segment. After seven days, the luminal surface of the covered stents was covered by a new endothelial layer in contrast to partial endothelial cell appearance in the control group. The angiographic parameters were similar between the two groups. Histologically, the covered stents were associated with less vascular injury compared to uncovered stents. In covered stents a trend towards reduction of maximal intimal hyperplasia was detected (covered: 116.6 +/- 47.75 vs uncovered: 150.25 +/- 46.81 microns, p = 0.08); also the thickness of the arterial media was reduced (covered: 21.34 +/- 10.28 vs uncovered: 102.63 +/- 18.71 microns, p = 0.02). The luminal and vessel areas were similar in the two groups.

CONCLUSIONS

The preparation and implantation of the autologous arterial graft-covered stent is technically safe and feasible. This type of covered stent results in accelerated endothelialization, less vascular injury, thinning of the arterial media and a trend to reduce the intimal hyperplasia in normal coronary arteries.

Coronary artery apoptosis in experimental hypercholesterolemia

The altered coronary vasoactivity detected in experimental hypercholesterolemia before lesion formation is presumably due to an imbalance between vasodilating and vasoconstricting factors. Apoptosis, which has been previously described in advanced atherosclerosis, is modulated by vascular derived peptides with vasoactive properties. We hypothesized that coronary apoptosis occurs in experimental hypercholesterolemia prior to lesion formation. Pigs were sacrificed after being on either a high-cholesterol diet for 10-16 weeks (n = 17) or a normal diet (n = 9). Identification of apoptosis in each layer of coronary arteries and arterioles was performed by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end-labeling (TUNEL). In additional animals, ligation-mediated polymerase chain reaction (PCR) and transmission electron and confocal microscopy were done. Plasma cholesterol levels were higher in the cholesterol-fed animals (86+/-9 mg/dl versus 342+/-20 mg/dl, P < 0.001). Atheromatous plaques were not evident in the high-cholesterol group. TUNEL was positive in 11 of 17 hypercholesterolemic animals, primarily in the intima (1-2% of cells) and adventitia (3% of cells), but not in control vessels. A similar distribution was detected in arterioles. DNA bands were detected only in experimental animals, as were morphological features of apoptosis by transmission electron and confocal microscopy. In experimental hypercholesterolemia, apoptosis occurred in coronary arteries and arterioles before lesion formation. Apoptosis may be an integral process of early coronary atherosclerosis.

Histological and ultrastructural features of atherosclerosis in progeria

This histological and ultrastructural study of a limited amount of vascular tissue from a progeric woman of 20 years who died of traumatic subdural hemorrhage supports the belief that the vascular changes are atherosclerotic. The unusual features observed were collagen fibrils with a relatively small diameter in the atherosclerotic intima and media, extensive loss of mural smooth muscle cells particularly in the aorta, and widespread contraction bands in smooth muscle cells in vascular and nonvascular tissues. Smooth muscle cells appear to be unusually susceptible to hemodynamic and ischemic stress. Further autopsy studies are required to elucidate the etiology and pathogenesis of this unique disease.

Accumulation of co-localised unesterified cholesterol and neutral lipids within vacuolised elastin fibres in athero-prone areas of the human aorta

To investigate whether there are alterations of elastin fibres in the arterial intima at the pre-atherosclerotic stage, grossly normal areas of human thoracic aorta were taken soon after death from 13 healthy trauma victims whose ages ranged from 16 to 40 years. Two areas were compared: atherosclerosis-prone (AP) areas localised to the dorsal aspect of the aorta along the rows of intercostal branch origins, and atherosclerosis-resistant (AR) areas from the ventral aorta. Electron microscopic analysis combined with cytochemical staining was applied. Unesterified cholesterol was identified using the filipin-staining technique while neutral lipids were visualised by the OTO-technique. Intimal features were studied by combining the filipin-staining and the OTO-technique. Electron microscopical examination showed that in both AR and AP areas, some elastin fibres in the intima were vacuolised. Unesterified cholesterol was found to be predominantly localised in the musculoelastic layer, in particular, inside the vacuolised elastin fibres. This localisation was seen in all 13 AP areas studied in contrast to the AR areas where it was observed in only four of 13 aortas studied (P < 0.0005, chi2-test). Accumulation of neutral lipids inside vacuolised elastin fibres was found in five out of 13 AP areas but was not observed in any of the AR areas (P=0.01, chi2). A combination of the filipin-staining and OTO-techniques showed that some deposits of neutral lipids and unesterified cholesterol within vacuolised elastin fibres were independently located from each other, but more frequently, neutral lipids were co-located with unesterified cholesterol. The present observations indicate a difference between AP and AR intimal areas which, in particular, relates to the structure of elastin fibres in the musculoelastic layer. The observations suggest that alterations of the extracellular matrix are involved in the trapping and retention of cholesterol and neutral lipids within the intima at an early stage in the development of atherosclerotic lesions.

Polyurethane vascular prostheses decreases neointimal formation compared with expanded polytetrafluoroethylene

PURPOSE

Synthetic grafts have been increasingly used for complex vascular reconstructions in patients with limited autologous vein availability. Materials currently in use induce increased stenosis and graft thrombosis compared with autologous vein, especially in smaller vessels. We examined whether grafts constructed of a porous biodegradation-resistant polycarbonate polyurethane (PU) exert better biocompatibility in terms of faster endothelialization and decreased chronic proliferation of intimal cells compared with expanded polytetrafluoroethylene (ePTFE).

METHODS

PU or ePTFE interposition grafts were implanted into the abdominal aortas of male Sprague-Dawley rats (PU, n = 37; ePTFE, n = 32). Grafts were removed at days 1, 7, 14, 28, and 56 and 6 months and were evaluated by immunohistochemical, electron microscopic, and morphometric techniques. Bromodeoxyuridine (BrdU) was injected at 1 and 24 hours before death to determine cellular proliferation. Endothelial cells and smooth muscle cells were identified with antibodies to von Willebrand factor and alpha-actin, respectively.

RESULTS

The luminal surface of PU grafts took 4 weeks to completely endothelialize, whereas ePTFE grafts took 24 weeks (P <.05). Neointimal cell proliferation was lower in PU grafts compared with ePTFE at 56 days (1.4 +/- 0.1 versus 8.6 +/- 1.5, P <.001) and at 6 months (0.15 +/- 0.002 versus 3.4 +/- 0.5, p <.001). Neointimal thickness at 6 months after implantation was 3.2 +/- 0.8 micrometer for PU compared with 10.3 +/- 3.1 micrometer for ePTFE (P <.05).

CONCLUSION

Polycarbonate polyurethane small vascular prostheses promoted faster luminal endothelialization, induced less chronic intimal proliferation, and produced a significantly thinner neointima than ePTFE grafts. These findings suggest that aliphatic-polycarbonate urethanes may offer advantages over standard materials such as ePTFE for vascular graft construction.

Endothelialization of biosynthetic vascular prostheses after laser perforation

OBJECTIVE

This study was undertaken to investigate the feasibility of transmural capillary ingrowth into the inner surface of biosynthetic vascular prostheses (Omniflow, BioNova, Melbourne, Australia) through perforations created by an excimer laser, thus inducing an endothelial cell coverage.

METHOD

Biosynthetic vascular prostheses (Omniflow, 10 cm length, 6 mm diameter) were perforated with an excimer laser (diameter of the holes 50 to 100 microm, distance 4 mm) and implanted into the carotid arteries of eight sheep. They were compared to untreated Omniflow prostheses implanted at the contralateral side. Three months after implantation the prostheses were explanted and evaluated by gross morphology, histologic examination, scanning electron microscopy, and immunohistochemical staining for factor VIII to identify endothelial cells.

RESULTS

All grafts remained patent. Gross morphologic examination revealed no significant difference in the thrombus-free surface between perforated and untreated prostheses. However, scanning electron microscopy showed endothelial cells in the midgraft portion of all perforated prostheses, whereas collagen fibers, fibrin meshwork, and activated platelets formed the inner layer in six of eight untreated Omniflow prostheses. Transmural capillary ingrowth in the laser group was verified by positive factor VIII staining for endothelial cells in the laser channels.

CONCLUSION

Spontaneous endothelialization of biosynthetic vascular prostheses can be achieved by transmural capillary ingrowth through perforations in the wall of the prostheses in an experimental sheep model.

Eliminating arterial pulsatile strain by external banding induces medial but not neointimal atrophy and apoptosis in the rabbit

We have examined the role of vessel pulsation and wall tension on remodeling and intimal proliferation in the rabbit infrarenal abdominal aorta. A rigid perivascular polyethylene cuff was used to reduce vessel systolic diameter by 25%, producing a region of reduced circumferential strain. At 6 weeks postoperatively, reduced circumferential strain caused medial atrophy, with 45% reduction of medial area and 30% loss of medial smooth muscle cells. Apoptotic cell death was indicated by DNA fragmentation, propidium iodide staining, and cell morphology. Cuffing the aorta after balloon denudation produced medial atrophy but did not inhibit neointimal growth. At 1 week postoperatively, intimal thickness was slightly decreased in regions with reduced strain; however, intimal thickening in regions of reduced strain was not different from control segments at 3 weeks postoperatively (intimal area was 0.37 +/- 0.05 mm2 with reduced strain and 0.50 +/- 0.08 for controls, mean +/- SEM). We conclude that circumferential strain is a major factor controlling medial structure and cell number, whereas growth of the neointima after injury is not significantly affected by either reduced strain or extensive medial cell death. Vessel cuffing represents a new model of blood vessel remodeling in vivo that involves extensive smooth muscle cell apoptosis.

Enhanced neointimal growth in cultured rabbit aorta following in vivo balloon angioplasty

We have used in vivo balloon catheterization in combination with in vitro organ culture to develop a model system for vascular neointima formation. A Fogarty balloon catheter was used to deendothelialize and rupture the internal elastic lamina of aortae in adult rabbits. After three d of recovery, aortae were harvested, divided into segments, and placed into organ culture. We obtained a daily index of cell proliferation in cultured vessels using [3H]thymidine incorporation into DNA. Also, segments were collected and processed for routine histology or immunohistochemistry. Aortic segments that had undergone ballooning 3 d before harvest and then cultured exhibited diffuse neointimal growth after several d in vitro, whereas those from sham-operated (nonballooned) rabbits showed generally only a single endothelial cell layer that is characteristic of normal intima. Aortae that were harvested, balloon-damaged in vitro, and then cultured exhibited no neointimal growth. The neointima that developed in cultured segments from in vivo ballooned rabbits was primarily of smooth muscle cell origin as determined by positive immunostaining for alpha-smooth muscle actin. The intima:media thickness ratios were significantly higher in aortic segments from ballooned rabbits at harvest and after 4 or 7 d in culture compared with those from nonballooned rabbits. Also, the [3H]thymidine index was higher in the in vivo ballooned aorta compared to non-ballooned or in vitro ballooned vessel. We conclude that ballooning in vivo followed by exposure to blood-borne elements produces an enhanced proliferative response in cultured vessels that is distinct from other in vitro models of neointimal growth.

G protein signaling and vein graft intimal hyperplasia: reduction of intimal hyperplasia in vein grafts by a Gbetagamma inhibitor suggests a major role of G protein signaling in lesion development

Vein grafting results in the development of intimal hyperplasia with accompanying changes in guanine nucleotide-binding (G) protein expression and function. Several serum mitogens that act through G protein-coupled receptors, such as lysophosphatidic acid, stimulate proliferative pathways that are dependent on the G protein betagamma subunit (Gbetagamma)-mediated activation of p21ras. This study examines the role of Gbetagamma signaling in intimal hyperplasia by targeting a gene encoding a specific Gbetagamma inhibitor in an experimental rabbit vein graft model. This inhibitor, the carboxyl terminus of the beta-adrenergic receptor kinase (betaARK(CT)), contains a Gbetagamma-binding domain. Vein graft intimal hyperplasia was significantly reduced by 37% (P<0.01), and physiological studies demonstrated that the normal alterations in G protein coupling phenotypically seen in this model were blocked by betaARK(CT) treatment. Thus, it appears that Gbetagamma-mediated pathways play a major role in intimal hyperplasia and that targeting inhibitors of Gbetagamma signaling offers novel intraoperative therapeutic modalities to inhibit the development of vein graft intimal hyperplasia and subsequent vein graft failure.

Structural changes in rat aortic intima due to transmural pressure

Huang et al. (1997) propose a new hypothesis and develop a mathematical model to explain rationally the in vitro and in situ measured changes (Tedgui and Lever, 1984; Baldwin and Wilson, 1993) in the hydraulic conductivity of the artery wall of rabbit aorta with transmural pressure. The model leads to the intriguing prediction that this hydraulic conductivity would decrease by one half if the thin intimal layer between the endothelium and the internal elastic lamina volume-compresses approximately fivefold. This paper presents the first measurements of the effect of transmural pressure on intimal layer thickness and shows that the intimal matrix is, indeed, surprisingly compressible. We perfusion-fixed rat thoracic aortas in situ with 2 percent glutaraldehyde solution at 0, 50, 100, or 150 mm Hg lumen pressure and sectioned for light and electron microscopic observations. Electron micrographs show a dramatic, nonlinear decrease in average intimal thickness, i.e., 0.62 +/- 0.26, 0.27 +/- 0.14, 0.15 +/- 0.10, and 0.12 +/- 0.07 (SD) micron for 0, 50, 100, and 150 mm Hg lumen pressure, respectively. The volume strain of the intima is more than 20 times greater than the radial strain of the artery wall due to hoop tension and two orders of magnitude greater than the consolidation of the artery wall as a whole assuming constant medial density (Chuong and Fung, 1984). Moreover, in both light and electron microscopic observations, it is easy to find numerous sites where the endothelium puckers into the fenestral pores at high lumen pressure, as predicted by the theory in Huang et al. (1997). In contrast, the average diameter of a fenestral pore increases only 10 percent as the lumen pressure is increased from 0 to 150 mm Hg. These results indicate that the thin intimal layer comprising less than 1 percent of the wall thickness can have a profound effect on the filtration properties of the wall due to the large change in Darcy permeability of the layer and the large reduction in the entrance area of the flow entering the fenestral pores, though the pores themselves experience only a minor enlargement due to hoop tension.

Local inhibition of tyrosine kinase activity markedly attenuates the development of intimal hyperplasia in experimental vein grafts

BACKGROUND

Intimal hyperplasia is due to the migration and proliferation of vascular smooth muscle cells after bypass surgery. Tyrosine kinases are involved in many signal transduction pathways including cell proliferation. This study examines the effects of local treatment with the tyrosine kinase inhibitor, tyrphostin AG-51, on the formation of intimal hyperplasia in vein grafts.

MATERIALS AND METHODS

Thirty-nine New Zealand White rabbits underwent interposition bypass grafting of the carotid artery using the jugular vein. In the first group (TKI), tyrphostin AG-51 (5 mg), dissolved in 600 microliter of dimethyl sulfoxide and Ringer's lactate (2:1, v:v), was used to incubate the veins ex vivo prior to grafting and delivered locally in 2.5 ml of 30% pluronic gel after grafting. The second group (DMSO) received the same treatment but without tyrphostin. In the third group (control), tyrphostin and DMSO were omitted from the incubation and gel delivery solutions. Postoperatively, vein grafts were harvested on Day 3 for Western analysis using an antiphosphotyrosine antibody (PY-20) to assess for tyrosine kinase activity, and on Day 28 for either morphologic or contractile function studies.

RESULTS

Local application of the TKI to vein grafts resulted in a 49% reduction in intimal hyperplasia compared to DMSO-treated vein grafts (31 +/- 4 micrometer vs. 61 +/- 5 micrometer, P < 0.01). Treatment with DMSO alone reduced intimal hyperplasia by 28% compared to control (85 +/- 4 micrometer, P < 0.05). The contractile responses in the DMSO and TKI-treated vein grafts were equivalent. Western analysis showed a 39-fold decrease in tyrosine phosphorylation with TKI treatment compared to control.

CONCLUSION

This study demonstrates that local short-term treatment with TKI produces a 49% reduction in intimal hyperplasia and suggests that phosphorylation of tyrosine residues is involved in the signaling pathways leading to the development of intimal hyperplasia in vein grafts.

Apoptosis and related proteins in different stages of human atherosclerotic plaques

BACKGROUND

The transition of a fatty streak into an atherosclerotic plaque is characterized by the appearance of focal and diffuse regions of cell death. We have investigated the distribution of apoptotic cell death and apoptosis-related proteins in early and advanced atherosclerotic lesions.

METHODS AND RESULTS

Human atherosclerotic plaques were studied by whole-mount carotid endarterectomy specimens (n=18). This approach allowed comparison of adaptive intimal thickenings, fatty streaks, and advanced atherosclerotic plaques of the same patient. The fatty streaks differed from adaptive intimal thickenings by the presence of BAX (P<0.01), a proapoptotic protein of the BCL-2 family. Both regions were composed mainly of smooth muscle cells (SMCs), and macrophage infiltration was low and not different. Apoptosis, as detected by DNA in situ end labeling (terminal deoxynucleotidyl transferase end labeling [TUNEL] and in situ nick translation) was not present in these regions. Apoptosis of SMCs and macrophages, however, was present in advanced atherosclerotic plaques that were present mainly in the carotid sinus. A dense infiltration of macrophages (5.8+/-3% surface area) was present in these advanced atherosclerotic plaques. Cytoplasmic remnants of apoptotic SMCs, enclosed by a cage of thickened basal lamina, were TUNEL negative and remained present in the plaques as matrix vesicles.

CONCLUSIONS

We conclude that SMCs within human fatty streaks express BAX, which increases the susceptibility of these cells to undergo apoptosis. The localization of these susceptible SMCs in the deep layer of the fatty streaks could be important in our understanding of the transition of fatty streaks into atherosclerotic plaques, which are characterized by regions of cell death. Matrix vesicles are BAX-immunoreactive cytoplasmic remnants of fragmented SMCs that can calcify and may be considered the graves of SMCs that have died in the plaques.

The electron microscopic morphology of the common carotid artery in rats

The common carotid arteries of normal adult rats were investigated electron-microscopically after tannic acid fixation. This fixation technique yields a better demonstrability of the structures of the connective tissue, the basal laminae and the surface coat of the cell membrane. The common carotid artery represents a vessel of the elastic type. The intima consists of an endothelium and a narrow gap of connective tissue (0.1-1 micron) which contains single collagenous fibrils and small elastic structures. This space is only occasionally as wide as 3 microns, especially beneath gaps of the internal elastic membrane. In these areas, single cells and structures of densely packed filaments are additionally observed which can neither be attributed to collagenous fibrils nor to elastic fibres. The intima is demarcated from the outside by an internal elastic membrane (1 micron) which shows a number of gaps. The media exhibits 3 to 4 elastic membranes without gaps. Smooth muscle cells of the contractile type stretch in an oblique direction between these membranes, i.e. they are not arranged in a circular or spiral manner. Most of their process-rich ends are inserted directly into the elastic material and not via a basal lamina. Processes from these smooth muscle cells, collagenous fibrils and elastic fibres are seen in the intercellular spaces. The muscle cells are occasionally interlinked by gap junctions. The basal lamina does not surround the muscle cells continuously. The adventitia contains bundles of collagenous fibrils, fibrocytes, a few small vessels and nerves with a perineuronal envelope. Nerves could not be demonstrated in the media. The oblique course of the smooth muscle cells and the insertion into the elastic membranes indicate that these cells do not predominantly contribute to changes in the width of the lumen but also serve the stabilisation and resetting of the elastic membranes. Contraction is probably induced by an opening of stretch-dependent Ca2+ channels. Due to the interlinkage with gap junctions, the muscle cells of one layer respond as a functional unit. Our findings provide a morphological basis for elucidating commonly encountered changes, such as smooth muscle migration through a normally interrupted inner elastic lamina.

Expression of extracellular matrix proteins accompanies lesion growth in a model of intimal reinjury

Reinjury of rat arterial lesions induces an increase in lesion size that is not associated with an increase in cell number. In this study, matrix volume was examined after reinjury to preexisting lesions, and the kinetics of matrix gene expression and activity of proteolytic enzymes in the lesion were evaluated. Volume densitometry in intima showed a significant increase in matrix volume 28 days after the reinjury, although no change was observed at 14 days. Three common vascular matrix molecules, alpha1(I)procollagen, tropoelastin, and fibronectin, were expressed highly at 7 days after the reinjury. Expression of tropoelastin remained upregulated for the entire 28 days after the reinjury, whereas alpha1(I)procollagen and fibronectin returned to the control level by 28 days. Protease activity was also increased after reinjury. Within days, a marked increase in urokinase plasminogen activator activity was observed in intima, and this activity decreased to control level by 14 days. The activity of tissue plasminogen activator did not change. The 95-kDa gelatinolytic activity was increased 1 to 2 days after the reinjury, but no change in other gelatinolytic activities was observed. These findings demonstrate that the accumulation of extracellular matrix is important in the increase in lesion size after reinjury and that a balance of matrix synthesis and degradation may explain why no change in matrix volume was detected until 28 days after the reinjury.

Long-term evaluation of the behavior of a polytetrafluoroethylene microprosthesis in the rat iliac artery: myointimal regression

The present study represents a long-term investigation of polytetrafluoroethylene (PTFE) vascular microprostheses implanted in the right common iliac artery of rats, with the aim of evaluating the degree of intimal hyperplasia and the changes produced in the vascular prosthesis. A follow-up study was performed between 3 months and 1 year post-implantation, using immunohistochemical techniques, light, and electron microscopy. Three months after implantation, the PTFE segment appeared sandwiched between two cell layers. A general endothelialization was observed on the luminal surface. The underlying myointima appeared as an irregular lining of decreasing thickness, from the distal anastomosis with the receptor artery to the proximal suture. A large number of white blood cells were found adherent to and infiltrating the endothelium. A neoformed adventitia covered the prosthesis on the external surface. At 4 months post-implantation, a destabilization of the luminal surface was observed induced by white blood cells. A progressive reduction in the thickness of the myointimal layer was also apparent, so that 1 year after implantation, the luminal surface of the PTFE prosthesis was fully lined by a thin cell covering. There is good long-term tolerance to implanted PTFE microprostheses. The white blood cells present in the implant region appeared to play an important role in the long-term regression of intimal hyperplasia.

Immunolabeling of type IV collagen, laminin, and alpha-smooth muscle actin cells in the intima of normal and varicose saphenous veins

Smooth muscle cells (SMC) of normal and varicose human saphenous intima were studied on cryostat sections by immunohistochemistry with alpha-smooth muscle actin (ASMA), type IV collagen, and laminin antibodies and also by transmission electron microscopy. The findings suggest two structurally distinct subtypes of smooth muscle cells with thin and thicker external lamina. Thin external lamina SMC were characterized by laminin, type IV collagen, weaker external lamina reactivity, and intense cytoplasmic alpha-smooth muscle actin immunoreactivity. Ultrastructurally, they exhibited abundant cytoplasmic microfilaments and thin external lamina. These cells were found isolated or, more frequently, clustered in fascicles close to the subendothelium in focal or zonal cushions, or in diffuse enlargement of the intima. In contrast, thicker external lamina smooth muscle cells were intensely immunolabeled for laminin and collagen IV, showing irregular cytoplasmic ASMA reaction. Single or clustered thicker external lamina SMC were seen predominantly in zonal cushions and in intima diffuse enlargement. It is very likely that these cells secrete these matrices in a nonpolarized fashion. The thicker external lamina of these SMCs showed a fine granular amorphous aspect sometimes intermingled with microfibrils. These external lamina were interposed between neighboring cells and exposed to collagen fibrils and elastic fibers. The cells also exhibited rarefaction of the cytoplasmic filaments. Intermediary cells exhibiting both features were rarely seen. Thicker external lamina SMC should be discussed in the context of an adaptive/proliferative response leading to dysfunction of the fibroelastic properties of the vein wall.

Participation of angiogenesis from rat femoral veins in the neovascularization of adjacent occluded arteries

The neovascularization of the arterial wall in human and experimental pathology has been demonstrated. The occlusion of the of the rat femoral artery is a suitable model for the study of these angiogenesis processes. Newly formed capillaries growing into the arterial wall have been described in this model. The origin of these ingrowing capillaries has been attribute to the preformed surrounding venules and capillaries. The contribution of the adjacent femoral vein with a supplementary population of vascular sprouts could also be possible. To test this hypothesis in half of the occluded arteries, the adventitia was removed from the side facing the femoral vein. Between 1 and 3 days after surgery several alterations were found both in the endothelial cells and the smooth muscle cells of the tunica media. Between 3 and 6 days, solid or canalized endothelial sprouts were observed arising from the femoral vein. By days 4 and 6, newly formed capillaries grew into the adventitia and tunica media of the femoral artery. Some of them, penetrated the internal elastic lamina. This microvascular penetration from the femoral vein was more prominent in the area of the ostium of the collateral and when the adventitia was removed. Some ingrowing capillaries were in continuity with the endothelial cells of the arterial neointima. At days 7 and 8, regressing capillaries were observed in the neomicrovasculature network between artery and vein, with a selective loss of the smaller vessels. From day 9 onwards, fewer and larger vascular channels were present between the femoral vein and the femoral artery. An arterial neolumen contained what appeared to be circulating "fresh" blood. Quantitatively, the venous neocapillary density increased from days 4 to 6 and then declined significantly by day 8. The arterial neocapillary density increased form days 4 to 8 and declined significantly by day 12. Moreover, both densities were significantly greater when the arterial adventitia was removed. The perfusion with barium solution showed the presence of the contrast material in the newly formed vessels, the lumen of the femoral vein, and the neolumen of the occluded arterial segment. The present findings indicate that putative angiogenic molecules released form the occluded arterial segment may reach the adjacent wall of the vein inducing neovascularization from it. The vein vascular sprouts are connected to the ingrowing capillaries in the occluded arterial wall and to the neocapillaries form the preexisting pericytic microvasculature. When the arterial adventitia were removed up to 2 times greater vein neocapillary's density was observed suggesting an easily access of the putative angiogenic factors to the vein.

Upregulation of connexin43 gap junctions between smooth muscle cells after balloon catheter injury in the rat carotid artery

Phenotypic transformation of smooth muscle cells (SMCs) to the synthetic state in vitro and in human coronary atherosclerosis is reported to be associated with upregulation of connexin43 gap junctions. To determine whether cellular interactions mediated by gap junctions participate in the phenotypic transformation of SMCs in arterial injury and disease in general and to establish the spatial and temporal pattern of any such change in relation to neointimal development, we investigated SMC connexin43 gap junction expression during vascular healing in the rat carotid artery after balloon catheter injury. Quantitative immunoconfocal microscopy was applied to localize and to quantify connexin43 gap junctions 1, 3, 9, and 14 days after injury. Parallel studies were conducted by electron microscopy (direct morphological demonstration of SMC gap junctions) and immunoconfocal microscopy (localization of altered actin expression). Synthetic-state SMCs in the neointima (first apparent from 9 days postinjury) revealed abundant expression of gap junctions, with levels of immunodetectable connexin43 threefold greater than those of medial cells. However, the first detectable changes were found in the media, before neointimal formation; at 1 to 3 days postinjury, an increase in SMC gap junction expression was apparent in the innermost (subluminal) zone, the major site from which the cells subsequently found in the neointima are recruited. We conclude that upregulation of connexin43 gap junctions is intimately linked to SMC phenotypic transition and that interactions mediated by gap junctions may be a hitherto unrecognized contributor to the cellular mechanisms underlying the vascular response to injury.

Inhibition of mononuclear cell recruitment in aortic intima by treatment with anti-ICAM-1 and anti-LFA-1 monoclonal antibodies in hypercholesterolemic rats: implications of the ICAM-1 and LFA-1 pathway in atherogenesis

To investigate the mechanism(s) for mononuclear cell recruitment in the arterial wall during the development of atherosclerosis, we studied intercellular adhesion molecule-1 (ICAM-1) and lymphocyte function-associated antigen-1 (LFA-1) expression in aortic intima from diet-induced hypercholesterolemic rats. ICAM-1 was barely found in the aortic walls from rats fed a normal chow diet; however, in rats on a cholesterol-rich diet for 4 weeks, ICAM-1 expression was markedly enhanced in the intimal endothelial cells of aortas. Enhanced expression of ICAM-1 on endothelial cells especially along the cellular borders in the abdominal aorta was almost invariably associated with increased adherence of mononuclear cells. Compared to control animals, in hypercholesterolemic rats, the numbers of intimal macrophages and T lymphocytes adhering to the "lesion-prone" areas of the abdominal aorta were significantly increased by 5.9-fold (p < 0.001) and 2.2-fold (p < 0.001), respectively. More than 85% of adherent macrophages exhibited LFA-1 antigen on the cellular membrane surface as assessed by immunostaining. To examine the participation of ICAM-1 and LFA-1 in adherence and migration of mononuclear cells, we administered monoclonal antibodies (mAb) against either ICAM-1 or LFA-1 into hypercholesterolemic rats after they were fed a cholesterol-rich diet for 2 weeks. Two weeks after the mAb treatment, the number of macrophages adhering to the intima was significantly inhibited by 42% (p < 0.001) with anti-ICAM-1 mAb and by 31% (p < 0.001) with anti-LFA-1 mAb compared to controls injected with mouse IgG. Combined injection with these two mAb increased the reduction of the number of macrophages in the intima to 58%. Furthermore, we found that the decrease in the number of macrophages that adhered to the intima was almost exclusively due to the reduction of LFA-1-positive macrophages. These results suggest that the ICAM-1 and LFA-1 pathway is involved in mononuclear-endothelial cell interaction during cholesterol-rich diet-induced atherogenesis.

Effect of short-term treatment with a monoclonal antibody to P-selectin on balloon catheter-induced: intimal hyperplasia, re-endothelialization, and attenuation of endothelial-dependent relaxation

The effects of an anti-P-selectin monoclonal antibody (MAb, PB1.3; Cytel Corporation) on neoendothelialization; neoendothelial function, as evidenced by acetylcholine-induced relaxation (nitric oxide formation); and intimal hyperplasia following embolectomy catheter-induced injury to the rabbit thoracic aorta were investigated. Catheter injury was induced in two groups of New Zealand White rabbits. One group received no treatment, while the second group received short-term treatment with the MAb (i.p., immediately before and 12 h after induction of catheter injury). A third group underwent a sham operation and served as uninjured controls. Following sacrifice at 2 weeks after injury, aortic rings were assessed for degree of intimal hyperplasia, neoendothelial morphology (scanning electron microscopy), and acetylcholine-induced relaxation. Aortic tissue from catheter-injured animals that received treatment exhibited improved neoendothelial morphology, as compared with tissue from untreated but catheterized animals; however, no statistically significant attenuation of the hyperplastic response or improvement in the attenuated neoendothelial-dependent acetylcholine-induced relaxant response that is characteristic of neoendothelium that forms after catheter denudation was observed. These data suggest that short-term attenuation of P-selectin-mediated polymorphonuclear leukocyte (PMN)/endothelium, PMN/platelet interactions, and/or thrombin formation beneficially affects neoendothelialization of the vascular wall following balloon catheter-induced injury.

Development of vasa vasorum in the arterially implanted autovein bypass graft and its anastomosis in the dog

Using stereomicroscopy, light microscopy, and scanning electron microscopy, we investigated the development of vasa vasorum in the proliferated neointima of the autovein graft and its anastomoses implanted in the canine femoral artery against a background of poor distal runoff. In the stereomicroscopic examination, a microfil silicone rubber compound (MF) was injected transluminally or via perivascular vasa, and the vascular specimen was prepared for clearing by immersion in a methyl-salicylate solution. Vessel interstices filled with MF were found adjacent to the suture materials within 5 days of grafting. Fourteen days after implantation, luminally originating vasa vasorum were often visible in the neointima along the suture line and distributed into the media and adventitia connecting to the original vasa vasorum. At 6 months or more after grafting, many orifices of luminally originating vasa vasorum were seen along the suture line of both proximal end-to-end and distal end-to-side anastomoses and distributed into the thickened neointima forming a vasa network when the neointima had proliferated to over 250 microm in depth. On the other hand, some clefts filled with MF were found in mural thrombi deposited on the vascular sinus of the graft within 5 days, and these appeared to be one of the sources of luminally originating vasa vasorum on the graft distant from the suture line. Moreover, the development of numerous vasa vasorum was constantly demonstrated in the neointima when it had proliferated to over 250 microm in depth.

Emergence and distribution of intimal smooth muscle cells in the postnatal rat aorta

The distribution of aortic intimal smooth muscle cells in the normal rat during postnatal development was studied by electron microscopy and by staining with fluorescence-labeled phalloidin. The phenotypes of intimal and medial smooth muscle cells were almost identical at first; however, during development, the former remained synthetic, whereas the latter became contractile. Confocal laser scanning microscopy was utilized to observe intimal and medial cells separately. Intimal smooth muscle cells were rarely observed in neonatal rats, but appeared by 10 days of age and increased during postnatal development. A combination of confocal and conventional fluorescent microscopy clearly demonstrated that the intimal smooth muscle cells were preferentially distributed in: (1) the right-lateral and dorsal wall of the upper thoracic aorta, (2) the left-lateral and ventral wall of distal two-thirds of the descending aorta, and (3) the downstream side of branch orifices. Intimal smooth muscle cells in group (1) were oriented randomly, whereas most in group (2) ran longitudinally. Intimal smooth muscle cells at branches in group (3) ran obliquely from the edges at the downstream side in an upstream direction. They tended to accumulate in regions of the aortic wall considered to be under high tensile stress.

An ultrastructural study of progressive intimal hyperplasia in rat vein grafts

PURPOSE

Intimal hyperplasia (IH) poses the greatest challenge for vein graft success. This fibroproliferative disorder causes obliterative stenosis and frequent graft occlusion. Although its causes remain poorly understood, it has been proposed that IH begins as a wound-healing response that cascades into a chronic state of unchecked proliferation. In this ultrastructural study, IH development and concomitant cell changes were evaluated in rat vein grafts.

METHODS

Epigastric vein-to-femoral artery grafts were placed in Lewis rats using standard microsurgical techniques. At various time points, grafts were harvested and processed for transmission electron microscopic, histologic, and immunohistochemical analyses. The proximal region, which displayed the most marked IH, was assessed for ultrastructural changes.

RESULTS

Our findings showed: (1) regeneration of the damaged endothelium by cells displaying an activated appearance; (2) early and complete smooth muscle cell death, with subsequent replacement by myofibroblastic cells; (3) extensive and sustained graft infiltration by monocytes/macrophages; and (4) intramural fibrin deposition.

CONCLUSIONS

The rat vein graft wall was substantially altered after implantation into the arterial circulation. During and after IH development, the cells in the graft did not resemble cells that are present in the nongrafted epigastric vein. Marked cell death, mononuclear cell infiltration, and the presence of myofibroblastic cells suggest a state of aberrant wound healing.

Cells in pseudointimal hyperplasia is migrated from extravascular space

BACKGROUND

The aim of this study was to investigate the origin of the pseudointima (PI) formed in polytetrafluoroethylene (PTFE) tube grafts after implantation into the inferior vena cava (IVC) of rabbits.

METHODS

A segment of the IVC of rabbits was replaced by PTFE tube graft (3 cm long, 3 mm inner diameter, 30 microns internodal distance, 0.3 mm thickness). The experimental group was divided into two groups as follows: (Group A) non-wrapped, (Group B) wrapped the outer wall of PTFE with impermeable vinyl.

RESULTS

Grafts were harvested at three weeks after implantation and subjected to the following studies: patency, ultrastructural studies by light microscopy (LM) and immunostaining, scanning and transmission electron microscopy (SEM & TEM). The grafts were patient but the lumen of the control group was narrowed by PI. LM and immunostaining studies revealed the presence of thick PI composed of spindle-type cells in Group A, bust almost no PI in Group B. Only few erythrocytes, macrophage and protein-fibrin matrix was found in Group B. Endothelial like cell coverage, judged by SEM, was observed in only Group A. Only some macrophages and platelets were shown in the graft surface in Group B. TEM of PI revealed the presence of VSMCs, myofibroblasts and outer surface of grafts revealed the presence of myofibroblast in Group A.

CONCLUSIONS

The formation of PI suppressed by blocking the cellular migration from perigraft space suggest that PI was mainly originated by myofibroblast located in the perigraft space.

Immunohistochemical and ultrastructural examination of smooth muscle cells in aortocoronary saphenous vein grafts

In this study, phenotypic modulation and remodulation of smooth muscle cells and associated intermediate filament expression were demonstrated by means of immunohistochemistry and ultrastructure to understand the development of intimal hyperplasia in aortocoronary saphenous vein grafts. In nongrafted saphenous veins, all smooth muscle cells expressed vimentin and desmin and were of a contractile form. In saphenous vein grafts showing stenotic intimal hyperplasia (luminal stenosis < 75%), expression of desmin was notably lower, whereas that of vimentin was higher. The cells were shown to be of a synthetic phenotype, suggesting modulation from the original contractile form. In saphenous vein grafts showing occlusive intimal hyperplasia (luminal stenosis > 76%), desmin expression in smooth muscle cells was increased again, and such cells were of a contractile form, suggesting remodulation from the synthetic phenotype. Some of the smooth muscle cells of the synthetic phenotype were positive for an antibody against proliferation cell nuclear antigen. Smooth muscle cells of the contractile form were negative for this antibody. The study suggests that smooth muscle cells of synthetic phenotype are highly responsible for "growing" intimal hyperplasia of aortocoronary saphenous vein grafts.

In vitro endothelialization of expanded polytetrafluoroethylene grafts: a clinical case report after 41 months of implantation

PURPOSE

Forty-one months after we performed bilateral implantation of in vitro endothelialized femoropopliteal bypass grafts in a 69-year-old patient, we obtained a central graft segment for histologic and ultrastructural investigation.

METHODS

Before implantation the grafts were confluently lined with autologous first passage mass cultures of pure cephalic vein endothelial cells. The precoating of the expanded polytetrafluoroethylene prosthesis was done with fibrinolytically inhibited fibrin glue. Reoperation became necessary because of symptomatic unilateral atherosclerotic lesions located in the center of one of the two in vitro lined grafts. A 21 cm long graft segment was removed and replaced by a new in vitro endothelialized expanded polytetrafluoroethylene graft.

RESULTS

On scanning electron microscopy a confluently covering mature endothelium was found throughout the whole length of the removed prosthesis. The endothelial identity was confirmed by a positive immunohistochemical CD 34, von Willebrand factor-staining, and the ultrastructural demonstration of Weibel Pallade bodies. The endothelium rested on a collagen IV positive basement membrane. Histologic cross sections revealed uniformly developed subintimal tissue of 1.21 +/- 0.19 mm thickness, which was separated from the intima by a distinct internal elastic membrane. The cells of this cell-rich matrix stained strongly positive for actin. Ultrastructurally, this matrix was dominated by highly contractile myofibroblasts loaded with peripherally located well-developed actin fillaments. A number of these cells also showed signs of secretory cells with a distinct endoplasmic reticulum and a Golgi complex. In areas of atherosclerotic lesions the subendothelial matrix was partially exposed, and the internal elastic membrane had to a certain extent disintegrated. Only in these areas KP-1 and MG-M1 positive foamy macrophages and CD 34 positive capillaries were found. The myofibroblasts of this diseased part of the subintimal tissue contained large lipid vacuoles.

CONCLUSIONS

We conclude that the confluent in vitro lining of synthetic vascular grafts with pure autologous endothelial cells facilitates graft healing, which may result in a hybrid structure with features of a native vessel.

Antisense oligonucleotide to proto-oncogene c-myb inhibits the formation of intimal hyperplasia in experimental vein grafts

BACKGROUND

The development of intimal hyperplasia is a major cause of early vein graft failure. The study examines the effects of locally delivered antisense oligonucleotides to the proto-oncogene c-myb on the development of vein graft intimal hyperplasia.

METHODS

Common carotid vein bypass grafting procedures were performed on 60 New Zealand White rabbits. Seventeen grafts were controls, 14 had grafts coated with a commercial gel, 17 had grafts coated with gel containing 200 micrograms of an antisense c-myb oligonucleotide, and 6 rabbits each had grafts coated with gel containing one of two control oligonucleotides. Grafts were harvested 28 days after surgery, and sections were taken for dimensional analysis, morphologic evaluation, and vasomotor function. Grafts were also harvested at 1 day for oligonucleotide uptake/localization analysis and at 3 days for c-myb mRNA analysis.

RESULTS

Oligonucleotides were uniformly distributed within the media and adventitia by 1 day. A 38% reduction occurred in mean intimal thickness in the vein grafts coated with antisense to c-myb compared with the other groups. No difference in medial thickness was seen among groups. By scanning and transmission electron microscopy all vein grafts showed a confluent endothelium. In contrast to control vein grafts, which did not relax to acetylcholine, most of the gel and all of the gel/oligonucleotide-coated grafts relaxed by more than 40% of precontracted tension. Responses to a panel of contractile agents were unchanged in the treated groups compared with those in the control group.

CONCLUSIONS

Locally delivered antisense oligonucleotides to proto-oncogene c-myb significantly reduces intimal hyperplasia with preservation of acetylcholine-mediated endothelium-dependent relaxation in experimental vein grafts. These findings suggest that targeting a common regulatory pathway of vascular smooth muscle mitogenesis can be successful in reducing the early development of intimal hyperplasia.

Absence of atherosclerosis evolution in the coronary arterial segment covered by myocardial tissue in cholesterol-fed rabbits

The evolution of atherosclerotic lesions is suppressed in the intima of the human coronary artery, beneath myocardial bridges. To elucidate the mechanism of the protective effect, we investigated morphological changes using the rabbit coronary artery as a model. Rabbit fed a 1%-cholesterol diet were killed at intervals up to 20 weeks. Two short segments of the left coronary arteries running in the epicardial adipose tissue (EpiLAD) and subsequently running in the myocardium (MyoLAD) were compared morphologically. The intima of the EpiLAD had flat endothelial cells with a polygonal shape, and demonstrated raised atherosclerotic lesions with increase in serum cholesterol level. In contrast, the intima of the MyoLAD was free of atherosclerotic lesions throughout the study, and the endothelial cells were spindle-shaped and engorged. While ferritin particles reached only the surroundings of the internal elastic lamina in the MyoLAD, they permeated into the media of the EpiLAD. We suggest that myocardial bridges suppress coronary atherosclerosis by an alteration of endothelial permeability, which may be due to changes in haemodynamic force tending towards a higher shear stress. The data provide an insight into the relationship between haemodynamics and the development of coronary atherosclerosis.

Histopathologic study of veins in steroid treated rabbits

Although arterial factors have been regarded as playing an important role in the pathogenesis of osteonecrosis, more attention has been given to venous factors because steroids cause an increase in the intraosseous pressure despite a decrease in blood flow in the femoral head. The authors examined changes in the veins of steroid treated rabbits. Forty rabbits were used: 30 rabbits (the steroid treated group) were injected with methylprednisolone acetate (4 mg/kg) weekly and 10 rabbits (the control group) were treated without steroids. The veins around the femoral head, ear veins, femoral veins, and inferior vena cava were obtained after 8 weeks of treatment, and the specimens were examined by immunohistochemical staining and electron microscopy. In the steroid treated group, proliferation of foam cells was observed in the intima of the vein in 7 of 30 rabbits. Immunohistochemical studies, using monoclonal antibodies for smooth muscle cells and macrophages, showed that the foam cells were derived from smooth muscle cells. Electron microscopy showed damage to the endothelial cells and smooth muscle cells. These results indicated that corticosteroids damaged the venous system. It is suggested that steroid induced disturbance of the draining veins causes stasis and that steroids are an important factor in osteonecrosis of the femoral head.

Long-term behavior of an arterial autograft: a new role for intimal hyperplasia?

The long-term behavior of an arterial autograft was studied with special attention to the evolution of intimal hyperplasia. An arterial autograft measuring approximately 5 mm in length was implanted in the right common iliac artery of female Sprague-Dawley rats. Animals were sacrificed at 90, 120, 150, 180, 240, 360, 400, 540 and 730 days after implantation. Grafts were evaluated by optical microscopy, electron microscopy, and morphometry. Myointimal cells were marked using an antiactin monoclonal antibody and studied by transmission electron microscopy. In the long term, the myointima of the arterial wall appeared as a consolidated layer formed by smooth muscle cells of contractile phenotype, abundant extracellular material consisting of clumps of elastin and collagen fibers. Cell maturity and degree of differentiation were demonstrated by the incorporation of antiactin antibody. The medial layer of the grafted segment suffered a marked long-term loss of cells and became an acellular layer sustained by the elastic layers. The adventitial layer was markedly cellular and had abundant vasa vasorum. Morphometry showed that the myointimal layer in the operated territory was not uniform and consisted of tongues of varying thickness. The total thickness of the arterial wall did not differ significantly (p > 0.05) between the graft and the proximal and distal areas. The results suggest that the intimal hyperplasia originating during the repair process could assume some functions of the degenerated medial layer, maintaining long-term vascular homeostasis.

Enhanced expression of tissue factor activity in the atherosclerotic aortas of cholesterol-fed rabbits

Tissue factor (TF) is an initiation cofactor of the extrinsic pathway of coagulation. Although the overexpression of TF antigen and mRNA have been previously demonstrated in atherosclerotic lesions using both immunohistochemical and in situ hybridization techniques, it still remains unclear as to whether TF activity is overexpressed in atherosclerotic plaque in vivo. In thoracic aortas obtained from cholesterol-fed rabbits for 10-20 weeks, the TF-mediated activation of factor X was quantitatively assessed on the intimal surface of the aortas ex vivo using a chromogenic substrate S-2222 and the findings were then compared with the immunohistochemical distribution of TF antigen. Non-atherosclerotic intimas showed only a weak amount of TF activity, while the adventitia contained a significantly high amount of activity. In the atherosclerotic intimas where TF antigen was overexpressed by foamy and non-foamy macrophages and smooth muscle cells but not by endothelial cells, TF activity was apparently enhanced to a level similar to that in the adventitia. Scanning electron microscopy revealed a perturbation of the intimal surface of the atherosclerotic aorta. These findings suggest that TF activity is apparently enhanced in subendothelial atherosclerotic lesions and, therefore, endothelial denudation, which results in the exposure of active TF to flowing blood, leads to thrombosis and its sequelae in atherosclerotic lesions.

Homocysteine induced arteriosclerosis-like alterations of the aorta in normotensive and hypertensive rats following application of high doses of methionine

Following oral administration of methionine in high doses to normotensive (NR) and spontaneously hypertensive (SHR) rats, its degradation product, homocysteine (HC), which is markedly elevated in serum, exerts an angiotoxic action directed to the aorta. This is accompanied by considerable loss of endothelium and degeneration, partly with dissolution of the media cells with formation of characteristic processes of the degenerating mitochondria, and by elevated HC and cystathion (CT) values in the aortic wall. At the arterial vessels of other organs similar alterations did not occur. There are quantitative differences between NR and SHR. In SHR, serum shows higher HC and CT concentrations than in NR, and the methionine-related aortic alterations are considerably more pronounced and develop earlier, with the additional formation of connective tissue. Here, a certain dependence on the methionine dose is noted, in contrast to NR, for which the magnitude of the reaction appears to be more related to the length of time of methionine application. Additional administration of atherogenic substances (cholestane-3 beta, 5 alpha, 6 beta-triol, cholesterol, angiotensin II, cholic acid with methylthiouracil) in SHR causes an exacerbation of the methionine-related aortic alterations. Only cholestane-triol has the same effect on the aortic wall in NR and SHR, with more accentuation in SHR. Cholestane-triol has, in NR as well as in SHR, a high coincidence with methionine-induced morphological reactions including the formation of mitochondrial processes. Simultaneous application of these two substances did not cause a potentiation of the effect. High doses of cholesterol bring about aortic alterations in SHR but not in NR. Thus, in addition to the disorder of fat and carbohydrate metabolism, disturbed protein metabolism is of decisive importance as a risk factor for coronary and other vascular diseases.

Atherosclerosis-prone branch regions in human aorta: microarchitecture and cell composition of intima

The microarchitecture and cell composition of intima were studied at the macroscopically unaffected branch regions of human thoracic aorta using en face preparations, scanning and transmission electron microscopy, and immunohistochemistry. The endothelial lining showed a heterogeneous pattern and altered morphology including the areas of deendothelialization covered with platelets and dilated intercellular clefts. Leukocyte adhesion, accumulation of subendothelial macrophages and lymphocytes were characteristic of proximal and lateral zones, while the flow divider showed no significant accumulation of blood cells. Smooth muscle cells (SMCs) on the flow divider were elongated, in a contractile state, contacted side-by-side and did not contain lipid inclusions. In the lateral and proximal zones, intima appeared to be a network of stellate SMCs which were in contact through their processes. Most of the SMCs were in a synthetic state and many of them contained small lipid droplets. The number of procollagen I positive cells and the volume of extracellular components were most significant at the lateral zones rather than at the flow divider. We did not observe any difference in the rate of proliferation. Our results suggest that the intimal layer at the lateral and proximal zones has some distinct structural peculiarities, which provoke the development of initial atherosclerotic lesions at these sites. Such an intimal structure is probably caused by different flow patterns at these zone. However, only the totality of different morphological features exhibited in the area of altered vascular wall shear stress may be considered as a prerequisite for atherosclerotic lesions.

Modifications induced by atherogenic diet in the capacity of the arterial wall in rats to respond to surgical insult

A study was made of events occurring in the arterial wall of the rat after administration of an atherogenic calcification-inducing diet and of vascular response in a model of combined metabolic aggression (atherogenic, calcification-inducing diet) and surgical aggression (adventitial resection). Female Sprague-Dawley rats were fed an atherogenic, calcification-inducing diet for 24 consecutive days, after which half the rats returned to standard diet (group I, n = 12) and the other half (group II) underwent resection of the adventitia on a segment of common iliac artery on day 25 before returning to standard diet. Normolipemic rats and rats that underwent adventitial resection without the atherogenic, calcification-inducing diet were used as the control groups. The rats were killed at 10 min, 1 and 24 h, 5, 14, 21, 30, 50, 70, 120 and 180 days. Morphologic studies were made with light microscopy and electron microscopy (scanning and transmission), as well as biochemical studies. Monocyte adherence and infiltration of the arterial intima, thickening of the subintimal space, the presence of monocyte-macrophages, calcification in the medial layer, intense adventitial fibrosis, and vacuolization of the endothelial cells of the adventitial microvessels were common findings in the two groups receiving the atherogenic, calcification-inducing diet. However, these groups differed in the intensity of calcification: the deep part of the medial layer did not become calcified when the adventitia was resected. Moreover, adventitial regeneration was delayed in group II with respect to the animals that underwent adventitial resection without atherogenic, calcification-inducing diet. We conclude that this diet induced atherosclerotic lesions in the vessel wall and inhibited adventitial regeneration in the rats that underwent resection.

Nature and origin of the neointima in whole vessel wall organ culture of the human saphenous vein

Intimal proliferation is a characteristic feature of arteriosclerosis. Whole vessel wall organ culture systems have been developed to study the early stages of neointima formation. We have cultured a large number of explants of human saphenous vein specimens for several weeks, and have identified the nature of the cells in the newly formed intima by a panel of monoclonal antibodies recognizing endothelial cells (von Willebrand factor, platelet endothelial cell adhesion molecule-1 and EN-4 antigen), smooth muscle cells (monoclonal antibodies HHF35 and CGA-7) and fibroblasts (5B5 antibody). In addition we determined the uptake of fluorescently labelled acetylated low density lipoprotein by the surface cells of the explants. We found that an apparent neointima was formed in the vein organ system, the cells of which were predominantly smooth muscle cells and originated from the cut edges and from the adventitia of the vein segment. The endothelial cells originally lining the luminal surface of the vessel segments became overgrown by these cells. They remained at the base of the newly formed neointima and a number of them reorganized into capillary-like structures. Our data suggest that explant culture of saphenous vein does not reflect the classical concept of neointima formation, in which intimal smooth muscle cells migrate through the internal elastic lamina and accumulate in the intima. Although it has this limitation, the model may serve well to study specific aspects of cell migration, smooth muscle cell differentiation and angiogenesis, and may reflect aspects of intimal thickening at surgical suture sites.

Effect of defective connective tissue on the formation of aneurysmal-like structures in the rat testicular artery

Microscopic aneurysmal-like structures (ALS) develop spontaneously in the convoluted rat testicular artery and have been previously proposed as a model relevant to cerebral aneurysms. The effect of defects in connective tissue fibres on ALS formation was investigated by microscopy using two approaches: (i) the study of the effect of beta-aminopropionitrile (BAPN), an inhibitor of the cross-linking of elastic and collagen fibres, on the incidence, size and morphology of ALS in spontaneously hypertensive rats (SHR) and their normotensive controls (WKY). The straight spermatic artery was studied for comparison. (ii) The determination of the incidence of spontaneous ALS in Brown Norway (BN) and Long Evans (LE) rats which are highly susceptible (BN) or resistant (LE) to the spontaneous rupture of the arterial internal elastic lamina. (i) BAPN increased the number and size of ALS in SHR and WKY rats and had no effect on the straight spermatic artery and (ii) ALS were more numerous and of greater size in BN than in LE rats. Taken together, these results show that defective connective tissue fibres may favour the formation and induce the enlargement of aneurysmal-like structures. By analogy, these data suggest that a lack of connective tissue fibre integrity may be of importance in cerebral aneurysm formation and development.

Relationship between chondroitin sulfate proteoglycan and coronary atherosclerosis in the youth

OBJECTIVE

To study the relationship between chondroitin sulfate proteoglycan (CSPG) and coronary atherosclerosis in youth.

MATERIAL AND METHODS

Immunohistochemistry of chondroitin sulfate proteoglycan and SM-alpha-actin was performed on 39 human coronary arteries, including normal vessels and vessels with fatty streaks, intermediate lesions and plaques. Some of the lesional vessels were taken for beta-lipoprotein immunohistochemical study. CSPG contents were quantitated by image analyzer and the coronary arteries from one heart were processed for immunoelectron microscopy.

RESULTS

The range of CSPG distribution was extensive and CSPG area density was increased significantly in the intima with atherosclerotic lesions. The increase of CSPG was parallel to the numbers of smooth muscle cell (SMC) with positive SM-alpha-actin reaction and was likely related to the phenotype transformation of SMC. Similar distribution of beta-lipoprotein and CSPG were found within the lesional regions.

CONCLUSIONS

The increase of CSPG in atherosclerotic lesion may be an important factor resulting in the deposition of lipids in the vascular wall so as to promote the formation and development of atherosclerosis.

Human saphenous vein organ culture: a useful model of intimal hyperplasia?

OBJECTIVES

Although cell culture techniques and animal models of intimal hyperplasia have increased our current understanding of the aetiology of vein graft stenosis, the results of such studies have been difficult to relate to the human situation.

DESIGN

The present study was designed to validate an organ culture of human saphenous vein by comparing the changes occurring in cultured vein with those seen in pathological vein graft stenoses and to identify a suitable marker of cell proliferation.

MATERIALS AND METHODS

Saphenous vein segments were cultured for 14 days, fixed in formalin and processed for immunohistochemistry. Freshly excised stenoses were fixed and processed similarly. A number of markers of cell proliferation were evaluated in the culture system in order to identify the one best suited to this particular model.

RESULTS

Marked similarities were observed in the cellular and extracellular matrix composition, and electron microscopy revealed that both the neointima of the cultured vein and the pathological lesion contained an abundance of smooth muscle cells of a secretory phenotype. Bromodeoxyuridine proved to be the most reliable proliferation marker and revealed that early proliferation in the superficial layers of the vein intima gave rise to the formation of neointima. Both proliferation and neointimal thickness were maximal by day 14 in culture. Proliferation declined rapidly thereafter, and the neointima was maintained.

CONCLUSIONS

The changes occurring in cultured vein and graft stenoses bore many similarities, thereby justifying the use of organ culture as a valuable experimental tool.

Diversity of the synthetic-state smooth-muscle cells proliferating in mechanically and hemodynamically injured rabbit arteries

Vascular smooth muscles contain at least three types of developmentally regulated myosin heavy-chain (MHC) isoforms; SM1, SM2, and SMemb. By investigating the expression of the three MHC isoforms, we previously demonstrated in rabbits that smooth muscles proliferating in the neointima of arterio- and atherosclerotic lesions regain an "embryonic" phenotype. In the present study, we examined if neointimal cells are morphologically similar to embryonal smooth muscles and if dedifferentiation of neointimal smooth muscles is a reversible process. Vascular injury was produced in rabbits either by endothelial cell denudation of the aorta or by poststenotic dilation of the carotid artery. We have demonstrated in this study that the proliferating neointimal cells expressed SM1 and SMemb, but not SM2, indicating smooth muscles of an "embryonic" phenotype. The dedifferentiation of neointimal smooth muscles was found to be reversible; at 4 to 8 weeks after injury, a majority of the cells reexpressed both SM1 and SM2, but not SMemb. By electron microscopy, we have revealed smooth-muscle phenotypes determined by MHC isoforms to correspond to the morphologic phenotypes as an increase in membranous organelles, and a decrease in myofilaments was associated with the reexpression of SMemb. Interestingly, we also found that in the medial wall at 4 to 8 weeks after ballooning injury, a number of SM1-negative cells proliferated rapidly, replacing normal smooth muscles. These cells were negative against SM1 and SM2 but positive for SMemb. These SM1-negative cells contained abundant membranous organelles and few myofilaments. These cells did not express SM1 or SM2 even after 8 weeks postinjury. We conclude from these results that the proliferating synthetic-type smooth muscles after vascular injury are composed of SM1-positive cells that are morphologically similar to embryonal smooth muscle and that maintain ability to redifferentiate, and SM1-negative cells that contain few myofilaments and remain dedifferentiated.