Narrow superficial injury to rabbit aortic endothelium. The healing process as observed by scanning electron microscopy

The Endothelial Cytoskeleton: Organization in Normal and Regenerating Endothelium*

The components of the endothelial cell cytoskeleton that have been shown to be important in maintaining endothelial structural integrity and in regulating endothelial repair include F-actin microfilament bundles, including stress fibers, and microtubules, and centrosomes. Endothelial cells contain peripheral and central actin microfilaments. The dense peripheral band (DPB) consists of peripheral actin microfilament bundles which are associated with vinculin adhesion plaques and are most prominent in low or no hemodynamic shear stress conditions. The central microfilaments are very prominent in areas of elevated hemodynamic shear stress. There is a redistribution of actin microfilaments characterized by a decrease of peripheral actin and an increase in central microfilaments under a variety of conditions, including exposure to thrombin, phorbol-esters, and hemodynamic shear stress. During reendothelialization, there is a sequential series of cytoskeletal changes. The DPB remains intact during the rapid lamellipodia mediated repair of very small wounds except at the base of the lamellipodia where it is splayed. The DPB is reduced or absent when cell locomotion occurs to repair a wound. In addition, when cell locomotion is required, the centrosome, in the presence of intact microtubules, redistributes to the front of the cell to establish cell polarity and acts as a modulator of the directionality of migration. This occurs prior to the loss of the DPB but does not occur in very small wounds that close without migration. Thus, the cytoskeleton is a dynamic intracellular system which regulates endothelial integrity and repair and is modulated by external stimuli that are present at the vessel wall-blood interface.

A microfluidics-based wound-healing assay for studying the effects of shear stresses, wound widths, and chemicals on the wound-healing process

Collective cell migration plays important roles in various physiological processes. To investigate this collective cellular movement, various wound-healing assays have been developed. In these assays, a “wound” is created mechanically, chemically, optically, or electrically out of a cellular monolayer. Most of these assays are subject to drawbacks of run-to-run variations in wound size/shape and damages to cells/substrate. Moreover, in all these assays, cells are cultured in open, static (non-circulating) environments. In this study, we reported a microfluidics-based wound-healing assay by using the trypsin flow-focusing technique. Fibroblasts were first cultured inside this chip to a cellular monolayer. Then three parallel fluidic flows (containing normal medium and trypsin solution) were introduced into the channels, and cells exposed to protease trypsin were enzymatically detached from the surface. Wounds of three different widths were generated, and subsequent wound-healing processes were observed. This assay is capable of creating three or more wounds of different widths for investigating the effects of various physical and chemical stimuli on wound-healing speeds. The effects of shear stresses, wound widths, and β-lapachone (a wound healing-promoting chemical) on wound-healing speeds were studied. It was found that the wound-healing speed (total area healed per unit time) increased with increasing shear stress and wound width, but under a shear stress of 0.174 mPa the linear healing speed (percent area healed per unit time) was independent of the wound width. Also, the addition of β-lapachone up to 0.5 μM did not accelerate wound healing. This microfluidics-based assay can definitely help in understanding the mechanisms of the wound-healing process and developing new wound-healing therapies.

Differential migration and proliferation of geometrical ensembles of cell clusters

Differential cell migration and growth drives the organization of specific tissue forms and plays a critical role in embryonic development, tissue morphogenesis, and tumor invasion. Localized gradients of soluble factors and extracellular matrix have been shown to modulate cell migration and proliferation. Here we show that in addition to these factors, initial tissue geometry can feedback to generate differential proliferation, cell polarity, and migration patterns. We apply layer by layer polyelectrolyte assembly to confine multicellular organization and subsequently release cells to demonstrate the spatial patterns of cell migration and growth. The cell shapes, spreading areas, and cell-cell contacts are influenced strongly by the confining geometry. Cells within geometric ensembles are morphologically polarized. Symmetry breaking was observed for cells on the circular pattern and cells migrate toward the corners and in the direction parallel to the longest dimension of the geometric shapes. This migration pattern is disrupted when actomyosin based tension was inhibited. Cells near the edge or corner of geometric shapes proliferate while cells within do not. Regions of higher rate of cell migration corresponded to regions of concentrated growth. These findings demonstrate that multicellular organization can result in spatial patterns of migration and proliferation.

Inhibition of neovascularization by a cartilage factor

Neovascularization of developing, repairing or neoplastic tissues is regulated, at least partially, by a family of proteins of low molecular mass (1000 less than mol mass less than 50 000 Da) which can be extracted from avascular tissues, such as hyaline cartilage, aorta or bladder epithelium, by mild salt solutions. These extractable proteins, functionally defined as anti-invasion factor (AIF), act as local regulators for some of the major mechanistic pathways by which endothelial cells are thought to invade tissues during neovascularization, mainly by matrix-degrading enzymes and by increased rates of migration and proliferation. AIF contains a spectrum of proteinase (collagenase) inhibitory activities, as well as an endothelial cell growth inhibitor. The endothelial cell growth inhibitor is directed against actively dividing endothelial cells in culture but has no effect on endothelial cell monolayers or any other cell lines tested. In tumours, the AIF-derived endothelial cell growth inhibitor may limit tumour growth to less than 2 mm in diameter by inhibiting tumour neovascularization.

Cell motility in a new single-cell wound model

Until now researchers have used a monolayer of cultured cells to investigate cell motility toward an injured cell. However, we suspect that, when using this method, adjacent cells move to the free space due to relief of contact inhibition. The current study was designed to investigate the cell motility nearby an injured cell in varying cell connectivity. A low-power laser beam was used to damage one cell selectively with the silver coating beads. After injury, we observed the cell motility in three different cell types: (1) those immediately adjacent to the injured cell, (2) those removed from the injured cell by interposition of another cell, and (3) those removed from the injured cell by free space. The cells that are in direct contact with the injured cell moved toward the injured cell within 1.5-3.0 h. Indirectly connected cells and cells with no contact, on the other hand, showed no significant movement toward the injured cell. This suggests that the cell motility toward the cell injury is not only due to relief of contact inhibition but might also be caused by cell-to-cell signaling via cell connection. The current method will provide a tool to create a cell injury without damaging adjacent cells.

Shear stress enhances human endothelial cell wound closure in vitro

Repair of the endothelium occurs in the presence of continued blood flow, yet the mechanisms by which shear forces affect endothelial wound closure remain elusive. Therefore, we tested the hypothesis that shear stress enhances endothelial cell wound closure. Human umbilical vein endothelial cells (HUVEC) or human coronary artery endothelial cells (HCAEC) were cultured on type I collagen-coated coverslips. Cell monolayers were sheared for 18 h in a parallel-plate flow chamber at 12 dyn/cm(2) to attain cellular alignment and then wounded by scraping with a metal spatula. Subsequently, the monolayers were exposed to a laminar shear stress of 3, 12, or 20 dyn/cm(2) under shear-wound-shear (S-W-sH) or shear-wound-static (S-W-sT) conditions for 6 h. Wound closure was measured as a percentage of original wound width. Cell area, centroid-to-centroid distance, and cell velocity were also measured. HUVEC wounds in the S-W-sH group exposed to 3, 12, or 20 dyn/cm(2) closed to 21, 39, or 50%, respectively, compared with only 59% in the S-W-sT cells. Similarly, HCAEC wounds closed to 29, 49, or 33% (S-W-sH) compared with 58% in the S-W-sT cells. Cell spreading and migration, but not proliferation, were the major mechanisms accounting for the increases in wound closure rate. These results suggest that physiological levels of shear stress enhance endothelial repair.

Evans blue dye modifies the ultrastructure of normal and regenerating arterial endothelium in rats

Evans blue dye (EBD) identifies areas of increased vascular permeability, which is usually indicative of endothelial damage. Most studies examine EBD-stained areas light-microscopically, but others analyze the cells with the electron microscope. Electron microscopic studies have assumed that EBD itself did not change the ultrastructure of endothelial cells and this hypothesis was tested in the following study. The left iliac arteries of 20 rats were injured with 1-mm vascular clamps for 5 minutes. At 7 and 14 days after clamping, 10 rats for each time were infused intravenously either with normal-saline or EBD, perfused 30 minutes later with fixatives. Then the clamp-injured arteries, contralateral (unclamped) arteries, aortae, and the aortic bifurcations were removed for EM morphometry. In an additional (control) group of 10 rats, with no clamp injuries, 5 were infused with EBD and 5 with normal-saline and all 10 rats were perfused 30 minutes later, as above. EBD caused a significant simplification of the junctional morphology in both normal and regenerating endothelium. It also increased the area fractions of cytoplasmic vesicles in regenerating endothelium. These data demonstrate that EBD causes measurable ultrastructural changes in normal and regenerating endothelium. This effect should be taken into account when using EBD to assess various insults to blood vessels.

Inhibitory effect of methylmercury on migration and tube formation by cultured human vascular endothelial cells

The effect of methylmercury chloride (MeHg) on migration and tube formation by cultured human umbilical vein endothelial cells (HUVECs) was quantitatively analyzed. The distance of endothelial cell outgrowth from the scraped edge of a monolayer was measured. HUVEC outgrowth was inhibited by MeHg (1.0-5.0 microM) treatment in a dose-dependent manner. Tube formation was studied by culturing the cells on gelled basement membrane matrix (Matrigel). Treatment of HUVECs with 0.1-5.0 microM MeHg for 24 h inhibited tube formation dose-dependently. These results suggest that migration and tube formation by HUVECs are susceptible to MeHg cytotoxicity, and that MeHg could be injurious to endothelial cell function, which may be involved in the pathogenesis of arteriosclerosis.

The effect of peroxides on the vascular endothelium of isolated pig aorta in vitro

The effect of peroxide on endothelial cells (perfused pig aorta) was examined using an in vitro perfusion model. Hydrogen peroxide was added to the perfusion medium (pig serum together with a buffer solution) which was expected to lead to an increased oxidation of lipids and lipoproteins. Oxidation processes of this type play a decisive role in the pathogenesis and progression of arteriosclerosis. The aim of the present investigation was to demonstrate by introducing hydrogen peroxide (H2O2) in varying concentrations (0.5-1.5%), the destructive impact of peroxides on the endothelium, while these cells are believed to play a key role in the pathogenesis of arteriosclerosis. The extent of endothelial cell impairment was assessed by means of silver staining visualisation of endothelial cell borders as well as light- and scanning-electronmicroscopic investigation. It was discovered that the endothelial cells show increasing impairment after 10 h of perfusion due to the effect of peroxide (hydrogen peroxide).

Role of thrombin in endothelial cell monolayer repair in vitro

PURPOSE

We examined the effect of thrombin on human iliac artery endothelial cell monolayer repair and proliferation after denuding vascular injury.

METHODS

Human iliac artery endothelial cell monolayer repair was determined by scrape wounding confluent monolayers and measuring the advancement of the cells into the wounded area for 3 days. Proliferation studies involved plating human iliac artery endothelial cells at one tenth confluence and counting the increase in cell number every 2 days for a 2-week period. Proliferation during monolayer repair was examined by determining bromodeoxyuridine uptake in cells located at the leading edge of a scrape-wounded monolayer.

RESULTS

Thrombin (1 to 8 U/ml) inhibited human iliac artery endothelial cell monolayer repair in a concentration-related, reversible manner. The effect was augmented by decreasing serum concentration and was independent of the presence of endothelial cell growth supplement. Inactivation of thrombin's proteolytic site with diisopropylfluorophosphate eliminated its effect on monolayer repair. Thrombin (0.5 to 8 U/ml) inhibited human iliac artery endothelial cell proliferation in a dose-related manner. This effect was augmented by decreasing serum concentration. Finally, thrombin (4 U/ml) inhibited the proliferative response of cells located at the leading edge of wounded monolayers compared with control groups.

CONCLUSION

Thrombin inhibits human arterial endothelial cell monolayer repair and proliferation after denuding vascular injury.

Enhanced detection of cardiac allograft arterial disease with intracoronary ultrasonographic imaging

Intracoronary ultrasonographic imaging was performed in 60 patients 0.3 to 9 years (mean 2.9 +/- 1.9) after heart transplantation. By using a 1.8 mm intravascular ultrasonographic catheter, 192 (80%) of 240 angiographically visualized major epicardial coronary arteries (right, left main, anterior descending, and circumflex) were imaged by ultrasonography. Coronary luminal irregularities were detected in 15% of arteries by angiography compared with 34% by ultrasonography (p < 0.0001). The typical abnormality detected by ultrasonography consisted of crescentic and/or concentric intimal and medial thickening. Calcification in vascular lesions was rare (< 1% of arteries studied). Although the prevalence of angiographic abnormalities tended to be time dependent, ultrasonographic abnormalities were more strongly associated with donor age (normal, 22 +/- 8 years, vs abnormal, 33 +/- 10 years; p < 0.0001). Cardiac allograft coronary arterial disease is significantly underestimated by contrast angiography. Intravascular ultrasonography may provide a useful adjunct for identification and serial follow-up of this significant problem.

Influence of mitomycin C on endothelial monolayer regeneration in vitro

This study examines the effect of Mitomycin C, a fungal toxin which inhibits DNA synthesis, on the regeneration of partially denuded large vessel endothelium in vitro. Monolayers of bovine pulmonary artery endothelial cells were treated with Mitomycin C prior to or immediately following partial denudation and were incubated in the continuing presence of Mitomycin C; the effects of this treatment on monolayer repair, cell proliferation, and other aspects of endothelial phenotype were monitored. Cell proliferation, DNA, RNA, and protein synthesis were all reduced in a dose dependent manner in treated cultures. Incubation with Mitomycin C for 48 h or longer resulted in reduced cell spreading, and rounding up and loss of cells from both intact and partially denuded cultures. Effects were less severe with lower doses and shorter incubation times. However, significant reductions in monolayer regeneration occurred within 8 h of incubation, sufficiently early to suggest that Mitomycin C may affect aspects of the regeneration process independent of cell proliferation. Polarization/spreading of cells at the denudation edge was monitored by fluorescence staining for golgi with C5-DMB-ceramide, and for centrioles with antibodies to tubulin. Centrioles and golgi rapidly reoriented to a location at the putative leading edge of control cultures. Mitomycin C treatment had no effect on centriole reorientation, but caused a significant delay in golgi localization. These results suggest that Mitomycin C inhibits endothelial monolayer regeneration by mechanisms independent of cell proliferation and DNA synthesis, perhaps by interfering with cell spreading or translocation at the wound edge.

Stimulatory effects of insulin and insulin-like growth factor I on migration and tube formation by vascular endothelial cells

The effects of insulin and insulin-like growth factor I (IGF-I) on migration, proliferation and tube-forming activity of endothelial cells were investigated, by using bovine carotid artery endothelial cells. Migration was assayed by a filter membrane technique and tube formation was assayed by a quantitative angiogenesis in vitro model which we have recently developed. In this model, endothelial cells are cultured between two layers of type I collagen gel and become organized into tube-like structures which mimic capillaries in vivo ultrastructurally. Insulin (50-1000 microunits/ml) and IGF-I (10-200 ng/ml) significantly stimulated migration of endothelial cells in a dose-dependent manner with a maximal stimulation of 3.0-fold at 1000 microunits/ml for insulin and 3.8-fold at 200 ng/ml for IGF-I (P less than 0.01). Insulin at concentrations up to 1000 microunits/ml and IGF-I up to 100 ng/ml did not affect proliferation of endothelial cells. When insulin or IGF-I was added in culture medium on collagen gels, tube-forming activity of endothelial cells was markedly stimulated. The specific lengths of tubes significantly increased with the increase in insulin concentration from 25 to 100 microunits/ml (P less than 0.01). At 100 microunits/ml, the stimulation was 1.77-fold (P less than 0.01). IGF-I (1-100 ng/ml) also stimulated the elongation of tubes dose-dependently with a maximal stimulation of 1.96-fold at 100 ng/ml (P less than 0.01). Thus, insulin and IGF-I at pathophysiological concentrations stimulate migration and tube-forming activity of endothelial cells, suggesting that these polypeptides may stimulate repair of endothelial injury in cases such as atherosclerosis and may act as a stimulator of angiogenesis.

A biological basis for re-stenosis after percutaneous transluminal angioplasty: possible underlying mechanisms

Intravascular catheterization is a commonly used diagnostic tool and percutaneous transluminal angioplasty is used to dilate stenosed blood vessels. Although these techniques are very successful diagnostically and therapeutically they may precipitate a number of acute and chronic complications. Chronic intimal changes following balloon angioplasty can result in re-stenosis. Intimal hyperplasia can be a long-term complication of both diagnostic and interventional vascular catheterization. This article details these long-term structural changes, specifically relating experimental in vivo and in vitro changes to those seen clinically.

Endothelial cell population dynamics in rat brain after local irradiation

The dynamics of the endothelial cell population was investigated in the rat brain after local irradiation with different doses of X rays. A fluorescent-histochemical technique was used for the visualization of the cells. A decrease in endothelial cell number was observed within 1 day of irradiation with doses of 5-200 Gy. At this time the endothelial cell number had decreased by up to 15% compared with the pre-treatment values. This early dose-independent loss in cell number was maintained for up to 1 month after irradiation. This was then followed by a slow dose-independent decrease in cell density up to 6 months after exposure. Subsequently the depletion of the endothelial cell population exposed to 40 and 60 Gy continued. After a dose of 25 Gy an abortive recovery of cell numbers occurred followed by an abrupt depletion of the endothelial cell population. The possible mechanisms of such changes are discussed.

Cytoskeleton in TFG-beta- and bFGF-modulated endothelial monolayer repair

Endothelial cell proliferation and migration in vitro is depressed by transforming growth factor beta (TFG-beta) and enhanced by basic fibroblast growth factor (bFGF) treatment. This study examines interactions between cytoskeletal changes and cell proliferation in regenerating endothelial monolayers treated with bFGF, TFG-beta, and both factors. As previously described by others, monolayer regeneration is enhanced by bFGF and reduced by TFG-beta. Endothelial cell morphology is altered by TFG-beta treatment. Cells lose their cobblestone appearance and assume a pleomorphic shape. Actin microfilament staining is modified in both intact and regenerating TFG-beta-treated monolayers as well. There is a loss of dense peripheral band staining and an enhancement in staining intensity of cytoplasmic stress fibers. No such alterations are seen in bFGF-treated cultures. Cell proliferation at the wound edge, as indicated by bromodeoxyuridine incorporation, is inhibited by TGF-beta. Although monolayer repair is modulated by growth factor treatment, centrosome reorientation and microtubule staining patterns are not altered by either factor. Thus these factors appear to have effects on a mechanism(s) other than centrosome reorientation which may be involved in repair of denuded endothelial monolayers.

Enhancement of migration in bovine endothelial cells by eicosapentaenoic acid pretreatment

It has been recognized that endothelial cell migration is an important process in the regeneration of injury in blood vessels. In this study, we examined the effects of polyunsaturated fatty acids on the migration of cultured endothelial cells using a modified Boyden chamber. When endothelial cells isolated from bovine carotid artery were pretreated for 2 days with 5 micrograms/ml of either arachidonic acid, eicosapentaenoic acid or docosahexaenoic acid, every polyunsaturated fatty acid was incorporated substantially into cellular phospholipids. The content of arachidonic acid increased from 9.27 to 23.9% by the arachidonic acid pretreatment, and that of eicosapentaenoic acid and docosahexaenoic acid increased from 9.57 to 11.85% by the eicosapentaenoic acid pretreatment and from 5.56 to 18.40% by the docosahexaenoic acid pretreatment, respectively. Pretreatment of the cells with 0.5-5.0 micrograms/ml of eicosapentaenoic acid resulted in a dose-dependent increase in endothelial migration in response to fetal bovine serum. In contrast, pretreatment of the cells with arachidonic acid and docosahexaenoic acid had no effects on the cell migration. If eicosapentaenoic acid, however, was added directly to the migration assay system instead of the pretreatment, it did not show a profile of chemotactic factor. The eicosapentaenoic acid pretreatment also potentiated cell migration activity in response to several other chemotactic factors such as basic fibroblast growth factor, tumor necrosis factor-alpha and leukotriene C4. The effect of eicosapentaenoic acid on porcine smooth muscle cell migration was also examined. Although eicosapentaenoic acid was similarly incorporated into cellular phospholipids of smooth muscle cells by the pretreatment for 2 days, no stimulative effect was observed in the migration of smooth muscle cells at any doses (0.5-5.0 microns/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Intimal lesion formation in rat carotid arteries after endothelial denudation in absence of medial injury

Injury of an artery by passage of a balloon catheter causes both endothelial denudation and medial damage and produces a marked smooth muscle cell (SMC) proliferative response. In this study, the endothelium from rat carotid arteries was removed by use of a rotating loop of 5/0 monofilament suture (gentle denudation technique), which did not cause any detectable damage to the underlying medial cells but did cause platelet adherence. Expression of platelet-derived growth factor (PDGF) A-chain and PDGF receptor mRNA was comparable to that seen in ballooned carotids, but the medial SMC proliferative response to gentle denudation was markedly reduced when compared to that observed after balloon denudation (1.4% vs. 13.6%). Intimal lesions were only observed in those zones that remained denuded for more than 7 days. These results demonstrate that a denuding injury with no medial trauma is sufficient to induce intimal lesions and that the significantly higher proliferation seen in ballooned vessels might reflect a response of the medial cells to trauma that occurred during denudation.

Syndromes of accelerated atherosclerosis: role of vascular injury and smooth muscle cell proliferation

Vascular injury represents a critical initiating event in the pathogenesis of various vascular diseases, including atherosclerosis. This review discusses 1) the current understanding and a new pathologic classification of vascular injury; 2) the resultant cellular pathophysiologic responses, specifically, lipid accumulation, platelet aggregation, thrombus formation and smooth muscle cell proliferation; 3) the role of vascular injury in the pathogenesis of spontaneous and accelerated atherosclerosis; and 4) emerging therapeutic approaches in preventing these vascular diseases. The process of type I vascular injury (nondenuding functional injury) followed by lipid accumulation, monocyte and platelet adhesion, smooth muscle cell proliferation and resultant plaque formation represents the prevalent view of the early stages of spontaneous atherogenesis. The syndromes of accelerated atherosclerosis (namely, heart transplant atherosclerosis, coronary vein graft disease and restenosis after percutaneous transluminal coronary angioplasty) appear to share etiologic mechanisms with spontaneous atherosclerosis by means of the "response to injury" hypothesis. However, type II and type III vascular injury (denuding endothelial and intimal injury with or without medial damage) followed by thrombus and its organization by smooth muscle cell proliferation and subsequent fibrosis appear to be responsible for the vascular process. This accelerated and premature occlusive process accounts for significant morbidity and mortality in patients with these conditions. Better understanding of the nature of vascular injury and its pathophysiologic responses in these clinical situations may aid in developing therapeutic strategies for preventing these vascular diseases.

In vitro endothelial wound repair. Interaction of cell migration and proliferation

Most re-endothelialization requires both cell migration and cell proliferation. To study the association between cell migration and the initiation of DNA synthesis in an in vitro wound model, confluent cultures of porcine aortic endothelial cells grown on glass coverslips were scraped to remove half of the monolayer. Treatment with 1 ng/ml of taxol, a microtubule stabilizing drug, for 24 hours resulted in no visible change in F-actin or microtubule organization as assessed by fluorescence and immunofluorescence microscopy. There was, however, a reduction of wound re-endothelialization and an associated reduction in the proportion of cells with centrosomes redistributed toward the wound edge. No significant differences, however, were seen in the labeling indices for the first two rows of cells at the wound edge as revealed by 3H-thymidine autoradiography. Labeling of nuclei in Rows 3 to 8 and in a zone deeper within the monolayer was reduced in treated cultures. The data suggest that endothelial proliferation in cells within an area bordering a wound is dependent on both denudation, which is sufficient to promote maximal proliferation in the two rows adjacent to the wound, and cell migration, which is required for the propagation of proliferation in cells further away from the wound edge.

Endothelial cell response to pulsed electromagnetic fields: stimulation of growth rate and angiogenesis in vitro

The effects of pulsed electromagnetic fields on the repopulation rate of denuded regions of endothelial cell monolayers and on endothelial cell reorganization into complex vessellike structures was monitored in vitro by using human umbilical vein and bovine aortic endothelial cells. A small (20-40%) but statistically significant enhancement in growth rate of partially denuded endothelial cell monolayers as determined by tritiated thymidine incorporation was observed in the presence of pulsed electromagnetic fields. Morphologically, endothelial cells entering the denuded regions were observed to be elongated, often connecting end to end to form a mycelial or "sprouting" pattern when exposed to pulsed electromagnetic fields. This was in contrast to cells outside of the field which had a more cuboidal morphology. Complete disruption of the endothelial cell monolayer by passaging the cells with EDTA-trypsin resulted in reorganization of some of the cells into three-dimensional vessellike structures after as little as 5-8 hours in the presence of the pulsed electromagnetic field. This reorganization occurred in the presence of heparin, endothelial cell growth factor, and a competent fibronectin matrix. Vascularization for comparable cultures outside of the field did not occur during the time-course of the experiments. Discrete stages of neovascularization were observed in the presence of the field that were qualitatively similar to stages of angiogenesis observed in vivo.

Methodological approaches for the study of the aortic endothelium of the rat

This report describes a new method for obtaining whole mount preparations of rat thoracic aorta which allows the study en face of the complete surface of the endothelium. A comparative study of the different techniques utilized for silver staining of endothelium has been performed. Included is the description of an apparatus for perfusion fixation of rat aorta which allows sequential perfusion of several fluids at a constant pressure. Conditions for perfusion fixation at physiological pressure and flow and for optimal nuclear staining and silver staining of the interendothelial junctions have been studied. The method is rapid and easy to perform and, in the same preparation, allows by optical microscopy the study of the most commonly described parameters for the characterization of normal and injured endothelium. Qualitative aspects of the endothelial lesions found in rats with antibodies to Mycoplasma pulmonis are presented.

Smooth muscle cell proliferation in the rat coronary artery induced by vitamin D

Ultrastructural changes induced in rat coronary arteries by oral administration of a large dose of vitamin D2 were examined by transmission and scanning electron microscopy. Our observations were that smooth muscle cell proliferation occurred without endothelial denudation and without exposure of the subendothelium. While the endothelial cells did show evidence of degeneration, the adjoining endothelial cells migrated beneath so that these degenerated cells could become detached without exposing the subendothelium. Therefore, factors other than platelets seem to participate in the phenotypic modulation and proliferation of the smooth muscle cell. Medial degeneration may be a prerequisite for formation of the lesion.

Injury and repair of smaller muscular and elastic arteries. A light microscopical study on the different healing patterns of rabbit femoral and carotid arteries following dilatation injuries by a balloon catheter

26 rabbits of the Danish country strain were subjected to mechanical dilatation injury of the left femoral and carotid arteries with Fogarty's embolectomy catheters F2 and F3 respectively. The rabbits were killed 2, 7, 14 and 28 days after the dilatation injury and the arteries examined histologically. Initially both of the arteries exhibited necrosis of the media and infiltration of the vessel wall with neutrophils and mononuclear cells. From day 7, intimal thickening was observed in both types of arteries, progressing in thickness during the later stages. However, thrombosis occurred in the majority of the carotid arteries, whereas this was only infrequently seen in the femoral arteries. In all of the dilated arteries, the elastic laminas were stretched or fragmented and never regained their normal appearance. In the carotid artery, giant cells accumulated around the fragmented elastin and calcified areas, located primarily at the intima-medial border. These changes were never observed in the femoral artery. At the twenty-eight days stage, proliferation of the smooth muscle cells more or less led to restitution of the media in the femoral artery, whereas the carotid artery showed medial restitution only to a lesser extent. The similarities between the injured carotid artery and human temporal arteritis, and the utility of the model as an animal model for the study of temporal arteritis are underlined.

Immunohistochemical studies of C-reactive protein and apolipoprotein B in inflammatory and arterial lesions

Interactions in vivo between C-reactive protein (CRP) and apolipoprotein B (apo-B)-containing lipoproteins were sought in inflammatory lesions and atherosclerosis. CRP was demonstrated immunohistochemically on the surface of some muscle fibres in locally induced inflammatory lesions in the rabbit, but apoB was not detected in the same distribution. CRP was not detected in catheter-induced aortic endothelial injuries in the rabbit, in arterial lesions containing apoB from cholesterol-fed rabbits, in apoB-containing human fatty streaks or in advanced human atherosclerotic lesions.

A less traumatic catheter for coronary arteriography

A deformable soft-tipped angiographic catheter has been designed and developed to reduce vascular trauma during coronary arteriography. In order to test the ability of the catheter tip glide over vascular endothelium, the coefficient of resistance was tested using fresh human aortic tissue. The mean frictional coefficients of resistance (FRc) for the soft-tipped catheter, as compared with two commonly used catheters (N = 10/group), were .78 +/- .08 units for the soft-tipped catheter and 1.10 +/- .10 (p less than .006) and .98 +/- .10 (p less than .034) for the conventional catheters. This demonstrates a significant 23% reduction in FRc with the soft-tipped catheter. The ease of penetration into a wax media was also measured using the soft-tipped catheter and compared with the same two conventional catheters. The indentation depths for the soft-tipped catheter and the two other catheter groups (N = 7/group) were 140 +/- 18 micron, 246 +/- 15 micron and 318 +/- 20 micron, respectively. This represents a 56% decrease in indentation depth with the soft-tipped catheter. Histologic studies in canines have demonstrated considerably less endothelial damage and subsequent intimal proliferation in the aorta and coronary ostia with the soft-tipped catheters compared with control catheters. It is concluded that a soft-tipped angiographic catheter is less traumatic to vascular tissue and may offer a safer approach to intravascular studies.

Monocytic origin of foam cells in human atherosclerotic plaques

Foam cells in 4 human atherosclerotic plaques reacted with 3 rat monoclonal antibodies directed against T.200 ('anti-leucocyte common' antibody), HLA-Class II molecules and macrophage cytoplasm, respectively. Smooth muscle cells did not react. The results support the view that foam cells are monocyte-derived macrophages.

Endothelial healing in the rabbit aorta and the effect of risk factors for atherosclerosis. Hypercholesterolemia

The effect of diet-induced moderate hypercholesterolemia on endothelial healing has been investigated in the rabbit following a narrow superficial injury to aortic endothelium without damage to the media of the vessel. The healing process was compared with that observed in normocholesterolemic animals. The degree of platelet involvement was similar in both normo- and hypercholesterolemic animals. Reendothelialization occurred within 48 hours in both groups of animals, showing that hypercholesterolemia did not delay endothelial healing. It was found that esterase-positive cells, which morphologically resembled monocyte-macrophages, adhered to and penetrated regenerated endothelium only in hypercholesterolemic animals. After reendothelialization in normocholesterolemic animals, there was no increase in the number of cells within the intima of the vessel and no evidence of lipid accumulation. In hypercholesterolemic animals, cells accumulated in the intima in areas of regeneration, and lipid accumulation occurred within both the intima and the media in areas of regeneration.

Porcine aortic organ culture: a model to study the cellular response to vascular injury

Organ cultures of porcine thoracic aorta were studied to define the characteristics of this system as a model to study the reaction of endothelial cells (ECs) and the underlying smooth muscle cells (SMCs) to injury. Both nonwounded and wounded cultures, the latter having had part of the endothelial surface gently denuded with a scalpel blade, were studied over a 7 d period by scanning and transmission electron microscopy. The results showed that the nonwounded ECs underwent a shape change from elongated to polygonal within 24 h in culture. In both nonwounded and wounded explants there was cell proliferation beneath the nondenuded endothelium so that by 7 d several layers of cells were present showing features of the secretory type of SMCs. This proliferation, however, did not occur if the endothelium was totally removed from the aorta. There was also evidence of gaps between the surface ECs, and by 7 d lamellipodia of cells beneath the surface were present in these gaps. Occasionally, elongated cells were seen to be present on the surface of the endothelium. In the wounded organ culture, cell migration and proliferation occurred extending from the wound edge and producing a covering of cells on the denuded area. There were also multilayered cells beneath the surface similar to the nonwounded area. Occasional foam cells were seen in the depth of the multilayered proliferating cells. The results indicate that organ culture of porcine thoracic aorta is a good model to study the reaction of ECs and underlying SMCs to injury.

In vitro reendothelialization. Microfilament bundle reorganization in migrating porcine endothelial cells

An experimentally induced wound made in a confluent monolayer culture of porcine thoracic aortic endothelial cells (ECs) was studied 22 hours after wounding using 7-nitrobenz-2-oxa-1,3-diazole (NBD) phallacidin and immunofluorescence microscopy to localize actin and myosin containing microfilament (MF) bundles. ECs extending from the wound edge back toward the confluent monolayer showed a specific change in cell shape and in MF bundle distribution and orientation, which correlated with the cell migration behavior observed using time-lapse cinemicrophotography. The migrating ECs in the first zone, the leading zone, were polygonal to partially elongated in shape, and contained distinct central MF bundles oriented both parallel and perpendicular to the wound edge. The second zone, the elongated zone, was characterized by elongated cells with central MF bundles oriented parallel to the direction of migration. A third zone, the transitional zone, showed nonmigrating polygonal ECs containing prominent central and dense peripheral bands (DPB) of MF bundles. The central MF bundles were oriented randomly with respect to the wound edge. The MF bundles of the confluent resting monolayer were both centrally and peripherally located with the latter being more prominent. The results indicate that the reorientation of central MF bundles and reduction in the peripheral MF bundles are probably important in the reorganization of the cytoskeletal system during the conversion of stationary cells to migrating cells.

Cellular proliferation in atherosclerosis and hypertension

We have tried to compare the proliferative responses seen in two vascular diseases: atherosclerosis and hypertension. Both diseases involve endothelial injury and proliferation, but our knowledge of this phenomenon is just beginning to emerge. In atherosclerosis the best evidence is that denudation does not occur in the normal young animal. Man, however, ages over a much longer time than our usual animal models, and the study of denudation during the chronic progression of atherosclerotic lesions remains to be done. We need to consider the possibility that repetitive, small lesions may occur at sites of endothelial turnover. We also need to know more about the possible role of nondenuding injuries, including death of endothelial cells in situ and the apparent increased stickiness of endothelial cells and monocytes during the early stages of hypercholesterolemia. The role of endothelial injury in hypertension also needs more study. We know that extensive denudation and thrombosis occur in small vessels subjected to high blood pressure. It is highly probable that release of PDGF occurs at these sites, possibly accounting for the characteristic hyperplasia seen in malignant hypertension. Whether this process is related to the more subtle changes in vessel wall mass seen in chronic hypertension remains unknown. Finally, there are remarkable differences in the proliferative behavior of the smooth muscle cells themselves in these two diseases. Hypertensive vascular disease is, in large part, a disease of the media. Atherosclerosis is characterized by intimal hyperplasia. Injury results in migration of smooth muscle cells from the media and cell division in the intima. It is possible to identify chemotactic factors using putative atherosclerosis risk factors or normal components of serum. This has already been done for one component of lesion formation, PDGF, and there is a report of a monocyte chemotactic factor released by smooth muscle cells. Factors released by other components of lesions may be of considerable interest. In contrast, changes in hypertension occur within a more orderly preservation of vessel wall structure. The wall thickens, but this occurs by increased synthesis of cell mass in the media. The cells themselves do not even divide, but they undergo a form of amitotic replication of their DNA.(ABSTRACT TRUNCATED AT 400 WORDS)

Endothelial regeneration in hypertensive and genetically hypercholesterolemic rats

Endothelial regeneration after a narrow, superficial aortic injury was studied in rats with chronic Goldblatt hypertension, genetic hypercholesterolemia, or a combination of hypertension and genetic hypercholesterolemia. In all groups, endothelial continuity was restored within 24 to 36 hours by a combination of endothelial migration and proliferation. A line of increased endothelial density covering the previous wound was seen through 16 weeks after injury. Intimal thickening after injury did not occur in any of the groups. These results indicate that hypertension and hypercholesterolemia neither delay endothelial regeneration nor cause intimal thickening after a small injury in the rat.

Endothelial healing following defined injury to rabbit aorta. Depth of injury and mode of repair

A study has been made of the healing of a narrow deep injury to rabbit aortic endothelium which also involves damage to the media of the vessel. The injury was produced using a nylon catheter containing a wire filament; the injury was approximately 150 micron in width and damaged up to 3 elastic lamellae. Immediately after injury platelet aggregates were observed over the injured areas, several hours later large numbers of leukocytes were also seen to adhere. Two days after injury a non-thrombogenic neointimal surface was observed over deeply injured areas; endothelial cells could be identified covering the injured area at 6 days. The healing process following the injury has been directly compared with the healing of rabbit aortic endothelium following a superficial injury of similar width, where endothelial cells are removed without significant damage to the media of the vessel [1]. The results show that (a) following a narrow injury to the aorta which causes damage to the media platelet aggregation and proliferation of smooth muscle cells occurs, (b) despite the disruption of subendothelial components, endothelium rapidly regenerates over the narrow injured area, although not as quickly as for a superficial injury.