Intimal proliferation in an organ culture of human internal mammary artery

PDGF regulates guanylate cyclase expression and cGMP signaling in vascular smooth muscle

The nitric oxide-cGMP (NO-cGMP) pathway is of outstanding importance for vascular homeostasis and has multiple beneficial effects in vascular disease. Neointimal hyperplasia after vascular injury is caused by increased proliferation and migration of vascular smooth muscle cells (VSMCs). However, the role of NO-cGMP signaling in human VSMCs in this process is still not fully understood. Here, we investigate the interaction between platelet derived growth factor (PDGF)-signaling, one of the major contributors to neointimal hyperplasia, and the cGMP pathway in vascular smooth muscle, focusing on NO-sensitive soluble guanylyl cyclase (sGC). We show that PDGF reduces sGC expression by activating PI3K and Rac1, which in turn alters Notch ligand signaling. These data are corroborated by gene expression analysis in human atheromas, as well as immunohistological analysis of diseased and injured arteries. Collectively, our data identify the crosstalk between PDGF and NO/sGC signaling pathway in human VSMCs as a potential target to tackle neointimal hyperplasia.

PDGF reduces expression of nitric oxide-sensitive soluble guanylyl cyclase (NO-sGC) through PI3K-P-Rex1-Rac1 signaling in vascular smooth muscle cells. These insights provide possible avenues to prevent dysregulation of NO/cGMP signaling in vascular disease.

Gene therapy with antisense oligonucleotides silencing c-myc reduces neointima formation and vessel wall thickness in a mouse model of vein graft disease

Gene therapy for avoiding intimal hyperplasia of vein grafts after coronary artery bypass grafting is still discussed controversially. A promising application of gene therapy in vein grafts is the use of antisense oligonucleotides to block the expression of genes encoding cell cycle regulatory proteins in vascular smooth muscle cells. C-myc, either directly or by regulating the expression of other proteins, controls cell proliferation, apoptosis and cell survival, tissue remodeling, angiogenesis, cell metabolism, production of inflammatory and anti-inflammatory cytokines, and also participates in cell transformation. Forty C57BL/6J mice underwent interposition of the inferior vena cava from isogenic donor mice into the common carotid artery using a previously described cuff technique. Twenty mice received periadventitial administration of antisense oligonucleotides directed against c-myc (treatment group), the other twenty mice received no treatment (control group). All vein grafts were harvested two weeks after surgery, dehydrated, wax embedded, cut into slides of 2 μm thickness, stained and histologically and immunohistochemically examined under light microscope. In our study, we could show the promising effects of antisense oligonucleotide treatment in a mouse model of vein graft disease including the significant reduction of neointimal, media and total vessel wall thickness with a significantly lower percentage of SMA positive cells, elastic fibres and acid mucopolysaccharides in the neointima and media, a decreased vascularization, and a lower expression of PDGFR ß, MMP-9 and VEGF-A positive cells throughout the whole vein graft wall.

The emerging issue of human resident arterial progenitors: the contribution of organ culture

Human femoral arteries were cultured up to 56 days. Samples were processed for light, immunohistochemical, and transmission electron microscopy. Arteries became rapidly depopulated; at day 42, an endothelial lining (CD31(+), Weibel-Palade bodies) developed on the intima; endothelium was in continuity with mesenchymal stromal cells (CD44(+), CD90(low), CD105(low)) placed on adventitia. The media-adventitia area showed heterogeneous cell populations. In long-term organ culture, femoral artery develops a continuous cell coverage that differentiates to endothelium on the intima exclusively. This suggests that distinct topographical factors, such as resident progenitors and/or matrix signals, are able to regulate vascular homeostasis in adult life.

SERCA2a gene transfer prevents intimal proliferation in an organ culture of human internal mammary artery

Coronary restenosis, a major complication of percutaneous balloon angioplasty, results from neointimal proliferation of vascular smooth muscle cells (VSMCs). The sarco/endoplasmic reticulum calcium ATPase isoform 2a (SERCA2a), specific to contractile VSMCs, has been reported previously to be involved in the control of the Ca²⁺-signaling pathways governing proliferation and migration. Moreover, SERCA2a gene transfer was reported to inhibit in vitro VSMC proliferation and to prevent neointimal thickening in a rat carotid injury model.

The aim of this study was to evaluate the potential therapeutic interest of SERCA2a gene transfer for prevention of in-stent restenosis using a human ex vivo model of left internal mammary artery (hIMA) intimal thickening.

Left hIMAs, obtained at the time of aorto-coronary bypass surgeries, were subjected to balloon dilatation followed by infection for 30 min with adenoviruses encoding either human SERCA2 and GFP or control gene (beta-galactosidase) and GFP. Proliferation of subendothelial VSMCs and neointimal thickening were observed in balloon-injured hIMA maintained 14 days in organ culture under constant pressure and perfusion. SERCA2a gene transfer prevented vascular remodeling and significantly (p<0.01, n=5) reduced neointimal thickening in injured arteries (intima/media ratio was 0.07 ± 0.01 vs 0.40 ± 0.03 in βGal-infected arteries).

These findings could have potential implications for treatment of pathological in stent-restenosis.

Human internal mammary artery (IMA) transplantation and stenting: a human model to study the development of in-stent restenosis

Preclinical in vivo research models to investigate pathobiological and pathophysiological processes in the development of intimal hyperplasia after vessel stenting are crucial for translational approaches (1,2). The commonly used animal models include mice, rats, rabbits, and pigs (3-5). However, the translation of these models into clinical settings remains difficult, since those biological processes are already studied in animal vessels but never performed before in human research models (6,7). In this video we demonstrate a new humanized model to overcome this translational gap. The shown procedure is reproducible, easy, and fast to perform and is suitable to study the development of intimal hyperplasia and the applicability of diverse stents. This video shows how to perform the stent technique in human vessels followed by transplantation into immunodeficient rats, and identifies the origin of proliferating cells as human.

Arterial pO₂ stimulates intimal hyperplasia and serum stimulates inward eutrophic remodeling in porcine saphenous veins cultured ex vivo

Ex vivo culture of arteries and veins is an established tool for investigating mechanically induced remodeling. Porcine saphenous veins (PSV) cultured ex vivo with a venous mechanical environment, serum-supplemented cell-culture medium and standard cell-culture conditions (5% CO₂ and 95% balance air ~140 mmHg pO₂) develop intimal hyperplasia (IH), increased cellular proliferation, decreased compliance and exhibit inward eutrophic remodeling thereby suggesting that nonmechanical factors stimulate some changes observed ex vivo. Herein we explore the contribution of exposure to greater than venous pO₂ and serum to these changes in cultured veins. Removing serum from culture medium did not inhibit development of IH, but did reduce cellular proliferation and inward eutrophic remodeling. In contrast, veins perfused using reduced pO₂ (75 mmHg) showed reduced IH. Among the statically cultured vessels, veins cultured at arterial pO₂ (95 mmHg) and above showed IH as well as increase in proliferation and vessel weight compared to fresh veins; veins cultured at venous pO₂ did not. Taken together, these data suggest that exposure of SV to arterial pO₂ stimulates IH and cellular proliferation independent of changes in the mechanical environment, which might provide insight into the etiology of IH in SV used as arterial grafts.

Enhanced cytomegalovirus infection in atherosclerotic human blood vessels

Human cytomegalovirus (CMV) is a possible co-factor in atherogenesis and vascular occlusion, but its ability to actively infect medium and large blood vessels is unclear. A vascular explant model was adapted to investigate CMV infection in human coronary artery, internal mammary artery (IMA), and saphenous vein (SV). Vascular explants were inoculated with CMV Towne or low-passage clinical isolate and examined in situ for CMV cytopathic effect and immediate-early and early antigens, as indicators of active infection. At 5 to 7 days after inoculation, we found that CMV Towne actively infected eight of eight different atherosclerotic blood vessel explants (coronary artery, n = 4; SV and IMA grafts, n = 4), whereas it only infected 2 of 14 nonatherosclerotic blood vessel explants (SV, n = 10; IMA, n = 4) (P = 0.001). The CMV clinical isolate actively infected none of six sets of nonatherosclerotic SV explants at 5 to 7 days after inoculation. The active CMV infections involved adventitial and, less frequently, intimal cells. A small subset of infected cells in atherosclerotic tissue expresses the endothelial cell marker CD31. Smooth muscle cells residing in both atherosclerotic and nonatherosclerotic blood vessels were free of active CMV infections even after all vascular tissue layers were exposed to the virus. In contrast, active CMV Towne infection was evident at 2 days after inoculation in smooth muscle cells and endothelial cells previously isolated from the SV tissues. We conclude that active CMV infection is enhanced in atherosclerotic blood vessels compared to atherosclerosis-free vascular equivalents, and this viral activity is restricted to subpopulations of intimal and adventitial cells.

Injury induced neointima formation and its inhibition by retrovirus-mediated transfer of nitride oxide synthase gene in an in-vitro human saphenous vein culture model

Human saphenous veins were cultured to characterize neointima formation and feasibility of gene transfer to inhibit the intimal proliferative response to injury. Mechanical injury was introduced by abrading the luminal surface of the vein patch with a sterile cotton bud. Both injured and non-injured vein patches were cultured and transduced with retroviral vectors carrying marker or therapeutic genes. After a 14-day culture, the thickness of the intimal layer of non-injured vein patches reached 90+/-28 microm at the edge and 61+/-22 microm at the center (n=29) from the original 22+/-12 microm at harvest (n=6, P=0.02). Mechanical injury to the intimal surface prior to culture resulted in an exaggerated proliferative response. The intimal thickness of injured vein patches increased from 3.4+/-1 microm right after injury to 128+/-23 microm (n=12, P<0.001) at the edge after 14-day culture. Genes were transduced efficiently into a luminal layer of cultured veins using a pseudotyped murine leukemia viral vector. Transduction of gene encoding nitric oxide synthase resulted in reduction of neointima formation to 33+/-7 microm (n=12) at the edge after 14-day culture compared to 90 microm (P<0.01) seen in untransduced non-injured vein patches. Marker gene transduction did not alter intimal proliferative response or its immunohistochemical profile. The data suggest that cultured vein can be used as a model for studying the effects of injury to blood vessels and to evaluate the effects of candidate therapeutic genes.

Marimastat inhibits neointimal thickening in a model of human arterial intimal hyperplasia

OBJECTIVE

matrix metalloproteases (MMPs) produced by vascular smooth-muscle cells (VSMCs) degrade extracellular matrix and facilitate the migration of these cells. This is a fundamental process in arterial intimal hyperplasia. This study investigated whether Marimastat (a selective but non-specific MMP inhibitor) can prevent intimal hyperplasia in cultured human internal mammary artery (IMA).

MATERIALS AND METHODS

segments of IMA from 8 patients were prepared and cultured for 14 days in serum-supplemented medium (control) or in medium supplemented with Marimastat at 2 concentrations (treatment groups). The tissue was fixed, sectioned, stained and neointimal thicknesses measured by computer-aided image analysis. Further sections were cultured in the same manner and prepared for gel enzymography to quantify the production of MMPs.

RESULTS

neointimal thickness was significantly reduced by Marimastat in a dose-dependent manner when compared to controls (p =0.008 Wilcoxon). Gel enzymography demonstrated a reduction in levels of MMP2 and MMP9. This was most significant for the active forms of the enzymes ( p =0.03).

CONCLUSIONS

our results suggest that there is a potential therapeutic role for specific inhibition of the gelatinases in the prevention of human arterial restenosis.

Long-term effects of Ca(2+) on structure and contractility of vascular smooth muscle

Culture of dispersed smooth muscle cells is known to cause rapid modulation from the contractile to the synthetic cellular phenotype. However, organ culture of smooth muscle tissue, with maintained extracellular matrix and cell-cell contacts, may facilitate maintenance of the contractile phenotype. To test the influence of culture conditions, structural, functional, and biochemical properties of rat tail arterial rings were investigated after culture. Rings were cultured for 4 days in the absence and presence of 10% FCS and then mounted for physiological experiments. Intracellular Ca(2+) concentration ([Ca(2+)](i)) after stimulation with norepinephrine was similar in rings cultured with and without FCS, whereas force development after FCS was decreased by >50%. The difference persisted after permeabilization with beta-escin. These effects were associated with the presence of vasoconstrictors in FCS and were dissociated from its growth-stimulatory action. FCS treatment increased lactate production but did not affect ATP, ADP, or AMP contents. The contents of actin and myosin were decreased by culture but similar for all culture conditions. There was no effect of FCS on calponin contents or myosin SM1/SM2 isoform composition, nor was there any appearance of nonmuscle myosin. FCS-stimulated rings showed evidence of cell degeneration not found after culture without FCS or with FCS + verapamil (1 microM) to lower [Ca(2+)](i). The decreased force-generating ability after culture with FCS is thus associated with increased [Ca(2+)](i) during culture and not primarily caused by growth-associated modulation of cells from the contractile to the synthetic phenotype.

Long-term effects of intracellular calcium and growth factors on excitation and contraction in smooth muscle

Modulation of vascular smooth muscle cells from a contractile to a synthetic phenotype is thought to be important in the development of the atherosclerotic lesion. Such modulation depends on growth factors and is influenced by cell-cell and cell-matrix interactions. Whereas smooth muscle cells in the vessel wall are contractile, dispersed cells in culture rapidly modulate to synthetic phenotype, which complicates long-term in vitro studies. In contrast, vascular segments or smooth muscle strips in organ culture can maintain contractility for at least a week, sufficient for studies involving altered metabolism or protein expression. Examples are effects of endogenous polyamines on membrane ion channels and excitation-contraction coupling. While smooth muscle tissue is well preserved in serum-free culture, growth stimulation with fetal calf serum (FCS) causes multiple effects, including decreased contractility, ultrastructural changes, decreased expression of L-type Ca2+ channels, and increased SR release of Ca2+ via ryanodine receptors. These are all consequences of increased basal [Ca2+]i caused by FCS, as they are reversed by culture with verapamil in a concentration (1 microM) that does not inhibit stimulation of DNA and protein synthesis by FCS. The effects of FCS on contractility and Ca2+ channel expression are mimicked in serum-free culture with increased [Ca2+]i. Contractile protein patterns, including myosin isoform composition, are unaffected by FCS, suggesting that reversal to synthetic phenotype is limited and not the immediate cause of decreased contractility.

Halofuginone inhibits neointimal formation of cultured rat aorta in a concentration-dependent fashion in vitro

Halofuginone, an anticoccidial quinoazolinone, can specifically inhibit collagen type alpha1 (I) synthesis and gene expression, and also inhibits cultured smooth muscle cell proliferation. The aim of this study was to investigate the effect of halofuginone on neointimal formation of rat aorta after culture in a concentration-dependent manner in vitro. Thoracic aorta of Wistar rats was removed and manipulated to damage the endothelium under sterile conditions, and culture for 15 days in halofuginone-free or halofuginone-added culture medium (n = 20). Segments of cultured aorta were studied by histologic and immunohistochemical methods. Proliferation of neointimal layers consisting of loose multilayer cellular structure was observed in the halofuginone-free control group after 15 days of rat aorta culture, and neointimal formation was significantly decreased as an increasing concentration of halofuginone was added. As with precultured fresh aorta, no intimal proliferation was observed in the cultured segments of aorta with 500 ng/ml halofuginone added to culture medium. The proliferation of cell nuclear antigen index was significantly higher in the halofuginone-free control group than that in the halofuginone-added groups. The present results suggest that halofuginone can inhibit neointimal formation of rat aorta after culture in a concentration-dependent fashion in vitro.

Short-term exposure to thapsigargin inhibits neointima formation in human saphenous vein

Vascular smooth muscle cell (VSMC) migration and proliferation are involved in the intimal thickening responsible for late vein graft failure. In addition to growth and chemotactic factors, VSMCs require expression of matrix-degrading enzymes, e.g., metalloproteinases (MMP), to relieve the antiproliferative and antimigratory constraints of the extra-cellular matrix. Thapsigargin irreversibly inhibits Ca(2+)-ATPase, eliciting an increase in intracellular Ca2- and depletion of the intracellular calcium pools that are thought to be involved in the control of VSMC migration, VSMC proliferation, and MMP activity. We therefore studied the effect of thapsigargin on VSMC migration, VSMC proliferation, and MMP expression in human saphenous vein organ cultures. Vein segments were cultured for 14 days, and VSMC proliferation and migration were determined by autoradiography. Cell death was assessed using in situ end-labeling and lactate dehydrogenase release. Using Western blotting, we examined MMP-2 and MMP-9 and tissue inhibitor of metalloproteinases (TIMP)-1 and TIMP-2 expression. Exposure to thapsigargin at 10 nmol/L for 60 minutes before culture significantly inhibited neointimal thickening (60%, P < .05), intimal and medial VSMC proliferation (32%, P < .05 and 37%, P < .05, respectively), and VSMC migration (36%, P < .05). Thapsigargin at 10 nmol/L did not significantly increase cell death or MMP-2, MMP-9, TIMP-1, and TIMP-2 expression. These results suggest that blockade of Ca(2+)-ATPase by thapsigargin inhibits VSMC migration and proliferation involved in neointimal formation without affecting MMP-2 and MMP-9 expression. Because short-term exposure to thapsigargin was sufficient to inhibit neointima formation, this drug may prove useful in the treatment of intimal thickening after arterial bypass graft surgery.

Myosin isoform expression and force generation in cultured resistance arteries

Organ culture of mesenteric resistance arteries results in a loss of force-generating ability, which is prevented by 1alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3]. We have tested the hypothesis that the culture-induced decrease in active stress is associated with altered myosin isoform expression. Rat mesenteric resistance arteries were studied immediately (fresh) or after incubation at 37 degrees C for 48 h in culture medium (control), with 300 pg/ml 1,25(OH)2D3, or with 5 microg/ml insulin. Isometric force was measured by myography; myosin heavy chain (MHC) and regulatory myosin light chain isoform (MLC) contents were determined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Maximal active stress to 100 mM K+ (mN/mm2) was greater for fresh (147.8 +/- 4.9) than control (109.2 +/- 4.6, P = 0.001) or insulin (79.6 +/- 8.6, P < 0.001) but not 1,25(OH)2D3 (137.4 +/- 9.5, P = 0.197). Organ culture did not alter MLC or MHC smooth muscle (SM)-1 isoform content. MHC SM-2 content (nmol/mg protein) was greater in fresh (0.038 +/- 0.003) than control (0.026 +/- 0.003, P = 0.012) and insulin (0.027 +/- 0.002, P = 0.018) but not 1,25(OH)2D3 (0.036 +/- 0.003, P = 0.693); nonmuscle MHC (NMM) was observed in insulin. The maximal active stress response to K+ significantly correlated with SM-2 MHC isoform content (r2 = 0.483, P < 0.001). We conclude that 1) arterial organ culture alters MHC isoform content, 2) SM-2 MHC isoform content positively correlates with active stress generation, 3) 1,25(OH)2D3 maintains force-generating capacity by preventing the shift of MHC isoform expression, and 4) insulin impairs force-generating ability by lowering MHC SM-2 content and stimulating NMM expression.

Organ culture of arteries for experimental studies of vascular endothelium in situ

The objective of this study was to determine whether organ culture of arteries could be used as a more physiological model than endothelial cell culture for the study of vascular endothelium in vitro. Small pieces of artery from rat, pig, piglet and man were cultured in 24-well plates for up to seven or eight days to study the characteristics of the vascular endothelial cell layer during the first week of culture, in particular its integrity, viability and propensity for cell division. Using conventional and confocal microscopy, silver-stained endothelial cell boundaries were shown to be intact at all time points, up to and including day 7. However, occasional very small gaps between endothelial cells were seen with the scanning electron microscope under high power at day 7. Using the bromodeoxyuridine technique, no endothelial cell division was seen at day 4 in any species, except for the occasional endothelial cell in rat aorta. At day 7, pig, piglet and human arteries showed only very occasional dividing endothelial cells, but many endothelial cells had divided by day 7 in rat aorta. Viability of the endothelium was assessed using fluorochromes and examination of the endothelial layer en face using confocal microscopy. Viability was always excellent (> 95%) up to day 4. By day 7, occasional patches of dead cells could be seen, which were most obvious in rat aorta. This study demonstrates that endothelial cells can be studied in situ in organ culture with intact morphology, lack of cell division and excellent viability for a minimum of four days. For many research questions involving vascular endothelium--for example the pathophysiology of hyperacute rejection--short-term organ culture of vessels is likely to represent a more physiological model than endothelial cell culture.

Lipopolysaccharide and interleukin 1 augment the effects of hypoxia and inflammation in human pulmonary arterial tissue

The combined effects of hypoxia and interleukin 1, lipopolysaccharide, or tumor necrosis factor alpha on the expression of genes encoding endothelial constitutive and inducible nitric oxide synthases, endothelin 1, interleukin 6, and interleukin 8 were investigated in human primary pulmonary endothelial cells and whole pulmonary artery organoid cultures. Hypoxia decreased the expression of constitutive endothelial nitric oxide synthase (NOS-3) mRNA and NOS-3 protein as compared with normoxic conditions. The inhibition of expression of NOS-3 corresponded with a reduced production of NO. A combination of hypoxia with bacterial lipopolysaccharide, interleukin 1 beta, or tumor necrosis factor alpha augmented both effects. In contrast, the combination of hypoxia and the inflammatory mediators superinduced the expression of endothelin 1, interleukin 6, and interleukin 8. Here, we have shown that inflammatory mediators aggravate the effect of hypoxia on the down-regulation of NOS-3 and increase the expression of proinflammatory cytokines in human pulmonary endothelial cells and whole pulmonary artery organoid cultures.

Experimental models of accelerated atherosclerosis syndromes

The processes of angioplasty restenosis, vein graft failure, and transplant atherosclerosis, collectively termed 'syndromes of accelerated atherosclerosis', have been the focus of significant clinical and experimental research. Limitations of clinical studies have forced emphasis onto experimental animal models for the purpose of determining pathophysiology and evaluation of potential therapeutic strategies. However, the apparent failure of many in vivo animal models to predict interventional outcome in humans has raised doubt over their suitability as models of these pathophysiological states. Similar criticism has befallen the use of in vitro techniques for elucidating pathophysiology of the cellular elements. An awareness of the shortcomings of the various experimental models in use would therefore seem prerequisite both to a more critical evaluation of data generated from their use, and to the development of truly effective therapeutic strategies for humans.

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.

An essential role for platelet-derived growth factor in neointima formation in human saphenous vein in vitro

The role of platelet-derived growth factor (PDGF), a potent vascular smooth muscle cells (SMC) mitogen and chemoattractant, was investigated during neointima formation in human saphenous vein organ culture. PDGFA and B messenger ribonucleic acid (mRNA) expression was detected by RNase protection assay and in situ hybridisation and PDGF protein by immunocytochemistry. The expression of PDGFA and B mRNA was low in veins before culture while PDGF protein was detected in all cell types. A neointima consisting of densely packed SMC developed after 14 days of culture. The dense packing and high expression of PDGFA and B mRNA in neointimal SMC led to higher PDGF protein concentrations in the neointima, the role of which was examined by culturing with neutralising anti-(human PDGF) antibodies. The anti-PDGF antibodies significantly reduced neointimal thickness by approximately 66% and the number of neointimal cells by approximately 50%, without affecting neointimal or medial proliferation indices or cell viability. These results suggest that PDGF played an essential role in SMC migration into the neointima in human saphenous vein.

Differential effects of pressure and flow on DNA and protein synthesis and on fibronectin expression by arteries in a novel organ culture system

Structural adaptation of the blood vessel wall occurs in response to mechanical factors related to blood pressure and flow. To elucidate the relative roles of pressure, flow, and medium composition, we have developed a novel organ culture system in which rabbit thoracic aorta, held at in vivo length, can be perfused and pressurized at independently varied flow and pressure for several days. Histology and histomorphometry, as well as scanning electron microscopy, revealed a well-preserved wall structure. In arteries perfused and pressurized at 80 mm Hg, endothelial injury led to a 2-fold increase in [3H]thymidine incorporation in the media, which peaked at 3 to 5 days and returned to baseline level at 6 to 8 days. In intact endothelialized vessels cultured for 3 days under no-flow conditions, pressure per se had no effect on DNA synthesis. In contrast, in the presence of serum, total protein synthesis, as assessed by [35S]methionine incorporation into the media, was enhanced 6-fold at 150 mm Hg compared with vessels pressurized at 0 or 80 mm Hg. In intact vessels perfused at a constant flow of 40 mL/min for 3 days, DNA synthesis was unchanged regardless of the pressure level when vessels were cultured in the presence of serum but increased 8-fold at both 80 and 150 mm Hg in the absence of serum. Unlike DNA synthesis, total protein synthesis was enhanced 12-fold by flow regardless of the presence or absence of serum. Expression of fibronectin was markedly enhanced at high transmural pressure, and serum potentiated its expression in the arterial wall. This novel organ culture system of perfused and pressurized vessels allowed identification of differential effects of pressure, flow, and serum on DNA and total protein synthesis, including cellular fibronectin expression.

Distension produces medial but not endothelial damage in porcine internal mammary artery

The influence of intraluminal distension on porcine internal mammary artery was studied using adenosine 5'-triphosphate (ATP) concentration and prostacyclin production as biochemical markers of medial and endothelial functional integrity respectively. Distension reduced mean (95% confidence limits) tissue ATP concentrations from 459 (337-581) nmol/g wet weight to 314 (193-435) nmol/g wet weight (n = 10, P < 0.01). Stimulated prostacyclin production was similar in undistended (25.8(15.9-35.9) pg/min per mg wet weight) and distended arteries (33.2(21.4-45.1) pg/min per mg wet weight) (n = 8, not significant). The data demonstrate that distension of the internal mammary artery results in acute medial but not endothelial damage. Distension-induced medial damage is unlikely to be rapidly reversible and might have implications for the early and long-term function of the artery as a bypass graft.

Comparison of response to injury in organ culture of human saphenous vein and internal mammary artery

Autologous saphenous vein grafts, unlike internal mammary artery grafts, suffer many late occlusions as a result of excessive proliferation of vascular smooth muscle cells and the superimposition of atheroma on the resulting thickened intima. We investigated the possible basis of this difference using organ cultures. Internal mammary artery segments and freshly isolated and surgically prepared saphenous vein segments were obtained from patients undergoing coronary artery bypass grafting. Internal mammary artery and freshly isolated vein segments showed a high degree of endothelial coverage and medial cell viability that were maintained during culture. Surgically prepared veins showed partial endothelial denudation and medial cell injury, both of which tended to be reversed during culture. Neointimal thickening was greater in surgically prepared vein (72 +/- 13 microns; n = 11) than in freshly isolated vein (44 +/- 8 microns; n = 10) or internal mammary artery (34 +/- 4 microns; n = 13) segments. The occurrence of proliferating cells in the medial layer was also significantly greater in surgically prepared vein (2.8 +/- 1.0/mm; n = 11) than in freshly isolated vein (0.8 +/- 0.3/mm; n = 9) or internal mammary artery (0.6 +/- 0.3/mm; n = 10) segments. The data show that although the smooth muscle proliferation was similar in undamaged saphenous vein and internal mammary artery, it was significantly greater in damaged vein. This implies that the greater intimal proliferation seen in saphenous vein grafts may arise not from intrinsic differences in arterial and venous smooth muscle cells but from a greater susceptibility to injury.