An endothelial cell-derived growth factor

Tissue-engineered 3D microvessel and capillary network models for the study of vascular phenomena

Advances in tissue engineering, cell biology, microfabrication, and microfluidics have led to the development of a wide range of vascular models. Here, we review platforms based on templated microvessel fabrication to generate increasingly complex vascular models of (i) the tumor microenvironment, (ii) occluded microvessels, and (iii) perfused capillary networks. We outline fabrication guidelines and demonstrate a number of experimental methods for probing vascular function such as permeability measurements, tumor cell intravasation, flow characterization, and endothelial cell morphology and proliferation.

Culture Medium Supplements Derived from Human Platelet and Plasma: Cell Commitment and Proliferation Support

Present cell culture medium supplements, in most cases based on animal sera, are not fully satisfactory especially for the in vitro expansion of cells intended for human cell therapy. This paper refers to (i) an heparin-free human platelet lysate (PL) devoid of serum or plasma components (v-PL) and (ii) an heparin-free human serum derived from plasma devoid of PL components (Pl-s) and to their use as single components or in combination in primary or cell line cultures. Human mesenchymal stem cells (MSC) primary cultures were obtained from adipose tissue, bone marrow, and umbilical cord. Human chondrocytes were obtained from articular cartilage biopsies. In general, MSC expanded in the presence of Pl-s alone showed a low or no proliferation in comparison to cells grown with the combination of Pl-s and v-PL. Confluent, growth-arrested cells, either human MSC or human articular chondrocytes, treated with v-PL resumed proliferation, whereas control cultures, not supplemented with v-PL, remained quiescent and did not proliferate. Interestingly, signal transduction pathways distinctive of proliferation were activated also in cells treated with v-PL in the absence of serum, when cell proliferation did not occur, indicating that v-PL could induce the cell re-entry in the cell cycle (cell commitment), but the presence of serum proteins was an absolute requirement for cell proliferation to happen. Indeed, Pl-s alone supported cell growth in constitutively activated cell lines (U-937, HeLa, HaCaT, and V-79) regardless of the co-presence of v-PL. Plasma- and plasma-derived serum were equally able to sustain cell proliferation although, for cells cultured in adhesion, the Pl-s was more efficient than the plasma from which it was derived. In conclusion, the cells expanded in the presence of the new additives maintained their differentiation potential and did not show alterations in their karyotype.

Investigational Approaches to Pulmonary Hypertension

Pulmonary vascular disease (PVD) revolves around a series of switches in the smooth muscle cell (SMC) phenotype. Differentiation of SMC from precursor cells causes muscularization of normally non-muscular peripheral arteries; hypertrophy and hyperplasia of existing SMC and increased connective tissue protein synthesis cause thickening of the wall, and migration of SMC into the subendothelial space is the basis of intimal proliferation. To uncover the pathophysiologic mechanisms of these changes, we have used a variety of animal models and cell culture systems. From rats in which hypertensive PVD was induced by exposure to chronic hypoxia or following injection of the pyrrolizidine alkaloid, monocrotaline, we have identified increased pulmonary artery (PA) elastolytic activity which occurs early and which accompanies progressive rather than reversible PVD. Inhibition of elastolytic activity prevents or reduces PVD. We are cloning the gene for this new enzyme to study its regulation in PVD. To address the mechanism of SMC proliferation under conditions of high PA pressure and flow, we cultured endothelial cells on Polyvinylchloride membranes and pulsated them at high pressure. This caused reduced synthesis of heparan sulfate. The resulting decrease binding of fibroblast growth factor would lessen its mitogenic effect and modulate SMC proliferation in response to other growth factors from platelets or serum. To study SMC migration, we cultured endothelial and SMC from the ductus arteriosus (a fetal vessel which spontaneously develops intimal proliferation in late gestation). The migratory SMC phenotype is a function of increased production of fibronectin governed by a translational control mechanism, and increased endothelial hyaluronan regulated by transforming growth factor β. SMC migration is also related to impaired assembly of elastin, the result of a chondroitin sulfate-induced decrease in elastin binding proteins and the production of a novel ‘defunct’ 52 kD tropoelastin.

Cardiovascular Adaptations to Exercise Training

Aerobic exercise training leads to cardiovascular changes that markedly increase aerobic power and lead to improved endurance performance. The functionally most important adaptation is the improvement in maximal cardiac output which is the result of an enlargement in cardiac dimension, improved contractility, and an increase in blood volume, allowing for greater filling of the ventricles and a consequent larger stroke volume. In parallel with the greater maximal cardiac output, the perfusion capacity of the muscle is increased, permitting for greater oxygen delivery. To accommodate the higher aerobic demands and perfusion levels, arteries, arterioles, and capillaries adapt in structure and number. The diameters of the larger conduit and resistance arteries are increased minimizing resistance to flow as the cardiac output is distributed in the body and the wall thickness of the conduit and resistance arteries is reduced, a factor contributing to increased arterial compliance. Endurance training may also induce alterations in the vasodilator capacity, although such adaptations are more pronounced in individuals with reduced vascular function. The microvascular net increases in size within the muscle allowing for an improved capacity for oxygen extraction by the muscle through a greater area for diffusion, a shorter diffusion distance, and a longer mean transit time for the erythrocyte to pass through the smallest blood vessels. The present article addresses the effect of endurance training on systemic and peripheral cardiovascular adaptations with a focus on humans, but also covers animal data.

A computational model of fibroblast growth factor-2 binding to endothelial cells under fluid flow

Fibroblast growth factor-2 (FGF2) is an angiogenic growth factor that binds to cell surface receptors (FGFR) and heparan sulfate proteoglycans (HSPG), as well as HSPG in the basement membrane. FGF2 plays a critical role in angiogenesis, yet clinical FGF2 trials demonstrated limited success perhaps due to inadequate understanding of FGF2 binding in physiological conditions. We developed a computational model of FGF2 binding to isolated (HSPG or FGFR) or combined (HSPG and FGFR) binding sites under physiological fluid flow and predicted the effects of FGF2 concentration, binding site density, fluid flow rate, and delivery mode (continuous vs. bolus) on FGF2 complex formation. The isolated binding site models showed increased binding with FGF2 and binding site density. However, in the triad model, increasing FGF2 concentration decreased triads (FGF2-HSPG-FGFR) and increased FGF2-HSPG complexes. Fluid flow decreased time to equilibrium and dissociation in isolated binding site models, yet flow effect in the triad model depended on binding site density. Similarly, FGF2 capture and complex stability in bolus delivery depended on bolus size, flow rate, association and dissociation rate constants, as well as binding site density. This model shows the integrated effects of FGF2 binding stoichiometry, fluid flow, and delivery mode, and enhances our understanding of FGF2 complex formation under physiological conditions.

Treatment with TNF-alpha or bacterial lipopolysaccharide attenuates endocardial endothelial cell-mediated stimulation of cardiac fibroblasts

Background

The endocardial endothelium that lines the inner cavity of the heart is distinct from the microvascular endothelial cells and modulates cardiac muscle performance in a manner similar to the vascular endothelial modulation of vascular structure and vasomotor tone. Although the modulatory effects of endocardial endothelium (EE) on cardiomyocytes are firmly established, the regulatory effects of endocardial endothelium on the cardiac interstitium and its cellular components remain ill defined.

Methods and Results

We investigated whether the stimulatory effect of EE on cardiac fibroblasts would be altered when EECs are activated by the cytokine tumor necrosis factor-α (TNF-α) or the endotoxin bacterial lipopolysaccharide (LPS). Both TNF-α and LPS were found to independently attenuate the stimulatory effect of EE on cardiac fibroblasts. These agents lowered the synthesis or release of ET-1 and increased the secretion of TGF-β and NO.

Conclusion

The findings of this study using endocardial endothelial cells (EECs) and neonatal cardiac fibroblasts demonstrate that pro-inflammatory cytokines cause altered secretion of paracrine factors by EECs and inhibit proliferation and lower collagen synthesis in fibroblasts. These changes may influence fibroblast response and extra cellular matrix remodeling in pathological conditions of the heart.

Endothelial cells provide feedback control for vascular remodeling through a mechanosensitive autocrine TGF-beta signaling pathway

Mechanical forces are potent modulators of the growth and hypertrophy of vascular cells. We examined the molecular mechanisms through which mechanical force and hypertension modulate endothelial cell regulation of vascular homeostasis. Exposure to mechanical strain increased the paracrine inhibition of vascular smooth muscle cells (VSMCs) by endothelial cells. Mechanical strain stimulated the production of perlecan and heparan sulfate glycosaminoglycans by endothelial cells. By inhibiting the expression of perlecan with an antisense vector we demonstrated that perlecan was essential to the strain-mediated effects on endothelial cell growth control. Mechanical regulation of perlecan expression in endothelial cells was governed by a mechanotransduction pathway requiring autocrine transforming growth factor beta (TGF-beta) signaling and intracellular signaling through the ERK pathway. Immunohistochemical staining of the aortae of spontaneously hypertensive rats demonstrated strong correlations between endothelial TGF-beta, phosphorylated signaling intermediates, and arterial thickening. Further, studies on ex vivo arteries exposed to varying levels of pressure demonstrated that ERK and TGF-beta signaling were required for pressure-induced upregulation of endothelial HSPG. Our findings suggest a novel feedback control mechanism in which net arterial remodeling to hemodynamic forces is controlled by a dynamic interplay between growth stimulatory signals from VSMCs and growth inhibitory signals from endothelial cells.

Cell interactions in post-traumatic fibrosis

Models of reparative fibrosis, or wound healing, disclose a basic spatial relationship between inflammatory cells, fibroblasts, dividing fibroblasts and angiogenic endothelial cells. Many components of the extracellular fluid, especially steep gradients of PO2, PCO2, pH, glucose and lactate, have been measured. After components of coagulation play out their role in the first few days after injury, macrophages sense excitatory substances and signs of respiratory distress, and secrete chemoattractants for endothelial cells and fibroblasts. If excitatory substances (such as silica) are eliminated, active fibrosis ends with the restoration of the energy supply. Some of the mitogens and chemoattractants acting as intercellular messengers between these cells have been isolated and identified.

Platelet-derived growth factor: its potential roles in wound healing, atherosclerosis, neoplasia, and growth and development

Platelet-derived growth factor (PDGF) has been found to be derived not only from platelets that have been induced to release their contents, but also from a number of transformed cells (including cells transformed by both DNA and RNA viruses, spontaneous transformation, and cells from various human tumours), from activated macrophages, from embryonic rat aortic smooth muscle cells, and from rat aortic smooth muscle cells derived from experimentally induced intimal proliferative lesions. The studies discussed demonstrate the potential role of platelets and macrophages in atherosclerosis and in wound repair, and indicate the ability of anti-PDGF IgG to inhibit proliferative responses in vitro. With the demonstration that the transforming protein derived from the oncogene from the simian sarcoma virus is highly homologous with PDGF, it was possible to show that a number of transformed cells secrete PDGF and show markedly decreased binding of PDGF. The same is true for embryonic rat aortic smooth muscle cells and for cells from experimentally induced proliferative lesions in the rat carotid artery. All these findings point to the role of PDGF in the formation of these lesions and can be correlated with the capacity of the cells noted above, as well as injured endothelial cells, to secrete PDGF or PDGF-like molecules. The biological significance of these observations is discussed and a model for atherogenesis is proposed.

Endocardial endothelial cells stimulate proliferation and collagen synthesis of cardiac fibroblasts

Given that vascular endothelial cells play an important role in the modulation of vascular structure and function, we hypothesized that endocardial endothelial cells (EECs) may have a modulator role in regulating the cardiac interstitial cells. Endocardial endothelial cells were isolated from freshly collected pig hearts and cardiac fibroblasts were isolated from 3- to 4-d-old Wistar rats. Fibroblasts were cultured in the presence or absence of conditioned medium from EECs. Proliferation of cardiac fibroblasts was measured by the incorporation of [3H]- Thymidine and collagen synthesis was assayed by the incorporation of [3H]-Proline. To determine the involvement of signaling mediators, in separate experiments, cardiac fibroblasts were incubated with BQ123 (selective ETA receptor antagonist), PD142893 (nonselective ETA/ETB receptor antagonist), Bis-indolylmaleimide (PKC inhibitor), PD 098059 (MEK inhibitor), or neutralizing anti-transforming growth factor (TGF)-beta-antibody. Endocardial endothelium-derived factors endothelin (ET)-1, TGF-beta, and Angiotensin (Ang)-II in the conditioned medium were assayed by enzyme-linked immunosorbent assay using commercially available kits. We report here evidence that suggest that endocardial endothelial cells stimulate both proliferation and collagen synthesis of cardiac fibroblasts. The response seems to be mediated by endothelin through its ETA receptor. Our results also indicate that protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) pathways are essential for the EEC-induced proliferation of cardiac fibroblasts.

Intrauterine growth restriction and the proliferation of smooth muscle cells in umbilical vessels

AIMS

The purpose of this study was to investigate the proliferation of smooth muscle cells in umbilical vessels of fetuses affected by intrauterine growth restriction (IUGR) and to compare the findings with gestational age-matched control cases.

METHODS

Sixty umbilical cords from fetuses at 36-37 weeks gestation were examined. Fetuses were divided into three groups: group I, appropriate for dates birthweight; group II, IUGR with reassuring fetal status; and group III, IUGR with abnormal umbilical Doppler waveforms. Umbilical cords were immunostained with an antibody to proliferating cell nuclear antigen and Ki-67; stained smooth muscle cells were subsequently counted. Smooth muscle cell density was determined by counting the total number of cells in a representative area of vessel wall and the wall thickness of each vessel was also measured.

RESULTS

Proliferation marker-positive cells were increased in the umbilical vessels of group II compared to group I, and there were more proliferating smooth muscle cells in the umbilical vessels of group III compared to the other two groups. The umbilical vessels of group III showed the highest smooth muscle cell density, but the wall thickness of all vessels was significantly thinner in group III than the other two groups.

CONCLUSIONS

This study showed overproliferation of smooth muscle cells in the umbilical vessel walls associated with IUGR. It is hypothesised that hypoxia might induce this overproliferation given the further proliferation in IUGR fetuses with abnormal umbilical Doppler waveforms. Coexistence of a high cell density and lean vessel walls suggests small smooth muscle cells in umbilical vessels with IUGR.

Role of Adenosine as Adjunctive Therapy in Acute Myocardial Infarction

Although early reperfusion and maintained patency is the mainstay therapy for ST elevation myocardial infarction, experimental studies demonstrate that reperfusion per se induces deleterious effects on viable ischemic cells. Thus "myocardial reperfusion injury" may compromise the full potential of reperfusion therapy and may account for unfavorable outcomes in high-risk patients. Although the mechanisms of reperfusion injury are complex and multifactorial, neutrophil-mediated microvascular injury resulting in a progressive decrease in blood flow ("no-reflow" phenomenon) likely plays an important role. Adenosine is an endogenous nucleoside found in large quantities in myocardial and endothelial cells. It activates four well-characterized receptors producing various physiological effects that attenuate many of the proposed mechanisms of reperfusion injury. The cardio-protective effects of adenosine are supported by its role as a mediator of pre- and post-conditioning. In experimental models, administration of adenosine in the peri-reperfusion period results in a marked reduction in infarct size and improvement in ventricular function. The cardioprotective effects in the canine model have a narrow time window with the drug losing its effect following three hours of ischemia. Several small clinical studies have demonstrated that administration of adenosine with reperfusion therapy reduces infarct size and improves ventricular function. In the larger AMISTAD and AMISTAD II trials a 3-h infusion of adenosine as an adjunct to reperfusion resulted in a striking reduction in infarct size (55-65%). Post hoc analysis of AMISTAD II showed that this was associated with significantly improved early and late mortality in patients treated within 3.17 h of symptoms. An intravenous infusion of adenosine for 3 h should be considered as adjunctive therapy in high risk-patients undergoing reperfusion therapy.

Endothelial heparan sulfate is necessary but not sufficient for control of vascular smooth muscle cell growth

The state of the endothelial cell (EC) determines the nature of its control of vascular smooth muscle cell (vSMC) biology. Conditioned medium from postconfluent ECs inhibits vSMC proliferation, whereas subconfluent conditioned medium from the same ECs has a stimulatory effect. We and others have identified confluent endothelial cells' production of heparan sulfate proteoglycans (HSPG) as critical to vSMC growth control. The question that arises is whether the stimulation that is observed with subconfluent cells is from (1) aberrant HSPG production, (2) elaboration of noninhibitory species of HSPG, or (3) production of other factors, such as mitogens, which counteract the inhibitory HSPG to stimulate vSMCs. We studied the relative effects of conditioned medium produced by both subconfluent and postconfluent EC cultures on vSMC growth. Conditioned medium was fractionated into nonproteoglycan (non-PG) and proteoglycan (PG) components by anion-exchange chromatography. The PG fractionation profile and the antiproliferative activity of the HSPGs isolated from both subconfluent and postconfluent EC-conditioned media were similar. However, the HSPG fraction alone could not approach the inhibitory potential of unfractionated conditioned medium from postconfluent EC cultures. Non-PG proteins produced by the endothelial cultures had no effect on vSMC growth on their own. Yet, when they were mixed together with HSPG fractions, from either subconfluent or postconfluent EC cultures, the full growth effects were returned. Non-PG protein fractions from postconfluent cultures with HSPG fractions gave maximal inhibition of vSMC growth, whereas non-PG protein fractions from subconfluent EC cultures with HSPG fractions produced the maximal stimulation. Thus, whereas the net stimulatory or inhibitory effect on vSMC growth of EC-conditioned medium is density dependent, this effect does not result from a difference in the antiproliferative heparan sulfate component but rather from non-PG proteins that interact with the heparan sulfates.

Immunohistochemical analysis of platelet-derived growth factor-B expression in myocardial tissues in hypertrophic cardiomyopathy

Intimal and/or medial hyperplasia of intramyocardial small vessels is thought to be one of the causes of myocardial ischemia in hypertrophic cardiomyopathy (HCM). However, the pathogenesis of such vascular lesions in HCM is not yet known. To evaluate the pathogenic role of platelet-derived growth factor (PDGF-B) and basic fibroblast growth factor (b-FGF), which have a potential to induce cellular and molecular changes observed in the vessels in HCM, we examined the expression of these molecules and PDGF receptors in cardiac tissues from six patients with HCM and seven controls using immunohistochemistry. The percentage of PDGF-B positive cells in the myocyte population in HCM was significantly higher than that in controls (52.6 +/- 16.2 (mean +/- SD) vs. 21.6 +/- 9.6, p < 0.01). PDGF-B was also observed in vascular regions in HCM (61.1 +/- 25.5% of arterioles) but not in controls. There were no significant differences in the expression of b-FGF and PDGF receptors in the myocyte and non-myocyte populations and the vascular regions between the HCM and control groups. Our study revealed that the expression of PDGF-B protein was up-regulated in HCM, suggesting the contribution of this molecule to the development of intramyocardial vasculopathy.

NG-hydroxy-L-arginine and nitric oxide inhibit Caco-2 tumor cell proliferation by distinct mechanisms

The objective of this study was to elucidate the role and mechanism of nitric oxide (NO) synthase (NOS) in modulating the growth of the Caco-2 human colon carcinoma cell line. The two novel observations reported here are, first, that NG-hydroxy-L-arginine (NOHA) inhibits Caco-2 tumor cell proliferation, likely by inhibiting arginase activity, and, second, that NO causes cytostasis by mechanisms that might involve inhibition of ornithine decarboxylase (ODC) activity. Both arginase and ODC are enzymes involved in the conversion of arginine to polyamines required for cell proliferation. Cell growth was monitored by cell count, cell protein analysis, and DNA synthesis. NOHA (1-30 microM) and NO in the form of DETA/NO (1-30 microM) inhibited cell proliferation by 30-85%. The cytostatic effect of NOHA was prevented by addition of excess ornithine, putrescine, spermidine, or spermine to cell cultures, whereas the cytostatic effect of NO (DETA/NO) and alpha-difluoromethylornithine (ODC inhibitor) was unaffected by ornithine but was prevented by putrescine, spermidine, or spermine. The cytostatic effect of NOHA appeared to be independent of its conversion to NO, and the effect of NO appeared to be independent of cGMP. NOHA inhibited urea production by Caco-2 cells and inhibited arginase catalytic activity (85% at 3 microM), whereas NO (DEA/NO and SNAP) inhibited ODC activity (>/=60% at 30 microM) without affecting arginase activity. Coculture of Caco-2 cells with lipopolysaccharide/cytokine-activated rat aortic endothelial cells markedly slowed Caco-2 cell proliferation, and this was blocked by NOS inhibitors. These observations that NOHA and NO may inhibit sequential steps in the arginine-polyamine pathway suggest a novel biological role for NOS in the inhibition of cell proliferation of certain tumor cells and possibly other cell types.

Fibroblast growth factor-2-toxin induced cytotoxicity: differential sensitivity of co-cultured vascular smooth muscle cells and endothelial cells

Recombinant FGF-2-SAP is a mitotoxin consisting of the plant-derived ribosome-inactivating toxin saporin (SAP) fused to basic fibroblast growth factor (FGF-2). FGF-2-SAP targets and kills cells bearing upregulated FGF receptors. In vivo, FGF-2-SAP inhibits smooth muscle cell hyperplasia in models of restenosis. The present study examined the potential for a differential effect of FGF-2-SAP on canine vascular endothelial cells (EC) and smooth muscle cells (SMC) separately as well as in a novel co-culture model. Canine vascular SMC and EC cultures were established separately and made quiescent once cells reached 80% confluence. Following the release from growth arrest, both cell types were treated with FGF-2-SAP, or FGF-2, or SAP alone for 48 h. [3H]TdR incorporation was used to determine the growth response of SMC and EC. The co-culture system was created by plating canine vascular SMC and EC on either side of a microporous 13 microm thick polyester membrane insert. Both cell types were grown to 80% confluence and independently made quiescent. Following the release from growth arrest, cells were treated with FGF-2-SAP, or FGF-2, or SAP alone. Negative and positive control groups were untreated wells containing phosphate buffered saline and complete growth media, respectively. After 48 h, both [3H]TdR incorporation and total DNA content, by fluorometric measurement, were quantitated in SMC and EC independently. FGF-2-SAP showed a concentration-dependent cytotoxicity in both canine SMC and EC but cytotoxicity for EC required substantially higher concentrations. In co-cultured SMC, FGF-2-SAP significantly decreased both [3H]TdR uptake and total DNA content at 0.5, 5, 50, and 500 ng/ml (0.01-10 nM) compared to positive controls. In co-cultured EC, FGF-2-SAP decreased [3H]TdR uptake at 50 and 500 ng/ml and total DNA content at 500 ng/ml compared to positive controls. Neither SAP alone nor FGF-2 alone showed a significant effect on [3H]TdR uptake or DNA content of either SMC or EC. In this unique co-culture model, which better replicates the relationship between SMC and EC in vivo, we demonstrated a dose-response range of FGF-2-SAP at which both the proliferation and total cell number of SMC, but not EC, is significantly reduced. These data suggest that FGF-2-SAP may have therapeutic utility in inhibiting myointimal hyperplasia in the absence of a deleterious effect on regenerating endothelium following vascular reconstructions.

Hemagglutinating virus of Japan-liposome-mediated gene transfer of endothelial cell nitric oxide synthase inhibits intimal hyperplasia of canine vein grafts under conditions of poor runoff

PURPOSE

Late graft failure is a critical problem, particularly in the presence of poor runoff vessels. Intimal hyperplasia is considered to be the main cause of graft failure. We have already reported that intimal thickening of experimental vein grafts in dogs with poor runoff vessels is more pronounced than that in dogs with normal vessels. We and others also have reported that production of nitric oxide (NO) in the endothelium of canine vein grafts is impaired. In the present study, we asked whether in vivo gene transfer of endothelial cell NO synthase (ecNOS) would inhibit intimal hyperplasia of autogenous vein grafts implanted in limbs with poor distal runoff in dogs.

METHODS

After exposing femoral veins, the nuclear-targeted lac Zgene, bovine ecNOS cDNA, or control vector plasmid encapsulated in the hemagglutinating virus of Japan-liposomes was infused intraluminally, followed by incubation for 10 minutes at room temperature under a distending pressure of 100 mm Hg. Twenty reversed vein grafts were implanted under normal runoff conditions, and 4 days later these were used to confirm gene transfer to the vein grafts. Twelve reversed vein grafts were implanted under conditions of poor runoff, and 4 weeks after the operation intimal thickening was evident.

RESULTS

In vein grafts under normal runoff conditions, lac Z gene transfer exhibited diffuse and frequent X-Gal-positive signals in both medial and adventitial layers 4 days after implantation (n = 3). In case of the ecNOS gene-transferred vein grafts, bovine ecNOS protein was mainly detected in medial smooth muscle cells and adventitial cells 4 days after implantation, determined using immunohistochemical techniques and bovine ecNOS specific antibody (n = 3). In addition, ecNOS-transferred vessels showed intense purple signals by reduced nicotinamide adenine dinucleotide phosphate diaphorase and nitroblue tetrazolium reaction, in both medial and adventitial layers, whereas weak NOS activity was recognized at the adventitial vasa vasorum of the untreated veins or control vector transferred veins (n = 3, respectively). In vein grafts under poor runoff conditions, the intimal thickness at 4 weeks after implantation was significantly reduced by ecNOS gene transfer (n = 4; 90.0 +/- 7.6 microns and 1.18 +/- 0.07 mm2) in comparison with buffer-treated vessels (n = 4; 195.8 +/- 25.7 microns and 2.62 +/- 0.48 mm2) or vector vehicle-treated vessels (n = 4; 193.0 +/- 15.8 microns and 2.65 +/- 0.22 mm2).

CONCLUSIONS

Our findings show that gene transfer of ecNOS inhibited intimal hyperplasia of canine vein grafts caused by poor runoff conditions, as a result of an increased local production of NO. Thus ecNOS gene transfer warrants further study as a possible approach to prevent late graft failure.

Heparin/heparan sulfate chelation inhibits control of vascular repair by tissue-engineered endothelial cells

The relative importance of heparin-like compounds in mediating vascular repair is unclear. We investigated how protamine, a chelator of heparin, affected endothelial cell inhibition of vascular smooth muscle cell growth and intimal hyperplasia. The 52% (P < 0.001) reduction in smooth muscle cell proliferation produced by postconfluent endothelial cell-conditioned medium was entirely reversed by pretreatment of medium with heparinase and heparitinase and was inhibited in a dose-dependent fashion by the coadministration of protamine. Pretreatment of conditioned medium with heparinase and heparitinase largely prevented protamine's mitogenic activity, suggesting that protamine affects growth by interacting with heparin-like compounds. Perivascular implantation of polymerengrafted endothelial cells reduced neointima formation in denuded rat carotid arteries by 92% (P < 0.001) and cell proliferation by 81% (P < 0.001). Coadministration of protamine abolished the inhibitory potential of the cell implants, resulting in a nearly twofold exacerbation of intimal hyperplasia compared with controls (P < 0.001). Thus heparin-like molecules are essential to the biochemical regulation of vascular repair provided by endothelial cells, and the continued routine clinical use of heparin chelators, like protamine, may be questionable.

Response of vascular smooth muscle cells to the neuropeptide secretoneurin. A functional role for migration and proliferation in vitro

Mesenchymal cell migration and replication are central biologic events involved in atherosclerosis and lung and hepatic fibrosis. Tissue repair and fibrosis are thought to be regulated by growth regulatory molecules, comprising both stimulators and inhibitors of mesenchymal cell functions, including platelet-derived growth factor (PDGF), transforming growth factor-beta (TGF-beta), fibroblast growth factors, and several neuropeptides such as substance P. Secretoneurin (SN), a novel 33-amino acid neuropeptide derived from secretogranin II (chromogranin C), is widely distributed in the central and peripheral nervous and neuroendocrine systems, including afferent C-fibers, and can be released in the periphery by capsaicin. Recently, we reported that SN triggers the selective migration of human monocytes and fibroblasts in vitro, implicating its involvement in inflammatory responses. We report herein that SN stimulates specific migration (maximal response at 10(-10) M) of cultured arterial smooth muscle cells (SMCs), originating from rat thoracic aorta, and initiates DNA synthesis and SMC growth (BrdU incorporation, MTT test) with a maximum at 10(-8) M SN to a similar extent as observed by PDGF. Both functional activities of SN were inhibited by specific anti-SN immunoglobulins (dilution, 1:1000), and furthermore, a trypsinized SN peptide (10(-8) M) was unable to provoke biologic effects. Our studies suggest that SN functions as a regulatory peptide to modulate SMC migration and proliferation, which in conjunction with other factors could serve to aggravate and accelerate the development of atherosclerotic or restenotic lesions at sites of vascular injury.

Inhibitory effect of type 1 collagen gel containing alpha-elastin on proliferation and migration of vascular smooth muscle and endothelial cells

The purpose of this study was to investigate in vitro the potential effect of type 1 collagen gel containing alpha-elastin on the proliferation of vascular smooth muscle cells and vascular endothelial cells, and on smooth muscle cell migration. Vascular smooth muscle cell and endothelial cell were cultured in 12-well plates precoated with collagen gels and alpha-elastin. Cell proliferation rates were measured by monitoring [3H]-thymidine incorporation. After 2, 3 or 4 days of culture, the proliferation rate of both smooth muscle cells and endothelial cells was significantly decreased on collagen gel containing 10 mg/ml alpha-elastin compared with collagen gel only as control. Smooth muscle cell proliferation on collagen gel containing alpha-elastin on the 4th day of culture was decreased dose-dependently, e.g. 1 mg/ml of alpha-elastin (74.8(2.3)% of control, P=n.s.); 5 mg/ml (56.7(2.1)%; P<0.05); 10 mg/ml (30.3(3.1)%; P<0.005). In the case of cultured endothelial cells, however, [3H]-thymidine incorporation was not decreased significantly in the presence of 5 mg/ml alpha-elastin (83.1(7.9)%, P=n.s.). After stimulation by platelet-derived growth factor, the smooth muscle cell migration rate on collagen gel containing alpha-elastin (5 mg/ml) was decreased over time. The area of migration on the 6th day of culture was also significantly decreased dose-dependently in the presence of alpha-elastin, e.g. 1 mg/ml (72.6(3.4)% of control, P<0.05), 5 mg/ml (56.9%(1.5)%; P<0.05); 10 mg/ml (37.3(2.7)%; P<0.0005). In conclusion, alpha-elastin inhibited the proliferation and migration of smooth muscle cell in a dose-dependent manner on collagen gel culture, however, at high concentrations of alpha-elastin (10 mg/ml), the endothelial cell proliferation rate was also inhibited. At 5 mg/ml, alpha-elastin significantly inhibited smooth muscle cell proliferation and migration but did not significantly inhibit endothelial cell proliferation. Incorporation of collagen gel containing alpha-elastin into the structure of arterial prosthesis offers the possibility of inhibiting smooth muscle cell hyperplasia without significant effect on endothelial cell formation.

Compartmentalized coculture of porcine arterial endothelial and smooth muscle cells on a microporous membrane

Endothelial and smooth muscle cells were harvested from porcine pulmonary arteries and grown to two passages from primary culture in serum-containing medium. Thereafter, the cells were plated on the opposite sides of microporous poly-(ethylene terephthalate) membrane and cultivated in a chemically defined, serum-free medium. The membrane with pores of 1 microgram diameter allowed the passage of molecules and the extension of cell processes, while maintaining separate homogeneous cell populations. Pores of 3 microgram diameter permitted the crossing of smooth muscle cells through the membrane. The coating of the polymer with constituents of the extracellular matrix optimized cell adhesion. Morphological analysis of the model showed typical cobblestone pattern and ultrastructure of endothelial cells, which lost rapidly the expression of von Willebrand factor but kept that of angiotensin-converting enzyme. Smooth muscle cells were spindle shaped and specific alpha-actin was revealed by immunochemistry and quantitated by enzyme-linked immunosorbent assay (ELISA). Their ultrastructure featured an intermediate contractile-synthetic phenotype. Permeability studies to different molecules showed a marked reduction of the albumin clearance. Finally, in coculture in the presence of endothelial cells, the smooth muscle cells proliferation was increased, whereas it was not the case in autologous cocultures. In conclusion, such a coculture model may help to a better understanding of the interactions between endothelial and smooth muscle cells that may be important in the pathogenesis of vascular diseases.

Coculture of endothelial cells and smooth muscle cells in bilayer and conditioned media models

Smooth muscle cell (SMC) growth characteristics are affected by endothelial cells (ECs) in vivo and in vitro. In this study, we compare a bilayer EC/SMC coculture model that allows cell contact with a model of SMCs growing in media continuously conditioned by ECs, but without physical contact. Bovine aortic SMCs were plated on one side of a 13-microns-thick, semipermeable membrane. Three models were compared: (1) SMCs cultured alone (with no cells on the opposite side of the membrane, O/SMC); (2) SMCs cultured with ECs on the opposite side of the membrane in a bilayer coculture system that allows physical contact between ECs and SMCs (EC/SMC); and (3) SMCs cultured in media continuously conditioned by adjacent ECs, without contact (conditioned media, CM). After cultures were established, SMCs were harvested at 7 and 14 days after plating (n = 5 cultures/day/group). SMC DNA and protein content and [3H]thymidine incorporation were measured in each group. On Days 7 and 14 after plating, ECs in both the EC/SMC and CM models stimulated SMC proliferation > 50% compared to O/SMC controls (P < 0.05). SMC density was similar for the EC/ SMC and CM models at Day 7, but SMC density was higher in the EC/SMC group at Day 14 in culture (P < 0.05). At Day 7, protein synthesis was similar in the three groups, but by Day 14, SMCs in the EC/SMC group had produced significantly less cellular protein/ DNA than SMCs in the CM group (P < 0.05), which in turn had less protein/DNA than the control (O/SMC) group (P < 0.05). SMCs in the EC/SMC and CM groups retained a thin, spindle shape with filamentous projections, compared to the hypertrophic appearance of SMCs in the absence of ECs. Electron microscopy revealed projections from SMCs which traversed the pores in the coculture membrane and made intimate contact with ECs. The degree of EC/SMC contact increased from 7 to 14 days (P < 0.05). Compared to SMCs alone, ECs in bilayer coculture or conditioned media altered SMCs growth characteristics similarly after 7 days in culture. By 14 days, however, the bilayer coculture had a significantly greater effect on SMC density and protein synthesis. The bilayer model is unique in terms of luminal/abluminal orientation of the cells, the proximity of the cell layers, and the presence of physical cell contact. Since the bilayer model amplifies the effect of ECs on SMCs, it may be more useful than conditioned media to study EC-SMC interactions.

Gamma radiation effect on vascular smooth muscle cells in culture

PURPOSE

Prior work in our laboratory demonstrated that external gamma irradiation administered within 48 h following balloon catheter carotid artery injury in rats produced a marked inhibition of intimal hyperplasia and restenosis. The current study used smooth muscle cells (SMC) in vitro to examine the radiation dose response and to investigate the cellular mechanism by which radiation inhibits SMC proliferation.

METHODS AND MATERIALS

Quiescent rat aortic SMC in plasma were refed with whole blood serum to stimulate synchronous proliferation and immediately irradiated with single fraction doses of 1.25-20 Gy.

RESULTS

Comparison between a micronucleus assay and a clonogenic assay indicated a dose-dependent inhibition of SMC growth, with an ED50 at 2-3 Gy. The micronucleus assay also demonstrated a dose-dependent increase in apparent chromosomal damage at 72 h after irradiation. Inhibition of SMC growth by radiation did not correlate with changes in intracellular or released mitogenic activity. Furthermore, there was no evidence of apoptosis in irradiated SMC up to 96 h after treatment.

CONCLUSION

Radiation likely inhibits SMC proliferation after arterial injury by a dose-dependent mechanism of lethal and/or sublethal cellular injury leading to clonogenic cell death.

Paracrine effect of human vascular endothelial cells on human vascular smooth muscle cell proliferation: transmembrane co-culture method

To investigate the role endothelial cells have on underlying smooth muscle cell proliferation, human aortic vascular smooth muscle cells were co-cultured with human aortic endothelial cells at different cell densities, using a transmembrane co-culture method. Subconfluent endothelial cells subseeded at low (0.5 x 10(4) cells/well) and medium densities (2.0 x 10(4) cells/well) stimulated smooth muscle cell proliferation by 43 +/- 14% (P < 0.01) and 39 +/- 8% (P < 0.02), respectively. However, this stimulatory effect on smooth muscle cell proliferation was not evident in confluent endothelial cells subseeded at high cell density (8.0 x 10(4) cells/well). Treatment of smooth muscle cells with trapidil, at 10(-6) M, for anti-platelet derived growth factor (PDGF) effect or with endothelin-1 receptor blocker FR 139317, at 10(-6) M failed to inhibit this stimulatory effect. These results imply that subconfluent human endothelial cells are able to exert a stimulatory effect on human smooth muscle cell proliferation, and that this endothelial paracrine growth effect may not be mediated by endothelin or PDGF.

Induction of tissue inhibitor and matrix metalloproteinase by serum in human heart-derived fibroblast and endomyocardial endothelial cells

To understand the regulatory mechanisms of extracellular matrix (ECM) turnover and proteinase expression in human cardiovascular tissue, we have isolated and characterized human heart fibroblast (HHF) and human heart endothelial (HHE) cells from endomyocardial biopsy specimens. HHE cell in culture exhibited the typical cobblestone growth pattern and positive immunofluorescent staining for factor VIII related antigen. HHF demonstrated the typical spindle shape during culture and were positive for vimentin. Both cell types were negative for alpha-actin, indicating that these cells were of nonmuscle origin. Cell growth studies revealed significant growth when maintained in limiting serum concentration, suggesting mitogenic activity of these cells, and demonstrated growth inhibitory activity when grown in serum-free medium. Serum-dependent matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinases (TIMPs) expression was measured by zymography, immunoblot, and Northern blot analysis. Results indicated that serum induces both the MMP and TIMP expression at the mRNA and protein levels in a dose-dependent manner. This induction was inhibited by actinomycin D and cycloheximide, suggesting transcriptional and translational regulation of MMP and TIMP. Indirect immunofluorescence labeling indicated expression of MMP and TIMP in HHF and HHE cells. These results suggested that the serum induces proliferation as well as expression of MMP and TIMP in HHE and HHF cells. The growth inhibitory activity of these cell cultures will enable us to explore further the nature of this response and compare this phenomenon with other growth inhibitors and growth promoters identified in other normal and transformed cells.

Effect of nonanticoagulant heparin (Astenose) on restenosis after balloon angioplasty in the atherosclerotic rabbit

PURPOSE

To determine whether intravenous administration of Astenose, a high-molecular-weight nonanticoagulant heparin, can reduce restenosis following balloon angioplasty in a rabbit model.

MATERIALS AND METHODS

Focal atherosclerosis was induced in 54 rabbits (89 vessel), and angioplasty was performed after animals were randomized into five groups. Group 1 vessels (control) were treated with lactated Ringer solution for 28 days (n = 19); group 2, Astenose at 0.10 mg/kg per hour for 28 days (n = 16); group 3, Astenose at 0.33 mg/kg per hour for 28 days (n = 16); group 4, Astenose at 0.60 mg/kg per hour for 28 days (n = 17); and group 5, Astenose at 0.33 mg/kg per hour for 14 days (n = 21). Arteriograms were obtained to measure minimal luminal diameters before, immediately after, and 28 days after angioplasty, and the rabbits were killed for histologic analysis.

RESULTS

Angiographically demonstrated restenosis was significantly reduced in groups 3 (18.9% +/- 3.7, P = .04) and 4 (20.2% +/- 3.1, P = .04) compared with the control group (32.4% +/- 4.8). Group 5 showed a nonsignificant trend toward reduced restenosis (23.1% +/- 2.9, P = .09), and group 2 showed restenosis similar to that in group 1 (31.0% +/- 2.5, P = .80). However, quantitative histopathologic analysis detected no differences among the groups in absolute plaque area. Medial area was significantly smaller in groups 2 and 5 (P < or = .002) than in group 1, and there was a nonsignificant trend toward reduced medial area in groups 3 and 4 (P = .12).

CONCLUSION

Long-term intravenous Astenose therapy resulted in a modest but statistically significant reduction in angiographically demonstrated restenosis after angioplasty in this atherosclerotic rabbit model.

Fish oil supplementation attenuates myointimal proliferation of the abdominal aorta after balloon injury in diet-induced hypercholesterolemic rabbits

The effects of supplementing with fish oil on the myointimal proliferation of the abdominal aorta after balloon injury were studied in control and in rabbits fed a 1% cholesterol-enriched diet, with and without 10% fish oil supplementation. Twenty-one animals in each group underwent a balloon injury of the abdominal aorta and left common iliac artery after 2 weeks of feeding. The animals remained on their respective diets thereafter. In 7 balloon-injured and 7 sham-operated animals of each group, the abdominal aorta was harvested 3 days later for the analysis of prostanoids, malondialdehyde, superoxide dismutase activity, [3H]thymidine uptake, and cholesterol levels. In the other 7 balloon-injured rabbits of each group, the tissue was harvested 3 weeks later for morphometric study. The fish oil-treated rabbits had the lowest aortic production of thromboxane B2 levels and the highest 6-keto-PGF1 alpha/thromboxane B2 ratios among the three groups after balloon injury. The aortic malondialdehyde levels of the cholesterol-fed rabbits were significantly higher than the other two groups (each P < 0.001) independent of balloon injury. The myointimal proliferation of the abdominal aorta and left common iliac artery in the fish oil-treated rabbits was less severe than in the cholesterol-fed animals (both P < 0.001) and was comparable with the controls. These results suggest that a fish oil supplement changes prostanoid metabolism to a favorable pattern and reduces lipid peroxidation on the abdominal aortic wall, thus attenuating myointimal proliferation after balloon injury in diet-induced hypercholesterolemic rabbits.

The protective effect of vein cuffed anastomoses is not mechanical in origin

PURPOSE

Intimal hyperplasia (IH) is a proliferative process of vascular smooth muscle cells that occurs after an arterial injury, particularly at outflow anastomoses of prosthetic bypass grafts. IH causes stenosis that leads ultimately to graft flow reduction and thrombosis. We have demonstrated previously that vein cuff interposition between an expanded polytetrafluoroethylene (e-PTFE) graft and artery at distal anastomoses diminished IH formation in the arterial outflow as compared with noncuffed anastomoses. Improved long-term patency rates associated with the placement of an interposition vein cuff at the distal anastomosis of e-PTFE grafts to infrageniculate arteries have also been demonstrated clinically. This study examined the mechanical factors that may contribute to the protective effect of cuffed anastomoses. These factors include the expansibility of the vein cuff as compared with e-PTFE, as well as the angle of the cuffed anastomosis.

METHODS

Compatible animals were selected by use of platelet aggregation studies. Nine dogs, group A, received a 4 mm e-PTFE graft plus a 1 cm long interposition vein cuff at the distal anastomosis in the left carotid artery. The same procedure was done on the right side, and in addition the vein cuff was encircled by an e-PTFE jacket incorporated into the anastomosis to prevent the expansion of the vein cuff with arterial pulsation. To study the effect of distal anastomotic angle and geometry on the formation of IH, five dogs, group B, received a 4 mm e-PTFE graft in both sides. On the left, the distal anastomosis was performed between the graft and the artery at an acute angle as it is commonly done when a bypass graft is placed. On the right side a 1 cm long, 6 mm diameter e-PTFE segment was interposed between the artery and the graft at a perpendicular angle. This geometry mimicked the right angle of a vein cuff-to-artery anastomosis. After 10 weeks the grafts were harvested, and the thickness of IH was measured with an ocular micrometer under light microscopy.

RESULTS

In group A, one dog had bilateral graft thrombosis (12%), and these grafts were discarded. In the remaining eight dogs there was no statistically significant difference in the thickness of IH between the right (jacketed group) and the left side (nonjacketed/control group), showing that vein cuff expansibility did not play a role in protecting against the formation of IH. In group B, bilateral graft thrombosis occurred in four of five dogs (80%), suggesting that the perpendicular anastomotic angle was not protective.

CONCLUSION

These results suggested that the protective effect of the vein cuff is not mechanical in origin.

Neutrophils may contribute to the morbidity and mortality of claudicants

Peripheral arterial occlusive disease is a common cause of morbidity in middle-aged men; 5 per cent of those aged over 50 years suffer from intermittent claudication. While claudication itself is not fatal, claudicants have a mortality rate approximately three times that of non-claudicating men of the same age, mainly from cardiovascular disease. This review examines the evidence for involvement of the neutrophil in this increased mortality and describes the possible pathogenesis. It also discusses how treatment of claudication may modify neutrophil behaviour, reducing subsequent mortality and morbidity rates.

L-arginine improves endothelium-dependent vasorelaxation and reduces intimal hyperplasia after balloon angioplasty

Reductions in nitric oxide (NO) activity persist after arterial intimal injury and may be a factor in the development of intimal hyperplasia. NO inhibits in vitro platelet aggregation, leukocyte adhesion, and smooth muscle cell growth, all of which are key components in the process of intimal hyperplasia. We hypothesized that long-term supplementation with L-arginine, the precursor of NO, would increase NO production and thereby improve endothelium-dependent vasorelaxation and simultaneously reduce intimal hyperplasia. Twenty-six New Zealand White male rabbits were fed standard rabbit chow either with or without 2.25% L-arginine in their drinking water for 3 weeks. Then the animals underwent unilateral iliac artery angioplasty and were continued on their respective diets. Four weeks after angioplasty, the iliac arteries were harvested for functional and morphometric studies. The iliac arteries from several animals from each group were processed for study by electron microscopy. Maximal endothelium-dependent vasorelaxation in injured arteries was significantly greater in L-arginine-supplemented animals (mean +/- SEM, 71.8 +/- 4.1%; n = 6) than controls (51.4 +/- 4.0%, n = 7; P < .05). Furthermore, the intimal area in injured arteries was significantly reduced in L-arginine-supplemented animals (0.22 +/- 0.03 mm2, n = 5) compared with controls (0.34 +/- 0.03 mm2, n = 6; P < .05). These data suggest that L-arginine supplementation enhances NO production at sites of vascular healing and may reduce intimal hyperplasia.

A definition of initial, fatty streak, and intermediate lesions of atherosclerosis. A report from the Committee on Vascular Lesions of the Council on Arteriosclerosis, American Heart Association

The compositions of lesion types that precede and that may initiate the development of advanced atherosclerotic lesions are described and the possible mechanisms of their development are reviewed. While advanced lesions involve disorganization of the intima and deformity of the artery, such changes are absent or minimal in their precursors. Advanced lesions are either overtly clinical or they predispose to the complications that cause ischemic episodes; precursors are silent and do not lead directly to complications. The precursors are arranged in a temporal sequence of three characteristic lesion types. Types I and II are generally the only lesion types found in children, although they may also occur in adults. Type I lesions represent the very initial changes and are recognized as an increase in the number of intimal macrophages and the appearance of macrophages filled with lipid droplets (foam cells). Type II lesions include the fatty streak lesion, the first grossly visible lesion, and are characterized by layers of macrophage foam cells and lipid droplets within intimal smooth muscle cells and minimal coarse-grained particles and heterogeneous droplets of extracellular lipid. Type III (intermediate) lesions are the morphological and chemical bridge between type II and advanced lesions. Type III lesions appear in some adaptive intimal thickenings (progression-prone locations) in young adults and are characterized by pools of extracellular lipid in addition to all the components of type II lesions.

A definition of initial, fatty streak, and intermediate lesions of atherosclerosis. A report from the Committee on Vascular Lesions of the Council on Arteriosclerosis, American Heart Association

The compositions of lesion types that precede and that may initiate the development of advanced atherosclerotic lesions are described and the possible mechanisms of their development are reviewed. While advanced lesions involve disorganization of the intima and deformity of the artery, such changes are absent or minimal in their precursors. Advanced lesions are either overtly clinical or they predispose to the complications that cause ischemic episodes; precursors are silent and do not lead directly to complications. The precursors are arranged in a temporal sequence of three characteristic lesion types. Types I and II are generally the only lesion types found in children, although they may also occur in adults. Type I lesions represent the very initial changes and are recognized as an increase in the number of intimal macrophages and the appearance of macrophages filled with lipid droplets (foam cells). Type II lesions include the fatty streak lesion, the first grossly visible lesion, and are characterized by layers of macrophage foam cells and lipid droplets within intimal smooth muscle cells and minimal coarse-grained particles and heterogeneous droplets of extracellular lipid. Type III (intermediate) lesions are the morphological and chemical bridge between type II and advanced lesions. Type III lesions appear in some adaptive intimal thickenings (progression-prone locations) in young adults and are characterized by pools of extracellular lipid in addition to all the components of type II lesions.

Molecular and cellular concepts in atherosclerosis

Atherosclerosis is a complex disease of uncertain cause. Its pathobiology is believed to represent an abnormal expression of the processes of vascular healing. Etiologic models derive from a 'response to injury' paradigm and can be divided into three separate disease stages: endothelial dysfunction, smooth muscle proliferation and architectural disruption. The initiating event of endothelial dysfunction is unknown, but is believed to be related to low-density lipoproteins and/or their oxidized derivatives. Endothelial injury is signalled to the smooth muscle cells of the media by three routes: direct cell-cell interaction, secretion of soluble growth factors and monocyte-derived cytokines. Monocytes are recruited by the endothelium and invade the subintimal space by a complex interaction of a variety of adhesion proteins and receptors on both cell types. Smooth muscle cell proliferation is initiated by a change in phenotype expression from 'contractile' to 'synthetic' resulting from the binding of fibronectin to specific integrin receptors. Three functionally distinct activities may represent separate subtypes of the 'synthetic phenotype': migration from the media to the intima, increased proliferation and inappropriate extracellular matrix synthesis. The loss of normal regulatory control and anchorage independence of proliferation suggest a relationship to oncogenic transformation. Both migration and proliferation result from the binding of platelet-derived growth factor-like factors to smooth muscle cell receptors, which initiates a cascade of intracellular molecular events leading either to cytoskeletal locomotory restructuring or cell cycle activation. Both pathways also appear to be coregulated by integrin receptors and both depend upon phosphorylation of cell membrane, cytosolic and nuclear regulatory proteins. Clinical expression of atherosclerosis may follow sudden loss of architectural integrity of the intimal plaque by three different mechanisms: plaque fissuring, intraluminal plaque rupture or intramural hemorrhage related to abnormal vessel wall stress and/or biochemistry.

Topical hyperbaric therapy for problem skin wounds

BACKGROUND

Hyperbaric oxygen remains the sole treatment capable of inducing growth of new blood vessels. However, systemic hyperbaric oxygen therapy risks central nervous system and pulmonary toxicity.

OBJECTIVE

To describe topical hyperbaric oxygen therapy for the treatment of recalcitrant open wounds.

METHODS

Topical and systemic hyperbaric oxygen treatments are described and contrasted from one another. Applications of topical hyperbaric oxygen therapy are described.

CONCLUSION

Topical hyperbaric oxygen therapy is useful only for open wounds. The advantages of topical hyperbaric oxygen therapy include low cost, the lack of systemic oxygen toxicity, and effectiveness, allowing this treatment to be prescribed for many patients early in the course of their disease rather than as a last resort.

Effects of platelet-derived growth factor isoforms on human lung fibroblast proliferation and procollagen gene expression

Platelet-derived growth factor (PDGF), a potent mitogen for fibroblasts, is a potentially important cytokine in the pathogenesis of fibroproliferative disorders of lung. Different isoforms of PDGF include a heterodimer composed of A and B chains and homodimers composed of A or B chains. The biological significance of the different isoforms is unknown, but they have been shown to differ in their mitogenic potency in some systems. Their effects on other fibroblast functions have not been fully examined. We undertook this study to determine the effect of PDGF isoforms on human lung fibroblast proliferation and procollagen synthesis. Cultured lung fibroblasts (IMR-90, WI-38, GeNA) were incubated in the presence of varying concentrations of highly purified PDGF-AB obtained from platelets or recombinant PDGF-AA or -BB homodimers. Incorporation of [3H]thymidine was determined as a measure of mitogenic activity. Fetal lung fibroblasts (IMR-90, WI-38) and an adult fibroblast strain (GeNA) responded similarly to the different isoforms, with maximum mitogenic activity observed at 5-10 ng/mL. Cell cycle analysis using three additional normal adult lung fibroblast strains indicated that all PDGF isoforms stimulated similar proportions of cells to cycle over a 7-day period. Fibroblast procollagen synthesis, measured after pulse labeling with [3H]proline, was not increased even at concentrations of the PDGF isoforms that were maximally mitogenic. Moreover, steady-state levels of alpha 1(I) and alpha 1(III) procollagen mRNA levels, determined by northern analysis and dot blot hybridization, were not changed after exposure to any of the PDGF isoforms. While all PDGF isoforms are potent mitogens for fetal and adult lung fibroblasts, it was concluded that they do not directly stimulate procollagen gene expression or procollagen synthesis in vitro. The results suggest that PDGF isoforms are potentially important mitogens for lung fibroblasts, but other factors are likely to be involved in the stimulation of fibroblast procollagen synthesis that is observed in fibroproliferative disorders of lung.

Pathophysiological mechanisms for restenosis following coronary angioplasty: possible preventive alternatives

Restenosis after successful percutaneous transluminal coronary angioplasty (PTCA) remains an unsolved medical problem. The search for the underlying pathophysiological mechanisms have identified intimal proliferation of smooth muscle cells (SMC) to be the prevailing cause of late restenosis, with endothelial cells (EC) and platelets being important participators in the process. According to the most accepted present theory, SMC would be stimulated to migrate and proliferate shortly after the angioplasty by the release of growth factors from injured EC and accumulated platelets. However, clinical trials of agents interfering with these mechanisms have not significantly diminished the rate of restenosis, which suggest both that our knowledge of the process is incomplete, and that new ways of administering the agents may be required.

Sequestration and secretion of insulin-like growth factor-I by bovine aortic endothelial cells

Endothelial cells elaborate growth promoting activities in culture medium that support limited smooth muscle cell and fibroblast growth in vitro in the absence of serum. We investigated whether insulin-like growth factor-I (IGF-I) was synthesized and secreted by bovine aortic endothelial cells in vitro. Subconfluent endothelial cell cultures in serum-free medium secreted severalfold higher IGF-I levels than confluent cultures by acid-sizing chromatography and IGF-I radioimmunoassay. The IGF-I secretory level was not sustained during a second serum-free incubation. In contrast, secretion of IGF binding proteins persisted and was maintained at constant levels throughout the same observation periods. Analysis of poly(A+)RNA by northern blots revealed hybridization of an IGF-I cDNA to a 7.5- to 7.0-kb transcript and superinduction of the 7.5-7.0-kb mRNA by the translational inhibitor, cyclohexamide. However, no endogenously labeled IGF-I was detected in conditioned media after incubation of cultures with [35S]cysteine or [3H]leucine. When cultures were incubated in the presence of serum supplemented with IGF-I, subconfluent cultures sequestered and released more IGF-I than confluent cultures. We concluded that the majority of IGF-I secreted in vitro was sequestered from serum.

Vascular injury and time course of smooth muscle cell proliferation after experimental holmium laser angioplasty

BACKGROUND

In vitro experiments have shown that holmium laser energy can effectively ablate even calcified plaque in human arterial vessels. Because high-energy densities from holmium lasers can easily be transmitted through quartz fibers, this solid-state laser has been suggested as an alternative intraluminal treatment of atherosclerotic plaque.

METHODS AND RESULTS

To develop an intimal plaque, 35 New Zealand White rabbits underwent electrical stimulation of their right carotid artery for 28 days. Subsequently, in 25 rabbits, holmium laser angioplasty (wavelength, 2.12 microns; pulse duration, 150 microseconds; energy density, 350 mJ/mm2) was performed. To study the morphological results, the vessels were excised after 7, 14, 28, and 42 days. Cross sections were analyzed in regard to laser-specific injury. Staining of alpha-actin was used to identify smooth muscle cells (SMCs). After bromodeoxyuridine labeling, the extent of proliferation (number of cells undergoing DNA synthesis) was determined by using a monoclonal antibody. Holmium laser ablation resulted in an initial decrease of the numbers of intimal cell layers in the early group (7 days after treatment: 5 +/- 1 cell layers with 76 +/- 39 microns; control: 13 +/- 3 cell layers with 144 +/- 44 microns). Quantification of SMCs undergoing DNA synthesis in the intima (control: 51 +/- 19 cells/mm2) showed a significant increase of labeled cells after 7 (216 +/- 74 cells/mm2, p = 0.003) and 14 days (281 +/- 139 cells/mm2, p = 0.011). Integrity of the internal elastic lamina was disrupted in all animals after intervention. Seven and 14 days after treatment, a considerable reduction of medial cell nuclei was found in 10 of 12 animals. SMC proliferation in the medial layer was increased within the first 2 weeks after laser ablation (168 +/- 113 cells/mm2; control: 8 +/- 4 cells/mm2; p = 0.023). Six weeks after holmium laser angioplasty, SMC proliferation had returned to control levels in the intima and remained increased in the medial layer. This proliferative response resulted in a significant increase of intimal thickening within 6 weeks after laser ablation (30 +/- 6 cell layers, 375 +/- 97 microns resp.; p = 0.001 each).

CONCLUSIONS

Holmium laser treatment leads to considerable vessel wall injury and results in SMC proliferation in the intimal and medial layer with a maximum of proliferative activity within the first 2 weeks. Subsequently, this results in considerable intimal and medial hyperplasia within 6 weeks after treatment.

Capillary endothelial cells secrete a heparin-binding mitogen for pericytes

The cells of the retinal microvasculature consist predominantly of mesodermally derived pericytes and endothelial cells, and the regulatory factors which govern their co-ordinated growth and define their phenotypic characteristics in vivo may be regarded as key elements of the angiogenic process. An investigation of these cells in co-culture experiments has led to the identification of a potent mitogen for pericytes in medium conditioned by retinal endothelial cells (EC-FBS). EC-FBS activity was shown to be non-dialyzable, and stable to both heat and acid treatment. EC-FBS was inactivated by passage over a heparin-Agarose column. The column-bound activity could be eluted as a single peak at approximately 1.0 M NaCl. Stimulation of pericyte growth was also achieved with platelet-derived growth factor (PDGF), acidic fibroblast growth factor (aFGF) and basic fibroblast growth factor (bFGF) and could be blocked by using the appropriate antiserum (anti-PDGF or anti-aFGF). Neither antisera, however, blocked the activity of EC-FBS. The EC-FBS mitogen markedly altered the phenotypic behavior of pericytes compared with PDGF and the FGFs; yet, unlike them, it failed to stimulate the growth of smooth muscle cells (SMC) and Balb/c 3T3 cells.

Effects of antithrombotic drug, Y-20811 on mural thrombus formation and intimal thickening following intimal injury

Inhibitory effect of Y-20811 on platelet thrombus formation induced by mechanical intimal injury and subsequent intimal fibrous thickening was studied. In the short term experiment, polyethylene tubing was inserted into the rabbit aorta and was drawn out one hour after with or without Y-20811 administration, then the rabbits were sacrificed. In the experiment for the quantitative analysis of platelet adhesion, 51Cr-labeled platelets were used. Radioactivities of 2cm length of the injured segment of the thoracic aorta and the proximal 2cm of the normal segment were measured. Radioactivity of the injured segment was significantly lower in rabbits treated with Y-20811 than the control ones. The mean thickness (area of thrombi/length of injured intima) and the maximal thickness of the mural thrombi in the Y-20811-treated rabbits were significantly lower than those in control rabbits. De-endothelialized area showed raised platelet thrombi in the control group and diffuse thin-layered platelet sheets in Y-20811-treated rabbits. In the long term experiment, polyethylene tubing was indwelled for 24 hours. Rabbits were sacrificed 10 days after drawing out the tubing. Through the experiment Y-20811 was injected intravenously every 24 hours. There was no significant difference between the control group and the Y-20811-treated one in both mean thickness and maximal thickness of the intimal fibromuscular thickening. The experiments indicate that Y-20811 has an inhibitory effect on platelet thrombus formation following intimal injury, but subsequent myointimal thickening is not inhibited by the drug.

Inhibition of pulmonary artery smooth muscle cell growth by hypoxanthine, xanthine, and uric acid

We have previously reported that medium conditioned by hypoxic pulmonary artery endothelial cells (ECCM) contains a factor of small molecular weight that inhibits the growth of pulmonary artery smooth muscle cells (SMC). We postulated that this factor might be a breakdown product of ATP and, therefore, measured the levels of hypoxanthine/xanthine (HX/X) and uric acid (UA) in ECCM and cell lysates from endothelial cells (EC) exposed to hypoxia and normoxia. Although hypoxic and normoxic cell lysates contained no UA and an equal amount of HX/X (2.9 +/- 0.3 and 2.9 +/- 0.5 microM, respectively), there was a 5-fold increase in the amount of HX/X present in hypoxic compared with normoxic ECCM (3.4 +/- 0.3 versus 0.6 +/- 0.4 microM, respectively; P less than 0.001) but no difference in UA levels (5 +/- 2 versus 5 +/- 1 microM, respectively). In separate experiments, we examined the effects of exogenous HX, X, and UA (doses ranging from 0.1 to 100 microM) on the proliferation of pulmonary and aortic SMC and pulmonary artery EC. Our results indicate that HX, X, and UA inhibit the proliferation of SMC in a dose-dependent manner without causing injury to the cells. The proliferation of EC, on the other hand, was not affected by UA and was significantly inhibited by HX and X only at doses of 100 microM. In conclusion, we have found that significant amounts of HX/X accumulate in hypoxic ECCM and that HX, X, and UA inhibit the proliferation of SMC. The relevance of these findings to conditions where hypoxia prevails is discussed.

Effects of endothelial-cell-derived growth factors on cultured astrocytes

To clarify the participation of endothelial-cell-derived growth factors (ECDGFs) in astrocytosis, the effects of endothelial-cell-conditioned medium (ECCM) derived either from normotensive rats or spontaneously hypertensive, stroke-prone rats (SHRSPs) on proliferation of C6 cells of an established rat glioma cell line were bioassayed. The ECCM from both strains stimulated proliferation of astrocytes, but the ECCM from SHRSPs showed a higher mitogenic activity for astrocytes than that from normotensive rats. Growth-promoting activity of the ECCM derived from SHRSPs showed an increase that was linear to the conditioning time. These results seem to indicate that endothelial cells produce and release factors that promote the growth of astrocytes. It seems also probable that chronic hypertension causes an increase in production and release of such ECDGFs that correlated with astrocytic proliferation.

Arterial response to mechanical injury: balloon catheter de-endothelialization

Coronary angioplasty has been used clinically for over a decade. Its initial promise as an alternative to coronary bypass surgery has only partially been fulfilled because of the high rate of post-operative restenosis. A number of animal models have been devised to study this phenomenon and although none is entirely satisfactory, they have, together with recent advances in molecular biology provided an insight into the cellular mechanisms that may contribute to this complication. This knowledge may ultimately lead to a means of therapeutic intervention. This review summarises our present understanding of the pathology of post-angioplasty re-stenosis as revealed by studies using the balloon catheter de-endothelialization model, and discusses some of the intervention strategies that have been attempted.

A new biodegradable patch for closure of atrial septal defect. An experimental study

Biodegradable patches made from polyhydroxybutyrate (PHB) were used to close experimentally induced atrial septal defect in six calves. The implants were evaluated after 3-12 months macroscopically and by light and scanning electron microscopy with regard to regeneration of tissue and degradation of the polymer. At implant degradation, complete endothelial layers facing the right and left atrium were observed, with a subendothelial layer of collagen and some smooth-muscle cells. The patch was degraded by polynucleated macrophages, and 12 months postoperatively no polymer material was identifiable at ordinary light microscopy, but in polarized light small particles of polymer with persisting foreign body reaction were still seen. Scanning electron microscopy revealed a complete layer of surface cells with morphologic signs of endothelium. There was no shunt or sign of infection. Biodegradable PHB patches implanted in atrial septal defects in this experimental model thus prompted formation of regenerated tissue that macroscopically and microscopically resembled native atrial septal wall. The total degradation time exceeded 12 months.

Fish oils in the prevention of atherosclerosis

The hypothesis that oils derived from the flesh of fish and marine mammals inhibit the atherosclerotic process is critically reviewed. Populations consuming a diet rich in fish have low rates of coronary heart disease. Dietary fish oil is associated with changes in serum lipids, prostaglandin and leukotriene metabolism, enhanced endothelial function and effects on growth factors released from platelets, leukocytes and endothelial cells. Dietary fish oil supplementation has been associated with inhibition of atherosclerosis experimentally induced by dietary hyperlipidemia and balloon injury. Results of studies of the use of fish oil to inhibit postangioplasty restenosis in human subjects have been inconclusive.

Biochemical properties of vascular endothelial cells

Present knowledge in the field of vascular endothelial cells is reviewed. The role of endothelial cells in the synthesis of matrix proteins and glycosaminoglycans is described. Endothelial cells play a considerable role in the processes of coagulation and fibrinolysis. They also interact with neurotransmitters and vasomotoric substances, and participate in inflammation and immunological responses. They produce several different growth factors. Their role in lipoprotein metabolism is of special importance to research into atherosclerosis.

Increased plasma immunoreactive endothelin-1 concentration in hypercholesterolemic rats

This study examined the influence of hypercholesterolemia on the concentration of plasma immunoreactive (ir) endothelin-1 in rats. Plasma ir-endothelin-1, total cholesterol, triglycerides, and lipoprotein fraction concentrations were measured in three groups of rats; ie, fed a standard diet, a high cholesterol diet, or a high cholesterol diet supplemented with the antihypercholesterolemic drug clinofibrate for 4 and 8 weeks. In the rats fed cholesterol for 8 weeks, morphological changes in thoracic and abdominal aortas were examined. Plasma total cholesterol, low density lipoprotein (LDL), very low density lipoprotein (VLDL) and ir-endothelin-1 concentrations increased significantly in the cholesterol-fed rats after both 4 and 8 weeks. In the clinofibrate-treated rats, these lipid parameters and plasma ir-endothelin-1 levels after 4 and 8 weeks were significantly lower than in the cholesterol-fed rats. The plasma ir-endothelin-1 concentration was correlated with plasma total cholesterol, LDL, and VLDL concentrations in the three study groups after 4 and 8 weeks. Morphologically, neither foam cells formation nor intimal thickening was observed in rats fed the high cholesterol diet for 8 weeks. These observations indicate that hypercholesterolemia without atherosclerosis elevates the plasma ir-endothelin-1 level in rats. The observed increase in plasma ir-endothelin-1 associated with hypercholesterolemia may play a role in the initiation or development of atherosclerotic vascular lesions.