Secretion of prostacyclin, tissue plasminogen activator and its inhibitor by cultured adult human endothelial cells grown on different matrices

A Review of Integrin-Mediated Endothelial Cell Phenotype in the Design of Cardiovascular Devices

Sustained biomaterial thromboresistance has long been a goal and challenge in blood-contacting device design. Endothelialization is one of the most successful strategies to achieve long-term thromboresistance of blood-contacting devices, with the endothelial cell layer providing dynamic hemostatic regulation. It is well established that endothelial cell behavior is influenced by interactions with the underlying extracellular matrix (ECM). Numerous researchers have sought to exploit these interactions to generate improved blood-contacting devices by investigating the expression of hemostatic regulators in endothelial cells on various ECM coatings. The ability to select substrates that promote endothelial cell-mediated thromboresistance is crucial to advancing material design strategies to improve cardiovascular device outcomes. This review provides an overview of endothelial cell regulation of hemostasis, the major components found within the cardiovascular basal lamina, and the interactions of endothelial cells with prominent ECM components of the basement membrane. A summary of ECM-mimetic strategies used in cardiovascular devices is provided with a focus on the effects of key adhesion modalities on endothelial cell regulators of hemostasis.

Functional stability of endothelial cells on a novel hybrid scaffold for vascular tissue engineering

Porous and pliable conduits made of biodegradable polymeric scaffolds offer great potential for the development of blood vessel substitutes but they generally lack signals for cell proliferation, survival and maintenance of a normal phenotype. In this study we have prepared and evaluated porous poly(ε-caprolactone) (PCL) integrated with fibrin composite (FC) to get a biomimetic hybrid scaffold (FC PCL) with the biological properties of fibrin, fibronectin (FN), gelatin, growth factors and glycosaminoglycans. Reduced platelet adhesion on a human umbilical vein endothelial cell-seeded hybrid scaffold as compared to bare PCL or FC PCL was observed, which suggests the non-thrombogenic nature of the tissue-engineered scaffold. Analysis of real-time polymerase chain reaction (RT-PCR) after 5 days of endothelial cell (EC) culture on a hybrid scaffold indicated that the prothrombotic von Willebrand factor and plasminogen activator inhibitor (PAI) were quiescent and stable. Meanwhile, dynamic expressions of tissue plasminogen activator (tPA) and endothelial nitric oxide synthase indicated the desired cell phenotype on the scaffold. On the hybrid scaffold, shear stress could induce enhanced nitric oxide release, which implicates vaso-responsiveness of EC grown on the tissue-engineered construct. Significant upregulation of mRNA for extracellular matrix (ECM) proteins, collagen IV and elastin, in EC was detected by RT-PCR after growing them on the hybrid scaffold and FC-coated tissue culture polystyrene (FC TCPS) but not on FN-coated TCPS. The results indicate that the FC PCL hybrid scaffold can accomplish a remodeled ECM and non-thrombogenic EC phenotype, and can be further investigated as a scaffold for cardiovascular tissue engineering.

The effect of locally administered anti-growth factor antibodies on neointimal hyperplasia formation in expanded polytetrafluoroethylene grafts

The selective blockage of platelet-derived growth factor BB (PDGF-BB), basic fibroblast growth factor (bFGF), and transforming growth factor beta1 (TGF-beta1) by specific antibodies coated into expanded polytetrafluoroethylene (ePTFE) grafts may diminish neointimal hyperplasia. Sixty pigs were divided into two groups (n = 30 each) and then further divided into five subgroups. Group 1 had a bilateral iliac artery ePTFE interposition graft precoated with Matrigel. Three subgroups (A, B, and C) received a specific monoclonal antibody against PDGF-BB, bFGF, or TGF-beta1. One (D) received all antibodies, and one served as control (nonimmune immunoglobulin G [IgG] isotypes) (E). Group 2 had a bilateral iliac artery endothelial cell (EC)-seeded ePTFE interposition graft precoated with Matrigel. Three subgroups (A, B, and C) received a specific antibody against PDGF-BB, bFGF, or TGF-beta1. One (D) received all antibodies, and one served as control (nonimmune IgG isotypes) (E). Light microscopy and immunohistochemical stain showed that neointimal hyperplasia formation was significantly reduced in subgroups D compared to the others (p < 0.05). In subgroups D, the different precoating influenced neointimal hyperplasia formation. It was more pronounced in the prosthesis precoated with EC and Matrigel (p < 0.05). In organ culture, the amount of PDGF-BB, bFGF, and TGF-beta1 release was reduced in subgroup D animals compared to the others (p < 0.05). In subgroups D, the release of PDGF-BB, bFGF, and TGF-beta1 depended on ePTFE seeding. A higher amount of these growth factors was released in the prostheses precoated with EC and Matrigel (p < 0.05), and the bromodeoxyuridine labeling index confirmed higher incorporation in this subgroup (p < 0.001). The combined use of locally administered anti-PDGF-BB, bFGF, and TGF-beta1 monoclonal antibodies reduces neointimal hyperplasia formation.

Isolation and characterization of human gingival microvascular endothelial cells

BACKGROUND AND OBJECTIVE

Endothelial cells have a substantial role in maintaining vascular homeostasis, and their dysregulation can contribute to the development of pathology. The plasminogen activators and their inhibitors may, arguably, be the single most important proteolytic system of the endothelium for vascular maintenance by controlling plasminogen activation and other proteolytic cascades that impact on clotting, hemodynamics, angiogenesis and the character of the vascular wall. In chronic periodontal disease, significant changes to the microvasculature occur in association with the severity of the disease. Investigation of the role played by endothelial cells in periodontal health and disease has been limited to in situ immunolocalization or to the use of endothelial cells of nongingival origin, such as human umbilical vein endothelial cells. The objective of this research was to establish a replicable protocol for isolating microvascular endothelial cells from the gingiva.

MATERIAL AND METHODS

From inflamed gingiva, isolated cells were characterized by morphology, the expression of factor VIII-related antigen, the expression of UEA-1 ligand, the uptake of acetylated low-density lipoprotein, network formation on Matrigel, and by the expression levels of urokinase plasminogen activator, tissue plasminogen activator, plasminogen activator inhibitor-1 and collagen IV.

RESULTS AND CONCLUSION

Gingival endothelial cells were most readily obtained from inflamed gingival tissues, and these endothelial cells, when isolated by the protocol established herein, demonstrated endothelial characteristics and constitutively secreted plasminogen activators and plasminogen activator inhibitor-1 in culture.

The influence of biomaterials on endothelial cell thrombogenicity

Driven by tissue engineering and regenerative medicine, endothelial cells are being used in combination with biomaterials in a number of applications for the purpose of improving blood compatibility and host integration. Endothelialized vascular grafts are beginning to be used clinically with some success in some centers, while endothelial seeding is being explored as a means of creating a vasculature within engineered tissues. The underlying assumption of this strategy is that when cultured on artificial biomaterials, a confluent layer of endothelial cells maintain their non-thrombogenic phenotype. In this review the existing knowledge base of endothelial cell thrombogenicity cultured on a number of different biomaterials is summarized. The importance of selecting appropriate endpoint measures that are most reflective of overall surface thrombogenicity is the focus of this review. Endothelial cells inhibit thrombosis through three interconnected regulatory systems (1) the coagulation cascade, (2) the cellular components of the blood such as leukocytes and platelets and (3) the complement cascade, and also through effects on fibrinolysis and vascular tone, the latter which influences blood flow. Thus, in order to demonstrate the thrombogenic benefit of seeding a biomaterial with EC, the conditions under which EC surfaces are more likely to exhibit lower thrombogenicity than unseeded biomaterial surfaces need to be consistent with the experimental context. The endpoints selected should be appropriate for the dominant thrombotic process that occurs under the given experimental conditions.

Tissue engineering of vascular conduits

BACKGROUND

Autologous conduits are not available in up to 40 per cent of patients with arteriopathy who require coronary or lower limb revascularization, and access sites for renal dialysis may eventually become exhausted. Synthetic prostheses achieve a poor patency rate in small-calibre anastomoses. This review examines how vascular tissue engineering may be used to address these issues.

METHODS

A Medline search was performed, using the keywords "vascular tissue engineering", "small diameter vascular conduit", "vascular cell biology", "biomechanics", "cell seeding" and "graft endothelialization". Key references were hand-searched for relevant papers.

RESULTS AND CONCLUSION

In vitro and in vivo approaches are currently being used for guided cell repopulation of both biological and synthetic scaffolds. The major clinical problem has been extended culture time (approximately 6 weeks), which precludes their use in the acute setting. However, recent advances have led not only to improved patency rates for prostheses, but also to a potential reduction in culture time. In addition, increased mobilization of endothelial progenitor cells in the presence of ischaemic tissue may increase the autologous cell yield for scaffold reseeding with further reduction in culture time.

Review: Endothelial Cells Cultured on Engineered Vascular Grafts Are Able to Transduce Shear Stress

In vitro endothelialization of small-diameter vascular prostheses confluently lined with cultured autologous endothelial cells (ECs) before clinical implantation improves their patency. Many authors have studied the effects of shear stress on ECs seeded on various substrates showing activation of mitogen-activated protein (MAP) kinases. Very few studies have reported any functional EC response to shear stress when they are seeded on vascular grafts. The purpose of this in vitro study was to investigate whether ECs were able to transduce shear stress. Human saphenous vein ECs were seeded on 6 mm fibrin-glue-coated grafts, then submitted to 15 dyn/cm(2) for 10, 30, and 120 min. Cell lysates were submitted to Western blot analysis to detect phosphorylated ERK 1/2 and p38. ERK 1/2 activation was observed at 10 min (1.6 fold) followed by a lower activation than under static conditions at 30 and 120 min. Shear stress induced a significant increase in p38 phosphorylation (2.5 fold) at 10 and 30 min, decreasing at 120 min. Thus, ECs are able to transduce shear stress in an in vitro model in closed clinical conditions, but the ERK 1/2 and p38 temporal activation profile is different. We provide new insights into the validity of the vascular tissue engineering approach.

Effect of streptavidin-biotin on endothelial vasoregulation and leukocyte adhesion

The current study examines whether the adhesion promoting arginine-glycine-aspartate-streptavidin mutant (RGD-SA) also affects two important endothelial cell (EC) functions in vitro: vasoregulation and leukocyte adhesion. EC adherent to surfaces via fibronectin (Fn) or Fn plus RGD-SA were subjected to laminar shear flow and media samples were collected over a period of 4h to measure the concentration of nitric oxide (NO), prostacyclin (PGI(2)), and endothelin-1 (ET-1). Western blot analysis was used to quantify the levels of endothelial-derived nitric oxide synthase (eNOS) and cyclooxygenase II (COX II). In a separate set of experiments, fluorescent polymorphonuclear leukocyte (PMN) adhesion to EC was quantified for EC with and without exposure to flow preconditioning. When cell adhesion was supplemented with the SA-biotin system, flow-induced production of NO and PGI(2) increased significantly relative to cells adherent on Fn alone. Previous exposure of EC to shear flow also significantly decreased PMN attachment to SA-biotin supplemented EC, but only after 2h of exposure to shear flow. The observed decrease in PMN-EC adhesion was negated by NG-nitro-L-arginine methyl ester (L-NAME), an antagonist of NO synthesis, but not by indomethacin, an inhibitor to PGI(2) synthesis, indicating the induced effect of PMN-EC interaction is primarily NO-dependent. Results from this study suggest that the use of SA-biotin to supplement EC adhesion encourages vasodilation and PMN adhesion in vitro under physiological shear-stress conditions. We postulate that the presence of SA-biotin more efficiently transmits the shear-stress signal and amplifies the downstream events including the NO and PGI(2) release and leukocyte-EC inhibition. These results may have ramifications for reducing thrombus-induced vascular graft failure.

Toward a new blood vessel

Strategies to treat atherosclerotic coronary artery disease include coronary artery bypass grafting (CABG), in which grafts are used to bypass atherosclerotic vessels and restore blood flow to the ischemic myocardium. The grafts used include healthy arteries or veins harvested from a separate site. Results with arterial grafts have been superior to venous grafts; promoting the practice of total arterial revascularization using only arterial grafts. Suitable arterial grafts, however, are scarce and harvest procedures add to morbidity and cost. Tissue engineering combines the principles of engineering with life sciences for the development of biological substitutes and restore, maintain or improve tissue function. Advances in this field have included the development of tissue-engineered blood vessels, with the potential to serve as arterial grafts, conduits or fistulae. This review describes the history of tissue engineering arteries, the techniques used, and progress to date. The source of cells and the future direction of this field are explored.

Relation between cell density and the secretion of von Willebrand factor and prostacyclin by human umbilical vein endothelial cells

In this study, the relation between the density of human umbilical vein endothelial cells (HUVECs) cultured on TCPS and (crosslinked) collagen, and the secretion of von Willebrand factor (vWF) and prostacyclin (PGI2) was determined. Collagen was crosslinked using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) in combination with N-hydroxy-succinimide (NHS), resulting in a matrix containing 14 free primary amino groups per 1000 amino acid residues after crosslinking (E/N14C). HUVECs were seeded on E/N14C, non-crosslinked collagen (N-Coll) and fibronectin-coated TCPS at densities ranging from 2500 to 50,000 cells/cm2. After 1 day of culture, both basal and A23187-stimulated secretion of vWF (expressed per 1,000,000 cells) was considerably increased at low cell densities (i.e. below 5000 cells/cm2) on all substrates. Secretion of PGI2 gradually increased with decreasing cell densities below 10,000 cells/cm2. After 10 days of proliferation, cell numbers on all substrates exceeded 50,000 cells/cm2, irrespective of the seeding density. Concomitantly, the initial higher secretion of PGI2 and vWF at the lowest seeding densities was decreased after longer times of culture, to values comparable to those obtained for higher seeding densities.

ENDOTHELIAL CELL CULTURE AND SEEDING OF PROSTHETIC VASCULAR GRAFTS: AN EXPERIMENTAL STUDY

Current synthetic vascular prostheses do not acquire lining of vascular endothelium in humans or dogs. Endothelial seeding of vascular grafts has been proposed as a means of reducing the thrombogenicity of these grafts. We examined feasibility of cultivating endothelial cells (EC) by tissue culture technique and their subsequent seeding onto small diameter polytetra fluoroethylene (PTFE) grafts. Twenty adult dogs underwent common carotid artery interposition with 4 mm PTFE grafts. Ten dogs received seeded and the remaining ten received unseeded grafts. Grafts were removed at 4 and 12 weeks and their gross/morphological features compared. Cumulative patency rates for seeded grafts were 70% as compared to unseeded ones 30%. Seeded grafts were completely surfaced with a mono-layer of endothelium by 4 weeks. Small graft patency appears to be related to the establishment of an endothelial surface, the development of which is clearly facilitated by seeding with autogenous endothelium.

Suppression of prostanoid formation and regulation of peripheral circulation after surgery using thrombin inhibitor (MD805)

We studied the effects of thrombin generation due to surgical stress on prostanoid formation and peripheral circulation in anesthetized dogs. Three experimental groups were used, consisting of a control group (group 1), a thoracotomized group (group 2), and a thoracotomized group treated with thrombin inhibitor (MD805: a synthetic arginine derivative) (group 3). The plasma concentrations of thrombin-antithrombin III complex (TAT) and prostanoids were measured along with the hemodynamic parameters. The plasma concentrations of TAT and thromboxane B2 significantly increased 1h after a thoracotomy in group 2. However, neither concentration increased after a thoracotomy in group 3. The flow ratio of the brachial and femoral arteries to cardiac output significantly decreased 1h after a thoracotomy in group 2. This study indicates that thromboxane A2 was thus synthesized by the stimulation of endogenous thrombin, while it also reduced the peripheral blood flow after surgery.

Release of PDGF-BB and bFGF by human endothelial cells seeded on expanded polytetrafluoroethylene vascular grafts

BACKGROUND

The majority of endothelial cell (EC) seeded graft failures are due to anastomotic neointimal fibrous hyperplasia. We investigated the PDGF-BB and bFGF release in vitro by umbilical vein EC seeded on precoated expanded polytetrafluoroethylene (ePTFE) prostheses.

MATERIALS

EC harvested from human umbilical veins were seeded into ePTFE (30 microns internodal distance, 1 cm2 in diameter) disks. ePTFE disks uncoated or precoated with collagen type I, fibronectin, and Matrigel were used, and EC seeded into plastic wells coated as ePTFE disks or uncoated plastic wells served as controls. Scanning electron microscopy study assessed EC coverage. The presence of bFGF and PDGF-BB in serum-free conditioned media from EC seeded into ePTFE grafts and EC seeded into wells was determined by the inhibition antibody-binding assay 72 h after seeding.

RESULTS

EC coverage was similar in uncoated and coated ePTFE grafts. The release of PDGF-BB and bFGF by EC seeded into ePTFE grafts was significantly higher than that observed in EC seeded into plastic wells. The release of PDGF-BB and bFGF was independent from the various substrates used in the experiments in EC seeded into either ePTFE grafts or plastic wells.

CONCLUSIONS

Our findings pointed out that in seeded ePTFE grafts, anastomotic smooth muscle cell proliferation and intimal thickening could take place underneath an intact endothelium because seeded EC may release several growth factors.

A completely biological tissue-engineered human blood vessel

Mechanically challenged tissue-engineered organs, such as blood vessels, traditionally relied on synthetic or modified biological materials for structural support. In this report, we present a novel approach to tissue-engineered blood vessel (TEBV) production that is based exclusively on the use of cultured human cells, i.e., without any synthetic or exogenous biomaterials. Human vascular smooth muscle cells (SMC) cultured with ascorbic acid produced a cohesive cellular sheet. This sheet was placed around a tubular support to produce the media of the vessel. A similar sheet of human fibroblasts was wrapped around the media to provide the adventitia. After maturation, the tubular support was removed and endothelial cells were seeded in the lumen. This TEBV featured a well-defined, three-layered organization and numerous extracellular matrix proteins, including elastin. In this environment, SMC reexpressed desmin, a differentiation marker known to be lost under standard culture conditions. The endothelium expressed von Willebrand factor, incorporated acetylated LDL, produced PGI2, and strongly inhibited platelet adhesion in vitro. The complete vessel had a burst strength over 2000 mmHg. This is the first completely biological TEBV to display a burst strength comparable to that of human vessels. Short-term grafting experiment in a canine model demonstrated good handling and suturability characteristics. Taken together, these results suggest that this novel technique can produce completely biological vessels fulfilling the fundamental requirements for grafting: high burst strength, positive surgical handling, and a functional endothelium.