Confluent durable endothelialization of endarterectomized baboon aorta by early attachment of cultured endothelial cells

Current usage and future directions for the bovine pericardial patch

Bovine pericardium (BP) is widely used in surgery and is commonly used as a patch after arteriotomy in cardiovascular surgery. BP patches have several advantages compared with prosthetic patches, including superior biocompatability, easy handling, less suture line bleeding, and possibly reduced rates of infection. These advantages of BP have led to its common use during carotid endarterectomy (CEA). However, long-term clinical results reported after CEA have suggested several issues that may be related to the patch, including restenosis, pseudoaneurysm formation, infection, fibrosis, calcification, and thrombosis. These complications may diminish the long-term efficacy of CEA and suggest potential areas for improvement of surgical patches. Understanding the mechanisms by which BP heals after patch angioplasty may lead to next generation tissue-engineered patches.

Porous tissue grafts sandwiched with multilayered mesenchymal stromal cell sheets induce tissue regeneration for cardiac repair

AIMS

To provide the basis for uniform cardiac tissue regeneration, a spatially uniform distribution of adhered cells within a scaffold is a prerequisite. To achieve this goal, a bioengineered tissue graft consisting of a porous tissue scaffold sandwiched with multilayered sheets of mesenchymal stromal cells was developed.

METHODS AND RESULTS

This tissue graft (sandwiched patch) was used to replace the infarcted wall in a syngeneic Lewis rat model with an experimentally chronic myocardial infarction (MI). There were four treatment groups (n >/= 10): sham, MI, empty patch, and sandwiched patch. After a 7 day culture of the sandwiched patch, a tissue graft with relatively uniform cell concentrations was obtained. The cells were viable and tightly adhered to the tissue scaffold, as the endogenous extracellular matrix inherent with multilayered cell sheets can act as an adhesive agent for cell attachment and retention. At retrieval, the area of the empty patch was relatively enlarged, suggesting reduced structural support, while that of the sandwiched patch remained about the same (P = 0.56). In the immunofluorescent staining, host cells together with neo-microvessels were clearly observed in the empty patch; however, there were still a large number of unfilled pores within the patch. In the sandwiched patch, besides host cells, originally seeded cells were populated within the entire patch. No apparent evidence of apoptotic cell death was found in both studied patches. Thus, the sandwiched-patch-treated hearts demonstrated a better heart function to the empty-patch-treated hearts (P < 0.05).

CONCLUSION

The results demonstrated that this novel bioengineered tissue graft can serve as a useful cardiac patch to restore the dilated left ventricle and stabilize heart functions after MI.

Approaches to heart valve tissue engineering scaffold design

Heart valve disease is a significant cause of mortality worldwide. However, to date, a nonthrombogenic, noncalcific prosthetic, which maintains normal valve mechanical properties and hemodynamic flow, and exhibits sufficient fatigue properties has not been designed. Current prosthetic designs have not been optimized and are unsuitable treatment for congenital heart defects. Research is therefore moving towards the development of a tissue engineered heart valve equivalent. Two approaches may be used in the creation of a tissue engineered heart valve, the traditional approach, which involves seeding a scaffold in vitro, in the presence of specific signals prior to implantation, and the guided tissue regeneration approach, which relies on autologous reseeding in vivo. Regardless of the approach taken, the design of a scaffold capable of supporting the growth of cells and extracellular matrix generation and capable of withstanding the unrelenting cardiovascular environment while forming a tight seal during closure, is critical to the success of the tissue engineered construct. This paper focuses on the quest to design, such a scaffold.

Tissue regeneration observed in a basic fibroblast growth factor-loaded porous acellular bovine pericardium populated with mesenchymal stem cells

OBJECTIVE

We sought to induce tissue regeneration within a porous patch for repair of a myocardial defect.

METHODS

A basic fibroblast growth factor-loaded porous bovine pericardium populated with 5-bromo-2'-deoxyuridine-labeled mesenchymal stem cells was used as a cardiac patch (the basic fibroblast growth factor/mesenchymal stem cell patch) to repair a defect created in a syngeneic rat model. The blank porous pericardium (the control patch) and the patch loaded with basic fibroblast growth factor were used as controls. The implanted patches were retrieved at 4 and 12 weeks postoperatively (n = 5 per group at each time point).

RESULTS

At retrieval, we found that none of the patches were thinned or dilated. Endothelialization and remesothelialization were observed on the endocardial and epicardial surfaces of patches in each of the studied groups, respectively. Additionally, newly regenerated muscle fibers, glycosaminoglycans, smooth muscle cells, and microvessels were seen in the middle layers of all patches, an indication of tissue regeneration. However, the extents of tissue regeneration in the basic fibroblast growth factor and basic fibroblast growth factor/mesenchymal stem cell patches were more pronounced than in those of the control patch. This may be attributed to the fact that the densities of neomicrovessels observed in the basic fibroblast growth factor and basic fibroblast growth factor/mesenchymal stem cell patches were significantly greater than in those of the control patch. 5-Bromo-2'-deoxyuridine-labeled cardiomyocytes, smooth muscle cells, and endothelial cells were identified in the basic fibroblast growth factor/mesenchymal stem cells patch, and no cardiomyocytes were observed in the control and basic fibroblast growth factor patches.

CONCLUSION

The results provided evidence of tissue regeneration within a porous bovine pericardium through a process involving cell recruitment and tissue-specific differentiation.

Role of the endothelium in modulating neointimal formation: vasculoprotective approaches to attenuate restenosis after percutaneous coronary interventions

Restenosis at the site of an endoluminal procedure remains a significant problem in the practice of interventional cardiology. We present current data on intimal hyperplasia, which identify the major role of endothelial cells (ECs) in the development of restenosis. Considering endothelial denudation as one of the most important mechanisms contributing to restenosis, we focus more attention on methods of accelerating restoration of endothelial continuity. Prevention of restenosis may be achieved by promoting endothelial regeneration through the use of growth factors, EC seeding, vessel reconstruction with autologous EC/fibrin matrix, and the use of estrogen-loaded stents and stents designed to capture progenitor ECs.

Decellularization protocols of porcine heart valves differ importantly in efficiency of cell removal and susceptibility of the matrix to recellularization with human vascular cells

OBJECTIVE

We compared 3 different decellularization protocols in porcine heart valves for efficiency of complete cell removal and potential for recellularization.

METHODS

Porcine aortic and pulmonary roots were treated with trypsin, sodium-dodecyl-sulphate, or a new method using 0.25% tert-octylphenyl-polyoxyethylen in combination with sodium-deoxycholate. After a subsequent ribonuclease digestion, specimens were seeded with in vitro expanded human saphenous vein endothelial cells and myofibroblasts.

RESULTS

After treatment with trypsin and subsequent ribonuclease digestion, endothelial attachment took place; however, xenogenic cells were still visible within the matrix. Unexpectedly, when human cells were seeded onto specimens that had been decellularized with sodium-dodecyl-sulphate, the matrices were surrounded by nonviable endothelial cell fragments, indicating a toxic influence of the ionic detergent; 0.25% tert-octylphenyl-polyoxyethylen together with sodium-deoxycholate completely removed porcine cells and enabled host recellularization.

CONCLUSION

Compared with trypsin and sodium-dodecyl-sulphate involving decellularization procedures, reported to be effective in cell removal and susceptible to recellularization with human cells, only the porcine matrix treated with a new detergent-based decellularization method using 0.25% tert-octylphenyl-polyoxyethylen/sodium-deoxycholate followed by nuclease digestion presented an excellent scaffold for recellularization with human cells.

Reconstruction of the right ventricular outflow tract with a bovine jugular vein graft fixed with a naturally occurring crosslinking agent (genipin) in a canine model

OBJECTIVE

This study was designed to evaluate a newly developed biologic valved conduit fixed with genipin used to reconstruct the right ventricular outflow tract in a canine model.

METHODS

Fresh bovine jugular veins with a retained native valve procured from a slaughterhouse were used as raw materials to fabricate the valved conduits. A naturally occurring crosslinking agent, genipin, was used to fix the procured jugular veins. The glutaraldehyde-fixed counterpart was used as a control. A canine model was used in the study.

RESULTS

Echocardiography revealed that the motion of the valvular leaflets in both the glutaraldehyde- and genipin-fixed conduits was satisfactory. The transvalvular pressure gradients of both studied groups were minimal. No endothelium-like cells were observed on the luminal surface of the conduit and the valvular leaflet for the glutaraldehyde-fixed group throughout the entire course of the study. In contrast, endothelium-like cells were observed on the entire surface of the genipin-fixed valved conduit retrieved at 6 months postoperatively in all the cases studied. There was no evidence of luminal fibrous peel in any the valved conduits studied. Degradation of valvular leaflet in one of the glutaraldehyde-fixed conduits was observed. In this particular case, thrombus formation was also observed on the surface of the valvular leaflet. On the other hand, no apparent degradation or thrombus formation was observed on the surfaces of the genipin-fixed valvular leaflet and conduit. A significantly more severe inflammatory reaction was observed for the glutaraldehyde-fixed conduit than for its genipin-fixed counterpart throughout the entire course of the study. The calcium contents of the samples before implantation and those retrieved at distinct implantation duration were minimal for both the glutaraldehyde- and genipin-fixed tissues.

CONCLUSION

Although further studies are necessary, the genipin-fixed valved conduit appears to have great potential in helping mitigate the complications observed in the commercially available conduits.

Endoluminal reconstruction of the arterial wall with endothelial cell/glue matrix reduces restenosis in an atherosclerotic rabbit

OBJECTIVES

The objectives of this study were 1) to improve the attachment of reimplanted endothelial cells (EC) using a fibrin glue, and 2) to assess the impact of endothelial reseeding on restenosis eight weeks after balloon angioplasty.

BACKGROUND

A possible mechanism contributing to restenosis after balloon angioplasty is the loss of the EC lining. Previous attempts to reseed EC had little effect due to rapid loss of the seeded cells.

METHODS

Twelve atherosclerotic rabbits were subjected to angioplasty of iliac arteries and reseeding procedure. One iliac artery was subjected to EC/glue reconstruction and a contralateral site to EC seeding without glue. The animals were sacrificed after 4 h. In another series 12 rabbits were treated in the same fashion and were restudied at eight weeks. Additionally, in 10 animals one iliac was subjected to glue treatment, and another served as control.

RESULTS

Histological examination demonstrated the ability of this method to reattach the EC/glue matrix circumferentially to 68.0 +/- 6.7% of the arterial wall in comparison with 13.5 +/- 3.9% reattachment after EC seeding. Morphometry at eight weeks showed that the lumen area was significantly greater in the EC/glue group (1.23 +/- 0.35 mm2) than in the EC seeding alone (0.65 +/- 0.02 mm2) and 0.72 +/- 0.41 mm2 in the glue group. This was principally accounted for by the statistically significant differences in the intimal area (0.76 +/- 0.18 mm vs. 1.25 +/-0.26 mm2 and 1.01 +/- 0.53 mm2, respectively).

CONCLUSIONS

The attachment of EC after angioplasty can be greatly improved with fibrin glue matrix. The near 70% endothelial coverage achieved by this method resulted in a significant reduction of restenosis in atherosclerotic rabbit.

Tissue engineering of vascular grafts: human cell seeding of decellularised porcine matrix

OBJECTIVES

To develop a biocompatible and mechanically stable vascular graft combining human cells and a xenogenic acellular matrix. DESIGN/MATERIALS: Decellularised matrix tubes were obtained by enzymatic cell extraction of native porcine aortas. Endothelial cells and myofibroblasts were isolated from human saphenous veins and grown in cell cultures. The inner surface of the tubes was seeded with endothelial cells or myofibroblasts and exposed to pulsatile flow.

RESULTS

After cell extraction, the absence of cellular components, as well as the maintenance of matrix integrity, was demonstrated by means of light microscopy and scanning electron microscopy. Furthermore, the porcine matrix was successfully seeded with human endothelial cells, which grew to a monolayer under flow conditions. Stable biomechanical properties were achieved at physiological perfusion pressures in vitro.

CONCLUSIONS

Cellular components can be extracted from native porcine blood vessels. Vascular grafts can be generated in vitro of animal acellular matrix and human cells.

Reduction in vascular lesion formation by hirudin secreted from retrovirus-transduced confluent endothelial cells on vascular grafts in baboons

BACKGROUND

The hypothesis that thrombin mediates the formation of neointimal vascular lesions at sites of mechanical vascular injury has been tested in baboons by measurement of the effects of hirudin delivered by retrovirus-transduced hirudin-secreting vascular endothelial cells (ECs) lining surgically implanted arterial vascular grafts (AVGs).

METHODS AND RESULTS

The antithrombotic efficacy of baboon ECs transduced with cDNA encoding hirudin was assessed in vitro and in vivo on thrombogenic segments in chronically exteriorized femoral arteriovenous (AV) shunts. Bilateral brachial AVGs lined with hirudin-transduced versus nonhirudin control ECs at confluent density were surgically implanted, and vascular lesion formations at distal graft-vessel anastomoses were compared after 30 days. Hirudin-transduced ECs secreted 20+/-6 ng x 10(6) cells(-1) x 24 h(-1) (range, 14 to 24 ng x 10(6) cells(-1) x 24 h(-1)) hirudin in supernatants of static cultures. Hirudin-secreting ECs on segments of collagen-coated graft interposed in chronic AV shunts decreased the accumulation of (111)In-labeled platelets to 0.52+/-0.34 x 10(9) platelets, compared with 0.82+/-0.49 x 10(9) platelets in controls (P = 0.03) and reduced platelet deposition in propagated thrombotic tails extending downstream from segments of vascular graft from 1.38+/-0.41 x 10(9) platelets in controls to 0.59+/-0.22 x 10(9) platelets (P = 0.04). ECs recovered from 30-day AVG implants generated 17+/-9 ng x 10(6) cells(-1) x 24 h(-1) (range, 9 to 25 ng x 10(6) cells(-1) x 24 h(-1)) hirudin. Hirudin-secreting ECs reduced neointimal lesion formation at distal graft-vessel anastomoses, ie, 1.02 mm(2) (range, 0.88 to 1.95 mm(2)) versus 1.82 mm(2) (range, 0.88 to 2.56 mm(2)) in contralateral AVGs bearing nonhirudin control ECs (P<0.01).

CONCLUSIONS

Viral vector-directed secretion of hirudin from ECs lining implanted AVGs significantly reduces the formation of thrombus and neointimal vascular lesions.

Tissue engineering of heart valves--human endothelial cell seeding of detergent acellularized porcine valves

OBJECTIVE

Tissue engineering of heart valves represents a new experimental concept to improve current modes of therapy in valvular heart disease. Drawbacks of glutaraldehyde fixed tissue valves or mechanical valves include the short durability or the need for life-long anticoagulation, respectively. Both have in common the inability to grow, which makes valvular heart disease especially problematic in children. The aim of this study was to develop a new methodology for a tissue engineered heart valve combining human cells and a xenogenic acellularized matrix.

METHODS

Porcine aortic valves were acellularized by deterging cell extraction using Triton without tanning. Endothelial cells were isolated in parallel from human saphenous veins and expanded in vitro. Specimens of the surface of the acellular matrix were seeded with endothelial cells. Analysis of acellularity was performed by light microscopy and scanning electron microscopy. Cell viability following seeding was assayed by fluorescence staining of viable cells.

RESULTS

The acellularization procedure resulted in an almost complete removal of the original cells while the 3D matrix was loosened at interfibrillar zones. However the 3D arrangement of the matrix fibers was grossly maintained. The porcine matrix could be seeded with in vitro expanded human endothelial cells and was maintained in culture for up to 3 days to document the formation of confluent cultures.

CONCLUSIONS

Porcine aortic valves can be almost completely acellularized by a non-tanning detergent extraction procedure. The xenogenic matrix was reseeded with human endothelial cells. This approach may eventually lead to the engineering of tissue heart valves repopulated with the patients own autologous cells.

Resistance of freshly adherent endothelial cells to detachment by shear stress is matrix and time dependent

PURPOSE

The placement of endothelial cells on the surfaces of arteries immediately after vascular interventions has the potential to limit restenosis by inhibiting intimal thickening and by stimulating arterial enlargement. Because such re-endothelialization is dependent on rapid formation of strong endothelial cell-matrix interactions, experiments were performed to identify the extracellular matrix that provided endothelial cells with the greatest resistance to detachment by a shear stress in the least amount of time.

MATERIALS AND METHODS

Rabbit microvascular endothelial cells were plated onto glass slides coated with collagen, laminin, vitronectin, or fibronectin. After allowing 5-45 minutes for cell adhesion, each slide was placed in a parallel plate chamber, and the number of cells present before and after exposure of the cells to shear stresses (1-25 dynes/cm2) were counted.

RESULTS

Endothelial cell retention to the matrix-coated slides was time and matrix dependent. The percentages of endothelial cells retained after adhesion times of 5, 15, 30, and 45 minutes followed by exposure to 15 dynes/cm2 were 9%, 20%, 32%*, and 38%* for collagen; 7%, 20%, 36%*, and 49%* for laminin; 35%, 47%, 62%, and 76%* for vitronectin; and 64%, 58%, 71%, and 78% for fibronectin, respectively (*P < .05 versus 5 minutes adhesion). Similar results were obtained for lower and higher shear stresses, indicating that cell retention was independent of shear stress above 1 dyne/cm2.

CONCLUSIONS

The resistance of freshly adherent endothelial cells to detachment by shear stress is matrix- (fibronectin approximately equal to vitronectin > laminin approximately equal to COL) and time-dependent. Fibronectin provided the greatest cell retention in the least amount of time.

Placement of endothelial cells on the luminal surface of denuded arteries in vitro and in vivo

PURPOSE

Experiments were performed to determine if the percutaneous placement of endothelial cells on denuded arterial surfaces is feasible.

MATERIALS AND METHODS

For in vitro adhesion assays, rabbit microvascular endothelial cells were stained with a fluorescent marker and placed on the luminal surface of disks of denuded rabbit aorta. At varying times thereafter, the nonadherent cells were removed, and the adherent cells were quantitated with use of fluorescence microscopy. For in vivo studies, angioplasty was performed on external iliac arteries in five rabbits, and a double-balloon catheter, positioned at the dilatation site, was used to deliver fluorescent rabbit microvascular endothelial cells. Ten minutes (n = 2), 1 hour (n = 2), 1 day (n = 1), or 3 days (n = 1) after cell placement, the number of fluorescent cells remaining on each artery was determined.

RESULTS

In vitro rabbit microvascular endothelial cell attachment was (a) serum-dependent, peaking with media containing 25% autologous serum; (b) time-dependent, peaking at 30 minutes; and (c) cell density-dependent. In vivo rabbit microvascular endothelial cell attachment was (a) noncircumferential, (b) appeared to be gravity-dependent, and (c) appeared unchanged over 3 days with respect to number of cells per cross-section and length of artery having endothelium.

CONCLUSIONS

Percutaneous delivery of endothelial cells onto denuded arterial surfaces with use of optimal conditions is feasible and these cells remain adherent for at least 3 days.

Early attachment of leucocytes, platelets and fibrinogen in endothelial cell-seeded Dacron venous conduits

BACKGROUND

There is a need for prosthetic venous conduits in surgery for trauma, cancer and thrombotic disease. Such conduits in use today have a low patency rate, leaving room for much improvement.

METHODS

This experimental study investigated the dynamics of the early attachment of radiolabelled platelets, leucocytes and fibrinogen to endothelial cell-seeded Dacron venous conduits in sheep. Grafts were placed as jugular vein interposition grafts, seeded on one side, not seeded on the other, and followed for 4 h.

RESULTS

No difference could be demonstrated between the two graft types. Platelets showed an increasing attachment during the whole period, leucocytes an immediate attachment followed by an undulating pattern, and fibrinogen an immediate attachment with a tendency to decrease. Measurements on the vein itself showed a high attachment and, for platelets, an extremely high attachment when measured after the graft in the direction of flow.

CONCLUSION

The seeding process did not seem to affect early thrombogenicity. The carefully dissected vein wall showed highly thrombogenic properties, in many ways as high as in the prosthetic graft.

Early attachment of platelets, leukocytes, and fibrinogen in endothelial cell seeded Dacron grafts

Endothelial cell seeding has been advocated as a method for reducing the thrombogenicity of prosthetic grafts. Principally two different techniques for endothelial cell seeding can be used: immediate seeding of grafts followed by implantation or initial growth and establishment of an endothelial cell-covered surface before subsequent late implantation. This study was designed to determine whether the immediate seeding technique altered thrombogenicity directly after graft implantation. Carotid arteries from 19 sheep were replaced with Dacron interposition grafts; one side was seeded with endothelial cells and the other side was left unseeded. The dynamics of thrombus formation involving radiolabeled platelets, leukocytes, and fibrinogen were studied for 4 hours with flow reduced to 35 ml/min. No difference in platelet uptake (approximately 6-fold increase compared to baseline values) was found between endothelial cell seeded and unseeded grafts. Likewise, there were no differences in leukocyte uptake (approximately 4-fold increase) or fibrinogen uptake (approximately 10- to 15-fold increase) between the two groups. No differences were demonstrated with regard to patency or thrombus weight. In this experimental investigation we were unable to verify any change in the uptake of platelets, white blood cells, or fibrinogen between endothelial cell seeded and unseeded Dacron grafts during the first 4 hours after graft placement. Immediate seeding does not affect the initial thrombogenicity of grafts.

Enhanced thrombolytic and antithrombotic potency of a fibrin-targeted plasminogen activator in baboons

BACKGROUND

Thrombolytic therapy reduces mortality in patients with acute myocardial infarction, but significant limitations exist with the use of currently available agents. In the present report, we describe the thrombolytic and antithrombotic potencies of a hybrid recombinant plasminogen activator consisting of an antifibrin antibody 59D8 (AFA) and low-molecular-weight single-chain urokinase-type plasminogen activator (scuPA).

METHODS AND RESULTS

A thrombolysis model in which thrombi are preformed in vivo in juvenile baboons was developed to compare the potencies of AFA-scuPA, recombinant tissue plasminogen activator (rTPA), and recombinant scuPA (rscuPA) in lysing nonocclusive 111In-labeled platelet-rich arterial-type thrombi and 125I-labeled fibrin-rich venous-type thrombi. Systemic infusion of 1.89 nmol/kg AFA-scuPA produced thrombolysis that was comparable to that obtained with much higher doses of TPA (14.2 nmol/kg) and rscuPA (28.5 nmol/kg). When steady-state plasma concentrations are normalized, AFA-scuPA lyses thrombi sixfold more rapidly than scuPA and TPA (P < .001) and reduces the rate of formation more than comparable doses of rscuPA (P < .0001). At equivalent thrombolytic doses, AFA-scuPA produced fewer antihemostatic effects than either rTPA or rscuPA. Template bleeding time measurements were shorter (3.5 +/- 0.12 minutes for AFA-scuPA versus 5.3 +/- 0.36 and 5.2 +/- 0.04 minutes for rTPA and rscuPA, respectively; P < .05), alpha 2-antiplasmin consumption was less (P < .05), and D-dimer generation was lower (P < .05).

CONCLUSIONS

We conclude that antibody targeting of scuPA to fibrin increases thrombolytic and antithrombotic potencies with less impairment of hemostasis compared with rTPA and rscuPA.

Endothelial cell seeding of de-endothelialised human arteries: improvement by adhesion molecule induction and flow-seeding technology

OBJECTIVES

To assess re-endothelialisation of denuded human arteries by two different seeding techniques using adhesion molecule induction and a dynamic flow-seeding.

DESIGN

Prospective, open study.

SETTING

University Department of Cardiovascular Surgery.

MATERIALS AND METHODS

In the first group (I) segments of human common carotid arteries (n = 4) were balloon-denuded, short-time seeded with cultured adult human venous endothelial cells (EC) and exposed to a mock circulation. In the second group (II) (n = 4), EC were incubated with a synthetic RGD peptide (arginine-glycine-aspartate) prior to seeding with the aim of upregulating the cellular adhesion molecules and increasing EC attachment. In the third group (III) (n = 4), EC were seeded not using the common technique of instillating cells and sequentially rotating the graft but by a dynamic flow application. The percentage of EC-covered luminal surface was assessed by image analysis of scanning electron micrographs.

RESULTS

EC attachment was significantly increased in groups II (73%) and III (94%) compared with group I (34%). In group III, a preconfluent monolayer could be established immediately after seeding. One hour of artificial perfusion resulted in no significant EC loss in any of the study groups.

CONCLUSIONS

RGD-peptide preincubation improves EC seeding of biological surfaces. Because of accelerated seeding times it may have good potential for clinical applications. The flow-seeding technology may be indispensable if EC seeding of the vascular surface of complete organ systems is required.

Enhanced in vivo antithrombotic effects of endothelial cells expressing recombinant plasminogen activators transduced with retroviral vectors

BACKGROUND

The effects of regulating endothelial cell (EC) plasminogen activator production on thrombus accumulation in vivo are incompletely understood. By overexpressing plasminogen activators in ECs via gene transfer, the hypothesis was tested that increased levels of plasminogen activators inhibit the accumulation of thrombus in vivo.

METHODS AND RESULTS

Cultured baboon ECs transduced with human cDNAs for wild-type tissue plasminogen activator (TPA) or for glycosylphosphatidylinositol-anchored urokinase-type plasminogen activator (a-UPA) were seeded onto collagen-coated segments of vascular graft (collagen segments) and exposed overnight to flow using an in vitro perfusion circuit. The antigenic levels of TPA and UPA each increased 10-fold in the media perfusing the corresponding transduced ECs compared with untransduced ECs (P < or = .05 in both cases). In baboons the antithrombotic effects of TPA-transduced or a-UPA-transduced ECs were measured as 111In-platelet deposition and 125I-fibrin accumulation on collagen segments bearing sparsely attached ECs (tarnsduced versus untransduced) interposed in exteriorized arteriovenous femoral shunts. Platelet-rich thrombus formed on the collagen segments with fibrin-rich thrombus propagated distally. The presence of TPA-transduced or a-UPA-transduced ECs on collagen segments at a density of 25,000 ECs/cm2 decreased 111AIn-platelet deposition and 125I-fibrin accumulation on collagen surfaces compared with untransduced ECs present at equivalent density (P < .05 for platelet deposition with TPA-transduced ECs and P < .05 for platelet deposition on the propagated tail, as well as fibrin accumulation on the graft with a-UPA-transduced ECs). The systemic levels of fibrinopeptide A, thrombin-antithrombin complex, D-dimer, and both local and systemic levels of TPA and UPA were not increased by transduced ECs compared with untransduced ECs. The focal antithrombotic effects of transduced ECs appear to be due to local enhancement of thrombolysis.

CONCLUSIONS

ECs transduced with recombinant TPA and a-UPA enhance local antithrombotic activity in vivo. This strategy of attaching transduced ECs overexpressing plasminogen activators may be therapeutically useful by preventing thrombo-occlusive failure of implanted cardiovascular devices or mechanically denuded vessels.

Culture of human adult endothelial cells on endarterectomy surfaces

OBJECTIVES

Endothelial cell seeding of prosthetic grafts has not been as successful as initially hoped and the application of seeding technology to alternative reconstructive procedures such as endarterectomy and angioplasty has been increasingly considered. The success of such seeding depends on the ability of the seeded cells to attach to, and form a monolayer on the endarterectomised vessel wall which was the aim of this study.

METHODS

Using a seeding chamber model, heterologous human adult endothelial cells were seeded onto fresh human endarterectomy specimens and cultured. Studies of endothelial call adherence to endarterectomy specimens were performed using 111-Indium oxine labelled cells using methodology analogous to graft seeding.

RESULTS

Mean endothelial cell adherence of 70% (S.D. 10%) after 1 h incubation was achieved and the successful development of a monolayer of human adult venous endothelial cells on endarterectomised arteries was demonstrated in vitro.

CONCLUSIONS

These results indicate that closed endarterectomy appears to offer a surface with cell attachment that is superior to prosthetic grafts. Where femoral endarterectomy is appropriate, endothelial seeding potentially offers a method of reducing thrombogenicity and intimal hyperplasia, improving patency and avoiding a prosthetic graft whilst preserving collateral circulation and autologous vein.

Effect of pulsatile shear stress on endothelial attachment to native vascular surfaces

An in vitro model of vascular damage was used to investigate the ability of seeded endothelial cells to resist shear stresses generated in a perfusion circuit. At perfusion rates of 100 ml/min the maximum shear stress reached 16.5 dyn/cm2. At this level the rate of cell detachment from the damaged vascular surface was 88 per cent per h for the first 20 min of flow but gradually decreased to 5 per cent per h after 90 min. These findings suggest that endothelial cells may be retained on damaged vascular surfaces in conditions that approximate to arterial flow.

Interruption of vascular thrombus formation and vascular lesion formation by dietary n-3 fatty acids in fish oil in nonhuman primates

BACKGROUND

Because of discrepant claims regarding the relative biological effects of n-3 fatty acids (n-3FAs), we have concurrently measured the effects of dietary n-3FAs on blood and vascular lipid composition, hemostatic function, blood thrombotic responses, vascular thrombus formation, and vascular lesion formation in baboons.

METHODS AND RESULTS

Dietary n-3FAs displaced n-6FAs in plasma, platelets, blood vessels, and corresponding urinary eicosanoid metabolites (p < 0.01 in all cases) within weeks after initiation of a semipurified diet containing 1 g/kg per day n-3FA-ethyl ester concentrate (composed of two thirds eicosapentanoic acid and one third docosahexanoic acid). Coincidentally, platelet hemostatic function became minimally impaired (template bleeding times prolonged from 4.3 +/- 0.5 minutes to 7.6 +/- 1.3 minutes, p = 0.039); concentrations of collagen producing half-maximal platelet aggregation increased (from 6.4 +/- 2.1 to 8.5 +/- 2.5 micrograms/mL, p = 0.045); and tissue factor expression by endotoxin-stimulated blood monocytes fell (from 6.5 +/- 1.2 to 1.7 +/- 0.14 mU/10(6) cells, p < 0.005). Dietary n-3FAs decreased deposition of platelets onto thrombogenic segments of Dacron vascular graft incorporated into chronic exteriorized femoral arteriovenous (AV) shunts, a thrombotic process resistant to the effects of both aspirin and heparin (111In-labeled platelet deposition decreased from 14.1 +/- 1.4 x 10(9) platelets/5-cm segment at 40-60 minutes with occlusion to 7.5 +/- 0.8 x 10(9) platelets/5-cm segment without occlusion; p < 0.001). Platelet deposition onto segments of endarterectomized homologous normal aorta in the AV shunts of n-3FA-treated animals was similarly reduced (from 4.4 +/- 0.9 to 1.8 +/- 0.4 x 10(9) platelets; p < 0.01). Dietary n-3FAs interrupted vascular thrombus formation at sites of surgical carotid endarterectomy (platelet deposition, 1.5 +/- 0.4 versus 4.4 +/- 1.0 x 10(9) platelets in untreated controls; p < 0.001). Moreover, endarterectomized aortic segments (EASs) from n-3FA-treated donors exhibited little capacity to induce thrombus formation when tested in the AV shunts of control recipient animals (0.24 +/- 0.10 versus 4.4 +/- 0.90 x 10(9) platelets). However, in the converse crossover experiments, EASs from control animals actively accumulated platelets when studied in the AV shunts of n-3FA-treated animals (1.8 +/- 0.4 x 10(9) platelets; p < 0.01 versus n-3FA-treated EASs in shunts of normal animals). Dietary n-3FAs also abolished vascular lesion formation at sites of carotid endarterectomy 6 weeks after surgery (cross-sectional area of neointima 0.048 +/- 0.031 mm2 compared with 0.428 +/- 0.104 mm2 in control arteries; p = 0.010).

CONCLUSIONS

In nonhuman primates, dietary n-3FAs in high doses eliminate both vascular thrombus formation and vascular lesion formation after mechanical vascular injury while largely sparing hemostatic function and modestly reducing blood thrombotic responses. These effects are attributed to selective n-3FA-dependent alterations in cellular membrane functions.

Endothelial cell seeding: a review

The concept of endothelial cell seeding, designed to provide vascular grafts with a nonthrombogenic lining, has progressed from crude animal experiments during the past two decades to detailed in vitro functional studies using human cells. Although favorable results have been obtained in animal studies this has yet to be translated to humans, where current application of these techniques has been limited to a very few clinical trials. The history, current status and future directions are reviewed herein.

Endothelial cell seeding of damaged native vascular surfaces: prostacyclin production

Endothelial cell seeding has been successful in reducing the thrombogenicity of prosthetic vascular grafts in animal and clinical studies. The reduction in thrombogenicity may be attributed to the intrinsic properties of endothelial cells themselves, and their ability to produce anti-thrombogenic mediators such as prostacyclin, and endothelium-derived relaxing factor. Endothelial seeding of damaged vascular surfaces produced during percutaneous transluminal angioplasty and endarterectomy is an attractive possibility due to the excellent attachment characteristics of the sub-endothelial tissue exposed during these procedures. The ability of endothelial seeded damaged vascular surfaces to produce prostacyclin was measured in an in vitro model of vascular injury. Endothelial-seeded damaged surfaces produced significantly higher prostacyclin release than did vessels damaged by balloon dilatation (265.5 pg cm-2 min-1 and 87.5 pg cm-2 min-1 respectively). This study provides evidence that endothelial seeding of damaged native vascular surfaces is technically feasible and that seeding may reduce the thrombogenicity of vascular surfaces following balloon dilatation.

Endothelial cell seeding after carotid endarterectomy in a canine model reduces platelet uptake

Post-endarterectomy platelet deposition may play an important role not only in vessel wall healing, but also in the development of progressive stenosis. Using a canine model, we investigated the effect of endothelial cell seeding on platelet deposition on endarterectomised arteries. Thirteen dogs underwent bilateral carotid intimectomy (5 cm long) and one side was seeded with an average of 2 x 10(6) viable freshly harvested endothelial cells. Blood flow was restored 20 min after seeding. On the contralateral side, a sham-seeding was performed. Deposition of 111indium-labelled autologous platelets was studied with sequential gamma camera images 3-5 h, 1, 2, 3, 4 days and 4 weeks after surgery. Platelet uptake was statistically reduced on the seeded side. Animals were killed at 4 weeks (nine dogs) and 5 weeks (four dogs) after surgery. Seven arteries for each group were found to be occluded. We conclude that endothelial cell seeding on endarterectomised arteries is feasible and reduces platelet uptake. Improvement in the efficiency of seeding and reduction of endothelial cell loss might permit clinical application of this technique.