(Circulation. 1995;92:2605-2616.)
© 1995 American Heart Association, Inc.
Articles |
Seeding With Omental Cells Prevents Late Neointimal Hyperplasia in Small-Diameter Dacron Grafts
From the Clinic for Cardiovascular Surgery, Department of Surgery, University Hospital (M.P., W.M.-G., M.L., M.T.), Zurich, Switzerland; the Laboratory for Special Techniques, Department of Pathology, University Hospital (B.O.), Zurich; and the Department of Biostatistics ISPM, University of Zurich (B.S.), Switzerland.
Correspondence to Miralem Pasic, MD, PhD, Deutsches Herzzentrum Berlin, Klinik für Herz-, Thorax-, und Gefässchirugie, Augustenburger Platz 1, D-13353 Berlin, Germany.
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Abstract |
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Background The influence of complete endothelialization of a prosthetic graft on development of late neointimal hyperplasia is unknown. This study was designed to investigate the effect of complete coverage with endothelial-like cells on late neointimal hyperplasia in small-diameter Dacron grafts seeded with omental cells in a canine model.
Methods and Results Four-mm-ID Dacron grafts were seeded with cells from omentum and implanted in the carotid arteries in 24 mongrel dogs. Each dog received one seeded and one nonseeded graft. The graft patencies were assessed by angiography at 1, 5, 12, 26, and 52 weeks after surgery. The prostheses were explanted at 5, 12, 26, and 52 weeks after surgery and underwent microscopic studies. The actuarial patency rates at 1, 5, 12, 26, and 52 weeks were 100%, 95%, 95%, 95%, and 95% for seeded grafts and 100%, 86%, 49%, 40%, and 13% for nonseeded grafts, respectively. The seeded grafts exhibited a uniform endothelial-like luminal monolayer without the development of late neointimal proliferation or anastomotic neointimal hyperplasia. Neointimal tissue thickness increased up to 6 months; no additional progression of the subendothelial tissue thickness was observed, in fact there was an insignificant decrease.
Conclusions Seeding with omental cells prevents development of late neointimal hyperplasia of small diameter prosthetic vascular grafts in a canine model.
Key Words: cells • grafting • anastomosis • arteries • endothelium • atherosclerosis
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Introduction |
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Neointimal hyperplasia, usually found in the area of the distal anastomoses, accounts for more than 20% of late failures of infrainguinal prosthetic graft revascularizations.1 2 3 4 Although endothelial cells play an important role in preventing or inhibiting neointimal hyperplasia by releasing inhibitors of smooth muscle cells,5 6 7 incomplete endothelialization seen at the anastomotic areas in nonseeded grafts may induce smooth muscle cell proliferation beneath endothelium8 9 due to platelet-derived growth factor and other mitogen production by perturbed endothelial cells.10 11 12 The influence of complete endothelialization of a prosthetic graft on development of late neointimal hyperplasia is unknown.
The aim of the present study was to test whether complete coverage with endothelial-like cells of a small vascular graft seeded with omentally derived cells might reduce or even prevent late neointimal proliferation and anastomotic hyperplasia.
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Methods |
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Animals
Studies were performed in 24 mongrel dogs (weight range, 20 to 30 kg; age range, 1 to 4 years). The dogs were cared for according to the European Convention on Animal Care. The experiments were reviewed and approved by the ethics committee of the University Hospital Zurich.
Surgical Procedure
The anesthesia was induced with sodium
thiopental
(20 mg/kg IV), and the dogs were intubated and ventilated with an
oxygen, nitrous oxide, and halothane mixture. The animals received
infusion of lactated Ringer's solution at the rate of 10 mL/kg per
hour during operation.
A small supraumbilical laparotomy was made and as much of the omentum as possible was removed and placed in a sterile 150-mL plate containing 60 mL of HEPES-buffered saline (HBS). Concomitantly, the omentum was further processed in the cell laboratory by the call-laboratory staff while the surgical staff closed the abdominal incision and performed exposure of the arteries for the implantation. Starch-free gloves were used throughout the study to avoid the cytotoxic effect of glove powder.13 Midline neck incision was made, and both common carotid arteries were dissected free. A 6-cm segment of each artery was isolated between the vascular bulldog clamps and excised, and then both ends were beveled to approximately 45°. A 4-mm-ID uncrimped Dacron graft (Sulzer Brother, Ltd) with an average water porosity of 700 mL/min per square centimeter at 120 mm Hg was simultaneously preclotted and seeded and immediately thereafter implanted into the right carotid artery. The oblique end-to-end anastomoses were performed with a continuous 7-0 polypropylene suture. The paired anatomic sites (the common carotid arteries) were used throughout the study; each dog received one seeded graft (inserted into the right carotid artery) and one nonseeded graft (inserted into the left carotid artery).
Harvesting of the Omental Cells
The cell harvesting procedure
was the modified method of Schmidt
et al.14 The omentum (mean±SD weight, 28.8±7.3 g)
was
rinsed with HBS, trimmed, minced with two scalpels into very small
pieces, and aspirated into a 10-mL pipette; then the tissue was
transferred into a 50-mL Erlenmayer flask containing 1500 U/mL
collagenase type II (Sigma Chemical Co). The ratio was 1 g
of omental tissue to 2 mL of collagenase. The suspension of
omental tissue and collagenase was incubated for 40 minutes
in a 37°C water bath at 100 shaking motions per minute. The digested
tissue was homogenized by repetitive pipeting, transferred
into a 15-mL tube, and centrifuged twice at 100g for
5 minutes. The supernatant contained mainly adipocytes and the
collagenase solution. The cell pellet was resuspended in 10
mL phosphate-buffered saline (PBS), filtered through a 250-µ
pore-size polyester mesh (Bolting Cloth) to remove nondigested
large tissue fragments, and then washed two times with HBS. Finally, a
2-mL suspension of the endothelial cells was added to
15 mL of autologous plasma and centrifuged at 45g
for 20 minutes onto the prosthesis using a rotation device
(Sulzer Brothers, Ltd) before implantation. After implantation, the
seeded grafts demonstrated clusters of cells that adhered to the Dacron
fibers covered with an additional formation of red thrombus against the
prosthetic lumen, preventing the washout and subsequent loss of
the seeded cells.15 Cell seeding density was 1.75 (95%
CI, 0.77 to 2.72) x106 cells per square centimeter
of graft surface ranging from 0.37x106 to
4.54x106 cells seeded per square centimeter of
graft surface.
An 
0.5-mL aliquot of the cells was removed for the
cell count of all
harvested cells assessed by fluorometric DNA measurements on cell
pellets,16 cell identification by specific perinuclear
uptake of acetylated LDL17 and by
immunohistochemical staining for von Willebrand
factor,18 cell culture,19 and the
determination of cell viability.20 Viability was defined
as the number of attached cells counted after 18 hours in the cell
culture and was attributed to those cells that resisted rinsing with
PBS. After washing, the cell culture was trypsinized, and the number of
cells was calculated by fluorometric DNA measurements on cell
pellets.16 The density of viable cells per square
centimeter of a seeded graft was estimated by the ratio of the number
of viable cells to the seeded graft surface.
Medication
All animals received prophylactic cephalosporin
antibiotics (cefalexinum monohydratum, 1200 mg/day) and analgesics
(buprenorphine hydrochloride 0.9 mg/day) for 4 days postoperatively, as
well as dipyridamole (75 mg/day) and
acetylsalicylic acid (325 mg/day) orally, beginning
on 1 and 4 days before surgery, respectively. The antiplatelet
medication was continued for 4 weeks postoperatively.
Patency Assessment
Serial patency determinations of the
grafts were performed by
angiography at 1, 5, 12, 26, and 52 weeks after surgery. The
angiographic catheter was introduced through the common femoral artery
and then forwarded into the common carotid artery. The angiographic
examination was performed by manual injection of 10 mL of diluted
nonionic angiographic dye (dilution 1:1 with 0.9% NaCl) (Iopromidum
Ultravist 370, Schering).
Explantation
The prostheses were explanted after 5 weeks
(n=6 dogs), 12 weeks
(n=6 dogs), 26 weeks (n=6 dogs), and 52 weeks (n=6 dogs).
After
transfemoral angiography, the grafts were dissected free and then
removed along with the adjacent 3 cm of the carotid artery. The grafts
underwent microscopic studies with light microscopy after staining with
hematoxylin-eosin. The grafts were processed by standard method for
scanning electron microscopy.21 Immunohistochemical
staining for von Willebrand factor was performed on
formalin-fixed paraffin-embedded tisssue. Sections were
predigested for 10 minutes with 0.1% pronase E (Merck) at 37°C.
After blocking, endogenous endoperoxidase with
methanol-H2O2, rabbit antiserum against
von Willebrand factor (factor VIII–related antigen) was
applied. Rabbit antibodies were detected using the ABC/peroxidase
method, with diaminobenzidine as a substrate of the color
reaction.18 Sections were counterstained with hemalaun.
(All immunological reagents were from DAKO A/S.) The maximum
thicknesses of the neointimal tissue within 10 mm of the
suture lines, as well as of the central part of the graft, were
measured on hematoxylin-eosin–stained cross section by means
of a computer-assisted automated image analysis system
(Video planimeter, Zeiss Inc).
Definition
Late neointimal hyperplasia was considered to be
present if the significant difference of the neointimal
thicknesses was found when comparing (1) the mean
neointimal thickness of the certain parts of the grafts
with the mean neointimal thicknesses of the other parts at
the same time point (eg, the mean value of the neointimal
thicknesses of all the distal parts of all grafts explanted at 3 months
after implantation versus the mean value of the proximal or central
part of the same group of grafts) and (2) the difference between the
mean neointimal thicknesses of the same parts of the grafts
at the different time points (eg, the mean value of the
neointimal thicknesses of all the distal parts of all
grafts explanted at 3 months after implantation versus the mean value
of the neointimal thicknesses of all the distal parts of
all grafts explanted at 6 months after implantation).
Statistics
Patency data determined by serial angiographic
studies were
tabulated and presented in the life-table format by the
method of Cutler and Ederer.22 Event-free proportions
at 1, 5, 12, 26, and 52 weeks postoperatively are reported with 95%
CIs.
The data are presented as mean values with 95% nonparametric CIs. Differences in mean values for neointimal thicknesses at different time points and between different locations were assessed by repeated-measures ANOVA; simple regression was used to evaluate the development of the neointimal thickness during the time at the same location. A value of P<.05 was considered to be significant.
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Results |
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The actuarial patency rates at 1, 5, 12, 26, and 52 weeks were 100%, 95%, 95%, 95%, and 95% for seeded grafts and 100%, 86%, 49%, 40%, and 13% for nonseeded grafts, respectively (Fig 1
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The obvious angiographic and histological differences
were found between the seeded and the nonseeded grafts regarding
neointimal hyperplasia, except when the nonseeded grafts
were totally covered with endothelial-like cells.
According to the fine anatomic details of the grafts seen on
angiography and later confirmed on histological
examinations, thrombotic process and neointimal hyperplasia
were found to be two main causes of graft occlusion. The early graft
occlusions were caused mainly by thrombotic processes because these
grafts showed smooth anastomotic regions with an intraluminal clot on
angiography (Fig 2A). Contrary to these
early findings, the progression of the late neointimal
proliferation found predominantly at the anastomotic regions (Fig
2B) was the dominant finding in the grafts that
occluded in the late period. First changes in terms of
neointimal hyperplasia were noted by angiographic studies
performed at 3 months after graft insertion, with a trend to
progression with time. However, this anastomotic stenosis was
not observed in the two nonseeded grafts that were totally covered with
endothelial-like cells (Fig 2C).
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Histological studies of the seeded grafts revealed a
neointima with luminal endothelial-like
lining and highly organized subendothelial layers
without anastomotic neointimal hyperplasia (Fig 3A through 3C).
The intima is covered by
a luminal monolayer of coherent epithelial-like flat cells
expressing von Willebrand factor (Fig 4A and
4B). Microscopic examinations confirmed that
neointimal hyperplasia caused anastomotic stenosis
seen by angiography (Fig 3D and 3E). Moreover,
the
nonseeded grafts occluded in the late period demonstrated anastomotic
fibrous tissue ingrowth, indicating neointimal hyperplasia
as the main cause for occlusion (Fig 5A), with different phases
of maturation
of a clot throughout the graft lumen. Histological
examinations revealed that the stenotic lesions seen on
angiography in the central parts were predominantly caused by a
thrombotic process (Fig 5B), although it was difficult
to distinguish hyperplasia from organized thrombus in some specimens of
the occluded nonseeded grafts. However, the neointimal
hyperplasia was not seen in the two nonseeded grafts totally covered
with endothelial-like cells.
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The nonseeded grafts showed a different degree of spontaneous coverage
with endothelial-like cells (so-called
spontaneous endothelialization, Fig 6).
The extent of this process was time dependent; the two nonseeded grafts
that were patent at 1 year were already totally covered with
endothelial-like cells. However, in these grafts we
could not find any neointimal hyperplasia. Scanning
electron microscopy of the seeded grafts showed complete coverage by a
uniform monolayer of endothelial-like cells and
minimal platelet or cellular deposition (Fig 7A and
7B). In patent nonseeded grafts, scanning electron
microscopy revealed large areas covered with coagulum consisting of
fibrin, platelets, and occasional leukocytes (Fig 7C) and
regions of spontaneous coverage with
endothelial-like cells. There was no difference in
the scanning microscopy findings of the seeded grafts and the findings
of the regions of the nonseeded grafts covered with
endothelial-like cells.
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The measurements of the maximum thicknesses of the
neointimal tissue within the anastomoses as well as within
the central parts of the seeded small-diameter Dacron grafts showed
neither late neointimal proliferation nor anastomotic
hyperplasia in the grafts. The mean neointimal tissue
thickness of the seeded grafts increased up to 26 weeks and then
remained stable or slightly reduced (Fig 8). Simple regression
analysis
showed progressive reduction of the mean neointimal
thickness (-0.5 µm/wk, Fig 9) but no significant
slope. Hence, there was no difference when comparing any part of the
grafts at any time point, as well as when comparing them with the two
nonseeded grafts that were totally covered with
endothelial-like cells. Repeated-measures ANOVA
revealed no significant differences among the mean
neointimal thicknesses of the seeded grafts at the
different time points (P=.51) or among the mean
neointimal thicknesses at the different locations
(Greenhouse-Geisser corrected P=.16).
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Discussion |
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Based on the combination of three highly conclusive parameters (patency rate, angiographic findings, and histological examinations), our study strongly supported the hypothesis that complete coverage with endothelial-like cells of a luminal side of a small vascular graft seeded with omentally derived cells might reduce or even prevent late neointimal proliferation and anastomotic hyperplasia. The prevention of late neointimal hyperplasia—one of the main causes of late occlusion of the synthetic vascular grafts—resulted consequently in the enhanced patency rate of the seeded grafts as compared with the nonseeded grafts.
Both the angiographic studies and histological examinations revealed that neointimal proliferation and anastomotic hyperplasia were the main factors leading to late occlusion of the nonseeded grafts. To obtain fine assessment of our implants, we used conventional angiography for routine long-term surveillance because this type of angiography provided fine anatomic details that enabled us to identify structural changes in grafts.1 Angiograms of the seeded grafts showed a smooth intimal surface without luminal narrowing, whereas angiographic examinations of most of the nonseeded grafts demonstrated different degrees of luminal stenosis at the anastomotic regions in the late phase after implantation.
The main factors for occlusion of a prosthetic vascular graft are increased graft surface thrombogenicity and technical error in the early postoperative course and progression of the atherosclerotic disease and neointimal hyperplasia in the late phase.23 In this study, technical error such as an incorrectly performed anastomosis was excluded by angiographic examination performed postoperatively, and atherosclerotic process as a possible cause for late occlusion was also excluded because the animals were not old. Therefore, thrombotic graft occlusion was found to be the cause of the early occlusion, as it was shown on angiography, on histological examination, and on explantation. It should be emphasized that the cause of occlusion was determined after considering the results of all diagnostic methods (angiographic, histological, and macroscopic findings) but not solely on the basis of only one method. Because the grafts were explanted according to the preoperative randomization and not immediately after occlusion was noted, it was difficult to distinguish hyperplasia from organized thrombus in some specimens of the occluded nonseeded grafts. Once thrombosis of a graft has occurred, the thrombus rapidly becomes organized and fibrotic so that it is difficult to distinguish from preexisting hyperplasia. The technique of quantitative histological analysis of neointimal hyperplasia used in our study permits accurate measurement only in grafts that are patent so that progression can be observed; however, the progressive course of hyperplasia can only be compared between different animals. Therefore, we performed two types of comparisons: first, simultaneous measurements and comparisons of the different locations at the same time point and, second, measurement and comparisons of the same locations on different specimens at different times.
Furthermore, the second important observation of our study is that complete coverage with endothelial-like cells per se, regardless of the method by which it has been achieved, was the most important factor for prevention of late neointimal hyperplasia and the subsequent improvement of the graft patency. This concept is supported by the fact that late neointimal hyperplasia was demonstrated if the nonseeded grafts were only partially covered spontaneously with endothelial-like cells, but hyperplasia was not found if the nonseeded grafts were totally covered with endothelial-like cells by a spontaneous process.
We could not find any difference in terms of intimal hyperplasia between the seeded grafts (all totally covered with endothelial-like cells) and the totally endothelialized nonseeded grafts, but we found the obvious difference between the seeded grafts and the nonseeded grafts partially covered with endothelial-like cells. These facts lead us to conclude that the omental seeding technique may reduce or prevent late neointimal hyperplasia via the mechanism of complete luminal coverage with endothelial-like cells. However, it should be emphasized that the improved patency rate of the seeded grafts can be achieved only in part via reduction or prevention of the late neointimal hyperplasia and in part by some other mechanisms, such as reduced thrombogenicity of the total coverage of the luminal surface of such grafts with endothelial-like cells. Thus, the omental seeding technique has an impact on graft patency by several possible mechanisms, and one of them is via the mechanism of neointimal hyperplasia.
The third important observation of our study is that we found no differences between the scanning microscopy findings of the seeded grafts and the findings of the regions of the nonseeded grafts covered with endothelial-like cells. Although the process of spontaneous endothelialization of nonseeded grafts is usually seen in animals, the precise origin of luminal endothelial-like cells in both endothelialized seeded and nonseeded grafts remains unclear. The origin of the cells covering the flow surface of nonseeded vascular grafts is still speculative. The findings of endothelialized anastomotic regions as well as islands of endothelium throughout the grafts indicate that spontaneous endothelialization can occur by several mechanisms, such as migration of endothelial cells from the host artery toward the prosthesis, ordinary endothelial cell division from capillaries that originate from outside the graft passing through the interstices of the fabric, or circulating blood cells.24 Coverage with endothelial-like cells of a synthetic vascular graft after seeding with pure endothelial cells or with the mixture of different cells from omentum is an unknown process, too. It probably requires cell duplication, although it has been shown that endothelial cells remained on the graft surface after cell transplantation.25 Because of the similarity of the scanning microscopy findings between the seeded grafts and the regions spontaneously covered with endothelial-like cells of the nonseeded grafts, it can be speculated that these two different processes probably have similar evolving processes leading ultimately to surface coverage with endothelial-like cells with consecutive athrombogenicity of the graft surface.
It should be emphasized that the term "late neointimal hyperplasia" does not mean the absence of any neointimal tissue on the luminal side of a seeded prosthetic vascular graft. It has been very well known that seeding with cells from the omentum produces a neointima in these grafts. Therefore, we defined "late neointimal hyperplasia" in our study as a significant increase of the neointimal thickness in certain parts of the seeded grafts (ie, proximal, central, distal) as compared with the other parts at the same time point, or the difference between the neointimal thicknesses of the same parts of the grafts at the different time points.
Neointimal hyperplasia in a nonseeded graft is a process of smooth muscle cell proliferation that occurs at both the proximal and distal anastomoses between a prosthetic nonseeded graft and an artery; however, it occurs to a significantly greater degree at the distal anastomosis as compared with the proximal anastomosis.26 In our study no difference was found in the thickness of the neointima when comparing any part (proximal, distal, or central) of the seeded grafts at any time point. If there is any late neointimal hyperplasia (progression of the neointimal thickness), it would be expected that any difference between the neointimal thicknesses should be found when looking at the following: (1) the mean thickness of the same parts of the grafts at the different time point (such as the neointimal thickness of the proximal parts at 6 months versus the neointimal thickness of the proximal parts at 12 months) and (2) the mean neointimal thickness of the different parts of the grafts at the same time point (such as comparison of the neointimal thicknesses of the central parts with the neointimal thicknesses of the distal parts at 6 months). The regular angiographic follow-up and microscopic examination revealed that there was a significant difference between the seeded and the nonseeded grafts concerning neointimal hyperplasia. The fact that no difference between the neointimal thicknesses was found when comparing the two nonseeded grafts that were patent at 1 year (and were totally covered with endothelial-like cells) with the seeded grafts does not speak against the hypothesis but rather emphasizes the impact of complete endothelialization on neointimal proliferation.
Intimal hyperplasia (intimal changes in a venous or arterial graft or native artery) and neointimal hyperplasia (the process in a new intimal building in a synthetic graft without previous intima) are characteristic fibromuscular cellular responses to vascular injury during vascular reconstruction.27 It is characterized by cellular proliferation and accumulation of extracellular matrix material that occur as a result of excessive proliferation of smooth muscle cells.28 All forms of vascular reconstruction cause injury and a wound healing response,29 leading to intimal or neointimal proliferation after reconstruction with vein or prosthetic grafts30 31 as well as in a host artery after endarterectomy, atherectomy, or coronary angioplasty.32 33 34 35 However, formation of neointimal hyperplasia occurring after implantation of prosthetic vascular grafts is not identical to intimal proliferation after endarterectomy or angioplasty, especially due to chronic inflammatory responses associated with implanted synthetic grafts. Early after implantation of a prosthetic graft, leukocytes are observed on the graft surface, with monocyte infiltration and formation of foreign body giant cells, characterizing the chronic inflammatory or foreign body response to vascular prostheses.36 Neointimal hyperplasia in a synthetic graft has already been recognized in the early phase of peripheral vascular surgery.4 37 It occurs both in Dacron and polytetrafluoroethylene (PTFE) grafts38 39 as early as 3 months and as late as 1 year after implantation.3 4 37 In contrast to occlusions after angioplasty or atherectomy that tend to appear in the first 6 months,40 the stenosing intimal lesions of autologous or prosthetic grafts usually appear later after surgery.1 2 Anastomotic hyperplasia involves both the proximal and distal anastomoses but it has a predilection for the distal anastomosis, with a tendency to progress with time.39 Neointimal hyperplasia in the area of the distal anastomoses accounts for between 20% and 50% of late lower extremity bypass graft failure.2 3 4
The regulation of cell migration, proliferation, and growth during intimal thickening appears to be regulated by factors from the blood, particularly platelets and leukocytes, and the interaction of vascular wall cells and graft themselves.41 Operative manipulation and hemodynamic factors such as high-flow and low-flow velocities, high and low wall shear stresses,42 and compliance and diameter mismatch between graft and host artery43 also influence smooth muscle cell proliferation and intimal thickening.
It has been proposed that growth factors, such as platelet-derived growth factor and basic fibroblast growth factor, released from activated platelets, leukocytes, altered smooth muscle cells, and endothelial cells may be involved in smooth muscle cell migration and proliferation after vascular injury.44 45 Basic fibroblast growth factor is a prototype of the family of heparin-binding growth factors that regulate a variety of cellular responses, including cell growth, morphogenesis, and differentiation of various cell types such as smooth muscle cells.46 Fibroblast growth factors deliver their signals to cells by binding to a dual receptor system that activates the bound growth factor before its delivery to the signal-transducer receptors.47 48 Signaling of growth and differentiation involves multiple pathways.49 At least two families of receptors bind basic fibroblast growth factor and mediate its response: tyrosine kinase–containing fibroblast growth factor receptors47 and heparan sulfate proteoglycans.50 Both are known to undergo internalization by different pathways.49 Heparan sulfate proteoglycans are obligate partners in the binding of basic fibroblast growth factors to their receptors; fibroblast growth factors do not bind to fibroblast growth factor receptors unless heparan sulfate, or its analog heparin, is present.51 The activation of intrinsic tyrosine kinase function of receptor tyrosine kinases on binding of growth factors can trigger cytoplasmatic signal transduction pathways.47 These regulatory mechanisms of specific cell behavior are not well understood. Thus, analysis of biological activity of growth factors on smooth muscle cell growth might be useful for antagonizing pathological smooth muscle cell migration and proliferation.44 45 52
The complexity of the pathways leading to formation of
neointimal hyperplasia suggests that the use of one agent
alone will not be likely to be entirely effective in preventing it. The
multifactorial cause is the reason that single medical therapy has
failed in preventing anastomotic hyperplasia. Since growth factors are
the main stimuli for smooth muscle cell migration and proliferation,
several pharmacological approaches to smooth muscle cell hyperplasia
might be useful.53 Different agents such as
antiinflammatory drugs,54 antihypertensive
medicaments,55 56 fish oil,57
prostaglandin analogues,58
1-adrenergic blocking agents,59
and anticoagulants60 have been shown to suppress the
process of intimal hyperplasia in animal studies. The role of
antiplatelet therapy in the prevention of intimal hyperplasia
after arterial reconstruction remains
controversial.61 62 Trials in human subjects have
demonstrated that aspirin and dipyridamole
significantly improve patency of prosthetic but not saphenous
vein femoropopliteal bypasses63 64 ; aspirin and
dipyridamole are particularly beneficial when started
before operation64 or within 24 hours of
operation.65 However, clinical trials of
antiplatelet agents suggest that platelet inhibition alone
does not prevent anastomotic intimal hyperplasia.66
This study showed that establishing the presence of an endothelial-like cell coverage on the luminal surface played an important role in reduction or prevention of late neointimal and anastomotic hyperplasias of small-diameter prosthetic vascular grafts. Anastomotic neointimal hyperplasia was suppressed in the grafts that were totally covered with endothelial-like cells regardless of whether they had been seeded or not. In contrast, occluded control grafts showed clearly visible anastomotic tissue ingrowth in the late phase. Therefore, seeding with omental cells may play an important role in preventing or inhibiting late smooth muscle cell proliferation by total coverage of the luminal surface with endothelial-like cells in a synthetic vascular graft. The characteristic of endothelial cells to exhibit both inhibitional and proliferative properties on smooth muscle cells may play an important role in the pathogenesis of neointimal hyperplasia.67 68 A possible explanation for the smooth muscle cell proliferation beneath endothelium in the nonseeded grafts is the production of smooth muscle cell mitogens by perturbed endothelial cells.36 By reaching luminal confluence of endothelial-like cells in a seeded graft, one possible factor for neointimal anastomotic hyperplasia, namely nonendothelialized luminal surface of the graft, might be excluded or might be converted into an active factor for prevention of late neointimal hyperplasia. Although the presence of an endothelial-like surface will not alter all factors potentially contributing to anastomotic intimal hyperplasia, it might lessen deposition and activation of circulating blood elements (including platelets, leukocytes, and components of the coagulation and complement system), decrease the release of mitogen factors for smooth muscle cells, and prevent thrombus formation by generation of prostacyclin, antithrombotic factors, and plasminogen activators.
Large numbers of cells can be harvested from the omentum. The cells derived from omental suspension are a mixture of microvascular endothelial cells and mesothelial cells, with a few other cell types.14 69 Contamination of a seeding suspension with nonendothelial cells depends on a harvesting method. A purer endothelial cell yield can be achieved by lowering the separation density during the harvesting procedure, but doing so leads to a lowering of the number of all cells available for seeding. Wang et al70 estimated that 10% or less of total cell numbers harvested from omentum were nonendothelial in origin. Kern et al71 obtained a completely pure microvascular endothelial-cell population harvested from omental tissue with no growth of other cell types in serially passaged cultures, but the endothelial cell yield was greatly reduced at only 103 endothelial cells per gram of omental tissue.
The identification of the cells derived from omentum poses a problem, and there is no consensus in the literature as to whether these cells are endothelial or nonendothelial in origin.72 73 It is difficult to rule out the identity of the isolated endothelial cells from other cells, especially from mesothelial74 because both types of cells are present in omental tissue. Like endothelial cells, mesothelial cells produce prostacyclin75 76 and possess fibrinolytic activity. In vitro these cells produce large amounts of tissue-type plasminogen activator, together with types 1 and 2 plasminogen activator inhibitors.77 Moreover, when seeded onto vascular prostheses, these cells acquire a confluent monolayer lining with no adherent platelets or amorphous material within 1 month after surgery.78 79 In a tissue culture, both types of cells show similar growth patterns under light microscopy.72 74 75 However, it has been shown that in a culture of mixtured cells derived from omentum, endothelial cells were rapidly displaced by mesothelial cells, resulting in a pure culture of mesothelial cells.73 Similarly, in a tissue culture of endothelial cells and fibroblasts, endothelial cells were suppressed by fibroblasts that proliferated, forming a confluent layer.80 In our study, we performed seeding of the grafts with cells immediately after harvesting from omentum and did not seed with cultered cells. In this way, the suppressive effect of mesothelial cells on endothelial cells in culture could be excluded in our study.
Although the origin of the omentally derived cells has been controversial, its endothelial nature has usually been proven by morphological and functional criteria. The most used methods for identification of endothelial cells are the demonstration of von Willebrand factor by immunofluorescence staining79 and the uptake of diacetylated LDL.17 The incorporation of [35S]methionine into von Willebrand factor demonstrates the ability of the cultured microvascular endothelial cells from human omental tissue to synthesize von Willebrand factor,81 which proves the identity of the cultured cells to be endothelial. However, it could be speculated that the extensive immunostaining seen in some of our specimens in the upper layers of the intima could be caused by previous platelet deposition and therefore previous thrombosis, which was supposedly prevented by seeding with omental cells. The other methods for identification of these cells and its differentiation from mesothelial are use of endothelial cell-specific monoclonal antibodies, such as antibody BMA 120,82 and characterization of different biological functions typical for these cells.81 Moreover, these cells express cofactor thrombomodulin for activation of protein C, thus endothelial cells stimulate the activation of protein C by thrombin83 and contain thrombomodulin within the cells.84 Furthermore, thrombomodulin has been identified immunologically on endothelial cells of veins, arteries, and capillaries as well as on endothelium of lymphatics and on syncytiotrophoblasts.85
When cells derived from human omental fat tissue were compared with those of human umbilical vein endothelial cells, Visser et al73 concluded that the cells from omental tissue were not endothelial but mesothelial in nature. Their statement was based on the observations that cells isolated from human omental tissue did not stain with endothelial-specific antibodies EN-4 and PAL-E; these cells contained abundant cytokeratins 8 and 18, which were absent in endothelial cells.77 Cytokeratins 8 and 18, determined with the monoclonal antibodies M20 and M9, were abundantly present in the cells derived from omentum but not in the human umbilical vein endothelial cells.73 Vimenten could be detected (with monoclonal antibody V9) in both types of cells, whereas desmine (detected with monoclonal antibody D33) was present only in omentally derived cells. A faint and diffuse staining of von Willebrand factor was seen in cells from omentum, whereas microvascular endothelial cells from subcutaneous fat displayed this factor as indistinct granular structures.77 In contrast to the human umbilical vein endothelial cells that were stained by both anti–von Willebrand factor antibodies, omentally derived cells could be stained for von Willebrand factor only by use of polyclonal anti–von Willebrand factor antibodies. Moreover, scanning electron microscopy revealed that cultured cells derived from omentum contained numerous surface microvilli, whereas human umbilical vein endothelial cells did not. All these findings suggested that the cells derived from omentum were a mixture of predominantly mesothelial cells with a low number of microvascular endothelial cells.73 In contrast to these findings, Stansby et al86 were not able to prove that the omental cells were mesothelial in origin. They supposed that human omental microvascular endothelial cells were pericytic in nature.86 Hernando et al75 proved the nonendothelial origin of the cells derived from human omentum, demonstrating that these cells showed positivity for monoclonal antibodies specific for endothelial cells (anti-CD34 QBEND10), antibodies to intermediate filaments (anti-vimentin and anti-desmin), and anti–smooth muscle cell antibodies (anti-actin and anti–total actin).
Endothelial cells from various organs in tissue culture and in vivo show various differences; human endothelial cells harvested from saphenous or umbilical vein exhibit distinctive features in transmission electron microscopy examination during cultivation on precoated PTFE grafts.87 Microvascular endothelial cells migrate more slowly than their large-vessel counterparts.88 Microvascular endothelial cells produce similar amounts of prostacyclin,89 factor VIII, angiotensin-converting enzyme, and a heparin-like molecule by microvascular endothelial cells is similar in comparison to the endothelial cells of large vessels.88 Human omental microvascular endothelial cells demonstrate a lesser amount of von Willebrand factor than human umbilical vein endothelial cells,90 with lower fluorescence in the cytoplasm than large-vessel endothelial cells as determined by the immunofluorescence staining to von Willebrand factor.79 In contrast to endothelial cells from umbilical vein, saphenous vein cells show typically tight junction at the marginal flaps. Umbilical venous cells regularly present dense condensations of microfibrillar networks at the apical and luminal sides, whereas saphenous vein cells show higher amounts of basal vesicles but rarely show basal and luminal condensations of the cytoskeleton.87 The presence or absence of Weibel-Palade bodies in transmission electron microscopy is one of the important morphological features that distinguish large-vessel from microvascular endothelial cells. Weibel-Palade bodies are endothelium-specific cytoplasmatic organelles found in abundance in large-vessel endothelium,91 but they are either absent or present in a lesser frequency in microvascular endothelial cells.71 Transmission electron microscopy of Dacron grafts seeded with omental microvascular cells reveals luminal lining cells with morphological features of an endothelial phenotype, including numerous pinocytotic vesicles within the cytoplasm on both basal and apical sides, closely interdigitated junctions with adjacent lining cells, large nuclei, and attenuated cytoplasmatic extension, but typically without Weibel-Palade bodies.70 However, macrovascular endothelial cells always exhibit the presence of Weibel-Palade bodies.91
Our experimental model with optimal conditions (high blood flow, short segment of a graft segment, and both anastomoses end-to-end) enabled us to achieve an excellent result regarding neointimal hyperplasia. However, further studies under more difficult conditions (eg, low blood flow, end-to-site anastomoses, longer grafts, and other location of implantation) are needed to determine the efficacy of the seeding with omental cells on neointimal hyperplasia and consequently on the patency of small-diameter grafts. Moreover, human investigations should be performed to determine the exact mechanisms of the endothelialization and the clinical efficacy. Animal data are not transferable directly to the clinical setting because of species differences in the healing of synthetic grafts; therefore, this experimental study requires validation by clinical trials. Our study showed safety and efficacy of the procedure, validating its use in prospective clinical studies.
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Acknowledgments |
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The study was supported by the Kommision zur Förderung der wissenschaftlichen Forschung, Bern, Switzerland, Project No. 1576, 1724.1, and 2178.1, and by Sulzer Medical Technology, Ltd, Winterthur, Switzerland. We are indebted to Prof P. Groscurth, MD, and Prof J. Auer, MD Vet, University of Zurich, Switzerland, for their active support and contribution to the study.
Received January 18, 1994; accepted May 25, 1995.
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TopAbstractIntroductionMethods Results Discussion References |
|---|
1. Idu MM, Truyen E, Buth J. Surveillance of lower extremity vein grafts. Eur J Vasc Surg. 1992;6:456-462. [Medline] [Order article via Infotrieve]
2. Quiñones-Baldrich WJ, Alfredo AP, Ahn SS, Baker JD, Machleder HI, Moore WS. Long-term results of infrainguinal revascularization with polytetrafluoroethylene: a ten-year experience. J Vasc Surg. 1992;16:209-217. [Medline] [Order article via Infotrieve]
3. Echave V, Koornick AR, Haimov M, Jacobson JH II. Intimal hyperplasia as a complication of the use of the polytetrafluoroethylene graft for femoral-popliteal bypass. Surgery. 1979;86:791-798. [Medline] [Order article via Infotrieve]
4. Imparato AM, Bracco A, Kim GE, Zeff R. Intimal and neointimal fibrous proliferation causing failure of arterial reconstructions. Surgery. 1972;72:1007-1017. [Medline] [Order article via Infotrieve]
5.
Fritze LMS, Reilly CF, Rosenberg RD. An
antiproliferative heparan sulfate species produced by postconfluent
smooth muscle cells. J Cell Biol. 1985;100:1041-1049.
6.
Castellot JJ, Addonizio ML, Rosenberg R, Karnovsky
MJ. Cultured endothelial cells produce
heparinlike inhibitor of smooth muscle cell growth.
J Cell Biol. 1981;90:372-378.
7. Jensen N, Brunkwall J, Fält K, Lindblat B, Bergquist D. Prostacyclin is produced from endothelial cell-seeded grafts: an experimental study in sheep. Eur J Vasc Surg. 1992;6:499-504. [Medline] [Order article via Infotrieve]
8. Angelini GD, Christie MI, Bryan AJ, Lewis MJ. Surgical preparation impairs release of endothelium derived relaxing factor from human saphenous vein. Ann Thorac Surg. 1989;48:417-420. [Abstract]
9. Graham LM, Fox PL. Growth factor production following prosthetic graft implantation. J Vasc Surg. 1991;13:742-744. [Medline] [Order article via Infotrieve]
10. Miossec P, Cavender D, Ziff M. Production of interleukin 1 by human endothelial cells. J Immunol. 1986;136:2486-2491. [Abstract]
11.
DiCorleto PE, Bowen-Pope DF. Cultured
endothelial cells produce a platelet-derived
growth factor-like protein. Proc Natl Acad Sci
U S A. 1983;80:1919-1923.
12. Kaufman BR, Fox PL, Graham LM. Platelet-derived growth factor production by canine aortic grafts seeded with endothelial cells. J Vasc Surg. 1992;15:699-707. [Medline] [Order article via Infotrieve]
13. Sharefkin JB, Fairchild KD, Albus RA, Cruess DF, Rich NM. The cytotoxic effect of surgical glove powder particles on adult human vascular endothelial cell cultures: implications for clinical uses of tissue culture techniques. J Surg Res. 1986;41:463-472. [Medline] [Order article via Infotrieve]
14. Schmidt SP, Monajjem N, Evancho MM, Pippert TR, Sharp WV. Microvascular endothelial cell seeding of small-diameter Dacron vascular grafts. J Invest Surg. 1988;1:35-44. [Medline] [Order article via Infotrieve]
15. Pasic M. Endothelial-cell seeding with microvascular omental cells onto small-diameter prosthetic vascular grafts in a canine model. Habilitation. Zurich, Switzerland: The University of Zurich; 1994:79-82.
16. Anderson JS, Price TM, Hanson SR, Harker LA. In vitro endothelialization of small-caliber vascular grafts. Surgery. 1987;101:577-586. [Medline] [Order article via Infotrieve]
17.
Vojta JC, Via DP, Butterfield CE, Zetter BR.
Identification and isolation of endothelial cells based
on their increased uptake of acetylated-low density
lipoprotein. J Cell Biol. 1984;99:2034-2040.
18. Hsu SU, Raine L, Fanger H. Use of avidin-biotin-peroxidase complex (ABC) in immunoperoxidase techniques: a comparison between ABC and unlabeled antibody (PAP) procedures. J Histochem Cytochem. 1981;29:577-580. [Abstract]
19. Müller-Glauser W, Bay U, Lehmann KH, Turina M. An improved procedure for enzymatic harvesting of highly purified canine venous endothelial cells for experimental small diameter vascular prostheses. Ann Vasc Surg. 1989;3:134-139. [Medline] [Order article via Infotrieve]
20. Zilla P, Siedler S, Fasol R, Sharefkin JB. Reduced reproductive capacity of freshly harvested endothelial cells in smokers: a possible shortcoming in the success of seeding. J Vasc Surg. 1989;10:143-148. [Medline] [Order article via Infotrieve]
21. Schrötter D, Spiess E, Paweletz N, Benker R. A procedure for rupture free preparation of confluently grown monolayer cells for scanning electron microscopy. J Electr Microsc Techn. 1984;1:219-225.
22. Cutler SJ, Ederer F. Minimum utilization of the life table method in analyzing survival. J Chron Dis. 1958;8:699-712. [Medline] [Order article via Infotrieve]
23. Rutherford RM, Nishikimi N. Graft thrombosis and thromboembolic complications. In: Rutherford RB, ed. Vascular Surgery. 3rd edition. Philadelphia, Pa: WB Saunders Co; 1989:501-510.
24. Scott SM, Barth MG, Gaddy LR, Ahl ET Jr. The role of circulating cells in the healing of vascular prostheses. J Vasc Surg. 1994;19:585-593. [Medline] [Order article via Infotrieve]
25. Williams SK, Kleinert LB, Rose D, McKenney S. Origin of endothelial cells that line expanded polytetrafluoroethylene vascular grafts sodded with cells from microvascularized fat. J Vasc Surg. 1994;19:594-604. [Medline] [Order article via Infotrieve]
26. Cantelmo NL, Quist WC, Lo Gerfo FW. Quantitative analysis of anastomotic intimal hyperplasia in paired Dacron and PTFE grafts. J Cardiovasc Surg. 1989;30:910-915. [Medline] [Order article via Infotrieve]
27. Chervu A, Moore WS. An overview of intimal hyperplasia. Surg Gynecol Obstet. 1990;171:433-447. [Medline] [Order article via Infotrieve]
28. Angelini GD, Bryan AJ, Williams HMJ, Soyombo AA, Williams A, Tovey J, Newby AC. Time-course of medial and intimal thickening in pig venous arterial grafts: relationship to endothelial injury and cholesterol accumulation. J Thorac Cardiovasc Surg. 1992;103:1093-1103. [Abstract]
29. Clowes AW, Clowes MM, Reidy MA. Kinetics of cellular proliferation after arterial injury, III: endothelial and smooth muscle growth in chronically denuded vessels. Lab Invest. 1986;54:295-303. [Medline] [Order article via Infotrieve]
30. Imparato AM, Bracco A, Geun EK, Zeff R. Intimal and neointimal fibrous proliferation causing failure of arterial reconstruction. Surgery. 1972;72:1007-1017.
31. Ip JH, Fuster V, Badimon L, Badimon J, Taubman MB, Chesebro JH. Syndromes of accelerated atherosclerosis: role of vascular injury and smooth muscle cell proliferation. J Am Coll Cardiol. 1990;15:1667-1687. [Abstract]
32. Clagett GP. Morphogenesis and clinicopathologic characteristics of recurrent carotid disease. J Vasc Surg. 1986;3:10-23. [Medline] [Order article via Infotrieve]
33. Healy DA, Zierler RE, Nicholls SC, Clowes AW, Primozich JF, Bergelin RO, Strandness DE Jr. Long-term follow-up and clinical outcome of carotid restenosis. J Vasc Surg. 1989;10:662-668. [Medline] [Order article via Infotrieve]
34. Vroegindeweij D, Kemper FJ, Tielbeek AV, Buth J, Landman G. Recurrence of stenoses following balloon angioplasty and Simpson atherectomy of the femoro-popliteal segment: a randomised comparative 1-year follow-up study using colour flow duplex. Eur J Vasc Surg. 1992;6:164-171. [Medline] [Order article via Infotrieve]
35. Kuntz RE, Safian RD, Levine MJ, Reis GJ, Diver DJ, Baim DS. Novel appproach to the analysis of restenosis after the use of three new coronary devices. J Am Coll Cardiol. 1992;19:1493-1499. [Abstract]
36. Graham LM, Brothers TE, Vincent CK, Burkel WE, Stanley JC. The role of an endothelial cell lining in limiting distal anastomotic intimal hyperplasia of 4-mm-I.D. Dacron grafts in a canine model. J Biomed Mater Res. 1991;25:525-533. [Medline] [Order article via Infotrieve]
37. Szilagyi DE, Smith RF, Elliott JP, Allen HM. Long-term behavior of a Dacron arterial substitute: clinical, roentgenologic and histologic correlations. Ann Surg. 1965;162:453-477. [Medline] [Order article via Infotrieve]
38. Selman SH, Rhodes RS, Anderson JM, DePalma RG, Clowes AW. Atheromatous changes in expanded polytetrafluoroethylene grafts. Surgery. 1980;87:630-637. [Medline] [Order article via Infotrieve]
39. Lo Gerfo FW, Quist WC, Nowak MD, Crawshaw HM, Haudenschild CC. Downstream anastomotic hyperplasia: a mechanism of filure in Dacron arterial grafts. Ann Surg. 1983;197:479-483. [Medline] [Order article via Infotrieve]
40. Block PC, Myler RK, Stertzer S, Fallon JT. Morphology after transluminal angioplasty in human beings. N Engl J Med. 1981;305:382-385. [Medline] [Order article via Infotrieve]
41. Clowes AW, Reidy MA. Prevention of stenosis after vascular reconstruction: pharmacologic control of intimal hyperplasia—a review. J Vasc Surg. 1991;13:886-891.
42. Morinaga K, Okadome K, Kuroki M, Miyazaki T, Muto Y, Inokuchi K. Effect of wall shear stress on intimal thickening of arterially transplanted autogenous veins in dogs. J Vasc Surg. 1985;2:430-433. [Medline] [Order article via Infotrieve]
43. Lyon RT, Runyon-Hass A, Davais HR, Glagov S, Zarins CK. Protection from atherosclerotic lesion formation by reduction of artery wall motion. J Vasc Surg. 1987;5:59-67. [Medline] [Order article via Infotrieve]
44.
Ferns GAA, Raines EW, Sprugel KH, Motani AY, Reidy MA,
Ross R. Inhibition of neointimal smooth muscle cell
accumulation after angioplasty by an antibody to PDGF.
Science. 1991;253:1129-1132.
45. Olson NE, Chao S, Lindner V, Reidy M. Intimal smooth muscle cell proliferation after balloon catheter injury: the role of basic fibroblast growth factor. Am J Pathol. 1992;140:1017-1023. [Abstract]
46. Burgess WH, Maciag T. The heparin-binding (fibroblast) growth factor family of proteins. Annu Rev Biochem. 1989;58:576-606.
47. Ullrich A, Schlessinger J. Signal tranduction by receptors with tyrosine kinase activity. Cell. 1990;61:203-212. [Medline] [Order article via Infotrieve]
48. Turnbull JE, Gallagher JT. Heparan sulfate: functional role as a modulator of fibroblast growth factor activity. Biochem Soc Trans. 1993;21:477-482. [Medline] [Order article via Infotrieve]
49. Reiland J, Rapraeger AC. Heparan sulphate proteoglycan and FGF receptor target basic FGF to different intracellular destination. J Cell Sci. 1993;105:1085-1093. [Abstract]
50. David G. Integral membrane heparan sulfate proteoglycans. FASEB J. 1993;7:1023-1030. [Abstract]
51.
Kan M, Wang F, Xu J, Crabb WC, Hou J, McKeehen
WL. An essential heparin-binding domain in the fibroblast
growth factor receptor kinase. Science. 1993;259:1918-1921.
52.
Lindner V, Reidy MA. Proliferation of smooth
muscle cells after vascular injury is inhibited by an antibody against
fibroblast growth factor. Proc Natl Acad Sci
U S A. 1991;88:3739-3743.
53. Schoen FJ, Castellot JJ Jr. Vascular graft intimal fibrous hyperplasia: prospects for pharmacological inhibition. J Vasc Surg. 1991;13:758-761. [Medline] [Order article via Infotrieve]
54. Chervu A, Moore WS, Quinones-Baldrich WJ, Henderson T. Efficacy of corticosteroids in suppression of intimal hyperplasia. J Vasc Surg. 1989;10:129-134. [Medline] [Order article via Infotrieve]
55. O'Malley MK, McDermott EW, Mehigan D, O'Higgins NJ. Role for prazosin in reducing the development of rabbit intimal hyperplasia after endothelial denudation. Br J Surg. 1989;76:936-938. [Medline] [Order article via Infotrieve]
56. El-Sanadiki MN, Cross KS, Murray JJ, Schuman RW, Mikat E, McCann RL, Hagen P-O. Reduction of intimal hyperplasia and enhanced reactivity of experimental vein bypass grafts with verapamil. Ann Surg. 1990;212:87-96. [Medline] [Order article via Infotrieve]
57. Fanelli C, Arnoff R. Restenosis following coronary angioplasty. Am Heart J. 1990;119:357-368. [Medline] [Order article via Infotrieve]
58. Kouchi Y, Esato K, O'Hara M, Zempo N. Effect of prostaglandin I2 analogue TRK-100 on the suppression of intimal fibrous proliferation. J Vasc Surg. 1992;16:232-238. [Medline] [Order article via Infotrieve]
59. Vashisht R, Sian M, Franks PJ, O'Malley MK. Long-term reduction of intimal hyperplasia by the selective alpha-1 adrenergic antagonist doxazosin. Br J Surg. 1992;79:1285-1288. [Medline] [Order article via Infotrieve]
60. Dryjski M, Mikat E, Bjornsson TD. Inhibition of intimal hyperplasia after arterial injury by heparins and heparinoid. J Vasc Surg. 1988;8:623-633. [Medline] [Order article via Infotrieve]
61. Hagen P-O, Wang Z-G, Mikat EM, Hackel DB. Antiplatelet therapy reduces aortic intimal hyperplasia distal to small diameter vascular prostheses (PTFE) in nonhuman primates. Ann Surg. 1982;195:328-339. [Medline] [Order article via Infotrieve]
62.
Murday AJ, Gershlick AH, Syndercombe-Court YD, Mills P,
Lewis CT. Intimal thickening in autogenous vein grafts in
rabbits: influence of aspirin and dipyridamole.
Thorax. 1984;39:457-461.
63. Clyne CAC, Archer TJ, Atuhaire LK, Chant AD, Webster JH. Random control trial of a short course of aspirin and dipyridamole (Persantin) for femorodistal grafts. Br J Surg. 1987;74:246-248. [Medline] [Order article via Infotrieve]
64. McCollum C, Alexander C, Kenchington G, Franks PJ, Greenhalgh R. Antiplatelet drugs in femoropopliteal vein bypasses: a multicenter trial. J Vasc Surg. 1991;13:150-161. [Medline] [Order article via Infotrieve]
65. Henderson WG, Goldman S, Copeland JG, Moritz TE, Harker LA. Antiplatelet or anticoagulant therapy after coronary artery bypass surgery. Ann Intern Med. 1989;111:743-750.
66. Clowes AW. The role of aspirin in enhancing arterial graft patency. J Vasc Surg. 1986;3:381-385. [Medline] [Order article via Infotrieve]
67. Allen KE, Varty K, Jones L, Sayers RD, Bell PRF, London NJM. Human venous endothelium can promote intimal hyperplasia in a paracrine manner. J Vasc Surg. 1994;19:577-584. [Medline] [Order article via Infotrieve]
68. Williams SR. Regulation of intimal hyperplasia: do endothelial cells participate? Lab Invest. 1991;64:721-723. [Medline] [Order article via Infotrieve]
69. Sterpetti AV, Hunter WJ, Schultz RD, Sugimoto JT, Blair EA, Hacker K, Chasan P, Valentine J. Seeding with endothelial cells derived from the microvessels of the omentum and from the jugular vein: a comparative study. J Vasc Surg. 1988;7:677-684. [Medline] [Order article via Infotrieve]
70. Wang Z, Du W, Li G, Pu L, Sharefkin JB. Rapid cellular luminal coverage of Dacron inferior vena cava prostheses in dogs by immediate seeding of autogenous endothelial cell derived from omental tissue: results of a preliminary trial. J Vasc Surg. 1990;12:168-179. [Medline] [Order article via Infotrieve]
71. Kern PA, Knedler A, Eckel RH. Isolation and culture of microvascular endothelium from human adipose tissue. J Clin Invest. 1983;71:1822-1829.
72. Takahashi K, Goto T, Mukai K, Sawasaki Y, Hata J. Cobblestone monolayer cells from human omental adipose tissue are possible mesothelial, not endothelial. In Vitro Cell Dev Biol. 1989;25:109-110. [Medline] [Order article via Infotrieve]
73. Visser MJT, van Bockel JH, van Muijen GNP, van Hinsbergh VWM. Cells derived from omental fat tissue and used for seeding vascular prostheses are not endothelial in origin: a study on the origin of epitheloid cells derived from omentum. J Vasc Surg. 1991;13:373-381. [Medline] [Order article via Infotrieve]
74. Nicholson LJ, Clarke JM, Pittilo RM, Machin SJ, Woolf N. The mesothelial cell as a non-thrombogenic surface. Thromb Haemost. 1984;52:102-104. [Medline] [Order article via Infotrieve]
75. Hernando A, Garcìa-Honduvilla N, Bellòn JM, Buàn J, Navlet J. Coating for vascular prostheses: mesothelial cells express specific markers for muscle cells and have biological activity similar to that of endothelial cells. Eur J Vasc Surg. 1994;8:531-536. [Medline] [Order article via Infotrieve]
76. Coene MC, Solheid C, Claeys M, Herman AG. Prostaglandin production by cultured mesothelial cells. Arch Int Pharmacodyn Ther. 1981;249:316-318. [Medline] [Order article via Infotrieve]
77.
van Hinsbergh VWM, Kooistra T, Scheffer MA, van Bockel
JH, van Muijen GNP. Characterization and fibrinolytic properties
of human omental tissue mesothelial cells: comparison with
endothelial cells. Blood. 1990;75:1490-1497.
78. Clarke JMF, Pittilo RM, Nicholson LJ, Woolf N, Marston A. Seeding Dacron arterial prostheses with peritoneal mesothelial cells: a preliminary morphological study. Br J Surg. 1984;71:492-494. [Medline] [Order article via Infotrieve]
79. Jaffe EA, Nachman RL, Becker CG, Minick CR. Culture of human endothelial cells derived from umbilical veins: identification by morphologic and immunologic criteria. J Clin Invest. 1973;52:2745-2756.
80. Noishiki Y, Yamane Y, Tolmizawa Y, Okoshi T, Satoh S, Wildevuur CRH, Suzuki K. Rapid endothelialization of vascular prostheses by seeding autologous venous tissue fragments. J Thorac Cardiovasc Surg. 1992;104:770-778. [Abstract]
81. Anders E, Alles JU, Delvos U, Poetzsch B, Preissner KT, Mueller-Berghaus G. Microvascular endothelial cells from human omental tissue: modified method for long-term cultivation and new aspects of characterization. Microvasc Res. 1987;34:239-249. [Medline] [Order article via Infotrieve]
82. Alles JR, Bosslet K. Immunohistochemical and immunochemical characterization of a new endothelial cell-specific antigen. J Histochem Cytochem. 1986;34:209-214. [Abstract]
83.
Owen WG, Esmon CT. Functional properties of an
endothelial cell cofactor for thrombin-catalyzed
activation of protein. J Biol Chem. 1981;256:5532-5535.
84. De Bault LE, Esmon NL, Smith GP, Esmon CT. Localization of thrombomodulin antigen in rabbit endothelial cells in culture. Lab Invest. 1986;54:179-187. [Medline] [Order article via Infotrieve]
85.
Maruyama I, Bell CE, Majerus PW.
Thrombomodulin is found on endothelium of arteries,
veins, capillaries, and lymphatics, and on syncytiotrophoblast of human
placenta. J Cell Biol. 1985;101:363-371.
86. Stansby G, Shukla N, Fuller B, Hamilton G. Cells derived from omental fat tissue and used for seeding vascular prostheses are not endothelial in origin. J Vasc Surg. 1992;15:583-584. Letter. [Medline] [Order article via Infotrieve]
87. Zilla P, Fasol R, Preiss P, Kadletz M, Deutsch M, Schima H, Tsangaris S, Groscurth P. Use of fibrin glue as a substrate for in vitro endothelialization of PTFE vascular grafts. Surgery. 1989;105:515-522. [Medline] [Order article via Infotrieve]
88. Zetter BR. The endothelial cell of large and small blood vessels. Diabetes. 1981;30:284-286.
89. Stansby G, Shukla N, Hamilton G, Jeremy J. Comparison prostanoid synthesis in cultured human vascular endothelial cells derived from omentum and umbilical vein. Eur J Vasc Surg. 1991;5:501-506. [Medline] [Order article via Infotrieve]
90.
Kwast TH, Stel HV, Cristen E, Bertina RM, Veerman
ECI. Localization of factor VIII-procoagulant antigen: an
immunohistological survey of the human body using
monoclonal antibodies. Blood. 1986;67:222-227.
91.
Weibel ER, Palade GE. New cytoplasmatic
components in arterial endothelium.
J Cell Biol. 1964;23:101-112.
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 B. S Lewis, M. Y Flugelman, A. Weisz, I. Keren-Tal, and W. Schaper Angiogenesis by gene therapy: a new horizon for myocardial revascularization? Cardiovasc Res, September 1, 1997; 35(3): 490 - 497. [Abstract] [Full Text] [PDF]
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