Gene Therapy (2012) 19, 630–636
& 2012 Macmillan Publishers Limited All rights reserved 0969-7128/12
www.nature.com/gt
REVIEW
Vein graft failure: current clinical practice and potential
for gene therapeutics
S Wan1, SJ George2, C Berry3,4 and AH Baker3
Autologous saphenous vein is commonly used as a conduit to bypass atherosclerotic lesions in coronary and femoral arteries.
Despite the wide use of arterial conduits, which are less susceptible to complications and failure, as alternative conduits, the
saphenous vein will continue to be used in coronary artery bypass grafting until acceptable alternative approaches are evaluated.
Hence, preservation of vein graft patency is essential for the long-term success. Gene therapy is attractive in this setting as an
ex-vivo technology to genetically manipulate the conduit before grafting. The use of safe and efficient vectors for delivery
is a necessity as well as a strategy to improve patency in the long term. Here, we review the current clinical practice, the
pathogenesis of bypass graft failure and adenovirus-mediated gene therapy strategies designed to improve late vein graft failure
by modulation of smooth muscle cells in the vein wall.
Gene Therapy (2012) 19, 630–636; doi:10.1038/gt.2012.29; published online 29 March 2012
Keywords: adenovirus; metalloproteinases; vein grafting; vascular disease
CLINICAL USE OF AUTOLOGOUS SAPHENOUS VEIN
Autologous saphenous vein is used as a conduit to bypass atherosclerotic lesions both in the coronary artery (coronary artery bypass
grafting (CABG))1–4 and in femoral arteries (infrainguinal bypass graft
surgery). Even with the rapid development of intracoronary stents,
certain advantages of CABG over percutaneous coronary intervention
(PCI) are likely to continue in the foreseeable future, particularly in
diabetic patients and in those with left main and multivessel coronary
diseases.5 The autologous saphenous vein remains a widely used
conduit for CABG (Figure 1); however, late vein graft failure is the
Achilles’ heel of this operation. Nearly, half of the patients may require
reoperation 10–15 years after CABG to alleviate symptoms and treat
vein graft occlusion.2,5 In the United States alone, the estimated direct
and indirect cost in treating coronary heart disease was more than
US$177 billion in 2010.6 To date, despite a very large number of
clinical trials, apart from lipid-lowering drugs,7 no other pharmacological agents appear effective in preventing early vein graft remodelling or subsequent accelerated atherosclerosis. As such, the fate of vein
grafts remains largely unchanged even after decades of technical
development. Some recent observations indicated that the vein graft
patency rates may be very poor. For instance, in the PREVENT IV
trial,8 1829 patients had follow-up angiography 12–18 months after
CABG that showed per-patient vein graft failure rate was 445% (each
patient had at least two vein grafts), while per-graft vein graft
occlusion rate was 426%. In the latest ROOBY trial,9 the incidence
of vein graft occlusion during the first postoperative year in 894
patients was 414% (following conventional harvesting) or up to 25%
(following endoscopic harvesting). Such failure rates are similar to
those reported in 1996 by Fitzgibbon et al.3 Knowledge about the
pathophysiology of vein graft failure has significantly enhanced
recently (this is discussed in detail below). Furthermore, distal
coronary ‘run-off’ can affect the long-term vein graft patency.10–12
As the severity of disease in the native coronary recipient artery
increases, distal run-off may reduce. In the Radial Artery Patency
and Clinical Outcomes (RAPCO) trial, saphenous vein graft patency
(measured by the protocol-directed angiograms) was demonstrated in
80% of subjects at 9 years.11 However, on closer examination it is
apparent that one of the predictors of vein graft patency was an
anastomosis with the left anterior descending coronary artery, which is
now rarely performed. The initial calibre of the recipient coronary
artery (that is, a diameter of at least 2 mm) is another predictor of
long-term graft patency.12 In a recent randomised controlled trial
conducted at 11 Veterans Affairs medical centres in United States
undergoing first-time elective CABG,13 the 1-year graft patency of the
radial artery conduits was not significantly greater than venous grafts.
In fact, the 7-year patency rates for the vein grafts were also similar to
the radial artery conduits in a randomised Australian trial11 as well as
in a retrospective French series with 20-year follow-up.14 The relevance
of vein graft failure, therefore, should not be overlooked.
Given the large number of CABG patients living with late vein graft
failure, and the complexities of their clinical management, their
cardiac morbidity and mortality is an increasing challenge for primary
and secondary care clinicians. When revascularisation is performed in
CABG patients, acute and long-term outcomes are much worse than
in patients without prior CABG.15 PCI in redo CABG carries a
fourfold higher risk of death compared with the index procedure.15
Patients with recurrent angina after CABG are usually elderly and
co-morbid health problems are very common.16–18 Redo CABG is
uncommon and only performed in o2% of invasively managed acute
coronary syndrome patients.17 In the United Kingdom, of 161 patients
who had PCI 126±65 months after CABG, cardiac death, myocardial
infarction or repeat PCI occurred in 14% of them by 13 months
1Division of Cardiothoracic Surgery, Prince of Wales Hospital, The Chinese University of Hong Kong, Hong Kong, China; 2School of Clinical Sciences, Bristol Heart Institute,
University of Bristol, Bristol, UK; 3Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK and 4Golden Jubilee National Hospital, Clydebank, UK
Correspondence: Professor AH Baker, Institute of Cardiovascular and Medical Sciences BHF Glasgow, Cardiovascular Research Centre, University of Glasgow, 126 University
Place, Glasgow G12 8TA, UK.
E-mail: [email protected]
Received 16 December 2011; revised 27 February 2012; accepted 27 February 2012; published online 29 March 2012
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(mainly related to repeat PCI (12%)). In the United Kingdom overall,
of the 33 652 PCIs performed in 1999/2000, 907 (2.7%) occurred in
patients with prior CABG. Only 1 in 10 procedures was reported as
successful and 1.3 and 1.0% of patients experienced in-hospital
myocardial infarction or death, respectively.19 Ten years on 2009/
2010, 8.4% of all patients undergoing PCI had a history of prior
CABG and procedure-related outcomes remained disappointingly
similar (1 in 10 procedural success, in-hospital death rate (1.0%)
and 30-day mortality (1.5%)).
By contrast secondary prevention drug therapies have beneficial effects
in symptomatic patients with prior CABG.20–23 In contrast to clinical
trials involving revascularisation, patients with prior CABG are usually
not excluded from drug trials and the evidence for secondary prevention
medical therapies in patients with prior CABG is fairly robust. In acute
coronary syndrome patients with prior CABG, health outcomes are also
improved by treatment with anti-platelet drug therapies.21–23 Furthermore, new evidence-based medicines continue to emerge including more
potent anti-platelet drugs such as prasugrel24 and ticagrelor25 and safer
anti-coagulants, such as fondaparinux.26 However, to a great extent,
these treatments have mainly palliative effects in patients with progressive
vein graft disease and more definitive preventative strategies are needed
to prevent vein graft disease occurring in the first place.
Figure 1 Autologous saphenous vein graft remains to be one of the most
commonly used conduits for CABG. (a) Saphenous vein harvesting during
CABG; (b) the proximal anastomoses (on the aorta) of two saphenous vein
grafts have been constructed.
PATHOGENESIS OF VEIN GRAFT DISEASE
Detailed studies using mainly pre-clinical in-vivo models have enabled
us to construct an approximate timeline of the events that occur in
vein grafts and ultimately lead to reduced patency (Figure 2). Immediately after implantation of the vein as a graft into the arterial
circulation a complex series of biological events is initiated in the
vein. Within the first few days after implantation many vein grafts fail
due to thrombosis, stimulated by endothelial injury.27 Additionally,
in the first 24 h vein grafts undergo a period of ischaemia followed by
EC injury → thrombosis
→ early failure
Vein
EC and VSMC injury
Ischaemia → O2− & ROS →
EC and SMC cytotoxicity
Superimposed
Atherosclerosis
Inflammation: neutrophils
and monocytes
→ oxidative stress
ECM remodelling,
VSMC migration and
proliferation, and
ECM synthesis
Late vein graft failure:
Intimal thickening
Figure 2 Processes involved in vein graft failure. Damage to the endothelium leads to thrombosis formation and early vein graft failure. Late vein graft failure
is predominantly due to intimal thickening and superimposed atherosclerosis. Vessel wall damage and ischaemia lead to inflammation and vessel wall
remodelling and intimal thickening.
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reperfusion, resulting in the generation of superoxide and other
reactive oxygen species that trigger cytotoxicity of endothelial and
vascular smooth muscle cells (VSMCs).28,29 The grafted vein is then
targeted by an acute inflammatory response involving neutrophil and
mononuclear cell recruitment and oxidative stress persists.28 Extracellular matrix (ECM) remodelling and migration of medial VSMCs
into the intima occurs within the first week after implantation. Once
in the intima the VSMCs proliferate at a heightened rate and deposit
newly synthesised ECM, thereby contributing further to the intimal
thickening (for a review, see Newby30). The resultant thickened intima
is highly susceptible to superimposed accelerated atherosclerosis due
to the infiltration of monocytes that differentiate into macrophages
and develop into foam cells after lipid uptake (for a review, see
Schwartz et al.31). The resultant lesions within the vein graft are
diffuse, concentric, friable plaques with poorly developed or absent
fibrous caps.32,33
The surgical preparation of saphenous veins for the surgical
procedure causes considerable removal of the endothelium34 and a
‘no touch’ surgical preparation of the vein leads to superior vein graft
patency.35 Endothelial denudation allows platelet and leukocyte adhesion immediately after graft implantation that precipitates thrombosis,
as well as acting as an initiating factor for intimal thickening.36–39
Adherent (activated) platelets generate a large number of substances,
including thromboxane A2, endothelin-1, serotonin, platelet-derived
growth factor, platelet factor IV, fibrinogen, fibronectin, thrombospondin, von Willebrand factor, b-thromboglobulin and reactive oxygen species, which activate VSMCs in the medial layer of the vein graft.
Activated VSMCs are more synthetic and have heightened proliferation and migration rates (for a review, see Owens et al.40). As a result,
VSMCs migrate from the media into the intima where they proliferate
and deposit ECM, leading to the thickening of the intimal layer.
Moreover, coagulation factors and fibrinolysis products are also
important factors that contribute to VSMC activation and intimal
thickening (for a review, see Jeremy et al.41).
Enhanced leukocyte binding is enabled due to increased adhesion
molecule expression within the vein graft after implantation.42,43
Consequently, soluble forms of the adhesion molecules such
as vascular cell adhesion molecule-1 and intercellular adhesion
molecule-1 have been proposed as potential inhibitors of vein graft
disease.44 Leukocytes (neutrophils and monocytes) also participate in
the induction of intimal thickening in the vein graft.37–39 Adherent
leukocytes, particularly neutrophils, release numerous pro-inflammatory substances, including leukotrienes, interleukins, histamine,
tumour necrosis factor, platelet activating factor and proteases, all of
which promote VSMC proliferation and migration (for a review,
see Segel et al.45). Monocyte adhesion also occurs early after vein graft
implantation and promotes intimal thickening.46 Monocytes invade
into the intima and differentiate into resident macrophages that
transform into the foam cells, after uptake of lipid, which are a
major contributor to atherogenesis. Similarly to adherent leukocytes,
macrophages release a plethora of factors that promote intimal
thickening including proteases such as matrix-degrading metalloproteinases (MMPs), growth factors, cytokines and reactive oxygen
species.
Endothelial denudation also results in the loss of vasculoprotective
systems (principally nitric oxide (NO) and prostacyclin as well as
heparin-like substances) that inhibit thrombosis and inflammation.
The loss of these systems permits thrombosis and inflammation
within the vein graft and renders the graft prone to intimal thickening
and subsequent atherogenesis. Moreover, in addition to the inhibition
of platelet and leukocyte adhesion, NO, prostacyclin and heparin-like
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substances inhibit other processes that contribute to intimal thickening such as VSMC proliferation and migration and protease expression (for a review, see Ramli et al.47).
The endothelial lining of the vein graft is in fact repaired within 1–2
weeks as a result of proliferation and migration of endothelial cells48
and this is thought to repress thrombogenicity and intimal thickening.49 The repaired endothelial lining is however markedly dysfunctional in part due to the arterial pressure that the vein is now subjected
to.50,51 After implantation, the vein graft, which has been subjected
only to an internal pressure of 10 mm Hg in the venous circulation, is
immediately subjected to the arterial pressure (100 mm Hg) as well as
immediate increases in flow, longitudinal wall (shear) stress, circumferential, radial and pulsatile deformation and stress.52 Numerous
genes are upregulated in response to the altered shear stress, including
adhesion molecules,53,54 and therefore this is a substantial promoter
of intimal thickening. Since the wall of the saphenous vein graft is
considerably thinner than the recipient artery and lacks connective
and elastic tissue layers that characterises arteries, it undergoes an
adaptation to the arterial environment by thickening or ‘remodelling’,
possibly to resist the altered haemodynamic stresses. This predominantly involves VSMC proliferation and deposition of ECM.55,56 This
process of vein graft remodelling also intrinsically alters intragraft
haemodynamics. The growth of the graft is asymmetric that may also
promote chaotic blood flow patterns,57 resulting in enhanced platelet
and leukocyte adhesion, and thrombosis that in turn can augment
intimal thickening.
The blood vessel wall is a highly organised structure of cells and
ECM (Figure 3; for a review, see Adiguzel et al.58). The ECM is
synthesised by the VSMCs within the arterial wall, which then
interacts with the VSMCs through cell-to-matrix contacts via integrins. In the medial layer of the blood vessel wall, VSMCs are
surrounded by basement membrane, which is in turn embedded in
fibrillar collagens type I, III and V, collagen type XVIII, elastin,
fibronectin and glycoproteins including proteoglycans and cartilage
oligomeric matrix protein (thrombospondin 5). Contact of VSMCs
with the ECM via integrins retards VSMC migration and proliferation
(for a review, see Newby59). More recently, it has been established that
cell-to-cell contacts via cadherins also retard VSMC proliferation.60,61
To enable VSMC migration and proliferation the ECM and cadherin
contacts must be digested by proteases including MMPs (for a review,
see Newby59). Upregulation and activation of MMPs occurs as a result
of surgical preparation of the saphenous vein, and during intimal
thickening in human organ cultures and experimental vein grafts.62,63
Furthermore, direct proof of the involvement of MMPs in vein graft
intimal thickening has been provided by the observation that overexpression of the endogenous MMP inhibitors tissue inhibitors of
MMPs (TIMPs) significantly retarded intimal thickening.64–67
Overproduction of superoxide (O2 ) is an important pathological
component of vein graft failure, the principal source being nicotinamide adenine dinucleotide phosphate oxidase (for a review, see Jeremy
et al.68). Nicotinamide adenine dinucleotide phosphate oxidase is
upregulated by many platelets and leukocytes factors such as entothelin-1, leukotrienes and serotonin.69 O2 promotes VSMC proliferation and migration and upregulates MMPs (for a review, see Jeremy
et al.68). O2 also reacts with NO to produce reactive nitrogen species
reducing NO bioavailability, which is itself associated with vein graft
disease as mentioned above. Medial and intimal regions of porcine
vein grafts contain high levels of nitrated tyrosine, an index of
peroxynitrite formation, indicating that both NO and O2 must be
present in order for the reaction to occur.70 Thus, it has been
suggested that O2 formation compromises vein graft patency
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Cell-cell contact:
Cadherins
Basement membrane:
Collagen type IV
Laminin
Perlecan
Nidogen
Contractile
VSMC
Interstitial ECM:
Collagen type I, III, V, XVIII
Elastin, Fibronectin
Glycoproteins
Cell-matrix contact:
Integrins
Dismantled
cell-cell contact
Cleaved interstitial
ECM
Cleaved
basement
membrane
Activated
synthetic
VSMC
MMPs
MMPs
Altered cellmatrix contact
TIMP gene
therapy
Transitional matrix: versican, osteopontin,
hyaluronan, fibronectin, collagen type VIII,
tenascin, syndecans, biglycan, lumican
Figure 3 Schematic diagram of VSMC and ECM proteins. (a) In the normal vessel, VSMC is in the contractile state. Through integrins they form cell-matrix
contacts with the basement membrane, which is in turn surrounded by interstitial ECM. Cell-cell contacts are mediated via cadherins. (b) In response to
injury of the vein graft, VSMCs become activated and synthetic. MMPs are secreted by VSMCs and inflammatory cells which have entered the vessel wall.
Cleavage of basement membrane and interstitial ECM proteins and cell-cell contacts by MMPs permits migration and proliferation. Activated VSMCs secrete
and form contacts with new ‘transitional ECM proteins’, which promotes VSMC migration and proliferation. Consequently, overexpression of the endogenous
MMP inhibitors, TIMPs, has been assessed as a therapy for late vein graft failure.
through a reduction of NO as well as direct effects mentioned above.
Hypoxia may also have a key role in mediating vein graft disease.71
Implicitly, surgical dissection of the saphenous vein disconnects the
vasa vasorum, a microvessel complex that infiltrates and oxygenates
the large blood vessels and therefore results in hypoxia within the graft
and intimal thickening. Hypoxia promotes O2 formation via
activation of nicotinamide adenine dinucleotide phosphate oxidase,
xanthine oxidase and mitochondrial respiratory chain and prolonged
hypoxia upregulates the expression of numerous genes that include
those that are key regulators of vein graft disease (for a review, see
Jeremy et al.68). Consequently, the regeneration of the vasa vasorum
may constitute an important adaptation of vein grafts to arterial
conditions and to repair and reintegration of the microvascular system. Support for this suggestion is gained from the
observation that in vein grafts subjected to external stenting increased
formation of adventitial microvessels occurs concurrently with
reduced intimal thickening.72
OPPORTUNITIES FOR GENE THERAPY IN BYPASS GRAFTING
Despite a very large number of clinical trials, no specific pharmacological agents appear to have beneficial effects on early vein graft
remodelling or subsequent accelerated atherosclerosis. For this reason,
alternative and novel therapeutic strategies are urgently required.
Accordingly, a number of gene transfer strategies, using specific
genes delivered intraoperatively to either limit VSMC proliferation
or inflammation, or to improve endothelial function, appear to be
effective pre-clinically.
The E2F decoy oligonucleotide approach from the Dzau laboratory
using pressure-mediated delivery of ‘decoy oligonucleotides’ to prevent E2F-mediated transcription of pro-proliferative genes to promote
vein ‘arterialisation’ failed in late clinical trials (PREVENT) for both
coronary and peripheral grafts, despite encouraging pre-clinical and
phase I/II trial data.48,73–76 This highlights a number of important
issues, including the possible lack of utility of the anti-proliferative
strategy in the human setting, the potential limitations in the decoy
approach, the delivery methodology and (possibly) the limitations of
animal models utilised for pre-clinical studies. Further research into
decoy oligonucleotides has been conducted recently.77 A strategy to
decoy Egr-1 was employed in a rabbit model of vein graft interposition
grafts using a single intraoperative approach. Multiple time points
were tested after intervention (acute and chronic). The authors found
that a 60% inhibition of Egr-1 was achieved with a concomitant
decrease in cellular proliferation and the study found a reduction in
intimal thickness for the Egr decoy-treated samples compared with
controls.77 This demonstrates that alternative decoys may hold value
in the setting of vein graft neointima formation but assigning
differences between the Egr-1 approach and the E2F approach already
tested clinically would be important for translational aspirations.
To date, no clinical gene therapy studies in the bypass graft setting
have been conducted.
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VECTORS FOR GENE DELIVERY TO BYPASS GRAFTS
Delivery of the therapeutic gene must occur within CABG surgery.
The ‘clinical window’ is short. Vector systems thus must be efficient to
achieve efficient gene transfer into the target graft within the window
of access. Many delivery systems have been evaluated and tested using
both reporter gene systems and therapeutic transgenes—these include
both viral and non-viral vectors, the latter more efficient in general
due to the higher level of cell gene transfer that can be achieved in
general. Adenovirus (Ad)-based vectors have become the most
favoured vectors for this task, albeit they come with some limitations
and have not yet been tested at the clinical level in the context of vein
graft gene therapy.
Ad is, however, a relatively efficient vector for gene delivery to the
vein. Pivotal studies in the 1990s described the role of the coxsackie
and adenovirus receptor and integrins in adenovirus type 5 (Ad5)
gene transfer.78,79 The interaction with coxsackie and adenovirus
receptor tethers the virus to the cell surface with subsequent engagement of the penton base RGD motif with integrins to mediate cellular
internalisation. However, the mechanism for gene transfer by Ad is not
clear since coxsackie and adenovirus receptor expression is not evident
on VSMCs.80,81 Early studies in the vasculature showed detrimental
effects of Ad vectors to the vasculature following the gene transfer.
For example, some early studies showed enhanced neointima formation following arterial gene transfer in rabbits as well as
high levels of inflammatory markers on endothelium;82 however, we
recently reported that there was no difference in inflammatory
markers in long-term pig grafts using Ad5 vectors.67 This may
represent differences in responses in different models (rabbit/pig)
and potential differences in virus quality control. Clearly, modulation
of virus infection to maintain/improve target cell infection within the
constraints imposed in the vein graft gene therapy setting would be
advantageous. Especially important are (1) considerations for maximal uptake into target cells within short time periods allowed for
access to the vein clinically, (2) reduction in the ability of human sera
to neutralise Ad5 through pre-existing immunity in many patients83
via specific modification of the Ad5 capsid or use of alternate
serotypes (although this may alter the efficiency of vascular
gene delivery), (3) use of helper-dependent Ad systems to provide
longer term gene therapy in the vasculature should this be a
requirement.84
STUDIES USING GENE THERAPY FOR VEIN GRAFTS
The majority of strategies for prevention of late vein graft failure have
focused on phenotypic modulation of the vessel wall, assessing
proliferation, migration and apoptosis. These aspects have been
discussed previously85 and reviewed recently in the context of graft
pathophysiology86 and here we bring the literature up to date with
recent original papers in this area. It has recently been demonstrated
that NogoB is a novel regulator of the vascular system87 and that
NogoB overexpression using the Ad5 approach significantly reduced
neointima formation in pig venous grafts.88 An interesting recently
published study89 focused on the concept that overexpression of
cyclooxygenase-1 might attenuate vein graft disease. The authors
utilised an Ad approach in rabbit jugular veins and assessed parameters at 4 weeks post grafting. It was shown that blood flow in
cyclooxygenase-1-treated vein grafts increased as well as in the lumen
area. Functional effects of cyclooxygenase-1 were observed when
assessed at 72 h. This demonstrates the benefit of short-term
Ad-mediated overexpression of relevant genes. In a rabbit model,
but using a different strategy, the effect of platelet-derived endothelial
cell growth factor gene transfer has also been evaluated.90 This strategy
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used polaxmer hydrogel at 20% to deliver plasmid DNA to the
adventitia of rabbit grafts in the presence of trypsin to further enhance
gene transfer. A significant reduction in neointima formation
was observed at both 2 and 8 weeks post grafting, primarily
through an anti-proliferative effect achieved through elevation of
haemoxygenase-1 mediated by therapeutic gene transfer.90
Since inflammation is also a key factor in vein graft disease,
chemokine receptor-2 has emerged as an effector of vein graft
pathology. Using a mouse model, a lentivirus expressing shRNA to
chemokine receptor-2 was evaluated. This intervention led to a
reduction in chemokine receptor-2 levels and a 38% reduction in
graft thickening, highlighting the potential of this knockdown strategy
and also the power of lentivirus vectors.91 However, production of
these vectors for assessment in larger animal models and ultimately in
man would be challenging but could be considered as an important
aim to achieve.
As discussed previously,85 the proteolytic system has a prominent
role in vein graft disease. A recent study developed an intriguing
system to probe this in the mouse in-vivo and human ex-vivo
models. The authors developed a chimeric gene consisting of the
receptor binding amino terminal fragment of urokinase-type
plasminogen activator and bovine trypsin inhibitor linked to
TIMP-1. Delivery of this vector blocked neointima formation in
both models.92
Targeting the TGFb system is also proven to be a popular approach
recently. Using a series of adenoviruses and the human ex-vivo model,
it was reported that fibromodullin was superior to decorin overexpression in reducing neointimal area and thickness in human
saphenous vein segments at 14 days.93 An alternate approach using
Activin A to alter the contractile properties of VSMCs, led to a
reduction in neointimal parameters in a rat model.94
Therefore, there remains a number of strategies of potential benefit
to the prevention of vein graft disease. Our focus has been on utilising
the properties of TIMP-3. TIMP-3, a member of the tissue inhibitors
of metalloproteinase family, has the ability to block both VSMC
migration and promote apoptosis, the latter requiring high concentrations of TIMP-3.95 First-generation Ad5-mediated overexpression
of TIMPs reduced neointimal formation in a human in-vitro model of
vein graft failure and ex-vivo adenoviral.66 It is important to note that
Ad-mediated overexpression of TIMP-3 leads to high levels of matrixassociated TIMP-3 around the VSMCs closest to lumen of the vessel. It
is likely that this provides an effective barrier to migration of the
VSMCs. In addition, VSMC apoptosis was observed but this occurred
only where high concentrations of TIMP-3 were observed and not
randomly throughout the vessel wall.66 We have recently performed
longer term experiments in a pig vein graft model and shown
sustained efficacy out to 3 months post gene transfer.67 This is
important since it illustrates that short-term transgene overexpression
leads to lasting effects on neointima formation. Taken together with
other studies, this presents a new opportunity to treat late vein graft
failure using an Ad gene therapy approach and is a goal that we are
aiming to test clinically in the future.
CONFLICT OF INTEREST
The authors declare no conflict of interest.
ACKNOWLEDGEMENTS
We thank the British Heart Foundation, the UK Medical Research Council and
the Hong Kong Research Grant Council Earmarked Grants for supporting
research on vein grafting in our laboratories. Professor Berry is supported by a
Senior Fellowship from the Scottish Funding Council.
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