Antisense oligonucleotide to proto-oncogene c-myb inhibits the formation of intimal hyperplasia in experimental vein grafts

miR579-3p is an inhibitory modulator of neointimal hyperplasia and transcription factors c-MYB and KLF4

Neointimal hyperplasia (IH) is a common vascular pathology that typically manifests in in-stent restenosis and bypass vein graft failure. Smooth muscle cell (SMC) phenotypic switching is central to IH, both regulated by some microRNAs, yet the role of miR579-3p, a scarcely studied microRNA, is not known. Unbiased bioinformatic analysis suggested that miR579-3p was repressed in human primary SMCs treated with different pro-IH cytokines. Moreover, miR579-3p was software-predicted to target both c-MYB and KLF4 - two master transcription factors known to promote SMC phenotypic switching. Interestingly, treating injured rat carotid arteries via local infusion of miR579-3p-expressing lentivirus reduced IH 14 days after injury. In cultured human SMCs, transfection with miR579-3p inhibited SMC phenotypic switching, as indicated by decreased proliferation/migration and increased SMC contractile proteins. miR579-3p transfection downregulated c-MYB and KLF4, and luciferase assays indicated miR579-3p's targeting of the 3'UTRs of the c-MYB and KLF4 mRNAs. In vivo, immunohistochemistry showed that treatment of injured rat arteries with the miR579-3p lentivirus reduced c-MYB and KLF4 and increased SMC contractile proteins. Thus, this study identifies miR579-3p as a previously unrecognized small-RNA inhibitor of IH and SMC phenotypic switch involving its targeting of c-MYB and KLF4. Further studies on miR579-3p may provide an opportunity for translation to develop IH-mitigating new therapeutics.

Gene Therapy for the Extension of Vein Graft Patency: A Review

The mainstay of treatment for long-segment small-vessel chronic occlusive disease not amenable to endovascular intervention remains surgical bypass grafting using autologous vein. The procedure is largely successful and the immediate operative results almost always favorable. However, the lifespan of a given vein graft is highly variable, and less than 50% will remain primarily patent after 5 years. The slow process of graft malfunction is a result of the vein's chronic maladaptive response to the systemic arterial environment, its primary component being the uncontrolled proliferation of vascular smooth muscle cells (SMCs). It has recently been suggested that this response might be attenuated through pre-implantation genetic modification of the vein, so-called gene therapy for the extension of vein graft patency. Gene therapy seems particularly well suited for the prevention or postponement of vein graft failure since: (1) the stimulation of SMC proliferation appears to largely be an early and transient process, matching the kinetics of current gene transfer technology; (2) most veins are relatively normal and free of disease at the time of bypass allowing for effective gene transfer using a variety of systems; and (3) the target tissue is directly accessible during operation because manipulation and irrigation of the vein is part of the normal workflow of the surgical procedure. This review briefly summarizes the current knowledge of the incidence and basic mechanisms of vein graft failure, the vector systems and molecular targets that have been proposed as possible pre-treatments, the results of experimental genetic modification of vein grafts, and the few available clinical studies of gene therapy for vascular proliferative disorders.

Gingerol Inhibits Serum-Induced Vascular Smooth Muscle Cell Proliferation and Injury-Induced Neointimal Hyperplasia by Suppressing p38 MAPK Activation

Purpose:

Gingerol inhibits growth of cancerous cells; however, its role in vascular smooth muscle cell (VSMC) proliferation is not known. The present study investigated the effect of gingerol on VSMC proliferation in cell culture and during neointima formation after balloon injury.

Method and Results:

Rat VSMCs or carotid arteries were harvested at 15 minutes, 30 minutes, 1, 6, 12, and 24 hours of fetal bovine serum (FBS; 10%) stimulation or balloon injury, respectively. Gingerol prevented FBS (10%)-induced proliferation of VSMCs in a dose-dependent manner (50 μmol/L-400 μmol/L). The FBS-induced proliferating cell nuclear antigen (PCNA) upregulation and p27Kip1 downregulation were also attenuated in gingerol (200 μmol/L) pretreated cells. Fetal bovine serum-induced p38 mitogen-activated protein kinase (MAPK) activation, PCNA upregulation, and p27Kip1 downregulation were abrogated in gingerol (200 μmol/L) and p38 MAPK inhibitor (SB203580, 10 μmol/L) pretreated cells. Balloon injury induced time-dependent p38 MAPK activation in the carotid artery. Pretreatment with gingerol (200 μmol/L) significantly attenuated injury-induced p38 MAPK activation, PCNA upregulation, and p27Kip1 downregulation. After 14 days of balloon injury, intimal thickening, neointimal proliferation, and endothelial dysfunction were significantly prevented in gingerol pretreated arteries. In isolated organ bath studies, gingerol (30 nmol/L-300 μmol/L) inhibited phenylephrine-induced contractions and induced dose-dependent relaxation of rat thoracic aortic rings in a partially endothelium-dependent manner.

Conclusion:

Gingerol prevented FBS-induced VSMC proliferation and balloon injury-induced neointima formation by regulating p38 MAPK. Vasodilator effect of gingerol observed in the thoracic aorta was partially endothelium dependent. Gingerol is thus proposed as an attractive agent for modulating VSMC proliferation, vascular reactivity, and progression of vascular proliferative diseases.

Gαq G proteins modulate MMP-9 gelatinase during remodeling of the murine femoral artery

BACKGROUND

Vessels heal after injury and G protein-coupled receptors are involved in the vascular smooth muscle cell proliferation required to form intimal hyperplasia. We have previously identified the role of Gαq in vascular smooth muscle cell proliferation in vitro. This study now examines the role of Gαq in the developing intimal hyperplasia in a murine model and the impact of disruption of Gαq signaling on intimal hyperplasia development.

METHODS

We employed a murine femoral wire injury model in which a micro-wire is passed through a branch of the femoral artery and used to denude the common femoral artery. We perfusion-fixed specimens and stained sections with hematoxylin-eosin and Movat's stains such that morphometric analysis could be performed using an Image-Pro system. We also harvested additional specimens of femoral artery and snap-froze them for Western blotting or zymography, to allow for the study of G protein expression and both protease expression and activity. We used contralateral vessels as controls. We immersed additional vessels in pluronic gel containing the chemical Gαq G protein inhibitors GP-2A, siRNA to Gαq or adenovirus containing mutant inactive Gαq.

RESULTS

Gαq expression increased in a time-dependent manner after femoral artery injury. Sham-operated vessels did not produce such a response. Inhibition of Gαq reduced cell proliferation without affecting cell migration. Interruption of Gαq signaling also inhibited the development of intimal hyperplasia. Inhibition of Gαq did not alter peak urinary-type plasminogen activator activity and expression, but did increase early plasminogen activator inhibitor-1 activity and expression. Inhibition of Gαq reduced peak metalloproteinase (MMP)-9 activity at Day 3 but did not influence peak MMP-2 activity at Day 7. Protein expression for MMP-9 was also decreased, but that of MMP-2 was not affected. There were no changes in the expression or the activity of the respective inhibitors for MMP-9 and MMP-2, and tissue inhibitor of metalloproteinases-1 and -2.

CONCLUSIONS

These data demonstrate that femoral wire injury in the mouse is associated with a time-dependent increase in Gαq expression. Inhibition of Gαq alters cell proliferation and is associated with decreased MMP-9 expression and activity.

Role for Gβγ G-proteins in protease regulation during remodeling of the murine femoral artery

BACKGROUND

Intimal hyperplasia remains the principal lesion in the development of restenosis after vessel wall injury. G-protein coupled receptors are involved in smooth muscle cell proliferation but the role of Gβγ in arterial intimal hyperplasia has not been well defined. The aim of this study is to characterize the expression of Gβγ G-proteins in the developing intimal hyperplasia in a murine model and the impact of disruption of Gβγ signaling on intimal hyperplasia development.

METHODS

The murine femoral wire injury model was employed. Specimens were perfusion-fixed and sections were stained with H&E and Movat's stains such that morphometry could be performed using an Image-Pro system. Additional specimens of femoral artery were also harvested and snap frozen for Western blotting for the Gβγ expression and for Western blotting and zymography to allow for the study of gelatinase and plasminogen activator expression and activation. Contralateral vessels were used as controls. Additional vessels were immersed in pluronic gel containing an adenovirus with the Gβγ inhibitor βARK(CT).

RESULTS

The injured femoral arteries developed intimal hyperplasia, while sham vessels did not produce such a response. Cell proliferation peaked at 3-5 d and cell migration at 7 d after injury. There was a marked time-dependent increase in Gβγ over the 28 d following injury. Inhibition of Gβγ with βARK(CT) inhibited cell proliferation, cell migration and the development of intimal hyperplasia. Inhibition of Gβγ decreased peak uPA activity and expression without increasing early PAI-1 activity and expression. Inhibition of Gβγ reduced peak MMP-2 activity at d 1 but not at d 7 and also reduced peak MMP-9 activity at d 3. Protein expression for both MMP-2 and MMP-9 was also transiently decreased. There were no changes in TIMP-1 and TIMP-2 expression and activity.

CONCLUSIONS

These data demonstrate a time-dependent increase in Gβγ G-protein expression following wire injury in the mouse. Inhibition of Gβγ alters cell proliferation and migration with associated changes in MMP-2, MMP-9, and uPA expression and activity.

Control of cell proliferation in atherosclerosis: insights from animal models and human studies

Excessive hyperplastic cell growth within occlusive vascular lesions has been recognized as a key component of the inflammatory response associated with atherosclerosis, restenosis post-angioplasty, and graft atherosclerosis after coronary artery bypass. Understanding the molecular mechanisms that regulate arterial cell proliferation is therefore essential for the development of new tools for the treatment of these diseases. Mammalian cell proliferation is controlled by a large number of proteins that modulate the mitotic cell cycle, including cyclin-dependent kinases, cyclins, and tumour suppressors. The purpose of this review is to summarize current knowledge about the role of these cell cycle regulators in the development of native and graft atherosclerosis that has arisen from animal studies, histological examination of specimens from human patients, and genetic studies.

Patterns of gelatinase activation induced by injury in the murine femoral artery

BACKGROUND

Intimal hyperplasia remains the principal lesion in the development of restenosis after vessel wall injury. Modulation of the extracellular matrix by proteases is a pivotal component of the response to injury. The aim of this study is to characterize the changes in gelatinase (MMP-2/TIMP-2 and MMP-9/TIMP-1) systems in a murine model.

METHODS

The murine femoral wire injury model was used in which a microwire is passed through a branch of the femoral and used to denude the common femoral artery. Pluronic gel was used to apply a proteass inhibitor (GM6001) to the exterior of the vessels. Specimens were perfusion-fixed and sections were stained with hematoxylin and eosin and Movat's stain such that morphometry could be performed by using an ImagePro system. Additional specimens of femoral artery were also harvested and snap frozen for Western blotting and zymography to allow for the study of gelatinase expression and activation. Contralateral vessels were used as controls.

RESULTS

MMP-2 activity increased significantly at day 1, peaked again at day 7, and then showed a continual decline in activity to day 56. MMP-9 activity peaked early at day 3 and declined thereafter. Protein expression for both MMP-2 and MMP-9 increased significantly after injury and both were maximal at day 14. There was an initial decrease in TIMP-1 and TIMP-2 expression and activity after injury until day 5. Both expression and activation gradually increased thereafter to level out by day 21 and correlated well with the early increases in MMP-2 and MMP-9 activity and their subsequent decline. Local application of protease inhibitor (GM6001) within a pluronic gel decreased cell proliferation, and at 14 d there was a decrease in intimal hyperplasia.

CONCLUSIONS

These data demonstrate that femoral wire injury in the mouse is associated with a time-dependent increase in gelatinase activity. Cell proliferation is associated with increased MMP-2/MMP-9 activity and decreased TIMP-2/TIMP-1 activity, whereas migration is associated with increased in MMP-2 activity. Modulation of proteases and their inhibitors control the vessels' response to injury.

Patterns of kinase activation induced by injury in the murine femoral artery

BACKGROUND

Intimal hyperplasia remains the principal lesion in the development of restenosis after vessel wall injury. Cell signaling in vascular smooth muscle cells remains a potential molecular target to modulate the development of intimal hyperplasia. The aim of this study was to define a baseline pattern of histological changes and kinase activation in a murine model.

METHODS

The murine femoral wire injury model was used in which a microwire was passed through a branch of the femoral artery and used to denude the common femoral artery. Pluronic gel was used to apply mitogen-activated protein kinases (MAPK) inhibitors (PD98059, SB230580, and SP600125) on the exterior of the vessels. Specimens were perfusion-fixed and sections were stained for morphometry using an ImagePro system. Additional specimens of femoral artery were also harvested and snap frozen for Western blotting and zymography to allow for the study of kinase and protease activation. Contralateral vessels were used as controls.

RESULTS

The injured femoral arteries developed intimal hyperplasia, which is maximal at 28 days and does not change substantially between day 28 and day 56. Sham-operated vessels did not produce such a response. Cell apoptosis peaked within 3 days and cell proliferation peaked at 7 days after injury. There is a time-dependent increase in kinase activity immediately after injury. MEK1/2 activation peaks at 20 min after injury and is followed by a peak in extracellular signal-regulated kinase-1/2 activation at 45 min. The stress kinases p38(MAPK) and JNK peak between 10 and 20 min. Activation of akt is later at 45 min and 120 min and activation of p70S6K was biphasic. There was a time-dependent increase in uPA/PAI-1 expression and activity after injury. Local application of MAPK inhibitors (PD98059, SB230580, and SP600125) within a pluronic gel reduced respective MAPK activity, decreased cell proliferation and enhanced cell apoptosis, increased PAI-1, and decreased uPA expression and activity; at 14 days there was a decrease in intimal hyperplasia.

CONCLUSIONS

These data demonstrate that femoral wire injury in the mouse induces a consistent model of intimal hyperplasia and that it is associated with a time dependent increase in signaling kinase activity. Interruption of these pathways will interrupt the uPA/PAI-1 pathway and decrease intimal hyperplasia development. Accurate characterization of cell signaling is a necessary step in the development of molecular therapeutics.

Controlled release of small interfering RNA targeting midkine attenuates intimal hyperplasia in vein grafts

OBJECTIVE

Intimal hyperplasia is a major obstacle to patency after vein grafting. Despite of a diverse array of trials to prevent it, a satisfactory therapeutic strategy for clinical use has not been established. However, sufficient inhibition of early stages of intimal hyperplasia may prevent this long-term progressive disease. Midkine (MK) is a heparin-binding growth factor that was originally discovered as the product of a retinoic acid-responsive gene. We previously demonstrated that MK-deficient mice exhibit a striking reduction of neointima formation in a restenosis model, which is reversed on systemic MK administration. In this study, we evaluated a strategy of using small interfering RNA (siRNA) targeting MK as a therapy for vein graft failure.

METHODS

We first made a highly effective siRNA to rabbit MK. Jugular vein-to-carotid artery interposition vein grafts, which are applied to a low flow condition, were made in Japanese white rabbits. Small interfering RNA mixed with atelocollagen was administrated to the external wall of grafted veins. Cy3-conjugated stabilized siRNA was used to confirm its stability and successful transfer into the vein graft wall. Neointimal hyperplasia was evaluated 4 weeks after the operation. The proliferation index and leukocyte infiltration were determined.

RESULTS

MK expression was induced and reached the maximum level 7 days after operation. Fluorescence of Cy3-labeled siRNA could be detected in the graft wall even 7 days after operation. Knockdown of the gradually increasing expression was achieved by perivascular application of siRNA using atelocollagen. The intima-media ratio and the intima thickness at 28 days after grafting were both reduced >90% by this treatment compared with controls. This phenomenon was preceded by significant reductions of inflammatory cell recruitment to the vessel walls and subsequent cell proliferation in MK siRNA-treated grafts.

CONCLUSIONS

These results suggest that midkine is a candidate molecular target for preventing vein graft failure. Furthermore, for clinical applications of siRNA, a single intraoperative atelocollagen-based nonviral delivery method could be a reliable approach to achieve maximal function of siRNA in vivo. This strategy may be a useful and practical form of gene therapy against human vein graft failure.

Conditional expression of a dominant-negative c-Myb in vascular smooth muscle cells inhibits arterial remodeling after injury

Inhibiting activity of the c-Myb transcription factor attenuates G1 to S phase cell cycle transitions in vascular smooth muscle cells (SMCs) in vitro. To determine the effects of arterial SMC-specific expression of a dominant-negative c-Myb molecule (Myb-Engrailed) on vascular remodeling in vivo, we performed carotid artery wire-denudation in 2 independent lines of binary transgenic mice with SM22alpha promoter-defined Doxycycline-suppressible expression of Myb-Engrailed. Adult mice with arterial SMC-specific expression of Myb-Engrailed were overtly normal in appearance and did not display any changes in cardiovascular structure or physiology. However, bromodeoxyuridine-defined arterial SMC proliferation, neointima formation, medial hyperplasia, and arterial remodeling were markedly decreased in mice expressing arterial SMC-restricted Myb-Engrailed after arterial injury. These data suggest that c-Myb activity in arterial SMCs is not essential for arterial structure or function during development, but is involved in the proliferation of arterial SMCs as occurs in vascular pathology, and that the expression of a dominant-negative c-Myb can dramatically reduce adverse arterial remodeling in an in vivo model of restenosis. As such, this model represents a novel tissue-specific strategy for the potential gene therapy of diseases characterized by arterial SMC proliferation.

Adenoviral-mediated gene transfer in human and animal vein grafts using clinically relevant exposure times, pressures, and viral concentrations

This study examined the efficiency of adenoviral-mediated gene transfer in experimental vein grafts and cultured human saphenous vein under physiologic conditions using clinically relevant exposure times, pressures, and viral concentrations. The external jugular veins of 25 male New Zealand White rabbits were exposed to 0.5 mL of replication-deficient adenovirus vectors encoding beta-galactosidase (AdlacZ), control adenovirus (AdBg/II), or vehicle at pressures ranging from 0 to 120 mmHg for 10 min. Veins were excised and grafted into the carotid circulation. After 5 days, the vessels were reexposed, excised, and stained with X-gal chromagen for beta-galactosidase (beta-gal) activity. Gene transfer was also performed in 13 segments of human saphenous vein discarded at the time of bypass grafting. The veins were cultured for 0-21 days and assayed for beta-gal activity as above. Rabbit vein grafts exposed to high-pressure AdlacZ transfection showed significant transgene expression in 100% of grafts (39 +/- 2% positive cells/hpf) while only 60% of those transfected at low pressure expressed beta-gal (9 +/- 3% positive cells/hpf). All human veins exposed to AdlacZ expressed beta-gal to a variable degree (range 10-50% positive cells/hpf). No control grafts or veins expressed the transgene. Efficient adenoviral-mediated gene transfer in experimental vein grafts and human saphenous vein segments can be achieved using clinically feasible parameters of exposure time, pressure, and viral concentration.

Long-term stabilization of vein graft wall architecture and prolonged resistance to experimental atherosclerosis after E2F decoy oligonucleotide gene therapy

OBJECTIVE

We tested the hypothesis that a single intraoperative transfection of rabbit vein grafts with a decoy oligonucleotide that blocks cell-cycle gene transactivation by the transcription factor E2F induces long-term stable adaptation that involves medial hypertrophy and a resistance to neointimal hyperplasia and atherosclerosis.

METHODS

Jugular vein to carotid artery interposition vein grafts in hypercholesterolemic rabbits were treated, using pressure-mediated delivery, with either E2F decoy oligonucleotide, scrambled oligonucleotide, or vehicle alone. E2F decoy inhibition of cell-cycle gene expression was determined by measuring proliferating cell nuclear antigen upregulation and bromodeoxyuridine incorporation in vascular smooth muscle cells. Neointimal hyperplasia and atherosclerosis were compared between groups at 6 months after operation. Wall stress was derived from the ratio of luminal radius to wall thickness. Normal rabbits exposed to 6 weeks of diet-induced hypercholesterolemia starting 6 months after operation were analyzed in the same manner.

RESULTS

The E2F decoy oligonucleotide, but not scrambled oligonucleotide or vehicle alone, inhibited proliferating cell nuclear antigen expression and smooth muscle cell proliferation. Furthermore, this manipulation of cell-cycle gene expression yielded an inhibition of neointimal hyperplasia and atherosclerotic plaque formation throughout the 6 months of cholesterol feeding. In normocholesterolemic rabbits, vehicle-treated and scrambled oligonucleotide-treated vein grafts remain susceptible to diet-induced atherosclerosis as well, whereas resistance to this disease induction remained stable in genetically engineered grafts.

CONCLUSION

A single intraoperative pressure-mediated delivery of E2F decoy effectively provides vein grafts with long-term resistance to neointimal hyperplasia and atherosclerosis. These findings suggest that long-term reduction in human vein graft failure rates may be feasible with this ex vivo gene therapy approach.

G-protein expression and intimal hyperplasia after arterial injury: a role for Galpha(i) proteins

PURPOSE

Guanine nucleotide binding protein (G-protein) coupled receptors are involved in smooth muscle cell proliferation, but the role of G-proteins in arterial intimal hyperplasia has not been defined. This study examines the expression of G-proteins in the developing intimal hyperplasia after balloon injury of the rat carotid artery and specifically tests the hypothesis that the pertussis toxin sensitive G(i) G-protein subunit plays a role in the initiation of intimal hyperplasia.

METHODS

In vitro responses to serum stimulation (10% fetal bovine serum) were examined in the presence and absence of pertussis toxin (PTx). After a standard balloon injury in male Sprague-Dawley rats, the expression of G-protein subunits (alpha(o), alpha(i), alpha(q), alpha(s), and betagamma) was determined by means of Western blotting in the first 28 days. Thereafter, a second set of animals was allocated to control and PTx-treated (a Galpha(i) inhibitor; 500 ng/mL in an externally applied 30% pluronic gel) groups. Smooth muscle cell proliferation was estimated by means of thymidine analogue 5-bromo-2' deoxyuridine incorporation 2 days after injury, and vessel dimensions were determined by means of videomorphometry 14 days after injury.

RESULTS

There was inhibition of DNA synthesis and smooth muscle cell proliferation in response to serum with an IC(50) of 100 ng/mL. Three days after balloon injury, there was an increase in Galpha(i3) expression, which decreased at days 7, 14, and 28, compared with the uninjured carotid. Galpha(q) expression increased in a time-dependent manner. There was a marked time-dependent increase in Gbetagamma in the 28 days. Galpha(i2) and Galpha(s) isoforms (45 and 52 kDa) did not change significantly with time. There was no major change in Galpha(i1) and Galpha(o) in the study period. At 14 days, PTx treatment reduced intimal hyperplasia by 52% (63 +/- 4 microm vs. 30 +/- 5 microm, control vs. PTx; P <.001). Medial smooth muscle cell proliferation at day 2 was decreased in the PTx group, compared with that in the gel-coated group (15% +/- 2% and 26% +/- 3%; P = .02).

CONCLUSION

After balloon injury, there is a time-dependent increase in G-protein expression, which is subunit specific. Activation of PTx sensitive G-proteins (Galpha(i)) is involved during the initiation of intimal hyperplasia after arterial injury, and their inhibition results in a decrease in early medial cell proliferation. This acute interruption of G(i) signaling produces a long-term decrease in intimal hyperplasia.

Local treatment with recombinant tissue factor pathway inhibitor reduces the development of intimal hyperplasia in experimental vein grafts

BACKGROUND

Tissue factor (TF)-initiated thrombin generation has been implicated in the development of intimal hyperplasia after arterial injury. An increase in intimal TF expression has been shown to precede the development of intimal hyperplasia in vein grafts. This study examines the effects of local treatment with recombinant human tissue factor pathway inhibitor (rTFPI) in experimental vein grafts.

METHODS

Thirty-six male New Zealand white rabbits underwent bypass grafting of the carotid artery by use of the reversed ipsilateral jugular vein and were divided into four groups. Twenty animals had ex vivo incubation with rTFPI treatment (50 microg x mL(-1); n = 10) or placebo vehicle (control; n = 10). Sixteen animals received both ex vivo incubation and in vivo gel treatment with rTFPI (50 microg. mL(-1); n = 8) or without rTFPI (gel-control; n = 8). After operation, vein grafts were harvested at 3 days for immunohistochemical and Western analyses and at 28 days for histomorphologic study.

RESULTS

Western analysis demonstrated a 6.2-fold reduction in the expression of TF protein with rTFPI treatment in comparison to without rTFPI treatment. CD-18 leukocyte staining was diminished, whereas Tie-2 endothelial staining was increased in all rTFPI-treated vein grafts, compared with control and gel-control vein grafts. Intimal thickness was reduced by 21% with ex vivo rTFPI treatment compared with placebo (69 +/- 4 versus 87 +/- 5 microm; P <.05) and by 30% with the addition of rTFPI in vivo compared with gel-control (60 +/- 4 versus 86 +/- 5 microm; P <.01).

CONCLUSION

Local administration of rTFPI exerts early beneficial effects and limits the development of intimal hyperplasia in vein grafts. Therefore blocking TF-mediated pathway may offer new therapeutic options to reduce vein graft failure.

Gene Therapy for Cardiovascular Disease

During the past decade, gene therapy for the treatment of many inherited and acquired medical problems has become the subject of increasing focus in both the scientific litera ture and the lay press. This review examines the history and current status of gene therapy for advanced chronic periph eral and myocardial ischemia.

A new animal model to study intimal hyperplasia in arteriovenous fistulas

BACKGROUND

Intimal hyperplasia (IH) plays a key role in the failure of arteriovenous (AV) fistulas. The animal models available to study IH in AV fistulas are expensive and do not mimic the development of truly stenotic IH. In this study we examined whether goats are a more suitable model to study IH in AV fistulas.

MATERIALS AND METHODS

Thirteen direct and four bridge graft AV fistulas between the carotid artery and the jugular vein of goats were explanted 10 to 195 days after creation. Immunohistochemical staining and morphometric measurements of intima and media were performed in the artery, the vein, the toe, and the heel of the venous anastomosis. Ratios of intimal to medial thickness (Ith/Mth) and area (Ia/Ma) were calculated.

RESULTS

IH developed in all goats, mainly at the anastomosis (Ia/Ma = 0.17) and the efferent vein (Ia/Ma = 0.31). The artery was almost free of lesions (Ia/Ma = 0.03). In the efferent vein, Ith/Mth varied between 0.59 and 0.68. In the anastomosis the largest value of Ith/Mth was measured at the suture lines (0.88 and 0.91). Absolute intimal area increased with time. IH contained many vascular smooth muscle cells with a patchy display of desmin positivity, an abundance of smooth muscle cell alpha-actin positivity, and almost complete endothelial cell coverage. Occlusion was due to thrombus formation on the IH.

CONCLUSION

A clear intimal hyperplasia developed in AV fistulas in goats at locations comparable to those in humans. Therefore, the AV fistula model in the goat may be seen as an effective model to study IH in hemodialysis AV fistulas.

Gene therapy as a therapeutic intervention for vascular disease

Gene therapy for the treatment of many medical problems, including vascular disease, has become the subject of increasing discussion in both the scientific literature and the national press over the past decade. This review will examine the history and current status of gene therapy for vascular proliferative disorders and advanced chronic peripheral and cardiac ischemia.

Reduction of lipid peroxidation with intraoperative superoxide dismutase treatment decreases intimal hyperplasia in experimental vein grafts

BACKGROUND

Vein graft failure is commonly attributed to the development of intimal hyperplastic lesions. Oxidative stress has been implicated in the initiation and progression of atherosclerosis. In this study we examined the effects of local intraoperative treatment with polyethylene glycolated superoxide dismutase (PEG-SOD) on lipid peroxidation and on the development of intimal hyperplasia in experimental vein grafts.

MATERIALS AND METHODS

Forty-one New Zealand White male rabbits had a right carotid interposition bypass graft using the ipsilateral reversed jugular vein. Sixteen animals received local PEG-SOD (4,100 units) treatment; 9 animals received the polyethylene glycol (PEG) vehicle without SOD; 16 animals were used as controls. Postoperatively, malondialdehyde (MDA, a product of lipid peroxidation) concentration and SOD activity were assessed in 3-day vein grafts by colorimetric spectrophotometry. To determine wall dimensions and vasomotor function, morphometric and isometric tension studies were performed on 28-day vein grafts.

RESULTS

MDA concentration was increased 5. 7-fold (P < 0.05) in 3-day control vein grafts compared to ungrafted jugular veins. Intraoperative PEG-SOD treatment raised SOD activity 5.0-fold (P < 0.05) and reduced MDA concentration 8-fold (P < 0.05) in 3-day vein grafts compared to controls. At 28 days, intimal thickness was reduced by 35% with PEG-SOD treatment (54 +/- 4 vs 83 +/- 5; P < 0.001) compared to control vein grafts, without a change in medial thickness (77 +/- 4 vs 88 +/- 5; P = ns). The vasomotor functions of 28-day PEG-SOD-treated vein grafts to norepinephrine, serotonin, bradykinin, nitroprusside, and acetylcholine were not significantly changed when compared to controls. Treatment with PEG alone did not significantly alter lipid peroxidation, wall dimensions, or vasomotor function of vein grafts.

CONCLUSION

This study demonstrates that intraoperative local treatment of vein grafts with PEG-SOD increases SOD activity and decreases lipid peroxidation for at least 3 days, resulting in reduced intimal hyperplasia at 28 days. These findings further implicate oxidative stress in the hyperplastic response of vein grafts and suggest a potential therapeutic role for PEG-SOD in the prevention of vein graft failure.

Plasminogen is not required for neointima formation in a mouse model of vein graft stenosis

Recent studies of mice that lack plasminogen have identified a critical role for this zymogen in arterial remodeling. To permit the use of these (and other) genetically modified mice in the analysis of venous injury, we developed a model in which a patch cut from the external jugular vein of a mouse is grafted to repair a surgically created defect in its carotid artery. In wild-type mice, the venous graft showed initial endothelial denudation and formation of a neointima that progressively and reproducibly expanded in a manner analogous to human vein graft disease, albeit at an accelerated pace. This neointima occupied 37+/-4.6% of the vessel lumen at day 7 and 66+/-5.7% at day 20. The proliferative index of neointimal cells assessed by proliferating cell nuclear antigen staining was 50.6+/-3. 6% at day 7 and 15.2+/-2.0% at day 20. CD45-positive leukocytes and alpha-actin-positive smooth muscle cells accounted for 9.5+/-1.0% and 9.9+/-1.1% of intimal area at day 7, respectively, with the latter increasing to 40.9+/-2.6% at day 20. Collagen accounted for 6.8+/-0.7% of intimal area at day 7 and 20.7+/-1.8% at day 20. Surprisingly, even though arterial neointima formation due to electrostatic and immune-mediated injury is impaired in plasminogen -/- mice, in our study vein graft neointima formation in these mice was not significantly different from that in controls (70.9+/-6.4 versus 65.6+/-4.4% luminal occlusion, P=NS). Thus, plasmin proteolysis, although critical in extracellular matrix degradation and cellular migration after arterial injury, does not appear to be so important in vein graft neointima formation, perhaps because of the relative lack of structural barriers to cellular migration in the normal vein wall. This novel model of vein graft injury should be useful for further studies of differences in the response to injury of arterial and venous tissues.

Characterization of the entire transcription unit of the mouse fibroblast growth factor 1 (FGF-1) gene. Tissue-specific expression of the FGF-1.A mRNA

Fibroblast growth factor 1 (FGF-1, also known as acidic FGF) is a mitogen for a variety of mesoderm- and neuroectoderm-derived cells, as well as an angiogenic factor in vivo. It has been implicated in angiogenic diseases including atherosclerosis, cancer and inflammatory diseases. In the present study, the entire transcriptional unit of the mouse FGF-1 gene, including four promoters, is characterized. By nucleotide sequence and RNase protection analyses, we have determined that its 3'-end resides 3.2 kilobase pairs downstream from the stop codon. We have previously cloned and characterized the mouse homologue of the human 1B promoter, as well as a novel upstream untranslated exon. In order to elucidate the regulatory mechanism of FGF-1 gene expression, the mouse promoter containing TATA and CAAT consensus sequences (FGF-1. A) was isolated from a P1 library and characterized. We further determined that the mouse heart is the most abundant source for the FGF-1.A mRNA. Finally, via both RNase protection analysis and 5'-rapid amplification of cDNA ends, we determined the transcription start site of the FGF-1.A mRNA.

Sustained reduction of neointima with c-myc antisense oligonucleotides in saphenous vein grafts

BACKGROUND

Treatment of saphenous veins with c-myc antisense oligomers during preparation for grafting reduces medial cellular proliferation and macrophage infiltration, and preserves medial smooth muscle content at 3 days. Accordingly, the purpose of this study was to examine whether c-myc antisense oligomers have an impact on late vein graft remodeling.

METHODS

Sixty-two pigs underwent unilateral saphenous vein-carotid artery interposition grafting. Harvested veins were incubated either in saline (control group) or 20-micromol/L or 200-micromol/L concentrations of c-myc antisense oligomers (treated groups) for 30 minutes intraoperatively. Three months after surgery, vein graft histology was assessed.

RESULTS

Forty-five of 62 randomized animals survived the experiment; no differences in animal survival or graft patency among the groups were observed (p = NS, chi2). C-myc antisense oligomers significantly decreased neointimal and wall thickness, as well as increased lumenal index, in treated groups (p<0.04, p<0.03, and p<0.001, respectively, analysis of variance). In contrast, there was no difference in medial thickness or perivascular wound healing.

CONCLUSION

Intraoperative treatment of saphenous veins with c-myc antisense oligomers decreased neointimal formation at 3 months after grafting. In conjunction with our previous reports, these findings suggest that early inhibition of cellular proliferation and inflammatory infiltration results in a sustained reduction in neointimal formation and favorable graft remodeling.

Local delivery of a tissue factor antibody reduces early leukocyte infiltration but fails to limit intimal hyperplasia in experimental vein grafts

BACKGROUND

Tissue Factor-mediated thrombin generation involves the generation of VIIa and Xa and has been implicated in the pathogenesis of intimal hyperplasia. In experimental vein grafts, Tissue Factor protein is increased over the first 3 days and colocalized with CD18-positive leukocytes; this increase in Tissue Factor precedes the development of intimal hyperplasia. This study further evaluates the potential role of Tissue Factor in vein graft intimal hyperplasia by directly inhibiting Tissue Factor protein.

METHODS

New Zealand white rabbits underwent interpositional bypass grafting of the common carotid artery using the external jugular vein. Perioperatively, murine anti-rabbit Tissue Factor antibody (109 microg/ml gel, 12,500x IC50 of Tissue Factor activity) was applied to the adventitial surface of the graft, using a pluronic gel (30% soln.). Tissue Factor antibody treated vein grafts were compared to control and empty gel-treated vein grafts. Vein grafts were examined at 3 days to assess CD18-positive leukocyte infiltration and the presence of residual antibody by Western blotting. At 28 days, intimal and medial dimensions were quantified using videomorphometry.

RESULTS

At day 3, there was marked reduction in CD18-positive leukocytes in the Tissue Factor antibody versus control vein grafts (6.3 +/- 4.7 vs 20.8 +/- 7.4 per 200x field, P < 0.05). At 28 days, intimal hyperplasia was similar for the control (70 +/- 4 microm, mean +/- SEM), gel (73 +/- 4 microm), and Tissue Factor antibody (75 +/- 4 microm) vein grafts. However, medial thickness (76 +/- 4 microm;, P < 0.05) was significantly increased compared to the gel treated vein graft (61 +/- 5 microm).

CONCLUSION

Local delivery of pharmacologic doses of an anti-rabbit Tissue Factor antibody decreased CD18-positive leukocyte infiltration but failed to limit intimal hyperplasia in experimental vein grafts. The results suggest that inhibition of Tissue Factor protein modulates polymorphonuclear leukocyte-endothelial interactions but not in the subsequent development of intimal hyperplasia. It implies that the relationship between the extrinsic coagulation cascade and intimal hyperplasia in vein grafts is complex.

Locally applied antisense oligonucleotide to proliferating cell nuclear antigen inhibits intimal thickening in experimental vein grafts

This study examines the effect of antisense oligonucleotide to proliferating cell nuclear antigen (PCNA) on the formation of vein graft intimal hyperplasia in vivo, using localized administration. Twenty-four New Zealand white rabbits had a right carotid interposition bypass graft using the external jugular vein and were sacrificed on the 28th postoperative day. To determine the effect of PCNA on the development of intimal hyperplasia, 6 animals had their grafts coated with a pluronic gel containing 18 base antisense oligonucleotide to PCNA (1 mg/ml), 6 received a pluronic gel containing an 18 base nonsense oligonucleotide (1 mg/ml), and 12 animals were controls (6 with and 6 without pluronic gel). These grafts were harvested for morphology and videomorphometry. There was no change in the intimal thickness between the control and gel-treated groups. (70 +/- 4 microm versus 72 +/- 4 microm; mean +/- s.e.m.; p = ns). The presence of nonsense oligonucleotide had no further effect. Antisense PCNA produced a 26% decrease in intimal thickness to 50 +/- 4 microm in the treated vein grafts (p < 0.03) without a change in medial thickness. This study shows that a local single application of antisense oligonucleotide to PCNA will reduce the intimal hyperplasia in experimental vein grafts over 28 days.

G protein signaling and vein graft intimal hyperplasia: reduction of intimal hyperplasia in vein grafts by a Gbetagamma inhibitor suggests a major role of G protein signaling in lesion development

Vein grafting results in the development of intimal hyperplasia with accompanying changes in guanine nucleotide-binding (G) protein expression and function. Several serum mitogens that act through G protein-coupled receptors, such as lysophosphatidic acid, stimulate proliferative pathways that are dependent on the G protein betagamma subunit (Gbetagamma)-mediated activation of p21ras. This study examines the role of Gbetagamma signaling in intimal hyperplasia by targeting a gene encoding a specific Gbetagamma inhibitor in an experimental rabbit vein graft model. This inhibitor, the carboxyl terminus of the beta-adrenergic receptor kinase (betaARK(CT)), contains a Gbetagamma-binding domain. Vein graft intimal hyperplasia was significantly reduced by 37% (P<0.01), and physiological studies demonstrated that the normal alterations in G protein coupling phenotypically seen in this model were blocked by betaARK(CT) treatment. Thus, it appears that Gbetagamma-mediated pathways play a major role in intimal hyperplasia and that targeting inhibitors of Gbetagamma signaling offers novel intraoperative therapeutic modalities to inhibit the development of vein graft intimal hyperplasia and subsequent vein graft failure.

Local inhibition of tyrosine kinase activity markedly attenuates the development of intimal hyperplasia in experimental vein grafts

BACKGROUND

Intimal hyperplasia is due to the migration and proliferation of vascular smooth muscle cells after bypass surgery. Tyrosine kinases are involved in many signal transduction pathways including cell proliferation. This study examines the effects of local treatment with the tyrosine kinase inhibitor, tyrphostin AG-51, on the formation of intimal hyperplasia in vein grafts.

MATERIALS AND METHODS

Thirty-nine New Zealand White rabbits underwent interposition bypass grafting of the carotid artery using the jugular vein. In the first group (TKI), tyrphostin AG-51 (5 mg), dissolved in 600 microliter of dimethyl sulfoxide and Ringer's lactate (2:1, v:v), was used to incubate the veins ex vivo prior to grafting and delivered locally in 2.5 ml of 30% pluronic gel after grafting. The second group (DMSO) received the same treatment but without tyrphostin. In the third group (control), tyrphostin and DMSO were omitted from the incubation and gel delivery solutions. Postoperatively, vein grafts were harvested on Day 3 for Western analysis using an antiphosphotyrosine antibody (PY-20) to assess for tyrosine kinase activity, and on Day 28 for either morphologic or contractile function studies.

RESULTS

Local application of the TKI to vein grafts resulted in a 49% reduction in intimal hyperplasia compared to DMSO-treated vein grafts (31 +/- 4 micrometer vs. 61 +/- 5 micrometer, P < 0.01). Treatment with DMSO alone reduced intimal hyperplasia by 28% compared to control (85 +/- 4 micrometer, P < 0.05). The contractile responses in the DMSO and TKI-treated vein grafts were equivalent. Western analysis showed a 39-fold decrease in tyrosine phosphorylation with TKI treatment compared to control.

CONCLUSION

This study demonstrates that local short-term treatment with TKI produces a 49% reduction in intimal hyperplasia and suggests that phosphorylation of tyrosine residues is involved in the signaling pathways leading to the development of intimal hyperplasia in vein grafts.

Local effects of nitric oxide supplementation and suppression in the development of intimal hyperplasia in experimental vein grafts

OBJECTIVES

The universal response of vein grafts after insertion into the arterial circulation is the development of intimal hyperplasia; smooth muscle cell proliferation and connective tissue deposition, which may be modulated in part by dysfunctional endothelial nitric oxide (NO) metabolism. This study examines the effects of single dose, local application by pluronic gel of a NO donor, S-nitroso-N-acetylpenicillamine (SNAP) and an NO synthase inhibitor nitro-L-arginine methyl ester (L-NAME) on the formation of intimal hyperplasia.

MATERIALS

Forty New Zealand white rabbits underwent jugular vein interposition grafting of the common carotid artery.

DESIGN

Ten animals were controls, 10 animals had the outer surface of the vein graft coated with 30% pluronic gel (2.5 ml), and 10 each were immersed for 15 min prior to insertion in Ringer lactate containing 10(-3) M of SNAP or L-NAME and then had their vein grafts coated with 2.5 ml of gel containing either SNAP (10(-3) M) or L-NAME (10(-3) M), which allows for sustained delivery for up to 6 h. On the 28th post operative day, the animals were sacrificed and vein grafts were harvested for morphology by electron microscopy (SEM and TEM) and dimensional analysis by videomorphometry.

RESULTS

All vein grafts developed intimal hyperplasia. On SEM the vein grafts had a confluent layer of endothelial cells with multiple layers of smooth muscle cells representing intimal hyperplasia in TEM. There were no demonstrable morphological differences between the four groups. Local treatment with SNAP produced a significant 36% decrease in mean intimal thickness (72 +/- 4 microns vs. 45 +/- 4 microns; mean +/- S.E.M.; p < 0.01) without a change in medial thickness compared to gel-only treated groups (58 +/- 6 microns vs. 61 +/- 7 microns; p = ns). Inhibition of NO synthase by L-NAME had no effect on the development of intimal hyperplasia (72 +/- 4 microns vs. 79 +/- 10 microns; p = ns); medial thickness was also unchanged.

CONCLUSION

These data confirm the protective effect of NO in vascular injury and suggest that NO synthase activity is either absent or reduced to such a level that further inhibition in this short time course is not relevant to the pathophysiology of vein graft intimal hyperplasia.