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

Efficient gene transfer and durable transgene expression in grafted rabbit veins

Venous bypass grafts are useful treatments for obstructive coronary artery disease. However, their usefulness is limited by accelerated atherosclerosis. Genetic engineering of venous bypass grafts that prevented atherosclerosis could improve long-term graft patency and clinical outcomes. We used a rabbit model of jugular vein-to-carotid interposition grafting to develop gene therapy for vein-graft atherosclerosis. Rabbit veins were easily transduced in situ with a first-generation adenoviral vector; however, most transgene expression (∼80%) was lost within 3 days after arterial grafting. This rapid loss of transgene expression was not prevented by transducing veins after grafting or by prolonged ex vivo transduction. However, delaying vein-graft transduction for 28 days (after the vein had adapted to the arterial circulation) prevented this early loss of transgene expression. We used the delayed transduction approach to test the durability of expression of a therapeutic transgene (apolipoprotein A-I) expressed from a helper-dependent adenoviral (HDAd) vector. HDAd DNA and apolipoprotein A-I mRNA were easily detectable in transduced vein grafts. Vector DNA and mRNA declined by 4 weeks, and then persisted stably for at least 6 months. Delaying transduction for 28 days after grafting permitted initiation of vein-graft neointimal growth and medial thickening before gene transfer. However, vein-graft lumen diameter was not compromised, because of gradual outward remodeling of grafted veins. Our data highlight the promise of HDAd-mediated gene therapy, delivered to arterialized vein grafts, for preventing vein-graft atherosclerosis.

The expanding roles of Gβγ subunits in G protein-coupled receptor signaling and drug action

Gβγ subunits from heterotrimeric G proteins perform a vast array of functions in cells with respect to signaling, often independently as well as in concert with Gα subunits. However, the eponymous term "Gβγ" does not do justice to the fact that 5 Gβ and 12 Gγ isoforms have evolved in mammals to serve much broader roles beyond their canonical roles in cellular signaling. We explore the phylogenetic diversity of Gβγ subunits with a view toward understanding these expanded roles in different cellular organelles. We suggest that the particular content of distinct Gβγ subunits regulates cellular activity, and that the granularity of individual Gβ and Gγ action is only beginning to be understood. Given the therapeutic potential of targeting Gβγ action, this larger view serves as a prelude to more specific development of drugs aimed at individual isoforms.

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.

Gene transfer of COX-1 improves lumen size and blood flow in carotid bypass grafts

BACKGROUND

In autologous saphenous vein grafts, prostacyclin (PGI(1)), a vasoprotective molecule produced by normal endothelial cells, is down-regulated compared with ungrafted saphenous veins and normal carotid arteries. Reduced PGI(2) synthesis may contribute to local platelet deposition, vascular smooth muscle cell (VSMC) accumulation, atherosclerosis, and ultimately failure of venous bypass grafts. We have examined whether gene transfer-mediated overexpression of COX-1 in grafted veins (1) increases PGI(2) and cyclic AMP (cAMP) production, (2) leads to vasodilation and improved local blood flow in the presence of hypercholesterolemia, and (3) reduces neointima formation.

MATERIALS AND METHODS

Jugular veins from New Zealand-White rabbits were incubated for 30 min ex vivo with 1 x 10(10) PFU/mL of an adenoviral vector encoding COX-1 (AdCOX-1; n = 10) or empty control (n = 10) and grafted to the carotid arteries. The rabbits were placed on a high-cholesterol diet for 4 w, and blood flow and histomorphometry of the grafts were assessed.

RESULTS

In the AdCOX-1 group, blood flow was significantly increased (16.0 +/- 3.3 versus 12.5 +/- 3.3 mL/min; P < 0.05) compared with controls, and luminal area (8.9 +/- 1.4 versus 5.3 +/- 1.2 mm(2); P < 0.01) and outer circumference were larger. In six identically treated rabbits, graft PGI(2) and cAMP synthesis was increased at 72 h in AdCOX-1 compared with controls.

CONCLUSION

Our data suggest a 30-min ex vivo exposure of vein grafts to AdCOX-1 increased local synthesis of PGI(2) and cAMP after graft surgery and resulted in better graft lumen and blood flow at 4 w.

A Gβγ inhibitor reduces intimal hyperplasia in aortocoronary saphenous vein grafts

OBJECTIVE

Approximately 50% of aortocoronary saphenous vein grafts are occluded 10 years after coronary revascularization surgery. Intimal hyperplasia, a critical component in saphenous vein graft failure, is defined by vascular smooth muscle cell proliferation, which is mediated in part by betagamma subunits of heterotrimeric G proteins (G(betagamma)) and downstream effectors such as mitogen-activated protein kinases. A peptide consisting of the carboxyl-terminus of the beta-adrenergic receptor kinase (betaARKct) binds G(betagamma), thereby inhibiting G(betagamma) signaling. Utilizing a recombinant adenovirus containing the coding sequence for the betaARKct peptide (AdbetaARKct), this study investigates whether treatment of the vein graft with AdbetaARKct reduces intimal hyperplasia in a large animal model of aortocoronary saphenous vein graft intimal hyperplasia.

METHODS

Twenty-seven dogs (27-32 kg) underwent aortocoronary bypass grafting to the left anterior descending artery using autologous saphenous vein. Vein grafts were treated with saline (n = 8), an empty adenovirus (n = 8), or AdbetaARKct (n = 8). A subset of dogs (n = 3) were sacrificed on postoperative day 7 and betaARKct expression confirmed by Northern blotting.

RESULTS

Arteriograms performed on postoperative day 90 confirmed that saphenous vein grafts were patent. At postoperative day 90, AdbetaARKct-treated grafts demonstrated reduced intimal area compared to empty virus and saline treated animals (P < .05). Additionally, AdbetaARKct treatment of isolated vascular smooth muscle cells in vitro inhibited mitogen-activated protein kinase activation and decreased overall vascular smooth muscle cell proliferation.

CONCLUSION

This study demonstrates that betaARKct expression in aortocoronary saphenous vein grafts reduces intimal hyperplasia and decreases vascular smooth muscle cell proliferation in vitro via inhibition of G(betagamma)-mediated mitogen-activated protein kinase activation. Modulation of G(betagamma) via betaARKct may represent a novel therapy to reduce intimal hyperplasia and saphenous vein graft failure.

Catheter-mediated delivery of adenoviral vectors expressing beta-adrenergic receptor kinase C-terminus inhibits intimal hyperplasia and luminal stenosis in rabbit iliac arteries

BACKGROUND

Previous studies have shown that incubation of balloon-injured rat carotid arteries with adenoviral vectors encoding the carboxyl terminus of the beta-adrenergic receptor kinase (Ad2/betaARKct) for 30 min reduces neointima formation. However, it is unclear whether this beneficial effect of betaARKct could be achieved using a catheter-based vector delivery system and whether the observed inhibition of neointima formation translated into a reduction of vessel stenosis.

METHODS

In this study, Ad2/betaARKct was infused into the balloon-injured site of rabbit iliac arteries using a porous infusion catheter over 2 min. Twenty-eight days after gene transfer, angiographic and histological assessments were performed.

RESULTS

Angiographic and histological assessments indicate significant (p < 0.05) inhibition of iliac artery neointima formation and lumen stenosis by Ad2/betaARKct. Our studies demonstrate that an inhibitory effect of Ad2/betaARKct on neointima formation is achievable using a catheter-based vector delivery system and that the inhibition of neointima formation translates into a gain in the vessel minimal luminal diameter. The extent of inhibition (35%) was comparable to that observed with adenoviral-mediated expression of thymidine kinase plus ganciclovir treatment, a cytotoxic gene therapy approach for restenosis.

CONCLUSIONS

These results suggest that adenoviral-mediated gene transfer of betaARKct is a clinically viable cytostatic gene therapy strategy for the treatment of restenosis.

Vascular Dysfunction of Venous Bypass Conduits Is Mediated by Reactive Oxygen Species in Diabetes: Role of Endothelin-1

Diabetes is associated with increased risk for complications following coronary bypass grafting (CABG) surgery. Augmented superoxide (*O2*) production plays an important role in diabetic complications by causing vascular dysfunction. The potent vasoconstrictor endothelin-1 (ET-1) is also elevated in diabetes and following CABG; however, the effect of ET-1 on *O2* generation and/or vascular dysfunction in bypass conduits remain unknown. Accordingly, this study investigated basal and ET-1-stimulated *O2* production in bypass conduits and determined the effect of *O2* on conduit reactivity. Saphenous vein specimens were obtained from nondiabetic (n = 24) and diabetic (n = 24) patients undergoing CABG. Dihydroethidium staining and NAD(P)H oxidase activity assays (5380 +/- 940 versus 16,362 +/- 2550 relative light units/microg) demonstrated increased basal *O2* levels in the diabetes group (p < 0.05). Plasma ET-1 levels were associated with elevated basal *O2* levels, and treatment of conduits with exogenous ET-1 further increased *O2* production and augmented vasoconstriction. Furthermore, vascular relaxation was impaired in the diabetic group (75 versus 40%), which was restored by *O2* scavenger superoxide dismutase. These findings suggest that ET-1 causes bypass conduits dysfunction via stimulation of *O2* production in diabetes. Novel therapies that attenuate *O2* generation in bypass conduits may improve acute and late outcome of CABG in diabetic patients.

Native matrix metalloproteinase characteristics may influence early stenosis of venous versus arterial coronary artery bypass grafting conduits

PURPOSE

Stenosis and occlusion rates of internal mammary artery (IMA) and saphenous vein (SV) coronary artery bypass grafts (CABGs) are markedly different, which result from respective disparities in vascular remodeling. Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) regulate vascular structure and may have important influence on graft patency. However, the MMP milieu and expression profile of the IMA and SV have not been contrasted. Therefore, the aim of this study was to assess and compare the native MMP systems in IMA vs SV conduits.

METHODS

IMA (n = 10) and SV (n = 10) specimens were obtained from patients undergoing CABG surgery. Protein levels of MMP-1, MMP-2, and MMP-9, TIMP-1, a membrane-bound MMP activator (MT1-MMP), and an extracellular MMP inducer protein (EMMPRIN) were determined by immunoblotting and quantified by densitometric analysis. MMP-2 and MMP-9 activity was determined by gelatin zymography.

RESULTS

MMP-2 levels were significantly higher in SV (2,218 +/- 351 pixels) vs IMA (1,012 +/- 213 pixels) specimens (mean +/- SEM]). There were no significant differences in MMP-1, MMP-9, or TIMP-1 content; however, MT1-MMP and EMMPRIN levels were significantly lower in SV (847 +/- 190 pixels, 1,742 +/- 461 pixels) vs IMA conduits (2,590 + 403 pixels, 5,606 + 678 pixels), respectively (p < 0.05). MMP-9 activity was similar while MMP-2 activity was significantly increased in SV vs IMA specimens.

CONCLUSIONS

SV and IMA conduits harbor the same MMP molecular constituents. However, MMP-2 levels and activity are significantly more abundant in the SV compared to the IMA. These differences may contribute to the early pathologic remodeling of the SV vs IMA conduit following CABG surgery.

Role of Gαq in smooth muscle cell proliferation

BACKGROUND

G protein-linked receptors are involved in the processes that lead to intimal hyperplasia. This study examined the role of Galphaq signaling pathways in vascular smooth muscle cell (SMC) proliferation in vitro.

METHODS

Rat pulmonary artery SMCs were cultured in vitro. Standard assays of cellular DNA synthesis, proliferation, phospholipase C-beta (PLCbeta) activation, and extracellular signal-regulated kinase (ERK1/2) phosphorylation were used to study the response to angiotensin II (a specific Galphaq agonist; 0.1-100 micromol/L) in the presence and absence of GP-2A (a competitive Galphaq inhibitor; 10 micromol/L) and the PLCbeta inhibitor U73122 (10micromol/L).

RESULTS

Angiotensin II induced SMC DNA synthesis and cell proliferation. DNA synthesis was inhibited by both Galphaq inhibitor, GP-2A, and PLCbeta inhibitor U73122, in a dose-dependent manner (66% +/- 7% of angiotensin II alone at 10 micromol/L for GP-2A [P <.05] and 63% +/- 6% for U73122). GP-2A completely inhibited angiotensin II-induced Galphaq-mediated PLCbeta phosphorylation. Activation of ERK1/2 by angiotensin II was significantly reduced by GP-2A (P <.05) and by PLCbeta inhibition (P <.05).

CONCLUSION

Inhibition of Galphaq decreases PLCbeta and ERK1/2 phosphorylation, leading to decreased SMC proliferation in vitro. Understanding specific signal transduction pathways will be an integral component of anti-restenosis therapy.Clinical Relevance The universal response of a blood vessel to injury is chronic wound healing, which includes the development of intimal hyperplasia and subsequent remodeling of the vessel wall. This can lead to luminal narrowing in as many as 30% of patients undergoing angioplasty. Neointimal formation is the principal cause of in-stent recurrent stenosis. Intimal hyperplasia is in part produced by smooth muscle cell (SMC) proliferation. Understanding the keys to the proliferation of SMCs will enable therapies to be developed that may inhibit the initial development of intimal hyperplasia. Whereas in the past many studies focused on the multiple mechanical, humoral, and cellular elements that induce SMC proliferation, molecular therapeutics focuses on key choke points within the cell that can be used to inhibit proliferation. One of these key choke points is signal transduction. Galphaq is one of the ubiquitous signal transduction proteins on the membrane of SMCs. Inhibiting G proteins, such as Galphaq, would enable interference with a significant amount of the mechanical, humeral, and cellular elements that produce SMC proliferation, and thus decrease the development of intimal hyperplasia. The present study identifies and begins to map out the role of Galphaq in SMC proliferation and investigates the possible use of a small peptide in its inhibition. Other data suggest that inhibition of other G proteins will also decrease intimal hyperplasia. This is therefore a fertile area for the development of therapeutics to inhibit intimal hyperplasia. The direct relevance to the clinician is that this study identifies a transduction pathway that may be inhibited, and points in the direction of a possible molecular therapeutic target that would be beneficial as an adjunct to angioplasty or as part of a drug-eluding stent regimen.

Gene delivery to aortocoronary saphenous vein grafts in a large animal model of intimal hyperplasia

OBJECTIVE

More than 50% of aortocoronary saphenous vein grafts are occluded 10 years after surgery. Intimal hyperplasia is an initial, critical step in the progression toward occlusion. To date, no clinically relevant large animal models of aortocoronary saphenous vein graft intimal hyperplasia have been fully characterized. Gene therapy holds promise as a novel treatment for aortocoronary saphenous vein graft intimal hyperplasia. The 2 objectives of this study are to characterize a canine model of aortocoronary saphenous vein graft intimal hyperplasia and to demonstrate that ex vivo gene delivery is possible in these grafts using adenoviral vectors.

METHODS

Ten dogs underwent aortocoronary bypass grafting using saphenous veins. Six dogs underwent serial arteriograms to monitor graft patency. On postoperative day 90, the dogs were killed and their grafted and nongrafted saphenous veins were studied histologically. Four dogs underwent the same procedure, but their saphenous veins were treated with 1 x 10(12) total viral particles of a replication-deficient, recombinant adenovirus containing beta-galactosidase (n = 2) or the beta-adrenergic receptor kinase carboxyl terminus (n = 2). These animals were killed on postoperative day 7 for determination of transgene expression.

RESULTS

All grafts were demonstrated patent by arteriogram before the animals were killed. The mean intimal area of the saphenous vein grafts was increased when compared with that of the nongrafted saphenous veins (2.83 mm(2) vs 0.09 mm(2), P <.0008). Adenoviral-treated saphenous vein grafts demonstrated positive transgene expression either by X-gal staining (beta-galactosidase) or Northern analysis (beta-adrenergic receptor kinase carboxyl terminus).

CONCLUSION

This study characterizes a clinically relevant canine model of aortocoronary saphenous vein graft intimal hyperplasia. In addition, it demonstrates that adenoviral vectors can be delivered ex vivo to the saphenous vein graft vessel wall at subphysiologic distension pressures. This model may be used in future studies to manipulate molecular targets critical in aortocoronary saphenous vein graft intimal hyperplasia.

The ras-binding domain of ral GDS-like protein-2 as a ras inhibitor in smooth muscle cells

This study was undertaken to determine whether the response of smooth muscle cells to mitogens can be inhibited by inactivating ras with the ral GDS like protein-2 ras-binding domain (RGL2-RBD). RGL2 is a member of the ral GDS family of proteins that contains a carboxy terminal ras-binding domain which binds the GTP ligated form of ras and rap and a CDC25 homology domain with the structural features of a guanine nucleotide exchange factor. The effect of ras signaling on the smooth muscle cell growth factor response was studied using rat aortic A10 smooth muscle cells transfected with a plasmid that encoded the RGL2-RBD. RGL2-RBD transfection resulted in a 12-fold reduction in the number of clonal colonies that were obtained after selection, and dramatically slowed cell cycle progression. RGBL2-RBD reduced DNA synthesis and inhibited platelet derived growth factor (PDGF)-mediated activation of the MAPK pathway. These findings indicated that interfering with ras signaling inhibits smooth muscle cell proliferation and raise the possibility that ras signaling inhibition might be used therapeutically to control smooth muscle proliferation after vascular injury.

Gene transfer to coronary artery bypass conduits

BACKGROUND

Gene therapy is a rational approach to prevention of stenosis in saphenous vein grafts used as conduits for coronary artery bypass grafting. To explore this possibility we developed methods for adenoviral-mediated gene transfer to canine saphenous veins.

METHODS

During a single procedure, autogenous canine saphenous vein segments were transduced ex vivo and used as coronary artery bypass grafts. The proximal end of each vein was ligated, adenovirus containing the Escherichia coli beta-galactosidase gene (Ad.CMVLacZ) was delivered at titers of 2.5 x 10(9) or 5 x 10(9) plaque-forming units (pfu)/mL to the lumen through a distal heparin lock, and the segment was immersed in the viral solution for 1 hour at 37 degrees C. Control segments were exposed to diluent alone in an identical manner. Aortocoronary anastomoses were made using cardiopulmonary bypass. Transgene expression was assessed qualitatively and quantitatively after 3 days.

RESULTS

Beta-galactosidase levels showed a dose-dependent increase: 0.00 +/- 0.00 ng/mg total protein for controls; 5.60 +/- 2.27 ng/mg total protein for a viral titer of 2.5 x 10(9) pfu/mL and 11.97 +/- 6.14 ng/mg for 5 x 10(9) pfu/mL. The two dosage groups differed significantly from each other (p = 0.035) and from controls (p = 0.003). X-gal staining demonstrated mostly endothelial and scattered adventitial transgene expression.

CONCLUSIONS

Transgene expression after ex vivo gene transfer into saphenous vein grafts in a canine coronary artery bypass model indicates that this method may be useful for delivery of therapeutic genes to prevent or retard vein graft arteriosclerosis.

Gene therapy for acute diseases

The use of gene transfer systems to study cell function makes it apparent that overexpression of a transgene can restore or improve the function of a protein and positively influence cell function in a predetermined manner for purposes of counterbalancing cellular pathophysiology. The ability of some gene transfer vehicles to produce transgene product within hours of delivery positions gene transfer as a unique pharmaceutical administration system that can quickly affect production of biologic response modifiers in a highly compartmentalized fashion. This approach can be expected to overcome many of the adverse effects and high costs of systemic delivery of recombinant pharmaceuticals. This review highlights recent advances toward development of gene therapies for acute illnesses with particular emphasis on preclinical models of disease. In this context, a growing body of data suggests that gene therapies for polygenic and non-genetic diseases such as asthma, cardiogenic and non-cardiogenic pulmonary edema, stroke, subarachnoid hemorrhage, seizures, acute myocardial infarction, endovascular thrombosis, and infections may someday be options for the treatment of patients.

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.

Gene therapy for vein graft disease

Applying gene therapeutics to vein graft disease requires foundational knowledge of the underlying pathophysiology. This review details a brief description of vein graft disease, examines published and unpublished data on gene transfer to veins, and reviews the genes, which have significantly altered vascular biology.

Characterization of dopamine-mediated relaxation in experimental vein bypass grafts

BACKGROUND

Dopamine is an endogenous inotropic agent commonly used during coronary artery surgery and in the medical therapy of a revascularized patient. In this study the responses of intimal hyperplastic vein grafts to dopamine are examined.

METHODS

The in vitro isometric tension responses to dopamine of common carotid jugular vein bypass grafts in New Zealand White rabbits were determined. The responses were compared to those obtained in the jugular vein and in the common carotid artery. Both endothelialized and denuded vessels were precontracted with prostaglandin F(2alpha) and the responses to dopamine were assessed. The contributions of nitric oxide and prostanoids to the response were also determined.

RESULTS

Each vessel showed a biphasic dose response to dopamine with relaxation at low concentrations followed by contraction at high concentrations. Dopamine relaxation in the jugular vein was endothelial independent while in the carotid artery it was endothelial dependent and decreased. The sensitivity of both vessels was significantly greater than the vein graft (6.62 +/- 0.12; P < 0. 05); however, after endothelial denudation, the sensitivity of dopamine-mediated relaxation of the vein graft (8.91 +/- 0.09) was significantly enhanced. Preincubation with L-NMMA (to block NO synthesis) inhibited vein graft relaxation to dopamine and preincubation with indomethacin (to block cyclooxygenase activity) inhibited carotid artery relaxation to dopamine. Addition of phenoxybenzamine, a broad alpha-adrenergic antagonist, enhanced dopamine relaxation in the jugular vein and depressed the relaxation in the carotid artery. There was no effect on the dopamine response in the vein graft. Jugular vein and carotid artery responded to dopamine with cholera toxin-sensitive (Galpha(s)) responses. In contrast, dopamine relaxation in the vein graft was enhanced by inhibition of Galpha(s).

CONCLUSION

Dopamine relaxation in vein grafts is mediated in part by NO but not by either prostanoids or alpha-adrenergic receptor activation. It is diminished compared to native vessels due to an endothelium-dependent, Galpha(s)-mediated pathway.

G protein beta3 subunit polymorphism and risk of thrombosis and restenosis following coronary stent placement

C825T polymorphism in the G protein beta3 subunit gene (GNB3) has been associated with arterial hypertension, coronary artery disease and myocardial infarction. On the cellular level, C825T polymorphism is associated with altered transmembrane signaling via adenylyl cyclase inhibiting (G(i)) G proteins. This study was designed to test whether C825T polymorphism has an impact on the processes leading to restenosis and thrombosis following coronary stenting. The primary endpoint of the study was angiographic restenosis (> or =50% diameter stenosis) at 6-month follow-up. Secondary endpoint was angiographically proven stent thrombosis within 30 days of implantation. In the 562 consecutive patients C825T genotype was CC, 46.1%, CT, 45.2% and TT, 8.7%. The incidence of angiographic restenosis was 32.7% in homozygous carriers of the C allele, 28.2% in CT patients and 33.3% in homozygous carriers of the T allele (P = 0.563). C825T genotype distribution in 34 consecutive patients with subacute stent thrombosis (44.0% CC, 50.0% CT, and 6.0% TT) was not different from that of 451 patients with angiographically patent stented vessel (45.4% CC, 44.6% CT, 10.0% TT; P = 0.644). In conclusion, C825T polymorphism has no appreciable impact on the mechanisms leading to thrombosis and restenosis following coronary stent placement.

Targets for gene therapy of vein grafts

Poor long-term patency and a lack of suitable systemic pharmacologic therapy for the prevention of vein graft failure have prompted the search for effective local gene therapy. Vein grafts are particularly well suited for gene transfer in the clinic because direct access to vein is available during surgical preparation for grafting. In this review, the available animal models are discussed and a new mouse model is highlighted. Recent advances in gene transfer technology are reviewed, including the use of adeno-associated virus and modified adenoviruses that can prolong in vivo transgene expression for months. Gene therapy is intended to reduce early thrombosis, reduce neointima formation, and prevent atherosclerosis in vein grafts. Promising antithrombotic targets include tissue plasminogen activator and thrombomodulin. Nitric oxide synthase, prostacyclin synthase, and tissue inhibitors of metalloproteinases have been used to reduce neointima formation, and vein graft atheroma remains a challenge for the future.