Rabbit Carotid Research Articles

Abstract 46: Differential Gene and Transcription Factor Binding Site Expression Between the Intima and Media Drives Intimal Hyperplasia

Background: Vein grafts (VG) fail due to rapid intimal expansion in the weeks to months following implantation. Histologically, this results in a metabolically active intima juxtaposed to a quiescent medial layer. In this study, we leverage this dichotomy to identify the key genes that control intimal growth and the critical transcription factors (TF) that drive their activation. Methods: Microsurgical techniques were used to separate the intima and media of rabbit carotid VGs harvested at 1 (n=4), 3 (n=6), and 6 (n=4) months (m) following implantation. Each layer was independently analyzed for differential mRNA expression using a whole-genome microarray. rVista and TRANSFAC were used to identify TF binding sites within 5000 bp of differentially expressed genes. Results: Early growth of the intima was driven by an enhanced proliferative response and an accumulation of cell mass (Fig). During this early hyperplastic phase, substantial differences in intimal and medial gene expression were observed (197 genes at 1m and 346 at 3m, p<0.001) that resolved by 6m (8 genes). Genes involved in cell cycle regulation and cellular movement dominated the 1 and 3m differences (Fig). TF binding site analysis of up-regulated intimal genes at 1 month revealed enrichment of ETS and HOX, while CREB and bHLH-ZIP were the most over-represented among up-regulated 3m intimal genes. In the medial layer, RXR and zinc finger TF binding sites were most prominent among up-regulated genes at 1 and 3m, respectively. Conclusion: Corresponding to the most active phase of intimal growth, smooth muscle cells demonstrated marked up-regulation of an array of genes that modulate cell proliferation and migration, with these genes under the control of a discrete set of TFs. While previous attempts at modifying TF binding (via an E2F decoy) in the initial days following VG implantation have been unsuccessful, manipulation of a broader set of TFs in the time frame of weeks to months may prove a more promising strategy.

OP-342 The Effect of Transforming Growth Factor –β on Regulation of Intimal Hyperplasia in a Rabbit Carotid Anastomosis Model

OP-342 The Effect of Transforming Growth Factor –β on Regulation of Intimal Hyperplasia in a Rabbit Carotid Anastomosis Model

Expression of NF-κB, MCP-1 and MMP-9 in a Cerebral Aneurysm Rabbit Model

We explored the early expression of NF-κB, MCP-1 and -MMP 9 in a rabbit carotid aneurysm model, and investigated the possible mechanism of aneurysm. twenty four adult new Zealand rabbits were divided into four groups. normal control (group a); rabbits received elastase induction for 1, 2 3 weeks (group b, C and d respectively); hematoxylin-eosin stains were performed for observation. the mrna and protein expression of NF-κB, MCP-1 and MMP-9 were analyzed using RT-PCR and immunohistochemical methods. the expression of NF-κB and MCp-1 reached their peaks after induction for one week, then decreased. their expression in week 1 and week 2 had no statistical difference. the expression of MMP-9 increased after induction. We observed the highest expression at week 3. as the induction time increased, the number of smooth muscles reduced. endothelial cells were damaged; the aneurysm wall elastic layer was damaged. activation of NF-κB may be one of the initiating factors contributing to the occurrence and development of cerebral aneurysm. MCP-1 induced macrophage adhesion and infiltration in the artery wall of cerebral aneurysms, and contributed to the occurrence and development of brain aneurysm. damage to elastic fibers is one of the key factors for aneurysm formation. increased infiltration of inflammatory cells and the secretion of MMP-9 are the main reasons for elastic fiber damage.

Correlation of restenosis after rabbit carotid endarterectomy and inflammatory cytokines

ObjectiveTo establish rabbit model of restenosis after carotid endarterectomy surgery, and to study tissue inflammatory cytokines (TNF-α, IL-6) involved in restenosis. MethodsA total of 32 rabbits were randomly divided into two groups: model group and control group. The right common carotid artery in rabbits was damaged by carotid endar terectomy in model group. The tissues were harvested at different time points respectively, the pathological changes of the vascular wall after operation were observed at different time points. The changes of expression of tissue vascular wall inflammatory cytokines (TNF-α, IL-6) at different time points after the surgery was observed by RT-PCR, and the changes of serum inflammatory cytokines (TNF-α, IL −6) were detected by ELISA. ResultsThe new intima appeared after 7 days of the injury and reached the peak on 28 d which is uneven and significantly thicker than the control group (P<0.01). The tissue inflammatory cytokines (TNF-α, IL-6) were significantly increased after the rabbit common carotid artery injury, which was significant difference compared with normal control group (P<0.05). ConclusionsThe tissue inflammatory factors significantly increase after the rabbit carotid artery injury, which suggests the mutual concurrent effects of inflammatory cytokines can result in the proliferation of vascular restenosis.

Establishment of an animal model of vascular restenosis with bilateral carotid artery grafting.

BackgroundVascular restenosis occurring after CABG is a major clinical problem that needs to be addressed. Vein grafts are associated with a higher degree of stenosis than artery grafts. However, the mechanism responsible for this effect has not been elucidated. We aimed to establish a rabbit model of vascular restenosis after bilateral carotid artery grafting, and to investigate the associated spatiotemporal changes of intimal hyperplasia in carotid artery and jugular vein grafts after surgery.Material/MethodsTwenty adult New Zealand white rabbits (10 males; 10 females), weighing 2.0–2.5 kg, were obtained from the Experimental Animal Center of Southern Medical University, Guangzhou, China (License No.: scxk-Guangdong-2006-0015). We quantitatively analyzed intimal thickness, area, and degree of stenosis in carotid artery and jugular vein bridges.ResultsAfter 8 weeks of a high-fat diet, rabbit carotid arteries showed early atherosclerotic lesions. With increasing time after surgery, carotid artery and jugular vein grafts showed histopathological and morphological changes, including smooth muscle cell migration, lipid deposition, intimal hyperplasia, and vascular stenosis. The degree of vascular stenosis was significantly higher in vein grafts than in artery grafts at all time points – 35.1±6.7% vs. 16.1±2.6% at Week 12, 56.2±8.5% vs. 23.4±3.4% at Week 16, and 71.2±1.3% vs. 25.2±5.3% at Week 20.ConclusionsRabbit bilateral carotid arteries were grafted with carotid artery and jugular vein bridges to simulate pathophysiological processes that occur in people after CABG surgery.

Relaxation Effect of Epimedium Koreanum Extract on Rabbit Carotid Artery

Relaxation Effect of Epimedium Koreanum Extract on Rabbit Carotid Artery

Carotid body chemotransduction gets the human touch

Carotid body chemotransduction gets the human touch

Nitric oxide-loaded echogenic liposomes for treatment of vasospasm following subarachnoid hemorrhage

Delayed cerebral vasospasm following subarachnoid hemorrhage causes severe ischemic neurologic deficits leading to permanent neurologic dysfunction or death. Reduced intravascular and perivascular nitric oxide (NO) availability is a primary pathophysiology of cerebral vasospasm. In this study, we evaluated NO-loaded echogenic liposomes (NO-ELIP) for ultrasound-facilitated NO delivery to produce vasodilation for treatment of vasospasm following subarachnoid hemorrhage. We investigated the vasodilative effects of NO released from NO-ELIP both ex vivo and in vivo. Liposomes containing phospholipids and cholesterol were prepared, and NO was encapsulated. The encapsulation and release of NO from NO-ELIP were determined by the syringe/vacuum method and ultrasound imaging. The ex vivo vasodilative effect of NO-ELIP was investigated using rabbit carotid arteries. Arterial vasodilation was clearly observed with NO-ELIP exposed to Doppler ultrasound whereas there was little vasodilative effect without exposure to Doppler ultrasound in the presence of red blood cells. Penetration of NO into the arterial wall was determined by fluorescent microscopy. The vasodilative effects of intravenously administered NO-ELIP in vivo were determined in a rat subarachnoid hemorrhage model. NO-ELIP with ultrasound activation over the carotid artery demonstrated effective arterial vasodilation in vivo resulting in improved neurologic function. This novel methodology for ultrasound-controlled delivery of NO has the potential for therapeutic treatment of vasospasm following subarachnoid hemorrhage. This ultrasound-controlled release strategy provides a new avenue for targeted bioactive gas and therapeutic delivery for improved stroke treatment.

Myosin filaments in smooth muscle cells do not have a constant length

Myosin molecules from smooth muscle and non-muscle cells are known to self-assemble into side-polar filaments in vitro. However, the in situ mechanism of filament assembly is not clear and the question of whether there is a unique length for myosin filaments in smooth muscle is still under debate. In this study we measured the lengths of 16,587 myosin filaments in three types of smooth muscle cells using serial electron microscopy (EM). Sheep airway and pulmonary arterial smooth muscle as well as rabbit carotid arterial smooth muscle were fixed for EM and serial ultra-thin (50-60 nm) sections were obtained. Myosin filaments were traced in consecutive sections to determine their lengths. The results indicate that there is not a single length for the myosin filaments; instead there is a wide variation in lengths. The plots of observation frequency versus myosin filament length follow an exponential decay pattern. Analysis suggests that in situ assembly of myosin filaments in smooth muscle is governed by random processes of linear polymerization and de-polymerization, and that the dynamic equilibrium of these processes determines the observed length distribution.

Heat shock protein 27 attenuates neointima formation and accelerates reendothelialization after arterial injury and stent implantation: importance of vascular endothelial growth factor up‐regulation

Elevated serum heat shock protein 27 (HSP27) levels are atheroprotective; however, the role of HSP27 after arterial injury is unknown. Human endothelial progenitor cells (EPCs) were treated with recombinant (r)HSP27 (50 μg/ml) or its inactive C1 terminus, and gene expression was characterized before functional studies were performed in vitro and in vivo. Vascular endothelial growth factor (VEGF) was markedly up-regulated by rHSP27 (10- and 6-fold increases in mRNA and secretion, respectively). Pretreatment of EPCs with rHSP27 resulted in a 60% reduction in reendothelialization (RE) time in a scratch assay, an effect that was blocked with VEGF-neutralizing antibodies. Mice overexpressing HSP27 demonstrated more robust mobilization of EPCs at the time of arterial injury, as well as a 67% increase in RE and a 45% reduction in neointima (NI) formation at 28 d. Implantation of rHSP27-eluting stents in rabbit carotid arteries resulted in a marked improvement in RE at 7 and 28 d and transient attenuation of NI formation by 42% at 7 d. Hence, extracellular HSP27 up-regulated VEGF and improved EPC migration in vitro. Augmented systemic or local levels of HSP27 markedly improved RE after vascular injury, an effect that is of particular relevance to the safety profile of vascular stents.

MRI-guided Sonothrombolysis of Rabbit Carotid Artery

The potential of magnetic resonance imaging-guided focused ultrasound (MRgFUS) combined with the thrombolytic drug recombinant tissue plasminogen activator (rt-PA) to dissolve clots in the carotid of a New Zealand rabbit in vivo is evaluated. A spherically focused transducer of 5-cm diameter, focusing at 10 cm and operating at 1 MHz, was used. A pulsed ultrasound protocol was used that maintains a tissue temperature increase of less than 1 °C in the clot (called safe temperature). MRgFUS has the potentials to dissolve clots that are injected in the carotid of rabbits in vivo. It was found that the time needed for opening the carotid artery using ultrasound and rt-PA was decreased compared with just using rt-PA. The time needed for opening the artery decreases with increasing acoustic intensity. With an intensity of 20 W/cm2 (spatial average temporal average), which is not causing artery heating, the time needed to completely open the artery was 70 minutes. The proposed protocol was monitored using magnetic resonance angiography every 1 minute.

Endothelium-Dependent Vasorelaxation Effects of Rubus Coreanus extract on Rabbit Carotid Artery

This study was investigated to evaluate the vasorelaxant effect of Rubus coreanus(RC) extract on contracted rabbit carotid artery and its mechanism. To study the effect of RC extract on contracted rabbit carotid arterial strips, arterial strips with intact or damaged endothelium were used for experiment using organ bath. The pre-contracted arterial strips with norepinephrine(NE) or potassium chloride(KCl) was treated with various concentrations of an extract of RC(0.01, 0.03, 0.1, 0.3 and 1.0 ㎎/㎖). To determine the mechanisms of RC-induced vasorelaxant, RC extract was infused into contracted arterial rings which had been pretreated by indomethacin(IM), tetraethylammonium chloride(TEA), Nω-nitro-L-arginine (L-NNA), methylene blue(MB). And calcium chloride(Ca) 1 mM was infused into precontracted arterial ring induced by NE or KCl after treatment of RC extract in Ca<SUP>2+</SUP>-free krebs solution. Cytotoxic activity of RC extract on human umbilical vein endothelial cell(HUVEC) was measured by MTT assay, and nitric oxide(NO) prodution was measured by Griess reagent. RC extract revealed significant relaxation on NE-induced arterial contraction, but didn"t relax on KCl-induced arterial contraction. RC extract also had an effective relaxation to the intact endothelium arterial ring, but not the damaged endothelium arterial ring. Treatment of IM, TEA, L-NNA, MB reduced the relaxation of RC extract. Pretreatment of RC extract inhibited the contraction by influx of extracellular Ca<SUP>2+</SUP> in contracted arterial ring induced by NE, but it didn"t work the contraction by influx of extracellular Ca<SUP>2+</SUP> in contracted arterial ring induced by KCl in Ca<SUP>2+</SUP>-free krebs solution. RC extract increased nitric oxide production on HUVEC. This study indicated that the relaxation effect of RC extract on contracted rabbit carotid artery is related with NO-cGMP pathway, EDHF, prostacyclin.

Effects of exercise training on adrenergic and cholinergic responses of rabbit carotid artery

Effects of exercise training on adrenergic and cholinergic responses of rabbit carotid artery

Treatment of rabbit carotid aneurysms by hybrid stents (microporous thin polyurethane-covered stents): Preservation of side-branches

ObjectiveWe sought to determine the patency of normal arterial branches from the covered segments of an artery after stenting.BackgroundMost intracranial aneurysms occur at arterial branching points (bifurcations, side-branches, or perforators). The post-stenting patency of normal arterial branches from the covered segments of the artery is important. We have previously developed a hybrid stent with micropores to prevent early parent artery occlusion by more early endothelialization, and mid- to long-term parent artery stenosis by control of intimal hyperplasia after aneurysm occlusion.MethodsWe created aneurysms in 10 rabbits by distal ligation and intraluminal incubation of elastase within an endovascularly trapped proximal segment of the common carotid artery. All animals were treated with hybrid stents having micropores. Four animals were observed for one month and three each for three and 12 months. The patency of the side-branches of the subclavian artery was evaluated angiographically and in some cases, histologically.ResultsAneurysms were completely occluded at all time points other than 12 months. The subclavian artery and brachiocephalic artery were patent, without significant stenosis. All the side-branches of the subclavian artery detected on the preoperative angiogram remained patent at the final assessment.ConclusionThe use of hybrid stents for aneurysm repair and side-branch patency seems to be effective, as per the long-term results obtained in an animal model.

In Vitro and In Vivo Imaging Characteristics Assessment of Polymeric Coils Compared with Standard Platinum Coils for the Treatment of Intracranial Aneurysms

Conventional platinum coils cause imaging artifacts that reduce imaging quality and therefore impair imaging interpretation on intraprocedural or noninvasive follow-up imaging. The purpose of this study was to evaluate imaging characteristics and artifact production of polymeric coils compared with standard platinum coils in vitro and in vivo. Polymeric coils and standard platinum coils were evaluated in vitro with the use of 2 identical silicon aneurysm models coiled with a packing attenuation of 20% each. DSA, flat panel CT, CT, and MR imaging were performed. In vivo evaluation of imaging characteristics of polymeric coils was performed in experimentally created rabbit carotid bifurcation aneurysms. DSA, CT/CTA, and MR imaging were performed after endovascular treatment of the aneurysms. Images were evaluated regarding visibility of individual coils, coil mass, artifact production, and visibility of residual flow within the aneurysm. Overall, in vitro and in vivo imaging showed relevantly reduced artifact production of polymeric coils in all imaging modalities compared with standard platinum coils. Image quality of CT and MR imaging was improved with the use of polymeric coils, which permitted enhanced depiction of individual coil loops and residual aneurysm lumen as well as the peri-aneurysmal area. Remarkably, CT images demonstrated considerably improved image quality with only minor artifacts compared with standard coils. On DSA, polymeric coils showed transparency and allowed visualization of superimposed vessel structures. This initial experimental study showed improved imaging quality with the use of polymeric coils compared with standard platinum coils in all imaging modalities. This might be advantageous for improved intraprocedural imaging for the detection of complications and posttreatment noninvasive follow-up imaging.

Involvement of inducible nitric oxide synthase in radiation-induced vascular endothelial damage

The use of radiation therapy has been linked to an increased risk of cardiovascular disease. To understand the mechanisms underlying radiation-induced vascular dysfunction, we employed two models. First, we examined the effect of X-ray irradiation on vasodilation in rabbit carotid arteries. Carotid arterial rings were irradiated with 8 or 16 Gy using in vivo and ex vivo methods. We measured the effect of acetylcholine-induced relaxation after phenylephrine-induced contraction on the rings. In irradiated carotid arteries, vasodilation was significantly attenuated by both irradiation methods. The relaxation response was completely blocked by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, a potent inhibitor of soluble guanylate cyclase. Residual relaxation persisted after treatment with L-Nω-nitroarginine (L-NA), a non-specific inhibitor of nitric oxide synthase (NOS), but disappeared following the addition of aminoguanidine (AG), a selective inhibitor of inducible NOS (iNOS). The relaxation response was also affected by tetraethylammonium, an inhibitor of endothelium-derived hyperpolarizing factor activity. In the second model, we investigated the biochemical events of nitrosative stress in human umbilical-vein endothelial cells (HUVECs). We measured iNOS and nitrotyrosine expression in HUVECs exposed to a dose of 4 Gy. The expression of iNOS and nitrotyrosine was greater in irradiated HUVECs than in untreated controls. Pretreatment with AG, L-N6-(1-iminoethyl) lysine hydrochloride (a selective inhibitor of iNOS), and L-NA attenuated nitrosative stress. While a selective target of radiation-induced vascular endothelial damage was not definitely determined, these results suggest that NO generated from iNOS could contribute to vasorelaxation. These studies highlight a potential role of iNOS inhibitors in ameliorating radiation-induced vascular endothelial damage.

Transplantation of human thrombomodulin gene-modified endothelial progenitor cells to prevent vascular restenosis after balloon injury

Objective To explore the feasibility of transplantation of human thrombomodulin (hTM) gene-modified endothelial progenitor cells (EPCs) to rabbit carotid artery balloon injury model locally to prevent vascular restenosis.Methods Rabbit peripheral blood mononuclear cells were isolated and EPCs were modified with hTM gene using X-tremeGENE HP DNA Transfection Reagent.Genetically modified EPCs were incubated with Fe2O3-arginine.Sixteen adult New Zealand white rabbits were divided into two groups.hTM gene-modified EPCs,nom-gene modified EPCs and equal volume of normal saline were transplanted to the balloon injury local via Fogarty balloon catheter,respectively.Serial nuclear magnetic resonance (MRI) was performed on 1st,3rd,7th and 14th day after transplantation to assess the loss of MRI signal intensity at the injured sites.Four months later,the carotid arteries were isolated and cut for hematoxylin and eosin (HE) staining and elastic tissue staining to evaluate restenosis.Results The hTM gene could be successfully transfected into EPCs using Transfection Reagent and the efficiency rate was about 10％-15％.EPCs could be partly adhered to the injured site locally via Fogarty balloon catheter and result in the loss of magnetic resonance (MR) signal intensity at the injured sites.The neointimal/media ratio (N/M) in gene modified group,non-gene modified group and injured group was 0.30 ± 0.02,0.62 ± 0.05 and 1.58 ± 0.10,respectively (P ＜ 0.01).Conclusion hTM gene-modified EPCs could effectively prevent vascular restenosis after balloon injury. Key words: Thrombomodulin; Endothelial progenitor cells; Balloon injury; Restenosis

In vitro and in vivo investigations on the effects of low-density lipoprotein concentration polarization and haemodynamics on atherosclerotic localization in rabbit and zebrafish

Atherosclerosis (AS) commonly occurs in the regions of the arterial tree with haemodynamic peculiarities, including local flow field disturbances, and formation of swirling flow and vortices. The aim of our study was to confirm low-density lipoprotein (LDL) concentration polarization in the vascular system in vitro and in vivo, and investigate the effects of LDL concentration polarization and flow field alterations on atherosclerotic localization. Red fluorescent LDL was injected into optically transparent Flk1: GFP zebrafish embryos, and the LDL distribution in the vascular lumen was investigated in vivo using laser scanning confocal microscopy. LDL concentration at the vascular luminal surface was found to be higher than that in the bulk. The flow field conditions in blood vessel segments were simulated and measured, and obvious flow field disturbances were found in the regions of vascular geometry change. The LDL concentration at the luminal surface of bifurcation was significantly higher than that in the straight segment, possibly owing to the atherogenic effect of disturbed flow. Additionally, a stenosis model of rabbit carotid arteries was generated. Atherosclerotic plaques were found to have occurred in the stenosis group and were more severe in the stenosis group on a high-fat diet. Our findings provide the first ever definite proof that LDL concentration polarization occurs in the vascular system in vivo. Both lipoprotein concentration polarization and flow field changes are involved in the infiltration/accumulation of atherogenic lipids within the location of arterial luminal surface and promote the development of AS.

Performance effect of rabbit carotid artery treated with decellularization and photo-oxidation

To analyze and discuss the feasibility of rabbit carotid artery treated with decellularization and photo-oxidation. Sixty vascular slices of rabbit carotid artery were divided into a fresh group, a cryopreservation group, a glutaraldehyde group, and a decellularization plus photo-oxidation group 15 in each group. To evaluate the physical properties of all the rabbit carotid arteries by testing heat-shrinking temperature, tensile stress and the max elongation of each group. Then by buliding subcutaneous embedding model in SD rats we evaluated the biological stability and the anti-calcification function property of the above rabbit carotid arteries, and the detection means included HE stain, atomic absorption spectrometry and Von-Kossa calcium salt stain. The heat-shrinking temperature, tensile stress and the max elongation in the cryopreservation group were lower or shorter than those of the other groups and the difference had statistical significance (P<0.05). Although the heat-shrinking temperature and the tensile stress in the decellularization plus photo-oxidation group were lower or shorter than those in the glutaraldehyde group (P<0.05), the max elongation in the decellularization plus photo-oxidation group was much longer than that in the glutaraldehyde group (P<0.05). The rabbit carotid artery treated with decellularization plus photo-oxidation showed lower immunogenicity and better biological stability and better anti-calcification property compared with the other groups. Decellularization associated with photo-oxidation is a suitable and novel protocol for small caliber artery allograft with a diameter of less than 6 mm which is unbreakable to mechanical properties and conducive to biological stability, which has a broad prospect.

Abstract 249: Delayed Gene Transfer Increases Transgene Expression in Vein Grafts

Background Autogenous vein grafts are effective therapies for obstructive arterial disease. However, their long-term utility is limited by stenosis and occlusion. Genetic engineering of veins that prevents intimal hyperplasia and atherosclerosis could significantly improve the clinical utility of vein grafts. We recently reported that a helper-dependent adenoviral vector (HDAd) reduces atherosclerosis 4 wks after gene transfer in fat-fed rabbits and can express a therapeutic transgene (apo AI) in normal rabbit carotids for at least 48 wks. Use of HDAd for vein graft gene therapy will depend on achievement of similarly high and persistent transgene expression in grafted veins. Hypothesis We tested the hypothesis that Ad-mediated transgene expression in grafted veins (at an early time point) can be increased by varying the timing of gene transfer. Methods Rabbit external jugular veins were transduced by exposure to a beta galactosidase (b-gal)-expressing Ad: in situ either without (a) or with (b) immediate arterial grafting; c) ex vivo with grafting after overnight incubation with Ad; d) in vivo immediately after grafting and e) in vivo 4 wks after grafting (n = 6 - 19 veins/group). Transgene expression was measured in veins removed 3 d after Ad exposure by PCR quantitation of b-gal mRNA and by en-face planimetry of blue-stained area. Results B-gal transgene expression was higher in ungrafted veins than in veins grafted immediately after gene transfer (84 ± 17 vs 9.4 ± 2.0 arbitrary units (AU); P &lt; 0.0001). Overnight incubation of veins with Ad increased gene expression ex vivo by 10-fold but neither this nor performing vector infusion immediately after grafting improved gene expression (11 ± 4.7 and 9.1 ± 1.8 AU; P &gt; 0.9 for both vs immediately grafted veins). Delaying gene transfer until 4 wks after grafting significantly increased gene expression, to a level equivalent to transgene expression in ungrafted veins (61 ± 11 AU; P = 0.3 vs ungrafted veins). En face planimetry yielded similar results. Conclusions Exposure of a transduced vein to arterial blood flow is associated with significant loss of transgene expression. Transgene expression in grafted veins is significantly higher when gene transfer is performed 4 wks after exposure of the vein to arterial blood flow.