Computational simulation method of intraluminal velocity profile proved by laser Doppler velocimeter

Angiotensin II-induced growth of vascular smooth muscle cells is associated with modulation of cell surface area and platelet-derived growth factor receptor expression

1. Excessive growth of vascular smooth muscle cells (VSMC) can lead to critical problems in the treatment of some vascular diseases. Recent studies suggest a connection between this abnormal growth of VSMC and the octapeptide hormone angiotensin (Ang) II. However, the growth-promotive potential of AngII on VSMC is unclear. 2. Using the novel AngII inhibitor E4177 and an original animal model, we confirmed that AngII does function in abnormal growth of VSMC induced after transplantation of vein grafts in an animal model. 3. Furthermore, using a primary culture of human aortic smooth muscle cells (HASMC), we found that AngII augmented the growth of HASMC in a serum-dependent manner and induced enlargement of the cell surface area in HASMC, both effects being nullified by E4177. The latter effect of AngII was associated with an increase in the expression level of platelet-derived growth factor (PDGF) receptors. In specimens obtained from the animal model, PDGF receptors were highly expressed. 4. These data obtained in vitro and in vivo imply that AngII has the potential to promote growth of VSMC and suggest that this growth promotion may be mediated by enlargement of the cell surface area.

Intramuscular gene transfer of FGF-2 attenuates endothelial dysfunction and inhibits intimal hyperplasia of vein grafts in poor-runoff limbs of rabbit

We previously demonstrated that sustained disturbance of endothelium-dependent vasorelaxation and poor distal runoff in ischemic limbs were critical factors affecting the neointimal development of autologous vein grafts (VGs). Also, we recently showed the superior therapeutic potential of basic fibroblast growth factor (bFGF/FGF-2) boosted by the recombinant Sendai virus (SeV) for severe limb ischemia compared with that of vascular endothelial growth factor. Here, the effect of FGF-2 on neointimal hyperplasia of VGs was examined in a rabbit model of poor-runoff limbs. Two weeks after initial surgery for the induction of poor-runoff, SeV-expressing human FGF-2 (SeV-hFGF2) or that encoding firefly luciferase (109 plaque-forming units/head) was injected into the thigh and calf muscle. At that time, the femoral vein was implanted in the femoral artery in an end-to-end manner in some groups. FGF-2 gene-transferred limbs demonstrated significantly increased blood flow assessed not only by laser Doppler flow image but also by ultrasonic transit-time flowmeter (USTF). USTF also showed a significant increase in the blood flow ratio of the deep femoral artery to external iliac artery, indicating that collateral flow was significantly restored in the thigh muscles (P < 0.01). Reduction of neointimal hyperplasia was also observed in the VGs treated by SeV-hFGF2; these grafts demonstrated significant restoration of endothelium-dependent vasorelaxation. These findings thus extend the indications of therapeutic angiogenesis using SeV-hFGF2 to include not only limb salvage but also prevention of late graft failure.

Gene therapy in vascular surgery comes of age

In the last decade, gene therapy for cardiovascular diseases has been becoming a reality. However, although numerous successful experimental studies have suggested possible strategies of gene therapy for cardiovascular disorders, the clinical outcome remains limited. Because cardiovascular diseases are the result of complex causes, there is no exact answer to the following question: Which is the best gene to treat vascular diseases? In addition, current limitations include less clinically relevant vectors regarding both gene-transfer efficiency and safety, and at present, most efforts are focused on identifying more effective therapeutic genes, as well as developing more effective vectors. Furthermore, greater pathophysiologic understanding of these diseases, including vein-graft remodeling and ischemic limbs, is required. Regarding the relevant vector, we recently developed a novel mononegavirus-based gene-transfer vector, namely recombinant Sendai virus, which has shown dramatically superior gene-transfer efficiency to other vectors, including adenovirus, in several organs (eg, the vessel wall and skeletal muscles). These efforts now offer new possibilities to get more fruits in the field of gene therapy for vascular surgery.

Inhibitory effect of prostaglandin E 1 on intimal thickening caused by poor runoff conditions in the canine autologous vein grafts

The efficacy of ONO-1608, a newly developed liposomal formulation of prostaglandin E 1 prodrug, was evaluated on intimal hyperplasia of experimental canine autologous vein grafts under distal poor runoff conditions. The femoral vein was implanted into the femoral artery, preparing a distal poor runoff canine model. After 4 weeks of preparing the poor runoff model, the femoral vein was implanted into the femoral artery. They were then divided into two groups consisting of the control group and the ONO-1608 group. At 4 weeks, the grafts were harvested and intimal hyperplasia of the graft was measured with an ocular cytometer. Intimal cell proliferation was determined by bromodeoxyuridine incorporation 2 weeks after surgery. In addition, the effect of ONO-1608 on the proliferation of platelet-derived growth factor (PDGF)-stimulated human aortic smooth muscle cells (HASMCs) in culture was also investigated. At 4 weeks, the degree of intimal hyperplasia of the graft in the ONO-1608 group was significantly less than that of the control group. The bromodeoxyuridine labeling index 2 weeks after grafting was significantly lower in the ONO-1608 group compared with that in the control group. In addition, ONO-1608 significantly inhibited the proliferation of PDGF-stimulated HASMCs in culture. These results demonstrate the efficacy of ONO-1608 in reducing the degree of intimal hyperplasia of canine autogenous vein grafts under poor runoff conditions. The mechanism of reducing the intimal hyperplasia may be that ONO-1608 inhibited PDGF-stimulated proliferation of the smooth muscle cell. These results suggest that the administration of ONO-1608 may be beneficial in patients who have undergone gone arterial reconstruction.

Non-penetrating Vascular Clips Anastomosis Inhibited Intimal Thickening Under Poor Runoff Conditions in Canine Autogenous Vein Grafts

OBJECTIVE

Late graft failure is still a significant problem, particularly in cases with poor runoff vessels. The main cause of late graft failure is intimal thickening of the anastomotic region. Vascular closure system (VCS) clips may provide ideal anastomosis, since they do not penetrate the wall. Therefore, we examined whether the VCS clips affect intimal thickening under poor runoff conditions in the canine autogenous vein grafts.

METHODS

A canine poor runoff model was prepared at both femoral veins. Four weeks after the first surgical procedure, two groups were established according to the two different methods of anastomosis employed. The right femoral vein graft was performed using polypropylene sutures, conventional surgical anastomosis (control group), while the left femoral vein graft was performed using VCS clips anastomosis (VCS group). Four weeks after grafting, the vein grafts were removed and the intimal thickening of proximal, distal anastomosis and midportion of the vein grafts were examined histologically.

RESULTS

In the control group, flow rate and variation were 26+/-8 ml/min and 51+/-10 dynes/cm(2), respectively. In the VCS group, the flow rate and variation were 23+/-11 ml/min and 44+/-14 dynes/cm(2), respectively. There were no significant differences between the two groups. The average value of intimal thickening of both the anastomotic region and the midportion of the vein graft in the VCS group was significantly inhibited compared to that of the control group. The number of positive cells of masson trichrome stain in the VCS group was significantly less than that of the control group.

CONCLUSIONS

These experiments indicate that VCS clips significantly inhibit intimal thickening under poor runoff conditions in canine autogenous vein grafts to a greater extent compared to suture-constructed anastomosis. One mechanism that may account for the decreased intimal thickening is the inhibition of the expression of transforming growth factor-beta (TGF-beta), because the number of positive cells of masson trichrome stain in the VCS group was significantly less than that of the control group.

Immunohistochemical phenotypic alterations of rabbit autologous vein grafts implanted under arterial circulation with or without poor distal runoff-implications of vein graft remodeling

Although intimal hyperplasia is a major cause limiting the long-term patency of the vein grafts, its precise mechanisms, including the effect of poor runoff, has not yet been well characterized. We thus designed the present study to try to determine the effect of poor runoff arterial flow to the phenotypic alterations of the graft wall by immnohistochemistry using anti-intermediate filaments (alpha-SM actin, desmin, and vimentin) and anti-myosin heavy chain (SM1, SM2, and SMemb) specific antibodies. Vein grafts implanted under the poor runoff hind limb of rabbits showed enhanced intimal hyperplasia, however, no apparent difference in the cytoskeleton expression, including intermediate filaments and MHC, between two groups until 4 weeks. Interestingly, six of eight vein grafts at 2 weeks after implantation in both groups showed the accumulations of perivascular fibroblast-like phenotype (negative for SM1, alpha-SM actin, and desmin) in some parts of the outer neointima, whereas the inner neointima at 2 weeks and the whole neointima at 4 weeks were mainly occupied by a smooth muscle phenotype (positive for these three). Although the cellular origin of these cells is still unknown, these results suggest that the migration of non-muscle mesenchymal cells is involved in the neointima and thus may provide a clue for better understanding vein graft remodeling.

Modulation of platelet aggregation after percutaneous transluminal angioplasty of the iliac artery for atherosclerosis obliterans

BACKGROUND

Platelet aggregation is modulated by blood flow. We investigated whether platelet function is altered during percutaneous transluminal balloon angioplasty in patients with atherosclerosis obliterans.

METHODS

Blood samples were obtained from the iliac artery in 9 lower limbs of 7 patients undergoing percutaneous balloon angioplasty of the iliac artery. An agonists-induced platelet aggregation test was performed with an aggregometer. Femoral blood flow was measured with a Doppler velocimeter before and after the procedure.

RESULTS

Before dilatation, the maximum platelet aggregation rates (+/- SEM) induced by adenosine phosphate, epinephrine, and arachidonic acid were 54.7% +/- 5.8%, 64.8% +/- 4.3%, and 60.5% +/- 6.1%, respectively. After angioplasty, these values reduced to 36.7% +/- 4.1%, 36.1% +/- 8.6%, and 40.1% +/- 5.0%, respectively (P < .05). The pre-procedural ankle-brachial pressure index, mean flow rate, mean velocity, and shear stress variation were 0.63 +/- 0.1, 218.1 +/- 32.1 mL/min, 9.4 +/- 1.1 cm/sec, and 60.6 +/- 17.7 dyne/cm2, respectively. The mean velocity at the stenotic lesion was 215.1 +/- 83.9 cm/sec, which was significantly greater than those of the distal artery or after angioplasty (P < .01). Both ankle-brachial pressure index and shear stress variation increased after angioplasty to 0.99 +/- 0.07 (P < .05) and 139.8 +/- 17.0 (P < .05) dyne/cm2, but the mean flow rate and the mean velocity (198.3 +/- 24.5 mL/min and 8.8 +/- 1.2 cm/sec after angioplasty) did not change significantly.

CONCLUSIONS

These results indicate that activated platelet function at a stenosed artery was decreased after angioplasty, possibly because of normalized blood flow with reduction of stenotic lesion.

Hemagglutinating virus of Japan-liposome-mediated gene transfer of endothelial cell nitric oxide synthase inhibits intimal hyperplasia of canine vein grafts under conditions of poor runoff

PURPOSE

Late graft failure is a critical problem, particularly in the presence of poor runoff vessels. Intimal hyperplasia is considered to be the main cause of graft failure. We have already reported that intimal thickening of experimental vein grafts in dogs with poor runoff vessels is more pronounced than that in dogs with normal vessels. We and others also have reported that production of nitric oxide (NO) in the endothelium of canine vein grafts is impaired. In the present study, we asked whether in vivo gene transfer of endothelial cell NO synthase (ecNOS) would inhibit intimal hyperplasia of autogenous vein grafts implanted in limbs with poor distal runoff in dogs.

METHODS

After exposing femoral veins, the nuclear-targeted lac Zgene, bovine ecNOS cDNA, or control vector plasmid encapsulated in the hemagglutinating virus of Japan-liposomes was infused intraluminally, followed by incubation for 10 minutes at room temperature under a distending pressure of 100 mm Hg. Twenty reversed vein grafts were implanted under normal runoff conditions, and 4 days later these were used to confirm gene transfer to the vein grafts. Twelve reversed vein grafts were implanted under conditions of poor runoff, and 4 weeks after the operation intimal thickening was evident.

RESULTS

In vein grafts under normal runoff conditions, lac Z gene transfer exhibited diffuse and frequent X-Gal-positive signals in both medial and adventitial layers 4 days after implantation (n = 3). In case of the ecNOS gene-transferred vein grafts, bovine ecNOS protein was mainly detected in medial smooth muscle cells and adventitial cells 4 days after implantation, determined using immunohistochemical techniques and bovine ecNOS specific antibody (n = 3). In addition, ecNOS-transferred vessels showed intense purple signals by reduced nicotinamide adenine dinucleotide phosphate diaphorase and nitroblue tetrazolium reaction, in both medial and adventitial layers, whereas weak NOS activity was recognized at the adventitial vasa vasorum of the untreated veins or control vector transferred veins (n = 3, respectively). In vein grafts under poor runoff conditions, the intimal thickness at 4 weeks after implantation was significantly reduced by ecNOS gene transfer (n = 4; 90.0 +/- 7.6 microns and 1.18 +/- 0.07 mm2) in comparison with buffer-treated vessels (n = 4; 195.8 +/- 25.7 microns and 2.62 +/- 0.48 mm2) or vector vehicle-treated vessels (n = 4; 193.0 +/- 15.8 microns and 2.65 +/- 0.22 mm2).

CONCLUSIONS

Our findings show that gene transfer of ecNOS inhibited intimal hyperplasia of canine vein grafts caused by poor runoff conditions, as a result of an increased local production of NO. Thus ecNOS gene transfer warrants further study as a possible approach to prevent late graft failure.

Acceleration of impairment of endothelium-dependent responses under poor runoff conditions in canine autogenous vein grafts

OBJECTIVES

To assess the effects of changes in shear stress on endothelium-dependent responses.

MATERIALS AND METHODS

Autologous vein grafts were implanted in poor or normal distal runoff limbs of 10 mongrel dogs. Six weeks after grafting the vein grafts were removed, cut into rings, and suspended in organ chambers for isometric tension recording.

RESULTS

The average value of intimal thickening was 110.7 +/- 45.2 microns in poor runoff limbs and 65.5 +/- 27.9 microns in control limbs, respectively. There was a significant difference between the two groups. Acetylcholine caused comparable endothelium-independent contractions in both groups. In the control group, adenosine diphosphate, thrombin and A23187 caused endothelium-dependent relaxations. In the poor runoff group, the endothelium-dependent relaxations caused by adenosine diphosphate and thrombin were impaired, while A23187 caused comparable endothelium-dependent relaxations. Direct relaxations in response to sodium nitroprusside were comparable between the two groups.

CONCLUSIONS

This dysfunction of the endothelium under conditions of abnormal flow may accelerate intimal thickening of the vein graft and result in late graft failure.

Preserved endothelial function and morphology in canine arterial grafts under conditions of poor distal runoff

Late graft failure is still a significant problem particularly in vessels with poor runoff. In the present study, we examined whether poor runoff conditions contributed to either functional or morphological changes in experimental canine autogenous arterial grafts. Four weeks after grafting, isometric tension studies were performed on rings obtained from femoral arterial grafts with poor runoff and the findings were compared to rings from grafts with normal runoff. The flow rate and tau variation (wall shear stress variation) in the limbs with poor runoff (18.5 +/- 4.2 ml/min, 52.9 +/- 7.0 dyne/cm2) were significantly lower than those of the control limb (66.4 +/- 9.2 ml/min, 201.1 +/- 9.6 dyne/cm2). Acetylcholine (ACh), adenosine 5'-diphosphate (ADP), and A23187 (calcium ionophore) caused comparable endothelium-dependent relaxations in the two groups. Smooth muscle relaxation in response to sodium nitroprusside was also comparable in the two groups. No apparent intimal thickening of the arterial grafts was observed in the canine arterial grafts with normal or poor runoff. Scanning electron microscopy demonstrated mild endothelial cell damage in implanted autogenous arterial grafts. At 7 to 14 days after grafting, the endothelial cell layer in both groups of grafts appeared to be normal. These results are markedly different from our previous findings with vein grafts in which pronounced intimal thickening was associated with an impairment of the endothelium-dependent responses under conditions of poor runoff. Based on these findings, the intact endothelial function and the absence of intimal thickening under conditions of poor runoff may thus explain the improved patency of autogenous arterial grafts compared to the vein grafts in aortocoronary revascularization.

Simulated blood flow and the effects on prostacyclin production in the dog femoral artery

Effects of blood flow on the production of prostacyclin (PGI2) were examined in the canine femoral artery perfused ex vivo. Each artery was perfused in situ with medium 199, under conditions of simulated blood flow. To simulate the normal and abnormal blood flow waveforms at the same mean flow rate, we developed a flow apparatus capable of making various waveforms by changing the duration when the electromagnetic valve in the circuit was open. Group I (n = 7) was exposed to a steep acceleration waveform followed by a steep deceleration, as the normal flow waveform; group II (n = 7) was exposed to a gentle sloping waveform in the deceleration phase, as the abnormal flow waveform. PGI2 was measured as 6-ketoprostaglandin F1 alpha. PGI2 production was estimated as the cumulative production for the first 5 minutes (acute response) and as the production rate after the first 30 minutes (stable production rate). Under conditions of normal flow, the acute response was 5.87 +/- 2.16 ng/cm2/5 min, whereas under conditions of abnormal flow, the rate was 2.20 +/- 0.27 ng/cm2/5 min (p less than 0.01). Stable production rates were 82.5 and 37.5 pg/cm2/min, respectively (p less than 0.05). Both the acute response and the stable production rate of PGI2 production were greater under conditions of simulated normal flow as compared with findings in the case of an abnormal flow. Our working hypothesis is that the decreased production of PGI2, as well as a deterioration in the implanted graft, under conditions of abnormal blood flow leads to a loss of late patency of the reconstructed arteries.