The rate of re-endothelialization correlates inversely with the degree of the following intimal thickening in vein grafts. Electron microscopic and immunohistochemical studies

External Biodegradable Supporting Conduit Protects Endothelium in Vein Graft in Arterial Interposition

The prevention of circumferential distension could reduce structural damage in arteriovenous grafts. We studied the effect of an external biodegradable supporting conduit on the endothelium and extracellular matrix in vein graft in a pig model. Cephalic vein control grafts (Group I) and jugular veins wrapped in a vicryl mesh tube (I.D. 4mm) (Group II) were implanted into autologous carotid arteries (n=14). The grafts were explanted after 1 and 24 hours and at 1 and 3 weeks and evaluated by ELISA for endothelial DNA synthesis and by immunohistoenzymic assays for cells and extracellular matrix. In group I an initial loss of endothelial and smooth muscle cells along with elastin breakdown was followed by an impaired endothelial regeneration and significant graft wall thickening. The elastic tissue was replaced by collagen type I and chondroitin sulfate accumulations, which included a disarray of α-smooth muscle actin positive cells. The endothelium was preserved in group II. After 3 weeks the circumferential elastin layers were densified, distended and separated from the endothelium by a neointimal growth of irregular thickness. Biodegradable perivenous conduit minimized endothelial injury and allowed the partial preservation of elastin fibers and smooth muscle cells in the arteriovenous graft. It did not however, prevent myofibroblastic cell proliferation and triggered a macrophagic reaction.

Suppression of postoperative intimal hyperplasia of vein grafts with edaravone in rat models - a scanning electron microscope study

PURPOSE

Postoperative intimal hyperplasia, the most common cause of vein graft occlusion, is initiated by endothelial injury. In the present study, the mechanism by which the free radical scavenger edaravone (Radicut, Mitsubishi Tanabe Pharma Co, Japan) protects against endothelial injury in postoperative intimal hyperplasia was investigated.

METHODS

In 18 male Lewis rats, a right epigastric vein graft was interposed into the common femoral artery. Nine rats received a pre-operative intraperitoneal administration of edaravone (3.0 mg/kg, edaravone group) and the other nine rats received an equal volume of saline (saline group). After 1 h, five vein grafts from each group were treated with Verhoeff-van Gieson elastica stain and subjected to a histological examination. The other four vein grafts from each group were examined with an S-800 Hitachi scanning electron microscope (SEM) (Hitachi High-Technologies Co, Japan) at ×1000 magnification, as were three unoperated right epigastric veins (unoperated vein group). The endothelial areas of the vein grafts were measured using computerized planimetry of the SEM images (ImageJ version 1.37, National Institutes of Health, USA). The mean endothelial areas (%) were compared between the two groups.

RESULTS

Verhoeff-van Gieson elastica stain revealed no significant differences between the two groups. SEM showed that endothelial cells in the unoperated epigastric vein had a cobblestone-like appearance. In the saline group, the endothelial cells were comb-shaped and had adherent monocytes. In the edaravone group, however, the cobblestone-like appearance of endothelial cells was well preserved, with little monocyte adhesion. Moreover, the mean (± standard error of the mean) endothelial area was significantly higher in vein grafts from the edaravone group than in those from the saline group (74±1.8% versus 56±4.3%, P<0.05), and was similar to those in the unoperated epigastric veins (72±1.9%).

CONCLUSION

These findings show that endothelial injury is present soon after placement of the interposition graft. The authors believe that edaravone suppresses postoperative intimal hyperplasia by alleviating endothelial injury.

Ex vivo electroporation as a potent new strategy for nonviral gene transfer into autologous vein grafts

Gene transfer to vein grafts has therapeutic potential to prevent late graft failure; however, certain issues, including efficacy and safety, have hindered the clinical application of this treatment modality. Here, we report the successful and efficient gene transfer of plasmid DNA via ex vivo electroporation into veins as well as into vein grafts. Two approaches were used: one involved transluminal in situ gene transfer using a T-shaped electrode (the “Lu” method), and the other was an adventitial ex vivo approach using an electroporation cuvette followed by vein grafting (the “Ad” method). The Lu method was carried out at 10 V, with optimal gene transfer efficiency in the in situ jugular veins of rabbits, and transgene expression was observed primarily in endothelial cells. However, when these veins were grafted into the arterial circulation, no luciferase activity was detected; this effect was probably due to the elimination of the gene-transferred cells as a result of endothelial denudation. In contrast, optimal and satisfactory gene transfer was obtained with the vein grafts subjected to the Ad method at 30 V, and transgene expression was seen primarily in adventitial fibroblasts. Gene transfer of endothelial nitric oxide synthase cDNA to the vein graft via the Ad method successfully limited the extent of intimal hyperplasia, even under hyperlipidemic conditions, at 4 wk after grafting. We thus propose that the Ad method via ex vivo electroporation may provide a novel, safe, and clinically available technique for nonviral gene transfer to sufficiently prevent late graft failure.

Intraluminal gene transfer of endothelial cell-nitric oxide synthase suppresses intimal hyperplasia of vein grafts in cholesterol-fed rabbit: a limited biological effect as a result of the loss of medial smooth muscle cells

BACKGROUND

The intimal hyperplasia of vein grafts is a major cause of late graft failure and is more pronounced under hyperlipidemia. We previously reported that endothelial cell (ec)-type nitric oxide synthase (NOS) gene transfer inhibited graft intimal hyperplasia under poor runoff conditions. However, little information is available on either ecNOS gene transfer or intimal thickening under hypercholesterolemia.

METHODS

Using the hemagglutinating virus of Japan liposomes, bovine ecNOS complentary DNA (5000 hemagglutinating activity units/mL) was transfected intraluminally to the right jugular vein, and these veins were then implanted as reversed vein grafts in an end-to-side fashion to the ipsilateral carotid artery.

RESULTS

The cyclic guanosine 3',5'-monophosphate content of the ecNOS vein significantly increased in the grafts at 4 days after gene transfer, but the levels were only 25% greater than those found in the untreated veins. An immunohistochemical analysis at the same time suggested a large loss of medial smooth muscle cells that might have led to a reduction in the exogenous gene expression. The neointima of the ecNOS grafts was significantly reduced 4 weeks after implantation (P <.05), but the effect of ecNOS was limited to about a 30% inhibition. This reduction was associated with a reduced population of proliferating cells and decreased macrophage accumulation in the graft wall.

CONCLUSIONS

These results demonstrated that the ecNOS gene transfer suppressed intimal hyperplasia of the vein grafts under hyperlipidemic conditions. However, this effect may be limited because of the smooth muscle cell loss related to the use of an intraluminal delivery methods. These data lead to speculation that the outcome of ecNOS gene transfer could be improved using different methods of gene delivery.

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.

Acute intraoperative arterial elongation: an experimental study

OBJECTIVES

small arterial defects resulting from either trauma or resection of an aneurysm often present difficult problems to the vascular surgeon.

DESIGN

to demonstrate that certain arterial gaps as a result of traumatic injury or aneurysm resection could be closed with acute intraoperative arterial elongation.

MATERIALS

fifteen mongrel dogs underwent acute intraoperative arterial elongation of the right superficial femoral artery, with the left side used for a control vessel.

METHODS

arterial defects created surgically (median 50 (range 25 to 60 mm) mm). Appropriate length of artery was then undermined. A Foley catheter was placed proximally and distally directly beneath this undermined portion of vessel. The vessel is lengthened following 3 expansion/relaxation cycle of Foley catheter. Arterial gaps were closed by end to end anastomosis. Arterial pressure study was performed in all vessels.

RESULTS

acutely, arterial pressure differences proximal and distal to the anastomosis were seen only when arterial gaps were exceeded 55 mm. There was no occlusion either acutely or after 4 weeks follow-up period. Light microscopic examination of arterial specimens revealed partial disruption of internal elastic lamina. At the end of the follow-up period, formation of neointima with regeneration of the internal elastic lamina was demonstrated. Scanning electron microscopy revealed minimal endothelial denudation.

CONCLUSIONS

we believe that, acute intraoperative elongation can be used as an alternative technique to vein grafting for the repair of small traumatic arterial defects in selected cases.

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.

Experimental studies on the endothelium ultrastructure of heart capillaries under moderate (28-30 degrees) and deep (22-24 degrees) hypothermia without perfusion

Ultrastructural changes in endothelial cells (EC) of myocardial capillaries were studied in 24 dogs which underwent hypothermia without perfusion. Biopsy specimens for electron microscopy were taken from the left ventricle of each dog in the control group, during anesthesia (prior to active cooling), and at the end of moderate (28-30 degrees ) and deep (22-24 degrees ) artificial body cooling. The following morphological types of the EC were identified both in the control group and in all test groups: those with moderately dense cytoplasm, light, dark, and irreversibly damaged cells. Dark cells showed increased numbers of plasmalemmal vesicles and appeared to be more transport-specialized as opposed to other types. In all stages of the experiment the amount of dark cells continuously increased (to 23.80, 34.62, and 47.17%, respectively). On cooling to 28-30 degrees, subcellular manifestation of reduced synthetic activity of organelles (nucleus, Golgi complex, and rough endoplasmic reticulum) was observed in all types of the EC. These changes persisted, or even increased, at the end of deep hypothermia. The transport activity of the EC changed differently in three experimental groups in all cell types. Micropinocytotic activity increased under spontaneous mild hypothermia (34-35 degrees ) during anesthesia and tended to decrease with subsequent artificial lowering of the temperature to 22-24 degrees. These ultrastructural changes seem to make up an integral part of the process of capillary endothelium adaptation to body surface cooling, and they might contribute to the development of tolerance to subsequent ischemic exposure during cardiac arrest.

An ultrastructural study of progressive intimal hyperplasia in rat vein grafts

PURPOSE

Intimal hyperplasia (IH) poses the greatest challenge for vein graft success. This fibroproliferative disorder causes obliterative stenosis and frequent graft occlusion. Although its causes remain poorly understood, it has been proposed that IH begins as a wound-healing response that cascades into a chronic state of unchecked proliferation. In this ultrastructural study, IH development and concomitant cell changes were evaluated in rat vein grafts.

METHODS

Epigastric vein-to-femoral artery grafts were placed in Lewis rats using standard microsurgical techniques. At various time points, grafts were harvested and processed for transmission electron microscopic, histologic, and immunohistochemical analyses. The proximal region, which displayed the most marked IH, was assessed for ultrastructural changes.

RESULTS

Our findings showed: (1) regeneration of the damaged endothelium by cells displaying an activated appearance; (2) early and complete smooth muscle cell death, with subsequent replacement by myofibroblastic cells; (3) extensive and sustained graft infiltration by monocytes/macrophages; and (4) intramural fibrin deposition.

CONCLUSIONS

The rat vein graft wall was substantially altered after implantation into the arterial circulation. During and after IH development, the cells in the graft did not resemble cells that are present in the nongrafted epigastric vein. Marked cell death, mononuclear cell infiltration, and the presence of myofibroblastic cells suggest a state of aberrant wound healing.

Preexisting vascular pathology in donor and recipient vessels during penile microvascular arterial bypass surgery

The quality of the anastomosed vessels before vascular grafting has been shown to influence long-term patency rates in arterial reconstructive procedures. A study was designed to assess vascular graft quality during microvascular artery bypass procedures for impotence, correlate identified vasculopathy with the clinical history and gain insight into vascular pathophysiological mechanisms. A total of 194 donor or recipient vessel segments was biopsied in 111 patients with impotence who underwent microvascular artery bypass surgery during a 10-year period. A prospective histological grading system was used in a blinded randomized fashion. A preexisting vascular pathological condition was identified in 48% of the patients. Proliferative lesions above the internal elastic lamina with luminal stenosis were identified in 38 of 69 dorsal penile artery segments (55%) and 8 of 69 inferior epigastric artery segments (12%). Venous hypertrophy or sclerosis was observed in 13 of 56 deep dorsal vein segments (23%). Systemic atherosclerosis was likely the underlying pathophysiology of vascular disease in the inferior epigastric artery. Vasculopathy in the deep dorsal vein and the dorsal penile artery segments was probably related to the consequences of blunt trauma to the pelvis, perineum or penis, which was considered to occur following direct vessel wall injury with immediate or delayed vascular disease or indirect vessel wall injury secondary to proximal arterial occlusion and delayed distal vascular disease. Future studies are needed to investigate the relationship between preexisting graft vasculopathy in microvascular artery bypass surgery for impotence and long-term clinical success rates.

The native venous architecture is preserved in an arterialized deep dorsal vein graft for arteriogenic impotence: a case report

Endothelial injury in a deep dorsal vein graft may result from thermal, ischemic or mechanical trauma during surgical preparation or following exposure to systemic blood pressures and flow. We removed a functioning in situ deep dorsal vein graft section 10 months after microvascular arterial bypass surgery due to glans hyperemia. This section was compared and contrasted histomorphologically with a preoperative deep dorsal vein section that was procured for routine histological examination before the arteriovenous anastomosis. Detailed examination of the vein graft tissues by light microscopy, computer morphometrics and immunological staining demonstrated no evidence of vascular pathology. In the normal, healthy deep dorsal vein graft exposure to systemic arterial blood pressures and flow for 10 months did not result in myointimal proliferative lesions. Such histological changes seem more likely to be attributable to endothelial injury following iatrogenic surgical trauma. In situ vein grafts offer the opportunity to use "no-touch" endothelium preserving vascular techniques. Use of these grafts may improve long-term clinical results in penile microvascular arterial bypass surgery for impotence as it has in other vascular beds.

The modulation of smooth muscle cell phenotype is an early event in human aorto-coronary saphenous vein grafts

The morphological changes in human vein grafts occurring in the first days after a coronary bypass operation (CBP) are rarely reported in the literature. Sections of aorto-coronary vein grafts from 11 patients who died during the first 10 days after a CBP were obtained at autopsy. The number of vein grafts per patient ranged from 1 to 4, yielding a total of 28 vein grafts. The early changes in the vein grafts have been studied by light microscopy, immunohistochemistry, transmission and scanning electron microscopy. The study demonstrates that soon after grafting, the vein wall is infiltrated by polymorphonuclear leucocytes (PMN). At 24 h the endothelium shows extensive desquamation. The massive migration of PMN through the venous wall occurs simultaneously with the endothelial damage. The circular layer of the media is severely damaged, resulting in a loss of smooth muscle cells (SMC). The remaining SMC in this layer show a change toward the synthetic phenotype and a reduced expression of alpha-smooth muscle actin. These early changes in the SMC function may initiate the process of fibrosis in the intima and the media of the vein grafts.

Endothelium-dependent responses in long-term human coronary artery bypass grafts

In the present study, responses of long-term human coronary artery bypass grafts (CABGs) to known endothelium-dependent vasodilators, acetylcholine, calcium ionophore A23187, thrombin, and histamine, as well as authentic nitric oxide, the putative endothelium-derived relaxing factor, were studied. Sixteen CAGBs were isolated within 1-2 hours from hearts of 14 patients receiving a cardiac transplant. A total of 109 ring segments were prepared from these CABGs and studied in vitro. The duration of the CABGs ranged from 7 months to 12 years. Addition of acetylcholine (0.01-10 microM), calcium ionophore A23187 (0.01-1.0 microM), thrombin (0.01-1.0 unit/ml), and histamine (0.01-1.0 microM) consistently produced a dose- and endothelium-dependent relaxation, reaching a maximum of -35.3 +/- 3.3%, -45.3 +/- 5.5%, -26.9 +/- 4.8%, and -17.8 +/- 2.5% (mean +/- SEM), respectively. No significant difference was observed among the CABGs with different duration of transplantation, whereas the relaxant responses of different segments along the entire length of a CABG were markedly different. These latter differences in the endothelium-dependent responses appear to correlate inversely with the development of intimal proliferative lesions in these CABGs. Addition of nitric oxide (0.01-10 microM) produced a potent dose- and endothelium-independent relaxation, which was also slightly depressed in CABGs with severe intimal proliferation. These results demonstrate that long-term transplanted human saphenous vein grafts retain their endothelium-dependent responses and that development of severe intimal proliferative lesions, rather than the duration of the grafts, result in marked alterations in the reactivity of these transplanted CABGs.