Modulation of phosphatidylinositol 3-kinase signaling reduces intimal hyperplasia in aortocoronary saphenous vein grafts

OBJECTIVES: Fifty percent of human aortocoronary saphenous vein grafts are occluded after 10 years. Intimal hyperplasia is an initial step in graft occlusion and consists of vascular smooth muscle cell proliferation. Phosphatidylinositol 3-kinase and its downstream regulator, the inositol 3-phosphatase PTEN (phosphatase and tensin homolog deleted on chromosome 10), are important regulators of vascular smooth muscle cell proliferation, migration, and cell death. This study tests whether overexpression of PTEN in aortocoronary saphenous vein grafts can reduce intimal hyperplasia. METHODS: Adult dogs underwent aortocoronary bypass grafting to the left anterior descending artery by using the autologous saphenous vein. Saphenous vein grafts were treated with phosphate-buffered saline (n = 9), empty adenovirus (n = 8), or adenovirus encoding for PTEN (n = 8). Arteriography at 30 and 90 days assessed saphenous vein graft patency. A subset received saphenous vein grafts treated with a marker transgene (beta-galactosidase, n = 3), empty adenovirus (n = 4), or adenovirus encoding for PTEN (n = 4) and were killed on postoperative day 3 to confirm expression. Vascular smooth muscle cells were isolated from canine saphenous vein infected with adenovirus encoding for PTEN, and immunoblotting and proliferation assays were performed. RESULTS: Saphenous vein graft transgene expression was confirmed by means of immunohistochemistry, immunoblotting, and polymerase chain reaction. Arteriograms revealed all saphenous vein grafts to be patent. Saphenous vein grafts treated with adenovirus encoding for PTEN demonstrated reduced intimal area compared with those treated with empty adenovirus and phosphate-buffered saline (1.39 +/- 0.11 vs 2.35 +/- 0.3 and 2.57 +/- 0.4 mm 2 , P < .05), and the intima/media ratio was lower in saphenous vein grafts treated with adenovirus encoding for PTEN (0.50 +/- 0.05 vs 1.43 +/- 0.18 and 1.11 +/- 0.14, P < .005). PTEN overexpression in vascular smooth muscle cells inhibited platelet-derived growth factor-induced phosphorylation of Akt, a downstream effector of phosphatidylinositol 3-kinase. PTEN-treated vascular smooth muscle cells demonstrated decreased basal, platelet-derived growth factor-stimulated, and serum-stimulated proliferation. CONCLUSION: This study demonstrates that PTEN overexpression in aortocoronary saphenous vein grafts reduces intimal hyperplasia. The mechanism of this antiproliferative effect in vascular smooth muscle cells is likely due to inhibition of phosphatidylinositol 3-kinase signaling through Akt, with resultant decreases in vascular smooth muscle cell growth and survival. Therefore modulation of the phosphatidylinositol 3-kinase pathway through PTEN overexpression might represent a novel therapy to prevent saphenous vein graft intimal hyperplasia after coronary artery bypass grafting.     

Reduction of intimal hyperplasia and enhanced reactivity of experimental vein bypass grafts with verapamil treatment.

Recent studies have shown that calcium antagonists exert an antiatherogenic effect in animals fed cholesterol. Vein graft intimal hyperplasia is believed to be an early event in atherosclerotic lesion formation, which is a significant cause of graft failure. Altered vasoreactivity has also been postulated in the etiology of vein graft failure. Therefore this study examined the effect of verapamil treatment on the development of intimal hyperplasia and the vasoreactivity of experimental vein bypass grafts. The right external jugular vein was grafted into the right carotid artery of 30 male New Zealand white rabbits fed normal rabbit chow. The left external jugular vein was used as the control vein. Fifteen animals received verapamil (1.25 mg/day for 28 days) via the femoral vein by means of an osmotic pump. In 15 control animals the pump contained saline. Plasma verapamil concentration was 50.9 +/- 13.2 ng/mL (x +/- SEM), a dose that showed no effect on either blood pressure, total serum cholesterol, or in vitro platelet aggregation to ADP. Fourteen of fifteen grafts were patent in each group, for a patency rate of 93%. Histologic examination using computer morphometry showed significant reduction of intimal hyperplasia at the proximal, middle, and distal graft segments (p less than 0.05). In addition in vitro isometric tension studies of the vein grafts and control veins showed that verapamil causes enhanced reactivity of both vein grafts and control veins in response to norepinephrine and histamine (p less than 0.05). Reactivity of vein grafts to serotonin was unaltered. While none of the normal veins in the control group responded to serotonin, normal veins treated with verapamil contracted readily in response to serotonin. Endothelial-dependent relaxation to acetylcholine was absent in both control and verapamil-treated vein grafts, while normal veins from both groups responded to the same extent to acetylcholine. Because we could not demonstrate any difference in platelet or endothelium function between untreated and verapamil-treated animals, we examined the direct effect of verapamil on smooth muscle. Verapamil significantly inhibited [3H]-thymidine incorporation into DNA in vascular smooth muscle cells in culture in a dose-dependent manner. Verapamil treatment significantly reduces intimal hyperplasia in experimental vein grafts and inhibits smooth muscle cell proliferation in culture. Furthermore the enhanced reactivity to norepinephrine and histamine in the verapamil-treated vessels has no detrimental effect on the patency rate at 4 weeks. Thus by inhibiting intimal hyperplasia, calcium antagonists may improve the long-term patency of vein bypass grafts.     

Adenoviral activin A expression prevents vein graft intimal hyperplasia in a rat model

Autologus vein grafts are used for coronary artery and infra-inguinal bypass procedures. Although initially successful, long-term patency rates are limited by lumen occlusion due to neointima formation by smooth muscle cell hyperplasia. Gene therapy to prevent this smooth muscle cell proliferation has been studied extensively with limited success. Activin A, a member of the transforming growth factor-beta super family, promotes the contractile phenotype of smooth muscle cells. Maintaining the contractile phenotype could be a novel strategy to prevent intimal hyperplasia. In an epigastric vein-to-common femoral artery interposition grafts rat model, activin A over-expression resulted in a significant decrease in intimal cross-sectional area and percentage stenosis as compared to the control group. BrdU staining identified lower proliferation rates of the smooth muscle cells in the group treated with activin A. We report for the first time evidence that activin A can diminish vein graft failure in a rat model supporting a novel strategy to prevent intimal hyperplasia.     

Vein to artery grafts: a morphological and histochemical study of the histogenesis of intimal hyperplasia.

Failure of vein to artery grafts has been associated with intimal thickening (hyperplasia) and atherosclerosis. Current theories of intimal development, derived from arterial studies, show that smooth muscle cells migrate from the media to the intima after endothelial damage, where they proliferate and produce intimal hyperplasia. However, little is known of the histogenesis of these lesions in vein grafts. Experimental ilio-lumbar vein to iliac artery autografts were placed in 52 rats and analysed by light microscopy and histochemistry from 2 to 140 days after surgery. On day 2 the grafts and adjacent artery were severely damaged. Regeneration of damaged arterial tissue occurred by day 5, and thickening was already evident in the arterial intima. The intimal cells had histochemical characteristics of smooth muscle. By day 15, this hyperplastic intima was continuous across the anastomosis from the artery into the graft. After day 28 a wedge of densely packed cells was present in the vein graft intima for approximately 2 mm into the graft. By day 140, all the grafts were fully re-endothelialized. Intimal hyperplasia was present in all grafts and varied in thickness from 3 to 20 cells. Histochemical staining of these cells showed them to be of smooth muscle origin.     

VEIN TO ARTERY GRAFTS: A MORPHOLOGICAL AND HISTOCHEMICAL STUDY OF THE HISTOGENESIS OF INTIMAL HYPERPLASIA

Failure of vein to artery grafts has been associated with intimal thickening (hyperplasia) and atherosclerosis. Current theories of intimal development, derived from arterial studies, show that smooth muscle cells migrate from the media to the intima after endothelial damage, where they proliferate and produce intimal hyperplasia. However, little is known of the histogenesis of these lesions in vein grafts. Experimental ilio-lumbar vein to iliac artery autografts were placed in 52 rats and analysed by light microscopy and histochemistry from 2 to 140 days after surgery. On day 2 the grafts and adjacent artery were severely damaged. Regeneration of damaged arterial tissue occurred by day 5, and thickening was already evident in the arterial intima. The intimal cells had histochemical characteristics of smooth muscle. By day 15, this hyperplastic intima was continuous across the anastomosis from the artery into the graft. After day 28 a wedge of densely packed cells was present in the vein graft intima for approximately 2 mm into the graft. By day 140, all the grafts were fully re-endothelialized. Intimal hyperplasia was present in all grafts and varied in thickness from 3 to 20 cells. Histochemical staining of these cells showed them to be of smooth muscle origin.     

Long-term inhibition of Rho kinase suppresses intimal thickening in autologous vein grafts in rabbits

BACKGROUND: Rho kinase plays an important role in vascular smooth muscle cell (VSMC) contraction and other cellular functions, such as proliferation, migration, and apoptosis. Recent studies have demonstrated that long-term inhibition of Rho kinase suppresses coronary artery spasm and vascular lesion formation after arterial injury. In the cardiovascular surgery field, intimal thickening in vein grafts is the major cause of late graft failure, for which no effective treatment has yet been developed. In this study, we examined whether long-term inhibition of Rho kinase suppresses intimal thickening in autologous vein grafts in rabbits. METHODS: Male rabbits were randomly divided into two groups and received normal chow (control group) or a special chow containing 0.09% fasudil (fasudil group). After oral administration, fasudil is metabolized to a specific Rho kinase inhibitor, hydroxyfasudil. Each group underwent reversed autologous vein graft surgery with the internal jugular vein into the left common carotid artery. At 1, 2, and 4 weeks after the operation, we examined the extent of intimal thickening of the graft and VSMC proliferation and apoptosis. RESULTS: The intimal thickening was significantly suppressed in the fasudil group compared with the control group at 2 and 4 weeks after the operation. In the fasudil group, VSMC proliferation was suppressed at 1 and 2 weeks after the operation, whereas VSMC apoptosis was enhanced at 2 weeks after the procedure. CONCLUSIONS: These results indicate that Rho kinase is substantially involved in the pathogenesis of intimal thickening of vein grafts and that it is an important therapeutic target for the prevention of graft failure.     

Heparin fails to suppress intimal proliferation in experimental vein grafts.

Heparin has been shown to suppress both vascular smooth muscle cell proliferation in vitro and intimal hyperplasia in animal models of arterial injury. We investigated the effect of heparin on early postoperative smooth muscle cell proliferation and intimal thickening in vein grafts placed in the rat infrarenal aorta. Experimental animals (n = 6) received subcutaneous heparin (800 units/kg with levels monitored by activated factor X assay) every 12 hours for 3 days after surgery to coincide with the known period of maximal vascular wall DNA synthesis after injury. Control animals (n = 7) received identical vein grafts but no heparin. Grafts were harvested with perfusion fixation 14 days after insertion. Tritiated thymidine autoradiography was used to derive a mitotic index in regions of interest along the grafts, and computerized planimetric measurements of intimal and medial thickness were made in the same regions. Evans blue lumenal staining at harvesting revealed confluent endothelial coverage of both experimental and control grafts. The mitotic index of the vein graft's midsection and perianastomotic regions was significantly higher (p less than 0.005) than that of the native aorta in all animals, indicating cellular proliferation within all grafts, with no differences noted between heparinized and control animals. Similarly, both groups exhibited vein graft intimal and medial thickening at the anastomoses relative to the midsection of the vein graft (p less than 0.001). Heparin, administered in the equivalent of pharmacologic clinical doses, failed to suppress cellular proliferation and intimal hyperplasia in this model of vein grafting.     

Hydrophilic statin suppresses vein graft intimal hyperplasia via endothelial cell-tropic Rho-kinase inhibition

BACKGROUND: Recent studies suggest that statins can protect the vasculature in a manner that is independent of their lipid-lowering activity through inhibition of the small guanosine triphosphate-binding protein, Rho, and Rho-associated kinase. Little information is available on the inhibitory effect of statins on vein graft intimal hyperplasia, the main cause of late graft failure after bypass grafting. We therefore examined the effects of a hydrophilic statin on vein graft intimal hyperplasia in vivo and Rho-kinase activity in vitro. METHODS: In the first experiment, rabbits were randomized to a control group (n = 7) that was fed regular rabbit chow or to a pravastatin group (n = 7) that was fed regular rabbit chow supplemented with 10 mg/kg pravastatin sodium. The branches of the jugular vein were ligated and an approximately 3-cm segment of the jugular vein was taken for an autologous reversed-vein graft. The carotid artery was cut and replaced with the harvested autologous jugular vein. At 2 and 4 weeks after the operation, vein grafts in both groups were harvested, and intimal hyperplasia of the vein grafts was assessed. In the second experiment, human umbilical vein endothelial cells and vascular smooth muscle cells were cultured and then treated with 1 micromol/L and 30 micromol/L pravastatin for 24 hours and harvested. Immunoblotting was performed on the resulting precipitates. Quantitative evaluation of phosphorylated myosin binding subunit and endothelial nitric oxide synthase was performed by densitometric analysis. RESULTS: We demonstrated that oral administration of the hydrophilic statin pravastatin to normocholesterolemic rabbits inhibited intimal hyperplasia of carotid interposition-reversed jugular vein grafts 4 weeks after implantation (pravastatin group, 39.5 +/- 3.5 microm vs control group, 64.0 +/- 7.1 microm; n = 7; P < .05) and suppressed cell proliferation and apoptosis in the neointima 2 weeks after implantation. In addition, we found that pravastatin inhibited Rho-kinase activity and accelerated endothelial nitric oxide synthase expression in human umbilical vein endothelial cells but did not inhibit Rho-kinase activity in vascular smooth muscle cells. CONCLUSIONS: These novel findings clearly demonstrate that a hydrophilic statin can suppress intimal hyperplasia of the vein graft in vivo and also show endothelial cell-tropic inhibition of Rho-kinase in vitro. Furthermore, these results strongly support the clinical use of hydrophilic statins to prevent intimal hyperplasia of the vein graft after bypass grafting. CLINICAL RELEVANCE: Late graft failure caused by neointimal hyperplasia limits the efficacy of vein grafting. Various treatments were examined to reduce neointimal hyperplasia, but a standard clinical treatment has not yet been established. We report here the inhibitory effect of pravastatin on the development of vein graft intimal hyperplasia. In addition, we demonstrate that pravastatin showed endothelial cell-tropic benefits through both the inhibition of Rho-kinase activity and acceleration of eNOS expression in vitro. Because the clinical benefits and safety of pravastatin have been established to a certain extent through long-term clinical usage, pravastatin may soon become standard treatment after vein bypass grafting.     

Possible roles of 5-HT in vein graft failure due to intimal hyperplasia 5-HT, nitric oxide and vein graft

For vascular occlusive disease, an autologous vein graft is the most suitable conduit for arterial reconstruction. Intimal hyperplasia, resulting from the migration and proliferation of vascular smooth muscle cells, is a major obstacle to patency after vein grafting. The degree to which the function of nitric oxide (NO) in the vein graft is preserved has been reported to be associated with the magnitude of intimal hyperplasia. Serotonin (5-HT) is released from platelets in the vascular system and plays physiological roles in controlling the vascular tone. The subtype receptors contributing to the 5-HT-induced mechanical responses vary by vessel type (artery and vein) and among species (dogs, rabbits, rats, and so on). Recent studies have demonstrated that 5-HT induces vasoconstriction through the activation of 5-HT_2A receptors in smooth muscle cells or vasodilatation through the activation of endothelial 5-HT_1B receptors in arteries from various animals. However, the effects of 5-HT have not been clarified in grafted veins. We herein demonstrate the responses to 5-HT in un-operated veins and then autogenous vein grafts. Next, we describe the effects of chronic in vivo administration of Rho-kinase inhibitors and 5-HT_2A receptor antagonists, both of which reduce the 5-HT-induced contraction and intimal hyperplasia in vein grafts. Further studies targeting 5-HT are required to evaluate its possible benefits for autologous vein grafts with respect to vasospasm, function, and patency.     

Therapeutic approach against intimal hyperplasia of vein grafts through endothelial nitric oxide synthase/nitric oxide (eNOS/NO) and the Rho/Rho-kinase pathway

Late graft failure of autologous vein grafts is associated with intimal hyperplasia resulting from the migration and proliferation of vascular smooth muscle cells (VSMCs). Endothelial nitric oxide synthase (eNOS) is an enzyme that synthesizes nitric oxide (NO). An impairment of NO-mediated vasorelaxation and increases in cell proliferation occurs in vein grafts after the surgery and these pathophysiological changes cause intimal thickening. The Rho/Rho-kinase pathway negatively regulates eNOS and is involved in intimal hyperplasia. Several studies have been conducted with the goal of controlling intimal hyperplasia targeting eNOS/NO and the Rho/Rho-kinase pathway. The oral administration of drugs, such as Rho-kinase inhibitor, l-arginine, beta-blocker and statins, significantly suppressed intimal thickening in animal models. This study revealed that statins upregulate eNOS through Rho-kinase inhibition to suppress intimal hyperplasia. The intraluminal gene transfer of eNOS inhibited intimal hyperplasia, thereby reducing the cell proliferation. These approaches are thus considered to be potentially promising therapeutic modalities for graft failure.     

Celiprolol reduces the intimal thickening of autogenous vein grafts via an enhancement of nitric oxide function through an inhibition of superoxide production

BACKGROUND: Beta-adrenoceptor antagonist celiprolol has been widely used as an effective antihypertensive agent. Some studies reported that celiprolol enhances nitric oxide production. The purpose of the present study is to examine the effects of celiprolol on vein graft intimal hyperplasia and endothelium-dependent nitric oxide (NO)-mediated relaxation. METHODS: Japanese white rabbits were randomized to a control group that was fed regular rabbit chow or to a celiprolol group that was fed regular rabbit chow supplemented with 100 mg/body celiprolol sodium. The reversed jugular vein was implanted into the carotid artery. At 2 and 4 weeks after the operation, vein grafts in both groups were harvested, and intimal hyperplasia of the vein grafts was assessed. At 4 weeks after the operation, harvested vein grafts from both the groups were examined on the endothelium-dependent relaxation by application of Ach and were examined to detect for endothelial NO synthase (eNOS) expression and superoxide anion production. RESULTS: Celiprolol inhibited intimal hyperplasia of carotid interposition-reversed jugular vein grafts 4 weeks after implantation (Intima/media index of celiprolol group, 0.48 +/- 0.01 vs control group, 1.07 +/- 0.08, P < .05) and suppressed cell proliferation in the neointima 2 weeks after implantation. In addition, celiprolol significantly enhanced endothelium-dependent NO-mediated relaxation in the vein graft with no change in eNOS expression and a reduction in superoxide production. CONCLUSIONS: These novel findings clearly demonstrate that beta-adrenoceptor antagonist celiprolol can suppress intimal hyperplasia of the vein graft, which may be due to the enhancement of nitric oxide function through an inhibition of superoxide production. These results strongly support the clinical usefulness of celiprolol administration for preventing intimal hyperplasia of the vein graft after bypass grafting.     

Initial histopathology of the autovein graft in late occlusion after arterial reconstruction

Five patients developed local stenosis of autologous vein grafts implanted for femoro-popliteal arterial occlusive lesions. This stenosis occurred in the vein grafts 2 months to 5 years after the initial operation. Histopathologic study revealed that the stenotic segments had a thickened intima with a prominent proliferation of smooth muscle cells associated with fibrous extracellular matrix. There were no findings showing deposition of mural thrombi, as has heretofore been reported. The intimal thickening due to excessive fibromuscular proliferative response of the vein graft may possibly play an important role in the development of late graft occlusion.     

Small-caliber heparin-coated ePTFE grafts reduce platelet deposition and neointimal hyperplasia in a baboon model

PURPOSE: Intimal hyperplasia and graft thrombosis are major causes of graft failure. Heparin prolongs graft patency and inhibits neointimal hyperplasia in animal models. The purpose of this study was to evaluate the effect of a heparin-coated expanded polytetrafluoroethylene (ePTFE) graft on platelet deposition and anastomotic neointimal hyperplasia after aortoiliac bypass grafting in a baboon model. METHODS: Heparin-coated ePTFE grafts (4-mm diameter) were incorporated into exteriorized femoral arteriovenous shunts placed in five baboons. Platelet deposition was analyzed by measuring the accumulation of indium 111-labeled platelets on the grafts, with dynamic scintillation camera imaging. Eight adult male baboons (mean weight, 9.3 kg) underwent bilateral aortoiliac bypass grafting with ePTFE grafts (4-mm internal diameter). In each animal a heparin-coated ePTFE graft was placed in one aortoiliac artery, and an uncoated graft, which served as the control, was placed in the contralateral aortoiliac artery. All grafts were harvested at 4 weeks, and were analyzed quantitatively for neointimal hyperplasia at graft-vessel anastomoses. RESULTS: Early platelet deposition on heparin-coated grafts after 1 to 4 hours of ex vivo circuitry was significantly reduced. All the harvested aortoiliac grafts were patent at 4 weeks. There was a significant reduction in neointimal area at both proximal (0.26 +/- 0.11 mm(2)) and distal (0.29 +/- 0.14 mm(2)) anastomoses in the heparin-coated grafts, compared with proximal (0.56 +/- 0.18 mm(2)) and distal (0.63 +/- 0.21 mm(2)) anastomoses in the untreated control grafts (P <.05). In addition, neointimal cell proliferation assayed with bromodeoxyuridine (BrdU) incorporation was reduced in the graft neointima (3.47% +/- 0.43%) in heparin-coated grafts compared with the graft neointima (6.21% +/- 0.59%) in untreated control grafts (P <.05). CONCLUSIONS: Small-caliber heparin-coated ePTFE grafts significantly reduce platelet deposition and anastomotic neointimal hyperplasia and cell proliferation, without measurable side effects, in baboons. Surface coating with heparin in small-caliber ePTFE grafts is useful for improving prosthetic bypass graft patency. Clinical relevance: An autologous vein graft is the ideal bypass conduit in peripheral arterial reconstruction; however, many patients who undergo bypass grafting do not have adequate or available autologous vein graft. As a result surgeons often must rely on prosthetic grafts as an alternative conduit in arterial bypass procedures. Clinical outcomes with prosthetic grafts in peripheral arterial reconstruction are generally inferior to those with autologous vein bypass grafts, in part because of anastomotic neointimal hyperplasia. This study evaluated the effect of small-caliber heparin-coated expandable polytetrafluoroethylene (ePTFE) grafts in aortoiliac reconstruction in a baboon model. The study found that heparin-coated ePTFE grafts resulted in less intimal hyperplasia and less platelet deposition after implantation, compared with noncoated control ePTFE grafts.     

聚对二氧环己酮血管外支架抑制移植静脉内膜增生的机制

目的 构建可降解性聚对二氧环己酮(PDS)血管外支架抑制移植静脉内膜增生的动物模型,探讨PDS外支架抑制移植静脉内膜增生的作用及其机制。方法 建立兔颈外静脉移植模型,24只新西兰大白兔分为单纯移植组(n=12)和PDS外支架组(n=12)。术后4周及12周取出移植静脉,测量移植静脉内膜、中层面积及厚度,免疫组织化学法和实时荧光定量逆转录-聚合酶链反应(RT-PCR)法检测增殖细胞核抗原(PCNA)、转化生长因子-β1(TGF-β1)和肾素-血管紧张素Ⅱ受体1( AT1 R)表达。结果 24只兔均存活,移植血管全部通畅。外支架组中膜面积、内膜面积、中膜厚度、内膜厚度各值皆小于单纯移植组,差异有统计学意义(P＜0.05)。免疫组织化学与RT-PCR检测表明血管外支架组TGF-β1在外膜中过度表达,而中膜和内膜表达减少。术后4周,外支架组AT1R表达水平低于对照组,12周时,两组AT1R表达水平都降低,差异无统计学意义(P＞0.05)。结论 大孔隙、非限制性PDS血管外支架通过形成新生外膜、调节细胞因子再分布等机制有效地抑制内膜和中膜的增生,其用于抑制移植静脉内膜增生是可行的。     

Intimal hyperplasia and neointima: An ultrastructural analysis of thrombosed grafts in humans

The distal anastomoses of thrombosed saphenous vein (11), bovine (4), Dacron (7), and polytetrafluoroethylene (PTFE) (27) grafts removed en bloc during reoperation or amputation were studied with light microscopy, scanning electron microscopy, and transmission electron microscopy. Analysis of the ultrastructures of the distal anastomostic regions was done to characterize morphogenesis of intimal hyperplasia and neointimal proliferation. Complete reendothelialization occurred in all vein grafts. In bovine heterografts, there were isolated areas of endothelia. Thrombosed PTFE grafts were lined with gelatinous, proteinaceous material with no consistent organized cellular pattern. In contrast, laminated fibrous tissue produced by fibroblasts lined the Dacron grafts. Intimal hyperplasia was found in 6 of 11 vein grafts and in all prosthetic grafts examined. Regardless of the type of graft used, intimal hyperplasia was found predominantly at the heel of the graft and on the floor of the artery. Beneath the endothelia, collagenous ground substance and myofibroblasts mixed with smooth muscle cells were seen, characterized by pyknotic nuclei, reduced cytoplasm/nuclei ratio, and loss of cytoplasmic organelles. Endothelialization occurred exclusively in vein grafts. Prosthetic grafts lacked endothelia, with the neointima consisting of fibroblasts and fibrous matrix. In intimal hyperplasia, two forms of smooth muscle cell pathomorphogenesis were recognized. Formation of myofibroblasts induced medial fibroplasia, whereas degeneration of muscle cells progressed to medial necrosis. Smooth muscle cells seem to play a role not previously recognized in the pathogenesis of graft failure.     

Vein cuff interposition prevents juxta-anastomotic neointimal hyperplasia.

This study sought to minimize juxta-anastomotic neointimal hyperplasia (JNIH) following the use of polytetrafluorethylene (PTFE) conduits. PTFE anastomoses to canine carotid arteries (noncuff grafts) were compared with grafts with vein cuffs interposed proximally and distally between the graft and native artery. This technique has been suggested clinically for below-knee PTFE femoropopliteal reconstruction. Twelve dogs received aspirin for 1 week before operation, which was continued after each animal received bilateral cuff and noncuff 4-mm PTFE grafts. At sacrifice, after 3-12 weeks, graft patency was assessed and luminal diameters measured with ophthalmic calipers at three sites along the anastomoses and 1 mm proximal or distal to graft toe (A' diameter). Specimens were perfusion fixed at arterial pressure for gross and histologic study; selected arteries were additionally fixed with 4% buffered glutaraldehyde, stored at 4 C, and examined immunochemically using antimyosin antibody immunopurified for smooth muscle. Overall patency of noncuff grafts in 11 long-term surviving dogs was 4 of 11; patency of the cuff grafts was 7 of 11. Regardless of graft thrombosis, antibody positive cellular proliferation occurred mainly at noncuffed PTFE anastomoses. Luminal encroachment was predominantly due to subintimal proliferation of cells highly reactive to smooth muscle derived antibody. JNIH was most prominent 1 mm distal to the graft toe (A' distal diameter). Average A' for noncuff grafts was 1.82 mm +/- 0.97 SEM; average A' diameter for cuff grafts was 3.41 mm +/- 0.74 SEM (p less than 0.001). Vein cuff inhibition of proliferation of smooth muscle or cells derived from smooth muscle possibly relates to wider distribution of kinetic energy (less compliance mismatch) or to interposition of venous endothelium.     

Long-term histological changes in 1 millimeter polytetrafluoroethylene (Gore-Tex) prosthetic arterial grafts

Vein grafts are used extensively to repair blood vessels. However, when suitable vein segments are unavailable, alternative graft materials must be used. This study tested the suitability of 1 mm diameter polytetrafluoroethylene (PTFE) grafts for small-calibre arterial replacements. Grafts of 4 mm length were inserted microsurgically into the iliac arteries of 26 rats. The grafts were removed between 3 and 22 months postoperatively and examined with light microscopy and scanning and transmission electron microscopy (SEM:TEM). Anastomotic intimal hyperplasia was minimal, consisting of a few smooth muscle cells extending 100-200 microns onto the graft. The rest of the PTFE was covered with endothelium. In a few isolated areas, there was a subendothelial layer of smooth muscle, 2-10 cells thick. The short segments used in this study were highly successful, with an overall long-term patency rate of 80%. These grafts showed no evidence of excessive neo-intimal hyperplasia.     

Elevated platelet-derived growth factor production by aortic grafts implanted on a long-term basis in a canine model.

An endothelial cell lining in a prosthetic vascular graft has been shown to decrease graft thrombogenicity. However, previous studies in our laboratory demonstrated that grafts seeded with endothelial cells produced platelet-derived growth factor, a potent smooth muscle cell mitogen that may promote intimal hyperplasia. This study was undertaken to assess temporal changes in platelet-derived growth factor production by grafts seeded with endothelial cells and unseeded grafts and adjacent arteries. Adult beagles underwent placement of 20 to 22 cm long, 8 mm inner diameter, expanded polytetrafluoroethylene thoracoabdominal aortic grafts that were either seeded with autologous jugular vein endothelial cells or were unseeded controls. Grafts and adjacent arteries were removed at times up to 2 years after implantation. The tissue was studied in organ culture and platelet-derived growth factor production was measured after 72 hours with use of a radioreceptor assay. Platelet-derived growth factor production by endothelialized grafts increased significantly over the period studied, especially at the anastomoses, whereas that by arterial segments did not change significantly. The increase in platelet-derived growth factor production was greater in the distal than the proximal anastomotic segment suggesting a possible explanation for the clinical finding of more severe intimal hyperplasia at the distal anastomosis.