Hyperplasia In Vein Grafts Research Articles

Controlled periadventitial administration of verapamil inhibits neointimal smooth muscle cell proliferation and ameliorates vasomotor abnormalities in experimental vein bypass grafts

Objective: Inhibition of early myointimal proliferation may improve long-term patency of vein grafts, but the clinical use of many experimental drugs is limited by systemic toxicity. To determine whether this goal can be achieved by low-dose targeted drug administration, we constructed a polymeric system delivering verapamil and evaluated the effects on local and downstream vein graft morphology, neointimal smooth muscle cell proliferation, and vasomotor function. Methods: Ethylene-vinyl acetate polymeric delivery systems were constructed, containing 2% verapamil by weight. These are flexible, biocompatible, and nonbiodegradable matrices, delivering the drug at a rate of 10 μg/day. The autologous external jugular vein was used to create a carotid artery bypass graft in hypercholesterolemic ( n = 22) rabbits. Verapamil-containing matrices ( n = 12) or plain polymers (control, n = 10) were wrapped around the proximal third of the veins after reperfusion. Graft vasomotor function was evaluated and was also compared with function of an additional group of normocholesterolemic vein grafts ( n = 8). Results: Twenty-eight days after grafting, intimal index (intima/media thickness ratio) was 31% lower, neointima/original lumen surface ratio was 26% lower, and residual luminal area was 71% greater (4.00 ± 1.2 mm 2 versus 2.34 ± 0.9 mm 2, all p < 0.01) under verapamil matrices compared with control grafts. Neointimal smooth muscle cell content was reduced from 45.4% to 28.2%, and net neointimal smooth muscle cell thickness was reduced by 47% (30 μm vs 15.8 μm, both p < 0.01). Verapamil-treated segments distal to the matrices also showed significantly lower neointimal smooth muscle cell density and increased lumen size. Sensitivity to serotonin and vasomotor responses to serotonin, norepinephrine, and sodium nitroprusside in distal segments were significantly lower in verapamil-treated grafts than in controls. Conclusions: Periadventitial controlled administration of verapamil below 1% of the systemic dose effectively inhibits myointimal hyperplasia in vein grafts. Local polymeric drug delivery may be readily applicable to coronary revascularization operations(J Thorac Cardiovasc Surg 1997;114:53-63)

Suppressors of oxygen metabolites fail to reduce vein graft intimal hyperplasia.

To evaluate the role of reactive oxygen metabolites in the initiation of intimal hyperplasia of vein grafts inserted into the arterial circulation. University pathologic research laboratory. Sprague-Dawley rats. Animals were randomized to receive either the xanthine oxidase inhibitor allopurinol, the iron chelating agent starch-conjugated deferoxamine, or the free-radical scavenger 21-aminosteroid U74389G. Control animals were included for each group. The epigastric vein was inserted into the right common femoral artery. Vein grafts were harvested 30 days postoperatively. The degree of intimal hyperplasia at the two anastomoses as well as at the midgraft was calculated. The vein grafts were divided into three sections designated proximal anastomosis, midgraft, and distal anastomosis. Intimal and medial areas were determined in an observer-blind fashion and expressed as intimal area-medial area ratios. Pretreatment of the animals with any of these agents resulted in no significant reduction in the degree of intimal hyperplasia in any treated groups compared with the control animals 30 days postoperatively. Arterial reconstruction often involves interposition of vein segments into the arterial circulation. These veins are subject to ischemia and reperfusion, with the potential for generation of reactive oxygen metabolites and subsequent vein graft injury, resulting in intimal hyperplasia. We hypothesized that perioperative pharmacologic intervention either to scavenge or to reduce the production of reactive oxygen metabolites would attenuate the initial vein graft injury and thus limit the subsequent development of intimal hyperplasia. These data create doubt as to the influence of reactive oxygen metabolites in the initiation of intimal hyperplasia in the vein graft.

Control of Accelerated Vein Graft Atheroma with the Nitric Oxide Precursor: l-Arginine

Hyperlipidemia contributes to the development of intimal hyperplasia and subsequent accelerated atherosclerosis in vein bypass grafts. This study examines the effect of dietary supplementation with l-arginine on the development of intimal hyperplasia and the vasomotor function of vein grafts in hypercholesterolemic animals. Thirty male New Zealand White rabbits had a right carotid vein bypass graft and were sacrificed at 28 days postoperatively. Twenty animals received a 1% cholesterol diet for 4 weeks prior to surgery and this diet was continued until harvest. Of these, 10 also received l -arginine (2.25%, 2 g/kg, p.o.) 7 days preoperatively and thereafter until harvest. The last 10 animals were controls. Vein grafts were harvested either for morphology or for in vitro isometric tension studies. Cumulative dose-response curves to norepinephrine, serotonin, and bradykinin were recorded, and following norepinephrine precontraction, relaxation to acetylcholine and sodium nitroprusside were determined. After in situ pressure fixation, intimal thicknesses of the vein grafts were measured by videomorphometry. The addition of l-arginine doubled the serum arginine concentrations. Intimal hyperplasia of both groups of hypercholesterolemic vein grafts contained foam cells and lipid-laden endothelial and smooth muscle cells. There was a 24% reduction in the intimal thickness of vein graft intimal hyperplasia in the l-arginine group compared to that in the hypercholesterolemia group (P < 0.05). All hypercholesterolemic vein grafts were twofold thicker than in the control group. l-arginine supplementation resulted in the preservation of acetylcholine-mediated relaxation but did not change hypercholesterolemia-induced contractile agonist supersensitivity. Therefore, l-arginine supplementation can slow the formation of atheromatous intimal hyperplasia in vein grafts; it can improve endothelial cell function but it does not prevent the persistence of the hypercholesterolemia-associated smooth muscle phenotype.

The Effect of ACE Inhibition on Vein Graft Hyperplasia

The Effect of ACE Inhibition on Vein Graft Hyperplasia

Postoperative reduction of high serum cholesterol concentrations and experimental vein bypass grafts

Hypercholesterolemia is an important contributor to the development of intimal hyperplasia and superimposed accelerated atherosclerosis in vein bypass grafts. This study examines the effect of dietary modification of serum cholesterol on the development of intimal hyperplasia and vasomotor function of vein grafts. Thirty male New Zealand White rabbits had a right carotid vein bypass graft and were put to death 28 days after the operation. Twenty animals received a 1% cholesterol diet for 4 weeks before the operation. In 10 animals this diet was continued until harvest (hypercholesterolemia group). In another 10 animals the diet was changed to standard rabbit chow on the day of the surgical procedure and continued until harvest (cholesterol reduction group). The last 10 animals were control subjects. Vein grafts were harvested either for histologic study or for in vitro isometric tension studies. Cumulative dose response curves to norepinephrine, serotonin, bradykinin, and endothelin-1 were determined. After in situ pressure fixation, intimal thicknesses of the vein grafts were measured by videomorphometry. The change in diet produced a 74% reduction in serum cholesterol concentration within 28 days. There was a 26% reduction in the intimal thickness of vein graft intimal hyperplasia and the macroscopic disappearance of atheromatous lesions from the graft wall, which are always observed in vein grafts from the hypercholesterolemia group. Cholesterol reduction did not change hypercholesterolemia-induced agonist supersensitivity. Therefore, cholesterol reduction slows the formation of intimal hyperplasia in vein grafts but does not prevent the persistence of the hypercholesterolemia-associated smooth muscle phenotype.

Systemic Hypertension and Hypercholesterolemia in Vein Grafts: Effects on the Function and Morphology of Experimental Vein Grafts

Hypertension and hypercholesterolemia are known risk factors for the development of atherosclerosis and are considered to influence the development of vein graft intimal hyperplasia. This study examines the effect of hypertension (two-kidney, one-clip model for 8 weeks) and hypercholesterolemia (1% cholesterol diet for 8 weeks) individually and in combination on the formation of intimal hyperplasia and the vasomotor function of vein grafts. Forty New Zealand White rabbits underwent a carotid vein bypass graft. Ten were controls, 10 were hypertensive, 10 were hypercholesterolemic, and 10 had both hypertension and hypercholesterolemia. Hypertension and/or hypercholesterolemia were present for 4 weeks prior to and for 4 weeks after surgery. All vein grafts were harvested at 4 weeks postoperatively for histology (n = 6) or contractility studies (n = 4). Compared to controls, hypercholesterolemia increased intimal but not medial thicknesses of the vein grafts and enhanced smooth muscle cell contractility. Hypertension did not increase vein graft intimal or medial thicknesses but did augment vein graft contractility compared to controls. Hypertension with hypercholesterolemia increased intimal and medial thicknesses and enhanced vasoreactivity in vein grafts. The results show that hypertension influences the vasoreactivity but not the development of intimal hyperplasia in vein grafts. When hypertension is combined with hypercholesterolemia, there is both an increase in the medial thickness and an attenuation of vasomotor function compared to hypercholesterolemia alone, although there is no further increase in intimal hyperplasia formation. Therefore, this study suggests that the combination of both atherogenic risk factors does not act synergistically in promoting either the formation of intimal hyperplasia or vasomotor dysfunction in vein grafts.

Increased concentrations of angiotensin-converting enzyme in the intimal hyperplasia of experimental vein grafts.

Local renin and angiotensin-converting enzyme (ACE) activity were recently implicated in development of intimal hyperplasia after vascular injury, but little is known about the local responses of angiotensin I/II (AI/AII) and local ACE activity in vein graft physiology. The activity of the local ACE system of experimental vein grafts was examined in this study. The right carotid artery was divided and bypassed in 21 New Zealand White rabbits, using the right external jugular vein. The left external jugular vein was used as a control. Veins and vein grafts were harvested after 14 days. Rings from both vessels were studied in vitro under isometric tension, and dose-response curves to AI and AII were obtained. AI responses were also measured in the presence of captopril. The tissue concentrations of ACE in both vessels were estimated by spectrophotometry and were localized by immunohistochemistry. The responses of the veins to AI and AII were multiphasic, whereas the responses of vein grafts were sigmoid-shaped. Incubation of vein grafts with captopril significantly decreased the sensitivity to AI (p < 0.0001). Immunohistochemical localization identified ACE in the endothelial layer of the veins and vein grafts, but also at a greater density in the intimal hyperplasia of the vein graft. The concentration of ACE was 1.92 +/- 0.16 U/g (wet weight; mean +/- SEM, n = 9) in vein grafts and 1.39 +/- 0.05 U/g in the veins (38% increase, p < 0.05, n = 9).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of low molecular weight heparin on intimal hyperplasia in vein grafts

Intimal hyperplasia due to smooth muscle cell proliferation is a well recognised cause of vascular graft failure. In experimental studies heparin and its low molecular weight derivatives can inhibit this proliferative response. This study examines the effect of subcutaneous low molecular weight heparin (LMWH) therapy on intimal hyperplasia in a model of arterial vein grafting. Twenty-four New Zealand White rabbits underwent interposition vein grafting of the carotid artery. Animals were randomly assigned to a control or treated group. Treated animals received 60 anti Xa units/kg of subcutaneous LMWH daily for 1 month. Animals were then sacrificed, graft patency assessed and the vessels then harvested for analysis of intimal hyperplasia. Intimal hyperplasia in carotid arteries and vein grafts was measured using a computerised image analysis system and was expressed as an intimal:medial area ratio. A statistically significant reduction in the degree of intimal hyperplasia seen in the arterial component of the distal anastomoses of carotid vein grafts was achieved using subcutaneous LMWH [Control 0.44 (0.37-0.55): LMWH 0.27 (0-0.37) p < 0.05]. There was no difference in the degree of intimal hyperplasia seen in the vein grafts themselves. [Control 0.21 (0-0.54): LMWH 0.23 (0-0.72)]. This study suggests that subcutaneous LMWH can inhibit the development of intimal hyperplasia in arteries undergoing vascular grafting but does not influence intimal hyperplasia within vein grafts. This has important implications for the further evaluation of antithrombotic agents following vascular surgery.

The effects of intraoperative vasodilators and angiographic contrast medium on the endothelium and smooth muscle cells of vein grafts

Cellular injury is a major cause of intimal hyperplasia in vein grafts. The effects of exposure of vein samples to iopamidol, papaverine and iloprost were studied in vitro in an organ chamber to determine whether these agents cause endothelial and/or smooth muscle cell injury. Smooth muscle cell function was assessed by eliciting a dose response curve to noradrenaline. Endothelial cell function was assessed by measuring the degree of endothelial-dependent relaxation of sub-maximally contracted vein samples. Iopamidol and iloprost did not have any deleterious effect on endothelial or smooth muscle cell function. Papaverine did not affect endothelial-dependent relaxation but did produce a significant decrease in smooth muscle contraction. The use of these intraoperative agents during femorodistal bypass does not appear to cause functional injury to the endothelial or smooth muscle cells.

Development of Luminally Originating Vasa Vasorum in Arterially Implanted Autogenous Vein Graft and Related Anastomosis in Dogs

Using light and scanning electron microscopes, the authors examined the development of luminally originating vasa vasorum in the course of intimal hyperplasia of vein grafts implanted to the canine femoral artery under conditions of abnormal blood flow with a high peripheral resistance. Five days after the implantation, the luminally originating vasa vasorum in the autogenous vein grafts developed dominantly near the anastomosis and often at the site of the area of valvular sinus. This vasa vasorum took the form of numerous small holes on the luminal surface of the graft and along the suture materials at the site of the anastomosis. These holes were lined with endothelial-like cells two weeks after the implantation, and four weeks later these cells were distributed in the thickened neointima connecting the vasa vasorum in the media and adventitia. This vasa vasorum observed on the thickened neointima at the area of the valvular sinus of the vein graft at more than five days after the implantation was considered to have developed in the course of organization of the mural thrombi deposited on the suture line at and on the area of the valvular sinus. Thus, numerous interstices of the vessel wall, formed along the suture materials at the anastomosis, and some clefts, formed with shrinkage of the deposited mural thrombi at the area of the valvular sinus, are the source of the luminally originating vasa vasorum.

Peptide inhibition of neointimal hyperplasia in vein grafts

Angiopeptin, a novel synthetic octapeptide, was evaluated as a new approach toward the inhibition of neointimal hyperplasia in vein grafts. Male New Zealand white rabbits (n = 22) underwent carotid artery interposition bypass grafting with autologous reversed jugular vein. Nine rabbits were in the treatment group, and 13 were in the control group. The treatment group received angiopeptin 20 μg/kg/day by subcutaneous injection beginning 1 day before operation and continuing for 3 weeks until they were killed. At death the vein grafts were fixed in situ with 10% buffered formalyn at 80mm Hg perfusion pressure. Histologic sections through each vein graft were analyzed by computerized morphometric analysis for area of neointimal hyperplasia (mm2). Neointimal hyperplasia in the control animals was 0.080 + 0.017 mm2 (mean + SEM), whereas neointimal hyperplasia in the group treated with angiopeptin was 0.022 + 0.006 mm2 (mean + SEM) (p = 0.02). This is the first time that peptide inhibition of neointimal hyperplasia has been demonstrated in vein grafts and may have significant implications for future use in vascular surgery.

Peptide inhibition of neointimal hyperplasia in vein grafts

Peptide inhibition of neointimal hyperplasia in vein grafts

Effects of low-dose marine oils on intimal hyperplasia in autologous vein grafts

The effects of low-dose cod-liver oil on intimal hyperplasia of vein grafts were examined in 45 adult mongrel dogs undergoing peripheral arterial reconstruction. Fifteen animals served as the control group, 15 animals were fed a fish-oil supplement containing 240 mg of eicosapentaenoic acid daily, and a further 15 animals received 480 mg of eicosapentaenoic acid daily. Segments of undistended external jugular vein were anastomosed to bilaterally divided femoral arteries. The grafts were harvested at 6 weeks and intimal thickness was measured with a computerized interactive image analyzing system. Serum cholesterol level, prothrombin time, partial thromboplastin time, bleeding time, and platelet counts were measured before the operation and at 2, 4, and 6 weeks after the operation. Plasma levels of thromboxane B2 and prostaglandin F1 alpha and serum levels of eicosapentaenoic acid were measured before and 4 weeks after the operation. Serum cholesterol level increased similarly and significantly in all animals. Serum levels of eicosapentaenoic acid rose proportionately with the oral ingestion of fish oil but did not affect coagulation parameters. Plasma thromboxane B2 and prostaglandin F1 alpha were not significantly affected by the ingestion of marine oils. Intimal thickness was 39 +/- 5 microns in the control dogs. Ingestion of 240 mg of eicosapentaenoic acid reduced intimal thickness to 24 +/- 3 microns at 6 weeks (p less than 0.01). Increasing the dose by a factor of 2 did not decrease intimal thickness further, the intima being 23 +/- 2 microns (p less than 0.005). Our data indicate that small doses of fish oil will reduce intimal proliferation in autologous vein grafts and that marine oils may exert their beneficial effects on intimal hyperplasia by a mechanism other than their known effects on prostanoid metabolism.

Expression of genes for platelet-derived growth factor in adult human venous endothelium: A possible non-platelet-dependent cause of intimal hyperplasia in vein grafts and perianastomotic areas of vascular prostheses

Neointimal fibromuscular hyperplasia (NFH) in vein grafts and perianastomotic zones of vascular prostheses has been attributed to the effects of platelet-derived growth factor (PDGF) released by platelets interacting with bypass conduits. But inhibition of platelet aggregation often fails to prevent NFH, and recurrent growth of intact, platelet-free endothelium over perianastomotic areas where NFH occurs is inconsistent with the concept of sustained PDGF release from platelets causing NFH progression at late times after surgical procedures. Cultured bovine aortic endothelial cells (ECs) and human umbilical vein ECs have been shown to release a PDGF-like molecule. We report that confluent cultured fourth passage adult human saphenous vein ECs (AHSVECs) grown in the presence of heparin (100 μg/ml) and retina-derived growth factor (RDGF) studied by Northern blotting transcribed a messenger ribonucleic acid (mRNA) of 3.9 kb, strongly hybridizing to PDGF B chain probes, and two species of 2.0 and 2.6 kb hybridizing to PDGF A chain probes. Withdrawal of RDGF and heparin from these cultures for 48 hours before mRNA extraction amplified the scanning densitometric mRNA signal per cell by 8.0 ± 7.6 fold (mean ± SD) (N = 4 cultures) for B chain mRNA and 5.2 ± 3.6 fold (N = 3 cultures) for A chain mRNA. In addition, AHSVEC cultures released a PDGF-like substance, because 50% vol/vol AHSVEC-conditioned serum-free medium increased tritiated thymidine uptake elevenfold in PDGF receptor-bearing 3T3 cells whereas an excess (50 μg/ml) of monospecific goat anti-human-PDGF antibody significantly reduced this increase by a mean of 30% to 7.0 ± 3.4 fold (N = 6 trials, p < 0.001). Flow cytometry determined AHSVEC cultures to be proliferating with a mean of 6.2% ± 1.9% (N = 3 culture lines) of ECs in S phase even at confluence when deprived of EC mitogens for 48 hours. Adult human ECs, which proliferate on bypass conduits and host vessels after perioperative injury, may play a role in causing NFH by stimulating proliferation of adjacent smooth muscle cells. Prevention of NFH may require not only antiplatelet agents but also ways to prevent EC release of smooth muscle cell mitogens in response to perioperative EC injury.

Kinetics of vein graft hyperplasia: Association with tangential stress

Vein grafts become thicker as they adapt to arterial circulation, and in large measure this is the consequence of cellular hyperplasia. The kinetics of smooth muscle cell (SMC) and endothelial cell (EC) replication were evaluated in rabbit jugular vein segments transplanted into the carotid arterial circulation to define the role of cell proliferation in this process, and these data were correlated with dimensional changes in grafts from 1 hour to 24 weeks after implantation. At 1 hour most of the perianastomotic endothelium was denuded, as were occasional cells in the graft away from the anastomosis. EC replication (thymidine labeling index) in the center of the graft increased 400 times during the first week and produced an intact endothelial surface by 2 weeks. The EC thymidine index then fell progressively to quiescent pretransplant levels by the twelfth week. SMC replication was maximal at 1 week after grafting and returned to near quiescent levels at 12 and 24 weeks. Graft wall thickness and cross-sectional area reached a maximum at 12 weeks and then remained constant. Deoxyribonucleic acid content exhibited a thirty-five-fold increase in the first 4 weeks, then did not change. Likewise, SMC mass did not increase after 4 weeks. Further increase in cross-sectional wall area between 4 and 12 weeks was accounted for by accumulation of connective tissue. The final ratio of luminal radius to wall thickness decreased to a level equal to that of normal artery. Since blood pressure did not change over the period of the study, this observation supports a possible regulatory role for wall tangential stress in the modification of vein graft structure after transplantation into the arterial circulation.

Kinetics of vein graft hyperplasia: Association with tangential stress

Kinetics of vein graft hyperplasia: Association with tangential stress

A morphometric study of vein graft intimal hyperplasia.

The extent of intimal hyperplasia in veins grafted into arteries is a major determinant of graft survival. The development of intimal hyperplasia in experimental iliolumbar vein grafts in iliac arteries of 36 rats was followed by light microscopy between 2 and 140 days after grafting. The increase in mean thickness of the graft intima was most rapid from 2 to 21 days and then more gradual to reach a maximum at 140 days, when the graft intima was the same thickness as the combined intima and media of the control artery. Grafts aged between 15 and 28 days showed a significant thickening at the anastomosis, but this was not evident in older grafts. Our results quantitate the arterialization of a vein graft and show that there is no significant anastomotic intimal hyperplasia in mature grafts in this model.

Cod-liver oil in the prevention of intimal hyperplasia in autogenous vein grafts used for arterial bypass

Cod-liver oil, rich in eicosapentaenoic acid, an unsaturated fatty acid, was administered to 14 mongrel dogs to determine if this acid would prevent platelet-mediated intimal hyperplasia. Twenty-eight 1 cm segments of undistended jugular vein were interposed between bilaterally divided femoral arteries. Seven control animals were fed a 2% cholesterol diet 1 week before and for 6 weeks after the operation. A further seven animals received cod-liver oil capsules containing 1.8 gm of eicosapentaenoic acid daily 1 week before and for 6 weeks after autogenous vein implantation, in addition to the lipid-supplemented diet. Baseline serum cholesterol was 4.6 +/- 0.4 mmol/L. The rise in serum cholesterol was similar in the two groups and increased to 7.4 +/- 0.6 mmol/L (control group) and to 6.8 +/- 0.2 mmol/L (eicosapentaenoic acid group) (p less than 0.001). Prothrombin time, partial thromboplastin time, bleeding time, and platelet counts were unchanged in the two groups. Vein grafts, harvested at 6 weeks, were fixed in formaldehyde. Mean intimal thickness was measured from multiple vein graft cross sections with a Zeiss computerized interactive image analyzing system. A mean of 140 +/- 11 measurements were computed from each graft. Marked intimal hyperplasia occurred in the control group and increased from 4.3 +/- 0.3 to 86.4 +/- 14 micron. In contrast, a high eicosapentaenoic acid diet inhibited intimal hyperplasia, with intimal thickness only increasing from 4.0 +/- 0.4 to 24.8 +/- 2.7 micron (p less than 0.001). These data indicate that eicosapentaenoic acid inhibits platelet-mediated intimal hyperplasia and suggest that cod-liver oil could be used to prevent intimal hyperplasia in vein grafts used for myocardial revascularization.