Molecular and cellular changes in vein grafts: influence of pulsatile stretch

The placental growth factor attenuates intimal hyperplasia in vein grafts by improving endothelial dysfunction

Saphenous vein grafts (SVG) patency is limited by intimal hyperplasia (IH) caused by endothelial dysfunction. This study aimed to explore the effect of placental growth factor (PlGF) on the endothelial function of SVG. In rat models of external jugular vein-carotid artery graft treated with PlGF or saline hydrogel, PlGF inhibited vein graft IH (day 28: 12.0 ± 1.9 vs. 61.7 ± 13.1 μm, P < 0.001), promoted microvessel proliferation (day 14: 33.3% 3+ vs. 50.0% 2+, P = 0.03), and increased nitric oxide (NO) production (P < 0.05 on days 1/3/5) and NO synthase (NOS) expression by immunohistochemistry. In human umbilical vein endothelial cells (HUVECs) cultured under hypoxia and treated or not with PlGF, PlGF restored the survival (50 ng/ml PlGF, 48 h: 91.7 ± 0.6% vs. 84.9 ± 0.5%, P < 0.01), migration (by Matrigel assay), and tube formation ability (junctions, tubules, and tubule total length; all P < 0.01) of HUVECs after hypoxia. PlGF increased NO production through increased eNOS expression (P < 0.05), without changes in iNOS expression. The mRNA expression of eNOS decreased after the addition of the PI3K inhibitor LY294002 (P < 0.05). PlGF promoted the protein expression of eNOS by up-regulating AKT, and the AKT and eNOS protein levels were decreased after adding LY294002 (all P < 0.05). In conclusion, PlGF is a candidate for the inhibition of IH in SVG after coronary artery bypass graft. The effects of PlGF are mediated by the upregulation of the eNOS mRNA and protein through the PI3K/AKT signaling pathway. PlGF promotes the secretion of NO by endothelial cells and thereby reduces the occurrence and development of IH.

Biomechanics and Mechanobiology of Saphenous Vein Grafts

Within several weeks of use as coronary artery bypass grafts (CABG), saphenous veins (SV) exhibit significant intimal hyperplasia (IH). IH predisposes vessels to thrombosis and atherosclerosis, the two major modes of vein graft failure. The fact that SV do not develop significant IH in their native venous environment coupled with the rapidity with which they develop IH following grafting into the arterial circulation suggests that factors associated with the isolation and preparation of SV and/or differences between the venous and arterial environments contribute to disease progression. There is strong evidence suggesting that mechanical trauma associated with traditional techniques of SV preparation can significantly damage the vessel and might potentially reduce graft patency though modern surgical techniques reduces these injuries. In contrast, it seems possible that modern surgical technique, specifically endoscopic vein harvest, might introduce other mechanical trauma that could subtly injure the vein and perhaps contribute to the reduced patency observed in veins harvested using endoscopic techniques. Aspects of the arterial mechanical environment influence remodeling of SV grafted into the arterial circulation. Increased pressure likely leads to thickening of the medial wall but its role in IH is less clear. Changes in fluid flow, including increased average wall shear stress, may reduce IH while disturbed flow likely increase IH. Nonmechanical stimuli, such as exposure to arterial levels of oxygen, may also have a significant but not widely recognized role in IH. Several potentially promising approaches to alter the mechanical environment to improve graft patency are including extravascular supports or altered graft geometries are covered.

Pulsatile Flow and Atherogenesis: Results from in Vivo Studies

Compliance mismatch between prosthetic vascular replacement (possibly stented) and native artery is considered to be an important factor in implant failure due, e.g., to vascular remodeling, tissutal growth or intimal hyperplasia (IH). From an in vivo study involving altered vascular mechanics (and, consequently, compliance mismatch), carried out using the Moncada model of atherosclerosis development and smooth muscle cell (SMC) proliferation, the hemodynamic assessment was followed by means of real-time multigated ultrasound profilometry, of collared carotid artery using two different models: nonconstrictive and costrictive plastic collars, wrapped around the vessel. The experiments provided the real-time measurement of velocity profiles in vivo and the subsequent estimation of wall shear stresses, locally responsible for the altered hemodynamics.

Endothelium modifications were correlated with local hemodynamic alterations by using statistical regression analysis of the development of intimal hyperplasia and the mechanical stimulus applied to the endothelium by means of the two different manipulation models. Different correlations were found between wall shear rate and IH in the two models, showing the importance of the vascular pulsatility in determining SMC proliferation. This result could be useful in minimizing the negative consequences of clinical interventions such as graft and/or stent implantation.

Aneurysmorrhaphy is an Easy Technique for Arteriovenous Fistula Salvage

The life-saving procedures for patients in chronic renal failure (CRF) are hemodialysis (HD) or successful kidney transplantation. HD requires a properly placed and functioning vascular access, most often obtained by creating an arteriovenous fistula (AVF). The long-term patency of AVFs is limited, in addition to other factors, by the development of intimal hyperplasia and the process results in venous wall thickening and progressive fistula occlusion. Another problem is limited patency, due to the development of pseudoaneurysm, which is associated with an increased risk of thrombosis, infection and bleeding, difficult cannulation for dialysis, pain and cosmetic defects. Treatment is focused on rapidly progressing pseudoaneurysms, which can predispose to rupture, technical problems during cannulation because of pseudoaneurysm size or a growing intraluminal thrombus. Most of these patients are scheduled for pseudoaneurysm removal and new fistula construction or, occasionally, an endovascular procedure involving stent graft implantation. This paper describes a simple and inexpensive technique of managing an AVF pseudoaneurysm, i.e. aneurysmorrhaphy. To offset the weakening of the venous wall by suture following aneurysmorrhaphy, an external polyethylene terephthalate (PET) prosthesis was implanted in the vein to prevent the development of intimal hyperplasia in the de novo created AVF.

Morphological Analysis of in Vivo Velocity Field in the Alteration of the Vasomotor Tone

Vessel wall remodeling is involved in atherogenesis and in several important vascular diseases affecting mainly aged and prosthetic implanted patients. This adaptive response to pathological states in arterial hemodynamics strongly suggests that flow-derived stresses act as mechanical stimuli to the release of endothelium-derived vasoactive factors, leading to vascular alterations. As the correlation of intimal hyperplasia (IH) with blood flow alterations in arteries has been shown to be significant, and as it is well-known that clinical procedures carry a substantial risk of development of vascular disease, the relevance of local hemodynamics must be investigated to describe changes in compliance matching in prosthetic applications. The aim of our research is to investigate the use of principal components analysis, together with varimax rotation, in the individuation process of morphological characteristics of real time ultrasound in in vivo recordings of blood flow velocities, as provided by two different carotid perivascular manipulations. This would be of use in the clinical assessment of atherogenesis, hypertension, prosthetic replacement or more in general in all applications in which vascular tone may be impaired. Data recordings refer to previous animal experiments where the Moncada model was investigated by means of an ultrasound profilometer. The present study confirms the feasibility of the proposed analysis to follow vascular pathology evolution, distiguishing between an in progress and a static situation.

A new design concept for knitted external vein-graft support mesh

Autologous vein-graft failure significantly limits the long-term efficacy of coronary artery bypass procedures. The major cause behind this complication is biomechanical mismatch between the vein and coronary artery. The implanted vein experiences a sudden increase (10-12 fold) in luminal pressures. The resulting vein over-distension or 'ballooning' initiates wall thickening phenomenon and ultimate occlusion. Therefore, a primary goal in improving the longevity of a coronary bypass procedure is to inhibit vein over-distension using mechanical constriction. The idea of using an external vein-graft support mesh has demonstrated sustained benefits and wide acceptance in experimental studies. Nitinol based knitted structures have offered more promising mechanical features than other mesh designs owing to their unique loosely looped construction. However, the conventional plain knit construction still exhibits limitations (radial compliance, deployment ease, flexibility, and bending stresses) which limit this design from proving its real clinical advantage. The new knitted mesh design presented in this study is based on the concept of composite knitting utilising high modulus (nitinol and polyester) and low modulus (polyurethane) material components. The experimental comparison of the new design with a plain knit design demonstrated significant improvement in biomechanical (compliance, flexibility, extensibility, viscoelasticity) and procedural (deployment limit) parameters. The results are indicative of the promising role of new mesh in restoring the lost compliance and pulsatility of vein-graft at high arterial pressures. This way it can assist in controlled vein-graft remodelling and stepwise restoration of vein mechanical homoeostasis. Also, improvement in deployment limit parameter offers more flexibility for a surgeon to use a wide range of vein diameters, which may otherwise be rendered unusable for a plain knit mesh.

Pulmonary hypertension caused by pulmonary venous hypertension

The effect of pulmonary venous hypertension (PVH) on the pulmonary circulation is extraordinarily variable, ranging from no impact on pulmonary vascular resistance (PVR) to a marked increase. The reasons for this are unknown. Both acutely reversible pulmonary vasoconstriction and pathological remodeling (especially medial hypertrophy and intimal hyperplasia) account for increased PVR when present. The mechanisms involved in vasoconstriction and remodeling are not clearly defined, but increased wall stress, especially in small pulmonary arteries, presumably plays an important role. Myogenic contraction may account for increased vascular tone and also indirectly stimulate remodeling of the vessel wall. Increased wall stress may also directly cause smooth muscle growth, migration, and intimal hyperplasia. Even long-standing and severe pulmonary hypertension (PH) usually abates with elimination of PVH, but PVH-PH is an important clinical problem, especially because PVH due to left ventricular noncompliance lacks definitive therapy. The role of targeted PH therapy in patients with PVH-PH is unclear at this time. Most prospective studies indicate that these medications are not helpful or worse, but there is ample reason to think that a subset of patients with PVH-PH may benefit from phosphodiesterase inhibitors or other agents. A different approach to evaluating possible pharmacologic therapy for PVH-PH may be required to better define its possible utility.

Saphenous vein graft failure after coronary artery bypass surgery: pathophysiology, management, and future directions

OBJECTIVE

To review our current understanding of the epidemiology and pathogenesis of vein graft failure (VGF), give an overview of current preventive and interventional measures, and explore strategies that may improve vein graft patency.

BACKGROUND

VGF and progression of native coronary artery disease limit the long-term efficacy of coronary artery bypass graft surgery.

METHODS

We reviewed the published literature on the pathophysiology, prevention, and/or treatment of VGF by searching the MEDLINE (January 1, 1966-January 1, 2012), EMBASE (January 1, 1980-January 1, 2012), and Cochrane (January 1, 1995-January 1, 2012) databases. In addition, we reviewed references from the selected articles for studies not identified in the initial search. Basic science and clinical studies were included; non-English language publications were excluded.

RESULTS

Acute thrombosis, neointimal hyperplasia, and accelerated atherosclerosis are the 3 mechanisms that lead to VGF. Preventive measures include matching and quality assessment of conduit and target vessel, lipid-lowering drugs, antithrombotic therapy, and cessation of smoking. Treatment of VGF includes medical therapy, percutaneous intervention, and redo coronary artery bypass graft surgery. In patients undergoing graft intervention, the use of drug-eluting stents, antiplatelet agents, and embolic protection devices may improve clinical outcomes.

CONCLUSIONS

Despite advances in management, VGF remains one of the leading causes of poor in-hospital and long-term outcomes after coronary artery bypass graft surgery. New developments in VGF prevention such as gene therapy, external graft support, fully tissue-engineered grafts, hybrid grafts, and synthetic conduits are promising but unproven. Future efforts to reduce VGF require a multidisciplinary approach with a primary focus on prevention.

Inhibition of neointimal formation and hyperplasia in vein grafts by external stent/sheath

Synthetic and to a lesser extent vein graft failure is still a major problem in the treatment of peripheral arterial disease, with neointimal hyperplasia being the main cause for graft occlusion in the medium and long term. This review aims to establish the current status of external stents or sheaths in the prevention of intimal hyperplasia in small diameter (< 6 mm) vein grafts.

On the biology of saphenous vein grafts fitted with external synthetic sheaths and stents

Autologous saphenous vein is used as a conduit to bypass atherosclerotic lesions in both the coronary artery (coronary artery bypass graft surgery [CABG]) and in femoral arteries (infrainguinal bypass graft surgery [IIBS]). Despite the undoubted success and benefits of the procedures, graft failure occurs in 50% of cases within 10 years after surgery. A principal cause of late vein graft failure is intimal and medial hyperplasia and superimposed atherogenesis. Apart from lipid lowering therapy, no intervention has hitherto proved clinically effective in preventing late vein graft failure which clearly constitutes a major clinical and economic problem that needs to be urgently resolved. However, we have studied the effect of external synthetic stents and sheaths in pig models of vein into artery interposition grafting and found them to have a profound effect on vein graft remodelling and thickening. In this review, therefore, we will summarise the mechanisms underlying vein graft failure and how these stents influence these processes and the possible mechanisms involved as well as the application of these devices in preventing vein graft failure clinically.

Perivenous Application of Fibrin Glue as External Support Enhanced Adventitial Adenovirus Transfection in Rabbit Model

BACKGROUND

Placement of an external support has been reported to prevent intimal hyperplasia of vein grafts. However, it's application limited by potential complications. Peri-adventitial gene delivery is a promising alternative therapy to reduce intimal hyperplasia, but it is limited by low and transient levels of gene transfection. To get more effective inhibition of intimal hyperplasia and to avoid the limitations associated with these two approaches, a study was undertaken to investigate whether mixing adenovirus with fibrin glue may increase the level and prolong the time period of gene expression.

METHODS

Right jugular vein to common carotid artery interposition grafting was performed in 36 male New Zealand white rabbits (2.5-3.0 kg) and the animals were divided into four groups: control group (n = 6); fibrin glue group (n = 6); Ad-GAL group (n = 12); fibrin glue/Ad-GAL group (n = 12). Commercially available fibrin glue and adenovirus expressing the gene for beta-galactosidase (Ad-GAL) was applied separately or in mixing around vein grafts. At 7th day and 14th day after implantation, the grafts were harvested to evaluate transfection rate. At 28th day the grafts were harvested for morphometric analysis.

RESULTS

Compared with weak staining in 2.1 +/- 0.5% in Ad-GAL alone grafts, a high level of beta-Galactosidase staining was evident in 13.2 +/- 4.6% in fibrin glue/Ad-GAL grafts at 7th day (P < 0.001). At 14th day, almost no staining (0%) was detected in Ad-GAL alone grafts. However, there was still a relative high level staining (6.3 +/- 3.8%) in fibrin glue/Ad-GAL grafts (P < 0.001 versus Ad-GAL alone group). At 28th day, a statistically significantly decrease in neointimal area (0.68 +/- 0.06 mm(2)versus 1.00 +/- 0.08 mm(2), P < 0.05) was shown in fibrin glue grafts compared with unsupported vein grafts (control group). The same statistically significantly difference was also existed in fibrin glue/Ad-GAL group and unsupported group in neointimal area (0.66 +/- 0.07 mm(2), P < 0.05).

CONCLUSIONS

A novel method of adventitial gene delivery using fibrin glue as external support is proposed. Fibrin glue may be an ideal candidate for controlled release delivery that would facilitate adventitial gene transfer.

Cyclic strain-mediated matrix metalloproteinase regulation within the vascular endothelium: a force to be reckoned with

The vascular endothelium is a dynamic cellular interface between the vessel wall and the bloodstream, where it regulates the physiological effects of humoral and biomechanical stimuli on vessel tone and remodeling. With respect to the latter hemodynamic stimulus, the endothelium is chronically exposed to mechanical forces in the form of cyclic circumferential strain, resulting from the pulsatile nature of blood flow, and shear stress. Both forces can profoundly modulate endothelial cell (EC) metabolism and function and, under normal physiological conditions, impart an atheroprotective effect that disfavors pathological remodeling of the vessel wall. Moreover, disruption of normal hemodynamic loading can be either causative of or contributory to vascular diseases such as atherosclerosis. EC-matrix interactions are a critical determinant of how the vascular endothelium responds to these forces and unquestionably utilizes matrix metalloproteinases (MMPs), enzymes capable of degrading basement membrane and interstitial matrix molecules, to facilitate force-mediated changes in vascular cell fate. In view of the growing importance of blood flow patterns and mechanotransduction to vascular health and pathophysiology, and considering the potential value of MMPs as therapeutic targets, a timely review of our collective understanding of MMP mechanoregulation and its impact on the vascular endothelium is warranted. More specifically, this review primarily summarizes our current knowledge of how cyclic strain regulates MMP expression and activation within the vascular endothelium and subsequently endeavors to address the direct and indirect consequences of this on vascular EC fate. Possible relevance of these phenomena to vascular endothelial dysfunction and pathological remodeling are also addressed.

Comparison of flow characteristics and vascular reactivity of radial artery and long saphenous vein grafts [NCT00139399]

Background

The morphological and functional differences between arteries and veins may have implications on coronary artery bypass graft (CABG) survival. Although subjective differences have been observed between radial artery (RA) and long saphenous venous (LSV) grafts, these have not been quantified. This study assessed and compared the flow characteristics and in-vivo graft flow responses of RA and LSV aorto-coronary grafts.

Methods

Angiograms from 52 males taken 3.7 ± 1.0 months after CABG surgery were analyzed using adjusted Thrombolysis in Myocardial Infarction (TIMI) frame count. Graft and target coronary artery dimensions were measured using quantitative coronary angiography. Estimated TIMI velocity (V_E) and volume flow (F_E) were then calculated. A further 7 patients underwent in-vivo graft flow responses assessments to adenosine, acetylcholine and isosorbide dinitrate (ISDN) using intravascular Doppler.

Results

The V_E for RA grafts was significantly greater than LSV grafts (P = 0.002), however there was no difference in volume F_E (P = 0.20). RA grafts showed positive endothelium-dependent and -independent vasodilatation, and LSV grafts showed no statistically significant response to adenosine and acetylcholine. There was no difference in flow velocity or volume responses. Seven RA grafts (11%) had compromised patency (4 (6%) ≥ 50% stenosis in the proximal/distal anastomoses, and 3 (5%) diffuse narrowing). Thirty-seven (95%) LSV grafts achieved perfect patency and 2 (5%) were occluded.

Conclusion

The flow characteristics and flow responses of the RA graft suggest that it is a more physiological conduit than the LSV graft. The clinical relevance of the balance between imperfect patency versus the more physiological vascular function in the RA graft may be revealed by the 5-year angiographic follow-up of this trial.

Shear stress and pressure modulate saphenous vein remodeling ex vivo

Vein graft failure remains an important clinical challenge, but factors contributing to vein graft failure have not clearly been defined. We investigated the role of the mechanical environment in vein remodeling in an ex vivo perfusion system. Porcine saphenous veins were subjected to five different ex vivo hemodynamic environments, including one mimicking an arterial bypass graft, for one week in order to independently assess the effects of shear stress and pressure on vein remodeling. The extent of intimal hyperplasia decreased with culture under increasing shear stress, with veins cultured under the lowest levels of shear stress exhibiting the greatest ratio of intimal/medial area, 0.15+/-0.03, which was greater than that of fresh veins (0.06+/-0.01, p<0.05). All perfused veins displayed characteristics of both medial hypertrophy and eutrophic remodeling, with those veins cultured under elevated pressures showing greater increases in mass and area than those cultured under venous pressures. Medial area correlated with the average pressure under which veins were cultured (R2=0.95, p<0.001), with veins cultured under bypass graft conditions, which were exposed to the greatest pressure during the one week culture, exhibiting the largest medial area (1.69+/-0.15 mm2), which was significantly greater than that of fresh veins (1.08+/-0.05 mm2, p<0.05). However, pulsatility was not a necessary stimulus for medial growth, as increases in medial area were observed in culture conditions in which steady flow and pressure were present. Our results suggest that pressure and shear stress act independently to regulate vein remodeling, influencing changes in vessel size as well as the nature of the remodeling.

Double thoracic artery?halved mid-term mortality?

The superior patency of ITA grafts to saphenous veins is conclusive. The aim of the study was to collate mid-term benefit between patients receiving bilateral ITA (BITA) or single ITA (SITA). Outcome of 1378 pts with isolated CABG operated between 1/97-8/99 was analyzed retrospectively. Follow-up was 4.0 to 6.6 years (average 5.3). A total of 716 pts received BITA, 662 SITA and additional saphenous veins. We evaluated mortality rate, freedom from reoperation, intervention (PTCA/stent), and incidence of cardiac events and quality of life with respect to pts risk factors. Demographic data: Male gender was more frequent in both groups (BITA females: n=115; males: n=601; SITA females: n=150; males: n=512; p<0.01). Mean age was comparable in both groups with 69.2 years (42.7 to 88.6 years) in the BITA group and 71.0 years (47.3 to 91.6 years) (n. s.) in the SITA group.

RISK FACTORS

Incidence of diabetes mellitus (26.0 vs 25.9%) as well as the mean BMI (27.4 vs 27.0%) did not differ statistically in both groups.

RESULTS

Clinical characteristics like NYHA/ CCS classifications showed a significant difference towards superior results only for stadium I in the BITA group. Mortality/cardiac events after 5.3 years average: Total mortality revealed 5.2% (n=37) in the BITA vs 9.1% (n=60) in the SITA group (p</=0.005). The cardiac-related mortality was 0.7% (n=5) in the BITA and 2.0% (n=13) in the SITA group (p<0.05). The non-cardiac-related mortality did not differ significantly (2.7 vs 2.9%). The incidence of redo-operations was 0.1% (BITA) vs 0.6% (SITA) (n. s). Cardiac interventions like PTCA or stent were performed in 3.1% (BITA) vs 4.7% (SITA) or 3.7% (BITA) vs 4.2% (SITA) (n. s.) respectively. Infarction-rate was 2.0% in the BITA and 3.0% in the SITA group (n. s.).

CONCLUSIONS

Mid- to long-term benefit of patients receiving bilateral ITA is superior to those with single ITA. Cardiac-related mortality and incidence of reoperation was reduced to less than half after BITA grafting. Freedom from cardiac interventions (PTCA/stent), NYHA/CCS classifications and quality of life were rarely influenced by BITA frequency.

F-actin capping (CapZ) and other contractile saphenous vein smooth muscle proteins are altered by hemodynamic stress: a proteonomic approach

Increased force generation and smooth muscle remodeling follow the implantation of saphenous vein as an arterial bypass graft. Previously, we characterized and mapped 129 proteins in human saphenous vein medial smooth muscle using two-dimensional (2-D) PAGE and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Here, we focus on actin filament remodeling in response to simulated arterial flow. Human saphenous vein was exposed to simulated venous or arterial flow for 90 min in vitro, and the contractile medial smooth muscle was dissected out and subjected to 2-D gel electrophoresis using a non-linear immobilized pH 3-10 gradient in the first dimension. Proteins were analyzed quantitatively using PDQuest 2-D software. The actin polymerization inhibitor cytochalasin B (1 microm) prevented increases in force generation after 90 min of simulated arterial flow. At this time point, there were several consistent changes in actin filament-associated protein expression (seven paired vein samples). The heat shock protein HSP27, identified as a three-spot charge train, showed a 1.6-fold increase in abundance (p = 0.01), but with reduced representation of the phosphorylated Ser(82) and Ser(15)Ser(82) isoforms (p = 0.018). The abundance of actin-capping protein alpha2 subunit CapZ had decreased 3-fold, p = 0.04. A 19-kDa proteolytic fragment of actin increased 2-fold, p = 0.04. For the four-spot charge train of gelsolin, there was reduced representation of the more acidic isoforms, p = 0.022. The abundance of other proteins associated with actin filaments, including cofilin and destrin, remained unchanged after arterial flow. Actin filament remodeling with differential expression and/or post-translational modification of proteins involved in capping the barbed end of actin filaments, HSP27 and CapZ, is an early response of contractile saphenous vein smooth muscle cells to hemodynamic stress. The observed changes would favor the generation of contractile stress fibers.

Proliferative activity in stenotic human aortocoronary bypass grafts

BACKGROUND

Aortocoronary bypass graft disease is responsible for long-term failure of autologous vein grafts. The analyses of proliferation and cell type characterisation in human bypass grafts harvested during re-do surgery make it possible to investigate the cellular processes leading to bypass graft failure.

METHODS

30 stenotic vein grafts and 25 control veins were explantated during re-do heart surgery procedures. The total area and cell count of the neointima, media and adventitia were calculated computer-assisted. Actively proliferating cells were identified using antibody to Ki-67 and positive cells were determined by double-label immunocytochemistry with SMC alpha-actin, CD 31 (endothelial cells), CD 68 (macrophages) and CD 45 (T-lymphocytes).

RESULTS

Active proliferation was detected in different cell types with an average proliferation index of 0.15%, 0.18% and 0.086% for neointima, media and adventitia. Only 9% of proliferating cells in the neointima were SMC (not identified cells 40%); correspondingly, 14% SMC (not identified cells 33%) were detected in the media. Endothelial cells turned out to be the predominant proliferating cell type in all sections of the vessel wall.

CONCLUSION

Proliferation in our series of stenotic vein grafts occurred at a low level, but was significantly higher compared to native control veins. While proliferation may play an important role in early lesions, our data clearly show low proliferation activity in advanced graft lesions. The identification of proliferating macrophages and T-lymphocytes implicate an additional inflammatory component in the development of human bypass graft disease.

SUMMARY

To clarify the role of cellular proliferation in human aortocoronary bypass grafts, we characterized the cellular composition and proliferation index in 30 stenotic saphenous vein grafts in comparison to 25 native veins. Proliferation in our series of stenotic vein grafts occurred at a low level, but was significantly higher compared to native control veins.

External supports and the prevention of neointima formation in vein grafts

AIMS AND METHODOLOGY

the aim of this review is to provide an overview of the aetiology of neointima formation in vein grafts and to highlight the use of an external support to modulate this phenomenon. A systematic literature review was performed via computerised search on MEDLINE, OVID and the Cochrane Library. The search terms initially employed were broad-based; "vein graft", "neointima" and "external stent". Subsequently, more specific search terms were utilised; "perivenous mesh", "external prosthesis" and "varicose vein". Articles from indexed journals relevant to the objective, external venous supports, from the earliest reports in the 1960's to the latest in 2001 were included to obtain an exhaustive list. Reviews, abstracts and proceedings of scientific meetings, case reports and the results of both animal model investigations and human clinical trials in all languages were included. Articles describing an external support employed in both peripheral and aortocoronary bypass investigations were included.

Expression of the proto-oncogene c-myc in human stenotic aortocoronary bypass grafts

Proliferation and differentiation of vascular smooth muscle cells (VSMC) are central events in vascular pathobiology and play a major role in the development of stenotic and restenotic lesions. The proto-oncogene c-myc and other early cell cycle-regulating genes have been implicated in the induction of cell proliferation and differentiation under diverse pathophysiological conditions. In the present study we analyzed c-myc mRNA expression by indirect nonradioactive in situ hybridization technique (NISH) in human stenotic venous bypass grafts (n = 32) retrieved during re-do operations of coronary artery disease and compared the results with 28 native veins (vena saphena magna) from the same patients. Stenotic bypass grafts showed enhanced c-myc expression located predominantly in VSMC in the media and neointima (severity score: ++-+++, 32/32 stenotic veins). In native veins we observed only low levels of c-myc mRNA (severity score: +, 28/28 native veins), all signals were restricted to endothelial cells of either the innermost intimal layer or of the vasa vasorum. Our in situ hybridization studies demonstrate enhanced mRNA expression of the proto-oncogene c-myc in stenotic venous bypass grafts. These results suggest that--in analogy to other pathophysiological conditions--c-myc exerts essential regulatory functions in cellular events operative during the initiation and progression of venous bypass graft disease.

Integrin and FAK-mediated MAPK activation is required for cyclic strain mitogenic effects in Caco-2 cells

Rhythmic strain stimulates Caco-2 proliferation. We asked whether mitogen-activated protein kinase (MAPK) activation mediates strain mitogenicity and characterized upstream signals regulating MAPK. Caco-2 cells were subjected to strain on collagen I-precoated membranes or antibodies to integrin subunits. Twenty-four hours of cyclic strain increased cell numbers compared with static conditions. MAPK-extracellular signal-regulated kinase (ERK) kinase inhibition (20 microM PD-98059) blocked strain mitogenicity. p38 Inhibition (10 microM SB-202190) did not. Strain rapidly and time-dependently activated focal adhesion kinase (FAK), paxillin, ERK1 and 2, and p38 on collagen. c-Jun NH(2)-terminal kinase (JNK)1 and 2 exhibited delayed activation. Similar activation occurred when Caco-2 cells were subjected to strain on a substrate of functional antibody to the alpha2-, alpha3-, alpha6-, or beta1-integrin subunits but not on a substrate of functional antibody to the alpha5-subunit. FAK inhibition by FAK397 transfection blocked ERK2 and JNK1 activation by in vitro kinase assays, but pharmacological protein kinase C inhibition did not block ERK1 or 2 activation by strain. Strain-induced ERK signals mediate strain's mitogenic effects and may require integrins and FAK activation.