Evaluation of the Stress-Growth Hypothesis in Saphenous Vein Perfusion Culture.

The great saphenous vein (GSV) has served as a coronary artery bypass graft (CABG) conduit for over 50 years. Despite prevalent use, first-year failure rates remain high compared to arterial autograft options. Amongst other factors, vein graft failure can be attributed to material and mechanical mismatching that lead to apoptosis, inflammation, and intimal-medial hyperplasia. Through the implementation of the continuum mechanical-based theory of "stress-mediated growth and remodeling," we hypothesize that the mechanical properties of porcine GSV grafts can be favorably tuned for CABG applications prior to implantation using a prolonged but gradual transition from venous to arterial loading conditions in an inflammatory and thrombogenic deficient environment. To test this hypothesis, we used a hemodynamic-mimetic perfusion bioreactor to guide remodeling through stepwise incremental changes in pressure and flow over the course of 21-day cultures. Biaxial mechanical testing of vessels pre- and post-remodeling was performed, with results fit to structurally-motivated constitutive models using non-parametric bootstrapping. The theory of "small-on-large" was used to describe appropriate stiffness moduli, while histology and viability assays confirmed microstructural adaptations and vessel viability. Results suggest that stepwise transition from venous-to-arterial conditions results in a partial restoration of circumferential stretch and circumferential, but not axial, stress through vessel dilation and wall thickening in a primarily outward remodeling process. These remodeled tissues also exhibited decreased mechanical isotropy and circumferential, but not axial, stiffening. In contrast, only increases in axial stiffness were observed using culture under venous perfusion conditions and those tissues experienced moderate intimal resorption.

A pilot study of venous duplex ultrasound parameters in healthy children.

OBJECTIVE: The spectrum of chronic venous disease (CVD) in adults is well documented, whereas there is a paucity of data published commenting on pediatric CVD. We previously identified that there is often venous reflux present in cases of pediatric lower extremity edema despite an alternative confirmed diagnosis. To further assess the clinical significance of this venous reflux, this study aimed to elicit venous parameters in healthy pediatric controls. METHODS: Healthy pediatric volunteers aged 5 to 17 years were recruited for venous reflux study. A comprehensive venous reflux study was performed with the patient standing. Vein diameter, patterns of valvular reflux, and accessory venous anatomy were examined in the deep and superficial venous systems. RESULTS: Eighteen children including 10 boys and 8 girls were studied. Five volunteers were aged 5 to 8 years, six volunteers were aged 9 to 12 years, and seven volunteers were aged 13 to 17 years. Great saphenous vein (GSV) diameter at the saphenofemoral junction significantly increased with age. Deep vein valve closure time (VCT) did not differ significantly between groups, whereas GSV VCT was significantly higher in the 9- to 12-year age group. Incidental venous insufficiency was identified in 60% of children aged 5 to 8 years (n = 3), 50% of children aged 9 to 12 years (n = 3), and 57% of children aged 13 to 17 years (n = 4). All superficial venous reflux was confined to the GSV; there were no cases of isolated deep venous reflux. Reflux was identified at multiple GSV stations in 60% of children. There was no significant difference in incompetent GSV VCT in comparing children with and without deep venous reflux. Accessory superficial veins were identified in 20% of children aged 5 to 8 years (n = 1), 50% of children aged 9 to 12 years (n = 3), and 43% of children aged 13 to 17 years (n = 3). The presence of an accessory saphenous vein was not associated with deep venous reflux in any patient, and only 29% of those with accessory saphenous venous anatomy had evidence of superficial venous (GSV) reflux. CONCLUSIONS: The GSV continues to grow in diameter through the teenage years. Incidental valvular incompetence and GSV reflux are common. The presence of accessory saphenous veins is similarly common and not associated with venous reflux. The clinical significance and natural history of this incidental venous reflux remain unclear. Future research should determine whether these changes seen in the pediatric age group lead to CVD during later years of life.

Adventitial vessel growth and progenitor cells activation in an ex vivo culture system mimicking human saphenous vein wall strain after coronary artery bypass grafting.

Saphenous vein graft disease is a timely problem in coronary artery bypass grafting. Indeed, after exposure of the vein to arterial blood flow, a progressive modification in the wall begins, due to proliferation of smooth muscle cells in the intima. As a consequence, the graft progressively occludes and this leads to recurrent ischemia. In the present study we employed a novel ex vivo culture system to assess the biological effects of arterial-like pressure on the human saphenous vein structure and physiology, and to compare the results to those achieved in the presence of a constant low pressure and flow mimicking the physiologic vein perfusion. While under both conditions we found an activation of Matrix Metallo-Proteases 2/9 and of microRNAs-21/146a/221, a specific effect of the arterial-like pressure was observed. This consisted in a marked geometrical remodeling, in the suppression of Tissue Inhibitor of Metallo-Protease-1, in the enhanced expression of TGF-ß1 and BMP-2 mRNAs and, finally, in the upregulation of microRNAs-138/200b/200c. In addition, the veins exposed to arterial-like pressure showed an increase in the density of the adventitial vasa vasorum and of cells co-expressing NG2, CD44 and SM22α markers in the adventitia. Cells with nuclear expression of Sox-10, a transcription factor characterizing multipotent vascular stem cells, were finally found in adventitial vessels. Our findings suggest, for the first time, a role of arterial-like wall strain in the activation of pro-pathologic pathways resulting in adventitial vessels growth, activation of vasa vasorum cells, and upregulation of specific gene products associated to vascular remodeling and inflammation.

Capillary-venous malformation in the lower limb.

Regional capillary malformation of a lower extremity is associated with the overgrowth of bone or soft tissue in several disorders, most commonly Klippel-Trenaunay syndrome and Parkes Weber syndrome. We have observed a subset of patients with a capillary malformation of the leg, minor growth disturbance, and prominent veins. The objective of the current study is to describe a series of patients with regional capillary malformation of the lower extremity in association with phlebectasia. This is a retrospective series of 17 patients diagnosed with capillary-venous malformation of the lower extremity. We excluded patients with clinical or radiographic evidence of lymphatic or arteriovenous malformation. Age, presentation, associated features, radiographic findings, and management were documented. In most patients the capillary malformation covered a large area without sharply demarcated borders. Four patients had one or more discrete, well-defined capillary stains involving less than 5% of the total surface area of the affected lower limb. Prominent veins were most common in the popliteal fossa and on the knee and dorsal foot. Approximately two-thirds of patients had a leg length discrepancy, with the affected leg being longer (n = 6) or shorter (n = 4); in many the affected leg was also slightly larger (n = 8) or smaller (n = 4) in girth. Radiographic imaging showed dilatation of superficial (n = 16), muscular (n = 9), and deep veins (n = 6). We characterize a subset of patients with regional capillary-venous malformation of the lower extremity with prominent veins and minor hypotrophy/hypertrophy that differs from Klippel-Trenaunay syndrome (capillary-lymphatic-venous malformation) but belongs at the minor end of the spectrum of vascular disorders with overgrowth.

An external, oversized, porous polyester stent reduces vein graft neointima formation, cholesterol concentration, and vascular cell adhesion molecule 1 expression in cholesterol-fed pigs.

BACKGROUND: Reducing neointima formation and atherosclerosis are key goals in preventing late vein graft failure. Although pharmacologic and mechanical solutions have been proposed, the demonstration that these influence both aspects of vein graft pathology have been lacking. Supporting grafts externally with an oversized, highly porous polyester stent dramatically reduces neointima formation in normocholesterolemic pigs. However, its effects in the presence of hypercholesterolemia are unknown. METHODS: We compared wall thickening, cholesterol concentration, foam-cell formation, and the expression of the leukocyte adhesion molecule vascular cell adhesion molecule 1 after 3 months in stented and unstented saphenous vein interposition grafts into the carotid arteries of pigs fed cholesterol to cause modest hypercholesterolemia (11.2 +/- 1.2 mmol/L). RESULTS: Stenting reduced neointima formation from 5.6 +/- 0.4 to 1.2 +/- 0.2 mm(2) (n = 7; P <.00002, paired t test) and graft cholesterol concentration from 4.7 +/- 1.2 to 2.1 +/- 1.3 mg/g wet weight (P <.02). Foam cells were observed in unstented grafts (mean, 1.5% +/- 0.5% of all cells) but never in stented grafts. Vascular cell adhesion molecule 1 was strongly expressed in 53% +/- 8% of intimal and medial cells in unstented grafts but was weakly expressed in only 19% +/- 3% (n = 4, P <.05) of stented grafts. CONCLUSIONS: We conclude that external stenting with polyester favorably influences both neointima formation and early atherosclerosis, both of which are key aspects of vein graft disease, and that decreased expression of vascular cell adhesion molecule 1 is part of the underlying mechanism.

Adenoviral delivery of a constitutively active retinoblastoma mutant inhibits neointima formation in a human explant model for vein graft disease.

Intimal hyperplasia resulting from vascular injury remains a major obstacle in the long-term success of coronary artery bypass grafts. Inhibition of smooth muscle cell (SMC) proliferation using adenoviral gene transfer of cell cycle inhibitors resulted in reduced neointima formation in various animal models. However, little is known about the effect on human SMCs and neointima formation. Here we report the effects of infection with an adenoviral vector encoding a constitutively active form of the retinoblastoma gene (Ad. delta Rb) on proliferation of human saphenous vein SMCs (HSVSMCs) and neointima formation in organ cultures of human saphenous vein. Proliferation of SMCs was inhibited dose-dependently after infection with Ad. delta Rb. A near-total inhibition was found at an Ad. delta Rb concentration of 10(8) pfu/ml. Organ cultures of human saphenous vein segments were used to evaluate the effect of Ad. delta Rb infection on neointima formation and vein graft disease. Segments cultured for 4 weeks develop a neointima that is morphologically highly similar to early initimal lesions found in pathological vein grafts in vivo. Infection of saphenous vein segments with 2 x 10(9) pfu/ml Ad. delta Rb resulted in a 59% reduction of neointimal area when compared to uninfected counterparts, whereas infection with control adenovirus, Ad.LacZ, had no significant effect. The results of this study show that Ad. delta Rb gene transfer might be an efficient approach to prevent neointima formation in human saphenous vein grafts.

Inhibition of neointima formation in an organ culture of human saphenous vein: a comparison of dual endothelin-converting enzyme/neutral endopeptidase and selective neutral endopeptidase inhibition.

PURPOSE: Endothelin-1 (ET-1) has been implicated in a variety of vascular pathologic conditions, although there is considerable controversy as to whether such effects are mediated by the ET-(A) or ET-(B) receptor. This study investigated whether inhibition of big ET-1 processing by inhibition of endothelin-converting enzyme (ECE) could, therefore, offer an alternative therapeutic strategy in the prevention of vein graft intimal hyperplasia. METHODS: Human saphenous vein (3 equal segments from 10 patients) were maintained in organ culture for 14 days with either 50 micromol/L CGS 26303 (a dual ECE/neutral endopeptidase [NEP] inhibitor), 50 micromol/L CGS 24592 (a selective NEP inhibitor), or vehicle (control). They were then processed for immunostaining and neointimal thickness measurements, and conditioned media was collected for enzyme-linked immunosorbent assay analysis. RESULTS: Neointimal thickness in the ECE/NEP-inhibited veins did not differ significantly from that of control segments. However, there was a highly significant augmentation in the NEP-inhibited segments, consistent with an inhibition of ET-1 degradation (median difference, 16.8; 95% CI, -23.5, -10.4; P =.002, Wilcoxon). ECE immunostaining was reduced in the ECE/NEP-inhibited veins, although ET-1 staining was also present. ET-1 expression was intense in the thickened neointimas of NEP-inhibited veins, which also showed significant ECE staining. Elevated levels of big ET-1 were measured in the ECE/NEP-inhibited veins, consistent with reduced ECE activity. However, mature ET-1 was still detectable in these segments. CONCLUSION: There is a requirement for potent and selective inhibitors of ECE to evaluate fully the potential therapeutic benefits of blocking ET-1 biosynthesis. The use of dual inhibitors complicates the interpretation of results, because the observed response is likely to be a combination of both ECE and NEP inhibition.

Differences in adaptation to growth of children between internal thoracic artery and saphenous vein coronary bypass grafts.

BACKGROUND: It is not known how the internal thoracic artery (ITA) and saphenous vein graft (SVG) adapts to somatic growth of pediatric patients who underwent coronary artery bypass grafting (CABG). METHODS: Twenty-two ITAs and 6 SVGs in 17 patients who underwent at least three postoperative catheterizations with biplanar cineangiography and followed for a minimum of 5 years were evaluated. We evaluated the length, diameter and curvature of the grafts by cineangiographies which were performed at 1 month, 1 year, 5 years and more than 5 years postoperatively. RESULTS: The length of the ITA (1-month: 117+/-31 mm, 1-year: 134+/-32 mm, 5-years: 146+/-28 mm, and >5-years: 155+/-34 mm, p=0.032) and diameter of the ITA (1.4+/-0.4 mm, 2.0+/-0.7 mm, 2.3+/-0.6 mm and 2.6+/-0.6 mm, p<0.0001) significantly increased over time, but neither the length nor diameter of the SVG length: 121+/-33 mm, 119+/-29 mm, 119+/-25 mm and 126+/-1 mm, p=0.9907; diameter: 4.1+/-1.0 mm, 3.9+/-0.7 mm, 4.0+/-0.8 mm and 3.3+/-0.4 mm, p=0.5784) increased. Although the ITA exhibited no change in curvature over time (1 month: 1.15+/-0.07, late: 1.15+/-0.07, p=0.8490), the curvature of the SVG significantly decreased over time (1 month: 1.42+/-0.19 and late: 1.25+/-0.16, p=0.0277). The percent segmental length of ITAs were changed little from early to late after CABG (1 month: proximal: 33.7+/-7.0%, middle: 33.3+/-7.9% and distal: 32.9+/-7.9%, vs late: 34.3+/-7.2%, 33.2+/-7.9% and 32.5+/-7.9%, p=0.937). CONCLUSIONS: ITAs grow in proportion to somatic growth, while SVGs course in a more linear fashion in adapting to patient growth.

Saphenous vein graft growth 13 years after coronary bypass in a child with Kawasaki disease.

The presumed limited growth potential of saphenous vein grafts has led many authorities to discourage their use in young children. We documented excellent growth and patency of a saphenous vein graft 13 years after operation in a 7-year-old child with coronary artery obstruction caused by Kawasaki disease.

Spontaneous rhythmic contractions of human saphenous veins isolated from old subjects are sensitive to cyclooxygenase inhibitors.

Spontaneous rhythmic contractions were observed in some preparations of human isolated saphenous veins from old (greater than 60 years) subjects. These contractions were insensitive to adrenergic and histaminergic blockers, but were abolished by the cyclooxygenase inhibitors, aspirin and indomethacin, indicating the participation of endogenous eicosanoids.