Cable, David G.

Background —Proliferation of the intima is an early lesion of saphenous vein graft disease. Early patency rates of radial artery grafts are acceptable, but little is known about their risk of intimal hyperplasia. Methods and Results —To develop a model of intimal hyperplasia, we incubated human saphenous veins, internal mammary arteries, and radial arteries (n=6, 8, and 10, respectively) in an organ culture with Rosewell Park Memorial Institute 1640 (30% serum) for 0, 4, 7, 10, and 14 days. Quantitative histological studies were performed, and the average intimal-to-medial (I/M) ratio was calculated for each incubation interval. After 10 and 14 days of culture, the I/M ratio increased in the saphenous veins ( P =0.03, P =0.04 versus 0 day, respectively). No significant increase occurred in the I/M ratio in either the internal mammary or radial arteries. Next, the ability of adenoviral gene transfers to inhibit intimal hyperplasia in the saphenous veins was evaluated. Adenoviral-mediated gene transfer of nitric oxide synthase significantly reduced the I/M ratio at 14 days compared with vehicle ( P =0.001) and virus ( P =0.004) controls. Conclusions —The human saphenous vein has a greater propensity for intimal hyperplasia than arterial grafts; the human radial artery behaves similarly to the internal mammary artery. In the future, gene therapy may augment nitric oxide synthase, limiting vein graft disease.

Background —Coronary arteries respond to hypoxia with transient relaxations, which increases coronary blood flow, in part, by release of nitric oxide. We hypothesized that increased expression of nitric oxide synthase might further augment blood vessel relaxation during hypoxia. The present study examined the effect of adenovirus-mediated transfer of bovine endothelial nitric oxide synthase (eNOS) on hypoxia-induced transient relaxations in canine coronary arteries. Methods and Results —Paired segments of coronary arteries were exposed to vehicle (phosphate-buffered saline with albumin) or an adenovirus encoding either E coli β-galactosidase (Ad.CMVLacZ, viral control; 10 10 pfu/mL) or eNOS (Ad.CMVeNOS; 10 10 pfu/mL) for 2 hours at 37°C. Immunohistochemistry with a monoclonal antibody specific for eNOS documented both endothelial and adventitial expression in Ad.CMVeNOS arteries, whereas vehicle and viral controls demonstrated only constitutive expression. Levels of cGMP were increased 5-fold in Ad.CMVeNOS arteries compared with controls. In arteries exposed to Ad.CMVeNOS, maximum contraction to prostaglandin F 2α was reduced compared with viral controls, and this effect was eliminated by pretreatment with a competitive inhibitor of eNOS ( N G -monomethyl- l -arginine, 10 −3 mol/L). Hypoxia-induced transient relaxation (95% N 2 -5% CO 2 ) in Ad.CMVeNOS arteries (45.2±8.8%, n=6) was augmented compared with vehicle (26.3±6.0%) or viral (27.2±7.1%) controls. Conclusions —Adenovirus-mediated gene transfer of nitric oxide synthase reduces receptor-dependent contractions and augments hypoxia-induced relaxations in canine coronary arteries; this method of augmentation of NO production might be advantageous for reduction of coronary artery vasospasm.

Select subsets of patients require prosthetic graft material for revascularization. Although arterial prosthetic grafts of large caliber perform acceptably, grafts of <6 mm exhibit a high attrition rate. Microvessel endothelial sodding, a method resulting in the lining of prosthetic grafts with autologous endothelium, improves graft patency; however, aggressive antiplatelet therapy is still required, because terminating an antiplatelet regimen accelerates graft attrition. The present investigation was designed to address the acute production of vasoactive substances in microvessel endothelial cell sodded expanded polytetrafluoroethylene (ePTFE) grafts in an attempt to delineate a possible mechanism behind the continued requirement for antiplatelet therapy. Equal lengths of acutely sodded ePTFE grafts (canine falciform ligament source) and saphenous veins (SV) (canine source) were evaluated by superfusion bioassay. Basal secretion from ePTFE grafts relaxed the biodetector ring 1 ± 3%, whereas SV relaxed the ring 10 ± 3% (p < 0.05, ePTFE vs. SV). Relaxation with acetylcholine stimulation was 49 ± 7% in grafts and 50 ± 10% in veins (p = NS). Calcium ionophore stimulation produced relaxation of 37 ± 9% from ePTFE grafts and 100 ± 23% from SV (p < 0.05). Indomethacin added to perfusate reduced relaxations from sodded ePTFE grafts to 20.2 ± 9.2% with acetylcholine stimulation and 12.5 + 4.3% with calcium ionophore (p < 0.05 vs. control); addition of N G -monomethyl-L-arginine (L-NMMA) had no effect on the release of vasoactive substances from ePTFE grafts. In contrast, relaxations of effluent from SV stimulated by acetylcholine and calcium ionophore were significantly attenuated with indomethacin and L-NMMA (p < 0.05 vs. control). Scanning electron microscopy demonstrated confluent endothelium in SV and a nonconfluent endothelial cell layer in grafts. Acutely sodded ePTFE grafts produce vasoactive substances that quantitatively and qualitatively differ from those produced by canine SV. The ePTFE grafts produce mainly prostanoids, whereas SV produce both nitric oxide and prostanoids. The endothelial cell isolation procedure and absence of immediate graft luminal confluence may contribute to the observed differences.