Recombinant endothelial nitric oxide synthase-transduced human saphenous veins: Gene therapy to augment nitric oxide production in bypass conduits

Background: Nitric oxide is a potent vasodilator that also inhibits platelet aggregation and smooth muscle cell proliferation, properties that may prevent early and late occlusion of saphenous vein coronary bypass conduits. We determined whether human saphenous veins can be transduced with adenovirus vector-encoding bovine endothelial nitric oxide synthase (Ad. CMVeNOS), resulting in functional expression of recombinant nitric oxide synthase. Methods and Results: Harvested segments of human saphenous vein were exposed for 1 hour at 37°C to replication-deficient Ad.CMVeNOS (5x10⁹ PFU/mL) or control adenovirus-encoding Escherichia coli β-galactosidase (Ad.CMVLacZ; 5x10⁹ PFU/mL). The vein segments were analyzed for recombinant endothelial nitric oxide synthase expression and activity 48 hours later. Histochemical staining for recombinant β-galactosidase activity was localized to the luminal endothelium and adventitia of vein segments transduced with Ad.CMVLacZ. Similarly, immunohistochemical staining with a monoclonal antibody for nitric oxide synthase localized recombinant gene expression to endothelial and adventitial cells in Ad. CMVeNOS veins; only endogenous nitric oxide synthase was identified in the endothelium of Ad.CMVLacZ veins. Nitrite generation after stimulation with calcium ionophore increased in Ad.CMVeNOS veins (1420.0±298.2 nM/mg versus 130.3±19.9 nM/mg; n=3; P<.05). Isometric tension recording demonstrated augmented maximal relaxation to calcium ionophore (32±4.5% versus 17.4±7.4%; n=6; P<.05) after precontraction with norepinephrine. Bioassay superfusion demonstrated a twofold augmentation of the biodetector ring relaxation during calcium ionophore stimulation of Ad.CMVeNOS veins. Conclusions: Adenovirus-mediated gene transfer to human saphenous veins resulted in functional transgene expression with increased nitric oxide release. These or similar molecular techniques to increase nitric oxide production may reduce the risk of early thrombosis in saphenous vein grafts.