Interactive effects of homocysteine and copper on angiogenesis in porcine isolated saphenous vein

BACKGROUND: After coronary artery bypass grafting procedures with saphenous vein, there is a protracted elevation of plasma homocysteine and copper. These interact to elicit endothelial dysfunction through promotion of superoxide. It has been suggested that angiogenesis and the formation of a neovasa vasorum is important in mediating vein graft patency. A novel in vitro model of angiogenesis in isolated pig saphenous veins was therefore developed to study the effect of homocysteine and copper and the role of superoxide on tubule growth, an index of angiogenesis. METHODS: Two-millimeter rings of porcine saphenous veins were embedded in fibrin, incubated for 2 weeks with homocysteine and copper chloride, and tubules counted. RESULTS: Tubule growth in cultured saphenous veins, which was inhibited by angiostatin, occurred in a time-dependent manner during a 14-day period. Copper chloride alone at 1 microM and 10 microM augmented microtubule formation, whereas homocysteine alone at up to 1 mM had no effect. Homocysteine and copper chloride together markedly inhibited microtubule formation. Significant inhibition of tubule formation and superoxide formation was elicited with inhibitors of nicotinamide adenine dinucleotide phosphate oxidase, mitochondrial respiration, and xanthine oxidase. Copper chloride augmented superoxide formation, but homocysteine had no effect. Homocysteine and copper chloride together also augmented superoxide formation. CONCLUSIONS: These data indicate that the increase in plasma homocysteine and copper may exert a deleterious effect on graft patency by preventing the formation of a neovasa vasorum, thereby promoting hypoxia. This effect is mediated by a mechanism independent of superoxide which actually promotes angiogenesis in this model.