Ex vivo carbon monoxide delivery inhibits intimal hyperplasia in arterialized vein grafts

Aims Veins are still the best conduits available for arterial bypass surgery. When these arterialized vein grafts fail, it is often due to the development of intimal hyperplasia (IH). We investigated the feasibility and efficacy of the ex vivo pre-treatment of vein grafts with soluble carbon monoxide (CO) in the inhibition of IH. Methods and results The inferior vena cava was excised from donor rats and placed as an interposition graft into the abdominal aorta of syngeneic rats. Prior to implantation, vein grafts were stored in cold Lactated Ringer (LR) solution with or without CO saturation (bubbling of 100% CO) for 2 h. Three and 6 weeks following grafting, vein grafts treated with cold LR for 2 h developed IH, whereas grafts implanted immediately after harvest demonstrated significantly less IH. Treatment in CO-saturated LR significantly inhibited IH and reduced vascular endothelial cell (VEC) apoptosis. Electron microscopy revealed improved VEC integrity with less platelet/white blood cell aggregation in CO-treated grafts. The effects of CO in preventing IH were associated with activation of hypoxia inducible factor-1 alpha (HIF-1 alpha) and an increase in vascular endothelial growth factor (VEGF) expression at 3-6 h after grafting. Treatment with a HIF-1 alpha inhibitor completely abrogated the induction of VEGF by CO and reversed the protective effects of CO on prevention of IH. Conclusion Ex vivo treatment of vein grafts in CO-saturated LR preserved VEC integrity perioperatively and significantly reduced neointima formation. These effects appear to be mediated through the activation of the HIF1 alpha/VEGF pathway.