Background: Cardiopulmonary bypass (CPB) applied during coronary artery bypass grafting (CABG), promotes inflammation, generation of reactive oxygen species (ROS) and up-regulation of matrix metalloproteinases (MMPs). All these complications may lead to contractile dysfunction, restenosis and early graft failure, restricting long-term efficacy of bypass grafts. Low-dose doxycycline is a potent MMP inhibitor and ROS scavenger. In this study, we aimed to investigate the effects of doxycycline on ROS generation, MMP regulation and contractile dysfunction induced by H 2 O 2 in human saphenous vein (HSV) grafts. Methods: HSV grafts (n=7) were divided into four groups after removing endothelial layer by mechanical scratching and incubated with 10 µM H 2 O 2 and/or 10 µM doxycycline for 16 hrs. Untreated segments served as control. Concentration–response curves to noradrenaline (NA), potassium chloride (KCl), serotonin (5-HT) and papaverine were performed. Superoxide anion and other ROS levels were determined by using lucigenin- and luminol-enhanced chemiluminescence assays, respectively. Expression/activity of gelatinases (MMP-2/MMP-9) was examined by gelatin zymography. MMP-13 expression was evaluated by immunostaining/immunoscoring. Results: H 2 O 2 incubation increased superoxide anion and other ROS levels. Doxycycline prevented these increments. H 2 O 2 suppressed contractile responses to NA, KCl and 5-HT. Doxycycline ameliorated contractions to NA and KCl but not to 5-HT. H 2 O 2 or doxycycline did not altered relaxation to papaverine. MMP-2 and MMP-13 expression increased with H 2 O 2 , but doxycycline inhibited MMP-2 up-regulation/activation. Conclusion: Low-dose doxycycline may have beneficial effects on increased oxidative stress, MMP up-regulation/activation and contractile dysfunction in HSV grafts.

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