Prevention of Vein Graft Failure: Mechanisms Involved and Therapeutic Strategies

Coronary artery bypass grafting (CABG) remains the "gold standard" for treating highrisk patients with unprotected left-main or multi-vessel coronary lesions. However, the long-term success of CABG is largely limited by an inadequate patency of saphenous vein grafts. To date, various therapeutic strategies targeting at the underlying mechanisms involved in the pathogenesis of vein graft failure (VGF) have been proposed and tested. However, apart from lipid-lowering therapy, no other intervention appears to have sustained benefits on improving vein graft patency in the clinical setting. Therefore, the aim of this study is to explore novel sets of molecular targets and effective therapeutic strategies to prevent VGF.;Novel molecules involved in the pathogenesis of vein graft failure: Using a porcine model, we assessed the involvement of osteopontin (OPN) in the venous arterialization and its relationship with the matrix metalloproteinases (MMPs). We found that the expression of OPN was significantly increased over the 3-month study period. Moreover, the expression of OPN at different time points well correlated with the fluctuating activities of MMP-2/9 and the number of proliferative cells. We also observed a time-dependent redistribution of OPN protein accumulating in different layers of the venous wall. These findings suggest a contributory role of OPN protein involved in the process of vein graft wall remodeling.;We used pig and human saphenous veins (SVs), as well as human umbilical endothelial cells (HUVECs), to investigate the changes of bone morphogenic protein-4 (BMP4) expression and its effects on endothelium-dependent relaxations (EDRs) under hyperglycemic conditions. Our results demonstrated a marked increase of BMP4 expression in SVs from diabetic patients and in HUVECs cultured with hyperglycemic medium. Moreover, such an increase of BMP4 contributes significantly to the impaired EDRs in venous conduits. Our findings add novel evidence that helps explain the high prevalence of VGF in diabetic patients undergoing CABG, and also suggest BMP4 as a potential therapeutic target to improve vein graft patency in this population.;Novel Therapeutic Strategy -- Gene Therapy: Aiming at blocking the development of neointima formation caused by vascular smooth muscle cells migration and proliferation, genetic transfection of tissue inhibitor of metalloproteinases-3 (TIMP-3) to vein grafts has shown promising results. Based on our previous study, we used recombinant adenoviruses that carry TIMP-3 (RAdTIMP-3) as a therapeutic gene to evaluate its long-term (3 months) effects on the pathological vein graft wall thickening in vivo. We found that the RAdTIMP-3-treated vein grafts had significantly reduced intimal and medial thickness compared with grafts from the control groups at 3 months, even after adenoviruses had already been cleared from transduced tissue. Furthermore, by assessing the amount of macrophages and the level of three inflammatory biomarkers within grafts harvested at 7 days and 3 months after implantation, we did not observe any detrimental effects of adenoviral transfection on the inflammatory status within the vein grafts. We therefore concluded that overexpression of TIMP-3 could effectively inhibit vein graft wall over-thickening in the longer-term. Our findings suggested the ex vivo RAdTIMP-3 gene therapy an attractive candidate for future clinical translation.