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Assessment of the efficacy of anti-fibrotic gene transfer as a means of suppressing neointima formation in venous-arterial interposition grafts.
[Thesis]. Manchester, UK: The University of Manchester; 2018.
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Abstract
Background Diseases of the heart and circulatory system are the main causes of deaths in the UK, and accounted for almost 180,000 deaths in 2010. Coronary artery bypass grafting remains one of the viable modalities of coronary revascularization. Autologous Saphenous vein (SVG) is the most frequently used conduit for coronary artery bypass grafting. Its long-term success is however limited by progressive luminal loss, resulting from neointimal hyperplasia (NIH) and superimposed atherosclerosis. Due to the lack of effective pharmacological therapies and lack of long term benefits from percutaneous vein interventions described in the literature, vein graft disease following coronary artery bypass graft, is a potential target for novel approaches like gene therapy. TGF-β1 is a key promoter of ECM deposition in the intima of the vessel by promoting phenotypic changes in the smooth muscle cells (SMC) of the media and stimulating ECM synthesis. Many preclinical studies have confirmed the role of TGF-β1 antagonists at inhibiting NIH in injured arteries but the same effect has not been studied in vein. The research group in the University of Manchester previously studied the effects of adenovirus-mediated delivery of anti-fibrotic transgenes like the Latency-associated peptide of TGF-β1 (LAP-β1) and of Fibromodulin in organ-cultured human long saphenous vein and the resulting suppression of neointimal hyperplasia ex-vivo. The next step was to demonstrate the same effect in-vivo where different factors like haemodynamic, rheological, inflammatory and immune responses may influence the effects seen already in organ-cultured human saphenous vein. The objective of this study was hence to develop a methodology for the saphenous vein interposition grafting in to internal carotid artery and harvesting of the same graft in pigs in Manchester. Under appropriate conditions, long saphenous vein obtained from the pigs were infected with the virus Ad5-lacZ, expressing the marker gene β-galactosidase. These prepared veins were anastomosed as interposition grafts to the internal carotid arteries. These segments of venous-arterial interposition grafts explanted later were stained with 5-bromo-4-chloro-indolyl-D-galactopyranoside for expression of β-galactosidase present in vein segments infected with Ad5-lacZ.We obtained consistent results at repetition of experiments. This confirmed the testing of an in vivo system, paving pathway for further experiments. LAP-β1 gene transfer offers potential therapeutic benefit in the vein graft failure by reduction in NIH. The results of this work will thus help to establish whether these antifibrotic gene therapies will be suitable for clinical application to neointimal suppression in vein grafts in-vivo.