Kyriakopoulou, K; (2016) Quantitative analysis of α-Gal trisaccharide content and its contribution to degeneration of bioprosthetic heart valves. Doctoral thesis , UCL (University College London).

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Abstract

Background: Commercial bioprosthetic heart valves (BHVs) are generally produced from porcine aortic heart valves or sewn from bovine pericardium. BHVs are durable in older patients, but in younger patients they are subject to age-dependent structural valve degeneration (SVD). SVD involves tissue calcification, which our research suggests is due in part to an immune mediated BHV injury caused by high levels of xenogeneic antigen galactose-alpha-1,3-galactose (α-Gal) on commercial valves and anti-Gal antibody universally present in patients. This suggests that α-Gal-free BHVs, unaffected by anti-Gal antibody could resist calcification and show improved durability in younger patients. Aim: This research was to develop quantitative methods to measure α-Gal antigen on animal tissue and further characterize the role of α-Gal-specific immune injury in tissue calcification. Methodology: I tested an α-galactosidase based colorimetric enzymatic assay for detecting galactose liberated from tissue and an α-Gal-specific inhibition ELISA (GIE) to measure α-Gal on fixed porcine pericardium. The α-Gal levels on wild type (WT), and α-Gal-free (GTKO) porcine tissue after glutaraldehyde fixation and after treating with various anticalcification processes were measured. The effects of anti-Gal antibody on WT and GTKO tissue calcification were measured using subcutaneous implants in anti-Gal antibody producing GTKO mice. Results: The α-galactosidase based colorimetric assay showed low sensitivity and was not pursued. The GIE, using two different anti-Gal reagents, was sensitive and reliable. A-Gal antigen levels, measured by GIE were not reduced by anticalcification processing. Minimal tissue calcification was observed in GTKO mice for both WT and GTKO tissue. There was no clear anti-Gal immune response to WT implants. Conclusion: This research shows that the current BHVs remain susceptible to immune injury as α-Gal antigen is not eliminated by the current anticalcification treatments. In addition caution is required when choosing the appropriate animal model to address the immune response factor in tissue calcification studies.

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