Abstract 14677: Oxidative Damage in Failed Clinical Bioprosthetic Heart Valve Explants

Abstract

Introduction: Bioprosthetic heart valves (BHVs), fabricated from glutaraldehyde-fixed bovine pericardium or porcine aortic valves, have been widely used in valve replacement surgery. However, BHVs fail over time due to structural degeneration. Despite frequent observations of calcification-associated BHV failure, more than 25% of BHV structural failures occur without calcification. Previously, we reported that oxidative stress may have a pivotal role in noncalcific BHV failure. Moreover, oxidation-induced formation of dityrosine (DT) crosslinks via hydroxyl- and tyrosyl-radical mediated pathways was only detected in clinical BHV explants. Yet the mechanism of DT formation and its role in structural degeneration of clinical BHV is incompletely understood. Hypothesis: Oxidative damage to BHV is due to a specific spatial localization of DT crosslink formation mediated by myeloperoxidase (MPO) and/or iron (Fe) deposition in clinical BHV explants Method & Results: BHVs from 7 human subjects were collected and subjected to mass spectrometry to measure DT in paraffin sections of BHV. 4 different regions of each BHV leaflet (free edge, sewing cushion, commissure, and middle region) were sampled as well as entire cross-sections of each cusp. DT was only detected in the mid–cusp (137.37±49.96 μmol/mol) and was not significantly different from DT quantitated in the cross-sections (191.29±65.98 μmol/mol). DT was not detected in other regions, implying a specific spatial localization of oxidative stress in BHV. MPO, a neutrophil derived enzyme, is responsible for reactive oxygen species (ROS) generation. Immunofluoresence microscopy demonstrated significant presence of MPO in the BHV, implying that MPO may be responsible for the DT formation in BHV. Fe deposition due to intracuspal hematomas and/or Fe-association with calcific deposits can also be responsible for ROS and DT formation. Fe was shown to be present in histology sections in failed BHV by Prussian Blue staining, indicating that Fe deposits may also in part be responsible for the observed DT formation. Conclusion: These results demonstrated a mid-leaflet localization of DT formation in clinically failed BHV explants. This may in part be mediated by MPO and/or Fe-deposits in clinical BHV.