Heart valve disease at this time can only be treated surgically, with either valve replacement or repair. Bioprosthetic heart valves (BHV), fabricated from glutaraldehyde fixed heterografts, such as bovine pericardium (BP) or porcine aortic valves (PAV), are widely used in both cardiac surgery and in transcatheter valve replacements. Despite outstanding short term outcomes, BHV dysfunction due to structural valve leaflet degeneration (SVD) develops over time, frequently necessitating device replacement. Calcification is observed in the majority of SVD cases; however, 25% or more SVD cases are not associated with calcification. Recent work from the applicants? laboratories utilizing the Penn Cardiac Valve Bioregistry demonstrated that BHV are susceptible to non-calcification induced failure mechanisms, involving the formation of unique oxidized amino acids (OxAA) in BHV, such as the crosslink, di-tyrosine (di-Tyr). Feasibility studies also recently documented in BHV explant samples the presence of advanced glycation end products (AGE). The contributions of both AGE and OxAA to SVD pathophysiology has not been previously investigated by our group or others. Hypotheses: The accumulation of AGE in BHV leaflets together with the receptor for AGE (RAGE) mediated inflammatory response, and OxAA modification of structural proteins contribute to BHV SVD. These mechanisms also are hypothesized to interact with BHV calcification and co-morbidities, such as diabetes and coronary artery disease to enhance SVD. To test these hypotheses, we will pursue the following specific aims:
Aim 1 : To investigate the primary role of AGE in BHV dysfunction. Working hypothesis?AGE/RAGE signaling, related inflammation and AGE-induced crosslinking contribute to SVD pathophysiology Subaim 1a: These investigations will utilize the Columbia-U.Penn-U.Ottawa Bioregistry to completely characterize the impact of AGE/RAGE mechanisms on the clinical pathophysiology of SVD.
Sub aim 1 b: To study RAGE/AGE formation and material-biomechanical effects using in vitro model systems Aim 2: Investigate AGE/RAGE mechanisms and the monocyte derived macrophage (MDM) response to BHV, calcification and OxAA. Working hypothesis?AGE/RAGE mediated mechanisms affect both OxAA and calcification in SVD.
Sub aim 2 a: In vitro MDM studies of AGE modified BHV leaflets. These studies will also investigate the effects on MDM of: 1) an inhibitor of AGE formation, 2) a RAGE antagonist, and 3) an AGE breaker.
Sub aim 2 b: In vivo model studies of calcification, OxAA and AGE. Rat subdermal BHV implants will also investigate the compounds used in Subaim2a for their effects in vivo on AGE, OxAA and calcification. The long term objective of these studies is to provide novel insights about the role of AGE and OxAA formation in SVD of BHV. The mechanistic advances from our program will provide critical directions for research to improve BHV durability and outcomes in surgical and transcatheter heart valve replacement.
Oxidation-mediated structural degeneration of bioprosthetic heart valves Bioprosthetic heart valves (BHV), fabricated from glutaraldehyde pretreated heterografts (bovine pericardium or porcine aortic valves) are used worldwide in cardiac surgery and transcatheter interventions for heart valve disease; however, these devices increasingly fail over time due to structural degeneration. We will investigate the hypothesis that BHV are susceptible to oxidative modifications that cause structural degeneration, contributing to their clinical failure. We will study oxidized amino acids (OxAA); advanced glycation end products (AGE), including carboxymethyl-lysine (CML) a ligand for the receptor for AGE (RAGE) and glucosepane, an AGE crosslink contributions to BHV structural failure. 1