Advanced Glycation End Products And The Pathophysiology Of Bioprosthetic Heart Valve Structural Degeneration

Introduction: Bioprosthetic heart valves (BHV) are widely used to treat severe heart valve disease. BHV function deteriorates after 10-15 years due to structural degeneration (SVD) often involving calcification. SVD occurs regardless of biomaterial, requiring prosthesis replacement. Advanced glycation end products (AGEs) are post-translational, non-enzymatic protein modifications associated with diabetic complications and cardiovascular disease. Serum proteins, such as albumin, are also AGE modified. Hypothesis: AGEs, exacerbated by serum protein infiltration, play a role in SVD. Methods: Clinical BHV explants (n = 45) of glutaraldehyde-crosslinked bovine pericardium (BP, n = 35) or porcine aortic valve (PAV, n = 10) and equivalent unimplanted BHV were probed by immunostaining per semi-quantitative scoring (range 0-4) for generalized AGE, N-carboxymethyllysine (CML, an AGE-receptor ligand), and human serum albumin (HSA), the most abundant serum protein. Demographics comprise ages 34 to 86 (mean: 64.95), 28 males and 17 females, 8 diabetics, and 15 previous and concomitant coronary artery bypass patients (both conditions associated with SVD). BHV calcification was quantified by atomic absorption spectroscopy. BHV glycation was modeled by exposing BP to 50mM glyoxal +/- 5% albumin for 24hr, followed by either immunostaining for CML and albumin or 14 C glyoxal scintillation. Albumin incorporation was verified by mass uptake. Results: All explants showed positive immunostaining for AGE (mean ± SE = 3.52 ± 0.10); most showed HSA (2.30 ± 0.18) and less intense CML (1.55 ± 0.16) staining; unimplanted BHV staining was negative. Score comparisons showed no significant differences for BP vs PAV, coronary bypass or diabetic patients vs all patients. BHV Ca levels (122.01 ± 18.01ug/mg, binned as <30 vs >100ug/mL) did not correlate with AGE immunostaining. In vitro, glyoxal-generated CML and infiltrated albumin were evident throughout BP per immunostaining. 14 C glyoxal uptake by BP was 12.01 ± 0.50nmol/mg after 28 days and was increased 57.2 ± 7.5% by albumin co-incubation. Albumin co-incubation increased BP mass by 4.10 ± 0.19%. Conclusions: AGEs are associated with SVD regardless of BHV type and SVD risk factors. Albumin exacerbates AGE accumulation.