Inhibition of adenosine deaminase and nucleoside transport. Utility in a model of homograft cardiac valve preimplantation processing.

Human cardiac valves are increasingly used in the reconstruction of ventricular outflow tracts and offer performance advantages over porcine and mechanical prostheses; the durability of these replacements has been associated with leaflet interstitial cell viability and a presumed sustained function after implantation. Preimplantation tissue preparation entails sequential steps that are potentially cytotoxic and may therefore affect functional cell survival at thaw. We defined the metabolic consequences of each interval using semilunar cusps from 118 porcine valves to model a homograft preparation with 40 minutes of fixed cadaveric (harvest) ischemia. Fifty-eight valves served as controls and were first processed according to standard cryopreservation protocol; nucleosides were extracted at the end of each step to differentiate independent contributions to high-energy phosphate depletion. Sixty simultaneously harvested leaflets were administered the nucleoside transport inhibitor p-nitrobenzy-thionosine (NBMPR) and the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA) at procurement, to attempt adenosine salvage and restitution of processing-incurred adenine nucleotide losses. High-performance liquid chromatography was used to compare adenosine triphosphate, diphosphate, and monophosphate and diffusible nucleopurines of the control and EHNA/NBMPR-treated groups. Control results indicate that disruption of the adenosine triphosphate-diphosphate cycle occurs independently with antibiotic disinfection and cryopreservation. However, throughout all preparation steps, adenine nucleotides were maintained at harvest (baseline) concentrations in the EHNA/NBMPR valves. This suggests that salvage therapy may protect a significant number of cells from net high-energy phosphate catabolism. If, with further study, the durability of transplanted valves is concluded to benefit from retained leaflet interstitial cell viability, such enhancement of metabolic tolerance to the obligatory processing may facilitate functional recovery.