Initial validation of Gal knockout pig tissues as materials for biological heart valves

Abstract

Introduction: All current biological heart valves (BHVs) have the Gal antigen and are subject to age-dependent structural valve degeneration characterized by tissue calcification. We have shown that human anti-Gal antibody, present in all patients, enhances calcification of fixed bioprosthetic tissue suggesting that valves made from Gal knockout pigs (GTKO), would eliminate anti-Gal antibody induced calcification and thereby improve BHV durability. Demonstration of physical and biological equivalence of GTKO with standard pig tissue, is necessary to show that the GTKO mutation has not affected structural integrity of GTKO tissues. Methods: Biochemical and biophysical testing compared standard and GTKO pig pericardium. Using a new surgical BHV as a vehicle, made from GTKO and standard porcine pericardial leaflets, we compared the hydrodynamic performance of valves made from each tissue type. Hydrodynamic performance was measured for three valve sizes (21, 25 and 29 mm) at cardiac outputs of 2–7 L/min in a commercial pulse duplicator (ViVitro Labs, Inc., Victoria, BC, Canada). This analysis conforms to the International Organization for Standardization (ISO) 5840 standards governing cardiac valve prostheses. We used accelerated wear testing to measure valve durability and subsequently implanted valves in juvenile sheep to explore their in vivo function. Results: Biochemical analysis showed similar detergent soluble and insoluble protein profiles and equal hydroxyproline content in both standard and GTKO pig pericardium. Uniaxial stress and suture retention testing showed equivalence between the tissue types (2). Valves made from standard or GTKO pericardium had excellent hydrodynamic properties, which met or exceeded the ISO5840 minimum performance requirements of an effective orifice area ≥1.45 cm2 and a regurgitant fraction ≤15% for a 25 mm valve. Proof-in-principle and ongoing durability testing indicates our novel GTKO surgical valve is durable and can achieve 200 million cycles (the ISO5840 durability requirement simulating over 6 years of function) in an accelerated wear test (3). Using the industry standard mitral valve replacement in juvenile sheep we compared early biological equivalence of our GTKO BHV. Valve function, measured by echocardiology on implantation and at explant, was excellent. Conclusions: Our analysis indicates that standard and GTKO pig pericardium have physical and biological equivalence indicating that the GTKO mutation, which eliminates the Gal antigen, has not significantly impacted the structural integrity of GTKO porcine pericardium. Our new GTKO pericardial BHV, in early studies, shows excellent hydrodynamic performance and acceptable durability which meets or exceeds the ISO5840 guidelines. These results indicate that GTKO pericardium can be used to produce a durable surgical BHV or substituted for standard pig pericardium in current transcatheter devices.