Reduced Complement and Granulocyte Activation by α-Gal Knockout Porcine Pericardium for Bioprosthetic Heart Valves: A Pilot Hemocompatibility Study

Abstract

Xenogeneic pericardium is the main source for biological aortic valve prostheses. Immune responses to α-Gal epitopes and free aldehyde groups after glutaraldehyde (GA) fixation are responsible for the graft deterioration and the need for reoperation. Genetically modified α-Gal-depleted porcine pericardium is evaluated in this pilot study as an alternative to avoid immunologic interactions and prevent degeneration. The absence of α-Gal epitopes was confirmed by both anti-α-Gal and IB4 isolectin staining in α-Gal-KO pericardia. Elastic Moduli, collagen and elastin composition, and in vitro calcification susceptibility were similar irrespective of the pericardium donor genotype. For testing the response of an α-Gal-negative recipient organism, incubation assays with human whole blood were performed. Native α-Gal-KO pericardium induced a lower inflammatory blood response than tissue without modification, regarding complement granulocyte activation. GA fixation enhanced the inflammatory response for both tissue types, but the lower granulocyte activation persisted for the α-Gal-KO tissue. Thrombogenicity, regarding coagulation cascade and platelet activation, was not affected by the genetic modification. Native tissues induced high activation of the coagulation cascade, attributed to tissue factor activity, which was abrogated by the GA fixation. Cell and fibrin deposits on the pericardia corroborated the blood phase observations. It is concluded that the distinct lower inflammatory potential of the α-Gal-KO pericardium makes it an attractive tissue for artificial heart valves; however, it requires a preparation method with sufficient inactivation of procoagulant tissue factor activity without providing an inflammatory stimulus. Prospectively, the removal of additional xeno-epitopes like Neu5Gc can be considered to reduce the inflammatory potential further.