Calcification of decellularized and alpha-galactosidase-treated bovine pericardial tissue in an alpha-Gal knock-out mouse implantation model: comparison with primate pericardial tissue.

Abstract

Immune reaction against the α-Gal(Galα1,3-Galβ1-4GlcNAc-R) epitope is known to be one of the important factors for calcification of bioprostheses. The genetically manipulated α-Gal knock-out (KO) mice lacking the α-Gal epitope and containing anti-α-Gal antibodies may simulate an immune response against xenoantigens in primates including humans. The aims of this study were (i) to compare calcification and immune reactions of glutaraldehyde (GA)-fixed bovine with primate pericardium and (ii) to assess the differences in bovine pericardium treated with decellularization and α-galactosidase, using an α-Gal KO mouse implantation model. Four types of GA-fixed xenogeneic tissues were implanted into α-Gal KO mice for 16 weeks (Group 1: primate pericardium, n = 14; Group 2: bovine pericardium, n = 19; Group 3: decellularized bovine pericardium, n = 20; Group 4: decellularized and α-galactosidase-treated bovine pericardium, n = 21). Serum enzyme-linked immunosorbent assays for immune response were performed before implantation and 2, 4, 8, 12 and 16 weeks after implantation. Implanted tissues were harvested and studied for histopathology and quantification of calcification. Anti-α-Gal IgG antibody titres of Groups 2-4 increased after implantation although the titres did not change in Group 1. When compared with preimplantation titres, the increased IgG titres were highest at 8 weeks after implantation in Groups 2-4 (0.4358 ± 0.0524 vs 0.5462 ± 0.0519 in Group 2, 0.4712 ± 0.0500 vs 0.6424 ± 0.0613 in Group 3 and 0.4892 ± 0.0801 vs 0.6112 ± 0.0339 in Group 4; P = 0.028 in each group). Median calcium levels were higher in Group 2 than in Group 1 (9.21 vs 3.86 μg/mg, P < 0.001), but were not significantly higher in Groups 3 and 4 than in Group 1 (4.09 μg/mg in Group 3, P = 0.904; 5.47 μg/mg in Group 4, P = 0.210). GA-fixed bovine pericardium showed higher calcium levels than primate pericardium. Increased IgG antibody titres in the bovine but not in the primate group suggested that an immune response was involved in implanted tissue. Differences in calcium levels of bovine pericardium treated with decellularization and α-galactosidase were insignificant compared with primate pericardium, suggesting those treatments to be effective methods in preventing calcification of the bioprostheses.