AlphaGal Residue in Xenograft Heart Valve Bioprostheses and Tissue Engineered Construct

Abstract

AbstractThe glutaraldehyde (GA) fixed heart valve bioprostheses (HVB) fail in the long term due to dystrophic degeneration. To avoid GA treatment, xenogenic tissues have been processed by detergent-based decellularization procedures (DBDP). However a complete immunogeneic tolerance by the host is not granted. Degenerative inflammatory process seems to be triggered by the persistent presence of reactive xenogeneic residual, specifically by the alpha-Gal antigen. Through the use of an ELISA assay we assessed and quantified the content of such xenoantigen in different commercial bioprosthetic heart valves and compare to that present in the native and decellularized tissues used for their manufacture. Four models of pericardial and two of porcine HVBs were investigated for the alpha-Gal content. Untreated porcine aortic leaflets (UPAL) were assessed before and after 3 different detergent-based decellularization procedure: TRICOL (Triton X100 and Sodium Cholate), DOC (Sodium Deoxycholate) and DOC-SDS (Sodium Deoxycholate and Sodium Dodecyl Sulfate). Moreover the total amount of alpha-Gal epitopes in native bovine pericardium (NBP) was determined. All the specimens react with the M86 primary monoclonal antibody and the exposed alpha-Gal epitopes is determined by an indirect ELISA assay. For each sample, the amount of alpha-Gal was expressed as numbers of epitopes *10e11 each 10 mg of wet tissue. The amount of alpha-Gal xenoantigen in pericardial HVB (1.5 ± 0.18 *10e11, n=15) was three and half times less with respect to NBP (5.1 ± 0.21 *10e11, n=9). In a model of porcine HVB the xenoantigen was not detected, in the second one the absolute value (1.37 ± 0.25 *10e11, n=9) was similar to that of the pericardial HVB and half of UPAL (2.5 ± 0.31 *10e11, n=9). DOC and DOC-SDS treatments leave on the tissue the 40% (1.02 ± 0.1 *10e11) of the epitopes originally present in the native cusps. TRICOL has proven to be able to eliminate all the alpha-Gal antigen. HVBs GA-treatment do not prevent the binding of resident alpha-Gal antigens with M86 antibodies. The investigated HVBs exhibited a non negligible amount of reactive epitopes accounting to 29.3% of those exposed by native pericardial tissue and 55% for the porcine one. Probably, the pericardial simpler structure allow a better action of the GA, which is able to ensure a greater, but non complete epitope masking. In one model of porcine HVB the alpha-Gal was not found. Regarding the different DBDPs, the removal of cell components is not a sufficient condition to ensure the elimination of the alpha-Gal epitopes. Up to date the TRICOL seems to be the only method capable of producing an alpha-Gal tissue free.