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Distribution And Quantification Of The Xenogeneic Alpha-gal Epitope In Commercially Bioprosthetic Heart Valves
Filippo Naso1, Michele Spina2, Laura Iop1,
Gino Gerosa1.
1University Hospital of Padova, Padova, Italy, 2University of Padova, Padova, Italy.

OBJECTIVE: For more than 30 years, glutaraldehyde (GLU) fixation has been considered as the standard chemical process able to ensure tissue biocompatibility, increased mechanical strength, sterilization, and safe storage of clinical bioprosthetic heart valves (BHVs). Nevertheless, the interplay of multiple factors leads to the replacement of GLU-treated BHVs after 8 to 10 years following the original implant. Important issue related to BHVs' degeneration takes into account the efficiency of the GLU in ensuring biocompatibility of the treated xenogeneic tissue. BHVs express different epitopes proper of the species (bovine, porcine or equine), whose elimination or inactivation is mandatory to meet the requirements for a requisite improvement in clinical application. Unfortunately, GLU fixation procedure is not able to provide their complete masking, particularly the residual presence of alpha-Gal xenoantigen significantly increases the human anti-galactose titers, starting from day 10 following bioprosthetic heart valve (BHV) implantation and reaching a peak at around 3 months for IgM and IgG isotype, respectively.
METHODS: Seven different models of BHVs were tested. The number of epitopes was determined with reference to a standard alpha-Gal source by an ELISA test. The presence of xenoantigen was subsequently confirmed by immunofluorescence analysis.
RESULTS: Epic™ valve was the only model among those tested, in which the alpha-Gal antigen appeared to be completely shielded. Composite Trifecta™ valve exhibited conflicting results: cusps of bovine pericardial tissue were devoid of reactive alpha-Gal epitopes, while the stent cover strip of porcine pericardium still maintained 30% of active antigens originally present in native tissue. All other tested BHVs express an alpha-Gal amount not significantly different from that exhibited by porcine Mosaic valve (5.2 ± 0.6*10e10 each 10 mg of tissue).
CONCLUSIONS: For the first time, the quantitative evaluation of the alpha-Gal epitope in heart valve bioprostheses, already in clinical practice for about 40 yrs, was finally determined. Such quantification might provide indications of biocompatibility relevant for the selection of bioprosthetic devices and an increase in the confidence of the patient. It might become a major quality control tool in the production and redirection of future investigation in the quest for alpha- Gal-free long-lasting substitutes.

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