Glutaraldehyde-Fixed Bioprosthetic Heart Valve Conduits Calcify and Fail From Xenograft Rejection

Abstract

Background— Glutaraldehyde fixation (G-F) decreases but likely does not eliminate the antigenicity of bioprosthetic heart valves. Rejection (with secondary dystrophic calcification) may be why G-F xenograft valves fail, especially in young patients, who are more immunocompetent than the elderly. Therefore, we sought to determine whether rejection of G-F xenograft occurs and to correlate this with graft calcification. Methods and Results— Ascending aortas/valves (from rats [syngeneic] or guinea pigs [xenogeneic]) were transplanted (fresh or after 48 hour of G-F) into the infrarenal aortas of young rat recipients for 20 days. A xenogeneic group was also treated with steroids until graft harvest. The valves and media/adventitia were scored blindly for inflammation (0 to 4). Percent graft infiltration by T cells/macrophages was determined (immunohistochemistry), and rat IgG ELISAs were performed. There was >3 times more valve inflammation, >10 times more valve T-cell/macrophage infiltrate, and >3 times antibody rise in the G-F xenogeneic groups compared with the fresh syngeneic or the G-F syngeneic groups ( P <0.05). There was >2 times more adventitial inflammation and T-cell/macrophage infiltrate in the xenogeneic groups ( P <0.05). Steroid treatment decreased inflammation and antibody rise in the xenogeneic groups ( P <0.05). Correlation analysis revealed media/adventitia inflammation ( P =0.02) and percent macrophage ( P =0.01) infiltration to be predictors of calcification. Conclusions— G-F xenografts have cellular/humoral rejection and calcify secondarily.

Immunoproteomic identification of bovine pericardium xenoantigens

“…Abundant evidence demonstrates that both glutaraldehyde-fixed and unfixed BP xenografts elicit an immune response [1][2][3][4][5][6][7][8][27][28][29][30][31]. However, little is known about the nature and identity of BP proteins eliciting the immune response.…”

“…It is now clear that both humoral and cell-mediated immune responses to glutaraldehyde-fixed xenografts occur [1][2][3][4][5][6][7]. Mounting evidence implicates chronic antibody formation and immune rejection in bioprosthetic heart valve degeneration and calcification [2,3,6,7].…”

Prosthetic Heart Valves

“…73 Hence, residual animal antigens could elicit humoral and cellular immune responses, leading to tissue mineralization and/or disruption. A more robust immune system might also explain the more rapid SVD usually observed in younger patients.…”

Bioprosthetic Valves and Laudable Inflammation?

“…I n this issue of Circulation, Dr Manji and colleagues 1 from the University of Alberta (Canada) report a series of animal experiments designed to test the mythic role of gluteraldehyde in preventing recognition of bioprosthetic heart valve antigenicity with subsequent rejection and failure. Gluteraldehyde-cross-linked xenograft tissues (initially porcine) have been used in the manufacturing of stented (and now stentless) heart valves since 1970.…”

“…This well-designed series of studies buttresses other studies demonstrating that gluteraldehyde fixation does not eliminate antigenicity of bioprosthetic heart valves and that one of the primary causes of fibrocalcific failure is immune rejection. 4 -6 Important implications are in 4 areas: (1) proper assessment of durability and clinical performance of manufactured valve xenograft bioprostheses; (2) recognition of inflammation-driven calcification potential of all types of biological valves, including allografts (homografts), autografts, and new treatments of xenograft tissues designed to make available donor structural proteins for turnover (eg, decellularized xenograft valves); (3) choice of appropriate preclinical surgical implant test species to qualify biological tissues for implantation in humans; and (4) thorough failure modes and effects analysis driving regulatory end points and clinical qualification of new valve options, including new treatments of cross-linked xenograft valves, decellularized allograft/xenograft valves, and "tissueengineered" in vivo recellularized or bioreactor cell-seeded valves based on allograft or xenograft scaffolds.…”