FK506, Denudation of Donor Endothelial Cells and Bafilomycin A_1, a Selective Inhibitor of Vacuolar H^+-ATPase, Inhibit Neointimal Hyperplasia in Rat Cryopreserved Aortic Allograft

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Cryopreserved allografts have been utilized as alternatives for autografts. However, quality of allografts has been compromised by neointimal hyperplasia (NH). Although allo-immune response and cryopreservation procedures have been implicated in the mechanism of cryopreserved allograftpathy, the exact nature of this pathophysiology remains unknown. We have, therefore, investigated the possible involvement of allo-immune response and V-ATPase in NH in rat cryopreserved aortic allografts.Cryopreserved thoracic aorta from donor rats were implanted to the infra-renal abdominal aorta of recipient rats. The grafts removed 14 days after surgery were evaluated for all-immune response by counting the number of lymphocytes with positive immunostainung for CD8^+(×10^4/mm^2), and for NH by calculating the area ratio of intima to media.Allo-immune response in untreated allografts and allografts treated with Bafilomycin A_1 (BA_1) were significantly higher than untreated isografts, allografts treated with FK506 and allografts of which endothelial cell (ETs) were denuded (p<0.05). Untreated isografts and allografts of which ETs were denuded before transplantation and treated with FK506 and with BA_1 showed significant inhibition of NH compared to untreated allografts (p<0.05). Neointimal cells showed positive immunostaining for vimentin, but negative for HF-35 and CGA-7, indicating that these cells were dedifferentiated SMCs.FK506, denudation of donor ETs and BA_1 inhibit NH early after transplantation of rat cryopreserved aortic allografts. The mechanism of inhibition of NH induced by inhibition of allo-immune response may involve immunosuppression whereas that exerted by BA_1 may be mediated through direct growth suppression of dedifferentiated SMCs via inhibition of V-ATPase.