Protective mechanisms of a metalloporphyrinic peroxynitrite decomposition catalyst, WW85, in rat cardiac transplants

Nitric oxide (NO) derived from inducible NO synthase has been implicated in cardiac rejection. However, little is known about the role of the reactive nitrogen species peroxynitrite. We examined the protective actions of a peroxynitrite decomposition catalyst, WW85, in an experimental model of acute cardiac rejection. Heterotopic, abdominal transplantation of rat donor hearts was performed. Groups included isografts, allografts, or allografts treated with WW85, cyclosporine, or cyclosporine + WW85. We determined graft survival, histological rejection, and graft function (by in situ sonomicrometry). Intragraft biochemical analysis of cytokines and proapoptotic and antiapoptotic gene expression using reverse transcriptase-polymerase chain reaction were determined. Treatment with WW85 or cyclosporine alone prolonged graft survival, improved graft function, and decreased histological rejection. Graft survival was further significantly (P < 0.001) enhanced by combination treatment. A decrease was also shown in nitrotyrosine, poly(ADP-ribose) polymerase (PARP) activation, and lipid peroxide formation by WW85 that was potentiated when given in combination with cyclosporine. Benefits could not be ascribed to changes in intragraft myeloperoxidase activity. Only combination therapy produced significant decreases in inflammatory cytokine gene expression, suggesting that WW85 acted primarily downstream of these stimuli. In general, WW85 had no direct action on expression of the proapoptotic gene, Fas ligand; however, WW85 given alone or with cyclosporine enhanced expression of antiapoptotic genes Bcl-2 and Bcl-xL. Collectively, these findings suggest a protective action of the peroxynitrite decomposition catalyst WW85 on graft rejection that is independent of any action on leukocyte sequestration and cytokine gene expression. Rather, effects seem to be downstream on decreased protein nitration, decreased lipid peroxidation, and decreased PARP activation.