363: Intraluminal Bone Marrow Cells Inhibit Allograft Fibrosis Via the Indoleamine Dioxygenase Pathway

Abstract

Purpose: Bilirubin is a final byproduct of the heme oxygenase system and is known to be a powerful antioxidant. In this study, we examined whether recipient hyperbilirubinemia would protect cardiac grafts from ischemia/reperfusion (I/R) injury and chronic rejection in a rat heart transplantation (HTx) model. Methods and Materials: Heterotopic HTx was performed using congenitally hyperbilirubinemic GUNN (j/j) and normobilirubinemic GUNN ( / ) rats. Serum bilirubin levels of j/j rats were 4.8 mg/dl, while / rats had bilirubin levels 0.1 mg/dl. To evaluate I/R injury, syngenic grafts from / were transplanted into / or j/j rats with 18 hrs cold storage in UW solution. To evaluate the effect on allograft rejection, fully allogenic BN heart grafts were transplanted into / or j/j rats under a short course of tacrolimus (0.5 mg/kg, d0-6). Results: The / grafts in j/j rats resulted in a significantly lower serum CPK level (5492 IU/L) with smaller infarct area determined by TTC stain, compared to those in / recipients 3 hrs after HTx (9617 IU/L). Graft function evaluated by Langendorf apparatus revealed higher left ventricular developed pressure than those in / at 3 hrs after HTx. Tissue MDA levels, a marker of lipid peroxidation, were significantly lower in j/j recipients (16.3 M/g) compared to those in / recipients (39.5 M/g). Graft survival in j/j recipients improved to 41.7% from 0% in / rats and was associated with reduction of the levels of inflammatory mediator mRNA (TNF and IL-6) and phosphorylation of ERK. The mean allograft survival in j/j recipients was prolonged to a median survival of 150 days from 84 days in / recipients. Prolongation of allograft survival was associated with less inflammatory infiltrates and decrease of intragraft inflammatory cytokine mRNA including IFN , TNF and IL-6 at d50. In vitro T cell proliferation was significantly inhibited in the presence of bilirubin. Conclusions: Recipient hyperbilirubinemia ameliorated cardiac I/R injury, as well as chronic allograft rejection following HTx via regulation of inflammatory responses or T cell proliferation.