Recipient hyperbilirubinaemia protects cardiac graft in rat heterotopic heart transplantation

OBJECTIVES: Since bilirubin is a known powerful antioxidant, this study examined whether recipient hyperbilirubinaemia protected heart grafts from ischaemia/reperfusion (I/R) injury and chronic rejection associated with rat cardiac transplantation. METHODS: Heterotopic heart transplantation (HTx) was performed using congenitally hyperbilirubinaemic GUNN (j/j) and normobilirubinaemic GUNN (+/+) rats. Syngenic grafts from +/+ rats were transplanted into +/+ or j/j rats with 6 or 18 h cold storage in University of Wisconsin solution to study I/R injury. To evaluate the effect on chronic rejection, Brown Norway rat heart grafts were transplanted into +/+ or j/j rats under short-course tacrolimus immunosuppression. RESULTS: The +/+ grafts in j/j rats demonstrated significantly lower serum creatine phosphokinase and higher left ventricular developed pressures and had smaller infarct areas than +/+ rats at 3 h after reperfusion. Graft survival with 18 h cold storage increased from 0% in +/+ rats to 41.7% in j/j rats. Malondialdehyde (a marker of lipid peroxidation), mRNA of the inflammatory mediators and phosphorylation of ERK1/2 were significantly decreased in the grafts transplanted into j/j rats compared with those transplanted into +/+ rats 1-3 h after reperfusion. The mean allograft survival in j/j recipients was prolonged to a median survival of 150 days from 84 days in +/+ recipients and was associated with less macrophage infiltrates and less intragraft inflammatory cytokine mRNA at d60. In vitro T-cell proliferation was significantly inhibited in the presence of bilirubin. CONCLUSIONS: Recipient hyperbilirubinaemia ameliorated cardiac I/R injury, as well as chronic allograft rejection following HTx via regulation of inflammatory responses or T-cell proliferation.