The effects of Bilirubin and Bilirubin-di-taurate on ischemia reperfusion injruy in a rat model of kidney transplantation

Background: Heme oxygenase-1 (HO-1) is the rate-limiting enzyme in
the conversion of heme into biliverdin, carbon monoxide (CO) and
free iron. Biliverdin is then subsequently reduced to bilirubin by
the enzyme bilverdin reductase. In the past decades a lot of effort
was conducted to investigate the beneficial effects of HO-1 and its
end products biliverdin/bilirubin and CO. Due to intensive
research, solid organ transplantation can nowadays be seen as
clinical routine. However ischemia reperfusion injury (IR), acute
rejection episodes and the occurrence of chronic rejection remain
main problems. The severity of IRI can be seen as a prognostic
factor for early graft function, immunogenecity of grafts as well
as for long term graft survival. The goal of our experiments was to
investigate the potential beneficial effects of bilirubin and
biliverdin on ischemia reperfusion in a kidney transplantation
model of the rat. Methods: Two different sets of experiments were
performed: First, kidneys of Lewis rats were exposed to 60 minutes
of warm ischemia by clamping the renal artery followed by a 24h
reperfusion period. This model was used to find the optimal dosing
regimen of bilirubin/biliverdin before the more clinical relevant
model of kidney transplantation in the rat was performed. We found
that three doses of 10mg/Kg bilirubin were the most effective dose
regimen to protect kidneys from ischemia reperfusion injury. In the
second set of experiments, kidney transplantation was performed in
Lewis rats. Kidneys were harvested and stored in 4C cold
UW-solution for 18h. Subsequently the kidneys were transplanted
isotopically into the recipient rat. Time of warm ischemia was kept
in all experiments constantly at 60 minutes. After 24h of
reperfusion tissue samples and serum were harvested for further
analyses. Results: Systemic treatment of bilirubin led to a
significant amelioration of organ function after ischemia
reperfusion injury as assessed by measuring serum creatinine levels
and BUN levels after 24h of reperfusion. In addition treated
animals showed increased eGFR and a better cell integrity as
histomorphological analyses could demonstrate. Conclusion: Systemic
treatment with bilirubin and bilverdin has beneficial effects on
graft function after ischemia rerperfusion injury.