Protective Effect Of Pretreated Rapamycin On Renal Ischemia-Reperfusion Injury In Rats

Backgroud: Renal ischemia-reperfusion injury leads to acute failure in both native kidneys and renal allografts. The calcineurin inhibitors have been the mainstays of immunosuppression in solid organ transplantation over the last two decades, but their therapeutic benefits are limited due to nephrotoxicity. It has also been shown that the calcineurin inhibitors therapy subsequent to renal ischemia-reperfusion injury may further exacerbate renal dysfunction. Rapamycin, a mTOR pathway inhibitor, has received increasing attention as a new immunosuppressant with a unique mechanism of action distinct from that of the calcineurin inhibitors. However, some evidence suggests that rapamycin may impair renal recovery from ischemia-reperfusion injury in rat models and delay graft function after clinical renal transplantation, but this has yet to be confirmed. The mechanism of rapamycin action is still not well understood. In this present study, the effect of rapamycin at low and high concentrations was investigated after ischemia-reperfusion injury in rat kidneys.Methods: Right nephrectomy was performed on the male Sprague-Dawley rats(200～220g) and left renal ischemia was induced by clamping left renal pedicle for 45 minutes. After the clamp was released, reperfusion was confirmed visually. The rats were subjected to renal ischemia-reperfusion injury or sham operation. They were pretreated with either vehicle or rapamycin(1mg/kg/d, 3mg/kg/d or 5mg/kg/d) by oral gavage, starting 3 days before the ischemia-reperfusion injury and continued daily till sacrifice. The rats were scarificed at 24h and 72h after the reperfusion. Blood sample and left kidney tissue were collected. The severity of the renal ischemia-reperfusion injury was assessed by serum creatinine levels and renal histology. Apoptosis of tubular epithelium was observed by TUNEL assay.Results: In sham operation group, no significant difference was observed in serum creatinine level, renal histological damage and number of TUNEL-positive cells between the rapamycin-pretreated rats and vehicle-pretreated rats. At 24 hours after renal ischemia-reperfusion injury, the serum creatinine level of rapamycin 5mg/kg/d was significantly lower than that of vehicle. Kidney sections from rapamycin 5mg/kg/d showed less histological damage and significantly lower number of TUNEL-positive cells than those of vehicle. Rapamycin 3mg/kg/d also reduced the histological damage of the kidneys, but rapamycin 1mg/kg/d didn't show the protective effect. There was no significant difference in either serum creatinine level or number of TUNEL-positive cells among rapamycin 3mg/kg/d, rapamycin 1mg/kg/d and vehicle. At 72 hours after renal ischemia-reperfusion injury, there was no significant difference in serum creatinine level, histological damage and number of TUNEL-positive cells among all the groups.Conclusion: This study indicated that in renal ischemia-reperfusion injury in rats, rapamycin can attenuate renal ischemia-reperfusion injury in a dose-dependent manner. This protective effect might be mediated by its inhibition of tubular epithelium apoptosis and thereby reducing the histological damage. We also showed that rapamycin did not impair the recovery of renal function after 72 hours of ischemia-reperfusion injury.