Postconditioning Attenuates Kidney Ischemia Reperfusion Injury Via P38 Mitogen-activited Protein Kinase And C-Jun N-terminal Protein Kinase In Rats

Ischemic postconditioning is a new pattern against ischemia reperfusion injury of target organs, which is defined as a series of brief interruptions between prereperfusions applied before whole regain of reperfusion. Some studies have confirmed that ischemic postconditioning has protective effect on target organs including heart, liver and brain. Our teams established rat model of ischemic postconditioning and improved it, then we found similar protective effect in rat kidney. Moreover, we researched protective effect and molecular mechanism of kidney ischemic postconditioning based on the rat model of ischemic postcon- ditioning.Objective To investigate ischemic postconditioning affects expressions of c-Jun N-terminal protein kinase and p38 mitogen- activited protein kinase in rats with kidney ischemia reperfusion injury(IRI).Methods 72 SD rats were randomized into 3 groups:sham operation(S) group, ischemic reperfusion(IR) group and ischemic postconditioning(IPO) group. Each group had 8 periods of time. In S group, left renal artery was separated and right renal pedicle was ligatured by line for exposing 45 min. In IR group, left renal artery was induced by clamping for 45 min and right renal pedicle was ligated. IPO group was sequential 20 sec reperfusion and another 20 sec ischemia for a 10 cycles after 45 min kidney ischemia. After operation, the blood samples were draw from the inferior vena cava and the nephridial tissues were fixed at each time stage. Then renal function by biochemistry analysator and urine NAG enzyme was detected by biochemical methods, and the expression of p38MAPK and JNK were studied by immunohistochemistry and westen blot in rat kidney tissues.Results1. Compared with the S group, the levels of blood urea nitrogen and the serum creatinine were increased significantly (P<0.05) in the IR group, which lightly increased at 1h stage and 24h stage was the most increasing [BUN(30.97±9.96) mmol/L, SCr (238.3±54.2)μmol/L (P <0.05)], then which was felled baseline level at 48h and unchanged until 72h. In the IPO group, blood urea nitrogen level and serum creatinine level were not significantly changed compared to the S group (P >0.05). Compared with the IR group, the levels of blood urea nitrogen and the serum creatinine were decreased significantly (P<0.05) in the IPO group, which peak appeared at 12h [BUN(15.8±0.9)mmol/L, SCr (44.7±3.5)μmol/L(P <0.05)], but 24h stage was the most decreasing [BUN(8.0±0.6)mmol/L, SCr(44.0±4.6)μmol/L (P <0.05)].2. Urine NAG enzyme of IR group and IPO group was higher than S group, which reached peak time at 6h [(98.47±2.69)U/L(P<0.05)] in the IR group. Then the NAG enzyme falled and went back to baseline at 48h. In the IPO group, which peak time appeared at 3h, but which droped obviously at 6h [(40.51± 1.44)U/L(P<0.05)] compared with the IR group and constanted to 24h.3. Under electron microscope, p38MAPK和JNK expressed in epithelial cell of proximal tubular and distal convoluted tubule, especially in proximal tubular epithelial cell. Compared with the S group, the expression of p38MAPK and JNK in the IR group started at 0.5h and arrived peak time at 1h [p38MAPK(96.6±3.7)%,JNK(89.8±6.1)% (P<0.05) ], which fallde at 3h and went back to baseline at 6h. Followed the reperfusion going, the expression of p38MAPK and JNK began to express greatly again and reached peak time at 24h, which went back at 48h and unchanged until 72h. In the IPO group, p38MAPK and JNK expressed significantly decreased compared to IR group, especially at 1h and 24h, which respectively were [p38MAPK(49.8±22.5)%,JNK(28.4±5.3)% (P<0.05) ] and [p38MAPK(44.4±19.5)%, JNK(50.4±10.2)% (P<0.05) ].The Western blot results showed that the expression intensity of p38MAPK and JNK in the IR group and the IPO group was higher than the S group. In the IR group, the expression of p38MAPK and JNK started at 0.5h, which expressed significantly at 1h [p38MAPK(1.03±0.08), JNK(0.68±0.03) (P<0.05) ] and 24h [p38MAPK(0.68±0.06), JNK(0.77±0.06) (P<0.05) ]. In the IPO group, p38MAPK and JNK expressed lower than the IR group, especially at 1h and 24h, which respectively were [p38MAPK(0.78±0.07), JNK(0.50±0.03) (P<0.05) ] and [p38MAPK(0.44±0.09), JNK(0.52±0.06) (P<0.05) ].Conclusion Postconditioning attenuates acute kidney ischemic reperfusion injury via p38MAPK and JNK pathway.