Protective mechanism of ischemic preconditioning on apoptosis induced by kidney ischemia-reperfusion

Objective To investigate the protective effect of ischemia preconditioning(IPC) on apoptosis induced by renal ischemia-reperfusion(IR) and relations to the changing expressions of Bcl-2, Bax in rat kidney. Methods Ischemia models were induced by clipping bilateral renal pedicles for 30 min by using the artery clamp; IPC group was induced by clipping bilateral renal pedicles for 15 min, 4 days later IR was performed again by clipping bila-teral renal pedicle for 30 min.Rats were randomly divided into 5 groups with 5 animals in each group: control group(C group), sham-operation group(S group), IR group, IPC group(IPC+ IR group), sham IPC group(S+ IR group), all groups were randomly divided into 9 sub groups (0 h, 3 h, 6 h, 12 h, 24 h, 48 h, 3 d, 5 d, 7 d) except C group according to the time points after reperfusion.Occurrence of apoptosis was detected by terminal deoxynuleotidyl transferase mediated dUTP nick end and labeling(TUNEL)method; the mRNA expression and protein levels of Bax and Bcl-2 were detected by reverse transcriptase-polymerase chain reaction and quantitave immunohistochemisty. Results (1)Compared with S group and S+ IR group, serum creatinine, blood urea nitrogen, kidney pathological damage scores in IR group gradually increased after IR, and peak point was 24 h after reperfusion; among all the subgroups there was a significant difference (all P<0.01). The expression of Bax, Bcl-2 mRNA raised sharply in IR group after reperfusion, peaking at 6 h, 24 h of reperfusion respectively, 2.66±0.12, 2.70±0.10, and among all the subgroups there was a significant difference (all P<0.01); the expression of Bax, Bcl-2 protein had significant difference (all P<0.05). TUNEL immunofluorescence staining showed C group and S group had no obvious apoptosis cells in renal tubular epithelium; epithelial cell apoptosis after IR gradually increased in IR group, peaking at 24 h of reperfusion[(25.07±2.29)%]. (2)Compared with IR group and S+ IR group, pathological injury was significantly decreased in IPC+ IR group; the expression of Bax, Bcl-2 mRNA and protein, apoptosis cells were significantly decreased in IPC+ IR group (all P<0.05). Conclusions Bax, Bcl-2 are closely associated with kidney injury induced by IR.IPC may regulate acute kidney injuries by regulating Bax/Bcl-2. Key words: Ischemia-reperfusion injury; Acute kidney injury; Ischemic preconditioning; Bax; Bcl-2; Apoptosis