Neuroprotective effect of cerebral ischemic preconditioning on ischemia/reperfusion injury in rats is associated with Nrf2/NQO1 signaling pathway

Objective To investigate the protective effect of cerebral ischemic preconditioning (CIPC) on ischemia/reperfusion (I/R) in rats and the impact of CIPC on nuclear factor E2-related factor 2 (Nrf2)/quinone oxidoreductase 1 (NQO1) signaling pathway. Methods A total of 198 healthy male Sprague-Dawley rats were randomly divided into 3 groups: a sham-operation group, an I/R group, and a cerebral ischemic preconditioning (CIPC group). Each group was also randomly redivided into 5 subgroups: 6 h, 12 h, 24 h, 48 h, and 72 h after modeling according to the I/R time points. The neurological function scores were evaluated at each time point. HE staining was used to conduct morphological analysis. Triphenyl tetrazolium chloride method was used to detect the cerebral infarction volume. Immunohistochemical staining was used to observe the expression of Nrf2 nuclear transfer on the ischemic side. Real-time reverse transcriptase polymerase chain reaction was used to detect the expression levels of Nrf2 and NQO1 mRNA. Results The rats in the I/R group and the CIPC group had varying degrees of hemiplegia. Neurological function scores in the CIPC group at 24 and 48 h were decreased significantly compared with the I/R group (all P<0.01). No ischemic changes in nerve cells in the sham-operation group. The ischemic changes in nerve cells in the CIPC group were significantly lighter than those in the I/R group. No infarcts were observed in the sham-operation group. The infarct volume percentage in the CIPC group was lower than that in the I/R group (33.20%±7.48% vs.21.40%±4.48%; t=11.043, P=0.001). The numbers of Nrf2 nuclear positive cells in the ischemic cortex in the I/R group and the CIPC group at 6 h were more than that in the sham-operation group (all P<0.01). It reached the peak at 24 h and was decreased gradually from 48 to 72 h. The numbers of nuclear positive cells at 6, 12, and 24 h in the CIPC group was significantly more than that in the I/R group (all P<0.01). The expression levels of Nrf2 and NQO-1 mRNA in the ischemic cortex at 6 h in the I/R group and CIPC group were significantly higher than those in the sham-operation group (all P<0.01). It reached the peak at 24 h and continued to 48 h and it was decreased slightly at 72 h. The expression levels of Nrf2 and NQO1 mRNA at each time points in the CICP group were significantly higher than those in the I/R group (all P<0.01). It was most obvious at 24 h. Conclusions CIPC has neuroprotective effect on ischemia/reperfusion in rats. Its mechanism is associated with the promotion of Nrf2 nuclear transfer and upregulation of Nrf2/NQO1 signaling pathway. Key words: Brain Ischemia; Reperfusion Injury; Ischemic Preconditioning; Neuroprotective Agents; NF-E2-Related Factor 2; NQO1 Protein, Rat; Oxidative Stress; Disease Models, Animal; Rats