Objective To investigate the effects of soybean isoflavones (SI) on the apoptosis of rat hippocampal neurons after global cerebral ischemia/reperfusion and relevant mechanisms. Methods A total of 60 adult healthy SD rats were randomly divided into the sham group, ischemia/reperfusion group (I/R group), SI low dose group(SI-L group, 60 mg/kg), SI medium dose group (SI-M group, 120 mg/kg), and SI high dose group (SI-H group, 240 mg/kg)(n=12 in each). The global ischemia/reperfusion model was established by 3-vessel occlusion. Rats were sacrificed after being reperfused for 1 h after 1 h of ischemia and the hippocampal tissue was collected. The morphological changes of hippocampal neurons were observed under the light microscope. Changes of the ultra-structure of hippocampal neurons were observed by the transmission electron microscope. Annexin V-FITC/PI double staining was adopted to detect the apoptosis rate of hippocampal neurons. The chemical colorimetry was employed to detect the activity of superoxide dismutase (SOD) and inducible nitric oxide synthase (iNOS) and contents of methane dicarboxylic aldehyde (MDA) and nitric oxide(NO). The expression of NF-κB/p65 mRNA of hippocampal tissue was detected by the semi-

quantitative RT-PCR. The protein expressions of TNF-α and NF-κB/p65 of hippocampal tissue were detected by the immunohistochemical method. Results Shrivel of hippocampal neurons, marginalization of nucleus chromatin, incompletion of nuclear membrane, disintegration of partial mitochondria membrane, disappearance of partial mitochondrial cristae, and apoptosis of partial neurons were observed in I/R group. Compared with the I/R group, the damage of ultrastructure of hippocampal neurons of SI-L, SI-M, and SI-H groups was relieved significantly and the rate of cell apoptosis decreased (P<0.01). The activity of SOD and iNOS and contents of MDA and NO of the I/R group were obviously higher than those of the Sham group (P<0.01). Compared with the I/R group, the activity

of SOD and iNOS and contents of MDA and NO of SI-L, SI-M, and SI-H groups decreased (P<0.05). The mRNA expression of NF-κB/p65 and protein expressions of TNF-α and NF-κB/p65 of the I/R group were significantly higher than those of the Sham group (P<0.01). Compared with the I/R group, the mRNA expression of NFκB/p65 and protein expressions of TNF-α and NF-κB/p65 of SI-L, SI-M, and SI-H groups decreased significantly (P<0.01). Conclusion SI can decrease the apoptosis of rat hippocampal neurons after global cerebral ischemia/reperfusion, which may be relevant to inhibiting the oxidative stress, decreasing the expression of TNF-α, and inhibiting the activity of NF-kB/p65.