The effect of soybean isoflavone on the dysregulation of NMDA receptor signaling pathway induced by β-amyloid peptides 1-42 in rats.

Synaptic damage is the key factor of cognitive impairment. The purpose of this study was to understand the effect of soybean isoflavone (SIF) on synaptic damage induced by β-amyloid peptide 1-42 (Aβ1-42) in rats. Adult male Wistar rats were randomly divided into control, Aβ1-42, SIF, and SIF + Aβ1-42 (SIF pretreatment) groups according to body weight. SIF was treated orally by gavage in SIF and SIF + Aβ1-42 groups. After 14 days pretreatment with SIF or vehicle, Aβ1-42 was injected into the lateral cerebral ventricle of rats in Aβ1-42 and SIF + Aβ1-42 groups using miniosmotic pump. The level of Aβ1-42 and the expression of N-methyl-D-aspartic-acid receptor (NMDAR) were observed by immunohistochemistry. Reverse transcriptase polymerase chain reaction was used to detect the mRNA levels of NMDAR, calmodulin (CaM), calcium/CaM-dependent protein kinase II (CaMKII), cAMP-response element binding protein (CREB), and brain-derived neurotrophic factor (BDNF). The results showed that Aβ1-42 down-regulated mRNA and protein expression of the NR1 and NR2B subunits of NMDAR, SIF pretreatment could reverse these changes. The mRNA expression of CaM, CaMKII, CREB, and BDNF were down-regulated by Aβ1-42, but they were all regulated by SIF pretreatment. These results suggest that SIF pretreatment could antagonize the neuron damage in rats induced by Aβ1-42, and its mechanism might be associated with the NMDA receptor and CaM/CaMKII/CREB/BDNF signaling pathway, which are the synaptic plasticity-related molecules.