Icariside Ⅱ Attenuates Learning And Memory Impairment Induced By β-amyloid 25-35 Fragment And Its Underlying Mechanisms In Rats

Objective: The present study was designed to investigate the neuroprotective effect of icariside Ⅱ(ICS Ⅱ) on learning and memory impairment, as well as neuronal apoptosis in hippocampus induced by injection of beta-amyloid25-35(Aβ25-35) in rat, and further explore the underlying potential mechanisms.Methods: Sixty male Sprague-Dawley(SD) rats were randomly divided into 5 groups: sham group, model group, ICS Ⅱ low- and high- dose groups and positive drug group(each n=12).The rats of model group were injected into the bilateral hippocampal with aggregation of 5 μL Aβ25-35(2 μg/μL) to establish the model of learning and memory impairment, while the rats of sham group were injected with volume-matched normal saline, instead. Rats in ICS Ⅱ low- and high- dose groups and positive drug group were intragastrically administered with ICS Ⅱ 3, 10 mg/kg and sildenafil 3 mg/kg once a day, while the sham and model group rats were administered with volume-matched vehicle for 15 days, instead. Morris water maze(MWM) test was applied to evaluate spatial learning and memory ability of rats on 11 th day for consecutive 5 days after surgery, then the rats were sacrificed. Nissl staining was used to evaluate the survival neurons in the CA1 region of rat hippocampus. Neuronal apoptosis of hippocampus was detected by TUNEL assays. PDE 5 and c GMP protein levels in hippocampus were determinate using ELISA. The protein expression of pro-caspase-3, Bax, Bcl-2, BDNF, Trk B and the protein level of active-caspase-3 and related signaling in the regulation of CREB, Erk and Akt phosphorylation levels were detected by Western blot, respectively.Results: The escape latency of model group rats was prolonged, time percentage in the target quadrant and target quadrant frequency were significantly decreased compared with sham group; pyramidal cells of hippocampal CA1 region arranged in disorder, the structure of cell was not complete, the amount of Nissl bodies significantly reduced and the number of apoptosis cell increased;the protein level of PDE 5 was increased and the protein level of c GMP was reduced; the protein expression of Bax and the protein level of active-caspase-3 were significantly increased and the protein expression of Bcl-2, pro-caspase-3, BDNF and Trk B were decresaed, the protein of CREB, Erk and Akt phosphorylation levels were decreased. However, compared with model, the escape latency of ICS Ⅱ high-dose group and positive drug group rats was shorter, time percentage in the target quadrant and target quadrant frequency were markedly increased; hippocampal neurons arranged with regular, structure was complete, the number of Nissl bodies was significantly increased and apoptosis cell was reduced; the protein level of PDE 5 of the hippocampus was significantly lower and the protein level of c GMP was higher; the level of apoptosis related protein Bax and active-caspase-3 were significantly reduced; the protein expression of Bcl-2, pro-caspase-3, BDNF and Trk B were significantly increased; the protein of CREB, Erk and Akt phosphorylation levels were significantly enhanced.Conclusion: Under the experimental conditions, ICS Ⅱ significantly ameliorates spatial learning and memory impairment and apoptosis induced by Aβ25-35 in rats, and its protential mechanism may be related to the reduction of phosphodiesterase 5 content and upregulation of BDNF/Trk B/CREB signal pathway.