| Objective:To establish rat model of Sporadic Alzheimer's disease(SAD),and treat with GETO (herbal extract), which have the role function of supplementing Qi, activating blood flow, invigorating the kidney and dissipating phlegm. In this paper, we observe the learning and memorizing ability of the rats,ultrastructure of hippocampal neurons, as well as the expression of enzymes related to phosphorylation of tau and insulin signal transduction pathway in hippocampal neurons of AD rats. So as to investigate the neuroprotective role of GETO on rats with AD, provide further theoretical and experimental evidence for new medicine in clinical applicationMethods:Experimental animals were randomly divided into six groups: sham-operated group, model group, Donepezil group and GETO large, middle and small dosage treated groups. To establish the Sporadic Alzheimer's disease model by intracerebroventricular injection of STZ (ICV-STZ) bilaterally, GETO groups were treated with gastric perfusion of GETO in three different dosage. The model group and sham group were given double distilled water respectively. 3 months later, Learning and memorizing ability of the rats were inspected through Morris water maze test. Immunohistochemistry(IHC), Western bolt, electron microscope and system of image pro-plus were used to determine ultramicrostructure of hippocampus CA1 region, and the expression of enzymes related to phosphorylation of tau(GSK-3β,PP-2A,PP-1), as well as protein expression of insulin signal transduction pathway(IR,IGF-I,IRS-1,IRS-2)in hippocampal neurons of AD rats.Results:1 GETO can ameliorate the ability of learning and memory of ICV-STZ rats. In place navigation test, Morris water maze test showed that the escape latency and swimming distance were significantly longer in the model group than that in the sham group (P<0.05 or P<0.01), but shorter in GETO groups and Donepezil group(P<0.05 or P<0.01).In spatial probe test, compared with the sham group, swimming time in the platform of previous quadrant was significantly shorter in model group(P<0.01), but significantly longer in GETO groups(P<0.01), and there was no difference between Donepezil group and GETO groups. 2 Compared with the sham group, the levels of phosphorylated tau protein at Ser199/202 epitope were elevated in ICV-STZ rat brain hippocampus, and the levels of non- phosphorylated tau protein at Ser199/202 epitope were decreased (P<0.01); but in GETO groups and donepezil group, the levels of phosphorylated tau at the same epitope were obviously decreased, and non-phosphorylated proteins were obviously increased (P<0.05/ P<0.01), especially in Large and Middle dosage treated groups.3 The microtubules of hippocampal neurons of ICV-STZ model showed prominent changes of fragmentation and dissolution, while the treatment of GETO can significantly ameliorate these changes. The hippocampal neurons of AD rats showed significant intracellular increase in the tau phosphokinase, GSK-3β(P<0.01)and decrease in the tau dephosphry- lating enzymes, PP-1 and PP-2A(P<0.01). Compared with model group, GETO can down- regulate the expression of GSK-3βand up-regulate the expression of PP-2A and PP-1 (P<0.05/P<0.01).4 GETO can regulate brain insulin/IGF signal transduction pathway, there was an insignificant decrease in IR, IGF-I, IRS-1 and IRS-2 in the GETO treated groups as compared to the Model(P<0.01), and GETO groups can up-regulate the expression of them (P<0.05/P<0.01).Conclusion:1 There was dysfunction in learning and memory ability, as well as insulin/IGF-I signal transduction pathway in ICV-STZ rats; this model can simulate the pathological features of AD.2 GETO can ameliorate phosphorylation extent at Ser199/202 sites, and thus prevent the formation and toxicity of hyperphosphorylation of tau protein; GETO can keep balance of protein kinase and phosphatase expression, to ensure normal level of tau protein phosphorylation in hippocampal neurons, protect structure of microtubule, and prevent axonal injury.3 GETO can regulate insulin/IGF-I signaling pathway, help insulin and IGF-I act on protecting neurons from damage and remarkably improving learning and memory function.
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