The Study Of The Underlying Mechanisms For Protective Effect Of Phytoestrogen On Alzheimer's Disease After Menopause

Epidemiological investigation reported a remarkable increase of the incidence of Alzheimer's disease (AD) in women after menopause. AD is a chronic degenerative disease in central nervous system, characterized with the clinical symptom that the cognitive abilities decline gradually. It is demonstrated that cell apoptosis induced by P-amyloid peptide (AP) contribute mainly to the neuron loss and certain pathological alterations. AD is currently incurable with any specific treatments. Estrogen can inhibit the neuron apoptosis induced by Ap, and could become one of the potential medications for women with AD. But the potential risk for endometrial and mammary cancer of estrogen replacement therapy (ERT) restricts its clinical application.It is found that phytoestrogen (PE), with natural plant source.and similar chemic structure to estradiol, perform dual effects as estrogenic and anti- estrogenic. It was showed that PE could alleviate women menopauses syndrome and protect or treat osteoporosis and cardiovascular diseases without the side effects of estrogen, showing its promising as-a new drug for future ERT. Can PE exhibit its protective effect on central nervous system toprevent and treat AD as efficiently as estrogen? What are the underlying mechanisms? With the goal in mind, we chose genistein (GST) as the trial drug, which is of the highest bioactivity in phytoestrogen, and is most abundant in soybean, so as to evaluate the efficiency of neuroprotective effect of PE to search for the new target drug for therapy.In our study, we first established the ovariectomized rat model, then the behavioral and morphological changes and the alterations of neurotransmitter in rat brain were examined in estrogen-deficient conditions and the influence of ERT on the above parameters was observed later. Secondly, the cellular mechanism for Ap to induce neuron impairment was studied on the cellular model by applying AB25-35 to PC 12 cells, mimicking the deposition of Ap in AD. The mechanism of PE to antagonize AB in inducing cell apoptosis was measured.1.The possible mechanism of GST affecting the learning and memory of ovx rats was explored in vivo.Adult female Sprague-Dawley rats were ovariectomized to mimick the patho-physiological changes in women after menopause. The rats were randomly divided into five groups: the sham-ovariectomized group (Sham-group), the ovariectomized group (OVX group), the OVX+17B-E2 (E2 group), the OVX+ high dosage of GST (GST-h group) and OVX+ low dosage of GST group (GST-L group). The treatment lasted for 6 weeks. PE activity was evaluated with multi-parameters.The results showed is as follows.(1) The ovariectomy(OVX) resulted in the decrease in learning and memory in female rats. The escape latency of the OVX group was significantly increased compared with that in the Sham group (88.9+35.1 s vs 51.7+36.9 s, P< 0.05), and the frequency of memory in the OVX group was significantly decreased (18.7+2.7 s-1 vs 24.9+4.5 s-1 P< 0.05) . A significant increase in AchE activity, MAO and MDA was also found in frontal cortex and hippocampus in the OVX group. Replacement of GST and E2 for 6wkcould reverse the above results.(2) Caspase-3 activity in hippocampus was elevated in ovx group, and large amount of TUNEL positive cells were shown in the hippocampus and cortex. After replacement of GST or E2, the caspase-3 activity declined and the number of TUNEL positive cells was reduced compared to ovx group.(3) Serum estrogen level was decreased in ovx rats in contrast with sham-operation group. Treatments with higher dosage of genistein did not alter the serum estradiol level, the uterus index and the endometrium morphology. Low dosage of genistein performed weak estrogenic effect, which was far from that of estrogen, while high dosage of genistein exhibited significant inhibition in reproductive system.2. The mechanism for GST to antagonize Ap in inducing the apoptosis of PC 12 cells was investigated in vitro(1) The influence of different concentrations of GST on PC 12 cells were obs...