The Study On The Neuroprotection Of Dual Receptor Agonist CI-1206 Against Aβ1-42-Induced Impairments In Spatial Memory And Synaptic Plasticity In Mice

Alzheimer’s disease(AD) is a slow progressing neurodegenerative disease that could remain asymptomatic for several decades at the early stage, but gradually develop into dementia. It is the most common form of dementia, accounting for over 70% of all cases.Aging is the most definitive risk factor for AD, and the incidence rate of AD greatly increased with the increase of population age year by year. The most prominent neuro-pathological features of AD are the appearance of senile plaques and neuro-fibrillary tangles(NFTs) in the brain. The amyloid cascade hypothesis has been the major pathogenic concept in the field of AD research for the past few decades. The accumulation of amyloid-β peptide(Aβ) leads to neuro injury, and then cognitive impairment, even dementia. Currently, over 40 million people are affected by this condition worldwide and this number will continue to rise. The disease not only seriously affects the quality of life of patients, but also seriously adds great burden to their families and the community.However, there is still lack of a breakthrough in the treatment and prevention of the disease.Interestingly, epidemiological survey demonstrated a strong association between AD and type 2 diabetes mellitus(T2DM). And type 2 diabetes mellitus has been identified as a risk factor for AD. So the methods controlling T2 DM was also used to intervene AD. It is a pity that insulin was not an ideal choice for the AD treatment. CI-1206, a single molecule that acts equally on the receptors for the GLP-1 and GIP, was recently demonstrated to be more effective in enhancing antihyperglycemic and insulinotropic efficacy relative to selective GLP-1 or GIP receptor mono-agonist in rodent models of obesity and diabetes.Multiple studies demonstrate that GLP-1 and GIP or its analogs are neuroprotective. But it is not well known whether CI-1206 have some neuroprotective effects in AD-related mouse model.Therefore, the present study, by establishing a mouse model of AD with intra-cerebral Aβ1-42 administration, explored the neuroprotective effects of CI-1206 and its possible mechanism by using Y-maze test, Morris water maze test and hippocampal long term potentiation(LTP) recording.Part Ⅰ Effects of CI-1206 treatment on spatial working memory of miceObject:To explore the neuroprotective effects of intraperitoneal injection CI-1206 against Aβ1-42-induced deficits in spatial working memory in mice.Method:Adult male C57 mice weighing 25-30 g at the beginning of the experiments were used in this study.The mice were divided into the following groups:(1) Control(vehicle+saline);(2) Aβ1-42 injection(Aβ1-42+ saline);(3) Aβ1-42 plus CI-1206(25 nmol/kg/day, i.p.)(Aβ1-42+ CI-1206) and(4) CI-1206 alone(25 nmol/kg/day(i.p.)(CI-1206+saline).The mice were anesthetized with an intraperitoneal injection of 5% chloral hydrate(0.007-0.008ml/g). Then Aβ1-42 or vehicle administered intracerebroventricularly according to the brain atlas. Twenty four hour after i.c.v. Aβ1-42 or vehicle injection,CI-1206(25 nmol/kg) or saline was administered(i.p.) for 3 weeks regularly afternoon,and the injections were carried out until the end of the experimental study. Spatial working memory performance was assessed on the 22 nd day after Aβ infusion, by recording spontaneous alternation performance in a Y-maze. The numbers of arm entries were recorded during 8 min of trial.Results:After a single injection of Aβ1-42(Aβ1-42+saline), the percentage of spontaneous alteration behavior was reduced compared to the control(vehicle + saline)(P <0.01),suggesting i.c.v Aβ1-42 impaired the working memory of mice. Treatment with CI-1206(CI-1206 + Aβ1-42) significantly increased the percentage of spontaneous alteration behavior compared to the Aβ1-42 alone(Aβ1-42 + saline), indicating that CI-1206 ameliorated Aβ1-42-induced memory dysfunction of mice. No significant difference in total number of arm entries was found among these groups.Conclusion:CI-1206 could reverse the detrimental effects of i. c. v. Aβ1-42 on spatial working memory in mice, while CI-1206 itself did not affect the spatial working memory in mice.Part Ⅱ CI-1206 reversed Aβ1-42-induced impairment of spatial reference memory in miceObject:To explore the positive protective effect of CI-1206 against spatial reference memory impairment induced by intracerebroventricular injection of Aβ1-42 in mice.Method:The spatial learning ability of mice was examined using the hidden platform test from the 1st to the 5th days. Spatial memory of mice was evaluated by 2 times of probe trials on the 6th day after removing the platform out of the pool. Visual and locomotor abilities of mice were examined using the visual platform test. The escape latency in the hidden platform test and swimming traces in all experiments were recorded for off-line analysis with software.Results:Aβ1-42-treated mice(Aβ1-42 + saline) showed longer escape latency to reach the hidden platform and the mice treated with CI-1206(25 nmol/kg, i.p., 3 weeks) took less latency time. In probe trial, Aβ1-42-treated mice(Aβ1-42+saline) showed less time spent in the target quadrant, showing that Aβ1-42-induced memory impairment. Treatment with CI-1206 reversed this Aβ1-42-induced memory impairment and significantly increasing time spent in the target quadrant. No significant difference in escape latency and swimming speed was found in the visible platform test among these groups.Conclusion:Spatial reference memory was significantly impaired by injection of Aβ1-42 in mice and this impairment could be reversed by CI-1206.Part Ⅲ CI-1206 effectively reversed Aβ1-42-induced LTP impairment in mice brain slicesObject:To observe the effects of CI-1206 and Aβ1-42 on the hippocampal LTP induction and maitainence in mice by using MED64 multi-channel recording system.Method:After Morris water maze test, mouse brains were immediately dissected after sacrifice for LTP recordings. Brain slices were prepared using a vibratome. The baseline and HFS induced LTP of the dendritic layer of the CA1 region were recorded using a MED64multi-channel recording system.Results:LTP in hippocampal CA1 region was significantly suppressed in Aβ1-42 + saline mice,compared with the control group(P <0.05). But this suppression could be reversed by CI-1206 through chronic intraperitoneal injection(P <0.05). CI-1206 itself does not affect hippocampal LTP, without any significant difference(P> 0.05) compared with the control group.Conclusion:Lateral ventricular injection of Aβ1-42 impaired the synaptic plasticity of mice in the hippocampus and CI-1206 chronic treatment could reverse the depressing effect.