| Objects In this study,rat model of type 1 diabetes was established to observe the effect of a novel hypoglycemic drug GLP-1 analogue,Liraglutide(Li),on the improvement of cognitive dysfunction and the relationship between this effect and the AGEs-RAGE-oxidative stress pathway.Methods1.Grouping and modeling: SD rats were randomly divided into normal control group(NC group)and diabetes Mellitus group(DM group),adopt streptozotocin(STZ)intraperitoneal injection induced type 1diabetic rats,the diabetic rats were randomly divided into DM group and the Liraglutide intervention group(DM+Li group).Based on the previous data of early experiments,100 μg/kg/qd dose of Liraglutide was used in this experiment.The DM+Li group was subcutaneously injected with Liraglutide(100 μg/kg/qd)for 10 weeks,while the NC group and the DM group with normal saline of the same volume.GLU,HDL-C,TG,HDL-C,and CHOL were measured to observe the effect of Liraglutide on glycolipid metabolism in rats.2.Morris water maze behavior: Observe the performance of each group in the positioning navigation and space exploration experiment.The differences in learning and memory ability were analyzed.3.Morphological and functional detection of hippocampus and synapses: To observe the effects of Liraglutide on the morphology and ultrastructure of pyramidal cells in the hippocampus CA1 region related to cognitive function in rats by light microscope and transmission electron microscope.To determine the effect of Liraglutide on hippocampal synaptic function in diabetic rats.Immunohistochemistry was used to detect Aβ in hippocampal tissue,and western-blot was used to to analysis the expression of PSD-95 and SYN proteins to determine the effect of Liraglutide on hippocampal synaptic function in diabetic rats.4.AGEs-RAGE-oxidative stress pathway: Serum and hippocampal tissues MDA and SOD levels were measured to observe the effect of Liraglutide on oxidative stress function in rats.Additionally,to observe the effect of Liraglutide on the age-rage pathway,the oxidative stress immunohistochemistry and ELISA were used to detect RAGE(Receptor for AGEs)expression and serum AGEs(Advanced glycation end products)and RAGE in hippocampal tissues,respectively.Results1.General conditions and biochemical test results of rats: Compared with the NC group,the weight of the DM group significantly decreased(P < 0.05),but the food and water intake increased significantly(P<0.05).After Liraglutide intervention,there was no significant difference in body weight,food and water intake between the DM+Li group and the DM group.Results of serum biochemical test showed GLU,TG,CHOL and LDL-C concentrations in the DM group was higher than NC group while the concentration of HDL-C was lower,suggesting that the glucose and lipid metabolism in the DM group was disordered.After 10 weeks of Liraglutide intervention,no significant difference was observed in the above indicators between the DM+Li and DM group,suggesting that Liraglutide intervention could not improve the symptoms of high fat and sugar in type 1 diabetes.2.Morris water maze test results: Morris water maze experiment showed that the incubation period of DM group was significantly longer than NC group(P < 0.05),and that of DM+Li group was significantly shorter than that of DM group.In the space exploration experiment,compared with NC group,the number of times that the DM group rats passed through the area of the platform was reduced significantly(P < 0.05);however,the number of times of DM+Li group was significantly higher(P < 0.05)than DM group,as well as their memory ability.3.Morphological and functional test results of hippocampus and synapses: Histomorphological HE staining showed the number of pyramidal cells in the CA1 region of the hippocampus in the DM group decreased,the cell morphology varied,cellular arrangement disordered,and nucleic was partially shrunk.The pyramidal cell number of the DM+Li group was in the middle of the NC and DM group,and the arrangement was more orderly than DM group.The results of transmission electron microscopy of hippocampal synapses showed that in the DM group,the synaptic structure was unclear,the number of neure was decreased,the synaptic cleft was narrowed,some membranes were indistinct,the dense layer was thinner,and edema vacuoles appeared.However,the synapses in the DM+Li group were,to some extent,improved.Immunohistochemistry in the hippocampus of rats showed that the DM group had a deeper and more intensive expression than the NC group,and the DM+Li group had a shlighter expression than the DM group.Compared to NC group,the expression levels of synaptic proteins PSD-95 and SYN in DM group were significantly decreased,but that in DM+Li group were higher than DM group(P < 0.05)used by Western-blot.The above results suggested that Liraglutide could improve the morphological structure and function of the hippocampus of type 1 diabetic rats.4.Results of AGEs-RAGE-oxidative stress pathway: Oxidative stress indicators showed that DM group has higher hippocampus MDA content than NC group(P < 0.05),but lower SOD activity(P < 0.05).The MDA content in the brain tissues of rats in the DM+Li group was lower than DM(P < 0.05),but higher the SOD activity(P < 0.05).These results suggested that Liraglutide could reduce the oxidative stress level of brain tissue in rats with type 1 diabetes.AGEs-RAGE detection showed that the hippocampal immunohistochemical analyses of RAGE showed that the expression of RAGE in DM group was more intensive than that in NC group,while this was more shallow in DM+Li group than DM group.Compared with NC group,the serum AGEs concentration and hippocampal AGEs concentration in DM group were significantly higher(P < 0.05).The serum AGEs concentration and hippocampal AGEs concentration in the DM+Li group were significantly lower than DM group(P < 0.05),showed that Liraglutide had an inhibitory effect on AGEs-RAGE pathway.Conclusions1.Liraglutide had no significant effects on glycolipid metabolism in type 1 diabetic rats.2.Liraglutide had a certain effect on the improvement of cognitive dysfunction in type 1 diabetic rats but without lowering blood glucose and lipid levels.3.The effect of Liraglutide on improving cognitive dysfunction in type1 diabetes may be related to the effect on the AGEs-RAGE-oxidative stress pathway,which may be a mechanism for the improvement of cognitive impairment. |
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