| Alzheimer’s disease(AD)is a central nervous system degenerative disease characterized by progressive cognitive dysfunction and memory impairment,and is an important source causing dementia.Although there is still much controversy about the pathogenesis of AD,amyloid protein(Aβ)has been recognized as the initiator of AD.Senile plaque(SP)caused by Aβ deposition in the brain,neurofibrillary tangles(NFT)formed by phosphorylation of tau protein,and neuronal loss are characteristic pathological changes.Studies have shown that Aβ deposition and neuronal loss are earlier than cognitive function decline,so research around Aβ production and metabolism has become a hot topic.Aβ is formed through hydrolysis of amyloid precursor protein(APP)located on the cell membrane of neurons by β and γ secretase.β-site amyloid precursor protein cleaving enzyme 1(BACE1)inhibitor,γ-secretase inhibitor,agent affecting Aβ-aggregation metabolism,Aβ vaccine,and therapeutic targets for tau have been entered into clinical trials,but the failure of nearly 200 clinical trials of new drugs for AD has led the US FDA to adjust guidelines that will support very early intervention studies.Clinical trials are mostly aimed at mild cognitive impairment(MCI)and dementia.It is speculated that the possible cause of failure is the long-term deposition of Aβ.In MCI and dementia,Aβ level has far exceeded the threshold inducing the pathological change.Reducing Aβ is too late in the MCI and dementia phases.Studies have found that Aβ deposition has undergone a long process,about 17 years before the onset of clinical dementia symptoms,about 12 years from detectable Aβ to threshold concentration,about 4.2 years inducing hippocampal atrophy,about 3.3 years inducing memory loss,this provides more time for early and long-term intervention,regulation of disease progression.Besides the late intervention,the failure of clinical trials target to Aβ is also related to the single-target effect.The Wang Yanjiang team also proposed a multi-target comprehensive intervention for the complexity of AD pathogenesis.As an aging neurodegenerative disease,oxidative stress and inflammatory response play an important role in the pathogenesis and progression of AD,so polyphenol flavonoids with antioxidant effects enter the researcher’s vision.It was found that the early intervention of total flavonoids of citronin and total flavonoids of persimmon on APPswe /PS△E9 mice could reduce β-secretase activity and inhibit Aβ production.Hesperetin is a natural flavonoid,a phenolic antioxidant.Hesperetin was administered to APPswe/PS1dE9 double transgenic mice for 6 months from 3 months to observe the effect of early intervention of hesperetin on Aβ production,neuronal loss and cognitive function,providing a theoretical basis for preventing the occurrence and progression of AD.Objective:To investigate the effect of early intervention of hesperetin on Aβ production,neuronal loss and learning and memory in APPswe/PS1dE9 double transgenic mice.Method:Wild-type C57BL/6J mice were used as control,APPswe/PS1dE9 double transgenic mice were divided into model and the three groups of hesperetin including high(80 mg/kg/d),medium(40 mg/kg/d)and low(20 mg/kg/d)groups.Hesperetin was administered for 6 months from the age of 3 months.Morris water maze,Barens maze were used to detect the learning and memory.Thionine-nissl body staining was used to observe the morphology of hippocampal CA1 neurons.Western Blotting(WB)was used to detect the expression of Tau protein.Enzyme linked immunosorbent assays(ELISA)was used to detect the contents of β-secretase,γ-secretase,Aβ40 and Aβ42 in serum and brain tissue.Results:1 Effect of hesperetin on learning and memoryMorris water mazeCompared with the control group,the latency of the model group in the space exploration experiment was longer from the third day of the experiment,(P<0.05),the latency of the hesperetin high and low groups were significantly shorter than that of the model group(P< 0.05).In the withdrawal experiment,the times crossing the platform of the model group was significantly decreased than that of the control group(P<0.05),the times crossing the platform of three hesperetin groups were significantly increased than that of model group(P<0.05).Barens mazeThe number of errors in model group was more than that in control group,the number of errors in three hesperetin groups were less than that in model group(P<0.05).On the 14 th day,the number of errors in high hesperetin group was less than that in model group(P<0.05).2 Effect of hesperetin on neuron of hippocampus CA1 region(Thionine-nissl body staining)There were about 2 to 3 layers of neurons in the hippocampal CA1 region in control group,the neurons were intact and clear.The neurons in the model group were obviously missing,the contour structure of the neurons was unclear,and the arrangement was disordered.There were about 3 to 5 layers of neurons in three hesperetin groups,the neuronal structures in the hippocampal CA1 region were neatly arranged,the morphology of neurons were intact.3 Effect of hesperetin on tau expression(WB)Compared with the control group(0.50±0.15),the tau protein expression level(0.81±0.23)significantly increased(P<0.05).Compared with the model group,the tau expression in high dose(0.52±0.17)and low dose hesperetin group(0.32±0.05)significantly decreased(P<0.05).4 Effect of hesperetin on Aβ content in serum and brain tissue(ELISA)4.1 Aβ40Compared with the control group,the total content of Aβ40 in serum and brain tissue of the model group was significantly increased(P<0.05),the total content of Aβ40 in serum and brain tissue of high dose hesperetin group was significantly decreased than that of the model group(P<0.05).In brain tissue,compared with the control group,the Aβ40 content of the model group was significantly increased(P<0.05).Compared with the model group,the Aβ40 content of the high,medium and low dose hesperetin were significantly decreased.(P<0.05).In serum,there was no significant difference between the model group and the control group in Aβ40 content(P>0.05).Compared with the model group,Aβ40 content in the high,medium and low dose hesperetin were significantly increased(P<0.05).The ratio of Aβ40 in brain tissue to that in serum was higher in the model group than that in the control group(P<0.05).Compared with the model group,the ratio in high,medium and low dose hesperetin were significantly decreased(P<0.05).4.2 Aβ42Compared with the control group,the total content of Aβ42 in serum and brain tissue of the model group was significantly increased(P<0.05).Compared with the model group,the total content of Aβ42 in serum and brain tissue of the high and low dose hesperetin was significantly decreased.In the brain tissue,the content of Aβ42 in the model group was significantly increased than that in the control group,(P<0.05).Compared with the model group,the content of Aβ42 in the high,middle and low dose hesperetin were significantly decreased(P<0.05).In serum,there was no significant difference in Aβ42 content between the model group and the control group(P>0.05).The content of Aβ42 in the middle and low dose hesperetin were significantly increased than that in the model group(P<0.05).Compared with the control group,the ratio of Aβ42 in brain tissue to that in serum was higher than that of the control group(P<0.05).Compared with the model group,the ratio of Aβ42 in high,medium and low dose hesperetin groups were significantly lower(P<0.05).4.3 Total Aβ(Aβ40+Aβ42)In the brain tissue,the total amount of Aβ in the model group was significantly higher than that in the control group(P<0.05).The total amount of Aβ in three hesperetin groups were significantly lower than that in the model group(P<0.05).In the serum,compared with the control group,the total amount of Aβ in the model group was significantly lower(P<0.05).The total amount of Aβ in three hesperetin groups were significantly higher than that in the model group(P<0.05).5 Effect of hesperetin on content of β-secretase and γ-secretase in serum and brain tissue(ELISA)5.1 β-secretaseIn the brain tissue,the content of β-secretase in the model group was significantly increased than that in the control group(P<0.05).Compared with the model group,the β-secretase content in the high,medium and low dose hesperetin were significantly decreased(P<0.05).In the serum,compared with the control group,the content of β-secretase in the model group was significantly increased(P<0.05).Compared with the model group,the serum β-secretase content in the high-dose hesperetin group was significantly decreased(P<0.05).5.2 γ-secretaseIn the brain tissue,compared with the control group,the content of γ-secretase in the model group was significantly increased(P<0.05).Compared with the model group,the content of γ-secretase in three hesperetin group were significantly decreased(P<0.05).There was no significant difference in serum γ-secretase content between the model group and the control group(P>0.05).The content of γ-secretase in the high-dose hesperetin group was significantly lower than that in the model group(P<0.05).Conclusion:Hesperetin early intervention could protect the brain neurons and improve the learning and memory ability of APPswe/PS1dE9 double transgenic mice.The possible mechanism might be reducing the activity of β-secretase and γ-secretase of brain tissue,reducing Aβ42 production of brain tissue,promoting metastasis Aβ42 from brain tissue to peripheral,reducing Aβ42 content of brain tissue. |
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