Optical Detection And Depolymerization Of ?-amyloid Oligomers In Alzheimer's Disease

Since 2000,China has been defined as a country with an aging population,with the elderly over 65 making up 7%of the total population.By 2010,according to the sixth national census,China's population over the age of 60 will account for 13.26 percent of the total population,with the aging of the population becoming more and more serious.What followed is the neurodegenerative disease in the elderly,with Alzheimer's disease?AD?the most common neurodegenerative disease,accounting for about 60⁸0 percent.So far,China has the largest AD group in the world,which will undoubtedly impose a heavy burden on the families of patients and the socioeconomics.AD is an irreversible neurodegenerative brain disease,which is one of the most common type of dementia.Its main pathological features are extracellular?-amyloid plaque deposition and phosphorylation of tau protein intracellular neurofibrillary tangles,causing brain neuronal loss and ultimately brain atrophy and memory loss.Genetic data suggest that the deposition of soluble monomers into oligomers,fibrous filaments,and other aggregation forms is the starting step for the pathogenesis of AD,occurring approximately 15²0 years before the onset of dementia.A?is the major component of senile plaques deposited in the brain of AD patients,derived from the continuous cleavage of amyloid precursor protein?APP?by?-and?-secretase.It can produce two different A?fragments.A?_1-40?about 80⁹0%?is the most abundant form and A?_1-42?about 5¹0%?is the main form of deposition of senile plaque in AD brain,which is more hydrophobic and fibrous,and is more likely to cause synaptic injury,nerve damage and neuronal death.The amyloid cascade hypothesis points out that impaired balance between A?production and clearance is the main cause of AD.Studies have reported that A?is also present in the normal human brain,its production and metabolism in the brain cells are in a balanced state,and normally intracellular production of A?is soluble and has little neurotoxicity.When under abnormal conditions,soluble A?will gradually self-aggregate to form oligomers and further form the original fiber and other aggregation forms.And studies have shown that soluble A?oligomers?A?o?are the most toxic than other abnormal aggregates.As a result,A?o have been regarded as important markers and main therapeutic targets for Alzheimer's disease.Thus,inhibition of oligomeric aggregation and dissociation of the formed aggregates has been considered as a potential therapeutic approach.Based on the above research background,this paper designs a“off-to-on”fluorescent probe based on molybdenum disulfide nanosheets and a colorimetric probe based on mesoporous silica nanoparticles and competitive release principle to achieve the detection of A?o,respectively.At the same time,the designed system can inhibit the production of A?o and accelerate the dissociation and clearance of A?aggregates.The performances of these two works help us to comprehensively understand AD from the two perspectives of diagnosis and treatment,and provide a certain basis for future AD research.The specific contents of the thesis are as follows:Charpter 1:OverviewThis chapter first summarized the current research status of AD and its pathological relationship with A?o.Subsequently,the detection methods of A?o and the inhibition assays of AD were introduced respectively.Finally,the significance and main contents of the research work were expounded.Charpter 2:Molybdenum Disulfide Nanosheets based Fluorescent“Off-to-On”Probe for Targeted Monitoring and Inhibition of?-Amyloid OligomersIn this chapter,molybdenum disulfide nanosheets?MoS₂ NSs?were used to construct a fluorescent probe based on the“off-to-on”sensing mechanism for the efficient and sensitive detection of A?o.In this system,we first prepared FAM-labeled single-stranded DNA?FAM-ssDNA?.Then,the ssDNA was adsorbed onto the surface of MoS₂ NSs to obtain a MoS₂ NSs/FAM-ssDNA fluorescent probe owing to the Van der Waals force between the nucleic acid group of ssDNA and MoS₂ NSs,resulting in the occurrence of energy transfer and the fluorescence quenching of FAM to the“off”state.When a certain concentration of the A?o was added to the MoS₂ NSs/FAM-ssDNA probe solution,the hybrid structure was formed by the specific recognition and binding between ssDNA and A?o,causing the FAM far away from the surface of MoS₂ NSs and the fluorescence state“on”state.Meanwhile,in this work,we further found that MoS₂ NSs demonstrated potential AD therapeutic capability by inhibiting A?self-aggregation and degradation of already formed A?fibers.Meanwhile,the MoS₂ NSs prepared in this experiment also showed low cytotoxicity and good biocompatibility.In conclusion,this work confirmed the potential advantages of two-dimension nanomaterials represented by molybdenum disulfide in the diagnosis and treatment of AD,providing an effective means for the study of the mechanism of AD.Charpter 3:Targeting Monitoring and Inhibition of?-Amyloid Oligomers by Colorimetric Analytical Method based on Mesoporous Silica Nanoparticles and Competitive Displacement ReactionIn this chapter,PEI functionalized mesoporous silica nanoparticles?PEI-MSN?containing glucose signal molecules inside was used to constructe a colorimetric probe named PEI-MSN/mApoE-AuNPs by combining the competitive displacement reaction and colorimetric analytical method together,which was capable of detecting A?o efficiently.Firstly,the negatively charged mApoE-labeled gold nanoparticles?mApoE-AuNPs?were electrostatically adsorbed on the positively charged PEI-MSN surface,allowing glucose molecules to enter the pores of MSN and blocked.When A?o were introduced to the system,due to the stronger interaction between the specific binding force of“antigen-antibody”than electrostatic force,the separation of mApoE-AuNPs from PEI-MSN will result in the release of glucose molecules loaded in MSN from the pores,and the concentration of the targeted A?o was positively correlated with the leaked glucose contents.The supernatant after the reaction was collected,and the peroxidase activity of molybdenum disulfide nanometer sheet?MoS₂ NSs?and the catalytic activity of glucose oxidase?GOX?on glucose were used to conduct sensitive colorimetric analysis of the leaked glucose using TMB as the colorimetric substrate,so as to indirectly realize the optical detection of A?o.Meanwhile,it has been reported that mApoE and AuNPs involved in this work have a potential therapeutic value on AD.Therefore,we further investigated the potential therapeutic values of the above colorimetric probe by inhibiting A?self-aggregation and degrading the already formed A?fibrils.The colorimetric analytical method constructed in this work was simple in principle,quick in response,sensitive and reliable,and provided a solid foundation for the development of colorimetric technology in the detection and treatment of AD.