Molecular Recognition And Intervention Of Aβ Protein Misfolding And Aggregation Process

Alzheimer’s disease(AD)is the most common form of dementia associated with the loss of memory,cogntive decline and behavioral or physical disability,and is characterized by synapse loss as well as some lesions throughout the brain.The cost in curing and taking care of AD patients will become a serious social problem as the society is aging rapidly.Besides,researching progress of AD might be helpful to cure other protein misfolding diseases,such as Parkinson’disease,Ⅱ-type diabetes and bovine spongiform encephalopathy(BSE).However,to date,no method can cure this neurodegenerative since the multiple pathogenic factors.There are no definitive etiology but four hypothesises are summaried from primary pathological hallmarks of AD.Recently,more and more evidences indicate that assemblies of amyloid-β peptide(Aβ)induced by d-block metal ions(mainly Zn2+ and Cu2+)or self-misfolded are the primary pathologic factor of AD.Hence,we described a serious of compounds to modulate the β-sheet-rich Aβ aggregates and inhibit the production of ROS and neurotoxicity induced by the Aβ aggregates.Chapter 1 four hypothesises summaried from primary pathological hallmarks of AD:amyloid cascade hypothesis,metal ion hypothesis,oxidative stress hypothesis,and cholinergic hypothesis are reviewed detailedly.The factors that influence the Aβmisfolding and aggregation are summarized.Based on the amyloid cascade hypothesis combined with metal ion and oxidative stress hypothesis,a rounded system in design anti-AD agents is established and elaborated.Chapter 2,to date,there are more and more evidences indicate that assemblies of amyloid-β peptide(Aβ)induced by d-block metal ions(mainly Zn2+and Cu2+)is the primary pathological hallmarks of AD.In this regard,Aβ aggregates have been considered as both therapeutic and biomarkers targets for AD treatment.In this study,a concise designed multifunctional diagnosis and treatment agent 2-(2((1H-benzo imidazol-2-yl)phenyl)benzothiazole(BPB),which merge two thioflavin(ThT)analogue 2-phenylbenzothizaole and 2-(phenoxymethyl)-1H-benzoimidazole.As predicted,the N and O atoms located on the structure mold BPB into a polydentate ligand,which can efficiently modulate ions induced Aβ aggregates,suppress the Cu-Aβ mediated generation of ROS and reduce the neurotoxicity in PC12 cells.Remarkably,BPB can not only targeting the Aβ aggregates,but also can simultaneously probe in situ the β-sheet level of the peptides,especially can monitor the soluble Aβ oligomers directly with a visible region emission.Furthermore,BPB may also exhibit blood brain barrier(BBB)penetration.As the rare multi-functional diagnosis and treatment agent who can meet all the needs of targeting,sensing and modulating aggregations of Aβ,such multifunctional design idea should potentially lead to develop more effective therapeutic agents as well as provide an increased understanding of the metal-Aβ associated neuropathology.Chapter 3,the misfolding of Aβ results in the formation of β-sheet-rich aggregates and damages the function of neuron cells.Since hydrogen bond is the major force maintaining the secondary structure of misfolded proteins,a modified polyoxometalate(POM),[CoL(H2O)]2[CoL]2[HAsⅤMoⅤ6MoⅥ6O40][CAM,L=2-(1H-pyrazol-3-yl)pyridine],was designed to disaggregate the Aβ aggregates,where L acts as an Aβ-targeting group while POM as a conformational modulator.X-ray crystallography shows that CAM is comprised of a ε-Keggin unit and four coordination units.CAM can disassemble the β-sheet-rich fibrils or aggregates of Aβinduced by metal ions or peptide self-aggregation,and further inhibit the production of ROS.As a result,CAM can protect the neuron cells from synaptic toxicity induced by Zn2+-or Cu2+-Aβ aggregates or Aβ self-aggregation.The mechanism of disaggregation mediated by CAM involved a transformation of the Aβ conformation from β-sheet to other conformers.The nature of the process is an interference of theβ-sheet conformation by CAM via the hydrogen bonding.CAM specifically interacts with the Aβ aggregates but does not disturb the cerebral metal homeostasis and the enzymatic system.Molecular simulation suggests that the appropriate sizes of CAM and the cavity of β-sheets facilitate the interaction between CAM and Aβ aggregates;and the H-bonding-favored amino acid residues in the cavity provide a precondition for the interaction.Finally,CAM is lipophilic and capable of penetrating the blood-brain barrier,and is metabolizable within 2 days without causing serious untoward effect to mice at high dosages.In view of the significant inhibitory effect on the Aβ aggregation and related neurotoxicity,CAM represents a new type of leading compounds with a distinctive mechanism of action for the treatment of Alzheimer’disease.The mechanism of action of CAM might be applicative to other protein misfolding diseases,such as Parkinson’disease,II-type diabetes and bovine spongiform encephalopathy(BSE).In this sense,CAM opens a new door to the design of drugs against AD and other similar diseases.Chapter 4,among various Aβ aggregations,soluble oligomers are believed to be the most toxic species,which are rich in β-sheet structure and induced by aberrant homeostasis of cerebral metals or self-assembly.Therefore,to reduce the soluble Aβoligomers is an effective measure to delay the progression of AD.In this study,a new multifunctional anti-ROS agent(3-((3-mercaptopropyl)thio)propyl)triphenylphospho nium bromide(TSS)has been designed,where the triphenylphosphine acts as a electrostatic interference group while the hydrosulfuryl act as chelation and anti-ROS group.Preliminary results indicate that TSS can inhibit the formation of soluble Aβoligomers and protofibrils by depositing soluble Aβ fastly;it can also suppress the Cu-Aβ mediated generation of reactive oxygen species and synaptic toxicity induced by Zn2+-or Cu2+-Aβ aggregates or Aβ self-aggregation.These results suggest that TSS is a potential anti-AD agent.