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Title: Potential covalent modification of amyloid-beta protein and its effect on aggregation
Author: Alsalahat, Izzeddin
ISNI:       0000 0004 2720 488X
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2012
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The pathogenesis of Alzheimer's disease (AD) is mainly correlated to the misfolding and aggregation of the beta-amyloid peptide. This causes extracellular amyloid-beta peptide deposition as monomers, oligomers, fibrils and plaques in the brain. Compounds that may covalently interact with amyloid-beta protein might have a role in altering the pathogenesis of AD. Some beta-lactam antibiotics (e.g. amoxicillin), orlistat, resveratrol, vanillin, o-vanillin and ethyl vanillin have been shown to modulate the process of amyloid-beta peptide aggregation using a range of techniques. Several approaches have been used to investigate modulation of amyloid-beta peptide by these compounds. These methods include molecular modelling using both covalent and non-covalent docking, investigation of covalent interaction by MALDI and LC-MS/MS mass spectrometry, and synthesis of model peptides representing key motifs in the amyloid-beta peptide, aggregation studies of amyloid-beta peptide by using the thioflavin T (ThT) fluorescence assay, studying the morphology of aggregation by atomic force microscopy (AFM), and investigating their ability to inhibit amyloid-beta peptide cell toxicity by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell toxicity assay. In non-covalent docking, amoxicillin gave the best results after curcumin when docked with amyloid-beta peptides, while in covalent docking, the binding of vanillin with Lys16 in amyloid-beta peptide was favourable. Except orlistat and resveratrol, the other compounds were found to modulate amyloid-beta peptide aggregation by covalent interaction as confirmed by mass spectrometry. Vanillin derivatives were found to interact with Lys16 in the full length amyloid-beta peptide and synthesised model peptide fragments of amyloid-beta peptide. Penicillins were also shown to covalently interact with amyloid-beta peptide, probably by interacting with a serine residue in the amyloid-beta peptide. Surprisingly, orlistat and resveratrol were shown to induce hydrolysis of amyloid-beta peptide after 10 days of incubation. All of the compounds were found to inhibit aggregation of amyloid-beta peptide as confirmed by both the ThT fluorescence assay and AFM. In addition, the compounds showed significant cytoprotective activity against amyloid-beta peptide (Aβ(1-42)) cell toxicity as shown by the MTT cell toxicity assay. The best inhibitor was orlistat, with complete cell protection, and then resveratrol. Vanillin derivatives showed similar activity, whilst the weakest inhibitor was amoxicillin.
Supervisor: Freeman, Sally Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available