title: Stabilization of nontoxic Aβ-oligomers: insights into the mechanism of action of hydroxyquinolines in Alzheimer's disease.
abstract: The extracellular accumulation of amyloid β (Aβ) peptides is characteristic of Alzheimer's disease (AD). However, formation of diffusible, oligomeric forms of Aβ, both on and off pathways to amyloid fibrils, is thought to include neurotoxic species responsible for synaptic loss and neurodegeneration, rather than polymeric amyloid aggregates. The 8-hydroxyquinolines (8-HQ) clioquinol (CQ) and PBT2 were developed for their ability to inhibit metal-mediated generation of reactive oxygen species from Aβ:Cu complexes and have both undergone preclinical and Phase II clinical development for the treatment of AD. Their respective modes of action are not fully understood and may include both inhibition of Aβ fibrillar polymerization and direct depolymerization of existing Aβ fibrils. In the present study, we find that CQ and PBT2 can interact directly with Aβ and affect its propensity to aggregate. Using a combination of biophysical techniques, we demonstrate that, in the presence of these 8-HQs and in the absence of metal ions, Aβ associates with two 8-HQ molecules and forms a dimer. Furthermore, 8-HQ bind Aβ with an affinity of 1-10 μm and suppress the formation of large (>30 kDa) oligomers. The stabilized low molecular weight species are nontoxic. Treatment with 8-HQs also reduces the levels of in vivo soluble oligomers in a Caenorhabditis elegans model of Aβ toxicity. We propose that 8-HQs possess an additional mechanism of action that neutralizes neurotoxic Aβ oligomer formation through stabilization of small (dimeric) nontoxic Aβ conformers.
authors.affiliation: Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville 3052, Victoria, Australia, tmryan@unimelb.edu.au.
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Ryan
authors.affiliation: Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville 3052, Victoria, Australia.
authors.forename: Blaine R
authors.initials: BR
authors.lastname: Roberts
authors.affiliation: Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville 3052, Victoria, Australia.
authors.forename: Gawain
authors.initials: G
authors.lastname: McColl
authors.affiliation: Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville 3052, Victoria, Australia, Elemental Bio-imaging Facility, University of Technology Sydney, Broadway 2007, New South Wales, Australia.
authors.forename: Dominic J
authors.identifier: http://orcid.org/0000-0002-5922-7643
authors.initials: DJ
authors.lastname: Hare
authors.affiliation: Elemental Bio-imaging Facility, University of Technology Sydney, Broadway 2007, New South Wales, Australia.
authors.forename: Philip A
authors.initials: PA
authors.lastname: Doble
authors.affiliation: Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville 3052, Victoria, Australia.
authors.forename: Qiao-Xin
authors.initials: QX
authors.lastname: Li
authors.affiliation: Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville 3052, Victoria, Australia.
authors.forename: Monica
authors.initials: M
authors.lastname: Lind
authors.affiliation: Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville 3052, Victoria, Australia.
authors.forename: Anne M
authors.initials: AM
authors.lastname: Roberts
authors.affiliation: Australian Synchrotron, Clayton 3168, Victoria, Australia.
authors.forename: Haydyn D T
authors.identifier: http://orcid.org/0000-0002-5664-744X
authors.initials: HD
authors.lastname: Mertens
authors.affiliation: Australian Synchrotron, Clayton 3168, Victoria, Australia.
authors.forename: Nigel
authors.initials: N
authors.lastname: Kirby
authors.affiliation: Department of Pharmacology, University of Melbourne, Parkville 3052, Victoria, Australia.
authors.forename: Chi L L
authors.initials: CL
authors.lastname: Pham
authors.affiliation: Bio21 Molecular Science and Technology Institute, University of Melbourne, Parkville 3052, Victoria, Australia, and School of Chemistry, University of Melbourne, Parkville 3052, Victoria, Australia.
authors.forename: Mark G
authors.initials: MG
authors.lastname: Hinds
authors.affiliation: Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville 3052, Victoria, Australia.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Adlard
authors.affiliation: Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville 3052, Victoria, Australia, Department of Pharmacology, University of Melbourne, Parkville 3052, Victoria, Australia, Bio21 Molecular Science and Technology Institute, University of Melbourne, Parkville 3052, Victoria, Australia, and.
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Barnham
authors.affiliation: Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville 3052, Victoria, Australia.
authors.forename: Cyril C
authors.initials: CC
authors.lastname: Curtain
authors.affiliation: Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville 3052, Victoria, Australia.
authors.forename: Colin L
authors.initials: CL
authors.lastname: Masters
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism*; D016229:Amyloid beta-Peptides / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D052160:Benzothiazoles; D001703:Biophysics; D017173:Caenorhabditis elegans; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D002850:Chromatography, Gel; D007464:Clioquinol / Q000031:analogs & derivatives / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D006912:Hydroxyquinolines / Q000378:metabolism*; D051379:Mice; D008854:Microscopy, Electron; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D011485:Protein Binding / Q000187:drug effects; D053838:Scattering, Small Angle; D013844:Thiazoles / Q000378:metabolism
chemical_list: D016229:Amyloid beta-Peptides; D052160:Benzothiazoles; D006912:Hydroxyquinolines; C531955:PBT2 compound; D010446:Peptide Fragments; D013844:Thiazoles; C075222:amyloid beta-protein (1-42); C009462:thioflavin T; D007464:Clioquinol
keywords: Alzheimer's disease; PBT2; amyloid beta peptide; hydroxyquinoline; oligomer; toxicity