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Brain mGluR5 in mice with amyloid beta pathology studied with in vivo [(11)C]ABP688 PET imaging and ex vivo immunoblotting
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Geriatrics.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Medicinal Chemistry, Preclinical PET-MRI Platform. PET Centre, Uppsala University Hospital, 751 85 Uppsala, Sweden.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Medicinal Chemistry, Preclinical PET-MRI Platform. Uppsala University Hospital, 751 85 Uppsala, SwedenUppsala University Hospital, 751 85 Uppsala, Sweden.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Medicinal Chemistry, Preclinical PET-MRI Platform. Uppsala University Hospital, 751 85 Uppsala, SwedenUppsala University Hospital, 751 85 Uppsala, Sweden.
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2017 (English)In: Neuropharmacology, ISSN 0028-3908, E-ISSN 1873-7064, Vol. 113, no Pt A, p. 293-300, article id S0028-3908(16)30459-2Article in journal (Refereed) Published
Abstract [en]

Alzheimer's disease (AD) is characterized by aggregation of amyloid beta (Aβ) into insoluble plaques. Intermediates, Aβ oligomers (Aβo), appear to be the mechanistic cause of disease. The de facto PET AD ligand, [(11)C]PIB, binds and visualizes Aβ plaque load, which does not correlate well with disease severity. Therefore, finding a dynamic target that changes with pathology progression in AD is of great interest. Aβo alter synaptic plasticity, inhibit long-term potentiation, and facilitate long-term depression; key mechanisms involved in memory and learning. In order to convey these neurotoxic effects, Aβo requires interaction with the metabotropic glutamate 5 receptor (mGluR5). The aim was to investigate in vivo mGluR5 changes in an Aβ pathology model using PET. Wild type C57/BL6 (wt) and AβPP transgenic mice (tg-ArcSwe), 4, 8, and 16 months old, were PET scanned with [(11)C]ABP688, which is highly specific to mGluR5, to investigate changes in mGluR5. Mouse brains were extracted postscan and mGluR5 and Aβ protofibril levels were assessed with immunoblotting and ELISA respectively. Receptor-dense brain regions (hippocampus, thalamus, and striatum) displayed higher [(11)C]ABP688 concentrations corresponding to mGluR5 expression pattern. Mice had similar uptake levels of [(11)C]ABP688 regardless of genotype or age. Immunoblotting revealed general decline in mGluR5 expression and elevated levels of mGluR5 in 16 months old tg-ArcSwe compared with wt mice. [(11)C]ABP688 could visualize mGluR5 in the mouse brain. In conclusion, mGluR5 levels were found to decrease with age and tended to be higher in tg-ArcSwe compared with wt mice, however these changes could not be quantified with PET.

Place, publisher, year, edition, pages
2017. Vol. 113, no Pt A, p. 293-300, article id S0028-3908(16)30459-2
Keyword [en]
Alzheimer's disease, PET, [(11)C]ABP688, mGluR5
National Category
Geriatrics Radiology, Nuclear Medicine and Medical Imaging Neurology Pharmacology and Toxicology
Identifiers
URN: urn:nbn:se:uu:diva-317721DOI: 10.1016/j.neuropharm.2016.10.009ISI: 000390502200028PubMedID: 27743932OAI: oai:DiVA.org:uu-317721DiVA, id: diva2:1082567
Available from: 2017-03-17 Created: 2017-03-17 Last updated: 2018-01-13Bibliographically approved
In thesis
1. Preclinical PET imaging of Alzheimer's disease progression
Open this publication in new window or tab >>Preclinical PET imaging of Alzheimer's disease progression
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Amyloid PET imaging with [11C]PIB enabled detection of Aβ for the first time in vivo. However, [11C]PIB is a small molecule that binds only the insoluble Aβ plaque. Rather, the soluble Aβ aggregates are considered the cause of Alzheimer’s disease (AD). As such, a more sensitive and specific PET tracer is needed for tracking longitudinal AD pathology.

Soluble Aβ aggregates likely interact with the metabotropic glutamate receptor 5 (mGluR5) to cause neurotoxic effects. However, with [11C]ABP688 PET we were unable to detect aberrant mGluR5 binding in AD mouse models, although we find elevated mGluR5 protein levels with immunoblotting.

Antibodies are highly specific large molecules that can bind specifically to soluble Aβ aggregates, thus they can be a good marker for AD pathology. Unfortunately, due to their large size they cannot cross the blood-brain barrier (BBB). However, it is possible to shuttle antibodies into the brain by taking advantage of endogenous transporter systems on the BBB. By creating bispecific antibodies binding both to soluble Aβ aggregates and to the transferrin receptor (BBB target), we successfully transported the antibody into the brain and could visually detect soluble Aβ aggregates with PET.

Recombinant expression further improved and optimized antibody design, creating smaller bispecific antibody-based constructs that had better pharmacokinetic properties allowing for earlier PET scanning (1 day instead of 3), and more sensitive signal.

Lastly, using TCO-tetrazine click chemistry, we indirectly labeled our antibodies with fluorine-18, and could successfully perform PET already 11 h post-injection with a fluorine-18 labeled antibody.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. p. 59
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1395
Keyword
Alzheimer's disease, transgenic mice, PET, antibody-based tracer, mGluR5, ABP688, di-scFv, amyloid-β
National Category
Neurosciences Pharmaceutical Sciences Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:uu:diva-333220 (URN)978-91-513-0151-8 (ISBN)
Public defence
2018-01-19, Rudbecksalen, Dag Hammarskjölds väg 20, Uppsala, 09:15 (English)
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Supervisors
Available from: 2017-12-21 Created: 2017-11-10 Last updated: 2018-03-08

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Fang, Xiaotian T.Eriksson, JonasAntoni, GunnarYngve, UlrikaCato, LindaLannfelt, LarsSehlin, DagSyvänen, Stina

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