Does inflammation precede tau aggregation in early Alzheimer's disease? A PET study

Peter Parbo, Rola Ismail, Michael Sommerauer, Morten G Stokholm, Allan K. Hansen, Kim V. Hansen, Ali Amidi, Jeppe L. Schaldemose, Hanne Gottrup, Hans Braendgaard, Simon F Eskildsen, Per Borghammer, Rainer Hinz, Joel Aanerud, David J. Brooks

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Abstract

Objective: Our aim was to assess with positron emission tomography (PET) the temporal and spatial inter-relationships between levels of cortical microglial activation and the aggregated amyloid-β and tau load in mild cognitive impairment (MCI) and early Alzheimer's disease (AD).

Methods: Six clinically probable AD and 20 MCI subjects had inflammation (11C-(R)-PK11195), amyloid (11C-PiB) and tau (18F-flortaucipir) PET, magnetic resonance imaging (MRI) and a neuropsychological assessment. Parametric images of tracer binding were interrogated at a voxel level and by region of interest analyses.

Results: 55% of MCI and 83% of AD subjects had a high amyloid-β load. We have previously reported that clusters of correlated amyloid and inflammation levels are present in cortex. Here we found no correlation between levels of inflammation (11C-(R)-PK11195 BPND) and tau (18F-flortaucipir SUVR) or MMSE scores in high amyloid-β cases.

Interpretation: While correlated levels of amyloid-β and inflammation can be seen in MCI, we did not detect an association between levels of cortical tau tangles and inflammation in our series of high amyloid-β cases. High levels of inflammation could be seen in amyloid-β positive MCI cases where 18F-flortaucipir signals were low suggesting microglial activation precedes tau tangle formation. Inflammation levels were higher in high amyloid-β MCI than in early AD cases, compatible with it initially playing a protective role.
Original languageEnglish
JournalNeurobiology of disease
Volume117
Early online date11 Jun 2018
DOIs
Publication statusPublished - Sept 2018

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