Amnestic mild cognitive impairment (aMCI) is defined as a transitional state between normal aging and Alzheimer's disease (AD). Given the replicated finding of increased microglial activation in AD, we sought to investigate whether microglial activation is also elevated in aMCI and whether it is related to amyloid beta (Aβ) burden in-vivo . Eleven aMCI participants and 14 healthy volunteers completed positron emission tomography (PET) scans with [18F]-FEPPA and [11C]-PIB. Given the known sensitivity in affinity of second-generation TSPO radioligands, participants were genotyped for the TSPO polymorphism and only high-affinity binders were included. Dynamic [18F]-FEPPA PET images were analyzed using the 2-tissue compartment model with arterial plasma input function. Additionally, a supplementary method, the standardized uptake value ratio (SUVR), was explored. [11C]-PIB PET images were analyzed using the Logan graphical method. aMCI participants had significantly higher [11C]-PIB binding in the cortical regions. No significant differences in [18F]-FEPPA binding were observed between aMCI participants and healthy volunteers. In the aMCI group, [18F]-FEPPA and [11C]-PIB bindings were correlated in the hippocampus. There were no correlations between our PET measures and cognition. Our findings demonstrate that while Aβ burden is evident in the aMCI stage, microglial activation may not be present.
Keywords: Alzheimer’s disease; amyloid; mild cognitive impairment; neuroinflammation; positron emission tomography.