Localized Accumulation of Tau without Amyloid-Beta in Aged Brains Measured with [11C]PBB3 and [11C]Pib Positron Emission Tomography

Objective: Different regional specificity in tau accumulation is well known in Alzheimer’s disease (AD) brains. However, little is known about such distribution in aging brains and mild cognitive impairment (MCI) brains. Methods: Cognitive functions and regional accumulation of tau and amyloid β (Aβ) were evaluated in 13 healthy controls (HCs), 3 patients with MCI and 4 AD patients. Tau and Aβ accumulation was semi-quantitatively measured with positron emission tomography (PET) using [11C]pyridinyl-butadienyl-benzothiazole 3 (PBB3) and [11C]Pittsburgh compound-B (PiB). Results: Age-dependent accumulation of tau was found in all predetermined regions characteristic of AD, especially in the parahippocampal gyrus, lateral temporal cortex, frontal cortex, and posterior cingulate gyrus, where age-dependency was statistically significant. In contrast, age-dependency in accumulation of Aβ was not observed in most regions assessed in HC. Moreover, the accumulation of tau in regions characteristic of AD in MCI patients was higher than that in HC, whereas tau accumulation was highest and statistically significant in AD patients. Unlike HC, the accumulation of tau was accompanied by that of Aβ in patients with MCI and AD. Conclusion: Mild and age-dependent accumulation of tau without Aβ was found in AD-related areas in aging brains. Considering age as a major risk for AD, higher accumulation of tau may trigger the neurodegenerative process of AD.