Reduction in [18F]Nifene Binding, a PET imaging Probe for α4β2* Nicotinic acetylcholinergic receptors in Hippocampus-Subiculum of postmortem human Alzheimer’s disease brain

Abstract

Nicotinic acetylcholinergic receptors (nAChRs), including the α4β2* subtype are involved in cognition, learning and memory and may be adversely affected in Alzheimer’s disease (AD). In our efforts to consider translational use of [¹⁸F]nifene PET in AD, we report quantitative autoradiographic evaluation of α4β2* nAChRs using hippocampus-subiculum (HP-SUB) from cognitively normal (CN) and AD subjects. Brain slices were incubated in [¹⁸F]nifene for α4β2* nAChRs and adjacent sections were tested with [¹⁸F]flotaza for Aβ plaques and [¹²⁵I]IPPI for tau. Anti-Aβ and anti-tau immunostaining were carried out on adjacent slices. Regions of interest were drawn and binding of [¹⁸F]nifene, [¹⁸F]flotaza and [¹²⁵I]IPPI were quantified. All CN subjects exhibited significant [¹⁸F]nifene binding in the HP-SUB regions. Average [¹⁸F]nifene ratios of SUB to HP was 1.9, suggesting higher α4β2* nAChRs in the SUB versus HP regions. [¹⁸F]nifene binding did not change with aging in the female subjects, while the male subjects exhibited a weak positive correlation. There was a significant decrease in the binding of [¹⁸F]nifene in AD subjects compared to CN. Braak stage comparisons showed a decrease of [¹⁸F]nifene in stages V and VI, while [¹⁸F]flotaza and [¹²⁵I]IPPI increased significantly. A negative correlation was observed between [¹⁸F]nifene vs [¹⁸F]flotaza and [¹⁸F]nifene vs [¹²⁵I]IPPI across Braak stages I-VI. These findings suggest that α4β2* nAChR availability was effectively measured by [¹⁸F]nifene in the HP-SUB and was adversely affected by the presence of Aβ plaques and tau.