Abnormal [18 F]NIFENE binding in transgenic 5xFAD mouse model of Alzheimer's disease: In vivo PET/CT imaging studies of α4ß2* nicotinic acetylcholinergic receptors and in vitro correlations with Aß plaques.

Since cholinergic dysfunction has been implicated in Alzheimer's disease (AD), the effects of Aß plaques on nicotinic acetylcholine receptors (nAChRs) α4ß2* subtype were studied using the transgenic 5xFAD mouse model of AD. Using the PET radiotracer [18 F]nifene for α4ß2* nAChRs, in vitro autoradiography and in vivo PET/CT studies in 5xFAD mice were carried out and compared with wild-type (C57BL/6) mice. Ratios of [18 F]nifene binding in brain regions versus cerebellum (CB) in 5xFAD mice brains were for thalamus (TH) = 17, hippocampus-subiculum = 7, frontal cortex (FC) = 5.5, and striatum = 4.7. [125 I]IBETA and immunohistochemistry (IHC) in 5xFAD brain slices confirmed Aß plaques. Nicotine and acetylcholine displaced [18 F]nifene in 5xFAD mice (IC50 nicotine = 31-73 nM; ACh = 38-83 nM) and C57BL/6 (IC50 nicotine = 16-18 nM; ACh = 34-55 nM). Average [18 F]nifene SUVR (CB as reference) in 5xFAD mice was significantly higher in FC = 3.04 compared to C57BL/6 mice FC = 1.92 (p = .001), whereas TH difference between 5xFAD mice (SUVR = 2.58) and C57BL/6 mice (SUVR = 2.38) was not significant. Nicotine-induced dissociation half life (t1/2 ) of [18 F]nifene for TH were 37 min for 5xFAD mice and 26 min for C57BL/6 mice. Dissociation half life  for FC in C57BL/6 mice was 77 min , while no dissociation of [18 F]nifene occurred in the medial prefrontal cortex (mFC) of 5xFAD mice. Coregistration of [18 F]nifene PET with MR suggested that the mPFC, and anterior cingulate (AC) regions exhibited high uptake in 5xFAD mice compared to C57BL/6 mice. Ex vivo [18 F]nifene and in vitro [125 I]IBETA Aß plaque autoradiography after in vivo PET/CT scan of 5xFAD mouse brain were moderately correlated (r2 = 0.68). In conclusion, 5xFAD mice showed increased non-displaceable [18 F]nifene binding in mPFC.

Measurement of Aß Amyloid Plaques and Tau Protein in Postmortem Human Alzheimer's Disease Brain by Autoradiography Using [18F]Flotaza, [125I]IBETA, [124/125I]IPPI and Immunohistochemistry Analysis Using QuPath.

High-resolution scans of immunohistochemical (IHC) stains of Alzheimer's disease (AD) brain slices and radioligand autoradiography both provide information about the distribution of Aß plaques and Tau, the two common proteinopathies in AD. Accurate assessment of the amount and regional location of Aß plaques and Tau is essential to understand the progression of AD pathology. Our goal was to develop a quantitative method for the analysis of IHC-autoradiography images. Postmortem anterior cingulate (AC) and corpus callosum (CC) from AD and control (CN) subjects were IHC stained with anti-Aß for Aß plaques and autoradiography with [18F]flotaza and [125I]IBETA for Aß plaques. For Tau, [124I]IPPI, a new radiotracer, was synthesized and evaluated in the AD brain. For Tau imaging, brain slices were IHC stained with anti-Tau and autoradiography using [125I]IPPI and [124I]IPPI. Annotations for Aß plaques and Tau using QuPath for training and pixel classifiers were generated to measure the percent of the area of Aß plaques and Tau in each slice. The binding of [124I]IPPI was observed in all AD brains with an AC/CC ratio > 10. Selectivity to Tau was shown by blocking [124I]IPPI with MK-6240. Percent positivity for Aß plaques was 4-15%, and for Tau, it was 1.3 to 35%. All IHC Aß plaque-positive subjects showed [18F]flotaza and [125I]IBETA binding with a positive linear correlation (r2 > 0.45). Tau-positive subjects showed [124/125I]IPPI binding with a stronger positive linear correlation (r2 > 0.80). This quantitative IHC-autoradiography approach provides an accurate measurement of Aß plaques and Tau within and across subjects.