Abstract
Purpose
Imaging of the 18-kDa translocator protein (TSPO) is a potential tool for examining microglial activation and neuroinflammation in early Alzheimer’s disease (AD). [18F]FEMPA is a novel high-affinity second-generation TSPO radioligand that has displayed suitable pharmacokinetic properties in preclinical studies. The aims of this study were to quantify the binding of [18F]FEMPA to TSPO in AD patients and controls and to investigate whether higher [18F]FEMPA binding in AD patients than in controls could be detected in vivo.
Methods
Ten AD patients (five men, five women; age 66.9 ± 7.3 years; MMSE score 25.5 ± 2.5) and seven controls (three men, four women; age 63.7 ± 7.2 years, MMSE score 29.3 ± 1.0) were studied using [18F]FEMPA at Turku (13 subjects) and at Karolinska Institutet (4 subjects). The in vitro binding affinity for TSPO was assessed using PBR28 in a competition assay with [3H]PK11195 in seven controls and eight AD patients. Cortical and subcortical regions of interest were examined. Quantification was performed using a two-tissue compartment model (2TCM) and Logan graphical analysis (GA). The outcome measure was the total distribution volume (V T). Repeated measures analysis of variance was used to assess the effect of group and TSPO binding status on V T.
Results
Five AD patients and four controls were high-affinity binders (HABs). Three AD patients and three controls were mixed-affinity binders. V T estimated with Logan GA was significantly correlated with V T estimated with the 2TCM in both controls (r = 0.97) and AD patients (r = 0.98) and was selected for the final analysis. Significantly higher V T was found in the medial temporal cortex in AD patients than in controls (p = 0.044) if the TSPO binding status was entered as a covariate. If only HABs were included, significantly higher V T was found in the medial and lateral temporal cortex, posterior cingulate, caudate, putamen, thalamus and cerebellum in AD patients than in controls (p < 0.05).
Conclusion
[18F]FEMPA seems to be a suitable radioligand for detecting increased TSPO binding in AD patients if their binding status is taken into account.
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Acknowledgments
This study was sponsored by Bayer Healthcare, Berlin, Germany. The work at Turku PET Centre and Karolinska Institutet was supported by the European Union’s Seventh Framework Programme (FP7/2007-2013) under grant agreement HEALTH-F2-2011-278850 (INMIND). The compound [18F]FEMPA is now part of the portfolio of the Piramal Imaging GmbH, Berlin, Germany. The authors thank the staff of the Turku PET Centre, the Karolinska Institutet PET Centre and the Karolinska University Hospital for technical support.
Conflicts of interest
Ray Valencia, Marcus Schultze-Mosgau, Andrea Thiele, Sonja Vollmer, Thomas Dyrks, Lutz Lehmann, Tobias Heinrich, Anja Hoffmann were employed by Bayer Healthcare, Berlin, Germany at the time of the study.
Financial support
Bayer Healthcare, Berlin, Germany; FP7/2007-2013 HEALTH-F2-2011-278850 (INMIND).
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Andrea Varrone and Vesa Oikonen contributed equally to this work.
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Varrone, A., Oikonen, V., Forsberg, A. et al. Positron emission tomography imaging of the 18-kDa translocator protein (TSPO) with [18F]FEMPA in Alzheimer’s disease patients and control subjects. Eur J Nucl Med Mol Imaging 42, 438–446 (2015). https://doi.org/10.1007/s00259-014-2955-8
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DOI: https://doi.org/10.1007/s00259-014-2955-8