title: Positron emission tomography imaging of the 18-kDa translocator protein (TSPO) with [18F]FEMPA in Alzheimer's disease patients and control subjects.
abstract: OBJECTIVE
  Imaging of the 18-kDa translocator protein (TSPO) is a potential tool for examining microglial activation and neuroinflammation in early Alzheimer's disease (AD). [(18)F]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 [(18)F]FEMPA to TSPO in AD patients and controls and to investigate whether higher [(18)F]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 [(18)F]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 [(3)H]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).
  
  
  CONCLUSIONS
  [(18)F]FEMPA seems to be a suitable radioligand for detecting increased TSPO binding in AD patients if their binding status is taken into account.
authors.affiliation: Karolinska Institutet, Department of Clinical Neuroscience, Centre for Psychiatry Research, Stockholm, Sweden, andrea.varrone@ki.se.
authors.forename: Andrea
authors.initials: A
authors.lastname: Varrone
authors.forename: Vesa
authors.initials: V
authors.lastname: Oikonen
authors.forename: Anton
authors.initials: A
authors.lastname: Forsberg
authors.forename: Juho
authors.initials: J
authors.lastname: Joutsa
authors.forename: Akihiro
authors.initials: A
authors.lastname: Takano
authors.forename: Olof
authors.initials: O
authors.lastname: Solin
authors.forename: Merja
authors.initials: M
authors.lastname: Haaparanta-Solin
authors.forename: Sangram
authors.initials: S
authors.lastname: Nag
authors.forename: Ryuji
authors.initials: R
authors.lastname: Nakao
authors.forename: Nabil
authors.initials: N
authors.lastname: Al-Tawil
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Wells
authors.forename: Eugenii A
authors.initials: EA
authors.lastname: Rabiner
authors.forename: Ray
authors.initials: R
authors.lastname: Valencia
authors.forename: Marcus
authors.initials: M
authors.lastname: Schultze-Mosgau
authors.forename: Andrea
authors.initials: A
authors.lastname: Thiele
authors.forename: Sonja
authors.initials: S
authors.lastname: Vollmer
authors.forename: Thomas
authors.initials: T
authors.lastname: Dyrks
authors.forename: Lutz
authors.initials: L
authors.lastname: Lehmann
authors.forename: Tobias
authors.initials: T
authors.lastname: Heinrich
authors.forename: Anja
authors.initials: A
authors.lastname: Hoffmann
authors.forename: Agneta
authors.initials: A
authors.lastname: Nordberg
authors.forename: Christer
authors.initials: C
authors.lastname: Halldin
authors.forename: Juha O
authors.initials: JO
authors.lastname: Rinne
mesh_terms: D000368:Aged; D000544:Alzheimer Disease / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D006845:Hydrocarbons, Fluorinated / Q000009:adverse effects / Q000493:pharmacokinetics; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography; D011485:Protein Binding; D011725:Pyridines / Q000009:adverse effects / Q000493:pharmacokinetics; D019275:Radiopharmaceuticals / Q000009:adverse effects / Q000493:pharmacokinetics; D018079:Receptors, GABA / Q000378:metabolism*
chemical_list: C000602344:(18F)FEMPA; D006845:Hydrocarbons, Fluorinated; D011725:Pyridines; D019275:Radiopharmaceuticals; D018079:Receptors, GABA; C499229:TSPO protein, human