Measurement of [123I]FP-CIT binding to the dopamine transporter (DAT) in healthy mouse striatum using dedicated small animal SPECT imaging: feasibility, optimization and validation.
BACKGROUND
In-vivo imaging of dopamine transporter (DAT), a reliable marker of degeneration of nigrostriatal dopaminergic innervation, has gained increasing interest in preclinical neurodegenerative research for studying disease mechanisms and testing new therapeutic strategies. We assessed the feasibility and the reliability of in vivo and ex vivo quantification of Methyl (3S,4S,5R)-8-(3-fluoropropyl)-3-(4-iodophenyl)-8-azabicyclo[3.2.1]octane-4-carboxylate ([123I]FP-CIT) binding to striatal DAT sites in mouse brain.


METHODS
Dedicated small animal single-photon emission computed tomography (SPECT) images of [123I]FP-CIT binding were obtained in 3 groups of healthy mice: untreated (N.=6), pre-treated with lugol solution (N.=4), and pre-treated with selective dopamine transporter uptake inhibitor GBR12909 (N.=4). Ex-vivo autoradiography studies were performed at the end of SPECT studies with phosphor image system in 4 out of the 6 untreated mice and in all mice pre-treated with lugol. Regions of interest were defined over the striatum. The specific binding (SB) was calculated using the cerebral cortex as reference region.


RESULTS
SPECT images in untreated mice showed high [123I]FP-CIT uptake in the striatum and extracerebral regions. Lugol pretreatment improved striatal images quality decreasing salivary and thyroid glands uptake. SB was higher (P<0.0001) in mice pre-treated with lugol (5.97±0.60) than in untreated mice (2.25±0.28). Autoradiography showed similar SB findings in untreated (2.27±0.33) and lugol-treated (4.27±0.57) mice (P<0.0001). In-vivo striatal 123I-FP-CIT SB and ex-vivo striatal 123I-FP-CIT SB were significantly correlated (r=0.87; P<0.0001). SPECT competition studies showed a significant (P<0.0001) reduction of [123I]FP-CIT SB in the striatum after GBR12909.


CONCLUSIONS
We demonstrated the feasibility of [123I]FP-CIT imaging of the normal mouse brain using small-animal SPECT without pinhole collimators. The reliability of quantitative measurement of striatal [123I]FP-CIT SB is supported by competition studies showing measurable inhibition of uptake induced by GBR12909 and by the strong correlation between in vivo and ex vivo striatal [123I]FP-CIT SB. Our data also demonstrate that pre-treatment with lugol might improve striatal [123I]FP-CIT SB in mice.
Department of Advanced Biomedical Sciences, Federico II University of Naples, Naples, Italy - adegreco@unina.it.|Institute of Biostructures and Bioimages CNR, Naples, Italy - adegreco@unina.it.|Ceinge, Advanced Biotechnologies, Scarl, Naples, Italy - adegreco@unina.it.
Adelaide
A
Greco
Institute of Biostructures and Bioimages CNR, Naples, Italy.
Antonella
A
Zannetti
Institute of Biostructures and Bioimages CNR, Naples, Italy.
Sabina
S
Pappatà
Institute of Biostructures and Bioimages CNR, Naples, Italy.
Sandra
S
Albanese
Institute of Biostructures and Bioimages CNR, Naples, Italy.
Anna R
AR
Coda
Institute of Biostructures and Bioimages CNR, Naples, Italy.
Monica
M
Ragucci
Institute of Biostructures and Bioimages CNR, Naples, Italy.
Anna
A
Nardelli
Department of Advanced Biomedical Sciences, Federico II University of Naples, Naples, Italy.|Ceinge, Advanced Biotechnologies, Scarl, Naples, Italy.
Arturo
A
Brunetti
Department of Advanced Biomedical Sciences, Federico II University of Naples, Naples, Italy.
Alberto
A
Cuocolo
IRCCS, SDN, Naples, Italy.
Marco
M
Salvatore
D000818:Animals; D001692:Biological Transport; D004298:Dopamine / Q000378:metabolism; D050483:Dopamine Plasma Membrane Transport Proteins / Q000378:metabolism*; D005240:Feasibility Studies; D051379:Mice; D017072:Neostriatum / Q000000981:diagnostic imaging* / Q000378:metabolism*; D011485:Protein Binding; D015203:Reproducibility of Results; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*; D014326:Tropanes / Q000378:metabolism*
D050483:Dopamine Plasma Membrane Transport Proteins; D014326:Tropanes; C087552:2-carbomethoxy-8-(3-fluoropropyl)-3-(4-iodophenyl)tropane; D004298:Dopamine