Evaluation of CLINDE as potent translocator protein (18 kDa) SPECT radiotracer reflecting the degree of neuroinflammation in a rat model of microglial activation.
BACKGROUND
The translocator protein (TSPO; 18 kDa), the new name of the peripheral-type benzodiazepine receptor, is localised in mitochondria of glial cells and expressed in very low concentrations in normal brain. Their expression rises after microglial activation following brain injury. Accordingly, TSPO are potential targets to evaluate neuroinflammatory changes in a variety of CNS disorders.


OBJECTIVE
To date, only a few effective tools are available to explore TSPO by SPECT. We characterised here 6-chloro-2-(4'iodophenyl)-3-(N,N-diethyl)-imidazo[1,2-a]pyridine-3-acetamide or CLINDE in a rat model with different stages of excitotoxic lesion.


METHODS
Excitotoxicity was induced in male Wistar rats by unilateral intrastriatal injection of different amounts of quinolinic acid (75, 150 or 300 nmol). Six days later, two groups of rats (n = 5-6/group) were i.v. injected with [(125)I]-CLINDE (0.4 MBq); one group being pre-injected with PK11195 (5 mg/kg). Brains were removed 30 min after tracer injection and the radioactivity of cerebral areas measured. Complementary ex vivo autoradiography, in vitro autoradiography ([(3)H]-PK11195) and immunohistochemical studies (OX-42) were performed on brain sections.


RESULTS
In the control group, [(125)I]-CLINDE binding was significantly higher (p < 0.001) in lesioned than that in intact side. This binding disappeared in rats pre-treated with PK11195 (p < 0.001), showing specific binding of CLINDE to TSPO. Ex vivo and in vitro autoradiographic studies and immunohistochemistry were consistent with this, revealing a spatial correspondence between radioactivity signal and activated microglia. Regression analysis yielded a positive relation between the ligand binding and the degree of neuroinflammation.


CONCLUSIONS
These results demonstrate that CLINDE is suitable for TSPO in vivo SPECT imaging to explore their involvement in neurodegenerative disorders associated with microglial activation.
Arlicot
Nicolas
N
Inserm, U930, Tours 37000, France.
Katsifis
Andrew
A
Garreau
Lucette
L
Mattner
Filomena
F
Vergote
Jackie
J
Duval
Stéphanie
S
Kousignian
Isabelle
I
Bodard
Sylvie
S
Guilloteau
Denis
D
Chalon
Sylvie
S
D000818:Animals; D001345:Autoradiography; D001921:Brain / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000493:pharmacokinetics; D004195:Disease Models, Animal; D007150:Immunohistochemistry; D007249:Inflammation / Q000000981:diagnostic imaging* / Q000378:metabolism* / Q000473:pathology; D007546:Isoquinolines; D008297:Male; D017628:Microglia / Q000378:metabolism*; D011859:Radiography; D051381:Rats; D018079:Receptors, GABA / Q000378:metabolism*; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon
C504993:6-chloro-2-(4'-iodophenyl)-3-(N,N-diethyl)imidazo(1,2-a)pyridine-3-acetamide; D019086:Bridged Bicyclo Compounds, Heterocyclic; D007546:Isoquinolines; D018079:Receptors, GABA; C499229:TSPO protein, human; C037850:PK 11195