Translocator protein (18 kDa), a potential molecular imaging biomarker for non-invasively distinguishing non-alcoholic fatty liver disease.
OBJECTIVE
Mitochondrial dysfunction is responsible for liver damage and disease progression in non-alcoholic fatty liver disease (NAFLD). Translocator protein (18 kDa) (TSPO), a mitochondrial transmembrane protein, plays important roles in modulating mitochondrial function. This study explored whether TSPO can be used as an imaging biomarker of non-invasive diagnosis and staging of NAFLD, monitored using positron emission tomography (PET) with a TSPO radioligand [(18)F]FEDAC.


METHODS
PET with [(18)F]FEDAC, non-enhanced computerized tomography (CT), autoradiography, histopathology, and gene analysis were performed to evaluate and quantify TSPO levels and NAFLD progression in methionine and choline-deficient diet-fed mice. Correlations were analyzed between uptake ratio of radioactivity and NAFLD activity score (NAS) in the liver.


RESULTS
Uptake of [(18)F]FEDAC obviously increased with disease progression from simple steatosis to non-alcoholic steatohepatitis (NASH) (p<0.01). A close correlation was identified between [(18)F]FEDAC uptake ratio and NAS in the liver (Pearson's r=0.922, p=0.000). Specific binding of [(18)F]FEDAC to TSPO in the NAFLD livers was assessed in competition studies with the unlabelled TSPO-selective ligand PK11195. Autoradiography and histopathology confirmed the PET imaging results. Further, the mRNA levels of the functional macromolecular signaling complex composed of TSPO were obviously higher compared to controls.


CONCLUSIONS
TSPO expression increases in NAFLD and closely correlates with NAFLD progression. TSPO as a specific molecular imaging biomarker may open a novel avenue for non-invasive, reliable, and quantitative diagnosis and staging of NAFLD.
Molecular Imaging Center, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan.
Lin
L
Xie
Joji
J
Yui
Akiko
A
Hatori
Tomoteru
T
Yamasaki
Katsushi
K
Kumata
Hidekatsu
H
Wakizaka
Yuichiro
Y
Yoshida
Masayuki
M
Fujinaga
Kazunori
K
Kawamura
Ming-Rong
MR
Zhang
D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D004195:Disease Models, Animal; D018450:Disease Progression; D005234:Fatty Liver / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology; D005462:Fluorine Radioisotopes; D008099:Liver / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D065626:Non-alcoholic Fatty Liver Disease; D049268:Positron-Emission Tomography / Q000379:methods*; D018079:Receptors, GABA / Q000378:metabolism*; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D014057:Tomography, X-Ray Computed
D015415:Biomarkers; D005462:Fluorine Radioisotopes; D018079:Receptors, GABA; C499229:TSPO protein, human