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      • Record: found
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      [ 18F]FEBMP: Positron Emission Tomography Imaging of TSPO in a Model of Neuroinflammation in Rats, and in vitro Autoradiograms of the Human Brain

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          Abstract

          We evaluated the efficacy of 2-[5-(4-[ 18F]fluoroethoxy-2-oxo-1,3-benzoxazol-3(2 H)-yl)- N-methyl- N-phenylacetamide] ([ 18F]FEBMP) for positron emission tomography (PET) imaging of translocator protein (18 kDa, TSPO). Dissection was used to determine the distribution of [ 18F]FEBMP in mice, while small-animal PET and metabolite analysis were used for a rat model of focal cerebral ischemia. [ 18F]FEBMP showed high radioactivity uptake in mouse peripheral organs enriched with TSPO, and relatively high initial brain uptake (2.67 ± 0.12% ID/g). PET imaging revealed an increased accumulation of radioactivity in the infarcted striatum, with a maximum ratio of 3.20 ± 0.12, compared to non-injured striatum. Displacement with specific TSPO ligands lowered the accumulation levels in infarcts to those on the contralateral side. This suggests that the increased accumulation reflected TPSO-specific binding of [ 18F]FEBMP in vivo. Using a simplified reference tissue model, the binding potential on the infarcted area was 2.72 ± 0.27. Metabolite analysis in brain tissues showed that 83.2 ± 7.4% and 76.4 ± 2.1% of radioactivity was from intact [ 18F]FEBMP at 30 and 60 min, respectively, and that this ratio was higher than in plasma (8.6 ± 1.9% and 3.9 ± 1.1%, respectively). In vitro autoradiography on postmortem human brains showed that TSPO rs6971 polymorphism did not affect binding sites for [ 18F]FEBMP. These findings suggest that [ 18F]FEBMP is a promising new tool for visualization of neuroinflammation.

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          Reactive astrocytes overexpress TSPO and are detected by TSPO positron emission tomography imaging.

          Sonia Lavisse, Martine Guillermier, Anne-Sophie Hérard … (2012)
          Astrocytes and microglia become reactive under most brain pathological conditions, making this neuroinflammation process a surrogate marker of neuronal dysfunction. Neuroinflammation is associated with increased levels of translocator protein 18 kDa (TSPO) and binding sites for TSPO ligands. Positron emission tomography (PET) imaging of TSPO is thus commonly used to monitor neuroinflammation in preclinical and clinical studies. It is widely considered that TSPO PET signal reveals reactive microglia, although a few studies suggested a potential contribution of reactive astrocytes. Because astrocytes and microglia play very different roles, it is crucial to determine whether reactive astrocytes can also overexpress TSPO and yield to a detectable TSPO PET signal in vivo. We used a model of selective astrocyte activation through lentiviral gene transfer of the cytokine ciliary neurotrophic factor (CNTF) into the rat striatum, in the absence of neurodegeneration. CNTF induced an extensive activation of astrocytes, which overexpressed GFAP and become hypertrophic, whereas microglia displayed minimal increase in reactive markers. Two TSPO radioligands, [(18)F]DPA-714 [N,N-diethyl-2-(2-(4-(2-[(18)F]fluoroethoxy)phenyl)-5,7-dimethylpyrazolo[1,5-a]pyrimidin-3-yl)acetamide] and [(11)C]SSR180575 (7-chloro-N,N-dimethyl-5-[(11)C]methyl-4-oxo-3-phenyl-3,5-dihydro-4H-pyridazino[4,5-b]indole-1-acetamide), showed a significant binding in the lenti-CNTF-injected striatum that was saturated and displaced by PK11195 [N-methyl-N-(1-methylpropyl)-1-(2-chlorophenyl)-isoquinoline-3-carboxamide]. The volume of radioligand binding matched the GFAP immunopositive volume. TSPO mRNA levels were significantly increased, and TSPO protein was overexpressed by CNTF-activated astrocytes. We show that reactive astrocytes overexpress TSPO, yielding to a significant and selective binding of TSPO radioligands. Therefore, caution must be used when interpreting TSPO PET imaging in animals or patients because reactive astrocytes can contribute to the signal in addition to reactive microglia.
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            Mixed-affinity binding in humans with 18-kDa translocator protein ligands.

            David R J Owen, Leanna P. Matthews, Masahiro Fujita … (2010)
            11C-PBR28 PET can detect the 18-kDa translocator protein (TSPO) expressed within macrophages. However, quantitative evaluation of the signal in brain tissue from donors with multiple sclerosis (MS) shows that PBR28 binds the TSPO with high affinity (binding affinity [Ki], ∼4 nM), low affinity (Ki, ∼200 nM), or mixed affinity (2 sites with Ki, ∼4 nM and ∼300 nM). Our study tested whether similar binding behavior could be detected in brain tissue from donors with no history of neurologic disease, with TSPO-binding PET ligands other than 11C-PBR28, for TSPO present in peripheral blood, and with human brain PET data acquired in vivo with 11C-PBR28. The affinity of TSPO ligands was measured in the human brain postmortem from donors with a history of MS (n=13), donors without any history of neurologic disease (n=20), and in platelets from healthy volunteers (n=13). Binding potential estimates from thirty-five 11C-PBR28 PET scans from an independent sample of healthy volunteers were analyzed using a gaussian mixture model. Three binding affinity patterns were found in brains from subjects without neurologic disease in similar proportions to those reported previously from studies of MS brains. TSPO ligands showed substantial differences in affinity between subjects classified as high-affinity binders (HABs) and low-affinity binders (LABs). Differences in affinity between HABs and LABs are approximately 50-fold with PBR28, approximately 17-fold with PBR06, and approximately 4-fold with DAA1106, DPA713, and PBR111. Where differences in affinity between HABs and LABs were low (∼4-fold), distinct affinities were not resolvable in binding curves for mixed-affinity binders (MABs), which appeared to express 1 class of sites with an affinity approximately equal to the mean of those for HABs and LABs. Mixed-affinity binding was detected in platelets from an independent sample (HAB, 69%; MAB, 31%), although LABs were not detected. Analysis of 11C-PBR28 PET data was not inconsistent with the existence of distinct subpopulations of HABs, MABs, and LABs. With the exception of 11C-PK11195, all TSPO PET ligands in current clinical application recognize HABs, LABs, and MABs in brain tissue in vitro. Knowledge of subjects' binding patterns will be required to accurately quantify TSPO expression in vivo using PET.
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              In vivo radioligand binding to translocator protein correlates with severity of Alzheimer's disease.

              Robert B. Innis, N. Kimura, Joseph Snow … (2013)
              Neuroinflammation is a pathological hallmark of Alzheimer's disease, but its role in cognitive impairment and its course of development during the disease are largely unknown. To address these unknowns, we used positron emission tomography with (11)C-PBR28 to measure translocator protein 18 kDa (TSPO), a putative biomarker for inflammation. Patients with Alzheimer's disease, patients with mild cognitive impairment and older control subjects were also scanned with (11)C-Pittsburgh Compound B to measure amyloid burden. Twenty-nine amyloid-positive patients (19 Alzheimer's, 10 mild cognitive impairment) and 13 amyloid-negative control subjects were studied. The primary goal of this study was to determine whether TSPO binding is elevated in patients with Alzheimer's disease, and the secondary goal was to determine whether TSPO binding correlates with neuropsychological measures, grey matter volume, (11)C-Pittsburgh Compound B binding, or age of onset. Patients with Alzheimer's disease, but not those with mild cognitive impairment, had greater (11)C-PBR28 binding in cortical brain regions than controls. The largest differences were seen in the parietal and temporal cortices, with no difference in subcortical regions or cerebellum. (11)C-PBR28 binding inversely correlated with performance on Folstein Mini-Mental State Examination, Clinical Dementia Rating Scale Sum of Boxes, Logical Memory Immediate (Wechsler Memory Scale Third Edition), Trail Making part B and Block Design (Wechsler Adult Intelligence Scale Third Edition) tasks, with the largest correlations observed in the inferior parietal lobule. (11)C-PBR28 binding also inversely correlated with grey matter volume. Early-onset (<65 years) patients had greater (11)C-PBR28 binding than late-onset patients, and in parietal cortex and striatum (11)C-PBR28 binding correlated with lower age of onset. Partial volume corrected and uncorrected results were generally in agreement; however, the correlation between (11)C-PBR28 and (11)C-Pittsburgh Compound B binding was seen only after partial volume correction. The results suggest that neuroinflammation, indicated by increased (11)C-PBR28 binding to TSPO, occurs after conversion of mild cognitive impairment to Alzheimer's disease and worsens with disease progression. Greater inflammation may contribute to the precipitous disease course typically seen in early-onset patients. (11)C-PBR28 may be useful in longitudinal studies to mark the conversion from mild cognitive impairment or to assess response to experimental treatments of Alzheimer's disease.
              Article 0 comments Cited 119 times – based on 0 reviews     Review now
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                Author and article information

                Journal
                Journal ID (nlm-ta): Theranostics
                Journal ID (iso-abbrev): Theranostics
                Journal ID (publisher-id): thno
                Title: Theranostics
                Publisher: Ivyspring International Publisher (Sydney )
                ISSN (Electronic): 1838-7640
                Publication date Collection: 2015
                Publication date (Electronic): 26 May 2015
                Volume: 5
                Issue: 9
                Pages: 961-969
                Affiliations
                1. Molecular Imaging Centre, National Institute of Radiological Sciences, Chiba, Japan
                2. Division of Cyclotron and Radiopharmaceutical Sciences, Institute of Nuclear Medicine and Allied Sciences, Delhi, India
                3. Department of Nuclear Medicine, Nanjing Hospital, Affiliated to Nanjing Medical University, Nanjing, China .
                Author notes
                ✉ Corresponding author: Ming-Rong Zhang, PhD., Molecular Probe Program, Molecular Imaging Centre, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan. Phone: 81-43-382-3709; Fax: 81-43-206-3261; E-mail: zhang@ 123456nirs.go.jp . Feng Wang, PhD., Department of Nuclear Medicine, Nanjing Hospital, Affiliated to Nanjing Medical University, 68 Chanle Road, Nanjing 210006, China. Phone: 86-25-52271456. E-mail: fengwangcn@ 123456hotmail.com

                *These authors contributed equally to this work

                Competing Interests: All experiments were conducted in compliance with the ARRIVE guidelines. The authors have declared that no competing interest exists.

                Article
                Publisher ID: thnov05p0961
                DOI: 10.7150/thno.12027
                PMC ID: 4493534
                PubMed ID: 26155312
                SO-VID: c84a029c-07d0-4c2e-8a05-586843627856
                Copyright © © 2015 Ivyspring International Publisher. Reproduction is permitted for personal, noncommercial use, provided that the article is in whole, unmodified, and properly cited. See http://ivyspring.com/terms for terms and conditions.
                History
                Date received : 3 March 2015
                Date accepted : 9 May 2015
                Categories
                Subject: Research Paper

                ScienceOpen disciplines: Molecular medicine
                Keywords: [18f]febmp,translocator protein (18 kda),neuroinflammation,binding potential,rs6971 polymorphism
                Data availability:
                ScienceOpen disciplines: Molecular medicine
                Keywords: [18f]febmp, translocator protein (18 kda), neuroinflammation, binding potential, rs6971 polymorphism

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