Abstract
Inflammation is a pathophysiological hallmark of many diseases of the brain. Specific imaging of cells and molecules that contribute to cerebral inflammation is therefore highly desirable, both for research and in clinical application. The 18 kDa translocator protein (TSPO) has been established as a suitable target for the detection of activated microglia/macrophages. A number of novel TSPO ligands have been developed recently. Here, we evaluated the high affinity TSPO ligand DPA-714 as a marker of brain inflammation in two independent animal models. For the first time, the specificity of radiolabeled DPA-714 for activated microglia/macrophages was studied in a rat model of epilepsy (induced using Kainic acid) and in a mouse model of stroke (transient middle cerebral artery occlusion, tMCAO) using high-resolution autoradiography and immunohistochemistry. Additionally, cold-compound blocking experiments were performed and changes in blood-brain barrier (BBB) permeability were determined. Target-to-background ratios of 2 and 3 were achieved in lesioned vs. unaffected brain tissue in the epilepsy and tMCAO models, respectively. In both models, ligand uptake into the lesion corresponded well with the extent of Ox42- or Iba1-immunoreactive activated microglia/macrophages. In the epilepsy model, ligand uptake was almost completely blocked by pre-injection of DPA-714 and FEDAA1106, another high-affinity TSPO ligand. Ligand uptake was independent of the degree of BBB opening and lesion size in the stroke model. We provide further strong evidence that DPA-714 is a specific ligand to image activated microglia/macrophages in experimental models of brain inflammation.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Autoradiography
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Blood-Brain Barrier
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Carrier Proteins / metabolism*
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Cells, Cultured
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Disease Models, Animal*
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Epilepsy / chemically induced
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Epilepsy / complications*
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Epilepsy / pathology
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Fluorine Radioisotopes
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Immunoenzyme Techniques
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Inflammation / diagnosis*
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Inflammation / etiology
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Inflammation / metabolism
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Kainic Acid / toxicity
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Macrophages / immunology
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Macrophages / metabolism
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Macrophages / pathology
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Male
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Mice
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Mice, Inbred C57BL
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Microglia / immunology
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Microglia / metabolism
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Microglia / pathology
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Positron-Emission Tomography
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Pyrazoles* / metabolism
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Pyrimidines* / metabolism
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Radiopharmaceuticals
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Rats
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Rats, Sprague-Dawley
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Receptors, GABA / metabolism*
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Receptors, GABA-A / metabolism*
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Stroke / chemically induced
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Stroke / complications*
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Stroke / pathology
Substances
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Bzrp protein, mouse
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Carrier Proteins
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Fluorine Radioisotopes
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N,N-diethyl-2-(2-(4-(2-fluoroethoxy)phenyl)-5,7-dimethylpyrazolo(1,5-a)pyrimidin-3-yl)acetamide
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Pyrazoles
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Pyrimidines
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Radiopharmaceuticals
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Receptors, GABA
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Receptors, GABA-A
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Tspo protein, rat
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Kainic Acid
Grants and funding
This work was supported by the European Union's Seventh Framework Programme (FP7/2008–2013) under Grant Agreements 201024 and 202213 (European Stroke Network); the Deutsche Forschungsgemeinschaft (NeuroCure Cluster of Excellence, Exc 257); and the Bundesministerium für Bildung und Forschung (Center for Stroke Research Berlin, 01 EO 08 01) and the TSB grant entitled “Development of diagnostic markers for the diagnosis of stroke and establishment of a center for small animal imaging research at the Charité Berlin.” Furthermore, this study was supported and conducted together with Bayer Pharma AG and relevant parties are co-authors. Thomas Dyrks, Andrea Thiele, Keith Graham, Violetta Sudmann are employees of Bayer Pharma AG, Berlin, Germany and they hereby declare that they participated in the preclinical preparation for this study as well as the manuscript preparation. They have seen and approved the final version. None of the products in the manuscript are under development or seeking patent approval. All the other funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.