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Nerella SG, Michaelides M, Minamimoto T, Innis RB, Pike VW, Eldridge MAG. PET reporter systems for the brain. Trends Neurosci 2023; 46:941-952. [PMID: 37734962 PMCID: PMC10592100 DOI: 10.1016/j.tins.2023.08.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2023] [Revised: 07/18/2023] [Accepted: 08/23/2023] [Indexed: 09/23/2023]
Abstract
Positron emission tomography (PET) can be used as a noninvasive method to longitudinally monitor and quantify the expression of proteins in the brain in vivo. It can be used to monitor changes in biomarkers of mental health disorders, and to assess therapeutic interventions such as stem cell and molecular genetic therapies. The utility of PET monitoring depends on the availability of a radiotracer with good central nervous system (CNS) penetration and high selectivity for the target protein. This review evaluates existing methods for the visualization of reporter proteins and/or protein function using PET imaging, focusing on engineered systems, and discusses possible approaches for future success in the development of high-sensitivity and high-specificity PET reporter systems for the brain.
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Affiliation(s)
- Sridhar Goud Nerella
- Molecular Imaging Branch, National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892, USA.
| | - Michael Michaelides
- Biobehavioral Imaging and Molecular Neuropsychopharmacology Unit, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD 21224, USA
| | - Takafumi Minamimoto
- Department of Functional Brain Imaging, National Institutes for Quantum Science and Technology, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan
| | - Robert B Innis
- Molecular Imaging Branch, National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892, USA
| | - Victor W Pike
- Molecular Imaging Branch, National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892, USA
| | - Mark A G Eldridge
- Laboratory of Neuropsychology, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA.
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2
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Frau R, Devoto P, Aroni S, Saba P, Sagheddu C, Siddi C, Santoni M, Carli M, Gessa GL. The potent α 2-adrenoceptor antagonist RS 79948 also inhibits dopamine D 2 -receptors: Comparison with atipamezole and raclopride. Neuropharmacology 2022; 217:109192. [PMID: 35850212 DOI: 10.1016/j.neuropharm.2022.109192] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2021] [Revised: 07/08/2022] [Accepted: 07/11/2022] [Indexed: 11/16/2022]
Abstract
Neurochemical, electrophysiological and behavioral evidence indicate that the potent α2-adrenoceptor antagonist RS 79948 is also a dopamine (DA) D2 receptor antagonist. Thus, results from ligand binding and adenylate cyclase activity indicate that RS 79948 binds to D2 receptors and antagonized D2 receptor-mediated inhibition of cAMP synthesis at nanomolar concentrations. RESULTS: from microdialysis indicated that RS 79948 shared with the selective α2-adrenergic antagonist atipamezole the ability to increase the co-release of DA and norepinephrine (NE) from noradrenergic terminals in the medial prefrontal cortex (mPFC), except that RS 79948-induced DA release persisted after noradrenergic denervation, unlike atipamezole effect, indicating that RS 79948 releases DA from dopaminergic terminals as well. Similarly to the D2 antagonist raclopride, but unlike atipamezole, RS 79948 increased extracellular DA and DOPAC in the caudate nucleus. Electrophysiological results indicate that RS 79948 shared with raclopride the ability to activate the firing of ventral tegmental area (VTA) DA neurons, while atipamezole was ineffective. RESULTS: from behavioral studies indicated that RS 79948 exerted effects mediated by independent, cooperative and contrasting inhibition of α2-and D2 receptors. Thus, RS 79948, but not atipamezole, prevented D2-autoreceptor mediated hypomotility produced by a small dose of quinpirole. RS 79948 potentiated, more effectively than atipamezole, quinpirole-induced motor stimulation. RS 79948 antagonized, less effectively than atipamezole, raclopride-induced catalepsy. Future studies should clarify if the dual α2-adrenoceptor- and D2-receptor antagonistic action might endow RS 79948 with potential therapeutic relevance in the treatment of schizophrenia, drug dependence, depression and Parkinson's disease.
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Affiliation(s)
- Roberto Frau
- Department of Biomedical Sciences, Section of Neurosciences and Clinical Pharmacology, University of Cagliari, Cittadella Universitaria, Monserrato, CA, Italy; The Guy Everett Laboratory for Neuroscience, University of Cagliari, Cittadella Universitaria, Monserrato, CA, Italy
| | - Paola Devoto
- Department of Biomedical Sciences, Section of Neurosciences and Clinical Pharmacology, University of Cagliari, Cittadella Universitaria, Monserrato, CA, Italy; The Guy Everett Laboratory for Neuroscience, University of Cagliari, Cittadella Universitaria, Monserrato, CA, Italy.
| | - Sonia Aroni
- Department of Biomedical Sciences, Section of Neurosciences and Clinical Pharmacology, University of Cagliari, Cittadella Universitaria, Monserrato, CA, Italy
| | - Pierluigi Saba
- Department of Biomedical Sciences, Section of Neurosciences and Clinical Pharmacology, University of Cagliari, Cittadella Universitaria, Monserrato, CA, Italy
| | - Claudia Sagheddu
- Department of Biomedical Sciences, Section of Neurosciences and Clinical Pharmacology, University of Cagliari, Cittadella Universitaria, Monserrato, CA, Italy
| | - Carlotta Siddi
- Department of Biomedical Sciences, Section of Neurosciences and Clinical Pharmacology, University of Cagliari, Cittadella Universitaria, Monserrato, CA, Italy
| | - Michele Santoni
- Department of Biomedical Sciences, Section of Neurosciences and Clinical Pharmacology, University of Cagliari, Cittadella Universitaria, Monserrato, CA, Italy
| | - Marco Carli
- Department of Translational Research and New Technologies in Medicine and Surgery, University of Pisa, Italy
| | - Gian Luigi Gessa
- Department of Biomedical Sciences, Section of Neurosciences and Clinical Pharmacology, University of Cagliari, Cittadella Universitaria, Monserrato, CA, Italy; The Guy Everett Laboratory for Neuroscience, University of Cagliari, Cittadella Universitaria, Monserrato, CA, Italy
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3
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Jakobsson JE, Telu S, Lu S, Jana S, Pike VW. Broad Scope and High-Yield Access to Unsymmetrical Acyclic [ 11 C]Ureas for Biomedical Imaging from [ 11 C]Carbonyl Difluoride. Chemistry 2021; 27:10369-10376. [PMID: 33890705 PMCID: PMC10134011 DOI: 10.1002/chem.202100690] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2021] [Indexed: 12/13/2022]
Abstract
Effective methods are needed for labelling acyclic ureas with carbon-11 (t1/2 =20.4 min) as potential radiotracers for biomedical imaging with positron emission tomography (PET). Herein, we describe the rapid and high-yield syntheses of unsymmetrical acyclic [11 C]ureas under mild conditions (room temperature and within 7 min) using no-carrier-added [11 C]carbonyl difluoride with aliphatic and aryl amines. This methodology is compatible with diverse functionality (e. g., hydroxy, carboxyl, amino, amido, or pyridyl) in the substrate amines. The labelling process proceeds through putative [11 C]carbamoyl fluorides and for primary amines through isolable [11 C]isocyanate intermediates. Unsymmetrical [11 C]ureas are produced with negligible amounts of unwanted symmetrical [11 C]urea byproducts. Moreover, the overall labelling method tolerates trace water and the generally moderate to excellent yields show good reproducibility. [11 C]Carbonyl difluoride shows exceptional promise for application to the synthesis of acyclic [11 C]ureas as new radiotracers for biomedical imaging with PET.
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Affiliation(s)
- Jimmy E Jakobsson
- Molecular Imaging Branch, National Institute of Mental Health, National Institutes of Health, 10 Center Drive, Bethesda, MD, 20892-1003, USA
| | - Sanjay Telu
- Molecular Imaging Branch, National Institute of Mental Health, National Institutes of Health, 10 Center Drive, Bethesda, MD, 20892-1003, USA
| | - Shuiyu Lu
- Molecular Imaging Branch, National Institute of Mental Health, National Institutes of Health, 10 Center Drive, Bethesda, MD, 20892-1003, USA
| | - Susovan Jana
- Molecular Imaging Branch, National Institute of Mental Health, National Institutes of Health, 10 Center Drive, Bethesda, MD, 20892-1003, USA
| | - Victor W Pike
- Molecular Imaging Branch, National Institute of Mental Health, National Institutes of Health, 10 Center Drive, Bethesda, MD, 20892-1003, USA
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Shetty HU, Zoghbi SS, Morse CL, Kowalski A, Hirvonen J, Innis RB, Pike VW. Development of a non-radiometric method for measuring the arterial input function of a 11C-labeled PET radiotracer. Sci Rep 2020; 10:17350. [PMID: 33060616 DOI: 10.1038/s41598-020-73646-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2020] [Accepted: 09/18/2020] [Indexed: 11/08/2022] Open
Abstract
Positron emission tomography (PET) uses radiotracers to quantify important biochemical parameters in human subjects. A radiotracer arterial input function (AIF) is often essential for converting brain PET data into robust output measures. For radiotracers labeled with carbon-11 (t1/2 = 20.4 min), AIF is routinely determined with radio-HPLC of blood sampled frequently during the PET experiment. There has been no alternative to this logistically demanding method, neither for regular use nor validation. A 11C-labeled tracer is always accompanied by a large excess of non-radioactive tracer known as carrier. In principle, AIF might be obtained by measuring the molar activity (Am; ratio of radioactivity to total mass; Bq/mol) of a radiotracer dose and the time-course of carrier concentration in plasma after radiotracer injection. Here, we implement this principle in a new method for determining AIF, as shown by using [11C]PBR28 as a representative tracer. The method uses liquid chromatography-tandem mass spectrometry for measuring radiotracer Am and then the carrier in plasma sampled regularly over the course of a PET experiment. Am and AIF were determined radiometrically for comparison. The new non-radiometric method is not constrained by the short half-life of carbon-11 and is an attractive alternative to conventional AIF measurement.
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Devoto P, Sagheddu C, Santoni M, Flore G, Saba P, Pistis M, Gessa GL. Noradrenergic Source of Dopamine Assessed by Microdialysis in the Medial Prefrontal Cortex. Front Pharmacol 2020; 11:588160. [PMID: 33071798 PMCID: PMC7538903 DOI: 10.3389/fphar.2020.588160] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2020] [Accepted: 09/07/2020] [Indexed: 01/03/2023] Open
Abstract
Previous results indicate that dopamine (DA) release in the medial prefrontal cortex (mPFC) is modified by α2 adrenoceptor- but not D2 DA receptor- agonists and antagonists, suggesting that DA measured by microdialysis in the mPFC originates from noradrenergic terminals. Accordingly, noradrenergic denervation was found to prevent α2-receptor-mediated rise and fall of extracellular DA induced by atipamezole and clonidine, respectively, in the mPFC. The present study was aimed to determine whether DA released by dopaminergic terminals in the mPFC is not detected by in vivo microdialysis because is readily taken up by norepinephrine transporter (NET). Accordingly, the D2-antagonist raclopride increased the electrical activity of DA neurons in the ventral tegmental area (VTA) and enhanced extracellular DOPAC but failed to modify DA in the mPFC. However, in rats whose NET was either inactivated by nisoxetine or eliminated by noradrenergic denervation, raclopride still elevated extracellular DOPAC and activated dopaminergic activity, but also increased DA. Conversely, the D2-receptor agonist quinpirole reduced DOPAC but failed to modify DA in the mPFC in control rats. However, in rats whose NET was eliminated by noradrenergic denervation or inhibited by locally perfused nisoxetine, quinpirole maintained its ability to reduce DOPAC but acquired that of reducing DA. Moreover, raclopride and quinpirole, when locally perfused into the mPFC of rats subjected to noradrenergic denervation, were able to increase and decrease, respectively, extracellular DA levels, while being ineffective in control rats. Transient inactivation of noradrenergic neurons by clonidine infusion into the locus coeruleus, a condition where NET is preserved, was found to reduce extracellular NE and DA in the mPFC, whereas noradrenergic denervation, a condition where NET is eliminated, almost totally depleted extracellular NE but increased DA. Both transient inactivation and denervation of noradrenergic neurons were found to reduce the number of spontaneously active DA neurons and their bursting activity in the VTA. The results indicate that DA released in the mPFC by dopaminergic terminals is not detected by microdialysis unless DA clearance from extracellular space is inactivated. They support the hypothesis that noradrenergic terminals are the main source of DA measured by microdialysis in the mPFC during physiologically relevant activities.
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Affiliation(s)
- Paola Devoto
- Section of Neuroscience and Clinical Pharmacology, Department of Biomedical Sciences, University of Cagliari, Cagliari, Italy.,"Guy Everett" Laboratory, University of Cagliari, Cagliari, Italy
| | - Claudia Sagheddu
- Section of Neuroscience and Clinical Pharmacology, Department of Biomedical Sciences, University of Cagliari, Cagliari, Italy
| | - Michele Santoni
- Section of Neuroscience and Clinical Pharmacology, Department of Biomedical Sciences, University of Cagliari, Cagliari, Italy
| | - Giovanna Flore
- Department of Medical Sciences and Public Health, University of Cagliari, Cagliari, Italy
| | - Pierluigi Saba
- Section of Neuroscience and Clinical Pharmacology, Department of Biomedical Sciences, University of Cagliari, Cagliari, Italy
| | - Marco Pistis
- Section of Neuroscience and Clinical Pharmacology, Department of Biomedical Sciences, University of Cagliari, Cagliari, Italy.,Section of Cagliari, Neuroscience Institute, National Research Council of Italy (CNR), Cagliari, Italy
| | - Gian Luigi Gessa
- "Guy Everett" Laboratory, University of Cagliari, Cagliari, Italy.,Section of Cagliari, Neuroscience Institute, National Research Council of Italy (CNR), Cagliari, Italy
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LaBella A, Cao X, Petersen E, Lubinsky R, Biegon A, Zhao W, Goldan AH. High-Resolution Depth-Encoding PET Detector Module with Prismatoid Light-Guide Array. J Nucl Med 2020; 61:1528-1533. [PMID: 32111684 DOI: 10.2967/jnumed.119.239343] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2019] [Accepted: 02/10/2020] [Indexed: 11/16/2022] Open
Abstract
Depth-encoding detectors with single-ended readout provide a practical, cost-effective approach for constructing high-resolution and high-sensitivity PET scanners. However, the current iteration of such detectors uses a uniform glass light-guide to achieve depth encoding, resulting in nonuniform performance throughout the detector array due to suboptimal intercrystal light sharing. We introduce Prism-PET, a single-ended-readout PET detector module with a segmented light-guide composed of an array of prismatoids that introduce enhanced, deterministic light sharing. Methods: High-resolution PET detector modules were fabricated with single-ended readout of polished multicrystal lutetium yttrium orthosilicate scintillator arrays directly coupled 4-to-1 and 9-to-1 to arrays of 3 × 3 mm silicon photomultiplier pixels. Each scintillator array was coupled at the nonreadout side to a light-guide (one 4-to-1 module with a uniform glass light-guide, one 4-to-1 Prism-PET module, and one 9-to-1 Prism-PET module) to introduce intercrystal light sharing, which closely mimics the behavior of dual-ended readout, with the additional benefit of improved crystal identification. Flood histogram data were acquired using a 3-MBq 22Na source to characterize crystal identification and energy resolution. Lead collimation was used to acquire data at specific depths to determine depth-of-interaction (DOI) resolution. Results: The flood histogram measurements showed excellent and uniform crystal separation throughout the Prism-PET modules, whereas the uniform glass light-guide module had performance degradation at the edges and corners. A DOI resolution of 5.0 mm full width at half maximum (FWHM) and an energy resolution of 13% FWHM were obtained in the uniform glass light-guide module. By comparison, the 4-to-1 coupled Prism-PET module achieved a DOI resolution of 2.5 mm FWHM and an energy resolution of 9% FWHM. Conclusion: PET scanners based on our Prism-PET modules with segmented prismatoid light-guide arrays can achieve high and uniform spatial resolution (9-to-1 coupling with ∼1-mm crystals), high sensitivity (20-mm-thick detectors and intercrystal Compton scatter recovery), good energy and timing resolutions (using polished crystals and after applying DOI correction), and compact size (depth encoding eliminates parallax error and permits smaller ring-diameter).
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Affiliation(s)
- Andy LaBella
- Department of Biomedical Engineering, College of Engineering and Applied Sciences, Stony Brook University, Stony Brook, New York
| | - Xinjie Cao
- Department of Electrical and Computer Engineering, College of Engineering and Applied Sciences, Stony Brook University, Stony Brook, New York; and
| | - Eric Petersen
- Department of Biomedical Engineering, College of Engineering and Applied Sciences, Stony Brook University, Stony Brook, New York
| | - Rick Lubinsky
- Department of Radiology, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York
| | - Anat Biegon
- Department of Radiology, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York
| | - Wei Zhao
- Department of Radiology, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York
| | - Amir H Goldan
- Department of Radiology, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York
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de Bartolomeis A, Avagliano C, Vellucci L, D’ambrosio L, Manchia M, D’urso G, Buonaguro EF, Iasevoli F. Translating preclinical findings in clinically relevant new antipsychotic targets: focus on the glutamatergic postsynaptic density. Implications for treatment resistant schizophrenia. Neurosci Biobehav Rev 2019; 107:795-827. [DOI: 10.1016/j.neubiorev.2019.08.019] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2019] [Revised: 07/20/2019] [Accepted: 08/22/2019] [Indexed: 02/07/2023]
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9
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Caravaggio F, Iwata Y, Kim J, Shah P, Gerretsen P, Remington G, Graff-Guerrero A. What proportion of striatal D2 receptors are occupied by endogenous dopamine at baseline? A meta-analysis with implications for understanding antipsychotic occupancy. Neuropharmacology 2019; 163:107591. [PMID: 30940535 DOI: 10.1016/j.neuropharm.2019.03.034] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2019] [Revised: 03/25/2019] [Accepted: 03/27/2019] [Indexed: 11/30/2022]
Abstract
Using molecular imaging techniques - positron emission tomography (PET) and single-photon emission computed tomography (SPECT) - in conjunction with an acute dopamine depletion challenge (alpha-methyl-para-tyrosine) it is possible to estimate endogenous dopamine levels occupying striatal dopamine D2 receptors (D2R) in humans in vivo. However, it is unclear what proportion of striatal D2R are occupied by endogenous dopamine under normal conditions. This is important since it has been suggested that in schizophrenia there may be a substantial proportion of striatal D2R which are occupied by endogenous dopamine and not accessible by therapeutic doses of antipsychotics. In order to clarify these issues, we conducted a meta-analysis of dopamine depletion studies using substituted benzamide radiotracers in healthy persons. This meta-analysis suggests that anywhere from 8 to 21% (weighted average 11%) of striatal D2R may be occupied by endogenous dopamine at baseline. Using these estimates, we propose an updated occupancy model and tentatively suggest that antipsychotics inhibit a smaller proportion of the total pool of striatal D2R in vivo than previously acknowledged. This article is part of the issue entitled 'Special Issue on Antipsychotics'.
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Affiliation(s)
- Fernando Caravaggio
- Research Imaging Centre, Centre for Addiction and Mental Health, 250 College Street, Toronto, Ontario, M5T 1R8, Canada; Department of Psychiatry, University of Toronto, 250 College Street, Toronto, Ontario, M5T 1R8, Canada.
| | - Yusuke Iwata
- Research Imaging Centre, Centre for Addiction and Mental Health, 250 College Street, Toronto, Ontario, M5T 1R8, Canada; Department of Psychiatry, University of Toronto, 250 College Street, Toronto, Ontario, M5T 1R8, Canada
| | - Julia Kim
- Research Imaging Centre, Centre for Addiction and Mental Health, 250 College Street, Toronto, Ontario, M5T 1R8, Canada; Institute of Medical Science, University of Toronto, 1 Kings College Circle, Toronto, Ontario, M5S 1A8, Canada
| | - Parita Shah
- Research Imaging Centre, Centre for Addiction and Mental Health, 250 College Street, Toronto, Ontario, M5T 1R8, Canada; Institute of Medical Science, University of Toronto, 1 Kings College Circle, Toronto, Ontario, M5S 1A8, Canada
| | - Philip Gerretsen
- Research Imaging Centre, Centre for Addiction and Mental Health, 250 College Street, Toronto, Ontario, M5T 1R8, Canada; Department of Psychiatry, University of Toronto, 250 College Street, Toronto, Ontario, M5T 1R8, Canada; Institute of Medical Science, University of Toronto, 1 Kings College Circle, Toronto, Ontario, M5S 1A8, Canada
| | - Gary Remington
- Research Imaging Centre, Centre for Addiction and Mental Health, 250 College Street, Toronto, Ontario, M5T 1R8, Canada; Department of Psychiatry, University of Toronto, 250 College Street, Toronto, Ontario, M5T 1R8, Canada; Institute of Medical Science, University of Toronto, 1 Kings College Circle, Toronto, Ontario, M5S 1A8, Canada
| | - Ariel Graff-Guerrero
- Research Imaging Centre, Centre for Addiction and Mental Health, 250 College Street, Toronto, Ontario, M5T 1R8, Canada; Department of Psychiatry, University of Toronto, 250 College Street, Toronto, Ontario, M5T 1R8, Canada; Institute of Medical Science, University of Toronto, 1 Kings College Circle, Toronto, Ontario, M5S 1A8, Canada
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Notter T, Coughlin JM, Sawa A, Meyer U. Reconceptualization of translocator protein as a biomarker of neuroinflammation in psychiatry. Mol Psychiatry 2018; 23:36-47. [PMID: 29203847 DOI: 10.1038/mp.2017.232] [Citation(s) in RCA: 94] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/23/2017] [Revised: 09/05/2017] [Accepted: 10/02/2017] [Indexed: 02/06/2023]
Abstract
A great deal of interest in psychiatric research is currently centered upon the pathogenic role of inflammatory processes. Positron emission tomography (PET) using radiolabeled ligands selective for the 18 kDa translocator protein (TSPO) has become the most widely used technique to assess putative neuroimmune abnormalities in vivo. Originally used to detect discrete neurotoxic damages, TSPO has generally turned into a biomarker of 'neuroinflammation' or 'microglial activation'. Psychiatric research has mostly accepted these denotations of TSPO, even if they may be inadequate and misleading under many pathological conditions. A reliable and neurobiologically meaningful diagnosis of 'neuroinflammation' or 'microglial activation' is unlikely to be achieved by the sole use of TSPO PET imaging. It is also very likely that the pathological meanings of altered TSPO binding or expression are disease-specific, and therefore, not easily generalizable across different neuropathologies or inflammatory conditions. This difficulty is intricately linked to the varying (and still ill-defined) physiological functions and cellular expression patterns of TSPO in health and disease. While altered TSPO binding or expression may indeed mirror ongoing neuroinflammatory processes in some cases, it may reflect other pathophysiological processes such as abnormalities in cell metabolism, energy production and oxidative stress in others. Hence, the increasing popularity of TSPO PET imaging has paradoxically introduced substantial uncertainty regarding the nature and meaning of neuroinflammatory processes and microglial activation in psychiatry, and likely in other neuropathological conditions as well. The ambiguity of conceiving TSPO simply as a biomarker of 'neuroinflammation' or 'microglial activation' calls for alternative interpretations and complimentary approaches. Without the latter, the ongoing scientific efforts and excitement surrounding the role of the neuroimmune system in psychiatry may not turn into therapeutic hope for affected individuals.
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Affiliation(s)
- T Notter
- Institute of Pharmacology and Toxicology, University of Zurich-Vetsuisse, Zurich, Switzerland.,Neuroscience Center Zurich, University of Zurich and ETH Zurich, Zurich, Switzerland
| | - J M Coughlin
- Department of Psychiatry and Behavioral Sciences, Johns Hopkins Medical Institutions, Baltimore, MD, USA.,Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Medical Institutions, Baltimore, MD, USA
| | - A Sawa
- Department of Psychiatry and Behavioral Sciences, Johns Hopkins Medical Institutions, Baltimore, MD, USA
| | - U Meyer
- Institute of Pharmacology and Toxicology, University of Zurich-Vetsuisse, Zurich, Switzerland.,Neuroscience Center Zurich, University of Zurich and ETH Zurich, Zurich, Switzerland
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Takano H. Cognitive Function and Monoamine Neurotransmission in Schizophrenia: Evidence From Positron Emission Tomography Studies. Front Psychiatry 2018; 9:228. [PMID: 29896132 PMCID: PMC5987676 DOI: 10.3389/fpsyt.2018.00228] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/01/2017] [Accepted: 05/09/2018] [Indexed: 12/12/2022] Open
Abstract
Positron emission tomography (PET) is a non-invasive imaging technique used to assess various brain functions, including cerebral blood flow, glucose metabolism, and neurotransmission, in the living human brain. In particular, neurotransmission mediated by the monoamine neurotransmitters dopamine, serotonin, and norepinephrine, has been extensively examined using PET probes, which specifically bind to the monoamine receptors and transporters. This useful tool has revealed the pathophysiology of various psychiatric disorders, including schizophrenia, and the mechanisms of action of psychotropic drugs. Because monoamines are implicated in various cognitive processes such as memory and executive functions, some PET studies have directly investigated the associations between monoamine neurotransmission and cognitive functions in healthy individuals and patients with psychiatric disorders. In this mini review, I discuss the findings of PET studies that investigated monoamine neurotransmission under resting conditions, specifically focusing on cognitive functions in patients with schizophrenia. With regard to the dopaminergic system, some studies have examined the association of dopamine D1 and D2/D3 receptors, dopamine transporters, and dopamine synthesis capacity with various cognitive functions in schizophrenia. With regard to the serotonergic system, 5-HT1A and 5-HT2A receptors have been studied in the context of cognitive functions in schizophrenia. Although relatively few PET studies have examined cognitive functions in patients with psychiatric disorders, these approaches can provide useful information on enhancing cognitive functions by administering drugs that modulate monoamine transmission. Moreover, another paradigm of techniques such as those exploring the release of neurotransmitters and further development of radiotracers for novel targets are warranted.
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Affiliation(s)
- Harumasa Takano
- Department of Clinical Neuroimaging, Integrative Brain Imaging Center, National Center of Neurology and Psychiatry, Tokyo, Japan
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12
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Abstract
Molecular neuroimaging with PET is an integrated tool in psychiatry research and drug-development for as long as this modality has been available, in particular for studying neurotransmission and endogenous neurotransmitter release. Pharmacologic, behavioral and other types of challenges are currently applied to induce changes in neurochemical levels that can be inferred through their effects on changes in receptor binding and related outcome measures. Based on the availability of tracers that are sensitive for measuring neurotransmitter release these experiments have focused on the brain's dopamine system, while recent developments have extended those studies to other targets such as the serotonin or choline system. With the introduction of hybrid, truly simultaneous PET/MRI systems, in-vivo imaging of the dynamics of neuroreceptor signal transmission in the brain using PET and functional MRI (fMRI) has become possible. fMRI has the ability to provide information about the effects of receptor function that are complementary to the PET measurement. Dynamic acquisition of both PET and fMRI signals enables not only an in-vivo real-time assessment of neurotransmitter or drug binding to receptors but also dynamic receptor adaptations and receptor-specific neurotransmission. While fMRI temporal resolution is comparatively fast in relation to PET, the timescale of observable biological processes is highly dependent on the kinetics of radiotracers and study design. Overall, the combination of the specificity of PET radiotracers to neuroreceptors, fMRI signal as a functional readout and integrated study design promises to expand our understanding of the location, propagation and connections of brain activity in health and disease.
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Affiliation(s)
- Christin Y Sander
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA -
- Harvard Medical School, Boston, MA, USA -
| | - Swen Hesse
- Department of Nuclear Medicine, University of Leipzig, Leipzig, Germany
- Integrated Treatment and Research Center (IFB) Adiposity Diseases, Leipzig University Medical Center, Leipzig, Germany
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de Lange ECM, van den Brink W, Yamamoto Y, de Witte WEA, Wong YC. Novel CNS drug discovery and development approach: model-based integration to predict neuro-pharmacokinetics and pharmacodynamics. Expert Opin Drug Discov 2017; 12:1207-1218. [PMID: 28933618 DOI: 10.1080/17460441.2017.1380623] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
INTRODUCTION CNS drug development has been hampered by inadequate consideration of CNS pharmacokinetic (PK), pharmacodynamics (PD) and disease complexity (reductionist approach). Improvement is required via integrative model-based approaches. Areas covered: The authors summarize factors that have played a role in the high attrition rate of CNS compounds. Recent advances in CNS research and drug discovery are presented, especially with regard to assessment of relevant neuro-PK parameters. Suggestions for further improvements are also discussed. Expert opinion: Understanding time- and condition dependent interrelationships between neuro-PK and neuro-PD processes is key to predictions in different conditions. As a first screen, it is suggested to use in silico/in vitro derived molecular properties of candidate compounds and predict concentration-time profiles of compounds in multiple compartments of the human CNS, using time-course based physiology-based (PB) PK models. Then, for selected compounds, one can include in vitro drug-target binding kinetics to predict target occupancy (TO)-time profiles in humans. This will improve neuro-PD prediction. Furthermore, a pharmaco-omics approach is suggested, providing multilevel and paralleled data on systems processes from individuals in a systems-wide manner. Thus, clinical trials will be better informed, using fewer animals, while also, needing fewer individuals and samples per individual for proof of concept in humans.
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Affiliation(s)
- Elizabeth C M de Lange
- a Leiden Academic Center of Drug Research, Translational Pharmacology , Leiden University , Leiden , The Netherlands
| | - Willem van den Brink
- a Leiden Academic Center of Drug Research, Translational Pharmacology , Leiden University , Leiden , The Netherlands
| | - Yumi Yamamoto
- a Leiden Academic Center of Drug Research, Translational Pharmacology , Leiden University , Leiden , The Netherlands
| | - Wilhelmus E A de Witte
- a Leiden Academic Center of Drug Research, Translational Pharmacology , Leiden University , Leiden , The Netherlands
| | - Yin Cheong Wong
- a Leiden Academic Center of Drug Research, Translational Pharmacology , Leiden University , Leiden , The Netherlands
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Dupont AC, Largeau B, Santiago Ribeiro MJ, Guilloteau D, Tronel C, Arlicot N. Translocator Protein-18 kDa (TSPO) Positron Emission Tomography (PET) Imaging and Its Clinical Impact in Neurodegenerative Diseases. Int J Mol Sci 2017; 18:ijms18040785. [PMID: 28387722 PMCID: PMC5412369 DOI: 10.3390/ijms18040785] [Citation(s) in RCA: 119] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2017] [Revised: 03/31/2017] [Accepted: 04/04/2017] [Indexed: 02/06/2023] Open
Abstract
In vivo exploration of activated microglia in neurodegenerative diseases is achievable by Positron Emission Tomography (PET) imaging, using dedicated radiopharmaceuticals targeting the translocator protein-18 kDa (TSPO). In this review, we emphasized the major advances made over the last 20 years, thanks to TSPO PET imaging, to define the pathophysiological implication of microglia activation and neuroinflammation in neurodegenerative diseases, including Parkinson’s disease, Huntington’s disease, dementia, amyotrophic lateral sclerosis, multiple sclerosis, and also in psychiatric disorders. The extent and upregulation of TSPO as a molecular biomarker of activated microglia in the human brain is now widely documented in these pathologies, but its significance, and especially its protective or deleterious action regarding the disease’s stage, remains under debate. Thus, we exposed new and plausible suggestions to enhance the contribution of TSPO PET imaging for biomedical research by exploring microglia’s role and interactions with other cells in brain parenchyma. Multiplex approaches, associating TSPO PET radiopharmaceuticals with other biomarkers (PET imaging of cellular metabolism, neurotransmission or abnormal protein aggregates, but also other imaging modalities, and peripheral cytokine levels measurement and/or metabolomics analysis) was considered. Finally, the actual clinical impact of TSPO PET imaging as a routine biomarker of neuroinflammation was put into perspective regarding the current development of diagnostic and therapeutic strategies for neurodegenerative diseases.
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Affiliation(s)
- Anne-Claire Dupont
- CHRU Tours, 2 Boulevard Tonnellé, 37044 Tours, France.
- Institut National de la Santé et de la Recherche Médicale U930, 10 Boulevard Tonnellé, 37032 Tours, France.
| | | | - Maria Joao Santiago Ribeiro
- CHRU Tours, 2 Boulevard Tonnellé, 37044 Tours, France.
- Institut National de la Santé et de la Recherche Médicale U930, 10 Boulevard Tonnellé, 37032 Tours, France.
| | - Denis Guilloteau
- CHRU Tours, 2 Boulevard Tonnellé, 37044 Tours, France.
- Institut National de la Santé et de la Recherche Médicale U930, 10 Boulevard Tonnellé, 37032 Tours, France.
| | - Claire Tronel
- Institut National de la Santé et de la Recherche Médicale U930, 10 Boulevard Tonnellé, 37032 Tours, France.
| | - Nicolas Arlicot
- CHRU Tours, 2 Boulevard Tonnellé, 37044 Tours, France.
- Institut National de la Santé et de la Recherche Médicale U930, 10 Boulevard Tonnellé, 37032 Tours, France.
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