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Kumar A, Scarpa M, Nordberg A. Tracing synaptic loss in Alzheimer's brain with SV2A PET-tracer UCB-J. Alzheimers Dement 2024; 20:2589-2605. [PMID: 38363009 PMCID: PMC11032538 DOI: 10.1002/alz.13720] [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: 11/03/2023] [Revised: 01/04/2024] [Accepted: 01/05/2024] [Indexed: 02/17/2024]
Abstract
INTRODUCTION Synaptic loss is an early prominent feature of Alzheimer's disease (AD). The recently developed novel synaptic vesicle 2A protein (SV2A) PET-tracer UCB-J has shown great promise in tracking synaptic loss in AD. However, there have been discrepancies between the findings and a lack of mechanistic insight. METHODS Here we report the first extensive pre-clinical validation studies for UCB-J in control (CN; n = 11) and AD (n = 11) brains using a multidimensional approach of post-mortem brain imaging techniques, radioligand binding, and biochemical studies. RESULTS AND DISCUSSION We demonstrate that UCB-J could target SV2A protein with high specificity and depict synaptic loss at synaptosome levels in AD brain regions compared to CNs. UCB-J showed highest synaptic loss in AD hippocampus followed in descending order by frontal cortex, temporal cortex, parietal cortex, and cerebellum. 3H-UCB-J large brain-section autoradiography and cellular/subcellular fractions binding studies indicated potential off-target interaction with phosphorylated tau (p-tau) species in AD brains, which could have subsequent clinical implications for imaging studies. HIGHLIGHTS Synaptic positron emission tomography (PET)-tracer UCB-J could target synaptic vesicle 2A protein (SV2A) with high specificity in Alzheimer's disease (AD) and control brains. Synaptic PET-tracer UCB-J could depict synaptic loss at synaptosome levels in AD brain regions compared to control. Potential off-target interaction of UCB-J with phosphorylated tau (p-tau) species at cellular/subcellular levels could have subsequent clinical implications for imaging studies, warranting further investigations.
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Affiliation(s)
- Amit Kumar
- Division of Clinical GeriatricsCenter for Alzheimer ResearchDepartment of NeurobiologyCare Sciences and SocietyKarolinska InstitutetStockholmSweden
| | - Miriam Scarpa
- Division of Clinical GeriatricsCenter for Alzheimer ResearchDepartment of NeurobiologyCare Sciences and SocietyKarolinska InstitutetStockholmSweden
| | - Agneta Nordberg
- Division of Clinical GeriatricsCenter for Alzheimer ResearchDepartment of NeurobiologyCare Sciences and SocietyKarolinska InstitutetStockholmSweden
- Theme Inflammation and AgingKarolinska University HospitalStockholmSweden
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Jacobsen SC, Speth NR, Xiong M, Herth MM, Kristensen JL, Palner M, Janfelt C. Desorption Electrospray Ionization Mass Spectrometry Imaging of Cimbi-36, a 5-HT 2A Receptor Agonist, with Direct Comparison to Autoradiography and Positron Emission Tomography. Mol Imaging Biol 2021; 23:676-685. [PMID: 33651266 DOI: 10.1007/s11307-021-01592-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Revised: 01/22/2021] [Accepted: 02/16/2021] [Indexed: 10/22/2022]
Abstract
PURPOSE The study demonstrates the use of Desorption Electrospray Ionization mass spectrometry imaging (DESI-MSI) for imaging of the PET tracer compound Cimbi-36 in brain tissue and compares imaging by DESI-MSI to imaging by autoradiography and PET. PROCEDURES Rats were dosed intraperitoneally with 3 mg/kg of Cimbi-36 and euthanized at t = 5, 10, 15, 30, 60 and 120 min post-injection. The brains were removed, frozen and sectioned, and sagittal sections were imaged by DESI-MSI in positive ion mode. Additionally, brain sections from a non-dosed animal were incubated with 14C-labelled Cimbi-36 and imaged by autoradiography. Finally, PET images were acquired from an animal dosed with 11C-labelled Cimbi-36. RESULTS DESI-MSI and autoradiography images of a sagittal brain sections showed similar distributions of Cimbi-36, with increased abundance in the frontal cortex and choroid plexus, regions which are high in 5-HT2A and 5-HT2C receptors. The PET image also showed increased abundance in cortex, but the spatial resolution was clearly inferior to DESI-MSI and autoradiography. The DESI-MSI results showed increased abundance of Cimbi-36 in brain tissue until 15 min, after which the abundance was declining. The PET-tracer was still clearly detectable at t = 120 min. Similar imaging of the kidneys showed the abundance of Cimbi-36 peaking at 30 min. Cimbi-36 was quantified in a t = 15 min brain section by quantitative DESI-MSI, resulting in tissue concentrations of 19.8 μg/g in cortex, 15.4 μg/g in cerebellum and 12.5 μg/g in whole brain. CONCLUSIONS DESI imaging from an in vivo dosing experiment showed distribution of the PET tracer remarkably similar to what was obtained by autoradiography of an in vitro incubation experiment, indicating that the obtained results represent actual binding to certain receptors in the brain. DESI-MSI is suggested as a cost-effective screening tool, which does not rely on labelling of compounds.
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Affiliation(s)
- Sophie C Jacobsen
- Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen, Denmark
| | - Nikolaj R Speth
- Neurobiology Research Unit, Copenhagen University Hospital, Blegdamsvej 9, 2200, Copenhagen, Denmark
| | - Mengfei Xiong
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen, Denmark
- Department of Clinical Physiology, Nuclear Medicine and PET, Copenhagen University Hospital, Blegdamsvej 9, 2200, Copenhagen, Denmark
| | - Matthias M Herth
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen, Denmark
- Department of Clinical Physiology, Nuclear Medicine and PET, Copenhagen University Hospital, Blegdamsvej 9, 2200, Copenhagen, Denmark
| | - Jesper L Kristensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen, Denmark
| | - Mikael Palner
- Neurobiology Research Unit, Copenhagen University Hospital, Blegdamsvej 9, 2200, Copenhagen, Denmark
- Center for Translational Neuromedicine, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, 2200, Copenhagen, Denmark
| | - Christian Janfelt
- Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen, Denmark.
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Abstract
Purinergic receptors play important roles in central nervous system (CNS). These receptors are involved in cellular neuroinflammatory responses that regulate functions of neurons, microglial and astrocytes. Based on their endogenous ligands, purinergic receptors are classified into P1 or adenosine, P2X and P2Y receptors. During brain injury or under pathological conditions, rapid diffusion of extracellular adenosine triphosphate (ATP) or uridine triphosphate (UTP) from the damaged cells, promote microglial activation that result in the changes in expression of several of these receptors in the brain. Imaging of the purinergic receptors with selective Positron Emission Tomography (PET) radioligands has advanced our understanding of the functional roles of some of these receptors in healthy and diseased brains. In this review, we have accumulated a list of currently available PET radioligands of the purinergic receptors that are used to elucidate the receptor functions and participations in CNS disorders. We have also reviewed receptors lacking radiotracer, laying the foundation for future discoveries of novel PET radioligands to reveal these receptors roles in CNS disorders.
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Affiliation(s)
- Hamideh Zarrinmayeh
- Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Paul R Territo
- Department of Radiology and Imaging Sciences, Indiana University School of Medicine, Indianapolis, IN, USA
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Abstract
Adenosine receptors, G protein-coupled receptors (GPCRs) that are activated by the endogenous ligand adenosine, have been considered potential therapeutic targets in several disorders. To date however, only very few adenosine receptor modulators have made it to the market. Increased understanding of these receptors is required to improve the success rate of adenosine receptor drug discovery. To improve our understanding of receptor structure and function, over the past decades, a diverse array of molecular probes has been developed and applied. These probes, including radioactive or fluorescent moieties, have proven invaluable in GPCR research in general. Specifically for adenosine receptors, the development and application of covalent or reversible probes, whether radiolabeled or fluorescent, have been instrumental in the discovery of new chemical entities, the characterization and interrogation of adenosine receptor subtypes, and the study of adenosine receptor behavior in physiological and pathophysiological conditions. This review summarizes these applications, and also serves as an invitation to walk another mile to further improve probe characteristics and develop additional tags that allow the investigation of adenosine receptors and other GPCRs in even finer detail.
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Affiliation(s)
- Xue Yang
- Division of Drug Discovery and Safety, Leiden Academic Centre for Drug Research, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands
| | - Laura H. Heitman
- Division of Drug Discovery and Safety, Leiden Academic Centre for Drug Research, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands
| | - Adriaan P. IJzerman
- Division of Drug Discovery and Safety, Leiden Academic Centre for Drug Research, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands
| | - Daan van der Es
- Division of Drug Discovery and Safety, Leiden Academic Centre for Drug Research, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands
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