PET-MRI Applications and Future Prospects in Psychiatry.

This article reviews the synergistic application of positron emission tomography-magnetic resonance imaging (PET-MRI) in neuroscience with relevance for psychiatry, particularly examining neurotransmission, epigenetics, and dynamic imaging methodologies. We begin by discussing the complementary insights that PET and MRI modalities provide into neuroreceptor systems, with a focus on dopamine, opioids, and serotonin receptors, and their implications for understanding and treating psychiatric disorders. We further highlight recent PET-MRI studies using a radioligand that enables the quantification of epigenetic enzymes, specifically histone deacetylases, in the brain in vivo. Imaging epigenetics is used to exemplify the impact the quantification of novel molecular targets may have, including new treatment approaches for psychiatric disorders. Finally, we discuss innovative designs involving functional PET using [18F]FDG (fPET-FDG), which provides detailed information regarding dynamic changes in glucose metabolism. Concurrent acquisitions of fPET-FDG and functional MRI provide a time-resolved approach to studying brain function, yielding simultaneous metabolic and hemodynamic information and thereby opening new avenues for psychiatric research. Collectively, the review underscores the potential of a multimodal PET-MRI approach to advance our understanding of brain structure and function in health and disease, which could improve clinical care based on objective neurobiological features and treatment response monitoring. EVIDENCE LEVEL: 1 TECHNICAL EFFICACY: Stage 1.

18 kDa Translocator protein (TSPO) is upregulated in rat brain after peripheral nerve injury and downregulated by diroximel fumarate.

Neuroimmune signaling is a key process underlying neuropathic pain. Clinical studies have demonstrated that 18 kDa translocator protein (TSPO), a putative marker of neuroinflammation, is upregulated in discrete brain regions of patients with chronic pain. However, no preclinical studies have investigated TSPO dynamics in the brain in the context of neuropathic pain and in response to analgesic treatments. We used positron emission tomography-computed tomography (PET-CT) and [18F]-PBR06 radioligand to measure TSPO levels in the brain across time after chronic constriction injury (CCI) of the sciatic nerve in both male and female rats. Up to 10 weeks post-CCI, TSPO expression was increased in discrete brain regions, including medial prefrontal cortex, somatosensory cortex, insular cortex, anterior cingulate cortex, motor cortex, ventral tegmental area, amygdala, midbrain, pons, medulla, and nucleus accumbens. TSPO was broadly upregulated across these regions at 4 weeks post CCI in males, and 10 weeks in females, though there were regional differences between the sexes. Using immunohistochemistry, we confirmed TSPO expression in these regions. We further demonstrated that TSPO was upregulated principally in microglia in the nucleus accumbens core, and astrocytes and endothelial cells in the nucleus accumbens shell. Finally, we tested whether TSPO upregulation was sensitive to diroximel fumarate, a drug that induces endogenous antioxidants via nuclear factor E2-related factor 2 (Nrf2). Diroximel fumarate alleviated neuropathic pain and reduced TSPO upregulation. Our findings indicate that TSPO is upregulated over the course of neuropathic pain development and is resolved by an antinociceptive intervention in animals with peripheral nerve injury.

Synthesis and preclinical evaluation of 11C-labeled 7-Oxo-2,4,5,7-tetrahydro-6H-pyrazolo[3,4-c]pyridine radioligands for RIPK1 positron emission tomography imaging.

Targeting receptor-interacting protein kinase 1 (RIPK1) has emerged as a promising therapeutic strategy for various neurodegenerative disorders. The development of a positron emission tomography (PET) probe for brain RIPK1 imaging could offer a valuable tool to assess therapeutic effectiveness and uncover the neuropathology associated with RIPK1. In this study, we present the development and characterization of two new PET radioligands, [11C]PB218 and [11C]PB220, which have the potential to facilitate brain RIPK1 imaging. [11C]PB218 and [11C]PB220 were successfully synthesized with a high radiochemical yield (34 % - 42 %) and molar activity (293 - 314 GBq/µmol). PET imaging characterization of two radioligands was conducted in rodents, demonstrating that both newly developed tracers have good brain penetration (maximum SUV = 0.9 - 1.0) and appropriate brain clearance kinetic profiles. Notably, [11C]PB218 has a more favorable binding specificity than [11C]PB220. A PET/MR study of [11C]PB218 in a non-human primate exhibited good brain penetration, desirable kinetic properties, and a safe profile, thus supporting the translational applicability of our new probe. These investigations enable further translational exploration of [11C]PB218 for drug discovery and PET probe development targeting RIPK1.

Amphetamine pretreatment blunts dopamine-induced D2/D3-receptor occupancy by an arrestin-mediated mechanism: A PET study in internalization compromised mice.

While all reversible receptor-targeting radioligands for positron emission tomography (PET) can be displaced by competition with an antagonist at the receptor, many radiotracers show limited occupancies using agonists even at high doses. [11C]Raclopride, a D2/D3 receptor radiotracer with rapid kinetics, can identify the direction of changes in the neurotransmitter dopamine, but quantitative interpretation of the relationship between dopamine levels and radiotracer binding has proven elusive. Agonist-induced receptor desensitization and internalization, a homeostatic mechanism to downregulate neurotransmitter-mediated function, can shift radioligand-receptor binding affinity and confound PET interpretations of receptor occupancy. In this study, we compared occupancies induced by amphetamine (AMP) in drug-naive wild-type (WT) and internalization-compromised ß-arrestin-2 knockout (KO) mice using a within-scan drug infusion to modulate the kinetics of [11C]raclopride. We additionally performed studies at 3 h following AMP pretreatment, with the hypothesis that receptor internalization should markedly attenuate occupancy on the second challenge, because dopamine cannot access internalized receptors. Without prior AMP treatment, WT mice exhibited somewhat larger binding potential than KO mice but similar AMP-induced occupancy. At 3 h after AMP treatment, WT mice exhibited binding potentials that were 15 % lower than KO mice. At this time point, occupancy was preserved in KO mice but suppressed by 60 % in WT animals, consistent with a model in which most receptors contributing to binding potential in WT animals were not functional. These results demonstrate that arrestin-mediated receptor desensitization and internalization produce large effects in PET [11C]raclopride occupancy studies using agonist challenges.

The Back Pain Consortium (BACPAC) Research Program: Structure, Research Priorities, and Methods.

In 2019, the National Health Interview survey found that nearly 59% of adults reported pain some, most, or every day in the past 3 months, with 39% reporting back pain, making back pain the most prevalent source of pain, and a significant issue among adults. Often, identifying a direct, treatable cause for back pain is challenging, especially as it is often attributed to complex, multifaceted issues involving biological, psychological, and social components. Due to the difficulty in treating the true cause of chronic low back pain (cLBP), an over-reliance on opioid pain medications among cLBP patients has developed, which is associated with increased prevalence of opioid use disorder and increased risk of death. To combat the rise of opioid-related deaths, the National Institutes of Health (NIH) initiated the Helping to End Addiction Long-TermSM (HEAL) initiative, whose goal is to address the causes and treatment of opioid use disorder while also seeking to better understand, diagnose, and treat chronic pain. The NIH Back Pain Consortium (BACPAC) Research Program, a network of 14 funded entities, was launched as a part of the HEAL initiative to help address limitations surrounding the diagnosis and treatment of cLBP. This paper provides an overview of the BACPAC research program's goals and overall structure, and describes the harmonization efforts across the consortium, define its research agenda, and develop a collaborative project which utilizes the strengths of the network. The purpose of this paper is to serve as a blueprint for other consortia tasked with the advancement of pain related science.

Shared intrinsic functional connectivity alterations as a familial risk marker for ADHD: a resting-state functional magnetic resonance imaging study with sibling design.

BACKGROUND: Although aberrant intrinsic functional connectivity has been reported in attention-deficit/hyperactivity disorder (ADHD), we have a limited understanding of whether connectivity alterations are related to the familial risk of ADHD. METHODS: Fifty-three probands with ADHD, their unaffected siblings (n = 53) and typically developing controls (n = 53) underwent resting-state functional magnetic resonance imaging scans. A seed-based approach with the bilateral precuneus/posterior cingulate cortex (PCC) was used to derive a whole-brain functional connectivity map in each subject. The differences in functional connectivity among the three groups were tested with one-way ANOVA using randomized permutation. Comparisons between two groups were also performed to examine the increase or decrease in connectivity. The severity of ADHD symptoms was used to identify brain regions where symptom severity is correlated to the strength of intrinsic functional connectivity. RESULTS: When compared to controls, both probands and unaffected siblings showed increased functional connectivity in the left insula and left inferior frontal gyrus. The connectivity in these regions was linked to better performance in response inhibition in the control group but absent in other groups. Higher ADHD symptom severity was correlated with increased functional connectivity in bilateral fronto-parietal-temporal regions only noted in probands with ADHD. CONCLUSIONS: Alterations in resting-state functional connectivities with the precuneus/PCC, hubs of default-mode network, account for the underlying familial risks of ADHD. Since the left insula and left inferior frontal gyri are key regions of the salience and frontoparietal network, respectively, future studies focusing on alterations of cross-network functional connectivity as the familial risk of ADHD are suggested.

Molecular imaging of NAD+ -dependent deacetylase SIRT1 in the brain.

INTRODUCTION: Aging is an inevitable physiological process and the biggest risk factor of Alzheimer's disease (AD). Developing an imaging tracer to visualize aging-related changes in the brain may provide a useful biomarker in elucidating neuroanatomical mechanisms of AD. METHODS: We developed and characterized a new tracer that can be used to visualize SIRT1 in brains related to aging and AD by positron emission tomography imaging. RESULTS: The SIRT1 tracer displayed desirable brain uptake and selectivity, as well as stable metabolism and proper kinetics and distribution in rodent and nonhuman primate brains. This new tracer was further validated by visualizing SIRT1 in brains of AD transgenic mice, compared to nontransgenic animals. DISCUSSION: Our SIRT1 tracer not only enables, for the first time, the demonstration of SIRT1 in animal brains, but also allows visualization and recapitulation of AD-related SIRT1 neuropathological changes in animal brains.

Synthesis and preliminary evaluation of 4-hydroxy-6-(3-[11C]methoxyphenethyl)pyridazin-3(2H)-one, a 11C-labeled d-amino acid oxidase (DAAO) inhibitor for PET imaging.

Selective DAAO inhibitors have demonstrated promising therapeutic effects in clinical studies, including clinically alleviating symptoms of schizophrenic patients and ameliorating cognitive function in Alzheimer's patients with early phase. Herein we report the synthesis and preliminary evaluation of a 11C-labeled positron emission tomography ligand based on a DAAO inhibitor, DAO-1903 (8). 11C-Isotopologue of 8 was prepared in high radiochemical yield with high radiochemical purity (>99%) and high molar activity (>37 GBq/µmol). In vitro autoradiography studies indicated that the ligand possessed high in vitro specific binding to DAAO, while in vivo dynamic PET studies demonstrated that [11C]8 failed to cross the blood-brain barrier possibly due to moderate brain efflux mechanism. Further chemical scaffold optimization is necessary to overcome limited brain permeability and improve specific binding.

A New Positron Emission Tomography Probe for Orexin Receptors Neuroimaging.

The orexin receptor (OX) is critically involved in motivation and sleep-wake regulation and holds promising therapeutic potential in various mood disorders. To further investigate the role of orexin receptors (OXRs) in the living human brain and to evaluate the treatment potential of orexin-targeting therapeutics, we herein report a novel PET probe ([11C]CW24) for OXRs in the brain. CW24 has moderate binding affinity for OXRs (IC50 = 0.253 µM and 1.406 µM for OX1R and OX2R, respectively) and shows good selectivity to OXRs over 40 other central nervous system (CNS) targets. [11C]CW24 has high brain uptake in rodents and nonhuman primates, suitable metabolic stability, and appropriate distribution and pharmacokinetics for brain positron emission tomography (PET) imaging. [11C]CW24 warrants further evaluation as a PET imaging probe of OXRs in the brain.

A population stereotaxic positron emission tomography brain template for the macaque and its application to ischemic model.

PURPOSE: Positron emission tomography (PET) is a non-invasive imaging tool for the evaluation of brain function and neuronal activity in normal and diseased conditions with high sensitivity. The macaque monkey serves as a valuable model system in the field of translational medicine, for its phylogenetic proximity to man. To translation of non-human primate neuro-PET studies, an effective and objective data analysis platform for neuro-PET studies is needed. MATERIALS AND METHODS: A set of stereotaxic templates of macaque brain, namely the Institute of High Energy Physics & Jinan University Macaque Template (HJT), was constructed by iteratively registration and averaging, based on 30 healthy rhesus monkeys. A brain atlas image was created in HJT space by combining sub-anatomical regions and defining new 88 bilateral functional regions, in which a unique integer was assigned for each sub-anatomical region. RESULTS: The HJT comprised a structural MRI T1 weighted image (T1WI) template image, a functional FDG-PET template image, intracranial tissue segmentations accompanied with a digital macaque brain atlas image. It is compatible with various commercially available software tools, such as SPM and PMOD. Data analysis was performed on a stroke model compared with a group of healthy controls to demonstrate the usage of HJT. CONCLUSION: We have constructed a stereotaxic template set of macaque brain named HJT, which standardizes macaque neuroimaging data analysis, supports novel radiotracer development and facilitates translational neuro-disorders research.

A Manganese-based Alternative to Gadolinium: Contrast-enhanced MR Angiography, Excretion, Pharmacokinetics, and Metabolism.

Purpose To compare intravascular contrast enhancement produced by the manganese-based magnetic resonance (MR) imaging contrast agent manganese-N-picolyl-N,N',N'-trans-1,2-cyclohexenediaminetriacetate (Mn-PyC3A) to gadopentetate dimeglumine (Gd-DTPA) and to evaluate the excretion, pharmacokinetics, and metabolism of Mn-PyC3A. Materials and Methods Contrast material-enhanced MR angiography was performed in baboons (Papio anubis; n = 4) by using Mn-PyC3A and Gd-DTPA. Dynamic imaging was performed for 60 minutes following Mn-PyC3A injection to monitor distribution and elimination. Serial blood sampling was performed to quantify manganese and gadolinium plasma clearance by using inductively coupled plasma mass spectrometry and to characterize Mn-PyC3A metabolism by using high-performance liquid chromatography. Intravascular contrast enhancement in the abdominal aorta and brachiocephalic artery was quantified by measuring contrast-to-noise ratios (CNRs) versus muscle at 9 seconds following Mn-PyC3A or Gd-DTPA injection. Plasma pharmacokinetics were modeled with a biexponential function, and data were compared with a paired t test. Results Aorta versus muscle CNR (mean ± standard deviation) with Mn-PyC3A and Gd-DTPA was 476 ± 77 and 538 ± 120, respectively (P = .11). Brachiocephalic artery versus muscle CNR was 524 ± 55 versus 518 ± 140, respectively (P = .95). Mn-PyC3A was eliminated via renal and hepatobiliary excretion with similar pharmacokinetics to Gd-DTPA (area under the curve between 0 and 30 minutes, 20.2 ± 3.1 and 17.0 ± 2.4, respectively; P = .23). High-performance liquid chromatography revealed no evidence of Mn-PyC3A biotransformation. Conclusion Mn-PyC3A enables contrast-enhanced MR angiography with comparable contrast enhancement to gadolinium-based agents and may overcome concerns regarding gadolinium-associated toxicity and retention. © RSNA, 2017 Online supplemental material is available for this article.

A regularized full reference tissue model for PET neuroreceptor mapping.

The full reference tissue model (FRTM) is a PET analysis framework that includes both free and specifically bound compartments within tissues, together with rate constants defining association and dissociation from the specifically bound compartment. The simplified reference tissue model (SRTM) assumes instantaneous exchange between tissue compartments, and this "1-tissue" approximation reduces the number of parameters and enables more robust mapping of non-displaceable binding potentials. Simulations based upon FRTM have shown that SRTM exhibits biases that are spatially dependent, because biases depend upon binding potentials. In this work, we describe a regularized model (rFRTM) that employs a global estimate of the dissociation rate constant from the specifically bound compartment (k4). The model provides an internal calibration for optimizing k4 through the reference-region outflow rate k2', a model parameter that should be a global constant but varies regionally in SRTM. Estimates of k4 by rFRTM are presented for four PET radioligands. We show that SRTM introduces bias in parameter estimates by assuming an infinite value for k4, and that rFRTM ameliorates bias with an appropriate choice of k4. Theoretical considerations and simulations demonstrate that rFRTM reduces bias in non-displaceable binding potentials. A two-parameter reduction of the model (rFRTM2) provides robust mapping at a voxel-wise level. With a structure similar to SRTM, the model is easily implemented and can be applied as a PET reference region analysis that reduces parameter bias without substantially altering parameter variance.

The modulation effect of longitudinal acupuncture on resting state functional connectivity in knee osteoarthritis patients.

UNLABELLED: Recent advances in brain imaging have contributed to our understanding of the neural activity associated with acupuncture treatment. In this study, we investigated functional connectivity across longitudinal acupuncture treatments in older patients with knee osteoarthritis (OA). Over a period of 4 weeks (six treatments), we collected resting state functional magnetic resonance imaging (fMRI) scans from 30 patients before and after their first, third and sixth treatments. Clinical outcome showed a significantly greater pain subscore on the Knee Injury and Osteoarthritis Outcome Score (KOOS) (indicative of improvement) with verum acupuncture than with sham acupuncture. Independent component analysis (ICA) of the resting state fMRI data showed that the right frontoparietal network (rFPN) and the executive control network (ECN) showed enhanced functional connectivity (FC) with the rostral anterior cingulate cortex/medial prefrontal cortex, a key region in the descending pain modulatory system, in the verum groups as compared to the sham group after treatments. We also found that the rFPN connectivity with the left insula is (1) significantly associated with changes in KOOS pain score after treatments, and (2) significantly enhanced after verum acupuncture treatments as compared to sham treatment. Analysis of the acupuncture needle stimulation scan showed that compared with sham treatment, verum acupuncture activated the left operculum/insula, which also overlaps with findings observed in resting state analysis. Our results suggest that acupuncture may achieve its therapeutic effect on knee OA pain by modulating functional connectivity between the rFPN, ECN and the descending pain modulatory pathway. CLINICAL TRIAL NUMBER: NCT01079390.

Dynamic functional imaging of brain glucose utilization using fPET-FDG.

Glucose is the principal source of energy for the brain and yet the dynamic response of glucose utilization to changes in brain activity is still not fully understood. Positron emission tomography (PET) allows quantitative measurement of glucose metabolism using 2-[(18)F]-fluorodeoxyglucose (FDG). However, FDG PET in its current form provides an integral (or average) of glucose consumption over tens of minutes and lacks the temporal information to capture physiological alterations associated with changes in brain activity induced by tasks or drug challenges. Traditionally, changes in glucose utilization are inferred by comparing two separate scans, which significantly limits the utility of the method. We report a novel method to track changes in FDG metabolism dynamically, with higher temporal resolution than exists to date and within a single session. Using a constant infusion of FDG, we demonstrate that our technique (termed fPET-FDG) can be used in an analysis pipeline similar to fMRI to define within-session differential metabolic responses. We use visual stimulation to demonstrate the feasibility of this method. This new method has a great potential to be used in research protocols and clinical settings since fPET-FDG imaging can be performed with most PET scanners and data acquisition and analysis are straightforward. fPET-FDG is a highly complementary technique to MRI and provides a rich new way to observe functional changes in brain metabolism.

Simultaneous fMRI-PET of the opioidergic pain system in human brain.

MRI and PET provide complementary information for studying brain function. While the potential use of simultaneous MRI/PET for clinical diagnostic and disease staging has been demonstrated recently; the biological relevance of concurrent functional MRI-PET brain imaging to dissect neurochemically distinct components of the blood oxygenation level dependent (BOLD) fMRI signal has not yet been shown. We obtained sixteen fMRI-PET data sets from eight healthy volunteers. Each subject participated in randomized order in a pain scan and a control (nonpainful pressure) scan on the same day. Dynamic PET data were acquired with an opioid radioligand, [(11)C]diprenorphine, to detect endogenous opioid releases in response to pain. BOLD fMRI data were collected at the same time to capture hemodynamic responses. In this simultaneous human fMRI-PET imaging study, we show co-localized responses in thalamus and striatum related to pain processing, while modality specific brain networks were also found. Co-localized fMRI and PET signal changes in the thalamus were positively correlated suggesting that pain-induced changes in opioid neurotransmission contribute a significant component of the fMRI signal change in this region. Simultaneous fMRI-PET provides unique opportunities allowing us to relate specific neurochemical events to functional hemodynamic activation and to investigate the impacts of neurotransmission on neurovascular coupling of the human brain in vivo.

PET imaging of fatty acid amide hydrolase with [(18)F]DOPP in nonhuman primates.

Fatty acid amide hydrolase (FAAH) regulates endocannabinoid signaling. [(11)C]CURB, an irreversibly binding FAAH inhibitor, has been developed for clinical research imaging with PET. However, no fluorine-18 labeled radiotracer for FAAH has yet advanced to human studies. [(18)F]DOPP ([(18)F]3-(4,5-dihydrooxazol-2-yl)phenyl (5-fluoropentyl)carbamate) has been identified as a promising (18)F-labeled analogue based on rodent studies. The goal of this work is to evaluate [(18)F]DOPP in nonhuman primates to support its clinical translation. High specific activity [(18)F]DOPP (5-6 Ci·µmol(-1)) was administered intravenously (iv) to three baboons (2M/1F, 3-4 years old). The distribution and pharmacokinetics were quantified following a 2 h dynamic imaging session using a simultaneous PET/MR scanner. Pretreatment with the FAAH-selective inhibitor, URB597, was carried out at 200 or 300 µg/kg iv, 10 min prior to [(18)F]DOPP administration. Rapid arterial blood sampling for the first 3 min was followed by interval sampling with metabolite analysis to provide a parent radiotracer plasma input function that indicated ∼95% baseline metabolism at 60 min and a reduced rate of metabolism after pretreatment with URB597. Regional distribution data were analyzed with 1-, 2-, and 3-tissue compartment models (TCMs), with and without irreversible trapping since [(18)F]DOPP covalently links to the active site of FAAH. Consistent with previous findings for [(11)C]CURB, the 2TCM with irreversible binding was found to provide the best fit for modeling the data in all regions. The composite parameter λk3 was therefore used to evaluate whole brain (WB) and regional binding of [(18)F]DOPP. Pretreatment studies showed inhibition of λk3 across all brain regions (WB baseline: 0.112 mL/cm(3)/min; 300 µg/kg URB597: 0.058 mL/cm(3)/min), suggesting that [(18)F]DOPP binding is specific for FAAH, consistent with previous rodent data.

Acute Effects of Hallucinogens on Functional Connectivity: Psilocybin and Salvinorin-A.

The extent of changes in functional connectivity (FC) within functional networks as a common feature across hallucinogenic drug classes is under-explored. This work utilized fMRI to assess the dissociative hallucinogens Psilocybin, a classical serotonergic psychedelic, and Salvinorin-A, a kappa-opioid receptor (KOR) agonist, on resting-state FC in nonhuman primates. We highlight overlapping and differing influence of these substances on FC relative to the thalamus, claustrum, prefrontal cortex (PFC), default mode network (DMN), and DMN subcomponents. Analysis was conducted on a within-subject basis. Findings support the cortico-claustro-cortical network model for probing functional effects of hallucinogens regardless of serotonergic potential, with a potential key paradigm centered around the claustrum, PFC, anterior cingulate cortices (ACC), and angular gyrus relationship. Thalamo-cortical networks are implicated but appear dependent on 5-HT2AR activation. Acute desynchronization relative to the DMN for both drugs was also shown. Our findings provide a framework to understand broader mechanisms at which hallucinogens in differing classes may impact subjects regardless of the target receptor.

Design and Discovery of Novel NLRP3 Inhibitors and PET Imaging Radiotracers Based on a 1,2,3-Triazole-Bearing Scaffold.

The NOD-like receptor (NLR) family pyrin-domain-containing 3 (NLRP3) inflammasome, an essential component of the innate immune system, has been emerging as a viable drug target and a potential biomarker for human diseases. In our efforts to develop novel small molecule NLRP3 inhibitors, a 1-(5-chloro-2-methoxybenzyl)-4-phenyl-1H-1,2,3-triazole scaffold was designed via a rational approach based on our previous leads. Structure-activity relationship studies and biophysical studies identified a new lead compound 8 as a potent (IC50: 0.55 ± 0.16 µM), selective, and direct NLRP3 inhibitor. Positron emission tomography (PET) imaging studies of [11C]8 demonstrated its rapid and high brain uptake as well as fast washout in mice and rhesus macaque. Notably, plasma kinetic analysis of this radiotracer from the PET/magnetic resonance imaging studies in rhesus macaque suggested radiometabolic stability. Collectively, our data not only encourage further studies of this lead compound but also warrant further optimization to generate additional novel NLRP3 inhibitors and suitable central nervous system PET radioligands with translational promise.

Investigating neuroepigenetic alterations in chronic low back pain with positron emission tomography.

ABSTRACT: Epigenetics has gained considerable interest as potential mediators of molecular alterations that could underlie the prolonged sensitization of nociceptors, neurons, and glia in response to various environmental stimuli. Histone acetylation and deacetylation, key processes in modulating chromatin, influence gene expression; elevated histone acetylation enhances transcriptional activity, whereas decreased acetylation leads to DNA condensation and gene repression. Altered levels of histone deacetylase (HDAC) have been detected in various animal pain models, and HDAC inhibitors have demonstrated analgesic effects in these models, indicating HDACs' involvement in chronic pain pathways. However, animal studies have predominantly examined epigenetic modulation within the spinal cord after pain induction, which may not fully reflect the complexity of chronic pain in humans. Moreover, methodological limitations have previously impeded an in-depth study of epigenetic changes in the human brain. In this study, we employed [ 11 C]Martinostat, an HDAC-selective radiotracer, positron emission tomography to assess HDAC availability in the brains of 23 patients with chronic low back pain (cLBP) and 11 age-matched and sex-matched controls. Our data revealed a significant reduction of [ 11 C]Martinostat binding in several brain regions associated with pain processing in patients with cLBP relative to controls, highlighting the promising potential of targeting HDAC modulation as a therapeutic strategy for cLBP.

Molecular Imaging of Alzheimer's Disease-Related Sigma-1 Receptor in the Brain via a Novel Ru-Mediated Aromatic 18F-deoxyfluorination Probe.

Sigma-1 receptor (σ1R) is an intracellular protein implicated in a spectrum of neurodegenerative conditions, notably Alzheimer's disease (AD). Positron emission tomography (PET) imaging of brain σ1R could provide a powerful tool for better understanding the underlying pathomechanism of σ1R in AD. In this study, we successfully developed a 18F-labeled σ1R radiotracer [18F]CNY-05 via an innovative ruthenium (Ru)-mediated 18F-deoxyfluorination method. [18F]CNY-05 exhibited preferable brain uptake, high specific binding, and slightly reversible pharmacokinetics within the PET scanning time window. PET imaging of [18F]CNY-05 in nonhuman primates (NHP) indicated brain permeability, metabolic stability, and safety. Moreover, autoradiography and PET studies of [18F]CNY-05 in the AD mouse model found a significantly decreased brain uptake compared to that in wild-type mice. Collectively, we have provided a novel 18F-radiolabeled σ1R PET probe, which enables visualizing brain σ1R in health and neurological diseases.