TSPO Ligands Research Articles

Novel TSPO Ligand 2-Cl-MGV-1 Can Counteract Lipopolysaccharide Induced Inflammatory Response in Murine RAW264.7 Macrophage Cell Line and Lung Models.

We assessed the anti-inflammatory activity of the TSPO ligand 2-Cl-MGV-1. Lipopolysaccharide (LPS) was used to induce inflammatory response in a murine RAW264.7 macrophage model (LPS: 100 ng/mL) and a mouse model (C57BL/6) of lung inflammation (LPS: 5 mg/kg). In the macrophage model, the presence of 2-Cl-MGV-1 (25 µM) caused the LPS-induced elevation in nitrite levels to decrease by 70% (p < 0.0001) and interleukin (IL)-6 by 50% (p < 0.05). In the mouse model, 2-Cl-MGV-1, administered 30 min before, or co-administered with, an LPS injection, significantly inhibited the elevation in serum IL-5 levels (both by 65%; p < 0.001 and p < 0.01, respectively). 2-Cl-MGV-1 administration to mice 30 min before LPS injection and 1 h thereafter significantly inhibited the elevation in IL-1β serum levels (both by 63%, p < 0.005). IL-6 elevation was inhibited by 73% (p < 0.005) when 2-Cl-MGV-1 was administered 30 min before LPS, by 60% (p < 0.05) when co-administered with LPS, and by 64% (p < 0.05) when administered 1 h after LPS. All cytokine assessments were conducted 6 h post LPS injection. Histological analyses showed decreased leukocyte adherence in the lung tissue of the ligand-treated mice. 2-Cl-MGV-1 administration 30 min prior to exposure to LPS inhibited inflammation-induced open field immobility. The beneficial effect of 2-Cl-MGV-1 suggests its potential as a therapeutic option for inflammatory diseases.

Neurosteroids and translocator protein 18kDa (TSPO) ligands as novel treatment options in depression.

Recently, the gamma-aminobutyric acid (GABA) system has come into focus for the treatment of anxiety, postpartum depression, and major depressive disorder. Endogenous 3α-reduced steroids such as allopregnanolone are potent positive allosteric modulators of GABAA receptors and have been known for decades. Current industry developments and first approvals by the U.S. food and drug administration (FDA) for the treatment of postpartum depression with exogenous analogues of these steroids represent a major step forward in the field. 3α-reduced steroids target both synaptic and extrasynaptic GABAA receptors, unlike benzodiazepines, which bind to synaptic receptors. The first FDA-approved 3α-reduced steroid for postpartum depression is brexanolone, an intravenous formulation of allopregnanolone. It has been shown to provide rapid relief of depressive symptoms. An orally available 3α-reduced steroid is zuranolone, which also received FDA approval in 2023 for the treatment of postpartum depression. Although a number of studies have been conducted, the efficacy data were not sufficient to achieve approval of zuranolone in major depressive disorder by the FDA in 2023. The most prominent side effects of these 3α-reduced steroids are somnolence, dizziness and headache. In addition to the issue of efficacy, it should be noted that current data limit the use of these compounds to two weeks. An alternative to exogenous 3α-reduced steroids may be the use of substances that induce endogenous neurosteroidogenesis, such as the translocator protein 18kDa (TSPO) ligand etifoxine. TSPO has been extensively studied for its role in steroidogenesis, in addition to other functions such as anti-inflammatory and neuroregenerative properties. Currently, etifoxine is the only clinically available TSPO ligand in France for the treatment of anxiety disorders. Studies are underway to evaluate its antidepressant potential. Hopefully, neurosteroid research will lead to the development of fast-acting antidepressants.

The mitochondrial TSPO ligand Atriol mitigates metabolic-associated steatohepatitis by downregulating CXCL1

Background and aimsThe mitochondrial translocator protein (TSPO, 18 kDa) is pivotal in binding cholesterol and facilitating its transfer from the outer to the inner mitochondrial membrane. Atriol is a TSPO ligand disrupting cholesterol binding by targeting the cholesterol-recognition amino acid consensus domain. Prior research has shown that TSPO deficiency improved metabolic-associated steatohepatitis (MASH). We hypothesized that Atriol may have the potential to alleviate MASH. Methods and resultsIn vitro cell culture studies revealed that Atriol treatment effectively mitigated MASH by restoring mitochondrial function, inhibiting the NF-κB signaling pathway, and reducing hepatic stellate cell (HSC) activation. SD male rats were fed a GAN diet for 10 months to induce MASH. During the final two weeks of feeding, rats received intraperitoneal Atriol administration daily. Atriol treatment significantly ameliorated MASH by reducing lipid accumulation, diminishing hepatic lobular inflammation and fibrosis, decreasing cell death, and inhibiting excessive bile acid synthesis. Moreover, Atriol restored mitochondrial function in primary hepatocytes isolated from MASH rats. In search of the mechanism(s) governing these effects, we found that Atriol downregulated the proinflammatory chemokine CXCL1 through the NF-κB signaling pathway or via myeloperoxidase (MPO) in HSCs and Kupffer cells. Additionally, in vitro, studies further suggested that CXCL1 treatment induced dysfunctional mitochondria, inflammation, HSCs activation, and macrophage migration, whereas Atriol countered these effects. Finally, the mitigating effects of Atriol on MASH were reproduced by pharmacological inhibition of NF-κB or MPO and neutralization of CXCL1. ConclusionAtriol ameliorates MASH both in vitro and in vivo, demonstrating its potential therapeutic benefits in managing MASH.

МИТОХОНДРИАЛЬНЫЙ БЕЛОК-ТРАНСЛОКАЗА 18 кДа КАК БИОМАРКЕР РАДИАЦИОННО-ИНДУЦИРОВАННОГО НЕЙРОВОСПАЛЕНИЯ

The review presents current knowledge about the structure of the18 kDa translocator protein TSPO, its polymorphic variants, regulation of its gene expression and function in the cells of CNS. Particular attention is paid to its role in mitochondrial homeostasis in microglia under neuroinflammation in the long-term period after ionizing radiation exposure. Data on the effectiveness of several TSPO ligands for diagnostic imaging and treatment of neuroinflammation for restoring cognitive functions in neurodegenerative pathologies are summarized. Based on the TSPO level in the brain and in the peripheral blood cells late after irradiation, TSPO is discussed as a potential marker of neuroinflammation development.

Local and global effects of sedation in resting-state fMRI: a randomized, placebo-controlled comparison between etifoxine and alprazolam

TSPO ligands are promising alternatives to benzodiazepines in the treatment of anxiety, as they display less pronounced side effects such as sedation, cognitive impairment, tolerance development and abuse potential. In a randomized double-blind repeated-measures study we compare a benzodiazepine (alprazolam) to a TSPO ligand (etifoxine) by assessing side effects and acquiring resting-state fMRI data from 34 healthy participants after 5 days of taking alprazolam, etifoxine or a placebo. To study the effects of the pharmacological interventions in fMRI in detail and across different scales, we combine in our study complementary analysis strategies related to whole-brain functional network connectivity, local connectivity analysis expressed in regional homogeneity, fluctuations in low-frequency BOLD amplitudes and coherency of independent resting-state networks. Participants reported considerable adverse effects such as fatigue, sleepiness and concentration impairments, related to the administration of alprazolam compared to placebo. In resting-state fMRI we found a significant decrease in functional connection density, network efficiency and a decrease in the networks rich-club coefficient related to alprazolam. While observing a general decrease in regional homogeneity in high-level brain networks in the alprazolam condition, we simultaneously could detect an increase in regional homogeneity and resting-state network coherence in low-level sensory regions. Further we found a general increase in the low-frequency compartment of the BOLD signal. In the etifoxine condition, participants did not report any significant side effects compared to the placebo, and we did not observe any corresponding modulations in our fMRI metrics. Our results are consistent with the idea that sedation globally disconnects low-level functional networks, but simultaneously increases their within-connectivity. Further, our results point towards the potential of TSPO ligands in the treatment of anxiety and depression.

The translocator protein 18kDa ligand etifoxine in the treatment of depressive disorders—a double-blind, randomized, placebo-controlled proof-of-concept study

BackgroundRecent developments suggest that neurosteroids may achieve rapid antidepressant effects. As such, neurosteroidogenesis mediated by the translocator protein 18 kDa (TSPO) might constitute a promising option for the treatment of depression. Therefore, the current clinical trial aims to get the first evidence of whether TPSO ligands promote rapid antidepressant effects. Furthermore, we study which mechanisms of action, e.g., modulation of distinct neuronal networks, neurosteroidogenesis, endocrinological mechanisms, TSPO expression or microbiome composition, contribute to their putative antidepressant effects.MethodsThis is a randomized, placebo-controlled, double-blind single-center trial of 2-week treatment with the TSPO ligand etifoxine versus placebo in depressive patients. Main eligibility criteria: male or female individuals aged 18 to 65 years with unipolar/bipolar depressive disorder with no other psychiatric main diagnosis or acute neurological/somatic disorder or drug/alcohol dependence during their lifetime.The primary endpoint is the time point at which 50% of the maximal effect has occurred (ET50) estimated by the scores of the Hamilton Depression Scale (HAMD-21). A total of 20 patients per group are needed to detect changes of therapeutic efficacy about 5% and changes of ET50 about 10% with a power of 70%. Assuming a drop-out rate of 10–20%, 50 patients will be randomized in total. The study will be conducted at the Department of Psychiatry and Psychotherapy of the University of Regensburg.DiscussionThis study will provide a first proof-of-concept on the potential of the TSPO ligand etifoxine in the treatment of depressive disorders.Trial registrationClinical Trials Register (EudraCT number: 2021-006773-38, registration date: 14 September 2022) and German Register of Clinical Studies (DRKS number: DRKS00031099, registration date: 23 January 2023).

Mild and deep hypothermia differentially affect cerebral neuroinflammatory and cold shock response following cardiopulmonary bypass in rat

IntroductionTargeted temperature management (TTM) is considered to be a neuroprotective strategy during cardiopulmonary bypass (CPB) assisted procedures, possibly through the activation of cold shock proteins. We therefore investigated the effects of mild compared with deep hypothermia on the neuroinflammatory response and cold shock protein expression after CPB in rats. MethodsWistar rats were subjected to 1 hr of mild (33 °C) or deep (18 °C) hypothermia during CPB or sham procedure. PET scan analyses using TSPO ligand [11C]PBR28 were performed on day 1 (short-term) or day 3 and 7 post-procedure (long-term) to assess neuroinflammation. Hippocampal and cortical samples were obtained at day 1 in the short-term group and at day 7 in the long-term group. mRNA expression of M1 and M2 microglia associated cytokines was analysed with RT-PCR. Cold shock protein RNA-binding motive 3 (RBM3) and tyrosine receptor kinase B (TrkB) receptor protein expression were determined with Western Blot and quantified. ResultsIn both groups target temperature was reached within an hour. Standard uptake values (SUV) of [11C]PBR28 in CPB rats at 1 day and 3 days were similar to that of sham animals. At 7 days after CPB the SUV was significantly higher in amygdala and hippocampal regions of the CPB 18 °C group as compared to the CPB 33 °C group. No differences were observed in the expression of M1 and M2 microglia-related cytokines between TTM 18 °C and 33 °C. RBM3 protein levels in cortex and hippocampus were significantly higher in CPB 33 °C compared to CPB 18 °C and sham 33 °C, at day 1 and day 7, respectively. ConclusionsTTM at 18 °C increased the neuroinflammatory response in amygdala and hippocampus compared to TTM at 33 °C in rats undergoing a CPB procedure. Additionally, TTM at 33 °C induced increased expression of TrkB and RBM3 in cortex and hippocampus of rats on CPB compared to TTM at 18 °C. Together, these data indicate that neuroinflammation is alleviated by TTM at 33 °C, possibly by recruiting protective mechanisms through cold shock protein induction.

TOM40 mediates the effect of TSPO on postpartum depression partially through regulating calcium homeostasis in microglia

AimsTo assess the effect of the translocator protein 18 kDa (TSPO) on postpartum depression and explore its mechanism. MethodsPostpartum depression (PPD) mouse model was established, and flow cytometry, immunofluorescence, Western blot analysis, real-time quantitative PCR, adeno-associated virus (AAV), co-immunoprecipitation-mass spectrometry and immunofluorescence co-staining were used to detect the effect of TSPO ligand ZBD-2 on PPD mice. ResultsZBD-2 inhibits the overactivation of microglia in the hippocampus and amygdala of PPD model mice. ZBD-2 not only inhibited the inflammation but also repressed the burst of reactive oxygen species (ROS) and mitochondrial ROS (mtROS). Meanwhile, ZBD-2 protects mitochondria from LPS-induced damages through inhibiting the influx of calcium. ZBD-2 modulated the calcium influx by increasing the level of translocase of the outer mitochondrial membrane 40 (TOM40) and reducing the interaction of TSPO and TOM40. In addition, the effect of ZBD-2 was partially dependent on anti-oxidative process. Knockdown of TOM40 by adeno-associated virus (AAV) in the hippocampus or amygdala dramatically reduced the effect of ZBD-2 on PPD, indicating that TOM40 mediates the effect of ZBD-2 on PPD. ConclusionsTOM40 is required for the effect of ZBD-2 on treating anxiety and depression in PPD mice. This study reveals the role of microglia TSPO in PPD development and provides the new therapeutic strategy for PPD.

Anxiolytic-like effects of YL-IPA08, a potent ligand for the translocator protein (18 kDa) via regulating the synaptic plasticity in hippocampus

TSPO, translocator protein (18 kDa) ligands have demonstrated consistent antidepression and anxiolytic effects in several preclinical studies. This study aimed to examine whether YL-IPA08[N-ethyl-N-(2-pyridinylmethyl)-2-(3,4-ichlorophenyl) -7-methylimidazo [1,2-a] pyridine-3-acetamide hydrochloride], a potent and selective TSPO ligand synthesized by our institute, could alleviate anxiety-related behaviors induced by electric shock (ES) and investigate its underlying mechanism. As expected, we showed that chronic treatment with YL-IPA08 significantly reversed anxiety-related behaviors induced by electrical stimulation (0.5 mA, 12 times, duration 1s, interval 10s) exposure. Using the analysis of RNA-sequencing (RNA-seq) technology, it was found that the differential genes associated with the anxiolytic effect of YL-IPA08 were mainly related to synaptic plasticity. Furthermore, YL-IPA08 restored the decreased levels of brain-derived neurotrophic factor (BDNF), synapse-related protein (e.g. synapsin-1 and post-synaptic density95, PSD95), and the number of doublecortin (DCX) + neurons in the hippocampus of post-ES mice. In addition, YL-IPA08 also enhanced the dendritic complexity and dendritic spine density of hippocampal dentate gyrus (DG) granule neurons. Meanwhile, the induction of long-term potentiation (LTP) was significantly enhanced by YL-IPA08. In summary, the findings from the current study showed that YL-IPA08 exerted a clear anxiolytic effect, which might be partially mediated by promoting hippocampal neuroplasticity.

Development of the optimal scheme for the synthesis of the dipeptide TSPO ligand, N-phenylpropionyl-L-tryptophanyl-L-leucine amide (GD-102), a potential anxiolytic drug

Previously at the Zakusov Research Institute of Pharmacology the first dipeptide ligand TSPO, the compound N-phenylpropionyl-L-tryptophanyl-L-leucine amide (laboratory code GD-102), was designed and synthesized. The anxiolytic activity was detected for this compound at the doses 0.01–1.0 mg/kg intraperitoneally (ip) in mice. Dipeptide GD-102 also possessed antidepressant-like activity at the doses 0.01 and 0.05 mg/kg ip in BALB/c mice in the Porsolt forced swim test. The ligand properties of dipeptide GD-102 to TSPO were confirmed by pharmacological inhibitory analysis and molecular docking. This work is devoted to the development of the optimal scheme for the synthesis of the GD-102. 3 methods were tried — 1 activated succinimide esters method, 2 activated pentafluorophenyl ethers method and 3 imidazolide method. These three synthesis schemes have been compared in terms of yield and optical purity of the final product. It was shown that the optimal synthesis scheme is the first one, using succinimide esters.

Anti‐inflammatory and anti‐apoptotic activity of a TSPO ligand in slowing retina neurodegeneration in a model of retinitis pigmentosa

Aims/Purpose: An evolutionary well‐conserved protein called translocator protein (TSPO, 18 kDa) is found on the outer mitochondrial membrane. Under typical physiological conditions, TSPO expression in the central nervous system is rather low. Changes in TSPO expression, however, can result from several clinical conditions, including neurodegenerative diseases, and neuroinflammation. In a previous study (1) we test the efficacy of a new class of TSPO ligands (PIGAs) (1), in an in vitro model (661W, photoreceptor‐like cell line) of Lipopolysaccharide (LPS)‐induced neuroinflammation. We demonstrate the TSPO expression in retinal photoreceptor and the activity of this ligands in an in vitro neurodegeneration. Here, we examined the anti‐inflammatory effects of the highest active TSPO ligand (PIGA‐1138) on heterozygous (±) Tvrm4 mice (RhoTvrm4/Rho+) an animal model of autosomal dominant retinitis pigmentosa (RP) highly sensitive to light‐induced photoreceptor degeneration. The inflammatory component plays a predominant role in RP progression towards cone death and complete blindness.Methods: Mice have been treated with 3 or 10 mg/kg/die for seven days, starting from the day of onset of retinal degeneration induced by exposure for 1 min to a white light of 12000lux intensity. At the end of the protocol retinal functionality was tested by recording Electroretinogram (ERG) flash response in both scotopic and photopic conditions. Retinal tissue was collected from recorded mice and the tissue was used for further analyses including biochemical and molecular biology assays.Results: PIGA‐treated animal group shows improved response to flash ERG, reduced damaged area measured by cone‐arrestin staining, and modulation of pro‐ and anti‐inflammatory markers.Conclusions: As conclusion, we were able to establish that the TSPO ligand can slow down photoreceptor degeneration and confirm the results of the in vitro study.

FGIN-1-27 Mitigates Radiation-induced Mitochondrial Hyperfunction and Cellular Hyperactivation in Cultured Astrocytes

Radiation-induced brain injury (RBI) poses a significant challenge in the context of radiotherapy for intracranial tumors, necessitating a comprehensive understanding of the cellular and molecular mechanisms involved. While prior investigations have underscored the role of astrocyte activation and excessive vascular endothelial growth factor production in microvascular damage associated with RBI, there remains a scarcity of studies examining the impact of radiation on astrocytes, particularly regarding organelles such as mitochondria. Thus, our study aimed to elucidate alterations in astrocyte and mitochondrial functionality following radiation exposure, with a specific focus on evaluating the potential ameliorative effects of translocator protein 18 kDa(TSPO) ligands. In this study, cultured astrocytes were subjected to X-ray irradiation, and their cellular states and mitochondrial functions were examined and compared to control cells. Our findings revealed that radiation-induced astrocytic hyperactivation, transforming them into the neurotoxic A1-type, concomitant with reduced cell proliferation. Additionally, radiation triggered mitochondrial hyperfunction, heightened the mitochondrial membrane potential, and increased oxidative metabolite production. However, following treatment with FGIN-1-27, a TSPO ligand, we observed a restoration of mitochondrial function and a reduction in oxidative metabolite production. Moreover, this intervention mitigated astrocyte hyperactivity, decreased the number of A1-type astrocytes, and restored cell proliferative capacity. In conclusion, our study has unveiled additional manifestations of radiation-induced astrocyte dysfunction and validated that TSPO ligands may serve as a promising therapeutic strategy to mitigate this dysfunction. It has potential clinical implications for the treatment of RBI.

Neurosteroids Mediate Neuroprotection in an In Vitro Model of Hypoxic/Hypoglycaemic Excitotoxicity via δ-GABAA Receptors without Affecting Synaptic Plasticity.

Neurosteroids and benzodiazepines are modulators of the GABAA receptors, thereby causing anxiolysis. Furthermore, benzodiazepines such as midazolam are known to cause adverse side-effects on cognition upon administration. We previously found that midazolam at nanomolar concentrations (10 nM) blocked long-term potentiation (LTP). Here, we aim to study the effect of neurosteroids and their synthesis using XBD173, which is a synthetic compound that promotes neurosteroidogenesis by binding to the translocator protein 18 kDa (TSPO), since they might provide anxiolytic activity with a favourable side-effect profile. By means of electrophysiological measurements and the use of mice with targeted genetic mutations, we revealed that XBD173, a selective ligand of the translocator protein 18 kDa (TSPO), induced neurosteroidogenesis. In addition, the exogenous application of potentially synthesised neurosteroids (THDOC and allopregnanolone) did not depress hippocampal CA1-LTP, the cellular correlate of learning and memory. This phenomenon was observed at the same concentrations that neurosteroids conferred neuroprotection in a model of ischaemia-induced hippocampal excitotoxicity. In conclusion, our results indicate that TSPO ligands are promising candidates for post-ischaemic recovery exerting neuroprotection, in contrast to midazolam, without detrimental effects on synaptic plasticity.

Design, Synthesis, and Study of Anxiolytic Activity of New Pyrrolo[1,2-a]Pyrazine-Containing TSPO Ligands

Design, Synthesis, and Study of Anxiolytic Activity of New Pyrrolo[1,2-a]Pyrazine-Containing TSPO Ligands

A complex bearing TSPO PIGA ligand coordinated to the [Au(PEt3)]+ pharmacophore is highly cytotoxic against ovarian cancer cells

Auranofin ([1-(thio-κS)-β-d-glucopyranose-2,3,4,6-tetraacetato](triethylphosphine)-gold) is a leading gold-based drug clinically used to treat arthritis. In the last years, it entered various drug reprofiling programs, and it has been found promising against various forms of tumor, including ovarian cancer. Evidence showed as its antiproliferative profile mainly depends on the inhibition of thioredoxin reductase (TrxR), being this mitochondrial system its main target. In this context, we report here the synthesis and biological evaluation of a novel complex designed as auranofin analogue obtained through the conjugation of a phenylindolylglyoxylamide ligand (which belongs to the so-called PIGA TSPO ligand family) with the auranofin-derived cationic fragment [Au(PEt3)]+. This complex is characterized by two parts. The phenylindolylglyoxylamide moiety, owing to its high affinity for TSPO (in the low nM range) should drive the compound to target mitochondria, whereas the [Au(PEt3)]+ cation is the actual anticancer-active molecular fragment. Overall, we wanted to offer the proof-of-concept that by coupling PIGA ligands to anticancer gold active moieties, it is possible to preserve and even improve anticancer effects, opening the avenue to a reliable approach for targeted therapy.

Neurosteroids and translocator protein 18kDa (TSPO) in depression: implications for synaptic plasticity, cognition, and treatment options.

There is need for novel fast acting treatment options in affective disorders. 3α-reduced neurosteroids such as allopregnanolone are powerful positive allosteric modulators of GABAA receptors and target also extrasynaptic receptors. Their synthesis is mediated by the translocator protein 18kDa (TSPO). TSPO ligands not only promote endogenous neurosteroidogenesis, but also exert a broad spectrum of functions involving modulation of mitochondrial activity and acting as anti-inflammatory and neuroregenerative agents. Besides affective symptoms, in depression cognitive impairment can be frequently observed, which may be ameliorated through targeting of extrasynaptic GABAA receptors either via TSPO ligands or exogenously administered 3α-reduced neurosteroids. Interestingly, recent findings indicate an enhanced activation of the complement system, e.g., enhanced expression of C1q, both in depression and dementia. It is of note that benzodiazepines have been shown to reduce long-term potentiation and to cause cognitive decline. Intriguingly, TSPO may be crucial in mediating the effects of benzodiazepines on synaptic pruning. Here, we discuss how benzodiazepines and TSPO may interfere with synaptic pruning. Moreover, we highlight recent developments of TSPO ligands and 3α-reduced neurosteroids as therapeutic agents. Etifoxine is the only clinically available TSPO ligand so far and has been studied in anxiety disorders. Regarding 3α-reduced neurosteroids, brexanolone, an intravenous formulation of allopregnanolone, has been approved for the treatment of postpartum depression and zuranolone, an orally available 3α-reduced neurosteroid, is currently being studied in major depressive disorder and postpartum depression. As such, 3α-reduced neurosteroids and TSPO ligands may constitute promising treatment approaches for affective disorders.

TSPO gene polymorphism in Korean population

AbstractBackground18‐kDA translocator protein (TSPO protein) expression increases in neuroinflammation. Specific ligands that binds to TSPO protein can be used to visualize neuroinflammation. Due to the reported dependency of binding properties of the second‐generation TSPO ligands on a genetic polymorphism of the TSPO gene, all individuals were genotyped and classified as low‐, medium‐, or high‐affinity binder (LAB, MAB, and HAB). The objective of this study is to investigate the rs6971 gene polymorphism in Korean population.MethodWe performed genetic testing in 109 subjects including Alzheimer’s disease, mild cognitive decline, Lewy body disease, subcortical vascular dementia, and cognitively unimpaired participants. All of them performed MRI and detailed neuropsychological test. 29 participants also took 18F‐DPA714 PET. Exon 4 of the TSPO gene containing the polymorphism rs6971 (Ala or Thr at position 147) as well as exon/intron junctions were PCR amplified and sequenced using Sanger method. The identified rs6971 genotypes (C/C, C/T, or T/T) code for the amino acids Ala/ Ala, Ala/Thr, or Thr/Thr at position 147 of the TSPO protein and were considered to generate a high‐, medium‐, or low‐affinity binding phenotype, respectively.ResultWe found 96.3% of the study subjects were HAB (105 out of 109 subjects), and 3.7% of the subjects were MAB (4 out of 109 subjects). There was no participant who was LAB. From HapMap data allele frequency, American group had 69.2%of HABs, 28% of MABs, and 2.8% of LABs. In African group, 67.4% was HABs, 29.4% was MABs, and 3.2% was LABs. In Asian group, 96.9% was HABs, 6.1% was MABs, and 0.1% was LABs. In Europe group, 45.7% was HABs, 43.8% was MABs, and 10.5% was LABs.ConclusionKorean population had lesser frequency of MABs and LABs like other Asian population. Therefore, availability of second‐generation TSPO PET related to rs6971 gene polymorphism would be lesser affected.

Dipeptide Ligands of TSPO

Dipeptide Ligands of TSPO

Microglial proteins Iba1 and TSPO (PBR) are differentially altered in the temporal cortex and cerebellum according to Braak stage

AbstractBackgroundMicroglia are the resident immune cells in the brain and contribute to the neuropathology of Alzheimer’s disease (AD) by mechanisms not completely known. Iba1 is a microglial marker associated with homeostatic and motility functions. Whereas TSPO (PBR) is a marker of the mitochondrial membrane in microglia, macrophages and endothelial cells and is proposed to be associated with the activated subtype of microglia.MethodTo assess both Iba1 and PBR, we retrieved human temporal cortex and cerebellum samples from 57 cases at different stages of the disease, based on the Braak staging (Group 0‐II n=19, Group III‐IV n=20, Group V‐VI n=18), using immunohistochemical analysis. Additionally, a V‐Plex Mesoscale Discovery (MSD) analysis was performed to assess the inflammatory environment.ResultThere was a significant increase in PBR percentage load (P&lt;0.001) across the Braak stages in the temporal cortex (average load 0.93%) but not in the cerebellum (average load 0.76%). Conversely, there was a significant increase in cerebellar Iba1 load (average load 0.96%, P=0.012) but not in the temporal cortex (average load 1.12%). Furthermore, it was observed that Iba1 forms clusters, putatively around amyloid plaques, whereas this phenomenon was not seen with the PBR marker. The only significant inflammatory molecule was the cytokine IL15 in the temporal cortex (P=0.024), which increased across all Braak stages. However, when the MSD data was correlated with the Iba1 and PBR markers it showed that GM‐CSF was significantly correlated with PBR in the temporal cortex (P&lt;0.0099) and IL‐16 was significantly correlated with Iba1 in the cerebellum (P&lt;0.0012).ConclusionThis emphasises the outcome that, in AD, PBR may contribute to inflammation in the temporal cortex and Iba1 may be correlated to inflammation in the cerebellum. The findings indicate that TSPO relates to microglial activation in the brain which is Braak‐stage specific and consequently supports the use of TSPO ligands for positron emission tomography (PET) imaging of Alzheimer’s disease‐relevant microglial activity in vivo. Moreover, the absence of an increase in PBR load in the cerebellum could qualify this structure as a reference region for PET quantification.

18F-Radiolabeled Translocator Protein (TSPO) PET Tracers: Recent Development of TSPO Radioligands and Their Application to PET Study.

Translocator protein 18 kDa (TSPO) is a transmembrane protein in the mitochondrial membrane, which has been identified as a peripheral benzodiazepine receptor. TSPO is generally present at high concentrations in steroid-producing cells and plays an important role in steroid synthesis, apoptosis, and cell proliferation. In the central nervous system, TSPO expression is relatively modest under normal physiological circumstances. However, some pathological disorders can lead to changes in TSPO expression. Overexpression of TSPO is associated with several diseases, such as neurodegenerative diseases, neuroinflammation, brain injury, and cancers. TSPO has therefore become an effective biomarker of related diseases. Positron emission tomography (PET), a non-invasive molecular imaging technique used for the clinical diagnosis of numerous diseases, can detect diseases related to TSPO expression. Several radiolabeled TSPO ligands have been developed for PET. In this review, we describe recent advances in the development of TSPO ligands, and 18F-radiolabeled TSPO in particular, as PET tracers. This review covers pharmacokinetic studies, preclinical and clinical trials of 18F-labeled TSPO PET ligands, and the synthesis of TSPO ligands.