RESUMO
Intramembrane cleavage of transmembrane proteins is a fundamental cellular process to produce important signals that elicit biological responses. These proteolytic events are known as regulated intramembrane proteolysis (RIP). ATF6 and BBF2H7 are transmembrane basic leucine zipper transcription factors and are subjected to RIP by site-1 protease (S1P) and site-2 protease (S2P) sequentially in response to endoplasmic reticulum (ER) stress. However, the detailed mechanisms responsible for RIP of the transcription factors, including the precise cutting sites, are still unknown. In this study, we demonstrated that S1P cleaves BBF2H7 just before the RXXL S1P recognition motif. Conversely, S2P cut at least three different sites in the membrane (next to Leu380, Met381, and Leu385), indicating that S2P cleaves the substrates at variable sites or via a multistep process. Interestingly, we found BBF2H7-derived small peptide (BSP) fragments located between the S1P and S2P cleavage sites in cells exposed to ER stress. Major type of BSP fragments was composed of 45 amino acid including partial transmembrane and luminal regions and easily aggregates like amyloid ß (Aß) protein. These results advance the understanding of poorly characterized ER stress-dependent RIP. Furthermore, the aggregable peptides produced by ER stress could link to the pathophysiology of neurodegenerative disorders.
Assuntos
Peptídeos beta-Amiloides/metabolismo , Fatores de Transcrição de Zíper de Leucina Básica/metabolismo , Estresse do Retículo Endoplasmático/fisiologia , Retículo Endoplasmático/metabolismo , Proteólise , Fator 6 Ativador da Transcrição/metabolismo , Fatores de Transcrição de Zíper de Leucina Básica/genética , Humanos , Fragmentos de Peptídeos/metabolismo , Proteína de Ligação a Elemento Regulador de Esterol 1/metabolismo , Transcrição Gênica/fisiologiaRESUMO
The radiotracer, [18 F]-THK-5351, is a highly selective and high-binding affinity PET imaging agent for aggregates of hyper-phosphorylated tau protein. Our report is a simplified 1-pot, 2-step radiosynthesis of [18 F]-THK-5351. This report is broadly applicable for routine clinical production and multi-center trials on account of favorable half-life of flourine-18 and the use of a commercially available radiosynthesis module, the GE TRACERlab™ FXFN . First, the O-THP protected tosyl precursor underwent nucleophilic fluorinating reaction with potassium cryptand fluoride ([18 F] fluoride (K[18 F]/K222 )) in Dimethyl sulfoxide at 110°C for 10 minutes followed by O-THP removal by using diluted hydrochloric acid (HCl) at same temperature. [18 F]-THK-5351 was purified via semi-preparative high-performance liquid chromatography and formulated by using 10% EtOH, United States Pharmacopeia (USP) in 0.9% sodium chloride for injection, USP and an uncorrected radiochemical yield of 21 ± 3.5%, with a specific activity of 153.11 ± 25.9 GBq/µmol (4138 ± 700 mCi/µmol) at the end of synthesis (63 minutes; n = 3).
Assuntos
Aminopiridinas/síntese química , Quinolinas/síntese química , Compostos Radiofarmacêuticos/síntese química , Aminopiridinas/química , Automação/métodos , Técnicas de Química Sintética/métodos , Quinolinas/química , Compostos Radiofarmacêuticos/químicaRESUMO
PURPOSE: 18F-THK5351 is a novel radiotracer developed for in vivo imaging of tau pathology in the brain. For the quantitative assessment of tau deposits in the brain, it is important that the radioactive metabolite does not enter the brain and that it does not bind to tau fibrils. The purpose of the study was to identify a radiolabeled metabolite of 18F-THK5351 in blood samples from human subjects and to characterize its pharmacological properties. METHODS: Venous blood samples were collected from three human subjects after injection of 18F-THK5351 and the plasma metabolite was measured by high performance thin layer chromatography. In addition, mass spectrometry analysis and enzymatic assays were used to identify this metabolite. Mice were used to investigate the blood-brain barrier permeability of the radioactive metabolite. Furthermore, the binding ability of the metabolite to tau aggregates was evaluated using autoradiography and binding assays using human brain samples. RESULTS: About 13 % of the unmetabolized radiotracer was detectable in human plasma at 60 min following the injection of 18F-THK5351. The isolated radiometabolite of 18F-THK5351 was the sulphoconjugate of THK5351. This metabolite could be produced in vitro by incubating THK5351 with liver but not brain homogenates. The metabolite did not penetrate the blood-brain barrier in mice, and exhibited little binding to tau protein aggregates in post-mortem human brain samples. CONCLUSIONS: These results suggest that the sole metabolite detectable in plasma seems to be generated outside the brain and does not cross into the brain, which does not affect quantitative analysis of PET images.
Assuntos
Aminopiridinas/sangue , Aminopiridinas/farmacocinética , Barreira Hematoencefálica/metabolismo , Imagem Molecular/métodos , Quinolinas/sangue , Quinolinas/farmacocinética , Proteínas tau/metabolismo , Idoso , Aminopiridinas/síntese química , Animais , Barreira Hematoencefálica/diagnóstico por imagem , Feminino , Humanos , Marcação por Isótopo/métodos , Masculino , Taxa de Depuração Metabólica , Camundongos , Camundongos Endogâmicos ICR , Quinolinas/síntese química , Compostos Radiofarmacêuticos/sangue , Compostos Radiofarmacêuticos/síntese química , Compostos Radiofarmacêuticos/farmacocinética , Distribuição TecidualRESUMO
Several promising tau imaging probes have been developed by Tohoku University ([18F]THK series), National Institute of Radiological Sciences([11C]PBB3), Eli Lilly ([18F]T807), and Hoffman-La Roche ([18F]R06958948). In this paper we discussed some of the criteria required for the tau imaging probe in Alzheimer's disease. It will be certain that tau imaging plays an important role in an accurate diagnosis and as companion diagnostics.
Assuntos
Doença de Alzheimer/diagnóstico , Proteínas tau/análise , Doença de Alzheimer/metabolismo , Cognição , Humanos , Tomografia por Emissão de Pósitrons , Compostos Radiofarmacêuticos/química , Proteínas tau/metabolismoRESUMO
Development of symptomatic treatment of Alzheimer s disease by cholinesterase inhibitors like donepezil was successful. However, it is a disappointment that development of disease-modifying drugs such as anti-amyloid drug based on amyloid-cascade theory has been interrupted or unsuccessful. Therefore, we have to be more cautious regarding inclusion criteria for clinical trials of new drugs. We agree that potentially curative drugs should be started before symptoms begin as a preemptive therapy or prevention trial. The concept of personalized medicine also is important when ApoE4-related amyloid reducing therapy is considered. Unfortunately, Japanese-ADNI has suffered a setback since 2014. However, Ministry of Health, Labour and Welfare gave a final remark that there was nothing wrong in the data managing process in the J-ADNI data center. We should pay more attention to worldwide challenges of speeding up new drug development.
Assuntos
Doença de Alzheimer/tratamento farmacológico , Envelhecimento , Amiloide/antagonistas & inibidores , Amiloide/metabolismo , Humanos , Proteínas tau/metabolismoRESUMO
PURPOSE: Visualization of the spatial distribution of neurofibrillary tangles would help in the diagnosis, prevention and treatment of dementia. The purpose of the study was to evaluate the clinical utility of [(18)F]THK-5117 as a highly selective tau imaging radiotracer. METHODS: We initially evaluated in vitro binding of [(3)H]THK-5117 in post-mortem brain tissues from patients with Alzheimer's disease (AD). In clinical PET studies, [(18)F]THK-5117 retention in eight patients with AD was compared with that in six healthy elderly controls. Ten subjects underwent an additional [(11)C]PiB PET scan within 2 weeks. RESULTS: In post-mortem brain samples, THK-5117 bound selectively to neurofibrillary deposits, which differed from the binding target of PiB. In clinical PET studies, [(18)F]THK-5117 binding in the temporal lobe clearly distinguished patients with AD from healthy elderly subjects. Compared with [(11)C]PiB, [(18)F]THK-5117 retention was higher in the medial temporal cortex. CONCLUSION: These findings suggest that [(18)F]THK-5117 provides regional information on neurofibrillary pathology in living subjects.
Assuntos
Doença de Alzheimer/diagnóstico por imagem , Compostos de Anilina/farmacocinética , Neurofibrilas/diagnóstico por imagem , Tomografia por Emissão de Pósitrons , Quinolinas/farmacocinética , Compostos Radiofarmacêuticos , Idoso , Idoso de 80 Anos ou mais , Doença de Alzheimer/patologia , Compostos de Anilina/farmacologia , Benzotiazóis , Estudos de Casos e Controles , Córtex Cerebral/diagnóstico por imagem , Córtex Cerebral/patologia , Feminino , Humanos , Masculino , Neurofibrilas/patologia , Quinolinas/farmacologia , TiazóisRESUMO
Non-invasive imaging of tau pathology in the living brain would be useful for accurately diagnosing Alzheimer's disease, tracking disease progression, and evaluating the treatment efficacy of disease-specific therapeutics. In this study, we evaluated the clinical usefulness of a novel tau-imaging positron emission tomography tracer 18F-THK5105 in 16 human subjects including eight patients with Alzheimer's disease (three male and five females, 66-82 years) and eight healthy elderly controls (three male and five females, 63-76 years). All participants underwent neuropsychological examination and 3D magnetic resonance imaging, as well as both 18F-THK5105 and 11C-Pittsburgh compound B positron emission tomography scans. Standard uptake value ratios at 90-100 min and 40-70 min post-injection were calculated for 18F-THK5105 and 11C-Pittsburgh compound B, respectively, using the cerebellar cortex as the reference region. As a result, significantly higher 18F-THK5105 retention was observed in the temporal, parietal, posterior cingulate, frontal and mesial temporal cortices of patients with Alzheimer's disease compared with healthy control subjects. In patients with Alzheimer's disease, the inferior temporal cortex, which is an area known to contain high densities of neurofibrillary tangles in the Alzheimer's disease brain, showed prominent 18F-THK5105 retention. Compared with high frequency (100%) of 18F-THK5105 retention in the temporal cortex of patients with Alzheimer's disease, frontal 18F-THK5105 retention was less frequent (37.5%) and was only observed in cases with moderate-to-severe Alzheimer's disease. In contrast, 11C-Pittsburgh compound B retention was highest in the posterior cingulate cortex, followed by the ventrolateral prefrontal, anterior cingulate, and superior temporal cortices, and did not correlate with 18F-THK5105 retention in the neocortex. In healthy control subjects, 18F-THK5105 retention was â¼10% higher in the mesial temporal cortex than in the neocortex. Notably, unlike 11C-Pittsburgh compound B, 18F-THK5105 retention was significantly correlated with cognitive parameters, hippocampal and whole brain grey matter volumes, which was consistent with findings from previous post-mortem studies showing significant correlations of neurofibrillary tangle density with dementia severity or neuronal loss. From these results, 18F-THK5105 positron emission tomography is considered to be useful for the non-invasive assessment of tau pathology in the living brain. This technique would be applicable to the longitudinal evaluation of tau deposition and allow a better understanding of the pathophysiology of Alzheimer's disease.
Assuntos
Doença de Alzheimer/patologia , Compostos de Anilina , Emaranhados Neurofibrilares/patologia , Placa Amiloide/patologia , Tomografia por Emissão de Pósitrons , Quinolinas , Idoso , Idoso de 80 Anos ou mais , Doença de Alzheimer/diagnóstico por imagem , Peptídeos beta-Amiloides/metabolismo , Mapeamento Encefálico/métodos , Radioisótopos de Carbono , Feminino , Humanos , Masculino , Emaranhados Neurofibrilares/diagnóstico por imagem , Tomografia por Emissão de Pósitrons/métodos , Compostos Radiofarmacêuticos , TiazóisRESUMO
PURPOSE: Diagnosis of tauopathies such as Alzheimer's disease (AD) still relies on post-mortem examination of the human brain. A non-invasive method of determining brain tau burden in vivo would allow a better understanding of the pathophysiology of tauopathies. The purpose of the study was to evaluate (18)F-THK523 as a potential tau imaging tracer. METHODS: Ten healthy elderly controls, three semantic dementia (SD) and ten AD patients underwent neuropsychological examination, MRI as well as (18)F-THK523 and (11)C-Pittsburgh compound B (PIB) positron emission tomography (PET) scans. Composite memory and non-memory scores, global and hippocampal brain volume, and partial volume-corrected tissue ratios for (18)F-THK523 and (11)C-PIB were estimated for all participants. Correlational analyses were performed between global and regional (18)F-THK523, (11)C-PIB, cognition and brain volumetrics. RESULTS: (18)F-THK523 presented with fast reversible kinetics. Significantly higher (18)F-THK523 retention was observed in the temporal, parietal, orbitofrontal and hippocampi of AD patients when compared to healthy controls and SD patients. White matter retention was significantly higher than grey matter retention in all participants. The pattern of cortical (18)F-THK523 retention did not correlate with Aß distribution as assessed by (11)C-PIB and followed the known distribution of tau in the AD brain, being higher in temporal and parietal areas than in the frontal region. Unlike (11)C-PIB, hippocampal (18)F-THK523 retention was correlated with several cognitive parameters and with hippocampal atrophy. CONCLUSION: (18)F-THK523 does not bind to Aß in vivo, while following the known distribution of paired helical filaments (PHF)-tau in the brain. Significantly higher cortical (18)F-THK523 retention in AD patients as well as the association of hippocampal (18)F-THK523 retention with cognitive parameters and hippocampal volume suggests (18)F-THK523 selectively binds to tau in AD patients. Unfortunately, the very high (18)F-THK523 retention in white matter precludes simple visual inspection of the images, preventing its use in research or clinical settings.
Assuntos
Doença de Alzheimer/diagnóstico por imagem , Compostos de Anilina , Quinolinas , Compostos Radiofarmacêuticos , Proteínas tau/metabolismo , Idoso , Idoso de 80 Anos ou mais , Peptídeos beta-Amiloides/metabolismo , Compostos de Anilina/farmacocinética , Encéfalo/diagnóstico por imagem , Estudos de Casos e Controles , Feminino , Demência Frontotemporal/diagnóstico por imagem , Humanos , Masculino , Pessoa de Meia-Idade , Tomografia por Emissão de Pósitrons , Ligação Proteica , Quinolinas/farmacocinética , Compostos Radiofarmacêuticos/farmacocinética , Tiazóis/farmacocinética , Distribuição TecidualRESUMO
In several neurodegenerative diseases that are collectively called tauopathies, progressive accumulation of tau in the brain is closely associated with neurodegeneration and cognitive impairment. Noninvasive detection of tau protein deposits in the brain would be useful to diagnose tauopathies as well as to track and predict disease progression. Recently, several tau PET tracers including T807, THK-5117, and PBB3 have been developed and succeeded in imaging neurofibrillary pathology in vivo. For use of tau PET as a biomarker of tau pathology in Alzheimer's disease, PET tracers should have high affinity to PHF-tau and high selectivity for tau over amyloid-ß and other protein deposits. PET tau imaging enables the longitudinal assessment of the spatial pattern of tau deposition and its relation to amyloid-ß pathology and neurodegeneration. This technology could also be applied to the pharmacological assessment of anti-tau therapy, thereby allowing preventive interventions.
Assuntos
Doença de Alzheimer/diagnóstico por imagem , Doença de Alzheimer/metabolismo , Tomografia por Emissão de Pósitrons/métodos , Compostos Radiofarmacêuticos , Proteínas tau/metabolismo , Humanos , Ligação Proteica/efeitos dos fármacosRESUMO
Two methods are commonly used in brain image voxel-based analyses widely used for dementia work-ups: 3-dimensional stereotactic surface projections (3D-SSP) and statistical parametric mapping (SPM). The methods calculate the Z-scores of the cortical voxels that represent the significance of differences compared to a database of brain images with normal findings, and visualize them as surface brain maps. The methods are considered useful in amyloid positron emission tomography (PET) analyses to detect small amounts of amyloid-ß deposits in early-stage Alzheimer's disease (AD), but are not fully validated. We analyzed the (11)C-labeled 2-(2-[2-dimethylaminothiazol-5-yl]ethenyl)-6-(2-[fluoro]ethoxy)benzoxazole (BF-227) amyloid PET imaging of 56 subjects (20 individuals with mild cognitive impairment [MCI], 19 AD patients, and 17 non-demented [ND] volunteers) with 3D-SSP and the easy Z-score imaging system (eZIS) that is an SPM-based method. To clarify these methods' limitations, we visually compared Z-score maps output from the two methods and investigated the causes of discrepancies between them. Discrepancies were found in 27 subjects (9 MCI, 13 AD, and 5 ND). Relatively high white matter uptake was considered to cause higher Z-scores on 3D-SSP in 4 subjects (1 MCI and 3 ND). Meanwhile, in 17 subjects (6 MCI, 9 AD, and 2 ND), Z-score overestimation on eZIS corresponded with high skull uptake and disappeared after removing the skull uptake ("scalping"). Our results suggest that non-specific uptakes in the white matter and skull account for errors in voxel-based amyloid PET analyses. Thus, diagnoses based on 3D-SSP data require checking white matter uptake, and "scalping" is recommended before eZIS analysis.
Assuntos
Doença de Alzheimer/diagnóstico por imagem , Amiloide , Artefatos , Tomografia por Emissão de Pósitrons , Crânio/diagnóstico por imagem , Substância Branca/diagnóstico por imagem , Idoso , Doença de Alzheimer/patologia , Benzoxazóis , Disfunção Cognitiva/diagnóstico por imagem , Demência/diagnóstico por imagem , Demografia , Feminino , Humanos , Masculino , Tiazóis , Substância Branca/patologiaRESUMO
Alzheimer's disease (AD) is the most common cause of dementia. Senile plaques, consisting of ß-amyloid, and neurofibrillary tangles (NFTs), composed of tau protein, are representative pathological hallmarks of AD. It is believed that the accumulation of NFTs precedes the onset of clinical symptoms of AD and correlates with the progression of memory dysfunction. Thus, the use of noninvasive detection techniques including radiolabeled probes and positron emission tomography (PET) will facilitate early diagnosis or staging of AD. In this study, we synthesized and evaluated novel hydroxylated 2-arylquinoline derivatives as tau imaging PET probes. The binding affinities of compounds for tau were evaluated by fluorescent staining of the AD hippocampal section and a competitive binding assay using [(18) F]THK-523. THK-951 showed high binding affinity for tau pathology in an AD brain section and K18Δ280K fibrils (Ki = 20.7 nM); thus, we radiosynthesized a (11) C-labeled THK-951 and further studied its potential as a tau PET probe. The [(11) C]THK-951 demonstrated excellent kinetics in a normal mouse brain (3.23% ID/g at 2 min postinjection and 0.15% ID/g at 30 min postinjection) and showed the labeling of NFTs in an AD brain section by autoradiography assay. These findings indicate the availability of [(11) C]THK-951 for in vivo PET imaging of tau pathology in AD.
Assuntos
Hidroxiquinolinas/síntese química , Tomografia por Emissão de Pósitrons/métodos , Proteínas tau/metabolismo , Idoso de 80 Anos ou mais , Animais , Radioisótopos de Carbono , Técnicas de Química Sintética , Feminino , Hipocampo/diagnóstico por imagem , Hipocampo/metabolismo , Humanos , Interações Hidrofóbicas e Hidrofílicas , Hidroxilação , Hidroxiquinolinas/química , Hidroxiquinolinas/farmacocinética , CamundongosRESUMO
PURPOSE: Extensive deposition of senile plaques and neurofibrillary tangles in the brain is a pathological hallmark of Alzheimer's disease (AD). Although several PET imaging agents have been developed for in vivo detection of senile plaques, no PET probe is currently available for selective detection of neurofibrillary tangles in the living human brain. Recently, [(18)F]THK-523 was developed as a potential in vivo imaging probe for tau pathology. The purpose of this study was to compare the binding properties of [(18)F]THK-523 and other amyloid imaging agents, including PiB, BF-227 and FDDNP, to synthetic protein fibrils and human brain tissue. METHODS: In vitro radioligand binding assays were conducted using synthetic amyloid ß(42) and K18ΔK280-tau fibrils. Nonspecific binding was determined by the addition of unlabelled compounds at a concentration of 2 µM. To examine radioligand binding to neuropathological lesions, in vitro autoradiography was conducted using sections of AD brain. RESULTS: [(18)F]THK-523 showed higher affinity for tau fibrils than for Aß fibrils, whereas the other probes showed a higher affinity for Aß fibrils. The autoradiographic analysis indicated that [(18)F]THK-523 accumulated in the regions containing a high density of tau protein deposits. Conversely, PiB and BF-227 accumulated in the regions containing a high density of Aß plaques. CONCLUSION: These findings suggest that the unique binding profile of [(18)F]THK-523 can be used to identify tau deposits in AD brain.
Assuntos
Doença de Alzheimer/diagnóstico por imagem , Amiloide/análise , Compostos de Anilina/metabolismo , Quinolinas/metabolismo , Compostos Radiofarmacêuticos/metabolismo , Idoso , Idoso de 80 Anos ou mais , Amiloide/metabolismo , Encéfalo/diagnóstico por imagem , Química Encefálica , Humanos , Tomografia por Emissão de Pósitrons , Ligação Proteica , Traçadores Radioativos , Ensaio RadioliganteRESUMO
PURPOSE: Noninvasive imaging of protein aggregates in the brain is critical for the early diagnosis, disease monitoring, and evaluation of the effectiveness of novel therapies for Alzheimer's disease (AD). Near-infrared fluorescence (NIRF) imaging with specific probes is a promising technique for the in vivo detection of protein deposits without radiation exposure. Comprehensive screening of fluorescent compounds identified a novel compound, THK-565, for the in vivo imaging of amyloid-ß (Aß) deposits in the mouse brain. This study assessed whether THK-565 could detect amyloid-ß deposits in vivo in the AD mouse model. PROCEDURES: The fluorescent properties of THK-565 were evaluated in the presence and absence of Aß fibrils. APP knock-in (APP-KI) mice were used as an animal model of AD. In vivo NIRF images were acquired after the intravenous administration of THK-565 and THK-265 in mice. The binding selectivity of THK-565 to Aß was evaluated using brain slices obtained from these mouse models. RESULTS: The fluorescence intensity of the THK-565 solution substantially increased by mixing with Aß fibrils. The maximum emission wavelength of the complex of THK-565 and Aß fibrils was 704 nm, which was within the optical window range. THK-565 selectively bound to amyloid deposits in brain sections of APP-KI mice After the intravenous administration of THK-565, the fluorescence signal in the head of APP-KI mice was significantly higher than that of wild-type mice and higher than that after administration of THK-265. Ex vivo analysis confirmed that the THK-565 signal corresponded to Aß immunostaining in the brain sections of these mice. CONCLUSIONS: A novel NIRF probe, THK-565, enabled the in vivo detection of Aß deposits in the brains of the AD mouse model, suggesting that NIRF imaging with THK-565 could non-invasively assess disease-specific pathology in AD.
Assuntos
Doença de Alzheimer , Camundongos , Animais , Doença de Alzheimer/metabolismo , Placa Amiloide/metabolismo , Amiloide/metabolismo , Peptídeos beta-Amiloides/metabolismo , Encéfalo/metabolismo , Modelos Animais de Doenças , Corantes Fluorescentes/química , Camundongos TransgênicosRESUMO
Astrogliosis is a crucial feature of neuroinflammation and is characterized by the significant upregulation of glial fibrillary acidic protein (GFAP) expression. Hence, visualizing GFAP in the living brain of patients with damaged central nervous system using positron emission tomography (PET) is of great importance, and it is expected to depict neuroinflammation more directly than existing neuroinflammation imaging markers. However, no PET radiotracers for GFAP are currently available. Therefore, neuroimaging with antibody-like affinity proteins could be a viable strategy for visualizing imaging targets that small molecules rarely recognize, such as GFAP, while we need to overcome the challenges of slow clearance and low brain permeability. The E9 nanobody, a small-affinity protein with high affinity and selectivity for GFAP, was utilized in this study. E9 was engineered by fusing a brain shuttle peptide that facilitates blood-brain barrier permeation via two different types of linker domains: E9-GS-ApoE (EGA) and E9-EAK-ApoE (EEA). E9, EGA and EEA were radiolabeled with fluorine-18 using cell-free protein radiosynthesis. In vitro autoradiography showed that all radiolabeled proteins exhibited a significant difference in neuroinflammation in the brain sections created from a rat model constructed by injecting lipopolysaccharide (LPS) into the unilateral striatum of wildtype rats, and an excess competitor displaced their binding. However, exploratory in vivo PET imaging and ex vivo biodistribution studies in the rat model failed to distinguish neuroinflammatory lesions within 3 h of 18F-EEA intravenous injection. This study contributes to a better understanding of the characteristics of small-affinity proteins fused with a brain shuttle peptide for further research into the use of protein molecules as PET tracers for imaging neuropathology.
Assuntos
Doenças Neuroinflamatórias , Tomografia Computadorizada por Raios X , Animais , Ratos , Apolipoproteínas E , Encéfalo/diagnóstico por imagem , Proteína Glial Fibrilar Ácida , Peptídeos , Distribuição Tecidual , Anticorpos de Domínio ÚnicoRESUMO
Quantification of in vivo reactive astrogliosis, which represents neural inflammation and remodeling in the brain, is an emerging methodology for the evaluation of patients with neurodegenerative diseases. [18F]THK-5351 is a positron emission tomography (PET) tracer for monoamine oxidase B (MAO-B), a molecular marker of reactive astrogliosis. We performed in vivo [18F]THK-5351 PET in a patient who at autopsy was found to have argyrophilic grain disease (AGD) with comorbid pathology to visualize reactive astrogliosis for the first time. We aimed to validate an imaging-pathology correlation using [18F]THK-5351 PET and the autopsy brain. The patient, a 78-year-old man, was pathologically diagnosed with AGD combined with limbic-predominant age-related transactive response DNA-binding protein of 43 kDa encephalopathy and Lewy body disease without Alzheimer disease-related neuropathological changes. Reactive astrogliosis in the postmortem brain was abundant in the inferior temporal gyrus, insular gyrus, entorhinal cortex, and ambient gyrus where premortem [18F]THK-5351 signals were high. We found a proportional correlation between the amount of reactive astrogliosis in the postmortem brain and the in vivo [18F]THK-5351 standardized uptake value ratio (r = 0.8535, p = 0.0004). These results indicated that reactive astrogliosis in AGD with comorbid pathology could be identified and quantified by in vivo MAO-B imaging.
Assuntos
Doença de Alzheimer , Doenças Neurodegenerativas , Masculino , Humanos , Idoso , Gliose/patologia , Doença de Alzheimer/patologia , Doenças Neurodegenerativas/complicações , Doenças Neurodegenerativas/diagnóstico por imagem , Doenças Neurodegenerativas/metabolismo , Encéfalo/patologia , Tomografia por Emissão de Pósitrons , Monoaminoxidase/metabolismo , Proteínas tau/metabolismoRESUMO
Tau PET tracers are expected to be sufficiently sensitive to track the progression of age-related tau pathology in the medial temporal cortex. The tau PET tracer N-(4-[18F]fluoro-5-methylpyridin-2-yl)-7-aminoimidazo[1,2-a]pyridine ([18F]SNFT-1) has been successfully developed by optimizing imidazo[1,2-a]pyridine derivatives. We characterized the binding properties of [18F]SNFT-1 using a head-to-head comparison with other reported 18F-labeled tau tracers. Methods: The binding affinity of SNFT-1 to tau, amyloid, and monoamine oxidase A and B was compared with that of the second-generation tau tracers MK-6240, PM-PBB3, PI-2620, RO6958948, JNJ-64326067, and flortaucipir. In vitro binding properties of 18F-labeled tau tracers were evaluated through the autoradiography of frozen human brain tissues from patients with diverse neurodegenerative disease spectra. Pharmacokinetics, metabolism, and radiation dosimetry were assessed in normal mice after intravenous administration of [18F]SNFT-1. Results: In vitro binding assays demonstrated that [18F]SNFT-1 possesses high selectivity and high affinity for tau aggregates in Alzheimer disease (AD) brains. Autoradiographic analysis of tau deposits in medial temporal brain sections from patients with AD showed a higher signal-to-background ratio for [18F]SNFT-1 than for the other tau PET tracers and no significant binding with non-AD tau, α-synuclein, transactiviation response DNA-binding protein-43, and transmembrane protein 106B aggregates in human brain sections. Furthermore, [18F]SNFT-1 did not bind significantly to various receptors, ion channels, or transporters. [18F]SNFT-1 showed a high initial brain uptake and rapid washout from the brains of normal mice without radiolabeled metabolites. Conclusion: These preclinical data suggest that [18F]SNFT-1 is a promising and selective tau radiotracer candidate that allows the quantitative monitoring of age-related accumulation of tau aggregates in the human brain.
Assuntos
Doença de Alzheimer , Doenças Neurodegenerativas , Humanos , Camundongos , Animais , Doenças Neurodegenerativas/metabolismo , Doença de Alzheimer/metabolismo , Piridinas/farmacocinética , Encéfalo/metabolismo , Proteínas tau/metabolismo , Tomografia por Emissão de PósitronsRESUMO
While considerable effort has focused on developing positron emission tomography ß-amyloid imaging radiotracers for the early diagnosis of Alzheimer's disease, no radiotracer is available for the non-invasive quantification of tau. In this study, we detail the characterization of (18)F-THK523 as a novel tau imaging radiotracer. In vitro binding studies demonstrated that (18)F-THK523 binds with higher affinity to a greater number of binding sites on recombinant tau (K18Δ280K) compared with ß-amyloid(1-42) fibrils. Autoradiographic and histofluorescence analysis of human hippocampal serial sections with Alzheimer's disease exhibited positive THK523 binding that co-localized with immunoreactive tau pathology, but failed to highlight ß-amyloid plaques. Micro-positron emission tomography analysis demonstrated significantly higher retention of (18)F-THK523 (48%; P < 0.007) in tau transgenic mice brains compared with their wild-type littermates or APP/PS1 mice. The preclinical examination of THK523 has demonstrated its high affinity and selectivity for tau pathology both in vitro and in vivo, indicating that (18)F-THK523 fulfils ligand criteria for human imaging trials.
Assuntos
Doença de Alzheimer/diagnóstico por imagem , Compostos de Anilina/farmacologia , Encéfalo/diagnóstico por imagem , Fluordesoxiglucose F18/farmacologia , Quinolinas/farmacologia , Compostos Radiofarmacêuticos/farmacologia , Proteínas tau/metabolismo , Doença de Alzheimer/metabolismo , Análise de Variância , Animais , Autorradiografia , Sítios de Ligação , Encéfalo/metabolismo , Feminino , Humanos , Imuno-Histoquímica , Masculino , Camundongos , CintilografiaRESUMO
Many neurodegenerative diseases are neuropathologically characterized by neuronal loss, gliosis, and the deposition of misfolded proteins such as ß-amyloid (Aß) plaques and tau tangles in Alzheimer's disease (AD). In postmortem AD brains, reactive astrocytes and activated microglia are observed surrounding Aß plaques and tau tangles. These activated glial cells secrete pro-inflammatory cytokines and reactive oxygen species, which may contribute to neurodegeneration. Therefore, in vivo imaging of glial response by positron emission tomography (PET) combined with Aß and tau PET would provide new insights to better understand the disease process, as well as aid in the differential diagnosis, and monitoring glial response disease-specific therapeutics. There are two promising targets proposed for imaging reactive astrogliosis: monoamine oxidase-B (MAO-B) and imidazoline2 binding site (I2BS), which are predominantly expressed in the mitochondrial membranes of astrocytes and are upregulated in various neurodegenerative conditions. PET tracers targeting these two MAO-B and I2BS have been evaluated in humans. [18F]THK-5351, which was originally designed to target tau aggregates in AD, showed high affinity for MAO-B and clearly visualized reactive astrocytes in progressive supranuclear palsy (PSP). However, the lack of selectivity of [18F]THK-5351 binding to both MAO-B and tau, severely limits its clinical utility as a biomarker. Recently, [18F]SMBT-1 was developed as a selective and reversible MAO-B PET tracer via compound optimization of [18F]THK-5351. In this review, we summarize the strategy underlying molecular imaging of reactive astrogliosis and clinical studies using MAO-B and I2BS PET tracers.
RESUMO
(S)-(2-Methylpyrid-5-yl)-6-[(3-[18F]fluoro-2-hydroxy)propoxy]quinoline ([18F]SMBT-1) was recently developed as a novel class of selective and reversible monoamine oxidase-B (MAO-B) tracers for in vivo imaging of reactive astrogliosis via positron emission tomography. To investigate the effect of the chirality of [18F]SMBT-1 on tracer performance, we synthesized (S)-[18F]6 ([18F]SMBT-1) and (R)-[18F]6 and compared their binding properties, pharmacokinetics, and metabolism. (S)-6 showed higher binding affinity to MAO-B and lower binding affinity to MAO-A than (R)-6, demonstrating a higher selectivity ratio (MAO-B/MAO-A). A pharmacokinetic study in mice demonstrated that both (S)-[18F]6 and (R)-[18F]6 showed sufficient initial brain uptake. However, (S)-[18F]6 was cleared significantly faster from the body. An abundant sulfoconjugate metabolite M2 was observed in plasma for (S)-[18F]6 but not for (R)-[18F]6. In vitro sulfation assays confirmed that (S)-6 was more reactive than (R)-6, consistent with the in vivo findings. Mefenamic acid, a selective sulfotransferase 1A1 (SULT1A1) inhibitor, strongly inhibited the in vitro sulfation of (S)-6 by mouse liver fractions, human liver cytosol fractions, and human recombinant SULT1A1 enzyme. Genetic polymorphisms of SULT1A1 did not affect the sulfation of (S)-6 in vitro. In conclusion, (S)-[18F]6 had a more favorable binding affinity and binding selectivity for MAO-B than (R)-[18F]6. Additionally, (S)-[18F]6 also possessed better pharmacological and metabolic properties than (R)-[18F]6. These results suggest that (S)-[18F]6 ([18F]SMBT-1) is a promising candidate for application in the imaging of MAO-B in vivo.