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Methods in Molecular Biology (Clifton,... 2024Autoradiography, the direct imaging of radioactive distribution in tissue sections, is a powerful technique that has several key advantages for the validation of PET...
Autoradiography, the direct imaging of radioactive distribution in tissue sections, is a powerful technique that has several key advantages for the validation of PET radiotracers. Using autoradiography, we can localize radiotracer uptake to neighbours of cells, and when multiplexed with additional radiotracers, fluorescent probes, or in situ tissue analysis, autoradiography can help to characterize the mechanism of radiotracer uptake and assess functional heterogeneity in tissue. In this chapter, the author outlines the basic ex vivo autoradiography protocol and shows how it can be multiplexed using dual radionuclides F and C. They also highlight where autoradiography can be combined with other technologies to provide synergistic information for interrogating spatial biology.
Topics: Positron-Emission Tomography; Autoradiography; Radioisotopes; Radiopharmaceuticals; Fluorescent Dyes; Fluorine Radioisotopes
PubMed: 38006510
DOI: 10.1007/978-1-0716-3499-8_24 -
Brain : a Journal of Neurology Jul 2023Reactive astrogliosis is a hallmark of Alzheimer's disease (AD). However, a clinically validated neuroimaging probe to visualize the reactive astrogliosis is yet to be...
Reactive astrogliosis is a hallmark of Alzheimer's disease (AD). However, a clinically validated neuroimaging probe to visualize the reactive astrogliosis is yet to be discovered. Here, we show that PET imaging with 11C-acetate and 18F-fluorodeoxyglucose (18F-FDG) functionally visualizes the reactive astrocyte-mediated neuronal hypometabolism in the brains with neuroinflammation and AD. To investigate the alterations of acetate and glucose metabolism in the diseased brains and their impact on the AD pathology, we adopted multifaceted approaches including microPET imaging, autoradiography, immunohistochemistry, metabolomics, and electrophysiology. Two AD rodent models, APP/PS1 and 5xFAD transgenic mice, one adenovirus-induced rat model of reactive astrogliosis, and post-mortem human brain tissues were used in this study. We further curated a proof-of-concept human study that included 11C-acetate and 18F-FDG PET imaging analyses along with neuropsychological assessments from 11 AD patients and 10 healthy control subjects. We demonstrate that reactive astrocytes excessively absorb acetate through elevated monocarboxylate transporter-1 (MCT1) in rodent models of both reactive astrogliosis and AD. The elevated acetate uptake is associated with reactive astrogliosis and boosts the aberrant astrocytic GABA synthesis when amyloid-β is present. The excessive astrocytic GABA subsequently suppresses neuronal activity, which could lead to glucose uptake through decreased glucose transporter-3 in the diseased brains. We further demonstrate that 11C-acetate uptake was significantly increased in the entorhinal cortex, hippocampus and temporo-parietal neocortex of the AD patients compared to the healthy controls, while 18F-FDG uptake was significantly reduced in the same regions. Additionally, we discover a strong correlation between the patients' cognitive function and the PET signals of both 11C-acetate and 18F-FDG. We demonstrate the potential value of PET imaging with 11C-acetate and 18F-FDG by visualizing reactive astrogliosis and the associated neuronal glucose hypometablosim for AD patients. Our findings further suggest that the acetate-boosted reactive astrocyte-neuron interaction could contribute to the cognitive decline in AD.
Topics: Mice; Humans; Rats; Animals; Alzheimer Disease; Fluorodeoxyglucose F18; Astrocytes; Carbon Radioisotopes; Gliosis; Brain; Positron-Emission Tomography; gamma-Aminobutyric Acid
PubMed: 37062541
DOI: 10.1093/brain/awad037 -
Drug Metabolism and Disposition: the... Jul 2023RNA-based therapeutics and vaccines represent a novel and expanding class of medicines, the success of which depends on the encapsulation and protection of mRNA...
RNA-based therapeutics and vaccines represent a novel and expanding class of medicines, the success of which depends on the encapsulation and protection of mRNA molecules in lipid nanoparticle (LNP)-based carriers. With the development of mRNA-LNP modalities, which can incorporate xenobiotic constituents, extensive biodistribution analyses are necessary to better understand the factors that influence their in vivo exposure profiles. This study investigated the biodistribution of heptadecan-9-yl 8-((2-hydroxyethyl)(8-(nonyloxy)-8-oxooctyl)amino)octanoate (Lipid 5)-a xenobiotic amino lipid-and its metabolites in male and female pigmented (Long-Evans) and nonpigmented (Sprague Dawley) rats by using quantitative whole-body autoradiography (QWBA) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) techniques. After intravenous injection of Lipid 5-containing LNPs, C-containing Lipid 5 ([C]Lipid 5) and radiolabeled metabolites ([C]metabolites) were rapidly distributed, with peak concentrations reached within 1 hour in most tissues. After 10 hours, [C]Lipid 5 and [C]metabolites concentrated primarily in the urinary and digestive tracts. By 24 hours, [C]Lipid 5 and [C]metabolites were localized almost exclusively in the liver and intestines, with few or no concentrations detected in non-excretory systems, which is suggestive of hepatobiliary and renal clearance. [C]Lipid 5 and [C]metabolites were completely cleared within 168 hours (7 days). Biodistribution profiles were similar between QWBA and LC-MS/MS techniques, pigmented and nonpigmented rats, and male and female rats, excluding the reproductive organs. In conclusion, the rapid clearance through known excretory systems, with no evidence of redistribution for Lipid 5 or accumulation of [C]metabolites, provides confidence for the safe and effective use of Lipid 5-containing LNPs. SIGNIFICANCE STATEMENT: This study demonstrates the rapid, systemic distribution of intact and radiolabeled metabolites of Lipid 5, a xenobiotic amino lipid component of novel mRNA-LNP medicines, and its effective clearance without substantial redistribution after intravenous administration; additionally, findings were consistent between different mRNAs encapsulated within LNPs of similar composition. This study confirms the applicability of current analytical methods for lipid biodistribution analyses, and taken together with appropriate safety studies, supports the continued use of Lipid 5 in mRNA-medicines.
Topics: Rats; Male; Female; Animals; Rats, Sprague-Dawley; Tissue Distribution; Chromatography, Liquid; Rats, Long-Evans; RNA, Messenger; Xenobiotics; Tandem Mass Spectrometry; Infusions, Intravenous; Nanoparticles; Lipids; RNA, Small Interfering
PubMed: 37208184
DOI: 10.1124/dmd.122.000980 -
Nature Communications Oct 2023A positron emission tomography (PET) tracer detecting α-synuclein pathology will improve the diagnosis, and ultimately the treatment of α-synuclein-related diseases....
A positron emission tomography (PET) tracer detecting α-synuclein pathology will improve the diagnosis, and ultimately the treatment of α-synuclein-related diseases. Here we show that the PET ligand, [F]ACI-12589, displays good in vitro affinity and specificity for pathological α-synuclein in tissues from patients with different α-synuclein-related disorders including Parkinson's disease (PD) and Multiple-System Atrophy (MSA) using autoradiography and radiobinding techniques. In the initial clinical evaluation we include 23 participants with α-synuclein related disorders, 11 with other neurodegenerative disorders and eight controls. In vivo [F]ACI-12589 demonstrates clear binding in the cerebellar white matter and middle cerebellar peduncles of MSA patients, regions known to be highly affected by α-synuclein pathology, but shows limited binding in PD. The binding statistically separates MSA patients from healthy controls and subjects with other neurodegenerative disorders, including other synucleinopathies. Our results indicate that α-synuclein pathology in MSA can be identified using [F]ACI-12589 PET imaging, potentially improving the diagnostic work-up of MSA and allowing for detection of drug target engagement in vivo of novel α-synuclein targeting therapies.
Topics: Humans; alpha-Synuclein; Multiple System Atrophy; Parkinson Disease; Positron-Emission Tomography
PubMed: 37891183
DOI: 10.1038/s41467-023-42305-3 -
BioRxiv : the Preprint Server For... Sep 2023Positron Emission Tomography (PET) ligands have advanced Alzheimer's disease (AD) diagnosis and treatment. Using autoradiography and cryo-EM, we identified AD brain...
Positron Emission Tomography (PET) ligands have advanced Alzheimer's disease (AD) diagnosis and treatment. Using autoradiography and cryo-EM, we identified AD brain tissue with elevated tau burden, purified filaments, and determined the structure of second-generation high avidity PET ligand MK-6240 at 2.31 Å resolution, which bound at a 1:1 ratio within the cleft of tau paired-helical filament (PHF), engaging with glutamine 351, lysine K353, and isoleucine 360. This information elucidates the basis of MK-6240 PET in quantifying PHF deposits in AD and may facilitate the structure-based design of superior ligands against tau amyloids.
PubMed: 37790438
DOI: 10.1101/2023.09.22.558671 -
Biomedicines Sep 2023Neuroinflammation is a complex biological process that typically originates as a protective response in the brain. This inflammatory process is triggered by the release... (Review)
Review
Neuroinflammation is a complex biological process that typically originates as a protective response in the brain. This inflammatory process is triggered by the release of pro-inflammatory substances like cytokines, prostaglandins, and reactive oxygen and nitrogen species from stimulated endothelial and glial cells, including those with pro-inflammatory functions, in the outer regions. While neuronal inflammation is common in various central nervous system disorders, the specific inflammatory pathways linked with different immune-mediated cell types and the various factors influencing the blood-brain barrier significantly contribute to disease-specific characteristics. The endocannabinoid system consists of cannabinoid receptors, endogenous cannabinoids, and enzymes responsible for synthesizing and metabolizing endocannabinoids. The primary cannabinoid receptor is CB1, predominantly found in specific brain regions such as the brainstem, cerebellum, hippocampus, and cortex. The presence of CB2 receptors in certain brain components, like cultured cerebellar granular cells, Purkinje fibers, and microglia, as well as in the areas like the cerebral cortex, hippocampus, and cerebellum is also evidenced by immunoblotting assays, radioligand binding, and autoradiography studies. Both CB1 and CB2 cannabinoid receptors exhibit noteworthy physiological responses and possess diverse neuromodulatory capabilities. This review primarily aims to outline the distribution of CB1 and CB2 receptors across different brain regions and explore their potential roles in regulating neuroinflammatory processes.
PubMed: 37893016
DOI: 10.3390/biomedicines11102642 -
Nature Neuroscience Jul 2023Dynamics and functions of neural circuits depend on interactions mediated by receptors. Therefore, a comprehensive map of receptor organization across cortical regions...
Dynamics and functions of neural circuits depend on interactions mediated by receptors. Therefore, a comprehensive map of receptor organization across cortical regions is needed. In this study, we used in vitro receptor autoradiography to measure the density of 14 neurotransmitter receptor types in 109 areas of macaque cortex. We integrated the receptor data with anatomical, genetic and functional connectivity data into a common cortical space. We uncovered a principal gradient of receptor expression per neuron. This aligns with the cortical hierarchy from sensory cortex to higher cognitive areas. A second gradient, driven by serotonin 5-HT receptors, peaks in the anterior cingulate, default mode and salience networks. We found a similar pattern of 5-HT expression in the human brain. Thus, the macaque may be a promising translational model of serotonergic processing and disorders. The receptor gradients may enable rapid, reliable information processing in sensory cortical areas and slow, flexible integration in higher cognitive areas.
Topics: Aged; Animals; Female; Humans; Male; Rats; Autoradiography; Brain Mapping; Cerebral Cortex; Cognition; Dendritic Spines; Gyrus Cinguli; Macaca fascicularis; Rats, Inbred Lew; Receptor, Serotonin, 5-HT1A; Receptors, Cholinergic; Receptors, Dopamine; Receptors, Neurotransmitter; Serotonin; Species Specificity; Myelin Sheath
PubMed: 37336976
DOI: 10.1038/s41593-023-01351-2 -
Brain : a Journal of Neurology Aug 2023Amyloid-β (Aβ) is hypothesized to facilitate the spread of tau pathology beyond the medial temporal lobe. However, there is evidence that, independently of Aβ,...
Amyloid-β (Aβ) is hypothesized to facilitate the spread of tau pathology beyond the medial temporal lobe. However, there is evidence that, independently of Aβ, age-related tau pathology might be present outside of the medial temporal lobe. We therefore aimed to study age-related Aβ-independent tau deposition outside the medial temporal lobe in two large cohorts and to investigate potential downstream effects of this on cognition and structural measures. We included 545 cognitively unimpaired adults (40-92 years) from the BioFINDER-2 study (in vivo) and 639 (64-108 years) from the Rush Alzheimer's Disease Center cohorts (ex vivo). 18F-RO948- and 18F-flutemetamol-PET standardized uptake value ratios were calculated for regional tau and global/regional Aβ in vivo. Immunohistochemistry was used to estimate Aβ load and tangle density ex vivo. In vivo medial temporal lobe volumes (subiculum, cornu ammonis 1) and cortical thickness (entorhinal cortex, Brodmann area 35) were obtained using Automated Segmentation for Hippocampal Subfields packages. Thickness of early and late neocortical Alzheimer's disease regions was determined using FreeSurfer. Global cognition and episodic memory were estimated to quantify cognitive functioning. In vivo age-related tau deposition was observed in the medial temporal lobe and in frontal and parietal cortical regions, which was statistically significant when adjusting for Aβ. This was also observed in individuals with low Aβ load. Tau deposition was negatively associated with cortical volumes and thickness in temporal and parietal regions independently of Aβ. The associations between age and cortical volume or thickness were partially mediated via tau in regions with early Alzheimer's disease pathology, i.e. early tau and/or Aβ pathology (subiculum/Brodmann area 35/precuneus/posterior cingulate). Finally, the associations between age and cognition were partially mediated via tau in Brodmann area 35, even when including Aβ-PET as covariate. Results were validated in the ex vivo cohort showing age-related and Aβ-independent increases in tau aggregates in and outside the medial temporal lobe. Ex vivo age-cognition associations were mediated by medial and inferior temporal tau tangle density, while correcting for Aβ density. Taken together, our study provides support for primary age-related tauopathy even outside the medial temporal lobe in vivo and ex vivo, with downstream effects on structure and cognition. These results have implications for our understanding of the spreading of tau outside the medial temporal lobe, also in the context of Alzheimer's disease. Moreover, this study suggests the potential utility of tau-targeting treatments in primary age-related tauopathy, likely already in preclinical stages in individuals with low Aβ pathology.
Topics: Adult; Humans; Alzheimer Disease; tau Proteins; Cognitive Dysfunction; Amyloid beta-Peptides; Tauopathies; Positron-Emission Tomography; Magnetic Resonance Imaging
PubMed: 37082959
DOI: 10.1093/brain/awad135 -
Journal of Nuclear Medicine : Official... Sep 2023Calcific aortic valve disease (CAVD) is a prevailing disease with increasing occurrence and no known medical therapy. mice have a high prevalence of bicuspid aortic...
Calcific aortic valve disease (CAVD) is a prevailing disease with increasing occurrence and no known medical therapy. mice have a high prevalence of bicuspid aortic valve (BAV), spontaneous aortic valve calcification, and aortic stenosis (AS). F-NaF PET/CT can detect the aortic valve calcification process in humans. However, its feasibility in preclinical models of CAVD remains to be determined. Here, we sought to validate F-NaF PET/CT for tracking murine aortic valve calcification and leveraged it to examine the development of calcification with aging and its interdependence with BAV and AS in mice. mice at 3-4 mo, 10-16 mo, and 18-24 mo underwent echocardiography, F-NaF PET/CT ( = 34, or autoradiography ( = 45)), and tissue analysis. A subset of mice underwent both PET/CT and autoradiography ( = 12). The aortic valve signal was quantified as SUV on PET/CT and as percentage injected dose per square centimeter on autoradiography. The valve tissue sections were analyzed by microscopy to identify tricuspid and bicuspid aortic valves. The aortic valve F-NaF signal on PET/CT was significantly higher at 18-24 mo ( < 0.0001) and 10-16 mo ( < 0.05) than at 3-4 mo. Additionally, at 18-24 mo BAV had a higher F-NaF signal than tricuspid aortic valves ( < 0.05). These findings were confirmed by autoradiography, with BAV having significantly higher F-NaF uptake in each age group. A significant correlation between PET and autoradiography data (Pearson = 0.79, < 0.01) established the accuracy of PET quantification. The rate of calcification with aging was significantly faster for BAV ( < 0.05). Transaortic valve flow velocity was significantly higher in animals with BAV at all ages. Finally, there was a significant correlation between transaortic valve flow velocity and aortic valve calcification by both PET/CT ( = 0.55, < 0.001) and autoradiography ( = 0.45, < 0.01). F-NaF PET/CT links valvular calcification to BAV and aging in mice and suggests that AS may promote calcification. In addition to addressing the pathobiology of valvular calcification, F-NaF PET/CT may be a valuable tool for evaluation of emerging therapeutic interventions in CAVD.
Topics: Humans; Mice; Animals; Aortic Valve; Bicuspid Aortic Valve Disease; Positron Emission Tomography Computed Tomography; Disease Models, Animal; Aortic Valve Stenosis
PubMed: 37321825
DOI: 10.2967/jnumed.123.265516 -
Brain Communications 2023A cerebral gyrus is made up of an external layer of folded cortex and an inner core of white matter. The architecture of the core has specific features that make it... (Review)
Review
A cerebral gyrus is made up of an external layer of folded cortex and an inner core of white matter. The architecture of the core has specific features that make it distinct from the white matter of the deep brain regions. Limited externally by the grey matter that covers the top of the gyrus and the neighbouring sulci, this gyral white matter is made up of a mix of fibre populations with multiple directions and destinations. The presence of densely packed fibres with multiple crossings, the proximity to the cortex and the existence of inter-regional and inter-individual variations make the task of depicting this microanatomy extremely challenging. The topic is, however, of paramount relevance for both fundamental and applied neurosciences. This fibre colocalization is crucial for the functional role of each cerebral region and is key to clinical manifestations in cases of parenchymal damage. As track tracing, imaging and dissection are based on different biological or physical principles, it is natural for their results to sometimes be different, but they are often complementary. As the amount of available information increases, it becomes fragmented due to the multiplicity of methods, target phenomena and studied species. In this scoping review, we present the key concepts and map the primary sources of evidence regarding identifying the fibre pathways that compose the gyral white matter, enabling the discussion of avenues for future research. The general pattern in which these pathways are distributed in the gyral white matter was detailed, and the main variations as a function of brain topography were explained and illustrated with typical examples.
PubMed: 38074075
DOI: 10.1093/braincomms/fcad265