Tau and Aβ assemblies of Alzheimer’s disease (AD) can be visualized in living subjects using positron emission tomography (PET). Tau assemblies comprise paired helical and straight filaments (PHFs ...and SFs). APN-1607 (PM-PBB3) is a recently described PET ligand for AD and other tau proteinopathies. Since it is not known where in the tau folds PET ligands bind, we used electron cryo-microscopy (cryo-EM) to determine the binding sites of APN-1607 in the Alzheimer fold. We identified two major sites in the β-helix of PHFs and SFs and a third major site in the C-shaped cavity of SFs. In addition, we report that tau filaments from posterior cortical atrophy (PCA) and primary age-related tauopathy (PART) are identical to those from AD. In support, fluorescence labelling showed binding of APN-1607 to intraneuronal inclusions in AD, PART and PCA. Knowledge of the binding modes of APN-1607 to tau filaments may lead to the development of new ligands with increased specificity and binding activity. We show that cryo-EM can be used to identify the binding sites of small molecules in amyloid filaments.
Accumulation of intracellular tau fibrils has been the focus of research on the mechanisms of neurodegeneration in Alzheimer’s disease (AD) and related tauopathies. Here, we have developed a class of ...tau ligands, phenyl/pyridinyl-butadienyl-benzothiazoles/benzothiazoliums (PBBs), for visualizing diverse tau inclusions in brains of living patients with AD or non-AD tauopathies and animal models of these disorders. In vivo optical and positron emission tomographic (PET) imaging of a transgenic mouse model demonstrated sensitive detection of tau inclusions by PBBs. A pyridinated PBB, 11CPBB3, was next applied in a clinical PET study, and its robust signal in the AD hippocampus wherein tau pathology is enriched contrasted strikingly with that of a senile plaque radioligand, 11CPittsburgh Compound-B (11CPIB). 11CPBB3-PET data were also consistent with the spreading of tau pathology with AD progression. Furthermore, increased 11CPBB3 signals were found in a corticobasal syndrome patient negative for 11CPIB-PET.
•Compounds were developed to image in vivo diverse types of tau inclusions•These compounds enabled optical and PET imaging of tau lesions in model mice•PET with one of these compounds illuminated tau-rich regions in Alzheimer’s disease•Our probe produced PET images consistent with spreading tau pathology
A new class of imaging agents developed by Maruyama et al. enables visualization of tau protein aggregates—pathological hallmarks of Alzheimer’s disease and related neurodegenerative disorders—in living brains of human subjects and mouse models.
Objective
Abnormal aggregation of tau in the brain is a major contributing factor in various neurodegenerative diseases. Florzolotau (18F) (florzolotau, APN-1607, PM-PBB3) has been shown to be a ...probe for tau fibrils in an animal model and patients with Alzheimer’s disease and those with non-Alzheimer’s disease tauopathies. The objective of this study is to evaluate the safety, pharmacokinetics, and radiation dose following a single intravenous administration of florzolotau in healthy Japanese subjects.
Methods
Three healthy male Japanese subjects aged between 20 and 64 were enrolled in this study. Subjects were determined to be eligible based on the screening assessments at the study site. Subjects received a single intravenous dose of 195.0 ± 0.5 MBq of florzolotau and underwent the whole-body PET scan 10 times in total to calculate absorbed doses to major organs/tissues and effective dose. Radioactivities in whole blood and urine were also measured for pharmacokinetic evaluation. Absorbed doses to major organs/tissues and effective dose were estimated using the medical internal radiation dose (MIRD) method. Vital signs, electrocardiography (ECG), and blood tests were done for safety evaluation.
Results
The intravenous injection of florzolotau was well tolerated. There were no adverse events or clinically detectable pharmacologic effects related to the tracer in any subjects. No significant changes in vital signs and ECG were observed. The highest mean initial uptake at 15 min after injection was in the liver (29.0 ± 4.0%ID), intestine (4.69 ± 1.65%ID), and brain (2.13 ± 0.18%ID). The highest absorbed dose was 508 μGy/MBq of the gallbladder wall, followed by the liver of 79.4 μGy/MBq, the pancreas of 42.5 μGy/MBq, and the upper large intestine of 34.2 μGy/MBq. The effective dose was calculated as 19.7 μSv/MBq according to the tissue weighting factor reported by ICRP-103.
Conclusion
Florzolotau intravenous injection was well tolerated in healthy male Japanese subjects. The effective dose was determined as 3.61 mSv when 185 MBq florzolotau was given.
Background
The need for a light stable 4R tau PET tracer for use in diverse tauopathies is widely appreciated. We aimed to assess the initial human imaging profile of 18FAPN‐1701 as such a tracer and ...to compare its imaging profile to the well‐established but light‐sensitive tracer 18F‐APN‐1607 that can detect 4R aggregates as well as 3R and mixed 3R/4R aggregates. 18FAPN‐1607 has progressed to a multicenter Phase 2 clinical trial for Alzheimer’s disease (AD); therefore, prior imaging data with it was considered valuable for comparison.
Method
One cognitively normal (CN) subject (male, 73yo) and one AD subject (female, 58 yo), who had undergone prior amyloid profiling using 18Fflorbetapir PET and subsequent imaging with 18FAPN‐1607 in a proof‐of‐concept study and a test‐retest study, respectively, participated in the current study. Dynamic imaging with 18FAPN‐1701 was performed over 180 min to obtain kinetic data.
Result
Overall, for both subjects 18FAPN‐1701 generally matched 18FAPN‐1607 findings, i.e., peak SUV values reached similar levels. The CN subject, who was amyloid negative, had slight, uniform cortical 18F‐APN‐1701 uptake and more substantial uptake in the pallidum, pons and midbrain. SUVr images for the AD subject showed retention in similar brain regions for both tau tracers with the same rank order of regional SUV/SUVr. Notably, for this subject 18FAPN‐1701 continued to accumulate up to the end of image acquisition.
Conclusion
18FAPN‐1701 demonstrates cortical uptake generally similar to 18FAPN‐1607 but its slow kinetics are unfavorable for further development.
Axonal transport is vital for neurons and deficits in this process have been previously reported in a few mouse models of Alzheimer's disease prior to the appearance of plaques and tangles. However, ...it remains to be determined whether axonal transport is defective prior to the onset of neurodegeneration. The rTg4510 mouse, a fronto-temporal dementia and parkinsonism-17 (FTDP-17) tauopathy model, over-express tau-P301L mutation found in familial forms of FTDP-17, in the forebrain driven by the calcium-calmodulin kinase II promoter. This mouse model exhibits tau pathology, neurodegeneration in the forebrain, and associated behavioral deficits beginning at 4-5 months of age.
rTg4510 transgenic mice were used in these studies. Mice were given 2 μL of MnCl2 in each nostril 1 h prior to Magnetic Resonance Imaging (MRI). Following MnCl2 nasal lavage, mice were imaged using Manganese enhanced Magnetic Resonance Imaging (MEMRI) Protocol with TE = 8.5 ms, TR = 504 ms, FOV = 3.0 cm, matrix size = 128 × 128 × 128, number of cycles = 15 with each cycle taking approximately 2 min, 9 s, and 24 ms using Paravision software (BrukerBioSpin, Billerica, MA). During imaging, body temperature was maintained at 37.0 °C using an animal heating system (SA Instruments, Stony Brook, NY).
Resulting images were analyzed using Paravision software. Regions of interest (ROI) within the olfactory neuronal layer (ONL) and the water phantom consisting of one pixel (ONL) and 9 pixels (water) were selected and copied across each of the 15 cycles. Signal intensities (SI) of ONL and water phantom ROIs were measured. SI values obtained for ONL were then normalized the water phantom SI values. The correlation between normalized signal intensity in the ONL and time were assessed using Prism (GraphPad Software, San Diego, CA).
Using the MEMRI technique on 1.5, 3, 5, and 10-month old rTg4510 mice and littermate controls, we found significant axonal transport deficits present in the rTg4510 mice beginning at 3 months of age in an age-dependent manner. Using linear regression analysis, we measured rates of axonal transport at 1.5, 3, 5, and 10 months of age in rTg4510 and WT mice. Axonal transport rates were observed in rTg4510 mice at 48% of WT levels at 3 months, 40% of WT levels at 5 months, and 30% of WT levels at 10 months of age. In order to determine the point at which tau appears in the cortex, we probed for phosphorylated tau levels, and found that pSer262 is present at 3 months of age, not earlier at 1.5 months of age, but observed no pathological tau species until 6 months of age, months after the onset of the transport deficits. In addition, we saw localization of tau in the ONL at 6 months of age.
In our study, we identified the presence of age-dependent axonal transport deficits beginning at 3 months of age in rTg4510 mice. We correlated these deficits at 3 months to the presence of hyperphosphorylated tau in the brain and the presence within the olfactory epithelium. We observed tau pathology not only in the soma of these neurons but also within the axons and processes of these neurons. Our characterization of axonal transport in this tauopathy model provides a functional time point that can be used for future therapeutic interventions.
J. Neurochem. (2011) 119, 486–496.
NMDA receptor (NMDAR)‐mediated excitatory synaptic transmission plays a critical role in synaptic plasticity and memory formation, whereas its dysfunction may ...underlie neuropsychiatric and neurodegenerative diseases. The neuroactive steroid pregnenolone sulfate (PS) acts as a cognitive enhancer in impaired animals, augments LTP in hippocampal slices by enhancing NMDAR activity, and may participate in the reduction of schizophrenia’s negative symptoms by systemic pregnenolone. We report that the effects of PS on NMDAR function are diverse, varying with subunit composition and NR1 splice variant. While PS potentiates NR1‐1a/NR2B receptors through a critical steroid modulatory domain in NR2B that also modulates tonic proton inhibition, potentiation of the NMDA response is not dependent upon relief of such inhibition, a finding that distinguishes it from spermine. In contrast, the presence of an NR2A subunit confers enhanced PS‐potentiation at reduced pH, suggesting that it may indeed act like spermine does at NR2B‐containing receptors. Additional tuning of the NMDAR response by PS comes via the N‐terminal exon‐5 splicing insert of NR1‐1b, which regulates the magnitude of proton‐dependent PS potentiation. For NR2C‐ and NR2D‐containing receptors, negative modulation at NR2C receptors is pH‐independent (like NR2B) while negative modulation at NR2D receptors is pH‐dependent (like NR2A). Taken together, PS displays a rich modulatory repertoire that takes advantage of the structural diversity of NMDARs in the CNS. The differential pH sensitivity of NMDAR isoforms to PS modulation may be especially important given the emerging role of proton sensors to both learning and memory, as well as brain injury.
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