Assessment of 18F-PI-2620 as a Biomarker in Progressive Supranuclear Palsy

Atypical Parkinsonian Disorders

Atypical parkinsonian disorders (APD) include progressive supranuclear palsy, corticobasal degeneration, and multiple system atrophy. Identifying APD is important because they have different pathogenesis, disease course, and prognosis than Parkinson's disease (PD), and require different treatments. Therefore, when encountering patients with parkinsonism, it is of crucial importance to look for "red flags" or signs, such as impairments in higher cortical function, visuomotor system, cerebellar and other motor abnormalities including dystonia, myoclonus, and apraxia that help differentiate them from PD. Although disease-modifying therapies are not yet available, treatments targeting specific symptoms may improve the quality of life in these patients.

Binding Sites of a PET Ligand in Tau Fibrils with the Alzheimer's Disease Fold from 19F and 13C Solid-State NMR

Aggregation of the tau protein into cross-β amyloid fibrils is a hallmark of Alzheimer's disease (AD) and many other neurodegenerative disorders. Developing small molecules that bind these tau fibrils is important for the diagnosis and treatment of tauopathies. Here, we report the binding sites of a positron emission tomography (PET) ligand, PI-2620, to a recombinant tau construct that adopts the C-shaped AD fold. Using solid-state NMR 13C-19F rotational-echo double-resonance (REDOR) experiments, we measured the proximity of protein residues to the fluorine atom of the ligand. These data indicate that PI-2620 binds at two main locations in the concave interior of the C-shaped structure. Molecular docking simulations constrained by these REDOR data identified five binding poses at these two locations. In addition, 2D 13C-13C correlation NMR spectra indicate that PI-2620 decreased the intensities of residues at the protofilament interfaces, indicating that the ligand disordered the filament packing. Quantitative analysis of the 19F NMR spectra indicates that PI-2620 binds these AD-fold tau fibrils with a stoichiometry of ∼20 mol %, in which 10 mol % are immobilized and the rest are mobile. These results provide experimental constraints to the interaction of this second-generation PET tracer with tau fibrils adopting the AD fold and should be useful for the development of future imaging agents with improved stoichiometry and specificity for AD tau.

Radiosynthesis, In Vitro Characterization, and In Vivo PET Neuroimaging of [18F]F-4 for Tau Protein: A First-in-Human PET Study

[18F]PI-2620 is a promising radiopharmaceutical for positron emission tomography (PET) imaging of both Alzheimer's disease (AD) and non-Alzheimer's disease (non-AD) tauopathies in humans. An array of fluorinated derivatives of the carbazole scaffold of PI-2620 were synthesized and evaluated. In vitro binding assays with [3H]PI-2620 in human tissues with AD, progressive supranuclear palsy, and corticobasal degeneration, combined with in silico predictions of blood-brain barrier permeability, led to the selection and radiosynthesis of [18F]F-4 as a promising radiotracer. In vivo PET imaging with [18F]F-4 in healthy rats showed brain uptake and kinetics suitable for neuroimaging, similar to those of [18F]PI-2620. A first-in-human PET imaging study in a healthy subject as well as a patient with AD, in comparison with [18F]PI-2620 in the same AD subject, confirmed that [18F]F-4 is an alternative radiopharmaceutical for imaging tau protein.

Exploring the origins of frequent tau-PET signal in vermal and adjacent regions

PURPOSE

Off-target binding remains a significant challenge in tau-PET neuroimaging. While off-targets including monoamine oxidase enzymes and neuromelanin-containing cells have been identified, recent studies indicated a relevant binding of novel tau tracers to melanin-containing structures. To date, little is known about the effect of melanocytes in the meninges on tracer signals in brain PET data. Thus, we aimed to identify the target structure causal for the frequently observed [18F]PI-2620 PET signal in the vermis and adjacent cerebellar regions.

METHODS

274 participants underwent dynamic [18F]PI-2620 tau-PET: 3/4R-tauopathies (n = 85), 4R-tauopathies (n = 147), tau-negative disease controls (n = 24), and healthy controls (n = 18). Standardized uptake value ratio (SUVR) and kinetic parameters including the distribution volume ratio (DVR), tracer clearance (k2) and relative perfusion (R1), were compared among the cohorts and sexes using the Automated Anatomical Labelling (AAL) atlas. Age and p-Tau levels in cerebrospinal fluid (CSF) were assessed for their relationship with vermal tau-PET signal. Furthermore, we combined autoradiographic and histochemical experiments on post-mortem brain tissue of deceased patients (n = 9).

RESULTS

Male participants revealed higher mean vermal [18F]PI-2620 DVR (0.95 ± 0.13; vs. females 0.88 ± 0.10, p < 0.0001). Sex-related differences were most pronounced in the 3/4R-tauopathy cohort (p < 0.0001). Mean SUVRVer/Cbl, k2 and correlation analyses of kinetic parameters did not differ among groups. Histological assessments revealed co-localization of leptomeningeal pigmented cells with strong autoradiography signal spots within the vermal fissures. Tau-related autoradiography signals, age or p-Tau levels did not correlate significantly with tau-PET signals. Iron deposits did not cause relevant autoradiography signals in the vermis.

CONCLUSION

Leptomeningeal melanocytes are the primary target structure for [18F]PI-2620 PET binding in anterior vermis, whereas iron and tau deposits do not contribute significantly.

Multi-parametric [18F]PI-2620 tau PET/MRI for the phenotyping of different Alzheimer's disease variants

PURPOSE

Heterogeneity in clinical phenotypes has led to the description of different phenotypes of Alzheimer's disease (AD). Besides the most frequent amnestic variant of AD (aAD), patients presenting with language deficits are diagnosed with logopenic variant primary progressive aphasia (lvPPA), whereas patients presenting with visual deficits are classified as posterior cortical atrophy (PCA).

METHODS

This study set out to investigate the value of a multi-parametric [18F]PI-2620 tau PET/MRI protocol to distinguish aAD, lvPPA and PCA to support clinical diagnosis in 32 patients. Phenotype-specific information about tau accumulation, relative perfusion, grey matter density, functional network alterations and white matter microstructural alterations was collected.

RESULTS

The aAD patients showed significantly higher tau accumulation, relative hypoperfusion and grey matter density loss in the temporal lobes compared to PCA and lvPPA patients. PCA patients, on the other hand, showed significantly higher tau accumulation in the occipital lobe as compared to aAD patients. Relative hypoperfusion in the occipital lobe and loss of functional connectivity of the posterior cingulate cortex to supplementary visual cortical regions helped to distinguish PCA from lvPPA. Tau accumulation in the cerebellum and microstructural changes in the cingulum were found to help differentiate lvPPA from aAD.

CONCLUSION

This study highlights structural and functional differences between patients with different AD phenotypes. Differences in regional tau PET signals suggest that refinements in the Braak staging system are needed for the non-aAD cases. These patterns of tau accumulation align with the cascading network failure hypothesis, though more research is needed to warrant the here presented results in larger patient cohorts.

Brainstem and cerebellar radiological findings in progressive supranuclear palsy

Progressive supranuclear palsy is a sporadic neurodegenerative 4-repeat tauopathy associated with significant morbidity. Heterogeneity of symptom expression among this group is increasingly recognized, reflecting variable tau spread and neurodegeneration. Clinical manifestations consist of debilitating and rapidly progressive motor, oculomotor, speech, cognitive and affective impairments. Core pathological changes are noted with a predominance in the midbrain and basal ganglia; however, spread to the more caudal brainstem and cerebellar regions is reported at various stages. Accordingly, whilst midbrain atrophy is the best recognized supportive imaging finding, quantitative neuroimaging studies using MRI and PET approaches have revealed a wider profile of brain abnormalities in cohorts of individuals with progressive supranuclear palsy. This expanded neurobiological scope of disease may account for individual heterogeneity and may highlight additional biological markers that are relevant to diagnosing and tracking the illness. Additionally, there is increasing understanding of the diverse cognitive, affective and speech functions of the cerebellum, which may be implicated in progressive supranuclear palsy beyond current recognition. In this review, we undertake a systematic literature search and summary of in vivo structural and functional neuroimaging findings in the brainstem and cerebellum in progressive supranuclear palsy to date. Novel and multimodal imaging techniques have emerged over recent years, which reveal several infratentorial alterations beyond midbrain atrophy in progressive supranuclear palsy. Most saliently, there is evidence for volume loss and microstructural damage in the pons, middle cerebellar peduncles and cerebellar cortex and deep nuclei, reported alongside recognized midbrain and superior cerebellar peduncle changes. Whilst the literature supporting the presence of these features is not unanimous, the evidence base is compelling, including correlations with disease progression, severity or variant differences. A smaller number of studies report on abnormalities in MRI measures of iron deposition, neuromelanin, viscoelasticity and the glymphatic system involving the infratentorial regions. Molecular imaging studies have also shown increased uptake of tau tracer in the midbrain and cerebellar dentate nucleus, although concern remains regarding possible off-target binding. Imaging of other molecular targets has been sparse, but reports of neurotransmitter, inflammatory and synaptic density alterations in cerebellar and brainstem regions are available. Taken together, there is an established evidence base of in vivo imaging alterations in the brainstem and cerebellum which highlights that midbrain atrophy is often accompanied by other infratentorial alterations in people with progressive supranuclear palsy. Further research examining the contribution of these features to clinical morbidity and inter-individual variability in symptom expression is warranted.

SLC9A6-Linked Parkinson Syndrome in Female Heterozygotes Is Associated With PET-Detectable Tau Pathology

Background and Objectives

A previous postmortem study of men with Christianson syndrome, a disorder caused by loss-of-function mutations in the gene SLC9A6, reported a mechanistic link between pathologic tau accumulation and progressive symptoms such as cerebellar atrophy and cognitive decline. This study aimed to characterize the relationships between neuropathologic manifestations and tau accumulation in heterozygous women with SLC9A6 mutation.

Methods

We conducted a multimodal neuroimaging and plasma biomarker study on 3 middle-aged heterozygous women with SLC9A6 mutations (proband 1: mid-50s; proband 2: early 50s; proband 3: mid-40s) presenting with progressive extrapyramidal symptoms. Examinations included 11C-PiB PET; 18F-florzolotau PET; structural MRI; and plasma measures of neurofilament light chain (NfL) polypeptide, glial fibrillary acidic protein, phosphorylated (p)Tau181, Aβ40, and Aβ42. Neuroimaging results of all 3 patients were compared with those of 12 healthy age-matched women (49.8 ± 4.7 years) while plasma biomarker levels of probands 1 and 2 were compared with those of 14 age-matched healthy women (54.1 ± 9.0 years).

Results

Proband 1 was diagnosed with Parkinson disease while probands 2 and 3 were diagnosed with atypical parkinsonism. 11C-PiB PET results were negative in all patients. 18F-florzolotau PET revealed focal tau accumulations in all 3 patients, predominantly in the striatum contralateral to motor symptoms. Moreover, greater extrapyramidal symptom severity was associated with higher standardized uptake value ratios (SUVRs) for 18F-florzolotau in the striatum. Multiple comparisons showed significantly higher 18F-florzolotau SUVR values in both the caudate and putamen of proband 1, who exhibited the most severe extrapyramidal signs, while no significant increases in 18F-florzolotau SUVR values were detected in any brain region of probands 2 and 3. Structural MRI revealed slightly lower regional subcortical and gray matter volumes in all patients but not significant after multiple comparisons. Finally, plasma NfL concentration was significantly higher in probands 1 and 2 compared with healthy controls.

Discussion

Our 18F-florzolotau PET analysis revealed greater tau accumulation in the striatum of heterozygous women with SLC9A6 mutation associated with worsening extrapyramidal symptom severity. The heterozygosity of loss-of-function SLC9A6 mutations further suggests that tauopathy may be a primary contributor to extrapyramidal signs.

Pragmatic algorithm for visual assessment of 4-Repeat tauopathies in [18F]PI-2620 PET Scans

AIM

Standardized evaluation of [18F]PI-2620 tau-PET scans in 4R-tauopathies represents an unmet need in clinical practice. This study aims to investigate the effectiveness of visual evaluation of [18F]PI-2620 images for diagnosing 4R-tauopathies and to develop a straight-forward reading algorithm to improve objectivity and data reproducibility.

METHODS

A total of 83 individuals with [18F]PI-2620 PET scans were included. Participants were classified as probable 4R-tauopathies (n = 29), Alzheimer's disease (AD) (n = 20), α-synucleinopathies (n = 15), and healthy controls (n = 19) based on clinical criteria. Visual assessment of tau-PET scans (choice: 4R-tauopathy, AD-tauopathy, no-tauopathy) was conducted using either 20-40-minute or 40-60-minute intervals, with raw (common) and cerebellar grey matter scaled standardized reading settings (intensity-scaled). Two readers evaluated scans independently and blinded, with a third reader providing consensus in case of discrepant primary evaluation. A regional analysis was performed using the cortex, basal ganglia, midbrain, and dentate nucleus. Sensitivity, specificity, and interrater agreement were calculated for all settings and compared against the visual reads of parametric images (0-60-minutes, distribution volume ratios, DVR).

RESULTS

Patients with 4R-tauopathies in contrast to non-4R-tauopathies were detected at higher sensitivity in the 20-40-minute frame (common: 79%, scaled: 76%) compared to the 40-60-minute frame (common: 55%, scaled: 62%), albeit with reduced specificity in the common setting (20-40-min: 78%, 40-60-min: 95%), which was ameliorated in the intensity-scaled setting (20-40-min: 91%, 40-60-min: 96%). Combined assessment of multiple brain regions did not significantly improve diagnostic sensitivity, compared to assessing the basal ganglia alone (76% each). Evaluation of intensity-scaled parametric images resulted in higher sensitivity compared to intensity-scaled static scans (86% vs. 76%) at similar specificity (89% vs. 91%).

CONCLUSION

Visual reading of [18F]PI-2620 tau-PET scans demonstrated reliable detection of 4R-tauopathies, particularly when standardized processing methods and early imaging windows were employed. Parametric images should be preferred for visual assessment of 4R-tauopathies.

Relationships Between Glymphatic System Activity and Tau Burden, Dopaminergic Impairment, Abnormal Glucose Metabolism in Progressive Supranuclear Palsy

BACKGROUND

Progressive supranuclear palsy (PSP) is a primary tauopathy characterized by dopaminergic impairment and abnormal glucose metabolism. The glymphatic system can promote the elimination of tau protein. The association between glymphatic function and pathological hallmark in neuroimaging remains unknown.

METHODS

Diffusion tensor imaging (DTI) and positron emission tomography (PET) scanning with 18F-Florzolotau, 18F-FPCIT, and 18F-FDG were performed in PSP patients. DTI analysis along the perivascular space (ALPS) index was computed to assess glymphatic function, while the semi-quantitative value was employed to measure tau burden and dopaminergic impairment. The PSP-related pattern (PSPRP) served as an indicator of abnormal metabolic brain network activity.

RESULTS

PSP patients exhibited changes in ALPS index and tau deposition. ALPS index, tau deposition, and PSPRP expression showed significant correlations with clinical scores. Additionally, ALPS index was correlated with tau deposition and PSPRP expression. However, neither ALPS index nor the clinical scores were correlated with striatum dysfunction. Finally, tau deposition in subcortical regions and PSPRP expression exhibited mediating effects between ALPS index and clinical scores.

CONCLUSION

The glymphatic dysfunction is associated with tau deposition and abnormal metabolic brain network activity and is independent of dopaminergic impairment in PSP.

Subcortical tau burden correlates with regional brain atrophy and plasma markers in four-repeat tauopathy parkinsonism

Background18F-florzolotau positron emission tomography (PET) assists in the in vivo diagnosis of progressive supranuclear palsy (PSP).ObjectiveWe aimed to investigate the relationship between 18F-florzolotau uptake and clinical severity, structural volume changes, and plasma markers in four-repeat tauopathies.MethodsA total of 80 participants were recruited: 35 with PSP (11 with PSP-Richardson syndrome and 24 with PSP non-Richardson syndrome), 9 with corticobasal syndrome (CBS), 10 with Alzheimer's disease (AD), 8 with Parkinson's disease, and 18 controls. All participants underwent 18F-florzolotau PET, brain magnetic resonance imaging (MRI), and plasma biomarker investigation (total and phosphorylated tau [pTau181], neurofilament light chain, and glial fibrillary acidic protein [GFAP]).Results18F-Florzolotau uptake was significantly higher in the subcortical regions of the pallidum, subthalamic nucleus (STN), midbrain, red nucleus, and raphe nucleus in PSP patients compared to the other groups (all p < 0.01). Subcortical tau tracer retention assisted in distinguishing PSP and CBS from controls (AUC = 0.836, p < 0.001). Tau tracer retention could differentiate PSP and CBS from AD in cortical (p < 0.001) and subcortical regions (p = 0.028). The motor severity of PSP positively correlated with tau burden in STN (p = 0.044) and substantia nigra (p = 0.035). Tau tracer uptake was associated with cortical volume changes in CBS (p = 0.031), PSP non-Richardson syndrome (p = 0.003), and AD (p = 0.044). Cortical tau retention correlated with plasma levels of GFAP (p = 0.001) and pTau181 (p = 0.036).ConclusionsSubcortical 18F-Florzolotau uptake assist the diagnosis of 4R tauopathy parkinsonism. Additionally, regional tau burden contributes to structural brain volume changes and correlates with plasma levels of GFAP and pTau181.

Current Progress and Future Directions in Non-Alzheimer's Disease Tau PET Tracers

Alzheimer's disease (AD) and non-AD tauopathies are dominant public health issues driven by several factors, especially in the aging population. The discovery of first-generation radiotracers, including [18F]FDDNP, [11C]PBB3, [18F]flortaucipir, and the [18F]THK series, for the in vivo detection of tauopathies has marked a significant breakthrough in the fields of neuroscience and radiopharmaceuticals, creating a robust new category of labeled compounds: tau positron emission tomography (PET) tracers. Subsequently, other tau PET tracers with improved binding properties have been developed using various chemical scaffolds to target the three-repeat/four-repeat (3R/4R) tau folds in AD. In 2020, [18F]flortaucipir was approved by the U.S. Food and Drug Administration for PET imaging of tau pathology in adult patients with cognitive deficits undergoing evaluation for AD. Despite remarkable progress in the development of AD tau PET tracers, imaging agents for rare non-AD tauopathies (4R tauopathies [predominantly expressing a 4R tau isoform], involved in progressive supranuclear palsy, corticobasal degeneration, argyrophilic grain disease, and globular glial tauopathy, and 3R tauopathies [predominantly expressing a 3R tau isoform], such as Pick's disease) remain substantially underdeveloped. In this review, we discuss recent progress in tau PET tracer development, with particular emphasis on clinically validated tracers for AD and their potential use for non-AD tauopathies. Additionally, we highlight the critical need for further development of tau PET tracers specifically designed for non-AD tauopathies, an area that remains significantly underexplored despite its importance in advancing the understanding and diagnosis of these disorders.

18F-Florzolotau PET Imaging Unveils Tau Pathology in Dementia with Lewy Bodies

BACKGROUND

Dementia with Lewy bodies (DLB) commonly exhibits a complex neuropathology, sharing characteristics with Alzheimer's disease (AD), including tau aggregates. However, studies using the 18F-AV-1451 tau tracer have shown inconsistent findings regarding both the extent and topographical distribution of tau pathology in DLB.

OBJECTIVES

Our aim was to elucidate the topographical patterns of tau deposition in DLB and to investigate the in vivo pathological distinction between DLB and AD in virtue of the 18F-Florzolotau positron emission tomography (PET) imaging.

METHODS

This cross-sectional study enrolled patients with DLB (n = 24), AD (n = 43), and cognitively healthy controls (n = 18). Clinical assessments and 18F-Florzolotau PET imaging were performed. 18F-Florzolotau binding was quantitatively assessed on PET images using standardized uptake value ratios and voxel-wise analysis.

RESULTS

18F-Florzolotau PET imaging revealed widespread tau deposition across various cortical regions in DLB, uncovering heterogeneous topographical patterns. Among patients, 54.17% showed patterns similar to AD, whereas 16.67% exhibited distinct patterns. Compared to AD, DLB exhibited a unique in vivo neuropathological profile, characterized by a lower tau protein burden, heterogeneous topographical distributions, and a specific role of the medial temporal lobe in tau pathology.

CONCLUSIONS

18F-Florzolotau PET imaging elucidated tau pathology patterns in DLB, providing valuable insights for future in vivo pathological differentiation and potential disease-modifying therapies. © 2024 International Parkinson and Movement Disorder Society.

Visual reading for [18F]Florzolotau Tau PET scans in progressive supranuclear palsy

PURPOSE

The identification of tau accumulation within living brains holds significant potential in facilitating accurate diagnosis of progressive supranuclear palsy (PSP). While visual assessment is frequently employed, standardized methods for tau positron emission tomography (PET) specifically in PSP are absent. We aimed to develop a visual reading algorithm dedicated to the evaluation of [18F]Florzolotau PET in PSP.

METHODS

148 PSP and 30 healthy volunteers were divided into a development set (for the establishment of the reading rules; n = 89) and a testing set (for the validation of the reading rules; n = 89). For differential diagnosis, 55 α-synucleinopathies were additionally included into the testing set. The visual reading method was established by an experienced assessor (Reader 0) and was then validated by Reader 0 and two additional readers on regional and overall binary manners. A positive binding in both midbrain and globus pallidus/putamen regions was characterized as a PSP-like pattern, whereas any other pattern was classified as non-PSP-like.

RESULTS

Reader 1 (94.4%) and Reader 2 (93.8%) showed excellent agreement for the overall binary determination against Reader 0. The regional binary determinations of midbrain and globus pallidus/putamen showed excellent agreement among readers (kappa > 0.80). The overall binary evaluation demonstrated reproducibility of 86.1%, 94.4% and 77.8% for three readers. The visual reading algorithm showed high agreement with regional standardized uptake value ratios and clinical diagnoses.

CONCLUSION

Through the application of the suggested visual reading algorithm, [18F]Florzorotau PET imaging demonstrated a robust performance for the imaging diagnosis of PSP.

Atypical Parkinsonian Syndromes: Structural, Functional, and Molecular Imaging Features

Atypical parkinsonian syndromes, also known as Parkinson-plus syndromes, are a heterogeneous group of movement disorders, including dementia with Lewy bodies (DLB), progressive supranuclear palsy (PSP), multisystem atrophy (MSA), and corticobasal degeneration (CBD). This review highlights the characteristic structural, functional, and molecular imaging features of these complex disorders. DLB typically demonstrates parieto-occipital hypometabolism with involvement of the cuneus on FDG-PET, whereas dopaminergic imaging, such as [123I]-FP-CIT SPECT (DaTscan) or fluorodopa (FDOPA)-PET, can be utilized as an adjunct for diagnosis. PSP typically shows midbrain atrophy on structural imaging, whereas FDG-PET may be useful to depict frontal lobe hypometabolism and tau-PET confirms underlying tauopathy. MSA typically demonstrates putaminal or cerebellar atrophy, whereas FDG-PET highlights characteristic nigrostriatal or olivopontocerebellar hypometabolism, respectively. Finally, CBD typically shows asymmetric atrophy in the superior parietal lobules and corpus callosum, whereas FDG and tau-PET demonstrate asymmetric hemispheric and subcortical involvement contralateral to the side of clinical deficits. Additional advanced neuroimaging modalities and techniques described may assist in the diagnostic work-up or are promising areas of emerging research.

Neuronal and oligodendroglial, but not astroglial, tau translates to in vivo tau PET signals in individuals with primary tauopathies

Tau PET has attracted increasing interest as an imaging biomarker for 4-repeat (4R)-tauopathy progressive supranuclear palsy (PSP). However, the translation of in vitro 4R-tau binding to in vivo tau PET signals is still unclear. Therefore, we performed a translational study using a broad spectrum of advanced methodologies to investigate the sources of [18F]PI-2620 tau PET signals in individuals with 4R-tauopathies, including a pilot PET autopsy study in patients. First, we conducted a longitudinal [18F]PI-2620 PET/MRI study in a 4-repeat-tau mouse model (PS19) and detected elevated [18F]PI-2620 PET signals in the presence of high levels of neuronal tau. An innovative approach involving cell sorting after radiotracer injection in vivo revealed higher tracer uptake in single neurons than in the astrocytes of PS19 mice. Regional [18F]PI-2620 tau PET signals during the lifetime correlated with the abundance of fibrillary tau and with autoradiography signal intensity in PSP patients and disease controls who underwent autopsy 2-63 months after tau PET. In autoradiography, tau-positive neurons and oligodendrocytes with a high AT8 density, but not tau-positive astrocytes, were the drivers of [18F]PI-2620 autoradiography signals in individuals with PSP. The high tau abundance in oligodendrocytes at the boundary of gray and white matter facilitated the identification of an optimized frontal lobe target region to detect the tau burden in patients with PSP. In summary, neuronal and oligodendroglial tau constitutes the dominant source of tau PET radiotracer binding in 4-repeat-tauopathies, translating to an in vivo signal.

Can the clinical sign "head-turning sign" and simple questions in "Neucop-Q" predict amyloid β pathology?

BACKGROUND

To establish simple screening tests to suspect Alzheimer's disease (AD) pathology, the clinical sign "head-turning sign" (HTS), which is a patient's behavior of turning their head towards their partner to seek assistance with questions posed by the examiner during the interview, and the simple screening questionnaire for dementia named "Neucop-Q" were validated in participants diagnosed with amyloid and tau positron emission tomography (PET).

METHODS

We enrolled 155 patients: 47 cognitive normal, 36 with mild cognitive impairment, 64 with dementia, and 8 with psychiatric disorders. All participants underwent Neucop-Q [three questions: Consciousness/self-awareness of cognitive disabilities (C) normal/impaired (nor/imp), Pleasure/pastime (P) nor/imp, and News/knowledge on current topics (N) nor/imp] and amyloid/tau PET. Additionally, we measured plasma amyloid β (Aβ) 42/40 ratio, phosphorylated tau 181 (pTau181), glial fibrillary acidic protein (GFAP), and neurofilament light (NFL) levels and compared with HTS and Neucop-Q results.

RESULTS

The specificity and positive predictive value (PPV) of HTS positivity (HTSpos) were the highest (amyloid PET: 0.930 and 0.870, tau PET: 0.944 and 0.957, respectively), while Cimp and Nimp had a high negative predictive value (NPV) for amyloid PET (negativity) (0.750 and 0.725). Pimp showed high specificity for predicting non-AD tau positivity among non-AD participants without amyloid PET positivity (0.854). To validate these findings with PET results, we examined the correlation between well-established AD blood biomarkers and results obtained from these screening tests. HTSpos, Cimp, and Nimp were strongly associated with Aβ42/40 ratio (P < 0.0001, P = 0.0022, and P = 0.001), pTau181 (P < 0.0001, P = 0.0095, and P = 0.001), GFAP (P = 0.0372, P = 0.0088, and P = 0.0002), and amyloid PET Centiloid (P < 0.0001, P = 0.0210, and P = 0.0006), whereas Pimp increased neuroinflammation (GFAP; P = 0.0061) and was associated with non-AD tauopathy. The combination of Neucop-Q questions showed that Cimp/Pnor/Nimp subjects have the highest specificity and PPV (0.972 and 0.833) and were strongly associated with Aβ42/40 ratio (P = 0.0006), pTau181 (P = 0.0006), and amyloid PET Centiloid (P < 0.0001).

CONCLUSION

HTSpos, Cimp, and Nimp have diagnostic utility in suspecting MCI due to AD and AD, and Pimp has diagnostic value in non-AD tauopathy. HTSpos, Cimp, and Nimp were associated with biomarkers of Aβ pathology. HTS and Neucop-Q may serve as powerful first-line screening in memory clinics.

TRIAL REGISTRATION

UMIN Clinical Trials Registry (UMIN-CTR) under registration numbers 000032027 (Registration date: 2018/03/31) and 000030248 (Registration date: 2018/01/01).

Guidelines for the use and interpretation of Alzheimer's disease biomarkers in clinical practice in Brazil: recommendations from the Scientific Department of Cognitive Neurology and Aging of the Brazilian Academy of Neurology

In recent years, the diagnostic accuracy of Alzheimer's disease has been enhanced by the development of different types of biomarkers that indicate the presence of neuropathological processes. In addition to improving patient selection for clinical trials, biomarkers can assess the effects of new treatments on pathological processes. However, there is concern about the indiscriminate and poorly supported use of biomarkers, especially in asymptomatic individuals or those with subjective cognitive decline. Difficulties interpreting these tests, high costs, and unequal access make this scenario even more challenging in healthcare. This article presents the recommendations from the Scientific Department of Cognitive Neurology and Aging of the Brazilian Academy of Neurology (Departamento Científico de Neurologia Cognitiva e Envelhecimento da Academia Brasileira de Neurologia) regarding the rational use and interpretation of Alzheimer's disease biomarkers in clinical practice. The clinical diagnosis of cognitive-behavioral syndrome is recommended as the initial step to guide the request for biomarkers.

Thai Guideline for Nuclear Medicine Investigations of Neurocognitive Disorders: Nuclear Medicine Society of Thailand, the Neurological Society of Thailand, and Thai Medical Physicist Society Collaboration

Nuclear medicine investigations play a significant role in diagnosing dementia, mainly using imaging techniques such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT). By providing functional and molecular data via brain imaging, nuclear medicine investigations offer valuable insights that complement clinical evaluations and structural imaging in the early detection, diagnosis, and differentiation of various types of dementia, leading to more accurate diagnosis and personalized treatment planning. Therefore, the Nuclear Medicine Society of Thailand, the Neurological Society of Thailand, and the Thai Medical Physicist Society have collaborated to establish these practical nuclear medicine investigation guidelines aiming to (1) identify the role of nuclear medicine studies in patients with neurocognitive disorders; (2) assist referrers in requesting the most appropriate procedure for diagnosis of each type of neurocognitive disorders; and (3) identify scientific evidence that is useful to assisting nuclear medicine professionals in recommending, performing, interpreting, and reporting the results of nuclear medicine investigations in patients with neurocognitive disorders.

Combining cerebrospinal fluid and PI-2620 tau-PET for biomarker-based stratification of Alzheimer's disease and 4R-tauopathies

INTRODUCTION

Recent advances in biomarker research have improved the diagnosis and monitoring of Alzheimer's disease (AD), but in vivo biomarker-based workflows to assess 4R-tauopathy (4RT) patients are currently missing. We suggest a novel biomarker-based algorithm to characterize AD and 4RTs.

METHODS

We cross-sectionally assessed combinations of cerebrospinal fluid measures (CSF p-tau181 and t-tau) and 18F-PI-2620 tau-positron emission tomography (PET) in patients with AD (n = 64), clinically suspected 4RTs (progressive supranuclear palsy or corticobasal syndrome, n = 82) and healthy controls (n = 19).

RESULTS

Elevated CSF p-tau181 and cortical 18F-PI-2620 binding was characteristic for AD while normal CSF p-tau181 with elevated subcortical 18F-PI-2620 binding was characteristic for 4RTs. 18F-PI-2620-assessed posterior cortical hypoperfusion could be used as an additional neuronal injury biomarker in AD.

DISCUSSION

The specific combination of CSF markers and 18F-PI-2620 tau-PET in disease-specific regions facilitates the biomarker-guided stratification of AD and 4RTs. This has implications for biomarker-aided diagnostic workflows and the advancement in clinical trials.

HIGHLIGHTS

Novel biomarker-based algorithm for differentiating AD and 4R-tauopathies. A combination of CSF p-tau181 and 18F-PI-2620 discriminates AD versus 4R tauopathies. Hypoperfusion serves as an additional neuronal injury biomarker in AD.

Biomarker discovery in progressive supranuclear palsy from human cerebrospinal fluid

BACKGROUND

Progressive supranuclear palsy (PSP) is a neurodegenerative disorder often misdiagnosed as Parkinson's Disease (PD) due to shared symptoms. PSP is characterized by the accumulation of tau protein in specific brain regions, leading to loss of balance, gaze impairment, and dementia. Diagnosing PSP is challenging, and there is a significant demand for reliable biomarkers. Existing biomarkers, including tau protein and neurofilament light chain (NfL) levels in cerebrospinal fluid (CSF), show inconsistencies in distinguishing PSP from other neurodegenerative disorders. Therefore, the development of new biomarkers for PSP is imperative.

METHODS

We conducted an extensive proteome analysis of CSF samples from 40 PSP patients, 40 PD patients, and 40 healthy controls (HC) using tandem mass tag-based quantification. Mass spectrometry analysis of 120 CSF samples was performed across 13 batches of 11-plex TMT experiments, with data normalization to reduce batch effects. Pathway, interactome, cell-type-specific enrichment, and bootstrap receiver operating characteristic analyses were performed to identify key candidate biomarkers.

RESULTS

We identified a total of 3,653 unique proteins. Our analysis revealed 190, 152, and 247 differentially expressed proteins in comparisons of PSP vs. HC, PSP vs. PD, and PSP vs. both PD and HC, respectively. Gene set enrichment and interactome analysis of the differentially expressed proteins in PSP CSF showed their involvement in cell adhesion, cholesterol metabolism, and glycan biosynthesis. Cell-type enrichment analysis indicated a predominance of neuronally-derived proteins among the differentially expressed proteins. The potential biomarker classification performance demonstrated that ATP6AP2 (reduced in PSP) had the highest AUC (0.922), followed by NEFM, EFEMP2, LAMP2, CHST12, FAT2, B4GALT1, LCAT, CBLN3, FSTL5, ATP6AP1, and GGH.

CONCLUSION

Biomarker candidate proteins ATP6AP2, NEFM, and CHI3L1 were identified as key differentiators of PSP from the other groups. This study represents the first large-scale use of mass spectrometry-based proteome analysis to identify cerebrospinal fluid (CSF) biomarkers specific to progressive supranuclear palsy (PSP) that can differentiate it from Parkinson's disease (PD) and healthy controls. Our findings lay a crucial foundation for the development and validation of reliable biomarkers, which will enhance diagnostic accuracy and facilitate early detection of PSP.

Assessment of [18F]PI-2620 Tau-PET Quantification via Non-Invasive Automatized Image Derived Input Function

PURPOSE

[18F]PI-2620 positron emission tomography (PET) detects misfolded tau in progressive supranuclear palsy (PSP) and Alzheimer's disease (AD). We questioned the feasibility and value of absolute [18F]PI-2620 PET quantification for assessing tau by regional distribution volumes (VT). Here, arterial input functions (AIF) represent the gold standard, but cannot be applied in routine clinical practice, whereas image-derived input functions (IDIF) represent a non-invasive alternative. We aimed to validate IDIF against AIF and we evaluated the potential to discriminate patients with PSP and AD from healthy controls by non-invasive quantification of [18F] PET.

METHODS

In the first part of the study, we validated AIF derived from radial artery whole blood against IDIF by investigating 20 subjects (ten controls and ten patients). IDIF were generated by manual extraction of the carotid artery using the average and the five highest (max5) voxel intensity values and by automated extraction of the carotid artery using the average and the maximum voxel intensity value. In the second part of the study, IDIF quantification using the IDIF with the closest match to the AIF was transferred to group comparison of a large independent cohort of 40 subjects (15 healthy controls, 15 PSP patients and 10 AD patients). We compared VT and VT ratios, both calculated by Logan plots, with distribution volume (DV) ratios using simplified reference tissue modelling and standardized uptake value (SUV) ratios.

RESULTS

AIF and IDIF showed highly correlated input curves for all applied IDIF extraction methods (0.78 < r < 0.83, all p < 0.0001; area under the curves (AUC): 0.73 < r ≤ 0.82, all p ≤ 0.0003). Regarding the VT values, correlations were mainly found between those generated by the AIF and by the IDIF methods using the maximum voxel intensity values. Lowest relative differences (RD) were observed by applying the manual method using the five highest voxel intensity values (max5) (AIF vs. IDIF manual, avg: RD = -82%; AIF vs. IDIF automated, avg: RD = -86%; AIF vs. IDIF manual, max5: RD = -6%; AIF vs. IDIF automated, max: RD = -26%). Regional VT values revealed considerable variance at group level, which was strongly reduced upon scaling by the inferior cerebellum. The resulting VT ratio values were adequate to detect group differences between patients with PSP or AD and healthy controls (HC) (PSP target region (globus pallidus): HC vs. PSP vs. AD: 1.18 vs. 1.32 vs. 1.16; AD target region (Braak region I): HC vs. PSP vs. AD: 1.00 vs. 1.00 vs. 1.22). VT ratios and DV ratios outperformed SUV ratios and VT in detecting differences between PSP and healthy controls, whereas all quantification approaches performed similarly in comparing AD and healthy controls.

CONCLUSION

Blood-free IDIF is a promising approach for quantification of [18F]PI-2620 PET, serving as correlating surrogate for invasive continuous arterial blood sampling. Regional [18F]PI-2620 VT show large variance, in contrast to regional [18F]PI-2620 VT ratios scaled with the inferior cerebellum, which are appropriate for discriminating PSP, AD and healthy controls. DV ratios obtained by simplified reference tissue modeling are similarly suitable for this purpose.

Neuroinflammation Parallels 18F-PI-2620 Positron Emission Tomography Patterns in Primary 4-Repeat Tauopathies

BACKGROUND

Preclinical, postmortem, and positron emission tomography (PET) imaging studies have pointed to neuroinflammation as a key pathophysiological hallmark in primary 4-repeat (4R) tauopathies and its role in accelerating disease progression.

OBJECTIVE

We tested whether microglial activation (1) progresses in similar spatial patterns as the primary pathology tau spreads across interconnected brain regions, and (2) whether the degree of microglial activation parallels tau pathology spreading.

METHODS

We examined in vivo associations between tau aggregation and microglial activation in 31 patients with clinically diagnosed 4R tauopathies, using 18F-PI-2620 PET and 18F-GE180 (translocator protein [TSPO]) PET. We determined tau epicenters, defined as subcortical brain regions with highest tau PET signal, and assessed the connectivity of tau epicenters to cortical regions of interest using a 3-T resting-state functional magnetic resonance imaging template derived from age-matched healthy elderly controls.

RESULTS

In 4R tauopathy patients, we found that higher regional tau PET covaries with elevated TSPO-PET across brain regions that are functionally connected to each other (β = 0.414, P < 0.001). Microglial activation follows similar distribution patterns as tau and distributes primarily across brain regions strongly connected to patient-specific tau epicenters (β = -0.594, P < 0.001). In these regions, microglial activation spatially parallels tau distribution detectable with 18F-PI-2620 PET.

CONCLUSIONS

Our findings indicate that the spatial expansion of microglial activation parallels tau distribution across brain regions that are functionally connected to each other, suggesting that tau and inflammation are closely interrelated in patients with 4R tauopathies. The combination of in vivo tau and inflammatory biomarkers could therefore support the development of immunomodulatory strategies for disease-modifying treatments in these conditions. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Alzheimer's Disease-Related Cerebrospinal Fluid Biomarkers in Progressive Supranuclear Palsy

Progressive Supranuclear Palsy (PSP) is the most common four-repeat tauopathy. PSP cases are typically characterized by vertical gaze palsy and postural instability; however, various phenotypes have been reported, making antemortem diagnosis based on clinical symptoms challenging. The development of biomarkers reflecting brain pathology and the ability to diagnose patients based on these biomarkers are essential for developing future intervention strategies, including disease-modifying therapies. However, despite many dedicated efforts, no highly specific fluid biomarker for PSP has yet been established. Conversely, several cerebrospinal fluid (CSF) biomarkers of Alzheimer's Disease (AD) have been established, and an AT(N) classification system has been proposed. Typically, among patients with AD, CSF amyloid β42 (Aβ42), but not Aβ40, is decreased, resulting in a reduction in the Aβ42/Aβ40 ratio, while tau phosphorylated at threonine 181 (p-tau181) and total tau (t-tau) are increased. Interestingly, the core CSF AD biomarkers show unique patterns in patients with PSP. Furthermore, reports have indicated that the CSF levels of both Aβ42 and Aβ40 are decreased independently of Aβ accumulation in PSP. Therefore, the Aβ42/Aβ40 ratio could potentially be used to differentiate PSP from AD. Additionally, studies have reported that CSF p-tau and t-tau are reduced in PSP, and that the neurofilament light chain is remarkably increased compared to healthy controls and patients with AD, even though PSP is a neurodegenerative disease associated with tau accumulation. These PSP-specific changes in AD-related core biomarkers may reflect the pathology of PSP and contribute to its diagnosis. As such, elucidating the mechanisms underlying the observed decreases in Aβ and tau levels could facilitate a better understanding of the pathogenesis of PSP.

Towards multicenter β-amyloid PET imaging in mouse models: A triple scanner head-to-head comparison

AIM

β-amyloid (Aβ) small animal PET facilitates quantification of fibrillar amyloidosis in Alzheimer's disease (AD) mouse models. Thus, the methodology is receiving growing interest as a monitoring tool in preclinical drug trials. In this regard, harmonization of data from different scanners at multiple sites would allow the establishment large collaborative cohorts and may facilitate efficacy comparison of different treatments. Therefore, we objected to determine the level of agreement of Aβ-PET quantification by a head-to-head comparison of three different state-of-the-art small animal PET scanners, which could help pave the way for future multicenter studies.

METHODS

Within a timeframe of 5 ± 2 weeks, transgenic APPPS1 (n = 9) and wild-type (WT) (n = 8) mice (age range: 13-16 months) were examined three times by Aβ-PET ([18F]florbetaben) using a Siemens Inveon DPET, a MedisonanoScan PET/MR, and a MedisonanoScan PET/CT with harmonized reconstruction protocols. Cortex-to-white-matter 30-60 min p.i. standardized uptake value ratios (SUVRCTX/WM) were calculated to compare binding differences, effect sizes (Cohen's d) and z-score values of APPPS1 relative to WT mice. Correlation coefficients (Pearson's r) were calculated for the agreement of individual SUVR between different scanners. Voxel-wise analysis was used to determine the agreement of spatial pathology patterns. For validation of PET imaging against the histological gold standard, individual SUVR values were subject to a correlation analysis with area occupancy of methoxy‑X04 staining.

RESULTS

All three small animal PET scanners yielded comparable group differences between APPPS1 and WT mice (∆PET=20.4 % ± 2.9 %, ∆PET/MR=18.4 % ± 4.5 %, ∆PET/CT=18.1 % ± 3.3 %). Voxel-wise analysis confirmed a high degree of congruency of the spatial pattern (Dice coefficient (DC)PETvs.PET/MR=83.0 %, DCPETvs.PET/CT=69.3 %, DCPET/MRvs.PET/CT=81.9 %). Differences in the group level variance of the three scanners resulted in divergent z-scores (zPET=11.5 ± 1.6; zPET/MR=5.3 ± 1.3; zPET/CT=3.4 ± 0.6) and effect sizes (dPET=8.5, dPET/MR=4.5, dPET/CT=4.1). However, correlations at the individual mouse level were still strong between scanners (rPETvs.PET/MR=0.96, rPETvs.PET/CT=0.91, rPET/MRvs.PET/CT=0.87; all p ≤ 0.0001). Methoxy-X04 staining exhibited a significant correlation across all three PET machines combined (r = 0.76, p < 0.0001) but also at individual level (PET: r = 0.81, p = 0.026; PET/MR: r = 0.89, p = 0.0074; PET/CT: r = 0.93, p = 0.0028).

CONCLUSIONS

Our comparison of standardized small animal Aβ-PET acquired by three different scanners substantiates the possibility of moving towards a multicentric approach in preclinical AD research. The alignment of image acquisition and analysis methods achieved good overall comparability between data sets. Nevertheless, differences in variance of sensitivity and specificity of different scanners may limit data interpretation at the individual mouse level and deserves methodological optimization.

Magnetic Resonance Imaging Measures to Track Atrophy Progression in Progressive Supranuclear Palsy in Clinical Trials

BACKGROUND

Several magnetic resonance imaging (MRI) measures have been suggested as progression biomarkers in progressive supranuclear palsy (PSP), and some PSP staging systems have been recently proposed.

OBJECTIVE

Comparing structural MRI measures and staging systems in tracking atrophy progression in PSP and estimating the sample size to use them as endpoints in clinical trials.

METHODS

Progressive supranuclear palsy-Richardson's syndrome (PSP-RS) patients with one-year-follow-up longitudinal brain MRI were selected from the placebo arms of international trials (NCT03068468, NCT01110720, NCT01049399) and the DescribePSP cohort. The discovery cohort included patients from the NCT03068468 trial; the validation cohort included patients from other sources. Multisite age-matched healthy controls (HC) were included for comparison. Several MRI measures were compared: automated atlas-based volumetry (44 regions), automated planimetric measures of brainstem regions, and four previously described staging systems, applied to volumetric data.

RESULTS

Of 508 participants, 226 PSP patients including discovery (n = 121) and validation (n = 105) cohorts, and 251 HC were included. In PSP patients, the annualized percentage change of brainstem and midbrain volume, and a combined index including midbrain, frontal lobe, and third ventricle volume change, were the progression biomarkers with the highest effect size in both cohorts (discovery: >1.6; validation cohort: >1.3). These measures required the lowest sample sizes (n < 100) to detect 30% atrophy progression, compared with other volumetric/planimetric measures and staging systems.

CONCLUSIONS

This evidence may inform the selection of imaging endpoints to assess the treatment efficacy in reducing brain atrophy rate in PSP clinical trials, with automated atlas-based volumetry requiring smaller sample size than staging systems and planimetry to observe significant treatment effects. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Subcortical tau is linked to hypoperfusion in connected cortical regions in 4-repeat tauopathies

Four-repeat (4R) tauopathies are neurodegenerative diseases characterized by cerebral accumulation of 4R tau pathology. The most prominent 4R tauopathies are progressive supranuclear palsy (PSP) and corticobasal degeneration characterized by subcortical tau accumulation and cortical neuronal dysfunction, as shown by PET-assessed hypoperfusion and glucose hypometabolism. Yet, there is a spatial mismatch between subcortical tau deposition patterns and cortical neuronal dysfunction, and it is unclear how these two pathological brain changes are interrelated. Here, we hypothesized that subcortical tau pathology induces remote neuronal dysfunction in functionally connected cortical regions to test a pathophysiological model that mechanistically links subcortical tau accumulation to cortical neuronal dysfunction in 4R tauopathies. We included 51 Aβ-negative patients with clinically diagnosed PSP variants (n = 26) or corticobasal syndrome (n = 25) who underwent structural MRI and 18F-PI-2620 tau-PET. 18F-PI-2620 tau-PET was recorded using a dynamic one-stop-shop acquisition protocol to determine an early 0.5-2.5 min post tracer-injection perfusion window for assessing cortical neuronal dysfunction, as well as a 20-40 min post tracer-injection window to determine 4R-tau load. Perfusion-PET (i.e. early window) was assessed in 200 cortical regions, and tau-PET was assessed in 32 subcortical regions of established functional brain atlases. We determined tau epicentres as subcortical regions with the highest 18F-PI-2620 tau-PET signal and assessed the connectivity of tau epicentres to cortical regions of interest using a resting-state functional MRI-based functional connectivity template derived from 69 healthy elderly controls from the ADNI cohort. Using linear regression, we assessed whether: (i) higher subcortical tau-PET was associated with reduced cortical perfusion; and (ii) cortical perfusion reductions were observed preferentially in regions closely connected to subcortical tau epicentres. As hypothesized, higher subcortical tau-PET was associated with overall lower cortical perfusion, which remained consistent when controlling for cortical tau-PET. Using group-average and subject-level PET data, we found that the seed-based connectivity pattern of subcortical tau epicentres aligned with cortical perfusion patterns, where cortical regions that were more closely connected to the tau epicentre showed lower perfusion. Together, subcortical tau-accumulation is associated with remote perfusion reductions indicative of neuronal dysfunction in functionally connected cortical regions in 4R-tauopathies. This suggests that subcortical tau pathology may induce cortical dysfunction, which may contribute to clinical disease manifestation and clinical heterogeneity.

Low-intensity vestibular noise stimulation improves postural symptoms in progressive supranuclear palsy

BACKGROUND

Postural imbalance and falls are an early disabling symptom in patients with progressive supranuclear palsy (PSP) of multifactorial origin that may involve abnormal vestibulospinal reflexes. Low-intensity noisy galvanic vestibular stimulation (nGVS) is a non-invasive treatment to normalize deficient vestibular function and attenuate imbalance in Parkinson's disease. The presumed therapeutic mode of nGVS is stochastic resonance (SR), a mechanism by which weak sensory noise stimulation can enhance sensory information processing.

OBJECTIVE

To examine potential treatment effects of nGVS on postural instability in 16 patients with PSP with a clinically probable and [18F]PI-2620 tau-PET-positive PSP.

METHODS

Effects of nGVS of varying intensity (0-0.7 mA) on body sway were examined, while patients were standing with eyes closed on a posturographic force plate. We assumed a bell-shaped response curve with maximal sway reductions at intermediate nGVS intensities to be indicative of SR. An established SR-curve model was fitted on individual patient outcomes and three experienced human raters had to judge whether responses to nGVS were consistent with the exhibition of SR.

RESULTS

We found nGVS-induced reductions of body sway compatible with SR in 9 patients (56%) with optimal improvements of 31 ± 10%. In eight patients (50%), nGVS-induced sway reductions exceeded the minimal clinically important difference (improvement: 34 ± 5%), indicative of strong SR.

CONCLUSION

nGVS yielded clinically relevant reductions in body sway compatible with the exhibition of SR in vestibular sensorimotor pathways in at least half of the assessed patients. Non-invasive vestibular noise stimulation may be thus a well-tolerated treatment strategy to ameliorate postural symptoms in PSP.

Ligand-based design of [18F]OXD-2314 for PET imaging in non-Alzheimer's disease tauopathies

Positron emission tomography (PET) imaging of tau aggregation in Alzheimer's disease (AD) is helping to map and quantify the in vivo progression of AD pathology. To date, no high-affinity tau-PET radiopharmaceutical has been optimized for imaging non-AD tauopathies. Here we show the properties of analogues of a first-in-class 4R-tau lead, [18F]OXD-2115, using ligand-based design. Over 150 analogues of OXD-2115 were synthesized and screened in post-mortem brain tissue for tau affinity against [3H]OXD-2115, and in silico models were used to predict brain uptake. [18F]OXD-2314 was identified as a selective, high-affinity non-AD tau PET radiotracer with favorable brain uptake, dosimetry, and radiometabolite profiles in rats and non-human primate and is being translated for first-in-human PET studies.

Improved Tau PET SUVR Quantification in 4-Repeat Tau Phenotypes with [18F]PI-2620

We used a new data-driven methodology to identify a set of reference regions that enhanced the quantification of the SUV ratio of the second-generation tau tracer 2-(2-([18F]fluoro)pyridin-4-yl)-9H-pyrrolo[2,3-b:4,5-c']dipyridine ([18F]PI-2620) in a group of patients clinically diagnosed with 4-repeat tauopathy, specifically progressive supranuclear palsy or cortical basal syndrome. The study found that SUV ratios calculated using the identified reference regions (i.e., fusiform gyrus and crus-cerebellum) were significantly associated with symptom severity and disease duration. This establishes, for the first time to our knowledge, the suitability of [18F]PI-2620 for tracking disease progression in this 4-repeat disease population. This is an important step toward increased clinical utility, such as patient stratification and monitoring in disease-modifying treatment trials. Additionally, the applied methodology successfully optimized reference regions for automated detection of brain imaging tracers. This approach may also hold value for other brain imaging tracers.

Tau accumulation is associated with dopamine deficiency in vivo in four-repeat tauopathies

PURPOSE

We hypothesized that severe tau burden in brain regions involved in direct or indirect pathways of the basal ganglia correlate with more severe striatal dopamine deficiency in four-repeat (4R) tauopathies. Therefore, we correlated [18F]PI-2620 tau-positron-emission-tomography (PET) imaging with [123I]-Ioflupane single-photon-emission-computed tomography (SPECT) for dopamine transporter (DaT) availability.

METHODS

Thirty-eight patients with clinically diagnosed 4R-tauopathies (21 male; 69.0 ± 8.5 years) and 15 patients with clinically diagnosed α-synucleinopathies (8 male; 66.1 ± 10.3 years) who underwent [18F]PI-2620 tau-PET and DaT-SPECT imaging with a time gap of 3 ± 5 months were evaluated. Regional Tau-PET signals and DaT availability as well as their principal components were correlated in patients with 4R-tauopathies and α-synucleinopathies. Both biomarkers and the residuals of their association were correlated with clinical severity scores in 4R-tauopathies.

RESULTS

In patients with 4R-tauopathies, [18F]PI-2620 binding in basal ganglia and midbrain regions was negatively associated with striatal DaT availability (i.e. globus pallidus internus and putamen (β =  - 0.464, p = 0.006, Durbin-Watson statistics = 1.824) in a multiple regression model. Contrarily, [18F]PI-2620 binding in the dentate nucleus showed no significant regression factor with DaT availability in the striatum (β = 0.078, p = 0.662, Durbin-Watson statistics = 1.686). Patients with α-synucleinopathies did not indicate any regional associations between [18F]PI-2620-binding and DaT availability. Higher DaT-SPECT binding relative to tau burden was associated with better clinical performance (β =  - 0.522, p = 0.011, Durbin-Watson statistics = 2.663) in patients with 4R-tauopathies.

CONCLUSION

Tau burden in brain regions involved in dopaminergic pathways is associated with aggravated dopaminergic dysfunction in patients with clinically diagnosed primary tauopathies. The ability to sustain dopamine transmission despite tau accumulation may preserve motor function.

Misfolded protein deposits in Parkinson's disease and Parkinson's disease-related cognitive impairment, a [11C]PBB3 study

Parkinson's disease (PD) is associated with aggregation of misfolded α-synuclein and other proteins, including tau. We designed a cross-sectional study to quantify the brain binding of [11C]PBB3 (a ligand known to bind to misfolded tau and possibly α-synuclein) as a proxy of misfolded protein aggregation in Parkinson's disease (PD) subjects with and without cognitive impairment and healthy controls (HC). In this cross-sectional study, nineteen cognitively normal PD subjects (CN-PD), thirteen cognitively impaired PD subjects (CI-PD) and ten HC underwent [11C]PBB3 PET. A subset of the PD subjects also underwent PET imaging with [11C](+)DTBZ to assess dopaminergic denervation and [11C]PBR28 to assess neuroinflammation. Compared to HC, PD subjects showed higher [11C]PBB3 binding in the posterior putamen but not the substantia nigra. There was no relationship across subjects between [11C]PBB3 and [11C]PBR28 binding in nigrostriatal regions. [11C]PBB3 binding was increased in the anterior cingulate in CI-PD compared to CN-PD and HC, and there was an inverse correlation between cognitive scores and [11C]PBB3 binding in this region across all PD subjects. Our results support a primary role of abnormal protein deposition localized to the posterior putamen in PD. This suggests that striatal axonal terminals are preferentially involved in the pathophysiology of PD. Furthermore, our findings suggest that anterior cingulate pathology might represent a significant in vivo marker of cognitive impairment in PD, in agreement with previous neuropathological studies.

Cortical Tau Aggregation Patterns associated with Apraxia in Alzheimer's Disease

Objectives

Apraxia is a core feature of Alzheimer's disease, but the pathomechanism of this characteristic symptom is not well understood. Here, we systematically investigated apraxia profiles in a well-defined group of patients with Alzheimer's disease (AD; N=32) who additionally underwent PET imaging with the second-generation tau PET tracer [18F]PI-2620. We hypothesized that specific patterns of tau pathology might be related to apraxic deficits.

Methods

Patients (N=32) with a biomarker-confirmed diagnosis of Alzheimer's disease were recruited in addition to a sample cognitively unimpaired controls (CU 1 ; N=41). Both groups underwent in-depth neuropsychological assessment of apraxia (Dementia Apraxia Screening Test; DATE and the Cologne Apraxia Screening; KAS). In addition, static PET imaging with [18F]PI-2620 was performed to assess tau pathology in the AD patients. To specifically investigate the association of apraxia with regional tau-pathology, we compared the PET-data from this group with an independent sample of amyloid-negative cognitively intact participants (CU 2; N=54) by generation of z-score-deviation maps as well as voxel- based multiple regression analyses.

Results

We identified significant clusters of tau-aggregation in praxis-related regions (e.g., supramarginal gyrus, angular gyrus, temporal, parietal and occipital regions) that were associated with apraxia. These regions were similar between the two apraxia assessments. No correlations between tau-tracer uptake in primary motor cortical or subcortical brain regions and apraxia were observed.

Conclusions

These results suggest that tau deposition in specific cortical brain regions may induce local neuronal dysfunction leading to a dose-dependent functional decline in praxis performance.

Acute ischemic stroke outcomes in patients with COVID-19: a systematic review and meta-analysis

BACKGROUND

Although patients with COVID-19 have a higher risk of acute ischemic stroke (AIS), the impact on stroke outcomes remains uncertain.

AIMS

To determine the clinical outcomes of patients with AIS and COVID-19 (AIS-COVID+).

METHODS

We performed a systematic review and meta-analysis following the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines. Our protocol was registered with the International Prospective Register of Systematic Reviews (CRD42020211977). Systematic searches were last performed on June 3, 2021 in EMBASE, PubMed, Web-of-Science, Scopus, and CINAHL Databases.

INCLUSION CRITERIA

(1) studies reporting outcomes on AIS-COVID+; (2) original articles published in 2020 or later; (3) study participants aged ≥18 years.

EXCLUSION CRITERIA

(1) case reports with <5 patients, abstracts, review articles; (2) studies analyzing novel interventions. Risk of bias was assessed using the Mixed Methods Appraisal Tool. Random-effects models estimated the pooled OR and 95% confidence intervals (95% CI) for mortality, modified Rankin Scale (mRS) score, length of stay (LOS), and discharge disposition.

RESULTS

Of the 43 selected studies, 46.5% (20/43) reported patients with AIS without COVID-19 (AIS-COVID-) for comparison. Random-effects model included 7294 AIS-COVID+ and 158 401 AIS-COVID-. Compared with AIS-COVID-, AIS-COVID+ patients had higher in-hospital mortality (OR=3.87 (95% CI 2.75 to 5.45), P<0.001), less mRS scores 0-2 (OR=0.53 (95% CI 0.46 to 0.62), P<0.001), longer LOS (mean difference=4.21 days (95% CI 1.96 to 6.47), P<0.001), and less home discharge (OR=0.31 (95% CI 0.21 to 0.47), P<0.001).

CONCLUSIONS

Patients with AIS-COVID had worse outcomes, with almost fourfold increased mortality, half the odds of mRS scores 0-2, and one-third the odds of home discharge. These findings confirm the significant impact of COVID-19 on early stroke outcomes.

In vitro evaluation of [3H]PI-2620 and structural derivatives in non-Alzheimer's tauopathies

Alzheimer's disease (AD) and non-AD tauopathies such as chronic traumatic encephalopathy (CTE), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD) are characterized by the abnormal aggregation of three-repeat (3R) and/or four-repeat (4R) tau isoforms. Several tau-PET tracers have been applied for human imaging of AD and non-AD tauopathies including [18F]PI-2620. Our objective is to evaluate [3H]PI-2620 and two promising structural derivatives, [3H]PI-2014 and [3H]F-4, using in vitro saturation assays and competitive binding assays against new chemical entities based on this scaffold in human AD tissues for comparison with PSP, CBD and CTE tissues. Thin section autoradiography was employed to assess specific binding and distribution of [3H]PI-2620 and [3H]F-4 in fresh-frozen human post-mortem AD, PSP, CBD and CTE tissues. Immunohistochemistry was performed for phospho-tau (AT8) and 4R-tau (RD4). Homogenate filtration binding assays were performed for saturation analysis and competitive binding studies against [3H]PI-2620. All compounds bound with high affinity in AD tissue. In PSP tissue [3H]PI-2620 demonstrated the highest affinity (5.3 nM) and in CBD tissue [3H]F-4 bound with the highest affinity (9.4 nM). Over 40 fluorinated derivatives based on PI-2620 and F-4 were screened in AD and PSP tissue. Notably, compound 2 was the most potent derivative in PSP tissue (Ki = 7.3 nM). By autoradiography, [3H]PI-2620 and [3H]F-4 demonstrated positive signals similar in intensity in AD, PSP and CTE tissues that were displaced by homologous blockade. Binding of both radiotracers aligned with immunostaining for 4R-tau. This work demonstrates that [3H]PI-2620 and [3H]F-4 show promise for imaging 4R-tau aggregates in non-AD tauopathies. PI-2620 continues to serve as a structural scaffold for PET radiotracers with higher affinity for non-AD tau over AD tau.

Probable 4-Repeat Tauopathy Criteria Predict Brain Amyloid Negativity, Distinct Clinical Features, and FDG-PET/MRI Neurodegeneneration Patterns in Corticobasal Syndrome

BACKGROUND

Corticobasal syndrome (CBS) is associated with diverse underlying pathologies, including the four-repeat (4R)-tauopathies. The Movement Disorders Society (MDS) criteria for progressive supranuclear palsy (PSP) proposed the novel category "probable 4R-tauopathy" to address the phenotypic overlap between PSP and corticobasal degeneration (CBD).

OBJECTIVES

To investigate the clinical ability of the MDS-PSP criteria for probable 4R-tauopathy in predicting a negative amyloid-PET in CBS. Additionally, this study aims to explore CBS patients classified as 4R-tauopathy concerning their clinical features and neuroimaging degeneration patterns.

METHODS

Thirty-two patients with probable CBS were prospectively evaluated and split into those who fulfilled or did not fulfill the 4R-tauopathy criteria (CBS-4RT+ vs. CBS-4RT-). All patients underwent positron emission tomographies (PET) with [18 F]fluorodeoxyglucose and [11 C]Pittsburgh Compound-B (PIB) on a hybrid PET-MRI scanner to perform multimodal quantitative comparisons with a control group.

RESULTS

Eleven patients were clinically classified as CBS-4RT+, and only one had a positive PIB-PET. The CBS-4RT+ classification had 92% specificity, 52% sensitivity, and 69% accuracy in predicting a negative PIB-PET. The CBS-4RT+ group presented with dysarthria and perseveration more often than the CBS-4RT- group. Moreover, the CBS-4RT+ group showed a prominent frontal hypometabolism extending to the supplementary motor area and striatum, and brain atrophy at the anterior cingulate and bilateral striata.

CONCLUSIONS

The 4R-tauopathy criteria were highly specific in predicting a negative amyloid-PET in CBS. Patients classified as 4R-tauopathy presented distinct clinical aspects, as well as brain metabolism and atrophy patterns previously associated with tauopathies.

In vivo PET classification of tau pathologies in patients with frontotemporal dementia

Frontotemporal dementia refers to a group of neurodegenerative disorders with diverse clinical and neuropathological features. In vivo neuropathological assessments of frontotemporal dementia at an individual level have hitherto not been successful. In this study, we aim to classify patients with frontotemporal dementia based on topologies of tau protein aggregates captured by PET with 18F-florzolotau (aka 18F-APN-1607 and 18F-PM-PBB3), which allows high-contrast imaging of diverse tau fibrils in Alzheimer's disease as well as in non-Alzheimer's disease tauopathies. Twenty-six patients with frontotemporal dementia, 15 with behavioural variant frontotemporal dementia and 11 with other frontotemporal dementia phenotypes, and 20 age- and sex-matched healthy controls were included in this study. They underwent PET imaging of amyloid and tau depositions with 11C-PiB and 18F-florzolotau, respectively. By combining visual and quantitative analyses of PET images, the patients with behavioural variant frontotemporal dementia were classified into the following subgroups: (i) predominant tau accumulations in frontotemporal and frontolimbic cortices resembling three-repeat tauopathies (n = 3), (ii) predominant tau accumulations in posterior cortical and subcortical structures indicative of four-repeat tauopathies (n = 4); (iii) amyloid and tau accumulations consistent with Alzheimer's disease (n = 4); and (iv) no overt amyloid and tau pathologies (n = 4). Despite these distinctions, clinical symptoms and localizations of brain atrophy did not significantly differ among the identified behavioural variant frontotemporal dementia subgroups. The patients with other frontotemporal dementia phenotypes were also classified into similar subgroups. The results suggest that PET with 18F-florzolotau potentially allows the classification of each individual with frontotemporal dementia on a neuropathological basis, which might not be possible by symptomatic and volumetric assessments.

One-Year Longitudinal Changes in Tau Accumulation on [18F]PI-2620 PET in the Alzheimer Spectrum

We investigated the longitudinal changes in cortical tau accumulation and their association with cognitive decline in patients in the Alzheimer disease (AD) continuum using 2-(2-([18F]fluoro)pyridin-4-yl)-9H-pyrrolo[2,3-b:4,5c']dipyridine ([18F]PI-2620) PET. Methods: We prospectively enrolled 52 participants (age, 69.7 ± 8.4 y; 18 men and 34 women): 7 with normal cognition, 28 with mild cognitive impairment, and 17 with AD. They all completed the [18F]PI-2620 and [18F]florbetaben PET, MRI, and neuropsychologic tests at baseline and, excepting the [18F]florbetaben PET, at the 1-y follow-up. Amyloid-β (Aβ) PET images were visually scored as positive (+) or negative (-). Patients on the AD continuum, including Aβ+ mild cognitive impairment and AD, were classified into early-onset (EO+) (<65 y old) or late-onset (LO+) (≥65 y old) groups. [18F]PI-2620 PET SUV ratios (SUVRs) were determined by calculating the cerebral-to-inferior cerebellar ratio. Cortical volumes were calculated using 3-dimensional T1-weighted MRI. The correlation between tau accumulation progression and cognitive decline was also investigated. Results: The global [18F]PI-2620 PET SUVRs were 1.04 ± 0.07 in 15 Aβ- patients, 1.18 ± 0.21 in 20 LO+ patients (age, 76.7 ± 3.8 y), and 1.54 ± 0.38 in 17 EO+ patients (age, 63.4 ± 5.4 y; P < 0.001) at baseline. The global SUVR increased over 1 y by 0.05 ± 0.07 (3.90%) and 0.13 ± 0.22 (8.41%) in the LO+ and EO+ groups, respectively, whereas in the Aβ- groups, it remained unchanged. The EO+ group showed higher global and regional tau deposition than did the Aβ- and LO+ groups (P < 0.05 for each) and rapid accumulation in Braak stage V (0.15 ± 0.25; 9.10% ± 12.27%; P = 0.016 and 0.008), Braak stage VI (0.08 ± 0.12; 7.16% ± 10.06%; P < 0.006 and 0.005), and global SUVR (P = 0.013) compared with the Aβ- group. In the EO+ group, the changes in SUVR in Braak stages II-VI were strongly correlated with the baseline and changes in verbal memory (P < 0.03). The LO+ group showed higher tau accumulation in Braak stage I-IV areas than did the Aβ- group (P < 0.001 for each). In the LO+ group, the change in SUVR in Braak stages III and IV moderately correlated with the change in attention (P < 0.05), and the change in SUVR in Braak stages V and VI moderately correlated with the change in visuospatial function (P < 0.005). Conclusion: These findings suggest that [18F]PI-2620 PET can be a biomarker to provide regional and chronologic information about tau pathology in the AD continuum.

Impact of the pandemic and concomitant COVID-19 on the management and outcomes of middle cerebral artery strokes: a nationwide registry-based study

OBJECTIVES

To investigate the impact of the COVID-19 pandemic as well as concomitant COVID-19 itself on stroke care, focusing on middle cerebral artery (MCA) territory infarctions.

DESIGN

Registry-based study.

SETTING

We used the National Inpatient Sample (NIS) database, which covers a wide range of hospitals within the USA.

PARTICIPANTS

The NIS was queried for patients with MCA strokes between 2016 and 2020. In total, 35 231 patients were included.

OUTCOME MEASURES

Outcome measures were postprocedural complications, length of stays (LOSs), in-hospital mortality and non-routine discharge. Propensity score matching using all available baseline variables was performed to reduce confounders when comparing patients with and without concomitant COVID-19.

RESULTS

Mechanical thrombectomy (MT) was performed in 48.4%, intravenous thrombolysis (IVT) in 38.2%, and both MT and IVT (MT+IVT) in 13.4% of patients. A gradual increase in the use of MT and an opposite decrease in the use of IVT (p<0.001) was detected during the study period. Overall, 25.0% of all patients were admitted for MCA strokes during the pandemic period (2020), of these 209 (2.4%) were concomitantly diagnosed with COVID-19. Patients with MCA strokes and concomitant COVID-19 were significantly younger (64.9 vs 70.0; p<0.001), had significantly worse NIH Stroke Severity scores, and worse outcomes in terms of LOS (12.3 vs 8.2; p<0.001), in-hospital mortality (26.3% vs 9.8%; p<0.001) and non-routine discharge (84.2% vs 76.9%; p=0.013), as compared with those without COVID-19. After matching, only in-hospital mortality rates remained significantly higher in patients with COVID-19 (26.7% vs 8.5%; p<0.001). Additionally, patients with COVID-19 had higher rates of thromboembolic (12.3% vs 7.6%; p=0.035) and respiratory (11.3% vs 6.6%; p=0.029) complications.

CONCLUSIONS

Among patients with MCA stroke, those with concomitant COVID-19 were significantly younger and had higher stroke severity scores. They were more likely to experience thromboembolic and respiratory complications and in-hospital mortality compared with matched controls.

Staging of progressive supranuclear palsy-Richardson syndrome using MRI brain charts for the human lifespan

Brain charts for the human lifespan have been recently proposed to build dynamic models of brain anatomy in normal aging and various neurological conditions. They offer new possibilities to quantify neuroanatomical changes from preclinical stages to death, where longitudinal MRI data are not available. In this study, we used brain charts to model the progression of brain atrophy in progressive supranuclear palsy-Richardson syndrome. We combined multiple datasets (n = 8170 quality controlled MRI of healthy subjects from 22 cohorts covering the entire lifespan, and n = 62 MRI of progressive supranuclear palsy-Richardson syndrome patients from the Four Repeat Tauopathy Neuroimaging Initiative (4RTNI)) to extrapolate lifetime volumetric models of healthy and progressive supranuclear palsy-Richardson syndrome brain structures. We then mapped in time and space the sequential divergence between healthy and progressive supranuclear palsy-Richardson syndrome charts. We found six major consecutive stages of atrophy progression: (i) ventral diencephalon (including subthalamic nuclei, substantia nigra, and red nuclei), (ii) pallidum, (iii) brainstem, striatum and amygdala, (iv) thalamus, (v) frontal lobe, and (vi) occipital lobe. The three structures with the most severe atrophy over time were the thalamus, followed by the pallidum and the brainstem. These results match the neuropathological staging of tauopathy progression in progressive supranuclear palsy-Richardson syndrome, where the pathology is supposed to start in the pallido-nigro-luysian system and spreads rostrally via the striatum and the amygdala to the cerebral cortex, and caudally to the brainstem. This study supports the use of brain charts for the human lifespan to study the progression of neurodegenerative diseases, especially in the absence of specific biomarkers as in PSP.

Polypathologic Associations with Gray Matter Atrophy in Neurodegenerative Disease

Mixed pathologies are common in neurodegenerative disease; however, antemortem imaging rarely captures copathologic effects on brain atrophy due to a lack of validated biomarkers for non-Alzheimer's pathologies. We leveraged a dataset comprising antemortem MRI and postmortem histopathology to assess polypathologic associations with atrophy in a clinically heterogeneous sample of 125 human dementia patients (41 female, 84 male) with T1-weighted MRI ≤ 5 years before death and postmortem ordinal ratings of amyloid-[Formula: see text], tau, TDP-43, and [Formula: see text]-synuclein. Regional volumes were related to pathology using linear mixed-effects models; approximately 25% of data were held out for testing. We contrasted a polypathologic model comprising independent factors for each proteinopathy with two alternatives: a model that attributed atrophy entirely to the protein(s) associated with the patient's primary diagnosis and a protein-agnostic model based on the sum of ordinal scores for all pathology types. Model fits were evaluated using log-likelihood and correlations between observed and fitted volume scores. Additionally, we performed exploratory analyses relating atrophy to gliosis, neuronal loss, and angiopathy. The polypathologic model provided superior fits in the training and testing datasets. Tau, TDP-43, and [Formula: see text]-synuclein burden were inversely associated with regional volumes, but amyloid-[Formula: see text] was not. Gliosis and neuronal loss explained residual variance in and mediated the effects of tau, TDP-43, and [Formula: see text]-synuclein on atrophy. Regional brain atrophy reflects not only the primary molecular pathology but also co-occurring proteinopathies; inflammatory immune responses may independently contribute to degeneration. Our findings underscore the importance of antemortem biomarkers for detecting mixed pathology.

Novel aspects of the phosphorylation and structure of pathological tau: implications for tauopathy biomarkers

The deposition of highly phosphorylated and aggregated tau is a characteristic of tauopathies, including Alzheimer's disease. It has long been known that different isoforms of tau are aggregated in different cell types and brain regions in each tauopathy. Recent advances in analytical techniques revealed the details of the biochemical and structural biological differences of tau specific to each tauopathy. In this review, we explain recent advances in the analysis of post-translational modifications of tau, particularly phosphorylation, brought about by the development of mass-spectrometry and Phos-tag technology. We then discuss the structure of tau filaments in each tauopathy revealed by the advent of cryo-EM. Finally, we describe the progress in biofluid and imaging biomarkers for tauopathy. This review summarizes current efforts to elucidate the characteristics of pathological tau and the landscape of the use of tau as a biomarker to diagnose and determine the pathological stage of tauopathy.

Head-to-head comparison of [18F]-Flortaucipir, [18F]-MK-6240 and [18F]-PI-2620 postmortem binding across the spectrum of neurodegenerative diseases

We and others have shown that [18F]-Flortaucipir, the most validated tau PET tracer thus far, binds with strong affinity to tau aggregates in Alzheimer's (AD) but has relatively low affinity for tau aggregates in non-AD tauopathies and exhibits off-target binding to neuromelanin- and melanin-containing cells, and to hemorrhages. Several second-generation tau tracers have been subsequently developed. [18F]-MK-6240 and [18F]-PI-2620 are the two that have garnered most attention. Our recent data indicated that the binding pattern of [18F]-MK-6240 closely parallels that of [18F]-Flortaucipir. The present study aimed at the direct comparison of the autoradiographic binding properties and off-target profile of [18F]-Flortaucipir, [18F]-MK-6240 and [18F]-PI-2620 in human tissue specimens, and their potential binding to monoamine oxidases (MAO). Phosphor-screen and high resolution autoradiographic patterns of the three tracers were studied in the same postmortem tissue material from AD and non-AD tauopathies, cerebral amyloid angiopathy, synucleopathies, transactive response DNA-binding protein 43 (TDP-43)-frontotemporal lobe degeneration and controls. Our results show that the three tracers show nearly identical autoradiographic binding profiles. They all strongly bind to neurofibrillary tangles in AD but do not seem to bind to a significant extent to tau aggregates in non-AD tauopathies pointing to their limited utility for the in vivo detection of non-AD tau lesions. None of them binds to lesions containing β-amyloid, α-synuclein or TDP-43 but they all show strong off-target binding to neuromelanin and melanin-containing cells, as well as weaker binding to areas of hemorrhage. The autoradiographic binding signals of the three tracers are only weakly displaced by competing concentrations of selective MAO-B inhibitor deprenyl but not by MAO-A inhibitor clorgyline suggesting that MAO enzymes do not appear to be a significant binding target of any of them. These findings provide relevant insights for the correct interpretation of the in vivo behavior of these three tau PET tracers.

Association of Neurofilament Light Chain, [18F]PI-2620 Tau-PET, TSPO-PET, and Clinical Progression in Patients With β-Amyloid-Negative CBS

BACKGROUND AND OBJECTIVES

Corticobasal syndrome (CBS) with underlying 4-repeat tauopathy is a progressive neurodegenerative disease characterized by declining cognitive and motor functions. Biomarkers for assessing pathologic brain changes in CBS including tau-PET, 18 kDa translocator protein (TSPO)-PET, structural MRI, neurofilament light chain (NfL), or glial fibrillary acidic protein (GFAP) have recently been evaluated for differential diagnosis and disease staging, yet their association with disease trajectories remains unclear. Therefore, we performed a head-to-head comparison of neuroimaging (tau-PET, TSPO-PET, structural MRI) and plasma biomarkers (NfL, GFAP) as prognostic tools for longitudinal clinical trajectories in β-amyloid (Aβ)-negative CBS.

METHODS

We included patients with clinically diagnosed Aβ-negative CBS with clinical follow-up data who underwent baseline structural MRI and plasma-NfL analysis for assessing neurodegeneration, [18F]PI-2620-PET for assessing tau pathology, [18F]GE-180-PET for assessing microglia activation, and plasma-GFAP analysis for assessing astrocytosis. To quantify tau and microglia load, we assessed summary scores of whole-brain, cortical, and subcortical PET signal. For structural MRI analysis, we quantified subcortical and cortical gray matter volume. Plasma NfL and GFAP values were assessed using Simoa-based immunoassays. Symptom progression was determined using a battery of cognitive and motor tests (i.e., Progressive Supranuclear Palsy Rating Scale [PSPRS]). Using linear mixed models, we tested whether the assessed biomarkers at baseline were associated with faster symptom progression over time (i.e., time × biomarker interaction).

RESULTS

Overall, 21 patients with Aβ-negative CBS with ∼2-year clinical follow-up data were included. Patients with CBS with more widespread global tau-PET signal showed faster clinical progression (PSPRS: B/SE = 0.001/0.0005, p = 0.025), driven by cortical rather than subcortical tau-PET. By contrast, patients with higher global [18F]GE-180-PET readouts showed slower clinical progression (PSPRS: B/SE = -0.056/0.023, p = 0.019). No association was found between gray matter volume and clinical progression. Concerning fluid biomarkers, only higher plasma-NfL (PSPRS: B/SE = 0.176/0.046, p < 0.001) but not GFAP was associated with faster clinical deterioration. In a subsequent sensitivity analysis, we found that tau-PET, TSPO-PET, and plasma-NfL showed significant interaction effects with time on clinical trajectories when tested in the same model.

DISCUSSION

[18F]PI-2620 tau-PET, [18F]GE-180 TSPO-PET, and plasma-NfL show prognostic potential for clinical progression in patients with Aβ-negative CBS with probable 4-repeat tauopathy, which can be useful for clinical decision-making and stratifying patients in clinical trials.

Progressive Supranuclear Palsy: Subcortical Tau Depositions Are Associated with Cortical Perfusion in Frontal and Limbic Regions

In progressive supranuclear palsy (PSP), subcortical tau and cortical perfusion can be assessed using the tracer [18F]PI-2620. We investigated if subcortical tau (globus pallidus internus, dentate nucleus) and frontal/limbic perfusion correlate in a cohort of 32 PSP patients. Tau in subcortical regions showed significant negative correlation with perfusion in limbic cortex. Perfusion in frontal regions was negatively associated with tau in both subcortical regions, but the significance threshold was only passed for the dentate nucleus. A reason could be a diaschisis-like phenomenon; that is, subcortical tau could lead to reduced connectivity to frontal regions and, thereby, to decreased perfusion.

Traumatic Encephalopathy Syndrome and Tauopathy in a 19-Year-Old With Child Abuse

The majority of traumatic encephalopathy syndrome (TES) cases have been reported in former contact sport athletes. This is the first case with TES in a 19-year-old male patient with progressive cognitive decline after daily domestic physical violence through repeated hits to the head for 15 years. The patient presented with a moderate depressive episode and progressive cognitive decline. Tau positron emission tomography (PET) with 220 MBq of [18F]PI-2620 revealed increased focal signal at the frontal and parietal white/gray matter border. Brain magnetic resonance imaging (MRI) showed a cavum septum pellucidum, reduced left-sided hippocampal volume, and a left midbrain lesion. Cerebrospinal fluid results showed elevated total and p-tau. Neurocognitive testing at admission showed memory deficits clearly below average, and hampered dysfunctions according to the slow processing speed with a low mistake rate, indicating the acquired, thus secondary, attentional deficits. We diagnosed the patient with a TES suggestive of chronic traumatic encephalopathy and classified him as having subtle/mild functional limitation with a most likely transition to mild dementia within the TES criteria. This report underlines child abuse as a relevant criterion in diagnosing TES in cases with repetitive hits to the head. In addition to clinical markers, we show the relevance of fluid tau biomarkers and tau-PET to support the diagnosis of TES according to the recently published diagnosis criteria for TES.

New Perspectives in Radiological and Radiopharmaceutical Hybrid Imaging in Progressive Supranuclear Palsy: A Systematic Review

Progressive supranuclear palsy (PSP) is a neurodegenerative disease characterized by four-repeat tau deposition in various cell types and anatomical regions, and can manifest as several clinical phenotypes, including the most common phenotype, Richardson's syndrome. The limited availability of biomarkers for PSP relates to the overlap of clinical features with other neurodegenerative disorders, but identification of a growing number of biomarkers from imaging is underway. One way to increase the reliability of imaging biomarkers is to combine different modalities for multimodal imaging. This review aimed to provide an overview of the current state of PSP hybrid imaging by combinations of positron emission tomography (PET) and magnetic resonance imaging (MRI). Specifically, combined PET and MRI studies in PSP highlight the potential of [18F]AV-1451 to detect tau, but also the challenge in differentiating PSP from other neurodegenerative diseases. Studies over the last years showed a reduced synaptic density in [11C]UCB-J PET, linked [11C]PK11195 and [18F]AV-1451 markers to disease progression, and suggested the potential role of [18F]RO948 PET for identifying tau pathology in subcortical regions. The integration of quantitative global and regional gray matter analysis by MRI may further guide the assessment of reduced cortical thickness or volume alterations, and diffusion MRI could provide insight into microstructural changes and structural connectivity in PSP. Challenges in radiopharmaceutical biomarkers and hybrid imaging require further research targeting markers for comprehensive PSP diagnosis.

[18F]PI-2620 Binding Patterns in Patients with Suspected Alzheimer Disease and Frontotemporal Lobar Degeneration

Tau PET has enabled the visualization of paired helical filaments of 3 or 4 C-terminal repeat tau in Alzheimer disease (AD), but its ability to detect aggregated tau in frontotemporal lobar degeneration (FTLD) spectrum disorders is uncertain. We investigated 2-(2-([18F]fluoro)pyridin-4-yl)-9H-pyrrolo[2,3-b:4,5c']dipyridine ([18F]PI-2620), a newer tracer with ex vivo evidence for binding to FTLD tau, in a convenience sample of patients with suspected FTLD and AD using a static acquisition protocol and parametric SUV ratio (SUVr) images. Methods: We analyzed [18F]PI-2620 PET data from 65 patients with clinical diagnoses associated with AD or FTLD neuropathology; most (60/65) also had amyloid-β (Aβ) PET. Scans were acquired 30-60 min after injection; SUVr maps (reference, inferior cerebellar cortex) were created for the full acquisition and for 10-min truncated sliding windows (30-40, 35-45,…50-60 min). Age- and sex-adjusted z score maps were computed for each patient, relative to 23 Aβ-negative cognitively healthy controls (HC). Mean SUVr in the globus pallidus, substantia nigra, subthalamic nuclei, dentate nuclei, white matter, and temporal gray matter was extracted for the full and truncated windows. Results: Patients with suspected AD neuropathology (Aβ-positive patients with mild cognitive impairment or AD dementia) showed high-intensity temporoparietal cortex-predominant [18F]PI-2620 binding. At the group level, patients with clinical diagnoses associated with FTLD (progressive supranuclear palsy with Richardson syndrome [PSP Richardson syndrome], corticobasal syndrome, and nonfluent-variant primary progressive aphasia) exhibited higher globus pallidus SUVr than did HCs; pallidal retention was highest in the PSP Richardson syndrome group, in whom SUVr was correlated with symptom severity (ρ = 0.53, P = 0.05). At the individual level, only half of PSP Richardson syndrome, corticobasal syndrome, and nonfluent-variant primary progressive aphasia patients had a pallidal SUVr above that of HCs. Temporal SUVr discriminated AD patients from HCs with high accuracy (area under the receiver operating characteristic curve, 0.94 [95% CI, 0.83-1.00]) for all time windows, whereas discrimination between patients with PSP Richardson syndrome and HCs using pallidal SUVr was fair regardless of time window (area under the receiver operating characteristic curve, 0.77 [95% CI, 0.61-0.92] at 30-40 min vs. 0.81 [95% CI, 0.66-0.96] at 50-60 min; P = 0.67). Conclusion: [18F]PI-2620 SUVr shows an intense and consistent signal in AD but lower-intensity, heterogeneous, and rapidly decreasing binding in patients with suspected FTLD. Further work is needed to delineate the substrate of [18F]PI-2620 binding and the usefulness of [18F]PI2620 SUVr quantification outside the AD continuum.

In Vivo Measurement of Tau Depositions in Anti-IgLON5 Disease Using [18F]PI-2620 PET

OBJECTIVES

Anti-IgLON5 disease is a recently discovered neurologic disorder combining autoimmunity and neurodegeneration. Core manifestations include sleep disorders, bulbar symptoms, gait abnormalities, and cognitive dysfunction, but other presentations have been reported. Hallmarks are autoantibodies targeting the neuronal surface protein IgLON5, a strong human leukocyte antigen system Class II association, and brainstem and hypothalamus-dominant tau deposits. The purpose of this cohort study was to visualize tau deposition in vivo with the second-generation tau-PET tracer.

METHODS

A cohort of 4 patients with anti-IgLON5 disease underwent a dynamic PET scan with [18F]PI-2620. One patient received a follow-up scan. Z-deviation maps and a 2-sample t test in comparison with healthy controls (n = 10) were performed. Antibody titers, neurofilament light chain, and disease duration were correlated with brainstem binding potentials.

RESULTS

Patients demonstrated increased [18F]PI2620 tau binding potentials in the pons, dorsal medulla, and cerebellum. The longitudinal scan after 28 months showed an increase of tracer uptake in the medulla despite immunotherapy. Higher antibody titers and neurofilament light chain correlated with higher tracer retention.

DISCUSSION

The results indicate that tau depositions in anti-IgLON5 disease can be visualized with [18F]PI-2620 and might correlate with the extent of disease. For validation, a larger longitudinal study is necessary.