18F-THK5351 Positron Emission Tomography Imaging in Neurodegenerative Tauopathies

Introduction: We aimed to determine whether in vivo tau deposits and monoamine oxidase B (MAO-B) detection using ¹⁸F-THK5351 positron emission tomography (PET) can assist in the differential distribution in patients with corticobasal syndrome (CBS), progressive supranuclear palsy (PSP), and Alzheimer's disease (AD) and whether ¹⁸F-THK5351 retention of lesion sites in CBS and PSP can correlate with clinical parameters. Methods: ¹⁸F-THK5351 PET was performed in 35 participants, including 7, 9, and 10 patients with CBS, PSP, and AD, respectively, and 9 age-matched normal controls. In CBS and PSP, cognitive and motor functions were assessed using the Montreal Cognitive Assessment, Addenbrooke's Cognitive Examination-Revised, and Frontal Assessment Battery, Unified Parkinson's Disease Rating Scale Motor Score, and PSP Rating Scale. Results: ¹⁸F-THK5351 retention was observed in sites susceptible to disease-related pathologies in CBS, PSP, and AD. ¹⁸F-THK5351 uptake in the precentral gyrus clearly differentiated patients with CBS from those with PSP and AD. Furthermore, ¹⁸F-THK5351 uptake in the inferior temporal gyrus clearly differentiated patients with AD from those with CBS and PSP. Regional ¹⁸F-THK5351 retention was associated with the cognitive function in CBS and PSP. Conclusion: Measurement of the tau deposits and MAO-B density in the brain using ¹⁸F-THK5351 may be helpful for the differential diagnosis of tauopathies and for understanding disease stages.

Cognitive Dysfunction in Cats: Update on Neuropathological and Behavioural Changes Plus Clinical Management

Cognitive dysfunction syndrome (CDS) is an established condition in cats that shares many similarities with human Alzheimer's disease (AD), where cognitive decline ultimately results in dementia. Cats with CDS display behavioural abnormalities, including excessive Vocalisation, altered Interaction with owners (increased affection/attention), altered Sleep-wake cycles, House-soiling, Disorientation (spatial and/or temporal), alterations in Activity, Anxiety, and/or Learning/memory deficits (i.e., VISHDAAL). These cats develop neuropathologies, such as accumulation of β-amyloid and hyperphosphorylated tau deposits. Because of its similarities to those in the brains of people with cognitive impairment and AD, the domestic cat could be a natural model for human dementia studies. It is important to diagnose CDS promptly in cats, ruling out other causes for these behavioural changes, to provide effective management. Interventions include environmental enrichment (e.g., easy access to key resources, calming pheromones), dietary supplementations (e.g., Senilife, Aktivait for cats, SAMe), specific diets (e.g., containing antioxidants, medium-chain triglycerides) and, potentially, medication (e.g., selegiline or propentofylline). This article reviews the literature about CDS in cats, its causes, neuropathology, clinical signs, diagnosis and potential management options. By doing so, it furthers our understanding of this condition and allows improved health, welfare and quality of life of affected cats.

Longitudinal changes in 18 F-THK5351 positron emission tomography in corticobasal syndrome

BACKGROUND AND PURPOSE

Corticobasal syndrome (CBS) is pathologically characterized by tau deposits in neuronal and glial cells and by reactive astrogliosis. In several neurodegenerative disorders, ¹⁸ F-THK5351 has been observed to bind to reactive astrocytes expressing monoamine oxidase B. In this study, the aim was to investigate the progression of disease-related pathology in the brains of patients with CBS using positron emission tomography with ¹⁸ F-THK5351.

METHODS

Baseline and 1-year follow-up imaging were acquired using magnetic resonance imaging and positron emission tomography with ¹⁸ F-THK5351 in 10 subjects: five patients with CBS and five age-matched normal controls (NCs).

RESULTS

The 1-year follow-up scan images revealed that ¹⁸ F-THK5351 retention had significantly increased in the superior parietal gyrus of the patients with CBS compared with the NCs. The median increases in ¹⁸ F-THK5351 accumulation in the patients with CBS were 6.53% in the superior parietal gyrus, 4.34% in the precentral gyrus and 4.33% in the postcentral gyrus. In contrast, there was no significant increase in the regional ¹⁸ F-THK5351 retention in the NCs.

CONCLUSIONS

Longitudinal increases in ¹⁸ F-THK5351 binding can be detected over a short interval in the cortical sites of patients with CBS. A monoamine oxidase B binding radiotracer could be useful in monitoring the progression of astrogliosis in CBS.

Characteristics of Tau and Its Ligands in PET Imaging

Tau deposition is one of the neuropathological hallmarks in Alzheimer’s disease as well as in other neurodegenerative disorders called tauopathies. Recent efforts to develop selective tau radiopharmaceuticals have allowed the visualization of tau deposits in vivo. In vivo tau imaging allows the assessment of the regional distribution of tau deposits in a single human subject over time for determining the pathophysiology of tau accumulation in aging and neurodegenerative conditions as well as for application in drug discovery of anti-dementia drugs as surrogate markers. However, tau deposits show complicated characteristics because of different isoform composition, histopathology, and ultrastructure in various neurodegenerative conditions. In addition, since tau radiopharmaceuticals possess different chemotype classes, they may show different binding characteristics with heterogeneous tau deposits. In this review, we describe the characteristics of tau deposits and their ligands that have β-sheet binding properties, and the status of tau imaging in clinical studies.