July 1, 2020
National Institutes for Quantum and Radiological Science and Technology
Keio University School of Medicine
Japan Agency for Medical Research and Development
Sho Moriguchi, a visiting researcher at the Department of Functional Brain Imaging, National Institute of Radiological Sciences, Quantum Medical Science Directorate, National Institutes for Quantum and Radiological Science and Technology (QST; President: Toshio Hirano), whose primary affiliation is the Department of Neuropsychiatry, Keio University School of Medicine, and Makoto Higuchi, Director of the department, in collaboration with Professor Masaru Mimura and others from the Department of Neuropsychiatry, Keio University School of Medicine, have visualized tau accumulation in the living brains of patients with geriatric depression. They revealed that this accumulation may be associated with the onset of depressive symptoms and that the amount of accumulation is related to the presence or absence of psychotic symptoms seen in geriatric depression.
Until now, there has been no objective diagnostic method for depression. Diagnosis has been based mainly on the evaluation of clinical symptoms confirmed through interviews. However, the symptoms and pathology are diverse and many aspects remain unclear, and the effectiveness of treatment has been limited. Furthermore, while depression is known to be a risk factor for dementia, including Alzheimer's disease, the common pathological mechanisms between depression and dementia have not been well understood.
Postmortem brain studies of patients with depression have revealed that abnormal proteins such as tau and amyloid-β protein (hereinafter referred to as amyloid-β), which are thought to accumulate in the brains of dementia patients and be involved in the development of neurological disorders, are also found in the brains of some patients with depression. This has led to the suspicion that, similar to dementia patients, the accumulation of these abnormal proteins in the brain may be involved in the onset of the disease in patients with depression, but clear evidence of a link to clinical symptoms has not been obtained.
In this study, we used positron emission tomography (PET) technology, pioneered by QST to visualize tau in the living brain, to non-invasively measure the amount of tau and amyloid-β accumulation in the brains of patients with geriatric depression and examined the relationship with clinical symptoms. The results showed that, compared to healthy elderly individuals of the same age group, some patients with geriatric depression had significantly more tau accumulation throughout the cerebral cortex. In particular, it was revealed that brain tau accumulation was prominent in patients with psychotic symptoms such as delusions and auditory hallucinations.
These findings indicate that objective diagnosis of geriatric depression may become possible using tau accumulation in the living brain, as captured by PET, as a biomarker. Furthermore, it is expected that new therapeutic drugs being developed as radical treatments for dementia, which suppress brain tau accumulation, may also be effective for geriatric depression.
This research was conducted with support from the Japan Agency for Medical Research and Development (AMED) program "Strategic Research Program for Brain Sciences (SRPBS)." The results were published in the online edition of "Molecular Psychiatry," a high-impact (impact factor 11.973) international academic journal in the field of psychiatry, on July 1, 2020, at 9:00 AM (JST).
For the full press release, please see below.