MedWire News: Plasma levels of β-amyloid 42 (Aβ42) peptide are reduced in patients with bipolar depression, and could serve a possible biomarker of cognitive decline in patients with mood disorders, say researchers.
Writing in the Journal of Affective Disorders, Armando Piccinni (University of Pisa, Italy) and team explain: "The risk for dementia and cognitive deterioration is greater in patients affected by mood disorders than in the general population, and correlates with the number of affective episodes, manic polarity, and the presence of psychotic symptoms."
They say that previous studies in patients with Alzheimer's disease and those with mild cognitive impairment have reported "a reduction of plasma Aβ42, and an increase of Aβ40 and Aβ40/Aβ42 ratio," but add that little is known about levels of these peptides in patients with bipolar disorder.
To investigate, the researchers studied 16 patients with bipolar depression and 16 mentally healthy individuals (controls) who were aged at least 18 years.
Blood samples were collected from all of the participants and assessed for plasma levels of Aβ42 and Aβ40 using an enzyme-linked immunosorbent assay.
The researchers found that mean plasma levels of Aβ42 were significantly lower in patients with bipolar depression compared with controls, at 18.75 versus 27.50 pg/mL. However, there were no significant differences between the groups regarding mean plasma levels of Aβ40, at 101.13 and 111.32 pg/mL, respectively.
Consequently, patients with bipolar depression had a significantly higher Aβ40/Aβ42 ratio than controls, at 5.35 versus 4.38.
The researchers also found that there was a significant negative correlation between mean plasma levels of Aβ42 and duration of illness in patients with bipolar depression, while there was a significant positive correlation between number of previous mood episodes and Aβ40/Aβ42 ratio.
There was no significant correlation between mean plasma levels of Aβ40 and Aβ42, or between the Aβ40/Aβ42 ratio and scores on the Hamilton Rating Scale for Depression, the team notes.
Piccinni and colleagues conclude: "Our study point[s] out for the first time that lower Aβ42 values and higher Aβ40/Aβ42 ratio may characterize depressed bipolar patients, when compared with healthy controls."
They add that changes in plasma levels of Aβ peptides may not only act as "a possible biomarker in the pathophysiology of mood disorders, but also as a parameter whose change might identify subgroups of patients with an increased risk for cognitive decline."
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