Plasma Amyloid-beta dynamics in late-life major depression: a longitudinal study

Depressed individuals are twice as likely to develop Alzheimer's disease (AD) as compared to controls. Brain amyloid-beta (A beta) deposition is believed to have a major role in AD pathogenesis but studies also suggest associations of A beta dynamics and depression. The aim of this study was to test if plasma A beta levels are longitudinally associated to late-life depression. We measured plasma levels of amyloid-beta(1-40) (A beta 40) and amyloid-beta(1-42) (A beta 42) peptides longitudinally for three consecutive years in 48 cognitively intact elderly subjects with late-life major depressive disorder (LLMD) and 45 age-matched cognitively healthy controls. We found that the A beta 42/A beta 40 plasma ratio was significantly and steadily lower in depressed subjects compared to controls (p < 0.001). At screening, A beta 42/A beta 40 plasma did not correlate with depression severity (as measured with Hamilton Depression Scale) or cognitive performance (as measured with Mini-Mental State Examination) but was associated to depression severity at 3 years after adjustment for age, education, cognitive performance, and antidepressants use. This study showed that reduced plasma A beta 42/A beta 40 ratio is consistently associated with LLMD diagnosis and that increased severity of depression at baseline predicted low A beta 42/A beta 40 ratio at 3 years. Future studies are needed to confirm these findings and examine if the consistently lower plasma A beta 42/A beta 40 ratio in LLMD reflects increased brain amyloid deposition, as observed in AD subjects, and an increased risk for progressive cognitive decline and AD.