Changes in plasma amyloid beta in a longitudinal study of aging and Alzheimer's disease

Background: A practical biomarker is required to facilitate the preclinical diagnosis of Alzheimer's disease (AD). Methods: Plasma amyloid beta (A beta)(1-40), A beta(1-42), A beta(n-40), and A beta(n-42) peptides were measured at baseline and after 18 months in 771 participants from the Australian Imaging Biomarkers and Lifestyle (AIBL) study of aging. A beta peptide levels were compared with clinical pathology, neuroimaging and neuropsychological measurements. Results: Although inflammatory and renal function covariates influenced plasma A beta levels significantly, a decrease in A beta(1-42)/A beta(1-40) was observed in patients with AD, and was also inversely correlated with neocortical amyloid burden. During the 18 months, plasma A beta(1-42) decreased in subjects with mild cognitive impairment (MCI) and in those transitioning from healthy to MCI. Conclusion: Our findings are consistent with a number of published plasma A beta studies and, although the prognostic value of individual measures in any given subject is limited, the diagnostic contribution of plasma A beta may demonstrate utility when combined with a panel of peripheral biomarkers. (C) 2014 The Alzheimer's Association. All rights reserved.