The relationship between plasma amyloid- Delta b peptides and the medial temporal lobe in the homebound elderly

Background The ratio of high amyloid- Delta *b peptide40 (A Delta *b40) and low A Delta *b42 in plasma predicts the risk of Alzheimer's disease (AD) and is associated with episodic recall in depression. We thus examined the relationship between plasma A Delta *b levels and brain volumes. Methods Homebound elders (N=352) who had undergone brain MRI were used. Plasma A Delta *b1-40 and A Delta *b1-42 were measured by ELISA. Volumes of medial temporal regions, including the amygdala and hippocampus, were manually measured. Results Amygdala volume was associated with log10 of plasma A Delta *b1-42 ( Delta *b=+0.19, SE=0.07, p=0.005) after adjusting for AD, infarcts, white matter hyperintensities and demographics. In the absence of dementia, decreasing quartiles of plasma A Delta *b1-42 (Mean+SD ml: Q4=4.1?0.8; Q3=3.9?0.7; Q2=3.6?0.8 and Q1=3.7?0.8, p=0.01) and increasing quartiles of plasma A Delta *b1-40/1-42 ratio were associated with smaller amygdala volume. Those depressed subjects with a high plasma A Delta *b1-40/1-42 ratio had smaller amygdala (Mean+SD ml: 3.3?0.8 vs. 3.6?0.8, p=0.04) and total brain volume (Mean+SD liter: 0.95?0.07 vs. 1.04?0.12, p=0.005), and had a higher rate of MCI (67 vs. 36%, p=0.02) than those with a low plasma A Delta *b1-40/1-42 ratio. Conclusions The combination of low plasma A Delta *b1-42 concentration and atrophy of the medial temporal lobe structures, which regulates mood and cognition, may represent a biomarker for a prodromal stage of AD.