A study by researchers at the Centre for Healthy Brain Ageing (CHeBA) detailed, reportedly for a first time, the relationship between plasma levels of two types of amyloid beta peptides and cognitive function and brain volume, factors known to be diminished in Alzheimer’s disease (AD). The findings suggested that blood plasma measures of such peptides constitute an easy-to-collect and viable biomarker for a risk analysis or early diagnosis of the disease.
Amyloid beta (Aβ) peptides are the main components of the amyloid plaques found in the brains of Alzheimer’s patients, and are known to contribute to progressive neurodegeneration and cognitive decline. Researches have theorized that measurements of levels of Aβ in blood plasma may constitute an Alzheimer’s biomarker, but stronger proof has been hampered by difficulties in collecting and measuring the peptides. “While Aβ has traditionally been measured using cerebrospinal fluid, plasma presents a more accessible sample for routine collection and screening, although results to date have been variable,” Dr. Anne Poljak, the study’s lead author and head of the CHeBA’s Proteomics Group, said in a press release.
Researchers analysed and compared the plasma levels of the Aβ1-40 and Aβ1-42 peptides in 89 individuals with amnestic mild cognitive impairment (aMCI), 39 people with Alzheimer’s disease, and 126 age-matched cognitively healthy controls, all participants in CHeBA’s Sydney Memory & Ageing study. Plasma levels of the two peptides and the Aβ1-42/Aβ1-40 ratio were lower in aMCI and Alzheimer’s patients compared to the healthy controls, with lower levels of Aβ1-42 associated with lower cognition and lower hippocampal volume, both characteristics of AD.
A genetic component was also observed, since a link between Aβ1-40 and cognitive and brain volume measures were mainly observed in people carrying the ε4 allele, while the opposite was observed in non-carriers. Moreover, there was a greater decline in global cognition and memory for the highest quintiles of Aβ1-42 and the ratio measure. The APOE ε4 gene is a genetic factor associated with a higher risk of developing AD, and a higher risk of early onset disease.
“These findings certainly suggest that plasma Aβ measures may serve as biomarkers of Alzheimer’s disease,” concluded Professor Perminder Sachdev, director of CHeBA and a study co-author.