Novel plasma biomarker surrogating cerebral amyloid deposition

Alzheimer's disease (AD) is the most common and devastating dementia. Simple and practical biomarkers for AD are urgently required for accurate diagnosis and to facilitate the development of disease-modifying interventions. The subjects for the study were selected on the basis of PiB amyloid imaging by PET. Forty PiB-positive (PiB+) individuals, including cognitively healthy controls (HC), and mild cognitive impairment and AD individuals, and 22 PiB-negative (PiB-) HC participated. Employing our novel highly sensitive immunoprecipitation-mass spectrometry, we measured plasma amyloid beta-proteins (A beta s; A beta 1-40 and A beta 1-42) and A beta-approximate peptides (A beta APs), which were cleaved from amyloid precursor protein (APP). Among the A beta APs, APP669-711 appeared to be a good reference for deciphering pathological change of A beta 1-42. We evaluated the performance of the ratio of APP669-711 to A beta 1-42 (APP669-711/A beta 1-42) as a biomarker. APP669-711/A beta 1-42 significantly increased in the PiB+ groups. The sensitivity and specificity to discriminate PiB+ individuals from PiB- individuals were 0.925 and 0.955, respectively. Our plasma biomarker precisely surrogates cerebral amyloid deposition.