Background: Plasma Ã?²-amyloid (AÃ?²) is a potential candidate for an Alzheimerââ?¬â?¢s disease (AD) biomarker because blood is\nan easily accessible bio-fluid, which can be collected routinely, and AÃ?² is one of the major hallmarks of AD pathogenesis\nin the brain. However, the association between plasma AÃ?² levels and AD diagnosis is still unclear due to the instability\nand inaccurate measurements of plasma AÃ?² levels in the blood of patients with AD. If a consistent value of plasma AÃ?²\nfrom the blood can be obtained, this might help determine whether plasma AÃ?² is a potential biomarker for AD diagnosis.\nMethods: We predicted the brain amyloid deposit by measuring the plasma AÃ?² levels. This cross-sectional study included\n353 participants (215 cognitively normal, 79 with mild cognitive impairment, and 59 with AD dementia) who underwent\nPittsburgh-compound B positron emission tomography (PiB-PET) scans. We treated a mixture of protease inhibitors and\nphosphatase inhibitors (MPP) and detected plasma AÃ?²42 and AÃ?²40 (MPP-AÃ?²42 and MPP-AÃ?²40) in a stable\nmanner using xMAP technology.\nResults: MPP-AÃ?²40 and MPP-AÃ?²42/40 (MPP-AÃ?²s) were significantly different between subjects with positive amyloid\ndeposition (PiB+) and those with negative amyloid deposition (PiBââ?¬â??) (P < 0.0001). Furthermore, MPP-AÃ?²40 (P < 0.0001,\nr = 0.23) and MPP-AÃ?²42/40 ratio (P < 0.0001, r = ââ?¬â??0.23) showed significant correlation with global PiB deposition\n(standardized uptake value ratio). In addition, our integrated multivariable (MPP-AÃ?²42/40, gender, age, and\napolipoprotein E genotypes) logistic regression model proposes a new standard for the prediction of cerebral amyloid\ndeposition.\nConclusions: MPP-AÃ?² might be one of the potential blood biomarkers for the prediction of PiB-PET positivity in the brain.
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