Abstract
BackgroundThe quantification of amyloid-beta (Aβ) peptides in blood plasma as potential biomarkers of Alzheimer’s disease (AD) is hampered by very low Aβ concentrations and the presence of matrix components that may interfere with the measurements.MethodsWe developed a two-step immunoassay for the simultaneous measurement of the relative levels of Aβ38, Aβ40 and Aβ42 in human EDTA plasma. The assay was employed for the study of 23 patients with dementia of the Alzheimer’s type (AD-D) and 17 patients with dementia due to other reasons (OD). We examined relationships with the clinical diagnosis, cerebral Aβ load as quantified by amyloid-positron emission tomography, apolipoprotein E genotype, Aβ levels and Tau protein in cerebrospinal fluid.ResultsPreconcentration of plasma Aβ peptides by immunoprecipitation substantially facilitated their immunological measurements. The Aβ42/Aβ40 and Aβ42/Aβ38 ratios were statistically significantly lower in the AD-D patients than in the OD group. The areas under the receiver operating characteristic curves reached 0.87 for the Aβ42/Aβ40 ratio and 0.80 for the Aβ42/Aβ38 ratio.ConclusionsThe measurement of plasma Aβ peptides with an immunological assay can be improved by preconcentration via immunoprecipitation with an antibody against the Aβ amino-terminus and elution of the captured peptides by heating in a mild detergent-containing buffer. Our findings support the Aβ42/Aβ40 ratio in blood plasma as a promising AD biomarker candidate which correlates significantly with the validated core biomarkers of AD. Further studies will be needed for technical advancement of the assay and validation of the biomarker findings.
Highlights
The quantification of amyloid-beta (Aβ) peptides in blood plasma as potential biomarkers of Alzheimer’s disease (AD) is hampered by very low Amyloid beta (Aβ) concentrations and the presence of matrix components that may interfere with the measurements
We tested immunoprecipitation (IP) from 400 or 800 μl of EDTA plasma followed by elution of preconcentrated Aβ from the immune complexes at 95 °C in bicine-CHAPS buffer
We report on the development of a prototypic novel two-step immunoassay for the simultaneous assessment of the relative concentrations of Aβ38, Aβ40 and Aβ42 in human EDTA blood plasma
Summary
The quantification of amyloid-beta (Aβ) peptides in blood plasma as potential biomarkers of Alzheimer’s disease (AD) is hampered by very low Aβ concentrations and the presence of matrix components that may interfere with the measurements. The diagnostic potential of Aβ peptides in blood plasma has been the subject of numerous studies These have produced conflicting results, and the authors of a recent comprehensive meta-analysis and review concluded that there were no significant differences in Aβ42 or Aβ40 levels in blood plasma or serum between Alzheimer’s disease patients and controls, in general [1]. Matrix components present in blood plasma and serum may cause interferences (“matrix effects”) contributing to errors or incorrect results in immunoassays [10] These technical challenges may explain, at least in part, the contradictory findings of previous studies addressing the diagnostic potential of Aβ peptides in blood as AD biomarker candidates
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