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.Electronic supplementary materialThe online version of this article (10.1186/s13195-018-0448-x) contains supplementary material, which is available to authorized users.

The cerebrospinal fluid (CSF) biomarkers amyloid-β (Aβ), total Tau, and phospho-181-Tau represent important diagnostic tools to support the clinical diagnosis of Alzheimer's disease (AD). Acquiring CSF by lumbar puncture is considered a moderately invasive procedure, while blood sampling is minimally invasive with calculable risks and can be performed by trained non-medical staff. Thus, the identification of reliable and robust blood biomarkers of AD-related neuropathology would be significantly advantageous in daily practice and would allow more patients to be screened. In this study, we performed a multiplex amyloid-β assay to simultaneously measure Aβ and Aβ. We analyzed how well Aβ, Aβ, and the Aβ to Aβ ratio (Aβ) could differentiate between patients suffering from dementia either due or not due to AD. In addition, we studied different factors affecting Aβ levels in plasma. Plasma Aβ level was significantly lower in patients with dementia due to AD than in those with dementia due to other causes. Aβ correlated weakly between plasma and CSF, but did not differ between amyloid-PET positive or negative patients. Furthermore, we found that kidney function influences Aβ and Aβ plasma levels, but not Aβ level. Liver function, age, and sex do not affect Aβ levels in plasma.

Synucleinopathies are a group of neurodegenerative diseases including Parkinson’s disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). These diseases are characterized by the aggregation and deposition of α-synuclein (α-syn) in Lewy bodies (LBs) in PD and DLB or as glial cytoplasmic inclusions in MSA. In healthy brains, only ∼4% of α-syn is phosphorylated at Ser129 (pS129-α-syn), whereas >90% pS129-α-syn may be found in LBs, suggesting that pS129-α-syn could be a useful biomarker for synucleinopathies. However, a widely available, robust, sensitive, and reproducible method for measuring pS129-α-syn in biological fluids is currently missing. We used Meso Scale Discovery (MSD)’s electrochemiluminescence platform to create a new assay for sensitive detection of pS129-α-syn. We evaluated several combinations of capture and detection antibodies and used semisynthetic pS129-α-syn as a standard for the assay at a concentration range from 0.5 to 6.6 × 104 pg/mL. Using the antibody EP1536Y for capture and an anti-human α-syn antibody (MSD) for detection was the best combination in terms of assay sensitivity, specificity, and reproducibility. We tested the utility of the assay for the detection and quantification of pS129-α-syn in human cerebrospinal fluid, serum, plasma, saliva, and CNS-originating small extracellular vesicles, as well as in mouse brain lysates. Our data suggest that the assay can become a widely used method for detecting pS129-α-syn in biomedical studies including when only a limited volume of sample is available and high sensitivity is required, offering new opportunities for diagnostic biomarkers, monitoring disease progression, and quantifying outcome measures in clinical trials.

Different tauopathies are characterized by the isoform‐specific composition of the aggregates found in the brain and by structurally distinct tau strains. Although tau oligomers have been implicated as important neurotoxic species, little is known about how the primary structures of the six human tau isoforms affect tau oligomerization because the oligomers are metastable and difficult to analyze. To address this knowledge gap, here, we analyzed the initial oligomers formed by the six tau isoforms in the absence of posttranslational modifications or other manipulations using dot blots probed by an oligomer‐specific antibody, native‐PAGE/western blots, photo‐induced cross‐linking of unmodified proteins, mass‐spectrometry, and ion‐mobility spectroscopy. We found that under these conditions, three‐repeat (3R) isoforms are more prone than four‐repeat (4R) isoforms to form oligomers. We also tested whether known inhibitors of tau aggregation affect its oligomerization using three small molecules representing different classes of tau aggregation inhibitors, Methylene Blue (MB), the molecular tweezer CLR01, and the all‐D peptide TLKIVW, for their ability to inhibit or modulate the oligomerization of the six tau isoforms. Unlike their reported inhibitory effect on tau fibrillation, the inhibitors had little or no effect on the initial oligomerization. Our study provides novel insight into the primary–quaternary structure relationship of human tau and suggests that 3R‐tau oligomers may be an important target for future development of compounds targeting pathological tau assemblies.

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