Search

Alzheimer’s disease has a preclinical stage when cerebral amyloid-β deposition occurs before symptoms emerge, and when amyloid-β-targeted therapies may have maximum benefits. Existing amyloid-β status measurement techniques, including amyloid PET and CSF testing, are difficult to deploy at scale, so blood biomarkers are increasingly considered for screening. We compared three different blood-based techniques—liquid chromatography-mass spectrometry measures of plasma amyloid-β, and single molecule array (Simoa) measures of plasma amyloid-β and phospho-tau181—to detect cortical 18F-florbetapir amyloid PET positivity (defined as a standardized uptake value ratio of >0.61 between a predefined cortical region of interest and eroded subcortical white matter) in dementia-free members of Insight 46, a substudy of the population-based British 1946 birth cohort. We used logistic regression models with blood biomarkers as predictors of amyloid PET status, with or without age, sex and APOE ε4 carrier status as covariates. We generated receiver operating characteristics curves and quantified areas under the curves to compare the concordance of the different blood tests with amyloid PET. We determined blood test cut-off points using Youden’s index, then estimated numbers needed to screen to obtain 100 amyloid PET-positive individuals. Of the 502 individuals assessed, 441 dementia-free individuals with complete data were included; 82 (18.6%) were amyloid PET-positive. The area under the curve for amyloid PET status using a base model comprising age, sex and APOE ε4 carrier status was 0.695 (95% confidence interval: 0.628–0.762). The two best-performing Simoa plasma biomarkers were amyloid-β42/40 (0.620; 0.548–0.691) and phospho-tau181 (0.707; 0.646–0.768), but neither outperformed the base model. Mass spectrometry plasma measures performed significantly better than any other measure (amyloid-β1-42/1-40: 0.817; 0.770–0.864 and amyloid-β composite: 0.820; 0.775–0.866). At a cut-off point of 0.095, mass spectrometry measures of amyloid-β1-42/1-40 detected amyloid PET positivity with 86.6% sensitivity and 71.9% specificity. Without screening, to obtain 100 PET-positive individuals from a population with similar amyloid PET positivity prevalence to Insight 46, 543 PET scans would need to be performed. Screening using age, sex and APOE ε4 status would require 940 individuals, of whom 266 would proceed to scan. Using mass spectrometry amyloid-β1-42/1-40 alone would reduce these numbers to 623 individuals and 243 individuals, respectively. Across a theoretical range of amyloid PET positivity prevalence of 10–50%, mass spectrometry measures of amyloid-β1-42/1-40 would consistently reduce the numbers proceeding to scans, with greater cost savings demonstrated at lower prevalence., Keshavan et al. show that plasma Aβ1-42/1-40 and a plasma Aβ composite measured by liquid chromatography–mass spectrometry perform better than various blood biomarkers measured by single molecular array, and better than age, sex and APOE ε4, in screening for preclinical Alzheimer’s disease in the British 1946 birth cohort.

Alzheimer's disease has a preclinical stage when cerebral amyloid-? deposition occurs before symptoms emerge, and when amyloid-?-targeted therapies may have maximum benefits. Existing amyloid-? status measurement techniques, including amyloid PET and CSF testing, are difficult to deploy at scale, so blood biomarkers are increasingly considered for screening. We compared three different blood-based techniques-liquid chromatography-mass spectrometry measures of plasma amyloid-?, and single molecule array (Simoa) measures of plasma amyloid-? and phospho-tau181-to detect cortical 18F-florbetapir amyloid PET positivity (defined as a standardized uptake value ratio of >0.61 between a predefined cortical region of interest and eroded subcortical white matter) in dementia-free members of Insight 46, a substudy of the population-based British 1946 birth cohort. We used logistic regression models with blood biomarkers as predictors of amyloid PET status, with or without age, sex and APOE ?4 carrier status as covariates. We generated receiver operating characteristics curves and quantified areas under the curves to compare the concordance of the different blood tests with amyloid PET. We determined blood test cut-off points using Youden's index, then estimated numbers needed to screen to obtain 100 amyloid PET-positive individuals. Of the 502 individuals assessed, 441 dementia-free individuals with complete data were included; 82 (18.6%) were amyloid PET-positive. The area under the curve for amyloid PET status using a base model comprising age, sex and APOE ?4 carrier status was 0.695 (95% confidence interval: 0.628-0.762). The two best-performing Simoa plasma biomarkers were amyloid-?42/40 (0.620; 0.548-0.691) and phospho-tau181 (0.707; 0.646-0.768), but neither outperformed the base model. Mass spectrometry plasma measures performed significantly better than any other measure (amyloid-?1-42/1-40: 0.817; 0.770-0.864 and amyloid-? composite: 0.820; 0.775-0.866). At a cut-off point of 0.095, mass spectrometry measures of amyloid-?1-42/1-40 detected amyloid PET positivity with 86.6% sensitivity and 71.9% specificity. Without screening, to obtain 100 PET-positive individuals from a population with similar amyloid PET positivity prevalence to Insight 46, 543 PET scans would need to be performed. Screening using age, sex and APOE ?4 status would require 940 individuals, of whom 266 would proceed to scan. Using mass spectrometry amyloid-?1-42/1-40 alone would reduce these numbers to 623 individuals and 243 individuals, respectively. Across a theoretical range of amyloid PET positivity prevalence of 10-50%, mass spectrometry measures of amyloid-?1-42/1-40 would consistently reduce the numbers proceeding to scans, with greater cost savings demonstrated at lower prevalence.

Effect of serum and plasma on Aβ degradation. PBS spiked with (A) Aβ1-40 Arg13C15N and 5% serum and (B) Aβ1-40 Arg13C15N and 5% plasma. (PPTX 58 kb)

This report describes the production of ERM®-DA480/IFCC, ERM®-DA481/IFCC and ERM®-DA482/IFCC, which are human cerebrospinal fluid (CSF) materials certified for the mass concentration of amyloid β1-42 peptide (Aβ1-42). These materials were produced by the European Commission, Joint Research Centre (EC-JRC) in collaboration with the International Federation for Clinical Chemistry and Laboratory Medicine (IFCC) following ISO Guide 34:2009 and are certified in accordance with ISO Guide 35:2006. The starting material used to prepare ERM-DA480/IFCC, ERM-DA481/IFCC and ERM-DA482/IFCC was human CSF collected from normal pressure hydrocephalus patients by continuous lumbar drainage. After collection, the CSF was aliquoted and frozen at -80 °C. For the preparation of each certified reference material (CRM) a selected number of CSF donations were thawed, pooled, mixed, filled in microvials and stored at (-70 ± 10) °C immediately thereafter. Between unit-homogeneity was quantified and stability during dispatch and storage were assessed in accordance with ISO Guide 35:2006 [ ]. The material was characterised by an interlaboratory comparison of laboratories of demonstrated competence and adhering to ISO/IEC 17025 [ ]. Technically invalid results were removed but no outlier was eliminated on statistical grounds only. Uncertainties of the certified values were calculated in accordance with the Guide to the Expression of Uncertainty in Measurement (GUM) [ ] and include uncertainties related to possible inhomogeneity, instability and characterisation. The materials are intended for the calibration of methods, quality control and/or the assessment of method performance. As with any reference material, they can be used for establishing control charts or validation studies. The CRMs are available in microvials containing at least 0.5 mL of frozen liquid. The minimum amount of sample to be used is 15 µL., JRC.F.6-Reference Materials

Alzheimer’s disease (AD) is the most common neurodegenerative disease among the elderly and accounts for 60-80% of all cases of dementia. Currently, the diagnosis of AD is based on cognitive tests and mental state exams, but the peptide amyloid-beta (Aβ) in cerebrospinal fluid (CSF) is increasingly used in clinical trials and settings. As for most protein and peptide biomarkers, quantification is performed using antibody-based techniques such as enzyme-linked immunosorbent assay (ELISA). However these immunoassays suffer from high variability in measurements of Aβ concentrations, hampering its use as a diagnostic marker. The aim of this thesis was to develop an antibody independent method for absolute quantification of Aβ in human CSF, free of the specificity and reproducibility issues associated with antibody-based quantification. The method was based on solid-phase extraction (SPE) and liquid chromatography (LC)-tandem mass spectrometry (MS/MS). Stable isotope labeled Aβ peptides were used as internal standards, enabling absolute quantification. The method was first tested in a pilot study with CSF samples from AD patients and controls. As expected, the level of the 42 amino acid variant of Aβ (Aβ1-42) was decreased in AD CSF as compared to controls (p

MALDI-TOF MS CSF Aβ peptide patterns of a patient (A) in the acute phase of BM and (B) after antibiotic treatment. (PPTX 74 kb)

Effect of serum and plasma on Aβ degradation. PBS spiked with (A) Aβ1-40 Arg13C15N and 5% serum and (B) Aβ1-40 Arg13C15N and 5% plasma. (PPTX 58 kb)