Mass-Spectrometry-Based Method To Quantify in Parallel Tau and Amyloid β 1–42 in CSF for the Diagnosis of Alzheimer’s Disease

Abstract

Alzheimer’s disease (AD), the most common form of dementia, afflicts about 50 million people worldwide. Currently, AD diagnosis is primarily based on psychological evaluation and can only be confirmed post-mortem. Reliable and objective biomarkers for prognosis and diagnosis have been sought for several years. Together, tau and amyloid β 1–42 (Aβ42) in cerebrospinal fluid (CSF) have been shown to provide good diagnostic sensitivity and specificity. Additionally, phosphorylated forms of tau, such as tau pS181, have also shown promising results. However, the measurement of such markers currently relies on antibody-based immunoassays that have shown variability, leading to discrepant results across laboratories. To date, mass spectrometry methods developed to evaluate CSF tau and Aβ42 are not compatible. We present in this article the development of a mass spectrometry-based method of quantification for CSF tau and Aβ42 in parallel. The absolute concentration of tau and Aβ42 we measured are on average 50 ng/mL (7–130 ng/mL) and 7.1 ng/mL (3–13 ng/mL), respectively. Analyses of CSF tau and Aβ42, in a cohort of patients with AD, mild cognitive impairment and healthy controls (30 subjects), provide significant group differences evaluated with ROC curves (AUC(control-AD) and AUC(Control-MCI)=1, AUC(MCI-AD)=0.76), with at least equivalent diagnostic utility to immunoassay measurements in the same sample set. Finally, a significant and negative correlation was found between the tau and Aβ peptide ratio and the disease severity.

Fluid‐based proteomics targeted on pathophysiological processes and pathologies in neurodegenerative diseases

“…Parallel LC–MS measurement of CSF tau and Aβ1–42 was recently reported, showing good sensitivity and specificity for separating AD from controls (Pottiez et al . ). Because of the relatively low abundance of tau in CSF, detection sensitivity presents a major hurdle for the detection of protein modifications of low stoichiometry such as phosphorylation, and it has been difficult to verify the presence of many of the post‐translational tau modifications existing in the brain.…”

Mass spectrometry is a multifaceted weapon to be used in the battle against Alzheimer's disease: Amyloid beta peptides and beyond

“…must be taken into account in order to obtain reliable quantitative data . Based on current data, as stated above, the use of CSF Aβ 1‐42 alone or in combination with total tau and phosphorylated tau protein seems to be one of the very few biochemical analysis capable to discriminate AD compared with healthy controls of the same age (see also above), with a sensitivity and a specificity of approximately 85‐90% …”

“…For example, although not properly highlighted in this review yet, protein accumulation in the form of neurofibrillary tangles of hyper‐phosphorylated tau protein is also an important hallmark of the disease. Indeed, hyper‐phosphorylated tau protein accumulation has been investigated with MS almost to the same level as Aβ accumulation . In all cases, it is very difficult to correlate the observed specific protein dyshomeostasis with severity of the disease and/or to draw conclusions about possible biomolecular mechanisms responsible for the development of the disease.…”

“…29,30 Based on current data, as stated above, the use of CSF Aβ 1-42 alone or in combination with total tau and phosphorylated tau protein seems to be one of the very few biochemical analysis capable to discriminate AD compared with healthy controls of the same age (see also above), with a sensitivity and a specificity of approximately 85-90%. [31][32][33] Although, in principle, it is possible to profile with high resolution differential MS complex mixtures of the proteins in CSF simultaneously and provide quantitative measurements without the need to pre-specify the analyte, 34,35 the most common experimental procedure to quantitate Aβ peptides in CSF requires a sample-preparation step. The latter is performed to extract and concentrate the peptides, which are otherwise difficult to detect because of their wide dynamic range and low abundance.…”

Mass spectrometry: A platform for biomarker discovery and validation for Alzheimer's and Parkinson's diseases

“…We found equivalent diagnostic utility to immunoassay measurements within the same sample set, with particular strength in the ratio of Aβ 42 to global Aβ expression (Pottiez et al . ). Together, these studies illustrate the capacity of SRM to apply both relative and absolute quantification of peptide targets for verification of AD candidate biomarkers.…”