Identification and Validation of Novel Cerebrospinal Fluid Biomarkers for Staging Early Alzheimer's Disease

Abstract

BackgroundIdeally, disease modifying therapies for Alzheimer disease (AD) will be applied during the ‘preclinical’ stage (pathology present with cognition intact) before severe neuronal damage occurs, or upon recognizing very mild cognitive impairment. Developing and judiciously administering such therapies will require biomarker panels to identify early AD pathology, classify disease stage, monitor pathological progression, and predict cognitive decline. To discover such biomarkers, we measured AD-associated changes in the cerebrospinal fluid (CSF) proteome.Methods and FindingsCSF samples from individuals with mild AD (Clinical Dementia Rating [CDR] 1) (n = 24) and cognitively normal controls (CDR 0) (n = 24) were subjected to two-dimensional difference-in-gel electrophoresis. Within 119 differentially-abundant gel features, mass spectrometry (LC-MS/MS) identified 47 proteins. For validation, eleven proteins were re-evaluated by enzyme-linked immunosorbent assays (ELISA). Six of these assays (NrCAM, YKL-40, chromogranin A, carnosinase I, transthyretin, cystatin C) distinguished CDR 1 and CDR 0 groups and were subsequently applied (with tau, p-tau181 and Aβ42 ELISAs) to a larger independent cohort (n = 292) that included individuals with very mild dementia (CDR 0.5). Receiver-operating characteristic curve analyses using stepwise logistic regression yielded optimal biomarker combinations to distinguish CDR 0 from CDR>0 (tau, YKL-40, NrCAM) and CDR 1 from CDR<1 (tau, chromogranin A, carnosinase I) with areas under the curve of 0.90 (0.85–0.94 95% confidence interval [CI]) and 0.88 (0.81–0.94 CI), respectively.ConclusionsFour novel CSF biomarkers for AD (NrCAM, YKL-40, chromogranin A, carnosinase I) can improve the diagnostic accuracy of Aβ42 and tau. Together, these six markers describe six clinicopathological stages from cognitive normalcy to mild dementia, including stages defined by increased risk of cognitive decline. Such a panel might improve clinical trial efficiency by guiding subject enrollment and monitoring disease progression. Further studies will be required to validate this panel and evaluate its potential for distinguishing AD from other dementing conditions.

P1–206: Quantitative label‐free proteomics for discovery of biomarkers in cerebrospinal fluid: Assessment of technical and inter‐individual variation

“…10). It is also encouraging that many of the 81 proteins have already been reported as potential biomarkers for AD by multiple independent groups [2,20,28,31,36,[58][59][60][61]. Indeed, because none of these previously reported candidate biomarkers have been vetted sufficiently to be applied in clinical trials, they will have to be studied further: individually and in combination; in larger cohorts and in different diseases.…”

“…Indeed, even proteins with relatively broad ranges of concentration among cognitively normal individuals (e.g. chromogranin A, NrCAM) can show potential for diagnosing AD and control samples as part of a biomarker panel [20]. Nevertheless, most proteomic fold-changes reported to date for CSF biomarkers have been rather modest (,1.5 fold) and would show far greater biomarker utility in a background of far lower inter-individual variability.…”

“…Imaging and fluid biomarker studies have also shown potential to predict cognitive decline by measuring amyloid deposition [5], regional volumetric and metabolic changes in the brain [15][16][17], or specific changes in the CSF proteome (including concentrations of tau, YKL-40, VILIP-1, and calbindin, each in association with Ab42) [2,3,18,19]. CSF analysis may even allow classification of disease stage [20] and monitoring of acute changes in response to disease modifying therapies, as illustrated recently with gamma-secretase inhibitors [21]. In spite of these advances, however, these techniques must still be improved.…”

“…Indeed, many increasingly more powerful yet complementary proteomics technologies have been leveled at CSF biomarker discovery in the past decade, including: variations of 2D gel electrophoresis [2,20,[22][23][24][25][26][27][28][29][30]; SELDI-TOF-MS [31][32][33][34]; offline LC -MALDI-TOF [35]; and LC-MS/MS with either isotopecoded affinity tags (ICAT) [36], Tandem Mass Tags [37] or iTRAQ (isobaric tag for relative and absolute quantification) [38,39]. These techniques have all been used successfully to identify candidate biomarkers because they provide accurate relative quantitative information between or among samples.…”

Cerebrospinal fluid biomarkers of Alzheimer’s disease

“…precursor, Aβ, apolipoprotein E precursor, serum albumin precursor, keratin type I cytoskeletal 9, and tetranectin) was able to discriminate AD patients from controls with a median accuracy of 95% (sensitivity 85% and specificity 97%) [90] . [91] . that augment the core CSF biomarkers (Aβ42, t-tau, and p-tau) for distinguishing very mildly/mildly demented from cognitively normal individuals [92] .…”