Maria Bjerke

CSF and blood biomarkers for the diagnosis of Alzheimer's disease: a systematic review and meta-analysis

BACKGROUND Alzheimers disease biomarkers are important for early diagnosis in routine clinical practice and research. Three core CSF biomarkers for the diagnosis of Alzheimers disease (Aβ42, T-tau, and P-tau) have been assessed in numerous studies, and several other Alzheimers disease markers are emerging in the literature. However, there have been no comprehensive meta-analyses of their diagnostic performance. We systematically reviewed the literature for 15 biomarkers in both CSF and blood to assess which of these were most altered in Alzheimers disease. METHODS In this systematic review and meta-analysis, we screened PubMed and Web of Science for articles published between July 1, 1984, and June 30, 2014, about CSF and blood biomarkers reflecting neurodegeneration (T-tau, NFL, NSE, VLP-1, and HFABP), APP metabolism (Aβ42, Aβ40, Aβ38, sAPPα, and sAPPβ), tangle pathology (P-tau), blood-brain-barrier function (albumin ratio), and glial activation (YKL-40, MCP-1, and GFAP). Data were taken from cross-sectional cohort studies as well as from baseline measurements in longitudinal studies with clinical follow-up. Articles were excluded if they did not contain a cohort with Alzheimers disease and a control cohort, or a cohort with mild cognitive impairment due to Alzheimers disease and a stable mild cognitive impairment cohort. Data were extracted by ten authors and checked by two for accuracy. For quality assessment, modified QUADAS criteria were used. Biomarker performance was rated by random-effects meta-analysis based on the ratio between biomarker concentration in patients with Alzheimers disease and controls (fold change) or the ratio between biomarker concentration in those with mild cognitive impariment due to Alzheimers disease and those with stable mild cognitive impairment who had a follow-up time of at least 2 years and no further cognitive decline. FINDINGS Of 4521 records identified from PubMed and 624 from Web of Science, 231 articles comprising 15 699 patients with Alzheimers disease and 13 018 controls were included in this analysis. The core biomarkers differentiated Alzheimers disease from controls with good performance: CSF T-tau (average ratio 2·54, 95% CI 2·44-2·64, p<0·0001), P-tau (1·88, 1·79-1·97, p<0·0001), and Aβ42 (0·56, 0·55-0·58, p<0·0001). Differentiation between cohorts with mild cognitive impairment due to Alzheimers disease and those with stable mild cognitive impairment was also strong (average ratio 0·67 for CSF Aβ42, 1·72 for P-tau, and 1·76 for T-tau). Furthermore, CSF NFL (2·35, 1·90-2·91, p<0·0001) and plasma T-tau (1·95, 1·12-3·38, p=0·02) had large effect sizes when differentiating between controls and patients with Alzheimers disease, whereas those of CSF NSE, VLP-1, HFABP, and YKL-40 were moderate (average ratios 1·28-1·47). Other assessed biomarkers had only marginal effect sizes or did not differentiate between control and patient samples. INTERPRETATION The core CSF biomarkers of neurodegeneration (T-tau, P-tau, and Aβ42), CSF NFL, and plasma T-tau were strongly associated with Alzheimers disease and the core biomarkers were strongly associated with mild cognitive impairment due to Alzheimers disease. Emerging CSF biomarkers NSE, VLP-1, HFABP, and YKL-40 were moderately associated with Alzheimers disease, whereas plasma Aβ42 and Aβ40 were not. Due to their consistency, T-tau, P-tau, Aβ42, and NFL in CSF should be used in clinical practice and clinical research. FUNDING Swedish Research Council, Swedish State Support for Clinical Research, Alzheimers Association, Knut and Alice Wallenberg Foundation, Torsten Söderberg Foundation, Alzheimer Foundation (Sweden), European Research Council, and Biomedical Research Forum.

Confounding Factors Influencing Amyloid Beta Concentration in Cerebrospinal Fluid

Background. Patients afflicted with Alzheimers disease (AD) exhibit a decrease in the cerebrospinal fluid (CSF) concentration of the 42 amino acid form of β-amyloid (Aβ 42). However, a high discrepancy between different centers in measured Aβ 42 levels reduces the utility of this biomarker as a diagnostic tool and in monitoring the effect of disease modifying drugs. Preanalytical and analytical confounding factors were examined with respect to their effect on the measured Aβ 42 level. Methods. Aliquots of CSF samples were either treated differently prior to Aβ 42 measurement or analyzed using different commercially available xMAP or ELISA assays. Results. Confounding factors affecting CSF Aβ 42 levels were storage in different types of test tubes, dilution with detergent-containing buffer, plasma contamination, heat treatment, and the origin of the immunoassays used for quantification. Conclusion. In order to conduct multicenter studies, a standardized protocol to minimize preanalytical and analytical confounding factors is warranted.

Neurogranin in cerebrospinal fluid as a marker of synaptic degeneration in Alzheimer's disease

Synaptic pathology occurs early in Alzheimers disease (AD) development, and cerebrospinal fluid biomarkers for synaptic damage may be altered early in the disease process. In the present study we examined cerebrospinal fluid levels of the postsynaptic protein neurogranin in patients with mild cognitive impairment (MCI) or AD and controls. The low neurogranin level in cerebrospinal fluid required enrichment by immunoprecipitation prior to mass spectrometric identification and semi-quantitative immunoblot analysis. Relative quantification revealed a significant increase of neurogranin in the AD group compared with controls, while the MCI group was not statistically different from either controls or the AD group. The concentrations of the AD biomarkers T-tau, P-tau(181) and Aβ(42) were significantly changed in the control and MCI groups compared with the AD group, but no significant differences were found between the MCI group and controls for the three biomarkers. Nevertheless, a trend towards increasing levels of neurogranin, T-tau and P-tau(181) was found in cerebrospinal fluid from MCI patients compared with controls. The elevated neurogranin levels in the MCI and AD groups might reflect synaptic degeneration. These results together suggest that cerebrospinal fluid neurogranin might be valuable together with the established AD biomarkers in the early diagnosis of AD and warrants further studies to determine the diagnostic value of neurogranin.

Cerebrospinal Fluid Matrix Metalloproteinases and Tissue Inhibitor of Metalloproteinases in Combination with Subcortical and Cortical Biomarkers in Vascular Dementia and Alzheimer's Disease

Alzheimers disease (AD) and vascular dementia (VaD) are intertwined by mixed dementia (MD) harboring varying degrees of AD pathology in combination with cerebrovascular disease. The aim was to assess whether there is a difference in the cerebrospinal fluid (CSF) profile, of selected proteins, between patients with VaD and MD with subcortical vascular disease (SVD), AD, and healthy controls that could contribute in the separation of the groups. The study included 30 controls, 26 SVD patients (9 VaD and 17 MD) and 30 AD patients. The protein panel included total tau (T-tau), hyperphosphorylated tau 181 (P-tau(181)), amyloid β 1-42 (Aβ(1-42)), neurofilament light (NF-L), myelin basic protein (MBP), heart fatty acid binding protein (H-FABP), matrix metalloproteinases (MMP-1, -2, -3, -9, and -10), and tissue inhibitors of metalloproteinases (TIMP-1 and -2). Immunochemical methods were utilized for quantification of the proteins in CSF and data analysis was performed with a multivariate discriminant algorithm. The concentrations of MBP, TIMP-1, P-tau(181), NF-L, T-tau, MMP-9, Aβ(1-42), and MMP-2 contributed the most to the separation between SVD and AD, with a sensitivity of 89% and a specificity of 90% (AUC = 0.92). MBP and NF-L performed the best in discriminating SVD from controls, while T-tau and Aβ(1-42) contributed the most in segregating AD from controls. The CSF biomarkers reflecting AD pathology (T-tau, P-tau(181), and Aβ(1-42)), white matter lesions (NF-L and MBP) and matrix remodeling (MMP-9 and TIMP-1) perform well in differentiating between SVD and AD patients.

Reference measurement procedures for Alzheimer’s disease cerebrospinal fluid biomarkers: definitions and approaches with focus on amyloid β42

Cerebrospinal fluid (CSF) biomarkers for Alzheimers disease (AD) are increasingly used in clinical settings, research and drug trials. However, their broad-scale use on different technology platforms is hampered by the lack of standardization at the level of sample handling, determination of concentrations of analytes and the absence of well-defined performance criteria for in vitro diagnostic or companion diagnostic assays, which influences the apparent concentration of the analytes measured and the subsequent interpretation of the data. There is a need for harmonization of CSF AD biomarker assays that can reliably, across centers, quantitate CSF biomarkers with high analytical precision, selectivity and stability over long time periods. In this position paper, we discuss reference procedures for the measurement of CSF AD biomarkers, especially amyloid β42 and tau. We describe possible technical approaches, focusing on a selected reaction monitoring mass spectrometry assay as a candidate reference method for quantification of CSF amyloid β42.

Reduced expression of hsa-miR-27a-3p in CSF of patients with Alzheimer disease

Objective: We evaluated microRNAs (miRNAs) as potential biomarkers for Alzheimer disease (AD) by analyzing the expression level of miRNAs in CSF of patients with AD dementia and nonaffected control subjects. Methods: Using quantitative PCR, we profiled the expression level of 728 miRNAs in CSF of nonaffected control subjects and patients with clinically ascertained AD dementia, and we further compared the expression level of candidate miRNAs in 37 control subjects and 35 patients with AD dementia. Results: The level of hsa-miR-27a-3p in CSF is reduced in patients with dementia due to AD in 2 different cohorts of subjects (cohort 1: p = 0.008; cohort 2: p = 0.015; 2-tailed unpaired Welch t test). Moreover, low levels of hsa-miR-27a-3p were accompanied by high CSF tau levels and low CSF β-amyloid levels. Conclusions: Our pilot study highlights hsa-miR-27a-3p as a candidate biomarker for AD and provides the groundwork for further confirmation studies in larger cohorts and in other hospitals.

Nonlinear Association Between Cerebrospinal Fluid and Florbetapir F-18 β-Amyloid Measures Across the Spectrum of Alzheimer Disease

IMPORTANCE Cerebrospinal fluid (CSF) and positron emission tomographic (PET) amyloid biomarkers have been proposed for the detection of Alzheimer disease (AD) pathology in living patients and for the tracking of longitudinal changes, but the relation between biomarkers needs further study. OBJECTIVE To determine the association between CSF and PET amyloid biomarkers (cross-sectional and longitudinal measures) and compare the cutoffs for these measures. DESIGN, SETTING, AND PARTICIPANTS Longitudinal clinical cohort study from 2005 to 2014 including 820 participants with at least 1 florbetapir F-18 (hereafter referred to as simply florbetapir)-PET scan and at least 1 CSF β-amyloid 1-42 (Aβ1-42) sample obtained within 30 days of each other (501 participants had a second PET scan after 2 years, including 150 participants with CSF Aβ1-42 measurements). Data were obtained from the Alzheimers Disease Neuroimaging Initiative database. MAIN OUTCOMES AND MEASURES Four different PET scans processing pipelines from 2 different laboratories were compared. The PET cutoff values were established using a mixture-modeling approach, and different mathematical models were applied to define the association between CSF and PET amyloid measures. RESULTS The values of the CSF Aβ1-42 samples and florbetapir-PET scans showed a nonlinear association (R2 = 0.48-0.66), with the strongest association for values in the middle range. The presence of a larger dynamic range of florbetapir-PET scan values in the higher range compared with the CSF Aβ1-42 plateau explained the differences in correlation with cognition (R2 = 0.36 and R2 = 0.25, respectively). The APOE genotype significantly modified the association between both biomarkers. The PET cutoff values derived from an unsupervised classifier converged with previous PET cutoff values and the established CSF Aβ1-42 cutoff levels. There was no association between longitudinal Aβ1-42 levels and standardized uptake value ratios during follow-up. CONCLUSIONS AND RELEVANCE The association between both biomarkers is limited to a middle range of values, is modified by the APOE genotype, and is absent for longitudinal changes; 4 different approaches in 2 different platforms converge on similar pathological Aβ cutoff levels; and different pipelines to process PET scans showed correlated but not identical results. Our findings suggest that both biomarkers measure different aspects of AD Aβ pathology.

Multimodal Markers of Inflammation in the Subcortical Ischemic Vascular Disease Type of Vascular Cognitive Impairment

Vascular cognitive impairment (VCI) is a heterogeneous disease that is caused by a wide variety of vascular factors.1 Pathological studies have shown that both large- and small-vessel damage occurs in patients with VCI.2,3 Large-vessel disease leads to strokes with a stepwise course as a result of multiple infarctions that result in concomitant loss of intellect. Small-vessel disease has several forms: it may either produce lacunes mainly in the basal ganglia without white matter damage or extensive changes in the white matter with or without lacunes (Table I in the online-only Data Supplement). The term subcortical ischemic vascular disease is often used for both lacunar state and white matter disease, but there may be different pathophysiologies involved, particularly when there is cerebral hypoperfusion, which has a major effect on the vulnerable deep white matter.4 Binswanger disease (BD) was first described in 1894 in patients with arteriolosclerotic demyelination.5 Patients with BD have a symptom complex that includes vascular risk factors, cognitive impairment, small stroke-like events, hyperreflexia, and imbalance (Table II in the online-only Data Supplement).6,7 Neuropsychological testing shows executive dysfunction, whereas difficulties with memory and language occur more commonly in Alzheimer disease (AD); overlap occurs in neuropsychological testing in BD and AD, making patterns of cognitive dysfunction only suggestive of diagnoses. The Montreal Cognitive Assessment, which includes tests of executive function, when compared with minimental status examination is more often abnormal in patients with BD, making it a better screening test.8 Clinical features alone may be insufficient to diagnose BD, and a multimodal approach with biomarkers may be helpful. The biomarkers that have been suggested include neuropsychological testing, brain imaging, and cerebrospinal fluid (CSF) studies. Routine MRI shows white matter hyperintensities (WMHs) on fluid-attenuated inversion recovery imaging, which are nonspecific and are …

Increased Levels of Chitotriosidase and YKL-40 in Cerebrospinal Fluid from Patients with Alzheimer's Disease

Background: The cerebrospinal fluid (CSF) biomarkers total tau, abnormally phosphorylated tau and amyloid β 1-42 are strongly associated with Alzheimers disease (AD). Apart from the pathologic hallmarks that these biomarkers represent, other processes such as inflammation and microglial activation are present in the brains of patients with AD. New biomarkers related to these processes could be valuable for the diagnosis and follow-up of AD patients and for the evaluation of inflammation-related pathologies. Aim: The aim of this study was to evaluate the association of inflammatory CSF biomarkers with AD. Methods: Twenty-five AD patients and 25 controls who had a pathological and normal CSF profile of the core AD biomarkers, respectively, were included in this study. CSF levels of chitotriosidase, YKL-40 (also known as chitinase-3-like protein 1) and monocyte chemoattractant protein-1 (MCP-1) were quantified and the levels compared between the groups. Results: AD patients had increased CSF levels of chitotriosidase and YKL-40 (both approximately twice higher than in controls), while the levels of MCP-1 were similar in the AD and control groups. Conclusion: The results indicate that chitotriosidase and YKL-40 may be helpful for the evaluation of cerebral inflammatory activity in AD patients.

Soluble amyloid precursor protein alpha and beta in CSF in Alzheimer's disease

OBJECTIVE Cerebral accumulation of amyloid β (Aβ) is a pathological hallmark of Alzheimers disease (AD). Proteolytic processing of amyloid precursor protein (APP) by α- or β-secretase results in two soluble metabolites, sAPPα and sAPPβ, respectively. However, previous data have shown that both α- and β-secretase have multiple cleavage sites. The aim of this study was to characterize the C-termini of sAPPα and sAPPβ in cerebrospinal fluid (CSF) by mass spectrometry (MS) and to evaluate whether different combinations of these fragments better separate between AD patients and controls by comparing two different sAPP immunoassays. METHODS Using immunoprecipitation and high resolution MS, the APP species present in CSF were investigated. CSF levels of sAPPα and sAPPβ from patients with AD (n=43) and from non-demented controls (n=44) were measured using AlphaLISA and MSD immunoassays that employ different antibodies for C-terminal recognition of sAPPα. RESULTS Four different C-terminal forms of sAPP were identified, sAPPβ-M671, sAPPβ-Y681, sAPPα-Q686, and sAPPα-K687 (APP770 numbering). Neither immunoassay for the sAPP species could separate the two patient groups. The correlation (R(2)) between the two immunoassays was 0.41 for sAPPα and 0.45 for sAPPβ. CONCLUSION Using high resolution MS, we show here for the first time that sAPPα in CSF ends at Q686 and K687. The findings also support the conclusion from several previous studies that sAPPα and sAPPβ levels are unaltered in AD.