Cerebrospinal fluid and positron emission tomography biomarkers accurately predict an underlying Alzheimer's disease (AD) pathology; however, they represent either invasive or expensive diagnostic tools. Therefore, a blood-based biomarker like plasma amyloid beta (Aβ) that could correlate with the underlying AD pathology and serve as a prognostic biomarker or an AD screening strategy is urgently needed as a cost-effective and non-invasive diagnostic tool. In this paper we review the demographic, biologic, genetic and technical aspects that affect plasma Aβ levels. Findings of cross-sectional and longitudinal studies of plasma Aβ, including autosomal dominant AD cases, sporadic AD cases, Down syndrome cases and population studies, are also discussed. Finally, we review the association between cerebrovascular disease and Aβ plasma levels and the responses observed in clinical trials. Based on our review of the current literature on plasma Aβ, we conclude that further clinical research and assay development are needed before measures of plasma Aβ can be interpreted so they can be applied as trait, risk or state biomarkers for AD.
Increasing evidence supports a connection between cancer and metabolism and emphasizes the need to understand how tumors respond to the metabolic microenvironment and how tumor cell metabolism is regulated. The insulin receptor (IR) and its close family member the insulin-like growth factor-1 receptor (IGF-1R) mediate the cellular response to insulin in normal cells and their function is tightly regulated to maintain metabolic homeostasis. These receptors are also expressed on tumor cells and their expression correlates with tumor progression and poor prognosis. Understanding how the IR/IGF-1R pathway functions in tumors is increasing in importance as the efficacy of drugs that target metabolic pathways, such as metformin, are investigated in prospective clinical trials. This review will focus on key signaling intermediates of the IR and IGF-1R, the Insulin Receptor Substrate (IRS) proteins, with an emphasis on IRS-2, and discuss how these adaptor proteins play a pivotal role at the intersection of metabolism and cancer.
IRS proteins; insulin receptor; IGF-1 receptor; metabolism; cancer; metformin
The interassay variability and inconsistency of plasma β-amyloid (Aβ) measurements among centers are major factors precluding the interpretation of results and a substantial obstacle in the meta-analysis across studies of this biomarker. The goal of this investigation was to address these problems by improving the performance of the bioanalytical method.
We used the Luminex immunoassay platform with a multiplex microsphere-based reagent kit from Innogenetics. A robotic pipetting system was used to perform crucial steps of the procedure. The performance of this method was evaluated using two kit control samples and two quality control plasma samples from volunteer donors, and by retesting previously assayed patient samples in each run. This setup was applied to process 2454 patient plasma samples from the Alzheimer's Disease Neuroimaging Initiative study biofluid repository. We have additionally evaluated the correlations between our results and cerebrospinal fluid (CSF) biomarker data using mixed-effects modeling.
The average precision values of the kit controls were 8.3% for Aβ1-40 and 4.0% for Aβ1-42, whereas the values for the plasma quality controls were 6.4% for Aβ1-40 and 4.8% for Aβ1-42. From the test–retest evaluation, the average precision was 7.2% for Aβ1-40 and 4.5% for Aβ1-42. The range of final plasma results for Alzheimer's Disease Neuroimaging Initiative patients was 13 to 372 pg/mL (median: 164 pg/mL) for Aβ1-40 and 3.5 to 103 pg/mL (median: 39.3 pg/mL) for Aβ1-42. We found that sample collection parameters (blood volume and time to freeze) have a small, but significant, influence on the result. No significant difference was found between plasma Aβ levels for patients with Alzheimer's disease and healthy control subjects. We have determined multiple significant correlations of plasma Aβ1-42 levels with CSF biomarkers. The relatively strongest, although modest, correlation was found between plasma Aβ1-42 levels and CSF p-tau181/Aβ1-42 ratio in patients with mild cognitive impairment. Plasma Aβ1-40 correlations with CSF biomarkers were weaker and diminished completely when we used longitudinal data. No significant correlations were found for the plasma Aβ1-42/Aβ1-40 ratio.
The precision of our robotized method represents a substantial improvement over results reported in the literature. Multiple significant correlations between plasma and CSF biomarkers were found. Although these correlations are not strong enough to support the use of plasma Aβ measurement as a diagnostic screening test, plasma Aβ1-42 levels are well suited for use as a pharmacodynamic marker.
β-amyloid; Longitudinal; Plasma; xMAP immunoassay; ADNI study subjects; Robotic pipetting
Weight changes are common in aging and Alzheimer’s disease (AD) and post-mortem findings suggested a relation between lower body mass index (BMI) and increased AD brain pathology. In the current multicenter study, we tested whether lower BMI is associated with higher core AD brain pathology as assessed by cerebrospinal fluid (CSF) based biological markers of AD in 751 living subjects: 308 patients with AD, 296 subjects with amnestic mild cognitive impairment (MCI), and 147 elderly healthy controls (HC). Based upon a priori cutoff values on CSF concentration of total tau and beta-amyloid (Aβ1-42), subjects were binarized into a group with abnormal CSF biomarker signature (CSF+) and those without (CSF−). Results showed that BMI was significantly lower in the CSF+ when compared to the CSF− group (F = 27.7, df = 746, p < 0.001). There was no interaction between CSF signature and diagnosis or ApoE genotype. In conclusion, lower BMI is indicative of AD pathology as assessed with CSF-based biomarkers in demented and non-demented elderly subjects.
Alzheimer’s disease; body mass index; cerebrospinal fluid; tau protein; Aβ1-42
To utilize values of cerebrospinal fluid (CSF) tau and ß-amyloid obtained from two different analytical immunoassays to differentiate Alzheimer’s disease (AD) from frontotemporal lobar degeneration (FTLD).
CSF values of total tau (t-tau) and ß-amyloid (Aß1-42) obtained using the INNOTEST® ELISA were transformed using a linear regression model to equivalent values obtained using the INNO-BIA AlzBio3™ (xMAP Luminex) assay. Cutoff values obtained from the xMAP assay were developed in a series of autopsy-confirmed cases and cross-validated in another series of autopsy-confirmed samples using transformed ELISA values to assess sensitivity and specificity for differentiating AD from FTLD.
Tertiary memory disorders clinics and neuropathological and biomarker core centers.
75 samples from patients with CSF data obtained from both assays were used for transformation of ELISA values. 40 autopsy-confirmed cases (30 AD, 10 FTLD) were used to establish diagnostic cutoff values, and then cross-validated in a second sample set of 21 autopsy-confirmed cases (11 AD, 10 FTLD) with transformed ELISA values.
Main outcome measure
Diagnostic accuracy using transformed biomarker values.
Data obtained from both assays were highly correlated. The t-tau:Aß1-42 ratio had the highest correlation between measures (r=0.928, p<0.001) and high reliability of transformation (ICC=0.89). A cutoff of 0.34 for the t-tau:Aß1-42 ratio had 90% and 100% sensitivity and 96.7% and 91% specificity to differentiate FTLD cases in the validation and cross-validation samples, respectively.
Values from two analytical platforms can be transformed into equivalent units, which can distinguish AD from FTLD more accurately than the clinical diagnosis.
There is epidemiological evidence that cardiovascular risk factors (CVRF) also are risk factors for Alzheimer’s disease, but there is limited information on this from neuro-pathological studies, and even less from in vivo studies. Therefore, we examined the relationship between CVRF and amyloid-β (Aβ) brain burden measured by Pittsburgh Compound B-positron emission tomography (PiB-PET) studies in the Alzheimer’s Disease Neuroimaging Initiative.
Ninety-nine subjects from the Alzheimer’s Disease Neuroimaging Initiative cohort who had a PiB-PET study measure, apolipoprotein E genotyping data, and information available on CVRF (body mass index [BMI], systolic blood pressure, diastolic blood pressure [DBP1 and cholesterol and fasting glucose test results) were included. Eighty-one subjects also had plasma cortisol C-reactive protein, and superoxide dismutase 1 measurements. Stepwise regression models were used to assess the relation between the CVRF and the composite PiB-PET score.
The first model included the following as baseline variables: age, clinical diagnosis, number of apolipoprotein ε4 alleles, BMI (P = .023), and DBP (P = .012). BMI showed an inverse relation with PiB-PET score, and DBP had a positive relation with PiB-PET score. In the second adjusted model, cortisol plasma levels were also associated with PiB-PET score (P = .004). Systolic blood pressure, cholesterol, or impaired fasting glucose were not found to be associated with PiB-PET values.
In this cross-sectional study, we found an association between Aβ brain burden measured in vivo and DBP and cortisol, indicating a possible link between these CVRF and Aβ burden measured by PiB-PET. These findings highlight the utility of biomarkers to explore potential pathways linking diverse Alzheimer’s disease risk factors.
Alzheimer disease; Vascular risk factors; PiB; Amyloid-β; Cortisol; Blood pressure; Body mass index
The best-studied biomarkers of Alzheimer’s disease (AD) are the pathologically linked CSF proteins β-amyloid 42 (Aβ1–42), total tau (t-tau), and tau phosphorylated on amino acid 181 (p-tau181). Many laboratories measure these proteins using Enzyme-Linked ImmunoSorbent Assay (ELISA). Multiplex xMAP Luminex is a semi-automated assay platform with reduced intra-sample variance, which could facilitate its use in CLIA-approved clinical laboratories. CSF concentrations of these three biomarkers reported using xMAP technology differ from those measured by the most commonly used ELISA, confounding attempts to compare results. To develop a model for converting between xMAP and ELISA levels of the three biomarkers, we analyzed CSF samples from 140 subjects (59 AD, 30 controls, 34 with mild cognitive impairment (MCI), and 17 with Parkinson Disease, including 1 with dementia). Log-transformation of ELISA and xMAP levels made the variance constant in all three biomarkers and improved the linear regression: t-tau concentrations were highly correlated (r=0.94); p-tau181 concentrations by ELISA can be better predicted using both the t-tau and p-tau181 xMAP values (r=0.96) as compared to p-tau181 concentrations alone (r=0.82); correlation of Aβ1–42 concentrations was relatively weaker but still high (r=0.77). Among all six protein/assay combinations, xMAP Aβ1–42 had the best accuracy for diagnostic classification (88%) between AD and control subjects. In conclusion, our study demonstrates that multiplex xMAP is an appropriate assay platform providing results that can be correlated with research-based ELISA values, facilitating the incorporation of this diagnostic biomarker into routine clinical practice.
Enzyme-Linked Immunosorbent Assay (ELISA); Cerebrospinal fluid (CSF); Alzheimer’s Disease
Insulin Receptor Substrate-2 (IRS-2) belongs to the IRS family of adaptor proteins that function as signaling intermediates for growth factor, cytokine and integrin receptors, many of which have been implicated in cancer. Although the IRS proteins share significant homology, distinct functions have been attributed to each family member in both normal and tumor cells. In cancer, IRS-2 is positively associated with aggressive tumor behavior. In the current study, we demonstrate that IRS-2 expression, but not IRS-1 expression, is positively regulated by hypoxia, which selects for tumor cells with increased metastatic potential. We identify IRS-2 as a novel hypoxia responsive gene and establish that IRS-2 gene transcription increases in a HIF-dependent manner in hypoxic environments. IRS-2 is active to mediate IGF-1-dependent signals in hypoxia, and enhanced activation of Akt in hypoxia is dependent upon IRS-2 expression. Functionally, the elevated expression of IRS-2 facilitates breast carcinoma cell survival and invasion in hypoxia. Collectively, our results reveal a novel mechanism by which IRS-2 contributes to the aggressive behavior of hypoxic tumor cells.
IRS-2; hypoxia; HIF; survival; invasion; breast cancer
The characterization of cells with tumour initiating potential is significant for advancing our understanding of cancer and improving therapy. Aggressive, triple-negative breast cancers (TNBCs) are enriched for tumour-initiating cells (TICs). We investigated that hypothesis that VEGF receptors expressed on TNBC cells mediate autocrine signalling that contributes to tumour initiation. We discovered the VEGF receptor neuropilin-2 (NRP2) is expressed preferentially on TICs, involved in the genesis of TNBCs and necessary for tumour initiation. The mechanism by which NRP2 signalling promotes tumour initiation involves stimulation of the α6β1 integrin, focal adhesion kinase-mediated activation of Ras/MEK signalling and consequent expression of the Hedgehog effector GLI1. GLI1 also induces BMI-1, a key stem cell factor, and it enhances NRP2 expression and the function of α6β1, establishing an autocrine loop. NRP2 can be targeted in vivo to retard tumour initiation. These findings reveal a novel autocrine pathway involving VEGF/NRP2, α6β1 and GLI1 that contributes to the initiation of TNBC. They also support the feasibility of NRP2-based therapy for the treatment of TNBC that targets and impedes the function of TICs.
breast cancer; GLI1; integrin; neuropilin-2; stem cells
Expression of the α6β4 integrin is associated with poor patient prognosis and reduced survival in a variety of human cancers. In recent years, a limited number of in vivo studies have examined the contribution of this integrin receptor to cancer progression and they have revealed that the α6β4 integrin plays a multifaceted role in regulating tumor development and progression. In the current study, we investigated the mechanism by which one tyrosine residue in the β4 subunit cytoplasmic domain, Y1494, contributes to the tumor-promoting functions of the α6β4 integrin in vivo. We demonstrate that Y1494 participates in the stimulation of diverse signaling pathways that promote α6β4-dependent tumor growth and invasion. Mutation of Y1494 inhibits the ability of the α6β4 integrin to support anchorage independent growth in vitro and tumor development and angiogenesis in vivo, a result that mimics the loss of total expression of the β4 subunit. Our results support the hypothesis that Y1494 regulates α6β4-dependent anchorage independent growth through activation of the ERK1/2 signaling pathway, and invasion through the combined activation of PI3K and Src. Collectively, our results identify Y1494 as a major regulatory site for signaling from the α6β4 integrin to promote tumor development and progression.
beta4 integrin; tumor growth; signal transduction; invasion; angiogenesis
There is a pressing need to develop effective prevention and disease-modifying treatments for Alzheimer’s disease (AD), a dreaded affliction whose incidence increases almost logarithmically with age starting at about 65 years. A key need in the field of AD research is the validation of imaging and biochemical biomarkers. Biomarker tests that are shown to reliably predict the disease before it is clinically expressed would permit testing of new therapeutics at the earliest time point possible in order to give the best chance for delaying the onset of dementia in these patients. In this review the current state of AD biochemical biomarker research is discussed. A new set of guidelines for the diagnosis of AD in the research setting places emphasis on the inclusion of selected imaging and biochemical biomarkers, in addition to neuropsychological behavioral testing. Importantly, the revised guidelines were developed to identify patients at the earliest stages prior to full-blown dementia as well as patients with the full spectrum of the disease. The Alzheimer’s Disease Neuroimaging Initiative is a multicenter consortium study that includes as one of its primary goals the development of standardized neuroimaging and biochemical biomarker methods for AD clinical trials, as well as using these to measure changes over time in mildly cognitively impaired patients who convert to AD as compared to the natural variability of these in control subjects and their further change over time in AD patients. Validation of the biomarker results by correlation analyses with neuropsychological and neurobehavioral test data is one of the primary outcomes of this study. This validation data will hopefully provide biomarker test performance needed for effective measurement of the efficacy of new treatment and prevention therapeutic agents.
Alzheimer’s disease; Alzheimer’s Disease Neuroimaging Initiative; Biomarkers
Objective: Our goal was to evaluate the association of APOE with amyloid deposition, cerebrospinal fluid levels (CSF) of Aβ, tau, and p-tau, brain atrophy, cognition and cognitive complaints in E-MCI patients and cognitively healthy older adults (HC) in the ADNI-2 cohort.
Methods: Two-hundred and nine E-MCI and 123 HC participants from the ADNI-2 cohort were included. We evaluated the impact of diagnostic status (E-MCI vs. HC) and APOE ε4 status (ε4 positive vs. ε4 negative) on cortical amyloid deposition (AV-45/Florbetapir SUVR PET scans), brain atrophy (structural MRI scans processed using voxel-based morphometry and Freesurfer version 5.1), CSF levels of Aβ, tau, and p-tau, and cognitive performance and complaints.
Results: E-MCI participants showed significantly impaired cognition, higher levels of cognitive complaints, greater levels of tau and p-tau, and subcortical and cortical atrophy relative to HC participants (p < 0.05). Cortical amyloid deposition and CSF levels of Aβ were significantly associated with APOE ε4 status but not E-MCI diagnosis, with ε4 positive participants showing more amyloid deposition and lower levels of CSF Aβ than ε4 negative participants. Other effects of APOE ε4 status on cognition and CSF tau levels were also observed.
APOE ε4 status is associated with amyloid accumulation and lower CSF Aβ, as well as increased CSF tau levels in early prodromal stages of AD (E-MCI) and HC. Alternatively, neurodegeneration, cognitive impairment, and increased complaints are primarily associated with a diagnosis of E-MCI. These findings underscore the importance of considering APOE genotype when evaluating biomarkers in early stages of disease.
apolipoprotein E (APOE); early mild cognitive impairment (E-MCI); Florbetapir/AV-45/Amyvid; positron emission tomography (PET); magnetic resonance imaging (MRI); cerebrospinal fluid (CSF); Alzheimer's disease neuroimaging initiative (ADNI)
Neuronal and glial changes associated with tau, TAR DNA binding protein of ~43 kD (TDP-43), and fused in sarcoma (FUS) together constitute the pathologic spectrum of frontotemporal lobar degeneration (FTLD). Most patients with FTLD present with prominent behavior or language changes, sometimes accompanied by extrapyramidal symptoms or motor neuron disease. Identification of FTLD patients with mutations in genes for tau, TDP-43, and FUS lends strong support for their pathogenic roles in FTLD, and elucidation of their dysfunction will pave the way for development of substrate specific therapy. However, there remains no reliable biomarker for early detection of FTLD or prediction of underlying FTLD pathologic change. Clinical syndromes usually reflects the earliest affected brain regions where atrophy can be visualized on structural MRI, but neither clinical nor structural imaging-based biomarkers has been accurately correlated with underlying pathology on the individual patient level. Biochemical markers in the cerebrospinal fluid (CSF) have also been investigated in FTLD and related disorders, including amyotrophic lateral sclerosis (ALS) and progressive supranuclear palsy (PSP). However, their accuracy and pathologic significance need to be confirmed in future multi-center studies. Here we review the progress made in FTLD biomarkers, including clinical phenotype/feature characterization, neuropsychological analysis, CSF and plasma analytes, and patterns of brain atrophy and network dysfunction detectable on brain imaging. Given the pathologic overlap of FTLD with ALS and PSP, collaboration with specialists in those fields will be essential in the translation of promising FTLD biomarkers into clinical practice.
Biomarker; diagnosis; frontotemporal dementia; tau; tauopathy; TDP-43
MRI patterns were examined together with cerebrospinal fluid (CSF) biomarkers in serial scans of ADNI participants with mild cognitive impairment (MCI). The SPARE-AD score, summarizing brain atrophy patterns, was tested as predictor of short-term conversion to AD. MCI individuals that converted to AD (MCI-C) had mostly positive baseline SPARE-AD and atrophy in temporal lobe grey (GM) and white (WM) matter, posterior cingulate/precuneous, insula. MCI-C had mostly AD-like baseline CSF biomarkers. MCI non-converters (MCI-NC) had mixed baseline SPARE-AD and CSF values, suggesting that some MCI-NC subjects may later convert. Those MCI-NC with most negative baseline SPARE-AD scores (normal brain structure) had significantly higher baseline MMSE scores (28.67) than others, and relatively low annual rate of MMSE decrease (−0.25). MCI-NC with mid-level baseline SPARE-AD displayed faster annual rates of SPARE-AD increase (indicating progressing atrophy). SPARE-AD and CSF combination improved prediction over individual values. In summary, both SPARE-AD and CSF biomarkers showed high baseline sensitivity, however, many MCI-NC had abnormal baseline SPARE-AD and CSF biomarkers. Longer follow-up will elucidate the specificity of baseline measurements.
Alzheimer’s disease; early detection; mild cognitive impairment; MCI; pattern classification; imaging biomarkers; CSF biomarkers; SPARE-AD
The prevalence of post-operative cognitive disturbance, coupled with growing in vitro, cell and animal evidence suggesting anesthetic effects on neurodegeneration, calls for further study of the interaction between surgical care and Alzheimer neuropathology. Here, we study human cerebral spinal fluid (CSF) biomarkers perioperatively.
Eleven patients undergoing idiopathic nasal CSF leak correction joined this Institutional Review Board approved study. Lumbar subarachnoid catheters were placed prior to the procedure. Anesthesia was total intravenous anesthesia (propofol/remifentanil) or inhalational (sevoflurane), depending on provider choice. CSF samples were taken after catheter placement (base), at procedure end (0h), and then at 6, 24 and 48h. CSF was analyzed using xMAP Luminex immunoassay (Luminex, Austin, TX).
Patients: 53±6 yrs old; 8 women; 4 received intravenous anesthesia, 6 sevoflurane, 1 mixed. Procedures lasted 6.4 ± 2h. Mean CSF amyloid-β1-42 remained unchanged, but total-tau and phosphorylated-tau181P increased progressively until at least 48h. Total-tau, phosphorylated-tau or amyloid-β1-42 levels were not different between anesthetic groups. CSF interleukin-10, S100B and tumor necrosis factor alpha were increased similarly in both anesthetic groups at 24h, but interleukin-6 was increased more in the inhalational group.
These data indicate a robust neuroinflammatory response, including not only the usual markers (interleukin-6, tumor necrosis factor α, interleukin-10), but also S100B and tau, markers of injury. The total-tau/amyloid-β1-42 ratio increased in a pattern consistent with Alzheimer disease, largely due to an increase in total-tau rather than a decline in amyloid-β1-42. The differences in CSF interleukin-6 levels, suggest that anesthetic management may make a difference in neuroinflammatory response.
To empirically assess the concept that Alzheimer’s disease (AD) biomarkers significantly depart from normality in a temporally ordered manner.
Multi-site, referral centers
We studied 401 elderly cognitively normal (CN), Mild Cognitive Impairment (MCI) and AD dementia subjects from the Alzheimer’s Disease Neuroimaging Initiative. We compared the proportions of three AD biomarkers – CSF Aβ42, CSF total tau (t-tau), and hippocampal volume adjusted by intra-cranial volume (HVa) - that were abnormal as cognitive impairment worsened. Cut-points demarcating normal vs. abnormal for each biomarker were established by maximizing diagnostic accuracy in independent autopsy samples.
Main Outcome measures
Within each clinical group in the entire sample (n=401) CSF Aβ42 was abnormal more often than t-tau or HVa. Among the 298 subjects with both baseline and 12 month data, the proportion of subjects with abnormal Aβ42 did not change from baseline to 12 months in any group. The proportion of subjects with abnormal t-tau increased from baseline to 12 months in CN (p=0.05) but not in MCI or dementia. In 209 subjects with abnormal CSF AB42 at baseline, the percent abnormal HVa, but not t-tau, increased from baseline to 12 months in MCI.
Reduction in CSF Aβ42 denotes a pathophysiological process that significantly departs from normality (i.e., becomes dynamic) early, while t-tau and HVa are biomarkers of downstream pathophysiological processes. T-tau becomes dynamic before HVa, but HVa is more dynamic in the clinically symptomatic MCI and dementia phases of the disease than t-tau.
Alzheimer’s disease biomarkers; Magnetic Resonance Imaging; CSF tau; CSF Abeta; Alzheimer’s disease staging
The current study tested the accuracy of primary MRI and cerebrospinal fluid (CSF) biomarker candidates and neuropsychological tests for predicting the conversion from mild cognitive impairment (MCI) to Alzheimer's disease (AD) dementia. In a cross-validation paradigm, predictor models were estimated in the training set of AD (N = 81) and elderly control subjects (N = 101). A combination of CSF t-tau/Aβ1-4 ratio and MRI biomarkers or neuropsychological tests (free recall and trail making test B (TMT-B)) showed the best statistical fit in the AD vs. HC comparison, reaching a classification accuracy of up to 64% when applied to the prediction of MCI conversion (3.3-year observation interval, mean = 2.3 years). However, several single-predictor models showed a predictive accuracy of MCI conversion comparable to that of any multipredictor model. The best single predictors were right entorhinal cortex (prediction accuracy = 68.5% (95% CI (59.5, 77.4))) and TMT-B test (prediction accuracy 64.6% (95% CI (55.5, 73.4%))). In conclusion, short-term conversion to AD is predicted by single marker models to a comparable degree as by multimarker models in amnestic MCI subjects.
Alzheimer's disease; Dementia; Mild cognitive impairment; Mild cognitive impairment (MCI); Autopsy-confirmation; Biomarkers; Early detection; Cerebrospinal fluid; Cerebrospinal fluid (CSF); Aβ1-42; Tau; p-tau; MRI; Hippocampus; Volumetry; Entorhinal cortex; Prodromal; ADNI
Most people with Parkinson's disease (PD) eventually develop cognitive impairment (CI). However, neither the timing of onset nor the severity of cognitive symptoms can be accurately predicted. We sought plasma-based biomarkers for CI in PD.
A discovery cohort of 70 PD patients was recruited. Cognitive status was evaluated with the Mattis Dementia Rating Scale-2 (DRS) at baseline and on annual follow-up visits, and baseline plasma levels of 102 proteins were determined with a bead-based immunoassay. Using linear regression, we identified biomarkers of CI in PD, i.e. proteins whose levels correlated with cognitive performance at baseline and/or cognitive decline at follow-up. We then replicated the association between cognitive performance and levels of the top biomarker, using a different technical platform, with a separate cohort of 113 PD patients.
Eleven proteins exhibited plasma levels correlating with baseline cognitive performance in the discovery cohort. The best candidate was epidermal growth factor (EGF, p<0.001); many of the other 10 analytes co-varied with EGF across samples. Low levels of EGF not only correlated with poor cognitive test scores at baseline, but also predicted an eightfold greater risk of cognitive decline to dementia-range DRS scores at follow-up for those with intact baseline cognition. A weaker, but still significant, relationship between plasma EGF levels and cognitive performance was found in an independent replication cohort of 113 PD patients.
Our data suggest that plasma EGF may be a biomarker for progression to CI in PD.
Epidermal growth factor; EGF; Parkinson's Disease; Parkinson's Disease with Dementia; Biomarker; Plasma
To examine the effect of specific “CSF profiles” on the rate of cognitive decline, disease progression, and risk of conversion to Alzheimer's disease (AD) dementia in patients with amnestic mild cognitive impairment (MCI).
Total tau (t-tau), tau phosphorylated at threonine 181 (p-tau181), and β-amyloid 1-42 peptide (Aβ42) were immunoassayed in CSF samples obtained from MCI patients enrolled in the Alzheimer's Disease Neuroimaging Initiative. Patients were then stratified by “CSF profiles”: (1) normal t-tau and Aβ42 levels (i.e., normal–t-tauAβ42), (2) normal t-tau but abnormal Aβ42 (i.e., abnormal–Aβ42), (3) abnormal t-tau but normal Aβ42 (i.e., abnormal–t-tau), and (4) abnormal t-tau and Aβ42 (i.e., abnormal–t-tauAβ42).
Fifty-eight sites in the US and Canada.
One hundred ninety-five MCI patients.
Main Outcome Measures
A composite cognitive measure, the CDR-Sum of Boxes, and conversion to AD.
MCI patients with a CSF profile of abnormal–Aβ42 or abnormal–t-tauAβ42 experienced a faster rate of decline on the composite cognitive measure and the CDR-Sum of Boxes compared to those with normal–t-tauAβ42. They also had a greater risk of converting to AD relative to the normal–t-tauAβ42 group. In contrast, those with a CSF profile of abnormal–t-tau did not differ from the normal–t-tauAβ42 group on any outcome. These findings were generally replicated when the sample was reclassified by patterns of p-tau181 and Aβ42 abnormalities.
β-amyloid abnormalities, but not tau alterations, are associated with cognitive deterioration, disease progression, and increased risk of conversion to AD dementia in patients with MCI. Patients with abnormal levels of Aβ42 may be prime targets for drug treatment and clinical trials in MCI.
CSF; MCI; cognitive decline; disease progression; conversion to AD
The close correlation between abnormally low pre-mortem cerebrospinal fluid (CSF) concentrations of amyloid-β1-42 (Aβ1–42) and plaque burden measured by amyloid imaging as well as between pathologically increased levels of CSF tau and the extent of neurode-generation measured by MRI has led to growing interest in using these biomarkers to predict the presence of AD plaque and tangle pathology. A challenge for the wide-spread use of these CSF biomarkers is the high variability in the assays used to measure these analytes which has been ascribed to multiple pre-analytical and analytical test performance factors. To address this challenge, we conducted a seven-center inter-laboratory standardization study for CSF total tau (t-tau), phospho-tau (p-tau181) and Aβ1–42 as part of the Alzheimer’s Disease Neuroimaging Initiative (ADNI). Aliquots prepared from five CSF pools assembled from multiple elderly controls (n = 3) and AD patients (n = 2) were the primary test samples analyzed in each of three analytical runs by the participating laboratories using a common batch of research use only immunoassay reagents (INNO-BIA AlzBio3, xMAP technology, from Innogenetics) on the Luminex analytical platform. To account for the combined effects on overall precision of CSF samples (fixed effect), different laboratories and analytical runs (random effects), these data were analyzed by mixed-effects modeling with the following results: within center %CV 95% CI values (mean) of 4.0–6.0% (5.3%) for CSF Aβ1–42; 6.4–6.8% (6.7%) for t-tau and 5.5–18.0% (10.8%) for p-tau181 and inter-center %CV 95% CI range of 15.9–19.8% (17.9%) for Aβ1–42, 9.6–15.2% (13.1%) for t-tau and 11.3–18.2% (14.6%) for p-tau181. Long-term experience by the ADNI biomarker core laboratory replicated this degree of within-center precision. Diagnostic threshold CSF concentrations for Aβ1–42 and for the ratio t-tau/Aβ1–42 were determined in an ADNI independent, autopsy-confirmed AD cohort from whom ante-mortem CSF was obtained, and a clinically defined group of cognitively normal controls (NCs) provides statistically significant separation of those who progressed from MCI to AD in the ADNI study. These data suggest that interrogation of ante-mortem CSF in cognitively impaired individuals to determine levels of t-tau, p-tau181 and Aβ1–42, together with MRI and amyloid imaging biomarkers, could replace autopsy confirmation of AD plaque and tangle pathology as the “gold standard” for the diagnosis of definite AD in the near future.
Alzheimer’s Disease Neuroimaging Initiative; Cerebrospinal fluid; Amyloid-β1-42; Total tau; p-tau181; Interlaboratory study; Mixed-effects modeling
Cerebrospinal fluid (CSF) biomarkers of Alzheimer’s disease (AD) are currently being considered for inclusion in revised diagnostic criteria for research and/or clinical purposes to increase the certainty of ante-mortem diagnosis. Establishing biomarker validity requires demonstration that the assays are true markers of underlying disease pathology (e.g., amyloid plaques and/or neurofibrillary tangles) in living individuals.
We compared the performances of the two most commonly used platforms, INNOTEST® ELISA and INNO-BIA AlzBio3 for measurement of CSF amyloid-beta (Aβ) and tau(s), for identifying the presence of amyloid plaques in a research cohort (n=103). Values obtained for CSF Aβ1-42, total tau and phosphorylated tau181 (p-tau181) using the two assay platforms were compared to brain amyloid load as assessed by positron emission tomography using the amyloid imaging agent, Pittsburgh Compound B (PIB).
Research volunteers who are cognitively normal or have very mild to moderate AD dementia.
The two assay platforms yielded different (~2–6-fold) absolute values for the various analytes, but relative values were highly correlated. CSF Aβ1-42 correlated inversely, and tau and p-tau181 correlated positively, with the amount of cortical PIB binding, albeit to differing degrees. Both assays yielded similar patterns of CSF biomarker correlations with amyloid load. The ratios of total tau/Aβ1-42 and p-tau181/Aβ1-42 outperformed any single analyte, including Aβ1-2, in discriminating individuals with versus without cortical amyloid.
The INNOTEST® and INNO-BIA CSF platforms performed equally well in identifying individuals with underlying amyloid plaque pathology. Differences in absolute values, however, point to the need for assay-specific diagnostic cut-point values.
Alzheimer’s disease; amyloid; biomarkers; cerebrospinal fluid; imaging (PET, MRI) in dementias; Pittsburgh Compound B
Quantitation of isoprostanes such as 8-iso-PGF2α and 8,12-iso-iPF2α-VI in biological fluids has been proposed as a reliable test of oxidant stress and inflammation in a variety of disorders. This paper presents a liquid chromatography method with tandem mass spectrometry detection for the simultaneous analysis of these two isoprostanes in human CSF and brain tissue samples. An API 5000 triple quadrupole instrument (AB Sciex, Foster City, CA, USA) with an APCI ion source was used in this study. Aliquots of CSF samples (0.25mL) were treated with a methanol:zinc sulfate mixture followed by on-line cleanup on an extraction column (Validated-C18) with 0.1% formic acid. The brain tissue samples were homogenized and lipids were extracted using Folch solution. Solid phase extraction columns (C18) were used for the purification of the brain isoprostane fraction. Chromatographic separation was achieved using an analytical column (Synergi C18 HydroRP) with 0.1% formic acid in water and a mixture of methanol:acetonitrile under isocratic conditions. The mass spectrometer was operated in the MRM scan and negative ion mode. The quadrupoles were set to detect the molecular ions [M-H]− and high mass fragments of isoprostanes: m/z 353→193 amu (8-iso-PGF2α) and m/z 353→115 amu (8,12-iso-iPF2α-VI) and their deuterated internal standards: m/z 357→197 amu (8-iso-PGF2α-d4) and m/z 364 → 115 amu (8,12-iso-iPF2α -VI-d11). The lower limit of quantification was 2.5 pg/mL for 8-iso-PGF2α and 5.0 pg/mL for 8,12-iso-PF2α-VI for the CSF method and 10.0 pg/0.1 g of tissue and 30.0 pg/0.1 g of tissue for 8-iso-PGF2α and 8,12-iso-iPF2α -VI, respectively, for the brain tissue method. No ion suppression or enhancement of the detection of 8-isoPGF2α, 8,12-isoPF2α-VI or both internal standards was found.
8-iso-PGF2α; 8, 12-iso-iPF2α-VI; HPLC-MS/MS; on-line cleanup; CSF; brain tissue samples
Cerebrospinal fluid (CSF) and structural magnetic resonance imaging (MRI) show patterns of change in Alzheimer’s disease (AD) that precede dementia. The Alzheimer’s Disease Neuroimaging Initiative (ADNI) studied normal controls (NC), subjects with mild cognitive impairment (MCI) and AD to identify patterns of biomarkers to aid in early diagnosis and effective treatment of AD.
222 NC underwent baseline MRI and clinical examination at baseline and at least one follow-up. 112 also provided CSF at baseline. Unsupervised clustering based on initial CSF and MRI measures was used to identify clusters of participants with similar profiles. Repeated measures regression modeling assessed the relationship of individual measures, and of cluster membership, to cognitive change over three years.
Most individuals showed little cognitive change. Individual biomarkers had limited predictive value for cognitive decline, but membership in the cluster with the most extreme profile was associated with more rapid decline in ADAS-COG.
Subtypes among NC based on multiple biomarkers may represent the earliest stages of subclinical cognitive decline and AD.
Alzheimer’s disease; Dementia; Early diagnosis; Cerebrospinal fluid; Tau protein; Amyloid beta-protein; Structural magnetic resonance imaging; Hippocampal volume; Cognition; Clustering; Normal controls
Previously it was reported that Alzheimer's disease (AD) patients have reduced amyloid (Aβ1-42) and elevated total tau (t-tau) and phosphorylated tau (p-tau181p) in the cerebrospinal fluid (CSF), suggesting that these same measures could be used to detect early AD pathology in healthy elderly (CN) and mild cognitive impairment (MCI). In this study, we tested the hypothesis that there would be an association among rates of regional brain atrophy, the CSF biomarkers Aβ1-42, t-tau, and p-tau181p and ApoE ε4 status, and that the pattern of this association would be diagnosis specific. Our findings primarily showed that lower CSF Aβ1-42 and higher tau concentrations were associated with increased rates of regional brain tissue loss and the patterns varied across the clinical groups. Taken together, these findings demonstrate that CSF biomarker concentrations are associated with the characteristic patterns of structural brain changes in CN and MCI that resemble to a large extent the pathology seen in AD. Therefore, the finding of faster progression of brain atrophy in the presence of lower Aβ1-42 levels and higher p-tau levels supports the hypothesis that CSF Aβ1-42 and tau are measures of early AD pathology. Moreover, the relationship among CSF biomarkers, ApoE ε4 status, and brain atrophy rates are regionally varying, supporting the view that the genetic predisposition of the brain to amyloid and tau mediated pathology is regional and disease stage specific.
MRI; Alzheimer's disease; cerebrospinal fluid; biomarkers; cortical thickness; atrophy; brain tissue volume; ApoE
Ideal biomarkers of Alzheimer's disease should correlate with accepted measures of pathology in the cerebrospinal fluid (CSF); they should also correlate with, or predict, future clinical decline, and should be readily measured in hundreds to thousands of subjects. Here we explored the utility of automated 3D maps of the lateral ventricles as a possible biomarker of AD. We used our multi-atlas fluid image alignment (MAFIA) method, to compute ventricular models automatically, without user intervention, from 804 brain MRI scans with 184 AD, 391 MCI, and 229 healthy elderly controls (446 men/338 women; age: 75.50+/-6.81 [SD] years). Radial expansion of the ventricles, computed pointwise, was strongly correlated with current cognition, depression ratings, Hachinski Ischemic scores, language scores and with future clinical decline after controlling for any effects of age, sex, and educational level. In statistical maps ranked by effect sizes, ventricular differences were highly correlated with CSF measures of Aβ1-42, and correlated with ApoE4 genotype. These statistical maps are highly automated, and offer a promising biomarker of AD for large-scale studies.