Amyloid-β(1–42), Total Tau, and Phosphorylated Tau as Cerebrospinal Fluid Biomarkers for the Diagnosis of Alzheimer Disease

Variability of CSF Alzheimer's disease biomarkers: implications for clinical practice

BACKGROUND

Cerebrospinal fluid (CSF) biomarkers are increasingly being used for diagnosis of Alzheimer's disease (AD).

OBJECTIVE

We investigated the influence of CSF intralaboratory and interlaboratory variability on diagnostic CSF-based AD classification of subjects and identified causes of this variation.

METHODS

We measured CSF amyloid-β (Aβ) 1-42, total tau (t-tau), and phosphorylated tau (p-tau) by INNOTEST enzyme-linked-immunosorbent assays (ELISA) in a memory clinic population (n = 126). Samples were measured twice in a single or two laboratories that served as reference labs for CSF analyses in the Netherlands. Predefined cut-offs were used to classify CSF biomarkers as normal or abnormal/AD pattern.

RESULTS

CSF intralaboratory variability was higher for Aβ1-42 than for t-tau and p-tau. Reanalysis led to a change in biomarker classification (normal vs. abnormal) of 26% of the subjects based on Aβ1-42, 10% based on t-tau, and 29% based on p-tau. The changes in absolute biomarker concentrations were paralleled by a similar change in levels of internal control samples between different assay lots. CSF interlaboratory variability was higher for p-tau than for Aβ1-42 and t-tau, and reanalysis led to a change in biomarker classification of 12% of the subjects based on Aβ1-42, 1% based on t-tau, and 22% based on p-tau.

CONCLUSIONS

Intralaboratory and interlaboratory CSF variability frequently led to change in diagnostic CSF-based AD classification for Aβ1-42 and p-tau. Lot-to-lot variation was a major cause of intralaboratory variability. This will have implications for the use of these biomarkers in clinical practice.

Brain volume and white matter hyperintensities as determinants of cerebral blood flow in Alzheimer's disease

To better understand whether decreased cerebral blood flow (CBF) in patients with Alzheimer's disease (AD) reflects neurodegeneration or cerebral small vessel disease, we investigated the associations of normalized brain volume (NBV) and white matter hyperintensity (WMH) volume with CBF. We included 129 patients with AD (66 ± 7 years, 53% female) and 61 age-matched controls (64 ± 5 years, 43% female). CBF was measured with pseudocontinuous arterial spin labeling at 3T in the whole brain and in partial volume corrected cortical maps. When NBV and WMH were simultaneously entered in age and sex adjusted models, smaller NBV was associated with lower whole brain (Stβ: 0.29; p < 0.01) and cortical CBF (Stβ: 0.28; p < 0.01) in patients with AD. Larger WMH volume was also associated with lower whole brain (Stβ: -0.22; p < 0.05) and cortical CBF (Stβ: -0.24; p < 0.05) in AD. Additional adjustments did not change these results. In controls, neither NBV nor WMH was associated with CBF. Our results indicate that in AD, lower CBF as measured using pseudocontinuous arterial spin labeling, reflects the combined disease burden of both neurodegeneration and small vessel disease.

The association of angiotensin-converting enzyme with biomarkers for Alzheimer's disease

Introduction

Lower angiotensin-converting enzyme (ACE) activity could increase the risk of Alzheimer’s disease (AD) as ACE functions to degrade amyloid-β (Aβ). Therefore, we investigated whether ACE protein and activity levels in cerebrospinal fluid (CSF) and serum were associated with CSF Aβ, total tau (tau) and tau phosphorylated at threonine 181 (ptau).

Methods

We included 118 subjects from our memory clinic-based Amsterdam Dementia Cohort (mean age 66 ± 8 years) with subjective memory complaints (n = 40) or AD (n = 78), who did not use antihypertensive drugs. We measured ACE protein levels (ng/ml) and activity (RFU) in CSF and serum, and amyloid β_1–42, tau and ptau (pg/ml) in CSF.

Results

Cross-sectional regression analyses showed that ACE protein level and activity in CSF and serum were lower in patients with AD compared to controls. Lower CSF ACE protein level, and to a lesser extent serum ACE protein level and CSF ACE activity, were associated with lower CSF Aβ, indicating more brain Aβ pathology; adjusted regression coefficients (B) (95% CI) per SD increase were 0.09 (0.04; 0.15), 0.06 (0.00; 0.12) and 0.05 (0.00; 0.11), respectively. Further, lower CSF ACE protein level was associated with lower CSF tau and ptau levels; adjusted B’s (95% CI) per SD increase were 0.15 (0.06; 0.25) and 0.17 (0.10; 0.25), respectively.

Conclusions

These results strengthen the hypothesis that ACE degrades Aβ. This could suggest that lowering ACE levels by for example ACE-inhibitors might have adverse consequences for patients with, or at risk for AD.

Cerebrospinal fluid biomarkers of Alzheimer's disease

Alzheimer's disease (AD) is a fatal neurodegenerative disorder that takes about a decade to develop, making early diagnosis possible. Clinically, the diagnosis of AD is complicated, costly, and inaccurate, so it is urgent to find specific biomarkers. Due to its multifactorial nature, a panel of biomarkers for the multiple pathologies of AD, such as cerebral amyloidogenesis, neuronal dysfunction, synapse loss, oxidative stress, and inflammation, are most promising for accurate diagnosis. Highly sensitive and high-throughput proteomic techniques can be applied to develop a panel of novel biomarkers for AD. In this review, we discuss the metabolism and diagnostic performance of the well-established core candidate cerebrospinal fluid (CSF) biomarkers (β-amyloid, total tau, and hyperphosphorylated tau). Meanwhile, novel promising CSF biomarkers, especially those identified by proteomics, updated in the last five years are also extensively discussed. Furthermore, we provide perspectives on how biomarker discovery for AD is evolving.

The cerebrospinal fluid "Alzheimer profile": easily said, but what does it mean?

BACKGROUND

We aimed to identify the most useful definition of the "cerebrospinal fluid Alzheimer profile," based on amyloid-ß1-42 (Aβ42), total tau, and phosphorylated tau (p-tau), for diagnosis and prognosis of Alzheimer's disease (AD).

METHODS

We constructed eight Alzheimer profiles with previously published combinations, including regression formulas and simple ratios. We compared their diagnostic accuracy and ability to predict dementia due to AD in 1385 patients from the Amsterdam Dementia Cohort. Results were validated in an independent cohort (n = 1442).

RESULTS

Combinations outperformed individual biomarkers. Based on the sensitivity of the best performing regression formulas, cutoffs were chosen at 0.52 for the tau/Aβ42 ratio and 0.08 for the p-tau/Aβ42 ratio. Ratios performed similar to formulas (sensitivity, 91%-93%; specificity, 81%-84%). The same combinations best predicted cognitive decline in mild cognitive impairment patients. Validation confirmed these results, especially regarding the tau/Aβ42 ratio.

CONCLUSIONS

A tau/Aβ42 ratio of >0.52 constitutes a robust cerebrospinal fluid Alzheimer profile. We recommend using this ratio to combine biomarkers.

Detection of misfolded Aβ oligomers for sensitive biochemical diagnosis of Alzheimer's disease

Alzheimer's disease (AD) diagnosis is hampered by the lack of early, sensitive, and objective laboratory tests. We describe a sensitive method for biochemical diagnosis of AD based on specific detection of misfolded Aβ oligomers, which play a central role in AD pathogenesis. The protein misfolding cyclic amplification assay (Aβ-PMCA), exploits the functional property of Aβ oligomers to seed the polymerization of monomeric Aβ. Aβ-PMCA allowed detection of as little as 3 fmol of Aβ oligomers. Most importantly, using cerebrospinal fluid, we were able to distinguish AD patients from control individuals affected by a variety of other neurodegenerative disorders or nondegenerative neurological diseases with overall sensitivity of 90% and specificity of 92%. These findings provide the proof-of-principle basis for developing a highly sensitive and specific biochemical test for AD diagnosis.

Quantification of clusterin in paired cerebrospinal fluid and plasma samples

BACKGROUND

Clusterin (ApoJ) is an amyloid-associated protein and plays an important role in Alzheimer's disease (AD) pathology. Recent genome-wide association studies have indicated that certain genetic variants increase the risk of developing AD. To determine if the expression of clusterin is different in AD patients, both systemically and locally in the brain, differs between (subgroups of) AD patients and non-AD cases, an assay available that detects clusterin in both plasma and cerebrospinal fluid (CSF) with equal sensitivity would be helpful.

METHODS

We compared four different commercially available antibodies in their ability to detect recombinant clusterin and immune-purified human clusterin. Specificity was tested on western blot and in ELISA systems, and selection was based on the ability to detect clusterin in CSF and plasma. A sandwich ELISA was developed and validated with monoclonal antibody G7 as capture, and rabbit polyclonal (Alexis) antibodies for detection.

RESULTS

Our ELISA measured clusterin concentrations in plasma and CSF with dynamic ranges of 2-70 mg/L and 0.5-40 mg/L, respectively. The assays showed 99.8% recovery in CSF and 97% recovery in plasma. Intra-assay coefficient of variation was 1.4% and inter-assay 8.8%. The assay shows no cross-reactivity with related apolipoproteins. Clusterin quantification is dependent on the type of storage for plasma samples. A single freeze/thaw cycle caused fluctuations of clusterin concentrations in plasma, while clusterin in CSF is stable for up to five cycles.

CONCLUSIONS

We have successfully developed a clusterin ELISA that reliably measures CSF and plasma clusterin concentrations. In a pilot study, all samples gave results that were well within the dynamic range of the assay, with low variations. Freshly stored plasma samples are crucial for accurate clusterin quantification.

The Janus face of the heme oxygenase/biliverdin reductase system in Alzheimer disease: it's time for reconciliation

Alzheimer disease (AD) is the most common form of dementia among the elderly and is characterized by progressive loss of memory and cognition. These clinical features are due in part to the increase of reactive oxygen and nitrogen species that mediate neurotoxic effects. The up-regulation of the heme oxygenase-1/biliverdin reductase-A (HO-1/BVR-A) system is one of the earlier events in the adaptive response to stress. HO-1/BVR-A reduces the intracellular levels of pro-oxidant heme and generates equimolar amounts of the free radical scavengers biliverdin-IX alpha (BV)/bilirubin-IX alpha (BR) as well as the pleiotropic gaseous neuromodulator carbon monoxide (CO) and ferrous iron. Two main and opposite hypotheses for a role of the HO-1/BVR-A system in AD propose that this system mediates neurotoxic and neuroprotective effects, respectively. This apparent controversy was mainly due to the fact that for over about 20years HO-1 was the only player on which all the analyses were focused, excluding the other important and essential component of the entire system, BVR. Following studies from the Butterfield laboratory that reported alterations in BVR activity along with decreased phosphorylation and increased oxidative/nitrosative post-translational modifications in the brain of subjects with AD and amnestic mild cognitive impairment (MCI) subjects, a debate was opened on the real pathophysiological and clinical significance of BVR-A. In this paper we provide a review of the main discoveries about the HO/BVR system in AD and MCI, and propose a mechanism that reconciles these two hypotheses noted above of neurotoxic and the neuroprotective aspects of this important stress responsive system.

CSF p-Tau levels in the prediction of Alzheimer's disease

The two hallmarks of Alzheimer's disease (AD) are neurofibrillary tangles and amyloid plaques. Neurofibrillary tangles are formed due to the hyperphosphorylation of tau protein. There is an urgent need to develop a reliable biomarker for the diagnosis of AD. Cerebrospinal fluid (CSF) is surrounding the brain and reflects the major neuropathological features in the AD brain. Diagnosis, disease progression and drug actions rely on the AD biomarkers. Mainly CSF tau and phosphorylated tau (p-Tau) have been observed to serve the purpose for early AD. Keeping in view the early appearance of p-Tau in CSF, we analyzed p-Tau levels in 23 AD, 23 Non AD type dementia (NAD), 23 Neurological control (NC) and 23 Healthy control (HC) North Indian patients. The levels of p-Tau were found to be increased in AD patients (67.87±18.05 pg/ml, SEM 3.76) compared with NAD (47.55±7.85 pg/ml, SEM 1.64), NC (34.42±4.51 pg/ml, SEM 0.94) and HC (27.09±7.18 pg/ml, SEM 1.50). The resulting sensitivity for AD with NAD was 80.27% whereas with respect to the NAD, NC and HC was 85.40%. Therefore elevated levels of p-Tau in AD can be exploited as a predictive biomarker in North Indian AD patients.

Brain network alterations in Alzheimer's disease measured by eigenvector centrality in fMRI are related to cognition and CSF biomarkers

Recent imaging studies have demonstrated functional brain network changes in patients with Alzheimer's disease (AD). Eigenvector centrality (EC) is a graph analytical measure that identifies prominent regions in the brain network hierarchy and detects localized differences between patient populations. This study used voxel-wise EC mapping (ECM) to analyze individual whole-brain resting-state functional magnetic resonance imaging (MRI) scans in 39 AD patients (age 67 ± 8) and 43 healthy controls (age 69 ± 7). Between-group differences were assessed by a permutation-based method. Associations of EC with biomarkers for AD pathology in cerebrospinal fluid (CSF) and Mini Mental State Examination (MMSE) scores were assessed using Spearman correlation analysis. Decreased EC was found bilaterally in the occipital cortex in AD patients compared to controls. Regions of increased EC were identified in the anterior cingulate and paracingulate gyrus. Across groups, frontal and occipital EC changes were associated with pathological concentrations of CSF biomarkers and with cognition. In controls, decreased EC values in the occipital regions were related to lower MMSE scores. Our main finding is that ECM, a hypothesis-free and computationally efficient analysis method of functional MRI (fMRI) data, identifies changes in brain network organization in AD patients that are related to cognition and underlying AD pathology. The relation between AD-like EC changes and cognitive performance suggests that resting-state fMRI measured EC is a potential marker of disease severity for AD.

MicroRNA in Alzheimer's disease: an exploratory study in brain, cerebrospinal fluid and plasma

MicroRNA (miRNA) may be potential biomarkers of Alzheimer's disease (AD). The objective of this investigation was to demonstrate that miRNAs in human brain or biofluids are differentially expressed according to disease status, tissue type, neuritic plaque score or Braak stage. Post-mortem brain (PMB) miRNA were profiled using arrays and validated using quantitative RT-PCR (qRT-PCR). Five qRT-PCR-validated miRNAs were measured in an independent sample of PMB, cerebrospinal fluid and plasma from the same subjects. Plasma miR-15a was found to be associated with plaque score in the independent sample. In conclusion, miRNA present in human biofluids may offer utility as biomarkers of AD.

Different patterns of gray matter atrophy in early- and late-onset Alzheimer's disease

We assessed patterns of gray matter atrophy according to-age-at-onset in a large sample of 215 Alzheimer's disease (AD) patients and 129 control subjects with voxel-based morphometry using 3-Tesla 3D T1-weighted magnetic resonance imaging. Local gray matter amounts were compared between late- and early-onset AD patients and older and younger control subjects, taking into account the effect of apolipoprotein E. Additionally, combined effects of age and diagnosis on volumes of hippocampus and precuneus were assessed. Compared with age-matched control subjects, late-onset AD patients exhibited atrophy of the hippocampus, right temporal lobe, and cerebellum, whereas early-onset AD patients showed gray matter atrophy in hippocampus, temporal lobes, precuneus, cingulate gyrus, and inferior frontal cortex. Direct comparisons between late- and early-onset AD patients revealed more pronounced atrophy of precuneus in early-onset AD patients and more severe atrophy in medial temporal lobe in late-onset AD patients. Age and diagnosis independently affected the hippocampus; moreover, the interaction between age and diagnosis showed that precuneus atrophy was most prominent in early-onset AD patients. Our results suggest that patterns of atrophy might vary in the spectrum of AD.

Measurements of medial temporal lobe atrophy for prediction of Alzheimer's disease in subjects with mild cognitive impairment

Our aim was to compare the predictive accuracy of 4 different medial temporal lobe measurements for Alzheimer's disease (AD) in subjects with mild cognitive impairment (MCI). Manual hippocampal measurement, automated atlas-based hippocampal measurement, a visual rating scale (MTA-score), and lateral ventricle measurement were compared. Predictive accuracy for AD 2 years after baseline was assessed by receiver operating characteristics analyses with area under the curve as outcome. Annual cognitive decline was assessed by slope analyses up to 5 years after baseline. Correlations with biomarkers in cerebrospinal fluid (CSF) were investigated. Subjects with MCI were selected from the Development of Screening Guidelines and Clinical Criteria for Predementia AD (DESCRIPA) multicenter study (n = 156) and the single-center VU medical center (n = 172). At follow-up, area under the curve was highest for automated atlas-based hippocampal measurement (0.71) and manual hippocampal measurement (0.71), and lower for MTA-score (0.65) and lateral ventricle (0.60). Slope analysis yielded similar results. Hippocampal measurements correlated with CSF total tau and phosphorylated tau, not with beta-amyloid 1-42. MTA-score and lateral ventricle volume correlated with CSF beta-amyloid 1-42. We can conclude that volumetric hippocampal measurements are the best predictors of AD conversion in subjects with MCI.

Plasma biomarkers for Alzheimer's disease: much needed but tough to find

Alzheimer's disease is a complex age-dependent neurodegenerative disease where definitive diagnosis is only possible after autopsy and where there is a long prodromal or preclinical phase. Biomarkers for both early diagnosis and prediction of disease progression are needed and extensive efforts to discover them have been undertaken. In this article, we have attempted to summarize the findings of current studies using proteomics and metabolomics approaches. We are also discussing how the use of emerging technologies and better study designs can support the identification of the much-needed Alzheimer's disease plasma biomarkers.

Recommendations to standardize preanalytical confounding factors in Alzheimer's and Parkinson's disease cerebrospinal fluid biomarkers: an update

Early diagnosis of neurodegenerative disorders such as Alzheimer's (AD) or Parkinson's disease (PD) is needed to slow down or halt the disease at the earliest stage. Cerebrospinal fluid (CSF) biomarkers can be a good tool for early diagnosis. However, their use in clinical practice is challenging due to the high variability found between centers in the concentrations of both AD CSF biomarkers (Aβ42, total tau and phosphorylated tau) and PD CSF biomarker (α-synuclein). Such a variability has been partially attributed to different preanalytical procedures between laboratories, thus highlighting the need to establish standardized operating procedures. Here, we merge two previous consensus guidelines for preanalytical confounding factors in order to achieve one exhaustive guideline updated with new evidence for Aβ42, total tau and phosphorylated tau, and α-synuclein. The proposed standardized operating procedures are applicable not only to novel CSF biomarkers in AD and PD, but also to biomarkers for other neurodegenerative disorders.

Novel methodologies in metabolic profiling with a focus on molecular diagnostic applications

The metabolome contains all the biological end points of genomic, transcriptomic and proteomic perturbations, also including the influence of gut microbiota and the environment, giving a direct picture of an organism's ongoing metabolic state. Metabolomics thus has the potential to be an effective tool for early diagnosis of disease, and also to be a predictor of treatment response and survival. In recent years, the development of instrumental systems has enabled more comprehensive coverage of the metabolome. Advances in mass spectrometry and chromatography have particularly improved both the efficiency of nontargeted metabolic profiling as well as the sensitivity and reliability of targeted analyses. Mass spectrometric techniques are also increasingly becoming accepted as a routine diagnostic tool in clinical laboratories. This review summarizes the most recent advances and current challenges in metabolomics, with a focus on mass spectrometric methods utilized in biomarker research, highlighted with selected examples.

A prediction model to calculate probability of Alzheimer's disease using cerebrospinal fluid biomarkers

BACKGROUND

We aimed to develop a prediction model based on cerebrospinal fluid (CSF) biomarkers, that would yield a single estimate representing the probability that dementia in a memory clinic patient is due to Alzheimer's disease (AD).

METHODS

All patients suspected of dementia in whom the CSF biomarkers had been analyzed were selected from a memory clinic database. Clinical diagnosis was AD (n = 272) or non-AD (n = 289). The prediction model was developed with logistic regression analysis and included CSF amyloid β42, CSF phosphorylated tau181, and sex. Validation was performed on an independent data set from another memory clinic, containing 334 AD and 157 non-AD patients.

RESULTS

The prediction model estimated the probability that AD is present as follows: p(AD) = 1/(1 + e (- [-0.3315 + score])), where score is calculated from -1.9486 × ln(amyloid β42) + 2.7915 × ln(phosphorylated tau181) + 0.9178 × sex (male = 0, female = 1). When applied to the validation data set, the discriminative ability of the model was very good (area under the receiver operating characteristic curve: 0.85). The agreement between the probability of AD predicted by the model and the observed frequency of AD diagnoses was very good after taking into account the difference in AD prevalence between the two memory clinics.

CONCLUSIONS

We developed a prediction model that can accurately predict the probability of AD in a memory clinic population suspected of dementia based on CSF amyloid β42, CSF phosphorylated tau181, and sex.

Changes in plasma and cerebrospinal fluid biomarkers in aged patients with early postoperative cognitive dysfunction following total hip-replacement surgery

PURPOSE

We hypothesized that different patterns of biomarkers of brain injury and inflammation exist in aged patients with postoperative cognitive dysfunction (POCD) after total hip-replacement with spinal anesthesia.

METHODS

Eighty-three patients older than 65 years undergoing elective total hip-replacement surgery were enrolled in this prospective observational study. The CSF levels of Tau, phosphorylated-tau (pTau), amyloidβ1-42 (Aβ1-42), Tau/Aβ1-42, pTau/Aβ1-42, BDNF, IL-6, and IL-1β were measured preoperatively. Perioperative plasma levels of IL-1β, IL-6, brain-derived neurotrophic factor (BDNF), C-reactive protein (CRP), and malonaldehyde (MDA) as well as neurocognitive tests were determined preoperatively and seven days postoperatively.

RESULTS

Sixty-one patients completed both the CSF and blood samples collection and the neurocognitive tests. POCD occurred in 24.6 % of patients at seven days after surgery. Patients with POCD had significantly higher IL-1β, Tau/Aβ1-42, pTau/Aβ1-42, and a lower level of Aβ1-42 in CSF when compared with the Non-POCD group (P < 0.05). Furthermore, POCD patients displayed significantly higher plasma levels of MDA when compared with Non-POCD patients at seven days after surgery (P < 0.05). There was no difference in preoperative CSF levels of Tau, IL-6, and pTau as well as plasma levels of IL-1β, IL-6, BDNF and CRP between POCD and Non-POCD groups (P > 0.05).

CONCLUSION

The POCD patients were associated with higher postoperative plasma levels of MDA, and higher IL-1β and lower Aβ1-42 levels in preoperative CSF that might predispose the development of POCD in aged patients following total hip-replacement surgery with spinal anesthesia.

Neurochemical dementia diagnostics for Alzheimer’s disease and other dementias: an ISO 15189 perspective

Dementia is one of the most common causes of health problems in the elderly populations of Western industrialized countries. A combined analysis of cerebrospinal fluid-based neurochemical dementia diagnostics biomarkers (amyloid-β peptides, total tau and phosphorylated forms of tau) provides sensitivity and specificity in the range of 85% for the diagnosis of Alzheimer’s disease, the most common cause of dementia. The alterations occur very early in the course of neurodegeneration, enabling medical follow-up of persons with increased risk of developing dementia. With a growing number of laboratories performing neurochemical dementia diagnostics routinely, it is important to standardize protocols and laboratory performance to enable comparisons of results and their interpretations. Together with the recently published expert guidelines for sample handling and preparation, as well as the interpretation (post-analytical) algorithms developed by experienced centers, ISO 15189 norm provides an extremely useful tool for standardization of neurochemical dementia diagnostics.

Injury markers predict time to dementia in subjects with MCI and amyloid pathology

OBJECTIVES

Alzheimer disease (AD) can now be diagnosed in subjects with mild cognitive impairment (MCI) using biomarkers. However, little is known about the rate of decline in those subjects. In this cohort study, we aimed to assess the conversion rate to dementia and identify prognostic markers in subjects with MCI and evidence of amyloid pathology.

METHODS

We pooled subjects from the VU University Medical Center Alzheimer Center and the Development of Screening Guidelines and Criteria for Predementia Alzheimer's Disease (DESCRIPA) study. We included subjects with MCI, an abnormal level of β-amyloid(1-42) (Aβ(1-42)) in the CSF, and at least one diagnostic follow-up visit. We assessed the effect of APOE genotype, CSF total tau (t-tau) and tau phosphorylated at threonine 181 (p-tau) and hippocampal volume on time to AD-type dementia using Cox proportional hazards models and on decline on the Mini-Mental State Examination (MMSE) using linear mixed models.

RESULTS

We included 110 subjects with MCI with abnormal CSF Aβ(1-42) and a mean MMSE score of 26.3 ± 2.8. During a mean follow-up of 2.2 ± 1.0 (range 0.4-5.0) years, 63 subjects (57%) progressed to AD-type dementia. Abnormal CSF t-tau (hazard ratio [HR] 2.3, 95% confidence interval [CI] 1.1-4.6, p = 0.03) and CSF p-tau (HR 3.5, 95% CI 1.3-9.2, p = 0.01) concentration and hippocampal atrophy (HR 2.5, 95% CI 1.1-5.6, p = 0.02) predicted time to dementia. For subjects with both abnormal t-tau concentration and hippocampal atrophy, HR was 7.3 (95% CI 1.0-55.9, p = 0.06). Furthermore, abnormal CSF t-tau and p-tau concentrations and hippocampal atrophy predicted decline in MMSE score.

CONCLUSIONS

In subjects with MCI and evidence of amyloid pathology, the injury markers CSF t-tau and p-tau and hippocampal atrophy can predict further cognitive decline.

Analytical aspects of molecular Alzheimer’s disease biomarkers

In general, a biomarker has multiple uses such as a diagnostic tool and a method to monitor therapy. The quality of a biomarker depends on how big the difference is between, for example, patients and healthy controls, but also on the capacity of the method used to measure it (the uncertainty in the method should be much less than the difference between the groups). A good biomarker should also be specific towards a disease, allowing for differentiation between clinically related syndromes. In addition, it is of importance that the stability of the methods used is high enough to establish cut-off levels both in individual laboratories and on a global scale. In the field of Alzheimer’s disease, there are currently three cerebrospinal fluid markers that have been verified in multiple studies and the analytical aspects of measuring them will be discussed.

Cognitive correlates of cerebrospinal fluid biomarkers in frontotemporal dementia

OBJECTIVE

In this study we investigated the relationships between cerebrospinal fluid (CSF) biomarkers (tau and amyloid-β1-42 [Aβ1-42]) and cognition or behavior in patients with frontotemporal dementia (the behavioral variant, bvFTD).

METHODS

We included 58 patients with bvFTD. All patients underwent a neuropsychological assessment and lumbar puncture. Relationships between CSF biomarkers and cognition or behavior were assessed with linear regression analysis.

RESULTS

After correction for age, sex, and education, CSF tau levels were found to be negatively related to the Visual Association Test (standardized β = -0.3, P < .05), whereas CSF Aβ1-42 levels were found to be positively related to the Mini-Mental State Examination (β = 0.3, P < .05), the frontal assessment battery (β = 0.5, P < .05), and digit span backwards test (β = 0.3, P = .01). We did not find relations between CSF biomarkers and behavior (measured by the neuropsychiatric inventory). After excluding all patients with a CSF biomarker profile often seen in Alzheimer's disease (high levels of tau and low levels of Aβ1-42), we still found relations between CSF Aβ1-42 levels and Visual Association Test object naming (β = 0.4, P < .05), as well as between CSF Aβ1-42 levels and the frontal assessment battery (β = 0.5, P < .05, but there was no relation between CSF tau and cognition.

CONCLUSION

Low CSF Aβ1-42 levels are associated with worse general cognitive function and worse executive function in patients with bvFTD. Our results provide circumstantial evidence for a pathophysiological role of Aβ1-42 in bvFTD.

The Relationship between Different Assays for Detection and Quantification of Amyloid Beta 42 in Human Cerebrospinal Fluid

Alzheimer's disease (AD), which is characterized by a degeneration of neurons and their synapses, is one of the most common forms of dementia. CSF levels of amyloid β(42) (Aβ(42)) have been recognized as a strong candidate to serve as an AD biomarker. There are a number of commercial assays that are routinely employed for measuring Aβ(42); however, these assays give diverse ranges for the absolute levels of CSF Aβ(42). In order to employ CSF Aβ(42) as a biomarker across multiple laboratories, studies need to be performed to understand the relationship between the different platforms. We have analyzed CSF samples from both diseased and nondiseased subjects with two different widely used assay platforms. The results showed that different values for the levels of CSF Aβ(42) were reported, depending on the assay used. Nonetheless, both assays clearly demonstrated statistically significant differences in the levels of Aβ(42) in CSF from AD relative to age-matched controls (AMC). This paper provides essential data for establishing the relationship between these assays and provides an important step towards the validation of Aβ(42) as a biomarker for AD.

Roles of AMP-activated protein kinase in Alzheimer's disease

AMP-activated protein kinase (AMPK), a master regulator of cellular energy homeostasis and a central player in glucose and lipid metabolism, is potentially implicated in the pathogenesis of Alzheimer's disease (AD). AMPK activity decreases in AD brain, indicating decreased mitochondrial biogenesis and function. Emerging evidence demonstrates that AMPK activation is a potential target for improving perturbed brain energy metabolism that is involved in the pathogenesis of AD. The roles of AMPK in the pathogenesis of AD include β-amyloid protein (Aβ) generation and tau phosphorylation. In particular, AMPK may regulate Aβ generation through modulating neuronal cholesterol and sphingomyelin levels and through regulating APP distribution in the lipid rafts. AMPK is activated by phosphorylation of Thr-172 by LKB1 complex in response to increase in the AMP/ATP ratio and by calmodulin-dependent protein kinase kinase-beta in response to elevated Ca(2+) levels, which contributes to regulating Aβ generation. AMPK is a physiological tau kinase and can increase the phosphorylation of tau at Ser-262. AMPK can also directly phosphorylate tau at Thr-231 and Ser-396/404. Furthermore, AMPK activation decreases mTOR signaling activity to facilitate autophagy and promotes lysosomal degradation of Aβ. However, AMPK activation has non-neuroprotective property and may lead to detrimental outcomes, including Aβ generation and tau phosphorylation. Therefore, it is still unclear whether AMPK could serve a potential therapeutic target for AD, and hence, further studies will be needed to clarify the role of AMPK in AD.

In vitro and in vivo comparisons of the effects of the fruiting body and mycelium of Antrodia camphorata against amyloid β-protein-induced neurotoxicity and memory impairment

Antrodia camphorata is a particular and precious medicinal mushroom, and its fruiting body was found to provide more efficient protection from oxidative stress and inflammation than its mycelium because of its higher content of triterpenoids, total phenols, and so on. In the previous in vitro studies, the mycelium of A. camphorata is proven to provide strong neuroprotection in neuron cells and suggested to have the potential of protection against neurotoxicity of amyloid β-protein (Aβ) known as the risk factor toward Alzheimer's disease (AD) development. However, the in vivo study and the comparison study with the fruiting body have not yet been investigated. This study compared the effect of the fruiting body and mycelium of A. camphorata on alleviating the Aβ40-induced neurocytotoxicity in the in vitro Aβ-damaged neuron cell model (PC-12 cell treated with Aβ40) and memory impairment in the in vivo AD animal model induced with a continuous brain infusion of Aβ40. In the results of in vitro and in vivo studies, the fruiting body possessed stronger anti-oxidative and anti-inflammatory abilities for inhibiting neurocytotoxicity in Aβ40-treated PC-12 cells and Aβ40 accumulation in Aβ40-infused brain than mycelium. Moreover, hyperphosphorylated tau (p-tau) protein expression, known as an important AD risk factor, was suppressed by the treatment of fruiting body rather than that of mycelium in the in vitro and in vivo studies. These comparisons supported the reasons why the fruiting body resulted in a more significant improvement effect on working memory ability than mycelium in the AD rats.

Alzheimer's disease in the retina: imaging retinal aβ plaques for early diagnosis and therapy assessment

BACKGROUND

Definite Alzheimer's disease (AD) diagnosis at early stages is vital for targeting intervention, yet currently unavailable. Noninvasive detection of the pathological hallmark, amyloid-β protein (Aβ) plaques, is limited in the brain. However, the existence of Aβ plaques in the retina, possibly at presymptomatic stages, may improve early detection of AD.

OBJECTIVE

To summarize clinical and preclinical evidence showing that the retina, an accessible part of the central nervous system, displays abnormalities in AD, especially Aβ plaque pathology. The ability to monitor in vivo retinal plaque dynamics in response to immunotherapy is also assessed.

METHODS

Literature analysis of retinal AD pathology and imaging is provided. In our studies, systemic curcumin is administered to enable monitoring of retinal Aβ plaques in live APP(SWE)/PS1(Δ)(E9) transgenic mice by optical imaging.

RESULTS

Visual and retinal abnormalities, including early manifestation of retinal Aβ plaque pathology, have been documented in AD patients and animal models. In mouse models, retinal Aβ plaques accumulate with age and decrease in response to immunotherapy, consistent with brain pathology. Here, we demonstrate that retinal plaques can be individually monitored in real time following glatiramer acetate immunization.

CONCLUSION

Translation of noninvasive retinal-plaque imaging to humans could eventually facilitate early and accurate AD diagnosis and therapy assessment.

Microbleeds relate to altered amyloid-β metabolism in Alzheimer's disease

Cerebral microbleeds (MBs) may relate to amyloid in dementia. We selected 26 probable Alzheimer's disease (AD) patients with MBs, 26 age- and sex-matched AD patients without MBs, 11 vascular dementia (VaD) patients, and 22 patients with subjective complaints. We measured amyloid beta 1-42 (Aβ42) and 1-40 (Aβ40) in cerebrospinal fluid (CSF) and plasma, and blood-brain barrier (BBB) function using albumin ratios. CSF Aβ42 was lowest in AD with MBs, whereas Aβ40 was selectively decreased in VaD. In plasma, amyloid-beta was nonsignificantly elevated in VaD compared with controls. Higher albumin ratios in VaD suggested blood-brain barrier dysfunction. A MB pattern suggestive of cerebral amyloid angiopathy (CAA) related to lower CSF Aβ42, while a non-cerebral amyloid angiopathy specific MB distribution related to higher plasma Aβ40. Amyloid-beta is differentially implicated in AD with MBs and VaD. MB distribution related to different amyloid profiles, supporting distinct etiologies. Our results suggest that Aβ42 is retained in cerebrovasculature of AD patients with MBs, while in contrast, VaD patients may possibly drain amyloid.

Human Alzheimer and inflammation biomarkers after anesthesia and surgery

BACKGROUND

The prevalence of postoperative cognitive disturbance, coupled with growing in vitro, cell, and animal evidence suggesting anesthetic effects on neurodegeneration, calls for additional study of the interaction between surgical care and Alzheimer neuropathology. The authors studied human cerebrospinal fluid (CSF) biomarkers during surgery.

METHODS

Eleven patients undergoing idiopathic nasal CSF leak correction were admitted to this Institutional Review Board-approved study. Lumbar subarachnoid catheters were placed before the procedure. Anesthesia was total intravenous propofol or remifentanil or inhalational sevoflurane, depending on provider choice. CSF samples were taken after catheter placement (base), at procedure end (0 h), and then at 6, 24, and 48 h. CSF was analyzed using xMAP Luminex immunoassay (Luminex, Austin, TX).

RESULTS

Of the 11 patients (age range, 53 ± 6 yr), 8 were women; 4 received intravenous anesthesia, 6 sevoflurane, and 1 mixed. Procedures lasted 6.4 ± 2 h. Mean CSF amyloid-β(1-42) remained unchanged, but total-tau and phosphorylated-tau181P increased progressively until at least 48 h. Total-tau, phosphorylated-tau, or amyloid-β(1-42) concentrations were not different between anesthetic groups. CSF interleukin-10, S100Beta, and tumor necrosis factor α were increased similarly in both anesthetic groups at 24 h, but interleukin-6 was increased more in the inhalational group.

CONCLUSION

These data indicate a robust neuroinflammatory response, including not only the usual markers (interleukin-6, tumor necrosis factor α, interleukin-10), but also S100Beta and tau, markers of injury. The total-tau/amyloid-β(1-42) ratio increased in a pattern consistent with Alzheimer disease, largely because of an increase in total-tau rather than a decline in amyloid-β(1-42). The differences in CSF interleukin-6 concentrations suggest that anesthetic management may make a difference in neuroinflammatory response.

Circulating biomarkers of protein oxidation for Alzheimer disease: expectations within limits

Alzheimer disease (AD), the most common dementing disorder, is a multifactorial disease with complex etiology. Among different hypotheses proposed for AD one of the most corroborated is the "oxidative stress hypothesis". Although recent studies extensively demonstrated the specific oxidative modification of selected proteins in the brain of AD patients and how their dysfunction possibly correlates with the pathology, there is still an urgent need to extend these findings to peripheral tissue. So far very few studies showed oxidative damage of proteins in peripheral tissues and current findings need to be replicated. Another limit in AD research is represented by the lack of highly specific diagnostic tools for early diagnosis. For a full screening and early diagnosis, biomarkers easily detectable in biological samples, such as blood, are needed. The search of reliable biomarkers for AD in peripheral blood is a great challenge. A few studies described a set of plasma markers that differentiated AD from controls and were shown to be useful in predicting conversion from mild cognitive impairment, which is considered a prodromal stage, to AD. We review the current state of knowledge on peripheral oxidative biomarkers for AD, including proteomics, which might be useful for early diagnosis and prognosis.

The plant sterol brassicasterol as additional CSF biomarker in Alzheimer's disease

OBJECTIVE

Plant sterols (sitosterol, campesterol, stigmasterol and brassicasterol) are solely dietary-derivable sterols that are structurally very similar to cholesterol. In contrast to peripheral cholesterol, plant sterols can cross the blood-brain barrier and accumulate within mammalian brain. As an impaired function of the cerebrospinal fluid (CSF)-blood barrier is linked to neurodegenerative disorders, i.e. Alzheimer's disease (AD), we investigated whether this results in altered plant sterol concentrations in CSF.

METHOD

Applying gas chromatography/mass spectrometry analysis, plant sterol concentrations were measured in plasma and CSF of patients with AD (n = 67) and controls (n = 29). Age, gender, plasma-to-CSF albumin ratio, CSF Aβ(42) , CSF pTau, APOE4 genotype, and serum creatinine were applied as covariates in the statistical analysis for individual plant sterols in order to compare plasma and CSF plant sterol concentrations between patients with AD and controls.

RESULTS

Albumin quotient was a consistent predictor in CSF for cholesterol and methyl plant sterols campesterol and brassicasterol. Comparison of lipid parameters per diagnosis based on relevant predictors revealed significantly lower concentrations of brassicasterol (P < 0.001) in CSF of patients with AD. Binary logistic regression analysis revealed that brassicasterol improved the predictive value when added to pTau and Aβ42 in a biomarker model.

CONCLUSION

Brassicasterol might be a relevant additional biomarker in AD.

In vivo demonstration of amyloid burden in posterior cortical atrophy: a case series with PET and CSF findings

Our objective was to evaluate amyloid deposition in posterior cortical atrophy (PCA), using both cerebrospinal fluid (CSF) biomarker analysis and amyloid imaging. Five PCA patients, selected based on their neuropsychological profile and atrophic changes in posterior regions on MRI, underwent CSF analysis. CSF amyloid-beta 1-42, total tau, and phosphorylated tau at threonine 181 levels were determined. They also had positron emission tomography (PET) with Pittsburgh Compound B ([(11)C]PIB). [(11)C]PIB ratio images were assessed with visual, regional and voxel-based analyses and compared to eight typical Alzheimer's disease (AD) patients and eight controls. The biological profile in the five PCA patients, resulting from CSF and [(11)C]PIB images analysis, was consistent with AD. Individual comparisons of PCA patients' [(11)C]PIB images with the AD group with Statistical Parametric Mapping (SPM) revealed a distinctive posterior uptake in four out of the five patients showing increased amyloid deposition in occipital, temporal, and/or parietal regions. ROI group analysis showed a tendency for higher amyloid deposition in occipital and temporal regions. However, this pattern was not found with SPM group analysis when the global level of [(11)C]PIB uptake was used as a covariate. Our results indicate that amyloid burden can be demonstrated in vivo in PCA suggesting a diagnosis of AD. PCA patients may present a higher global amyloid load than AD that was not related to age at onset, disease severity, disease duration, or educational level in our study. Combined CSF and PET biomarkers seem helpful for in vivo diagnosis of this focal syndrome with underlying AD pathology.

Tau and p-tau as CSF biomarkers in dementia: a meta-analysis

BACKGROUND

To evaluate the value of total tau (tau) and phosphorylated tau (p-tau) in cerebrospinal fluid (CSF) in the differential diagnosis of dementia, more specifically: dementia with Lewy Bodies (DLB), frontotemporal lobar degeneration (FTLD), vascular dementia (VaD), and Creutzfeldt-Jacob disease (CJD).

METHODS

A systematic literature search was performed to identify studies on tau and p-tau in DLB, FTLD, VaD and CJD. Tau concentrations were compared to healthy controls and to subjects with Alzheimer's disease (AD) using random effect meta-analysis. Outcome measures were Cohen's delta, sensitivity and specificity.

RESULTS

Compared to controls, tau concentrations are moderately elevated in DLB, FTLD and VaD, while p-tau concentrations are only slightly elevated in DLB and not elevated in FTLD and VaD. Compared to AD, lower tau concentrations differentiated DLB with a sensitivity of 73% and a specificity of 90%, FTLD with sensitivity and specificity of 74%, and VaD with a sensitivity of 73% and a specificity of 86%. Relative to AD, lower p-tau values differentiated FTLD with a sensitivity of 79% and specificity of 83%, and VaD with a sensitivity of 88% and a specificity of 78%. CJD is characterized by extremely elevated tau concentrations with a sensitivity of 91% and a specificity of 98% vs. AD.

CONCLUSIONS

CSF tau concentrations in DLB, FTLD and VaD are intermediate between controls and AD patients. Overlap with both controls and AD patients results in insufficient diagnostic accuracy, and the development of more specific biomarkers for these disorders is needed. CJD is characterized by extremely increased tau values, resulting in a sensitivity and specificity that exceeds 90%.

Early-onset versus late-onset Alzheimer's disease: the case of the missing APOE ɛ4 allele

Some patients with early-onset Alzheimer's disease (AD) present with a distinct phenotype. Typically, the first and most salient characteristic of AD is episodic memory impairment. A few patients, however, present with focal cortical, non-memory symptoms, such as difficulties with language, visuospatial, or executive functions. These presentations are associated with specific patterns of atrophy and frequently with a young age at onset. Age is not, however, the only determinant of phenotype; underlying factors, especially genetic factors, seem also to affect phenotype and predispose patients to younger or older age at onset. Importantly, patients with atypical early-onset disease seldom carry the APOE ɛ4 allele, which is the most important risk factor for lowering the age of onset in patients with AD. Additionally, theAPOE ɛ4 genotype seems to predispose patients to vulnerability in the medial temporal areas, which leads to memory loss. Conversely, patients negative for the APOE ɛ4 allele and with early-onset AD are more likely to be predisposed to vulnerability of cerebral networks beyond the medial temporal lobes. Other factors are probably involved in determining the pattern of atrophy, but these are currently unknown.

Standardization of Assay Procedures for Analysis of the CSF Biomarkers Amyloid β((1-42)), Tau, and Phosphorylated Tau in Alzheimer's Disease: Report of an International Workshop

Large variation in assay performance and outcomes of CSF Aβ1-42, total Tau (Tau), and phosphorylated Tau (pTau) (at amino acid 181) levels is observed between laboratories. The aim of this study was to assess the differences in assay procedures between several experienced international laboratories, as potential sources of error. 14 groups performed the Aβ42, Tau, and pTau assays according to the guidelines of the manufacturer. Differences in analytical procedures between the laboratories were monitored. At least 23 items in assay procedures were identified that varied between the laboratories, including procedures for washing, pipetting, incubation, finishing, and sample handing. In general, the inter- and intra-assay variation between the groups was generally below 10% for all three assays. We concluded that 17 international centers that use the same assays for Aβ42, Tau and pTau on a regular basis do not uniformly adhere to the procedures recommended by the manufacturer. For harmonization of intercenter results of these biomarkers standardization of protocols is highly needed.

Batch prepared protein standards for cerebrospinal fluid (CSF) biomarkers for neurodegeneration

Immuno-assays are increasingly used for quantification of protein biomarkers for neurodegeneration. It has been proposed to use such cerebrospinal fluid (CSF) protein biomarkers as diagnostic tests for Alzheimer's disease. In two recent world-wide validation studies we found the analytical accuracy to be poor (inter-laboratory coefficient of variation, CV>10%) for CSF tau protein, CSF phospho-tau protein, CSF amyloid beta protein and the CSF neurofilament light chain protein. Retrospectively we suspected that the lack of preparation of accurate and consistent protein standards may have been one reason for the poor inter-laboratory CV. Here we confirm this hypothesis prospectively under standardised and optimised conditions. The CVs for CSF tau, CSF phospho-tau and CSF amyloid beta of individually prepared standards are 8%, 12% and 12% compared to significantly lower CVs for batch prepared standards (5%, 8%, 7%, respectively, p<0.05). This issue will need to be solved in order to ensure that the attempts to include these CSF protein biomarkers either as a diagnostic tool or a secondary outcome measure for treatment trials will be successful.

Cerebrospinal fluid biomarkers in human prion diseases

Cerebrospinal fluid (CSF) is the main component of the brain extracellular space and participates in the exchange of many biochemical products in the CNS. Consequently, CSF contains a dynamic and complex mixture of proteins that reflect the physiological or pathological state of the CNS. Changes in the CSF proteome have been described in various neurodegenerative disorders. These alterations are also thought to reflect pathological changes in the brain, and thus understanding them will contribute to a better awareness of the pathophysiology that underlies these disorders. Proteomics offers a new methodology for the analysis of pathological changes and mechanisms occurring in neurodegenerative processes and provides the possibility of novel biomarker discovery in order to supplement faster, earlier and more precise diagnosis. In general, the following criteria have to be applied in order to qualify a protein or a gene as a potential biomarker: the selected parameters have to be sensitive (able to detect the abnormalities at early stage of disease), specific (to allow differential diagnosis), reproducible with a high positive predictive value, and should allow for disease monitoring as well as a potential therapeutic response. In Creutzfeldt–Jakob disease, two major approaches have been followed that aim to detect the pathological form of the prion protein (PrPSc) in various peripheral tissues, while other approaches look for surrogate parameters that are a consequence of the neurodegenerative process. While the amount of abnormal disease-related PrPSc in CSF and blood in human transmissible spongiform encephalopathies appears to be extremely low, the development of a PrPSc-based biomarker was hampered by technical problems and detection limits. However, a variety of other proteins have been investigated in the CSF, and recently a variety of potential biomarkers have been reported that contribute to clinical diagnosis. Already established markers are 14-3-3, β-amyloid, tau-protein and phosphorylated isoforms, S100b, as well as neuron-specific enolase. Since some of these markers display certain limitations, the search continues. This review summarizes current knowledge of biomarker development in prion diseases and discusses perspectives for new approaches.