Cerebrospinal fluid amyloid-β 2-42 is decreased in Alzheimer's, but not in frontotemporal dementia

Chemical signatures delineate heterogeneous amyloid plaque populations across the Alzheimer's disease spectrum

Amyloid plaque deposition is recognized as the primary pathological hallmark of Alzheimer's disease(AD) that precedes other pathological events and cognitive symptoms. Plaque pathology represents itself with an immense polymorphic variety comprising plaques with different stages of amyloid fibrillization ranging from diffuse to fibrillar, mature plaques. The association of polymorphic Aβ plaque pathology with AD pathogenesis, clinical symptoms and disease progression remains unclear. Advanced chemical imaging tools, such as functional amyloid microscopy combined with MALDI mass spectrometry imaging (MSI), are now enhanced by deep learning algorithms. This integration allows for precise delineation of polymorphic plaque structures and detailed identification of their associated Aβ compositions. We here set out to make use of these tools to interrogate heterogenic plaque types and their associated biochemical architecture. Our findings reveal distinct Aβ signatures that differentiate diffuse plaques from fibrilized ones, with the latter showing substantially higher levels of Aβx-40. Notably, within the fibrilized category, we identified a distinct subtype known as coarse-grain plaques. Both in sAD and fAD brain tissue, coarse grain plaques contained more Aβx-40 and less Aβx-42 compared with cored plaques. The coarse grain plaques in both sAD and fAD also showed higher levels of neuritic content including paired helical filaments (PHF-1)/phosphorylated phospho Tau-immunopositive neurites. Finally, the Aβ peptide content in coarse grain plaques resembled that of vascular Aβ deposits (CAA) though with relatively higher levels of Aβ1-42 and pyroglutamated Aβx-40 and Aβx-42 species in coarse grain plaques. This is the first of its kind study on spatial in situ biochemical characterization of different plaque morphotypes demonstrating the potential of the correlative imaging techniques used that further increase the understanding of heterogeneous AD pathology. Linking the biochemical characteristics of amyloid plaque polymorphisms with various AD etiologies and toxicity mechanisms is crucial. Understanding the connection between plaque structure and disease pathogenesis can enhance our insights. This knowledge is particularly valuable for developing and advancing novel, amyloid-targeting therapeutics.

The Need for Biomarkers in the ALS-FTD Spectrum: A Clinical Point of View on the Role of Proteomics

Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are severely debilitating and progressive neurodegenerative disorders. A distinctive pathological feature of several neurodegenerative diseases, including ALS and FTD, is the deposition of aberrant protein inclusions in neuronal cells, which leads to cellular dysfunction and neuronal damage and loss. Despite this, to date, the biological process behind developing these protein inclusions must be better clarified, making the development of disease-modifying treatment impossible until this is done. Proteomics is a powerful tool to characterize the expression, structure, functions, interactions, and modifications of proteins of tissue and biological fluid, including plasma, serum, and cerebrospinal fluid. This protein-profiling characterization aims to identify disease-specific protein alteration or specific pathology-based mechanisms which may be used as markers of these conditions. Our narrative review aims to highlight the need for biomarkers and the potential use of proteomics in clinical practice for ALS-FTD spectrum disorders, considering the emerging rationale in proteomics for new drug development. Certainly, new data will emerge in the near future in this regard and support clinicians in the development of personalized medicine.

Meprin β knockout reduces brain Aβ levels and rescues learning and memory impairments in the APP/lon mouse model for Alzheimer's disease

β-Site amyloid precursor protein (APP) cleaving enzyme-1 (BACE1) is the major described β-secretase to generate Aβ peptides in Alzheimer's disease (AD). However, all therapeutic attempts to block BACE1 activity and to improve AD symptoms have so far failed. A potential candidate for alternative Aβ peptides generation is the metalloproteinase meprin β, which cleaves APP predominantly at alanine in p2 and in this study we can detect an increased meprin β expression in AD brain. Here, we report the generation of the transgenic APP/lon mouse model of AD lacking the functional Mep1b gene (APP/lon × Mep1b-/-). We examined levels of canonical and truncated Aβ species using urea-SDS-PAGE, ELISA and immunohistochemistry in brains of APP/lon mouse × Mep1b-/-. Additionally, we investigated the cognitive abilities of these mice during the Morris water maze task. Aβ1-40 and 1-42 levels are reduced in APP/lon mice when meprin β is absent. Immunohistochemical staining of mouse brain sections revealed that N-terminally truncated Aβ2-x peptide deposition is decreased in APP/lon × Mep1b-/- mice. Importantly, loss of meprin β improved cognitive abilities and rescued learning behavior impairments in APP/lon mice. These observations indicate an important role of meprin β within the amyloidogenic pathway and Aβ production in vivo.

Beta Amyloid, Tau Protein, and Neuroinflammation: An Attempt to Integrate Different Hypotheses of Alzheimer’s Disease Pathogenesis

Abstract

Alzheimer’s disease (AD) is a neurodegenerative disease that inevitably results in dementia and death. Currently, there are no pathogenetically grounded methods for the prevention and treatment of AD, and all current treatment regimens are symptomatic and unable to significantly delay the development of dementia. The accumulation of β-amyloid peptide (Aβ), which is a spontaneous, aggregation-prone, and neurotoxic product of the processing of signaling protein APP (Amyloid Precursor Protein), in brain tissues, primarily in the hippocampus and the frontal cortex, was for a long time considered the main cause of neurodegenerative changes in AD. However, attempts to treat AD based on decreasing Aβ production and aggregation did not bring significant clinical results. More and more arguments are arising in favor of the fact that the overproduction of Aβ in most cases of AD is not the initial cause, but a concomitant event of pathological processes in the course of the development of sporadic AD. The concept of neuroinflammation has come to the fore, suggesting that inflammatory responses play the leading role in the initiation and development of AD, both in brain tissue and in the periphery. The hypothesis about the key role of neuroinflammation in the pathogenesis of AD opens up new opportunities in the search for ways to treat and prevent this socially significant disease.

Infiltrating Hematogenous Macrophages Aggregate Around β-Amyloid Plaques in an Age- and Sex-Dependent Manner in a Mouse Model of Alzheimer Disease

β-Amyloid (Aβ) plaques can trigger chronic inflammation in the cellular environment that recruits infiltrating macrophages during the course of Alzheimer disease (AD). Activated macrophages release pro-inflammatory cytokines that increase neurotoxicity associated with AD. A major impediment to investigating neuroinflammation involving macrophage activity is the inability to discriminate resident microglial macrophages (mMϕ) from hematogenous macrophages (hMϕ), as they are morphologically and phenotypically similar when activated. To distinguish between mMϕ and hMϕ and to determine their respective roles in chronic inflammation associated with the progression of amyloidosis, we used lys-EGFP-ki transgenic mice that express enhanced green fluorescent protein in hMϕ, but not in mMϕ. These mice were crossed with 5XFAD mice. The offspring demonstrated robust AD pathology and enabled visual discrimination of mMϕ from hMϕ. Mutant mice demonstrated robust increases in Aβ1-42, area of Aβ plaques, gliosis and deficits in spatial learning by age 5 months. The time-course of Aβ accumulation, paralleled by the accumulation of hMϕ around Aβ plaques, was more robust in female compared with male mice and preceded behavioral changes. Thus, the accumulation of infiltrating hMϕ around Aβ plaques was age- and sex-dependent and preceded cognitive impairment.

Significance of Blood and Cerebrospinal Fluid Biomarkers for Alzheimer's Disease: Sensitivity, Specificity and Potential for Clinical Use

Alzheimer's disease (AD) is the most common type of dementia, affecting more than 5 million Americans, with steadily increasing mortality and incredible socio-economic burden. Not only have therapeutic efforts so far failed to reach significant efficacy, but the real pathogenesis of the disease is still obscure. The current theories are based on pathological findings of amyloid plaques and tau neurofibrillary tangles that accumulate in the brain parenchyma of affected patients. These findings have defined, together with the extensive neurodegeneration, the diagnostic criteria of the disease. The ability to detect changes in the levels of amyloid and tau in cerebrospinal fluid (CSF) first, and more recently in blood, has allowed us to use these biomarkers for the specific in-vivo diagnosis of AD in humans. Furthermore, other pathological elements of AD, such as the loss of neurons, inflammation and metabolic derangement, have translated to the definition of other CSF and blood biomarkers, which are not specific of the disease but, when combined with amyloid and tau, correlate with the progression from mild cognitive impairment to AD dementia, or identify patients who will develop AD pathology. In this review, we discuss the role of current and hypothetical biomarkers of Alzheimer's disease, their specificity, and the caveats of current high-sensitivity platforms for their peripheral detection.

Novel fluid biomarkers to differentiate frontotemporal dementia and dementia with Lewy bodies from Alzheimer's disease: A systematic review

RATIONALE

Frontotemporal dementia (FTD) and dementia with Lewy bodies (DLB) are two common forms of neurodegenerative dementia, subsequent to Alzheimer's disease (AD). AD is the only dementia that includes clinically validated cerebrospinal fluid (CSF) biomarkers in the diagnostic criteria. FTD and DLB often overlap with AD in their clinical and pathological features, making it challenging to differentiate between these conditions.

AIM

This systematic review aimed to identify if novel fluid biomarkers are useful in differentiating FTD and DLB from AD. Increasing the certainty of the differentiation between dementia subtypes would be advantageous clinically and in research.

METHODS

PubMed and Scopus were searched for studies that quantified and assessed diagnostic accuracy of novel fluid biomarkers in clinically diagnosed patients with FTD or DLB, in comparison to patients with AD. Meta-analyses were performed on biomarkers that were quantified in 3 studies or more.

RESULTS

The search strategy yielded 614 results, from which, 27 studies were included. When comparing bio-fluid levels in AD and FTD patients, neurofilament light chain (NfL) level was often higher in FTD, whilst brain soluble amyloid precursor protein β (sAPPβ) was higher in patients with AD. When comparing bio-fluid levels in AD and DLB patients, α-synuclein ensued heterogeneous findings, while the noradrenaline metabolite (MHPG) was found to be lower in DLB. Ratios of Aβ42/Aβ38 and Aβ42/Aβ40 were lower in AD than FTD and DLB and offered better diagnostic accuracy than raw amyloid-β (Aβ) concentrations.

CONCLUSIONS

Several promising novel biomarkers were highlighted in this review. Combinations of fluid biomarkers were more often useful than individual biomarkers in distinguishing subtypes of dementia. Considering the heterogeneity in methods and results between the studies, further validation, ideally with longitudinal prospective designs with large sample sizes and unified protocols, are fundamental before conclusions can be finalised.

Cerebrospinal Fluid Amyloid-β Subtypes in Confirmed Frontotemporal Lobar Degeneration Cases: A Pilot Study

To investigate amyloid-β (Aβ) in frontotemporal dementia (FTD), cerebrospinal fluid (CSF) Aβ38, Aβ40, and Aβ42 in frontotemporal lobar degeneration (FTLD; N = 18 genetically and/or pathologically confirmed and N = 8 FTD with concomitant amyotrophic lateral sclerosis) were compared with Alzheimer's disease (AD; pathological or Pittsburgh-compound-B Positron-emission-tomography (PIB-PET) positive; N = 25) and controls (N = 24). For all the Aβ subtypes, group difference was seen and post-hoc analysis revealed lower levels in FTLD compared to controls (p≤0.05). Aβ42/40 ratio showed no difference between FTLD and controls; however, a difference was seen between AD versus FTLD (p < 0.01). This is an intriguing finding, suggesting a possible role of Aβ in FTLD pathogenesis.

Diagnosis of Alzheimer's disease utilizing amyloid and tau as fluid biomarkers

Current technological advancements in clinical and research settings have permitted a more intensive and comprehensive understanding of Alzheimer’s disease (AD). This development in knowledge regarding AD pathogenesis has been implemented to produce disease-modifying drugs. The potential for accessible and effective therapeutic methods has generated a need for detecting this neurodegenerative disorder during early stages of progression because such remedial effects are more profound when implemented during the initial, prolonged prodromal stages of pathogenesis. The aggregation of amyloid-β (Aβ) and tau isoforms are characteristic of AD; thus, they are considered core candidate biomarkers. However, research attempting to establish the reliability of Aβ and tau as biomarkers has culminated in an amalgamation of contradictory results and theories regarding the biomarker concentrations necessary for an accurate diagnosis. In this review, we consider the capabilities and limitations of fluid biomarkers collected from cerebrospinal fluid, blood, and oral, ocular, and olfactory secretions as diagnostic tools for AD, along with the impact of the integration of these biomarkers in clinical settings. Furthermore, the evolution of diagnostic criteria and novel research findings are discussed. This review is a summary and reflection of the ongoing concerted efforts to establish fluid biomarkers as a diagnostic tool and implement them in diagnostic procedures.

Markers from body fluids could help clinicians diagnose Alzheimer’s disease before cognitive decline appears. After numerous setbacks in treating advanced Alzheimer’s, researchers are eager to identify biological indicators that facilitate earlier disease detection and interception. A review by YoungSoo Kim and colleagues at Yonsei University in South Korea, explores the promise of ‘fluid biomarkers,’ which enables diagnosis using cerebrospinal fluid (CSF), blood, oral, ocular, and olfactory fluid samples. Shifts in CSF levels of amyloid beta and tau, two proteins central to Alzheimer’s pathology, can reliably monitor at-risk individuals. Although CSF collection is unpleasant for patients, it remains more promising than blood, where current data for candidate fluid biomarkers are relatively inconclusive. In this review, investigations to discover safer, cheaper, and more reliable diagnostic tools to shift treatment from alleviation to prevention are introduced.

Correction to: Cerebrospinal fluid amyloid-β 2-42 is decreased in Alzheimer's, but not in frontotemporal dementia

The respective first and last authors of this article, Mirko Bibl and Jens Wiltfang, would like to clarify the issue of the seeming duplicate publication of a figure in two articles.

Are N- and C-terminally truncated Aβ species key pathological triggers in Alzheimer's disease?

The histopathology of Alzheimer's disease (AD) is characterized by neuronal loss, neurofibrillary tangles, and senile plaque formation. The latter results from an exacerbated production (familial AD cases) or altered degradation (sporadic cases) of 40/42-amino acid-long β-amyloid peptides (Aβ peptides) that are produced by sequential cleavages of Aβ precursor protein (βAPP) by β- and γ-secretases. The amyloid cascade hypothesis proposes a key role for the full-length Aβ42 and the Aβ40/42 ratio in AD etiology, in which soluble Aβ oligomers lead to neurotoxicity, tau hyperphosphorylation, aggregation, and, ultimately, cognitive defects. However, following this postulate, during the last decade, several clinical approaches aimed at decreasing full-length Aβ42 production or neutralizing it by immunotherapy have failed to reduce or even stabilize AD-related decline. Thus, the Aβ peptide (Aβ40/42)-centric hypothesis is probably a simplified view of a much more complex situation involving a multiplicity of APP fragments and Aβ catabolites. Indeed, biochemical analyses of AD brain deposits and fluids have unraveled an Aβ peptidome consisting of additional Aβ-related species. Such Aβ catabolites could be due to either primary enzymatic cleavages of βAPP or secondary processing of Aβ itself by exopeptidases. Here, we review the diversity of N- and C-terminally truncated Aβ peptides and their biosynthesis and outline their potential function/toxicity. We also highlight their potential as new pharmaceutical targets and biomarkers.

Cerebrospinal Fluid Biomarkers for the Differential Diagnosis between Alzheimer's Disease and Frontotemporal Lobar Degeneration: Systematic Review, HSROC Analysis, and Confounding Factors

BACKGROUND

Differential diagnosis in dementia is at present one of the main challenges both in clinical practice and research. Cerebrospinal fluid (CSF) biomarkers are included in the current diagnostic criteria of Alzheimer's disease (AD) but their clinical utility is still unclear.

OBJECTIVE

We performed a systematic review of studies analyzing the diagnostic performance of CSF Aβ42, total tau (t-tau), and phosphorylated tau (p-tau) in the discrimination between AD and frontotemporal lobar degeneration (FTLD) dementias.

METHODS

The following electronic databases were consulted until May 2016: Medline and PreMedline, EMBASE, PsycInfo, CINAHL, Cochrane Library, and CRD. For the first-time in the field, a Hierarchical Summary Receiver Operating Characteristic (HRSOC) model was applied, which avoids methodological problems of meta-analyses based on summary points of sensitivity and specificity values. We also investigated relevant confounders of CSF biomarkers' diagnostic performance such as age, disease duration, and global cognitive impairment.

RESULTS

The p-tau/Aβ42 ratio showed the best diagnostic performance. No statistically significant effects of the confounders were observed. Nonetheless, the p-tau/Aβ42 ratio may be especially indicated for younger patients. P-tau may be preferable for less cognitively impaired patients (high MMSE scores) and the t-tau/Aβ42 ratio for more cognitively impaired patients (low MMSE scores).

CONCLUSION

The p-tau/Aβ42 ratio has potential for being implemented in the clinical routine for the differential diagnosis between AD and FTLD. It is of utmost importance that future studies report information on confounders such as age, disease duration, and cognitive impairment, which should also stimulate understanding of the role of these factors in disease mechanisms and pathophysiology.

An UHPLC-MS/MS method for simultaneous quantification of human amyloid beta peptides Aβ1-38, Aβ1-40 and Aβ1-42 in cerebrospinal fluid using micro-elution solid phase extraction

Amyloid beta (Aβ) peptides in cerebrospinal fluid are extensively estimated for identification of Alzheimer's disease (AD) as diagnostic biomarkers. Unfortunately, their pervasive application is hampered by interference from Aβ propensity of self-aggregation, nonspecifically bind to surfaces and matrix proteins, and by lack of quantitive standardization. Here we report on an alternative Ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method for simultaneous measurement of human amyloid beta peptides Aβ1-38, Aβ1-40 and Aβ1-42 in cerebrospinal fluid (CSF) using micro-elution solid phase extraction (SPE). Samples were pre-processing by the mixed-mode micro-elution solid phase extraction and quantification was performed in the positive ion multiple reaction monitoring (MRM) mode using electrospray ionization. The stable-isotope labeled Aβ peptides ¹⁵N₅₁- Aβ1-38, ¹⁵N₅₃- Aβ1-40 and ¹⁵N₅₅- Aβ1-42 peptides were used as internal standards. And the artificial cerebrospinal fluid (ACSF) containing 5% rat plasma was used as a surrogate matrix for calibration curves. The quality control (QC) samples at 0.25, 2 and 15ng/mL were prepared. A "linear" regression (1/x² weighting): y=ax+b was used to fit the calibration curves over the concentration range of 0.1-20ng/mL for all three peptides. Coefficient of variation (CV) of intra-batch and inter-batch assays were all less than 6.44% for Aβ1-38, 6.75% for Aβ1-40 and 10.74% for Aβ1-42. The precision values for all QC samples of three analytes met the acceptance criteria. Extract recoveries of Aβ1-38, Aβ1-40 and Aβ1-42 were all greater than 70.78%, both in low and high QC samples. The stability assessments showed that QC samples at both low and high levels could be stable for at least 24h at 4°C, 4h at room temperature and through three freeze-thaw cycles without sacrificing accuracy or precision. And no significant carryover effect was observed. This validated UHPLC/MS/MS method was successfully applied to the quantitation of Aβ peptides in real human CSF samples. Our work may provide a reference method for simultaneous quantitation of human Aβ1-38, Aβ1-40 and Aβ1-42 from CSF.

Generation and Partial Characterization of Rabbit Monoclonal Antibody to Amyloid-β Peptide 1-37 (Aβ37)

Secreted soluble amyloid-β 1-37 (Aβ37) peptide is one of the prominent Aβ forms next to Aβ40, and is found in cerebrospinal fluid (CSF) and blood. Recent studies have shown the importance of quantitation of CSF Aβ37 levels in combination with Aβ38, Aβ40, and Aβ42 to support the diagnosis of patients with probable Alzheimer's disease (AD), and the value of antibody to Aβ37 to facilitate drug discovery studies. However, the availability of reliable and specific monoclonal antibody to Aβ37 is very limited. Our aims were: 1) to generate and partially characterize rabbit monoclonal antibody (RabmAb) to Aβ37, and 2) to determine whether the antibody detects changes in Aβ37 levels produced by a γ-secretase modulator (GSM). Our generated RabmAb to Aβ37 was found to be specific to Aβ37, since it did not react with Aβ36, Aβ38, Aβ39, Aβ40, and Aβ42 in an ELISA or immunoblotting. The epitope of the antibody was contained in the seven C-terminal residues of Aβ37. The antibody was sensitive enough to measure CSF and plasma Aβ37 levels in ELISA. Immunohistological studies showed the presence of Aβ37-positive deposits in the brain of AD, and Down syndrome persons diagnosed with AD. Our studies also showed that the antibody detected Aβ37 increases in CSF and brains of rodents following treatment with a GSM. Thus, our antibody can be widely applied to AD research, and in a panel based approach it may have potential to support the diagnosis of probable AD, and in testing the effect of GSMs to target AD.

Selecting Aβ isoforms for an Alzheimer's disease cerebrospinal fluid biomarker panel

Although the core cerebrospinal fluid Alzheimer's disease (AD) biomarkers amyloid-β (Aβ_1-42) and tau show a high diagnostic accuracy, there are still limitations due to overlap in the biomarker levels with other neurodegenerative and dementia disorders. During Aβ_1-42 production and clearance in the brain, several other Aβ peptides and amyloid precursor protein fragments are formed that could potentially serve as biomarkers for this ongoing disease process. Therefore, this review will present the current status of the findings for amyloid precursor protein and Aβ peptide isoforms in AD and clinically related disorders. In conclusion, adding new Aβ isoforms to the AD biomarker panel may improve early differential diagnostic accuracy and increase the cerebrospinal fluid biomarker concordance with AD neuropathological findings in the brain.

The Metalloprotease Meprin β Is an Alternative β-Secretase of APP

The membrane bound metalloprotease meprin β is important for collagen fibril assembly in connective tissue formation and for the detachment of the intestinal mucus layer for proper barrier function. Recent proteomic studies revealed dozens of putative new substrates of meprin β, including the amyloid precursor protein (APP). It was shown that APP is cleaved by meprin β in distinct ways, either at the β-secretase site resulting in increased levels of Aβ peptides, or at the N-terminus releasing 11 kDa, and 20 kDa peptide fragments. The latter event was discussed to be rather neuroprotective, whereas the ectodomain shedding of APP by meprin β reminiscent to BACE-1 is in line with the amyloid hypothesis of Alzheimer's disease, promoting neurodegeneration. The N-terminal 11 kDa and 20 kDa peptide fragments represent physiological cleavage products, since they are found in human brains under different diseased or non-diseased states, whereas these fragments are completely missing in brains of meprin β knock-out animals. Meprin β is not only a sheddase of adhesion molecules, such as APP, but was additionally demonstrated to cleave within the prodomain of ADAM10. Activated ADAM10, the α-secretase of APP, is then able to shed meprin β from the cell surface thereby abolishing the β-secretase activity. All together meprin β seems to be a novel player in APP processing events, even influencing other enzymes involved in APP cleavage.

Insulin Resistance is Associated with Higher Cerebrospinal Fluid Tau Levels in Asymptomatic APOEɛ4 Carriers

BACKGROUND

Insulin resistance (IR) is linked with the occurrence of pathological features observed in Alzheimer's disease (AD), including neurofibrillary tangles and amyloid plaques. However, the extent to which IR is associated with AD pathology in the cognitively asymptomatic stages of preclinical AD remains unclear.

OBJECTIVE

To determine the extent to which IR is linked with amyloid and tau pathology in late-middle-age.

METHOD

Cerebrospinal fluid (CSF) samples collected from 113 participants enrolled in the Wisconsin Registry for Alzheimer's Prevention study (mean age = 60.6 years), were assayed for AD-related markers of interest: Aβ₄₂, P-Tau181, and T-Tau. IR was determined using the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR). Linear regression was used to test the effect of IR, and APOEɛ4, on tau and amyloid pathology. We hypothesized that greater IR would be associated with higher CSF P-Tau181 and T-Tau, and lower CSF Aβ₄₂.

RESULTS

No significant main effects of HOMA-IR on P-Tau181, T-Tau, or Aβ₄₂ were observed; however, significant interactions were observed between HOMA-IR and APOEɛ4 on CSF markers related to tau. Among APOEɛ4 carriers, higher HOMA-IR was associated with higher P-Tau181 and T-Tau. Among APOEɛ4 non-carriers, HOMA-IR was negatively associated with P-Tau181 and T-Tau. We found no effects of IR on Aβ₄₂ levels in CSF.

CONCLUSION

IR among asymptomatic APOEɛ4 carriers was associated with higher P-Tau181 and T-Tau in late-middle age. The results suggest that IR may contribute to tau-related neurodegeneration in preclinical AD. The findings may have implications for developing prevention strategies aimed at modifying IR in mid-life.

CSF Aβ42/Aβ40 and Aβ42/Aβ38 ratios: better diagnostic markers of Alzheimer disease

Objective

The diagnostic accuracy of cerebrospinal fluid (CSF) biomarkers for Alzheimer's disease (AD) must be improved before widespread clinical use. This study aimed to determine whether CSF Aβ42/Aβ40 and Aβ42/Aβ38 ratios are better diagnostic biomarkers of AD during both predementia and dementia stages in comparison to CSF Aβ42 alone.

Methods

The study comprised three different cohorts (n = 1182) in whom CSF levels of Aβ42, Aβ40, and Aβ38 were assessed. CSF Aβs were quantified using three different immunoassays (Euroimmun, Meso Scale Discovery, Quanterix). As reference standard, we used either amyloid (¹⁸F‐flutemetamol) positron emission tomography (PET) imaging (n = 215) or clinical diagnosis (n = 967) of well‐characterized patients.

Results

When using three different immunoassays in cases with subjective cognitive decline and mild cognitive impairment, the CSF Aβ42/Aβ40 and Aβ42/Aβ38 ratios were significantly better predictors of abnormal amyloid PET than CSF Aβ42. Lower Aβ42, Aβ42/Aβ40, and Aβ42/Aβ38 ratios, but not Aβ40 and Aβ38, correlated with smaller hippocampal volumes measured by magnetic resonance imaging. However, lower Aβ38, Aβ40, and Aβ42, but not the ratios, correlated with non‐AD‐specific subcortical changes, that is, larger lateral ventricles and white matter lesions. Further, the Aβ42/Aβ40 and Aβ42/Aβ38 ratios showed increased accuracy compared to Aβ42 when distinguishing AD from dementia with Lewy bodies or Parkinson's disease dementia and subcortical vascular dementia, where all Aβs (including Aβ42) were decreased.

Interpretation

The CSF Aβ42/Aβ40 and Aβ42/Aβ38 ratios are significantly better than CSF Aβ42 to detect brain amyloid deposition in prodromal AD and to differentiate AD dementia from non‐AD dementias. The ratios reflect AD‐type pathology better, whereas decline in CSF Aβ42 is also associated with non‐AD subcortical pathologies. These findings strongly suggest that the ratios rather than CSF Aβ42 should be used in the clinical work‐up of AD.

Diagnostic value of cerebrospinal fluid Aβ ratios in preclinical Alzheimer's disease

INTRODUCTION

In this study of preclinical Alzheimer's disease (AD) we assessed the added diagnostic value of using cerebrospinal fluid (CSF) Aβ ratios rather than Aβ42 in isolation for detecting individuals who are positive on amyloid positron emission tomography (PET).

METHODS

Thirty-eight community-recruited cognitively intact older adults (mean age 73, range 65-80 years) underwent (18)F-flutemetamol PET and CSF measurement of Aβ1-42, Aβ1-40, Aβ1-38, and total tau (ttau). (18)F-flutemetamol retention was quantified using standardized uptake value ratios in a composite cortical region (SUVRcomp) with reference to cerebellar grey matter. Based on a prior autopsy validation study, the SUVRcomp cut-off was 1.57. Sensitivities, specificities and cut-offs were defined based on receiver operating characteristic analysis with CSF analytes as variables of interest and (18)F-flutemetamol positivity as the classifier. We also determined sensitivities and CSF cut-off values at fixed specificities of 90 % and 95 %.

RESULTS

Seven out of 38 subjects (18 %) were positive on amyloid PET. Aβ42/ttau, Aβ42/Aβ40, Aβ42/Aβ38, and Aβ42 had the highest accuracy to identify amyloid-positive subjects (area under the curve (AUC) ≥ 0.908). Aβ40 and Aβ38 had significantly lower discriminative power (AUC = 0.571). When specificity was fixed at 90 % and 95 %, Aβ42/ttau had the highest sensitivity among the different CSF markers (85.71 % and 71.43 %, respectively). Sensitivity of Aβ42 alone was significantly lower under these conditions (57.14 % and 42.86 %, respectively).

CONCLUSION

For the CSF-based definition of preclinical AD, if a high specificity is required, our data support the use of Aβ42/ttau rather than using Aβ42 in isolation.

Cerebrospinal fluid Aβ40 is similarly reduced in patients with Frontotemporal Lobar Degeneration and Alzheimer's Disease

Cerebrospinal fluid (CSF) biomarkers have been increasingly studied for dementia diagnosis, however the accuracy to distinguish between different forms of dementia is still unsatisfactory. In this study, the added value of another CSF Aβ-peptide (Aβ40), along with the core CSF markers t-Tau, p-Tau, and Aβ42, in the discrimination between two large dementia groups of Frontotemporal Lobar Degeneration (FTLD; n=107), Alzheimer's Disease (AD; n=107) and non-demented subjects (n=33) was evaluated. In FTLD, t-Tau and p-Tau were significantly increased in relation to controls, but lower than in AD, while Aβ42 was similar in FTLD and controls, but higher than in AD. Equally reduced Aβ40 levels were seen in both dementia groups, and therefore the combination of Aβ40 with core CSF biomarkers optimally discriminated FTLD and AD patients from controls. Aβ42 and t-Tau were selected as the best biomarker subset to differentiate FTLD from AD, with no added value of Aβ40 to the model. Diagnostic accuracy between FTLD and AD was still sub-optimal, with a significant percentage (23%) of FTLD patients, in particularly women, carrying an ApoE-ε4 allele, showing a CSF-AD biomarkers profile. Although CSF Aβ40 does not appear to have an additional value in the distinction between FTLD and AD, it increases the discrimination between subjects with dementia from controls. A CSF-AD biomarker profile can be seen in patients with a clinical phenotype of FTLD, reinforcing the need for autopsy confirmation.

Neutral polymers as coatings for high resolution electrophoretic separation of Aβ peptides on glass microchips

This study reports a comparison of the performances of two neutral polymers, poly ethylene-oxide (PEO) and poly(dimethylacrylamide-co-allyl glycidyl ether) (EpDMA), in glass microchips to achieve zone electrophoresis separation of several truncated forms of beta amyloid (Aβ) peptides, sharing very similar structures. The peptides were derivatized by FluoProbes 488 NHS to allow their fluorescence detection. Two protocols based either on PEO or EpDMA led to good pH stabilities in addition to a significant reduction of the electroosmotic flow. These two polymer coatings allowed repeatable analyses and high resolution for the simultaneous analysis of three Aβ peptides, Aβ 1-38, Aβ 1-40 and Aβ 1-42, considered as potential biomarkers of Alzheimer's disease. A recovery study showed that EpDMA was superior in reducing the adsorption of the Aβ peptides on the coated inner wall. Finally, the separation method relying on the EpDMA coated microchips was validated as linear using a calibration curve and the LOD was estimated to be close to 200 nM. Despite very short migration distances, different N-terminal or C-terminal truncated Aβ peptides, corresponding to promising biomarker combinations for the future diagnostic, were fully resolved. The method was successfully applied to detect these peptides in spiked cerebrospinal fluid and has provided a first achievement towards the development of a microsystem that would integrate preconcentration and separation steps.

Supportive CSF biomarker evidence to enhance the National Institute on Aging-Alzheimer's Association criteria for diagnosis of Alzheimer's type dementia--a study from Southern India

The present study was undertaken to validate the measurement of biomarkers as a supplement to the latest diagnostic criteria for Alzheimer disease (AD) dementia by National Institute on Aging-Alzheimer's Association (NIA-AA) work group using a sample attending a tertiary care center in Southern India. A total of 20 subjects diagnosed clinically as Alzheimer's dementia according to the NIA-AA criteria for AD were included in the study. The CSF biomarkers Aβ42, t-tau, and p-tau181 were assessed. The biomarker results were compared among mild and moderate to severe AD as defined in the NIA-AA work group guidelines. The results revealed that the amount of Aβ42 was very low in all the 20 samples (<50pg/ml) collected from mild AD cases with CDR score of 1 (n=8), and moderate to severe AD cases with CDR >1 (n=12). t-tau and p-tau levels were in the range of 39.45±5.09pg/ml and 13.06±7.32pg/ml for CDR 1 group. t-tau and p-tau levels were in the range of 49.9±11.28pg/ml and 33.94±15.13pg/ml for moderate to severe cases. Analysis of the data revealed statistically significant differences in the p-tau/t-tau ratio and p-tau/Aβ ratio between CDR 1and CDR >1 AD cases (p<0.001) suggesting that p-tau/t-tau and p-tau/Aβ ratio are good indicators of severity of dementia with discriminative value in differentiating mild AD from moderate to severe AD.

Magneto-immunocapture with on-bead fluorescent labeling of amyloid-β peptides: towards a microfluidized-bed-based operation

Novel combination of Magneto-immunocapture and on-beads fluorescent labeling of Aβ peptides for their sensitive determination in cerebro spinal fluid samples.

Cerebrospinal fluid proteomics and protein biomarkers in frontotemporal lobar degeneration: Current status and future perspectives

Frontotemporal lobar degeneration (FTLD) comprises a spectrum of rare neurodegenerative diseases with an estimated prevalence of 15-22 cases per 100,000 persons including the behavioral variant of frontotemporal dementia (bvFTD), progressive non-fluent aphasia (PNFA), semantic dementia (SD), FTD with motor neuron disease (FTD-MND), progressive supranuclear palsy (PSP) and corticobasal syndrome (CBS). The pathogenesis of the diseases is still unclear and clinical diagnosis of FTLD is hampered by overlapping symptoms within the FTLD subtypes and with other neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). Intracellular protein aggregates in the brain are a major hallmark of FTLD and implicate alterations in protein metabolism or function in the disease's pathogenesis. Cerebrospinal fluid (CSF) which surrounds the brain can be used to study changes in neurodegenerative diseases and to identify disease-related mechanisms or neurochemical biomarkers for diagnosis. In the present review, we will give an overview of the current literature on proteomic studies in CSF of FTLD patients. Reports of targeted and unbiased proteomic approaches are included and the results are discussed in regard of their informative value about disease pathology and the suitability to be used as diagnostic biomarkers. Finally, we will give some future perspectives on CSF proteomics and a list of candidate biomarkers which might be interesting for validation in further studies. This article is part of a Special Issue entitled: Neuroproteomics: Applications in neuroscience and neurology.

Plasma phosphorylated TDP-43 levels are elevated in patients with frontotemporal dementia carrying a C9orf72 repeat expansion or a GRN mutation

OBJECTIVES

About a half of patients with frontotemporal dementia (FTD) has deposition of phosphorylated TDP-43 protein (pTDP-43) in the brain. We studied pTDP-43 and total TDP-43 levels in plasma and cerebrospinal fluid (CSF) in healthy controls and patients with FTD, including those carrying a repeat expansion in the C9orf72 gene or a mutation in GRN.

METHODS

We included 88 plasma samples of 10 C9orf72 expansion carriers, 5 GRN mutation carriers, 51 patients with FTD without a known mutation and 22 healthy controls. We also obtained CSF samples from 25 patients with FTD (2 with C9orf72 expansion and 3 with a GRN mutation) and 22 healthy controls. We measured pTDP-43 and total TDP-43 levels using sandwich ELISA.

RESULTS

Patients carrying the C9orf72 repeat expansion or a GRN mutation had significantly higher plasma and CSF levels of pTDP-43 than the remaining patients with FTD (p<0.05). In addition, plasma pTDP-43 levels were higher in patients with FTD carrying a C9orf72 expansion or GRN mutations than in healthy controls (p<0.05).

CONCLUSIONS

Our study shows that plasma pTDP-43 levels may be increased in some genetic forms of FTD known to be associated with TDP-43 proteinopathies.

Truncated and modified amyloid-beta species

Alzheimer’s disease pathology is closely connected to the processing of the amyloid precursor protein (APP) resulting in the formation of a variety of amyloid-beta (Aβ) peptides. They are found as insoluble aggregates in senile plaques, the histopathological hallmark of the disease. These peptides are also found in soluble, mostly monomeric and dimeric, forms in the interstitial and cerebrospinal fluid. Due to the combination of several enzymatic activities during APP processing, Aβ peptides exist in multiple isoforms possessing different N-termini and C-termini. These peptides include, to a certain extent, part of the juxtamembrane and transmembrane domain of APP. Besides differences in size, post-translational modifications of Aβ – including oxidation, phosphorylation, nitration, racemization, isomerization, pyroglutamylation, and glycosylation – generate a plethora of peptides with different physiological and pathological properties that may modulate disease progression.

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.

Meta-Review of CSF Core Biomarkers in Alzheimer's Disease: The State-of-the-Art after the New Revised Diagnostic Criteria

BACKGROUND

Current research criteria for Alzheimer's disease (AD) include cerebrospinal fluid (CSF) biomarkers into the diagnostic algorithm. However, spreading their use to the clinical routine is still questionable.

OBJECTIVE

To provide an updated, systematic and critical review on the diagnostic utility of the CSF core biomarkers for AD.

DATA SOURCES

MEDLINE, PreMedline, EMBASE, PsycInfo, CINAHL, Cochrane Library, and CRD.

ELIGIBILITY CRITERIA

(1a) Systematic reviews with meta-analysis; (1b) Primary studies published after the new revised diagnostic criteria; (2) Evaluation of the diagnostic performance of at least one CSF core biomarker.

RESULTS

The diagnostic performance of CSF biomarkers is generally satisfactory. They are optimal for discriminating AD patients from healthy controls. Their combination may also be suitable for mild cognitive impairment (MCI) prognosis. However, CSF biomarkers fail to distinguish AD from other forms of dementia.

LIMITATIONS

(1) Use of clinical diagnosis as standard instead of pathological postmortem confirmation; (2) variability of methodological aspects; (3) insufficiently long follow-up periods in MCI studies; and (4) lower diagnostic accuracy in primary care compared with memory clinics.

CONCLUSION

Additional work needs to be done to validate the application of CSF core biomarkers as they are proposed in the new revised diagnostic criteria. The use of CSF core biomarkers in clinical routine is more likely if these limitations are overcome. Early diagnosis is going to be of utmost importance when effective pharmacological treatment will be available and the CSF core biomarkers can also be implemented in clinical trials for drug development.

Biomarkers of Alzheimer's disease: the present and the future

A paradigm shift has occurred in the last ten years in the diagnostic field of Alzheimer's disease (AD). Scientific thought has enriched the concept of AD as a pathophysiological continuum and emphasized contribution of biological, morphological and functional brain imaging biomarkers for diagnosis, in particular during the early stages of the disease. We address here the present and the future of these biological biomarkers. Most of them are linked to the pathophysiological lesions of the Alzheimer process: aggregates of hyperphosphorylated tau proteins, also called neurofibrillary tangles (NFT), and extracellular deposit of amyloid-beta peptides (Aβ), also called senile plaques. The detection in the cerebrospinal fluid (CSF) of tau and Aβ represents the current diagnostic practice of AD. Improvement for a more accurate and earlier biological diagnosis is however expected using a new generation of biomarkers, mostly in relation with tau and Aβ metabolism.

CSF Aβ1-42 combined with neuroimaging biomarkers in the early detection, diagnosis and prediction of Alzheimer's disease

The development of validated, qualified, and standardized biomarkers for Alzheimer's disease (AD) that allow for an early presymptomatic diagnosis and discrimination (classification) from other types of dementia and neurodegenerative diseases is warranted to accelerate the successful development of novel disease-modifying therapies. Here, we focus on the value of the 42-residue-long amyloid β isoform (Aβ1-42) peptide in the cerebrospinal fluid as the core, feasible neurobiochemical marker for the amyloidogenic mechanisms in early-onset familial and late-onset sporadic AD. We discuss the role and use of Aβ1-42 in combination with evolving neuroimaging biomarkers in AD detection and diagnosis. Multimodal neuroimaging techniques, directly providing structural-functional-metabolic aspects of brain pathophysiology, are supportive to predict and monitor the progression of the disease. Advances in multimodal neuroimaging provide new insights into brain organization and enable the detection of specific proteins and/or protein aggregates associated with AD. The combination of biomarkers from different methodologies is believed to be of incrementally added risk-value to accurately identify asymptomatic and prodromal individuals who will likely progress to dementia and represent rational biomarker candidates for preventive and symptomatic pharmacological intervention trials.

Cerebrospinal fluid biomarkers for differentiation of frontotemporal lobar degeneration from Alzheimer's disease

Accurate ante mortem diagnosis in frontotemporal lobar degeneration (FTLD) is crucial to the development and implementation of etiology-based therapies. Several neurodegenerative disease-associated proteins, including the major protein constituents of inclusions in Alzheimer's disease (AD) associated with amyloid-beta (Aβ(1-42)) plaque and tau neurofibrillary tangle pathology, can be measured in cerebrospinal fluid (CSF) for diagnostic applications. Comparative studies using autopsy-confirmed samples suggest that CSF total-tau (t-tau) and Aβ(1-42) levels can accurately distinguish FTLD from AD, with a high t-tau to Aβ(1-42) ratio diagnostic of AD; however, there is also an urgent need for FTLD-specific biomarkers. These analytes will require validation in large autopsy-confirmed cohorts and face challenges of standardization of within- and between-laboratory sources of error. In addition, CSF biomarkers with prognostic utility and longitudinal study of CSF biomarker levels over the course of disease are also needed. Current goals in the field include identification of analytes that are easily and reliably measured and can be used alone or in a multi-modal approach to provide an accurate prediction of underlying neuropathology for use in clinical trials of disease modifying treatments in FTLD. To achieve these goals it will be of the utmost importance to view neurodegenerative disease, including FTLD, as a clinicopathological entity, rather than exclusively a clinical syndrome.