Association of Plasma Total Tau Level With Cognitive Decline and Risk of Mild Cognitive Impairment or Dementia in the Mayo Clinic Study on Aging

Dysregulation of Exosome Cargo by Mutant Tau Expressed in Human-induced Pluripotent Stem Cell (iPSC) Neurons Revealed by Proteomics Analyses

Accumulation and propagation of hyperphosphorylated Tau (p-Tau) is a common neuropathological hallmark associated with neurodegeneration of Alzheimer's disease (AD), frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), and related tauopathies. Extracellular vesicles, specifically exosomes, have recently been demonstrated to participate in mediating Tau propagation in brain. Exosomes produced by human induced pluripotent stem cell (iPSC)-derived neurons expressing mutant Tau (mTau), containing the P301L and V337M Tau mutations of FTDP-17, possess the ability to propagate p-Tau pathology after injection into mouse brain. To gain an understanding of the mTau exosome cargo involved in Tau pathogenesis, these pathogenic exosomes were analyzed by proteomics and bioinformatics. The data showed that mTau expression dysregulates the exosome proteome to result in 1) proteins uniquely present only in mTau, and not control exosomes, 2) the absence of proteins in mTau exosomes, uniquely present in control exosomes, and 3) shared proteins which were significantly upregulated or downregulated in mTau compared with control exosomes. Notably, mTau exosomes (not control exosomes) contain ANP32A (also known as I1PP2A), an endogenous inhibitor of the PP2A phosphatase which regulates the phosphorylation state of p-Tau. Several of the mTau exosome-specific proteins have been shown to participate in AD mechanisms involving lysosomes, inflammation, secretases, and related processes. Furthermore, the mTau exosomes lacked a substantial portion of proteins present in control exosomes involved in pathways of localization, vesicle transport, and protein binding functions. The shared proteins present in both mTau and control exosomes represented exosome functions of vesicle-mediated transport, exocytosis, and secretion processes. These data illustrate mTau as a dynamic regulator of the biogenesis of exosomes to result in acquisition, deletion, and up- or downregulation of protein cargo to result in pathogenic mTau exosomes capable of in vivo propagation of p-Tau neuropathology in mouse brain.

A longitudinal examination of plasma neurofilament light and total tau for the clinical detection and monitoring of Alzheimer's disease

We examined baseline and longitudinal associations between plasma neurofilament light (NfL) and total tau (t-tau), and the clinical presentation of Alzheimer's disease (AD). A total of 579 participants (238, normal cognition [NC]; 185, mild cognitive impairment [MCI]; 156, AD dementia) had baseline blood draws; 82% had follow-up evaluations. Plasma samples were analyzed for NfL and t-tau using Simoa technology. Baseline plasma NfL was higher in AD dementia than MCI (standardized mean difference = 0.55, 95% CI: 0.37-0.73) and NC (standardized mean difference = 0.68, 95% CI: 0.49-0.88), corresponded to Clinical Dementia Rating scores (OR = 1.94, 95% CI: 1.35-2.79]), and correlated with all neuropsychological tests (r's = 0.13-0.42). Longitudinally, NfL did not predict diagnostic conversion but predicted decline on 3/10 neuropsychological tests. Baseline plasma t-tau was higher in AD dementia than NC with a small effect (standardized mean difference = 0.33, 95% CI: 0.10-0.57) but not MCI. t-tau did not statistically significant predict any longitudinal outcomes. Plasma NfL may be useful for the detection of AD dementia and monitoring of disease progression. In contrast, there was minimal evidence in support of plasma t-tau.

Future avenues for Alzheimer's disease detection and therapy: liquid biopsy, intracellular signaling modulation, systems pharmacology drug discovery

When Alzheimer's disease (AD) disease-modifying therapies will be available, global healthcare systems will be challenged by a large-scale demand for clinical and biological screening. Validation and qualification of globally accessible, minimally-invasive, and time-, cost-saving blood-based biomarkers need to be advanced. Novel pathophysiological mechanisms (and related candidate biomarkers) - including neuroinflammation pathways (TREM2 and YKL-40), axonal degeneration (neurofilament light chain protein), synaptic dysfunction (neurogranin, synaptotagmin, α-synuclein, and SNAP-25) - may be integrated into an expanding pathophysiological and biomarker matrix and, ultimately, integrated into a comprehensive blood-based liquid biopsy, aligned with the evolving ATN + classification system and the precision medicine paradigm. Liquid biopsy-based diagnostic and therapeutic algorithms are increasingly employed in Oncology disease-modifying therapies and medical practice, showing an enormous potential for AD and other brain diseases as well. For AD and other neurodegenerative diseases, newly identified aberrant molecular pathways have been identified as suitable therapeutic targets and are currently investigated by academia/industry-led R&D programs, including the nerve-growth factor pathway in basal forebrain cholinergic neurons, the sigma1 receptor, and the GTPases of the Rho family. Evidence for a clinical long-term effect on cognitive function and brain health span of cholinergic compounds, drug candidates for repositioning programs, and non-pharmacological multidomain interventions (nutrition, cognitive training, and physical activity) is developing as well. Ultimately, novel pharmacological paradigms, such as quantitative systems pharmacology-based integrative/explorative approaches, are gaining momentum to optimize drug discovery and accomplish effective pathway-based strategies for precision medicine. This article is part of the special issue on 'The Quest for Disease-Modifying Therapies for Neurodegenerative Disorders'.

Serum tau levels are increased in patients with hyperthyroidism

Hyperthyroidism may cause cognitive decline and increases the risk of Alzheimer's disease (AD), the major form of dementia; however, the underlying mechanism of this relationship is unclear. AD is associated with increased serum levels of tau. In this study, we investigated the relationship between serum thyroid hormones (THs) and tau. Fifty participants diagnosed with hyperthyroidism and fifty euthyroid counterparts were included and received clinical examinations. Serum concentrations of thyroid-stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3) and tau protein were assessed. The total tau protein level was significantly higher in hyperthyroidism participants than in their euthyroid counterparts. The level of circulating total tau had a significant positive association with the serum concentrations of FT3 and FT4. Total tau level was increased in the low TSH group and the serum THs decreased with the increase of age. These findings reveal that peripheral THs are associated with the serum concentration of tau, which may be involved in the pathogenesis of AD, suggesting a potential therapeutic target of AD via hyperthyroidism therapy.

An update on blood-based biomarkers for non-Alzheimer neurodegenerative disorders

Cerebrospinal fluid analyses and neuroimaging can identify the underlying pathophysiology at the earliest stage of some neurodegenerative disorders, but do not have the scalability needed for population screening. Therefore, a blood-based marker for such pathophysiology would have greater utility in a primary care setting and in eligibility screening for clinical trials. Rapid advances in ultra-sensitive assays have enabled the levels of pathological proteins to be measured in blood samples, but research has been predominantly focused on Alzheimer disease (AD). Nonetheless, proteins that were identified as potential blood-based biomarkers for AD, for example, amyloid-β, tau, phosphorylated tau and neurofilament light chain, are likely to be relevant to other neurodegenerative disorders that involve similar pathological processes and could also be useful for the differential diagnosis of clinical symptoms. This Review outlines the neuropathological, clinical, molecular imaging and cerebrospinal fluid features of the most common neurodegenerative disorders outside the AD continuum and gives an overview of the current status of blood-based biomarkers for these disorders.

Blood-based systems biology biomarkers for next-generation clinical trials in Alzheimer's disease

Alzheimer's disease (AD)-a complex disease showing multiple pathomechanistic alterations-is triggered by nonlinear dynamic interactions of genetic/epigenetic and environmental risk factors, which, ultimately, converge into a biologically heterogeneous disease. To tackle the burden of AD during early preclinical stages, accessible blood-based biomarkers are currently being developed. Specifically, next-generation clinical trials are expected to integrate positive and negative predictive blood-based biomarkers into study designs to evaluate, at the individual level, target druggability and potential drug resistance mechanisms. In this scenario, systems biology holds promise to accelerate validation and qualification for clinical trial contexts of use-including proof-of-mechanism, patient selection, assessment of treatment efficacy and safety rates, and prognostic evaluation. Albeit in their infancy, systems biology-based approaches are poised to identify relevant AD "signatures" through multifactorial and interindividual variability, allowing us to decipher disease pathophysiology and etiology. Hopefully, innovative biomarker-drug codevelopment strategies will be the road ahead towards effective disease-modifying drugs.
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Diagnostic value of plasma phosphorylated tau181 in Alzheimer's disease and frontotemporal lobar degeneration

With the potential development of new disease-modifying Alzheimer's disease (AD) therapies, simple, widely available screening tests are needed to identify which individuals, who are experiencing symptoms of cognitive or behavioral decline, should be further evaluated for initiation of treatment. A blood-based test for AD would be a less invasive and less expensive screening tool than the currently approved cerebrospinal fluid or amyloid β positron emission tomography (PET) diagnostic tests. We examined whether plasma tau phosphorylated at residue 181 (pTau181) could differentiate between clinically diagnosed or autopsy-confirmed AD and frontotemporal lobar degeneration. Plasma pTau181 concentrations were increased by 3.5-fold in AD compared to controls and differentiated AD from both clinically diagnosed (receiver operating characteristic area under the curve of 0.894) and autopsy-confirmed frontotemporal lobar degeneration (area under the curve of 0.878). Plasma pTau181 identified individuals who were amyloid β-PET-positive regardless of clinical diagnosis and correlated with cortical tau protein deposition measured by 18F-flortaucipir PET. Plasma pTau181 may be useful to screen for tau pathology associated with AD.

Assessment of Plasma Total Tau Level as a Predictive Biomarker for Dementia and Related Endophenotypes

Importance

Blood-based biomarkers have the potential to improve the identification of persons with the greatest dementia risk for inclusion in dementia prevention trials through low-cost and minimally invasive screening.

Objective

To investigate the use of plasma total tau as a blood biomarker for dementia and related endophenotypes.

Design, Setting, and Participants

This prospective cohort study used data from the US community-based Framingham Heart Study with replication in the Memento study, a multicenter cohort of persons with mild cognitive impairment or subjective cognitive complaints recruited from memory clinics across France. Total tau levels were measured from stored plasma samples in Framingham Heart Study participants during 2004 to 2011. Dementia follow-up occurred across a median of 6 years (interquartile range, 5-8 years) for persons 65 years and older who were dementia free at baseline. Plasma and/or cerebrospinal fluid samples were obtained from Memento study participants from April 19, 2011, to June 22, 2016. Dementia follow-up took place over a median of 4 years (interquartile range, 3-5 years). Data analysis was performed from January to November 2018.

Exposures

Plasma total tau level measured using single-molecule array technology.

Main Outcomes and Measures

Incidence of dementia of any cause (all dementia) and dementia due to clinical Alzheimer disease (AD dementia).

Results

Among the 1453 participants in the Framingham dementia study sample, the mean (SD) age was 75 (7) years; 792 (54.5%) were female. Among the 367 individuals in the replication cohort, the mean (SD) age was 69 (9) years; 217 (59.1%) were female. Of 134 cases of incident all dementia in the Framingham sample, 105 were AD dementia. After adjustment for age and sex, each SD unit increase in the log of plasma total tau level was associated with a 35% increase in AD dementia risk (hazard ratio [HR], 1.35; 95% CI, 1.10-1.67). The addition of plasma total tau to a model including age and sex improved the stratification of participants for risk of AD dementia (net reclassification improvement, 0.382; 95% CI, 0.030-0.716). Higher plasma total tau level was associated with poorer cognition across 7 cognitive tasks (P < .05) and smaller hippocampi (hippocampal volume: β [SE] = 0.002 [0.001]; P = .003) as well as neurofibrillary tangles (β [SE] = 0.95 [0.45]; P = .04) and microinfarcts (odds ratio, 3.04; 95% CI, 1.26-7.37) at autopsy. In the replication cohort, plasma total tau level weakly correlated with cerebrospinal fluid total tau level (Spearman correlation coefficient, 0.16; P = .07), but plasma total tau was at least as strongly associated with incident AD dementia as cerebrospinal fluid total tau (log plasma total tau: HR, 2.33; 95% CI, 1.00-5.48; log cerebrospinal fluid total tau: HR, 2.14; 95% CI, 1.33-3.44) after adjustment for age and sex.

Conclusions and Relevance

The findings suggest that plasma total tau levels may improve the prediction of future dementia, are associated with dementia endophenotypes, and may be used as a biomarker for risk stratification in dementia prevention trials.

Blood biomarkers as surrogate endpoints of treatment responses to aerobic exercise and cognitive training (ACT) in amnestic mild cognitive impairment: the blood biomarkers study protocol of a randomized controlled trial (the ACT Trial)

BACKGROUND

Alzheimer's disease (AD) is an epidemic with tremendous public health impacts because there are currently no disease-modifying therapeutics. Randomized controlled trials (RCTs) for prevention of AD dementia often use clinical endpoints that take years to manifest (e.g., cognition) or surrogate endpoints that are costly or invasive (e.g., magnetic resonance imaging [MRI]). Blood biomarkers represent a clinically applicable alternative surrogate endpoint for RCTs that would be both cost-effective and minimally invasive, but little is known about their value as surrogate endpoints for treatment responses in the prevention of AD dementia.

METHODS

The objective of this study is to investigate blood neuropathological, neurodegenerative, and neurotrophic biomarkers as surrogate endpoints for treatment responses to three interventions in older adults with amnestic mild cognitive impairment (aMCI, a prodromal stage of AD): aerobic exercise, cognitive training, and combined aerobic exercise and cognitive training (ACT). We chose these three sets of biomarkers for their unique mechanistic associations with AD pathology, neurodegeneration and neurogenesis. This study is built on the ACT Trial (1R01AG055469), a single-blinded, multi-site, 2 × 2 factorial phase II RCT that examines the synergistic effects of a 6-month ACT intervention on cognition and MRI biomarkers (AD-signature cortical thickness and hippocampal volume) (n = 128). In this ACT Trial blood biomarkers study, we will enroll 120 ACT Trial participants with aMCI and measure blood biomarkers at baseline and at 3, 6, 12, and 18 months. The goals are to (1) determine the effect of interventions on blood biomarkers over 6 months, (2) evaluate blood biomarkers as surrogate endpoints for predicting cognitive responses to interventions over 18 months, and (3, exploratory) examine blood biomarkers as surrogate endpoints for predicting brain MRI biomarker responses to interventions over 18 months.

DISCUSSION

This study aims to identify new blood biomarkers that can track cognitive decline or AD-related brain atrophy among patients with aMCI subjected to a regimen of aerobic exercise and cognitive training. Findings from this study will drive the further use of blood biomarkers in developing effective prevention and treatment strategies for AD dementia.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03313895. Registered on 18 October 2017.

From the prion-like propagation hypothesis to therapeutic strategies of anti-tau immunotherapy

The term “propagon” is used to define proteins that may transmit misfolding in vitro, in tissues or in organisms. Among propagons, misfolded tau is thought to be involved in the pathogenic mechanisms of various “tauopathies” that include Alzheimer's disease, progressive supranuclear palsy, and argyrophilic grain disease. Here, we review the available data in the literature and point out how the prion-like tau propagation has been extended from Alzheimer's disease to tauopathies. First, in Alzheimer’s disease, the progression of tau aggregation follows stereotypical anatomical stages which may be considered as spreading. The mechanisms of the propagation are now subject to intensive and controversial research. It has been shown that tau may be secreted in the interstitial fluid in an active manner as reflected by high and constant concentration of extracellular tau during Alzheimer’s pathology. Animal and cell models have been devised to mimic tau seeding and propagation, and despite their limitations, they have further supported to the prion-like propagation hypothesis. Finally, such new ways of thinking have led to different therapeutic strategies in anti-tau immunotherapy among tauopathies and have stimulated new clinical trials. However, it appears that the prion-like propagation hypothesis mainly relies on data obtained in Alzheimer’s disease. From this review, it appears that further studies are needed (1) to characterize extracellular tau species, (2) to find the right pathological tau species to target, (3) to follow in vivo tau pathology by brain imaging and biomarkers and (4) to interpret current clinical trial results aimed at reducing the progression of these pathologies. Such inputs will be essential to have a comprehensive view of these promising therapeutic strategies in tauopathies.

Exploring Relationships Among Peripheral Amyloid Beta, Tau, Cytokines, Cognitive Function, and Psychosomatic Symptoms in Breast Cancer Survivors

OBJECTIVE

Accelerated brain aging has been proposed to explain cancer-related cognitive impairment, but empirical evidence for this relationship is lacking. The purpose of this study was to evaluate amyloid beta (Aβ) and tau, biomarkers of neurodegeneration, in relation to cognition in breast cancer survivors (BCSs). We explored relationships among peripheral concentrations of Aβ42, Aβ-40, tau, and cytokines; cognitive function; and psychosomatic symptoms in a cohort of BCSs post-chemotherapy.

METHODS

This secondary analysis of a cross-sectional study was conducted with 65 BCSs. Serum total Aβ-42, Aβ-40, and tau levels were measured with single molecule array technology. Cytokines (interleukin [IL]-6, tumor necrosis factor [TNF]-α, granulocyte-macrophage colony-stimulating factor [GM-CSF], interferon [IFN]-g, IL-10, IL-12, IL-13, IL1-b, IL-2, IL-4, IL-5, IL-7, and IL-8) were simultaneously measured in serum using multiplex assays. Cognitive function was measured with five standardized neuropsychological tests and psychosomatic symptoms (stress, loneliness, anxiety, depressive symptoms, fatigue, sleep quality, and daytime sleepiness) with self-report questionnaires. Data analyses included correlations and random forest regression (RFR).

RESULTS

Significant correlations were identified among hip-to-waste ratio, number of treatment modalities, Aβ-42, Aβ-40, and tau levels (rs = .27-.35, ps < .05). RFR modeling including Aβ-42, Aβ-40, tau, and cytokines as features explained significant variance in cognitive function (R2 = .71, F = 9.01, p < .0001) and psychosomatic symptoms (R2 = .74, F = 10.22, p < .0001).

CONCLUSIONS

This study suggests that neurodegenerative biomarkers interact with cytokines to influence cognitive functioning and psychosomatic symptoms in BCSs following chemotherapy, but additional research is needed.

Tau inhibits PKA by nuclear proteasome-dependent PKAR2α elevation with suppressed CREB/GluA1 phosphorylation

Intraneuronal accumulation of wild-type tau plays a key role in Alzheimer's disease, while the mechanisms underlying tauopathy and memory impairment remain unclear. Here, we report that overexpressing full-length wild-type human tau (hTau) in mouse hippocampus induces learning and memory deficits with remarkably reduced levels of multiple synapse- and memory-associated proteins. Overexpressing hTau inhibits the activity of protein kinase A (PKA) and decreases the phosphorylation level of cAMP-response element binding protein (CREB), GluA1, and TrkB with reduced BDNF mRNA and protein levels both in vitro and in vivo. Simultaneously, overexpressing hTau increased PKAR2α (an inhibitory subunit of PKA) in nuclear fraction and inactivated proteasome activity. With an increased association of PKAR2α with PA28γ (a nuclear proteasome activator), the formation of PA28γ-20S proteasome complex remarkably decreased in the nuclear fraction, followed by a reduced interaction of PKAR2α with 20S proteasome. Both downregulating PKAR2α by shRNA and upregulating proteasome by expressing PA28γ rescued hTau-induced PKA inhibition and CREB dephosphorylation, and upregulating PKA improved hTau-induced cognitive deficits in mice. Together, these data reveal that intracellular tau accumulation induces synapse and memory impairments by inhibiting PKA/CREB/BDNF/TrkB and PKA/GluA1 signaling, and deficit of PA28γ-20S proteasome complex formation contributes to PKAR2α elevation and PKA inhibition.

Latest advances in cerebrospinal fluid and blood biomarkers of Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease and its diagnosis has classically been based on clinical symptoms. Recently, a biological rather than a syndromic definition of the disease has been proposed that is based on biomarkers that reflect neuropathological changes. In AD, there are two main biomarker categories, namely neuroimaging and fluid biomarkers [cerebrospinal fluid (CSF) and blood]. As a complex and multifactorial disease, AD biomarkers are important for an accurate diagnosis and to stage the disease, assess the prognosis, test target engagement, and measure the response to treatment. In addition, biomarkers provide us with information that, even if it does not have a current clinical use, helps us to understand the mechanisms of the disease. In addition to the pathological hallmarks of AD, which include amyloid-β and tau deposition, there are multiple concomitant pathological events that play a key role in the disease. These include, but are not limited to, neurodegeneration, inflammation, vascular dysregulation or synaptic dysfunction. In addition, AD patients often have an accumulation of other proteins including α-synuclein and TDP-43, which may have a pathogenic effect on AD. In combination, there is a need to have biomarkers that reflect different aspects of AD pathogenesis and this will be important in the future to establish what are the most suitable applications for each of these AD-related biomarkers. It is unclear whether sex, gender, or both have an effect on the causes of AD. There may be differences in fluid biomarkers due to sex but this issue has often been neglected and warrants further research. In this review, we summarize the current state of the principal AD fluid biomarkers and discuss the effect of sex on these biomarkers.

An update on fluid biomarkers for neurodegenerative diseases: recent success and challenges ahead

Over the last twenty years, the characterization of Alzheimer's disease (AD) patients has progressed from a description of clinical symptomatology followed by neuropathological findings at autopsy to in vivo pathophysiological signatures using cerebrospinal fluid (CSF) and positron emission tomography (PET). Additionally, CSF biomarkers now reflect synaptic pathology, axonal injury and neuroinflammation. Novel techniques are capable of measuring proteins of pathophysiological importance at femtomolar concentrations in blood (e.g. amyloid, tau species and neurofilaments), which enable screening of large populations in the near future. This will be essential for secondary prevention trials and clinical management. However, common diseases such as dementia with Lewy bodies, Parkinson's disease and frontotemporal dementias, are still without reliable diagnostic biomarkers, although emerging techniques show promising pilot results for some of these diseases. This is likely to change in the next few years, which will be crucial to stratify populations enrolling in clinical trials, since pathologies often coexist.

Advances and considerations in AD tau-targeted immunotherapy

The multifactorial and complex nature of Alzheimer’s disease (AD) has made it difficult to identify therapeutic targets that are causally involved in the disease process. However, accumulating evidence from experimental and clinical studies that investigate the early disease process point towards the required role of tau in AD etiology. Importantly, a large number of studies investigate and characterize the plethora of pathological forms of tau protein involved in disease onset and propagation. Immunotherapy is one of the most clinical approaches anticipated to make a difference in the field of AD therapeutics. Tau –targeted immunotherapy is the new direction after the failure of amyloid beta (Aß)-targeted immunotherapy and the growing number of studies that highlight the Aß-independent disease process. It is now well established that immunotherapy alone will most likely be insufficient as a monotherapy. Therefore, this review discusses updates on tau-targeted immunotherapy studies, AD-relevant tau species, updates on promising biomarkers and a prospect on combination therapies to surround the disease propagation in an efficient and timely manner.

Predictive Value of Routine Peripheral Blood Biomarkers in Alzheimer's Disease

Background

Biomarker screening is of major significance for the early diagnosis and prevention of Alzheimer’s disease (AD). Routine peripheral blood parameters are easy to collect and detect, making them ideal potential biomarkers. Thus, we aimed to evaluate the parameters from routine blood as potential biomarkers for AD.

Methods

We enrolled 56 AD patients, 57 mild cognitive impairment (MCI) patients, and 59 healthy elderly controls. Receiver operating characteristic (ROC) curves were used to assess the diagnostic values of routine blood biomarkers in patients with cognitive impairment.

Results

There were significant differences in eight parameters between the groups. Logistic regression revealed that the neutrophil% (odds ratio (OR) 1.34, 95% confidence interval [CI] 1.03–1.75, p = 0.031) and neutrophil-to-lymphocyte ratio (NLR; OR 6.27, 95% CI 3.98–9.82, p = 0.003) differentiated AD patients and controls (areas under the curve [AUCs], 0.728 and 0.721) and that the NLR (OR 1.93, 95% CI 1.07–3.47, p = 0.028) and mean platelet volume (OR 1.67, 95% CI 1.04–2.70, p = 0.036) differentiated MCI patients and controls (AUCs, 0.60 and 0.638). There were no effective diagnostic biomarkers to distinguish AD from MCI.

Conclusion

Some routine blood biomarkers may correlate with cognitive impairment. Analysis of these biomarkers, such as the NLR, may be useful for the identification of patients with cognitive impairment.

Plasma tau correlates with basal forebrain atrophy rates in people at risk for Alzheimer disease

Objective

To investigate whether baseline concentrations of plasma total tau (t-tau) and neurofilament light (NfL) chain proteins are associated with annual percent change (APC) of the basal forebrain cholinergic system (BFCS) in cognitively intact older adults at risk for Alzheimer disease (AD).

Methods

This was a large-scale study of 276 cognitively intact older adults from the monocentric INSIGHT-preAD (Investigation of Alzheimer's Predictors in Subjective Memory Complainers) cohort. Participants underwent baseline assessment of plasma t-tau and NfL concentrations as well as baseline and 24-month follow-up MRI scans. Linear models with and without influential observations (calculated using the Cook distance) were carried out to investigate the effect of plasma NfL and t-tau concentrations, and their interaction effect with β-amyloid status and APOE genotype, on the APC of the whole BFCS and its anterior (Ch1/2) and posterior (Ch4) subdivisions separately.

Results

Higher plasma t-tau concentrations at baseline were associated with higher BFCS rate of atrophy (model without influencers: n = 251, F value = 4.6815; p value = 0.031). Subregional analyses showed similar results for both the APC of the Ch1/2 (model without influencers: n = 256, F value = 3.9535, p corrected = 0.047) and Ch4 BFCS sectors (model without influencers: n = 253, F value = 4.9090, p corrected = 0.047). Baseline NfL, β-amyloid load, and APOE ε4 carrier status did not affect APC of the BFCS.

Conclusion

Increased concentrations of baseline plasma t-tau may predict in vivo structural BFCS atrophy progression in older adults at risk for AD, independently of β-amyloid status and APOE genotype.

Neuroinflammation as a Factor of Neurodegenerative Disease: Thalidomide Analogs as Treatments

Neuroinflammation is initiated when glial cells, mainly microglia, are activated by threats to the neural environment, such as pathogen infiltration or neuronal injury. Although neuroinflammation serves to combat these threats and reinstate brain homeostasis, chronic inflammation can result in excessive cytokine production and cell death if the cause of inflammation remains. Overexpression of tumor necrosis factor-α (TNF-α), a proinflammatory cytokine with a central role in microglial activation, has been associated with neuronal excitotoxicity, synapse loss, and propagation of the inflammatory state. Thalidomide and its derivatives, termed immunomodulatory imide drugs (IMiDs), are a class of drugs that target the 3'-untranslated region (3'-UTR) of TNF-α mRNA, inhibiting TNF-α production. Due to their multi-potent effects, several IMiDs, including thalidomide, lenalidomide, and pomalidomide, have been repurposed as drug treatments for diseases such as multiple myeloma and psoriatic arthritis. Preclinical studies of currently marketed IMiDs, as well as novel IMiDs such as 3,6'-dithiothalidomide and adamantyl thalidomide derivatives, support the development of IMiDs as therapeutics for neurological disease. IMiDs have a competitive edge compared to similar anti-inflammatory drugs due to their blood-brain barrier permeability and high bioavailability, with the potential to alleviate symptoms of neurodegenerative disease and slow disease progression. In this review, we evaluate the role of neuroinflammation in neurodegenerative diseases, focusing specifically on the role of TNF-α in neuroinflammation, as well as appraise current research on the potential of IMiDs as treatments for neurological disorders.

Advance in Plasma AD Core Biomarker Development: Current Findings from Immunomagnetic Reduction-Based SQUID Technology

New super-sensitive biomarker assay platforms for measuring Alzheimer's disease (AD) core pathological markers in plasma have recently been developed and tested. Research findings from these technologies offer promising evidence for identifying the earliest stages of AD and correlating them with brain pathological progression. Here, we review findings using immunomagnetic reduction, one of these ultrasensitive technologies. The principles, technology and assays developed, along with selected published findings will be discussed. The major findings from this technology were significant increases of amyloid beta (Aβ) 42 and total tau (t-tau) levels in subjects clinically diagnosed with early AD when compared with cognitively normal control (NC) subjects. The composite marker of the product of Aβ42 and t-tau discriminated subjects with early AD from NC subjects with high accuracy. The potential of this technology for the purpose of early or preclinical disease stage detection has yet to be explored in subjects who have also been assessed with brain imaging and cerebrospinal fluid AD core biomarker measurements.

Soluble TREM1 concentrations are increased and positively correlated with total tau levels in the plasma of patients with Alzheimer's disease

BACKGROUND/AIMS

Recently, we showed that triggering receptor expressed on myeloid cells 1 (TREM1) was involved in the pathogenesis of Alzheimer's disease (AD) since it modulated microglial phagocytic functions and thus affected amyloid-β clearance in the brain. Interestingly, a soluble form of TREM1 (sTREM1) can be detected in the plasma of human. To date, whether sTREM1 concentrations were altered in the plasma under AD context remained unclear.

METHODS

In this study, we compared the plasma concentrations of sTREM1 between 110 AD patients and 128 age- and gender-matched controls. Meanwhile, the relationship of sTREM1 concentrations with total tau levels in the plasma of AD patients was also assessed.

RESULTS

We revealed that the concentrations of sTREM1 were significantly increased in AD patients. Meanwhile, the sTREM1 concentrations were gradually increased during disease progression. More importantly, we showed that the sTREM1 concentrations were positively correlated with the levels of total tau in the plasma of AD patients (r = 0.61, P < 0.001). The subsequent subgroup analysis indicated that this correlation was more pronounced in patients with severe dementia (Mini-Mental State Exam score < 10, r = 0.81, P < 0.01).

CONCLUSION

These findings indicate a potential association between sTREM1 and tau pathology, and further confirm an involvement of this immune receptor in AD pathogenesis.

An Update on Blood-Based Markers of Alzheimer's Disease Using the SiMoA Platform

The development of blood-based biomarkers of Alzheimer's disease (AD) pathology as tools for screening the general population, and as the first step in a multistep process to determine which non-demented individuals are at greatest risk of developing AD dementia, is essential. Proteins that are reflective of AD pathology, such as amyloid beta 42 (Aβ42), tau proteins [total tau (T-tau) and phosphorylated tau (P-tau)], and neurofilament light chain (NfL), are detectable in the blood. However, a major challenge in measuring these blood-based proteins is that their concentrations are much lower in plasma or serum than in the cerebrospinal fluid. Single molecule array (SiMoA) is an ultrasensitive technology that can detect proteins in blood at sub-femtomolar concentrations (i.e., 10-16 M). In this review, we focus on the utility of SiMoA assays for the measurement of plasma or serum Aβ42, P-tau, T-tau, and NfL levels and discuss future directions.

Occupational metals exposure and cognitive performance among foundry workers using tau protein as a biomarker

INTRODUCTION

Human exposure to heavy metals is a potential risk for developing cognitive impairment. Aluminum (Al) foundry is one of industries that involve occupational exposure to different metals.

AIM OF THE WORK

to evaluate the cognitive performance of Aluminum foundry workers in relation to different metals exposure.

MATERIALS AND METHODS

a cross sectional study conducted on 75 Al foundry workers and 75 non-occupationally exposed subjects as controls. Personal interview with specially designed questionnaire, Assessment of cognitive functions done using Montreal cognitive assessment (MocA), Stress, depression and sleep were also assessed. Serum levels of Aluminum (AL), Lead (Pb), manganese (Mn), Zinc (Zn) and tau protein were measured.

RESULTS

Exposed group showed significant increase in serum levels of Aluminum, lead, Manganese and tau protein, p value < 0.005 (mean ± SD 0.56 ± 0.18, 22.3 ± 5.01, 42.04 ± 7.4, 1.53 ± 0.58 Vs 0.36 ± 0.11, 13.4 ± 1.29, 39.4 ± 4.4, 1.03 ± 0.44 respectively) with significant decrease of zinc level compared to control (mean ± SD 46.4 ± 5.2 Vs 88.8 ± 6.04, p value 0.005). There was a significant decrease MocA scores among exposed population, (mean ± SD 24.4 ± 3.4 compared to 28.4 ± 1.3 in non exposed, p value < 0.005). which was affected by serum levels of lead, aluminum, manganese and tau protein (β -0.165, -8.958, -.286, -2.341 respectively and p < 0.005).Stress scores was higher in exposed workers than control but not affecting cognitive performance.

CONCLUSION

occupational exposure to metals can cause cognitive dysfunction which may be subtle, so there is a need for formal cognitive testing at baseline, and on regular intervals during working period. Serum tau protein could be used as a prognostic biomarker for the hazardous effect of occupational exposure to these metals on the neuronal cells.

Association of Blood and Cerebrospinal Fluid Tau Level and Other Biomarkers With Survival Time in Sporadic Creutzfeldt-Jakob Disease

IMPORTANCE

Fluid biomarkers that can predict survival time in sporadic Creutzfeldt-Jakob disease (sCJD) will be critical for clinical care and for treatment trials.

OBJECTIVE

To assess whether plasma and cerebrospinal fluid (CSF) biomarkers are associated with survival time in patients with sCJD.

DESIGN, SETTING, AND PARTICIPANTS

In this longitudinal cohort study, data from 193 patients with probable or definite sCJD who had codon 129 genotyping referred to a tertiary national referral service in the United States were collected from March 2004 to January 2018. Participants were evaluated until death or censored at the time of statistical analysis (range, 0.03-38.3 months). We fitted Cox proportional hazard models with time to event as the outcome. Fluid biomarkers were log-transformed, and models were run with and without nonfluid biomarkers of survival. Five patients were excluded because life-extending measures were performed.

MAIN OUTCOMES AND MEASURES

Biomarkers of survival included sex, age, codon 129 genotype, Barthel Index, Medical Research Council Prion Disease Rating Scale, 8 CSF biomarkers (total tau [t-tau] level, phosphorylated tau [p-tau] level, t-tau:p-tau ratio, neurofilament light [NfL] level, β-amyloid 42 level, neuron-specific enolase level, 14-3-3 test result, and real-time quaking-induced conversion test), and 3 plasma biomarkers (t-tau level, NfL level, and glial fibrillary acidic protein level).

RESULTS

Of the 188 included participants, 103 (54.8%) were male, and the mean (SD) age was 63.8 (9.2) years. Plasma t-tau levels (hazard ratio, 5.8; 95% CI, 2.3-14.8; P < .001) and CSF t-tau levels (hazard ratio, 1.6; 95% CI, 1.2-2.1; P < .001) were significantly associated with survival after controlling for codon 129 genotype and Barthel Index, which are also associated with survival time. Plasma and CSF t-tau levels were correlated (r = 0.74; 95% CI, 0.50-0.90; P < .001). Other fluid biomarkers associated with survival included plasma NfL levels, CSF NfL levels, t-tau:p-tau ratio, 14-3-3 test result, and neuron-specific enolase levels. In a restricted subset of 23 patients with data for all significant biomarkers, the hazard ratio for plasma t-tau level was more than 40% larger than any other biomarkers (hazard ratio, 3.4; 95% CI, 1.8-6.4).

CONCLUSIONS AND RELEVANCE

Cerebrospinal fluid and plasma tau levels, along with several other fluid biomarkers, were significantly associated with survival time in patients with sCJD. The correlation between CSF and plasma t-tau levels and the association of plasma t-tau level with survival time suggest that plasma t-tau level may be a minimally invasive fluid biomarker in sCJD that could improve clinical trial stratification and guide clinical care.

Plasma tau complements CSF tau and P-tau in the diagnosis of Alzheimer's disease

Introduction

Plasma tau may be an accessible biomarker for Alzheimer's disease (AD), but the correlation between plasma and cerebrospinal fluid (CSF) tau and the value of combining plasma tau with CSF tau and phospho-tau (P-tau) are still unclear.

Methods

Plasma-tau, CSF-tau, and P-tau were measured in 97 subjects, including elderly cognitively normal controls (n = 68) and patients with AD (n = 29) recruited at the NYU Center for Brain Health, with comprehensive neuropsychological and magnetic resonance imaging evaluations.

Results

Plasma tau was higher in patients with AD than cognitively normal controls (P < .001, area under the receiver operating characteristic curve = 0.79) similarly to CSF tau and CSF P-tau and was negatively correlated with cognition in AD. Plasma and CSF tau measures were poorly correlated. Adding plasma tau to CSF tau or CSF P-tau significantly increased the areas under the receiver operating characteristic curve from 0.80 and 0.82 to 0.87 and 0.88, respectively.

Discussion

Plasma tau is higher in AD independently from CSF-tau. Importantly, adding plasma tau to CSF tau or P-tau improves diagnostic accuracy, suggesting that plasma tau may represent a useful biomarker for AD, especially when added to CSF tau measures.

Blood amyloid levels and risk of dementia in the Ginkgo Evaluation of Memory Study (GEMS): A longitudinal analysis

INTRODUCTION

Both high or low plasma amyloid levels have been associated with risk of dementia in nondemented subjects.

METHODS

We examined baseline plasma β-amyloid (Aβ) levels in relationship to incident dementia during a period of 8.5 years in 2840 subjects age >75 years; 2381 were cognitively normal (CN) and 450 mild cognitive impairment.

RESULTS

Increased plasma Aβ1-40 and Aβ1-42 levels were associated with gender (women), age, low education, creatinine levels, history of stroke, and hypertension. CN participants who developed dementia had lower levels of Aβ1-42 and Aβ1-42/Aβ1-40 ratio compared with those who did not. Aβ levels did not predict dementia in mild cognitive impairment participants.

DISCUSSION

There was an inverse association between Aβ1-42 and Aβ1-42/Aβ1-40 ratio to risk of dementia in CN participants. Cerebral and cardiovascular disease and renal function are important determinants of increased Aβ levels and must be considered in evaluations of relationship of plasma Aβ and subsequent risk of dementia.

Plasma Tau and Amyloid Are Not Reliably Related to Injury Characteristics, Neuropsychological Performance, or White Matter Integrity in Service Members with a History of Traumatic Brain Injury

The aim of this study was to examine the relationship between plasma tau and amyloid beta-42 (Aβ42), neuropsychological functioning, and white matter integrity in U.S. military service members with (n = 155) and without (n = 42) a history of uncomplicated mild (n = 83), complicated mild (n = 26), or moderate, severe, or penetrating (n = 46) traumatic brain injury (TBI). We hypothesized that higher levels of tau and Aβ42 would be related to reduced neurocognitive performance and white matter integrity. Participants were enrolled prospectively from Walter Reed National Military Medical Center. Participants completed a blood draw, neuropsychological assessment, and diffusion tensor imaging (General Electric 3T) of the whole brain. From 20 neuropsychological test scores, five cognitive domain scores were computed. Measures of fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were generated for 18 regions of interest (ROIs). There was no relationship found between the plasma biomarkers and neurocognitive performance in any of the three TBI groups (all ps >0.05; all R² changes <0.146). Although not reaching statistical significance after correction for multiple comparisons, higher tau and Aβ42 tended to be related to higher FA and lower MD, RD, and AD in patients with a history of moderate, severe, or penetrating TBI. There was no consistent relationship between either of the biomarkers and white matter integrity in the complicated and uncomplicated mild TBI groups. In addition, there was no significant relationship between the biomarkers and age, education, sex, race, bodily injury severity, time since injury, TBI severity, or number of TBIs (all ps >0.15). Future investigation in larger samples of moderate, severe, and penetrating TBI are needed. Other plasma biomarkers, including phosphorylated tau, exosomal tau, and interleukin-10, may be more promising measures to use in the diagnosis, management, and treatment of TBI.

Blood-based molecular biomarkers for Alzheimer's disease

A major barrier to the effective conduct of clinical trials of new drug candidates against Alzheimer’s disease (AD) and to identifying patients for receiving future disease-modifying treatments is the limited capacity of the current health system to find and diagnose patients with early AD pathology. This may be related in part to the limited capacity of the current health systems to select those people likely to have AD pathology in order to confirm the diagnosis with available cerebrospinal fluid and imaging biomarkers at memory clinics. In the current narrative review, we summarize the literature on candidate blood tests for AD that could be implemented in primary care settings and used for the effective identification of individuals at increased risk of AD pathology, who could be referred for potential inclusion in clinical trials or future approved treatments following additional testing. We give an updated account of blood-based candidate biomarkers and biomarker panels for AD-related brain changes. Our analysis centres on biomarker candidates that have been replicated in more than one study and discusses the need of further studies to achieve the goal of a primary care-based screening algorithm for AD.

Learnings about the complexity of extracellular tau aid development of a blood-based screen for Alzheimer's disease

INTRODUCTION

The tau protein plays a central role in Alzheimer's disease (AD), and there is huge interest in measuring tau in blood and cerebrospinal fluid (CSF).

METHODS

We developed a set of immunoassays to measure tau in specimens from humans diagnosed based on current best clinical and CSF biomarker criteria.

RESULTS

In CSF, mid-region- and N-terminal-detected tau predominated and rose in disease. In plasma, an N-terminal assay (NT1) detected elevated levels of tau in AD and AD-mild cognitive impairment (MCI). Plasma NT1 measurements separated controls from AD-MCI (area under the curve [AUC] = 0.88) and AD (AUC = 0.96) in a discovery cohort and in a Validation Cohort (with AUCs = 0.79 and 0.75, respectively).

DISCUSSION

The forms of tau in CSF and plasma are distinct, but in each specimen type, the levels of certain fragments are increased in AD. Measurement of plasma NT1 tau should be aggressively pursued as a potential blood-based screening test for AD/AD-MCI.

Increased plasma neurofilament light chain concentration correlates with severity of post-mortem neurofibrillary tangle pathology and neurodegeneration

Alzheimer’s disease (AD) is pathologically characterized by the accumulation of amyloid-β (Aβ) plaques, neurofibrillary tangles and widespread neuronal loss in the brain. In recent years, blood biomarkers have emerged as a realistic prospect to highlight accumulating pathology for secondary prevention trials. Neurofilament light chain (NfL), a marker of axonal degeneration, is robustly elevated in the blood of many neurological and neurodegenerative conditions, including AD. A strong relationship with cerebrospinal fluid (CSF) NfL suggests that these biomarker modalities reflect the same pathological process. Yet, the connection between blood NfL and brain tissue pathology has not been directly compared. In this study, longitudinal plasma NfL from cognitively healthy controls (n = 12) and AD participants (n = 57) were quantified by the Simoa platform. On reaching post-mortem, neuropathological assessment was performed on all participants, with additional frozen and paraffin-embedded tissue acquired from 26 participants for further biochemical (Aβ_1–42, Aβ_1–40, tau) and histological (NfL) evaluation. Plasma NfL concentrations were significantly increased in AD and correlated with cognitive decline, independent of age. Retrospective stratification based on Braak staging revealed that baseline plasma NfL concentrations were associated with higher neurofibrillary tangle pathology at post-mortem. Longitudinal increases in plasma NfL were observed in all Braak groupings; a significant negative association, however, was found between plasma NfL at time point 1 and both its rate of change and annual percentage increase. Immunohistochemical evaluation of NfL in the medial temporal gyrus (MTG) demonstrated an inverse relationship between Braak stages and NfL staining. Importantly, a significant negative correlation was found between the plasma NfL measurement closest to death and the level of NfL staining in the MTG at post-mortem. For the first time, we demonstrate that plasma NfL associates with the severity of neurofibrillary tangle pathology and neurodegeneration in the post-mortem brain.

Biomarkers for tau pathology

The aggregation of fibrils of hyperphosphorylated and C-terminally truncated microtubule-associated tau protein characterizes 80% of all dementia disorders, the most common neurodegenerative disorders. These so-called tauopathies are hitherto not curable and their diagnosis, especially at early disease stages, has traditionally proven difficult. A keystone in the diagnosis of tauopathies was the development of methods to assess levels of tau protein in vivo in cerebrospinal fluid, which has significantly improved our knowledge about these conditions. Tau proteins have also been measured in blood, but the importance of tau-related changes in blood is still unclear. The recent addition of positron emission tomography ligands to visualize, map and quantify tau pathology has further contributed with information about the temporal and spatial characteristics of tau accumulation in the living brain. Together, the measurement of tau with fluid biomarkers and positron emission tomography constitutes the basis for a highly active field of research.

This review describes the current state of biomarkers for tau biomarkers derived from neuroimaging and from the analysis of bodily fluids and their roles in the detection, diagnosis and prognosis of tau-associated neurodegenerative disorders, as well as their associations with neuropathological findings, and aims to provide a perspective on how these biomarkers might be employed prospectively in research and clinical settings.

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Biomarkers for tau pathology are now essential to the research framework in the diagnosis of Alzheimer's disease (AD)

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Measurement of t- and p-tau has been possible in cerebrospinal fluid (CSF) for some time, the recent development of positron emission tomography (PET) ligands binding to tau has added the possibility to map and quantify tau in the living brain

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First-generation tau PET ligands bind predominantly to AD-typical 3R/4R tau isoforms and exhibit off-target binding that can limit accurate ligand uptake quantification

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Second-generation tau PET ligands appear to bind to comparable binding sites but exhibit fewer issues with brain off-target binding

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Biomarkers for tau derived from CSF analysis and PET could provide complementary information about disease state and stage

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At this time, T-tau, but not p-tau, can be reliably measured in plasma using ultra-sensitive immunoassays.

Biomarkers of dementia in obstructive sleep apnea

Epidemiologic and mechanistic evidence is increasingly supporting the notion that obstructive sleep apnea is a risk factor for dementia. Hence, the identification of patients at risk of cognitive decline due to obstructive sleep apnea may significantly improve preventive strategies and treatment decision-making. Cerebrospinal fluid and blood biomarkers obtained through genomic, proteomic and metabolomic approaches are improving the ability to predict incident dementia. Therefore, fluid biomarkers have the potential to predict vulnerability to neurodegeneration in individuals with obstructive sleep apnea, as well as deepen our understanding of pathophysiological processes linking obstructive sleep apnea and dementia. Many fluid biomarkers linked to Alzheimer's disease and vascular dementia show abnormal levels in individuals with obstructive sleep apnea, suggesting that these conditions share common underlying mechanisms, including amyloid and tau protein neuropathology, inflammation, oxidative stress, and metabolic disturbances. Markers of these processes include amyloid-β, tau proteins, inflammatory cytokines, acute-phase proteins, antioxydants and oxidized products, homocysteine and clusterin (apolipoprotein J). Thus, these biomarkers may have the ability to identify adults with obstructive sleep apnea at high risk of dementia and provide an opportunity for therapeutic intervention. Large cohort studies are necessary to establish a specific fluid biomarker panel linking obstructive sleep apnea to dementia risk.

Current state of Alzheimer's fluid biomarkers

Alzheimer’s disease (AD) is a progressive neurodegenerative disease with a complex and heterogeneous pathophysiology. The number of people living with AD is predicted to increase; however, there are no disease-modifying therapies currently available and none have been successful in late-stage clinical trials. Fluid biomarkers measured in cerebrospinal fluid (CSF) or blood hold promise for enabling more effective drug development and establishing a more personalized medicine approach for AD diagnosis and treatment. Biomarkers used in drug development programmes should be qualified for a specific context of use (COU). These COUs include, but are not limited to, subject/patient selection, assessment of disease state and/or prognosis, assessment of mechanism of action, dose optimization, drug response monitoring, efficacy maximization, and toxicity/adverse reactions identification and minimization. The core AD CSF biomarkers Aβ42, t-tau, and p-tau are recognized by research guidelines for their diagnostic utility and are being considered for qualification for subject selection in clinical trials. However, there is a need to better understand their potential for other COUs, as well as identify additional fluid biomarkers reflecting other aspects of AD pathophysiology. Several novel fluid biomarkers have been proposed, but their role in AD pathology and their use as AD biomarkers have yet to be validated. In this review, we summarize some of the pathological mechanisms implicated in the sporadic AD and highlight the data for several established and novel fluid biomarkers (including BACE1, TREM2, YKL-40, IP-10, neurogranin, SNAP-25, synaptotagmin, α-synuclein, TDP-43, ferritin, VILIP-1, and NF-L) associated with each mechanism. We discuss the potential COUs for each biomarker.

Blood-based biomarkers for Alzheimer disease: mapping the road to the clinic

Biomarker discovery and development for clinical research, diagnostics and therapy monitoring in clinical trials have advanced rapidly in key areas of medicine - most notably, oncology and cardiovascular diseases - allowing rapid early detection and supporting the evolution of biomarker-guided, precision-medicine-based targeted therapies. In Alzheimer disease (AD), breakthroughs in biomarker identification and validation include cerebrospinal fluid and PET markers of amyloid-β and tau proteins, which are highly accurate in detecting the presence of AD-associated pathophysiological and neuropathological changes. However, the high cost, insufficient accessibility and/or invasiveness of these assays limit their use as viable first-line tools for detecting patterns of pathophysiology. Therefore, a multistage, tiered approach is needed, prioritizing development of an initial screen to exclude from these tests the high numbers of people with cognitive deficits who do not demonstrate evidence of underlying AD pathophysiology. This Review summarizes the efforts of an international working group that aimed to survey the current landscape of blood-based AD biomarkers and outlines operational steps for an effective academic-industry co-development pathway from identification and assay development to validation for clinical use.

Blood-based biomarkers for Alzheimer's disease-An update

Cerebrospinal fluid (CSF) biomarkers for Alzheimer's disease (AD) are in clinical use in many parts of the world and show good to excellent diagnostic accuracy in regards to identifying cerebral amyloid β (Aβ) and tau pathology irrespective of the clinical stage of the disease. However, CSF sampling is more difficult than a blood draw and a procedure only rarely performed by general practitioners. Since AD is such a common disease and since intense research on novel treatments that hopefully will be directed against underlying pathologies is moving forward, it would be excellent if the CSF tests for AD could be transformed into blood tests, as well as if novel blood biomarkers could be discovered. Brain-derived molecules are, however, present at much lower concentrations in blood than in CSF, which poses an analytical challenge. There are also additional issues with blood as a biofluid in which to measure biomarkers for central nervous system disease. Nevertheless, the past few years have seen an enormous development in the field of ultrasensitive measurement techniques. There is also much better availability of deeply phenotyped clinical cohorts for biomarker discovery and validation. This review gives an updated account of the current state of research on blood biomarkers for AD and related neurodegenerative dementias with special emphasis on findings that have been replicated by more than one research group.

AMYPAD Diagnostic and Patient Management Study: Rationale and design

INTRODUCTION

Reimbursement of amyloid-positron emission tomography (PET) is lagging due to the lack of definitive evidence on its clinical utility and cost-effectiveness. The Amyloid Imaging to Prevent Alzheimer's Disease-Diagnostic and Patient Management Study (AMYPAD-DPMS) is designed to fill this gap.

METHODS

AMYPAD-DPMS is a phase 4, multicenter, prospective, randomized controlled study. Nine hundred patients with subjective cognitive decline plus, mild cognitive impairment, and dementia possibly due to Alzheimer's disease will be randomized to ARM1, amyloid-PET performed early in the diagnostic workup; ARM2, amyloid-PET performed after 8 months; and ARM3, amyloid-PET performed whenever the physician chooses to do so.

ENDPOINTS

The primary endpoint is the difference between ARM1 and ARM2 in the proportion of patients receiving a very-high-confidence etiologic diagnosis after 3 months. Secondary endpoints address diagnosis and diagnostic confidence, diagnostic/therapeutic management, health economics and patient-related outcomes, and methods for image quantitation.

EXPECTED IMPACTS

AMYPAD-DPMS will supply physicians and health care payers with real-world data to plan management decisions.

Plasma Amyloid as Prescreener for the Earliest Alzheimer Pathological Changes

Objective

We investigated the association of plasma amyloid beta (Abeta)40, Abeta42, and total tau (tTau) with the presence of Alzheimer pathological changes in cognitively normal individuals with subjective cognitive decline (SCD).

Methods

We included 248 subjects with SCD (61 ± 9 years, 42% female, Mini‐Mental State Examination = 28 ± 2) from the SCIENCe project and Amsterdam Dementia Cohort. Subjects were dichotomized as amyloid abnormal by cerebrospinal fluid (CSF) and positron emission tomography (PET). Baseline plasma Abeta40, Abeta42, and tTau were measured using Simoa technology. Associations between plasma levels and amyloid status were assessed using logistic regression analyses and receiver operating characteristic analyses. Association of plasma levels with risk of clinical progression to mild cognitive impairment (MCI) or dementia was assessed using Cox proportional hazard models.

Results

Fifty‐seven (23%) subjects were CSF‐amyloid abnormal. Plasma Abeta42/Abeta40 ratio and plasma Abeta42 alone, but not tTau, identified abnormal CSF‐amyloid status (plasma ratio: area under the curve [AUC] = 77%, 95% confidence interval [CI] = 69–84%; plasma Abeta42: AUC = 66%, 95% CI: 58–74%). Combining plasma ratio with age and apolipoprotein E resulted in AUC = 83% (95% CI = 77–89%). The Youden cutoff of the plasma ratio gave a sensitivity of 76% and specificity of 75%, and applying this as a prescreener would reduce the number of lumbar punctures by 51%. Using PET as outcome, a comparable reduction in number of PET scans would be achieved when applying the plasma ratio as prescreener. In addition, low plasma ratio was associated with clinical progression to MCI or dementia (hazard ratio = 2.0, 95% CI = 1.4–2.3).

Interpretation

Plasma Abeta42/Abeta40 ratio has potential as a prescreener to identify Alzheimer pathological changes in cognitively normal individuals with SCD. Ann Neurol 2018;84:656–666

Association of telomere length with general cognitive trajectories: a meta-analysis of four prospective cohort studies

To investigate the association of telomere length (TL) with trajectories of general cognitive abilities, we used data on 5955 participants from the Sex Differences in Health and Aging Study and the Swedish Adoption/Twin Study of Aging in Sweden, and the Mayo Clinic Study of Aging, and the Health and Retirement Study in the United States. TL was measured at baseline, while general cognitive ability was assessed repeatedly up to 7 occasions. Latent growth curve models were used to examine the associations. One standard deviation increase of TL was associated with 0.021 unit increase (95% confidence interval [CI]: 0.001, 0.042) of standardized mean general cognitive ability. After controlling for sex, the point estimate remained similar (0.019) with a wider CI (95% CI: -0.002, 0.039). The association was attenuated with adjustment for educational attainment (0.009, 95% CI: -0.009, 0.028). No strong evidence was observed for the association of TL and decline in general cognitive ability. Longer TL was associated with higher general cognitive ability levels in the age-adjusted models but not in the models including all covariates, nor with cognitive decline.

Plasma phospho-tau181 increases with Alzheimer's disease clinical severity and is associated with tau- and amyloid-positron emission tomography

INTRODUCTION

We examined and compared plasma phospho-tau181 (pTau181) and total tau: (1) across the Alzheimer's disease (AD) clinical spectrum; (2) in relation to brain amyloid β (Aβ) positron emission tomography (PET), tau PET, and cortical thickness; and (3) as a screening tool for elevated brain Aβ.

METHODS

Participants included 172 cognitively unimpaired, 57 mild cognitively impaired, and 40 AD dementia patients with concurrent Aβ PET (Pittsburgh compound B), tau PET (AV1451), magnetic resonance imaging, plasma total tau, and pTau181.

RESULTS

Plasma total tau and pTau181 levels were higher in AD dementia patients than those in cognitively unimpaired. Plasma pTau181 was more strongly associated with both Aβ and tau PET. Plasma pTau181 was a more sensitive and specific predictor of elevated brain Aβ than total tau and was as good as, or better than, the combination of age and apolipoprotein E (APOE).

DISCUSSION

Plasma pTau181 may have utility as a biomarker of AD pathophysiology and as a noninvasive screener for elevated brain Aβ.

Blood biomarkers in Alzheimer's disease

INTRODUCTION

The early diagnosis of Alzheimer's disease (AD) via the use of biomarkers could facilitate the implementation and monitoring of early therapeutic interventions with the potential capacity to significantly modify the course of the disease.

DEVELOPMENT

Classic cerebrospinal fluid biomarkers and approved structural and functional neuroimaging have a limited clinical application given their invasive nature and/or high cost. The identification of more accessible and less costly biomarkers, such as blood biomarkers, would facilitate application in clinical practice. We present a literature review of the main blood biochemical biomarkers with potential use for diagnosing Alzheimer's disease.

CONCLUSIONS

Blood biomarkers are cost and time effective with regard to cerebrospinal fluid biomarkers. However, the immediate applicability of blood biochemical biomarkers in clinical practice is not very likely. The main limitations come from the difficulties in measuring and standardising thresholds between different laboratories and in failures to replicate results. Among all the molecules studied, apoptosis and neurodegeneration biomarkers and the biomarker panels obtained through omics approaches, such as isolated or combined metabolomics, offer the most promising results.