Plasma total-tau as a biomarker of stroke risk in the community

A critical appraisal of blood-based biomarkers for Alzheimer's disease

Biomarkers that predict the clinical onset of Alzheimer's disease (AD) enable the identification of individuals in the early, preclinical stages of the disease. Detecting AD at this point may allow for more effective therapeutic interventions and optimized enrollment for clinical trials of novel drugs. The current biological diagnosis of AD is based on the AT(N) classification system with the measurement of brain deposition of amyloid-β (Aβ) ("A"), tau pathology ("T"), and neurodegeneration ("N"). Diagnostic cut-offs for Aβ1-42, the Aβ1-42/Aβ1-40 ratio, tau and hyperphosphorylated-tau concentrations in cerebrospinal fluid have been defined and may support AD clinical diagnosis. Blood-based biomarkers of the AT(N) categories have been described in the AD continuum. Cross-sectional and longitudinal studies have shown that the combination of blood biomarkers tracking neuroaxonal injury (neurofilament light chain) and neuroinflammatory pathways (glial fibrillary acidic protein) enhance sensitivity and specificity of AD clinical diagnosis and improve the prediction of AD onset. However, no international accepted cut-offs have been identified for these blood biomarkers. A kit for blood Aβ1-42/Aβ1-40 is commercially available in the U.S.; however, it does not provide a diagnosis, but simply estimates the risk of developing AD. Although blood-based AD biomarkers have a great potential in the diagnostic work-up of AD, they are not ready for the routine clinical use.

Serum total tau, neurofilament light, and glial fibrillary acidic protein are associated with mortality in a population study

BACKGROUND

Total tau (t-tau), neurofilament light (NfL), and glial fibrillary acidic protein (GFAP) are neuronal cytoskeletal biomarkers that may indicate greater risk of poor outcomes in age-related conditions, including mortality. Health disparities experienced by some racial minority subgroups may influence biomarker expression and effects on longevity. We aimed to examine (a) associations of serum t-tau, NfL, and GFAP with overall and cardiovascular mortality and (b) differences in associations by racial background.

METHODS

Data came from 1327 older participants from the Chicago Health and Aging Project (CHAP), a longitudinal population-based study. Cox proportional hazards regression models were used to examine associations between concentrations of serum t-tau, NfL, and GFAP biomarker(s) and mortality (overall/cardiovascular mortality based on age at death). Interaction terms were used to examine differences between African-American and European-American participants. Models were adjusted for age, sex, education, the APOE-ε4 allele, body mass index, chronic health conditions, and cognitive and physical functioning.

RESULTS

Models showed that fivefold higher concentrations of t-tau (HR = 1.46, 95% CI: 1.27, 1.68), NfL (HR = 2.13, 95% CI: 1.76, 2.58), and GFAP (HR = 1.43, 95% CI: 1.08, 1.90) were separately associated with increased risk of overall mortality, with higher risk in African Americans in t-tau or NfL. In models with all biomarkers, NfL (HR = 2.17, 95% CI: 1.65, 2.85) was associated with risk of overall mortality, with racial differences in t-tau. Higher concentrations of t-tau (HR = 1.32, 95% CI: 1.02, 1.70), NfL (HR = 1.95, 95% CI: 1.40, 2.72), and GFAP (HR = 1.87, 95% CI: 1.18, 2.98) were separately associated with risk of cardiovascular mortality, with racial differences in t-tau, NfL, or GFAP. In combined models, NfL (HR = 1.73, 95% CI: 1.08, 2.78) was associated with cardiovascular mortality.

CONCLUSIONS

Serum t-tau, NfL, and GFAP may be early indicators for mortality outcomes among older adults, with racial differences among associations.

Brain-derived tau: a novel blood-based biomarker for Alzheimer's disease-type neurodegeneration

Blood-based biomarkers for amyloid beta and phosphorylated tau show good diagnostic accuracies and agreements with their corresponding CSF and neuroimaging biomarkers in the amyloid/tau/neurodegeneration [A/T/(N)] framework for Alzheimer's disease. However, the blood-based neurodegeneration marker neurofilament light is not specific to Alzheimer's disease while total-tau shows lack of correlation with CSF total-tau. Recent studies suggest that blood total-tau originates principally from peripheral, non-brain sources. We sought to address this challenge by generating an anti-tau antibody that selectively binds brain-derived tau and avoids the peripherally expressed 'big tau' isoform. We applied this antibody to develop an ultrasensitive blood-based assay for brain-derived tau, and validated it in five independent cohorts (n = 609) including a blood-to-autopsy cohort, CSF biomarker-classified cohorts and memory clinic cohorts. In paired samples, serum and CSF brain-derived tau were significantly correlated (rho = 0.85, P < 0.0001), while serum and CSF total-tau were not (rho = 0.23, P = 0.3364). Blood-based brain-derived tau showed equivalent diagnostic performance as CSF total-tau and CSF brain-derived tau to separate biomarker-positive Alzheimer's disease participants from biomarker-negative controls. Furthermore, plasma brain-derived tau accurately distinguished autopsy-confirmed Alzheimer's disease from other neurodegenerative diseases (area under the curve = 86.4%) while neurofilament light did not (area under the curve = 54.3%). These performances were independent of the presence of concomitant pathologies. Plasma brain-derived tau (rho = 0.52-0.67, P = 0.003), but not neurofilament light (rho = -0.14-0.17, P = 0.501), was associated with global and regional amyloid plaque and neurofibrillary tangle counts. These results were further verified in two memory clinic cohorts where serum brain-derived tau differentiated Alzheimer's disease from a range of other neurodegenerative disorders, including frontotemporal lobar degeneration and atypical parkinsonian disorders (area under the curve up to 99.6%). Notably, plasma/serum brain-derived tau correlated with neurofilament light only in Alzheimer's disease but not in the other neurodegenerative diseases. Across cohorts, plasma/serum brain-derived tau was associated with CSF and plasma AT(N) biomarkers and cognitive function. Brain-derived tau is a new blood-based biomarker that outperforms plasma total-tau and, unlike neurofilament light, shows specificity to Alzheimer's disease-type neurodegeneration. Thus, brain-derived tau demonstrates potential to complete the AT(N) scheme in blood, and will be useful to evaluate Alzheimer's disease-dependent neurodegenerative processes for clinical and research purposes.

Plasma extracellular vesicles reveal early molecular differences in amyloid positive patients with early-onset mild cognitive impairment

In the clinical course of Alzheimer's disease (AD) development, the dementia phase is commonly preceded by a prodromal AD phase, which is mainly characterized by reaching the highest levels of Aβ and p-tau-mediated neuronal injury and a mild cognitive impairment (MCI) clinical status. Because of that, most AD cases are diagnosed when neuronal damage is already established and irreversible. Therefore, a differential diagnosis of MCI causes in these prodromal stages is one of the greatest challenges for clinicians. Blood biomarkers are emerging as desirable tools for pre-screening purposes, but the current results are still being analyzed and much more data is needed to be implemented in clinical practice. Because of that, plasma extracellular vesicles (pEVs) are gaining popularity as a new source of biomarkers for the early stages of AD development. To identify an exosome proteomics signature linked to prodromal AD, we performed a cross-sectional study in a cohort of early-onset MCI (EOMCI) patients in which 184 biomarkers were measured in pEVs, cerebrospinal fluid (CSF), and plasma samples using multiplex PEA technology of Olink^© proteomics. The obtained results showed that proteins measured in pEVs from EOMCI patients with established amyloidosis correlated with CSF p-tau¹⁸¹ levels, brain ventricle volume changes, brain hyperintensities, and MMSE scores. In addition, the correlations of pEVs proteins with different parameters distinguished between EOMCI Aβ( +) and Aβ(-) patients, whereas the CSF or plasma proteome did not. In conclusion, our findings suggest that pEVs may be able to provide information regarding the initial amyloidotic changes of AD. Circulating exosomes may acquire a pathological protein signature of AD before raw plasma, becoming potential biomarkers for identifying subjects at the earliest stages of AD development.

Machine Learning Reveals a Multipredictor Nomogram for Diagnosing the Alzheimer's Disease Based on Chemiluminescence Immunoassay for Total Tau in Plasma

Background

Predicting amnestic mild cognitive impairment (aMCI) in conversion and Alzheimer's disease (AD) remains a daunting task. Standard diagnostic procedures for AD population are reliant on neuroimaging features (positron emission tomography, PET), cerebrospinal fluid (CSF) biomarkers (Aβ1-42, T-tau, P-tau), which are expensive or require invasive sampling. The blood-based biomarkers offer the opportunity to provide an alternative approach for easy diagnosis of AD, which would be a less invasive and cost-effective screening tool than currently approved CSF or amyloid β positron emission tomography (PET) biomarkers.

Methods

We developed and validated a sensitive and selective immunoassay for total Tau in plasma. Robust signatures were obtained based on several clinical features selected by multiple machine learning algorithms between the three participant groups. Subsequently, a well-fitted nomogram was constructed and validated, integrating clinical factors and total Tau concentration. The predictive performance was evaluated according to the receiver operating characteristic (ROC) curves and area under the curve (AUC) statistics. Decision curve analysis and calibration curves are used to evaluate the net benefit of nomograms in clinical decision-making.

Results

Under optimum conditions, chemiluminescence analysis (CLIA) displays a desirable dynamic range within Tau concentration from 7.80 to 250 pg/mL with readily achieved higher performances (LOD: 5.16 pg/mL). In the discovery cohort, the discrimination between the three well-defined participant groups according to Tau concentration was in consistent agreement with clinical diagnosis (AD vs. non-MCI: AUC = 0.799; aMCI vs. non-MCI: AUC = 0.691; AD vs. aMCI: AUC = 0.670). Multiple machine learning algorithms identified Age, Gender, EMPG, Tau, ALB, HCY, VB12, and/or Glu as robust signatures. A nomogram integrated total Tau concentration and clinical factors provided better predictive performance (AD vs. non-MCI: AUC = 0.960, AD vs. aMCI: AUC = 0.813 in discovery cohort; AD vs. non-MCI: AUC = 0.938, AD vs. aMCI: AUC = 0.754 in validation cohort).

Conclusion

The developed assay and a satisfactory nomogram model hold promising clinical potential for early diagnosis of aMCI and AD participants.

Meta-analysis of genome-wide association studies identifies ancestry-specific associations underlying circulating total tau levels

Circulating total-tau levels can be used as an endophenotype to identify genetic risk factors for tauopathies and related neurological disorders. Here, we confirmed and better characterized the association of the 17q21 MAPT locus with circulating total-tau in 14,721 European participants and identified three novel loci in 953 African American participants (4q31, 5p13, and 6q25) at P < 5 × 10-8. We additionally detected 14 novel loci at P < 5 × 10-7, specific to either Europeans or African Americans. Using whole-exome sequence data in 2,279 European participants, we identified ten genes associated with circulating total-tau when aggregating rare variants. Our genetic study sheds light on genes reported to be associated with neurological diseases including stroke, Alzheimer's, and Parkinson's (F5, MAP1B, and BCAS3), with Alzheimer's pathological hallmarks (ADAMTS12, IL15, and FHIT), or with an important function in the brain (PARD3, ELFN2, UBASH3B, SLIT3, and NSD3), and suggests that the genetic architecture of circulating total-tau may differ according to ancestry.

Plasma Amyloid Beta, Total-Tau and Neurofilament Light Chain Levels and the Risk of Stroke: A Prospective Population-Based Study

BACKGROUND AND OBJECTIVES

To unravel whether Alzheimer's disease-related pathology or neurodegeneration play a role in stroke etiology, we determined the effect of plasma levels amyloid β (Aβ), total-tau and neurofilament light chain (NfL) on risk of stroke and its subtypes.

METHODS

Between 2002 and 2005, we measured plasma Aβ40, Aβ42, total-tau, and NfL in 4,661 stroke-free participants from the population-based Rotterdam Study. We used Cox proportional-hazards models to determine the association between these markers with incident stroke for the entire cohort, per stroke subtype, and by median age, sex, Apolipoprotein E (APOE) ε4 carriership, and education.

RESULTS

After a mean follow-up of 10.8 ± 3.3 years, 379 participants suffered a first-ever stroke. Log2 total-tau at baseline showed a non-linear association with risk of any stroke and ischemic stroke: compared to the first (lowest) quartile the adjusted hazard ratio for the highest quartile total-tau was 1.68, 95% CI: 1.18-2.40 for any stroke. Log2 NfL was associated with an increased risk of any stroke (HR per SD increase 1.27, 95% CI: 1.12-1.44), ischemic stroke, and hemorrhagic stroke (HR 1.56, 95% CI: 1.14-2.12). Log2 Aβ40, Aβ42, and Aβ42/40 ratio levels were not associated with stroke risk.Discussion Participants with higher total-tau and NfL at baseline had a higher risk of stroke and several stroke subtypes. These findings support the role of markers of neurodegeneration in the etiology of stroke.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that higher plasma levels of total-tau and NfL are associated with an increased risk of subsequent stroke.

Protein Aggregation in the Pathogenesis of Ischemic Stroke

Despite the distinction between ischemic stroke and neurodegenerative disorders, they share numerous pathophysiologies particularly those mediated by inflammation and oxidative stress. Although protein aggregation is considered to be a hallmark of neurodegenerative diseases, the formation of protein aggregates can be also induced within a short time after cerebral ischemia, aggravating cerebral ischemic injury. Protein aggregation uncovers a previously unappreciated molecular overlap between neurodegenerative diseases and ischemic stroke. Unfortunately, compared with neurodegenerative disease, mechanism of protein aggregation after cerebral ischemia and how this can be averted remain unclear. This review highlights current understanding on protein aggregation and its intrinsic role in ischemic stroke.

An Introduction to Ultrasensitive Assays for Plasma Tau Detection

The detection of plasma tau and its phosphorylation is technically challenging due to the relatively low sensitivity. However, in Alzheimer’s disease and other tauopathies, it is hypothesized that tau in the biofluid may serve as a biomarker. In recent years, several ultrasensitive assays have been developed, which can successfully detect tau and its phosphorylation in various biofluids, and collectively demonstrated the prognostic and diagnostic value of plasma tau/phosphorylated tau. Here we have summarized the principle of four ultrasensitive assays newly developed suitable for plasma tau detection, namely single-molecule array, immunomagnetic reduction assay, enhanced immunoassay using multi-arrayed fiber optics, and meso scale discovery assay, with their advantages and applications. We have also compared these assays with traditional enzyme-linked-immunosorbent serologic assay, hoping to facilitate future tau-based biomarker discovery for Alzheimer’s disease and other neurodegenerative diseases.

Association between plasma tau and postoperative delirium incidence and severity: a prospective observational study

BACKGROUND

Postoperative delirium is associated with increases in the neuronal injury biomarker, neurofilament light (NfL). Here we tested whether two other biomarkers, glial fibrillary acidic protein (GFAP) and tau, are associated with postoperative delirium.

METHODS

A total of 114 surgical patients were recruited into two prospective biomarker cohort studies with assessment of delirium severity and incidence. Plasma samples were sent for biomarker analysis including tau, NfL, and GFAP, and a panel of 10 cytokines. We determined a priori to adjust for interleukin-8 (IL-8), a marker of inflammation, when assessing associations between biomarkers and delirium incidence and severity.

RESULTS

GFAP concentrations showed no relationship to delirium. The change in tau from preoperative concentrations to postoperative Day 1 was greater in patients with postoperative delirium (P<0.001) and correlated with delirium severity (ρ=0.39, P<0.001). The change in tau correlated with increases in IL-8 (P<0.001) and IL-10 (P=0.0029). Linear regression showed that the relevant clinical predictors of tau changes were age (P=0.037), prior stroke/transient ischaemic attack (P=0.001), and surgical blood loss (P<0.001). After adjusting for age, sex, preoperative cognition, and change in IL-8, tau remained significantly associated with delirium severity (P=0.026). Using linear mixed effect models, only tau (not NfL or IL-8) predicted recovery from delirium (P<0.001).

CONCLUSIONS

The change in plasma tau was associated with delirium incidence and severity, and resolved over time in parallel with delirium features. The impact of this putative perioperative neuronal injury biomarker on long-term cognition merits further investigation.

CLINICAL TRIAL REGISTRATION

NCT02926417 and NCT03124303.

TDZD-8 alleviates delayed neurological sequelae following acute carbon monoxide poisoning involving tau protein phosphorylation

Objective: Acute carbon monoxide （CO）poisoning can cause delayed neurological sequelae (DNS). Glycogen synthase kinase 3β (GSK-3β) /Tau protein pathway is reported to play a key role in neurological abnormalities. In the present study, we aimed to determine the role of GSK-3β/Tau in DNS following acute CO poisoning.Methods: 4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione (TDZD-8), a specific non-competitive inhibitor of GSK-3β, was used to inhibit GSK-3β. Twenty-four male Sprague-Dawley rats were randomly assigned to the three groups: Control group, CO group and CO-TDZD-8 group. Rats breathed 1000 ppm CO for 40 minutes and then 3000 ppm for up to 20 minutes until they lost consciousness. TDZD-8 (1 mg/kg) was administered intravenously three times after the end of CO exposure at 0, 24, 48 hours late. Learning and memory abilities were observed using the Morris Water Maze (MWM). Brain histological changes were evaluated by hematoxylin-eosin staining. Moreover, the expression levels of Tau and GSK-3β were detected after acute carbon monoxide poisoning.Results: TDZD-8 significantly attenuated the learning and memory dysfunction induced by acute CO poisoning, ameliorated the histology structure of damaged neural cells in cortex and hippocampus CA1 area. TDZD-8 clearly decreased p-Tau expression, reversed the reduction of p-GSK-3β induced by acute CO poisoning.Conclusions: The therapeutic effect of TDZD-8 in alleviating DNS caused by acute CO poisoning is related to the inactivation of Tau by intensifying the level of GSK-3β phosphorylation.

A soluble truncated tau species related to cognitive dysfunction is elevated in the brain of cognitively impaired human individuals

Neurofibrillary tangles are a pathological hallmark of Alzheimer’s disease, and their levels correlate with the severity of cognitive dysfunction in humans. However, experimental evidence suggests that soluble tau species cause cognitive deficits and memory impairment. Our recent study suggests that caspase-2 (Casp2)-catalyzed tau cleavage at aspartate 314 mediates synaptic dysfunction and memory impairment in mouse and cellular models of neurodegenerative disorders. Δtau314, the C-terminally-truncated cleavage products, are soluble and present in human brain. In addition, levels of Δtau314 proteins are elevated in the brain of the cognitively impaired individuals compared to the cognitively normal individuals, indicating a possible role for Δtau314 proteins in cognitive deterioration. Here we show that (1) Δtau314 proteins are present in the inferior temporal gyrus of human brains; (2) Δtau314 proteins are generated from all six tau splicing isoforms, (3) levels of both Casp2 and Δtau314 proteins are elevated in cognitively impaired individuals compared to cognitively normal individuals, and (4) levels of Δtau314 proteins show a modest predictive value for dementia. These findings advance our understanding of the characteristics of Δtau314 proteins and their relevance to cognitive dysfunction and shed light on the contribution of Casp2-mediated Δtau314 production to cognitive deterioration.