Specific associations between plasma biomarkers and postmortem amyloid plaque and tau tangle loads

Multimorbidity and fluid biomarkers of Alzheimer's disease: a systematic review

PURPOSE

This systematic review aimed to summarize the evidence on the association between multimorbidity and fluid biomarkers of Alzheimer's disease (AD).

METHODS

We systematically searched PubMed, Web of Science, and Embase for studies investigating the association between multimorbidity-defined as the co-occurrence of multiple chronic conditions in the same individual-and levels of cerebrospinal fluid (CSF) or blood biomarkers of AD, focusing on the most established AD biomarkers (amyloid-beta, phosphorylated-tau, total-tau, neurofilament light chain, and glial fibrillary acidic protein). Studies were selected following PRISMA guidelines.

RESULTS

Out of 3,104 records, we identified 10 cross-sectional studies. Four studies assessed CSF biomarkers in dementia-free participants with mean age between 61.8 and 66.6 years, yielding mixed findings with no consistent association between multimorbidity and CSF biomarkers. Six studies focused on blood biomarkers in participants with mean age ranging from 66.5 to 76.4 years, five of which included individuals with dementia. Most of these studies reported an association between multimorbidity and elevated blood biomarker levels.

CONCLUSIONS

This review suggests a significant association between multimorbidity and AD blood biomarkers in older populations, while the results on CSF are mixed and inconsistent. Further research is needed, particularly longitudinal studies assessing both CSF and blood biomarkers within the same populations.

How well do plasma Alzheimer's disease biomarkers reflect the CSF amyloid status?

BACKGROUND

Can plasma biomarkers as well as cerebrospinal fluid (CSF) perform in the separation of amyloid-beta-positive (Aβ+) vs amyloid-beta-negative (Aβ-) groups across an age range seen in an NHS cognitive disorder clinic?

METHODS

As part of the routine diagnostic investigation of 111 clinic patients who had contemporaneous blood and CSF samples taken, patients were categorised into Aβ+ and Aβ- groups based on their CSF in an Aβ42/40 ratio. We then evaluated four single molecule array (Simoa) Quanterix assays, quantifying single plasma analytes and ratios (p-tau217, p-tau217/Aβ42 ratio, p-tau181, p-tau181/Aβ42 ratio and Aβ42/40 ratio) in their ability to distinguish between these groups and the effect of age.

RESULTS

The median (range) age of participants was 66 (55-79) years with 48 females (43.2%). The areas under the curve (AUC), not accounting for age, for the ability to discriminate Aβ+ from Aβ- groups were plasma p-tau217 AUC=0.94, Aβ42/40 AUC=0.78 and p-tau181 AUC=0.77. Combining p-tau217/Aβ42 increased the AUC to 0.97. The difference between the groups was influenced by age with less separation in older individuals: a significant negative interaction term between age and group for plasma p-tau217 concentrations (-0.037, p=0.013) and p-tau217/Aβ42 ratio (-0.007, p=0.008).

CONCLUSIONS

There was variable performance of plasma biomarkers to recapitulate the CSF assay. Both p-tau217 and p-tau217/Aβ42 showed excellent promise as surrogates of CSF amyloid status, although with slightly reduced performance in older individuals. There was poorer discriminatory ability for p-tau181 and Aβ42/40. Further research is needed to address potential age-related confounds.

Promising clinical tools for specific Alzheimer disease diagnosis from plasma pTau217 and ApoE genotype in a cognitive disorder unit

Alzheimer's disease (AD) diagnosis relies on cerebrospinal fluid (CSF) biomarkers or amyloid PET. Alternatives for AD diagnosis from blood samples are needed to develop a fully-automated early-diagnosis approach, potentially implemented in a cognitive disorder unit. Plasma p-Tau217 was determined in patients diagnosed with AD (n = 134) or non-AD (n = 132), from CSF biomarkers (Aβ42/Aβ40). A logistic regression model was developed. The predictive performance was assessed using a training set (70% of data) and internally validated with a test set (30% of data) and 1000 iterations. A nomogram and a double cut-off strategy were proposed to visualize the model results, and stratify patients (AD, non-AD, uncertain), respectively. The model (plasma p-Tau217, ApoE, age) showed satisfactory performance (AUC 0.94, sensitivity 0.85, specificity 0.89); so, together with the corresponding nomogram, it could be applied in specialized clinical contexts. The model including only plasma p-Tau217 (AUC 0.93, sensitivity 0.72, specificity 0.96) would be a useful approach in less specialized clinics. The corresponding two-cut-off strategy for the first model were as AD probability (< 0.41 non-AD, > 0.57 AD). This study provided clinical tools (nomogram, double cut-off) for identifying Aβ positivity at a cognitive disorder unit, which would lead to reduce the CSF analysis.

Plasma p-tau217 and tau-PET predict future cognitive decline among cognitively unimpaired individuals: implications for clinical trials

Plasma p-tau217 and tau positron emission tomography (PET) are strong prognostic biomarkers in Alzheimer's disease (AD), but their relative performance in predicting future cognitive decline among cognitively unimpaired (CU) individuals is unclear. In a head-to-head comparison study including nine cohorts and 1,474 individuals, we show that plasma p-tau217 and medial temporal lobe tau-PET signal display similar associations with cognitive decline on a global cognitive composite test (R2PET = 0.34 versus R2plasma = 0.33, Pdifference = 0.653) and with progression to mild cognitive impairment (hazard ratio (HR)PET = 1.61 (1.48-1.76) versus HRplasma = 1.57 (1.43-1.72), Pdifference = 0.322). Combined plasma and PET models were superior to the single-biomarker models (R2 = 0.35, P < 0.01). Sequential selection using plasma phosphorylated tau at threonine 217 (p-tau217) and then tau-PET reduced the number of participants required for a clinical trial by 94%, compared to a 76% reduction when using plasma p-tau217 alone. Thus, plasma p-tau217 and tau-PET showed similar performance for predicting future cognitive decline in CU individuals, and their sequential use enhances screening efficiency for preclinical AD trials.

Biomarker discovery in Alzheimer's and neurodegenerative diseases using Nucleic Acid Linked Immuno-Sandwich Assay

INTRODUCTION

Recent advancements in immunological methods accurately quantify biofluid biomarkers for Alzheimer's disease (AD) pathology. Despite progress, more biomarkers, ideally in blood, are needed for effective disease monitoring for AD and other neurodegenerative proteinopathies.

METHODS

We used the Nucleic Acid Linked Immuno-Sandwich Assay (NULISA) central nervous system panel for biomarker quantification in plasma, serum, and cerebrospinal fluid of patients with AD, mild cognitive impairment, Lewy body dementia, progranulin (GRN) mutation carriers.

RESULTS

NULISA identified phosphorylated tau217 and neurofilament light chain as the most deregulated biomarkers in the AD continuum and GRN mutation carriers, respectively. Importantly, numerous novel proteomic changes were observed in each disease endophenotype, which included synaptic processing, inflammation, microglial reactivity, TAR DNA-binding protein 43, and α-synuclein pathology.

DISCUSSION

We underline the potential of next-generation biomarker identification tools to detect novel proteomic features that also incorporate established biomarkers. These findings highlight the importance of continued biomarker discovery to improve treatment decisions and help us better understand the complexities of neurodegenerative disorders.

HIGHLIGHTS

The, direct, or indirect, measures in blood that complement phosphorylated tau (p-tau)217 for other proteinopathies or disease progression are urgently needed. Significant novel proteomic changes were observed in each disease endophenotype in plasma, serum, and cerebrospinal fluid, which included proteins involved in synaptic processing, inflammation, microglial reactivity, TAR DNA-binding protein 43, and α-synuclein pathology. Nucleic Acid Linked Immuno-Sandwich Assay continued to unbiasely highlight p-tau217 and neurofilament light chain as the most significantly deregulated blood biomarkers in the Alzheimer's disease continuum and progranulin mutation carriers, respectively.

Lecanemab-Associated Amyloid-β Protofibril in Cerebrospinal Fluid Correlates with Biomarkers of Neurodegeneration in Alzheimer's Disease

OBJECTIVE

The Clarity AD phase III trial showed that lecanemab reduced amyloid markers in early Alzheimer's disease (AD) and resulted in less decline on measures of cognition and function than placebo. Herein, we aimed to characterize amyloid-β (Aβ) protofibril (PF) captured by lecanemab in human cerebrospinal fluid (CSF) from living participants with different stages in AD, which enable an enhanced understanding of the dynamic changes of lecanemab-associated Aβ-PF (Lec-PF) in vivo.

METHODS

We newly developed a unique and highly sensitive immunoassay method using lecanemab that selectively captures Lec-PF. The CSF level of Lec-PF, Aβ42, Aβ40, p-tau181, p-tau 217, total tau, and neurogranin were measured in Japanese participants (n = 163). The participants in this study consisted of 48 cognitively unimpaired Aβ-negative (CU-), 8 cognitively impaired diagnosed as suspected non-Alzheimer's disease pathophysiology, 9 cognitively unimpaired Aβ-positive (CU+), 34 Aβ-positive with mild cognitive impairment (MCI+), and 64 Aβ-positive with AD dementia (AD+).

RESULTS

The CSF Lec-PF levels significantly increased in the groups of MCI+ and AD+ compared with CU- group. Notably, CSF Lec-PF showed modest correlation with plaque-associated biomarkers in Aβ-positive participants and stronger correlation with neurodegeneration biomarkers, such as CSF total tau and neurogranin, suggesting that CSF Lec-PF levels proximally reflect neurodegeneration as well as the amount of senile amyloid plaques.

INTERPRETATION

This is the first report describing Aβ-PF species captured by lecanemab in human CSF and supporting that Lec-PF is correlated with neurodegeneration in AD and may explain the mechanism of the clinical effect of lecanemab. ANN NEUROL 2025;97:993-1006.

Dysregulated calcium signaling in the aged macaque entorhinal cortex associated with tau hyperphosphorylation

Introduction

Tau pathology in sporadic Alzheimer's disease (AD) follows a distinct pattern, beginning in the entorhinal cortex (ERC) and spreading to interconnected brain regions. Early-stage tau pathology, characterized by soluble phosphorylated tau, is difficult to study in human brains post-mortem due to rapid dephosphorylation.

Methods

Rhesus macaques, which naturally develop age-related tau pathology resembling human AD, provide an ideal model for investigating early tau etiology. This study examines the molecular processes underlying tau pathology in the macaque ERC, focusing on calcium and inflammatory signaling pathways using biochemical and immunohistochemistry.

Results

Our findings reveal an age-related decrease in PDE4 phosphodiesterase that hydrolyzes cAMP and increases in calpain-2 and glutamate carboxypeptidase II that occur in parallel with early-stage tau hyperphosphorylation at multiple epitopes (pS214-tau, pT181-tau, pT217-tau).

Discussion

These findings suggest that dysregulated calcium signaling in ERC, beginning in middle-age, may prime tau for hyperphosphorylation, potentially driving the early stages of AD, advancing our understanding of how ERC vulnerabilities contribute to neurodegeneration in AD.

The Current Role of Tau PET Imaging in Neurodegeneration

Neurodegenerative tauopathies are characterized by the pathological hyperphosphorylation of tau proteins that subsequently form aggregates. Tau PET tracers with affinity to bind these pathological tau aggregates have been developed to measure disease progression and to support therapeutic drug development. In this review, we summarize the pathophysiology of tau throughout the range of neurodegenerative tauopathies. We outline the available first- and second-generation tau PET tracers, with a focus on new tau PET tracer developments, and discuss the quantification of tau PET images. Next, we summarize how tau PET relates to cerebrospinal fluid and plasma tau biomarkers. Finally, we review the current recommendations on the clinical use of tau PET versus fluid tau biomarkers in diagnosis, prognosis and treatment development.

Exploring inflammation-related protein expression and its relationship with TSPO PET in Alzheimer's disease

INTRODUCTION

To understand the role of neuroinflammation in Alzheimer's disease (AD), we characterized immune-related proteins in central and peripheral biofluids.

METHODS

Selection of participants from the Translational Biomarker of Aging and Dementia (TRIAD) cohort with available translocator protein (TSPO) positron emission tomography (PET), cerebrospinal fluid (CSF) (n = 97), and plasma (n = 165). Biofluid samples analyzed with Olink technology (368 inflammation proteins).

RESULTS

Elevated proteins levels in CSF of TSPO-positive individuals were identified. Functional enrichment analysis of CSF proteins revealed processes implicated in AD (MAPK, ERK cascades, cytokine, and leukocyte signaling). Selected candidates (CXCL1 and TNFRSF11B) showed high correlation with each other in CSF and with TSPO PET signal, but weaker associations with amyloid and tau PET. No significantly changed proteins in plasma between TSPO groups were found.

DISCUSSION

This explorative study identified two potential targets in CSF showing correlations with TSPO, amyloid and tau PET, suggesting a direct link between neuroinflammation, expression of these proteins and their potential implication in AD.

HIGHLIGHTS

Several proteins are elevated in CSF of TSPO PET-positive individuals, linking them to neuroinflammation. Elevated CSF proteins were enriched in pathways such as MAPK, ERK, and cytokine signaling, linking them to the AD pathophysiology. Candidate proteins (CXCL1 and TNFRSF11B) correlated strongly with TSPO PET, particularly in brain regions known to be affected in AD. Although none of the plasma proteins remained significant after multiple comparisons correction when comparing their expression between TSPO groups, as done for CSF, candidate CSF proteins were found to correlate with plasmatic proteins, highlighting the complexity of the immune system.

Plasma biomarkers as core mediators in functional network abnormalities: Evidence from a two-cohort study

INTRODUCTION

Researchers have reported an association among amyloid beta (Aβ), tau deposition, and functional networks. Nevertheless, whether plasma biomarkers mediate this process remains unclear.

METHODS

Three hundred and forty-eight participants with available plasma biomarkers, Aβ positron emission tomography (PET), and resting-state functional magnetic resonance imaging were obtained from two independent cohorts: SILCODE (n = 147) and ADNI (n = 201). Correlations among plasma biomarkers, functional connectivity, and global standardized uptake value ratio (SUVR) were assessed, and mediating effects were analyzed to explore underlying pathways.

RESULTS

Plasma biomarkers (p-tau181, p-tau217, neurofilament light, glial fibrillary acidic protein, Aβ42/40) demonstrated significant correlations with global SUVR and functional connectivity across networks (p < 0.05). Significant functional connectivity variations in different networks were observed across various Aβ stages, with differences mediated by plasma biomarkers. The crucial pathway exhibited fully mediated effects: Aβ PET SUVR-plasma biomarkers (mainly p-tau181 and p-tau217) - various functional networks.

DISCUSSION

Our study highlights the core mediating role of plasma biomarkers (mainly p-tau181 and p-tau217) in the progression of Aβ accumulation and in various functional network alterations.

HIGHLIGHTS

Plasma biomarkers demonstrated significant mediating effects on Aβ deposition and functional network alterations across different Aβ stages in both East Asian and Western cohorts. Significant functional connectivity variations in different brain networks were observed throughout AD progression in two cohorts, particularly across various Aβ stages. Among all plasma biomarkers, p-tau217 and p-tau181 demonstrated more comprehensive and fully mediating effects compared to other biomarkers, influencing connectivity alterations in the various functional networks. The plasma biomarkers exhibited great potential for tracking pathologic progression, functional network alterations, and early disease identification in East Asian and Western cohorts.

Higher plasma soluble TREM2 correlates with reduced cerebral tau accumulation in Alzheimer's disease

Loss-of-function mutation of triggering receptor expressed on myeloid cell 2 (TREM2) is associated with increased risks for Alzheimer's disease (AD). Recent animal studies reveal that the activation of peripheral TREM2 signaling may affect cerebral β-amyloid (Aβ) and tau aggregates. However, the underlying relationship between peripheral TREM2 and brain AD pathology has not yet been well-elucidated in the aging population. In this study, we collected 318 Chinese older adults with Aβ PET and plasma biomarker measures, including soluble TREM2 (sTREM2) and glial fibrillary acidic protein (GFAP), a proxy for astrocyte reactivity. Additionally, 129 participants underwent tau PET scans. We explored the association between plasma sTREM2, GFAP, and primary AD pathology. Plasma sTREM2 was negatively associated with reduced temporal tau PET burden in participants with abnormal Aβ and tau pathology. Higher plasma sTREM2 was related to the weaker association of Aβ pathology and plasma phosphorylated tau with tau PET increases. In contrast, elevated plasma GFAP was related to greater Aβ and tau PET burden along with stronger Aβ-related tau accumulation. Finally, higher plasma sTREM2 was linked to attenuated strength of the association between plasma GFAP and tau PET increases at both pre-defined regions of interest and voxel levels. Altogether, our findings suggest distinct relationships between plasma sTREM2 and GFAP with cerebral tau pathology, providing novel insights into the roles of peripheral TREM2 signaling and astrocytic reactivity in AD neuropathological development. This study has important implications, such as targeting the peripheral TREM2 signature, which may be a potential strategy for future AD therapies.

Plasma MTBR-tau243 biomarker identifies tau tangle pathology in Alzheimer's disease

Insoluble tau aggregates within neurofibrillary tangles are a defining neuropathological feature of Alzheimer's disease (AD) and closely correlate with clinical symptoms. Although tau pathology can be assessed using tau positron emission tomography, a more accessible biomarker is needed for diagnosis, prognosis and tracking treatment effects. Here we present a new plasma tau species, the endogenously cleaved, microtubule-binding region containing residue 243 (eMTBR-tau243), which specifically reflects tau tangle pathology. Across the AD spectrum in three different cohorts (n = 108, 55 and 739), plasma eMTBR-tau243 levels were significantly elevated at the mild cognitive impairment stage and increased further in dementia. Plasma eMTBR-tau243 showed strong associations with tau positron emission tomography binding (β = 0.72, R2 = 0.56) and cognitive performance (β = 0.60, R2 = 0.40), outperforming other plasma tau (%p-tau217 and %p-tau205) biomarkers. These results suggest that plasma eMTBR-tau243 may be useful for estimating the tauopathy load in AD, thereby improving the diagnostic evaluation of AD in clinical practice and monitoring the efficacy of tau-targeted therapies in clinical trials.

Diagnostic performance of plasma p-tau217 in a memory clinic cohort using the Lumipulse automated platform

BACKGROUND

Plasma biomarkers for Alzheimer's disease (AD) are a promising tool for accessible and accurate biological diagnostics. However, data in clinical practice are needed to better understand their diagnostic and prognostic ability in memory unit patients.

METHODS

We analyzed plasma phosphorylated tau at threonine 217 (p-tau217) and neuroflament light chain (NfL) levels and AD cerebrospinal fluid (CSF) biomarkers in a group of 493 subjects using the Lumipulse G600II platform. The sample includes 340 patients from our memory unit (142 dementia, 186 mild cognitive impairment, and 12 with subjective complaints) and 153 cognitively unimpaired volunteers. We have correlated plasma and CSF biomarkers; we have analyzed plasma biomarker levels as a function of clinical diagnosis, cognitive status and amyloid status. We have also studied the ability of p-tau217 to discriminate between amyloid-positive and -negative subjects according to CSF using receiver operating characteristic curves.

RESULTS

Plasma p-tau217 correlated significantly with CSF Aβ42/Aβ40 (Rho = -0.75; p-value < 0.001), p-tau181 (r = 0.66; p-value < 0.001), and t-tau (r = 0.59; p-value < 0.001). Plasma NfL correlated with CSF NfL (r = 0.48; p-value < 0.001). By clinical diagnosis, plasma p-tau217 levels showed to be higher in AD patients than in healthy controls (difference = 0.63 pg/ml; p-value < 0.001), FTD (difference = 0.60 pg/ml; p-value < 0.001), and nondegenerative dementias (difference = 0.61 pg/ml; p-value < 0.001). Plasma p-tau217 showed an area under the curve of 0.95 to discriminate between A + and A- subjects (95%CI 0.93-0.97).

CONCLUSION

Plasma p-tau217 shows excellent results for detecting amyloid pathology at brain level in a clinical setting with an AUC of 0.95. It is a highly specific marker of AD and increases progressively along the disease continuum. Using plasma p-tau217 as an initial diagnostic tool with cut-offs at sensitivities and specificities of 95 or 97.5% could save between 57.4-84.8% of LP/PETs with diagnostic accuracies of 95-97%. Plasma NfL increases progressively at different cognitive stages.

Performance of plasma biomarkers for diagnosis and prediction of dementia in a Brazilian cohort

Despite remarkable progress in the biomarker field in recent years, local validation of plasma biomarkers of Alzheimer's disease (AD) and dementia is still lacking in Latin America. In this longitudinal cohort study of 145 elderly Brazilians, we assess the diagnostic performance of plasma biomarkers, based on clinical diagnosis and CSF biomarker positivity. Follow-up data of up to 4.7 years were used to determine performance in predicting diagnostic conversions. Participants were clinically categorized as cognitively unimpaired (n = 49), amnestic mild cognitive impairment (n = 29), AD (n = 38), Lewy body dementia (n = 22), or vascular dementia (n = 7). Plasma Tau, Aβ40, Aβ42, NfL, GFAP, pTau231, pTau181 and pTau217 were measured on the SIMOA HD-X platform. Plasma pTau217 showed excellent performance determining CSF biomarker status in the cohort, either alone (ROC AUC = 0.94, 95% CI: [0.88-1.00]) or as a ratio to Aβ42 (ROC AUC = 0.98, 95% CI: [0.94-1.00]). This study comprises an initial step towards local validation and adoption of dementia biomarkers in Brazil.

Biofluid-based staging of Alzheimer's disease

Recently, conceptual systems for the in vivo staging of Alzheimer's disease (AD) using fluid biomarkers have been suggested. Thus, it is important to assess whether available fluid biomarkers can successfully stage AD into clinically and biologically relevant categories. In the TRIAD cohort, we explored whether p-tau217, p-tau205 and NTA-tau (biomarkers of early, intermediate and late AD pathology, respectively) have potential for biofluid-based staging in cerebrospinal fluid (CSF; n = 219) and plasma (n = 150), and compared them in a paired CSF and plasma subset (n = 76). Our findings suggest a good concordance between biofluid staging and underlying pathology when classifying amyloid-positivity into three categories based on neurofibrillary pathology: minimal/non-existent (p-tau217 positive), early-to-intermediate (p-tau217 and p-tau205 positivity), and advanced tau tangle deposition (p-tau217, p-tau205 and NTA-tau positive), as indexed by tau-PET. Discordant cases accounted for 4.6% and 13.3% of all CSF and plasma measurements respectively (9.2% and 11.8% in paired samples). Notably, CSF- and plasma-based staging matched one another in 61.7% of the cases, while approximately 32% of the remaining participants were one to three biofluid stages higher in CSF as compared to plasma. Overall, these exploratory results suggest that biofluid staging of AD holds potential for offering valuable insights into underlying AD hallmarks and disease severity. However, its applicability beyond molecular characterization at research settings has yet to be demonstrated.

Alzheimer's disease neuropathology and its estimation with fluid and imaging biomarkers

Alzheimer's disease (AD) is neuropathologically characterized by the extracellular deposition of the amyloid-β peptide (Aβ) and the intraneuronal accumulation of abnormal phosphorylated tau (τ)-protein (p-τ). Most frequently, these hallmark lesions are accompanied by other co-pathologies in the brain that may contribute to cognitive impairment, such as vascular lesions, intraneuronal accumulation of phosphorylated transactive-response DNA-binding protein 43 (TDP-43), and/or α-synuclein (αSyn) aggregates. To estimate the extent of these AD and co-pathologies in patients, several biomarkers have been developed. Specific tracers target and visualize Aβ plaques, p-τ and αSyn pathology or inflammation by positron emission tomography. In addition to these imaging biomarkers, cerebrospinal fluid, and blood-based biomarker assays reflecting AD-specific or non-specific processes are either already in clinical use or in development. In this review, we will introduce the pathological lesions of the AD brain, the related biomarkers, and discuss to what extent the respective biomarkers estimate the pathology determined at post-mortem histopathological analysis. It became evident that initial stages of Aβ plaque and p-τ pathology are not detected with the currently available biomarkers. Interestingly, p-τ pathology precedes Aβ deposition, especially in the beginning of the disease when biomarkers are unable to detect it. Later, Aβ takes the lead and accelerates p-τ pathology, fitting well with the known evolution of biomarker measures over time. Some co-pathologies still lack clinically established biomarkers today, such as TDP-43 pathology or cortical microinfarcts. In summary, specific biomarkers for AD-related pathologies allow accurate clinical diagnosis of AD based on pathobiological parameters. Although current biomarkers are excellent measures for the respective pathologies, they fail to detect initial stages of the disease for which post-mortem analysis of the brain is still required. Accordingly, neuropathological studies remain essential to understand disease development especially in early stages. Moreover, there is an urgent need for biomarkers reflecting co-pathologies, such as limbic predominant, age-related TDP-43 encephalopathy-related pathology, which is known to modify the disease by interacting with p-τ. Novel biomarker approaches such as extracellular vesicle-based assays and cryptic RNA/peptides may help to better detect these co-pathologies in the future.

Blood phosphorylated Tau217 distinguishes amyloid-positive from amyloid-negative subjects in the Alzheimer's disease continuum. A systematic review and meta-analysis

BACKGROUND

Alzheimer's disease (AD) is the leading cause of dementia worldwide, and cost-effective tools to detect amyloid pathology are urgently needed. Blood-based Tau phosphorylated at threonine 217 (pTau217) seems promising, but its reliability as a proxy for cerebrospinal fluid (CSF) status and ability to identify patients within the AD spectrum remain unclear.

METHODS

We performed a systematic review and meta-analysis on the potential of blood pTau217 to differentiate amyloid-positive (A+) and amyloid-negative (A-) subjects. We included original studies reporting quantitative data on pTau217 concentrations in both blood and CSF in the AD continuum. The single-group meta-analysis computed the pooled pTau217 levels in blood and in CSF, separately in the A+ and A- groups, while the head-to-head meta-analysis compared the mean pTau217 concentrations in the A+ versus A- subjects, both in blood and CSF, stratifying by assessment method in both cases.

RESULTS

Ten studies (819 A+; 1055 A-) were included. The mean pTau217 levels resulted higher in CSF than in blood and, crucially, in A+ individuals than in A- ones, regardless of the laboratory method employed. Most importantly, all laboratory techniques reliably distinguished A+ from A- subjects, whether applied to CSF or blood samples.

CONCLUSIONS

These results confirm that blood-based pTau217 is a reliable marker of amyloid pathology with significant implications for clinical practice in the AD continuum. Indeed, pTau217 might be a non-invasive, scalable biomarker for early AD detection, reducing the reliance on more invasive, expansive, and less accessible methods.

CLINICAL TRIAL REGISTRATION

Prospero CRD42024565187.

Considerations in the clinical use of amyloid PET and CSF biomarkers for Alzheimer's disease

Amyloid-β (Aβ) positron emission tomography (PET) imaging and cerebrospinal fluid (CSF) biomarkers are now established tools in the diagnostic workup of patients with Alzheimer's disease (AD), and their use is anticipated to increase with the introduction of new disease-modifying therapies. Although these biomarkers are comparable alternatives in research settings to determine Aβ status, biomarker testing in clinical practice requires careful consideration of the strengths and limitations of each modality, as well as the specific clinical context, to identify which test is best suited for each patient. This article provides a comprehensive review of the pathologic processes reflected by Aβ-PET and CSF biomarkers, their performance, and their current and future applications and contexts of use. The primary aim is to assist clinicians in making better-informed decisions about the suitability of each biomarker in different clinical situations, thereby reducing the risk of misdiagnosis or incorrect interpretation of biomarker results. HIGHLIGHTS: Recent advances have positioned Aβ PET and CSF biomarkers as pivotal in AD diagnosis. It is crucial to understand the differences in the clinical use of these biomarkers. A team of experts reviewed the state of Aβ PET and CSF markers in clinical settings. Differential features in the clinical application of these biomarkers were reviewed. We discussed the role of Aβ PET and CSF in the context of novel plasma biomarkers.

Accuracy of plasma biomarkers to detect Alzheimer's disease proteinopathy prior to dementia

INTRODUCTION

Plasma biomarkers sensitive to Alzheimer's disease (AD) proteinopathy prior to the onset of dementia have significant implications for early detection.

METHODS

In 304 individuals without dementia, we investigated whether C2N Diagnostics' mass spectrometry (MS)-based plasma biomarkers (amyloid beta 42/40, %phosphorylated tau [p-tau]181, and %p-tau217) and amyloid probability scores (APS, PrecivityAD and APS2, PrecivityAD2) are associated with brain amyloid, brain tau, or preclinical cognitive decline.

RESULTS

In this cohort study, %p-tau217 and the APS2 had high discriminative accuracy (area under the curve > 0.93) for identifying elevated brain amyloid and tau and were associated with faster preclinical cognitive decline. Using %p-tau217 or the APS2 in a theoretical AD trial screening scenario reduced amyloid positron emission tomography imaging costs up to 41% or 45%, respectively.

DISCUSSION

These findings suggest that C2N Diagnostics' MS-based plasma biomarkers can detect brain amyloid and tau with high accuracy prior to dementia and could aid in identifying candidates for clinical trials or therapeutic intervention.

HIGHLIGHTS

C2N plasma biomarkers differentiated Alzheimer's disease proteinopathy status prior to dementia. Plasma %phosphorylated tau (p-tau)217 and the C2N Diagnostics PrecivityAD2 (APS2) were concordant with amyloid and tau positron emission tomography status. Plasma %p-tau217 and the APS2 were associated with preclinical cognitive decline.

Temporal Dynamics and Biological Variability of Alzheimer Biomarkers

Importance

Understanding the characteristics of discordance between plasma biomarkers and positron emission tomography (PET) results in Alzheimer disease (AD) is crucial for accurate interpretation of the findings.

Objective

To compare (1) medical comorbidities affecting plasma biomarker concentrations, (2) imaging and clinical features, and (3) cognitive changes between plasma biomarker and PET discordant and concordant cases.

Design, Setting, and Participants

This multicenter cohort study, conducted between 2016 and 2023, included individuals with unimpaired cognition, mild cognitive impairment, or Alzheimer-type dementia, who had both amyloid β (Aβ) PET imaging and plasma biomarkers. A subset of participants also underwent tau PET imaging.

Exposures

Participants were categorized into 4 groups based on their plasma and PET biomarker results: plasma-/PET-, plasma+/PET-, plasma-/PET+, and plasma+/PET+.

Main Outcomes and Measures

Clinical characteristics were compared between the 4 groups, focusing on the discordant groups.

Results

A total of 2611 participants (mean [SD] age was 71.2 [8.7] years; 1656 female [63.4%]), of whom 124 additionally underwent tau PET, were included. Among the plasma biomarkers, phosphorylated tau (p-tau) 217 exhibited the highest concordance rate with Aβ (2326 of 2571 [90.5%]) and tau (100 of 120 [83.3%]) PET. The p-tau217+/Aβ PET- group was older (mean [SD] age, 75.8 [7.2] years vs 70.0 [8.8] years; P < .001) with a higher prevalence of hypertension (56 of 152 [36.8%] vs 266 of 1073 [25.0%]), diabetes (40 of 152 [26.3%] vs 156 of 1059 [14.7%]), and chronic kidney disease (17 of 152 [11.2%] vs 21 of 1073 [2.0%]) compared with the p-tau217-/Aβ PET- group (P < .001 for all). Body mass index was higher in p-tau217-/Aβ PET+ than in p-tau217+/Aβ PET+ (mean [SD], 24.1 [2.8] vs 23.1 [3.1], respectively; P = .001; calculated as weight in kilograms divided by height in meters squared). The p-tau217+/Aβ PET- group had lower hippocampal volume (mean [SD], 2555.4 [576.9] vs 2979.1 [545.8]; P < .001) and worse clinical trajectory compared with p-tau217-/Aβ PET- (β = -0.53; P < .001). In contrast, tau PET discordant cases did not show significant differences in medical comorbidities or clinical outcomes compared with the p-tau217-/tau PET- group. Only the p-tau 217+/tau PET+ group demonstrated faster cognitive deterioration compared with the p-tau 217-/tau PET- group (β = -1.66; P < .001).

Conclusions and Relevance

Results of this cohort study suggest that the mechanisms underlying the discordance between plasma biomarkers and PET findings may be multifaceted, underscoring the need to consider the temporal dynamics and biological variability of plasma biomarkers.

Detection of Alzheimer Neuropathology in Alzheimer and Non-Alzheimer Clinical Syndromes With Blood-Based Biomarkers

Importance

Blood-based biomarkers for Alzheimer disease (AD) are clinically available, but their value is not well understood in syndromes typically associated with frontotemporal lobar degeneration syndromes (FTLD).

Objective

To investigate the clinical importance and detectability of AD in FTLD-related neurodegenerative syndromes using 3 plasma biomarkers, phosphorylated tau 217 (p-tau217), neurofilament light chain (NfL), and glial fibrillary acidic protein (GFAP).

Design, Setting, and Participants

This clinicopathological study took place at the University of California San Francisco Alzheimer Disease Research Center from August 2008 to July 2022. Autopsied individuals with clinical evaluation and neuropathological examination, diagnosed with clinical syndromes related to AD (n = 125), frontotemporal lobar degeneration (FTLD; n = 198), or cognitively unimpaired (CU) at the time of evaluation (n = 16) were included.

Exposures

AD-related or FTLD-related clinical syndromes or CU.

Main Outcomes and Measures

P-tau217, NfL, and GFAP were measured with single-molecule array (SIMOA). AD was defined as intermediate or high AD neuropathological change (ADNC) at autopsy. Clinical biomarker associations were evaluated using linear regressions. Imaging analyses used bayesian linear mixed-effects modeling.

Results

A total of 349 individuals (191 [55%] male; mean [SD] age at death, 72 [11] years) were included. AD was common in both AD-related syndromes (110/125 [88%]) and FTLD-related syndromes (45/198 [23%]). Neuropathological stage at autopsy was higher in AD-related syndromes (high ADNC: 82/88 [93%] AD vs 13/23 [56%] FTLD), and AD was frequently considered a copathology in FTLD-related syndromes (30/198 [15%]). Plasma p-tau217 concentrations were higher in AD-related syndromes (mean [SD], 0.28 [0.16] pg/mL) than FTLD-related syndromes (mean [SD], 0.10 [0.09] pg/mL) (P < .05). Plasma p-tau217 concentrations were highest in atypical AD-related syndromes (mean [SD], 0.33 [0.02] pg/mL), followed by typical late-onset amnestic syndromes (mean [SD], 0.27 [0.03] pg/mL). FTLD-related syndromes with AD (mean [SD], 0.19 [0.02] pg/mL) were higher compared to without (mean [SD], 0.07 [0.00] pg/mL). Plasma p-tau217 detected AD neuropathology across syndromes (area under the receiver operating characteristic curve [AUC], 0.95; 95% CI, 0.93-0.97), with slightly better performance in AD-related syndromes (AUC, 0.98; 95% CI, 0.95-1.00) compared to FTLD-related syndromes (AUC, 0.89; 95% CI, 0.83-0.94). NfL and GFAP had lower performance for detecting AD (AUC, 0.73; 95% CI, 0.68-0.78 and AUC, 0.75; 95% CI, 0.67-0.80, respectively) and added little to no diagnostic value either alone or in combinations with p-tau217. The presence of AD in FTLD-related syndromes was associated with lower Mini-Mental State Examination score (mean [SD], -2.90 [1.09]; P < .05), worse performance on memory (mean [SD] z score, -0.64 [0.32]), executive (mean [SD] z score, -0.74 [0.19]), and visuospatial composites (mean [SD] z score, -0.88 [0.37]) as well as increased rates of posterior cortical atrophy.

Conclusion

Clinically relevant AD was prevalent across neurodegenerative syndromes and detectable with plasma p-tau217. Plasma p-tau217 may be a useful tool to investigate the clinical impact of AD copathology in non-AD neurodegenerative syndromes, including the effect of disease-modifying therapies.

Alzheimer Disease Blood Biomarkers and Cognition Among Individuals With Diabetes and Overweight or Obesity

Importance

Blood-based biomarkers (BBMs) are clinically available to aid in the diagnosis of Alzheimer disease (AD) and AD-related dementias (ADRD), but their association with cognition among older adults with specific chronic conditions has not been examined.

Objective

To longitudinally examine associations between baseline AD and ADRD BBMs and change in BBMs with cognition among participants with type 2 diabetes (T2D) and overweight or obesity.

Design, Setting, and Participants

The Look AHEAD (Action for Health in Diabetes) study was a clinical trial of older adults with T2D and overweight or obesity randomized to a 10-year intensive lifestyle intervention for weight loss or a diabetes support and education condition. Participants were recruited and followed up at 16 clinical sites across the US. Enrollment occurred from January 1, 2001, to December 31, 2004. The primary intervention spanned the first 4 years after participants' enrollment (January 1, 2008, to December 31, 2011). The clinical trial was stopped in September 2012 and was converted to an observational study. Blood samples were drawn at baseline and 8 to 12 years later. Cognitive assessments were performed from January 1, 2013, to December 31, 2014, and from January 1, 2018, to December 31, 2020. Data for the present cohort study were analyzed between January and August 2024.

Exposures

Baseline and 8- to 12-year change in plasma levels of amyloid-β (Aβ)40, Aβ42, Aβ42/40 ratio, phosphorylated tau 181 (pTau-181), glial fibrillary acidic protein (GFAP), and neurofilament light chain (NfL).

Main Outcomes and Measures

Cognitive composite z score and adjudicated mild cognitive impairment or probable dementia.

Results

The mean (SD) baseline age of 758 participants was 61.5 (6.1) years, and 424 participants [55.9%] were female. Mean (SD) body mass index was 34.8 (5.3). Of the participants, 373 were randomized to diabetes support and education and 385 to intensive lifestyle intervention. Increasing baseline BBM levels were not associated with any cognitive composite z score. Increasing levels of NfL (β = -0.032 [SE, 0.013]; P = .01) and GFAP (β = -0.087 [SE, 0.025]; P < .001), but not the Aβ42/40 ratio (β = 0.006 [SE, 0.040]; P = .88) or pTau-181 (β = 0.026 [SE, 0.025]; P = .31), were associated with worsening cognitive function and incident mild cognitive impairment or probable dementia. The intervention had no association with 8- to 12-year change in BBM levels.

Conclusions and Relevance

In this study of participants with T2D and overweight or obesity, increasing plasma NfL and GFAP levels over time, but not Aβ42/40 or pTau-181 levels, were associated with cognitive decline and incident cognitive impairment. These results suggest that plasma NfL and GFAP may be important biomarkers of cognitive change among this patient population.

The Alzheimer's Association Global Biomarker Standardization Consortium (GBSC) plasma phospho-tau Round Robin study

INTRODUCTION

The Alzheimer's Association Global Biomarker Standardization Consortium conducted a blinded case-control study to learn which phosphorylated tau (p-tau) assays provide the largest fold-changes in Alzheimer's disease (AD) versus non-AD and show commutability in measuring patient samples and candidate certified reference materials (CRMs).

METHODS

Thirty-three different p-tau assays measured paired plasma and cerebrospinal fluid (CSF) from 40 participants (25 with "AD pathology" and 15 with "non-AD pathology" by CSF amyloid beta [Aβ]42/Aβ40 and p-tau181 criteria). Four CRMs were assessed.

RESULTS

Plasma p-tau217 demonstrated higher fold-changes between AD and non-AD than other p-tau epitopes. Fujirebio LUMIPULSE G, UGOT IPMS, and Lilly MSD p-tau217 provided the highest fold-changes. Plasma p-tau217 showed the strongest correlations between plasma assays (rho = 0.81-0.97). The CRMs were not commutable across assays.

DISCUSSION

Plasma p-tau217 showed larger fold-changes and better accuracy for detecting AD pathology in symptomatic individuals, with greater cross-platform agreement than other p-tau variants. Further work is needed to develop suitable CRMs facilitating cross-assay standardization.

HIGHLIGHTS

Paired plasma and cerebrospinal fluid (CSF) samples from twenty-five Alzheimer's disease (AD) and 15 non-AD patients were measured blind. Thirty-three plasma assays were compared, for phosphorylated tau-181 (p-tau181), 205, 212, 217 and 231. Plasma p-tau217 consistently had the highest fold-change and was best correlated between assays. Plasma-CSF correlations were weak to moderate. There was lack of commutability for four candidate reference materials.

Differential roles of Alzheimer's disease plasma biomarkers in stepwise biomarker-guided diagnostics

INTRODUCTION

This study aimed to investigate the differential roles of various plasma biomarkers in a stepwise diagnostic strategy for Alzheimer's disease (AD).

METHODS

A total of 2984 participants, including 666 cognitively unimpaired (CU), 2032 with Alzheimer's clinical syndrome (ACS), and 286 non-ACS individuals, were recruited. Plasma amyloid beta (Aβ) 42/40, four phosphorylated tau (p-tau) epitopes, glial fibrillary acidic protein (GFAP), and neurofilament light chain (NfL) levels were measured using immunoassays.

RESULTS

NfL demonstrated fair to excellent accuracy in differentiating non-ACS from CU groups (area under the curve [AUC], 0.79 to 0.94). p-tau217 had the highest accuracy for identifying Aβ (AUC 0.94) and tau positron emission tomography status (AUC 0.91). In the ACS group, p-tau217 was the strongest predictor of cognitive decline (p < .001).

DISCUSSION

NfL may serve as a useful screening tool, while p-tau217 is particularly valuable for confirming AD pathology and prognosis.

HIGHLIGHTS

Plasma NfL could screen for cognitive impairment. p-tau217 reliably detects AD pathology, regardless of diagnosis. p-tau217 and GFAP predict prognosis in ACS. Each plasma biomarker plays a distinct role in stepwise AD diagnostics.

The etiology and prevention of early-stage tau pathology in higher cortical circuits: Insights from aging rhesus macaques

Aging rhesus macaques provide a unique model for learning how age and inflammation drive early-stage pathology in sporadic Alzheimer's disease, and for testing potential therapeutics. Unlike mice, aging macaques have extensive association cortices and inflammatory signaling similar to humans, are apolipoprotein E ε4 homozygotes, and naturally develop tau and amyloid pathology with marked cognitive deficits. Importantly, monkeys provide the unique opportunity to study early-stage, soluble hyperphosphorylated tau (p-tau), including p-tau217. As soluble p-tau is rapidly dephosphorylated post mortem, it is not captured in human brains except with biopsy material. However, new macaque data show that soluble p-tau is toxic to neurons and capable of seeding across cortical circuits. Extensive evidence indicates that age-related inflammatory signaling contributes to calcium dysregulation, which drives tau hyperphosphorylation and amyloid beta generation. Pharmacological studies in aged macaques suggest that inhibiting inflammation and restoring calcium regulation can reduce tau hyperphosphorylation with minimal side effects, appropriate for potential preventive therapeutics. HIGHLIGHTS: Aging monkeys provide a unique window into early stage, soluble phosphorylated tau (p-tau). Inflammation with advancing age leads to calcium dysregulation, p-tau, and amyloid beta (Aβ). Macaque research shows p-tau undergoes transsynaptic seeding early in the cortex. p-tau traps amyloid precursor protein-containing endosomes, which may increase Aβ and drive vicious cycles. Restoring calcium regulation in cortex reduced p-tau217 levels in aged macaques.

Accuracy and clinical applicability of plasma tau 181 and 217 for Alzheimer's disease diagnosis in a memory clinic cohort

Plasma tau phosphorylated at threonine 181 (p-tau181) and 217 (p-tau217) have demonstrated high accuracy for Alzheimer's disease (AD) diagnosis, defined by CSF/PET amyloid beta (Aβ) positivity, but most studies have been performed in research cohorts, limiting their generalizability. We studied plasma p-tau217 and p-tau181 for CSF Aβ status discrimination in a cohort of consecutive patients attending an academic memory clinic in Spain (July 2019-June 2024). All patients had CSF AD biomarkers performed as part of their routine clinical assessment. Aβ positivity was defined with a local cut-off of CSF Aβ1-42 < 600 pg/mL; in patients with borderline Aβ1-42 values or when there was a mismatch between the Aβ and the T status (T + if CSF p-tau181 ≥ 65 pg/mL), a ratio Aβ1-42/Aβ1-40 < 0.07 was used. Plasma p-tau217 and p-tau181 were measured retrospectively, from blood samples collected at first visit, with Fujirebio Lumipulse and Quanterix Simoa assays, respectively. We included 468 patients (mean age 67 years, 50% female, 61% Aβ positive). Plasma p-tau217 outperformed plasma p-tau181 in discriminating CSF Aβ status (AUC 0.95 vs 0.90, p = 0.005). A 97.5% sensitivity and specificity plasma p-tau217 algorithm, classifying patients into three groups of Aβ probability (Low, Intermediate and High), resulted in 67% of patients in the Low and High groups, having their Aβ status predicted (as negative and positive, respectively) with 96% accuracy. The remaining 33% in the Intermediate group were candidates to undergo CSF/PET testing. A model with a 10% variation in p-tau217 levels yielded small changes in accuracy (95%). In conclusion, plasma p-tau217 could have discriminated CSF Aβ status in two-thirds of patients with very high accuracy in a memory clinic cohort. These results support the implementation of plasma p-tau217 as an initial diagnostic tool in memory clinics for AD diagnosis, reducing the need for more invasive/expensive testing.

Ethnic and racial influences on blood biomarkers for Alzheimer's disease: A systematic review

BACKGROUND

Little is known about confounding factors influencing Alzheimer's disease (AD) blood biomarker concentrations.

OBJECTIVE

The objective of this systematic review was to explore the available evidence for the influences of ethnicity and race on AD blood biomarker concentrations.

METHODS

We conducted a comprehensive systematic search in PubMed and Web of Science databases spanning from inception until 15 June 2023. We included studies that utilized plasma or serum biomarkers (amyloid-β [Aβ], total tau [t-tau], phosphorylated tau [p-tau], neurofilament light [NfL], and glial fibrillary acidic protein [GFAP]), compared individuals with AD to healthy controls, and included a minimum of two ethnic or racial groups for comparison. A total of 10 studies were included in the qualitative synthesis. All studies were conducted in the US.

RESULTS

Seven studies reported differences in blood biomarker concentrations between ethnic or racial groups. However, after adjusting for medical conditions and social determinants of health, the differences became non-significant in two of the studies. The included studies differed in their included covariates and their statistical approaches, which complicated the interpretation of the observed differences.

CONCLUSIONS

The available evidence suggests that ethnicity and race may influence blood biomarker concentrations. However, it remains unclear to what extent these differences are mediated by differences in social determinants of health and medical conditions. Future studies are needed to explore ethnic and racial differences in blood biomarkers, including studies in diverse samples outside the US.

Plasma Alzheimer's disease biomarker variability: Amyloid-independent and amyloid-dependent factors

INTRODUCTION

We aimed to investigate which factors affect plasma biomarker levels via amyloid beta (Aβ)-independent or Aβ-dependent effects and improve the predictive performance of these biomarkers for Aβ positivity on positron emission tomography (PET).

METHODS

A total of 2935 participants underwent blood sampling for measurements of plasma Aβ42/40 ratio, phosphorylated tau 217 (p-tau217; ALZpath), glial fibrillary acidic protein (GFAP), and neurofilament light chain (NfL) levels using single-molecule array and Aβ PET. Laboratory findings were collected using a routine blood test battery.

RESULTS

Aβ-independent factors included hemoglobin and estimated glomerular filtration rate (eGFR) for p-tau217 and hemoglobin, eGFR, and triiodothyronine (T3) for GFAP and NfL. Aβ-dependent factors included apolipoprotein E genotypes, body mass index status for Aβ42/40, p-tau217, GFAP, and NfL. However, these factors exhibited negligible or modest effects on Aβ positivity on PET.

DISCUSSION

Our findings highlight the importance of accurately interpreting plasma biomarkers for predicting Aβ uptake in real-world settings.

HIGHLIGHTS

We investigated factor-Alzheimer's disease plasma biomarker associations in a large Korean cohort. Hemoglobin and estimated glomerular filtration rate affect the biomarkers independently of brain amyloid beta (Aβ). Apolipoprotein E genotypes and body mass index status affect the biomarkers dependent on brain Aβ. Addition of Aβ-independent factors shows negligible effect in predicting Aβ positivity. Adjusting for Aβ-dependent factors shows a modest effect in predicting Aβ positivity.

Alzheimer's disease biomarkers and their current use in clinical research and practice

While blood-based tests are readily available for various conditions, including cardiovascular diseases, type 2 diabetes, and common cancers, Alzheimer's disease (AD) and other neurodegenerative diseases lack an early blood-based screening test that can be used in primary care. Major efforts have been made towards the investigation of approaches that may lead to minimally invasive, cost-effective, and reliable tests capable of measuring brain pathological status. Here, we review past and current technologies developed to investigate biomarkers of AD, including novel blood-based approaches and the more established cerebrospinal fluid and neuroimaging biomarkers of disease. The utility of blood as a source of AD-related biomarkers in both clinical practice and interventional trials is discussed, supported by a comprehensive list of clinical trials for AD drugs and interventions that list biomarkers as primary or secondary endpoints. We highlight that identifying individuals in early preclinical AD using blood-based biomarkers will improve clinical trials and the optimization of therapeutic treatments as they become available. Lastly, we discuss challenges that remain in the field and address new approaches being developed, such as the examination of cargo packaged within extracellular vesicles of neuronal origin isolated from peripheral blood.

Longitudinal trajectory of plasma p-tau217 in cognitively unimpaired subjects

BACKGROUND

The advent of Alzheimer's disease-modifying drugs requires accurate biological diagnosis to identify candidates for these therapies. So far, the most promising single plasma biomarker is phosphorylated tau at threonine 217 (p-tau217). To understand its biological features, it is essential to know its longitudinal trajectory and factors influencing it in cognitively unimpaired subjects with no brain pathology.

METHODS

We analyzed longitudinal plasma p-tau217 values (mean follow-up time = 768.3 days) in a cohort of 209 healthy volunteers. We have studied factors associated with plasma p-tau217 changes by using different linear mixed-effects models.

RESULTS

In amyloid-negative cognitively healthy subjects (n = 151) carriers of ApoE ε4 allele had significantly higher p-tau217 values than non-carriers (0.85 pg/mL; p-value < 0.001) and also a greater rate of change (0.01 pg/mL/year; p-value < 0.001). In the overall sample, including subjects with amyloid and tau pathology we have seen that amyloid positive subjects had higher predicted baseline plasma p-tau217 values than amyloid negative subjects (0.16 pg/mL; p-value < 0.001) and a greater rate of change (0.00004 pg/mL/day; p-value < 0.001). Subjects considered tau positive also showed a greater rate of change of p-tau217 with respect to tau negative (0.00005 pg/mL/day; p-value < 0.001). A + T + N + participants showed a higher baseline p-tau217 levels than A-T-N- subjects (0.2 pg/mL; p-value < 0.001) and also a greater rate of change (0.00006 pg/mL/day; p-value = 0.002). ApoE ε4 carriers had a greater rate of change than non-carriers (0.00003 pg/mL/day; p-value = 0.03).

CONCLUSION

In amyloid-negative cognitively unimpaired subjects, ApoE4 status influenced both baseline levels and rate of change of plasma p-tau217. Other factors such as age, sex or glomerular filtration rate have not shown significant influence on plasma p-tau217 levels in this group.

Dysregulated calcium signaling in the aged macaque entorhinal cortex associated with tau hyperphosphorylation

Tau pathology in sporadic Alzheimer's disease (AD) follows a distinct pattern, beginning in the entorhinal cortex (ERC) and spreading to interconnected brain regions. Early-stage tau pathology, characterized by soluble phosphorylated tau, is difficult to study in human brains post-mortem due to rapid dephosphorylation. Rhesus macaques, which naturally develop age-related tau pathology resembling human AD, provide an ideal model for investigating early tau etiology. This study examines the molecular processes underlying tau pathology in the macaque ERC, focusing on calcium and inflammatory signaling pathways. Our findings reveal age-related decreases in PDE4 phosphodiesterases that hydrolyze cAMP and increases in calpain-2 and GCPII that occur in parallel with early-stage tau hyperphosphorylation at multiple epitopes (pS214-tau, pT181-tau, pT217-tau). These findings suggest that dysregulated calcium signaling in ERC, beginning in middle-age, primes tau for hyperphosphorylation, potentially driving the early stages of AD, advancing our understanding of how ERC vulnerabilities contribute to neurodegeneration in AD.

Plasma p-tau181 and GFAP reflect 7T MR-derived changes in Alzheimer's disease: A longitudinal study of structural and functional MRI and MRS

BACKGROUND

Associations between longitudinal changes of plasma biomarkers and cerebral magnetic resonance (MR)-derived measurements in Alzheimer's disease (AD) remain unclear.

METHODS

In a study population (n = 127) of healthy older adults and patients within the AD continuum, we examined associations between longitudinal plasma amyloid beta 42/40 ratio, tau phosphorylated at threonine 181 (p-tau181), glial fibrillary acidic protein (GFAP), neurofilament light chain (NfL), and 7T structural and functional MR imaging and spectroscopy using linear mixed models.

RESULTS

Increases in both p-tau181 and GFAP showed the strongest associations to 7T MR-derived measurements, particularly with decreasing parietal cortical thickness, decreasing connectivity of the salience network, and increasing neuroinflammation as determined by MR spectroscopy (MRS) myo-inositol.

DISCUSSION

Both plasma p-tau181 and GFAP appear to reflect disease progression, as indicated by 7T MR-derived brain changes which are not limited to areas known to be affected by tau pathology and neuroinflammation measured by MRS myo-inositol, respectively.

HIGHLIGHTS

This study leverages high-resolution 7T magnetic resonance (MR) imaging and MR spectroscopy (MRS) for Alzheimer's disease (AD) plasma biomarker insights. Tau phosphorylated at threonine 181 (p-tau181) and glial fibrillary acidic protein (GFAP) showed the largest changes over time, particularly in the AD group. p-tau181 and GFAP are robust in reflecting 7T MR-based changes in AD. The strongest associations were for frontal/parietal MR changes and MRS neuroinflammation.

Pathologic and clinical correlates of region-specific brain GFAP in Alzheimer's disease

Plasma glial fibrillary acidic protein (GFAP) is an emerging biomarker of Alzheimer's disease (AD), with higher blood GFAP levels linked to faster cognitive decline, particularly among individuals with high brain amyloid burden. However, few studies have examined brain GFAP expression to clarify if peripheral associations reflect brain changes. This study aimed to correlate region-specific GFAP mRNA expression (n = 917) and protein abundance (n=386) with diverse neuropathological measures at autopsy in the Religious Orders Study and Rush Memory and Aging Project (ROS/MAP) and to characterize the interaction between brain GFAP and brain amyloid burden on downstream outcomes. We assessed GFAP gene expression in the dorsolateral prefrontal cortex, caudate nucleus, and posterior cingulate cortex with respect to core AD pathology (amyloid-β and tau), cerebrovascular (microinfarcts, macroinfarcts, and cerebral amyloid angiopathy [CAA]), proteinopathic (TDP-43, Lewy bodies), and cognitive outcomes. These associations were further examined at the protein level using tandem-mass tag proteomic measurements from the dorsolateral prefrontal cortex. We also assessed GFAP interactions with AD neuropathology on downstream outcomes. Cortical GFAP gene and protein expression were significantly upregulated in participants with a neuropathologically confirmed AD diagnosis at autopsy (all PFDR < 3.5e-4), but not in individuals positive for tau pathology and negative for amyloid pathology (all PFDR > 0.05). Higher cortical GFAP levels were associated with increased amyloid pathology, CAA pathology, and faster cognitive decline (all PFDR < 3.3e-3). GFAP's associations with phosphorylated tau burden and cognition were influenced by amyloid burden, being most pronounced among amyloid-positive individuals, confirming previous in vivo biomarker observations. No associations were observed between GFAP gene expression and outcomes in the caudate nucleus. Our results support previous biomarker findings and suggest that higher brain GFAP levels are associated with higher brain amyloid burden and faster cognitive decline among amyloid-positive individuals.

Post hoc analysis of ADAMANT, a phase 2 clinical trial of active tau immunotherapy with AADvac1 in patients with Alzheimer's disease, positive for plasma p-tau217

BACKGROUND

The spread of tau pathology closely correlates with the disease course and cognitive decline in Alzheimer's disease (AD). Tau-targeting immunotherapies are being developed to stop the spread of tau pathology and thus halt disease progression. In this post hoc analysis of the ADAMANT clinical trial, we examined the performance of AADvac1, an active immunotherapy targeting the microtubule-binding region (MTBR) of tau, in a subgroup of participants with elevated plasma p-tau217, indicating AD-related neuropathological changes.

METHODS

ADAMANT was a 24-month, randomized, placebo-controlled, parallel-group, double-blinded, multicenter, phase 2 clinical trial in subjects with mild AD. The trial participants were randomized 3:2 to receive six doses of AADvac1 or placebo at 4-week intervals, followed by five booster doses at 14-week intervals. The primary outcome was safety. The secondary outcomes were the Clinical Dementia Rating-Sum of Boxes (CDR-SB), the Alzheimer's Disease Cooperative Study - Activities of Daily Living score for Mild Cognitive Impairment 18-item version (ADCS-ADL-MCI-18), and immunogenicity. Volumetric MRI, plasma neurofilament light (NfL), and glial fibrillary acidic protein (GFAP) were exploratory outcomes. The inclusion criterion for this post-hoc analysis was a baseline plasma p-tau217 level above the cutoff for AD.

RESULTS

Among 196 ADAMANT participants, 137 were positive for plasma p-tau217 (mean age 71.4 years, 59% women). AADvac1 was safe and well tolerated in this subgroup. AADvac1 reduced the rate of accumulation of log-plasma NfL by 56% and that of GFAP by 73%. The treatment differences in the CDR-SB and ADCS-ADL-MCI-18 scores favored AADvac1 but were not statistically significant. AADvac1 had no effect on whole-brain volume but nonsignificantly reduced the loss of brain cortical tissue in several regions. Importantly, the impact on the study outcomes was more pronounced in participants with higher anti-tau antibody levels.

CONCLUSIONS

These results suggest that AADvac1 tau immunotherapy can reduce plasma biomarkers of neurodegeneration and neuroinflammation. These findings and possible observations on brain atrophy and cognition are hypothesis-generating and warrant further evaluation in a larger clinical trial.

TRIAL REGISTRATION

EudraCT 2015-000630-30 (primary) and NCT02579252.

Comparative neurofilament light chain trajectories in CSF and plasma in autosomal dominant Alzheimer's disease

Disease-modifying therapies for Alzheimer's disease (AD) are likely to be most beneficial when initiated in the presymptomatic phase. To track the benefit of such interventions, fluid biomarkers are of great importance, with neurofilament light chain protein (NfL) showing promise for monitoring neurodegeneration and predicting cognitive outcomes. Here, we update and complement previous findings from the Dominantly Inherited Alzheimer Network Observational Study by using matched cross-sectional and longitudinal cerebrospinal fluid (CSF) and plasma samples from 567 individuals, allowing timely comparative analyses of CSF and blood trajectories across the entire disease spectrum. CSF and plasma trajectories were similar at presymptomatic stages, discriminating mutation carriers from non-carrier controls 10-20 years before the estimated onset of clinical symptoms, depending on the statistical model used. However, after symptom onset the rate of change in CSF NfL continued to increase steadily, whereas the rate of change in plasma NfL leveled off. Both plasma and CSF NfL changes were associated with grey-matter atrophy, but not with Aβ-PET changes, supporting a temporal decoupling of Aβ deposition and neurodegeneration. These observations support NfL in both CSF and blood as an early marker of neurodegeneration but suggest that NfL measured in the CSF may be better suited for monitoring clinical trial outcomes in symptomatic AD patients.

Examination of plasma biomarkers of amyloid, tau, neurodegeneration, and neuroinflammation in former elite American football players

INTRODUCTION

Blood-based biomarkers offer a promising approach for the detection of neuropathologies from repetitive head impacts (RHI). We evaluated plasma biomarkers of amyloid, tau, neurodegeneration, and inflammation in former football players.

METHODS

The sample included 180 former football players and 60 asymptomatic, unexposed male participants (aged 45-74). Plasma assays were conducted for beta-amyloid (Aβ) 40, Aβ42, hyper-phosphorylated tau (p-tau) 181+231, total tau (t-tau), neurofilament light (NfL), glial fibrillary acidic protein (GFAP), interleukin-6 (IL-6), Aβ42/p-tau181 and Aβ42/Aβ40 ratios. We evaluated their ability to differentiate the groups and associations with RHI proxies and traumatic encephalopathy syndrome (TES).

RESULTS

P-tau181 and p-tau231(padj = 0.016) were higher and Aβ42/p-tau181 was lower(padj = 0.004) in football players compared to controls. Discrimination accuracy for p-tau was modest (area under the curve [AUC] = 0.742). Effects were not attributable to AD-related pathology. Younger age of first exposure (AFE) correlated with higher NfL (padj = 0.03) and GFAP (padj = 0.033). Plasma GFAP was higher in TES-chronic traumatic encephalopathy (TES-CTE) Possible/Probable (padj = 0.008).

DISCUSSION

Plasma p-tau181 and p-tau231, GFAP, and NfL may offer some usefulness for the characterization of RHI-related neuropathologies.

HIGHLIGHTS

Former football players had higher plasma p-tau181 and p-tau231 and lower Aβ42/ptau-181 compared to asymptomatic, unexposed men. Younger age of first exposure was associated with increased plasma NfL and GFAP in older but not younger participants. Plasma GFAP was higher in participants with TES-CTE possible/probable compared to TES-CTE no/suggestive.

Diagnosis of Alzheimer's disease using plasma biomarkers adjusted to clinical probability

Recently approved anti-amyloid immunotherapies for Alzheimer's disease (AD) require evidence of amyloid-β pathology from positron emission tomography (PET) or cerebrospinal fluid (CSF) before initiating treatment. Blood-based biomarkers promise to reduce the need for PET or CSF testing; however, their interpretation at the individual level and the circumstances requiring confirmatory testing are poorly understood. Individual-level interpretation of diagnostic test results requires knowledge of disease prevalence in relation to clinical presentation (clinical pretest probability). Here, in a study of 6,896 individuals evaluated from 11 cohort studies from six countries, we determined the positive and negative predictive value of five plasma biomarkers for amyloid-β pathology in cognitively impaired individuals in relation to clinical pretest probability. We observed that p-tau217 could rule in amyloid-β pathology in individuals with probable AD dementia (positive predictive value above 95%). In mild cognitive impairment, p-tau217 interpretation depended on patient age. Negative p-tau217 results could rule out amyloid-β pathology in individuals with non-AD dementia syndromes (negative predictive value between 90% and 99%). Our findings provide a framework for the individual-level interpretation of plasma biomarkers, suggesting that p-tau217 combined with clinical phenotyping can identify patients where amyloid-β pathology can be ruled in or out without the need for PET or CSF confirmatory testing.

Proteomic changes in Alzheimer's disease associated with progressive Aβ plaque and tau tangle pathologies

Proteomics can shed light on the dynamic and multifaceted alterations in neurodegenerative disorders like Alzheimer's disease (AD). Combining radioligands measuring β-amyloid (Aβ) plaques and tau tangles with cerebrospinal fluid proteomics, we uncover molecular events mirroring different stages of AD pathology in living humans. We found 127 differentially abundant proteins (DAPs) across the AD spectrum. The strongest Aβ-related proteins were mainly expressed in glial cells and included SMOC1 and ITGAM. A dozen proteins linked to ATP metabolism and preferentially expressed in neurons were independently associated with tau tangle load and tau accumulation. Only 20% of the DAPs were also altered in other neurodegenerative diseases, underscoring AD's distinct proteome. Two co-expression modules related, respectively, to protein metabolism and microglial immune response encompassed most DAPs, with opposing, staggered trajectories along the AD continuum. We unveil protein signatures associated with Aβ and tau proteinopathy in vivo, offering insights into complex neural responses and potential biomarkers and therapeutics targeting different disease stages.

Application of the revised criteria for diagnosis and staging of Alzheimer's disease: Drug development and clinical practice

The newly proposed revised criteria for diagnosis and staging of Alzheimer's disease (AD) by the Alzheimer's Association (AA) Workgroup represent a significant milestone in the field. These criteria offer objective measures for diagnosing and staging biological AD, bridging the gap between research and clinical care. Although implementation feasibility may vary across regions and settings, improving the availability and accuracy of biomarkers, especially plasma biomarkers, is expected to enhance the applicability of these criteria in clinical practice. The Fall 2023 Alzheimer's Association Research Roundtable (AARR) meeting served as a forum for gathering industry perspectives and feedback on these revised criteria, ensuring that the new criteria inform research, clinical trial design, and clinical care. In this article, we outline a summary of the newly proposed "Revised Criteria for Diagnosis and Staging of AD: AA Workgroup" and provide highlights from the AARR meeting in fall 2023.

Highlights

The Alzheimer's Association Research Roundtable (AARR) convened leaders from industry, academia, and government, to review the Revised Criteria for Diagnosis and Staging of AD: AA Workgroup, and gather industry perspectives and feedback on these revised criteria before its publication.The newly proposed revised criteria for diagnosis and staging of Alzheimer's disease (AD) by the AA's Workgroup represent a significant milestone, offering objective measures for the biological and staging of AD and bridging the gap between research and clinical care.Improving the availability and accuracy of biomarkers, especially blood-based biomarkers (BBMs) is expected to improve clinical research and enhance the applicability of these criteria in clinical practice.

Plasma pTau181 Reveals a Pathological Signature that Predicts Cognitive Outcomes in Lewy Body Disease

OBJECTIVE

To determine whether plasma phosphorylated-Tau181 (pTau181) could be used as a diagnostic biomarker of concurrent Alzheimer's disease neuropathologic change (ADNC) or amyloidosis alone, as well as a prognostic, monitoring, and susceptibility/risk biomarker for clinical outcomes in Lewy body disease (LBD).

METHODS

We studied 565 participants: 94 LBD with normal cognition, 83 LBD with abnormal cognition, 114 with Alzheimer's disease, and 274 cognitively normal. Plasma pTau181 levels were measured with the Lumipulse G platform. Diagnostic accuracy for concurrent ADNC and amyloidosis was assessed with Receiver Operating Characteristic curves in a subset of participants with CSF pTau181/Aβ42, and CSF Aβ42/Aβ40 or amyloid-β PET, respectively. Linear mixed effects models were used to examine the associations between baseline and longitudinal plasma pTau181 levels and clinical outcomes.

RESULTS

Plasma pTau181 predicted concurrent ADNC and amyloidosis in LBD with abnormal cognition with 87% and 72% accuracy, respectively. In LBD patients with abnormal cognition, higher baseline plasma pTau181 was associated with worse baseline MoCA and CDR-SB, as well as accelerated decline in CDR-SB. Additionally, in this group, rapid increases in plasma pTau181 over 3 years predicted a faster decline in CDR-SB and memory. In LBD patients with normal cognition, there was no association between baseline or longitudinal plasma pTau181 levels and clinical outcomes; however, elevated pTau181 at baseline increased the risk of conversion to cognitive impairment.

INTERPRETATION

Our findings suggest that plasma pTau181 is a promising biomarker for concurrent ADNC and amyloidosis in LBD. Furthermore, plasma pTau181 holds potential as a prognostic, monitoring, and susceptibility/risk biomarker, predicting disease progression in LBD. ANN NEUROL 2024;96:526-538.

The Alzheimer's Association Global Biomarker Standardization Consortium (GBSC) plasma phospho-tau Round Robin study

BACKGROUND

Phosphorylated tau (p-tau) is a specific blood biomarker for Alzheimer's disease (AD) pathology. Multiple p-tau biomarkers on several analytical platforms are poised for clinical use. The Alzheimer's Association Global Biomarker Standardisation Consortium plasma phospho-tau Round Robin study engaged assay developers in a blinded case-control study on plasma p-tau, aiming to learn which assays provide the largest fold-changes in AD compared to non-AD, have the strongest relationship between plasma and cerebrospinal fluid (CSF), and show the most consistent relationships between methods (commutability) in measuring both patient samples and candidate reference materials (CRM).

METHODS

Thirty-three different p-tau biomarker assays, built on eight different analytical platforms, were used to quantify paired plasma and CSF samples from 40 participants. AD biomarker status was categorised as "AD pathology" (n=25) and "non-AD pathology" (n=15) by CSF Aβ42/Aβ40 (US-FDA; CE-IVDR) and p-tau181 (CE-IVDR) methods. The commutability of four CRM, at three concentrations, was assessed across assays.

FINDINGS

Plasma p-tau217 consistently demonstrated higher fold-changes between AD and non-AD pathology groups, compared to other p-tau epitopes. Fujirebio LUMIPULSE G, UGOT IPMS, and Lilly MSD p-tau217 assays provided the highest median fold-changes. In CSF, p-tau217 assays also performed best, and exhibited substantially larger fold-changes than their plasma counterparts, despite similar diagnostic performance. P-tau217 showed the strongest correlations between plasma assays (rho=0.81 to 0.97). Plasma p-tau levels were weakly-to-moderately correlated with CSF p-tau, and correlations were non-significant within the AD group alone. The evaluated CRM were not commutable across assays.

INTERPRETATION

Plasma p-tau217 measures had larger fold-changes and discriminative accuracies for detecting AD pathology, and better agreement across platforms than other plasma p-tau variants. Plasma and CSF markers of p-tau, measured by immunoassays, are not substantially correlated, questioning the interchangeability of their continuous relationship. Further work is warranted to understand the pathophysiology underlying this dissociation, and to develop suitable reference materials facilitating cross-assay standardisation.

FUNDING

Alzheimer's Association (#ADSF-24-1284328-C).

Rationale and design of the BeyeOMARKER study: prospective evaluation of blood- and eye-based biomarkers for early detection of Alzheimer's disease pathology in the eye clinic

BACKGROUND

Alzheimer's disease (AD) is a common, complex and multifactorial disease that may require screening across multiple routes of referral to enable early detection and subsequent future implementation of tailored interventions. Blood- and eye-based biomarkers show promise as low-cost, scalable and patient-friendly tools for early AD detection given their ability to provide information on AD pathophysiological changes and manifestations in the retina, respectively. Eye clinics provide an intriguing real-world proof-of-concept setting to evaluate the performance of these potential AD screening tools given the intricate connections between the eye and brain, presumed enrichment for AD pathology in the aging population with eye disorders, and the potential for an accelerated diagnostic pathway for under-recognized patient groups.

METHODS

The BeyeOMARKER study is a prospective, observational, longitudinal cohort study aiming to include individuals visiting an eye-clinic. Inclusion criteria entail being ≥ 50 years old and having no prior dementia diagnosis. Excluded eye-conditions include traumatic insults, superficial inflammation, and conditions in surrounding structures of the eye that are not engaged in vision. The BeyeOMARKER cohort (n = 700) will undergo blood collection to assess plasma p-tau217 levels and a brief cognitive screening at the eye clinic. All participants will subsequently be invited for annual longitudinal follow-up including remotely administered cognitive screening and questionnaires. The BeyeOMARKER + cohort (n = 150), consisting of 100 plasma p-tau217 positive participants and 50 matched negative controls selected from the BeyeOMARKER cohort, will additionally undergo Aβ-PET and tau-PET, MRI, retinal imaging including hyperspectral imaging (primary), widefield imaging, optical coherence tomography (OCT) and OCT-Angiography (secondary), and cognitive and cortical vision assessments.

RESULTS

We aim to implement the current protocol between April 2024 until March 2027. Primary outcomes include the performance of plasma p-tau217 and hyperspectral retinal imaging to detect AD pathology (using Aβ- and tau-PET visual read as reference standard) and to detect cognitive decline. Initial follow-up is ~ 2 years but may be extended with additional funding.

CONCLUSIONS

We envision that the BeyeOMARKER study will demonstrate the feasibility of early AD detection based on blood- and eye-based biomarkers in alternative screening settings, and will improve our understanding of the eye-brain connection.

TRIAL REGISTRATION

The BeyeOMARKER study (Eudamed CIV ID: CIV-NL-23-09-044086; registration date: 19th of March 2024) is approved by the ethical review board of the Amsterdam UMC.

P-tau217 as a Reliable Blood-Based Marker of Alzheimer's Disease

Amyloid plaques and tau tangles are the hallmark pathologic features of Alzheimer's disease (AD). Traditionally, these changes are identified in vivo via cerebrospinal fluid (CSF) analysis or positron emission tomography (PET) scans. However, these methods are invasive, expensive, and resource-intensive. To address these limitations, there has been ongoing research over the past decade to identify blood-based markers for AD. Despite the challenges posed by their extremely low concentrations, recent advances in mass spectrometry and immunoassay techniques have made it feasible to detect these blood markers of amyloid and tau deposition. Phosphorylated tau (p-tau) has shown greater promise in reflecting amyloid pathology as evidenced by CSF and PET positivity. Various isoforms of p-tau, distinguished by their differential phosphorylation sites, have been recognized for their ability to identify amyloid-positive individuals. Notable examples include p-tau181, p-tau217, and p-tau235. Among these, p-tau217 has emerged as a superior and reliable marker of amyloid positivity and, thus, AD in terms of accuracy of diagnosis and ability for early prognosis. In this narrative review, we aim to elucidate the utility of p-tau217 as an AD marker, exploring its underlying basis, clinical diagnostic potential, and relevance in clinical care and trials.

Association between treatment with sacubitril/valsartan and the risk of Alzheimer's disease: a clinical update

Since 2014, sacubitril/valsartan (Entresto®) is widely prescribed for heart failure. Despite neprilysin inhibition's benefits in heart failure, concerns about potential amyloid-beta (Aβ) accumulation and Alzheimer's disease (AD) risk have persisted. This narrative review, a decade post-approval, evaluates the risk of amyloid pathology and neurocognitive disorders in long-term sacubitril/valsartan use. Clinical trials, real-world studies, and pharmacovigilance data do not indicate an increased risk of cognitive decline. In patients treated with sacubitril/valsartan blood-based amyloid biomarkers show perturbations, while neuroimaging biomarkers reveal no significant increase in amyloid load. Despite a theoretical risk of amyloid accumulation and AD under treatment with sacubitril/valsartan, current clinical data appears reassuring, and there is no signal indicating an increased risk of cognitive decline, but a perturbation of amyloid blood-based biomarkers, which implies great caution when interpreting biomarkers in this context.

Sleep, 24-Hour Activity Rhythms, and Subsequent Amyloid-β Pathology

Importance

Sleep disturbances are common among older adults and have been associated with the development of Alzheimer disease (AD), such as amyloid-β (Aβ) pathology. For effective AD prevention, it is essential to pinpoint the specific disturbances in sleep and the underlying 24-hour activity rhythms that confer the highest risk of Aβ deposition.

Objective

To determine the associations of 24-hour activity rhythms and sleep with Aβ deposition in adults without dementia, to evaluate whether disrupted 24-hour activity and sleep may precede Aβ deposition, and to assess the role of the apolipoprotein E ε4 (APOE4) genotype.

Design, Setting, and Participants

This was an observational cohort study using data from the Rotterdam Study. Of 639 participants without dementia who underwent Aβ positron emission tomography (PET) from September 2018 to November 2021, 319 were included in the current study. Exclusion criteria were no APOE genotyping and no valid actigraphy data at the baseline visits from 2004 to 2006 or from 2012 to 2014. The mean (SD) follow-up was 7.8 (2.4) years. Data were analyzed from March 2023 to April 2024.

Exposures

Actigraphy (7 days and nights, objective sleep, and 24-hour activity rhythms), sleep diaries (self-reported sleep), Aβ42/40, phosphorylated tau (p-tau)181 and p-tau217 plasma assays, 18F-florbetaben PET (mean standard uptake value ratio [SUVR] in a large cortical region of interest), and APOE4 genotype.

Main Outcomes and Measures

Association of objective and self-reported sleep and 24-hour activity rhythms at baseline with brain Aβ PET burden at follow-up.

Results

The mean (range) age in the study population was 61.5 (48-80) years at baseline and 69.2 (60-88) years at follow-up; 150 (47%) were women. Higher intradaily variability at baseline, an indicator of fragmented 24-hour activity rhythms, was associated with higher Aβ PET burden at follow-up (β, 0.15; bootstrapped 95% CI, 0.04 to 0.26; bootstrapped P = .02, false discovery rate [FDR] P = .048). APOE genotype modified this association, which was stronger in APOE4 carriers (β, 0.38; bootstrapped 95% CI, 0.05 to 0.64; bootstrapped P = .03) compared to noncarriers (β, 0.07; bootstrapped 95% CI, -0.04 to 0.18; bootstrapped P = .19). The findings remained largely similar after excluding participants with AD pathology at baseline, suggesting that a fragmented 24-hour activity rhythm may have preceded Aβ deposition. No other objective or self-reported measure of sleep was associated with Aβ.

Conclusions and Relevance

Among community-dwelling adults included in this study, higher fragmentation of the 24-hour activity rhythms was associated with greater subsequent Aβ burden, especially in APOE4 carriers. These results suggest that rest-activity fragmentation could represent a modifiable risk factor for AD.

Revised criteria for diagnosis and staging of Alzheimer's disease: Alzheimer's Association Workgroup

The National Institute on Aging and the Alzheimer's Association convened three separate work groups in 2011 and single work groups in 2012 and 2018 to create recommendations for the diagnosis and characterization of Alzheimer's disease (AD). The present document updates the 2018 research framework in response to several recent developments. Defining diseases biologically, rather than based on syndromic presentation, has long been standard in many areas of medicine (e.g., oncology), and is becoming a unifying concept common to all neurodegenerative diseases, not just AD. The present document is consistent with this principle. Our intent is to present objective criteria for diagnosis and staging AD, incorporating recent advances in biomarkers, to serve as a bridge between research and clinical care. These criteria are not intended to provide step-by-step clinical practice guidelines for clinical workflow or specific treatment protocols, but rather serve as general principles to inform diagnosis and staging of AD that reflect current science. HIGHLIGHTS: We define Alzheimer's disease (AD) to be a biological process that begins with the appearance of AD neuropathologic change (ADNPC) while people are asymptomatic. Progression of the neuropathologic burden leads to the later appearance and progression of clinical symptoms. Early-changing Core 1 biomarkers (amyloid positron emission tomography [PET], approved cerebrospinal fluid biomarkers, and accurate plasma biomarkers [especially phosphorylated tau 217]) map onto either the amyloid beta or AD tauopathy pathway; however, these reflect the presence of ADNPC more generally (i.e., both neuritic plaques and tangles). An abnormal Core 1 biomarker result is sufficient to establish a diagnosis of AD and to inform clinical decision making throughout the disease continuum. Later-changing Core 2 biomarkers (biofluid and tau PET) can provide prognostic information, and when abnormal, will increase confidence that AD is contributing to symptoms. An integrated biological and clinical staging scheme is described that accommodates the fact that common copathologies, cognitive reserve, and resistance may modify relationships between clinical and biological AD stages.

The Crossroads Between Alzheimer's Disease Pathophysiology and Epilepsy

Association of Plasma Aβ42/Aβ40 Ratio and Late-Onset Epilepsy: Results From the Atherosclerosis Risk in Communities Study Johnson EL, Sullivan KJ, Schneider ALC, Simino J, Mosley TH, Kucharska-Newton A, Knopman DS, Gottesman RF. Neurology . 2023 Sep 26;101(13):e1319-e1327. doi:10.1212/WNL.0000000000207635 . Epub 2023 Aug 4. PMID: 37541842 Background and Objectives: The objective of this study was to determine the relationship between plasma β-amyloid (Aβ), specifically the ratio of 2 Aβ peptides (the Aβ42/Aβ40 ratio, which correlates with increased accumulation of Aβ in the central nervous system [CNS]), and late-onset epilepsy (LOE). Methods: We used Medicare fee-for-service claims codes from 1991 to 2018 to identify cases of LOE among 1424 Black and White men and women enrolled in the Atherosclerosis Risk in Communities (ARIC) study cohort. The Aβ42/Aβ40 ratio was calculated from plasma samples collected from ARIC participants from 1993 to 1995 (age 50-71 years) and 2011 to 2013 (age 67-90 years). We used survival analysis accounting for the competing risk of death to determine the relationship between late-life plasma Aβ42/Aβ40, and its change from midlife to late life, and the subsequent development of epilepsy. We adjusted for demographics, the apolipoprotein e4 genotype, and comorbidities, including stroke, dementia, and head injury. A low plasma ratio of 2 Aβ peptides, the Aβ42/Aβ40 ratio, correlates with low CSF Aβ42/Aβ40 and with increased accumulation of Aβ in the CNS. Results: A decrease in plasma Aβ42/Aβ40 ratio from midlife to late life, but not an isolated measurement of Aβ42/Aβ40, was associated with the development of epilepsy in later life. For every 50% reduction in Aβ42/Aβ40, there was a 2-fold increase in the risk of epilepsy (adjusted subhazard ratio 2.30, 95% CI: 1.27-4.17). Discussion: A reduction in plasma Aβ42/Aβ40 is associated with an increased risk of subsequent epilepsy. Our observations provide a further validation of the link between Aβ, hyperexcitable states, and LOE. Similar Brain Proteomic Signatures in Alzheimer's Disease and Epilepsy Leitner D, Pires G, Kavanagh T, Kanshin E, Askenazi M, Ueberheide B, Devinsky O, Wisniewski T, Drummond E. Acta Neuropathol . 2024 Jan 30;147(1):27. doi:10.1007/s00401-024-02683-4 . PMID: 38289539 The prevalence of epilepsy is increased among Alzheimer's disease (AD) patients and cognitive impairment is common among people with epilepsy. Epilepsy and AD are linked but the shared pathophysiological changes remain poorly defined. We aim to identify protein differences associated with epilepsy and AD using published proteomics datasets. We observed a highly significant overlap in protein differences in epilepsy and AD: 89% (689/777) of proteins altered in the hippocampus of epilepsy patients were significantly altered in advanced AD. Of the proteins altered in both epilepsy and AD, 340 were altered in the same direction, while 216 proteins were altered in the opposite direction. Synapse and mitochondrial proteins were markedly decreased in epilepsy and AD, suggesting common disease mechanisms. In contrast, ribosome proteins were increased in epilepsy but decreased in AD. Notably, many of the proteins altered in epilepsy interact with tau or are regulated by tau expression. This suggests that tau likely mediates common protein changes in epilepsy and AD. Immunohistochemistry for Aβ and multiple phosphorylated tau species (pTau396/404, pTau217, and pTau231) showed a trend for increased intraneuronal pTau217 and pTau231 but no phosphorylated tau aggregates or amyloid plaques in epilepsy hippocampal sections. Our results provide insights into common mechanisms in epilepsy and AD and highlight the potential role of tau in mediating common pathological protein changes in epilepsy and AD.

Diagnostic performance of plasma pTau217, pTau181, Aβ1-42 and Aβ1-40 in the LUMIPULSE automated platform for the detection of Alzheimer disease

BACKGROUND

Recently developed blood markers for Alzheimer's disease (AD) detection have high accuracy but usually require ultra-sensitive analytic tools not commonly available in clinical laboratories, and their performance in clinical practice is unknown.

METHODS

We analyzed plasma samples from 290 consecutive participants that underwent lumbar puncture in routine clinical practice in a specialized memory clinic (66 cognitively unimpaired, 130 participants with mild cognitive impairment, and 94 with dementia). Participants were classified as amyloid positive (A +) or negative (A-) according to CSF Aβ1-42/Aβ1-40 ratio. Plasma pTau217, pTau181, Aβ1-42 and Aβ1-40 were measured in the fully-automated LUMIPULSE platform. We used linear regression to compare plasma biomarkers concentrations between A + and A- groups, evaluated Spearman's correlation between plasma and CSF and performed ROC analyses to assess their diagnostic accuracy to detect brain amyloidosis as determined by CSF Aβ1-42/Aβ1-40 ratio. We analyzed the concordance of pTau217 with CSF amyloidosis.

RESULTS

Plasma pTau217 and pTau181 concentration were higher in A + than A- while the plasma Aβ1-42/Aβ1-40 ratio was lower in A + compared to A-. pTau181 and the Aβ1-42/Aβ1-40 ratio showed moderate correlation between plasma and CSF (Rho = 0.66 and 0.69, respectively). The areas under the ROC curve to discriminate A + from A- participants were 0.94 (95% CI 0.92-0.97) for pTau217, and 0.88 (95% CI 0.84-0.92) for both pTau181 and Aβ1-42/Aβ1-40. Chronic kidney disease (CKD) was related to increased plasma biomarker concentrations, but ratios were less affected. Plasma pTau217 had the highest fold change (× 3.2) and showed high predictive capability in discriminating A + from A-, having 4-7% misclassification rate. The global accuracy of plasma pTau217 using a two-threshold approach was robust in symptomatic groups, exceeding 90%.

CONCLUSION

The evaluation of blood biomarkers on an automated platform exhibited high diagnostic accuracy for AD pathophysiology, and pTau217 showed excellent diagnostic accuracy to identify participants with AD in a consecutive sample representing the routine clinical practice in a specialized memory unit.

Prediction of future cognitive decline among cognitively unimpaired individuals using measures of soluble phosphorylated tau or tau tangle pathology

Plasma p-tau217 and Tau-PET are strong prognostic biomarkers in Alzheimer's disease (AD), but their relative performance in predicting future cognitive decline among cognitively unimpaired (CU) individuals is unclear. In this head-to-head comparison study including 9 cohorts and 1534 individuals, we found that plasma p-tau217 and medial temporal lobe Tau-PET signal showed similar associations with cognitive decline on a global cognitive composite test (R2 PET=0.32 vs R2 PLASMA=0.32, pdifference=0.812) and with progression to mild cognitive impairment (Hazard ratio[HR]PET=1.56[1.43-1.70] vs HRPLASMA=1.63[1.50-1.77], pdifference=0.627). Combined plasma and PET models were superior to the single biomarker models (R2=0.36, p<0.01). Furthermore, sequential selection using plasma p-tau217 and then Tau-PET reduced the number of participants required for a clinical trial by 94%, compared to a 75% reduction when using plasma p-tau217 alone. We conclude that plasma p-tau217 and Tau-PET showed similar performance for predicting future cognitive decline in CU individuals, and their sequential use (i.e., plasma p-tau217 followed by Tau-PET in a subset with high plasma p-tau217) is useful for screening in clinical trials in preclinical AD.

Donanemab in Japanese Patients with Early Alzheimer's Disease: Subpopulation Analysis of the TRAILBLAZER-ALZ 2 Randomized Trial

INTRODUCTION

Donanemab, a monoclonal antibody directed against an insoluble, modified, N-terminal truncated form of amyloid beta, demonstrated efficacy and safety in patients with early, symptomatic Alzheimer's disease (AD) in the phase 3 TRAILBLAZER-ALZ 2 trial. Here, we report clinical outcomes, biomarkers, and safety results for the Japanese subpopulation.

METHODS

TRAILBLAZER-ALZ 2 (N = 1736) was conducted in eight countries, including Japan (enrollment June 2020-November 2021; database lock April 2023). Participants (60-85 years) with early, symptomatic AD (mild cognitive impairment/mild dementia), Mini-Mental State Examination score 20-28, and confirmed amyloid and tau pathology were randomized 1:1 (stratified by tau status) to intravenous donanemab (700 mg for three doses, then 1400 mg/dose) or placebo every 4 weeks for 72 weeks. Primary outcome was change from baseline to week 76 in integrated Alzheimer's Disease Rating Scale (iADRS) score. Other outcomes included clinical measures of cognitive and functional impairment, biomarkers, and safety.

RESULTS

Of 88 Japanese participants (43 placebo, 45 donanemab), 7 in each group discontinued. Least-squares mean (LSM) change from baseline in iADRS score at week 76 was smaller with donanemab than with placebo in the combined (low-medium tau and high tau) and low-medium tau (N = 76) subpopulations (LSM change difference: 4.43 and 3.99, representing 38.8% and 40.2% slowing of disease progression, respectively). Slowing of AD progression with donanemab was also observed for other clinical outcomes. Marked decreases in amyloid plaque and plasma phosphorylated tau 217 were observed; amyloid clearance (< 24.1 Centiloids) was observed in 83.3% of the combined donanemab and 0% of the combined placebo groups. Amyloid-related imaging abnormalities of edema/effusions occurred in ten (22.2%) donanemab-treated participants (one [2.2%] symptomatic) and one (2.3%) placebo-treated participant.

CONCLUSIONS

The overall efficacy and safety of donanemab in Japanese participants were similar to the global TRAILBLAZER-ALZ 2 population.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT04437511.