Current state of Alzheimer's fluid biomarkers

"Advances in biomarker discovery and diagnostics for alzheimer's disease"

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by intracellular neurofibrillary tangles with tau protein and extracellular β-amyloid plaques. Early and accurate diagnosis is crucial for effective treatment and management.

OBJECTIVE

The purpose of this review is to investigate new technologies that improve diagnostic accuracy while looking at the current diagnostic criteria for AD, such as clinical evaluations, cognitive testing, and biomarker-based techniques.

METHODS

A thorough review of the literature was done in order to assess both conventional and contemporary diagnostic methods. Multimodal strategies integrating clinical, imaging, and biochemical evaluations were emphasised. The promise of current developments in biomarker discovery was also examined, including mass spectrometry and artificial intelligence.

RESULTS

Current diagnostic approaches include cerebrospinal fluid (CSF) biomarkers, imaging tools (MRI, PET), cognitive tests, and new blood-based markers. Integrating these technologies into multimodal diagnostic procedures enhances diagnostic accuracy and distinguishes dementia from other conditions. New technologies that hold promise for improving biomarker identification and diagnostic reliability include mass spectrometry and artificial intelligence.

CONCLUSION

Advancements in AD diagnostics underscore the need for accessible, minimally invasive, and cost-effective techniques to facilitate early detection and intervention. The integration of novel technologies with traditional methods may significantly enhance the accuracy and feasibility of AD diagnosis.

Accurate Diagnosis of Alzheimer's Disease Using Specific Breath Volatile Organic Compounds

Whether volatile organic compounds (VOCs) from exhaled breath can be used as a novel biomarker for Alzheimer's disease (AD) diagnosis is unclear. To determine the significantly distinctive VOCs for AD, a total of 970 participants were enrolled, including 60 individuals in data set 1 (AD, 30; controls, 30), 164 individuals in data set 2 (AD, 82; controls, 82), 637 individuals in data set 3 (AD, 31; controls, 606), and 109 individuals in data set 4 (frontotemporal dementia, 19; vascular dementia, 21; Parkinson's disease, 69). The participants in data sets 1, 2, and 4 were from Xiangya Hospital, Central South University. Participants in data set 3 were from a two-year follow-up cohort. VOCs in breath and plasma, neuropsychological scores, plasma p-tau181 levels, metabolites in plasma, and brain functional connectivity were detected. We found that six VOCs were significantly different between the two groups in data set 1 and were verified in data set 2 and data set 3. Ethanol (m/z = 46) and pyrrole (m/z = 67) presented AUC values of 0.907 and 0.895 in data sets 1 and 2 (clinical data sets) and 0.849 and 0.974 in data set 3 (community data set), respectively. The six VOCs were associated with cognitive decline as reflected by neuropsychological tests; five of them were correlated with plasma p-tau181, and these five plasma VOCs were consistently altered as breath VOCs. Correlation between metabolites and five VOCs in plasma was noted, and the five VOCs may originate from blood metabolites. Moreover, four breath VOCs were associated with altered brain connectivity. In conclusion, specific breath VOCs may be used as biomarkers for AD detection.

Analysis and interpretation of inflammatory fluid markers in Alzheimer's disease: a roadmap for standardization

Growing interest in the role of the immune response in Alzheimer's Disease and related dementias (ADRD) has led to widespread use of fluid inflammatory markers in research studies. To standardize the use and interpretation of inflammatory markers in AD research, we build upon prior guidelines to develop consensus statements and recommendations to advance application and interpretation of these markers. In this roadmap paper, we propose a glossary of terms related to the immune response in the context of biomarker discovery/validation, discuss current conceptualizations of inflammatory markers in research, and recommend best practices to address key knowledge gaps. We also provide consensus principles to summarize primary conceptual, methodological, and interpretative issues facing the field: (1) a single inflammatory marker is likely insufficient to describe an entire biological cascade, and multiple markers with similar or distinct functions should be simultaneously measured in a panel; (2) association studies in humans are insufficient to infer causal relationships or mechanisms; (3) neuroinflammation displays time-dependent and disease context-dependent patterns; (4) neuroinflammatory mechanisms should not be inferred based solely on blood inflammatory marker changes; and (5) standardized reporting of CSF inflammatory marker assay validation and performance will improve incorporation of inflammatory markers into the biological AD criteria.

Impact of hemolysis on the levels of proteins associated with aging and age-related neurodegenerative diseases in a multicentric clinical research

Introduction

Hemolysis is a known interference factor that has been found to show erroneous effect. Present study analyzes the impact of hemolysis on the concentrations of protein biomarkers of Alzheimer's disease (Aβ42, t-Tau, p-Tau181) along with novel proteins which are currently under investigation (SIRT1,SIRT2,SIRT6,FOXO3A, NFL, Aβ40, GFAP).

Methods

Plasma samples were grouped into two categories: hemolyzed and non-hemolyzed groups. Degree of hemolysis (in percentage) was separately analyzed using Single molecule array (SIMOA) technology. Quantitative analysis for hemolyzed and non-hemolyzed samples were done using surface plasmon resonance (SPR) technology.

Results

The SIMOA analysis indicated that at high levels of hemolysis (1000 mg/dL) there was an increase in NFL protein level up to approximately 30 % whereas p-Tau181 did not show much interference even at higher hemolysate concentration. Aβ40, Aβ42 and GFAP showed modest effect up to hemolysis of 250mg/dL-500 mg/dL. SPR analysis of total Tau (t-Tau), p-Tau181, SIRT1, SIRT6 showed the consistency in the result and there was no significant difference in hemolyzed plasma compared to non-hemolyzed samples. Aβ42 and FOXO3A showed decline in hemolyzed plasma compared to non-hemolyzed samples (4.34 ± 0.18ng/ul; 4.95 ± 0.19ng/ul) and (3.83 ± 0.34ng/ul; 5.12 ± 0.46ng/ul), respectively whereas, a significant increase in the concentration was observed for SIRT2; 2.4 ± 0.10ng/ul in hemolyzed compared to 1.30 ± 0.22ng/ul in non-hemolyzed group.

Conclusions

High grade hemolysis leads to altered protein concentration associated with neurodegeneration. Present study emphasizes the need to have pre-analytical inspection for hemolysis detection especially in a multicentric biomarker study.

Changes in transcriptional regulation in the temporal lobe in patients with Alzheimer's disease

BackgroundAlzheimer's disease (AD) is a complex neurodegenerative disorder with intricate pathophysiological mechanisms. Transcriptome analysis has been used to investigate the pathogenesis of AD from the perspectives of mRNA expression, alternative splicing, and alternative polyadenylation. However, these 3 transcriptomic regulatory layers have not been comprehensively explored, limiting our understanding of the transcriptomic landscapes of AD pathogenesis.ObjectiveWe aimed to describe the transcriptomic landscapes of AD pathogenesis, detect the contributions of different regulatory layers to the total transcriptional variance, and identify diagnostic candidates for AD prediction.MethodsWe collected RNA sequencing data derived from the temporal lobes of 257 patients with AD and 97 controls, performed joint transcriptional analysis with multi-omics factor analysis (MOFA2) and weighted gene co-expression network analysis (WGCNA), and evaluated the signals with regression models.ResultsWe found that increasing Braak stage is associated with progressive downregulation of SYT1, CHN1, SNAP25, VSNL1, and ENC1 as well as upregulation of TNS1, SGK1, CPM, PPFIBP, and CLMN. Subsequent MOFA2 revealed that alternative splicing contributes most (R2 = 0.558) to the transcriptional variance between patients with AD and controls followed by alternative polyadenylation (R2 = 0.449) and mRNA expression (R2 = 0.438). In addition, the regression model constructed with SNAP25, VSNL1, and ENC1 expression could distinguish between patients with AD and controls (AUC = 0.752).ConclusionsWe systematically detailed the transcriptional landscapes in patients with AD and report mRNA signals associated with AD, offering novel insights into AD pathogenesis and therapeutic development.

Exploring the association between mild behavioral impairment and plasma p-tau217: Implications for early detection of Alzheimer's disease

INTRODUCTION

Mild behavioral impairment (MBI), marked by late-onset persistent neuropsychiatric symptoms (NPS), may signal early dementia risk. While MBI is linked to previously established amyloid-beta (Aβ) and tau biomarkers, its association with plasma p-tau217, a promising blood-based biomarker for Alzheimer's disease (AD), remains unexplored. Here, we investigated the association between MBI and plasma p-tau217 in dementia-free individuals from the Alzheimer's Disease Neuroimaging Initiative.

METHODS

MBI was defined using the Neuropsychiatric Inventory (NPI) data. Linear regression assessed the association between NPS status and continuous p-tau217 levels, while logistic regression modeled the association between NPS status and p-tau217 positivity, using a study-specific cutoff. Models adjusted for age, sex, education, and cognitive diagnosis.

RESULTS

Among 101 participants (mean age = 72.0 ± 6.5; 44.6% female), those with MBI had higher plasma p-tau217 levels (β = 36.4%; 95% confidence interval [CI]: 2.2-82.0, p = 0.04) and higher odds of being p-tau217 positive (odds ratio [OR] = 3.06, 95% CI: 1.14-8.70, p = 0.03) than MBI- participants.

DISCUSSION

Findings support the role of MBI in AD risk stratification.

Highlights

Mild behavioral impairment (MBI) is linked to elevated plasma p-tau217, a specific Alzheimer's disease biomarker.MBI increases the odds of plasma p-tau217 positivity in dementia-free individuals.Findings support MBI as an early indicator for Alzheimer's disease risk.MBI assessment can improve biomarker-based screening and clinical trial efficiency.

Diagnostic value of fluid-based non-amyloid biomarkers for Alzheimer's disease and related dementias in a clinic-based cohort from South Asia

INTRODUCTION

The rising dementia burden and limited knowledge of fluid biomarkers in South Asians highlights this study's aim on evaluating their utility for the diagnosis of Alzheimer's disease and related dementias (ADRD).

METHODS

Participants with ADRD were recruited from a cognitive disorders clinic in India. We performed cognitive assessments and severity evaluations using standard tests. Serum and cerebrospinal fluid (CSF) levels of glial fibrillary acidic protein (GFAP), neurofilament light chain (NfL), total tau, and ubiquitin C-terminal hydrolase L1 (UCHL1) were quantified using a Simoa HD analyzer.

RESULTS

Among the 101 participants, serum GFAP and NfL levels were significantly greater in dementia participants (n = 70) than controls. Serum biomarkers significantly correlated with their corresponding CSF levels. Significant correlations were noted for serum and CSF GFAP and NfL in Alzheimer's disease (ρ = 0.492, 0.664) and between serum and CSF NfL in frontotemporal dementia (ρ = 0.727). Serum GFAP, NfL, and UCHL1 demonstrated high diagnostic accuracy (area under the curve = 0.765-0.806).

DISCUSSION

Our results emphasize the role of fluid biomarkers in diagnosing dementia in low-resource settings in South Asians.

Highlights

Serum glial fibrillary acidic protein (GFAP) and neurofilament light chain (NfL) levels were significantly greater in patients with dementia than in healthy controls.Significant correlation was observed between the serum and cerebrospinal fluid levels of GFAP, NfL, and total tau independent of the baseline demographics or co-morbidities, indicating their potential role in clinical practice.Serum biomarker levels were related to the severity of dementia.This is one of few studies on fluid-based biomarkers in diverse cohorts with Alzheimer's disease and related dementias in the South Asian cohort with limited resources.

Older Amyloid Beta as a Candidate Blood Biomarker of Early Cognitive Decline in the Elderly-A Preliminary Study

(1) Background/Objectives: The pathogenic process of Alzheimer's disease (AD) is known to begin decades before its clinical onset. This period, although imperceptible to the patient, encompasses a gradual neuronal loss. The first symptoms of dementia, often classified as mild cognitive impairment (MCI), in many cases converts into incipient AD, but can also remain stable or even reverse to cognitive norm. An easy and fast blood-based method of identifying patients at risk of conversion to AD would allow for the application of disease-altering therapies. This preliminary study focuses on the identification and assessment of the relationship between plasma amyloid beta (Aβ) and cognitive performance in older Polish adults with respect to its adequacy as a biomarker of an early cognitive deterioration. (2) Methods: The preliminary research sample consisted of 230 participants, 109 females and 121 males, aged 65 plus. The association between plasma Aβ concentrations with cognitive status, gender, and age were assessed. The analyses were conducted in three categories of cognitive performance: cognitive norm, mild cognitive impairment, and mild dementia, based on results of the Mini-Mental State Examination (MMSE) and functional tests. (3) Results: No significant differences in plasma Aβ levels for different cognitive statuses were identified. No significant differences were found in Aβ levels based on age or gender. (4) Conclusions: In order to thoroughly explore the power of research on plasma Aβ with respect to early cognitive deterioration, further prospective studies are required.

Elevated cerebrospinal fluid biomarkers of neuroinflammation and neuronal damage in essential hypertension with secondary insomnia: Implications for Alzheimer's disease risk

Essential hypertension (EH) with secondary insomnia is associated with increased risks of neuroinflammation, neuronal damage, and Alzheimer's disease (AD). However, its relationship with specific cerebrospinal fluid (CSF) biomarkers of neuronal damage and neuroinflammation remains unclear. This case-control study compared CSF biomarker levels across three groups: healthy controls (HC, n = 64), hypertension-controlled (HTN-C, n = 54), and hypertension-uncontrolled (HTN-U, n = 107) groups, all EH participants experiencing secondary insomnia. CSF samples from knee replacement patients were analyzed for key biomarkers, and sleep quality was assessed via the Pittsburgh Sleep Quality Index (PSQI). Our findings showed that the HTN-U group had significantly higher CSF levels of proinflammatory cytokines IL-6, TNF-α, and IL-17 than the HC and HTN-C groups (all p < 0.01). These cytokines correlated positively with secondary insomnia measures, with IL-6 (r = 0.285, p = 0.003), IL-17 (r = 0.324, p = 0.001), and TNF-α (r = 0.274, p = 0.005) linked to PSQI scores. In the HTN-U group, elevated IL-6, TNF-α, and IL-17 levels were also positively associated with neurofilament light (NF-L) and negatively with β-amyloid 42 (Aβ42), both key AD markers (all p < 0.05). Additionally, secondary insomnia was negatively correlated with Aβ42 (r = -0.225, p = 0.021) and positively with NF-L (r = 0.261, p = 0.007). Higher CSF palmitic acid (PA) levels observed in the HTN-U group were linked to poorer sleep quality (r = 0.208, p = 0.033). In conclusion, EH with secondary insomnia is associated with CSF biomarkers of neuronal damage, neuroinflammation, and neurodegeneration, suggesting a potential increase in AD risk among this population.

Improvements in Exercise for Alzheimer's Disease: Highlighting FGF21-Induced Cerebrovascular Protection

Alzheimer's disease (AD) is the most common neurodegenerative disease. Currently, it has shown a trend of earlier onset, with most patients experiencing a progressive decline in cognitive function following the disease's onset, which places a heavy burden on society and family. Since no drug cure for AD exists, exploring new ways for its treatment and prevention has become critical. Early vascular damage is an initial trigger for neuronal injury in AD, underscoring the importance of vascular health in the early stages of the disease. Patients with early AD experience abnormal blood-brain barrier transport of amyloid-β (Aβ) peptides, with excess Aβ being deposited in the cerebral vasculature. The toxic effects of Aβ lead to abnormalities in cerebrovascular structure and function. Fibroblast growth factor21 (FGF21) is an endocrine factor that positively regulates energy homeostasis and glucose-lipid metabolism. Notably, it is one of the effective targets for metabolic disease prevention and treatment. Recent studies have found that FGF21 has anti-aging and vasoprotective effects, with receptors for FGF21 present in the brain. Exercise stimulates the liver to produce large amounts of FGF21, which enters the blood-brain barrier with the blood to exert neurovascular protection. Therefore, we review the biological properties of FGF21, its role in the cerebrovascular structure and function in AD, and the mechanism of exercise-regulated FGF21 action on AD-related cerebrovascular changes, aiming to provide a new theoretical basis for using exercise to ameliorate degenerative neurological diseases.

Guidelines for the standardization of pre-analytical variables for salivary biomarker studies in Alzheimer's disease research: An updated review and consensus of the Salivary Biomarkers for Dementia Research Working Group

There is a pressing need for accessible biomarkers with high diagnostic accuracy for Alzheimer's disease (AD) diagnosis to facilitate widespread screening, particularly in underserved groups. Saliva is an emerging specimen for measuring AD biomarkers, with distinct contexts of use that could complement blood and cerebrospinal fluid and detect various analytes. An interdisciplinary, international group of AD and related dementias (ADRD) researchers convened and performed a narrative review of published studies on salivary AD biomarkers. We critically appraised the current state of the literature, examining both consistencies and discrepancies in existing pre-analytical variables and methodologies. We discussed how various pre-analytical variables could influence the detection and quantification of salivary biomarkers, showed technologies available to standardize collection procedures, and proposed a standardized pre-analytical protocol to guide future studies on salivary AD biomarker examinations. We identified potential contexts of use, gaps, and priorities and proposed future research directions. HIGHLIGHTS: Given its non-invasive nature, wider accessibility, and cultural acceptability, particularly in low-resourced settings, saliva is a biofluid complementary to blood and CSF. Current salivary AD biomarker studies do not control for many confounding pre-analytical variables during the sampling process, potentially leading to inaccurate salivary biomarker readings and conclusions, contributing to conflicting findings. Reviewing the current literature, including the consistencies and non-consistencies observed in the existing parameters and methodologies, discussing how they can affect salivary AD biomarker detection and quantification. Proposing a standardized salivary pre-analytical protocol, identifying the gaps and prioritizations needed to move this area forward, proposing future directions and potential contexts of use.

"My Biomarkers Are Fine, Thank You": On the Biomarkerization of Modern Medicine

Biomarkers are becoming crucial in ever more medical tasks and are proposed to change medicine in profound ways. By biomarking ever more attributes of human life, they tend to blur the distinction between health and disease and come to characterize life as such. Not only do biomarkers strongly influence the professional conception of disease by pervading ever more diagnoses, but they also impact patients' experience of illness. To manage how biomarkers influence patients, professionals, and societies, we urgently need to move from identifying potentially relevant biomarkers to determine their meaning and value to individuals, professionals, and public health.

An overview of the genes and biomarkers in Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia and neurodegenerative disease characterized by neurofibrillary tangles (NFTs) and amyloid plaque. Familial AD is caused by mutations in the APP, PSEN1, and PSEN2 genes and these mutations result in the early onset of the disease. Sporadic AD usually affects older adults over the age of 65 years and is, therefore classified as late-onset AD (LOAD). Several risk factors associated with LOAD including the APOE gene have been identified. Moreover, GWAS studies have identified a wide array of genes and polymorphisms that are associated with LOAD risk. Currently, the diagnosis of AD involves the evaluation of memory and personality changes, cognitive impairment, and medical and family history to rule out other diseases. Laboratory tests to assess the biomarkers in the body fluids as well as MRI, CT, and PET scans to analyze the presence of plaques and NFTs are also included in the diagnosis of AD. It is important to diagnose AD before the onset of clinical symptoms, i.e. during the preclinical stage, to delay the progression and for better management of the disease. Research has been conducted to identify biomarkers of AD in the CSF, serum, saliva, and urine during the preclinical stage. Current research has identified several biomarkers and potential biomarkers in the body fluids that enhance diagnostic accuracy. Aside from genetics, other factors such as diet, physical activity, and lifestyle factors may influence the risk of developing AD. Clinical trials are underway to find potential biomarkers, diagnostic measures, and treatments for AD mainly in the preclinical stage. This review provides an overview of the genes and biomarkers of AD.

Inflammatory signaling pathways in Alzheimer's disease: Mechanistic insights and possible therapeutic interventions

The complex pathophysiology of Alzheimer's disease (AD) poses challenges for the development of therapies. Recently, neuroinflammation has been identified as a key pathogenic mechanism underlying AD, while inflammation has emerged as a possible target for the management and prevention of AD. Several prior studies have demonstrated that medications modulating neuroinflammation might lessen AD symptoms, mostly by controlling neuroinflammatory signaling pathways such as the NF-κB, MAPK, NLRP3, etc, and their respective signaling cascade. Moreover, targeting these inflammatory modalities with inhibitors, natural products, and metabolites has been the subject of intensive research because of their anti-inflammatory characteristics, with many studies demonstrating noteworthy pharmacological capabilities and potential clinical applications. Therefore, targeting inflammation is considered a promising strategy for treating AD. This review comprehensively elucidates the neuroinflammatory mechanisms underlying AD progression and the beneficial effects of inhibitors, natural products, and metabolites in AD treatment.

Methylated cell-free DNA as a novel biomarker in Alzheimer's disease

Due to an aging population, Alzheimer's disease (AD), a neurodegenerative disorder, has affected more than 40 million people worldwide, a figure predicted to significantly increase in the coming decades. Despite much effort to understand AD pathogenesis, effective diagnosis and treatment remain a challenge. However, the development of liquid biopsy including the analysis of cell-free DNA (cfDNA) and methylation thereof has provided an alternative source of investigation to further explore the pathophysiology of AD. Herein, we discuss the research progress to date and highlight clinical applications of methylated cfDNA in AD.

Serum β-secretase 1 (sBACE1) activity in subjective cognitive decline: an exploratory study

β-Secretase-1 (BACE1) plays a key role in the regulation of cerebral amyloid-β homeostasis, being involved in amyloidogenic and, as recently found, amyloidolytic pathways. Growing evidence indicates that increased serum BACE1 (sBACE1) activity might represent an early biomarker for Alzheimer's disease. Here, we tested the hypothesis that an increase in sBACE1 activity may already occur in individuals with subjective cognitive decline (SCD). We found that sBACE1 activity was significantly higher in individuals with SCD (n 118) compared to cognitively normal subjects (controls, n 137) (p < 0.001). Moreover, compared with SCD, sBACE1 activity was even higher in patients affected by amnestic (n 179) or non-amnestic mild cognitive impairment (MCI) (n 99) (p < 0.001 and p 0.02, respectively). In all cases, the respective increase in sBACE1 activity was significant after adjustment for possible confounders including age, sex, and comorbidities. We also found a significant sexual dimorphism, with women affected by either type of MCI, but not by SCD, having higher levels of serum BACE1 activity compared to men. These results provide evidence supporting the potential use of sBACE1 activity as tool for blood-based screening of cognitively healthy individuals at clinical risk of MCI and dementia.

Alterations of amino acids in older adults with Alzheimer's Disease and Vascular Dementia

Metabolomics provide a promising tool for understanding dementia pathogenesis and identifying novel biomarkers. This study aimed to identify amino acid biomarkers for Alzheimer's Disease (AD) and Vascular Dementia (VD). By amino acid metabolomics, the concentrations of amino acids were determined in the serum of AD and VD patients as well as age-matched healthy controls. Several differences in the concentration of amino acids were observed in AD patients compared to both healthy controls and VD patients. However, no significant distinction was found between healthy controls and VD patients. Considering comorbidities, cystine levels were higher in AD than in VD among non-diabetic patients, but not in those with diabetes. Notably, creatine, spermidine, cystine, and tyrosine demonstrated favorable results in decision curve analyses and good discriminative performances, suggesting their potential for clinical application. These fundings give novel perspectives of serum amino acids for predicting metabolic pathways in AD and VD pathogenesis.

Brain injury biomarkers and applications in neurological diseases

ABSTRACT

Neurological diseases are a major health concern, and brain injury is a typical pathological process in various neurological disorders. Different biomarkers in the blood or the cerebrospinal fluid are associated with specific physiological and pathological processes. They are vital in identifying, diagnosing, and treating brain injuries. In this review, we described biomarkers for neuronal cell body injury (neuron-specific enolase, ubiquitin C-terminal hydrolase-L1, αII-spectrin), axonal injury (neurofilament proteins, tau), astrocyte injury (S100β, glial fibrillary acidic protein), demyelination (myelin basic protein), autoantibodies, and other emerging biomarkers (extracellular vesicles, microRNAs). We aimed to summarize the applications of these biomarkers and their related interests and limits in the diagnosis and prognosis for neurological diseases, including traumatic brain injury, status epilepticus, stroke, Alzheimer's disease, and infection. In addition, a reasonable outlook for brain injury biomarkers as ideal detection tools for neurological diseases is presented.

The Alzheimer's Association clinical practice guideline for the Diagnostic Evaluation, Testing, Counseling, and Disclosure of Suspected Alzheimer's Disease and Related Disorders (DETeCD-ADRD): Executive summary of recommendations for specialty care

US clinical practice guidelines for the diagnostic evaluation of cognitive impairment due to Alzheimer's disease (AD) or a related dementia (ADRD) are two decades old. This evidence-based guideline was developed to empower all clinicians to implement a structured approach for evaluating a patient with symptoms that may represent clinical AD/ADRD. An expert workgroup conducted a review of 7374 publications (133 met inclusion criteria) and developed recommendations as steps in an evaluation process. This summary briefly reviews core recommendations and details specialist recommendations of a high-quality, evidence-supported evaluation process aimed at characterizing, diagnosing, and disclosing the patient's cognitive functional status, cognitive-behavioral syndrome, and likely underlying brain disease so that optimal care plans to maximize patient/care partner dyad quality of life can be developed; a companion article summarizes primary care recommendations. If clinicians use the recommendations in this guideline and health-care systems provide adequate resources, outcomes should improve in most patients in most practice settings. HIGHLIGHTS: US clinical practice guidelines for the diagnostic evaluation of cognitive impairment due to Alzheimer's disease (AD) or related dementias (ADRD) are decades old and aimed at specialists. This evidence-based guideline was developed to empower all-including primary care-clinicians to implement a structured approach for evaluating a patient with symptoms that may represent clinical AD/ADRD. This summary focuses on recommendations appropriate for specialty practice settings, forming key elements of a high-quality, evidence-supported evaluation process aimed at characterizing, diagnosing, and disclosing the patient's cognitive functional status, cognitive-behavioral syndrome, and likely underlying brain disease so that optimal care plans to maximize patient/care partner dyad quality of life can be developed; a companion article summarizes primary care recommendations. If clinicians use this guideline and health-care systems provide adequate resources, outcomes should improve in most patients in most practice settings.

TREM2 bridges microglia and extracellular microenvironment: Mechanistic landscape and therapeutical prospects on Alzheimer's disease

Neuroinflammation is closely related to the pathogenesis of Alzheimer's disease (AD). One of its prominent cellular components, microglia, is a potent coordinator of neuroinflammation in interplay with the characteristic AD pathological alterations including Aβ, tau, and neuronal defects, which constitute the AD-unique extracellular microenvironment. Mounting evidence implicates Triggering Receptors Expressed on Myeloid Cells 2 (TREM2) in the center of microglial activation, a vital event in the pathogenesis of AD. TREM2 is a pivotal microglial receptor that interacts with specific elements present in the AD microenvironment and induces microglial intracellular signallings contributing to phagocytosis, migration, cytokine production, metabolism, and survival, which shapes the microglial activation profile. It follows that TREM2 builds up a bridge between microglia and the extracellular microenvironment. This review illustrates how TREM2 modulates microglia to affect AD pathogenesis. Mainly presented facets in the review are i. the development of AD-specific microglial phenotypes (disease-associated microglia, DAM), ii. microglial interactions with major AD pathologies, and iii. the underlying intracellular signallings of microglial activation. Also, outstanding controversies regarding the nature of neuroinflammation are discussed. Through our illustration, we attempt to establish a TREM2-centered network of AD pathogenesis, in the hope as well to provide insights into the potential therapeutic strategies based on the underlying mechanisms.

Interval-specific likelihood ratios and probability-based models for interpreting combined CSF biomarkers for Alzheimer's disease

BACKGROUND

In Alzheimer's disease (AD) diagnosis, a cerebrospinal fluid (CSF) biomarker panel is commonly interpreted with binary cutoff values. However, these values are not generic and do not reflect the disease continuum. We explored the use of interval-specific likelihood ratios (LRs) and probability-based models for AD using a CSF biomarker panel.

METHODS

CSF biomarker (Aβ1-42, tTau and pTau181) data for both a clinical discovery cohort of 241 patients (measured with INNOTEST) and a clinical validation cohort of 129 patients (measured with EUROIMMUN), both including AD and non-AD dementia/cognitive complaints were retrospectively retrieved in a single-center study. Interval-specific LRs for AD were calculated and validated for univariate and combined (Aβ1-42/tTau and pTau181) biomarkers, and a continuous bivariate probability-based model for AD, plotting Aβ1-42/tTau versus pTau181 was constructed and validated.

RESULTS

LR for AD increased as individual CSF biomarker values deviated from normal. Interval-specific LRs of a combined biomarker model showed that once one biomarker became abnormal, LRs increased even further when another biomarker largely deviated from normal, as replicated in the validation cohort. A bivariate probability-based model predicted AD with a validated accuracy of 88% on a continuous scale.

CONCLUSIONS

Interval-specific LRs in a combined biomarker model and prediction of AD using a continuous bivariate biomarker probability-based model, offer a more meaningful interpretation of CSF AD biomarkers on a (semi-)continuous scale with respect to the post-test probability of AD across different assays and cohorts.

Shared and distinct changes in the molecular cargo of extracellular vesicles in different neurodegenerative diseases

Neurodegenerative disorders such as Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS) and Parkinson's disease (PD) affect millions of people worldwide. Curative treatment for these neurodegenerative disorders is still lacking and therefore a further understanding of their cause and progression is urgently needed. Extracellular vesicles (EVs) are nanosized vesicles loaded with cargo, such as proteins and miRNAs, that are released by cells and play an important role in intercellular communication. Intercellular communication through EVs can contribute to the spread of pathological proteins, such as amyloid-beta and tau, or cause pathogenesis through other mechanisms. In addition, EVs may serve as potential biomarkers for diagnosis and for monitoring disease progression. In this review, we summarize and discuss recent advances in our understanding of the role of EVs in AD, ALS an PD with an emphasis on dysregulated cargo in each disease. We highlight shared dysregulated cargo between these diseases, discuss underlying pathways, and outline future implications for therapeutic strategies.

Association of Serum Ferritin with Total and Regional Fat Measured by Dual-Energy X-Ray Absorptiometry in a Nationally Representative Survey

INTRODUCTION

Fat distribution is a stronger predictor for cardiometabolic morbidity and mortality. We aimed to investigate the association of elevated iron stores, measured as serum ferritin levels, with total and regional body fat.

METHODS

Data from 2,646 adults from the National Health and Nutrition Examination Survey 2017-2018 were analyzed. Dual-energy X-ray absorptiometry was used to measure overall and regional body fat. The fat mass index (FMI) was calculated by dividing the fat mass (kg) by the square of body height (m2). The leg fat mass to trunk fat mass ratio (LTR) was used to assess the relative distribution of leg fat compared to trunk fat.

RESULTS

Medians (IQR) of serum ferritin levels were 0.168 μg/mL (0.104-0.269) for men and 0.053 μg/mL (0.026-0.102) for women. After adjusting for sociodemographic, lifestyle, and metabolic factors, serum ferritin showed a significant positive association with total FMI (β = 2.662) and trunk FMI (β = 0.983), and a negative association with leg FMI (β = -0.324) and LTR (β = -0.160) in men. In women, serum ferritin showed a significant positive association with total FMI (β = 4.658), trunk FMI (β = 2.085), and negative association with LTR (β = -0.312). Significant positive trends were observed for serum ferritin with total and trunk FMI in men and women, using the lowest serum ferritin quartile as the reference group. Additionally, significant negative trends were observed for serum ferritin with leg FMI and LTR in men. The mediation analysis revealed that C-reactive protein mediated 16.4% and 22.6% of the potential effects of serum ferritin on trunk FMI in men and women, respectively.

CONCLUSION

Higher ferritin levels were associated with greater total and trunk fat but lower leg fat. Further prospective and mechanistic studies are warranted to confirm the study results.

The early diagnosis of Alzheimer's disease: Blood-based panel biomarker discovery by proteomics and metabolomics

Diagnosis and prediction of Alzheimer's disease (AD) are increasingly pressing in the early stage of the disease because the biomarker-targeted therapies may be most effective. Diagnosis of AD largely depends on the clinical symptoms of AD. Currently, cerebrospinal fluid biomarkers and neuroimaging techniques are considered for clinical detection and diagnosis. However, these clinical diagnosis results could provide indications of the middle and/or late stages of AD rather than the early stage, and another limitation is the complexity attached to limited access, cost, and perceived invasiveness. Therefore, the prediction of AD still poses immense challenges, and the development of novel biomarkers is needed for early diagnosis and urgent intervention before the onset of obvious phenotypes of AD. Blood-based biomarkers may enable earlier diagnose and aid detection and prognosis for AD because various substances in the blood are vulnerable to AD pathophysiology. The application of a systematic biological paradigm based on high-throughput techniques has demonstrated accurate alterations of molecular levels during AD onset processes, such as protein levels and metabolite levels, which may facilitate the identification of AD at an early stage. Notably, proteomics and metabolomics have been used to identify candidate biomarkers in blood for AD diagnosis. This review summarizes data on potential blood-based biomarkers identified by proteomics and metabolomics that are closest to clinical implementation and discusses the current challenges and the future work of blood-based candidates to achieve the aim of early screening for AD. We also provide an overview of early diagnosis, drug target discovery and even promising therapeutic approaches for AD.

A pentavalent peptide vaccine elicits Aβ and tau antibodies with prophylactic activity in an Alzheimer's disease mouse model

Amyloid-β (Aβ) and hyperphosphorylated tau protein are targets for Alzheimer's Disease (AD) immunotherapies, which are generally focused on single epitopes within Aβ or tau. However, due to the complexity of both Aβ and tau in AD pathogenesis, a multipronged approach simultaneously targeting multiple epitopes of both proteins could overcome limitations of monotherapies. Herein, we propose an active AD immunotherapy based on a nanoparticle vaccine comprising two Aβ peptides (1-14 and pyroglutamate pE3-14) and three tau peptides (centered on phosphorylated pT181, pT217 and pS396/404). These correspond to both soluble and aggregated targets and are displayed on the surface of immunogenic liposomes in an orientation that maintains reactivity with epitope-specific monoclonal antibodies. Intramuscular immunization of mice with individual epitopes resulted in minimally cross-reactive antibody induction, while simultaneous co-display of 5 antigens ("5-plex") induced antibodies against all epitopes without immune interference. Post-immune sera recognized plaques and neurofibrillary tangles from human AD brain tissue. Vaccine administration to 3xTg-AD mice using a prophylactic dosing schedule inhibited tau and amyloid pathologies and resulted in improved cognitive function. Immunization was well tolerated and did not induce antigen-specific cellular responses or persistent inflammatory responses in the peripheral or central nervous system. Antibody levels could be reversed by halting monthly vaccinations. Altogether, these results indicate that active immune therapies based on nanoparticle formulations of multiple Aβ and tau epitopes warrant further study for treating early-stage AD.

Association of Neurogranin and BACE1 With Clinical Cognitive Decline in Individuals With Subjective Cognitive Decline

BACKGROUND AND OBJECTIVES

CSF biomarkers have immense diagnostic and prognostic potential for Alzheimer disease (AD). However, AD is still diagnosed relatively late in the disease process, sometimes even years after the initial manifestation of cognitive symptoms. Thus, further identification of biomarkers is required to detect related pathology in the preclinical stage and predict cognitive decline. Our study aimed to assess the association of neurogranin and β-site amyloid precursor protein-cleaving enzyme 1 (BACE1) with cognitive decline in individuals with subjective cognitive decline (SCD).

METHODS

We enrolled participants with available neurogranin and BACE1 measurements in CSF from the DELCODE (DZNE-Longitudinal Cognitive Impairment and Dementia, Germany) cohort. The longitudinal change of Preclinical Alzheimer's Cognitive Composite score was assessed as the primary outcome in participants with SCD and controls. The secondary outcome was defined as conversion of SCD to mild cognitive impairment (MCI) during follow-up. Levels of neurogranin, BACE1, and neurogranin/BACE1 ratio across groups were compared by analysis of covariance after adjustment for demographics. The linear mixed-effects model and Cox regression analysis were applied to evaluate their association with cognitive decline and progression of SCD to MCI, respectively.

RESULTS

A total of 530 participants (mean age: 70.76 ± 6.01 years, 48.7% female) were analyzed in the study. The rate of cognitive decline was faster in individuals with SCD with higher neurogranin and neurogranin/BACE1 ratio (β = -0.138, SE = 0.065, p = 0.037, and β = -0.293, SE = 0.115, p = 0.013). Higher baseline neurogranin and neurogranin/BACE1 ratio were associated with an increased rate of conversion from SCD to MCI (hazard ratio [HR] 1.35 per SD, 95% CI 1.03-1.77, p = 0.028, and HR 1.53 per SD, 95% CI 1.13-2.07, p = 0.007). In addition, the impact of higher neurogranin levels on accelerating the rate of cognitive decline was more pronounced in the SCD group than in cognitively unimpaired controls (β = -0.077, SE = 0.033, p = 0.020).

DISCUSSION

Our findings suggest that CSF neurogranin and BACE1 begin to change in the preclinical stage of AD and they are associated with clinical progression in individuals with SCD.

Nanomaterials that Aid in the Diagnosis and Treatment of Alzheimer's Disease, Resolving Blood-Brain Barrier Crossing Ability

As a form of dementia, Alzheimer's disease (AD) suffers from no efficacious cure, yet AD treatment is still imperative, as it ameliorates the symptoms or prevents it from deteriorating or maintains the current status to the longest extent. The human brain is the most sensitive and complex organ in the body, which is protected by the blood-brain barrier (BBB). This yet induces the difficulty in curing AD as the drugs or nanomaterials that are much inhibited from reaching the lesion site. Thus, BBB crossing capability of drug delivery system remains a significant challenge in the development of neurological therapeutics. Fortunately, nano-enabled delivery systems possess promising potential to achieve multifunctional diagnostics/therapeutics against various targets of AD owing to their intriguing advantages of nanocarriers, including easy multifunctionalization on surfaces, high surface-to-volume ratio with large payloads, and potential ability to cross the BBB, making them capable of conquering the limitations of conventional drug candidates. This review, which focuses on the BBB crossing ability of the multifunctional nanomaterials in AD diagnosis and treatment, will provide an insightful vision that is conducive to the development of AD-related nanomaterials.

Reduced platelet activation and thrombus formation in male transgenic model mice of Alzheimer's disease suggests early sex-specific differences in platelet pathophysiology

Alzheimer's disease (AD) is the most common form of dementia and characterized by extracellular amyloid-β (Aβ) plaques, intracellular neurofibrillary tau tangles and neurodegeneration. Over 80 % of AD patients also exhibit cerebral amyloid angiopathy (CAA). CAA is a cerebrovascular disease caused by deposition of Aβ in the walls of cerebral blood vessels leading to vessel damage and impairment of normal blood flow. To date, different studies suggest that platelet function, including activation, adhesion and aggregation, is altered in AD due to vascular Aβ deposition. For example, the transgenic AD model mice APP23 mice that exhibit CAA and parenchymal Aβ plaques, show pre-activated platelets in the blood circulation and increased platelet integrin activation leading to a pro-thrombotic phenotype in these mice late stages of AD. However, it is still an open question whether or not platelets exhibit changes in their activation profile before they are exposed to vascular Aβ deposits. Therefore, the present study examined platelets from middle-aged transgenic APP23 mice at the age of 8-10 months. At this age, APP23 mice show amyloid plaques in the brain parenchyma but not in the vasculature. Our analyses show that these APP23 mice have unaltered platelet numbers and size, and unaltered surface expression of glycoproteins. However, the number of dense granules in transgenic platelets was increased while the release was unaltered. Male, but not female APP23 mice, exhibited reduced platelet activation after stimulation of the thrombin receptor PAR4 and decreased thrombus stability on collagen under flow conditions ex vivo compared to control mice. In an arterial thrombosis model in vivo, male APP23 mice showed attenuated occlusion of the injured artery compared to controls. These findings provide clear evidence for early changes in platelet activation and thrombus formation in male mice before development of overt CAA. Furthermore, reduced platelet activation and thrombus formation suggest sex-specific differences in platelet physiology in AD that has to be considered in future studies of platelets and their role in AD.

Exploring advancements in early detection of Alzheimer's disease with molecular assays and animal models

Alzheimer's Disease (AD) is a challenging neurodegenerative condition, with overwhelming implications for affected individuals and healthcare systems worldwide. Animal models have played a crucial role in studying AD pathogenesis and testing therapeutic interventions. Remarkably, studies on the genetic factors affecting AD risk, such as APOE and TREM2, have provided valuable insights into disease mechanisms. Early diagnosis has emerged as a crucial factor in effective AD management, as demonstrated by clinical studies emphasizing the benefits of initiating treatment at early stages. Novel diagnostic technologies, including RNA sequencing of microglia, offer promising avenues for early detection and monitoring of AD progression. Therapeutic strategies remain to evolve, with a focus on targeting amyloid beta (Aβ) and tau pathology. Advances in animal models, such as APP-KI mice, and the advancement of anti-Aβ drugs signify progress towards more effective treatments. Therapeutically, the focus has shifted towards intricate approaches targeting multiple pathological pathways simultaneously. Strategies aimed at reducing Aβ plaque accumulation, inhibiting tau hyperphosphorylation, and modulating neuroinflammation are actively being explored, both in preclinical models and clinical trials. While challenges continue in developing validated animal models and translating preclinical findings to clinical success, the continuing efforts in understanding AD at molecular, cellular, and clinical levels offer hope for improved management and eventual prevention of this devastating disease.

Potential application of aptamers combined with DNA nanoflowers in neurodegenerative diseases

The efficacy of neurotherapeutic drugs hinges on their ability to traverse the blood-brain barrier and access the brain, which is crucial for treating or alleviating neurodegenerative diseases (NDs). Given the absence of definitive cures for NDs, early diagnosis and intervention become paramount in impeding disease progression. However, conventional therapeutic drugs and existing diagnostic approaches must meet clinical demands. Consequently, there is a pressing need to advance drug delivery systems and early diagnostic methods tailored for NDs. Certain aptamers endowed with specific functionalities find widespread utility in the targeted therapy and diagnosis of NDs. DNA nanoflowers (DNFs), distinctive flower-shaped DNA nanomaterials, are intricately self-assembled through rolling ring amplification (RCA) of circular DNA templates. Notably, imbuing DNFs with diverse functionalities becomes seamlessly achievable by integrating aptamer sequences with specific functions into RCA templates, resulting in a novel nanomaterial, aptamer-bound DNFs (ADNFs) that amalgamates the advantageous features of both components. This article delves into the characteristics and applications of aptamers and DNFs, exploring the potential or application of ADNFs in drug-targeted delivery, direct treatment, early diagnosis, etc. The objective is to offer prospective ideas for the clinical treatment or diagnosis of NDs, thereby contributing to the ongoing efforts in this critical field.

The Evaluation of Clinical Applications for the Detection of the Alzheimer's Disease Biomarker GFAP

One of the most prevalent neurodegenerative diseases is Alzheimer's disease (AD). The hallmarks of AD include the accumulation of amyloid plaques and neurofibrillary tangles, which cause related secondary diseases, progressive neurodegeneration, and ultimately death. The most prevalent cell type in the human central nervous system, astrocytes, are crucial for controlling neuronal function. Glial fibrillary acidic protein (GFAP) is released from tissue into the bloodstream due to astrocyte breakdown in neurological diseases. Increased levels of GFAP in the serum can function as blood markers and be an effective prognostic indicator to help diagnose neurological conditions early on, from stroke to neurodegenerative diseases. The human central nervous system (CNS) is greatly affected by diseases associated with blood GFAP levels. These include multiple sclerosis, intracerebral hemorrhage, glioblastoma multiforme, traumatic brain injuries, and neuromyelitis optica. GFAP demonstrates a strong diagnostic capacity for projecting outcomes following an injury. Furthermore, the increased ability to identify GFAP protein fragments helps facilitate treatment, as it allows continuous screening of CNS injuries and early identification of potential recurrences. GFAP has recently gained attention due to data showing that the plasma biomarker is effective in identifying AD pathology. AD accounts for 60-70% of the approximately 50 million people with dementia worldwide. It is critical to develop molecular markers for AD, whose number is expected to increase to about 3 times and affect humans by 2050, and to investigate possible targets to confirm their effectiveness in the early diagnosis of AD. In addition, most diagnostic methods currently used are image-based and do not detect early disease, i.e. before symptoms appear; thus, treatment options and outcomes are limited. Therefore, recently developed methods such as point-of-care (POC), on-site applications, and enzyme-linked immunosorbent assay-polymerase chain reaction (ELISA-PCR) that provide both faster and more accurate results are gaining importance. This systematic review summarizes published studies with different approaches such as immunosensor, lateral flow, POC, ELISA-PCR, and molecularly imprinted polymer using GFAP, a potential blood biomarker to detect neurological disorders. Here, we also provide an overview of current approaches, analysis methods, and different future detection strategies for GFAP, the most popular biosensing field.

Alzheimer Disease Cerebrospinal Fluid Biomarkers in a Tertiary Neurology Practice

OBJECTIVE

To evaluate the performance of Alzheimer disease (AD) cerebrospinal fluid (CSF) biomarkers in a tertiary neurology clinic setting with high frequency of non-AD cases, including normal pressure hydrocephalus (NPH).

METHODS

There were 534 patients who underwent AD CSF biomarkers (Roche Elecsys Aβ42, p-Tau181, total-Tau) from April 1, 2020, through April 23, 2021. A behavioral neurologist blinded to CSF results assigned a clinical diagnosis retrospectively on the basis of consensus criteria, and a neuroradiologist blinded to the diagnosis and CSF studies graded brain magnetic resonance images for indicators of CSF dynamics disorders. Associations between biomarkers, diagnoses, and imaging were assessed by χ2, analysis of covariance, and linear regression methods.

RESULTS

Median age at time of testing was 67 years (range, 19 to 96 years), median symptom duration was 2 years (range, 0.4 to 28 years), and median Short Test of Mental Status score was 30 (range, 0 to 38). Clinical diagnoses significantly correlated with different CSF biomarker values (χ2=208.3; P=10e-4). p-Tau181/Aβ42 ratios above 0.023 positively correlated with Alzheimer dementia (more than individual measures). This ratio also had the best performance for differentiating Alzheimer dementia from NPH (area under the curve, 0.869). Imaging markers supportive of CSF dynamics disorders correlated with low Aβ42, p-Tau181, and total-Tau.

CONCLUSION

In a heterogeneous clinical population, abnormal p-Tau181/Aβ42 ratios (>0.023) have the strongest association with Alzheimer dementia and probably represent a comorbid AD pathologic component in persons clearly matching non-AD neurodegenerative syndromes. Altered CSF dynamics were associated with lower concentrations of AD CSF biomarkers regardless of clinical diagnosis, but the ratio compensates for these changes. In the appropriate clinical setting, an isolated abnormal Aβ42 should prompt consideration of NPH.

Serum Beta-Secretase 1 Activity Is a Potential Marker for the Differential Diagnosis between Alzheimer's Disease and Frontotemporal Dementia: A Pilot Study

Alzheimer's disease (AD) and frontotemporal dementia (FTD) are the two major neurodegenerative diseases causing dementia. Due to similar clinical phenotypes, differential diagnosis is challenging without specific biomarkers. Beta-site Amyloid Precursor Protein cleaving enzyme 1 (BACE1) is a β-secretase pivotal in AD pathogenesis. In AD and mild cognitive impairment subjects, BACE1 activity is increased in brain/cerebrospinal fluid, and plasma levels appear to reflect those in the brain. In this study, we aim to evaluate serum BACE1 activity in FTD, since, to date, there is no evidence about its role. The serum of 30 FTD patients and 30 controls was analyzed to evaluate (i) BACE1 activity, using a fluorescent assay, and (ii) Glial Fibrillary Acid Protein (GFAP) and Neurofilament Light chain (NfL) levels, using a Simoa kit. As expected, a significant increase in GFAP and NfL levels was observed in FTD patients compared to controls. Serum BACE1 activity was not altered in FTD patients. A significant increase in serum BACE1 activity was shown in AD vs. FTD and controls. Our results support the hypothesis that serum BACE1 activity is a potential biomarker for the differential diagnosis between AD and FTD.

Recent advances in N-glycan biomarker discovery among human diseases

N-glycans play important roles in a variety of biological processes. In recent years, analytical technologies with high resolution and sensitivity have advanced exponentially, enabling analysts to investigate N-glycomic changes in different states. Specific glycan and glycosylation signatures have been identified in multiple diseases, including cancer, autoimmune diseases, nervous system disorders, and metabolic and cardiovascular diseases. These glycans demonstrate comparable or superior indicating capability in disease diagnosis and prognosis over routine biomarkers. Moreover, synchronous glycan alterations concurrent with disease initiation and progression provide novel insights into pathogenetic mechanisms and potential treatment targets. This review elucidates the biological significance of N-glycans, compares the existing glycomic technologies, and delineates the clinical performance of N-glycans across a range of diseases.

Lipid nanoparticle mediated small interfering RNA delivery as a potential therapy for Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative condition that exhibits a gradual decline in cognitive function and is prevalent among a significant number of individuals globally. The use of small interfering RNA (siRNA) molecules in RNA interference (RNAi) presents a promising therapeutic strategy for AD. Lipid nanoparticles (LNPs) have been developed as a delivery vehicle for siRNA, which can selectively suppress target genes, by enhancing cellular uptake and safeguarding siRNA from degradation. Numerous research studies have exhibited the effectiveness of LNP-mediated siRNA delivery in reducing amyloid beta (Aβ) levels and enhancing cognitive function in animal models of AD. The feasibility of employing LNP-mediated siRNA delivery as a therapeutic approach for AD is emphasized by the encouraging outcomes reported in clinical studies for other medical conditions. The use of LNP-mediated siRNA delivery has emerged as a promising strategy to slow down or even reverse the progression of AD by targeting the synthesis of tau phosphorylation and other genes linked to the condition. Improvement of the delivery mechanism and determination of the most suitable siRNA targets are crucial for the efficacious management of AD. This review focuses on the delivery of siRNA through LNPs as a promising therapeutic strategy for AD, based on the available literature.

Tau- and α-synuclein-targeted gold nanoparticles: applications, opportunities, and future outlooks in the diagnosis and therapy of neurodegenerative diseases

The use of nanomaterials in medicine offers multiple opportunities to address neurodegenerative disorders such as Alzheimer's and Parkinson's disease. These diseases are a significant burden for society and the health system, affecting millions of people worldwide without sensitive and selective diagnostic methodologies or effective treatments to stop their progression. In this sense, the use of gold nanoparticles is a promising tool due to their unique properties at the nanometric level. They can be functionalized with specific molecules to selectively target pathological proteins such as Tau and α-synuclein for Alzheimer's and Parkinson's disease, respectively. Additionally, these proteins are used as diagnostic biomarkers, wherein gold nanoparticles play a key role in enhancing their signal, even at the low concentrations present in biological samples such as blood or cerebrospinal fluid, thus enabling an early and accurate diagnosis. On the other hand, gold nanoparticles act as drug delivery platforms, bringing therapeutic agents directly into the brain, improving treatment efficiency and precision, and reducing side effects in healthy tissues. However, despite the exciting potential of gold nanoparticles, it is crucial to address the challenges and issues associated with their use in the medical field before they can be widely applied in clinical settings. It is critical to ensure the safety and biocompatibility of these nanomaterials in the context of the central nervous system. Therefore, rigorous preclinical and clinical studies are needed to assess the efficacy and feasibility of these strategies in patients. Since there is scarce and sometimes contradictory literature about their use in this context, the main aim of this review is to discuss and analyze the current state-of-the-art of gold nanoparticles in relation to delivery, diagnosis, and therapy for Alzheimer's and Parkinson's disease, as well as recent research about their use in preclinical, clinical, and emerging research areas.

Present and Future of Blood-Based Biomarkers of Alzheimer's Disease: Beyond the Classics

The field of blood-based biomarkers for Alzheimer's disease (AD) has advanced at an incredible pace, especially after the development of sensitive analytic platforms that can facilitate large-scale screening. Such screening will be important when more sophisticated diagnostic methods are scarce and expensive. Thus, blood-based biomarkers can potentially reduce diagnosis inequities among populations from different socioeconomic contexts. This large-scale screening can be performed so that older adults at risk of cognitive decline assessed using these methods can then undergo more complete assessments with classic biomarkers, increasing diagnosis efficiency and reducing costs to the health systems. Blood-based biomarkers can also aid in assessing the effect of new disease-modifying treatments. This paper reviews recent advances in the area, focusing on the following leading candidates for blood-based biomarkers: amyloid-beta (Aβ), phosphorylated tau isoforms (p-tau), neurofilament light (NfL), and glial fibrillary acidic (GFAP) proteins, as well as on new candidates, Neuron-Derived Exosomes contents (NDEs) and Transactive response DNA-binding protein-43 (TDP-43), based on data from longitudinal observational cohort studies. The underlying challenges of validating and incorporating these biomarkers into routine clinical practice and primary care settings are also discussed. Importantly, challenges related to the underrepresentation of ethnic minorities and socioeconomically disadvantaged persons must be considered. If these challenges are overcome, a new time of cost-effective blood-based biomarkers for AD could represent the future of clinical procedures in the field and, together with continued prevention strategies, the beginning of an era with a lower incidence of dementia worldwide.

Serum NFL and tau, but not serum UCHL-1 and GFAP or CSF SNAP-25, NPTX2, or sTREM2, correlate with delirium in a 3-year retrospective analysis

Delirium represents a common terminal pathway of heterogeneous neurological conditions characterized by disturbances in consciousness and attention. Contemporary theories highlight the acute impairment of synaptic function and network connectivity, driven by neuroinflammation, oxidative stress, and neurotransmitter imbalances. However, established biomarkers are still missing. Innovative diagnostic techniques, such as single-molecule array analysis, enable the detection of biomarkers in blood at picomolar concentrations. This approach paves the way for deeper insights into delirium and potentially therapeutic targets for tailored medical treatments. In a retrospective 3-year study, we investigated seven biomarkers indicative of neuroaxonal damage [neurofilament light chain (NFL), ubiquitin carboxyl-terminal hydrolase (UCHL-1), and tau protein], microglial activation [glial fibrillary acidic protein (GFAP) and soluble triggering receptor expressed on myeloid cells 2 (sTREM2)], and synaptic dysfunction [synaptosomal-associated protein 25 (SNAP-25) and neuronal pentraxin 2 (NPTX2)]. The analysis of 71 patients with delirium, Alzheimer's disease (AD), and non-AD controls revealed that serum NFL levels are higher in delirium cases compared to both AD and non-AD. This suggests that elevated NFL levels in delirium are not exclusively the result of dementia-related damage. Serum tau levels were also elevated in delirium cases compared to controls. Conversely, cerebrospinal fluid (CSF) SNAP-25 showed higher levels in AD patients compared to controls only. These findings add to the increasing body of evidence suggesting that serum NFL could be a valuable biomarker of neuroaxonal damage in delirium research. Although SNAP-25 and NPTX2 did not exhibit significant differences in delirium, the exploration of synaptic biomarkers remains promising for enhancing our understanding of this condition.

Predicting mild cognitive impairment in older adults: A machine learning analysis of the Alzheimer's Disease Neuroimaging Initiative

AIM

Mild cognitive impairment (MCI) in older adults is potentially devastating, but an accurate prediction model is still lacking. We hypothesized that neuropsychological tests and MRI-related markers could predict the onset of MCI early.

METHODS

We analyzed data from 306 older adults who were cognitive normal (CN) attending the Alzheimer's Disease Neuroimaging Initiative sequentially (474 pairs of visits) within 3 years. There were 231 pairs of MCI conversion (CN to MCI), and 242 pairs of CN maintenance (CN to CN). Variables on demographic, neuropsychological tests, genetic, and MRI-related markers were collected. Machine learning was used to construct MCI prediction models, comparing the area under the receiver operating characteristic curve (AUC) as the primary metric of performance. Important predictors were ranked for the optimal model.

RESULTS

The baseline age of the study sample was 74.8 years old. The best-performing model (gradient boosting decision tree) with 13 variables predicted MCI with an AUC of 0.819, and the rank of variable importance showed that intracranial volume, hippocampal volume, and score from task 4 (word recognition) of the Alzheimer's Disease Assessment Scale were important predictors of MCI.

CONCLUSIONS

With the help of machine learning, fewer neuropsychological tests and MRI-related markers are required to accurately predict MCI within 3 years, thereby facilitating targeted intervention. Geriatr Gerontol Int 2024; 24: 96-101.

Biomarker Changes during 20 Years Preceding Alzheimer's Disease

BACKGROUND

Biomarker changes that occur in the period between normal cognition and the diagnosis of sporadic Alzheimer's disease have not been extensively investigated in longitudinal studies.

METHODS

We conducted a multicenter, nested case-control study of Alzheimer's disease biomarkers in cognitively normal participants who were enrolled in the China Cognition and Aging Study from January 2000 through December 2020. A subgroup of these participants underwent testing of cerebrospinal fluid (CSF), cognitive assessments, and brain imaging at 2-year-to-3-year intervals. A total of 648 participants in whom Alzheimer's disease developed were matched with 648 participants who had normal cognition, and the temporal trajectories of CSF biochemical marker concentrations, cognitive testing, and imaging were analyzed in the two groups.

RESULTS

The median follow-up was 19.9 years (interquartile range, 19.5 to 20.2). CSF and imaging biomarkers in the Alzheimer's disease group diverged from those in the cognitively normal group at the following estimated number of years before diagnosis: amyloid-beta (Aβ)42, 18 years; the ratio of Aβ42 to Aβ40, 14 years; phosphorylated tau 181, 11 years; total tau, 10 years; neurofilament light chain, 9 years; hippocampal volume, 8 years; and cognitive decline, 6 years. As cognitive impairment progressed, the changes in CSF biomarker levels in the Alzheimer's disease group initially accelerated and then slowed.

CONCLUSIONS

In this study involving Chinese participants during the 20 years preceding clinical diagnosis of sporadic Alzheimer's disease, we observed the time courses of CSF biomarkers, the times before diagnosis at which they diverged from the biomarkers from a matched group of participants who remained cognitively normal, and the temporal order in which the biomarkers became abnormal. (Funded by the Key Project of the National Natural Science Foundation of China and others; ClinicalTrials.gov number, NCT03653156.).

Salivary Biomarkers for Parkinson's Disease: A Systematic Review with Meta-Analysis

Parkinson's Disease (PD) is a common neurodegenerative disease which manifests with motor features, such as bradykinesia, resting tremor, rigidity, and postural instability. Using the non-invasive technique of saliva collection, we designed a systematic review to answer the question "Are salivary biomarkers reliable for the diagnosis of Parkinson's Disease?". Following inclusion and exclusion criteria, 30 studies were included in this systematic review (according to the PRISMA statement guidelines). Mostly proteins were reported as potential biomarkers in saliva. Based on meta-analysis, in PD patients, salivary levels of total alpha-synuclein were significantly decreased, and those of oligomeric alpha-synuclein were significantly increased. Also, according to pooled AUC, heme oxygenase-1 demonstrated significant predictive value for saliva-based PD diagnosis. In conclusion, some potential biomarkers, especially alpha-synuclein, can be altered in the saliva of PD patients, which could be reliably useful for early diagnosis of this neurodegenerative disease differentiating other synucleopathies.

Alzheimer's Disease Biomarker Analysis Using Targeted Mass Spectrometry

Alzheimer's disease (AD) is characterized by several neuropathological changes, mainly extracellular amyloid aggregates (plaques), intraneuronal inclusions of phosphorylated tau (tangles), as well as neuronal and synaptic degeneration, accompanied by tissue reactions to these processes (astrocytosis and microglial activation) that precede neuronal network disturbances in the symptomatic phase of the disease. A number of biomarkers for these brain tissue changes have been developed, mainly using immunoassays. In this review, we discuss how targeted mass spectrometry (TMS) can be used to validate and further characterize classes of biomarkers reflecting different AD pathologies, such as tau- and amyloid-beta pathologies, synaptic dysfunction, lysosomal dysregulation, and axonal damage, and the prospect of using TMS to measure these proteins in clinical research and diagnosis. TMS advantages and disadvantages in relation to immunoassays are discussed, and complementary aspects of the technologies are discussed.

Small RNA Changes in Plasma Have Potential for Early Diagnosis of Alzheimer's Disease before Symptom Onset

Alzheimer's disease (AD), due to its multifactorial nature and complex etiology, poses challenges for research, diagnosis, and treatment, and impacts millions worldwide. To address the need for minimally invasive, repeatable measures that aid in AD diagnosis and progression monitoring, studies leveraging RNAs associated with extracellular vesicles (EVs) in human biofluids have revealed AD-associated changes. However, the validation of AD biomarkers has suffered from the collection of samples from differing points in the disease time course or a lack of confirmed AD diagnoses. Here, we integrate clinical diagnosis and postmortem pathology data to form more accurate experimental groups and use small RNA sequencing to show that EVs from plasma can serve as a potential source of RNAs that reflect disease-related changes. Importantly, we demonstrated that these changes are identifiable in the EVs of preclinical patients, years before symptom manifestation, and that machine learning models based on differentially expressed RNAs can help predict disease conversion or progression. This research offers critical insight into early disease biomarkers and underscores the significance of accounting for disease progression and pathology in human AD studies.

Improving Regression Analysis with Imputation in a Longitudinal Study of Alzheimer's Disease

Background

Missing data is prevalent in the Alzheimer's Disease Neuroimaging Initiative (ADNI). It is common to deal with missingness by removing subjects with missing entries prior to statistical analysis; however, this can lead to significant efficiency loss and sometimes bias. It has yet to be demonstrated that the imputation approach to handling this issue can be valuable in some longitudinal regression settings.

Objective

The purpose of this study is to demonstrate the importance of imputation and how imputation is correctly done in ADNI by analyzing longitudinal Alzheimer's Disease Assessment Scale -Cognitive Subscale 13 (ADAS-Cog 13) scores and their association with baseline patient characteristics.

Methods

We studied 1,063 subjects in ADNI with mild cognitive impairment. Longitudinal ADAS-Cog 13 scores were modeled with a linear mixed-effects model with baseline clinical and demographic characteristics as predictors. The model estimates obtained without imputation were compared with those obtained after imputation with Multiple Imputation by Chained Equations (MICE). We justify application of MICE by investigating the missing data mechanism and model assumptions. We also assess robustness of the results to the choice of imputation method.

Results

The fixed-effects estimates of the linear mixed-effects model after imputation with MICE yield valid, tighter confidence intervals, thus improving the efficiency of the analysis when compared to the analysis done without imputation.

Conclusions

Our study demonstrates the importance of accounting for missing data in ADNI. When deciding to perform imputation, care should be taken in choosing the approach, as an invalid one can compromise the statistical analyses.

An activatable small-molecule fluorogenic probe for detection and quantification of beta-amyloid aggregates

Extracellular accumulation of β amyloid (Aβ) peptides in the brain is thought to be a pathological hallmark and initial event before the symptom starts of Alzheimer's patients. Herein, we developed two series of benzo[d]thiazole-based small-molecule compounds (BM1-BM4, BPM1-BPM4) with a donor-acceptor (D-A) or donor-π-acceptor (D-π-A) architecture, respectively, based on structure-activity relationship. Among them, the optimized BPM1 not only displayed the highest binding affinity to Aβ aggregates over other proteins or Aβ monomers, but was readily activated its fluorescence with 10-fold fluorescence enhancement, allowing for specifically and sensitively detecting Aβ aggregates. BPM1 also exhibits several other advantages including low molecular weight, low cytotoxicity and excellent biological stability. Besides, cell staining results confirmed that SK-N-BE(2) cells can be fluorescently lighted up as well as cell permeability and damage when treated with BPM1-bound Aβ1-42 aggregates.

Cerebrospinal and Blood Biomarkers in Alzheimer's Disease: Did Mild Cognitive Impairment Definition Affect Their Clinical Usefulness?

Despite Alzheimer's Disease (AD) being known from the times of Alois Alzheimer, who lived more than one century ago, many aspects of the disease are still obscure, including the pathogenesis, the clinical spectrum definition, and the therapeutic approach. Well-established biomarkers for AD come from the histopathological hallmarks of the disease, which are Aβ and phosphorylated Tau protein aggregates. Consistently, cerebrospinal fluid (CSF) Amyloid β (Aβ) and phosphorylated Tau level measurements are currently used to detect AD presence. However, two central biases affect these biomarkers. Firstly, incomplete knowledge of the pathogenesis of diseases legitimates the search for novel molecules that, reasonably, could be expressed by neurons and microglia and could be detected in blood simpler and earlier than the classical markers and in a higher amount. Further, studies have been performed to evaluate whether CSF biomarkers can predict AD onset in Mild Cognitive Impairment (MCI) patients. However, the MCI definition has changed over time. Hence, the studies on MCI patients seem to be biased at the beginning due to the imprecise enrollment and heterogeneous composition of the miscellaneous MCI subgroup. Plasma biomarkers and novel candidate molecules, such as microglia biomarkers, have been tentatively investigated and could represent valuable targets for diagnosing and monitoring AD. Also, novel AD markers are urgently needed to identify molecular targets for treatment strategies. This review article summarizes the main CSF and blood AD biomarkers, underpins their advantages and flaws, and mentions novel molecules that can be used as potential biomarkers for AD.

Understanding the Episodic Memory and Executive Functioning Axis Impairment in MCI Patients: A Multicenter Study in Comparison with CSF Biomarkers

BACKGROUND

This study aimed to explore the association between a verbal learning task that evaluates the potential mutual dependency between memory and executive functions (i.e., the Test of Memory Strategies, TMS) and cerebrospinal fluid (CSF) Alzheimer's Disease (AD) biomarkers.

METHODS

A sample of 47 mild cognitive impairment (MCI) participants from Poland and Spain were classified according to the Erlangen Score Diagnostic Algorithm (ESA) into CSF- (n = 16) and CSF+ (n = 31) groups. Correlation analyses between TMS word-list conditions and CSF biomarkers were conducted. Additionally, an analysis of covariance was performed to define the effect on ESA classification in the sample, using as a covariable the country of origin of the participants.

RESULTS

Significant associations between the TMS-3 condition and Aβ42, t-tau, and p-tau were observed for the whole sample. In addition, the CSF- participants obtained higher cognitive performance in TMS-3 compared to the CSF+ group. This outcome persisted if the groups were based on Aβ42 scores, but not t-tau or p-tau values.

CONCLUSIONS

These findings could indicate that poor performance on verbal learning tests may be affected by executive dysfunctions. Therefore, future intervention plans focused on training executive functions would be of interest to improve the ability of MCI patients to encode and organize information.

CSF 14-3-3β is associated with progressive cognitive decline in Alzheimer's disease

Alzheimer's disease is a neurodegenerative disorder characterized pathologically by amyloid-beta plaques, tau tangles and neuronal loss. In clinical practice, the 14-3-3 isoform beta (β) is a biomarker that aids in the diagnosis of sporadic Creutzfeldt-Jakob disease. Recently, a proteomics study found increased CSF 14-3-3β levels in Alzheimer's disease patients, suggesting a potential link between CSF 14-3-3β and Alzheimer's disease. Our present study aimed to further investigate the role of CSF 14-3-3β in Alzheimer's disease by analysing the data of 719 participants with available CSF 14-3-3β measurements from the Alzheimer's Disease Neuroimaging Initiative. Higher CSF 14-3-3β levels were observed in the mild cognitive impairment group compared to the cognitively normal group, with the highest CSF 14-3-3β levels in the Alzheimer's disease dementia group. This study also found significant associations between CSF 14-3-3β levels and CSF biomarkers of p-tau, t-tau, pTau/Aβ42 ratios and GAP-43, as well as other Alzheimer's disease biomarkers such as Aβ-PET. An early increase in CSF 14-3-3β levels was observed prior to Aβ-PET-positive status, and CSF 14-3-3β levels continued to rise after crossing the Aβ-PET positivity threshold before reaching a plateau. The diagnostic accuracy of CSF 14-3-3β (area under the receiver operating characteristic curve = 0.819) was moderate compared to other established Alzheimer's disease biomarkers in distinguishing cognitively normal Aβ pathology-negative individuals from Alzheimer's disease Aβ pathology-positive individuals. Higher baseline CSF 14-3-3β levels were associated with accelerated cognitive decline, reduced hippocampus volumes and declining fluorodeoxyglucose-PET values over a 4-year follow-up period. Patients with mild cognitive impairment and high CSF 14-3-3β levels at baseline had a significantly increased risk [hazard ratio = 2.894 (1.599-5.238), P < 0.001] of progression to Alzheimer's disease dementia during follow-up. These findings indicate that CSF 14-3-3β may be a potential biomarker for Alzheimer's disease and could provide a more comprehensive understanding of the underlying pathological changes of Alzheimer's disease, as well as aid in the diagnosis and monitoring of disease progression.

CSF biomarker analysis of ABCA7 mutation carriers suggests altered APP processing and reduced inflammatory response

BACKGROUND

The Alzheimer's disease (AD) risk gene ABCA7 has suggested functions in lipid metabolism and the immune system. Rare premature termination codon (PTC) mutations and an expansion of a variable number of tandem repeats (VNTR) polymorphism in the gene, both likely cause a lower ABCA7 expression and hereby increased risk for AD. However, the exact mechanism of action remains unclear. By studying CSF biomarkers reflecting different types of AD-related pathological processes, we aim to get a better insight in those processes and establish a biomarker profile of mutation carriers.

METHODS

The study population consisted of 229 AD patients for whom CSF was available and ABCA7 sequencing and VNTR genotyping had been performed. This included 28 PTC mutation and 16 pathogenic expansion carriers. CSF levels of Aβ1-42, Aβ1-40, P-tau181, T-tau, sAPPα, sAPPβ, YKL-40, and hFABP were determined using ELISA and Meso Scale Discovery assays. We compared differences in levels of these biomarkers and the Aβ ratio between AD patients with or without an ABCA7 PTC mutation or expansion using linear regression on INT-transformed data with APOE-status, age and sex as covariates.

RESULTS

Carriers of ABCA7 expansion mutations had significantly lower Aβ1-42 levels (P = 0.022) compared with non-carrier patients. The effect of the presence of ABCA7 mutations on CSF levels was especially pronounced in APOE ε4-negative carriers. In addition, VNTR expansion carriers had reduced Aβ1-40 (P = 0.023), sAPPα (P = 0.047), sAPPβ (P = 0.016), and YKL-40 (P = 0.0036) levels.

CONCLUSIONS

Our results are suggestive for an effect on APP processing by repeat expansions given the changes in the amyloid-related CSF biomarkers that were found in carriers. The decrease in YKL-40 levels in expansion carriers moreover suggests that these patients potentially have a reduced inflammatory response to AD damage. Moreover, our findings suggest the existence of a mechanism, independent of lowered expression, affecting neuropathology in expansion carriers.

Computational saturation mutagenesis to explore the effect of pathogenic mutations on extra-cellular domains of TREM2 associated with Alzheimer's and Nasu-Hakola disease

CONTEXT

The specialised family of triggering receptors expressed on myeloid cells (TREMs) plays a pivotal role in causing neurodegenerative disorders and activating microglial anti-inflammatory responses. Nasu-Hakola disease (NHD), a rare autosomal recessive disorder, has been associated with mutations in TREM2, which is also responsible for raising the risk of Alzheimer's disease (AD). Herein, we have made an endeavour to differentiate the confirmed pathogenic variants in TREM2 extra-cellular domain (ECD) linked with NHD and AD using mutation-induced fold stability change (∆∆G), with the computation of 12distinct structure-based methods through saturation mutagenesis. Correlation analysis between relative solvent accessibility (RSA) and ∆∆G expresses the discrete distributive behaviour of mutants associated with TREM2 in AD (R2 = 0.061) and NHD (R2 = 0.601). Our findings put an emphasis on W50 and V126 as major players in maintaining V-like domain in TREM2. Interestingly, we discern that both of them interact with a common residue Y108, which is dissolved upon mutation. This Y108 could have structural or functional role for TREM2 which can be an ideal candidate for further study. Furthermore, the residual interaction network highlights the importance of R47 and R62 in maintaining the CDR loops that are crucial for ligand binding. Future studies using biophysical characterisation of ligand interactions in TREM2-ECD would be helpful for the development of novel therapeutics for AD and NHD.

METHODS

ConSurf algorithm and ENDscript were used to determine the position and conservation of each residue in the wild-type ECD of TREM2. The mutation-induced fold stability change (∆∆G) of confirmed pathogenic mutants associated with NHD and AD was estimated using 12 state-of-the-art structure-based protein stability tools. Furthermore, we also computed the effect of random mutation on these sites using computational saturation mutagenesis. Linear regression analysis was performed using mutants ∆∆G and RSA through GraphPad software. In addition, a comprehensive non-bonded residual interaction network (RIN) of wild type and its mutants of TREM2-ECD was enumerated using RING3.0.