Blood neuro-exosomal synaptic proteins predict Alzheimer's disease at the asymptomatic stage

Evolution of Detecting Early Onset of Alzheimer's Disease: From Neuroimaging to Optical Immunoassays

Alzheimer's disease (AD) is a pathological disorder defined by the symptoms of memory loss and deterioration of cognitive abilities over time. Although the etiology is complex, it is mainly associated with the accumulation of toxic amyloid-β peptide (Aβ) aggregates and tau protein-induced neurofibrillary tangles (NFTs). Even now, creating non-invasive, sensitive, specific, and cost-effective diagnostic methods for AD remains challenging. Over the past few decades, polymers, and nanomaterials (e.g., nanodiamonds, nanogold, quantum dots) have become attractive and practical tools in nanomedicine for diagnosis and treatment. This review focuses on current developments in sensing methods such as enzyme-linked immunosorbent assay (ELISA) and surface-enhanced Raman scattering (SERS) to boost the sensitivity in detecting related biomarkers for AD. In addition, optical analysis platforms such as ELISA and SERS have found increasing popularity among researchers due to their excellent sensitivity and specificity, which may go as low as the femtomolar range. While ELISA offers easy technological usage and high throughput, SERS has the advantages of improved mobility, simple electrical equipment integration, and lower cost. Both portable optical sensing techniques are highly superior in terms of sensitivity, specificity, human application, and practicality, enabling the early identification of AD biomarkers.

Bioengineered exosomal-membrane-camouflaged abiotic nanocarriers: neurodegenerative diseases, tissue engineering and regenerative medicine

A bio-inspired strategy has recently been developed for camouflaging nanocarriers with biomembranes, such as natural cell membranes or subcellular structure-derived membranes. This strategy endows cloaked nanomaterials with improved interfacial properties, superior cell targeting, immune evasion potential, and prolonged duration of systemic circulation. Here, we summarize recent advances in the production and application of exosomal membrane-coated nanomaterials. The structure, properties, and manner in which exosomes communicate with cells are first reviewed. This is followed by a discussion of the types of exosomes and their fabrication methods. We then discuss the applications of biomimetic exosomes and membrane-cloaked nanocarriers in tissue engineering, regenerative medicine, imaging, and the treatment of neurodegenerative diseases. Finally, we appraise the current challenges associated with the clinical translation of biomimetic exosomal membrane-surface-engineered nanovehicles and evaluate the future of this technology.

Plasma Extracellular Vesicle MicroRNA Analysis of Alzheimer's Disease Reveals Dysfunction of a Neural Correlation Network

Small extracellular vesicle (sEV) is an emerging source of potential biomarkers of Alzheimer's disease (AD), but the role of microRNAs (miRNAs) in sEV is not well understood. In this study, we conducted a comprehensive analysis of sEV-derived miRNAs in AD using small RNA sequencing and coexpression network analysis. We examined a total of 158 samples, including 48 from AD patients, 48 from patients with mild cognitive impairment (MCI), and 62 from healthy controls. We identified an miRNA network module (M1) that was strongly linked to neural function and showed the strongest association with AD diagnosis and cognitive impairment. The expression of miRNAs in the module was decreased in both AD and MCI patients compared to controls. Conservation analysis revealed that M1 was highly preserved in the healthy control group but dysfunctional in the AD and MCI groups, suggesting that changes in the expression of miRNAs in this module may be an early response to cognitive decline prior to the appearance of AD pathology. We further validated the expression levels of the hub miRNAs in M1 in an independent population. The functional enrichment analysis showed that 4 hub miRNAs might interact with a GDF11-centered network and play a critical role in the neuropathology of AD. In summary, our study provides new insights into the role of sEV-derived miRNAs in AD and suggests that M1 miRNAs may serve as potential biomarkers for the early diagnosis and monitoring of AD.

A blood mRNA panel that differentiates Alzheimer's disease from other dementia types

BACKGROUND

Messenger RNAs (mRNAs) have been reported to be associated with Alzheimer's disease (AD). In this study, we investigated whether plasma-based mRNAs could distinguish AD from cognitively normal controls and other types of dementia, including vascular dementia (VaD), Parkinson's disease dementia (PDD), behavioral variant frontotemporal dementia (bvFTD), and dementia with Lewy body (DLB).

METHODS

Plasma mRNA expression was measured in three independent datasets. Dataset 1 (n = 40; controls, 20; AD, 20) was used to identify the differentially expressed mRNAs. Dataset 2 (n = 122; controls: 60; AD: 62) was used to develop a diagnostic AD model using an mRNA panel. Furthermore, we applied the model to Dataset 3 (n = 334; control, 57; AD, 58; VaD, 55; PDD, 54; bvFTD, 55; DLB, 55) to verify its ability to identify AD and other types of dementia.

RESULTS

Dataset 1 showed 22 upregulated and 21 downregulated mRNAs. A panel of six mRNAs distinguished AD from the control group in Dataset 2. The panel was used to successfully differentiate AD from other types of dementia in Dataset 3.

CONCLUSIONS

An AD-specific panel of six mRNAs was created that can be used for AD diagnosis.

Neuronal Exosomes as a New Signaling System

Number of studies devoted to investigation of neuronal exosomes increases significantly each year. Potential of exosomes as diagnostic markers of neurodegenerative diseases has been examined thoroughly and similar protocols were used to search for the markers of other psychiatric disorders. Biogenesis of exosomes in various types of cells has been studied, physiological role of exosomes has been actively investigated, and many features of their signaling cascades have been clarified. The accumulated data indicate important role of the exosome signaling in interneuronal communication. Do we have enough grounds to recognize exosomes as new non-canonical neurotransmitters in the brain? In this review we discuss this issue and present a concept on the possible role of brain exosomes as a new signaling system to the scientific community.

Modern Approaches to the Diagnosis of Cognitive Impairment and Alzheimer's Disease: A Narrative Literature Review

BACKGROUND

The aging of the worlds population leads to an increase in the prevalence of age-related diseases, including cognitive impairment. At the stage of dementia, therapeutic interventions become usually ineffective. Therefore, researchers and clinical practitioners today are looking for methods that allow for early diagnosis of cognitive impairment, including techniques that are based on the use of biological markers.

AIM

The aim of this literature review is to delve into scientific papers that are centered on modern laboratory tests for Alzheimers disease, including tests for biological markers at the early stages of cognitive impairment.

METHODS

The authors have carried out a descriptive review of scientific papers published from 2015 to 2023. Studies that are included in the PubMed and Web of Science electronic databases were analyzed. A descriptive analysis was used to summarized the gleaned information.

RESULTS

Blood and cerebrospinal fluid (CSF) biomarkers, as well as the advantages and disadvantages of their use, are reviewed. The most promising neurotrophic, neuroinflammatory, and genetic markers, including polygenic risk models, are also discussed.

CONCLUSION

The use of biomarkers in clinical practice will contribute to the early diagnosis of cognitive impairment associated with Alzheimers disease. Genetic screening tests can improve the detection threshold of preclinical abnormalities in the absence of obvious symptoms of cognitive decline. The active use of biomarkers in clinical practice, in combination with genetic screening for the early diagnosis of cognitive impairment in Alzheimers disease, can improve the timeliness and effectiveness of medical interventions.

A combination model of AD biomarkers revealed by machine learning precisely predicts Alzheimer's dementia: China Aging and Neurodegenerative Initiative (CANDI) study

INTRODUCTION

To test the utility of the "A/T/N" system in the Chinese population, we study core Alzheimer's disease (AD) biomarkers in a newly established Chinese cohort.

METHODS

A total of 411 participants were selected, including 96 cognitively normal individuals, 94 patients with mild cognitive impairment (MCI) patients, 173 patients with AD, and 48 patients with non-AD dementia. Fluid biomarkers were measured with single molecule array. Amyloid beta (Aβ) deposition was determined by 18F-Flobetapir positron emission tomography (PET), and brain atrophy was quantified using magnetic resonance imaging (MRI).

RESULTS

Aβ42/Aβ40 was decreased, whereas levels of phosphorylated tau (p-tau) were increased in cerebrospinal fluid (CSF) and plasma from patients with AD. CSF Aβ42/Aβ40, CSF p-tau, and plasma p-tau showed a high concordance in discriminating between AD and non-AD dementia or elderly controls. A combination of plasma p-tau, apolipoprotein E (APOE) genotype, and MRI measures accurately predicted amyloid PET status.

DISCUSSION

These results revealed a universal applicability of the "A/T/N" framework in a Chinese population and established an optimal diagnostic model consisting of cost-effective and non-invasive approaches for diagnosing AD.

Exosomes for the diagnosis and treatment of dementia

PURPOSE OF REVIEW

Dementia is a syndrome with several possible pathologies. To date, definitive methods for diagnosis and treatment of sub-types of dementia have not been established. Emerging evidence suggests that exosomes can provide important information for the diagnosis and treatment of several subtypes of dementia. This article reviews recent studies on the application of exosomes in dementia.

RECENT FINDINGS

Exosomes are involved in the pathogenesis of Alzheimer's disease (AD) and Parkinson's disease (PD) through transporting toxic proteins such as amyloid beta (Aβ), tau, and α-synuclein. Exosomal microRNAs (miR) and proteins reflect the disease state, and therefore, exosomes can be used as diagnostic markers for diseases such as AD, PD, Huntington's disease (HD), vascular dementia (VaD), dementia with Lewy bodies (DLB), and frontotemporal dementia (FTD). Mesenchymal stem cell (MSC)-derived exosomes have been shown to ameliorate disease pathology, and improve cognitive function in AD, PD, and VAD.

SUMMARY

Recent studies have shown that exosomes could be novel diagnostic agents for dementia because they contain molecules that could be potential biomarker candidates indicative of the type and stage of dementia. Therapeutic application of exosomes in dementia has revealed that exosomes only, or exosomes loaded with an active pharmaceutical ingredient (API), ameliorate disease phenotype of dementia. Further work is needed to exploit this potential.

Advanced Overview of Biomarkers and Techniques for Early Diagnosis of Alzheimer's Disease

The development of early non-invasive diagnosis methods and identification of novel biomarkers are necessary for managing Alzheimer's disease (AD) and facilitating effective prognosis and treatment. AD has multi-factorial nature and involves complex molecular mechanism, which causes neuronal degeneration. The primary challenges in early AD detection include patient heterogeneity and lack of precise diagnosis at the preclinical stage. Several cerebrospinal fluid (CSF) and blood biomarkers have been proposed to show excellent diagnosis ability by identifying tau pathology and cerebral amyloid beta (Aβ) for AD. Intense research endeavors are being made to develop ultrasensitive detection techniques and find potent biomarkers for early AD diagnosis. To mitigate AD worldwide, understanding various CSF biomarkers, blood biomarkers, and techniques that can be used for early diagnosis is imperative. This review attempts to provide information regarding AD pathophysiology, genetic and non-genetic factors associated with AD, several potential blood and CSF biomarkers, like neurofilament light, neurogranin, Aβ, and tau, along with biomarkers under development for AD detection. Besides, numerous techniques, such as neuroimaging, spectroscopic techniques, biosensors, and neuroproteomics, which are being explored to aid early AD detection, have been discussed. The insights thus gained would help in finding potential biomarkers and suitable techniques for the accurate diagnosis of early AD before cognitive dysfunction.

Assembled Photonic Crystal/Gold Nanoparticle Interface: A Dual Amplifying Electrochemiluminescent Aptasensor for the Ultrasensitive Detection of an Amyloid-β Monomer

Amyloid-β (Aβ) protein is considered to be a key biomarker that is closely associated with Alzheimer's disease (AD). The level of Aβ, particularly its subtle fluctuation, indicates early neuropathological changes, which poses a considerable challenge in predicting AD, considering the detection limit of sensing technologies. Herein, a new label-free sensor based on luminol electrochemiluminescence (ECL) was proposed by developing a close-packed monolayered-SiO2 array with gold (Au) nanoparticles (NPs) entrapped in their gaps as the basal electrode. The well-organized SiO2 NPs with a quasiphotonic crystal structure amplified the ECL signal via light scattering, while Au NPs amplified the signal by directly catalyzing luminol oxidation. Owing to the dual signal amplification, the proposed electrode furnished an ∼64-fold-intensified ECL signal of luminol as the sensing background. Further, the as-prepared ECL electrode served as the substrate to develop an aptasensor for the sensitive detection of Aβ. The inhibition of the ECL signal due to the suppressed diffusion of luminol to the sensor surface acts as an indicator to quantify the amount of Aβ. The transfer dynamics mechanism provides a label-free sensing strategy and facilitates the high sensitivity of the aptasensor for Aβ detection. Under optimal conditions, the developed aptasensor exhibits an ultrasensitive performance for Aβ with a very low limit of detection of 5 fM, providing a new prospect for clinical research on Aβ and a promising approach in the field of ECL sensing.

The Roles of Exosomal Proteins: Classification, Function, and Applications

Exosome, a subpopulation of extracellular vesicles, plays diverse roles in various biological processes. As one of the most abundant components of exosomes, exosomal proteins have been revealed to participate in the development of many diseases, such as carcinoma, sarcoma, melanoma, neurological disorders, immune responses, cardiovascular diseases, and infection. Thus, understanding the functions and mechanisms of exosomal proteins potentially assists clinical diagnosis and targeted delivery of therapies. However, current knowledge about the function and application of exosomal proteins is still limited. In this review, we summarize the classification of exosomal proteins, and the roles of exosomal proteins in exosome biogenesis and disease development, as well as in the clinical applications.

A Group of Long Non-coding RNAs in Blood Acts as a Specific Biomarker of Alzheimer's Disease

Long non-coding RNAs (lncRNAs) have been identified to be involved in the pathogenesis of Alzheimer's disease (AD). In this study, we evaluated whether lncRNAs can be used to discriminate AD patients from controls and patients with other dementias, such as vascular, Parkinson's disease, behavioral variant frontotemporal, and dementia with Lewy body. In this study, we used three datasets to measure the blood lncRNA levels. A pilot study (dataset 1, n = 40; controls, 20; AD, 20) was used to screen for differentially expressed lncRNAs. Dataset 2 (n = 174; controls, 86; AD, 88) was used to identify a lncRNA panel for the diagnostic model. Dataset 3 (n = 333; control, 60; AD, 54; vascular dementia, 53; Parkinson's disease dementia, 55; behavioral variant frontotemporal dementia, 56; and dementia with Lewy body, 55) was used to validate the diagnostic model. In dataset 1, 12 upregulated and 15 downregulated lncRNAs were identified. In dataset 2, a panel of seven lncRNAs was found to have the ability to differentiate AD patients from controls. Finally, this panel was applied to dataset 3 to successfully distinguish AD from other dementias. This study proposes a panel of seven lncRNAs as specific and promising biomarker for AD diagnosis.

miRNAs and Alzheimer's Disease: Exploring the Role of Inflammation and Vitamin E in an Old-Age Population

Alzheimer's disease (AD) is the most frequent cause of dementia worldwide and represents one of the leading factors for severe disability in older persons. Although its etiology is not fully known yet, AD may develop due to multiple factors, including inflammation and oxidative stress, conditions where microRNAs (miRNAs) seem to play a pivotal role as a molecular switch. All these aspects may be modulated by nutritional factors. Among them, vitamin E has been widely studied in AD, given the plausibility of its various biological functions in influencing neurodegeneration. From a cohort of old-aged people, we measured eight vitamin E forms (tocopherols and tocotrienols), thirty cytokines/chemokines, and thirteen exosome-extracted miRNAs in plasma of subjects suffering from subjects affected by AD and age-matched healthy controls (HC). The sample population included 80 subjects (40 AD and 40 HC) with a mean age of 77.6 ± 3.8 years, mostly women (45; 56.2%). Of the vitamin E forms, only α-tocopherol differed between groups, with significantly lower levels in AD. Regarding the examined inflammatory molecules, G-CSF, GM-CSF, INF-α2, IL-3, and IL-8 were significantly higher and IL-17 lower in AD than HC. Among all miRNAs examined, AD showed downregulation of miR-9, miR-21, miR29-b, miR-122, and miR-132 compared to controls. MiR-122 positively and significantly correlated with some inflammatory molecules (GM-CSF, INF-α2, IL-1α, IL-8, and MIP-1β) as well as with α-tocopherol even after correction for age and gender. A final binary logistic regression analysis showed that α-tocopherol serum levels were associated with a higher AD probability and partially mediated by miR-122. Our results suggest an interplay between α-tocopherol, inflammatory molecules, and microRNAs in AD, where miR-122 may be a good candidate as modulating factor.

Detecting Early Cognitive Decline in Alzheimer's Disease with Brain Synaptic Structural and Functional Evaluation

Early cognitive decline in patients with Alzheimer's (AD) is associated with quantifiable structural and functional connectivity changes in the brain. AD dysregulation of Aβ and tau metabolism progressively disrupt normal synaptic function, leading to loss of synapses, decreased hippocampal synaptic density and early hippocampal atrophy. Advances in brain imaging techniques in living patients have enabled the transition from clinical signs and symptoms-based AD diagnosis to biomarkers-based diagnosis, with functional brain imaging techniques, quantitative EEG, and body fluids sampling. The hippocampus has a central role in semantic and episodic memory processing. This cognitive function is critically dependent on normal intrahippocampal connections and normal hippocampal functional connectivity with many cortical regions, including the perirhinal and the entorhinal cortex, parahippocampal cortex, association regions in the temporal and parietal lobes, and prefrontal cortex. Therefore, decreased hippocampal synaptic density is reflected in the altered functional connectivity of intrinsic brain networks (aka large-scale networks), including the parietal memory, default mode, and salience networks. This narrative review discusses recent critical issues related to detecting AD-associated early cognitive decline with brain synaptic structural and functional markers in high-risk or neuropsychologically diagnosed patients with subjective cognitive impairment or mild cognitive impairment.

Identification and validation of oxidative stress and immune-related hub genes in Alzheimer's disease through bioinformatics analysis

Alzheimer's disease (AD) is the leading cause of dementia in aged population. Oxidative stress and neuroinflammation play important roles in the pathogenesis of AD. Investigation of hub genes for the development of potential therapeutic targets and candidate biomarkers is warranted. The differentially expressed genes (DEGs) in AD were screened in GSE48350 dataset. The differentially expressed oxidative stress genes (DEOSGs) were analyzed by intersection of DEGs and oxidative stress-related genes. The immune-related DEOSGs and hub genes were identified by weighted gene co-expression network analysis (WGCNA) and protein-protein interaction (PPI) analysis, respectively. Enrichment analysis was performed by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes. The diagnostic value of hub genes was assessed by receiver operating characteristic analysis and validated in GSE1297. The mRNA expression of diagnostic genes was determined by qRT-PCR analysis. Finally, we constructed the drug, transcription factors (TFs), and microRNA network of the diagnostic genes. A total of 1160 DEGs (259 up-regulated and 901 down-regulated) were screened in GSE48350. Among them 111 DEOSGs were identified in AD. Thereafter, we identified significant difference of infiltrated immune cells (effector memory CD8 T cell, activated B cell, memory B cell, natural killer cell, CD56 bright natural killer cell, natural killer T cell, plasmacytoid dendritic cell, and neutrophil) between AD and control samples. 27 gene modules were obtained through WGCNA and turquoise module was the most relevant module. We obtained 66 immune-related DEOSGs by intersecting turquoise module with the DEOSGs and identified 15 hub genes through PPI analysis. Among them, 9 hub genes (CCK, CNR1, GAD1, GAP43, NEFL, NPY, PENK, SST, and TAC1) were identified with good diagnostic values and verified in GSE1297. qRT-PCR analysis revealed the downregulation of SST, NPY, GAP43, CCK, and PENK and upregulation of NEFL in AD. Finally, we identified 76 therapeutic agents, 152 miRNAs targets, and 91 TFs regulatory networks. Our study identified 9 key genes associated with oxidative stress and immune reaction in AD pathogenesis. The findings may help to provide promising candidate biomarkers and therapeutic targets for AD.

Biomarkers of Activity-Dependent Plasticity and Persistent Enhancement of Synaptic Transmission in Alzheimer Disease: A Review of the Current Status

Alzheimer disease (AD) is a chronic and heterogeneous neurodegenerative disorder characterized by complex pathological processes involving neuroinflammation, neurodegeneration, and synaptic dysfunction. Understanding the exact neurobiological mechanisms underlying AD pathology may help to provide a biomarker for early diagnosis or at least for assessment of vulnerability to dementia development. Neural plasticity is defined as a capability of the brain to respond to alterations including aging, injury, or learning, with a crucial role of synaptic elements. Long-term potentiation (LTP) and long-term depression (LTD) are important in regulating synaptic connections between neural cells in functional plasticity. Synaptic loss and impairment of the brain's plasticity in AD leads to cognitive impairment, and one of important roles of synaptic biomarkers is monitoring synaptic dysfunction, response to treatment, and predicting future development of AD. Synaptic biomarkers are undoubtedly very promising in developing novel approach to AD treatment and control, especially in the era of aging of societies, which is one of the most common risk factor of AD. Implementing a widespread measurement of synaptic biomarkers of AD will probably be crucial in early diagnosis of AD, early therapeutic intervention, monitoring progression of the disease, or response to treatment. One of the most important challenges is finding a biomarker whose blood concentration correlates with its level in the central nervous system (CNS). This review aims to present the current status of biomarkers of activity-dependent plasticity and persistent enhancement of synaptic transmission in Alzheimer disease.

Neurogranin as an important regulator in swimming training to improve the spatial memory dysfunction of mice with chronic cerebral hypoperfusion

BACKGROUND

Vascular cognitive impairment caused by chronic cerebral hypoperfusion (CCH) has become a hot issue worldwide. Aerobic exercise positively contributes to the preservation or restoration of cognitive abilities; however, the specific mechanism has remained inconclusive. And recent studies found that neurogranin (Ng) is a potential biomarker for cognitive impairment. This study aims to investigate the underlying role of Ng in swimming training to improve cognitive impairment.

METHODS

To test this hypothesis, the clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein 9 (Cas9) system was utilized to construct a strain of Ng conditional knockout (Ng cKO) mice, and bilateral common carotid artery stenosis (BCAS) surgery was performed to prepare the model. In Experiment 1, 2-month-old male and female transgenic mice were divided into a control group (wild-type littermate, n = 9) and a Ng cKO group (n = 9). Then, 2-month-old male and female C57BL/6 mice were divided into a sham group (C57BL/6, n = 12) and a BCAS group (n = 12). In Experiment 2, 2-month-old male and female mice were divided into a sham group (wild-type littermate, n = 12), BCAS group (n = 12), swim group (n = 12), BCAS + Ng cKO group (n = 12), and swim + Ng cKO group (n = 12). Then, 7 days after BCAS, mice were given swimming training for 5 weeks (1 week for adaptation and 4 weeks for training, 5 days a week, 60 min a day). After intervention, laser speckle was used to detect cerebral blood perfusion in the mice, and the T maze and Morris water maze were adopted to test their spatial memory. Furthermore, electrophysiology and Western blotting were conducted to record long-term potential and observe the expressions of Ca²⁺ pathway-related proteins, respectively. Immunohistochemistry was applied to analyze the expression of relevant markers in neuronal damage, inflammation, and white matter injury.

RESULTS

The figures showed that spatial memory impairment was detected in Ng cKO mice, and a sharp decline of cerebral blood flow and an impairment of progressive spatial memory were observed in BCAS mice. Regular swimming training improved the spatial memory impairment of BCAS mice. This was achieved by preventing long-term potential damage and reversing the decline of Ca²⁺ signal transduction pathway-related proteins. At the same time, the results suggested that swimming also led to improvements in neuronal death, inflammation, and white matter injury induced by CCH. Further study adopted the use of Ng cKO transgenic mice, and the results indicated that the positive effects of swimming training on cognitive impairments, synaptic plasticity, and related pathological changes caused by CCH could be abolished by the knockout of Ng.

CONCLUSION

Swimming training can mediate the expression of Ng to enhance hippocampal synaptic plasticity and improve related pathological changes induced by CCH, thereby ameliorating the spatial memory impairment of vascular cognitive impairment.

Applications of Extracellular Vesicles in Nervous System Disorders: An Overview of Recent Advances

Diseases affecting the brain and spinal cord fall under the umbrella term "central nervous system disease". Most medications used to treat or prevent chronic diseases of the central nervous system cannot cross the blood-brain barrier (BBB) and hence cannot reach their intended target. Exosomes facilitate cellular material movement and signal transmission. Exosomes can pass the blood-brain barrier because of their tiny size, high delivery efficiency, minimal immunogenicity, and good biocompatibility. They enter brain endothelial cells via normal endocytosis and reverse endocytosis. Exosome bioengineering may be a method to produce consistent and repeatable isolation for clinical usage. Because of their tiny size, stable composition, non-immunogenicity, non-toxicity, and capacity to carry a wide range of substances, exosomes are indispensable transporters for targeted drug administration. Bioengineering has the potential to improve these aspects of exosomes significantly. Future research into exosome vectors must focus on redesigning the membrane to produce vesicles with targeting abilities to increase exosome targeting. To better understand exosomes and their potential as therapeutic vectors for central nervous system diseases, this article explores their basic biological properties, engineering modifications, and promising applications.

Methylmalonic acid levels in serum, exosomes, and urine and its association with cblC type methylmalonic acidemia-induced cognitive impairment

Background

The cblC type methylmalonic acidemia is the most common methylmalonic acidemia (MMA) in China. The biochemical characteristics of this disease include elevated methylmalonic acid and homocysteine (HCY), increased propionylcarnitine (C3), decreased free carnitine (C0). In this study, we aimed to clarify the roles of these biomarkers in cblC-MMA induced cognitive impairment and evaluate the capacity of methylmalonic acid in different fluids or exosomes to distinguish cblC-MMA induced cognitive impairment.

Methods

15 non-inherited hyperhomocysteinemia (HHcy) patients, 42 cblC-MMA patients and 57 age- and sex-matched healthy children were recruited in this study. The levels of HCY were detected by an automatic immune analyzer. The levels of acylcarnitines and methylmalonic acid were detected by tandem mass spectrometer.

Results

The main findings were all biomarkers as HCY, acylcarnitines and methylmalonic acid had capacities for distinguishing patients with cblC-MMA induced cognitive impairment from healthy children. The methylmalonic acid in different fluids or exosomes had good performances for distinguishing patients with cblC-MMA induced cognitive impairment from HHcy patients. The methylmalonic acid in serum exosomes and neuronal-derived exosomes were able to distinguishing cblC-MMA patients with cognitive impairment from patients without cognitive impairment. The methylmalonic acid in neuronal-derived exosomes might be helpful to evaluate the severity of cblC-MMA induced cognitive impairment.

Discussion

Methylmalonic acid levels in serum exosomes, especially in serum neuronal-derived exosomes, serve as potential biomarkers for distinguishing cblC-MMA induced cognitive impairment.

Proteomic profiling of circulating plasma exosomes reveals novel biomarkers of Alzheimer's disease

BACKGROUND

Neuronal- and astrocyte-derived exosomes have been identified as an optimal source for screening biomarkers for Alzheimer's disease (AD). However, few studies focus on the bulk exosome population isolated from plasma of AD. This study investigated whether proteins in bulk exosomes can aid in the diagnosis of AD.

METHODS

The plasma exosomes were collected by ultracentrifuge. Protein samples were extracted from exosomes. Cerebrospinal fluid levels of amyloid β (Aβ)42 and phosphorylated tau (P-tau)181 were measured for diagnostic purposes. A pilot study (controls, 20; AD, 20) followed by a second dataset (controls, 56; AD, 58) was used to establish a diagnostic model of AD. Mass spectrometry-based proteomics was performed to profile the plasma exosomal proteome. Parallel reaction monitoring was used to further confirm the differentially expressed proteins.

RESULTS

In total, 328 proteins in plasma exosomes were quantified. Among them, 31 proteins were altered in AD patients, and 12 were validated. The receiver operating characteristic curve analysis revealed a combination of six proteins (upregulated: Ig-like domain-containing protein (A0A0G2JRQ6), complement C1q subcomponent subunit C (C1QC), complement component C9 (CO9), platelet glycoprotein Ib beta chain (GP1BB), Ras suppressor protein 1 (RSU1); downregulated: disintegrin and metalloproteinase domain 10 (ADA10)) has the capacity to differentiate AD patients from healthy controls with high accuracy. Linear correlation analysis showed that the combination was significantly correlated with cognitive performance.

CONCLUSIONS

The combination of plasma exosomal proteins A0A0G2JRQ6, C1QC, CO9, GP1BB, RSU1, and ADA10 acts as a novel candidate biomarker to differentiate AD patients from healthy individuals.

Extracellular vesicles and Alzheimer's disease in the novel era of Precision Medicine: implications for disease progression, diagnosis and treatment

Extracellular vesicles (EVs), secreted membranous nano-sized particles, are critical intercellular messengers participating in nervous system homeostasis, while recent evidence implicates EVs in Alzheimer's disease (AD) pathogenesis. Specifically, small EVs have been shown to spread toxic proteins, induce neuronal loss, and contribute to neuroinflammation and AD progression. On the other hand, EVs can reduce amyloid-beta deposition and transfer neuroprotective substances between cells, mitigating disease mechanisms. In addition to their roles in AD pathogenesis, EVs also exhibit great potential for the diagnosis and treatment of other brain disorders, representing an advantageous tool for Precision Medicine. Herein, we summarize the contribution of small EVs to AD-related mechanisms and disease progression, as well as their potential as diagnostic and therapeutic agents for AD.

Multipronged diagnostic and therapeutic strategies for Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and a major contributor to dementia cases worldwide. AD is clinically characterized by learning, memory, and cognitive deficits. The accumulation of extracellular amyloid β (Aβ) plaques and neurofibrillary tangles (NFTs) of tau are the pathological hallmarks of AD and are explored as targets for clinical diagnosis and therapy. AD pathology is poorly understood and there are no fully approved diagnosis and treatments. Notwithstanding the gap, decades of research in understanding disease mechanisms have revealed the multifactorial nature of AD. As a result, multipronged and holistic approaches are pertinent to targeting multiple biomarkers and targets for developing effective diagnosis and therapeutics. In this perspective, recent developments in Aβ and tau targeted diagnostic and therapeutic tools are discussed. Novel indirect, combination, and circulating biomarkers as potential diagnostic targets are highlighted. We underline the importance of multiplexing and multimodal detection of multiple biomarkers to generate biomarker fingerprints as a reliable diagnostic strategy. The classical therapeutics targeting Aβ and tau aggregation pathways are described with bottlenecks in the strategy. Drug discovery efforts targeting multifaceted toxicity involving protein aggregation, metal toxicity, oxidative stress, mitochondrial damage, and neuroinflammation are highlighted. Recent efforts focused on multipronged strategies to rationally design multifunctional modulators targeting multiple pathological factors are presented as future drug development strategies to discover potential therapeutics for AD.

Associations between cerebrospinal fluid markers and cognition in ageing and dementia: A systematic review

A biomarker associated with cognition in neurodegenerative dementias would aid in the early detection of disease progression, complement clinical staging and act as a surrogate endpoint in clinical trials. The current systematic review evaluates the association between cerebrospinal fluid protein markers of synapse loss and neuronal injury and cognition. We performed a systematic search which revealed 67 studies reporting an association between cerebrospinal fluid markers of interest and neuropsychological performance. Despite the substantial heterogeneity between studies, we found some evidence for an association between neurofilament-light and worse cognition in Alzheimer's diseases, frontotemporal dementia and typical cognitive ageing. Moreover, there was an association between cerebrospinal fluid neurogranin and cognition in those with an Alzheimer's-like cerebrospinal fluid biomarker profile. Some evidence was found for cerebrospinal fluid neuronal pentraxin-2 as a correlate of cognition across dementia syndromes. Due to the substantial heterogeneity of the field, no firm conclusions can be drawn from this review. Future research should focus on improving standardization and reporting as well as establishing the importance of novel markers such as neuronal pentraxin-2 and whether such markers can predict longitudinal cognitive decline.

Emerging blood exosome-based biomarkers for preclinical and clinical Alzheimer's disease: a meta-analysis and systematic review

Blood exosomes, which are extracellular vesicles secreted by living cells into the circulating blood, are regarded as a relatively noninvasive novel tool for monitoring brain physiology and disease states. An increasing number of blood cargo-loaded exosomes are emerging as potential biomarkers for preclinical and clinical Alzheimer's disease. Therefore, we conducted a meta-analysis and systematic review of molecular biomarkers derived from blood exosomes to comprehensively analyze their diagnostic performance in preclinical Alzheimer's disease, mild cognitive impairment, and Alzheimer's disease. We performed a literature search in PubMed, Web of Science, Embase, and Cochrane Library from their inception to August 15, 2020. The research subjects mainly included Alzheimer's disease, mild cognitive impairment, and preclinical Alzheimer's disease. We identified 34 observational studies, of which 15 were included in the quantitative analysis (Newcastle-Ottawa Scale score 5.87 points) and 19 were used in the qualitative analysis. The meta-analysis results showed that core biomarkers including Aβ1-42, P-T181-tau, P-S396-tau, and T-tau were increased in blood neuron-derived exosomes of preclinical Alzheimer's disease, mild cognitive impairment, and Alzheimer's disease patients. Molecules related to additional risk factors that are involved in neuroinflammation (C1q), metabolism disorder (P-S312-IRS-1), neurotrophic deficiency (HGF), vascular injury (VEGF-D), and autophagy-lysosomal system dysfunction (cathepsin D) were also increased. At the gene level, the differential expression of transcription-related factors (REST) and microRNAs (miR-132) also affects RNA splicing, transport, and translation. These pathological changes contribute to neural loss and synaptic dysfunction. The data confirm that the above-mentioned core molecules and additional risk-related factors in blood exosomes can serve as candidate biomarkers for preclinical and clinical Alzheimer's disease. These findings support further development of exosome biomarkers for a clinical blood test for Alzheimer's disease. This meta-analysis was registered at the International Prospective Register of Systematic Reviews (Registration No. CRD4200173498, 28/04/2020).

Defective mitochondria-lysosomal axis enhances the release of extracellular vesicles containing mitochondrial DNA and proteins in Huntington's disease

Mitochondrial and autophagy dysfunction are mechanisms proposed to be involved in the pathogenesis of several neurodegenerative diseases. Huntington's disease (HD) is a progressive neurodegenerative disorder associated with mutant Huntingtin-induced abnormalities in neuronal mitochondrial dynamics and quality control. Former studies suggest that the removal of defective mitochondria may be compromised in HD. Mitochondrial quality control (MQC) is a complex, well-orchestrated pathway that can be compromised through mitophagy dysregulation or impairment in the mitochondria-lysosomal axis. Another mitochondrial stress response is the generation of mitochondrial-derived vesicles that fuse with the endolysosomal system and form multivesicular bodies that are extruded from cells as extracellular vesicles (EVs). In this work, we aimed to study the presence of mitochondrial components in human EVs and the relation to the dysfunction of both mitochondria and the autophagy pathway. We comprehensively characterized the mitochondrial and autophagy alterations in premanifest and manifest HD carriers and performed a proteomic and genomic EVs profile. We observed that manifest HD patients exhibit mitochondrial and autophagy impairment associated with enhanced EVs release. Furthermore, we detected mitochondrial DNA and proteins in EVs released by HD cells and in neuronal-derived EVs including VDAC-1 and alpha and beta subunits of ATP synthase F1. HD-extracellular vesicles transport higher levels of mitochondrial genetic material in manifest HD patients, suggesting an alternative pathway for the secretion of reactive mitochondrial components. This study provides a novel framework connecting EVs enhanced release of mitochondrial components to mitochondrial and lysosomal dysfunction in HD.

An Update on Diagnostic Laboratory Biomarkers for Multiple Sclerosis

PURPOSE

For many patients, the multiple sclerosis (MS) diagnostic process can be lengthy, costly, and fraught with error. Recent research aims to address the unmet need for an accurate and simple diagnostic process through discovery of novel diagnostic biomarkers. This review summarizes recent studies on MS diagnostic fluid biomarkers, with a focus on blood biomarkers, and includes discussion of technical limitations and practical applicability.

RECENT FINDINGS

This line of research is in its early days. Accurate and easily obtainable biomarkers for MS have not yet been identified and validated, but several approaches to uncover them are underway. Continue efforts to define laboratory diagnostic biomarkers are likely to play an increasingly important role in defining MS at the earliest stages, leading to better long-term clinical outcomes.

A circular RNA blood panel that differentiates Alzheimer's disease from other dementia types

Background

Circular RNAs (circRNAs) have been demonstrated to be associated with Alzheimer’s disease (AD). Here, we conducted a study to explore whether circRNAs have the ability to differentiate AD from cognitively normal controls and other types of dementia, such as vascular dementia (VaD), Parkinson’s disease dementia (PDD), behavioral variant frontotemporal dementia (bvFTD), and dementia with Lewy body (DLB).

Methods

Three datasets were included in this study to measure blood circRNAs. The pilot study (Dataset 1, n = 40; controls, 20; AD, 20) was used to screen differentially expressed circRNAs. Dataset 2 (n = 124; controls, 61; AD, 63) was recruited for the establishment of the diagnostic model using a circRNA panel. Further, the Dataset 3 (n = 321; control, 58; AD, 60; VaD, 50; PDD, 51; bvFTD, 52; DLB, 50) was used to verify the diagnostic model.

Results

In Dataset 1, 22 upregulated and 19 downregulated circRNAs were revealed. In Dataset 2, a six-circRNA panel was found to be able to distinguish patients with AD from controls. Then this panel was applied to Dataset 3 and successfully differentiated AD from other types of dementia.

Conclusion

This study suggested that a six-circRNA panel is AD-specific and a promising biomarker of AD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40364-022-00405-0.

Diagnostic and Therapeutic Roles of Extracellular Vesicles in Aging-Related Diseases

Aging shows a decline in overall physical function, and cellular senescence is the powerful catalyst leading to aging. Considering that aging will be accompanied with the emergence of various aging-related diseases, research on new antiaging drugs is still valuable. Extracellular vesicles (EVs), as tools for intercellular communication, are important components of the senescence-associated secretory phenotype (SASP), and they can play pathological roles in the process of cellular senescence. In addition, EVs are similar to their original cells in functions. Therefore, EVs derived from pathological tissues or body fluids may be closely related to the progression of diseases and become potential biomarkers, while those from healthy cells may have therapeutic effects. Moreover, EVs are satisfactory drug carriers. At present, numerous studies have supported the idea that engineered EVs could improve drug targeting ability and utilization efficiency. Here, we summarize the characteristics of EVs and cellular senescence and focus on the diagnostic and therapeutic potential of EVs in various aging-related diseases, including Alzheimer disease, osteoporosis, cardiovascular disease, diabetes mellitus and its complications, and skin aging.

Review on the roles of specific cell-derived exosomes in Alzheimer's disease

Alzheimer's disease (AD) is the sixth leading cause of death worldwide and cannot be effectively cured or prevented; thus, early diagnosis, and intervention are important. The importance of exosomes, membrane-bound extracellular vesicles produced in the endosome of eukaryotic cells, in the development, diagnosis, and treatment of AD has been recognized; however, their specific functions remain controversial and even unclear. With the development of exosome extraction, isolation, and characterization, many studies have focused on exosomes derived from different cells and body fluids. In this study, we summarized the roles of exosomes derived from different body fluids and cells, such as neuron, glial, stem, and endothelial cells, in the development, diagnosis, monitoring, and treatment of AD. We also emphasize the necessity to focus on exosomes from biological fluids and specific cells that are less invasive to target. Moreover, aside from the concentrations of classic and novel biomarkers in exosomes, the size and number of exosomes may also influence early and differential diagnosis of AD.

Cerebrospinal Fluid Synaptosomal-Associated Protein 25 Levels in Patients with Alzheimer’s Disease: A Meta-Analysis

Background: Several studies have shown increased levels of cerebrospinal fluid (CSF) synaptosomal-associated protein 25 (SNAP-25) in patients with Alzheimer’s disease (AD). However, results have been inconsistent thus far. Objective: We conducted meta-analyses summarizing the associations of CSF SNAP-25 levels with AD to assess the utility of SNAP-25 as a novel biomarker for AD. Methods: We conducted a meta-analysis of differences in CSF SNAP-25 levels in patients with AD or mild cognitive impairment (MCI) and in cognitively healthy controls (HC). We calculated pooled correlation coefficients comparing SNAP-25 levels and total tau (T-tau) or hyperphosphorylated tau (P-tau) in CSF. Results: Eight studies enrolling 1,162 individuals (423 AD, 275 MCI, 464 HC) were included for quantitative analysis. Patients with AD (ratio of means [RoM] = 1.50, 95% confidence interval [CI]: 1.30,1.74) and MCI (RoM = 1.45, 95% CI: 1.12,1.87) had increased levels of CSF SNAP-25 as compared to HC. The difference in CSF SNAP-25 levels when comparing AD and MCI (RoM = 1.05, 95% CI: 0.96,1.14) was not statistically significant but showed a trend toward significance. Statistically significant correlations were found when comparing CSF SNAP-25 with CSF T-tau (Spearman correlation coefficient, ρ=0.78; ρ=0.66; ρ=0.69, respectively) and P-tau (ρ=0.66; ρ=0.70; ρ=0.62, respectively) levels in patients with AD, MCI, and HC. Conclusion: Increased CSF SNAP-25 levels differentiated patients with AD or MCI from controls, suggesting the utility of this biomarker in the early diagnosis of AD.

Exosomal MicroRNA-Based Predictive Model for Preclinical Alzheimer's Disease: A Multicenter Study

BACKGROUND

Exosomal microRNAs (miRNAs) have been demonstrated to be biomarkers of Alzheimer's disease (AD). However, whether exosomal miRNAs can predict AD at the asymptomatic stage remains unclear.

METHODS

This study is a multicenter study with four independent datasets to verify the capacity of exosomal miRNAs to identify preclinical AD. Subjects were recruited from a Beijing center in the pilot study (dataset 1: subjects with AD, n = 20; control subjects, n = 20), from other centers across China (dataset 2: subjects with AD, n = 95; control subjects, n = 93), a longitudinal cohort (dataset 3: subjects with preclinical AD, n = 101; control subjects, n = 102), and a confirmation study on familial AD (dataset 4: mutation carriers, n = 56; nonmutation carriers, n = 57).

RESULTS

A panel of miRNAs was changed in subjects with AD and can detect preclinical AD 5 to 7 years before the onset of cognitive impairment (areas under the curve = 0.85-0.88).

CONCLUSIONS

Exosomal miRNAs can be effective biomarkers for predicting AD 5 to 7 years prior to cognitive impairment onset.

Role of exosomes in the pathogenesis, diagnosis, and treatment of central nervous system diseases

Central nervous system (CNS) diseases, such as multiple sclerosis, Alzheimer's disease (AD), and Parkinson’s disease (PD), affect millions of people around the world. Great efforts were put in disease related research, but few breakthroughs have been made in the diagnostic and therapeutic approaches. Exosomes are cell-derived extracellular vesicles containing diverse biologically active molecules secreted by their cell of origin. These contents, including nucleic acids, proteins, lipids, amino acids, and metabolites, can be transferred between different cells, tissues, or organs, regulating various intercellular cross-organ communications and normal and pathogenic processes. Considering that cellular environment and cell state strongly impact the content and uptake efficiency of exosomes, their detection in biological fluids and content composition analysis potentially offer a multicomponent diagnostic readout of several human diseases. Recently, studies have found that aberrant secretion and content of exosomes are closely related to the pathogenesis of CNS diseases. Besides, loading natural cargoes, exosomes can deliver drugs cross the blood brain barrier, making them emerging candidates of biomarkers and therapeutics for CNS diseases. In this review, we summarize and discuss the advanced research progress of exosomes in the pathological processes of several CNS diseases in regarding with neuroinflammation, CNS repair, and pathological protein aggregation. Moreover, we propose the therapeutic strategies of applying exosomes to the diagnosis, early detection, and treatment of CNS diseases.

Recent progresses in exosome-based systems for targeted drug delivery to the brain

Despite the multiple ongoing and novel initiatives for developing brain-targeted drug delivery systems, insurmountable obstacles remain. A perfect drug delivery device that can bypass the brain-blood barrier and boost therapeutic efficacy is urgently needed for clinical applications. Exosomes hold unrivaled benefits as a drug delivery vehicle for treating brain diseases due to their endogenous and innate attributes. Unique properties, such as the ability to penetrate physical barriers, biocompatibility, innate targeting features, ability to leverage natural intracellular trafficking pathways, favored tumor homing, and stability, make exosomes suitable for brain-targeted drug delivery. Herein, we provide an overview of recent exosome-based drug delivery nanoplatforms and discuss how these inherent vesicles can be used to deliver therapeutic agents to the brain to cure neurodegenerative diseases, brain tumors, and other brain disorders. Moreover, we review the current roadblocks associated with exosomes and other brain-targeted drug delivery systems and discuss future directions for achieving successful therapy outcomes.

Serum Neurogranin Measurement as a Biomarker of Central Nervous System Infections: A Preliminary Study

The early diagnosis of central nervous system infections is of great importance to minimize morbidity and mortality. Neurogranin is a postsynaptic neural protein, and when the blood-brain barrier is damaged, neurogranin levels increase in both the cerebrospinal fluid and serum. The aim of this study was to evaluate the level of serum neurogranin and to investigate its utility in the diagnosis of central nervous system infections. This study was conducted as a prospective case-control study of patients diagnosed with meningitis. The study initially included 55 patients, and 15 patients with proven central nervous system infection were ultimately included in the patient group. The results in the patient group were compared with those of the control group of 15 healthy subjects. The 15 patients comprised 4 women and 11 men with a mean cerebrospinal fluid neurogranin level of 432.4 ± 123.5 ng/ml. Correlation analysis revealed a moderate positive correlation between cerebrospinal fluid neurogranin levels and serum neurogranin levels. The mean serum neurogranin level was 198.6 ± 51.7 ng/ml in the control group but was significantly higher at 429.2 ± 104.3 ng/ml in the patient group. In conclusion, it may be useful to measure blood neurogranin levels in patients suspected of having central nervous system infections, especially in those for whom computed tomography, magnetic resonance imaging, or lumbar puncture cannot be performed.

Phosphorylated Tau 181 Serum Levels Predict Alzheimer’s Disease in the Preclinical Stage

Background

There is an urgent need for cost-effective, easy-to-measure biomarkers to identify subjects who will develop Alzheimer’s disease (AD), especially at the pre-symptomatic stage. This stage can be determined in autosomal dominant AD (ADAD) which offers the opportunity to observe the dynamic biomarker changes during the life-course of AD stages. This study aimed to investigate serum biomarkers during different AD stages and potential novel protein biomarkers of presymptomatic AD.

Methods

In the first stage, 32 individuals [20 mutation carriers including 10 with AD, and 10 with mild cognitive impairment (MCI), and 12 healthy controls] from ADAD families were analyzed. All subjects underwent a complete clinical evaluation and a comprehensive neuropsychological battery. Serum samples were collected from all subjects, and antibody arrays were used to analyze 170 proteins in these samples. The most promising biomarkers were identified during this screening and were then measured in serum samples of 12 subjects with pre-MCI and 20 controls.

Results

The serum levels of 13 proteins were significantly different in patients with AD or MCI compared to controls. Of the 13 proteins, cathepsin D, immunoglobulin E, epidermal growth factor receptor (EGFR), matrix metalloproteinase-9 (MMP-9), von Willebrand factor (vWF), haptoglobin, and phosphorylated Tau-181 (p-Tau181) correlated with all cognitive measures (R² = −0.69–0.76). The areas under the receiver operating characteristic curve of these seven proteins were 0.71–0.93 for the classification of AD and 0.57–0.95 for the classification of MCI. Higher levels of p-Tau181 were found in the serum of pre-MCI subjects than in the serum of controls. The p-Tau181 serum level might detect AD before symptoms occur (area under the curve 0.85, sensitivity 75%, specificity 81.67%).

Conclusions

A total of 13 serum proteins showed significant differences between subjects with AD and MCI and healthy controls. The p-Tau181 serum level might be a broadly available and cost-effective biomarker to identify individuals with preclinical AD and assess the severity of AD.

Exosome: The “Off-the-Shelf” Cellular Nanocomponent as a Potential Pathogenic Agent, a Disease Biomarker, and Neurotherapeutics

Exosomes are nanosized “off-the-shelf” lipid vesicles released by almost all cell types and play a significant role in cell–cell communication. Exosomes have already been proven to carry cell-specific cargos of proteins, lipids, miRNA, and noncoding RNA (ribonucleic acid). These vesicles can be selectively taken up by the neighboring cell and can regulate cellular functions. Herein, we have discussed three different roles of exosomes in neuroscience. First, we have discussed how exosomes play the role of a pathogenic agent as a part of cell–cell communication and transmit pathogens such as amyloid-beta (Aβ), further helping in the propagation of neurodegenerative and other neurological diseases. In the next section, the review talks about the role of exosomes in biomarker discovery in neurological disorders. Toward the end, we have reviewed how exosomes can be harnessed and engineered for therapeutic purposes in different brain diseases. This review is based on the current knowledge generated in this field and our comprehension of this domain.

Association of plasma apolipoproteins and levels of inflammation-related factors with different stages of Alzheimer's disease: a cross-sectional study

OBJECTIVE

Blood-based biomarkers for the early diagnosis of Alzheimer's disease (AD) are a 'Holy Grail' of AD research. Growing evidence shows that levels of apolipoproteins and various inflammation-related factors are altered in the peripheral blood of patients with AD. The purpose of this study was to clear and definite whether these biomarkers are differentially expressed at the early stages of AD, and could be a biomarker as an early diagnosis of the disease.

DESIGN

Observation study.

SETTING

This study was a part of the Sino Longitudinal Study on Cognitive Decline, an ongoing prospective cohort study (ClinicalTrials.gov identifier: NCT03370744) that centres on Xuanwu Hospital (Beijing, China) in cooperation with an alliance of 94 hospitals from 50 cities across China.

PARTICIPANTS

In the present study, 416 right-handed Chinese Han subjects were recruited through standardised public advertisements from 2014 to 2019.

OUTCOME MEASURES

Concentrations of plasma apolipoprotein A1, apolipoprotein CIII (ApoCIII), apolipoprotein E (ApoE), A-2-macroglobulin (A2M), complement C3 (C3) and complement factor H (FH) were determined using a commercial multiplex Luminex-based panel in normal controls (NC), subjective cognitive decline (SCD), mild cognitive impairment and AD groups.

RESULTS

For individual analysis, pairwise comparisons showed that: (1) For SCD versus NC, no biomarker showed significant difference; (2) For amnestic mild cognitive impairment (aMCI) versus NC, levels of ApoCIII, ApoE, A2M, C3 and FH increased significantly; and (3) For AD versus NC, amounts of C3 increased. For models differentiating clinical groups, discriminant analysis was performed by including all protein markers, age, sex, genotype and education level in the model. This approach could distinguish between patients with aMCI (area under the curve (AUC): 0.743) and AD (AUC: 0.837) from NC.

CONCLUSION

Our results suggest that concentrations of certain apolipoproteins and inflammation-related factors are altered at the early stage of AD, and could be useful biomarkers for early diagnosis.

TRIAL REGISTRATION NUMBER

NCT03370744.

Biomarkers and Tools for Predicting Alzheimer's Disease in the Preclinical Stage

Alzheimer's disease (AD) is the only leading cause of death for which no disease-modifying therapy is currently available. Over the past decade, a string of disappointing clinical trial results has forced us to shift our focus to the preclinical stage of AD, which represents the most promising therapeutic window. However, the accurate diagnosis of preclinical AD requires the presence of brain β- amyloid deposition determined by cerebrospinal fluid or amyloid-positron emission tomography, significantly limiting routine screening and diagnosis in non-tertiary hospital settings. Thus, an easily accessible marker or tool with high sensitivity and specificity is highly needed. Recently, it has been discovered that individuals in the late stage of preclinical AD may not be truly "asymptomatic" in that they may have already developed subtle or subjective cognitive decline. In addition, advances in bloodderived biomarker studies have also allowed the detection of pathologic changes in preclinical AD. Exosomes, as cell-to-cell communication messengers, can reflect the functional changes of their source cell. Methodological advances have made it possible to extract brain-derived exosomes from peripheral blood, making exosomes an emerging biomarker carrier and liquid biopsy tool for preclinical AD. The eye and its associated structures have rich sensory-motor innervation. In this regard, studies have indicated that they may also provide reliable markers. Here, our report covers the current state of knowledge of neuropsychological and eye tests as screening tools for preclinical AD and assesses the value of blood and brain-derived exosomes as carriers of biomarkers in conjunction with the current diagnostic paradigm.

Biofluid Biomarkers of Alzheimer’s Disease: Progress, Problems, and Perspectives

Since the establishment of the biomarker-based A-T-N (Amyloid/Tau/Neurodegeneration) framework in Alzheimer’s disease (AD), the diagnosis of AD has become more precise, and cerebrospinal fluid tests and positron emission tomography examinations based on this framework have become widely accepted. However, the A-T-N framework does not encompass the whole spectrum of AD pathologies, and problems with invasiveness and high cost limit the application of the above diagnostic methods aimed at the central nervous system. Therefore, we suggest the addition of an “X” to the A-T-N framework and a focus on peripheral biomarkers in the diagnosis of AD. In this review, we retrospectively describe the recent progress in biomarkers based on the A-T-N-X framework, analyze the problems, and present our perspectives on the diagnosis of AD.

The China Alzheimer Report 2022

China’s population has rapidly aged over the recent decades of social and economic development as neurodegenerative disorders have proliferated, especially Alzheimer’s disease (AD) and related dementias (ADRD). AD’s incidence rate, morbidity, and mortality have steadily increased to make it presently the fifth leading cause of death among urban and rural residents in China and magnify the resulting financial burdens on individuals, families and society. The ‘Healthy China Action’ plan of 2019–2030 promotes the transition from disease treatment to health maintenance for this expanding population with ADRD. This report describes related epidemiological trends, evaluates the economic burden of the disease, outlines current clinical diagnosis and treatment status and delineates existing available public health resources. More specifically, it examines the public health impact of ADRD, including prevalence, mortality, costs, usage of care, and the overall effect on caregivers and society. In addition, this special report presents technical guidance and supports for the prevention and treatment of AD, provides expertise to guide relevant governmental healthcare policy development and suggests an information platform for international exchange and cooperation.

Diagnostic Accuracy of Blood-Based Biomarker Panels: A Systematic Review

Background

Because of high prevalence of Alzheimer's disease (AD) in low- and middle-income countries (LMICs), there is an urgent need for inexpensive and minimally invasive diagnostic tests to detect biomarkers in the earliest and asymptomatic stages of the disease. Blood-based biomarkers are predicted to have the most impact for use as a screening tool and predict the onset of AD, especially in LMICs. Furthermore, it has been suggested that panels of markers may perform better than single protein candidates.

Methods

Medline/Pubmed was searched to identify current relevant studies published from January 2016 to December 2020. We included all full-text articles examining blood-based biomarkers as a set of protein markers or panels to aid in AD's early diagnosis, prognosis, and characterization.

Results

Seventy-six articles met the inclusion criteria for systematic review. Majority of the studies reported plasma and serum as the main source for biomarker determination in blood. Protein-based biomarker panels were reported to aid in AD diagnosis and prognosis with better accuracy than individual biomarkers. Conventional (amyloid-beta and tau) and neuroinflammatory biomarkers, such as amyloid beta-42, amyloid beta-40, total tau, phosphorylated tau-181, and other tau isoforms, were the most represented. We found the combination of amyloid beta-42/amyloid beta-40 ratio and APOEε4 status to be most represented with high accuracy for predicting amyloid beta-positron emission tomography status.

Conclusion

Assessment of Alzheimer's disease biomarkers in blood as a non-invasive and cost-effective alternative will potentially contribute to early diagnosis and improvement of therapeutic interventions. Given the heterogeneous nature of AD, combination of markers seems to perform better in the diagnosis and prognosis of the disease than individual biomarkers.

Exosomes in Age-Related Cognitive Decline: Mechanistic Insights and Improving Outcomes

Aging is the most prominent risk factor for cognitive decline, yet behavioral symptomology and underlying neurobiology can vary between individuals. Certain individuals exhibit significant age-related cognitive impairments, while others maintain intact cognitive functioning with only minimal decline. Recent developments in genomic, proteomic, and functional imaging approaches have provided insights into the molecular and cellular substrates of cognitive decline in age-related neuropathologies. Despite the emergence of novel tools, accurately and reliably predicting longitudinal cognitive trajectories and improving functional outcomes for the elderly remains a major challenge. One promising approach has been the use of exosomes, a subgroup of extracellular vesicles that regulate intercellular communication and are easily accessible compared to other approaches. In the current review, we highlight recent findings which illustrate how the analysis of exosomes can improve our understanding of the underlying neurobiological mechanisms that contribute to cognitive variation in aging. Specifically, we focus on exosome-mediated regulation of miRNAs, neuroinflammation, and aggregate-prone proteins. In addition, we discuss how exosomes might be used to enhance individual patient outcomes by serving as reliable biomarkers of cognitive decline and as nanocarriers to deliver therapeutic agents to the brain in neurodegenerative conditions.

Biomarkers used in Alzheimer's disease diagnosis, treatment, and prevention

Alzheimer's disease (AD), being the number one in terms of dementia burden, is an insidious age-related neurodegenerative disease and is presently considered a global public health threat. Its main histological hallmarks are the Aβ senile plaques and the P-tau neurofibrillary tangles, while clinically it is marked by a progressive cognitive decline that reflects the underlying synaptic loss and neurodegeneration. Many of the drug therapies targeting the two pathological hallmarks namely Aβ and P-tau have been proven futile. This is probably attributed to the initiation of therapy at a stage where cognitive alterations are already obvious. In other words, the underlying neuropathological changes are at a stage where these drugs lack any therapeutic value in reversing the damage. Therefore, there is an urgent need to start treatment in the very early stage where these changes can be reversed, and hence, early diagnosis is of primordial importance. To this aim, the use of robust and informative biomarkers that could provide accurate diagnosis preferably at an earlier phase of the disease is of the essence. To date, several biomarkers have been established that, to a different extent, allow researchers and clinicians to evaluate, diagnose, and more specially exclude other related pathologies. In this study, we extensively reviewed data on the currently explored biomarkers in terms of AD pathology-specific and non-specific biomarkers and highlighted the recent developments in the diagnostic and theragnostic domains. In the end, we have presented a separate elaboration on aspects of future perspectives and concluding remarks.