A Strategy for Discovery and Verification of Candidate Biomarkers in Cerebrospinal Fluid of Preclinical Alzheimer's Disease

Involvement of the VGF/BDNF axis in the neuropathology of Alzheimer's disease and its potential role in diagnosis and treatment

The brain is a highly plastic organ that continually receives and integrates signals to generate functional and structural changes and homeostatic adaptations throughout life. Alterations in some signaling pathways that mediate these responses can impact brain plasticity, accelerate brain aging and potentially lead to neurodegeneration. There is substantial evidence that two important signaling pathways activated by neurotrophins, nonacronymic (VGF) and brain-derived neurotrophic factor (BDNF), are involved in substantial functions stimulating neuronal growth, differentiation, and circuit establishment during development and neuronal maintenance and plasticity in the mature brain. In this review, we present evidence that these two pathways and their interactions are central players in cognitive performance and alterations in pathological aging, particularly in conditions such as Alzheimer's disease (AD). Finally, we suggest specific avenues for future research on the basis of recent findings suggesting these molecules are diagnostic biomarkers and putative therapeutic tools to prevent, delay or improve AD neuropathology.

Boost-DiLeu: Enhanced Isobaric N,N-Dimethyl Leucine Tagging Strategy for a Comprehensive Quantitative Glycoproteomic Analysis

Intact glycopeptide analysis has been of great interest because it can elucidate glycosylation site information and glycan structural composition at the same time. However, mass spectrometry (MS)-based glycoproteomic analysis is hindered by the low abundance and poor ionization efficiency of glycopeptides. Relatively large amounts of starting materials are needed for the enrichment, which makes the identification and quantification of intact glycopeptides from samples with limited quantity more challenging. To overcome these limitations, we developed an improved isobaric labeling strategy with an additional boosting channel to enhance N,N-dimethyl leucine (DiLeu) tagging-based quantitative glycoproteomic analysis, termed as Boost-DiLeu. With the integration of a one-tube sample processing workflow and high-pH fractionation, 3514 quantifiable N-glycopeptides were identified from 30 μg HeLa cell tryptic digests with reliable quantification performance. Furthermore, this strategy was applied to human cerebrospinal fluid (CSF) samples to differentiate N-glycosylation profiles between Alzheimer's disease (AD) patients and non-AD donors. The results revealed processes and pathways affected by dysregulated N-glycosylation in AD, including platelet degranulation, cell adhesion, and extracellular matrix, which highlighted the involvement of N-glycosylation aberrations in AD pathogenesis. Moreover, weighted gene coexpression network analysis (WGCNA) showed nine modules of glycopeptides, two of which were associated with the AD phenotype. Our results demonstrated the feasibility of using this strategy for in-depth glycoproteomic analysis of size-limited clinical samples. Taken together, we developed and optimized a strategy for the enhanced comprehensive quantitative intact glycopeptide analysis with DiLeu labeling, showing significant promise for identifying novel therapeutic targets or biomarkers in biological systems with a limited sample quantity.

VGF: A prospective biomarker and therapeutic target for neuroendocrine and nervous system disorders

Neuroendocrine regulatory polypeptide VGF (nerve growth factor inducible) was firstly found in the rapid induction of nerve growth factor on PC12 cells. It was selectively distributed in neurons and many neuroendocrine tissues. This paper reviewed the latest literatures on the gene structure, transcriptional regulation, protein processing, distribution and potential receptors of VGF. The neuroendocrine roles of VGF and its derived polypeptides in regulating energy, water electrolyte balance, circadian rhythm and reproductive activities were also summarized. Furthermore, based on the experimental evidence in vivo and in vitro, dysregulation of VGF in different neuroendocrine diseases and the possible mechanism mediated by VGF polypeptides were discussed. We next discussed the potential as the clinical diagnosis and therapy for VGF related diseases in the future.

Molecular pharmacology and therapeutic advances of the pentacyclic triterpene lupeol

BACKGROUND

Plant triterpenoids are major sources of nutraceuticals that provide many health benefits to humans. Lupeol is one of the pentacyclic dietary triterpenoids commonly found in many fruits and vegetables, which is highly investigated for its pharmacological effect and benefit to human health.

PURPOSE

This systematic review critically discussed the potential pharmacological benefits of lupeol and its derivatives as evidenced by various cellular and animal model studies. To gain insight into the pharmacological effects of lupeol, the network pharmacological approach is applied. Pharmacokinetics and recent developments in nanotechnology-based approaches to targeted delivery of lupeol along with its safety use are also discussed.

METHODS

This study is dependent on the systematic and non-exhaustive literature survey for related research articles, papers, and books on the chemistry, pharmacological benefits, pharmacokinetics, and safety of lupeol published between 2011 and 2021. For online materials, the popular academic search engines viz. Google Scholar, PubMed, Science Direct, Scopus, ResearchGate, Springer, as well as official websites were explored with selected keywords.

RESULTS

Lupeol has shown promising benefits in the management of cancer and many other human diseases such as diabetes, obesity, cardiovascular diseases, kidney and liver problems, skin diseases, and neurological disorders. The pharmacological effects of lupeol primarily rely on its capacity to revitalize the cellular antioxidant, anti-inflammatory and anti-apoptotic mechanisms. Network pharmacological approach revealed some prospective molecular targets and pathways and presented some significant information that could help explain the pharmacological effects of lupeol and its derivatives. Despite significant progress in molecular pharmacology, the clinical application of lupeol is limited due to poor bioavailability and insufficient knowledge on its mode of action. Structural modification and nanotechnology-guided targeted delivery of lupeol improve the bioavailability and bioactivity of lupeol.

CONCLUSION

The pentacyclic triterpene lupeol possesses numerous human health-benefiting properties. This review updates current knowledge and critically discusses the pharmacological effects and potential applications of lupeol and its derivatives in human health and diseases. Future studies are needed to evaluate the efficacies of lupeol and its derivatives in the management and pathobiology of human diseases.

Isotopic N,N-dimethyl leucine tags for absolute quantification of clusterin and apolipoprotein E in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia and one of the leading causes of death in the United States. In the past decades, extensive efforts have been devoted to biomarker discovery for early diagnosis and treatment of AD. Herein, this study aims to quantify clusterin (CLU) and apolipoprotein E (APOE) in blood samples from AD patients and evaluate these two proteins as potential biomarkers in AD diagnosis. In-house synthesized 5-plex isotopic N,N-dimethyl leucine (iDiLeu) tags were used to label target peptide standards at different concentrations to construct standard curves. Our study revealed that the levels of CLU and APOE exhibited clear differences in male vs. female AD groups but not in male vs. female non-AD groups. In contrast, the levels of serum CLU and APOE did not show statistically significant differences in the AD groups and non-AD groups. Principal component analysis (PCA) with CLU and APOE showed some separation between the AD and non-AD participants. Significance: Dissecting CLU and APOE heterogeneity in AD pathogenesis may therefore facilitate delineating the pathological relevance for sex-related pathways, leading to personalized medicine in the future. Collectively, this study introduces a cost-effective absolute quantitative proteomics strategy for target protein quantitation and lays the foundation for future investigation of CLU and APOE as potential biomarkers for AD. SIGNIFICANCE STATEMENT: As blood-based biomarkers for AD diagnosis are cost-effective and introduce less invasiveness, discovery and validation of biomarkers in the blood samples of AD patients have become a hot topic in Alzheimer's and dementia research. Thus far, amyloid β (Aβ), total-tau and phosphorylated tau (p-tau) in blood show great accuracy and specificity in diagnosis of AD. However, the underlying mechanism of AD pathology remains to be elusive and complex. Besides these well studied proteins, many other proteins, such as clusterin (CLU) and apolipoprotein E (APOE) have also been found to be related to AD development. It has been implicated that these two proteins are involved in Aβ clearance and deposition. In this study, we measure the absolute concentrations of these two proteins in blood and shed some light on the potential roles of CLU and APOE in AD pathology. Dissecting CLU and APOE heterogeneity in AD pathogenesis may therefore facilitate delineating the pathological relevance for specific pathways between different genders, leading to personalized medicine in the future. Collectively, this study introduces a cost-effective absolute quantitative proteomics strategy for target protein quantitation and lays the foundation for future investigation of CLU and APOE as potential biomarkers for AD.

Mass spectrometry-based methods for robust measurement of Alzheimer's disease biomarkers in biological fluids

Alzheimer's disease (AD) is the most common form of dementia affecting 60%-70% of people afflicted with this disease. Accurate antemortem diagnosis is urgently needed for early detection of AD to enable reliable estimation of prognosis, intervention, and monitoring of the disease. The National Institute on Aging/Alzheimer's Association sponsored the 'Research Framework: towards a biological definition of AD', which recommends using different biomarkers in living persons for a biomarker-based definition of AD regardless of clinical status. Fluid biomarkers represent one of key groups of them. Since cerebrospinal fluid (CSF) is in direct contact with brain and many proteins present in the brain can be detected in CSF, this fluid has been regarded as the best biofluid in which to measure AD biomarkers. Recently, technological advancements in protein detection made possible the effective study of plasma AD biomarkers despite their significantly lower concentrations versus to that in CSF. This and other challenges that face plasma-based biomarker measurements can be overcome by using mass spectrometry. In this review, we discuss AD biomarkers which can be reliably measured in CSF and plasma using targeted mass spectrometry coupled to liquid chromatography (LC/MS/MS). We describe progress in LC/MS/MS methods' development, emphasize the challenges, and summarize major findings. We also highlight the role of mass spectrometry and progress made in the process of global standardization of the measurement of Aβ42/Aβ40. Finally, we briefly describe exploratory proteomics which seek to identify new biomarkers that can contribute to detection of co-pathological processes that are common in sporadic AD.

In-depth Site-specific Analysis of N-glycoproteome in Human Cerebrospinal Fluid and Glycosylation Landscape Changes in Alzheimer's Disease

As the body fluid that directly interchanges with the extracellular fluid of the central nervous system (CNS), cerebrospinal fluid (CSF) serves as a rich source for CNS-related disease biomarker discovery. Extensive proteome profiling has been conducted for CSF, but studies aimed at unraveling site-specific CSF N-glycoproteome are lacking. Initial efforts into site-specific N-glycoproteomics study in CSF yield limited coverage, hindering further experimental design of glycosylation-based disease biomarker discovery in CSF. In the present study, we have developed an N-glycoproteomic approach that combines enhanced N-glycopeptide sequential enrichment by hydrophilic interaction chromatography (HILIC) and boronic acid enrichment with electron transfer and higher-energy collision dissociation (EThcD) for large-scale intact N-glycopeptide analysis. The application of the developed approach to the analyses of human CSF samples enabled identifications of a total of 2893 intact N-glycopeptides from 511 N-glycosites and 285 N-glycoproteins. To our knowledge, this is the largest site-specific N-glycoproteome dataset reported for CSF to date. Such dataset provides molecular basis for a better understanding of the structure-function relationships of glycoproteins and their roles in CNS-related physiological and pathological processes. As accumulating evidence suggests that defects in glycosylation are involved in Alzheimer's disease (AD) pathogenesis, in the present study, a comparative in-depth N-glycoproteomic analysis was conducted for CSF samples from healthy control and AD patients, which yielded a comparable N-glycoproteome coverage but a distinct expression pattern for different categories of glycoforms, such as decreased fucosylation in AD CSF samples. Altered glycosylation patterns were detected for a number of N-glycoproteins including alpha-1-antichymotrypsin, ephrin-A3 and carnosinase CN1 etc., which serve as potentially interesting targets for further glycosylation-based AD study and may eventually lead to molecular elucidation of the role of glycosylation in AD progression.

Recent Advances in Analytical Approaches for Glycan and Glycopeptide Quantitation

Growing implications of glycosylation in physiological occurrences and human disease have prompted intensive focus on revealing glycomic perturbations through absolute and relative quantification. Empowered by seminal methodologies and increasing capacity for detection, identification, and characterization, the past decade has provided a significant increase in the number of suitable strategies for glycan and glycopeptide quantification. Mass-spectrometry-based strategies for glycomic quantitation have grown to include metabolic incorporation of stable isotopes, deposition of mass difference and mass defect isotopic labels, and isobaric chemical labeling, providing researchers with ample tools for accurate and robust quantitation. Beyond this, workflows have been designed to harness instrument capability for label-free quantification, and numerous software packages have been developed to facilitate reliable spectrum scoring. In this review, we present and highlight the most recent advances in chemical labeling and associated techniques for glycan and glycopeptide quantification.

Effect of neurological screening on early dementia detection in southern Italy

OBJECTIVE

Population screening can facilitate early diagnosis of dementia and improve disease management. This study examined the effects of a screening campaign for neurodegenerative disorders on the early diagnosis of dementia using 2-year follow-up data.

METHODS

A 5-day screening campaign was conducted that comprised neurological, neuropsychological and other specialist examinations. Identification of alterations during the neurological examination was followed-up by further diagnostic examinations to confirm the neurological impairment.

RESULTS

Neurological alterations were observed in 39% of the screened subjects, who were mostly diagnosed with mild cognitive impairment and referred to a dementia and cognitive disorders centre. Suspicion of neurological impairment was a risk factor for inclusion in a specific neurological ambulatory follow-up and a condition for exemption from payment for medical examinations.

CONCLUSIONS

Neurodegenerative screening initiatives should include subjects selected by general practitioners. It would be useful to create a network including primary care physicians and cognitive disorder centres. Telemedicine tools (e.g., teleconsulting) could also be used to facilitate early diagnosis.

Mass Defect-Based DiLeu Tagging for Multiplexed Data-Independent Acquisition

The unbiased selection of peptide precursors makes data-independent acquisition (DIA) an advantageous alternative to data-dependent acquisition (DDA) for discovery proteomics, but traditional multiplexed quantification approaches employing mass difference labeling or isobaric tagging are incompatible with DIA. Here, we describe a strategy that permits multiplexed quantification by DIA using mass defect-based N,N-dimethyl leucine (mdDiLeu) tags and high-resolution tandem mass spectrometry (MS2) analysis. Millidalton mass differences between mdDiLeu isotopologues produce fragment ion multiplet peaks separated in mass by as little as 5.8 mDa, enabling up to 4-plex quantification in DIA MS2 spectra. Quantitative analysis of yeast samples displayed comparable accuracy and precision for MS2-based DIA and MS1-based DDA methods. Multiplexed DIA analysis of cerebrospinal fluid revealed the dynamic proteome changes in Alzheimer's disease, demonstrating its utility for discovery of potential clinical biomarkers. We show that the mdDiLeu tagging approach for multiplexed DIA is a viable methodology for investigating proteome changes, particularly for low-abundance proteins, in different biological matrices.

Neuroprotective Potentials of Marine Algae and Their Bioactive Metabolites: Pharmacological Insights and Therapeutic Advances

Beyond their significant contribution to the dietary and industrial supplies, marine algae are considered to be a potential source of some unique metabolites with diverse health benefits. The pharmacological properties, such as antioxidant, anti-inflammatory, cholesterol homeostasis, protein clearance and anti-amyloidogenic potentials of algal metabolites endorse their protective efficacy against oxidative stress, neuroinflammation, mitochondrial dysfunction, and impaired proteostasis which are known to be implicated in the pathophysiology of neurodegenerative disorders and the associated complications after cerebral ischemia and brain injuries. As was evident in various preclinical studies, algal compounds conferred neuroprotection against a wide range of neurotoxic stressors, such as oxygen/glucose deprivation, hydrogen peroxide, glutamate, amyloid β, or 1-methyl-4-phenylpyridinium (MPP+) and, therefore, hold therapeutic promise for brain disorders. While a significant number of algal compounds with promising neuroprotective capacity have been identified over the last decades, a few of them have had access to clinical trials. However, the recent approval of an algal oligosaccharide, sodium oligomannate, for the treatment of Alzheimer's disease enlightened the future of marine algae-based drug discovery. In this review, we briefly outline the pathophysiology of neurodegenerative diseases and brain injuries for identifying the targets of pharmacological intervention, and then review the literature on the neuroprotective potentials of algal compounds along with the underlying pharmacological mechanism, and present an appraisal on the recent therapeutic advances. We also propose a rational strategy to facilitate algal metabolites-based drug development.

The anatomy and metabolome of the lymphatic system in the brain in health and disease

Recent studies have demonstrated that the brain is equipped with a lymphatic drainage system that is actively involved in parenchymal waste clearance, brain homeostasis and immune regulation. However, the exact anatomic drainage routes of brain lymph fluid (BLF) remain elusive, hampering the physiological study and clinical application of this system. In this study, we systematically dissected the anatomy of the BLF pathways in a rat model. Moreover, we developed a protocol to collect BLF from the afferent lymphatic vessels of deep cervical lymph nodes (dcLNs) and cerebrospinal fluid (CSF) from the fourth ventricle. Nuclear magnetic resonance spectroscopy showed that BLF contains more metabolites than CSF, suggesting that BLF might be a more sensitive indicator of brain dynamics under physiological and pathological conditions. Finally, we identified several metabolites as potential diagnostic biomarkers for glioma, Parkinson's disease and CNS infectious diseases. Together, these data may provide insight into the physiology of the lymphatic system in the brain and into the clinical diagnosis of CNS disorders.