Cerebrospinal fluid S100B is elevated in the earlier stages of Alzheimer's disease

Osteoclasts Link Dysregulated Peripheral Degradation Processes and Accelerated Progression in Alzheimer's Disease

Background

The amyloid-β (Aβ) enhances the number and activity of blood monocyte-derived osteoclasts (OCs). Individuals with osteoporosis (OP) face an increased risk of developing dementia or Alzheimer's disease (AD). Despite this association, the contribution of bone-resorbing OCs to the progression of AD pathology remains unclear.

Objective

Our objective was to investigate the potential impacts of OCs on the development of AD pathology.

Methods

We conducted targeted analysis of publicly available whole blood transcriptomes from patients with AD to characterize the blood molecular signatures and pathways associated with hyperactive OCs. In addition, we used APP23 transgenic (APP23 TG) AD mouse model to assess the effects of OCs pharmacological blockade on AD pathology and behavior.

Results

Patients with AD exhibited increased osteoclastogenesis signature in their blood cells, which appears to be positively correlated with dysfunction of peripheral clearance of Aβ mediated by immune cells. Long-term anti-resorptive intervention with Alendronate inhibited OC activity in APP23 mice, leading to improvements in peripheral monocyte Aβ-degrading enzyme expression, Aβ-deposition, and memory decline.

Conclusions

Our findings suggest that OCs have a disease-promoting role in the development and progression of AD, possibly linked to their modulation of peripheral immunity. These findings guide future research to further elucidate the connection between OP and AD pathogenesis, highlighting the potential benefits of preventing OP in alleviating cognitive burden.

S100B and Neuron-Specific Enolase Levels as Brain Injury Biomarkers in Internet Addiction: Effect of Sleep

BACKGROUND

Comorbidity of Internet addiction (IA) with sleep disruptions is common in adolescents. There is evidence that the levels of brain injury markers could be affected by sleep disruptions. In this study, we aimed to evaluate the relationship between sleep quality and these biomarkers within the framework of the relationship between IA and sleep disruptions.

METHODS

A total of 65 drug-free adolescents with newly diagnosed IA, aged 12 to 18 years, were included in the study, and they were divided into two groups considering the comorbidities of attention-deficit/hyperactivity disorder (ADHD) and social anxiety. The control group consisted of 30 healthy children. The participants were asked to complete the Young Internet Addiction Scale, Pittsburgh Sleep Quality Index (PSQI), Morningness Eveningness Questionnaire, Beck's Depression Inventory, Beck's Anxiety Inventory, and Barratt Impulsiveness Scale-11. Blood samples were taken between 8 and 9 am to analyze S100 calcium-binding protein B (S100B) and neuron-specific enolase (NSE) levels with enzyme-linked immunosorbent assay.

RESULTS

Plasma S100B and NSE levels were found to be statistically significantly higher in the IA with ADHD and the IA with anxiety groups than in healthy controls. NSE and S100B levels were found to be correlated with PSQI scores in both the IA groups. Also, there was a positive correlation between these biomarkers and IA severity.

CONCLUSIONS

Decreased sleep quality and daily sleep duration in IA might cause brain injury, resulting in an increase in the severity of the addiction. Prospective studies with large samples are needed to better explain the IA-sleep-brain injury relationship.

Spinal cord injury immunosensor: Sensitive detection of S100β on interdigitated electrode sensor

A spinal cord injury is damage to the nerves and cells that receive and provide a signal from the brain to the rest of the body. Spinal injury causes changes in movement, sensation, and strength, affect the body functions near the injury site, and may lead to paralysis. S100β was found as a suitable biomarker for identifying spinal cord injury and its causing problem. Herein, S100β immunoassay was developed on interdigitated electrode sensor to diagnose spinal cord injury. For effective anti-S100β antibody immobilization, the antibody was premixed with 3-Aminopropyl)triethoxsilane and then attached to the hydroxylated interdigitated electrode surface. This method of antibody immobilization enhanced the antibody attachment two-times than the method without premix. Antibody-attached surfaces increased current responses as S100 concentrations increased, and the limit of detection was seen to be 1 pg/mL on the linearity until 3000 pg/mL at an R2 value of 0.9907 [y = 7x - 6.4667]. Further, biofouling experiments with glial fibrillary acidic protein and γ-aminobutyric acid failed to enhance the current response, indicating the specific detection of S100β. This immunoassay identifies S100β at its lower level and helps to diagnose spinal cord injury and its related problem.

Secondary neurodegeneration following Stroke: what can blood biomarkers tell us?

Stroke is one of the leading causes of death and the primary source of disability in adults, resulting in neuronal necrosis of ischemic areas, and in possible secondary degeneration of regions surrounding or distant to the initial damaged area. Secondary neurodegeneration (SNDG) following stroke has been shown to have different pathogenetic origins including inflammation, neurovascular response and cytotoxicity, but can be associated also to regenerative processes. Aside from focal neuronal loss, ipsilateral and contralateral effects distal to the lesion site, disruptions of global functional connectivity and a transcallosal diaschisis have been reported in the chronic stages after stroke. Furthermore, SNDG can be observed in different areas not directly connected to the primary lesion, such as thalamus, hippocampus, amygdala, substantia nigra, corpus callosum, bilateral inferior fronto-occipital fasciculus and superior longitudinal fasciculus, which can be highlighted by neuroimaging techniques. Although the clinical relevance of SNDG following stroke has not been well understood, the identification of specific biomarkers that reflect the brain response to the damage, is of paramount importance to investigate in vivo the different phases of stroke. Actually, brain-derived markers, particularly neurofilament light chain, tau protein, S100b, in post-stroke patients have yielded promising results. This review focuses on cerebral morphological modifications occurring after a stroke, on associated cellular and molecular changes and on state-of-the-art of biomarkers in acute and chronic phase. Finally, we discuss new perspectives regarding the implementation of blood-based biomarkers in clinical practice to improve the rehabilitation approaches and post stroke recovery.

Mini review: Current status and perspective of S100B protein as a biomarker in daily clinical practice for diagnosis and prognosticating of clinical outcome in patients with neurological diseases with focus on acute brain injury

Prognosticating the clinical outcome of neurological diseases is essential to guide treatment and facilitate decision-making. It usually depends on clinical and radiological findings. Biomarkers have been suggested to support this process, as they are deemed objective measures and can express the extent of tissue damage or reflect the degree of inflammation. Some of them are specific, and some are not. Few of them, however, reached the stage of daily application in clinical practice. This mini review covers available applications of the S100B protein in prognosticating clinical outcome in patients with various neurological disorders, particularly in those with traumatic brain injury, spontaneous subarachnoid hemorrhage and ischemic stroke. The aim is to provide an understandable picture of the clinical use of the S100B protein and give a brief overview of the current limitations that require future solutions.

Reactive astrogliosis: A friend or foe in the pathogenesis of Alzheimer's disease

Astrocytes are highly efficient homeostatic glial cells playing a crucial role in optimal brain functioning and homeostasis. Astrocytes respond to changes in brain homoeostasis following central nervous system (CNS) injury/diseased state by a specific defence mechanism called reactive astrogliosis. Recent studies have implicated and placed reactive astrogliosis in the centre of pathophysiology of Alzheimer's disease (AD) and other neurodegenerative disorders. The AD biomarker field is evolving rapidly with new findings providing strong evidence which supports the notion that a reactive astrogliosis is an early event in the time course of AD progression which may precede other pathological hallmarks of AD. Clinical/translational in vivo PET and in vitro postmortem brain imaging studies demonstrated 'a first and second wave' of reactive astrogliosis in AD with distinct close-loop relationships with other pathological biomarkers at different stages of the disease. At the end stages, reactive astrocytes are found to be associated, or in proximity, with amyloid plaque and tau pathological deposits in postmortem AD brains. Several new PET-tracers, which are being in pipeline and validated at a very fast pace for mapping and visualising reactive astrogliosis in the brain, will provide further invaluable mechanistic insights into AD and other non-AD dementia pathologies. The complementary roles of microglia and astrocyte activation in AD progression, along with the clinical value of new fluid astrocytes biomarkers in the context of existing biomarkers, are the latest avenue that needs further exploration.

Glial Cell-Mediated Neuroinflammation in Alzheimer’s Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder; it is the most common cause of dementia and has no treatment. It is characterized by two pathological hallmarks, the extracellular deposits of amyloid beta (Aβ) and the intraneuronal deposits of Neurofibrillary tangles (NFTs). Yet, those two hallmarks do not explain the full pathology seen with AD, suggesting the involvement of other mechanisms. Neuroinflammation could offer another explanation for the progression of the disease. This review provides an overview of recent advances on the role of the immune cells’ microglia and astrocytes in neuroinflammation. In AD, microglia and astrocytes become reactive by several mechanisms leading to the release of proinflammatory cytokines that cause further neuronal damage. We then provide updates on neuroinflammation diagnostic markers and investigational therapeutics currently in clinical trials to target neuroinflammation.

Increased Serum NSE and S100B Indicate Neuronal and Glial Alterations in Subjects Under 71 Years With Mild Neurocognitive Disorder/Mild Cognitive Impairment

Background

Mild cognitive impairment (MCI) is considered a pre-stage of different dementia syndromes. Despite diagnostic criteria refined by DSM-5 and a new term for MCI – “mild neurocognitive disorder” (mild NCD) – this diagnosis is still based on clinical criteria.

Methods

To link mild NCD to the underlying pathophysiology we assessed the degree of white matter hyperintensities (WMH) in the brain and peripheral biomarkers for neuronal integrity (neuron-specific enolase, NSE), plasticity (brain-derived neurotrophic factor, BDNF), and glial function (S100B) in 158 community-dwelling subjects with mild NCD and 82 healthy controls. All participants (63–79 years old) were selected from the Leipzig-population-based study of adults (LIFE).

Results

Serum S100B levels were increased in mild NCD in comparison to controls (p = 0.007). Serum NSE levels were also increased but remained non-significant after Bonferroni-Holm correction (p = 0.04). Furthermore, age by group interaction was significant for S100B. In an age-stratified sub-analysis, NSE and S100B were higher in younger subjects with mild NCD below 71 years of age. Some effects were inconsistent after controlling for potentially confounding factors. The discriminatory power of the two biomarkers NSE and S100B was insufficient to establish a pathologic threshold for mild NCD. In subjects with mild NCD, WMH load correlated with serum NSE levels (r = 0.20, p = 0.01), independently of age.

Conclusion

Our findings might indicate the presence of neuronal (NSE) and glial (S100B) injury in mild NCD. Future studies need to investigate whether younger subjects with mild NCD with increased biomarker levels are at risk of developing major NCD.

Development of Alzheimer’s Disease Biomarkers: From CSF- to Blood-Based Biomarkers

In the 115 years since the discovery of Alzheimer’s disease (AD), our knowledge, diagnosis, and therapeutics have significantly improved. Biomarkers are the primary tools for clinical research, diagnostics, and therapeutic monitoring in clinical trials. They provide much insightful information, and while they are not clinically used routinely, they help us to understand the mechanisms of this disease. This review charts the journey of AD biomarker discovery and development from cerebrospinal fluid (CSF) amyloid-beta 1-42 (Aβ42), total tau (T-tau), and phosphorylated tau (p-tau) biomarkers and imaging technologies to the next generation of biomarkers. We also discuss advanced high-sensitivity assay platforms for CSF Aβ42, T-tau, p-tau, and blood analysis. The recently proposed Aβ deposition/tau biomarker/neurodegeneration or neuronal injury (ATN) scheme might facilitate the definition of the biological status underpinning AD and offer a common language among researchers across biochemical biomarkers and imaging. Moreover, we highlight blood-based biomarkers for AD that offer a scalable alternative to CSF biomarkers through cost-saving and reduced invasiveness, and may provide an understanding of disease initiation and development. We discuss different groups of blood-based biomarker candidates, their advantages and limitations, and paths forward, from identification and analysis to clinical validation. The development of valid blood-based biomarkers may facilitate the implementation of future AD therapeutics and diagnostics.

Effects of mobile phone electromagnetic radiation on rat hippocampus proteome

Worldwide, the number of mobile phone users has increased from 5.57 billion in 2011 to 6.8 billion in 2019. However, short- and long-term impact of the electromagnetic radiation emitting from mobile phones on tissue homeostasis with particular to brain proteome composition needs further investigation. In this study, we attempted a global proteome profiling study of rat hippocampus exposed to mobile phone radiation for 20 weeks (for 3 h/day for 5 days/week) to identify deregulated proteins and western blot analysis for validation. As a result, we identified 358 hippocampus proteins, of which 16 showed deregulation (log₂ (exposed/sham) ≥ ±1.0, p-value <.05). Majority of these deregulated proteins grouped into three clusters sharing similar molecular pathways. A set of four proteins (Succinate-semialdehyde dehydrogenase: Aldh5a1, Na⁺ K⁺ transporting ATPase: Atp1b2, plasma membrane calcium transporting ATPase: PMCA and protein S100B) presenting each functional pathway were selected for validation. Western blot analysis of these proteins, in an independent sample set, corroborated the mass spectrometry findings. Aldh5a1 involve in cellular energy metabolism, both Atp1b2 and PMCA responsible for membrane transport and protein S100B have a neuroprotective role. In conclusion, we present a deregulated hippocampus proteome upon mobile phone radiation exposure, which might influence the healthy functioning of the brain.

Old and New Biomarkers for Infection, Inflammation, and Autoimmunity in Treatment-Resistant Affective and Schizophrenic Spectrum Disorders

Affective (AF) and Schizophrenic (SZ) Spectrum disorders manifest with risk factors, involving inflammatory processes linked to infections and autoimmunity. This study searched for novel biomarkers in cerebrospinal fluid (CSF) and peripheral blood. A total of 29 AF and 39 SZ patients with treatment-resistant disease were included. In CSF, the chemokine IL-8 was significantly elevated in AF and SZ patients. IL-8 promotes chemotaxis by neutrophils and may originate from different tissues. S100B, a glia-derived brain damage marker, was higher in CSF from AF than SZ patients. Among the plasma-derived biomarkers, ferritin was elevated in AF and SZ. Soluble CD25, indicating Treg dysfunction, was higher in SZ than in AF patients. Interferon-γ, implying virus-specific immune activation, was positive in selective AF patients, only. Both groups showed elevated expression of immunosuppressive CD33 on monocytes, but higher amounts of CD123+ plasmacytoid dendritic cells were restricted to SZ. In conclusion, chemotactic IL-8 indicates neuronal stress and inflammation in the CSF of both groups. Novel plasma-derived biomarkers such as sCD25 and monocytic CD33 distinguish SZ from AF with an autoimmune phenotype.

Microglia and Astrocyte Function and Communication: What Do We Know in Humans?

Microglia and astrocytes play essential roles in the central nervous system contributing to many functions including homeostasis, immune response, blood–brain barrier maintenance and synaptic support. Evidence has emerged from experimental models of glial communication that microglia and astrocytes influence and coordinate each other and their effects on the brain environment. However, due to the difference in glial cells between humans and rodents, it is essential to confirm the relevance of these findings in human brains. Here, we aim to review the current knowledge on microglia-astrocyte crosstalk in humans, exploring novel methodological techniques used in health and disease conditions. This will include an in-depth look at cell culture and iPSCs, post-mortem studies, imaging and fluid biomarkers, genetics and transcriptomic data. In this review, we will discuss the advantages and limitations of these methods, highlighting the understanding these methods have brought the field on these cells communicative abilities, and the knowledge gaps that remain.

The genetic and epigenetic profile of serum S100β in the Lothian Birth Cohort 1936 and its relationship to Alzheimer’s disease

Background: Circulating S100 calcium-binding protein (S100β) is a marker of brain inflammation that has been associated with a range of neurological conditions. To provide insight into the molecular regulation of S100β and its potential causal associations with Alzheimer’s disease, we carried out genome- and epigenome-wide association studies (GWAS/EWAS) of serum S100β levels in older adults and performed Mendelian randomisation with Alzheimer’s disease. Methods: GWAS (N=769, mean age 72.5 years, sd = 0.7) and EWAS (N=722, mean age 72.5 years, sd = 0.7) of S100β levels were performed in participants from the Lothian Birth Cohort 1936. Conditional and joint analysis (COJO) was used to identify independent loci. Expression quantitative trait locus (eQTL) analyses were performed for lead loci that had genome-wide significant associations with S100β. Bidirectional, two-sample Mendelian randomisation was used to test for causal associations between S100β and Alzheimer’s disease. Colocalisation between S100β and Alzheimer’s disease GWAS loci was also examined. Results: We identified 154 SNPs from chromosome 21 that associated (P<5x10-8) with S100β protein levels. The lead variant was located in the S100β gene (rs8128872, P=5.0x10-17). We found evidence that two independent causal variants existed for both transcription of S100β and S100β protein levels in our eQTL analyses. No CpG sites were associated with S100β levels at the epigenome-wide significant level (P<3.6x10-8); the lead probe was cg06833709 (P=5.8x10-6), which mapped to the LGI1 gene. There was no evidence of a causal association between S100β levels and Alzheimer’s disease or vice versa and no evidence for colocalisation between S100β and Alzheimer’s disease loci. Conclusions: These data provide insight into the molecular regulators of S100β levels. This context may aid in understanding the role of S100β in brain inflammation and neurological disease.

The genetic and epigenetic profile of serum S100β in the Lothian Birth Cohort 1936 and its relationship to Alzheimer's disease

Background: Circulating S100 calcium-binding protein (S100β) is a marker of brain inflammation that has been associated with a range of neurological conditions. To provide insight into the molecular regulation of S100β and its potential causal associations with Alzheimer's disease, we carried out genome- and epigenome-wide association studies (GWAS/EWAS) of serum S100β levels in older adults and performed Mendelian randomisation with Alzheimer's disease. Methods: GWAS (N=769, mean age 72.5 years, sd = 0.7) and EWAS (N=722, mean age 72.5 years, sd = 0.7) of S100β levels were performed in participants from the Lothian Birth Cohort 1936. Conditional and joint analysis (COJO) was used to identify independent loci. Expression quantitative trait locus (eQTL) analyses were performed for lead loci that had genome-wide significant associations with S100β. Bidirectional, two-sample Mendelian randomisation was used to test for causal associations between S100β and Alzheimer's disease. Colocalisation between S100β and Alzheimer's disease GWAS loci was also examined. Results: We identified 154 SNPs from chromosome 21 that associated (P<5x10 ^-8) with S100β protein levels. The lead variant was located in the S100β gene (rs8128872, P=5.0x10 ^-17). We found evidence that two independent causal variants existed for both transcription of S100β and S100β protein levels in our eQTL analyses . No CpG sites were associated with S100β levels at the epigenome-wide significant level (P<3.6x10 ^-8); the lead probe was cg06833709 (P=5.8x10 ^-6), which mapped to the LGI1 gene. There was no evidence of a causal association between S100β levels and Alzheimer's disease or vice versa and no evidence for colocalisation between S100β and Alzheimer's disease loci. Conclusions: These data provide insight into the molecular regulators of S100β levels. This context may aid in understanding the role of S100β in brain inflammation and neurological disease.

S100B dysregulation during brain development affects synaptic SHANK protein networks via alteration of zinc homeostasis

Autism Spectrum Disorders (ASD) are caused by a combination of genetic predisposition and nongenetic factors. Among the nongenetic factors, maternal immune system activation and zinc deficiency have been proposed. Intriguingly, as a genetic factor, copy-number variations in S100B, a pro-inflammatory damage-associated molecular pattern (DAMP), have been associated with ASD, and increased serum S100B has been found in ASD. Interestingly, it has been shown that increased S100B levels affect zinc homeostasis in vitro. Thus, here, we investigated the influence of increased S100B levels in vitro and in vivo during pregnancy in mice regarding zinc availability, the zinc-sensitive SHANK protein networks associated with ASD, and behavioral outcomes. We observed that S100B affects the synaptic SHANK2 and SHANK3 levels in a zinc-dependent manner, especially early in neuronal development. Animals exposed to high S100B levels in utero similarly show reduced levels of free zinc and SHANK2 in the brain. On the behavioral level, these mice display hyperactivity, increased stereotypic and abnormal social behaviors, and cognitive impairment. Pro-inflammatory factors and zinc-signaling alterations converge on the synaptic level revealing a common pathomechanism that may mechanistically explain a large share of ASD cases.

Amyloid-β Processing in Aged S100B Transgenic Mice Is Sex Dependent

(1) Background: Calcium-binding protein S100B is involved in neuroregeneration but has also been associated with neurodegeneration. These contrasting effects may result from concentration or duration of exposure. We investigated the effect of long-term increased S100B levels on amyloid-β processing in one-year-old transgenic (tg) mice with 12 copies of the murine S100B gene with specific consideration of sex and specific brain regions. (2) Methods: S100B and amyloid-β 42 (Aβ42) were quantified in serum, cerebrospinal fluid (CSF), adipose tissue, and different brain regions by ELISA in wild-type (wt) and S100Btg mice (each n = 7 per group). Thioflavin T (ThT) and Aβ immunostaining were performed for visualization of Aβ deposition. (3) Results: S100B in serum, CSF, and brain was significantly increased in S100Btg mice of both sexes. Aβ42 was significantly increased in the hippocampus of male S100Btg mice (p = 0.0075), and the frontal cortex of female S100Btg mice (p = 0.0262). ThT and Aβ immunostaining demonstrated Aβ deposition in different brain regions in S100Btg mice of both sexes and female wt. (4) Conclusion: Our data validate this experimental model for studying the role of S100B in neurodegeneration and indicate that Aβ processing is sex-dependent and brain region-specific, which deserves further investigation of signaling pathways and behavioral responses.

New Frontiers in the Prevention, Diagnosis, and Treatment of Alzheimer's Disease

One of the major puzzles in medical research and public health systems worldwide is Alzheimer's disease (AD), reaching nowadays a prevalence near 50 million people. This is a multifactorial brain disorder characterized by progressive cognitive impairment, apathy, and mood and neuropsychiatric disorders. The main risk of AD is aging; a normal biological process associated with a continuum dynamic involving a gradual loss of people's physical capacities, but with a sound experienced view of life. Studies suggest that AD is a break from normal aging with changes in the powerful functional capacities of neurons as well as in the mechanisms of neuronal protection. In this context, an important path has been opened toward AD prevention considering that there are elements of nutrition, daily exercise, avoidance of toxic substances and drugs, an active social life, meditation, and control of stress, to achieve healthy aging. Here, we analyze the involvement of such factors and how to control environmental risk factors for a better quality of life. Prevention as well as innovative screening programs for early detection of the disease using reliable biomarkers are becoming critical to control the disease. In addition, the failure of traditional pharmacological treatments and search for new drugs has stimulated the emergence of nutraceutical compounds in the context of a "multitarget" therapy, as well as mindfulness approaches shown to be effective in the aging, and applied to the control of AD. An integrated approach involving all these preventive factors combined with novel pharmacological approaches should pave the way for the future control of the disease.

Recent Advancements in Electrochemical Biosensors for Alzheimer's Disease Biomarkers Detection

Background

It is estimated that the average time between the diagnosis of Alzheimer’s disease (AD) and the patient’s death is 5-9 years. Therefore, both the initial phase of the disease and the preclinical state can be included in the critical period in disease diagnosis. Accordingly, huge progress has recently been observed in biomarker research to identify risk factors for dementia in older people with normal cognitive functions and mild cognitive impairments.

Methods

Electrochemical biosensors are excellent analytical tools that are used in the detection of AD biomarkers as they are easy to use, portable, and can do analysis in real time.

Results

This review presents the analytical techniques currently used to determine AD biomarkers in terms of their advantages and disadvantages; the most important clinical biomarkers of AD and their role in the disease. All recently used biorecognition molecules in electrochemical biosensor development, i.e., receptor protein, antibodies, aptamers and nucleic acids, are summarized for the first time. Novel electrochemical biosensors for AD biomarker detection, as ideal analytical platforms for point-of-care diagnostics, are also reviewed.

Conclusion

The article focuses on various strategies of biosensor chemical surface modifications to immobilize biorecognition molecules, enabling specific, quantitative AD biomarker detection in synthetic and clinical samples. In addition, this is the first review that presents innovative single-platform systems for simultaneous detection of multiple biomarkers and other important AD-associated biological species based on electrochemical techniques. The importance of these platforms in disease diagnosis is discussed.

Astrocyte Biomarkers in Alzheimer Disease: A Systematic Review and Meta-analysis

OBJECTIVE

To perform a systematic review and meta-analysis to determine whether fluid and imaging astrocyte biomarkers are altered in Alzheimer disease (AD).

METHODS

PubMed and Web of Science databases were searched for articles reporting fluid or imaging astrocyte biomarkers in AD. Pooled effect sizes were determined with standardized mean differences (SMDs) using the Hedge G method with random effects to determine biomarker performance. Adapted questions from the Quality Assessment of Diagnostic Accuracy Studies were applied for quality assessment. A protocol for this study has been previously registered in PROSPERO (registration number: CRD42020192304).

RESULTS

The initial search identified 1,425 articles. After exclusion criteria were applied, 33 articles (a total of 3,204 individuals) measuring levels of glial fibrillary acidic protein (GFAP), S100B, chitinase-3-like protein 1 (YKL-40), and aquaporin 4 in the blood and CSF, as well as monoamine oxidase-B indexed by PET 11C-deuterium-l-deprenyl, were included. GFAP (SMD 0.94, 95% confidence interval [CI] 0.71-1.18) and YKL-40 (SMD 0.76, 95% CI 0.63-0.89) levels in the CSF and S100B levels in the blood (SMD 2.91, 95% CI 1.01-4.8) were found to be significantly increased in patients with AD.

CONCLUSIONS

Despite significant progress, applications of astrocyte biomarkers in AD remain in their early days. This meta-analysis demonstrated that astrocyte biomarkers are consistently altered in AD and supports further investigation for their inclusion in the AD clinical research framework for observational and interventional studies.

The Impact of High Glucose or Insulin Exposure on S100B Protein Levels, Oxidative and Nitrosative Stress and DNA Damage in Neuron-Like Cells

Alzheimer’s disease (AD) is attracting considerable interest due to its increasing number of cases as a consequence of the aging of the global population. The mainstream concept of AD neuropathology based on pathological changes of amyloid β metabolism and the formation of neurofibrillary tangles is under criticism due to the failure of Aβ-targeting drug trials. Recent findings have shown that AD is a highly complex disease involving a broad range of clinical manifestations as well as cellular and biochemical disturbances. The past decade has seen a renewed importance of metabolic disturbances in disease-relevant early pathology with challenging areas in establishing the role of local micro-fluctuations in glucose concentrations and the impact of insulin on neuronal function. The role of the S100 protein family in this interplay remains unclear and is the aim of this research. Intracellularly the S100B protein has a protective effect on neurons against the toxic effects of glutamate and stimulates neurites outgrowth and neuronal survival. At high concentrations, it can induce apoptosis. The aim of our study was to extend current knowledge of the possible impact of hyper-glycemia and -insulinemia directly on neuronal S100B secretion and comparison to oxidative stress markers such as ROS, NO and DBSs levels. In this paper, we have shown that S100B secretion decreases in neurons cultured in a high-glucose or high-insulin medium, while levels in cell lysates are increased with statistical significance. Our findings demonstrate the strong toxic impact of energetic disturbances on neuronal metabolism and the potential neuroprotective role of S100B protein.

S100B gene polymorphisms are associated with the S100B level and Alzheimer's disease risk by altering the miRNA binding capacity

To examine the role of S100B in genetic susceptibility to Alzheimer’s disease (AD), we conducted a case-control study to analyze four polymorphism loci (rs2839364, rs1051169, rs2300403, and rs9722) of the S100B gene and AD risk. We found an independent increased risk of AD in ApoE ε4(-) subjects carrying the rs9722 AA-genotype (OR = 2.622, 95% CI = 1.399–4.915, P = 0.003). Further investigation revealed the serum S100B levels to be lower in rs9722 GG carriers than in rs9722 AA carriers (P = 0.003). We identified three miRNAs (miR-340-3p, miR-593-3p, miR-6827-3p) in which the seed match region covered locus rs9722. Luciferase assays indicated that the rs9722 G allele has a higher binding affinity to miR-6827-3p than the rs9722 A allele, leading to a significantly decreased fluorescence intensity. Subsequent western blot analysis showed that the S100B protein level of SH-SY5Y cells, which carry the rs9722 G allele, decreased significantly following miR-6827-3p stimulation (P = 0.009). The present study suggests that the rs9722 polymorphism may upregulate the expression of S100B by altering the miRNA binding capacity and may thus increase the AD risk. This finding would be of great help for the early diagnosis of AD.

Short-Term Alterations in Behavior and Astroglial Function After Intracerebroventricular Infusion of Methylglyoxal in Rats

Methylglyoxal (MG) is a by-product of glycolysis. In pathological conditions, particularly diabetes mellitus, this molecule is unbalanced, causing widespread protein glycation. In addition to protein glycation, other effects resulting from high levels of MG in the central nervous system may involve the direct modulation of GABAergic and glutamatergic neurotransmission, with evidence suggesting that the effects of MG may be related to behavioral changes and glial dysfunction. In order to evaluate the direct influence of MG on behavioral and biochemical parameters, we used a high intracerebroventricular final concentration (3 μM/μL) to assess acute effects on memory and locomotor behavior in rats, as well as the underlying alterations in glutamatergic and astroglial parameters. MG induced, 12 h after injection, a decrease in locomotor activity in the Open field and anxiolytic effects in rats submitted to elevated plus-maze. Subsequently, 36 h after surgery, MG injection also induced cognitive impairment in both short and long-term memory, as evaluated by novel object recognition task, and in short-term spatial memory, as evaluated by the Y-maze test. In addition, hippocampal glutamate uptake decreased and glutamine synthetase activity and glutathione levels diminished during seventy-two hours after infusion of MG. Interestingly, the astrocytic protein, S100B, was increased in the cerebrospinal fluid, accompanied by decreased hippocampal S100B mRNA expression, without any change in protein content. Taken together, these results may improve our understanding of how this product of glucose metabolism can induce the brain dysfunction observed in diabetic patients, as well as in other neurodegenerative conditions, and further defines the role of astrocytes in disease and therapeutics.

Emerging role of S100B protein implication in Parkinson's disease pathogenesis

The exact etiology of Parkinson's disease (PD) remains obscure, lacking effective diagnostic and prognostic biomarkers. In search of novel molecular factors that may contribute to PD pathogenesis, emerging evidence highlights the multifunctional role of the calcium-binding protein S100B that is widely expressed in the brain and predominantly in astrocytes. Preclinical evidence points towards the possible time-specific contributing role of S100B in the pathogenesis of neurodegenerative disorders including PD, mainly by regulating neuroinflammation and dopamine metabolism. Although existing clinical evidence presents some contradictions, estimation of S100B in the serum and cerebrospinal fluid seems to hold a great promise as a potential PD biomarker, particularly regarding the severity of motor and non-motor PD symptoms. Furthermore, given the recent development of S100B inhibitors that are able to cross the blood brain barrier, novel opportunities are arising in the research field of PD therapeutics. In this review, we provide an update on recent advances in the implication of S100B protein in the pathogenesis of PD and discuss relevant studies investigating the biomarker potential of S100B in PD, aiming to shed more light on clinical targeting approaches related to this incurable disorder.

Association of Cerebrospinal Fluid S100B Protein with Core Biomarkers and Cognitive Deficits in Prodromal and Mild Alzheimer's Disease

BACKGROUND

Increased expression of the astroglial Ca2+-binding protein S100B has been observed in various neurodegenerative diseases and also seems to play a role in the unfolding of pathophysiological events at early stages of Alzheimer's disease (AD).

OBJECTIVE

To examine the association of cerebrospinal fluid (CSF) levels of S100B with 1) established CSF core biomarkers total tau (tau), hyperphosphorylated tau (p-tau), and amyloid β1-42 (Aβ1-42) as well as neuron-specific enolase (NSE) CSF levels and 2) cognition in early AD and mild cognitive impairment (MCI) due to AD (MCI-AD).

METHODS

Retrospective study assessing 49 pooled charts of Memory Clinic and inpatients diagnosed with AD (N = 26) and MCI-AD (N = 23) according to the National Institute of Aging and Alzheimer's Disease Association (NIA-AA) criteria. Neuropsychological testing was performed with the Consortium to Establish a Registry for AD (CERAD)-Plus battery.

RESULTS

CSF levels of S100B correlated with NSE, but not the other CSF parameters. Stepwise multiple linear regression, adjusted for age, sex, and educational level, revealed that only increased CSF S100B was independently associated with lower CERAD-Plus total and Mini-Mental Status Examination scores together with poorer performance in wordlist learning (delayed recall and overall performance). We found no independent associations with other CSF biomarkers or cognitive domains.

CONCLUSION

Our data suggest that CSF S100B may have a diagnostic value particularly at early stages of AD reflecting the significance of neuroinflammatory/astroglial processes. Thus, CSF S100B may complement the established array of available AD biomarkers to improve early stage diagnosis.

Impact of routine S100B protein assay on CT scan use in children with mild traumatic brain injury

OBJECTIVES

To evaluate the impact of implementing a modified Pediatric Emergency Care Applied Research Network (PECARN) rule including the S100B protein assay for managing mild traumatic brain injury (mTBI) in children.

METHODS

A before-and-after study was conducted in a paediatric emergency department of a French University Hospital from 2013 to 2015. We retrospectively included all consecutive children aged 4 months to 15 years who presented mTBI and were at intermediate risk for clinically important traumatic brain injury (ciTBI). We compared the proportions of CT scans performed and of in-hospital observations before (2013-2014) and after (2014-2015) implementation of a modified PECARN rule including the S100B protein assay.

RESULTS

We included 1,062 children with mTBI (median age 4.5 years, sex ratio [F/M] 0.73) who were at intermediate risk for ciTBI: 494 (46.5%) during 2013-2014 and 568 (53.5%) during 2014-2015. During 2014-2015, S100B protein was measured in 451 (79.4%) children within 6 h after mTBI. The proportion of CT scans and in-hospital observations significantly decreased between the two periods, from 14.4 to 9.5% (p=0.02) and 73.9-40.5% (p<0.01), respectively. The number of CT scans performed to identify a single ciTBI was reduced by two-thirds, from 18 to 6 CT scans, between 2013-2014 and 2014-2015. All children with ciTBI were identified by the rules.

CONCLUSIONS

The implementation of a modified PECARN rule including the S100B protein assay significantly decreased the proportion of CT scans and in-hospital observations for children with mTBI who were at intermediate risk for ciTBI.

Cerebrospinal Fluid YKL-40 and Chitotriosidase Levels in Frontotemporal Dementia Vary by Clinical, Genetic and Pathological Subtype

BACKGROUND

Chronic glial dysfunction may contribute to the pathogenesis of frontotemporal dementia (FTD). Cerebrospinal fluid (CSF) levels of glia-derived proteins YKL-40 and chitotriosidase are increased in Alzheimer's disease (AD) but have not been explored in detail across the spectrum of FTD.

METHODS

We investigated whether CSF YKL-40 and chitotriosidase levels differed between FTD patients and controls, across different clinical and genetic subtypes of FTD, and between individuals with a clinical FTD syndrome due to AD versus non-AD (frontotemporal lobar degeneration, FTLD) pathology (based on CSF neurodegenerative biomarkers). Eighteen healthy controls and 64 people with FTD (behavioural variant FTD, n = 20; primary progressive aphasia [PPA], n = 44: nfvPPA, n = 16, svPPA, n = 11, lvPPA, n = 14, PPA-NOS, n = 3) were included. 10/64 had familial FTD, with mutations in GRN(n = 3), MAPT(n = 4), or C9orf72 (n = 3). 15/64 had neurodegenerative biomarkers consistent with AD pathology. Levels were measured by immunoassay and compared using multiple linear regressions. We also examined relationships of YKL-40 and chitotriosidase with CSF total tau (T-tau), phosphorylated tau 181 (P-tau) and β-amyloid 1-42 (Aβ42), with each other, and with age and disease du-ration.

RESULTS

CSF YKL-40 and chitotriosidase levels were higher in FTD, particularly lvPPA (both) and nfvPPA (YKL-40), compared with controls. GRN mutation carriers had higher levels of both proteins than controls and C9orf72 expansion carriers, and YKL-40 was higher in MAPT mutation carriers than controls. Individuals with underlying AD pathology had higher YKL-40 and chitotriosidase levels than both controls and those with likely FTLD pathology. CSF YKL-40 and chitotriosidase levels were variably associated with levels of T-tau, P-tau and Aβ42, and with each other, depending on clinical syndrome and underlying pathology. CSF YKL-40 but not chitotriosidase was associated with age, but not disease duration.

CONCLUSION

CSF YKL-40 and chitotriosidase levels are increased in individuals with clinical FTD syndromes, particularly due to AD pathology. In a preliminary analysis of genetic groups, levels of both proteins are found to be highly elevated in FTD due to GRN mutations, while YKL-40 is increased in individuals with MAPT mutations. As glia-derived protein levels generally correlate with T-tau and P-tau levels, they may reflect the glial response to neurodegeneration in FTLD.

The role of innate immunity in Alzheimer's disease

The amyloid hypothesis has dominated Alzheimer's disease (AD) research for almost 30 years. This hypothesis hinges on the predominant clinical role of the amyloid beta (Aβ) peptide in propagating neurofibrillary tangles (NFTs) and eventual cognitive impairment in AD. Recent research in the AD field has identified the brain-resident macrophages, known as microglia, and their receptors as integral regulators of both the initiation and propagation of inflammation, Aβ accumulation, neuronal loss, and memory decline in AD. Emerging studies have also begun to reveal critical roles for distinct innate immune pathways in AD pathogenesis, which has led to great interest in harnessing the innate immune response as a therapeutic strategy to treat AD. In this review, we will highlight recent advancements in our understanding of innate immunity and inflammation in AD onset and progression. Additionally, there has been mounting evidence suggesting pivotal contributions of environmental factors and lifestyle choices in AD pathogenesis. Therefore, we will also discuss recent findings, suggesting that many of these AD risk factors influence AD progression via modulation of microglia and immune responses.

Increased Cerebrospinal Fluid S100B and NSE Reflect Neuronal and Glial Damage in Parkinson's Disease

Introduction: The diagnosis of Parkinson’s disease (PD) mainly relies on clinical manifestation, but may be difficult to make in very early stages of the disease, especially in pre-motor PD. Thus, there is great interest in finding a biomarker for PD. Among diagnostic biomarkers, the most promising molecules are those which reflect the pathophysiological mechanisms of the disease. Until now, only α-synuclein, a classical CSF Alzheimer’s disease biomarker, and neurofilament light (NFL) chains have turned out to be helpful in differential diagnosis between PD and healthy control subjects.

Aim: To assess whether CSF molecules related to some pathological processes present in PD might be of interest in the diagnosis of PD and whether they correlate with disease severity.

Methods: CSF levels of S100B and neuron-specific enolase (NSE) were measured in 58 PD patients and in 28 healthy control subjects. Correlations were determined between the levels of these CSF molecules and measures of disease severity (Hoehn–Yahr scale and UPDRS part III), as well as disease duration and levodopa dose.

Results: CSF S100B and CSF NSE were both significantly increased in PD subjects vs. healthy controls (p = 0.007 and p = 0.00035, respectively). CSF S100B was significantly positively correlated with measures of disease severity (H-Y score and UPDRS part III), as well as disease duration (p < 0.05). No correlation was found between CSF NSE levels and disease severity or disease duration (p > 0.05). CSF S100B levels alone provided a relatively high discrimination (AUC 0.77) between PD and healthy controls, with 60.7% sensitivity and 88.5% specificity (p < 0.001) at a cut-off value of 123.22 pg/ml. Similarly, CSF NSE levels alone provided a relatively high discrimination (AUC 0.775) between PD and healthy controls, with 78.6% sensitivity and 74.1% specificity at a cut-off value of 51.56 ng/ml (p < 0.001).

Conclusions: Our results show that both CSF S100B and CSF NSE seem to be promising markers of the axonal and glial degeneration present in PD. Additionally CSF S100B may be a promising marker of PD progression.

Cerebrospinal fluid myelin basic protein is elevated in multiple system atrophy

INTRODUCTION

Parkinson's disease (PD) and multiple system atrophy (MSA) have overlapping symptoms, challenging an early diagnosis. Diagnostic accuracy is important because PD and MSA have a different prognosis and response to treatment. Here, we aimed to evaluate the diagnostic value of brain-specific structural proteins in cerebrospinal fluid (CSF) of PD and MSA patients, as well as their association with cognitive decline.

METHODS

CSF samples were collected from patients with clear signs of parkinsonism, but with uncertain diagnosis at the time of inclusion. Clinical diagnoses of PD (n = 55) and MSA (n = 22) were established after 3 and 10 years of follow-up and re-evaluated after 12 years, according to the most updated clinical criteria. CSF from controls (n = 118) was studied for comparison. Neuron-specific enolase (NSE), glial fibrillary acidic protein (GFAP), S100 calcium-binding protein B (S100B) and myelin basic protein (MBP) levels in CSF were measured using ELISA. Protein levels were also correlated with cognitive decline, i.e. worsening of the mini mental state examination (MMSE) over a period of three years.

RESULTS

MBP concentrations were increased in MSA compared to PD and controls (p < 0.005) and could differentiate MSA and PD with high accuracy (AUC = 0.781; p < 0.001). Concentrations of MPB, GFAP and S100B, but not NSE, were significantly elevated in PD patients compared to controls (p = 0.05). None of the brain-specific structural proteins correlated with MMSE progression.

CONCLUSIONS

Our results demonstrate that MBP differentiates PD from MSA at early stages of the disease, indicating that demyelination and axonal damage may already occur in early stages of MSA.

Cerebrospinal fluid markers analysis in the differential diagnosis of dementia with Lewy bodies and Parkinson's disease dementia

Dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD) share a couple of clinical similarities that is often a source of diagnostic pitfalls. We evaluated the discriminatory potential of brain-derived CSF markers [tau, p-tau (181P), Aβ_1-42, NSE and S100B] across the spectrum of Lewy body disorders and assessed whether particular markers are associated with cognitive status in investigated patients. The tau CSF level, amyloid β_1-42 and p-tau/tau ratio were helpful in the distinction between DLB and PDD (p = 0.04, p = 0.002 and p = 0.02, respectively) as well as from PD patients (p < 0.001, p = 0.001 and p = 0.002, respectively). Furthermore, the p-tau/tau ratio enabled the differentiation of DLB with mild dementia from PDD patients (p = 0.02). The CSF tau and p-tau levels in DLB and CSF tau and p-tau/tau ratio in PDD patients reflected the severity of dementia. Rapid disease course was associated with the decrease of Aβ_1-42 in DLB but not in PDD. Elevation of S100B in DLB (p < 0.0001) as well as in PDD patients (p = 0.002) in comparison to controls was estimated. Hence, with the appropriate clinical context; the CSF marker profile could be helpful in distinguishing DLB from PDD patients even in early stages of dementia.

The Interplay between Diabetes and Alzheimer's Disease-In the Hunt for Biomarkers

The brain is an organ in which energy metabolism occurs most intensively and glucose is an essential and dominant energy substrate. There have been many studies in recent years suggesting a close relationship between type 2 diabetes mellitus (T2DM) and Alzheimer’s disease (AD) as they have many pathophysiological features in common. The condition of hyperglycemia exposes brain cells to the detrimental effects of glucose, increasing protein glycation and is the cause of different non-psychiatric complications. Numerous observational studies show that not only hyperglycemia but also blood glucose levels near lower fasting limits (72 to 99 mg/dL) increase the incidence of AD, regardless of whether T2DM will develop in the future. As the comorbidity of these diseases and earlier development of AD in T2DM sufferers exist, new AD biomarkers are being sought for etiopathogenetic changes associated with early neurodegenerative processes as a result of carbohydrate disorders. The S100B protein seem to be interesting in this respect as it may be a potential candidate, especially important in early diagnostics of these diseases, given that it plays a role in both carbohydrate metabolism disorders and neurodegenerative processes. It is therefore necessary to clarify the relationship between the concentration of the S100B protein and glucose and insulin levels. This paper draws attention to a valuable research objective that may in the future contribute to a better diagnosis of early neurodegenerative changes, in particular in subjects with T2DM and may be a good basis for planning experiments related to this issue as well as a more detailed explanation of the relationship between the neuropathological disturbances and changes of glucose and insulin concentrations in the brain.

Levels of serum S100B are associated with cognitive dysfunction in patients with type 2 diabetes

Objective: Previous studies have provided robust evidence that cognitive impairment exists in patients with type 2 diabetes. The predictive role of S100B in a variety of neurodegenerative diseases such as Alzheimer’s disease, has been shown to be closely related to cognitive function. The purpose of this study was to investigate the correlation between serum S100B levels and cognitive function in type 2 diabetes patients.

Results: The type 2 diabetes group scored lower than the healthy control group in all domains of cognitive function except language and attention, and the former group also had lower serum levels of S100B. Besides, serum S100B levels were lower in the type 2 diabetes patients with impaired cognition than in those with normal cognition. In addition, the moderate to severe cognitive impairment group had significantly lower levels than that in mild cognitive impairment group. After adjusting for confounding factors, serum S100B levels were positively correlated with cognitive function in type 2 diabetes patients.

Conclusions: Serum S100B levels were positively correlated with cognitive function in type 2 diabetes patients with cognitive impairment. It is suggested that S100B may be involved in the occurrence and development of cognitive dysfunction in type 2 diabetes patients and play a protective role.

Methods: The clinical data and biochemical indexes of ninety-six patients with type 2 diabetes and sixty-eight healthy subjects were collected. The levels of serum S100B were detected by enzyme-linked immunosorbent assay. Ninety-six type 2 diabetes patients were divided into a cognitive dysfunction group and a normal cognition group according to Mini-mental State Examination scores. To better understand the differences in various aspects of cognition, we used the Repeatable Battery for the Assessment of Neuropsychological Status scale for further evaluation. To study the relationship between serum S100B levels and cognitive impairment, the cognitive dysfunction group was divided into a mild cognitive impairment group and a moderate to severe cognitive impairment group for further study.

Early and reversible changes to the hippocampal proteome in mice on a high-fat diet

Background

The rise in global obesity makes it crucial to understand how diet drives obesity-related health conditions, such as premature cognitive decline and Alzheimer's disease (AD). In AD hippocampal-dependent episodic memory is one of the first types of memory to be impaired. Previous studies have shown that in mice fed a high-fat diet (HFD) episodic memory is rapidly but reversibly impaired.

Methods

In this study we use hippocampal proteomics to investigate the effects of HFD in the hippocampus. Mice were fed either a low-fat diet (LFD) or HFD containing either 10% or 60% (Kcal) from fat for 3 days, 1 week or 2 weeks. One group of mice were fed the HFD for 1 week and then returned to the LFD for a further week. Primary hippocampal cultures were challenged with palmitic acid (PA), the most common long-chain saturated FA in the Western diet, and with the anti-inflammatory, n-3 polyunsaturated FA, docosahexaenoic acid (DHA), or a combination of the two to ascertain effects of these fatty acids on dendritic structure.

Results

HFD-induced changes occur in hippocampal proteins involved in metabolism, inflammation, cell stress, cell signalling, and the cytoskeleton after 3 days, 1 week and 2 weeks of HFD. Replacement of the HFD after 1 week by a low-fat diet (LFD) for a further week resulted in partial recovery of the hippocampal proteome. Microtubule-associated protein 2 (MAP2), one of the earliest proteins changed, was used to investigate the impact of fatty acids (FAs) on hippocampal neuronal morphology. PA challenge resulted in shorter and less arborised dendrites while DHA had no effect when applied alone but counteracted the effects of PA when FAs were used in combination. Dendritic morphology recovered when PA was removed from the cell culture media.

Conclusion

This study provides evidence for the rapid and reversible effects of diet on the hippocampal proteome and the impact of PA and DHA on dendritic structure.

Distribution and Relative Abundance of S100 Proteins in the Brain of the APP23 Alzheimer's Disease Model Mice

Increasing evidence links proteins of the S100 family to the pathogenesis of Alzheimer's disease (AD). S100 proteins are EF-hand calcium-binding proteins with intra- and extracellular functions related to regulation of proliferation, differentiation, apoptosis, and trace metal homeostasis, and are important modulators of inflammatory responses. For example, S100A6, S100A8, and S100B expression levels were found increased in inflammatory diseases, but also neurodegenerative disorders, and S100A8/A9 complexes may provide a mechanistic link between amyloid-beta (Aβ) plaque formation and neuroinflammation. On the other hand, S100B, a proinflammatory protein that is chronically up-regulated in AD and whose elevation precedes plaque formation, was recently shown to suppress Aβ aggregation. Here, we report expression of S100A6 and S100B in astrocytes and less so in neurons, and low level of expression of S100A8 in both neurons and glial cells in vitro. In vivo, S100A8 expression is almost absent in the brain of aged wildtype mice, while S100A6 and S100B are expressed in all brain regions and most prominently in the cortex and cerebellum. S100B seems to be enriched in Purkinje cells of the cerebellum. In contrast, in the brain of APP23 mice, a mouse model for Alzheimer's disease, S100B, S100A6, and S100A8 show co-localization with Aβ plaques, compatible with astrocyte activation, and the expression level of S100A8 is increased in neural cells. While S100A6 and S100B are enriched in the periphery of plaques where less fibrillar Aβ is found, S100A8 is more intense within the center of the inclusion. In vitro assays show that, similarly to S100B, S100A6, and S100A8 also delay Aβ aggregation suggesting a regulatory action over protein aggregation. We posit that elevated expression levels and overlapping spatial distribution of brain S100 proteins and plaques translates functional relationships between these inflammatory mediators and AD pathophysiology processes that uncover important molecular mechanisms linking the aggregation and neuroinflammation cascades.

S100 Proteins in Alzheimer's Disease

S100 proteins are calcium-binding proteins that regulate several processes associated with Alzheimer's disease (AD) but whose contribution and direct involvement in disease pathophysiology remains to be fully established. Due to neuroinflammation in AD patients, the levels of several S100 proteins are increased in the brain and some S100s play roles related to the processing of the amyloid precursor protein, regulation of amyloid beta peptide (Aβ) levels and Tau phosphorylation. S100 proteins are found associated with protein inclusions, either within plaques or as isolated S100-positive puncta, which suggests an active role in the formation of amyloid aggregates. Indeed, interactions between S100 proteins and aggregating Aβ indicate regulatory roles over the aggregation process, which may either delay or aggravate aggregation, depending on disease stage and relative S100 and Aβ levels. Additionally, S100s are also known to influence AD-related signaling pathways and levels of other cytokines. Recent evidence also suggests that metal-ligation by S100 proteins influences trace metal homeostasis in the brain, particularly of zinc, which is also a major deregulated process in AD. Altogether, this evidence strongly suggests a role of S100 proteins as key players in several AD-linked physiopathological processes, which we discuss in this review.

AGE-RAGE stress: a changing landscape in pathology and treatment of Alzheimer's disease

Numerous hypotheses including amyloid cascade, cholinergic, and oxidative have been proposed for pathogenesis of Alzheimer's disease (AD). The data suggest that advanced glycation end products (AGEs) and its receptor RAGE (receptor for AGE) are involved in the pathogenesis of AD. AGE-RAGE stress, defined as a balance between stressors (AGE, RAGE) and anti-stressors (sRAGE, AGE degraders) in favor of stressors, has been implicated in pathogenesis of diseases. AGE and its interaction with RAGE-mediated increase in the reactive oxygen species (ROS) damage brain because of its increased vulnerability to ROS. AGE and ROS increase the synthesis of amyloid β (Aβ) leading to deposition of Aβ and phosphorylation of tau, culminating in formation of plaques and neurofibrillary tangles. ROS increase the synthesis of Aβ, high-mobility group box 1(HMGB1), and S100 that interacts with RAGE to produce additional ROS resulting in enhancement of AD pathology. Elevation of ROS precedes the Aβ plaques formation. Because of involvement of AGE and RAGE in AD pathology, the treatment should be targeted at lowering AGE levels through reduction in consumption and formation of AGE, and lowering expression of RAGE, blocking of RAGE ligand binding, increasing levels of soluble RAGE (sRAGE), and use of antioxidants. The above treatment aspect of AD is lacking. In conclusion, AGE-RAGE stress initiates, and Aβ, HMGB1, and S100 enhance the progression of AD. Reduction of levels of AGE and RAGE, elevation of sRAGE, and antioxidants would be beneficial therapeutic modalities in the prevention, regression, and slowing of progression of AD.

Astrocyte Biomarkers in Alzheimer's Disease

Astrocytic contributions to Alzheimer's disease (AD) progression were, until recently, largely overlooked. Astrocytes are integral to normal brain function and astrocyte reactivity is an early feature of AD, potentially providing a promising target for preclinical diagnosis and treatment. Several in vivo AD biomarkers already exist, but presently there is a paucity of specific and sensitive in vivo astrocyte biomarkers that can accurately measure preclinical AD. Measuring monoamine oxidase-B with neuroimaging and glial fibrillary acidic protein from bodily fluids are biomarkers that are currently available. Developing novel, more specific, and sensitive astrocyte biomarkers will make it possible to pharmaceutically target chemical pathways that preserve beneficial astrocytic functions in response to AD pathology. This review discusses astrocyte biomarkers in the context of AD.

Clinical Use of the Calcium-Binding S100B Protein, a Biomarker for Head Injury

S100B is a calcium-binding protein most abundant in neuronal tissue. It is expressed in glial cells and Schwann cells and exerts both intra- and extracellular effects. Depending on the concentration, secreted S100B exerts either trophic or toxic effects. Its functions have been extensively studied but are still not fully understood. It can be measured in cerebrospinal fluid and in blood, and increased S100B level in blood can be seen after, e.g., traumatic brain injury, certain neurodegenerative disorders, and malignant melanoma. This chapter provides a short background of protein S100B, commercially available methods of analysis, and its clinical use, especially as a biomarker in minor head injury.

Longitudinal serum S100β and brain aging in the Lothian Birth Cohort 1936

Elevated serum and cerebrospinal fluid concentrations of S100β, a protein predominantly found in glia, are associated with intracranial injury and neurodegeneration, although concentrations are also influenced by several other factors. The longitudinal association between serum S100β concentrations and brain health in nonpathological aging is unknown. In a large group (baseline N = 593; longitudinal N = 414) of community-dwelling older adults at ages 73 and 76 years, we examined cross-sectional and parallel longitudinal changes between serum S100β and brain MRI parameters: white matter hyperintensities, perivascular space visibility, white matter fractional anisotropy and mean diffusivity (MD), global atrophy, and gray matter volume. Using bivariate change score structural equation models, correcting for age, sex, diabetes, and hypertension, higher S100β was cross-sectionally associated with poorer general fractional anisotropy (r = -0.150, p = 0.001), which was strongest in the anterior thalamic (r = -0.155, p < 0.001) and cingulum bundles (r = -0.111, p = 0.005), and survived false discovery rate correction. Longitudinally, there were no significant associations between changes in brain imaging parameters and S100β after false discovery rate correction. These data provide some weak evidence that S100β may be an informative biomarker of brain white matter aging.

Early and Persistent O-GlcNAc Protein Modification in the Streptozotocin Model of Alzheimer's Disease

 O-GlcNAc transferase (OGT), an enzyme highly expressed in brain tissue, catalyzes the addition of N-acetyl-glucosamine (GlcNAc) to hydroxyl residues of serine and threonine of proteins. Brain protein O-GlcNAcylation is diminished in Alzheimer's disease (AD), and OGT targets include proteins of the insulin-signaling pathway (e.g., insulin receptor susbtrate-1, IRS-1). We hypothesized that ICV streptozotocin (STZ) also affects O-GlcNAc protein modification. We investigated hippocampal metabolic changes in Wistar rats, particularly OGT levels and insulin resistance, as well as related astroglial activities, immediately after ICV STZ administration (first week) and later on (fourth week). We found an early (at one week) and persistent (at fourth week) decrease in OGT in the ICV STZ model of AD, characterized by a spatial cognitive deficit. Consistent with this observation, we observed a decrease in protein O-GlnNAc modification at both times. Increased phosphorylation at serine-307 of IRS-1, which is related to insulin resistance, was observed on the fourth week. The decrease in OGT and consequent protein O-GlnNAc modifications appear to precede the decrease in glucose uptake and increment of the glyoxalase system observed in the hippocampus. Changes in glial fibrillary acidic protein and S100B in the hippocampus, as well as the alterations in cerebrospinal fluid S100B, confirm the astrogliosis. Moreover, decreases in glutamine synthetase and glutathione content suggest astroglial dysfunction, which are likely implicated in the neurodegenerative cascade triggered in this model. Together, these data contribute to the understanding of neurochemical changes in the ICV STZ model of sporadic AD, and may explain the decreases in protein O-GlcNAc levels and insulin resistance observed in AD.

Proteome profiling in the hippocampus, medial prefrontal cortex, and striatum of aging rat

Decrease in multiple functions occurs in the brain with aging, all of which can contribute to age-related cognitive and locomotor impairments. Brain atrophy specifically in hippocampus, medial prefrontal cortex (mPFC), and striatum, can contribute to this age-associated decline in function. Our recent metabolomics analysis showed age-related changes in these brain regions. To further understand the aging processes, analysis using a proteomics approach was carried out. This study was conducted to identify proteome profiles in the hippocampus, mPFC, and striatum of 14-, 18-, 23-, and 27-month-old rats. Proteomics analysis using ultrahigh performance liquid chromatography coupled with Q Exactive HF Orbitrap mass spectrometry identified 1074 proteins in the hippocampus, 871 proteins in the mPFC, and 241 proteins in the striatum. Of these proteins, 97 in the hippocampus, 25 in mPFC, and 5 in striatum were differentially expressed with age. The altered proteins were classified into three ontologies (cellular component, molecular function, and biological process) containing 44, 38, and 35 functional groups in the hippocampus, mPFC, and striatum, respectively. Most of these altered proteins participate in oxidative phosphorylation (e.g. cytochrome c oxidase and ATP synthase), glutathione metabolism (e.g. peroxiredoxins), or calcium signaling pathway (e.g. protein S100B and calmodulin). The most prominent changes were observed in the oldest animals. These results suggest that alterations in oxidative phosphorylation, glutathione metabolism, and calcium signaling pathway are involved in cognitive and locomotor impairments in aging.

Intérêt clinique des concentrations sériques de la protéine S100β dans l’évaluation des patients traumatisés crâniens

Les recommandations de la Société française de médecine d’urgence concernant la prise en charge des patients traumatisés crâniens légers ont été éditées en 2012, complétées par des recommandations sur la bonne utilisation du biomarqueur S100β deux ans plus tard. Grâce à son excellente valeur prédictive négative, la protéine S100β utilisée à travers des règles strictes de prescription a été définie comme une alternative solide à la tomodensitométrie. Cependant, plusieurs questions restent en suspens concernant le délai maximum de réalisation du prélèvement par rapport à l’heure du traumatisme, l’impact médicoéconomique, les variations en rapport avec l’âge du patient, l’impact des agents anticoagulants ou antiagrégants plaquettaires et l’utilité du dosage sérique de cette protéine dans d’autres cadres nosologiques.