Cerebrospinal fluid and blood biomarkers in Alzheimer’s disease

Predicting the diagnosis of various mental disorders in a mixed cohort using blood-based multi-protein model: a machine learning approach

The lack of objective diagnostic methods for mental disorders challenges the reliability of diagnosis. The study aimed to develop an easily accessible and useable objective method for diagnosing major depressive disorder (MDD), schizophrenia (SZ), bipolar disorder (BPD), and panic disorder (PD) using serum multi-protein. Serum levels of brain-derived neurotrophic factor (BDNF), VGF (non-acronymic), bicaudal C homolog 1 (BICC1), C-reactive protein (CRP), and cortisol, which are generally recognized to be involved in different pathogenesis of various mental disorders, were measured in patients with MDD (n = 50), SZ (n = 50), BPD (n = 55), and PD along with 50 healthy controls (HC). Linear discriminant analysis (LDA) was employed to construct a multi-classification model to classify these mental disorders. Both leave-one-out cross-validation (LOOCV) and fivefold cross-validation were applied to validate the accuracy and stability of the LDA model. All five serum proteins were included in the LDA model, and it was found to display a high overall accuracy of 96.9% when classifying MDD, SZ, BPD, PD, and HC groups. Multi-classification accuracy of the LDA model for LOOCV and fivefold cross-validation (within-study replication) reached 96.9 and 96.5%, respectively, demonstrating the feasibility of the blood-based multi-protein LDA model for classifying common mental disorders in a mixed cohort. The results suggest that combining multiple proteins associated with different pathogeneses of mental disorders using LDA may be a novel and relatively objective method for classifying mental disorders. Clinicians should consider combining multiple serum proteins to diagnose mental disorders objectively.

The association of obstructive sleep apnea with blood and cerebrospinal fluid biomarkers of Alzheimer's dementia - A systematic review and meta-analysis

Alzheimer's disease (AD) is the most common type of dementia and is characterized by the aggregation of extracellular amyloid-beta and intracellular hyperphosphorylation of tau proteins. Obstructive Sleep Apnea (OSA) is associated with increased AD risk. We hypothesize that OSA is associated with higher levels of AD biomarkers. The study aims to conduct a systematic review and meta-analysis of the association between OSA and levels of blood and cerebrospinal fluid biomarkers of AD. Two authors independently searched PubMed, Embase, and Cochrane Library for studies comparing blood and cerebrospinal fluid levels of dementia biomarkers between patients with OSA and healthy controls. Meta-analyses of the standardized mean difference were conducted using random-effects models. From 18 studies with 2804 patients, meta-analysis found that cerebrospinal fluid amyloid beta-40 (SMD:-1.13, 95%CI:-1.65 to -0.60), blood total amyloid beta (SMD:0.68, 95%CI: 0.40 to 0.96), blood amyloid beta-40 (SMD:0.60, 95%CI: 0.35 to 0.85), blood amyloid beta-42 (SMD:0.80, 95%CI: 0.38 to 1.23) and blood total-tau (SMD: 0.664, 95% CI: 0.257 to 1.072, I² = 82, p<0.01, 7 studies) were significantly higher in OSA patients compared with healthy controls. These findings suggest that OSA is associated with an elevation of some biomarkers of AD.

MicroRNA super-resolution imaging in blood for Alzheimer's disease

We propose a novel blood biomarker detection method that uses miRNA super-resolution imaging to enable the early diagnosis of Alzheimer's disease (AD). Here, we report a singlemolecule detection method for visualizing disease-specific miRNA in tissue from an AD mice model, and peripheral blood mononuclear cells (PBMCs) from AD patients. Using optimized Magnified Analysis of Proteome (MAPs), we confirmed that five miRNAs contribute to neurodegenerative disease in the brain hippocampi of 5XFAD and wild-type mice. We also assessed PBMCs isolated from the whole blood of AD patients and a healthy control group, and subsequently analyzed those samples using miRNA super-resolution imaging. We detected more miR-200a-3p expression in the cornu ammonis 1 and dentate gyrus regions of 3 month-old 5XFAD mice than in wild-type mice. Additionally, miRNA super-resolution imaging of blood provides AD diagnosis platform for studying miRNA regulation inside cells at the single molecule level. Our results present a potential liquid biopsy method that could improve the diagnosis of early stage AD and other diseases. [BMB Reports 2023; 56(3): 190-195].

Synaptic degeneration in Alzheimer disease

Alzheimer disease (AD) is characterized by progressive cognitive decline in older individuals accompanied by the presence of two pathological protein aggregates - amyloid-β and phosphorylated tau - in the brain. The disease results in brain atrophy caused by neuronal loss and synapse degeneration. Synaptic loss strongly correlates with cognitive decline in both humans and animal models of AD. Indeed, evidence suggests that soluble forms of amyloid-β and tau can cause synaptotoxicity and spread through neural circuits. These pathological changes are accompanied by an altered phenotype in the glial cells of the brain - one hypothesis is that glia excessively ingest synapses and modulate the trans-synaptic spread of pathology. To date, effective therapies for the treatment or prevention of AD are lacking, but understanding how synaptic degeneration occurs will be essential for the development of new interventions. Here, we highlight the mechanisms through which synapses degenerate in the AD brain, and discuss key questions that still need to be answered. We also cover the ways in which our understanding of the mechanisms of synaptic degeneration is leading to new therapeutic approaches for AD.

Recent advances in understanding depressive disorder: Possible relevance to brain stimulation therapies

Recent research has provided novel insights into the major depressive disorder (MDD) and identified certain biomarkers of this disease. There are four main mechanisms playing a key role in the related pathophysiology, namely (1) monoamine systems dysfunction, (2) stress response, (3) neuroinflammation, and (4) neurotrophic factors alteration. Robust evidence on the decreased homovanillic acid in the cerebrospinal fluid (CSF) of patients with MDD supports a rationale for therapeutic stimulation of the medial forebrain bundle activating the dopamine reward system. Both activation and suppression of the hypothalamic-pituitary-adrenal (HPA) axis in MDD and related conditions indicate usefulness of its evaluation for the disease subtyping. Elevated proinflammatory cytokines (specifically, interleukin-6) in CSF imply the role of neuroinflammation resulting in activation of the tryptophan-kynurenine pathway. Finally, neuroplasticity and trophic effects of the brain-derived neurotrophic factor (BDNF) may be related to both structural abnormalities of the brain in MDD and the underlying mechanisms of various therapies. In addition, the gut-brain interaction is pivotal, since lack of beneficial microbes confer the risk of MDD through negative effects on the dopamine system, HPA axis, and vagal nerve. All these factors may be highly relevant to treatment of MDD with contemporary brain stimulation therapies.

Axonal plasma membrane-mediated toxicity of cholesterol in Alzheimer's disease: A microsecond molecular dynamics study

Alzheimer's disease is increasingly being recognized as an immune-mediated disease of brain. Since physiological brain health and brain immune function is dependent upon homeostatic neuronal membrane structure and function, alterations in membrane lipid biochemistry may predispose to disease. Brain is rich in cholesterol, and cholesterol metabolism dysfunction is a known risk factor for AD. Employing extensive microsecond all-atom molecular dynamics simulations, we investigated the properties of model neuronal membranes as a function of cholesterol concentration; phospholipid and phospholipid/cholesterol bilayers were also simulated to compare against available experimental data. Increased cholesterol concentrations compact and stiffen the lipid membrane, reducing permeability while modulating local water densities in the peri-membranous environment. Conversely, lower cholesterol mole fraction yields membranes with increased molecular disorder, enhanced fluidity, higher molecular tilting, and augmented interdigitation between bilayer leaflet lipids. Our findings provide a molecular insight on effect of cholesterol composition on various biochemical processes occurring at neuronal axon plasma membrane. These calculations also endeavor to establish a membrane-based link between cholesterol as an AD risk factor and possible AD pathology.

Rare variants in the endocytic pathway are associated with Alzheimer's disease, its related phenotypes, and functional consequences

Late-onset Alzheimer's disease (LOAD) is the most common type of dementia causing irreversible brain damage to the elderly and presents a major public health challenge. Clinical research and genome-wide association studies have suggested a potential contribution of the endocytic pathway to AD, with an emphasis on common loci. However, the contribution of rare variants in this pathway to AD has not been thoroughly investigated. In this study, we focused on the effect of rare variants on AD by first applying a rare-variant gene-set burden analysis using genes in the endocytic pathway on over 3,000 individuals with European ancestry from three large whole-genome sequencing (WGS) studies. We identified significant associations of rare-variant burden within the endocytic pathway with AD, which were successfully replicated in independent datasets. We further demonstrated that this endocytic rare-variant enrichment is associated with neurofibrillary tangles (NFTs) and age-related phenotypes, increasing the risk of obtaining severer brain damage, earlier age-at-onset, and earlier age-of-death. Next, by aggregating rare variants within each gene, we sought to identify single endocytic genes associated with AD and NFTs. Careful examination using NFTs revealed one significantly associated gene, ANKRD13D. To identify functional associations, we integrated bulk RNA-Seq data from over 600 brain tissues and found two endocytic expression genes (eGenes), HLA-A and SLC26A7, that displayed significant influences on their gene expressions. Differential expressions between AD patients and controls of these three identified genes were further examined by incorporating scRNA-Seq data from 48 post-mortem brain samples and demonstrated distinct expression patterns across cell types. Taken together, our results demonstrated strong rare-variant effect in the endocytic pathway on AD risk and progression and functional effect of gene expression alteration in both bulk and single-cell resolution, which may bring more insight and serve as valuable resources for future AD genetic studies, clinical research, and therapeutic targeting.

Serum Metabolomics Profiling of Commercially Mixed Functional Foods—Effects in Beta-Amyloid Induced Rats Measured Using 1H NMR Spectroscopy

Functional foods such as pomegranate, dates and honey were shown by various previous studies to individually have a neuroprotective effect, especially in neurodegenerative disease such as Alzheimer’s disease (AD). In this novel and original study, an ¹H NMR spectroscopy tool was used to identify the metabolic neuroprotective mechanism of commercially mixed functional foods (MFF) consisting of pomegranate, dates and honey, in rats injected with amyloid-beta 1-42 (Aβ-42). Forty-five male albino Wistar rats were randomly divided into five groups: NC (0.9% normal saline treatment + phosphate buffer solution (PBS) solution injection), Abeta (0.9% normal saline treatment + 0.2 µg/µL Aβ-42 injection), MFF (4 mL/kg MFF treatment + PBS solution injection), Abeta–MFF (4 mL/kg MFF treatment + 0.2 µg/µL Aβ-42 injection) and Abeta–NAC (150 mg/kg N-acetylcysteine + 0.2 µg/µL Aβ-42 injection). Based on the results, the MFF and NAC treatment improved the spatial memory and learning using Y-maze. In the metabolic analysis, a total of 12 metabolites were identified, for which levels changed significantly among the treatment groups. Systematic metabolic pathway analysis found that the MFF and NAC treatments provided a neuroprotective effect in Aβ-42 injected rats by improving the acid amino and energy metabolisms. Overall, this finding showed that MFF might serve as a potential neuroprotective functional food for the prevention of AD.

Genome-wide transcriptome analysis identifies novel dysregulated genes implicated in Alzheimer's pathology

INTRODUCTION

Abnormal gene expression patterns may contribute to the onset and progression of late-onset Alzheimer's disease (LOAD).

METHODS

We performed transcriptome-wide meta-analysis (N = 1440) of blood-based microarray gene expression profiles as well as neuroimaging and cerebrospinal fluid (CSF) endophenotype analysis.

RESULTS

We identified and replicated five genes (CREB5, CD46, TMBIM6, IRAK3, and RPAIN) as significantly dysregulated in LOAD. The most significantly altered gene, CREB5, was also associated with brain atrophy and increased amyloid beta (Aβ) accumulation, especially in the entorhinal cortex region. cis-expression quantitative trait loci mapping analysis of CREB5 detected five significant associations (P < 5 × 10^-8 ), where rs56388170 (most significant) was also significantly associated with global cortical Aβ deposition measured by [¹⁸ F]Florbetapir positron emission tomography and CSF Aβ_1-42 .

DISCUSSION

RNA from peripheral blood indicated a differential gene expression pattern in LOAD. Genes identified have been implicated in biological processes relevant to Alzheimer's disease. CREB, in particular, plays a key role in nervous system development, cell survival, plasticity, and learning and memory.

Mechanistic Modeling of Soluble Aβ Dynamics and Target Engagement in the Brain by Anti-Aβ mAbs in Alzheimer’s Disease

Background:

Anti-amyloid-β (Aβ) monoclonal antibodies (mAbs) are currently in development for treating Alzheimer’s disease.

Objectives:

To address the complexity of Aβ target engagement profiles, improve the understanding of crenezumab Pharmacokinetics (PK) and Aβ Pharmacodynamics (PD) in the brain, and facilitate comparison of anti-Aβ therapies with different binding characteristics.

Methods:

A mechanistic mathematical model was developed describing the distribution, elimination, and binding kinetics of anti-Aβ mAbs and Aβ (monomeric and oligomeric forms of Aβ1-40 and Aβ1-42) in the brain, Cerebrospinal Fluid (CSF), and plasma. Physiologically meaningful values were assigned to the model parameters based on the previous data, with remaining parameters fitted to clinical measurements of Aβ concentrations in CSF and plasma, and PK/PD data of patients undergoing anti-Aβ therapy. Aβ target engagement profiles were simulated using a Monte Carlo approach to explore the impact of biological uncertainty in the model parameters.

Results:

Model-based estimates of in vivo affinity of the antibody to monomeric Aβ were qualitatively consistent with the previous data. Simulations of Aβ target engagement profiles captured observed mean and variance of clinical PK/PD data.

Conclusion:

This model is useful for comparing target engagement profiles of different anti-Aβ therapies and demonstrates that 60 mg/kg crenezumab yields a significant increase in Aβ engagement compared with lower doses of solanezumab, supporting the selection of 60 mg/kg crenezumab for phase 3 studies. The model also provides evidence that the delivery of sufficient quantities of mAb to brain interstitial fluid is a limiting step with respect to the magnitude of soluble Aβ oligomer neutralization.

Epidermal growth factor treatment of female mice that express APOE4 at an age of advanced pathology mitigates behavioral and cerebrovascular dysfunction

APOE4 is a major genetic risk factor for Alzheimer's disease and high amyloid-β (Aβ) levels in the brain are a pathological hallmark of the disease. However, the contribution of specific APOE-modulated Aβ-dependent and Aβ-independent functions to cognitive decline remain unclear. Increasing evidence supports a role of APOE in modulating cerebrovascular function, however whether ameliorating this dysfunction can improve behavioral function is still under debate. We have previously demonstrated that systemic epidermal growth factor (EGF) treatment, which is important for vascular function, at early stages of pathology (treatment from 6 to 8 months) is beneficial for recognition and spatial memory and cerebrovascular function in female mice that express APOE4. These data raise the important question of whether EGF can improve APOE4-associated cerebrovascular and behavioral dysfunction when treatment is initiated at an age of advanced pathology. Positive findings would support the development of therapies that target cerebrovascular dysfunction associated with APOE4 in aging and AD in individuals with advanced cognitive impairment. Therefore, in this study female mice that express APOE4 in the absence (E4FAD- mice) or presence (E4FAD+ mice) of Aβ overproduction were treated from 8 to 10 months of age systemically with EGF. EGF treatment mitigated behavioral dysfunction in recognition memory and spatial learning and improved hippocampal neuronal function in both E4FAD+ and E4FAD- mice, suggesting that EGF treatment improves Aβ-independent APOE4-associated deficits. The beneficial effects of EGF treatment on behavior occurred in tandem with improved markers of cerebrovascular function, including lower levels of fibrinogen, lower permeability when assessed by MRI and higher percent area coverage of laminin and CD31 in the hippocampus. These data suggest a mechanistic link among EGF signaling, cerebrovascular function and APOE4-associated behavioral deficits in mice with advanced AD-relevant pathology.

Cholesterol and Dementia: A Long and Complicated Relationship

BACKGROUND

There is a huge demand for efficient strategies for maintaining cognitive wellbeing with age, especially in the context of population aging. Dementia constitutes the main reason for disability and dependency in the elderly. Identification of potential risk and protective factors, as well as determinants of conversion from MCI to dementia, is therefore crucial. In case of Alzheimer's disease, the most prevalent dementia syndrome amongst the members of modern societies, neurodegenerative processes in the brain can begin many years before first clinical symptoms appear. First functional changes typically mean advanced neuron loss, therefore, the earliest possible diagnosis is critical for implementation of promising early pharmaceutical interventions.

OBJECTIVE

The study aimed to discuss the relationships between both circulating and brain cholesterol with cognition, and explore its potential role in early diagnosis of cognitive disorders.

METHODS

Literature review.

RESULTS

The causal role of high cholesterol levels in AD or MCI has not been confirmed. It has been postulated that plasma levels of 24(S)-OHC can potentially be used as an early biochemical marker of altered cholesterol homeostasis in the CNS. Some studies brought conflicting results, finding normal or lowered levels of 24(S)-OHC in dementia patients compared to controls. In spite of decades of research on the relationship between cholesterol and dementia, so far, no single trusted indicator of an early cognitive deterioration has been identified.

CONCLUSION

The current state of knowledge makes the use of cholesterol markers of cognitive decline in clinical practice impossible.

Biomarkers of dementia in obstructive sleep apnea

Epidemiologic and mechanistic evidence is increasingly supporting the notion that obstructive sleep apnea is a risk factor for dementia. Hence, the identification of patients at risk of cognitive decline due to obstructive sleep apnea may significantly improve preventive strategies and treatment decision-making. Cerebrospinal fluid and blood biomarkers obtained through genomic, proteomic and metabolomic approaches are improving the ability to predict incident dementia. Therefore, fluid biomarkers have the potential to predict vulnerability to neurodegeneration in individuals with obstructive sleep apnea, as well as deepen our understanding of pathophysiological processes linking obstructive sleep apnea and dementia. Many fluid biomarkers linked to Alzheimer's disease and vascular dementia show abnormal levels in individuals with obstructive sleep apnea, suggesting that these conditions share common underlying mechanisms, including amyloid and tau protein neuropathology, inflammation, oxidative stress, and metabolic disturbances. Markers of these processes include amyloid-β, tau proteins, inflammatory cytokines, acute-phase proteins, antioxydants and oxidized products, homocysteine and clusterin (apolipoprotein J). Thus, these biomarkers may have the ability to identify adults with obstructive sleep apnea at high risk of dementia and provide an opportunity for therapeutic intervention. Large cohort studies are necessary to establish a specific fluid biomarker panel linking obstructive sleep apnea to dementia risk.

Gout and dementia in the elderly: a cohort study of Medicare claims

Background

Conflicting data in the literature raise the question whether gout, independent of its treatment, increases the risk of dementia in the elderly. Our objective was to assess whether gout in older adults is associated with the risk of incident dementia.

Methods

We used the 5% Medicare claims data for this observational cohort study. We used multivariable-adjusted Cox proportional hazard models to assess the association of gout with a new diagnosis of dementia (incident dementia), adjusting for potential confounders/covariates including demographics (age, race, sex), comorbidities (Charlson-Romano comorbidity index), and medications commonly used for cardiac diseases (statins, beta-blockers, diuretics, and angiotensin converting enzyme (ACE)-inhibitors) and gout (allopurinol and febuxostat).

Results

In our cohort of 1.71 million Medicare beneficiaries, 111,656 had incident dementia. The crude incidence rates of dementia in people without and with gout were 10.9 and 17.9 per 1000 person-years, respectively. In multivariable-adjusted analyses, gout was independently associated with a significantly higher hazard ratio of incident dementia, with a HR of 1.15 (95% CI, 1.12, 1.18); sensitivity analyses confirmed the main findings. Compared to age 65 to < 75 years, age 75 to < 85 and ≥ 85 years were associated with 3.5 and 7.8-fold higher hazards of dementia; hazards were also higher for females, black race or people with higher medical comorbidity.

Conclusion

Gout was independently associated with a 15% higher risk of incident dementia in the elderly. Future studies need to understand the pathogenic pathways involved in this increased risk.

Cerebrospinal fluid monoamine metabolite concentrations in depressive disorder: A meta-analysis of historic evidence

Altered monoaminergic functions have been implicated in the pathophysiology of depressive disorder. However, previously reported cerebrospinal fluid (CSF) monoamine metabolite concentrations in major depression have been inconsistent. We performed a meta-analysis of historic evidence to determine whether CSF monoamine metabolite levels were different between patients with depression and normal controls, and could be used as depression biomarkers. Relevant studies that investigated CSF 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid (HVA), and 3-methoxy-4-hydroxyphenylglycol (MHPG) levels in patients with depression and normal controls were identified in PubMed, Web of Science, PsycINFO, and Embase databases through September 5, 2017, using a synonymous search for depression, CSF, normal, control, and each monoamine metabolite name, and in the reference lists of the acquired articles. Obtained records were individually scrutinized for eligibility. Our search strategy identified 26 studies, including our own. We employed random effects modeling and adopted "Hedges's g" as an index of effect size. In the meta-analyses, no significant difference was observed in CSF 5-HIAA or MHPG levels between patients with depressive disorder and controls. In contrast, CSF HVA was significantly decreased in patients with depression (Hedges's g = -0.30, P = 0.0000025), and these results remained significant after patients with bipolar disorder were excluded (Hedges's g = -0.37, P = 0.000061). In the meta-regression, sex was significantly associated with the Hedges's g of CSF HVA (Q = 4.41, P = 0.036). This meta-analysis revealed that only CSF HVA, and not 5-HIAA or MHPG, levels were decreased in depressive disorder. The reduction in the CSF HVA concentration in patients with depression may guide future studies on depression and serve as a useful biomarker of depressive disorder.

Sirtuin 1 and Alzheimer's disease: An up-to-date review

Sirtuins are NAD+-dependent enzymes that regulate a large number of cellular pathways and are related to aging and age-associated diseases. In recent years, the role of sirtuins in Alzheimer's disease (AD) has become increasingly apparent. Growing evidence demonstrates that sirtuin 1 (SIRT1) regulates many processes that go amiss in AD, such as: APP processing, neuroinflammation, neurodegeneration, and mitochondrial dysfunction. Here we review how SIRT1 affects AD and cognition, the main mechanisms in which SIRT1 is related to AD pathology, and its importance for the prevention and possible diagnosis of AD.

The Role of Immunosenescence in Neurodegenerative Diseases

Aging is characterized by the progressive decline of physiological function and tissue homeostasis leading to increased vulnerability, degeneration, and death. Aging-related changes of the innate and adaptive immune system include decline in the preservation and enhancement of many immune functions, such as changes in the number of circulating monocytic and dendritic cells, thymic involution, T cell polyfunctionality, or production of proinflammatory cytokines, and are defined as immunosenescence. Inflammatory functions are increased with age, causing the chronic low-grade inflammation, referred to as inflamm-aging, that contribute, together with immunosenescence, to neurodegenerative diseases. In this review, we discuss the link between the immune and nervous systems and how the immunosenescence and inflamm-aging can contribute to neurodegenerative diseases.

The interplay between inflammation, oxidative stress, DNA damage, DNA repair and mitochondrial dysfunction in depression

A growing body of evidence suggests that inflammation, mitochondrial dysfunction and oxidant-antioxidant imbalance may play a significant role in the development and progression of depression. Elevated levels of reactive oxygen and nitrogen species - a result of oxidant-antioxidant imbalance - may lead to increased damage of biomolecules, including DNA. This was confirmed in depressed patients in a research study conducted by our team and other scientists. 8-oxoguanine - a marker of oxidative DNA damage - was found in the patients' lymphocytes, urine and serum. These results were confirmed using a comet assay on lymphocytes. Furthermore, it was shown that the patients' cells repaired peroxide-induced DNA damage less efficiently than controls' cells and that some single nucleotide polymorphisms (SNP) of the genes involved in oxidative DNA damage repair may modulate the risk of depression. Lastly, less efficient DNA damage repair observed in the patients can be, at least partly, attributed to the presence of specific SNP variants, as it was revealed through a genotype-phenotype analysis. In conclusion, the available literature shows that both oxidative stress and less efficient DNA damage repair may lead to increased DNA damage in depressed patients. A similar mechanism may result in mitochondrial dysfunction, which is observed in depression.

Role of Pro-Inflammatory Cytokines and Vitamin D in Probable Alzheimer's Disease with Depression

Symptoms of depression are present in a significant proportion of Alzheimer's disease (AD) patients. While epidemiological studies have shown a strong association between depression and AD, it has not been established whether depression is a risk factor or merely a co-morbidity of AD. It is also uncertain if depression affects the pathogenesis of AD. In this paper, we address these questions by measuring the serum levels of two common metabolic risk factors of AD and depression, inflammatory cytokines (IL 6 and TNF alpha) and serum 25-hydroxyvitamin D, in a case-control study. We measured the serum levels of IL 6, TNF α and 25-hydroxyvitamin D in age-matched healthy controls (n= 60) and in AD patients without depression (n=26) or AD patients with depression (n=34), and statistically analyzed the changes in these parameters among different groups under this study. Our results show that in AD there is a significant increase in IL 6 and TNF α and a marked decrease in 25-hydroxyvitamin D in the peripheral circulation compared to age-matched healthy controls. Furthermore, AD patients with depression have even significantly higher levels of IL 6 or TNF α and a lower level of 25-hydroxyvitamin D in circulation than in AD patients without depression. We also found a strong statistical correlation between the disease severity and the serum levels of IL 6, TNF α and 25-hydroxyvitamin D in AD patients with depression. These results suggest that altered circulating levels of common metabolic risk factors lead to the co-existence of depression with AD in many patients, and when they co-exist, the depression presumably affects the severity of AD presentations through more aggravated changes in these risk factors.

Epidermal growth factor prevents APOE4 and amyloid-beta-induced cognitive and cerebrovascular deficits in female mice

Cerebrovascular (CV) dysfunction is emerging as a critical component of Alzheimer's disease (AD), including altered CV coverage. Angiogenic growth factors (AGFs) are key for controlling CV coverage, especially during disease pathology. Therefore, evaluating the effects of AGFs in vivo can provide important information on the role of CV coverage in AD. We recently demonstrated that epidermal growth factor (EGF) prevents amyloid-beta (Aβ)-induced damage to brain endothelial cells in vitro. Here, our goal was to assess the protective effects of EGF on cognition, CV coverage and Aβ levels using an AD-Tg model that incorporates CV relevant AD risk factors. APOE4 is the greatest genetic risk factor for sporadic AD especially in women and is associated with CV dysfunction. EFAD mice express human APOE3 (E3FAD) or APOE4 (E4FAD), overproduce human Aβ42 and are a well characterized model of APOE pathology. Thus, initially the role of APOE and sex in cognitive and CV dysfunction was assessed in EFAD mice in order to identify a group for EGF treatment. At 8 months E4FAD female mice were cognitively impaired, had low CV coverage, high microbleeds and low plasma EGF levels. Therefore, E4FAD female mice were selected for an EGF prevention paradigm (300 μg/kg/wk, 6 to 8.5 months). EGF prevented cognitive decline and was associated with lower microbleeds and higher CV coverage, but not changes in Aβ levels. Collectively, these data suggest that EGF can prevent Aβ-induced damage to the CV. Developing therapeutic strategies based on AGFs may be particularly efficacious for APOE4-induced AD risk.

Comorbidity Factors and Brain Mechanisms Linking Chronic Stress and Systemic Illness

Neuropsychiatric symptoms and mental illness are commonly present in patients with chronic systemic diseases. Mood disorders, such as depression, are present in up to 50% of these patients, resulting in impaired physical recovery and more intricate treatment regimen. Stress associated with both physical and emotional aspects of systemic illness is thought to elicit detrimental effects to initiate comorbid mental disorders. However, clinical reports also indicate that the relationship between systemic and psychiatric illnesses is bidirectional, further increasing the complexity of the underlying pathophysiological processes. In this review, we discuss the recent evidence linking chronic stress and systemic illness, such as activation of the immune response system and release of common proinflammatory mediators. Altogether, discovery of new targets is needed for development of better treatments for stress-related psychiatric illnesses as well as improvement of mental health aspects of different systemic diseases.

Effects of ketone bodies in Alzheimer's disease in relation to neural hypometabolism, β-amyloid toxicity, and astrocyte function

Diet supplementation with ketone bodies (acetoacetate and β-hydroxybuturate) or medium-length fatty acids generating ketone bodies has consistently been found to cause modest improvement of mental function in Alzheimer's patients. It was suggested that the therapeutic effect might be more pronounced if treatment was begun at a pre-clinical stage of the disease instead of well after its manifestation. The pre-clinical stage is characterized by decade-long glucose hypometabolism in brain, but ketone body metabolism is intact even initially after disease manifestation. One reason for the impaired glucose metabolism may be early destruction of the noradrenergic brain stem nucleus, locus coeruleus, which stimulates glucose metabolism, at least in astrocytes. These glial cells are essential in Alzheimer pathogenesis. The β-amyloid peptide Aβ interferes with their cholinergic innervation, which impairs synaptic function because of diminished astrocytic glutamate release. Aβ also reduces glucose metabolism and causes hyperexcitability. Ketone bodies are similarly used against seizures, but the effectively used concentrations are so high that they must interfere with glucose metabolism and de novo synthesis of neurotransmitter glutamate, reducing neuronal glutamatergic signaling. The lower ketone body concentrations used in Alzheimer's disease may owe their effect to support of energy metabolism, but might also inhibit release of gliotransmitter glutamate. Alzheimer's disease is a panglial-neuronal disorder with long-standing brain hypometabolism, aberrations in both neuronal and astrocytic glucose metabolism, inflammation, hyperexcitability, and dementia. Relatively low doses of β-hydroxybutyrate can have an ameliorating effect on cognitive function. This could be because of metabolic supplementation or inhibition of Aβ-induced release of glutamate as gliotransmitter, which is likely to reduce hyperexcitability and inflammation. The therapeutic β-hydroxybutyrate doses are too low to reduce neuronally released glutamate.

Reduced cerebrospinal fluid ethanolamine concentration in major depressive disorder

Amino acids play key roles in the function of the central nervous system, and their alterations are implicated in psychiatric disorders. In the search for a biomarker for major depressive disorder (MDD), we used high-performance liquid chromatography to measure amino acids and related molecules in the cerebrospinal fluid (CSF) of 52 patients with MDD (42 depressed and 10 remitted; DSM-IV) and 54 matched controls. Significant differences were found in four amino acid concentrations between the depressed patients and controls. After Bonferroni correction, only ethanolamine (EA) levels remained significantly reduced in depressed patients (nominal P = 0.0000011). A substantial proportion of the depressed patients (40.5%) showed abnormally low CSF EA levels (<12.1 μM) (P = 0.000033; OR = 11.6, 95% CI: 3.1–43.2). When patients with low EA and those with high EA levels were compared, the former had higher scores for overall depression severity (P = 0.0033) and ‘Somatic Anxiety’ symptoms (P = 0.00026). In unmedicated subjects, CSF EA levels showed a significant positive correlation with levels of homovanillic acid (P = 0.0030) and 5-hydroxyindoleacetic acid (P = 0.019). To our knowledge, this is the first study showing that patients with MDD have significantly lower CSF EA concentrations compared with control subjects. CSF EA could be a state-dependent biomarker for a subtype of MDD.

Raised serum proinflammatory cytokines in Alzheimer's disease with depression

The purpose of the present study was to identify the changes in the levels of proinflammatory cytokines like IL-1β, IL-6 and TNF-α in peripheral circulation in Alzheimer's disease (AD) subjects and to correlate these with associated depression and cognitive deficit. Fifty five AD subjects and thirty seven age and sex matched controls were included in the study. The AD patients were grouped as AD with depression (n= 31) and AD without depression (n= 24). The serum levels of IL-1β, IL-6 and TNF-α were determined by immunoassay by commercially available kits. The serum levels of IL-6 and TNF-α were elevated in AD patients with depression compared to control (p<0.001) or AD without depression (p<0.001). The serum level of IL-1β was higher in AD patients with or without depression as compared to controls. Furthermore, a strong inverse correlation was observed between the MMSE scores and serum levels of IL-6 or TNF-α in AD subjects with depression. The study highlights the important role of peripheral IL-6 and TNF-α in AD associated depression and cognitive deficits.

Biomarkers in Alzheimer's disease: a review

Alzheimer's disease is the most common form of dementia affecting millions of individuals worldwide. It is currently diagnosed only via clinical assessments and confirmed by postmortem brain pathology. The development of validated biomarkers for Alzheimer's disease is essential to improve diagnosis and accelerate the development of new therapies. Biochemical and neuroimaging markers could facilitate diagnosis, predict AD progression from a pre-AD state of mild cognitive impairment (MCI), and be used to monitor efficacies of disease-modifying therapies. Cerebrospinal fluid (CSF) levels of Aβ40, Aβ42, total tau, and phosphorylated tau have diagnostic values in AD. Measurements of the above CSF markers in combination are useful in predicting the risk of progression from MCI to AD. New potential biomarkers are emerging, and CSF or plasma marker profiles may eventually become part of the clinician's toolkit for accurate AD diagnosis and management. These biomarkers along with clinical assessment, neuropsychological testing, and neuroimaging could achieve a much higher diagnostic accuracy for AD and related disorders in the future.