Plasma cortisol in Alzheimer's disease with or without depressive symptoms

Unlocking the potential of exercise: harnessing myokines to delay musculoskeletal aging and improve cognitive health

Objectives

This review aims to summarize the common physiological mechanisms associated with both mild cognitive impairment (MCI) and musculoskeletal aging while also examining the relevant literature on how exercise regulation influences the levels of shared myokines in these conditions.

Methods

The literature search was conducted via databases such as PubMed (including MEDLINE), EMBASE, and the Cochrane Library of Systematic Reviews. The searches were limited to full-text articles published in English, with the most recent search conducted on 16 July 2024. The inclusion criteria for this review focused on the role of exercise and myokines in delaying musculoskeletal aging and enhancing cognitive health. The Newcastle‒Ottawa Scale (NOS) was utilized to assess the quality of nonrandomized studies, and only those studies with moderate to high quality scores, as per these criteria, were included in the final analysis. Data analysis was performed through narrative synthesis.

Results

The primary outcome of this study was the evaluation of myokine expression, which included IL-6, IGF-1, BDNF, CTSB, irisin, and LIF. A total of 16 studies involving 633 older adults met the inclusion criteria. The current exercise modalities utilized in these studies primarily consisted of resistance training and moderate-to high-intensity cardiovascular exercise. The types of interventions included treadmill training, elastic band training, aquatic training, and Nordic walking training. The results indicated that both cardiovascular exercise and resistance exercise could delay musculoskeletal aging and enhance the cognitive functions of the brain. Additionally, different types and intensities of exercise exhibited varying effects on myokine expression.

Conclusion

Current evidence suggests that exercise mediates the secretion of specific myokines, including IL-6, IGF-1, BDNF, CTSB, irisin, and LIF, which establish self-regulatory circuits between the brain and muscle. This interaction enhances cognitive function in the brain and improves skeletal muscle function. Future research should focus on elucidating the exact mechanisms that govern the release of myokines, the correlation between the intensity of exercise and the secretion of these myokines, and the distinct processes by which myokines influence the interaction between muscle and the brain.

Alzheimer's disease early screening and staged detection with plasma proteome using machine learning and convolutional neural network

Alzheimer's disease (AD) stands as the prevalent progressive neurodegenerative disease, precipitating cognitive impairment and even memory loss. Amyloid biomarkers have been extensively used in the diagnosis of AD. However, amyloid proteins offer limited information about the disease process and accurate diagnosis depends on the presence of a substantial accumulation of amyloid deposition which significantly impedes the early screening of AD. In this study, we have combined plasma proteomics with an ensemble learning model (CatBoost) to develop a cost-effective and non-invasive diagnostic method for AD. A longitudinal panel has been identified that can serve as reliable biomarkers across the entire progression of AD. Simultaneously, we have developed a neural network algorithm that utilizes plasma proteins to detect stages of Alzheimer's disease. Based on the developed longitudinal panel, the CatBoost model achieved an area under the operating curve of at least 0.90 in distinguishing mild cognitive impairment from cognitively normal. The neural network model was utilized for the detection of three stages of AD, and the results demonstrated that the neural network model exhibited an accuracy as high as 0.83, surpassing that of the traditional machine learning model.

An Insight into Cellular and Molecular Mechanisms Underlying the Pathogenesis of Neurodegeneration in Alzheimer's Disease

Alzheimer's disease (AD) is the most prominent neurodegenerative disorder in the aging population. It is characterized by cognitive decline, gradual neurodegeneration, and the development of amyloid-β (Aβ)-plaques and neurofibrillary tangles, which constitute hyperphosphorylated tau. The early stages of neurodegeneration in AD include the loss of neurons, followed by synaptic impairment. Since the discovery of AD, substantial factual research has surfaced that outlines the disease's causes, molecular mechanisms, and prospective therapeutics, but a successful cure for the disease has not yet been discovered. This may be attributed to the complicated pathogenesis of AD, the absence of a well-defined molecular mechanism, and the constrained diagnostic resources and treatment options. To address the aforementioned challenges, extensive disease modeling is essential to fully comprehend the underlying mechanisms of AD, making it easier to design and develop effective treatment strategies. Emerging evidence over the past few decades supports the critical role of Aβ and tau in AD pathogenesis and the participation of glial cells in different molecular and cellular pathways. This review extensively discusses the current understanding concerning Aβ- and tau-associated molecular mechanisms and glial dysfunction in AD. Moreover, the critical risk factors associated with AD including genetics, aging, environmental variables, lifestyle habits, medical conditions, viral/bacterial infections, and psychiatric factors have been summarized. The present study will entice researchers to more thoroughly comprehend and explore the current status of the molecular mechanism of AD, which may assist in AD drug development in the forthcoming era.

Linking the Amyloid, Tau, and Mitochondrial Hypotheses of Alzheimer's Disease and Identifying Promising Drug Targets

Damage or loss of brain cells and impaired neurochemistry, neurogenesis, and synaptic and nonsynaptic plasticity of the brain lead to dementia in neurodegenerative diseases, such as Alzheimer's disease (AD). Injury to synapses and neurons and accumulation of extracellular amyloid plaques and intracellular neurofibrillary tangles are considered the main morphological and neuropathological features of AD. Age, genetic and epigenetic factors, environmental stressors, and lifestyle contribute to the risk of AD onset and progression. These risk factors are associated with structural and functional changes in the brain, leading to cognitive decline. Biomarkers of AD reflect or cause specific changes in brain function, especially changes in pathways associated with neurotransmission, neuroinflammation, bioenergetics, apoptosis, and oxidative and nitrosative stress. Even in the initial stages, AD is associated with Aβ neurotoxicity, mitochondrial dysfunction, and tau neurotoxicity. The integrative amyloid-tau-mitochondrial hypothesis assumes that the primary cause of AD is the neurotoxicity of Aβ oligomers and tau oligomers, mitochondrial dysfunction, and their mutual synergy. For the development of new efficient AD drugs, targeting the elimination of neurotoxicity, mutual potentiation of effects, and unwanted protein interactions of risk factors and biomarkers (mainly Aβ oligomers, tau oligomers, and mitochondrial dysfunction) in the early stage of the disease seems promising.

Cerebrospinal Fluid Cortisol and Dehydroepiandrosterone Sulfate, Alzheimer’s Disease Pathology, and Cognitive Decline

Introduction

Elevated cortisol levels have been reported in Alzheimer’s disease (AD) and may accelerate the development of brain pathology and cognitive decline. Dehydroepiandrosterone sulfate (DHEAS) has anti-glucocorticoid effects and it may be involved in the AD pathophysiology.

Objectives

To investigate associations of cerebrospinal fluid (CSF) cortisol and DHEAS levels with (1) cognitive performance at baseline; (2) CSF biomarkers of amyloid pathology (as assessed by CSF Aβ levels), neuronal injury (as assessed by CSF tau), and tau hyperphosphorylation (as assessed by CSF p-tau); (3) regional brain volumes; and (4) clinical disease progression.

Materials and Methods

Individuals between 49 and 88 years (n = 145) with mild cognitive impairment or dementia or with normal cognition were included. Clinical scores, AD biomarkers, brain MRI volumetry along with CSF cortisol and DHEAS were obtained at baseline. Cognitive and functional performance was re-assessed at 18 and 36 months from baseline. We also assessed the following covariates: apolipoprotein E (APOE) genotype, BMI, and education. We used linear regression and mixed models to address associations of interest.

Results

Higher CSF cortisol was associated with poorer global cognitive performance and higher disease severity at baseline. Cortisol and cortisol/DHEAS ratio were positively associated with tau and p-tau CSF levels, and negatively associated with the amygdala and insula volumes at baseline. Higher CSF cortisol predicted more pronounced cognitive decline and clinical disease progression over 36 months. Higher CSF DHEAS predicted more pronounced disease progression over 36 months.

Conclusion

Increased cortisol in the CNS is associated with tau pathology and neurodegeneration, and with decreased insula and amygdala volume. Both CSF cortisol and DHEAS levels predict faster clinical disease progression. These results have implications for the identification of patients at risk of rapid decline as well as for the development of interventions targeting both neurodegeneration and clinical manifestations of AD.

The Tryptophan Catabolite or Kynurenine Pathway in Alzheimer's Disease: A Systematic Review and Meta-Analysis

BACKGROUND

Alzheimer's disease (AD), which is characterized by progressive brain dysfunction and memory loss, is one of the most significant global health concerns for older adults. Neuroinflammation and increased oxidative stress contribute to the pathophysiology of AD, thereby presumably inducing tryptophan (TRP) degradation through the TRP catabolite (TRYCAT) pathway.

OBJECTIVE

To delineate the activity of the TRYCAT pathway along with levels of TRP and tryptophan catabolites (TRYCATs) in AD patients.

METHODS

We used PubMed, Google Scholar, Web of Science, and SciFinder during the month of January 2022 to gather the pertinent publications. We found 19 eligible articles which involved 738 patients and 665 healthy controls.

RESULTS

Our results revealed a significant difference (p = 0.008) in the kynurenine (KYN)/TRP ratio (standardized mean difference, SMD = 0.216, 95% confidence interval, CI: 0.057; 0.376), and a significant decrease in TRP in AD patients (SMD = -0.520, 95% CI: -0.738; -0.302, p < 0.0001). Moreover, we also found a significant increase in the central nervous system (CNS), brain, and cerebrospinal fluid kynurenic acid (KA)/KYN ratio but not in peripheral blood, as well as a significant decrease in plasma KA and xanthurenic acid in the CNS and blood.

CONCLUSION

AD is characterized by TRP depletion but not by an overactivity of the TRYCAT pathway. IDO-induced production of neurotoxic TRYCATs is not a key factor in the pathophysiology of AD.

Escalated (Dependent) Oxycodone Self-Administration Is Associated with Cognitive Impairment and Transcriptional Evidence of Neurodegeneration in Human Immunodeficiency Virus (HIV) Transgenic Rats

Substance use disorder is associated with accelerated disease progression in people with human immunodeficiency virus (HIV; PWH). Problem opioid use, including high-dose opioid therapy, prescription drug misuse, and opioid abuse, is high and increasing in the PWH population. Oxycodone is a broadly prescribed opioid in both the general population and PWH. Here, we allowed HIV transgenic (Tg) rats and wildtype (WT) littermates to intravenously self-administer oxycodone under short-access (ShA) conditions, which led to moderate, stable, "recreational"-like levels of drug intake, or under long-access (LgA) conditions, which led to escalated (dependent) drug intake. HIV Tg rats with histories of oxycodone self-administration under LgA conditions exhibited significant impairment in memory performance in the novel object recognition (NOR) paradigm. RNA-sequencing expression profiling of the medial prefrontal cortex (mPFC) in HIV Tg rats that self-administered oxycodone under ShA conditions exhibited greater transcriptional evidence of inflammation than WT rats that self-administered oxycodone under the same conditions. HIV Tg rats that self-administered oxycodone under LgA conditions exhibited transcriptional evidence of an increase in neuronal injury and neurodegeneration compared with WT rats under the same conditions. Gene expression analysis indicated that glucocorticoid-dependent adaptations contributed to the gene expression effects of oxycodone self-administration. Overall, the present results indicate that a history of opioid intake promotes neuroinflammation and glucocorticoid dysregulation, and excessive opioid intake is associated with neurotoxicity and cognitive impairment in HIV Tg rats.

Spousal caregiving, widowhood, and cognition: A systematic review and a biopsychosocial framework for understanding the relationship between interpersonal losses and dementia risk in older adulthood

Accumulating research suggests that stressful life events, especially those that threaten close intimate bonds, are associated with an increased risk of dementia. Grieving the loss of a spouse, whether in the form of caregiving or after the death, ranks among 'life's most significant stressors', evoking intense psychological and physiological distress. Despite numerous studies reporting elevated dementia risk or poorer cognition among spousal caregivers and widow(er)s compared to controls, no review has summarized findings across cognitive outcomes (i.e., dementia incidence, cognitive impairment rates, cognitive performance) or proposed a theoretical model for understanding the links between partner loss and abnormal cognitive decline. The current systematic review summarizes findings across 64 empirical studies. Overall, both cross-sectional and longitudinal studies revealed an adverse association between partner loss and cognitive outcomes. In turn, we propose a biopsychosocial model of cognitive decline that explains how caregiving and bereavement may position some to develop cognitive impairment or Alzheimer's disease and related dementias. More longitudinal studies that focus on the biopsychosocial context of caregivers and widow(er)s are needed.

Intact circadian rhythm despite cortisol hypersecretion in Alzheimer's disease: A meta-analysis

Hypersecretion of the glucocorticoid steroid hormone cortisol by individuals with Alzheimer's disease (AD) has been suspected for several decades, during which time dozens of examinations of this phenomenon have been conducted and published. The goals of this investigation were to summarize this sizeable body of literature, test whether participant and methodological characteristics modify the magnitude of the AD-associated basal cortisol hypersecretion, and examine whether cortisol circadian rhythmicity is maintained among individuals with AD. To this end, the present meta-analysis and systematic review examined over 300 comparisons of indices of basal HPA-axis functioning between individuals with AD and cognitively normal older adults. AD was associated with basal cortisol elevations (g = 0.45) but the magnitude of the effect was not systematically impacted by any of the participant characteristics considered or the time-of-day of the cortisol sampling. Further, there was no evidence of group differences among direct indices of circadian rhythmicity such as the cortisol awakening response or the diurnal cortisol slope. These results suggest that basal hypersecretion of cortisol, but not circadian dysrhythmia, is characteristic of individuals with AD. Mechanistically, the observed hypersecretion is consistent with the theorized AD-driven deterioration of the hippocampus and subsequent reduction in hypothalamic-pituitary-adrenal axis inhibition. Further investigation is warranted to elucidate the role and timing of cortisol elevations in the progression of AD.

Development of Classification Models for the Prediction of Alzheimer's Disease Utilizing Circulating Sex Hormone Ratios

BACKGROUND

While sex hormones are essential for normal cognitive health, those individuals with greater endocrine dyscrasia around menopause and with andropause are more likely to develop cognitive loss and Alzheimer's disease (AD).

OBJECTIVE

To assess whether circulating sex hormones may provide an etiologically significant, surrogate biomarker, for cognitive decline.

METHODS

Plasma (n = 152) and serum (n = 107) samples from age- and gender-matched AD and control subjects from the Wisconsin Alzheimer's Disease Research Center (ADRC) were analyzed for 11 steroids and follicle-stimulating hormone. Logistic regression (LR), correlation analyses, and recursive partitioning (RP) were used to examine the interactions of hormones and hormone ratios and their association with AD. Models generated were then tested on an additional 43 ADRC samples.

RESULTS

The wide variation and substantial overlap in the concentrations of all circulating sex steroids across control and AD groups precluded their use for predicting AD. Classification tree analyses (RP) revealed interactions among single hormones and hormone ratios that associated with AD status, the most predictive including only the hormone ratios identified by LR. The strongest associations were observed between cortisol, cortisone, and androstenedione with AD, with contributions from progesterone and 17β-estradiol. Utilizing this model, we correctly predicted 81% of AD test cases and 64% of control test cases.

CONCLUSION

We have developed a diagnostic model for AD, the Wisconsin Hormone Algorithm Test for Cognition (WHAT-Cog), that utilizes classification tree analyses of hormone ratios. Further refinement of this technology could provide a quick and cheap diagnostic method for screening those with AD.

Investigation on the influence of isolated environment on human psychological and physiological health

Crewmembers are working and living in isolated environment lacking natural light and perception. Although their health problems have been documented, the mechanism has not been thoroughly investigated. The aim of the present study is to investigate the psychological and physiological influences of isolated environment on crewmember's health. On account of complexity of the isolated environment, it is necessary to have a manually controllable system to simulate research platform-Bioregenerative Life Support System (BLSS). Symptom checklist 90 (SCL-90) was used to complete emotional status test. Urine samples were collected for metabonomics and hormone secretion analysis. Fecal samples were collected for intestinal microorganisms analysis. Crewmembers (n = 4) followed strict daily schedule during the experimental period. Five emotional factors were significantly (P < 0.05) increased, differential metabolites were enriched in tryptophan metabolism pathway, the relative abundance of Prevotella decreased significantly (P < 0.0001) when crewmembers in isolated environment without natural light. Hormone (melatonin, cortisol) secretion rhythm also changed. Significant positive correlation (r = 0.805, P < 0.05) between cortisol secretion and anxiety was observed. In conclusion, natural light simulation in an isolated environment may have a positive effect on the physiological and psychological health of the crewmember.

Stress and verbal memory in patients with Alzheimer's disease: different role of cortisol and anxiety

Objectives: Chronic stress has shown to have marked effects on learning and memory. A broader understanding of these effects has special interest in the context of Alzheimer's disease (AD). This study aims to analyze the moderating effect of cognitive impairment in the relationships between stress and verbal memory performance by considering biological and psychological measures of stress. Method: The sample consisted of 80 AD patients and 104 healthy controls. Salivary cortisol and state anxiety was measured as stress markers. Memory Alteration test (M@T) and Hopkins verbal learning test (HVLT-R) were used to measure verbal memory. Results: In controls, cortisol level was negatively associated with HVLT-R total, learning and delayed recall scores as well as M@T free recall scores, while in patients, such associations were not significant. In this group, cortisol negative effects were limited to HVLT-R learning and M@T semantic memory scores. In both groups, anxiety was associated with better M@T encoding and free recall scores. Besides, inverted U-shaped relationships were observed between anxiety and HVLT-R total recall and learning scores as well as M@T orientation scores. Conclusion: Cortisol levels and anxiety are differentially associated with memory performance in older adults. In general, the negative relationship between cortisol levels and memory observed in healthy elderly weakens in AD. However, moderate state anxiety levels seem to be associated with a better memory performance in AD patients and in healthy elderly.

Past to Future: What Animal Models Have Taught Us About Alzheimer's Disease

Alzheimer's disease (AD) impairs memory and causes significant cognitive deficits. The disease course is prolonged, with a poor prognosis, and thus exacts an enormous economic and social burden. Over the past two decades, genetically engineered mouse models have proven indispensable for understanding AD pathogenesis, as well as for discovering new therapeutic targets. Here we highlight significant studies from our laboratory that have helped advance the AD field by elucidating key pathogenic processes operative in AD and exploring a variety of aspects of the disease which may yield novel therapeutic strategies for combatting this burdensome disease.

Neuropsychological assessment and cortisol levels in biofluids from early Alzheimer's disease patients

Cortisol dysregulation is proposed as a factor in the development of Alzheimer's disease (AD). AD patients can show high cortisol levels in prodromal phases of AD, early enough that neuropsychological alterations exist but activities of daily living remain unimpaired. Nevertheless, it is unknown if biofluid cortisol levels can have some AD predictive power together with neuropsychological assessment in prodromal stages in comparison with other cognitive disorders. In this work, an analytical method based on ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) was applied to determine the cortisol levels in different biofluids (urine, plasma, saliva, cerebrospinal fluid). Early AD patients and non-AD patients recruited at out-patient neurological unit were classified from the standard cerebrospinal fluid biomarkers levels (β-amyloid, tau, phosphorylated tau), and studied with an extensive neuropsychological assessment including global, neuropsychological, functional and affective scales. We used a logistic regression model to discriminate between the AD and non-AD groups. Higher plasma cortisol levels were found in the AD group than in the non-AD group (p < 0.001). Regarding neuropsychological evaluation, delayed memory was used as representative of the neuropsychological status, and lower scores were obtained in the AD group (p < 0.001). The prediction model, including plasma cortisol levels and delayed memory scores, achieved an AUC of 0.93, as well as a sensitivity of 97% and a specificity of 69.4%. In conclusion, plasma cortisol levels and delayed memory scores were specifically impaired in early AD, allowing the development of a new diagnostic model which could be employed as a very satisfactory screening system.

Alzheimer's disease: risk factors and potentially protective measures

Alzheimer's disease (AD) is the most common type of dementia and typically manifests through a progressive loss of episodic memory and cognitive function, subsequently causing language and visuospatial skills deficiencies, which are often accompanied by behavioral disorders such as apathy, aggressiveness and depression. The presence of extracellular plaques of insoluble β-amyloid peptide (Aβ) and neurofibrillary tangles (NFT) containing hyperphosphorylated tau protein (P-tau) in the neuronal cytoplasm is a remarkable pathophysiological cause in patients' brains. Approximately 70% of the risk of developing AD can be attributed to genetics. However, acquired factors such as cerebrovascular diseases, diabetes, hypertension, obesity and dyslipidemia increase the risk of AD development. The aim of the present minireview was to summarize the pathophysiological mechanism and the main risk factors for AD. As a complement, some protective factors associated with a lower risk of disease incidence, such as cognitive reserve, physical activity and diet will also be addressed.

Neuroimmune nexus of depression and dementia: Shared mechanisms and therapeutic targets

Dysfunctional immune activity is a physiological component of both Alzheimer's disease (AD) and major depressive disorder (MDD). The extent to which altered immune activity influences the development of their respective cognitive symptoms and neuropathologies remains under investigation. It is evident, however, that immune activity affects neuronal function and circuit integrity. In both disorders, alterations are present in similar immune networks and neuroendocrine signalling pathways, immune responses persist in overlapping neuroanatomical locations, and morphological and structural irregularities are noted in similar domains. Epidemiological studies have also linked the two disorders, and their genetic and environmental risk factors intersect along immune-activating pathways and can be synonymous with one another. While each of these disorders individually contains a large degree of heterogeneity, their shared immunological components may link distinct phenotypes within each disorder. This review will therefore highlight the shared immune pathways of AD and MDD, their overlapping neuroanatomical features, and previously applied, as well as novel, approaches to pharmacologically manipulate immune pathways, in each neurological condition. LINKED ARTICLES: This article is part of a themed section on Therapeutics for Dementia and Alzheimer's Disease: New Directions for Precision Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.18/issuetoc.

High Cortisol and the Risk of Dementia and Alzheimer's Disease: A Review of the Literature

Introduction: Cortisol effects on the brain are exerted through two distinct receptors, inducing complex and even opposite effects on the cerebral structures implicated in the various cognitive functions. High cortisol may also have deleterious effects on the brain structures and contribute to neurodegeneration, in particular Alzheimer’s disease (AD), via different mechanisms.

Objective: To examine the interrelationships between cortisol, cognitive impairment and AD.

Methods: Review of the literature.

Results: Clinical studies found that elevated cortisol was associated with poorer overall cognitive functioning, as well as with poorer episodic memory, executive functioning, language, spatial memory, processing speed, and social cognition; while in animals, glucocorticoid administration resulted in cognitive impairment and abnormal behavior. In cognitively healthy subjects, higher cortisol levels have been associated with an increased risk of cognitive decline and AD. Subjects with dementia and Mild Cognitive Impairment (MCI) due to AD have been found to have higher CSF cortisol levels than cognitively healthy controls. Elevated CSF cortisol may also be associated with a more rapid cognitive decline in MCI due to AD. Elevated cortisol levels have been also found in delirium. High cortisol may mediate the impact of stressful life events, high neuroticism, depression, sleep disturbances, as well as cardiovascular risk factors on cognitive performance, neurodegeneration, and cognitive decline. High cortisol may also exert neurotoxic effects on the hippocampus, and promote oxidative stress and amyloid β peptide toxicity. Further possible underlying mechanisms include the interactions of cortisol with inflammatory mediators, neurotransmitters, and growth factors.

Conclusion: Elevated cortisol levels may exert detrimental effects on cognition and contribute to AD pathology. Further studies are needed to investigate cortisol-reducing and glucocorticoidreceptor modulating interventions to prevent cognitive decline.

Peripheral adaptive immunity of the triple transgenic mouse model of Alzheimer's disease

Background

Immunologic abnormalities have been described in peripheral blood and central nervous system of patients suffering from Alzheimer’s disease (AD), yet their role in the pathogenesis still remains poorly defined.

Aim and methods

We used the triple transgenic mouse model (3xTg-AD) to reproduce Aβ (amyloid plaques) and tau (neurofibrillary tangles) neuropathologies. We analyzed important features of the adaptive immune system in serum, primary (bone marrow) as well as secondary (spleen) lymphoid organs of 12-month-old 3xTg-AD mice using flow cytometry and ELISPOT. We further investigated serum cytokines of 9- and 13-month-old 3xTg-AD mice using multiplex ELISA. Results were compared to age-matched non-transgenic controls (NTg).

Results

In the bone marrow of 12-month-old 3xTg-AD mice, we detected decreased proportions of short-term reconstituting hematopoietic stem cells (0.58-fold, P = 0.0116), while lymphocyte, granulocyte, and monocyte populations remained unchanged. Our results also point to increased activation of both B and T lymphocytes. Indeed, we report elevated levels of plasma cells in bone marrow (1.3-fold, P = 0.0405) along with a 5.4-fold rise in serum IgG concentration (P < 0.0001) in 3xTg-AD animals. Furthermore, higher levels of interleukin (IL)-2 were detected in serum of 9- and 13-month-old 3xTg-AD mice (P = 0.0018). Along with increased concentrations of IL-17 (P = 0.0115) and granulocyte-macrophage colony-stimulating factor (P = 0.0085), these data support helper T lymphocyte activation with Th17 polarization.

Conclusion

Collectively, these results suggest that the 3xTg-AD model mimics modifications of the adaptive immunity changes previously observed in human AD patients and underscore the activation of both valuable and harmful pathways of immunity in AD.

Levels of Cortisol in CSF Are Associated With SNAP-25 and Tau Pathology but Not Amyloid-β

Objective: Preclinical studies have found both hyperactivity of hypothalamic- pituitary- adrenal (HPA) axis and synaptic degeneration are involved in the pathogenesis of Alzheimer's disease (AD). However, the data on the relationship of activity of HPA axis and synaptic degeneration in humans are limited. Methods: We compared CSF cortisol levels in 310 subjects, including 92 cognitively normal older people, 149 patients with mild cognitive impairment (MCI), and 69 patients with mild AD. Several linear and logistic regression models were conducted to investigate associations between CSF cortisol and synaptosomal-associated protein 25 (SNAP-25, reflecting synaptic degeneration) and other AD-related biomarkers. Results: We found that levels of cortisol in CSF were associated with SNAP-25 levels and tau pathologies but not amyloid-β protein. However, there were no significant differences in CSF cortisol levels among the three diagnostic groups. Conclusion: The HPA axis may play a crucial role in synaptic degeneration in AD pathogenesis.

Stress induced neural reorganization: A conceptual framework linking depression and Alzheimer's disease

Chronic stress is a risk factor for a number of physiological disorders including cardiovascular disease, obesity and gastrointestinal disorders, as well as psychiatric and neurodegenerative disorders. There are a number of underlying molecular and cellular mechanisms altered in the course of chronic stress, which may increase the vulnerability of individuals to develop psychiatric disorders such as depression, and neurodegenerative disorders such as Alzheimer's Disease (AD). This is evident in the influence of stress on large-scale brain networks, including the resting state Default Mode Network (DMN), the effects of stress on neuronal circuitry and architecture, and the cellular and molecular adaptations to stress, which may render individuals with stress related psychiatric disorders more vulnerable to neurodegenerative disease later in life. These alterations include decreased negative feedback inhibition of the hypothalamic pituitary axis (HPA) axis, decreased dendritic arborization and spine density in the prefrontal cortex (PFC) and hippocampus, and the release of proinflammatory cytokines, which may suppress neurogenesis and promote neuronal cell death. Each of these factors are thought to play a role in stress-related psychiatric disease as well as AD, and have been observed in clinical and post-mortem studies of individuals with depression and AD. The goal of the current review is to summarize clinical and preclinical evidence supporting a role for chronic stress as a putative link between neuropsychiatric and neurodegenerative disease. Moreover, we provide a rationale for the importance of taking a medical history of stress-related psychiatric diseases into consideration during clinical trial design, as they may play an important role in the etiology of AD in stratified patient populations.

Elevated serum levels of malondialdehyde and cortisol are associated with major depressive disorder: A case-control study

Objectives:

Major depressive disorder is diagnosed on the basis of patient’s self-reported experiences, behavior reported by relatives, and a mental status examination, and yet we do not have any reliable biomarker for this. Mood-regulating pathways are affected by oxidative injury to lipids and cortisol is released into the blood due to stimulation of corticotrophin receptors in the adrenal cortex. Here, we aimed to determine serum levels of malondialdehyde and cortisol in major depressive disorder patients and controls.

Methods:

We collected blood samples from 247 major depressive disorder patients and 248 controls. Serum levels of malondialdehyde and cortisol were measured by ultraviolet spectrophotometry and enzyme-linked immunosorbent assay kit, respectively.

Results:

We found malondialdehyde levels were significantly higher in patients than controls, with mean ± standard deviation at 4.49 ± 1.37 and 2.87 ± 0.82 µmol/L, respectively, p < 0.001. Cortisol levels were also found significantly higher in patients than controls, with mean ± SD at 19.22 ± 1.64 and 17.37 ± 1.34 µg/dL, respectively, p < 0.001. Significant negative correlation was observed between serum levels of malondialdehyde and cortisol in patients (r =−0.170, p = 0.021). Receiver operating characteristic analysis showed good diagnostic value for malondialdehyde and cortisol, with the area under the curve at 0.853 and 0.819, respectively.

Conclusion:

The present study suggests that increased serum levels of malondialdehyde and cortisol are strongly associated with major depressive disorder. We believe elevations of malondialdehyde and cortisol in serum level arise independently and they could serve as biomarkers for major depressive disorder.

Interactions Among Polymorphisms of Susceptibility Loci for Alzheimer's Disease or Depressive Disorder

Background

Several genetic susceptibility loci for major depressive disorder (MDD) or Alzheimer’s disease (AD) have been described. Interactions among polymorphisms are thought to explain the differences between low- and high-risk groups. We tested for the contribution of interactions between multiple functional polymorphisms in the risk of MDD or AD.

Material/Methods

A genetic association case-control study was performed in 68 MDD cases, 84 AD cases (35 of them with comorbid depression), and 90 controls. The contribution of 7 polymorphisms from 5 genes (APOE, HSPA1A, SLC6A4, HTR2A, and BDNF) related to risk of MDD or AD development was analyzed.

Results

Significant associations were found between MDD and interactions among polymorphisms in HSPA1A, SLC6A4, and BDNF or HSPA1A, BDNF, and APOE genes. For polymorphisms in the APOE gene in AD, significant differences were confirmed on the distributions of alleles and genotype rates compared to the control or MDD. Increased probability of comorbid depression was found in patients with AD who do not carry the ɛ4 allele of APOE.

Conclusions

Assessment of the interactions among polymorphisms of susceptibility loci in both MDD and AD confirmed a synergistic effect of genetic factors influencing inflammatory, serotonergic, and neurotrophic pathways at these heterogenous complex diseases. The effect of interactions was greater in MDD than in AD. A presence of the ɛ4 allele was confirmed as a genetic susceptibility factor in AD. Our findings indicate a role of APOE genotype in onset of comorbid depression in a subgroup of patients with AD who are not carriers of the APOE ɛ4 allele.

Stress and Cognitive Reserve as independent factors of neuropsychological performance in healthy elderly

Exposure to high levels of cortisol and self-reported stress, as well as cognitive reserve, have been linked to Alzheimer's disease pathology. However, there are no studies on the interaction of these variables. The present study aims to assess the associations of measures of cortisol, self-reported stress, and cognitive reserve with neuropsychological performance in healthy elderly people; besides, to test the interactions between these variables. Cross-sectional analyzes were conducted using data on stress, cognitive reserve and clinical conditions in 145 healthy elderly adults. A neuropsychological battery was used to assess executive functions, verbal memory and processing speed. Measurement of salivary cortisol at the circadian nadir was taken. A negative association between different stress measures and performance on tasks of memory, executive functions and processing speed was observed. Elderly people with higher cognitive reserve showed superior performance on all neuropsychological measures. No significant interaction between stress and cognitive reserve to neuropsychological performance was observed. These results indicate that older adults with high levels of stress and reduced cognitive reserve may be more susceptible to cognitive impairment.

ATP-sensitive potassium-channel inhibitor glibenclamide attenuates HPA axis hyperactivity, depression- and anxiety-related symptoms in a rat model of Alzheimer's disease

Affective disorders including depression and anxiety are among the most prevalent behavioral abnormalities in patients with Alzheimer's disease (AD), which affect the quality of life and progression of the disease. Dysregulation of the hypothalamic-pituitary-adrenal-(HPA) axis has been reported in affective disorders and AD. Recent studies revealed that current antidepressant drugs are not completely effective for treating anxiety- and depression-related disorders in people with dementia. ATP-sensitive-potassium-(K_ATP) channels are well-known to be involved in AD pathophysiology, HPA axis function and the pathogenesis of depression and anxiety-related behaviors. Thus, targeting of K_ATP channel may be a potential therapeutic strategy in AD. Hence, we investigated the effects of intracerebroventricular injection of Aβ25-35 alone or in combination with glibenclamide, K_ATP channel inhibitor on depression- and anxiety-related behaviors as well as HPA axis response to stress in rats. To do this, non-Aβ25-35- and Aβ25-35-treated rats were orally treated with glibenclamide, then the behavioral consequences were assessed using sucrose preference, forced swim, light-dark box and plus maze tests. Stress-induced corticosterone levels following forced swim and plus maze tests were also evaluated as indicative of abnormal HPA-axis-function. Aβ25-35 induced HPA axis hyperreactivity and increased depression- and anxiety-related symptoms in rats. Our results showed that blockade of K_ATP channels with glibenclamide decreased depression- and anxiety-related behaviors by normalizing HPA axis activity in Aβ25-35-treated rats. This study provides additional evidence that Aβ administration can induce depression- and anxiety-like symptoms in rodents, and suggests that K_ATP channel inhibitors may be a plausible therapeutic strategy for treating affective disorders in AD patients.

Glucocorticoid may influence amyloid β metabolism in patients with depression

Epidemiological studies have demonstrated that depression may be a risk factor for Alzheimer's disease (AD); however, the biological mechanisms of the transition from depression to AD are still not clear. Changes of amyloid β protein (Aβ) metabolism and increased glucocorticoid (GC) levels have been found in both depression and AD. Moreover, several studies in animal models have demonstrated that GC administration changes Aβ metabolism. To reveal whether GC affects amyloid metabolism in patients with depression, we evaluated serum levels of Aβ40, Aβ42 and cortisol at admission in 187 inpatients with major depressive disorder (MDD) and 224 healthy comparisons. Additionally, we re-evaluated the serum levels of Aβs in 27 patients with MDD 1 year later. The results of multiple regression analyses revealed that serum cortisol and Aβ levels are not correlated at the time of admission. However, serum cortisol levels at admission correlated with serum Aβ42 levels and Aβ40/Aβ42 ratio 1 year later. These findings suggest that increased cortisol in patients with MDD may influence the metabolism of Aβ over prolonged periods of time.

Influence of Perceived Stress on Incident Amnestic Mild Cognitive Impairment: Results From the Einstein Aging Study

Stress is a potentially remediable risk factor for amnestic mild cognitive impairment (aMCI). Our objective is to determine whether perceived stress predicts incident aMCI and to determine if the influence of stress on aMCI is independent of known aMCI risk factors, particularly demographic variables, depression, and apolipoprotein genotype. The Einstein Aging Study is a longitudinal community-based study of older adults. The Perceived Stress Scale (PSS) was administered annually in the Einstein Aging Study to participants (N=507; 71 developed incident aMCI; mean follow-up time=3.6 y, SD=2.0) who were aged 70 years and older, free of aMCI and dementia at baseline PSS administration, and had at least 1 subsequent annual follow-up. Cox hazard models were used to examine time to aMCI onset adjusting for covariates. High levels of perceived stress are associated with a 30% greater risk of incident aMCI (per 5-point increase in PSS: hazard ratio=1.30; 95% confidence interval, 1.08-1.58) independent of covariates. The consistency of results after covariate adjustment and the lack of evidence for reverse causation in longitudinal analyses suggest that these findings are robust. Understanding of the effect of perceived stress on cognition may lead to intervention strategies that prevent the onset of aMCI and Alzheimer dementia.

Cortisol: Mediator of association between Alzheimer's disease and diabetes mellitus?

Numerous epidemiologic studies have identified an independent association between Alzheimer's disease (AD) and diabetes mellitus (DM), which remains unexplained. This review contends that the association is mediated by mild hypercortisolemia that is manifested in AD by early stages, as empirical evidence indicates that hypercortisolemia is diabetogenic even at subclinical levels. Subclinical Cushing's syndrome is discussed as the paradigm. It is proposed that hypercortisolemia increases the risk of pre-diabetes and DM during early AD and the preceding decades. That hypercortisolemia is exhibited during the AD prodromal stage has yet to be determined, but may be inferred from concurrent metabolic parameters as documented in the literature. Studies refuting association between AD and DM also are evaluated, and the relationship between AD and DM is deduced to be more complex than directly causal, with DM of longstanding duration having a protective role. Association between DM and AD may require reappraisal by APOE ε4 carrier status, in view of newly identified roles of APOE ε4 in pre-diabetes. That association of APOE ε4 with DM in AD may have been underestimated in epidemiologic studies also is highlighted. At the core of arguments and mechanisms presented in this review is the circadian rhythm of cortisol secretion, which is the main determinant of glycemic control in humans. Alterations to that rhythm and to the hypothalamic-pituitary-adrenal axis occurring in AD are examined. Consequently the cause of hypercortisolemia in AD, and therefore of association between AD and DM, is proposed to be adrenal hyper-responsiveness to adrenocorticotropic hormone.

Short-term modern life-like stress exacerbates Aβ-pathology and synapse loss in 3xTg-AD mice

Alzheimer's disease (AD) is a progressive neurological disorder that impairs memory and other cognitive functions in the elderly. The social and financial impacts of AD are overwhelming and are escalating exponentially as a result of population aging. Therefore, identifying AD-related risk factors and the development of more efficacious therapeutic approaches are critical to cure this neurological disorder. Current epidemiological evidence indicates that life experiences, including chronic stress, are a risk for AD. However, it is unknown if short-term stress, lasting for hours, influences the onset or progression of AD. Here, we determined the effect of short-term, multi-modal 'modern life-like' stress on AD pathogenesis and synaptic plasticity in mice bearing three AD mutations (the 3xTg-AD mouse model). We found that combined emotional and physical stress lasting 5 h severely impaired memory in wild-type mice and tended to impact it in already low-performing 3xTg-AD mice. This stress reduced the number of synapse-bearing dendritic spines in 3xTg-AD mice and increased Aβ levels by augmenting AβPP processing. Thus, short-term stress simulating modern-life conditions may exacerbate cognitive deficits in preclinical AD by accelerating amyloid pathology and reducing synapse numbers. Epidemiological evidence indicates that life experiences, including chronic stress, are a risk for Alzheimer disease (AD). However, it is unknown if short stress in the range of hours influences the onset or progression of AD. Here, we determined the effect of short, multi-modal 'modern-lifelike'stress on AD pathogenesis and synaptic plasticity in mice bearing three AD mutations (the 3xTg-AD mouse model). We found that combined emotional and physical stress lasting 5 h severely impaired memory in wild-type mice and tended to impact it in already low-performing 3xTg-AD mice. This stress reduced the number of synapse-bearing dendritic spines in 3xTg-AD mice and increased Aβ levels by augmenting AβPP processing. Thus, short stress simulating modern-life conditions may exacerbate cognitive deficits in preclinical AD by accelerating amyloid pathology and reducing synapse numbers.

Meta-analysis of Ubiquilin1 gene polymorphism and Alzheimer's disease risk

BACKGROUND

Some studies have evaluated the association between the Ubiquilin 1 (UBQLN1) gene UBQ-8i polymorphism and Alzheimer's disease (AD). However, the results remain uncertain. We carried out a meta-analysis to derive a more comprehensive estimation of this association.

MATERIAL/METHODS

Case-control studies were identified by searching databases of PubMed, EMBASE, Web of Science, CNKI, CBM, Wanfang, and VIP. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the strength of the association.

RESULTS

The UBQ-8i polymorphism was significantly associated with an increased AD risk (OR=1.15; 95%CI 1.05-1.25; P=0.002). The combination of adjusted ORs also found UBQ-8i polymorphism was significantly associated with AD risk (OR=1.15; 95%CI 1.02-1.30; P=0.02). When stratified by APOE ε4 status, both APOE ε4 carriers and APOE non-ε4 carriers with UBQ-8i polymorphism had significantly increased AD risk (OR=1.28; 95%CI 1.05-1.56; P=0.01 and OR=1.25; 95%CI 1.04-1.50; P=0.02). In the subgroup analysis according to age, UBQ-8i polymorphism was significantly associated with LOAD risk (OR=1.17; 95%CI 1.05-1.31; P=0.005), but not with EOAD risk (OR=1.12; 95%CI 0.95-1.31; P=0.17).

CONCLUSIONS

These results suggest that the UBQ-8i polymorphism is associated with AD risk.