Cortisol, Amyloid-β, and Reserve Predicts Alzheimer’s Disease Progression for Cognitively Normal Older Adults

Convergent effects of synthetic glucocorticoid dexamethasone and amyloid beta in human olfactory neurosphere-derived cells

Stressful life events and glucocorticoid (stress) hormones appear to increase the risk of Alzheimer's disease and hasten its progression, but the reasons for this remain unclear. One potential explanation is that when amyloid β (Aβ) pathology is accumulating in the preclinical disease stage, glucocorticoid receptor signalling during stressful events exacerbates cellular dysfunction caused by Aβ. Alternatively, Aβ may disrupt glucocorticoid receptor signalling. To explore these possibilities, we investigated whether the synthetic glucocorticoid dexamethasone and Aβ have overlapping effects on the cellular proteome and whether Aβ influences canonical glucocorticoid receptor function. Human olfactory neurosphere-derived (ONS) cells, collected from the olfactory mucosa of six adult donors, were treated with soluble Aβ40 or Aβ42 followed by dexamethasone. Proteins were quantified by mass spectrometry. After 32 h treatment, Aβ40 and Aβ42 both induced profound changes in innate immunity-related proteins. After 72 h, Aβ42 formed widespread aggregates and induced few proteomic changes, whereas Aβ40 remained soluble and altered expression of mitochondrial and innate immunity-related proteins. ONS cells revealed overlapping impacts of Aβ40 and dexamethasone, with 23 proteins altered by both treatments. For 16 proteins (including eight mitochondrial proteins) dexamethasone counteracted the effects of Aβ40. For example, caspase 4 and methylmalonate-semialdehyde dehydrogenase were increased by Aβ40 and decreased by dexamethasone. Consistent with this finding, Aβ40 increased, but dexamethasone decreased, ONS cell proliferation. For seven proteins, including superoxide dismutase [Mn] mitochondrial, dexamethasone exacerbated the effects of Aβ40. For some proteins, including complement C3, the effects of dexamethasone differed depending on whether Aβ40 was present or absent. Neither Aβ species influenced glucocorticoid receptor nuclear translocation. Overall, this study revealed that glucocorticoid receptor signalling modifies the intracellular effects of Aß40, counteracting some effects and exacerbating others. It suggests that cellular mechanisms through which glucocorticoid receptor signalling influences Alzheimer's disease risk/progression are complex and determined by the balance of beneficial and detrimental glucocorticoid effects.

Association between occupational complexity and cognitive function in older adults from Brazil and Mexico

More complex occupations during adulthood may be associated with better cognition in later life. We used data from the Brazilian Longitudinal Study of Aging (ELSI) and the Mexican Health and Aging Study (MHAS) to investigate the association between occupational complexity and cognitive function. Using a regression-based approach, participants were classified as cognitively impaired or not. Occupation was categorized into four levels using the 2008 International Standard of Classification of Occupations. We used logistic regression models for separate and pooled analysis. The odds of cognitive impairment decreased with higher occupation skill levels in the ELSI, but this trend was not seen in the MHAS, where the highest skill level was not associated with cognitive impairment. ELSI participants had a lower probability of cognitive impairment compared to MHAS participants with the same occupation skill level. The results of this study suggest that programs addressing the negative consequences of lower-complexity occupations need to be tailored to specific regional contexts, considering their unique socioeconomic, cultural, and occupational landscapes.

Association between apolipoprotein E ε4 status and the risk of Alzheimer's disease: a meta-analysis

BACKGROUND

The apolipoprotein E ε4 (APOE ε4) status has a controversial role in predicting Alzheimer's disease (AD) factors. This meta-analysis assessed AD event risk in patients with APOE ε4 status.

MATERIALS AND METHODS

The relevant English-language articles were identified by searching the Cochrane Library, EMBASE, and PubMed databases. The prognostic significance of APOE ε4 status in AD patients was examined on the basis of pooled hazard ratios (HRs).

RESULTS

A total of 22 studies published after 1987, including 571,800 patients, were included. Consequently, APOE ε4 status was a risk factor for disease-free survival (DFS, HR = 2.033; 95% confidence interval [CI] = 1.589-2.602; P = 0.000; I 2 = 93.1%) in patients with AD. Additionally, subgroup analysis suggested that the ROC curve was the main risk factor among patients with AD.

CONCLUSIONS

AD patients with different events are managed via different methods; however, the present meta-analysis suggests an increased risk of AD events in patients with different APOE ε4 statuses.

Allostatic load measures in older adults with subjective cognitive decline and mild cognitive impairment: A cross-sectional analysis from the Brazilian Memory and Aging Study

INTRODUCTION

An increasing body of research suggests that stress and allostatic load are related to cognitive dysfunction and neurodegeneration.

OBJECTIVES

to determine the relationship between allostatic load (AL) and cognitive status in older adults classified with subjective cognitive decline (SCD) and mild cognitive impairment (MCI).

METHODOLOGY

Using the Brazilian Memory and Aging Study (BRAMS) database, we analyzed data from 57 older adults with SCD and MCI. Blood neuroendocrine (cortisol, DHEA-s), inflammatory (C-reactive protein, fibrinogen), metabolic (HbA1c, HDL-cholesterol, total cholesterol, creatinine), and cardiovascular (blood pressure, waist/hip ratio) were transformed into an AL index.

RESULTS

Despite a significant difference in the univariate analysis between waist/hip ratio (0.94 in the MCI group vs. 0, 88 in the SCD group, p = 0.03), total cholesterol levels (194 vs. 160, p = 0.02), and AL index (36.9 % in the MCI group vs. 27.2 % in the SCD group, p = 0.04), AL was not associated with SCD or MCI in the multivariate analysis.

CONCLUSION

Our data suggest that different profiles of AL in MCI compared to individuals with SCD could be due to cofounding factors. These findings need to be confirmed in longitudinal studies investigating profiles of AL changes at preclinical and prodromal stages of Alzheimer's disease.

Progress on early diagnosing Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that affects both cognition and non-cognition functions. The disease follows a continuum, starting with preclinical stages, progressing to mild cognitive and behavioral impairment, ultimately leading to dementia. Early detection of AD is crucial for better diagnosis and more effective treatment. However, the current AD diagnostic tests of biomarkers using cerebrospinal fluid and/or brain imaging are invasive or expensive, and mostly are still not able to detect early disease state. Consequently, there is an urgent need to develop new diagnostic techniques with higher sensitivity and specificity during the preclinical stages of AD. Various non-cognitive manifestations, including behavioral abnormalities, sleep disturbances, sensory dysfunctions, and physical changes, have been observed in the preclinical AD stage before occurrence of notable cognitive decline. Recent research advances have identified several biofluid biomarkers as early indicators of AD. This review focuses on these non-cognitive changes and newly discovered biomarkers in AD, specifically addressing the preclinical stages of the disease. Furthermore, it is of importance to explore the potential for developing a predictive system or network to forecast disease onset and progression at the early stage of AD.

Experimental laboratory models as tools for understanding modifiable dementia risk

Experimental laboratory research has an important role to play in dementia prevention. Mechanisms underlying modifiable risk factors for dementia are promising targets for dementia prevention but are difficult to investigate in human populations due to technological constraints and confounds. Therefore, controlled laboratory experiments in models such as transgenic rodents, invertebrates and in vitro cultured cells are increasingly used to investigate dementia risk factors and test strategies which target them to prevent dementia. This review provides an overview of experimental research into 15 established and putative modifiable dementia risk factors: less early-life education, hearing loss, depression, social isolation, life stress, hypertension, obesity, diabetes, physical inactivity, heavy alcohol use, smoking, air pollution, anesthetic exposure, traumatic brain injury, and disordered sleep. It explores how experimental models have been, and can be, used to address questions about modifiable dementia risk and prevention that cannot readily be addressed in human studies. HIGHLIGHTS: Modifiable dementia risk factors are promising targets for dementia prevention. Interrogation of mechanisms underlying dementia risk is difficult in human populations. Studies using diverse experimental models are revealing modifiable dementia risk mechanisms. We review experimental research into 15 modifiable dementia risk factors. Laboratory science can contribute uniquely to dementia prevention.

Diurnal cortisol, neuroinflammation, and neuroimaging visual rating scales in memory clinic patients

BACKGROUND

Neuroinflammation is a hallmark of the Alzheimer's disease (AD) pathogenic process. Cortisol dysregulation may increase AD risk and is related to brain atrophy. This cross-sectional study aims to examine interactions of cortisol patterns and neuroinflammation markers in their association with neuroimaging correlates.

METHOD

134 participants were recruited from the Karolinska University Hospital memory clinic (Stockholm, Sweden). Four visual rating scales were applied to magnetic resonance imaging or computed tomography scans: medial temporal lobe atrophy (MTA), global cortical atrophy (GCA), white matter lesions (WML), and posterior atrophy. Participants provided saliva samples for assessment of diurnal cortisol patterns, and underwent lumbar punctures for cerebrospinal fluid (CSF) sampling. Three cortisol measures were used: the cortisol awakening response, total daily output, and the ratio of awakening to bedtime levels. Nineteen CSF neuroinflammation markers were categorized into five composite scores: proinflammatory cytokines, other cytokines, angiogenesis markers, vascular injury markers, and glial activation markers. Ordinal logistic regressions were conducted to assess associations between cortisol patterns, neuroinflammation scores, and visual rating scales, and interactions between cortisol patterns and neuroinflammation scores in relation to visual rating scales.

RESULT

Higher levels of angiogenesis markers were associated with more severe WML. Some evidence was found for interactions between dysregulated diurnal cortisol patterns and greater neuroinflammation-related biomarkers in relation to more severe GCA and WML. No associations were found between cortisol patterns and visual rating scales.

CONCLUSION

This study suggests an interplay between diurnal cortisol patterns and neuroinflammation in relation to brain structure. While this cross-sectional study does not provide information on causality or temporality, these findings suggest that neuroinflammation may be involved in the relationship between HPA-axis functioning and AD.

Association of Lifelong Cognitive Reserve with Dementia and Mild Cognitive Impairment among Older Adults with Limited Formal Education: A Population-Based Cohort Study

INTRODUCTION

Early-life educational attainment contributes to cognitive reserve (CR). We investigated the associations of lifelong CR with dementia and mild cognitive impairment (MCI) among older people with limited formal education.

METHODS

This population-based cohort study included 2,127 dementia-free participants (≥60 years; 59.4% women; 81.5% with no or elementary school) who were examined at baseline (August-December 2014) and follow-up (March-September 2018). Lifelong CR score at baseline was generated from six lifespan intellectual factors. Dementia, MCI, and their subtypes were defined according to the international criteria. Data were analyzed using Cox proportional-hazards models.

RESULTS

During the total of 8,330.6 person-years of follow-up, 101 persons were diagnosed with dementia, including 74 with Alzheimer's disease (AD) and 26 with vascular dementia (VaD). The high (vs. low) tertile of lifelong CR score was associated with multivariable-adjusted hazards ratios (95% confidence interval) of 0.28 (0.14-0.55) for dementia and 0.18 (0.07-0.48) for AD. The association between higher CR and reduced AD risk was significant in people aged 60-74 but not in those aged ≥75 years (p for interaction = 0.011). Similarly, among MCI-free people at baseline (n = 1,635), the high (vs. low) tertile of lifelong CR score was associated with multivariable-adjusted hazard ratios of 0.51 (0.38-0.69) for MCI and 0.46 (0.33-0.64) for amnestic MCI. Lifelong CR was not related to VaD or non-amnestic MCI.

DISCUSSION

High lifelong CR is associated with reduced risks of dementia and MCI, especially AD and amnestic MCI. It highlights the importance of lifelong CR in maintaining late-life cognitive health even among people with no or limited education.

Lifelong Cognitive Reserve, Imaging Markers of Brain Aging, and Cognitive Function in Dementia-Free Rural Older Adults: A Population-Based Study

BACKGROUND

Cognitive reserve (CR) partly explains cognitive variability in the presence of pathological brain aging.

OBJECTIVE

We investigated the interplay of lifelong CR with age, sex, and brain aging markers in cognitive phenotypes among older adults with very limited education.

METHODS

This population-based cross-sectional study included 179 dementia-free participants (age ≥65 years; 39.7% women; 67.0% had no or elementary education) examined in 2014-2016. We assessed lacunes and volumes of hippocampus, ventricles, grey matter, white matter (WM), and white matter hyperintensities. Lifelong CR score was generated from six lifespan intellectual factors (e.g., education and social support). We used Mini-Mental State Examination (MMSE) score to assess cognition and Petersen's criteria to define mild cognitive impairment (MCI). Data were analyzed using general linear and logistic models.

RESULTS

The association of higher lifelong CR score (range: -4.0-5.0) with higher MMSE score was stronger in women (multivariable-adjusted β-coefficient and 95% CI: 1.75;0.99-2.51) than in men (0.68;0.33-1.03) (pinteraction = 0.006). The association of higher CR with MCI (multivariable-adjusted odds ratio and 95% CI: 0.77;0.60-0.99) did not vary by age or sex. Among participants with low CR (<1.4[median]), greater hippocampal and WM volumes were related to higher MMSE scores with multivariable-adjusted β-coefficients being 1.77(0.41-3.13) and 0.44(0.15-0.74); the corresponding figures in those with high CR were 0.15(-0.76-1.07) and -0.17(-0.41-0.07) (pinteraction <0.01). There was no statistical interaction of CR with MRI markers on MCI.

CONCLUSION

Greater lifelong CR capacity is associated with better late-life cognition among people with limited education, possibly by compensating for impact of neurodegeneration.

The role of plasma cortisol in dementia, epilepsy, and multiple sclerosis: A Mendelian randomization study

BACKGROUND

Many clinical studies have shown a correlation between plasma cortisol and neurological disorders. This study explored the causal relationship between plasma cortisol and dementia, epilepsy and multiple sclerosis based on Mendelian randomization (MR) method.

METHODS

Data were taken from the summary statistics of a genome-wide association study, FinnGen consortium and United Kingdom Biobank. Dementia, epilepsy, and multiple sclerosis were used as outcomes, and genetic variants associated with plasma cortisol were used as instrumental variables. The main analysis was performed using the inverse variance weighted method, and the results were assessed according to the odds ratio (OR) and 95% confidence interval. Heterogeneity tests, pleiotropy tests, and leave-one-out method were conducted to evaluate the stability and accuracy of the results.

RESULTS

In two-sample MR analysis, the inverse variance weighted method showed that plasma cortisol was associated with Alzheimer's disease (AD) [odds ratio (95% confidence interval) = 0.99 (0.98-1.00), P = 0.025], vascular dementia (VaD) [odds ratio (95% confidence interval) = 2.02 (1.00-4.05), P = 0.049)], Parkinson's disease with dementia (PDD) [odds ratio (95% confidence interval) = 0.24 (0.07-0.82), P = 0.023] and epilepsy [odds ratio (95% confidence interval) = 2.00 (1.03-3.91), P = 0.042]. There were no statistically significant associations between plasma cortisol and dementia with Lewy bodies (DLB), frontotemporal dementia (FTD) and multiple sclerosis.

CONCLUSION

This study demonstrates that plasma cortisol increase the incidence rates of epilepsy and VaD and decrease the incidence rates of AD and PDD. Monitoring plasma cortisol concentrations in clinical practice can help prevent diseases, such as AD, PDD, VaD and epilepsy.

Midlife occupational cognitive requirements protect cognitive function in old age by increasing cognitive reserve

Introduction

Several lifestyle factors promote protection against Alzheimer's disease (AD) throughout a person's lifespan. Although such protective effects have been described for occupational cognitive requirements (OCR) in midlife, it is currently unknown whether they are conveyed by brain maintenance (BM), brain reserve (BR), or cognitive reserve (CR) or a combination of them.

Methods

We systematically derived hypotheses for these resilience concepts and tested them in the population-based AgeCoDe cohort and memory clinic-based AD high-risk DELCODE study. The OCR score (OCRS) was measured using job activities based on the O*NET occupational classification system. Four sets of analyses were conducted: (1) the interaction of OCR and APOE-ε4 with regard to cognitive decline (N = 2,369, AgeCoDe), (2) association with differentially shaped retrospective trajectories before the onset of dementia of the Alzheimer's type (DAT; N = 474, AgeCoDe), (3) cross-sectional interaction of the OCR and cerebrospinal fluid (CSF) AD biomarkers and brain structural measures regarding memory function (N = 873, DELCODE), and (4) cross-sectional and longitudinal association of OCR with CSF AD biomarkers and brain structural measures (N = 873, DELCODE).

Results

Regarding (1), higher OCRS was associated with a reduced association of APOE-ε4 with cognitive decline (mean follow-up = 6.03 years), consistent with CR and BR. Regarding (2), high OCRS was associated with a later onset but subsequently stronger cognitive decline in individuals converting to DAT, consistent with CR. Regarding (3), higher OCRS was associated with a weaker association of the CSF Aβ42/40 ratio and hippocampal volume with memory function, consistent with CR. Regarding (4), OCR was not associated with the levels or changes in CSF AD biomarkers (mean follow-up = 2.61 years). We found a cross-sectional, age-independent association of OCRS with some MRI markers, but no association with 1-year-change. OCR was not associated with the intracranial volume. These results are not completely consistent with those of BR or BM.

Discussion

Our results support the link between OCR and CR. Promoting and seeking complex and stimulating work conditions in midlife could therefore contribute to increased resistance to pathologies in old age and might complement prevention measures aimed at reducing pathology.

Cortisol, cognition and Alzheimer's disease biomarkers among memory clinic patients

Objective

This study aims to investigate the relationship between diurnal cortisol patterns, cognition and Alzheimer's disease (AD) biomarkers in memory clinic patients.

Method

Memory clinic patients were recruited from Karolinska University Hospital in Sweden (n=155). Diurnal cortisol patterns were assessed using five measures: awakening levels, cortisol awakening response, bedtime levels, the ratio of awakening to bedtime levels (AM/PM ratio) and total daily output. Cognition was measured in five domains: memory, working memory, processing speed, perceptual reasoning and overall cognition. AD biomarkers Aβ42, total tau and phosphorylated tau were assessed from cerebrospinal fluid (CSF). Cognition was measured at follow-up (average 32 months) in a subsample of participants (n=57).

Results

In assessing the associations between cortisol and cognition, higher awakening cortisol levels were associated with greater processing speed at baseline. No relationship was found between diurnal cortisol patterns and change in cognition over time or CSF AD biomarkers in the total sample. After stratification by CSF Aβ42 levels, higher awakening cortisol levels were associated with worse memory performance in amyloid-positive participants. In amyloid-negative participants, higher bedtime cortisol levels and a lower AM/PM ratio were associated with lower overall cognition, greater awakening cortisol levels were associated with better processing speed, and a higher AM/PM ratio was associated with better perceptual reasoning. Additionally, higher awakening cortisol levels were associated with lower CSF Aβ42 levels in amyloid-positive participants, while higher bedtime cortisol levels and a lower AM/PM ratio were associated with higher CSF total tau in amyloid-negative participants.

Conclusions

Our findings suggest that diurnal cortisol patterns are associated with cognitive function and provide new insights into the association between diurnal cortisol patterns and AD-related CSF biomarkers. Further research is needed to examine the complex relationship between cortisol, cognition and brain pathology.

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.

Influence of Cortisol on the Fibril Formation Kinetics of Aβ42 Peptide: A Multi-Technical Approach

Amyloid-β peptide (Aβ) aggregates are known to be correlated with pathological neurodegenerative diseases. The fibril formation process of such peptides in solution is influenced by several factors, such as the ionic strength of the buffer, concentration, pH, and presence of other molecules, just to mention a few. In this paper, we report a detailed analysis of in vitro Aβ42 fibril formation in the presence of cortisol at different relative concentrations. The thioflavin T fluorescence assay allowed us to monitor the fibril formation kinetics, while a morphological characterization of the aggregates was obtained by atomic force microscopy. Moreover, infrared absorption spectroscopy was exploited to investigate the secondary structure changes along the fibril formation path. Molecular dynamics calculations allowed us to understand the intermolecular interactions with cortisol. The combined results demonstrated the influence of cortisol on the fibril formation process: indeed, at cortisol-Aβ42 concentration ratio (ρ) close to 0.1 a faster organization of Aβ42 fragments into fibrils is promoted, while for ρ = 1 the formation of fibrils is completely inhibited.

Computerized Cognitive Training in Amnestic Mild Cognitive Impairment: A Randomized Clinical Trial

OBJECTIVE

Computerized cognitive training has been successful in healthy older adults, but its efficacy has been mixed in patients with amnestic Mild Cognitive Impairment (MCI).

METHODS

In a randomized, placebo-controlled, double-blind, parallel clinical trial, we examined the short- and long-term efficacy of a brain-plasticity computerized cognitive training in 113 participants with amnestic MCI.

RESULTS

Immediately after 40-hours of training, participants in the active control group who played computer games performed better than those in the experimental group on the primary cognitive outcome (p = 0.02), which was an auditory memory/attention composite score. There were no group differences on 2 secondary outcomes (global cognitive composite and rating of daily functioning). After 1 year, there was no difference between the 2 groups on primary or secondary outcomes. No adverse events were noted.

CONCLUSIONS

Although the experimental cognitive training program did not improve outcomes in those with MCI, the short-term effects of the control group should not be dismissed, which may alter treatment recommendations for these patients.

Depression and Dementia: The Role of Cortisol and Vascular Brain Lesions. AGES-Reykjavik Study

BACKGROUND

Late-life depression (LLD) is related to an increased risk of developing dementia; however, the biological mechanisms explaining this relationship remain unclear.

OBJECTIVE

To determine whether the relationship between LLD and dementia can be best explained by the glucocorticoid cascade or vascular hypothesis.

METHODS

Data are from 4,354 persons (mean age 76±5 years) without dementia at baseline from the AGES-Reykjavik Study. LLD was assessed with the MINI diagnostic interview (current and remitted major depressive disorder [MDD]) and the Geriatric Depression Scale-15. Morning and evening salivary cortisol were collected (glucocorticoid cascade hypothesis). White matter hyperintensities (WMH; vascular hypothesis) volume was assessed using 1.5T brain MRI. Using Cox proportional hazard models, we estimated the associations of LLD, cortisol levels, and WMH volume with incident all-cause dementia, AD, and non-AD dementia.

RESULTS

During 8.8±3.2 years of follow-up, 843 persons developed dementia, including 397 with AD. Current MDD was associated with an increased risk of developing all-cause dementia (HR = 2.17; 95% CI 1.66-2.67), with risks similar for AD and non-AD, while remitted MDD was not (HR = 1.02; 95% CI 0.55-1.49). Depressive symptoms were also associated with increased risk of dementia, in particular non-AD dementias. Higher levels of evening cortisol increased risk of dementia, but this was independent of MDD. WMH partially explained the relation between current MDD and dementia risk but remained increased (HR = 1.71; 95% CI 1.34-2.08).

CONCLUSION

The current study highlights the importance of LLD in developing dementia. However, neither the glucocorticoid cascade nor the vascular hypotheses fully explained the relation between depression and dementia.

Cognitive Reserve and Anxiety Interactions Play a Fundamental Role in the Response to the Stress

The aims of the present study were to assess the possible interaction between Cognitive Reserve (CR) and State Anxiety (SA) on adrenocortical and physiological responses in coping situations. Forty healthy, middle-aged men completed the Cognitive Reserve Scale and the State-Trait Anxiety Inventory. We used an Observational Fear Conditioning (OFC) paradigm in order to assess emotional learning and to induce stress. Electrodermal activity (EDA) and salivary cortisol concentrations were measured throughout the conditions. Our results indicate that those who indicated having higher state anxiety showed a lower capacity for learning the contingency, along with presenting higher salivary cortisol peak response following the observational fear-conditioning paradigm. The most prominent finding was the interaction between cognitive reserve and state anxiety on cortisol response to the post observational fear-conditioning paradigm. Thus, those who showed a high anxiety-state and, at the same time, a high cognitive reserve did not present an increased salivary cortisol response following the observational fear-conditioning paradigm. Given these results, we postulate that the state anxiety reported by participants, reflects emotional activation that hinders the attention needed to process and associate emotional stimuli. However, cognitive reserve has an indirect relation with conditioning, enabling better emotional learning. In this context, cognitive reserve demonstrated a protective effect on hormonal response in coping situations, when reported anxiety or emotional activation were high. These findings suggest that cognitive reserve could be used as a tool to deal with the effects of stressors in life situations, limiting development of the allostatic load.

Air Pollution Neurotoxicity in the Adult Brain: Emerging Concepts from Experimental Findings

Epidemiological studies are associating elevated exposure to air pollution with increased risk of Alzheimer's disease and other neurodegenerative disorders. In effect, air pollution accelerates many aging conditions that promote cognitive declines of aging. The underlying mechanisms and scale of effects remain largely unknown due to its chemical and physical complexity. Moreover, individual responses to air pollution are shaped by an intricate interface of pollutant mixture with the biological features of the exposed individual such as age, sex, genetic background, underlying diseases, and nutrition, but also other environmental factors including exposure to cigarette smoke. Resolving this complex manifold requires more detailed environmental and lifestyle data on diverse populations, and a systematic experimental approach. Our review aims to summarize the modest existing literature on experimental studies on air pollution neurotoxicity for adult rodents and identify key gaps and emerging challenges as we go forward. It is timely for experimental biologists to critically understand prior findings and develop innovative approaches to this urgent global problem. We hope to increase recognition of the importance of air pollution on brain aging by our colleagues in the neurosciences and in biomedical gerontology, and to support the immediate translation of the findings into public health guidelines for the regulation of remedial environmental factors that accelerate aging processes.

Cognitive Reserve, Alzheimer's Neuropathology, and Risk of Dementia: A Systematic Review and Meta-Analysis

Cognitive reserve (CR) may reduce the risk of dementia. We summarized the effect of CR on progression to mild cognitive impairment (MCI) or dementia in studies accounting for Alzheimer's disease (AD)-related structural pathology and biomarkers. Literature search was conducted in Web of Science, PubMed, Embase, and PsycINFO. Relevant articles were longitudinal, in English, and investigating MCI or dementia incidence. Meta-analysis was conducted on nine articles, four measuring CR as cognitive residual of neuropathology and five as composite psychosocial proxies (e.g., education). High CR was related to a 47% reduced relative risk of MCI or dementia (pooled-hazard ratio: 0.53 [0.35, 0.81]), with residual-based CR reducing risk by 62% and proxy-based CR by 48%. CR protects against MCI and dementia progression above and beyond the effect of AD-related structural pathology and biomarkers. The finding that proxy-based measures of CR rivaled residual-based measures in terms of effect on dementia incidence underscores the importance of early- and mid-life factors in preventing dementia later.

Cortisol hypersecretion and the risk of Alzheimer's disease: A systematic review and meta-analysis

BACKGROUND

Morning cortisol levels have been reported to be elevated among patients with Alzheimer's disease (AD); yet no meta-analysis has been conducted to confirm the existence and magnitude of this association. It also remains unclear whether hypercortisolism is a risk factor for AD.

METHODS

PubMed, EMBASE, and PsycINFO were systematically searched for eligible studies. Cross-sectional data were pooled using random-effects meta-analyses; the differences in morning cortisol levels between patients and cognitively normal controls were quantified. Longitudinal studies were qualitatively synthesised due to methodological heterogeneity.

RESULTS

17,245 participants from 57 cross-sectional studies and 19 prospective cohort studies were included. Compared with cognitively normal controls, AD patients had moderately increased morning cortisol in blood (g = 0.422, P < 0.001; I² = 48.5 %), saliva (g = 0.540, P < 0.001; I² = 13.6 %), and cerebrospinal fluids (g = 0.565, P = 0.003; I² = 75.3 %). A moderate elevation of morning cortisol was also detected in cerebrospinal fluids from patients with mild cognitive impairment (MCI) versus controls (g = 0.309, P = 0.001; I² = 0.0 %). Cohort studies suggested that higher morning cortisol may accelerate cognitive decline in MCI or mild AD patients, but the results in cognitively healthy adults were inconsistent.

CONCLUSIONS

Morning cortisol was confirmed to be moderately elevated in AD patients and may have diagnostic and prognostic values for AD.

Determination of neurosteroids in human cerebrospinal fluid in the 21st century: A review

Determination of steroid hormones synthesized by the human body plays an important role in various fields of endocrinology. Neurosteroids (NS) are steroids that are synthesized in the central (CNS) or peripheral nervous system (PNS), which is not only a source but also a target for neurosteroids. They are discussed as possible biomarkers in various cognitive disorders and research interest in this topic raises continuously. Nevertheless, knowledge on functions and metabolism is still limited, although the concept of neurosteroids was already introduced in the 1980s. Until today, the analysis of neurosteroids is truly challenging. The only accessible matrix for investigations of brain metabolism in living human beings is cerebrospinal fluid (CSF), which therefore becomes a very interesting specimen for analysis. However, neurosteroid concentrations are expected to be very low and the available amount of cerebrospinal fluid is limited. Further, high structural similarities of endogenous neurosteroids challenges analysis. Therefore, comprehensive methods, highly selective and sensitive for a large range of concentrations for different steroids in one aliquot are required and under continuous development. Although research has been increasingly intensified, still only few data are available on reference levels of neurosteroids in human cerebrospinal fluid. In this review, published literature of the last twenty years, as a period with relatively contemporary analytical methods, was systematically investigated. Considerations on human cerebrospinal fluid, different analytical approaches, and available data on levels of in analogy to periphery conceivable occurring neurosteroids, including (pro-) gestagens, androgens, corticoids, estrogens, and steroid conjugates, and their interpretation are intensively discussed.

11β-hydroxysteroid dehydrogenase type 1 inhibitor use in human disease-a systematic review and narrative synthesis

INTRODUCTION

11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) is an intracellular enzyme that catalyses conversion of cortisone into cortisol; correspondingly, 11β-HSD1 inhibitors inhibit this conversion. This systematic review focuses on the use of 11β-HSD1 inhibitors in diseases known to be associated with abnormalities in hypothalamic pituitary adrenal (HPA) axis function.

METHODS

The databases screened for suitable papers were: MedLine, EMBASE, Web of Science, ClinicalTrials.gov, and Cochrane Central.

RESULTS

1925 papers were identified, of which 29 were included in the final narrative synthesis. 11β-HSD1 and its inhibitors have been studied in diabetes, obesity, metabolic syndrome (MetS), and Alzheimer's disease (AD). Higher expression of 11β-HSD1 is seen in obesity and MetS, but has not yet been described in obesity or AD. Genetic studies identify 11β-HSD1 SNPs of interest in populations with diabetes, MetS, and AD. One phase II trial successfully reduced HbA1c in a diabetic population, however trials in MetS, obesity, and AD have not met primary endpoints.

CONCLUSIONS

Translation of this research from preclinical studies has proved challenging so far, however this is a growing area of research and more studies should focus on understanding the complex relationships between 11β-HSD1 and disease pathology, especially given the therapeutic potential of 11β-HSD1 inhibitors in development.

Comparison of mortality rate in older adults with and without functional awareness: the Neurological Disorders in Central Spain (NEDICES) population-based study

OBJECTIVES

The main aim of the study was to compare the rates of mortality in older adults with and without functional unawareness (FU). We also tested a possible interaction effect between levels of awareness and education, as a single cognitive reserve proxy, on mortality.

STUDY DESIGN

The study design is a longitudinal population-based cohort study.

METHODS

The Neurological Disorders in Central Spain is epidemiological study to detect main age-associated conditions in people aged 65 years and older. Participants were collected from updated population-based registers of residents in three areas of central Spain. Awareness of functional limitations was established in accordance with the discrepancy between two sources of information on functional impairments: reliable informants versus the participants themselves. Three mutually exclusive groups were formed, namely, Functional Limitation Complaints (FCs), FU, and Functional Awareness (FA). Cox's regression models, adjusted by different covariates, were used to calculate the risk of mortality for each group at 5-year follow-up (vs. reference group without limitations).

RESULTS

Of 1818 selected individuals, 229 (12.5%) showed FA, 254 (13.9%) showed FC, and 96 (5%) were classified as FU. All these groups showed an increased risk of mortality at 5-year follow-up [adjusted hazard ratio (HR) for FC < FU < FA]. However, the association of FU with mortality remained significant only for highly educated individuals.

CONCLUSIONS

Functional impairment was associated with increased mortality rates, regardless of the presence of unawareness. This study extends the role of education in modulating the symptoms and prognosis of individuals at very mild or preclinical dementia stages.

Cortisol reactivity to a psychosocial stressor significantly increases the risk of developing Cognitive Impairment no Dementia five years later

Alzheimer's disease (AD) patients show high cortisol levels suggesting that biological mediators of stress may play a role in the neurodegenerative process of cognitive disorders. However, there is no consensus as to whether cortisol concentrations represent a risk factor for the development of cognitive impairment. We analyzed the potential association between the incidence of cognitive impairment and cortisol concentrations under basal and acute stress conditions in 129 individuals aged 50 years or older, with preserved cognitive and functional abilities. All participants were recruited in 2011 for assessment of cognitive performance and cortisol levels. Cortisol was analyzed in saliva samples collected during two typical and consecutive days, in the morning, afternoon, and night, and also during exposure to an acute psychosocial stressor (Trier Social Stress Test - TSST). After a five-year follow-up, 69 of these volunteers were reassessed for cognitive performance, functional evaluation, memory complaints, and depression. The incidence of cognitive impairment not dementia (CIND) was 26.1 %, and was positively associated with greater TSST-induced cortisol release (responsiveness) [(95 % CI = 1.001-1.011; B = 0.006), p = 0.023]. Moreover, five years before diagnosis, participants who later developed CIND had greater responsiveness to TSST (p = 0.019) and lower cortisol awakening response (CAR: p = 0.018), as compared to those who did not develop CIND. These findings suggest that higher psychosocial stress responsiveness profiles may represent a preclinical sign of cognitive impairment.

Cognitive Reserve from the Perspective of Preclinical Alzheimer Disease: 2020 Update

The concept of cognitive reserve (CR) was proposed to account for the discrepancy between levels of brain pathologic process or damage and clinical and cognitive function. We provide a detailed review of prospective longitudinal studies that have investigated the interaction between CR and Alzheimer disease (AD) biomarkers on clinical and cognitive outcomes among individuals with normal cognition at baseline. Current evidence is consistent with the view that higher levels of CR are associated with a delay in the onset of symptoms of mild cognitive impairment and that there may be multiple pathways by which CR exerts its protective effects.