Testosterone reduces neuronal secretion of Alzheimer's beta-amyloid peptides

Sex-specific associations of serum testosterone with gray matter volume and cerebral blood flow in midlife individuals at risk for Alzheimer's disease

Testosterone, an essential sex steroid hormone, influences brain health by impacting neurophysiology and neuropathology throughout the lifespan in both genders. However, human research in this area is limited, particularly in women. This study examines the associations between testosterone levels, gray matter volume (GMV) and cerebral blood flow (CBF) in midlife individuals at risk for Alzheimer's disease (AD), according to sex and menopausal status. A cohort of 294 cognitively normal midlife participants, 83% female, ages 35-65 years, with an AD family history and/or Apolipoprotein E epsilon 4 (APOE-4) genotype, underwent volumetric Magnetic Resonance Imaging (MRI) to measure GMV and MR-Arterial Spin Labeling (ASL) for measurement of CBF. We used voxel-based analysis and volumes of interest to test for associations between testosterone (both total and free testosterone) and brain imaging outcomes, stratified by sex and menopausal status. Higher total and free testosterone levels were associated with larger GMV in men, with peak effects in frontal and temporal regions. Conversely, in women, higher testosterone levels correlated with higher CBF, with peak effects in frontal and limbic regions, subcortical areas and hypothalamus. Among women, associations between testosterone and GMV were observed at the premenopausal and perimenopausal stages, but not postmenopause, whereas associations of testosterone with CBF were significant starting at the perimenopausal stage and were more pronounced among hormone therapy non-users. Results were independent of age, APOE-4 status, midlife health indicators, and sex hormone-binding globulin levels. These findings indicate sex-specific neurophysiological effects of testosterone in AD-vulnerable regions in midlife individuals at risk for AD, with variations observed across sex and menopausal status. This underscores the need for further research focusing on the neuroprotective potential of testosterone in both sexes.

Biological Sex Disparities in Alzheimer's Disease

Alzheimer's disease is a highly complex and multifactorial neurodegenerative disorder, with age being the most significant risk factor. The incidence of Alzheimer's disease doubles every 5 years after the age of 65. Consequently, one of the major challenges in Alzheimer's disease research is understanding how the brain changes with age. Gaining insights into these changes could help identify individuals who are more prone to developing Alzheimer's disease as they age. Over the past 25 years, studies on brain aging have examined thousands of human brains to explore the neuronal basis of age-related cognitive decline. However, most of these studies have focused on adults over 60, often neglecting the critical menopause transition period. During menopause, women experience a substantial decline in ovarian sex hormone production, with a decrease of about 90% in estrogen levels. Estrogen is known for its neuroprotective effects, and its significant loss during menopause affects various biological systems, including the brain. Importantly, despite known differences in dementia risk between sexes, the impact of biological sex and sex hormones on brain aging and the development of Alzheimer's disease remains underexplored.

Low testosterone levels relate to poorer cognitive function in women in an APOE-ε4-dependant manner

BACKGROUND

Past research suggests that low testosterone levels relate to poorer cognitive function and higher Alzheimer's disease (AD) risk; however, these findings are inconsistent and are mostly derived from male samples, despite similar age-related testosterone decline in females. Both animal and human studies demonstrate that testosterone's effects on brain health may be moderated by apolipoprotein E ε4 allele (APOE-ε4) carrier status, which may explain some previous inconsistencies. We examined how testosterone relates to cognitive function in older women versus men across healthy aging and the AD continuum and the moderating role of APOE-ε4 genotype.

METHODS

Five hundred and sixty one participants aged 55-90 (155 cognitively normal (CN), 294 mild cognitive impairment (MCI), 112 AD dementia) from the Alzheimer's Disease Neuroimaging Initiative (ADNI), who had baseline cognitive and plasma testosterone data, as measured by the Rules Based Medicine Human DiscoveryMAP Panel were included. There were 213 females and 348 males (self-reported sex assigned at birth), and 52% of the overall sample were APOE-ε4 carriers. We tested the relationship of plasma testosterone levels and its interaction with APOE-ε4 status on clinical diagnostic group (CN vs. MCI vs. AD), global, and domain-specific cognitive performance using ANOVAs and linear regression models in sex-stratified samples. Cognitive domains included verbal memory, executive function, processing speed, and language.

RESULTS

We did not observe a significant difference in testosterone levels between clinical diagnostic groups in either sex, regrardless of APOE-ε4 status. Across clinical diagnostic group, we found a significant testosterone by APOE-ε4 interaction in females, such that lower testosterone levels related to worse global cognition, processing speed, and verbal memory in APOE-ε4 carriers only. We did not find that testosterone, nor its interaction with APOE-ε4, related to cognitive outcomes in males.

CONCLUSIONS

Findings suggest that low testosterone levels in older female APOE-ε4 carriers across the aging-MCI-AD continuum may have deleterious, domain-specific effects on cognitive performance. Although future studies including additional sex hormones and longitudinal cognitive trajectories are needed, our results highlight the importance of including both sexes and considering APOE-ε4 carrier status when examining testosterone's role in cognitive health.

Water extract of moschus alleviates erastin-induced ferroptosis by regulating the Keap1/Nrf2 pathway in HT22 cells

ETHNOPHARMACOLOGICAL RELEVANCE

Moschus, first described in the Shennong's Classic of the Materia medicine, is a scarce and precious animal medicine. Modern pharmacological researches have suggested that Moschus has neuroprotective actions, and its mechanism is related to anti-inflammatory, antioxidant, and anti-apoptosis effects. Ferroptosis is one of the major pathologies of Alzheimer's disease (AD) and is widely implicated in the pathogenesis and progression of AD. Although previous studies have suggested that Moschus possesses neuroprotective effect, whether Moschus could mitigate neuronal damages by inhibiting the onset of ferroptosis is unknown in model cells of AD.

AIM OF THE STUDY

The aim of study was to explore the water extract of Moschus (WEM) on ferroptosis caused by erastin and the potential mechanism.

MATERIALS AND METHODS

Erastin was used to stimulate HT22 cells to form ferroptosis model to evaluate the anti-ferroptosis effect of WEM by cell counting kit-8 and lactic dehydrogenase (LDH) tests. The malondialdehyde (MDA) and glutathione (GSH) kits are used for detection of MDA and GSH levels, and 2',7'-dichlorofluorescein diacetate and C11 BODIPY 581/591 fluorescence probe are used for evaluation of reactive oxygen species (ROS) and lipid peroxide (LOOH) levels. And Western blot was used to test nuclear factor erythroid 2-related factor 2 (Nrf2), Kelch-like ECH-associated protein 1 (Keap1), heme oxygenase-1 (HO-1), and ferroptosis associated proteins including glutathione peroxidase 4 (GPX4), cystine/glutamate antiporter subunit (SLC7A11), ferritin heavy chain 1 (FTH1), ferroportin1 (FPN1), transferrin receptor (TFRC). In addition, the Nrf2 inhibitor ML385 was applied to verify whether WEM prevents erastin-induced ferroptosis by activating the Keap1/Nrf2 pathway.

RESULTS

After WEM treatment, erastin-induced HT22 cell survival was significantly elevated, the accumulation of intracellular MDA, ROS, and LOOH were significantly reduced, the level of GSH and expressions of ferroptosis inhibitors GPX4 and SLC7A11 were significantly increased, and iron metabolism-related proteins TFRC, FPN1, and FTH1 were regulated. These effects of WEM are implemented by activating the Keap1/Nrf2 pathway.

CONCLUSIONS

This study demonstrated that WEM could perform neuroprotective effects by alleviating ferroptosis, verified that WEM treatment of AD can be mediated by the Keap1/Nrf2 pathway, and provided theoretical support for the application of WEM in the treatment of AD.

Association between human blood metabolites and cerebral cortex architecture: evidence from a Mendelian randomization study

Background

Dysregulation of circulating metabolites may affect brain function and cognition, associated with alterations in the cerebral cortex architecture. However, the exact cause remains unclear. This study aimed to determine the causal effect of circulating metabolites on the cerebral cortex architecture.

Methods

This study utilized retrieved data from genome-wide association studies to investigate the relationship between blood metabolites and cortical architecture. A total of 1,091 metabolites and 309 metabolite ratios were used for exposure. The brain cortex surface area and cortex thickness were selected as the primary outcomes in this study. In this study, the inverse variance weighting method was used as the main analytical method, complemented by sensitivity analyses that were more robust to pleiotropy. Furthermore, metabolic pathway analysis was performed via MetaboAnalyst 6.0. Finally, reverse Mendelian randomization (MR) analysis was conducted to assess the potential for reverse causation.

Results

After correcting for the false discovery rate (FDR), we identified 37 metabolites and 9 metabolite ratios that showed significant causal associations with cortical structures. Among these, Oxalate was found to be most strongly associated with cortical surface area (β: 2387.532, 95% CI 756.570-4018.495, p = 0.037), while Tyrosine was most correlated with cortical thickness (β: -0.015, 95% CI -0.005 to -0.025, p = 0.025). Furthermore, pathway analysis based on metabolites identified six significant metabolic pathways associated with cortical structures and 13 significant metabolic pathways based on metabolite ratios.

Conclusion

The identified metabolites and relevant metabolic pathways reveal potential therapeutic pathways for reducing the risk of neurodegenerative diseases. These findings will help guide health policies and clinical practice in treating neurodegenerative diseases.

Association of genetically predicted 486 blood metabolites on the risk of Alzheimer's disease: a Mendelian randomization study

Background

Studies have reported that metabolic disturbance exhibits in patients with Alzheimer's disease (AD). Still, the presence of definitive evidence concerning the genetic effect of metabolites on AD risk remains insufficient. A systematic exploration of the genetic association between blood metabolites and AD would contribute to the identification of new targets for AD screening and prevention.

Methods

We conducted an exploratory two-sample Mendelian randomization (MR) study aiming to preliminarily identify the potential metabolites involved in AD development. A genome-wide association study (GWAS) involving 7,824 participants provided information on 486 human blood metabolites. Outcome information was obtained from a large-scale GWAS meta-analysis of AD, encompassing 21,982 cases and 41,944 controls of Europeans. The primary two-sample MR analysis utilized the inverse variance weighted (IVW) model while supplementary analyses used Weighted median (WM), MR Egger, Simple mode, and Weighted mode, followed by sensitivity analyses such as the heterogeneity test, horizontal pleiotropy test, and leave-one-out analysis. For the further identification of metabolites, replication and meta-analysis with FinnGen data, steiger test, linkage disequilibrium score regression, confounding analysis, and were conducted for further evaluation. Multivariable MR was performed to assess the direct effect of metabolites on AD. Besides, an extra replication analysis with EADB data was conducted for final evaluation of the most promising findings.

Results

After rigorous genetic variant selection, IVW, complementary analysis, sensitivity analysis, replication and meta-analysis with the FinnGen data, five metabolites (epiandrosterone sulfate, X-12680, pyruvate, docosapentaenoate, and 1-stearoylglycerophosphocholine) were identified as being genetically associated with AD. MVMR analysis disclosed that genetically predicted these four known metabolites can directly influence AD independently of other metabolites. Only epiandrosterone sulfate and X-12680 remained suggestive significant associations with AD after replication analysis with the EADB data.

Conclusion

By integrating genomics with metabonomics, this study furnishes evidence substantiating the genetic association of epiandrosterone sulfate and X-12680 with AD. These findings hold significance for the screening, prevention, and treatment strategies for AD.

The underlying roles and neurobiological mechanisms of music-based intervention in Alzheimer's disease: A comprehensive review

Non-pharmacological therapy has gained popularity in the intervention of Alzheimer's disease (AD) due to its apparent therapeutic effectiveness and the limitation of biological drug. A wealth of research indicates that music interventions can enhance cognition, mood and behavior in individuals with AD. Nonetheless, the underlying mechanisms behind these improvements have yet to be fully and systematically delineated. This review aims to holistically review how music-based intervention (MBI) ameliorates abnormal emotion, cognition decline, and behavioral changes in AD patients. We cover several key dimensions: the regulation of MBIs on cerebral blood flow (CBF), their impact on neurotransmission (including GABAergic and monoaminergic transmissions), modulation of synaptic plasticity, and hormonal release. Additionally, we summarize the clinical applications and limitations of active music-based intervention (AMBI), passive music-based intervention (PMBI), and hybrid music-based intervention (HMBI). This thorough analysis enhances our understanding of the role of MBI in AD and supports the development of non-pharmacological therapeutic strategies.

Does Sex Matter? High Semantic Autobiographical Retrieval in Women and Men With Alzheimer's Disease

The decline of autobiographical memory in Alzheimer's disease (AD) is mainly characterized by overgenerality. While there is a large body of research on autobiographical overgenerality in AD, this research has mainly assessed retrieval with a dichotomy between specific vs. general retrieval. To go beyond this dichotomy, we assessed several degrees of autobiographical specificity in patients with AD, namely, we assessed specific vs. categoric vs. extended vs. semantic retrieval. We also assessed sex differences regarding these degrees of autobiographical specificity. We invited patients with mild AD and control participants to complete sentences (e. g., "When I think back to/of…") with autobiographical memories. Memories were categorized into specific, categoric, extended, or semantic memories. Results demonstrated more semantic than specific, categoric or extended memories in men and women with AD. In control participants, analysis demonstrated more specific than categoric, extended, and semantic memories in men and women. Also, no significant differences were observed between women and men with AD, or between control women and men, regarding specific, categoric, extended, and semantic memoires. This study offers not only a nuanced analysis of autobiographical specificity in patients with mild AD, but also an original analysis regarding this specificity by sex.

Sarcopenic obesity is part of obesity paradox in dementia development: evidence from a population-based cohort study

BACKGROUND

Sarcopenic obesity, a clinical and functional condition characterized by the coexistence of obesity and sarcopenia, has not been investigated in relation to dementia risk and its onset.

METHODS

We included 208,867 participants from UK biobank, who aged 60 to 69 years at baseline. Dementia diagnoses were identified using hospital records and death register data. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using Cox proportional hazards models to evaluate the associations of obesity, sarcopenia, and sarcopenic obesity with dementia risk, stratified by sex. Stratified analyses were performed across dementia-related polygenic risk score (PRS). Restricted mean survival time models were established to estimate the difference and 95%CIs of dementia onset across different status. Additionally, linear regression models were employed to estimate associations of different status with brain imaging parameters. The mediation effects of chronic diseases were also examined.

RESULTS

Obese women with high PRS had a decreased risk (HR = 0.855 [0.761-0.961]), but obese men with low PRS had an increased risk (HR = 1.223 [1.045-1.431]). Additionally, sarcopenia was associated with elevated dementia risk (HRwomen = 1.323 [1.064-1.644]; HRmen = 2.144 [1.753-2.621]) in those with low PRS. Among those with high PRS, however, the association was only significant in early-life (HRwomen = 1.679 [1.355-2.081]; HRmen = 2.069 [1.656-2.585]). Of note, sarcopenic obesity was associated with higher dementia risk (HRwomen = 1.424 [1.227-1.653]; HRmen = 1.989 [1.702-2.323]), and results remained similar stratified by PRS. Considering dementia onset, obesity was associated with dementia by 1.114 years delayed in women, however, 0.170 years advanced in men. Sarcopenia (women: 0.080 years; men: 0.192 years) and sarcopenic obesity (women: 0.109 years; men: 0.511 years) respectively advanced dementia onset. Obesity, sarcopenia, and sarcopenic obesity were respectively related to alterations in different brain regions. Association between sarcopenic obesity and dementia was mediated by chronic diseases.

CONCLUSIONS

Sarcopenic obesity and sarcopenia were respectively associated with increased dementia risk and advanced dementia onset to vary degree. The role of obesity in dementia may differ by sex and genetic background.

Sex-Specific Differences in Serum Kallikrein-8 (KLK8): An Exploratory Study

Background

There are indications for sex-specific differences regarding the association between kallikrein-8 (KLK8) and cognitive impairment in early stages of Alzheimer's disease for which KLK8 may be an early blood-based biomarker. These may be due to different levels of sex hormones. To correctly interpret KLK8 blood concentrations, sex-specific analyses are needed.

Objective

The aim of our exploratory study was to investigate sex-specific differences in blood-based KLK8 in participants of the population-based Heinz Nixdorf Recall study with different cognitive status and the association between KLK8 and sex hormones.

Methods

In 290 participants (45% women, 69.7±7.4 years (mean±SD)) we investigated sex-specific serum KLK8 differences between cognitively unimpaired (CU, 43%) and cognitively impaired (CI) participants and the association between KLK8 and dehydroepiandrosteronsulfate (DHEAS), estradiol and testosterone, using adjusted multiple linear regression.

Results

The mean±SD KLK8 was similar for CU men (808.1±729.6 pg/ml) and women (795.9±577.7 pg/ml); adjusted mean-difference [95%-CI]: -95.3 [-324.1;133.5] pg/ml. KLK8 was lower in CI women (783.5±498.7 pg/ml) than men (1048.4±829 pg/ml); -261 [-493.1; -29] pg/ml. In men but not women, there was a weak indication for a positive slope between estradiol (11.9 [-0.4;24.3] pg/ml) and DHEAS (1.4 [-0.5;3.3] pg/ml) with KLK8, while testosterone had no impact.

Conclusions

The results suggested a different role for KLK8 in the development of cognitive impairment in men and women, potentially influenced by sex hormones. To use blood KLK8 as an early biomarker, further research on hormonal regulation of KLK8 expression is needed as a part of the investigation of the KLK8 involvement in cognitive impairment and Alzheimer's disease pathology.

Testosterone, cognitive decline and dementia in ageing men

As men grow older, circulating testosterone concentrations decline, while prevalence of cognitive impairment and dementia increase. Epidemiological studies of middle-aged and older men have demonstrated associations of lower testosterone concentrations with higher prevalence and incidence of cognitive decline and dementia, including Alzheimer's disease. In observational studies, men with prostate cancer treated by androgen deprivation therapy had a higher risk of dementia. Small intervention studies of testosterone using different measures of cognitive function have provided inconsistent results, with some suggesting improvement. A randomised placebo-controlled trial of one year's testosterone treatment conducted in 788 men aged ≥ 65 years, baseline testosterone < 9.54 nmol/L, showed an improvement in sexual function, but no improvement in cognitive function. There is a known association between diabetes and dementia risk. A randomised placebo-controlled trial of two year's testosterone treatment in 1,007 men aged 50-74 years, waist circumference ≥ 95 cm, baseline testosterone ≤ 14 nmol/L, showed an effect of testosterone in reducing type 2 diabetes risk. There were no cognitive endpoints in that trial. Additional research is warranted but at this stage lower testosterone concentrations in ageing men should be regarded as a biomarker rather than a proven therapeutic target for risk reduction of cognitive decline and dementia, including Alzheimer's disease.

Lower serum testosterone concentrations are associated with a higher incidence of dementia in men: The UK Biobank prospective cohort study

INTRODUCTION

The association of testosterone concentrations with dementia risk remains uncertain. We examined associations of serum testosterone and sex hormone-binding globulin (SHBG) with incidence of dementia and Alzheimer's disease.

METHODS

Serum total testosterone and SHBG were measured by immunoassay. The incidence of dementia and Alzheimer's disease (AD) was recorded. Cox proportional hazards regression was adjusted for age and other variables.

RESULTS

In 159,411 community-dwelling men (median age 61, followed for 7 years), 826 developed dementia, including 288 from AD. Lower total testosterone was associated with a higher incidence of dementia (overall trend: P = .001, lowest vs highest quintile: hazard ratio [HR] = 1.43, 95% confidence interval [CI] = 1.13-1.81), and AD (P = .017, HR = 1.80, CI = 1.21-2.66). Lower SHBG was associated with a lower incidence of dementia (P < .001, HR = 0.66, CI = 0.51-0.85) and AD (P = .012, HR = 0.53, CI = 0.34-0.84).

DISCUSSION

Lower total testosterone and higher SHBG are independently associated with incident dementia and AD in older men. Additional research is needed to determine causality.

Association Between Human Blood Metabolome and the Risk of Alzheimer's Disease

OBJECTIVE

Alzheimer's disease (AD) is the most common degenerative neurological disorder with limited therapeutic options. Therefore, it is particularly important to explore the potential biomarkers implicated in the occurrence and progression of AD prior to clinical testing.

METHODS

We selected 119 unique blood metabolites from 3 metabolome genome-wide association studies (GWASs) with 147,827 European participants. Summary data about AD were obtained from a GWAS meta-analysis with 63,926 European individuals from the International Genomics of Alzheimer's Project. MR analyses were performed to assess the associations of blood metabolites with AD, and a phenome-wide MR analysis was further applied to ascertain the potential on-target side effects of metabolite interventions.

RESULTS

Four metabolites were identified as causal mediators for AD, including epiandrosterone sulfate (odds ratio [OR] per SD increase: 0.60; 95% confidence interval [CI]: 0.51-0.71; P=6.14×10^-9 ), 5alpha-androstan-3beta-17beta-diol disulfate (OR per SD increase: 0.69; 95% CI: 0.57-0.84; P=1.98×10^-4 ), sphingomyelin (OR per SD increase: 2.53; 95% CI: 1.78-3.59; P=2.10×10^-7 ), and glutamine (OR per SD increase: 0.83; 95% CI: 0.77-0.89; P=2.09×10^-6 ). Phenome-wide MR analysis showed that epiandrosterone sulfate, 5alpha-androstan-3beta-17beta-diol disulfate and sphingomyelin mediated the risk of multiple diseases, and glutamine had beneficial effects on the risk of 4 diseases.

INTERPRETATION

Genetically predicted increased epiandrosterone sulfate, 5alpha-androstan-3beta-17beta-diol disulfate and glutamine might be associated with a decreased risk of AD, while sphingomyelin was associated with an increased risk. Side-effect profiles were characterized to help inform drug target prioritization, and glutamine might be a promising target for the prevention and treatment of AD with no predicted detrimental side effects. This article is protected by copyright. All rights reserved.

A Personal Prospective on Testosterone Therapy in Women—What We Know in 2022

Hormone replacement therapy continues to be a controversial topic in medicine, with certain narratives regarding safety concerns that are not scientifically established in peer-reviewed literature. These negative narratives, specifically undermining the use of testosterone in women, have caused women to remain without any Food and Drug Administration (FDA)-approved testosterone therapies, while more than 30 FDA-approved testosterone therapies are available for men in the United States. This has resulted in millions of women suffering in silence with very common symptoms of perimenopause and menopause that could easily be addressed with the use of testosterone. There is growing evidence to support the use of physiologic doses of testosterone for sexual function, osteoporosis prevention, brain protection, and breast protection. The safety of testosterone use in women has been evaluated for the past 80 years. A recent publication on the complications of subcutaneous hormone-pellet therapy, looking at a large cohort of patients over 7 years, demonstrated long-term safety. In addition, there have been two large long-term peer-reviewed studies showing a significant reduction in the incidence of invasive breast cancer in women on testosterone therapy. Perhaps it is time for the FDA to consider approving products that would benefit testosterone-deficient women.

Transcriptional and Post-Transcriptional Regulations of Amyloid-β Precursor Protein (APP) mRNA

Alzheimer’s disease (AD) is an age-associated neurodegenerative disorder characterized by progressive impairment of memory, thinking, behavior, and dementia. Based on ample evidence showing neurotoxicity of amyloid-β (Aβ) aggregates in AD, proteolytically derived from amyloid precursor protein (APP), it has been assumed that misfolding of Aβ plays a crucial role in the AD pathogenesis. Additionally, extra copies of the APP gene caused by chromosomal duplication in patients with Down syndrome can promote AD pathogenesis, indicating the pathological involvement of the APP gene dose in AD. Furthermore, increased APP expression due to locus duplication and promoter mutation of APP has been found in familial AD. Given this background, we aimed to summarize the mechanism underlying the upregulation of APP expression levels from a cutting-edge perspective. We first reviewed the literature relevant to this issue, specifically focusing on the transcriptional regulation of APP by transcription factors that bind to the promoter/enhancer regions. APP expression is also regulated by growth factors, cytokines, and hormone, such as androgen. We further evaluated the possible involvement of post-transcriptional regulators of APP in AD pathogenesis, such as RNA splicing factors. Indeed, alternative splicing isoforms of APP are proposed to be involved in the increased production of Aβ. Moreover, non-coding RNAs, including microRNAs, post-transcriptionally regulate the APP expression. Collectively, elucidation of the novel mechanisms underlying the upregulation of APP would lead to the development of clinical diagnosis and treatment of AD.

Androgens Regulate Tau Phosphorylation Through Phosphatidylinositol 3-Kinase-Protein Kinase B-Glycogen Synthase Kinase 3β Signaling

Age-related testosterone depletion in men is a risk factor for Alzheimer's disease (AD). How testosterone modulates AD risk remains to be fully elucidated, although regulation of tau phosphorylation has been suggested as a contributing protective action. To investigate the relationship between testosterone and tau phosphorylation, we first evaluated the effect of androgen status on tau phosphorylation in 3xTg-AD mice. Depletion of endogenous androgens via gonadectomy resulted in increased tau phosphorylation that was prevented by acute testosterone treatment. Parallel alterations in the phosphorylation of both glycogen synthase kinase 3β (GSK3β) and protein kinase B (Akt) suggest possible components of the underlying signaling pathway. To further explore mechanism, primary cultured neurons were treated with a physiological concentration of testosterone or its active metabolite dihydrotestosterone (DHT). Results showed that testosterone and DHT induced significant decreases in phosphorylated tau and significant increases in phosphorylation of Akt and GSK3β. Pharmacological inhibition of phosphatidylinositol 3-kinase (PI3K) effectively inhibited androgen-induced increases in Akt and GSK3β phosphorylation, and decreases in tau phosphorylation. In addition, androgen receptor (AR) knock-down by small interfering RNA prevented androgen-induced changes in the phosphorylation of Akt, GSK3β and tau, suggesting an AR-dependent mechanism. Additional experiments demonstrated androgen-induced changes in Akt, GSK3β and tau phosphorylation in AR-expressing PC12 cells but not in AR-negative PC12 cells. Together, these results suggest an AR-dependent pathway involving PI3K-Akt-GSK3β signaling through which androgens can reduce tau phosphorylation. These findings identify an additional protective mechanism of androgens that can improve neural health and inhibit development of AD.

Sex Differences in Vitamin D Status as a Risk Factor for Incidence of Disability in Instrumental Activities of Daily Living: Evidence from the ELSA Cohort Study

Vitamin D deficiency compromises elements underlying the disability process; however, there is no evidence demonstrating the association between vitamin D deficiency and the incidence of disability in instrumental activities of daily living (IADL). We investigated the association between vitamin D deficiency and the risk of incidence of IADL disability separately in men and women. A total of 4768 individuals aged ≥50 years from the English Longitudinal Study of Aging (ELSA) and without IADL disability according to the Lawton scale were available. Vitamin D was evaluated at baseline by serum 25(OH)D concentrations and classified as sufficient (>50 nmol/L), insufficient (>30 to ≤50 nmol/L) or deficient serum (≤30 nmol/L). IADL were reassessed after 4 years. Poisson models stratified by sex and controlled by covariates demonstrated that deficient serum 25(OH)D was a risk factor for the incidence of IADL disability in men (IRR: 1.43; 95% CI 1.02, 2.00), but not in women (IRR: 1.23; 95% CI 0.94, 1.62). Men appear to be more susceptible to the effect of vitamin D deficiency on the incidence of IADL disability, demonstrating the importance of early clinical investigation of serum 25(OH)D concentrations to prevent the onset of disability.

Lower Plasma Total Testosterone Levels Were Associated With Steeper Decline in Brain Glucose Metabolism in Non-demented Older Men

OBJECTIVE

There is growing evidence that testosterone may be implicated in the pathogenesis of Alzheimer's disease (AD). We aimed to examine the relationship between plasma total testosterone levels and change in brain glucose metabolism over time among non-demented older people.

METHODS

The association of plasma total testosterone levels with change in brain glucose metabolism among non-demented older people was investigated cross-sectionally and longitudinally. Given a significant difference in levels of plasma total testosterone between gender, we performed our analysis in a sex-stratified way. At baseline, 228 non-demented older people were included: 152 males and 76 females.

RESULTS

In the cross-sectional analysis, no significant relationship between plasma total testosterone levels and brain glucose metabolism was found in males or females. In the longitudinal analysis, we found a significant association of plasma total testosterone levels with change in brain glucose metabolism over time in males, but not in females. More specifically, in males, higher levels of total testosterone in plasma at baseline were associated with slower decline in brain glucose metabolism.

CONCLUSION

We found that higher levels of total testosterone in plasma at baseline were associated with slower decline in brain glucose metabolism in males without dementia, indicating that testosterone may have beneficial effects on brain function.

Blood-based Biomarkers of Alzheimer's Disease: The Long and Winding Road

BACKGROUND

Blood-based biomarkers can be very useful in formulating new diagnostic and treatment proposals in the field of dementia, especially in Alzheimer's disease (AD). However, due to the influence of several factors on the reproducibility and reliability of these markers, their clinical use is still very uncertain. Thus, up-to-date knowledge about the main blood biomarkers that are currently being studied is extremely important in order to discover clinically useful and applicable tools, which could also be used as novel pharmacological strategies for the AD treatment.

METHODS

A narrative review was performed based on the current candidates of blood-based biomarkers for AD to show the main results from different studies, focusing on their clinical applicability and association with AD pathogenesis.

OBJECTIVE

The aim of this paper was to carry out a literature review on the major blood-based biomarkers for AD, connecting them with the pathophysiology of the disease.

RESULTS

Recent advances in the search of blood-based AD biomarkers were summarized in this review. The biomarkers were classified according to the topics related to the main hallmarks of the disease such as inflammation, amyloid, and tau deposition, synaptic degeneration and oxidative stress. Moreover, molecules involved in the regulation of proteins related to these hallmarks were described, such as non-coding RNAs, neurotrophins, growth factors and metabolites. Cells or cellular components with the potential to be considered as blood-based AD biomarkers were described in a separate topic.

CONCLUSION

A series of limitations undermine new discoveries on blood-based AD biomarkers. The lack of reproducibility of findings due to the small size and heterogeneity of the study population, different analytical methods and other assay conditions make longitudinal studies necessary in this field to validate these structures, especially when considering a clinical evaluation that includes a broad panel of these potential and promising blood-based biomarkers.

Association of Androgens and Gonadotropins with Amnestic Mild Cognitive Impairment and Probable Alzheimer’s Disease in Chinese Elderly Men

Background: Age-related hormone changes play important roles in cognitive decline in older men, and apolipoprotein E ɛ4 (APOE ɛ4) is a risk factor for Alzheimer’s disease (AD). Objective: This study aimed to investigate the interactive role of androgen decline and APOE ɛ4 genotype in the pathogenesis of amnestic mild cognitive impairment (aMCI) and AD. Methods: In total, 576 elderly men over 65 years old from communities in Shijiazhuang were enrolled in this study, including 243 with normal cognition (NC), 271 with aMCI, and 62 with probable AD. Cognitive function was evaluated with a battery of neuropsychological tests. The serum levels of androgen and gonadotropin were detected by ELISA and chemiluminescence immunoassay. Results: The levels of free testosterone (FT) and dihydrotestosterone (DHT) were lower in the aMCI group (p < 0.05), and even lower in the AD group (p < 0.001), but the levels of follicle stimulating hormone (FSH) and luteinizing hormone (LH) were higher in AD group (p < 0.01), comparing with that in NC or aMCI group. The interaction of lower FT or DHT levels with APOE ɛ4 had a risk role in global cognitive impairment (p < 0.05). The area under the curve (AUC) of the ROC curve for predicting aMCI by serum FT levels was 0.745. Conclusion: These results indicated that the interaction of androgen decline and APOE ɛ4 genotype play a role in aMCI and AD. Serum FT levels have a predictive value for aMCI and might be a potential biomarker for prodromal AD.

Age-Related Male Hypogonadism and Cognitive Impairment in the Elderly: Focus on the Effects of Testosterone Replacement Therapy on Cognition

BACKGROUND

Epidemiological data report that male hypogonadism may play a role in cognitive impairment in elderly. However, the effect of testosterone replacement therapy (TRT) on cognitive abilities in this cluster of patients has not been well established. Methods. PubMed/MEDLINE, Google Scholar, Cochrane Library, and Web of Science were searched by using free text words and medical subject headings terms related with "male hypogonadism", "late-onset hypogonadism", elderly, cognition, "mild cognitive impairment", memory, "testosterone replacement therapy" used in various combinations according to the specific clinical questions. Original articles, reviews, and randomized controlled trials written in English were selected. Results. A long-term TRT could improve specific cognitive functions, such as verbal and spatial memory, cognitive flexibility, and physical vitality. However, randomized controlled trials do not provide positive results, and in most of the cases TRT might not induce beneficial effects on cognitive function in elderly men. Discussion and conclusions. Since the lengthening of life expectancy, the prevalence rate of cognitive decline in elderly men is expected to increase remarkably over the next decade with considerable healthcare and economical concerns. Therefore, this remains a relevant clinical topic and further investigations are needed for clarifying the role of TRT especially in elderly men with hypogonadism.

Androgen Therapy in Neurodegenerative Diseases

Neurodegenerative diseases, including Alzheimer disease (AD), Parkinson disease (PD), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), and Huntington disease, are characterized by the loss of neurons as well as neuronal function in multiple regions of the central and peripheral nervous systems. Several studies in animal models have shown that androgens have neuroprotective effects in the brain and stimulate axonal regeneration. The presence of neuronal androgen receptors in the peripheral and central nervous system suggests that androgen therapy might be useful in the treatment of neurodegenerative diseases. To illustrate, androgen therapy reduced inflammation, amyloid-β deposition, and cognitive impairment in patients with AD. As well, improvements in remyelination in MS have been reported; by comparison, only variable results are observed in androgen treatment of PD. In ALS, androgen administration stimulated motoneuron recovery from progressive damage and regenerated both axons and dendrites. Only a few clinical studies are available in human individuals despite the safety and low cost of androgen therapy. Clinical evaluations of the effects of androgen therapy on these devastating diseases using large populations of patients are strongly needed.

On the Etiopathogenesis and Pathophysiology of Alzheimer's Disease: A Comprehensive Theoretical Review

Alzheimers' disease (AD) is the most common cause of dementia, with an estimated 5 million new cases occurring annually. Among the elderly, AD shortens life expectancy, results in disability, decreases quality of life, and ultimately, leads to institutionalization. Despite extensive research in the last few decades, its heterogeneous pathophysiology and etiopathogenesis have made it difficult to develop an effective treatment and prevention strategy. Aging is the biggest risk factor for AD and evidence suggest that the total number of older people in the population is going to increase astronomically in the next decades. Also, there is evidence that air pollution and increasing income inequality may result in higher incidence and prevalence of AD. This makes the need for a comprehensive understanding of the etiopathogenesis and pathophysiology of the disease extremely critical. In this paper, a quintuple framework of thyroid dysfunction, vitamin D deficiency, sex hormones, and mitochondria dysfunction and oxidative stress are used to provide a comprehensive description of AD etiopathogenesis and pathophysiology. The individual role of each factor, their synergistic and genetic interactions, as well as the limitations of the framework are discussed.

Testosterone, sex steroids, and aging in neurodegenerative disease after acquired brain injury: a commentary

PRIMARY OBJECTIVE

Traumatic brain injury (TBI) is associated with higher incidence of neurodegenerative disease and the effects of aging appear more pronounced after TBI. This paper examines the potential interaction of aging, TBI, and change in male testosterone production.

METHODS AND PROCEDURES

An abbreviated review of literature documenting hypogonadism after TBI is provided. Potential mechanisms of endocrine dysgrasia associated with aging are reviewed as they relate and interact with endocrine change after TBI in males. These factors align to suggest the need for development of surveillance guidelines for male individuals living with TBI.

OUTCOMES AND RESULTS

The neuroprotectant, neuroactivation, growth, and cell therapy characteristics of testosterone in the central nervous system are considerable. Age-related decrements in testosterone production may be accelerated after TBI.

CONCLUSIONS

Testosterone deficiency in male individuals after TBI can be present after TBI or can develop during aging. Age-related decreases in testosterone production after TBI may act to amplify endocrine dysfunction after TBI. Ongoing clinical surveillance for testosterone deficiency associated with both TBI and aging may be reasonable.

Sex and gender differences in Alzheimer's disease: current challenges and implications for clinical practice: Position paper of the Dementia and Cognitive Disorders Panel of the European Academy of Neurology

Alzheimer's disease (AD) is characterized by high heterogeneity in disease manifestation, progression and risk factors. High phenotypic variability is currently regarded as one of the largest hurdles in early diagnosis and in the design of clinical trials; there is therefore great interest in identifying factors driving variability that can be used for patient stratification. In addition to genetic and lifestyle factors, the individual's sex and gender are emerging as crucial drivers of phenotypic variability. Evidence exists on sex and gender differences in the rate of cognitive deterioration and brain atrophy, and in the effect of risk factors as well as in the patterns of diagnostic biomarkers. Such evidence might be of high relevance and requires attention in clinical practice and clinical trials. However, sex and gender differences are currently seldom appreciated; importantly, consideration of sex and gender differences is not currently a focus in the design and analysis of clinical trials for AD. The objective of this position paper is (i) to provide an overview of known sex and gender differences that might have implications for clinical practice, (ii) to identify the most important knowledge gaps in the field (with a special regard to clinical trials) and (iii) to provide conclusions for future studies. This scientific statement is endorsed by the European Academy of Neurology.

The Implication of Androgens in the Presence of Protein Kinase C to Repair Alzheimer’s Disease-Induced Cognitive Dysfunction

Aging, as a major risk factor of memory deficiency, affects neural signaling pathways in hippocampus. In particular, age-dependent androgens deficiency causes cognitive impairments. Several enzymes like protein kinase C (PKC) are involved in memory deficiency. Indeed, PKC regulatory process mediates α-secretase activation to cleave APP in β-amyloid cascade and tau proteins phosphorylation mechanism. Androgens and cortisol regulate PKC signaling pathways, affecting the modulation of receptor for activated C kinase 1. Mitogen-activated protein kinase/ERK signaling pathway depends on CREB activity in hippocampal neurons and is involved in regulatory processes via PKC and androgens. Therefore, testosterone and PKC contribute in the neuronal apoptosis. The present review summarizes the current status of androgens, PKC, and their influence on cognitive learning. Inconsistencies in experimental investigations related to this fundamental correlation are also discussed, with emphasis on the mentioned contributors as the probable potent candidates for learning and memory improvement.

Testosterone and Adult Neurogenesis

It is now well established that neurogenesis occurs throughout adulthood in select brain regions, but the functional significance of adult neurogenesis remains unclear. There is considerable evidence that steroid hormones modulate various stages of adult neurogenesis, and this review provides a focused summary of the effects of testosterone on adult neurogenesis. Initial evidence came from field studies with birds and wild rodent populations. Subsequent experiments with laboratory rodents have tested the effects of testosterone and its steroid metabolites upon adult neurogenesis, as well as the functional consequences of induced changes in neurogenesis. These experiments have provided clear evidence that testosterone increases adult neurogenesis within the dentate gyrus region of the hippocampus through an androgen-dependent pathway. Most evidence indicates that androgens selectively enhance the survival of newly generated neurons, while having little effect on cell proliferation. Whether this is a result of androgens acting directly on receptors of new neurons remains unclear, and indirect routes involving brain-derived neurotrophic factor (BDNF) and glucocorticoids may be involved. In vitro experiments suggest that testosterone has broad-ranging neuroprotective effects, which will be briefly reviewed. A better understanding of the effects of testosterone upon adult neurogenesis could shed light on neurological diseases that show sex differences.

Poor Diet, Stress, and Inactivity Converge to Form a "Perfect Storm" That Drives Alzheimer's Disease Pathogenesis

North American incidence of Alzheimer's disease (AD) is expected to more than double over the coming generation. Although genetic factors surrounding the production and clearance of amyloid-β and phosphorylated tau proteins are known to be responsible for a subset of early-onset AD cases, they do not explain the pathogenesis of the far more prevalent sporadic late-onset variant of the disease. It is thus likely that lifestyle and environmental factors contribute to neurodegenerative processes implicated in the pathogenesis of AD. Herein, we review evidence that (1) excess sucrose consumption induces AD-associated liver pathologies and brain insulin resistance, (2) chronic stress overdrives activity of locus coeruleus neurons, leading to loss of function (a common event in neurodegeneration), (3) high-sugar diets and stress promote the loss of neuroprotective sex hormones in men and women, and (4) Western dietary trends set the stage for a lithium-deficient state. We propose that these factors may intersect as part of a "perfect storm" to contribute to the widespread prevalence of neurodegeneration and AD. In addition, we put forth the argument that exercise and supplementation with trace lithium can counteract many of the deleterious consequences associated with excessive caloric intake and perpetual stress. We conclude that lifestyle and environmental factors likely contribute to AD pathogenesis and that simple lifestyle and dietary changes can help counteract their effects.

Supraphysiologic-dose anabolic-androgenic steroid use: A risk factor for dementia?

Supraphysiologic-dose anabolic-androgenic steroid (AAS) use is associated with physiologic, cognitive, and brain abnormalities similar to those found in people at risk for developing Alzheimer's Disease and its related dementias (AD/ADRD), which are associated with high brain β-amyloid (Aβ) and hyperphosphorylated tau (tau-P) protein levels. Supraphysiologic-dose AAS induces androgen abnormalities and excess oxidative stress, which have been linked to increased and decreased expression or activity of proteins that synthesize and eliminate, respectively, Aβ and tau-P. Aβ and tau-P accumulation may begin soon after initiating supraphysiologic-dose AAS use, which typically occurs in the early 20s, and their accumulation may be accelerated by other psychoactive substance use, which is common among non-medical AAS users. Accordingly, the widespread use of supraphysiologic-dose AAS may increase the numbers of people who develop dementia. Early diagnosis and correction of sex-steroid level abnormalities and excess oxidative stress could attenuate risk for developing AD/ADRD in supraphysiologic-dose AAS users, in people with other substance use disorders, and in people with low sex-steroid levels or excess oxidative stress associated with aging.

On the central role of mitochondria dysfunction and oxidative stress in Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is the commonest cause of dementia, with approximately 5 million new cases occurring annually. Despite decades of research, its complex pathophysiology and etiopathogenesis presents a major hindrance to the development of an effective treatment and prevention strategy. Aging is the biggest risk factor for the development of AD, and the total number of older people in the population is going to significantly increase in the next decades, suggesting that AD incidence and prevalence is likely to increase in the future. This makes the need for a better understanding of the disease to be extremely urgent.

METHODS

A search was done by accessing PubMed/Medline, EBSCO, and PsycINFO databases. The search string used was "(dementia* OR Alzheimer's) AND (pathophysiology* OR pathogenesis)". New key terms were identified (new term included "vitamin D, thyroid hormone, mitochondria dysfunction, oxidative stress, testosterone, estrogen, melatonin, progesterone, luteinizing hormone, amyloid-β (Aβ), and hyperphosphorylated tau"). The electronic databases were searched for titles or abstracts containing these terms in all published articles between January 1, 1965, and January 31, 2019. The search was limited to studies published in English and other languages involving both animal and human subjects.

RESULTS

Mitochondria dysfunction and oxidative stress play a critical role in AD etiopathogenesis and pathophysiology.

CONCLUSION

AD treatment and prevention strategies must be geared towards improving mitochondrial function and attenuating oxidative stress.

Sleep Mediates the Relationship Between Depression and Cognitive Impairment in Older Men

Sleep and depression are strongly associated with cognitive impairment. The role of sleep disturbances in the adverse effect of depression on cognitive dysfunction in older adults remains unclear. This study explored the mediating effect of self-reported sleep disturbances on the relationship between depression and cognitive impairment in older adults according to sex differences. This study derived data from the 2009 Taiwan National Health Interview Survey and included 2,175 community-dwelling adults aged 65 years and older (men = 991; women = 1,184). Sleep disturbances were measured using self-reported survey questions. The Center for Epidemiological Studies Depression scale was used to assess depression. The Mini-Mental State Examination was used to evaluate cognitive impairment. A higher proportion of female older persons had cognitive impairment and depression than male older persons (cognition: 24.4% vs. 11.5%; depression: 17.0% vs. 10.8%). The meditating effect of sleep was detected in only men. Difficulty in initiating sleep was a complete mediator of the adverse effect of depression on cognitive impairment (Sobel test: p = .03). In summary, difficultly in initiating sleep may be a crucial, treatable mediator of the adverse effect of depression on cognitive impairment in older men.

Effects of Androgens on the Amyloid-β Protein in Alzheimer's Disease

Age-related androgen depletion has been implicated in compromised neuroprotection and is involved in the pathogenesis of neurodegenerative disease, including Alzheimer's disease (AD), the leading cause of dementia. Emerging data revealed that reduction of both serum and brain androgen levels in males is associated with increased amyloid-β (Aβ) accumulation, a putative cause of AD. It has been demonstrated that androgens can function as the endogenous negative regulators of Aβ. However, the mechanisms by which androgens regulate Aβ production, degradation, and clearance, as well as the Aβ-induced pathological process in AD, are still elusive. This review emphasizes the contributions of androgen to Aβ metabolism and toxicity in AD and thus may provide novel strategies for prevention and therapeutics.

Increasing use of cognitive measures in the operational definition of frailty-A systematic review

Ageing is associated both with frailty and cognitive decline. The quest for a unifying approach has led to a new concept: cognitive frailty. This systematic review explores the contribution of cognitive assessment in frailty operationalization. PubMed, Web of Knowledge and PsycINFO were searched until December 2016 using the keywords aged; frail elderly; aged, 80 and over; frailty; diagnosis; risk assessment and classification, yielding 2863 hits. Seventy-nine articles were included, describing 94 frailty instruments. Two instruments were not sufficiently specified and excluded. 46% of the identified frailty instruments included cognition. Of these, 85% were published after 2010, with a significant difference for publication date (X² = 8.45, p < .05), indicating increasing awareness of the contribution of cognitive deficits to functional decline. This review identified 7 methods of cognitive assessment: dementia as co-morbidity; objective cognitive-screening instruments; self-reported; specific signs and symptoms; delirium/clouding of consciousness; non-specific cognitive terms and mixed assessments. Although cognitive assessment has been increasingly integrated in recently published frailty instruments, this has been heterogeneously operationalized. Once the domains most strongly linked to functional decline will have been identified and operationalized, this will be the groundwork for the identification of reversible components, and for the development of preventive interventional strategies.

Higher levels of kallikrein-8 in female brain may increase the risk for Alzheimer's disease

Women seem to have a higher vulnerability to Alzheimer's disease (AD), but the underlying mechanisms of this sex dichotomy are not well understood. Here, we first determined the influence of sex on various aspects of Alzheimer's pathology in transgenic CRND8 mice. We demonstrate that beta-amyloid (Aβ) plaque burden starts to be more severe around P180 (moderate disease stage) in female transgenics when compared to males and that aging aggravates this sex-specific difference. Furthermore, we show that female transgenics suffer from higher levels of neurovascular dysfunction around P180, resulting in impaired Aβ peptide clearance across the blood-brain-barrier at P360. Female transgenics show also higher levels of diffuse microgliosis and inflammation, but the density of microglial cells surrounding Aβ plaques is less in females. In line with this finding, testosterone compared to estradiol was able to improve microglial viability and Aβ clearance in vitro. The spatial memory of transgenics was in general poorer than in wildtypes and at P360 worse in females irrespective of their genotype. This difference was accompanied by a slightly diminished dendritic complexity in females. While all the above-named sex-differences emerged after the onset of Aβ pathology, kallikrein-8 (KLK8) protease levels were, as an exception, higher in female than in male brains very early when virtually no plaques were detectable. In a second step, we quantified cerebral KLK8 levels in AD patients and healthy controls, and could ascertain, similar to mice, higher KLK8 levels not only in AD-affected but also in healthy brains of women. Accordingly, we could demonstrate that estradiol but not testosterone induces KLK8 synthesis in neuronal and microglial cells. In conclusion, multiple features of AD are more pronounced in females. Here, we show for the first time that this sex-specific difference may be meditated by estrogen-induced KLK8 overproduction long before AD pathology emerges.

Androgen alleviates neurotoxicity of β-amyloid peptide (Aβ) by promoting microglial clearance of Aβ and inhibiting microglial inflammatory response to Aβ

AIMS

Lower androgen level in elderly men is a risk factor of Alzheimer's disease (AD). It has been reported that androgen reduces amyloid peptides (Aβ) production and increases Aβ degradation by neurons. Activated microglia are involved in AD by either clearing Aβ deposits through uptake of Aβ or releasing cytotoxic substances and pro-inflammatory cytokines. Here, we investigated the effect of androgen on Aβ uptake and clearance and Aβ-induced inflammatory response in microglia, on neuronal death induced by Aβ-activated microglia, and explored underlying mechanisms.

METHODS

Intracellular and extracellular Aβ were examined by immunofluorescence staining and Western blot. Amyloid peptides (Aβ) receptors, Aβ degrading enzymes, and pro-inflammatory cytokines were detected by RT-PCR, real-time PCR, and ELISA. Phosphorylation of MAP kinases and NF-κB was examined by Western blot.

RESULTS

We found that physiological concentrations of androgen enhanced Aβ42 uptake and clearance, suppressed Aβ42 -induced IL-1β and TNFα expression by murine microglia cell line N9 and primary microglia, and alleviated neuronal death induced by Aβ42 -activated microglia. Androgen administration also reduced Aβ42 -induced IL-1β expression and neuronal death in murine hippocampus. Mechanistic studies revealed that androgen promoted microglia to phagocytose and degrade Aβ42 through upregulating formyl peptide receptor 2 and endothelin-converting enzyme 1c expression, and inhibited Aβ42 -induced pro-inflammatory cytokines expression via suppressing MAPK p38 and NF-κB activation by Aβ42 , in an androgen receptor independent manner.

CONCLUSION

Our study demonstrates that androgen promotes microglia to phagocytose and clear Aβ42 and inhibits Aβ42 -induced inflammatory response, which may play an important role in reducing the neurotoxicity of Aβ.

Sex hormones and brain volumes in a longitudinal study of middle-aged men in the CARDIA study

INTRODUCTION

Several findings suggest that testosterone (T) is neuroprotective and that declining T levels during aging are associated with cognitive and brain pathologies; however, little is known on T and brain health in middle-age. We examined the relationships of total T, bioavailable T, and sex hormone binding globulin (SHBG) levels with total and regional gray matter (GM) and white matter (WM) volumes in middle-aged men. We also evaluated the association of sex hormone levels with cognitive function.

METHODS

Analysis included 267 community-dwelling men participating in the Coronary Artery Risk Development in Young Adults (CARDIA) brain magnetic resonance imaging (MRI) substudy. Total T, bioavailable T, and SHBG levels were measured at three times from the 2nd to 4th decade of life; brain volumes were measured at the ages of 42-56. Associations were estimated using linear regression models, adjusted for several potential confounders.

RESULTS

Higher SHBG levels were associated with greater total WM volume (+3.15 cm3 [95% confidence interval [CI] = 0.01, 6.28] per one standard deviation higher SHBG). Higher SHBG levels were associated with lower total and regional GM volumes overall and significantly with smaller parietal GM volume (-0.96 cm3 [95%CI = -1.71, -0.21]). T levels were not related to brain volumes. Neither T nor SHBG levels were associated with cognitive function.

CONCLUSION

Results suggest a role for SHBG in structural brain outcomes in men and emphasize the value of investigating SHBG levels as modulators of sex hormone and metabolic pathways regulating brain and behavioral characteristics in men.

Postmenopausal cognitive changes and androgen levels in the context of apolipoprotein E polymorphism

INTRODUCTION

The focus of this study was to assess cognitive functions in relation to androgens and specifically testosterone and dehydroepiandrosterone in postmenopausal women as well as the correlation between cognitive functions and these two androgens according to polymorphism of the apolipoprotein E gene (APOE).

MATERIAL AND METHODS

A group of 402 women was recruited to the study (minimum 2 years after the last menstruation, follicle-stimulating hormone (FSH) more than 30 U/ml and no dementia signs on Montreal Cognitive Assessment). The computerized battery of the Central Nervous System Vital Signs test was used to diagnose cognitive functions. APOE genotyping was performed by multiplex polymerase chain reaction (PCR). Testosterone (TTE) and dehydroepiandrosterone (DHEA) in the blood serum were assessed for further statistical correlations analysis.

RESULTS

In the group of postmenopausal women, higher testosterone concentration was associated with lower scores for Neurocognition Index (NCI) (p = 0.028), memory (p = 0.008) and psychomotor speed (p < 0.001). Presence of at least one APOE ε4 allele potentiated testosterone's negative influence on cognitive functions (p < 0.05). Woman with a high normal level of DHEA scored significantly better in verbal (p = 0.027) and visual memory (p < 0.001) than other participants. APOE polymorphism did not modify the relationship between DHEA concentration and scores for cognitive functions.

CONCLUSIONS

Hormonal balance variations after menopause may influence brain processes concerned with cognition, especially memory and psychomotor speed. The observed effects may be related to androgens' influence on higher cortical functions in the changed hormonal dynamics of the postmenopausal period.

Metabolomics and cognition in African American adults in midlife: the atherosclerosis risk in communities study

Clinical studies have shown alterations in metabolic profiles when patients with mild cognitive impairment and Alzheimer's disease dementia were compared to cognitively normal subjects. Associations between 204 serum metabolites measured at baseline (1987-1989) and cognitive change were investigated in 1035 middle-aged community-dwelling African American participants in the biracial Atherosclerosis Risk in Communities (ARIC) Study. Cognition was evaluated using the Delayed Word Recall Test (DWRT; verbal memory), the Digit Symbol Substitution Test (DSST; processing speed) and the Word Fluency Test (WFT; verbal fluency) at visits 2 (1990-1992) and 4 (1996-1998). In addition, Cox regression was used to analyze the metabolites as predictors of incident hospitalized dementia between baseline and 2011. There were 141 cases among 1534 participants over a median 17.1-year follow-up period. After adjustment for established risk factors, one standard deviation increase in N-acetyl-1-methylhistidine was significantly associated with greater 6-year change in DWRT scores (β=-0.66 words; P=3.65 × 10-4). Two metabolites (one unnamed and a long-chain omega-6 polyunsaturated fatty acid found in vegetable oils (docosapentaenoate (DPA, 22:5 n-6)) were significantly associated with less decline on the DSST (DPA: β=1.25 digit-symbol pairs, P=9.47 × 10-5). Two unnamed compounds and three sex steroid hormones were associated with an increased risk of dementia (all P<3.9 × 10-4). The association of 4-androstene-3beta, 17beta-diol disulfate 1 with dementia was replicated in European Americans. These results demonstrate that screening the metabolome in midlife can detect biologically plausible biomarkers that may improve risk stratification for cognitive impairment at older ages.

Sexual dimorphism of frailty and cognitive impairment: Potential underlying mechanisms (Review)

The aim of the present study was to assess systematically gender differences in susceptibility to frailty and cognitive performance decline, and the underlying mechanisms. A systematic assessment was performed of the identified reviews of cohort, mechanistic and epidemiological studies. The selection criteria of the present study included: i) Sexual dimorphism of frailty, ii) sexual dimorphism of subjective memory decline (impairment) and atrophy of hippocampus during early life, iii) sexual dimorphism of late‑onset Alzheimer's disease and iv) sexual dimorphism mechanisms underlying frailty and cognitive impairment. Males exhibit a susceptibility to poor memory performance and a severe atrophy of the hippocampus during early life and females demonstrate a higher prevalence for frailty and late‑life dementia. The different alterations within the hypothalamic‑pituitary‑gonadal/adrenal axis, particularly with regard to gonadal hormones, cortisol and dehydroepiandrosterone/sulfate‑bound dehydroepiandrosterone prior to and following andropause in males and menopause in females, serve important roles in sexual dimorphism of frailty and cognitive impairment. These endocrine changes may accelerate immunosenescence, weaken neuroprotective and neurotrophic effects, and promote muscle catabolism. The present study suggested that these age‑associated endocrine alterations interact with gender‑specific genetic and epigenetic factors, together with immunosenescence and iron accumulation. Environment factors, including psychological factors, are additional potential causes of the sexual dimorphism of frailty and cognitive impairment.