Oxidative stress, testosterone, and cognition among Caucasian and Mexican-American men with and without Alzheimer's disease

Plant extracts and omega-3 improve short-term memory and modulate the microbiota-gut-brain axis in D-Galactose model mice

BACKGROUND

Aging, characterized by a slow and progressive alteration of cognitive functions, is associated with gut microbiota dysbiosis, low-grade chronic inflammation, as well as increased oxidative stress and neurofunctional alterations. Some nutrients, such as polyphenols, carotenoids, and omega-3, are good candidates to prevent age-related cognitive decline, due to their immunomodulatory, antioxidant and neuroprotective properties.

OBJECTIVE

The objective of this study was to demonstrate the preventive effect of a combination of plant extracts (PE) containing Memophenol™ (grapes and blueberries polyphenols) and a patented saffron extract (saffron carotenoids and safranal), and omega-3 (om-3) on cognitive function in a mice model of accelerated aging and to understand the biological mechanisms involved.

METHODS

We used an accelerated aging model by injecting 3-month-old male C57Bl6/J mice with D-galactose for 8 weeks, during which they were fed with a balanced control diet, supplemented or not with PE and/or om-3 (n=15-16/group). Short-term memory was evaluated by Y-maze test, following by analyses of hippocampal and intestinal RNA expressions, brain fatty acid and oxylipin amounts and gut microbiota composition (16S rRNA gene sequencing). Statistical analyses were performed (t-test, ANOVA and Pearson's correlation).

RESULTS

Our results showed that oral administration of PE, om-3, or both (mix) prevented hippocampus-dependent short-term memory deficits induced by D-galactose (p<0.05). This effect was accompanied by the modulation of gut microbiota, altered by the treatment. PE and the mix increased the expression of antioxidative and neurogenesis markers, such as catalase and DCX, in hippocampus (p<0.05 for both). Moreover, om-3 and the mix showed a higher omega-3 level (p<0.05) and EPA-derived 18-HEPE (p<0.001) in prefrontal cortex. These changes may contribute to the improvement in memory.

CONCLUSIONS

These results suggest that the mix of PE and om-3 could be more efficient at attenuating age-related cognitive decline than individual supplementations because it targeted, in mice, the different pathways impaired with aging.

Involvement of P2X7R-mediated microglia polarization and neuroinflammation in the response to electroacupuncture on post-stroke memory impairment

PURPOSE

Post-stroke cognitive impairment (PSCI) is a common complication of ischemic stroke episodes. Memory impairment is an important component of the poststroke cognitive syndrome. Microglial activation plays a critical role in stroke-induced neuroinflammation. Previous studies have reported that electroacupuncture (EA) provides neuroprotective effects by reducing the expression levels of the Purinergic receptor P2X ligand-gated ion channel 7 (P2X7) and inhibiting neuroinflammation in rat model of ischemic stroke. Further understanding of the role and connections between P2X7R and microglial activation in EA-induced anti-inflammatory can reveal novel targets for post-stroke memory impairment treatment.

METHODS

A Middle cerebral artery occlusion and reperfusion (MCAO/R) model was established. We used 2'(3')-O-(4-benzoyl) benzoyl ATP (BzATP) as a P2X7R agonist. Following MCAO/R injury, the rats underwent EA therapy at the Baihui (DU20) and Shenting (DU24) acupoints for seven consecutive days. The Barnes maze test was used to evaluate memory function. Following intervention, a T2 weighted images (T2WI) scan was performed to identify changes in cerebral infarction volume in MCAO/R rats. The levels of Interleukin-1β (IL-1β), Interleukin-6 (IL-6) and Interleukin-4 (IL-4), Interleukin-10 (IL-10) in the peri-infarct hippocampal were examined by ELISA. Immunofluorescence was employed to evaluate Iba-1+ / P2X7R+, Iba-1+/ iNOS+ and Iba-1+/ Arg-1+ cell populations in the peri-infarct hippocampal DG area. The protein expression of P2X7R, Nuclear factor E2-related factor 2 (Nrf2), Recombinant nlr family, pyrin domain containing protein 3 (NLRP3), Inducible nitric oxide synthase (iNOS) and Arginase-1 (Arg-1) in the peri-infarct hippocampal were investigated using western blot assays. Besides, we also measured the levels of reactive oxygen species (ROS), superoxide dismutase (SOD) and malondialdehyde (MDA).

RESULTS

We found EA treatment reduced inflammation and oxidative stress, which is consistent with a decrease in P2X7R expression and improved learning and memory functions. In contrast, we found BzATP enhanced inflammation and oxidative stress. Moreover, our results showed EA treatment up-regulated Nrf2, down-regulated NLRP3, and promoted microglia M2 polarization. Finally, EA-mediated positive effects were reversed by intracerebroventricular injection of BzATP, which is consistent with an increase in P2X7R expression.

CONCLUSION

EA ameliorates memory impairment in a rat model of ischemic stroke by reducing inflammation and ROS through the inhibition of P2X7R expression. In turn, this mechanism regulates Nrf2 and NLRP3 expression, suggesting EA is beneficial for ischemic stroke treatment using P2X7R as target.

Testosterone deficiency worsens mitochondrial dysfunction in APP/PS1 mice

Background

Recent studies show testosterone (T) deficiency worsens cognitive impairment in Alzheimer's disease (AD) patients. Mitochondrial dysfunction, as an early event of AD, is becoming critical hallmark of AD pathogenesis. However, currently, whether T deficiency exacerbates mitochondrial dysfunction of men with AD remains unclear.

Objective

The purpose of this study is to explore the effects of T deficiency on mitochondrial dysfunction of male AD mouse models and its potential mechanisms.

Methods

Alzheimer's disease animal model with T deficiency was performed by castration to 3-month-old male APP/PS1 mice. Hippocampal mitochondrial function of mice was analyzed by spectrophotometry and flow cytometry. The gene expression levels related to mitochondrial biogenesis and mitochondrial dynamics were determined through quantitative real-time PCR (qPCR) and western blot analysis. SH-SY5Y cells treated with flutamide, T and/or H2O2 were processed for analyzing the potential mechanisms of T on mitochondrial dysfunction.

Results

Testosterone deficiency significantly aggravated the cognitive deficits and hippocampal pathologic damage of male APP/PS1 mice. These effects were consistent with exacerbated mitochondrial dysfunction by gonadectomy to male APP/PS1 mice, reflected by further increase in oxidative damage and decrease in mitochondrial membrane potential, complex IV activity and ATP levels. More importantly, T deficiency induced the exacerbation of compromised mitochondrial homeostasis in male APP/PS1 mice by exerting detrimental effects on mitochondrial biogenesis and mitochondrial dynamics at mRNA and protein level, leading to more defective mitochondria accumulated in the hippocampus. In vitro studies using SH-SY5Y cells validated T's protective effects on the H2O2-induced mitochondrial dysfunction, mitochondrial biogenesis impairment, and mitochondrial dynamics imbalance. Administering androgen receptor (AR) antagonist flutamide weakened the beneficial effects of T pretreatment on H2O2-treated SH-SY5Y cells, demonstrating a critical role of classical AR pathway in maintaining mitochondrial function.

Conclusion

Testosterone deficiency exacerbates hippocampal mitochondrial dysfunction of male APP/PS1 mice by accumulating more defective mitochondria. Thus, appropriate T levels in the early stage of AD might be beneficial in delaying AD pathology by improving mitochondrial biogenesis and mitochondrial dynamics.

Oxidative damage in neurodegeneration: roles in the pathogenesis and progression of Alzheimer disease

Alzheimer disease (AD) is associated with multiple etiologies and pathological mechanisms, among which oxidative stress (OS) appears as a major determinant. Intriguingly, OS arises in various pathways regulating brain functions, and it seems to link different hypotheses and mechanisms of AD neuropathology with high fidelity. The brain is particularly vulnerable to oxidative damage, mainly because of its unique lipid composition, resulting in an amplified cascade of redox reactions that target several cellular components/functions ultimately leading to neurodegeneration. The present review highlights the "OS hypothesis of AD," including amyloid beta-peptide-associated mechanisms, the role of lipid and protein oxidation unraveled by redox proteomics, and the antioxidant strategies that have been investigated to modulate the progression of AD. Collected studies from our groups and others have contributed to unraveling the close relationships between perturbation of redox homeostasis in the brain and AD neuropathology by elucidating redox-regulated events potentially involved in both the pathogenesis and progression of AD. However, the complexity of AD pathological mechanisms requires an in-depth understanding of several major intracellular pathways affecting redox homeostasis and relevant for brain functions. This understanding is crucial to developing pharmacological strategies targeting OS-mediated toxicity that may potentially contribute to slow AD progression as well as improve the quality of life of persons with this severe dementing disorder.

Bioinformatics analysis of diagnostic biomarkers for Alzheimer's disease in peripheral blood based on sex differences and support vector machine algorithm

Background

The prevalence of Alzheimer's disease (AD) varies based on gender. Due to the lack of early stage biomarkers, most of them are diagnosed at the terminal stage. This study aimed to explore sex-specific signaling pathways and identify diagnostic biomarkers of AD.

Methods

Microarray dataset for blood was obtained from the Gene Expression Omnibus (GEO) database of GSE63060 to conduct differentially expressed genes (DEGs) analysis by R software limma. Gene Ontology (GO) analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis and Gene set enrichment analysis (GSEA) were conducted. Immune checkpoint gene expression was compared between females and males. Using CytoHubba, we identified hub genes in a protein–protein interaction network (PPI). Then, we evaluated their distinct effectiveness using unsupervised hierarchical clustering. Support vector machine (SVM) and ten-fold cross-validation were used to further verify these biomarkers. Lastly, we confirmed our findings by using another independent dataset.

Results

A total of 37 female-specific DEGs and 27 male-specific DEGs were identified from GSE63060 datasets. Analyses of enrichment showed that female-specific DEGs primarily focused on energy metabolism, while male-specific DEGs mostly involved in immune regulation. Three immune-checkpoint-relevant genes dysregulated in males. In females, however, these eight genes were not differentially expressed. SNRPG, RPS27A, COX7A2, ATP5PO, LSM3, COX7C, PFDN5, HINT1, PSMA6, RPS3A and RPL31 were regarded as hub genes for females, while SNRPG, RPL31, COX7C, RPS27A, RPL35A, RPS3A, RPS20 and PFDN5 were regarded as hub genes for males. Thirteen hub genes mentioned above was significantly lower in both AD and mild cognitive impairment (MCI). The diagnostic model of 15-marker panel (13 hub genes with sex and age) was developed. Both the training dataset and the independent validation dataset have area under the curve (AUC) with a high value (0.919, 95%CI 0.901–0.929 and 0.803, 95%CI 0.789–0.826). Based on GSEA for hub genes, they were associated with some aspects of AD pathogenesis.

Conclusion

DEGs in males and females contribute differently to AD pathogenesis. Algorithms combining blood-based biomarkers may improve AD diagnostic accuracy, but large validation studies are needed.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41065-022-00252-x.

The Role of Lipid Rafts and Membrane Androgen Receptors in Androgen’s Neurotoxic Effects

Sex differences have been observed in multiple oxidative stress–associated neurodegenerative diseases. Androgens, such as testosterone, can exacerbate oxidative stress through a membrane androgen receptor (mAR), AR45, localized to lipid rafts in the plasma membrane. The goal of this study is to determine if interfering with mAR localization to cholesterol-rich lipid rafts decreases androgen induced neurotoxicity under oxidative stress environments. We hypothesize that cholesterol-rich caveolar lipid rafts are necessary for androgens to induce oxidative stress generation in neurons via the mAR localized within the plasma membrane. Nystatin was used to sequester cholesterol and thus decrease cholesterol-rich caveolar lipid rafts in a neuronal cell line (N27 cells). Nystatin was applied prior to testosterone exposure in oxidatively stressed N27 cells. Cell viability, endocytosis, and protein analysis of oxidative stress, apoptosis, and mAR localization were conducted. Our results show that the loss of lipid rafts via cholesterol sequestering blocked androgen-induced oxidative stress in cells by decreasing the localization of mAR to caveolar lipid rafts.

Neurodegenerative Disease: Roles for Sex, Hormones, and Oxidative Stress

Neurodegenerative diseases cause severe impairments in cognitive and motor function. With an increasing aging population and the onset of these diseases between 50 and 70 years, the consequences are bound to be devastating. While age and longevity are the main risk factors for neurodegenerative diseases, sex is also an important risk factor. The characteristic of sex is multifaceted, encompassing sex chromosome complement, sex hormones (estrogens and androgens), and sex hormone receptors. Sex hormone receptors can induce various signaling cascades, ranging from genomic transcription to intracellular signaling pathways that are dependent on the health of the cell. Oxidative stress, associated with aging, can impact the health of the cell. Sex hormones can be neuroprotective under low oxidative stress conditions but not in high oxidative stress conditions. An understudied sex hormone receptor that can induce activation of oxidative stress signaling is the membrane androgen receptor (mAR). mAR can mediate nicotinamide adenine dinucleotide-phosphate (NADPH) oxidase (NOX)-generated oxidative stress that is associated with several neurodegenerative diseases, such as Alzheimer disease. Further complicating this is that aging can alter sex hormone signaling. Prior to menopause, women experience more estrogens than androgens. During menopause, this sex hormone profile switches in women due to the dramatic ovarian loss of 17β-estradiol with maintained ovarian androgen (testosterone, androstenedione) production. Indeed, aging men have higher estrogens than aging women due to aromatization of androgens to estrogens. Therefore, higher activation of mAR-NOX signaling could occur in menopausal women compared with aged men, mediating the observed sex differences. Understanding of these signaling cascades could provide therapeutic targets for neurodegenerative diseases.

Testosterone and Cognitive Impairment or Dementia in Middle-Aged or Aging Males: Causation and Intervention, a Systematic Review and Meta-Analysis

BACKGROUND AND PURPOSE

To investigate the association between testosterone levels and the risk of dementia and to assess the effectiveness of testosterone supplement treatment in patients with cognitive impairment or dementia.

METHODS

We searched Pubmed, Cochrane Library, and EMBASE on September 30, 2019.

RESULTS

The risk factor portion of the review included 27 studies with 18 599 participants. Studies revealed inconsistent findings on the association between testosterone levels and the risk of all-cause dementia or Alzheimer disease (AD). The result from our meta-analysis showed an increased risk of all-cause dementia with decreasing total testosterone (total-T, 4572 participants, hazard ratio: 1.14, 95% CI: 1.04-1.26). Some studies also found an increased risk of AD with a lower level of total-T, free testosterone, and bioavailable testosterone. Testosterone supplement treatment may improve general cognitive function and motor response in the short term as measured by the Developmental Test of Visual-Motor Integration (mean difference [MD]: 4.4, 95% CI: 1.20-7.59) and the Mini-Mental State Examination (MD: 3.4, 95% CI: 0.83-5.97) and verbal memory as measured by story recall delay at 3 months (MD: 8.4, 95% CI: 0.49-16.3).

CONCLUSION

Lower levels of testosterone may be associated with an increased risk of all-cause dementia or AD. Testosterone supplement treatment may or may not improve general cognitive function in patients with cognitive impairment/AD.

Breast cancer type 1 and neurodegeneration: consequences of deficient DNA repair

Numerous cellular processes, including toxic protein aggregation and oxidative stress, have been studied extensively as potential mechanisms underlying neurodegeneration. However, limited therapeutic efficacy targeting these processes has prompted other mechanisms to be explored. Previous research has emphasized a link between cellular senescence and neurodegeneration, where senescence induced by excess DNA damage and deficient DNA repair results in structural and functional changes that ultimately contribute to brain dysfunction and increased vulnerability for neurodegeneration. Specific DNA repair proteins, such as breast cancer type 1, have been associated with both stress-induced senescence and neurodegenerative diseases, however, specific mechanisms remain unclear. Therefore, this review explores DNA damage-induced senescence in the brain as a driver of neurodegeneration, with particular focus on breast cancer type 1, and its potential contribution to sex-specific differences associated with neurodegenerative disease.

Involvement of Testosterone Signaling in the Integrity of the Neurovascular Unit in the Male: Review of Evidence, Contradictions, and Hypothesis

Age-related central nervous system function decline and increased susceptibility of females compared to males with respect to prevalence of several neurodegenerative and neuropsychiatric diseases are both based on the principle that hormonal factors could be involved. These cerebral disorders are characterized by an alteration of blood-brain barrier (BBB) properties and chronic neuroinflammation, which lead to disease progression. Neuroinflammation, in turn, contributes to BBB dysfunction. The BBB and its environment, called the neurovascular unit (NVU), are crucial for cerebral homeostasis and neuronal function. Interestingly, sex steroids influence BBB properties and modulate neuroinflammatory responses. To date however, the majority of work reported has focused on the effects of estrogens on BBB function and neuroinflammation in female mammals. In contrast, the effects of testosterone signaling on the NVU in males are still poorly studied. The aim of this review was to summarize and discuss the literature, providing insights and contradictions to highlight hypothesis and the need for further investigations.

Aging, Life History, and Human Evolution

Aging occurs in all sexually reproducing organisms. That is, physical degradation over time occurs from conception until death. While the life span of a species is often viewed as a benchmark of aging, the pace and intensity of physical degradation over time varies owing to environmental influences, genetics, allocation of energetic investment, and phylogenetic history. Significant variation in aging within mammals, primates, and great apes, including humans, is therefore common across species. The evolution of aging in the hominin lineage is poorly known; however, clues can be derived from the fossil record. Ongoing advances continue to shed light on the interactions between life-history variables such as reproductive effort and aging. This review presents our current understanding of the evolution of aging in humans, drawing on population variation, comparative research, trade-offs, and sex differences, as well as tissue-specific patterns of physical degradation. Implications for contemporary health challenges and the future of human evolutionary anthropology research are also discussed.

Representation of Older Latinxs in Cohort Studies at the Rush Alzheimer's Disease Center

The Rush Alzheimer's Disease Center (RADC) conducts 5 harmonized prospective clinical-pathologic cohort studies of aging - with 1 study, the Latino Core, focused exclusively on Latinxs, 2 studies consisting of mostly non-Latinx whites, and 2 studies of mostly non-Latinx blacks. This paper contextualizes the Latino Core within the other 4 harmonized RADC cohort studies. The overall aim of the paper is to provide information from the RADC, so that researchers can learn from our participants and procedures to better advance the science of Alzheimer's disease and related dementias in Latinxs. We describe an annual clinical evaluation that assesses risk factors for Alzheimer's dementia among older adults without known dementia at enrollment. As all RADC cohort studies offer brain donation as a part of research participation, we discuss our approach to brain donation and subsequent participant decision-making among older Latinxs. We also summarize baseline characteristics of older Latinxs across the 5 RADC cohort studies in relation to the baseline characteristics of non-Latinx blacks and non-Latinx whites. Finally, we outline challenges and considerations as well as potential next steps in cognitive aging research with older Latinxs.

Neuroprotective and neurotoxic outcomes of androgens and estrogens in an oxidative stress environment

BACKGROUND

The role of sex hormones on cellular function is unclear. Studies show androgens and estrogens are protective in the CNS, whereas other studies found no effects or damaging effects. Furthermore, sex differences have been observed in multiple oxidative stress-associated CNS disorders, such as Alzheimer's disease, depression, and Parkinson's disease. The goal of this study is to examine the relationship between sex hormones (i.e., androgens and estrogens) and oxidative stress on cell viability.

METHODS

N27 and PC12 neuronal and C6 glial phenotypic cell lines were used. N27 cells are female rat derived, whereas PC12 cells and C6 cells are male rat derived. These cells express estrogen receptors and the membrane-associated androgen receptor variant, AR45, but not the full-length androgen receptor. N27, PC12, and C6 cells were exposed to sex hormones either before or after an oxidative stressor to examine neuroprotective and neurotoxic properties, respectively. Estrogen receptor and androgen receptor inhibitors were used to determine the mechanisms mediating hormone-oxidative stress interactions on cell viability. Since the presence of AR45 in the human brain tissue was unknown, we examined the postmortem brain tissue from men and women for AR45 protein expression.

RESULTS

Neither androgens nor estrogens were protective against subsequent oxidative stress insults in glial cells. However, these hormones exhibited neuroprotective properties in neuronal N27 and PC12 cells via the estrogen receptor. Interestingly, a window of opportunity exists for sex hormone neuroprotection, wherein temporary hormone deprivation blocked neuroprotection by sex hormones. However, if sex hormones are applied following an oxidative stressor, they exacerbated oxidative stress-induced cell loss in neuronal and glial cells.

CONCLUSIONS

Sex hormone action on cell viability is dependent on the cellular environment. In healthy neuronal cells, sex hormones are protective against oxidative stress insults via the estrogen receptor, regardless of sex chromosome complement (XX, XY). However, in unhealthy (e.g., high oxidative stress) cells, sex hormones exacerbated oxidative stress-induced cell loss, regardless of cell type or sex chromosome complement. The non-genomic AR45 receptor, which is present in humans, mediated androgen's damaging effects, but it is unknown which receptor mediated estrogen's damaging effects. These differential effects of sex hormones that are dependent on the cellular environment, receptor profile, and cell type may mediate the observed sex differences in oxidative stress-associated CNS disorders.

Chronic Testosterone Deprivation Sensitizes the Middle-Aged Rat Brain to Damaging Effects of Testosterone Replacement

INTRODUCTION

An increasing number of middle-aged men are being screened for low testosterone levels and the number of prescriptions for various forms of testosterone replacement therapy (TRT) has increased dramatically over the last 10 years. However, the safety of TRT has come into question with some studies suggesting increased morbidity and mortality.

OBJECTIVE

Because the benefits of estrogen replacement in postmenopausal women and ovariectomized rodents are lost if there is an extended delay between estrogen loss and replacement, we hypothesized that TRT may also be sensitive to delayed replacement.

METHODS

We compared the effects of testosterone replacement after short-term (2 weeks) and long-term testosterone deprivation (LTTD; 10 weeks) in middle-aged male rats on cerebral ischemia, oxidative stress, and cognitive function. We hypothesized that LTTD would increase oxidative stress levels and abrogate the beneficial effects of TRT.

RESULTS

Hypogonadism itself and TRT after short-term castration did not affect stroke outcome compared to intact rats. However, after long-term hypogonadism in middle-aged male Fischer 344 rats, TRT exacerbated the detrimental behavioral effects of experimental focal cerebral ischemia, whereas this detrimental effect was prevented by administration of the free-radical scavenger tempol, suggesting that TRT exacerbates oxidative stress. In contrast, TRT improved cognitive performance in non-stroked rats regardless of the length of hypogonadism. In the Morris water maze, peripheral oxidative stress was highly associated with decreased cognitive ability.

CONCLUSIONS

Taken together, these data suggest that TRT after long-term hypogonadism can exacerbate functional recovery after focal cerebral ischemia, but in the absence of injury can enhance cognition. Both of these effects are modulated by oxidative stress levels.

The Longitudinal Effects of Expressive Writing on Victims of Relational Transgressions

This study investigated the longitudinal effects of written disclosure on physiological and communicative health outcomes for victims of severe relational transgressions in dating relationships. Participants were assigned to a two-step writing condition, a benefit-finding condition, or a control condition to write once a day for three consecutive days on the same topic. Testosterone and forgiveness communication were assessed twice over the course of one-month. The results demonstrate that conditional forgiveness levels were higher for participants in both experimental conditions than in the control condition, whereas neither of the experimental conditions reduced testosterone levels. Across the writing conditions, testosterone levels were negatively associated with conditional forgiveness and positively associated with direct forgiveness. Finally, the results revealed that linguistic features in the writing predicted levels of testosterone and conditional forgiveness.

Effects of aging, high-fat diet, and testosterone treatment on neural and metabolic outcomes in male brown Norway rats

Risk for Alzheimer's disease (AD) is affected by multiple factors, including aging, obesity, and low testosterone. We previously showed that obesity and low testosterone independently and interactively exacerbate AD-related outcomes in young adult rodents. The goals of the present study are two-fold: to examine whether the effects of an obesogenic diet differ with increasing age and to determine if testosterone treatment in middle-aged and aged animals mitigates negative effects of the diet. Male brown Norway rats were maintained on control or high-fat diets for 12 weeks beginning in young adulthood, middle age, or advanced age. Separate cohorts of middle-aged and aged animals were treated with testosterone during dietary manipulations. Endpoints included metabolic indices, inflammation, cognitive performance, and neural health outcomes. Aging was associated with poorer outcomes that were generally exacerbated by high-fat diet, especially at middle age. Testosterone treatment was largely without benefit, exerting only subtle effects on a select number of measures. Understanding how the deleterious effects of obesity are affected by advancing age and the ability of protective strategies such as testosterone to reduce these effects may provide significant insight into both the development and prevention of age-related cognitive decline and AD.

The testosterone metabolite 3α-androstanediol inhibits oxidative stress-induced ERK phosphorylation and neurotoxicity in SH-SY5Y cells through an MKP3/DUSP6-dependent mechanism

Testosterone exerts neuroprotective effects on the brain, but the mechanisms by which these effects are exerted appear to be different in males and females. While in females they involve local conversion to estradiol, in males they may be androgen receptor-dependent, or mediated through metabolism to neurosteroids such as 5α-androstane-3α,17β-diol (3α-diol), which acts through different mechanisms than testosterone itself. Recently, we demonstrated that 3α-diol can protect neurons and neuronal-like cells against oxidative stress-induced neurotoxicity associated with prolonged phosphorylation of the extracellular signal-regulated kinase (ERK). The mechanism(s) responsible for these effects remain unknown. In the present study, we sought to determine whether the ERK-specific phosphatase, mitogen-activated protein kinase phosphatase 3/dual specificity phosphatase 6 (MKP3/DUSP6), is involved in the cytoprotective effects of 3α-diol in SH-SY5Y human female neuroblastoma cells. 3α-diol inhibited ERK phosphorylation and ameliorated cell death induced by the oxidative stressor hydrogen peroxide (H₂O₂). These protective effects were significantly reduced by pre-treatment with the MKP3/DUSP6 inhibitor BCI. In addition, H₂O₂ decreased expression of MKP3/DUSP6, and this was prevented by co-treatment with 3α-diol. These findings suggest that the protective effects of 3α-diol are mediated through regulation of ERK phosphorylation in neurotoxic conditions and indicate that these effects may be exerted through modulation of MKP3/DUSP6. Targeting the regulation of MKP3/DUSP6 may be beneficial in reducing toxicity under conditions of oxidative stress.

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.

Androgens modulate chronic intermittent hypoxia effects on brain and behavior

Sleep apnea is associated with testosterone dysregulation as well as increased risk of developing neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD). A rodent model of the hypoxemic events of sleep apnea, chronic intermittent hypoxia (CIH), has been previously documented to impair cognitive function and elevate oxidative stress in male rats, while simultaneously decreasing testosterone. Therefore, androgens may modulate neuronal function under CIH. To investigate the role of androgens during CIH, male rats were assigned to one of four hormone groups: 1) gonadally intact, 2) gonadectomized (GDX), 3) GDX + testosterone (T) supplemented, or 4) GDX + dihydrotestosterone (DHT) supplemented. Each group was exposed to either normal room air or CIH exposure for one week, followed by memory and motor task assessments. Brain regions associated with AD and PD (entorhinal cortex, dorsal hippocampus, and substantia nigra) were examined for oxidative stress and inflammatory markers, key characteristics of AD and PD. Gonadally intact rats exhibited elevated oxidative stress due to CIH, but no significant memory and motor impairments. GDX increased memory impairments, regardless of CIH exposure. T preserved memory function and prevented detrimental CIH-induced changes. In contrast, DHT was not protective, as evidenced by exacerbated oxidative stress under CIH. Further, CIH induced significant spatial memory impairment in rats administered DHT. These results indicate androgens can have both neuroprotective and detrimental effects under CIH, which may have clinical relevance for men with untreated sleep apnea.

Sex-related differences in oxidative stress and neurodegeneration

Oxidative stress has been implicated in a number of neurodegenerative diseases spanning various fields of research. Reactive oxygen species can be beneficial or harmful, depending on their concentration. High levels of reactive oxygen species can lead to oxidative stress, which is an imbalance between free radicals and antioxidants. Increased oxidative stress can result in cell loss. Interestingly, sex differences have been observed in oxidative stress generation, which may underlie sex differences observed in neurodegenerative disorders. An enhanced knowledge of the role of sex hormones on oxidative stress signaling and cell loss can yield valuable information, leading to sex-based mechanistic approaches to neurodegeneration.

Chronic intermittent hypoxia induces hormonal and male sexual behavioral changes: Hypoxia as an advancer of aging

Sleep apnea is a common sleep disorder characterized by intermittent periods of low blood oxygen levels. The risk for sleep apnea increases with age and is more prevalent in men than women. A common comorbidity of sleep apnea includes male sexual dysfunction, but it is not clear if a causal relationship exists between sleep apnea and sexual dysfunction. Possible mechanisms that link these two disorders include oxidative stress and testosterone. Oxidative stress is elevated in clinical patients with sleep apnea and in rodents exposed to chronic intermittent hypoxia (CIH), an animal model for apnea-induced hypopnea. Further, oxidative stress levels increase with age. Therefore, age may play a role in sleep apnea-induced sexual dysfunction and oxidative stress generation. To investigate this relationship, we exposed gonadally intact 3 (young) and 12 (middle-aged) month old male F344/BN F1 hybrid male rats to 8 days of CIH, and then examined male sexual function. Plasma was used to assess circulating oxidative stress and hormone levels. Middle-aged male rats had lower testosterone levels with increased sexual dysfunction and oxidative stress, independent of CIH. However, CIH decreased testosterone levels and increased sexual dysfunction and oxidative stress only in young gonadally intact male rats, but not in gonadectomized young rats with physiological testosterone replacement. In sum, CIH had a greater impact on younger gonadally intact animals, with respect to sexual behaviors, testosterone, and oxidative stress. Our data indicate CIH mimics the effects of aging on male sexual behavior in young gonadally intact male rats.

Role of Estrogen and Other Sex Hormones in Brain Aging. Neuroprotection and DNA Repair

Aging is an inevitable biological process characterized by a progressive decline in physiological function and increased susceptibility to disease. The detrimental effects of aging are observed in all tissues, the brain being the most important one due to its main role in the homeostasis of the organism. As our knowledge about the underlying mechanisms of brain aging increases, potential approaches to preserve brain function rise significantly. Accumulating evidence suggests that loss of genomic maintenance may contribute to aging, especially in the central nervous system (CNS) owing to its low DNA repair capacity. Sex hormones, particularly estrogens, possess potent antioxidant properties and play important roles in maintaining normal reproductive and non-reproductive functions. They exert neuroprotective actions and their loss during aging and natural or surgical menopause is associated with mitochondrial dysfunction, neuroinflammation, synaptic decline, cognitive impairment and increased risk of age-related disorders. Moreover, loss of sex hormones has been suggested to promote an accelerated aging phenotype eventually leading to the development of brain hypometabolism, a feature often observed in menopausal women and prodromal Alzheimer's disease (AD). Although data on the relation between sex hormones and DNA repair mechanisms in the brain is still limited, various investigations have linked sex hormone levels with different DNA repair enzymes. Here, we review estrogen anti-aging and neuroprotective mechanisms, which are currently an area of intense study, together with the effect they may have on the DNA repair capacity in the brain.

Role of Estrogen and Other Sex Hormones in Brain Aging. Neuroprotection and DNA Repair

Aging is an inevitable biological process characterized by a progressive decline in physiological function and increased susceptibility to disease. The detrimental effects of aging are observed in all tissues, the brain being the most important one due to its main role in the homeostasis of the organism. As our knowledge about the underlying mechanisms of brain aging increases, potential approaches to preserve brain function rise significantly. Accumulating evidence suggests that loss of genomic maintenance may contribute to aging, especially in the central nervous system (CNS) owing to its low DNA repair capacity. Sex hormones, particularly estrogens, possess potent antioxidant properties and play important roles in maintaining normal reproductive and non-reproductive functions. They exert neuroprotective actions and their loss during aging and natural or surgical menopause is associated with mitochondrial dysfunction, neuroinflammation, synaptic decline, cognitive impairment and increased risk of age-related disorders. Moreover, loss of sex hormones has been suggested to promote an accelerated aging phenotype eventually leading to the development of brain hypometabolism, a feature often observed in menopausal women and prodromal Alzheimer's disease (AD). Although data on the relation between sex hormones and DNA repair mechanisms in the brain is still limited, various investigations have linked sex hormone levels with different DNA repair enzymes. Here, we review estrogen anti-aging and neuroprotective mechanisms, which are currently an area of intense study, together with the effect they may have on the DNA repair capacity in the brain.

A comparative study of the effect of the dose and exposure duration of anabolic androgenic steroids on behavior, cholinergic regulation, and oxidative stress in rats

The aim of this study was to assess if the dose and exposure duration of the anabolic androgenic steroids (AAS) boldenone (BOL) and stanazolol (ST) affected memory, anxiety, and social interaction, as well as acetylcholinesterase (AChE) activity and oxidative stress in the cerebral cortex (CC) and hippocampus (HC). Male Wistar rats (90 animals) were randomly assigned to three treatment protocols: (I) 5 mg/kg BOL or ST, once a week for 4 weeks; (II) 2.5 mg/kg BOL or ST, once a week for 8 weeks; and (III) 1.25 mg/kg BOL or ST, once a week for 12 weeks. Each treatment protocol included a control group that received an olive oil injection (vehicle control) and AAS were administered intramuscularly (a total volume of 0.2 ml) once a week in all three treatment protocols. In the BOL and ST groups, a higher anxiety level was observed only for Protocol I. BOL and ST significantly affected social interaction in all protocols. Memory deficits and increased AChE activity in the CC and HC were found in the BOL groups treated according to Protocol III only. In addition, BOL and ST significantly increased oxidative stress in both the CC and HC in the groups treated according to Protocol I and III. In conclusion, our findings show that the impact of BOL and ST on memory, anxiety, and social interaction depends on the dose and exposure duration of these AAS.

Multiple Mechanisms Linking Type 2 Diabetes and Alzheimer's Disease: Testosterone as a Modifier

Evidence in support of links between type-2 diabetes mellitus (T2DM) and Alzheimer's disease (AD) has increased considerably in recent years. AD pathological hallmarks include the accumulation of extracellular amyloid-β (Aβ) and intracellular hyperphosphorylated tau in the brain, which are hypothesized to promote inflammation, oxidative stress, and neuronal loss. T2DM exhibits many AD pathological features, including reduced brain insulin uptake, lipid dysregulation, inflammation, oxidative stress, and depression; T2DM has also been shown to increase AD risk, and with increasing age, the prevalence of both conditions increases. In addition, amylin deposition in the pancreas is more common in AD than in normal aging, and although there is no significant increase in cerebral Aβ deposition in T2DM, the extent of Aβ accumulation in AD correlates with T2DM duration. Given these similarities and correlations, there may be common underlying mechanism(s) that predispose to both T2DM and AD. In other studies, an age-related gradual loss of testosterone and an increase in testosterone resistance has been shown in men; low testosterone levels can also occur in women. In this review, we focus on the evidence for low testosterone levels contributing to an increased risk of T2DM and AD, and the potential of testosterone treatment in reducing this risk in both men and women. However, such testosterone treatment may need to be long-term, and would need regular monitoring to maintain testosterone at physiological levels. It is possible that a combination of testosterone therapy together with a healthy lifestyle approach, including improved diet and exercise, may significantly reduce AD risk.

Effects of Oxidative Stress and Testosterone on Pro-Inflammatory Signaling in a Female Rat Dopaminergic Neuronal Cell Line

Parkinson's disease, a progressive neurodegenerative disorder, is associated with oxidative stress and neuroinflammation. These pathological markers can contribute to the loss of dopamine neurons in the midbrain. Interestingly, men have a 2-fold increased incidence for Parkinson's disease than women. Although the mechanisms underlying this sex difference remain elusive, we propose that the primary male sex hormone, testosterone, is involved. Our previous studies show that testosterone, through a putative membrane androgen receptor, can increase oxidative stress-induced neurotoxicity in dopamine neurons. Based on these results, this study examines the role of nuclear factor κ B (NF-κB), cyclooxygenase-2 (COX2), and apoptosis in the deleterious effects of androgens in an oxidative stress environment. We hypothesize, under oxidative stress environment, testosterone via a putative membrane androgen receptor will exacerbate oxidative stress-induced NF-κB/COX2 signaling in N27 dopaminergic neurons, leading to apoptosis. Our data show that testosterone increased the expression of COX2 and apoptosis in dopamine neurons. Inhibiting the NF-κB and COX2 pathway with CAPE and ibuprofen, respectively, blocked testosterone's negative effects on cell viability, indicating that NF-κB/COX2 cascade plays a role in the negative interaction between testosterone and oxidative stress on neuroinflammation. These data further support the role of testosterone mediating the loss of dopamine neurons under oxidative stress conditions, which may be a key mechanism contributing to the increased incidence of Parkinson's disease in men compared with women.

Lipid peroxidation and apoptotic response in rat brain areas induced by long-term administration of nandrolone: the mutual crosstalk between ROS and NF-kB

The aim of this study was to evaluate the played by oxidative stress in the apoptotic response in different brain areas of rats chronically treated with supra-physiological doses of nandrolone decanoate (ND). Immunohistochemical study and Western blot analysis were performed to evaluate cells' apoptosis and to measure the effects of expression of specific mediators, such as NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells), Bcl-2 (B-cell lymphoma 2), SMAC/DIABLO (second mitochondria-derived activator of caspases/direct IAP-binding protein with low PI) and VMAT2 (vesicular monoamine transporter 2) on apoptosis. The results of the present study indicate that a long-term administration of ND promotes oxidative injury in rat brain specific areas. A link between oxidative stress and NF-κB signalling pathways is supported by our results. In addition to high levels of oxidative stress, we consistently observed a strong immunopositivity to NF-κB. It has been argued that one of the pathways leading to the activation of NF-κB could be under reactive oxygen species (ROS)-mediated control. In fact, growing evidence suggests that although in limited doses, endogenous ROS may play an activating role in NF-κB signalling, while above a certain threshold, they may negatively impact upon this signalling. However, a mutual crosstalk between ROS and NF-κB exists and recent studies have shown that ROS activity is subject to negative feedback regulation by NF-κB, and that this negative regulation of ROS is the means through which NF-κB counters programmed cells.

Reactive oxygen species: players in the cardiovascular effects of testosterone

Androgens are essential for the development and maintenance of male reproductive tissues and sexual function and for overall health and well being. Testosterone, the predominant and most important androgen, not only affects the male reproductive system, but also influences the activity of many other organs. In the cardiovascular system, the actions of testosterone are still controversial, its effects ranging from protective to deleterious. While early studies showed that testosterone replacement therapy exerted beneficial effects on cardiovascular disease, some recent safety studies point to a positive association between endogenous and supraphysiological levels of androgens/testosterone and cardiovascular disease risk. Among the possible mechanisms involved in the actions of testosterone on the cardiovascular system, indirect actions (changes in the lipid profile, insulin sensitivity, and hemostatic mechanisms, modulation of the sympathetic nervous system and renin-angiotensin-aldosterone system), as well as direct actions (modulatory effects on proinflammatory enzymes, on the generation of reactive oxygen species, nitric oxide bioavailability, and on vasoconstrictor signaling pathways) have been reported. This mini-review focuses on evidence indicating that testosterone has prooxidative actions that may contribute to its deleterious actions in the cardiovascular system. The controversial effects of testosterone on ROS generation and oxidant status, both prooxidant and antioxidant, in the cardiovascular system and in cells and tissues of other systems are reviewed.

Testosterone deficiency, insulin-resistant obesity and cognitive function

Testosterone is an androgenic steroid hormone, which plays an important role in the regulation of male reproduction and behaviors, as well as in the maintenance of insulin sensitivity. Several studies showed that testosterone exerted beneficial effects in brain function, including preventing neuronal cell death, balancing brain oxidative stress and antioxidant activity, improving synaptic plasticity and involving cognitive formation. Although previous studies showed that testosterone deficiency is positively correlated with cognitive impairment and insulin-resistant obesity, several studies demonstrated contradictory findings. Thus, this review comprehensively summarizes the current evidence from in vitro, in vivo and clinical studies of the relationship between testosterone deficiency and insulin-resistant obesity as well as the correlation between either insulin-resistant obesity or testosterone deficiency and cognitive impairment. Controversial reports and the mechanistic insights regarding the roles of testosterone in insulin-resistant obesity and cognitive function are also presented and discussed.

Oxidative stress and cognition amongst adults without dementia or stroke: Implications for mechanistic and therapeutic research in psychiatric disorders

Oxidative stress has been implicated in cognitive deficits in disease states such as dementia and stroke. However, growing evidence shows similar associations in individuals without these conditions. We therefore set out to systematically review the literature on this topic. MEDLINE searches were conducted of medical subject-headings neuropsychology, cognition, cognition disorders, or neuropsychological tests, cross-referenced with oxidative stress, or superoxide. Exclusion criteria were dementia and stroke studies, absence of human subjects, and absence of quantifiable oxidative stress/cognition measures. The search yielded 883 results, of which 19 studies (consisting of 3662 total subjects) were included in this review. The majority of studies indicated that frontal cognitive functions were most often impaired, and lipid peroxidation was most commonly associated with impairments. Literature on learning, memory, and general cognitive function was less robust. A substantial proportion of the literature on this topic is based on psychiatric populations. Frontal-executive dysfunction implicates frontal brain regions, which are known to be susceptible to oxidative damage. Further studies are needed, and those examining psychiatric populations may be especially fruitful. Focusing on youth may yield enhanced signal detection. Further study is needed to identify which antioxidant interventions work best for which cognitive functions and for which patients.

Total testosterone and neuropsychiatric symptoms in elderly men with Alzheimer's disease

Introduction

There has been a significant increase in the use of testosterone in aging men, but little investigation into its impact on men with Alzheimer’s disease (AD). The findings of the few studies that have been done are inconsistent. In the present study, we investigated the relationship between total testosterone (TT) and neuropsychiatric symptoms (NPS) in a well-characterized sample of elderly men with mild to moderate AD.

Methods

The sample, which was drawn from the Texas Alzheimer’s Research Care Consortium Longitudinal Research Cohort, included 87 men who met the criteria for mild to moderate AD. The occurrence of NPS was gathered from caregivers and/or family members with the Neuropsychiatric Inventory. TT was analyzed, and the sample was divided into a low-testosterone group (TT ≤2.5 ng/ml; n = 44) and a borderline/normal group (TT ≥2.6 ng/ml; n = 43).

Results

TT was correlated with symptoms of hallucinations, delusions, agitation, irritability and motor activity. The borderline/normal group was significantly more likely to have hallucinations (odds ratio (OR) = 5.56), delusions (OR = 3.87), motor activity (OR = 3.13) and irritability (OR = 2.77) than the low-testosterone group. Health status and apolipoprotein E ε4 status were not significant factors.

Conclusions

The findings of the present study have implications for the use of testosterone replacement therapy in men with AD or the prodromal stage of the disease.

Relationships between testosterone levels and cognition in patients with Alzheimer disease and nondemented elderly men

BACKGROUND/AIMS

Previous research suggests that low levels of testosterone may be associated with the development of Alzheimer disease (AD), as well as poorer performance on certain neuropsychological tests and increased risk of depression.

METHODS

This study utilized data from 61 nondemented older men and 68 men with probable AD.

RESULTS

Testosterone levels did not differ between the groups. Regression analyses in men with AD revealed that testosterone levels did not significantly predict performance on neuropsychological tests or a measure of depression. Among controls, testosterone levels predicted estimated premorbid verbal IQ and performance on a verbal fluency test.

CONCLUSION

Findings suggest that testosterone is not associated with most neuropsychological test performances in patients with AD.

GSTM1 Null Genotype and GSTP1 Ile105Val Polymorphism Are Associated with Alzheimer's Disease: a Meta-Analysis

Published studies on the associations between glutathione S-transferase (GST) polymorphisms and Alzheimer's disease reported controversial findings. A meta-analysis of published studies was performed to assess the associations between polymorphisms of GSTM1, GSTT1 and GSTP1, and Alzheimer's disease. PubMed, Embase, and other databases were searched for case-control on the associations between polymorphisms of GSTM1, GSTT1 and GSTP1, and Alzheimer's disease. The odds ratio (OR) and 95% confidence interval (95% CI) were used to assess the associations. Eleven articles were finally included into the meta-analysis, including eight studies on GSTM1 null genotype, six studies on GSTT1 null genotype, and six studies on GSTP1 Ile105Val polymorphism. Overall, GSTM1 null genotype was associated with increased risk of Alzheimer's disease (fixed effect OR = 1.34, 95% CI 1.10-1.64, P = 0.004). GSTT1 null genotype was not associated with risk of Alzheimer's disease (random effect OR = 1.15, 95% CI 0.68-1.92, P = 0.60). Besides, GSTP1 Ile105Val polymorphism was significantly associated with increased risk of Alzheimer's disease (Val vs Ile: OR = 1.45, 95% CI 1.05-1.99, P = 0.023; ValVal vs IleIle: OR = 1.87, 95% CI 1.30-2.69, P = 0.001; ValVal vs IleIle + IleVal: OR = 1.76, 95% CI 1.24-2.51, P = 0.002). No obvious risk of publication bias was observed in the meta-analysis. GSTM1 null genotype and GSTP1 Ile105Val polymorphism are associated with increased risk of Alzheimer's disease. More studies with large sample size are needed to validate the findings in the meta-analysis.

A model for the induction of autism in the ecosystem of the human body: the anatomy of a modern pandemic?

Background

The field of autism research is currently divided based on a fundamental question regarding the nature of autism: Some are convinced that autism is a pandemic of modern culture, with environmental factors at the roots. Others are convinced that the disease is not pandemic in nature, but rather that it has been with humanity for millennia, with its biological and neurological underpinnings just now being understood.

Objective

In this review, two lines of reasoning are examined which suggest that autism is indeed a pandemic of modern culture. First, given the widely appreciated derailment of immune function by modern culture, evidence that autism is strongly associated with aberrant immune function is examined. Second, evidence is reviewed indicating that autism is associated with ‘triggers’ that are, for the most part, a construct of modern culture. In light of this reasoning, current epidemiological evidence regarding the incidence of autism, including the role of changing awareness and diagnostic criteria, is examined. Finally, the potential role of the microbial flora (the microbiome) in the pathogenesis of autism is discussed, with the view that the microbial flora is a subset of the life associated with the human body, and that the entire human biome, including both the microbial flora and the fauna, has been radically destabilized by modern culture.

Conclusions

It is suggested that the unequivocal way to resolve the debate regarding the pandemic nature of autism is to perform an experiment: monitor the prevalence of autism after normalizing immune function in a Western population using readily available approaches that address the well-known factors underlying the immune dysfunction in that population.

Neurotoxicity by synthetic androgen steroids: oxidative stress, apoptosis, and neuropathology: A review

Anabolic-androgenic steroids (AAS) are synthetic substances derived from testosterone that are largely employed due to their trophic effect on muscle tissue of athletes at all levels. Since a great number of organs and systems are a target of AAS, their adverse effects are primarily on the following systems: reproductive, hepatic, musculoskeletal, endocrine, renal, immunological, infectious, cardiovascular, cerebrovascular, and hematological. Neuropsychiatric and behavioral effects as a result of AAS abuse are well known and described in the literature. Mounting evidence exists suggesting that in addition to psychiatric and behavioral effects, non-medical use of AAS carries neurodegenerative potential. Although, the nature of this association remains largely unexplored, recent animal studies have shown the recurrence of this AAS effect, ranging from neurotrophin unbalance to increased neuronal susceptibility to apoptotic stimuli. Experimental and animal studies strongly suggest that apoptotic mechanisms are at least in part involved in AAS-induced neurotoxicity. Furthermore, a great body of evidence is emerging suggesting that increased susceptibility to cellular oxidative stress could play a pivotal role in the pathogenesis of many neurodegenerative disorders and cognitive impairment. As in other drug-evoked encephalopathies, the key mechanisms involved in AAS - induced neuropathology could represent a target for future neuroprotective strategies. Progress in the understanding of these mechanisms will provide important insights into the complex pathophysiology of AAS-induced neurodegeneration, and will pave the way for forthcoming studies. Supplementary to abandoning the drug abuse that represents the first step in reducing the possibility of irreversible brain damage in AAS abusers, neuroprotective strategies have to be developed and implemented in future.