Estrogen and Alzheimer's disease: the story so far

The role of estrogen in Alzheimer's disease pathogenesis and therapeutic potential in women

Estrogens are pivotal regulators of brain function throughout the lifespan, exerting profound effects from early embryonic development to aging. Extensive experimental evidence underscores the multifaceted protective roles of estrogens on neurons and neurotransmitter systems, particularly in the context of Alzheimer's disease (AD) pathogenesis. Studies have consistently revealed a greater risk of AD development in women compared to men, with postmenopausal women exhibiting heightened susceptibility. This connection between sex factors and long-term estrogen deprivation highlights the significance of estrogen signaling in AD progression. Estrogen's influence extends to key processes implicated in AD, including amyloid precursor protein (APP) processing and neuronal health maintenance mediated by brain-derived neurotrophic factor (BDNF). Reduced BDNF expression, often observed in AD, underscores estrogen's role in preserving neuronal integrity. Notably, hormone replacement therapy (HRT) has emerged as a sex-specific and time-dependent strategy for primary cardiovascular disease (CVD) prevention, offering an excellent risk profile against aging-related disorders like AD. Evidence suggests that HRT may mitigate AD onset and progression in postmenopausal women, further emphasizing the importance of estrogen signaling in AD pathophysiology. This review comprehensively examines the physiological and pathological changes associated with estrogen in AD, elucidating the therapeutic potential of estrogen-based interventions such as HRT. By synthesizing current knowledge, it aims to provide insights into the intricate interplay between estrogen signaling and AD pathogenesis, thereby informing future research directions and therapeutic strategies for this debilitating neurodegenerative disorder.

Breast cancer therapies reduce risk of Alzheimer's disease and promote estrogenic pathways and action in brain

Worldwide, an ever-increasing number of women are prescribed estrogen-modulating therapies (EMTs) for the treatment of breast cancer. In parallel, aging of the global population of women will contribute to risk of both breast cancer and Alzheimer's disease. To address the impact of anti-estrogen therapies on risk of Alzheimer's and neural function, we conducted medical informatic and molecular pharmacology analyses to determine the impact of EMTs on risk of Alzheimer's followed by determination of EMT estrogenic mechanisms of action in neurons. Collectively, these data provide both clinical and mechanistic data indicating that select EMTs exert estrogenic agonist action in neural tissue that are associated with reduced risk of Alzheimer's disease while simultaneously acting as effective estrogen receptor antagonists in breast.

The Role of Estrogen Therapy as a Protective Factor for Alzheimer's Disease and Dementia in Postmenopausal Women: A Comprehensive Review of the Literature

The complete cessation of menstruation for 12 months with associated vasomotor symptoms is termed menopause. Apart from playing a role in reproduction, estrogen significantly affects the central nervous system (CNS). Population-based studies highlighted a substantial difference in the prevalence of dementia between men and women, with Alzheimer-associated dementia being more prevalent in women, indicating that estrogen deficiency might be a risk factor for neurodegenerative diseases. Patients with dementia experience a progressive decline in neurocognitive function, beginning with short-term memory loss that progresses to long-term memory loss and the inability to perform everyday activities, leading ultimately to death. There is currently no cure for dementia, so preventing or slowing the disease's progression is paramount. Accordingly, researchers have widely studied the role of estrogen as a neuroprotective agent. Estrogen prevents dementia by augmenting Hippocampal and prefrontal cortex function, reducing neuroinflammation, preventing degradation of estrogen receptors, decreasing oxidative damage to the brain, and increasing cholinergic and serotonergic function. According to the window phase hypothesis, estrogen's effect on preventing dementia is more pronounced if therapy is started early, during the first five years of menopause. Other studies like The Woman's Health Initiative Memory Study (WHIMS) showed unfavorable effects of estrogen on the brain. This review aims to establish an understanding of the currently available data on estrogen's effect on neurodegeneration, namely, dementia and Alzheimer's disease.

Calcium regulation by SERC-A before and during Alzheimer disease

There are many factors involved in the incidence of Alzheimer’s disease that, in combination, impede or hinder normal neuronal functions. Little is currently known about calcium regulation before and during the disease. Internal instability of calcium levels is associated with increased vascular risk, a prevalent condition in a high number of individuals already compromised by Alzheimer’s disease. This review provides a reevaluation of the molecular mechanism of the sarcoendoplasmic reticulum calcium ATPase (SERC-A) in the disease and discusses salient aspects of voltage-gated calcium channel function; in these way new alternatives could be open for its treatment. These regulation mechanisms are clinically relevant since the irregular functions of SERC+A has been implicated in pathologies of brain function.

The Interaction Between NF-κB and Estrogen in Alzheimer's Disease

Post-menopausal women are at a higher risk of developing Alzheimer's disease (AD) than males. The higher rates of AD in women are associated with the sharp decline in the estrogen levels after menopause. Estrogen has been shown to downregulate inflammatory cytokines in the central nervous system (CNS), which has a neuroprotective role against neurodegenerative diseases including AD. Sustained neuroinflammation is associated with neurodegeneration and contributes to AD. Nuclear factor kappa-B (NF-κB) is a transcription factor involved with the modulation of inflammation and interacts with estrogen to influence the progression of AD. Application of 17β-estradiol (E2) has been shown to inhibit NF-κB, thereby reducing transcription of NF-κB target genes. Despite accumulating evidence showing that estrogens have beneficial effects in pre-clinical AD studies, there are mixed results with hormone replacement therapy in clinical trials. Furthering our understanding of how NF-κB interacts with estrogen and alters the progression of neurodegenerative disorders including AD, should be beneficial and result in the development of novel therapeutics.

Aggregate Trends of Apolipoprotein E on Cognition in Transgenic Alzheimer's Disease Mice

Background:

Apolipoprotein E (APOE) genotypes typically increase risk of amyloid-β deposition and onset of clinical Alzheimer’s disease (AD). However, cognitive assessments in APOE transgenic AD mice have resulted in discord.

Objective:

Analysis of 31 peer-reviewed AD APOE mouse publications (n = 3,045 mice) uncovered aggregate trends between age, APOE genotype, gender, modulatory treatments, and cognition.

Methods:

T-tests with Bonferroni correction (significance = p < 0.002) compared age-normalized Morris water maze (MWM) escape latencies in wild type (WT), APOE2 knock-in (KI2), APOE3 knock-in (KI3), APOE4 knock-in (KI4), and APOE knock-out (KO) mice. Positive treatments (t+) to favorably modulate APOE to improve cognition, negative treatments (t–) to perturb etiology and diminish cognition, and untreated (t0) mice were compared. Machine learning with random forest modeling predicted MWM escape latency performance based on 12 features: mouse genotype (WT, KI2, KI3, KI4, KO), modulatory treatment (t+, t–, t0), mouse age, and mouse gender (male = g_m; female = g_f, mixed gender = g_mi).

Results:

KI3 mice performed significantly better in MWM, but KI4 and KO performed significantly worse than WT. KI2 performed similarly to WT. KI4 performed significantly worse compared to every other genotype. Positive treatments significantly improved cognition in WT, KI4, and KO compared to untreated. Interestingly, negative treatments in KI4 also significantly improved mean MWM escape latency. Random forest modeling resulted in the following feature importance for predicting superior MWM performance: [KI3, age, g_m, KI4, t0, t+, KO, WT, g_mi, t–, g_f, KI2] = [0.270, 0.094, 0.092, 0.088, 0.077, 0.074, 0.069, 0.061, 0.058, 0.054, 0.038, 0.023].

Conclusion:

APOE3, age, and male gender was most important for predicting superior mouse cognitive performance.

Structural volume and cortical thickness differences between males and females in cognitively normal, cognitively impaired and Alzheimer's dementia population

We investigated differences due to sex in brain structural volume and cortical thickness in older cognitively normal (N=742), cognitively impaired (MCI; N=540) and Alzheimer's Dementia (AD; N=402) individuals from the ADNI and AIBL datasets (861 Males and 823 Females). General linear models were used to control the effect of relevant covariates including age, intracranial volume, magnetic resonance imaging (MRI) scanner field strength and scanner types. Significant volumetric differences due to sex were observed within different cortical and subcortical regions of the cognitively normal group. The number of significantly different regions was reduced in the MCI group, and no region remained different in the AD group. Cortical thickness was overall thinner in males than females in the cognitively normal group, and likewise, the differences due to sex were reduced in the MCI and AD groups. These findings were sustained after including cerebrospinal fluid (CSF) Tau and phosphorylated tau (pTau) as additional covariates.

Therapeutic Potential of Phosphodiesterase Inhibitors against Neurodegeneration: The Perspective of the Medicinal Chemist

Increasing human life expectancy prompts the development of novel remedies for cognitive decline: 44 million people worldwide are affected by dementia, and this number is predicted to triple by 2050. Acetylcholinesterase and N-methyl-d-aspartate receptors represent the targets of currently available drugs for Alzheimer’s disease, which are characterized by limited efficacy. Thus, the search for therapeutic agents with alternative or combined mechanisms of action is wide open. Since variations in 3′,5′-cyclic adenosine monophosphate, 3′,5′-cyclic guanosine monophosphate, and/or nitric oxide levels interfere with downstream pathways involved in memory processes, evidence supporting the potential of phosphodiesterase (PDE) inhibitors in contrasting neurodegeneration should be critically considered. For the preparation of this Review, more than 140 scientific papers were retrieved by searching PubMed and Scopus databases. A systematic approach was adopted when overviewing the different PDE isoforms, taking into account details on brain localization, downstream molecular mechanisms, and inhibitors currently under study, according to available in vitro and in vivo data. In the context of drug repurposing, a section focusing on PDE5 was introduced. Original computational studies were performed to rationalize the emerging evidence that suggests the role of PDE5 inhibitors as multi-target agents against neurodegeneration. Moreover, since such compounds must cross the blood–brain barrier and reach inhibitory concentrations in the central nervous system to exert their therapeutic activity, physicochemical parameters were analyzed and discussed. Taken together, literature and computational data suggest that some PDE5 inhibitors, such as tadalafil, represent promising candidates.

Quality of life and psychological functioning in postmenopausal women undergoing aromatase inhibitor treatment for early breast cancer

INTRODUCTION

Aromatase inhibitors (AIs) dramatically increased breast cancer (BC) survival, leading to enhanced attention to their long-term consequences on psychological functioning. Conflicting data has been examined regarding the association between AIs administration and the clinical psychological features in BC survivors (BCSs).

PURPOSE

As psychological symptoms often occur in such chronic diseases, our study aimed at exploring anxious and depressive symptoms and the perceived quality of life (QoL) in BCSs assessed for osteoporosis.

METHODS

The total sample consisted of a clinical sample of 51 outpatient postmenopausal women, diagnosed with BC, and a control group composed of 51 healthy postmenopausal women. All recruited participants were evaluated through the clinical gold standard interview and completed the following self-rating scales: the Hamilton Anxiety Rating Scale, Beck Depression Inventory II edition, and 36-Item Short Form Health Survey, which were administered at baseline and after 6 months in BCSs in AIs treatment, compared with controls. Moreover, all participants were assessed for vitamin D status, bone mineral density (BMD) and subclinical vertebral fractures. Data regarding age, age at menopause, body mass index (BMI), smoking habits and alcohol consumption was collected.

RESULTS

BCSs (n = 51) showed higher anxious and depressive symptoms, and lower perceived QoL vs. controls (n = 51) (p<0.05 for all). After 6 months of treatment with AIs, BCSs showed significant reduction of anxious and depressive symptoms and a significantly higher perceived QoL for both physical and mental components, vs. controls.

CONCLUSIONS

The improvement of clinical psychological features and perceived QoL was associated with AIs treatment in women being treated with, for early breast cancer. Further studies are needed to obtain a deeper comprehension of the correlation between clinical psychological and physical features in BCSs.

Association Between Hormone-Modulating Breast Cancer Therapies and Incidence of Neurodegenerative Outcomes for Women With Breast Cancer

Importance

The association between exposure to hormone-modulating therapy (HMT) as breast cancer treatment and neurodegenerative disease (NDD) is unclear.

Objective

To determine whether HMT exposure is associated with the risk of NDD in women with breast cancer.

Design, Setting, and Participants

This retrospective cohort study used the Humana claims data set from January 1, 2007, to March 31, 2017. The Humana data set contains claims from private-payer and Medicare insurance data sets from across the United States with a population primarily residing in the Southeast. Patient claims records were surveyed for a diagnosis of NDD starting 1 year after breast cancer diagnosis for the duration of enrollment in the claims database. Participants were 57 843 women aged 45 years or older with a diagnosis of breast cancer. Patients were required to be actively enrolled in Humana claims records for 6 months prior to and at least 3 years after the diagnosis of breast cancer. The analyses were conducted between January 1 and 15, 2020.

Exposure

Hormone-modulating therapy (selective estrogen receptor modulators, estrogen receptor antagonists, and aromatase inhibitors).

Main Outcomes and Measures

Patients receiving HMT for breast cancer treatment were identified. Survival analysis was used to determine the association between HMT exposure and diagnosis of NDD. A propensity score approach was used to minimize measured and unmeasured selection bias.

Results

Of the 326 485 women with breast cancer in the Humana data set between 2007 and 2017, 57 843 met the study criteria. Of these, 18 126 (31.3%; mean [SD] age, 76.2 [7.0] years) received HMT, whereas 39 717 (68.7%; mean [SD] age, 76.8 [7.0] years) did not receive HMT. Mean (SD) follow-up was 5.5 (1.8) years. In the propensity score-matched population, exposure to HMT was associated with a decrease in the number of women who received a diagnosis of NDD (2229 of 17 878 [12.5%] vs 2559 of 17 878 [14.3%]; relative risk, 0.89; 95% CI, 0.84-0.93; P < .001), Alzheimer disease (877 of 17 878 [4.9%] vs 1068 of 17 878 [6.0%]; relative risk, 0.82; 95% CI, 0.75-0.90; P < .001), and dementia (1862 of 17 878 [10.4%] vs 2116 of 17 878 [11.8%]; relative risk, 0.88; 95% CI, 0.83-0.93; P < .001). The number needed to treat was 62.51 for all NDDs, 93.61 for Alzheimer disease, and 69.56 for dementia.

Conclusions and Relevance

Among patients with breast cancer, tamoxifen and steroidal aromatase inhibitors were associated with a decrease in the number who received a diagnosis of NDD, specifically Alzheimer disease and dementia.

Domain-specific contributions of biological sex and sex hormones to what, where and when components of episodic-like memory in adult rats

Episodic memory involves the integration and recall of discrete events that include information about what happened, where it happened and when it occurred. Episodic memory function is critical to daily life, and its dysfunction is both a first identifiable indicator and an enduring core feature of cognitive decline in ageing and in neuropsychiatric disorders including Alzheimer's disease and schizophrenia. Available evidence from human studies suggests that biological sex and sex hormones modulate episodic memory function in health and disease. However, knowledge of how this occurs is constrained by the limited availability and underutilization of validated animal models in investigating hormone impacts on episodic-like memory function. Here, adult female, adult male and gonadally manipulated adult male rats were tested on the what-where-when episodic-like memory task to determine whether rats model human sex differences in episodic memory and how the hormonal milieu impacts episodic-like memory processes in this species. These studies revealed salient ways in which rats model human sex differences in episodic memory, including a male advantage in spatial episodic memory performance. They also identified domain-specific roles for oestrogens and androgens in modulating what, where and when discriminations in male rats that were unlike those engaged in corresponding novel object recognition and novel object location tasks. These studies thus identify rats and the what-where-when task as suitable for investigating the neuroendocrine bases of episodic-like memory, and provide new information about the unique contributions that sex and sex hormones make to this complex mnemonic process.

Possible Existence of the Hypothalamic-Pituitary-Hippocampal (HPH) Axis: A Reciprocal Relationship Between Hippocampal Specific Neuroestradiol Synthesis and Neuroblastosis in Ageing Brains with Special Reference to Menopause and Neurocognitive Disorders

The hippocampus-derived neuroestradiol plays a major role in neuroplasticity, independent of circulating estradiol that originates from gonads. The response of hypothalamus-pituitary regions towards the synthesis of neuroestradiol in the hippocampus is an emerging scientific concept in cognitive neuroscience. Hippocampal plasticity has been proposed to be regulated via neuroblasts, a major cellular determinant of functional neurogenesis in the adult brain. Defects in differentiation, integration and survival of neuroblasts in the hippocampus appear to be an underlying cause of neurocognitive disorders. Gonadotropin receptors and steroidogenic enzymes have been found to be expressed in neuroblasts in the hippocampus of the brain. However, the reciprocal relationship between hippocampal-specific neuroestradiol synthesis along neuroblastosis and response of pituitary based feedback regulation towards regulation of estradiol level in the hippocampus have not completely been ascertained. Therefore, this conceptual article revisits (1) the cellular basis of neuroestradiol synthesis (2) a potential relationship between neuroestradiol synthesis and neuroblastosis in the hippocampus (3) the possible involvement of aberrant neuroestradiol production with mitochondrial dysfunctions and dyslipidemia in menopause and adult-onset neurodegenerative disorders and (4) provides a hypothesis for the possible existence of the hypothalamic-pituitary-hippocampal (HPH) axis in the adult brain. Eventually, understanding the regulation of hippocampal neurogenesis by abnormal levels of neuroestradiol concentration in association with the feedback regulation of HPH axis might provide additional cues to establish a neuroregenerative therapeutic management for mood swings, depression and cognitive decline in menopause and neurocognitive disorders.

Engineering poly(lactic-co-glycolic acid) (PLGA) micro- and nano-carriers for Controlled Delivery of 17β-Estradiol

With menopause, circulating levels of 17β-estradiol (E2) markedly decrease. E2-based hormone therapy is prescribed to alleviate symptoms associated with menopause. E2 is also recognized for its beneficial effects in the central nervous system (CNS), such as enhanced cognitive function following abrupt hormonal loss associated with ovariectomy. For women with an intact uterus, an opposing progestogen component is required to decrease the risk of developing endometrial hyperplasia. While adding an opposing progestogen attenuates these detrimental effects on the uterus, it can attenuate the beneficial effects of E2 in the CNS. Poly(lactic-co-glycolic acid) (PLGA) micro- and nano- carriers (MNCs) have been heavily investigated for their ability to enhance the therapeutic activity of hydrophobic agents following exogenous administration, including E2. Multiple PLGA MNC formulation parameters, such as composition, molecular weight, and type of solvent used, can be altered to systematically manipulate the pharmacokinetic and pharmacodynamic profiles of encapsulated agents. Thus, there is an opportunity to enhance the therapeutic activity of E2 in the CNS through controlled delivery from PLGA MNCs. The aim of this review is to consider the fate of exogenously administered E2 and discuss how PLGA MNCs and route of administration can be used as strategies for controlled E2 delivery.

17β-Estradiol augments antidepressant efficacy of escitalopram in ovariectomized rats: Neuroprotective and serotonin reuptake transporter modulatory effects

The prevalence or recurrence of depression is seriously increased in women during the transition to and after menopause. The chronic hypo-estrogenic state of menopause may reduce the response to antidepressants; however the influence of estrogen therapy on their efficacy is still controversial. This study aimed at investigating the effects of combining escitalopram with 17β-estradiol on depression and cognitive impairment induced by ovariectomy, an experimental model of human menopause. Young adult female Wistar rats were subjected to either sham operation or ovariectomy. Ovariectomized animals were treated chronically with escitalopram (10mg/kg/day, i.p) alone or with four doses of 17β-estradiol (40μg/kg, s.c) given prior to the behavioral tests. Co-administration of 17β-estradiol improved escitalopram-induced antidepressant effect in forced swimming test verified as more prominent decrease in the immobility time without opposing its memory enhancing effect in Morris water maze. 17β-estradiol augmented the modulatory effects of escitalopram on the hippocampal levels of brain-derived neurotrophic factor and serotonin reuptake transporter as well as tumor necrosis factor-alpha without altering its effects on the gene expressions of serotonin receptor 1A, estrogen receptors alpha and beta, or acetylcholinestearase content. This combined therapy afforded synergistic protective effects on the brain histopathological architecture, particularly, the hippocampus. The antidepressant effect of 17β-estradiol was abolished by pretreatment with estrogen receptor antagonist, tamoxifen (10mg/kg, p.o). In conclusion, 17β-estradiol-induced antidepressant effect was confined to intracellular estrogen receptors activation. Moreover, 17β-estradiol enhanced escitalopram's efficiency in ameliorating menopausal-like depression, via exerting synergistic neuroprotective and serotonin reuptake transporter modulatory effects, without impeding escitalopram-mediated cognitive improvement.

Sex and estrous cycle influence diazepam effects on anxiety and memory: Possible role of progesterone

Studies with rodents and humans show the relationship between female sex hormones and cognitive/emotional tasks. However, despite the greater incidence of anxiety disorders in women, the data are still inconclusive regarding the mechanisms related to this phenomenon. We evaluated the effects of a classical anxiolytic/amnestic drug (diazepam; DZP) on female (at different estrous cycle phases) and male rats tested in the plus-maze discriminative avoidance task (PMDAT), that allows the concomitant evaluation of memory and anxiety-like behavior. Further, in order to investigate the role of progesterone and its metabolites in the effects of DZP in the PMDAT, female rats were pre-treated with the progesterone receptor antagonist mifepristone or the 5-alpha-reductase inhibitor finasteride. The main findings were: (1) DZP caused memory impairment and anxiolysis in both sexes, but only the highest dose induced the anxiolytic effect in females; (2) females in proestrus did not present the amnestic and anxiolytic effects of DZP (at 2.0 and 4.0mg/kg, respectively) and (3) the co-administration of mifepristone reestablished both amnestic and anxiolytic effects of DZP, while finasteride reinstated the amnestic effect in proestrus female rats. These results suggest that changes in the endogenous levels of progesterone and its metabolites are important in the modulation of emotional/cognitive behavior in female rats. Based on the influence on different aspects of DZP action, the mechanisms related to this modulation are probably linked to GABAergic transmission, but this point remains to be investigated. Further, the variation in therapeutic and adverse effects of DZP depending on sex and hormonal state is of great relevance considering the higher prevalence of anxiety disorders in women.

Neurobiological Consequences of Long-Term Estrogen Therapy

Postmenopausal women demonstrate an increased incidence of Alzheimer's disease (AD). Epidemiological evidence suggests that estrogen replacement therapy (ERT) may reduce the risk or delay the onset of AD, yet recent clinical trials found no cognitive benefits of ERT in women with mild to moderate AD. This review suggests that the timing of estrogen administration may explain these conflicting results. Chronic administration has neurobiological consequences that can affect neural and immune function, but a therapy designed to mimic the natural cycle of fluctuating hormones may more effectively slow the progression of AD in postmenopausal women.

Expression of early growth response 1 affects miR-106a/signal transducer and activator of transcription 3 regulating cognitive impairment in ovariectomized mice

OBJECTIVE

This study aims to investigate the effects of early growth response 1 (Egr1) on miR-106a/signal transducer and activator of transcription 3 (STAT3) regulating cognitive impairment in an ovariectomy model.

METHODS

Using the Morris water maze test, we assessed escape latency and time spent in a quadrant among mice at 6, 8, and 12 weeks after ovariectomy and their age-matched controls (n = 15 each group). Egr1, miR-106a, and STAT3 messenger RNA expression (n = 7) in the hippocampus and cortex of mice at 6, 8, and 12 weeks after ovariectomy was detected by quantitative real-time polymerase chain reaction, whereas Egr1, phospho-STAT3 (p-STAT3), and STAT3 protein expression (n = 8) was evaluated by Western blot analysis. Moreover, alterations in miR-106a and STAT3 expression were investigated in neuroblastoma (SH-SY5Y) cells transfected with a human Egr1 interference fragment (si-Egr1) or an Egr1-overexpressing plasmid (GV141-Egr1), respectively.

RESULTS

Escape latency was significantly increased and time spent in a platform quadrant was reduced in mice at 12 weeks after ovariectomy compared with age-matched controls. Egr1 and miR-106a expression was obviously increased in the hippocampus and cortex at 12 weeks after ovariectomy, whereas STAT3 levels were decreased compared with 12-week controls. After SH-SY5Y cell transfection with the si-Egr1 fragment, miR-106a levels decreased and STAT3/p-STAT3 levels increased, whereas cotransfection of the miR-106a mimic caused a significant decrease in STAT3 levels. MiR-106a messenger RNA expression was significantly increased and STAT3/p-STAT3 protein levels were decreased by Egr1 overexpression, whereas simultaneous transfection with the miR-106a inhibitor inhibited alterations in STAT3 levels.

CONCLUSIONS

This study suggests that Egr1 decreases STAT3 expression via miR-106a in ovariectomized mice with cognitive impairment, indicating that Egr1 represents a potential target for therapeutic intervention in postmenopausal cognitive decline.

Estrogen levels modify scopolamine-induced amnesia in gonadally intact rats

Previous studies suggested that estrogen plays a role in cognitive function by modulating the cholinergic transmission. However, most of the studies dealing with this subject have been conducted using ovariectomized rats. In the present study we evaluated the effects of physiological and supra-physiological variation of estrogen levels on scopolamine-induced amnesia in gonadally intact female rats. We used the plus-maze discriminative avoidance task (PMDAT) in order to evaluate anxiety levels and motor activity concomitantly to the memory performance. In experiment 1, female Wistar rats in each estrous cycle phase received scopolamine (1 mg/kg) or saline i.p. 20 min before the training session in the PMDAT. In experiment 2, rats in diestrus received estradiol valerate (1 mg/kg) or sesame oil i.m., and scopolamine (1 mg/kg) or saline i.p., 45 min and 20 min before the training, respectively. In experiment 3, rats in diestrus received scopolamine (1 mg/kg) or saline i.p. 20 min before the training, and estradiol valerate (1 mg/kg) or sesame oil i.m. immediately after the training session. In all experiments, a test session was performed 24 h later. The main results showed that: (1) scopolamine impaired retrieval and induced anxiolytic and hyperlocomotor effects in all experiments; (2) this cholinergic antagonist impaired acquisition only in animals in diestrus; (3) acute administration of estradiol valerate prevented the learning impairment induced by scopolamine and (4) interfered with memory consolidation process. The results suggest that endogenous variations in estrogen levels across the estrous cycle modulate some aspects of memory mediated by the cholinergic system. Indeed, specifically in diestrus, a stage with low estrogen levels, the impairment produced by scopolamine on the acquisition was counteracted by exogenous administration of the hormone, whereas the posttraining treatment potentiated the negative effects of scopolamine during the consolidation phase of memory.

Therapeutic options in Alzheimer’s disease

Alzheimer's disease (AD) places an enormous burden on individuals, families and society. Consequently, a tremendous effort is being devoted to the development of drugs that prevent or delay neurodegeneration. Current pharmacological treatments are based on the use of acetylcholinesterase inhibitors or memantine, a N-methyl-D-aspartate channel blocker. However, new therapeutic approaches, including those more closely targeted to the pathogenesis of the disease, are being developed. These potentially disease-modifying therapeutics include secretase inhibitors, cholesterol-lowering drugs, amyloid-beta immunotherapy, nonsteroidal anti-inflammatory drugs, hormonal modulation and the use of antioxidants. The possibility that oxidative stress is a primary event in AD indicates that antioxidant-based therapies are perhaps the most promising weapons against this devastating neurodegenerative disorder.

Androgen receptor gene and sex-specific Alzheimer's disease

Women are at a 2-fold risk of developing late-onset Alzheimer's disease (AD) (onset at 65 years of age or older) compared with men. During perimenopausal years, women undergo hormonal changes that are accompanied by metabolic, cardiovascular, and inflammatory changes. These all together have been suggested as risk factors for late-onset AD. However, not all perimenopausal women develop AD; we hypothesize that certain genetic factors might underlie the increased susceptibility for developing AD in postmenopausal women. We investigated the Androgen Receptor gene (AR) in a clinical cohort of male and female AD patients and normal control subjects by sequencing all coding exons and evaluating the length and distribution of the CAG repeat in exon 1. We could not establish a correlation between the repeat length, sex, and the disease status, nor did we identify possible pathogenic variants. AR is located on the X chromosome; to assess its role in AD, X-inactivation patterns will need to be studied to directly correlate the actual expressed repeat length to a possible sex-specific phenotypic effect.

Cognitive decline and dementia in the oldest-old

The oldest-old are the fastest growing segment of the Western population. Over half of the oldest-old will have dementia, but the etiology is yet unknown. Age is the only risk factor consistently associated with dementia in the oldest-old. Many of the risk and protective factors for dementia in the young elderly, such as ApoE genotype, physical activity, and healthy lifestyle, are not relevant for the oldest-old. Neuropathology is abundant in the oldest-old brains, but specific pathologies of Alzheimer's disease (AD) or vascular dementia are not necessarily correlated with cognition, as in younger persons. It has been suggested that accumulation of both AD-like and vascular pathologies, loss of synaptic proteins, and neuronal loss contribute to the cognitive decline observed in the oldest-old. Several characteristics of the oldest-old may confound the diagnosis of dementia in this age group. A gradual age-related cognitive decline, particularly in executive function and mental speed, is evident even in non-demented oldest-old. Hearing and vision losses, which are also prevalent in the oldest-old and found in some cases to precede/predict cognitive decline, may mechanically interfere in neuropsychological evaluations. Difficulties in carrying out everyday activities, observed in the majority of the oldest-old, may be the result of motor or physical dysfunction and of neurodegenerative processes. The oldest-old appear to be a select population, who escapes major illnesses or delays their onset and duration toward the end of life. Dementia in the oldest-old may be manifested when a substantial amount of pathology is accumulated, or with a composition of a variety of pathologies. Investigating the clinical and pathological features of dementia in the oldest-old is of great importance in order to develop therapeutic strategies and to provide the most elderly of our population with good quality of life.

The Significance of Age-Related Androgen Depletion in Cognitive Impairment: A Review

The potential role of supplementing sex steroids for the prevention and delay of age-related cognitive decline has received a great deal of recent interest. Although the biological plausibility of hormone treatment has received considerable support, clinical studies of cognitive functioning after hormonal treatment in postmenopausal women with and without dementia have produced mixed results. Much less attention has been given to the corresponding role of androgens in men. In order to establish the relevance of hormonal supplementation for men in delaying or preventing cognitive decline, it is of importance to evaluate both adrenal and gonadal contributions to androgen status. Additionally, consideration must also be given to the potential interactions of androgens with risk and protective factors (e.g., apolipoprotein E genotype and education). Here we review experimental and epidemiological studies of the significance of androgens for cognitive function.

Brain levels of sex steroid hormones in men and women during normal aging and in Alzheimer's disease

We examined the relationships between normal aging, Alzheimer's disease (AD), and brain levels of sex steroid hormones in men and women. In postmortem brain tissue from neuropathologically normal, postmenopausal women, we found no age-related changes in brain levels of either androgens or estrogens. In comparing women with and without AD at different ages, brain levels of estrogens and androgens were lower in AD cases aged 80 years and older but not significantly different in the 60-79 year age range. In male brains, we observed that normal aging was associated with significant decreases in androgens but not estrogens. Further, in men aged 60-79 years, brain levels of testosterone but not estrogens were lower in cases with mild neuropathological changes as well as those with advanced AD neuropathology. In male cases over age 80, brain levels hormones did not significantly vary by neuropathological status. To begin investigating the relationships between hormone levels and indices of AD neuropathology, we measured brain levels of soluble β-amyloid (Aβ). In male cases with mild neuropathological changes, we found an inverse relationship between brain levels of testosterone and soluble Aβ. Collectively, these findings demonstrate sex-specific relationships between normal, age-related depletion of androgens and estrogens in men and women, which may be relevant to development of AD.

Low luteinizing hormone enhances spatial memory and has protective effects on memory loss in rats

Though several studies have suggested that estradiol improves hippocampal-dependent spatial memory, the effects of other hormones in the hypothalamic-pituitary-gonadal axis on memory have largely been ignored. Estradiol and luteinizing hormone (LH) are generally inversely related and LH may significantly affect spatial memory. Ovariectomized (ovx) rats treated with Antide (a gonadotropin releasing hormone receptor antagonist) had low LH levels and showed enhanced spatial memory, comparable to treatment with estradiol. Antide-treated ovx females retained spatial memory longer than estradiol-treated ovx females. Deficits in spatial memory are a primary symptom of neurodegenerative disorders including Alzheimer's disease (AD). Treatment with Antide prevented spatial memory deficits in a neurotoxin-induced model typical of early AD. These data suggest that memory impairments seen in female rats after ovariectomy or women after menopause may be due to high LH levels and that a reduction in LH enhances memory. These results also implicate an LH lowering agent as a potential preventative therapy for AD.

Phosphodiesterase-5 inhibitors: novel weapons against Alzheimer's disease?

Although Alzheimer's disease (AD) poses a major health problem in both developing and developed countries, no definite treatment is available for its cure; hence efforts are being focused on introducing disease-modifying agents for slowing down its course. Recent studies on the effects of sildenafil on different organs have shown that PDE-5 inhibitors may offer new horizons in therapeutic treatment of pulmonary hypertension, multiple sclerosis, neuropathic pain, and age-related memory impairment. In this paper we introduce PDE-5 inhibitors as novel disease-modifying agents against AD and review the different impacts of PDE-5 inhibition on various pathogenic mechanisms leading to AD, including neuronal apoptosis, neurovascular dysfunction, neurotransmitter modulation, and impairment of neurogenesis.

Statin-associated adverse cognitive effects: survey results from 171 patients

STUDY OBJECTIVE

To characterize the adverse cognitive effects of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins).

DESIGN

Patient survey-based analysis.

PATIENTS

One hundred seventy-one patients (age range 34-86 yrs) who self-reported memory or other cognitive problems associated with statin therapy while participating in a previous statin effects study.

MEASUREMENTS AND MAIN RESULTS

Patients completed a survey assessing statin-associated, cognitive-specific adverse drug reaction (ADR) characteristics, relation of the ADR to specific statin and dose (or potency), and time course of symptom onset and recovery. Visual analog scales were used to assess the effect of the cognitive ADRs on seven quality-of-life domains. Demographic and clinical data were also collected. To target cognitive ADRs with a probable or definite causal relationship to statins, the Naranjo adverse drug reaction probability scale was used: 128 patients (75%) experienced cognitive ADRs determined to be probably or definitely related to statin therapy. Of 143 patients (84%) who reported stopping statin therapy, 128 (90%) reported improvement in cognitive problems, sometimes within days of statin discontinuation (median time to first-noted recovery 2.5 wks). Of interest, in some patients, a diagnosis of dementia or Alzheimer's disease reportedly was reversed. Nineteen patients whose symptoms improved or resolved after they discontinued statin therapy and who underwent rechallenge with a statin exhibited cognitive problems again (multiple times in some). Within this vulnerable group, a powerful relationship was observed between potency of the statin and fraction of trials with that agent resulting in cognitive ADRs (p<0.00001). Quality of life was significantly adversely affected for each of the seven assessed domains (all p<0.00000001).

CONCLUSION

Findings from the survey suggest that cognitive problems associated with statin therapy have variable onset and recovery courses, a clear relation to statin potency, and significant negative impact on quality-of-life. Administration of a patient-targeted questionnaire is a feasible approach that provides a useful complement to other ADR surveillance approaches.

Estradiol prevents ozone-induced increases in brain lipid peroxidation and impaired social recognition memory in female rats

There is increasing concern about the neurodegenerative and behavioral consequences of ozone pollution in industrialized urban centers throughout the world and that women may be more susceptible to brain neurodegenerative disorders. In the present study we have investigated the effects of chronic (30 or 60 days) exposure to ozone on olfactory perception and memory and on levels of lipid peroxidation, alpha and beta estrogen receptors and dopamine beta-hydroxylase in the olfactory bulb in ovariectomized female rats. The ability of 17beta-estradiol to prevent these effects was then assessed. Results showed that ozone exposure for 30 or 60 days impaired formation/retention of a selective olfactory recognition memory 120 min after exposure to a juvenile stimulus animal with the effect at 60 days being significantly greater than at 30 days. They also showed impaired speed in locating a buried chocolate reward after 60 days of ozone exposure indicating some loss of olfactory perception. These functional impairments could all be prevented by coincident estradiol treatment. In the olfactory bulb, levels of lipid peroxidation were increased at both 30- and 60-day time-points and numbers of cells with immunohistochemical staining for alpha and beta estrogen receptors, and dopamine beta-hydroxylase were reduced as were alpha and beta estrogen receptor protein levels. These effects were prevented by estradiol treatment. Oxidative stress damage caused by chronic exposure to ozone does therefore impair olfactory perception and social recognition memory and may do so by reducing noradrenergic and estrogen receptor activity in the olfactory bulb. That these effects can be prevented by estradiol treatment suggests increased susceptibility to neurodegenerative disorders in aging women may be contributed to by reduced estrogen levels post-menopause.

Effects of estrogen and estrogenic compounds on cognition in ovariectomized rats

OBJECTIVES

To evaluate the effects of estrogen and estrogenic compounds on cognition in ovariectomized rats.

METHODS

Female Sprague-Dawley rats (3-5 months old) weighing 250-300 g were randomly divided into seven groups: Sham, ovariectomized (OVX), OVX plus estradiol valerate, OVX plus ipriflavone, OVX plus raloxifene, OVX plus tibolone, OVX plus low-dose estradiol valerate and ipriflavone. All treatments were given orally for 3 months; whereas the drug groups received indicated drugs, the Sham and OVX control groups received saline. The escape latency of rats was tested by the Morris water maze test and the expression of amyloid precursor protein (APP) in hippocampus was determined by reverse transcription polymerase chain reaction. The level of serum estradiol and the diameter of the endometrial gland and the thickness of endometrium were also evaluated.

RESULTS

The latency of the OVX group was noticeably longer than that of the Sham group, and the latency of all treatment groups was lower than that of OVX rats. The expression of APP mRNA in the hippocampii of OVX rats was significantly increased relative to that in Sham rats; interestingly, expression of APP in treatment groups was significantly reduced relative to OVX rats.

CONCLUSIONS

Our data indicate that estrogenic compounds can antagonize cognitive impairment and that all these compounds cause only mild stimulation on the endometrium compared to estrogen. Inhibition of APP expression in the hippocampus may account for, at least partially, the protective effects of these estrogenic compounds against cognitive defects. Our data suggest that estrogenic compounds (raloxifene, tibolone and ipriflavone) may be a promising approach to antagonize cognitive impairment in postmenopausal women.

[Stem cells use in the treatment of neurologic disorders--has the future already arrived?]

<zakljucak> Buducnost celijske terapije u lecenju neuroloskih bolesti je pocela. Ostaju vazna pitanja na koja odgovor mogu dati samo dobro osmisljene medjunarodne studije, a ticu se vrste celija, nacina njihovog umnozavanja i aplikacije, kao i optimalnog vremenskog okvira za ovakvu vrstu lecenja.

Plasma growth hormones, P300 event-related potential and test of variables of attention (TOVA) are important neuroendocrinological predictors of early cognitive decline in a clinical setting: evidence supported by structural equation modeling (SEM) parameter estimates

A review of the literature in both animals and humans reveals that changes in sex hormone have often been associated with changes in behavioral and mental abilities. Previously published research from our laboratory, and others, provides strong evidence that P300 (latency) event-related potential (ERP), a marker of neuronal processing speed, is an accurate predictor of early memory impairment in both males and females across a wide age range. It is our hypothesis, given the vast literature on the subject, that coupling growth hormones (insulin-like growth factor-I, (IGF-I) and insulin-like growth factor binding protein 3 (IGF-BP3)), P300 event-related potential and test of variables of attention (TOVA) are important neuroendocrinological predictors of early cognitive decline in a clinical setting. To support this hypothesis, we utilized structural equation modeling (SEM) parameter estimates to determine the relationship between aging and memory, as mediated by growth hormone (GH) levels (indirectly measured through the insulin-like growth factor system), P300 latency and TOVA, putative neurocognitive predictors tested in this study. An SEM was developed hypothesizing a causal directive path, leading from age to memory, mediated by IGF-1 and IGF-BP3, P300 latency (speed), and TOVA decrements. An increase in age was accompanied by a decrease in IGF-1 and IGF-BP3, an increase in P300 latency, a prolongation in TOVA response time, and a decrease in memory functioning. Moreover, independent of age, decreases in IGF-1 and IGF-BP3, were accompanied by increases in P300 latency, and were accompanied by increases in TOVA response time. Finally, increases in P300 latency were accompanied by decreased memory function, both directly and indirectly through mediation of TOVA response time. In summary, this is the first report utilizing SEM to reveal the finding that aging affects memory function negatively through mediation of decreased IGF-1 and IGF-BP3, and increased P300 latency (delayed attention and processing speed).

Progesterone reverses the spatial memory enhancements initiated by tonic and cyclic oestrogen therapy in middle-aged ovariectomized female rats

While some research has indicated that ovarian hormone therapy (HT) benefits memory and decreases risk of Alzheimer's disease in menopausal women, several newer studies have shown null or detrimental effects. Despite the null and negative cognitive findings, the numerous studies showing positive effects beg the question of what factors determine whether HT acts as a neuroprotectant or a risk factor for brain functioning. Using middle-aged female rats, we directly compared six HTs. We evaluated the effects of ovariectomy, tonic low-dose, tonic high-dose and biweekly cyclic estradiol treatment, as well as whether progesterone altered the effectiveness of any one of these oestrogen regimens. Animals were tested on spatial and complex cued (intramaze patterns) reference memory using variants of the Morris maze. The tonic low-dose and cyclic estradiol treatments improved spatial performance, while the addition of progesterone reversed these beneficial cognitive effects of estradiol. Additionally, all groups learned to locate the platform on the cued task; however, an egocentric circling strategy was used with sham ovary-intact and hormone-replacement groups showing the most efficient search strategy. Although the question of memory retention 8 weeks after the first cognitive assessment was addressed, a large number of animals died between the first and second test, rendering the retest uninterpretable for many group comparisons. Specifically, both doses of tonic estradiol dramatically increased the number of deaths during the 17-week experiment, while the cyclic estradiol treatment did not. Progesterone decreased the number of deaths due to tonic estradiol treatment. Our findings suggest that the dose of estradiol replacement as well as the presence of progesterone influences the cognitive outcome of estradiol treatment. Further, there appears to be a dissociation between HT effects on cognition and mortality rates.

Development of 17alpha-estradiol as a neuroprotective therapeutic agent: rationale and results from a phase I clinical study

17alpha-estradiol (17alpha-E2) differs from its isomer, the potent feminizing hormone 17beta-estradiol (17beta-E2), only in the stereochemistry at one carbon, but this is sufficient to render it at least 200-fold less active as a transactivating hormone. Despite its meager hormonal activity, 17alpha-E2 is as potent as 17beta-E2 in protecting a wide variety of cell types, including primary neurons, from a diverse array of lethal and etiologically relevant stressors, including amyloid toxicity, serum withdrawal, oxidative stress, excitotoxicity, and mitochondrial inhibition, among others. Moreover, both estradiol isomers have shown efficacy in animal models of stroke, Alzheimer's disease (AD), and Parkinson's disease (PD). Data from many labs have yielded a mechanistic model in which 17alpha-E2 intercalates into cell membranes, where it terminates lipid peroxidation chain reactions, thereby preserving membrane integrity, and where it in turn is redox cycled by glutathione or by NADPH through enzymatic coupling. Maintaining membrane integrity is critical to mitochondrial function, where loss of impermeability of the inner membrane initiates both necrotic and apoptotic pathways. Thus, by serving as a mitoprotectant, 17alpha-E2 forestalls cell death and could correspondingly provide therapeutic benefit in a host of degenerative diseases, including AD, PD, Friedreich's ataxia, and amyotrophic lateral sclerosis, while at the same time circumventing the common adverse effects elicited by more hormonally active analogues. Positive safety and pharmacokinetic data from a successful phase I clinical study with oral 17alpha-E2 (sodium sulfate conjugate) are presented here, and several options for its future clinical assessment are discussed.

Androgens, aging, and Alzheimer's disease

Testosterone depletion is a normal consequence of aging in men that is associated with senescent effects in androgen- responsive tissues. We discuss new evidence that one consequence of testosterone depletion in men is an increased risk for the development of Alzheimer's disease (AD). Furthermore, we discuss two candidate mechanisms by which testosterone may affect AD pathogenesis. First, testosterone has been identified as an endogenous regulator of beta-amyloid, a protein that abnormally accumulates in AD brain and is implicated as a causal factor in the disease. Second, findings from several different paradigms indicate that testosterone has both neurotrophic and neuroprotective functions. These new findings support the clinical evaluation of androgen-based therapies for the prevention and treatment of AD.

Age-related changes in the oestrous cycle and reproductive hormones in senescence-accelerated mouse

To investigate age-related changes in the oestrous cycle and reproductive hormone levels in senescence-accelerated mouse (SAM), we examined these parameters in 3-, 5-, 7-, 9- and 11-month-old female SAM-prone/8 (SAMP8) and SAM-resistant/1 (SAMR1) strains. Levels of beta-endorphin (beta-EP) and substance P (SP) in the hypothalamus were also measured. The oestrous cycle and dioestrus of 9-month-old SAMP8 mice were significantly prolonged compared with age-matched SAMR1 mice. Furthermore, the concentration of serum oestradiol was lower and the level of pituitary luteinising hormone was higher in SAMP8 mice compared with SAMR1 mice. This characterises the hypothalamus-pituitary-ovary (HPO) axis of the SAMP8 strain as hypergonadotropic-hypogonad. The levels of beta-EP and SP in the SAMP8 hypothalamus were lower than in the SAMR1 hypothalamus. These results indicate that the function of the HPO axis in SAMP8 mice declines early and this may be attributed, in part, to the decline in beta-EP and SP concentrations in the hypothalamus.

Role of astrocytes in reproduction and neuroprotection

Hypothalamic astrocytes secrete TGF-beta and 3 alpha,5 alpha-tetrahydro progesterone (3 alpha,5 alpha-THP) in culture. When the astrocyte-conditioned medium (ACM) was incubated with the hypothalamic cell line GT1-7, it resulted in the secretion of GnRH. Immunoneutralization with TGF-beta antibody or ultra-filteration with a 10 kDa cut off filter resulted in attenuation of the GnRH releasing ability of ACM, indicating that TGF-beta was a major factor involved with GnRH release. Treatment with estrogens increases TGF-beta secretion. These observations indicate a significant role of astrocytes in GnRH secretion. Serum-deprivation results in the death of GT1-7 neurons in culture and addition of ACM or TGF-beta to the culture, attenuates cell death. The mechanism of protection from cell death appears to involve phosphorylation of MKK4, JNK, c-Jun(Ser63), and enhancement of AP-1 binding. Co-administration of JNK inhibitors, but not MEK inhibitors attenuated ACM or TGF-beta-induced c-Jun(Ser63) phosphorylation and their neuroprotective effects. These studies suggest that astrocytes can protect neurons, at least in part, by the release of TGF-beta and activation of a c-Jun/AP-1 protective pathway.

Beneficial effects of melatonin in experimental models of Alzheimer disease

Alzheimer's disease (AD), a progressive degenerative disorder, is characterized by the presence of amyloid deposits, neurofibrillary tangles and neuron loss. Emerging evidence indicates that antioxidants could be useful either for the prevention or treatment of AD. It has been shown that melatonin is a potent antioxidant and free radical scavenger. Additionally, melatonin stimulates several antioxidative enzymes and improves mitochondrial energy metabolism. These findings led us to study amyloid precursor protein transgenic mice, ovariectomized rats, and pheochromocytoma and astroglioma cell lines, to observe whether melatonin had any effect on Alzheimer's symptoms or pathological changes. We found that melatonin had many beneficial effects in experimental models of AD, including improvement of cognitive function, anti-oxidative injury, anti-apoptosis, inhibition of beta-amyloid (Abeta) deposition and Abeta fiber formation. Several groups have shown that melatonin has an inhibitory effect on tau protein hyperphosphorylation. These actions may potentially slow down or stop the progression of dementia.

Long-term melatonin or 17beta-estradiol supplementation alleviates oxidative stress in ovariectomized adult rats

Melatonin is an endogenously generated potent antioxidant. Our previous results indicated that melatonin improved learning and memory deficits in the transgenic mouse model of Alzheimer's disease (AD) and ovariectomized (OVX) rats by improving cholinergic nerve system dysfunction, preventing apoptosis. In this study we aim to investigate the antioxidative effects of melatonin or estradiol in the brains of ovariectomized rats. OVX Sprague-Dawley rats received daily injections of melatonin (5, 10, or 20 mg/kg), 17beta-estradiol (80 microg/kg), or sesame oil for 16 weeks. We found an increase in brain mitochondrial thiobarbituric acid-reactive substances (TBARS) levels, a decrease in mitochondrial glutathione (GSH) content as well as mitochondrial superoxide dismutase (SOD) activity and upregulation of the apoptotic-related factors, such as Bax, Caspase-3, and Prostate apoptosis response-4 (Par-4) in the frontal cortex of OVX rats. In addition to oxidative stress, OVX also caused decreased activities of mitochondrial respiration complex I and complex IV, which implicated mitochondrial dysfunction. Melatonin or 17beta-estradiol antagonized the detrimental effects induced by OVX. Furthermore, immunohistochemistry results revealed that the abnormal upregulation of the apoptotic related factor such as Bax, Caspase-3, and (Par-4) greatly reduced expression after melatonin or 17beta-estradiol supplement action. These findings demonstrate the important effects of melatonin or 17beta-estradiol on postmenopausal neuropathy and support the potential application of melatonin in the treatment of dementia in postmenopausal women. Early, long-term melatonin application is a promising strategy which could potentially be applied in a clinical setting.

Astrocyte-derived transforming growth factor-{beta} mediates the neuroprotective effects of 17{beta}-estradiol: involvement of nonclassical genomic signaling pathways

17beta-Estradiol (E2) and selective estrogen receptor modulators (SERMs), such as tamoxifen, mediate numerous effects in the brain, including neurosecretion, neuroprotection, and the induction of synaptic plasticity. Astrocytes, the most abundant cell type in the brain, influence many of these same functions and thus may represent a mediator of estrogen action. The present study examined the regulatory effect and underlying cell signaling mechanisms of E2-induced release of neurotropic growth factors from primary rat cortical astrocyte cultures. The results revealed that E2 (0.5, 1, and 10 nm) and tamoxifen (1 mum) increased both the expression and release of the neuroprotective cytokines, TGF-beta1 and TGF-beta2 (TGF-beta), from cortical astrocytes. The stimulatory effect of E2 was attenuated by the estrogen receptor (ER) antagonist, ICI182,780, suggesting ER dependency. The effect of E2 also appeared to involve mediation by the phosphotidylinositol 3-kinase (PI3K)/Akt signaling pathway, because E2 rapidly induced Akt phosphorylation, and pharmacological or molecular inhibition of the PI3K/Akt pathway prevented E2-induced release of TGF-beta. Additionally, the membrane-impermeant conjugate, E2-BSA, stimulated the release of TGF-beta, suggesting the potential involvement of a membrane-bound ER. Finally, E2, tamoxifen, and E2-BSA were shown to protect neuronal-astrocyte cocultures from camptothecin-induced neuronal cell death, effects that were attenuated by ICI182,780, Akt inhibition, or TGF-beta immunoneutralization. As a whole, these studies suggest that E2 induction of TGF-beta release from cortical astrocytes could provide a mechanism of neuroprotection, and that E2 stimulation of TGF-beta expression and release from astrocytes occurs via an ER-dependent mechanism involving mediation by the PI3K/Akt signaling pathway.

Implications of statin adverse effects in the elderly

The elderly differ from younger people in the relation of cholesterol to heart disease and mortality. Clinical trial evidence supports epidemiological findings in showing that high cholesterol weakens in its relationship to heart disease with age and loses (and in older age reverses) its relation to mortality. Randomised trial data confirm that lowering cholesterol no longer extends life in the elderly, even those at high risk of heart disease, and no evidence supports the presumption that the impact on all-cause morbidity is any more favourable. These findings increase the importance of statin adverse effects (AEs) in this group. Furthermore, the elderly may be more vulnerable to known AEs, and evidence provides cause for concern that new risks may supervene, including cancer, neurodegenerative disease and heart failure. Physiological evidence regarding the impact of statins on mitochondrial function, and mitochondrial function on ageing, support these concerns. Additionally, the impact of statin AEs (e.g., muscle and cognitive problems) may be amplified in this group. Effects may be misattributed to ageing. Even modestly lower cognitive and physical function in older elderly prognosticates increased disability, hospitalisation, institutionalisation, and mortality. Disability, once present, is less likely to recover. Because the risk for AEs is unattended by evidence of net benefit to the person, the use of statins in the elderly should be undertaken, if at all, with circumspection and close scrutiny for adverse effects.

Benefits and risks of sex hormone replacement in postmenopausal women

Because cardiovascular disease (CVD), which is far less common in young women than in men, but increases in prevalence in the postmenopausal years to that of men, estrogen repletion therapy (ERT) or combined hormone replacement therapy (HRT), has been widely used to protect against development of both CVD and osteoporosis, and possibly to delay or prevent cognitive loss or Alzheimer's disease (AD). To test the validity of favorable findings in many small-scale studies, and in clinical practice, a large-scale trial: the Women's Health Initiative (WHI) was undertaken by the National Institutes of Health (NIH), a trial that was prematurely ended because of increased CVD complications, despite some lessening of hip fractures. This paper suggests that the customary high intake of calcium (Ca)-advised to protect against osteoporosis, and the marginal magnesium (Mg) intake in the USA, might well be contributory to the adverse CV effects, that were all thromboembolic in nature. The procoagulant effect of estrogen is intensified by Ca; Mg-which counteracts many steps in the coagulation cascade and inhibits platelet aggregation and adhesion-is commonly consumed in sub-optimal amounts. The high American dietary Ca/Mg ratio might also be contributory to the WHI failure to confirm ERT's favorable mental effects. Discussed are mechanisms by which Mg enhances estrogen's central nervous system protective effects. Mg's improvement of cerebral blood flow, which improves brain metabolism, can also enhance removal of the beta amyloid peptide, accumulation of which is implicated in AD.

Pharmacotherapeutic approaches to the prevention of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is the most common cause of cognitive impairment in older patients and is expected to increase greatly in prevalence. Interventions that could delay disease onset would have a major public health impact.

OBJECTIVE

The objective of this article is to review evidence from epidemiologic studies and controlled trials addressing whether AD can be prevented.

METHODS

Data were gathered through a comprehensive, systematic search of MEDLINE using focused search criteria and spanning a 6-year period from January 1998 through January 2004; a hand search of reference lists from these studies and reviews; a review of the Cochrane Database of Systematic Reviews; and a hand search of relevant journals. Selection of articles was based on the clinical focus. Additional inclusion criteria were used to select key articles that contained higher-level evidence in accordance with explicit, validated criteria.

RESULTS

Preventive interventions for AD include vitamins, nonsteroidal anti-inflammatory drugs, and agents that protect the endothelium (eg, statins). Good control of hypertension with angiotensin-converting enzyme inhibitors and long-acting dihydropyridines also confers neuroprotective benefits.

CONCLUSIONS

The paradigm that AD is pharmacologically unresponsive is shifting as more effective pharmacotherapies for prevention and treatment rapidly emerge. Our understanding of the molecular mechanisms of neurodegeneration will soon allow us to more specifically target and interrupt the processes that contribute to this progressive dementia.

Long-term effects of melatonin or 17 beta-estradiol on improving spatial memory performance in cognitively impaired, ovariectomized adult rats

Melatonin is an endogenously generated potent antioxidant. Our previous studies indicate that melatonin improved learning and memory deficits in APP695 transgenic mouse of Alzheimer's disease. An ovariectomized (OVX) rat model which is characterized by progressive memory deficits, central cholinergic nerve system degeneration and differentiation/apoptosis imbalance is the ideal in vivo model in which to test the neuroprotective effects of melatonin. OVX Sprague-Dawley rats received daily injections of melatonin (5, 10 and 20 mg/kg) or 17 beta-estradiol (E2, 80 microg/kg) or sesame oil for 16 wk. Morris water maze results showed that ovarian steroid deprivation resulted in spatial memory impairment, while melatonin and E2 significantly ameliorated spatial memory deficits in OVX rats. The latency to find the hidden platform and the distance to reach the platform become shorter in both melatonin and E2-treated rats compared with those that were only OVX. Four months after OVX, the choline acetyltransferase activity in the frontal cortex and hippocampus were greatly decreased in comparison with the controls. Melatonin and E2 antagonized the effects induced by OVX. Interestingly, the activity of the acetylcholinesterase was not altered in any group of rats. DNA fragmentation was presented in the front cortex of the OVX rats. Melatonin and E2 reduced the number of apoptotic neurons. These findings demonstrate the important effects of melatonin and E2 on cholinergic neurons and support the potential application of melatonin in the treatment of dementia in postmenopausal women. Our results indicate that neuroprotection by melatonin partly correlated to modulation of apoptosis and protection of the cholinergic system. Early long-term melatonin application is a promising strategy which could potentially be applied in a clinic setting.

The presenilin-1 familial Alzheimer disease mutant P117L impairs neurogenesis in the hippocampus of adult mice

The functions of presenilin 1 (PS1) and how PS1 mutations cause familial Alzheimer's disease (FAD) are incompletely understood. PS1 expression is essential for neurogenesis during embryonic development and may also influence neurogenesis in adult brain. We examined how increasing PS1 expression or expressing an FAD mutant would affect neurogenesis in the adult hippocampus. A neuron-specific enolase (NSE) promoter was used to drive neuronal overexpression of either wild-type human PS1 or the FAD mutant P117L in transgenic mice, and the animals were studied under standard-housing conditions or after environmental enrichment. As judged by bromodeoxyuridine (BrdU) labeling, neural progenitor proliferation rate was mostly unaffected by increasing expression of either wild-type or FAD mutant PS1. However, in both housing conditions, the FAD mutant impaired the survival of BrdU-labeled neural progenitor cells leading to fewer new beta-III-tubulin-immunoreactive neurons being generated in FAD mutant animals during the 4-week postlabeling period. The effect was FAD mutant specific in that neural progenitor survival and differentiation in mice overexpressing wild-type human PS1 were similar to nontransgenic controls. Two additional lines of PS1 wild-type and FAD mutant transgenic mice showed similar changes indicating that the effects were not integration site-dependent. These studies demonstrate that a PS1 FAD mutant impairs new neuron production in adult hippocampus by decreasing neural progenitor survival. They also identify a new mechanism whereby PS1 FAD mutants may impair normal neuronal function and may have implications for the physiological functioning of the hippocampus in FAD.

Gender differences in the amount and deposition of amyloidbeta in APPswe and PS1 double transgenic mice

Transgenic mice carrying both the human amyloid precursor protein (APP) with the Swedish mutation and the presenilin-1 A246E mutation (APP/PS1 mice) develop Alzheimer's disease-like amyloidbeta protein (Abeta) deposits around 9 months of age. These mice show an age-dependent increase in the level of Abeta40 and Abeta42 and in the number of amyloid plaques in the brain. Abeta40 and Abeta42 levels were measured, and amyloid burden and plaque number were quantified, in the hippocampus at the age of 4, 12, and 17 months in both male and female APP/PS1 mice. In all mice, amyloid burden and plaque number increased markedly with age, with female mice bearing a heavier amyloid burden and higher plaque number compared to male mice of the same age, both at 12 and at 17 months of age. The level of both Abeta40 and Abeta42 significantly increased in female mice with age and was always significantly higher in female than in male mice of the same age. Further, there were significant correlations between amyloid burden and Abeta42 level in female mice and between amyloid burden and plaques in both female and male mice. Together these data show that female APP/PS1 mice accumulate amyloid at an earlier age and that they build up more amyloid deposits in the hippocampus than age-matched male mice. Together, these results provide new insights in the potential mechanisms of the observed gender differences in the pathogenesis of AD.