Protective effects of estrogen and selective estrogen receptor modulators in the brain

Screening of orthopedic medicines identifies raloxifene hydrochloride as a novel ferroptosis inhibitor for spinal cord injury therapy

Spinal cord injury (SCI) is a severe condition that can lead to irreversible central nervous system damage. Spinal cord injury patients frequently present with coexisting orthopedic conditions, and many of them also have underlying bone and joint diseases. Recent studies have identified ferroptosis as a significant contributor that exacerbates the progression of spinal cord injury. This study conducted a screening in common orthopedic medications, which includes anti-osteoporosis agents and calcium supplements, in order to identify potential ferroptosis inhibitors and investigate their therapeutic effects on spinal cord injury. Among the 8 drugs screened, raloxifene hydrochloride was found to significantly inhibit ferroptosis induced by RSL3 in neural cells. Subsequent studies confirmed its inhibitory effect on ferroptosis both in vitro and in vivo. It was also demonstrated that Nrf2 inhibitor Brusatol could reverse the anti-ferroptotic effect of Raloxifene hydrochloride in neural cells in vitro as well as its therapeutic effect on SCI in vivo, suggesting its inhibitory effect on ferroptosis is through Nrf2. This study identifies a novel ferroptosis inhibitor among orthopedic medicines and also confirms the therapeutic effect of Raloxifene hydrochloride on SCI. The results of the current study may provide reference for the clinical administration of SCI.

Association of age at menopause and suicide risk in postmenopausal women: a nationwide cohort study

Introduction

Early age at menopause has been linked to various adverse health outcomes, but its association with suicide risk remains underexplored. This study aims to assess the relationship between age at menopause and suicide risk among postmenopausal women.

Methods

This retrospective cohort study analyzed data from the Korean National Health Insurance System (NHIS), covering 1,315,795 postmenopausal women aged 30 years and above, from 2009 to 2021. Menopausal age was classified as primary ovarian insufficiency (under 40 years), early menopause (40-44 years), average menopause (45-49 and 50-54 years), and late menopause (55 years and older). Suicide incidence was identified using ICD-10 codes for primary cause of death. Multivariable Cox proportional hazards models were utilized to estimate hazard ratios (HRs) and 95% confidence intervals (CIs).

Results

Across the 12-year follow-up, there were 2,986 suicides. Women with primary ovarian insufficiency exhibited the highest suicide risk (HR, 1.43; 95% CI, 1.14-1.78, p < 0.001), followed by those with early menopause (HR, 1.31; 95% CI, 1.15-1.50, p < 0.001), and those with menopause between 45 and 49 (HR, 1.13; 95% CI, 1.04-1.23, p < 0.001) compared to the reference group undergoing menopause at age of 50-54.

Discussion

Early onset of menopause, particularly primary ovarian insufficiency, is associated with a significantly elevated risk of suicide. These findings underscore the need for targeted interventions and support for women experiencing early menopause. This study highlights the importance of monitoring mental health in postmenopausal women and suggests further research to explore the underlying mechanisms linking early menopause to increased suicide risk.

Natural flavonoids as potential therapeutics in the management of Alzheimer's disease: a review

Alzheimer's disease (AD) is an age-dependent neurodegenerative disorder which is associated with the accumulation of proteotoxic Aβ peptides, and pathologically characterized by the deposition of Aβ-enriched plaques and neurofibrillary tangles. Given the social and economic burden caused by the rising frequency of AD, there is an urgent need for the development of appropriate therapeutics. Natural compounds are gaining popularity as alternatives to synthetic drugs due to their neuroprotective properties and higher biocompatibility. While natural compound's therapeutic effects for AD have been recently investigated in numerous in vitro and in vivo studies, only few have developed to clinical trials. The present review aims to provide a brief overview of the therapeutic effects, new insights, and upcoming perspectives of the preclinical and clinical trials of flavonoids for the treatment of Alzheimer's disease.

Gene-dosage- and sex-dependent differences in the prodromal-Like phase of the F344tgHD rat model for Huntington disease

In Huntington disease (HD) the prodromal phase has been increasingly investigated and is currently in focus for early interventional treatments. Also, the influence of sex on disease progression and severity in patients is under discussion, as a sex-specific impact has been reported in transgenic rodent models for HD. To this end, we have been studying these aspects in Sprague Dawley rats transgenic for HD. Here, we took up on the congenic F344tgHD rat model, expressing a fragmented Htt construct with 51 CAG repeats on an inbred F344 rat background and characterized potential sexual dimorphism and gene-dosage effects in rats during the pre-symptomatic phase (1-8 months of age). Our study comprises a longitudinal phenotyping of motor function, emotion and sensorimotor gating, as well as screening of metabolic parameters with classical and automated assays in combination with investigation of molecular HD hallmarks (striatal cell number and volume estimation, appearance of HTT aggregates). Differences between sexes became apparent during middle age, particularly in the motor and sensorimotor domains. Female individuals were generally more active, demonstrated different gait characteristics than males and less anxiolytic-like behavior. Alterations in both the time course and affected behavioral domains varied between male and female F344tgHD rats. First subtle behavioral anomalies were detected in transgenic F344tgHD rats prior to striatal MSN cell loss, revealing a prodromal-like phase in this model. Our findings demonstrate that the congenic F344tgHD rat model shows high face-validity, closely resembling the human disease's temporal progression, while having a relatively low number of CAG repeats, a slowly progressing pathology with a prodromal-like phase and a comparatively subtle phenotype. By differentiating the sexes regarding HD-related changes and characterizing the prodromal-like phase in this model, these findings provide a foundation for future treatment studies.

Estradiol mediates colonic epithelial protection in aged mice after stroke and is associated with shifts in the gut microbiome

The gut is a major source of bacteria and antigens that contribute to neuroinflammation after brain injury. Colonic epithelial cells (ECs) are responsible for secreting major cellular components of the innate defense system, including antimicrobial proteins (AMP) and mucins. These cells serve as a critical regulator of gut barrier function and maintain host-microbe homeostasis. In this study, we determined post-stroke host defense responses at the colonic epithelial surface in mice. We then tested if the enhancement of these epithelial protective mechanisms is beneficial in young and aged mice after stroke. AMPs were significantly increased in the colonic ECs of young males, but not in young females after experimental stroke. In contrast, mucin-related genes were enhanced in young females and contributed to mucus formation that maintains the distance between the host and gut bacteria. Bacterial community profiling was done using universal amplification of 16S rRNA gene sequences. The sex-specific colonic epithelial defense responses after stroke in young females were reversed with ovariectomy and led to a shift from a predominately mucin response to the enhanced AMP expression seen in males after stroke. Estradiol (E2) replacement prior to stroke in aged females increased mucin gene expression in the colonic ECs. Interestingly, we found that E2 treatment reduced stroke-associated neuronal hyperactivity in the insular cortex, a brain region that interacts with visceral organs such as the gut, in parallel to an increase in the composition of Lactobacillus and Bifidobacterium in the gut microbiota. This is the first study demonstrating sex differences in host defense mechanisms in the gut after brain injury.

Neuroprotective astroglial response to neural damage and its relevance to affective disorders

Astrocytes not only support neuronal function with essential roles in synaptic neurotransmission, action potential propagation, metabolic support, or neuroplastic and developmental adaptations. They also respond to damage or dysfunction in surrounding neurons and oligodendrocytes by releasing neurotrophic factors and other molecules that increase the survival of the supported cells or contribute to mechanisms of structural and molecular restoration. The neuroprotective responsiveness of astrocytes is based on their ability to sense signals of degeneration, metabolic jeopardy and structural damage, and on their aptitude to locally deliver specific molecules to remedy threats to the molecular and structural features of their cellular partners. To the extent that neuronal and other glial cell disturbances are known to occur in affective disorders, astrocyte responsiveness to those disturbances may help to better understand the roles astrocytes play in affective disorders. The astrocytic sensing apparatus supporting those responses involves receptors for neurotransmitters, purines, cell adhesion molecules and growth factors. Astrocytes also share with the immune system the capacity of responding to cytokines released upon neuronal damage. In addition, in responses to specific signals astrocytes release unique factors such as clusterin or humanin that have been shown to exert potent neuroprotective effects. Astrocytes integrate the signals above to further deliver structural lipids, removing toxic metabolites, stabilizing the osmotic environment, normalizing neurotransmitters, providing anti-oxidant protection, facilitating synaptogenesis and acting as barriers to contain varied deleterious signals, some of which have been described in brain regions relevant to affective disorders and related animal models. Since various of the injurious signals that activate astrocytes have been implicated in different aspects of the etiopathology of affective disorders, particularly in relation to the diagnosis of depression, potentiating the corresponding astrocyte neuroprotective responses may provide additional opportunities to improve or complement available pharmacological and behavioral therapies for affective disorders.

Sex differences in brainstem structure volumes in patients with schizophrenia

Patients with schizophrenia (SZ) display moderate reductions in brainstem volumes, including the midbrain, pons, superior cerebellar peduncle, and medulla oblongata. Here, we investigated alterations in brainstem volumes between SZ patients and healthy controls (HCs) stratified by sex. T1-weighted MRI brain scans were processed with FreeSurfer v6.0 in 156 SZ patients (61 males/95 females) and 205 HCs (133/72). Of the brainstem structures, pons volumes were significantly reduced, particularly in male SZ patients. The decreased pons volumes were correlated with lower levels of education but not duration of illness in male patients. These findings suggest that the reduction in pons volume in male patients might be occurred before or around the onset of the disorder.

Tamoxifen offers long-term neuroprotection after hippocampal silent infarct in male rats

Silent infarcts (SI) are a cerebral small vessel disease characterized by small subcortical infarcts. These occur in the absence of typical ischemia symptoms but are linked to cognitive decline and dementia. While there are no approved treatments for SI, recent results from our laboratory suggest that tamoxifen, a selective estrogen receptor modulator, is a viable candidate. In the present study, we induced SI in the dorsal hippocampal CA1 region of rats and assessed the effects of systemic administration of tamoxifen (5 mg/kg, twice) 21 days after injury on cognitive and pathophysiological measures, including cell loss, apoptosis, gliosis and estrogen receptors (ERs). We found that tamoxifen protected against the SI-induced cognitive dysfunction on the hippocampal-dependent, place recognition task, cell and ER loss, and increased apoptosis and gliosis in the CA1. Exploratory data analyses using a scatterplot matrix and principal component analysis indicated that SI-tamoxifen rats were indistinguishable from sham controls while they differed from SI rats, who were characterized by enhanced cell loss, apoptosis and gliosis, lower ERs, and recognition memory deficit. Supervised machine learning using support vector machine (SVM) determined predictors of progression from the early ischemic state to the dementia-like state. It showed that caspase-3 and ERα in the CA1 and exploration proportion were reliable and accurate predictors of this progression. Importantly, tamoxifen ameliorated SI-induced effects on all three of these variables, providing further evidence for its viability as a candidate treatment for SI and prevention of associated dementia.

The selective estrogen receptor modulator tamoxifen protects against subtle cognitive decline and early markers of injury 24 h after hippocampal silent infarct in male Sprague-Dawley rats

Silent infarcts (SI) are subcortical cerebral infarcts occurring in the absence of typical ischemia symptoms and are linked to cognitive decline and dementia development. There are no approved treatments for SI. One potential treatment is tamoxifen, a selective estrogen receptor modulator. It is critical to establish whether treatments effectively target the early consequences of SI to avoid progression to complete injury. We induced SI in the dorsal hippocampal CA1 of rats and assessed whether tamoxifen is protective 24 h later against cognitive deficits and injury responses including gliosis, apoptosis, inflammation and changes in estrogen receptors (ERs). SI led to subtle cognitive impairment on the object place task, an effect ameliorated by tamoxifen administration. SI did not lead to detectable hippocampal cell loss but increased apoptosis, astrogliosis, microgliosis and inflammation. Tamoxifen protected against the effects of SI on all measures except microgliosis. SI increased ERα and decreased ERβ in the hippocampus, which were mitigated by tamoxifen. Exploratory data analyses using scatterplot matrices and principal component analysis indicated that SI rats given tamoxifen were indistinguishable from controls. Further, SI rats were significantly different from all other groups, an effect associated with low levels of ERα and increased apoptosis, gliosis, inflammation, ERβ, and time spent with the unmoved object. The results demonstrate that tamoxifen is protective against the early cellular and cognitive consequences of hippocampal SI 24 h after injury. Tamoxifen mitigates apoptosis, gliosis, and inflammation and normalization of ER levels in the CA1, leading to improved cognitive outcomes after hippocampal SI.

Involvement of the Protein Ras Homolog Enriched in the Striatum, Rhes, in Dopaminergic Neurons' Degeneration: Link to Parkinson's Disease

Rhes is one of the most interesting genes regulated by thyroid hormones that, through the inhibition of the striatal cAMP/PKA pathway, acts as a modulator of dopamine neurotransmission. Rhes mRNA is expressed at high levels in the dorsal striatum, with a medial-to-lateral expression gradient reflecting that of both dopamine D₂ and adenosine A_2A receptors. Rhes transcript is also present in the hippocampus, cerebral cortex, olfactory tubercle and bulb, substantia nigra pars compacta (SNc) and ventral tegmental area of the rodent brain. In line with Rhes-dependent regulation of dopaminergic transmission, data showed that lack of Rhes enhanced cocaine- and amphetamine-induced motor stimulation in mice. Previous studies showed that pharmacological depletion of dopamine significantly reduces Rhes mRNA levels in rodents, non-human primates and Parkinson's disease (PD) patients, suggesting a link between dopaminergic innervation and physiological Rhes mRNA expression. Rhes protein binds to and activates striatal mTORC1, and modulates L-DOPA-induced dyskinesia in PD rodent models. Finally, Rhes is involved in the survival of mouse midbrain dopaminergic neurons of SNc, thus pointing towards a Rhes-dependent modulation of autophagy and mitophagy processes, and encouraging further investigations about mechanisms underlying dysfunctions of the nigrostriatal system.

Phytosterols: Targeting Neuroinflammation in Neurodegeneration

Plant-derived sterols, phytosterols, are well known for their cholesterol-lowering activity in serum and their anti-inflammatory activities. Recently, phytosterols have received considerable attention due to their beneficial effects on various non-communicable diseases, and recommended use as daily dietary components. The signaling pathways mediated in the brain by phytosterols have been evaluated, but little is known about their effects on neuroinflammation, and no clinical studies have been undertaken on phytosterols of interest. In this review, we discuss the beneficial roles of phytosterols, including their attenuating effects on inflammation, blood cholesterol levels, and hallmarks of the disease, and their regulatory effects on neuroinflammatory disease pathways. Despite recent advancements made in phytosterol pharmacology, some critical questions remain unanswered. Therefore, we have tried to highlight the potential of phytosterols as viable therapeutics against neuroinflammation and to direct future research with respect to clinical applications.

A Report of Tamoxifen and Parkinson's Disease in a US Population and a Review of the Literature

BACKGROUND

Tamoxifen, a selective estrogen receptor modulator, has been shown to variably affect Parkinson's disease (PD) risk.

OBJECTIVE

The aim of this study was to review epidemiological literature and evaluate the rate of PD in women with breast cancer with tamoxifen exposure in a US population.

METHODS

A literature search was conducted to identify relevant studies. We performed a retrospective cohort analysis using the Nurses' Health Study Version One to report descriptive statistics.

RESULTS

Most studies suggest there may be a time-dependent effect of tamoxifen on PD risk, with the risk increasing with time from exposure. However, rates of PD in persons exposed to tamoxifen overall appear to be low. In our cohort, PD was evident in 6.2 per 1,000 of those with tamoxifen use and 3.6 per 1,000 of those without tamoxifen use. Time from breast cancer to PD diagnosis was 9.7 years among women with tamoxifen exposure and 11.7 among women without.

CONCLUSIONS

Tamoxifen may be associated with an increased risk for PD. Further research is needed to elucidate the role of estrogen and selective estrogen antagonism in PD. © 2021 International Parkinson and Movement Disorder Society.

Protective mechanism of kaempferol against Aβ25-35-mediated apoptosis of pheochromocytoma (PC-12) cells through the ER/ERK/MAPK signalling pathway

INTRODUCTION

Progressive accumulation of amyloid-β (Aβ) is a pathological trait of Alzheimer's disease (AD). Amyloid-β increases free radical production in neuronal cells, leading to neuronal cell death. Hormone replacement therapy can reduce the incidence of AD, and oestrogen significantly improves the clinical signs in patients with AD. However, the long-term use of oestrogen causes a variety of diseases. Phytoestrogens have been reported to bind and activate oestrogen receptors in mammals and humans to produce oestrogen-like or anti-oestrogen-like effects. Kaempferol is a flavonoid phytoestrogen that can produce a certain protective effect in neurons. However, the molecular mechanism of kaempferol in AD is unclear.

MATERIAL AND METHODS

This study used pheochromocytoma (PC-12) cells that were damaged by Aβ_25-35 as an in vitro model of AD, and oestradiol was a positive control. The cells were incubated with kaempferol alone or in combination with fulvestrant (an antagonist of ER) and U0126 (an inhibitor of ERK) in Aβ_25-35 culture. Cell activity was measured by the MTT method. Cell apoptosis was evaluated by flow cytometry. Gene and protein expression levels were tested by qRT-PCR and Western blotting.

RESULTS

This study demonstrated that kaempferol protected PC-12 cells from Aβ_25-35-induced cell death and apoptosis in a dose-dependent manner. Treatment with fulvestrant (an antagonist of ER) and U0126 (an inhibitor of ERK) significantly increased the apoptosis of PC-12 cells. Moreover, kaempferol promoted the expression of anti-apoptotic molecules and inhibited the expression of pro-apoptotic molecules, which were blocked by fulvestrant and U0126.

CONCLUSIONS

Kaempferol protected PC-12 cells against Aβ_25-35-induced cell apoptosis through the ER/ERK/MAPK signalling pathway.

Raloxifene as Treatment for Various Types of Brain Injuries and Neurodegenerative Diseases: A Good Start

Recent studies have shown that the selective estrogen receptor modulator (SERM) raloxifene had pronounced protective effects against progressing brain damage after traumatic brain injury (TBI) in mice. These studies, indicating beneficial effects of raloxifene for brain health, prompted the study of the history and present state of knowledge of this topic. It appears that, apart from raloxifene, to date, four nonrelated compounds have shown comparable beneficial effects—fucoidan, pifithrin, SMM-189 (5-dihydroxy-phenyl]-phenyl-methanone), and translocator protein (TSPO) ligands. Raloxifene, however, is ahead of the field, as for more than two decades it has been used in medical practice for various chronic ailments in humans. Thus, apart from different types of animal and cell culture studies, it has also been assessed in various human clinical trials, including assaying its effects on mild cognitive impairments. Regarding cell types, raloxifene protects neurons from cell death, prevents glial activation, ameliorates myelin damage, and maintains health of endothelial cells. At whole central nervous system (CNS) levels, raloxifene ameliorated mild cognitive impairments, as seen in clinical trials, and showed beneficial effects in animal models of Parkinson’s disease. Moreover, with stroke and TBI in animal models, raloxifene showed curative effects. Furthermore, raloxifene showed healing effects regarding multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS) in cell culture. The adverse biological signals typical of these conditions relate to neuronal activity, neurotransmitters and their receptors, plasticity, inflammation, oxidative stress, nitric oxide, calcium homeostasis, cell death, behavioral impairments, etc. Raloxifene favorably modulates these signals toward cell health—on the one hand, by modulating gene expression of the relevant proteins, for example by way of its binding to the cell nuclear estrogen receptors ERα and ERβ (genomic effects) and, on the other hand (nongenomic effects) by modulation of mitochondrial activity, reduction of oxidative stress and programmed cell death, maintaining metabolic balance, degradation of Abeta, and modulation of intracellular cholesterol levels. More specifically regarding Alzheimer’s disease, raloxifene may not cure diagnosed Alzheimer’s disease. However, the onset of Alzheimer’s disease may be delayed or arrested by raloxifene’s capability to attenuate mild cognitive impairment. Mild cognitive impairment is a condition that may precede diagnosis of Alzheimer’s disease. In this review, relatively new insights are addressed regarding the notion that Alzheimer’s disease can be caused by bacterial (as well as viral) infections, together with the most recent findings that raloxifene can counteract infections of at least some bacterial and viral strains. Thus, here, an overview of potential treatments of neurodegenerative disease by raloxifene is presented, and attention is paid to subcellular molecular biological pathways that may be involved.

Sex Differences and the Role of Estradiol in Mesolimbic Reward Circuits and Vulnerability to Cocaine and Opiate Addiction

Although both men and women become addicted to drugs of abuse, women transition to addiction faster, experience greater difficulties remaining abstinent, and relapse more often than men. In both humans and rodents, hormonal cycles are associated with females' faster progression to addiction. Higher concentrations and fluctuating levels of ovarian hormones in females modulate the mesolimbic reward system and influence reward-directed behavior. For example, in female rodents, estradiol (E2) influences dopamine activity within the mesolimbic reward system such that drug-directed behaviors that are normally rewarding and reinforcing become enhanced when circulating levels of E2 are high. Therefore, neuroendocrine interactions, in part, explain sex differences in behaviors motivated by drug reward. Here, we review sex differences in the physiology and function of the mesolimbic reward system in order to explore the notion that sex differences in response to drugs of abuse, specifically cocaine and opiates, are the result of molecular neuroadaptations that differentially develop depending upon the hormonal state of the animal. We also reconsider the notion that ovarian hormones, specifically estrogen/estradiol, sensitize target neurons thereby increasing responsivity when under the influence of either cocaine or opiates or in response to exposure to drug-associated cues. These adaptations may ultimately serve to guide the motivational behaviors that underlie the factors that cause women to be more vulnerable to cocaine and opiate addiction than men.

Targeting BKCa Channels in Migraine: Rationale and Perspectives

Large (big)-conductance calcium-activated potassium (BK_Ca) channels are expressed in migraine-related structures such as the cranial arteries, trigeminal ganglion and trigeminal spinal nucleus, and they play a substantial role in vascular tonus and neuronal excitability. Using synthetic BK_Ca channels openers was associated with headache as a frequent adverse effect in healthy volunteers. Additionally, BK_Ca channels are downstream molecules in migraine signalling pathways that are activated by several compounds known to provoke migraine, including calcitonin gene-related peptide (CGRP), pituitary adenylate cyclase-activating polypeptide (PACAP) and glyceryl trinitrate (GTN). Also, there is a high affinity and a close coupling between BK_Ca channels and ATP-sensitive potassium (K_ATP) channels, the role of which has recently been established in migraine pathophysiology. These observations raise the question as to whether direct BK_Ca channel activation can provoke migraine in migraine patients, and whether the BK_Ca channel could be a potential novel anti-migraine target. Hence, randomized and placebo-controlled clinical studies on BK_Ca channel openers or blockers in migraine patients are needed.

Astrocytes Mediate Protective Actions of Estrogenic Compounds after Traumatic Brain Injury

Traumatic brain injury (TBI) is a serious public health problem. It may result in severe neurological disabilities and in a variety of cellular metabolic alterations for which available therapeutic strategies are limited. In the last decade, the use of estrogenic compounds, which activate protective mechanisms in astrocytes, has been explored as a potential experimental therapeutic approach. Previous works have suggested estradiol (E2) as a neuroprotective hormone that acts in the brain by binding to estrogen receptors (ERs). Several steroidal and nonsteroidal estrogenic compounds can imitate the effects of estradiol on ERs. These include hormonal estrogens, phytoestrogens and synthetic estrogens, such as selective ER modulators or tibolone. Current evidence of the role of astrocytes in mediating protective actions of estrogenic compounds after TBI is reviewed in this paper. We conclude that the use of estrogenic compounds to modulate astrocytic properties is a promising therapeutic approach for the treatment of TBI.

Nootropic and Anti-Alzheimer's Actions of Medicinal Plants: Molecular Insight into Therapeutic Potential to Alleviate Alzheimer's Neuropathology

Medicinal plants are the backbone of modern medicine. In recent times, there is a great urge to discover nootropic medicinal plants to reverse cognitive dysfunction owing to their less adverse effects. Alzheimer's disease (AD) is an age-related neurodegenerative disorder characterized by the inevitable loss of cognitive function, memory and language impairment, and behavioral disturbances, which turn into gradually more severe. Alzheimer's has no current cure, but symptomatic treatments are available and research continues. The number of patients suffering from AD continues to rise and today, there is a worldwide effort under study to find better ways to alleviate Alzheimer's pathogenesis. In this review, the nootropic and anti-Alzheimer's potentials of 6 medicinal plants (i.e., Centella asiatica, Clitoria ternatea, Crocus sativus, Terminalia chebula, Withania somnifera, and Asparagus racemosus) were explored through literature review. This appraisal focused on available information about neuroprotective and anti-Alzheimer's use of these plants and their respective bioactive compounds/metabolites and associated effects in animal models and consequences of its use in human as well as proposed molecular mechanisms. This review progresses our existing knowledge to reveal the promising linkage of traditional medicine to halt AD pathogenesis. This analysis also avowed a new insight to search the promising anti-Alzheimer's drugs.

Can distinctly different rapid estrogen actions share a common mechanistic step?

Contribution to Special Issue on Fast effects of steroids. This paper reviews early evidence for the existence of rapid, non-genomic effects of estrogens on neurons, and, further, proposes that these rapid effects are often synergistic with later, genomic effects. Finally, suggestions about potential molecular mechanisms underlying the rapid effects of estrogens are offered. A mechanistic step we propose to be common among rapid estrogenic actions includes membrane ER's binding to histamine, and NMDA receptors and subsequent dimerization, and clustering (respectively) in a manner that enhances histamine and NMDA actions.

Development of selective androgen receptor modulators (SARMs)

The Androgen Receptor (AR), a member of the steroid hormone receptor family, plays important roles in the physiology and pathology of diverse tissues. AR ligands, which include circulating testosterone and locally synthesized dihydrotestosterone, bind to and activate the AR to elicit their effects. Ubiquitous expression of the AR, metabolism and cross reactivity with other receptors limit broad therapeutic utilization of steroidal androgens. However, the discovery of selective androgen receptor modulators (SARMs) and other tissue-selective nuclear hormone receptor modulators that activate their cognate receptors in a tissue-selective manner provides an opportunity to promote the beneficial effects of androgens and other hormones in target tissues with greatly reduced unwanted side-effects. In the last two decades, significant resources have been dedicated to the discovery and biological characterization of SARMs in an effort to harness the untapped potential of the AR. SARMs have been proposed as treatments of choice for various diseases, including muscle-wasting, breast cancer, and osteoporosis. This review provides insight into the evolution of SARMs from proof-of-concept agents to the cusp of therapeutic use in less than two decades, while covering contemporary views of their mechanisms of action and therapeutic benefits.

Role of Plant-Derived Flavonoids and Their Mechanism in Attenuation of Alzheimer's and Parkinson's Diseases: An Update of Recent Data

Neurodegeneration is a progressive loss of neuronal cells in certain regions of the brain. Most of the neurodegenerative disorders (NDDs) share the communal characteristic such as damage or reduction of various cell types typically including astrocytes and microglial activity. Several compounds are being trialed to treat NDDs but they possess solitary symptomatic advantages along with copious side effects. The finding of more enthralling and captivating compounds to suspend and standstill the pathology of NDDs will be considered as a hallmark of present times. Phytochemicals possess the potential to alternate the synthetic line of therapy against NDDs. The present review explores the potential efficacy of plant-derived flavonoids against most common NDDs including Alzheimer's disease (AD) and Parkinson's disease (PD). Flavonoids are biologically active phytochemicals which possess potential pharmacological effects, including antiviral, anti-allergic, antiplatelet, anti-inflammatory, anti-tumor, anti-apoptotic and anti-oxidant effects and are able to attenuate the pathology of various NDDs through down-regulating the nitric oxide (NO) production, by reducing the tumor necrosis factor-α (TNF-α), by reducing the excitotoxicity of superoxide as well as acting as tyrosine kinase (TK) and monoamine oxidase (MAO) inhibiting enzyme.

Administration of 17β-Estradiol Improves Motoneuron Survival and Down-regulates Inflammasome Activation in Male SOD1(G93A) ALS Mice

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease manifested by the progressive loss of upper and lower motoneurons. The pathomechanism of ALS is complex and not yet fully understood. Neuroinflammation is believed to significantly contribute to disease progression. Inflammasome activation was recently shown in the spinal cord of human sporadic ALS patients and in the SOD1(G93A) mouse model for ALS. In the present study, we investigated the neuroprotective and anti-inflammatory effects of 17β-estradiol (E2) treatment in pre-symptomatic and symptomatic male SOD1(G93A) mice. Symptomatic mice with E2 substitution exhibited improved motor performance correlating with an increased survival of motoneurons in the lumbar spinal cord. Expression of NLRP3 inflammasome proteins and levels of activated caspase 1 and mature interleukin 1 beta were significantly reduced in SOD1(G93A) mice supplemented with E2.

Tamoxifen Administration Immediately or 24 Hours after Spinal Cord Injury Improves Locomotor Recovery and Reduces Secondary Damage in Female Rats

Spinal cord injury (SCI) is a condition with no available cure. The initial physical impact triggers a cascade of molecular and cellular events that generate a nonpermissive environment for cell survival and axonal regeneration. Spinal cord injured patients often arrive at the clinic hours after the initial insult. This indicates the need to study and develop treatments with a long therapeutic window of action and multiactive properties, which target the complex set of events that arise after the initial trauma. We provide evidence that tamoxifen (TAM), a drug approved by the Food and Drug Administration, exerts neuroprotective effects in an animal model when applied up-to 24 h after SCI. We hypothesized that continuous TAM administration will improve functional locomotor recovery by favoring myelin preservation and reducing secondary damage after SCI. Adult female Sprague-Dawley rats (∼230 g) received a moderate contusion to the thoracic (T9-T10) spinal cord, using the MASCIS impactor device. To determine the therapeutic window available for TAM treatment, rats were implanted with TAM pellets (15 mg) immediately or 24 h after SCI. Locomotor function (Basso, Beattie, Bresnahan open field test, grid walk, and beam crossing tests) was assessed weekly for 35 days post-injury. TAM-treated rats showed significant functional locomotor recovery and improved fine movements when treated immediately or 24 h after SCI. Further, TAM increased white matter preservation and reduced secondary damage caused by astrogliosis, axonal degeneration, and cell death after trauma. These results provide evidence for TAM as a potential therapeutic agent to treat SCI up to 24 h after the trauma.

Estrogens and Coronary Artery Disease: New Clinical Perspectives

In premenopausal women, endogenous estrogens are associated with reduced prevalence of arterial hypertension, coronary artery disease, myocardial infarction, and stroke. Clinical trials conducted in the 1990s such as HERS, WHI, and WISDOM have shown that postmenopausal treatment with horse hormone mixtures (so-called conjugated equine estrogens) and synthetic progestins adversely affects female cardiovascular health. Our understanding of rapid (nongenomic) and chronic (genomic) estrogen signaling has since advanced considerably, including identification of a new G protein-coupled estrogen receptor (GPER), which like the "classical" receptors ERα and ERβ is highly abundant in the cardiovascular system. Here, we discuss the role of estrogen receptors in the pathogenesis of coronary artery disease and review natural and synthetic ligands of estrogen receptors as well as their effects in physiology, on cardiovascular risk factors, and atherosclerotic vascular disease. Data from preclinical and clinical studies using nonselective compounds activating GPER, which include selective estrogen receptor modulators such as tamoxifen or raloxifene, selective estrogen receptor downregulators such as Faslodex™ (fulvestrant/ICI 182,780), vitamin B3 (niacin), green tea catechins, and soy flavonoids such as genistein or resveratrol, strongly suggest that activation of GPER may afford therapeutic benefit for primary and secondary prevention in patients with or at risk for coronary artery disease. Evidence from preclinical studies suggest similar efficacy profiles for selective small molecule GPER agonists such as G-1 which are devoid of uterotrophic activity. Further clinical research in this area is warranted to provide opportunities for future cardiovascular drug development.

Inhibition of p38 pathway-dependent MPTP-induced dopaminergic neurodegeneration in estrogen receptor alpha knockout mice

Approximately, 7-10 million people in the world suffer from Parkinson's disease (PD). Recently, increasing evidence has suggested the protective effect of estrogens against nigrostriatal dopaminergic damage in PD. In this study, we investigated whether estrogen affects 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced behavioral impairment in estrogen receptor alpha (ERα)-deficient mice. MPTP (15mg/kg, four times with 1.5-h interval)-induced dopaminergic neurodegeneration was evaluated in ERα wild-type (WT) and knockout (KO) mice. Larger dopamine depletion, behavioral impairments (Rotarod test, Pole test, and Gait test), activation of microglia and astrocytes, and neuroinflammation after MPTP injection were observed in ERα KO mice compared to those in WT mice. Immunostaining for tyrosine hydroxylase (TH) after MPTP injection showed fewer TH-positive neurons in ERα KO mice than WT mice. Levels of dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC, metabolite of dopamine) were also lowered in ERα KO mice after MPTP injection. Interestingly, a higher immunoreactivity for monoamine oxidase (MAO) B was found in the substantia nigra and striatum of ERα KO mice after MPTP injection. We also found an increased activation of p38 kinase (which positively regulates MAO B expression) in ERα KO mice. In vitro estrogen treatment inhibited neuroinflammation in 1-methyl-4-phenyl pyridium (MPP+)-treated cultured astrocyte cells; however, these inhibitory effects were removed by p38 inhibitor. These results indicate that ERα might be important for dopaminergic neuronal survival through inhibition of p38 pathway.

Tamoxifen Promotes Axonal Preservation and Gait Locomotion Recovery after Spinal Cord Injury in Cats

We performed experiments in cats with a spinal cord penetrating hemisection at T13-L1 level, with and without tamoxifen treatment. The results showed that the numbers of the ipsilateral and contralateral ventral horn neurons were reduced to less than half in the nontreated animals compared with the treated ones. Also, axons myelin sheet was preserved to almost normal values in treated cats. On the contrary, in the untreated animals, their myelin sheet was reduced to 28% at 30 days after injury (DAI), in both the ipsilateral and contralateral regions of the spinal cord. Additionally, we made hindlimb kinematics experiments to study the effects of tamoxifen on cat locomotion after the injury: at 4, 16, and 30 DAI. We observed that the ipsilateral hindlimb angular displacement (AD) of the pendulum-like movements (PLM) during gait locomotion was recovered to almost normal values in treated cats. Contralateral PLM acquired similar values to those obtained in intact cats. At 4 DAI, untreated animals showed a compensatory increment of PLM occurring in the contralateral hindlimb, which was partially recovered at 30 DAI. Our findings indicate that tamoxifen exerts a neuroprotective effect and preserves or produces myelinated axons, which could benefit the locomotion recovery in injured cats.

A Quantification of the Injury-Induced Changes in Central Aromatase, Oestrogenic Milieu and Steroid Receptor Expression in the Zebra Finch

In songbirds and mammals, brain injury results in the up-regulation of aromatase (oestrogen synthase) expression in astroglia. The resulting presumed synthesis of neural oestradiol (E2 ) has neuroprotective effects including a decrease in neurodegeneration, neuroinflammation and apoptosis. The development of therapeutic tools that exploit oestrogenic neuroprotection in the treatment of neurotrauma requires a precise quantification of the endogenous changes in neural aromatase and E2 following brain injury. Surprisingly, the expected increase in neural oestrogens following brain injury has not been demonstrated. Furthermore, we are just beginning to unravel the mechanisms behind the protective effects of centrally synthesised E2 . In the present study, levels of aromatase immunoprotein, neural E2 and steroid receptor mRNA were quantified in adult male and female zebra finches 48 h following a unilateral penetrating brain injury. Both aromatase and E2 were up-regulated in the injured hemisphere of the brain compared to the uninjured hemisphere, demonstrating for the first time a robust increase in neural E2 levels following injury. We did not detect an effect of injury on mRNA expression of the oestrogen receptors (ER)-α, ER-β or GPER-1, but observed a significant decrease in androgen receptor transcription in the injured lobe relative to the contralateral uninjured hemisphere. We conclude that mechanical damage causes a dramatic increase in local aromatisation, and the resultant high levels of central E2 are available to modulate steroid sensitive targets. Studies using alternate methods of receptor detection and/or time points may be necessary to understand the complete suite of mechanisms underlying the neuroprotective effects of induced oestrogen synthesis in this animal model.

Neuroprotective effects of estrogens: the role of cholesterol

INTRODUCTION

Experimental and clinical evidence suggests that estrogens have protective effects in the brain. Nevertheless, their potential role against neurodegenerative diseases, in particular Alzheimer's disease (AD), is still a matter of debate. The identification of the seladin-1 gene (for SELective Alzheimer's Disease INdicator-1), which appeared to be significantly less expressed in brain region affected in AD, opened a new scenario in the field of neuroprotective mechanisms. Seladin-1 was found to have neuroprotective properties through its anti-apoptotic activity. In addition, it was subsequently demonstrated that seladin-1 also has enzymatic activity, because it catalyzes the conversion of desmosterol into cholesterol. Several studies have shown that an appropriate amount of membrane cholesterol plays a pivotal role to protect nerve cells against β-amyloid toxicity in AD and to counteract the synthesis of β-amyloid.

METHODS AND RESULTS

We demonstrated that the expression of seladin-1, as well as the synthesis of cell cholesterol, is stimulated by estrogens in human neuronal precursor cells. Cholesterol enriched cells became more resistant against oxidative stress and β-amyloid toxicity. We thus hypothesized that seladin-1 might be a mediator of the neuroprotective effects of estrogens. Indeed, in cells in which seladin-1 gene expression had been silenced by siRNA the protective effects of estrogens were lost. This finding indicates that seladin-1 is a crucial mediator of the neuroprotective effects of these hormones, at least in our cell model.

CONCLUSIONS

In summary, these results establish a new link between estrogens and cholesterol, which is represented by the neuroprotective factor seladin-1.

Effects of Gender and Estrogen Receptors on Iron-Induced Brain Edema Formation

Our previous studies have shown that female mice have less brain edema and better recovery in neurological deficits after intracerebral hemorrhage (ICH) and that 17β-estradiol treatment in male mice markedly reduces ICH-induced brain edema. In this study, we investigated the role of gender and the estrogen receptors (ERs) in iron-induced brain edema. There were three parts in this study: (1) either male or female mice received an injection of 10 μL FeCl2 (1 mM) into the right caudate; (2) females received an intracaudate injection of FeCl2 or saline with 1 μg of ICI 182,780 (antagonists of ERs) or vehicle; and (3) males were treated with the ER regulator tamoxifen (5 mg/kg subcutaneously) or vehicle 1 h after FeCl2 injection. Mice were euthanized 24 h later for brain edema determination. FeCl2 induced lower brain edema in females than in males. Co-injection of ICI 182,780 with FeCl2 aggravated iron-induced brain edema in female mice. ICI 182,780 itself did not induce brain edema at the dose of 1 μg. Tamoxifen treatment reduced FeCl2-induced brain edema in male mice. In conclusion, iron induced less brain edema in female mice than in males. ER modification can affect iron-induced brain edema.

Tamoxifen and Src kinase inhibitors as neuroprotective/neuroregenerative drugs after spinal cord injury

Spinal cord injury (SCI) is a devastating condition that produces significant changes in the lifestyle of patients. Many molecular and cellular events are triggered after the initial physical impact to the cord. Two major phases have been described in the field of SCI: an acute phase and late phase. Most of the therapeutic strategies are focused on the late phase because this provides an opportunity to target cellular events like apoptosis, demyelination, scar formation and axonal outgrowth. In this mini-review, we will focus on two agents (tamoxifen and a Src kinase family inhibitor known as PP2) that have been shown in our laboratory to produce neuroprotective (increase cell survival) and/or regenerative (axonal outgrowth) actions. The animal model used in our laboratory is adult female rat (~250 g) with a moderate contusion (12.5 mm) to the spinal cord at the T₁₀ level, using the MASCIS impactor device. Tamoxifen or PP2 was administered by implantation of a 15 mg pellet (Innovative Research of America, Sarasota, FL, USA) or by intraperitoneal injections (1.5 mg/kg, every 3 days), respectively, to produce a long-term effect (28 days). Tamoxifen and the Src kinase inhibitor, PP2, are drugs that in rats with a moderate spinal cord injury promote functional locomotor recovery, increase spared white matter tissue, and stimulate axonal outgrowth. Moreover, tamoxifen reduces the formation of reactive oxygen species. Therefore, these drugs are possible therapeutic agents that have a neuroprotective/regenerative activity in vertebrates with SCI.

Raloxifene protects against seizures and neurodegeneration in a mouse model mimicking epilepsy in postmenopausal woman

Epilepsy in menopausal women presents several challenges in the treatment including an increased risk of seizures due to hormone replacement therapy. We investigated the hypothesis if raloxifene, a selective oestrogen receptor modulator, could be employed to prevent behavioural seizures and morphological alterations in a mouse model mimicking epilepsy in postmenopausal women. Female mice were made ovotoxic by treatment with 4-vinylcyclohexene diepoxide (VCD) to mimic a postmenopausal state. They were then subjected to kainic acid (KA)-induced seizures and neurotoxicity, as assessed by microscopic examination of hippocampus, relevant to human temporal lobe epilepsy. VCD administration (for 15days followed by a drug-free period of 30days) induced ovotoxicity in mice as evidenced by reduced number of primary ovarian follicles. This was accompanied by a 62.4% reduction in serum oestradiol levels. The bone mineral density of ovotoxic mice, however, remained unaffected. Raloxifene (8mg/kg) reduced the seizure severity score in both normal and ovotoxic mice and protected against degeneration induced by KA in the CA3, CA1 sub-fields and hilus of the DG. Hippocampal TGF-β3 levels were not affected by any of the treatments. We show the potential protective role of raloxifene in preventing seizures and neuronal damage in a mouse model mimicking epilepsy in postmenopausal women which was found unrelated to hippocampal TGF-β3. Raloxifene might represent a novel therapeutic option for postmenopausal temporal lobe epileptic woman.

Tibolone protects T98G cells from glucose deprivation

The steroidal drug Tibolone is used for the treatment of climacteric symptoms and osteoporosis in post-menopausal women. Although Tibolone has been shown to exert neuroprotective actions after middle cerebral artery occlusion, its specific actions on glial cells have received very little attention. In the present study we have assessed whether Tibolone exerts protective actions in a human astrocyte cell model, the T98G cells, subjected to glucose deprivation. Our findings indicate that Tibolone decreases the effects of glucose deprivation on cell death, nuclear fragmentation, superoxide ion production, mitochondrial membrane potential, cytoplasmic calcium concentration and morphological parameters. These findings suggest that glial cells may participate in the neuroprotective actions of Tibolone in the brain.

New perspectives on using brain imaging to study CNS stimulants

While the recent application of brain imaging to study CNS stimulants has offered new insights into the fundamental factors that contribute to their use and abuse, many gaps remain. Brain circuits that mediate pleasure, dependence, craving and relapse are anatomically, neurophysiologically and neurochemically distinct from one another, which has guided the search for correlates of stimulant-seeking and taking behavior. However, unlike other drugs of abuse, metrics for tolerance and physical dependence on stimulants are not obvious. The dopamine theory of stimulant abuse does not sufficiently explain this disorder as serotonergic, GABAergic and glutamagergic circuits are clearly involved in stimulant pharmacology and so tracking the source of the "addictive" processes must adopt a more multimodal, multidisciplinary approach. To this end, both anatomical and functional magnetic resonance imaging (MRI), MR spectroscopy (MRS) and positron emission tomography (PET) are complementary and have equally contributed to our understanding of how stimulants affect the brain and behavior. New vistas in this area include nanotechnology approaches to deliver small molecules to receptors and use MRI to resolve receptor dynamics. Anatomical and blood flow imaging has yielded data showing that cognitive enhancers might be useful adjuncts in treating CNS stimulant dependence, while MRS has opened opportunities to examine the brain's readiness to accept treatment as GABA tone normalizes after detoxification. A desired outcome of the above approaches is being able to offer evidence-based rationales for treatment approaches that can be implemented in a more broad geographic area, where access to brain imaging facilities may be limited. This article is part of the Special Issue entitled 'CNS Stimulants'.

Estrogen-mediated renoprotection following cardiac arrest and cardiopulmonary resuscitation is robust to GPR30 gene deletion

Introduction

Acute kidney injury is a serious,sexually dimorphic perioperative complication, primarily attributed to hypoperfusion. We previously found that estradiol is renoprotective after cardiac arrest and cardiopulmonary resuscitation in ovariectomized female mice. Additionally, we found that neither estrogen receptor alpha nor beta mediated this effect. We hypothesized that the G protein estrogen receptor (GPR30) mediates the renoprotective effect of estrogen.

Methods

Ovariectomized female and gonadally intact male wild-type and GPR30 gene-deleted mice were treated with either vehicle or 17β-estradiol for 7 days, then subjected to cardiac arrest and cardiopulmonary resuscitation. Twenty four hours later, serum creatinine and urea nitrogen were measured, and histologic renal injury was evaluated by unbiased stereology.

Results

In both males and females, GPR30 gene deletion was associated with reduced serum creatinine regardless of treatment. Estrogen treatment of GPR30 gene-deleted males and females was associated with increased preprocedural weight. In ovariectomized female mice, estrogen treatment did not alter resuscitation, but was renoprotective regardless of GPR30 gene deletion. In males, estrogen reduced the time-to-resuscitate and epinephrine required. In wild-type male mice, serum creatinine was reduced, but neither serum urea nitrogen nor histologic outcomes were affected by estrogen treatment. In GPR30 gene-deleted males, estrogen did not alter renal outcomes. Similarly, renal injury was not affected by G1 therapy of ovariectomized female wild-type mice.

Conclusion

Treatment with 17β-estradiol is renoprotective after whole-body ischemia-reperfusion in ovariectomized female mice irrespective of GPR30 gene deletion. Treatment with the GPR30 agonist G1 did not alter renal outcome in females. We conclude GPR30 does not mediate the renoprotective effect of estrogen in ovariectomized female mice. In males, estrogen therapy was not renoprotective. Estrogen treatment of GPR30 gene-deleted mice was associated with increased preprocedural weight in both sexes. Of significance to further investigation, GPR30 gene deletion was associated with reduced serum creatinine, regardless of treatment.

Mechanism of raloxifene-induced upregulation of glutamate transporters in rat primary astrocytes

Raloxifene (RX), a selective estrogen receptor modulator (SERM), exerts neuroprotection in multiple clinical and experimental settings. Astrocytic glutamate transporters GLT-1 (EAAT2) and GLAST (EAAT1) are the main glutamate transporters in the central nervous system, taking up most of excess glutamate from the synaptic cleft to prevent excitotoxic neuronal death. Since drugs targeting astrocytic glutamate transporters to enhance their expression and function represent potential therapeutics for neurodegenerative disorders associated with excitotoxicity, we tested if RX modulates the expression and function of GLT-1 and GLAST in rat primary astrocytes. The results showed that RX significantly increased glutamate uptake and expression of GLT-1 mRNA and protein levels. RX enhanced GLT-1 expression by the activation of multiple signaling pathways including ERK, EGFR, and CREB mediated by estrogen receptors (ERs) ER-α, ER-β, and GPR30. At the transcriptional level, NF-κB played a critical role in RX-induced GLT-1 expression as RX increased NF-κB reporter activity and induced binding of NF-κB p65 and p50 to the GLT-1 promoter. RX attenuated the reduction of GLT-1 expression and glutamate uptake induced by manganese (Mn) whose chronic high levels of exposure cause manganism. RX also upregulated GLAST by increasing its promoter activity and protein levels via the NF-κB pathway and ERs. Our findings provide new insight into the mechanism of RX-induced enhancement of GLT-1 and GLAST expression, as well as the attenuation of Mn-reduced expression of these transporters. These findings will be highly valuable for developing therapeutics of neurodegenerative diseases associated with impaired astrocytic glutamate transporters.

Tamoxifen and estradiol improved locomotor function and increased spared tissue in rats after spinal cord injury: their antioxidant effect and role of estrogen receptor alpha

17β-Estradiol is a multi-active steroid that imparts neuroprotection via diverse mechanisms of action. However, its role as a neuroprotective agent after spinal cord injury (SCI), or the involvement of the estrogen receptor-alpha (ER-α) in locomotor recovery, is still a subject of much debate. In this study, we evaluated the effects of estradiol and of Tamoxifen (an estrogen receptor mixed agonist/antagonist) on locomotor recovery following SCI. To control estradiol cyclical variability, ovariectomized female rats received empty or estradiol filled implants, prior to a moderate contusion to the spinal cord. Estradiol improved locomotor function at 7, 14, 21, and 28 days post injury (DPI), when compared to control groups (measured with the BBB open field test). This effect was ER-α mediated, because functional recovery was blocked with an ER-α antagonist. We also observed that ER-α was up-regulated after SCI. Long-term treatment (28 DPI) with estradiol and Tamoxifen reduced the extent of the lesion cavity, an effect also mediated by ER-α. The antioxidant effects of estradiol were seen acutely at 2 DPI but not at 28 DPI, and this acute effect was not receptor mediated. Rats treated with Tamoxifen recovered some locomotor activity at 21 and 28 DPI, which could be related to the antioxidant protection seen at these time points. These results show that estradiol improves functional outcome, and these protective effects are mediated by the ER-α dependent and independent-mechanisms. Tamoxifen׳s effects during late stages of SCI support the use of this drug as a long-term alternative treatment for this condition.

Effects of estradiol on high-voltage-activated Ca(2+) channels in cultured rat cortical neurons

OBJECTIVES

Estrogen regulates a wide variety of nonreproductive functions in the central nervous system. Cortical neurons contain a diverse range of voltage-gated ion channels, including calcium (Ca(2+)) channels, and Ca(2+) channels play an important role in the regulation of action potential generation and neuronal excitability. In this study, the effect of estradiol (E2) on high-voltage-activated (HVA) Ca(2+) channels in cultured rat cortical neurons was examined.

METHODS

We used the whole-cell patch-clamp technique to measure the HVA Ca(2+) channels.

RESULTS

We found that HVA Ca(2+) channel currents was inhibited by 17β-E2 in a rapid, reversible and concentration-dependent manner. Moreover, 17β-E2 shifted the steady-state inactivation curve in the hyperpolarizing direction without changing the activation curve. We also found that the inhibitory effects of 17β-E2 on Ca(2+) currents were unaffected by the estrogen receptor (ER) antagonist ICI 182780; however, the protein kinase C (PKC) inhibitor rottlerin and protein kinase A (PKA) inhibitor H-89 blocked the 17β-E2-induced inhibition of Ca(2+) currents.

CONCLUSIONS

E2 inhibited HVA Ca(2+) currents via PKC and PKA-dependent signaling pathway in cortical neurons, and the effects of BPA were independent of classical ER.

Neuroprotection by gonadal steroid hormones in acute brain damage requires cooperation with astroglia and microglia

The neuroactive steroids 17β-estradiol and progesterone control a broad spectrum of neural functions. Besides their roles in the regulation of classical neuroendocrine loops, they strongly influence motor and cognitive systems, behavior, and modulate brain performance at almost every level. Such a statement is underpinned by the widespread and lifelong expression pattern of all types of classical and non-classical estrogen and progesterone receptors in the CNS. The life-sustaining power of neurosteroids for tattered or seriously damaged neurons aroused interest in the scientific community in the past years to study their ability for therapeutic use under neuropathological challenges. Documented by excellent studies either performed in vitro or in adequate animal models mimicking acute toxic or chronic neurodegenerative brain disorders, both hormones revealed a high potency to protect neurons from damage and saved neural systems from collapse. Unfortunately, neurons, astroglia, microglia, and oligodendrocytes are comparably target cells for both steroid hormones. This hampers the precise assignment and understanding of neuroprotective cellular mechanisms activated by both steroids. In this article, we strive for a better comprehension of the mutual reaction between these steroid hormones and the two major glial cell types involved in the maintenance of brain homeostasis, astroglia and microglia, during acute traumatic brain injuries such as stroke and hypoxia. In particular, we attempt to summarize steroid-activated cellular signaling pathways and molecular responses in these cells and their contribution to dampening neuroinflammation and neural destruction. This article is part of a Special Issue entitled 'CSR 2013'.

Estrogen prevents cardiac and vascular failure in the 'listless' zebrafish (Danio rerio) developmental model

The presence of a robust estrogen (E2) response system throughout heart and blood vessel tissues of vertebrates, including humans, has led to the speculation that this ubiquitous hormone may play a prominent role in the health and maintenance of the adult cardiovascular system (CVS). We previously established an embryonic zebrafish model called 'listless', which results from the inhibition of E2 synthesis by treatment with aromatase enzyme inhibitors (AI). These fish have outward symptoms similar to the human condition of congestive heart failure and tamponade. E2 replacement therapy (1) reduced the severity of cardiac sac abnormalities, (2) protected heart function, (3) prevented reduction in heart size, and (4) reduced blood vessel deterioration. Nitric oxide may be a critical downstream mediator of these events. We also demonstrate that removal of fluid around the heart increases survival of AI-treated fish. These results strongly indicate the importance of E2 in the developing CVS of the zebrafish and offer a potential model for the study of its role in CVS development, maintenance, and disease conditions.

Incorporation of beta-sitosterol into the membrane increases resistance to oxidative stress and lipid peroxidation via estrogen receptor-mediated PI3K/GSK3beta signaling

BACKGROUND

Brain lipid peroxidation has long been considered a potential therapeutic target for Alzheimer's disease (AD). beta-sitosterol (BS), a plant sterol that is prevalent in plant plasma membrane, has been suggested to have antioxidant activity. Previous studies have demonstrated that dietary BS can enter the brain and accumulates in the plasma membrane of brain cells. However, it is unknown whether and how BS exerts its antioxidant activity in plasma membrane.

METHODS

To incorporate BS into the plasma membrane in vitro, HT22 cells and primarily cultured hippocampal cells were supplemented with BS using 2-hydroxypropyl-beta-cyclodextrin (HPbetaCD) as a carrier. The present study then tested the antioxidant effect of membrane BS against glucose oxidase (GOX)-induced oxidative stress and lipid peroxidation, and whether the antioxidant effect of membrane BS was associated with estrogen receptor (ER)-mediated phosphatidyl inositol 3-kinase (PL3K)/glycogen synthase kinase 3 (GSK3beta) signaling.

RESULTS

Incorporation of BS into cell membrane prevented GOX-induced oxidative stress and lipid peroxidation, which could be suppressed by the ER antagonists and PI3K inhibitor. Additional experiments showed that incorporation of BS into cell membrane induced an up-regulation of PI3K activity and a recruitment of PI3K to lipid rafts, which could be inhibited by the ER antagonist. Membrane BS also increased the expression of p-GSK3beta, which could be suppressed in the presence of the ER antagonist and PI3K inhibitor.

GENERAL SIGNIFICANCE

Given that BS is prevalent in foods such as plant oil, the results provide a better understanding of the beneficial effects of these BS-enriched nutrients on neurodegenerative diseases such as AD.

Cholesterol and perhaps estradiol protect against corticosterone-induced hippocampal CA3 dendritic retraction in gonadectomized female and male rats

Chronic stress or glucocorticoid exposure simplifies hippocampal Cornu Ammonis region 3 (CA3) apical dendritic arbors in male rats. In contrast to males, chronic stress either reduces CA3 basal branching or exerts no observable morphological effects in gonadally intact female rats. Under conditions that females display stress-induced CA3 dendritic retraction, such as that following ovariectomy, chronic exposure to 17β-estradiol or cholesterol can negate these changes. Whether glucocorticoids produce CA3 dendritic retraction in ovariectomized females and whether neuroprotection from 17β-estradiol or cholesterol is sex-specific remains unknown. The current study examined the effects of chronic glucocorticoid exposure, in conjunction with 17β-estradiol or cholesterol administration, on hippocampal CA3 dendritic complexity. Adult male and female Sprague-Dawley rats were gonadectomized and implanted with 25% 17β-estradiol in cholesterol, 100% cholesterol, or blank Silastic capsules. Rats were then assigned to either a 21-day corticosterone (CORT) drink (400μg/ml CORT, 2.4% ethanol in tap water) or tap water (Tap, 2.4% ethanol in tap water) treatment. Brains were processed for Golgi staining, and hippocampal CA3 dendritic architecture was quantified. Results showed 21-day CORT administration reduced hippocampal CA3 apical dendritic branch points, CA3 apical dendritic length, body weight gain, and adrenal weights compared to male and female control counterparts. Furthermore, male and female rats implanted with Silastic capsules containing cholesterol or 25% 17β-estradiol in cholesterol were protected from CORT-induced CA3 apical dendritic branch reduction. No effects were observed in the CA3 basal dendritic arbors. The present results demonstrate that CORT produces hippocampal CA3 dendritic retraction in gonadectomized male and female rats and that cholesterol and 25% 17β-estradiol in cholesterol prevent this dendritic simplification.

Neuroprotective effects of estradiol on motoneurons in a model of rat spinal cord embryonic explants

Amyotrophic lateral sclerosis (ALS) is an adult-onset degenerative disorder characterized by motoneuron death. Clinical and experimental studies in animal models of ALS have found gender differences in the incidence and onset of disease, suggesting that female hormones may play a beneficial role. Cumulative evidence indicates that 17β-estradiol (17βE2) has a neuroprotective role in the central nervous system. We have previously developed a new culture system by using rat spinal cord embryonic explants in which motoneurons have the singularity of migrating outside the spinal cord, growing as a monolayer in the presence of glial cells. In this study, we have validated this new culture system as a useful model for studying neuroprotection by estrogens on spinal cord motoneurons. We show for the first time that spinal cord motoneurons express classical estrogen receptors and that 17βE2 activates, specifically in these cells, the Akt anti-apoptotic signaling pathway and two of their downstream effectors: GSK-3β and Bcl-2. To further validate our system, we demonstrated neuroprotective effects of 17βE2 on spinal cord motoneurons when exposed to the proinflammatory cytokines TNF-α and IFN-γ. These effects of 17βE2 were fully reverted in the presence of the estrogen receptor antagonist ICI 182,780. Our new culture model and the results presented here may provide the basis for further studies on the effects of estrogens, and selective estrogen receptor modulators, on spinal cord motoneurons in the context of ALS or other motoneuron diseases.

Decreased frontal lobe phosphocreatine levels in methamphetamine users

BACKGROUND

Mitochondria-related mechanisms have been suggested to mediate methamphetamine (METH) toxicity. However, changes in brain energetics associated with high-energy phosphate metabolism have not been investigated in METH users. Phosphorus-31 ((31)P) magnetic resonance spectroscopy (MRS) was used to evaluate changes in mitochondrial high energy phosphates, including phosphocreatine (PCr) and β-nucleoside triphosphate (β-NTP, primarily ATP in brain) levels. We hypothesized that METH users would have decreased high-energy PCr levels in the frontal gray matter.

METHODS

Study participants consisted of 51 METH (age=32.8±6.7) and 23 healthy comparison (age=31.1±7.5) subjects. High-energy phosphate metabolite levels were compared between the groups and potential gender differences were explored.

RESULTS

METH users had lower ratios of PCr to total pool of exchangeable phosphate (PCr/TPP) in the frontal lobe as compared to the healthy subjects (p=.001). The lower PCr levels in METH subjects were significantly associated with lifetime amount of METH use (p=.003). A sub-analysis for gender differences revealed that female METH users, who had lower daily amounts (1.1±1.0g) of METH use than males (1.4±1.7g), had significantly lower PCr/TPP ratios than male METH users, controlling for the amount of METH use (p=.02).

CONCLUSIONS

The present findings suggest that METH compromises frontal lobe high-energy phosphate metabolism in a dose-responsive manner. Our findings also suggest that the abnormality in frontal lobe high-energy phosphate metabolism might be more prominent in female than in male METH users. This is significant as decreased PCr levels have been associated with depressive symptoms, and poor responses to antidepressant treatment have been reported in those with decreased PCr levels.