Neuroprotective effects of an estratriene analog are estrogen receptor independent in vitro and in vivo

Protection against APOE4 -associated aging phenotypes with the longevity-promoting intervention 17α-estradiol in male mice

The apolipoprotein ε4 allele ( APOE4 ) is associated with decreased longevity, increased vulnerability to age-related declines, and disorders across multiple systems. Interventions that promote healthspan and lifespan represent a promising strategy to attenuate the development of APOE4 -associated aging phenotypes. Here we studied the ability of the longevity-promoting intervention 17α-estradiol (17αE2) to protect against age-related impairments in APOE4 versus the predominant APOE3 genotype using early middle-aged mice with knock-in of human APOE alleles. Beginning at age 10 months, male APOE3 or APOE4 mice were treated for 20 weeks with 17αE2 or vehicle then compared for indices of aging phenotypes body-wide. Across peripheral and neural measures, APOE4 was associated with poorer outcomes. Notably, 17αE2 treatment improved outcomes in a genotype-dependent manner favoring APOE4 mice. These data demonstrate a positive APOE4 bias in 17αE2-mediated healthspan actions, suggesting that longevity-promoting interventions may be useful in mitigating deleterious age-related risks associated with APOE4 genotype.

Role of Estrogen Receptor α in Aging and Chronic Disease

Estrogen receptor alpha (ERα) plays a crucial role in reproductive function in both sexes. It also mediates cellular responses to estrogens in multiple nonreproductive organ systems, many of which regulate systemic metabolic homeostasis and inflammatory processes in mammals. The loss of estrogens and/or ERα agonism during aging is associated with the emergence of several comorbid conditions, particularly in females undergoing the menopausal transition. Emerging data also suggests that male mammals likely benefit from ERα agonism if done in a way that circumvents feminizing characteristics. This has led us, and others, to speculate that tissue-specific ERα agonism may hold therapeutic potential for curtailing aging and chronic disease burden in males and females that are at high-risk of cancer and/or cardiovascular events with traditional estrogen replacement therapies. In this mini-review, we emphasize the role of ERα in the brain and liver, summarizing recent evidence that indicates these two organs systems mediate the beneficial effects of estrogens on metabolism and inflammation during aging. We also discuss how 17α-estradiol administration elicits health benefits in an ERα-dependent manner, which provides proof-of-concept that ERα may be a druggable target for attenuating aging and age-related disease burden.

Kinetic Study of 17α-Estradiol Mechanism during Rat Sperm Capacitation

17α-Estradiol (αE2) is a natural diastereoisomer of 17β-estradiol (E2). It is well known that αE2 can bind to estrogen receptors. However, its biological activity is less than that of E2 and is species and tissue specific. The goal of our study was to propose the mechanism of αE2 hormonal response in rat sperm during their capacitation in vitro and compare it with a previously studied mouse model. Concentration changes in externally added αE2 during capacitation of rat sperm were monitored by the high-performance liquid chromatographic method with tandem mass spectrometric detection (HPLC-MS/MS). The calculated values of relative concentrations B_t were subjected to kinetic analysis. The findings indicated that αE2 in rat sperm did not trigger autocatalytic reaction, in contrast to the mouse sperm, and that the initiation of the hormone penetration through the sperm plasma membrane was substantially faster in rats.

Kinetic Study of 17α-Estradiol Activity in Comparison with 17β-Estradiol and 17α-Ethynylestradiol

17α-estradiol (αE2), an endogenous stereoisomer of the hormone 17β-estradiol (E2), is capable of binding to estrogen receptors (ER). We aimed to mathematically describe, using experimental data, the possible interactions between αE2 and sperm ER during the process of sperm capacitation and to develop a kinetic model. The goal was to compare the suggested kinetic model with previously published results of ER interactions with E2 and 17α-ethynylestradiol (EE2). The HPLC-MS/MS method was developed to monitor the changes of αE2 concentration during capacitation. The calculated relative concentrations Bt were used for kinetic analysis. Rate constants k and molar ratio n were optimized and used for the construction of theoretical B(t) curves. Modifications in αE2–ER interactions were discovered during comparison with models for E2 and EE2. These new interactions displayed autocatalytic formation of an unstable adduct between the hormone and the cytoplasmic receptors. αE2 accumulates between the plasma membrane lipid bilayer with increasing potential, and when the critical level is reached, αE2 penetrates through the inner layer of the plasma membrane into the cytoplasm. It then rapidly reacts with the ER and creates an unstable adduct. The revealed dynamics of αE2–ER action may contribute to understanding tissue rejuvenation and the cancer-related physiology of αE2 signaling.

The Role of Estradiol in Traumatic Brain Injury: Mechanism and Treatment Potential

Patients surviving traumatic brain injury (TBI) face numerous neurological and neuropsychological problems significantly affecting their quality of life. Extensive studies over the past decades have investigated pharmacological treatment options in different animal models, targeting various pathological consequences of TBI. Sex and gender are known to influence the outcome of TBI in animal models and in patients, respectively. Apart from its well-known effects on reproduction, 17β-estradiol (E2) has a neuroprotective role in brain injury. Hence, in this review, we focus on the effect of E2 in TBI in humans and animals. First, we discuss the clinical classification and pathomechanism of TBI, the research in animal models, and the neuroprotective role of E2. Based on the results of animal studies and clinical trials, we discuss possible E2 targets from early to late events in the pathomechanism of TBI, including neuroinflammation and possible disturbances of the endocrine system. Finally, the potential relevance of selective estrogenic compounds in the treatment of TBI will be discussed.

Treating Senescence like Cancer: Novel Perspectives in Senotherapy of Chronic Diseases

The WHO estimated around 41 million deaths worldwide each year for age-related non-communicable chronic diseases. Hence, developing strategies to control the accumulation of cell senescence in living organisms and the overall aging process is an urgently needed problem of social relevance. During aging, many biological processes are altered, which globally induce the dysfunction of the whole organism. Cell senescence is one of the causes of this modification. Nowadays, several drugs approved for anticancer therapy have been repurposed to treat senescence, and others are under scrutiny in vitro and in vivo to establish their senomorphic or senolytic properties. In some cases, this research led to a significant increase in cell survival or to a prolonged lifespan in animal models, at least. Senomorphics can act to interfere with a specific pathway in order to restore the appropriate cellular function, preserve viability, and to prolong the lifespan. On the other hand, senolytics induce apoptosis in senescent cells allowing the remaining non–senescent population to preserve or restore tissue function. A large number of research articles and reviews recently addressed this topic. Herein, we would like to focus attention on those chemical agents with senomorphic or senolytic properties that perspectively, according to literature, suggest a potential application as senotherapeutics for chronic diseases.

17α-Estradiol prevents ovariectomy-mediated obesity and bone loss

Menopause is a natural physiological process in older women that is associated with reduced estrogen production and results in increased risk for obesity, diabetes, and osteoporosis. 17α-estradiol (17α-E2) treatment in males, but not females, reverses several metabolic conditions associated with advancing age, highlighting sexually dimorphic actions on age-related pathologies. In this study we sought to determine if 17α-E2 could prevent ovariectomy (OVX)-mediated detriments on adiposity and bone parameters in females. Eight-week-old female C57BL/6J mice were subjected to SHAM or OVX surgery and received dietary 17α-E2 during a six-week intervention period. We observed that 17α-E2 prevented OVX-induced increases in body weight and adiposity. Similarly, uterine weight and luminal cell thickness were decreased by OVX and prevented by 17α-E2 treatment. Interestingly, 17α-E2 prevented OVX-induced declines in tibial metaphysis cancellous bone. And similarly, 17α-E2 improved bone density parameters in both tibia and femur cancellous bone, primarily in OVX mice. In contrast, to the effects on cancellous bone, cortical bone parameters were largely unaffected by OVX or 17α-E2. In the non-weight bearing lumbar vertebrae, OVX reduced trabecular thickness but not spacing, while 17α-E2 increased trabecular thickness and reduced spacing. Despite this, 17α-E2 did improve bone volume/tissue volume in lumbar vertebrae. Overall, we found that 17α-E2 prevented OVX-induced increases in adiposity and changes in bone mass and architecture, with minimal effects in SHAM-operated mice. We also observed that 17α-E2 rescued uterine tissue mass and lining morphology to control levels without inducing hypertrophy, suggesting that 17α-E2 could be considered as an adjunct to traditional hormone replacement therapies.

Ipriflavone and Ipriflavone loaded albumin nanoparticles reverse lipopolysaccharide induced neuroinflammation in rats

BACKGROUND

Neuroinflammation causes neurodegenerative conditions like Alzheimer's disease (AD). Ipriflavone (IP), therapeutic compound to postmenopausal osteoporosis, has limited estrogenic activity and is accounted as AChE inhibitor. The developing of drug delivery systems to enable drug targeting to specific sites increases the drug therapeutic effect.

OBJECTIVE

The aim of the present study was to formulate and evaluate ipriflavone loaded albumin nanoparticles (IP-Np) along with free ipriflavone against lipopolysaccharide (LPS) induced neuroinflammation in rats.

METHODS

Neuroinflammation was induced by intra-peritoneal (i.p) injection of LPS (250 μg/kg rat body weight) then treatments were conducted with (1) ipriflavone at two doses 50 mg/kg and 5 mg/kg, (2) IP-Np (5 mg ipriflavone/kg) or (3) IP-Np coated with polysorbate 80 (IP-Np-T80) (5 mg ipriflavone/kg). The alteration of the inflammatory response in male adult Wistar rats' brain hippocampus was investigated by examining associated indices using biochemical and molecular analyses.

RESULTS

A significant upsurge in inflammatory mediators and decline in antioxidant status were observed in LPS-induced rats. In one hand, ipriflavone (50 mg/kg), IP-Np and IP-Np-T80 ameliorated LPS induced brain hippocampal inflammation where they depreciated the level of pro-inflammatory cytokines (TNF-α, IL-6, IL-1β) and enhanced antioxidant status. In another hand, ipriflavone at dose (5 mg/kg) didn't show the same therapeutic effect.

CONCLUSION

The current study provides evidence for the potential neuroprotective effect of ipriflavone (50 mg/kg) against LPS-induced neuroinflammation in rats through its anti-inflammatory and antioxidant activities. Moreover, nanoparticles significantly attenuated neuroinflammation in concentration lower than the effective therapeutic dose of free drug ten times.

Estrogen Formation and Inactivation Following TBI: What we Know and Where we Could go

Traumatic brain injury (TBI) is responsible for various neuronal and cognitive deficits as well as psychosocial dysfunction. Characterized by damage inducing neuroinflammation, this response can cause an acute secondary injury that leads to widespread neurodegeneration and loss of neurological function. Estrogens decrease injury induced neuroinflammation and increase cell survival and neuroprotection and thus are a potential target for use following TBI. While much is known about the role of estrogens as a neuroprotective agent following TBI, less is known regarding their formation and inactivation following damage to the brain. Specifically, very little is known surrounding the majority of enzymes responsible for the production of estrogens. These estrogen metabolizing enzymes (EME) include aromatase, steroid sulfatase (STS), estrogen sulfotransferase (EST/SULT1E1), and some forms of 17β-hydroxysteroid dehydrogenase (HSD17B) and are involved in both the initial conversion and interconversion of estrogens from precursors. This article will review and offer new prospective and ideas on the expression of EMEs following TBI.

Sex differences in lifespan extension with acarbose and 17-α estradiol: gonadal hormones underlie male-specific improvements in glucose tolerance and mTORC2 signaling

Interventions that extend lifespan in mice can show substantial sexual dimorphism. Here, we show that male‐specific lifespan extension with two pharmacological treatments, acarbose (ACA) and 17‐α estradiol (17aE2), is associated, in males only, with increased insulin sensitivity and improved glucose tolerance. Females, which show either smaller (ACA) or no lifespan extension (17aE2), do not derive these metabolic benefits from drug treatment. We find that these male‐specific metabolic improvements are associated with enhanced hepatic mTORC2 signaling, increased Akt activity, and phosphorylation of FOXO1a – changes that might promote metabolic health and survival in males. By manipulating sex hormone levels through gonadectomy, we show that sex‐specific changes in these metabolic pathways are modulated, in opposite directions, by both male and female gonadal hormones: Castrated males show fewer metabolic responses to drug treatment than intact males, and only those that are also observed in intact females, while ovariectomized females show some responses similar to those seen in intact males. Our results demonstrate that sex‐specific metabolic benefits occur concordantly with sexual dimorphism in lifespan extension. These sex‐specific effects can be influenced by the presence of both male and female gonadal hormones, suggesting that gonadally derived hormones from both sexes may contribute to sexual dimorphism in responses to interventions that extend mouse lifespan.

Estrogens as neuroprotectants: Estrogenic actions in the context of cognitive aging and brain injury

There is ample empirical evidence to support the notion that the biological impacts of estrogen extend beyond the gonads to other bodily systems, including the brain and behavior. Converging preclinical findings have indicated a neuroprotective role for estrogen in a variety of experimental models of cognitive function and brain insult. However, the surprising null or even detrimental findings of several large clinical trials evaluating the ability of estrogen-containing hormone treatments to protect against age-related brain changes and insults, including cognitive aging and brain injury, led to hesitation by both clinicians and patients in the use of exogenous estrogenic treatments for nervous system outcomes. That estrogen-containing therapies are used by tens of millions of women for a variety of health-related applications across the lifespan has made identifying conditions under which benefits with estrogen treatment will be realized an important public health issue. Here we provide a summary of the biological actions of estrogen and estrogen-containing formulations in the context of aging, cognition, stroke, and traumatic brain injury. We have devoted special attention to highlighting the notion that estrogen appears to be a conditional neuroprotectant whose efficacy is modulated by several interacting factors. By developing criteria standards for desired beneficial peripheral and neuroprotective outcomes among unique patient populations, we can optimize estrogen treatments for attenuating the consequences of, and perhaps even preventing, cognitive aging and brain injury.

Neuroprotective effect of ipriflavone against scopolamine-induced memory impairment in rats

BACKGROUND

Alzheimer's disease is an age-related neurodegenerative disorder characterized clinically by a progressive loss of memory and cognitive functions resulting in severe dementia. Ipriflavone (IPRI) is a non-hormonal, semi-synthetic isoflavone, clinically used in some countries for the treatment and prevention of postmenopausal osteoporosis. Moreover, ipriflavone is a non-peptidomimetic small molecule AChE inhibitor with an improved bioavailability after systemic administration, due to its efficient blood-brain barrier permeability in comparison with peptidomimetic inhibitors.

OBJECTIVE

The present study aimed to evaluate the possible enhancing effects of IPRI on memory impairments caused by scopolamine administration.

METHODS

Male rats were administered IPRI (50 mg/kg, oral) 2 h before scopolamine injection (2 mg/kg, intraperitoneally injected) daily for 4 weeks. Effects of IPRI on acetylcholinesterase activity, amyloid-β precursor processing, and neuroplasticity in the rats' hippocampus were investigated.

RESULTS

Daily administration of IPRI reverted memory impairment caused by scopolamine as measured by the reduction of the escape latency. IPRI significantly alleviated the oxidative stress and restored the mRNA expression of both cAMP-response element-binding protein and brain-derived neurotrophic factor in the hippocampus. Furthermore, it significantly increased the expression of ADAM10 and ADAM17 (two putative α-secretase enzymes) and phosphorylated extracellular signal-regulated kinase 1/2 (pERK1/2) that associated with decreased expression of β-secretase (BACE) in the hippocampus. Finally, both the amyloid-β (Aβ) and Tau pathologies were reduced.

CONCLUSIONS

IPRI showed promising neuroprotective effects against scopolamine-induced memory dysfunction in rats. These findings contributed to the stimulation of α-secretase enzymes, the activation of MAPK/ERK1/2, and the alleviation of oxidative stress.

Anti-aging drugs reduce hypothalamic inflammation in a sex-specific manner

Aging leads to hypothalamic inflammation, but does so more slowly in mice whose lifespan has been extended by mutations that affect GH/IGF‐1 signals. Early‐life exposure to GH by injection, or to nutrient restriction in the first 3 weeks of life, also modulate both lifespan and the pace of hypothalamic inflammation. Three drugs extend lifespan of UM‐HET3 mice in a sex‐specific way: acarbose (ACA), 17‐α‐estradiol (17αE2), and nordihydroguaiaretic acid (NDGA), with more dramatic longevity increases in males in each case. In this study, we examined the effect of these anti‐aging drugs on neuro‐inflammation in hypothalamus and hippocampus. We found that age‐associated hypothalamic inflammation is reduced in males but not in females at 12 months of age by ACA and 17αE2 and at 22 months of age in NDGA‐treated mice. The three drugs blocked indices of hypothalamic reactive gliosis associated with aging, such as Iba‐1‐positive microglia and GFAP‐positive astrocytes, as well as age‐associated overproduction of TNF‐α. This effect was not observed in drug‐treated female mice or in the hippocampus of the drug‐treated animals. On the other hand, caloric restriction (CR; an intervention that extends the lifespan in both sexes) significantly reduced hypothalamic microglia and TNF‐α in both sexes at 12 months of age. Together, these results suggest that the extent of drug‐induced changes in hypothalamic inflammatory processes is sexually dimorphic in a pattern that parallels the effects of these agents on mouse longevity and that mimics the changes seen, in both sexes, of long‐lived nutrient restricted or mutant mice.

The effects of oestrogens and their receptors on cardiometabolic health

Cardiovascular disease (CVD) is one of the leading causes of mortality in developed countries. The incidence of CVD is sexually dimorphic, and research has focused on the contribution of sex steroids to the development and progression of the cardiometabolic syndrome, which is defined as a clustering of interrelated risk factors that promote the development of atherosclerosis (which can lead to CVD) and type 2 diabetes mellitus. Data are inconclusive as to how sex steroids and their respective receptors increase or suppress the risk of developing the cardiometabolic syndrome and thus CVD. In this Review, we discuss the potential role, or roles, of sex hormones in cardiometabolic health by first focusing on the influence of oestrogens and their receptors on the risk of developing cardiometabolic syndrome and CVD. We also highlight what is known about testosterone and its potential role in protecting against the development of the cardiometabolic syndrome and CVD. Given the inconclusive nature of the data regarding the direct effects of each sex hormone, we advocate and highlight the importance of studying the relative levels and the ratio of sex hormones to each other, as well as the use of cross sex hormone therapy and its effect on cardiometabolic health.

A novel mechanism of non-feminizing estrogens in neuroprotection

Estrogens are potent and efficacious neuroprotectants both in vitro and in vivo in a variety of models of neurotoxicity. We determined the structural requirements for neuroprotection in an in vitro assay using a panel of >70 novel estratrienes, synthesized to reduce or eliminate estrogen receptor (ER) binding. We observed that neuroprotection could be enhanced by as much as 200-fold through modifications that positioned a large bulky group at the C2 or C4 position of the phenolic A ring of the estratriene. Further, substitutions on the B, C or D rings either reduced or did not markedly change neuroprotection. Collectively, there was a negative correlation between binding to ERs and neuroprotection with the more potent compounds showing no ER binding. In an in vivo model for neuroprotection, transient cerebral ischemia, efficacious compounds were active in protection of brain tissue from this pro-oxidant insult. We demonstrated that these non-feminizing estrogens engage in a redox cycle with glutathione, using the hexose monophosphate shunt to apply cytosolic reducing potential to cellular membranes. Together, these results demonstrate that non-feminizing estrogens are neuroprotective and protect brain from the induction of ischemic- and Alzheimer's disease (AD)-like neuropathology in an animal model. These features of non-feminizing estrogens make them attractive compounds for assessment of efficacy in AD and stroke, as they are not expected to show the side effects of chronic estrogen therapy that are mediated by ER actions in the liver, uterus and breast.

Structure-activity studies of non-steroid analogues structurally-related to neuroprotective estrogens

Estrone and 17β-estradiol are phenolic steroids that are known to be neuroprotective in multiple models of neuronal injury. Previous studies have identified the importance of their phenolic steroid A-ring for neuroprotection and have identified ortho substituents at the C-2 and C-4 positions on the phenol ring that enhance this activity. To investigate the importance of the steroid ring system for neuroprotective activity, phenolic compounds having the cyclopent[b]anthracene, cyclopenta[b]phenanthrene, benz[f]indene, benz[e]indene, indenes linked to a phenol, and a phenolic spiro ring system were prepared. New synthetic methods were developed to make some of the cyclopent[b]anthracene analogues as well as the spiro ring system. Compounds were evaluated for their ability to protect HT-22 hippocampal neurons from glutamate neurotoxicity and their activity relative to a potent neuroprotective analogue of 17β-estradiol was determined. An adamantyl substituent placed ortho to the phenolic hydroxyl group gave neuroprotective analogues in all ring systems studied.

Longer lifespan in male mice treated with a weakly estrogenic agonist, an antioxidant, an α-glucosidase inhibitor or a Nrf2-inducer

The National Institute on Aging Interventions Testing Program (ITP) evaluates agents hypothesized to increase healthy lifespan in genetically heterogeneous mice. Each compound is tested in parallel at three sites, and all results are published. We report the effects of lifelong treatment of mice with four agents not previously tested: Protandim, fish oil, ursodeoxycholic acid (UDCA) and metformin - the latter with and without rapamycin, and two drugs previously examined: 17-α-estradiol and nordihydroguaiaretic acid (NDGA), at doses greater and less than used previously. 17-α-estradiol at a threefold higher dose robustly extended both median and maximal lifespan, but still only in males. The male-specific extension of median lifespan by NDGA was replicated at the original dose, and using doses threefold lower and higher. The effects of NDGA were dose dependent and male specific but without an effect on maximal lifespan. Protandim, a mixture of botanical extracts that activate Nrf2, extended median lifespan in males only. Metformin alone, at a dose of 0.1% in the diet, did not significantly extend lifespan. Metformin (0.1%) combined with rapamycin (14 ppm) robustly extended lifespan, suggestive of an added benefit, based on historical comparison with earlier studies of rapamycin given alone. The α-glucosidase inhibitor, acarbose, at a concentration previously tested (1000 ppm), significantly increased median longevity in males and 90th percentile lifespan in both sexes, even when treatment was started at 16 months. Neither fish oil nor UDCA extended lifespan. These results underscore the reproducibility of ITP longevity studies and illustrate the importance of identifying optimal doses in lifespan studies.

A sex difference in oxidative stress and behavioral suppression induced by ethanol withdrawal in rats

Ethanol withdrawal (EW) is referred to the abrupt termination of long-term heavy drinking, and provokes oxidative brain damage. Here, we investigated whether the cerebellum and hippocampus of female rats are less affected by prooxidant EW than male rats due to the antioxidant effect of 17β-estradiol (E2). Female and male rats received a four-week ethanol diet and three-week withdrawal per cycle for two cycles. Some female rats were ovariectomized with E2 or antioxidant (Vitamin E+Co-Q10) treatment. Measurements were cerebellum (Rotarod) and hippocampus (water-maze)-related behaviors, oxidative markers (O2(-), malondialdehyde, protein carbonyls), mitochondrial membrane swelling, and a key mitochondrial enzyme, cytochrome c oxidase (CcO). Separately, HT22 (hippocampal) cells were subjected to ethanol-exposure and withdrawal for two cycles to assess the effect of a CcO inhibitor on E2's protection for mitochondrial respiration and cell viability. Ethanol-withdrawn female rats showed a smaller increase in oxidative markers in cerebellum and hippocampus than male rats, and E2 treatment decreased the oxidative markers. Compared to male counterparts, ethanol-withdrawn female rats showed better Rotarod but poorer water-maze performance, accompanied by more severe mitochondrial membrane swelling and CcO suppression in hippocampus. E2 or antioxidant treatment improved Rotarod but not water-maze performance. In the presence of a CcO inhibitor, E2 treatment failed to protect mitochondrial respiration and cell viability from EW. These data suggest that antioxidant E2 contributes to smaller oxidative stress in ethanol-withdrawn female than male rats. They also suggest that EW-induced severe mitochondrial damage in hippocampus may blunt E2's antioxidant protection for hippocampus-related behavior.

Reprint of: From the 90׳s to now: A brief historical perspective on more than two decades of estrogen neuroprotection

Historical perspective abstract:From the 90׳s to now: a historical perspective on more than two decades of estrogen neuroprotection: In the early 90׳s, estrogens were known to exert organizational and activational effects on reproductive tissues and sexual behavior. As well, the role of sex and gonadal hormones in altering the risk for developing Alzheimer׳s Disease (AD) was only beginning to be elucidated. Preliminary investigations suggested that estrogen-containing therapies typically given for the management of disruptive menopausal symptoms could reduce AD risk, attenuate disease-associated cognitive deficits, and modulate brain substrates known to be dysregulated by the condition, such as the cholingeric system. The findings from our seminal paper demonstrating cognitive benefits and cholinergic impacts with exogenous estrogen treatment in a rodent model of surgical hormone depletion provided initial support for use of estrogen-containing therapies as a treatment for age-related brain disorders. We then went on to demonstrate neuroprotective actions of estrogen in several other in vivo and in vitro models of neurological challenge, including stroke and AD. Further, our findings of the chemical structure requirements for estrogen׳s neuroprotective effects identified a novel approach for optimizing future estrogen-containing hormone therapy options. These early efforts laid the groundwork for later, large-scale clinical investigations into the potential of estrogen-based menopausal hormone therapies for the prevention of a variety of age-related disorders. Although findings of these studies were equivocal, the neuroprotective actions of estrogen, and specifically 17β-estradiol, identified by early investigations, remain well-documented. Future development of interventions that optimize cognitive aging are crucial and, with proper understanding of the factors that influence the realization of beneficial impacts, estrogen-containing treatments may still be among these.

ORIGINAL ARTICLE ABSTRACT

Ovarian steroid deprivation results in a reversible learning impairment and compromised cholinergic function in female Sprague-Dawley rats: We hypothesized that estradiol (E2) serves as a neurotrophomodulatory substance for basal forebrain cholinergic neurons thought to be involved in learning and memory. Learning/memory was assessed using the two-way active avoidance paradigm and the Morris water task. Female Sprague-Dawley rats were either ovariectomized (OVX) or OVX for 3 weeks, followed by s.c. implantation of a Silastic pellet containing 17-βE2 (E2 pellet), resulting in a replacement of E2 to physiological levels. Ovary-intact (INTACT) animals served as our positive control. Active avoidance behavior and choline acetyltransferase (ChAT) activity in the frontal cortex and hippocampus were assessed at 5 and 28 weeks postovariectomy while performance on the Morris water task and high-affinity choline uptake (HACU) were measured only at the 5-week time point. At the 5-week time point, E2 replacement caused a significant elevation in the level of active avoidance performance relative to OVX animals. At the 28-week time point, OVX animals demonstrated a significantly lower number of avoidances relative to controls (61%) whereas E2-pellet animals not only demonstrated superior performance relative to OVX animals but also showed an accelerated rate of learning. Morris water task performance, on the other hand, was not significantly affected by estrogenic milieu despite a trend towards better performance in the E2-pellet group. Neurochemical analyses revealed that 5 weeks of ovariectomy was sufficient to reduce HACU in both the frontal cortex and hippocampus by 24 and 34%, respectively, while E2 replacement was successful in elevating HACU relative to OVX animals in both regions. ChAT activity was decreased in the hippocampus but not the frontal cortex of 5-week OVX animals. E2 replacement resulted in a reversal of this effect. At the 28-week time period, an unexpected decrease in ChAT activity was observed across all treatment groups. Interestingly, E2-pellet animals demonstrated the least severe decline in ChAT. This phenomenon was most evident in the frontal cortex where ChAT decreased by 61 and 56% in INTACT and OVX animals, respectively, whereas the decline in E2-pellet animals was only 16% over the same time period, suggesting a previously unreported cytoprotective effect of E2. Taken together, these findings demonstrate important effects of estrogens on cholinergic neurons and support the potential use of estrogen therapy in treatment of dementias in postmenopausal women. © 1994. This article is part of a Special Issue entitled SI:50th Anniversary Issue.

The Role of Presenilin-1 in the Excitotoxicity of Ethanol Withdrawal

Presenilin-1 (PS1) is a core component of γ-secretase that is involved in neurodegeneration. We have previously shown that PS1 interacts with a mitogen-activated protein kinase [(MAPK) jun-NH2-terminal-kinase], and another MAPK (p38) is activated by ethanol withdrawal (EW), abrupt termination from chronic ethanol exposure. EW is excitotoxic in nature, induces glutamate upregulation, and provokes neuronal damage. Here, we explored a potential mechanistic pathway involving glutamate, p38 (p38α isozyme), and PS1 that may mediate EW-induced excitotoxic stress. We used the prefrontal cortex of male rats withdrawn from a chronic ethanol diet. Additionally, we used ethanol-withdrawn HT22 cells (mouse hippocampal) treated with the inhibitor of glutamate receptors [dizocilpine (MK-801)], p38α (SB203580; 4-[4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-1H-imidazol-5-yl]pyridine), or γ-secretase [N-[N- (3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester (DAPT)] during EW. Separately, ethanol-free HT22 cells were exposed to glutamate with or without SB203580 or DAPT. Protein levels, mRNA levels, and cell viability were assessed using immunoblotting, qualitative polymerase chain reaction, and calcein assay, respectively. The prefrontal cortex of ethanol-withdrawn rats or HT22 cells showed an increase in PS1 and p38α, which was attenuated by MK-801 and SB203580, but mimicked by glutamate treatment to ethanol-free HT22 cells. DAPT attenuated the toxic effect of EW or glutamate on HT22 cells. These results suggest that PS1 expression is triggered by glutamate through p38α, contributing to the excitotoxic stimulus of EW.

Finding Ponce de Leon's Pill: Challenges in Screening for Anti-Aging Molecules

Aging is characterized by the progressive accumulation of degenerative changes, culminating in impaired function and increased probability of death. It is the major risk factor for many human pathologies - including cancer, type 2 diabetes, and cardiovascular and neurodegenerative diseases - and consequently exerts an enormous social and economic toll. The major goal of aging research is to develop interventions that can delay the onset of multiple age-related diseases and prolong healthy lifespan (healthspan). The observation that enhanced longevity and health can be achieved in model organisms by dietary restriction or simple genetic manipulations has prompted the hunt for chemical compounds that can increase lifespan. Most of the pathways that modulate the rate of aging in mammals have homologs in yeast, flies, and worms, suggesting that initial screening to identify such pharmacological interventions may be possible using invertebrate models. In recent years, several compounds have been identified that can extend lifespan in invertebrates, and even in rodents. Here, we summarize the strategies employed, and the progress made, in identifying compounds capable of extending lifespan in organisms ranging from invertebrates to mice and discuss the formidable challenges in translating this work to human therapies.

17α-Estradiol Alleviates Age-related Metabolic and Inflammatory Dysfunction in Male Mice Without Inducing Feminization

Aging is associated with visceral adiposity, metabolic disorders, and chronic low-grade inflammation. 17α-estradiol (17α-E2), a naturally occurring enantiomer of 17β-estradiol (17β-E2), extends life span in male mice through unresolved mechanisms. We tested whether 17α-E2 could alleviate age-related metabolic dysfunction and inflammation. 17α-E2 reduced body mass, visceral adiposity, and ectopic lipid deposition without decreasing lean mass. These declines were associated with reductions in energy intake due to the activation of hypothalamic anorexigenic pathways and direct effects of 17α-E2 on nutrient-sensing pathways in visceral adipose tissue. 17α-E2 did not alter energy expenditure or excretion. Fasting glucose, insulin, and glycosylated hemoglobin were also reduced by 17α-E2, and hyperinsulinemic-euglycemic clamps revealed improvements in peripheral glucose disposal and hepatic glucose production. Inflammatory mediators in visceral adipose tissue and the circulation were reduced by 17α-E2. 17α-E2 increased AMPKα and reduced mTOR complex 1 activity in visceral adipose tissue but not in liver or quadriceps muscle, which is in contrast to the generalized systemic effects of caloric restriction. These beneficial phenotypic changes occurred in the absence of feminization or cardiac dysfunction, two commonly observed deleterious effects of exogenous estrogen administration. Thus, 17α-E2 holds potential as a novel therapeutic for alleviating age-related metabolic dysfunction through tissue-specific effects.

From the 90's to now: A brief historical perspective on more than two decades of estrogen neuroprotection

Historical perspective abstract:From the 90's to now: a historical perspective on more than two decades of estrogen neuroprotection: In the early 90's, estrogens were known to exert organizational and activational effects on reproductive tissues and sexual behavior. As well, the role of sex and gonadal hormones in altering the risk for developing Alzheimer's Disease (AD) was only beginning to be elucidated. Preliminary investigations suggested that estrogen-containing therapies typically given for the management of disruptive menopausal symptoms could reduce AD risk, attenuate disease-associated cognitive deficits, and modulate brain substrates known to be dysregulated by the condition, such as the cholingeric system. The findings from our seminal paper demonstrating cognitive benefits and cholinergic impacts with exogenous estrogen treatment in a rodent model of surgical hormone depletion provided initial support for use of estrogen-containing therapies as a treatment for age-related brain disorders. We then went on to demonstrate neuroprotective actions of estrogen in several other in vivo and in vitro models of neurological challenge, including stroke and AD. Further, our findings of the chemical structure requirements for estrogen's neuroprotective effects identified a novel approach for optimizing future estrogen-containing hormone therapy options. These early efforts laid the groundwork for later, large-scale clinical investigations into the potential of estrogen-based menopausal hormone therapies for the prevention of a variety of age-related disorders. Although findings of these studies were equivocal, the neuroprotective actions of estrogen, and specifically 17β-estradiol, identified by early investigations, remain well-documented. Future development of interventions that optimize cognitive aging are crucial and, with proper understanding of the factors that influence the realization of beneficial impacts, estrogen-containing treatments may still be among these.

ORIGINAL ARTICLE ABSTRACT

Ovarian steroid deprivation results in a reversible learning impairment and compromised cholinergic function in female Sprague-Dawley rats: We hypothesized that estradiol (E2) serves as a neurotrophomodulatory substance for basal forebrain cholinergic neurons thought to be involved in learning and memory. Learning/memory was assessed using the two-way active avoidance paradigm and the Morris water task. Female Sprague-Dawley rats were either ovariectomized (OVX) or OVX for 3 weeks, followed by s.c. implantation of a Silastic pellet containing 17-βE2 (E2 pellet), resulting in a replacement of E2 to physiological levels. Ovary-intact (INTACT) animals served as our positive control. Active avoidance behavior and choline acetyltransferase (ChAT) activity in the frontal cortex and hippocampus were assessed at 5 and 28 weeks postovariectomy while performance on the Morris water task and high-affinity choline uptake (HACU) were measured only at the 5-week time point. At the 5-week time point, E2 replacement caused a significant elevation in the level of active avoidance performance relative to OVX animals. At the 28-week time point, OVX animals demonstrated a significantly lower number of avoidances relative to controls (61%) whereas E2-pellet animals not only demonstrated superior performance relative to OVX animals but also showed an accelerated rate of learning. Morris water task performance, on the other hand, was not significantly affected by estrogenic milieu despite a trend towards better performance in the E2-pellet group. Neurochemical analyses revealed that 5 weeks of ovariectomy was sufficient to reduce HACU in both the frontal cortex and hippocampus by 24 and 34%, respectively, while E2 replacement was successful in elevating HACU relative to OVX animals in both regions. ChAT activity was decreased in the hippocampus but not the frontal cortex of 5-week OVX animals. E2 replacement resulted in a reversal of this effect. At the 28-week time period, an unexpected decrease in ChAT activity was observed across all treatment groups. Interestingly, E2-pellet animals demonstrated the least severe decline in ChAT. This phenomenon was most evident in the frontal cortex where ChAT decreased by 61 and 56% in INTACT and OVX animals, respectively, whereas the decline in E2-pellet animals was only 16% over the same time period, suggesting a previously unreported cytoprotective effect of E2. Taken together, these findings demonstrate important effects of estrogens on cholinergic neurons and support the potential use of estrogen therapy in treatment of dementias in postmenopausal women. © 1994. This article is part of a Special Issue entitled SI:50th Anniversary Issue.

Estrogen receptor-β in mitochondria: implications for mitochondrial bioenergetics and tumorigenesis

Estrogen enhances mitochondrial function by enhancing mitochondrial biogenesis and sustaining mitochondrial energy-transducing capacity. Shifts in mitochondrial bioenergetic pathways from oxidative phosphorylation to glycolysis have been hypothesized to be involved in estrogen-induced tumorigenesis. Studies have shown that mitochondria are an important target of estrogen. Estrogen receptor-β (ERβ) has been shown to localize to mitochondria in a ligand-dependent or -independent manner and can affect mitochondrial bioenergetics and anti-apoptotic signaling. However, the functional role of mitochondrial ERβ in tumorigenesis remains unclear. Clinical studies of ERβ-related tumorigenesis have shown that ERβ stimulates mitochondrial metabolism to meet the high energy demands of processes such as cell proliferation, cell survival, and transformation. Thus, in elucidating the precise role of mitochondrial ERβ in cell transformation and tumorigenesis, it will be particularly valuable to explore new approaches for the development of medical treatments targeting mitochondrial ERβ-mediated mitochondrial function and preventing apoptosis.

Aberrant histone acetylation promotes mitochondrial respiratory suppression in the brain of alcoholic rats

The acetylation of histone proteins in the core of DNA regulates gene expression, including those affecting mitochondria. Both histone acetylation and mitochondrial deficit have been implicated in neuronal damage associated with drinking problems. Many alcoholics will repeat unsuccessful attempts at abstaining, developing a pattern of repeated drinking and withdrawal. We investigated whether aberrant histone acetylation contributes to mitochondrial and cellular damage induced by repeated ethanol withdrawal (EW). We also investigated whether this effect of histone acetylation involves let-7f, a small noncoding RNA (microRNA). Male rats received two cycles of an ethanol/control diet (7.5%, 4 weeks) and withdrawal. Their prefrontal cortex was collected to measure the mitochondrial respiration and histone acetylation using extracellular flux (XF) real-time respirometry and gold immunostaining, respectively. Separately, HT22 (mouse hippocampal) cells received two cycles of ethanol exposure (100 mM, 20 hours) and withdrawal. Trichostatin A (TSA) as a histone acetylation promoter and let-7f antagomir were applied during withdrawal. The mitochondrial respiration, let-7f level, and cell viability were assessed using XF respirometry, quantitative polymerase chain reaction, TaqMan let-7f primers, and a calcein-acetoxymethyl assay, respectively. Repeated ethanol withdrawn rats showed a more than 2-fold increase in histone acetylation, accompanied by mitochondrial respiratory suppression. EW-induced mitochondrial respiratory suppression was exacerbated by TSA treatment in a manner that was attenuated by let-7f antagomir cotreatment. TSA treatment did not alter the increasing effect of EW on the let-7f level but dramatically exacerbated the cell death induced by EW. These data suggest that the multiple episodes of withdrawal from chronic ethanol impede mitochondrial and cellular integrity through upregulating histone acetylation, independent of or additively with let-7f.

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.

Non-feminizing estrogens: a novel neuroprotective therapy

While the conflict between basic science evidence for estrogen neuroprotection and the lack of effectiveness in clinical trials is only now being resolved, it is clear that strategies for estrogen neuroprotection that avoid activation of ERs have the potential for clinical application. Herein we review the evidence from both in vitro and in vivo studies that describe high potency neuroprotection with non-feminizing estrogens. We have characterized many of the essential chemical features of non-feminizing estrogens that eliminate or reduce ER binding while maintaining or enhancing neuroprotection. Additionally, we provide evidence that these non-feminizing estrogens have efficacy in protecting the brain from AD neuropathology and traumatic brain injury. In conclusion, it appears that the non-feminizing estrogen strategy for neuroprotection is a viable option to achieve the beneficial neuroprotective effects of estrogens while eliminating the toxic off-target effects of chronic estrogen administration.

Acarbose, 17-α-estradiol, and nordihydroguaiaretic acid extend mouse lifespan preferentially in males

Four agents — acarbose (ACA), 17-α-estradiol (EST), nordihydroguaiaretic acid (NDGA), and methylene blue (MB) — were evaluated for lifespan effects in genetically heterogeneous mice tested at three sites. Acarbose increased male median lifespan by 22% (P < 0.0001), but increased female median lifespan by only 5% (P = 0.01). This sexual dimorphism in ACA lifespan effect could not be explained by differences in effects on weight. Maximum lifespan (90th percentile) increased 11% (P < 0.001) in males and 9% (P = 0.001) in females. EST increased male median lifespan by 12% (P = 0.002), but did not lead to a significant effect on maximum lifespan. The benefits of EST were much stronger at one test site than at the other two and were not explained by effects on body weight. EST did not alter female lifespan. NDGA increased male median lifespan by 8–10% at three different doses, with P-values ranging from 0.04 to 0.005. Females did not show a lifespan benefit from NDGA, even at a dose that produced blood levels similar to those in males, which did show a strong lifespan benefit. MB did not alter median lifespan of males or females, but did produce a small, statistically significant (6%, P = 0.004) increase in female maximum lifespan. These results provide new pharmacological models for exploring processes that regulate the timing of aging and late-life diseases, and in particular for testing hypotheses about sexual dimorphism in aging and health.

Impact of methodology on estrogens' effects on cerebral ischemia in rats: an updated meta-analysis

Background

Although most animal stroke studies have demonstrated potent neuroprotective effects of estrogens, there are a number of articles reporting the opposite. In 2009, we made the case that this dichotomy was related to administered estrogen dose. Several other suggestions for the discordant results have also been propagated, including the age of the experimental animals and the length of hypoestrogenicity prior to estrogen administration. These two suggestions have gained much popularity, probably because of their kinship with the window of opportunity hypothesis, which is commonly used to explain the analogous dichotomy among human studies. We were therefore encouraged to perform an updated meta-analysis, and to improve it by including all relevant variables in a large multiple regression model, where the impact of confounders could be controlled for.

Results

The multiple regression model revealed an indisputable impact of estrogen administration mode on the effects of estrogens in ischemic stroke. Subcutaneous slow-release pellets differed from the injection and silastic capsule treatments in terms of impact of estrogens on ischemic stroke, showing that the first mentioned were more prone to render estrogens damaging. Neither the use of elderly animals nor the adoption of longer wash-out periods influenced estrogens’ effects on experimental ischemic stroke in rats.

Conclusions

We conclude that the discordant results regarding estrogens’ effects in rat models of ischemic stroke are a consequence of differences in estrogen administration modes. These results are not only of importance for the ongoing debate regarding menopausal hormone therapy, but also have an important bearing on experimental stroke methodology and the apparent translational roadblock for suggested stroke interventions.

Neuroprotection with non-feminizing estrogen analogues: an overlooked possible therapeutic strategy

Although many of the effects of estrogens on the brain are mediated through estrogen receptors (ERs), there is evidence that neuroprotective activity of estrogens can be mediated by non-ER mechanisms. Herein, we review the substantial evidence that estrogens neuroprotection is in large part non-ER mediated and describe in vitro and in vivo studies that support this conclusion. Also, we described our drug discovery strategy for capitalizing on enhancement in neuroprotection while at the same time, reducing ER binding of a group of synthetic non-feminizing estrogens. Finally, we offer evidence that part of the neuroprotection of these non-feminizing estrogens is due to enhancement in redox potential of the synthesized compounds.

Neuroprotection and estrogen receptors

This review is intended to assess the state of current knowledge on the role of estrogen receptors (ERs) in the neuroprotective effects of estrogens in models for acute neuronal injury and death. We evaluate the overall evidence that estrogens are neuroprotective in acute injury and critically assess the role of ERα, ERβ, GPR 30, and nonreceptor-mediated mechanisms in these robust neuroprotective effects of this ovarian steroid hormone. We conclude that all three receptors, as well as nonreceptor-mediated mechanisms can be involved in neuroprotection, depending on the model used, the level of estrogen administrated, and the mode of administration of the steroid. Also, the signaling pathways used by both ER-dependent and ER-independent mechanisms to exert neuroprotection are considered. Finally, further studies that are needed to parse out the relative contribution of receptor versus nonreceptor-mediated signaling are discussed.

Neuroprotective effects of nonfeminizing estrogens in retinal photoreceptor neurons

PURPOSE

Retinal diseases such as macular degeneration and glaucoma are disorders that target specific retinal neurons that can ultimately lead to vision loss. Under these conditions and pathologies, retinal neurons can die via apoptosis that may be due to increased oxidative stress. The neuroprotective effects of 17β-estradiol (E2) and three synthetic nonfeminizing estrogen analogs (ZYC-26, ZYC-23, and ZYC-3) were investigated to examine their abilities to protect retinal neurons against glutamate toxicity.

METHODS

Using an in vitro model of glutamate-induced cell death in 661W cells, a mouse cone photoreceptor cell line, shown to express both estrogen receptors (ERs) via immunoblotting, was pretreated with E2 and its analogs and cell viability were assessed.

RESULTS

It was observed that E2 and estrogen analogs, ZYC-26 and ZYC-3, were protective against a 5 mM glutamate insult in 661W cells. The neuroprotective abilities of ZYC-26 and ZYC-3 were autonomous of estrogen receptor-α (ERα) and ERβ demonstrated by their ability to protect in the presence of ICI 182780, a pan-ER antagonist with a high affinity for the estrogen receptor. Treatment with PPT and DPN, ERα- and ERβ-specific agonists, respectively, did not protect the 661W cells from the glutamate insult. Studying the membrane ER (mER) or GPR30 did show that activation of the receptor by G1 protected the retinal neuron from insult, whereas G15, an antagonist of the mER was not able to antagonize the protection previously seen.

CONCLUSIONS

These data demonstrate that nonfeminizing estrogens may emerge as useful compounds for neuroprotection of retinal cells.

Estrone is neuroprotective in rats after traumatic brain injury

In various animal and human studies, early administration of 17β-estradiol, a strong antioxidant, anti-inflammatory, and anti-apoptotic agent, significantly decreases the severity of injury in the brain associated with cell death. Estrone, the predominant estrogen in postmenopausal women, has been shown to be a promising neuroprotective agent. The overall goal of this project was to determine if estrone mitigates secondary injury following traumatic brain injury (TBI) in rats. Male rats were given either placebo (corn oil) or estrone (0.5 mg/kg) at 30 min after severe TBI. Using a controlled cortical impact device in rats that underwent a craniotomy, the right parietal cortex was injured using the impactor tip. Non-injured control and sham animals were also included. At 72 h following injury, the animals were perfused intracardially with 0.9% saline followed by 10% phosphate-buffered formalin. The whole brain was removed, sliced, and stained for TUNEL-positive cells. Estrone decreased cortical lesion volume (p<0.01) and neuronal injury (p<0.001), and it reduced cerebral cortical levels of TUNEL-positive staining (p<0.0001), and decreased numbers of TUNEL-positive cells in the corpus callosum (p<0.03). We assessed the levels of β-amyloid in the injured animals and found that estrone significantly decreased the cortical levels of β-amyloid after brain injury. Cortical levels of phospho-ERK1/2 were significantly (p<0.01) increased by estrone. This increase was associated with an increase in phospho-CREB levels (p<0.021), and brain-derived neurotrophic factor (BDNF) expression (p<0.0006). In conclusion, estrone given acutely after injury increases the signaling of protective pathways such as the ERK1/2 and BDNF pathways, decreases ischemic secondary injury, and decreases apoptotic-mediated cell death. These results suggest that estrone may afford protection to those suffering from TBI.

Intermittent hypoxia conditioning protects mitochondrial cytochrome c oxidase of rat cerebellum from ethanol withdrawal stress

Intermittent hypoxia (IH) conditioning minimizes neurocognitive impairment and stabilizes brain mitochondrial integrity during ethanol withdrawal (EW) in rats, but the mitoprotective mechanism is unclear. We investigated whether IH conditioning protects a key mitochondrial enzyme, cytochrome c oxidase (COX), from EW stress by inhibiting mitochondrially directed apoptotic pathways involving cytochrome c, Bax, or phosphor-P38 (pP38). Male rats completed two cycles of a 4-wk ethanol diet (6.5%) and 3 wk of EW. An IH program consisting of 5-10 bouts of 5-8 min of mild hypoxia (9.5-10% inspired O(2)) and 4 min of reoxygenation for 20 consecutive days began 3 days before the first EW period. For some animals, vitamin E replaced IH conditioning to test the contributions of antioxidant mechanisms to IH's mitoprotection. During the second EW, cerebellar-related motor function was evaluated by measuring latency of fall from a rotating rod (Rotarod test). After the second EW, COX activity in cerebellar mitochondria was measured by spectrophotometry, and COX, cytochrome c, Bax, and pP38 content were analyzed by immunoblot. Mitochondrial protein oxidation was detected by measuring carbonyl contents and by immunochemistry. Earlier IH conditioning prevented motor impairment, COX inactivation, depletion of COX subunit 4, protein carbonylation, and P38 phosphorylation during EW. IH did not prevent cytochrome c depletion during EW, and Bax content was unaffected by EW ± IH. Vitamin E treatment recapitulated IH protection of COX, and P38 inhibition attenuated protein oxidation during EW. Thus IH protects COX and improves cerebellar function during EW by limiting P38-dependent oxidative damage.

Neuroprotective effects of high affinity Σ1 receptor selective compounds

We previously reported that the antipsychotic drug haloperidol, a multifunctional D2-like dopamine and sigma receptor subtype antagonist, has neuroprotective properties. In this study we further examined the association between neuroprotection and receptor antagonism by evaluating a panel of novel compounds with varying affinity at sigma and D2-like dopamine receptors. These compounds were evaluated using an in vitro cytotoxicity assay that utilizes a hippocampal-derived cell line, HT-22, in the presence or absence of varying concentrations (5 to 20 mM) of glutamate. While haloperidol was found to be a potent neuroprotective agent in this in vitro cell assay, the prototypic sigma 1 receptor agonist (+)-pentazocine was found not to be neuroprotective. Subsequently, the potency for the neuroprotection of HT-22 cells was evaluated for a) three SV series indoles which have nMolar affinity at D2-like receptors but varying affinity at sigma 1 receptor and b) two benzyl phenylacetamides sigma 1 receptor selective compounds which bind with low affinity at D2-like receptors but have nMolar affinity for the sigma 1 receptor. We observed that cytoprotection correlated with the affinity of the compounds for sigma 1 receptors. Based upon results from the HT-22 cell-based in vitro assay, two phenylacetamides, LS-127 and LS-137, were further evaluated in vivo using a transient middle cerebral artery occlusion (t-MCAO) model of stroke. At a dose of 100 μg/kg, both LS-127 and LS-137 attenuated infarct volume by approximately 50%. These studies provide further evidence that sigma 1 receptor selective compounds can provide neuroprotection in cytotoxic situations. These results also demonstrate that sigma 1 receptor selective benzyl phenylacetamides are candidate pharmacotherapeutic agents that could be used to minimize neuronal death after a stroke or head trauma.

The potential for estrogens in preventing Alzheimer's disease and vascular dementia

Estrogens are the best-studied class of drugs for potential use in the prevention of Alzheimer's disease (AD). These steroids have been shown to be potent neuroprotectants both in vitro and in vivo, and to exert effects that are consistent with their potential use in prevention of AD. These include the prevention of the processing of amyloid precursor protein (APP) into beta-amyloid (Aß), the reduction in tau hyperphosphorylation, and the elimination of catastrophic attempts at neuronal mitosis. Further, epidemiological data support the efficacy of early postmenopausal use of estrogens for the delay or prevention of AD. Collectively, this evidence supports the further development of estrogen-like compounds for prevention of AD. Several approaches to enhance brain specificity of estrogen action are now underway in an attempt to reduce the side effects of chronic estrogen therapy in AD.

Divergent mechanisms for trophic actions of estrogens in the brain and peripheral tissues

17β-estradiol (E(2)) can enhance reproductive, cognitive, and affective functions; however, the mechanisms by which E(2) has these effects need to be better understood. Pleiotrophic effects of E(2) can occur via traditional and novel actions at various forms of estrogen receptors (ERs). In the central nervous system, trophic effects of E(2) may be related to beneficial effects of hormone replacement therapy (HRT). However, in peripheral reproductive tissues, E(2)'s capacity to evoke growth can increase risk of cancers. This review focuses on investigations aimed at elucidating divergent mechanisms of steroids to promote trophic effects in the brain, independent of effects on peripheral reproductive tissues. First, actions of estrogens via ERα or ERβ for peripheral growth (carcinogen-induced tumors, uterine growth) and hippocampus-dependent behaviors (affect, cognition) are described. Second, factors that influence these effects of estrogens are described (e.g. experience, timing/critical windows, non-ER mechanisms). Third, effects of estrogens at ERβ related to actions of progestogens, such as 5α-pregnan-3α-ol-20-one (3α,5α-THP) are described. In summary, effects of E(2) may occur via multiple mechanisms, which may underlie favorable effects in the brain with minimal peripheral trophic effects.

The assessment of non-feminizing estrogens for use in neuroprotection

Menopause is associated with a precipitous decline in circulating estrogens and a resulting loss of the neuroprotective actions of this steroid hormone. In view of the results of the Women's Health Initiative and the preceding knowledge that orally administered estrogens has a variety of adverse side effects, likely through actions on peripheral estrogen receptor alpha (ERα), we initiated a program of research to synthesis and assess a group of non-feminizing estrogens that lack ability to interact with ERs but retain much of the neuroprotective action of feminizing estrogens. This program of research is aimed at the identification of compounds which do not stimulate ERs but are potentially neuroprotective in vitro and in animal models of neuronal cell death. We discovered that the most effective non-feminizing estrogens were those with large bulky groups in the 2 and/or 4 carbon of the phenolic A ring of the steroid. These compounds were 8- to 114-fold more potent than 17 β-estradiol (βE2), but lacked ER binding capacity in vitro and feminizing effects in vivo. The success of this program of research suggests that strategies to optimize non-feminizing estrogens for use in postmenopausal women can be successful.

Androgens selectively protect against apoptosis in hippocampal neurones

Androgens can protect neurones from injury, although androgen neuroprotection is not well characterised in terms of either specificity or mechanism. In the present study, we compared the ability of androgens to protect neurones against a panel of insults, empirically determined to induce cell death by apoptotic or non-apoptotic mechanisms. Three criteria defining but not inclusive of apoptosis are: protection by caspase inhibition, protection by protein synthesis inhibition and the presence of pyknotic nuclei. According to these criteria, beta-amyloid, staurosporine, and Apoptosis Activator II induced cell death involving apoptosis, whereas hydrogen peroxide (H(2)O(2)), iron, calcium ionophore and 3-nitropropionic acid induced cell death featuring non-apoptotic characteristics. Pretreatment of hippocampal neurones with testosterone or dihydrotestosterone attenuated cell death induced by beta-amyloid, staurosporine and Apoptosis Activator II, but none of the other insults. The anti-oxidant Trolox did not reduce cell death induced by beta-amyloid, staurosporine and Apoptosis Activator II, but did protect against H(2)O(2) and iron. Similarly, a supra-physiological concentration of oestrogen reduced cell death induced by H(2)O(2) and iron, an effect not observed with androgens. We also show that activation of oestrogen pathways was not necessary for androgen neuroprotection. These data suggest that androgens directly activate a neuroprotective mechanism specific to inhibition of cell death involving apoptosis. Determining the specificity of androgen neuroprotection may enable the development of androgen compounds for the treatment of neurodegenerative disorders.

Therapeutic implications of brain steroidogenesis

The nervous system is a steroidogenic tissue and several steroids synthesized locally in the brain, such as pregnenolone, progesterone and estradiol, modulate neuronal and glial physiology and are neuroprotective. The brain upregulates steroidogenesis at sites of injury as part of a program triggered by neural tissue to cope with neurodegenerative insults. Pharmacological targets to increase brain steroidogenesis and promote neuroprotection include the molecules that transport cholesterol to the inner mitochondrial membrane, where the first enzyme for steroidogenesis is located. Furthermore, the human gene encoding aromatase, the enzyme that synthesizes estradiol, is under the control of different tissue-specific promoters, and it is therefore conceivable that selective aromatase modulators can be developed that will enhance the expression of the enzyme and the consequent increase in estrogen formation in the brain but not in other tissues.

Low doses of 17alpha-estradiol and 17beta-estradiol facilitate, whereas higher doses of estrone and 17alpha- and 17beta-estradiol impair, contextual fear conditioning in adult female rats

Estrogens are known to exert significant structural and functional effects in the hippocampus of adult rodents. In particular, 17beta-estradiol can improve, impair, or have no effect on hippocampus-dependent learning and memory depending on dose and time of administration. The effects of other forms of estrogen, such as estrone and 17alpha-estradiol, on hippocampus-dependent learning have not been as thoroughly investigated. Therefore, the purpose of this study was to investigate the effects of 17beta-estradiol, estrone, and 17alpha-estradiol at three different doses on two different tasks: hippocampus-dependent contextual fear conditioning and hippocampus-independent cued fear conditioning. Adult ovariectomized female rats were injected with one of the estrogens at one of the three doses 30 mins before conditioning to assess the rapid effects of these estrogens on acquisition. Twenty-four hours later memory for the context was examined and 1 h later memory for the cue (tone) was assessed. Levels of synaptophysin were examined in the dorsal hippocampus of rats to identify a potential synaptic correlate of hormonal effects on contextual fear conditioning. Low 17beta-estradiol and 17alpha-estradiol enhanced, whereas high 17beta-estradiol and 17alpha-estradiol impaired, contextual fear conditioning. Only the middle dose of estrone severely impaired contextual fear conditioning. Estrogens did not alter performance in the hippocampus-independent cued task. Synaptophysin expression was increased by estrone (at a middle and high dose) and 17beta-estradiol (at a middle dose) in the CA3 region of the hippocampus and was not correlated with cognition. The results of this study indicate that estradiol can positively or negatively influence hippocampus-dependent learning and memory, whereas estrone impairs hippocampus-dependent learning and memory in a dose-dependent manner. These results have important therapeutic implications, as estrone, a main component of a widely used hormone replacement therapy, was shown to have either a negative effect or no effect on learning and memory. It may be possible to use 17alpha-estradiol and lower doses of estrogens as potential alternatives in hormone replacement therapies.