Modulation of Bcl-2 expression: a potential component of estrogen protection in NT2 neurons

Neurotrophic and neuroprotective actions of estrogen: basic mechanisms and clinical implications

Estrogen is an important hormone signal that regulates multiple tissues and functions in the body. This review focuses on the neurotrophic and neuroprotective actions of estrogen in the brain, with particular emphasis on estrogen actions in the hippocampus, cerebral cortex and striatum. Sex differences in the risk, onset and severity of neurodegenerative disease such as Alzheimer's disease, Parkinson's disease and stroke are well known, and the potential role of estrogen as a neuroprotective factor is discussed in this context. The review assimilates a complex literature that spans research in humans, non-human primates and rodent animal models and attempts to contrast and compare the findings across species where possible. Current controversies regarding the Women's Health Initiative (WHI) study, its ramifications, concerns and the new studies needed to address these concerns are also addressed. Signaling mechanisms underlying estrogen-induced neuroprotection and synaptic plasticity are reviewed, including the important concepts of genomic versus nongenomic mechanisms, types of estrogen receptor involved and their subcellular targeting, and implicated downstream signaling pathways and mediators. Finally, a multicellular mode of estrogen action in the regulation of neuronal survival and neurotrophism is discussed, as are potential future directions for the field.

Gender differences in the disposition and toxicity of metals

There is increasing evidence that health effects of toxic metals differ in prevalence or are manifested differently in men and women. However, the database is small. The present work aims at evaluating gender differences in the health effects of cadmium, nickel, lead, mercury and arsenic. There is a markedly higher prevalence of nickel-induced allergy and hand eczema in women compared to men, mainly due to differences in exposure. Cadmium retention is generally higher in women than in men, and the severe cadmium-induced Itai-itai disease was mainly a woman's disease. Gender differences in susceptibility at lower exposure are uncertain, but recent data indicate that cadmium has estrogenic effects and affect female offspring. Men generally have higher blood lead levels than women. Lead accumulates in bone and increased endogenous lead exposure has been demonstrated during periods of increased bone turnover, particularly in women in pregnancy and menopause. Lead and mercury, in the form of mercury vapor and methylmercury, are easily transferred from the pregnant women to the fetus. Recent data indicate that boys are more susceptible to neurotoxic effects of lead and methylmercury following exposure early in life, while experimental data suggest that females are more susceptible to immunotoxic effects of lead. Certain gender differences in the biotransformation of arsenic by methylation have been reported, and men seem to be more affected by arsenic-related skin effect than women. Experimental studies indicate major gender differences in arsenic-induced cancer. Obviously, research on gender-related differences in health effects caused by metals needs considerable more focus in the future.

Mitochondrial mechanisms of estrogen neuroprotection

Oxidative stress, bioenergetic failure and mitochondrial dysfunction are all implicated in the etiology of neurodegenerative diseases such as Alzheimer's disease (AD). The mitochondrial involvement in neurodegenerative diseases reflects the regulatory role mitochondrial failure plays in both necrotic cell death and apoptosis. The potent feminizing hormone, 17 beta-estradiol (E2), is neuroprotective in a host of cell and animal models of stroke and neurodegenerative diseases. The discovery that 17alpha-estradiol, an isomer of E2, is equally as neuroprotective as E2 yet is >200-fold less active as a hormone, has permitted development of novel, more potent analogs where neuroprotection is independent of hormonal potency. Studies of structure-activity relationships and mitochondrial function have led to a mechanistic model in which these steroidal phenols intercalate into cell membranes where they block lipid peroxidation reactions, and are in turn recycled. Indeed, the parental estrogens and novel analogs stabilize mitochondria under Ca(2+) loading otherwise sufficient to collapse membrane potential. The neuroprotective and mitoprotective potencies for a series of estrogen analogs are significantly correlated, suggesting that these compounds prevent cell death in large measure by maintaining functionally intact mitochondria. This therapeutic strategy is germane not only to sudden mitochondrial failure in acute circumstances, such as during a stroke or myocardial infarction, but also to gradual mitochondrial dysfunction associated with chronic degenerative disorders such as AD.

Implications for estrogens in Parkinson's disease: an epidemiological approach

Evidence from experimental and epidemiological studies suggests a role of sex hormones in the pathogenic process leading to neurodegenerative diseases, (i.e., Alzheimer's and Parkinson's disease). The effects of sexual steroid hormones are complex and vary with the events of women's fertile life. Estrogens are supposed to influence dopamine synthesis, metabolism, and transport; however, there is no consensus regarding the direction, locus, and mechanism of the effect of estrogens on the dopaminergic system. A neuroprotective effect of estrogens has been demonstrated in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-animal models of Parkinson's disease (PD). Epidemiological studies indicate gender differences regarding the onset and the prognosis of PD. Most of the analytical studies explored the relationship between PD and exogenous estrogens. Only three studies investigated the role of endogenous estrogens in the risk of developing PD. These studies reported an increased risk of PD in conditions causing an early reduction in endogenous estrogens (early menopause, reduced fertile life length). Longer cumulative length of pregnancies has also been associated with an increased PD risk. A lack of consensus still exists on the effect of the type of menopause (surgical vs. natural) on PD risk. Finally, the effect of postmenopausal estrogen replacement therapy is still debated. Inconsistencies across studies are in part explained by the complexity of the mechanisms of action of sexual hormones and by the paucity of analytical studies.

Estrogen regulates Bcl-w and Bim expression: role in protection against beta-amyloid peptide-induced neuronal death

Estrogen is neuroprotective against a variety of insults, including beta-amyloid peptide (Abeta); however, the underlying mechanism(s) is not fully understood. Here, we report that 17beta-estradiol (E2) selectively regulates neuronal expression of the Bcl-2 family (bcl-2, bcl-x, bcl-w, bax, bak, bad, bik, bnip3, bid, and bim). In primary cerebrocortical neuron cultures under basal conditions, we observe that E2 upregulates expression of antiapoptotic Bcl-w and downregulates expression of proapoptotic Bim in an estrogen receptor (ER)-dependent manner. In the presence of toxic levels of Abeta, we observe that E2 attenuates indices of neuronal apoptosis: c-Jun N-terminal kinase (JNK)-dependent downregulation of Bcl-w and upregulation of Bim, mitochondrial release of cytochrome c and Smac, and cell death. These neuroprotective effects of E2 against Abeta-induced apoptosis are mimicked by the JNK inhibitor SP600125 (anthra[1,9-cd]pyrazol-6(2H)-one). In addition, E2 attenuates Abeta-induced JNK phosphorylation in an ER-dependent manner, but does not affect basal levels of JNK phosphorylation. These results suggest that E2 may reduce Abeta-induced neuronal apoptosis at least in part by two complementary pathways: (1) ER-dependent, JNK-independent upregulation of Bcl-w and downregulation of Bim under basal conditions, and (2) ER-dependent inhibition of Abeta-induced JNK activation and subsequent JNK-dependent downregulation of Bcl-w and upregulation of Bim, resulting in mitochondrial release of cytochrome c and Smac and eventual cell death. These data provide new understanding into the mechanisms contributing to estrogen neuroprotection, a neural function with potential therapeutic relevance to Alzheimer's disease.

Anatomical measurements of the orbitofrontal cortex in child and adolescent patients with bipolar disorder

Imaging studies indicate smaller orbitofrontal cortex (OFC) volume in mood disorder patients compared with healthy subjects. We sought to determine whether child and adolescent patients with bipolar disorder have smaller OFC volumes than healthy controls. Fourteen children and adolescents meeting DSM-IV criteria for bipolar disorder (six males and eight females with a mean age+/-S.D.=15.5+/-3.2 years) and 20 healthy controls (11 males and nine females with mean age+/-S.D.=16.9+/-3.8 years) were studied. Orbitofrontal cortex volume was measured using magnetic resonance imaging. Male bipolar patients had smaller gray matter volumes in medial (p=0.044), right medial (0.037) and right (p=0.032) lateral OFC subdivisions compared to male controls. In contrast, female patients had larger gray matter volumes in left (p=0.03), lateral (p=0.012), left lateral (p=0.007), and trends for larger volumes in right lateral and left medial OFC subdivisions compared with female controls. Male patients exhibit smaller gray matter volumes, while female patients exhibit larger volumes in some OFC sub-regions. Gender differences in OFC abnormalities may be involved in illness pathophysiology among young bipolar patients.

Structure-nongenomic neuroprotection relationship of estrogens and estrogen-derived compounds

Nongenomic estrogen signaling pathways involve extranuclear estrogen receptors or function independently from estrogen receptors. These pathways participate in neuroprotection elicited by the hormone. Additional nongenomic neuroprotective effects are attributable to antioxidant and antiinflammatory actions of estrogens. Numerous chemical modifications to afford neuroprotective compounds from estrogens while eliminating estrogenicity and maintaining or enhancing nongenomic neuroprotection have been described. This review highlights recent structure-activity studies that revealed the importance of antioxidant effects for neuroprotective estrogen analogues and derivatives.

Estrogen protects neuronal cells from amyloid beta-induced apoptosis via regulation of mitochondrial proteins and function

BACKGROUND

Neurodegeneration in Alzheimer's disease is associated with increased apoptosis and parallels increased levels of amyloid beta, which can induce neuronal apoptosis. Estrogen exposure prior to neurotoxic insult of hippocampal neurons promotes neuronal defence and survival against neurodegenerative insults including amyloid beta. Although all underlying molecular mechanisms of amyloid beta neurotoxicity remain undetermined, mitochondrial dysfunction, including altered calcium homeostasis and Bcl-2 expression, are involved in neurodegenerative vulnerability.

RESULTS

In this study, we investigated the mechanism of 17beta-estradiol-induced prevention of amyloid beta-induced apoptosis of rat hippocampal neuronal cultures. Estradiol treatment prior to amyloid beta exposure significantly reduced the number of apoptotic neurons and the associated rise in resting intracellular calcium levels. Amyloid beta exposure provoked down regulation of a key antiapoptotic protein, Bcl-2, and resulted in mitochondrial translocation of Bax, a protein known to promote cell death, and subsequent release of cytochrome c. E2 pretreatment inhibited the amyloid beta-induced decrease in Bcl-2 expression, translocation of Bax to the mitochondria and subsequent release of cytochrome c. Further implicating the mitochondria as a target of estradiol action, in vivo estradiol treatment enhanced the respiratory function of whole brain mitochondria. In addition, estradiol pretreatment protected isolated mitochondria against calcium-induced loss of respiratory function.

CONCLUSION

Therefore, we propose that estradiol pretreatment protects against amyloid beta neurotoxicity by limiting mitochondrial dysfunction via activation of antiapoptotic mechanisms.

Complex actions of sex steroids in adipose tissue, the cardiovascular system, and brain: Insights from basic science and clinical studies

Recent publications describing the results of the Women's Health Initiative (WHI) and other studies reporting the impact of hormone therapy on aging women have spurred reexamination of the broad use of estrogens and progestins during the postmenopausal years. Here, we review the complex pharmacology of these hormones, the diverse and sometimes opposite effects that result from the use of different estrogenic and progestinic compounds, given via different delivery routes in different concentrations and treatment sequence, and to women of different ages and health status. We examine our new and growing appreciation of the role of estrogens in the immune system and the inflammatory response, and we pose the concept that estrogen's interface with this system may be at the core of some of the effects on multiple physiological systems, such as the adipose/metabolic system, the cardiovascular system, and the central nervous system. We compare and contrast clinical and basic science studies as we focus on the actions of estrogens in these systems because the untoward effects of hormone therapy reported in the WHI were not expected. The broad interpretation and publicity of the results of the WHI have resulted in a general condemnation of all hormone replacement in postmenopausal women. In fact, careful review of the extensive literature suggests that data resulting from the WHI and other recent studies should be interpreted within the narrow context of the study design. We argue that these results should encourage us to perform new studies that take advantage of a dialogue between basic scientists and clinician scientists to ensure appropriate design, incorporation of current knowledge, and proper interpretation of results. Only then will we have a better understanding of what hormonal compounds should be used in which populations of women and at what stages of menopausal/postmenopausal life.

17beta-estradiol is protective in spinal cord injury in post- and pre-menopausal rats

The neuroprotective effects of 17 beta -estradiol have been shown in models of central nervous system injury, including ischemia, brain injury, and more recently, spinal cord injury (SCI). Recent epidemiological trends suggest that SCIs in elderly women are increasing; however, the effects of menopause on estrogen-mediated neuroprotection are poorly understood. The objective of this study was to evaluate the effects of 17beta-estradiol and reproductive aging on motor function, neuronal death, and white matter sparing after SCI of post- and pre-menopausal rats. Two-month-old or 1- year-old female rats were ovariectomized and implanted with a silastic capsule containing 180 microg/mL of 17beta-estradiol or vehicle. Complete crush SCI at T8-9 was performed 1 week later. Additional animals of each age group were left ovary-intact but were spinal cord injured. The Basso, Beattie, Bresnahan (BBB) locomotor test was performed. Spinal cords were collected on post-SCI days 1, 7, and 21, and processed for histological markers. Administration of 17beta-estradiol to ovariectomized rats improved recovery of hind-limb locomotion, increased white matter sparing, and decreased apoptosis in both the post- and pre-menopausal rats. Also, ovary-intact 1-year-old rats did worse than ovary-intact 2-month-old rats, suggesting that endogenous estrogen confers neuroprotection in young rats, which is lost in older animals. Taken together, these data suggest that estrogen is neuroprotective in SCI and that the loss of endogenous estrogen-mediated neuroprotective seen in older rats can be attenuated with exogenous administration of 17beta-estradiol.

Neuroprotective effects of 17beta-estradiol and nonfeminizing estrogens against H2O2 toxicity in human neuroblastoma SK-N-SH cells

Neuroprotective effects of estrogens have been shown in various in vitro and in vivo models, but the mechanisms underlying protection by estrogen are not clear. Mounting evidence suggests antioxidant effects contribute to the neuroprotective effects of estrogens. In the present study, we assessed the protective effects of estrogens against H2O2-induced toxicity in human neuroblastoma cells and the potential mechanisms involved in this protection. We demonstrate that 17beta-estradiol (17beta-E2) increases cell survival against H2O2 toxicity in human neuroblastoma cells. 17beta-E2 effectively reduced lipid peroxidation induced by 5-min H2O2 exposure. Furthermore, 17beta-E2 exerts the protective effects by maintaining intracellular Ca2+ homeostasis, attenuating ATP depletion, ablating mitochondrial calcium overloading, and preserving mitochondrial membrane potential. Two nonfeminizing estrogens, 17alpha- and ent-estradiol, were as effective as 17beta-E2 in increasing cell survival, alleviating lipid peroxidation, preserving mitochondrial function, and maintaining intracellular glutathione levels and Ca2+ homeostasis against H2O2 insult. Moreover, the estrogen receptor antagonist fulvestrant (ICI 182,780) did not block effects of 17beta-E2, but increased cell survival and blunted intracellular Ca2+ increases. However, these estrogens failed to reduce cytosolic reactive oxygen species, even at concentrations as high as 10 microM. In conclusion, estrogens exert protective effects against oxidative stress by inhibiting lipid peroxidation and subsequently preserving Ca2+ homeostasis, mitochondrial membrane potential, and ATP levels.

Gender disparities in Parkinson's disease

Parkinson's disease is a chronic neurodegenerative disorder of unknown etiology. There are sparse data on gender differences in this disorder, but it is clear that there are gender discrepancies in incidence, symptoms, medication effects and treatments. There also appear to be lifecycle fluctuations in the disease course of female Parkinson's disease patients. The effect of estrogen in this disorder is multifold and its role in the development and treatment of PD will be discussed.

Differential modulation of estrogen receptors (ERs) in ischemic brain injury: a role for ERalpha in estradiol-mediated protection against delayed cell death

Estradiol enhances plasticity and survival of the injured brain. Our previous work demonstrates that physiological levels of estradiol protect against cerebral ischemia in the young and aging brain through actions involving estrogen receptors (ERs) and alterations in gene expression. The major goal of this study was to establish mechanisms of neuroprotective actions induced by low levels of estradiol. We first examined effects of estradiol on the time-dependent evolution of ischemic brain injury. Because estradiol is known to influence apoptosis, we hypothesized that it acts to decrease the delayed phase of cell death observed after middle cerebral artery occlusion (MCAO). Furthermore, because ERs are pivotal to neuroprotection, we examined the temporal expression profiles of both ER subtypes, ERalpha and ERbeta, after MCAO and delineated potential roles for each receptor in estradiol-mediated neuroprotection. We quantified cell death in brains at various times after MCAO and analyzed ER expression by RT-PCR, in situ hybridization, and immunohistochemistry. We found that during the first 24 h, the mechanisms of estradiol-induced neuroprotection after MCAO are limited to attenuation of delayed cell death and do not influence immediate cell death. Furthermore, we discovered that ERs exhibit distinctly divergent profiles of expression over the evolution of injury, with ERalpha induction occurring early and ERbeta modulation occurring later. Finally, we provide evidence for a new and functional role for ERalpha in estradiol-mediated protection of the injured brain. These findings indicate that physiological levels of estradiol protect against delayed cell death after stroke-like injury through mechanisms requiring ERalpha.

Gender-related differences in recovery of locomotor function after spinal cord injury in mice

STUDY DESIGN

In order to study the role of gender in recovery, we induced a thoracic compression spinal cord injury (SCI) separately in 2-month-old male and female C57Bl/6 mice.

OBJECTIVES

We intended to assess effects of gender on recovery of hindlimb motor function and to correlate these with histomorphologic profiles of injured spinal cord tissue.

METHODS

Locomotor function was evaluated by three means: a modified locomotor scoring system for rodents, beam walking and computerized activity meter. Histology was analyzed by comparison of hematoxylin and eosin-stained perfused specimens.

RESULTS

Locomotor scores were 2.2+/-0.9 on day 1 in male mice, while, in contrast, they were significantly higher, 7.3+/-1.7, in females (P<0.02). On day 14 Basso, Beattie and Bresnahan scores were 9.5+/-2.2 in male mice and 16.0+/-2.2 in females (P<0.03). Terminal histology showed that the spinal cord architecture was relatively better preserved in female mice and that the extent of necrosis and infiltration of inflammatory cells was less compared to males.

SETTING

Neurobiology Research Laboratory of University of Kansas Medical School in US Department of Veterans Affairs Medical Center, Kansas City, Missouri.

CONCLUSION

We found that the severity of the initial injury as well as the ultimate recovery of motor function after SCI is significantly influenced by gender, being remarkably better in females. The mechanism(s) of neuroprotection in females, although not yet elucidated, may be associated with the effects of estrogen on pathophysiological processes (blood flow, leukocyte migration inhibition, antioxidant properties, and inhibition of apoptosis).

SPONSORSHIP

Medical Research, US Department of Veterans Affairs, the Christopher Reeve Paralysis Foundation and NIH.

Estradiol alters only GAD67 mRNA levels in ischemic rat brain with no consequent effects on GABA

The present study tested the hypothesis that estradiol reduces tissue infarction after middle cerebral artery occlusion (MCAO) in estradiol-deficient females by augmenting glutamic acid decarboxylase (GAD) expression and thus activity, leading to increases in gamma-amino-butyric acid (GABA) tissue levels. Glutamic acid decarboxylase is the principal enzyme for GABA synthesis and has two isoforms, GAD65 and GAD67, which differ in size and cellular distribution. Rats were ovariectomized 7 to 8 days before receiving no hormone, placebo, or 25 microg estradiol via subcutaneous implant 7 to 10 days before harvesting tissue in either ischemic cohorts after 2 h of MCAO (end-ischemia) or in nonischemic cohorts. Selected cortical and striatal regions were microdissected from harvested brains. GAD65/67 mRNA levels were determined by microlysate ribonuclease protection assay. End-ischemic GABA concentrations were determined by HPLC. Steroid treatment selectively decreased ischemic cortical GAD67 mRNA levels. In most brain regions evaluated, regional GABA concentrations increased with ischemia regardless of treatment. Estradiol blocked MCAO-induced increases in GABA concentration only in dorsomedial cortex. These data suggest that estradiol repletion in ischemic rat brain selectively decreases GAD67 mRNA levels but does not alter steady-state GABA concentrations. It may be that estradiol under ischemic conditions is attenuating GABA metabolism rather than enhancing synthesis or is augmenting other aspects of GABAergic transmission such as GABA transporters and receptors.

Estrogen down-regulates glial activation in male mice following 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine intoxication

Emerging evidence suggests beneficial effect of estrogen for Parkinson's disease (PD), yet the exact mechanisms implicated remain obscured. Activated glia observed in MPTP mouse model and in PD may participate in the cascade of deleterious events that ultimately leads to dopaminergic nigral neuronal death. In vitro studies demonstrate that estrogen can modify the microglial and astroglial expression of inflammatory mediator, such as cytokines and chemokines implicated in neuroinflammation and neurodegeneration. To determine whether estrogen-elicited neuroprotection in PD is mediated through glia, adult male C57Bl/6 mice were treated with 17beta-estradiol (E2) for a total of 11 days. Following 5 days of pretreatment with E2, they were injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on the sixth day. The brains were collected on day 11. Immunohistochemistry and quantitative study were used to assess the number of tyrosine hydroxylase-immunoreactive (TH-IR) neurons in the substantia nigra pars compacta (SNpc) and that of activated astrocytes and activated microglia in the SNpc and the striatum. Pretreatment with E2 decreased the loss of TH-IR nigral neurons and diminished the deficit of TH-IR striatal fibers triggered by MPTP. The neuroprotective effect of E2 was coincident with an attenuation of a glial response within the nigra and the striatum. These findings suggest that the neuroprotective effects of E2 evidenced in MPTP mouse model might mediate through an inhibition of reactive glia. However, direct neuroprotective effects of E2 upon TH-IR neurons cannot be excluded.

Multiple pathways transmit neuroprotective effects of gonadal steroids

Numerous preclinical studies suggest that gonadal steroids, particularly estrogen, may be neuroprotective against insult or disease progression. This paper reviews the mechanisms contributing to estrogen-mediated neuroprotection. Rapid signaling pathways, such as MAPK, PI3K, Akt, and PKC, are required for estrogen's ability to provide neuroprotection. These rapid signaling pathways converge on genomic pathways to modulate transcription of E2-responsive genes via ERE-dependent and ERE-independent mechanisms. It is clear that both rapid signaling and transcription are important for estrogen's neuroprotective effects. A mechanistic understanding of estrogen-mediated neuroprotection is crucial for the development of therapeutic interventions that enhance quality of life without deleterious side effects.

The role of the phosphatidylinositide 3-kinase–protein kinase B pathway in schizophrenia

Neuroanatomical studies of brains from schizophrenic patients report evidence for neuronal dystrophy, while in genetic studies in schizophrenia there is evidence for mutations in growth factors and the downstream enzymes phosphatidylinositide 3-kinase (PI3K) and protein kinase B (PKB). Since the PI3K-PKB pathway is involved in cellular growth and proliferation, reduced activity of this cascade in schizophrenia could at least partly explain the neuronal dystrophy. Risk factors for schizophrenia, such as corticosteroids and cannabis, suppress the activity of the PI3K-PKB pathway. Conversely, estrogen and vitamin D, 2 factors with a moderate protective activity in schizophrenia, electroconvulsive shock therapy, and chronic treatment with antipsychotic compounds stimulate the pathway. Reduced activity of the PI3K-PKB pathway makes the brain more susceptible to virus infections, anoxia, and obstetric complications (recognized risk factors for schizophrenia), whereas a diminution of growth factor levels towards the end of puberty could contribute to an increase in schizophrenia symptoms observed around that time. On the other hand, constitutive (over)activation of the PI3K-PKB pathway increases cancer risk. Consequently, the presumed hypoactivity of the PI3K-PKB cascade might provide a partial explanation for the remarkable epidemiological finding of a reduced cancer rate in schizophrenic patients. Recognition of the role of a dysfunctional PI3K-PKB pathway in schizophrenia might help in the discovery of hitherto undetected causative gene mutations and could also lead to novel therapeutic approaches. However, a major challenge that remains to be solved is how the PI3K-PKB pathway can be activated without increasing the risk of cancer.

Dehydroepiandrosterone sulfate is neuroprotective when administered either before or after injury in a focal cortical cold lesion model

Dehydroepiandrosterone and its sulfate (DHEAS) are sex hormone precursors that exert marked neurotrophic and/or neuroprotective activity in the central nervous system. The present study evaluated the effects of DHEAS and 17beta-estradiol (E2) in a focal cortical cold lesion model, in which DHEAS (50 mg/kg, sc) and E2 (35 mg/kg, sc) were administered either as pretreatment (two subsequent injections 1 d and 1 h before lesion induction) or posttreatment (immediately after lesion induction). The focal cortical cold lesion was induced in the primary motor cortex by means of a cooled copper cylinder placed directly onto the cortical surface. One hour later, the animals were killed, the brains cut into 0.4-mm-thick slices, and the sections stained with 1% triphenyltetrazolium chloride. The volume of the hemispheric lesion was calculated for each animal. The results demonstrated that the lesion area was significantly attenuated in both the DHEAS- and E2- pre- and posttreated groups and that in the presence of letrozole, a nonsteroidal aromatase inhibitor, no neuroprotection was observed, suggesting that the beneficial effect of DHEAS on the cold injury might depend on the conversion of DHEAS to E2 within the brain. It is concluded that even a single posttraumatic administration of DHEAS may be of substantial therapeutic benefit in the treatment of focal brain injury with vasogenic edema.

Estrogen Modulates Bcl-2 Family Proteins in Ischemic Brain Injury

Estradiol acts as a neuroprotective factor against brain injury. This study investigated whether estradiol modulates the Bcl-2 family proteins in ischemic brain injury. Adult female rats were ovariectomized and treated with estradiol prior to middle cerebral artery occlusion (MCAO). Brains were collected 24 hr after MCAO, and infarct volumes were analyzed. Estradiol significantly reduces the infarct volume and decreases the positive cells of TUNEL staining in cerebral cortex. In ischemic cerebral cortex, the level of Bcl-2 was decreased, and the level of Bax was significantly increased. Estradiol prevents the injury-induced decrease of Bcl-2 and increase of Bax. In conclusion, our findings suggest that estradiol plays a potent protective role in brain injury through the regulation of Bcl-2 family proteins.

Endogenously expressed estrogen receptors mediate neuroprotection in hippocampal cells (HT22)

Discovery of estrogen receptors (ER) in the central nervous system and the ability of estrogens to modulate neural circuitry and act as neurotrophic factors, suggest a therapeutic role of this steroid. To gain better understanding of the specificity and cellular mechanisms involved in estrogen-mediated neuroprotection, a mouse hippocampal neuronal cell line (HT22) was evaluated. Earlier reports indicated this cell line was devoid of ERs. Contrary to these findings, characterization of HT22 cells using RT-PCR, immunoblot, immunocytochemical, and radioligand binding techniques revealed endogenous expression of ER. The predominant subtype appeared to be ERalpha with functional activity confirmed using an ERE-tk-luciferase assay. The ability of an ER antagonist, ICI-182780, to block the neuroprotective effects of estrogens confirmed ER was involved mechanistically in neuroprotection. In conclusion, HT22 cells express functional ERalpha or a closely related ER enabling this cell line to be used to profile estrogens for neuroprotective properties acting via an ER-dependent mechanism.

From clinical evidence to molecular mechanisms underlying neuroprotection afforded by estrogens

Recent studies have highlighted that female sex hormones represent potential neuroprotective agents against damage produced by acute and chronic injuries in the adult brain. Clinical reports have documented the effectiveness of estrogens to attenuate symptoms associated with Parkinson's disease, and to reduce the risk of Alzheimer's disease and cerebrovascular stroke. This evidence is corroborated by numerous experimental studies documenting the protective role of female sex hormones both in vitro and in vivo. Accordingly, estrogens have been shown to promote survival and differentiation of several neuronal populations maintained in culture, and to reduce cell death associated with excitotoxicity, oxidative stress, serum deprivation or exposure to beta-amyloid. The neuroprotective effects of estrogens have been widely documented in animal models of neurological disorders, such as Alzheimer's and Parkinson's diseases, as well as cerebral ischemia. Although estrogens are known to exert several direct effects on neurones, the cellular and molecular mechanisms implicated in their protective actions on the brain are not completely understood. Thus, on the basis of clinical and experimental evidence, in this review, we discuss recent findings concerning the neuronal effects of estrogens that may contribute to their neuroprotective actions. Both estrogen receptor-dependent and -independent mechanisms will be described. These include modulation of cell death regulators, such as Bcl-2, Akt and calpain, as well as interaction with growth factors, such as BDNF, NGF, IGF-I and their receptors. The anti-inflammatory effects of estrogens will also be described, namely their ability to reduce brain levels of inflammatory mediators, cytokines and chemokines. Finally, a brief overview about receptor-independent mechanisms of neuroprotection will aim at describing the antioxidant effects of estrogens, as well as their ability to modulate neurotransmission.

Sex differences and the effect of hormonal therapy on ischemic brain injury

Epidemiological data emphasize the importance of sex differences in the mortality and morbidity of stroke and cardiovascular disease. The importance of hormonal influences on stroke outcome has pointed out the importance of gender, age, and presence of neural hormones. This clinical data has been substantiated by various experimental studies using clinically relevant models of cerebral ischemia and stroke. Published findings emphasize that male and female animals respond differently to periods of cerebral ischemia and that various combinations of hormonal treatments can provide protection, both histopathological and behavioral. Mechanisms underlying the hormonal effects on ischemic outcome are multifactorial. These include effects on vascular integrity and cerebral blood flow, excitotoxicity, oxidation pathways, inflammation, and apoptosis. Although many studies have shown positive results with hormonal treatments, negative findings have also been presented. Explanations for the limitations of hormonal treatment include uncertainties regarding therapeutic window, specific therapeutic dose range, as well as the specific pathophysiological processes being targeted. Additional studies are therefore required to clarify under what conditions hormonal therapy is most protective or not warranted. Experimental studies utilizing a variety of cerebral ischemia and stroke models are reviewed to indicate under what conditions sex differences and hormonal therapy are most important in terms of functional outcome.

Gonadal steroids differentially modulate neurotoxicity of HIV and cocaine: testosterone and ICI 182,780 sensitive mechanism

Background

HIV Associated Dementia (HAD) is a common complication of human immunodeficiency virus (HIV) infection that erodes the quality of life for patients and burdens health care providers. Intravenous drug use is a major route of HIV transmission, and drug use is associated with increased HAD. Specific proteins released as a consequence of HIV infection (e.g., gp120, the HIV envelope protein and Tat, the nuclear transactivating protein) have been implicated in the pathogenesis of HAD. In primary cultures of human fetal brain tissue, subtoxic doses of gp120 and Tat are capable of interacting with a physiologically relevant dose of cocaine, to produce a significant synergistic neurotoxicity. Using this model system, the neuroprotective potential of gonadal steroids was investigated.

Results

17β-Estradiol (17β-E₂), but not 17α-estradiol (17α-E₂), was protective against this combined neurotoxicity. Progesterone (PROG) afforded limited neuroprotection, as did dihydrotestosterone (DHT). The efficacy of 5α-testosterone (T)-mediated neuroprotection was robust, similar to that provided by 17β-E_2. In the presence of the specific estrogen receptor (ER) antagonist, ICI-182,780, T's neuroprotection was completely blocked. Thus, T acts through the ER to provide neuroprotection against HIV proteins and cocaine. Interestingly, cholesterol also demonstrated concentration-dependent neuroprotection, possibly attributable to cholesterol's serving as a steroid hormone precursor in neurons.

Conclusion

Collectively, the present data indicate that cocaine has a robust interaction with the HIV proteins gp120 and Tat that produces severe neurotoxicity, and this toxicity can be blocked through pretreatment with ER agonists.

Lack of a Gender Difference in Post-Traumatic Neurodegeneration in the Mouse Controlled Cortical Impact Injury Model

Recent studies using a mouse model of weight-drop-induced "diffuse" traumatic brain injury (TBI) have demonstrated a substantial gender difference in the time course and magnitude of post-traumatic neurodegeneration following a severe level of injury. The time of maximal damage, as assessed by the de Olmos aminocupric silver staining method, occurred at 72 h in male mice, whereas the peak of neurodegeneration was not observed until 14 days in females and was less in magnitude compared to males. This difference, favoring females, has been postulated to relate to the neuroprotective actions of estrogen and progesterone. In the presently reported experiments, we compared the time course and peak of neurodegeneration in male and female mice after a severe level of "focal" controlled cortical impact (CCI; 1 mm, 3.5 m/sec) TBI using the same strain (CF-1) and weight (29-31 g) as employed in the "diffuse" TBI study. The volume of silver staining was measured using image analysis methods at 24, 48, and 72 h, and 1, 2 and 4 weeks. In male and female mice, a significant increase in neurodegeneration was observed at 24 h, and the volume was not significantly different between the two genders. In both gender groups, the maximal neurodegeneration was seen at 48 h after injury. Although the female mice exhibited a trend toward higher mean volumes of silver staining, this difference was not significantly different compared to males. Furthermore, the rate of resolution of staining between 48 h and 4 weeks was similar. However, injured females still exhibited a significantly higher volume of staining compared to sham, non-injured females at 4 weeks, whereas the difference in staining volume between sham and injured males was no longer significant at that time point. These results show that, following a "focal" CCI, there is no gender difference that favors females, in contrast to that seen with the "diffuse" injury paradigm. The disparity between the effects of gender in the two models may be due to the fact that, in the "focal" CCI model, the timing of post-traumatic neurodegeneration is significantly more rapid than that seen in the "diffuse" model, which may overwhelm the neuroprotective effects of estrogen and progesterone and obscure the appearance of a gender difference.

Neuroprotective Anti-Apoptosis Effect of Estrogens in Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading cause of death and functional disability in western countries, affecting mostly young patients. Despite intense and sustained efforts deployed for the development of new therapeutic strategies, no clinical benefit has been shown by any of the investigated compounds. Increasing attention has been drawn during the past two decades to the neuroprotective effects of estrogens, although most of the available data relate to ischemic brain injury. The purpose of the present study was to investigate the potential neuroprotective value of estrogens in TBI as a therapeutic modality. For this purpose, a contusion was created in the parietal cortex by dynamic cortical deformation in two groups of 10 Sprague-Dawley male rats. Following the injury, treated animals received conjugated estrogens for 3 days, using a subcutaneously implanted osmotic pump. Animals were then sacrificed, and TUNEL, anti-active Caspase 3, bcl-2, and bax labeling were performed in paraffin-embedded brain sections, allowing for comparative and quantitative analysis. In estrogen-treated animals, there was a marked and significant reduction of apoptosis in comparison with non-treated animals. The reduction in TUNEL and active Caspase 3 staining was similar and close to 50%. Optical analysis of histological slides prepared by bcl-2 labeling showed a significant increase in bcl-2 expression in estrogen-treated animals compared to non-treated animals. On the contrary, bax expression was not influenced by hormonal treatment, and no difference could be noticed between the two groups. These results support the potential therapeutic value of estrogens in TBI and further clarify their mode of action.

Estrogen neuroprotection against the neurotoxic effects of ethanol withdrawal: potential mechanisms

Ethanol withdrawal (EW) produces substantial neurotoxic effects, whereas estrogen is neuroprotective. Given observations that both human and nonhuman female subjects often show less impairment following EW, it is reasonable to hypothesize that estrogens may protect females from the neurotoxic effects of ethanol. This article is based on the assumption that the behavioral deficits seen following EW are produced in part by neuronal death triggered by oxidative insults produced by EW. The EW leads to activation of protein kinase C, especially PKCepsilon, which subsequently triggers apoptotic downstream events such as phosphorylation of nuclear factor-kappaB (NFkappaB) complex. On phosphorylation, active NFkappaB translocates to the nucleus, binds to DNA, and activates caspases, which trigger DNA fragmentation and apoptosis. In contrast, estrogens are antioxidant, inhibit overexpression of PKCepsilon, and suppress expression of NFkappaB and caspases. Estrogen treatment reduces the behavioral deficits seen during EW and attenuates molecular signals of apoptosis. The effects of ethanol and estrogen on each step in the signaling cascade from ethanol exposure to apoptosis are reviewed, and potential mechanisms by which estrogen could produce neuronal protection against the neurotoxicity produced by EW are identified. These studies serve as a guide for continuing research into the mechanisms of the neuroprotective effects of estrogen during EW and for the development of potential estrogen-based treatments for male and female alcoholics.

Estradiol Protects Against Oxygen and Glucose Deprivation in Rat Hippocampal Organotypic Cultures and Activates Akt and Inactivates GSK-3?

Here we investigated the neuroprotective effect of 17beta-estradiol in an in vitro model of ischemia. We used organotypic hippocampal slice cultures, acute or chronically treated with 17beta-estradiol (10 nM), and exposed to oxygen and glucose deprivation (OGD). Cellular death was quantified by measuring uptake of propidium iodide (PI), a marker of dead cells. In OGD exposed cultures, treated only with vehicle, about 70% of the CA1 area of hippocampus was labeled with PI, indicating a great percentage of cellular death. When cultures were treated with 17beta-estradiol (acute or chronically), this cellular death was reduced to 15%. This effect was prevented by LY294002 but was not by PD98059. Immunoblotting revealed that both, chronic and acute, treatments with 17beta-estradiol induced the phosphorylation/activation of Akt and the phosphorylation/inactivation of GSK-3beta. Our results show a clear neuroprotective effect of 17beta-estradiol and suggest that this effect could involve PI3-K pathway.

Estradiol reduces cytochrome c translocation and minimizes hippocampal damage caused by transient global ischemia in rat

It is well-established that 17beta-estradiol (17beta-E(2)) confers neuroprotection to male and female rats exposed to focal cerebral ischemia, while less is known about the effects of the hormone under conditions of transient global ischemia. Since translocation of cytochrome c from the mitochondria to the cytosol is a critical step in apoptotic cell death after cerebral ischemia, we have investigated whether 17beta-E(2) interferes with such mechanism to exert neuroprotection. Global ischemia, induced in male Wistar rats by 5-min 4 vessel occlusion (4VO), resulted in a significant increase of cytosolic cytochrome c (cyt-c) levels as detected by Western blotting at 6h after reperfusion. 17beta-E(2) (0.2mg/kg, i.p.) given 1h before ischemia minimized cytochrome c translocation and the latter effect was partially reversed by tamoxifen (0.25mg/kg, i.p.). Bilateral cell counting revealed that delayed hippocampal damage typically caused by 4VO was abolished by 17beta-E(2) and this was partially reversed by tamoxifen in the CA3 subregion, but not in CA1/CA2 or CA4. These findings provide the original observation that 17beta-E(2) reduces delayed hippocampal damage caused by 4VO in male rats and blocks cytochrome c translocation during the early stages of neuronal death, thus providing an important mechanism involved in estrogen-mediated neuroprotection.

17beta-estradiol protects oligodendrocytes from cytotoxicity induced cell death

During pregnancy, changes in circulating levels of hormones, including estrogens, correlates with a significant decrease in the relapse incidence in women with Multiple Sclerosis (MS). In the present study, we demonstrate that both primary and cell line cultures of rat oligodendrocytes express the estrogen receptor (ER)-alpha and ERbeta estrogen receptors in the cytosol and nucleus, and that nuclear compartmentalization becomes more pronounced as the cells mature. Moreover, 17beta-estradiol significantly decreases the cytotoxic effects of the peroxynitrite generator 3-(4-morpholinyl)-sydnonimine (SIN-1) in both immature and mature oligodendrocytes in a dose dependent manner. This protective mechanism requires pretreatment with 17beta-estradiol and is blocked by ICI 182,780, a selective ERalpha/ERbeta antagonist. These results strongly suggest that 17beta-estradiol protects oligodendrocytes against SIN-1 mediated cytotoxicity through the activation of the estrogen receptors and provides new insights into the roles of the estrogen signaling pathways in myelin forming cells that are lost in demyelinating disorders.

Estrogen and neuroprotection: higher constitutive expression of glutaredoxin in female mice offers protection against MPTP-mediated neurodegeneration

Incidence of Parkinson's disease is lower in women as compared with men. Although neuroprotective effect of estrogen is recognized, the underlying molecular mechanisms are unclear. MPTP (1-methyl-4-phenyl-1, 2, 3, 6, tetrahydro-pyridine), a neurotoxin that causes Parkinson's disease-like symptoms acts through inhibition of mitochondrial complex I. Administration of MPTP to male mice results in loss of dopaminergic neurons in substantia nigra, whereas female mice are unaffected. Oxidation of critical thiol groups by MPTP disrupts mitochondrial complex I, and up-regulation of glutaredoxin (a thiol disulfide oxidoreductase) is essential for recovery of complex I. Early events following MPTP exposure, such as increased AP1 transcription, loss of glutathione, and up-regulation of glutaredoxin mRNA is seen only in male mice, indicating that early response to neurotoxic insult does not occur in females. Pretreatment of female mice with ICI 182,780, estrogen receptor (ER) antagonist sensitizes them to MPTP-mediated complex I dysfunction. Constitutive expression of glutaredoxin is significantly higher in female mice as compared with males. ICI 182,780 down-regulates glutaredoxin activity in female mouse brain regions (midbrain and striatum), indicating that glutaredoxin expression is regulated through estrogen receptor signaling. Higher constitutive expression of glutaredoxin could potentially contribute to the neuroprotection seen in female mouse following exposure to neurotoxins, such as MPTP.

Systemic Administration of 17β-Estradiol Reduces Apoptotic Cell Death and Improves Functional Recovery following Traumatic Spinal Cord Injury in Rats

Recent evidence indicates that estrogen exerts neuroprotective effects in both brain injury and neurodegenerative diseases. We examined the protective effect of estrogen on functional recovery after spinal cord injury (SCI) in rats. 17beta-estradiol (3, 100, or 300 microg/kg) was administered intravenously 1-2 h prior to injury (pre-treatment), and animals were then subjected to a mild, weight-drop spinal cord contusion injury. Estradiol treatment significantly improved hind limb motor function as determined by the Basso-Beattie-Bresnahan (BBB) locomotor open field behavioral rating test. Fifteen to 30 days after SCI, BBB scores were significantly higher in estradiol-treated (100 microg/kg) rats when compared to vehicle-treated rats. Morphological analysis showed that lesion sizes increased progressively in either vehicle-treated or 17beta-estradiol-treated spinal cords. However, in response to treatment with 17beta-estradiol, the lesion size was significantly reduced 18-28 days after SCI when compared to vehicle-treated controls. Terminal deoxynucleotidyl transferase-mediated UTP nickend labeling (TUNEL) staining and DNA gel electrophoresis revealed that apoptotic cell death peaked 24-48 h after injury. Also, SCI induced a marked increase in activated caspase-3 in the spinal cord, evident by 4 h after injury. However, administration of 17beta-estradiol significantly reduced the SCI-induced increase in apoptotic cell death and caspase-3 activity after SCI. Furthermore, 17beta-estradiol significantly increased expression of the anti-apoptotic genes, bcl-2 and bcl-x, after SCI while expression of the pro-apoptotic genes, bad and bax, was not affected by drug treatment. Finally, intravenous administration of 17beta-estradiol (100 microg/kg) immediately after injury (post-treatment) also significantly improved hind limb motor function 19-30 days after SCI compared to vehicle-treated controls. These data suggest that after SCI, 17 beta-estradiol treatment improved functional recovery in the injured rat, in part, by reducing apoptotic cell death.

Estrogen interacts with the IGF-1 system to protect nigrostriatal dopamine and maintain motoric behavior after 6-hydroxdopamine lesions

The most prominent neurochemical hallmark of Parkinson's disease (PD) is the loss of nigrostriatal dopamine (DA). Animal models of PD have concentrated on depleting DA and therapies have focused on maintaining or restoring DA. Within this context estrogen protects against 6-hydroxdopamine (6-OHDA) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesions of the nigrostriatal DA pathway. Present studies tested the hypothesis that neuroprotective estrogen actions involve activation of the insulin-like growth factor-1 (IGF-1) system. Ovariectomized rats were treated with either a single subcutaneous injection of 17beta-estradiol benzoate or centrally or peripherally IGF-1. All rats were infused unilaterally with 6-OHDA into the medial forebrain bundle (MFB) to lesion the nigrostriatal DA pathway. Tyrosine hydroxylase (TH) immunocytochemistry confirmed that rats injected with 6-OHDA had a massive loss of TH immunoreactivity in both the ipsilateral substantia nigra compacta (60% loss) and the striatum (>95% loss) compared to the contralateral side. Loss of TH immunoreactivity was correlated with loss of asymmetric forelimb movements, a behavioral assay for motor deficits. Pretreatment with estrogen or IGF-1 significantly prevented 6-OHDA-induced loss of substantia nigra compacta neurons (20% loss) and TH immunoreactivity in DA fibers in the striatum (<20% loss) and prevented the loss of asymmetric forelimb use. Blockage of IGF-1 receptors by intracerebroventricular JB-1, an IGF-1 receptor antagonist, attenuated both estrogen and IGF-1 neuroprotection of nigrostriatal DA neurons and motor behavior. These findings suggest that IGF-1 and estrogen acting through the IGF-1 system may be critical for neuroprotective effects of estrogen on nigrostriatal DA neurons in this model of PD.

Anatomic evaluation of the orbitofrontal cortex in major depressive disorder

BACKGROUND

The orbitofrontal cortex (OFC) plays a major role in neuropsychologic functioning including exteroceptive and interoceptive information coding, reward-guided behavior, impulse control, and mood regulation. This study examined the OFC and its subdivisions in patients with MDD and matched healthy control subjects.

METHODS

Magnetic resonance imaging (MRI) was performed on 31 unmedicated MDD and 34 control subjects matched for age, gender, and race. Gray matter volumes of the OFC and its lateral and medial subdivisions were measured blindly.

RESULTS

The MDD patients had smaller gray matter volumes in right medial [two-way analysis of covariance F(1,60) = 4.285; p =.043] and left lateral OFC [F(1,60) = 4.252; p =.044]. Left lateral OFC volume correlated negatively with age in patients but not in control subjects. Male, but not female patients exhibited smaller left and right medial OFC volumes compared with healthy control subjects of the same gender.

CONCLUSIONS

These findings suggest that patients with MDD have reduced OFC gray matter volumes. Although this reduction might be important in understanding the pathophysiology of MDD, its functional and psychopathologic consequences are as yet unclear. Future studies examining the relationship between specific symptomatic dimensions of MDD and OFC volumes could be especially informative.

Effects of estrone on N-METHYL-d-aspartic acid- and staurosporine-induced changes in caspase-3-like protease activity and lactate dehydrogenase-release: time- and tissue-dependent effects in neuronal primary cultures

A growing body of evidence indicates that estrogens affect apoptotic processes in neuronal cells. However, their effects seem to depend on type of neuronal tissue, stage of development and apoptosis inducing factors. In the present study we compared effects of estrone (100 and 500 nM) on N-methyl-D-aspartic acid (NMDA) (1 mM)- and staurosporine (1 microM)-induced caspase-3-like activity and lactate dehydrogenase (LDH)-release in primary cultures of rat hippocampal and neocortical neurons. Fluorometric and colorimetric determination of enzyme activity was performed 6 h, 14 h, and 24 h after exposure to apoptotic agents. In the hippocampal cell cultures on 7 days in vitro (DIV), a time-dependent NMDA-induced activation of caspase-3-like proteases was accompanied by increased LDH-release. In neocortical cell cultures on 7 DIV NMDA did not affect caspase activity and decreased LDH-release. In neocortical cell cultures on 12 DIV NMDA inhibited spontaneous caspase activity, but was toxic to neurons after 24 h exposure suggesting that these cells underwent necrotic rather than apoptotic death. Estrone has attenuated both pro- and anti-apoptotic NMDA-induced changes in rat primary neuronal cultures acting independently of estrogen receptors, as detected with ICI 182, 780. In hippocampal neurons estrone antagonized not only the NMDA-induced caspase-3-like activity, but also NMDA-mediated LDH-release. However, in neocortical neurons estrone either attenuated NMDA-induced inhibition of caspase-3-like activity (12 DIV) or partly blocked NMDA-mediated decrease in LDH-release (7 DIV). In contrast to NMDA, staurosporine elevated caspase-3-like activity and LDH-release in a time-dependent manner in all used culture systems. Estrone inhibited pro-apoptotic effects of staurosporine in neocortical neurons, but only at later stage of development in vitro, which points to the protective role of estrogens during the brain tissue maturation. Since estrone triggered its effects via non-genomic mechanisms, it suggests that the other estradiol metabolites exhibiting low affinity to hormone receptors may be potent neuroprotective agents, which could retain the favorable and minimize the adverse side effects of estrogens.

Neuroimmunoprotective effects of estrogen and derivatives in experimental autoimmune encephalomyelitis: Therapeutic implications for multiple sclerosis

The extensive literature and the work from our laboratory illustrate the large number of complex processes affected by estrogen that might contribute to the striking ability of 17beta-estradiol (E2) and its derivatives to inhibit clinical and histological signs of experimental autoimmune encephalomyelitis (EAE) in mice. These effects require sustained exposure to relatively low doses of exogenous hormone and offer better protection when initiated prior to induction of EAE. However, oral ethinyl estradiol (EE) and fluasterone, which lacks estrogenic side effects, could partially reverse clinical EAE when given after the onset of disease. The three main areas discussed in this review include E2-mediated inhibition of encephalitogenic T cells, inhibition of cell migration into central nervous system tissue, and neuroprotective effects that promote axon and myelin survival. E2 effects on EAE were mediated through Esr1 (alpha receptor for E2) but not Esr2 (beta receptor for E2), as were its antiinflammatory and neuroprotective effects. A novel finding is that E2 up-regulated the expression of Foxp3 and CTLA-4 that contribute to the activity of CD4+CD25+ Treg cells. The protective effects of E2 in EAE suggest its use as therapy for MS, although the risk of cardiovascular disease may complicate treatment in postmenopausal women. This risk could be minimized by using subpregnancy levels of exogenous E2 that produced synergistic effects when used in combination another immunoregulatory therapy. Alternatively, one might envision using EE or fluasterone metabolites alone or in combination therapies in both male and female MS patients.

Role of the GABAA system in behavioral, motoric, and cerebellar protection by estrogen during ethanol withdrawal

Results of studies from our laboratory have shown that administration of 17beta-estradiol (E(2)) reduces cerebellar neuronal damage during ethanol withdrawal (EW). In the current study, we investigated whether the GABAergic system is involved in the protective effects of E(2) against the EW syndrome. To test this hypothesis, we examined the effects of GABAergic drugs, with and without E(2), on EW sign scores, motoric capacity, and caspase activation. Ovariectomized rats implanted with an E(2) or an oil pellet received liquid ethanol [7.5% weight/volume (wt./vol.)] for 5 weeks or dextrin diet, followed by 2 weeks of EW. A gamma-aminobutyric acid type A (GABA(A)) agonist, muscimol (0.125 or 0.25 mg/kg), and antagonist, bicuculline (1.25 mg/kg), were administered (intraperitoneally; three times a day for 4 days) starting 1 day before the onset of EW. On termination of chronic administration of ethanol diet, rats were tested for overt withdrawal signs and latency to fall from a rotarod. The initial latency was measured separately to assess motoric capacity before learning occurred. Cerebelli were subsequently collected for immunohistochemistry to detect caspase activation. Results showed that treatment with E(2) lowered EW sign scores and improved initial as well as subsequent rotarod latencies compared with findings without treatment with E(2) (control group). These effects of E(2) were enhanced by combined treatment with muscimol and diminished by bicuculline. Results also showed that ethanol-withdrawn rats had more caspase-3-positive cells than observed for the dextrin diet-fed group in a manner reversed by E(2) and exacerbated by bicuculline. Bicuculline also caused partial antagonism of the protective effect of E(2). These findings support the suggestion that GABA(A) agonists ameliorate, and GABA(A) antagonists exacerbate, EW signs, cerebellar neuronal damage, and motoric impairment in ethanol-withdrawn rats. Also, results of the current study provide indirect evidence that the GABAergic system is involved in protective effects of E(2) against the EW syndrome.

Sex differences in response to kainic acid and estradiol in the hippocampus of newborn rats

Premature and full-term human infants are at considerable risk of excitotoxic-mediated brain damage due to hypoxia-ischemia, infection or other trauma. Glutamate receptor activation is a major source of excitoxicity in the adult and developing brain, and the hippocampus is particularly vulnerable to damage. The seven-day-old rat is a widely used model of pediatric brain damage, in large part due to the relative insensitivity of the brain to exogenous glutamate treatment prior to this age. We have reexamined the possible role of glutamate in pediatric brain damage in the newborn rat using kainic acid treatment and attending to the sex of the animal as well as the effects of pretreatment with the gonadal steroid estradiol. Consistent with previous studies, we found no evidence of damage 7 days posttreatment in the CA1 region of the hippocampus in males or females. There was also little to no damage in the CA2/3 or dentate gyrus of males. In females, however, kainic-acid treatment induced substantial damage in the dentate gyrus and moderate damage in CA2/3, as assessed by neuron number and regional volume. Pretreatment with estradiol was protective against kainic acid-induced damage in females but was permissive for damage in the dentate gyrus of males. Estradiol treatment in the absence of kainic acid treatment was also neuroprotective in females in that it increased neuron number and volume throughout the hippocampal formation, suggesting that the basis of the sex difference observed in hippocampal volume was hormonally mediated. There was no effect of exogenous estradiol given to males in the absence of kainic acid. We conclude that the newborn female rat brain, but not the male, is sensitive to glutamate-mediated toxicity and that gonadal steroids play a complex role in both naturally occurring sex differences in hippocampal volume and response to injury.

Cytoskeletal protein degradation and neurodegeneration evolves differently in males and females following experimental head injury

The resulting neuropathological degeneration that occurs following a traumatic brain injury (TBI) is a consequence of both immediate and secondary neurochemical sequelae. Proteolysis of cytoskeletal proteins, triggered by calcium-mediated events, is believed to be a particularly significant contributor to TBI-induced neuronal death. To date, efforts to associate cytoskeletal degradation and neurodegeneration in TBI have been primarily qualitative or semiquantitative. The objectives of this study were (1). to quantitatively describe, over a posttraumatic time course, the relationship and mechanisms of cytoskeletal degradation (Western blot) and neurodegeneration (silver staining) in male and female mice following a moderately severe weight-drop impact-acceleration head injury; (2). to evaluate gender differences in the response to TBI; and (3). to examine the potential therapeutic window for future pharmacological treatment strategies. In male and female mice, we report a close correlation in the time courses of neurofilament M protein degradation and alpha-spectrin breakdown products (SBDP 150 and 145) with the peak magnitude of neurodegeneration, as quantified by silver staining. Evidence from the increased patterns of SBDPs suggests that both calpain and caspase-3 are involved. In general, males incurred peak protein degradation and neurodegeneration within 3 days after injury, while in females this did not occur until 14 days. The neuroprotective effects of estrogen are believed to be key factors in the superior outcome of female vs male mice following TBI. In mice, the therapeutic window of opportunity for pharmacological intervention aimed at limiting cytoskeletal degradation might be as much as 24 h following injury. Evidence of a protracted time course of cytoskeletal degradation, especially in females, suggests a potential for an extended treatment-duration following TBI.

Estrogen activates protein kinase C in neurons: role in neuroprotection

It has been previously demonstrated that estrogen can protect neurons from a variety of insults, including beta-amyloid (Abeta). Recent studies have shown that estrogen can rapidly modulate intracellular signaling pathways involved in cell survival. In particular, estrogen activates protein kinase C (PKC) in a variety of cell types. This enzyme plays a key role in many cellular events, including regulation of apoptosis. In this study, we show that 17beta-estradiol (E2) rapidly increases PKC activity in primary cultures of rat cerebrocortical neurons. A 1 h pre-treatment with E2 or phorbol-12-myristate-13-acetate (PMA), a potent activator of PKC, protects neurons against Abeta toxicity. Protection afforded by both PMA and E2 is blocked by pharmacological inhibitors of PKC. Further, depletion of PKC levels resulting from prolonged PMA exposure prevents subsequent E2 or PMA protection. Our results indicate that E2 activates PKC in neurons, and that PKC activation is an important step in estrogen protection against Abeta. These data provide new understanding into the mechanism(s) underlying estrogen neuroprotection, an action with therapeutic relevance to Alzheimer's disease and other age-related neurodegenerative disorders.

Estrogens: protective or risk factors in brain function?

Over the past century, the average lifespan of women has increased from 50 to over 80 years, but the age of the menopause has remained fixed at 51 years. This "change of life" is marked by a dramatic and permanent decrease in circulating levels of ovarian estrogens. Therefore, more women will live a greater proportion of their lives in a chronic hypoestrogenic state. Ovarian steroid hormones are pleiotropic and have multiple, diverse, and possibly opposing actions in different contexts. In light of recent reports of the possible health risks of hormone replacement therapy (HRT) on several different physiological systems, the question of whether estrogens are protective or risk factors must be carefully re-evaluated.

Estrogen receptor-mediated neuroprotection from oxidative stress requires activation of the mitogen-activated protein kinase pathway

It is well documented that estrogen mediates responses by both genomic and nongenomic mechanisms, both of which are important for cell survival. Because direct evidence showing that the estrogen receptors (ERs) alpha and/or beta can activate rapid signaling that may mediate neuroprotection is lacking, the hippocampal-derived cell line, HT22, was stably transfected with ERalpha (HTERalpha), ERbeta (HTERbeta), or a mutated form of ERalpha (HTERalphaHE27), which lacks the ability to mediate ER element-mediated transcription. Treatment of HT22, HTERalpha, HTERbeta, and HTERalphaHE27 cells with glutamate (5 mM) resulted in a significant decrease in cell viability. Pretreatment for 15 min with 10 nM 17beta-estradiol resulted in a 50% increase in the number of living cells in HTERalpha and HTERbeta cells but not in HT22 cells. The ER antagonist ICI 182,780 and the MEK inhibitor PD98059 prevented 17beta-estradiol-mediated protection. In HTERalphaHE27 cells, 17beta-estradiol rapidly phosphorylated ERK2 (within 15 min), in the absence of estrogen response element-mediated transcription. Treatment of HTERalphaHE27 cells with 10 nM 17beta-estradiol partially reversed the cell death produced by glutamate treatment. This study demonstrates that activation of either ERalpha or ERbeta can result in neuroprotection and that activation of the MAPK pathway is an important part of the neuroprotective mechanism.

Acute and chronic alterations in calcium homeostasis in 3-nitropropionic acid-treated human NT2-N neurons

3-Nitropropionic acid (3-NP), an irreversible inhibitor of succinate dehydrogenase, induced ATP depletion and both necrosis and apoptosis in human NT2-N neurons. Necrosis occurred predominantly within the first two days, and increased in a dose-dependent fashion with the concentration of 3-NP, whereas apoptosis was observed after 24 h or later at a similar rate in 0.1 mM and 5 mM 3-NP. We focused our efforts on intracellular calcium homeostasis during the first 48 h in 1 mM 3-NP, a period during which 10% of the neurons died by necrosis and 3% by apoptosis. All NT2-N neurons showed a stereotyped [Ca(2+)](i) rise, from 48+/-2 to 140+/-12 nM (mean +/-S.E.M.), during the first 2 h in 3-NP. Despite severe ATP depletion, however, [Ca(2+)](i) remained above 100 nM in only 17% and 25% of the NT2-N neurons after 24 and 48 h in 3-NP, respectively, indicating that most neurons were able to recover from acute [Ca(2+)](i) rise, and suggesting that chronic [Ca(2+)](i) dysregulation is a better indicator of subsequent necrosis. Blockade of N-methyl-D-aspartate-glutamate receptor by MK-801 substantially ameliorated 3-NP-induced ATP depletion, subsequent chronic [Ca(2+)](i) elevation, and survival. Moreover, xestospongin C, an inhibitor of endoplasmic reticulum Ca(2+) release, enhanced the capacity of NT2-N neurons to maintain [Ca(2+)](i) homeostasis and resist necrosis while subjected to sustained energy deprivation. As far as we know, this report is the first to employ human neurons to study the pathophysiology of 3-NP neurotoxicity.

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

Within the last few years, there has been a growing interest in the neuroprotective effects of estrogen and the possible beneficial effects of estrogen in neurodegenerative diseases such as stroke, Alzheimer disease, and Parkinson disease. Here, we review the progress in this field, with a particular focus upon estrogen-induced protection from stroke-induced ischemic damage. The important issue of whether clinically relevant selective estrogen receptor modulators (SERMs) such as tamoxifen and raloxifene and estrogen replacement therapy can exert neuroprotection is also addressed. Although the mechanism of estrogen and SERM neuroprotection is not clearly resolved, we summarize the leading possibilities, including 1) a genomic estrogen receptor-mediated pathway that involves gene transcription, 2) a nongenomic signaling pathway involving activation of cell signalers such as mitogen-activated protein kinases and/or phosphatidylinositol-3-kinase /protein kinase B, and 3) a nonreceptor antioxidant free-radical scavenging pathway that is primarily observed with pharmacological doses of estrogen. The role of other potential mediatory factors such as growth factors and the possibility of an astrocyte role in neuroprotection is also discussed.

The effect of oxidative stress on ERalpha and ERbeta expression

The formation of intracellular reactive oxygen and nitrogen species (ROS and RNS) has been implicated in the pathogenesis of a variety of diseases. In excess, ROS and their byproducts may cause oxidative damage and be cytotoxic to cells. Recently, it has been established that these oxidants can also act as subcellular messengers in gene regulatory and signal transduction pathways. Estrogen, on the other hand, is known to offer protection from coronary artery diseases in post-menopausal women and to be involved in various ROS-related diseases, such as Alzheimer's and Parkinson's diseases, diabetes and aging. The existence of estrogen receptors in these tissues lead us to investigate whether ROS can regulate their expression. We demonstrated here, for the first time, that oxidative stress induced by hydrogen peroxide (H(2)O(2)), Fe(2+), 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH) and activated macrophages, affect the expression of estrogen receptors alpha and beta (ERalpha and ERbeta) differently, demonstrating cell-specific response which can be blocked by antioxidants. This data suggest that oxidative stress and the production of ROS/RNS function as physiological regulators of ERalpha and ERbeta expression. This may provide a new insight into the ERbeta-dependent protective action of estrogen and phytoestrogens in inflammation involving diseases, and may contribute to the development of novel therapeutic treatment strategies.

Prevalence of dementia in users of hormone replacement therapy as defined by prescription data

BACKGROUND

Studies of hormone replacement therapy (HRT) and dementia and cognitive impairment show mixed results. This study assessed the prevalence of dementia and cognitive impairment in users and nonusers of HRT defined using computer-stored prescription information.

METHODS

The study involved 3924 women 75 years of age and older who were members of the Southern California Kaiser Permanente Medical Care Program in 1998. HRT use was determined based on prescription data for 1992-1998. Cognitive function and dementia were assessed using the Telephone Interview of Cognitive Status supplemented by the Telephone Dementia Questionnaire and medical record review.

RESULTS

Odds ratios (ORs) for cognitive impairment/dementia showed expected associations with age, education, ethnicity, and a history of stroke or Parkinson's disease. After adjustment, the OR for cognitive impairment or dementia in HRT users compared with HRT nonusers was 0.91 (95% confidence interval 0.75-1.10). The adjusted ORs for all dementia and dementia without cause in HRT users compared with nonusers were 0.77 (95% confidence interval 0.59- 1.00) and 0.78 (0.58-1.05), respectively. Twenty percent of women with cognitive impairment or dementia who had been classified as HRT users by prescription (one prescription each year from 1992-1998) denied hormone use compared with 8.8% of women without impairment. Medical record review validated prescription information for the impaired women.

CONCLUSIONS

The study identified an important methodologic problem in studies of HRT and cognitive impairment and dementia that depend on recalled information about drug exposure. A protective effect of HRT for cognitive impairment and dementia was neither established nor ruled out based on the prescription data.

Estrogen-mediated neuroprotection against beta-amyloid toxicity requires expression of estrogen receptor alpha or beta and activation of the MAPK pathway

It is well documented that estrogen can activate rapid signaling pathways in a variety of cell types. These non-classical effects of estrogen have been reported to be important for cell survival after exposure to a variety of neurotoxic insults. Since direct evidence of the ability of the estrogen receptors (ERs) alpha and/or beta to mediate such responses is lacking, the hippocampal-derived cell line HT22 was stably transfected with either ERalpha (HTERalpha) or ERbeta (HTERbeta). In HTERalpha and HTERbeta cells, but not untransfected cells, an increase in ERK2 phosphorylation was measured within 15 min of 17beta-estradiol treatment. The ER antagonist ICI 182, 780 (1 microm) and the MEK inhibitor, PD98059 (50 microm) blocked this increase in ERK2 phosphorylation. Treatment of HT22, HTERalpha and HTERbeta cells with the beta-amyloid peptide (25-35) (10 micro m) resulted in a significant decrease in cell viability. Pre-treatment for 15 min with 10 nm 17beta-estradiol resulted in a 50% increase in the number of living cells in HTERalpha and HTERbeta cells, but not in HT22 cells. Finally, ICI 182, 780 and PD98059 prevented 17beta-estradiol-mediated protection. This study demonstrates that both ERalpha and ERbeta can couple to rapid signaling events that mediate estrogen-elicited neuroprotection.

Androgen supplementation in older women: too much hype, not enough data

Androgen supplementation in women has received enormous attention in the scientific and lay communities. That it enhances some aspects of cognitive function, sexual function, muscle mass, strength, and sense of well-being is not in question. What is not known is whether physiological testosterone replacement can improve health-related outcome in older women without its virilizing side effects. Although it is assumed that the testosterone dose-response relationship is different in women than in men and that clinically relevant outcomes on the above-mentioned effects can be achieved at lower testosterone doses, these assumptions have not been tested rigorously. Androgen deficiency has no clear-cut definition. Clinical features may include impaired sexual function, low energy, depression, and a total testosterone level of less than 15 ng/dL, the lower end of the normal range. Measurement of free testosterone is ideal, because it provides a better estimate of the biologically relevant fraction. It is not widely used in clinical practice, because some methods of measuring free testosterone assay are hampered by methodological difficulties. In marked contrast to the abrupt decline in estrogen and progesterone production at menopause, serum testosterone is lower in older women than in menstruating women, with the decline becoming apparent a decade before menopause. This article reviews testosterone's effects on sexual function, cognitive function, muscle mass, body composition, and immune function in postmenopausal women.

Oestrogen as a neuroprotective hormone

In addition to its role as a sex hormone, oestrogen affects the structure and function of the nervous system. Oestrogen receptors are expressed in brain regions that are involved in sex differentiation and maturation. But in addition to its well-known effects, oestrogen also has important neuroprotective actions that are both dependent and independent of a nuclear oestrogen-receptor activity. Furthermore, oestrogen can interact with neuroprotective intracellular signalling pathways and is itself a neuroprotective antioxidant. Understanding the mechanisms of oestrogen action will be crucial to determine its potential as a therapeutic agent, particularly in the elderly.