Glutamate receptor requirement for neuronal death from anoxia-reoxygenation: an in Vitro model for assessment of the neuroprotective effects of estrogens

Exosomes derived from HUVECs alleviate ischemia-reperfusion induced inflammation in neural cells by upregulating KLF14 expression

Neuroinflammation plays a key role in the progression of secondary brain injury after ischemic stroke, and exosomes have been increasingly recognized to eliminate inflammatory responses through various mechanisms. This study aimed to explore the effect and possible mechanism of human umbilical vein endothelial cells derived exosomes (H-EXOs) on neuroinflammation. We established a transient middle cerebral artery occlusion/reperfusion (tMCAO/R) in male rats and oxygen-glucose-deprivation/reoxygenation (OGD/R) model in cultured neurons to mimic secondary brain injury after ischemic stroke in vivo. H-EXOs were administered at the same time of reperfusion. Results showed that the production of pro-inflammatory cytokines TNF-α, IL-1β, and IL-6, and the transcription factor Krüppel-like factor 14 (KLF14) were significantly increased both in rat brain tissue and cultured neural cells after ischemic-reperfusion (I/R) injury. H-EXOs treatment significantly improved the cultured cell viability, reduced infarct sizes, mitigated neurobehavioral defects, and alleviated the expression of pro-inflammatory cytokines compared with the control group, indicating that H-EXOs exerted anti-inflammatory effect against I/R injury. Further studies revealed that the anti-inflammatory effect of H-EXOs could be weakened by small-interfering RNA (siKLF4) transfection. KLF14 was a protective factor produced during cerebral ischemia-reperfusion injury. In conclusion, H-EXOs protect neurons from inflammation after I/R injury by enhancing KLF14 expression.

Negative modulation of mitochondrial calcium uniporter complex protects neurons against ferroptosis

Ferroptosis is an iron- and reactive oxygen species (ROS)-dependent form of regulated cell death, that has been implicated in Alzheimer's disease and Parkinson's disease. Inhibition of cystine/glutamate antiporter could lead to mitochondrial fragmentation, mitochondrial calcium ([Ca2+]m) overload, increased mitochondrial ROS production, disruption of the mitochondrial membrane potential (ΔΨm), and ferroptotic cell death. The observation that mitochondrial dysfunction is a characteristic of ferroptosis makes preservation of mitochondrial function a potential therapeutic option for diseases associated with ferroptotic cell death. Mitochondrial calcium levels are controlled via the mitochondrial calcium uniporter (MCU), the main entry point of Ca2+ into the mitochondrial matrix. Therefore, we have hypothesized that negative modulation of MCU complex may confer protection against ferroptosis. Here we evaluated whether the known negative modulators of MCU complex, ruthenium red (RR), its derivative Ru265, mitoxantrone (MX), and MCU-i4 can prevent mitochondrial dysfunction and ferroptotic cell death. These compounds mediated protection in HT22 cells, in human dopaminergic neurons and mouse primary cortical neurons against ferroptotic cell death. Depletion of MICU1, a [Ca2+]m gatekeeper, demonstrated that MICU is protective against ferroptosis. Taken together, our results reveal that negative modulation of MCU complex represents a therapeutic option to prevent degenerative conditions, in which ferroptosis is central to the progression of these pathologies.

Alcohol Withdrawal and Cerebellar Mitochondria

Cerebellar disorders trigger the symptoms of movement problems, imbalance, incoordination, and frequent fall. Cerebellar disorders are shown in various CNS illnesses including a drinking disorder called alcoholism. Alcoholism is manifested as an inability to control drinking in spite of adverse consequences. Human and animal studies have shown that cerebellar symptoms persist even after complete abstinence from drinking. In particular, the abrupt termination (ethanol withdrawal) of long-term excessive ethanol consumption has shown to provoke a variety of neuronal and mitochondrial damage to the cerebellum. Upon ethanol withdrawal, excitatory neurotransmitter molecules such as glutamate are overly released in brain areas including cerebellum. This is particularly relevant to the cerebellar neuronal network as glutamate signals are projected to Purkinje neurons through granular cells that are the most populated neuronal type in CNS. This excitatory neuronal signal may be elevated by ethanol withdrawal stress, which promotes an increase in intracellular Ca(2+) level and a decrease in a Ca(2+)-binding protein, both of which result in the excessive entry of Ca(2+) to the mitochondria. Subsequently, mitochondria undergo a prolonged opening of mitochondrial permeability transition pore and the overproduction of harmful free radicals, impeding adenosine triphosphate (ATP)-generating function. This in turn provokes the leakage of mitochondrial molecule cytochrome c to the cytosol, which triggers a cascade of adverse cytosol reactions. Upstream to this pathway, cerebellum under the condition of ethanol withdrawal has shown aberrant gene modifications through altered DNA methylation, histone acetylation, or microRNA expression. Interplay between these events and molecules may result in functional damage to cerebellar mitochondria and consequent neuronal degeneration, thereby contributing to motoric deficit. Mitochondria-targeting research may help develop a powerful new therapy to manage cerebellar disorders associated with hyperexcitatory CNS disorders like ethanol withdrawal.

Researching glutamate - induced cytotoxicity in different cell lines: a comparative/collective analysis/study

Although glutamate is one of the most important excitatory neurotransmitters of the central nervous system, its excessive extracellular concentration leads to uncontrolled continuous depolarization of neurons, a toxic process called, excitotoxicity. In excitotoxicity glutamate triggers the rise of intracellular Ca²⁺ levels, followed by up regulation of nNOS, dysfunction of mitochondria, ROS production, ER stress, and release of lysosomal enzymes. Excessive calcium concentration is the key mediator of glutamate toxicity through over activation of ionotropic and metabotropic receptors. In addition, glutamate accumulation can also inhibit cystine (CySS) uptake by reversing the action of the CySS/glutamate antiporter. Reversal of the antiporter action reinforces the aforementioned events by depleting neurons of cysteine and eventually glutathione’s reducing potential. Various cell lines have been employed in the pursuit to understand the mechanism(s) by which excitotoxicity affects the cells leading them ultimately to their demise. In some cell lines glutamate toxicity is exerted mainly through over activation of NMDA, AMPA, or kainate receptors whereas in other cell lines lacking such receptors, the toxicity is due to glutamate induced oxidative stress. However, in the greatest majority of the cell lines ionotropic glutamate receptors are present, co-existing to CySS/glutamate antiporters and metabotropic glutamate receptors, supporting the assumption that excitotoxicity effect in these cells is accumulative. Different cell lines differ in their responses when exposed to glutamate. In this review article the responses of PC12, SH-SY5Y, HT-22, NT-2, OLCs, C6, primary rat cortical neurons, RGC-5, and SCN2.2 cell systems are systematically collected and analyzed.

The effect of aromatase inhibition on the cognitive function of older patients with breast cancer

INTRODUCTION

This study evaluated the association between aromatase inhibitor (AI) therapy and cognitive function (over a 6-month period) in a cohort of patients aged ≥ 60 years compared with an age-matched healthy control group, and it evaluated changes in regional cerebral metabolism as measured by positron emission tomography (PET) scans of the brain done in a subset of the patient cohort.

PATIENTS AND METHODS

Thirty-five patients (32 evaluable) and 35 healthy controls were recruited to this study. Patients with breast cancer completed a neuropsychological battery, self-reported memory questionnaire, and geriatric assessment before initiation of AI therapy and again 6 months later. Age-matched healthy control participants completed the same assessments at the same time points as the patient group.

RESULTS

No significant decline in cognitive function was seen among individuals receiving an AI from pretreatment to 6 months later compared with healthy controls. In the PET cohort over the same period, both standardized volume of interest and statistical parametric mapping analyses detected specific changes in metabolic activity between baseline and follow-up uniquely in the AI patients, most significantly in the medial temporal lobes.

CONCLUSION

Although patients undergoing AI treatment had few changes in neuropsychological performance compared with healthy controls over a 6-month period, regionally specific changes in cerebral metabolic activity were identified during this interval in the patient group. Additional longitudinal follow-up is needed to understand the potential clinical implications of these findings.

17Beta-estradiol suppresses AMPA-induced increases in regional cerebral O2consumption

We tested the hypothesis that 17 beta-estradiol would reduce the cerebral O2 consumption response resulting from glutamate receptor stimulation by alpha amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA). Fourteen ovariectomized rats were separated into 17 beta-estradiol (0.5 mg 21 day release pellet) and control (placebo pellet) groups to determine cerebral blood flow (14C-iodoantipyrine) and O2 consumption (microspectrophotometry). After topical cortical stimulation with 10(-3) M and 10(-4) M AMPA, cerebral blood flow increased significantly in both groups in a concentration-dependent manner. Cerebral O2 extraction was not significantly different in any region of the 17 beta-estradiol treated group. In the placebo treated group, the O2 extraction in the saline treated cortex and in the 10(-3) M AMPA treated cortex was significantly higher when compared to the 10(-4) M AMPA treated cortex. Cerebral O2 consumption in the control group increased by 20%, from 5.2 +/- 0.6 to 6.1 +/- 0.7, with 10(-4) M AMPA and significantly increased by 64% to 8.5 +/- 0.8 ml O2 min-1 100 g-1 with 10(-3) M AMPA. The 17 beta-estradiol group demonstrated no statistically significant difference in O2 consumption between the saline treated and AMPA treated cortex. Thus, 17 beta-estradiol reduced the effects of AMPA in increasing cerebral O2 consumption.

Estrogen and neuroprotection: from clinical observations to molecular mechanisms

We now appreciate that estrogen is a pleiotropic gonadal steroid that exerts profound effects on the plasticity and cell survival of the adult brain. Over the past century, the life span of women has increased, but the age of the menopause remains constant. This means that women may now live over one third of their lives in a hypoestrogenic, postmenopausal state. The impact of prolonged hypoestrogenicity on the brain is now a critical health concern as we realize that these women may suffer an increased risk of cognitive dysfunction and neurodegeneration due to a variety of diseases. Accumulating evidence from both clinical and basic science studies indicates that estrogen exerts critical protective actions against neurodegenerative conditions such as Alzheimer's disease and stroke. Here, we review the discoveries that comprise our current understanding of estrogen action against neurodegeneration. These findings carry far-reaching possibilities for improving the quality of life in our aging population.

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.

Neuroprotective effects of 17β-estradiol rely on estrogen receptor membrane initiated signals

Besides its crucial role in many physiological events, 17β-estradiol (E2) exerts protective effects in the central nervous system. The E2 effects are not restricted to the brain areas related with the control of reproductive function, but rather are widespread throughout the developing and the adult brain. E2 actions are mediated through estrogen receptors (i.e., ERα and ERβ) belonging to the nuclear receptor super-family. As members of the ligand-regulated transcription factor family, classically, the actions of ERs in the brain were thought to mediate only the E2 long-term transcriptional effects. However, a growing body of evidence highlighted rapid, membrane initiated E2 effects in the brain that are independent of ER transcriptional activities and are involved in E2-induced neuroprotection. The aim of this review is to focus on the rapid effects of E2 in the brain highlighting the specific role of the signaling pathway(s) of the ERβ subtype in the neuroprotective actions of E2.

Functional and morphological effects of β-estradiol in eyes with N-methyl-D-Aspartate-induced retinal neurotoxicity in rats

Glutamate-mediated excitotoxicity, mainly induced by N-methyl-d-aspartate (NMDA) receptors, is known to cause retinal ganglion cell death in retinal ischemia, glaucoma, and several other retinal diseases. We evaluated the effects of β-estradiol (E2) against a single intravitreal injection of NMDA using a functional and morphological approach. Male rats were randomly divided into 3 treatment groups: (1) Control; (2) NMDA (intravitreal injection of 5 mM NMDA); and (3) NMDA + E2 (intravitreal injection of 5 mM NMDA and pretreatment with subcutaneous E2 implantation). Seven days after NMDA injection, full-field electroretinograms (ERGs) and quantitative morphological analyses using transverse sections of the retina were conducted. In the NMDA group, full-field ERGs showed reductions in the amplitudes of the negative-scotopic threshold response, rod response b-wave, oscillatory potentials, flicker response second b-wave and cone response b-wave. Morphological evaluations of transverse sections of the retina demonstrated a reduction in the thickness of the inner plexiform layer, increases in the thickness of the outer plexiform and outer nuclear layers, and a loss of cells in the ganglion cell layer. In the NMDA + E2 group, pretreatment with E2 prevented the aggravations in the amplitudes of the ERGs except for oscillatory potential 2 (OP2); however, no morphological differences between the NMDA and NMDA + E2 groups were seen. These findings indicate that E2 can protect retinal function against NMDA-induced neurotoxicity. In addition, these indications suggested that the effect of E2 may have therapeutic benefits in NMDA related diseases, such as retinal ischemia and glaucoma.

Estrogen receptor beta selective nonsteroidal estrogens: seeking clinical indications

IMPORTANCE OF THE FIELD

Nonsteroidal estrogens have been known since the 1930s. However, the relatively recent (1996) discovery of estrogen receptor subtype beta (ERbeta) suggested a possible paradigm shift away from SERM-like selectivity. Selective ERbeta agonism would potentially allow expansion of estrogenic targeting into new indications (discussed herein) currently precluded by the thrombogenic and hyperproliferative effects of nonselective estrogens.

AREAS COVERED IN THIS REVIEW

ERbeta agonist design has been very successful. Pharmacophores for ERbeta selective nonsteroidal estrogens are generally diphenolic compounds that achieve an inter-phenolic distance and geometry similar to 17beta-estradiol with few restraints on the nature of the element linking the phenols (or phenol mimetics). The tremendously chemodiverse ERbeta agonist patent literature is reviewed, segregating the agonists into structurally similar compounds based on their interphenolic linking elements.

WHAT THE READER WILL GAIN

A comprehensive understanding of the chemotype landscape of this field and an assessment of its maturation.

TAKE HOME MESSAGE

Subtype selective ERbeta agonist therapy seems very promising. However, more clinical testing is needed to firmly establish its therapeutic potential. At this point, ERbeta is a promising target in search of an indication.

Ethanol withdrawal acts as an age-specific stressor to activate cerebellar p38 kinase

We investigated whether protein kinase p38 plays a role in the brain-aging changes associated with repeated ethanol withdrawal (EW). Ovariectomized young, middle-age and older rats, with or without 17β-estradiol (E2) implantation, received a 90-day ethanol with repeated withdrawal. They were tested for active pP38 expression in cerebellar Purkinje neurons and whole-cerebellar lysates using immunohistochemistry and enzyme-linked immunosorbent assay, respectively. They were also tested for the Rotarod task to determine the behavioral manifestation of cerebellar neuronal stress and for reactive oxygen species (ROS) and mitochondrial protein carbonyls to determine oxidative mechanisms. Middle-age EW rats showed higher levels of pP38-positive Purkinje neurons/cerebellar lysates, which coincided with increased mitochondrial protein oxidation than other diet/age groups. Exacerbated motor deficit due to age-EW combination also began at the middle-age. In comparison, ROS contents peaked in older EW rats. E2 treatment mitigated each of the EW effects to a different extent. Collectively, pP38 may mediate the brain-aging changes associated with pro-oxidant EW at vulnerable ages and in vulnerable neurons in a manner protected by estrogen.

Mitochondrial damage: a target for new therapeutic horizons

Traumatic brain injury (TBI) represents a leading cause of death and morbidity, as well as a considerable social and economical burden in western countries, and has thus emerged as a formidable therapeutic challenge. Yet despite tremendous efforts enlightening the mechanisms of neuronal death, hopes for the "magic bullet" have been repeatedly deceived, and TBI management has remained focused on the control of increased intracranial pressure. Indeed, impairment of cerebral metabolism is traditionally attributed to impaired oxygen delivery mediated by reduced cerebral perfusion in the swollen cerebral parenchyma. Although intuitively appealing, this hypothesis is not entirely supported by physiological facts and does not take into consideration mitochondrial dysfunction that has been repeatedly reported in both human and animal TBI. Although the nature and origin of the events leading to mitochondrial damage may be different, most share a permeabilization of mitochondrial membrane, which therefore may represent a logical target for new therapeutic strategies. Therefore, the proteins mediating these events may represent promising targets for new TBI therapies. Furthermore, mimicking anti-apoptotic proteins, such as Bcl-2 or XIAP, or inhibiting mitochondrial pro-apoptotic proteins, such as Smac/DIABLO, Omi/HTRA2, and ARTS (septin 4 isoform 2) may represent useful novel therapeutic strategies. This review focuses on mechanisms of the mitochondrial membrane permeabilization and its consequences and discusses the current and possible future therapeutic implications of this key event of neuronal death.

Effects of estrogen on AF64A-induced apoptosis in NG108-15 cells

In this study, we show that pretreatment with physiological concentrations (1-100 nM) of 17beta-estradiol decreased apoptosis induced by ethylcholine aziridinium (AF64A), a choline toxin, in the cholinergic neuronal cell line NG108-15. These protective effects were observed after short-term (30 min) pretreatment, and were blocked by treatment with an estrogen receptor antagonist and inhibitors of phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase kinase (MEK). The protective effects were, however, not reversed by a protein synthesis inhibitor. Furthermore, we examined the effects of 17beta-estradiol on choline uptake in NG108-15 cells. Although choline uptake was inhibited by a selective inhibitor of choline uptake, hemicholinium-3, it was not altered by treatment with 17beta-estradiol. These results indicated that the protective effect of 17beta-estradiol on AF64A-induced apoptosis could be nongenomic, and that this effect may be due to the activation of PI3K/Akt and/or MEK/extracellular signal-regulated kinase (ERK) pathways.

Oestrogen and progestins differently prevent glutamate toxicity in cortical neurons depending on prior hormonal exposure via the induction of neural nitric oxide synthase

Sex steroids are important for brain function and protection. However, growing evidence suggests that these actions might depend on the timing of exposure to steroids. We have studied the effects of steroid administration on the survival of neural cells and we have partially characterized the possible mechanisms. The effect of a 24h pre-treatment with 17beta-estradiol or 17beta-estradiol plus progesterone or medroxyprogesterone acetate on the toxic action of l-glutamate was used to test the experimental hypothesis. Pre-exposure to either steroid combinations turned in enhanced cell survival. Instead, addition of sex steroids together with l-glutamate, in the absence of a pre-exposure had no protective effect. Pre-treatment with the steroid combinations resulted in increased neural NOS expression and activity and blockade of NOS abolished the cytoprotective effects of steroids. These results suggest that NOS induction might be involved in sex steroid-induced neuroprotection. Furthermore, these data supports the hypothesis that prolonged and continued exposure to oestrogen and progesterone, leading to changes in gene expression, is necessary to obtain neuroprotection induced by sex steroids.

Phenolic compounds protect cultured hippocampal neurons against ethanol-withdrawal induced oxidative stress

Ethanol withdrawal is linked to elevated oxidative damage to neurons. Here we report our findings on the contribution of phenolic antioxidants (17beta-estradiol, p-octyl-phenol and 2,6-di-tert-butyl-4-methylphenol) to counterbalance sudden ethanol withdrawal-initiated oxidative events in hippocampus-derived cultured HT-22 cells. We showed that ethanol withdrawal for 4 h after 24-h ethanol treatment provoked greater levels of oxidative damage than the preceding ethanol exposure. Phenolic antioxidant treatment either during ethanol exposure or ethanol withdrawal only, however, dose-dependently reversed cellular oxidative damage, as demonstrated by the significantly enhanced cell viability, reduced malondialdehyde production and protein carbonylation, compared to untreated cells. Interestingly, the antioxidant treatment schedule had no significant impact on the observed neuroprotection. In addition, the efficacy of the three phenolic compounds was practically equipotent in protecting HT-22 cells in spite of predictions based on an in silico study and a cell free assay of lipid peroxidation. This finding implies that free-radical scavenging may not be the sole factor responsible for the observed neuroprotection and warrants further studies to establish, whether the HT-22 line is indeed a suitable model for in vitro screening of antioxidants against EW-related neuronal damage.

Ethanol withdrawal provokes opening of the mitochondrial membrane permeability transition pore in an estrogen-preventable manner

We have reported that the major endogenous estrogen, 17beta-estradiol (E2), protects against oxidative injury during ethanol withdrawal (EW) in a cultured hippocampal cell line (HT22). Here, we investigated whether the pro-oxidant nature of EW mediates opening of the mitochondrial membrane permeability transition pore (PTP) in a manner protected by E2. Excess PTP opening provokes mitochondrial membrane swelling (MMS) and the collapse of membrane potential (DeltaPsim). HT22 cells were collected at the end of ethanol exposure (100 mM) for 24 h or at 4 h of EW to assess MMS by monitoring absorbance decline at 540 nm and to assess DeltaPsim using flow cytometry. Protective effects of E2 on PTP were compared with an antioxidant butylated hydroxytoluene (BHT) and an E2 analog, ZYC26 [(3-hydroxy-2-adamantyl(1)-4-methyl-estra-1,3,5(10)-17-one], with higher antioxidant potency than E2. To assess cellular consequences of PTP opening, effects of a PTP inhibitor (cyclosporin A) on EW-induced cell death were assessed using the calcein assay. Major findings were that: 1) EW resulted in rapid MMS and DeltaPsim collapse; 2) cyclosporin A attenuated EW-induced cell death; and 3) E2 treatment restricted to the EW phase protected against the PTP opening more prominently than BHT and to a similar degree to ZYC26. These findings suggest that EW provokes PTP opening partly but not entirely through the pro-oxidant nature and that E2 counteracts EW-associated factors to protect against the PTP opening.

17Beta-estradiol prevents retinal ganglion cell loss induced by acute rise of intraocular pressure in rat

Glaucoma, is a progressive optic neuropathy often associated with increased intraocular pressure (IOP) and characterized by progressive death of retinal ganglion cells (RGCs). High acute rise of IOP is a model for retinal ischemia and may represent a model of acute angle closure glaucoma. Here we have used this experimental model in combination with a neurochemical and neuropathological approach to gain more insight in the neuroprotective profile of 17beta-estradiol (E2), a steroid hormone, which has been shown to increase the viability, survival, and differentiation of primary neuronal cultures from different brain areas including amygdala, hypothalamus, and neocortex. Our data demonstrate that systemic administration of E2 significantly reduces RGC loss induced by high IOP in rat. In addition, pretreatment with E2, 30 min before ischemia, minimizes the elevation of glutamate observed during the reperfusion period. These effects seem to be in part mediated by the activation of the estrogen receptor, since a pretreatment with ICI 182-780, a specific estrogen receptor antagonist, partially counteracts the neuroprotection afforded by the estrogen.

Estrogen receptor-independent neuroprotection via protein phosphatase preservation and attenuation of persistent extracellular signal-regulated kinase 1/2 activation

The mechanism of estrogen-mediated neuroprotection is not yet clear. Estrogens have a variety of modes of action, including transducing signaling events such as activation and/or suppression of the mitogen-activated protein kinase (MAPK) pathway. We have previously shown protein phosphatases to be involved in 17beta-estradiol-mediated neuroprotection. In the present study, we assessed the role of estrogen receptors (ERs) in estrogen-mediated neuroprotection from oxidative/excitotoxic stress and the consequential effects on MAPK signaling. Okadaic acid and calyculin A, nonspecific serine/threonine phosphatase inhibitors, were exposed to cells at various concentrations in the presence or absence of 17alpha-estradiol, the enantiomer of 17beta-estradiol, 2-(1-adamantyl)-3-hydroxyestra-1,3,5(10)-trien-17-one (ZYC3; non-ER-binding estrogen analog), and/or glutamate. All three compounds, which we have shown to have little or no binding to ERalpha and ERbeta, were protective against glutamate toxicity but not against okadaic acid and calyculin A toxicity. In addition, in the presence of effective concentrations of these inhibitors, the protective effects of these estrogen analogs were lost. Glutamate treatment caused a 50% decrease in levels of protein phosphatase 1 (PP1), protein phosphatase 2A (PP2A), and protein phosphatase 2B (calcineurin) (PP2B). Coadministration of ZYC3 with glutamate prevented the decreases in PP1, PP2A, and PP2B levels. Furthermore, glutamate treatment caused a persistent increase in phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 that corresponds with the decrease protein levels of serine/threonine phosphatases. ZYC3 blocked this persistent increase in ERK phosphorylation. These results suggest that estrogens protect cells against glutamate-induced oxidative stress through an ER-independent mediated mechanism that serves to preserve phosphatase activity in the face of oxidative insults, resulting in attenuation of the persistent phosphorylation of ERK associated with neuronal death.

A prototypical Sigma-1 receptor antagonist protects against brain ischemia

Previous studies indicate that the Sigma-1 ligand 4-phenyl-1-(4-phenylbutyl) piperidine (PPBP) protects the brain from ischemia. Less clear is whether protection is mediated by agonism or antagonism of the Sigma-1 receptor, and whether drugs already in use for other indications and that interact with the Sigma-1 receptor might also prevent oxidative damage due to conditions such as cerebral ischemic stroke. The antipsychotic drug haloperidol is an antagonist of Sigma-1 receptors and in this study it potently protects against oxidative stress-related cell death in vitro at low concentrations. The protective potency of haloperidol and a number of other butyrophenone compounds positively correlate with their affinity for a cloned Sigma-1 receptor, and the protection is mimicked by a Sigma-1 receptor-selective antagonist (BD1063), but not an agonist (PRE-084). In vivo, an acute low dose (0.05 mg/kg s.c.) of haloperidol reduces by half the ischemic lesion volume induced by a transient middle cerebral artery occlusion. These in vitro and in vivo pre-clinical results suggest that a low dose of acutely administered haloperidol might have a novel application as a protective agent against ischemic cerebral stroke and other types of brain injury with an ischemic component.

Possible anti-oxidant and neuroprotective mechanisms of zolpidem in attenuating typical anti-psychotic-induced orofacial dyskinesia: a biochemical and neurochemical study

Tardive dyskinesia is a serious motor side effect of chronic anti-psychotic therapy. The pathophysiology of this disabling and commonly irreversible movement disorder continues obscure and may be caused due to GABAergic hypofunction or increased oxidative damage and free radical generation. Chronic treatment with typical antipsychotics leads to the development of abnormal hyperkinetic orofacial movements (vacuous chewing movements, tongue protrusions and facial jerking) in rats and is widely accepted as the animal model for tardive dyskinesia. Zolpidem, a GABA-mimetic drug is structurally related to melatonin and has been reported to possess anti-oxidant and neuroprotective effects both in vivo and in vitro. The study was carried out to investigate whether zolpidem can be used in the treatment of typical anti-psychotic-induced orofacial dyskinesia. Chronic haloperidol (1 mg/kg, i.p. for 21 days) and chlorpromazine (5 mg/kg, i.p. for 21 days) treatment significantly induced orofacial hyperkinetic movements and zolpidem [N, N, 6-trimethyl-2-p-tolyl-imidazo (1, 2-a) pyridine 3-acetamideL-(+)] dose dependently (1, 2, 5 mg/kg i.p. for 21 days) reduced these haloperidol and chlorpromazine-induced hyperkinetic orofacial movements. Biochemical analysis revealed that haloperidol and chlorpromazine treatment significantly induced increase in lipid peroxidation and decrease in the levels of total nitric oxide levels, non-protein thiols (NPSH) and of anti-oxidant defense enzymes, superoxide dismutase (SOD) and catalase in the striatum of rat brain. Co-administration of zolpidem (1, 2, 5 mg/kg i.p. for 21 days) significantly reduced the lipid peroxidation and restored the non-protein thiols and total nitric oxide levels induced by chronic haloperidol and chlorpromazine treatment. It also significantly reversed the haloperidol and chlorpromazine-induced decrease in brain SOD and catalase activity. Neurochemical analysis (Neurotransmitter and their metabolite level estimation) revealed that haloperidol and chlorpromazine significantly decreased the dopamine, norepinephrine and serotonin levels in brain homogenates where as it caused a significant increase in the metabolite (VMA and HVA) levels in urine, which were significantly reversed by zolpidem at higher doses. Result of the present study support the therapeutic use of zolpidem in the treatment of typical anti-psychotic-induced orofacial dyskinesia.

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.

The effects of glutamate can be attenuated by estradiol via estrogen receptor dependent pathway in rat adrenal pheochromocytoma cells

Estrogens have been suggested to exhibit neuroprotective activities against several insults including beta-amyloid and glutamate, one of the excitatory neurotransmitters in the central nervous system. In the present study, we showed that exposure to glutamate not only inhibited the cell growth of exponentially growing rat pheochromocytoma PC12 cells in a time- and dose-dependent manner, but also influenced cell adherence capacity. Glutamate-induced growth inhibition was significantly attenuated by the co-administration of estradiol in PC12 cells. Pre-exposure of the PC12 cells to the estradiol was not required for protection against glutamate-induced growth inhibition. Administration of anti-estrogen ICI182,780 efficiently blocked the neuroprotective effects of estradiol. Glutamate-induced changes in cell adherence, on the other hand, were not significantly affected by estradiol. These data indicate that the neuroprotective effects of estradiol against glutamate-induced insults in PC12 cells, at least in part, involve estrogen receptor-dependent pathways.

Sex differences in behavior and striatal ascorbate release in the 140 CAG knock-in mouse model of Huntington's disease

Ethological assessment of murine models of Huntington's disease (HD), an inherited neurodegenerative disorder, enables correlation between phenotype and pathophysiology. Currently, the most characterized model is the R6/2 line that develops a progressive behavioral and neurological phenotype by 6 weeks of age. A recently developed knock-in model with 140 CAG repeats (KI) exhibits a subtle phenotype with a longer progressive course, more typical of adult-onset HD in humans. We evaluated rotarod performance, open-field behavior, and motor activity across the diurnal cycle in KI mice during early to mid-adulthood. Although we did not observe any effects of age, relative to wild-type (WT) mice, KI mice showed significant deficits in both open-field climbing behavior and home-cage running wheel activity during the light phase of the diurnal cycle. An interesting sex difference also emerged. KI females spent more time in the open-field grooming and more time running during the diurnal dark phase than KI males and WT mice of both sexes. In striatum, the primary site of HD pathology, we measured behavior-related changes in extracellular ascorbate (AA), which is abnormally low in the R6/2 line, consistent with a loss of antioxidant protection in HD. KI males exhibited a 20-40% decrease in striatal AA from anesthesia baseline to behavioral activation that was not observed in other groups. Collectively, our results indicate behavioral deficits in KI mice that may be specific to the diurnal cycle. Furthermore, sex differences observed in behavior and striatal AA release suggest sex-dependent variation in the phenotype and neuropathology of HD.

Pyruvate protects mitochondria from oxidative stress in human neuroblastoma SK-N-SH cells

Oxidative stress is implicated in neurodegenerative diseases including stroke, Alzheimer's disease and Parkinson's disease, and has been extensively studied as a potential target for therapeutic intervention. Pyruvate, a natural metabolic intermediate and energy substrate, exerts antioxidant effects in brain and other tissues susceptible to oxidative stress. We tested the protective effects of pyruvate on hydrogen peroxide (H(2)O(2)) toxicity in human neuroblastoma SK-N-SH cells and the mechanisms underlying its protection. Hydrogen peroxide insult resulted in 85% cell death, but co-treatment with pyruvate dose-dependently attenuated cell death. At concentrations of >or=1 mM, pyruvate totally blocked the cytotoxic effects of H(2)O(2). Pyruvate exerted its protective effects even when its administration was delayed up to 2 h after H(2)O(2) insult. As a scavenger of reactive oxygen species (ROS), pyruvate dose-dependently attenuated H(2)O(2)-induced ROS formation, assessed from 2,7-dichlorofluorescein diacetate fluorescence. Furthermore, pyruvate suppressed superoxide production by submitochondrial particles, and attenuated oxidative stress-induced collapse of the mitochondrial membrane potential. Collectively, these results suggest that pyruvate protects neuronal cells through its antioxidant actions on mitochondria.

Induction of transcription factor CEBP homology protein mediates hypoglycaemia-induced necrotic cell death in human neuroblastoma cells

Oxygen and glucose deprivation are direct consequences of tissue ischaemia. We explored the interaction of hypoxia and hypoglycaemia on cell survival and gene expression in the absence of glutamatergic signalling using human SH-SY5Y neuroblastoma cells as a model. In agreement with previous investigations in non-neural cells, prolonged hypoxia (0.5% O(2)) failed to induce significant cell death in this system. In contrast, exposure to hypoglycaemia induced significant necrotic cell death (> 80% after 72 h). Interestingly, hypoglycaemia-induced cell death was completely abrogated by simultaneous exposure to hypoxia, suggesting strong cytoprotective effects of hypoxia. Subsequent microarray analysis of the underlying transcriptional responses revealed that the transcription factor CEBP homology protein (CHOP) was strongly induced by hypoglycaemia, and suppressed by simultaneous hypoxia. RNA interference against CHOP significantly protected cells from glucose deprivation-induced cell death. Hypoxia-induced vascular endothelial growth factor (VEGF) activation also protected cells against hypoglycaemia-induced cell death, but VEGF failed to modify hypoglycaemia-induced CHOP induction. Our data suggest that hypoglycaemia-induced necrotic cell death of neuroblastoma cells is an active process mediated via the induction of the transcription factor CHOP, and that hypoxia counteracts this cell death via at least two distinct mechanisms: repression of CHOP and induction of VEGF.

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.

A nonfeminizing estrogen analog protects against ethanol withdrawal toxicity in immortalized hippocampal cells

We have shown that 17beta-estradiol protects against ethanol withdrawal toxicity in rats. Here, we investigated whether a cellular model of ethanol withdrawal could be developed in a cultured hippocampal cell line (HT22) and whether an adamantyl-containing nonfeminizing estrogen analog, ZYC26 [(3-hydroxy-2-adamantyl(1)-4-methyl-estra-1,3,5(10)-17-one], protects against ethanol withdrawal toxicity. HT22 cells were exposed to ethanol (0-500 mM) for 24 h in the presence or absence of ZYC26 or 17beta-estradiol. The ethanol solution was then removed from the cells for 4 h to create ethanol withdrawal. Samples were collected at the end of a 24-h ethanol exposure or at 4 h of ethanol withdrawal to assess cell viability using a calcein assay, lipid peroxidation by measuring malondialdehyde, and protein oxidation by measuring carbonyl contents. When tested, ethanol concentrations were constantly maintained during a 24-h ethanol exposure and eliminated at 4 h of ethanol withdrawal. Ethanol withdrawal decreased cell viability and increased the levels of malondialdehyde and carbonyls more than ethanol exposure. ZYC26 reduced the cell death and malondialdehyde levels at a lower dose (1 microM) than 17beta-estradiol (10 microM). The increased carbonyl contents were reduced only by ZYC26 treatment. These data suggest that ethanol withdrawal can be created in HT22 cells in a manner that is more toxic than ethanol exposure and that ZYC26 is a more potent cytoprotectant than 17beta-estradiol against cell death and oxidative damage induced by ethanol withdrawal. Therefore, ZYC26 can be a potential alternative estrogen therapy for a cellular and oxidative imbalance associated with ethanol withdrawal.

Glutamate-induced apoptosis in neuronal cells is mediated via caspase-dependent and independent mechanisms involving calpain and caspase-3 proteases as well as apoptosis inducing factor (AIF) and this process is inhibited by equine estrogens

BACKGROUND

Glutamate, a major excitatory amino acid neurotransmitter, causes apoptotic neuronal cell death at high concentrations. Our previous studies have shown that depending on the neuronal cell type, glutamate-induced apoptotic cell death was associated with regulation of genes such as Bcl-2, Bax, and/or caspase-3 and mitochondrial cytochrome c. To further delineate the intracellular mechanisms, we have investigated the role of calpain, an important calcium-dependent protease thought to be involved in apoptosis along with mitochondrial apoptosis inducing factor (AIF) and caspase-3 in primary cortical cells and a mouse hippocampal cell line HT22.

RESULTS

Glutamate-induced apoptotic cell death in neuronal cells was associated with characteristic DNA fragmentation, morphological changes, activation of calpain and caspase-3 as well as the upregulation and/or translocation of AIF from mitochondria into cytosol and nuclei. Our results reveal that primary cortical cells and HT22 cells display different patterns of regulation of these genes/proteins. In primary cortical cells, glutamate induces activation of calpain, caspase-3 and translocation of AIF from mitochondria to cytosol and nuclei. In contrast, in HT22 cells, only the activation of calpain and upregulation and translocation of AIF occurred. In both cell types, these processes were inhibited/reversed by 17beta-estradiol and Delta8,17beta-estradiol with the latter being more potent.

CONCLUSION

Depending upon the neuronal cell type, at least two mechanisms are involved in glutamate-induced apoptosis: a caspase-3-dependent pathway and a caspase-independent pathway involving calpain and AIF. Since HT22 cells lack caspase-3, glutamate-induced apoptosis is mediated via the caspase-independent pathway in this cell line. Kinetics of this apoptotic pathway further indicate that calpain rather than caspase-3, plays a critical role in the glutamate-induced apoptosis. Our studies further indicate that glutamate- induced changes of these proteins can be inhibited by estrogens, with Delta8,17beta-estradiol, a novel equine estrogen being more potent than 17beta-estradiol. To our knowledge, this is the first demonstration that glutamate-induced apoptosis involves regulation of multiple apoptotic effectors that can be inhibited by estrogens. Whether these observations can help in the development of novel therapeutic approaches for the prevention of neurodegenerative diseases with estrogens and calpain inhibitors remains to be investigated.

Novel mechanisms for estrogen-induced neuroprotection

Estrogens are gonadal steroid hormones that are present in the circulation of both males and females and that can no longer be considered within the strict confines of reproductive function. In fact, the bone, the cardiovascular system, and extrahypothalamic regions of the brain are now well-established targets of estrogens. Among the numerous aspects of brain function regulated by estrogens are their effects on mood, cognitive function, and neuronal viability. Here, we review the supporting evidence for estrogens as neuroprotective agents and summarize the various mechanisms that may be involved in this effect, focusing particularly on the mitochondria as an important target. On the basis of this evidence, we discuss the clinical applicability of estrogens in treating various age-related disorders, including Alzheimer disease and stroke, and identify the caveats that must be considered.

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.

Estrogen attenuates gp120- and tat1-72-induced oxidative stress and prevents loss of dopamine transporter function

Postmenopausal women who are infected with HIV are at risk for experiencing dementia and Parkinson's-like symptoms associated with low levels of estrogen. Neurotoxic damage leading to these symptoms may involve HIV-associated proteins gp120 and/or tat(1-72) (tat). Our hypothesis is that 17beta-Estradiol (E(2)) is an effective agent for protection against gp120/tat-induced damage associated with increased oxidative stress, with particular focus on peroxynitrite-induced oxidative stress. We used SK-N-SH cells and striatal synaptosomes from Sprague-Dawley rats as model systems to assess neuroprotection by E(2). Cells coincubated with SIN-1(3-morpholinosydnonimine) or tat and gp120, together or separately, significantly increased oxidative stress on the SK-N-SH cells, as indicated by the increase in the levels of dichlorofluorescein (DCFH) fluorescence. These data suggest that a component of tat and gp120 neurotoxicity may be due to increased oxidative stress. Coincubation with E(2) attenuated tat- and gp120-induced increase in fluorescence. Coincubation with progesterone had no effect on tat-induced fluorescence, whereas coincubation with the E(2) antagonist ICI 182,780 and E(2) completely prevented the effects observed with E(2) alone. Both gp120 and tat decreased [(3)H] dopamine uptake into striatal synaptosomes by decreasing the V(max) of the dopamine transporter (DAT). Pretreatment of synaptosomes with E(2) (100 nM) partially reversed this reduction. In conclusion, E(2) appears to be effective for preventing the oxidative stress and loss of DAT function associated with gp120/tat neurotoxicity.

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.

Suppression of protein kinase Cepsilon mediates 17beta-estradiol-induced neuroprotection in an immortalized hippocampal cell line

Although estrogens are neuroprotective in a variety of neuroprotection models, the precise underlying mechanisms are currently not well understood. Here, we examined the role of protein kinase C (PKC) in mediating estrogen-induced neuroprotection in the HT-22 immortalized hippocampal cell line. The neuroprotection model utilized calcein fluorescence to quantitate cell viability following glutamate insults. 17beta-Estradiol (betaE2) protected HT-22 cells when treatment was initiated before or after the glutamate insult. The inhibition of PKC by bis-indolylmaleimide mimicked and enhanced betaE2-induced neuroprotection. In contrast, the inhibition of specific PKC isozymes (alpha and beta) by Go6976, inhibition of 1-phosphatidylinositol 3 kinase by wortmannin, or inhibition of protein kinase A by H-89, did not alter cell viability, suggesting a specific involvement of PKC in an isozyme-dependent manner. We further examined whether estrogen interacts with PKC in a PKC isozyme-specific manner. Protein levels and activity of PKC isozymes (alpha, delta, epsilon, and zeta) were assessed by western blot analysis and radiolabeled phosphorylation assays respectively. Among the isozymes tested, betaE2 altered only PKCepsilon; it reduced the activity and membrane translocation of PKCepsilon in a manner that correlated with its protection against glutamate toxicity. Furthermore, betaE2 reversed the increased activity of membrane PKCepsilon induced by glutamate. These data suggest that the neuroprotective effects of estrogens are mediated in part by inhibition of PKCepsilon activity and membrane translocation.

Estradiol Prevents Neural Tau Hyperphosphorylation Characteristic of Alzheimer's Disease

Alzheimer's disease (AD) is three times more prevalent in women than men, and epidemiological studies have shown that estrogen replacement in aging women forestalls the onset of AD. Hyperphosphorylation of the tau protein that forms the neurofibrillary tangles found in AD brains might be responsible for the breakdown of microtubules in affected neurons. The mechanisms by which tau protein is phosphorylated in the AD brain are not fully understood. Using a human neuroblastoma cell line (SH-SY5Y) and primary cultures of newborn male or female rat cerebral cortical neurons, we investigated the effect of 17beta-estradiol on tau protein expression and phosphorylation. We found that estradiol increased total tau and induced dephosphorylation at the proline-directed site of the molecule. Further, estradiol prevented okadaic acid-induced hyperphosphorylation of tau in both proline- and non-proline-directed sites, and antiestrogens blocked this effect. To our knowledge, this is the first report of an effect of estradiol on naturally occurring and induced tau phosphorylation. This assumes special significance because the estrogen action was found to be sexually dimorphic in rat cortical neurons and differentiation-sensitive in human neuroblastoma cells.

Antioxidant activity and neuroprotective effects of zolpidem and several synthesis intermediates

Structural relationship between the antioxidant melatonin and the non-benzodiazepine hypnotic zolpidem (ZPD) suggests possible direct antioxidant and neuroprotective properties of this compound. In the present work, these effects were analyzed for zolpidem and four of its synthesis intermediates. In vitro assays include lipid peroxidation and protein oxidation studies in liver and brain homogenates. Intracellular antioxidant effects were analyzed by evaluation of free radical formation prevention in HT-22 hippocampal cells treated with glutamate 10mM and measured by flow cytometer DCF fluorescence. The neuroprotective effect of these compounds was evaluated as neuronal death prevention of HT-22 cells treated with the same concentration of glutamate. Zolpidem was found to prevent induced lipid peroxidation in rat liver and brain homogenates showing figures similar to melatonin, although it failed to prevent protein oxidation. ZPD-I was the most effective out of the several zolpidem intermediates studied as it prevented lipid peroxidation with an efficiency higher than melatonin or zolpidem and with an effectiveness similar to estradiol and trolox. ZPD-I prevents protein oxidation, which trolox is known to be unable to prevent. When cellular experiments were undertaken, ZPD-I prevented totally the increase of intracellular free radicals induced by glutamate 10mM in culture medium for 12h, while zolpidem and ZPD-III partially prevented this increase. Also the three compounds protected hippocampal neurons from glutamate-induced death in the same conditions, being their comparative efficacy, ZPD-III > ZPD-I = ZPD.

Sex hormones and brain aging

Sex steroids exert pleiotropic effects in the nervous system, preserving neural function and promoting neuronal survival. Therefore, the age-related decrease in sex steroids may have a negative impact on neural function. Progesterone, testosterone and estradiol prevent neuronal loss in the central nervous system in different experimental animal models of neurodegeneration. Furthermore, progesterone and its reduced derivatives dihydroprogesterone and tetrahydroprogesterone reduce aging-associated morphological abnormalities of myelin and aging-associated myelin fiber loss in rat peripheral nerves. However, the results from hormone replacement studies in humans are thus far inconclusive. A possible alternative to hormonal replacement therapy is to increase local steroidogenesis by neural tissues, which express enzymes for steroid synthesis and metabolism. Proteins involved in the intramitochondrial trafficking of cholesterol, the first step in steroidogenesis, such as the peripheral-type benzodiazepine receptor and the steroidogenic acute regulatory protein, are up-regulated in the nervous system after injury. Furthermore, steroidogenic acute regulatory protein expression is increased in the brain of 24-month-old rats compared with young adult rats. This suggests that brain steroidogenesis may be modified in adaptation to neurodegenerative conditions and to the brain aging process. Furthermore, recent studies have shown that local formation of estradiol in the brain, by the enzyme aromatase, is neuroprotective. Therefore, steroidogenic acute regulatory protein, peripheral-type benzodiazepine receptor and aromatase are attractive pharmacological targets to promote neuroprotection in the aged brain.

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.

1-trichloromethyl-1,2,3,4-tetrahydro-beta-carboline (TaClo) induces apoptosis in human neuroblastoma cell lines

The former popular hypnotic chloral hydrate has been known to spontaneously condense with tryptamine in the body to give rise to a highly unpolar 1-trichloromethyl-1,2,3,4-tetrahydro-beta-carboline (TaClo) derivative. Earlier studies have revealed the relative permeability of the molecule through the body, and its ability to induce Parkinson-like symptoms in rats. In this study, we report that TaClo is a highly cytotoxic agent that leads to apoptosis in human neuroblastoma cells involving caspase-3 activation.

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.

Equine estrogens differentially inhibit DNA fragmentation induced by glutamate in neuronal cells by modulation of regulatory proteins involved in programmed cell death

BACKGROUND

Recent data indicate that excitotoxicity of high levels of neurotransmitter glutamate may be mediated via programmed cell death (apoptosis) and that it can be prevented in HT22 mouse hippocampal cells by various equine estrogens with Delta8,17beta-estradiol (Delta8,17beta-E2) being the most potent. In order to delineate the mechanism(s), glutamate-induced cell death of HT22 cells was assessed by measuring (a) DNA fragmentation in the presence or absence of 11 equine estrogens (components of the drug CEE); (b) cell death and (c) levels of anti-apoptotic (Bcl-2) and proapoptotic (Bax) proteins in the presence or absence of two equine estrogens, Delta8,17beta-E2 and 17beta-estradiol (17beta-E2) by LDH release assay and Western blot analysis respectively.

RESULTS

Glutamate treatment induced cell death was time and dose-dependent. After 18 to 24 h, glutamate induced DNA fragmentation and morphological characteristics of apoptotic cell death. DNA fragmentation and morphological changes induced by 10 mM glutamate were completely inhibited by some equine estrogens. Exposure of cells to various concentrations of glutamate, resulted in a significant increase in cell death associated LDH release that was time-dependent. Both Delta8,17beta-E2 and 17beta-E2 inhibited the glutamate-induced LDH release and cell death in a dose-dependent manner with Delta8,17beta-E2 being 10 times more potent than 17beta-E2. Western blot analysis indicated that glutamate also significantly decreased the levels of Bcl-2 and increased Bax levels. This glutamate-induced change in the ratio of Bcl-2 to Bax was reversed by estrogens with Delta8,17beta-E2 being more potent.

CONCLUSIONS

In HT22 mouse hippocampal cells, glutamate induced apoptosis that was associated with DNA fragmentation, morphological changes and up-regulation of the pro-apoptotic protein Bax and down-regulation of the anti-apoptotic protein Bcl-2. This apoptotic process was differentially prevented by some equine estrogens with Delta8,17beta-E2 being more potent than 17beta-E2. Since HT22 cells lacked both glutamate and estrogen receptors, the neuroprotective effects of estrogens most likely involve both genomic and non-genomic mechanisms. Since Delta8-estrogens are less feminizing estrogens than 17beta-E2, further chemical modifications of these Delta8-estrogens may provide more selective estrogens that will be useful in the prevention of neurodegenerative diseases such as Alzheimer's and Parkinson's in both aging men and women.

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.