Neuroprotective Effects Of E2 Research Articles

Effects of 2-methoxyestradiol on hydrogen peroxide induced neuronal cell death and tau hyperphosphorylation

AimsAlzheimer's Disease (AD) is characterized by progressive cognitive impairment, and memory loss. It has been shown that depletion of estrogens renders women vulnerable to AD with menopause women presenting higher risk for AD development than men. However, women under hormone replacement therapy (HRT) with 17β-estradiol (E2) show lower risk for AD, implying that E2 may be protective. It has been shown that E2 exerts its effects through the estrogen receptor (ER) but also via its biologically active metabolites, 2-hydroxyestradiol (2OH), and 2-methoxyestradiol (2ME). We hypothesized that the neuroprotective effects of E2 are partly attributed to its metabolites. Materials and methodsSH-SY5Y neuronal cells were subjected oxidative stress (OS) cell death by hydrogen peroxide (H2O2), in the presence or absence of E2, 2ME and 2OH. Viability was assessed by trypan blue and thiazolyl blue tetrazolium bromide assays, intracellular OS with the Dichlorodihydrofluorescein Diacetate (DCFDA) assay, and Bax, p53 and PUMA quantified by RT-PCR. Tau hyperphosphorylation was studied by western blot. Key findingsE2 and its metabolites 2OH and 2ME protect from cell death as assessed by the viability assays. Their effect was partly attributed to their antioxidant properties evidenced by the reduction of intracellular OS. Treatment with 2ME resulted in a reduction of Bax, but not p53 or PUMA in cells challenged with OS. Finally, 2ME was able to inhibit tau hyperphosphorylation as well. SignificanceE2 protects neuron cells partly through its metabolites. Further studies are needed to fully delineate the mechanism for this protection.

N-myc Downstream-Regulated Gene 2 (Ndrg2): A Critical Mediator of Estrogen-Induced Neuroprotection Against Cerebral Ischemic Injury.

Growing evidence indicates that estrogen plays a pivotal role in neuroprotection against cerebral ischemia, but the molecular mechanism of this protection is still elusive. N-myc downstream-regulated gene 2 (Ndrg2), an estrogen-targeted gene, has been shown to exert neuroprotective effects against cerebral ischemia in male mice. However, the role of Ndrg2 in the neuroprotective effect of estrogen remains unknown. In this study, we first detected NDRG2 expression levels in the cortex and striatum in both female and male mice with western blot analyses. We then detected cerebral ischemic injury by constructing middle cerebral artery occlusion and reperfusion (MCAO-R) models in Ndrg2 knockout or conditional knockdown female mice. We further implemented estrogen, ERα, or ERβ agonist replacement in the ovariectomized (OVX) Ndrg2 knockout or conditional knockdown female mice, then tested for NDRG2 expression, glial fibrillary acidic protein (GFAP) expression, and extent of cerebral ischemic injury. We found that NDRG2 expression was significantly higher in female than in male mice in both the cortex and striatum. Ndrg2 knockouts and conditional knockdowns showed significantly aggravated cerebral ischemic injury in female mice. Estrogen and ERβ replacement treatment (DPN) led to NDRG2 upregulation in both the cortex and striatum of OVX mice. Estrogen and DPN also led to GFAP upregulation in OVX mice. However, the effect of estrogen and DPN in activating astrocytes was lost in Ndrg2 knockout OVX mice and primary cultured astrocytes, but partially retained in conditional knockdown OVX mice. Most importantly, we found that the neuroprotective effects of E2 and DPN against cerebral ischemic injury were lost in Ndrg2 knockout OVX mice but partially retained in conditional knockdown OVX mice. These findings demonstrate that estrogen alleviated cerebral ischemic injury via ERβ upregulation of Ndrg2, which could activate astrocytes, indicating that Ndrg2 is a critical mediator of E2-induced neuroprotection against cerebral ischemic injury.

Downregulation of G‑protein‑coupled receptor 30 in the hippocampus attenuates the neuroprotection of estrogen in the critical period hypothesis.

The aim of the present study was to investigate the role of G-protein-coupled receptor 30 (GPR30) in long-term 17β-estradiol (E2) deprivation (LTED) in a rat model with global cerebral ischemia (GCI), and its therapeutic target for ischemic stroke in the clinical setting. Following bilateral ovariectomy, GCI was induced in rats 1 or 10 weeks post-surgery. To determine the protein and mRNA expression levels of GPR30 in the hippocampal CA1 region of LTED rats, short-term E2 deprivation (STED) rats and naturally aging rats, western blot analysis and reverse transcription-quantitative polymerase chain reaction were performed. The results of the present study demonstrated that E2 treatment revealed significant neuroprotection post-GCI in STED rats, but not in LTED rats, as well as a decrease in the expression levels of GPR30 in the hippocampal CA1 region. In LTED rats,. Notably, no effects were observed on the ubiquitination of GPR30 following investigation in STED or LTED rats. While the protein and mRNA expression levels of GPR30 were also decreased in the hippocampal CA1 region of female 24-month-old rats compared with 3-month-old rats. E2 treatment initiated for the entire ovariectomy period elevated GPR30 mRNA and protein expression levels, and attenuated the loss of hippocampal neurons in the GCI-induced CA1 region, indicating that E2 treatment exerted robust neuroprotection within LTED rats. However, the neuroprotective effect of E2 may be blocked by G15. The results of the present study revealed that downregulation of GPR30 expression may attenuate the neuroprotection of E2 within LTED conditions in rats post-ovariectomy by leading to neuronal insensitivity to E2 neuroprotection following cerebral ischemia. These results provide evidence that GPR30 may have potential as a novel therapeutic target for the treatment of clinical ischemic stroke.

Pretreatment with 17β-Estradiol Attenuates Cerebral Ischemia-Induced Blood-Brain Barrier Disruption in Aged Rats: Involvement of Antioxidant Signaling

Background/Aims: Blood-brain barrier (BBB) disruption is often induced in brain injury and particularly associated with cerebral ischemia in stroke. Estradiol (17β-estradiol 3-benzoate, E2), an endogenous steroid hormone, has been reported to play a protective role against cerebrovascular pathologies. Here we aimed to determine the potential effects of E2 on the integrity of BBB and brain damage following middle cerebral artery occlusion (MCAO). Methods: Aged (24- month-old) ovariectomized female rats were administered E2 for 2 months through daily intraperitoneal injections prior to induction of MCAO. Results: Compared to vehicle controls, E2 had a dose-dependent effect in reducing the severity of brain injuries while maintaining the integrity of the BBB in aged rats. The neuroprotective effects of E2 were associated with the rescued tight junction loss, decreased oxidative stress, and attenuated ERK activation in the ischemic brains. Conclusion: Our data suggest a beneficial role of E2 in aged stroke patients, associated with a protective effect of E2 against BBB disruption in aging-related brain ischemia.

Neuroprotective effects of estrogen in CNS injuries: insights from animal models.

Among the estrogens that are biosynthesized in the human body, 17β-estradiol (estradiol or E2) is the most common and the best estrogen for neuroprotection in animal models of the central nervous system (CNS) injuries such as spinal cord injury (SCI), traumatic brain injury (TBI), and ischemic brain injury (IBI). These CNS injuries are not only serious health problems, but also enormous economic burden on the patients, their families, and the society at large. Studies from animal models of these CNS injuries provide insights into the multiple neuroprotective mechanisms of E2 and also suggest the possibility of translating the therapeutic efficacy of E2 in the treatment SCI, TBI, and IBI in humans in the near future. The pathophysiology of these injuries includes loss of motor function in the limbs, arms and their extremities, cognitive deficit, and many other serious consequences including life-threatening paralysis, infection, and even death. The potential application of E2 therapy to treat the CNS injuries may become a trend as the results are showing significant therapeutic benefits of E2 for neuroprotection when administered into the animal models of SCI, TBI, and IBI. This article describes the plausible mechanisms how E2 works with or without the involvement of estrogen receptors and provides an overview of the known neuroprotective effects of E2 in these three CNS injuries in different animal models. Because activation of estrogen receptors has profound implications in maintaining and also affecting normal physiology, there are notable impediments in translating E2 therapy to the clinics for neuroprotection in CNS injuries in humans. While E2 may not yet be the sole molecule for the treatment of CNS injuries due to the controversies surrounding it, the neuroprotective effects of its metabolite and derivative or combination of E2 with another therapeutic agent are showing significant impacts in animal models that can potentially shape the new treatment strategies for these CNS injuries in humans.

Estrogen is neuroprotective against hypoglycemic injury in murine N38 hypothalamic cells.

Estrogen (E2) has been demonstrated to possess protective effects from hypoglycemic toxicity, particularly in the pancreas. In the central nervous system, several brain regions, such as the hypothalamus, are highly vulnerable to hypoglycemic injuries that may lead to seizures, coma, and mortality. The present study performed a novel invitro assay of hypoglycemic injury to hypothalamic cells, and is the first study, to the best of our knowledge, to demonstrate that E2 protects hypothalamic cells from hypoglycemic toxicity. The toxic effects of hypoglycemia on hypothalamic cells invitro was determined by performing cell counts, together with MTT and lactate dehydrogenase assays, using the N38 murine hypothalamic cell line. Following 24 and 48h in hypoglycemic conditions, a 60 and 75% reduction in cell number and mitochondrial function was observed, which reached 80 and ~100% by 72 and 96h, respectively. E2 treatment prevented the hypoglycemia‑induced loss in cell number and mitochondrial toxicity at 24 and 48h. However at 72 and 96h of hypoglycemic conditions, the neuroprotective effects of E2 on cell number or mitochondrial function was not significant or not present at all. In order to determine whether E2 exerted its effects through the AKT signaling pathway, the expression of proline‑rich AKT substrate of 40kDa (PRAS40) was analyzed. No alterations in PRAS40 expression were observed when N38 cells were exposed to hypoglycemic shock. From the biochemical and molecular data obtained, the authors speculated that E2 exhibits neuroprotective effects against hypoglycemic shock in hypothalamic cells, which dissipates with time. Despite demonstrating no significant effect on total AKT/PRS40 activity, it is possible that E2 may mediate these neuroprotective effects by upregulating the phosphorylated‑AKT/pPRAS40 signaling pathway. The present study presented, to the best of our knowledge, the first invitro model for hypoglycemic toxicity to hypothalamic cells, and provided evidence to suggest that E2 may protect hypothalamic cells from the damaging effects of hypoglycemia.

Inhibition of Autophagy by Estradiol Promotes Locomotor Recovery after Spinal Cord Injury in Rats.

17β-estradiol (E2) has been shown to have neuroprotective effects in different central nervous system diseases. The mechanisms underlying estrogen neuroprotection in spinal cord injury (SCI) remain unclear. Previous studies have shown that autophagy plays a crucial role in the course of nerve injury. In this study, we showed that E2 treatment improved the restoration of locomotor function and decreased the loss of motor neurons in SCI rats. Real-time PCR and western blot analysis revealed that the protective function of E2 was related to the suppression of LC3II and beclin-1 expression. Immunohistochemical study further confirmed that the immunoreactivity of LC3 in the motor neurons was down-regulated when treated with E2. In vitro studies demonstrated similar results that E2 pretreatment decreased the autophagic activity induced by rapamycin (autophagy sensitizer) and increased viability in a PC12 cell model. These results indicated that the neuroprotective effects of E2 in SCI are partly related to the suppression of excessive autophagy.

17β-estradiol suppresses hyperoxia-induced apoptosis of oligodendrocytes through paired-immunoglobulin-like receptor B.

Hyperoxia is a high risk factor for neurodevelopmental disorders and can cause nerve cell death. 17β‑Estradiol (E2) has been demonstrated as a neuroprotective agent. In the present study, the effect of hyperoxia on rat oligodendrocyte precursor cells (OPCs) in vivo and the neuroprotective effects of E2 on these cells were investigated. OPCs were treated with various concentrations of E2 and were harvested for reverse transcription‑quantitiative polymerase chain reaction (RT‑qPCR) analysis at various time‑points. RT‑qPCR analysis demonstrated that paired immunoglobin‑like receptor B (PriB) PriB mRNA expression levels were markedly decreased following treatment with 10(‑6), 10(‑7) and 10(‑8) M E2. Cells treated with 10(‑7) M E2 for 24 h were selected for subsequent experiments. PriB was silenced with small interfering (si)RNA and the effects of E2 treatment and silencing of PriB on the viability and apoptosis of OPCs under hyperoxic stimulation was detected using 3‑(4,5‑dimethyl‑2‑thiazolyl)‑2,5‑diphenyl‑2‑H‑tetrazoliu‑bromide (MTT) assay and flow cytometry analysis. The results revealed that hyperoxia induced apoptosis in OPCs and decreased their viability. Hyperoxia also induced the expression of caspases‑3 and ‑8, and Fas cell surface death receptor (Fas). E2 treatment markedly downregulated the expression of PirB. E2 treatment or PirB silencing markedly decreased hyperoxia‑induced apoptosis, increased cell viability and decreased the expression of caspases‑3 and ‑8, and Fas in OPCs, indicating that E2 protects OPCs from hyperoxia‑induced apoptosis, predominantly through the downregulation of PirB The results of the present study provide a theoretical basis for the reasonable use of oxygen in Neonatal Intensive Care Units.

The role of lysosomal proteinases and estradiol in neurodegeneration induced by beta-amyloid.

Activation of lysosomal degradation process in nervous tissue may be neuroprotective. One of the factors that may influence on expression of lysosomal proteinases is the sex hormone, estradiol (E2). In this regard the expression of lysosomal proteinases after intracerebral injection of beta-amyloid peptide (Aβ) was investigated as well as the neuroprotective effect of E2 in Aβ-induced neurodegeneration. Intracerebral injection of Aβ was shown to cause the significant increase in expression of cathepsin D in rat hippocampus and cerebral cortex. On the background of Aβ intoxication, E2 treatment resulted in further increase in cathepsin D gene expression in hippocampus region and in its lowering to the control level in cerebral cortex. It was demonstrated for the first time that neuroprotective effect of E2 may be mediated by cathepsin D up-regulation.

17β-estradiol inhibits MMP-9 and SUR1/TrpM4 expression and activation and thereby attenuates BSCB disruption/hemorrhage after spinal cord injury in male rats.

Blood-spinal cord barrier (BSCB) disruption and progressive hemorrhage after spinal cord injury (SCI) lead to secondary injury and the subsequent apoptosis and/or necrosis of neuron and glia, causing permanent neurological deficits. In this study, we examined the effect of 17β-estradiol (E2) on BSCB breakdown and hemorrhage as well as subsequent inflammation after SCI. After a moderate contusion injury at the 9th thoracic segment of spinal cord, E2 (300 μg/kg) was administered by iv injection immediately after SCI, and the same dose of E2 was then administered 6 and 24 hours after injury. Our data show that E2 attenuated BSCB permeability and hemorrhage and reduced the infiltration of neutrophils and macorphages after SCI. Consistent with this finding, the expression of inflammatory mediators was significantly reduced by E2. Furthermore, E2 treatment significantly inhibited the expression of sulfonylurea receptor 1 and transient receptor potential melastatin 4 after injury, which are known to mediate hemorrhage at an early stage after SCI. Moreover, the expression and activation of matrix metalloprotease-9 after injury, which is known to disrupt BSCB, and the degradation of tight junction proteins, such as zona occludens-1 and occludin, were significantly inhibited by E2 treatment. Furthermore, the protective effects of E2 on BSCB disruption and functional improvement were abolished by an estrogen receptor antagonist, ICI 182780 (3 mg/kg). Thus, our study provides evidence that the neuroprotective effect of E2 after SCI is, in part, mediated by inhibiting BSCB disruption and hemorrhage through the down-regulation of sulfonylurea receptor 1/transient receptor potential melastatin 4 and matrix metalloprotease-9, which is dependent on estrogen receptor.

Impact of continuous versus discontinuous progesterone on estradiol regulation of neuron viability and sprouting after entorhinal cortex lesion in female rats.

Because the estrogen-based hormone therapy (HT) in postmenopausal women typically contains a progestogen component, understanding the interactions between estrogens and progestogens is critical for optimizing the potential neural benefits of HT. An important issue in this regard is the use of continuous vs discontinuous hormone treatments. Although sex steroid hormone levels naturally exhibit cyclic fluctuation, many HT formulations include continuous delivery of hormones. Recent findings from our laboratory and others have shown that coadministration of progesterone (P4) can either attenuate or augment beneficial actions of 17β-estradiol (E2) in experimental models depending in part upon the delivery schedule of P4. In this study, we demonstrate that the P4 delivery schedule in combined E2 and P4 treatments alters degenerative and regenerative outcomes of unilateral entorhinal cortex lesion. We assessed how lesion-induced degeneration of layer II neurons in entorhinal cortex layer and deafferentation in dentate gyrus are affected by ovariectomy and treatments with E2 alone or in combination with either continuous or discontinuous P4. Our results demonstrate the combined efficacy of E2 and P4 is dependent on the administration regimen. Importantly, the discontinuous-combined E2+P4 regimen had the greatest neuroprotective efficacy for both end points. These data extend a growing literature that indicates qualitative differences in the neuroprotective effects of E2 as a function of cotreatment with continuous versus discontinuous P4, the understanding of which has important implications for HT in postmenopausal women.

Neuroprotective effect of estradiol-loaded poly(lactic-co-glycolic acid) nanoparticles on glutamate-induced excitotoxic neuronal death.

Different concentrations of estradiol (E2)-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles (E2-PLGA-NPs) were synthesized using the emulsion-diffusion method. Transmission electron microscopy results showed that the average particle size of E2-PLGA-NPs was 98 ± 1.9 nm when stabilized with polyvinyl alcohol and 103 ± 4.9 nm when stabilized with Tween-80. Fourier transform-infrared spectroscopy with diamond attenuated total reflectance was used to identify the presence or absence of E2 molecules in PLGA nanocapsules. Cell proliferation was assessed after treating SH-SY5Y neuroblastoma cells with 1 nM-1 μM of E2 and E2-PLGA-NPs. The neuroprotective efficacy against glutamate-induced excitotoxicity was also investigated in SH-SY5Y neuroblastoma cells. Neuroprotection was greater in E2-PLGA-NP-treated cells than in cells treated with the same concentration of E2. Furthermore, E2- and E2-PLGA-NP-treated cells expressed more p-ERK1/2 and p-CREB than cells treated with glutamate only. Moreover, the expression of p-ERK1/2 was higher than that of p-CREB. In this study, p-ERK1/2 had a greater influence on the neuroprotective effect of E2 and E2-PLGA-NPs than p-CREB.

Neuroprotective Effects of Non-Classical Estrogen-Like Signaling Activators: From Mechanism to Potential Implications

The gonadal steroid 17β-estradiol (E2) has shown powerful cytoprotective effect on cells. In addition to classical genomic mechanisms of action, E2 also exerts non-classical effects on intracellular signal transduction. Extensive studies during the past two decades have provided evidence that the E2-induced non-classical signaling on second messenger molecules plays a critical role in the neuroprotective effect of E2. These observations provide a unique basis for developing non-classical estrogen-like signaling activators that may have potential for clinical use in neuroprotection. In spite of the extensive research over the past decade reviewed here, we are just starting to appreciate the importance and potential of these compounds. Hence, we first describe the molecular characteristics and effects of these activators. Second, we survey recent data as to possible mechanisms underlying the ameliorative actions of selective non-classical estrogen-like signaling activation. In addition, the pitfalls and future aspects of "non-classical"-line activators and its clinical relevance will also be discussed.

17β-Estradiol Attenuates Neural Cell Apoptosis Through Inhibition of JNK Phosphorylation in SCI Rats and Excitotoxicity Induced by Glutamate In Vitro

ABSTRACTWe investigated whether 17β-estradiol (E2) treatment could prevent the apoptosis of neural cells after spinal cord injury (SCI) and cultured cortical cells through inhibition of JNK (c-Jun N-terminal kinase) phosphorylation. SCI-induced rats were randomly divided into three groups: control, E2-treated, and sham-treated. Five rats from each group were sacrificed at 2, 4, 6, 12, or 24 h postinjury. Apoptotic neural cells were assessed using the TUNEL method. JNK phosphorylation was detected with immunohistochemistry. Cultured cortical cells were pretreated with E2 and the specific JNK inhibitor SP600125 and then treated with glutamate-induced cytotoxicity in vitro. Neuron viability was determined with an methyl thiazolyl tetrazolium (MTT) assay, morphology of apoptotic cells was observed with 4′,6-diamidino-2-phenylindole (DAPI) staining, and JNK phosphorylation was detected using Western blot analysis. Treatment with E2 reduced neuron apoptosis and inhibited JNK phosphorylation. Moreover, the number of apoptotic cells was correlated with JNK phosphorylation 24 h after the rats suffered the SCI. Pretreatment with E2 significantly maintained neural cell viability, attenuated apoptosis, and inhibited JNK phosphorylation induced by glutamate in vitro. These neuroprotective effects of E2 on neural cells were blocked by the co-administration of SP600125. Our results suggest that neuroprotection from E2 is partially mediated by the inhibition of JNK phosphorylation.

17β-Estradiol Protects Dopaminergic Neurons in Organotypic Slice of Mesencephalon by MAPK-Mediated Activation of Anti-apoptosis Gene BCL2

Both clinical and experimental studies provide growing evidences that marked sex differences in certain neurological disorders or disease models are largely attributed to the neuroprotective effects of estrogen. The purposes of this study were to assess the neuroprotective effect of 17β-estradiol (E2) on dopaminergic neurons against 6-hydroxydopamine (6-OHDA) in organotypic mesencephalic slice culture and to elucidate the possible mechanism underlying neuroprotection. It was found that long-term exposure to E2 exerted marked effects on restoring the number of dopaminergic neurons, maintaining normal morphology of dopaminergic neurons, and preserving their ability to release dopamine at the presence of 6-OHDA. The neuroprotective effect of E2 could be dramatically blocked by an estrogen receptor antagonist ICI 182, 780 (ICI). The expression of GFAP, TLR4, and anti-apoptosis gene BCL2 were elevated at the presence of E2, whereas only BCL2 activation was blocked by ICI, dominantly responsible for E2-induced neuroprotection. Furthermore, activation of BCL2 was speculated to be mainly mediated through mitogen-activated protein kinase (MAPK) pathways, yet phosphatidylinositol-3-kinase signaling contributed largely to GFAP and TLR4 upregulation. Taken together, MAPK pathway-mediated BCL2 expression accounted for one of the key mechanisms involved in E2 neuroprotective effect on dopaminergic neurons against 6-OHDA insult. This finding provides new insight into controversial estrogen replacement therapy.

Estrogen Regulates Bcl-w and Bim Expression: Role in Protection against β-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.

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 17β-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.

Therapeutic effects of Ginkgo biloba extract EGB 761 in animal models of Alzheimer’s disease

assessed for mitochondrial respiratory activity and enzymatic activity in the presence and absence of toxic calcium exposure. Primary hippocampal rat neurons exposed to E2 or vehicle control were assessed for cytochrome c release and Bax translocation by immunocytochemistry and western blot analysis. Conclusions: E2-treated mitochondria displayed enhanced respiratory function coupled to increased expression and activity of the electron transport chain complex IV (cytochrome c oxidase). This enhancement of basal mitochondrial function was paralleled by the neuroprotective effects of E2, which were evidenced by an attenuation of the calcium-induced decline in mitochondrial respiratory function. Apoptosis during neurodegeneration is preceded by release of cytochrome c from the mitochondrial intermembrane space. This translocation is regulated by the expression and localization of the Bcl-2 family of proteins. We showed that E2 prevents the glutamateand A-induced reciprocal mitochondrial/cytosolic translocation of cytochrome c and Bax. These data suggest a mechanism of E2 neuroprotection involving an increase in Ca sequestration by mitochondria coupled with an increase in mitochondrial Ca load tolerability and an increase in mitochondrial respiratory function.

Estrogen protects against beta-amyloid-induced neurotoxicity in rat hippocampal neurons by activation of Akt.

The cellular mechanisms underlying the neuroprotective effects of estrogen are only beginning to be elucidated. Here we examined the role of protein kinase B (Akt) activation in 17beta-estradiol (E2) inhibition of beta-amyloid peptide (31-35) (Abeta31-35)-induced neurotoxicity in cultured rat hippocampal neurons. Abeta31-35 (25-30 betaM) significantly decreased the total number of microtubule associated protein-2 positive cells (MAP2+). This decrease was significantly reversed by pre-treatment with 100 nM E2. Further, 100 nM E2 alone significantly increased the total number of protein kinase B and microtubule associated protein-2 positive cells compared with controls. Such E2-induced increases were inhibited by LY294002 (20 microM), a specific PI3-K inhibitor, as well as by tamoxifen, an estrogen receptor antagonist/selective estrogen receptor modulator. These results indicate that the neuroprotective effects of E2 may be mediated at least in part via estrogen receptor-mediated protein kinase B activation.