Neuroprotective action of acute estrogens: animal models of brain ischemia and clinical implications

Polydopamine-modified black phosphorus nanosheet drug delivery system for the treatment of ischemic stroke

Black phosphorus (BP), as a representative metal-free semiconductor, has been extensively explored. It has a higher drug loading capacity in comparison to conventional materials and also possesses excellent biocompatibility and biodegradability. Furthermore, BP nanosheets can enhance the permeability of the blood-brain barrier (BBB) upon near-infrared (NIR) irradiation, owing to their photothermal effect. However, the inherent instability of BP poses a significant limitation, highlighting the importance of surface modification to enhance its stability. Ischemic stroke (IS) is caused by the occlusion of blood vessels, and its treatment is challenging due to the hindrance caused by the BBB. Therefore, there is an urgent need to identify improved methods for bypassing the BBB for more efficient IS treatment. This research devised a novel drug delivery approach based on pterostilbene (Pte) supported by BP nanosheets, modified with polydopamine (PDA) to form BP-Pte@PDA. This system shows robust stability and traverses the BBB using effective photothermal mechanisms. This enables the release of Pte upon pH and NIR stimuli, offering potential therapeutic advantages for treating IS. In a middle cerebral artery occlusion mouse model, the BP-Pte@PDA delivery system significantly reduced infarct size, and brain water content, improved neurological deficits, reduced the TLR4 inflammatory factor expression, and inhibited cell apoptosis. In summary, the drug delivery system fabricated in this study thus demonstrated good stability, therapeutic efficacy, and biocompatibility, rendering it suitable for clinical application.

Development of a new cerebral ischemia reperfusion model of Mongolian gerbils and standardized evaluation system

BACKGROUND

The Mongolian gerbil is an excellent laboratory animal for preparing the cerebral ischemia model due to its inherent deficiency in the circle of Willis. However, the low incidence and unpredictability of symptoms are caused by numerous complex variant types of the circle. Additionally, the lack of an evaluation system for the cerebral ischemia/reperfusion (I/R) model of gerbils has shackled the application of this model.

METHODS

We created a symptom-oriented principle and detailed neurobehavioral scoring criteria. At different time points of reperfusion, we analyzed the alteration in locomotion by rotarod test and grip force score, infarct volume by triphenyltetrazolium chloride (TTC) staining, neuron loss using Nissl staining, and histological characteristics using hematoxylin-eosin (H&E) straining.

RESULTS

With a successful model rate of 56%, 32 of the 57 gerbils operated by our method harbored typical features of cerebral I/R injury, and the mortality rate in the male gerbils was significantly higher than that in the female gerbils. The successfully prepared I/R gerbils demonstrated a significant reduction in motility and grip strength at 1 day after reperfusion; formed obvious infarction; exhibited typical pathological features, such as tissue edema, neuronal atrophy and death, and vacuolated structures; and were partially recovered with the extension of reperfusion time.

CONCLUSION

This study developed a new method for the unilateral common carotid artery ligation I/R model of gerbil and established a standardized evaluation system for this model, which could provide a new cerebral I/R model of gerbils with more practical applications.

Cerebroprotective Effect of 17β-Estradiol Replacement Therapy in Ovariectomy-Induced Post-Menopausal Rats Subjected to Ischemic Stroke: Role of MAPK/ERK1/2 Pathway and PI3K-Independent Akt Activation

Despite the overwhelming advances in the understanding of the pathogenesis of stroke, a devastating disease affecting millions of people worldwide, currently there are only a limited number of effective treatments available. Preclinical and clinical studies show that stroke is a sexually dimorphic disorder, affecting males and females differently. Strong experimental evidence indicates that estrogen may play a role in this difference and that exogenous 17β-estradiol (E2) is neuroprotective against stroke in both male and female rodents. However, the molecular mechanisms by which E2 intervenes in ischemia-induced cell death, revealing these sex differences, remain unclear. The present study was aimed to determine, in female rats, the molecular mechanisms of two well-known pro-survival signaling pathways, MAPK/ERK1/2 and PI3K/Akt, that mediate E2 neuroprotection in response to acute ischemic stroke. E2 pretreatment reduced brain damage and attenuated apoptotic cell death in ovariectomized female rats after an ischemic insult. Moreover, E2 decreased phosphorylation of ERK1/2 and prevented ischemia/reperfusion-induced dephosphorylation of both Akt and the pro-apoptotic protein, BAD. However, MAPK/ERK1/2 inhibitor PD98059, but not the PI3K inhibitor LY294002, attenuated E2 neuroprotection. Thus, these results suggested that E2 pretreatment in ovariectomized female rats modulates MAPK/ERK1/2 and activates Akt independently of PI3K to promote cerebroprotection in ischemic stroke. A better understanding of the mechanisms and the influence of E2 in the female sex paves the way for the design of future successful hormone replacement therapies.

The novel estrogen receptor modulator STX attenuates Amyloid-β neurotoxicity in the 5XFAD mouse model of Alzheimer's disease

Based on previous evidence that the non-steroidal estrogen receptor modulator STX mitigates the effects of neurotoxic Amyloid-β (Aβ) in vitro, we have evaluated its neuroprotective benefits in a mouse model of Alzheimer's disease. Cohorts of 5XFAD mice, which begin to accumulate cerebral Aβ at two months of age, were treated with orally-administered STX starting at 6 months of age for two months. After behavioral testing to evaluate cognitive function, biochemical and immunohistochemical assays were used to analyze key markers of mitochondrial function and synaptic integrity. Oral STX treatment attenuated Aβ-associated mitochondrial toxicity and synaptic toxicity in the brain, as previously documented in cultured neurons. STX also moderately improved spatial memory in 5XFAD mice. In addition, STX reduced markers for reactive astrocytosis and microgliosis surrounding amyloid plaques, and also unexpectedly reduced overall levels of cerebral Aβ in the brain. The neuroprotective effects of STX were more robust in females than in males. These results suggest that STX may have therapeutic potential in Alzheimer's Disease.

Neuroprotective Effects of Treadmill Exercise in Hippocampus of Ovariectomized and Diabetic Rats

To determine detrimental effects of estrogen and insulin deficiencies on hippocampus, we examined apoptosis-induced neuronal damage and cholinergic system in ovariectomized and/or diabetic rat hippocampus. Possible neuroprotective effects of treadmill exercise were also investigated. Adult female Wistar rats were randomly divided into four groups (n = 5 rats/group) as follows: control, ovariectomized (Ovx), diabetic (Dia, streptozotocin (STZ) 60 mg/kg; i.p.), and Ovx + Dia groups. Each group was further subdivided into exercise and non-exercise groups. Animals in exercise groups were subjected to treadmill training, while those in non-exercise groups were placed on the stationary treadmill for 4 weeks (5 days/week). Apoptosis-related protein levels (i.e. Bax, Bcl-2, and caspase-3), number of survived neurons, and acetylcholinesterase (AChE) activity in the hippocampus were measured using Western blotting, Cresyl Violet staining, and Ellman assay, respectively. Both ovariectomy and diabetes increased expression of Bax and caspase-3 and decreased expression of Bcl-2 at protein levels. In addition, a significant decrease in the number of survived neurons was observed in both Ovx and Dia groups, while AChE activity was lower only in the Dia group. The Ovx + Dia group showed stronger apoptosis-induced neuropathology and inhibition of AChE activity. Treadmill exercise attenuated apoptosis-induced neuropathology in the Ovx and Dia groups and recovered AChE activity in the Dia group. Neuroprotective effects of treadmill exercise were mediated by inhibition of apoptosis. Moderate exercise protocol had no beneficial anti-apoptotic and neuroprotective effects in ovariectomized-diabetic rats.

Sex differences in the cerebroprotection by Nestorone intranasal delivery following stroke in mice

Our previous studies showed that intranasal delivery of progesterone offers a good bioavailability and neuroprotective efficacy after experimental stroke. We have also demonstrated that progesterone receptors (PR) are essential for cerebroprotection by endogenous progesterone and by progesterone treatment. The identification of PR as a potential drug target for stroke therapy opens new therapeutic indications for selective synthetic progestins. Nestorone® (16-methylene-17α-acetoxy-19-nor-pregn-4-ene-3, 20-dione, also known as segesterone acetate) is a 19-norprogesterone derivative that more potently targets PR than progesterone. The objective of this study was to evaluate the cerebroprotective efficiency of intranasal administration of Nestorone after middle cerebral occlusion (MCAO) in mice. We show here that intranasal administration is a very efficient route to achieve a preferential delivery of Nestorone to the brain and confers a slow elimination and a sustained bioavailability. Furthermore, intranasal administration of Nestorone (at 0.08 mg/kg) improved the functional outcomes and decreased the ischemic lesion in male but not in female mice at 48 h post MCAO. Use of PR^NesCre mice, selectively lacking expression of PR in neural cells, and their control PR^loxP/loxP littermates showed that the cerebroprotective effects of Nestorone in male mice depended on neural PR as they were not observed in PR^NesCre mice. Our findings show that intranasal delivery of Nestorone may be an efficient strategy to promote recovery after stroke in males and confirm the key role of PR in cerebroprotection. Furthermore, they point to sex differences in the response to Nestorone treatment and emphasize the necessity to include males and females in experimental studies.

A Review of Plant Extracts and Plant-Derived Natural Compounds in the Prevention/Treatment of Neonatal Hypoxic-Ischemic Brain Injury

Neonatal hypoxic-ischemic (HI) brain injury is one of the major drawbacks of mortality and causes significant short/long-term neurological dysfunction in newborn infants worldwide. To date, due to multifunctional complex mechanisms of brain injury, there is no well-established effective strategy to completely provide neuroprotection. Although therapeutic hypothermia is the proven treatment for hypoxic-ischemic encephalopathy (HIE), it does not completely chang outcomes in severe forms of HIE. Therefore, there is a critical need for reviewing the effective therapeutic strategies to explore the protective agents and methods. In recent years, it is widely believed that there are neuroprotective possibilities of natural compounds extracted from plants against HIE. These natural agents with the anti-inflammatory, anti-oxidative, anti-apoptotic, and neurofunctional regulatory properties exhibit preventive or therapeutic effects against experimental neonatal HI brain damage. In this study, it was aimed to review the literature in scientific databases that investigate the neuroprotective effects of plant extracts/plant-derived compounds in experimental animal models of neonatal HI brain damage and their possible underlying molecular mechanisms of action.

Animal models of transient ischemic attack: a review

Transient ischemic attack (TIA) is defined as a brief episode of neurological dysfunction caused by focal cerebral ischemia. TIA is a critical early warning signal of stroke. Patients with TIA may have long-term cognitive decline. The pathogenesis and pathological changes of TIA have not been fully elucidated. Animal models can simulate the process of human diseases and are essential tools to investigate injury mechanisms and therapeutic approaches of TIA. Most TIA animal models are based on ischemic stroke models and the definition of TIA. Each model has unique strengths and weaknesses. The establishment of a successful and reliable TIA model should follow three criteria: (1) objective evidence of cerebral arteries occlusion and reperfusion, (2) no permanent neurological deficit, and (3) no acute cerebral infarction. However, experimental animal models are impossible to be completely consistent with human TIA, because TIA itself is a heterogeneous disease. In the present review, the selection of animals, methodological development, and evaluation of cerebral blood flow of animal models of TIA are comprehensively evaluated.

Chlorogenic acid ameliorates memory loss and hippocampal cell death after transient global ischemia

Chlorogenic acid (CGA) is known to have antioxidant potentials, yet the effect of CGA on brain ischemia has not been sufficiently understood. Brain ischemia such as transient global ischemia disrupts many areas of the brain of rats, including the hippocampus. Male Wistar rats were randomly assigned into five groups, that is, sham-operated (SO), bilateral common carotid occlusion (BCCO), and BCCO+ 15, 30, and 60 mg/kg bw CGA groups (CGA15, CGA30, and CGA60, respectively). Brain ischemia was induced in Wistar rats with BCCO for 20 min followed by intraperitoneal injection of CGA. The rats were examined for the spatial memory in a Morris water maze test on the 3rd day and were euthanized on the 10th day after BCCO. The total number of pyramidal cells was estimated, and the mRNA expressions of Bcl2, Bax, caspase-3, SOD2, SOD1, GPx, ET-1, eNOS, CD31, and VEGF-A were measured. The BCCO group spent less time and distance in the target quadrant than any other group in the spatial memory retention test. The CA1 pyramidal cell numbers in the BCCO and CGA15 groups were lower than in the CGA30 and CGA60 groups. The mRNA expressions of Bcl2, SOD2, and CD31 in the BCCO group were lower than in the CGA15, CGA30, and CGA60 groups. The ET-1 expression was higher in the BCCO and CGA15 groups than in the SO, CGA30, and CGA60 groups. CGA improves the spatial memory and prevents the CA1 pyramidal cell death after BCCO by increasing Bcl2, SOD2, and CD31 expressions and decreasing ET-1 expression.

Sex steroid hormones as neuroprotective elements in ischemia models

Among sex steroid hormones, progesterone and estradiol have a wide diversity of physiological activities that target the nervous system. Not only are they carried by the blood stream, but also they are locally synthesized in the brain and for this reason, estradiol and progesterone are considered 'neurosteroids'. The physiological actions of both hormones range from brain development and neurotransmission to aging, illustrating the importance of a deep understanding of their mechanisms of action. In this review, we summarize key roles that estradiol and progesterone play in the brain. As numerous reports have confirmed a substantial neuroprotective role for estradiol in models of neurodegenerative disease, we focus this review on traumatic brain injury and stroke models. We describe updated data from receptor and signaling events triggered by both hormones, with an emphasis on the mechanisms that have been reported as 'rapid' or 'cytoplasmic actions'. Data showing the therapeutic effects of the hormones, used alone or in combination, are also summarized, with a focus on rodent models of middle cerebral artery occlusion (MCAO). Finally, we draw attention to evidence that neuroprotection by both hormones might be due to a combination of 'cytoplasmic' and 'nuclear' signaling.

17β-Estradiol Regulates Microglia Activation and Polarization in the Hippocampus Following Global Cerebral Ischemia

17β-Estradiol (E2) is a well-known neuroprotective hormone, but its role in regulation of neuroinflammation is less understood. Recently, our lab demonstrated that E2 could regulate the NLRP3 (NOD-like receptor protein 3) inflammasome pathway in the hippocampus following global cerebral ischemia (GCI). Here, we examined the ability of E2 to regulate activation and polarization of microglia phenotype in the hippocampus after global cerebral ischemia (GCI). Our in vivo study in young adult ovariectomized rats showed that exogenous low-dose E2 profoundly suppressed microglia activation and quantitatively shifted microglia from their "activated," amoeboid morphology to a "resting," ramified morphology after GCI. Further studies using M1 "proinflammatory" and M2 "anti-inflammatory" phenotype markers showed that E2 robustly suppressed the "proinflammatory" M1 phenotype, while enhancing the "anti-inflammatory" M2 microglia phenotype in the hippocampus after GCI. These effects of E2 may be mediated directly upon microglia, as E2 suppressed the M1 while enhancing the M2 microglia phenotype in LPS- (lipopolysaccharide-) activated BV2 microglia cells in vitro. E2 also correspondingly suppressed proinflammatory while enhancing anti-inflammatory cytokine gene expression in the LPS-treated BV2 microglia cells. Finally, E2 treatment abolished the LPS-induced neurotoxic effects of BV2 microglia cells upon hippocampal HT-22 neurons. Collectively, our study findings suggest a novel E2-mediated neuroprotective effect via regulation of microglia activation and promotion of the M2 "anti-inflammatory" phenotype in the brain.

Proteomics in plasma of ovariectomized rats and those exposed to estradiol valerate

The menopausal period, an inevitable physiological process for women, is frequently associated with physiological and psychological dysfunction attributable to substantial fluctuation and gradual decrease in female hormones induced by ovarian failure, leading to corresponding symptoms and diseases that impact multiple systems in the body to varying degrees. As prior studies have focused primarily on menopausal syndrome-related pathophysiological changes and hormone replacement therapy effects, here we approached menopausal disease incidence risk and pathogenesis through systemic plasma proteomics analysis. Female Sprague-Dawley rats were randomly divided into sham, ovariectomized, and estrogen treatment after ovariectomy groups (n=9 per group). Tandem Mass Tag quantitative proteomics analysis of their plasma identified over 900 proteins by MS. Between group fold change of >1.2 and p<0.05 (Student's t-test) identified 121 (including 36 up-regulated and 85 down-regulated), 117 (69 up-regulated and 48 down-regulated), and 109 (41 up-regulated and 68 down-regulated) differentially expressed proteins between groups, respectively. Of these, 5 (GHR, LIFR, apoA IV, RTN, and Lin28b) were verified by parallel reaction monitoring to be reliable. Further application of optimized screening criteria and performance of a series of bioinformatics analyses allowed the selection of 35 optimal differentially expressed proteins. Gene ontology annotation results suggested that the differentially expressed proteins are mainly annotated as protein binding, cell, and single organism process in terms of molecular function, cell composition, and biological process, respectively. KEGG pathway analysis indicated that the PI3-Akt pathway has the highest aggregation degree of differentially expressed proteins. Protein-protein interaction analysis noted GLUT4 as an important node protein. This research is the first to comprehensively analyze plasma protein changes, together with estrogen efficacy, in ovariectomized rats. The findings facilitate our understanding of the molecular mechanism of systemic menopausal changes and provide valuable clues for developing diagnostic biomarkers for menopausal dysfunctions and selecting clinical therapeutic strategies.

Aromatase and neuroinflammation in rat focal brain ischemia

Accumulating evidence suggests that expression of aromatase, the enzyme responsible for the conversion of androgens to estrogens, is transiently upregulated in rat stroke models. It was further suggested that increased aromatase expression is linked to neuroinflammation and that it is neuroprotective in females. Our goal was to investigate aromatase upregulation in male rats subjected to experimental stroke in relationship to neuroinflammation, infarct and response to treatment with different putative neuroprotective agents. Intact male rats were subjected to transient (90min) middle cerebral artery occlusion (MCAO) and administered selfotel (N-methyl-d-aspartic acid (NMDA) receptor competitive antagonist), TPEN (a zinc chelator), a combination of the two drugs or vehicle, injected immediately after reperfusion. Animals were killed 14days after MCAO and consecutive brain sections used to measure aromatase expression, cerebral infarct volume and neuroinflammation. Quantitative immunohistochemistry (IHC) demonstrated increased brain aromatase expression in the peri-infarct area relative to contralesional area, which was partially abrogated by neuroprotective agents. There was no correlation between aromatase expression in the peri-infarct zone and infarct volume, which was reduced by neuroprotective agents. Microglial activation, measured by quantitative autoradiography, was positively correlated with infarct and inversely correlated with aromatase expression in the peri-infarct zone. Our findings indicate that focal ischemia upregulates brain aromatase in the male rat brain at 14days post surgery, which is within the time frame documented in females. However, the lack of negative correlation between aromatase expression and infarct volume and lack of positive correlation between microgliosis and aromatase do not support a major role for aromatase as a mediator of neuroprotection or a causal relationship between microglial activation and increased aromatase expression in male focal ischemia.

Semi-synthetic sapogenin exerts neuroprotective effects by skewing the brain ischemia reperfusion transcriptome towards inflammatory resolution

Stroke represents one of the first causes of mortality and morbidity worldwide. We evaluated the therapeutic potential of a novel semi-synthetic spirosteroid sapogenin derivative "S15" in a transient middle cerebral artery occlusion (tMCAO) focal ischemia model in rat. S15-treated rats had significantly reduced infarct volumes and improved neurological functions at 24h post-reperfusion, compared with ischemia. Corresponding gene expression changes in brain were characterized by mRNA sequencing and qPCR approaches. Next, we applied geneset, pathway and transcription factor motif enrichment analysis to identify relevant signaling networks responsible for neuronal damage upon ischemia-reperfusion or neuroprotection upon pretreatment with S15. As expected, ischemia-reperfusion brain damage strongly modulates transcriptional programs associated with immune responses, increased differentiation of immune cells as well as reduced (cat)ion transport and synaptic activity. Interestingly, S15-dependent neuroprotection regulates inflammation-associated genes involved in phagosome specific resolution of tissue damage, chemotaxis and anti-inflammatory alternative activation of microglia. Altogether our transcriptome wide RNA sequencing and integrated pathway analysis provides new clues in the neuroprotective properties of a novel spirosteroid S15 or neuronal damage in rat brains subjected to ischemia, which opens new perspectives for successful treatment of stroke.

In Vitro Neuroprotective and Anti-Inflammatory Activities of Natural and Semi-Synthetic Spirosteroid Analogues

Two spirosteroid analogues were synthesized and evaluated for their in vitro neuroprotective activities in PC12 cells, against glutamate-induced excitotoxicity and mitochondrial damage in glucose deprivation conditions, as well as their anti-inflammatory potential in LPS/IFNγ-stimulated microglia primary cultures. We also evaluated the in vitro anti-excitotoxic and anti-inflammatory activities of natural and endogenous steroids. Our results show that the plant-derived steroid solasodine decreased PC12 glutamate-induced excitotoxicity, but not the cell death induced by mitochondrial damage and glucose deprivation. Among the two synthetic spirosteroid analogues, only the (25R)-5α-spirostan-3,6-one (S15) protected PC12 against ischemia-related in vitro models and inhibited NO production, as well as the release of IL-1β by stimulated primary microglia. These findings provide further insights into the role of specific modifications of the A and B rings of sapogenins for their neuroprotective potential.

Astrocytic response to cerebral ischemia is influenced by sex differences and impaired by aging

Ischemic stroke occurs more often among the elderly, and within this demographic, women are at an increased risk for stroke and have poorer functional recovery than men. This is also well replicated in animal studies where aging females are shown to have more extensive brain tissue loss as compared to adult females. Astrocytes provide nutrients for neurons, regulate glutamate levels, and release neurotrophins and thus play a key role in the events that occur following ischemia. In addition, astrocytes express receptors for gonadal hormones and synthesize several neurosteroids suggesting that the sex differences in stroke outcome may be mediated through astrocytes. This review discusses key astrocytic responses to ischemia including, reactive gliosis, excitotoxicity, and neuroinflammation. In light of the age and sex differences in stroke outcomes, this review highlights how aging and gonadal hormones influence these responses. Lastly, astrocyte specific changes in gene expression and epigenetic modifications during aging and following ischemia are discussed as possible molecular mechanisms for impaired astrocytic functioning.

Estrogen administration modulates hippocampal GABAergic subpopulations in the hippocampus of trimethyltin-treated rats

Given the well-documented involvement of estrogens in the modulation of hippocampal functions in both physiological and pathological conditions, the present study investigates the effects of 17-beta estradiol (E2) administration in the rat model of hippocampal neurodegeneration induced by trimethyltin (TMT) administration (8 mg/kg), characterized by loss of pyramidal neurons in CA1, CA3/hilus hippocampal subfields, associated with astroglial and microglial activation, seizures and cognitive impairment. After TMT/saline treatment, ovariectomized animals received two doses of E2 (0.2 mg/kg intra-peritoneal) or vehicle, and were sacrificed 48 h or 7 days after TMT-treatment. Our results indicate that in TMT-treated animals E2 administration induces the early (48 h) upregulation of genes involved in neuroprotection and synaptogenesis, namely Bcl2, trkB, cadherin 2 and cyclin-dependent-kinase-5. Increased expression levels of glutamic acid decarboxylase (gad) 67, neuropeptide Y (Npy), parvalbumin, Pgc-1α and Sirtuin 1 genes, the latter involved in parvalbumin (PV) synthesis, were also evident. Unbiased stereology performed on rats sacrificed 7 days after TMT treatment showed that although E2 does not significantly influence the extent of TMT-induced neuronal death, significantly enhances the TMT-induced modulation of GABAergic interneuron population size in selected hippocampal subfields. In particular, E2 administration causes, in TMT-treated rats, a significant increase in the number of GAD67-expressing interneurons in CA1 stratum oriens, CA3 pyramidal layer, hilus and dentate gyrus, accompanied by a parallel increase in NPY-expressing cells, essentially in the same regions, and of PV-positive cells in CA1 pyramidal layer. The present results add information concerning the role of in vivo E2 administration on mechanisms involved in cellular plasticity in the adult brain.

Changes in the gene expression of estrogen receptors involved in the protective effect of estrogen in rat's trumatic brain injury

It has been demonstrated that estradiol has neuroprotective effects after traumatic brain injury (TBI) in female rats. Since estrogen receptors have an important role in estradiol effects at the cellular level and the exact mechanism(s) of estradiol-induced neuroprotection has not yet been fully clarified, the present study was designed to determine the changes in the levels of estrogen receptors mRNAs and proteins involved in this phenomenon. All experiments were carried out on female Wistar rats. The brain edema and blood-brain-barrier (BBB) disruption were assessed. The TBI method was diffuse type and induced by the Marmarou method. Semiquantitative RT-PCR and immunoblotting were used to assess ERα and ERβ gene expression. The data showed that the level of brain water content was significantly increased in TBI group. The increased water content was significantly attenuated in estradiol-treated (1mg/kg) TBI rats. Disruption of BBB after TBI was significantly inhibited just by estradiol treatment. Estrogen-treated animals showed a significant increase in ERα mRNA (18%) and protein (35%) levels in the brain tissue. Furthermore, in the brain-injured rats the levels of ERβ mRNA were lower than those in control rats. Following estrogen treatment, the protein levels of ERβ were closed to those in control group. In conclusion, the data demonstrate that estrogen treatment can protect brain against traumatic brain injury. Estrogen treatment increases ER mRNA and protein levels which were coincident with its protective effects. It seems that such phenomenon participates in the induction of neuroprotective effects of estrogen. This article is part of a Special Issue entitled 1618.

The neuroprotective actions of oestradiol and oestrogen receptors

Hormones regulate homeostasis by communicating through the bloodstream to the body's organs, including the brain. As homeostatic regulators of brain function, some hormones exert neuroprotective actions. This is the case for the ovarian hormone 17β-oestradiol, which signals through oestrogen receptors (ERs) that are widely distributed in the male and female brain. Recent discoveries have shown that oestradiol is not only a reproductive hormone but also a brain-derived neuroprotective factor in males and females and that ERs coordinate multiple signalling mechanisms that protect the brain from neurodegenerative diseases, affective disorders and cognitive decline.

Estradiol pretreatment ameliorates impaired synaptic plasticity at synapses of insulted CA1 neurons after transient global ischemia

Global ischemia in humans or induced experimentally in animals causes selective and delayed neuronal death in pyramidal neurons of the hippocampal CA1. The ovarian hormone estradiol administered before or immediately after insult affords histological protection in experimental models of focal and global ischemia and ameliorates the cognitive deficits associated with ischemic cell death. However, the impact of estradiol on the functional integrity of Schaffer collateral to CA1 (Sch-CA1) pyramidal cell synapses following global ischemia is not clear. Here we show that long term estradiol treatment initiated 14 days prior to global ischemia in ovariectomized female rats acts via the IGF-1 receptor to protect the functional integrity of CA1 neurons. Global ischemia impairs basal synaptic transmission, assessed by the input/output relation at Sch-CA1 synapses, and NMDA receptor (NMDAR)-dependent long term potentiation (LTP), assessed at 3 days after surgery. Presynaptic function, assessed by fiber volley and paired pulse facilitation, is unchanged. To our knowledge, our results are the first to demonstrate that estradiol at near physiological concentrations enhances basal excitatory synaptic transmission and ameliorates deficits in LTP at synapses onto CA1 neurons in a clinically-relevant model of global ischemia. Estradiol-induced rescue of LTP requires the IGF-1 receptor, but not the classical estrogen receptors (ER)-α or β. These findings support a model whereby estradiol acts via the IGF-1 receptor to maintain the functional integrity of hippocampal CA1 synapses in the face of global ischemia. This article is part of a Special Issue entitled SI: Brain and Memory.

Fracture as an independent risk factor of dementia: a nationwide population-based cohort study

Dementia is among various diseases affecting the elderly, who is also at a high risk for fractures. This study aimed to evaluate the association between fracture history and sequential risk of dementia in Taiwan.A retrospective cohort study was designed using the claims data of the entire insured residents covered by Taiwan's universal health insurance from 1998 to 2010. A total of 66,797 patients with fractures and 133,594 control subjects without fractures were matched in terms of age (±5 years), sex, and index year and then recruited. Fractures and dementia were defined in accordance with the International Classification of Diseases, 9th Revision, Clinical Modification. The influence of fractures on the risk of dementia was analyzed using a Cox proportional hazards model.After a 12-year follow-up period, 2775 and 3991 incident cases of dementia were reported in exposed and unexposed cohorts, respectively. The overall incidence rate of dementia in individuals with fractures was 41% higher than that in individuals without fractures (6.05 vs 4.30 per 1000 person-years) at an adjusted hazard ratio of 1.38 (95% confidence interval 1.32-1.45) after age, sex, urbanization, and individual disorders or comorbidities were adjusted. Considering fracture location, we found that patients with hip fractures were at a slightly high risk for dementia. The occurrence of multiple fractures at a single visit was also significantly associated with an increased risk of dementia.Fracture history is regarded as an independent risk factor of dementia in individuals aged ≥65 years, particularly those who suffered from multiple fractures and/or fractures located in the hip. Further studies are needed to support an independent role of fracture in dementia considering the clinical information and other comorbidities.

Long-term effects of post-ischaemic oestrogen on brain injury in a rat transient forebrain ischaemia model

BACKGROUND

The current study was conducted to compare the effects of post-treatment with oestrogen on histological and neurological outcomes after short (7-day) and long (28-day) recovery periods in rats subjected to transient forebrain ischaemia.

METHODS

Male Sprague-Dawley rats were randomly assigned to one of five groups: vehicle (7-day recovery period), vehicle (28-day recovery period), oestrogen (17β-estradiol 200 μg/kg, 7-day), oestrogen (17β-estradiol 200 μg /kg, 28-day), or sham surgical (n = 8 in each group). After forebrain ischaemia was induced with bilateral carotid artery occlusion and haemorrhagic hypotension (mean arterial pressure = 40 mmHg) for 10 min, the brain was reperfused for 7 or 28 days. Either 17β-estradiol or vehicle was injected intravenously during the initial 2 min of reperfusion. To evaluate histological damage, the number of intact neurons per 1 mm in the hippocampal CA1 subfield was counted at 7 or 28 days after transient forebrain ischaemia.

RESULTS

At 7 days after ischaemia, the number of intact neurons in the hippocampal CA1 subfield was significantly greater in the oestrogen group [57.5 (46.5)/mm: median (interquartile range)] than in the vehicle group [10 (19.5) /mm; P = 0.014]. However, there was no difference between groups at 28 days after ischaemia [vehicle: 11 (20)/mm vs. oestrogen: 6 (11)/mm]. The neurological deficit scores in the oestrogen and vehicle groups were not different from the sham group at any point post-ischaemia.

CONCLUSION

The current study indicates that post-ischaemic administration of oestrogen provided short-term but not long-term neuroprotective effects in transient forebrain ischaemia in rats.