Evidence to Implicate Early Modulation of Interleukin‐1β Expression in the Neuroprotection Afforded by 17β‐Estradiol in Male Rats Undergone Transient Middle Cerebral Artery Occlusion

Sexual Dimorphism in Neurodegenerative Diseases and in Brain Ischemia

Epidemiological studies and clinical observations show evidence of sexual dimorphism in brain responses to several neurological conditions. It is suggested that sex-related differences between men and women may have profound effects on disease susceptibility, pathophysiology, and progression. Sexual differences of the brain are achieved through the complex interplay of several factors contributing to this phenomenon, such as sex hormones, as well as genetic and epigenetic differences. Despite recent advances, the precise link between these factors and brain disorders is incompletely understood. This review aims to briefly outline the most relevant aspects that differ between men and women in ischemia and neurodegenerative disorders (AD, PD, HD, ALS, and SM). Recognition of disparities between both sexes could aid the development of individual approaches to ameliorate or slow the progression of intractable disorders.

Dietary genistein and 17β-estradiol implants differentially influence locomotor and cognitive functions following transient focal ischemia in middle-aged ovariectomized rats at different lengths of estrogen deprivation

Genistein possesses estrogenic activity and has been considered a potential replacement for estrogen replacement therapy after menopause. In the current study, we investigated the neuroprotective effects of dietary genistein at varied lengths of estrogen deprivation in middle-aged ovariectomized Sprague-Dawley rats under ischemic conditions. Two weeks of treatment with dietary genistein at 42 mg/kg but not 17β-estradiol implants improved cognitive flexibility (Morris water maze test) after short-term estrogen deprivation (2 weeks) but not long-term estrogen deprivation (12 weeks). 17β-estradiol implants but not dietary genistein improved locomotor asymmetry (cylinder test) after long-term but not short-term estrogen deprivation. Dietary genistein but not 17β-estradiol implant improved early phase motor learning (rotarod test) after long-term estrogen deprivation. Neither 17β-estradiol implant nor dietary genistein reduced infarct size after either short-term or long-term estrogen deprivation. Genistein, however, reduced ionized calcium-binding adaptor molecule-1 (Iba1) expression, a marker of brain inflammation, at the ipsilateral side of stroke injury after short-term but not long-term estrogen deprivation. This study suggests that the neuroprotective effects of dietary genistein on motor and cognitive functions are distinctly influenced by the length of estrogen deprivation following focal ischemia. SIGNIFICANCE: There is an increasing postmenopausal population opting for homeopathic medicines for the management of menopausal symptoms due to the perceived distrust in estrogen use as hormone replacement. Basic and clinical studies support the notion that early, but not delayed, hormone replacement after menopause is beneficial. Furthermore, evidence suggests that delaying hormone replacement augments the detrimental, rather than the beneficial effects of estrogens. Because of the active consideration of soy isoflavones including genistein as alternatives to estrogen replacement, it is necessary to understand the ramifications of soy isoflavones use when their administration is begun at various times after menopause.

Long-term hypogonadism diminishes the neuroprotective effects of dietary genistein in young adult ovariectomized rats after transient focal ischemia

Increasing age disproportionately increases the risk of stroke among women compared to men of similar age, especially after menopause. One of the reasons for this observation is a sharp drop in circulating estrogens. However, the timing of initiation of estrogen replacement after menopause is associated with mixed beneficial and detrimental effects, hence contributing to widespread mistrust of estrogen use. Agents including soy isoflavones are being assessed as viable alternatives to estrogen therapy. In this study, we hypothesized that the neuroprotective effects of genistein, a soy isoflavone are less sensitive to the length of hypogonadism in young adult ovariectomized rats following cerebral ischemia. We expected that long-term hypogonadism will worsen motor and cognitive function, increase post-stroke inflammation with no effect on the neuroprotection of genistein. We compared the effect of treatment with dietary genistein (GEN) on short-term (2 weeks) and long-term hypogonadism (12 weeks) in young adult ovariectomized Sprague-Dawley rats on sensorimotor function, cognition and inflammation after focal ischemia. Dorsal Silastic implant of 17β-estradiol (E2) was used as a control for hormone therapy. Long-term hypogonadism stroked rats performed worse than the short-term hypogonadism stroked rats on the motor and cognitive function tests. GEN did not improve neurological assessment and motor learning after either short-term or long-term hypogonadism. GEN improved cognitive flexibility after short-term hypogonadism but not after the long-term. Both GEN and E2 reduced tissue loss after short-term hypogonadism and reduced GFAP expression at the contralateral side of ischemia after long-term hypogonadism. The length of hypogonadism may differentially influence the neuroprotective effects of both GEN and E2 on the motor and cognitive functions in young adult rats.

Concentrations of estradiol, progesterone and testosterone in sefrum and cerebrospinal fluid of patients with aneurysmal subarachnoid hemorrhage correlate weakly with transcranial Doppler flow velocities

Background

The implication of the steroids estradiol, progesterone and testosterone in cerebral vasospasm after aneurysmal subarachnoid hemorrhage (aSAH) has not been comprehensively assessed. In rodents, studies suggested beneficial effects of steroids on cerebral vasospasm after experimental SAH. Studies in humans are warranted, however, a general dilemma of human studies on neuroactive substances is that the brain is not directly accessible and that concentrations in the periphery may not adequately parallel concentrations in the central compartments. In the present study, concentrations of estradiol, progesterone and testosterone in serum and cerebrospinal fluid (CSF) of patients with aSAH were determined. Blood flow velocities in cerebral arteries were measured by transcranial Doppler sonography (TCD). The aim of this study was to evaluate the correlations between the cerebral blood flow velocities and levels of estradiol, progesterone and testosterone in CSF and serum.

Results

Samples of serum and CSF of 42 patients with aSAH were collected concomitantly daily or every other day via the arterial line and the external ventricular drainage for two weeks after the hemorrhage. Blood flow velocities in the cerebral arteries were determined by TCD. Total estradiol, progesterone and testosterone concentrations were measured by electro-chemiluminescence immunoassay. The strength of correlation was assessed by Spearman’s rank correlation coefficient. The correlation analysis revealed very weak correlations between cerebral blood flow velocities and concentrations of estradiol, progesterone and testosterone levels in both compartments with correlation coefficients below 0.2.

Conclusions

In humans with aSAH, merely very weak correlations between flow velocities in cerebral arteries and concentrations of estradiol, progesterone and testosterone in serum and CSF were demonstrated. These results suggest a limited influence of the respective steroids on cerebral vascular tone although vasodilatory effects were described in rodent studies. Thus, the implication of steroids in processes of neurological deterioration warrants further clarification.

Age and sex differences in the pathophysiology of acute CNS injury

Despite the immeasurable burden on patients and families, no effective therapies to protect the CNS after an acute injury are available yet. Furthermore, the underlying mechanisms that promote neuronal death and functional deficits after injury remain to be poorly understood. The prevalence, age of onset, pathophysiology, and symptomatology of many CNS insults differ significantly between males and females. In the case of stroke, younger males tend to show a higher risk than younger females, while this trend reverses with age. Accumulating evidence from preclinical studies have shown that sex hormones play a crucial role in providing neuroprotection following ischemic stroke and other acute CNS injuries. Estrogen, in particular, exerts a neuroprotective effect by modulating the immune responses after injury. In addition, there exists a sexual dimorphism in cell death pathways between males and females that are independent of hormones. Meanwhile, recent studies suggest that microRNAs are critically involved in the sex-specific mechanisms of cell death. This review discusses the current knowledge on the contribution of sex and age to outcome after stroke. Implication of the interplay between these two factors on other CNS injuries (spinal cord injury and traumatic brain injury) from the experimental evidence were also discussed.

The regulatory role of Toll-like receptors after ischemic stroke: neurosteroids as TLR modulators with the focus on TLR2/4

Ischemic stroke is the most common cerebrovascular disease and considered as a worldwide leading cause of death. After cerebral ischemia, different pathophysiological processes including neuroinflammation, invasion and aggregation of inflammatory cells and up-regulation of cytokines occur simultaneously. In this respect, Toll-like receptors (TLRs) are the first identified important mediators for the activation of the innate immune system and are widely expressed in glial cells and neurons following brain trauma. TLRs are also able to interact with endogenous and exogenous molecules released during ischemia and can increase tissue damage. Particularly, TLR2 and TLR4 activate different downstream inflammatory signaling pathways. In addition, TLR signaling can alternatively play a role for endogenous neuroprotection. In this review, the gene and protein structures, common genetic polymorphisms of TLR2 and TLR4, TLR-related molecular pathways and their putative role after ischemic stroke are delineated. Furthermore, the relationship between neurosteroids and TLRs as neuroprotective mechanism is highlighted in the context of brain ischemia.

Ischemic stroke across sexes: What is the status quo?

Stroke prevalence is expected to increase in the next decades due to the aging of the Western population. Ischemic stroke (IS) shows an age- and sex-dependent distribution in which men represent the most affected population within 65 years of age, being passed by post-menopausal women in older age groups. Furthermore, a sexual dimorphism concerning risk factors, presentation and treatment of IS has been widely recognized. In order to address these phenomena, a number of issue have been raised involving both socio-economical and biological factors. The latter can be either dependent on sex hormones or due to intrinsic factors. Although women have poorer outcomes and are more likely to die after a cerebrovascular event, they are still underrepresented in clinical trials and this is mirrored by the lack of sex-tailored therapies. A greater effort is needed in the future to ensure improved treatment and quality of life to both sexes.

Ischemic stroke across sexes: what is the status quo?

Stroke prevalence is expected to increase in the next decades due to the aging of the Western population. Ischemic stroke (IS) shows an age- and sex-dependent distribution in which men represent the most affected population within 65 years of age, being passed by post-menopausal women in older age groups. Furthermore, a sexual dimorphism concerning risk factors, presentation and treatment of IS has been widely recognized. In order to address these phenomena, a number of issue have been raised involving both socio-economical and biological factors. The latter can be either dependent on sex hormones or due to intrinsic factors. Although women have poorer outcomes and are more likely to die after a cerebrovascular event, they are still underrepresented in clinical trials and this is mirrored by the lack of sex-tailored therapies. A greater effort is needed in the future to ensure improved treatment and quality of life to both sexes.

Administration of 17β-Estradiol Improves Motoneuron Survival and Down-regulates Inflammasome Activation in Male SOD1(G93A) ALS Mice

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease manifested by the progressive loss of upper and lower motoneurons. The pathomechanism of ALS is complex and not yet fully understood. Neuroinflammation is believed to significantly contribute to disease progression. Inflammasome activation was recently shown in the spinal cord of human sporadic ALS patients and in the SOD1(G93A) mouse model for ALS. In the present study, we investigated the neuroprotective and anti-inflammatory effects of 17β-estradiol (E2) treatment in pre-symptomatic and symptomatic male SOD1(G93A) mice. Symptomatic mice with E2 substitution exhibited improved motor performance correlating with an increased survival of motoneurons in the lumbar spinal cord. Expression of NLRP3 inflammasome proteins and levels of activated caspase 1 and mature interleukin 1 beta were significantly reduced in SOD1(G93A) mice supplemented with E2.

The Effects of Estrogen Receptors' Antagonist on Brain Edema, Intracranial Pressure and Neurological Outcomes after Traumatic Brain Injury in Rat

Background:

In previous studies, the neuroprotective effect of 17β-estradiol in diffuse traumatic brain injury has been shown. This study used ICI 182,780, a non-selective estrogen receptor antagonist, to test the hypothesis that the neuroprotective effect of 17β-estradiol in traumatic brain injury is mediated by the estrogen receptors.

Methods:

The ovariectomized rats were divided into eight groups. Brain injury was induced by Marmarou’s method. Estrogen was injected 30 minutes after traumatic brain injury, and ICI 182,780 was injected before traumatic brain injury and also before estrogen treatment. In one group only ICI 182,780 was injected. The brain water content and Evans blue dye content were measured 24 and 5 hours after traumatic brain injury, respectively. The neurologic outcomes and intracranial pressure were assessed before, 4, and 24 hours after traumatic brain injury.

Results:

Brain water content and Evans blue content were less in estrogen-treated group comparison to vehicle group. ICI 182,780 eliminated the effects of estrogen on brain edema and brain blood barrier permeability. Intracranial pressure was increased significantly after trauma, and estrogen decreased intracranial pressure at 4 and 24 hours after traumatic brain injury in comparison to vehicle. This inhibitory effect was also eliminated by treatment with ICI182,780. ICI 182,780 also inhibited the estrogen induced increase in neurologic outcomes following traumatic brain injury. However, the use of ICI 182,780 alone had no neuroprotective effect after traumatic brain injury.

Conclusion:

The results suggest that classical estrogen receptors have probably a role in the neuroprotective function of estrogen following traumatic brain injury.

Central inflammatory response to experimental stroke is inhibited by a neuroprotective dose of dietary soy

Dietary soy and soy isoflavones are neuroprotective in experimental cerebral ischemia. Because the isoflavones in soy that are responsible for this neuroprotective effect act as phytoestrogens, we hypothesized that they would mimic the beneficial effects of estrogens on the innate inflammatory response to cerebral ischemia. Ovariectomized Sprague-Dawley rats were fed a soy free diet or a diet containing high dietary levels of soy for 5 weeks, after which they were subjected to transient middle cerebral artery occlusion (tMCAO) for 90min. Dietary soy was associated with a reduced inflammatory response in the cerebral cortex during the acute innate period 4 and 24h after tMCAO, including significant (>2-fold) reductions in interleukins 1 beta, 2, and 13, and the chemokine CXCL1. However, there was no effect of soy on tumor necrosis factor-alpha or interferon-gamma. Dietary soy was also associated with a 40 percent reduction in the nuclear translocation of p65 nuclear factor kappa B despite an increase in the expression of p65 RELA mRNA. In support of an early effect on the innate immune response to stroke, soy-fed rats had 44 percent fewer activated microglia in the infarct core than soy free rats. Interestingly, despite increased expression following injury, the steady state mRNA levels of inflammatory factors were not altered in soy-fed rats even though inflammatory proteins were. These data suggest that dietary soy isoflavones, like estrogens, inhibit of the innate immune response to injury. However, post-transcriptional mechanisms may play an important role in the mechanism of this action. Coupled with previously published data, these results support an early and rapid effect of dietary soy on the evolution of brain injury following stroke.

Adult stem cell transplantation: is gender a factor in stemness?

Cell therapy now constitutes an important area of regenerative medicine. The aging of the population has mandated the discovery and development of new and innovative therapeutic modalities to combat devastating disorders such as stroke. Menstrual blood and Sertoli cells represent two sources of viable transplantable cells that are gender-specific, both of which appear to have potential as donor cells for transplantation in stroke. During the subacute phase of stroke, the use of autologous cells offers effective and practical clinical application and is suggestive of the many benefits of using the aforementioned gender-specific cells. For example, in addition to being exceptionally immunosuppressive, testis-derived Sertoli cells secrete many growth and trophic factors and have been shown to aid in the functional recovery of animals transplanted with fetal dopaminergic cells. Correspondingly, menstrual blood cells are easily obtainable and exhibit angiogenic characteristics, proliferative capability, and pluripotency. Of further interest is the ability of menstrual blood cells, following transplantation in stroke models, to migrate to the infarct site, secrete neurotrophic factors, regulate the inflammatory response, and be steered towards neural differentiation. From cell isolation to transplantation, we emphasize in this review paper the practicality and relevance of the experimental and clinical use of gender-specific stem cells, such as Sertoli cells and menstrual blood cells, in the treatment of stroke.

The battle of the sexes for stroke therapy: female- versus male-derived stem cells

Cell therapy is a major discipline of regenerative medicine that has been continually growing over the last two decades. The aging of the population necessitates discovery of therapeutic innovations to combat debilitating disorders, such as stroke. Menstrual blood and Sertoli cells are two gender-specific sources of viable transplantable cells for stroke therapy. The use of autologous cells for the subacute phase of stroke offers practical clinical application. Menstrual blood cells are readily available, display proliferative capacity, pluripotency and angiogenic features, and, following transplantation in stroke models, have the ability to migrate to the infarct site, regulate the inflammatory response, secrete neurotrophic factors, and have the possibility to differentiate into neural lineage. Similarly, the testis-derived Sertoli cells secrete many growth and trophic factors, are highly immunosuppressive, and exert neuroprotective effects in animal models of neurological disorders. We highlight the practicality of experimental and clinical application of menstrual blood cells and Sertoli cells to treat stroke, from cell isolation and cryopreservation to administration.

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

Background

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

Results

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

Conclusions

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

Neuroprotection by gonadal steroid hormones in acute brain damage requires cooperation with astroglia and microglia

The neuroactive steroids 17β-estradiol and progesterone control a broad spectrum of neural functions. Besides their roles in the regulation of classical neuroendocrine loops, they strongly influence motor and cognitive systems, behavior, and modulate brain performance at almost every level. Such a statement is underpinned by the widespread and lifelong expression pattern of all types of classical and non-classical estrogen and progesterone receptors in the CNS. The life-sustaining power of neurosteroids for tattered or seriously damaged neurons aroused interest in the scientific community in the past years to study their ability for therapeutic use under neuropathological challenges. Documented by excellent studies either performed in vitro or in adequate animal models mimicking acute toxic or chronic neurodegenerative brain disorders, both hormones revealed a high potency to protect neurons from damage and saved neural systems from collapse. Unfortunately, neurons, astroglia, microglia, and oligodendrocytes are comparably target cells for both steroid hormones. This hampers the precise assignment and understanding of neuroprotective cellular mechanisms activated by both steroids. In this article, we strive for a better comprehension of the mutual reaction between these steroid hormones and the two major glial cell types involved in the maintenance of brain homeostasis, astroglia and microglia, during acute traumatic brain injuries such as stroke and hypoxia. In particular, we attempt to summarize steroid-activated cellular signaling pathways and molecular responses in these cells and their contribution to dampening neuroinflammation and neural destruction. This article is part of a Special Issue entitled 'CSR 2013'.

Sex, stroke, and inflammation: the potential for estrogen-mediated immunoprotection in stroke

Stroke is the third leading cause of death and the primary cause of disability in the developed world. Experimental and clinical data indicate that stroke is a sexually dimorphic disease, with males demonstrating an enhanced intrinsic sensitivity to ischemic damage throughout most of their lifespan. The neuroprotective role of estrogen in the female brain is well established, however, estrogen exposure can also be deleterious, especially in older women. The mechanisms for this remain unclear. Our current understanding is based on studies examining estrogen as it relates to neuronal injury, yet cerebral ischemia also induces a robust sterile inflammatory response involving local and systemic immune cells. Despite the potent anti-inflammatory effects of estrogen, few studies have investigated the contribution of estrogen to sex differences in the inflammatory response to stroke. This review examines the potential role for estrogen-mediated immunoprotection in ischemic injury.

Sex steroids control neuroinflammatory processes in the brain: relevance for acute ischaemia and degenerative demyelination

Sex steroids have been demonstrated as powerful compounds to protect neurones and neural tissue from neurotoxic challenges and during neurodegeneration. A multitude of cellular actions have been attributed to female gonadal steroid hormones, including the regulation of pro-survival and anti-apoptotic factors, bioenergetic demands and radical elimination, growth factor allocation and counteracting against excitotoxicity. In recent years, immune-modulatory and anti-inflammatory characteristics of oestrogen and progesterone have also come under scrutiny. To date, each of these physiological responses has been considered to be partially and selectively integrated in the mediation of steroid-mediated cell protection and tested in suitable animal models and in vitro systems. To what extent these individual effects contribute to the overall neural protection remains sketchy. One idea is that a battery of cellular mechanisms operates at the same time. On the other hand, interactions and the control of the brain-intrinsic and peripheral immune system may play an additional and perhaps pioneering function in this scenario, notwithstanding the importance of secondary adjuvant mechanisms. In the present review, we highlight neuroprotective effects of oestrogen and progesterone in two different disease models of the brain, namely acute ischaemic and demyelination damage, which represent the most common acute and degenerative neurological disorders in humans. Besides other inflammatory parameters, we discuss the idea that chemokine expression and signalling appear to be early hallmarks in both diseases and are positively affected by sex steroids. In addition, the complex interplay with local brain-resident immune-competent cells appears to be controlled by the steroid environment.

Hormesis and Female Sex Hormones

Hormone replacement after menopause has in recent years been the subject of intense scientific debate and public interest and has sparked intense research efforts into the biological effects of estrogens and progestagens. However, there are reasons to believe that the doses used and plasma concentrations produced in a large number of studies casts doubt on important aspects of their validity. The concept of hormesis states that a substance can have diametrically different effects depending on the concentration. Even though estrogens and progestagens have proven prone to this kind of dose-response relation in a multitude of studies, the phenomenon remains clearly underappreciated as exemplified by the fact that it is common practice to only use one hormone dose in animal experiments. If care is not taken to adjust the concentrations of estrogens and progestagens to relevant biological conditions, the significance of the results may be questionable. Our aim is to review examples of female sexual steroids demonstrating bidirectional dose-response relations and to discuss this in the perspective of hormesis. Some examples are highlighted in detail, including the effects on cerebral ischemia, inflammation, cardiovascular diseases and anxiety. Hopefully, better understanding of the hormesis phenomenon may result in improved future designs of studies of female sexual steroids.

Gonadal steroids prevent cell damage and stimulate behavioral recovery after transient middle cerebral artery occlusion in male and female rats

17β-estradiol (E) and progesterone (P) are neuroprotective factors in the brain preventing neuronal death under different injury paradigms. Our previous work demonstrates that both steroids compensate neuronal damage and activate distinct neuroprotective strategies such as improving local energy metabolism and abating pro-inflammatory responses. The current study explored steroid hormone-mediated protection from brain damage and restoration of behavioral function after 1h transient middle cerebral artery occlusion (tMCAO). Male and ovariectomized female rats were studied 24h after stroke. Both steroid hormones reduced the cortical infarct area in males and females to a similar extent. A maximum effect of ~60-70% reduction of the infarct size was evident after P and a combined treatment with both hormones. No infarct protection was seen in the basal ganglia. Testing of motor and sensory behavioral revealed an equal high degree of functional recovery in all three hormone groups. Gene expression studies in the delineated penumbra revealed that estrogen receptor (ER) alpha and beta are locally up-regulated. tMCAO-mediated induction of the pro-inflammatory chemokines CCL2, CCL5 and interleukin 6 was attenuated by E and P, whereas the expression of vascular endothelial growth factor (VEGF) was fortified. Local expression of microglia/macrophage/lymphocyte markers, i.e. Iba1, CD68 and CD3, were significantly reduced in the penumbra after hormone treatment suggesting attenuation of microglia and lymphocyte attraction. These results demonstrate the neuroprotective potency of a combined treatment with E and P under ischemic conditions in both sexes and point at the regulation of chemokine-microglia/lymphocyte interactions as a supposable mechanism implicated in cell protection.

Mechanisms of estrogens' dose-dependent neuroprotective and neurodamaging effects in experimental models of cerebral ischemia

Ever since the hypothesis was put forward that estrogens could protect against cerebral ischemia, numerous studies have investigated the mechanisms of their effects. Despite initial studies showing ameliorating effects, later trials in both humans and animals have yielded contrasting results regarding the fundamental issue of whether estrogens are neuroprotective or neurodamaging. Therefore, investigations of the possible mechanisms of estrogen actions in brain ischemia have been difficult to assess. A recently published systematic review from our laboratory indicates that the dichotomy in experimental rat studies may be caused by the use of insufficiently validated estrogen administration methods resulting in serum hormone concentrations far from those intended, and that physiological estrogen concentrations are neuroprotective while supraphysiological concentrations augment the damage from cerebral ischemia. This evidence offers a new perspective on the mechanisms of estrogens’ actions in cerebral ischemia, and also has a direct bearing on the hormone replacement therapy debate. Estrogens affect their target organs by several different pathways and receptors, and the mechanisms proposed for their effects on stroke probably prevail in different concentration ranges. In the current article, previously suggested neuroprotective and neurodamaging mechanisms are reviewed in a hormone concentration perspective in an effort to provide a mechanistic framework for the dose-dependent paradoxical effects of estrogens in stroke. It is concluded that five protective mechanisms, namely decreased apoptosis, growth factor regulation, vascular modulation, indirect antioxidant properties and decreased inflammation, and the proposed damaging mechanism of increased inflammation, are currently supported by experiments performed in optimal biological settings.

Acute effects of 17 β-estradiol and genistein on insulin sensitivity and spatial memory in aged ovariectomized female rats

Aging is characterized by decline in metabolic function and insulin resistance, and both seem to be in the basis of neurodegenerative diseases and cognitive dysfunction. Estrogens prevent age-related changes, and phytoestrogens influence learning and memory. Our hypothesis was that estradiol and genistein, using rapid-action mechanisms, are able to modify insulin sensitivity, process of learning, and spatial memory. Young and aged ovariectomized rats received acute treatment with estradiol or genistein. Aged animals were more insulin-resistant than young. In each age, estradiol and genistein-treated animals were less insulin-resistant than the others, except in the case of young animals treated with high doses of genistein. In aged rats, no differences between groups were found in spatial memory test, showing a poor performance in the water maze task. However, young females treated with estradiol or high doses of genistein performed well in spatial memory task like the control group. Only rats treated with high doses of genistein showed an optimal spatial memory similar to the control group. Conversely, acute treatment with high doses of phytoestrogens improved spatial memory consolidation only in young rats, supporting the critical period hypothesis for the beneficial effects of estrogens on memory. Therefore, genistein treatment seems to be suitable treatment in aged rats in order to prevent insulin resistance but not memory decline associated with aging. Acute genistein treatment is not effective to restore insulin resistance associated to the early loss of ovarian function, although it can be useful to improve memory deficits in this condition.

Estradiol regulation of lipocalin-type prostaglandin D synthase promoter activity: evidence for direct and indirect mechanisms

In the CNS, lipocalin-type prostaglandin D synthase (L-PGDS) is predominantly a non-neuronal enzyme responsible for the production of PGD(2), an endogenous sleep promoting substance. We have previously demonstrated that estradiol differentially regulates L-PGDS transcript levels in the rodent brain. In hypothalamic nuclei, estradiol increases L-PGDS transcript expression, whereas in the ventrolateral preoptic area L-PGDS gene expression is reduced after estradiol treatment. In the present study, we have used an immortalized glioma cell line transfected with a L-PGDS reporter construct and estrogen receptor (ER) alpha and ERbeta expression plasmids to further elucidate the mechanisms underlying estradiol regulation of L-PGDS gene expression. We found that physiologically relevant concentrations of estradiol evoked an inverted U response in cells expressing ERalpha. The most effective concentration of estradiol (10(-11)M) increased the promoter activity 3-fold over baseline. Expression of ERbeta did not increase activity over control and when ERbeta was co-expressed with ERalpha there was a significant attenuation of the promoter activity. While ERalpha significantly increased L-PGDS promoter activity, our previous in vivo studies demonstrate a greater magnitude of change in L-PGDS gene expression in the presences of estradiol. This led us to ask whether estradiol is signaling via a paracrine factor released by the neighboring neurons. Conditioned media from estradiol treated neurons applied to the glioma cell line resulted in a significant 7-fold increase in L-PGDS promoter activity supporting the possibility that neuronal-glial interactions are involved in estradiol regulation of L-PGDS.

Dose-related neuroprotective versus neurodamaging effects of estrogens in rat cerebral ischemia: a systematic analysis

Numerous studies of the effects of estrogens for stroke prevention have yielded conflicting results in human and animal studies alike. We present a systematical analysis of study design and methodological differences between 66 studies where estrogens' impact on ischemic brain damage in rat models has been investigated, providing evidence that the differences in results may be explained by high estrogen doses produced by slow-release pellets. These pellets have been used in all studies showing increased neurologic damage because of estrogens. Our data indicate that the increased neurologic damage is related to the pellets' plasma concentration profile with an early, prolonged, supraphysiological peak. Neither the method of inducing the ischemic brain lesions, the choice of variables for measuring outcome, the measured plasma concentrations of estrogens at the time of ischemia nor rat population attributes (sex, strain, age, and diseases) are factors contributing to the discrepancies in results. This suggests that the effects of estrogens for stroke prevention are concentration related with a complex dose-response curve, and underscores the importance of carefully validating the experimental methods used. Future studies of hormone-replacement therapy in women may have to take dosage and administration regimens into account.

Attenuation of cerebral vasospasm and secondary injury by 17beta-estradiol following experimental subarachnoid hemorrhage

OBJECT

Cerebral vasospasm remains a major complication in patients who have suffered a subarachnoid hemorrhage (SAH). Previous studies have shown that 17beta-estradiol (E2) attenuates experimental SAH-induced cerebral vasospasm. Moreover, E2 has been shown to reduce neuronal apoptosis and secondary injury following cerebral ischemia. Adenosine A1 receptor (AR-A1) expression is increased following ischemia and may represent an endogenous neuroprotective effect. This study was designed to evaluate the efficacy of E2 in preventing cerebral vasospasm and reducing secondary injury, as evidenced by DNA fragmentation and AR-A1 expression, following SAH.

METHODS

A double-hemorrhage model of SAH in rats was used, and the degree of vasospasm was determined by averaging the cross-sectional areas of the basilar artery 7 days after the first SAH. A cell death assay was used to detect apoptosis. Changes in the protein expression of AR-A1 in the cerebral cortex, hippocampus, and dentate gyrus were compared with levels in normal controls and E2-treated groups (subcutaneous E2, 0.3 mg/ml).

RESULTS

The administration of E2 prevented vasospasm (p < 0.05). Seven days after the first SAH, DNA fragmentation and protein levels of AR-A1 were significantly increased in the dentate gyrus. The E2 treatment decreased DNA fragmentation and prevented the increase in AR-A1 expression in the dentate gyrus. There were no significant changes in DNA fragmentation and the expression of AR-A1 after SAH in the cerebral cortex and hippocampus in the animals in the control and E2-treated groups.

CONCLUSIONS

The E2 was effective in attenuating SAH-induced cerebral vasospasm, decreasing apoptosis in the dentate gyrus, and reducing the expression of AR-A1 in the dentate gyrus after SAH. Interestingly, E2 appears to effectively prevent cerebral vasospasm subsequent to SAH as well as attenuate secondary injury by reducing both apoptosis and a compensatory increase in AR-A1 expression in the dentate gyrus.

Sex-dependent regulation of hypoxic ventilation in mice and humans is mediated by erythropoietin

Acclimatization to hypoxic exposure relies on an elevated ventilation and erythropoietic activity. We recently proposed that erythropoietin (Epo) links both responses: apart from red blood cell production, cerebral and plasma Epo interact with the central and peripheral respiratory centers. Knowing that women cope better than men with reduced oxygen supply (as observed at high altitude), we analyzed the hypoxic ventilatory response in Epo-overexpressing transgenic male and female mice with high Epo levels in brain and plasma (Tg6) or in wild-type animals injected with recombinant human Epo (rhEpo). Exposure to moderate and severe hypoxia as well as to hyperoxia and injection of domperidone, a potent peripheral ventilatory stimulant, revealed that the presence of transgenic or rhEpo extensively increased the hypoxic ventilatory response in female mice compared with their corresponding male siblings. Alterations of catecholamines in the brain stem's respiratory centers were also sex dependent. In a proof-of-concept study, human volunteers were intravenously injected with 5,000 units rhEpo and subsequently exposed to 10% oxygen. Compared with men, the hypoxic ventilatory response was significantly increased in women. We conclude that Epo exerts a sex-dependent impact on hypoxic ventilation improving the response in female mice and in women that most probably involves sexual hormones. Our data provides an explanation as to why women are less susceptible to hypoxia-associated syndromes than men.

Effects of estrogen on temporal expressions of IL-1beta and IL-1ra in rat organotypic hippocampal slices exposed to oxygen-glucose deprivation

Anti-inflammatory action of estrogen is involved in neuroprotection but the effects of estrogen on IL-1beta and its endogenous antagonist (IL-1 ra) have not been clearly defined in the ischemic brain. This study was performed to evaluate whether estrogen affects the expression of IL-1beta or IL-1ra and the ratio of the two in the ischemic hippocampus. Rat organotypic hippocampal slices were treated with 17beta estradiol (E2, 1 nM) for 7 days, exposed to oxygen-glucose deprivation (OGD) for 30 min, and then reperfused for 72 h. CA1 neuronal death quantified by propidium iodide (PI) staining and expressions of IL-1beta and IL-1ra in slices measured by real-time PCR and Western blotting were examined. PI intensities in CA1 in slices treated with E2 were significantly reduced at 24 h and 72 h post-OGD, and IL-1beta mRNA expressions were reduced at 6 h and 24 h post-OGD. In addition, IL-1ra mRNA was significantly overexpressed and the ratio of IL-1beta to IL-1ra mRNA expression was reduced by E2 especially at 24 h. In terms of protein levels, E2 downregulated IL-1beta but upregulated IL-1ra and thereby decreased the IL-1beta/IL-1 ra ratio at 24h. These findings demonstrate that estrogen-induced protection is associated with a decrease in IL-1beta and an increase in IL-1ra expression in the ischemic hippocampus during early reperfusion periods, which suggests that modulation of IL-1beta/IL-1ra might be a part of anti-inflammatory effects of estrogen.