Testosterone increases neurotoxicity of glutamate in vitro and ischemia-reperfusion injury in an animal model

Pretreatment with oleuropein protects the neonatal brain from hypoxia-ischemia by inhibiting apoptosis and neuroinflammation

Hypoxic-ischemic (HI) encephalopathy is a cerebrovascular injury caused by oxygen deprivation to the brain and remains a major cause of neonatal mortality and morbidity worldwide. Therapeutic hypothermia is the current standard of care but it does not provide complete neuroprotection. Our aim was to investigate the neuroprotective effect of oleuropein (Ole) in a neonatal (seven-day-old) mouse model of HI. Ole, a secoiridoid found in olive leaves, has previously shown to reduce damage against cerebral and other ischemia/reperfusion injuries. Here, we administered Ole as a pretreatment prior to HI induction at 20 or 100 mg/kg. A week after HI, Ole significantly reduced the infarct area and the histological damage as well as white matter injury, by preserving myelination, microglial activation and the astroglial reactive response. Twenty-four hours after HI, Ole reduced the overexpression of caspase-3 and the proinflammatory cytokines IL-6 and TNF-α. Moreover, using UPLC-MS/MS we found that maternal supplementation with Ole during pregnancy and/or lactation led to the accumulation of its metabolite hydroxytyrosol in the brains of the offspring. Overall, our results indicate that pretreatment with Ole confers neuroprotection and can prevent HI-induced brain damage by modulating apoptosis and neuroinflammation.

Sex differences in treatment effect in neuroprotectant trials for acute ischemic stroke: A systematic review

BACKGROUND

Pre-clinical data suggest sex differences in mechanisms of cerebral ischemic injury. This might result in differential outcomes of putative neuroprotectants by sex, though little systematic data is available to assess this.

METHODS

We performed a systematic review of multicenter randomized controlled trials published from January 1980-June 2022 enrolling >100 subjects and testing neuroprotectants in acute ischemic stroke (AIS). For each trial, reported treatment effect by sex was extracted. When published results by sex were not available, we contacted individual authors to attempt to retrieve these data.

RESULTS

We identified 59 publications reporting 64 trials that met inclusion criteria. Of these, data on treatment effect by sex were published for 14/64 trials. Unpublished data for an additional 5 trials were obtained from trial investigators (19/64, or 29.7%). Two trials (one testing uric acid and one dexborneol) reported treatment benefit in women but not men. Pooled analysis of six trials of tirilazad reported worse treatment outcomes in women and no effect in men. No clear difference was apparent in the other trials.

CONCLUSIONS

Most trials did not report treatment effect by sex. Of those that did, there was little evidence of systematic sex differences in treatment response.

TrkB-mediated neuroprotection in female hippocampal neurons is autonomous, estrogen receptor alpha-dependent, and eliminated by testosterone: a proposed model for sex differences in neonatal hippocampal neuronal injury

BACKGROUND

Neonatal hypoxia ischemia (HI) related brain injury is one of the major causes of learning disabilities and memory deficits in children. In both human and animal studies, female neonate brains are less susceptible to HI than male brains. Phosphorylation of the nerve growth factor receptor TrkB has been shown to provide sex-specific neuroprotection following in vivo HI in female mice in an estrogen receptor alpha (ERα)-dependent manner. However, the molecular and cellular mechanisms conferring sex-specific neonatal neuroprotection remain incompletely understood. Here, we test whether female neonatal hippocampal neurons express autonomous neuroprotective properties and assess the ability of testosterone (T) to alter this phenotype.

METHODS

We cultured sexed hippocampal neurons from ERα+/+ and ERα-/- mice and subjected them to 4 h oxygen glucose deprivation and 24 h reoxygenation (4-OGD/24-REOX). Sexed hippocampal neurons were treated either with vehicle control (VC) or the TrkB agonist 7,8-dihydroxyflavone (7,8-DHF) following in vitro ischemia. End points at 24 h REOX were TrkB phosphorylation (p-TrkB) and neuronal survival assessed by immunohistochemistry. In addition, in vitro ischemia-mediated ERα gene expression in hippocampal neurons were investigated following testosterone (T) pre-treatment and TrkB antagonist therapy via q-RTPCR. Multifactorial analysis of variance was conducted to test for significant differences between experimental conditions.

RESULTS

Under normoxic conditions, administration of 3 µM 7,8-DHF resulted an ERα-dependent increase in p-TrkB immunoexpression that was higher in female, as compared to male neurons. Following 4-OGD/24-REOX, p-TrkB expression increased 20% in both male and female ERα+/+ neurons. However, with 3 µM 7,8-DHF treatment p-TrkB expression increased further in female neurons by 2.81 ± 0.79-fold and was ERα dependent. 4-OGD/24-REOX resulted in a 56% increase in cell death, but only female cells were rescued with 3 µM 7,8-DHF, again in an ERα dependent manner. Following 4-OGD/3-REOX, ERα mRNA increased ~ 3 fold in female neurons. This increase was blocked with either the TrkB antagonist ANA-12 or pre-treatment with T. Pre-treatment with T also blocked the 7,8-DHF- dependent sex-specific neuronal survival in female neurons following 4-OGD/24-REOX.

CONCLUSIONS

OGD/REOX results in sex-dependent TrkB phosphorylation in female neurons that increases further with 7,8-DHF treatment. TrkB phosphorylation by 7,8-DHF increased ERα mRNA expression and promoted cell survival preferentially in female hippocampal neurons. The sex-dependent neuroprotective actions of 7,8-DHF were blocked by either ANA-12 or by T pre-treatment. These results are consistent with a model for a female-specific neuroprotective pathway in hippocampal neurons in response to hypoxia. The pathway is activated by 7,8-DHF, mediated by TrkB phosphorylation, dependent on ERα and blocked by pre-exposure to T.

Revealing the Influences of Sex Hormones and Sex Differences in Atrial Fibrillation and Vascular Cognitive Impairment

The impacts of sex differences on the biology of various organ systems and the influences of sex hormones on modulating health and disease have become increasingly relevant in clinical and biomedical research. A growing body of evidence has recently suggested fundamental sex differences in cardiovascular and cognitive function, including anatomy, pathophysiology, incidence and age of disease onset, symptoms affecting disease diagnosis, disease severity, progression, and treatment responses and outcomes. Atrial fibrillation (AF) is currently recognized as the most prevalent sustained arrhythmia and might contribute to the pathogenesis and progression of vascular cognitive impairment (VCI), including a range of cognitive deficits, from mild cognitive impairment to dementia. In this review, we describe sex-based differences and sex hormone functions in the physiology of the brain and vasculature and the pathophysiology of disorders therein, with special emphasis on AF and VCI. Deciphering how sex hormones and their receptor signaling (estrogen and androgen receptors) potentially impact on sex differences could help to reveal disease links between AF and VCI and identify therapeutic targets that may lead to potentially novel therapeutic interventions early in the disease course of AF and VCI.

Gender differences involved in the pathophysiology of the perinatal hypoxic-ischemic damage

Hypoxic-ischemic encephalopathy (HIE) is a neonatal condition that occurs as a consequence of perinatal asphyxia, which is caused by a number of factors, commonly via compression of the umbilical cord, placental abruption, severe meconium aspiration, congenital cardiac or pulmonary anomalies and birth trauma. Experimental studies have confirmed that male rat pups show a higher resistance to HIE treatment. Moreover, the long-term consequences of hypoxia in male are more severe in comparison to female rat pups. These sex differences can be attributed to the pathophysiology of hypoxia-ischemia, whereby studies are beginning to establish such gender-specific distinctions. The current and sole treatment for HIE is hypothermia, in which a reduction in temperature prevents long-term effects, such as cerebral palsy or seizures. However, in most cases hypothermia is not a sufficient treatment as indicated by a high mortality rate. In the present review, we discuss the gender differences within the pathophysiology of hypoxia-ischemia and delve into the role of gender in the incidence, progression and severity of the disease. Furthermore, this may result in the development of potential novel treatment approaches for targeting and preventing the long-term consequences of HIE.

Androgens' effects on cerebrovascular function in health and disease

Androgens affect the cerebral vasculature and may contribute to sex differences in cerebrovascular diseases. Men are at a greater risk for stroke and vascular contributions to cognitive impairment and dementia (VCID) compared to women throughout much of the lifespan. The cerebral vasculature is a target for direct androgen actions, as it expresses several sex steroid receptors and metabolizing enzymes. Androgens’ actions on the cerebral vasculature are complex, as they have been shown to have both protective and detrimental effects, depending on factors such as age, dose, and disease state. When administered chronically, androgens are shown to be pro-angiogenic, promote vasoconstriction, and influence blood-brain barrier permeability. In addition to these direct effects of androgens on the cerebral vasculature, androgens also influence other vascular risk factors that may contribute to sex differences in cerebrovascular diseases. In men, low androgen levels have been linked to metabolic and cardiovascular diseases including hypertension, diabetes, hyperlipidemia, and obesity, which greatly increase the risk of stroke and VCID. Thus, a better understanding of androgens’ interactions with the cerebral vasculature under physiological and pathological conditions is of key importance.

Insight into the molecular sex dimorphism of ischaemic stroke in rat cerebral cortex: Focus on neuroglobin, sex steroids and autophagy

Including sex is of paramount importance in preclinical and clinical stroke researches, and molecular studies dealing in depth with sex differences in stroke pathophysiology are needed. To gain insight into the molecular sex dimorphism of ischaemic stroke in rat cerebral cortex, male and female adult rats were subjected to transient middle cerebral artery occlusion. The expression of neuroglobin (Ngb) and other functionally related molecules involved in sex steroid signalling (oestrogen and androgen receptors), steroidogenesis (StAR, TSPO and aromatase) and autophagic activity (LC3B-II/LC3B-I ratio, UCP2 and HIF-1α) was assessed in the ipsilateral ischaemic and contralateral non-ischaemic hemispheres. An increased expression of Ngb was detected in the injured female cerebral cortex. In contrast, increased expression of oestrogen receptor α, GPER, StAR, TSPO and UCP2, and decreased androgen receptor expression were detected in the injured male cortex. In both sexes, the ischaemic insult induced an upregulation of LC3B-II/-I ratio, indicative of increased autophagy. Therefore, the cerebral cortex activates both sex-specific and common molecular responses with neuroprotective potential after ischaemia-reperfusion, which globally results in similar stroke outcome in both sexes. Nonetheless, these different potential molecular targets should be taken into account when neuroprotective drugs aiming to reduce brain damage in ischaemic stroke are investigated.

Chronic Testosterone Deprivation Sensitizes the Middle-Aged Rat Brain to Damaging Effects of Testosterone Replacement

INTRODUCTION

An increasing number of middle-aged men are being screened for low testosterone levels and the number of prescriptions for various forms of testosterone replacement therapy (TRT) has increased dramatically over the last 10 years. However, the safety of TRT has come into question with some studies suggesting increased morbidity and mortality.

OBJECTIVE

Because the benefits of estrogen replacement in postmenopausal women and ovariectomized rodents are lost if there is an extended delay between estrogen loss and replacement, we hypothesized that TRT may also be sensitive to delayed replacement.

METHODS

We compared the effects of testosterone replacement after short-term (2 weeks) and long-term testosterone deprivation (LTTD; 10 weeks) in middle-aged male rats on cerebral ischemia, oxidative stress, and cognitive function. We hypothesized that LTTD would increase oxidative stress levels and abrogate the beneficial effects of TRT.

RESULTS

Hypogonadism itself and TRT after short-term castration did not affect stroke outcome compared to intact rats. However, after long-term hypogonadism in middle-aged male Fischer 344 rats, TRT exacerbated the detrimental behavioral effects of experimental focal cerebral ischemia, whereas this detrimental effect was prevented by administration of the free-radical scavenger tempol, suggesting that TRT exacerbates oxidative stress. In contrast, TRT improved cognitive performance in non-stroked rats regardless of the length of hypogonadism. In the Morris water maze, peripheral oxidative stress was highly associated with decreased cognitive ability.

CONCLUSIONS

Taken together, these data suggest that TRT after long-term hypogonadism can exacerbate functional recovery after focal cerebral ischemia, but in the absence of injury can enhance cognition. Both of these effects are modulated by oxidative stress levels.

Anti-apoptotic and Immunomodulatory Effect of CB2 Agonist, JWH133, in a Neonatal Rat Model of Hypoxic-Ischemic Encephalopathy

Introduction: Neonatal HIE is associated with high morbidity and mortality. Current research, is focused on developing alternative treatments to therapeutic hypothermia for treatment of HIE. The endocannabinoid system is known to be influential in neuronal protection. Activation of brain CB2 receptors, has been shown to reduce inflammatory markers and decrease infarct volume in adult cerebral ischemic models. Methods: Rat pups were divided into six groups: 1-Placebo; 2-JWH133; 3-HIE + Placebo; 4-HIE + JWH133; 5-HIE + Hypothermia + Placebo; and 6-HIE + Hypothermia + JWH133. HIE was induced in in groups 3-6 by right carotid ligation on postnatal day 7 followed by placement in a hypoxic chamber. Pups in groups 5 and 6 were treated with hypothermia. Western blot analysis was used to analyze brain tissue for acute inflammatory markers (IL-6, TNFα, MIP1α, and RANTES), immunoregulatory cytokines (TGFβ and IL-10), and CB2 receptor expression. DNA fragmentation in the brains of pups was determined via TUNEL staining post HIE. Results: The combination of JWH133 and hypothermia significantly reduced tumor necrosis factor α (TNFα) (-57.7%, P = 0.0072) and macrophage inflammatory protein 1α (MIP1α) (-50.0%, P = 0.0211) as compared to placebo. DNA fragmentation was also significantly reduced, with 6.9 ± 1.4% TUNEL+ cells in HIE+JWH133 and 12.9 ± 2.2% in HIE+Hypothermia + JWH133 vs. 16.6 ± 1.9% in HIE alone. No significant difference was noted between groups for the expression of interleukins 6 and 10, RANTES, or TGFβ. After 8 h, CB2 receptor expression increased nearly 2-fold in the HIE and HIE + JWH133 groups (+214%, P = 0.0102 and +198%, P = 0.0209, respectively) over placebo with no significant change in the hypothermia groups. By 24 h post HIE, CB2 receptor expression was elevated over five times that of placebo in the HIE (P < 0.0001) and HIE + JWH133 (P = 0.0002) groups, whereas hypothermia treatment maintained expression similar to that of placebo animals. Conclusion: These results indicate that the combination of CB2 agonist and hypothermia may be neuroprotective in treating HIE, opening the door for further studies to examine alternative or adjuvant therapies to hypothermia.

Sex hormones and stroke: Beyond estrogens

Stroke risk and poor stroke outcomes in postmenopausal women have usually beeen attributed to decreased levels of estrogen. However, two lines of evidence suggest that this hormone may not be solely responsible for elevated stroke risk in this population. First, the increased risk for CVD and stroke occurs much earlier than menopause at a time when estrogen levels are not yet reduced. Second, estrogen therapy has not successfully reduced stroke risk in all studies. Other sex hormones may therefore also contribute to stroke risk. Prior to menopause, levels of the gonadotrophin Follicle Stimulating Hormone (FSH) are elevated while levels of the gonadal peptide inhibin are lowered, indicating an overall decrease in ovarian reserve. Similarly, reduced estrogen levels at menopause significantly increase the ratio of androgens to estrogens. In view of the evidence that androgens may be unfavorable for CVD and stroke, this elevated ratio of testosterone to estrogen may also contribute to the postmenopause-associated stroke risk. This review synthesizes evidence from different clinical populations including natural menopause, surgical menopause, women on chemotherapy, and preclinical stroke models to dissect the role of ovarian hormones and stroke risk and outcomes.

Contributions of sex to cerebrovascular function and pathology

Sex differences exist in how cerebral blood vessels function under both physiological and pathological conditions, contributing to observed sex differences in risk and outcomes of cerebrovascular diseases (CBVDs), such as vascular contributions to cognitive impairment and dementia (VCID) and stroke. Throughout most of the lifespan, women are protected from CBVDs; however, risk increases following menopause, suggesting sex hormones may play a significant role in this protection. The cerebrovasculature is a target for sex hormones, including estrogens, progestins, and androgens, where they can influence numerous vascular functions and pathologies. While there is a plethora of information on estrogen, the effects of progestins and androgens on the cerebrovasculature are less well-defined. Estrogen decreases cerebral tone and increases cerebral blood flow, while androgens increase tone. Both estrogens and androgens enhance angiogenesis/cerebrovascular remodeling. While both estrogens and androgens attenuate cerebrovascular inflammation, pro-inflammatory effects of androgens under physiological conditions have also been demonstrated. Sex hormones exert additional neuroprotective effects by attenuating oxidative stress and maintaining integrity and function of the blood brain barrier. Most animal studies utilize young, healthy, gonadectomized animals, which do not mimic the clinical conditions of aging individuals likely to get CBVDs. This is also concerning, as sex hormones appear to mediate cerebrovascular function differently based on age and disease state (e.g. metabolic syndrome). Through this review, we hope to inspire others to consider sex as a key biological variable in cerebrovascular research, as greater understanding of sex differences in cerebrovascular function will assist in developing personalized approaches to prevent and treat CBVDs.

Sex differences in risk factors for vascular contributions to cognitive impairment & dementia

Vascular contributions to cognitive impairment and dementia (VCID) is the second most common cause of dementia. While males overall appear to be at a slightly higher risk for VCID throughout most of the lifespan (up to age 85), some risk factors for VCID more adversely affect women. These include female-specific risk factors associated with pregnancy related disorders (e.g. preeclampsia), menopause, and poorly timed hormone replacement. Further, presence of certain co-morbid risk factors, such as diabetes, obesity and hypertension, also may more adversely affect women than men. In contrast, some risk factors more greatly affect men, such as hyperlipidemia, myocardial infarction, and heart disease. Further, stroke, one of the leading risk factors for VCID, has a higher incidence in men than in women throughout much of the lifespan, though this trend is reversed at advanced ages. This review will highlight the need to take biological sex and common co-morbidities for VCID into account in both preclinical and clinical research. Given that there are currently no treatments available for VCID, it is critical that we understand how to mitigate risk factors for this devastating disease in both sexes.

Molecular differences in Alzheimer's disease between male and female patients determined by integrative network analysis

Alzheimer's disease (AD) is a complex neurodegenerative disease and the most common cause of dementia among the elderly. There has been increasing recognition of sex differences in AD prevalence, clinical manifestation, disease course and prognosis. However, there have been few studies on the molecular mechanism underlying these differences. To address this issue, we carried out global gene expression and integrative network analyses based on expression profiles (GSE84422) across 17 cortical regions of 125 individuals with AD. There were few genes that were differentially expressed across the 17 regions between the two sexes, with only four (encoding glutamate metabotropic receptor 2, oestrogen‐related receptor beta, kinesin family member 26B, and aspartoacylase) that were differentially expressed in three regions. A pan‐cortical brain region co‐expression network analysis identified pathways and genes (eg, glycogen synthase kinase 3β) that were significantly associated with clinical characteristics of AD (such as neurofibrillary score) in males only. Similarity analyses between region‐specific networks indicated that male patients exhibited greater variability, especially in the superior parietal lobule, dorsolateral prefrontal cortex and occipital visual cortex. A network module analysis revealed an association between clinical traits and crosstalk of sex‐specific modules. An examination of temporal and spatial patterns of sex differences in AD showed that molecular networks were more conserved in females than in males in different cortical regions and at different AD stages. These findings provide insight into critical molecular pathways governing sex differences in AD pathology.

Estradiol to Androstenedione Ratios Moderate the Relationship between Neurological Injury Severity and Mortality Risk after Severe Traumatic Brain Injury

Early declines in gonadotropin production, despite elevated serum estradiol, among some individuals with severe traumatic brain injury (TBI) suggests amplified systemic aromatization occurs post-injury. Our previous work identifies estradiol (E2) as a potent mortality marker. Androstenedione (A), a metabolic precursor to E2, estrone (E1), and testosterone (T), is a steroid hormone substrate for aromatization that has not been explored previously as a biomarker in TBI. Here, we evaluated serum A, E1, T, and E2 values for 82 subjects with severe TBI. Daily hormone values were calculated, and E2:A and E1:T ratios were generated and then averaged for days 0-3 post-injury. After data inspection, mean E2:A values were categorized as above (high aromatization) and below (low aromatization) the 50th percentile for 30-day mortality assessment using Kaplan-Meier survival analysis and a multivariable Cox proportional hazard model adjusting for age, and Glasgow Coma Scale (GCS) to predict 30-day mortality status. Daily serum T, E1, and E2 were graphed by E2:A category. Serum E1 and E2 significantly differed over time (p < 0.05); the high aromatization group had elevated levels and a significantly lower probability of survival within the first 30 days (p = 0.0274). Multivariable Cox regression showed a significant E2:A*GCS interaction (p = 0.0129), wherein GCS predicted mortality only among those in the low aromatization group. E2:A may be a useful mortality biomarker representing enhanced aromatization after TBI. E2:A ratios may represent non-neurological organ dysfunction after TBI and may be useful in defining injury subgroups in which GCS has variable capacity to serve as an accurate early prognostic marker.

Physiological basis behind ergogenic effects of anabolic androgens

Anabolic androgenic steroids (AAS) are widely abused by the sporting community. Demonstrating performance enhancing effects of AAS in rigorous scientific studies is fraught with difficulty. In controlled studies, AAS have consistently been reported to increase muscle mass and strength. The clinical evidence that these anabolic effects are independent of, and additive to exercise are supported by preclinical studies suggesting that AAS and exercise affect muscle by overlapping, yet distinct mechanisms. AAS may also improve performance by their actions on other organ systems, such as the vasculature, and the erythropoietic and central nervous system, although this evidence is less strong. While most of the actions of AAS are thought to be mediated via classical androgen receptor-mediated genomic signalling, AAS may also produce rapid effects via non-genomic mechanisms.

Sex differences in the brain: Implications for behavioral and biomedical research

Biological differences between males and females are found at multiple levels. However, females have too often been under-represented in behavioral neuroscience research, which has stymied the study of potential sex differences in neurobiology and behavior. This review focuses on the study of sex differences in the neurobiology of social behavior, memory, emotions, and recovery from brain injury, with particular emphasis on the role of estrogens in regulating forebrain function. This work, presented by the authors at the 2016 meeting of the International Behavioral Neuroscience Society, emphasizes varying approaches from several mammalian species in which sex differences have not only been documented, but also become the focus of efforts to understand the mechanistic basis underlying them. This information may provide readers with useful experimental tools to successfully address recently introduced regulations by granting agencies that either require (e.g. the National Institutes of Health in the United States and the Canadian Institutes of Health Research in Canada) or recommend (e.g. Horizon 2020 in Europe) the inclusion of both sexes in biomedical research.

Magnesium Sulfate Prevents Neurochemical and Long-Term Behavioral Consequences of Neonatal Excitotoxic Lesions: Comparison Between Male and Female Mice

Magnesium sulfate (MgSO4) administration to mothers at risk of preterm delivery is proposed as a neuroprotective strategy against neurological alterations such as cerebral palsy in newborns. However, long-term beneficial or adverse effects of MgSO4 and sex-specific sensitivity remain to be investigated. We conducted behavioral and neurochemical studies of MgSO4 effects in males and females, from the perinatal period to adolescence in a mouse model of cerebral neonatal lesion. The lesion was produced in 5-day-old (P5) pups by ibotenate intracortical injection. MgSO4 (600 mg/kg, i.p.) prior to ibotenate prevented lesion-induced sensorimotor alterations in both sexes at P6 and P7. The lesion increased glutamate level at P10 in the prefrontal cortex, which was prevented by MgSO4 in males. In neonatally lesioned adolescent mice, males exhibited more sequelae than females in motor and cognitive functions. In the perirhinal cortex of adolescent mice, the neonatal lesion induced an increase in vesicular glutamate transporter 1 density in males only, which was negatively correlated with cognitive scores. Long-term sequelae were prevented by neonatal MgSO4 administration. MgSO4 never induced short- or long-term deleterious effect on its own. These results also strongly suggest that sex-specific neuroprotection should be foreseen in preterm infants.

Menopause and Ischemic Stroke: A Brief Review

Ischemic stroke is one of the leading causes of morbidity and mortality worldwide. Females are protected against stroke before the onset of menopause. Menopause results in increased incidence of stroke when compared to men. The mechanisms of these differences remain to be elucidated. Considering that there is a postmenopausal phenomenon and females in general, are living longer sex hormone-dependent mechanisms have been postulated to be the primary factors responsible for the premenopausal protection from stroke and later to be responsible for the higher incidence and increased the severity of stroke after menopause. Animal studies suggest that administration of estrogen and progesterone is neuroprotective and decreases the incidence of stroke. However, the real-world outcomes of hormone replacement therapy have failed to decrease the stroke risk. Despite the multifactorial nature of sex differences in stroke, here, we briefly discuss the pathophysiology of sex steroid hormones, the molecular mechanisms of estrogen receptor-dependent signaling pathways in stroke, and the potential factors that determine the discrepant effects of hormone replacement therapy in stroke.

Differential effects of neonatal SSRI treatments on hypoxia-induced behavioral changes in male and female offspring

Prenatal hypoxia induced by transient intrauterine ischemia is a serious clinical problem, and at present, effective treatments are lacking. Currently, it is unknown how prenatal hypoxia affects behaviors in adulthood. Therefore, we developed a mouse model that mimics prenatal hypoxia in humans using uterine artery occlusion in late gestation. We examined whether prenatal hypoxia induces behavioral changes in adult male and female offspring by conducting a series of behavioral tests. In adulthood, longer immobility was observed in the forced swim test in males, whereas females showed decreased inhibition in the prepulse inhibition test. We then investigated the effects of two different selective serotonin reuptake inhibitors (SSRIs), fluoxetine (FLX) and escitalopram (ESC), on these behavioral changes. These drugs affect the neurodevelopmental process and have long-term neurological consequences. FLX treatment from postnatal day 3 (P3) to P21 ameliorated the behavioral changes in both male and female mice. In comparison, ESC treatment ameliorated the behavioral changes only in female mice. Neurochemical analysis revealed that dopamine was increased in the female hippocampus, but not in males. Thus, neonatal SSRI treatment decreases dopamine levels in the hippocampus in females selectively. Our findings suggest that prenatal hypoxia is a risk factor for behavioral abnormalities in adulthood, and that neonatal SSRI treatment might have clinical potential for alleviating these long-term behavioral deficits.

Sex differences in stroke therapies

Stroke is the fifth leading cause of death and acquired disability in aged populations. Women are disproportionally affected by stroke, having a higher incidence and worse outcomes than men. Numerous preclinical studies have discovered novel therapies for the treatment of stroke, but almost all of these have been shown to be unsuccessful in clinical trials. Despite known sex differences in occurrence and severity of stroke, few preclinical or clinical therapeutics take into account possible sex differences in treatment. Reanalysis of data from studies of tissue plasminogen activator (tPA), the only currently FDA-approved stroke therapy, has shown that tPA improves stroke outcomes for both sexes and also shows sexual dimorphism by more robust improvement in stroke outcome in females. Experimental evidence supports the inclusion of sex as a variable in the study of a number of novel stroke drugs and therapies, including preclinical studies of anti-inflammatory drugs (minocycline), stimulators of cell survival (insulin-like growth factor-1), and inhibitors of cell death pathways (pharmacological inhibition of poly[ADP-ribose] polymerase-1, nitric oxide production, and caspase activation) as well as in current clinical trials of stem cell therapy and cortical stimulation. Overall, study design and analysis in clinical trials as well as in preclinical studies must include both sexes equally, consider possible sex differences in the analyses, and report the differences/similarities in more systematic/structured ways to allow promising therapies for both sexes and increase stroke recovery. © 2016 Wiley Periodicals, Inc.

Animal models of hypoxic-ischemic encephalopathy: optimal choices for the best outcomes

Hypoxic-ischemic encephalopathy (HIE), a serious disease leading to neonatal death, is becoming a key area of pediatric neurological research. Despite remarkable advances in the understanding of HIE, the explicit pathogenesis of HIE is unclear, and well-established treatments are absent. Animal models are usually considered as the first step in the exploration of the underlying disease and in evaluating promising therapeutic interventions. Various animal models of HIE have been developed with distinct characteristics, and it is important to choose an appropriate animal model according to the experimental objectives. Generally, small animal models may be more suitable for exploring the mechanisms of HIE, whereas large animal models are better for translational studies. This review focuses on the features of commonly used HIE animal models with respect to their modeling strategies, merits, and shortcomings, and associated neuropathological changes, providing a comprehensive reference for improving existing animal models and developing new animal models.

Effects of sex steroid hormones and their metabolites on neuronal injury caused by oxygen-glucose deprivation/reoxygenation in organotypic hippocampal slice cultures

In this study, protective actions of the sex steroid hormones, progesterone, testosterone, and 17β-estradiol, against oxygen-glucose deprivation (OGD)/reoxygenation-induced neuronal cell death were examined using rat organotypic hippocampal slice cultures. Progesterone, testosterone, and 17β-estradiol significantly attenuated neuronal cell death elicited by OGD/reoxygenation. While the neuroprotection conferred by progesterone was not affected by SU-10603, an inhibitor of cytochrome P45017α, finasteride, a 5α-reductase inhibitor that blocks the conversion of progesterone to allopregnanolone, partially reversed the neuroprotection induced by progesterone. The progesterone metabolite, allopregnanolone attenuated neuronal injury induced by OGD/reoxygenation. Pretreatment with letrozole, a cytochrome P450 aromatase inhibitor or 4-hydroxyphenyl-1-naphthol, a 17β-hydroxysteroid dehydrogenase 2 inhibitor showed no effect on testosterone-mediated neuroprotection, while finasteride completely abolished the protective action of testosterone. Treatment with 5α-dihydrotestosterone significantly suppressed neuronal injury. Pretreatment with mifepristone, a progesterone receptor antagonist and hydroxyflutamid, an androgen receptor antagonist significantly diminished the neuroprotective effects of progesterone and testosterone, respectively. ICI182,780, an estrogen receptor antagonist, showed no effect on neuroprotection mediated by 17β-estradiol. Pretreatment with actinomycin D or cycloheximide clearly abolished the neuroprotective effects of progesterone and testosterone, while actinomycin D and cycloheximide did not show any effect on neuroprotection mediated by 17β-estradiol. Taken together, progesterone protects neurons via progesterone receptor-dependent genomic pathway, and allopregnanolone is involved in progesterone-mediated neuroprotection. Testosterone and its metabolite 5α-dihydrotestosterone protect neurons via the genomic pathway of the androgen receptor. Metabolism of sex steroid hormones in the brain might complicate their protective actions in the brain.

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.

Androgen receptor (AR) in cardiovascular diseases

Cardiovascular diseases (CVDs) are still the highest leading cause of death worldwide. Several risk factors have been linked to CVDs, including smoking, diabetes, hyperlipidemia, and gender among others. Sex hormones, especially the androgen and its receptor, androgen receptor (AR), have been linked to many diseases with a clear gender difference. Here, we summarize the effects of androgen/AR on CVDs, including hypertension, stroke, atherosclerosis, abdominal aortic aneurysm (AAA), myocardial hypertrophy, and heart failure, as well as the metabolic syndrome/diabetes and their impacts on CVDs. Androgen/AR signaling exacerbates hypertension, and anti-androgens may suppress hypertension. Androgen/AR signaling plays dual roles in strokes, depending on different kinds of factors; however, generally males have a higher incidence of strokes than females. Androgen and AR differentially modulate atherosclerosis. Androgen deficiency causes elevated lipid accumulation to enhance atherosclerosis; however, targeting AR in selective cells without altering serum androgen levels would suppress atherosclerosis progression. Androgen/AR signaling is crucial in AAA development and progression, and targeting androgen/AR profoundly restricts AAA progression. Men have increased cardiac hypertrophy compared with age-matched women that may be due to androgens. Finally, androgen/AR plays important roles in contributing to obesity and insulin/leptin resistance to increase the metabolic syndrome.

New steps forward in the neuroactive steroid field

Evidence accumulated in recent years suggests that the systemic treatment with neuroactive steroids, or the pharmacological modulation of its production by brain cells, represent therapeutic options to promote neuroprotection. However, new findings, which are reviewed in this paper, suggest that the factors to be considered for the design of possible therapies based on neuroactive steroids are more complex than previously thought. Thus, although as recently reported, the nervous system regulates neuroactive steroid synthesis and metabolism in adaptation to modifications in peripheral steroidogenesis, the neuroactive steroid levels in the brain do not fully reflect its levels in plasma. Even, in some cases, neuroactive steroid level modifications occurring in the nervous tissues, under physiological and pathological conditions, are in the opposite direction than in the periphery. This suggests that the systemic treatment with these molecules may have unexpected outcomes on neural steroid levels. In addition, the multiple metabolic pathways and signaling mechanisms of neuroactive steroids, which may change from one brain region to another, together with the existence of regional and sex differences in its neural levels are additional sources of complexity that should be clarified. This complexity in the levels and actions of these molecules may explain why in some cases these molecules have detrimental rather than beneficial actions for the nervous system. This article is part of a Special Issue entitled 'Steroid Perspectives'.

Testosterone deficiency, insulin-resistant obesity and cognitive function

Testosterone is an androgenic steroid hormone, which plays an important role in the regulation of male reproduction and behaviors, as well as in the maintenance of insulin sensitivity. Several studies showed that testosterone exerted beneficial effects in brain function, including preventing neuronal cell death, balancing brain oxidative stress and antioxidant activity, improving synaptic plasticity and involving cognitive formation. Although previous studies showed that testosterone deficiency is positively correlated with cognitive impairment and insulin-resistant obesity, several studies demonstrated contradictory findings. Thus, this review comprehensively summarizes the current evidence from in vitro, in vivo and clinical studies of the relationship between testosterone deficiency and insulin-resistant obesity as well as the correlation between either insulin-resistant obesity or testosterone deficiency and cognitive impairment. Controversial reports and the mechanistic insights regarding the roles of testosterone in insulin-resistant obesity and cognitive function are also presented and discussed.

Soluble epoxide hydrolase gene deletion improves blood flow and reduces infarct size after cerebral ischemia in reproductively senescent female mice

Soluble epoxide hydrolase (sEH), a key enzyme in the metabolism of vasodilatory epoxyeicosatrienoic acids (EETs), is sexually dimorphic, suppressed by estrogen, and contributes to underlying sex differences in cerebral blood flow and injury after cerebral ischemia. We tested the hypothesis that sEH inhibition or gene deletion in reproductively senescent (RS) female mice would increase cerebral perfusion and decrease infarct size following stroke. RS (15–18 month old) and young (3–4 month old) female sEH knockout (sEHKO) mice and wild type (WT) mice were subjected to 45 min middle cerebral artery occlusion (MCAO) with laser Doppler perfusion monitoring. WT mice were treated with vehicle or a sEH inhibitor t-AUCB at the time of reperfusion and every 24 h thereafter for 3 days. Differences in regional cerebral blood flow were measured in vivo using optical microangiography (OMAG). Infarct size was measured 3 days after reperfusion. Infarct size and cerebral perfusion 24 h after MCAO were not altered by age. Both sEH gene deletion and sEH inhibition increased cortical perfusion 24 h after MCAO. Neither sEH gene deletion nor sEH inhibition reduced infarct size in young mice. However, sEH gene deletion, but not sEH inhibition of the hydrolase domain of the enzyme, decreased infarct size in RS mice. Results of these studies show that sEH gene deletion and sEH inhibition enhance cortical perfusion following MCAO and sEH gene deletion reduces damage after ischemia in RS female mice; however this neuroprotection in absent is young mice.

Sex- and gender-specific research priorities in cardiovascular resuscitation: proceedings from the 2014 Academic Emergency Medicine Consensus Conference Cardiovascular Resuscitation Research Workgroup

Significant sex and gender differences in both physiology and psychology are readily acknowledged between men and women; however, data are lacking regarding differences in their responses to injury and treatment and in their ultimate recovery and survival. These variations remain particularly poorly defined within the field of cardiovascular resuscitation. A better understanding of the interaction between these important factors may soon allow us to dramatically improve outcomes in disease processes that currently carry a dismal prognosis, such as sudden cardiac arrest. As part of the 2014 Academic Emergency Medicine consensus conference "Gender-Specific Research in Emergency Medicine: Investigate, Understand, and Translate How Gender Affects Patient Outcomes," our group sought to identify key research questions and knowledge gaps pertaining to both sex and gender in cardiac resuscitation that could be answered in the near future to inform our understanding of these important issues. We combined a monthly teleconference meeting of interdisciplinary stakeholders from largely academic institutions with a focused interest in cardiovascular outcomes research, an extensive review of the existing literature, and an open breakout session discussion on the recommendations at the consensus conference to establish a prioritization of the knowledge gaps and relevant research questions in this area. We identified six priority research areas: 1) out-of-hospital cardiac arrest epidemiology and outcome, 2) customized resuscitation drugs, 3) treatment role for sex steroids, 4) targeted temperature management and hypothermia, 5) withdrawal of care after cardiac arrest, and 6) cardiopulmonary resuscitation training and implementation. We believe that exploring these key topics and identifying relevant questions may directly lead to improved understanding of sex- and gender-specific issues seen in cardiac resuscitation and ultimately improved patient outcomes.

Testosterone and dihydrotestosterone and incident ischaemic stroke in men in the Cardiovascular Health Study

OBJECTIVE

Ischaemic stroke is a major cause of morbidity and mortality in elderly men. Our main objective was to examine whether testosterone (T) or dihydrotestosterone (DHT) was associated with incident ischaemic stroke in elderly men.

DESIGN

Cohort study.

PARTICIPANTS

Elderly men in the Cardiovascular Health Study who had no history of stroke, heart disease or prostate cancer as of 1994 and were followed until December 2010.

MEASUREMENTS

Adjudicated ischaemic stroke.

RESULTS

Among 1032 men (mean age 76, range 66-97), followed for a median of 10 years, 114 had an incident ischaemic stroke. Total T and free T were not significantly associated with stroke risk, while DHT had a nonlinear association with incident stroke (P = 0·006) in analyses adjusted for stroke risk factors. The lowest risk of stroke was at DHT levels of 50-75 ng/dl, with greater risk of stroke at DHT levels above 75 ng/dl or below 50 ng/dl. Results were unchanged when SHBG was added to the model. Calculated free DHT had an inverse linear association with incident ischaemic stroke with HR 0·77 (95% CI, 0·61, 0·98) per standard deviation in analyses adjusted for stroke risk factors.

CONCLUSIONS

Dihydrotestosterone had a nonlinear association with stroke risk in which there was an optimal DHT level associated with the lowest stroke risk. Further studies are needed to confirm these results and to clarify whether there is an optimal androgen range associated with the least risk of adverse outcomes in elderly men.

Sex differences in cognitive impairment and Alzheimer's disease

Studies have shown differences in specific cognitive ability domains and risk of Alzheimer's disease between the men and women at later age. However it is important to know that sex differences in cognitive function during adulthood may have their basis in both organizational effects, i.e., occurring as early as during the neuronal development period, as well as in activational effects, where the influence of the sex steroids influence brain function in adulthood. Further, the rate of cognitive decline with aging is also different between the sexes. Understanding the biology of sex differences in cognitive function will not only provide insight into Alzheimer's disease prevention, but also is integral to the development of personalized, gender-specific medicine. This review draws on epidemiological, translational, clinical, and basic science studies to assess the impact of sex differences in cognitive function from young to old, and examines the effects of sex hormone treatments on Alzheimer's disease in men and women.

Biological sex and mechanisms of ischemic brain injury

Cerebrovascular disease is a leading cause of death-from-disease and of disability worldwide, affecting some 15 million people. The incidence of stroke or "brain attack" is unlikely to recede for a decade at minimum by most predictions, despite large public health initiatives in stroke prevention. It has been well established that stroke is also one of the most strikingly sex-specific diseases in its epidemiology, and in some cases, in patient outcomes. For example, women sustain lower rates of ischemic stroke relative to men, even beyond their menopausal years. In contrast, outcomes are worse in women in many clinical studies. The biological basis for this sexual dimorphism is a compelling story, and both hormone-dependent and hormone-independent factors are involved, the latter of which is the subject of this brief review. Understanding the molecular and cell-based mechanisms underlying sex differences in ischemic brain injury is an important step toward personalized medicine and effective therapeutic interventions in patients of both sexes.

Major cardiac surgery induces an increase in sex steroids in prepubertal children

While the neuroprotective benefits of estrogen and progesterone in critical illness are well established, the data regarding the effects of androgens are conflicting. Surgical repair of congenital heart disease is associated with significant morbidity and mortality, but there are scant data regarding the postoperative metabolism of sex steroids in this setting. The objective of this prospective observational study was to compare the postoperative sex steroid patterns in pediatric patients undergoing major cardiac surgery (MCS) versus those undergoing less intensive non-cardiac surgery. Urinary excretion rates of estrogen, progesterone, and androgen metabolites (μg/mmol creatinine/m(2) body surface area) were determined in 24-h urine samples before and after surgery using gas chromatography-mass spectrometry in 29 children undergoing scheduled MCS and in 17 control children undergoing conventional non-cardiac surgery. Eight of the MCS patients had Down's syndrome. There were no significant differences in age, weight, or sex between the groups. Seven patients from the MCS group showed multi-organ dysfunction after surgery. Before surgery, the median concentrations of 17β-estradiol, pregnanediol, 5α-dihydrotestosterone (DHT), and dehydroepiandrosterone (DHEA) were (control/MCS) 0.1/0.1 (NS), 12.4/11.3 (NS), 4.7/4.4 (NS), and 2.9/1.1 (p=0.02). Postoperatively, the median delta 17β-estradiol, delta pregnanediol, delta DHT, and delta DHEA were (control/MCS) 0.2/6.4 (p=0.0002), -3.2/23.4 (p=0.013), -0.6/3.7 (p=0.0004), and 0.5/4.2 (p=0.004). Postoperative changes did not differ according to sex. We conclude that MCS, but not less intensive non-cardiac surgery, induced a distinct postoperative increase in sex steroid levels. These findings suggest that sex steroids have a role in postoperative metabolism following MCS in prepubertal children.

Androgens and stroke: good, bad or indifferent?

Cerebral ischemia caused by loss of blood supply to the brain during cardiac arrest or stroke are major causes of death and disability. Biological sex is an important factor in predicting vulnerability of the brain to an ischemic insult, with males being at higher risk for cardio-cerebrovascular events than females of the same age. However, relative incidence of stroke between the genders appears to normalize at advanced ages. Therefore, many scientists have focused on the mechanisms of sex differences in outcome following brain ischemic injury, with a particular emphasis on the role of sex steroids. The majority of studies indicate that female sex steroids, such as estrogen and progesterone, play important roles in the relative neuroprotection following cerebral ischemia observed in females. However, less is known about male sex steroids and brain damage. This review describes the state of our knowledge of androgen-related contributions to neurological injury and recovery following cerebral ischemia that occurs following stroke. Experimental studies examining the effects of castration, androgenic agonists and antagonists and aging provide valuable insights into the role of androgens in clinical outcome following cerebrovascular events.

Sex stratified neuronal cultures to study ischemic cell death pathways

Sex differences in neuronal susceptibility to ischemic injury and neurodegenerative disease have long been observed, but the signaling mechanisms responsible for those differences remain unclear. Primary disassociated embryonic neuronal culture provides a simplified experimental model with which to investigate the neuronal cell signaling involved in cell death as a result of ischemia or disease; however, most neuronal cultures used in research today are mixed sex. Researchers can and do test the effects of sex steroid treatment in mixed sex neuronal cultures in models of neuronal injury and disease, but accumulating evidence suggests that the female brain responds to androgens, estrogens, and progesterone differently than the male brain. Furthermore, neonate male and female rodents respond differently to ischemic injury, with males experiencing greater injury following cerebral ischemia than females. Thus, mixed sex neuronal cultures might obscure and confound the experimental results; important information might be missed. For this reason, the Herson Lab at the University of Colorado School of Medicine routinely prepares sex-stratified primary disassociated embryonic neuronal cultures from both hippocampus and cortex. Embryos are sexed before harvesting of brain tissue and male and female tissue are disassociated separately, plated separately, and maintained separately. Using this method, the Herson Lab has demonstrated a male-specific role for the ion channel TRPM2 in ischemic cell death. In this manuscript, we share and discuss our protocol for sexing embryonic mice and preparing sex-stratified hippocampal primary disassociated neuron cultures. This method can be adapted to prepare sex-stratified cortical cultures and the method for embryo sexing can be used in conjunction with other protocols for any study in which sex is thought to be an important determinant of outcome.

The effect of hemorrhage on the development of the postnatal mouse cerebellum

Recent studies have shown that hemorrhagic injury in the preterm cerebellum leads to long-term neurological sequelae, such as motor, affective, and cognitive dysfunction. How cerebellar hemorrhage (CBH) affects the development and function of the cerebellum is largely unknown. Our study focuses on developing a mouse model of CBH to determine the anatomical, behavioral, and molecular phenotypes resulting from a hemorrhagic insult to the developing cerebellum. To induce CBH in the postnatal mouse cerebellum, we injected bacterial collagenase, which breaks down surrounding blood vessel walls, into the fourth ventricle at postnatal day two. We found a reduction in cerebellar size during postnatal growth, a decrease in granule cells, and persistent neurobehavioural abnormalities similar to abnormalities reported in preterm infants with CBH. We further investigated the molecular pathways that may be perturbed due to postnatal CBH and found a significant upregulation of genes in the inflammatory and sonic hedgehog pathway. These results point to an activation of endogenous mechanisms of injury and neuroprotection in response to postnatal CBH. Our study provides a preclinical model of CBH that may be used to understand the pathophysiology of preterm CBH and for potential development of preventive therapies and treatments.

Oxidative stress defines the neuroprotective or neurotoxic properties of androgens in immortalized female rat dopaminergic neuronal cells

Males have a higher risk for developing Parkinson's disease and parkinsonism after ischemic stroke than females. Although estrogens have been shown to play a neuroprotective role in Parkinson's disease, there is little information on androgens' actions on dopamine neurons. In this study, we examined the effects of androgens under conditions of oxidative stress to determine whether androgens play a neuroprotective or neurotoxic role in dopamine neuronal function. Mitochondrial function, cell viability, intracellular calcium levels, and mitochondrial calcium influx were examined in response to androgens under both nonoxidative and oxidative stress conditions. Briefly, N27 dopaminergic cells were exposed to the oxidative stressor, hydrogen peroxide, and physiologically relevant levels of testosterone or dihydrotestosterone, applied either before or after oxidative stress exposure. Androgens, alone, increased mitochondrial function via a calcium-dependent mechanism. Androgen pretreatment protected cells from oxidative stress-induced cell death. However, treatment with androgens after the oxidative insult increased cell death, and these effects were, in part, mediated by calcium influx into the mitochondria. Interestingly, the negative effects of androgens were not blocked by either androgen or estrogen receptor antagonists. Instead, a putative membrane-associated androgen receptor was implicated. Overall, our results indicate that androgens are neuroprotective when oxidative stress levels are minimal, but when oxidative stress levels are elevated, androgens exacerbate oxidative stress damage.

Impact of aromatase genetic variation on hormone levels and global outcome after severe TBI

Although experimental traumatic brain injury (TBI) studies support estradiol as a neuroprotectant and potent stimulator of neuroplasticity, clinical studies suggest a negative association between endogenous estradiol profiles and mortality/poor outcomes. However, no studies have evaluated associations with cerebral spinal fluid (CSF) hormone profiles and aromatase gene (cytochrome P450 [CYP]19A1) variability on clinical TBI outcomes. We evaluated 110 adults with severe TBI. Average and daily estradiol, testosterone, and estradiol/testosterone ratios (E2:T) were measured using CSF and serum samples and compared to healthy controls. Eighteen tagging and four functional single-nucleotide polymorphisms (SNPs) for CYP19A1 were genotyped and compared to hormones, acute mortality, and Glasgow Outcome Scale (GOS) scores 6 months post-TBI. TBI subjects had lower CSF estradiol over time versus controls. CSF testosterone was initially high, but declined over time. E2/T ratios were initially low, compared to controls, but rose over time. Higher mean E2/T ratio in bivariate analysis was associated with lower mortality (p=0.019) and better GOS-6 scores (p=0.030). rs2470152 influenced CSF E2/T ratio and also serum and CSF testosterone (p≤0.05 all comparisons). Multiple-risk SNPs rs2470152, rs4646, and rs2470144 were associated with worse GOS-6 scores (p≤0.05, all comparisons), and those with>1 risk SNP variant had a higher risk for poor outcome, compared with those with ≤1 risk variant. TBI results in low CSF estradiol and dynamic CSF testosterone and E2/T ratio. In contrast to clinical serum hormone studies, higher CSF E2/T ratio was associated with better outcome. Further, genetic variation in CYP19A1 influences both hormone dynamics and outcome post-TBI.

The effects of craniocerebral and extracranial trauma on the changes in serum testosterone and estradiol in the early stage and their clinical significance

BACKGROUND

This study aimed to examine the correlation between the alterations in serum sex hormones testosterone (T) and estradiol (E2) in the early stages after craniocerebral and extracranial injuries, to assess the Injury Severity Score (ISS) and Glasgow Coma Scale (GCS) score in patients with multiple injuries, and to investigate the significance of the posttrauma changes in ISS and GCS as well as their ratio.

METHODS

The serum levels of T and E(2) in 95 patients with multiple injuries in the early stages after trauma (within 24 hours) were determined by radioimmune double-antibody method. All the patients were classified by ISS, and among them, those complicated with craniocerebral injury were classified by GCS. The serum sex hormone levels and their ratio in the patients with trauma were compared with those in the control group consisting of 15 healthy persons.

RESULTS

In patients with multiple injuries, in the early stage after injury, the serum T level decreased in proportion with the severity of the trauma, whereas the E2 level increased. There was a significant difference in T, E(2), and the ratio of E(2) and T in the severely traumatic group (ISS > 25) as compared with the other groups (p < 0.01). Among the groups complicated with craniocerebral injury that were classified by GCS, there were significant differences in the groups of 5 ≥ GCS ≥ 3 and 8 ≥ GCS > 5, compared with the control group (p < 0.01).

CONCLUSION

The alterations in the serum sex hormones T and E2 levels and their ratio is correlated with the severity of trauma and craniocerebral injury and, thus probably, could serve as an indicator for the evaluation of the trauma severity and possibly in prognosis.

LEVEL OF EVIDENCE

Prognostic study, level III.

Stroke: understanding the differences between males and females

Stroke is a significant cause of death and long-term disability in the USA. The incidence, mortality, and outcomes of stroke are significantly different between men and women. As with many diseases that affect men and women differently, an understanding on the reasons underlying those differences is critical to effective diagnosis and treatment. This review will examine the sex differences in stroke in both humans and animal models of stroke and review what is known about potential mechanisms underlying these differences. It is clear that there is a complex interaction between hormonal, genetic, and unknown factors at play in generating the sex differences in stroke.

Gonadal hormones and the control of reactive gliosis

Astrocytes and microglia respond to central nervous system (CNS) injury with changes in morphology, proliferation, migration and expression of inflammatory regulators. This phenomenon is known as reactive gliosis. Activation of astrocytes and microglia after acute neural insults, such as stroke or traumatic CNS injury, is considered to be an adaptive response that contributes to minimize neuronal damage. However, reactive gliosis may amplify CNS damage under chronic neurodegenerative conditions. Progesterone, estradiol and testosterone have been shown to control reactive gliosis in different models of CNS injury, modifying the number of reactive astrocytes and reactive microglia and the expression of anti-inflammatory and proinflammatory mediators. The actions of gonadal hormones on reactive gliosis involve different mechanisms, including the modulation of the activity of steroid receptors, such as estrogen receptors α and β, the regulation of nuclear factor-κB mediated transcription of inflammatory molecules and the recruitment of the transcriptional corepressor c-terminal binding protein to proinflammatory promoters. In addition, the Parkinson's disease related gene parkin and the endocannabinoid system also participate in the regulation of reactive gliosis by estradiol. The control exerted by gonadal hormones on reactive gliosis may affect the response of neural tissue to trauma and neurodegeneration and may contribute to sex differences in the manifestation of neurodegenerative diseases. However, the precise functional consequences of the regulation of reactive gliosis by gonadal hormones under acute and chronic neurodegenerative conditions are still not fully clarified.

Gender, sex steroid hormones, and Alzheimer's disease

Age-related loss of sex steroid hormones is a established risk factor for the development of Alzheimer's disease (AD) in women and men. While the relationships between the sex steroid hormones and AD are not fully understood, findings from both human and experimental paradigms indicate that depletion of estrogens in women and androgens in men increases vulnerability of the aging brain to AD pathogenesis. We review evidence of a wide range of beneficial neural actions of sex steroid hormones that may contribute to their hypothesized protective roles against AD. Both estrogens and androgens exert general neuroprotective actions relevant to a several neurodegenerative conditions, some in a sex-specific manner, including protection from neuron death and promotion of select aspects of neural plasticity. In addition, estrogens and androgens regulate key processes implicated in AD pathogenesis, in particular the accumulation of β-amyloid protein. We discuss evidence of hormone-specific mechanisms related to the regulation of the production and clearance of β-amyloid as critical protective pathways. Continued elucidation of these pathways promises to yield effective hormone-based strategies to delay development of AD.

Flutamide Enhances Neuroprotective Effects of Testosterone during Experimental Cerebral Ischemia in Male Rats

Testosterone has been shown to worsen histological and neurological impairment during cerebral ischemia in animal models. Cell culture studies revealed that testosterone is implicated in protecting neural and glial cells against insults, and they started to elucidate testosterone pathways that underlie these protective effects. These studies support the hypothesis that testosterone can be neuroprotective throughout an episode of cerebral ischemia. Therefore, we evaluated the mechanisms underlying the shift between testosterone protective and deleterious effects via block testosterone aromatization and androgen receptors in rats subjected to 60-minute middle cerebral artery occlusion. Fifty rats were divided into five equal groups: gonadally intact male; castrated male; intact male + flutamide; intact male + letrozole; intact male + combination flutamide and letrozole. Our results indicated that castration has the ability to reduce histological damage and to improve neurological score 24 hours after middle cerebral artery occlusion. Moreover, flutamide improved histologic and neurological impairment better than castration. Letrozole induced increases in striatal infarct volume and seizures in gonadally intact rats. Combination of flutamide and letrozole showed that letrozole can reverse beneficial effects of flutamide. In conclusion, it seems that the beneficial effects of flutamide are the prevention of the deleterious effects and enhancement of neuroprotective effects of testosterone during cerebral ischemia.

Sex differences in mechanisms and outcome of neonatal hypoxia-ischemia in rodent models: implications for sex-specific neuroprotection in clinical neonatal practice

Clinical findings show that male infants with hypoxic-ischemic injury (HI) fare more poorly than matched females on cognitive outcomes. Rodent models of neonatal hypoxia-ischemia support this difference, with data showing that perinatal brain injury leads to long-term behavioral deficits primarily in male rodents and in female rodents treated with early androgens. Results support the idea that sex-specific gonadal hormones may modulate developmental response to injury and dovetail with overwhelming evidence of developmental androgen effects on typical brain morphology and behavior. However, mechanisms underlying sex differences in response to early brain injury may be more complicated. Specifically, activation of cell death pathways in response to HI may also differ by sex. In females, the preferential activation of the caspase-dependent apoptotic pathway may actually afford greater protection, potentially due to the actions of X-linked inhibitor of apoptosis (XIAP) within this pathway. This contrasts the pattern of preferential activation of the caspase-independent pathway in males. While an integrated model of sex-specific hormonal and genetic modulation of response to early injury remains to be fully elucidated, these findings suggest that infants might benefit from sex-specific neuroprotection following HI injury.

Reprint of "Early testosterone modulated sex differences in behavioral outcome following neonatal hypoxia ischemia in rats"

Hypoxia ischemia (HI; reduced blood oxygenation and/or flow to the brain) represents one of the most common injuries for both term and preterm/very low birth weight (VLBW) infants. These children experience elevated incidence of cognitive and/or sensory processing disabilities, including language based learning disabilities. Clinical data also indicate more substantial long-term deficits for HI injured male babies as compared to HI injured females. Previously, we reported significant deficits in rapid auditory processing and spatial learning in male rats with postnatal day 1 (P1), P7, or P10 HI injury. We also showed sex differences in HI injured animals, with more severe deficits in males as compared to females. Given these findings, combined with extant clinical data, the current study sought to assess a putative role for perinatal testosterone in modulating behavioral outcome following early hypoxic-ischemic injury in rats. Male, female, and testosterone-propionate (TP) treated females were subjected to P7 HI or sham surgery, and subsequently (P30+) underwent a battery of auditory testing and water maze assessment. Results confirm previous reports of sex differences following HI, and add new findings of significantly worse performance in TP-treated HI females compared to vehicle treated HI females. Post mortem anatomic analyses showed consistent effects, with significant brain weight decreases seen in HI male and TP-treated HI females but not female HI or sham groups. Further neuromorphometric analysis of brain structures showed that HI male animals exhibited increased pathology relative to HI females as reflected in ventricular enlargement. Findings suggest that neonatal testosterone may act to enhance the deleterious consequences of early HI brain injury, as measured by both neuropathology and behavior.

Neuroprotective effects of testosterone in a naturally occurring model of neurodegeneration in the adult avian song control system

Seasonal regression of the avian song control system, a series of discrete brain nuclei that regulate song learning and production, serves as a useful model for investigating the neuroprotective effects of steroids. In seasonally breeding male songbirds, the song control system regresses rapidly when males are transferred from breeding to nonbreeding physiological conditions. One nucleus in particular, the HVC, regresses in volume by 22% within days of castration and transfer to a nonbreeding photoperiod. This regression is mediated primarily by a 30% decrease in neuron number, a result of a caspase-dependent process of programmed cell death. Here we examine whether testosterone (T) can act locally in the brain to prevent seasonal-like neurodegeneration in HVC. We began to infuse T intracerebrally near HVC on one side of the brain in breeding-condition male white-crowned sparrows 2 days prior to T withdrawal and shifting them to short-day photoperiods. The birds were killed 3 or 7 days later. Local T infusion significantly protected ipsilateral HVC from volume regression and neuron loss. In addition, T infusion significantly reduced the number, density, and number/1,000 neurons of activated caspase-3 cells and cells positive for cleaved PARP, both markers for programmed cell death, in the ipsilateral HVC. T infusion near HVC also prevented regression of ipsilateral efferent targets of HVC neurons, including the volumes of robust nucleus of the arcopallium (RA) and Area X and the soma area and density of RA neurons. Thus T can act locally in the brain to have a neuroprotective effect and act transsynaptically to prevent regression of efferent nuclei.

Acute serum hormone levels: characterization and prognosis after severe traumatic brain injury

Experimental traumatic brain injury (TBI) studies report the neuroprotective effects of female sex steroids on multiple mechanisms of injury, with the clinical assumption that women have hormonally mediated neuroprotection because of the endogenous presence of these hormones. Other literature indicates that testosterone may exacerbate injury. Further, stress hormone abnormalities that accompany critical illness may both amplify or blunt sex steroid levels. To better understand the role of sex steroid exposure in mediating TBI, we 1) characterized temporal profiles of serum gonadal and stress hormones in a population with severe TBI during the acute phases of their injury; and 2) used a biological systems approach to evaluate these hormones as biomarkers predicting global outcome. The study population was 117 adults (28 women; 89 men) with severe TBI. Serum samples (n=536) were collected for 7 days post-TBI for cortisol, progesterone, testosterone, estradiol, luteinizing hormone (LH), and follicle-stimulating hormone (FSH). Hormone data were linked with clinical data, including acute care mortality and Glasgow Outcome Scale (GOS) scores at 6 months. Hormone levels after TBI were compared to those in healthy controls (n=14). Group based trajectory analysis (TRAJ) was used to develop temporal hormone profiles that delineate distinct subpopulations in the cohort. Structural equations models were used to determine inter-relationships between hormones and outcomes within a multivariate model. Compared to controls, acute serum hormone levels were significantly altered after severe TBI. Changes in the post-TBI adrenal response and peripheral aromatization influenced hormone TRAJ profiles and contributed to the abnormalities, including increased estradiol in men and increased testosterone in women. In addition to older age and greater injury severity, increased estradiol and testosterone levels over time were associated with increased mortality and worse global outcome for both men and women. These findings represent a paradigm shift when thinking about the role of sex steroids in neuroprotection clinically after TBI.

Early testosterone modulated sex differences in behavioral outcome following neonatal hypoxia ischemia in rats

Hypoxia ischemia (HI; reduced blood oxygenation and/or flow to the brain) represents one of the most common injuries for both term and preterm/very low birth weight (VLBW) infants. These children experience elevated incidence of cognitive and/or sensory processing disabilities, including language based learning disabilities. Clinical data also indicate more substantial long-term deficits for HI injured male babies as compared to HI injured females. Previously, we reported significant deficits in rapid auditory processing and spatial learning in male rats with postnatal day 1 (P1), P7, or P10 HI injury. We also showed sex differences in HI injured animals, with more severe deficits in males as compared to females. Given these findings, combined with extant clinical data, the current study sought to assess a putative role for perinatal testosterone in modulating behavioral outcome following early hypoxic-ischemic injury in rats. Male, female, and testosterone-propionate (TP) treated females were subjected to P7 HI or sham surgery, and subsequently (P30+) underwent a battery of auditory testing and water maze assessment. Results confirm previous reports of sex differences following HI, and add new findings of significantly worse performance in TP-treated HI females compared to vehicle treated HI females. Post mortem anatomic analyses showed consistent effects, with significant brain weight decreases seen in HI male and TP-treated HI females but not female HI or sham groups. Further neuromorphometric analysis of brain structures showed that HI male animals exhibited increased pathology relative to HI females as reflected in ventricular enlargement. Findings suggest that neonatal testosterone may act to enhance the deleterious consequences of early HI brain injury, as measured by both neuropathology and behavior.