Estrogen therapy: does it help or hurt the adult and aging brain? Insights derived from animal models

Age and Sex-Related Effects on Single-Subject Gray Matter Networks in Healthy Participants

Recent developments in image analysis have enabled an individual’s brain network to be evaluated and brain age to be predicted from gray matter images. Our study aimed to investigate the effects of age and sex on single-subject gray matter networks using a large sample of healthy participants. We recruited 812 healthy individuals (59.3 ± 14.0 years, 407 females, and 405 males) who underwent three-dimensional T1-weighted magnetic resonance imaging. Similarity-based gray matter networks were constructed, and the following network properties were calculated: normalized clustering, normalized path length, and small-world coefficients. The predicted brain age was computed using a support-vector regression model. We evaluated the network alterations related to age and sex. Additionally, we examined the correlations between the network properties and predicted brain age and compared them with the correlations between the network properties and chronological age. The brain network retained efficient small-world properties regardless of age; however, reduced small-world properties were observed with advancing age. Although women exhibited higher network properties than men and similar age-related network declines as men in the subjects aged < 70 years, faster age-related network declines were observed in women, leading to no differences in sex among the participants aged ≥ 70 years. Brain age correlated well with network properties compared to chronological age in participants aged ≥ 70 years. Although the brain network retained small-world properties, it moved towards randomized networks with aging. Faster age-related network disruptions in women were observed than in men among the elderly. Our findings provide new insights into network alterations underlying aging.

Artificial intelligence-based computational framework for drug-target prioritization and inference of novel repositionable drugs for Alzheimer's disease

BACKGROUND

Identifying novel therapeutic targets is crucial for the successful development of drugs. However, the cost to experimentally identify therapeutic targets is huge and only approximately 400 genes are targets for FDA-approved drugs. As a result, it is inevitable to develop powerful computational tools that can identify potential novel therapeutic targets. Fortunately, the human protein-protein interaction network (PIN) could be a useful resource to achieve this objective.

METHODS

In this study, we developed a deep learning-based computational framework that extracts low-dimensional representations of high-dimensional PIN data. Our computational framework uses latent features and state-of-the-art machine learning techniques to infer potential drug target genes.

RESULTS

We applied our computational framework to prioritize novel putative target genes for Alzheimer's disease and successfully identified key genes that may serve as novel therapeutic targets (e.g., DLG4, EGFR, RAC1, SYK, PTK2B, SOCS1). Furthermore, based on these putative targets, we could infer repositionable candidate-compounds for the disease (e.g., tamoxifen, bosutinib, and dasatinib).

CONCLUSIONS

Our deep learning-based computational framework could be a powerful tool to efficiently prioritize new therapeutic targets and enhance the drug repositioning strategy.

Hippocampal Shape Maturation in Childhood and Adolescence

The hippocampus is a subcortical structure critical for learning and memory, and a thorough understanding of its neurodevelopment is important for studying these processes in health and disease. However, few studies have quantified the typical developmental trajectory of the structure in childhood and adolescence. This study examined the cross-sectional age-related changes and sex differences in hippocampal shape in a multisite, multistudy cohort of 1676 typically developing children (age 1-22 years) using a novel intrinsic brain mapping method based on Laplace-Beltrami embedding of surfaces. Significant age-related expansion was observed bilaterally and nonlinear growth was observed primarily in the right head and tail of the hippocampus. Sex differences were also observed bilaterally along the lateral and medial aspects of the surface, with females exhibiting relatively larger surface expansion than males. Additionally, the superior posterior lateral surface of the left hippocampus exhibited an age-sex interaction with females expanding faster than males. Shape analysis provides enhanced sensitivity to regional changes in hippocampal morphology over traditional volumetric approaches and allows for the localization of developmental effects. Our results further support evidence that hippocampal structures follow distinct maturational trajectories that may coincide with the development of learning and memory skills during critical periods of development.

Sex steroid hormone function in the brain niche: Implications for brain metastatic colonization and progression

BACKGROUND

While sex hormones and their receptors play well-known roles in progression of primary tumors through direct action on sex steroid hormone-responsive cancer cells, emerging evidence suggest that hormones also play important roles in metastatic progression by modulating the tumor microenvironment. Estrogens and androgens synthesized in gonads and within the brain influence memory, behavior, and outcomes of brain pathologies. Yet, their impact on brain metastatic colonization and progression is just beginning to be explored.

RECENT FINDINGS

Estradiol and testosterone cross the blood-brain barrier and are synthesized de novo in astrocytes and other cells within the adult brain. Circulating and brain-synthesized estrogens have been shown to promote brain metastatic colonization of tumors lacking estrogen receptors (ERs), through mechanisms involving the upregulation of growth factors and neurotrophins in ER+ reactive astrocytes. In this review, we discuss additional mechanisms by which hormones may influence brain metastases, through modulation of brain endothelial cells, astrocytes, and microglia.

CONCLUSION

A greater understanding of hormone-brain-tumor interactions may shed further light on the mechanisms underlying the adaptation of cancer cells to the brain niche, and provide therapeutic alternatives modulating the brain metastatic niche.

Long-term use of tamoxifen reduces the risk of dementia: a nationwide population-based cohort study

BACKGROUND

To assess the possible association between tamoxifen treatment and the subsequent risk of dementia in patients with breast cancer, a population-based cohort study was conducted using the Taiwanese National Health Insurance Research Database.

METHODS

The study cohort contained 24 197 patients diagnosed with breast cancer between 1 January 2000 and 31 December 2004. Among them, 16 556 cases received tamoxifen treatment and 7641 did not. Four women without breast cancer were frequency matched to each case by age and index-year as the cancer-free group. The outcome of the analysis of is dementia. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using multivariate Cox proportional hazards regression models.

RESULTS

Patients with breast cancer exhibited a similar risk of developing dementia (adjusted HR = 0.95, 95% CI = 0.86-1.04) compared with the cancer-free group. In addition, among women diagnosed with breast cancer, tamoxifen users exhibited a significant 17% lower risk of dementia compared with those not using tamoxifen (adjusted HR = 0.83, 95% CI = 0.69-0.98), but the significant difference was limited to 5 years or more use (adjusted HR = 0.47, 95% CI = 0.32-0.69). Both tamoxifen and aromatase inhibitor use had a joint effect, with a significantly lower risk of dementia among patients.

CONCLUSION

The results of this population-based cohort study suggest that long-term use of tamoxifen in patients with breast cancer is associated with a lower risk of dementia.

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.

17α-Oestradiol-induced neuroprotection in the brain of spontaneously hypertensive rats

17β-oestradiol is a powerful neuroprotective factor for the brain abnormalities of spontaneously hypertensive rats (SHR). 17α-Oestradiol, a nonfeminising isomer showing low affinity for oestrogen receptors, is also endowed with neuroprotective effects in vivo and in vitro. We therefore investigated whether treatment with 17α-oestradiol prevented pathological changes of the hippocampus and hypothalamus of SHR. We used 20-week-old male SHR with a blood pressure of approximately 170 mmHg receiving s.c. a single 800 μg pellet of 17α-oestradiol dissolved in cholesterol or vehicle only for 2 weeks Normotensive Wistar-Kyoto (WKY) rats were used as controls. 17α-Oestradiol did not modify blood pressure, serum prolactin, 17β-oestradiol levels or the weight of the testis and pituitary of SHR. In the brain, we analysed steroid effects on hippocampus Ki67+ proliferating cells, doublecortin (DCX) positive neuroblasts, glial fibrillary acidic protein (GFAP)+ astrocyte density, aromatase immunostaining and brain-derived neurotrophic factor (BDNF) mRNA. In the hypothalamus, we determined arginine vasopressin (AVP) mRNA. Treatment of SHR with 17α-oestradiol enhanced the number of Ki67+ in the subgranular zone and DCX+ cells in the inner granule cell layer of the dentate gyrus, increased BDNF mRNA in the CA1 region and gyrus dentatus, decreased GFAP+ astrogliosis in the CA1 subfield, and decreased hypothalamic AVP mRNA. Aromatase expression was unmodified. By contrast to SHR, normotensive WKY rats were unresponsive to 17α-oestradiol. These data indicate a role for 17α-oestradiol as a protective factor for the treatment of hypertensive encephalopathy. Furthermore, 17α-oestradiol is weakly oestrogenic in the periphery and can be used in males.

Estradiol increases dendritic length and spine density in CA1 neurons of the hippocampus of spontaneously hypertensive rats: a Golgi impregnation study

Increased neuronal vulnerability has been described in the brain of spontaneously hypertensive rats (SHR), models of primary hypertension. Previous data indicate that estradiol treatment corrects several dysfunctions of the hippocampus and hypothalamus of SHR. Considering this evidence we analyzed the dendritic arborization and spine density of the CA1 subfield in SHR and Wistar-Kyoto (WKY) normotensive rats with and without estradiol treatment. Five month old male SHR and WKY rats received single estradiol or cholesterol pellets (sham treatment) for 2 weeks. A substantial rise of circulating estradiol (>25 fold) and testicular atrophy was present in all estradiol-receiving rats. In both SHR and WKY rats, estradiol decreased blood pressure by ~20 mm Hg; however, a moderate hypertension persisted in SHR (164 mm Hg). Using a modified Golgi impregnation technique, apical and basal dendrites of the CA1 subfield were subjected to Sholl analysis. Spine density was also statistically analyzed. Apical dendritic length was significantly lower in SHR compared to WKY rats (p<0.01), whereas estradiol treatment increased dendritic length in the SHR group only (SHR vs SHR+estradiol; p<0.01). Apical dendritic length plotted against the shell distances 20-100, 120-200 and 220-300 μm, revealed that changes were more pronounced in the range 120-200 μm between SHR vs. WKY rats (p<0.05) and SHR vs. SHR+estradiol (p<0.05). Instead, basal dendrites were not significantly modified by hypertension or steroid treatment. Spine density of apical dendrites was lower in SHR than WKY (p<0.05) and was up-regulated in the SHR+estradiol group compared to the SHR group (p<0.001). Similar changes were obtained for basal dendritic spines. These data suggest that changes of neuronal processes in SHR are plastic events restorable by estradiol treatment. In conjunction with previous results, the present data reveal new targets of estradiol neuroprotection in the brain of hypertensive rats.

Neurocognitive effects of chemotherapy and endocrine therapies in the treatment of breast cancer: recent perspectives

With an estimated 207,090 patients diagnosed with breast cancer in 2010, the role of chemotherapy-induced cognitive impairment is of growing importance. Studies to determine the impact of chemotherapy-induced cognitive impairment have been hindered by difficulties in study-design, in particular, study methodology. Here, we present a review of existing studies and discuss several mechanisms for chemotherapy-induced neurocognitive impairment in breast cancer patients, such as direct neurotoxic injury, telomere shortening, oxidative stress, cytokine dysregulation, estrogen-mediated effects, and the role of certain genetic polymorphisms. Decreased estrogen levels may serve as a link between multiple mechanisms potentiating the effects of the chemotherapy-induced cognitive impairment.

Estrogen regulation of mitochondrial bioenergetics: implications for prevention of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease with a complex and progressive pathological phenotype characterized first by hypometabolism and impaired mitochondrial bioenergetics followed by pathological burden. Increasing evidence indicates an antecedent and potentially causal role of mitochondrial bioenergetic deficits and brain hypometabolism coupled with increased mitochondrial oxidative stress in AD pathogenesis. Compromised aerobic glycolysis pathway coupled with oxidative stress is first accompanied by a shift toward a ketogenic pathway that eventually progresses into fatty acid oxidation (FAO) pathways and leads to white matter degeneration and overproduction and mitochondrial accumulation of β-amyloid. Estrogen-induced signaling pathways converge upon the mitochondria to enhance mitochondrial function and to sustain aerobic glycolysis coupled with citric acid cycle-driven oxidative phosphorylation to potentiate ATP (Adenosine triphosphate) generation. In addition to potentiated mitochondrial bioenergetics, estrogen also enhances neural survival and health through maintenance of calcium homeostasis, promotion of antioxidant defense against free radicals, efficient cholesterol trafficking, and beta amyloid clearance. Significantly, the convergence of E2 mechanisms of action onto mitochondria is also a potential point of vulnerability when activated in diseased neurons that exacerbates degeneration through increased load on dysregulated calcium homeostasis. The "healthy cell bias of estrogen action" hypothesis examines the role that regulating mitochondrial function and bioenergetics play in promoting neural health and the mechanistic crossroads that lead to divergent outcomes following estrogen exposure. As the continuum of neurological health progresses from healthy to unhealthy, so too do the benefits of estrogen or hormone therapy.

Sex steroids and connectivity in the human brain: a review of neuroimaging studies

Our brain operates by the way of interconnected networks. Connections between brain regions have been extensively studied at a functional and structural level, and impaired connectivity has been postulated as an important pathophysiological mechanism underlying several neuropsychiatric disorders. Yet the neurobiological mechanisms contributing to the development of functional and structural brain connections remain to be poorly understood. Interestingly, animal research has convincingly shown that sex steroid hormones (estrogens, progesterone and testosterone) are critically involved in myelination, forming the basis of white matter connectivity in the central nervous system. To get insights, we reviewed studies into the relation between sex steroid hormones, white matter and functional connectivity in the human brain, measured with neuroimaging. Results suggest that sex hormones organize structural connections, and activate the brain areas they connect. These processes could underlie a better integration of structural and functional communication between brain regions with age. Specifically, ovarian hormones (estradiol and progesterone) may enhance both cortico-cortical and subcortico-cortical functional connectivity, whereas androgens (testosterone) may decrease subcortico-cortical functional connectivity but increase functional connectivity between subcortical brain areas. Therefore, when examining healthy brain development and aging or when investigating possible biological mechanisms of 'brain connectivity' diseases, the contribution of sex steroids should not be ignored.

Brain levels of sex steroid hormones in men and women during normal aging and in Alzheimer's disease

We examined the relationships between normal aging, Alzheimer's disease (AD), and brain levels of sex steroid hormones in men and women. In postmortem brain tissue from neuropathologically normal, postmenopausal women, we found no age-related changes in brain levels of either androgens or estrogens. In comparing women with and without AD at different ages, brain levels of estrogens and androgens were lower in AD cases aged 80 years and older but not significantly different in the 60-79 year age range. In male brains, we observed that normal aging was associated with significant decreases in androgens but not estrogens. Further, in men aged 60-79 years, brain levels of testosterone but not estrogens were lower in cases with mild neuropathological changes as well as those with advanced AD neuropathology. In male cases over age 80, brain levels hormones did not significantly vary by neuropathological status. To begin investigating the relationships between hormone levels and indices of AD neuropathology, we measured brain levels of soluble β-amyloid (Aβ). In male cases with mild neuropathological changes, we found an inverse relationship between brain levels of testosterone and soluble Aβ. Collectively, these findings demonstrate sex-specific relationships between normal, age-related depletion of androgens and estrogens in men and women, which may be relevant to development of AD.

Protective effect of estrogens on the brain of rats with essential and endocrine hypertension

Estrogen neuroprotection has been shown in pathological conditions damaging the hippocampus, such as trauma, aging, neurodegeneration, excitotoxicity, oxidative stress, hypoglycemia, amyloid-β peptide exposure and ischemia. Hypertensive encephalopathy also targets the hippocampus; therefore, hypertension seems an appropriate circumstance to evaluate steroid neuroprotection. Two experimental models of hypertension, spontaneously hypertensive rats (SHR) and deoxycorticosterone (DOCA)-salt hypertensive rats, develop hippocampal abnormalities, which include decreased neurogenesis in the dentate gyrus, astrogliosis, low expression of brain-derived neurotrophic factor (BDNF) and decreased number of neurons in the hilar region, with respect of their normotensive strains Wistar Kyoto (WKY) and Sprague-Dawley rats. After estradiol was given for 2 weeks to SHR and DOCA-treated rats, both hypertensive models normalized their faulty hippocampal parameters. Thus, estradiol treatment positively modulated neurogenesis in the dentate gyrus of the hippocampus, according to bromodeoxyuridine incorporation and doublecortin immunocytochemistry, decreased reactive astrogliosis, increased BDNF mRNA and protein expression in the dentate gyrus and increased neuronal number in the hilar region of the dentate gyrus. A role of local estrogen biosynthesis is suggested in SHR, because basal aromatase mRNA in the hippocampus and immunoreactive aromatase protein in cell processes of the dentate gyrus were highly expressed in these rats. Estradiol further stimulated aromatase-related parameters in SHR but not in WKY. These observations strongly support that a combination of exogenous estrogens to those locally synthesized might better alleviate hypertensive encephalopathy. These studies broaden estrogen neuroprotective functions to the hippocampus of hypertensive rat models.

Involvement of brain-derived neurotrophic factor and neurogenesis in oestradiol neuroprotection of the hippocampus of hypertensive rats

The hippocampus of spontaneously hypertensive rats (SHR) and deoxycorticosterone (DOCA)-salt hypertensive rats shows decreased cell proliferation and astrogliosis as well as a reduced number of hilar cells. These defects are corrected after administration of 17β-oestradiol (E(2) ) for 2 weeks. The present work investigated whether E(2) treatment of SHR and of hypertensive DOCA-salt male rats modulated the expression of brain-derived neurotrophic factor (BDNF), a neurotrophin involved in hippocampal neurogenesis. The neurogenic response to E(2) was simultaneously determined by counting the number of doublecortin-immunopositive immature neurones in the subgranular zone of the dentate gyrus. Both hypertensive models showed decreased expression of BDNF mRNA in the granular zone of the dentate gyrus, without changes in CA1 or CA3 pyramidal cell layers, decreased BDNF protein levels in whole hippocampal tissue, low density of doublecortin (DCX)-positive immature neurones in the subgranule zone and decreased length of DCX+ neurites in the dentate gyrus. After s.c. implantation of a single E(2) pellet for 2 weeks, BDNF mRNA in the dentate gyrus, BDNF protein in whole hippocampus, DCX immunopositive cells and the length of DCX+ neurites were significantly raised in both SHR and DOCA-salt-treated rats. These results indicate that: (i) low BDNF expression and deficient neurogenesis distinguished the hippocampus of SHR and DOCA-salt hypertensive rats and (ii) E(2) was able to normalise these biologically important functions in the hippocampus of hypertensive animals.

Effects of tamoxifen and exemestane on cognitive functioning of postmenopausal patients with breast cancer: results from the neuropsychological side study of the tamoxifen and exemestane adjuvant multinational trial

PURPOSE

To evaluate the influence of adjuvant tamoxifen and exemestane on cognitive functioning in postmenopausal patients with breast cancer (BC).

PATIENTS AND METHODS

Neuropsychological assessments were performed before the start (T1) and after 1 year of adjuvant endocrine treatment (T2) in Dutch postmenopausal patients with BC, who did not receive chemotherapy. Patients participated in the international Tamoxifen and Exemestane Adjuvant Multinational trial, a prospective randomized study investigating tamoxifen versus exemestane as adjuvant therapy for hormone-sensitive BC.

RESULTS

Participants included 80 tamoxifen users (mean age, 68.7 years; range 51 to 84), 99 exemestane users (mean age, 68.3 years; range, 50 to 82), and 120 healthy controls (mean age, 66.2 years; range, 49 to 86). At T2, after adjustment for T1 performance, exemestane users did not perform statistically significantly worse than healthy controls on any cognitive domain. In contrast, tamoxifen users performed statistically significantly worse than healthy controls on verbal memory (P < .01; Cohen's d = .43) and executive functioning (P = .01; Cohen's d = .40), and statistically significantly worse than exemestane users on information processing speed (P = .02; Cohen's d = .36). With respect to visual memory, working memory, verbal fluency, reaction speed, and motor speed, no significant differences between the three groups were found.

CONCLUSION

After 1 year of adjuvant therapy, tamoxifen use is associated with statistically significant lower functioning in verbal memory and executive functioning, whereas exemestane use is not associated with statistically significant lower cognitive functioning in postmenopausal patients with BC. Our results accentuate the need to include assessments of cognitive effects of adjuvant endocrine treatment in long-term safety studies.

Progesterone treatment for brain injury: an update

Traumatic brain injury is a significant clinical problem for which there is still no effective treatment. Recent laboratory and clinical data demonstrate a potentially beneficial role for neurosteroids, such as progesterone and allopregnanolone, in the treatment of traumatic brain injury, ischemic stroke and some neurodegenerative disorders. Unlike single-target agents, progesterone affects many of the molecular and physiological processes in the cascade of secondary damage after a traumatic brain injury. This article updates a 2006 Future Neurology review of the research on progesterone and its metabolites in the treatment of traumatic brain injury, and presents new evidence that vitamin D deficiency can reduce progesterone neuroprotection, while combining progesterone with vitamin D produces better functional outcomes after TBI compared with eithertreatment alone.

Neuroprotective effects of estrogen therapy for cognitive and neurobiological profiles of monkey models of menopause

Many postmenopausal women question whether to start or continue hormone therapy because of recent clinical trial negative results. However, evidence from other studies of postmenopausal women, and from studies in menopausal monkeys, indicate that estrogen has neurocognitive protective effects, particularly when therapy is initiated close to the time of menopause before neural systems become increasingly compromised with age. In this review, we present studies of menopausal women and female monkeys that support the concept that estrogen therapies protect both cognitive function and neurobiological processes.

Estradiol reduces anxiety- and depression-like behavior of aged female mice

Beneficial effects of the ovarian steroid, 17beta-estradiol (E(2)), for affective behavior have been reported in young individuals, but less is known about the effects of E(2) among older individuals, and the capacity of older individuals to respond to E(2) following its decline. In the present study, the effects of acute E(2) administration to aged mice for anxiety-like and depression-like behaviors were investigated. Intact female C57BL/6 mice (N=18) that were approximately 24 months old were administered vehicle (sesame oil, n=9) or E(2) (10 microg, n=9) subcutaneously 1h prior to behavioral testing. Mice were tested for anxiety-like behavior (open field, elevated plus maze, mirror chamber, light-dark transition task, Vogel conflict task) and depression-like behavior (forced swim task). To assess the role of general motor behavior and coordination in these aged mice, performance in an activity monitor and rotarod task, and total entries made in tasks (open field, elevated plus maze, light-dark transition task) were determined. Mice administered E(2), compared to vehicle, demonstrated anti-anxiety behavior in the open field, mirror chamber, and light-dark transition task, and anti-depressive-like behavior in the forced swim task. E(2) also tended to have anti-anxiety effects in the elevated plus maze and Vogel task compared to vehicle administration, but these effects did not reach statistical significance. E(2) did not alter motor behavior and/or coordination in the activity monitor, open field, or rotarod tasks. Thus, an acute E(2) regimen produced specific anti-anxiety and anti-depressant effects, independent of effects on motor behavior, when administered to aged female C57BL/6 mice.

Sex-different effect of angiotensin II type 2 receptor on ischemic brain injury and cognitive function

We previously reported that angiotensin II type 2 (AT(2)) receptor signaling prevents neural damage and cognitive impairment after focal cerebral ischemia. We investigated the possible roles of the AT(2) receptor in the sex difference, focusing on cognitive function and ischemic brain damage using AT(2) receptor-deficient mice (Agtr2(-)). In Agtr2(-), spatial memory evaluated by the Morris water maze test was impaired in female compared with that in male Agtr2(-) and female wild-type (Agtr2(+)), while no significant sex-different change was observed in Agtr2(+). Interestingly, bromodeoxyuridine incorporation assay showed a significant decrease of hippocampal neurogenesis in female Agtr2(-) compared with that in female Agtr2(+). In contrast, ischemic area after middle cerebral artery (MCA) occlusion was significantly increased in male compared with female mice in Agtr2(-), while no significant sex-different change was observed in Agtr2(+). Male Agtr2(-) mice showed higher AT(1) receptor expression and significantly impaired cerebral blood flow (CBF) in the ipsilateral side 24 hours after MCA occlusion compared with female Agtr2(-) mice. In conclusion, deletion of the AT(2) receptor showed a sex-different effect such as a severe cognitive impairment with a decrease of hippocampal neurogenesis in females and a larger ischemic brain damage with a decrease of CBF in males.

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

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

Estrogen, aging and the cardiovascular system

Estrogen is a powerful hormone with pleiotropic effects. Estrogens have potent antioxidant effects and are able to reduce inflammation, induce vasorelaxation and alter gene expression in both the vasculature and the heart. Estrogen treatment of cultured cardiac myocytes and endothelial cells rapidly activates NFkappaB, induces heat-shock protein (HSP)-72, a potent intracellular protective protein, and protects cells from simulated ischemia. In in vivo models, estrogens protect against ischemia and trauma/hemorrhage. Estrogens may decrease the expression of soluble epoxide hydrolase, which has deleterious effects on the cardiovascular system through metabolism of epoxyeicosatrienoic acids. Natural (endogenous) estrogens in premenopausal women appear to protect against cardiovascular disease and yet controlled clinical trials have not indicated a benefit from estrogen replacement postmenopause. Much remains to be understood in regards to the many properties of this powerful hormone and how changes in this hormone interact with aging-associated changes. The unexpected negative results of trials of estrogen replacement postmenopause probably arise from our lack of understanding of the many effects of this hormone.

Neuropsychological functioning in postmenopausal breast cancer patients treated with tamoxifen or exemestane after AC-chemotherapy: cross-sectional findings from the neuropsychological TEAM-side study

BACKGROUND

Previous studies have indicated that a subset of cancer patients treated with chemotherapy show cognitive deficits and/or experience cognitive complaints, whereas literature about the influence of hormonal therapies on cognition is sparse. Because of the accumulating knowledge about the importance of estrogen for cognitive functioning, there is growing concern about adjuvant hormonal therapy for breast cancer (BC) affecting cognition. We examined the cognitive functioning of postmenopausal BC patients who were, following doxorubicin/cyclophosphamide (AC) chemotherapy, randomized to tamoxifen or exemestane, and compared their performance with that of non-cancer controls.

MATERIALS AND METHODS

Thirty BC patients using tamoxifen and 50 patients using exemestane underwent interviews, questionnaires and cognitive tests, on average two years after completion of AC chemotherapy. Forty eight healthy controls were tested with similar measures.

RESULTS

Memory complaints were reported by 28% of AC/tamoxifen users, 24% of AC/exemestane users and 6% of healthy controls (p=0.02). Cognitive testing revealed no statistically significant differences between tamoxifen and exemestane users, but suggested that tamoxifen use is possibly related to worse verbal functioning, while exemestane use is possibly related to slower manual motor speed. Both patient groups performed significantly worse than healthy controls on verbal fluency and information processing speed.

DISCUSSION

Our findings show that sequential treatment of AC-chemotherapy and hormonal therapy in postmenopausal, primary BC is associated with lower test scores for certain cognitive functions, and provide indications for possibly distinctive associations for different types of hormonal treatment. Future research with larger groups is recommended to obtain a more definite picture.

Combination treatment with progesterone and vitamin D hormone may be more effective than monotherapy for nervous system injury and disease

More than two decades of pre-clinical research and two recent clinical trials have shown that progesterone (PROG) and its metabolites exert beneficial effects after traumatic brain injury (TBI) through a number of metabolic and physiological pathways that can reduce damage in many different tissues and organ systems. Emerging data on 1,25-dihydroxyvitamin D(3) (VDH), itself a steroid hormone, have begun to provide evidence that, like PROG, it too is neuroprotective, although some of its actions may involve different pathways. Both agents have high safety profiles, act on many different injury and pathological mechanisms, and are clinically relevant, easy to administer, and inexpensive. Furthermore, vitamin D deficiency is prevalent in a large segment of the population, especially the elderly and institutionalized, and can significantly affect recovery after CNS injury. The combination of PROG and VDH in pre-clinical and clinical studies is a novel and compelling approach to TBI treatment.

Protective actions of sex steroid hormones in Alzheimer's disease

Risk for Alzheimer's disease (AD) is associated with age-related loss of sex steroid hormones in both women and men. In post-menopausal women, the precipitous depletion of estrogens and progestogens is hypothesized to increase susceptibility to AD pathogenesis, a concept largely supported by epidemiological evidence but refuted by some clinical findings. Experimental evidence suggests that estrogens have numerous neuroprotective actions relevant to prevention of AD, in particular promotion of neuron viability and reduction of beta-amyloid accumulation, a critical factor in the initiation and progression of AD. Recent findings suggest neural responsiveness to estrogen can diminish with age, reducing neuroprotective actions of estrogen and, consequently, potentially limiting the utility of hormone therapies in aged women. In addition, estrogen neuroprotective actions are also modulated by progestogens. Specifically, continuous progestogen exposure is associated with inhibition of estrogen actions whereas cyclic delivery of progestogens may enhance neural benefits of estrogen. In recent years, emerging literature has begun to elucidate a parallel relationship of sex steroid hormones and AD risk in men. Normal age-related testosterone loss in men is associated with increased risk to several diseases including AD. Like estrogen, testosterone has been established as an endogenous neuroprotective factor that not only increases neuronal resilience against AD-related insults, but also reduces beta-amyloid accumulation. Androgen neuroprotective effects are mediated both directly by activation of androgen pathways and indirectly by aromatization to estradiol and initiation of protective estrogen signaling mechanisms. The successful use of hormone therapies in aging men and women to delay, prevent, and or treat AD will require additional research to optimize key parameters of hormone therapy and may benefit from the continuing development of selective estrogen and androgen receptor modulators.

Estrogen Regulation of MicroRNA Expression

Women outlive men, but life expectancy is not influenced by hormone replacement (estrogen + progestin) therapy. Estrogens appear to protect brain, cardiovascular tissues, and bone from aging. Estrogens regulate genes directly through binding to estrogen receptors alpha and beta (ERalpha and ERbeta) that are ligand-activated transcription factors and indirectly by activating plasma membrane-associated ER which, in turns, activates intracellular signaling cascades leading to altered gene expression. MicroRNAs (miRNAs) are short (19-25 nucleotides), naturally-occurring, non-coding RNA molecules that base-pair with the 3' untranslated region of target mRNAs. This interaction either blocks translation of the mRNA or targets the mRNA transcript to be degraded. The human genome contains ~ 700-1,200 miRNAs. Aberrant patterns of miRNA expression are implicated in human diseases including breast cancer. Recent studies have identified miRNAs regulated by estrogens in human breast cancer cells, human endometrial stromal and myometrial smooth muscle cells, rat mammary gland, and mouse uterus. The decline of estradiol levels in postmenopausal women has been implicated in various age-associated disorders. The role of estrogen-regulated miRNA expression, the target genes of these miRNAs, and the role of miRNAs in aging has yet to be explored.

Estrogen receptor beta as a mitochondrial vulnerability factor

We recently demonstrated mitochondrial localization of estrogen receptor beta (ERbeta). We herein confirm the mitochondrial localization of ERbeta by the loss of mitochondrial ERbeta immunoreactivity in ERbeta knockdown cells. A phenotype change characterized as an increase in resistance to oxidative stressors is associated with ERbeta knockdown. ERbeta knockdown results in a lower resting mitochondrial membrane potential (Deltapsim) and increase in resistance to hydrogen peroxide-induced Deltapsim depolarization in both immortal hippocampal cells and primary hippocampal neurons. ERbeta knockdown cells maintained ATP concentrations despite insults that compromise ATP production and produce less mitochondrial superoxide under oxidative stress. Furthermore, similar mitochondrial phenotype changes were identified in primary hippocampal neurons derived from ERbeta knock-out mice. These data demonstrate that ERbeta is expressed in mitochondria and function as a mitochondrial vulnerability factor involved in Deltapsim maintenance, potentially through a mitochondrial transcription dependent mechanism.

Estrogen-induced plasticity from cells to circuits: predictions for cognitive function

Controversy regarding estrogen action in the brain remains at the forefront of basic, translational and clinical science for women's health. Here, I provide an integrative analysis of estrogen-inducible plasticity and posit it as a strategy for predicting cognitive domains affected by estrogen in addition to sources of variability. Estrogen enhancement of plasticity is evidenced by increases in neurogenesis, neural network connectivity and synaptic transmission. In parallel, estrogen increases glucose transport, aerobic glycolysis and mitochondrial function to provide the ATP necessary to sustain increased energetic demand. The pattern of plasticity predicts that estrogen would preferentially affect cognitive tasks of greater complexity, temporal demand and associative challenge. Thus, estrogen deprivation should be associated with decrements in these functions. Estrogen regulation of plasticity and bioenergetics provides a framework for predicting estrogen-dependent cognitive functions while also identifying sources of variability and potential biomarkers for identifying women appropriate for hormone therapy.

Estrogen regulation of glucose metabolism and mitochondrial function: therapeutic implications for prevention of Alzheimer's disease

Estrogen-induced signaling pathways in hippocampal and cortical neurons converge upon the mitochondria to enhance mitochondrial function and to sustain aerobic glycolysis and citric acid cycle-driven oxidative phosphorylation and ATP generation. Data derived from experimental and clinical paradigms investigating estrogen intervention in healthy systems and prior to neurodegenerative insult indicate enhanced neural defense and survival through maintenance of calcium homeostasis, enhanced glycolysis coupled to the citric acid cycle (aerobic glycolysis), sustained and enhanced mitochondrial function, protection against free radical damage, efficient cholesterol trafficking and beta amyloid clearance. The convergence of E(2) mechanisms of action onto mitochondrial is also a potential point of vulnerability when activated in a degenerating neural system and could exacerbate the degenerative processes through increased load on dysregulated calcium homeostasis. The data indicate that as the continuum of neurological health progresses from healthy to unhealthy so too do the benefits of estrogen or hormone therapy. If neurons are healthy at the time of estrogen exposure, their response to estrogen is beneficial for both neuronal survival and neurological function. In contrast, if neurological health is compromised, estrogen exposure over time exacerbates neurological demise. The healthy cell bias of estrogen action hypothesis provides a lens through which to assess the disparities in outcomes across the basic to clinical domains of scientific inquiry and on which to predict future applications of estrogen and hormone therapeutic interventions sustain neurological health and to prevent age-associated neurodegenerative diseases such as Alzheimer's. Overall, E(2) promotes the energetic capacity of brain mitochondria by maximizing aerobic glycolysis (oxidative phosphorylation coupled to pyruvate metabolism). The enhanced aerobic glycolysis in the aging brain would be predicted to prevent conversion of the brain to using alternative sources of fuel such as the ketone body pathway characteristic of Alzheimer's.

Progesterone blocks estrogen neuroprotection from kainate in middle-aged female rats

The neuroprotective effects of estrogen in young adult rodents are well established. Less well understood is how estrogen neuroprotection is affected by aging and interactions with progesterone. In this study, we investigated the effects of estrogen and continuous progesterone, both alone and in combination, on hippocampal neuron survival following kainate lesion in 14-month-old female rats entering reproductive senescence. Our results show that ovariectomy-induced hormone depletion did not significantly affect the extent of kainate-induced neuron loss. Treatment of ovariectomized rats with estrogen significantly reduced neuron loss, however this effect was blocked by co-administration of continuous progesterone. Treatment of ovariectomized rats with progesterone alone did not significantly affect kainate toxicity. These results provide new insight into factors that regulate estrogen neuroprotection, which has important implications for hormone therapy in postmenopausal women.

The healthy cell bias of estrogen action: mitochondrial bioenergetics and neurological implications

The 'healthy cell bias of estrogen action' hypothesis examines the role that regulating mitochondrial function and bioenergetics play in promoting neural health and the mechanistic crossroads that lead to divergent outcomes following estrogen exposure. Estrogen-induced signaling pathways in hippocampal and cortical neurons converge upon the mitochondria to enhance aerobic glycolysis coupled to the citric acid cycle, mitochondrial respiration and ATP generation. Convergence of estrogen-induced signaling onto mitochondria is also a point of vulnerability when activated in diseased neurons which exacerbates degeneration through increased load on dysregulated calcium homeostasis. As the continuum of neurological health progresses from healthy to unhealthy so too do the benefits of estrogen or hormone therapy. The healthy cell bias of estrogen action hypothesis provides a lens through which to assess disparities in outcomes across basic and clinical science and on which to predict outcomes of estrogen interventions for sustaining neurological health and preventing age-associated neurodegenerative diseases such as Alzheimer's.

Sex differences and the impact of steroid hormones on the developing human brain

Little is known about the hormonal effects of puberty on the anatomy of the developing human brain. In a voxel-based morphometry study, sex-related differences in gray matter (GM) volume were examined in 46 subjects aged 8-15 years. Males had larger GM volumes in the left amygdala, whereas females had larger right striatal and bilateral hippocampal GM volumes than males. Sexually dimorphic areas were related to Tanner stages (TS) of pubertal development and to circulating level of steroid hormones in a subsample of 30 subjects. Regardless of sex, amygdala and hippocampal volumes varied as a function of TS and were associated with circulating testosterone (TEST) levels. By contrast, striatal GM volumes were unrelated to pubertal development and circulating steroid hormones. Whole-brain regression analyses revealed positive associations between circulating estrogen levels and parahippocampal GM volumes as well as between TEST levels and diencephalic brain structures. In addition, a negative association was found between circulating TEST and left parietal GM volumes. These data suggest that GM development in certain brain regions is associated with sexual maturation and that pubertal hormones might have organizational effects on the developing human brain.

Regional variability in age-related loss of neurons from the primary visual cortex and medial prefrontal cortex of male and female rats

During aging, changes in the structure of the cerebral cortex of the rat have been seen, but potential changes in neuron number remain largely unexplored. In the present study, stereological methods were used to examine neuron number in the medial prefrontal cortex and primary visual cortex of young adult (85-90 days of age) and aged (19-22 months old) male and female rats in order to investigate any age-related losses. Possible sex differences in aging were also examined since sexually dimorphic patterns of aging have been seen in other measures. An age-related loss of neurons (18-20%), which was mirrored in volume losses, was found to occur in the primary visual cortex in both sexes in all layers except IV. Males, but not females, also lost neurons (15%) from layer V/VI of the ventral medial prefrontal cortex and showed an overall decrease in volume of this region. In contrast, dorsal medial prefrontal cortex showed no age-related changes. The effects of aging clearly differ among regions of the rat brain and to some degree, between the sexes.

Androgen administration to aged male mice increases anti-anxiety behavior and enhances cognitive performance

Although androgen secretion is reduced with aging, and may underlie decrements in cognitive and affective performance, the effects and mechanisms of androgens to mediate these behaviors are not well understood. Testosterone (T), the primary male androgen, is aromatized to estrogen (E(2)), and reduced to dihydrotestosterone (DHT), which is converted to 5alpha-androstane, 3alpha, 17beta-diol (3alpha-diol). To ascertain whether actions of the neuroactive metabolite of T, 3alpha-diol, mediates cognitive and affective behaviors, intact, aged male C57/B6 mice (24 month old) as well as young, intact and gonadectomized (GDX; 12 week old) mice were administered s.c. T, 3alpha-diol, E(2), or sesame oil vehicle (1 mg/kg; n=4-5/group) at weekly intervals and 1 h later mice were tested in the activity box, roto-rod, open field, elevated plus maze, zero maze, mirror maze, dark-light transition, forced swim, or Vogel tasks. Mice were trained in the inhibitory avoidance or conditioned contextual fear and were administered hormones following training and then were tested. After the last test occasion, tissues were collected for evaluation of hormone levels and effects on gamma-aminobutyric acid (GABA)-stimulated chloride flux. T, 3alpha-diol, or E(2) increased anti-anxiety and antidepressant behavior of aged, intact mice in the open field, light-dark transition, mirror maze, and forced swim tasks. T or 3alpha-diol, but not E(2), enhanced anti-anxiety behavior in the elevated plus maze, zero maze, and the Vogel task, and increased motor behavior in the activity monitor, latency to fall in the Roto-rod task, and cognitive performance in the hippocampally-mediated, but not the amygdala-mediated, portion of the conditioned fear task and in the inhibitory avoidance task. Anti-anxiety and enhanced cognitive performance was associated with regimen that increased plasma and hippocampal 3alpha-diol levels and GABA-stimulated chloride flux. Similar patterns were seen among young, adult GDX but not in intact mice. Thus, 3alpha-diol can enhance affective and cognitive behavior of male mice.

Inhibition of injury-induced glial aromatase reveals a wave of secondary degeneration in the songbird brain

Mechanical or anoxic/ischemic brain insult results in reactive gliosis and a pronounced wave of apoptotic secondary degeneration (WSD). Reactive glia express aromatase (estrogen synthase) and glial estrogen synthesis decreases apoptosis and the volume of degeneration. Whether aromatization by glia affects gliosis itself or the initiation/maintenance of the WSD remains unknown. Adult male zebra finches (Taeniopygia guttata) were injured with a needle that contained the aromatase inhibitor fadrozole or vehicle into contralateral hemispheres. Birds were killed at 0, 2, 6, 24, 72h, 2 or 6 weeks postinjury. Gliosis and degeneration were measured with vimentin- and Fluoro-Jade B-expression, respectively. Reactive gliosis was detectable at 6 h, reached asymptote at 72 h, and continued until 6 weeks postinsult. Gliosis extended further around fadrozole-injury than vehicle, an effect driven by a larger area of gliosis around fadrozole- relative to vehicle-injury at 72 h postinsult. Glial aromatase was inhibited for about 2 weeks postinjury since aromatase relative optical density was higher around fadrozole-injury relative to vehicle-injury until this time-point. Degeneration around vehicle-injury reached asymptote at 2 h postinsult, but that around fadrozole-injury peaked 24-72 h postinjury and decreased thereafter. Thus, the injury-induced WSD as described in mammals is detectable in zebra finches only following glial aromatase inhibition. In the zebra finch, injury-induced estrogen provision may decrease reactive gliosis and severely dampen the WSD, suggesting that songbirds are powerful models for understanding the role of glial aromatization in secondary brain damage.

Cellular and molecular events underlying the dysregulated response of the aged brain to stroke: a mini-review

BACKGROUND

Age-related brain injuries, including stroke, are a major cause of physical and mental disabilities.

OBJECTIVE

Therefore, studying the basic mechanism underlying functional recovery after brain stroke in aged subjects is of considerable clinical interest.

METHODS

This review summarizes the effects of age on recovery after stroke in an animal model, with emphasis on the underlying cellular mechanisms.

RESULTS

Data from our laboratory and elsewhere indicate that, behaviorally, aged rats were more severely impaired by stroke than young rats, and they also showed diminished functional recovery. Infarct volume did not differ significantly between young and aged animals, but critical differences were apparent in the cytological response to stroke, most notably an age-related acceleration in the development of the glial scar. Early infarct in older rats is associated with premature accumulation of BrdU-positive microglia and astrocytes, persistence of activated oligodendrocytes, a high incidence of neuronal degeneration and accelerated apoptosis. In aged rats, neuroepithelial-positive cells were rapidly incorporated into the glial scar, but these neuroepithelial-like cells did not make a significant contribution to neurogenesis in the infarcted cortex in young or aged animals. The response of plasticity-associated proteins like MAP1B, was delayed in aged rats. Tissue recovery was further delayed by an age-related increase in the amount of the neurotoxic C-terminal fragment of the beta-amyloid precursor protein (A-beta) at 2 weeks poststroke.

CONCLUSION

The available evidence indicates that the aged brain has the capability to mount a cytoproliferative response to injury, but the timing of the cellular and genetic response to cerebral insult is dysregulated in aged animals, thereby further compromising functional recovery. Elucidating the molecular basis for this phenomenon in the aging brain could yield novel approaches to neurorestoration in the elderly.

Progesterone: Therapeutic opportunities for neuroprotection and myelin repair

Progesterone and its metabolites promote the viability of neurons in the brain and spinal cord. Their neuroprotective effects have been documented in different lesion models, including traumatic brain injury (TBI), experimentally induced ischemia, spinal cord lesions and a genetic model of motoneuron disease. Progesterone plays an important role in developmental myelination and in myelin repair, and the aging nervous system appears to remain sensitive to some of progesterone's beneficial effects. Thus, the hormone may promote neuroregeneration by several different actions by reducing inflammation, swelling and apoptosis, thereby increasing the survival of neurons, and by promoting the formation of new myelin sheaths. Recognition of the important pleiotropic effects of progesterone opens novel perspectives for the treatment of brain lesions and diseases of the nervous system. Over the last decade, there have been a growing number of studies showing that exogenous administration of progesterone or some of its metabolites can be successfully used to treat traumatic brain and spinal cord injury, as well as ischemic stroke. Progesterone can also be synthesized by neurons and by glial cells within the nervous system. This finding opens the way for a promising therapeutic strategy, the use of pharmacological agents, such as ligands of the translocator protein (18 kDa) (TSPO; the former peripheral benzodiazepine receptor or PBR), to locally increase the synthesis of steroids with neuroprotective and neuroregenerative properties. A concept is emerging that progesterone may exert different actions and use different signaling mechanisms in normal and injured neural tissue.

Effects of estrogen against LPS-induced inflammation and toxicity in primary rat glial and neuronal cultures

Several lines of evidence link inflammation with neurodegenerative diseases, which are aggravated by the age-related decline in estrogen levels in postmenopausal women. Lipopolysaccharide (LPS) is used widely to stimulate glial cells to produce pro-inflammatory mediators such as NO, PGE(2), and TNF-alpha, and was found to be toxic in high doses. We examined the effects of a physiological dose of 17beta-estradiol (E2) against LPS-induced inflammation and toxicity (cell death) in rat primary glial and neuronal cultures. Cultures were treated with 0.1 nM E2 for 24 h and then exposed to LPS 0.5-200 microg/ml for another 24 h. Levels of NO, PGE(2), and TNF-alpha in the culture medium were determined by the Griess reaction assay, radio-immunoassay, and enzyme-linked immunoassay, respectively. Cell death was quantified by measuring the leakage of lactate dehydrogenase (LDH) into the medium from dead or dying cells using the non-radioactive cytotoxicity assay. E2 significantly reduced the LPS-induced increase in NO and TNF-alpha (but not PGE(2)) production in glial cells. PGE(2) and TNF-alpha were undetectable in neuronal cultures, while only basal levels of NO were detected, even after stimulation with LPS. Moreover, pretreatment with E2 significantly reduced LPS-induced cell death, as measured by the release of LDH, in both glial and neuronal cultures. These results suggest that the neuroprotective effects attributed to E2 are derived, at least in part, from its anti-inflammatory and cytoprotective effects in both glial and neuronal cells.

The anti-apoptosis effects of daidzein in the brain of D-galactose treated mice

The purpose of this study was to explore the neuroprotective effects of daidzein on the apoptotic pathway in the hippocampus and cortex of D-galactose treated mice. For this purpose we have examined the expression of bcl-2 mRNA, bax mRNA and caspase-3 in the hippocampus and cortex of D-galactose-treated mice after fed with 10 or 5 mg/kg of daidzein. The results of in situ hybridization experiments indicate that daidzein could help increase the transcriptions of bcl-2 and decrease the transcriptions of bax in those brain regions of D-galactose-treated mice. Furthermore, immunohistochemical studies showed that daidzein could reduce the expression of caspase-3 in both brain regions. These results suggest that daidzein in soybean can inhibit the D-gal induced apoptosis via Bcl-2/Bax apoptotic pathway and be a potential medical candidate for neurodegeneration therapy.

Neuroprotective effects of estradiol in hippocampal neurons and glia of middle age mice

During aging the hippocampus experiences structural, molecular, and functional alterations. Protection from age-related disorders is provided by several factors, including estrogens. Since aging defects start at middle age, we studied if 17 beta-estradiol (E(2)) protected the hippocampus at this age period. Middle age (10-12 month old) male C57Bl/6 mice were implanted sc with E(2) (15 microg) or cholesterol pellets. Ten days afterwards they received bromodeoxyuridine (BrdU) 4 and 2h before killing to study cell proliferation in the dentate gyrus (DG). A pronounced depletion of BrdU+cells in the DG was found in cholesterol-treated middle age mice, accompanied by astrocytosis, and by neuronal loss in the hilus. Middle age mice receiving E(2) showed increased number of BrdU+cells while the other parameters were remarkably attenuated. When steroid treatment was prolonged for 2 months to study migration of cells in the granular layer of the DG, cell migration was unaffected by E(2). However, E(2)-treated middle age mice presented higher cell density and increased staining for doublecortin, a marker for differentiating neurons. Thus, from the three basic steps of adult neurogenesis (proliferation, migration, and differentiation), E(2) stimulated progenitor proliferation - even after long exposure to E(2) studied by Ki67 immunocytochemistry - and differentiation towards a neuronal lineage. This result, in conjunction with recovery from other aging indicators as increased deposits of the aging pigment lipofuscin in DG cells, loss of hilar neurons and astrocytosis supports a wide range protection of hippocampal function of middle age mice by estrogenic hormones.

Novel perspectives for progesterone in hormone replacement therapy, with special reference to the nervous system

The utility and safety of postmenopausal hormone replacement therapy has recently been put into question by large clinical trials. Their outcome has been extensively commented upon, but discussions have mainly been limited to the effects of estrogens. In fact, progestagens are generally only considered with respect to their usefulness in preventing estrogen stimulation of uterine hyperplasia and malignancy. In addition, various risks have been attributed to progestagens and their omission from hormone replacement therapy has been considered, but this may underestimate their potential benefits and therapeutic promises. A major reason for the controversial reputation of progestagens is that they are generally considered as a single class. Moreover, the term progesterone is often used as a generic one for the different types of both natural and synthetic progestagens. This is not appropriate because natural progesterone has properties very distinct from the synthetic progestins. Within the nervous system, the neuroprotective and promyelinating effects of progesterone are promising, not only for preventing but also for reversing age-dependent changes and dysfunctions. There is indeed strong evidence that the aging nervous system remains at least to some extent sensitive to these beneficial effects of progesterone. The actions of progesterone in peripheral target tissues including breast, blood vessels, and bones are less well understood, but there is evidence for the beneficial effects of progesterone. The variety of signaling mechanisms of progesterone offers exciting possibilities for the development of more selective, efficient, and safe progestagens. The recognition that progesterone is synthesized by neurons and glial cells requires a reevaluation of hormonal aging.

Metabolism of exogenous sex steroids and effect on brain functions with a focus on tibolone

Around the menopause, changes in ovarian secretion of steroids result in changes in brain function: hot flushes and sweating later followed by changes in mood, libido and cognition. The relationship between sex steroids and brain functions are reviewed, with focus on hormonal treatments, in particular tibolone, on the postmenopausal brain and on associations between tissue levels and brain functions. Data on steroid levels in human brain are limited. Exogenous oestrogens alone or combined with progestagens reduce hot flushes and sweating, and may favourably affect anxiety, depression and mood. Testosterone alone or combined with E(2) improves libido and mood. Tibolone reduces hot flushes and sweating, and improves mood and libido, but does not stimulate endometrium or breast, like oestrogens. Tibolone is an ideal compound for studying steroid levels and metabolism in brain in view of its structural differences from endogenous steroids and its extensive metabolism required to express its endocrine effects. Brain levels of tibolone metabolites were measured in ovariectomized cynomolgus monkeys receiving tibolone for 36 days. Compared to serum, higher levels of the oestrogenic 3alpha/beta-hydroxytibolone and the androgenic/progestagenic Delta(4)-tibolone, and lower levels of sulphated metabolites are found in various brain regions. The high levels of oestrogenic metabolites in the hypothalamus explain hot flush reduction. Combined with the presence of Delta(4)-tibolone, the tibolone-induced increase in free testosterone through SHBG reduction explains androgenic effects of tibolone on mood and libido. The levels of tibolone metabolites in the monkey brain support tibolone's effects on brain functions.