Positive effects of 17beta-estradiol on insulin sensitivity in aged ovariectomized female rats

The effects of estrogens on spatial learning and memory in female rodents - A systematic review and meta-analysis

Estrogens have inconsistent effects on learning and memory in both the clinical and preclinical literature. Preclinical literature has the advantage of investigating an array of potentially important factors contributing to the varied effects of estrogens on learning and memory, with stringently controlled studies. This study set out to identify specific factors in the animal literature that influence the effects of estrogens on cognition, for possible translation back to clinical practice. The literature was screened and studies meeting strict inclusion criteria were included in the analysis. Eligible studies included female ovariectomized rodents with an adequate vehicle for the estrogen treatment, with an outcome of spatial learning and memory in the Morris water maze. Training days of the Morris water maze were used to assess acquisition of spatial learning, and the probe trial was used to evaluate spatial memory recall. Continuous outcomes were pooled using a random effects inverse variance method and reported as standardized mean differences with 95 % confidence intervals. Subgroup analyses were developed a priori to assess important factors. The overall analysis favoured treatment for the later stages of training and for the probe trial. Factors including the type of estrogen, route, schedule of administration, age of animals, timing relative to ovariectomy, and duration of treatment were all found to be important. The subgroup analyses showed that chronic treatment with 17β-estradiol, either cyclically or continuously, to young animals improved spatial recall. These results, observed in animals, can inform and guide further clinical research on hormone replacement therapy for cognitive benefits.

The Metabolic Syndrome, a Human Disease

This review focuses on the question of metabolic syndrome (MS) being a complex, but essentially monophyletic, galaxy of associated diseases/disorders, or just a syndrome of related but rather independent pathologies. The human nature of MS (its exceptionality in Nature and its close interdependence with human action and evolution) is presented and discussed. The text also describes the close interdependence of its components, with special emphasis on the description of their interrelations (including their syndromic development and recruitment), as well as their consequences upon energy handling and partition. The main theories on MS's origin and development are presented in relation to hepatic steatosis, type 2 diabetes, and obesity, but encompass most of the MS components described so far. The differential effects of sex and its biological consequences are considered under the light of human social needs and evolution, which are also directly related to MS epidemiology, severity, and relations with senescence. The triggering and maintenance factors of MS are discussed, with especial emphasis on inflammation, a complex process affecting different levels of organization and which is a critical element for MS development. Inflammation is also related to the operation of connective tissue (including the adipose organ) and the widely studied and acknowledged influence of diet. The role of diet composition, including the transcendence of the anaplerotic maintenance of the Krebs cycle from dietary amino acid supply (and its timing), is developed in the context of testosterone and β-estradiol control of the insulin-glycaemia hepatic core system of carbohydrate-triacylglycerol energy handling. The high probability of MS acting as a unique complex biological control system (essentially monophyletic) is presented, together with additional perspectives/considerations on the treatment of this 'very' human disease.

Gender Difference in the Association of Hyperuricemia with Insulin Resistance and beta-cell Function in Nondiabetic Korean Adults: The 2019 Korea National Health and Nutrition Examination Survey

AIMS

This study was conducted to assess the association of uric acid (UA) with the homeostasis model assessment of insulin resistance (HOMA-IR) and beta-cell function (HOMA-B) by gender in nondiabetic Korean adults.

MATERIALS AND METHODS

The study was carried out using data from the 2019 Korean National Health and Nutrition Examination Survey and included nondiabetic Korean men, premenopausal women, and postmenopausal women aged 20 years or older.

RESULTS

First, after adjusted for the related variables (excluding obesity), the prevalence of hyperuricemia (UA ≥ 7.0 mg/dL in men or UA ≥ 6.0 mg/dL in women) was positively associated with the quartiles of HOMA-IR and HOMA-B in men, premenopausal women, and postmenopausal women. Second, when further adjusted for obesity, hyperuricemia was positively associated with the quartiles of HOMA-IR and HOMA-B in men and postmenopausal women but not in premenopausal women. Third, after adjusted for the related variables (including obesity), UA level was positively associated with the quartiles of HOMA-IR and HOMA-B in men and postmenopausal women but not in premenopausal women.

CONCLUSIONS

hyperuricemia is positively associated with insulin resistance and beta-cell function in nondiabetic Korean men and postmenopausal women but not in premenopausal women.

Ursolic acid ameliorates adipose tissue insulin resistance in aged rats via activating the Akt-glucose transporter 4 signaling pathway and inhibiting inflammation

Ageing often results in insulin resistance (IR) and chronic inflammation, and adipose is one of the tissues in which inflammation and IR occur earliest during this process. The present study investigated the effect and underlying mechanisms of ursolic acid (UA) on adipose IR and inflammation in ageing rats. Specific pathogen-free male Sprague-Dawley rats were randomly divided into 4 groups: i) Young normal (young); ii) untreated ageing (aged); and groups supplemented with UA either iii) low-UA 10 mg/kg (UA-L) or iv) high-50 mg/kg (UA-H). Animals in the UA-treated groups received 10 or 50 mg/kg UA (suspended in 5% Gum Arabic solution). The rats in the corresponding aged group and young groups received vehicle (5% Gum Arabic) alone. All rats were intragastrically treated once daily by oral gavage for 7 weeks. The day before the experiment terminated, overnight fasting blood (~700 µl) was collected and plasma was prepared to measure biochemical indicators; western blotting was performed to analyze the expression of insulin signaling proteins [(insulin receptor substrate 1 (IRS-1), phosphorylated (p)-IRS-1, PI3K, glucose transporter 4 (GLUT4), Akt and p-Akt)] and inflammatory factors (NF-κB, IL-6 and IL-1β) in the epididymis white adipose tissue (eWAT). The results revealed that treatment with UA-H decreased eWAT weight, the ratio of eWAT weight/body weight, fasted insulin and triglyceride levels, the homeostasis model assessment of insulin resistance and adipose tissue insulin resistance index in ageing rats, indicating the amelioration of systemic and adipose tissue IR, compared with the aged group. Mechanistically, UA-H administration upregulated p-protein kinase B, the ratio of p-Akt to protein kinase B and total and cellular membrane GLUT4 protein levels in eWAT of ageing rats. Conversely, UA inhibited the increase in NF-κB expression and proinflammatory cytokines IL-6 and IL-1β. However, these alterations were not observed in the rats of the aged group. Taken together, the findings of the present study indicated that UA may ameliorate adipose IR, which is associated with activation of the Akt-GLUT4 signaling pathway and inhibition of inflammation in ageing rats. These data provide a basis for the development of effective and safe drugs or functional substances, such as UA, for the prevention and treatment of metabolic diseases.

17β-Estradiol improves insulin signalling and insulin resistance in the aged female hearts: Role of inflammatory and anti-inflammatory cytokines

Aging effects in energy balance in all tissues and organs, including the cardiovascular. The risk of cardiovascular disease is drastically higher in postmenopausal women than in premenopausal women. Estrogen plays an important role in the cardiac function and body's metabolism. The aim of this study was to determine whether 17β-estradiol (E2) has beneficial effects on insulin resistance and some key stages of the insulin signalling pathway in the aged hearts. Young and aged female Wistar rats were ovariectomized and were randomly divided into three groups: young (YS) and aged (AS) sham, young (YV) and aged (AV) vehicle, and young (YE2) and aged (AE2) E2 treatment groups. E2 (1 mg/kg) was administrated every four days for four weeks. Results showed that ovariectomy increased fasting blood glucose, insulin, and HOMAIR in young, while none of these parameters was affected in aged animals. On the other hand, aging itself increased these variables. Furthermore, E2 therapy alleviated these changes in both young and aged animals. Moreover, aging also decreased the p-IRS1, p-Akt level, and translocation of GLUT4 to the plasma membrane. E2 reduced the negative impact of menopause and aging on insulin sensitivity by favoring increase in the level of IL-10 and decrease in the levels of TNF-α and IL-1β. Our results indicated that the heart response to E2 depended on age, and E2 increased insulin sensitivity in the heart of both young and aged animals by altering inflammatory conditions. Determining the exact mechanism of this action is suggested in future studies.

Do women expose themselves to more health-related risks in certain phases of the menstrual cycle? A meta-analytic review

Researchers have increasingly examined the menstrual cycle as a potential source of day-to-day variation in women's cognitions, motivations, and behavior. Within this literature, several lines of research have examined the impact of the menstrual cycle on women's engagement in activities that could negatively affect their health (alcohol and tobacco consumption, sexual behavior, risk recognition). However, findings have been mixed, leaving it unclear whether women may expose themselves to more health-related risks during certain phases of the cycle. We conducted a meta-analysis of 22 published and four unpublished studies (N = 7529, https://osf.io/xr37j/). The meta-analysis revealed shifts across the menstrual cycle in women's sexual behavior with others and risk recognition (higher in ovulatory phase), whereas there was no consistent pattern of difference for alcohol and cigarette consumption. These findings help to clarify the proximate physiological and evolutionary mechanisms underlying women's health-related risk-taking and may inform new interventions.

Sex Differences in Age-Associated Type 2 Diabetes in Rats-Role of Estrogens and Oxidative Stress

Females live longer than males, and the estrogens are one of the reasons for this difference. We reported some years ago that estrogens are able to protect rats against oxidative stress, by inducing antioxidant genes. Type 2 diabetes is an age-associated disease in which oxidative stress is involved, and moreover, some studies show that the prevalence is higher in men than in women, and therefore there are sex-associated differences. Thus, the aim of this study was to evaluate the role of estrogens in protecting against oxidative stress in type 2 diabetic males and females. For this purpose, we used Goto-Kakizaki rats, which develop type 2 diabetes with age. We found that female diabetic rats showed lower glycaemia levels with age than did diabetic males and that estrogens enhanced insulin sensitivity in diabetic females. Moreover, glucose uptake, measured by positron emission tomography, was higher in the female brain, cerebellum, and heart than in those from male diabetic rats. There were also sex-associated differences in the plasma metabolic profile as determined by metabolomics. The metabolic profile was similar between estrogen-replaced and control diabetic rats and different from ovariectomized diabetic rats. Oxidative stress is involved in these differences. We showed that hepatic mitochondria from females produced less hydrogen peroxide levels and exhibited lower xanthine oxidase activity. We also found that hepatic mitochondrial glutathione oxidation and lipid oxidation levels were lower in diabetic females when compared with diabetic males. Ovariectomy induced oxidative stress, and estrogen replacement therapy prevented it. These findings provide evidence for estrogen beneficial effects in type 2 diabetes and should be considered when prescribing estrogen replacement therapy to menopausal women.

Estrogen replacement enhances insulin-induced AS160 activation and improves insulin sensitivity in ovariectomized rats

Menopause predisposes women to impaired glucose metabolism, but the role of estrogen remains unclear. In this study, we examined the effects of chronic estrogen replacement on whole body insulin sensitivity and insulin signaling in ovariectomized rats. Female Wistar rats aged 9 wk were ovariectomized under anesthesia. After 4 wk, pellets containing either 17β-estradiol (E₂) or placebo (Pla) were subcutaneously implanted in the rats. After 4 wk of treatment, the intra-abdominal fat accumulation was greater in the Pla group than that in the E₂ group. Hyperinsulinemic-euglycemic clamp analysis and intravenous glucose tolerance test revealed that insulin sensitivity was significantly lower in the Pla group than in the E₂ group. In addition, Western blotting showed that in vivo insulin stimulation increased protein kinase B (Akt) phosphorylation to a similar degree in the gastrocnemius and liver of both groups, but phosphorylated Akt2 Ser⁴⁷⁴ was enhanced in the muscle of the E₂ group compared with the Pla group. Moreover, insulin-stimulated phosphorylation of Akt substrate of 160 kDa (AS160) Thr⁶⁴² was observed only in the E₂ group, resulting in the difference between the two groups. Additionally, AS160 protein and mRNA levels were higher in muscle of the E₂ group than the Pla group. In contrast, E₂ replacement had no effect on glucose transporter 4 protein levels in muscle and glycogen synthase kinase-3β in muscle and liver. These results suggest that estrogen replacement improves insulin sensitivity by activating the Akt2/AS160 pathway in the insulin-stimulated muscle of ovariectomized rats.

Estrogen signaling in the medial amygdala decreases emotional stress responses and obesity in ovariectomized rats

Declining estradiol (E2), as occurs during menopause, increases risk for obesity and psychopathology (i.e., depression, anxiety). E2 modulates mood and energy homeostasis via binding to estrogen receptors (ER) in the brain. The often comorbid and bidirectional relationship between mood and metabolic disorders suggests shared hormonal and/or brain networks. The medial amygdala (MeA) is abundant in ERs and regulates mood, endocrine, and metabolic stress responses; therefore we tested the hypothesis that E2 in the MeA mitigates emotional and metabolic dysfunction in a rodent model of surgical menopause. Adult female rats were ovariectomized (OVX) and received bilateral implants of E2 or cholesterol micropellets aimed at the MeA. E2-MeA decreased anxiety-like (center entries, center time) and depression-like (immobility) behaviors in the open field and forced swim tests (FST), respectively in ovariectomized rats. E2-MeA also prevented hyperphagia, body weight gain, increased visceral adiposity, and glucose intolerance in ovariectomized rats. E2-MeA decreased caloric efficiency, suggestive of increased energy expenditure. E2-MeA also modulated c-Fos neural activity in amygdalar (central and medial) and hypothalamic (paraventricular and arcuate) brain regions that regulate mood and energy homeostasis in response to the FST, a physically demanding task. Given the shared neural circuitry between mood and body weight regulation, c-Fos expression in discrete brain regions in response to the FST may be due to the psychologically stressful and/or metabolic demands of the task. Together, these findings suggest that the MeA is a critical node for mediating estrogenic effects on mood and energy homeostasis.

Using the cerebrospinal fluid to understand ingestive behavior

The cerebrospinal fluid (CSF) offers a window into the workings of the brain and blood-brain barrier (BBB). Molecules that enter into the central nervous system (CNS) by passive diffusion or receptor-mediated transport through the choroid plexus often appear in the CSF prior to acting within the brain. Other molecules enter the CNS by passing through the BBB into the brain's interstitial fluid prior to appearing in the CSF. This pattern is also often observed for molecules synthesized by neurons or glia within the CNS. The CSF is therefore an important conduit for the entry and clearance of molecules into/from the CNS and thereby constitutes an important window onto brain activity and barrier function. Assessing the CSF basally, under experimental conditions, or in the context of challenges or metabolic diseases can provide powerful insights about brain function. Here, we review important findings made by our labs, as influenced by the late Randall Sakai, by interrogating the CSF.

Estrogen and insulin transport through the blood-brain barrier

Obesity is associated with insulin resistance and reduced transport of insulin through the blood-brain barrier (BBB). Reversal of high-fat diet-induced obesity (HFD-DIO) by dietary intervention improves the transport of insulin through the BBB and the sensitivity of insulin in the brain. Although both insulin and estrogen (E2), when given alone, reduce food intake and body weight via the brain, E2 actually renders the brain relatively insensitive to insulin's catabolic action. The objective of these studies was to determine if E2 influences the ability of insulin to be transported into the brain, since the receptors for both E2 and insulin are found in BBB endothelial cells. E2 (acute or chronic) was systemically administered to ovariectomized (OVX) female rats and male rats fed a chow or a high-fat diet. Food intake, body weight and other metabolic parameters were assessed along with insulin entry into the cerebrospinal fluid (CSF). Acute E2 treatment in OVX female and male rats reduced body weight and food intake, and chronic E2 treatment prevented or partially reversed high-fat diet-induced obesity. However, none of these conditions increased insulin transport into the CNS; rather, chronic E2 treatment was associated less-effective insulin transport into the CNS relative to weight-matched controls. Thus, the reduction of brain insulin sensitivity by E2 is unlikely to be mediated by increasing the amount of insulin entering the CNS.

Obesity accelerates cognitive decline by aggravating mitochondrial dysfunction, insulin resistance and synaptic dysfunction under estrogen-deprived conditions

Chronic consumption of a high-fat diet (HF) causes peripheral insulin resistance, brain insulin resistance, brain mitochondrial dysfunction and cognitive impairment. Estrogen deprivation has also been found to impair cognition. However, the combined effect of both conditions on the brain is unclear. We hypothesized that estrogen deprivation causes brain insulin resistance, brain mitochondrial dysfunction, hippocampal synaptic dysfunction and cognitive impairment, and that consumption of a HF accelerates these impairments in an estrogen-deprived condition. Seventy-two female rats were divided into sham (S) and ovariectomized (O) groups. Rats in each group were further divided into two subgroups to be fed with either a normal diet (ND) or HF for 4, 8 and 12 weeks. At the end of each period, the Morris water maze test was carried out, after which the blood and brain were collected for metabolic and brain function analysis. Obesity, peripheral insulin resistance, increased brain oxidative stress and hippocampal synaptic dysfunction were observed at the eighth week in the NDO, HFS and HFO rats. However, these impairments were worse in the HFO rats. Interestingly, brain insulin resistance, brain mitochondrial dysfunction and cognitive impairment developed earlier (week eight) in the HFO rats, whereas these conditions were observed later at week 12 in the NDO and HFS rats. Either estrogen deprivation or HF appears to cause peripheral insulin resistance, increased brain oxidative stress, hippocampal synaptic dysfunction, brain mitochondrial dysfunction and brain insulin resistance, which together can lead to cognitive impairment. A HF accelerates and aggravates these deleterious effects under estrogen-deprived conditions.

Novel Aspects Concerning the Functional Cross-Talk between the Insulin/IGF-I System and Estrogen Signaling in Cancer Cells

The insulin/IGF system plays an important role in cancer progression. Accordingly, elevated levels of circulating insulin have been associated with an increased cancer risk as well as with aggressive and metastatic cancer phenotypes. Numerous studies have documented that estrogens cooperate with the insulin/IGF system in multiple pathophysiological conditions. The biological responses to estrogens are mainly mediated by the estrogen receptors (ER)α and ERβ, which act as transcription factors; however, several studies have recently demonstrated that a member of the G protein-coupled receptors, named GPR30/G-protein estrogen receptor (GPER), is also involved in the estrogen signaling in normal and malignant cells as well as in cancer-associated fibroblasts (CAFs). In this regard, novel mechanisms linking the action of estrogens through GPER with the insulin/IGF system have been recently demonstrated. This review recapitulates the relevant aspects of this functional cross-talk between the insulin/IGF and the estrogenic GPER transduction pathways, which occurs in various cell types and may account for cancer progression.

GPER1 is regulated by insulin in cancer cells and cancer-associated fibroblasts

Elevated insulin levels have been associated with an increased cancer risk as well as with aggressive and metastatic cancer phenotypes characterized by a poor prognosis. Insulin stimulates the proliferation, migration, and invasiveness of cancer cells through diverse transduction pathways, including estrogen signaling. As G protein estrogen receptor 1 (GPER1) mediates rapid cell responses to estrogens, we evaluated the potential of insulin to regulate GPER1 expression and function in leiomyosarcoma cancer cells (SKUT-1) and breast cancer-associated fibroblasts (CAFs), which were used as a model system. We found that insulin transactivates the GPER1 promoter sequence and increases the mRNA and protein expression of GPER1 through the activation of the PRKCD/MAPK1/c-Fos/AP1 transduction pathway, as ascertained by means of specific pharmacological inhibitors and gene-silencing experiments. Moreover, cell migration triggered by insulin occurred through GPER1 and its main target gene CTGF, whereas the insulin-induced expression of GPER1 boosted cell-cycle progression and the glucose uptake stimulated by estrogens. Notably, a positive correlation between insulin serum levels and GPER1 expression was found in cancer fibroblasts obtained from breast cancer patients. Altogether, our data indicate that GPER1 may be included among the complex network of transduction signaling triggered by insulin that drives cells toward cancer progression.

Effects of estradiol and genistein on the insulin signaling pathway in the cerebral cortex of aged female rats

Menopause leads to a decrease in estrogen production that increases central insulin resistance, contributing to the development of neurodegenerative diseases. We have evaluated the influence of aging and estradiol or genistein treatments on some key stages of the insulin signaling pathway in the cerebral cortex. Young and aged female Wistar rats were ovariectomized and treated acutely with 17β-estradiol (1.4μg/kg body weight), two doses of genistein (10 or 40mg/kg body weight), or vehicle. The cortical expression of several key insulin signaling pathway components was analyzed by western blotting. Our results showed an age-related deterioration in the interactions between the regulatory subunit of phosphatidylinositol 3-kinase (p85α) and the activated form of insulin receptor substrate 1 (p-IRS1tyr612), as well as between p85α and the 46kDa isoform of the estrogen receptor α (ERα46). Moreover, aging also decreased the translocation of glucose transporter-4 (GLUT4) to the plasma membrane. 17β-Estradiol but not genistein reduced the negative impact of aging on central insulin sensitivity by favoring this GLUT4 translocation, and therefore could be neuroprotective against the associated neurodegenerative diseases. However, protein kinase B (Akt) activation by genistein suggests that other possible mechanisms are involved in the neuroprotective effects of this phytoestrogen during the aging process.

Estrogen restores brain insulin sensitivity in ovariectomized non-obese rats, but not in ovariectomized obese rats

OBJECTIVE

We previously demonstrated that obesity caused the reduction of peripheral and brain insulin sensitivity and that estrogen therapy improved these defects. However, the beneficial effect of estrogen on brain insulin sensitivity and oxidative stress in either ovariectomy alone or ovariectomy with obesity models has not been determined. We hypothesized that ovariectomy alone or ovariectomy with obesity reduces brain insulin sensitivity and increases brain oxidative stress, which are reversed by estrogen treatment.

MATERIALS/METHODS

Thirty female rats were assigned as either sham-operated or ovariectomized. After the surgery, each group was fed either a normal diet or high-fat diet for 12 weeks. At week 13, rats in each group received either the vehicle or estradiol for 30 days. At week 16, blood and brain were collected for determining the peripheral and brain insulin sensitivity as well as brain oxidative stress.

RESULTS

We found that ovariectomized rats and high-fat diet fed rats incurred obesity, reduced peripheral and brain insulin sensitivity, and increased brain oxidative stress. Estrogen ameliorated peripheral insulin sensitivity in these rats. However, the beneficial effect of estrogen on brain insulin sensitivity and brain oxidative stress was observed only in ovariectomized normal diet-fed rats, but not in ovariectomized high fat diet-fed rats.

CONCLUSIONS

Our results suggested that reduced brain insulin sensitivity and increased brain oxidative stress occurred after either ovariectomy or obesity. However, the reduced brain insulin sensitivity and the increased brain oxidative stress in ovariectomy with obesity could not be ameliorated by estrogen treatment.

Impaired PI3 K Akt expression in liver and skeletal muscle of ovariectomized rats

It is well established that estrogen deficiency is strongly linked to the development of insulin resistance (IR), but the mechanism is still unclear. Since IR is characterized by a marked reduction in insulin-stimulated PI3 K-mediated activation of Akt in liver and skeletal muscle, we hypothesized that ovariectomized rats (OVX) would exhibit reductions in the expression of proteins in PI3 K signaling pathway, including PI3 K and Akt. As hypothesized, after observing for 12 weeks, compared with the SHAM rats, ovariectomy led to decreased plasma estrogen level and increased HOMA-IR index; in addition, ovariectomy also caused decreased PI3 K and Akt expression levels in the liver and skeletal muscle. Interestingly, the expression patterns differed in tissue-dependent fashion: Akt1 was only found reduction in liver, whereas Akt2 decreased in muscle; these changes can be reversed by estrogen supplement (OVXE). In conclusion, data demonstrate that estrogen withdrawals may cause IR at least in part by impaired PI3 K/Akt signaling proteins in liver and skeletal muscle, and Akt1 and Akt2 might be tissue-specific expressions.

17β-estradiol activates glucose uptake via GLUT4 translocation and PI3K/Akt signaling pathway in MCF-7 cells

The relationship between estrogen and some types of breast cancer has been clearly established. However, although several studies have demonstrated the relationship between estrogen and glucose uptake via phosphatidylinositol 3-kinase (PI3K)/Akt in other tissues, not too much is known about the possible cross talk between them for development and maintenance of breast cancer. This study was designed to test the rapid effects of 17β-estradiol (E2) or its membrane-impermeable form conjugated with BSA (E2BSA) on glucose uptake in a positive estrogen receptor (ER) breast cancer cell line, through the possible relationship between key components of the PI3K/Akt signaling pathway and acute steroid treatment. MCF-7 human breast cancer cells were cultured in standard conditions. Then 10 nM E2 or E2BSA conjugated were administered before obtaining the cell lysates. To study the glucose uptake, the glucose fluorescent analog 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-d-glucose was used. We report an ER-dependent activation of some of the key steps of the PI3K/Akt signaling pathway cascade that leads cells to improve some mechanisms that finally increase glucose uptake capacity. Our data suggest that both E2 and E2BSA enhance the entrance of the fluorescent glucose analog 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-d-glucose, and also activates PI3K/Akt signaling pathway, leading to translocation of glucose transporter 4 to the plasma membrane in an ERα-dependent manner. E2 enhances ER-dependent rapid signaling triggered, partially in the plasma membrane, allowing ERα-positive MCF-7 breast cancer cells to increase glucose uptake, which could be essential to meet the energy demands of the high rate of proliferation.

17β-Estradiol and genistein acute treatments improve some cerebral cortex homeostasis aspects deteriorated by aging in female rats

Aging is associated with decreased insulin sensitivity and impaired cerebral glucose homeostasis. These changes increase neural sensitivity to metabolic damage contributing to cognitive decline, being the decrease in plasma estrogen following menopause one of the main factors involved in aged females. Phytoestrogens as genistein are structurally similar to 17β-estradiol, bind to estrogen receptors, and can evoke both estrogenic and anti-estrogenic effects. Estrogens and phytoestrogens have neuroprotective potential, but the physiological mechanisms are not fully understood. Young and aged female Wistar rats were ovariectomized and treated acutely with 17β-estradiol (1.4μg/kg body weight), genistein (10 or 40 mg/kg body weight), or vehicle. Cortical expression of glucose transporter-3 (GLUT-3) and -4 (GLUT-4), cytochrome c oxidase (CO), estrogen receptor-α (ERα) and -β (ERβ) was measured by Western blotting. There was an age-related decline in GLUT-4, CO and ERβ levels. Both drugs, estradiol and genistein, were able to reverse GLUT-3 downregulation in the cortex following late ovariectomy. However, genistein was the only treatment able to restore completely GLUT-4 levels in aged rats. In contrast, estradiol was more potent than genistein at increasing CO, a marker of cerebral oxidative metabolism. As regards ER levels, estradiol increased the ERα67 quantity diminished by late ovariectomy, while genistein did the same with the other ERα isoform, ERα46, highlighting drug-specific differences in expression changes for both isoforms. On the other hand, no treatment-related differences were found regarding ERβ levels. Therefore, genistein like estradiol could be suitable treatments against cortical metabolic dysfunction caused by aging. These treatments may hold promise as neuroprotective strategies against diabetes and age-related neurodegenerative diseases.

Estradiol favors glucose oxidation in gastrocnemius muscle through modulation of insulin signaling molecules in adult female rats

INTRODUCTION

Estrogens are steroid compounds that are synthesized in ovary, testis, adrenal cortex and other tissues. Several surveys have shown the potential relationship between estradiol and glucose homeostasis in physiological and pathological states such as the menstrual cycle, gestation, gestational diabetes mellitus and polycystic ovarian syndrome (PCOS). All these states are characterized by variability in estradiol level and some degree of insulin resistance. Skeletal muscle plays a crucial role in maintaining systemic glucose metabolism through activation of assorted signaling molecules.

OBJECTIVES

The present study is to evaluate the aftermath of ovariectomy and estradiol replacement on few insulin signaling molecules and GLUT4 protein expression and glucose oxidation in gastrocnemius muscle of adult albino rat.

DESIGN

In the present study, Wistar strain albino rats were selected and divided into three groups. Group I: Control (sham-operated). Group II: Ovariectomized and Group III: Estradiol was replaced 7 days after ovariectomy at a dose of 6 μg/kg boxpression of insulin signaling molecules (western blot) and glucose oxidation were assessed.

RESULTS

Ovariectomy significantly depleted the expression of insulin signaling molecules and glucose oxidation whereas estradiol replacement improved them. Thus, estradiol helps in maintaining glucose level in ovariectomized rats. Results of this study suggest that estradiol improves the expression of insulin signaling molecules in skeletal muscle and thereby it prevents the onset of insulin resistance as a result of estradiol deficiency.

In vivo stimulation of oestrogen receptor α increases insulin-stimulated skeletal muscle glucose uptake

Previous studies suggest oestrogen receptor α (ERα) is involved in oestrogen-mediated regulation of glucose metabolism and is critical for maintenance of whole body insulin action. Despite this, the effect of direct ERα modulation in insulin-responsive tissues is unknown. The purpose of the current study was to determine the impact of ERα activation, using the ER subtype-selective ligand propylpyrazoletriyl (PPT), on skeletal muscle glucose uptake. Two-month-old female Sprague-Dawley rats, ovariectomized for 1 week, were given subcutaneous injections of PPT (10 mg kg⁻¹), oestradiol benzoate (EB; 20 μg kg⁻¹), the ERβ agonist diarylpropionitrile (DPN, 10 mg kg⁻¹) or vehicle every 24 h for 3 days. On the fourth day, insulin-stimulated skeletal muscle glucose uptake was measured in vitro and insulin signalling intermediates were assessed via Western blotting.Activation of ERα with PPT resulted in increased insulin-stimulated glucose uptake into the slow-twitch soleus and fast-twitch extensor digitorum longus (EDL)muscles, activation of insulin signalling intermediates (as measured by phospho-Akt (pAkt) and pAkt substrate (PAS)) and phosphorylation of AMP-activated protein kinase (AMPK). GLUT4 protein was increased only in the EDL muscle. Rats treated with EB or DPN for 3 days did not show an increase in insulin-stimulated skeletal muscle glucose uptake compared to vehicle-treated animals. These new findings reveal that direct activation of ERα positively mediates glucose uptake and insulin action in skeletal muscle. Evidence that oestrogens and ERα stimulate glucose uptake has important implications for understanding mechanisms of glucose homeostasis, particularly in postmenopausal women.

Chronic treatment with the nitric oxide synthase inhibitor, L-NAME, attenuates estradiol-mediated improvement of learning and memory in ovariectomized rats

INTRODUCTION

The role of ovarian hormones and nitric oxide in learning and memory has been widely investigated.

OBJECTIVE

The present study was carried out to evaluate the effect of the nitric oxide synthase (NOS) inhibitor, N (G)-nitro-L-arginine methyl ester (L-NAME), on the ability of estradiol to improve learning in OVX rats using the Morris water maze.

METHODS

Forty rats were divided into five groups: (1) ovariectomized (OVX), (2) ovariectomized-estradiol (OVX-Est), (3) ovariectomized-L-NAME 10 (OVX-LN 10), (4) ovariectomized-L-NAME 50 (OVX-LN 50) and (5) ovariectomized-estradiol-L-NAME 50 (OVX-Est-LN 50). The animals in the OVX-Est group were treated with a weekly injection of estradiol valerate (2 mg/kg; i.m.). The OVX-LN 10 and OVX-LN 50 groups were treated with daily injections of 10 and 50 mg/kg L-NAME (i.p.), respectively. The animals in the OVX-Est-LN 50 group received a weekly injection of estradiol valerate and a daily injection of 50 mg/kg L-NAME. After 8 weeks, all animals were tested in the Morris water maze.

RESULTS

The animals in the OVX-Est group had a significantly lower latency in the maze than the OVX group (p<0.001). There was no significant difference in latency between the OVX-LN 10 and OVX-LN 50 groups in comparison with the OVX group. The latency in the OVX-Est-LN 50 group was significantly higher than that in the OVX-Est group (p<0.001).

CONCLUSION

These results show that L-NAME treatment attenuated estradiol-mediated enhancement of spatial learning and memory in OVX rats, but it had no significant effect in OVX rats without estrogen, suggesting an interaction of nitric oxide and estradiol in these specific brain functions.

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

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

Chronic 17beta-estradiol treatment improves skeletal muscle insulin signaling pathway components in insulin resistance associated with aging

Insulin resistance is a common feature of aging in both humans and rats. In the case of females, it seems to be related to loss of gonadal function, due mainly due to a decrease in plasma estrogen levels. Several causes have been postulated for this insulin resistance, among them changes in several steps of the insulin pathway. In view of these findings, the purpose of the present study was to examine the role of chronic 17beta-estradiol treatment on insulin sensitivity during the aging process, and its effects on levels of the insulin-sensitive glucose transporter Glut4 (both total and plasma membrane localized), the interaction between p85alpha subunit of PI3-k and IRS-1, Tyr- and Ser-612 phosphorylation of IRS-1 levels, and Ser-473 phosphorylation of Akt. The present findings indicate that 17beta-estradiol treatment is able to minimize the deleterious effect of aging on insulin sensitivity, at least at the level of plasma membrane localized Glut4. Nevertheless further research is needed to determine this conclusively.

17beta-estradiol treatment is unable to reproduce p85 alpha redistribution associated with gestational insulin resistance in rats

Maternal metabolic adaptations are essential to ensure proper fetal development. According to changes in insulin sensitivity, pregnancy can be divided into two periods: early pregnancy, characterized by an increase in maternal insulin sensitivity, and late pregnancy, in which there is a significant increase in insulin resistance. The aims of the present work were two-fold: firstly, the molecular mechanisms associated with the development of pregnancy-related insulin resistance in peripheral tissues, mainly retroperitoneal adipose tissue and skeletal muscle, were studied in pregnant rats at 6, 11, and 16 days gestation. Secondly, the role of 17beta-estradiol in this process was elucidated in an animal model consisting of ovariectomized rats treated with 17beta-estradiol to mimic plasma gestational levels. The results support the conclusion that retroperitoneal adipose tissue plays a pivotal role in the decrease in insulin sensitivity during pregnancy, through a mechanism that involves p85 alpha redistribution to the insulin receptor and impairment of Glut4 translocation to the plasma membrane. Treatment with 17beta-estradiol did not reproduce the molecular adaptations that occur during pregnancy, suggesting that other hormonal factors presents in gestation but absent in our experimental model are responsible for p85 alpha redistribution to the insulin receptor.

Estradiol restores diabetes-induced reductions in sex steroid receptor expression and distribution in the vagina of db/db mouse model

Sex steroid hormones and receptors play an important role in maintaining vaginal physiology. Disruptions in steroid receptor signaling adversely impact vaginal function. Limited studies are available investigating the effects of diabetic complications on steroid receptor expression and distribution in the vagina. The goals of this study were to investigate type 2 diabetes-induced changes in expression, localization and distribution of estrogen (ER), progesterone (PR) and androgen receptors (AR) in the vagina and to determine if estradiol treatment ameliorates these changes. Eight-week-old female diabetic (db/db) mice (strain BKS.Cg-m+/+ Lepr(db)/J) were divided into two subgroups: untreated diabetic and diabetic animals treated with pellets containing estradiol. Control normoglycemic littermates were subcutaneously implanted with pellets devoid of estradiol. At 16 weeks of age, animals were sacrificed, vaginal tissues excised and analyzed by Western blot and immunohistochemical methods. Diabetes produced marked reductions in protein expression of ER, PR, and AR. Diabetes also resulted in marked differences in the distribution, staining intensity and proportion of immunoreactive cells containing these steroid receptors in the epithelium, lamina propria and muscularis. Treatment of diabetic animals with estradiol restored receptor protein expression and distribution similar to those levels observed in control animals. This study demonstrates that type 2 diabetes markedly reduces steroid receptor protein expression and distribution in the vagina. Estradiol treatment of diabetic animals ameliorates these diabetes-induced changes.

Muscular transcriptome in postmenopausal women with or without hormone replacement

The loss of muscle mass and strength with aging is well characterized, but our knowledge of the molecular mechanisms underlying the development of sarcopenia remains incomplete. Although menopause is often accompanied with first signs of age-associated changes in muscle structure and function, the effects of hormone replacement therapy (HRT) or menopause-related decline in estrogen production in the muscles of postmenopausal women is not well understood. Furthermore the knowledge of the global transcriptional changes that take place in skeletal muscle in relation to estrogen status has thus far been completely lacking. We used a randomized double-blinded study design together with an explorative microarray experiment to characterize possible effects of continuous, combined HRT and estrogen deprivation on the skeletal muscle of fifteen women. Here, we report the differential response of both Gene Ontology-annotated biological processes and some individual genes responding differentially to the use or non-use of HRT. Our results revealed transcription level changes in, for example, muscle protein and energy metabolism. In particular, the ubiquitine-proteosome system was found to be effected at several levels. HRT seemed to partially counteract the postmenopause-related transcriptional changes. Our results suggest that during the early postmenopausal years, when there is no counteracting medication available, muscle transcriptome changes notably, whereas HRT appears to slow down this phenomenon and could therefore aid in maintaining proper muscle mass and function after menopause.

Chronic estradiol treatment improves brain homeostasis during aging in female rats

Aging is associated with a reduction in metabolic function, insulin resistance, increased incidence of neurodegenerative diseases, and memory or cognitive dysfunction. In aging females, loss of gonadal function determines the beginning of the period of reduced metabolic function. Estrogens have neuroprotective effects, but the mechanisms by which they exert these effects remain unclear. The effects of estradiol treatment on the activation of the insulin receptor substrate (IRS)-1 signaling pathway, the interactions between estrogen receptor (ER)-alpha and IRS-1 and the p85alpha subunit of phosphatidylinositol-3 kinase, together with the possible effects of estradiol treatment on glucose transporter-3 and -4 levels, were investigated in female rats. The level of expression of each glucose transporter was greater in control and estradiol-treated groups than in the ovariectomized group. Interactions of ERalpha46-IRS-1, ERalpha46-p85alpha, and p85alpha-IRS-1, as well as IRS-1 phosphorylation, appeared to increase with estradiol treatment. The results indicate that estradiol treatment improves some aspects of neuronal homeostasis that are affected by aging; this may indicate that estradiol has neuroprotective effects in female rats. Additional animal studies are required to clarify the neuroprotective role of estradiol in relation to other important molecules involved in the IRS-1-phosphatidylinositol-3 kinase signaling pathway.

The effects of estrogen and testosterone on gene expression in the rat mesenteric arteries

A dramatic difference exists in the timing of development of cardiovascular disease in men vs. women. The primary candidates underlying the cause of this gender difference are the sex steroids, estrogen and testosterone. The vasculature is considered to be a site of action of these steroids. In spite of these concepts there is little data on the direct effects of estrogen and testosterone on gene expression in the vasculature. In this study, ovariectomized Sprague Dawley rats were treated for 4 days with vehicle (sesame oil), estradiol benzoate (0.15 mg/kg/day), or testosterone (1 mg/kg/day). The mesenteric arteries were obtained, total RNA was extracted, and CodeLink Uniset Rat I DNA microarrays were used to identify differential gene expression. Seven genes were identified as differentially expressed from the DNA microarray data and confirmed by real time RT-PCR. The expression of D site albumin promoter binding protein and fatty acid synthase were increased in response to both estrogen and testosterone. 3 alpha-hydroxysteroid dehydrogenase, interleukin 4 receptor, JunB and c-Fos expression were increased by estrogen but not by testosterone. Aryl hydrocarbon nuclear translocator-like gene was reduced by testosterone. These data identify genes not previously known to be responsive to estrogen and testosterone in the vasculature.