Tissue-selective estrogen complexes with bazedoxifene prevent metabolic dysfunction in female mice

Sex differences in lipid and lipoprotein metabolism

BACKGROUND

Endogenous sex hormones are important for metabolic health in men and women. Before menopause, women are protected from atherosclerotic cardiovascular disease (ASCVD) relative to men. Women have fewer cardiovascular complications of obesity compared to men with obesity. Endogenous estrogens have been proposed as a mechanism that lessens ASCVD risk, as risk of glucose and lipid abnormalities increases when endogenous estrogens decline with menopause. While baseline risk is higher in males than females, endogenously produced androgens are also protective against fatty liver, diabetes and ASCVD, as risk goes up with androgen deprivation and with the decline in androgens with age.

SCOPE OF REVIEW

In this review, we discuss evidence of how endogenous sex hormones and hormone treatment approaches impact fatty acid, triglyceride, and cholesterol metabolism to influence metabolic and cardiovascular risk. We also discuss potential reasons for why treatment strategies with estrogens and androgens in older individuals fail to fully recapitulate the effects of endogenous sex hormones.

MAJOR CONCLUSIONS

The pathways that confer ASCVD protection for women are of potential therapeutic relevance. Despite protection relative to men, ASCVD is still the major cause of mortality in women. Additionally, diabetic women have similar ASCVD risk as diabetic men, suggesting that the presence of diabetes may offset the protective cardiovascular effects of being female through unknown mechanisms.

The Role of Estrogens in Pancreatic Islet Physiopathology

In rodent models of insulin-deficient diabetes, 17β-estradiol (E2) protects pancreatic insulin-producing β-cells against oxidative stress, amyloid polypeptide toxicity, gluco-lipotoxicity, and apoptosis. Three estrogen receptors (ERs)-ERα, ERβ, and the G protein-coupled ER (GPER)-have been identified in rodent and human β-cells. This chapter describes recent advances in our understanding of the role of ERs in islet β-cell function, nutrient homeostasis, survival from pro-apoptotic stimuli, and proliferation. We discuss why and how ERs represent potential therapeutic targets for the maintenance of functional β-cell mass.

Long-Term Administration of Conjugated Estrogen and Bazedoxifene Decreased Murine Fecal β-Glucuronidase Activity Without Impacting Overall Microbiome Community

Conjugated estrogens (CE) and Bazedoxifene (BZA) combination is used to alleviate menopause-associated symptoms in women. CE+BZA undergo first-pass-metabolism in the liver and deconjugation by gut microbiome via β-glucuronidase (GUS) enzyme inside the distal gut. To date, the impact of long-term exposure to CE+BZA on the gut microbiome or GUS activity has not been examined. Our study using an ovariectomized mouse model showed that CE+BZA administration did not affect the overall cecal or fecal microbiome community except that it decreased the abundance of Akkermansia, which was identified as a fecal biomarker correlated with weight gain. The fecal GUS activity was reduced significantly and was positively correlated with the abundance of Lactobacillaceae in the fecal microbiome. We further confirmed in Escherichia coli K12 and Lactobacillus gasseri ADH that Tamoxifen-, 4-hydroxy-Tamoxifen- and Estradiol-Glucuronides competed for GUS activity. Our study for the first time demonstrated that long-term estrogen supplementation directly modulated gut microbial GUS activity. Our findings implicate that long-term estrogen supplementation impacts composition of gut microbiota and microbial activity, which affects estrogen metabolism in the gut. Thus, it is possible to manipulate such activity to improve the efficacy and safety of long-term administered estrogens for postmenopausal women or breast cancer patients.

Central regulation of energy metabolism by estrogens

BACKGROUND

Estrogenic actions in the brain prevent obesity. Better understanding of the underlying mechanisms may facilitate development of new obesity therapies.

SCOPE OF REVIEW

This review focuses on the critical brain regions that mediate effects of estrogens on food intake and/or energy expenditure, the molecular signals that are involved, and the functional interactions between brain estrogens and other signals modulating metabolism. Body weight regulation by estrogens in male brains will also be discussed.

MAJOR CONCLUSIONS

17β-estradiol acts in the brain to regulate energy homeostasis in both sexes. It can inhibit feeding and stimulate brown adipose tissue thermogenesis. A better understanding of the central actions of 17β-estradiol on energy balance would provide new insight for the development of therapies against obesity in both sexes.

Towards optimization of estrogen receptor modulation in medicine

Women now spend more than one-third of their lives in the postmenopausal years, and the decline of endogenous estrogen production during menopause is accompanied by a series of functional disorders that affect the quality of life. These symptoms could be alleviated or even totally suppressed by menopausal hormone therapy (MHT), initially based on natural estrogens extracted from the urine of pregnant mares (mainly in the USA, using the oral route) and later from the synthesis of the natural estrogen, 17β-estradiol (mainly in Europe, in particular using the transdermal route). Estrogen receptor (ER) α is the main receptor mediating the physiological effects of estrogens. ERα belongs to the nuclear receptor superfamily and activates gene transcription in a time and tissue-specific manner through two distinct activation functions (AF), AF1 and AF2. In addition to these classical genomic actions, ERα also mediates membrane initiated signaling enabling rapid actions of estrogen, potentially along or in interaction with other receptors. Here, we provide a brief historical overview of MHT, and we then highlight recent advances in the characterization of new treatments based on the association of estrogens with selective estrogen receptor modulators (SERMs) or on the modulation of nuclear or membrane ERα.

Estrogens and female liver health

Due to declining estrogen levels during menopause, NAFLD prevalence is higher in postmenopausal women compared to in premenopausal women or in men. Postmenopausal women are more susceptible to weight gain, fat redistribution and dyslipidemia, all major hallmarks of metabolic syndrome associated with increased NAFLD risk. Gut microbiota plays important roles in development of gastrointestinal tract, metabolism and immunity. Host-microbe interactions allows regulation of a wide range of pathways that affect healthy and diseased physiology. Recent advances in - omics technologies, such as microbiome, transcriptome and metabolome analysis, provided evidence that estrogens and intestinal microbiota (IM) can collectively influence obesity, inflammatory disease, diabetes, and cancers. By understanding underlying mechanisms of estrogens and microbiota crosstalk, we might design dietary and pharmacological interventions to alleviate the metabolic syndrome and NAFLD.

Roles of G protein-coupled estrogen receptor GPER in metabolic regulation

Metabolic homeostasis is differentially regulated in males and females. The lower incidence of obesity and associated diseases in pre-menopausal females points towards the beneficial role of the predominant estrogen, 17β-estradiol (E2). The actions of E2 are elicited by nuclear and extra-nuclear estrogen receptor (ER) α and ERβ, as well as the G protein-coupled estrogen receptor (GPER, previously termed GPR30). The roles of GPER in the regulation of metabolism are only beginning to emerge and much remains unclear. The present review highlights recent advances implicating the importance of GPER in metabolic regulation. Assessment of the specific metabolic roles of GPER employing GPER-deficient mice and highly selective GPER-targeted pharmacological agents, agonist G-1 and antagonists G-15 and G36, is also presented. Evidence from in vitro and in vivo studies involving either GPER deficiency or selective activation suggests that GPER is involved in body weight regulation, glucose and lipid homeostasis as well as inflammation. The therapeutic potential of activating GPER signaling through selective ligands for the treatment of obesity and diabetes is also discussed.

Bazedoxifene and conjugated estrogen combination maintains metabolic homeostasis and benefits liver health

The bazedoxifene and conjugated estrogens (CE+BZA) combination has been shown to prevent visceral adiposity and weight gain after ovariectomy. However, its impact on the liver transcriptomes associated with prevention of hepatosteatosis is yet to be determined. In the present study, we use liver transcriptomics and plasma metabolomics analysis to characterize the effects of various estrogens on liver. The CE+BZA combination was very effective at preventing ovariectomy-induced weight gain in mice fed a high-fat diet (HFD). In CE+BZA treated animals, liver weight and hepatic lipid deposition were significantly lower than in Vehicle (Veh) treated animals. Additionally, CE+BZA induced unique liver transcriptome and plasma metabolome profiles compared to estradiol, conjugated estrogens alone, and bazedoxifene alone. Blood plasma metabolite analysis identified several metabolites similar to and distinct from other estrogen treatments. Integrated pathway analysis showed that gene networks that were associated with inflammation, reactive oxygen species pathway and lipid metabolism and their relevant metabolites were regulated significantly by CE+BZA treatment. Thus, long-term CE+BZA treatment modulated hepatic metabolic gene networks and their associated metabolites and improves hepatic health without stimulating the uterus.

AMPK activation caused by reduced liver lactate metabolism protects against hepatic steatosis in MCT1 haploinsufficient mice

Objective

Hepatic steatosis is the first step leading to non-alcoholic fatty liver disease, which represents a major complication of obesity. Here, we show that MCT1 haploinsufficient mice resist to hepatic steatosis development when fed a high fat diet. They exhibit a reduced hepatic capacity to metabolize monocarboxylates such as lactate compared to wildtype mice.

Methods

To understand how this resistance to steatosis develops, we used HFD fed wildtype mice with hepatic steatosis and MCT1 haploinsufficient mice to study hepatic metabolism.

Results

AMPK is constitutively activated in the liver of MCT1 haploinsufficient mice, leading to an inactivation of SREBP1. Therefore, expression of key transcription factors for lipid metabolism, such as PPARα and γ, CHREB, or SREBP1 itself, as well as several enzymes including FAS and CPT1, was not upregulated in these mice when fed a high fat diet. It is proposed that reduced hepatic lactate metabolism is responsible for the protection against hepatic steatosis in MCT1 haploinsufficient mice via a constitutive activation of AMPK and repression of several major elements involved in hepatic lipid metabolism.

Conclusion

Our results support a role of increased lactate uptake in hepatocytes during HFD that, in turn, induce a metabolic shift stimulating SREBP1 activity and lipid accumulation.

•

Lactate uptake causes a shift in LDH isoform expression during HFD.

•

LDH isoform shift favors a decrease in AMPK activity.

•

Lactate uptake reduction in MCT1+/− mice blocks LDH isoform shift and leads to AMPK activation.

•

SREBP activation is prevented in MCT1+/− mice due to AMPK activation.

•

Decreased expression of SREBP targets involved in lipid metabolism protects against NAFLD.

Sex-specific association between fibroblast growth factor 21 and type 2 diabetes: a nested case-control study in Singapore Chinese men and women

Background

Fibroblast growth factor 21 (FGF-21) is mainly secreted by liver and has been reported to be involved in the pathogenesis of type 2 diabetes. Some prospective studies have shown a positive association between FGF-21 and diabetes risk. However, no study has examined whether the association differed by sex, which has been reported between FGF-21 and atherosclerosis. Therefore, we prospectively evaluated the sex-specific association between FGF-21 and diabetes in a Chinese population.

Methods

Serum FGF-21 concentration was measured in a case-control study comprising of 251 incident diabetes cases and 251 age-sex-matched controls nested within a prospective population-based cohort, the Singapore Chinese Health Study. At blood collection between 1999 and 2004, participants were free of diagnosed diabetes, cardiovascular disease, and cancer. Incident self-reported diabetes cases were identified at follow-up II interview (2006–2010). Odds ratio (OR) and 95% confidence interval (CI) were calculated using multivariable logistic regression models.

Results

After adjustment for risk biomarkers of diabetes including lipids, liver enzymes and inflammatory marker, the OR of type 2 diabetes with per one unit increment in log FGF-21 concentration was 1.16 (95% CI 0.90–1.50). Significant interaction was found with sex (P-interaction = 0.029): the OR (95% CI) was 1.50 (1.00-2.25) in women and 0.89 (0.52–1.53) in men.

Conclusions

Higher serum FGF-21 level was associated with an increased risk of diabetes in Chinese women but not in men. The sex difference in the association between FGF-21 and diabetes risk deserves further investigation and replication in other populations.

Electronic supplementary material

The online version of this article (10.1186/s12986-017-0216-0) contains supplementary material, which is available to authorized users.

A Guide for the Design of Pre-clinical Studies on Sex Differences in Metabolism

In animal models, the physiological systems involved in metabolic homeostasis exhibit a sex difference. Investigators often use male rodents because they show metabolic disease better than females. Thus, females are not used precisely because of an acknowledged sex difference that represents an opportunity to understand novel factors reducing metabolic disease more in one sex than the other. The National Institutes of Health (NIH) mandate to consider sex as a biological variable in preclinical research places new demands on investigators and peer reviewers who often lack expertise in model systems and experimental paradigms used in the study of sex differences. This Perspective discusses experimental design and interpretation in studies addressing the mechanisms of sex differences in metabolic homeostasis and disease, using animal models and cells. We also highlight current limitations in research tools and attitudes that threaten to delay progress in studies of sex differences in basic animal research.

Menopausal Hormone Therapy and Type 2 Diabetes Prevention: Evidence, Mechanisms, and Clinical Implications

Type 2 diabetes has reached epidemic proportions in the United States. Large, randomized controlled trials suggest that menopausal hormone therapy (MHT) delays the onset of type 2 diabetes in women. However, the mechanisms and clinical implications of this association are still a matter of controversy. This review provides an up-to-date analysis and integration of epidemiological, clinical, and basic studies, and proposes a mechanistic explanation for the effect of menopause and MHT on type 2 diabetes development and prevention. We discuss the beneficial effects of endogenous estradiol with respect to insulin secretion, insulin sensitivity, and glucose effectiveness; we also discuss energy expenditure and adipose distribution, both of which are affected by menopause and improved by MHT, which thereby decreases the incidence of type 2 diabetes. We reconcile differences among studies that investigated the effect of menopause and MHT formulations on type 2 diabetes. We argue that discrepancies arise from physiological differences in methods used to assess glucose homeostasis, ranging from clinical indices of insulin sensitivity to steady-state methods to assess insulin action. We also discuss the influence of the route of estrogen administration and the addition of progestogens. We conclude that, although MHT is neither approved nor appropriate for the prevention of type 2 diabetes due to its complex balance of risks and benefits, it should not be withheld from women with increased risk of type 2 diabetes who seek treatment for menopausal symptoms.

The effect of selective estrogen receptor modulators on type 2 diabetes onset in women: Basic and clinical insights

Selective estrogen receptor modulators (SERMs) are a class of compounds that interact with estrogen receptors (ERs) and exert agonist or antagonist effects on ERs in a tissue-specific manner. Tamoxifen, a first generation SERM, is used for treatment of ER positive breast cancer. Raloxifene, a second generation SERM, was used to prevent postmenopausal osteoporosis. The third-generation SERM bazedoxifene (BZA) effectively prevents osteoporosis while preventing estrogenic stimulation of breast and uterus. Notably, BZA combined with conjugated estrogens (CE) is a new menopausal treatment. The menopausal state predisposes to metabolic syndrome and type 2 diabetes, and therefore the effects of SERMs on metabolic homeostasis are gaining attention. Here, we summarize knowledge of SERMs' impacts on metabolic, homeostasis, obesity and diabetes in rodent models and postmenopausal women.

Role of Estrogens in the Regulation of Liver Lipid Metabolism

Before menopause, women are protected from atherosclerotic heart disease associated with obesity relative to men. Sex hormones have been proposed as a mechanism that differentiates this risk. In this review, we discuss the literature around how the endogenous sex hormones and hormone treatment approaches after menopause regulate fatty acid, triglyceride, and cholesterol metabolism to influence cardiovascular risk.The important regulatory functions of estrogen signaling pathways with regard to lipid metabolism have been in part obscured by clinical trials with hormone treatment of women after menopause, due to different formulations, routes of delivery, and pairings with progestins. Oral hormone treatment with several estrogen preparations increases VLDL triglyceride production. Progestins oppose this effect by stimulating VLDL clearance in both humans and animals. Transdermal estradiol preparations do not increase VLDL production or serum triglycerides.Many aspects of sex differences in atherosclerotic heart disease risk are influenced by the distributed actions of estrogens in the muscle, adipose, and liver. In humans, 17β-estradiol (E2) is the predominant circulating estrogen and signals through estrogen receptor alpha (ERα), estrogen receptor beta (ERβ), and G-protein-coupled estrogen receptor (GPER). Over 1000 human liver genes display a sex bias in their expression, and the top biological pathways are in lipid metabolism and genes related to cardiovascular disease. Many of these genes display variation depending on estrus cycling in the mouse. Future directions will likely rely on targeting estrogens to specific tissues or specific aspects of the signaling pathways in order to recapitulate the protective physiology of premenopause therapeutically after menopause.

Estradiol Regulation of Brown Adipose Tissue Thermogenesis

Physiologically, estrogens carry out a myriad of functions, the most essential being the regulation of the reproductive axis. Currently, it is also dogmatic that estrogens play an important role modulating energy balance and metabolism. In this sense, it is well known that low estrogens levels, occurring due to ovarian insufficiency, in conditions such as menopause or ovariectomy (OVX), are associated with increased food intake and decreased energy expenditure, leading to weight gain and obesity at long term. Concerning energy expenditure, the main effect of estradiol (E2) is on brown adipose tissue (BAT) thermogenesis. Thus, acting through a peripheral or a central action, E2 activates brown fat activity and increases body temperature, which is negatively associated with body weight. Centrally, the hypothalamic AMP-activated protein kinase (AMPK) mediates the E2 action on BAT thermogenesis. In this chapter, we will summarize E2 regulation of BAT thermogenesis and how this can influence energy balance and metabolism in general.

Role of Sex Steroids in β Cell Function, Growth, and Survival

The gonads have long been considered endocrine glands, producing sex steroids such as estrogens, androgens, and progesterone (P4) for the sole purpose of sexual differentiation, puberty, and reproduction. Reproduction and energy metabolism are tightly linked, however, and gonadal steroids play an important role in sex-specific aspects of energy metabolism in various physiological conditions. In that respect, gonadal steroids also influence the secretion of insulin in a sex-specific manner. This review presents a perspective on the physiological roles of estrogens, androgens, and P4 via their receptors in pancreatic β cells in the gender-specific tuning of insulin secretion. I also discuss potential gender-specific therapeutic avenues that this knowledge may open in the future.

Western-style diet, sex steroids and metabolism

The evolutionary transition from hunting to farming was associated with introduction of carbohydrate-rich diets. Today, the increased consumption of simple sugars and high-fat food brought about by Western-style diet and physical inactivity are leading causes of the growing obesity epidemic in the Western society. The extension of human lifespan far beyond reproductive age increased the burden of metabolic disorders associated with overnutrition and age-related hypogonadism. Sex steroids are essential regulators of both reproductive function and energy metabolism, whereas their imbalance causes infertility, obesity, glucose intolerance, dyslipidemia, and increased appetite. Clinical and translational studies suggest that dietary restriction and weight control can improve metabolic and reproductive outcomes of sex hormone-related pathologies, including testosterone deficiency in men and natural menopause and hyperandrogenemia in women. Minimizing metabolic and reproductive decline through rationally designed diet and exercise can help extend human reproductive age and promote healthy aging. This article is part of a Special Issue entitled: Oxidative Stress and Mitochondrial Quality in Diabetes/Obesity and Critical Illness Spectrum of Diseases - edited by P. Hemachandra Reddy.

Effect of menopausal hormone therapy on components of the metabolic syndrome

The world population is aging, and women will spend an increasing share of their lives in a postmenopausal state that predisposes to metabolic dysfunction. Thus, the prevalence of metabolic syndrome (MetS) in women is likely to increase dramatically. This article summarizes the effects of menopause in predisposing to components of MetS including visceral obesity, dyslipidemia, type 2 diabetes (T2D) and hypertension (HTN). We also summarize the effects of menopausal hormone therapy (MHT) in reversing these metabolic alterations and discuss therapeutic advances of novel menopausal treatment on metabolic function.

Differential utilization of nuclear and extranuclear receptor signaling pathways in the actions of estrogens, SERMs, and a tissue-selective estrogen complex (TSEC)

Estrogens act through nuclear and extranuclear initiated pathways involving estrogen receptors (ERs) to regulate gene expression and activate protein kinases. We investigated the involvement of extracellular signal-regulated kinase2 (ERK2) and ERα in the activities of estradiol (E2), conjugated estrogens (CEs), selective estrogen receptor modulators (SERMs), and a Tissue-Selective Estrogen Complex (TSEC), a combination of a SERM and CE that has a blended activity. We found that CE and individual CE components were generally less effective than E2 in ERK2 recruitment to chromatin binding sites of E2-regulated genes. Likewise, CE was much less agonistic than E2 in stimulation of proliferation of ERα-positive breast cancer cells. The SERM bazedoxifene (BZA) fully suppressed proliferation stimulated by E2 or CE and reversed gene stimulation by CE or E2, as did the antiestrogen Faslodex. Thus, the balance of biological activities mediated through nuclear ERα vs. ERK2-mediated activities is different for CE vs. E2, with CE showing lower stimulation of kinase activity. Furthermore, at the BZA to CE concentrations in TSEC, BZA antagonized CE stimulation of gene expression and proliferation programs in ERα-positive breast cancer cells. The studies provide molecular underpinnings of the different ways in which SERMs and estrogens support or antagonize one another in regulating the chromatin binding of ERα and ERK2, and modulating gene and cell activities. They illuminate how the combined actions of two classes of ER ligands (SERM and CE, present in TSEC) can achieve unique modes of regulation and efficacy.

Mitochondrial Quality Control as a Therapeutic Target

In addition to oxidative phosphorylation (OXPHOS), mitochondria perform other functions such as heme biosynthesis and oxygen sensing and mediate calcium homeostasis, cell growth, and cell death. They participate in cell communication and regulation of inflammation and are important considerations in aging, drug toxicity, and pathogenesis. The cell's capacity to maintain its mitochondria involves intramitochondrial processes, such as heme and protein turnover, and those involving entire organelles, such as fusion, fission, selective mitochondrial macroautophagy (mitophagy), and mitochondrial biogenesis. The integration of these processes exemplifies mitochondrial quality control (QC), which is also important in cellular disorders ranging from primary mitochondrial genetic diseases to those that involve mitochondria secondarily, such as neurodegenerative, cardiovascular, inflammatory, and metabolic syndromes. Consequently, mitochondrial biology represents a potentially useful, but relatively unexploited area of therapeutic innovation. In patients with genetic OXPHOS disorders, the largest group of inborn errors of metabolism, effective therapies, apart from symptomatic and nutritional measures, are largely lacking. Moreover, the genetic and biochemical heterogeneity of these states is remarkably similar to those of certain acquired diseases characterized by metabolic and oxidative stress and displaying wide variability. This biologic variability reflects cell-specific and repair processes that complicate rational pharmacological approaches to both primary and secondary mitochondrial disorders. However, emerging concepts of mitochondrial turnover and dynamics along with new mitochondrial disease models are providing opportunities to develop and evaluate mitochondrial QC-based therapies. The goals of such therapies extend beyond amelioration of energy insufficiency and tissue loss and entail cell repair, cell replacement, and the prevention of fibrosis. This review summarizes current concepts of mitochondria as disease elements and outlines novel strategies to address mitochondrial dysfunction through the stimulation of mitochondrial biogenesis and quality control.

Retraction: Protective effects of bazedoxifene paired with conjugated estrogens on pancreatic β-cell dysfunction

This article has been retracted by the Editorial Committee of The Pharmaceutical Society of Japan because it contains scientific misconduct. Although the data published in this article were generated in part by the first author, the authors violated authorship and sponsorship protocol.

Progestogens' effects and mechanisms for object recognition memory across the lifespan

This review explores the effects of female reproductive hormones, estrogens and progestogens, with a focus on progesterone and allopregnanolone, on object memory. Progesterone and its metabolites, in particular allopregnanolone, exert various effects on both cognitive and non-mnemonic functions in females. The well-known object recognition task is a valuable experimental paradigm that can be used to determine the effects and mechanisms of progestogens for mnemonic effects across the lifespan, which will be discussed herein. In this task there is little test-decay when different objects are used as targets and baseline valance for objects is controlled. This allows repeated testing, within-subjects designs, and longitudinal assessments, which aid understanding of changes in hormonal milieu. Objects are not aversive or food-based, which are hormone-sensitive factors. This review focuses on published data from our laboratory, and others, using the object recognition task in rodents to assess the role and mechanisms of progestogens throughout the lifespan. Improvements in object recognition performance of rodents are often associated with higher hormone levels in the hippocampus and prefrontal cortex during natural cycles, with hormone replacement following ovariectomy in young animals, or with aging. The capacity for reversal of age- and reproductive senescence-related decline in cognitive performance, and changes in neural plasticity that may be dissociated from peripheral effects with such decline, are discussed. The focus here will be on the effects of brain-derived factors, such as the neurosteroid, allopregnanolone, and other hormones, for enhancing object recognition across the lifespan.

Effect of selective estrogen receptor modulators on metabolic homeostasis

Selective estrogen receptor modulators (SERMs) are estrogen receptor (ER) ligands that exhibit either estrogen agonistic or antagonistic activity in a tissue-specific manner. The first and second generation SERMs, tamoxifen and raloxifene, are used for treatment of ER positive breast cancer and postmenopausal osteoporosis respectively. The third-generation SERM, bazedoxifene (BZA), effectively prevents osteoporosis while blocking the estrogenic stimulation in breast and uterus. Notably, BZA combined with conjugated estrogens (CE) in a tissue-selective estrogen complex (TSEC) is a new menopausal treatment. Postmenopausal estrogen deficiency predisposes to metabolic syndrome and type 2 diabetes, and therefore the effects of SERMs and TSECs on metabolic homeostasis are gaining attention. In this article, we summarize current knowledge about the impact of SERMs on metabolic homeostasis and metabolic disorders in animal models and postmenopausal women.

Short-Term Estrogen Replacement Effects on Insulin Sensitivity and Glucose Tolerance in At-Risk Cats for Feline Diabetes Mellitus

Male domestic cats that are neutered and overweight are at an increased risk for developing a type-2-like diabetes mellitus. Beneficial effects of 17β-estradiol (E2) on glucose homeostasis may be lost with neutering and thereby account for increased diabetes risk. To evaluate this, adult male neutered overweight cats (n=6) were given daily E2 (1.0 μg/kg) or vehicle (Vh; ethanol, 1.0μL/kg) in a single crossover trial of 14-day periods with a 7-day washout. The E2 and Vh were voluntarily ingested on food. The E2 dosage was determined in a pre-trial to significantly and transiently reduce food intake with no measurable change in plasma E2 concentration. During treatments, physical activity was assessed with collar-mounted accelerometers on days 9-11, and tests of intravenous insulin tolerance and intravenous glucose tolerance were conducted on days 13 and 14, respectively. Over the 14 days, E2 compared to Vh treatment reduced (p=0.03) food intake (- 22%) but not enough to significantly reduce body weight; activity counts were not significantly changed. With E2 compared to Vh treatment, the late-phase plasma insulin response of the glucose tolerance test was less (p=0.03) by 31%, while glucose tolerance and insulin sensitivity indexes were not significantly changed. The results indicate that oral E2 at a dosage that moderately affects food intake may reduce insulin requirement for achieving glucose homeostasis in neutered male cats. Further investigation is needed to identify the mechanism underlying the E2 effect.

Effect of targeted estrogen delivery using glucagon-like peptide-1 on insulin secretion, insulin sensitivity and glucose homeostasis

The female estrogen 17β-estradiol (E2) enhances pancreatic β-cell function via estrogen receptors (ERs). However, the risk of hormone dependent cancer precludes the use of general estrogen therapy as a chronic treatment for diabetes. To target E2 to β-cells without the undesirable effects of general estrogen therapy, we created fusion peptides combining active or inactive glucagon-like peptide-1 (GLP-1) and E2 in a single molecule (aGLP1-E2 and iGLP1-E2 respectively). By combining the activities of GLP-1 and E2, we envisioned synergistic insulinotropic activities of these molecules on β-cells. In cultured human islets and in C57BL/6 mice, both aGLP1 and aGLP1-E2 enhanced glucose-stimulated insulin secretion (GSIS) compared to vehicle and iGLP1-E2 without superior efficacy of aGLP1-E2 compared to GLP-1 alone. However, aGLP1-E2 decreased fasting and fed blood glucose to a greater extent than aGLP1 and iGLP1-E2 alone. Further, aGLP1-E2 exhibited improved insulin sensitivity compared to aGLP1 and iGLP1-E2 alone (HOMA-IR and insulin tolerance test). In conclusion, targeted estrogen delivery to non-diabetic islets in the presence of GLP-1 does not enhance GSIS. However, combining GLP-1 to estrogen delivers additional efficacy relative to GLP-1 alone on insulin sensitivity and glucose homeostasis in non-diabetic mice.

Progress in the molecular understanding of central regulation of body weight by estrogens

OBJECTIVE

Estrogens can act in the brain to prevent body weight gain. Tremendous research efforts have been focused on estrogen physiology in the brain in the context of body weight control; estrogen receptors and the related signals have been attractive targets for development of new obesity therapies. The objective is to review recent findings on these aspects.

METHODS

Recent studies that used conventional and conditional knockout mouse strains to delineate the cellular and molecular mechanisms for the beneficial effects of estrogens on body weight balance are reviewed. Emerging genetic tools that could further benefit the field of estrogen research and a newly developed estrogen-based regimen that produces body weight-lowering benefits also are discussed.

RESULTS

The body weight-lowering effects of estrogens are mediated by multiple forms of estrogen receptors in different brain regions through distinct but coordinated mechanisms. Both rapid signals and "classic" nuclear receptor actions of estrogen receptors appear to contribute to estrogenic regulation of body weight.

CONCLUSIONS

Estrogen receptors and associated signal networks are potential targets for obesity treatment, and further investigations are warranted.

Blueberries improve glucose tolerance without altering body composition in obese postmenopausal mice

OBJECTIVE

Metabolic syndrome (MetS) risk increases significantly during menopause and remains elevated postmenopause. Several botanicals, including blueberries (BB), have been shown to delay MetS progression, but few studies have been conducted in postmenopausal animal models. Here, the effects of BB supplementation on obese postmenopausal mice using a chemically induced menopause model were examined.

METHODS

After induction of menopause, mice were fed a high-fat diet or the same diet supplemented with 4% BB powder for 12 weeks. Body weight and body composition were measured, and mice were subjected to glucose and insulin tolerance tests. Serum triglycerides and adiponectin were measured, and liver histology and hepatic gene expression were assessed.

RESULTS

Menopausal and BB-supplemented mice had significantly higher body weights and fat mass than control mice, while menopausal mice had impaired glucose tolerance and higher serum triglycerides when compared with control and BB-supplemented mice. Menopausal mice also had hepatic steatosis that was prevented by BB supplementation and correlated with expression of genes involved in hepatic fatty acid oxidation.

CONCLUSIONS

BB supplementation prevents the glucose intolerance and hepatic steatosis that occur in obese postmenopausal mice, and these effects are independent of body weight.

Effects of genistein in combination with conjugated estrogens on endometrial hyperplasia and metabolic dysfunction in ovariectomized mice

Tissue-selective estrogen complex (TSEC), which combines a selective estrogen receptor modulator (SERM) with one or more estrogens, is a novel approach to menopausal therapy. It has been demonstrated that the phytoestrogen genistein (GEN) exhibits mixed estrogen receptor agonist and antagonist activity, suggesting that GEN may have potential for use as a natural SERM. We evaluated, for the first time, the effects of GEN, conjugated estrogens (CE), and their pairing effects as a TSEC treatment on estrogen-induced endometrial hyperplasia and metabolic dysfunction in ovariectomized (OVX) mice fed a high-fat diet. CE replacement prevented fat accumulation in the adipose tissue and liver, improved glucose homeostasis, and induced endometrial hyperplasia in OVX mice. GEN at 100 mg/kg showed CE mimetic effects in preventing ovariectomy-induced metabolic dysfunctions without endometrial stimulation. Combination treatments with CE and GEN prevented metabolic dysfunctions more strongly than CE alone, but at both low and high doses, GEN did not reverse CE-induced endometrial hyperplasia. In addition, we found that in a TSEC regimen, a typical SERM raloxifene maintains the metabolic benefits of CE while simultaneously protecting the endometrium in OVX mice. These findings indicate that GEN acts as an estrogen agonist in metabolic regulation, but has no SERM function in the uteri of OVX mice.

Estrogen: an emerging regulator of insulin action and mitochondrial function

Clinical trials and animal studies have revealed that loss of circulating estrogen induces rapid changes in whole body metabolism, fat distribution, and insulin action. The metabolic effects of estrogen are mediated primarily by its receptor, estrogen receptor-α; however, the detailed understanding of its mechanisms is incomplete. Recent investigations suggest that estrogen receptor-α elicits the metabolic effects of estrogen by genomic, nongenomic, and mitochondrial mechanisms that regulate insulin signaling, substrate oxidation, and energetics. This paper reviews clinical and experimental studies on the mechanisms of estrogen and the current state of knowledge regarding physiological and pathobiological influences of estrogen on metabolism.

Experimental study of the effect on bone metabolism and bone histomorphometry of osteoporosis rats with birdpecking and revolving moxibustion on twelve back-shu points

The aim of the study was to explore the effect of birdpecking and revolving moxibustion on twelve back shenshu points on the bone metabolism and bone histomorphometry of osteoporosis rats. The 50 female rats of 8 months old that did not pregnant were collected and randomly divided into sham-operation group, model group, moxibustion group, moxibustion and estrogen group, and estrogen group. All the rats, except for the rats in the sham-operation group, received ovarian surgery to establish the models. After 10 days postoperatively (healing), the rats received moxibustion and estrogen therapy. According to the different groups, the rats received rat femur in vivo bone mineral density assessment at 90 days after surgery. After that, the rats were sacrificed, and then the left femoral bones were collected for bone histomorphometry test; blood was taken for bone alkaline phosphatase (BALP) testing, and urine was collected for hydroxyproline testing. The urine hydroxyproline was tested once at 24 h after ovarian surgery. At 24 h after ovarian surgery, the urine hydroxyproline in the ovariectomy group was significantly higher than that in the sham-operation group (P < 0.05), indicating that after ovarian surgery, the collagen broke down which accelerated the process of osteoporosis. After the intervention therapy with moxibustion and estrogen, the BALP, urinary hydroxyproline and femoral bone histomorphometry were comparatively analyzed, and the results showed that the intervention groups were higher than the model group (P < 0.05). But when compared with the sham-operation group, the indexes in the intervention groups were decreased, and the differences were significant (P < 0.05), indicating that intervention could only delay the incidence of osteoporosis. The Chinese traditional measure of "birdpecking and revolving moxibustion on twelve back-shu points" can effectively prevent the recession of bone metabolism of osteoporosis rats, and slow down the degeneration of bone morphology, which can be used to delay the incidence of osteoporosis.

Estrogen signaling prevents diet-induced hepatic insulin resistance in male mice with obesity

The development of insulin resistance in the liver is a key event that drives dyslipidemia and predicts diabetes and cardiovascular risk with obesity. Clinical data show that estrogen signaling in males helps prevent adiposity and insulin resistance, which may be mediated through estrogen receptor-α (ERα). The tissues and pathways that mediate the benefits of estrogen signaling in males with obesity are not well defined. In female mice, ERα signaling in the liver helps to correct pathway-selective insulin resistance with estrogen treatment after ovariectomy. We assessed the importance of liver estrogen signaling in males using liver ERα-knockout (LKO) mice fed a high-fat diet (HFD). We found that the LKO male mice had decreased insulin sensitivity compared with their wild-type floxed (fl/fl) littermates during hyperinsulinemic euglycemic clamps. Insulin failed to suppress endogenous glucose production in LKO mice, indicating liver insulin resistance. Insulin promoted glucose disappearance in LKO and fl/fl mice similarly. In the liver, insulin failed to induce phosphorylation of Akt-Ser(473) and exclude FOXO1 from the nucleus in LKO mice, a pathway important for liver glucose and lipid metabolism. Liver triglycerides and diacylglycerides were also increased in LKO mice, which corresponded with dysregulation of insulin-stimulated ACC phosphorylation and DGAT1/2 protein levels. Our studies demonstrate that estrogen signaling through ERα in the liver helps prevent whole body and hepatic insulin resistance associated with HFD feeding in males. Augmenting hepatic estrogen signaling through ERα may lessen the impact of obesity on diabetes and cardiovascular risk in males.

The role of estrogen in adipose tissue metabolism: insights into glucose homeostasis regulation

Adipose tissue is an organ with active endocrine function involved in the regulation of energy balance and glucose homeostasis via multiple metabolic signaling pathways targeting the brain, liver, skeletal muscle, pancreas, and other organs. There is increasing evidence demonstrating that the female sex hormone, estrogen, regulates adipose development and improves systemic glucose homeostasis in both males and females. The underlying mechanism linking estrogenic regulation in adipose tissue and systemic glucose metabolism has not been fully elucidated, but is thought to include interactions of estrogen receptor signaling events involving lipolytic and/or lipogenic enzyme activity, free fatty acid metabolism, and adipocytokine production. Thus, understanding the effects of estrogen replacement on adipose tissue biology and metabolism is important in determining the risk of developing obesity-related metabolic disorders in patients undergoing treatment for sex hormone deficiency. In this report, we review literature regarding the role of estrogens and their corresponding receptors in the control of adipose metabolism and glucose homeostasis in both rodents and humans. We also discuss the effects of selective estrogen receptor modulators on glucose metabolism.