Mechanisms of antidiabetogenic and body weight-lowering effects of estrogen in high-fat diet-fed mice

Estradiol In Vivo Induces Changes in Cardiomyocytes Size in Obese Rats

We studied the in vivo effects of estradiol on size and biochemical parameters of cardiomyocytes in pathophysiological conditions such as obesity and insulin resistance. Male Wistar rats were normally fed (controls, n = 7) or fed with high-fat diet (obese, n = 14). Half of the obese rats (obese + estradiol, n = 7) were treated with a single dose of estradiol (40 μg/kg, intraperitoneally) and 24 hours after treatment all the rats were killed. Estradiol in vivo in obese rats resulted in a significant increase in protein kinase B (Akt) activation ( P < .05) and decrease in heart mass ( P < .05), ratio of the heart mass/body mass ( P < .05), transverse diameters of cardiomyocytes ( P < .001), concentration of serum high-sensitivity C-reactive protein ( P < .001), and total cholesterol ( P < .01) compared with obese nontreated rats. Our results suggest that estradiol in obese/IR rats affects the size of cardiomyocytes and its actions lead in vivo to a reduction in obesity-induced cardiac hypertrophy, via Akt.

Prevention of obesity and insulin resistance by estrogens requires ERα activation function-2 (ERαAF-2), whereas ERαAF-1 is dispensable

The beneficial metabolic actions of estrogen-based therapies are mainly mediated by estrogen receptor α (ERα), a nuclear receptor that regulates gene transcription through two activation functions (AFs): AF-1 and AF-2. Using mouse models deleted electively for ERαAF-1 (ERαAF-1°) or ERαAF-2 (ERαAF-2°), we determined their respective roles in the actions of estrogens on body composition and glucose homeostasis in response to either a normal diet or a high-fat diet (HFD). ERαAF-2° males and females developed accelerated weight gain, massive adiposity, severe insulin resistance, and glucose intolerance--quite reminiscent of the phenotype observed in mice deleted for the entire ERα protein (ERα(-/-)). In striking contrast, ERαAF-1° and wild-type (wt) mice shared a similar metabolic phenotype. Accordingly, 17β-estradiol administration regulated key metabolic genes in insulin-sensitive tissues and conferred a strong protection against HFD-induced metabolic disturbances in wt and ERαAF-1° ovariectomized mice, whereas these actions were totally abrogated in ERαAF-2° and ERα(-/-) mice. Thus, whereas both AFs have been previously shown to contribute to endometrial and breast cancer cell proliferation, the protective effect of estrogens against obesity and insulin resistance depends on ERαAF-2 but not ERαAF-1, thereby delineating new options for selective modulation of ERα.

Molecular effects of ER alpha- and beta-selective agonists on regulation of energy homeostasis in obese female Wistar rats

The molecular mechanisms underlying the effects of selective ER subtype activation on lipogenesis, adipogenesis, lipid utilization and storage as well as glucose metabolism are currently largely unknown and were analyzed in female OVX Wistar rats on a high-fat diet. Rats received estradiol (E2), ER subtype-selective agonists (Alpha and Beta), and genistein (Gen) for 10 weeks. In adipose tissue, treatment with E2, Alpha, and Beta significantly decreased lipogenic (SREBP-1c, FAS) and adipogenic genes (LPL, PPAR gamma). In liver and skeletal muscle of E2-, Alpha-, Beta-, and Gen-treated animals, lipogenesis and triglyceride accumulation were significantly reduced. Increased hepatic and muscular PPAR gamma mRNA expression was observed in untreated, Beta- and Gen-treated animals, which correlates with increased hepatic glucose uptake. However, only untreated animals showed impaired insulin sensitivity compared to all other groups. Therefore, PPAR gamma up-regulation in untreated animals suggests a compensatory mechanism, probably due to increased triglyceride accumulation in non-adipose tissues. Beta- and Gen-treated animals may benefit from the anabolic potency of ER beta that ameliorates lipid and glucose utilization in muscle. Activation of either ER subtype reduces fat enrichment and improves insulin sensitivity. Depending on the investigated tissue, different molecular pathways seem to be involved.

The role of estrogens in control of energy balance and glucose homeostasis

Estrogens play a fundamental role in the physiology of the reproductive, cardiovascular, skeletal, and central nervous systems. In this report, we review the literature in both rodents and humans on the role of estrogens and their receptors in the control of energy homeostasis and glucose metabolism in health and metabolic diseases. Estrogen actions in hypothalamic nuclei differentially control food intake, energy expenditure, and white adipose tissue distribution. Estrogen actions in skeletal muscle, liver, adipose tissue, and immune cells are involved in insulin sensitivity as well as prevention of lipid accumulation and inflammation. Estrogen actions in pancreatic islet β-cells also regulate insulin secretion, nutrient homeostasis, and survival. Estrogen deficiency promotes metabolic dysfunction predisposing to obesity, the metabolic syndrome, and type 2 diabetes. We also discuss the effect of selective estrogen receptor modulators on metabolic disorders.

Estrogen reduces lipid content in the liver exclusively from membrane receptor signaling

Estrogen induces signal transduction through estrogen receptor α (ERα), which localizes to both the plasma membrane and nucleus. Using wild-type mice, ERα knockout (ERKO) mice, or transgenic mice expressing only the ligand-binding domain of ERα exclusively at the plasma membrane (MOER), we compared the transcriptional profiles of liver tissue extracts after mice were injected with the ERα agonist propyl-pyrazole-triol (PPT). The expression of many lipid synthesis-related genes was comparably decreased in livers from MOER or wild-type mice but was not suppressed in ERKO mice, indicating that only membrane-localized ERα was necessary for their suppression. Cholesterol, triglyceride, and fatty acid content was decreased only in livers from wild-type and MOER mice exposed to PPT, but not in the livers from the ERKO mice, validating the membrane-driven signaling pathway on a physiological level. PPT-triggered activation of ERα at the membrane induced adenosine monophosphate-activated protein kinase to phosphorylate sterol regulatory element-binding factor 1 (Srebf1), preventing its association with and therefore its proteolytic cleavage by site-1 protease. Consequently, Srebf1 was sequestered in the cytoplasm, preventing the expression of cholesterol synthesis-associated genes. Thus, we showed that inhibition of gene expression mediated by membrane-localized ERα caused a metabolic phenotype that did not require nuclear ERα.

Cellular mechanism by which estradiol protects female ovariectomized mice from high-fat diet-induced hepatic and muscle insulin resistance

Estrogen replacement therapy reduces the incidence of type 2 diabetes in postmenopausal women; however, the mechanism is unknown. Therefore, the aim of this study was to evaluate the metabolic effects of estrogen replacement therapy in an experimental model of menopause. At 8 weeks of age, female mice were ovariectomized (OVX) or sham (SHAM) operated, and OVX mice were treated with vehicle (OVX) or estradiol (E2) (OVX+E2). After 4 weeks of high-fat diet feeding, OVX mice had increased body weight and fat mass compared with SHAM and OVX+E2 mice. OVX mice displayed reduced whole-body energy expenditure, as well as impaired glucose tolerance and whole-body insulin resistance. Differences in whole-body insulin sensitivity in OVX compared with SHAM mice were accounted for by impaired muscle insulin sensitivity, whereas both hepatic and muscle insulin sensitivity were impaired in OVX compared with OVX+E2 mice. Muscle diacylglycerol (DAG), content in OVX mice was increased relative to SHAM and OVX+E2 mice. In contrast, E2 treatment prevented the increase in hepatic DAG content observed in both SHAM and OVX mice. Increases in tissue DAG content were associated with increased protein kinase Cε activation in liver of SHAM and OVX mice compared with OVX+E2 and protein kinase Cθ activation in skeletal muscle of OVX mice compared with SHAM and OVX+E2. Taken together, these data demonstrate that E2 plays a pivotal role in the regulation of whole-body energy homeostasis, increasing O(2) consumption and energy expenditure in OVX mice, and in turn preventing diet-induced ectopic lipid (DAG) deposition and hepatic and muscle insulin resistance.

Estrogen signalling and the metabolic syndrome: targeting the hepatic estrogen receptor alpha action

An increasing body of evidence now links estrogenic signalling with the metabolic syndrome (MS). Despite the beneficial estrogenic effects in reversing some of the MS symptoms, the underlying mechanisms remain largely undiscovered. We have previously shown that total estrogen receptor alpha (ERα) knockout (KO) mice exhibit hepatic insulin resistance. To determine whether liver-selective ablation of ERα recapitulates metabolic phenotypes of ERKO mice we generated a liver-selective ERαKO mouse model, LERKO. We demonstrate that LERKO mice have efficient reduction of ERα selectively within the liver. However, LERKO and wild type control mice do not differ in body weight, and have a comparable hormone profile as well as insulin and glucose response, even when challenged with a high fat diet. Furthermore, LERKO mice display very minor changes in their hepatic transcript profile. Collectively, our findings indicate that hepatic ERα action may not be the responsible factor for the previously identified hepatic insulin resistance in ERαKO mice.

Intrahypothalamic estradiol regulates glucose metabolism via the sympathetic nervous system in female rats

Long-term reduced hypothalamic estrogen signaling leads to increased food intake and decreased locomotor activity and energy expenditure, and ultimately results in obesity and insulin resistance. In the current study, we aimed to determine the acute obesity-independent effects of hypothalamic estrogen signaling on glucose metabolism. We studied endogenous glucose production (EGP) and insulin sensitivity during selective modulation of systemic or intrahypothalamic estradiol (E2) signaling in rats 1 week after ovariectomy (OVX). OVX caused a 17% decrease in plasma glucose, which was completely restored by systemic E2. Likewise, the administration of E2 by microdialysis, either in the hypothalamic paraventricular nucleus (PVN) or in the ventromedial nucleus (VMH), restored plasma glucose. The infusion of an E2 antagonist via reverse microdialysis into the PVN or VMH attenuated the effect of systemic E2 on plasma glucose. Furthermore, E2 administration in the VMH, but not in the PVN, increased EGP and induced hepatic insulin resistance. E2 administration in both the PVN and the VMH resulted in peripheral insulin resistance. Finally, sympathetic, but not parasympathetic, hepatic denervation blunted the effect of E2 in the VMH on both EGP and hepatic insulin sensitivity. In conclusion, intrahypothalamic estrogen regulates peripheral and hepatic insulin sensitivity via sympathetic signaling to the liver.

G protein-coupled estrogen receptor in energy homeostasis and obesity pathogenesis

Obesity and its related metabolic diseases have reached a pandemic level worldwide. There are sex differences in the prevalence of obesity and its related metabolic diseases, with men being more vulnerable than women; however, the prevalence of these disorders increases dramatically in women after menopause, suggesting that sex steroid hormone estrogens play key protective roles against development of obesity and metabolic diseases. Estrogens are important regulators of several aspects of metabolism, including body weight and body fat, caloric intake and energy expenditure, and glucose and lipid metabolism in both males and females. Estrogens act in complex ways on their nuclear estrogen receptors (ERs) ERα and ERβ and transmembrane ERs such as G protein-coupled estrogen receptor. Genetic tools, such as different lines of knockout mouse models, and pharmacological agents, such as selective agonists and antagonists, are available to study function and signaling mechanisms of ERs. We provide an overview of the evidence for the physiological and cellular actions of ERs in estrogen-dependent processes in the context of energy homeostasis and body fat regulation and discuss its pathology that leads to obesity and related metabolic states.

Estrogens regulate the hepatic effects of growth hormone, a hormonal interplay with multiple fates

The liver responds to estrogens and growth hormone (GH) which are critical regulators of body growth, gender-related hepatic functions, and intermediate metabolism. The effects of estrogens on liver can be direct, through the direct actions of hepatic ER, or indirect, which include the crosstalk with endocrine, metabolic, and sex-differentiated functions of GH. Most previous studies have been focused on the influence of estrogens on pituitary GH secretion, which has a great impact on hepatic transcriptional regulation. However, there is strong evidence that estrogens can influence the GH-regulated endocrine and metabolic functions in the human liver by acting at the level of GHR-STAT5 signaling pathway. This crosstalk is relevant because the widespread exposition of estrogen or estrogen-related compounds in human. Therefore, GH or estrogen signaling deficiency as well as the influence of estrogens on GH biology can cause a dramatic impact in liver physiology during mammalian development and in adulthood. In this review, we will summarize the current status of the influence of estrogen on GH actions in liver. A better understanding of estrogen-GH interplay in liver will lead to improved therapy of children with growth disorders and of adults with GH deficiency.

High stearoyl-CoA desaturase 1 expression is associated with shorter survival in breast cancer patients

Stearoyl-CoA desaturase 1 (SCD1) is an essential regulator of fatty acid synthesis. We have previously shown that overexpression of SCD1 increases the growth of breast cancer cell lines. The purpose of this study was to determine the relationship between SCD1 expression level and clinical-pathologic characteristics and survival of patients with breast cancer. Fine-needle aspirates were collected from the primary tumors of 250 patients with stage I-III breast cancer. Demographic and clinical characteristics including patient age, ethnicity, and menopausal status and tumor clinical stage, grade, and subtype were reviewed. SCD1 expression was analyzed using reverse-phase protein arrays. Samples were divided into high or low SCD1 expression levels based on a cut-off determined from martingale residual plots and regression tree analysis. SCD1 levels were significantly higher in tumors from patients >50-years old compared to patients ≤50-years old and were lower in triple-negative (estrogen/progesterone receptor-negative and human epidermal growth factor receptor-2-negative) breast cancers than other tumor subtypes. After adjusting for patient age, tumor subtype, tumor grade, and clinical stage, we found that patients with primary breast cancers expressing high SCD1 levels had significantly shorter relapse-free survival (RFS) (P = 0.0140) and overall survival (OS) (P = 0.039) in multivariable analysis. We conclude that SCD1 expression varies by breast cancer subtype and that high levels of SCD1 expression are associated with significantly shorter RFS and OS in multivariable analysis. Future studies are needed to define the role of SCD1 in the malignant phenotype of breast cancer and to evaluate the potential for SCD1 as a therapeutic target.

Hepatic and plasma sex differences in saturated and monounsaturated fatty acids are associated with differences in expression of elongase 6, but not stearoyl-CoA desaturase in Sprague-Dawley rats

Monounsaturated fatty acids (MUFA) have been viewed as either beneficial or neutral with respect to health; however, recent evidence suggests that MUFA may be associated with obesity and cardiovascular disease. Sex differences in MUFA composition have been reported in both rats and humans, but the basis for this sexual dimorphism is unknown. In the current study, enzymes involved in MUFA biosynthesis are examined in rat and cell culture models. Male and female rats were maintained on an AIN-93G diet prior to killing at 14 weeks of age after an overnight fast. Concentrations of 16:0 (2,757 ± 616 vs. 3,515 ± 196 μg fatty acid/g liver in males), 18:1n-7 (293 ± 66 vs. 527 ± 49 μg/g) and 18:1n-9 (390 ± 80 vs. 546 ± 47 μg/g) were lower, and concentrations of 18:0 (5,943 ± 1,429 vs. 3,987 ± 325 μg/g) were higher in phospholipids in livers from female rats compared with males. Hepatic elongase 6 mRNA and protein were 5.9- and 2.0-fold higher, respectively, in females compared with males. Stearoyl-CoA desaturase expression did not differ. Specific hormonal effects were examined in HepG2 cells cultured with varying concentrations of 17β-estradiol, progesterone and testosterone (0, 10, 30 and 100 nM) for 72 h. Progesterone and 17β-estradiol treatments increased, while testosterone decreased, elongase 6 protein. Sex differences in MUFA composition were associated with increased expression of hepatic elongase 6 in females relative to male rats, which appears to be mediated by sex hormones based on observations of hormonal treatments of HepG2 cells.

Targeted estrogen delivery reverses the metabolic syndrome

We report the development of a new combinatorial approach that allows for peptide-mediated selective tissue targeting of nuclear hormone pharmacology while eliminating adverse effects in other tissues. Specifically, we report the development of a glucagon-like peptide-1 (GLP-1)-estrogen conjugate that has superior sex-independent efficacy over either of the individual hormones alone to correct obesity, hyperglycemia and dyslipidemia in mice. The therapeutic benefits are driven by pleiotropic dual hormone action to improve energy, glucose and lipid metabolism, as shown by loss-of-function models and genetic action profiling. Notably, the peptide-based targeting strategy also prevents hallmark side effects of estrogen in male and female mice, such as reproductive endocrine toxicity and oncogenicity. Collectively, selective activation of estrogen receptors in GLP-1-targeted tissues produces unprecedented efficacy to enhance the metabolic benefits of GLP-1 agonism. This example of targeting the metabolic syndrome represents the discovery of a new class of therapeutics that enables synergistic co-agonism through peptide-based selective delivery of small molecules. Although our observations with the GLP-1-estrogen conjugate justify translational studies for diabetes and obesity, the multitude of other possible combinations of peptides and small molecules may offer equal promise for other diseases.

Endogenous sex hormones, blood pressure change, and risk of hypertension in postmenopausal women: the Multi-Ethnic Study of Atherosclerosis

OBJECTIVE

Sex steroid hormones have been postulated to involve in blood pressure (BP) regulation. We examine the association of endogenous sex hormone levels with longitudinal change of BP and risk of developing hypertension in initially normotensive postmenopausal women.

METHODS

We conducted prospective analysis among 619 postmenopausal women free of hypertension at baseline in the Multi-Ethnic Study of Atherosclerosis (MESA). Change of BP and development of incident hypertension were assessed during a mean of 4.8 years follow-up.

RESULTS

After adjusting for age, race/ethnicity, and lifestyle factors, baseline serum estradiol (E(2)), total and bioavailable testosterone (T), dehydroepiandrosterone (DHEA) were each positively associated and sex-hormone binding globulin (SHBG) was inversely associated with risk of hypertension. Additional adjustment for body mass index eliminated the associations for E(2) and T but only attenuated the associations for DHEA and SHBG. The corresponding multivariable hazard ratios (95% CIs) in the highest quartile were 1.28 (0.83-1.97) for E(2), 1.38 (0.89-2.14) for total T, 1.42 (0.90-2.23) for bioavailable T, 1.54 (1.02-2.31) for DHEA, and 0.48 (0.30-0.76) for SHBG. Adjustment for fasting glucose, insulin, and C-reactive protein further attenuated the association for DHEA but not for SHBG. Associations of sex hormones with longitudinal BP change were similar.

CONCLUSION

In postmenopausal women, higher endogenous E(2), T, and DHEA and lower SHBG were associated with higher incidence of hypertension and greater longitudinal rise in BP. The associations for E(2), T, and DHEA were mostly explained by adiposity, while the association for SHBG was independent of measures of adiposity, insulin resistance, and systemic inflammation.

Central versus peripheral impact of estradiol on the impaired glucose metabolism in ovariectomized mice on a high-fat diet

Age-related loss of ovarian function promotes adiposity and insulin resistance in women. Estrogen (E(2)) directly enhances insulin sensitivity and suppresses lipogenesis in peripheral tissues. Recently, the central actions of E(2) in the regulation of energy homeostasis are becoming clearer; however, the functional relevance and degree of contribution of the central vs. peripheral actions of E(2) are currently unknown. Therefore, we prepared and analyzed four groups of mice. 1) CONTROL: sham-operated mice fed a regular diet, 2) OVX-HF: ovariectomized (OVX) mice fed a 60% high-fat diet (HF), 3) E2-SC: OVX-HF mice subcutaneously treated with E(2), and 4) E2-ICV: OVX-HF mice treated with E(2) intracerebroventricularly. OVX-HF mice showed increased body weight with both visceral and subcutaneous fat volume enlargement, glucose intolerance, and insulin resistance. Both E2-SC and E2-ICV equally ameliorated these abnormalities. Although the size of adipocytes and number of CD11c-positive macrophages in perigonadal fat in OVX-HF were reduced by both E(2) treatments, peripherally administered E(2) decreased the expression of TNFα, lipoprotein lipase, and fatty acid synthase in the white adipose tissue (WAT) of OVX-HF. In contrast, centrally administered E(2) increased hormone-sensitive lipase in WAT, decreased the hepatic expression of gluconeogenic enzymes, and elevated core body temperature and energy expenditure with marked upregulation of uncoupling proteins in the brown adipose tissue. These results suggest that central and peripheral actions of E(2) regulate insulin sensitivity and glucose metabolism via different mechanisms, and their coordinated effects may be important to prevent the development of obesity and insulin resistance in postmenopausal women.

Tetradian oscillation of estrogen receptor α is necessary to prevent liver lipid deposition

In the liver of female mice, the transcriptional activity of estrogen receptor (ER) α oscillates in phase with the 4-d-long estrous cycle. Here systemic, genome-wide analysis demonstrates that ER tetradian oscillation is necessary to generate pulses of expression in genes for fatty acid and cholesterol synthesis. This ER-dependent metabolic programming changes with pregnancy and after cessation of ovarian function due to age or surgical menopause, suggesting that ER signaling is optimized to coordinate liver functions with the energetic requirements of each reproductive stage. Alterations of amplitude and frequency of the tetradian cycle, as observed after surgical menopause, age, or specific ablation of the hepatic Igf-1 gene, are associated with liver fat deposition. Appropriate hormone replacement therapy reinstating the oscillatory activity of liver ER prevents the effect of surgical menopause on fat deposition in liver.

Effect of oral contraceptive use on lipid profile in Korean women aged 35-55 years

BACKGROUND

Although oral contraceptives (OCs) are widely used, their effects on lipid profile need monitoring according to current usage in different populations.

STUDY DESIGN

A cross-sectional study was conducted using data from 1541 participants aged 35-55 years collected by the 2005-2009 Korea National Health and Nutrition Examination Surveys. OC use, demographic characteristics and dietary intake were obtained from the participants by questionnaire, and lipid levels were determined by analysis of blood samples.

RESULTS

Longer duration of OC use was positively associated with increasing levels of high-density lipoprotein cholesterol (HDL-C) and decreasing levels of low-density lipoprotein cholesterol (LDL-C). After adjusting for demographic and dietary factors, the odds ratio (OR) of low HDL-C (<50 mg/dL) was significantly decreased in the longer-term (>12 months) OC users (OR=0.36, 95% confidence interval 0.24-0.52) compared with those who never used OCs. However, use of OCs was not associated with a risk of high total cholesterol (≥ 240 mg/dL), high LDL-C (≥ 130 mg/dL), high triglycerides (≥ 150 mg/dL) or high ratio of triglycerides to HDL-C (>3.8).

CONCLUSIONS

These data suggest that the use of OCs may reduce the risk of dyslipidemia, mainly due to the decreased risk of low HDL-C, in Korean women.

Nuclear receptors reverse McGarry's vicious cycle to insulin resistance

Several pathways and pathologies have been suggested as connections between obesity and diabetes, including inflammation of adipose and other tissues, toxic lipids, endoplasmic reticulum stress, and fatty liver. One specific proposal is that insulin resistance induces a vicious cycle in which hyperinsulinemia increases hepatic lipogenesis and exacerbates fatty liver, in turn further increasing insulin resistance. Here I suggest that reversing this cycle via suppression of the lipogenic transcription factor SREBP-1c is a common thread that connects the antidiabetic effects of a surprising number of nuclear hormone receptors, including CAR, LRH-1, TRβ, ERα, and FXR/SHP.

Metabolic effects of estrogen substitution in combination with targeted exercise training on the therapy of obesity in ovariectomized Wistar rats

Postmenopausal women tend to have a higher risk in developing obesity and thus metabolic syndrome. Recently we could demonstrate that physical activity and estrogen replacement are effective strategies to prevent the development of nutritional induced obesity in an animal model. The aim of this study was to determine the combined effects of estrogen treatment and exercise training on already established obesity. Therefore ovariectomized (OVX) and sham-operated (SHAM) female Wistar rats were exposed to a high fat diet for ten months. After this induction period obese SHAM and OVX rats either remained sedentary or performed treadmill training for six weeks. In addition OVX rats were treated with 17β-Estradiol (E(2)) alone, or in combination with training. Before and after intervention effects on lipid and glucose metabolism were investigated. Training resulted in SHAM and OVX rats in a significant decrease of body weight, subcutaneous and visceral body fat, size of adipocytes and the serum levels of leptin, cholesterol, low-density lipoprotein and triglycerides. In OVX animals E(2) treatment resulted in similar effects. Often the combination of E(2) treatment and training was most effective. Analysis of the respiratory quotient indicates that SHAM animals had a better fat burning capacity than OVX rats. There was a tendency that training in SHAM animals and E(2) treatment in OVX animals could improve this capacity. Analysis of glucose metabolism revealed that obese SHAM animals had higher glucose tolerance than OVX animals. Training improved glucose tolerance in SHAM and OVX rats, E(2) treatment in OVX rats. The combination of both was most effective. Our results indicate that even after a short intervention period of six weeks E(2) treatment and exercise training improve parameters related to lipid as well as glucose metabolism and energy expenditure in a model of already established obesity. In conclusion a combination of hormone replacement therapy and exercise training could be a very effective strategy to encourage the therapy of diet-induced obesity and its metabolic consequences in postmenopausal women.

Selective estrogen receptor modulator promotes weight loss in ovariectomized female rhesus monkeys (Macaca mulatta) by decreasing food intake and increasing activity

The effect of hormone replacement therapy (HRT) on body weight in postmenopausal women is controversial, with studies reporting an increase, a decrease, and no change in body weight. To examine estrogen receptor actions on body weight, we investigated the effects of treatment with a selective estrogen receptor modulator (SERM) on body weight, food intake, and activity and metabolic rate in a nonhuman primate model. Eighteen ovariectomized female rhesus monkeys were treated with a nonsteroidal SERM (GSK232802A, 5 mg/kg po) for 3 mo. GSK232802A decreased lutenizing hormone (P < 0.0001) and follicle-stimulating hormone levels (P < 0.0001), consistent with the estrogenic action of the compound. GSK232802A treatment produced a small but sustained weight loss (4.6 ± 1.0%, P < 0.0001) and reduced adiposity (P < 0.0001), which was due at least in part to a suppression of food intake (3.6 ± 3.7%, P < 0.0001). Physical activity increased during the 3rd mo of treatment (P = 0.04). Baseline activity level and the change in activity due to treatment were correlated, with the most sedentary individuals exhibiting increased physical activity during the 1st mo of treatment (P = 0.02). Metabolic rate did not change (P = 0.58). These results indicate that GSK232802A treatment reduces body weight and adiposity in ovariectomized nonhuman primates by suppressing food intake and increasing activity, particularly in the most sedentary individuals. These findings suggest that SERM treatment may counteract weight gain in postmenopausal women.

The diversity of sex steroid action: regulation of metabolism by estrogen signaling

The metabolic syndrome is a complex condition characterized by obesity, insulin resistance, decreased high-density lipoproteins, and hypertension associated with high risk of developing type 2 diabetes and cardiovascular disease. A major increase in the incidence of developing metabolic syndrome and related diseases is observed worldwide in association with a change toward a less active lifestyle and increased food consumption. Estrogen and the estrogen receptors (ERs) are well-known regulators of several aspects of metabolism, including glucose and lipid metabolism, and impaired estrogen signaling is associated with the development of metabolic diseases. This review will describe the key effects of estrogen signaling in metabolic and glucose sensing tissues, including the liver, pancreatic β cells, adipose tissue, and skeletal muscle. The impact on metabolic processes of impaired estrogen signaling and knock out of each ER subtype will also be discussed.

Estrogenic plant extracts reverse weight gain and fat accumulation without causing mammary gland or uterine proliferation

Long-term estrogen deficiency increases the risk of obesity, diabetes and metabolic syndrome in postmenopausal women. Menopausal hormone therapy containing estrogens might prevent these conditions, but its prolonged use increases the risk of breast cancer, as wells as endometrial cancer if used without progestins. Animal studies indicate that beneficial effects of estrogens in adipose tissue and adverse effects on mammary gland and uterus are mediated by estrogen receptor alpha (ERα). One strategy to improve the safety of estrogens to prevent/treat obesity, diabetes and metabolic syndrome is to develop estrogens that act as agonists in adipose tissue, but not in mammary gland and uterus. We considered plant extracts, which have been the source of many pharmaceuticals, as a source of tissue selective estrogens. Extracts from two plants, Glycyrrhiza uralensis (RG) and Pueraria montana var. lobata (RP) bound to ERα, activated ERα responsive reporters, and reversed weight gain and fat accumulation comparable to estradiol in ovariectomized obese mice maintained on a high fat diet. Unlike estradiol, RG and RP did not induce proliferative effects on mammary gland and uterus. Gene expression profiling demonstrated that RG and RP induced estradiol-like regulation of genes in abdominal fat, but not in mammary gland and uterus. The compounds in extracts from RG and RP might constitute a new class of tissue selective estrogens to reverse weight gain, fat accumulation and metabolic syndrome in postmenopausal women.

Obesity-induced metabolic stresses in breast and colon cancer

Epidemiological studies have suggested that excess body weight gain may be a major risk factor for colon and breast cancer. A positive energy balance creates metabolic stresses, including the excess production of reactive oxygen species (ROS), hyperinsulinemia, the elevated adipokine secretion, and increased gut permeability. Obesity is a risk factor for breast cancer in postmenopausal women, and overweight women are more likely to have poor outcomes. The higher circulating concentration of insulin-like growth factor 1 (IGF-1) in overweight and obese women is thought to be an important mediator to promote cell proliferation and survival via the activation of phosphatidylinositol 3-kinase (PI3K)/Akt and mitogen-activated protein kinase (MAPK)/p38 signaling pathways. In an animal model of colon carcinogenesis, overweight mice fed a high-fat diet exhibited a greater number of colon tumors than lean animals. The increased abdominal fat was associated with higher concentrations of leptin, insulin, and IGF-1, which possibly mediate tumor growth. These data suggest that the metabolic burden created by excess adiposity accelerates uncontrolled cell growth and survival, thereby increasing the risk of developing breast and colon cancer.

Wheel running prevents the accumulation of monounsaturated fatty acids in the liver of ovariectomized mice by attenuating changes in SCD-1 content

Decreases in female sex steroids enhance the accumulation of visceral fat mass, leading to a predisposition to developing metabolic diseases. The purpose of this study was to determine whether loss of ovarian function alters the amount and (or) the fatty acid (FA) composition of triacylglycerol (TAG) levels in the liver of ovary-intact (SHAM) or ovariectomized (OVX) mice. We also sought to determine whether voluntary wheel running could attenuate the associated changes in the liver. Twenty-two C57/BL6 female mice were divided into 2 groups (SHAM, OVX) and were then subdivided into sedentary and exercising groups (SHAM-Sed, SHAM-Ex, OVX-Sed, OVX-Ex). Visceral fat mass significantly increased in the OVX-Sed animals; however, the effect was attenuated in the OVX-Ex animals. Total hepatic TAG content did not significantly increase in the OVX-Sed animals; however, SHAM-Ex and OVX-Ex animals demonstrated significant decreases in TAG levels. A significant increase in the FA desaturase index (18:1/18:0 and 16:1/16:0) was detected in the OVX-Sed animals compared with all other groups, which corresponded to increases in stearoyl-CoA desaturase (SCD-1) content. These results indicate that loss of ovarian function alters FA composition of hepatic TAG mediated by increases in SCD-1. These data indicate that female sex steroids influence lipid metabolism in the liver and provide important insight concerning the influence of exercise on hepatic function.

Estrogen receptors and the metabolic network

The metabolic syndrome has reached pandemic level worldwide, and evidence is that estradiol plays a key role in its development. The discovery of the second estrogen receptor, ERβ, in tissues previously not considered targets of estradiol was a breakthrough in endocrinology. In the present review, we discuss how the presence of ERβ and the previously described ERα in tissues involved in glucose and lipid homeostasis (brain, skeletal muscle, adipose tissue, pancreas, liver, and heart) may have important implications to risk factors associated with the metabolic syndrome. Imbalance of ERα/ERβ ratio in this "metabolic network" may lead to the metabolic syndrome.

Body mass index and its correlation to metabolic and hormone parameters in postmenopausal Spanish women

OBJECTIVE

To assess body weight composition in postmenopausal women and determine correlations with metabolic and hormonal parameters.

METHODS

Medical records of 574 postmenopausal Caucasian Spanish women first time attending a menopause clinic were retrospectively reviewed. Retrieved information included general demographic data, type of menopause, time since menopause onset and baseline hormonal and metabolic parameters. A body mass index (BMI) value of >28.8 kg/m(2) was used to define obesity. The metabolic syndrome (METS) was diagnosed with three or more criteria: fasting glycemia ≥ 100 mg/dL, high density lipoprotein cholesterol (HDL-C) <50 mg/dL, triglycerides (TG) ≥ 150 mg/dL, blood pressure ≥ 130/85 mmHg and obesity (as defined above).

RESULTS

Mean age of the whole cohort was 49.9 ± 6.1 years, with 66% having a natural menopause. A 38.9% and 23.1% of all women were obese or had the METS, respectively. Obese women were older, had a higher parity, smoked less, had more time since menopause onset and a higher rate of surgical menopause as compared to non-obese ones (p = 0.001). BMI values positively correlated with age, time since menopause, parity, and glucose, TG and systolic blood pressure levels; displaying an inverse correlation with HDL-C and SHBG levels. SHBG levels inversely correlated with glucose, TG, HDL-C and systolic blood pressure levels.

CONCLUSION

In this Spanish postmenopausal population BMI significantly increased with age, time since menopause and parity displaying significant correlations with hormonal and metabolic parameters.

Estrogen sulfotransferase is expressed in subcutaneous adipose tissue of obese humans in association with TNF-alpha and SOCS3

CONTEXT AND OBJECTIVE

Estrogen sulfotransferase (EST) catalyzes the inactivation of estrone and estradiol in numerous tissues. Animal studies suggest that EST modulates glucose and lipid metabolism in adipose tissue, but it is unknown whether EST is expressed in human adipose tissue and, if so, how its expression relates to features of the metabolic syndrome.

DESIGN AND PARTICIPANTS

Cross-sectional data from 16 obese men and women with metabolic dysregulation were collected as part of a larger randomized trial at an academic medical center.

OUTCOME MEASURES

Participants underwent assessment of body composition, oral glucose tolerance testing, measurement of serum hormones and inflammatory markers, and sc fat biopsy to assess adipose expression of TNF-α, suppressor of cytokine signaling 3 (SOCS3), leptin, adiponectin, and EST.

RESULTS

EST expression was detectable in sc adipose tissue from both men and women. Log(10) EST mRNA was not significantly associated with age, race, sex or menopausal status, or circulating levels of estrogen or testosterone. In univariate analysis, log(10) EST mRNA was significantly associated with visceral adipose tissue area (r = 0.57, P = 0.02) as well as adipose tissue expression of TNF-α (r = 0.94, P < 0.0001) and SOCS3 mRNA (r = 0.93, P < 0.0001). The associations between EST expression and TNF-α and SOCS3 held in multivariate modeling controlling for age, race, sex and menopausal status, and visceral adiposity. EST expression was not significantly associated with the adipose tissue levels of leptin or adiponectin expression.

CONCLUSIONS

EST is expressed in abdominal sc adipose tissue of both obese males and females in association with expression of TNF-α and SOCS3, suggesting potential roles in inflammation. Further studies are needed to determine the specific metabolic roles of EST expression in human adipose tissue.

A high fructose diet does not affect amphetamine self-administration or spatial water maze learning and memory in female rats

High energy diets can have a detrimental effect on brain plasticity. For example, a high fructose diet impairs spatial memory in male rats. The aim of the present study was to determine whether a high fructose diet impairs another form of learning and memory: drug reinforcement learning. Female Sprague-Dawley rats were fed a high fructose diet (60%) from weaning at postnatal day (PND) 21, then allowed to acquire lever-pressing maintained by intravenous (i.v.) amphetamine at PND 68, 109, or 165. Acquisition was tested on a fixed ratio one (FR1) schedule of reinforcement (0.025 mg/kg/infusion, 1h daily sessions, 10 sessions over 14 days), followed by testing for reinforcing efficacy on a progressive ratio (PR) schedule (0.025, 0.01, and 0.1mg/kg/infusion), 14 days of abstinence, and within-session extinction and reinstatement tests. Subsequently, water maze acquisition and retention were tested in these subjects as well as a separate cohort tested in the water maze only. The diet had no effect on acquisition, reinforcing efficacy, extinction, or reinstatement of amphetamine seeking. Nor did the diet alter any measures of spatial memory. The high fructose diet did decrease body mass and increase relative liver and spleen mass, but did not affect plasma triglyceride concentrations consistently. Together with prior research on males, these results suggest that the metabolism of fructose and the effects of a high fructose diet on learning and memory may be sex-dependent.

Murine models of obesity and hormonal therapy

Obesity is a common disorder, and related diseases such as diabetes, atherosclerosis, hypertension, cardiovascular disease and cancer are a major cause of mortality and morbidity in Westerntype societies. Development of obesity is associated with extensive modifications in adipose tissue involving adipogenesis, angiogenesis and extracellular matrix proteolysis. The fibrinolytic (plasminogen/plasmin) and matrix metalloproteinase (MMP) systems cooperate in these processes. Adipogenesis is tightly associated with angiogenesis, as shown by the findings that adipose tissue expiants trigger blood vessel formation, whereas in turn adipose tissue endothelial cells promote preadipocyte differentiation. A nutritionally induced obesity model in transgenic mice has been used extensively to study the role of the fibrinolytic and MMP systems and of angiogenesis in the development of obesity. Most studies support a role of these systems in adipogenesis and obesity, and suggest that their modulation may affect development of adipose tissue. Such models have also shown that treatment of obese female mice with estrogens has the potential to improve obesity, insulin resistance and glucose intolerance, via decreased expression of lipogenic genes. Thus, murine models of obesity have been very useful tools to study mechanisms of adipose tissue development, as well as effects of hormonal therapy.

The fatty acid desaturation index of blood lipids, as a biomarker of hepatic stearoyl-CoA desaturase expression, is a predictive factor of breast cancer risk

PURPOSE OF REVIEW

This review summarizes epidemiological data linking the fatty acid desaturation index measured in blood lipids, as a biomarker of hepatic stearoyl-CoA desaturase activity, the key enzyme involved in the synthesis of monounsaturated fatty acids from saturated fatty acids, to breast cancer risk. The biological plausibility of this association is discussed.

RECENT FINDINGS

Epidemiological cohort studies reported an association between a high saturated to monounsaturated fatty acid ratio measured in blood lipids, indicating low stearoyl-CoA desaturase-1 activity, and decreased breast cancer risk. The suppression of stearoyl-CoA desaturase expression reduces cancer cell proliferation and in-vitro invasiveness, and dramatically impairs tumor formation and growth. These effects could not be overcome by supplying exogenous monounsaturated fatty acids.

SUMMARY

Epidemiological findings, in accordance with experimental data, suggested that decreased hepatic stearoyl-CoA desaturase expression/activity may be related to decreased risk of breast cancer.

Altered estrogen receptor expression in skeletal muscle and adipose tissue of female rats fed a high-fat diet

Estrogen receptors (ERs) are expressed in adipose tissue and skeletal muscle, with potential implications for glucose metabolism and insulin signaling. Previous studies examining the role of ERs in glucose metabolism have primarily used knockout mouse models of ERα and ERβ, and it is unknown whether ER expression is altered in response to an obesity-inducing high-fat diet (HFD). The purpose of the current study was to determine whether modulation of glucose metabolism in response to a HFD in intact and ovariectomized (OVX) female rats is associated with alterations in ER expression. Our results demonstrate that a 6-wk HFD (60% calories from fat) in female rats induces whole body glucose intolerance with tissue-specific effects isolated to the adipose tissue, and no observed differences in insulin-stimulated glucose uptake, GLUT4, or ERα protein expression levels in skeletal muscle. In chow-fed rats, OVX resulted in decreased ERα with a trend toward decreased GLUT4 expression in adipose tissue. Sham-treated and OVX rats fed a HFD demonstrated a decrease in ERα and GLUT4 in adipose tissue. The HFD also increased activation of stress kinases (c-jun NH₂-terminal kinase and inhibitor of κB kinase β) in the sham-treated rats and decreased expression of the protective heat shock protein 72 (HSP72) in both sham-treated and OVX rats. Our findings suggest that decreased glucose metabolism and increased inflammation in adipose tissue with a HFD in female rats could stem from a significant decrease in ERα expression.

Estrogen and androgen receptors: regulators of fuel homeostasis and emerging targets for diabetes and obesity

Because of increasing life expectancy, the contribution of age-related estrogen or androgen deficiency to obesity and type 2 diabetes will become a new therapeutic challenge. This review integrates current concepts on the mechanisms through which estrogen receptors (ERs) and androgen receptor (AR) regulate energy homeostasis in rodents and humans. In females, estrogen maintains energy homeostasis via ERα and ERβ, by suppressing energy intake and lipogenesis, enhancing energy expenditure, and ameliorating insulin secretion and sensitivity. In males, testosterone is converted to estrogen and maintains fuel homeostasis via ERs and AR, which share related functions to suppress adipose tissue accumulation and improve insulin sensitivity. We suggest that ERs and AR could be potential targets in the prevention of age-related metabolic disorders.

Energy balance modulates colon tumor growth: Interactive roles of insulin and estrogen

Obesity increases colorectal cancer (CRC) risk and progression. However, the impact of obesity on CRC in women is dependent on ovarian hormone status. The purpose of this study was to determine the interactive roles of obesity and ovarian hormones on serum markers of inflammation, cell signaling, and transplanted colon tumor growth. Female C57BL/6 mice (6 wk) were either ovariectomized (OVX) or ovaries left intact (nonovariectomized, NOVX) and randomized to receive a (1) control, (2) 30% calorie-restricted (CR), or (3) diet-induced obese (DIO) diet regimen for 20 wk to induce differing levels of adiposity. Serum was collected and inflammatory and metabolic markers were measured using an antibody array (62 proteins) and ELISAs. Mice were subcutaneously injected with syngeneic MC38 colon cancer cells after 20 wk and sacrificed 4 wk later. CR mice had the smallest tumors irrespective of hormone status, whereas the largest tumors were observed in DIO-OVX mice. Glucose tolerance was impaired in OVX mice, being most severe in the DIO-OVX group. Cytokine arrays suggested that in CR animals, inhibition of tumor growth paralleled insulin sensitivity and associated changes in leptin, adiponectin, and IGF-BPs. Conversely, in DIO-OVX animals, tumor growth was associated with insulin and leptin resistance as well as higher levels of pro-inflammatory proteins. In vitro, leptin and adiponectin had no effect, whereas insulin induced MC38 cell proliferation and MAPK activation. Co-treatment with estrogen blocked the stimulatory effects of insulin. Thus, our in vitro and in vivo data indicate female reproductive hormones have a modulating effect on obesity-induced insulin resistance and inflammation, which may directly or indirectly influence CRC progression.

Body weight decreases induced by estradiol in female rhesus monkeys are dependent upon social status

Gonadal steroids regulate appetite and thus body weight. In addition, continuous exposure to stressors negatively influences appetite through circuits likely distinct from those of gonadal steroids. The occurrence of adverse metabolic consequences due to chronic exposure to psychosocial stressors is twice as frequent in women as men, implicating a role for ovarian hormones, estradiol (E2) and progesterone (P4), in modulating stress-induced changes in appetite. Using social subordination in female macaques as a model of social stress, the current study tested the hypothesis that subordinate females would lose more weight during E2 treatment and gain less weight during P4 administration than dominant females. Because polymorphisms in the gene encoding the serotonin transporter (5HTT; SCL6A4) are known to alter responsivity to stress, we hypothesized that weight loss during E2 administration would be greatest in females with the short variant (s-variant) allele of 5HTT. Dominant females were significantly heavier than subordinate animals throughout the study, a result consistent with previous accounts of food intake when animals are fed a low-fat, high-fiber diet. Females with the s-variant 5HTT genotype weighed significantly less than l/l animals. Dominant animals lost significantly more weight than subordinate animals during E2 treatment. Administration of P4 blocked the weight-reducing effects of E2 in all females, regardless of social status. These data provide evidence that social subordination modulates the influence of ovarian steroid hormones on body weight in female rhesus monkeys independent of 5HTT genotype. Given the prosocial effects of these steroids, future studies are necessary to determine whether status differences in E2-induced weight loss are due to diminished food intake and or increases in energy expenditure and how the change in energy availability during E2 treatments relates to a female's motivation to interact with conspecifics.

Puerarin improves insulin resistance and modulates adipokine expression in rats fed a high-fat diet

The link between obesity and insulin resistance largely accounts for the pathogenesis of metabolic syndrome and diabetes mellitus, in which adipokine expression plays a key role. Puerarin, a major active isoflavone extracted from the traditional Chinese medicine Radix Puerariae, has been studied for its comprehensive biological actions. However, its effect on high-fat diet (HFD)-induced insulin resistance and adipokine expression in rat has not been well investigated. In the present study, male Sprague-Dawley rats were fed on a normal control diet (NCD) or HFD for 6 weeks, followed by administration of puerarin (100 and 200 mg/kg) for up to 8 weeks. Compared to NCD, HFD feeding for 6 weeks led to increased body weight gain and impaired glucose/insulin tolerance manifested by oral glucose/intraperitoneal insulin tolerance tests in rats. These exacerbations prolonged through HFD feeding, but were effectively reversed by puerarin administration. Enzyme-linked immunosorbent assay demonstrated that, serum levels of leptin and resistin, but not that of adiponectin, were markedly augmented by HFD and retarded by puerarin treatment. Real-time reverse transcription polymerase chain reaction results showed that, in agreement with the circulating levels, mRNA expression of leptin and resistin in epididymal white adipose tissue was modified by HFD and improved by puerarin in the same pattern. Collectively, we revealed that puerarin could improve body weight gain, glucose/insulin intolerance and adipokine expression in HFD-induced insulin resistant rats, indicating its potential value for treatment of metabolic syndrome.

Lactobacillus plantarum strain No. 14 reduces adipocyte size in mice fed high-fat diet

Because gut microbiota has recently attracted much attention as an environmental factor involved in the development of obesity, probiotics may be useful in preventing and/or improving obesity and its related disorders. The present study aimed to investigate the effects of Lactobacillus plantarum strain No. 14 (LP14), a bacterial strain reported to decrease body fat percentage in healthy volunteers, on adipocyte size in mice. Female C57BL/6 mice were fed either normal- or high-fat diet and administered intragastrically with LP14 (1 x 10(8) colony-forming units/mouse) or vehicle daily for 11 weeks. High dietary fat intake increased body weight gain, white adipose tissue weight, mean adipocyte size and serum total cholesterol and leptin concentrations, and decreased serum adiponectin concentration. In mice fed the high-fat diet, LP14 administration significantly reduced the mean adipocyte size and tended to reduce the white adipose tissue weight and serum total cholesterol and leptin concentrations as compared with the vehicle-administered mice. All mice had undetectable serum levels of conjugated linoleic acids that reportedly exert antiobesity action. In a separate experiment, LP14 ingestion had no influence on serum triacylglycerol accumulation following olive oil administration in Triton WR1339-treated mice, suggesting that dietary fat absorption is unaffected by LP14. In conclusion, we propose that LP14 may exert a beneficial effect on the onset of diet-induced obesity by reducing the cell size of white adipose tissues, and it seems unlikely that previously reported mechanisms for other bacterial strains are involved in the action of LP14.

Male and female rats with severe protein restriction present delayed wound healing

Malnutrition remains a significant problem, not only in developing countries, but also in the developed world. The aim of this study was to investigate the effects of protein restriction on rat excisional cutaneous healing. Male and female rats (12 weeks old) were exposed to different degrees of protein restriction (23%, 12% (slight restriction), and 0% (severe restriction)) for 12 weeks. On week 9, a full-thickness excisional skin lesion was performed, and the lesion area was measured to evaluate wound contraction and re-epithelialization. Euthanasia was performed after 12 weeks, and the lesion and adjacent skin were removed, fixed in formalin, and embedded in paraffin. Sections were stained with hematoxylin-eosin, toluidine blue, picro-mallory, and sirius red, and were immunostained for alpha-smooth muscle actin. Animals (males and females) exposed to severe protein restriction (0% protein) presented impairment of wound contraction. Inflammatory cells were present in higher amounts in the protein-restricted groups than in the 23% group. Extracellular matrix was poorly deposited in the severely restricted group (0%), but only mildly disturbed in the slightly restricted group (12%). Neovascularization was disturbed in both restricted groups. Our study demonstrates that animals exposed to slight protein restriction present disturbed wound healing, but animals exposed to severe protein restriction present impaired wound healing.

Bisphenol-A: a new diabetogenic factor?

The aim of this review was to analyze the potential effects of environmental chemicals on homeostatic control related to glycemia and energy balance. Many of the environmental chemicals can mimic or interfere with the action of hormones and are generally referred to as "endocrine disruptors". Among these compounds, polychlorinated biphenyls, dioxins, phthalates and bisphenol-A have been correlated with alterations in blood glucose homeostasis in humans. In rodents it has been demonstrated that small doses of bisphenol-A have profound effects on glucose metabolism. Therefore, this altered blood glucose homeostasis may enhance the development of type 2 diabetes.

Minireview: Estrogenic protection of beta-cell failure in metabolic diseases

The prevalence of diabetes is lower in premenopausal women, especially diabetic syndromes with insulin deficiency, suggesting that the female hormone 17beta-estradiol protects pancreatic beta-cell function. In classical rodent models of beta-cell failure, 17beta-estradiol at physiological concentrations protects pancreatic beta-cells against lipotoxicity, oxidative stress, and apoptosis. In this review, we integrate evidence showing that estrogens and their receptors have direct effects on islet biology. The estrogen receptor (ER)-alpha, ER beta, and the G-protein coupled ER are present in beta-cells and enhance islet survival. They also improve islet lipid homeostasis and insulin biosynthesis. We also discuss evidence that ERs modulate insulin sensitivity and energy homeostasis, which indirectly alter beta-cell biology in diabetic and obese conditions.

The association of endogenous sex hormones, adiposity, and insulin resistance with incident diabetes in postmenopausal women

CONTEXT

In postmenopausal women, endogenous bioavailable testosterone (T) and estradiol (E2) have been positively associated, and SHBG has been negatively associated, with incident type 2 diabetes (T2DM). Previous studies have not explored possible factors explaining these relationships.

OBJECTIVE

Our objective was to examine the association of endogenous sex hormones with incident T2DM in postmenopausal women and possible explanatory factors.

DESIGN, SETTING, AND PARTICIPANTS

The Multi-Ethnic Study of Atherosclerosis (MESA) is a prospective study that included 1612 postmenopausal women aged 45-84 yr, followed between the years 2000-2006, who were not taking hormone replacement therapy, had no prevalent cardiovascular disease or diabetes, and had complete ascertainment of sex hormones.

MAIN OUTCOME MEASURES

T2DM was defined based on fasting glucose and/or treatment for diabetes.

RESULTS

There were 116 incident cases of diabetes during follow-up. Across higher quartiles of bioavailable T and E2 and lower quartiles of SHBG, we found significantly greater hazards of developing incident T2DM (all P for trend <or=0.001). After adjustment for body mass index and insulin resistance estimated by homeostasis model assessment of insulin resistance, bioavailable T was no longer associated with incident T2DM. The associations of E2 and SHBG with incident T2DM were partially explained by body mass index and insulin resistance but persisted in fully adjusted models (both P for trend <0.02). Dehydroepiandrosterone had no relationship with incident T2DM.

CONCLUSIONS

Adiposity and insulin resistance explained most of the association of bioavailable T but only partially explained the associations of E2 and SHBG with incident T2DM among postmenopausal women.

Biochemical and physiological function of stearoyl-CoA desaturase

A key and highly regulated enzyme that is required for the biosynthesis of monounsaturated fatty acids is stearoyl-CoA desaturase (SCD), which catalyzes the D(9)-cis desaturation of a range of fatty acyl-CoA substrates. The preferred substrates are palmitoyl- and stearoyl-CoA, which are converted into palmitoleoyl- and oleoyl-CoA respectively. Oleate is the most abundant monounsaturated fatty acid in dietary fat and is therefore readily available. Studies of mice that have a naturally occurring mutation in the SCD-1 gene isoform as well as a mouse model with a targeted disruption of the SCD gene (SCD-1(-/-)) have revealed the role of de novo synthesized oleate and thus the physiological importance of SCD-1 expression. SCD-1 deficiency results in reduced body adiposity, increased insulin sensitivity, and resistance to diet-induced obesity. The expression of several genes of lipid oxidation are upregulated, whereas lipid synthesis genes are downregulated. SCD-1 was also found to be a component of the novel metabolic response to the hormone leptin. Therefore, SCD-1 appears to be an important metabolic control point, and inhibition of its expression could be of benefit for the treatment of obesity, diabetes, and other metabolic diseases. In this article, we summarize the recent and timely advances concerning the important role of SCD in the biochemistry and physiology of lipid metabolism.