Mechanisms behind insulin resistance in rat skeletal muscle after oophorectomy and additional testosterone treatment

Association between sex steroid hormones and subsequent hyperglycemia during pregnancy

Objective

Sex steroid hormones may play a role in insulin resistance and glucose dysregulation. However, evidence regarding associations between early-pregnancy sex steroid hormones and hyperglycemia during pregnancy is limited. The primary objective of this study was to assess the relationships between first trimester sex steroid hormones and the subsequent development of hyperglycemia during pregnancy; with secondary evaluation of sex steroid hormones levels in mid-late pregnancy, concurrent with and subsequent to diagnosis of gestational diabetes.

Methods

Retrospective analysis of a prospective pregnancy cohort study was conducted. Medically low-risk participants with no known major endocrine disorders were recruited in the first trimester of pregnancy (n=319). Sex steroid hormones in each trimester, including total testosterone, free testosterone, estrone, estradiol, and estriol, were assessed using high-performance liquid chromatography and tandem mass spectrometry. Glucose levels of the 1-hour oral glucose tolerance test and gestational diabetes diagnosis were abstracted from medical records. Multivariable linear regression models were fitted to assess the associations of individual first trimester sex steroids and glucose levels.

Results

In adjusted models, first trimester total testosterone (β=5.24, 95% CI: 0.01, 10.46, p=0.05) and free testosterone (β=5.98, 95% CI: 0.97, 10.98, p=0.02) were positively associated with subsequent glucose concentrations and gestational diabetes diagnosis (total testosterone: OR=3.63, 95% CI: 1.50, 8.78; free testosterone: OR=3.69; 95% CI: 1.56, 8.73). First trimester estrone was also positively associated with gestational diabetes (OR=3.66, 95% CI: 1.56, 8.55). In mid-late pregnancy, pregnant people with gestational diabetes had lower total testosterone levels (β=-0.19, 95% CI: -0.36, -0.02) after adjustment for first trimester total testosterone.

Conclusion

Early-pregnancy sex steroid hormones, including total testosterone, free testosterone, and estrone, were positively associated with glucose levels and gestational diabetes in mid-late pregnancy. These hormones may serve as early predictors of gestational diabetes in combination with other risk factors.

The Association of Carbohydrate Antigen (CA) 19-9 Levels and Low Skeletal Muscle Mass in Healthy Adults

Carbohydrate antigen 19-9 (CA 19-9) is a commonly used tumor marker for pancreatic cancer. However, CA 19-9 can be overexpressed in several benign inflammatory diseases. We investigated the relationship between high CA 19-9 level and low muscle mass (LMM) in healthy adults without cancer. Participants who underwent evaluation of muscle mass and CA 19-9 were included. Exclusion criteria were any malignancy, cardiovascular disease, tuberculosis, and chronic lung/liver disease. Participants were classified into "normal", "mild LMM", and "severe LMM" groups based on the skeletal muscle mass index. Multivariable logistic regression analyses were conducted to assess the association of high CA 19-9 with muscle mass status. A total of 263,061 adults were included. The mean age and SMI were 41.03 years and 7.13 kg/m2. After adjustments for various confounders, high CA 19-9 was independently associated with mild LMM (adjusted odds ratio, 1.677 [95% confidence interval, 1.533-1.834]) and severe LMM (2.651 [2.126-3.306]) compared to the normal group. Furthermore, the association between high CA 19-9 and severe LMM was stronger in men than in women. Elevated CA 19-9 levels were independently associated with a higher prevalence of LMM in healthy adults without cancer. Therefore, increased CA 19-9 could be utilized as a novel biomarker for sarcopenia.

Specific Alteration of Branched-Chain Amino Acid Profile in Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is one of the most common endocrinopathies in reproductive age women; it is a complex health issue with numerous comorbidities. Attention has recently been drawn to amino acids as they are molecules essential to maintain homeostasis. The aim of the study was to investigate the branch chain amino acid (BCAA) profile in women with PCOS. A total of 326 women, 208 diagnosed with PCOS and 118 healthy controls, participated in the study; all the patients were between 18 and 40 years old. Anthropometrical, biochemical and hormonal parameters were assessed. Gas-liquid chromatography combined with tandem mass spectrometry was used to investigate BCAA levels. Statistical analysis showed significantly higher plasma levels of BCAAs (540.59 ± 97.23 nmol/mL vs. 501.09 ± 85.33 nmol/mL; p < 0.001) in women with PCOS. Significant correlations (p < 0.05) were found between BCAA and BMI, HOMA-IR, waist circumference and total testosterone levels. In the analysis of individuals with abdominal obesity, there were significant differences between PCOS and controls in BCAA (558.13 ± 100.51 vs. 514.22 ± 79.76 nmol/mL) and the concentrations of all the analyzed amino acids were higher in the PCOS patients. Hyperandrogenemia in PCOS patients was associated with significantly higher leucine, isoleucine and total BCAA levels. The increase of BCAA levels among PCOS patients in comparison to healthy controls might be an early sign of metabolic alteration and a predictive factor for other disturbances.

Does the weight loss efficacy of alternate day fasting differ according to sex and menopausal status?

BACKGROUND AND AIMS

This study examined if the weight loss and metabolic benefits of alternate day fasting (ADF) varies according to sex and menopausal status in adults with obesity.

METHODS AND RESULTS

This secondary analysis pooled the data of men and women (n = 75) who participated in three 12-week ADF studies (500 kcal fast day; alternated with an ad libitum intake feast day). Body weight decreased in premenopausal women (-4.6 ± 3.2%), postmenopausal women (-6.5 ± 3.2%) and men (-6.2 ± 4.4%) (main effect of time, P < 0.001), with no difference between groups (no group × time interaction). Energy intake on fast days was higher than prescribed in all groups (∼400-500 excess kcal consumed), with no differences between groups. Fat mass, lean mass, fasting insulin, and insulin resistance, and blood pressure decreased similarly in all groups (main effect of time, P < 0.05 for all comparisons). LDL cholesterol decreased more in postmenopausal versus premenopausal women (group × time interaction, P = 0.01). Fasting glucose, HDL cholesterol, and triglycerides remained unchanged in all groups.

CONCLUSION

These findings suggest that the weight loss and metabolic benefits of ADF do not generally vary according to sex or menopausal status in adults with obesity.

TRIAL REGISTRATION

Clinicaltrials.gov, NCT00960505; NCT03528317.

Association between relative handgrip strength and prediabetes among South Korean adults

BACKGROUND

Diabetes is a progressive disease, and thus, it is important to prevent diabetes at the prediabetes stage. Although the loss of muscle strength and prediabetes are associated, few studies have examined relative handgrip strength (RHGS), which can be an indicator of both muscle strength and adiposity. Therefore, our study aimed to examine the association between RHGS and prediabetes (HbA1c level >5.7%) stratified by sex due to sex differences in strength.

METHODS

We analyzed data from the 2016-2018 Korean National Health and Nutrition Examination Survey. Prediabetes was defined using the HbA1c cut-off level of 5.7-6.4%, identified by the American Diabetes Association. RHGS was calculated as the maximal absolute handgrip strength of both hands divided by body mass index and was divided into sex-specific quartiles. Multiple logistic regression analysis was performed to determine the association between sex-specific RHGS and prediabetes.

RESULTS

Among the total participants, 13,384 did not have diabetes. In men, the low and mid-low RHGS groups had increased odds of prediabetes (low group, odds ratio [OR]: 1.42, 95% confidence interval [CI]: 1.10-1.82; mid-low group, OR: 1.32, 95% CI: 1.04-1.67). However, no significant differences were observed between the corresponding female groups. Moreover, central obesity and lower RHGS were strongly associated with prediabetes in men (low group, OR: 2.40, 95% CI: 1.52-3.80; mid-low group, OR: 2.00, 95% CI: 1.26-3.17; mid-high group, OR: 1.76, 95% CI: 1.11-2.81), and a trend was observed (p = 0.0026).

CONCLUSION

RHGS could be a practical and inexpensive tool for predicting diabetes in men. Programs aimed at preventing diabetes need to include exercise routines for improving muscle strength, and further research through longitudinal studies is required to investigate the causality of RHGS on the risk of prediabetes.

Persistent Poor Metabolic Profile in Postmenopausal Women With Ovarian Hyperandrogenism After Testosterone Level Normalization

Context

Data on prevalence of metabolic risk factors in hyperandrogenic postmenopausal women are limited. Also, the correlation between metabolic disorders and androgen excess in this scenario is poorly understood.

Objectives

We aimed to assess the prevalence of obesity, hypertension, type 2 diabetes (T2D), and dyslipidemia (DLP) in postmenopausal women with hyperandrogenism of ovarian origin before and after surgical normalization of testosterone (T) levels, as well as the impact of androgen normalization on body mass index (BMI), glucose, and lipid metabolism.

Design

Retrospective study.

Setting

Tertiary health center.

Participants

Twenty-four Brazilian women with postmenopausal hyperandrogenism who underwent bilateral oophorectomy between 2004 and 2014 and had histologically confirmed virilizing ovarian tumor (VOT) or ovarian hyperthecosis (OH) and T-level normalization after surgery were selected.

Main Outcome Measures

FSH, LH, total and calculated free T, BMI, fasting plasma glucose (FPG), glycated hemoglobin (HbA1c), total cholesterol, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and triglyceride (TG) serum levels were accessed before (n = 24) and 24 months after (n = 19) bilateral oophorectomy.

Results

At baseline, the overall prevalence rates of obesity, T2D, DLP, and hypertension were 58.3%, 83.3%, 66.7%, and 87.5%, respectively. No significant difference in prevalence was found between patients with OH and VOTs. At follow-up, FSH, LH, and total and free T levels had returned to menopausal physiologic levels, but mean BMI and mean FPG, HbA1c, LDL-C, HDL-C, and TG levels did not differ from baseline.

Conclusions

Postmenopausal hyperandrogenism is associated with adverse metabolic risk. Long-term normalization of testosterone levels did not improve BMI, glucose, or lipid metabolism.

Sex differences and correlates of poor glycaemic control in type 2 diabetes: a cross-sectional study in Brazil and Venezuela

OBJECTIVE

Examine whether glycaemic control varies according to sex and whether the latter plays a role in modifying factors associated with inadequate glycaemic control in patients with type 2 diabetes (T2D) in Brazil and Venezuela.

DESIGN, SETTING AND PARTICIPANTS

This was a cross-sectional, nationwide survey conducted in Brazil and Venezuela from February 2006 to June 2007 to obtain information about glycaemic control and its determinants in patients with diabetes mellitus attending outpatient clinics.

MAIN OUTCOME MEASURES

Haemoglobin A1c (HbA1c) level was measured by liquid chromatography, and patients with HbA1c ≥7.0% (53 mmol/mol) were considered to have inadequate glycaemic control. The association of selected variables with glycaemic control was analysed by multivariate linear regression, using HbA1c as the dependent variable.

RESULTS

A total of 9418 patients with T2D were enrolled in Brazil (n=5692) and in Venezuela (n=3726). They included 6214 (66%) women and 3204 (34%) men. On average, HbA1c levels in women were 0.13 (95% CI 0.03 to 0.24; p=0.015) higher than in men, after adjusting for age, marital status, education, race, country, body mass index, duration of disease, complications, type of healthcare, adherence to diet, adherence to treatment and previous measurement of HbA1c. Sex modified the effect of some factors associated with glycaemic control in patients with T2D in our study, but had no noteworthy effect in others.

CONCLUSIONS

Women with T2D had worse glycaemic control than men. Possible causes for poorer glycaemic control in women compared with men include differences in glucose homeostasis, treatment response and psychological factors. In addition, sex modified factors associated with glycaemic control, suggesting the need to develop specific treatment guidelines for men and women.

Metformin improves ovarian insulin signaling alterations caused by fetal programming

Insulin resistance is the decreased ability of insulin to mediate metabolic actions. In the ovary, insulin controls ovulation and oocyte quality. Alterations in ovarian insulin signaling pathway could compromise ovarian physiology. Here, we aimed to investigate the effects of fetal programming on ovarian insulin signaling and evaluate the effect of metformin treatment. Pregnant rats were hyperandrogenized with testosterone and female offspring born to those dams were employed; at adulthood, prenatally hyperandrogenized (PH) offspring presented two phenotypes: irregular ovulatory (PHiov) and anovulatory (PHanov). Half of each group was orally treated with metformin. Metformin treatment improved the estrous cyclicity in both PH groups. Both PH groups showed low mRNA levels of IR, IRS1 and Glut4. IRS2 was decreased only in PHanov. Metformin upregulated the mRNA levels of some of the mediators studied. Protein expression of IR, IRS1/2 and GLUT4 was decreased in both PH groups. In PHiov, metformin restored the expression of all the mediators, whereas, in PHanov, metformin restored only that of IR and IRS1/2. IRS1 phosphorylation was measured in tyrosine residues, which activates the pathway, and in serine residues, which impairs insulin action. PHiov presented high IRS1 phosphorylation on tyrosine and serine residues, whereas PHanov showed high serine phosphorylation and low tyrosine phosphorylation. Metformin treatment lowered serine phosphorylation only in PHanov rats. Our results suggest that PHanov rats have a defective insulin action, partially restored with metformin. PHiov rats had less severe alterations, and metformin treatment was more effective in this phenotype.

Female sex hormones are necessary for the metabolic effects mediated by loss of Interleukin 18 signaling

OBJECTIVE

Interleukin (IL)-18 plays a crucial role in maintaining metabolic homeostasis and levels of this cytokine are influenced by gender, age, and sex hormones. The role of gender on IL-18 signaling, however, is unclear. We hypothesized that the presence of female sex hormone could preserve the metabolic phenotype of the IL-18R^-/- animals.

METHODS

We studied female mice with a global deletion of the α isoform of the IL-18 receptor (IL-18R^-/-) and littermates control. Three studies were done: 1) animals fed a high fat diet (HFD) for 16 weeks; 2) animals fed chow diet for 72 weeks and 3) animals (3 weeks-old) randomized to either bilateral ovariectomy (OVX) or control surgery (SHAM) and followed for 16 weeks.

RESULTS

Female IL-18R^-/- mice gained less weight and maintained glucose homeostasis on a chow diet compared with HFD, but no differences between genotypes were observed. The maintenance of body weight and glucose homeostasis in IL-18R^-/- mice was lost with aging. By 72 weeks of age, IL-18R^-/- mice became heavier compared with WT mice due to an increase in both visceral and subcutaneous adiposity and displayed glucose intolerance. OVX did not affect body weight in IL-18R^-/- mice but exacerbated glucose intolerance and impaired liver insulin signaling when compared with SHAM mice.

CONCLUSIONS

Female mice harboring a global deletion of the IL-18R, only present the same phenotype as reported in male IL-18R^-/- mice if they are aged or have undergone OVX, in which circulating estrogen is likely to be blunted. The role of estrogen signaling in the protection against altered metabolic homeostasis in IL-18R^-/- mice appears to be mediated by liver insulin signaling. We therefore suggest that the metabolic effects mediated by loss of IL-18 signaling are only present in a female sex hormone free environment.

Risk of Diabetes After Hysterectomy With or Without Oophorectomy in Postmenopausal Women

The aim of this study was to determine the associations between hysterectomy, bilateral salpingo-oophorectomy (BSO), and incidence of diabetes in postmenopausal women participating in the Women's Health Initiative (WHI), a series of trials conducted in the United States, during the period 1993-1998. A total of 67,130 postmenopausal women aged 50-79 years were followed for a mean of 13.4 years. Among them, 7,430 cases of diabetes were diagnosed. Multivariable Cox proportional hazards models were used to assess the association between hysterectomy/oophorectomy status and diabetes incidence. Compared with women without hysterectomy, women with hysterectomy had a significantly higher risk of diabetes (hazard ratio = 1.13, 95% confidence interval: 1.06, 1.21). The increased risk of diabetes was similar for women with hysterectomy only and for women with hysterectomy with concomitant BSO. Compared with hysterectomy alone, hysterectomy with BSO was not associated with additional risk of diabetes after stratification by age at hysterectomy and hormone therapy status. In our large, prospective study, we observed that hysterectomy, regardless of oophorectomy status, was associated with increased risk of diabetes among postmenopausal women. However, our data did not support the hypothesis that early loss of ovarian estrogens is a risk factor for type 2 diabetes. The modest increased risk of diabetes associated with hysterectomy may be due to residual confounding, such as the reasons for hysterectomy.

Effects of 17β-Estradiol and Androgen on Glucose Metabolism in Skeletal Muscle

Diabetes develops predominantly in males in experimental models, and extensive evidence suggests that 17β-estradiol (E2) modulates progression of diabetes in humans. We previously developed a severely diabetic transgenic (Tg) mouse model by β-cell-specific overexpression of inducible cAMP early repressor (ICER) and found that male ICER-Tg mice exhibit sustained severe hyperglycemia, but female ICER-Tg mice gradually became normoglycemic with aging. This implies that differences in circulating androgen and E2 levels might influence skeletal muscle glucose uptake and glycemic status. Here we examined whether a decrease of androgen or E2 excess can improve muscle glucose uptake in hyperglycemic male ICER-Tg mice and, conversely, whether a decrease of E2 or androgen excess can elevate blood glucose levels and impair muscle glucose uptake in normoglycemic female ICER-Tg mice. We treated hyperglycemic male ICER-Tg mice with orchiectomy (ORX) or ORX+E2 pellet implantation and normoglycemic female ICER-Tg mice with ovariectomy (OVX) or OVX+5α-DHT pellet implantation to alter the androgen to E2 ratio. ORX+E2 treatment of male ICER-Tg mice caused a rapid drop in blood glucose via both a dramatic increase of β-cells and significantly improved muscle glucose uptake due to the induction of glucose transporter type 4 (GLUT4) expression and translocation of GLUT4 to the cell membrane. In contrast, OVX+5α-DHT-treated female ICER-Tg mice showed an elevation of blood glucose without any decrease of β-cells; instead, they showed decreased muscle glucose uptake due to decreased activation of serine/threonine-specific protein kinase AKT and GLUT4 expression. These findings suggest that androgen (5α-DHT) promotes insulin resistance in females, whereas E2 improves insulin sensitivity in severely diabetic male mice.

Free androgen index and Irisin in polycystic ovary syndrome

PURPOSE

PCOS is associated with hyperandrogenism and insulin resistance (IR). Recent studies have shown that circulating Irisin levels increase in PCOS women. However, no report has demonstrated a relationship between Irisin and hyperandrogenism in PCOS women. The purpose of the study was to compare interrelationship between Irisin or androgen excess with IR in PCOS and normal subjects.

METHODS

166 PCOS and 103 control women were prospectively studied. Euglycemic- hyperinsulinemic clamps were preformed to assess their insulin sensitivity, which was expressed as M value. Circulating Irisin was determined by ELISA kit. Circulating androgens were measured using ultrasensitive assays.

RESULTS

PCOS women with high FAI had significantly higher BMI, FAT%, TC, DHEA-S and HOMA-IR, and significantly lower levels of M values and SHBG than PCOS women with low FAI or the controls. Pearson correlations showed that in the entire population, FAI correlated positively with BMI, WHR, FAT%, blood pressure, TG, DHEA-S, LH/FSH, AUCinsulin, HOMA-IR and Irisin, and negatively with M values. In multiple stepwise regression analysis, only FAT%, DHEA-S and LH/FSH were independent related factors with FAI.

CONCLUSION

The elevated Irisin levels in PCOS women were associated with androgen excess. Circulating Irisin is a primary predictor of hyperandrogenism, MetS and IR in PCOS women.

Effects of Hormone Replacement Therapy on Insulin Resistance in Postmenopausal Diabetic Women

BACKGROUND

Insulin resistance (IR) is closely associated with diabetes mellitus. On the other hand, increased visceral fat in menopause is also associated with IR, which makes postmenopausal diabetic women in a big risk for cardiovascular diseases. There are conflicting reports about the effects on hormone replacement therapy (HRT) on IR.

AIM

The aim of the study was to investigate the effects of HRT on IR.

METHODS

A total of 40 postmenopausal women with type 2 diabetes were enrolled and followed for 12 months. Half of them were assigned to take HRT, while the other half made the control group. Fasting plasma glucose (FPG) and insulinemia were measured in both groups at baseline and after 12 months. IR was represented by Homeostatic model assessment for IR (HOMA-IR).

RESULTS

HRT was associated with significant decrease in HOMA-IR, FPG and insulinemia in the examined group. There was no significant reduction in FPG and no significant increase in insulinemia levels and HOMA-IR values in control group after 12 months.

CONCLUSION

HRT was associated with statistically signifficant increase of insulin sensitivity. Larger clinical trials will be necessary to understand whether HRT may improve insulin resistance and glucose homeostasis in women with diabetes, especially when given shortly after entering menopause.

Genetic Rodent Models of Obesity-Associated Ovarian Dysfunction and Subfertility: Insights into Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is the most common endocrinopathy affecting women and a leading cause of female infertility worldwide. Defined clinically by the presence of hyperandrogenemia and oligomenorrhoea, PCOS represents a state of hormonal dysregulation, disrupted ovarian follicle dynamics, and subsequent oligo- or anovulation. The syndrome's prevalence is attributed, at least partly, to a well-established association with obesity and insulin resistance (IR). Indeed, the presence of severe PCOS in human genetic obesity and IR syndromes supports a causal role for IR in the pathogenesis of PCOS. However, the molecular mechanisms underlying this causality, as well as the important role of hyperandrogenemia, remain poorly elucidated. As such, treatment of PCOS is necessarily empirical, focusing on symptom alleviation. The generation of knockout and transgenic rodent models of obesity and IR offers a promising platform in which to address mechanistic questions about reproductive dysfunction in the context of metabolic disease. Similarly, the impact of primary perturbations in rodent gonadotrophin or androgen signaling has been interrogated. However, the insights gained from such models have been limited by the relatively poor fidelity of rodent models to human PCOS. In this mini review, we evaluate the ovarian phenotypes associated with rodent models of obesity and IR, including the extent of endocrine disturbance, ovarian dysmorphology, and subfertility. We compare them to both human PCOS and other animal models of the syndrome (genetic and hormonal), explore reasons for their discordance, and consider the new opportunities that are emerging to better understand and treat this important condition.

A Dietary Medium-Chain Fatty Acid, Decanoic Acid, Inhibits Recruitment of Nur77 to the HSD3B2 Promoter In Vitro and Reverses Endocrine and Metabolic Abnormalities in a Rat Model of Polycystic Ovary Syndrome

Hyperandrogenism is the central feature of polycystic ovary syndrome (PCOS). Due to the intricate relationship between hyperandrogenism and insulin resistance in PCOS, 50%-70% of these patients also present with hyperinsulinemia. Metformin, an insulin sensitizer, has been used to reduce insulin resistance and improve fertility in women with PCOS. In previous work, we have noted that a dietary medium-chain fatty acid, decanoic acid (DA), improves glucose tolerance and lipid profile in a mouse model of diabetes. Here, we report for the first time that DA, like metformin, inhibits androgen biosynthesis in NCI-H295R steroidogenic cells by regulating the enzyme 3β-hydroxysteroid dehydrogenase/Δ5-Δ4-isomerase type 2 (HSD3B2). The inhibitory effect on HSD3B2 and androgen production required cAMP stimulation, suggesting a mechanistic action via the cAMP-stimulated pathway. Specifically, both DA and metformin reduced cAMP-enhanced recruitment of the orphan nuclear receptor Nur77 to the HSD3B2 promoter, coupled with decreased transcription and protein expression of HSD3B2. In a letrozole-induced PCOS rat model, treatment with DA or metformin reduced serum-free testosterone, lowered fasting insulin, and restored estrous cyclicity. In addition, DA treatment lowered serum total testosterone and decreased HSD3B2 protein expression in the adrenals and ovaries. We conclude that DA inhibits androgen biosynthesis via mechanisms resulting in the suppression of HSD3B2 expression, an effect consistently observed both in vitro and in vivo. The efficacy of DA in reversing the endocrine and metabolic abnormalities of the letrozole-induced PCOS rat model are promising, raising the possibility that diets including DA could be beneficial for the management of both hyperandrogenism and insulin resistance in PCOS.

Scientific Statement on the Diagnostic Criteria, Epidemiology, Pathophysiology, and Molecular Genetics of Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a heterogeneous and complex disorder that has both adverse reproductive and metabolic implications for affected women. However, there is generally poor understanding of its etiology. Varying expert-based diagnostic criteria utilize some combination of oligo-ovulation, hyperandrogenism, and the presence of polycystic ovaries. Criteria that require hyperandrogenism tend to identify a more severe reproductive and metabolic phenotype. The phenotype can vary by race and ethnicity, is difficult to define in the perimenarchal and perimenopausal period, and is exacerbated by obesity. The pathophysiology involves abnormal gonadotropin secretion from a reduced hypothalamic feedback response to circulating sex steroids, altered ovarian morphology and functional changes, and disordered insulin action in a variety of target tissues. PCOS clusters in families and both female and male relatives can show stigmata of the syndrome, including metabolic abnormalities. Genome-wide association studies have identified a number of candidate regions, although their role in contributing to PCOS is still largely unknown.

Metabolic Syndrome and Menopause: Pathophysiology, Clinical and Diagnostic Significance

Menopause is a risk factor for cardiometabolic diseases, including metabolic syndrome (MetS), type 2 diabetes, and cardiovascular diseases. MetS is a constellation of interdependent factors such as insulin resistance, abdominal obesity, dyslipidemia, and hypertension. The prevalence of MetS in postmenopause is due to loss of the protective role of estrogens and increased circulating androgens resulting in changes to body fat distribution and development of abdominal obesity. Excessive visceral adipose tissue plays an important role due to synthesis and secretion of bioactive substances such as adipocytokines, proinflammatory cytokines, reactive oxygen species, prothrombotic, and vasoconstrictor factors. MetS may also impact risk assessment of breast cancer, osteoporosis and chronic kidney disease, and quality of life during the menopausal transition. Increased MetS has stimulated the exploration of new laboratory tests for early detection and therapies.

Protective effects of melatonin against metabolic and reproductive disturbances in polycystic ovary syndrome in rats

OBJECTIVES

This study was undertaken to study the effects of melatonin on metabolic and reproductive aspects of polycystic ovary syndrome (PCOS) in rats.

METHODS

PCOS was induced by daily subcutaneous administration of testosterone (20 mg/kg) to 21-day-old female rats for 35 days. Rats were given metformin (500 mg/kg), melatonin (1 mg/kg) or melatonin (2 mg/kg) along with testosterone. One group served as vehicle control. On the 36th day, the animals were euthanised, and anthropometrical, biochemical (glucose, insulin, lipids, testosterone, C reactive protein (CRP)), oral glucose tolerance test, and histopathological evaluation of ovaries, uterus and intraabdominal fat (IAF), were carried out. Daily colpocytological examination was carried out from 14(th) day of study until termination.

KEY FINDINGS

Both the doses of melatonin significantly reduced body weight, body mass index, IAF, insulin and CRP. A favourable lipid profile, normal glucose tolerance and a decrease in the percentage of estrus smears were observed. Histopathological examination of ovary, uterus and IAF revealed a decrease in the number of cystic follicles, decrease in neoplastic endometrial glands, and decrease in adipocyte hypertrophy, respectively. The effects observed with melatonin were comparable to that with metformin.

CONCLUSION

The study provides evidence of the potential beneficial effects of melatonin in PCOS.

In vitro palmitate treatment of myotubes from postmenopausal women leads to ceramide accumulation, inflammation and affected insulin signaling

Menopause is associated with an increased incidence of insulin resistance and metabolic diseases. In a chronic palmitate treatment model, we investigated the role of skeletal muscle fatty acid exposure in relation to the metabolic deterioration observed with menopause. Human skeletal muscle satellite cells were isolated from premenopausal (n = 6) and postmenopausal (n = 5) women. In an in vitro model, the myotubes were treated with palmitate (300 µM) for one-, two- or three days during differentiation. Effects on lipid accumulation, inflammation and insulin signaling were studied. Palmitate treatment led to a 108% (CI 95%: 50%; 267%) increase in intramyocellular ceramide in the myotubes from the postmenopausal women (post-myotubes) compared with a 26% (CI 95%: -57%; 96%) increase in myotubes from the premenopausal women (pre-myotubes), (p<0.05). Furthermore, post-myotubes had a 22% (CI 95%: 4%; 34%) increase in pJNK (p = 0.04) and a 114% (CI 95%: 50%; 177%) increase in Hsp70 protein expression (p = 0.03) after three days of palmitate treatment, compared with pre-myotubes, in which no increase in either pJNK (-12% (CI 95: -26%; 2%)) or Hsp70 (7% (CI 95: -78%; 91%)) was detected. Furthermore, post-myotubes showed a blunted insulin stimulated phosphorylation of AS160 in response to chronic palmitate treatment compared with pre-myotubes (p = 0.02). The increased intramyocellular ceramide content in the post-myotubes was associated with a significantly higher mRNA expression of Serine Palmitoyltransferase1 (SPT1) after one day of palmitate treatment (p = 0.03) in post-myotubes compared with pre-myotubes. Our findings indicate that post-myotubes are more prone to develop lipid accumulation and defective insulin signaling following chronic saturated fatty acid exposure as compared to pre-myotubes.

Bilateral oophorectomy and the risk of incident diabetes in postmenopausal women

OBJECTIVE

Ovarian hormones regulate glucose uptake and insulin sensitivity. Despite the high frequency of surgical menopause, its relationship with diabetes has not been extensively investigated. We assessed the association between hysterectomy with or without bilateral oophorectomy (BSO) status, menopausal age, and reproductive life span with incident diabetes.

RESEARCH DESIGN AND METHODS

Data were from a cohort of 2,597 postmenopausal women enrolled in the National Health and Nutrition Examination Survey I Epidemiologic Follow-up Study without diabetes mellitus at baseline. Cox proportional hazards regression models were used to calculate adjusted hazard ratios (HRs) and 95% CIs.

RESULTS

After a median follow-up time of 9.2 years, the incidence of diabetes (in cases per 1,000 person-years) was 7.4 for women with no hysterectomy or BSO, 8.2 for hysterectomy alone, and 8.5 for hysterectomy with BSO. Hysterectomy status was associated positively with diabetes (HR 1.66, 95% CI 1.23-2.23). However, the elevated risk was restricted to women with both hysterectomy and BSO after adjustment for relevant confounders (HR 1.57, 95% CI 1.03-2.41). An earlier age at menopause and a shorter reproductive life span also exhibited a linear relationship with the development of diabetes irrespective of type of menopause (P for trend = 0.001).

CONCLUSIONS

Women with hysterectomy concomitant with BSO may represent a unique population with elevated risk for diabetes and other chronic diseases. Therefore, the decision to remove the ovaries at the time of hysterectomy for benign conditions during the premenopausal years should be balanced with the risk of diabetes and its potential complications. Furthermore, the mechanism linking BSO to diabetes mellitus needs to be clarified.

Sex differences in type 2 diabetes: focus on disease course and outcomes

BACKGROUND

Women with type 2 diabetes (T2D) are less likely to reach the goals for hemoglobin A1c compared with men, and have higher all-cause mortality. The risk of cardiovascular disease is elevated among both men and women with T2D, however, the risk has declined among men over recent years while it remains stationary in women. Reasons for these sex differences remain unclear, and guidelines for diabetes treatment do not differentiate between sexes. Possible causes for varying outcome include differences in physiology, treatment response, and psychological factors. This review briefly outlines sex differences in hormonal pathophysiology, and thereafter summarizes the literature to date on sex differences in disease course and outcome.

METHODS

Systematic searches were performed on PubMed using "sex", "gender", and various glucose-lowering therapies as keywords. Earlier reviews are summarized and results from individual studies are reported. Reference lists from studies were used to augment the search.

RESULTS

There is an increased risk of missing the diagnosis of T2D when screening women with only fasting plasma glucose instead of with an oral glucose tolerance test. The impact of various risk factors for complications may differ by sex. Efficacy and side effects of some glucose-lowering drugs differ between men and women. Men with T2D appear to suffer more microvascular complications, while women have higher morbidity and mortality in cardiovascular disease and also fare worse psychologically.

CONCLUSION

Few studies to date have focused on sex differences in T2D. Several questions demand further study, such as whether risk factors and treatment guidelines should be sex-specific. There is a need for clinical trials designed specifically to evaluate sex differences in efficacy and outcome of the available treatments.

Using a novel coculture model to dissect the role of intramuscular lipid load on skeletal muscle insulin responsiveness under reduced estrogen conditions

Reductions in estrogen function lead to adiposity and peripheral insulin resistance. Significant metabolic changes have been found in adipocytes and skeletal muscle with disruptions in the estrogen-signaling axis; however, it is unclear if intercellular communication exists between these tissues. The purpose of this study was to examine the impact of isolated adipocytes cocultured with single adult skeletal muscle fibers (SMF) collected from control female (SHAM) and ovariectomized female (OVX) mice. In addition, a second purpose was to compare differential effects of primary adipocytes from omental and inguinal adipose depots on SMF from these same groups. OVX SMF displayed greater lipid content, impaired insulin signaling, and lower insulin-induced glucose uptake compared with SHAM SMF without coculture. In the SHAM group, regardless of the adipose depot of origin, coculture induced greater intracellular lipid content compared with control SHAM SMF. The increased lipid in the SMF was associated with impaired insulin-induced glucose uptake when adipocytes were of omental, but not inguinal, origin. Coculture of OVX SMF with omental or inguinal adipocytes resulted in higher lipid content but no further reduction in insulin-induced glucose uptake compared with control OVX SMF. The data indicate that, in the OVX condition, there is a threshold for lipid accumulation in skeletal muscle beyond which there is no further impairment in insulin responsiveness. These results also demonstrate depot-specific effects of adipocyte exposure on skeletal muscle glucose uptake and further implicate a role for increased intracellular lipid storage in the pathogenesis of insulin resistance when estrogen levels are reduced.

Recent progress in the use of genetics to understand links between type 2 diabetes and related metabolic traits

Genome-wide association studies have identified genetic variants associated with increased risk of type 2 diabetes. The aim of this review is to highlight some of the insights into the mechanism underlying type 2 diabetes provided by genetic association studies.

Study of carbohydrate metabolism indices and adipocytokine profile and their relationship with androgens in polycystic ovary syndrome after menopause

OBJECTIVE

Hyperandrogenism, insulin resistance, and altered adipocytokine levels characterize polycystic ovary syndrome (PCOS) women of reproductive age. Hyperandrogenism persists in postmenopausal PCOS women. In the latter, this study aimed at investigating carbohydrate metabolism, adipocytokines, androgens, and their relationships.

SUBJECTS AND METHODS

Blood sampling from overweight postmenopausal women (25 PCOS and 24 age- and BMI-matched controls) at baseline and during oral glucose tolerance test for measurement of insulin and glucose levels, baseline leptin, adiponectin, visfatin, retinol-binding protein 4, lipocalin-2, androgen, and high-sensitivity C-reactive protein (hs-CRP) levels and for calculation of insulin sensitivity (glucose-to-insulin ratio (G/I), quantitative insulin sensitivity check index, and insulin sensitivity index (ISI)), resistance (homeostasis mathematical model assessment-insulin resistance (HOMA-IR)), secretion (Δ of the area under the curve of insulin (ΔAUCI), first-phase insulin secretion (1st PHIS), and second-phase insulin secretion (2nd PHIS)), and free androgen indices (FAI).

RESULTS

PCOS women had higher insulin secretion indices, hs-CRP, androgen, and FAI levels than controls without differing in baseline glucose, insulin and adipocytokines levels, insulin sensitivity, and resistance indices. In PCOS women, FAI levels correlated positively with baseline insulin, ΔAUCI, HOMA-IR, and ΔAUCG and negatively with G/I; hs-CRP levels correlated positively with ΔAUCI and negatively with ISI. PCOS status, waist circumference, and 17-hydroxyprogesterone (17-OHP) levels were positive predictors for ΔAUCI. In all women, waist circumference was a negative predictor for ISI; 17-OHP and FAI levels were positive predictors respectively for baseline insulin levels and for 1st PHIS and 2nd PHIS.

CONCLUSIONS

Early postmenopausal PCOS women are characterized by hyperinsulinemia but attenuated insulin resistance. PCOS status and waist circumference are predictors of hyperinsulinemia while insulin sensitivity correlates negatively with FAI. The differences reported in adipocytokine levels between PCOS and non-PCOS women in reproductive years seem to disappear after menopause.

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

INTRODUCTION

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

OBJECTIVES

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

DESIGN

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

RESULTS

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

Insulin resistance and the polycystic ovary syndrome revisited: an update on mechanisms and implications

Polycystic ovary syndrome (PCOS) is now recognized as an important metabolic as well as reproductive disorder conferring substantially increased risk for type 2 diabetes. Affected women have marked insulin resistance, independent of obesity. This article summarizes the state of the science since we last reviewed the field in the Endocrine Reviews in 1997. There is general agreement that obese women with PCOS are insulin resistant, but some groups of lean affected women may have normal insulin sensitivity. There is a post-binding defect in receptor signaling likely due to increased receptor and insulin receptor substrate-1 serine phosphorylation that selectively affects metabolic but not mitogenic pathways in classic insulin target tissues and in the ovary. Constitutive activation of serine kinases in the MAPK-ERK pathway may contribute to resistance to insulin's metabolic actions in skeletal muscle. Insulin functions as a co-gonadotropin through its cognate receptor to modulate ovarian steroidogenesis. Genetic disruption of insulin signaling in the brain has indicated that this pathway is important for ovulation and body weight regulation. These insights have been directly translated into a novel therapy for PCOS with insulin-sensitizing drugs. Furthermore, androgens contribute to insulin resistance in PCOS. PCOS may also have developmental origins due to androgen exposure at critical periods or to intrauterine growth restriction. PCOS is a complex genetic disease, and first-degree relatives have reproductive and metabolic phenotypes. Several PCOS genetic susceptibility loci have been mapped and replicated. Some of the same susceptibility genes contribute to disease risk in Chinese and European PCOS populations, suggesting that PCOS is an ancient trait.

PET imaging reveals distinctive roles for different regional adipose tissue depots in systemic glucose metabolism in nonobese humans

Excess amounts of abdominal subcutaneous (SAT) and visceral (VAT) adipose tissue (AT) are associated with insulin resistance, even in normal-weight subjects. In contrast, gluteal-femoral AT (GFAT) is hypothesized to offer protection against insulin resistance. Dynamic PET imaging studies were undertaken to examine the contributions of both metabolic activity and size (volume) of these depots in systemic glucose metabolism. Nonobese, healthy volunteers (n = 15) underwent dynamic PET imaging uptake of [¹⁸F]FDG at a steady-state (20 mU·m⁻²·min⁻¹) insulin infusion. PET images of tissue [¹⁸F]FDG activity were coregistered with MRI to derive K values for insulin-stimulated rates of fractional glucose uptake within tissue. Adipose tissue volume was calculated from DEXA and MRI. VAT had significantly higher rates of fractional glucose uptake per volume than SAT (P < 0.05) or GFAT (P < 0.01). K(GFAT) correlated positively (r = 0.67, P < 0.01) with systemic insulin sensitivity [glucose disappearance rate (R(d))] and negatively with insulin-suppressed FFA (r = -0.71, P < 0.01). SAT (r = -0.70, P < 0.01) and VAT mass (r = -0.55, P < 0.05) correlated negatively with R(d), but GFAT mass did not. We conclude that rates of fractional glucose uptake within GFAT and VAT are significantly and positively associated with systemic insulin sensitivity in nonobese subjects. Furthermore, whereas SAT and VAT amounts are confirmed to relate to systemic insulin resistance, GFAT amount is not associated with insulin resistance. These dynamic PET imaging studies indicate that both quantity and quality of specific AT depots have distinct roles in systemic insulin resistance and may help explain the metabolically obese but normal-weight phenotype.

Orchidectomy of middle-aged rats decreases liver deiodinase 1 and pituitary deiodinase 2 activity

Endogenous androgens are involved in regulation of thyroid function and metabolism of thyroid hormones. As serum testosterone level progressively declines with age, this regulation may change. We tested how androgen deprivation, achieved by orchidectomy, affects thyroid homeostasis in middle-aged rats. Fifteen-month-old Wistar rats were orchidectomized (Orx) or sham-operated under ketamine anesthesia (15 mg/kg body weight). Five weeks after the surgery, animals were decapitated. Thyroids were used for histomorphometric and ultrastructural examinations and together with livers and pituitaries for real-time quantitative PCR and deiodinase (DIO) activity measurements. Serum testosterone, TSH, l-thyroxine (T(4)), and cholesterol (Chol) levels were determined. As expected, middle-aged control rats had lower (P<0.05) testosterone and T(4) compared with 3-month-old males. In the Orx middle-aged group, we detected diminished serum testosterone (P<0.05), no change in TSH and T(4) levels, and higher Chol level (P<0.05), in comparison with age-matched controls. Histomorphometric analysis of thyroid tissue revealed decreased relative volume densities of follicles and colloid (P<0.05). Relevant gene expressions and DIO1 enzyme activity were not changed in the thyroids of Orx rats. Liver Dio1 gene expression and DIO1 activity were decreased (P<0.05) in comparison with the control values. Pituitary levels of TSHβ, Dio1, and Dio2 mRNAs did not change, while DIO2 activity decreased (P<0.05). In conclusion, orchidectomy of middle-aged rats affected thyroid structure with no effect on serum T(4) and TSH. However, decreased liver DIO1 and pituitary DIO2 enzyme activities indicate compensatory-adaptive changes in local T(3) production.

Effect of pregnancy for females born small on later life metabolic disease risk

There is a strong inverse relationship between a females own birth weight and her subsequent risk for gestational diabetes with increased risk of developing diabetes later in life. We have shown that growth restricted females develop loss of glucose tolerance during late pregnancy with normal pancreatic function. The aim of this study was to determine whether growth restricted females develop long-term impairment of metabolic control after an adverse pregnancy adaptation. Uteroplacental insufficiency was induced by bilateral uterine vessel ligation (Restricted) or sham surgery (Control) in late pregnancy (E18) in F0 female rats. F1 Control and Restricted female offspring were mated with normal males and allowed to deliver (termed Ex-Pregnant). Age-matched Control and Restricted Virgins were also studied and glucose tolerance and insulin secretion were determined. Pancreatic morphology and hepatic glycogen and triacylglycerol content were quantified respectively. Restricted females were born lighter than Control and remained lighter at all time points studied (p<0.05). Glucose tolerance, first phase insulin secretion and liver glycogen and triacylglycerol content were not different across groups, with no changes in β-cell mass. Second phase insulin secretion was reduced in Restricted Virgins (-34%, p<0.05) compared to Control Virgins, suggestive of enhanced peripheral insulin sensitivity but this was lost after pregnancy. Growth restriction was associated with enhanced basal hepatic insulin sensitivity, which may provide compensatory benefits to prevent adverse metabolic outcomes often associated with being born small. A prior pregnancy was associated with reduced hepatic insulin sensitivity with effects more pronounced in Controls than Restricted. Our data suggests that pregnancy ameliorates the enhanced peripheral insulin sensitivity in growth restricted females and has deleterious effects for hepatic insulin sensitivity, regardless of maternal birth weight.

MicroRNAs in pancreatic cancer metabolism

Advances in understanding the biology of tumour progression and metastasis have clearly highlighted the importance of aberrant tumour metabolism, which supports not only the energy requirements but also the enormous biosynthetic needs of tumour cells. Such metabolic alterations modulate glucose, amino acid and fatty-acid-dependent metabolite biosynthesis and energy production. Although much progress has been made in understanding the somatic mutations and expression genomics behind these alterations, the regulation of these processes by microRNAs (miRNAs) is only just beginning to be appreciated. This Review focuses on the miRNAs that are potential regulators of the expression of genes whose protein products either directly regulate metabolic machinery or serve as master regulators, indirectly modulating the expression of metabolic enzymes. We focus particularly on miRNAs in pancreatic cancer.

Sex hormone-binding globulin and type 2 diabetes mellitus

Sex hormone-binding globulin (SHBG) has emerged as one of the multiple genetic and environmental factors that potentially contribute to the pathophysiology of type 2 diabetes mellitus (T2DM). In addition to epidemiologic studies demonstrating a consistent relationship between decreased levels of serum SHBG and incident T2DM, recent genetic studies also reveal that transmission of specific polymorphisms in the SHBG gene influence the risk of T2DM. At the molecular level, the multiple interactions between SHBG and its receptors in various target tissues suggest physiologic roles for SHBG that are more complex than the simple transport of sex hormones in serum. Taken together, these data provide support for an expanded role of SHBG in the pathophysiology of insulin resistance and T2DM.

Melatonin supplementation therapy as a potent alternative to ERT in ovariectomized rats

AIM

To evaluate the efficacy of melatonin supplementation therapy as an alternative to estrogen replacement therapy in an ovariectomized rat model and to assess diabetogenic metabolic dysregulation caused by estrogen deficiency in postmenopausal individuals.

METHODS

Ovariectomized adult Wistar rats were treated with either estrogen/progesterone, melatonin or a combination of estrogen and melatonin. Body weight gain, feed efficiency, serum glucose, insulin, glucose tolerance and insulin response, serum and tissue lipids, tissue glycogen contents and activities of glycogen phosphorylase and glucose-6-phosphatase were analyzed in all the experimental groups.

RESULTS

Ovariectomized animals showed increased body weight gain, feed efficiency, fasting insulin resistance, greater area under curve for the glucose tolerance test, higher serum and tissue lipids and reduced glycogen content and insulin sensitivity. A low dose of melatonin was more efficient than estrogen in reversing all the ovariectomy-induced changes. The combination of estrogen + melatonin was found to be best in correcting glycemic dysregulation while high doses of melatonin could effectively regulate dyslipidemia.

CONCLUSION

The present study provides strong evidence for melatonin supplementation therapy to be more potent and effective in comparison to estrogen replacement therapy due to its single-handed ability to revert all the ovariectomy-induced changes. No reported side-effect or long-term effect of melatonin, against the known effects of estrogen replacement therapy, make it more attractive as a candidate to treat postmenopausal symptoms.

NAFLD, Estrogens, and Physical Exercise: The Animal Model

One segment of the population that is particularly inclined to liver fat accumulation is postmenopausal women. Although nonalcoholic hepatic steatosis is more common in men than in women, after menopause there is a reversal in gender distribution. At the present time, weight loss and exercise are regarded as first line treatments for NAFLD in postmenopausal women, as it is the case for the management of metabolic syndrome. In recent years, there has been substantial evidence coming mostly from the use of the animal model, that indeed estrogens withdrawal is associated with modifications of molecular markers favouring the activity of metabolic pathways ultimately leading to liver fat accumulation. In addition, the use of the animal model has provided physiological and molecular evidence that exercise training provides estrogens-like protective effects on liver fat accumulation and its consequences. The purpose of the present paper is to present information relative to the development of a state of NAFLD resulting from the absence of estrogens and the role of exercise training, emphasizing on the contribution of the animal model on these issues.

NAFLD, Estrogens, and Physical Exercise: The Animal Model

One segment of the population that is particularly inclined to liver fat accumulation is postmenopausal women. Although nonalcoholic hepatic steatosis is more common in men than in women, after menopause there is a reversal in gender distribution. At the present time, weight loss and exercise are regarded as first line treatments for NAFLD in postmenopausal women, as it is the case for the management of metabolic syndrome. In recent years, there has been substantial evidence coming mostly from the use of the animal model, that indeed estrogens withdrawal is associated with modifications of molecular markers favouring the activity of metabolic pathways ultimately leading to liver fat accumulation. In addition, the use of the animal model has provided physiological and molecular evidence that exercise training provides estrogens-like protective effects on liver fat accumulation and its consequences. The purpose of the present paper is to present information relative to the development of a state of NAFLD resulting from the absence of estrogens and the role of exercise training, emphasizing on the contribution of the animal model on these issues.

Coffee and caffeine consumption in relation to sex hormone-binding globulin and risk of type 2 diabetes in postmenopausal women

OBJECTIVE

Coffee consumption has been inversely associated with type 2 diabetes risk, but its mechanisms are largely unknown. We aimed to examine whether plasma levels of sex hormones and sex hormone-binding globulin (SHBG) may account for the inverse association between coffee consumption and type 2 diabetes risk.

RESEARCH DESIGN AND METHODS

We conducted a case-control study nested in the prospective Women's Health Study (WHS). During a median follow-up of 10 years, 359 postmenopausal women with newly diagnosed type 2 diabetes were matched with 359 control subjects by age, race, duration of follow-up, and time of blood draw.

RESULTS

Caffeinated coffee was positively associated with SHBG but not with sex hormones. Multivariable-adjusted geometric mean levels of SHBG were 26.6 nmol/l among women consuming ≥4 cups/day of caffeinated coffee and 23.0 nmol/l among nondrinkers (P for trend = 0.01). In contrast, neither decaffeinated coffee nor tea was associated with SHBG or sex hormones. The multivariable-adjusted odds ratio (OR) of type 2 diabetes for women consuming ≥4 cups/day of caffeinated coffee compared with nondrinkers was 0.47 (95% CI 0.23-0.94; P for trend = 0.047). The association was largely attenuated after further adjusting for SHBG (OR 0.71 [95% CI 0.31-1.61]; P for trend = 0.47). In addition, carriers of rs6259 minor allele and noncarriers of rs6257 minor allele of SHBG gene consuming ≥2 cups/day of caffeinated coffee had lower risk of type 2 diabetes in directions corresponding to their associated SHBG.

CONCLUSIONS

Our findings suggest that SHBG may account for the inverse association between coffee consumption and type 2 diabetes risk among postmenopausal women.

Intense electroacupuncture normalizes insulin sensitivity, increases muscle GLUT4 content, and improves lipid profile in a rat model of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is associated with hyperandrogenism and insulin resistance, possibly reflecting defects in skeletal muscle and adipocyte insulin signaling. Low-frequency (2 Hz) electroacupuncture (EA) increases insulin sensitivity in female rats with dihydrotestosterone (DHT)-induced PCOS, but the mechanism is unclear. We hypothesized that low-frequency EA regulates mediators involved in skeletal muscle glucose uptake and metabolism and alters the lipid profile in rats with DHT-induced PCOS. To test this hypothesis, we implanted in prepubescent female rats 90-day continuous-release pellets containing DHT (PCOS). At 70 days of age, the rats were randomly subdivided into two groups: one received low-frequency EA (evoking muscle twitches) for 20-25 min five times/wk for 4-5 wk; the other did not. Controls were implanted with pellets containing vehicle only. All three groups were otherwise handled similarly. Lipid profile was measured in fasting blood samples. Insulin sensitivity was determined by euglycemic hyperinsulinemic clamp, soleus muscle protein expression of glucose transporter 4 (GLUT4), and phosphorylated and nonphosphorylated Akt, and Akt substrate of 160 kDa was determined by Western blot analysis and GLUT4 location by immunofluorescence staining. PCOS EA rats had normalized insulin sensitivity, lower levels of total high-density lipoprotein and low-density lipoprotein cholesterol, and increased expression of GLUT4 in different compartments of skeletal muscle compared with PCOS rats. Total weight and body composition did not differ in the groups. Thus, in rats with DHT-induced PCOS, low-frequency EA has systemic and local effects involving intracellular signaling pathways in muscle that may, at least in part, account for the marked improved insulin sensitivity.

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

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

Genetic evidence that raised sex hormone binding globulin (SHBG) levels reduce the risk of type 2 diabetes

Epidemiological studies consistently show that circulating sex hormone binding globulin (SHBG) levels are lower in type 2 diabetes patients than non-diabetic individuals, but the causal nature of this association is controversial. Genetic studies can help dissect causal directions of epidemiological associations because genotypes are much less likely to be confounded, biased or influenced by disease processes. Using this Mendelian randomization principle, we selected a common single nucleotide polymorphism (SNP) near the SHBG gene, rs1799941, that is strongly associated with SHBG levels. We used data from this SNP, or closely correlated SNPs, in 27 657 type 2 diabetes patients and 58 481 controls from 15 studies. We then used data from additional studies to estimate the difference in SHBG levels between type 2 diabetes patients and controls. The SHBG SNP rs1799941 was associated with type 2 diabetes [odds ratio (OR) 0.94, 95% CI: 0.91, 0.97; P = 2 x 10(-5)], with the SHBG raising allele associated with reduced risk of type 2 diabetes. This effect was very similar to that expected (OR 0.92, 95% CI: 0.88, 0.96), given the SHBG-SNP versus SHBG levels association (SHBG levels are 0.2 standard deviations higher per copy of the A allele) and the SHBG levels versus type 2 diabetes association (SHBG levels are 0.23 standard deviations lower in type 2 diabetic patients compared to controls). Results were very similar in men and women. There was no evidence that this variant is associated with diabetes-related intermediate traits, including several measures of insulin secretion and resistance. Our results, together with those from another recent genetic study, strengthen evidence that SHBG and sex hormones are involved in the aetiology of type 2 diabetes.

Polycystic Ovary Syndrome, Obesity and Reproductive Implications

Polycystic ovary syndrome (PCOS) is one of the most common causes of female infertility, affecting 5–10% of women of reproductive age. The syndrome is characterized by anovulation, hyperandrogenism and polycystic ovaries. Furthermore, PCOS is associated with insulin resistance and obesity, which is present in approximately 50% of women with PCOS. Reproductive function in women with PCOS is strongly dependent on bodyweight and metabolic status. Obesity is associated with an increased risk of infertility and may also have a negative influence on pregnancy outcome. Considering the worldwide epidemic of obesity, clinical problems relating to PCOS may worsen and increase in frequency. Lifestyle interventions resulting in weight loss comprise the most successful strategy to improve symptoms of PCOS. However, many patients fail to lose weight or may quickly regain weight. It is an important challenge to develop effective lifestyle programs and adjuvant pharmacologic treatments in order to improve reproductive and metabolic health among women with PCOS.

Interrelation between sex hormones and plasma sex hormone-binding globulin and hemoglobin A1c in healthy postmenopausal women

BACKGROUND

Androgenicity, as measured by low sex hormone-binding globulin (SHBG) and elevations in testosterone and free androgen index (FAI), is associated with adverse cardiovascular (CV) outcomes, possibly due to effects on insulin resistance and glycemia.

METHODS

Glycosylated hemoglobin (HbA1c) concentration, SHBG, and sex hormones were available in 200 nondiabetic postmenopausal women who were not using hormone therapy (HT) in the Women's Health Study. Of these, 98 were cardiovascular disease (CVD) cases; the remainders were matched controls. To achieve normality, continuous values were log transformed and geometric means were calculated. Associations between sex hormones and HbA1c were examined using general linear models (GLM), partial correlations, and multiple linear regression analyses.

RESULTS

Lower SHBG levels and higher FAI and HbA1c values were found among the CVD cases, and all analyses were adjusted for this factor. In GLM, higher values of HbA1c were observed in the highest quartiles of FAI and the lowest quartiles of SHBG. However, the correlation between SHBG and HbA1c across quartiles was eliminated after adjusting for body mass index (BMI). In partial correlations, HbA1c values were inversely associated with SHBG (r = -0.19, P = 0.008) and positively associated with FAI (r = 0.19, P = 0.01), even after adjusting for age, CVD case-control status, and BMI. In multivariate models, a significant inverse association between SHBG and HbA1c persisted, as well as a significant positive association between FAI and HbA1c.

CONCLUSIONS

Androgenicity, as measured by low SHBG and high FAI, is associated with glycemia, and thereby may contribute to CVD risk in postmenopausal women.

Gender differences in insulin resistance, body composition, and energy balance

BACKGROUND

Men and women differ substantially in regard to degrees of insulin resistance, body composition, and energy balance. Adipose tissue distribution, in particular the presence of elevated visceral and hepatic adiposity, plays a central role in the development of insulin resistance and obesity-related complications.

OBJECTIVE

This review summarizes published data on gender differences in insulin resistance, body composition, and energy balance, to provide insight into novel gender-specific avenues of research as well as gender-tailored treatments of insulin resistance, visceral adiposity, and obesity.

METHODS

English-language articles were identified from searches of the PubMed database through November 2008, and by reviewing the references cited in these reports. Searches included combinations of the following terms: gender, sex, insulin resistance, body composition, energy balance, and hepatic adipose tissue.

RESULTS

For a given body mass index, men were reported to have more lean mass, women to have higher adiposity. Men were also found to have more visceral and hepatic adipose tissue, whereas women had more peripheral or subcutaneous adipose tissue. These differences, as well as differences in sex hormones and adipokines, may contribute to a more insulin-sensitive environment in women than in men. When normalized to kilograms of lean body mass, men and women had similar resting energy expenditure, but physical energy expenditure was more closely related to percent body fat in men than in women.

CONCLUSION

Greater amounts of visceral and hepatic adipose tissue, in conjunction with the lack of a possible protective effect of estrogen, may be related to higher insulin resistance in men compared with women.

Role of androgen excess on metabolic aberrations and cardiovascular risk in women with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is associated with a clustering of metabolic and cardiovascular risk factors. Insulin resistance is implicated as the major player in the metabolic abnormalities and contributes to the increased cardiovascular risk associated with the syndrome. However, androgen excess appears to participate as an independent parameter, which further aggravates the cardiovascular and metabolic aberrations in affected women with PCOS. The resultant impact of hyperandrogenemia possibly acquires clinical significance for women's health in the context of PCOS, particularly since recent data support an increased incidence of coronary artery disease and of cardiovascular events directly related to androgen levels in women with the syndrome.

Effect of testosterone on insulin stimulated IRS1 Ser phosphorylation in primary rat myotubes--a potential model for PCOS-related insulin resistance

Background

Polycystic ovary syndrome (PCOS) is characterized by a hyperandrogenic state and frequently develops skeletal muscle insulin resistance. We determined whether testosterone adversely affects insulin action by increasing serine phosphorylation of IRS-1^636/639 in differentiated rat skeletal muscle myotubes. The phosphorylation of Akt, mTOR, and S6K, downstream targets of the PI3-kinase-IRS-1 complex were also studied.

Methods

Primary differentiated rat skeletal muscle myotubes were subjected to insulin for 30 min after 16-hour pre-exposure to either low (20 ng/ml) or high (200 ng/ml) doses of testosterone. Protein phosphorylation of IRS-1 Ser^636/639, Akt Ser⁴⁷³, mTOR-Ser²⁴⁴⁸, and S6K-Thr³⁸⁹ were measured by Western blot with signal intensity measured by immunofluorescence.

Results

Cells exposed to 100 nM of insulin had increased IRS-1 Ser^636/639 and Akt Ser⁴⁷³ phosphorylation. Cells pre-exposed to low-dose testosterone had significantly increased insulin-induced mTOR-Ser²⁴⁴⁸ and S6K-Thr³⁸⁹ phosphorylation (p<0.05), and further increased insulin-induced IRS-1 Ser^636/639 phosphorylation (p = 0.042) compared to control cells. High-dose testosterone pre-exposure attenuated the insulin-induced mTOR-Ser²⁴⁴⁸ and S6K-Thr³⁸⁹ phosphorylation.

Conclusions

The data demonstrated an interaction between testosterone and insulin on phosphorylation of intracellular signaling proteins, and suggests a link between a hyperandrogenic, hyperinsulinemic environment and the development of insulin resistance involving serine phosphorylation of IRS-1 Ser^636/639. These results may guide further investigations of potential mechanisms of PCOS-related insulin resistance.

Modulation of insulin resistance in ovariectomized rats by endurance exercise training and estrogen replacement

Estrogen is known to play a role in fat metabolism, but its role in carbohydrate metabolism remains controversial. We investigated alterations in carbohydrate and fat metabolism after prolonged estrogen deprivation by determining body weight, food intake, visceral fat content, serum lipids, glucose tolerance, and insulin action on glucose transport activity in isolated soleus and extensor digitorum longus muscles. In addition, effects of endurance exercise training with or without estrogen replacement on metabolic alterations occurring under estrogen deficiency were examined. Female Sprague-Dawley rats were ovariectomized (OVX) or sham-operated (SHAM). The OVX rats remained sedentary, received 5 microg of 17beta-estradiol (E(2)), performed exercise training (ET), or underwent both estrogen treatment and exercise training (E(2) + ET) for 12 weeks. Compared with SHAM, OVX animals had greater final body weights, visceral fat content, and serum levels of total and low-density lipoprotein cholesterol (P < .05). Exercise training and E(2) significantly reduced body weights (6% and 25%), visceral fat (37% and 51%), and low-density lipoprotein cholesterol level (19% and 26%). Exercise training alone improved whole-body glucose tolerance (29%), which was enhanced to the greatest extent (51%) in the ET rats that also received E(2). Insulin-stimulated glucose transport activity in OVX group was lower than that in SHAM by 29% to 44% (P < .05). Exercise training and E(2) corrected the diminished insulin action on skeletal muscle glucose transport in OVX animals, which was partly due to elevated glucose transporter-4 protein expression. These findings indicate that 12 weeks of ovariectomy caused metabolic alterations mimicking features of the insulin resistance syndrome. Furthermore, these metabolic disturbances were attenuated by ET or E(2), whereas the beneficial interactive effects of ET and E(2) on these defects were not apparent.