Effect of chronically elevated androgen or estrogen on the glucose tolerance test and insulin response in female rhesus monkeys

Naturally Occurring and Experimentally Induced Rhesus Macaque Models for Polycystic Ovary Syndrome: Translational Gateways to Clinical Application

Indian rhesus macaque nonhuman primate models for polycystic ovary syndrome (PCOS) implicate both female hyperandrogenism and developmental molecular origins as core components of PCOS etiopathogenesis. Establishing and exploiting macaque models for translational impact into the clinic, however, has required multi-year, integrated basic-clinical science collaborations. Paradigm shifting insight has accrued from such concerted investment, leading to novel mechanistic understanding of PCOS, including hyperandrogenic fetal and peripubertal origins, epigenetic programming, altered neural function, defective oocytes and embryos, adipogenic constraint enhancing progression to insulin resistance, pancreatic decompensation and type 2 diabetes, together with placental compromise, all contributing to transgenerational transmission of traits likely to manifest in adult PCOS phenotypes. Our recent demonstration of PCOS-related traits in naturally hyperandrogenic (High T) female macaques additionally creates opportunities to employ whole genome sequencing to enable exploration of gene variants within human PCOS candidate genes contributing to PCOS-related traits in macaque models. This review will therefore consider Indian macaque model contributions to various aspects of PCOS-related pathophysiology, as well as the benefits of using macaque models with compellingly close homologies to the human genome, phenotype, development and aging.

Western-style diet, sex steroids and metabolism

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

Role of androgens in normal and pathological ovarian function

Androgens mediate their actions via the androgen receptor (AR), a member of the nuclear receptor superfamily. AR-mediated androgen action is essential in male reproductive development and function; however, only in the last decade has the suspected but unproven role for AR-mediated actions in female reproduction been firmly established. Deciphering the specific roles and precise pathways by which AR-mediated actions regulate ovarian function has been hindered by confusion on how to interpret results from pharmacological studies using androgens that can be converted into oestrogens, which exert actions via the oestrogen receptors. The generation and analysis of global and cell-specific femaleArknockout mouse models have deduced a role for AR-mediated actions in regulating ovarian function, maintaining female fertility, and have begun to unravel the mechanisms by which AR-mediated androgen actions regulate follicle health, development and ovulation. Furthermore, observational findings from human studies and animal models provide substantial evidence to support a role for AR-mediated effects not only in normal ovarian function but also in the development of the frequent ovarian pathological disorder, polycystic ovarian syndrome (PCOS). This review focuses on combining the findings from observational studies in humans, pharmacological studies and animal models to reveal the roles of AR-mediated actions in normal and pathological ovarian function. Together these findings will enable us to begin understanding the important roles of AR actions in the regulation of female fertility and ovarian ageing, as well as providing insights into the role of AR actions in the androgen-associated reproductive disorder PCOS.

Sex-specific differences in lipid and glucose metabolism

Energy metabolism in humans is tuned to distinct sex-specific functions that potentially reflect the unique requirements in females for gestation and lactation, whereas male metabolism may represent a default state. These differences are the consequence of the action of sex chromosomes and sex-specific hormones, including estrogens and progesterone in females and androgens in males. In humans, sex-specific specialization is associated with distinct body-fat distribution and energy substrate-utilization patterns; i.e., females store more lipids and have higher whole-body insulin sensitivity than males, while males tend to oxidize more lipids than females. These patterns are influenced by the menstrual phase in females, and by nutritional status and exercise intensity in both sexes. This minireview focuses on sex-specific mechanisms in lipid and glucose metabolism and their regulation by sex hormones, with a primary emphasis on studies in humans and the most relevant pre-clinical model of human physiology, non-human primates.

Diabetes and the female reproductive system

The insulin/insulin-like growth factor (IGF) pathways and glucose metabolism act as mediators of human ovarian function and female fertility. In normal insulin action, insulin binds to its own receptors in the ovary to mediate steroidogenesis and act as a co-gonadotropin. Insulin with other factors may influence ovarian growth and cyst formation. The IGF pathway also seems to influence normal ovarian function. Insulin signaling affects reproductive function. Dysregulation of this pathway leads to altered puberty, ovulation, and fertility. Better understanding of the normal physiology and pathophysiology of insulin, IGF, and glucose effects on the human reproductive system will allow for better outcomes.

Nonhuman primate models of polycystic ovary syndrome

With close genomic and phenotypic similarity to humans, nonhuman primate models provide comprehensive epigenetic mimics of polycystic ovary syndrome (PCOS), suggesting early life targeting for prevention. Fetal exposure to testosterone (T), of all nonhuman primate emulations, provides the closest PCOS-like phenotypes, with early-to-mid gestation T-exposed female rhesus monkeys exhibiting adult reproductive, endocrinological and metabolic dysfunctional traits that are co-pathologies of PCOS. Late gestational T exposure, while inducing adult ovarian hyperandrogenism and menstrual abnormalities, has less dysfunctional metabolic accompaniment. Fetal exposures to dihydrotestosterone (DHT) or diethylstilbestrol (DES) suggest androgenic and estrogenic aspects of fetal programming. Neonatal exposure to T produces no PCOS-like outcome, while continuous T treatment of juvenile females causes precocious weight gain and early menarche (high T), or high LH and weight gain (moderate T). Acute T exposure of adult females generates polyfollicular ovaries, while chronic T exposure induces subtle menstrual irregularities without metabolic dysfunction.

Age-related differences in the reproductive and metabolic implications of polycystic ovarian syndrome: findings in an obese, United States population

The objective of this study was to explore age-related differences in the reproductive and metabolic manifestations of polycystic ovarian syndrome (PCOS). Using a prospective cross-sectional design, we compared metabolic and reproductive findings in women attending a multidisciplinary clinic for PCOS, stratified across the following age groups: 18-25 (n = 71), 26-35 (n = 129), and 36-45 (n = 29). The study included primarily overweight and obese women, with a mean BMI of 31.1 in the entire study group. Older women had a decreased prevalence of biochemical hyperandrogenemia (p-trend: 0.0005). Of women meeting diagnostic criteria for PCOS, older women (n = 15) had larger median waist circumference and higher median diastolic blood pressure, total cholesterol, LDL cholesterol and fasting glucose compared to younger women (p-trend: 0.03, 0.01, 0.01, 0.01 and 0.06, respectively). The odds of metabolic syndrome for women ages 36-45 are increased four-fold relative to the younger groups (OR: 4.01; 95% CI: 1.04-15.4; p = 0.04). We conclude that there are significant age-related differences in both the clinical presentation and metabolic manifestations of PCOS.

Fetal, infant, adolescent and adult phenotypes of polycystic ovary syndrome in prenatally androgenized female rhesus monkeys

Old World monkeys provide naturally occurring and experimentally induced phenotypes closely resembling the highly prevalent polycystic ovary syndrome (PCOS) in women. In particular, experimentally induced fetal androgen excess in female rhesus monkeys produces a comprehensive adult PCOS-like phenotype that includes both reproductive and metabolic dysfunction found in PCOS women. Such a reliable experimental approach enables the use of the prenatally androgenized (PA) female rhesus monkey model to (1) examine fetal, infant and adolescent antecedents of adult pathophysiology, gaining valuable insight into early phenotypic expression of PCOS, and (2) to understand adult pathophysiology from a mechanistic perspective. Elevated circulating luteinizing hormone (LH) levels are the earliest indication of reproductive dysfunction in late gestation nonhuman primate fetuses and infants exposed to androgen excess during early (late first to second trimester) gestation. Such early gestation-exposed PA infants also are hyperandrogenic, with both LH hypersecretion and hyperandrogenism persisting in early gestation-exposed PA adults. Similarly, subtle metabolic abnormalities appearing in young nonhuman primate infants and adolescents precede the abdominal adiposity, hyperliplidemia and increased incidence of type 2 diabetes that characterize early gestation-exposed PA adults. These new insights into the developmental origins of PCOS, and progression of the pathophysiology from infancy to adulthood, provide opportunities for clinical intervention to ameliorate the PCOS phenotype thus providing a preventive health-care approach to PCOS-related abnormalities. For example, PCOS-like traits in PA monkeys, as in PCOS women, can improve with better insulin-glucose homeostasis, suggesting that lifestyle interventions preventing increased adiposity in adolescent daughters of PCOS mothers also may reduce their risk of acquiring many PCOS-related metabolic abnormalities in adulthood.

Normalization of hyperinsulinemia by chronic opioid receptor blockade in hyperandrogenemic women

OBJECTIVE

Evaluation of the effects of naltrexone on hyperinsulinemia and hyperandrogenemia in hyperandrogenemic, hyperinsulinemic women.

DESIGN

Controlled clinical study.

SETTING

Department of Gynecologic Endocrinology and Reproductive Medicine, Center of Obstetrics and Gynecology, Medical University of Innsbruck, Austria.

PATIENT(S)

Thirty-nine hyperandrogenemic, hyperinsulinemic women were studied.

INTERVENTION(S)

Women were treated with naltrexone (50 mg/d) for >or=3 weeks.

MAIN OUTCOME MEASURE(S)

Body mass index (BMI), gonadotropin (LH, FSH) and androgen (T, free T, DHEAS) levels, and plasma levels of glucose, insulin, and C-peptide, during a standard 75-g oral glucose tolerance test (OGTT), were determined before and during chronic opiate receptor blockade.

RESULT(S)

The BMI did not change during therapy. When OGTT was repeated after treatment with naltrexone, glucose levels were not different from those before treatment. Insulin response, however, had dramatically declined. We also observed a significant decrease in the levels of serum androgens.

CONCLUSION(S)

Hyperinsulinemia associated with hyperandrogenemia can be improved or completely abolished by chronic opiate receptor blockade. This observation suggests that endogenous opiates play a critical role in the process leading to hyperinsulinemia in hyperandrogenemia.

Effect of gonadotropin-releasing-hormone-induced hypogonadism on insulin action as assessed by euglycemic clamp studies in men

OBJECTIVE

In view of the relationship between hyperandrogenism and impaired insulin action in women with polycystic ovarian syndrome, we sought to investigate the effects of decreasing androgen levels on insulin action in men.

DESIGN

Prospective clinical study.

SETTING

University hospital.

PATIENT(S)

Ten normal healthy men.

INTERVENTION(S)

GnRH agonist, 3.75 mg monthly for 3 months.

MAIN OUTCOME MEASURE(S)

Rate of glucose uptake, serum insulin, and glucose levels.

RESULT(S)

GnRH treatment caused a significant fall in circulating testosterone levels, from 572 +/- 58 ng/dL to 178 +/- 66 ng/dL (P<.05). However, as assessed by euglycemic hyperinsulinemic clamp studies, there was no significant change in glucose uptake.

CONCLUSION(S)

In normal men, administration of a GnRH analogue was associated with a decrease in testosterone levels but not in insulin action.

Sex hormones, insulin sensitivity, and diabetes mellitus

Sex differences and the role of gonadal hormones in modulating insulin sensitivity and glucose tolerance are of increasing interest and importance because of the increasing prevalence of type 2 diabetes mellitus and the metabolic abnormalities associated with aging. Body composition is closely associated with insulin sensitivity, and increased body fat, particularly in the visceral compartment, is a risk factor for developing type 2 diabetes mellitus. Sex differences in body composition and/or insulin sensitivity are evident in humans throughout the lifespan. Ovarian hormones influence insulin sensitivity across the menstrual cycle, during pregnancy, and in the menopausal transition. Similarly, estrogens and progestins used for contraception and hormone replacement therapy affect glucoregulation. Nonhuman primates and humans have similar life histories and reproductive characteristics. As a result, nonhuman primates provide a valuable model for investigating factors related to insulin sensitivity. Studies of nonhuman primates have contributed significantly to our understanding of sex differences and the influence of sex steroids in this context. This brief review surveys present knowledge of the sex differences in body composition, insulin sensitivity, and risk for development of type 2 diabetes mellitus derived from studies in humans and nonhuman primates. The influences of endogenous and exogenous gonadal steroids are emphasized.

Testosterone effect on insulin content, messenger ribonucleic acid levels, promoter activity, and secretion in the rat

Coexistence of hyperinsulinemia and hyperandrogenism in women has been frequently described. Most of the studies addressing this issue have focused on the mechanisms by which insulin produces hyperandrogenism. In the present study, we analyzed the effects of testosterone in vivo and in vitro upon insulin gene expression and release in the rat. Our studies demonstrate that testosterone increases insulin messenger RNA (mRNA) levels in vitro as well as in vivo. In both prepuberal and intact adult rats, serum testosterone concentrations were positively correlated with insulin mRNA levels and insulin concentration in serum. Testosterone deprivation after gonadectomy decreased both insulin gene expression and serum insulin concentration. Insulin mRNA levels were partially restored after 3 days of testosterone administration and serum insulin was 80% and 27% above baseline values at 5 and 7 days posttreatment. Primary cultured pancreatic islets treated with the sexual steroid increased about 80% insulin mRNA, as well as protein, and release. In transfected islets, testosterone increased the activity of the -410 bp rat insulin promoter I by 154%. These data demonstrate that testosterone has a direct effect upon pancreatic islet function by favoring insulin gene expression and release.

Hyperinsulinism and its interaction with hyperandrogenism in polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in women of reproductive age. It has become increasingly evident that insulin resistance plays a significant role both as a cause and result of the syndrome. The purpose of this review is to summarize the possible mechanisms leading to insulin resistance and resultant hyperinsulinism (HI) and their interaction with hyperandrogenism (HA) in PCOS. We conducted a computerized search of MEDLINE for relevant studies in the English literature published between January 1966 and January 2000. We reviewed all studies that investigated the roles of insulin, insulin receptor, and insulin gene in insulin resistance and its interaction with hyperandrogenism in PCOS. Insulin resistance in PCOS seems to involve a postbinding defect in the insulin receptor and/or in the receptor signal transduction. Current research has focused on identifying a genetic predisposition for insulin resistance in this syndrome. The answer to the question whether HI or HA is the initiating event is still unclear inasmuch as there are clinical and molecular evidences to support both of these approaches. Our view is that whichever is the triggering insult, a vicious cycle is established where HI acts to aggravate HA and vice versa. In this model, obesity and genetic predisposition seem to be the independent factors that can give rise or contribute to HI, HA, or both simultaneously. It seems that "hyperinsulinemic hyperandrogenism" represents a significant subgroup of PCOS, which probably needs to be renamed and reclassified in the light of this new approach.

Insulin sensitivity and antiandrogenic therapy in women with polycystic ovary syndrome

Polycystic ovary (PCO) syndrome is strongly associated with insulin resistance and the accompanying adverse metabolic profile. To distinguish the mechanisms of this association, we determined the interactions of PCO with obesity and the influence of ameliorating direct androgenic actions via short-term treatment with the antiandrogen flutamide. Insulin sensitivity was determined by the hyperinsulinemic euglycemic clamp in groups of lean and obese PCO women and weight-matched controls. Compared with control values, insulin-mediated glucose utilization in PCO women was significantly lower in lean (1.96 +/- 0.17 v 1.24 +/- 0.10, P < .01) and obese (1.23 +/- 0.18 v 1.03 +/- 0.09 mmol/m2/min, P < .01) subjects. ANOVA indicated that the effects of obesity and androgenicity are independent and additive. In both lean and obese PCO women, treatment with flutamide for 1 or 3 months markedly improved the clinical and biochemical androgenic features, but did not significantly influence the overall insulin sensitivity. A large disparity between individuals in the response to treatment correlated significantly with a simultaneous reduction in plasma levels of dehydroepiandrosterone sulfate (DHEA-S). Thus in women, PCO and obesity exert synergistic effects on insulin resistance. The decreased insulin sensitivity is mediated via indirect androgenic actions or nonandrogenic mechanisms. In some individuals, a direct effect of androgens might have been masked by a decrease in DHEA-S levels.

The use of the intravenous glucose tolerance test to evaluate nonobese hyperandrogenemic women

To better define the association of hyperandrogenemia and insulin resistance, we evaluated nonobese, nonacanthotic hyperandrogenemic women utilizing intravenous glucose tolerance tests (IVGTT). Six women (group 1) all of whom had elevated serum testosterone (T) and were less than 5% above their ideal body weight for height underwent IVGTTs. A control group (group 2, n = 5) with equivalent weight and height but normal levels of T were similarly tested. The T values (normal 0.1 to 0.6 ng/mL) in group 1 (0.93 +/- 0.05 ng/mL, mean +/- SEM) were significantly different from those in group 2 (0.34 +/- 0.03 ng/mL). Area under the curve (AUC) was calculated for the glucose and insulin values. The glucose AUC for group 1 (15,000 +/- 1,100) was not significantly different from the glucose AUC for group 2 (15,853 +/- 788). Interestingly, the insulin AUC for group 1 (3,829 +/- 583) was not significantly different from the insulin AUC for group 2 (2,987 +/- 456). Within group 1, a correlation between serum T and insulin AUC could not be established. We conclude that in these nonobese, nonacanthotic hyperandrogenemic females, although individual variation exists, collectively a significantly increased insulin response to an IVGTT challenge cannot be demonstrated. This data further challenges the concept of androgens being etiologic in insulin resistance.

Effects of parenteral testosterone administration on insulin action in perfused hindlimb muscle of female rats

The effects of 14 days of testosterone (T) administration (1 mg/kg/d) on insulin-regulated phenylalanine release and glucose uptake by perfused hindquarters of intact and ovariectomized (OVX) female rats were studied. Results were compared with control groups that did not receive T. In the absence of exogenous insulin, T treatment significantly suppressed phenylalanine release (an index of net protein degradation) from hindquarters of intact and OVX rats below that of the intact control group (P less than .01). In perfusions containing insulin (100 or 500 microU/mL), phenylalanine efflux from intact and OVX control hindquarters was significantly lower as compared with hindquarters perfused without exogenous insulin (P less than .01). Insulin also reduced the phenylalanine release by T-treated groups to the efflux rates of control rats perfused at the same insulin concentration. Basal glucose uptake by perfused hindquarters was similar in all four treatment groups. In perfusions containing 100 or 500 microU insulin/mL, glucose uptake by hindlimbs of intact and OVX control rats was increased 2.7-fold and 5-fold, respectively, above that observed in perfusions without insulin (P less than .01). T treatment did not alter glucose uptake by perfused hindquarters in the absence or presence of insulin under these experimental conditions. The results of these studies suggest that T has anabolic effects on skeletal muscle that are independent of exogenous insulin action.