Spotted hyaenas and the sexual spectrum: reproductive endocrinology and development

The spotted hyaena (Crocuta crocuta) is a unique species, even amongst the Hyaenidae. Extreme clitoral development in female spotted hyaenas challenges aspects of the accepted framework of sexual differentiation and reproductive function. They lack a vulva and instead urinate, copulate and give birth through a single, long urogenital canal that traverses a clitoris superficially resembling a penis. Recent and historical evidence is reviewed to describe our changing understanding of the biology of this species. Expanding upon observations from hyaenas in nature, much has been learned from studies utilising the captive colony at the University of California, Berkeley. The steroid environment of pregnancy is shaped by placental androgen and oestrogen secretion and a late gestational increase in sex hormone binding globulin, the regulated expression and steroid-binding characteristics of which are unique within the Hyaenidae. While initial external genital development is largely free of androgenic influence, the increase in testosterone concentrations in late gestation influences foetal development. Specifically, anti-androgen (AA) treatment of pregnant females reduced the developmental influence of androgens on their foetuses, resulting in reduced androstenedione concentrations in young females and easier birth through a 'feminised' clitoris, but precluded intromission and mating by 'feminised' male offspring, and altered social interactions. Insight into the costs and benefits of androgen exposure on spotted hyaena reproductive development, endocrinology and behaviour emphasises the delicate balance that sustains reproductive success, forces a re-evaluation of how we define masculine vs feminine sexual characteristics, and motivates reflection about the representative value of model species.

The imbalance of sex-hormones related to depressive symptoms in obese men

Obese men may present hypogonadothrofic hypogonadism, mainly related to higher insulinemia and aromatase activity. Our objectives were to evaluate the relationship of sex-hormones profiles and frequency of depressive symptoms in 43 obese men, in a cross-sectional study. They had 19-60 years, and body mass index 30-50 kg/m(2). LH, total and free testosterone (TT and FT), estradiol (E2), sex hormone binding globulin, estradiol/total testosterone ratio (E2/T) were analyzed. Depressive symptoms were evaluated by "beck depression inventory" (BDI), and significant depression was considered if BDI ≥ 16.Thirty-four (80%) presented low TT levels, but only 4 (14%) had low free testosterone and hypogonadism symptoms; 12 of 43 (28%) presented increased E2. Forty five (56%) presented depressive symptoms, but 16 (28% of the 45) had significant depression. BDI correlated positively with E2 (r = 0.407; p = 0.001) and E2/T (r = 0.473; p = 0.001), but not TT or FT. Patients with significant depressive showed higher levels of estradiol (136 ± 48 versus 103 ± 48 pg/ml, p = 0.02) and E2/T (16.0 ± 9.9 versus 9.8 ± 4.6; p = 0.002) (mean ± SD).In conclusion, obese men may present relatively excess of estradiol and deficiency in testosterone, leading to an imbalance between these two hormones. The greater this imbalance, the more depressive symptoms had our patients.

Menopausal obesity and metabolic syndrome - PolSenior study

Obesity is a common problem and its health consequences depend on the phenotype of obesity. Clinical aspects of three phenotypes of obesity: upper body (visceral), lower body (healthy) and metabolic obesity with normal weight are discussed. The PolSenior study and other data show that the incidence of obesity increases during hormonal climacteric transformation with special emphasis on visceral (72%) and metabolic obesity with normal weight (16%). The etiology of menopausal obesity and fat redistribution with an increase incidence of menopausal metabolic syndrome is presented. The role of sex hormones and SHBG of fat mass and fat distribution in postmenopausal women is discussed on the basis of PolSenior study. The diagnostic-therapeutic algorithm for climacteric women is recommended according to cardiovascular diseases risk (CVD), elevated waist circumference, serum triglicerides, decreased HDL cholesterol, elevated fasting glucose, HOMA over 1.69 and BP over 130/80 mmHg. In women with CVD risk factors the metformin therapy is a golden standard.

Potential role of tumor necrosis factor-α in downregulating sex hormone-binding globulin

Low plasma sex hormone-binding globulin (SHBG) levels are associated with obesity and predict the development of type 2 diabetes. The reason why obese individuals have low circulating SHBG has been attributed to hyperinsulinemia, but no mechanistic evidence has been described. The aim of the current study is to explore whether tumor necrosis factor-α (TNF-α) rather than insulin could be the main factor accounting for low SHBG levels in obesity. We performed in vitro and in vivo studies using human HepG2 cells and human SHBG transgenic mice. In addition, a cross-sectional study to explore the relationship between TNF-α and SHBG in obese patients and an interventional study to examine the effect of insulin administration on circulating SHBG in type 2 diabetic patients were performed. We provide evidence that TNF-α, but not insulin, is the main factor by which SHBG is reduced in obesity. Plasma SHBG was significantly increased rather than decreased after insulin treatment in diabetic patients. TNF-α-induced reduction of SHBG expression was mediated by downregulating HNF4A. Finally, a negative and independent correlation was found between plasma TNF-α receptor 1 and SHBG levels in obese patients. Our results suggest that TNF-α plays an important role downregulating SHBG in chronic low-grade inflammatory diseases such as obesity and type 2 diabetes.

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.

Endocrinology of the aging male

The endocrinology of the aging male is complex, with multiple hormones along the hypothalamic-pituitary-testicular (HPT) axis interacting with one another in feedback. As men age, there is a small and progressive (not precipitous, as in women) decline in several sex hormones, in particular testosterone and dehydroepiandrosterone, and related increases in luteinizing hormone, follicle-stimulating hormone, and sex hormone-binding globulin. The importance of these changes is wide-ranging because of the ubiquitous role of sex hormones in male physiology. This chapter discusses the endocrinology of the aging male. We provide an overview of the regulation of the HPT axis with an emphasis on the changes that occur with aging and the measurement of gonadal steroids, including hormone pulsatility, within-subject and circadian variations. The difficulties of assessing the symptoms of late-onset hypogonadism are highlighted. There is a comprehensive discussion of the epidemiology of sex hormone changes, including their age associations, prevalence of symptomatic hypogonadism, secular changes, risk factors, and the association of sex hormones with outcomes.

Sex hormone-binding globulin genetic variation: associations with type 2 diabetes mellitus and polycystic ovary syndrome

Sex hormone-binding globulin (SHBG) is the primary plasma transport protein for sex steroid hormones and regulates the bioavailability of these hormones to target tissues. The gene encoding SHBG is complex and any of several polymorphisms in SHBG have been associated with alterations in circulating SHBG levels. Epidemiological studies have revealed that low plasma SHBG levels are an early indicator of insulin resistance and predict the development of type 2 diabetes mellitus (T2DM) in both men and women. Although associations between low SHBG levels and risk of diabetes could be explained by the observation that elevations in insulin suppress hepatic SHBG production, recent studies documenting that the transmission of SHBG-altering polymorphisms are associated with risk of T2DM suggest that SHBG may have a more direct physiologic role in glucose homeostasis. However, the exact mechanism(s) underlying this association is not known. Non-diabetic women with the polycystic ovary syndrome (PCOS), a common endocrine disorder that is associated with insulin resistance, similarly demonstrate lower levels of SHBG. In light of studies investigating polymorphisms in SHBG and T2DM, our group and others have hypothesized that SHBG may represent a candidate gene for PCOS. In this manuscript, we review studies investigating the association between SHBG polymorphisms and PCOS. In summary, multiple studies in women with PCOS confirm that certain genetic polymorphisms are associated with circulating SHBG levels, but they are not consistently associated with PCOS per se.

[The influence of testosterone on cardiovascular disease in men]

The influence of testosterone on cardiovascular disease is recently discussed question. Testosterone modulates vascular reactivity by genomic and nongenomic modes of action, it has an impact on endothelial function, production of proinflamatory cytokines and lipid profiles. The possible role of sex hormone binding globulin (SHBG) in androgen action by plasmatic membrane receptors breaks "the free hormone hypothesis", especially when clinical trials reveal strong association between SHBG and risk factors of cardiovascular disease. The results of last clinical trials mention that androgen deficiency is associated with obesity, insulin resistance and dyslipidaemia. Large clinical trials demonstrated that androgen deficiency predict mortality in elderly men. Testosterone substitution restores vasoreactivity and endothelial function and could potentially reduce cardiovascular disease in men but to confirm this theory more large clinical trials are needed.

Testosterone and type 2 diabetes

PURPOSE OF REVIEW

To describe the relationship between testosterone levels and type 2 diabetes (T2D).

RECENT FINDINGS

Multiple epidemiological studies have shown that low testosterone levels are associated with and predict the future development of T2D and the metabolic syndrome. Although this relationship is confounded by the association of total testosterone with sex hormone-binding globulin, free testosterone remains associated with measures of insulin resistance and T2D in some, but not all studies. Although the link between low testosterone levels and insulin resistance is not solely a consequence of adiposity, current studies suggest that a substantial component is mediated through its association with body fat, in particular abdominal visceral adipose tissue. This testosterone-fat relationship is bi-directional, as both weight loss and testosterone therapy increase testosterone levels, reduce fat mass, and decrease insulin resistance.

SUMMARY

Low testosterone levels are very commonly found in men with T2D and are associated with aging and obesity. Whether testosterone treatment in men with T2D decreases insulin resistance above that attributable to its fat-reducing effect is currently unknown. Future studies should compare testosterone treatment with lifestyle changes (exercise and weight loss measures), and other insulin-sensitizing agents. Until further evidence is available, testosterone therapy outside clinical trials should be reserved for diabetic men with unequivocal hypogonadism.

Sex hormone-binding globulin in osteoporosis

Sex hormone-binding globulin (SHBG) is a plasma glycoprotein that binds with high affinity to sex steroids, most notably 5alpha-dihydrotestosterone, testosterone, and 17beta-estradiol, thereby regulating their bioavailability and access to target cells. SHBG modulates the sex-steroid signaling system by binding to a specific membrane receptor (SHBG-R). Plasma SHBG levels vary in health and disease due to the effects of multiple regulation factors (age, body weight, sex steroids, insulin, and others). SHBG is involved in a number of diseases, including osteoporosis. Several studies found an inverse correlation between serum SHBG levels and bone mineral density in both males and females. SHBG levels may predict a number of macro-architectural characteristics of cortical bone. Weaker links have been reported between SHBG and bone turnover markers. Finally, high SHBG levels predict the occurrence of osteoporotic fractures of the vertebras and peripheral bones, most notably the proximal femur. Together with estradiol, SHBG plays a key role in the genesis of bone loss and osteoporotic fractures. Given that serum SHBG elevation is associated with the occurrence of multiple fractures, determination of the serum SHBG level, which can be readily performed in everyday clinical practice, may constitute a useful new marker for predicting the severity of osteoporosis.

Sex steroids and the male skeleton: a tale of two hormones

Traditionally, the stronger male skeleton was considered to result from higher androgen levels in men compared to women. However, the regulation of male bone growth by sex steroids appears more complex than originally anticipated. Based on clinical observations and studies in animal models, not only androgens and androgen receptor (AR), but also estrogens and estrogen receptor-alpha (not ERbeta) are required for optimal bone mineral acquisition during male growth. In addition, both sex steroids are involved in the maintenance of male skeletal health. In fact, bone loss and fracture risk have been associated with estrogen exposure in elderly men. Overall, a compelling body of evidence suggests that both androgens and estrogens are crucial for male skeletal growth and maintenance.

Intracellular sex hormone-binding globulin (SHBG) in normal and neoplastic breast tissue--an additional marker for hormone dependency?

Recent studies indicate that in addition to free diffusion, uptake of sex hormones into target cells is mediated by sex hormone-binding globulin (SHBG). The purpose of this study was to investigate localization and distribution of SHBG in normal and neoplastic breast tissue. We examined 31 normal, 21 non-invasive, 52 invasive breast cancer tissues and 33 cases of recurrences and metastases of breast cancer immunohistochemically for SHBG by the ABC-peroxidase method, using a polyclonal, monospecific antiserum derived from rabbit. The proportion of stained cells was evaluated semiquantitatively. In 81 malignant cases the oestrogen receptor (ER) content was evaluated by the ER-ICA method. Positive staining for SHBG was found exclusively in epithelial cell cytoplasm. Benign tissue was focally SHBG-positive and showed more stained cells in proliferating epithelium. Staining of neoplastic tissue was more heterogeneous. Half of the non-invasive carcinomas were SHBG-positive; particularly the highly differentiated. Independent of subtype and differentiation, invasive tumours were SHBG-negative in 32.5% of cases, while 19.3% were SHBG-positive in most cells. In 13 cases of invasive carcinomas, associated intraductal parts showed more staining for SHBG than the invasive tissue. Recurrences and metastases of breast cancer were SHBG-negative in 45.5% of cases, while only 3% were positive in most cells. SHBG-staining was unrelated to ER content. These results suggest that the demonstration of cytoplasmic SHBG represents a physiological feature of breast epithelium and its presence is compatible with a mechanism for cellular uptake of SHBG-bound sex hormones preceding their interaction with nuclear receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Sex hormone binding globulin and aging

New and more active concepts of steroid binding globulin action are emerging from recent research. As a result, examination of steroid levels in aging humans and the role of steroid binding globulins need to be re-visited. This review will discuss the possibility that sex hormone binding globulin (SHBG) plays an active role in the aging process. It will discuss the changes in blood levels of SHBG in aging humans in association with sexual activity, prostate hypertrophy and cancer, uterine leiomyoma, breast cancer, obesity and particularly the relationship between SHBG and HDL-cholesterol, Alzheimer's disease, osteoporosis, and cardiovascular disease. Starting with the idea that SHBG is an active participant in steroid action demands a re-evaluation of data demonstrating a primary change in blood SHBG levels in association with various pathologies. Here we discuss the postulate that SHBG may act at its own receptor at the plasma membrane level to influence other receptors such as scavenger receptors and HDL-cholesterol receptors. We will also suggest that SHBG is a critical marker for mating and thus may be an important physiological molecule in control of aging.

Hormonal profiles behind the heart of a man

This study focuses on the role of sex steroids on the libido, sexual life, emotional and physiological heart of men of all ages. Sex steroids play a significant role throughout a man's life, with a gradual decline in old age. The foetal testis secretes testosterone and dehydroepiandrosterone at about nine weeks gestation. At puberty, testosterone increases dramatically in boys. Changes in weight and height of boys across this period are associated with increasing testosterone concentration and sex hormone binding globulin (SHBG). Romantic thoughts, fantasy, and sexual pleasure-seeking behaviour in adolescents are associated with exposure to high androgens secretion. Thus, the libido and sexual life of a man is initiated and maintained by testosterone and SHBG. Lower testosterone levels are associated with erectile dysfunction among other risk factors: diabetes, hypertension, heart disease, psychological stress and obesity. Men with proven coronary atherosclerosis have lower levels of testosterone and SHBG, which have negative correlation with very low-density lipoprotein, triglycerides, body mass index and body fat mass. These are some of the risk factors for cardiovascular diseases. Thus, in men, endogenous sex steroids impart beneficial effects on the heart. How exactly endogenous sex steroids act on the heart is not clear. Further study is needed to understand the interaction between endogenous sex steroids, higher centers in the brain and the heart of a man.

Sex hormone-binding globulin in fish gills is a portal for sex steroids breached by xenobiotics

As in most vertebrates, plasma sex hormone-binding globulin (SHBG) is produced in fish liver and regulates sex steroid access to target tissues. Low levels of SHBG mRNA are present in zebra fish gills but are unlikely to account for the high amounts of immunoreactive SHBG in filaments and lamellae. Although the uptake of steroids by fish from water has been reported to correlate with their affinity for SHBG, it is not known how this occurs. Our studies of zebra fish SHBG have revealed its preference for biological active androgen (testosterone), as well as for androstenedione, a sex steroid precursor that also acts as a pheromone in some fish. In addition to natural steroids, zebra fish SHBG has a high affinity for synthetic steroids, such as ethinylestradiol and progestins (levonorgestrel and norethindrone), that are present in waste water systems. Because steroids can pass across fish gills, we examined whether SHBG serves as a portal for natural and synthetic steroids controlling their flux between the blood and aquatic environment. The results indicate that SHBG ligands are rapidly and specifically removed from water by the fish through their gills, whereas the accumulated steroids are released slowly. The capacity of fish to sequester SHBG ligands from water is similar between sexes, independent of size, and characterized by a wide dynamic range. We conclude that SHBG controls the flux of sex steroids across fish gills and that this highly specialized function can be hijacked by xenobiotic ligands of fish SHBGs.

Role of sex hormone-binding globulin in the relationship between sex hormones and antisocial and aggressive personality in inmates

Plasma total testosterone (TT), free bioavailable testosterone (BT), sex hormone-binding globulin (SHGB), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) were analysed in a sample of 89 inmates. Also, the tendency towards an Antisocial Personality Disorder (AAPS) and Aggressiveness (based on an index containing three scales of the Buss-Durkee Hostility Inventory; BDHI) was assessed. Results showed strong correlations between SHBG, total testosterone and free bioavailable testosterone. SHBG and total testosterone correlated with Aggressiveness (0.39 and 0.29, respectively), though the latter turned out not to be significant when SHBG level was controlled. The group with a high probability of Antisocial Personality Disorder and the group with high scores in Aggressiveness obtained higher SHBG levels. Recidivists and subjects already sentenced presented higher concentrations of SHBG. No significant relation was found for the free bioavailable testosterone. It is argued that the relationship between testosterone and antisocial personality and aggressiveness is mediated by the role of SHBG. We conclude that subjects with a disinhibited life-style tend to abuse intoxicants affecting the production of SHBG in the liver. This effect is observed in healthy subjects and delinquents, but more strongly in the population of delinquents.

Relationship between androgen levels and blood pressure in young women with polycystic ovary syndrome

The role of testosterone on the development of hypertension is controversial, especially in women with polycystic ovary syndrome (PCOS) who have higher prevalence of obesity and insulin resistance than women without PCOS. Little is known about the association between serum testosterone level and blood pressure in young women with PCOS. In the 151 young Taiwanese women with PCOS enrolled in this cross-sectional study, we measured the body mass index, waist circumference, blood pressure, fasting glucose, fasting insulin, lipid profile, and hormone profiles. The free androgen index, total testosterone, and sex hormone-binding globulin, but not the level of dehydroepiandrosterone sulfate, significantly correlated with both systolic blood pressure (SBP) and diastolic blood pressure (DBP). In multiple linear regression models adjusted for age, body mass index, and other anthropometric, metabolic, and hormonal variables, the level of serum free androgen index or total testosterone, but not the sex hormone-binding globulin, were independently related to SBP and DBP. The age- and body mass index-adjusted least-square mean of serum-free androgen index levels were significantly different between the highest quartile and other quartiles of the SBP and DBP levels. The high bioavailable testosterone levels (free androgen index: >or=19%) in women with PCOS increased the risk of elevated blood pressure (SBP >or=130 mm Hg and/or DBP >or=85 mm Hg) with an odds ratio of 3.817 (P=0.029; 95% CI: 1.14 to 12.74) after adjustment for age, anthropometric measures, and metabolic profiles. Our results suggest that the characteristic hyperandrogenemia in young women with PCOS was associated with an elevated SBP and DBP independent of age, insulin resistance, obesity, or dyslipidemia.

Molecular epidemiology of prostate cancer: hormone-related genetic loci

Prostate cancer is the most common non-skin cancer and the second leading cause of cancer deaths among men in most Western countries. Despite its high morbidity and mortality, the etiology of prostate cancer remains obscure. Although compelling laboratory data suggest a role for androgens in prostate carcinogenesis, most epidemiologic data, including serological and genetic studies, are inconclusive. In this chapter, we review the status of serologic studies and discuss the importance of intra-prostatic hormone levels in possibly clarifying the often-contradictory data on serologic studies. To provide insights and directions for epidemiologic research on hormones and prostate cancer, this review centers on the molecular epidemiology of hormone-related genetic loci. These loci have been investigated in a number of studies to date and will undoubtedly expand even further as rich new genetic information sources and high-throughput genotyping and analysis methods become available. Due to the enormous number of these loci, we recommend careful analysis and cautious interpretation of studies of genetic markers, including microsatellites and single nucleotide polymorphisms (SNPs), as false positive and negative results are likely due to limited statistical power, multiple hypothesis testing, population stratification, or non-representative population sampling. This review also highlights the need for replication in various populations, as well as reasons for performing functional analyses of SNPs, a critical and often under-appreciated component of molecular epidemiologic investigations. The time is ripe for concerted, large-scale multidisciplinary investigations that incorporate molecular genetics, biochemistry, histopathology, and endocrinology into traditional epidemiologic studies. Such collaboration will lead to a deeper understanding of the etiologic pathways of prostate cancer, ultimately yielding better preventive, diagnostic, and therapeutic strategies.

Hypogonadism in male patients with cancer

BACKGROUND

Patients with cancer often develop anorexia, fatigue, and decreased muscle mass. These signs and symptoms are nonspecific, and they frequently occur in other conditions, including hypogonadism.

METHODS

The objectives of this study were 1) to measure testosterone levels in patients with cancer and 2) to examine the correlations between testosterone, tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), insulin-like growth factor-1 (IGF-1), ghrelin levels, and appetite in patients with cancer patients and in a noncancer control group. This was designed as a cross-sectional study in the setting of a university-affiliated Veterans Affairs Medical Center. The study population included 31 male patients with cancer and 25 gender-matched noncancer controls of similar age. The variables total testosterone (TT), calculated free testosterone (cFT), calculated bioavailable testosterone (cBT), sex hormone-binding globulin (SHBG), luteinizing hormone (LH), TNF-alpha, IL-6, IGF-1, and active ghrelin were measured in fasting morning plasma samples. Appetite was measured according to a visual analog scale. The main outcome measures were cFT and cBT.

RESULTS

Cancer patients had mean TT levels similar to levels in the noncancer control group but significantly lower levels of cFT, cBT, IGF-1, and appetite. SHBG, LH, TNF-alpha, IL-6, and ghrelin levels were increased in patients with cancer compared with the control group. cFT and cBT levels were correlated inversely with IL-6 and ghrelin levels and were correlated directly with IGF-1 levels and appetite.

CONCLUSIONS

Patients with cancer had lower levels of biologically active testosterone. TT was not adequate for the evaluation of hypogonadism, because SHBG levels were increased. A reliable measurement of FT and/or BT should be used. LH was elevated in the patients with cancer, indicating that low FT levels were caused by primary testicular dysfunction. The authors postulated that high IL-6 or ghrelin levels inhibit testosterone synthesis, although a secondary effect at the hypothalamic-pituitary levels cannot be excluded.

Potential anabolic effects of androgens on bone

Sex steroid hormones are essential to normal skeletal growth and maintenance throughout life in both men and women. The importance of estrogens to bone health in women becomes obvious at menopause when estrogen deficiency occurs and results in accelerated bone loss. After menopause, estrogen deficiency results in drastic changes in the androgen-estrogen ratio. Thus, the relative importance of androgens after menopause may increase. Androgens also appear to be important for bone health in pre-menopausal women. Evidence from human, animal, and laboratory studies is leading to a better understanding of the effects of androgens on bone in women.

Hypogonadism and diabetes

Clinicians have been aware of the increased prevalence of low testosterone levels in patients with type II diabetes for several years, but how these two conditions are associated is difficult to determine. Older age and obesity may be factors, as both are associated with type II diabetes and both decrease testosterone levels. Sex hormone-binding globulin (SHBG), the major serum carrier protein for testosterone, also may have an impact. SHBG levels fall with obesity and increase with aging. Some studies indicate lower SHBG levels in type II diabetes. Most of the differences in testosterone levels between diabetic and nondiabetic patients may be due to reduced SHBG, rather than reduced testosterone production. However, free testosterone levels fall with increasing age and obesity, rendering many type II diabetic patients testosterone deficient. Testosterone replacement may improve insulin sensitivity in hypogonadal, overweight men with type II diabetes by altering body composition, but studies are conflicting.

Structure/function analyses of human sex hormone-binding globulin: effects of zinc on steroid-binding specificity

In humans, sex hormone-binding globulin (SHBG) binds and transports the biologically most important androgens and estrogens in the blood, and regulates the access of these steroids to their targets tissues. In addition to binding sex steroids, SHBG has specific binding sites for divalent cations including calcium and zinc. Zinc binding to a site at the entrance of the steroid-binding pocket in human SHBG has been shown to reduce its affinity for estrogens, while having no impact on the binding of C19 steroids. Crystallographic studies indicate that C18 and C19 steroids are bound in opposite orientations within the SHBG steroid-binding site, and we have obtained new information that supports a molecular model explaining the mechanism by which zinc alters the affinity of human SHBG for estrogens, by studying directly the estradiol-binding properties SHBG variants created by site-directed mutagenesis. In this model, the coordination of a zinc ion by the side chains of residues Asp65 and His136 eliminates a critical hydrogen bond between Asp65 and the hydroxyl at C3 of estrogens, such as estradiol and 2-methoxyestradiol, and causes disorder in a polypeptide loop segment that covers the steroid-binding site. The combination of these structural changes explains the specific decrease in the affinity of human SHBG for C18 steroids in the presence of a zinc ion.

Obesity and the polycystic ovary syndrome

The polycystic ovary syndrome (PCOS) is a condition characterized by hyperandrogenism and chronic oligo-anovulation. However, many features of the metabolic syndrome are inconsistently present in the majority of women with PCOS. Approximately 50% of PCOS women are overweight or obese and most of them have the abdominal phenotype. Obesity may play a pathogenetic role in the development of the syndrome in susceptible individuals. In fact, insulin possesses true gonadotrophic function and an increased insulin availability at the level of ovarian tissue may favour excess androgen synthesis. Obesity, particularly the abdominal phenotype, may be partly responsible for insulin resistance and associated hyperinsulinemia in women with PCOS. Therefore, obesity-related hyperinsulinemia may play a key role in favouring hyperandrogenism in these women. Other factors such as increased estrogen production rate, increased activity of the opioid system and of the hypothalamic-pituitary-adrenal axis, decreased sex hormone binding globulin synthesis and, possibly, high dietary lipid intake, may be additional mechanisms by which obesity favours the development of hyperandrogenism in PCOS. Irrespective of the pathogenetic mechanism involved, obese PCOS women have more severe hyperandrogenism and related clinical features (such as hirsutism, menstrual abnormalities and anovulation) than normal-weight PCOS women. This picture tends to be more pronounced in obese PCOS women with the abdominal phenotype. Body weight loss is associated with beneficial effects on hormones, metabolism and clinical features. A further clinical and endocrinological improvement can also be achieved by adding insulin-sensitizing agents and/or antiandrogens to weight reduction programmes. These obviously emphasize the role of obesity in the pathophysiology of PCOS.

Cardiovascular risk factors in men: The role of gonadal steroids and sex hormone-binding globulin

Males have higher risk of cardiovascular disease (CVD) than premenopausal females. Gonadal steroids are probably involved in the gender difference in CVD, but previous results have been conflicting. We investigated the associations between CVD risk factors and sex hormones in a cross-sectional designed study of 508 healthy males, aged 41 to 72 years. We determined total testosterone (T), sex hormone-binding globulin (SHBG), free androgen index (FAI), and estradiol (E2) and studied their relationship to body fat mass (BF), blood pressure (BP), aortic compliance, left ventricular mass (LVM), and plasma lipids (total cholesterol, high-density lipoprotein [HDL], low-density lipoprotein [LDL], very--low-density lipoprotein [VLDL], and triglycerides). In quartile analyses after adjustment for confounders (age, body mass index [BMI], alcohol consumption, and smoking), SHBG and E2 were positively associated with HDL, while FAI was negatively associated with HDL. T and SHBG were negatively associated with VLDL and triglycerides, while FAI was positively associated with VLDL and triglycerides. T and SHBG were negatively associated with BMI and BF, while FAI and E2 were positively associated with BMI and BF. E2 was negatively associated with LVM. No hormone varied with total cholesterol, LDL, BP, and aortic compliance in the adjusted analyses. In multiple regression analyses, SHBG was the main predictive variable of HDL, VLDL, and triglycerides explaining 12%, 17%, and 17% of the variation, respectively. No other hormones were selected as predictive variables for VLDL and triglycerides, but E2, T, and FAI were selected in the HDL regression, explaining 3%, 2%, and less than 1%, respectively. Our regression analyses illustrate the diverging results when investigating associations between gonadal steroids and lipids with and without SHBG adjustment. Atherogenic lipid profile in males is associated with low SHBG, low T levels, and a high FAI. Males with high E2 levels may have a less atherogenic lipid profile and lower LVM. SHBG is a key hormone in the association between sex hormones and plasma lipids. We suggest that conflicting results of cross-sectional and intervention studies of sex hormones and lipids, in part, may be explained by interindividual differences or changes in SHBG. Thus, further studies on the potential role of SHBG in the development of ischemic heart disease (IHD) should be performed.

Physiologic aspects of natural and surgical menopause

With oophorectomy, the physiologic changes associated with menopause occur quickly and with a significant impact on a woman's quality of life. In naturally menopausal women, ovarian hormone biosynthesis provides low circulating levels of estrogen and androgen. In the surgically menopausal woman, estrogen and androgen levels are significantly reduced. In surgically menopausal women for whom supplemental estrogen is prescribed, sex hormone binding globulin levels increase dramatically, resulting in reduced bioavailability of the remaining estrogens and androgens that result from peripheral conversion. This paper reviews the physiologic changes associated with natural and surgical menopause and the effects of estrogens and androgens at the cellular level. It describes the effects of hormone replacement on endogenous hormones and on the symptoms of menopause that result from physiologic changes, including vasomotor instability, sexual dysfunction and urinary complications. It also addresses the effects of estrogen/androgen therapy on physiologic symptoms.

Testosterone deficiency in women

Testosterone (T) is an important component of female sexuality, enhancing interest in initiating sexual activity and response to sexual stimulation. Testosterone is also associated with greater well-being and with reduced anxiety and depression. Clinical and biochemical definitions of T deficiency have not been established; hence, the prevalence of this condition is not known. However, surgically menopausal women are among the populations most likely to experience T deficiency, a syndrome characterized by blunted or diminished motivation; persistent fatigue; decreased sense of personal well-being; sufficient plasma estrogen levels; and low circulating bioavailable T (either a low total T/sex hormone binding globulin (SHBG) ratio or free T in the lower one-third of the female reproductive range); and low libido. Exogenous estrogen, particularly when administered orally, increases SHBG, which, in turn, reduces free T and estradiol (E2). After oophorectomy, levels of T and its precursor, androstenedione, decline by approximately 50%. T replacement continues to be evaluated as an adjunct to estrogen replacement therapy, particularly for women with androgen deficiency symptoms, surgically menopausal women and women with premature ovarian failure. In the United States, oral methyltestosterone is the common product currently approved for androgen replacement in women. The best product specifically designed for women has yet to be determined, as standardized, long-term, randomized, control clinical studies are lacking and product refinement continues.

Role of androgens in female-pattern androgenetic alopecia, either alone or associated with other symptoms of hyperandrogenism

The roles of androgen hypersecretion, in situ enzyme activity, and androgen receptors in androgenetic alopecia in women are still a matter of debate. We studied 187 women with alopecia, which we graded I, II, or III, according to Ludwig's classification, and 21 healthy control women. All participants were subjected to full basal and 1 h post-beta-1-24 corticotropin stimulation endocrine profiles. Abnormal hormone profiles were observed in 67% of the patients with alopecia alone (group A, n = 110) and in 84% of the patients with alopecia plus other symptoms of hyperandrogenism including acne, hirsutism, and menstrual cycle disturbances (group B, n = 77). Mean serum 5alpha-androstane-3alpha,17beta-diol glucuronide (3alpha-AdiolG) levels in all three patient groups (6.50+/-4.10, 8.90+/-5.80, and 14.70+/-8.90 nmol/l, respectively) correlated with the grade of alopecia (I-III) and were significantly higher than in the control group (4.80+/-2.05 nmol/l, P < 0.005). Mean serum sex hormone-binding globulin (SHBG) levels were inversely correlated with the grade of alopecia (I-III) and were significantly lower in all three patient groups (50.55+/-23.50, 40.00+/-17.65, and 38.80+/-14.10 nmol/l, respectively) than in the control group (61.15+/-17.65 nmol/l, P < 0.05). Mean serum levels of delta4-androstenedione, dehydroepiandrosterone, dehydroepiandrosterone sulfate, and 3alpha-AdiolG were higher in group B than in group A, and higher in group A than in the control group. The significant correlations found between adrenal secretion - either positive (with 3alpha-AdiolG levels and the body mass index) or negative (with SHBG levels) - might reflect the important contribution of secretory and metabolic components in the development of alopecia, the severity of which has been shown to be very closely related to observed levels of two of these parameters (3alpha-AdiolG and SHBG).

Sex steroid hormones, sex hormone-binding globulin, and obesity in men and women

Sex steroid hormones in both males and females have been closely related to the regulation of adiposity, either through direct or indirect physiological mechanisms. Evidence also suggests a direct relationship between sex hormones and risk factors for cardiovascular disease. In the present review article, we will discuss recent studies that have examined the complex interrelationships between sex hormones, SHBG, obesity and risk factors for cardiovascular disease. Male obesity and excess abdominal adipose tissue accumulation is associated with reductions in gonadal androgen and low adrenal C19 steroid concentrations. Reduced C19 steroids are also related to an altered metabolic risk factor profile including glucose intolerance and an atherogenic dyslipidemic state. However, the concomitant visceral obese state appears as a major correlate in these associations. In women, menopause-induced estrogen deficiency and increased androgenicity are associated with increased abdominal obesity and with the concomitant alterations in the metabolic risk profile. The accelerated accretion of adipose tissue in the intra-abdominal region coincident with the onset of menopause may explain part of the increased risk of cardiovascular disease in postmenopausal women. In both men and women, plasma levels of sex hormone-binding globulin are strong correlates of obesity and risk factors for cardiovascular disease, and more importantly, the relationships between low SHBG and altered plasma lipid levels appear to be independent from the concomitant increased levels of visceral adipose tissue. SHBG concentration may, therefore, represent the most important and reliable marker of the sex hormone profile in the examination of the complex interrelation of sex steroid hormones, obesity, and cardiovascular disease risk.

A steroid-binding protein mediates estrogen-dependent inhibition of growth of MCF-7 breast cancer cells

We have described two different proteins that mediate MCF-7 cell growth inhibition (1). One is estrogen-dependent and is a heterodimer consisting of a heavy (54 kDa) and light (29 kDa) chain. This protein is distinct from cortisol-binding globulin (CBG), sex hormone-binding protein (SBP or SHBG) and albumin (HSA). It may be fetal steroid binding protein (FSBP). The other is not estrogen dependent, but may be related to the estrogen-dependent protein. Since these are large proteins they must be acting at the level of the plasma membrane, not traditional intracellular estrogen receptors, and inhibit MCF-7 cell growth.

Synthesis and regulation of sex hormone-binding globulin in obesity

Sex hormone-binding globulin (SHBG) is a plasma glycoprotein with high binding affinity for testosterone and dihydrotestosterone and lower affinity for estradiol. SHBG is synthesized in the liver, and its plasma level is important in the regulation of plasma free and albumin-bound androgens and estrogens. Obesity and particularly excess visceral fat, known risk factors for cardiovascular and metabolic diseases, are associated with decreased testosterone levels in males and SHBG levels in both sexes. SHBG is usually positively correlated with high-density lipoprotein cholesterol and negatively correlated with triglyceride and insulin concentrations. A positive association between SHBG and various measures of insulin sensitivity has been demonstrated in both sexes, suggesting that decreased SHBG levels may be one of the components of the metabolic syndrome. We have examined pituitary-adrenocortical function, glucose tolerance, and lipoprotein and hormone levels in a large cohort of Finnish males. Abdominal obesity appears to be associated with slight hypocortisolemia and increased sensitivity to exogenous adrenocorticotropin stimulation, which may contribute to the hyperinsulinemia and related metabolic changes including decreased SHBG levels in males.

The rabbit sex hormone-binding globulin gene: structural organization and characterization of its 5-flanking region

Sex hormone-binding globulin (SHBG) transports sex steroids in the blood. In humans and rabbits, the gene encoding SHBG (shbg) is expressed primarily in the liver and testis, whereas the testis is the major site of shbg expression in rodents postnatally. Sequence analysis has revealed that rabbit shbg (rbshbg) spans 2.5 kb and comprises eight exons with consensus splice sites at all exon-intron junctions. The major transcription start site ofrbshbg is located 52 bp upstream from the translation initiation codon for the rabbit SHBG precursor. Unlike the situation in humans and rats, rbshbg transcripts contain no alternative exon 1 sequences in the liver or testis, and this suggests that the rbshbg 5'-flanking region plays an equally important role in controlling transcription of this gene in these tissues. Like the human and rat shbg promoter sequences, the rbshbg proximal promoter lacks a typical TATA box. It also contains several transcription factor-binding sites, but deoxyribonuclease I footprinting experiments indicated that the human and rabbit shbg proximal promoters interact quite differently with proteins extracted from rabbit liver nuclei. However, the predominant footprint on the rbshbg promoter is conserved at the same position within the human shbg (hshbg) promoter and includes consensus binding sites for the transcription factor nuclear factor- 1. Transient transfection studies of the rbshbg 5'-flanking sequence (893 bp) revealed regions that actively enhance and repress its activity in human hepatoblastoma and mouse Sertoli cells, but not in Chinese hamster ovary cells. Like the rat shbg proximal promoter, the rbshbg 5'-flanking sequence lacks a region that corresponds to a cis-element, designated footprinted region 4 in the hshbg proximal promoter. Furthermore, the hshbg promoter footprinted region 3 sequence is poorly conserved in rbshbg, and when mutated to resemble the corresponding human sequence it increased the transcriptional activity of the rbshbg promoter by 7-fold in hepatoblastoma cells. Thus, the rabbit and hshbg promoters appear to be controlled by a different set of transcriptional regulators. Further comparisons of their functional activities may shed light on species-specific differences in the spatial and temporal expression of this gene, the products of which play important roles in regulating sex steroid access to target cells.

Androgen receptors in prostate and skeletal muscle

Regulatory control of the androgen receptor has been studied most extensively in prostatic tissue. Additional information has been obtained from the study of androgen receptors in pituitary and hypothalamic tissues, and these results can be extrapolated to regulatory mechanisms in both prostate and skeletal muscle. The present work provides a brief summary of studies on androgen action on muscle, gives an overview of mechanisms of androgen action on target tissues, and focuses on several aspects of regulation of androgen receptor (AR) gene expression. These include some characteristics of AR gene transcription start sites; the role of the cyclic adenosine monophosphate, protein kinase C, and protein kinase A pathways in mediating androgen receptor function; and tissue-variable regulatory elements inhibiting AR gene expression.

[Reference values of FSH, LH, total testosterone, free testosterone, 17-beta-estradiol and SHBG in healthy children in Zaragoza]

OBJECTIVE

Our purpose was to estimate reference values for basal serum concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH), total testosterone, free testosterone, 17-beta-estradiol (E2) and sex steroid binding globulin (SHBG) in healthy children of Zaragoza.

PATIENTS AND METHODS

The reference population consisted of healthy children between 0 and 14 years of age with normal weight and height and living in the metropolitan area of Zaragoza (Spain). It was a transversal study. Basal serum concentrations of FSH, LH and SHBG were measured by immunoradiometric assay. Basal serum concentrations of total testosterone, free testosterone and E2 were analyzed by radioimmunoassay. Reference values and ranges were estimated according to the recommendations of the International Federation of Clinical Chemistry.

RESULTS

Reference values have been classified by age, sex and pubertal stage. Serum concentrations of FSH, LH, total testosterone, free testosterone and E2 increase during the first six months, remain low in infancy and rise during puberty. All of these concentrations showed marked differences according to sex. Serum SHBG levels are influenced by age and during puberty by sex.

CONCLUSIONS

Differences in reference values for gonadotrophins, sex steroids and SHBG during infancy, childhood and adolescence makes it necessary for every population to establish their own reference values according to age, sex and pubertal stage.

Sex hormone-binding globulin mediates steroid hormone signal transduction at the plasma membrane

Sex hormone-binding globulin is a plasma glycoprotein that binds certain estrogens and androgens with high affinity. Over the past several years it has been shown that, in addition to functioning as a regulator of the free concentration of a number of steroid hormones, SHBG plays a central role in permitting certain steroid hormones to act without entering the cell. The system is complex. SHBG interacts with a specific, high affinity receptor (R(SHBG)) on cell membranes that appears to transduce its signal via a G protein. The SHBG-R(SHBG) complex causes the activation of adenylyl cyclase and the generation of cAMP within a matter of minutes after exposure to an appropriate steroid. Only steroids that bind to SHBG can activate SHBG-R(SHBG), but not all steroids that bind have this function, e.g. are agonists. All steroids that bind to SHBG but do not activate adenylyl cyclase are antagonists. The signals generated by the steroid-SHBG-R(SHBG) complex generate messages that have effects on the transcriptional activity of classic, intracellular receptors for steroid hormones. These and other downstream effects of this system are reviewed.

Levels of sex hormone-binding globulin and corticosteroid-binding globulin mRNAs in corpus luteum of human subjects: correlation with serum steroid hormone levels

To understand regulation of the function of human ovarian corpus luteum by sex steroid-binding proteins, the levels of luteal intracellular sex hormone-binding globulin (SHBG) and corticosteroid-binding globulin (CBG) mRNAs and serum steroid hormones were simultaneously determined. The expression of SHBG and CBG mRNAs was detected in all samples analyzed. SHBG mRNA level was positively correlated with serum estradiol-17 beta level (p < 0.05), but not with serum progesterone level. There was a positive correlation between SHBG mRNA level and serum estradiol-17 beta/progesterone ratio (p < 0.01). On the other hand, CBG mRNA level was positively correlated with serum estradiol-17 beta and progesterone level (p < 0.01 and p < 0.01, respectively). There was no correlation between CBG mRNA level and serum estradiol-17 beta/progesterone ratio. SHBG and CBG mRNA levels were not correlated with the levels of serum testosterone, free testosterone or cortisol. These findings suggest that the synthesis of luteal SHBG and CBG is complexly regulated by estrogen and progesterone, and that SHBG and CBG interact with estrogen and progesterone, respectively, for luteal steroidal activity.

Sex hormone-binding globulin: not only a transport protein. What news is around the corner?

The plasma Sex Hormone-Binding Globulin (SHBG) transports androgens and estradiol in the blood and regulates their bioavailable fraction and access to target cells. The recent advances in the knowledge of its structure and gene expression, and notabily the demonstration of a specific receptor (SHBG-R) located on membranes of sex steroid responsive cells, gave support to the thesis that SHBG has much more sophisticated functions at cell site. In particular, the receptor-mediated action of SHBG, which uses as a second messenger cAMP, has been linked to the effects of androgens and estradiol. It is conceivable that the SHBG/SHBG-R system works as an additional control mechanism which inhibits or amplifies the effects of DHT and estradiol in cells. In the prostate, it has been suggested that the estradiol-activated SHBG/SHBG-R complex cross-talks with the androgen receptor, and is able to activate AR even in the absence of DHT. Of great interest, for its potential clinical applications, is the observation that in estrogen-dependent breast cancer SHBG, through SHBG-R, cAMP and PKA, specifically inhibits the estradiol-induction of cell proliferation. This anti-proliferative, anti-estrogenic effect of human SHBG has not only increased and continues to increase our understanding of the molecular mechanisms involved in the biology of breast cancer, but could also be exploited as a future therapeutic strategy in the managing of estrogen-dependent tumours.

Comparative breast tumor imaging and comparative in vitro metabolism of 16alpha-[18F]fluoroestradiol-17beta and 16beta-[18F]fluoromoxestrol in isolated hepatocytes

16beta-[18F]Fluoromoxestrol ([18]betaFMOX) is an analog of 16alpha-[18F]fluoroestradiol-17beta ([18F]FES), a radiopharmaceutical known to be an effective positron emission tomography (PET) imaging agent for estrogen receptor-positive (ER+) human breast tumors. Based on comparisons of target tissue uptake efficiency and selectivity in a rat model, [18F]betaFMOX was predicted to be as effective an imaging agent as [18F]FES. However, in a preliminary PET imaging study with [18F]FMOX of 12 patients, 3 of whom had ER+ breast cancer, no tumor localization of [18F]betaFMOX was observed. In search for an explanation for the unsuccessful [18F]betaFMOX clinical trial, we have examined the rate of metabolism of [18F]FMOX and [18F]FES in isolated rat, baboon, and human hepatocytes. We have also studied the effect of the serum protein sex hormone-binding globulin (SHBG), which binds [18F]FES better than [18F]betaFMOX, on these rates of metabolism. Immature rat hepatocytes were found to metabolize [18F]FES 31 times faster than [18F]betaFMOX, whereas mature rat cells metabolized [18F]FES only 3 times faster, and baboon and human hepatocytes only 2 times faster than [18F]betaFMOX. In the presence of SHBG, the metabolic consumption rate for [18F]FES in mature rat hepatocytes decreased by 26%. Thus, the very favorable target tissue uptake characteristics of [18F]betaFMOX determined in the rat probably result from its comparative resistance to metabolism (vis-a-vis [18F]FES) in this species, an advantage that is strongly reflected in comparative metabolism rates in rat hepatocytes. In the baboon and human, [18F]FES is extensively protein bound and protected from metabolism, an effect that may be reflected to a degree as a decrease in the rate of metabolism of this compound in baboon and human hepatocytes relative to [18F]betaFMOX. Thus in primates, SHBG may potentiate the ER-mediated uptake of [18F]FES in ER+ tumors by selectively protecting this ligand from metabolism and ensuring its delivery to receptor-containing cells. In addition to current screening methods for 18F-estrogens that involve evaluating in vivo ER-mediated uptake in the immature female rat, studies comparing the metabolism of the new receptor ligands in isolated hepatocytes, especially those from primates or humans, may assist in predicting the potential of these ligands for human PET imaging.

Sex hormone binding globulin inhibits strongly the uptake of estradiol by human breast carcinoma cells via a deprivative mechanism

A controversy exists for many years about the role of sex hormone binding globulin (SHBG) in the uptake of estradiol by the cells. Using the estradiol-sensitive human breast carcinoma cell line MCF-7 and SHBG isolated from human serum by a new method, we observed a strong inhibition of estradiol uptake. The inhibition was higher when the concentration of the hormone was low. On the other hand, there seemed to be a lag period in inhibition when the concentrations of SHBG were very low, followed by an exponential increase, when the concentration exceeded a critical value. The inhibitory activity was higher when SHBG was added before or along with estradiol in the cell culture, as well as when the incubation period was elongated, while was dramatically minimized by the presence of dihydrotestosterone. Despite the inhibition of estradiol uptake caused by SHBG, the distribution of the hormone in various cell components remained practically the same. In conclusion, all indications from experimental data seem to suggest a simple deprivative mechanism being responsible for the inhibitory activity of SHBG on estradiol uptake by MCF-7 cells in culture.

Sex differences in the control of sex-hormone-binding globulin in the elderly: role of insulin-like growth factor-I and insulin

OBJECTIVE

Serum levels of sex-hormone-binding globulin (SHBG) have been reported in the literature to increase with age in both sexes. We have investigated the variations in levels of androgens, insulin and IGF-I with age and have evaluated their putative roles to obtain a better understanding of the increase in SHBG.

DESIGN

Cross-sectional pilot study of blood samples in healthy elderly subjects aged 50 to 90 years.

PATIENTS AND METHODS

Forty-four postmenopausal women and 40 men were classified into three age groups. Subjects who were obese, undernourished or smokers and postmenopausal women receiving hormone replacement therapy were excluded from the study. Body mass index and waist/hip ratio were evaluated in each subject. Fasting levels of blood glucose, insulin, triglycerides, cholesterol, SHBG, testosterone, dehydroepiandrosterone sulfate (DHEAS) and IGF-I were measured. Free testosterone and glucose/insulin ratio were calculated.

RESULTS

The results are based on variance analysis of the mean of each parameter in the three age groups. Multiple regression analysis was performed to define the role of age, insulin and IGF-I in the increase in SHBG. The increase in SHBG with age in older men was significant but that in postmenopausal women was not. Decreasing DHEAS with age was confirmed. No significant variations in glucose and insulin were observed with age in our selected population. A positive correlation was observed between insulin and triglycerides in elderly men and women. IGF-I decreased significantly with age in both sexes. Insulin was the main factor explaining SHBG increase with age in women. In men, both age and IGF-I contributed to the SHBG increase.

CONCLUSIONS

The factors regulating the increase in SHBG with age appear to be different in the two sexes. Insulin plays a major role in women, whereas a decrease in IGF-I is the predominant regulating factor in men. These results should be thought of as a working hypothesis rather than a reflection of physiology.

Control of the membrane sex hormone-binding globulin-receptor (SHBG-R) in MCF-7 cells: effect of locally produced SHBG

The interaction between plasma sex hormone-binding globulin (SHBG) and its receptor (SHBG-R) inhibits estradiol-induced proliferation of MCF-7 cells (human estrogen-dependent breast cancer) through cAMP and PKA. Thus, SHBG can modulate estradiol action in breast cancer, but the implications of this require a more detailed knowledge of the SHBG-R. To this end, we have transfected MCF-7 cells with an expression vector carrying the human SHBG cDNA (S-MCF-7) and studied the effects of this on both SHBG-R binding and cell proliferation. Control cells were parental MCF-7 (P-MCF-7) and MCF-7 cells transfected with the beta-galactosidase gene (B-MCF-7). Transfections were mediated by lipofectin followed by selection of transfected cells with G418. The amounts of SHBG in culture medium were evaluated by IRMA assay, with only S-MCF-7 cells shown to secrete SHBG; SHBG-R levels were evaluated by tracer binding technique. In P-MCF-7 and B-MCF-7 cells, SHBG-R was detectable as a two-binding site receptor, but no binding of SHBG was observed in S-MCF-7 cells. Proliferation of cells treated with estradiol was evaluated by [3H]thymidine incorporation in the three cell lines and in cells pretreated with SHBG (1 nM) purified from human serum or with conditioned medium from S-MCF-7 cells (medium S). In all three lines, cell proliferation increased after estradiol treatment. Preincubation with purified SHBG was effective in reducing estrogen-induced cell proliferation to basal levels in P-MCF-7 and B-MCF-7 but not in S-MCF-7 cells. The estradiol effect was also inhibited in P-MCF-7 cells treated with medium S. In conclusion, 1) SHBG inhibits estradiol-induced proliferation in cells containing a functional SHBG-R, whereas it has no detectable effect in cells in which the SHBG-R is either absent or not available to bind SHBG; and 2) S-MCF-7 cells are insensitive to SHBG (locally produced or exogenous) because their SHBG-R is occupied by SHBG.

Testosterone as a biological marker in psychopathy and alcoholism

The aim of the present study was to clarify the relationships between testosterone and alcohol abuse, alcohol dependence and specific personality characteristics and behaviors in a forensic psychiatric population. Serum levels of total testosterone (TT), free testosterone (FT-DPC) and sex hormone-binding globulin (SHBG) were determined in 61 male subjects undergoing forensic psychiatric examinations. All subjects had been detoxified from drugs and alcohol during previous incarceration in jail or hospital. TT and FT-DPC were found to be highly correlated (r=0.63, P < 0.0001). High concentrations of TT and SHBG were consistently related to type II alcoholism, but not pure alcohol dependence. TT and SHBG were also related to antisocial personality disorder. Furthermore, TT and SHBG were related to socially deviant behavior, reflected in factor 2 in the Psychopathy Checklist (PCL-R). In a multiple regression, FT-DPC was also clearly associated with the psychopathy-related scales of the Karolinska Scales of Personality (KSP) when age and signs of hepatic damage were kept under control.

Sex hormone-binding globulin mediates prostate androgen receptor action via a novel signaling pathway

Estradiol (E2) and 5alpha-androstan-3alpha,17beta-diol (3alpha-diol) have been implicated in prostate hyperplasia in man and dogs, but neither of these steroids bind to androgen receptors (ARs). Recently, we reported that E2 and 3alpha-diol stimulated generation of intracellular cAMP via binding to a complex of sex hormone-binding globulin (SHBG) and its receptor (R(SHBG)) on prostate cells. We speculated that this pathway, involving steroids normally found in the prostate, was involved in the indirect activation of ARs. Using the dog as a model to test this hypothesis in normal prostate, we investigated whether E2, 3alpha-diol, and SHBG stimulated the production of the androgen-responsive protein, arginine esterase (AE), the canine equivalent of human prostate-specific antigen. In cultured dog prostate tissue preincubated with SHBG, E2 and 3alpha-diol stimulated AE activity. These effects were blocked by hydroxyflutamide, an AR antagonist, and by 2-methoxyestradiol, a competitive inhibitor of E2 and 3alpha-diol binding to SHBG. In the absence of exogenous steroids and SHBG, AE also was significantly increased by treatment with forskolin or 8-Bromoadenosine-cAMP. These observations support the hypothesis that in normal prostate, E2 and 3alpha-diol can amplify or substitute for androgens, with regard to activation of the AR via the R(SHBG) by a signal transduction pathway involving cAMP. Because both E2 and 3alpha-diol are involved in the pathogenesis of benign prostatic hyperplasia in dogs and implicated in benign prostatic hyperplasia in man, antagonism of the prostatic SHBG pathway may offer a novel and attractive therapeutic target.