Access of reproductive steroids to target tissues

Genetic correlations of alcohol consumption and alcohol use disorder with sex hormone levels in females and males

Background

Alcohol consumption behaviors and alcohol use disorder risk and presentation differ by sex, and these complex traits are associated with blood concentrations of the steroid sex hormones, testosterone and estradiol, and their regulatory binding proteins, sex hormone binding globulin (SHBG) and albumin. Genetic variation is associated with alcohol consumption and alcohol use disorder, as well as levels of steroid sex hormones and their binding proteins.

Methods

To assess the contribution of genetic factors to previously described phenotypic associations between alcohol-use traits and sex-hormone levels, we estimated genetic correlations (rg) using summary statistics from prior published, large sample size genome-wide association studies (GWAS) of alcohol consumption, alcohol dependence, testosterone, estradiol, SHBG, and albumin.

Results

For alcohol consumption, we observed positive genetic correlation (i.e. genetic effects in the same direction) with total testosterone in males (rg = 0.084, p = 0.007) and trends toward positive genetic correlation with bioavailable testosterone (rg = 0.060, p = 0.084) and SHBG in males (rg = 0.056, p = 0.086) and with albumin in a sex-combined cohort (rg = 0.082, p = 0.015); however in females, we observed positive genetic correlation with SHBG (rg = 0.089, p = 0.004) and a trend toward negative genetic correlation (i.e. genetic effects in opposite directions) with bioavailable testosterone (rg = -0.064, p = 0.032). For alcohol dependence, we observed a trend toward negative genetic correlation with total testosterone in females (rg = -0.106, p = 0.024) and positive genetic correlation with BMI-adjusted SHBG in males (rg = 0.119, p = 0.017). Several of these genetic correlations differed between females and males and were not in the same direction as the corresponding phenotypic associations.

Conclusions

Findings suggest that shared genetic effects may contribute to positive associations of alcohol consumption with albumin in both sexes, as well as positive associations between alcohol consumption and bioavailable testosterone and between alcohol dependence and SHBG in males. However, relative contributions of heritable and environmental factors to associations between alcohol-use traits and sex-hormone levels may differ by sex, with genetic factors contributing more in males and environmental factors contributing more in females.

An antibody-free LC-MS/MS method for the quantification of sex hormone binding globulin in human serum and plasma

OBJECTIVES

Sex hormone binding globulin (SHBG) is a hormone binding protein which plays an important role in regulating the transport and availability of biologically active androgens and estradiol to target cells and used to calculate free testosterone concentrations.

METHODS

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed, featuring an albumin removal step followed by a tryptic digestion. After a reduction step with dithiothreitol and alkylation with iodoacetamide three signature peptides were used for the quantification of SHBG.

RESULTS

The method enables the quantification of serum and plasma SHBG over the clinically relevant range of 200-20,000 ng/mL and was validated according to the most recent guidelines. The LC-MS/MS method correlates well with the Abbott Alinity immunoassay (R2>0.95), but the LC-MS/MS results are on average 16-17% lower than the immunoassay results, which is consistent for all three signature peptides.

CONCLUSIONS

The LC-MS/MS method which includes an albumin depletion step allows quantification of SHBG in serum and plasma without an immunocapture step at clinically relevant SHBG levels, thus contributing to better lab-to-lab consistency of results.

Effect of SHBG Polymorphism on the Levels of Bioavailable Testosterone and Lipid Metabolism in Older Men of the Kazakh Population

This study is aimed at investigating the effect of SHBG (rs727428; rs10822184) and LPL (rs754493647) single nucleotide polymorphisms on the concentration of the bioavailable fraction of testosterone in older men. Materials and methods To study gene mutations, 417 residents of the East Kazakhstan region of Kazakh nationality were examined. The main group included 135 men with signs of hypogonadism (AMS 37-49), and the control group consisted of 282 healthy men (AMS 17-26) of the corresponding age (p = 0.5). Single nucleotide polymorphisms rs 727428 [C / T]; rs10822184 [T / C]; rs754493647 [T / C], was determined by the TaqMan method. Results Analysis of the rs727428 polymorphism has revealed that the TT allele (rs727428) has a lower level of albumin (p = 0.03), bioavailable testosterone (p = 0.04), and free testosterone (p = 0.6) than in carriers of the CC and CT genotypes. Also, it has shown a decrease in total testosterone (p = 0.001) and an increase in SHBG levels (p = 0.07) in men with the TT genotype of the rs727428 gene polymorphism. The rs10822184 polymorphism demonstrated an increase in triglyceride and LDL levels in TT genotype (p ≤ 0.04), in comparison with CC and CT genotypes. Conclusion It has been proven that rs727428 (p = 0.001) is associated with testosterone levels and therefore can determine the concentration of bioavailable testosterone. Decreased levels of bioavailable testosterone are a sign of male hypogonadism. This study confirms the effect of rs10822184 on LDL (p = 0.01) and triglyceride (p = 0.04) levels, but its association with androgen levels has not been proven. Our results may be of interest for understanding the etiology of early development of hypogonadism and lipid metabolism disorders in men. To confirm the conclusions, a more detailed study with a large sample of men from the Kazakh population may be required.

Accurate measurement of total and free testosterone levels for the diagnosis of androgen disorders

The circulating concentrations of total and free testosterone vary substantially in people over time due to biologic factors as well as due to measurement variation. Accurate measurement of total and free testosterone is essential for making the diagnosis of androgen disorders. Total testosterone should ideally be measured in a fasting state in the morning using a reliable assay, such as liquid chromatography tandem mass spectrometry, in a laboratory that is certified by an accuracy-based benchmark. Free testosterone levels should be measured in men in whom alterations in binding protein concentrations are suspected or in whom total testosterone levels are only slightly above or slightly below the lower limit of the normal male range for testosterone.

Genome-wide Association Study of Estradiol Levels and the Causal Effect of Estradiol on Bone Mineral Density

CONTEXT

Estradiol is the primary female sex hormone and plays an important role for skeletal health in both sexes. Several enzymes are involved in estradiol metabolism, but few genome-wide association studies (GWAS) have been performed to characterize the genetic contribution to variation in estrogen levels.

OBJECTIVE

Identify genetic loci affecting estradiol levels and estimate causal effect of estradiol on bone mineral density (BMD).

DESIGN

We performed GWAS for estradiol in males (n = 147 690) and females (n = 163 985) from UK Biobank. Estradiol was analyzed as a binary phenotype above/below detection limit (175 pmol/L). We further estimated the causal effect of estradiol on BMD using Mendelian randomization.

RESULTS

We identified 14 independent loci associated (P < 5 × 10-8) with estradiol levels in males, of which 1 (CYP3A7) was genome-wide and 7 nominally (P < 0.05) significant in females. In addition, 1 female-specific locus was identified. Most loci contain functionally relevant genes that have not been discussed in relation to estradiol levels in previous GWAS (eg, SRD5A2, which encodes a steroid 5-alpha reductase that is involved in processing androgens, and UGT3A1 and UGT2B7, which encode enzymes likely to be involved in estradiol elimination). The allele that tags the O blood group at the ABO locus was associated with higher estradiol levels. We identified a causal effect of high estradiol levels on increased BMD in both males (P = 1.58 × 10-11) and females (P = 7.48 × 10-6).

CONCLUSION

Our findings further support the importance of the body's own estrogen to maintain skeletal health in males and in females.

Correlational analysis of bone health status and vitamin D-related biomarkers in women working in agriculture

The purpose of this study was to investigate the status of bone health in women working in agriculture and analyze the associations between bone health and various vitamin D-related biomarkers.This observational study enrolled women working in agriculture (n = 210) and control occupations (n = 180). The concentration of serum total 25-hydroxy vitamin D [25(OH)D] was measured using the Elecsys Vitamin D Total Kit, and serum vitamin D-binding protein (VDBP) was measured by enzyme-linked immunosorbent assay. Along with albumin, 25(OH)D and VDBP were used to calculate the concentrations of bioavailable and free 25(OH)D. Bone mineral density (BMD) and T-score were measured at lumbar 1 to 4 and the femur neck using dual-energy X-ray absorptiometry. To identify factors affecting BMD, log-linear model and linear regression analysis were performed for statistical analysis.Agricultural women workers showed higher serum concentrations of bioavailable 25(OH)D (12.8 ± 3.7 vs 8.7 ± 5.1 ng/mL) and lower VDBP concentrations (201.8 ± 45.0 vs 216.0 ± 68.2 μg/mL) than control women. The association between these 2 vitamin D related-biomarkers and femur neck BMD were confirmed through univariable and multivariable linear model analysis. Although lumbar BMD did not differ between groups, the agricultural group displayed a lower femur BMD and a 4.3-fold increase in the risk of osteoporosis compared with the control group.Women working in agriculture showed lower femur BMD than the control group. Of the vitamin D-related biomarkers tested, bioavailable 25(OH)D and VDBP were associated with BMD. As bioavailable 25(OH)D levels are affected mainly by VDBP levels, VDBP may play a role in the lower femur neck BMD values observed in the agricultural group. Thus, the measurement of VDBP concentration might be considered a simple and non-invasive method for measuring bone health status.

Comparative analysis of the association between various serum vitamin D biomarkers and sarcopenia

Background

Vitamin D status is associated with muscle strength and maintenance of muscle fibers. However, which serum vitamin D biomarker better reflects sarcopenia remains unclear. The aim of this study was to investigate associations between various serum vitamin D biomarkers (total 25‐hydroxy vitamin D [25(OH)D], bioavailable 25(OH)D, 24,25‐dihydroxyvitamin D [24,25(OH)₂D], and vitamin D metabolite ratio [VMR]) and sarcopenia.

Methods

The data for 83 hip fracture patients were finally included in the analysis. Sarcopenia was defined according to the Asia Working Group for Sarcopenia (AWGS) criteria. Measurements of 24,25(OH)₂D and 25(OH)D were made using solid‐phase extraction (SPE) and subsequent liquid chromatography‐tandem mass spectrometry (LC‐MS/MS). Vitamin D binding protein (VDBP) concentration was measured using an enzyme‐linked immunosorbent assay. The VMR was calculated by dividing serum 24,25(OH)₂D by serum 25(OH)D and then multiplying by 100. Based on total 25(OH)D, VDBP, and albumin concentrations, bioavailable 25(OH)D concentrations were calculated using the equations from the other previous studies.

Results

Bioavailable 25(OH)D levels were significantly (p = 0.030) decreased in the sarcopenia group compared with the non‐sarcopenia group. Results of ROC analysis for the diagnosis of sarcopenia using serum level of bioavailable of 25(OH)D revealed that the cutoff point for bioavailable 25(OH)D was 1.70 ng/ml (AUC = 0.649, p < 0.001). In the group with a bioavailable 25(OH)D less than 1.70 ng/ml, the incidence of sarcopenia increased by 3.3 times (odds ratio: 3.33, p = 0.013).

Conclusion

We demonstrated that bioavailable 25(OH)D was associated with sarcopenia among the various serum vitamin D biomarkers. Bioavailable vitamin D might be helpful for assessing the risk of sarcopenia.

Considering Sex as a Biological Variable in Basic and Clinical Studies: An Endocrine Society Scientific Statement

In May 2014, the National Institutes of Health (NIH) stated its intent to "require applicants to consider sex as a biological variable (SABV) in the design and analysis of NIH-funded research involving animals and cells." Since then, proposed research plans that include animals routinely state that both sexes/genders will be used; however, in many instances, researchers and reviewers are at a loss about the issue of sex differences. Moreover, the terms sex and gender are used interchangeably by many researchers, further complicating the issue. In addition, the sex or gender of the researcher might influence study outcomes, especially those concerning behavioral studies, in both animals and humans. The act of observation may change the outcome (the "observer effect") and any experimental manipulation, no matter how well-controlled, is subject to it. This is nowhere more applicable than in physiology and behavior. The sex of established cultured cell lines is another issue, in addition to aneuploidy; chromosomal numbers can change as cells are passaged. Additionally, culture medium contains steroids, growth hormone, and insulin that might influence expression of various genes. These issues often are not taken into account, determined, or even considered. Issues pertaining to the "sex" of cultured cells are beyond the scope of this Statement. However, we will discuss the factors that influence sex and gender in both basic research (that using animal models) and clinical research (that involving human subjects), as well as in some areas of science where sex differences are routinely studied. Sex differences in baseline physiology and associated mechanisms form the foundation for understanding sex differences in diseases pathology, treatments, and outcomes. The purpose of this Statement is to highlight lessons learned, caveats, and what to consider when evaluating data pertaining to sex differences, using 3 areas of research as examples; it is not intended to serve as a guideline for research design.

Vitamin D binding protein/GC-globulin: a novel regulator of alpha cell function and glucagon secretion

The contribution of glucagon to type 1 and type 2 diabetes has long been known, but the underlying defects in alpha cell function are not well-described. During both disease states, alpha cells respond inappropriately to stimuli, leading to dysregulated glucagon secretion, impaired glucose tolerance and hypoglycaemia. The mechanisms involved in this dysfunction are complex, but possibly include changes in alpha cell glucose-sensing, alpha cell de-differentiation, paracrine feedback, as well as alpha cell mass. However, the molecular underpinnings of alpha cell failure are still poorly understood. Recent transcriptomic analyses have identified vitamin D binding protein (DBP), encoded by GC/Gc, as an alpha cell signature gene. DBP is highly localized to the liver and alpha cells and is virtually absent from other tissues and cell types under non-pathological conditions. While the vitamin D transportation role of DBP is well characterized in the liver and circulation, its function in alpha cells remains more enigmatic. Recent work reveals that loss of DBP leads to smaller and hyperplastic alpha cells, which secrete less glucagon in response to low glucose concentration, despite vitamin D sufficiency. Alpha cells lacking DBP display impaired Ca²⁺ fluxes and Na⁺ conductance, as well as changes in glucagon granule distribution. Underlying these defects is an increase in the ratio of cytoskeletal F-actin to G-actin, highlighting a novel intracellular actin scavenging role for DBP in islets.

Assessment of free testosterone concentration

Testosterone (T) is strongly bound to sex hormone binding globulin and measurement of free T may be more appropriate than measuring total serum T, according to the free hormone theory. This view remains controversial and it has its detractors who claim that little extra benefit is gained than simply measuring total T, but it is endorsed by recent clinical practice guidelines for investigation of androgen disorders in both men and women. Free T measurement is very challenging. The gold standard equilibrium dialysis methods are too complex for use in routine clinical laboratories, assays are not harmonized and consequently there are no common reference intervals to aid result interpretation. The algorithms derived for calculating free T are inaccurate because they were founded on faulty models of testosterone binding to SHBG, however they can still give clinically useful results. To negate the effects of differences in binding protein constants, some equations for free T have been derived from accurate measurement of testosterone in large population studies, however a criticism is that the equations may not hold true in different patient populations. The free androgen index is not recommended for use in men because of inaccuracy at extremes of SHBG concentration, and in women it can also give inaccurate results when SHBG concentrations are low. If the free hormone hypothesis is to be believed, then calculated free testosterone may offer the best way forward but better equations are needed to improve accuracy and these should be derived from detailed knowledge of testosterone binding to SHBG. There is still much work to be done to improve harmonization of T and SHBG assays between laboratories because these can have a profound effect on the equations used to calculate free testosterone.

Sex hormone-binding globulin provides a novel entry pathway for estradiol and influences subsequent signaling in lymphocytes via membrane receptor

The complex effects of estradiol on non-reproductive tissues/cells, including lymphoid tissues and immunocytes, have increasingly been explored. However, the role of sex hormone binding globulin (SHBG) in the regulation of these genomic and non-genomic actions of estradiol is controversial. Moreover, the expression of SHBG and its internalization by potential receptors, as well as the influence of SHBG on estradiol uptake and signaling in lymphocytes has remained unexplored. Here, we found that human and mouse T cells expressed SHBG intrinsically. In addition, B lymphoid cell lines as well as both primary B and T lymphocytes bound and internalized external SHBG, and the amount of plasma membrane-bound SHBG decreased in B cells of pregnant compared to non-pregnant women. As potential mediators of this process, SHBG receptor candidates expressed by lymphocytes were identified in silico, including estrogen receptor (ER) alpha. Furthermore, cell surface-bound SHBG was detected in close proximity to membrane ERs while highly colocalizing with lipid rafts. The SHBG-membrane ER interaction was found functional since SHBG promoted estradiol uptake by lymphocytes and subsequently influenced Erk1/2 phosphorylation. In conclusion, the SHBG-SHBG receptor-membrane ER complex participates in the rapid estradiol signaling in lymphocytes, and this pathway may be altered in B cells in pregnant women.

Measured free 25-hydroxyvitamin D in healthy children and relationship to total 25-hydroxyvitamin D, calculated free 25-hydroxyvitamin D and vitamin D binding protein

BACKGROUND

vitamin D deficiency in children is still a global health problem. Measuring free 25-hydroxyvitamin D concentrations could provide a better estimate of the vitamin D status than total 25-hydroxyvitamin D (25(OH)D) levels.

OBJECTIVE

To assess the relationship between measured free vitamin D (m-f25(OH)D) and calculated free 25(OH)D (c-f25(OH)D), total 25(OH)D, intact parathyroid hormone (iPTH) and other markers of phosphocalcic metabolism. To establish serum m-f25(OH)D concentrations corresponding to a total 25(OH)D > 50 nmol/L which is accepted as vitamin D-sufficiency status in children.

DESIGN

Prospective cohort study.

SETTING

January and February 2017 in a Mediterranean population.

PATIENTS

healthy children.

MEASUREMENTS

m-f25(OH)D and vitamin D binding protein (VDBP) by ELISA. Free 25(OH)D was calculated using the formula described by Bikle.

RESULTS

m-f25(OH)D directly correlated with total 25(OH)D (r:0.804,p < .001), serum calcium (r:0.26,p:0.035), and c-f25(OH)D (r:0.553,p:0.016); and inversely with iPTH (r:-0.374, p:0.002), alkaline phosphatase (r:-0.28, p:0.026), and age (r:-0.289, p:0.018). Total 25(OH)D correlated with the same parameters as m-f25(OH)D except for serum calcium. However, c-f25(OH)D correlated only with total 25(OH)D and VDBP, both included in the calculation formula. Multiple regression analysis showed that m-f25(OH)D variations were independently explained by calcium (β:0.156, p:0.026) and total 25(OH)D (β:0.043, p < .001). The optimal m-f25(OH)D cut-off for discriminating between insufficient and sufficient total 25(OH)D was >9.8 pmol/L (Area Under Curve (AUC): 0.897 (95% confidence interval (CI): (0.798-0.958); p < .001; sensitivity:72.7% (95%CI: 49.8-89.3); specificity: 95.5% (95%CI: 84.5-99.4)).

CONCLUSIONS

Directly measured free vitamin D correlated better with markers of phosphocalcic metabolism than total 25(OH)D and c-f25(OH)D in a population of healthy children.

Reassessing Free-Testosterone Calculation by Liquid Chromatography-Tandem Mass Spectrometry Direct Equilibrium Dialysis

CONTEXT

Assessment of free testosterone (FT) might help evaluate androgen status in patients with borderline total testosterone (T) and/or altered sex hormone-binding globulin (SHBG) levels. However, the validity of different methods to measure FT is debatable.

METHODS

Serum from 183 women and 146 men was analyzed using equilibrium dialysis (ED), with FT directly measured by liquid chromatography-tandem mass spectrometry. FT calculation was re-evaluated for the mass action law-based equation according to Vermeulen (cFT-V), empirical equations according to Ly (cFT-L), and a proposed calculation based on a multistep, dynamic, allosteric model according to Zakharov (cFT-Z).

RESULTS

FT level analyzed by ED [median,13 pmol/L (1.2% of T) in women; 248 pmol/L (1.5% of T) in men] was strongly inversely correlated to SHBG level, significantly to albumin level in women, and only weakly to SHBG level in men. The median [percentile (p) range, 2.5 to 97.5] ratios of calculated FT (cFT) over ED-FT (from European Male Aging Study samples) were 1.19 (0.9 to 1.47), 1.00 (0.69 to 1.42), and 2.05 (1.26 to 3.26) for cFT-V, cFT-L, and cFT-Z, respectively. The ratio for cFT-V was not significantly affected by SHBG, T, or albumin levels (ρ range, 0.17 to -0.01); ratios for cFT-L and cFT-Z were affected (P < 0.05 and P < 0.001, respectively) and strongly correlated with SHBG levels (ρ = 0.72 and 0.75, respectively). Rank correlations between cFT% and ED-FT% (for men) were 0.62, 0.74, and 0.89 for cFT-Z, cFT-L, and cFT-V, respectively.

CONCLUSION

FT results by direct ED confirm prior FT data from indirect ED and ultrafiltration methodologies. Calculations have inherent limitations, with clinically important differences among evaluated equations: cFT-V, although overestimating FT level, appears the most robust approximation, largely independent of SHBG, albumin, and T levels.

Reduced levels of stromal sex hormone-binding globulin and androgen receptor dysfunction in the sperm storage region of the rat epididymis

The cauda epididymidis is the major sperm storage region whose androgenic supply, essential for the sperm viability, is provided by the vasculature and is dependent upon testosterone diffusion through the stromal tissue to reach the epithelial cells. We have focused our efforts on examining the regulation of this important epididymal region by evaluating the impact of the androgen disrupter cimetidine on the epithelial–stromal androgenic microenvironment. Male rats received 100 mg/kg cimetidine (CMTG) or saline (CG) for 50 days, serum testosterone levels were measured and the epididymal cauda region was processed for light and transmission electron microscopy. In the proximal cauda region, the duct diameter was measured and birefringent collagen in the stroma was quantified. TUNEL-labeled epithelial cells were quantified, and androgen receptor (AR), karyopherin alpha (KPNA) and sex hormone-binding globulin (SHBG) levels were analyzed by immunofluorescence and Western blot. CMTG showed reduced duct diameter and high number of apoptotic epithelial cells. In the epithelium, the total AR concentration and the KPNA immunoreactivity were reduced, and a weak/absent AR nuclear immunofluorescence was observed in contrast to the enhanced AR immunolabeling observed in the cytoplasm of the epithelial cells. A significant reduction of collagen and SHBG levels in the stroma was also observed. Cimetidine treatment impairs AR nuclear import in the epithelium, causing androgenic dysfunction and subsequent epithelial cell apoptosis and duct atrophy. The connective tissue atrophy and reduction of SHBG stromal levels associated with epithelial androgenic dysfunction indicate a possible role of stromal SHBG in the androgenic supply of the sperm storage region of the epididymis.

Steroid Hormones and Their Action in Women's Brains: The Importance of Hormonal Balance

Sex hormones significantly impact women's lives. Throughout the different stages of life, from menarche to menopause and all stages in between, women experience dramatic fluctuations in the levels of progesterone and estradiol, among other hormones. These fluctuations affect the body as a whole, including the central nervous system (CNS). In the CNS, sex hormones act via steroid receptors. They also have an effect on different neurotransmitters such as GABA, serotonin, dopamine, and glutamate. Additionally, studies show that sex hormones and their metabolites influence brain areas that regulate mood, behavior, and cognitive abilities. This review emphasizes the benefits a proper hormonal balance during the different stages of life has in the CNS. To achieve this goal, it is essential that hormone levels are evaluated considering a woman's age and ovulatory status, so that a correct diagnosis and treatment can be made. Knowledge of steroid hormone activity in the brain will give women and health providers an important tool for improving their health and well-being.

Free Testosterone Reflects Metabolic as well as Ovarian Disturbances in Subfertile Oligomenorrheic Women

BACKGROUND

Diagnosing polycystic ovary syndrome (PCOS) is based on ovulatory dysfunction, ovarian ultrasound data, and androgen excess. Total testosterone is frequently used to identify androgen excess, but testosterone is mainly bound to sex hormone-binding globulin (SHBG) and albumin. Only 1-2% of nonprotein-bound testosterone (so-called free testosterone) is biologically active and responsible for androgen action. Moreover, automated immunoassays which are frequently used for female testosterone measurements are inaccurate.

OBJECTIVE

To assess the clinical usefulness of liquid chromatography-tandem mass spectrometry measured testosterone and calculated free testosterone in subfertile women attending a fertility clinic with oligomenorrhea and suspected PCOS.

METHODS

Hormonal and metabolic parameters were evaluated, and ovarian ultrasound was performed. Total testosterone was measured by liquid chromatography-tandem mass spectrometry. Free testosterone was calculated from total testosterone and SHBG.

RESULTS

Sixty-six women were included in the study. Total testosterone was associated with ovarian volume and antral follicle count but not with metabolic parameters. However, SHBG and calculated free testosterone were associated with both ovarian ultrasound and metabolic parameters, such as BMI and insulin resistance.

CONCLUSIONS

Assessing SHBG and free testosterone is important in evaluating androgen excess in subfertile women with ovulatory dysfunction and suspected PCOS, as it reflects both ovarian and metabolic disturbances.

Sex Hormone Decline and Amyloid β Synthesis, Transport and Clearance in the Brain

Sex hormones (SH) are essential regulators of the central nervous system. The decline in SH levels along with ageing may contribute to compromised neuroprotection and set the grounds for neurodegeneration and cognitive impairments. In Alzheimer's disease, besides other pathological features, there is an imbalance between amyloid β (Aβ) production and clearance, leading to its accumulation in the brain of older subjects. Aβ accumulation is a primary cause for brain inflammation and degeneration, as well as concomitant cognitive decline. There is mounting evidence that SH modulate Aβ production, transport and clearance. Importantly, SH regulate most of the molecules involved in the amyloidogenic pathway, their transport across brain barriers for elimination, and their degradation in the brain interstitial fluid. This review brings together data on the regulation of Aβ production, metabolism, degradation and clearance by SH.

Differential Responses to Vitamin D2 and Vitamin D3 Are Associated With Variations in Free 25-Hydroxyvitamin D

25-Hydroxyvitamin D (25D) circulates bound primarily to serum vitamin D binding protein (DBP), with DBP showing higher binding affinity for 25D3 than 25D2. We therefore hypothesized that vitamin D2 (D2) promotes higher serum levels of unbound 25D (free 25D), with different functional responses, relative to vitamin D3 (D3). Week 3 C56BL/6 mice were placed on diets containing either D2 or D3 alone (both 1000 IU/kg). At week 8 and week 16, D2 mice had only 25D2 in circulation (26.6 ± 1.9 and 33.3 ± 4.4 ng/mL), and D3 mice had only 25D3 (28.3 ± 2.0 and 31.7 ± 2.1 ng/mL). At week 8 (44.5 ± 6.4 vs 62.4 ± 11.6 pg/mL, P < .05) and week 16 (78.4 ± 12.6 vs 95.5 ± 11.6), D2 mice had lower serum 1,25-dihydroxyvitamin D relative to D3 mice. By contrast, measured free 25D was significantly higher in D2 mice at week 8 (16.8 ± 0.65 vs 8.4 ± 0.63 pg/mL, P < .001) and week 16 (17.4 ± 0.43 vs 8.4 ± 0.44, P < .001). A two-way ANOVA of bone histomorphometry showed that week 8 D2 mice had significantly higher osteoclast surface/bone surface, eroded surface/bone surface, and mineral apposition rate compared with D3 mice. Osteoblast surface/bone surface was higher in week 8 D2 females but not week 8 D2 males. At week 16, D2 mice had significantly higher bone volume/total volume and trabecular number compared with D3 mice. Differences in bone phenotype were observed despite D2 mice reaching similar serum 25D levels and lower 1,25D levels compared with D3 mice. These data indicate that 25D2 binds less well to DBP than 25D3, with resulting higher levels of free 25D promoting differential effects on bone in mice exposed to D2 alone.

The other side of progestins: effects in the brain

Progestins are a broad class of progestational agents widely differing in their chemical structures and pharmacological properties. Despite emerging data suggest that progestins, besides their action as endometrial protection, can also have multiple nonreproductive functions, much remains to be discovered regarding the actions exerted by these molecules in the nervous system. Here, we report the role exerted by different progestins, currently used for contraception or in postmenopausal hormone replacement therapies, in regulating cognitive functions as well as social behavior and mood. We provide evidence that the effects and mechanisms underlying their actions are still confusing due to the use of different estrogens and progestins as well as different doses, duration of exposure, route of administration, baseline hormonal status and age of treated women. We also discuss the emerging issue concerning the relevant increase of these substances in the environment, able to deeply affect aquatic wildlife as well as to exert a possible influence in humans, which may be exposed to these compounds via contaminated drinking water and seafood. Finally, we report literature data showing the neurobiological action of progestins and in particular their importance during neurodegenerative events. This is extremely interesting, since some of the progestins currently used in clinical practice exert neuroprotective and anti-inflammatory effects in the nervous system, opening new promising opportunities for the use of these molecules as therapeutic agents for trauma and neurodegenerative disorders.

Plasma steroid-binding proteins: primary gatekeepers of steroid hormone action

Biologically active steroids are transported in the blood by albumin, sex hormone-binding globulin (SHBG), and corticosteroid-binding globulin (CBG). These plasma proteins also regulate the non-protein-bound or 'free' fractions of circulating steroid hormones that are considered to be biologically active; as such, they can be viewed as the 'primary gatekeepers of steroid action'. Albumin binds steroids with limited specificity and low affinity, but its high concentration in blood buffers major fluctuations in steroid concentrations and their free fractions. By contrast, SHBG and CBG play much more dynamic roles in controlling steroid access to target tissues and cells. They bind steroids with high (~nM) affinity and specificity, with SHBG binding androgens and estrogens and CBG binding glucocorticoids and progesterone. Both are glycoproteins that are structurally unrelated, and they function in different ways that extend beyond their transportation or buffering functions in the blood. Plasma SHBG and CBG production by the liver varies during development and different physiological or pathophysiological conditions, and abnormalities in the plasma levels of SHBG and CBG or their abilities to bind steroids are associated with a variety of pathologies. Understanding how the unique structures of SHBG and CBG determine their specialized functions, how changes in their plasma levels are controlled, and how they function outside the blood circulation provides insight into how they control the freedom of steroids to act in health and disease.

Sex Hormone Binding Globulin Modifies Testosterone Action and Metabolism in Prostate Cancer Cells

Sex Hormone Binding Globulin (SHBG) is the major serum carrier of sex hormones. However, growing evidence suggests that SHBG is internalised and plays a role in regulating intracellular hormone action. This study was to determine whether SHBG plays a role in testosterone uptake, metabolism, and action in the androgen sensitive LNCaP prostate cancer cell line. Internalisation of SHBG and testosterone, the effects of SHBG on testosterone uptake, metabolism, regulation of androgen responsive genes, and cell growth were assessed. LNCaP cells internalised SHBG by a testosterone independent process. Testosterone was rapidly taken up and effluxed as testosterone-glucuronide; however this effect was reduced by the presence of SHBG. Addition of SHBG, rather than reducing testosterone bioavailability, further increased testosterone-induced expression of prostate specific antigen and enhanced testosterone-induced reduction of androgen receptor mRNA expression. Following 38 hours of testosterone treatment cell morphology changed and growth declined; however, cotreatment with SHBG abrogated these inhibitory effects. These findings clearly demonstrate that internalised SHBG plays an important regulatory and intracellular role in modifying testosterone action and this has important implications for the role of SHBG in health and disease.

What maintains the high intra-follicular estradiol concentration in pre-ovulatory follicles?

PURPOSE

The purpose of the study was to establish the mechanism by which the estrogen concentration difference between the follicular fluid and the serum is maintained.

METHODS

We used dialysis membrane with a pore size of <3 KD to characterize the estrogen-binding capacity of the follicular fluid. We performed PCR, western blot, and ELISA on luteinized granulosa cells to determine if sex hormone-binding globulin (SHBG) is produced by granulosa cells, and finally we used affinity columns and mass spectrometry to identify the estrogen-binding protein in the follicular fluid.

RESULTS

We found that a significant estrogen concentration difference is maintained in a cell-free system and is lost with proteolysis of the follicular fluid proteins. Luteinized granulosa cells are likely not a source of SHBG, as we were not able to detect expression of SHBG in these cells. Perlecan was the most highly enriched follicular fluid protein in the affinity columns.

CONCLUSIONS

We were able to identify perlecan as the most likely candidate for the major estrogen-binding protein in the follicular fluid.

Human sex hormone-binding globulin binding affinities of 125 structurally diverse chemicals and comparison with their binding to androgen receptor, estrogen receptor, and α-fetoprotein

One endocrine disruption mechanism is through binding to nuclear receptors such as the androgen receptor (AR) and estrogen receptor (ER) in target cells. The concentration of a chemical in serum is important for its entry into the target cells to bind the receptors, which is regulated by the serum proteins. Human sex hormone-binding globulin (SHBG) is the major transport protein in serum that can bind androgens and estrogens and thus change a chemical's availability to enter the target cells. Sequestration of an androgen or estrogen in the serum can alter the chemical elicited AR- and ER-mediated responses. To better understand the chemical-induced endocrine activity, we developed a competitive binding assay using human pregnancy plasma and measured the binding to the human SHBG for 125 structurally diverse chemicals, most of which were known to bind AR and ER. Eighty seven chemicals were able to bind the human SHBG in the assay, whereas 38 chemicals were nonbinders. Binding data for human SHBG are compared with that for rat α-fetoprotein, ER and AR. Knowing the binding profiles between serum and nuclear receptors will improve assessment of a chemical's potential for endocrine disruption. The SHBG binding data reported here represent the largest data set of structurally diverse chemicals tested for human SHBG binding. Utilization of the SHBG binding data with AR and ER binding data could enable better evaluation of endocrine disrupting potential of chemicals through AR- and ER-mediated responses since sequestration in serum could be considered.

Vitamin D and DBP: the free hormone hypothesis revisited

The last five years have witnessed a remarkable renaissance in vitamin D research and a complete re-evaluation of its benefits to human health. Two key factors have catalyzed these changes. First, it now seems likely that localized, tissue-specific, conversion of 25-hydroxyvitamin D (25OHD) to 1,25-dihydroxyvitamin D (1,25(OH)2D) drives many of the newly recognized effects of vitamin D on human health. The second key factor concerns the ongoing discussion as to what constitutes adequate or optimal serum vitamin D (25OHD) status, with the possibility that vitamin D-deficiency is common to communities across the globe. These two concepts appear to be directly linked when low serum concentrations of 25OHD compromise intracrine generation of 1,25(OH)2D within target tissues. But, is this an over-simplification? Pro-hormone 25OHD is a lipophilic molecule that is transported in the circulation bound primarily to vitamin D binding protein (DBP). While the association between 25OHD and DBP is pivotal for renal handling of 25OHD and endocrine synthesis of 1,25(OH)2D, what is the role of DBP for extra-renal synthesis of 1,25(OH)2D? We hypothesize that binding to DBP impairs delivery of 25OHD to the vitamin D-activating enzyme 1α-hydroxylase in some target cells. Specifically, it is unbound, 'free' 25OHD that drives many of the non-classical actions of vitamin D. Levels of 'free' 25OHD are dependent on the concentration of DBP and alternative serum binding proteins such as albumin, but will also be influenced by variations in DBP binding affinity for specific vitamin D metabolites. The aim of this review will be to discuss the merits of 'free 25OHD' as an alternative marker of vitamin D status, particularly in the context of non-classical responses to vitamin D. This article is part of a Special Issue entitled '16th Vitamin D Workshop'.

Polymorphisms in estrogen receptors predict the risk of male infertility: a meta-analysis

BACKGROUND

Estrogen receptors play an important role in mediating estrogen action on target tissues, and the estrogen is relevant to male infertility. Single nucleotide polymorphisms (SNPs) in estrogen receptors may be associated with the risk of male infertility. A variety of case control studies have been published evaluating this association. However, the accumulated studies have shown inconsistent conclusions.

METHODS

To further determine the potential association between the four common SNPs (rs2234693, rs9340799, rs1256049 and rs4986938) in estrogen receptors gene and male infertility, this meta-analysis was performed according to the 10 published case control studies. The odds ratio (OR) and 95% confidence interval (CI) were used to evaluate the strength of the associations.

RESULTS

It was revealed that the sub-group analysis by the ethnicity, for the rs2234693, a significant association in the comparison of CC vs. TT (OR = 0.61, 95% CI: 0.40-0.93), CT vs. TT (OR = 0.67, 95% CI: 0.49-0.93) and CC + CT vs. TT (OR = 0.66, 95% CI: 0.49-0.89) in the Asian population with male infertility. For rs9340799 polymorphism, increased risks were observed for the comparison of AA vs. GG (OR = 1.75, 95% CI: 1.15-2.68) and AA vs. GA + GG (OR = 1.38, 95% CI: 1.02-1.88). For rs1256049 polymorphism, the comparison of the GA vs. GG (OR = 1.52, 95% CI: 1.00-2.31) and AA + GA vs. GG (OR = 1.74, 95% CI: 1.03-2.94), also increased risks present in Asian and Caucasian population, respectively.

CONCLUSIONS

The rs2234693C allele was associated with the decreased risk for male infertility; however, the rs9340799AA genotype and the rs1256049GA genotype were associated with an increased risk for male infertility.

Naturally occurring mutants inform SHBG structure and function

SHBG transports and regulates the activities of androgens and estrogens. Several single nucleotide polymorphisms in the human SHBG gene have been linked to sex steroid-dependent diseases, including those associated with the metabolic syndrome. The N-terminal laminin G-like domain of SHBG includes binding sites for calcium, sex steroids, and fibulin family members, as well as a dimerization domain. We have found that 8 of 18 uncharacterized nonsynonymous single nucleotide polymorphisms within this domain alter the production or biochemical properties of SHBG in ways not previously recognized. O-Linked glycosylation at Thr7 is disrupted in SHBG T7N, whereas abnormal glycosylation of SHBG G195E limits its secretion. Three SHBG mutants (R135C, L165M, and E176K) bind estradiol with abnormally high affinity. SHBG R135C also has an increased interaction with fibulin-2. Two different substitutions within the dimer interface at R123 (R123H and R123C) reduce the affinity for 5α-dihydrotestosterone, while increasing the relative binding affinity for estradiol. SHBG T48I is defective in calcium binding, which leads to a defect in dimerization, reduced affinity for sex steroids, and an enhanced interaction with fibulin-2, which can all be restored by calcium supplementation. These naturally occurring mutants provide insight into SHBG structure and function, and defects in SHBG production or function need to be considered in the context of its utility as a biomarker of diseases.

Testicular function during adolescence in boys with type 1 diabetes mellitus (T1D): absence of hypogonadism and differences in endocrine profile at the beginning and end of puberty

AIM

Conflicting results regarding testicular function in adults with type 1 diabetes (T1D) have been reported, but little is known about Leydig and Sertoli cell function during puberty in boys treated with multiple daily insulin doses. Our aim was to assess testicular function in boys with T1D.

METHODS

Pubertal boys with T1D (n = 71) and healthy control boys (Control group; n = 104) who were 10-18 years were studied. Both groups were matched by pubertal stage, age, and BMI. Total testosterone (TT), calculated free testosterone (cfT), SHBG, inhibin B, AMH, and gonadotropin levels were determined.

RESULTS

At the beginning of puberty, the T1D group had higher levels of SHBG (p = 0.003) and similar androgen levels than the Control group. At the end of puberty, higher TT, and cfT were observed in T1D compared to the Control group (p < 0.01 and p < 0.001, respectively). Gonadotropins and AMH were similar in both groups. Regression analysis showed that T1D was a significant factor, even after adjusting for Tanner stage and BMI-SDS, affecting TT, cFT, and SHBG levels. BMI-SDS was a significant factor affecting TT and SHBG levels. Higher HbA1c had a negative effect on total testosterone and cFT and a positive effect on SHBG levels in T1D boys.

CONCLUSION

Adolescents with T1D do not exhibit hypogonadism, as shown by normal gonadotropin, testosterone, inhibin B, and AMH levels. However, in T1D boys, HbA1c and BMI-SDS had a negative association with testosterone levels. Elevated testosterone levels are observed during late puberty, which were not present earlier.

Single-nucleotide polymorphism, rs1799941 in the Sex Hormone-Binding Globulin (SHBG) gene, related to both serum testosterone and SHBG levels and the risk of myocardial infarction, type 2 diabetes, cancer and mortality in men: the Tromsø Study

Low testosterone levels are associated with metabolic and cardiovascular disease risk factor, and have been shown to predict type 2 diabetes mellitus (T2DM), myocardial infarction (MI) and all-cause mortality. It is not known if these associations are causal or not. Recently, it has been shown that the serum testosterone levels are associated with single-nucleotide polymorphisms (SNPs), and we therefore studied the associations between one of these SNPs, rs1799941 on the Sex Hormone-Binding Globulin (SHBG) gene, and MI, T2DM, cancer and death. DNA was prepared from men who participated in the fourth survey of the Tromsø Study in 1994-1995 and who were registered with the endpoints MI, T2DM, cancer or death and a randomly selected control group. For mortality, the observation time was set from 1994, and for the other endpoints from birth. The endpoint data were completed up to 2010-2013. Genetic analyses were successfully performed in 5309 men, of whom 1454 were registered with MI, 638 with T2DM, 1534 with cancer and in 2226 who had died. Men with the minor homozygote genotype had significantly higher levels of total testosterone (14.7%) and SHBG (24.7%) compared with men with the major homozygote genotype, whereas free testosterone levels did not differ significantly between the genotypes. The SNP rs1799941 was not significantly associated with MI, T2DM, cancer or mortality. Thus, our result does not support a causal relationship between total testosterone and SHBG and MI, T2DM, cancer or mortality, suggesting that low testosterone more likely is a marker of poor health.

Apolipoprotein A-IV reduces hepatic gluconeogenesis through nuclear receptor NR1D1

We showed recently that apoA-IV improves glucose homeostasis by enhancing pancreatic insulin secretion in the presence of elevated levels of glucose. Therefore, examined whether apolipoprotein A-IV (apoA-IV) also regulates glucose metabolism through the suppression of hepatic gluconeogenesis. The ability of apoA-IV to lower gluconeogenic gene expression and glucose production was measured in apoA-IV(-/-) and wild-type mice and primary mouse hepatocytes. The transcriptional regulation of Glc-6-Pase and phosphoenolpyruvate carboxykinase (PEPCK) by apoA-IV was determined by luciferase activity assay. Using bacterial two-hybrid library screening, NR1D1 was identified as a putative apoA-IV-binding protein. The colocalization and interaction between apoA-IV and NR1D1 were confirmed by immunofluorescence, in situ proximity ligation assay, and coimmunoprecipitation. Enhanced recruitment of NR1D1 and activity by apoA-IV to Glc-6-Pase promoter was verified with ChIP and a luciferase assay. Down-regulation of apoA-IV on gluconeogenic genes is mediated through NR1D1, as illustrated in cells with NR1D1 knockdown by siRNA. We found that apoA-IV suppresses the expression of PEPCK and Glc-6-Pase in hepatocytes; decreases hepatic glucose production; binds and activates nuclear receptor NR1D1 and stimulates NR1D1 expression; in cells lacking NR1D1, fails to inhibit PEPCK and Glc-6-Pase gene expression; and stimulates higher hepatic glucose production and higher gluconeogenic gene expression in apoA-IV(-/-) mice. We conclude that apoA-IV inhibits hepatic gluconeogenesis by decreasing Glc-6-Pase and PEPCK gene expression through NR1D1. This novel regulatory pathway connects an influx of energy as fat from the gut (and subsequent apoA-IV secretion) with inhibition of hepatic glucose production.

Progestogens used in postmenopausal hormone therapy: differences in their pharmacological properties, intracellular actions, and clinical effects

The safety of progestogens as a class has come under increased scrutiny after the publication of data from the Women's Health Initiative trial, particularly with respect to breast cancer and cardiovascular disease risk, despite the fact that only one progestogen, medroxyprogesterone acetate, was used in this study. Inconsistency in nomenclature has also caused confusion between synthetic progestogens, defined here by the term progestin, and natural progesterone. Although all progestogens by definition have progestational activity, they also have a divergent range of other properties that can translate to very different clinical effects. Endometrial protection is the primary reason for prescribing a progestogen concomitantly with postmenopausal estrogen therapy in women with a uterus, but several progestogens are known to have a range of other potentially beneficial effects, for example on the nervous and cardiovascular systems. Because women remain suspicious of the progestogen component of postmenopausal hormone therapy in the light of the Women's Health Initiative trial, practitioners should not ignore the potential benefits to their patients of some progestogens by considering them to be a single pharmacological class. There is a lack of understanding of the differences between progestins and progesterone and between individual progestins differing in their effects on the cardiovascular and nervous systems, the breast, and bone. This review elucidates the differences between the substantial number of individual progestogens employed in postmenopausal hormone therapy, including both progestins and progesterone. We conclude that these differences in chemical structure, metabolism, pharmacokinetics, affinity, potency, and efficacy via steroid receptors, intracellular action, and biological and clinical effects confirm the absence of a class effect of progestogens.

Sex and gonadal hormones in mouse models of Alzheimer's disease: what is relevant to the human condition?

Biologic sex and gonadal hormones matter in human aging and diseases of aging such as Alzheimer's - and the importance of studying their influences relates directly to human health. The goal of this article is to review the literature to date on sex and hormones in mouse models of Alzheimer's disease (AD) with an exclusive focus on interpreting the relevance of findings to the human condition. To this end, we highlight advances in AD and in sex and hormone biology, discuss what these advances mean for merging the two fields, review the current mouse model literature, raise major unresolved questions, and offer a research framework that incorporates human reproductive aging for future studies aimed at translational discoveries in this important area. Unraveling human relevant pathways in sex and hormone-based biology may ultimately pave the way to novel and urgently needed treatments for AD and other neurodegenerative diseases.

Evolving utility of sex hormone-binding globulin measurements in clinical medicine

PURPOSE OF REVIEW

Sex hormone-binding globulin (SHBG) regulates the plasma levels and biological actions of the sex steroids: testosterone and estradiol. Advances in our understanding of how plasma SHBG levels are determined, and how SHBG functions, have provided insight into how SHBG should be used to assess the actions of its sex-steroid ligands, and as a biomarker of metabolic and endocrine abnormalities.

RECENT FINDINGS

Plasma SHBG levels fluctuate throughout life in response to the changes in metabolic and physiologic states, and are altered by natural hormones and synthetic steroids. Interindividual differences in plasma SHBG levels and activity are also influenced by polymorphisms within the structural and regulatory regions of the SHBG gene.

SUMMARY

Measurements of SHBG are widely used to predict plasma free testosterone levels in patients suffering from excess androgen exposures, but have broader utility in assessing the risk for endocrine diseases and clinical sequelae of the metabolic syndrome, namely, type 2 diabetes and cardiovascular disease. It is anticipated that new genetic and functional data regarding SHBG will reveal whether SHBG is simply a biomarker of these diseases or participants in their cause.

Direct measurement of free estradiol in human serum by equilibrium dialysis-liquid chromatography-tandem mass spectrometry and reference intervals of free estradiol in women

BACKGROUND

Measurement of free estradiol offers a better representation of the bioactive fraction of the hormone. We describe a direct equilibrium dialysis-liquid chromatography-tandem mass spectrometry (ED-LC-MS/MS) method for serum free estradiol.

METHODS

Two hundred fifty microliter aliquots of serum were dialyzed for 22h followed by liquid-liquid extraction and derivatization with dansyl chloride. Free estradiol was measured using LC-MS/MS with an AB SCIEX 5500 mass spectrometer in positive ion and multiple reaction monitoring (MRM) mode.

RESULTS

The limits of detection and quantification for free estradiol were 0.25 and 0.5pg/ml (0.9 and 1.8pmol/l) respectively. Total imprecision was less than 10%. Results of method comparison showed 3 times overestimation using indirect methods of measurement. Reference intervals in pre-menopausal women in follicular, mid-cycle, and luteal phases of cycle were <2.4, <3.1 and <2.6pg/ml (8.8, 11.4, 9.5pmol/l) respectively; in post menopausal women the concentrations were ≤0.5pg/ml (1.8pmol/l).

CONCLUSIONS

ED-LC-MS/MS is a direct method for accurately measuring free estradiol, independent of total estradiol or sex hormone binding globulin concentrations. Imprecision and sensitivity of the method are adequate for clinical diagnostic applications. The degree of variation observed in the method comparison reinforces the relevance of method specific reference ranges.

Vitamin D binding protein and monocyte response to 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D: analysis by mathematical modeling

Vitamin D binding protein (DBP) plays a key role in the bioavailability of active 1,25-dihydroxyvitamin D (1,25(OH)₂D) and its precursor 25-hydroxyvitamin D (25OHD), but accurate analysis of DBP-bound and free 25OHD and 1,25(OH)₂D is difficult. To address this, two new mathematical models were developed to estimate: 1) serum levels of free 25OHD/1,25(OH)₂D based on DBP concentration and genotype; 2) the impact of DBP on the biological activity of 25OHD/1,25(OH)₂D in vivo. The initial extracellular steady state (eSS) model predicted that 50 nM 25OHD and 100 pM 1,25(OH)₂D), <0.1% 25OHD and <1.5% 1,25(OH)₂D are ‘free’ in vivo. However, for any given concentration of total 25OHD, levels of free 25OHD are higher for low affinity versus high affinity forms of DBP. The eSS model was then combined with an intracellular (iSS) model that incorporated conversion of 25OHD to 1,25(OH)₂D via the enzyme CYP27B1, as well as binding of 1,25(OH)₂D to the vitamin D receptor (VDR). The iSS model was optimized to 25OHD/1,25(OH)₂D-mediated in vitro dose-responsive induction of the vitamin D target gene cathelicidin (CAMP) in human monocytes. The iSS model was then used to predict vitamin D activity in vivo (100% serum). The predicted induction of CAMP in vivo was minimal at basal settings but increased with enhanced expression of VDR (5-fold) and CYP27B1 (10-fold). Consistent with the eSS model, the iSS model predicted stronger responses to 25OHD for low affinity forms of DBP. Finally, the iSS model was used to compare the efficiency of endogenously synthesized versus exogenously added 1,25(OH)₂D. Data strongly support the endogenous model as the most viable mode for CAMP induction by vitamin D in vivo. These novel mathematical models underline the importance of DBP as a determinant of vitamin D ‘status’ in vivo, with future implications for clinical studies of vitamin D status and supplementation.

Molecular mechanisms of steroid receptor-mediated actions by synthetic progestins used in HRT and contraception

Synthetic progestins are used by millions of women as contraceptives and in hormone replacement therapy (HRT), although their molecular mechanisms of action are not well understood. The importance of investigating these mechanisms, as compared to those of progesterone, has been highlighted by clinical evidence showing that medroxyprogesterone acetate (MPA), a first generation progestin, increases the risk of breast cancer and coronary heart disease in HRT users. A diverse range of later generation progestins with varying structures and pharmacological properties is available for therapeutic use and it is becoming clear that different progestins elicit beneficial and adverse effects to different extents. These differences in biological activity are likely to be due to many factors including variations in dose, metabolism, pharmacokinetics, bioavailability, and regulation of, and/or binding, to serum-binding proteins and steroidogenic enzymes. Since the intracellular effects on gene expression and cell signaling of steroids are mediated via intracellular steroid receptors, differential actions via the progesterone and other steroid receptors and their isoforms, are likely to be the major cause of differential intracellular actions of progestins. Since many progestins bind not only to the progesterone receptor, but also to the glucocorticoid, androgen, mineralocorticoid, and possibly the estrogen receptors, it is plausible that synthetic progestins exert therapeutic actions as well as side-effects via some of these receptors. Here we review the molecular mechanisms of intracellular actions of old (MPA, norethisterone, levonorgestrel, gestodene) vs. new (drospirenone, dienogest, trimegestone) generation progestins, via steroid receptors.

Diverse roles for sex hormone-binding globulin in reproduction

Sex hormone-binding globulin (SHBG) transports androgens and estrogens in blood and regulates their access to target tissues. Hepatic production of SHBG fluctuates throughout the life cycle and is influenced primarily by metabolic and hormonal factors. Genetic differences also contribute to interindividual variations in plasma SHBG levels. In addition to controlling the plasma distribution, metabolic clearance, and bioavailability of sex steroids, SHBG accumulates in the extravascular compartments of some tissues and in the cytoplasm of specific epithelial cells, where it exerts novel effects on androgen and estrogen action. In mammals, the gene-encoding SHBG is expressed primarily in the liver but also at low levels in other tissues, including the testis. In subprimate species, Shbg expression in Sertoli cells is under the control of follicle-stimulating hormone and produces the androgen-binding protein that influences androgen actions in the seminiferous tubules and epididymis. In humans, the SHBG gene is not expressed in Sertoli cells, but its expression in germ cells produces an SHBG isoform that accumulates in the acrosome. In fish, Shbg is produced by the liver but has a unique function in the gill as a portal for natural steroids and xenobiotics, including synthetic steroids. However, salmon have retained a second, poorly conserved Shbg gene that is expressed only in ovary, muscle, and gill and that likely exerts specialized functions in these tissues. The present review compares the production and functions of SHBG in different species and its diverse effects on reproduction.

Association of polymorphisms in the estrogen receptors alpha, and beta (ESR1, ESR2) with the occurrence of male infertility and semen parameters

Male infertility is a multifactorial condition with a strong genetic component. In the last decade a large number of investigations focused on the identification of gene variants affecting spermatogenesis in human. Polymorphisms of the estrogen receptor (ER) genes, have been implicated in male infertility, however, comprehensive data are lacking. We investigated the association between the ER-α gene (ESR1) PvuII and XbaI and ER-β gene (ESR2) RsaI and Alul polymorphisms and the idiopathic male infertility in Iranian males. Polymerase chain reaction (PCR) method and restriction fragment length polymorphism (RFLP) were used to detect the ER-α, and ER-β gene polymorphisms in 164 infertile men and 164 age-matched healthy controls. Reproductive hormones were measured and at least two semen analyses were performed in each subject. Significant differences were observed in the frequency distribution of Pvull and XbaI in the ESR-α gene and RsaI and Alul in the ER-β gene between patients and controls. The presence of the ER-α Pvull TC (OR = 0.56, 95% CI: 0.26-0.80; P = 0.011), ER-α XbaI AG (OR = 0.51, 95% CI: 0.31-0.84; P = 0.017), and ER-β Alul GG (OR = 0.48, 95% CI: 0.265-0.84; P = 0.012) genotypes suggest a protective effect for infertility. The ER-β RsaI AG (OR = 2.32, 95% CI: 1.61-3.22; P = 0.012) and ER-β Alul AG (OR=2.76, 95% CI: 1.64-3.66; P=0.014) genotypes are associated with increased infertility risk. Subjects (both fertile and infertile) with ER-α Pvull TT, ER-α XbaI AA, ER-β RsaI AG, and ER-β Alul AG genotypes had significantly lower levels of serum sex hormone binding globulin (SHBG), and luteinizing hormone (LH), but, higher serum levels of free estradiol and follicle stimulating hormone (FSH). The same genotypes had significantly lower values for sperm density, sperm motility, and percentage of sperm with normal morphology. Our results further suggest a possible role of ESR-α, and ER-β variants on male infertility. Further studies are needed to replicate our findings as well as to better elucidate the biological mechanisms of the modulation of ESR-α, and ER-β on male infertility.

Vitamin D-binding protein directs monocyte responses to 25-hydroxy- and 1,25-dihydroxyvitamin D

BACKGROUND

Serum 25-hydroxyvitamin D (25OHD) is a key factor in determining monocyte induction of the antimicrobial protein cathelicidin, which requires intracrine conversion of 25OHD to 1,25-dihydroxyvitamin D [1,25(OH)(2)D]. Both vitamin D metabolites circulate bound to vitamin D-binding protein (DBP), but the effect of this on induction of monocyte cathelicidin remains unclear.

METHODS

Human monocytes were cultured in medium containing 1) serum from DBP knockout (DBP(-/-)) or DBP(+/-) mice, 2) serum-free defined supplement reconstituted with DBP or albumin (control), and 3) human serum with different DBP [group-specific component [Gc]] genotypes with varying affinities for vitamin D metabolites. In each case, response to added 1,25(OH)(2)D(3) or 25OHD(3) was determined by measuring expression of mRNA for cathelicidin and 24-hydroxylase. Monocyte internalization of DBP was assessed by fluorescent tagging followed by microscopic and flow cytometric analysis of tagged DBP.

RESULTS

Monocytes cultured in DBP(-/-) serum showed more potent induction of cathelicidin by 25OHD(3) or 1,25(OH)(2)D(3) when compared with DBP(+/-) serum. Likewise, DBP added to serum-free medium attenuated 25OHD(3)/1,25(OH)(2)D(3) responses. Fluorescently tagged DBP showed low-level uptake by monocytes, but this did not appear to involve a megalin-mediated mechanism. Human serum containing low-affinity Gc2-1S or Gc2-2, respectively, supported 2.75-fold (P = 0.003) and 2.43-fold (P = 0.016) higher induction of cathelicidin by 25OHD relative to cells cultured with high affinity Gc1F-1F.

CONCLUSION

These data indicate that DBP plays a pivotal role in regulating the bioavailablity of 25OHD to monocytes. Vitamin D-dependent antimicrobial responses are therefore likely to be strongly influenced by DBP polymorphisms.

Structural analyses of sex hormone-binding globulin reveal novel ligands and function

Plasma sex hormone-binding globulin (SHBG) regulates the access of androgens and estrogens to their target tissues and cell types. An SHBG homologue, known as the androgen-binding protein, is expressed in Sertoli cells of many mammalians, but testicular expression of human SHBG is restricted to germ cells. The primary structure of SHBG comprises tandem laminin G-like (LG) domains. The amino-terminal LG-domain includes the steroid-binding site and dimerization interface, and its tertiary structure, resolved in complex with natural and synthetic sex steroids, has revealed unanticipated mechanisms of steroid binding at the atomic level. This LG-domain interacts with fibulin-1D and fibulin-2 in a ligand-specific manner, and this is attributed to the unique way estrogens reside within the steroid-binding site, and the ordering of an otherwise flexible loop structure covering the entrance of the steroid-binding pocket. This mechanism enables estradiol to enhance the sequestration of plasma SHBG by the stroma of some tissues through binding to these extra-cellular matrix-associated proteins. The human SHBG amino-terminal LG-domain also contains several cation-binding sites, and occupancy of a zinc-binding site influences its affinity for estradiol. The complete quaternary structure of SHBG remains unresolved but structural predictions suggest that the carboxy-terminal LG-domains extend laterally from the dimerized amino-terminal LG-domains. The carboxy-terminal LG-domain contains two N-glycosylation sites, but their biological significance remains obscure. Knowledge of the SHBG tertiary structure has helped develop computational techniques based on the use of a "bench-mark data set" of steroid ligands, and created novel drug discovery and toxicology risk assessment platforms.

Some sex hormone profiles are consistent over time in normal menstruating women: implications for sports injury epidemiology

PURPOSE

It is unclear whether sex hormone profiles obtained in two consecutive months are consistent within women. Month-to-month consistency in daily, nadir, peak and mean hormone concentrations during the early follicular and luteal phases in recreationally active, young eumenorrheic women was prospectively examined.

METHODS

60 healthy, non-smoking women who reported normal and consistent menstrual cycles lasting 26-32 days for the past 6 months were followed prospectively to obtain serum samples for the first 6 days of menses and for 8 days after a positive ovulation test over two consecutive months. Month-to-month consistency of daily concentrations of oestradiol (pg/ml), progesterone (ng/ml), testosterone (ng/dl), sex hormone-binding globulin (nmol/l) and free androgen index were determined using linear mixed models. Month-to-month consistency in nadir, peak and mean concentrations were then assessed using intraclass correlation coefficients and SEM to more precisely examine intraindividual consistency.

RESULTS

Linear mixed models revealed stable hormone concentrations across cycles and cycles by day. Reliability estimates for nadir, peak, mean menses and mean postovulatory concentrations range from 0.56 to 0.86 for oestradiol, 0.44 to 0.91 for progesterone, 0.60 to 0.86 for testosterone, 0.88 to 0.97 for sex hormone-binding globulin and 0.78 to 0.91 for free androgen index.

CONCLUSIONS

Hormone profiles were reproducible over two consecutive months. To reduce month-to-month intraindividual variations and improve measurement consistency, it is recommended that multiple samples be taken over consecutive days as opposed to a single sample.

Effects of aggressive encounters on plasma corticosteroid-binding globulin and its ligands in white-crowned sparrows

In birds, corticosteroid-binding globulin (CBG) binds corticosterone, progesterone and testosterone. The concentration of each ligand can alter the binding of the other ligands through competitive interactions. Thus, an increase in corticosterone or progesterone may displace testosterone bound to CBG, leading to an increase in bioactive free testosterone levels without affecting total testosterone levels in the circulation. Aggressive interactions increase plasma total testosterone levels in some birds but not in others. Here, we tested the hypothesis that aggressive encounters in the late breeding season would not increase total testosterone levels in plasma, but would alter CBG, total corticosterone or total progesterone levels in such a way as to modify the number of available binding sites and therefore occupancy by testosterone. A marked decrease in CBG occupancy by testosterone would indirectly suggest an increase in free testosterone levels in plasma. Wild male white-crowned sparrows were exposed to a simulated territorial intrusion (STI) or control for 30 min. Subjects were then caught and bled. We measured CBG using a ligand-binding assay and corticosterone, progesterone and testosterone using highly sensitive radioimmunoassays. STI significantly increased aggressive behaviors but did not affect plasma total testosterone levels. STI significantly increased plasma CBG and total corticosterone levels and decreased plasma total progesterone levels. We predict that CBG occupancy by corticosterone will increase slightly following an aggressive encounter. However, this small change is unlikely to increase free testosterone levels, because of the large number of seemingly unoccupied CBG binding sites in these subjects.

Residues in the human corticosteroid-binding globulin reactive center loop that influence steroid binding before and after elastase cleavage

Corticosteroid-binding globulin (CBG) is a non-inhibitory serine proteinase inhibitor (serpin) that transports cortisol and progesterone in blood. Crystal structures of rat CBG and a thrombin-cleaved human CBG:anti-trypsin (Pittsburgh) chimera show how structural transitions after proteolytic cleavage of the CBG reactive center loop (RCL) could disrupt steroid binding. This ligand release mechanism is assumed to involve insertion of the cleaved RCL into the beta-sheet A of the serpin structure. We have, therefore, examined how amino acid substitutions in the human CBG RCL influence steroid binding before and after its cleavage by neutrophil elastase. Elastase-cleaved wild-type CBG or variants with substitutions at P15 and/or P16 (E334G/G335N or E334A) lost steroid binding completely, whereas deletion of Glu-334 resulted in no loss of steroid binding after RCL cleavage, presumably because this prevents its insertion into beta-sheet A. Similarly, the steroid binding properties of CBG variants with substitutions at P15 (G335P), P14 (V336R), or P12 (T338P) in the RCL hinge were largely unaffected after elastase cleavage, most likely because the re-orientation and/or insertion of the cleaved RCL was blocked. Substitutions at P10 (G340P, G340S) or P8 (T342P, T342N) resulted in a partial loss of steroid binding after proteolysis which we attribute to incomplete insertion of the cleaved RCL. Remarkably, several substitutions (E334A, V336R, G340S, and T342P) increased the steroid binding affinities of human CBG even before elastase cleavage, consistent with the concept that CBG normally toggles between a high affinity ligand binding state where the RCL is fully exposed and a lower affinity state in which the RCL is partly inserted into beta-sheet A.

Osteoporosis in men

With the aging of the population, there is a growing recognition that osteoporosis and fractures in men are a significant public health problem, and both hip and vertebral fractures are associated with increased morbidity and mortality in men. Osteoporosis in men is a heterogeneous clinical entity: whereas most men experience bone loss with aging, some men develop osteoporosis at a relatively young age, often for unexplained reasons (idiopathic osteoporosis). Declining sex steroid levels and other hormonal changes likely contribute to age-related bone loss, as do impairments in osteoblast number and/or activity. Secondary causes of osteoporosis also play a significant role in pathogenesis. Although there is ongoing controversy regarding whether osteoporosis in men should be diagnosed based on female- or male-specific reference ranges (because some evidence indicates that the risk of fracture is similar in women and men for a given level of bone mineral density), a diagnosis of osteoporosis in men is generally made based on male-specific reference ranges. Treatment consists both of nonpharmacological (lifestyle factors, calcium and vitamin D supplementation) and pharmacological (most commonly bisphosphonates or PTH) approaches, with efficacy similar to that seen in women. Increasing awareness of osteoporosis in men among physicians and the lay public is critical for the prevention of fractures in our aging male population.

Individual variation and the endocrine regulation of behaviour and physiology in birds: a cellular/molecular perspective

Investigations of the cellular and molecular mechanisms of physiology and behaviour have generally avoided attempts to explain individual differences. The goal has rather been to discover general processes. However, understanding the causes of individual variation in many phenomena of interest to avian eco-physiologists will require a consideration of such mechanisms. For example, in birds, changes in plasma concentrations of steroid hormones are important in the activation of social behaviours related to reproduction and aggression. Attempts to explain individual variation in these behaviours as a function of variation in plasma hormone concentrations have generally failed. Cellular variables related to the effectiveness of steroid hormone have been useful in some cases. Steroid hormone target sensitivity can be affected by variables such as metabolizing enzyme activity, hormone receptor expression as well as receptor cofactor expression. At present, no general theory has emerged that might provide a clear guidance when trying to explain individual variability in birds or in any other group of vertebrates. One strategy is to learn from studies of large units of intraspecific variation such as population or sex differences to provide ideas about variables that might be important in explaining individual variation. This approach along with the use of newly developed molecular genetic tools represents a promising avenue for avian eco-physiologists to pursue.

Estrogen receptor α gene polymorphisms are associated with idiopathic premature ovarian failure

OBJECTIVE

To assess the role of hormone receptor/binding protein variants in genetic predisposition to premature ovarian failure (POF).

DESIGN

Case-control study.

SETTING

Academic.

PATIENT(S)

Fifty-five POF patients, 107 control women from the general population, and 27 control women who had proven fertility after age 37.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Allele distributions in cases and controls were assessed for genetic association.

RESULT(S)

Allele distributions of polymorphisms at the androgen receptor (AR) gene, estrogen receptor beta (ESR2) gene, sex hormone-binding globulin (SHBG) gene, and FSH receptor (FSHR) gene did not differ between patients and controls. At a repeat in a promoter of the estrogen receptor alpha(ESR1) gene, POF patients had fewer (<18) short repeat alleles than did controls (P=.004 vs. combined controls). Genotypes consisting of two short alleles were found in 36.4% of control women but only 5.5% of POF patients (P<.0001 vs. combined controls). The ESR1 repeat may confer risk for POF in a simple dominant manner in which carriers of a long repeat have a relative risk of 9.7 (95% CI = 2.6 - 35.6).

CONCLUSION(S)

Polymorphisms at the ESR1 gene are associated with POF in this patient population, while those in AR, ESR2, SHBG, and FSHR showed no association. Further studies are necessary to confirm these findings in larger patient samples and to identify the specific predisposing lesion.