SHBG gene promoter polymorphisms in men are associated with serum sex hormone-binding globulin, androgen and androgen metabolite levels, and hip bone mineral density

Circulating Metabolites and Dental Traits: A Mendelian Randomization Study

It is of great importance to uncover causal biomarkers to gain insight into the pathogenesis of oral diseases and identify novel treatment targets for prevention and treatment thereof. This study aimed to systematically evaluate the causal effects of hundreds of metabolites on 10 dental traits using a 2-sample Mendelian randomization (MR) approach. Genetic variants from genome-wide association studies of 309 known metabolites were used as instrumental variables. We selected 10 dental traits, including clinical measures of dental diseases, from the Gene-Lifestyle Interactions in Dental Endpoints Consortium and self-reported oral health data from the UK Biobank. The causal relationships between metabolites and dental traits were inferred using the inverse variance-weighted approach and further controlled for horizontal pleiotropy using 5 additional MR methods. After correcting for multiple tests, 5 metabolites were identified as causal biomarkers. Genetically predicted increased levels of mannose were associated with lower risk of bleeding gums (odds ratio [OR] = 0.72; 95% confidence interval [CI], 0.61-0.85; P = 9.9 × 10-5). MR also indicated 4 metabolites on the causal pathway to dentures, with fructose (OR = 0.50; 95% CI, 0.36-0.70; P = 5.2 × 10-5) and 1-palmitoleoyl-glycerophosphocholine (OR = 0.67; 95% CI, 0.56-0.81; P = 4.8 × 10-5) as potential protective factors and glycine (OR = 1.22; 95% CI, 1.11-1.35; P = 5.6×10-5) and 1,5-anhydroglucitol (OR = 1.32; 95% CI, 1.14-1.52; P = 1.5 × 10-4) as risk factors. The causal associations were robust in various sensitivity analyses. We further observed some shared metabolites among different dental traits, implying similar biological mechanisms underlying the pathogenic processes. Finally, the pathway analysis revealed several significant metabolic pathways that may be involved in the development of dental disorders. Our study provides novel insights into the combination of metabolomics and genomics to reveal the pathogenesis of and therapeutic strategies for dental disorders. It highlighted 5 metabolites and several pathways as causal candidates, warranting further investigation.

Genetic Correlation, Shared Loci, and Causal Association Between Sex Hormone-Binding Globulin and Bone Mineral Density: Insights From a Large-Scale Genomewide Cross-Trait Analysis

Although the impact of sex hormones on bone metabolism is well-documented, effect of their primary modulator, sex hormone-binding globulin (SHBG), remains inconclusive. This study aims to elucidate the genetic overlap between SHBG and heel estimated bone mineral density (eBMD), a widely-accepted tool for osteoporosis management and fracture risk assessment. Using summary statistics from large-scale genomewide association studies conducted for SHBG (N = 370,125), SHBG adjusted for body mass index (SHBGa, N = 368,929), and eBMD (N = 426,824), a comprehensive genomewide cross-trait approach was performed to quantify global and local genetic correlations, identify pleiotropic loci, and infer causal associations. A significant overall inverse genetic correlation was found for SHBG and eBMD (rg  = -0.11, p = 3.34 × 10-10 ), which was further supported by the significant local genetic correlations observed in 11 genomic regions. Cross-trait meta-analysis revealed 219 shared loci, of which seven were novel. Notably, four novel loci (rs6542680, rs8178616, rs147110934, and rs815625) were further demonstrated to colocalize. Mendelian randomization identified a robust causal effect of SHBG on eBMD (beta = -0.22, p = 3.04 × 10-13 ), with comparable effect sizes observed in both men (beta = -0.16, p = 1.99 × 10-6 ) and women (beta = -0.19, p = 2.73 × 10-9 ). Replacing SHBG with SHBGa, the observed genetic correlations, pleiotropic loci and causal associations did not change substantially. Our work reveals a shared genetic basis between SHBG and eBMD, substantiated by multiple pleiotropic loci and a robust causal relationship. Although SHBG has been implicated in preventing and screening aging-related diseases, our findings support its etiological role in osteoporosis. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Bone health in ageing men

Osteoporosis does not only affect postmenopausal women, but also ageing men. The burden of disease is projected to increase with higher life expectancy both in females and males. Importantly, osteoporotic men remain more often undiagnosed and untreated compared to women. Sex steroid deficiency is associated with bone loss and increased fracture risk, and circulating sex steroid levels have been shown to be associated both with bone mineral density and fracture risk in elderly men. However, in contrast to postmenopausal osteoporosis, the contribution of relatively small decrease of circulating sex steroid concentrations in the ageing male to the development of osteoporosis and related fractures, is probably only minor. In this review we provide several clinical and preclinical arguments in favor of a 'bone threshold' for occurrence of hypogonadal osteoporosis, corresponding to a grade of sex steroid deficiency that in general will not occur in many elderly men. Testosterone replacement therapy has been shown to increase bone mineral density in men, however data in osteoporotic ageing males are scarce, and evidence on fracture risk reduction is lacking. We conclude that testosterone replacement therapy should not be used as a sole bone-specific treatment in osteoporotic elderly men.

Role of sex hormone-binding globulin in the free hormone hypothesis and the relevance of free testosterone in androgen physiology

According to the free hormone hypothesis, biological activity of a certain hormone is best reflected by free rather than total hormone concentrations. A crucial element in this theory is the presence of binding proteins, which function as gatekeepers for steroid action. For testosterone, tissue exposure is governed by a delicate equilibrium between free and total testosterone which is determined through interaction with the binding proteins sex hormone-binding globulin and albumin. Ageing, genetics and various pathological conditions influence this equilibrium, hereby possibly modulating hormonal exposure to the target tissues. Despite ongoing controversy on the subject, strong evidence from recent in vitro, in vivo and human experiments emphasizes the relevance of free testosterone. Currently, however, clinical possibilities for free hormone diagnostics are limited. Direct immunoassays are inaccurate, while gold standard liquid chromatography with tandem mass spectrometry (LC-MS/MS) coupled equilibrium dialysis is not available for clinical routine. Calculation models for free testosterone, despite intrinsic limitations, provide a suitable alternative, of which the Vermeulen calculator is currently the preferred method. Calculated free testosterone is indeed associated with bone health, frailty and other clinical endpoints. Moreover, the added value of free testosterone in the clinical diagnosis of male hypogonadism is clearly evident. In suspected hypogonadal men in whom borderline low total testosterone and/or altered sex hormone-binding globulin levels are detected, the determination of free testosterone avoids under- and overdiagnosis, facilitating adequate prescription of hormonal replacement therapy. As such, free testosterone should be integrated as a standard biochemical parameter, on top of total testosterone, in the diagnostic workflow of male hypogonadism.

Ageing male (part I): Pathophysiology and diagnosis of functional hypogonadism

This narrative review summarizes key points of the pathogenesis and diagnosis of the ageing-related decline of testosterone (T) in men. The condition is commonly termed late-onset hypogonadism (LOH), but because it is more often caused by other factors than chronological ageing (obesity and other comorbidities), a more appropriate term is functional hypogonadism (FH). Unlike the classical organic hypogonadism, no anatomical or genetic aberrations are found in FH, and the suppression of T is milder. Moreover, FH can be reversible if the underlying cause (e.g. obesity, chronic disease) is removed/treated. Low serum total T in connection with more specific hypogonadism-associated symptoms (primarily sexual) form the basis of the diagnosis of FH. When T concentrations are borderline, the accuracy of diagnosis can be improved by assessment of free or calculated free T, especially when suppressed SHBG levels (usually related to obesity) are likely. Current data indicate that FH (low T and sexual symptoms) is not a common condition, and it is detectable in about 2% of community-dwelling men aged 40-80 years.

Decreased risk of ovarian cancer associated with rs9898876 sex hormone-binding globulin gene variant

BACKGROUND

Ovarian cancer (OC) is one of the most common gynecologic cancers,with significant morbidity and mortality. The risk of OC is influenced by hormone status, of which sex hormone-binding globulin (SHBG), which influences the serum availability of steroid sex hormones, is implicated in the pathogenesis and evolution of OC. The aim of this study is to evaluate the involvement of common SHBG gene variants in OC susceptibility and evolution.

MATERIALS

A case control study including 71 OC patients and 74 cancer-free controls, who were genotyped for rs9898876, rs13894, rs1799941 and rs6257 SHBG SNP. Genotyping was done by the allelic discrimination method, using VIC- and FAM-labeled primers.

RESULTS

The minor allele frequencies of rs9898876, rs13894, rs1799941 and rs6257 SHBG SNP was comparable between OC cases and control women, implying no significant associations of the tested variants and overall OC risk. Taking homozygous wild-type genotype as reference (OR = 1.00), heterozygous rs9898876 (G/T), and minor allele-carrying genotypes [G/T + T/T] were associated with reduced risk of OC. While rs9898876 heterozygosity (G/T) was predictive of OC occurrence, no significant association of the remaining three tested SNPs was noted with altered risk of OC. Irrespective of FIGO staging, the four tested SHBG SNPs were not associated with the clinical progression of OC.

CONCLUSIONS

In conclusion, SHBG rs9898876 is associated with a decreased risk of OC, and thus constitutes a potential diagnostic biomarker of OC.

A Capra hircus chromosome 19 locus linked to milk production influences mammary conformation

Background

Economically important milk production traits including milk volume, milk fat and protein yield vary considerably across dairy goats in New Zealand. A significant portion of the variation is attributable to genetic variation. Discovery of genetic markers linked to milk production traits can be utilised to drive selection of high-performance animals.

A previously reported genome wide association study across dairy goats in New Zealand identified a quantitative trait locus (QTL) located on chromosome 19. The most significantly associated single nucleotide polymorphism (SNP) marker for this locus is located at position 26,610,610 (SNP marker rs268292132). This locus is associated with multiple milk production traits including fat, protein and volume. The predicted effect of selection for the beneficial haplotype would result in an average production increase of 2.2 kg fat, 1.9 kg protein and 73.6 kg milk yield.

An outstanding question was whether selection for the beneficial allele would co-select for any negative pleiotropic effects. An adverse relationship between milk production and udder health traits has been reported at this locus. Therefore, a genome wide association study was undertaken looking for loci associated with udder traits.

Results

The QTL and production associated marker rs268292132 was identified in this study to also be associated with several goat udder traits including udder depth (UD), fore udder attachment (FUA) and rear udder attachment (RUA). Our study replicates the negative relationship between production and udder traits with the high production allele at position 19:26,610,610 (SNP marker rs268292132) associated with an adverse change in UD, FUA and RUA.

Conclusions

Our study has confirmed the negative relationship between udder traits and production traits in the NZ goat population. We have found that the frequency of the high production allele is relatively high in the NZ goat population, indicating that its effect on udder conformation is not significantly detrimental on animal health. It will however be important to monitor udder conformation as the chromosome 19 locus is progressively implemented for marker assisted selection. It will also be of interest to determine if the gene underlying the production QTL has a direct effect on mammary gland morphology or whether the changes observed are a consequence of the increased milk volume.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-021-00667-y.

Associations of Sex Hormone-binding Globulin with Bone Mineral Density Among US Adults, NHANES 2013-2016

Background

Bone metabolism can be influenced by sex steroid hormones. However, the relationship between sex steroid hormones and bone mineral density (BMD) remains inconsistent. Our study explored existing evidence of the association between sex hormones, blood glucose and BMD.

Methods

We conducted a cross-sectional study of 6434 participants aged 18–80 years in the National Health and Nutrition Examination Survey (NHANES) 2013–2016 to assess the association between SHBG and BMD. The multivariable linear regression models were performed to evaluate the associations between testosterone, estrogen, sex hormone-binding globulin (SHBG) and BMD.

Results

On adjustment for traditional risk factors (age, BMI, ALB, ALK, ASP, calcium, cholesterol, potassium, sodium, total protein, uric acid), SHBG could be regarded as an independent predictor for BMD, while fasting blood glucose did not. SHBG levels were significant associated with BMD in the multivariate model; however, it will be a different effect between the genders. On comparative analysis, high level SHBG was predictive of lumbar BMD irrespective of other two sex steroid hormones.

Conclusion

This study indicated that SHBG may improve the predictive value for bone loss in adults.

Impact of sex hormone-binding globulin on the human phenome

Background: Sex hormone-binding globulin (SHBG) is a circulating glycoprotein and a regulator of sex hormone levels, which has been shown to influence various traits and diseases. The molecular nature of SHBG makes it a feasible target for preventative or therapeutic interventions. A systematic study of its effects across the human phenome may uncover novel associations. Methods: We used a Mendelian randomization phenome-wide association study (MR-pheWAS) approach to systematically appraise the potential functions of SHBG while reducing potential biases such as confounding and reverse causation common to the literature. We searched for potential causal effects of SHBG in UK Biobank (N = 334 977) and followed-up our top findings using two-sample MR analyses to evaluate whether estimates may be biased due to horizontal pleiotropy. Results: Results of the MR-pheWAS across over 21 000 outcome phenotypes identified 12 phenotypes associated with genetically elevated SHBG after Bonferroni correction for multiple testing. Follow-up analysis using two-sample MR indicated the associations of increased natural log SHBG with higher impedance of the arms and whole body, lower pulse rate, lower bone density, higher odds of hip replacement, lower odds of high cholesterol or cholesterol medication use and higher odds of gallbladder removal. Conclusions: Our systematic MR-pheWAS of SHBG, which was comprehensive to the range of phenotypes available in UK Biobank, suggested that higher circulating SHBG affects the body impedance, bone density and cholesterol levels, among others. These phenotypes should be prioritized in future studies aiming to investigate the biological effects of SHBG or develop targets for therapeutic intervention.

Classic and Novel Sex Hormone Binding Globulin Effects on the Cardiovascular System in Men

In men, 70% of circulating testosterone binds with high affinity to plasma sex hormone binding globulin (SHBG), which determines its bioavailability in their target cells. In recent years, a growing body of evidence has shown that circulating SHBG not only is a passive carrier for steroid hormones but also actively regulates testosterone signaling through putative plasma membrane receptors and by local expression of androgen-binding proteins apparently to reach local elevated testosterone concentrations in specific androgen target tissues. Circulating SHBG levels are influenced by metabolic and hormonal factors, and they are reduced in obesity and insulin resistance, suggesting that SHBG may have a broader clinical utility in assessing the risk for cardiovascular diseases. Importantly, plasma SHBG levels are strongly correlated with testosterone concentrations, and in men, low testosterone levels are associated with an adverse cardiometabolic profile. Although obesity and insulin resistance are associated with an increased incidence of cardiovascular disease, whether they lead to abnormal expression of circulating SHBG or its interaction with androgen signaling remains to be elucidated. SHBG is produced mainly in the liver, but it can also be expressed in several tissues including the brain, fat tissue, and myocardium. Expression of SHBG is controlled by peroxisome proliferator-activated receptor γ (PPARγ) and AMP-activated protein kinase (AMPK). AMPK/PPAR interaction is critical to regulate hepatocyte nuclear factor-4 (HNF4), a prerequisite for SHBG upregulation. In cardiomyocytes, testosterone activates AMPK and PPARs. Therefore, the description of local expression of cardiac SHBG and its circulating levels may shed new light to explain physiological and adverse cardiometabolic roles of androgens in different tissues. According to emerging clinical evidence, here, we will discuss the potential mechanisms with cardioprotective effects and SHBG levels to be used as an early metabolic and cardiovascular biomarker in men.

Research progress on the relationship between sex hormone-binding globulin and male reproductive system diseases

Sex hormone-binding globulin, also known as testosterone-estradiol-binding globulin, is a multifunctional protein synthesised by hepatocytes. Sex hormone-binding globulin specifically binds and transports sex hormones to regulate plasma bioactive sex hormone levels and affects their bioavailability. As male sex hormone expression is dominated by testosterone, the binding of sex hormone-binding globulin with testosterone leads to the reduction in bioavailable testosterone, which cannot fulfil its physiological roles, thereby resulting in male infertility, erectile and gonadal dysfunction, prostate cancer and other male reproductive system diseases. Sex hormone-binding globulin may be involved in the pathogenesis of male reproductive system diseases, seriously affecting the quality of life of men. In this article, we review the association between sex hormone-binding globulin and male reproductive system diseases.

U-Shaped Association of Plasma Testosterone, and no Association of Plasma Estradiol, with Incidence of Fractures in Men

PURPOSE

Whether androgens, distinct from estrogen, maintain bone health during male aging has implications for understanding osteoporosis. We assessed associations of different sex hormones with incidence of any bone fracture or hip fracture in older men.

PARTICIPANTS AND METHODS

Analysis of 3307 community-dwelling men aged 76.8 ± 3.5 years, median follow-up period of 10.6 years. Plasma testosterone (T), dihydrotestosterone (DHT), and estradiol (E2) assayed by mass spectrometry, sex hormone-binding globulin (SHBG), and luteinizing hormone (LH) using immunoassay. Incident fractures determined via data linkage. We analyzed probability of fracture and performed Cox regression adjusted for age, medical comorbidities, and frailty.

RESULTS

Incident fractures occurred in 330 men, including 144 hip fractures. Probability plots suggested nonlinear relationships between hormones and risk of any fracture and hip fracture, with higher risk at lower and higher plasma T, lower E2, higher SHBG, and higher LH. In fully adjusted models, there was a U-shaped association of plasma T with incidence of any fracture (Quartile 2 [Q2] versus Q1: fully adjusted hazard ratio [HR] = 0.69, 95% confidence interval [CI] 0.51-0.94, P = .020; Q3: HR 0.59, 95% CI 0.42-0.83, P = .002) and hip fracture (Q2 versus Q1: HR 0.60, 95% CI 0.37-0.93, P = .043; Q3: HR 0.52, 95% CI 0.31-0.88, P = .015). DHT, E2, and LH were not associated with fracture. Higher SHBG was associated with hip fracture (Q4 versus Q1: HR 1.76, 95% CI 1.05-2.96, P = .033).

CONCLUSIONS

Midrange plasma T was associated with lower incidence of any fracture and hip fracture, and higher SHBG with increased risk of hip fracture. Circulating androgen rather than estrogen represents a biomarker for hormone effects on bone driving fracture risk.

Aging and the Male Reproductive System

This narrative review presents an overview of current knowledge on fertility and reproductive hormone changes in aging men, the factors driving and modulating these changes, their clinical consequences, and the benefits and risks of testosterone (T) therapy. Aging is accompanied by moderate decline of gamete quality and fertility. Population mean levels show a mild total T decline, an SHBG increase, a steeper free T decline, and a moderate LH increase with important contribution of comorbidities (e.g., obesity) to these changes. Sexual symptoms and lower hematocrit are associated with low T and are partly responsive to T therapy. The relationship of serum T with body composition and metabolic health is bidirectional; limited beneficial effects of T therapy on body composition have only marginal effects on metabolic health and physical function. Skeletal changes are associated primarily with estradiol and SHBG. Cognitive decline is not consistently linked to low T and is not improved by T therapy. Although limited evidence links moderate androgen decline with depressive symptoms, T therapy has small beneficial effects on mood, depressive symptoms, and vitality in elderly patients with low T. Suboptimal T (and/or DHT) has been associated with increased risk of stroke, but not of ischemic heart disease, whereas an association with mortality probably reflects that low T is a marker of poor health. Globally, neither severity of clinical consequences attributable to low T nor the nature and magnitude of beneficial treatment effects justify the concept of some broadly applied "T replacement therapy" in older men with low T. Moreover, long-term safety of T therapy is not established.

Effects of SHBG rs1799941 Polymorphism on Free Testosterone Levels and Hypogonadism Risk in Young Non-Diabetic Obese Males

Introduction: Obesity has been associated with increased risk of presenting hypogonadism. Free testosterone (FT) is the fraction of testosterone that carries out the biological function of testosterone, and is determined from total testosterone (TT) and sex-hormone binding globulin (SHBG) levels. We aimed to study the SHBG polymorphism rs1799941 in a cohort of young non-diabetic obese males to unravel the possible implication of this polymorphism in obesity-related hypogonadism. Methodology: 212 young (<45 years) non-diabetic obese (BMI ≥ 30 kg/m²) males participated in this study. Subjects were classified according to TT and FT levels in: Eugonadal (n = 55, TT > 3.5 ng/mL and FT ≥ 70 pg/mL; EuG), normal FT hypogonadism (n = 40, TT < 3.5 and FT ≥ 70 pg/mL; normal FT HG) and hypogonadism (n = 117, TT < 3.5 ng/mL and TL < 70 pg/mL; HG). The SHBG rs1799941 polymorphism (GG/GA/AA) was analyzed using the Taqman Open Array (Applied biosystem). Results: The rs1799941 frequencies were different among the groups. Higher proportion of the allele (A) was found in HG, compared to EuG and normal FT HG. Among the genotypes, the rare homozygous (AA) were found in the normal FT HG group and higher levels of serum SHBG and lower of FT were observed. The presence of the allele A was related (according to lineal regression models) to an increased of SHBG levels ((GA) β = 3.28; (AA) β = 12.45) and a decreased of FT levels ((GA) β = −9.19; (AA) β = −18.52). The presence of the allele (A) increased the risk of presenting HG compared to normal FT HG (OR = 2.54). Conclusions: The rs1799941 of the SHBG gene can partially determine the presence of obesity-related hypogonadism in young non-diabetic males and whether these subjects have normal FT HG.

Genetic polymorphisms of the SHBG gene can be the effect on SHBG and HDL-cholesterol levels in Coronary Heart Disease: a case-control study

Sex hormone binding globulin (SHBG) level is positively associated with the high-density lipoprotein cholesterol (HDL-C) levels. The aim of this study was to investigate the effects of the SHBG gene variations (D356N, rs1799941, and P156L) on SHBG and HDL-C levels and Coronary Heart Disease (CHD) risk. The SHBG D356 N (rs6259,G > A), P156L (rs6258,C > T), and rs1799941(G > A) polymorphisms were determined in 131 male CHD patients and 55 male controls by PCR-RFLP and real-time PCR techniques. SHGB levels were measured by Electro-chemiluminescence immunoassay (ECLIA). In the patients who had SHBG levels lower than threshold 35 nmol/l value, the risk of being HDL-C levels lower than threshold 0.90 mmol/l value was observed statistically significant (p = 0.017; OR 2.522, 95% CI 1.170-5.438). The rs1799941 GG was associated with increased CHD risk when compared with the A allele carriers (GA + AA) (p = 0.019, OR 2.222, 95% CI 1.130-4.371). In addition, the rs1799941 GG genotype and D356 N N allele were associated with lower SHBG in the CHD group (p < 0.01). The logistic regression analysis also revealed the rs1799941 GG genotype was significantly associated with low SHBG in CHD patients. It was observed that Haplotype-1(rs1799941 G allele-P156L P allele-D356 N D allele) was associated with increased CHD risk, while Haplotype-2 (rs1799941 rare A allele-P156L C allele- D356 N G allele) was correlated with the decreased CHD risk (p = 0.0167). Our findings suggest that there is a positive correlation between SHBG and HDL-C levels in CHD patients, and this association might be affected by SHBG gene variations.

Effect of sex hormone-binding globulin polymorphisms on the outcome of in vitro fertilization-embryo transfer for polycystic ovary syndrome patients: A case-control study

Polycystic ovary syndrome (PCOS), known as a common endocrine disorder among females, plagues many PCOS patients. The current study aimed to explore the correlations of sex hormone-binding globulin (SHBG) polymorphisms with the outcome of in vitro fertilization-embryo transfer (IVF-ET) in PCOS patients. PCOS patients who underwent IVF-ET and patients with non-PCOS-related infertility were selected in the study. Correlations of SHBG rs6259 and rs727428 with the risk factors in PCOS were analyzed, followed by the evaluation of the effect of SHBG polymorphisms on the outcome of IVF-ET in PCOS patients. At last, unconditional logistic regression analysis was performed to study the risk factors for IVF-ET treatment outcome. Compared with SHBG rs6259 GG carriers, the incidence of PCOS was found to be elevated in SHBG rs6259 GA+AA carriers which indicated that the A allele was a risk factor for PCOS. Compared with SHBG rs6259 TT carriers, the number of retrieved oocytes and embryo as well as the fertility rate in SHBG rs6259 GA+AA carriers was found to be decreased, while the abortion rate, incidence of ovarian hyperstimulation syndrome, transplant rejection rate, estradiol, and testosterone in serum, as well as testosterone in follicular fluid were elevated. The luteal hormone, serum testosterone, and progesterone and GA+AA genotype of rs6259 were the risk factors for IVF-ET treatment outcome. Taken together, the study showed that SHBG rs6259 polymorphisms might be correlated with the risk of PCOS and the outcome of IVF-ET treatment.

Testosterone treatment in older men: clinical implications and unresolved questions from the Testosterone Trials

A decrease in the concentration of circulating testosterone in many older men is a biomarker and possibly a rectifiable contributing factor to ill health. Low circulating testosterone concentration has been associated with cardiovascular disease, reduced cognition, fracture risk, and anaemia. However, randomised placebo-controlled trials are essential to clarify the benefits and possible risks of testosterone treatment in men without hypothalamic, pituitary, or testicular disease. The Testosterone Trials (T-Trials) were a coordinated set of trials that, following a screening-to-enrolment ratio of 65:1, randomly assigned 790 men aged 65 years or older who had a baseline testosterone concentration of less than 9·54 nmol/L and symptoms consistent with hypogonadism, but no recognisable hypothalamic-pituitary-testicular axis pathology, to daily transdermal testosterone or placebo for 12 months. In the main trial, testosterone treatment resulted in a modest benefit for sexual function, whereas the other primary outcomes of vitality and physical function were not met. Data from concomitant substudies raised a possible concern over changes in coronary plaque volume, showed a neutral effect on memory and other cognitive functions, and revealed improvements in volumetric bone mineral density and anaemia. Although insufficient to alter the existing clinical equipoise, the T-Trials provided substantial new data on organ-specific outcomes for testosterone treatment in older men. Further clinical trials are necessary to determine whether testosterone treatment will translate into patient-valued health outcomes and to clarify effects on the cardiovascular system.

Effect of placental sex hormone-binding globulin single nucleotide polymorphism rs6259 on protein and function in gestational diabetes mellitus

Sex hormone-binding globulin (SHBG) has a key role in the occurrence and development of the gestational diab-etes mellitus (GDM). Single nucleotide polymorphism (SNP) rs6259 is a functional site in SHBG gene, which is suspected to regulate the SHBG level. The present study explored the placental SHBG SNP rs6259 distribution in Chinese pregnant women and the influence on placental SHBG concentrations, to assess the relationship of SHBG rs6259 in the occurrence and development of GDM. We screened the SHBG rs6259 allele in 210 healthy and 180 GDM gravidas by PCR-RFLP and restriction enzyme and measured placental SHBG concentrations in each genotypic group with western blot analysis. The mechanisms of SHBG rs6259 function were analyzed by cell culture, recombinant lentivirus transfection, real-time PCR, and western blot analysis. We found the differences of SHBG Asn327 allele frequency and the genotype distribution in GDM and control groups were statistically significant (P<0.05). Western blot analysis results showed that the Asn327 allele group was associated with a higher placental SHBG level than the Asp327 allele homozygote group (P<0.05). In HTR8-SVneo cell transfection, the positive transfection groups (SHBG-rs6259 Asn) led to an obviously higher tendency of SHBG mRNA and protein expression than the negative control groups (SHBG-rs6259 Asp), the normal cell group, and the blank control group (blank lentivirus LV-5) (P<0.05). Our data, therefore, reflected that SHBG SNP rs6259 causes changes in placental SHBG concentration and may play a functional role in the molecular mechanisms of GDM etiology.

Genetics of Sex Hormone-Binding Globulin and Testosterone Levels in Fertile and Infertile Men of Reproductive Age

Context

Testosterone (T) is a central androgenic hormone, and sex hormone-binding globulin (SHBG) is the major determinant of its bioactivity. There are no acknowledged genetic variants with clear-cut clinical implications, modulating T levels in men.

Objective

To confirm genetic associations of top loci (SHBG, GCKR, SLCO1B1, and JMJD1C) from genome-wide association (GWA) studies for serum SHBG and T.

Design Patients

Groups differing in general and reproductive parameters: young men (n = 540; 19.3 ± 1.8 years), severe idiopathic male infertility patients (n = 641; 31.6 ± 6.0 years), and male partners of pregnant women (n = 324; 31.9 ± 6.6 years). All patients were recruited at the Andrology Centre, Tartu University Hospital, Estonia.

Main Outcome Measures

Genetic associations with reproductive hormones, testicular and sperm parameters (linear regression, additive model); intergroup allele/genotype distribution comparisons.

Results

Associations with serum SHBG levels were robust for SHBG -68 G>A [rs1799941; meta-analysis: P = 3.7 × 10^-14; allelic effect (standard error) = 4.67 (0.62) nmol/L], SHBG +1091 C>T [rs727428; P = 7.3 × 10^-11; -3.74 (0.57)], SHBG Pro185Leu [rs6258; P = 1.2 × 10^-4, -12.2 (3.17)], and GCKR Pro446Leu [rs1260326; P = 1.5 × 10^-4; -2.2 (0.59)]. Measured T concentrations correlated with genetically modulated levels of SHBG (r = 0.48 to 0.74, P < 0.0001), guaranteeing stable availability of free T. Among infertile men, SHBG Pro185Leu substitution showed additional downstream effect on luteinizing hormone [P = 5.1 × 10^-5; -1.66 (0.57) IU/L] and follicle-stimulating hormone [P = 3.4 × 10^-3; -2.48 (1.23) IU/L]. No associations with male reproductive parameters were detected for SHBG Asp327Asn (rs6259), SLCO1B1 Val174Ala (rs4149056), and JMJD1C intronic variant rs7910927.

Conclusions

Claims were replicated and additional associations were detected for four of seven tested GWAS top loci. Perspective clinical investigations of these variants are hypotestosteronemia among aging men and pharmacogenetics of hormone replacement therapy.

Sex hormone-binding globulin regulation of androgen bioactivity in vivo: validation of the free hormone hypothesis

Sex hormone-binding globulin (SHBG) is the high-affinity binding protein for androgens and estrogens. According to the free hormone hypothesis, SHBG modulates the bioactivity of sex steroids by limiting their diffusion into target tissues. Still, the in vivo physiological role of circulating SHBG remains unclear, especially since mice and rats lack circulating SHBG post-natally. To test the free hormone hypothesis in vivo, we examined total and free sex steroid concentrations and bioactivity on target organs in mice expressing a human SHBG transgene. SHBG increased total androgen and estrogen concentrations via hypothalamic-pituitary feedback regulation and prolonged ligand half-life. Despite markedly raised total sex steroid concentrations, free testosterone was unaffected while sex steroid bioactivity on male and female reproductive organs was attenuated. This occurred via a ligand-dependent, genotype-independent mechanism according to in vitro seminal vesicle organ cultures. These results provide compelling support for the determination of free or bioavailable sex steroid concentrations in medicine, and clarify important comparative differences between translational mouse models and human endocrinology.

The association between sex hormone-binding globulin gene polymorphism with bone mineral density

To investigate the impact of single nucleotide polymorphisms (SNPs) of SHBG gene the neighboring genes on SHBG levels, bone mineral density (BMD) and osteoporosis in Chinese males. A group of Chinese men, aged ⩾ 45 years were included in the analysis. BMD was measured with dual-energy X-ray absorptiometry (DXA), SHBG and total testosterone (TT) was measured using chemiluminescent immunoassay, and free testosterone (FT) was calculated. SNPs of SHBG gene and the neighboring genes were studied by means of improved multiple ligase detection reaction (iMLDR). A total of 404 men were included in our study. In the single locus analysis, significant associations were found between SHBG levels and four polymorphisms (rs11078701, rs9901675, rs9898876 and rs2541012) in age- and BMI-adjusted models. In addition, statistically significant difference was found between osteoporosis patients and control subjects in genotype distributions of rs9898876, rs2541012, rs6259 and rs3853894. In the models with or without adjustment for confounders (age, BMI, SHBG and free testosterone (FT) levels), carriers of variant genotype of rs9898876, rs2541012 and rs6259 had lower BMD and were more likely to suffer from osteoporosis, as compare to carriers of common genotype. Subjects with variant genotype of rs3853894 had higher BMD and were less likely to suffer from osteoporosis, as compared to subjects with common genotype. In the haplotypes analysis, CCGGT (constituted by rs11078701C, rs1017163C, rs9898876G, rs62059836G and rs2541012T) and haplotype CGGT (constituted by rs858521C, rs858518G, rs6259G and rs727428T) was associated with a significant risk effect for osteoporosis. Polymorphisms of SHBG or the neighboring genes were associated with SHBG levels or BMD and osteoporosis, suggesting the involvement of genetic variation of SHBG in bone health.

Genetic influence on the association between bone mineral density and testosterone in Korean men

Low bone mineral density (BMD) leads to an increased risk of osteoporotic fracture. Total testosterone and free testosterone were positively associated with BMD, which was significantly influenced by the additive genetic effects.

INTRODUCTION

This cross-sectional study aimed to evaluate an association between testosterone and BMD and the influence of genetic factors on the association.

METHODS

Study subjects were 1070 Korean men including 144 pairs of monozygotic twins and their family members. Levels of serum total testosterone and sex hormone binding globulin (SHBG) were measured by chemiluminescence immunoassay. Calculated free testosterone (cFT) was then determined using Vermeulen's method. BMDs of the whole body and specific regions were measured using dual-energy X-ray absorptiometry.

RESULTS

Linear mixed regression analyses showed that total testosterone and cFT were positively associated with BMD at most regions, after considering intra-familial relationship and covariates including fat mass, lean mass, and SHBG. SHBG had an inverse association with BMD at the pelvis but not with the BMD at other regions after adjusting for all covariates and cFT. Co-twin control analysis in monozygotic twins found no association between pairwise difference of testosterone and pairwise difference of BMD. Bivariate variance component analysis showed that both total testosterone and cFT had a significant positive additive genetic correlation with BMD at rib, spine, and arm, whereas SHBG had no significant genetic correlation with BMD. Inverse environmental correlations were seen between total testosterone and BMDs at the lumbar spine and arm.

CONCLUSIONS

This Korean twin and family study showed that both total testosterone and free testosterone were positively associated with BMD and that genetic effects were significant on the association between testosterone and BMD.

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.

Study of Sex Hormone-binding Globulin Gene Polymorphism and Risk of Type 2 Diabetes Mellitus in Egyptian Men

OBJECTIVES

Conditions of hypoandrogenism in men have been linked to insulin resistance, suggesting that alterations in normal sex steroid physiology could play a role in the pathogenesis of Type 2 diabetes mellitus (T2DM). Sex hormone-binding globulin (SHBG) gene polymorphisms may be the cause of sex steroid alteration. The aim of this work is to study the effect of SHBG gene polymorphisms on the risk of T2DM through its impact on testosterone and oestradiol level in Egyptian men.

SUBJECTS AND METHODS

A case control study was performed in the diabetes clinic at Zagazig University Hospital on 185 males with Type 2 diabetes and their matched healthy controls. Two polymorphisms (rs6257 and rs6259) of the gene encoding SHBG were genotyped and serum levels of SHBG, testosterone and oestradiol were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Carriers of rs6257 variant allele (CC or CT) and carriers of rs6259 wild allele (GG) appear to have a high risk of diabetes than carriers of other alleles (OR 2.241, 1.585 and 2.391, respectively). They also showed a significant decrease in plasma level of both SHBG and testosterone and a significant increase in oestradiol blood level compared with carriers of other alleles.

CONCLUSIONS

Sex hormone-binding globulin gene polymorphisms at position rs6257 and rs6259 are associated with higher risk of T2DM in Egyptian men, through lowering circulating levels of SHBG and consequently, lowering testosterone and elevating oestradiol level.

A systems genetics approach to dyslipidemia in children and adolescents

Elevated triglycerides (TG) or low high density lipoprotein cholesterol (HDL-C) levels are common cardiometabolic risk factors in children. From a systems genetics standpoint, Visualization of Statistical Epistasis Networks (ViSEN) is a nonparametric entropy-based method that can characterize the global structure of interacting genetic factors. We identified a novel set of connected genetic and cardiometabolic risk factors with strong and significant interaction effects on two important dyslipidemia phenotypes (low HDL-C and high TG) in children and adolescents. Study participants were recruited from five schools in Istanbul, Turkey (n=360; 170 boys, 190 girls). Participants with TG levels≥75th and HDL-C levels≤25th percentile were defined as 'high TG' and 'low HDL-C', respectively. We genotyped participants for six single nucleotide polymorphisms (SNPs) in five genes with known associations to lipid levels (rs328 in LPL, rs708272 in CETP, rs1800588 in LIPC, rs1800977 in ABCA1, rs1799941 and rs6257 in SHBG gene). ViSEN was used to identify associations with dyslipidemia phenotypes. There were 71 (50 males, 21 females) and 93 (60 males and 33 females) subjects with low HDL-C and high TG, respectively. Biological variables including age, gender, and BMI were significantly associated with both phenotypes (p<0.001). Importantly, a single SNP, rs708272, was associated with low HDL-C (IG=2.24%, p=0.026). Pairwise and higher order interaction analyses in the full dataset for low HDL-C and high TG revealed the largest effects in the models containing rs1800977, rs708272, age (IG=6.20%, p=0.046) and rs1800588, age, BMI (IG, 3.06%, p=0.022), respectively. In conclusion, the present study brings us a step closer to a systems genetic approach in understanding lipid phenotypes in children. Further efforts can integrate population and laboratory-based studies, hence accelerate the preventive medicine efforts.

In women, no significant variances of calculated free testosterone (cFT) are observed when a fixed value of albumin (Alb: 4.3 g/dL) is used instead of measured albumin values

BACKGROUND

Calculated free testosterone (cFT) is determined from the values of total testosterone (TT), sex hormone binding globulin (SHBG), and albumin (Alb) using mathematical formulae. We evaluated any potential cFT variance when determined with fixed Alb (4.3 g/dL) compared to measured Alb, and the point at which low SHBG and Alb combinations produced significant cFT variance.

MATERIALS

We analyzed 2050 data points in 1222 women. cFT values with fixed vs. the actual measured Alb values were evaluated and contrasted. cFT levels were determined theoretically for all possible combinations of TT, SHBG, and Alb.

METHODS

Agreement between the two measures was assessed with Lin's concordance coefficient. Statistical analyses were performed using R software version 2.12.1.

RESULTS

Mean Alb was 4.05 ± 0.30 g/dL. Mean SHBG 73.0 ± 53.3 nmol/L. A fixed Alb of 4.3 g/dL produced no significant variance for most evaluations of cFT. The accuracy decreased with Alb ≤ 3.5 g/dL in combination with SHBG ≤ 30 nmol/L and exists in 1.0% of the samples.

CONCLUSIONS

A fixed Alb of 4.3 g/dL is acceptable for most clinical evaluations. If Alb is ≤ 3.5 g/dL, along with SHBG ≤ 30 nmol/L, the variance increases and a free testosterone (FT) measurement by equilibrium dialysis is warranted for better accuracy.

The relationship of sex hormone-binding globulin (SHBG) gene polymorphisms with serum SHBG level and metabolic syndrome in Chinese Han males

OBJECTIVE

Epidemiological studies have shown that circulating sex hormone-binding globulin (SHBG) levels are lower in metabolic syndrome (MetS) patients than in non-MetS individuals. In this study, we investigated the relationship of polymorphisms in the SHBG gene with the serum SHBG levels and MetS in Han Chinese.

METHODS

We performed a cross-sectional study of 316 subjects who were recruited from a health checkup population at Zhongshan Hospital, Fudan University. Anthropometric measurements, blood pressure, fasting plasma glucose, lipid levels, total testosterone, and SHBG levels were obtained in addition to the seven SHBG single-nucleotide polymorphisms (SNPs).

RESULTS

The variant allele (AG or AA) carriers in rs6259, compared to the wild-type allele carriers (GG), have a lower risk for MetS [OR 0.56, 95% confidence interval (CI) 0.33-0.96] and higher serum SHBG and TT levels (P = 0.016, 0.004). CT or TT allele carriers in rs3760213, compared to CC allele carriers, also have a lower risk for MetS (OR 0.59, 95 % CI 0.34-1.00) and significantly higher SHBG and TT levels (P = 0.029, 0.009). Carriers having both of the variant alleles had the lowest risk of MetS (OR 0.51, 95 % CI 0.275-0.950) and the highest SHBG levels. The risk of MetS rose with the decrease in serum SHBG levels for rs6259 and rs376021 carriers.

CONCLUSION

rs6259 and rs3760213 SNPs are associated with the risk of MetS and lower serum SHBG level in Chinese Han males.

Sex steroid actions in male bone

Sex steroids are chief regulators of gender differences in the skeleton, and male gender is one of the strongest protective factors against osteoporotic fractures. This advantage in bone strength relies mainly on greater cortical bone expansion during pubertal peak bone mass acquisition and superior skeletal maintenance during aging. During both these phases, estrogens acting via estrogen receptor-α in osteoblast lineage cells are crucial for male cortical and trabecular bone, as evident from conditional genetic mouse models, epidemiological studies, rare genetic conditions, genome-wide meta-analyses, and recent interventional trials. Genetic mouse models have also demonstrated a direct role for androgens independent of aromatization on trabecular bone via the androgen receptor in osteoblasts and osteocytes, although the target cell for their key effects on periosteal bone formation remains elusive. Low serum estradiol predicts incident fractures, but the highest risk occurs in men with additionally low T and high SHBG. Still, the possible clinical utility of serum sex steroids for fracture prediction is unknown. It is likely that sex steroid actions on male bone metabolism rely also on extraskeletal mechanisms and cross talk with other signaling pathways. We propose that estrogens influence fracture risk in aging men via direct effects on bone, whereas androgens exert an additional antifracture effect mainly via extraskeletal parameters such as muscle mass and propensity to fall. Given the demographic trends of increased longevity and consequent rise of osteoporosis, an increased understanding of how sex steroids influence male bone health remains a high research priority.

Androgens and estrogens in skeletal sexual dimorphism

Bone is an endocrine tissue expressing androgen and estrogen receptors as well as steroid metabolizing enzymes. The bioactivity of circulating sex steroids is modulated by sex hormone-binding globulin and local conversion in bone tissue, for example, from testosterone (T) to estradiol (E2) by aromatase, or to dihydrotestosterone by 5α-reductase enzymes. Our understanding of the structural basis for gender differences in bone strength has advanced considerably over recent years due to increasing use of (high resolution) peripheral computed tomography. These microarchitectural insights form the basis to understand sex steroid influences on male peak bone mass and turnover in cortical vs trabecular bone. Recent studies using Cre/LoxP technology have further refined our mechanistic insights from global knockout mice into the direct contributions of sex steroids and their respective nuclear receptors in osteoblasts, osteoclasts, osteocytes, and other cells to male osteoporosis. At the same time, these studies have reinforced the notion that androgen and estrogen deficiency have both direct and pleiotropic effects via interaction with, for example, insulin-like growth factor 1, inflammation, oxidative stress, central nervous system control of bone metabolism, adaptation to mechanical loading, etc., This review will summarize recent advances on these issues in the field of sex steroid actions in male bone homeostasis.

Associations between Salivary Testosterone Levels, Androgen-Related Genetic Polymorphisms, and Self-Estimated Ejaculation Latency Time

Introduction

Recently, testosterone (T) has been shown to be associated with premature ejaculation (PE) symptoms in the literature. Furthermore, studies suggest that the etiology of PE is partly under genetic control.

Aim

The aim of this study was to reassess findings suggesting an association between testosterone (T) and a key symptom of PE, ejaculation latency time (ELT), as well as exploratively investigating associations between six androgen-related genetic polymorphisms and ELT.

Materials and Methods

Statistical analyses were performed on a population-based sample of 1,429 Finnish men aged 18–45 years (M = 26.9, SD = 4.7). Genotype information was available for 1,345–1,429 of these (depending on the polymorphism), and salivary T samples were available from 384 men. Two androgen receptor gene-linked, two 5-alpha-reductase type 2-gene-linked, and two sex hormone-binding globuline gene-linked polymorphisms were genotyped.

Main Outcome Measures

Ejaculatory function was assessed using self-reported ELT.

Results

We found no association between salivary T levels and ELT. We found a nominally significant association between a 5-alpha-reductase type 2-gene-linked polymorphism (rs2208532) and ELT, but this association did not remain significant after correction for multiple testing. One single nucleotide polymorphism in the sex hormone-binding globulin gene (rs1799941) moderated (significantly after correction for multiple testing) the association between salivary T and ELT, so that A:A genotype carriers had significantly lower salivary T levels as a function of increasing ELT compared with other genotype groups.

Conclusions

We were unable to find support for the hypothesis suggesting an association between T levels and ELT, possibly because of the low number of phenotypically extreme cases (the sample used in the present study was population based). Our results concerning genetic associations should be interpreted with caution until replication studies have been conducted. Jern P, Westberg L, Ankarberg-Lindgren C, Johansson A, Gunst A, Sandnabba NK, and Santtila P. Associations between salivary testosterone levels, androgen-related genetic polymorphisms, and self-estimated ejaculation latency time. Sex Med 2014;2:107–114.

Genome-wide association studies on serum sex steroid levels

Even though the levels of circulating sex steroid hormones are to a large extent heritable, their genetic determinants are largely unknown. With the advent of genome-wide association studies (GWAS), much progress has been made and several genetic loci have been identified to be associated with serum levels of dehydroepiandrosterone sulfate, testosterone and sex hormone-binding globulin. The variants identified so far only explain a small amount of the overall heritability, but may help to elucidate the role of sex steroid hormones in common disorders such as hypogonadism, type 2 diabetes and hormone-sensitive cancers. This review provides an overview of the current state of knowledge of the genetic determinants of sex steroid hormones, with a focus on recent GWAS and brief directions for elucidating the remaining heritability.

Multi-locus candidate gene analyses of lipid levels in a pediatric Turkish cohort: lessons learned on LPL, CETP, LIPC, ABCA1, and SHBG

Cardiovascular risk factors and atherosclerosis precursors were examined in 365 Turkish children and adolescents. Study participants were recruited at five different state schools. We tested single and multi-locus effects of six polymorphisms from five candidate genes, chosen based on prior known association with lipid levels in adults, for association with low (≤10th percentile) high density lipoprotein cholesterol (HDL-C) and high (≥90th percentile) triglycerides (TG), and the related continuous outcomes. We observed an association between CETP variant rs708272 and low HDL-C (allelic p=0.020, genotypic p=0.046), which was supported by an independent analysis, PRAT (PRAT control p=0.027). Sex-stratified logistic regression analysis showed that the B2 allele of rs708272 decreased odds of being in the lower tenth percentile of HDL-C measurements (OR=0.36, p=0.02) in girls; this direction of effect was also seen in boys but was not significant (OR=0.64, p=0.21). Logistic regression analysis also revealed that the T allele of rs6257 (SHBG) decreased odds of being in the top tenth percentile of TG measurements in boys (OR=0.43, p=0.03). Analysis of lipid levels as a continuous trait revealed a significant association between rs708272 (CETP) and LDL-C levels in males (p=0.02) with the B2B2 genotype group having the lowest mean LDL-C; the same direction of effect was also seen in females (p=0.05). An effect was also seen between rs708272 and HDL-C levels in girls (p=0.01), with the B2B2 genotype having the highest mean HDL-C levels. Multi-locus analysis, using quantitative multifactor dimensionality reduction (qMDR) identified the previously mentioned CETP variant as the best single locus model, and overall model, for predicting HDL-C levels in children. This study provides evidence for association between CETP and low HDL-C phenotype in children, but the results appear to be weaker in children than previous results in adults and may also be subject to gender effects.

High serum testosterone is associated with reduced risk of cardiovascular events in elderly men. The MrOS (Osteoporotic Fractures in Men) study in Sweden

OBJECTIVES

We tested the hypothesis that serum total testosterone and sex hormone-binding globulin (SHBG) levels predict cardiovascular (CV) events in community-dwelling elderly men.

BACKGROUND

Low serum testosterone is associated with increased adiposity, an adverse metabolic risk profile, and atherosclerosis. However, few prospective studies have demonstrated a protective link between endogenous testosterone and CV events. Polymorphisms in the SHBG gene are associated with risk of type 2 diabetes, but few studies have addressed SHBG as a predictor of CV events.

METHODS

We used gas chromatography/mass spectrometry to analyze baseline levels of testosterone in the prospective population-based MrOS (Osteoporotic Fractures in Men) Sweden study (2,416 men, age 69 to 81 years). SHBG was measured by immunoradiometric assay. CV clinical outcomes were obtained from central Swedish registers.

RESULTS

During a median 5-year follow-up, 485 CV events occurred. Both total testosterone and SHBG levels were inversely associated with the risk of CV events (trend over quartiles: p = 0.009 and p = 0.012, respectively). Men in the highest quartile of testosterone (≥550 ng/dl) had a lower risk of CV events compared with men in the 3 lower quartiles (hazard ratio: 0.70, 95% confidence interval: 0.56 to 0.88). This association remained after adjustment for traditional CV risk factors and was not materially changed in analyses excluding men with known CV disease at baseline (hazard ratio: 0.71, 95% confidence interval: 0.53 to 0.95). In models that included both testosterone and SHBG, testosterone but not SHBG predicted CV risk.

CONCLUSIONS

High serum testosterone predicted a reduced 5-year risk of CV events in elderly men.

Androgens and doping tests: genetic variation and pit-falls

The large variation in disposition known for most drugs is also true for anabolic androgenic steroids. Genetic factors are probably the single most important cause of this variation. Further, there are reasons to believe that there is a corresponding variation in efficacy of doping agents. Doped individuals employ a large variety of doping strategies in respect of choice of substance, dose, dose interval, duration of treatment and use of other drugs for enforcement of effects or correction of side effects. Metabolic steps up-stream and down-stream of testosterone are genetically variable and contribute substantially to the variation in disposition of testosterone, the most common doping agent in sports and in society. Large inter- and intra-ethnic variation in testosterone glucuronidation and excretion is described as well as the pit-falls in evaluation of testosterone doping test results. The hydrolysis and bioactivation of testosterone enanthate is also genetically variable yielding a 2-3 fold variation in excretion rate and serum concentration, thereby implicating a substantial variation in 'efficacy' of testosterone. Given this situation it is logical to adopt the new findings in the doping control programme. The population based cut-off level for the testosterone : epitestosterone ratio should be replaced by a Bayesian interpretation of consecutive tests in the same individual. When combined with the above genetic information the sensitivity of the test is considerably improved. The combination of the three approaches should reduce the rate of falsely negative or positive results and the number of expensive follow-up tests, stipulated by the World Anti-Doping Agency.

Genome-wide association study identifies a new locus JMJD1C at 10q21 that may influence serum androgen levels in men

Circulating androgen levels are often used as indicators of physiological or pathological conditions. More than half of the variance for circulating androgen levels is thought to be genetically influenced. A genome-wide association study (GWAS) has identified two loci, SHBG at 17p13 and FAM9B at Xp22, for serum testosterone (T) levels; however, these explain only a small fraction of inter-individual variability. To identify additional genetic determinants of androgen levels, a GWAS of baseline serum T and dihydrotestosterone (DHT) levels was conducted in 3225 men of European ancestry from the REduction by DUtasteride of Prostate Cancer Events (REDUCE) study. Cross-validation was used to confirm the observed associations between the drug (n = 1581) and placebo (n = 1644) groups of REDUCE. In addition to confirming the associations of two known loci with serum T levels (rs727428 in SHBG: P = 1.26 × 10(-12); rs5934505 in FAM9B: P = 1.61 × 10(-8)), we identified a new locus, JMJD1C at 10q21 that was associated with serum T levels at a genome-wide significance level (rs10822184: P = 1.12 × 10(-8)). We also observed that the SHBG locus was associated with serum DHT levels (rs727428: P = 1.47 × 10(-11)). Moreover, two additional variants in SHBG [rs72829446, in strong linkage equilibrium with the missense variant D356N (rs6259), and rs1799941] were also independently associated with circulating androgen levels in a statistical scale. These three loci (JMJD1C, SHBG and FAM9B) were estimated to account for ~5.3 and 4.1% of the variance of serum T and DHT levels. Our findings may provide new insights into the regulation of circulating androgens and potential targets for androgen-based therapy.

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.

Influence of bone remodelling rate on quantitative ultrasound parameters at the calcaneus and DXA BMDa of the hip and spine in middle-aged and elderly European men: the European Male Ageing Study (EMAS)

OBJECTIVE

To assess the influence of sex hormones on markers of bone turnover and to explore the association between these markers and bone health in middle-aged and elderly European men.

DESIGN

A cross-sectional population-based survey.

METHODS

Men aged 40-79 years were recruited from population registers in eight European centres. Subjects completed a postal questionnaire which included questions concerning lifestyle and were invited to undergo quantitative ultrasound (QUS) of the calcaneus and to provide a fasting blood sample from which the bone markers serum N-terminal propeptide of type 1 procollagen (P1NP) and crosslinks (β C-terminal cross-linked telopeptide (β-cTX)), total testosterone, total oestradiol (E(2)), sex hormone-binding globulin (SHBG) and insulin-like growth factor 1 (IGF1) were measured. Dual-energy X-ray absorptiometry (DXA) of the hip and lumbar spine was performed in two centres.

RESULTS

A total of 3120, mean age 59.9 years (s.d.=11.0) were included. After adjustment for centre, age, height, weight, lifestyle factors, season and other hormones, total and free E(2) were negatively associated with β-cTX but not P1NP while SHBG, IGF1 and parathyroid hormone (PTH) were positively associated with both β-cTX and P1NP. Total or free testosterone was not independently associated with either bone marker. After the same adjustments, higher levels of both bone markers were significantly associated with lower QUS parameters and lower DXA-assessed bone density at the total hip and lumbar spine.

CONCLUSIONS

E(2), SHBG, IGF1 and PTH contribute significantly to the regulation/rate of bone turnover in middle-aged and older European men. Higher rates of bone remodelling are negatively associated with male bone health.

Genetic determinants of serum testosterone concentrations in men

Testosterone concentrations in men are associated with cardiovascular morbidity, osteoporosis, and mortality and are affected by age, smoking, and obesity. Because of serum testosterone's high heritability, we performed a meta-analysis of genome-wide association data in 8,938 men from seven cohorts and followed up the genome-wide significant findings in one in silico (n = 871) and two de novo replication cohorts (n = 4,620) to identify genetic loci significantly associated with serum testosterone concentration in men. All these loci were also associated with low serum testosterone concentration defined as <300 ng/dl. Two single-nucleotide polymorphisms at the sex hormone-binding globulin (SHBG) locus (17p13-p12) were identified as independently associated with serum testosterone concentration (rs12150660, p = 1.2×10(-41) and rs6258, p = 2.3×10(-22)). Subjects with ≥ 3 risk alleles of these variants had 6.5-fold higher risk of having low serum testosterone than subjects with no risk allele. The rs5934505 polymorphism near FAM9B on the X chromosome was also associated with testosterone concentrations (p = 5.6×10(-16)). The rs6258 polymorphism in exon 4 of SHBG affected SHBG's affinity for binding testosterone and the measured free testosterone fraction (p<0.01). Genetic variants in the SHBG locus and on the X chromosome are associated with a substantial variation in testosterone concentrations and increased risk of low testosterone. rs6258 is the first reported SHBG polymorphism, which affects testosterone binding to SHBG and the free testosterone fraction and could therefore influence the calculation of free testosterone using law-of-mass-action equation.

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.

Osteoporosis in Men

The prevalence of osteoporosis is estimated to be 18% in men, but 30% of all fractures occur in men. With age, men experience a gradual decline in testosterone production and bone density. The rate of trabecular bone loss in the lumbar spine in men over age 50 can be double the rate of loss in men under age 50. Endogenous testosterone, estradiol, and their metabolites play a role in maintaining bone health, but their specific effects on bone turnover have been difficult to elucidate. Recently, large cohort studies have provided more detailed information confirming estrogen’s associations and further characterizing the effect of endogenous testosterone and its metabolites on bone mineral density and fractures. Very few clinical trials have assessed the impact of testosterone replacement therapy (TRT) on bone density and fractures in men. The few studies that have been conducted are generally small and not robust enough to show the true treatment effect of TRT and adequately determine its safety. In the absence of data on patient outcomes, it is important for pharmacists to understand the impact of drug therapy on biomarkers and surrogate markers of disease for optimal pharmacotherapy selection and monitoring.

Association of the (TAAAA)n repeat and Asp327Asn polymorphisms in the sex hormone-binding globulin (SHBG) gene with idiopathic male infertility and relation to serum SHBG concentrations

Sex hormone binding globulin (SHBG) is involved in delivering sex hormones to target tissues. We investigated the association between the (TAAAA)n repeat polymorphism, and Asp327Asn polymorphism in the SHBG gene with semen quality and idiopathic male infertility. We studied 168 men with idiopathic infertility [oligoasthenoteratozoospermia (OAT)] and equal number of age-matched normal controls. The serum levels of SHBG, reproductive and thyroid hormones, and Inhibin B were measured. Semen parameters were also assessed. The genotype assays for the SHBG polymorphism were done using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique. Baseline SHBG levels tended to be lower in infertile men (21.1±7.2nmol/l) compared to normal fertile men (24.7±7.9nmol/l). SHBG levels tended to be higher among the subjects with the Asn/Asn (25.84±3.6nmol/l) and S/S (24.50±5.4nmol/l) genotypes compared to subjects with the Asp/Asn (24.38±3.2nmol/l) and L/L (18.44±4.2nmol/l) genotypes of the SHBG gene. The genotype frequencies of Asp/Asp were 80.9% in cases and 71.4% in controls (P=0.001). The variant Asp/Asn genotype was associated with a more than 50% reduced risk of infertility (OR: 0.46, 95% CI: 0.25-0.80, P=0.001). Genotype analysis demonstrated six SHBG (TAAAA)n alleles with 6-11 repeats. Long SHBG (TAAAA)n alleles (>8 repeats) were at greater frequency in infertile men than fertile subjects (P=0.001), whereas short SHBG (TAAAA)n alleles (≤8 repeats) tended to be more frequent in fertile men than cases (P=0.001). Men with the 9/X TAAAA repeat genotype displayed a 2.82-fold increased risk of infertility (95% CI: 1.27-4.79, P=0.01). There were strong and significant positive correlations between plasma SHBG and sperm count (r=0.672, P=0.01), sperm motility (r=0.721, P=0.01) and sperm morphology (r=0.574, P=0.02). We concluded that the SHBG Asp237Asn and (TAAAA)n polymorphisms may influence SHBG levels and as a result, male infertility. Multicenter large scale studies are warranted to better elucidate the role of SHBG gene polymorphism in male infertility.

Menstrual irregularity and bone mass in premenopausal women: cross-sectional associations with testosterone and SHBG

Background

There have been few studies examining the associations between menstrual irregularity, androgens and bone mass in population-based samples of premenopausal women. This study aimed to describe the associations between menstrual pattern, testosterone, sex hormone binding globulin (SHBG) and bone mass in a population-based sample of premenopausal women.

Methods

Cross-sectional study (N = 382, mean age 31.5 years). Menstrual pattern was assessed by questionnaire, bone mass measured by quantitative ultrasound (QUS) and androgen status was assessed by levels of serum testosterone, SHBG and the free androgen index (FAI).

Results

Women with irregular cycles (n = 41, 11%) had higher free androgen index (FAI, P = 0.01) and higher QUS measurements including speed of sound (SOS, 1%, P < 0.05), quantitative ultrasound index (QUI, 7%, p < 0.05), and broadband ultrasound attenuation (BUA, 7%, p = 0.10). These associations persisted after adjustment for age and body mass index (BMI). After further adjustment for hormonal factors (either testosterone, SHBG or FAI), the strength of the associations was moderately attenuated, however, women with irregular cycles still had a 6% increase in mean QUS. Total testosterone, FAI and SHBG were also associated with QUS measures (testosterone and FAI, r +0.11 to +0.21, all p < 0.05; SHBG r -0.14 to -0.16, all p < 0.05) and the associations remained significant after adjustment.

Conclusion

Irregular menstrual cycles were associated with higher bone mass in this population-based sample of premenopausal women suggesting menstrual disturbance should continue to be evaluated but may be less harmful for bone mass. The association between menstrual irregularity and bone mass was partially mediated by markers of androgen status especially free testosterone.

The C282Y polymorphism of the hereditary hemochromatosis gene is associated with increased sex hormone-binding globulin and normal testosterone levels in men

BACKGROUND

Hereditary hemochromatosis resulting either from homozygosity for the C282Y polymorphism of the HFE gene, or compound heterozygosity for C282Y and H63D, manifests with liver disease and hypogonadism. However, it is unclear whether men who are heterozygotes for C282Y or H63D exhibit subtle abnormalities of sex hormone status.

AIMS

To evaluate whether heterozygosity for either of the HFE gene polymorphisms C282Y or H63D is associated with circulating testosterone and SHBG in men.

SUBJECTS AND METHODS

We performed a cross-sectional analysis of 388 community-dwelling men. Men were genotyped for C282Y and H63D. Sera were analysed for testosterone and SHBG, and insulin resistance was estimated using a homeostatic model (HOMA2-IR).

RESULTS

Mean age of men in the cohort was 56.9 yr. Men who were heterozygous for the C282Y polymorphism in the HFE gene had higher SHBG levels than men who did not carry this polymorphism (mean ± SE, 38.2 ± 1.64 vs 32.8 ± 0.71 nmol/l, p=0.006). Total and free testosterone levels did not differ in the two groups. In multivariate analysis adjusting for potential confounders including age, waist circumference, testosterone, and HOMA2-IR, C282Y heterozygosity remained associated with SHBG levels (p<0.001).

CONCLUSION

The C282Y polymorphism is associated with SHBG levels in men who do not manifest iron overload. Further studies are needed to clarify potential mechanisms and determine the clinical relevance of this finding.

Sex steroid metabolism in the regulation of bone health in men

The growth and maintenance of both the female and the male skeleton are influenced by sex steroids. Although the regulation of the female skeleton by estrogens is well established, the relative importance of androgens and estrogens for the male skeleton remains uncertain. Evidence from cross-sectional and longitudinal studies suggests that serum estradiol levels are more strongly associated with bone mineral density, bone turnover and bone loss than testosterone levels are in adult men. In addition, it appears that a threshold level of serum estradiol exists for optimal skeletal maturation and prevention of both bone loss and fractures. Also, the specificity of the assay technique should be considered when examining serum sex steroid levels in epidemiological cohorts, with a preference for the gold standard mass spectrometry. Additionally, serum levels of sex steroid metabolites, rather than the bio-active sex steroids, may be better markers of local sex steroid action at the target tissue level. In this respect, serum levels of glucuronidated androgen metabolites appear to provide additional information as markers of local androgenic activity in bone than the bio-active androgens. Taken together, even though an important role of testosterone is not excluded, estradiol is an important regulator of bone health in men.

Genetic variants of sex hormone-binding globulin and their biological consequences

Several hormonal and metabolic factors have been found to influence the production of sex hormone-binding globulin (SHBG). In addition, twin studies have suggested that genetic factors may also contribute to variation in SHBG levels. Given the clinical significance of SHBG in regulating bioavailable sex steroid hormones, a number of studies examined the potential association between polymorphisms of SHBG gene and serum SHBG levels as well as their possible contribution in the pathogenesis of common diseases. Thus, polymorphisms of SHBG, altering either the production or the metabolism of the protein, may represent part of the genetic background of sex steroid hormone activity in humans. There is considerable heterogeneity in the results of these studies indicating the multiplicity of the factors influencing SHBG variation. However, the weight of evidence suggests that some common genetic variants of SHBG may influence SHBG levels and in part contribute to the phenotypic expression of human diseases.

Sex hormone-binding globulin gene expression in the liver: drugs and the metabolic syndrome

Sex hormone-binding globulin (SHBG) is the main transport binding protein for sex steroid hormones in plasma and regulates their accessibility to target cells. Plasma SHBG is secreted by the liver under the control of hormones and nutritional factors. In the human hepatoma cell line (HepG2), thyroid and estrogenic hormones, and a variety of drugs including the antioestrogen tamoxifen, the phytoestrogen, genistein and mitotane (Op'DDD) increase SHBG production and SHBG gene promoter activity. In contrast, monosaccharides (glucose or fructose) effectively decrease SHBG expression by inducing lipogenesis, which reduces hepatic HNF-4alpha levels, a transcription factor that play a critical role in controlling the SHBG promoter. Interestingly, diminishing hepatic lipogenesis and free fatty acid liver biosynthesis also appear to be associated with the positive effects of thyroid hormones and PPARgamma antagonists on SHBG expression. This mechanism provides a biological explanation for why SHBG is a sensitive biomarker of insulin resistance and the metabolic syndrome, and why low plasma SHBG levels are a risk factor for developing hyperglycemia and type 2 diabetes, especially in women. These important advances in our knowledge of the regulation of SHBG expression in the liver open new approaches for identifying and preventing metabolic disorder-associated diseases early in life.

Genetic variation in androgen disposition: implications in clinical medicine including testosterone abuse

BACKGROUND

Testosterone replacement therapy in hypogonadal men has been used for > 60 years. The use of testosterone substitution is continuously growing and is given to aging men to improve the quality of life. Because testosterone use is associated with muscle strength enhancing effects, it has become a popular drug to abuse. Doping with anabolic steroids, such as testosterone, is a severe challenge to the vision, moral and ethics in sports and has also become a significant and increasing problem in society.

OBJECTIVE

The primary aim of this review is to summarize and discuss the contribution of genetic components to inter-individual variation in androgen disposition.

CONCLUSION

Genetic variation has a large impact on androgen disposition. This variation is of the utmost importance for the interpretation of doping test results and may modulate the effects of testosterone replacement therapy and testosterone doping.

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.