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.

Unlocking the potential of forensic traces: Analytical approaches to generate investigative leads

Forensic investigation involves gathering the information necessary to understand the criminal events as well as linking objects or individuals to an item, location or other individual(s) for investigative purposes. For years techniques such as presumptive chemical tests, DNA profiling or fingermark analysis have been of great value to this process. However, these techniques have their limitations, whether it is a lack of confidence in the results obtained due to cross-reactivity, subjectivity and low sensitivity; or because they are dependent on holding reference samples in a pre-existing database. There is currently a need to devise new ways to gather as much information as possible from a single trace, particularly from biological traces commonly encountered in forensic casework. This review outlines the most recent advancements in the forensic analysis of biological fluids, fingermarks and hair. Special emphasis is placed on analytical methods that can expand the information obtained from the trace beyond what is achieved in the usual practices. Special attention is paid to those methods that accurately determine the nature of the sample, as well as how long it has been at the crime scene, along with individualising information regarding the donor source of the trace.

Modulation of SHBG binding to testosterone and estradiol by sex and morbid obesity

OBJECTIVE

Sex hormone-binding globulin (SHBG) binds and transports testosterone and estradiol in plasma. The possibility that SHBG is a mixture of transporting proteins has been postulated. We analyzed in parallel the effects of obesity status on the levels and binding capacity of circulating SHBG and their relationship with testosterone and estradiol.

DESIGN

Anthropometric measures and plasma were obtained from apparently healthy young (i.e. 35 ± 7 years) premenopausal women (n = 32) and men (n = 30), with normal weight and obesity (BMI >30 kg/m²).

METHODS

SHBG protein (Western blot), as well as the plasma levels of testosterone, estradiol, cortisol and insulin (ELISA) were measured. Specific binding of estradiol and testosterone to plasma SHBG was analyzed using tritium-labeled hormones.

RESULTS

Significant differences in SHBG were observed within the obesity status and gender, with discordant patterns of change in testosterone and estradiol. In men, testosterone occupied most of the binding sites. Estrogen binding was much lower in all subjects. Lower SHBG of morbidly obese (BMI >40 kg/m²) subjects affected testosterone but not estradiol. The ratio of binding sites to SHBG protein levels was constant for testosterone, but not for estradiol. The influence of gender was maximal in morbid obesity, with men showing the highest binding/SHBG ratios.

CONCLUSIONS

The results reported here are compatible with SHBG being a mixture of at least two functionally different hormone-binding globulins, being affected by obesity and gender and showing different structure, affinities for testosterone and estradiol and also different immunoreactivity.

Determining Gender by Raman Spectroscopy of a Bloodstain

The development of novel methods for forensic science is a constantly growing area of modern analytical chemistry. Raman spectroscopy is one of a few analytical techniques capable of nondestructive and nearly instantaneous analysis of a wide variety of forensic evidence, including body fluid stains, at the scene of a crime. In this proof-of-concept study, Raman microspectroscopy was utilized for gender identification based on dry bloodstains. Raman spectra were acquired in mapping mode from multiple spots on a bloodstain to account for intrinsic sample heterogeneity. The obtained Raman spectroscopic data showed highly similar spectroscopic features for female and male blood samples. Nevertheless, support vector machines (SVM) and artificial neuron network (ANN) statistical methods applied to the spectroscopic data allowed for differentiating between male and female bloodstains with high confidence. More specifically, the statistical approach based on a genetic algorithm (GA) coupled with an ANN classification showed approximately 98% gender differentiation accuracy for individual bloodstains. These results demonstrate the great potential of the developed method for forensic applications, although more work is needed for method validation. When this method is fully developed, a portable Raman instrument could be used for the infield identification of traces of body fluids and to obtain phenotypic information about the donor, including gender and race, as well as for the analysis of a variety of other types of forensic evidence.

Estrogen: a master regulator of bioenergetic systems in the brain and body

Estrogen is a fundamental regulator of the metabolic system of the female brain and body. Within the brain, estrogen regulates glucose transport, aerobic glycolysis, and mitochondrial function to generate ATP. In the body, estrogen protects against adiposity, insulin resistance, and type II diabetes, and regulates energy intake and expenditure. During menopause, decline in circulating estrogen is coincident with decline in brain bioenergetics and shift towards a metabolically compromised phenotype. Compensatory bioenergetic adaptations, or lack thereof, to estrogen loss could determine risk of late-onset Alzheimer's disease. Estrogen coordinates brain and body metabolism, such that peripheral metabolic state can indicate bioenergetic status of the brain. By generating biomarker profiles that encompass peripheral metabolic changes occurring with menopause, individual risk profiles for decreased brain bioenergetics and cognitive decline can be created. Biomarker profiles could identify women at risk while also serving as indicators of efficacy of hormone therapy or other preventative interventions.

Relationship of sex steroid hormones with bone mineral density (BMD) in a nationally representative sample of men

OBJECTIVE

Sex steroid hormones influence bone mineral density (BMD) in women, but are less well-studied in men. We evaluated the association of serum total and free sex steroid hormones and SHBG with osteopaenia in a nationally representative sample of men aged 20-90 years.

DESIGN

BMD and sex steroid hormones were measured among participants in NHANES III, a cross-sectional study of the US population.

POPULATION

A total of 1185 adult men in morning examination session of Phase I of NHANES III (1988-91).

MEASUREMENTS

Relation of oestradiol (E(2)), testosterone, and SHBG concentrations with BMD. Osteopaenia was defined as 1-2.5 SD below the mean for white men aged 20-29 years.

RESULTS

Men in the lowest quartile of free E(2) had 70% increased odds (OR = 1.69, 95% CI 0.95-2.98) of osteopaenia compared with men in the highest quartile. Men in the lowest quartile of free testosterone had nearly four times the odds of osteopaenia than those in the highest quartile (OR = 3.82, 95% CI 1.87-7.78). Lower concentrations of SHBG appeared protective against osteopaenia (P-trend = 0.01). Neither total testosterone nor total E(2) was associated with BMD, although men with clinically low E(2) (< 20 ng/l) had lower BMD (0.930 g/cm(2), 95% CI 0.88-0.98) than men with normal-range E(2) (1.024 g/cm(2), 95% CI 1.01-1.04; P = 0.004). Findings for free E(2) were most pronounced among elderly men, while the findings for free testosterone were most pronounced among younger men.

CONCLUSIONS

In this nationally representative study, men with lower free E(2), lower free testosterone, and higher SHBG concentrations in circulation were more likely to have low BMD.

Serum sex hormone-binding globulin levels in healthy children and girls with precocious puberty before and during gonadotropin-releasing hormone agonist treatment

CONTEXT

The regulation of SHBG is complex and influenced by sex steroids and insulin.

OBJECTIVE

Our objective was to describe serum levels and evaluate determinants of SHBG levels in healthy children and in girls with central precocious puberty (CPP) before and during GnRH analog (GnRHa) treatment.

DESIGN

We conducted a cross-sectional study on healthy subjects and a 2-yr longitudinal study in girls with CPP.

SETTING

The study took place at a tertiary referral center for pediatric endocrinology.

PARTICIPANTS/PATIENTS

A total of 903 healthy schoolchildren served as healthy subjects, and 25 girls with precocious/early puberty participated.

INTERVENTIONS

Girls with CPP were treated with the long-acting GnRHa triptorelin.

RESULTS

SHBG levels declined with increasing age in both sexes until adulthood. In healthy children, SHBG was significantly negatively correlated with testosterone, estradiol, dehydroepiandrosterone sulfate, and body mass index (BMI) in boys (total model R(2) = 0.71) but only with dehydroepiandrosterone sulfate and BMI in girls (total model R(2) = 0.26). Body fat percentage was significantly negatively correlated with SHBG levels (P < 0.001) in both boys (R(2) = 0.18) and girls (R(2) = 0.23). Girls with CPP had significantly lower pretreatment SHBG levels compared with age-matched controls [SHBG sd score, -1.29 (-4.48; 0.01)], which declined even further during GnRHa treatment [-2.75 (-5.9; 0.53); P < 0.001]. Even after adjustment for BMI and pubertal stage, girls with CPP had lower SHBG levels (P < 0.001) compared with healthy controls.

CONCLUSIONS

SHBG levels were strongly dependent on body composition and sex steroid levels in children with normal and precocious puberty. Studies on insulin sensitivity and SHBG in puberty are needed to better understand the interaction between body composition and gonadal maturation.

Calculation of bioavailable and free testosterone in men: a comparison of 5 published algorithms

BACKGROUND

Estimation of serum concentrations of free testosterone (FT) and bioavailable testosterone (bioT) by calculation is an inexpensive and uncomplicated method. We compared results obtained with 5 different algorithms.

METHODS

We used 5 different published algorithms [described by Sodergard et al. (bioTS and FTS), Vermeulen et al. (bioTV and FTV), Emadi-Konjin et al. (bioTE), Morris et al. (bioTM), and Ly et al. (FTL)] to estimate bioT and FT concentrations in samples obtained from 399 independently living men (ages 40-80 years) participating in a cross-sectional, single-center study.

RESULTS

Mean bioT was highest for bioTS (10.4 nmol/L) and lowest for bioT(E) (3.87 nmol/L). Mean FT was highest for FTS (0.41 nmol/L), followed by FTV (0.35 nmol/L), and FTL (0.29 nmol/L). For bioT concentrations, the Pearson correlation coefficient was highest for the association between bioTS and bioTV (r = 0.98) and lowest between bioTM and bioTE (r = 0.66). FTL was significantly associated with both FTS (r = 0.96) and FTV (r = 0.88). The Pearson correlation coefficient for the association between FTL and bioTM almost reached 1.0. Bland-Altman analysis showed large differences between the results of different algorithms. BioTM, bioTE, bioTV, and FTL were all significantly associated with sex hormone binding globulin (SHBG) concentrations.

CONCLUSION

Algorithms to calculate FT and bioT must be revalidated in the local setting, otherwise over- or underestimation of FT and bioT concentrations can occur. Additionally, confounding of the results by SHBG concentrations may be introduced.

Evaluation of a new automated electrochemiluminescent sex hormone-binding globulin (SHBG) immunoassay

Serum sex hormone-binding globulin (SHBG) regulates the cellular bioavailability of SHBG-bound steroid hormones. Since variations in SHBG levels may affect the concentration of free, i.e., biologically active testosterone in serum, SHBG levels are commonly measured as a supplement to total testosterone determination. The recently developed electrochemiluminescence Elecsys SHBG immunoassay was evaluated analytically on a Modular E170 (Roche Diagnostics, Mannheim, Germany) immunoanalyzer. Major differences in SHBG concentrations have been described among the commercially available methods; we therefore compared the new method with an established SHBG immunoradiometric assay (IRMA) in 99 routine serum samples. To provide reference values to clinicians, SHBG concentration was measured by Elecsys in 304 serum samples from healthy volunteers and several relevant clinical subgroups. The within-run and total imprecision coefficients of variation were </=2.9% and </=3.3%, respectively. Functional sensitivity was at least 0.74 nmol/L. Recoveries after dilution of high-concentration samples in low-titer human serum or in assay diluent were within the range of 85-110%. The Elecsys SHBG assay correlated well (r=0.98) with the SHBG immunoradiometric assay, but values were higher for the Elecsys assay (Passing Bablok regression analysis: slope 1.14, intercept +2.5). In healthy subjects and clinical subgroups, we confirmed the differences in SHBG values reported in the literature. The Elecsys SHBG immunoassay provides precision and reliability in combination with reduced turnaround time.

Reflections concerning biochemical parameters of androgenicity

Due to the highly variable concentration of sex hormone binding globulin (SHBG) and the many factors affecting it, the evaluation of the androgen status may require the measurement of a parameter of bioactive plasma testosterone. As, however, no practical, clinical useful direct method for measurement of plasma androgen bioactivity is available, indirect biochemical parameters are used. All have their limitations and pitfalls. In this paper are discussed some of the factors influencing the values obtained with different methods (direct measurement of free testosterone by analog radioimmunoassay, dialysis, ammonium sulfate precipitation, free testosterone index, calculated free and bioavailable testosterone), all of which may explain the variability of data reported in the literature. It is concluded that, whereas determination of bioavailable testosterone by dialysis or ammonium sulfate precipitation of SHBG-bound testosterone is work-intensive and not really suitable for clinical routine, while direct measurement of free testosterone by analog immunoassay yields unreliable results, only the free testosterone index and calculated bioavailable testosterone are adapted for clinical routine. The limitations of the free testosterone index, a dimensionless parameter which does not reflect a defined bioavailable testosterone concentration, are discussed. As the same measurements of testosterone and SHBG required for determination of the free testosterone index permit the calculation of bioavailable testosterone, which yields a defined androgen concentration, it is advisable to prefer the latter over the free testosterone index, which should no longer be used.

Androgen treatment of male hypogonadism in older males

The treatment of primary and secondary hypogonadism with testosterone is well established. Recently, there has been increased awareness that low testosterone levels also occur in chronically ill persons and aging males. Because of sex hormone binding globulin changes, it is more appropriate to make the diagnosis using either free or bioavailable testosterone. A small number of controlled studies have suggested that testosterone replacement in older men improves libido, quality of erections, some aspects of cognition, muscle mass, muscles strength, and bone mineral density. It also decreases fat mass and leptin levels. A number of screening questionnaires for the andropause have been developed. Insufficient numbers of older men have been treated with testosterone to characterize the true incidence of side effects. There is a desperate need for well designed, large controlled trials to establish the value or otherwise of testosterone treatment in older males.