Direct Measurement of Free Estradiol in Human Serum and Plasma by Equilibrium Dialysis-Liquid Chromatography-Tandem Mass Spectrometry

Clinical Utility and Analytical Aspects of Direct Measurements of Free Hormones Using Mass Spectrometry-Based Methods

BACKGROUND

The free hormone (FH) hypothesis states that hormone action and the corresponding biological effects are mediated by the unbound (free) fraction of hormone in circulation. The in vivo relationship between protein-bound and FH is complex and dynamic. In most individuals, measurement of total hormone (TH) is usually adequate to reflect the hormone status; however, certain physiological conditions and/or medications can affect protein binding and alter FH concentration. In these cases, measurement of FH will provide a better measure of the bioactive hormone status than measurement of the TH. Measurement of FH presents many challenges, as the concentrations are very low and there are number of pitfalls, which may affect the measured concentrations.

CONTENT

In this review, we discuss techniques used in the separation and direct quantitation of FH concentrations in biological samples using mass spectrometry for analysis. We also highlight clinical situations in which FH analysis is warranted and when mass spectrometry should be the preferred methodology over immunoassays.

SUMMARY

Equilibrium dialysis, ultrafiltration, or size-exclusion separation coupled with liquid chromatography-tandem mass spectrometry provides a sensitive and specific method to measure FH concentrations. These direct methods are useful in iatrogenic or physiological states that alter hormone binding or metabolism.

The importance of estradiol measurement in patients undergoing in vitro fertilization

Successful outcomes of in vitro fertilization (IVF) are dependent in part on successful oocyte maturation and retrieval during a controlled ovarian stimulation process, which is guided by serial ultrasound and estradiol measurements. Yet, laboratory analysis of estradiol poses challenges due to the need for accuracy and specificity across concentrations that span multiple orders of magnitude. The Endocrine Society released a 2013 position statement that called for improvements in methods to analyze estradiol, and while some progress has been made in standardization and assay specificity, further work is needed to meet the needs of patients in both the IVF setting and in other clinical contexts. This review highlights the capabilities and challenges of current laboratory methods for the analysis of estradiol in the IVF setting, including automated immunoassays and liquid chromatography-tandem mass spectrometry, and discusses current efforts to improve the analytical sensitivity and standardization of estradiol assays. Clinical laboratorians should be aware of the limitations of current estradiol assays and select appropriate methods for the measurement of estradiol in their patient population.

Simultaneous measurement of total estradiol and testosterone in human serum by isotope dilution liquid chromatography tandem mass spectrometry

Reliable measurement of total testosterone and estradiol is critical for their use as biomarkers of hormone-related disorders in patient care and translational research. We developed and validated a mass spectrometry method to simultaneously quantify these analytes in human serum without chemical derivatization. Serum is equilibrated with isotopic internal standards and treated with acidic buffer to release hormones from their binding proteins. Lipids are isolated and polar impurities are removed by two serial liquid-liquid extraction steps. Total testosterone and estradiol are measured using liquid chromatography tandem mass spectrometry (LC-MS/MS) in combination of positive and negative electrospray ionization modes. The method shows broad analytical measurement range for both testosterone 0.03-48.5 nM (0.75-1400 ng/dL) and estradiol 11.0-5138 pM (2.99-1400 pg/mL) and excellent agreement with certified reference materials (mean bias less than 2.1% to SRM 971, BCR 576, 577, and 578) and a high order reference method (mean bias 1.25% for testosterone and -0.84% for estradiol). The high accuracy of the method was monitored and certified by CDC Hormone Standardization (HoSt) Program for 2 years with mean bias -0.7% (95% CI -1.6% to 0.2%) for testosterone and 0.1% (95% CI -2.2% to 2.3%) for estradiol. The method precision over a 2-year period for quality control pools at low, medium, and high concentrations was 2.7-2.9% for testosterone and 3.3-5.3% for estradiol. With the consistently excellent accuracy and precision, this method is readily applicable for high-throughput clinical and epidemiological studies.

Effects of chronic administration of the phosphodiesterase inhibitor vardenafil on serum levels of adrenal and testicular steroids in men with type 2 diabetes mellitus

To investigate whether long-term, chronic treatment with the phosphodiesterase-5 inhibitor vardenafil affects adrenal and testicular steroidogenesis in diabetic men, using liquid chromatography-tandem mass spectrometry. A longitudinal, prospective, investigator-started, randomized, placebo-controlled, double-blind, clinical-trial was carried out, enrolling 54 male patients affected by type 2 diabetes mellitus diagnosed within the last 5 years. In total, 26 and 28 patients were followed for 1 year and assigned to the study and placebo group, respectively. Progesterone, 17-hydroxyprogesterone, androstenedione, testosterone, dehydroepiandrosterone, dehydroepiandrosterone sulfate, corticosterone, 11-deoxycortisol and cortisol, were evaluated using liquid chromatography-tandem mass spectrometry. No differences were seen in sex testicular steroids between study and control group. As for the adrenal gland, steroids were considered according to the zona in which they are produced. No significant differences were seen in steroid produced in zona fasciculata. For the zona reticularis, dehydroepiandrosterone significantly decreased during treatment only in the study group (p = 0.007), with higher levels at visit 2 and 8 than other visits. The dehydroepiandrosterone sulfate/dehydroepiandrosterone ratio significantly increased during treatment only in the verum group. Considering the adrenal zona glomerulosa, corticosterone significantly changed among visits both in both groups (p < 0.001), with higher levels at visit 2 (p = 0.028), 8 (p = 0.003), and 10 (p = 0.044), i.e., in coincidence with the complete clinical and instrumental examination performed only at these visits according to the study protocol. Chronically administered vardenafil reduces dehydroepiandrosterone levels and increases dehydroepiandrosterone sulfate/dehydroepiandrosterone ratio as possible consequences of modulation of steroidogenic enzymes by tissue changes in cyclic adenosine monophosphate and cyclic guanosine monophosphate availability. A possibly stress-related increase in corticosterone is suggested for the first time.

SHBG, Sex Steroids, and Kyphosis in Older Men: The MrOS Study

Accentuated kyphosis is associated with adverse health outcomes, including falls and fractures. Low bone density is a risk factor for hyperkyphosis, and each vertebral fracture adds roughly 4° to forward spine curvature. Sex steroids, in particular low bioavailable estradiol and high sex hormone-binding globulin (SHBG), are associated with bone loss and high SHBG is associated with vertebral fractures in older men. We, therefore, hypothesized that low bioavailable estradiol and high SHBG would be associated with worse kyphosis. To test this hypothesis, we examined the cross-sectional associations between individual bioavailable sex hormones and SHBG with radiographically assessed kyphosis. Participants included 1500 men aged 65 and older from the Osteoporotic Fractures in Men (MrOS) Study, in whom baseline measures of kyphosis and sex hormones were available. Modified Cobb angle of kyphosis, calculated from T4 through T12, was assessed from supine lateral spine radiographs. Serum total estradiol and total testosterone were measured by mass spectrometry, and bioavailable sex steroids were calculated from mass action equations. After adjustment for age and other confounding variables, no association was found between bioavailable estradiol or testosterone and Cobb angle, either when kyphosis was analyzed as a continuous variable or dichotomized into highest versus lower three quartiles. In linear regression models adjusted for age and clinic site, there was a significant association between SHBG and kyphosis (parameter estimate = 0.76 per SD increase, p = 0.01). In the fully adjusted model, this association was weakened and of only borderline statistical significance (parameter estimate = 0.61 per SD, p = 0.05). Logistic models demonstrated similar findings. Although associated with bone loss, we did not demonstrate that low bioavailable estradiol translates into worse kyphosis in older men. High SHBG is associated with bone loss and vertebral fractures. Our results suggest that high SHBG may also be a risk factor for hyperkyphosis. © 2016 American Society for Bone and Mineral Research.