Conjugated steroids: analytical approaches and applications

A novel LC-MS/MS-based assay for the simultaneous quantification of aldosterone-related steroids in human urine

OBJECTIVES

Primary aldosteronism is the most common cause of endocrine hypertension and is associated with significant cardiovascular morbidities. The diagnostic workup depends on determinations of plasma aldosterone and renin which are highly variable and associated with false-positive and false-negative results. Quantification of aldosterone in 24 h urine may provide more reliable results, but the methodology is not well established. We aimed to establish an assay for urinary aldosterone and related steroids with suitability for clinical routine implementation.

METHODS

Here, we report on the development and validation of a quantitative LC-MS/MS method for six urinary steroids: aldosterone, cortisol, 18-hydroxycorticosterone, 18-hydroxycortisol, 18-oxocortisol, tetrahydroaldosterone. After enzymatic deconjugation, total steroids were extracted using SepPak tC18 plates and quantified in positive electrospray ionization mode on a QTRAP 6500+ mass spectrometer.

RESULTS

Excellent linearity was demonstrated with R2>0.998 for all analytes. Extraction recoveries were 89.8-98.4 % and intra- and inter-day coefficients of variations were <6.4 and <9.0 %, establishing superb precision. Patients with primary aldosteronism (n=10) had higher mean 24 h excretions of aldosterone-related metabolites than normotensive volunteers (n=20): 3.91 (95 % CI 2.27-5.55) vs. 1.92 (1.16-2.68) µmol/mol for aldosterone/creatinine, 2.57 (1.49-3.66) vs. 0.79 (0.48-1.10) µmol/mol for 18-hydroxycorticosterone/creatinine, 37.4 (13.59-61.2) vs. 11.61 (10.24-12.98) µmol/mol for 18-hydroxycortisol/creatinine, 1.56 (0.34-2.78) vs. 0.13 (0.09-0.17) µmol/mol for 18-oxocortisol/creatinine, and 21.5 (13.4-29.6) vs. 7.21 (4.88-9.54) µmol/mol for tetrahydroaldosterone/creatinine.

CONCLUSIONS

The reported assay is robust and suitable for routine clinical use. First results in patient samples, though promising, require clinical validation in a larger sample set.

Detection of DHCMT long-term metabolite glucuronides with LC-MSMS as an alternative approach to conventional GC-MSMS analysis

Dehydrochloromethyltestosterone (DHCMT) is one of the most detected illicit used anabolic-androgenic steroids in professional sports. Therefore, a fast and accurate analysis of this substance is of great importance for a constructive fight against doping abuse. The conventional method for the analysis of this drug, GC-MSMS, is very sensitive and selective but also very time- and resource-consuming. With the presented work, a new approach for simple detection with LC-HRMSMS without any sample preparation is introduced. The method is based on the direct analysis of two newly described phase-II metabolites of the DHCMT long-term metabolite 4-chloro-18-nor-17β-hydroxymethyl-17α-methyl-5β-androst-13-en-3α-ol (M3). LC-HRMSMS, GC-MSMS, fractionation and derivatization experiments are combined to identify and characterize for the first time two different glucuronide-acid conjugates of this metabolite in positive human urine samples. In addition, a third glucuronide metabolite was identified, however without isomeric structure determination. The detection of these metabolites is particularly interesting for confirmation analyses, as the method is rapid and requires little sample material.

Stanozolol-N-glucuronide metabolites in human urine samples as suitable targets in terms of routine anti-doping analysis

The exogenous anabolic-androgenic steroid (AAS) stanozolol stays one of the most detected substances in professional sports. Its detection is a fundamental part of doping analysis, and the analysis of this steroid has been intensively investigated for a long time. This contribution to the detection of stanozolol doping describes for the first time the unambiguous proof for the existence of 17-epistanozolol-1'N-glucuronide and 17-epistanozolol-2'N-glucuronide in stanozolol-positive human urine samples due to the access to high-quality reference standards. Examination of excretion study samples shows large detection windows for the phase-II metabolites stanozolol-1'N-glucuronide and 17-epistanozolol-1'N-glucuronide up to 12 days and respectively up to almost 28 days. In addition, we present appropriate validation parameters for the analysis of these metabolites using a fully automatic method online solid-phase extraction (SPE) method already published before. Limits of identification (LOIs) as low as 100 pg/ml and other validation parameters like accuracy, precision, sensitivity, robustness, and linearity are given.

Long-term stability study and evaluation of intact steroid conjugate ratios after the administration of endogenous steroids

The most frequently detected substances prohibited by the World Anti-Doping Agency (WADA) belong to the anabolic steroids class. The most challenging compounds among this class are the endogenous anabolic steroids, which are detected by quantitative measurement of testosterone (T) and its metabolites with a so-called "steroid profiling" method. The current steroid profile is based on the concentrations and ratios of the sum of free and glucuronidated steroids. Recently, our group developed a steroid profiling method for the detection of three free steroids and 14 intact steroid conjugates, including both the glucuronic acid conjugated and sulfated fraction. The study aimed at evaluating the long-term stability of steroid conjugate concentrations and ratios, and the influence of different endogenous steroids on this extended steroid profile. A single dose of oral T undecanoate (TU), topical T gel, topical dihydrotestosterone (DHT) gel, and oral dehydroepiandrosterone (DHEA) was administered to six healthy male volunteers. One additional volunteer with a homozygote deletion of the UGT2B17 gene (del/del genotype) received a single topical dose of T gel. An intramuscular dose of TU was administered to another volunteer. To avoid fluctuation of steroid concentrations caused by variations in urinary flow rates, steroid ratios were calculated and evaluated as possible biomarkers for the detection of endogenous steroid abuse with low doses. Overall, sulfates do not have substantial additional value in prolonging detection times for the investigated endogenous steroids and administration doses. The already monitored glucuronides were overall the best markers and were sufficient to detect the administered steroids.

A method for determination of one hundred endogenous steroids in human serum by gas chromatography-tandem mass spectrometry

Steroid profiling helps various pathologies to be rapidly diagnosed. Results from analyses investigating steroidogenic pathways may be used as a tool for uncovering pathology causations and proposals of new therapeutic approaches. The purpose of this study was to address still underutilized application of the advanced GC-MS/MS platform for the multicomponent quantification of endogenous steroids. We developed and validated a GC-MS/MS method for the quantification of 58 unconjugated steroids and 42 polar conjugates of steroids (after hydrolysis) in human blood. The present method was validated not only for blood of men and non-pregnant women but also for blood of pregnant women and for mixed umbilical cord blood. The spectrum of analytes includes common hormones operating via nuclear receptors as well as other bioactive substances like immunomodulatory and neuroactive steroids. Our present results are comparable with those from our previously published GC-MS method as well as the results of others. The present method was extended for corticoids and 17alpha-hydroxylated 5alpha/ß-reduced pregnanes, which are useful for the investigation of alternative "backdoor" pathway. When comparing the analytical characteristics of the present and previous method, the first exhibit by far higher selectivity, and generally higher sensitivity and better precision particularly for 17alpha-hydroxysteroids.

Applicability of an innovative steroid-profiling method to determine synthetic growth promoter abuse in cattle

A robust LC-MS/MS method was developed to quantify a large number of phase I and phase II steroids in urine. The decision limit is for most compounds lower than 1ngml^-1 with a measurement uncertainty smaller than 30%. The method is fully validated and was applied to assess the influence of administered synthetic steroids and beta-agonists on the steroidogenesis. From three animal experiments, clenbuterol, diethylstilbestrol and stanozolol, the steroid profiles in urine of bovine animals were compared before and after treatment. It was demonstrated that the steroid profiles were altered due to these treatments. A predictive multivariate model was built to identify deviations from normal population steroid profiles. The abuse of synthetic steroids can be detected in urine samples from bovine animals using this model. The samples from the animal experiments were randomly analysed using this method and predictive model. It was shown that these samples were predicted correctly in the exogenous steroids group.

Simultaneous quantitation of nine hydroxy-androgens and their conjugates in human serum by stable isotope dilution liquid chromatography electrospray ionization tandem mass spectrometry

Castration resistant prostate cancer (CRPC), the fatal form of prostate cancer, remains androgen dependent despite castrate levels of circulating testosterone (T) and 5α-dihydrotestosterone (DHT). To investigate mechanisms by which the tumor can synthesize its own androgens and develop resistance to abiraterone acetate and enzalutamide, methods to measure a complete androgen profile are imperative. Here, we report the development and validation of a stable isotope dilution liquid chromatography electrospray ionization tandem mass spectrometric (SID-LC-ESI-MS/MS) method to quantify nine human hydroxy-androgens as picolinates, simultaneously with requisite specificity and sensitivity. In the established method, the fragmentation patterns of all nine hydroxy-androgen picolinates were identified, and [13C3]-5α-androstane-3α, 17β-diol and [13C3]-5α-androstane-3β, 17β-diol used as internal standards were synthesized enzymatically. Intra-day and inter-day precision and accuracy corresponds to the U.S. Food and Drug Administration Criteria for Bioanalytical Method Validation. The lower limit of quantitation (LLOQ) of nine hydroxy-androgens is 1.0pg to 2.5pg on column. Diols which have been infrequently measured: 5-androstene-3β, 17β-diol and 5α-androstane-3α, 17β-diol can be determined in serum at values as low as 1.0pg on column. The method also permits the quantitation of conjugated hydroxy-androgens following enzymatic digestion. While direct detection of steroid conjugates by electrospray-ionization tandem mass spectrometry has advantages the detection of unconjugated and conjugated steroids would require separate methods for each set of analytes. Our method was applied to pooled serum from male and female donors to provide reference values for both unconjugated and conjugated hydroxy-androgens. This method will allow us to interrogate the involvement of the conversion of 5-androstene-3β, 17β-diol to T, the backdoor pathway involving the conversion of 5α-androstane-3α, 17β-diol to DHT and the inactivation of DHT to 5α-androstane-3β, 17β-diol in advanced prostate cancer.

Comparison of sulfo-conjugated and gluco-conjugated urinary metabolites for detection of methenolone misuse in doping control by LC-HRMS, GC-MS and GC-HRMS

Methenolone (17β-hydroxy-1-methyl-5α-androst-1-en-3-one) misuse in doping control is commonly detected by monitoring the parent molecule and its metabolite (1-methylene-5α-androstan-3α-ol-17-one) excreted conjugated with glucuronic acid using gas chromatography-mass spectrometry (GC-MS) and liquid chromatography mass spectrometry (LC-MS) for the parent molecule, after hydrolysis with β-glucuronidase. The aim of the present study was the evaluation of the sulfate fraction of methenolone metabolism by LC-high resolution (HR)MS and the estimation of the long-term detectability of its sulfate metabolites analyzed by liquid chromatography tandem mass spectrometry (LC-HRMSMS) compared with the current practice for the detection of methenolone misuse used by the anti-doping laboratories. Methenolone was administered to two healthy male volunteers, and urine samples were collected up to 12 and 26 days, respectively. Ethyl acetate extraction at weak alkaline pH was performed and then the sulfate conjugates were analyzed by LC-HRMS using electrospray ionization in negative mode searching for [M-H](-) ions corresponding to potential sulfate structures (comprising structure alterations such as hydroxylations, oxidations, reductions and combinations of them). Eight sulfate metabolites were finally detected, but four of them were considered important as the most abundant and long term detectable. LC clean up followed by solvolysis and GC/MS analysis of trimethylsilylated (TMS) derivatives reveal that the sulfate analogs of methenolone as well as of 1-methylene-5α-androstan-3α-ol-17-one, 3z-hydroxy-1β-methyl-5α-androstan-17-one and 16β-hydroxy-1-methyl-5α-androst-1-ene-3,17-dione were the major metabolites in the sulfate fraction. The results of the present study also document for the first time the methenolone sulfate as well as the 3z-hydroxy-1β-methyl-5α-androstan-17-one sulfate as metabolites of methenolone in human urine. The time window for the detectability of methenolone sulfate metabolites by LC-HRMS is comparable with that of their hydrolyzed glucuronide analogs analyzed by GC-MS. The results of the study demonstrate the importance of sulfation as a phase II metabolic pathway for methenolone metabolism, proposing four metabolites as significant components of the sulfate fraction.

Method for the Compound Annotation of Conjugates in Nontargeted Metabolomics Using Accurate Mass Spectrometry, Multistage Product Ion Spectra and Compound Database Searching

Owing to biotransformation, xenobiotics are often found in conjugated form in biological samples such as urine and plasma. Liquid chromatography coupled with accurate mass spectrometry with multistage collision-induced dissociation provides spectral information concerning these metabolites in complex materials. Unfortunately, compound databases typically do not contain a sufficient number of records for such conjugates. We report here on the development of a novel protocol, referred to as ChemProphet, to annotate compounds, including conjugates, using compound databases such as PubChem and ChemSpider. The annotation of conjugates involves three steps: 1. Recognition of the type and number of conjugates in the sample; 2. Compound search and annotation of the deconjugated form; and 3. In silico evaluation of the candidate conjugate. ChemProphet assigns a spectrum to each candidate by automatically exploring the substructures corresponding to the observed product ion spectrum. When finished, it annotates the candidates assigning a rank for each candidate based on the calculated score that ranks its relative likelihood. We assessed our protocol by annotating a benchmark dataset by including the product ion spectra for 102 compounds, annotating the commercially available standard for quercetin 3-glucuronide, and by conducting a model experiment using urine from mice that had been administered a green tea extract. The results show that by using the ChemProphet approach, it is possible to annotate not only the deconjugated molecules but also the conjugated molecules using an automatic interpretation method based on deconjugation that involves multistage collision-induced dissociation and in silico calculated conjugation.

A simple method for the small scale synthesis and solid-phase extraction purification of steroid sulfates

Steroid sulfates are a major class of steroid metabolite that are of growing importance in fields such as anti-doping analysis, the detection of residues in agricultural produce or medicine. Despite this, many steroid sulfate reference materials may have limited or no availability hampering the development of analytical methods. We report simple protocols for the rapid synthesis and purification of steroid sulfates that are suitable for adoption by analytical laboratories. Central to this approach is the use of solid-phase extraction (SPE) for purification, a technique routinely used for sample preparation in analytical laboratories around the world. The sulfate conjugates of sixteen steroid compounds encompassing a wide range of steroid substitution patterns and configurations are prepared, including the previously unreported sulfate conjugates of the designer steroids furazadrol (17β-hydroxyandrostan[2,3-d]isoxazole), isofurazadrol (17β-hydroxyandrostan[3,2-c]isoxazole) and trenazone (17β-hydroxyestra-4,9-dien-3-one). Structural characterization data, together with NMR and mass spectra are reported for all steroid sulfates, often for the first time. The scope of this approach for small scale synthesis is highlighted by the sulfation of 1μg of testosterone (17β-hydroxyandrost-4-en-3-one) as monitored by liquid chromatography-mass spectrometry (LCMS).

Comparison of CID versus ETD-based MS/MS fragmentation for the analysis of doubly derivatized steroids

Electrospray ionization coupled with collision-induced dissociation (CID) and tandem mass spectrometry (MS/MS) is a commonly used technique to analyze the chemical composition of steroids. However, steroids are structurally similar compounds, making it difficult to interpret their product-ion spectra. Electron transfer dissociation (ETD), a relatively new technique for protein and peptide fragmentation, has been shown to provide more detailed structural information. In this study, we compared the ability of CID with that of ETD to differentiate between eight 3,20-dioxosteroids that had been derivatizated with a quaternary ammonium salt, Girard reagent P (GirP), at room temperature or after exposure to microwave irradiation to generate doubly charged ions. We found that the derivatization of steroid with GirP hydrazine occurred in less than 10 min when the reaction was carried out in the presence of microwave irradiation compared to 30 min when the reaction was carried out at room temperature. According to the MS/MS spectra, CID provided rich, structurally informative ions; however, the spectra were complex, thereby complicating the peak assignment. In contrast, ETD generated simpler spectra, making it easier to recognize individual peaks. Remarkably, both CID and ETD were allowed to differentiate of steroid isomers, 17α-hydroxyprogesterone (17OHP) and deoxycorticosterone (DOC), but the signature ions obtained from CID were less intense than those generated by ETD, which generated much clearer spectra. These results indicate that ETD in conjunction with CID can provide more structural information for precise characterization of steroids.

Use of isotope ratio mass spectrometry to differentiate between endogenous steroids and synthetic homologues in cattle: a review

Although substantial technical advances have been achieved during the past decades to extend and facilitate the analysis of growth promoters in cattle, the detection of abuse of synthetic analogs of naturally occurring hormones has remained a challenging issue. When it became clear that the exogenous origin of steroid hormones could be traced based on the (13)C/(12)C isotope ratio of the substances, GC/C/IRMS has been successfully implemented to this aim since the end of the past century. However, due to the costly character of the instrumental setup, the susceptibility of the equipment to errors and the complex and time consuming sample preparation, this method is up until now only applied by a limited number of laboratories. In this review, the general principles as well as the practical application of GC/C/IRMS to differentiate between endogenous steroids and exogenously synthesized homologous compounds in cattle will be discussed in detail, and will be placed next to other existing and to be developed methods based on isotope ratio mass spectrometry. Finally, the link will be made with the field of sports doping, where GC/C/IRMS has been established within the World Anti-Doping Agency (WADA) approved methods as the official technique to differentiate between exogenous and endogenous steroids over the past few years.

Novel fragmentation pathways of anionic adducts of steroids formed by electrospray anion attachment involving regioselective attachment, regiospecific decompositions, charge-induced pathways, and ion-dipole complex intermediates

The analysis of several bifunctional neutral steroids, 5-α-pregnane diol (5-α-pregnane-3α-20βdiol), estradiol (3,17α-dihydroxy-1,3,5(10)-estratriene), progesterone (4-pregnene-3,20-dione), lupeol (3β-hydroxy-20(29)-lupene), pregnenolone (5-pregnen-3β-ol-20-one), and pregnenolone acetate (5-pregnen-3β-ol-20-one acetate) was accomplished by negative ion electrospray mass spectrometry (ESI-MS) employing adduct formation with various anions: fluoride, bicarbonate, acetate, and chloride. Fluoride yielded higher abundances of anionic adducts and more substantial abundances of deprotonated molecules compared with other investigated anions. Collision-induced dissociation (CID) of precursor [M + anion](-) adducts of these steroids revealed that fluoride adduct [M + F](-) precursors first lose HF to produce [M - H](-) and then undergo consecutive decompositions to yield higher abundances of structurally-informative product ions than the other tested anions. In addition to charge-remote fragmentations, the majority of CID pathways of estradiol are deduced to occur via charge-induced fragmentation. Most interestingly, certain anions exhibit preferential attachment to a specific site on these bifunctional steroid molecules, which we are calling "regioselective anion attachment." Regioselective anion attachment is evidenced by subsequent regiospecific decomposition. Regioselective attachment of fluoride (and acetate) anions to low (and moderate) acidity functional groups of pregnenolone, respectively, is demonstrated using deuterated compounds. Moreover, the formation of unique intermediate ion-dipole complexes leading to novel fragmentation pathways of fluoride adducts of pregnenolone acetate, and bicarbonate adducts of d(4)-pregnenolone, are also discussed.

Metabolism of anabolic steroids and their relevance to drug detection in horseracing

The fight against doping in sport using analytical chemistry is a mature area with a history of approximately 100 years in horseracing. In common with human sport, anabolic/androgenic steroids (AASs) are an important group of potential doping agents. Particular issues with their detection are extensive metabolism including both phase I and phase II. A number of the common AASs are also endogenous to the equine. A further issue is the large number of synthetic steroids produced as pharmaceutical products or as 'designer' drugs intended to avoid detection or for the human supplement market. An understanding of the metabolism of AASs is vital to the development of effective detection methods for equine sport. The aim of this paper is to review current knowledge of the metabolism of appropriate steroids, the current approaches to their detection in equine sport and future trends that may affect equine dope testing.

Simultaneous quantification of four native estrogen hormones at trace levels in human cerebrospinal fluid using liquid chromatography-tandem mass spectrometry

Estrogens are known to exhibit neuroprotective effects on the brain. Their importance in this regard and in others has been emphasized in many recent studies, which increases the need to develop reliable analytical methods for the measurement of estrogen hormones. A heart-cutting two-dimensional liquid chromatography separation method coupled with electrospray ionization-tandem mass spectrometry (ESI-MS/MS) has been developed for simultaneous measurement of four estrogens, including estriol (E3), estrone (E1), 17β-estradiol (17β-E2), and 17α-estradiol (17α-E2), in human cerebrospinal fluid (CSF). The method was based on liquid-liquid extraction and derivatization of estrogens with dansyl chloride to enhance the sensitivity of ESI-based detection in conjunction with tandem mass spectrometry. Dansylated estriol and estrone were separated in the first dimension by an amide-C18 column, while dansylated 17β- and 17α-estradiol were resolved on the second dimension by two C18 columns (175 mm total length) connected in series. This is the first report of a method for simultaneous quantification of all four endogenous estrogen compounds in their dansylated form. The detection limits for E1, 17α-E2, 17β-E2, and E3 were 19, 35, 26, and 61pg/mL, respectively. Due to matrix effects, validation and calibration was carried out in charcoal-stripped CSF. The precision and accuracy were more than 86% for the two E2 compounds and 79% for E1 and E3 while the extraction recovery ranged from 91% to 104%. The method was applied to measure estrogens obtained in a clinical setting, from the CSF of ischemic trauma patients. While 17β-estradiol was present at a significant level in the CSF of some samples, other estrogens were present at lower levels or were undetectable.

Preclinical challenges in steroid analysis of human samples

Preclinical challenges in the analysis of steroid hormones are primarily determined by biological factors involved in the physiology and pathophysiology of hormone secretion. Major biologically influencing factors like age, sex, pubertal stage, pregnancy, phase of the menstruation, and diurnal rhythm have to be considered in the definition of reference ranges for steroids and their clinical interpretation. Hitherto, in clinical routine laboratories steroids were mainly determined by direct immunoassays applied on automated platforms, which are simple, rapid and cheap if a high number of samples are measured. However, technical factors like cross-reactivity of related steroid metabolites or limited analytical ranges have to be taken in account and may impair accuracy and precision of these direct methods. The actual development of mass spectrometry based analytical platforms for the determination of single steroid or steroid patterns seems to be an alternative analytical approach combining multi-parametric analysis, high sensitivity and specificity as well simple sample pre-treatment, robustness and low running costs for steroid analysis. This short review will give an overview about biological influencing factors and technical disturbing factors of routinely used immunoassay for the analysis of steroids. The application of LC-MS/MS as an alternative routine high-throughput platform for steroid analysis and its perspective role in the standardization and harmonisation of steroid measurements in clinical routine application will be discussed.

Development of carbon plasma-coated multiwell plates for high-throughput mass spectrometric analysis of highly lipophilic fermentation products

Classical approaches to strain improvement and metabolic engineering rely on rapid qualitative and quantitative analyses of the metabolites of interest. As an analytical tool, mass spectrometry (MS) has proven to be efficient and nearly universally applicable for timely screening of metabolites. Furthermore, gas chromatography (GC)/MS- and liquid chromatography (LC)/MS-based metabolite screens can often be adapted to high-throughput formats. We recently engineered a Saccharomyces cerevisiae strain to produce taxa-4(5),11(12)-diene, the first pathway-committing biosynthetic intermediate for the anticancer drug Taxol, through the heterologous and homologous expression of several genes related to isoprenoid biosynthesis. To date, GC/MS- and LC/MS-based high-throughput methods have been inherently difficult to adapt to the screening of isoprenoid-producing microbial strains due to the need for extensive sample preparation of these often highly lipophilic compounds. In the current work, we examined different approaches to the high-throughput analysis of taxa-4(5),11(12)-diene biosynthesizing yeast strains in a 96-deep-well format. Carbon plasma coating of standard 96-deep-well polypropylene plates allowed us to circumvent the inherent solvent instability of commonly used deep-well plates. In addition, efficient adsorption of the target isoprenoid product by the coated plates allowed rapid and simple qualitative and quantitative analyses of the individual cultures.