Characterization and quantitation of a sulfoconjugated metabolite for detection of methyltestosterone misuse and direct identification by LC-MS

Methyltestosterone (MT) is one of the most frequently misused anabolic androgenic steroids detected in doping control analysis. The metabolism of MT in humans leads to several phase І metabolites and their corresponding phase Ⅱ conjugates. Previous studies have postulated the 3α-sulfoconjugate of 17α-methyl-5β-androstane-3α,17β-diol (S2) as principal sulfate metabolite of MT, with a detection window exceeding 10 days. However, a final direct and unambiguous confirmation of the structure of this metabolite is missing until now. In this study, we established an approach to detect and identify S2, using intact analysis by liquid chromatography hyphenated with tandem mass spectrometry (LC-MS/MS) without complex sample pretreatment. An in vitro study yielded the LC-MS/MS reference retention times of all 3-sulfated 17-methylandrostane-3,17-diol diastereomers, allowing for accurate structure assignment of potentially detected metabolites. In an in vivo excretion study with a single healthy male volunteer, the presence of the metabolite S2 was confirmed after a single oral dose of 10 mg MT. The reference standard was chemically synthesized, characterized by accurate mass mass spectrometry (MS) and nuclear magnetic resonance (NMR), and quantified by quantitative NMR (qNMR). Thus, this study finally provides accurate structure information on the S2 metabolite and a direct analytical method for detection of MT misuse. The availability of the reference material is expected to facilitate further evaluation and subsequent analytical method validation in anti-doping research.

SFC-MS/MS for orthogonal separation of hydroxylated 17α-methyltestosterone isomers

Because of their performance-enhancing effect, anabolic androgenic steroids (AAS) are often misused in sports. Nearly half of the adverse analytical findings (AAF) in 2022 doping controls are correlated to AAS misuse. Metabolites play a crucial role in the bioanalysis of endogenous and exogenous steroids. Therefore, one important field in antidoping research is the investigation on drug metabolizing and steroidogenic enzymes. The introduction of a hydroxy group is the most common reaction, which is catalyzed by cytochrome P450 (CYP) enzymes in phase-I metabolism. Analysis of AAS metabolites is commonly performed using gas chromatography mass spectrometry (GC-MS) systems. Laborious sample preparation and extended run times compared to liquid chromatography (tandem) mass spectrometry (LC-MS/MS) methods are usually correlated with this type of analysis. On the other hand, liquid chromatography (tandem) mass spectrometry (LC-MS[/MS]) methods have a lower separation efficiency than GC-MS methods. Both techniques lack selectivity for hydroxylated 17α-methyltestosterone metabolites. Therefore, as an orthogonal analytical approach, a supercritical fluid chromatography tandem mass spectrometry method was developed to separate four hydroxy metabolites of 17α-methyltestosterone (2α-/2β-/4-/6β-hydroxy-17α-methyltestosterone). This project aimed to get a more in-depth look at the metabolization and analysis of 17α-methyltestosterone and its hydroxylated metabolites. The developed method revealed lower limits of quantitation between 0.6 and 6 ng/ml at an accuracy of 85-115% using a matrix matched calibration. An in vitro study with human liver microsomes shows 6β-hydroxy-17α-methyltestosterone as main metabolite (15.9%) as well as the metabolite 2β-hydroxy-17α-methyltestosterone (0.5%). The results show that the developed method is sensitive and robust. In addition, the method allows a previously missing discrimination of the hydroxylated metabolites in a short analysis time without prior, complex derivatizations.

New long-standing metabolites of 17α-methyltestosterone are detected in HepG2 cell in vitro metabolic model and in human urine

Novel metabolites of the anabolic androgenic steroid 17α-methyltestosterone have been detected in HepG2 cell in vitro metabolic model and in human urine. Their detection was accomplished through targeted gas chromatography-(tandem) mass spectrometry analysis that has been based on microscale synthesized standards. The related synthesis and the gas chromatography-(tandem) mass spectrometry characterization of the analytical standards are described. All newly presented metabolites have a fully reduced steroid A-ring with either an 17,17-dimethyl-18-nor-Δ13 structure or they have been further oxidized at position 16 of the steroid backbone. Metabolites with 17,17-dimethyl-18-nor-Δ13 structure may be considered as side products of phase II metabolic sulfation of the 17β-hydroxy group of methyltestosterone or its reduced tetrahydro-methyltestosterone metabolites 17α-methyl-5β-androstane-3α,17β-diol and 17α-methyl-5α-androstane-3α,17β-diol that produce the known epimeric 17β-methyl-5β-androstane-3α,17α-diol and 17β-methyl-5α-androstane-3α,17α-diol metabolites. The prospective of these new metabolites to increase detection time windows and improve identification was investigated by applying the World Anti-doping Agency TD2021IDCR criteria. The new metabolites, presented herein, complement the current knowledge on the 17α-methyltestosterone metabolism and in some cases can be used as additional long-term markers in the frame of sport doping drug testing.

Biotransformation of anabolic androgenic steroids in human skin cells

In comparison to well-known drug-metabolizing organs such as the liver, the metabolic capacity of human skin is still not well elucidated despite the widespread use of topical drug application. To gain a comprehensive insight into anabolic steroid metabolism in the skin, six structurally related anabolic androgenic steroids, testosterone, metandienone, methyltestosterone, clostebol, dehydrochloromethyltestosterone, and methylclostebol, were applied to human keratinocytes and fibroblasts derived from the juvenile foreskin. Phase I metabolites obtained from incubation media were analyzed by gas chromatography-mass spectrometry. The 5α-reductase activity was predominant in the metabolic pathways as supported by the detection of 5α-reduced metabolites after incubation of testosterone, methyltestosterone, clostebol, and methylclostebol. Additionally, the stereochemistry structures of fully reduced metabolites (4α,5α-isomers) of clostebol and methylclostebol were newly confirmed in this study by the help of inhouse synthesized reference materials. The results provide insights into the steroid metabolism in human skin cells with respect to the characteristics of the chemical structures.

Simultaneous determination of methyltestosterone and its metabolite in fish by gas chromatography-mass spectrometry

Methyltestosterone is one of the banned drugs in aquaculture, and it should be monitored in food-producing animals. 17α-Methyl-5β-androstane-3α,17β-diol, as the main metabolite of methyltestosterone in vertebrates, could be used as another marker for controlling the administration of methyltestosterone, due to its high residual concentration and slow elimination rate. In this study, an analytical method based on gas chromatography-mass spectrometry (GC-MS) was developed and validated for the simultaneous determination of methyltestosterone and its main metabolite in fish. After pretreatment by liquid-liquid extraction with n-hexane and solid phase extraction with C18 and NH2 columns, the target analytes in the muscle tissues were extracted and concentrated, and the influence of the sample matrix was eliminated. Then, the prepared samples were separated and detected with GC-MS in the selected ion monitoring (SIM) mode. Methyltestosterone-D3 was chosen as the internal standard for quantitation. After optimization, the limits of detection for methyltestosterone and 17α-methyl-5β-androstane-3α,17β-diol were 20 μg kg-1 and 15 μg kg-1, respectively. The limits of quantitation were both 50 μg kg-1. The calibration curves showed good linearity in the concentration range from 50.0 ng mL-1 to 500.0 ng mL-1. The correlation coefficients of methyltestosterone and 17α-methyl-5β-androstane-3α,17β-diol were more than 0.9990. The recoveries of the analytes in real samples were in the range of 99.7-116.6% with the relative standard deviation of 5.2-8.3%. The established method could meet the demand for simultaneous detection of methyltestosterone and its major metabolite, and it could be used to provide more information on the abuse of methyltestosterone in food-producing animals.

Metabolites identification of anabolic steroid bolasterone in vitro and in rats by high resolution liquid chromatography mass spectrometry

Bolasterone (7α,17α-dimethyltestosterone) and anabolic androgenic steroids are included in the World Anti-Doping Agency's Prohibited list of substances. This study aimed to evaluate the metabolism of bolasterone through in vitro experiments using rat liver microsomes and in vivo experiments using rat urine after oral administration. Urine samples were collected over a 168-h period. Bolasterone and its metabolites were detected by liquid chromatography coupled with a Q-Exactive Obitrap mass spectrometry (LC-HRMS). Ultimately 16 hydroxylated metabolites (M1-M16), one metabolite from the reduction of the 3-keto function and 4-ene (M17), and one glucuronic acid conjugated metabolite (M18) were detected. Metabolites M17 and M18 were confirmed by comparison with available reference or authentic standards. Metabolic modifications in the structure of the parent bolasterone result in different fragmentation patterns. Based on the sensitivity of the HRMS data, characteristic ions such as m/z 121.064 (C8 H9 O) generated from ring A of the mono-hydroxylated metabolites and 121.101 (C9 H13 ) generated from ring D of the di-hydroxylated metabolites were observed that helped differentiate between the obtained metabolites. The structures of fragment ions were tentatively proposed based on their fragmentation pathways, where the significant ions were correlated to the possible structural fragments. In conclusion, new metabolites of bolasterone were detected and characterized by the use of the full-scan and dd-MS/MS using LC-HRMS, and this data can be useful for providing metabolite information for the interpretation of mass spectra of anabolic bolasterone analogues for doping screening tests.

Evaluation of alternative gas chromatographic and mass spectrometric behaviour of trimethylsilyl-derivatives of non-hydrolysed sulfated anabolic steroids

Sulfated metabolites have shown to have potential as long-term markers (LTMs) of anabolic-androgenic steroid (AAS) abuse. The compatibility of gas chromatography-mass spectrometry (GC-MS) with trimethylsilyl (TMS)-derivatives of non-hydrolysed sulfated steroids has been demonstrated, where, after derivatisation, generally, two closely eluting isomers are formed that both have the same molecular ion [M-H2 SO4 ]•+ . Sulfated reference standards are in limited commercial availability, and therefore, the current knowledge of the GC-MS behaviour of these compounds is mainly based on sulfating and analysing the available standard reference material. This procedure can unfortunately not cover all of the current known LTMs as these are often not available as pure substance. Therefore, in theory, some metabolites could be missed as they exhibit alternative behaviour. To investigate the matter, in-house sulfated reference materials that bear resemblance to known sulfated LTMs were analysed on GC-MS in their TMS-derivatised non-hydrolysed state. The (alternative) gas chromatographic and mass spectrometric behaviour was mapped, evaluated and linked to the corresponding steroid structures. Afterwards, using fraction collection, known sulfated LTMs were isolated from excretion urine to confirm the observed findings. The categories that were selected were mono-hydroxy-diones, 17-methyl-3,17-diols and 17-keto-3,16-diols as these are commonly encountered AAS conformations. The ability to predict the GC-MS behaviour of non-hydrolysed sulfated AAS metabolites is the corner stone of finding new metabolites. This knowledge is also essential, for example, for understanding AAS detection analyses, for the mass spectrometric characterization of metabolites of new designer steroids or when one needs to characterize an unknown steroid structure.

Detection time comparison of non-hydrolysed sulphated metabolites of metenolone, mesterolone and 17α-methyltestosterone analysed by four different mass spectrometric techniques

The frequent detection of anabolic androgenic steroids (AAS) indicates their popularity among rule-breaking athletes. The so called long-term metabolites play a crucial role in their detection, and non-hydrolysed sulphated metabolites have gained renewed interest, as research has demonstrated their extended detection time compared to the more conventional markers (e.g., for metenolone and mesterolone). Their potential has been investigated using liquid and gas chromatography-mass spectrometry (LC- and GC-MS). However, due to their complementary nature, chances are that the most promising metabolite on one technique does not necessarily exhibit the same behaviour on the other and vice versa. Therefore, a comparison was carried out where as a trial model, metenolone, mesterolone and 17α-methyltestosterone were selected and the most likely long-term sulphated metabolites identified on four mass spectrometric instruments. Additionally, using a modified sample preparation procedure, comparison between conventional and non-hydrolysed sulphated metabolites between different GC-MS instruments was also included. When focusing on each individual marker, no cases were observed where a single metabolite provided a superior detection time on all instruments. Furthermore, for each AAS, there were incidences where a metabolite provided the best detection time on one instrument but could only be detected for a shorter period or not at all on other instruments. This demonstrates that metabolite detection windows and hence their added-value as target substance are unique and dependent on the analytical technique and not only on their pharmacokinetic behaviour. Consequently, in each case, a metabolite versus instrument evaluation is needed to maximise the probabilities of detecting doping offences.

Medaka embryos as a model for metabolism of anabolic steroids

In anti-doping science, the knowledge of drug metabolism is a prerequisite to identify analytical targets for the detection of misused prohibited substances. As the most obvious way to study xenobiotic metabolism, the administration to human volunteers, faces ethical concerns, there is a need for model systems. In the present study, we investigated whether Oryzias latipes (medaka) embryos might be an alternative, non-animal test model to study human-like metabolism. In the present study, we exposed medaka embryos at the morula stage to the anabolic steroid metandienone (10 µM or 50 µM) for a period of 2 or 8 days. According to the fish embryo toxicity test (OECD test), we assessed the developmental status of the embryos. We further investigated metandienone metabolites by high-performance liquid chromatography- and gas chromatography-mass spectrometry. Medaka embryos produced three mono-hydroxylated and one reduced metabolite known from human biotransformation. Developmental malformations were observed for the exposition to 50 µM metandienone, while a significant elevation of the heart beat was also present in those individuals exposed to the lower dose for 8 days. The present study demonstrates that the medaka embryo represents a promising model to study human-like metabolism. Moreover, the judgement of developmental parameters of the fish embryos enables for the simultaneous assessment of toxicity.

A Withanolide-rich Fraction of Athenaea velutina Induces Apoptosis and Cell Cycle Arrest in Melanoma B16F10 Cells

Athenaea velutina is a promising Brazilian shrub with cytotoxic and antimigratory properties against cancer cells. However, the mechanism of induction of cancer cell death and the compounds involved remain unknown. To ascertain these bioactive compounds, bioassay-guided fractionation was performed, alongside the appropriate in vitro tests. A withanolide-rich fraction (FAv_5) from the dichloromethane extract increased cytotoxic activity by 1.5-fold (IC₅₀ = 2.1 µg/mL). Fourteen withanolide steroids were tentatively identified for the first time for this species by mass spectrometry coupled to liquid chromatography (LC MS/MS), including withanolide A, aurelianolide A, and aurelianolide B. FAv_5 significantly decreased cell proliferation, migration, and invasion with a selectivity index greater than 8 for B16F10 cells. Furthermore, flow cytometry with annexin V fluorescein isothiocyanate/propidium iodide (V-FITC/PI) staining showed FAv_5 to promote cell cycle arrest at the G0/G1-phase as well as apoptotic cell death. Overall, these findings highlight A. velutina as a source of withanolide-steroids that inhibit cancer cell proliferation through apoptosis and cell cycle blockade mechanisms. Details on the geographic distribution of A. velutina and species conservation strategies have also been highlighted.

New Insights into the Metabolism of Methyltestosterone and Metandienone: Detection of Novel A-Ring Reduced Metabolites

Metandienone and methyltestosterone are orally active anabolic-androgenic steroids with a 17α-methyl structure that are prohibited in sports but are frequently detected in anti-doping analysis. Following the previously reported detection of long-term metabolites with a 17ξ-hydroxymethyl-17ξ-methyl-18-nor-5ξ-androst-13-en-3ξ-ol structure in the chlorinated metandienone analog dehydrochloromethyltestosterone ("oral turinabol"), in this study we investigated the formation of similar metabolites of metandienone and 17α-methyltestosterone with a rearranged D-ring and a fully reduced A-ring. Using a semi-targeted approach including the synthesis of reference compounds, two diastereomeric substances, viz. 17α-hydroxymethyl-17β-methyl-18-nor-5β-androst-13-en-3α-ol and its 5α-analog, were identified following an administration of methyltestosterone. In post-administration urines of metandienone, only the 5β-metabolite was detected. Additionally, 3α,5β-tetrahydro-epi-methyltestosterone was identified in the urines of both administrations besides the classical metabolites included in the screening procedures. Besides their applicability for anti-doping analysis, the results provide new insights into the metabolism of 17α-methyl steroids with respect to the order of reductions in the A-ring, the participation of different enzymes, and alterations to the D-ring.

UPLC-ESI-MRM/MS for Absolute Quantification and MS/MS Structural Elucidation of Six Specialized Pyranonaphthoquinone Metabolites From Ventilago harmandiana

Pyranonaphthoquinones (PNQs) are important structural scaffolds found in numerous natural products. Research interest in these specialized metabolites lies in their natural occurrence and therapeutic activities. Nonetheless, research progress has thus far been hindered by the lack of analytical standards and analytical methods for both qualitative and quantitative analysis. We report here that various parts of Ventilago harmandiana are rich sources of PNQs. We developed an ultraperformance liquid chromatography-electrospray ionization multiple reaction monitoring/mass spectrometry method to quantitatively determine six PNQs from leaves, root, bark, wood, and heartwood. The addition of standards in combination with a stable isotope of salicylic acid-D₆ was used to overcome the matrix effect with average recovery of 82% ± 1% (n = 15). The highest concentration of the total PNQs was found in the root (11,902 μg/g dry weight), whereas the lowest concentration was found in the leaves (28 μg/g dry weight). Except for the root, PNQ-332 was found to be the major compound in all parts of V. harmandiana, accounting for ∼48% of the total PNQs quantified in this study. However, PNQ-318A was the most abundant PNQ in the root sample, accounting for 27% of the total PNQs. Finally, we provide novel MS/MS spectra of the PNQs at different collision induction energies: 10, 20, and 40 eV (POS and NEG). For structural elucidation purposes, we propose complete MS/MS fragmentation pathways of PNQs using MS/MS spectra at collision energies of 20 and 40 eV. The MS/MS spectra along with our discussion on structural elucidation of these PNQs should be very useful to the natural products community to further exploring PNQs in V. harmandiana and various other sources.

A further insight into methyltestosterone metabolism: New evidences from in vitro and in vivo experiments

RATIONALE

Although the metabolism of methyltestosterone (MT) has been extensively studied since the 1950s using different techniques, the aim of this study was to investigate the hydroxylation in positions C2, C4 and C6 after in vitro experiments and in vivo excretion studies using gas chromatography time-of-flight (GC/TOF) and gas chromatography/tandem mass spectrometry (GC/MS/MS). The results could be influenced by the mass spectrometric analyser used.

METHODS

Incubations were carried out with human liver microsomes and six enzymes belonging to the cytochrome P450 family using MT as a substrate. The trimethylsilyl derivatives of the samples were analysed using GC/TOF and GC/MS/MS once the correct MS/MS transitions had been selected, mainly for 6-hydroxymethyltestosterone (6-OH-MT) to avoid artefact interferences. A urinary excretion study was then performed after the administration of a 10 mg single oral dose of MT to a volunteer.

RESULTS

The formation of hydroxylated metabolites of MT in the C6, C4 and C2 positions after both in vitro and in vivo experiments was observed. Sample evaluation using GC/TOF showed an interference for 6-OH-MT that could only be resolved in GC/MS/MS by monitoring specific transitions. The transitory detection of these hydroxylated metabolites in urine agrees with previous investigations that had described this metabolic route as being of little significance.

CONCLUSIONS

In doping analysis, the formation of 4-hydroxymethyltestosterone (oxymesterone) from MT cannot be underestimated. Although it is only detected as a minor and short-term excretion metabolite, it cannot be overlooked as it was found in both in vitro and in vivo experiments. The use of a combination of different mass spectrometric instruments allowed reliable conclusions to be reached, and it was shown that special attention must be given to artefact formation.

Mass spectral fragmentation analyses of isotopically labelled hydroxy steroids using gas chromatography/electron ionization low-resolution mass spectrometry: A practical approach

RATIONALE

Gas chromatography coupled to electron ionization mass spectrometry (GC/EI-MS) is used for routine screening of anabolic steroids in many laboratories after the conversion of polar groups into trimethylsilyl (TMS) derivatives. The aim of this work is to elucidate the origin and formation of common and subclass-specific fragments in the mass spectra of TMS-derivatized steroids. Especially in the context of metabolite identification or analysis of designer drugs, isotopic labelling is helpful to better understand fragment ion generation, identify unknown compounds and update established screening methods.

METHODS

Stable isotope labelling procedures for the introduction of [² H₉ ]-TMS or ¹⁸ O were established to generate perdeuterotrimethylsilylated, mixed deuterated and ¹⁸ O-labelled derivatives for 13 different hydroxy steroids. Fragmentation proposals were substantiated by comparison of the abundances of isotopically labelled and unlabelled fragment ions in unit mass resolution GC/MS. Specific fragmentations were also investigated by high-resolution MS (GC/quadrupole time-of-flight MS, GC/QTOFMS).

RESULTS

Methyl radical cleavage occurs primarily from the TMS groups in saturated androstanes and from the steroid nucleus in the case of enol-TMS of oxo or α,β-unsaturated steroid ketones. Loss of trimethylsilanol (TMSOH) is dependent on steric factors, degree of saturation of the steroid backbone and the availability of a hydrogen atom and TMSO group in the 1,3-diaxial position. For the formation of the [M - 105]⁺ fragment ion, methyl radical cleavage predominates from the angular methyl groups in position C-18 or C-19 and is independent of the site of TMSOH loss. The common [M - 15 - 76]⁺ fragment ion was found in low abundance and identified as [M - CH₃ - (CH₃ )₂ SiH - OH]⁺ . For the different steroid subclasses further diagnostic fragment ions were discussed and structure proposals postulated.

CONCLUSIONS

Stable isotope labelling of oxo groups as well as derivatization with deuterated TMS groups enables the detection of structure-related fragment ion generation in unit mass resolution GC/EI-MS. This may in turn allow us to propose isomeric assignments that are otherwise almost impossible using MS only.

Reconsidering mass spectrometric fragmentation in electron ionization mass spectrometry - new insights from recent instrumentation and isotopic labelling exemplified by ketoprofen and related compounds

RATIONALE

In various fields of chemical analyses, structurally unknown analytes are considered. Proper structure confirmation may be challenged by the low amounts of analytes that are available, e.g. in early stage drug development, in metabolism studies, in toxicology or in environmental analyses. In these cases, mass spectrometric techniques are often used to build up structure proposals for these unknowns. Fragmentation reactions in mass spectrometry are known to follow definite pathways that may help to assign structural elements by fragment ion recognition. This work illustrates an investigation of fragmentation reactions for gas chromatography/electron ionization mass spectrometric characterization of benzophenone derivatives using the analgesic drug ketoprofen and seven of its related compounds as model compounds.

METHODS

Deuteration and ¹⁸ O-labelling experiments along with high-resolution accurate mass and tandem mass spectrometry (MS/MS) were used to further elucidate fragmentation pathways and to substantiate rationales for structure assignments. Low-energy ionization was investigated to increase confidence in the identity of the molecular ion.

RESULTS

The high-resolution mass analyses yielded unexpected differences that led to reconsideration of the proposals. Site-specific isotopic labelling helped to directly trace back fragment ions to their respective structural elements. The proposed fragmentation pathways were substantiated by MS/MS experiments.

CONCLUSIONS

The described method may offer a perspective to increase the level of confidence in unknown analyses, where reference material is not (yet) available.

P450-Humanized and Human Liver Chimeric Mouse Models for Studying Xenobiotic Metabolism and Toxicity

Preclinical evaluation of drug candidates in experimental animal models is an essential step in drug development. Humanized mouse models have emerged as a promising alternative to traditional animal models. The purpose of this mini-review is to provide a brief survey of currently available mouse models for studying human xenobiotic metabolism. Here, we describe both genetic humanization and human liver chimeric mouse models, focusing on the advantages and limitations while outlining their key features and applications. Although this field of biomedical science is relatively young, these humanized mouse models have the potential to transform preclinical drug testing and eventually lead to a more cost-effective and rapid development of new therapies.

Application of α- and β-naphthoflavones as monooxygenase inhibitors of Absidia coerulea KCh 93, Syncephalastrum racemosum KCh 105 and Chaetomium sp. KCh 6651 in transformation of 17α-methyltestosterone

In this work, 17α-methyltestosterone was effectively hydroxylated by Absidia coerulea KCh 93, Syncephalastrum racemosum KCh 105 and Chaetomium sp. KCh 6651. A. coerulea KCh 93 afforded 6β-, 12β-, 7α-, 11α-, 15α-hydroxy derivatives with 44%, 29%, 6%, 5% and 9% yields, respectively. S. racemosum KCh 105 afforded 7α-, 15α- and 11α-hydroxy derivatives with yields of 45%, 19% and 17%, respectively. Chaetomium sp. KCh 6651 afforded 15α-, 11α-, 7α-, 6β-, 9α-, 14α-hydroxy and 6β,14α-dihydroxy derivatives with yields of 31%, 20%, 16%, 7%, 5%, 7% and 4%, respectively. 14α-Hydroxy and 6β,14α-dihydroxy derivatives were determined as new compounds. Effect of various sources of nitrogen and carbon in the media on biotransformations were tested, however did not affect the degree of substrate conversion or the composition of the products formed. The addition of α- or β-naphthoflavones inhibited 17α-methyltestosterone hydroxylation but did not change the percentage composition of the resulting products.

Successful Engraftment of Human Hepatocytes in uPA-SCID and FRG® KO Mice

Mice with humanized chimeric liver are promising in vivo tools to evaluate the efficacy of novel compounds or vaccine induced antibodies directed against pathogens that infect the human liver. In addition they can be used to study the human-type metabolism of medicinal compounds and hepatotoxicity.

Stability-Indicating TLC-Densitometric Assay for Methyltestosterone and Quantum Chemical Calculations

Methyltestosterone is a synthetic testosterone derivative commonly used for the treatment of testosterone deficiency in males and one the anabolic steroids whose use is banned by World Anti-Doping Agency (WADA). This study presents a simple, cost-effective and rapid stability-indicating assay for densitometric quantification of methyltestosterone in pharmaceutical formulation. The developed method employed pre-coated TLC plates with mobile phase hexane:acetone (6.5:3.5 v/v). Limit of detection and limit of quantitation were found to be 2.06 and 6.24 ng/spot, respectively. Stress degradation study of methyltestosterone was conducted by applying various stress conditions such as hydrolysis under acidic, basic and neutral conditions, heating in anhydrous conditions and exposure to light. Methyltestosterone was found to be susceptible to photodegradation, acidic and basic hydrolysis. Degraded products were well resolved with significantly different Rf values. Acid degraded product was identified as 17,17-dimethyl-18-norandrosta-4,13(14)-dien-3-one through spectroscopic methods. The reactivity of methyltestosterone under applied stress conditions was also explained by quantum chemical calculations. The developed method is found to be repeatable, selective and accurate for quantification of methyltestosterone and can be employed for routine analysis.

Current LC-MS methods and procedures applied to the identification of new steroid metabolites

The study of the metabolism of steroids has a long history; from the first characterizations of the major metabolites of steroidal hormones in the pre-chromatographic era, to the latest discoveries of new forms of excretions. The introduction of mass spectrometers coupled to gas chromatography at the end of the 1960's represented a major breakthrough for the elucidation of new metabolites. In the last two decades, this technique is being complemented by the use of liquid chromatography-mass spectrometry (LC-MS). In addition of becoming fundamental in clinical steroid determinations due to its excellent specificity, throughput and sensitivity, LC-MS has emerged as an exceptional tool for the discovery of new steroid metabolites. The aim of the present review is to provide an overview of the current LC-MS procedures used in the quest of novel metabolic products of steroidal hormones and exogenous steroids. Several aspects regarding LC separations are first outlined, followed by a description of the key processes that take place in the mass spectrometric analysis, i.e. the ionization of the steroids in the source and the fragmentation of the selected precursor ions in the collision cell. The different analyzers and approaches employed together with representative examples of each of them are described. Special emphasis is placed on triple quadrupole analyzers (LC-MS/MS), since they are the most commonly employed. Examples on the use of precursor ion scan, neutral loss scan and theoretical selected reaction monitoring strategies are also explained.

Efficient approach for the detection and identification of new androgenic metabolites by applying SRM GC-CI-MS/MS: a methandienone case study

Identification of anabolic androgenic steroids (AAS) is a vital issue in doping control and toxicology, and searching for metabolites with longer detection times remains an important task. Recently, a gas chromatography chemical ionization triple quadrupole mass spectrometry (GC-CI-MS/MS) method was introduced, and CI, in comparison with electron ionization (EI), proved to be capable of increasing the sensitivity significantly. In addition, correlations between AAS structure and fragmentation behavior could be revealed. This enables the search for previously unknown but expected metabolites by selection of their predicted transitions. The combination of both factors allows the setup of an efficient approach to search for new metabolites. The approach uses selected reaction monitoring which is inherently more sensitive than full scan or precursor ion scan. Additionally, structural information obtained from the structure specific CI fragmentation pattern facilitates metabolite identification. The procedure was demonstrated by a methandienone case study. Its metabolites have been studied extensively in the past, and this allowed an adequate evaluation of the efficiency of the approach. Thirty three metabolites were detected, including all relevant previously discovered metabolites. In our study, the previously reported long-term metabolite (18-nor-17β-hydroxymethyl,17α-methyl-androst-1,4,13-trien-3-one) could be detected up to 26 days by using GC-CI-MS/MS. The study proves the validity of the approach to search for metabolites of new synthetic AAS and new long-term metabolites of less studied AAS and illustrates the increase in sensitivity by using CI. Copyright © 2016 John Wiley & Sons, Ltd.

Animal models for the study of HCV

The development and evaluation of effective therapies and vaccines for the hepatitis C virus (HCV) and the study of its interactions with the mammalian host have been hindered for a long time by the absence of suitable small animal models. Immune compromised mouse models that recapitulate the complete HCV life cycle have been useful to investigate many aspects of the HCV life cycle including antiviral interventions. However, HCV has a high propensity to establish persistence and associated histopathological manifestations such as steatosis, fibrosis, cirrhosis and hepatocellular carcinoma (HCC). Better understanding of these processes requires the development of a permissive and fully immunocompetent small animal model. In this review we summarize the in vivo models that are available for the study of HCV.

Detection and characterization of prednisolone metabolites in human urine by LC-MS/MS

Glucocorticosteroids are prohibited in sports when used by systemic administrations (e.g. oral), whereas they are allowed using other administration ways. Strategies to discriminate between administrations routes have to be developed by doping control laboratories. For this reason, the metabolism of prednisolone (PRED) was studied using liquid chromatography coupled to tandem mass spectrometry. A single oral (10 mg) dose of PRED was administered to two healthy male volunteers. Urine samples were collected up to 6 days after administration. Samples were hydrolyzed with β-glucuronidase and subjected to liquid-liquid extraction with ethyl acetate in alkaline conditions. The extracts were analyzed by liquid chromatography coupled to tandem mass spectrometry. Precursor ion scan methods (m/z 77, 91, 105, 121, 147 and 171) in positive ionization and neutral loss scan methods (76 and 94 Da) in negative ionization modes were applied for the open detection of PRED metabolites. Using these methods, PRED parent compound plus 20 metabolites were detected. PRED and 11 metabolites were characterized by comparison with standards of the compounds (PRED, prednisone, 20β-dihydro-PRED and 20α-dihydro-PRED, 20β-dihydro-prednisone and 20α-dihydro-prednisone, 6β-hydroxy-PRED and 6α-hydroxy-PRED, 20β isomers and 20α isomers of 6β,11β,17α,20,21-pentahydroxypregnan-1,4-diene-3-one, 6α,11β,17α,20β,21-pentahydroxypregnan-1,4-diene-3-one and Δ(6) -PRED). Using mass spectrometric data, feasible structures were proposed for seven of the remaining nine detected metabolites, including several 6-hydroxy-metabolites. Eleven of the characterized metabolites have not been previously described. Maximum excretion rates for PRED metabolites were achieved in first 24 h; however, most of the metabolites were still detectable in the last collected samples (day 6).

HCV animal models and liver disease

The development and evaluation of effective therapies and vaccines for the hepatitis C virus (HCV) and the study of its interactions with the mammalian host have been hindered for a long time by the absence of suitable small animal models. Due to the narrow host tropism of HCV, the development of mice that can be robustly engrafted with human hepatocytes was a major breakthrough since they recapitulate the complete HCV life cycle. This model has been useful to investigate many aspects of the HCV life cycle, including antiviral interventions. However, studies of cellular immunity, immunopathogenesis and resulting liver diseases have been hampered by the lack of a small animal model with a functional immune system. In this review, we summarize the evolution of in vivo models for the study of HCV.

Molecular detection and quantification of Plasmodium falciparum-infected human hepatocytes in chimeric immune-deficient mice

BACKGROUND

Chimeric mice with humanized livers represent a promising tool for infections with Plasmodium falciparum to evaluate novel methods for prevention and treatment of pre-erythrocytic stages. Adequate assessment of hepatic infections is generally compromised by the limited number of human hepatocytes infected by developing parasites.

METHODS

A qPCR-based method has been developed that sensitively and reliably detects P. falciparum liver stage infection of humanized mice and quantitatively expresses the results as the number of parasites per human hepatocyte.

RESULTS

This assay allows for detection of liver stage parasites after challenging humanized mice with infected mosquito bites or after intravenous injection with sporozoites. The sensitivity of the protocol, which comprises approximately 25% of the total chimeric liver, allows for the detection of a single infected hepatocyte in the analysed tissue.

CONCLUSIONS

This method allows for the detection and quantification of P. falciparum parasites in chimeric mice repopulated with human hepatocytes. It will be a useful tool when studying the in vivo therapeutic and/or prophylactic qualities of novel compounds, small molecules or antibodies directed against the liver stage of P. falciparum infections.

Current status and bioanalytical challenges in the detection of unknown anabolic androgenic steroids in doping control analysis

Androgenic anabolic steroids (AAS) are prohibited in sports due to their anabolic effects. Doping control laboratories usually face the screening of AAS misuse by target methods based on MS detection. Although these methods allow for the sensitive and specific detection of targeted compounds and metabolites, the rest remain undetectable. This fact opens a door for cheaters, since different AAS can be synthesized in order to evade doping control tests. This situation was evidenced in 2003 with the discovery of the designer steroid tetrahydrogestrinone. One decade after this discovery, the detection of unknown AAS still remains one of the main analytical challenges in the doping control field. In this manuscript, the current situation in the detection of unknown AAS is reviewed. Although important steps have been made in order to minimize this analytical problem and different analytical strategies have been proposed, there are still some drawbacks related to each approach.

Detection, synthesis and characterization of metabolites of steroid hormones conjugated with cysteine

The occurrence of several polyunsaturated testosterone related compounds (including 4,6-androstadien-3,17-dione and 4,6-androstadien-17β-ol-3-one) in urine after alkaline treatment of the sample has been recently reported. Although several experiments seem to indicate that they are testosterone metabolites, their origin is still unknown. In this study, it is demonstrated that these metabolites are produced from the degradation of cysteine conjugates. Several testosterone metabolites conjugated with cysteine have been synthesized and characterized by NMR techniques. Their detection in human urine has been performed by LC-MS/MS. The acquisition of several transitions in the SRM mode and the comparison between ion ratios and retention times allowed for the unequivocal confirmation of the presence of cysteine conjugates in urine. The analysis of urine samples collected after testosterone administration confirmed that synthesized cysteine conjugates are testosterone metabolites. The fact that these conjugates result in polyunsaturated compounds in urine after alkaline treatment was demonstrated by fraction collection and alkaline treatment of each fraction. Besides, the presence of these metabolites was also confirmed in human plasma. The formation of these metabolites implies an unreported metabolic biotransformation: 6,7-dehydrogenation as phase I metabolism followed by conjugation with glutathione and subsequent transformation to cysteine conjugates. Finally, the existence of similar metabolites for cortisol and progesterone was also confirmed by LC-MS/MS indicating that the presented metabolic pathway is not exclusively active in androgens, but common to progestagens and glucocorticoids.

Tandem mass spectrometry approach for the investigation of the steroidal metabolism: structure-fragmentation relationship (SFR) in anabolic steroids and their metabolites by ESI-MS/MS analysis

Electrospray ionization tandem mass spectrometry (ESI-MS/MS) was used to investigate the effect of different substitutions introduced during metabolism on fragmentation patterns of four anabolic steroids including methyltestosterone, methandrostenolone, cis-androsterone and adrenosterone, along with their metabolites. Collision-induced dissociation (CID) analysis was performed to correlate the major product ions of 19 steroids with structural features. The analysis is done to portray metabolic alteration, such as incorporation or reduction of double bonds, hydroxylations, and/or oxidation of hydroxyl moieties to keto functional group on steroidal skeleton which leads to drastically changed product ion spectra from the respective classes of steroids, therefore, making them difficult to identify. The comparative ESI-MS/MS study also revealed some characteristic peaks to differentiate different steroidal metabolites and can be useful for the unambiguous identification of anabolic steroids in biological fluid. Moreover, LC-ESI-MS/MS analysis of fermented extract of methyltestosterone, obtained by Macrophomina phaseolina was also investigated.

Alternative long-term markers for the detection of methyltestosterone misuse

Methyltestosterone (MT) is one of the most frequently detected anabolic androgenic steroids in doping control analysis. MT misuse is commonly detected by the identification of its two main metabolites excreted as glucuronide conjugates, 17α-methyl-5α-androstan-3α,17β-diol and 17α-methyl-5β-androstan-3α,17β-diol. The detection of these metabolites is normally performed by gas chromatography-mass spectrometry, after previous hydrolysis with β-glucuronidase enzymes, extraction and derivatization steps. The aim of the present work was to study the sulphate fraction of MT and to evaluate their potential to improve the detection of the misuse of the drug in sports. MT was administered to healthy volunteers and urine samples were collected up to 30days after administration. After an extraction with ethyl acetate, urine extracts were analysed by liquid chromatography tandem mass spectrometry using electrospray ionisation in negative mode by monitoring the transition m/z 385 to m/z 97. Three diol sulphate metabolites (S1, S2 and S3) were detected. Potential structures for these metabolites were proposed after solvolysis and mass spectrometric experiments: S1, 17α-methyl-5β-androstan-3α,17β-diol 3α-sulphate; S2, 17β-methyl-5α-androstan-3α,17α-diol 3α-sulphate; and S3, 17β-methyl-5β-androstan-3α,17α-diol 3α-sulphate. Synthesis of reference compounds will be required in order to confirm the structures. The retrospectivity of these sulphate metabolites in the detection of MT misuse was compared with the obtained with previously described metabolites. Metabolite S2 was detected up to 21days after MT administration, improving between 2 and 3 times the retrospectivity of the detection compared to the last long-term metabolite of MT previously described, 17α-hydroxy-17β-methylandrostan-4,6-dien-3-one.

New potential markers for the detection of boldenone misuse

Boldenone is one of the most frequently detected anabolic androgenic steroids in doping control analysis. Boldenone misuse is commonly detected by the identification of the active drug and its main metabolite, 5β-androst-1-en-17β-ol-3-one (BM1), by gas chromatography-mass spectrometry (GC-MS), after previous hydrolysis with β-glucuronidase enzymes, extraction and derivatization steps. However, some cases of endogenous boldenone and BM1 have been reported. Nowadays, when these compounds are detected in urine at low concentrations, isotope ratio mass spectrometry (IRMS) analysis is needed to confirm their exogenous origin. The aim of the present study was to identify boldenone metabolites conjugated with sulphate and to evaluate their potential to improve the detection of boldenone misuse in sports. Boldenone was administered to a healthy volunteer and urine samples were collected up to 56h after administration. After a liquid-liquid extraction with ethyl acetate, urine extracts were analysed by liquid chromatography tandem mass spectrometry (LC-MS/MS) using electrospray ionisation in negative mode by monitoring the transition of m/z 365-350, specific for boldenone sulphate. Boldenone sulphate was identified in the excretion study urine samples and, moreover, another peak with the same transition was observed. Based on the MS/MS behaviour the metabolite was identified as epiboldenone sulphate. The identity was confirmed by isolation of the LC peak, solvolysis and comparison of the retention time and MS/MS spectra with an epiboldenone standard. These sulphated metabolites have not been previously reported in humans and although they account for less than 1% of the administered dose, they were still present in urine when the concentrations of the major metabolites, boldenone and BM1, were at the level of endogenous origin. The sulphated metabolites were also detected in 10 urine samples tested positive to boldenone and BM1 by GC-MS. In order to verify the usefulness of these new metabolites to discriminate between endogenous and exogenous origin of boldenone, four samples containing endogenous boldenone and BM1, confirmed by IRMS, were analysed. In 3 of the 4 samples, neither boldenone sulphate nor epiboldenone sulphate were detected, confirming that these metabolites were mainly detected after exogenous administration of boldenone. In contrast, boldenone sulphate and, in some cases, epiboldenone sulphate were present in samples with low concentrations of exogenous boldenone and BM1. Thus, boldenone and epiboldenone sulphates are additional markers for the exogenous origin of boldenone and they can be used to reduce the number of samples to be analysed by IRMS. In samples with boldenone and BM1 at the concentrations suspicion for endogenous origin, only if boldenone and epiboldenone sulphates are present, further analysis by IRMS will be needed to confirm exogenous origin.

Identification of budesonide metabolites in human urine after oral administration

Budesonide (BUD) is a glucocorticoid widely used for the treatment of asthma, rhinitis, and inflammatory bowel disease. Its use in sport competitions is prohibited when administered by oral, intravenous, intramuscular, or rectal routes. However, topical preparations are not prohibited. Strategies to discriminate between legal and forbidden administrations have to be developed by doping control laboratories. For this reason, metabolism of BUD has been re-evaluated using liquid chromatography-tandem mass spectrometry (LC-MS/MS) with different scan methods. Urine samples obtained after oral administration of 3 mg of BUD to two healthy volunteers have been analyzed for metabolite detection in free and glucuronide metabolic fractions. Structures of the metabolites have been studied by LC-MS/MS using collision induced dissociation and gas chromatography-mass spectrometry (GC/MS) in full scan mode with electron ionization. Combination of all structural information allowed the proposition of the most comprehensive picture for BUD metabolism in humans to this date. Overall, 16 metabolites including ten previously unreported compounds have been detected. The main metabolite is 16α-hydroxy-prednisolone resulting from the cleavage of the acetal group. Other metabolites without the acetal group have been identified such as those resulting from reduction of C20 carbonyl group, oxidation of the C11 hydroxyl group and reduction of the A ring. Metabolites maintaining the acetal group have also been identified, resulting from 6-hydroxylation (6α and 6β-hydroxy-budesonide), 23-hydroxylation, reduction of C6-C7, oxidation of the C11 hydroxyl group, and reduction of the C20 carbonyl group. Metabolites were mainly excreted in the free fraction. All of them were excreted in urine during the first 24 h after administration, and seven of them were still detected up to 48 h after administration for both volunteers.

Using complementary mass spectrometric approaches for the determination of methylprednisolone metabolites in human urine

RATIONALE

The metabolism of methylprednisolone is revisited in order to find new metabolites that could be important for distinguishing between different routes of administration. Recently developed liquid chromatography/tandem mass spectrometry (LC/MS/MS) strategies for the detection of corticosteroid metabolites have been applied to the study of methylprednisolone metabolism.

METHODS

The structures of these metabolites were studied using two complementary mass spectrometric techniques: LC/MS/MS in product ion scan mode with electrospray ionization and gas chromatography/mass spectrometry (GC/MS) in full scan mode with electron ionization. Metabolites were also isolated by semipreparative liquid chromatography fractionation. Each fraction was divided into two aliquots; one was studied by LC/MS/MS and the other by GC/MS after methoxyamine-trimethylsilyl derivatization.

RESULTS

The combination of all the structural information allowed us to propose a comprehensive picture of methylprednisolone metabolism in humans. Overall, 15 metabolites including five previously unreported compounds have been detected. Specifically, 16β,17α,21-trihydroxy-6α-methylpregna-1,4-diene-3,11,20-trione, 17α,20β,21-trihydroxy-6α-methylpregna-1,4-diene-3, 11-dione, 11β,17α,21-trihydroxy-6α-hydroxymethylpregna-1,4-diene-3,20-dione, 11β,17α,20ξ,21-tetrahydroxy-6α-hydroxymethylpregna-1,4-diene-3-one, and 17α,21-dihydroxy-6α-hydroxymethylpregna-1,4-diene-3,11,20-trione are proposed as feasible structures for the novel metabolites. In addition to the expected biotransformations: reduction of the C20 carbonyl, oxidation of the C11 hydroxy group, and further 6β-hydroxylation, we propose that hydroxylation of the 6α-methyl group can also take place.

CONCLUSIONS

New metabolites have been identified in urine samples collected after oral administration of 40 mg of methylprednisolone. All identified metabolites were found in all samples collected up to 36 h after oral administration. However, after topical administration of 5 g of methylprednisolone aceponate, neither the parent compound nor any of the metabolites were detected.

Recent developments in MS for small molecules: application to human doping control analysis

Recent developments in MS for the detection of small molecules in the context of doping control analysis are reviewed. Doping control analysis is evolving together with MS, which is the technique of choice in order to accomplish the analytical requirements in this field. Since these analytical requirements for the detection of a doping agent depend on the substance, in the first section we review the different scenarios. The commonly established approaches, together with their achievements and drawbacks are described. New developments in hyphenated MS techniques (both GC–MS/MS and LC–MS/MS) concerning interfaces and analyzers are mentioned. The use (or potential use) of these developments in order to minimize the limitations of the commonly established approaches in the doping control field is discussed. Finally, a brief discussion about trends and remaining limitations is presented.

Comparison between triple quadrupole, time of flight and hybrid quadrupole time of flight analysers coupled to liquid chromatography for the detection of anabolic steroids in doping control analysis

Triple quadrupole (QqQ), time of flight (TOF) and quadrupole-time of flight (QTOF) analysers have been compared for the detection of anabolic steroids in human urine. Ten anabolic steroids were selected as model compounds based on their ionization and the presence of endogenous interferences. Both qualitative and quantitative analyses were evaluated. QqQ allowed for the detection of all analytes at the minimum required performance limit (MRPL) established by the World Anti-Doping Agency (between 2 and 10 ng mL(-1) in urine). TOF and QTOF approaches were not sensitive enough to detect some of the analytes (3'-hydroxy-stanozolol or the metabolites of boldenone and formebolone) at the established MRPL. Although a suitable accuracy was obtained, the precision was unsatisfactory (RSD typically higher than 20%) for quantitative purposes irrespective of the analyser used. The methods were applied to 30 real samples declared positives either for the misuse of boldenone, stanozolol and/or methandienone. Most of the compounds were detected by every technique, however QqQ was necessary for the detection of some metabolites in a few samples. Finally, the possibility to detect non-target steroids has been explored by the use of TOF and QTOF. The use of this approach revealed that the presence of boldenone and its metabolite in one sample was due to the intake of androsta-1,4,6-triene-3,17-dione. Additionally, the intake of methandienone was confirmed by the post-target detection of a long-term metabolite.