Quantification of clenbuterol at trace level in human urine by ultra-high pressure liquid chromatography-tandem mass spectrometry

Recent advances in mass spectrometry for the detection of doping

INTRODUCTION

The analysis of doping control samples is preferably performed by mass spectrometry, because obtained results meet the highest analytical standards and ensure an impressive degree of reliability. The advancement in mass spectrometry and all its associated technologies thus allow for continuous improvements in doping control analysis.

AREAS COVERED

Modern mass spectrometric systems have reached a status of increased sensitivity, robustness, and specificity within the last decade. The improved sensitivity in particular has, on the other hand, also led to the detection of drug residues that were attributable to scenarios where the prohibited substances were not administered consciously but rather by the unconscious ingestion of or exposure to contaminated products. These scenarios and their doubtless clarification represent a great challenge. Here, too, modern MS systems and their applications can provide good insights in the interpretation of dose-related metabolism of prohibited substances. In addition to the development of new instruments itself, software-assisted analysis of the sometimes highly complex data is playing an increasingly important role and facilitating the work of doping control laboratories.

EXPERT OPINION

The sensitive analysis and evaluation of a higher number of samples in a shorter time is made possible by the ongoing developments in mass spectrometry.

Rapid and High-Throughput Determination of Sixteen β-agonists in Livestock Meat Using One-Step Solid-Phase Extraction Coupled with UHPLC-MS/MS

β-agonists are illegally added to animal feed because they can greatly increase carcasses' leanness, which impairs the safety of animal-derived foods and indirectly endangers human health. This study aimed to develop an ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method for determining sixteen β-agonists in livestock meat. The homogenized samples were subjected to enzymatic hydrolysis using β-glucuronidase/sulfatase at 40 °C for 2 h, extracted with acetonitrile containing 1% acetic acid (v/v), and purified by the one-step Qvet-AG extraction column. The residue was redissolved by 0.1% aqueous formic acid/methanol (9:1, v/v) after blow-drying by nitrogen, and then determined by UHPLC-MS/MS. The results demonstrated that the well linearity was in the range of 0.1-50 μg/L with the correlation coefficient (R²) ≥0.9928, and the limits of detection (LOD) and quantification (LOQ) were 0.01-0.11 μg/kg and 0.04-0.38 μg/kg, respectively. With intraday and interday relative standard deviations (RSDs) being less than 10%, the average recoveries of pork, beef, and lamb at various spiked levels ranged from 62.62-115.93%, 61.35-106.34%, and 62.00-111.83%, respectively. In conclusion, the established method is simple, efficient, sensitive, and suitable for the simultaneous detection of several β-agonist residues in livestock meat.

Simple and Sensitive Analysis of Clenbuterol in Urine Matrices by UHPLC-MS/MS Method with Online-SPE Sample Preparation

Clenbuterol is one of the most misused anabolic agents in professional sports. Therefore, the monitoring of clenbuterol in body fluids such as human urine is related to the development of rapid, selective and sensitive analytical methods that produce reliable results. In this work, these requirements were met by a two-dimensional separation method based on online solid-phase extraction coupled with ultra-high performance liquid chromatography–tandem mass spectrometry (SPE–UHPLC–MS/MS). The developed method provides favorable performance parameters, and it is characterized by minimum manual steps (only dilution and the addition of an internal standard) in the sample preparation. A limit of quantification (LOQ) of 0.1 ng/mL, excellent linearity (0.9999), remarkable precision (1.26% to 8.99%) and high accuracy (93.1% to 98.7%) were achieved. From a practical point of view, the analytical performance of the validated SPE–UHPLC–MS/MS method was demonstrated on blinded spiked urine samples from ten healthy volunteers. The estimated concentrations of clenbuterol were in accordance with their corresponding nominal values, as supported by the precision and accuracy data (relative standard deviation ≤5.4%, relative error ≤11%). The fulfillment of the World Anti-Doping Agency’s screening and confirmation criteria indicates that the proposed method is suitable for implementation in routine use in toxicologic and antidoping laboratories. Due to its high orthogonality and separation efficiency, the SPE–UHPLC–MS/MS method should also be easily adapted to the separation of structurally related compounds (such as clenbuterol metabolites). Thus, future antidoping applications could also include monitoring of clenbuterol metabolites, providing a longer detection widow.

Electromembrane extraction of clenbuterol from swine urine for monitoring illegal use in livestock

The illegal use of clenbuterol seriously endangers food safety and human health. Accurate monitoring the illegal use of clenbuterol in livestock can efficiently prevent the clenbuterol residue pork products from entering the consumer market. Thus, in this study, a simple, rapid and sensitive method for the determination of clenbuterol in swine urine was developed using electromembrane extraction combined with liquid chromatography-tandem mass spectrometry. It should be noted that the electromembrane extraction method presented many advantages of simple operation, fast mass transfer rate, good sample clean-up capability and less organic solvent consumption. The effect of important factors on the extraction efficiency of clenbuterol was investigated. Under the optimal conditions, good linearity was achieved for clenbuterol over the range of 1-1000 ng/mL (R² = 0.9996). The recoveries of clenbuterol in swine urine at three spiked levels ranged from 83.7 to 110.0% with relative standard deviation values lower than 9.7% (n = 4). Limits of detection and quantification for clenbuterol were 0.07 and 0.25 ng/mL, respectively. These results suggested that the proposed method has great potential on the extraction and determination of trace analyte in complex sample matrix for monitoring the illegal use in livestock. This article is protected by copyright. All rights reserved.

[Cardiovascular Risks Associated with the use of Performance-Enhancing Stimulants]

The number of people involved in regular exercise and sports is increasing. Not infrequently, this is associated with intake of sports biologically active food supplements (BAS) and stimulators of physical ability. Data has been reported on the frequency of use of physical ability stimulators among professional athletes and on the use of the most popular food supplements among young people. Special attention is paid to the effect of such use on the cardiovascular system of athletes. This review describes negative cardiac effects and clinical cases of death of athletes due to the use of such supplements and stimulators.

VAMS and StAGE as innovative tools for the enantioselective determination of clenbuterol in urine by LC-MS/MS

Clenbuterol is a chiral, selective β₂-adrenergic agonist. It is administered as a racemic mixture for therapeutic purposes (as a bronchodilator or prospective neuroprotective agent), but also for non-therapeutic uses (athletic performance enhancement, cattle growth promotion). Aim of the present study is to develop an original, enantioselective workflow for the analysis of clenbuterol enantiomers in urine microsamples. An innovative miniaturised sampling procedure by volumetric absorptive microsampling (VAMS) and a microsample pretreatment strategy based on stop-and-go extraction (StAGE) tips were developed and coupled to an original, chiral analytical method, exploiting liquid chromatography with triple quadrupole detection (LC-MS/MS). The method was validated, with satisfactory results: good linearity (r² ≥ 0.9995) and LOQ values (0.3 ng/mL) were found over suitable concentration ranges. Extraction yield (>87 %), precision (RSD < 4.3 %) and matrix effect (85-90 %) were all within acceptable levels of confidence. After validation, the method was applied to the determination of clenbuterol in dried urine sampled by VAMS from patients taking the drug for therapeutic reasons. Analyte content ranged from 0.8 to 2.5 ng/mL per single enantiomer, with substantial retention of the original drug racemic composition. The VAMS-StAGE-LC-MS/MS workflow seems to be suitable for future application to anti-doping testing of clenbuterol in urine.

Sensitive detection of clenbuterol by hybrid iridium/silicon nanowire-enhanced laser desorption/ionization mass spectrometry

There is increasing demand for anti-doping drug monitoring in sports and food safety checks by developing sensitive and fast analytical methods. Here we report the development of hybrid Ir/SiNW as a new MALDI matrix for the detection of small molecules. This matrix is characterized by sufficient UV absorption, low-noise background, and high efficiency in ionization of small molecules. Sensitive detection of clenbuterol (LOD: 0.18 pmol) and a variety of other small molecules has been achieved using the Ir/SiNW matrix with a reproducible performance. Compared to the individual components separately, the matrix of hybrid Ir/SiNW synthesized via in situ growth can promote the MS signal intensity by up to 10 fold under identical experimental conditions. We provide a unique mechanism for the high performance of the hybrid Ir/SiNW matrix with the characteristic properties of hydrogen atom transfer and enhanced protonation at the interface of the hybrid nanostructures. Our approach of using a hybrid Ir/SiNW matrix enables detection of clenbuterol quantitatively in complicated biological samples and in vivo experiments, promising a useful tool for food security and anti-doping drug monitoring in sports.

Dietary Supplement and Food Contaminations and Their Implications for Doping Controls

A narrative review with an overall aim of indicating the current state of knowledge and the relevance concerning food and supplement contamination and/or adulteration with doping agents and the respective implications for sports drug testing is presented. The identification of a doping agent (or its metabolite) in sports drug testing samples constitutes a violation of the anti-doping rules defined by the World Anti-Doping Agency. Reasons for such Adverse Analytical Findings (AAFs) include the intentional misuse of performance-enhancing/banned drugs; however, also the scenario of inadvertent administrations of doping agents was proven in the past, caused by, amongst others, the ingestion of contaminated dietary supplements, drugs, or food. Even though controversial positions concerning the effectiveness of dietary supplements in healthy subjects exist, they are frequently used by athletes, anticipating positive effects on health, recovery, and performance. However, most supplement users are unaware of the fact that the administration of such products can be associated with unforeseeable health risks and AAFs in sports. In particular anabolic androgenic steroids (AAS) and stimulants have been frequently found as undeclared ingredients of dietary supplements, either as a result of cross-contaminations due to substandard manufacturing practices and missing quality controls or an intentional admixture to increase the effectiveness of the preparations. Cross-contaminations were also found to affect therapeutic drug preparations. While the sensitivity of assays employed to test pharmaceuticals for impurities is in accordance with good manufacturing practice guidelines allowing to exclude any physiological effects, minute trace amounts of contaminating compounds can still result in positive doping tests. In addition, food was found to be a potential source of unintentional doping, the most prominent example being meat tainted with the anabolic agent clenbuterol. The athletes’ compliance with anti-doping rules is frequently tested by routine doping controls. Different measures including offers of topical information and education of the athletes as well as the maintenance of databases summarizing low- or high-risk supplements are important cornerstones in preventing unintentional anti-doping rule violations. Further, the collection of additional analytical data has been shown to allow for supporting result management processes.

Construction, expression and functional analysis of anti-clenbuterol codon-optimized scFv recombinant antibody

The construction, expression and functional analysis of codon-optimized single-chain variable fragment (coscFv) against clenbuterol (CBL) prepared from the Escherichia coli system is described. First, the ionic concentration for coscFv expression was optimized through single-factor experiments. Then, the extraction conditions of inclusion bodies were optimized, and coscFv was affinity-purified. Finally, the functional analysis of coscFv was elucidated by indirect competitive enzyme-linked immunosorbent assay (icELISA) and molecular docking. After optimizing the ionic concentration, the yield of coscFv increased from 21.69% to 23.26%. The molecular weight of coscFv was determined to be approximately 27 kDa according to the SDS-PAGE and Western blot assay. The percentage of coscFv was as high as 43.9% after the inclusion bodies were extracted, washed, and dissolved. Functional analysis indicated that the coscFv recognized CBL, and the 50% inhibition average concentration of CBL (IC₅₀) was 4.22 ± 0.01 (n = 3) ng/mL. The binding site between coscFv and CBL consisted of Asp33H, Met34H, Ser50H, Arg52H, Tyr57H, Leu59H, Asp99H, and Tyr93L. Our study confirms that coscFv can bind with CBL through the key amino acid residues and can be used to sensitively detect CBL.

Quantification and Stereochemical Composition of R-(−) and S-(+)-Clenbuterol Enantiomers in Bovine Urine by Liquid Chromatography–Tandem Mass Spectrometry

Clenbuterol (4-amino-α-[(tert-butylamino)methyl]-3,5-dichlorobenzylalcohol) is a β2-adrenergic agonist. The consumption of meat contaminated with clenbuterol can lead to increased heart rate, blood pressure, anxiety, palpitations and skeletal muscle tremors. Several analytical methods have been developed to identify and quantify clenbuterol in different biological matrices. In this report, we have developed a specific and sensitive analytical method for quantifying clenbuterol and performed an in-depth enantiomeric analysis in bovine urine. The method was evaluated in accordance with international guidelines, and we used an isotopically labeled analog as an internal standard. The extraction efficiency for clenbuterol in bovine urine was &gt; 98%, the limit of detection was 0.05 ng/mL and the limit of quantification was 0.10 ng/mL. Our assay showed high specificity, no carryover was observed and the assay was linear in the range 0.10–8.0 ng/mL. Fifteen bovine urine samples were analyzed (containing clenbuterol), and an enantiomeric analysis was performed. The clenbuterol concentration range was 0.10–10.56 ng/mL across these samples. The levorotatory enantiomer was detected at greater concentrations than the dextrorotatory enantiomer, the ratio being 1.7 ± 0.6 (n = 15), and a statistical difference was observed (P &lt; 0.05) using the Wilcoxon test.

Enhancing a clenbuterol immunosensor based on poly(3,4-ethylenedioxythiophene)/multi-walled carbon nanotube performance using response surface methodology

Clenbuterol (CLB) is an illegal antibiotic for livestock, which is misused as a growth promoter drug. In this study, an immunosensor modified with poly(3,4-ethylenedioxythiophene) (PEDOT), multi-walled carbon nanotubes (MWCNT) and anti-clenbuterol antibody (Ab) was developed for the detection of CLB. A screen-printed carbon electrode (SPCE) was modified with PEDOT/MWCNT as a sensor platform before immobilizing Ab for specific CLB binding through a competitive-type immunoassay. Free CLB in the sample solution competed with clenbuterol-horseradish peroxide (CLB-HRP) to bind with Ab. A high current signal was obtained after optimization of the electrochemical immunoassay conditions (pH, incubation temperature, antigen (Ag) incubation time and % blocking) using the response surface methodology/central composite design (RSM/CCD). The developed immunosensor is highly reproducible and sensitive with good storage stability, which are necessary for practical application. In real sample application, this immunosensor produces comparable results with liquid chromatography-mass spectrometry; thus, it is useful for CLB screening and monitoring in real meat samples.

Abuse of Prescription Drugs in the Context of Novel Psychoactive Substances (NPS): A Systematic Review

Recently, a range of prescription and over-the-counter drugs have been reportedly used as Novel Psychoactive Substances (NPS), due to their potential for abuse resulting from their high dosage/idiosyncratic methods of self-administration. This paper provides a systematic review of the topic, focusing on a range of medications which have emerged as being used recreationally, either on their own or in combination with NPS. Among gabapentinoids, pregabalin may present with higher addictive liability levels than gabapentin, with pregabalin being mostly identified in the context of opioid, polydrug intake. For antidepressants, their dopaminergic, stimulant-like, bupropion activities may explain their recreational value and diversion from the therapeutic intended use. In some vulnerable clients, a high dosage of venlafaxine (‘baby ecstasy’) is ingested for recreational purposes, whilst the occurrence of a clinically-relevant withdrawal syndrome may be a significant issue for all venlafaxine-treated patients. Considering second generation antipsychotics, olanzapine appears to be ingested at very large dosages as an ‘ideal trip terminator’, whilst the immediate-release quetiapine formulation may possess proper abuse liability levels. Within the image- and performance- enhancing drugs (IPEDs) group, the beta-2 agonist clenbuterol (‘size zero pill’) is reported to be self-administered for aggressive slimming purposes. Finally, high/very high dosage ingestion of the antidiarrhoeal loperamide has shown recent increasing levels of popularity due to its central recreational, anti-withdrawal, opiatergic effects. The emerging abuse of prescription drugs within the context of a rapidly modifying drug scenario represents a challenge for psychiatry, public health and drug-control policies.

Distinction of clenbuterol intake from drug or contaminated food of animal origin in a controlled administration trial - the potential of enantiomeric separation for doping control analysis

The differentiation of clenbuterol abuse and unintentional ingestion from contaminated meat is crucial with respect to the valuation of an adverse analytical finding in human sports doping control. The proportion of the two enantiomers of clenbuterol may serve as potential discriminating parameter. For the determination of the individual enantiomers, specific methods were developed and validated for the different matrices under investigation based on chiral chromatography coupled to tandem mass spectrometry. Data are presented from the administration to humans of clenbuterol from a pharmaceutical preparation, and from cattle meat and liver containing residues. A shift in the proportion of the enantiomers in cattle meat is detected and this signature is also found in human urine after ingestion. Thus, an altered enantiomeric composition of clenbuterol may be used to substantiate athletes' claims following adverse analytical findings in doping control. However, in meat, the enantiomeric composition was found to be highly variable. Species as well as tissue dependent variances need to be considered in interpreting enantiomer discrimination. Analysis of post administration urines from a controlled experiment comparing the administration of racemic clenbuterol from a registered pharmaceutical preparation and the administration of residue-containing meat and liver (nonracemic mixture) from treated animals is reported. Furthermore doping control samples from Mexican U17 World Championship 2011 of the Fédération Internationale de Football Association (FIFA), with adverse analytical findings for clenbuterol, were re-analysed.

Applications and challenges in using LC–MS/MS assays for quantitative doping analysis

LC–MS/MS is useful for qualitative and quantitative analysis of ‘doped’ biological samples from athletes. LC–MS/MS-based assays at low-mass resolution allow fast and sensitive screening and quantification of targeted analytes that are based on preselected diagnostic precursor–product ion pairs. Whereas LC coupled with high-resolution/high-accuracy MS can be used for identification and quantification, both have advantages and challenges for routine analysis. Here, we review the literature regarding various quantification methods for measuring prohibited substances in athletes as they pertain to World Anti-Doping Agency regulations.

Rapid screening of toxic salbutamol, ractopamine, and clenbuterol in pork sample by high-performance liquid chromatography—UV method

A rapid and simple high-performance liquid chromatography–UV method was developed for the separation and quantification of salbutamol, ractopamine, and clenbuterol in pork. A mixture of acetonitrile–formic acid–ammonium acetate was used as the mobile phase to separate three β-agonists on a C18 column with gradient. The effects of the addition of formic acid and ammonium acetate to mobile phases on the separation of β-agonists were investigated. These additives can greatly improve the resolution and sensitivity. Under the optimized chromatographic condition, this separation does not need extra sample preparation. Complete baseline separation of three β-agonists was achieved in < 20 minutes; the linear range is 0.2–50 μg/L with a correlation coefficient R² value of > 0.99. Excellent method reproducibility was found by intra- and interday precisions with a relative standard deviation of < 3%. The detection limit (S/N = 3) was found to be <0.05 μg/L; this method can be used for routine screening of the β-agonist residues in foods of animal origin before being identified by confirmatory methods.

Antidoping programme and biological monitoring before and during the 2014 FIFA World Cup Brazil

Background

The FIFA has implemented an important antidoping programme for the 2014 FIFA World Cup.

Aim

To perform the analyses before and during the World Cup with biological monitoring of blood and urine samples.

Methods

All qualified players from the 32 teams participating in the World Cup were tested out-of-competition. During the World Cup, 2–8 players per match were tested. Over 1000 samples were collected in total and analysed in the WADA accredited Laboratory of Lausanne.

Results

The quality of the analyses was at the required level as described in the WADA technical documents. The urinary steroid profiles of the players were stable and consistent with previously published papers on football players. During the competition, amphetamine was detected in a sample collected on a player who had a therapeutic use exemption for attention deficit hyperactivity disorder. The blood passport data showed no significant difference in haemoglobin values between out-of-competition and postmatch samples.

Conclusions

Logistical issues linked to biological samples collection, and the overseas shipment during the World Cup did not impair the quality of the analyses, especially when used as the biological passport of football players.

Development of a Efficient and Sensitive Dispersive Liquid-Liquid Microextraction Technique for Extraction and Preconcentration of 10 β2-Agonists in Animal Urine

Dispersive liquid–liquid microextraction (DLLME) coupled with ultra-performance liquid chromatography with tandem mass spectrometry (UPLC-MS/MS) was developed for the extraction and determination of 10 β₂-agonists in animal urine. Some experimental parameters, such as the type and volume of the extraction solvent, the concentration of the dispersant, the salt concentration, the pH value of the sample solution, the extraction time and the speed of centrifugation, were investigated and optimized. Under the optimized conditions, a good enrichment factors (4.8 to 32.3) were obtained for the extraction. The enrichment factor show that the concentration rate of DLLME is significantly higher than other pretreatment methods, and the detection sensitivity has been greatly improved. The calibration curves were linear, the correlation coefficient ranged from 0.9928 to 0.9999 for the concentration range of 0.05 to 50 ngmL^-1 and 0.1 to 50 ngmL^-1, and the relative standard deviations (RSDs, n = 15, intra and inter-day precision) at a concentration of 5 ngmL^-1 were in the range of 1.8 to 14.6%. The limits of detection (LODs) for the 10 β₂-agonists, based on a signal-to-noise ratio (S/N) of 3, were in the range of 0.01 to 0.03 ngmL^-1. The proposed method was used to identify β₂-agonists in three types of animal urine (swine, cattle, sheep), and the relative recoveries from each matrix were in the range of 89.2 to 106.8%, 90.0 to 109.8% and 89.2 to 107.2%, respectively.

Detection of clenbuterol hydrochloride residuals in pork liver using a customized surface plasmon resonance bioanalyzer

A surface plasmon resonance (SPR) immunoassay with an immobilization of self-assembled molecular identification membrane for the detection of residual Clenbuterol Hydrochloride (CLB) in pork liver was systematically investigated and experimentally validated for its high performance. SPR immunoassay with a regular competitive inhibition assay cannot be directly verified to detect CLB residuals. In this study, the binding of Au film with mercaptopropionic acid was investigated using the known form of the strong S-Au covalent bonds formed by the chemical radical of the mercaptopropionic acid and the Au film. After that, the immunoglobulin IgG of swine (SwIgG-CLB) was bonded with the mercaptopropionic acid by covalent -CO-NH- amide bonding. The modified comprehensive analysis of how the membrane structure works was introduced together with the customized SPR bioanalyzer. In order to evaluate the performance of this biomembrane structure, the concentrations of CLB-contained solutions of 0 ng•mL^-1, 10 ng•mL^-1, 20 ng•mL^-1, 33.3 ng•mL^-1, and 40 ng•mL^-1 were prepared by adding CLB reagents into the solutions of CLB antibody (Clenbuterol Hydrochloride Antibody, CLB-Ab), successively and then the response unit (RU) was measured individually. Using the data collected from the linear CCD array, the fitting curve was established with the R-Square value of 0.9929. Correspondingly, the recovery rate ranged from 88.48% to 103.21% was experimented and the limit of detection of CLB in 1.26 ng•mL^-1 was obtained efficiently. It was concluded that the detection method associated with biomembrane properties is expected to contribute much to the determination of residual CLB in pork liver quantitatively by using the customized SPR bioanalyzer.

Time for change: a roadmap to guide the implementation of the World Anti-Doping Code 2015

A medical and scientific multidisciplinary consensus meeting was held from 29 to 30 November 2013 on Anti-Doping in Sport at the Home of FIFA in Zurich, Switzerland, to create a roadmap for the implementation of the 2015 World Anti-Doping Code. The consensus statement and accompanying papers set out the priorities for the antidoping community in research, science and medicine. The participants achieved consensus on a strategy for the implementation of the 2015 World Anti-Doping Code. Key components of this strategy include: (1) sport-specific risk assessment, (2) prevalence measurement, (3) sport-specific test distribution plans, (4) storage and reanalysis, (5) analytical challenges, (6) forensic intelligence, (7) psychological approach to optimise the most deterrent effect, (8) the Athlete Biological Passport (ABP) and confounding factors, (9) data management system (Anti-Doping Administration & Management System (ADAMS), (10) education, (11) research needs and necessary advances, (12) inadvertent doping and (13) management and ethics: biological data. True implementation of the 2015 World Anti-Doping Code will depend largely on the ability to align thinking around these core concepts and strategies. FIFA, jointly with all other engaged International Federations of sports (Ifs), the International Olympic Committee (IOC) and World Anti-Doping Agency (WADA), are ideally placed to lead transformational change with the unwavering support of the wider antidoping community. The outcome of the consensus meeting was the creation of the ad hoc Working Group charged with the responsibility of moving this agenda forward.

Anabolic agents: recent strategies for their detection and protection from inadvertent doping

According to the World Anti-Doping Agency (WADA) Prohibited List, anabolic agents consist of exogenous anabolic androgenic steroids (AAS), endogenous AAS and other anabolic agents such as clenbuterol and selective androgen receptor modulators (SARMs). Currently employed strategies for their improved detection include the prolongation of the detection windows for exogenous AAS, non-targeted and indirect analytical approaches for the detection of modified steroids (designer steroids), the athlete's biological passport and isotope ratio mass spectrometry for the detection of the misuse of endogenous AAS, as well as preventive doping research for the detection of SARMs. The recent use of these strategies led to 4-80-fold increases of adverse analytical findings for exogenous AAS, to the detection of the misuse of new designer steroids, to adverse analytical findings of different endogenous AAS and to the first adverse analytical findings of SARMs. The strategies of the antidoping research are not only focused on the development of methods to catch the cheating athlete but also to protect the clean athlete from inadvertent doping. Within the past few years several sources of inadvertent doping with anabolic agents have been identified. Among these are nutritional supplements adulterated with AAS, meat products contaminated with clenbuterol, mycotoxin (zearalenone) contamination leading to zeranol findings, and natural products containing endogenous AAS. The protection strategy consists of further investigations in case of reasonable suspicion of inadvertent doping, publication of the results, education of athletes and development of methods to differentiate between intentional and unintentional doping.