Resolution of R‐(−) and S‐(+)‐ enantiomers of clenbuterol in pharmaceutical preparations and black‐market products using liquid chromatography–tandem mass spectrometry

A LC-MS/MS method for determination of clenbuterol enantiomers in animal tissues and its application to the enantioselective distribution in Bama mini-pigs

OBJECTIVES

To establish and validate a simple and reliable analytical method for separation and determination of clenbuterol enantiomers (R-(-)-clenbuterol & S-(+)-clenbuterol) in animal tissues, and apply it to the enantioselective distribution of clenbuterol in Bama mini-pigs.

METHODS

A LC-MS/MS analytical method was developed and validated in positive multiple reaction monitoring mode with electrospray ionization. After perchloric acid deproteinization, samples were pretreated only by one step liquid-liquid extraction using tert-butyl methyl ether under strong alkaline condition. Teicoplanin was used as chiral selector and 10 mM ammonium formate methanol solution was used as mobile phase. The optimized chromatographic separation conditions were completed in 8 min. Two chiral isomers in 11 edible tissues from Bama mini-pigs were investigated.

RESULTS

R-(-)-clenbuterol and S-(+)-clenbuterol can be baseline separated and accurately analyzed with a linear range of 5-500 ng/g. Accuracies ranged from -11.9-13.0% for R-(-)-clenbuterol and -10.2-13.2% for S-(+)-clenbuterol, intra-day and inter-day precisions were between 0.7 and 6.1% for R-(-)-clenbuterol and 1.6-5.9% for S-(+)-clenbuterol. R/S ratios in edible tissues of pigs were all significantly lower than 1.

CONCLUSIONS

The analytical method has good specificity and robustness in determination of R-(-)-clenbuterol and S-(+)-clenbuterol in animal tissues, and can be used as a routine analysis method for food safety and doping control. There is a significant difference in R/S ratio between pig feeding tissues and pharmaceutical preparations (racemate with R/S ratio of 1), which makes it possible to identify the source of clenbuterol in doping control and investigation.

Quantification and enantiomeric distribution of clenbuterol in several bovine tissues using UHPLC-tandem mass spectrometry: Evaluation of a risk factor associated with meat contamination

Clenbuterol (Clb) (4-amino-α-[(tert-butylamine) methyl]-3,5-dichlorobenzyl alcohol) is a sympathomimetic agent that exhibits β2-agonist activity. It is applied as a bronchodilatory, tocolytic, and mucolytic agent and is authorized for clinical management in both human and veterinary therapeutics as a racemic mixture. However, its use is strictly prohibited in animals destined for food production in countries in the European Union and in the United States and Mexico, among many others. The R-(-) enantiomer in clenbuterol stimulates β2-receptors, whereas the S-(+) enantiomer blocks the effect of β1-receptors. The aims of this study were to develop a method for detecting and quantifying Clb and its enantiomeric distribution in several bovine tissues. The UHPLC-MS/MS method developed to quantify the target compound at trace levels in these tissues combines high sensitivity with good selectivity and short chromatographic run time. The tissue samples tested were found to contain racemic Clb in concentrations of 5-447 pg g^-1 . The enantiomeric analysis of Clb showed that R-(-)-Clb is present at higher concentrations in some tissues, whereas S-(+)-Clb was detected in a ratio of 55/45 in the liver and heart tissues.

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.

Determination of clenbuterol at trace levels in raw gelatin powder and jellies using ultra-high-performance liquid chromatography coupled to triple quadrupole mass spectrometry

Clenbuterol is present in animal tissues and organs and, therefore, potentially present in gelatin derived from animal sources. The objective of this study was to develop a method for identify an quantify traces of clenbuterol in gelatin and jellies. The clenbuterol calibration curve showed linearity in the range of 20-1000 pg mL^-1. The detection and quantification limits were 5 pg g^-1 and 10 pg g^-1, respectively. The recovery of the analyte ranged from 93.4 to 98.7% with an intra-day RSD% (n = 4) of 1.25%-3.25%, and an inter-day RSD% (n = 12) of 0.5%-2.25%, with good linearity (R² = 0.99). The method developed and validated was successfully applied in 54 gelatin samples, 57.4% of which showed clenbuterol. This UHPLC-MS/MS method combines high sensitivity with good selectivity and short chromatographic run time.

Detection of clenbuterol residues in beef sausages and its enantiomeric analysis using UHPLC-MS/MS. A risk of unintentional doping in sport field

Clenbuterol (Clb) can be present in Mexico often but not all over the world in animal tissues and organs, therefore, potentially is derived from animal sources as well. The aims of this study were to develop and validate a method for detecting traces of clenbuterol in beef sausages. A calibration curve showed linearity in the range of 20–500 pg ml⁻¹. The limit of detection (LOD) and lower limit of quantification (LLOQ) were 5 and 10 pg g⁻¹, respectively. The analyte recovery was from 95.70% to 100.40% with an intraday relative standard deviation (RSD%) of 0.99%–2.10% and an interday RSD% of 0.54%–2.34%, R² = 0.9998. The methodology developed was applied successfully in 15 samples of beef sausage, and 73.3% of the samples tested contained racemic clenbuterol in concentrations between 30 and 471 pg g⁻¹. The UHPLC–MS/MS method developed combines high sensitivity with good selectivity and short chromatographic run time. Additionally, the enantiomeric analysis of clenbuterol performed in beef sausages showed a 59% for R‐(−)‐Clb and 41% for S‐(+)‐Clb. The presence of clenbuterol in beef sausages could represent a risk of unintentional doping in sport field, because the clenbuterol is a banned substance included in the World Anti‐Doping Agency's (WADA) list of prohibited substances.

Sports drug testing and the athletes' exposome

Similar to the general population, elite athletes are exposed to a complex set of environmental factors including chemicals and radiation and also biological and physical stressors, which constitute an exposome that is, unlike for the general population, subjected to specific scrutiny for athletes due to applicable antidoping regulations and associated (frequent) routine doping controls. Hence, investigations into the athlete's exposome and how to distinguish between deliberate drug use and different contamination scenarios has become a central topic of antidoping research, as a delicate balance is to be managed between the vital and continually evolving developments of sensitive analytical techniques on the one hand, and the risk of the athletes' exposome potentially causing adverse analytical findings on the other.

Do dried blood spots have the potential to support result management processes in routine sports drug testing?-Part 2: Proactive sampling for follow-up investigations concerning atypical or adverse analytical findings

Capillary blood sampled as dried blood spot (DBS) has shown substantial potential as test matrix in sports drug testing in various different settings, enabling the analysis of numerous different drugs and/or their respective metabolites. In addition to established beneficial aspects of DBS specimens in general (such as the minimally invasive and non-intrusive nature, and simplified sample transport), a yet unexplored advantage of DBS in the anti-doping context could be the opportunity of preserving a source of information complementary to routine doping controls performed in urine or venous blood. Whenever follow-up investigations are warranted or required, frequently collected and stored (but yet not analyzed) DBS samples could be target-tested for the compound(s) in question, in order to contribute to results management and decision-making processes.

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.

Enantiomeric analysis of clenbuterol in Chinese people by LC–MS/MS to distinguish doping abuse from meat contamination

Aim: Follow-up investigations are often required for clenbuterol-positive cases. A method to distinguish doping abuse from meat contamination was developed. Materials & methods: A total of 26 volunteers were recruited to ingest clenbuterol contaminated-pork and clenbuterol tablets. Results: For 20 volunteers, after ingestion of contaminated-pork, R-(-)/S-(+)-clenbuterol ratio was <1.0, while the value was >1.0 after taking clenbuterol tablets. However, after taking clenbuterol tablets, some ratio points of the other six volunteers were between 0.9 and 1.0. A case of an abnormal cold and fever, which returned to normal after recovery, was also reported firstly. Conclusion: A change in R-(-)/S-(+)-clenbuterol was reported in the Chinese population initially. A ratio of 0.9 was recommended in doping related cases for the Chinese population.

Screening and confirmatory analysis of recombinant human erythropoietin for racing camels' doping control

Recombinant human erythropoietin (rHuEPO) belongs to the therapeutic class of erythropoiesis stimulating agents (ESAs) due to its implication in the creation pathway of red blood cells and thus enhancement of oxygenation. Because of this bioactivity, rHuEPO has been considered as a major doping agent in sports competitions for decades. Over the years, doping control laboratories designed several analytical strategies applied to human and animal samples to highlight any misuse. Even though multiple analytical approaches have been reported, none has yet been dedicated to racing camels. Here, we describe an analytical strategy to test camel plasma samples at screening using an ELISA assay and a targeted nano-liquid chromatography-high-resolution tandem mass spectrometry for confirmatory analysis. The method was validated and has been successfully applied to post-race samples, allowing the detection of a positive case of rHuEPO administration.

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.

Evaluation of R- (-) and S- (+) Clenbuterol enantiomers during a doping cycle or continuous ingestion of contaminated meat using chiral liquid chromatography by LC-TQ-MS

Clenbuterol is known to improve competition resistance and muscular growth in athletes. Although it is an illegal drug, its use by farmers is widely spread to induce growth of their cattle. Thus, when clenbuterol is found in the urine of an athlete, there is doubt whether it was consumed with doping purposes or if it is due to the consumption of meat from a clenbuterol-fed animal. Previous studies suggest that enantiomeric relationship of clenbuterol may be different according to the intake source. However, the enantiomeric relationship throughout a doping cycle or a continuous intake of contaminated meat has not yet been explored. In this first approximation, our aim was the development and validation of a sensitive and rapid method for the determination of S- (+) and R- (─) clenbuterol enantiomers to be used in a controlled study in rats fed for one week with contaminated meat or simulating a doping cycle. Enantiomers were measured using liquid chromatography coupled to mass spectrometry with a triple quadrupole analyzer (LC-TQ-MS) and were separated on an AGP Chiralpak column. The method was fully validated following the VICH (Veterinary International Conference on Harmonization guidelines) and was linear in the range of 12.5-800 pg/mL with a correlation coefficient of ≥0.98 for each enantiomer, and with a limit of quantitation and detection (LOQ and LOD) of 12.5 pg/mL and 6.5 pg/mL, respectively, for both enantiomers. The application of this method pointed out the shift of the enantiomeric relationship in urine from rats during the first five days of the doping cycle compared to those fed with contaminated meat. This finding can be of substantial importance in further doping studies.