Stereochemical composition of clenbuterol residues in edible tissues of swine

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.

Simultaneous determination of fourteen β2-agonist enantiomers in food animal muscles by liquid chromatography coupled with tandem mass spectrometry

Illegal drug residues in animal derived foods are closely related to human's life and health. Studies on illegal drug residues and the metabolism, such as β2-agonists in animals have attracted more and more attention. In most cases, β2-agonists are suppliedand used astheracemate. The metabolic process and distribution of the two enantiomers in animal tissues are different. Therefore, it is very necessary to develop a simple and fast method for chiral resolution of these drugs in animal tissues. In this paper, a reliable resolution and determination method was presented using liquid chromatography-tandem mass spectrometry (LC-MS/MS) for fourteen enantiomers of seven β2-agonist racemates, clenbuterol (CLE), salbutamol (SAL), cimaterol (CIM), terbutaline (TER), clorprenaline (CLO), tulobuterol (TUL), penbuterol (PEN) in pork, beef, and lamb muscle samples. The samples were added the internal standard solution (IS) and extracted in the alkaline medium with acetonitrile. The further sample purification was accomplished through MCX solid phase extraction cartridge. Chromatographic chiral separation was carried out on a VancoShell chiral column (100 mm × 4.6 mm, 2.7 μm) with an isocratic mobile phase consisting of methanol and 10 mmol mL-1 ammonium formate aqueous solution (85:15, v/v). Under the optimized conditions, the resolution (R) of CIM was 2.0, CLE and PEN were 1.5, the others were all greater than 1.0. Enantiomeric determination was performed in the positive electrospray ionization mode using multiple reaction monitoring (MRM). The correlation coefficient (r) in the range of 0.2-25.0 μg L-1 was above 0.993. The average recoveries at the three spiking levels ranged from 95.3% to 117.7% with the relative standard deviation (RSD) lower than 15%. The limit of detection (LOD) and the limit of quantification (LOQ) of β2-agonist enantiomers was 0.2 μg kg-1 and 0.5 μg kg-1 respectively. The method was successfully applied in the analysis and evaluation of β2-agonist enantiomers in positive food animal muscle samples, CLE, SAL, TEB and CIM enantiomers were detected. The concentrations of the corresponding enantiomers were in the range of 1.06-17.3 μg kg-1, the lowest enantiomer fraction (EF) value was 0.42, and the highest value was 0.69. The work is expected to provide a method for chiral separation and enantiomeric determination of the further study of pharmacology, toxicity and residue elimination of β2-agonist enantiomers.

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.

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.

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.

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.

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.

Enantioselective disposition of clenbuterol in rats

Clenbuterol is a long-acting β2-adrenoceptor agonist and bronchodilator that is used for the treatment of asthma, but the desired activities reside almost exclusively in the (-)-R-enantiomer. This study examined enantioselectivity in the disposition of clenbuterol following administration of clenbuterol racemate to rats. Concentrations of clenbuterol enantiomers in plasma, urine and bile were determined by LC-MS/MS assay with a Chirobiotic T column. This method was confirmed to show high sensitivity, specificity and precision, and clenbuterol enantiomers in 0.1 ml volumes of plasma were precisely quantified at concentrations as low as 0.25 ng/ml. The pharmacokinetic profiles of clenbuterol enantiomers following intravenous and intraduodenal administration of clenbuterol racemate (2 mg/kg) in rats were significantly different. The distribution volume of (-)-R-clenbuterol (9.17 l/kg) was significantly higher than that of (+)-S-clenbuterol (4.14 l/kg). The total body clearance of (-)-R-clenbuterol (13.5 ml/min/kg) was significantly higher than that of the (+)-S-enantiomer (11.5 ml/min/kg). An in situ absorption study in jejunal loops showed no difference in the residual amount between the (-)-R- and (+)-S-enantiomers. Urinary clearance was the same for the two enantiomers, but biliary excretion of (-)-R-clenbuterol was higher than that of the (+)-S-enantiomer. The fractions of free (non-protein-bound) (-)-R- and (+)-S-clenbuterol in rat plasma were 48.8% and 33.1%, respectively. These results indicated that there are differences in the distribution and excretion of the clenbuterol enantiomers, and these may be predominantly due to enantioselective protein binding.

Does the analysis of the enantiomeric composition of clenbuterol in human urine enable the differentiation of illicit clenbuterol administration from food contamination in sports drug testing?

RATIONALE

Clenbuterol (4-amino-α-[(tert-butylamino)methyl]-3,5-dichlorobenzyl alcohol) is approved for human and veterinary use primarily for the treatment of pulmonary afflictions. Despite the authorized administration in cases of medical indications, the misuse of clenbuterol in animal husbandry as well as elite and amateur sport has frequently been reported, arguably due to growth-promoting properties. Due to various recent incidences of doping control specimens containing clenbuterol, strategies towards the discrimination of a surreptitious application from unintended intake via animal-derived edibles or dietary supplements were required.

METHODS

The enantiomeric compositions of clenbuterol in human urine samples derived from administration studies with therapeutic amounts of the β(2)-agonist and authentic doping control specimens were determined. Due to the facts that therapeutic clenbuterol consists of a racemic mixture of (+)- and (-)-stereoisomers and that the first mentioned (dextrorotatory) stereoisomer is retained to a greater extent in edible animal tissue, the differentiation of a recent administration of therapeutic (and thus racemic) clenbuterol from food contamination (stereoisomerically depleted clenbuterol) was considered. Employing deuterated clenbuterol as internal standard, the target analytes were extracted from human urine by means of concerted liquid-liquid and solid-phase extractions and subjected to chiral liquid chromatography hyphenated to high resolution/high accuracy mass spectrometry with electrospray ionization.

RESULTS

Both enantiomers of clenbuterol were baseline separated and relative abundances of corresponding labeled and unlabeled stereoisomers were determined, demonstrating that the therapeutic use of clenbuterol results in racemic mixtures in urine for at least 24 h while adverse analytical findings presumably originating from food contaminations can yield (-)-clenbuterol-depleted pairs of analytes.

CONCLUSIONS

The determination of relative abundances of clenbuterol enantiomers can indicate the ingestion of clenbuterol via contaminated food; however, depletion of (-)-clenbuterol in edible animal tissue is time-dependent and thus results can still be inconclusive as to the inadvertent ingestion of clenbuterol when clenbuterol administration to animals was conducted until slaughter.

Analytical methods for the detection of clenbuterol

Clenbuterol is therapeutically used for the treatment of pulmonary diseases such as bronchial asthma or for tocolytic reasons. In cattle feeding as well as in sports it is illicitly misused due to its anabolic properties to promote muscle growth. Sample preparation procedures and analytical techniques used for the detection of clenbuterol are manifold and vary with the objectives of the investigation. Methods for its detection in biological specimens, drug preparations, the environment, food and feed products are reported. They are mainly based on immunochemical, chromatographic and mass spectrometric techniques, or on capillary electrophoresis. Sample preparation primarily includes liquid-liquid extraction and solid-phase extraction. Depending on the aim of the method clenbuterol can be determined in single- or multi-analyte methods. In biological and environmental samples concentrations are generally low due to the potency of the drug. Thus, highly sensitive procedures are required for expedient analyses.

Competitive immunoassay for clenbuterol using capillary electrophoresis with laser-induced fluorescence detection

A competitive immunoassay for detecting clenbuterol in urine was established by capillary electrophoresis (CE) with laser-induced fluorescence (LIF). The clenbuterol was conjugated with bovine serum albumin (BSA), and then the derivative was labeled with fluorescein isothiocyanate (FITC) and competes for antibody with free clenbuterol in the sample. Under the optimal conditions, Free and bound FITC labeled clenbuterol was separated within 8 min with the relative standard deviation (R.S.D.) 0.72% for migration time and 2.8% for peak area. The detection limit reached 0.7 ng/ml.

Stereoselectivity of porcine beta-adrenergic receptors for ractopamine stereoisomers

Ractopamine HCl is a beta-adrenergic receptor ((betaAR) ligand approved for use in swine to enhance carcass leanness. Ractopamine is produced commercially as a mixture of four stereoisomers (RR, RS, SR, SS). In order to determine which stereoisomers are active in the pig and whether they exhibit betaAR subtype selectivity, receptor affinity and adenylyl cyclase activation were determined using cloned porcine beta1- and beta2AR expressed in Chinese hamster ovary (CHO) cells. Dissociation constants (Kd) were determined by competitive displacement of [125I]iodocyanopindolol binding by ractopamine stereoisomers. The RR isomer had the highest affinity for both beta1- and betaAR (Kd of 29 and 26 nM, respectively). Dissociation constants for the other stereoisomers were higher (RS = 463 and 78 nM, SR = 3,230 and 831 nM, SS = 16,600 and 3,530 nM for the beta1- and beta2AR, respectively) relative to the RR stereoisomer. Isoproterenol stimulated adenylyl cyclase activity 600% relative to basal rates in CHO cells, regardless of betaAR subtype. Ractopamine stereoisomers did not significantly (P > 0.05) stimulate adenylyl cyclase through the beta1AR at moderate (near Kd) or high (10(-4) M) concentrations. In contrast, the RR isomer increased adenylyl cyclase activity 200 to 300% relative to basal rates through the beta2AR at moderate and hiconcentrations; the SR stereoisomer increased adenylyl cyclase activity nearly 100%. Neither the RS nor SS stereoisomers were effective in activating adenylyl cyclase activity through the beta2AR. A pattern of stereoselective activation similar to that for adenylyl cyclase also was exhibited for lipolysis using porcine adipocytes. The RR stereoisomer was equal to isoproterenol in stimulating lipolysis, whereas the SR isomer was 50% as effective; the RS and SR stereoisomers did not stimulate lipolysis in porcine adipocytes. The porcine betaAR exhibited stereoselectivity toward ractopamine stereoisomers with the RR isomer exhibiting the highest affinity for the (beta1- and beta2AR. In contrast, ractopamine stereoisomers seemed to be more effective at eliciting adenosine cyclic 3',5'-phosphate responses from beta2AR than beta1AR. The RR isomer ilikely the functional stereoisomer of ractopamine, but its effectiveness may be compromised by the presence of competing isomers, in particular the RS stereoisomer.

Stereoselective chromatography of cardiovascular drugs: an update

This review reports the latest achievements in chromatographic enantioseparations of various classes of cardiovascular drugs and selected applications of these methods in pharmaceutical and clinical analysis. The use of these drugs as test compounds for new chiral stationary phases and different parameters of chromatographic processes is also presented.

Recent applications of stereoselective chromatography

Some recent applications of stereoselective chromatography in the fields of clinical pharmacy, drug analysis, food, and natural products are reviewed. The review is documented with up-to-date literature, which will assist further expansion of research in these areas.