The ionization mechanism in dopant-assisted atmospheric pressure photoionization and the effect of solvent on the ionization efficiency was studied using 7 naphthalenes and 13 different solvent systems. The ionization efficiency was 1-2 orders of magnitude higher with dopant than without, indicating that the photoionization of the dopant initiates the ionization process. In positive ion mode, the analytes were ionized either by charge exchange or by proton transfer. Charge exchange was favored for low proton affinity solvents (water, hexane, chloroform), whereas the addition of methanol or acetonitrile to the solvent initiated proton transfer. In negative ion mode, the compounds with high electron affinity were ionized by electron capture or by charge exchange and the compounds with high gas-phase acidity were ionized by proton transfer. In addition, some oxidation reactions were observed. All the reactions leading to ionization of analytes in negative ion mode are initiated by thermal electrons formed in photoionization of toluene. The testing of different solvents showed that addition of buffers such as ammonium acetate, ammonium hydroxide, or acetic acid may suppress ionization in APPI. The reactions are discussed in detail in light of thermodynamic data.

The study of the metabolic fate of drugs is an essential and important part of the drug development process. The analysis of metabolites is a challenging task and several different analytical methods have been used in these studies. However, after the introduction of the atmospheric pressure ionization (API) technique, electrospray and atmospheric pressure chemical ionization, liquid chromatography/mass spectrometry (LC/MS) has become an important and widely used method in the analysis of metabolites owing to its superior specificity, sensitivity and efficiency. In this paper the feasibility of LC/API-MS techniques in the identification, structure characterization and quantitation of drug metabolites is reviewed. Sample preparation, LC techniques, isotope labeling, suitability of different MS techniques, such as tandem mass spectrometry, and high-resolution MS in drug metabolite analysis, are summarized and discussed. Automation of data acquisition and interpretation, special techniques and possible future trends are also the topics of the review.

The applicability of liquid chromatography/tandem mass spectrometry (LC/MS/MS) for the detection of the free anabolic steroid fraction in human urine was examined. Electrospray ionization (ESI), atmospheric pressure chemical ionization and atmospheric pressure photoionization methods were optimized regarding eluent composition, ion source parameters and fragmentation. The methods were compared with respect to specificity and detection limit. Although all methods proved suitable, LC/ESI-MS/MS with a methanol-water gradient including 5 mM ammonium acetate and 0.01% acetic acid was found best for the purpose. Multiple reaction monitoring allowed the determination of steroids in urine at low nanogram per milliliter levels. LC/MS/MS exhibited high sensitivity and specificity for the detection of free steroids and may be a suitable technique for screening for the abuse of anabolic steroids in sports.

ABSTRACT:Testosterone and epitestosterone are endogenous steroids that differ in the configuration of the hydroxyl-bearing carbon at C-17. Testosterone is the predominant male sex hormone, whereas the role of epitestosterone is largely unclear. In humans, both androgens are excreted mainly as glucuronide conjugates and the urinary ratio of testosterone to epitestosterone (T/E), used to expose illicit testosterone abuse by male athletes, indicates the relative concentrations of the respective glucuronides. Some male athletes have T/E values greater than the accepted threshold value (4.0), even without testosterone abuse. We have analyzed athletes' urine samples and found that the main reason for such false-positive results in doping tests was a low epitestosterone glucuronide concentration not a high level of testosterone glucuronide. Sulfate conjugates of both testosterone and epitestosterone were also detected in the different urine samples. Glucuronidation assays with the 19 human UDP-glucuronosyltransferases (UGTs) of subfamilies UGT1A, UGT2A, and UGT2B revealed that UGT2B17 is the most active enzyme in testosterone glucuronidation. UGT2B17 does not glucuronidate epitestosterone, but inhibition studies revealed that it binds epitestosterone with affinity similar to that of testosterone. Epitestosterone glucuronidation is catalyzed mainly by UGT2B7, and the K m of this reaction is significantly lower than the K m of UGT2B17 for testosterone. Although UGT2B7 and UGT2B17 exhibited high, although converse, stereoselectivity in testosterone and epitestosterone glucuronidation, UGT2A1, an extrahepatic enzyme that is expressed mainly in the nasal epithelium, catalyzed the glucuronidation of both steroids at considerable rates and similar kinetics. The results shed new light on the substrate specificity and stereoselectivity of human UGTs.

In the fight against doping, steroid profiling is a powerful tool to detect drug misuse with endogenous anabolic androgenic steroids. To establish sensitive and reliable models, the factors influencing profiling should be recognised. We performed an extensive literature review of the multiple factors that could influence the quantitative levels and ratios of endogenous steroids in urine matrix. For a comprehensive and scientific evaluation of the urinary steroid profile, it is necessary to define the target analytes as well as testosterone metabolism. The two main confounding factors, that is, endogenous and exogenous factors, are detailed to show the complex process of quantifying the steroid profile within WADA-accredited laboratories. Technical aspects are also discussed as they could have a significant impact on the steroid profile, and thus the steroid module of the athlete biological passport (ABP). The different factors impacting the major components of the steroid profile must be understood to ensure scientifically sound interpretation through the Bayesian model of the ABP. Not only should the statistical data be considered but also the experts in the field must be consulted for successful implementation of the steroidal module.

A detailed understanding of equine drug metabolism is important for detection of drug abuse in horseracing and also in veterinary drug development and practice. To date, however, no comprehensive review of equine drug metabolism has been published. The majority of literature regarding equine drug metabolite profiles is derived from sports drug detection research and is generally targeted at detecting marker metabolites of drug abuse. However, the bulk of the literature on equine drug metabolism enzymology is derived from veterinary studies aimed at determining the molecular basis of metabolism. In this article, the phase 1 and 2 metabolisms of seven of the most important classes of drugs monitored in horseracing are reviewed, including: anabolic-androgenic steroids (AAS), β₂ -agonists, stimulants, sedatives/tranquilizers, local anesthetics, non-steroidal anti-inflammatory analgesics (NSAIDS)/cyclooxygenase-2 (COX-2) inhibitors, and opioid analgesics. A summary of the literature relating to the enzymology of drug metabolism in this species is also be presented. The future of equine drug metabolism in the area of doping research will be influenced by several factors, including: a possible move towards the increased use of blood and other alternative testing matrices; the development of assays based on intact drug conjugates; the increasing threat of 'designer' and herbal- based products; advances in the use of in vitro technologies; the increased use of liquid-chromatography/high-resolution mass spectrometry; and the possibility of screening using 'omics' approaches. Also, the recent cloning of a range of equine cytochrome P450 (CYP) enzymes opens up the potential for carrying out more detailed mechanistic pharmacological and toxicological veterinary studies.

ABSTRACT:Selective androgen receptor modulators (SARM) are a prominent group of compounds for being misused in sports owing to their advantageous anabolic properties and reduced side effects. To target the preventive doping control analysis in relevant compounds, the challenge is to predict the metabolic fate of a new compound. For aryl-propionamide-derived SARM, an in vitro assay employing microsomal and S9 human liver enzymes was developed to simulate phase-I and phase-II metabolic reactions. In vitro metabolic profiles and the structure-metabolic relationship were compared between four structurally modified substrates. Accurate mass measurements were used to characterize the synthesized metabolites, and also collision-induced dissociation was examined to suggest the methodological approach to monitor the prohibited use of aryl-propionamide-derived drug candidates. Subsequent phase-I and phase-II metabolic reactions were successfully combined in one in vitro assay. The main routes of phase-I modifications involved the hydrolysis of ether linkage, monohydroxylation, and hydrolytic cleavage of the amide bond. Nitro-reduction and deacetylation were reactions observed for substrates possessing the corresponding functionality. SARM metabolites were analyzed in negative ion electrospray ionization and detected as deprotonated species [M-H]؊ . The main metabolic modifications were observed to occur in the B-ring side, and collision-induced dissociation resulted in the product ions originating from the A-ring side of the compound. These structure-specific ions may be monitored as target ions in the routine doping control.For decades, steroidal androgens have been clinically used in the treatment of diseases related to androgen deficiency, including muscle-wasting, osteoporosis, and benign prostate hyperplasia, but recently their suitability for hormone replacement therapy of aging men and regulation of male fertility has been under investigation (NegroVilar, 1999;Gao and Dalton, 2007). Traditional anabolic-androgenic therapies, applying steroid-structured compounds such as testosterone, are often limited due to low oral bioavailability, cross-reactivity with steroid receptors other than the androgen receptor, hepatic toxicity, and other undesirable side effects on the prostate and cardiovascular system (Bhasin and Bremner, 1997). To overcome these drawbacks, a series of nonsteroidal selective androgen receptor modulators (SARM) have been developed. SARM represent enhanced tissue selectivity, binding to the androgen receptor (AR) with affinity similar to testosterone, but exhibiting only partial agonist properties in androgenic tissue. Based on their chemical structure, most prominent pharmacophores of SARM can be categorized at least in four classes: 1) aryl-propionamide, 2) bicyclic hydantoin, 3) quinoline, and 4) tetrahydroquinoline analogs, which all have also entered different stages of clinical studies (Chen et al., 2005a;Thevis and Schänzer, 2007). Among the published data on SARM research, the series of aryl-pr...

ABSTRACT:A multidimensional study on the glucuronidation of anabolic androgenic steroids and their phase I metabolites by 11 recombinant human UDP-glucuronosyltransferases (UGTs) was carried out using liquid chromatographic-tandem mass spectrometric analyses. Large differences between the enzymes with respect to the conjugation profiles of the 11 tested aglycones were detected. Two UGTs, 1A6 and 1A7, did not exhibit measurable activity toward any of the aglycones that were examined in this study. Regioselectivity was demonstrated by UGTs 1A8, 1A9, and 2B15 that preferentially catalyzed hydroxyl glucuronidation at the 17␤-position. Most of the other enzymes glucuronidated hydroxyl groups at both the 3␣-and the 17␤-positions. Clear stereoselectivity was observed in glucuronidation of diastereomeric nandrolone metabolites (5␣-estran-3␣-ol-17-one and 5␤-estran-3␣-ol-17-one), whereas such specificity was not seen when analogous methyltestosterone metabolites were assayed. UGTs 1A1, 1A3, 1A4, 1A8, 1A9, 1A10, 2B4, 2B7, and 2B15 readily glucuronidated 5␣-androstane-3␣,17␤-diol, but none of them exhibited methyltestosterone glucuronidation activity. In agreement with the latter observations, we found that the methyltestosterone glucuronidation activity of human liver microsomes is extremely low, whereas in induced rat liver microsomes it was significantly higher. The homology among UGTs 1A7 to 1A10 at the level of amino acid sequence is very high, and it was thus surprising to find large differences in their activity toward this set of aglycones. Furthermore, the high activity of UGT1A8 and 1A10 toward some of the substrates indicates that extrahepatic enzymes might play a role in the metabolism of anabolic androgenic steroids.