Drug metabolism: in vitro biotransformation of anabolic steroids in canines

The in vivo metabolism of Furazadrol in greyhounds

Samples of the 'dietary supplement' Furazadrol sourced through the internet have been reported to contain the designer anabolic androgenic steroids [1',2']isoxazolo[4',5':2,3]-5α-androstan-17β-ol (furazadrol F) and [1',2']isoxazolo[4',3':2,3]-5α-androstan-17β-ol (isofurazadrol IF). These steroids contain an isoxazole fused to the A-ring and were designed to offer anabolic activity while evading detection, raising concerns over the potential for abuse of this preparation in sports. The metabolism of Furazadrol (F:IF, 10:1) was studied by in vivo methods in greyhounds. Urinary phase II Furazadrol metabolites were detected as glucuronides after a controlled administration. These phase II metabolites were subjected to enzymatic hydrolysis by Escherichia coli β-glucuronidase to afford the corresponding phase I metabolites. Using a library of synthetically derived reference materials, the identities of seven urinary Furazadrol metabolites were confirmed. Major confirmed metabolites were isofurazadrol IF, 4α-hydroxyfurazadrol 4α-HF and 16α-hydroxy oxidised furazadrol 16α-HOF, whereas the minor confirmed metabolites were furazadrol F, 4β-hydroxyfurazadrol 4β-HF, 16β-hydroxyfurazadrol 16β-HF and 16β-hydroxy oxidised furazadrol 16β-HOF. One major hydroxyfurazadrol and two dihydroxyfurazadrol metabolites remained unidentified. Qualitative excretion profiles, limits of detection and extraction recoveries were established for furazadrol F and major confirmed metabolites. These investigations identify the key urinary metabolites of Furazadrol following oral administration, which can be incorporated into routine screening by anti-doping laboratories to aid the regulation of greyhound racing.

The metabolism of anabolic-androgenic steroids in the greyhound

BACKGROUND

Effective control of the use of anabolic-androgenic steroids (AASs) in animal sports is essential in order to ensure both animal welfare and integrity. In order to better police their use in Australian and New Zealand greyhound racing, thorough metabolic studies have been carried out on a range of registered human and veterinary AASs available in the region.

RESULTS

Canine metabolic data are presented for the AASs boldenone, danazol, ethylestrenol, mesterolone, methandriol, nandrolone and norethandrolone. The principal Phase I metabolic processes observed were the reduction of A-ring unsaturations and/or 3-ketones with either 3α,5β- or 3β,5α-stereochemistry, the oxidation of secondary 17β-hydroxyl groups and 16α-hydroxylation. The Phase II β-glucuronylation of sterol metabolites was extensive.

CONCLUSION

The presented data have enabled the effective analysis of AASs and their metabolites in competition greyhound urine samples.

Metabolism of stanozolol: chemical synthesis and identification of a major canine urinary metabolite by liquid chromatography-electrospray ionisation ion trap mass spectrometry

The canine phase I and phase II metabolism of the synthetic anabolic-androgenic steroid stanozolol was investigated following intramuscular injection into a male greyhound. The major phase I biotransformation was hydroxylation to give 6alpha-hydroxystanozolol which was excreted as a glucuronide conjugate and was identified by comparison with synthetically derived reference materials. An analytical procedure was developed for the detection of this stanozolol metabolite in canine urine using solid phase extraction, enzyme hydrolysis of glucuronide conjugates and analysis by positive ion electrospray ionisation ion trap LC-MS.

In vitro metabolism of polychlorinated biphenyls and cytochrome P450 monooxygenase activities in dietary-exposed Greenland sledge dogs

The in vitro metabolism of a polychlorinated biphenyl (PCB) mixture was examined using hepatic microsomes of dietary-exposed Greenland sledge dogs (Canis familiaris) to an organohalogen-rich diet (Greenland minke whale blubber: EXP cohort) or a control diet (pork fat: CON cohort). The associations between in vitro PCB metabolism, activity of oxidative hepatic microsomal cytochrome P450 (CYP) isoenzymes and concentrations of PCBs and hydroxylated metabolites were investigated. The CON dogs exhibited a 2.3-fold higher depletion percentage for the PCB congeners having at least two pairs of vicinal meta-para Cl-unsubstituted carbons (PCB-18 and -33) relative to the EXP dogs. This depletion discrepancy suggests that there exist substrates in liver of the organohalogen-contaminated EXP dogs that can competitively bind and/or interfere with the active sites of CYP isoenzymes, leading to a lower metabolic efficiency for these PCBs. Testosterone (T) hydroxylase activity, determined via the formation of 6beta-OH-T, 16alpha-OH-T, 16beta-OH-T and androstenedione, was strongly correlated with the depletion percentages of PCB-18 and -33 in both cohorts. Based on documented hepatic microsomal CYP isoenzyme substrate specificities in canines, present associations suggest that primarily CYP2B/2C and CYP3A were inducible in sledge dogs and responsible for the in vitro metabolism of PCB-18 and -33.

Metabolism of methyltestosterone in the greyhound

Gas chromatography/mass spectrometry and selective derivatisation techniques have been used to identify urinary metabolites of methyltestosterone following oral administration to the greyhound. Several metabolites were identified including reduced, mono-, di- and trihydroxylated steroids. The major metabolites observed were 17alpha-methyl-5beta-androstane-3alpha-17beta-diol, 17alpha-methyl-5beta-androstane-3alpha,16alpha,17beta-triol, and a further compound tentatively identified as 17alpha-methyl-5z-androstane-6z,17beta-triol. The most abundant of these was the 17alpha-methyl-5beta-androstane-3alpha,16alpha,17beta-triol. This metabolite was identified by comparison with a reference standard synthesised using a Grignard procedure and characterised using trimethylsilyl (TMS) and acetonide-TMS derivatisation techniques. There did not appear to be any evidence for 16beta-hydroxylation as a phase I metabolic transformation in the greyhound. However, significant quantities of 16alpha-hydroxy metabolites were detected. Selective enzymatic hydrolysis procedures indicated that the major metabolites identified were excreted as glucuronic acid conjugates. Metabolic transformations observed in the greyhound have been compared with those of other mammalian species and are discussed here.

Determination of testosterone metabolites in human hepatocytes. I. Development of an on-line sample preparation liquid chromatography technique and mass spectroscopic detection of 6beta-hydroxytestosterone

A rapid and sensitive RP-HPLC assay for determination of 6beta-hydroxytestosterone in human hepatocytes with corticosterone as the internal standard is described. The procedure employs on-line sample enrichment using a BioTrap 500 MS (20x4 mm I.D.) extraction pre-column and subsequent gradient separation on a Prontosil 60-5 C(18)-H (250x2 mm I.D., 5 micrometer particle size) analytical column in the back-flush mode using a ternary eluent system composed of methanol, tetrahydrofuran and water. Signal monitoring was done by measurement of the responses from liquid chromatography coupled to mass spectroscopy (LC-MS/MS) using an atmospheric pressure chemical ionization (APCI) source conducted in the selected reaction monitoring (SRM) mode. Mean recoveries of 6beta-hydroxytestosterone from an estimate of the biological matrix, i.e., Dulbecco's modified Eagle medium "High Glucose", ranged from 101.8-104.4% for samples containing the target analyte at the 250, 500 and 1000 ng/ml level. The limit of quantitation (LOQ) was 20 ng/ml at an injection volume of 100 microliter determined in the same matrix. Linearity of signal responses versus concentration for all three analytes was accomplished in the range of 100-4000 ng/ml. Mean values of the coefficients of variation (C.V.) for the target analyte obtained for the concentrations 250, 500 and 1000 ng/ml at 5 different days in quintuplicate ranged from 1.5-7.7% (within-day) and 4.8-7.3% (between-day). The corresponding values for the accuracy ranged from 87.7-106.1% for the within-day and from 98.8-102.5% for the between-day measurements. The target analyte was sufficiently stable at both storage and sample preparation conditions because no substantial deviations between analyte concentrations measured before and after subsequently performed freeze and thaw cycles were observed.

Steroid analysis for medical diagnosis

Steroid assays are important for medical diagnosis of diseases related to steroid disturbances and abuse. This article reviews the recent progress in analytical methods for steroids in the clinical laboratory. The requirements for these methods are rapid, highly sensitive, specific, direct assay of conjugated steroids, the simultaneous analysis, identification of unknown steroids, and ultra-miniaturization of the separation system.