β2-Agonist abuse in food producing animals: use of in vitro liver preparations to assess biotransformation and potential target residues for surveillance

• Published in: Xenobiotica Vol. 29; no. 5; pp. 483 - 497
• Main Authors: SAUER, M. J., DAVE, M., LAKE, B. G., MANCHEE, G. R., HOWELLS, L. C., COLDHAM, N. G.
• Format: Journal Article
• Language: English
• Published: London Informa UK Ltd 1999; Taylor & Francis
• Subjects: Biological and medical sciences; Food toxicology; Medical sciences; Toxicology; Agonist; Farming animal; Bovine; Liver; HPLC chromatography; β2-Adrenergic receptor; β-Adrenergic receptor agonist; Illicit traffic; Metabolism; In vitro; Contamination; Meat; Vertebrata; Mammalia; Residue; Biotransformation; Illicit preparation; Artiodactyla; Detection; Veterinary; Adulteration; Ungulata; Food
• ISSN: 0049-8254; 1366-5928
• DOI: 10.1080/004982599238498

1. The biotransformation of [3H]clenbuterol, [3H]salbutamol, [14C]salmeterol and 7-ethoxycoumarin by bovine liver was investigated by incubation with freshly prepared microsomes, suspension and monolayer cultures of isolated hepatocytes, precision-cut (250 μm) and chopped (600 μm) tissue slices. 2. Radio-HPLC analysis indicated that the saligenin β2-agonists salmeterol and salbutamol were extensively metabolized by all intact cell preparations. A single major product (SmM1) was evident for salmeterol and two unresolved products for salbutamol (SbM1 and SbM2). Differential enzyme hydrolysis studies with Helix pomatia β-glucuronidase/aryl sulphatase indicated that the main metabolites were glucuronide conjugates. Consistent with this, analysis of metabolites by liquid chromatography-mass spectrometry showed molecular ions ([M+H]+) at m/z 592 for Sm1 and 416 for both Sb1 and Sb2. 3. Comparable studies with clenbuterol revealed three minor metabolites. Prolonged incubations generated products representing, at maximum, 27% biotransformation. Two of the products have been identified as a glucuronide ([M+H]+, m/z 453) and hydroxyclenbuterol ([M+H]+, m/z 293). 4. These findings indicate that in vitro studies provide simple and cost-effective means of evaluating xenobiotic metabolism, and thus of identifying potential target residues to enable surveillance of use of unlicensed veterinary drugs, or prohibited substances in farm animals.