beta2-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, Howell, L.C, Coldham, N.G
• Format: Journal Article
• Language: English
• Published: England 01.05.1999
• Subjects: 7-ethoxycoumarin; Adrenergic beta-Agonists - analysis; Adrenergic beta-Agonists - metabolism; Adrenergic beta-Agonists - pharmacokinetics; Albuterol - analogs & derivatives; Albuterol - analysis; Albuterol - metabolism; Animals; beta-adrenergic agonists; Biotransformation; Cattle; clenbuterol; Clenbuterol - analysis; Clenbuterol - metabolism; coumarins; Coumarins - metabolism; drug metabolism; Food Contamination - prevention & control; Foodborne Diseases - metabolism; hepatocytes; liver; Liver - chemistry; Liver - cytology; Liver - metabolism; Male; Meat Products; metabolites; Microsomes, Liver - chemistry; Microsomes, Liver - metabolism; salbutamol; salmeterol; Salmeterol Xinafoate
• ISSN: 0049-8254; 1366-5928

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 microm) and chopped (600 microm) tissue slices. 2. Radio-HPLC analysis indicated that the saligenin beta2-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 beta-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.