Metabolism of tilmicosin by rabbit liver microsomes and hepatocytes.
We investigated tilmicosin (TIM) metabolism, at 25, 50 or 100 microM, in cultures of primary hepatocytes from rabbits bred commercially for food and in liver microsomes prepared from both untreated and rifampicin (RIF)-treated rabbits. RIF is a well-known cytochrome P4503A (CYP 3A) inducer in rabbits and most macrolides are known to be substrates of CYP 3A. No peaks in addition to those of the cis and trans forms of TIM were observed by high performance liquid chromatography (HPLC) in extracts of microsomes from untreated rabbits. When TIM was incubated with induced microsomes, at least two peaks were found by HPLC and an additional peak, eluting at shorter retention time was isolated from hepatocytes incubated for 24h with the macrolide. The structures of the metabolites were then estimated by liquid chromatography-mass spectrometry (LC-MS) in concentrated extracts from induced microsomes. Five metabolites were separated and putatively identified: cis and trans demethylated tilmicosin, tilmicosin N-oxide and cis and trans tilmicosin epoxide. The overall amount of metabolites produced in vitro using livers of untreated and RIF treated rabbits was very low, has also been observed in vivo and in vitro in cattle, chickens and pigs.
Montesissa
C
C
Dipartimento di Sanità pubblica Patologia comparata ed Igiene veterinaria, Agripolis, I-35020 Legnaro, Padua, Italy. clara.montesissa@unipd.it
Capolongo
F
F
Santi
A
A
Biancotto
G
G
Dacasto
M
M
D000818:Animals; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid / Q000662:veterinary; D046508:Culture Techniques; D003577:Cytochrome P-450 Enzyme System / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D022781:Hepatocytes / Q000378:metabolism*; D018942:Macrolides / Q000378:metabolism*; D013058:Mass Spectrometry / Q000662:veterinary; D008862:Microsomes, Liver / Q000378:metabolism*; D011817:Rabbits / Q000378:metabolism*; D012293:Rifampin / Q000008:administration & dosage / Q000009:adverse effects; D015645:Tylosin / Q000031:analogs & derivatives* / Q000378:metabolism*
D018942:Macrolides; D003577:Cytochrome P-450 Enzyme System; D012293:Rifampin; C052319:tilmicosin; D015645:Tylosin