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Updated: Aug 30, 2026
Human Liver Microphysiological System for Assessing Drug-Induced Liver Toxicity In Vitro
Published on: January 31, 2022
Metabolism of tilmicosin by rabbit liver microsomes and hepatocytes
C Montesissa1, F Capolongo, A Santi
1Dipartimento di Sanità pubblica Patologia comparata ed Igiene veterinaria, Agripolis, I-35020 Legnaro, Padua, Italy. clara.montesissa@unipd.it
Abstract:
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.
Insights
Tilmicosin metabolism in rabbit liver microsomes and hepatocytes was studied. Rifampicin induction revealed low levels of five metabolites, including demethylated, N-oxide, and epoxide forms.
Area of Science:
- Veterinary Pharmacology
- Drug Metabolism and Pharmacokinetics
- Biochemistry
Background:
- Tilmicosin (TIM) is a macrolide antibiotic used in food-producing animals.
- Cytochrome P450 3A (CYP 3A) enzymes are crucial for drug metabolism, and rifampicin (RIF) is a known inducer.
- Understanding TIM metabolism is essential for assessing its efficacy and safety in animal agriculture.
Purpose of the Study:
- To investigate the metabolic pathways of tilmicosin in rabbit liver preparations.
- To determine the effect of cytochrome P450 3A induction on tilmicosin metabolism.
- To identify and characterize the major metabolites of tilmicosin in rabbits.
Main Methods:
- Incubation of tilmicosin with primary rabbit hepatocytes and liver microsomes from untreated and RIF-treated rabbits.
- Analysis of metabolites using high-performance liquid chromatography (HPLC).
- Structural elucidation of metabolites using liquid chromatography-mass spectrometry (LC-MS).
Main Results:
- No significant metabolism of tilmicosin was observed in microsomes from untreated rabbits.
- Incubation with RIF-induced microsomes and hepatocytes revealed the formation of at least five metabolites.
- Identified metabolites include cis and trans demethylated tilmicosin, tilmicosin N-oxide, and cis and trans tilmicosin epoxide.
- Overall metabolite production was low, consistent with observations in other species.
Conclusions:
- Rabbit liver CYP 3A enzymes play a role in tilmicosin metabolism, particularly after induction.
- The identified metabolites suggest specific biotransformation pathways for tilmicosin.
- The low overall metabolic yield indicates that tilmicosin may have a relatively stable pharmacokinetic profile in rabbits.
- Findings contribute to the understanding of tilmicosin's fate in a key food-producing animal model.
