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Tiamulin inhibits human CYP3A4 activity in an NIH/3T3 cell line stably expressing CYP3A4 cDNA
E M De Groene1, S M Nijmeijer, G J Horbach
1Research Institute of Toxicology, Utrecht University, The Netherlands.
Abstract:
Tiamulin is an antibiotic frequently used in veterinary medicine. The drug has been shown to produce clinically important interactions with other compounds that are administered simultaneously. An NIH/3T3 cell line, stably expressing human cytochrome P450 (EC 1.14.14.1) cDNA (CYP3A4), was used to study the effect of tiamulin on CYP3A4 activity. The 6 beta-hydroxylation activity of testosterone, which is increased in CYP3A4-expressing cells compared to vector-transfected cells, showed reduced activity after incubation with 1 microM tiamulin and was completely reduced to background level after incubation with 2, 5 and 10 microM tiamulin. The CYP3A4-expressing cell line was used in combination with a shuttle vector containing the bacterial lacZ' gene to study the effect of tiamulin on CYP3A4-mediated mutagenicity of aflatoxin B1. The mutation frequency of aflatoxin B1 could be completely inhibited by tiamulin in CYP3A4-expressing cells, but no effect was observed on the mutation frequency of the direct mutagen ethylmethanesulphonate. Western blotting of homogenates of the CYP3A4-expressing cell line showed stabilization of CYP3A4 protein after incubation with tiamulin, supporting the hypothesis that the mechanism of inhibition is by binding of tiamulin to the cytochrome.
Insights
Tiamulin, a veterinary antibiotic, inhibits human cytochrome P450 (CYP3A4) activity and blocks CYP3A4-mediated aflatoxin B1 mutagenicity. This suggests tiamulin binds to the cytochrome, impacting drug metabolism and safety.
Area of Science:
- Pharmacology
- Biochemistry
- Drug Metabolism
Background:
- Tiamulin is a veterinary antibiotic with known drug interaction potential.
- Cytochrome P450 enzymes, particularly CYP3A4, are crucial for drug metabolism.
- Understanding tiamulin's impact on CYP3A4 is vital for veterinary drug safety.
Purpose of the Study:
- To investigate the effect of tiamulin on human CYP3A4 activity.
- To determine if tiamulin affects CYP3A4-mediated mutagenicity.
- To elucidate the mechanism of tiamulin's interaction with CYP3A4.
Main Methods:
- Utilized an NIH/3T3 cell line stably expressing human CYP3A4.
- Assessed testosterone 6 beta-hydroxylation activity in the presence of varying tiamulin concentrations.
- Evaluated tiamulin's effect on aflatoxin B1 mutagenicity using a bacterial lacZ' gene assay.
- Performed Western blotting to analyze CYP3A4 protein levels.
Main Results:
- Tiamulin significantly reduced CYP3A4-mediated testosterone 6 beta-hydroxylation in a dose-dependent manner.
- Tiamulin completely inhibited CYP3A4-mediated aflatoxin B1 mutagenicity.
- No effect of tiamulin was observed on the mutagenicity of ethylmethanesulphonate.
- Western blot analysis indicated tiamulin stabilizes CYP3A4 protein.
Conclusions:
- Tiamulin inhibits human CYP3A4 activity and its metabolic activation of aflatoxin B1.
- The mechanism of inhibition appears to involve tiamulin binding to the cytochrome.
- These findings highlight potential drug interactions and safety concerns for tiamulin in co-administered therapies.