title: Tiamulin inhibits human CYP3A4 activity in an NIH/3T3 cell line stably expressing CYP3A4 cDNA.
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.
authors.affiliation: Research Institute of Toxicology, Utrecht University, The Netherlands.
authors.forename: E M
authors.initials: EM
authors.lastname: De Groene
authors.forename: S M
authors.initials: SM
authors.lastname: Nijmeijer
authors.forename: G J
authors.initials: GJ
authors.lastname: Horbach
authors.forename: R F
authors.initials: RF
authors.lastname: Witkamp
mesh_terms: D016475:3T3 Cells; D016604:Aflatoxin B1 / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001711:Biotransformation / Q000187:drug effects; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism*; D004224:Diterpenes / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D051379:Mice; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D016296:Mutagenesis; D013250:Steroid Hydroxylases / Q000378:metabolism; D014162:Transfection
chemical_list: D000900:Anti-Bacterial Agents; D065607:Cytochrome P-450 Enzyme Inhibitors; D018076:DNA, Complementary; D004224:Diterpenes; D003577:Cytochrome P-450 Enzyme System; D016604:Aflatoxin B1; C014224:tiamulin; D006899:Mixed Function Oxygenases; D013250:Steroid Hydroxylases; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C022657:steroid hormone 6-beta-hydroxylase; C510163:CYP3A4 protein, human