title: Trimethoprim: novel reactive intermediates and bioactivation pathways by cytochrome p450s.
abstract: Trimethoprim (TMP) is a widely used antibacterial agent that is usually considered as a safe drug. TMP has, however, been implicated in rare adverse drug reactions (ADRs) in humans. Bioactivation to a reactive iminoquinone methide intermediate has been proposed as a possible cause for the toxicity of the drug. However, little is known about the cytochrome P450s (P450s) involved in this bioactivation and in the metabolism of TMP in general. In this study, we have investigated the metabolism and bioactivation of TMP by human liver microsomes (HLM) and rat liver microsomes, by recombinant human cytochrome P450s, and by the bacterial P450 BM3 mutant M11(his). In addition to non GSH-dependent metabolites, five GSH adducts were identified in the HLM incubations. Next to two major GSH adducts probably originating from the iminoquinone methide intermediate described previously, three minor GSH adducts were also identified, indicating that other types of reactive intermediates are formed by HLM, such as ortho-quinones and para-quinone methide intermediates. The major GSH adducts were produced by P450 1A2 and P450 3A4, while the minor GSH adducts were mainly formed by P450 1A2, P450 3A4, and P450 2D6. Although preliminary, these results might implicate that genetic polymorphisms in P450 enzymes could play a role in the onset of TMP-related ADRs in humans.
authors.affiliation: LACDR/Division of Molecular Toxicology, Department of Pharmacochemistry, Vrije Universiteit, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.
authors.forename: Micaela C
authors.initials: MC
authors.lastname: Damsten
authors.forename: Jon S B
authors.initials: JS
authors.lastname: de Vlieger
authors.forename: Wilfried M A
authors.initials: WM
authors.lastname: Niessen
authors.forename: Hubertus
authors.initials: H
authors.lastname: Irth
authors.forename: Nico P E
authors.initials: NP
authors.lastname: Vermeulen
authors.forename: Jan N M
authors.initials: JN
authors.lastname: Commandeur
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism*; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D013058:Mass Spectrometry; D008862:Microsomes, Liver / Q000378:metabolism; D014295:Trimethoprim / Q000009:adverse effects / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D003577:Cytochrome P-450 Enzyme System; D014295:Trimethoprim; D005978:Glutathione