d-Isomer of gly-tyr-pro-cys-pro-his-pro peptide: A novel and sensitive in vitro trapping agent to detect reactive metabolites by electrospray mass spectrometry

This paper describes a d-peptide isomer-based trapping assay using an LC/MS ion-trap spectrometer with an electrospray ionization (ESI) source as the analytical tool to study bioactivation of xenobiotics. Reactive metabolites were generated from parent compounds in in vitro incubations with different sources of CYP enzymes. A short d-isomer of gly-tyr-pro-cys-pro-his-pro proved to be a sensitive trapping agent and resistant to proteases. This method was tested with 16 probe substances. Acetaminophen, 1-chloro 2,4-dinitrobenzene, clozapine, diclofenac, imipramine, menthofuran, propranolol, pulegone and ticlopidine all formed d-peptide adducts, which were analogous to the GSH adducts previously described in the literature. New adducts were identified with clopidogrel (–Cl + peptide), nicotine (–CH 3+H + peptide), nimesulide (+peptide) and tolcapone (+peptide), i.e., no GSH adducts of those drugs have been described in the literature. No adducts were identified with ciprofloxacin, ketoconazole and verapamil. In the literature no GSH adducts have been described with ciprofloxacin and verapamil. d-Peptide-based trapping proved to be a reliable and reproducible method to identify bioactivated intermediates. d-Peptide is a new and convenient protein trapping agent for use in early phase screening of bioactivation of new chemical entities and evaluation of toxic properties of chemicals.