Multiple Cytochrome P450 Isoforms Are Involved in the Generation of a Pharmacologically Active Thiol Metabolite, whereas Paraoxonase 1 and Carboxylesterase 1 Catalyze the Formation of a Thiol Metabolite Isomer from Ticlopidine

• DOI: 10.1124/dmd.113.053017
• Publication Date: 2013-10-30T03:38:56Z
• Authors: Min-Jung Kim; Eun Sook Jeong; Jung-Soon Park; Su-Jun Lee; Jong Lyul Ghim; Chang-Soo Choi; Jae-Gook Shin; Dong-Hyun Kim
• Keywords: Carboxylesterase; Thiol; Paraoxonase; Active metabolite

Ticlopidine is a first-generation thienopyridine antiplatelet drug that prevents adenosine 5′-diphosphate (ADP)-induced platelet aggregation. We identified the enzymes responsible for two-step metabolic bioactivation of ticlopidine in human liver microsomes and plasma. Formation 2-oxo-ticlopidine, an intermediate metabolite, was NADPH dependent cytochrome P450 (CYP) 1A2, 2B6, 2C19, 2D6 were involved this reaction. Conversion 2-oxo-ticlopidine to thiol metabolites observed both (M1 M2) plasma (M1). These two considered as isomers, mass spectral analysis suggested M2 metabolite bearing exocyclic double bond, whereas M1 isomer which bond migrated endocyclic position piperidine ring. The conversion significantly increased by addition 1 mM CaCl₂. In contrast, activity not changed presence formation inhibited EDTA but other esterase inhibitors, substantially carboxylesterase (CES) inhibitors such bis-(<i>p</i>-nitrophenyl)phosphate (BNPP), diisopropylphosphorofluoride (DFP), clopidogrel. further confirmed with recombinant paraoxonase (PON1) CES1. However, detected only NADPH-dependent microsomal incubation, multiple CYP isoforms highest contribution CYP2B6. vitro aggregation assay demonstrated pharmacologically active. results collectively indicated mediated M1, M2, generated either PON1 or CES1 liver.