TY - JOUR T1 - Metabolic Activation of Mefenamic Acid Leading to Mefenamyl-<em>S</em>-Acyl-Glutathione Adduct Formation In Vitro and In Vivo in Rat JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 1515 LP - 1526 DO - 10.1124/dmd.112.046102 VL - 40 IS - 8 AU - Mark P. Grillo AU - Michelle Tadano Lohr AU - Jill C. M. Wait Y1 - 2012/08/01 UR - http://dmd.aspetjournals.org/content/40/8/1515.abstract N2 - Carboxylic acid-containing nonsteroidal anti-inflammatory drugs (NSAIDs) can be metabolized to chemically reactive acyl glucuronide and/or S-acyl-CoA thioester metabolites capable of transacylating GSH. We investigated the metabolism of the NSAID mefenamic acid (MFA) to metabolites that transacylate GSH, leading to MFA-S-acyl-GSH thioester (MFA-SG) formation in incubations with rat and human hepatocytes and in vivo in rat bile. Thus, incubation of MFA (1–500 μM) with rat hepatocytes led to the detection of MFA-1-β-O-acyl glucuronide (MFA-1-β-O-G), MFA-S-acyl-CoA (MFA-SCoA), and MFA-SG by liquid chromatography-tandem mass spectrometric analysis. The Cmax of MFA-SG (330 nM; 10-min incubation with 100 μM MFA) was 120- to 1400-fold higher than the Cmax of drug S-acyl-GSH adducts detected from studies with other carboxylic acid drugs to date. MFA-SG was also detected in incubations with human hepatocytes, but at much lower concentrations. Inhibition of MFA acyl glucuronidation in rat hepatocytes had no effect on MFA-SG formation, whereas a 58 ± 1.7% inhibition of MFA-SCoA formation led to a corresponding 66 ± 3.5% inhibition of MFA-SG production. Reactivity comparisons with GSH in buffer showed MFA-SCoA to be 80-fold more reactive than MFA-1-β-O-G forming MFA-SG. MFA-SG was detected in MFA-dosed (100 mg/kg) rat bile, where 17.4 μg was excreted after administration. In summary, MFA exhibited bioactivation in rat and human hepatocytes and in vivo in rat, leading to reactive acylating derivatives that transacylate GSH. The formation of MFA-SG in hepatocytes was shown not to be mediated by reaction with MFA-1-β-O-G, and not solely by MFA-SCoA, but perhaps also by intermediary MFA-acyl-adenylate formation, which is currently under investigation. ER -