TY - JOUR T1 - BIOACTIVATION OF THE NONTRICYCLIC ANTIDEPRESSANT NEFAZODONE TO A REACTIVE QUINONE-IMINE SPECIES IN HUMAN LIVER MICROSOMES AND RECOMBINANT CYTOCHROME P450 3A4 JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 243 LP - 253 DO - 10.1124/dmd.104.001735 VL - 33 IS - 2 AU - Amit S. Kalgutkar AU - Alfin D. N. Vaz AU - Mary E. Lame AU - Kirk R. Henne AU - John Soglia AU - Sabrina X. Zhao AU - Yuri A. Abramov AU - Franco Lombardo AU - Claire Collin AU - Zachary S. Hendsch AU - Cornelis E. C. A. Hop Y1 - 2005/02/01 UR - http://dmd.aspetjournals.org/content/33/2/243.abstract N2 - The therapeutic benefits of the antidepressant nefazodone have been hampered by several cases of acute hepatotoxicity/liver failure. Although the mechanism of hepatotoxicity remains unknown, it is possible that reactive metabolites of nefazodone play a causative role. Studies were initiated to determine whether nefazodone undergoes bioactivation in human liver microsomes to electrophilic intermediates. Following incubation of nefazodone with microsomes or recombinant P4503A4 in the presence of sulfydryl nucleophiles, conjugates derived from the addition of thiol to a monohydroxylated nefazodone metabolite were observed. Product ion spectra suggested that hydroxylation and sulfydryl conjugation occurred on the 3-chlorophenylpiperazine-ring, consistent with a bioactivation pathway involving initial formation of p-hydroxynefazodone, followed by its two-electron oxidation to the reactive quinone-imine intermediate. The formation of novel N-dearylated nefazodone metabolites was also discernible in these incubations, and 2-chloro-1,4-benzoquinone, a by-product of N-dearylation, was trapped with glutathione to afford the corresponding hydroquinone-sulfydryl adduct. Nefazodone also displayed NADPH-, time-, and concentration-dependent inactivation of P4503A4 activity, suggesting that reactive metabolites derived from nefazodone bioactivation are capable of covalently modifying P4503A4. A causative role for 2-chloro-1,4-benzoquinone and/or the quinone-imine intermediate(s) in nefazodone hepatotoxicity is speculated. Although the antianxiety agent buspirone, which contains a pyrimidine ring in place of the 3-chlorophenyl-ring, also generated p-hydroxybuspirone in liver microsomes, no sulfydryl conjugates of this metabolite were observed. This finding is consistent with the proposal that two-electron oxidation of p-hydroxybuspirone to the corresponding quinone-imine is less favorable due to differences in the protonation state at physiological pH and due to weaker resonance stabilization of the oxidation products as predicted from ab initio measurements. The American Society for Pharmacology and Experimental Therapeutics ER -