title: Role of enzymatic N-hydroxylation and reduction in flutamide metabolite-induced liver toxicity.
abstract: Flutamide is used for prostate cancer therapy but occasionally induces severe liver injury. Flutamide is hydrolyzed in the body into 5-amino-2-nitrobenzotrifluoride (FLU-1) and then further oxidized. In our previous study, N-hydroxy FLU-1 (FLU-1 N-OH) was detected in the urine of patients and exhibited cytotoxicity in rat primary hepatocytes. In the present study, we have assessed the roles of FLU-1 N-oxidation and hepatic glutathione (GSH) depletion in liver injury. FLU-1 (200 mg/kg p.o.) was administered to C57BL/6 mice for 5 days together with 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) (3 mg/kg i.p.) for the first 3 days. Mice were fasted for the last 2 days to deplete hepatic GSH. Administration of FLU-1 alone did not affect serum alanine aminotransferase activities (ALT), whereas coadministration of FLU-1 and TCPOBOP significantly increased ALT in fasted mice but not in nonfasted mice. Microsomal FLU-1 N-hydroxylation was enhanced approximately 5 times by TCPOBOP treatment. Flutamide metabolite-protein adducts were detected in liver microsomes incubated with FLU-1 N-OH, but not with FLU-1 and flutamide, by immunoblotting using antiflutamide antiserum. In the presence of mouse liver cytosol, FLU-1 N-OH was reduced back into FLU-1. This enzymatic reduction required NAD(P)H as a cofactor. The reduction was enhanced by the coexistence of NAD(P)H and GSH, whereas it was markedly inhibited by allopurinol (20 microM). By using purified bovine xanthine oxidase, the reduction was observed in the presence of NAD(P)H. These results suggest that FLU-1 N-OH is involved in flutamide-induced hepatotoxicity and that cytosolic reduction of FLU-1 N-OH plays a major role in protection against flutamide-induced hepatotoxicity.
authors.affiliation: Division of Drug Metabolism and Molecular Toxicology, Graduate School of Pharmaceutical Sciences, Tohoku University, Aramaki, Aoba-ku, Sendai, 980-8578, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Ohbuchi
authors.forename: Masaaki
authors.initials: M
authors.lastname: Miyata
authors.forename: Daichi
authors.initials: D
authors.lastname: Nagai
authors.forename: Miki
authors.initials: M
authors.lastname: Shimada
authors.forename: Kouichi
authors.initials: K
authors.lastname: Yoshinari
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Yamazoe
mesh_terms: D000726:Androgen Antagonists / Q000378:metabolism* / Q000633:toxicity; D000818:Animals; D015153:Blotting, Western; D002851:Chromatography, High Pressure Liquid; D005485:Flutamide / Q000378:metabolism* / Q000633:toxicity; D005978:Glutathione / Q000378:metabolism; D006900:Hydroxylation; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D013056:Spectrophotometry, Ultraviolet
chemical_list: D000726:Androgen Antagonists; D005485:Flutamide; D005978:Glutathione