Identification of CYP isozymes involved in benzbromarone metabolism in human liver microsomes

Abstract

Benzbromarone (BBR) is metabolized to 1'-hydroxy BBR and 6-hydroxy BBR in the liver. 6-Hydroxy BBR is further metabolized to 5,6-dihydroxy BBR. The aim of this study was to identify the CYP isozymes involved in the metabolism of BBR to 1'-hydroxy BBR and 6-hydroxy BBR and in the metabolism of 6-hydroxy BBR to 5,6-dihydroxy BBR in human liver microsomes. Among 11 recombinant P450 isozymes examined, CYP3A4 showed the highest formation rate of 1'-hydroxy BBR. The formation rate of 1'-hydroxy BBR significantly correlated with testosterone 6β-hydroxylation activity in a panel of 12 human liver microsomes. The formation of 1'-hydroxy BBR was completely inhibited by ketoconazole in pooled human liver microsomes. On the other hand, the highest formation rate of 6-hydroxy BBR was found in recombinant CYP2C9. The highest correlation was observed between the formation rate of 6-hydroxy BBR and diclofenac 4'-hydroxylation activity in 12 human liver microsomes. The formation of 6-hydroxy BBR was inhibited by tienilic acid in pooled human liver microsomes. The formation of 5,6-dihydroxy BBR from 6-hydroxy BBR was catalysed by recombinant CYP2C9 and CYP1A2. The formation rate of 5,6-dihydroxy BBR was significantly correlated with diclofenac 4'-hydroxylation activity and phenacetin O-deethylation activity in 12 human liver microsomes. The formation of 5,6-dihydroxy BBR was inhibited with either tienilic acid or α-naphthoflavone in human liver microsomes. These results suggest that (i) the formation of 1'-hydroxy BBR and 6-hydroxy BBR is mainly catalysed by CYP3A4 and CYP2C9, respectively, and (ii) the formation of 5,6-dihydroxy BBR is catalysed by CYP2C9 and CYP1A2 in human liver microsomes.

Novel Bioactivation Pathway of Benzbromarone Mediated by Cytochrome P450

“…This result is consistent with the previous reports that CYP2C9 and CYP2C19 are the major isozymes capable of catalyzing the formation of 6-OH-BBR (McDonald and Rettie, 2007;Kobayashi et al, 2012). CYP2C9 was also responsible for the formation of DBH from BBR.…”

“…Early metabolic studies identified that the major metabolites of BBR are 6-hydroxybenzbromarone (6-OH-BBR) formed by cytochrome P450 isoforms CYP2C9 and CYP2C19, and 1ʹ-hydroxybenzbromarone (1ʹ-OH-BBR) produced by CYP3A4 (McDonald and Rettie, 2007;Kobayashi et al, 2012). It has been reported that human hepatocarcinoma HepG2 cells infected with adenovirus vector expressing CYP2C9 significantly increase the cytotoxicity of BBR, suggesting that CYP2C9 is associated with BBR-induced cytotoxicity (Iwamura et al, 2011).…”

PharmGKB summary

“…Due to reports of fatal hepatotoxicity, benzbromarone was withdrawn from the market by one of its main manufacturers, though it is still available from other drug companies in several countries across the globe [87, 94]. Genetics could be a factor that influences toxicity risk.…”

“…Genetics could be a factor that influences toxicity risk. Benzbromarone is metabolized by CYP2C9 to form the active metabolite 6-hydroxybenzbromarone (which has inhibitory activity upon URAT1 uric acid uptake) and by CYP3A4 to form 1′-hydroxybenzbromarone [75, 87, 94, 95]. 6-hydroxybenzbromarone is further metabolized to 5,6-dihydroxybenzbromarone by CYP2C9 and CYP1A2 [94].…”

“…Benzbromarone is metabolized by CYP2C9 to form the active metabolite 6-hydroxybenzbromarone (which has inhibitory activity upon URAT1 uric acid uptake) and by CYP3A4 to form 1′-hydroxybenzbromarone [75, 87, 94, 95]. 6-hydroxybenzbromarone is further metabolized to 5,6-dihydroxybenzbromarone by CYP2C9 and CYP1A2 [94]. A small study in 20 healthy individuals saw reduced metabolism and clearance of benzbromarone in an individual with the CYP2C9*3/*3 genotype compared to those with *1/*1 or *1/*3 genotypes, and a significantly higher elimination half life of 6-hydroxybenzbromarone in patients with the *1/*3 genotype compared to *1/*1 [96].…”