Characterisation of metabolites of the food mutagens 2-amino-3-methylimidazo[4,5- f]quinoline and 2-amino-3,4-dimethylimidazo[4,5- f]quinoline formed after incubation with isolated rat liver cells

Abstract

The metabolism of 14C-labelled 2-amino-3-methylimidazo[4,5- f]quinoline (IQ) and 2-amino-3,4-dimethylimidazo[4,5- f]quinoline (MeIQ) was studied in suspensions of hepatocytes isolated from PCB-pretreated rats. The metabolites found after incubation of IQ/MeIQ (0.1 mM) with PCB-pretreated hepatocytes for 3 h were separated into three principal groups: ethyl acetate-extractable metabolites (2–4%), water soluble metabolites (94–98%) and covalently bound metabolites (0.4–0.5%). The water soluble metabolites were separated by HPLC. The metabolites were evaluated by β-glucuronidase lability, sulphate incorporation and compared with glucuronides formed by microsomes. Mass spectroscopy and proton NMR were also run. The major metabolites formed were a N 2 -sulphamate, an O-sulphate in position 5 for IQ and 5 for MeIQ and an O-glucuronide in the same position. The MeIQ N 2 -sulphamate was much less abundant than the IQ N 2 -sulphamate. When compared with hepatocytes from uninduced rats, it was found that primarily the formation of ring-hydroxylated conjugates increased after PCB-pretreatment. The major ethyl acetate-extractable metabolites were the N 2 -acetyl derivatives and an unidentified metabolite. A small peak representing the 5-hydroxy-IQ or 5-hydroxy-MeIQ could also be seen in the HPLC chromatogram of the ethyl acetate extractable metabolites. All major water soluble products described in hepatocytes were also found in urine and bile of uninduced rats exposed to IQ/MeIQ in vivo.