2,2',5,5'-Tetrachlorobiphenyl: isolation and identification of metabolites generated by rat liver microsomes

The in vitro metabolism of 2,2',5,5'-tetrachloro[3H]biphenyl (TCB) by control and phenobarbital-induced rat liver microsomes has been investigated. Phenobarbital induction was found to significantly increase (30-fold) the NADPH-dependent, microsomal metabolism of TCB above that observed with control microscomes. The metabolites generated by microsomes of phenobarbital-induced rats were separated by Sephadex LH-20 and gas-liquid chromatography (GLC) and were subsequently characterized by infrared and mass spectral (MS) analyses and techniques of catalytic dechlorination with GLC/MS comparison to biphenylol standards. The major metablite, representing 90% of all metabolic products, was identified as 3-hydroxy-TCB. 3,4-Dihydro-3,4-dihydroxy-TCB was identified as a minor metabolite (5%), and trace amounts of two chromatographically and spectrally distinct dihydroxy-TCB's (4% and 1%) were also found. This in vitro metabolic profile is consistent with that found in vivo and suggests a mechanism of TCB metabolism incorporating both direct hydroxylation and an arene oxide intermediate.