Biodehalogenation of Para-Substituted Aromatic Halides.

Abstract

Biodehalogenation plays a small but significant role in aromatic halide metabolism. Para-substituted benzenes containing iodine-125, chlorine-36, bromine or chlorine were used to study the extent and mechanism of dehalogenation in vivo in in vitro in the rat by direct halide measurement. A reverse phase HPLC technique was developed for separation of inorganic halide from nontransformed substrates and metabolites. Liquid scintillation counting of HPLC eluent was used for inorganic iodide-125 and chloride-36 determination. Neutron activation analysis(NAA) of eluent was used for in vitro debromination studies of 4-bromobiphenyl. In vitro microsomal deiodination of para-nitro, benzoic acid, aldehyde, hydroxyl(phenol) and phenyl(biphenyl) substrates exhibited statistically significant deiodination above control values consistent with mixed function oxidase activity while the benzonitrile did not. Cytosolic deiodination resulted in significant deiodination for all six substrates mentioned above. The phenol and biphenyl deiodinated in cytosol containing N-ethylmaleimide(NEM) or in glutathione(GSH)-depleted cytosol indicating the presence of a non-GSH-mediated cytosolic dehalogenase. Deiodination of p-iodophenol using cytosol with NEM was about two-thirds that using normal cytosol while no statistical difference was observed in deiodination using either cytosol with the phenol. Deiodination using GSH-depleted cytosol was less than for NEM studies indicating degradation of this dehalogenase. Cytosolic debromination of 4-bromobiphenyl was not significant above controls. High background levels of chloride precluded in vitro dechlorination studies of 4-chlorobiphenyl via NAA. In vivo dechlorination of {4-('36)Cl}-chlorobiphenyl was 1.68% (+OR-) 0.485 compared to 11.45% (+OR-) 2.68 for {4,4'-('36)Cl}-dichlorobiphenyl for a ten day period. This appears to be the first report of dechlorination of 4-chlorobiphenyl. Results of dechlorination of {4,4'-('36)Cl}-dichlorobiphenyl agree with literature values determined by isolation of metabolites. Mutagenicity studies using GSH-depleted cytosol were undertaken to see if inhibition of GSH-S-transferase would result in greater mutagenicity compared to normal cytosol. No mutagenicity above background was observed with 4-chlorobiphenyl or 4-iodobiphenyl using S./typhimurium strain TA-100 at doses of 50, 100, 250, 500 or 1000 (mu)g with either cytosol. Indications of increased cytotoxicity using GSH-depleted cytosol were observed but were not quantitatively reproducible due to solubility problems.