title: Effects of individual terphenyls and polychlorinated terphenyls on rat hepatic microsomal cytochrome P-450-dependent monooxygenases: structure-activity relationships.
abstract: The effects of o-, m- and p-terphenyl, 2,4-dichloro-, 2,4,6-trichloro-, 2,3,5,6-tetrachloro-, 2,3,4,6-tetrachloro-, 2,4,4''',6- tetrachloro- and 2,3,4,5-tetrachloro-p-terphenyl, 2,3,4,5-tetrachloro-m- and o-terphenyl as inducers of hepatic drug-metabolizing enzymes were determined in immature male Wistar rats. o-Terphenyl, 2,4-dichloro-, 2,4,6-trichloro-p-terphenyl and 2,3,4,5-tetrachloro-o-terphenyl induced 4,4'-dimethylamino antipyrine N-demethylase at total dose levels of 300 mumol/kg and the 2,3,4,5-tetrachloro-p-terphenyl induced ethoxyresorufin O-deethylase (EROD). In contrast, none of the other terphenyls or polychlorinated terphenyls (PCTs) induced these enzyme activities. Previous studies have demonstrated that 2,3,4,5-tetrachloro-p-terphenyl did not exhibit a high affinity for the 2,3,7,8-tetrachlorodibenzo-p-trachlorodibenzo-p-dioxin (TCDD) receptor protein (EC50 = 6.6 X 10(-6) M). In contrast, this study showed that 2,3,4,5-tetrachloro-p-terphenyl was more active than either 2,3,4,5-tetrachloro-o- or m-terphenyl as an inducer of EROD. Moreover, the competitive receptor binding EC50 values for the latter two isomers were greater than 10(-5) M and this result was also consistent with their lack of EROD induction activity. Previous studies showed that analysis of the data for a series of 4'-substituted-2,3,4,5-tetrachlorobiphenyls indicated that the p-terphenyl structural moiety (i.e. 4'-substituent = phenyl) did not interact with high affinity with the receptor protein binding site. Since the 2,3,4,5-tetrachloro o- and m-terphenyls are also poor ligands for the receptor protein, this data and results from other studies indicate that PCT congeners (and commercial mixtures) are therefore unlikely to elicit significant 2,3,7,8-TCDD-like biologic or toxic effects in target species.
mesh_terms: D000818:Animals; D001579:Benzopyrene Hydroxylase / Q000378:metabolism; D019363:Cytochrome P-450 CYP1A1; D003577:Cytochrome P-450 Enzyme System; D003600:Cytosol / Q000378:metabolism; D007536:Isomerism; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D010088:Oxidoreductases / Q000378:metabolism; D010089:Oxidoreductases, N-Demethylating / Q000378:metabolism; D010105:Oxygenases / Q000378:metabolism*; D011080:Polychloroterphenyl Compounds / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D018336:Receptors, Aryl Hydrocarbon; D011955:Receptors, Drug / Q000378:metabolism; D013329:Structure-Activity Relationship; D013730:Terphenyl Compounds / Q000494:pharmacology*
chemical_list: D011080:Polychloroterphenyl Compounds; D018336:Receptors, Aryl Hydrocarbon; D011955:Receptors, Drug; D013730:Terphenyl Compounds; D003577:Cytochrome P-450 Enzyme System; D010088:Oxidoreductases; D010105:Oxygenases; D001579:Benzopyrene Hydroxylase; D019363:Cytochrome P-450 CYP1A1; D010089:Oxidoreductases, N-Demethylating; C023680:dimethylaminoantipyrine N-demethylase