Xenobiotic and steroid biotransformation enzymes in Atlantic salmon (Salmo salar) liver treated with an estrogenic compound, 4-nonylphenol

Hepatic microsomal biotransformation reactions with xenobiotic and steroid substrates have been investigated in 4-non-ylphenol (NP; 1, 5, 25, and 125 mg/kg body weight)-treated juvenile Atlantic salmon (Salmo salar), in addition to control and estradiol-17β (5 mg/kg, positive control)-treated fish. Treatment of juvenile salmon with NP caused an initial increase and an apparent dose-dependent decrease in progesterone 6β-, 16α, and 17α-hydroxylase activities in liver microsomes. 7-Ethoxyresorufin O-deethylase and UDP-glucuronosyltransferase activities were also reduced. Plasma levels of estradiol-17β (E2) were lowered 24–43% as a result of NP treatment. Immunochemical analysis of CYP1A, CYP2K-like, and CYP3A-like proteins showed 18%, 47%, and 30% reductions in enzyme-linked immunosorbent assay absorbance levels, respectively, in the groups treated with 125 mg NP/kg fish. The group treated with E2 also showed similar reductions. In summary, the present study has demonstrated variations in steroid hydroxylases, cytochrome P450 isozymes, and conjugating enzyme levels in NP-treated juvenile salmon. These results represent a novel aspect of NP effects not previously demonstrated with an environmental estrogen in any fish species or lower vertebrate.