Xenobiotic and steroid biotransformation activities in rainbow trout gill epithelial cells in culture

The biotransformation of xenobiotics and steroids was investigated in cultu red respiratory epithelial cells from rainbow trout (Oncorhynchus mykiss) g ills. As a first approach, ethoxyresorufin-O-deethylase (EROD), chosen as a marker of CYPIA activity, was measured in monolayers of adherent cells. Th e induction of this enzyme was studied in cells exposed to beta-naphthoflav one (BNF) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in concentrations r anging from 10(-6) to 10(-12) M. After 24 h, TCDD showed a maximal inductio n at a concentration of 10(-9) M while BNF showed a maximal induction at a concentration of 10(-7) M. Concurrently, a variety of substrates involved i n cytochrome P450-dependent metabolism as well as phase II reactions, namel y ethoxycoumarin, aniline and testosterone were incubated with cultured gil l cells for 2 or 8 h and with freshly isolated hepatocytes for comparison. Our results revealed a significant cytochrome P450-dependent activity in gi ll cells with ethoxycoumarin and aniline, but no hydroxylation was observed with testosterone as substrate. No trace of sulfate conjugate was detected . With 2.5 mu M aniline as substrate, 2-hydroxyaniline accounted for 32.1% of the radioactivity after 2 h incubation whereas acetanilide amounted to 6 .4%. Significant differences were found between gill cells and isolated hep atocytes in the capacity of these systems to conduct oxidative and conjugat ing metabolic pathways. Qualitatively, the main difference was observed for testosterone which is hydroxylated in position 6 beta and 16 beta and conj ugated to glucuronic acid in liver cells, whereas reductive biotransformati on giving rise to dihydrotestosterone and androstanediol and traces of andr ostenedione were observed in gill cells. Quantitatively, the biotransformat ion activity in gill epithelial cells, expressed as pmol/h per mg protein, was between 1.5 and 14% of the activity level observed in isolated hepatocy tes, depending on the substrate. (C) 2000 Elsevier Science B.V. All rights reserved.