Induction of cytochrome P450 1A and DNA damage in isolated rainbow trout (Oncorhynchus mykiss) hepatocytes by 2,3,7,8-tetrachlorodibenzo-p-dioxin

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on hepatocytes isolat ed from immature rainbow trout (Oncorhynchus mykiss) by collagenase perfusi on vc ere investigated with respect to induction of cytochrome P450 1A (CYP 1A) enzyme activities and protein contents as well as DNA damage. Exposure of primary rainbow trout hepatocytes to TCDD resulted in increased CYP1A co ntents, as determined by immunoblotting enhanced activities of 7-ethoxyreso rufin-O-deethylase (EROD) and increased DNA damage as determined by the com et assay. By means of electron microscopy, no symptoms of cytotoxicity coul d be observed except for slight increases of lysosomal components and the s mooth endoplasmic reticulum. Whereas CYP1A contents constantly increased ov er the duration of the entire experiment, EROD activities remained constant from day 3 of exposure to 1 nM TCDD; maximum induction of CYP1A activities was reached with 0.1 nM TCDD after 5 days. DNA damage increased in a time- and dose-dependent fashion until day 3. After 5 days, DNA damage was less pronounced, and the number of damaged nuclei declined in all TCDD concentra tions. Since TCDD has been shown to not directly react with DNA, metabolism of TCDD or TCDD-induced changes in other metabolic pathways are suspected to result in the production of DNA-reactive (endogenous) substances.