A comparison of the dose and time response of CYP1A1 mRNA induction in chemically treated Atlantic tomcod from two populations

Quantification of cytochrome P4501A1 (CYP1A1) mRNA levels in environmentall y exposed Atlantic tomcod (Microgadus tomcod) has revealed significantly in duced gene expression in fish from contaminated locales including the Hudso n River, New York, and the Miramichi River, New Brunswick. In order to cali brate this response, determine its sensitivity and dose-responsiveness, lev els of hepatic CYP1A1 mRNA were quantified in depurated Atlantic tomcod int raperitoneally (i.p.) injected with various concentrations of: beta-naphtho flavone (beta-NF), the PAH benzo[a]pyrene (B[a]P), the non-ortho coplanar P CB congener-3,3',4,4'- tetrachlorobiphenyl (IUPAC: PCB-77), and the dioxin 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). Additionally, the rates of CYP1A1 mRNA induction and disappearance were quantified in depurated At lantic tomcod i.p. injected with single doses of these chemicals and sacrif iced at times ranging up to 72 days. Levels of CYP1A1 mRNA were dose-respon sive for all four chemicals with maximum induction ranging from 50- to 460- fold and first significant induction being observed in the low mg per kg fi sh (wet weight) range for beta-NF and B[a]P, mu g/kg range for PCB-77 and n g/kg range for 2,3,7,8-TCDD. However, while tomcod from the Miramichi River responded to both PAHs and halogenated aromatic hydrocarbons (HAHs), Hudso n River tomcod responded only to PAHs indicating population level differenc es in CYP1A1 mRNA inducibility in tomcod. Furthermore, differences in the r esponsiveness to PAHs and HAHs suggest that more than one molecular mechani sm mediates CYP1A1 transcription in Atlantic tomcod. Kinetic profiles of CY P1A1 mRNA induction differed greatly between tomcod treated with HAHs and P AHs. Initial induction occurred within hours of treatment with PAHs and pea ked after 1-3 days, compared to initial induction 4-7 days after treatment with HAHs, and maximum induction not occuring for up to 72 days after expos ure. Quantification of halogenated aromatic hydrocarbons (HAH) in the liver s of tomcod caught in the Hudson and Miramichi Rivers confirmed exposure an d accumulation of known CYP1A1 inducing chemicals including 2,3,7,8-TCDD at concentrations as high as 1.5 mu g/kg lipid (554 ng/kg w.w.) and PCB-77 at concentrations as high as 108 mu g/kg lipid (15 mu g/kg w.w.). These resul ts suggest that hepatic CYP1A1 mRNA concentration can be a useful bioindica tor of exposure to some aromatic hydrocarbon compounds in the aquatic envir onment and that profiles of gene induction and disappearance may help ident ify environmental inducers provided that gene responsiveness is also evalua ted under controlled laboratory conditions. (C) 1999 Elsevier Science B.V. All rights reserved.