CYP1A Induction by β-Naphthoflavone, Aroclor 1254, and 2,3,7,8-Tetrachlorodibenzo-p-dioxin and Its Influence on Aflatoxin B1Metabolism and DNA Adduction in Zebrafish (Danio rerio)

Abstract

This study investigated the inductive response of cytochrome P4501A (CYP1A) in the zebrafish (Danio rerio) following exposure to Aroclor 1254, β-naphthoflavone (βNF), and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and then investigated TCDD modulation of aflatoxin B1(AFB1) metabolism and hepatic AFB1–DNA adduction. Aroclor 1254 fed at 500 ppm for 1 to 9 days or intraperitoneal (ip) injection of 75–200 mg Aroclor 1254/kg body weight failed to induce CYP1A protein or associated 7-ethoxyresorufin-O-deethylase (EROD) activity. By contrast, dietary βNF at 500 ppm for 3 or 7 days induced CYP1A protein and EROD activity approximately threefold above controls. A single ip injection of 150 mg/kg βNF showed maximal induction of CYP1A protein and EROD activity near 24 hr, both of which decreased to control levels during the next 6 days. Single ip administration of 25, 50, 100, or 150 mg βNF/kg body weight provided dose-responsive increases in CYP1A and EROD activity. Dietary exposure to 0.75 ppm TCDD for 3 days also significantly induced CYP1A and EROD. The effect of TCDD on the metabolism of [3H]AFB1in zebrafish was then investigated. The major [3H]AFB1metabolites excreted in water over 24 hr in the control group were aflatoxicol, aflatoxicol-glucuronide, and parent AFB1. By contrast, the predominant metabolites in the TCDD-pretreated group were aflatoxicol-M1-glucuronide, aflatoxicol, aflatoxin M1plus aflatoxicol-M1(unresolved), aflatoxicol-glucuronide, and parent AFB1. Surprisingly, hepatic AFB1–DNA adduction was approximately fourfold higher in the TCDD treated group than in controls. This significant difference could not be explained by increased capacity for bioactivation of AFB1as measured by anin vitroAFB1-exo-8,9-epoxide trapping assay. However, it was demonstrated that both control and induced zebrafish have high capacity to bioactivate aflatoxin M1to a reactive intermediate, such that secondary bioactivation of this genotoxic intermediate may be responsible for the increased DNA binding.