Inhibition of CYP1A1-Dependent Activity by the Polynuclear Aromatic Hydrocarbon (PAH) Fluoranthene

• Published in: Biochemical pharmacology Vol. 55; no. 6; pp. 831 - 839
• Main Authors: Willett, Kristine L, Randerath, Kurt, Zhou, Guo-Dong, Safe, Stephen H
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 15.03.1998; Elsevier Science
• Subjects: Ah receptor; Animals; Biological and medical sciences; Biological Assay; Carcinogenesis, carcinogens and anticarcinogens; Chemical agents; Chemical and industrial products toxicology. Toxic occupational diseases; CYP1A1; Cytochrome P-450 CYP1A1 - antagonists & inhibitors; Cytochrome P-450 CYP1A1 - biosynthesis; DNA adducts; DNA Adducts - isolation & purification; DNA, Neoplasm - isolation & purification; Enzyme Induction; Enzyme Inhibitors - pharmacology; Female; fluoranthene; Fluorenes - pharmacology; H4IIE cells; Linear Models; Medical sciences; Microsomes, Liver - enzymology; PAHs; Rats; Rats, Sprague-Dawley; Toxicology; Tumor Cells, Cultured; Tumors; Various organic compounds; H4IIE cells; CYP1A1; Ah receptor; PAHs; fluoranthene; DNA adducts; Rat; Digestive system; Toxicity; Cytochrome P450; Liver; Rodentia; Enzyme inhibitor; Microsome; Halocarbon; Carcinogen; Vertebrata; Mammalia; Animal; DNA; Fluoranthene
• ISSN: 0006-2952; 1873-2968
• DOI: 10.1016/S0006-2952(97)00561-3

Polynuclear aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants, and recently bioassay-based induction studies have been used to determine exposures to complex mixtures of PAHs. Induction of CYP1A1-dependent activity in H4IIE rat hepatoma cells has been used extensively as a bioassay for halogenated aromatic hydrocarbons and more recently for PAHs. Fluoranthene (FL) is a prevalent PAH contaminant in diverse environmental samples, and FL did not induce CYP1A1-dependent ethoxyresorufin O-deethylase (EROD) activity significantly in H4IIE cells. However, in cells cotreated with 2 × 10 −5 M FL plus the potent inducers 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) or benzo[ k]fluoranthene (BkF) (2 × 10 −8 M), there was a significant decrease in EROD activities. Furthermore, treatment of TCDD-induced rat microsomes with FL caused an 80% decrease in EROD activity. Studies showed that FL did not affect induction of CYP1A1 protein or mRNA levels in H4IIE cells, and analysis of enzyme inhibition data using microsomal CYP1A1 indicated that FL noncompetitively inhibited CYP1A1-dependent activity. 32P-Postlabeling revealed no significant FL–DNA adduct formation in H4IIE cells treated with FL. However, in cells cotreated with FL plus BkF or benzo[ a]pyrene (BaP), certain PAH–DNA adducts were induced 2-fold. This study demonstrated that FL is an inhibitor of CYP1A1-dependent enzyme activity in rat hepatoma H4IIE cells and that the genotoxic potency of some carcinogenic PAHs may be modulated by FL in mixtures containing relatively high levels of this compound.