Toxicological Sciences 57, 217-228 (2000)
Copyright © 2000 by the Society of Toxicology
Carcinogenicity |
Influence of ß-Naphthoflavone on 7,12-Dimethylbenz(a)anthracene Metabolism, DNA Adduction, and Tumorigenicity in Rainbow Trout
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* Department of Pharmacology and Toxicology, West Virginia University, Morgantown, West Virginia 26506;
Department of Environmental and Molecular Toxicology, Oregon State University, Corvallis, Oregon 97331;
Environmental Toxicology Center, Department of Pharmacology, University of Wisconsin, Madison, Wisconsin 53705;
§ Department of Biochemistry, West Virginia University, Morgantown, West Virginia 26506;
¶ CDC/NIOSH, Health Effects Laboratory Division, Physiology Pathology Research Branch, Morgantown, West Virginia 26505; and
|| Environmental Health Sciences Center, Oregon State University, Corvallis, Oregon 97331
Metabolism, DNA adduction, and tumor induction by 7,12-dimethylbenz(a)anthracene (DMBA) were examined in cultured trout liver cells and in vivo in trout. Modulating CYP1A1 activity indicated this enzyme plays a significant role in metabolizing DMBA to water-soluble compounds in isolated trout liver cells. The major DMBA metabolites identified in trout liver cells were 10-, 11-, 8,9-, and 5,6-DMBA dihydrodiols, and DMBA, 2- or 3- or 4-phenol; 7-OH-methyl-12-methyl-benz(a)anthracene and 12-OH-methyl-7-methyl-benz(a)anthracene were minor metabolites. A very small amount of DMBA-3,4-dihydrodiol was detected, and polar metabolites, which did not migrate with any DMBA metabolite standards, were observed. Incubating trout hepatocytes with DMBA-3,4-dihydrodiol produced three prominent, nonpolar adducts indistinguishable from those in mouse embryo cells. However, DMBA-DNA adducts, formed in trout in vivo or in trout liver cells exposed to DMBA, were predominantly more polar than those formed in mouse embryo fibroblasts, and levels of DMBA-DNA adducts formed in trout liver cells were not significantly altered by modulating CYP1A1 activity. No significant repair of DMBA-DNA adducts was detected in cultured trout liver cells over a 48-h period, supporting previous studies indicating that fish are less efficient than mammals in repairing polyaromatic hydrocarbon DNA adducts. Compared to animals receiving DMBA alone, ß-naphthoflavone pretreatment in vivo did not affect hepatic CYP1A1, DMBA-DNA adducts, nor hepatic tumor response; but did significantly reduce tumor response in two other target organs. These results collectively indicate that DMBA bioactivation to DNA-binding metabolites in trout liver cells and mouse embryo cells predominantly involve different metabolic pathways to form the DNA-binding intermediates.
Key Words: 7,12-dimethylbenz(a)anthracene; trout; liver cells; CYP1A1; DNA adducts.