N-heterocyclic aromatics are environmentally important pollutants, however, little is known of their mechanism of action or biological effects. The objective is to investigate the metabolic activation of 7H-dibenz(c,g)carbazole (DBC) which is a potent carcinogen in mouse lung, liver, and skin, with respect to dibenz(a,j)acridine (DBA) a moderate to weak carcinogen in mouse lung and skin. Since the structural difference between the well characterized polycyclic aromatic hydrocarbons and the N-heterocyclic analogs is the existence of a nitrogen atom in the aromatic ring system of the latter, it is hypothesized that any differences in metabolism, metabolic activation, DNA binding, or carcinogenic potency is due not only to the presence of a nitrogen atom but to the aromaticity of the heteroatom containing ring.
The specific aims i nvolve the characterization of the metabolic activation and DNA binding of DBC and DBA in mouse skin and liver as follows: 1) determine the modulation of metabolism of DBC and DBA incubated with liver preparations using a variety of inducing agents, 2) determine the modulation of DNA binding of DBC and DBA with induced liver preparations, 3) determine the modulation of metabolism of DBC and DBA with induced skin preparations, 4) characterize the covalent binding of selected metabolites of DBC and DBA to DNA in vitro with liver preparations, 5) characterize the covalent binding of DBC and DBA to DNA in skin and liver in vivo and 6) undertake chronic dose response carcinogenicity studies for DBC and DBA relative to benzo(a)pyrene and mixtures thereof. Phenobarbital, Aroclor 1254, DBC, DBA and 3-methylcholanthrene will be used for enzyme induction and subcellular liver and skin fractions will be prepared. Metabolism of DBC and DBA will be analyzed by HPLC and alumina column chromatography. In vitro DNA binding and DNA adducts (as standards) will be analyzed by radiometry, HPLC, and analytical techniques. In vivo studies will involve the development of finger prints of DNA adducts using (32)P-postlabeling techniques and dephosphorylation of the adducts for comparison with in vitro adducts. Lastly, analysis of the biological responses of mixtures will determine whether additive, synergistic or inhibitory effects are involved. This approach will provide valuable information concerning the disposition of an important class of carcinogens and will lead to a better understanding of the mechanism(s) of action of N-heterocyclic aromatic carcinogenesis.
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