32P-postlabelling in studies of polycyclic aromatic hydrocarbon activation

Polycyclic aromatic hydrocarbons (PAHs) undergo metabolic activation reactions to yield intermediates that react with DNA to form covalent adducts. PAH administration leads to the formation of various types of DNA adducts that may differ between species, strains and tissues due to differences in metabolic activation and repair. The structures of PAH-DNA adducts can be identified by three approaches: co-chromatography with synthetic mononucleotide adduct standards; examining the adducts resulting from metabolism of pathway intermediates; or chemically blocking metabolic activation at specific sites on the PAH. Administration of putative metabolic intermediates of a PAH leads to enhanced formation of DNA adducts resulting from further activation along that pathway. Conversely, chemically blocking a bond or position on a PAH prevents adducts arising from activation at that site. By comparing the DNA adduct spectra generated by metabolites, blocked forms, and parent PAH administration, the pathways important in the metabolic activation of the PAH in each tissue may be deduced. Partial identification of these adducts may also be made by co-chromatography with the products of reactions between synthetic reactive intermediates and defined polydeoxynucleotides, and more thorough identification by using synthetic DNA adduct standards. These approaches have all been successfully applied to studies of PAH activation, and are reviewed here.