Coal tar residues produce both DNA adducts and oxidative DNA damage in human mammary epithelial cells

In the present study we compare the metabolic activation of coal tar, as measured by the production of both DNA adducts and oxidative DNA damage, with that of a single carcinogen that is a constituent of this complex mixture in human mammary epithelial cells (HMEC). We find that a significant level of DNA adducts, detected by 32P-postlabeling, are formed in HMEC following exposure to coal tar residues. This treatment also results in the generation of high levels of oxidative DNA damage, as measured by the production of one type of oxidative base modification, thymine glycols. The amounts of both DNA adducts and thymine varied considerably between the various coal tar residues and did not correlate with either the total amount of polycyclic aromatic hydrocarbons (PAH) or the amount of benzo[a]pyrene (B[a]P) present in the residue. Fractionating the residue from one of the sites by sequential extraction with organic solvents indicated that while the ability to produce both types of DNA damage was contained mostly in a hexane-soluble fraction, a benzene-soluble fraction produced high levels of reactive oxygens relative to the number of total DNA adducts. We find that the total amount of PAH or B[a]P present in the coal tars from the various sites was not a predictor of the level of total DNA damage formed.