Covalent binding of components of coal-tar, creosote and bitumen to the DNA of the skin and lungs of mice following topical application.
In order to assess the DNA damaging ability of complex carcinogenic mixtures, male Parkes mice were treated topically with solutions of (i) pharmaceutical coal-tar, (ii) creosote, a blend of coal-tar fractions or (iii) bitumen, a product of oil-refining. DNA was isolated from the treated skin and analysed by 32P-post-labelling. A band of radioactivity was obtained on polyethyleneimine--cellulose TLC indicating the formation of DNA adducts by a large number of different chemical compounds present in these fossil fuel products. The chromatographic properties of the adducts were broadly characteristic of those formed by polycyclic aromatic hydrocarbons. The levels of DNA binding were approximately 0.4 fmol total adducts/micrograms DNA 24 h after treatment for coal-tar and creosote and 0.09 fmol/micrograms DNA for bitumen treatment. The persistence of adducts in mouse skin following a single dose of either coal-tar or creosote was found to exhibit a phase of rapid removal, in which one half to two thirds of the initial levels of adducts, detected at 24 h after treatment, were removed by 7 days followed by a second phase in which one half to two thirds of the remainder was removed in the succeeding 25 days. When mice were treated topically with multiple carcinogenic doses of coal-tar, creosote or bitumen for up to 5 weeks, a steady accumulation of adducts was seen in skin DNA during the course of the treatment, approaching a steady-state level towards the end of the treatment period in some instances. A similar accumulation of adducts was also evident in lung DNA, the levels being approximately half those attained in skin. The results demonstrate the application of 32P-post-labelling to the detection of DNA adducts formed in vivo by complex carcinogenic mixtures of the type to which humans are exposed.