Dosimetry of PAH skin carcinogenesis: covalent binding of benzo[a]pyrene to mouse epidermal DNA.

Benzo[a]pyrene (BaP) is metabolized to the chemically reactive anti and syn isomers of the 7,8-diol-9,10-epoxides of BaP (BPDE) which bind covalently to DNA to form DNA/BPDE complexes. Tetrols liberated from the DNA/BPDE complex by acid hydrolysis are easily quantified by h.p.l.c. using fluorescence detection. This approach allows femtomole amounts of BPDE associated with the DNA isolated from a single mouse to be detected using conventional instrumentation. The usefulness of this technique to estimate the interaction of BaP with DNA of mouse skin, both in the intact animal and in organ culture, was investigated. With mouse skin in organ culture it could be demonstrated that: (i) upon a single topical application of 5 micrograms of BaP, binding to DNA occurred via BPDE at a linear rate for up to 65 h, (ii) the amount of binding was dose dependent at concentrations of BaP less than 10 micrograms.