Comparison of hydrocarbon-DNA adducts formed in mouse skin in vivo and in organ culture in vitro following treatment with benzo[a]pyrene.
Species differences in the metabolism of toxic chemicals can confound the extrapolation of experimentally determined risk data to man. However, it is often difficult to obtain reliable information on human metabolism, particularly of genotoxic agents. In this study, comparisons of chromatographic profiles of DNA adducts formed in vivo and in vitro have been applied to develop and validate in vitro systems as models for the bioactivation of precursor genotoxic agents in vivo. Reversed phase h.p.l.c. analysis showed that the DNA adducts obtained from the skin (epidermal and dermal) of mice (CD1, CF1 and athymic nude mice) treated topically with [3H] or [14C]benzo[a]pyrene (BP) were qualitatively very similar to those formed in mouse (CD1) skin explant cultures. In each case the principal product was the N2-deoxyguanosine adduct, (+)-N2-(7R,8S,9R-trihydroxy-7,8,9,10-tetrahydrobenzo[a]-pyrene-10S- yl)-2'-deoxyguanosine, derived from (+)-7R,8S-dihydroxy-9R,10R-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene. The use of [14C]BP has provided an accurate reference profile of BP-DNA adducts formed in mouse skin in vivo. These findings show that mouse skin explants maintained in organ culture effectively mimic the bioactivation of BP and the binding of the products to the DNA of mouse skin in vivo. Such culture techniques are readily transferable to human skin thus permitting the indirect determination of bioactivation pathways in human skin in vivo for comparison with those of mouse skin and other models used to determine the human hazard. In principle, this approach to validate in vitro bioactivation systems may be applied to all human tissues.