Comparative metabolism of dibenz[a,j]anthracene and 7-methyldibenz[a,j]anthracene in primary cultures of mouse keratinocytes.

The identification of several metabolites formed from dibenz[aj]anthracene (DB[aj]A) and 7-methyldibenz[aj]anthracene (7MeDB[aj]A) in primary cultures of mouse keratinocytes is presented. The metabolites were analyzed by coelution with known synthetic standards using high-pressure liquid chromatography. The metabolite identifications were further facilitated by comparisons of fluorescence excitation and emission spectra obtained for isolated metabolites with those for the synthetic standards. Both DB[aj]A and its 7-methyl analog were converted by mouse keratinocytes to the corresponding 3,4- as well as 5,6-dihydrodiols. The 5,6-dihydrodiol of DB[aj]A was the major intracellular metabolite found at all time points up to 24 h. By 48 h, the relative proportion of both intracellular dihydrodiols had decreased, and they were found in approximately equal proportions. In contrast, 7MeDB[aj]A-3,4- dihydrodiol was the major intracellular metabolite of 7MeDB[aj]A at all time points examined up to 48 h. The decreased intracellular retention of DB[aj]A-3,4-dihydrodiol was due, in part, to glucuronide conjugation and subsequent excretion of this metabolite. In this regard, both the 3,4- as well as the 5,6-dihydrodiols of DB[aj]A were found as glucuronides in the extracellular medium, whereas no such conjugates were detected extracellularly in cultures exposed to the 7-methyl derivative. The chromatographic profiles of cell- and medium-associated metabolites from both hydrocarbons also exhibited several other metabolite peaks that remain to be identified. The observed differences in dihydrodiol metabolism by mouse keratinocytes could explain, in part, the greater biological activity of 7MeDB[aj]A relative to DB[aj]A.