Formation and persistence of safrole-DNA adducts over a 10,000-fold dose range in mouse liver

The spice constituent safrole (1-allyl-3,4-methylenedioxybenzene) and related allylbenzenes form DNA adducts and are rodent carcinogens. This study examined both dose and time dependence of hepatic safrole-DNA adduct formation over a 10,000-fold dose range up to 30 days after single administration. Female CD-1 mice were treated with safrole i.p. at 0.001, 0.01, 0.1, 1.0, and 10.0 mg/mouse in 0.2 ml tricaprylin or with vehicle alone. Liver DNA was analyzed at 0.5, 1, 2, 3, 7, 15 and 30 days via the dinucleotide/monophosphate version of the 32P-postlabeling assay. An approximately 10-fold increase in total safrole adduct levels with each successive 10-fold increase in dose was observed, giving relative adduct labeling (RAL) values of 10(-9)-10(-5). Each dose elicited identical kinetics of adduct formation, showing peak levels at 2 days and only slight decreases thereafter. The time course of adduct persistence was independent of the dose (0.01-10 mg/mouse). An in vitro experiment established that the assay responded in strictly linear fashion to adduct concentration over a 10,000-fold range, and thus was suitable for in vivo dosimetry. DNA synthesis, as measured by [3H]thymidine incorporation, was enhanced only for the 10.0 mg dose at 2, 3 and 7 days. These results indicate a linear response of safrole-DNA adduct formation and persistence in mouse liver following administration of minute (0.001 mg/mouse) to high (10.0 mg/mouse) doses of the carcinogen.