Formation and persistence of DNA adducts of 2-amino-3-methylimidazo[4,5-f] quinoline in male Fischer-344 rats.

The mutagenic heterocyclic amine 2-amino-3-methylimidazo[4,5-f] quinoline (IQ) is carcinogenic in the Fischer-344 rat, affecting the liver and small and large intestines, as well as several other organs. In male animals the incidences of tumors in the liver, small intestine, and large intestine were reported to be 67.5, 30.0, and 62.5%, respectively. Using 32P-postlabeling assays, the formation and persistence of IQ-DNA adducts in the liver and small and large intestines were studied in male Fischer-344 rats. Young, adult animals were either given a single p.o. dose (5, 25, or 50 mg/kg) of IQ and were killed 24 h later or were given a single p.o. or i.p. dose (50 mg/kg) of IQ and were killed at different time points, from 6 h to 31 days after p.o. treatment and from 6 h to 6 days after i.p. treatment, to follow adduct persistence. Up to five specific adducts could be isolated, and adduct formation was dose related in all three organs. Adduct 1, previously shown to be N-(hydroxyguanosin-8-yl)-IQ, was the major adduct in all cases, comprising up to 78% of the total. After p.o. administration (6-24 h) adduct levels in the liver were 3- to 4-fold higher than after i.p. administration, while levels in the intestines during this time period were independent of the route of administration. At 24 h after p.o. administration total adduct levels in the liver were 13.5-41.4 and 9.2-18.4 times higher than those in the small intestine and large intestine, respectively. Maximum adduct levels were observed between 6 and 24 h after administration, and from 1 to 6 days later, rates of removal from the liver were 7-fold and 2-fold slower, respectively, than from the small and large intestine. Rates of adduct removal from the intestines after i.p. administration were similar to those after p.o. administration. Beyond day 15 adduct levels in all organs constituted less than 12% of those on day 1, and low levels of adducts persisted for up to 31 days. In all cases there was no preferential loss or persistence of any of the adducts. It is concluded that total adduct levels and persistence in target organs may, in part, be related to susceptibility to IQ-induced carcinogenesis in the Fischer-344 rat.