DEPURINATING AND STABLE BENZO[A]PYRENE-DNA ADDUCTS FORMED IN ISOLATEDRAT-LIVER NUCLEI

Polycyclic aromatic hydrocarbons are bound to DNA by two major pathway s, one-electron oxidation and monooxygenation, to form adducts that ar e stable in DNA under normal conditions of isolation and depurinating adducts that are released from DNA by cleavage of the bond between the purine base and deoxyribose. Isolated rat liver nuclei have been used as an in vitro model for studying covalent binding of aromatic hydroc arbons to DNA, but the depurinating adducts formed by nuclei have not been identified or compared to those formed by the more commonly used rat liver microsomes. To examine the profiles of stable and depurinati ng adducts, nuclei from the livers of 3-methylcholanthrene-induced mal e MRC Wistar rats were incubated with [H-3]benzo[a]pyrene (BP) and NAD PH. Three depurinating adducts, 8-(BP-6-yl)Gua, 7-(BP-6-yl)Gua, and 7- (BP-6-yl)Ade, were obtained from the nuclei, as seen previously with r at liver microsomes or in mouse skin. The profile of stable adducts an alyzed by the P-32-postlabeling method was qualitatively similar to th at found in the microsomal activation of BP or in mouse skin treated w ith BP. Low-temperature fluorescence studies of the nuclear DNA reveal ed the presence of stable BP adducts originating from syn- and anti-BP diol epoxide.