The different genotoxicity of p-dichlorobenzene in mouse and rat: measurement of the in vivo and in vitro covalent interaction with nucleic acids.

Twenty-two hours after i.p. injection to male Wistar rats and BALB/c mice para-dichlorobenzene (p-DCB) is bound covalently to DNA from liver, kidney, lung and stomach of mice but not of rats. DNA adducts in mouse liver are repaired in seventy-two hours. The covalent binding index value, calculated on the labelling of mouse liver DNA, classifies p-DCB as a weak initiator with an oncogenic activity lower than that of chlorobenzene. The labelling of RNA and proteins from the different organs of both species is, however, low. In vitro interaction with calf thymus DNA mediated by mouse and rat microsomes from liver and lung did occur. Binding extent was strongly reduced by addition of 2-diethylaminoethyl-2,2-diphenylvalerate hydrochloride (SKF 525-A) to the microsomal standard incubation mixture, whereas it was enhanced by adding GSH. Cytosolic fractions from kidney and lung were able to induce binding of p-DCB to DNA to a lower extent with respect to microsome-mediated binding. These results indicate that microsomal mixed function oxidase system and microsomal GSH-transferases can be involved in overall activating metabolism whereas cytosolic GSH-transferases play a minor role. This study, which is a part of a structure-activity relationship approach on benzene and its haloderivatives, provides the first evidence of genotoxicity of p-DCB in mammalian cell. It allows to partly explain variations of susceptibility of different species to hepatocarcinogenesis and of hepatotoxicity of different isomers.