Genotoxicity of various nitroarenes in DNA repair tests with human hepatocytes

Inhibition of dinitropyrene mutagenicity in vitro and in vivo using Salmonella typhimurium and the intrasanguinous host-mediated assay

Dinitropyrenes (DNP), present in polluted air, are potent direct-acting mutagens in Salmonella typhimurium TA98. This mutagenicity is markedly reduced in the presence of rat-liver S9 or microsomes. This has now been confirmed using mouse hepatic fractions. Since most in vitro test systems do not adequately simulate conditions encountered in the intact animal, we have investigated dinitropyrene mutagenicity to Salmonella in the host-mediated assay. 1,8-Dinitropyrene (1,8-DNP) given p.o. to BALB/c mice induced a weak mutagenic effect in S. typhimurium TA98 recovered from the liver 1 h after i.v. administration (optimum time). Over the entire dose range tested no toxicity to bacterial cells was detected. Mutation induction in vivo was dose-related with maximum response at 1 mg DNP/kg body weight. This optimum dose, however, was non-mutagenic to strains TA98/1,8-DNP6 (O-transacetylase-deficient) or TA98NR/1,8-DNP6 (nitroreductase- and O-transacetylase-deficient). 1,3-Dinitropyrene and 1,6-dinitropyrene were weakly mutagenic to TA98 at doses similar to 1,8-DNP. Studies with [14C]1,8-DNP showed that 1 h after oral dosing (1 mg/kg), over 100 ng of 1,8-DNP equivalents were present in the liver (= 0.73% dose). However, only about 5.5 ng were present in the bacterial pellet, suggesting that hepatic components in vivo, as in vitro, bind to DNP, thus interfering with its interaction with Salmonella.

The clastogenic activity of 1,6-dinitropyrene in peripheral human lymphocytes

The ability of 1,6-dinitropyrene to induce chromosome damage in peripheral human lymphocyte cultures has been demonstrated. Low levels of clastogenic activity were detected following 3-h treatments with 1,6-dinitropyrene in the presence of a rat-liver cytosol fraction. The clastogenic activity reached a peak at a concentration of 1.25 micrograms/ml of 1,6-dinitropyrene after which the frequency of aberrations decreased. This unusual genotoxic dose response is similar to that found previously in yeast and rat-liver cells. The fact that a positive result was obtained using human lymphocytes shows that, in the presence of the appropriate activation system, dinitropyrene is genotoxic in human cells.