The mutagenicity of 1-nitropyrene and its reduced metabolite 1-nitrosopyrene was determined in the lambda cI gene of an Escherichia coli uvr- lysogen. 1-Nitropyrene induced a mutation frequency of 3.8 x 10(-6), which was approximately 2-fold higher than the background mutation frequency, whereas an equimolar dose of 1-nitrosopyrene induced a much higher mutation frequency of 1.4 x 10(-4). Previous studies have established that both compounds form the same premutagenic lesion, viz. N-(deoxyguanosin-8-yl)-1-aminopyrene in bacterial DNA. In order to determine how this initial premutational lesion is converted to a stable heritable mutation, DNA sequences were determined for 30 mutations induced by 1-nitrosopyrene that mapped between bp 1 and 352 in the lambda cI gene of E.coli lysogens. We show here that these mutations are mainly frameshifts involving the addition or deletion of a single GC or CG base pair. A small proportion of mutations were base substitutions which were equally divided between transitions and transversions. These also occurred primarily at GC or CG sites.

[3H]1-Nitropyrene was administered at a dose of 25 mg/kg by i.p. injection to female Wistar rats. Animals were killed 24 h later and DNA was isolated from kidney, liver and mammary gland, enzymically hydrolysed and analysed by reverse-phase h.p.l.c. A major adduct peak was detected in DNA from each of the three organs. Enzymic hydrolysates of DNA, which had been reacted in vitro with 1-nitropyrene in the presence of xanthine oxidase, were similarly analysed by h.p.l.c. One major adduct peak was obtained which had the same retention time as the in vivo product. Confirmatory evidence that the in vivo adduct and the in vitro adduct were structurally similar was obtained from the determination of the pH-dependent solvent partitioning profiles. Further, treatment of the in vivo adduct from liver, kidney or mammary gland DNA hydrolysates and the in vitro adduct with sodium hydroxide resulted in the formation of a more polar product which eluted earlier on h.p.l.c. This behaviour is consistent with scission of the imidazole ring of a deoxyguanosine adduct. The major DNA adduct formed in vitro following xanthine oxidase reduction of 1-nitropyrene has previously been identified by others as N-(deoxyguanosin-8-yl)-1-aminopyrene. The present data suggest that the in vivo 1-nitropyrene-DNA adduct has the same structure.

Aflatoxin B1 (AFB1)-8,9-oxide, the proposed ultimate carcinogen is conjugated enzymically with glutathione (GSH) to give 8-(S-glutathionyl)-9-hydroxy-8,9-dihydro AFB1 (AFB1-SG). The GSH conjugate isolated from rat bile was shown, on the basis of 1H n.m.r. to be identical to AFB1-SG. Of the seven soluble rat liver GSH transferases tested, namely GSH transferases 1-1, 1-2, 2-2, 3-3, 3-4, 4-4 and 5-5 (see reference 1 for the new system of nomenclature), only the first three were active with microsomally generated AFB1-8,9-oxide, their rates of conjugation being 1.1, 0.61 and 0.64 nmol/min/mg enzyme, respectively. AFB1-SG is a thioacetal, but it was not formed from the incubation of the hemiacetal, AFB1-8,9-dihydrodiol, with GSH or GSH plus GSH transferase 1-1 plus 1-2. The covalent binding of in vitro microsomally activated AFB1 to DNA and the formation of AFB1-SG were linearly related to AFB1 concentration in the range of 0.2-2 micrograms/ml. DNA binding was decreased by 38% by the competing formation of AFB1-SG throughout this range of concentrations. These results are in accord with the observation of Scott Appleton et al. (Cancer Res., 42, 3659-3662) that, in the rat in vivo, there is no evident threshold for the binding of AFB1 to DNA. These findings are also consistent with the further observation, reported in this paper that GSH and GSH transferases have no effect on the mutagenicity of microsomally activated AFB1 to Salmonella typhimurium TA 100.

Snow and air particulate samples collected in Upper Frankonia, Federal Republic of Germany, have been analyzed for nitro-polycyclic aromatic hydrocarbons (PAH) and PAH content. A novel clean-up technique has been developed enabling interfering organochlorine environmental contaminants to be removed prior to analysis of the hydrocarbons by GC-MS. Mass fragmentation patterns are presented for 1-nitropyrene, 6-nitrobenzo(a)pyrene, 6-nitrochrysene, and 3-nitrofluoranthene. The level of these compounds found in air samples was in the range of 0.2-2.0 ng.m-3 with the exception of 6-nitrobenzo(a)pyrene, which was not detected. This compares with PAH values of between 1 and 6 ng.m-3. The freshly fallen snow sample collected at the side of a motorway had no detectable PAHs or nitro-PAHs. Parallel studies on the bacterial mutagenicity of the collected air samples using Salmonella typhimurium TA98 and TA100 in the presence and absence of aroclor-induced rat liver "S9" revealed both "direct" and "indirect" activity. Larger numbers of mutants were induced in the presence of S9 than in its absence. The snow sample was devoid of mutagenic activity. These studies show the utility of the biological approach to screen environmental samples prior to expensive and time-consuming chemical analysis.