1,3-butadiene: cancer, mutations, and adducts. Part II: Roles of two metabolites of 1,3-butadiene in mediating its in vivo genotoxicity.
1,3-Butadiene (BD) is carcinogenic in mice and rats, with mice being more susceptible than rats to its carcinogenic effects. 1,3-Butadiene is mutagenic in the bone marrow and spleen cells of B6C3F1 lacI transgenic mice. The goal of this research was to assess the roles of two BD metabolites, 1,2-epoxy-3-butene (BDO) and 1,2,3,4-diepoxybutane (BDO2), in the mutagenicity and mutational spectrum of the parent compound BD by determining the mutagenicity and mutational spectra of BDO and BDO2 in human and rodent cells in vitro and in vivo. In human TK6 lymphoblastoid cells (TK6 cells), BDO exposure increased the frequency of G.C-->A.T transitions and A.T-->T.A transversions (Fisher exact test; p < 0.05). The most striking difference in the type of base-substitution mutations between BDO-exposed and BDO-unexposed TK6 cells was the 19-fold increase in A.T-->T.A transversions. 1,2,3,4-Diepoxybutane increased the frequency of A.T-->T.A transversions (Fisher exact test; p < 0.05) and the frequency of deletions in exposed TK6 cells compared with unexposed controls. Exposure of Rat2 lacI transgenic fibroblasts (Rat2 cells) to BDO increased the frequency of three types of base-substitution mutations: G.C-->A.T transitions, G.C-->T.A transversions, and A.T-->T.A transversions. Exposure of Rat2 cells to BDO2-induced dose-dependent increases in micronuclei at exposure levels that apparently did not induce mutagenicity at the lacI transgene. The lack of detectable mutagenicity at the lacI transgene in Rat2 cells exposed to BDO2 probably reflects the poor recovery of large deletions by this lambda phage-based mutagenicity assay. Inhalation exposure of B6C3F1 lacI transgenic mice (lacI mice) and F344 lacI transgenic rats (lacI rats) to BDO (29.9 parts per million [ppm]; 6 hours/day; 5 days/week for 2 weeks) did not increase the lacI mutant frequency (MF) in bone marrow or spleen cells of mice and rats, but in the cells of mouse lung (a tumor target organ for BD), significant mutagenicity was observed. An increased lacI MF was also observed in the bone marrow cells of rats exposed to BDO. Inhalation exposure of lacI mice and lacI rats to BDO2 (3.8 ppm; 6 hours/day; 5 days/week for 2 weeks) did not increase the lacI MF in bone marrow or spleen cells of mice or in the spleen cells of rats. An increased lacI MF was observed in the bone marrow cells of rats exposed to BDO2. In the present study, BDO specifically induced G.C-->A.T and A.T-->T.A transversions in vitro at both the endogenous hypoxanthine phosphoribosyltransferase (hprt) gene and the lacI transgene in Rat2 cells. It also induced an increased frequency of G.C-->T.A transversions in Rat2 cells. These types of mutations also occur at an increased frequency in mice exposed to the parent compound, BD. This finding demonstrates the induction of consistent mutational types across biological systems by BDO and indicates that BDO, but not BDO2, probably has a role in mediating the mutations recovered at the lacI transgene in animals exposed to the parent compound, BD. Therefore, it is apparent that in mice exposed to BD at carcinogenic levels, BDO and BDO2 act in concert to mediate the range of genotoxic responses. These data demonstrate that certain DNA adducts (guanine or adenine) may be useful biomarkers for BD genetic effects. However, other DNA lesions that can account for BDO2-induced deletions and chromosomal alterations also need to be considered as biomarkers for BD-induced genotoxicity.
Chemical Industry Institute of Toxicology, Research Triangle Park, NC 27709-2137, USA.
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D000818:Animals; D030801:Animals, Genetically Modified; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D002070:Butadienes / Q000378:metabolism / Q000633:toxicity*; D002273:Carcinogens / Q000378:metabolism / Q000633:toxicity; D004247:DNA; D018736:DNA Adducts; D004252:DNA Mutational Analysis; D029968:Escherichia coli Proteins; D006801:Humans; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics; D056968:Lac Repressors; D051379:Mice; D009152:Mutagenicity Tests; D009153:Mutagens / Q000378:metabolism / Q000633:toxicity*; D009154:Mutation; D009374:Neoplasms, Experimental / Q000139:chemically induced*; D051381:Rats; D011916:Rats, Inbred F344; D012097:Repressor Proteins / Q000235:genetics
D001426:Bacterial Proteins; D002070:Butadienes; D002273:Carcinogens; D018736:DNA Adducts; D029968:Escherichia coli Proteins; D056968:Lac Repressors; D009153:Mutagens; D012097:Repressor Proteins; D004247:DNA; D007041:Hypoxanthine Phosphoribosyltransferase; C031763:1,3-butadiene