Micronuclei and gene mutations in transgenic Big Blue® mouse and rat fibroblasts after exposure to the epoxide metabolites of 1,3-butadiene

1,3-Butadiene (BD) is a commodity compound and by-product in the manufacture of synthetic rubber that elicits a differential carcinogenic response in rodents after chronic exposure. Mice are up to approximately 1000-fold more sensitive to the tumorigenicity of inhaled ED than rats, thereby confounding human risk assessment analyses. Rodent transgenic in vivo and in vitro models have been recently utilized for generating genetic toxicology data in support of risk assessment studies. However, studies have not been extended to investigate multiple endpoints of genetic damage using in vitro transgenic models. The goal of this study was to evaluate possible differences in the production of genetic damage in transgenic Big Blue(R) mouse IBBM1) and rat (BBR1) fibroblasts exposed to three predominant epoxide metabolites of ED. Analyses of cytotoxicity, micronucleus (MN) formation, cll mutant frequency (MF) and apoptosis were assessed after in vitro exposure of BBM1 and BBR1 cells exposed to various concentrations of butadiene monoepoxide (BMO), diepoxybutane (DEB) and butadiene diolepoxide (BDE). Both BMO and DEB reduced cell survival in BBM1 and BBR1 cells. However, BDE decreased cell survival only in BBM1 cells at the concentrations evaluated. Concentration-dependent increases in the formation of MN was observed in both BBM1 and BBR1 cells, with DEB being the most potent followed by BDE and then BMO. The dose-response for mutations induced at the cll locus was essentially equal after DEB exposure of BBM 1 and BBR1 fibroblasts. In contrast, the cll MF was significantly increased only in BBM1 cells after exposure to either BMO or BDE. These data demonstrate a differential genetic response for gene mutations but not for MN formation in transgenic BBM1 and BBR1 fibroblasts and suggest a rodent species-specific difference in the persistence of DNA damage that results in gene mutations. In addition, apoptosis was observed in BBR1 cells but not in BBM1 cells when treated with any of the three ED epoxide metabolites. This response may partially explain the differential response to mutations induced by BMO and BDE. These data offer insight into specific differences in mouse and rat cells with respect to their response to ED epoxide metabolites. Such data may help to explain the different tumorigenicity results observed in rodent ED carcinogenicity studies. (C) 2000 Elsevier Science B.V. All rights reserved.