In vitro genotoxicity testing of (1-chloroethenyl)oxirane, a metabolite ofbeta-chloroprene

(1-Chloroethenyl)oxirane (CEO) is a metabolite of beta -chloroprene (2-chlo ro-1,3-butadiene, CD). The purpose of this study was to evaluate the in vit ro mutagenic and clastogenic (chromosome breaking) potential of CEO. For co mparative purposes, the study also included an evaluation of the racemic co mpounds, 3,4-epoxy-1-butene (EB) and 1,2:3,4-diepoxybutane (DEB). Mutagenic ity was evaluated in a bacterial reverse mutation test (Ames), using the pr e-incubation method in the presence and absence of an exogenous metabolism system (Aroclor(R)-induced rat liver S9). Four Salmonella typhimurium teste r strains, TA97a, TA98, TA100 and TA1535 were used. The exposure concentrat ions in the sealed incubation vials ranged from 0 to 69 mM for CEO, 0 to 10 2 mM for EB, and 0 to 83 mM for DEB. All three compounds showed signs of to xicity, with DEB being substantially more toxic than either CEO or EB. Muta genic activity was observed with all three chemicals in primarily the base pair substitution strains (S. typhimurium TA100 and TA1535), but some activ ity was also seen in the frameshift elimination strains (S. typhimurium TA9 7a and TA98). The observed mutagenic responses after exposure with CEO or E B were greater than the observed response for DEB, most likely because of t he higher toxicity of DEB. Generally, the mutagenic responses were unchange d in the frameshift strains and base pair substitution strains in the prese nce of S9 metabolism. In vitro clastogenicity was evaluated using the cytoc halasin-B blocked micronucleus test in cultured Chinese hamster V79 cells. The test was conducted without S9 metabolism because of the absence of subs tantial changes in the Ames test. Exposure concentrations ranged from 0 to 0.943 mM for CEO, 0 to 3.0 mM for EB, and 0 to 0.035 mM for DEB, with the u pper exposure concentrations dictated by cytotoxicity. Cytotoxicity, measur ed as a reduction in the proportion of binucleated cells and altered cell m orphology, was observed for CEO at concentrations greater than or equal to0 .175 mM. Exposure to EB led to a reduced proportion of binucleated cells at concentrations greater than or equal to2.0 mM, and cell death was observed after DEB exposure at concentrations greater than or equal to0.025 mM. No clastogenicity was observed in the V79 cells when tested up to cytotoxic: c oncentrations of CEO, whereas an elevated frequency of micronuclei was obse rved after exposure to either EB (greater than or equal to 1.0 mM) or DEB ( greater than or equal to 0.0125 mM). These results suggest that CEO-induced mutagenicity, but not clastogenicity, may contribute to the observed P-chl oroprene-induced carcinogenicity in the rodent bioassay studies. (C) 2001 E lsevier Science Ireland Ltd. All rights reserved.