Mutation spectrum of 1,2-dibromo-3-chloropropane, an endocrine disruptor, in the lacI transgenic Big Blue Rat2 fibroblast cell line

Abstract

1,2-Dibromo-3-chloropropane (DBCP), a soil fumigant against nematodes, has been extensively studied for genotoxicity, carcinogenicity and damage to male reproduction-related organs, as a possible endocrine disruptor. However, the precise mechanisms involved in DBCP-induced mutagenesis and carcinogenesis are as yet unknown. Thus, in this study the mutagenicity and mutation spectrum of DBCP was determined using the lacI transgenic Big Blue Rat2 fibroblast cell line. In determining the optimal concentration of DBCP in Big Blue Rat2 fibroblast cells, the 50% inhibition concentration was calculated to be 0.75 mM. When cells were exposed to DBCP concentrations of 0.21, 0.39 and 0.75 mM, the respective relative survival rates were similar to80, 70 and 50%. The mean mutant frequencies (MFs) (x 10(-5), +/- SEM) of the medium and 1% DMSO solvent controls were determined as 6.43 +/- 0.616 and 5.28 +/- 1.086, respectively. The MFs (x 10(-5), +/- SEM) of cells exposed to 0.21, 0.39 and 0.75 mM DBCP were 8.09 +/- 1.02, 10.86 +/- 2.17 and 12.26 +/- 0.79, respectively, with a dose-dependent effect (ANOVA, P = 0.007). Moreover, MF values for the 0.75 and 0.39 mM DBCP-treated groups were statistically significant (ANOVA, P < 0.05). The majority of recovered mutations (31/40, 77.5%) were single base pair substitutions in the DBCP-induced groups. Among 31 single base pair substitutions, 25 (62.5%) occurred at G:C base pairs, while six (15%) were at A:T base pairs. The predominant mutation was G:C-->A:T transitions (16/40, 40%), followed by G:C-->T:A transversions (9/40, 22.5%). We conclude that DBCP is a possible base substitution mutagen, especially at guanine bases.