Genotoxic and Mutagenic Assays of Halothane Metabolites in Bacillus subtilis and Salmonella typhimurium

Reactions of N-acetylcysteine with the halothane metabolite, 2-chloro-1,1-difluoroethylene (CF2CHCl), and two related probable metabolites, 2-bromo-1,1-difluoroethylene (CF2CHBr) and 2-bromo-2-chloro-1,1difluoroethylene (CF2CBrCl), afforded the saturated conjugates, RSCF2CH2Cl, RSCF2CH2Br, and RSCF2CHBrCl, as well as the unsaturated analogs, RSCFCHCl and RSCFCHBr; R = −CH2CH(COOH)NHCOCH3. The mutagenic and genotoxic potential of these conjugates was evaluated in the Salmonella/microsome system described by Ames and a “rec” DNA repair system developed by Kada employing recombination proficient and deficient strains of Bacillus subtilis. When screened for mutagenicity with Salmonella typhimurium strains TA1535 and TA100, the saturated and the unsaturated conjugates were found to be nonmutagenic. However, in a preliminary test using strain TA100 in logarithmic growth, compounds RSCF2CHBrCl and RSCFCHCl were mutagenic. Furthermore, screening for DNA-damaging ability in the B. subtilis “rec” assay with strains H17 and M45 revealed that the urinary halothane metabolite, RSCF2CHBrCl, and the unsaturated analogs, RSCFCHCl and RSCFCHBr, preferentially inhibited the growth of strain M45, which is deficient in its ability to repair DNA. In view of the reported correlation between known mutagens and their differential lethal action on rec− versus rec+ bacteria, the present findings of the DNA-damaging effects of the nonvolatile halothane metabolites and related probable metabolites suggest a possible relationship between halothane metabolism and reported toxic effects associated with occupational anesthetic exposure.