Amberg, A; Braun, K; Kauffmann, H; Spirkl, H; Stammberger, I; Czich, A
Carboxylic acid halides are known as potential mutagenic toxicophores, which are detected by the software for prediction of toxicity DEREK (Deductive Estimation of Risk from Existing Knowledge). This is based on several examples of Ames positive alkyl or aryl substituted carboxylic acid chlorides available from the NTP Salmonella database. To investigate the influence of solvents on results of mutagenicity assays, we tested some of these Ames positive carboxylic acid chlorides and additionally other carboxylic acid halides in the Ames II assay, a liquid microtiter modification of the standard Ames plate incorporation test, using deionized water and DMSO as solvents. The tested compounds were acetyl chloride, acetyl bromide, acetyl iodide, octanoyl chloride, benzoyl chloride, benzoyl bromide, phenylacetyl chloride and 3-phenylpropionyl chloride. When using water as solvent, all carboxylic acid halides were negative in Ames II, except acetyl bromide, which was positive in strains TAMix (TA7001-7006) without metabolic activation at 1600 g/ml. But in contrast to these results, using DMSO as solvent lead to positive Ames II results for all compounds with and without metabolic activation beginning at 16 ug/ml, with higher mutagenic activity in strains TAMix than in TA98. These results may be explained by different reactions of the compounds in the solvents. Carboxylic acid halides in water should completely react to the corresponding and non-mutagenic carboxylic acids and hydrohalide acids. But when using DMSO as solvent, besides the corresponding carboxylic acids, dimethylsulfide halides are also formed as reaction products of DMSO. These dimethylsulfide halides are alkylating agents, which are more stable in aqueous conditions and more likely to react with DNA, resulting in a positive Ames II. As a consequence of these results, we recommend using other solvents than DMSO to test the mutagenic potential of carboxylic acid halides, to avoid false positive results from DMSO reaction products, not relevant for aqueous, physiological conditions.