Evaluation of bioanalytical assays for toxicity assessment and mode of toxic action classification of reactive chemicals

The toxicity of electrophiles, including reactive organochlorines, epoxides, and compounds with an activated double bond was investigated. A set of different bioanalytical assays based on genetically modified Escherichia coli strains was set up quantify cytotoxicity and specific reactivity toward the important biological nucleophiles DNA and glutathione (GSH). The significance of GSH for detoxification was assessed by cellular GSH depletion as well as by growth inhibition of a GSH-deficient strain. Tests for DNA damage comprised the measurement of induction of DNA repair systems, DNA fragmentation, and growth inhibition of a strain deficient in major DNA repair mechanisms. The most suitable assays for detection of mechanisms that underlie the observable cytotoxicity of the tested electrophiles were two sets of strains either lacking GSH or DNA repair in combination with their corresponding parent strains. Comparison of toxicity observed in those strains suggests three clearly distinguishable modes of toxic action for electrophilic chemicals: "DNA damage", "GSH depletion-related toxicity", and "unspecific reactivity". The class of chemicals causing DNA damage includes the epoxides 1,2-epoxybutane, (2,3-epoxypropyl)benzene, and styrene oxide. The class of chemicals with GSH depletion-related toxicity includes compounds with an activated double bond, like acrylates and acrolein. All reactive organochlorines and some epoxides were classified as unspecifically reactive because their toxicity is initiated by reactions with both biological nucleophiles. The work presented here is a contribution for an alternative hazard and effect assessment of organic pollutants based on mode of toxic action classification.