10.1021/es050758o.s001
Manuela Richter
Manuela
Richter
Beate I. Escher
Beate I.
Escher
Mixture Toxicity of Reactive
Chemicals by Using Two Bacterial
Growth Assays as Indicators of
Protein and DNA Damage
American Chemical Society
2005
reactive chemicals
compound
prediction
concentration addition
Bacterial Growth Assays
mixture toxicity
DNA
mixture components
electrophile
nucleophile
2005-11-15 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Mixture_Toxicity_of_Reactive_Chemicals_by_Using_Two_Bacterial_Growth_Assays_as_Indicators_of_Protein_and_DNA_Damage/3257119
The mixture toxicity of reactive chemicals was investigated
with a set of bioanalytical tests that quantify not only the
toxic effects but also allow the identification of the
preferred target of reactive chemicals in bacterial cells.
Softer electrophiles such as acrylates react preferentially
with thiol groups in proteins and peptides, and harder
electrophiles such as epoxides preferentially attack DNA.
In addition, some compounds, e.g., benzyl chloride,
have no preference for a biological target and damage
both DNA and proteins. A thiophenol was used as a model
compound representing nucleophiles. We explored if the
paradigms of mixture toxicity also hold true for reactive
chemicals. Compounds with the same targets and the same
modes of action should act concentration additive in
mixtures, and compounds with different modes of action
should act according to the concept of independent action.
In addition, we investigated the potential for interaction
of compounds of mixtures of electrophiles or electrophiles
plus nucleophiles, which might lead to synergistic or
antagonistic effects. The toxicity of mixtures of electrophiles
with a single preferred target was consistent with the
prediction for concentration addition. Unfortunately, the
predictions for independent action did not differ much from
those for concentration addition; therefore it was not
possible to differentiate between these two models. Mixtures
of two groups with different preferred target sites
clearly showed concentration addition. In contrast, mixtures
of compounds with multiple targets, i.e., compounds that
show nonspecific reactivity toward any biological nucleophile,
exhibited effects that lay distinctly between the predictions
for concentration addition and independent action. We
observed neither synergism (higher toxicity than predicted
by concentration addition) nor antagonism (lower toxicity
than predicted by independent action) for mixtures of
electrophiles. Binary combinations of different electrophiles
with the nucleophile 4-chlorothiophenol yielded smaller
effects than those expected from the prediction for
independent action. The degree of antagonism was
correlated with the reaction rate constant of the electrophile
with the thiol group of glutathione, which indicates that
the interaction between the mixture components occur in
the toxicokinetic phase and is purely a result of chemical
reactivity between the mixture components. Overall,
we conclude that the concepts of mixture toxicity apply
not only for baseline toxicity and receptor-mediated
mechanisms, as has been shown in a large number of
studies, but also for reactive mechanisms of toxicity, provided
that one has checked beforehand that no chemical
reactions occur between the mixture components.