The Good, the Bad, and the Toxic: Approaching Hormesis
in <i>Daphnia magna</i> Exposed to an Energetic Compound
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Abstract
A hormetic
response is characterized by an opposite effect in small
and large doses of chemical exposure, often resulting in seemingly
beneficial effects at low doses. Here, we examined the potential mechanisms
underlying the hormetic response of <i>Daphnia magna</i> to the energetic trinitrotoluene (TNT). <i>Daphnia magna</i> were exposed to TNT for 21 days, and a significant increase in adult
length and number of neonates was identified at low concentrations
(0.002–0.22 mg/L TNT), while toxic effects were identified
at high concentrations (0.97 mg/L TNT and above). Microarray analysis
of <i>D. magna</i> exposed to 0.004, 0.12, and 1.85 mg/L
TNT identified effects on lipid metabolism as a potential mechanism
underlying hormetic effects. Lipidomic analysis of exposed <i>D. magna</i> supported the hypothesis that TNT exposure affected
lipid and fatty acid metabolism, showing that hormetic effects could
be related to changes in polyunsaturated fatty acids known to be involved
in <i>Daphnia</i> growth and reproduction. Our results show
that <i>Daphnia</i> exposed to low levels of TNT presented
hormetic growth and reproduction enhancement, while higher TNT concentrations
had an opposite effect. Our results also show how a systems approach
can help elucidate potential mechanisms of action and adverse outcomes