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The good, the bad, and the toxic: approaching hormesis in Daphnia magna exposed to an energetic compound.

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 Daphnia magna to the energetic trinitrotoluene (TNT). Daphnia magna 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 D. magna 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 D. magna 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 Daphnia growth and reproduction. Our results show that Daphnia 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.

SUBMITTER: Stanley JK

PROVIDER: S-EPMC4120942 | biostudies-literature | 2013 Aug

REPOSITORIES: biostudies-literature

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The good, the bad, and the toxic: approaching hormesis in Daphnia magna exposed to an energetic compound.

Stanley Jacob K JK Perkins Edward J EJ Habib Tanwir T Sims Jerre G JG Chappell Pornsawan P Escalon B Lynn BL Wilbanks Mitchell M Garcia-Reyero Natàlia N

Environmental science & technology 20130730 16

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 Daphnia magna to the energetic trinitrotoluene (TNT). Daphnia magna 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 i ...[more]

PMID: 23898970

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Project description:Hormesis is a dose response phenomenon characterized by a stimulation of an organismal response at low doses of a chemical and inhibition of the response (toxicity) at a higher dose. In the present study, Daphnia magna were exposed to the energetic compound 2,4,6-trinitrotoluene (TNT) for 21 days, and the endpoints survival, growth (length and dry weight), and reproduction (number of neonates per survivor) were assesed, identifying hormetic responses at the lower treatment levels. In order to elucidate the mechanisms leading to hormesis, microarray analysis was performed at 0.004 (hormetic), 0.12 (sometimes hormetic), and 1.85 (toxic) mg/L TNT. Functional and transcriptional benchmark dose analyses performed on differentially expressed genes suggested the involvement of lipid metabolism in hormetic responses and subsequently lipidomic analysis was performed on the same treatments. Lipid analysis supported the hypothesis that TNT exposure affected lipid metabolism, and showed that hormetic effects could be related to increases in some polyunsaturated fatty acids and ecosanoids known to be involved in Daphnia growth and reproduction. Chronic toxicity tests was designed to identify the hormetic range of D. magna responses to TNT. Daphnia magna younger than 24 h old and obtained from in-house cultures at the U.S. Army Engineer Research and Development Center, Environmental Laboratory (Vicksburg, MS) were used to initiate the bioassay. The experimental design consisted of one D. magna per test chamber and 10 test chambers per treatment level. In the microarray mass exposure, nominal treatment levels were 0.004, 0.02, 0.12, 0.44, and 1.85 mg/L. Based on the results of the testing in the 50 ml beakers, organisms from three treatments were selected for analysis of gene expression: 0.004, 0.12, and 1.85 mg/L. These treatments were selected to represent a hormetic concentration (0.004 mg/L), a toxic concentration (1.85 mg/L), and an intermediate concentration (0.12 mg/L). A total of 23 arrays used, with 5-6 replicates per each dose (solvent control, 0.004 mg/L, 0.12 mg/L, and 1.85 mg/L).

Dataset Information

The good, the bad, and the toxic: approaching hormesis in Daphnia magna exposed to an energetic compound.

Publications

The good, the bad, and the toxic: approaching hormesis in Daphnia magna exposed to an energetic compound.

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