Citation:

Catron, T., A. Swank, L. Wehmas, D. Phelps, J. McCord, R. Singh, J. Sobus, S. Keely, N. Brinkman, C. Wood, M. Strynar, AND T. Tal. Estradiol exposure disrupts the microbiota-gut-brain axis during zebrafish development. Society of Toxicology, Baltimore, Maryland, March 10 - 14, 2019.

Impact/Purpose:

Intestinal microbes are thought to play important roles in development of the nervous system. It has been proposed that microbiota can 1) interact with environmental chemicals through bioactivation or detoxification, or 2) be targeted by chemical exposures. This work shows that exposure to estradiol, a potent estrogen receptor agonist and reference chemical for estrogen receptor activation, causes behavioral toxicity only in zebrafish with microbes. Following exposure, zebrafish colonized with microbes also contain three times less parent estradiol and direct estradiol metabolites relative to microbe-free zebrafish. These data demonstrate for the first time that chemical-induced behavioral toxicity is dependent on the presence of microbes. These findings also show that chemical metabolism is influenced by microbial colonization. More broadly, this work supports the concept that current hazard identification strategies may misestimate toxicological risk if microbe interactions with environmental chemicals are not considered.

Description:

Estrogenic chemicals are widespread environmental contaminants. During early vertebrate development, estrogen receptor signaling is critical for nervous system function. Because host-associated microbiota influence neurodevelopment and can metabolize xenobiotics, we hypothesized that microbiota can biotransform exogenous estradiol (E2) and modify the E2 effect on neurobehavioral development. To test this hypothesis, colonized zebrafish were continuously exposed to five non-teratogenic E2 concentrations (0.34–3.5 µM) from 1 to 10 days post-fertilization (dpf). At 10 dpf, 16S rRNA gene sequencing was used to evaluate changes in microbial community composition and predicted metagenomic function. Locomotor activity was assessed in colonized and axenic (microbe-free) zebrafish exposed to 0.4 or 1.2 µM E2 using a standard light/dark behavioral assay and zebrafish tissue was collected to conduct targeted and non-targeted mass spectrometry. E2 exposure did not alter microbial composition or function in colonized larvae. However, light-phase locomotor hypoactivity was observed in E2-exposed colonized larvae as opposed to normal behavior in axenic larvae exposed to E2. Both colonized and axenic larvae exposed to E2 exhibited hypoactivity in the dark phase. Measured parent E2 concentrations and abundance of predicted direct E2 metabolites (E2 sulfate and E2 glucuronide) were significantly higher in axenic relative to colonized zebrafish, while abundance of putative secondary metabolites (estrone sulfate and estrone glucuronide) was similar in axenic and colonized zebrafish. These data suggest a correlation between chemical-induced neurobehavioral effects and microbiota-based metabolism of exogenous chemicals. More broadly, this work supports the inclusion of chemical-microbiota interactions when estimating chemical hazard. This abstract does not necessarily reflect EPA policy.

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