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Sensitivity of the vitellogenin assay to diagnose exposure of fathead minnows to 17α-ethynylestradiol
Citation:
Flick, R., D. Bencic, MaryJean See, AND A. Biales. Sensitivity of the vitellogenin assay to diagnose exposure of fathead minnows to 17α-ethynylestradiol. AQUATIC TOXICOLOGY. Elsevier Science Ltd, New York, NY, 152(2014):353-360, (2014).
Impact/Purpose:
The purpose of this work was to characterize the expression of vitellogenin in adult fathead minnows exposed to EE2 for two, four and seven days in the laboratory under controlled conditions. These data will help provide guidance regarding the number of fish to expose and the duration of exposures in order to have the statistical power necessary to determine if fish have been exposed to estrogens. Exposure of too-few individuals, or for too short a time, reduces the likelihood of detecting a positive response to an exposure. Unnecessarily lengthy exposures, both in the field, where mortality becomes an issue with caged fish, or in the laboratory, where the volume of water collected becomes unmanageable, should also be avoided. Understanding the concentration-response curve for vitellogenin at multiple time points would assist in guiding the design of experiments. In the present work, EE2 was used as a model estrogen because its potency makes it a substantial contributor to the estrogenicity of many surface waters. Additionally, we analyzed both plasma VTG protein and hepatic vtg mRNA to determine if one biomarker has greater resolution than the other at the low concentrations of estrogens often found in surface waters.
Description:
Vitellogenin is frequently used as a biomarker of exposure to environmental estrogens. When designing an experiment using vitellogenin, investigators must decide whether to deploy fish in the field or expose fish in the lab, how many fish to expose, and how long to expose the fish. They must also choose between using the vitellogenin gene or the protein. Without data on the sensitivity of vitellogenin under different exposure scenarios, experiments may lack the statistical power necessary to determine if an exposure has occurred. We exposed male fathead minnows to 17α-ethynylestradiol (EE2) in a flow-through system and quantified both vitellogenin gene mRNA transcripts in liver (vtg) and plasma protein (VTG). Exposures of 2, 4 and 7 days at multiple EE2 concentrations were performed in order to provide information regarding the sensitivity of each of these biomarkers to diagnose exposure to estrogens. Both vitellogenin gene and protein were able to reliably detect exposures to EE2 at concentrations of 5 ng/L and higher at all time points. At any given time point, vtg mRNA appears to be more sensitive than plasma VTG. For lower concentrations, sensitivity was improved with increasing exposure duration. A sample size of ~12 fish was sufficient in many cases to produce a statistically significant increase in vitellogenin, but larger sample sizes may provide more sensitivity at low concentrations. These data will assist in designing experiments that have sufficient statistical power necessary to determine if fish have been exposed to estrogens.
