Direct Effects, Compensation, and Recovery in Female Fathead Minnows Exposed to a Model Aromatase Inhibitor

Abstract

BackgroundSeveral chemicals in the environment have the potential to inhibit aromatase, an enzyme critical to estrogen synthesis.ObjectivesThe objective of this study was to provide a detailed characterization of molecular and biochemical responses of female fathead minnows to a model aromatase inhibitor, fadrozole (FAD).MethodsFish were exposed via water to 0, 3, or 30 μg FAD/L for 8 days and then held in clean water for 8 days, with samples collected at four time points during each 8-day period. We quantified ex vivo steroid production, plasma steroids, and plasma vitellogenin (Vtg) concentrations and analyzed relative transcript abundance of 10 key regulatory genes in ovaries and 3 in pituitary tissue by real-time polymerase chain reaction.ResultsEx vivo 17β-estradiol (E2) production and plasma E2 and Vtg concentrations were significantly reduced after a single day of exposure to 3 μg or 30 μg FAD/L. However, plasma E2 concentrations recovered by the eighth day of exposure in the 3-μg/L group and within 1 day of cessation of exposure in the 30-μg/L group, indicating concentration- and time-dependent physiologic compensation and recovery. Concentration-dependent increases in transcripts coding for aromatase (A isoform), cytochrome P450 side-chain cleavage, steroidogenic acute regulatory protein, and follicle-stimulating hormone receptor all coincided with increased E2 production and recovery of plasma E2 concentrations.ConclusionsResults of this research highlight the need to consider compensation/adaptation and recovery when developing and interpreting short-term bioassays or biomarkers or when trying to predict the effects of chemical exposures based on mode of action.

Dynamic Nature of Alterations in the Endocrine System of Fathead Minnows Exposed to the Fungicide Prochloraz

“…The basic experimental design used for this study was described by Villeneuve et al, (2009). There were 16 replicate tanks per treatment (48 tanks total), each containing four male and four female fathead minnows.…”

“…Ex vivo production of T (testis and ovary) and E2 (ovary) was determined with an adaptation of the method of McMaster et al (1995), as described by Villeneuve et al (2009), using radioimmunoassay (RIA) to measure steroids in the culture medium. Plasma concentrations of T and E2 in the fish also were determined by RIA (Jensen et al, 2001), and plasma concentrations of VTG were measured using an ELISA with a polyclonal fathead minnow antibody and fathead minnow VTG as a standard (Korte et al, 2000).…”

“…Consistent with its mechanism of action, fadrozole strongly inhibited synthesis of E2 by female fish and depressed production of the estrogen-responsive protein vitellogenin (VTG; egg yolk precursor) within 24 h of exposure. However, there was a subsequent time/dose-dependent compensatory response relative to E2 production by the fish, coincident with upregulation of several HPG axis genes that would contribute to increased steroid production (Villeneuve et al, 2009). Termination of the fadrozole exposure resulted in recovery of the fish in terms of gene expression and steroid (and to some degree VTG) production.…”

“…Therefore, a component of predicting effects involves understanding how chemicals interact with the HPG axis temporally, in terms of both direct impacts and compensation during dosing, and recovery after cessation of chemical exposure. Some of our initial research on temporal changes in the HPG axis was described by Villeneuve et al (2009). That work assessed effects of a model aromatase inhibitor, fadrozole, on reproductive endocrine function in the fathead minnow (Pimephales promelas).…”

“…The objective of the present study was to employ an experimental design similar to that used by Villeneuve et al (2009) to investigate responses of the fathead minnow HPG axis to prochloraz. Because prochloraz affects other targets in addition to aromatase, it provides a useful comparison to fadrozole in terms of revealing commonalities and differences in effects of the two chemicals on steroid synthesis and HPG function.…”