Effects of androstenedione exposure on fathead minnow (Pimephales promelas) reproduction and embryonic development

Abstract

High concentrations (300 ng/L) of androstenedione (A4) were identified in snowmelt runoff from fields fertilized with manure from livestock feeding operations in Wisconsin, USA. In fishes, A4 is an active androgen and substrate for biosynthesis of functional androgens (e.g., testosterone and 11-ketotestosterone) and estrogens (e.g., estradiol-17β). Thus, A4 has the potential to be a powerful endocrine disruptor. This hypothesis was tested by exposing reproductively mature fathead minnows to 0.0 ng/L, 4.5 ng/L, 74 ng/L, and 700 ng/L A4 for 26 d in a flow-through system. Various reproductive endpoints were measured including fecundity, fertilization success, secondary sexual characteristics, gonadosomatic index (GSI), and hepatic vitellogenin messenger RNA (mRNA) expression. In addition, fertilized embryos from the reproduction assay were used in an embryonic development assay to assess A4 effects on development and hatchability. In males, A4 significantly increased Vtg mRNA expression (estrogenic effect), significantly reduced GSI, and had no effect on tubercle expression (p = 0.067). In females, A4 induced tubercle development (androgenic effect) with no effects on GSI. Fecundity was not significantly impacted. Exposure to A4 had no effect on fertilization, embryonic development, or hatchability. These data indicate that exogenous A4, at environmentally relevant concentrations, can significantly modulate the reproductive physiology of the fathead minnows in a sex-specific manner and that A4 should be monitored as an endocrine disruptor.

Histological and transcriptional effects of androstenedione in adult zebrafish (Danio rerio)

“…This was in line with our previous results from a synthetic progestin, norgestrel 22 . In a flow‐through exposure system, AED measured concentrations also went down in adult test, with 45% to 70% of their nominal concentrations 16 . This further demonstrated AED was easily degraded in adult exposure experiment due to biological degradation by microorganisms from feces.…”

“…As known, early developmental stage was more sensitive than adult fish when exposed to environmental pollutants. AED exposure did not impact egg production, as well as fertilization, embryonic development in mature fathead minnow 16 . Therefore, these reproductive endpoints including fecundity and histology of the gonad were not sensitive to AED exposure in adult fish.…”

“…Long‐term exposure to 0.4 μg/L of AED from embryos to adults for 180 days suppressed growth and ovarian development in female mosquitofish 15 . However, exposure from 4.5 to 700 ng/L of AED for 26 days did not impact egg production, as well as embryonic development (eg, heart rate, blood circulation, edema and hatch) in adult fathead minnow 16 . Transcriptional alterations were also observed in zebrafish ( Danio rerio ) embryos following exposure to different concentrations of AED 17,18 .…”

“…Jenkins et al proposed that the androgenic effects of AED in female fish might be due to its metabolites like T and 11‐KT 13 . Laboratory findings also supported that AED could induce masculinization of female mosquitofish, 14,15 as well as female fathead minnow ( Pimephales promelas ) 16 . Long‐term exposure to 0.4 μg/L of AED from embryos to adults for 180 days suppressed growth and ovarian development in female mosquitofish 15 .…”

Blockage of androgen and administration of estrogen induce transdifferentiation of testis into ovary

“…The upper the enzyme located in the steroidogenic pathway, the higher SSR rate was induced with E2 when it was inhibited A4 is an active androgen and substrate for biosynthesis of functional androgens (DeQuattro et al 2015). Its product 11-hydroxyandrostenedione (11-OHA) induced sex reversal in the rainbow trout, by downregulation of Cyp19a1a (Govoroun et al 2001).…”