Estrogenic environmental contaminants alter the mRNA abundance profiles of genes involved in gonadal differentiation of the American bullfrog

Abstract

Wildlife and human populations are exposed to anthropogenic mixtures of chemicals in the environment that may adversely influence normal reproductive function and development. We determined the effects of exposure to estrogenic chemicals and wastewater effluent (WWE) on developing gonads of the American bullfrog, Rana (Lithobates) catesbeiana, a species whose widespread distribution make it an ideal model for environmental monitoring for endocrine effects of chemical contaminants. Premetamorphic bullfrog tadpoles were exposed to treatment vehicle, 17β-estradiol (E2; 10−9 M) or 4-tert-octylphenol (OP; 10−9 M, 10−8 M, and 10−7 M). Additionally, gonadal differentiation was evaluated in bullfrog tadpoles from a WWE-containing site versus those from a reference location receiving no WWE. In both studies, phenotypic sex, steroidogenic factor-1 (nr5a1), and aromatase (cyp19a1) mRNA levels using quantitative real-time PCR were determined. Exposure to E2 or OP did not alter sex ratios. In controls, both nr5a1 and cyp19a1 transcript levels exhibited sexual dimorphism, with males demonstrating higher levels of nr5a1 and females greater abundance of cyp19a1. However, E2 exposure increased cyp19a1 mRNA abundance in testes and decreased levels in ovaries, eliminating the sexual dimorphism observed in controls. E2-exposed males exhibited increased nr5a1 transcript levels in the testes compared to controls, while females demonstrated no E2 effect. OP treatment had no effect on female cyp19a1 mRNA abundance, but exposure to 10−7 M OP increased testicular transcript levels. Treatment with 10−9 and 10−8 M OP, but not 10−7 M, resulted in decreased abundance of nr5a1 transcript in both ovaries and testes. Animals from the field had sexually dimorphic gonadal levels of cyp19a1, but both sexes from the WWE site exhibited elevated cyp19a1 transcript abundance compared to the reference location. Individual chemical compounds and anthropogenic wastewater effluent dispersed within the environment influence the levels of gonadal mRNA encoding key proteins involved in gonadal differentiation.

Nitrate: An Environmental Endocrine Disruptor? A Review of Evidence and Research Needs

“…Byproducts of the fertilizers, pesticides, and pharmaceuticals that we rely on for health and to enhance food production are dispersed into the environment. Many of these products are toxic or mimic natural biomolecules causing endocrine disruption in humans and wildlife. − …”

“…During the past decades, deviations in reproductive hormone levels and sex ratios in wildlife have been reported in organisms ranging from alligators, newts, fish. and frogs to small crustaceans. ,,− Many suspects have been implicated, such as pesticides, biocides, and chemicals discharged from urban wastewater treatment plants . In addition, more apparent suspects have been identified, such as estrogens from human contraceptives, hormone residues in livestock waste, , or even phytoestrogens released into agricultural drainage systems during soy and red-clover productions .…”

Toxicity Effects of the Environmental Hormone 4-Tert-Octylphenol in Zebrafish (Danio Rerio)

“…In addition to fish model, 4-t-OP also has been proved to alter cyp19a1 expression profiles involving in gonadal differentiation of male American bullfrog [19], and susceptible to vascular function and led to the reduction of vascular contractile in rats [20]. Due to the toxicity of 4-t-OP and harmful effects over diverse species, many countries including European Union members have legislated to restrict the use of APEOs in domestic application.…”

Photodegradation of 17α-ethynylestradiol in nitrate aqueous solutions

“…Steroid estrogens (SEs), including estrone (E1), 17β-estradiol (E2), estriol (E3) and 17α-ethynylestradiol (EE2), have been widely detected in environmental waters [1] and gotten increasing focus in recent years due to their detrimental effects on both human and wildlife endocrine systems [2,3]. As an active ingredient of oral contraceptives, EE2 has been extensively used and discharged into natural waters through the effluents of sewage treatment plants [4][5][6].…”