Conversion of Estrone to 17β-Estradiol: A Potential Confounding Factor in Assessing Risks of Environmental Estrogens to Fish.

Feminization of male fish and the role of endocrine-active chemicals in this phenomenon has been an area of intense study for many years. Estrone (E1), a natural steroid, is found in aquatic environments sometimes at high concentrations relative to the estrogenic steroids 17 beta-estradiol (E2) and 17 alpha-ethynylestradiol. However, E1 has been less thoroughly studied than E2 or 17 alpha-ethynylestradiol due in part to a relatively lower potency in metabolically limited estrogen receptor (ER) binding/activation assays. Recent evidence suggests that in vivo biotransformation of E1 to E2 may occur in fathead minnows (Pimephales promelas) residing in environments with high concentrations of E1, such as near wastewater treatment plants. The enzymes likely responsible for this biotransformation, 17 beta-hydroxysteroid dehydrogenases (17 beta HSDs), have been well characterized in mammals but to a lesser extent in fish species. In the present study, a novel systematic analysis of amino acid sequence data from the National Center for Biotechnology Information database demonstrated that multiple 17 beta HSD isoforms are conserved across different fish species. Experimentally, we showed that metabolically active hepatic cytosolic preparations from 2 commercially important salmonid species, rainbow trout and lake trout, biotransformed E1 to E2 to a degree sufficient to alter results of competitive ER binding assays. These results from in silico and in vitro analyses indicate that E1 and biotransformation may play a significant role in adverse effects on development and reproduction of a variety of fish species in contaminated aquatic environments. Environ Toxicol Chem 2020;00:1-13. Published 2020. This article is a US Government work and is in the public domain in the USA.