Two complementary bioassays for screening the estrogenic potency of xenobiotics: recombinant yeast for trout estrogen receptor and trout hepatocyte cultures

Abstract

A relation between the chemical structure of a xenobiotic and its steroidal action has not yet been clearly established. Thus, it is not possible to define the estrogenic potency of different xenobiotics. An assessment may be accomplished by the use of different bioassays. We have previously developed a yeast system highly and stably expressing rainbow trout estrogen receptor (rtER) in order to analyze the biological activity of the receptor. The recombinant yeast system appears to be a reliable, rapid and sensitive bioassay for the screening and determination of the direct interaction between ER and estrogenic compounds. This system was used in parallel with a more elaborate biological system, trout hepatocyte aggregate cultures, to examine the estrogenic potency of a wide spectrum of chemicals commonly found in the environment. In hepatocyte cultures, the vitellogenin gene whose expression is principally dependent upon estradiol was used as a biomarker. Moreover, competitive binding assays were performed to determine direct interaction between rtER and xenobiotics. In our study, 50%of the 49 chemical compounds tested exhibited estrogenic activity in the two bioassays: the herbicide diclofop-methyl; the fungicides biphenyl, dodemorph, and triadimefon; the insecticides lindane, methyl parathion, chlordecone, dieldrin, and endosulfan; polychlorinated biphenyl mixtures; the plasticizers or detergents alkylphenols and phthalates; and phytoestrogens. To investigate further biphenyl estrogenic activity, its principal metabolites were also tested in both bioassays. Among these estrogenic compounds, 70% were able to activate rtER in yeast and hepatocytes with variable induction levels according to the system. Nevertheless, 30% of these estrogenic compounds exhibited estrogenic activity in only one of the bioassays, suggesting the implication of metabolites or different pathways in the activation of gene transcription. This paper shows that it is important to combine in vivo bioassays with in vitro approaches to elucidate the mechanism of xenoestrogen actions.

Evaluation of estrogenic activities and mechanism of action of perfluorinated chemicals determined by vitellogenin induction in primary cultured tilapia hepatocytes

“…The structure of PFCs is not similar to E2, but there may be other mechanisms by which these compounds elicit a response. Petit et al (1997) pointed out that certain xenobiotics may interact directly with the ER without disturbing E2 binding. Anti-estrogenic activities have also been observed by co-exposure of other chemicals with E2.…”

Xenoestrogens are potent activators of nongenomic estrogenic responses

“…For many years the mechanisms via which many xenoestrogens act remained a mystery. This lack of a mechanistic explanation existed because while these compounds can affect animal functions and development at relatively low concentrations, experimental systems for testing the classical nuclear transcriptional activities of xenoestrogens showed weak or no activity [3][4][5][6][7][8][9][10]. Therefore, the question remained, via what cellular mechanisms do xenoestrogens act?…”

Morphological sex reversal upon short-term exposure to endocrine modulators in juvenile fathead minnow (Pimephales promelas)

“…estrogen/androgen receptor transfected cell lines (e.g. Petit et al, 1997), receptor binding assays (e.g. Danzo, 1997) or in vivo assays in mammalians (e.g.…”