Elsevier

Toxicology

Volume 205, Issues 1–2, 1 December 2004, Pages 65-73
Toxicology

Whole body action of xenoestrogens with different chemical structures in estrogen reporter male mice

https://doi.org/10.1016/j.tox.2004.06.038Get rights and content

Abstract

The present work tested the estrogenic activity of three weak environmental estrogens p,p′DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane], p,p′DDE [1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene] and βBHC [β-benzene-hexachloride] in the transgenic estrogen-reporter mouse model (ERE-tK-LUC). By a time dependent analysis of the transgenic reporter expression (luciferase), we showed that all these chemicals modulated the estrogen receptors (ERs) in the whole body, although with a different efficacy and depending upon the tissue analyzed. Peak activity was registered at 16 h of treatment with 5000 μg/kg of each compound.

Organochlorines are lipophylic molecules that accumulate in fat. During weight loss they are mobilized and their concentration increases in blood. We tested whether after experimental accumulation in fat tissue, followed by a 48 h period of fasting, these compounds could be modulated to reach sufficient levels to activate the ERs in target tissues. This experimental setting produced results that were different from those obtained following acute treatments. In loaded mice, fasting induced βBHC mobilization resulted in strong ER activation in the liver, lung, eye, cerebellum, hypothalamus and cortex. p,p′DDT mobilization had no effect in these tissues, but efficiently acted in the testis, where, on the contrary, βBHC inhibited reporter expression. During fasting, βBHC, p,p′DDT and the metabolite p,p′DDE increased in blood concentration, from 2.7 ± 0.36, 0.65 ± 0.01 and 0.48 ± 0.06 μg/ml to 9.51 ± 1.1, 4.98 ± 0.77 and 6.0 ± 0.71 μg/ml, respectively. We conclude that these organochlorines modulate differently the expression of estrogen regulated genes in a tissue- and compound-specific manner and that their action is dependent on the energy balance. Moreover, we show that this mouse model is suitable to detect the estrogenic activity of chemicals with variable structures such as alkyl phenols and polychlorobiphenyls.

Introduction

The actual concern on the activity of environmental estrogens regards in part their action as ER modulators in the whole body (Di Lorenzo et al., 2002, Palanza et al., 2001, Nagel et al., 2001, Den Hond et al., 2001, Hoyer, 2001). They may interfere with ER-ligands such as endogenous estrogens, therapeutics and with beneficial estrogens present in food. Recent acquisitions allow to hyphotesize that negative effects on normal endocrine function and on hormone dependent pathologies may be caused by blood concentration of estrogenic chemicals as low as those released from fat depots during diets or diseases (Pelletier et al., 2003).

The availability of reporter mice in which the state of transcriptonal activity of estrogen receptors can be investigated in all the estrogen target organs (ERE-tK-LUC mice) (Ciana et al., 2001), provides an opportunity to measure the tissue specific activity of xenoestrogens at relatively low doses and after mobilization out of fat tissue induced by dietary restriction. Here we demonstrate that three compounds βBHC, p,p′DDT and p,p′-DDE are mobilized differently during weight loss and exert compound-specific effects in ERs expressing tissues of male mice.

Section snippets

Experimental animals

The procedures involving the animals and their care were conducted in accord to institutional guidelines, which comply with national and international laws and policies [National Institutes of Health, Guide for the Care and Use of Laboratory Animals, 1996 (7th edition) (Washington, D.C.); National Academy Press, National Research Council Guide, htpp://www.nap.edu/readingroom/books/labrats]. ERE-tk-LUC transgenic mice were kept in animal rooms maintained at a temperature of 23 °C, with natural

Time dependent ER activation by βBHC, p,p′DDT and p,p′DDE in mouse organs

A time dependent analysis was determined in several tissues of transgenic ERE-iK-LUC reporter male mice (Ciana et al., 2003) injected i.p. with 5000 μg/kg of βBHC, p,p′DDT and p,p′DDE separately. The response was quantified by assaying the enzymatic activity of the transgenic marker, luciferase. In parallel, mice were also treated with 17β-estradiol (50 μg/kg) as a reference compound.

As reported in Fig. 1, all the compounds showed ability to modulate the ERs, time dependently and in a tissue

Discussion

The organochlorines βBHC, p,p′DDT and its main metabolite p,p′DDE, have in common a low toxicity, the ability to concentrate in the food chain and to be extremely long-lived in the adipose tissues of animals and humans (Jaga and Dharmani, 2003).

Previous reports have shown a variable mobilization capacity of environmental chemicals (Diel et al., 2000) from sites of accumulation and a consequential different biological action in the uterus (Bigsby et al., 1997). Here we have shown, that the blood

Acknowledgments

We are grateful to Francesca Piazza, Alessandro Bulla and Rosa Di Lorenzo for their helpful English writing and secretarial assistance. This work was partially supported by the European Union “EDERA”, grant no. QLK4-CT-2002-02221, by Istituto Superiore di Sanità (ARACNA Project) and by the FIRB grant n.er RBNE0157EH.

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