Estrogens in vitro

Meng QH, Hockerstedt A, Heinonen S et al. Antioxidant protection of lipoproteins containing estrogens in vitro evidence for low- and high-density lipoproteins as estrogen carriers. Biochim. Biophys. Acta 1439, 331-340, 1999. 

Key words Endocrine, Endocrine disruption, Adrenal, Thyroid, Reproductive, Estrogenic, In vitro, Toxicity... 

The transport of estrogens in vitro has not been studied extensively. Smith el al. (1963) studied the ability of everted rat gut sacs to transport steroids using estradiol-17/3- C as a model estrogen. With this compound, net transport of radioactivity to the serosal medium was accomplished by oxidation of the estradiol to estrone, followed by conjugation of the estrone as a glucosiduronate. Accumulation of this conjugate in the serosal sac fluid resulted in radioactivity levels as much as seven times those in th(i mucosal medium. 

A large number of molecules have provided experimental evidence of neuroprotection in in vitro and in vivo models of Parkinson s disease and many of these putative neuroprotective substances are now the objects of clinical trials. Recently, a team of experts has identified potential neuroprotective agents to be tested in pilot studies [4]. Twelve compounds have been considered for clinical trials caffeine, coenzyme Q 10, creatine, estrogen, GPI1485, GM-1 ganglioside, minocycline, nicotine, pramipexole, ropinirol, rasagiline, and selegiline (for individual discussion see [4]). 

Mayr U, Butsch A and Schneider S. 1992. Validation of two in vitro test systems for estrogenic activities with zearalenone, phytoestrogens and cereal extracts. Toxicology 74 135-149. 

As discussed in the Endocrine Effects section, endosulfan has shown weak estrogenic properties in some in vitro assays, but no such properties could be confirmed in studies in vivo. 

In vivo studies in animals suggest that endosulfan may disrupt normal reproductive hormone levels in male animals, but that it is not an endocrine disrupter in females. Persistent depressed testicular testosterone was seen in male rats after intermediate duration oral exposures to endosulfan. In ovariectomized female rats, orally administered endosulfan did not induce normal development of female reproductive tissues, and in female mice and immature female rats, acute parenteral exposure to endosulfan did not affect several endocrine-related end points. In vitro studies have evaluated endosulfan for estrogen receptor (ER) and cytosolic protein binding affinity, ER-mediated reporter gene expression, estrogenic induction of cell proliferation, and alteration of relative abundance of active estradiol metabolites. Overall, in vitro evidence in favor of endosulfan estrogenicity indicates relatively weak potency compared to 17[3-estradiol. Apparently contradictory results were reported in different... 

The test system was considerably less sensitive to endosulfan when mouse ER, rather than human ER, was used to mediate (3-gal activity (Ramamoorthy et al. 1997). In similar assays, endosulfan at 10 jM had no effect on (3-gal activity in yeast Saccharomyces) transfected with either the human or rainbow trout ER (Andersen et al. 1999). In addition, no effect was observed on transcriptional activation of HeLa cells transfected with plasmids containing an estrogen receptor as a responsive element (Shelby et al. 1996). Endosulfan also did not induce transient reporter gene expression in MCF-7 human breast cancer cells at an incubation concentration of 2.5 pM (Andersen et al. 1999). Maximum endosulfan-induced ER-mediated luciferase reporter gene expression occurred in vitro in a T47D human breast adenocarcinoma cell line at approximately 10 pM, while 50% expression of luciferase occurred at about 5.9 pM the maximum expression was approximately 59% of the effect from exposure to 0.03 nM estradiol (0.00003 pM) (Legler et al. 1999). Luciferase expression from combined treatment with endosulfan and dieldrin was additive over concentrations ranging from 3 to 8 pM. 

The overall evidence indicates that endosulfan administered in vivo may be disruptive of reproductive hormone levels in male animals. On the other hand, endosulfan is neither estrogenic nor disruptive of thyroid or pituitary hormone levels in females in vivo, despite its weak estrogenicity in several in vitro test systems. 

Agarwal et al. 1978), the quantification of these specific enzymes may indicate that exposure to endosulfan has occurred. Blood tests, such as decay curves for aminopyrine in plasma, which are semiquantitative indices of liver enzyme induction, have been used successfully in the past to demonstrate enzyme induction in pesticide-exposed workers. Because numerous chemicals found at hazardous waste sites also induce these hepatic enzymes, these measurements are not specific for endosulfan exposure. However, measurements of enzyme activity, together with the detection of the parent compound or its metabolites in tissue or excreta, can be useful indicators of exposure. All of these potential biomarkers require further verification in epidemiological studies. Further studies with focus on the development of methods to separate and measure the estrogenicity of endosulfan in in vitro assays would be valuable since these assays are more sensitive and discriminative than other conventional biomarkers. Preliminary results have been presented by Sonnenschein et al. (1995). 

Shelby MD, Newbold RR, Tully DB, etal. 1996. Assessing environmental chemicals for estrogenicity using a combination of in vitro and in vivo assays. Environ Health Perspect 104(12) 1296-1300. 

Wade MG, Desaulniers D, Leingartner K, et al. 1997. Interactions between endosulfan and dieldrin on estrogen-mediated processes in vitro and in vivo. Reprod Toxicol 11(6) 791-798. 

The yeast reporter gene assays not only assess for the interaction of the chemical with the hormone receptor, but also the ability of that receptor-chemical ligand interaction to activate the hormone DNA response element. It should be realized, however, that most of these systems have been developed with human and mammalian hormone receptors and differences in ligand potencies can occur between different animal species. A comprehensive review of in vitro assays for measuring estrogenic activity, and some of the issues of comparability, is provided by Zacharewski (1997). 

Desbrow, C., Routledge, E.J., and Brighty, G.C. et al. (1998). Identification of estrogenic chemicals in STW effluent. 1. Chemical fractionation and in vitro biological screening. Environmental Science and Technology 32, 1549-1558. 

Pelissero, C., Flouriot, G., and Foucher, J.L. (1993). Vitellogenin Synthesis in Cultured-Hepatocytes—an in vitro Test for the Estrogenic Potency of Chemicals. Journal of Steroid Biochemistry and Molecular Biology 44, 263-272. 

Zacharewski, T. (1997). In vitro bioassays for assessing estrogenic substances. Environmental Science and Technology 31, 613-623. 

---