Monitoring of estrogen mimics by a recombinant yeast assay: synergy between natural and synthetic compounds?

Properties of mixtures of compounds exhibiting estrogenic potential have been questioned in the past. Synergistic effects of endocrine disrupters have been proposed, but could never be confirmed. In this study, the transactivational potential of xenoestrogens and phytoestrogens has been evaluated in a yeast test system. Pesticides such as endosulfan, dieldrin, atrazine, and the main metabolites, desethylatrazine and desisopropylatrazine, have been tested and their behavior as mixtures is compared to the behavior of the single compounds. Our results are in contrast to a report (Tran et al., 1996) on the inhibitive effects of xenoestrogens on 17β-estradiol-dependent transactivation. Phytoestrogens have been investigated in a similar manner. A synergistic effect could not be confirmed for both, xenoestrogens and phytoestrogens. These compounds are either weak estrogens or completely lack estrogenic potential. Their endocrine disrupting potential in more complex systems must be therefore attributed to other molecular mechanisms such as to metabolic modification or interference with steroidogenesis. This study shows that yeast systems are useful tools for monitoring pure estrogenic properties.