Estrogenic potencies of several environmental pollutants, as determined by vitellogenin induction in a carp hepatocyte assay

Abstract

Estrogenic potencies of several xenoestrogens were determined in vitro, using cultured hepatocytes from a genetically uniform male carp strain (Cyprinus carpio). Estrogenicity was measured as induction of the yolk protein precursor vitellogenin (Vtg), and compared to Vtg induction by 17β- estradiol (E2). The order of estrogenic potency was: methoxychlor (MXCL) > o,p-DDT > chlordecone ≃ bisphenol-A ≃ 4-t-pentylphenol. Estrogenic potencies of these compounds varied from 1 x 10-3 to 1 x 10-4 relative to E2. The synthetic estrogen DES had a relative estrogenic potency of 0.5, whereas dieldrin, β-endosulfan, o,p-DDE, and toxaphene (technical mixture) did not induce vitellogenesis at concentrations up to 100 μM. Experiments in which cells were simultaneously exposed to E2 and these xenoestrogens showed that the Vtg-inducing activities of E2 and 4-t-pentylphenol or bisphenol-A were (partially) additive, whereas E2 antagonized the estrogenic effects of MXCL and o,p-DDT. The effect of cytochrome P4501A (CYP1A)-induction on the estrogenicity of MXCL was studied by co-exposing cells to 2,3,7,8- tetrachlorodibenzo-p-dioxin (TCDD). TCDD (10 pM) caused a greater than 50- fold induction of CYP1A, measured as ethoxyresorufin O-deethylase (EROD) activity, but Vtg induction by MXCL was not significantly affected. This indicates that CYP1A is not involved in the bioactivation of MXCL to more potent estrogenic metabolites in carp. The CARP-HEP (hepatocyte) assay can detect xenoestrogens with a potency ≥ 2 x 10-5 relative to E2. It allows simultaneous testing of more than 10 compounds for both estrogenic and antiestrogenic effects, which makes it a promising tool for the screening of suspected xenoestrogens.