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

Estrogenic potencies of several xenoestrogens were determined in vitro, usi ng cultured hepatocytes from a genetically uniform male carp strain (Cyprin us carpio). Estrogenicity was measured as induction of the yolk protein pre cursor vitellogenin (Vtg), and compared to Vtg induction by 17 beta-estradi ol (E2). The order of estrogenic potency was: methoxychlor (MXCL) > o,p-DDT > chlordecone approximate to bisphenol-A approximate to 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 pote ncy of 0.5, whereas dieldrin, beta-endosulfan, o,p-DDE, and toxaphene (tech nical mixture) did not induce vitellogenesis at concentrations up to 100 mu M. Experiments in which cells were simultaneously exposed to E2 and these xenoestrogens showed that the Vtg-inducing activities of E2 and 4-t-pentylp henol or bisphenol-A were (partially) additive, whereas E2 antagonized the estrogenic effects of MXCL and o,p-DDT. The effect of cytochrome P4501A (CY P1A)-induction on the estrogenicity of MXCL was studied by co-exposing cell s to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). TCDD (10 pM) caused a grea ter than 50-fold induction of CYP1A, measured as ethoxyresorufin O-deethyla se (EROD) activity, hut Vtg induction by MXCL was not significantly affecte d. This indicates that CYP1A is not involved in the bioactivation of MXCL t o more potent estrogenic metabolites in carp. The CARP-HEP (hepatocyte) ass ay can detect xenoestrogens with a potency greater than or equal to 2 x 10( -5) relative to E2. It allows simultaneous testing of more than 10 compound s for both estrogenic and antiestrogenic effects, which makes it a promisin g tool for the screening of suspected xenoestrogens.