A sensitive zonagenetic assay for rapid in vitro assessment of estrogenic potency of xenobiotics and mycotoxins

Mounting evidence confirms that hepatic biosynthetic processes are essentia l for female sexual maturation in fish, which is directly controlled by est rogens. These oogenetic events (zonagenesis and vitellogenesis) are induced in both sexes by estrogens. In this paper, we report the induction of zona radiata (zr) proteins and vitellogenin in primary hepatocytes from Atlanti c salmon (Salmo salar L.) exposed to xenoestrogens and mycotoxins. Cells we re treated with doses of 1, 5, and 10 mu M 4-nonylphenol (4-NP), o,p'-DDT, lindane (gamma-HCH), and bisphenol A (BPA), which all induced zr proteins a nd vitellogenin in an approximate dose-dependent manner. Hepatocytes were a lso treated with combinations of xenoestrogens at 1 or 2 mu M, resulting in elevated levels of both zr proteins and vitellogenin, compared to single t reatment. The estrogenic activity of the mycotoxin zearalenone (ZEA) and it s metabolites [alpha-zearalenol (alpha-ZEA) and beta-zearalenol (beta-ZEA)] , with regard to zonagenesis and vitellogenesis, was assessed in this assay system. Mycotoxins were used at concentrations of 10, 100, or 1,000 nM. Al l induced zr proteins and vitellogenin, with a-ZEA being the strongest indu cer. When cells were treated with xenoestrogens or mycotoxins in combinatio n with an estrogen receptor inhibitor (ICI 182,780), the induction of both zr proteins and vitellogenin was inhibited in all cases. Thus, the reported estrogen effects are bonafide estrogen responses. Zona radiata proteins we re more responsive than vitellogenin to both xenoestrogens and mycotoxins. The versatility and sensitivity of the hepatocyte assay demonstrates that b iosynthesis of zr proteins provides a new supplementary method for estimati ng xenoestrogenicity and mycotoxin action.