USE OF XENOPUS LAEVIS AS A MODEL FOR INVESTIGATING IN VITRO AND IN VIVO ENDOCRINE DISRUPTION IN AMPHIBIANS

摘要

The estrogenic activity of 17β-estradiol (E_2), α-zearalenol (α-ZEA), genistein (GEN), and 4-t-octylphenol (4-t-OP) was investigated using Xenopus laevis-based assays. All test compounds competed with [~3H]E_2 for binding to a recombinant Xenopus estrogen receptor (xER) with the following relative affinities: E_2 > α-ZEA > 4-t-OP > GEN. The ability of these compounds to induce xER-mediated reporter gene expression was then assessed in MCF-7 human breast cancer cells cotransfected with a Gal4-xERdef chimeric estrogen receptor and a Gal4-regulated luciferase reporter gene. Luciferase activity was increased 30- to 50-fold by 10 nM E_2 relative to that in solvent control. Maximal reporter gene activity induced by 10 nM α-ZEA was 54% of that induced by E_2; however, the activity did not increase following doses of up to 10 μM. A dose of 1 μM 4-t-OP induced 23% of the maximal reporter gene activity induced by E_2, whereas 10 μM GEN induced activity to the same level as E_2. A dose-dependent increase in vitellogenin (VTG) mRNA expression was observed in Xenopus treated intraperitoneally with E_2 at 0.05 to 5 mg/kg/d for three consecutive days, with the maximal induction observed in the group receiving 1 mg/kg/d. The α-ZEA, GEN, and 4-t-OP also significantly induced VTG mRNA expression, although at higher doses. These results demonstrate the utility of X. laevis as an amphibian model to assess the estrogenic activity of endocrine disruptors.