Use of Xenopus laevis as a model for investigating in vitro and in vivo endocrine disruption in amphibians.
The estrogenic activity of 17beta-estradiol (E2), alpha-zearalenol (alpha-ZEA), genistein (GEN), and 4-t-octylphenol (4-t-OP) was investigated using Xenopus laevis-based assays. All test compounds competed with [3H]E2 for binding to a recombinant Xenopus estrogen receptor (xER) with the following relative affinities: E2 > alpha-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 E2 relative to that in solvent control. Maximal reporter gene activity induced by 10 nM alpha-ZEA was 54% of that induced by E2; however, the activity did not increase following doses of up to 10 microM. A dose of 1 microM 4-t-OP induced 23% of the maximal reporter gene activity induced by E2, whereas 10 microM GEN induced activity to the same level as E2. A dose-dependent increase in vitellogenin (VTG) mRNA expression was observed in Xenopus treated intraperitoneally with E2 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 alpha-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.
Huang
Yue-wern
YW
Department of Biochemistry and Molecular Biology, National Food Safety and Toxicology Center, Michigan State University, East Lansing, Michigan 48824, USA. huangy@umr.edu
Matthews
Jason B
JB
Fertuck
Kirsten C
KC
Zacharewski
Tim R
TR
D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D052244:Endocrine Disruptors / Q000633:toxicity*; D066298:In Vitro Techniques; D008024:Ligands; D008297:Male; D008954:Models, Biological; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014819:Vitellogenins / Q000235:genetics; D014982:Xenopus laevis
D052244:Endocrine Disruptors; D008024:Ligands; D012333:RNA, Messenger; D014819:Vitellogenins