Screening of chemicals with anti-estrogenic activity using in vitro and in vivo vitellogenin induction responses in zebrafish (Danio rerio)

Growing concern over possible adverse effects of endocrine-disrupting chemicals (EDCs) has driven the development of associated screening methods. The use of the vitellogenin (VTG) induction response in cultured teleost hepatocytes has been suggested as an in vitro screening assay for EDCs. However, current data do not sufficiently support this assay in the routine screening of chemicals. This study established and validated the use of primary cultured hepatocytes from zebrafish to screen chemicals for anti-estrogenic activities. Here we measured the transcript levels of selected hepatic estrogen-response genes, including vtg1, vtg2 and erα. Two model anti-estrogens, letrozole (LET), an aromatase inhibitor, and tamoxifen (TAM), a competitive estrogen receptor, were selected as representative chemicals. Additionally, comparisons between in vitro and in vivo assays were performed. As expected, there were concentration-dependent decreases for all three genes in the liver of female zebrafish exposed to LET in vivo for 72 h. Similar responses were observed in males. As for in vitro testing, no discernable alterations in the gene transcripts were found in hepatocytes from males or females. In the case of TAM, exposure for 72 h caused transcriptional reduction of hepatic estrogen-response genes in females in vivo and in vitro. In males, low concentrations of TAM resulted in increased expression of genes, while the expression decreased slightly at higher concentrations. Since these observations were in agreement with the pharmaceutical properties of two tested chemicals, the primary hepatocyte culture could be a promising tool for screening suspected EDCs.