Physiological and Transcriptional Effects of Mixtures of Environmental Estrogens, Androgens, Progestins, and Glucocorticoids in Zebrafish

Fishes are exposed to mixtures of different classes of steroids, but ecotoxicological implications are not sufficiently known. Here, we systematically analyze effects of different combinations of steroid mixtures in zebrafish embryos to assess their joint activities on physiology and transcriptional alterations of steroid-specific target genes at 96 and 120 h post fertilization. In binary mixtures of clobetasol propionate (CLO) with estradiol (E2) or androstenedione (A4), each steroid exhibited its own expression profile. This was also the case in mixtures of 5-, 8-, and 13-different classes of steroids in exposure concentrations of 10-10,000 ng/L. The transcriptional expression of most genes in different mixtures was steroid-specific except for genes encoding aromatase (cypl9b), sulfotransferase (sult2st3), and cyp2k22 that were induced by androgens, progestins, and glucocorticoids. Marked alterations occurred for sult2st3 in binary mixtures of CLO + E2 and CLO + A4. Glucocorticoids increased the heart rate and muscle contractions. In mixtures containing estrogens, induction of the cypl9b transcript occurred at 10 ng/L and protc from the anticoagulation system at 100 ng/L. Our study demonstrates that steroids can act independently in mixtures; the sum of individual steroid profiles is expressed. However, some genes, including cypl9b, sult2st3, and cyp2k22, are regulated by several steroids. This joint effect on different pathways may be of concern for fish development.