The domestic fowl (Gallus gallus domesticus) embryo as an alternative for mammalian experiments – Validation of a test method for the detection of endocrine disrupting chemicals

Abstract

In recent decades the embryo of Gallus g. domesticus has been widely used as a model for the study of early sexual development and the potential impact of substances affecting development, including endocrine disrupting chemicals (EDCs). Since there is no standardized procedure available for experiments with the chicken embryo, the objective of our project is to expedite the protocol to assess the potential effects of EDCs on early sexual differentiation. The main aim of the present study was to systematically investigate the natural variability of individual developmental and histological key parameters in untreated and solvent-treated control groups, since this has been insufficiently addressed so far. A further aim was to provide robust values for all parameters investigated in control and substance experiments, using two known estrogenic compounds, bisphenol A (75/150/300 μg/g egg) and 17α-ethinylestradiol (20 ng/g egg). On embryonic day 1 eggs were injected with the estrogenic compounds. On embryonic day 19 histological gonadal data as well as morphological parameters were noted. In baseline experiments with control groups the selected endpoints showed reproducible results with low variabilities. Furthermore, gonadal endpoints responded sensitively to the treatment with the two model EDCs. Thus, these endpoints are recommended for the assessment of suspected EDCs in which the values provided for all parameters can serve as validity criteria in future experiments. The embryo of G. domesticus has shown to be a suitable alternative to currently accepted mammalian bioassays for the impact assessment of EDCs on reproductive tissues.

A suggested bisphenol A metabolite (MBP) interfered with reproductive organ development in the chicken embryo while a human-relevant mixture of phthalate monoesters had no such effects

“…The males in the MBP group developed a left ovotestis. Similar results have been obtained with BPA (Berg, Halldin, and Brunström 2001a;Jessl, Scheider, and Oehlmann 2018a). Berg, Halldin, and Brunström (2001a) found that BPA induced ovotestis formation in male chicken embryos as determined histologically at 200 µg/g egg but not at 67 µg/g egg.…”

“…All 12 males exposed to 100 µg MBP/g egg in our study developed a left ovotestis, while approximately half of the males developed ovotestis at 200 µg BPA/g egg in the study by Berg, Halldin, and Brunström (2001a). Jessl, Scheider, and Oehlmann (2018a) observed an effect of BPA on cortex thickness already at 75 µg/g egg in both sexes, but there no marked effect on gonad size in males at this dose. These results suggest that MBP is at least as potent as BPA in terms of inducing ovotestis in chicken embryos.…”

“…Berg, Halldin, and Brunström (2001a) found that BPA induced ovotestis formation in male chicken embryos as determined histologically at 200 µg/g egg but not at 67 µg/g egg. Jessl, Scheider, and Oehlmann (2018a) noted an increase in cortex thickness in the left testis and reduction in cortex thickness in the left ovary after exposure to 75, 100, or 300 µg BPA/g egg. All 12 males exposed to 100 µg MBP/g egg in our study developed a left ovotestis, while approximately half of the males developed ovotestis at 200 µg BPA/g egg in the study by Berg, Halldin, and Brunström (2001a).…”

“…Chicken and quail embryos have been widely used for studying effects of xenoestrogens on sex differentiation (Berg et al 1998(Berg et al , 1999Brunström et al 2009;Jessl, Scheider, and Oehlmann 2018a). Development of the reproductive tract of females Figure 4.…”

“…In the presence of xenoestrogens, the left gonad in male embryos develops into an ovotestis, and retention and malformations of Müllerian ducts occur in both sexes (Berg et al 1999;Mattsson, Olsson, and Brunström 2011). The hormone-dependent differentiation of reproductive organs makes the avian embryo a suitable model in studies of EDCs (Jessl, Scheider, and Oehlmann 2018a).…”