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

Bisphenol A (BPA) and phthalate diesters are ubiquitous environmental contaminants. While thesecompounds have been reported as reproductive toxicants, their effects may partially be attributedto metabolites. The aim of this study was to examine reproductive organ development in chickenembryos exposed to the BPA metabolite, 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP;100 μg/g egg) or a human-relevant mixture of 4 phthalate monoesters (85 μg/g egg). The mixturewas designed within the EU project EDC-MixRisk based upon a negative association with anogenitaldistance in boys at 21 months of age in a Swedish pregnancy cohort. Chicken embryoswere exposed in ovo from an initial stage of gonad differentiation (embryonic day 4) anddissected two days prior to anticipated hatching (embryonic day 19). No discernible effectswere noted on reproductive organs in embryos exposed to the mixture. MBP-treated malesexhibited retention of Müllerian ducts and feminization of the left testicle, while MBPadministeredfemales displayed a diminished the left ovary. In the left testicle of MBP-treatedmales, mRNA expression of female-associated genes was upregulated while the testicular markergene SOX9 was downregulated, corroborating a feminizing effect by MBP. Our results demonstratethat MBP, but not the phthalate monoester mixture, disrupts both male and femalereproductive organ development in an avian embryo model