Transcriptomic changes upon epoxiconazole exposure in a human stem cell-based model of developmental toxicity.

Conazole fungicides such as epoxiconazole are mostly used on cereals of crops to inhibit fungal growth through direct inhibition of sterol 14α-demethylase (CYP51A1). However, this enzyme is highly conserved and in humans it is part of the steroid hormone biosynthesis pathway. Endocrine disrupting effects of epoxiconazole have been shown in rodents and have been substantiated by in vitro data, however, the underlying molecular mechanisms are not clear. We took advantage of a human stem cell based in vitro model for developmental toxicity to study the molecular effects of epoxiconazole. This model is based on 3D cultures of embryoid bodies and differentiation into cardiomyocytes, which mimics the early stages of embryonic development. We have previously shown that epoxiconazole impairs differentiation of these embryoid bodies and therefore has the potential to affect human embryonic development. We employed global transcriptome analysis using RNA sequencing and found that the steroid biosynthesis pathway including CYP51A1, the human sterol 14α-demethylase, was highly deregulated by epoxiconazole in our model. We confirmed that most genes of the steroid biosynthesis pathway were upregulated, including CYP51A1, suggesting a compensatory mechanism at the gene expression level. Our data suggest that epoxiconazole acts mainly by decreasing cholesterol biosynthesis in the cells. We conclude that epoxiconazole bears the potential to harm human embryonic development through inhibition of the steroid biosynthesis pathway. As this may be a common feature of compounds that target sterol 14α-demethylase, we add evidence to the assumption that conazole fungicides may be human developmental toxicants.