Investigating BPDE-induced embryonic toxicity employing hiPSC-based models

Benzo[a]pyrene diol epoxide (BPDE) is a metabolite of the environmental contaminant Benzo[a]pyrene- a byproduct of incomplete combustion of organic matter. BPDE reacts with DNA to form BPDE-DNA bulky adducts which if not removed can lead to mutations due to DNA base-pair substitutions. While the effects of BPDE on somatic cells are fairly well described, its effects on early human development are currently unknown. In this study, we investigated for the first time the effect of BPDE on human induced pluripotent stem cells (hiPSCs) and their differentiated neuroprogenitor cells (NPCs) as a model for early embryonic development. Furthermore, we compared hiPSCs and NPCs derived from cells of patients suffering from Nijmegen Breakage Syndrome (NBS), which is a chromosomal instability disorder characterized by defective DNA repair and increased risk of malignancies. Transcriptome analysis, coupled with protein content analysis employing immunostaining and Western blots, revealed that hiPSCs are more sensitive to BPDE exposure when compared to NPCs with an enhanced expression of several genes associated with p53-mediated DNA damage response, including DNA repair by lesion bypass, cell cycle checkpoints and extrinsic apoptosis. We also identified that cells from NBS patients showed less apoptotic response and a distinct p53 response than their healthy counterparts. This iPSC-based study enhances our meagre knowledge of the effects of BPDE on early human development in both healthy individuals and NBS patients. Furthermore, our model conforms with the 3Rs principle.