Cytotoxicity induced by iodinated haloacetamides via ROS accumulation and apoptosis in HepG-2 cells

Iodinated haloacetamides (I-HAcAms) are emerging disinfection by-products and have received great concern due to their extremely high health risk. Previous studies have demonstrated the cytotoxicity of I-HAcAms, but the biological mechanism remained unclear. In this study, cytotoxicity mechanisms of 4 I-HAcAms species were preliminarily examined using HepG-2 cells. The results showed that the cytotoxicity could be ranked as follows: diiodoacetamide (DIAcAm)> iodoacetamide (IAcAm)> bromoiodoacetamide (BIAcAm)> chloroiodoacetamide (CIAcAm). Reactive oxygen species (ROS) and apoptosis played an important role in the cytotoxicity for all I-HAcAms species. Moreover, the ROS and cytotoxicity could be completely reversed by the addition of an antioxidant (N-acetylcysteine (NAC)), but the apoptosis could not. Specifically, the apoptosis induced by DIAcAm and IAcAm was partially reversed by NAC, suggesting that in addition to ROS, other pathways were also possible; While For BIAcAm and CIAcAm, the apoptosis was not reversed by NAC at all, which is potentially due to ROS-independent pathways. The apoptosis mechanisms were further analyzed via Bax and Bcl-2 gene expression and the corresponding protein expression in HepG-2 cells, that mitochondrial pathway was important in the apoptosis of HepG-2 cells induced by all I-HAcAms species. Overall, the mitochondrial pathway provided a potential explanation for BIAcAm and CIAcAm-induced apoptosis, while both ROS and mitochondrial pathways explained DIAcAm and IAcAm-induced apoptosis.