The alternation of halobenzoquinone disinfection byproduct on toxicogenomics of DNA damage and repair in uroepithelial cells

In vivo oxidative stress responses and mechanism to chlorinated and methylated p-benzoquinone oxidation byproducts: A comparison study

Halogen-substituted para-benzoquinones (p-BQs) are emerging disinfection byproducts known to induce oxidative damage both in vitro and in vivo. However, as ubiquitous oxidation byproducts, the in vivo toxicity and transport mechanism of non-halogenated p-BQs with similar structure of α, β-unsaturated ketones to halogenated p-BQs have not been thoroughly investigated. In this study, the effect of substituents on toxicity and transportation of 2-chloro-1,4-benzoquinone (CBQ) and 2-methyl-1,4-benzoquinone (MBQ) was systematically investigated. The results show that MBQ exhibits slightly lower acute toxicity to zebrafish embryos compared to CBQ. Exposure to both CBQ and MBQ at concentration of 10 μg/L and 100 μg/L significantly increased the levels of reactive oxygen species, and enhanced the activities of total superoxide dismutase, catalase, and glutathione peroxidase, while malformations were primarily observed in the 100 μg/L exposure groups. The varying developmental toxicity was associated with significant upregulation of 10 genes by CBQ compared to only 6 by MBQ. Using the high-resolution mass spectrometry and electron paramagnetic resonance spectroscopy, the hydroxylation of both CBQ and MBQ, and the production of semiquinone radicals and hydroxyl radicals in aqueous environments have been revealed. This study has demonstrated that the toxicity of non-halogenated p-BQs should not be overlooked and contributes to the understanding of the generated radicals, leading to excessive oxidative-stress in vivo.

Halobenzoquinone-induced potential carcinogenicity associated with p53-mediated cell cycle pathway

2,6-Dibromo-1,4-benzoquinone (2,6-DBBQ) and 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ), two emerging halobenzoquinones (HBQs), have the highest detection frequencies and levels in drinking water among all HBQs. They are more toxic than the regulated disinfection byproducts. Quantitative structure toxicity relationship analysis predicted that HBQs are a class of potential bladder carcinogens. However, direct experimental evidence for the carcinogenicity of 2,6-DBBQ and 2,6-DCBQ is lacking and the associated toxicity mechanisms remain unclear. In this study, we confirmed the potential carcinogenicity of 2,6-DBBQ and 2,6-DCBQ using an in vitro malignant transformation assay, evaluated their cytotoxicity and genotoxicity, and investigated their toxicity mechanisms. The results showed that 2,6-DBBQ and 2,6-DCBQ significantly decreased the viability of human uroepithelial SV-HUC-1 cells and induced DNA damage in SV-HUC-1 cells, and chromosomal damage in HepG2 cells, and malignant transformation of SV-HUC-1 cells. Moreover, transcriptome sequencing revealed that 2,6-DBBQ and 2,6-DCBQ activated the p53-mediated cell cycle pathway in bladder cancer. In the p53-mediated cell cycle pathway, 2,6-DBBQ and 2,6-DCBQ induced cell cycle arrest at the S phase by downregulating p53 and upregulating p21. Additionally, 2,6-DBBQ and 2,6-DCBQ may have produced excessive reactive oxygen species, damaging DNA and chromosomes. These results not only first confirm the potential carcinogenicity of 2,6-DBBQ and 2,6-DCBQ but also provide an important reference for exploring the cytotoxicity and genotoxicity mechanisms of these HBQs.