Elevated 8-oxo-7,8-dihydro-2'-deoxyguanosine in genome of T24 bladder cancer cells induced by halobenzoquinones

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.

Metabolite identification of emerging disinfection byproduct dibromo-benzoquinone in vivo and in vitro: Multi-strategy mass-spectrometry annotation and toxicity characterization

Halobenzoquinones (HBQs) are emerging disinfection byproducts (DBPs) of high toxicity and also are shared active toxic intermediates of multiple halogenated organic pollutants. Due to the strong oxidizing property and electrophilicity, HBQs exhibit extremely diverse metabolism pathways in organisms. The identification of toxic-decisive metabolites is pivotal, albeit challenging, for understanding the toxicity mechanisms of HBQs. We employed dibromo-benzoquinone (DBBQ) as a representative HBQ, and established a systematic analytical strategy using high-resolution mass spectrometry, which collectively coupled suspect screening (SS), mass defect filtering (MDF), product ion filtering (PIF), isotopic signature filtering (ISF), and molecular networking (MN). As a result, 20 biotransformation products of DBBQ were identified in vivo and in vitro, involving metabolism reactions such as hydroxylation, methylation, methoxylation, acetylation, sulfonation, glucuronidation, glutathionylation, dimerization, and conjugation with amino acids or fatty acids. Quantitative structure-activity relationship (QSAR) analysis and cytotoxicity experiments consistently demonstrated the significantly high toxicity of the fatty acid conjugate compared to the parent compound DBBQ and other metabolites, pinpointing the important role of the fatty acid conjugation in determining the metabolism and toxicity of HBQs. The research conducted a comprehensive evaluation of the metabolism of a typical HBQ with the combination of multiple analytical and toxicity characterization methods, therefore screen out the most important metabolism pathway of HBQs.

Chlorobenzoquinones Aggravate RSL3-Induced Ferroptosis in ROS-Dependent Manner

Chlorobenzoquinones (CBQs) are a class of emerging water disinfection byproducts that pose significant risks to public health. In this study, we found that three CBQs (tetrachloro-1,4-benzoquinone, 2,5-dichloro-1,4-benzoquinone, and 2-chloro-1,4-benzoquinone) can significantly aggravate cell death caused by Ras-selective lethal small molecule 3 (RSL3). Further study showed that the cell death caused by CBQs, either alone or in combination with RSL3, was related to iron accumulation and GPX4 inactivation, suggesting the occurrence of ferroptosis. Furthermore, reactive oxygen species are found to play a potential key role in mediating the toxicity of CBQs in CBQs and RSL3-induced ferroptosis. These findings will be helpful in understanding the toxic mechanism of CBQs to mammalian cells.

Comprehensive Toxicological Assessment of Halobenzoquinones in Drinking Water at Environmentally Relevant Concentration

Halobenzoquinones (HBQs), an emerging unregulated category of disinfection byproduct (DBP) in drinking water, have aroused an increasing concern over their potential health risks. However, the chronic toxicity of HBQs at environmentally relevant concentrations remains largely unknown. Here, the occurrence and concentrations of 13 HBQs in drinking water from a northern megacity in China were examined using ultrahigh performance liquid chromatography coupled with triple-quadrupole tandem mass spectrometry (UHPLC-MS/MS). Four HBQs, including 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ), 2,6-dibromo-1,4-benzoquinone (2,6-DBBQ), 2,3,6-trichloro-1,4-benzoquinone (TriCBQ), and 2,5-dibromo-1,4-benzoquinone (2,5-DBBQ), were detected beyond 50% occurrence frequency and at median concentrations from 4 to 50 ng/L. The chronic toxicity of these four HBQs to normal human colon and liver cells (FHC and THLE-2) was investigated at these concentrations. After 90 days of exposure, 2,5-DBBQ and 2,6-DCBQ induced the highest levels of oxidative stress and deoxyribonucleic acid (DNA) damage in colon and liver cells, respectively. Moreover, 2,5-DBBQ and 2,6-DCBQ were also found to induce epithelial-mesenchymal transition (EMT) in normal human liver cells via the extracellular signal regulated kinase (ERK) signaling pathway. Importantly, heating to 100 °C (boiling) was found to efficiently reduce the levels of these four HBQs in drinking water. These results suggested that environmentally relevant concentrations of HBQs could induce cytotoxicity and genotoxicity in normal human cells, and boiling is a highly efficient way of detoxification for HBQs.

Recent advances in high-performance liquid chromatography tandem mass spectrometry techniques for analysis of DNA damage and epigenetic modifications

Environmental exposure would cause DNA damage and epigenetic modification changes, potentially resulting in physiological dysfunction, thereby triggering diseases and even cancer. DNA damage and epigenetic modifications are thus promising biomarkers for environmental exposures and disease states. Benefiting from its high sensitivity and accuracy, high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) is considered the "gold standard technique" for investigating epigenetic DNA modifications. This review summarizes the recent advancements of UHPLC-MS/MS-based technologies for DNA damage and epigenetic modifications analysis, mainly focusing on the innovative methods developed for UHPLC-MS/MS-related pretreatment technologies containing efficient genomic DNA digestion and effective removal of the inorganic salt matrix, and the new strategies for improving detection sensitivity of liquid chromatography-mass spectrometry. Moreover, we also summarized the novel hyphenated techniques of the advanced UHPLC-MS/MS coupled with other separation and analysis methods for the measurement of DNA damage and epigenetic modification changes in special regions and fragments of chromosomes.

Transcriptomic analysis of adult zebrafish heart and brain in response to 2, 6-dichloro-1, 4-benzoquinone exposure

Halobenzoquinones (HBQs) are emerging and widespread disinfection byproducts (DBPs), but their toxicological mechanisms to aquatic organisms remain elusive. Herein, we evaluated oxidative stress, cardiac toxicity, and cerebral toxicity after 2, 6-dichloro-1, 4-benzoquinone (2,6-DCBQ) exposure in zebrafish. Adult zebrafish were respectively exposed to 0.25, 0.5, and 1 μM 2,6-DCBQ for 96 h. The mortality rate of 2,6-DCBQ (1 μM) was 10%, while the LC50 value was 1.532 μM. Besides, 2,6-DCBQ exposure caused irregularity and elimination of myocardial fiber in the heart, and the pyknosis of nuclears and the agglutination of chromatin in the brain. We measured the 2,6-DCBQ-induced oxidative stresses in the heart and brain. Additionally, the glutathione (GSH) content, superoxide dismutase (SOD) activity, catalase (CAT) activity, and total antioxidant capacity (T-AOC) were significantly inhibited. To better understand the potential toxicity of 2,6-DCBQ, transcriptomic analysis was performed in the control and 1 μM group after 96 h exposure. As a result, 545 and 1228 differentially expressed genes (DEGs) were detected in the heart and brain, respectively. GO analysis revealed that these DEGs were primarily enriched in blood vessel development, vasculature development, and oxidoreductase activity in the heart; response to stimulus, nervous system development, and oxidoreductase activity in the brain. KEGG enrichment analysis indicated that the DEGs were mainly enriched in VEGF signaling pathway and vascular smooth muscle contraction pathway in the heart; neuroactive ligand-receptor interaction, and NOD-like receptor signaling pathway in the brain. These findings exposed the underlying toxicity mechanism of 2,6-DCBQ exposure on zebrafish cardiovascular and brain systems.

Dummy template based molecularly imprinted solid-phase microextraction coating for analysis of trace disinfection by-product of 2,6-dichloro-1,4-benzoquinone using high-performance liquid chromatography

Trace disinfection by-products (DBPs) produced during the disinfection of drinking water are potentially carcinogenic, teratogenic and mutagenic, which has aroused much attention recently. In this study, a molecularly imprinted (MIP) solid -phase microextraction (SPME) fiber coating was prepared by an in-situ polymerization method using a dummy template molecule for the analysis of trace 2,6-dichloroindole-1,4-benzoquinone (2,6-DCBQ), a typical DBP. The characterization results suggested that this monolithic SPME fiber under the optimized conditions had the porous structure, large surface area and good thermal stability. Due to the strong structural recognition and molecular interaction between MIP SPME coating and target molecule, it showed good extraction selectivity and capacity to trace 2,6-DCBQ with an imprinting factor of 4.7. Then, coupling with high-performance liquid chromatography (HPLC)-ultraviolet (UV) detection, a sensitive analytical method for trace 2,6-DCBQ in water samples was successfully established with a detection limit down to 2.3 ng/mL. The recoveries of the proposed method were in range of 84.4-122% with the relative standard deviations of 1.0-13% (n = 3). The results showed that this MIP SPME-HPLC-UV method possessed high analytical selectivity and sensitivity for trace 2,6-DCBQ in water, which would benefit the improvement of the practicability of DBPs monitoring and detection methodology.

Analytical discovery of water disinfection byproducts of toxicological relevance: highlighting halobenzoquinones

Analytical advancement enables discoveries in water research, and challenges in the identification and determination of a wide range of trace level toxic compounds in water drives the development of new analytical platforms and tools. The identification of toxic disinfection byproducts (DBPs) in disinfected drinking water is an excellent example. Water disinfection is necessary to protect the public from waterborne disease. However, an unintentional consequence is the formation of DBPs resulting from reactions of disinfectants with natural organic matter in source water. To date, regulated DBPs do not account for the increased bladder cancer risk estimated in epidemiological studies. The majority of halogenated DBPs remain unidentified and the discovery of unknown DBPs of toxicological relevance continues to be a major focus of current water research. This review will highlight halobenzoquinones as a class of DBPs that serves as an example of analytical development and toxicological studies. We will feature recent trends and gaps in analytical technologies for identification of unknown DBPs and bioassays for evaluation of the toxicological effects of specific DBPs and their mixtures.

Occurrence and toxicity of halobenzoquinones as drinking water disinfection byproducts

Halobenzoquinones (HBQs) are emerging unregulated drinking water disinfection byproducts (DBPs) that are more toxic than regulated DBPs. This study aimed to determine the distribution and formation of HBQs in drinking water from water treatment plants in China, compare their chronic cytotoxicity and their induction of chromosomal damage in Chinese hamster ovary cells, and analyze the correlation of HBQ toxicity with their physicochemical parameters. Two HBQs, 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ) and 2,6-dibromo-1,4-benzoquinone (2,6-DBBQ), were detected in finished water and tap water in China. The concentrations were in the ranges of <2.6-19.70 ng/L for 2,6-DCBQ and <0.38-1.8 ng/L for 2,6-DBBQ. Chemical oxygen demand and residual chlorine were positively correlated with HBQ formation. The HBQ concentration was lower in a drinking water treatment plant using chlorine dioxide. High Ca²⁺ in tap water decreased the HBQ level. The rank order of HBQ by cytotoxicity was 2-chloro-1,4-benzoquinone > 2,3-diiodo-1,4-benzoquinone > 2,6-diiodo-1,4-benzoquinone > 2,6-dibromo-1,4-benzoquinone > 2,5-dibromo-1,4-benzoquinone > 2,5-dichloro-1,4-benzoquinone > 2,6-dichloro-1,4-benzoquinone > tetrachloro-1,4-benzoquinone > 2,3,6-trichloro-1,4-benzoquinone, and for their genotoxicity, 2,5-dichloro-1,4-benzoquinone > 2,6-dichloro-1,4-benzoquinone > 2,3-diiodo-1,4-benzoquinone > 2,6-diiodo-1,4-benzoquinone > tetrachloro-1,4-benzoquinone > 2,5-dibromo-1,4-benzoquinone > 2,6-dibromo-1,4-benzoquinone > 2,3,6-trichloro-1,4-benzoquinone. The cytotoxicity of six dihalo-HBQs was negatively correlated with the octanol-water partition coefficient (r = -0.971, P < 0.05), molar refractivity (r = -0.956, P < 0.05), energy of the highest occupied molecular orbital (E_HOMO) (r = -0.943, P < 0.05), and polar surface area (r = -0.829, P < 0.05). The genotoxicity of these three pairs of dihalo-HBQ isomers followed the same order as their E_HOMO values. This study reveals the occurrence and formation of HBQs in drinking water in China and systematically evaluates the chromosomal damage caused by nine HBQs in mammalian cells.

Profiling of the assembly of RecA nucleofilaments implies a potential target for environmental factors to disturb DNA repair

Double-strand breaks (DSBs), one class of the most harmful DNA damage forms that bring elevated health risks, need to be repaired timely and effectively. However, an increasing number of environmental pollutants have been identified to impair DSB repair from various mechanisms. Our previous work indicated that the formation of unsaturated RecA nucleofilaments plays an essential role in homology recombination (HR) pathway which can accurately repair DSBs. In this study, by developing a benzonase cutting protection assay and combining it with traditional electrophoretic mobility shift assay (EMSA) analysis, we further investigated the assembly patterns of four RecA mutants that display differential DSB repair ability and ATPase activity. We observed that the mutants (G204S and S69G) possessing both ATP hydrolysis and DSB repair activities form unsaturated nucleofilaments similar to that formed by the wild type RecA, whereas the other two ATP hydrolysis-deficient mutants (K72R and E96D) that fail to mediate HR form more compacted nucleofilaments in the presence of ATP. These results establish a coupling of ATPase activity and effective DSB repair ability via the assembly status of RecA nucleofilaments. This linkage provides a potential target for environmental factors to disturb the essential HR pathway for DSB repair by suppressing the ATPase activity and altering the assembly pattern of nucleofilaments.

Multienzyme Cascade Bioreactor for a 10 min Digestion of Genomic DNA into Single Nucleosides and Quantitative Detection of Structural DNA Modifications in Cellular Genomic DNA

Identification and quantification of chemical DNA modifications provide essential information on genomic DNA changes, for example, epigenetic modifications and abnormal DNA lesions. In this vein, it requires to digest genomic DNA strands into single nucleosides, facilitating the mass spectrometry analysis. However, rapid digestion of such supramacromolecule DNA of several millions Daltons (molecular weight) into single nucleosides remains very challenging. Here, we constructed an immobilized benzonase capillary bioreactor and further tandemly coupled with immobilized snake venom phosphodiesterase and alkaline phosphatase capillary bioreactor to form a novel three-enzyme cascade bioreactor (BenzoSAC bioreactor). In these constructions, the chosen enzymes were immobilized onto synthetic porous capillary silica monoliths. With the tailor-made porous structure and high immobilized capacity and high digestion rate of benzonase, genomic DNA of >99.5% can be digested into single nucleosides within only 10 min when passing through the BenzoSAC bioreactor by microinjection pump. In contrast, traditional digestion requires 8-24 h. By offline coupling this benzoSAC bioreactor with liquid chromatography-tandem mass spectrometry, we detected 5-hydroxymethylcytosine, a major oxidation product of the epigenetically crucial 5-methylcytosine, in genomic DNA isolated from ladder cancer (T24) cells. The newly synthesized BenzoSAC bioreactor and the proposed mass spectrometry detection are promising for fast identification and analysis of structural modifications in DNA.

Halobenzoquinone-Induced Alteration of Gene Expression Associated with Oxidative Stress Signaling Pathways

Halobenzoquinones (HBQs) are emerging disinfection byproducts (DBPs) that effectively induce reactive oxygen species and oxidative damage in vitro. However, the impacts of HBQs on oxidative-stress-related gene expression have not been investigated. In this study, we examined alterations in the expression of 44 genes related to oxidative-stress-induced signaling pathways in human uroepithelial cells (SV-HUC-1) upon exposure to six HBQs. The results show the structure-dependent effects of HBQs on the studied gene expression. After 2 h of exposure, the expression levels of 9 to 28 genes were altered, while after 8 h of exposure, the expression levels of 29 to 31 genes were altered. Four genes ( HMOX1, NQO1, PTGS2, and TXNRD1) were significantly upregulated by all six HBQs at both exposure time points. Ingenuity pathway analysis revealed that the Nrf2 pathway was significantly responsive to HBQ exposure. Other canonical pathways responsive to HBQ exposure included GSH redox reductions, superoxide radical degradation, and xenobiotic metabolism signaling. This study has demonstrated that HBQs significantly alter the gene expression of oxidative-stress-related signaling pathways and contributes to the understanding of HBQ-DBP-associated toxicity.