Mass spectrometric determination of N7-HPTE-dG and N7-HPTE-Gua in mammalian cells and mice exposed to methoxychlor, an emergent persistent organic pollutant

An integrated LC-MS/MS platform for noninvasive urinary nucleus acid adductomics: A pilot study for tobacco exposure

Tobacco smoke exposure significantly increases the level of global nucleoside damage. To evaluate all aspects of nucleic acid (NA) modifications, NA adductomics analyzes DNA, RNA and nucleobase adducts and provides comprehensive data. Liquid chromatography-tandem triple quadrupole mass spectrometry (LC-QQQ-MS/MS) and LC-Zeno-TOF-MS/MS were employed to screen for DNA, RNA and nucleobase adducts, as part of the analytical platform that was designed to combine high sensitivity and high resolution detection. We identified and distinguished urine nucleoside adducts via precursor ion and neutral loss scanning. A total of 245 potential adducts were detected, of which 28 were known adducts. The smoking group had significantly higher concentrations of nucleoside adducts in rat urine than the control group, based on MRM scanning, which was then used to perform relative quantitative analysis of these adducts. Urine nucleoside adducts were further confirmed using LC-Zeno-TOF-MS/MS. This highlights the potential of untargeted detection methods to provide comprehensive data on both known and unknown adducts. These approaches can be used to investigate the interactions among oxidative and alkylation stresses, and epigenetic modifications caused by exposure to tobacco smoke.

DNA adductomics aided rapid screening of genotoxic impurities using nucleosides and 3D bioprinted human liver organoids

Current genotoxicity assessment methods are mainly employed to verify the genotoxic safety of drugs, but do not allow for rapid screening of specific genotoxic impurities (GTIs). In this study, a new approach for the recognition of GTIs has been proposed. It is to expose the complex samples to an in vitro nucleoside incubation model, and then draw complete DNA adduct profiles to infer the structures of potential genotoxic impurities (PGIs). Subsequently, the genotoxicity is confirmed in human by 3D bioprinted human liver organoids. To verify the feasibility of the approach, lansoprazole chloride compound (Lanchlor), a PGI during the synthesis of lansoprazole, was selected as the model drug. After confirming genotoxicity by Comet assay, it was exposed to different models to map and compare the DNA adduct profiles by LC-MS/MS. The results showed Lanchlor could generate diverse DNA adducts, revealing firstly its genotoxicity at molecular mechanism of action. Furthermore, the largest variety and content of DNA adducts were observed in the nucleoside incubation model, while the human liver organoids exhibited similar results with rats. The results showed that the combination of DNA adductomics and 3D bioprinted organoids were useful for the rapid screening of GTIs.

Pyrite-assisted degradation of methoxychlor by laccase immobilized on Fe3S4/earthworm-like mesoporous SiO2

Laccase immobilized and cross-linked on Fe3S4/earthworm-like mesoporous SiO2 (Fe3S4/EW-mSiO2) was used to degrade methoxychlor (MXC) in aqueous environments. The effects of various parameters on the degradation of MXC were determined using free and immobilized laccase. Immobilization improved the thermal stability and reuse of laccase significantly. Under the conditions of pH 4.5, temperature 40 °C, and reaction time 8 h, the degradation rate of MXC by immobilized laccase reached a maximum value of 40.99% and remained at 1/3 of the original after six cycles. The excellent degradation performance of Fe3S4/EW-mSiO2 was attributable to the pyrite (FeS2) impurity in Fe3S4, which could act as an electron donor in reductive dehalogenation. Sulfide groups and Fe2+ reduced the activation energy of the system resulting in pyrite-assisted degradation of MXC. The degradation mechanism of MXC in aqueous environments by laccase immobilized on Fe3S4/EW-mSiO2 was determined via mass spectroscopy of the degradation products. This study is a new attempt to use pyrite to support immobilized laccase degradation.

Hydrolytic degradation of methoxychlor by immobilized cellulase on LDHs@Fe3O4 nanocomposites

In this study, we synthesized Fe3O4 using the co-precipitation method and then prepared magnetic carrier LDHs@Fe3O4 by immobilizing layered double hydroxide on Fe3O4 by in situ growth method. Cellulase was immobilized on this magnetic carrier by using glutaraldehyde as a coupling agent, which can be used for degrading Methoxychlor (MXC). The results demonstrated the maximum MXC removal efficiency of 73.4% at 45 °C and pH = 6.0 with excellent reusability. Through kinetic analysis, it was found that the degradation reaction conforms to the Langmuir-Hinshelwood model and is a first-order reaction. Finally, according to the EPR analysis, the active radicals in the system were found to be OH· and the degradation mechanism was proposed in combination with LC-MS. This study provides a feasible method for degrading organochlorine pesticides, which can be used for groundwater purification.

DNA damage resulting from human endocrine disrupting chemical exposure: Genotoxicity, detection and dietary phytochemical intervention

In recent years, exposure to endocrine disrupting chemicals (EDCs) has posed an increasing threat to human health. EDCs are major risk factors in the occurrence and development of many diseases. Continuous DNA damage triggers severe pathogenic consequences, such as cancer. Beyond their effects on the endocrine system, EDCs genotoxicity is also worthy of attention, owing to the high accessibility and bioavailability of EDCs. This review investigates and summarizes nearly a decade of DNA damage studies on EDC exposure, including DNA damage mechanisms, detection methods, population marker analysis, and the application of dietary phytochemicals. The aims of this review are (1) to systematically summarize the genotoxic effects of environmental EDCs (2) to comprehensively summarize cutting-edge measurement methods, thus providing analytical solutions for studies on EDC exposure; and (3) to highlight critical data on the detoxification and repair effects of dietary phytochemicals. Dietary phytochemicals decrease genotoxicity by playing a major role in the detoxification system, and show potential therapeutic effects on human diseases caused by EDC exposure. This review may support research on environmental toxicology and alternative chemo-prevention for human EDC exposure.

Toxicity and mutagenicity studies of 6PPD-quinone in a marine invertebrate species and bacteria

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-quinone), an oxidation product of the tire additive, 6PPD, has been associated with high mortality of salmonids (0.1 μg/L). The objective of this study was to determine the acute toxicity using neonates and mutagenicity (micronuclei in hemolymph of exposed adults) of 6PPD-quinone in the marine amphipod Parhyale hawaiensis. Also, we studied its mutagenicity in the Salmonella/microsome assay using five strains of Salmonella with and without metabolic system (rat liver S9, 5%). 6PPD-quinone did not present acute toxicity to P. hawaiensis from 31.25 to 500 μg/L. Micronuclei frequency increased after 96 h-exposure to 6PPD-quinone (250 and 500 μg/L) when compared to the negative control. 6PPD-quinone also showed a weak mutagenic effect for TA100 only in the presence of S9. We conclude that 6PPD-quinone is mutagenic to P. hawaiensis and weakly mutagenic to bacteria. Our work provides information for future risk assessment of the presence of 6PPD-quinone in the aquatic environment.

A new toxicity mechanism of N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone: Formation of DNA adducts in mammalian cells and aqueous organisms

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPDQ), one of the oxidation products of rubber antioxidant 6PPD, has been identified as a novel toxicant to many organisms. However, an understanding of its underlying toxicity mechanisms remained elusive. In this study, we reported that 6PPDQ could react with deoxyguanosine to form one isomer of 3-hydroxy-1, N²-6PPD-etheno-2'-deoxyguanosine (6PPDQ-dG). Next, by employing an ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS) method, we found that 6PPDQ-dG could be detected in genomic DNA from 6PPDQ-treated mammalian cells and Chlamydomonas reinhardtii. We observed positive correlations between concentrations of exogenous 6PPDQ and the amounts of 6PPDQ-dG, and a recovery period after removal of 6PPDQ also led to decreased levels of the adduct in both organisms, which suggested potential repair pathways for this adduct in mammalian cells and unicellular algae. Additionally, we extracted the genomic DNA from tissues of frozen capelin and observed substantial amounts of the adduct in roe and gills, as well as livers at a relatively lower level. These results provided insights into the target organs and tissues that 6PPDQ might accumulate or harm fish. Overall, our study provides a new understanding of the mechanisms of toxicity of 6PPDQ in mammalian cells and aqueous organisms.

Enrichment of nucleobase adducts from genomic DNA in the cytoplasm by solid-phase extraction

The exact levels of some DNA adducts, like N7-deoxyguanosine (N7-dG), can be under-calculated since these adducts may depurinate due to their chemical instability, leading to corresponding nucleobase adducts being released into the cytoplasm. To accurately quantify the levels of DNA adducts, it is necessary to consider those modified nucleobases. However, high levels and diversity of cytoplasmic small molecule metabolites (SMMs) can strongly interfere with the detection of adducts, and it is almost impossible to remove them with nucleobase adducts being well retained. Therefore, we aimed to establish an optimized enrichment method based on solid-phase extraction (SPE) to reduce the co-elution of SMMs with target analytes. In this vein, we employed three bisphenols (BPA, BPF, and BPAF) as examples, prepared corresponding N7-guanine (N7-Gua) adducts, loaded on an Oasis hydrophilic-lipophilic balance ® (HLB) cartridge, used a series of mobile phases containing different percentage of methanol for elution, and evaluated the levels of these adducts in each eluent. First, we found that neutral samples led to the best retention for all three adducts compared with acidified or basified ones. We next employed normal distribution fitting model to characterize the elution of analytes from H₂O/methanol with different pHs and observed that neutral mobile phases resulted in more hydrophobic elution for all three adducts. Besides, N7-BPA-Gua and N7-BPF-Gua obtained narrow fitted peaks at neutral pH, while N7-BPAF-Gua had minimized elution windows at low pH. After optimization, we exposed 293T cells to the aforementioned bisphenols and quantified the N7-Gua adducts in the cytoplasm and the corresponding N7-dG adducts in genomic DNA. The results revealed that with the same levels of BPs exposure, BPAF led to the highest levels of adducts in both cytoplasm and genomic DNA samples, followed by BPA and BPF in order. In summary, our research established an appropriate model to describe the elution of DNA adducts in the SPE, applied it to optimize the loading and elution conditions, and discussed the genotoxicity of bisphenols by accurate quantification of both cleaved and uncleaved N7-dG adducts.