Multidrug Resistance Protein 4 (MRP4/ABCC4) Protects Cells from the Toxic Effects of Halobenzoquinones

Investigation of the nephrotoxicity of 2,6-dichloro-1,4-benzoquinone disinfection by-product in mice through a 28-day toxicity test

In recent years, 2,6-dichloro-1,4-benzoquinone (DCBQ) has become an emerging water disinfection by-product and widely distributed in disinfected water. Although kidney is a potential target of DCBQ, a systematic study of the in vivo nephrotoxicity of DCBQ is rare. In this study, a 28-day oral toxicity test was used to assess the nephrotoxic effects of DCBQ on mice. And the potential mechanisms of nephrotoxicity induced by DCBQ were explored through inflammation, oxidative stress, apoptosis and gut microbiota. The results showed that the kidney indexes of mice were not altered in DCBQ-exposed group in comparison with the control group. The histopathological investigation revealed that DCBQ caused swollen of renal tube, destruction of the renal structure, and infiltration of inflammatory cell in kidney. DCBQ has induced oxidative damage in kidney, as the observation of the increase of the renal superoxide dismutase (SOD) and catalase (CAT) activity. Also, DCBQ has triggered the inflammatory response in kidney through the increased expression of IL-1β, NF-κB and iNOS. Moreover, DCBQ has activated the apoptosis pathway, as indicated by the increased mRNA expression of Caspase-3 and Caspase-9. We eventually found an association between gut microbiota and nephrotoxic variables, demonstrating the importance of gut-kidney axis in DCBQ toxicity. Our results suggested that exposure to DCBQ in disinfected water might be a risk factor for kidney and provided novel insights into the underlying mechanisms of DCBQ-induced kidney injury, contributing to better interpretation of the health impact of the environmentally emerging contaminant DCBQ.

Untargeted metabolomics of human keratinocytes reveals the impact of exposure to 2,6-dichloro-1,4-benzoquinone and 2,6-dichloro-3-hydroxy-1,4-benzoquinone as emerging disinfection by-products

INTRODUCTION

The 2,6-dichloro-1,4-benzoquinone (DCBQ) and its derivative 2,6-dichloro-3-hydroxy-1,4-benzoquinone (DCBQ-OH) are disinfection by-products (DBPs) and emerging pollutants in the environment. They are considered to be of particular importance as they have a high potential of toxicity and they are likely to be carcinogenic.

OBJECTIVES

In this study, human epidermal keratinocyte cells (HaCaT) were exposed to the DCBQ and its derivative DCBQ-OH, at concentrations equivalent to their IC20 and IC50, and a study of the metabolic phenotype of cells was performed.

METHODS

The perturbations induced in cellular metabolites and their relative content were screened and evaluated through a metabolomic study, using 1H-NMR and MS spectroscopy.

RESULTS

Changes in the metabolic pathways of HaCaT at concentrations corresponding to IC20 and IC50 of DCBQ-OH involved the activation of cell membrane α-linolenic acid, biotin, and glutathione and deactivation of glycolysis/gluconeogenesis at IC50. The changes in metabolic pathways at IC20 and IC50 of DCBQ were associated with the activation of inositol phosphate, pertaining to the transfer of messages from the receptors of the membrane to the interior as well as with riboflavin. Deactivation of biotin metabolism was recorded, among others. The cells exposed to DCBQ exhibited a concentration-dependent decrease in saccharide concentrations. The concentration of steroids increased when cells were exposed to IC20 and decreased at IC50. Although both chemical factors stressed the cells, DCBQ led to the activation of transporting messages through phosphorylated derivatives of inositol.

CONCLUSION

Our findings provided insights into the impact of the two DBPs on human keratinocytes. Both chemical factors induced energy production perturbations, oxidative stress, and membrane damage.

Multidrug resistance protein 4 (MRP4/ABCC4) is overexpressed in clear cell renal cell carcinoma (ccRCC) and is essential to regulate cell proliferation

Kidney cancer accounts for 2.5% of all cancers, with an annual global incidence of almost 300,000 cases leading to 111,000 deaths. Approximately 85% of kidney tumors are renal cell carcinoma (RCC) and their major histologic subtype is clear cell renal cell carcinoma (ccRCC). Although new therapeutic treatments are being designed and applied based on the combination of tyrosine kinase inhibitors and immunotherapy, no major impact on the mortality has been reported so far. MRP4 is a pump efflux that transporters multiple endogenous and exogenous substances. Recently it has been associated with tumoral persistence and cell proliferation in several types of cancer including pancreas, lung, ovary, colon, ostesarcoma, etc. Herein, we demonstrate for the first time, that MRP4 is overexpressed in ccRCC tumors, compared to control renal tissues. In addition, using cell culture models, we observed that MRP4 pharmacological inhibition produces an imbalance in cAMP metabolism, induces cell arrest, changes in lipid composition, increase in cytoplasmic lipid droplets and finally apoptosis. These data provide solid evidence for the future evaluation of MRP4 as a possible new therapeutic target in ccRCC.

Cytotoxicity of Halogenated Tyrosyl Compounds, an Emerging Class of Disinfection Byproducts

Halogenated amino acids and peptides are an emerging class of disinfection byproducts (DBPs), having been detected in drinking water and in washed food products. However, the toxicological significance of these emerging DBPs remains unclear. In this study, the cytotoxicity of eight halogenated tyrosyl compounds was investigated in Chinese hamster ovary (CHO) cells using real-time cell analysis (RTCA). Dihalogenated tyrosyl compounds are more cytotoxic than their monohalogenated analogues. The cytotoxicity of the dihalogenated compounds is associated with their ability to induce intracellular reactive oxygen species (ROS), suggesting that oxidative stress is an important toxicity pathway of these compounds. Pearson correlation analysis of the cytotoxicity (IC₅₀ values) of these compounds with eight physicochemical parameters showed strong associations with their lipophilicity (logP) and reactivity (polarizability, E_LUMO). Finally, cytotoxicity testing of the concentrated extracts of a chloraminated mixture of eight dipeptides with bromide or iodide showed the cytotoxicity of these mixtures in the order: iodinated peptides > brominated peptides ≥ chlorinated peptides. These results demonstrate that halogenated peptide DBPs are toxicologically relevant, and further research is needed to understand the implications of long-term exposure for human health.

Assessment of the in vitro toxicity of the disinfection byproduct 2,6-dichloro-1,4-benzoquinone and its transformed derivatives

An emerging class of unregulated disinfection byproducts, halobenzoquinones (HBQs), has gained recent interest following suggestions of enhanced toxicity compared to regulated disinfection byproducts. While the kinetics of HBQ hydrolysis in water have been well characterized, the stability of HBQs in cell culture media, a critical parameter when evaluating toxicity in vitro, has been overlooked. The objective of this study was: (1) to contrast the stability of a prevalent HBQ, 2,6-dichloro-1,4-benzoquinone (DCBQ), in cell culture media and water, and (2) to evaluate the cytotoxicity of parent and transformed DCBQ compounds as well as the ability of these compounds to generate intracellular reactive oxygen species (ROS) in normal human colon cells (CCD 841 CoN) and human liver cancer cells (HepG2). The half-life of DCBQ in cell media was found to be less than 40 min, compared to 7.2 h in water at pH 7. DCBQ induced a concentration-dependent decrease in cell viability and increase in ROS production in both cell lines. The parent DCBQ compound was found to induce significantly greater cytotoxicity compared to transformed DCBQ products. We demonstrate that the study design used by most published studies (i.e., extended exposure periods) has led to a potential underestimation of the cytotoxicity of HBQs by evaluating the toxicological profile primarily of transformed HBQs, rather than corresponding parent compounds. Future in vitro toxicological studies should account for HBQ stability in media to evaluate the acute cytotoxicity of parent HBQs.

The toxic potentials and focus of disinfection byproducts based on the human embryonic kidney (HEK293) cell model

Disinfection byproducts (DBPs) are inevitably generated during drinking water disinfection processes, and their hazards have not been well characterized. Because they plausibly cause toxicological and pathological damage to human kidney, we selected the human embryonic kidney (HEK293) cell, instead of the commonly used CHO cell, as a model to investigate the toxic potential and target of 10 DBPs, including 3 haloacetamides, 2 trihaloacetaldehydes and 5 iodomethanes. Based on the chronic toxicity parameter EC₁₀ of the cell viability test, we obtained a toxic rank of the tested DBPs different from previous studies and calculated their risk quotients by combining their actual concentrations in drinking water systems. Then, dichloroacetamide (DCAM), trichloroacetaldehyde (TCAL), and bromochloroiodomethane (BCIM) were selected to conduct multiple mechanistic bioassays, including cellular lactate dehydrogenase (LDH) assay, ATP metabolism, ROS production, mitochondria-derived apoptosis and qRT-PCR assay. All bioassays revealed the effects of interrupting the molecular, physiological and biochemical processes relevant to mitochondrial functions, such as oxidative respiration, apoptosis, and energy metabolism. Our study improved the human risk assessment of DBPs with the help of a convenient model and parameter and revealed that mitochondrion is a potential toxic focus of DBPs exposure at the cellular level.

Genetic Basis of Phenotypic Differences Between Chinese Yunling Black Goats and Nubian Goats Revealed by Allele-Specific Expression in Their F1 Hybrids

Chinese Yunling black goats and African Nubian goats are divergent breeds showing significant differences in body size, milk production, and environmental adaptation. However, the genetic mechanisms underlying these phenotypic differences remain to be elucidated. In this report, we provide a detailed portrait of allele-specific expression (ASE) from 54 RNA-Seq analyses across six tissues from nine F1 hybrid offspring generated by crossing the two breeds combined with 13 genomes of the two breeds. We identified a total of 524 genes with ASE, which are involved in bone development, muscle cell differentiation, and the regulation of lipid metabolic processes. We further found that 38 genes with ASE were also under directional selection by comparing 13 genomes of the two breeds; these 38 genes play important roles in metabolism, immune responses, and the adaptation to hot and humid environments. In conclusion, our study shows that the exploration of genes with ASE in F1 hybrids provides an efficient way to understand the genetic basis underlying the phenotypic differences of two diverse goat breeds.

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.

Drinking Water Disinfection Byproducts (DBPs) and Human Health Effects: Multidisciplinary Challenges and Opportunities

While drinking water disinfection has effectively prevented waterborne diseases, an unintended consequence is the generation of disinfection byproducts (DBPs). Epidemiological studies have consistently observed an association between consumption of chlorinated drinking water with an increased risk of bladder cancer. Out of the >600 DBPs identified, regulations focus on a few classes, such as trihalomethanes (THMs), whose concentrations were hypothesized to correlate with the DBPs driving the toxicity of disinfected waters. However, the DBPs responsible for the bladder cancer association remain unclear. Utilities are switching away from a reliance on chlorination of pristine drinking water supplies to the application of new disinfectant combinations to waters impaired by wastewater effluents and algal blooms. In light of these changes in disinfection practice, this article discusses new approaches being taken by analytical chemists, engineers, toxicologists and epidemiologists to characterize the DBP classes driving disinfected water toxicity, and suggests that DBP exposure should be measured using other DBP classes in addition to THMs.