Oral Exposure to 1,4-Dioxane Induces Hepatic Inflammation in Mice: The Potential Promoting Effect of the Gut Microbiome.

1,4-Dioxane is a widely used industrial solvent that has been frequently detected in aquatic environments. However, the hepatotoxicity of long-term dioxane exposure at environmentally relevant concentrations and underlying mechanisms of liver damage remain unclear. In this study, male mice were exposed to dioxane at concentrations of 0.5, 5, 50, and 500 ppm for 12 weeks, followed by histopathological examination of liver sections and multiomics investigation of the hepatic transcriptome, serum metabolome, and gut microbiome. Results showed that dioxane exposure at environmentally relevant concentrations induced hepatic inflammation and caused changes in the hepatic transcriptome and serum metabolic profiles. However, no inflammatory response was observed after in vitro exposure to all concentrations of dioxane and its in vivo metabolites. The gut microbiome was considered to be contributing to this apparently contradictory response. Increased levels of lipopolysaccharide (LPS) may be produced by some gut microbiota, such as Porphyromonadaceae and Helicobacteraceae, after in vivo 500 ppm of dioxane exposure. LPS may enter the blood circulation through an impaired intestinal wall and aggravate hepatic inflammation in mice. This study provides novel insight into the underlying mechanisms of hepatic inflammation induced by dioxane and highlights the need for concerns about environmentally relevant concentrations of dioxane exposure.

A comparative evaluation of the immunotoxicity and immunomodulatory effects on macrophages exposed to aromatic trihalogenated DBPs.

Objective: 2,4,6-trichlorophenol (TCP), 2,4,6-tribromophenol (TBP), and 2,4,6-triiodophenol (TIP) are three aromatic halogenated disinfection byproducts (DBPs) identified in chlorinated saline effluents. This study aimed to evaluate and compare their immunotoxicity and immunomodulatory effects on macrophages. Materials and methods: CCK-8 assay was used to evaluate cytotoxicity of TCP, TBP, and TIP in mouse macrophage RAW264.7 cells. A light microscope and digital camera were used to record the morphological changes of RAW264.7 cells. qRT-PCR was used to measure the mRNA levels of polarization markers and secreted cytokines. Cytokine production was also detected by ELISA. Flow cytometry was performed to analyze the expression of M1 and M2 markers on macrophages. Results: TCP, TBP, and TIP had different cytotoxic effects on macrophages. The rank order of cytotoxicity was TIP > TBP > TCP. Furthermore, the three halogenated DBPs displayed different preferences for macrophage polarization. Intriguingly, 200 µM TIP remarkably induced the M2-dominant polarization of macrophages, while 200 µM TCP induced an M1-dominant polarization of macrophages. TBP has a moderate ability in inducing M1 and M2 polarization compared with TCP and TIP. Conclusions: TIP displayed higher cytotoxicity against macrophages than TBP and TCP, its brominated and chlorinated analogs. Since M1 and M2 macrophages facilitate the inflammatory and anti-inflammatory responses, respectively, the discrepancy of TCP, TBP, and TIP in inducing macrophage polarization may lead to distinct immunomodulatory and toxicological outcomes, thus giving rise to different types of diseases. This finding may provide novel insights into evaluating the toxicity of environmental pollutants on the immune system.

In vivo toxicity evaluations of halophenolic disinfection byproducts in drinking water: A multi-omics analysis of toxic mechanisms.

Halophenolic disinfection byproducts (DBPs) in drinking water have attracted considerable concerns in recent years due to their wide occurrence and high toxicity. The liver has been demonstrated as a major target organ for several halophenolic DBPs. However, little is known about the underlying mechanisms of liver damage caused by halophenolic DBPs. In this study, 2,4,6-trichlorophenol (TCP), 2,4,6-tribromophenol (TBP) and 2,4,6-triiodiophenol (TIP) were selected as representative halophenolic DBPs and exposed to C57BL/6 mice at an environmentally-relevant concentration (0.5 µg/L) and two toxicological concentrations (10 and 200 µg/L) for 12 weeks. Then, a combination of histopathologic and biochemical examination, liver transcriptome, serum metabolome, and gut microbiome was adopted. It was found that trihalophenol exposure significantly elevated the serum levels of alkaline phosphatase and albumin. Liver inflammation was observed at toxicological concentrations in the histopathological examination. Transcriptome results showed that the three trihalophenols could impact immune-related pathways at 0.5 µg/L, which further contributed to the disturbance of pathways in infectious diseases and cancers. Notably, TBP and TIP had higher immunosuppressive effects than TCP, which might lead to uncontrolled infection and cancer. In terms of serum metabolic profiles, energy metabolism pathway of citrate cycle and amino acid metabolism pathways of valine, leucine, and isoleucine were also significantly affected. Integration of the metabolomic and transcriptomic data suggested that a 12-week trihalophenol exposure could prominently disturb the glutathione metabolism pathway, indicating the impaired antioxidation and detoxification abilities in liver. Moreover, the disorder of the intestinal flora could interfere with immune regulation and host metabolism. This study reveals the toxic effects of halophenolic DBPs on mammalian liver and provides novel insights into the underlying mechanisms of hepatotoxicity.

The involvement of branched-chain amino acids (BCAAs) in aromatic trihalogenated DBP exposure-induced kidney damage in mice.

Disinfection by-products (DBPs) are inevitably generated in the process of disinfection. Among them, aromatic halogenated DBPs, such as 2,4,6-trichlorophenol (TCP), 2,4,6-tribromophenol (TBP) and 2,4,6-triiodophenol (TIP), have attracted considerable interest for their high toxicity. A systematic nephrotoxicity evaluation of 2,4,6-trihalophenols is still lacking. In this study, mice were exposed to TCP, TBP and TIP ranging from environmental-related low concentration to high concentration that commonly used in animal study (0.5-200 µg/L). Kidney histopathology, urine protein detection and urine metabolomics were performed. Remarkable changes including kidney damage, proteinuria and glomerular mesangial cell proliferation were observed after three 2,4,6-trihalophenol exposure, even at low concentration of 0.5 µg/L. The nephrotoxicity rank order was TIP > TBP > TCP. Additionally, in vivo exposure to 2,4,6-trihalophenols also led to apparent changes in urinary metabolic profiles. Biosynthesis pathways of branched-chain amino acids (BCAAs, containing valine, leucine and isoleucine) were disturbed even at the early stage of exposure (4 weeks). Intriguingly, it has been reported that BCAAs could promote the proliferation of glomerular mesangial cells. Thus, in vitro cell experiments were further performed on mouse glomerular mesangial cell line MES-13. Consistently with in vivo results, cell proliferation was observed in MES-13 cells after exposure to 2,4,6-trihalophenols, especially to TBP and TIP. Meanwhile, TCP at high concentration, TBP and TIP at not only high concentration but also low concentration, induced BCAAs accumulation in glomerular mesangial cells, which was completely commensurate to that observed in cell proliferation assay. Then the proliferation of MES-13 cells induced by 2,4,6-trihalophenols was remarkably inhibited after BCAAs interference. Here we provide direct link between disturbed BCAAs and the nephrotoxicity of 2,4,6-trihalophenols. 2,4,6-trihalophenols could induce excess BCAAs, which further led to proliferation of glomerular mesangial cells and renal injury. This study revealed the nephrotoxicity of aromatic trihalogenated DBPs and provided new insights into the potential toxic mechanisms.

1,4-Dioxane exposure induces kidney damage in mice by perturbing specific renal metabolic pathways: An integrated omics insight into the underlying mechanisms.

1,4-Dioxane (dioxane), an industrial solvent widely detected in environmental and biological matrices, has potential nephrotoxicity. However, the underlying mechanism by which dioxane induces kidney damage remains unclear. In this study, we used an integrated approach, combining kidney transcriptomics and urine metabolomics, to explore the mechanism for the toxic effects of dioxane on the mouse kidney. Transcriptomics profiling showed that exposure to 0.5 mg/L dioxane induced perturbations of multiple signaling pathways in kidneys, such as MAPK and Wnt, although no changes in oxidative stress indicators or anatomical pathology were observed. Exposure to 500 mg/L dioxane significantly disrupted various metabolic pathways, concomitantly with observed renal tissue damage and stimulated oxidant defense system. Urine metabolomic analysis using NMR indicated that exposure to dioxane gradually altered the metabolic profile of urine. Within the full range of altered metabolites, the metabolic pathway containing glycine, serine and threonine was the most significantly altered pathway at the early stage of exposure (3 weeks) in both 0.5 and 500 mg/L dioxane-treated groups. However, with prolonged exposure (9 and 12 weeks), the level of taurine significantly decreased after treatment of 0.5 mg/L dioxane, while exposure to 500 mg/L dioxane significantly increased glutathione levels in urine and decreased arginine metabolism. Furthermore, integrated omics analysis showed that 500 mg/L dioxane exposure induced arginine deficiency by perturbing several genes involved in renal arginine metabolism. Shortage of arginine coupled with increased oxidative stress could lead to renal dysfunction. These findings offer novel insights into the toxicity of dioxane.