Dysregulation of Intestinal Health by Environmental Pollutants: Involvement of the Estrogen Receptor and Aryl Hydrocarbon Receptor

Comprehensive binding analysis of polybrominated diphenyl ethers and aryl hydrocarbon receptor via an integrated molecular modeling approach

Polybrominated diphenyl ethers (PBDEs) are often suspected to activate the signal transduction pathway of aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, for the induction of toxicity. Hence, the binding property of PBDEs with AhR is assumed to be associated with the ligand-dependent activation of AhR that may introduce many drug-metabolizing enzymes of genes encoding. However, the binding mechanism and the structural effect of PBDEs on their binding properties of AhR still need to be unraveled for toxicology research. A comprehensive study of the PBDEs-AhR binding mechanism was investigated using an integrated molecular modeling approach with two-dimensional quantitative structure-activity relationships (2D-QSAR), three-dimensional QSAR (3D-QSAR), and molecular docking simulation. Molecular docking revealed the differences in binding domains among 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-AhR complex and two PBDE-AhR complexes. A 2D-QSAR model was developed to analyze the overall structural effects of PBDEs on the binding affinity of AhR. It provided an insight into major physico-chemical properties by multiple linear regression based on genetic algorithm with reasonable results. The 3D-QSAR modeling discovered the detailed interaction features of binding sites, configurations and interaction fields of AhR with different PBDE ligands. This study demonstrated that the descriptors of Smin69 and MoRSEC15 were related to electronic properties and had a great effect on the relative binding affinities. The position of Br substitutions exhibited a significant influence on the interactions between AhR and PBDEs, including halogen interaction, π-S interaction, π-π stacking interaction, and hydrophobic effect. This integrated molecular modeling approach provided a comprehensive analysis of the structural effects of PBDEs on their binding properties with AhR at molecular level.

Low-concentration of dichloroacetonitrile (DCAN) in drinking water perturbs the health-associated gut microbiome and metabolic profile in rats

Dichloroacetonitrile (DCAN) is one of the emerging nitrogenous disinfection by-products (DBPs) in drinking water. However, its potential toxicological effects remain poorly understood, especially at a low concentration found in the environment. In the present study, we investigated whether the consumption of low-concentration DCAN through drinking water would produce significant effects in male SD rats, with particular focus on their physiological traits and changes in their gut microbiome and metabolite profiles. After a 4-weeks DCAN intervention, significant changes were observed in the body weight, blood indices, and histology in DCAN-treated (100 μg/L) group. Proteobacteria was relatively less abundant in 20 and 100 μg/L DCAN-treated groups compared with that in the control group at phylum level. At genus level, Parasutterella and Anaerotruncus were significantly less abundant in both 20 and 100 μg/L DCAN-treated groups than that in the control group. Furthermore, the gut microbiota-related metabolites were dramatically perturbed after DCAN consumption. In the 20 and 100 μg/L DCAN-treated groups, there were 48 and 95 altered metabolites, respectively, and were found to be involved in sphingolipid signaling pathway, fatty acid biosynthesis, and cGMP-PKG signaling pathway. In summary, we demonstrated that consumption of low-concentration DCAN through drinking water could impair host health and induce gut microbiota dysbiosis and gut microflora-related metabolic disorders in male SD rats. Our findings highlight the potential toxicity of low-concentration DBPs and provide new insight into potential causal relationship between low concentration DBPs found in the drinking water and the host health.

Sub-chronic carbendazim exposure induces hepatic glycolipid metabolism disorder accompanied by gut microbiota dysbiosis in adult zebrafish (Daino rerio)

Carbendazim (CBZ) as a broad spectrum fungicide is widely used in the whole world to contorl plant diseases. With the application of CBZ in the agriculture, it has been detected in vegetables and fruits. Nowadays, it even has been detected in the watercourse and indoor dust. However, the toxic effects of CBZ on aquatic organisms have received limited attention. In this study, male adult zebrafish were exposed at 0, 30 and 100 μg/L CBZ for 21 days to assess its effects on hepatic glycolipid metabolism. After exposure, the body weight and length decreased, but the condition factor increased significantly. Some hepatic biochemical parameters including the levels of glucose, pyruvate, low density lipoprotein (LDL) and triglyceride (TG) decreased significantly in the liver of zebrafish after exposure with CBZ. Two transaminases alanine transaminase (ALT) and aspartate transaminase (AST) also increased significantly, indicating that subchronic CBZ exposure influenced the liver function. Moreover, the relative mRNA levels of some key genes related to the glycolysis and lipid metabolism in the liver also changed significantly. Furthermore, the transcriptome analysis showed that the carbon metabolism, lipid metabolism and detoxification metabolism were also affected in the liver of CBZ exposed zebrafish. Interestingly, we also found the amounts of the Firmicutes, Bacteroidetes, Actinobacteria, α-Proteobacteria, γ-Proteobacteria and Verrucomicrobia at phylum level significantly decreased in the gut. Sequencing V3-V4 region of 16S rRNA also demonstrated gut microbiota composition changed significantly according to weighted UniFrac distance analysis. Consequently, subchronic CBZ exposure induced hepatic metabolic disorder accompanied by gut microbiota dysbiosis in adult male zebrafish.

Immunotoxicological effects of dioxin-like polychlorinated biphenyls extracted from Zhanjiang Bay sediments in zebrafish

Dioxin-like polychlorinated biphenyls (DLPCBs) are ubiquitous environmental contaminants spread all over the world. They can cause disorders in the reproductive, nervous, gut, and immune systems. We investigated the effects of DL-PCB extracted from Zhanjiang (Guangdong Province, China) offshore area on the immune functions of adult zebrafish. Zebrafish were exposed to different levels of DL-PCBs, i.e., control, positive control (PCB77 at 16.0 μg/L), low (LD; PCB81 + PCB118 at 0.32 μg/L), and high-dose (HD; PCB81 + PCB118 at 16.0 μg/L) groups for 28 days. Compared with the control group, positive control and HD group showed a significant decrease (P < 0.05) in the number of red blood cells (RBC) on day 7 and the same decrease was observed in the LD group (P < 0.05) on day 21. The results of white blood cell (WBC) profiles were opposite to that of RBCs. Moreover, the serum lysozyme activity was significantly lower in positive control and HD group (P < 0.05) on day 21 but no significant effect was observed in the LD group. The mucus lysozyme activity and immunoglobulin concentration in positive control and HD group decreased significantly (P < 0.05) from day 14. A similar effect was observed in the LD group but was significant (P < 0.05) only on day 28. Additionally, histopathological examination showed accumulation of hemosiderin in the spleen of experimental animals, which was significant in positive control and HD group. Further, renal tubular epithelial cells of head kidney were swollen in the positive control and HD group while the expansion of lumen and renal interstitial edema was observed in the LD group on day 21 and with significant presence on 28 days. Therefore, these findings suggest that the exposure of zebrafish to DL-PCBs at > 16.0 μg/L can impair their immune functions.

Probiotic Modulation of Lipid Metabolism Disorders Caused by Perfluorobutanesulfonate Pollution in Zebrafish

To determine whether and how probiotic supplement can alter gut microbiota dysbiosis and lipid metabolism disorders caused by perfluorobutanesulfonate (PFBS), the present study exposed adult zebrafish to 0, 10, and 100 μg/L PFBS for 28 days, with or without dietary administration of probiotic Lactobacillus rhamnosus. Regarding intestinal health and gut microbiota, probiotic supplement altered the innate toxicities of PFBS, depending on exposure concentration and the sex of the fish. Lactobacillus genus correlated positively (P < 0.001; r > 0.5) with other beneficial bacteria in the gut microbiota, thereby indirectly regulating host metabolic activities. In female fish, the PFBS and probiotic combination enhanced fatty acid synthesis and β-oxidation, but mitigated the accumulation of cholesterol in the blood compared with PFBS single exposure, highlighting the benefits of the probiotic to host health. In male zebrafish, probiotic administration antagonized the PFBS-induced disturbances of bile acid metabolism, presumably via farnesoid X receptor signaling. However, coexposure to PFBS and probiotic caused significant accumulation of triglyceride in male livers (2.6-fold relative to the control), implying the induction of hepatic steatosis. Overall, the present study underlined the potential of probiotics to modulate gut microbial dysbiosis and lipid metabolism disorders caused by PFBS exposure, which could provide implications to the application of probiotics in aquaculture.

Homeostasis of gut microbiota protects against polychlorinated biphenyl 126-induced metabolic dysfunction in liver of mice

Polychlorinated biphenyls (PCBs) exposure is closely associated with the prevalence of metabolic diseases, including fatty liver and dyslipidemia. Emerging literature suggests that disturbance of gut microbiota is related to PCB126-induced metabolic disorders. However, the causal role of dysbiosis in PCB126-induced fatty liver is still unknown. To clarify the role of the gut microbiome in the detoxification of PCB126 in intestine or PCB126-induced toxicity in liver, mice were administrated with drinking water containing antibiotics (ampicillin, vancomycin, neomycin, and metronidazole) or Inulin. We showed that PCB126 resulted in significant hepatic lipid accumulation, inflammation, and fibrosis. PCB126, Antibiotics, and Inulin significantly affected the structure and shifted community membership of gut microbiome. 7 KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways at level 2 and 39 KEGG pathways at level 3 were significantly affected. Antibiotics alleviated PCB126-induced fibrosis in the liver but increased inflammation. Inulin treatment ameliorated both inflammation and fibrosis in the liver of PCB126-treated mice. Neither Antibiotics nor Inulin had significant effect on PCB126-induced hepatic steatosis. The more specific intervention of gut microbiota is needed to alleviate PCB126-induced fatty liver. These data demonstrate that homeostasis of gut microbiota is critical for the defense against PCB126 toxicity and dysbiosis plays a fundamental role in the development of inflammation and fibrosis in liver of PCB126-treated mice.

Sex-dependent and organ-specific toxicity of silver nanoparticles in livers and intestines of adult zebrafish

Silver nanoparticles (AgNPs) have been increasingly manufactured and thus are increasingly detected in aquatic systems. However, there are still some overlooked factors (e.g., organism sex) in the field of nano-toxicological assessment. In this study, to explore the role of sex in nanotoxicity, adult male and female zebrafish were exposed to 100 μg/L of two uncoated commercial AgNPs with primary sizes 20 nm and 80 nm for 2 weeks, after which the impacts of AgNPs on intestines and livers of both male and female zebrafish were assessed using a suite of biomarkers. Results demonstrated that the intestinal Na/K-ATPase activity as well as the superoxide dismutase activity in male zebrafish differed significantly between 20-nm AgNPs and 80-nm AgNPs treatments (p < 0.05), indicating 20-nm AgNPs showing higher toxicity to zebrafish than the 80-nm AgNPs. Also, we noted that the used AgNPs induced sex-dependent effects on growth indices, oxidative/anti-oxidative status, neural signaling and hepatic lipid metabolism, with the male zebrafish being more sensitive to AgNPs than the females. Further, the tested AgNPs impaired the intestine much more seriously than the liver, as evidenced by the disruptions of Na/K-ATPase and antioxidant system in intestine but not in liver. These findings imply that prolonged exposure to AgNPs might induce size-related, sex-dependent, and organ-specific toxicity to adult zebrafish, thereby may significantly extend our understanding of the toxic effects of AgNPs in aquatic environment.

Endocrine Disruptors in Food: Impact on Gut Microbiota and Metabolic Diseases

Endocrine disruptors (EDCs) have been associated with the increased incidence of metabolic disorders. In this work, we conducted a systematic review of the literature in order to identify the current knowledge of the interactions between EDCs in food, the gut microbiota, and metabolic disorders in order to shed light on this complex triad. Exposure to EDCs induces a series of changes including microbial dysbiosis and the induction of xenobiotic pathways and associated genes, enzymes, and metabolites involved in EDC metabolism. The products and by-products released following the microbial metabolism of EDCs can be taken up by the host; therefore, changes in the composition of the microbiota and in the production of microbial metabolites could have a major impact on host metabolism and the development of diseases. The remediation of EDC-induced changes in the gut microbiota might represent an alternative course for the treatment and prevention of metabolic diseases.

Activation of aryl hydrocarbon receptor by dioxin directly shifts gut microbiota in zebrafish

Gut microbiota is of critical importance to host health. Aryl hydrocarbon receptor (AhR) is found to be closely involved in the regulation of gut microbial dynamics. However, it is still not clear how AhR signaling shapes the gut microbiota. In the present study, adult zebrafish were acutely exposed to an AhR antagonist (CH223191), an AhR agonist (polychlorinated biphenyl 126; PCB126) or their combination for 7 d. Overall intestinal health and gut microbial community were temporally monitored (1 d, 3 d and 7 d) and inter-compared among different groups. The results showed that single exposure to PCB126 significantly disrupted the overall health of intestines (i.e., neural signaling, inflammation, epithelial barrier integrity, oxidative stress). However, CH223191 failed to inhibit but enhanced the physiological toxicities of PCB126, implying the involvement of extra mechanisms rather than AhR in the regulation of intestinal physiological activities. Dysbiosis of gut microbiota was also caused by PCB126 over time as a function of sex. It is intriguing that CH223191 successfully abolished the holistic effects of dioxin on gut microbiota, which inferred that growth of gut microbes was directly controlled by AhR activation without the involvement of host feedback modulation. When coming to detailed alterations at certain taxon, both antagonistic and synergistic interactions existed between CH223191 and dioxin, depending on fish sex, exposure duration and bacterial species. Correlation analysis found that gut inflammation was positively associated with pathogenic Legionella bacteria, but was negatively associated with epithelial barrier integrity, suggesting that integral intestinal epithelial barrier can prevent the influx of pathogenic bacteria to induce inflammatory response. Overall, this study has deciphered, for the first time, the direct regulative effects of AhR activity on gut microbiota. Future research is warranted to elucidate the specific mechanisms of AhR action on certain bacterial population.

Exploring interactions between xenobiotics, microbiota, and neurotoxicity in zebrafish

Susceptibility to xenobiotic exposures is variable. One factor that might account for this is the microbiome, which encompasses all microorganisms, their encoded genes, and associated functions that colonize a host organism. Microbiota harbor the capacity to affect the toxicokinetics and toxicodynamics of xenobiotic exposures. The neurotoxicological effects of environmental chemicals may be modified by intestinal microbes via the microbiota-gut-brain axis. This is a complex, bi-directional signaling pathway between intestinal microbes and the host nervous system. As a model organism, zebrafish are extremely well-placed to illuminate mechanisms by which microbiota modify the developmental neurotoxicity of environmental chemicals. The goal of this review article is to examine the microbiota-gut-brain axis in a toxicological context, specifically focusing on the strengths and weaknesses of the zebrafish model for the investigation of interactions between xenobiotic agents and host-associated microbes. Previous studies describing the relationship between intestinal microbes and host neurodevelopment will be discussed. From a neurotoxicological perspective, studies utilizing zebrafish to assess links between neurotoxicological outcomes and the microbiome are emphasized. Overall, there are major gaps in our understanding the mechanisms by which microbiota interact with xenobiotics to cause or modify host neurotoxicity. In this review, we demonstrate that zebrafish are an ideal model system for studying the complex relationship between chemical exposures, microorganisms, and host neurotoxicological outcomes.

The Dynamic Interplay between the Gut Microbiota and Autoimmune Diseases

The human gut-resident commensal microbiota is a unique ecosystem associated with various bodily functions, especially immunity. Gut microbiota dysbiosis plays a crucial role in autoimmune disease pathogenesis as well as in bowel-related diseases. However, the role of the gut microbiota, which causes or influences systemic immunity in autoimmune diseases, remains elusive. Aryl hydrocarbon receptor, a ligand-activated transcription factor, is a master moderator of host-microbiota interactions because it shapes the immune system and impacts host metabolism. In addition, treatment optimization while minimizing potential adverse effects in autoimmune diseases remains essential, and modulation of the gut microbiota constitutes a potential clinical therapy. Here, we present evidence linking gut microbiota dysbiosis with autoimmune mechanisms involved in disease development to identify future effective approaches based on the gut microbiota for preventing autoimmune diseases.

The Dynamic Interplay between the Gut Microbiota and Autoimmune Diseases

The human gut-resident commensal microbiota is a unique ecosystem associated with various bodily functions, especially immunity. Gut microbiota dysbiosis plays a crucial role in autoimmune disease pathogenesis as well as in bowel-related diseases. However, the role of the gut microbiota, which causes or influences systemic immunity in autoimmune diseases, remains elusive. Aryl hydrocarbon receptor, a ligand-activated transcription factor, is a master moderator of host-microbiota interactions because it shapes the immune system and impacts host metabolism. In addition, treatment optimization while minimizing potential adverse effects in autoimmune diseases remains essential, and modulation of the gut microbiota constitutes a potential clinical therapy. Here, we present evidence linking gut microbiota dysbiosis with autoimmune mechanisms involved in disease development to identify future effective approaches based on the gut microbiota for preventing autoimmune diseases.

Effects of 2,2-dichloroacetamide (DCAcAm), an emerging disinfection by-product in drinking water, on the intestinal microbiota of adult zebrafish

The presence of disinfection by-products (DBPs) increases the mutagenicity of water and may pose adverse health effects. Gut microbiota exerts a fundamental role on host physiology, and how extrinsic perturbations influence its composition has been increasingly examined. However, the effect of DBPs on gut microbiota is still poorly understood. In the present study, adult zebrafish were exposed to different concentrations of dichloroacetamide (DCAcAm, an emerging nitrogenous DBP) for 30 days. Sequencing of 16S rRNA amplicons revealed a significant change in the richness and diversity of microbiota in the gut of DCAcAm-exposed zebrafish. At the phylum level, the abundance of Proteobacteria decreased and the abundance of Fusobacteria and Firmicutes increased significantly in the gut after exposure to 100 and 500 μg/L DCAcAm. At the genus level, the abundances of several bacteria which are considered pathogens or opportunistic pathogens in fish and closely related to fish metabolism, disease and inflammation (Aeromonas, Stenotrophomonas, Bacteroides and Ralstonia) increased in the DCAcAm-treated groups. Our results reveal that DBPs in drinking water potentially affect gut microbiota composition, which may contribute to the toxicity assessment of DBPs in future and provide new insight into the complex interactions between the DBPs in drinking water and host health.

The role of the gut microbiome in mediating neurotoxic outcomes to PCB exposure

A series of complex physiological processes underlie the development of the microbiota, gut, and brain in early life, which together communicate via the microbiota-gut-brain axis to maintain health and homeostasis. Disruption of these processes can lead to dysbiosis of the microbiota, pathophysiology of the gut and behavioral deficits including depression, anxiety and cognitive deficits. Environmental exposures, particularly in early life, can interfere with development and impact these pathways. This review will focus on the role of the microbiome and the gut in neurodevelopment and neurodegeneration as well as the impacts of environmental exposures, particularly to the neurotoxicant polychlorinated biphenyls (PCBs), given that the gut serves as the primary exposure route. There exists extensive research on the importance of the microbiome in the developing brain and connections with autism spectrum disorder (ASD) and increasing links being established between the microbiome and development of Alzheimer's disease (AD) in the elderly. Finally, we will speculate on the mechanisms through which PCBs can induce dysbiosis and dysregulate physiology of the gut and brain.

Gut microbiome: An intermediary to neurotoxicity

There is growing recognition that the gut microbiome is an important regulator for neurological functions. This review provides a summary on the role of gut microbiota in various neurological disorders including neurotoxicity induced by environmental stressors such as drugs, environmental contaminants, and dietary factors. We propose that the gut microbiome remotely senses and regulates CNS signaling through the following mechanisms: 1) intestinal bacteria-mediated biotransformation of neurotoxicants that alters the neuro-reactivity of the parent compounds; 2) altered production of neuro-reactive microbial metabolites following exposure to certain environmental stressors; 3) bi-directional communication within the gut-brain axis to alter the intestinal barrier integrity; and 4) regulation of mucosal immune function. Distinct microbial metabolites may enter systemic circulation and epigenetically reprogram the expression of host genes in the CNS, regulating neuroinflammation, cell survival, or cell death. We will also review the current tools for the study of the gut-brain axis and provide some suggestions to move this field forward in the future.

Microbiota alter metabolism and mediate neurodevelopmental toxicity of 17β-estradiol

Estrogenic chemicals are widespread environmental contaminants associated with diverse health and ecological effects. During early vertebrate development, estrogen receptor signaling is critical for many different physiologic responses, including nervous system function. Recently, host-associated microbiota have been shown to influence neurodevelopment. Here, we hypothesized that microbiota may biotransform exogenous 17-βestradiol (E2) and modify E2 effects on swimming behavior. Colonized zebrafish were continuously exposed to non-teratogenic E2 concentrations from 1 to 10 days post-fertilization (dpf). Changes in microbial composition and predicted metagenomic function were evaluated. Locomotor activity was assessed in colonized and axenic (microbe-free) zebrafish exposed to E2 using a standard light/dark behavioral assay. Zebrafish tissue was collected for chemistry analyses. While E2 exposure did not alter microbial composition or putative function, colonized E2-exposed larvae showed reduced locomotor activity in the light, in contrast to axenic E2-exposed larvae, which exhibited normal behavior. Measured E2 concentrations were significantly higher in axenic relative to colonized zebrafish. Integrated peak area for putative sulfonated and glucuronidated E2 metabolites showed a similar trend. These data demonstrate that E2 locomotor effects in the light phase are dependent on the presence of microbiota and suggest that microbiota influence chemical E2 toxicokinetics. More broadly, this work supports the concept that microbial colonization status may influence chemical toxicity.

Chronic Toxic Effects of Flutolanil on the Liver of Zebrafish ( Danio rerio)

Flutolanil is a broad-spectrum amide fungicide that is widely used to prevent fungal pathogens in agriculture. However, its usage may have a potential environmental impact on organisms. So far, few literatures have investigated the chronic toxicity of flutolanil at concentrations relevant to environmental conditions in the nontarget aquatic organisms. This study was aimed at evaluating whether the long-term exposure of flutolanil affects oxidative stress, immune response, and apoptosis in the liver of zebrafish ( Danio rerio). The results showed that the activity of catalase (CAT) was significantly decreased in the liver in all flutolanil-treated groups. Interestingly, the malondialdehyde (MDA) contents were remarkably increased following the flutolanil exposure. Deoxyribonucleic acid (DNA) damage was increased with a concentration-dependent manner. The transcription level of genes involved in apoptosis and the immune system were significantly altered following flutolanil chronic exposure in zebrafish liver. Furthermore, the caspase-3 enzyme activity was significantly increased. Taken together, this study demonstrated that the resulting effects on oxidative stress, immune toxicity, and apoptosis may be responsible for the pathological alterations in zebrafish liver after flutolanil exposure at concentrations relevant to environmental conditions, advancing the knowledge of pesticide environmental risk assessment.

Sex-specific alterations of lipid metabolism in zebrafish exposed to polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are persistent organic pollutants (POPs) mixtures exerting environmental health risk. In mammals, PCBs have been shown to disrupt metabolic state, especially lipid metabolism, and energy balance, but their effects on lipid metabolism in fish are largely unknown. The zebrafish were selected as model and both male and female adult zebrafish were exposed to different concentrations of PCBs at gradient concentrations of 0.2, 2.0 and 20.0 μg/L for 6 weeks. PCB exposure did not affect survival, but a significant inhibition of growth was observed in the males after exposure to 20.0 μg/L. The lower concentrations of 0.2 and 2.0 μg/L increased hepatic lipid accumulation to a greater extent in male fish, but the higher concentration of 20.0 μg/L did not cause significant fat accumulation in either male or female fish. In males, the expression of genes related to lipogenesis and lipid catabolism was upregulated in a concentration-dependent manner in the liver and visceral mass without liver and gonad; the effects of exposure on lipid metabolism-related genes in female fish were less pronounced. PCB exposure did not induce significant oxidative stress, but did upregulate the expression of stress- and apoptosis-related genes, mostly in male fish. The low concentrations of PCBs (0.2 μg/L and 2.0 μg/L) exerted sex-specific effects on zebrafish lipid metabolism, and male fish were more sensitive to the exposure. This study provides new mechanistic insights into the complex interactions between PCBs, lipid metabolism, and sex in zebrafish, and may contribute to a future systematic assessment of the effects of PCBs on aquatic ecosystems.

Gut microbiota dysbiosis correlates with a low-dose PCB126-induced dyslipidemia and non-alcoholic fatty liver disease

There is growing evidence that polychlorinated biphenyl 126 (PCB126) not only has adverse effects on host health but also has the ability to shift gut microbiota, which is recently recognized as a crucial factor determining numerous physiological processes. However, the interplay between the gut microbiota and host health remains largely unknown. Herein, adult female C57BL/6 mice were orally exposed to environmentally relevant low-dose of PCB126, at 50 μg/kg body weight once per week for 6 weeks. This study aims to illuminate how PCB126 influences gut microbiota variations and host disorders and to further identify the correlation between the gut microbiota and metabolic markers of host disorders. Obtained results demonstrated that the PCB126 administration induced gut microbiota dysbiosis in mice, with changes both in the gut microbiota constitution and structure. PCB126 administration also simultaneously altered the physiological status of serum and liver, as evaluated by dyslipidemia, liver lipid accumulation and injury, and non-alcoholic fatty liver disease. Importantly, Spearman's correlation analysis suggested that several specific bacterial taxa were positively and significantly related to metabolic markers of the mentioned disorders. Moreover, based on the co-occurrence network map, some of the bacterial taxa may synergistically regulate host physiology. This work provides new insight into the mechanism underlying the interaction between the gut microbiota and host disorders. It is expected that gut microbiota modulation should be another novel way used for the prevention and treatment of PCB126-triggered diseases.

Associations of prenatal exposure to polybrominated diphenyl ethers and polychlorinated biphenyls with long-term gut microbiome structure: a pilot study

Supplemental Digital Content is available in the text.

The gut microbiome is influenced by early-life exposures, but—despite potentially enormous implications for child health—is understudied in environmental epidemiology. This pilot study is one of the first to explore in utero exposures and long-term gut microbiome profiles. We examined the association between exposure to polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) during pregnancy and the mid-childhood gut microbiome.

Potassium sorbate suppresses intestinal microbial activity and triggers immune regulation in zebrafish (Danio rerio)

Potassium sorbate (PS) is a class of bacteriostatic antiseptic agent widely used in the food industry; the effects of its intake on host health are currently unclear.

Dioxin-like PCB 126 increases intestinal inflammation and disrupts gut microbiota and metabolic homeostasis

The gut microbiome is sensitive to diet and environmental exposures and is involved in the regulation of host metabolism. Additionally, gut inflammation is an independent risk factor for the development of metabolic diseases, specifically atherosclerosis and diabetes. Exposures to dioxin-like pollutants occur primarily via ingestion of contaminated foods and are linked to increased risk of developing cardiometabolic diseases. We aimed to elucidate the detrimental impacts of dioxin-like pollutant exposure on gut microbiota and host gut health and metabolism in a mouse model of cardiometabolic disease. We utilized 16S rRNA sequencing, metabolomics, and regression modeling to examine the impact of PCB 126 on the microbiome and host metabolism and gut health. 16S rRNA sequencing showed that gut microbiota populations shifted at the phylum and genus levels in ways that mimic observations seen in chronic inflammatory diseases. PCB 126 reduced cecum alpha diversity (0.60 fold change; p = 0.001) and significantly increased the Firmicutes to Bacteroidetes ratio (1.63 fold change; p = 0.044). Toxicant exposed mice exhibited quantifiable concentrations of PCB 126 in the colon, upregulation of Cyp1a1 gene expression, and increased markers of intestinal inflammation. Also, a significant correlation between circulating Glucagon-like peptide-1 (GLP-1) and Bifidobacterium was evident and dependent on toxicant exposure. PCB 126 exposure disrupted the gut microbiota and host metabolism and increased intestinal and systemic inflammation. These data imply that the deleterious effects of dioxin-like pollutants may be initiated in the gut, and the modulation of gut microbiota may be a sensitive marker of pollutant exposures.

Acute exposure to PBDEs at an environmentally realistic concentration causes abrupt changes in the gut microbiota and host health of zebrafish

Contamination from lower brominated PBDEs is ubiquitous in the environments. However, their effects on gut microbiota and intestinal health have not yet been investigated. This study exposed adult zebrafish to an environmentally realistic concentration of pentaBDE mixture (DE-71) at 5.0 ng/L for 7 days, after which metagenomic sequencing of the intestinal microbiome was conducted and host physiological activities in the intestine and liver were also examined. The results showed that acute exposure to DE-71 significantly shifted the gut microbial community in a sex-specific manner. Certain genera (e.g., Mycoplasma, Ruminiclostridium, unclassified Firmicutes sensu stricto, and Fusobacterium) disappeared from the DE-71-exposed intestines, resulting in decreased bacterial diversity. Bacterial metabolic functions in guts were also affected by DE-71, namely those covering energy metabolism, virulence, respiration, cell division, cell signaling, and stress response. In addition, measurement of diverse sensitive biomarkers showed that the health of male intestines was remarkably compromised by the DE-71 exposure, as indicated by the disruption to its neural signaling (serotonin), epithelial barrier integrity (tight junction protein 2), inflammatory response (interleukin 1β), oxidative stress and antioxidant capacity, as well as detoxifying potential (ethoxyresorufin-O-deethylase activity). However, female intestines maintained intact physiological activities. Compared to the direct impact on intestines, a latent effect of DE-71 was observed in livers. Co-occurrence network analysis demonstrated that the gut bacteria vigorously interacted to establish the fittest community under DE-71 stress by promoting the reproduction of favorable genera, while diminishing the survival of unfavorable ones. Significant correlations between the zebrafish gut microbiota and physiological activities (e.g., oxidative stress, detoxification, neurotransmission, and epithelial integrity) were also observed. Overall, this study has demonstrated, for the first time, the high susceptibility of gut microbiota and intestinal health of zebrafish to DE-71, thus warranting more work to reveal its mode of toxicity.

PCBs-high-fat diet interactions as mediators of gut microbiota dysbiosis and abdominal fat accumulation in female mice

Polychlorinated biphenyls (PCBs), one type of lipophilic pollutant, are ubiquitous in daily life. PCBs exposure has been implicated in the alterations of gut microbial community which is profoundly associated with diverse metabolic disorders, including obesity. High-fat diet (H) is a dietary pattern characterized by a high percentage of fat. According to the theory that similarities can be easily solvable in each other, PCBs and H exposures are inevitably and objectively coexistent in a real living environment, prompting great concerns about their individual and combined effects on hosts. However, the effects of PCBs-H interactions on gut microbiota and obesity are still incompletely understood. In the present study, the effects of PCBs and/or H on the gut microbiota alteration and obesity risk in mice were examined and the interactions between PCBs and H were investigated. Obtained results showed that PCBs and/or H exposure induced prominent variations in the gut microbiota composition and diversity. Exposure to PCBs also resulted in higher body fat percentage, greater size of abdominal subcutaneous adipocytes and increased expression of proinflammatory cytokines including TNF-α, iNOS and IL-6. Such PCBs-induced changes could be further enhanced upon the co-exposure of H, implying that obese individuals may be vulnerable to PCBs exposure. Taken together, the present study is helpful for a better understanding of the gut microbiota variation influenced by PCBs and/or H exposure, and furthermore, provides a novel insight into the mechanism of PCBs-H interactions on host adiposity.