Sex-Dependent Effects on Liver Inflammation and Gut Microbial Dysbiosis After Continuous Developmental Exposure to Trichloroethylene in Autoimmune-Prone Mice

RISING STARS: Sex differences in toxicant-associated fatty liver disease

Based on biological sex, the consequential health outcomes from exposures to environmental chemicals or toxicants can differ in disease pathophysiology, progression, and severity. Due to basal differences in cellular and molecular processes resulting from sexual dimorphism of organs including the liver and additional factors influencing 'gene-environment' interactions, males and females can exhibit different responses to toxicant exposures. Associations between environmental/occupational chemical exposures and fatty liver disease (FLD) have been well-acknowledged in human epidemiologic studies and their causal relationships demonstrated in experimental models. However, studies related to sex differences in liver toxicology are still limited to draw any inferences on sex-dependent chemical toxicity. The purpose of this review is to highlight the present state of knowledge on the existence of sex differences in toxicant-associated FLD (TAFLD), discuss potential underlying mechanisms driving these differences, implications of said differences on disease susceptibility, and emerging concepts. Chemicals of interest include various categories of pollutants that have been investigated in TAFLD, namely persistent organic pollutants, volatile organic compounds, and metals. Insight into research areas requiring further development is also discussed, with the objective of narrowing the knowledge gap on sex differences in environmental liver diseases. Major conclusions from this review exercise are that biological sex influences TAFLD risks, in part due to (i) toxicant disruption of growth hormone and estrogen receptor signaling, (ii) basal sex differences in energy mobilization and storage, and (iii) differences in chemical metabolism and subsequent body burden. Finally, further sex-dependent toxicological assessments are warranted for the development of sex-specific intervention strategies.

Oral ingestion of the environmental toxicant trichloroethylene in rats induces alterations in the gut microbiome: Relevance to idiopathic Parkinson's disease

Microbial alterations within the gut microbiome appear to be a common feature of individuals with Parkinson's disease (PD), providing further evidence for the role of the gut-brain axis in PD development. As a major site of contact with the environment, questions have emerged surrounding the cause and effect of alterations to the gut microbiome by environmental contaminants associated with PD risk, such as pesticides, metals, and organic solvents. Recent data from our lab shows that ingestion of the industrial byproduct and environmental pollutant trichloroethylene (TCE) induces key Parkinsonian pathology within aged rats, including the degeneration of dopaminergic neurons, α-synuclein accumulation, neuroinflammation, and endolysosomal deficits. As TCE is the most common organic contaminant within drinking water, we postulated that ingestion of TCE associated with PD-related neurodegeneration may alter the gut microbiome to a similar extent as observed in persons with PD. To assess this, we collected fecal samples from adult rats treated with 200 mg/kg TCE over 6 weeks via oral gavage - the dose that produced nigrostriatal neurodegeneration - and analyzed the gut microbiome via whole genome shotgun sequencing. Our results showed changes in gut microorganisms reflective of the microbial signatures observed in individuals with idiopathic PD, such as decreased abundance of short-chain fatty acid producing Blautia and elevated lactic-acid producing Bifidobacteria, as well as genera who contain species previously reported as opportunistic pathogens such as Clostridium. From these experimental data, we postulate that TCE exposure within contaminated drinking water could induce alterations of the gut microbiome that contributes to chronic disease risk, including idiopathic PD.

Gut microbiome-host interactions in driving environmental pollutant trichloroethene-mediated autoimmunity

Trichloroethene (TCE), a widely used industrial solvent, is associated with the development of autoimmune diseases (ADs), including systemic lupus erythematosus and autoimmune hepatitis. Increasing evidence support a linkage between altered gut microbiome composition and the onset of ADs. However, it is not clear how gut microbiome contributes to TCE-mediated autoimmunity, and initial triggers for microbiome-host interactions leading to systemic autoimmune responses remain unknown. To achieve this, female MRL+/+ mice were treated with 0.5 mg/ml TCE for 52 weeks and fecal samples were subjected to 16S rRNA sequencing to determine the microbiome composition. TCE exposure resulted in distinct bacterial community revealed by β-diversity analysis. Notably, we observed reduction in Lactobacillaceae, Rikenellaceae and Bifidobacteriaceae families, and enrichment of Akkermansiaceae and Lachnospiraceae families after TCE exposure. We also observed significantly increased colonic oxidative stress and inflammatory markers (CD14 and IL-1β), and decreased tight junction proteins (ZO-2, occludin and claudin-3). These changes were associated with increases in serum antinuclear and anti-smooth muscle antibodies and cytokines (IL-6 and IL-12), together with increased PD1 + CD4+ T cells in TCE-exposed spleen and liver tissues. Importantly, fecal microbiota transplantation (FMT) using feces from TCE-treated mice to antibiotics-treated mice induced increased anti-dsDNA antibodies and hepatic CD4+ T cell infiltration in the recipient mice. Our studies thus delineate how imbalance in gut microbiome and mucosal redox status together with gut inflammatory response and permeability changes could be the key factors in contributing to TCE-mediated ADs. Furthermore, FMT studies provide a solid support to a causal role of microbiome in TCE-mediated autoimmunity.