Alterations in immune and renal biomarkers among workers occupationally exposed to low levels of trichloroethylene below current regulatory standards

Trichloroethylene exposure, multi-organ injury, and potential mechanisms: A narrative review

Trichloroethylene (TCE) is a common environmental pollutant and industrial chemical that has been associated with adverse health effects, especially on organ systems. The purpose of this review is to summarize the current findings on organ system damage caused by TCE exposure and the underlying mechanisms involved. Numerous studies have shown that TCE exposure may cause damage to multiple organ systems, mainly the skin, liver, kidney, and circulatory system. The mechanisms leading to TCE-induced organ system damage are complex and diverse. TCE is metabolized in vivo to reactive intermediates, through which TCE can induce oxidative stress, interfere with cell signaling pathways, and promote inflammatory responses. In addition, studies have shown that TCE interferes with DNA repair mechanisms, leading to genotoxicity and potentially carcinogenic effects. This review highlights the importance of understanding the deleterious effects of TCE exposure on organ systems and provides insights into the underlying mechanisms involved. Further research is needed to elucidate the full range of organ system damage caused by TCE and to develop effective prevention and treatment strategies.

Targeted proteomic scan identifies alteration of serum proteins among workers occupationally exposed to low levels of trichloroethylene

Occupational exposure to trichloroethylene (TCE) has been associated with alterations in B-cell activation factors and an increased risk of non-Hodgkin's lymphoma (NHL). Here, we aimed to examine the biological processes influenced by TCE exposure to understand the underlying molecular mechanisms. This cross-sectional molecular epidemiology study included data of 1317 targeted proteins in the serum from 42 TCE exposed and 34 unexposed factory workers in Guangdong, China. We used multivariable linear regressions to identify proteins associated with TCE exposure and examined their exposure-response relationship across categories of TCE exposure (unexposed, low exposed: <10 ppm, high exposed: ≥10 ppm). We further examined pathway enrichment of TCE-related proteins to understand their biological response. Occupational exposure to TCE was associated with lower levels of tumor necrosis factor receptor superfamily member 17 (TNFRSF17; β = -.08; p-value = .0003) and kynureninase (KYNU; β = -.10, p-value = .002). These proteins also showed a significant exposure-response relation across the unexposed, low exposed, and high exposed workers (all p-trends < .001, false discovery rate [FDR] < 0.20). Pathway analysis of TCE-related proteins showed significant enrichment (FDR < 0.05) for several inflammatory and immune pathways. TCE exposure was associated with TNFRSF17, a key B-cell maturation antigen that mediates B-cell survival and KYNU, an enzyme that plays a role in T-cell mediated immune response. Given that altered immunity is an established risk factor for NHL, our findings support the biological plausibility of linking TCE exposure with NHL.

Glomerular Damage in Trichloroethylene-Sensitized Mice: Targeting Cathepsin L-Induced Hyperactive mTOR Signaling

Trichloroethylene (TCE) is a serious health hazard for workers with daily exposure, causing occupational medicamentosa-like dermatitis due to TCE (OMDT) and glomerular damage. Recent studies suggest that mTORC1 signaling is activated in various glomerular disorders; however, the role of mTORC1 signaling in TCE-induced glomerular damage remains to be explored. In the present study, 6 OMDT patients were enrolled and a TCE-sensitized mouse model was established to investigate molecular mechanisms underlying the glomerular damage associated with OMDT. Glomerular damage was assessed by levels of urine nephrin, H&E staining, and renal function test. Ultrastructural change of podocyte was investigated by transmission electron microscopy. The podocyte-related molecules including nephrin, α-actinin-4, and integrin β1 were visualized by immunofluorescence. The activation of mTORC1 signaling was confirmed by Western blot. Glomerular apoptosis was examined by the TUNEL test and Western blotting. Expression and location of cathepsin L (CTSL) were assessed by RT-PCR and immunofluorescence. Our results showed that TCE sensitization caused damage to glomerular structural integrity and also increased the activation of mTORC1 signaling, which was accompanied by podocyte loss, hypertrophy, and glomerular apoptosis. Importantly, we also found that over-expressed CTSL was mainly located in podocyte and CTSL inhibition could partially block the activation of mTORC1 signaling. Thus, our findings suggested a novel mechanism whereby hyperactive mTOR signaling contributes to TCE sensitization–induced and immune-mediated glomerular damage via CTSL activation.

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

Trichloroethylene (TCE) is a common environmental toxicant linked with hypersensitivity and autoimmune responses in humans and animal models. While autoimmune diseases are more common in females, mechanisms behind this disparity are not clear. Recent evidence suggests that autoimmunity may be increasing in males, and occupational studies have shown that TCE-mediated hypersensitivity responses occur just as often in males. Previous experimental studies in autoimmune-prone MRL^+/+ mice have focused on responses in females. However, it is important to include both males and females in order to better understand sex-disparity in autoimmune disease. In addition, because of an alarming increase in autoimmunity in adolescents, developmental and/or early life exposures to immune-enhancing environmental pollutants should also be considered. Using MRL^+/+ mice, we hypothesized that TCE would alter markers related to autoimmunity to a greater degree in female mice relative to male mice, and that TCE would enhance these effects. Mice were continuously exposed to either TCE or vehicle beginning at gestation, continuing during lactation, and directly in the drinking water. Both male and female offspring were evaluated at 7 weeks of age. Sex-specific effects were evident. Female mice were more likely than males to show enhanced CD4⁺ T cell cytokine responses (e.g., IL-4 and IFN-γ). Although none of the animals developed pathological or serological signs of autoimmune hepatitis-like disease, TCE-exposed female mice were more likely than males in either group to express higher levels of biomarkers in the liver related to regeneration/repair and proliferation. Levels of bacterial populations in the intestinal ileum were also altered by TCE exposure and were more prominent in females as compared to males. Thus, our expectations were correct in that young adult female mice developmentally exposed to TCE were more likely to exhibit alterations in immunological and gut/liver endpoints compared to male mice.

Continuous Developmental and Early Life Trichloroethylene Exposure Promoted DNA Methylation Alterations in Polycomb Protein Binding Sites in Effector/Memory CD4+ T Cells

Trichloroethylene (TCE) is an industrial solvent and drinking water pollutant associated with CD4⁺ T cell-mediated autoimmunity. In our mouse model, discontinuation of TCE exposure during adulthood after developmental exposure did not prevent immunotoxicity. To determine whether persistent effects were linked to epigenetic changes we conducted whole genome reduced representation bisulfite sequencing (RRBS) to evaluate methylation of CpG sites in autosomal chromosomes in activated effector/memory CD4⁺ T cells. Female MRL+/+ mice were exposed to vehicle control or TCE in the drinking water from gestation until ~37 weeks of age [postnatal day (PND) 259]. In a subset of mice, TCE exposure was discontinued at ~22 weeks of age (PND 154). At PND 259, RRBS assessment revealed more global methylation changes in the continuous exposure group vs. the discontinuous exposure group. A majority of the differentially methylated CpG regions (DMRs) across promoters, islands, and regulatory elements were hypermethylated (~90%). However, continuous developmental TCE exposure altered the methylation of 274 CpG sites in promoters and CpG islands. In contrast, only 4 CpG island regions were differentially methylated (hypermethylated) in the discontinuous group. Interestingly, 2 of these 4 sites were also hypermethylated in the continuous exposure group, and both of these island regions are associated with lysine 27 on histone H3 (H3K27) involved in polycomb complex-dependent transcriptional repression via H3K27 tri-methylation. CpG sites were overlapped with the Open Regulatory Annotation database. Unlike the discontinuous group, continuous TCE treatment resulted in 129 DMRs including 12 unique transcription factors and regulatory elements; 80% of which were enriched for one or more polycomb group (PcG) protein binding regions (i.e., SUZ12, EZH2, JARID2, and MTF2). Pathway analysis of the DMRs indicated that TCE primarily altered the methylation of genes associated with regulation of cellular metabolism and cell signaling. The results demonstrated that continuous developmental exposure to TCE differentially methylated binding sites of PcG proteins in effector/memory CD4⁺ cells. There were minimal yet potentially biologically significant effects that occurred when exposure was discontinued. These results point toward a novel mechanism by which chronic developmental TCE exposure may alter terminally differentiated CD4⁺ T cell function in adulthood.