Transcriptome analysis of 3D primary mouse liver spheroids shows that long-term exposure to hexafluoropropylene oxide trimer acid disrupts hepatic bile acid metabolism

Shift from legacy to emerging per- and polyfluoroalkyl substances for watershed management along the coast of China

Per- and polyfluoroalkyl substances and their short-chain alternatives have attracted world-wide attention due to their widespread presence and persistence in the environment. However, the sources, environmental fate, and driving forces of PFAS in coastal ecosystems remain poorly understood. In this study, the spatial distribution, source apportionment, and driving mechanisms of PFAS were investigated through a comprehensive analysis of water samples collected along the China's coastline. The concentrations of Σ25PFAS in water samples followed a general pattern, with higher levels observed in northern coastal zones of China than the south, ranging from 0.72 to 1872.21 ng L-1. PFOA and PFBA were dominant. Emerging short-chain PFAS, such as PFBS, PFBA, F-53B and GenX, were frequently detected, with detection rates of 97%, 99%, 95% and 77%, respectively. This indicated a shift in coastal PFAS contamination from legacy compounds to emerging short-chain alternatives. Source apportionment using the Positive Matrix Factorization model identified key contributors to PFAS pollution, including textile production, volatile precursors, precious metal industries, aqueous film-forming foam, metal-plating, electrochemical fluorination, and fluoropolymer manufacturing. Additionally, PFAS concentrations were significantly positively correlated with cultivated land, urban area, and wastewater discharge, while negatively correlated with annual precipitation and woodland coverage (p < 0.05). Socio-economic development was identified as a major driver of PFAS emissions, while the hydrological factors and vegetation coverage can significantly enhance watershed resilience against PFAS pollution.

Effects of per- and polyfluoroalkyl substances on the liver: Human-relevant mechanisms of toxicity

Per- and polyfluoroalkyl substances (PFAS) are abundantly used in a plethora of products with applications in daily life. As a result, PFAS are widely distributed in the environment, thus providing a source of exposure to humans. The majority of human exposure to PFAS is attributed to the human diet, which encompasses drinking water. Their chemical nature grants persistent, accumulative and toxic properties, which are currently raising concerns. Over the past few years, adverse effects of PFAS on different organs have been repeatedly documented. Numerous epidemiological studies established a clear link between PFAS exposure and liver toxicity. Likewise, effects of PFAS on liver homeostasis, lipid metabolism, bile acid metabolism and hepatocarcinogenesis have been reported in various in vitro and in vivo studies. This review discusses the role of PFAS in liver toxicity with special attention paid to human relevance as well as to the mechanisms underlying the hepatotoxic effects of PFAS. Future perspectives and remaining knowledge gaps were identified to enhance future PFAS risk assessment.

Impact of hexafluoropropylene oxide trimer acid (HFPO-TA) on sex differentiation after exposures during different development stages of zebrafish (Danio rerio)

Hexafluoropropylene oxide trimer acid (HFPO-TA), a novel alternative to perfluorooctanoic acid (PFOA), has been widely used and ubiquitously detected in aquatic environments. However, its potential effects on sex differentiation of aquatic organisms are not well known. Therefore, in this study, zebrafish were exposed to HFPO-TA at different development stages (0-21, 21-42, and 42-63 dpf) to investigate the effects on sex differentiation and its underlying mechanisms. All three exposures to HFPO-TA resulted in the feminization of zebrafish, and the impact of Stage II was most significant. The transcription levels of key genes related to female differentiation (bpm15, cyp19a1a, esr1, vtg1, and sox9b) were up-regulated, while those of key genes related to male differentiation (dmrt1, gata4, amh, and sox9a) were down-regulated, which could lead to the feminization. In addition, it was found that the dysregulations of these genes were prolonged in adult zebrafish even through a long recovery, which could cause sex imbalance in populations. Therefore, HFPO-TA might not be a safe alternative to PFOA, and more evidences from multi- and transgenerational toxicology are warranted.

Perfluorooctanoic acid (PFOA) and its alternative perfluorobutanoic acid (PFBA) alter hepatic bile acid profiles via different pathways

The disruption of per- and polyfluoroalkyl substances (PFASs) on bile acid (BA) homeostasis has raised public concerns, making the evaluation of their effects and underlying mechanisms a high priority. Although the use of perfluorooctanoic acid (PFOA) has been restricted, it remains a widespread legacy PFAS in the environment. Concurrently, the use of its prevalent short-chain alternative, perfluorobutanoic acid (PFBA), is increasing, yet the toxicity assessment of PFBA remains inadequate. In this study, C57BL/6N mice were exposed to PFOA and PFBA (0.4 or 10 mg/kg body weight) by gavage for 28 days. The results showed that both PFOA and PFBA significantly increased hepatic weight, although PFBA exhibited lower bioaccumulation than PFOA in the liver. Targeted metabolomics revealed that PFOA significantly decreased total BA levels and altered their composition. Conversely, PFBA, without significantly altering total BA levels, notably changed their composition, such as increasing the proportion of cholic acid. Further investigations using in vivo and in vitro assays suggested that PFOA inhibited the expression of Cyp7A1, a key BA synthetase, potentially via PPARα activation, thereby reducing BA levels. In contrast, PFBA enhanced Cyp7A1 expression, associated with the inhibition of intestinal Farnesoid X receptor-fibroblast growth factor 15 (FXR-FGF15) pathway. This study evaluated the differences in the BA-interfering effects of PFOA and PFBA and shed light on the potential mechanisms, which will provide new insights into the health risks of legacy PFASs and their alternatives.

Transcriptomics-based analysis reveals hexafluoropropylene oxide trimer acid (HFPO-TA) induced kidney damage and lipid metabolism disorders in SD rats

Hexafluoropropylene oxide trimer acid (HFPO-TA) is an emerging environmental pollutant that can accumulate in air and surface water. Currently, it has been widely used in fluoropolymer industry, which could cause serious environmental pollution. Due to the high bioaccumulation, the accumulation of pollutants may have an adverse effect on the normal physiological function of the kidneys. However, the toxic effects of HFPO-TA on the kidney are unknown. In this study, we investigated the toxic effects of HFPO-TA exposure on the rat kidney and its mechanism of action. Male SD rats were divided into 4 groups: control group (Ctrl group), L group (0.125 mg/kg/d), M group (0.5 mg/kg/d) and H group (2 mg/kg/d). After 14 consecutive days of gavage, periodic acid‑silver methenamine (PASM) and hematoxylin-eosin (HE) staining were used to examine the structure of the kidneys. We also used transcriptome sequencing (RNA-seq) to identify differentially expressed genes (DEGs) in the testes of rats in both the control and high dose groups. Besides, expression of key proteins was analyzed by immunohistochemistry. The results indicated that HFPO-TA can lead to injured renal capsule, change glomerular shape and have a significant impact on the protein expression levels of AQP2, p-AQP2 and PPARα. Additionally, the level of total cholesterol (TC) was obviously decreased after HFPO-TA exposure. RNA-seq analysis showed that HFPO-TA primarily affected peroxisome proliferator-activated receptor (PPAR) signaling pathway that is associated with lipid metabolism and cyclic adenosine monophosphate (cAMP) signaling pathway. In summary, exposure to HFPO-TA can lead to kidney damage and lipid metabolism disorders.

Comparative steroidogenic effects of hexafluoropropylene oxide trimer acid (HFPO-TA) and perfluorooctanoic acid (PFOA): Regulation of histone modifications

As a widely used alternative to perfluorooctanoic acid (PFOA), hexafluoropropylene oxide trimer acid (HFPO-TA) has been detected in the environment and humans; however, little is known regarding its male reproductive toxicity. To compare the effects of HFPO-TA on steroid hormone synthesis with PFOA, we exposed Leydig cells (MLTC-1) to non-lethal doses (0.1, 1, and 10 μM) of PFOA and HFPO-TA for 48 h. It was found that the levels of steroid hormones, 17α-hydroxyprogesterone (OHP), androstenedione (ASD), and testosterone (T) were significantly increased in 1 and 10 μM of PFOA and HFPO-TA groups, with greater elevation being observed in the HFPO-TA groups than in the PFOA groups at 10 μM. We further showed that the two rate-limiting steroidogenic genes (Star and Cyp11a1) were up-regulated, while Hsd3b, Cyp17a1, and Hsd17b were down-regulated or unchanged after PFOA/HFPO-TA exposure. Moreover, PFOA exposure significantly up-regulated histone H3K4me1/3 and H3K9me1, while down-regulated H3K4me2 and H3K9me2/3 levels. By contrast, H3K4me2/3 and H3K9me2/3 were enhanced, while H3K4me1 and H3K9me1 were repressed after HFPO-TA treatment. It was further confirmed that H3K4me1/3 were increased and H3K9me2 was decreased in Star and Cyp11a1 promoters by PFOA, while HFPO-TA increased H3K4me2/3 and decreased H3K9me1 in the two gene promoters. Therefore, we propose that low levels of PFOA/HFPO-TA enhance the expression of Star and Cyp11a1 by regulating H3K4 and H3K9 methylation, thus stimulating the production of steroid hormones in MLTC-1 cells. Collectively, HFPO-TA exhibits stronger effects on steroidogenesis compared to PFOA, which may be ascribed to the distinct regulation of histone modifications. These data suggest that HFPO-TA does not appear to be a safer alternative to PFOA on the aspect of male reproductive toxicity.

Prenatal exposure to hexafluoropropylene oxide trimer acid (HFPO-TA) disrupts the maternal gut microbiome and fecal metabolome homeostasis

Initially considered a "safe" substitute for perfluorooctanoic acid (PFOA), hexafluoropropylene oxide trimer acid (HFPO-TA) has been extensively used in the production of fluoropolymers for several years, leading to its environmental ubiquity and subsequent discovery of its significant bio-accumulative properties and toxicological effects. However, the specific impact of HFPO-TA on females, particularly those who are pregnant, remains unclear. In the present study, pregnant mice were exposed to 0.63 mg/kg/day HFPO-TA from gestational day (GD) 2 to GD 18. We then determined the potential effects of exposure on gut microbiota and fecal metabolites at GD 12 (mid-pregnancy) and GD 18 (late pregnancy). Our results revealed that, in addition to liver damage, HFPO-TA exposure during the specified window altered the structure and function of cecal gut microbiota. Notably, these changes showed the opposite trends at GD 12 and GD 18. Specifically, at GD 12, HFPO-TA exposure primarily resulted in the down-regulation of relative abundances within genera from the Bacteroidetes and Proteobacteria phyla, as well as associated Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. With extended exposure time, the down-regulated genera within Proteobacteria became significantly up-regulated, accompanied by corresponding up-regulation of human disease- and inflammation-associated pathways, suggesting that HFPO-TA exposure can induce intestinal inflammation and elevate the risk of infection during late pregnancy. Pearson correlation analysis revealed that disturbances in the gut microbiota were accompanied by abnormal fecal metabolite. Additionally, alterations in hormones related to the steroid hormone biosynthesis pathway at both sacrifice time indicated that HFPO-TA exposure might change the steroid hormone level of pregnant mice, but need further study. In conclusion, this study provides new insights into the mechanisms underlying HFPO-TA-induced adverse effects and increases awareness of potential persistent health risks to pregnant females.

Dietary exposure to per- and polyfluoroalkyl substances: Potential health impacts on human liver

Per- and polyfluoroalkyl substances (PFAS), dubbed "forever chemicals", are widely present in the environment. Environmental contamination and food contact substances are the main sources of PFAS in food, increasing the risk of human dietary exposure. Numerous epidemiological studies have established the link between dietary exposure to PFAS and liver disease. Correspondingly, PFAS induced-hepatotoxicity (e.g., hepatomegaly, cell viability, inflammation, oxidative stress, bile acid metabolism dysregulation and glycolipid metabolism disorder) observed from in vitro models and in vivo rodent studies have been extensively reported. In this review, the pertinent literature of the last 5 years from the Web of Science database was researched. This study summarized the source and fate of PFAS, and reviewed the occurrence of PFAS in food system (natural and processed food). Subsequently, the characteristics of human dietary exposure PFAS (population characteristics, distribution trend, absorption and distribution) were mentioned. Additionally, epidemiologic evidence linking PFAS exposure and liver disease was alluded, and the PFAS-induced hepatotoxicity observed from in vitro models and in vivo rodent studies was comprehensively reviewed. Lastly, we highlighted several critical knowledge gaps and proposed future research directions. This review aims to raise public awareness about food PFAS contamination and its potential risks to human liver health.

Rutin ameliorate PFOA induced renal damage by reducing oxidative stress and improving lipid metabolism

Perfluorooctanoic acid (PFOA) is a persistent environmental pollutant that can accumulate in the kidneys and eventually cause kidney damage. Rutin (RUTIN) is a natural flavonoid with multiple biological activities, and its use in against kidney damage has been widely studied in recent years. It is not yet known whether rutin protects against kidney damage caused by PFOA. In this study, 30 ICR mice were randomly divided into three groups: CTRL group, PFOA group and PFOA+RUTIN group. The mice were fed continuously by gavage for 28 days. Renal pathological changes were assessed by HE and PASM staining, and serum renal function and lipid indicators were measured. RNA-seq and enrichment analysis using GO, KEGG and PPI to detect differential expression of genes in treatment groups. Kidney tissue protein expression was determined by Western blot. Research has shown that rutin can improve glomerular and tubular structural damage, and increase serum CREA, HDL-C levels and decrease LDH, LDL-C levels. The expression of AQP1 and ACOT1 was up-regulated after rutin treatment. Transcriptomic analysis indicated that PFOA and rutin affect the transcriptional expression of genes related to lipid metabolism and oxidative stress, and may affected by PI3K-Akt, PPAR, NRF2/KEAP1 signaling pathways. In conclusion, rutin ameliorated renal damage caused by PFOA exposure, and this protective effect may be exerted by ameliorating oxidative stress and regulating lipid metabolism.

Different Life-Stage Exposure to Hexafluoropropylene Oxide Trimer Acid Induces Reproductive Toxicity in Adult Zebrafish (Danio rerio)

As a novel alternative to perfluorooctanoic acid (PFOA), hexafluoropropylene oxide trimer acid (HFPO-TA) has been widely used and has caused ubiquitous water pollution. However, its adverse effects on aquatic organisms are still not well known. In the present study, zebrafish at different life stages were exposed to 0, 5, 50, and 100 μg/L of HFPO-TA for 21 days to investigate reproductive toxicity in zebrafish. The results showed that HFPO-TA exposure significantly inhibited growth and induced reproductive toxicity in zebrafish, including a decrease of the condition factor, gonadosomatic index, and the average number of eggs. Histological section observation revealed that percentages of mature oocytes and spermatozoa were reduced, while those of primary oocytes and spermatocytes increased. In addition, exposure to HFPO-TA at three stages induced a significant decrease in the hatching rate, while the heart rate and normal growth rate of F1 offspring were only significantly inhibited for the exposure from fertilization to 21 days postfertilization (dpf). Compared with the exposure from 42 to 63 dpf, the reproductive toxicity induced by HFPO-TA was more significant for the exposure from fertilization to 21 dpf and from 21 to 42 dpf. Expression of the genes for cytochrome P450 A1A, vitellogenin 1, estrogen receptor alpha, and estrogen receptor 2b was significantly up-regulated in most cases after exposure to HFPO-TA, suggesting that HFPO-TA exhibited an estrogen effect similar to PFOA. Therefore, HFPO-TA might disturb the balance of sex steroid hormones and consequently induce reproductive toxicity in zebrafish. Taken together, the results demonstrate that exposure to HFPO-TA at different life stages could induce reproductive toxicity in zebrafish. However, the underlying mechanisms deserve further investigation. Environ Toxicol Chem 2023;42:2490-2500. © 2023 SETAC.

Per- and Poly-fluoroalkyl Substances and Bile Acid Profiles in Pregnant Women

Alterations in bile acid (BA) profiles are closely associated with adverse outcomes in pregnant women and their offspring and may be one potential pathway underlying the related metabolic effects of per- and poly-fluoroalkyl substances (PFAS) exposure. However, evidence of associations between PFAS exposure and BA profiles in pregnant women is scarce. This study examined the associations of individual PFAS and PFAS mixture with BA profiles of pregnant women. We obtained quantitative data on the plasma concentrations of 13 PFAS and 15 BAs in 645 pregnant women from the Jiashan birth cohort. In Bayesian kernel machine regression models, the PFAS mixture was associated with increased plasma CA, TCA, TCDCA, and GLCA levels but with decreased GCA and LCA concentrations. Furthermore, the PFAS mixture was associated with increased concentrations of total BAs and the secondary/primary BA ratio but with decreased conjugated/unconjugated and glycine/taurine-conjugated BA ratios. PFHxS, PFUdA, PFOS, PFNA, and PFDA were the dominant contributors. The results of the linear regression analysis of individual PFAS were generally similar. Our findings provide the first epidemiological evidence for the associations of a PFAS mixture with BA profiles in pregnant women and may provide explanatory insights into the biological pathways underlying the related metabolic effects of PFAS exposure.

Effect of dietary antioxidants on excretion of perfluorooctanoic acid (PFOA) via regulating uptake transporters expression and intestinal permeability in mice

Dietary antioxidants, including 2,6-di-tert-butyl-hydroxytoluene (BHT), α-tocopherol (αT) and tea polyphenol (TP), have been widely used in food. However, no data about the effect of food antioxidants on PFOA excretion were available. In this study, excretion of PFOA toward mice (four mice in each group) under the influence of co-ingested food antioxidants (i.e., BHT, αT, and TP) were investigated, and mechanism involved in excretion of PFOA, including RNA expression of uptake and efflux transporters in kidneys and liver involved in PFOA transport and intestinal permeability were also investigated. Chronic exposure to BHT (1.56 mg/kg) increased urinary PFOA excretion from 1795 ± 340 ng/mL (control) to 3340 ± 29.9 ng/mL (BHT treatment). TP treatment (12.5 mg/kg) decreased urinary excretion of PFOA, i.e., with a decrease percentage of 70% compared to the control. Organic anion transporting polypeptides (Oatps) act as uptake transporter mediate renal elimination or reabsorption of PFOA in the kidney. The decrease in urinary excretion of PFOA under TP treatment was associated with significantly (p < 0.05) enhanced expression of Oatp1a1 in the kidney (1.78 ± 0.58 vs 1.00 ± 0.18 in control), which facilitated renal reabsorption of PFOA and in turn decreased urinary excretion of PFOA. αT treatment (12.5 mg/kg) increased fecal PFOA excretion with a value of 228 ± 95.8 ng/g vs control (96.8 ± 22.7 ng/g). Mechanistic investigation revealed that αT treatment reduced intestinal permeability, resulting in increased fecal PFOA excretion.

Bile acid metabolism disorder mediates hepatotoxicity of Nafion by-product 2 and perfluorooctane sulfonate in male PPARα-KO mice

Perfluorooctane sulfonate (PFOS) and Nafion by-product 2 (H-PFMO2OSA) induce hepatotoxicity in male mice via activation of the peroxisome proliferator-activated receptor α (PPARα) pathway; however, accumulating evidence suggests that PPARα-independent pathways also play a vital role in hepatotoxicity after exposure to per- and polyfluoroalkyl substances (PFASs). Thus, to assess the hepatotoxicity of PFOS and H-PFMO2OSA more comprehensively, adult male wild-type (WT) and PPARα knockout (PPARα-KO) mice were exposed to PFOS and H-PFMO2OSA (1 or 5 mg/kg/d) for 28 d via oral gavage. Results showed that although elevations in alanine transaminase (ALT) and aspartate aminotransferase (AST) were alleviated in PPARα-KO mice, liver injury, including liver enlargement and necrosis, was still observed after PFOS and H-PFMO2OSA exposure. Liver transcriptome analysis identified fewer differentially expressed genes (DEGs) in the PPARα-KO mice than in the WT mice, but more DEGs associated with the bile acid secretion pathway after PFOS and H-PFMO2OSA treatment. Total bile acid content in the liver was increased in the 1 and 5 mg/kg/d PFOS-exposed and 5 mg/kg/d H-PFMO2OSA-exposed PPARα-KO mice. Furthermore, in PPARα-KO mice, proteins showing changes in transcription and translation levels after PFOS and H-PFMO2OSA exposure were involved in the synthesis, transportation, reabsorption, and excretion of bile acids. Thus, exposure to PFOS and H-PFMO2OSA in male PPARα-KO mice may disturb bile acid metabolism, which is not under the control of PPARα.

Toxicological Mechanisms of Emerging Per-/poly-fluoroalkyl Substances: Focusing on Transcriptional Activity and Gene Expression Disruption

Environmental and human monitoring studies have witnessed increasing occurrence of emerging per-/poly-fluoroalkyl substances (ePFASs) worldwide. Three classes of ePFASs, namely chlorinated polyfluoroalkylether sulfonic acids, hexafluoropropylene oxide homologues and short-chain perfluoroalkyl acids attracted the most attention. It is, therefore, the goal of this review to systematically and critically analyse the toxicity and toxicological mechanisms of these ePFASs based on the papers published between 2017 and 2022. The review summarized the main findings from both in vivo and in vitro studies, covering the hepatotoxicity of ePFASs and their interference with the endocrine system, including reproductive, developmental and thyroid toxicity. It also summarized the changes in gene expression in the hypothalamic-pituitary-thyroid axis and hypothalamic-pituitary-gonad axis of the model organisms after ePFASs exposure. The changes in gene expression in vitro and in vivo provide a clearer understanding of the toxicological mechanisms of ePFASs interference on hormonal levels (i.e., estradiol, testosterone, and thyroid hormones), developmental disturbance (e.g., swim bladder dysfunction) and lipid metabolism disruption (e.g., lipid droplet accumulation and hepatomegaly). In the end, future research directions on the toxicological mechanisms of ePFASs are suggested.

Effects of Perfluorooctanoic Acid on Gut Microbiota and Microbial Metabolites in C57BL/6J Mice

Perfluorooctanoic acid (PFOA) represents an increasing public health concern due to its persistence in the environment and its toxic effects. The gut microbiota is known to produce various metabolites that assist the host to maintain metabolic homeostasis. However, few studies have explored the effects of PFOA on gut-microbiota-related metabolites. In the present study, male C57BL/6J mice were exposed to 1 ppm of PFOA in drinking water for four weeks and integrative analysis of the gut microbiome and metabolome was performed to reveal the health effects of PFOA. Our results showed that PFOA disturbed both the gut microbiota composition and the metabolic profiles of the feces, serum, and liver in mice. A correlation was found between Lachnospiraceae UCG004, Turicibacter, Ruminococcaceae, and different fecal metabolites. Significant alterations of gut-microbiota-related metabolites were induced by PFOA exposure, including bile acids and tryptophan metabolites such as 3-indoleacrylic acid and 3-indoleacetic acid. The findings of this study are helpful to improve the understanding of the health effects of PFOA, which might be mediated through the gut microbiota and its related metabolites.

Recent advances in liver-on-chips: Design, fabrication, and applications

The liver is a multifunctional organ and the metabolic center of the human body. Most drugs and toxins are metabolized in the liver, resulting in varying degrees of hepatotoxicity. The damage of liver will seriously affect human health, so it is very important to study the prevention and treatment of liver diseases. At present, there are many research studies in this field. However, most of them are based on animal models, which are limited by the time-consuming processes and species difference between human and animals. In recent years, liver-on-chips have emerged and developed rapidly and are expected to replace animal models. Liver-on-chips refer to the use of a small number of liver cells on the chips to simulate the liver microenvironment and ultrastructure in vivo. They hold extensive applications in multiple fields by reproducing the unique physiological functions of the liver in vitro. In this review, we first introduced the physiology and pathology of liver and then described the cell system of liver-on-chips, the chip-based liver models, and the applications of liver-on-chips in liver transplantation, drug screening, and metabolic evaluation. Finally, we discussed the currently encountered challenges and future trends in liver-on-chips.

Emerging trends in the methodology of environmental toxicology: 3D cell culture and its applications

Human diseases and health concerns caused by environmental pollutants are globally emerging. Therefore, rapid and efficient evaluation of the effects of environmental pollutants on human health is essential. Due to the significant differences between humans and animals and the lack of physiologically related environments, animal models and two-dimensional (2D) culture cannot accurately describe toxicological effects and predict actual in vivo responses. To make up for the limitations of traditional environmental toxicology screening, three-dimensional (3D) culture has been developed. The 3D culture could provide a good organizational structure comparable to the complex internal environment of humans and produce a more realistic response to environmental pollutants, which has been used in drug development, toxicity evaluation, personalized therapy and biological mechanism research. The goal of environmental toxicology is to provide clues and support for the risk assessment and management of environmental pollutants. With the development of 3D culture that can reproduce specific physiological aspects loaded with specific cells that reflect human biology, interactions between pollutants and target tissues and organs can be explored to assess the acute and chronic adverse health effects of exposure to various environmental toxins. The 3D culture with great potential shows broad prospects in toxicology research and is expected to bridge the gap between 2D culture and animal models eventually. In this sense, we strongly recommend that 3D culture be used to identify and understand environmental toxins, which will greatly facilitate the public's comprehensive understanding of environmental toxins.

Lead and copper led to the dysregulation of bile acid homeostasis by impairing intestinal absorption in Bufo gargarizans larvae: An integrated metabolomics and transcriptomics approach

Bile acids, as metabolic regulators and signaling molecules, play key roles in the regulation of host metabolism and immune responses. Heavy metals such as lead (Pb) and copper (Cu) are widespread environmental pollutants that threaten public health. However, the effects of heavy metals on bile acid metabolism and the underlying molecular mechanisms remain unclear, particularly for ecologically important amphibian species. In the present research, the effects of exposure to environmentally-relevant concentrations of Pb (250 μg/L), Cu (50 μg/L), and a mixture of both (Mix) on bile acid metabolism and the underlying molecular mechanisms in the intestines of Bufo gargarizans larvae were comprehensively investigated using histopathology, metabolomics and transcriptomics analysis. Our results suggested that Pb and/or Cu caused histopathological damage to the intestine and liver, such as decreased intestinal epithelial cell height and dilated hepatic sinusoid. The total bile acid level was decreased in the Pb and Mix exposure groups but elevated in the Cu treatment. A significant decrease in the ratio of conjugated to unconjugated bile acids was present in all treatment groups. Also, the level of GCA was increased while TCA and TCDCA were decreased in all exposure groups. In addition, exposure to Pb and Cu altered the expression levels of genes related to intestinal absorption. For example, mrp2, mrp3 and aqp4 had higher expression in the Pb and Mix treatment groups, and aqp1 and mrp4 were increased in the Cu treatment group. Overall, we speculated that the dysregulation of bile acid homeostasis induced by Pb and Cu exposure may be due to impaired intestinal absorption. These findings raise further concerns about the hazards of Pb and/or Cu in influencing bile acid metabolism that might lead to the development of metabolic diseases and inflammatory disorders.