Transcriptional inhibition of TCDD-mediated induction of cytochrome P450 1A1 and alteration of protein expression in a zebrafish hepatic cell line following the administration of TCDD and Cd2

2,2',4,4'-Tetrabromodiphenyl ether and cadmium co-exposure activates aryl hydrocarbon receptor pathway to induce ROS and GSDME-dependent pyroptosis in renal tubular epithelial cells

We have previously found that a mixture exposure of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and cadmium (Cd) causes kidney damage; however, the mechanism was not fully understood. The aryl hydrocarbon receptor (AhR) is a ligand-receptor transcription factor that plays an important role in the adaptive response or metabolic detoxification of environmental toxins. Thus, this study aimed to examine the role of AhR in kidney toxicity. BDE-47 (50 μM) or Cd (5 μM) exposure reduced cell viability in renal tubular epithelial cells (HKC), with a larger effect observed in co-treatment. The cell morphology presented pyroptotic changes, including swollen cells, large bubbles, and plasma membrane pore formation. The gene expressions of AhR, heat shock protein 90 (Hsp90), AhR nuclear translocator (ARNT), and cytochrome P450 1B1 (CYP1B1) were increased, while CYP1A1 was decreased. Reactive oxygen species (ROS) were generated, which was reduced by the AhR antagonist CH223191. The apoptosis, necrosis, and intracellular lactated hydrogenase (LDH) release was elevated, and this was attenuated by N-acetylcysteine (NAC). Furthermore, the pyroptosis pathway was activated with increased protein levels of cleaved-caspase-3 and gasdermin E N-terminal (GSDME-NT), while caspase-8, caspase-3, and GSDME were decreased. These effects were alleviated by NAC and CH223191. Our data demonstrate a combined effect of BDE-47 and Cd on nephrotoxicity by activating AhR to induce ROS contributing to GSDME-dependent pyroptosis, and retardation of the AhR pathway could reduce this toxicity.

Development, scrutiny, and modulation of transient reporter gene assays of the xenobiotic metabolism pathway in zebrafish hepatocytes

The "toxicology in the twenty-first century" paradigm shift demands the development of alternative in vitro test systems. Especially in the field of ecotoxicology, coverage of aquatic species-specific assays is relatively scarce. Transient reporter gene assays could be a quick, economical, and reliable bridging technology. However, the user should be aware of potential pitfalls that are influenced by reporter vector geometry. Here, we report the development of an AhR-responsive transient reporter-gene assay in the permanent zebrafish hepatocytes cell line (ZFL). Additionally, we disclose how viral, constitutive promoters within reporter-gene assay cassettes induce squelching of the primary signal. To counter this, we designed a novel normalization vector, bearing an endogenous zebrafish-derived genomic promoter (zfEF1aPro), which rescues the squelching-delimited system, thus, giving new insights into the modulation of transient reporter systems under xenobiotic stress. Finally, we uncovered how the ubiquitously used ligand BNF promiscuously activates multiple toxicity pathways of the xenobiotic metabolism and cellular stress response in an orchestral manner, presumably leading to a concentration-related inhibition of the AhR/ARNT/XRE-toxicity pathway and non-monotonous concentration-response curves. We named such a multi-level inhibitory mechanism that might mask effects as "maisonette squelching." A transient reporter gene assay in zebrafish cell lines utilizing endogenous regulatory gene elements shows increased in vitro toxicity testing performance. Synthetic and constitutive promotors interfere with signal transduction ("squelching") and might increase cellular stress (cytotoxicity). The squelching phenomenon might occur on multiple levels (toxicity pathway crosstalk and normalization vector), leading to a complete silencing of the reporter signal.

Whole-transcriptome sequencing (RNA-seq) study of the ZFL zebrafish liver cell line after acute exposure to Cd2+ ions

Cadmium (Cd) is a non-essential metal with no known biological function and a broad range of toxic effects in biological systems. We used whole-transcriptome sequencing (RNA-seq) to study the effects of Cd²⁺ toxicity in zebrafish liver cells, ZFL. The results of an RNA-Seq analysis of ZFL cells exposed to 5, 10 or 20 μM Cd²⁺ for 4- or 24-h. The differentially expressed genes affected by Cd²⁺ were analyzed by using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis to study the regulated pathways. Cd²⁺ regulated the expression of genes associated with cellular Cu, Zn, and Fe homeostasis, DNA replication leading to cell cycle arrest and apoptosis, and glutathione metabolism. Cd²⁺ boosted up the amino acid synthesis, possibly to support the glutathione metabolism for tackling the oxidative stress generated from Cd²⁺. Cd²⁺ stimulation was similar to heat or xenobiotics, based on the responses from ZFL such as endoplasmic reticulum stress and protein folding. We linked also those finding of gene activations relating to carcinogenesis of Cd. This paper provides a comprehensive analysis of the expression profiles induced by Cd²⁺ exposure in ZFL cells, as well as useful insights into the specific toxic effects.

Are we forgetting the "proteomics" in multi-omics ecotoxicology?

Proteomics plays a significant role in discerning the effects of chemical exposures in animal taxa. Multi-omics applications have become more pervasive in toxicology, however questions remain about whether proteomics is being utilized by the community to its full potential - are we placing too much stock in transcriptomics and other omics approaches for developing adverse outcome pathways? Proteins are more relevant than transcripts because they are direct mediators of the resulting phenotype. There is also rarely perfect stoichiometry between transcript and protein abundance and transcript abundance may not accurately predict physiologic response. Proteins direct all levels of phenotype: structural proteins dictate physical form, enzymes catalyze biochemical reactions, and proteins act as signaling proteins, antibodies, transporters, ion pumps, and transcription factors to control gene expression. Molecular initiating events (MIEs) of AOPs predominantly occur at the level of the protein (e.g. ligand-receptor binding) and proteomics can elucidate novel MIEs and mapping KEs in AOPs. This critical review highlights the need for proteomics in multi-omics studies in environmental toxicology and outlines steps required for inclusion and wider acceptance in chemical risk assessment. We also present case studies of multi-omics approaches that utilize proteomics and discuss some of the challenges and opportunities for proteomics in comparative ecotoxicology. Our intention is not to minimize the importance of other omics technologies, as each has strengths and limitations, but rather to encourage researchers to consider proteomics-based methods in multi-omics studies and AOP development.

Association between blood cadmium and vitamin D levels in the Yangtze Plain of China in the context of rapid urbanization

BACKGROUND

China has experienced rapid urbanization in the past 30 years. We aimed to report blood cadmium level (BCL) in the rapidly urbanized Yangtze Plain of China, and explore the association between BCL and 25-hydroxyvitamin D (25(OH)D).

METHODS

Our data source was the Survey on Prevalence in East China for Metabolic Diseases and Risk Factors (SPECT-China) cross-sectional study (ChiCTR-ECS-14005052, www.chictr.org). We enrolled 3234 subjects from 12 villages in the Yangtze Plain. BCLs were measured by atomic absorption spectrometry. 25(OH)D was measured with a chemiluminescence assay.

RESULTS

A total of 2560 (79.2%) subjects were diagnosed with vitamin D deficiency. The median (interquartile range) BCL was 1.80 μg/L (0.60-3.42) for men and 1.40 μg/L (0.52-3.10) for women. In women, mean 25(OH)D concentrations were inversely associated with BCL (0.401, 95% confidence interval: -0.697 to -0.105 nmol/L lower with each doubling of the BCL) after adjustment for age, educational status, current smoking, body mass index, diabetes, and season. However, there was no significant difference in 25(OH)D across the BCL tertiles for men.

CONCLUSIONS

BCL in Chinese residents in the Yangtze Plain were much higher than that in developed countries. An inverse association between BCL and 25(OH)D was found in general Chinese women after multivariable adjustment. Future prospective cohort and animal studies are warranted to resolve the direction and temporality of these relationships, and to elucidate the exact mechanisms involved.

Oxidative stress and apoptotic effects of copper and cadmium in the zebrafish liver cell line ZFL

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Oxidative stress and apoptosis created by Cu²⁺ and Cd²⁺ insults were studied in ZFL.

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Cu²⁺ and Cd²⁺ both created lipid peroxidation, causing oxidative stress in cytoplasm.

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Mitochondrial superoxide was induced by Cd²⁺ but supressed by Cu²⁺.

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Cu²⁺ suppressed Casp3 activity, resulting in suppressed the apoptosis.

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Pre-treatments of low concentration of Cu²⁺ protected the cell from Cd²⁺ insults.

Copper (Cu) and cadmium (Cd) are widely used in industrial activities, resulting in Cu and Cd contamination in aquatic systems worldwide. Although Cu plays an essential role in many biological functions, an excessive amount of the metal causes cytotoxicity. In contrast, Cd is a non-essential metal that usually co-exists with Cu. Together, they cause oxidative stress in cells, leading to cell damage. These metal ions are also believed to cause cell apoptosis. In this study, we used a zebrafish liver cell line, ZFL, to study combined Cu and Cd cytotoxicity. Although Cd is more toxic than Cu, both were found to regulate the expression of oxidative stress related genes, and neither significantly altered the activity of oxidative stress related enzymes. Co-exposure tests with the antioxidant N-acetyl-l-cysteine and the Cu chelator bathocuproinedisulfonic acid disodium salt demonstrated that Cd toxicity was due to the oxidative stress caused by Cu, and that Cu at a low concentration could in fact exert an antioxidant effect against the oxidative stress in ZFL. Excessive Cu concentration triggered the expression of initiator caspases (caspase 8 and caspase 9) but suppressed that of an executioner caspase (caspase 3), halting apoptosis. Cd could only trigger the expression of initiator caspases; it could not halt apoptosis. However, a low concentration of Cu reduced the mitochondrial superoxide level, suppressing the Cd-induced apoptotic effects in ZFL.

Interference of goethite in the effects of glyphosate and Roundup® on ZFL cell line

Goethite (α-FeOOH) brings important perspectives in environmental remediation, as, due to its physicochemical properties, this iron oxide can adsorb a wide variety of compounds, including glyphosate. This study aimed to evaluate the effects of goethite nanoparticles (NPs), glyphosate (Gly), Roundup® (Rd), and co-exposures (Gly + NPs and Rd + NPs) on zebrafish liver cell line (ZFL). ZFL cells were exposed to NPs (1, 10, and 100 mg L-1), Gly (3.6 mg L-1), Rd (10 mg L-1), and co-exposures (Gly + NPs and Rd + NPs), or only to saline for 1, 6, and 12 h. Cell viability was assessed by Trypan blue, MTT, and neutral red assays. The generation of reactive oxygen species and total antioxidant capacity were also determined, while genotoxicity was quantified by the comet assay. Both NPs and Rd in isolation produced cytotoxic effects at 6 h and genotoxic effects at 1 and 6 h. Rd + NPs resulted in synergistic effects, intensifying the toxicity. Cells exposed to Gly did not present toxic effects and Gly + NPs resulted in the suppression of toxic effects observed for NPs. The presence of other components in Roundup® seems to favor its toxicity compared to the active ingredient. In conclusion, according to the in vitro model, the concentrations used were not safe for the ZFL lineage.

Microcystin-LR-regulated transcriptome dynamics in ZFL cells

Microcystin-LR (MC-LR) is a highly toxic hepatotoxin that poses great hazards to aquatic organisms and even human health. The zebrafish liver cell line (ZFL) is a valuable model for investigating toxicity and metabolism of toxicants. However, the toxicity of MC-LR and its effects on gene transcription of ZFL cells remains to be characterized. In this study, we determined the toxicity of MC-LR for ZFL cells and investigated the effects of MC-LR on cellular transcriptome dynamics. The EC₅₀ of MC-LR for ZFL cells was 80.123 μg/mL. The ZFL cells were exposed to 10 μg/mL MC-LR for 0, 1, 3, 6, 12 or 24 h, and RNA-sequencing was performed to analyze gene transcription. A total of 10,209 genes were found to be regulated by MC-LR. The numbers of up- and down-regulated genes at different time points ranged from 2179 to 3202 and from 1501 to 2597, respectively. Furthermore, 1543 genes underwent differential splicing (AS) upon MC-LR exposure, of which 620 were not identified as differentially expressed gene (DEG). The effects of MC-LR on cellular functions were highly time-dependent. MAPK (mitogen-activated protein kinase) and FoxO (forkhead box O) signaling pathways were the most prominent pathways activated by MC-LR. Steroid biosynthesis and terpenoid backbone biosynthesis were the most enriched for the down-regulated genes. A gene regulatory network was constructed from the expression profile datasets and the candidate master transcription factors were identified. Our results shed light on the molecular mechanisms of MC-LR cellular toxicity and the transcriptome landscapes of ZFL cells upon MC-LR toxicity.

Modulations of TCDD-mediated induction of zebrafish cyp1a1 and the AHR pathway by administering Cd2+in vivo

Trace metal ions such as cadmium (Cd²⁺) and trace organics typified by 2,3,7,8- tetrachlorodibenzo-p-dioxin (TCDD) are common co-contaminants in the environment and cause toxic effects in aquatic organisms that pose serious health risks. We studied the effects of Cd²⁺ on the regulation of cytochrome P450 1A1 (cyp1a1) gene-induction by TCDD using zebrafish embryos and larvae and adult zebrafish tissues. Our results showed that TCDD induced the cyp1a1 gene in all developmental stages and tissues of zebrafish, and the induction was higher in females than males. However, for the upstream genes (ahr2 and arnt2b) that mediate cyp1a1 gene induction in the zebrafish liver cell line was not induced by TCDD similar to the pattern of cyp1a1 in all investigated groups. After co-treatment with Cd²⁺, induction of the aryl hydrocarbon receptor pathway by TCDD was inhibited in the zebrafish larvae and the livers, intestines, kidneys and gills of adult zebrafish, but not in the embryos or brains of adult zebrafish, indicating that the toxicological effects of Cd²⁺ on TCDD are dependent on the developmental stages and tissue types. The present study confirms that Cd²⁺ blocks the TCDD-induced cyp1a1 gene in vivo but emphasizes that the effects are specific to the developmental stage, type of tissue and sex. The combined effects of Cd²⁺ and TCDD must be taken into consideration together with these parameters to accurately predict and assess cadmium and TCDD-induced toxicity in fish and carcinogenesis in animals in general.

Norisoboldine, a natural AhR agonist, promotes Treg differentiation and attenuates colitis via targeting glycolysis and subsequent NAD+/SIRT1/SUV39H1/H3K9me3 signaling pathway

Norisoboldine (NOR), a natural aryl hydrocarbon receptor (AhR) agonist, has been demonstrated to attenuate ulcerative colitis (UC) and induce the generation of Treg cells. Under UC condition, hypoxia widely exists in colonic mucosa, and secondary changes of microRNAs (miRs) expressions and glycolysis contribute to Treg differentiation. At present, we worked for exploring the deep mechanisms for NOR-promoted Treg differentiation in hypoxia and its subsequent anti-UC action from the angle of AhR/miR or AhR/glycolysis axis. Results showed that NOR promoted Treg differentiation in hypoxia and the effect was stronger relative to normoxia. It activated AhR in CD4⁺ T cells under hypoxic microenvironment; CH223191 (a specific AhR antagonist) and siAhR-3 abolished NOR-promoted Treg differentiation. Furthermore, the progress of glycolysis, levels of Glut1 and HK2, and expression of miR-31 rather than miR-219 and miR-490 in CD4⁺ T cells were downregulated by NOR treatment under hypoxic microenvironment. However, HK2 plasmid but not miR-31 mimic significantly interfered NOR-enhanced Treg polarization. In addition, NOR reduced NAD⁺ and SIRT1 levels, facilitated the ubiquitin-proteasomal degradation of SUV39H1 protein, and inhibited the enrichment of H3K9me3 at -1, 201 to -1,500 region of Foxp3 promoter in CD4⁺ T cells under hypoxic microenvironment, which was weakened by HK2 plasmid, CH223191, and siAhR-3. Finally, the correlation between NOR-mediated activation of AhR, repression of glycolysis, regulation of NAD⁺/SIRT1/SUV39H1/H3K9me3 signals, induction of Treg cells, and remission of colitis was confirmed in mice with DSS-induced colitis by using CH223191 and HK2 plasmid. In conclusion, NOR promoted Treg differentiation and then alleviated the development of colitis by regulating AhR/glycolysis axis and subsequent NAD⁺/SIRT1/SUV39H1/H3K9me3 signaling pathway.