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Comparison of the modes of action of p-dialkoxy chlorobenzenes in rat primary hepatocytes

ABSTRACT: It is considered that read-across based on only structure similarity has a risk of error on risk assessment. Under this circumstances, considering biological similarity based on adverse outcome pathways (AOPs) using in vitro omics technologies is expected to enhance the accuracy and robustness of conclusions in read-across. However, because of a lack of practical case studies, it is not well discussed key considerations and how to use these technologies for data gap filling. In the present case study, we elucidated and compared the mode of action for structural analogs ; p-dialkoxy chlorobenzenes including 1,4-dichloro-2,5-dimethoxybenzene (DDMB), 2,5-dichloro-1,4-diethoxybenzene (DDEB), 2-chloro-1,4-dimethoxybenzene (CDMB), and 1-chloro-2,5-diethoxybenzene (CDEB) using in vitro omics technologies. To reveal the modes of action, we conducted microarray analysis with rat primary hepatocytes.

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE137379 | GEO | 2020/04/01

REPOSITORIES: GEO

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Project description:1,4-Dioxane (1,4-DX) is an environmental contaminant found in drinking water throughout the United States (US). While it is a suspected liver carcinogen, there is no federal or state maximum contaminant level for 1,4-DX in drinking water. Very little is known about the mechanisms by which this chemical elicits liver carcinogenicity. In the present study, we performed chronic and short-term dosing studies in female BDF-1 mice to explore the toxic effects of 1,4-DX. Histopathology studies and a multi-omics approach (transcriptomics and metabolomics) were performed to investigate potential mechanisms of toxicity. Mice were exposed to various concentrations of 1,4-DX (0, 50, 500 and 5,000 mg/L) in their drinking water for one or four weeks. Immunohistochemical analysis of the liver revealed an increase in the number of H2AXγ-positive hepatocytes (a marker of DNA double strand breaks) in mice exposed to 5,000 mg/L 1,4-DX for one and four weeks. In addition, an expansion of precholangiocytes was observed after four weeks of 5,000 mg/L 1,4-DX exposure, as reflected by CK-7 immunostaining. An increase in these markers reflect both DNA damage and repair mechanisms. Liver transcriptomics profiling showed that exposure to 5,000 mg/L 1,4-DX for four weeks resulted in the differential expression of 65 genes compared to controls. Pathway analysis of the transcriptomic data revealed 1,4-DX-induced perturbations in multiple signaling pathways in the liver, including those involved in xenobiotic metabolism, nicotine degradation and glutathione-mediated detoxification. Changes to these pathways as a result of 1,4-DX exposure reflect would be predicted to impact the oxidative stress response, detoxification, and DNA damage. Liver, kidney, stool and urine metabolomics profiling revealed no effect of 5,000 mg/L 1,4-DX exposure for one or four weeks on metabolites. We speculate that this may be reflective of DNA damage being counterbalanced by the repair response, with the net result being a null overall effect on the systemic biochemistry of the exposed mice. Our results show a novel approach for the investigation of environmental chemicals that do not elicit cell death, but have activated the repair systems in response to 1,4-DX exposure

Project description:The objective of this work was to use transcriptional profiling to assess the biological activity of structurally related chemicals to define their biological similarity and with that, substantiate the validity of a read-across approach usable in risk assessment. Two case studies are presented, one with 4 short alkyl chain parabens: methyl (MP), ethyl (EP), butyl (BP), and propyl paraben (PP), as well as their main metabolite, p-Hydroxybenzoic acid (pHBA) with the assumption that PP was the target chemical; and a second one with caffeine (CA) and its main metabolites theophylline (TP), theobromine (TB) and paraxanthine (PX), where caffeine was the target chemical. The comprehensive transcriptional response of MCF7, HepG2, A549 and ICell cardyomiocytes was evaluated (TempO-Seq) after exposure to vehicle-control, each paraben or pHBA, caffeine or its metabolites, at 3 non-cytotoxic concentrations, for 6h. Differentially expressed genes (FDR ≥ 0.05, and fold change ±1.2≥) were identified for each chemical, at each dose of exposure, and used to determine similarities between them. Each of the chemicals is able to elicit changes in the expression of a number of genes, as compared to controls, particularly at the highest dose tested. Importantly, the transcriptional profile elicited by each of the parabens shares a high degree of similarities across the category members. The highest number of genes commonly affected by the parabens was found between BP and PP. The transcriptional profile of the parabens is similar to the one elicited by some estrogen receptor agonist, among other actives. Pathway enrichment analysis (MSigDB v7.0) of the transcriptional profile for each paraben indicated a significant overlap in the up- and down-regulated pathways across the four parabens.The highest similarity in biological activity was found between BP and PP. This was indicative of their biological similarity, and thus the validity of the read across among the group, with BT being the closest structural and biological analogue for PP. In the caffeine case and its main metabolites, the transcriptional profile elicited of all four compounds had a high degree of similarity across the cell types, with CA and TP being the most active. The most robust response was obtained in the cardiomyocytes with the highest transcriptional profile similarity between CA and TP. The transcriptional profile of the methylxantines is similar to the one elicited by inhibitors of phosphatidylinositol 3-kinase as well as other actives. Pathway enrichment analysis (MSigDB v7.0) of the transcriptional profile for each compound indicated a significant overlap in the up- and down-regulated pathways across the four methylxanthines. The highest similarity in biological activity was found between CA and TP, supporting the conclusion that from the group of methylxantines evaluated TP is the most appropriate analogue to read-across for CA. Overall, our results support the approach of incorporating transcriptional profiling in well-designed in vitro tests to support biological similarity driven read-across procedures and strengthening the traditional structure-based approaches useful in risk assessment.

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Comparison of the modes of action of p-dialkoxy chlorobenzenes in rat primary hepatocytes

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