Unknown,Transcriptomics,Genomics,Proteomics

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Temporal Concordance between Apical and Transcriptional Points-of-Departure for Chemical Risk Assessment

ABSTRACT: The number of legacy chemicals without toxicity reference values combined with the rate of new chemical development are overwhelming the capacity of the traditional risk assessment paradigm. More efficient approaches are needed to quantitatively estimate chemical risks. In this study, rats were dosed orally with multiple doses of six chemicals for 5 days, 2, 4, and 13 weeks. Target organs were analyzed for traditional histological and organ weight changes and transcriptional changes using microarrays. Histological and organ weight changes in this study and the tumor incidences in the original cancer bioassays were analyzed using benchmark dose (BMD) methods to identify noncancer and cancer points-of-departure. The dose-response changes in gene expression were also analyzed using BMD methods and the responses grouped based on signaling pathways. A comparison of transcriptional BMD values for the most sensitive pathway with BMD values for the noncancer and cancer apical endpoints showed a high degree of correlation at all time points. When the analysis included data from an earlier study with 8 additional chemicals, transcriptional BMD values for the most sensitive pathway were significantly correlated with noncancer (r = 0.827, p = 0.0031) and cancer-related (r = 0.940, p = 0.0002) BMD values at 13 weeks. The average ratio of apical-to-transcriptional BMD values was less than two suggesting that for the current chemicals, transcriptional perturbation did not occur at significantly lower doses than apical responses. Based on our results, we propose a practical framework for application of transcriptomic data to chemical risk assessment. Four to five week-old rats were exposed in dose-response and for multiple durations to 6 chemicals. The chemicals were 1,2,4-tribromobenzene (CAS No. 615-54-3), 2,3,4,6-tetrachlorophenol (CAS No. 58-90-2), bromobenzene (CAS No. 108-86-1), 4,4'-methylenebis(N,N-dimethyl)benzenamine (CAS No. 101-61-1), hydrazobenzene (CAS No. 122-66-7), N-nitrosodiphenylamine (CAS No. 86-30-6). For 1,2,4-tribromobenzene and 2,3,4,6-tetrachlorophenol, male Sprague Dawley (Rat/Crl:CD(SD)) rats were used. For bromobenzene and hydroazobenzene, male F344/DuCrl rats were used. For 4,4'-methylenebis(N,N-dimethyl)benzenamine and N-nitrosodiphenylamine, female F344/DuCrl rats were used. The exposure durations were 5 days, 2 weeks, 4 weeks, and 13 weeks. The dose and route of exposure are provided with the individual sample annotations. With each chemical treatment, a matched vehicle control group was run concurrently with the exposure. Gavage exposures were administered 7 days per week and feed exposures were provided 7 days per week. At the appropriate time point, animals were euthanized with a lethal intraperitoneal injection of sodium pentobarbital. For the liver, slices from each of the lobes were mixed together and used for microarray analysis. For the thyroid, the gland was transversely sectioned and the bottom portion was used for microarray analysis. For the bladder, the organ was longitudinally bisected, a slice was removed for histology and the remainder of the organ was minced and used for microarray analysis. Microarrays were run on five rats per dose per time point.

ORGANISM(S): Rattus norvegicus

SUBMITTER: Longlong Yang

PROVIDER: E-GEOD-45892 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Two-year rodent bioassays play a central role in evaluating both the carcinogenic potential of a chemical and generating quantitative information on the dose-response behavior for chemical risk assessments. The bioassays involved are expensive and time-consuming, requiring nearly lifetime exposures (two years) in mice and rats and costing $2 to $4 million per chemical. Since there are approximately 80,000 chemicals registered for commercial use in the United States and 2,000 more are added each year, applying animal bioassays to all chemicals of concern is clearly impossible. To efficiently and economically identify carcinogens prior to widespread use and human exposure, alternatives to the two-year rodent bioassay must be developed. In this study, animals were exposed for 13 weeks to 10 chemicals that were positive for liver tumors in the two-year rodent bioassay, 14 chemicals that were negative for liver tumors, and two chemicals that produced an equivocal response. Matched vehicle control groups were run concurrently with each chemical treatment. Gene expression analysis was performed on the livers of the animals to assess the potential for identifying gene expression biomarkers and signaling pathways that can predict tumor formation in a two-year bioassay following a 13 week exposure. Five-week-old female B6C3F1 mice were exposed for 13 weeks to 26 chemicals. The chemical and dose information are provided with the individual sample annotations. With each chemical treatment, a matched vehicle control group was run concurrently with the exposure. A subset of five chemicals, methylene chloride, naphthalene, 1,2,3-trichloropropane, propylene glycol mono-t-butyl ether, and 1,4-dichlorobenzene, were performed in a five-point dose response with matched control groups. The concentrations for these exposures overlapped those in the original cancer bioassay. Gavage exposures were administered 5 days per week and feed exposures were provided 7 days per week. For inhalation exposures, mice were exposed 6 hr per day, 5 days per week. After 13 weeks, animals were euthanized and livers were collected. The right, caudate and median liver lobes were minced together and used for microarray analysis. Microarray analysis was performed on the livers of three to five mice per treatment group.

Project description:ß-chloroprene (2-chloro-1,3-butadiene), a monomer used in the production of neoprene elastomers, is of regulatory interest due to the production of multi-organ tumors in mouse and rat cancer bioassays. A significant increase in female mouse lung tumors was observed at the lowest exposure concentration of 12.8 ppm while a small, but not statistically significant, increase was observed in female rats only at the highest exposure concentration of 80 ppm. The metabolism of chloroprene results in the generation of reactive epoxides and the rate of overall chloroprene metabolism is highly species dependent. To identify potential key events in the mode-of-action of chloroprene lung tumorigenesis, dose response and time course gene expression microarray measurements were made in the lungs of female mice and female rats. The gene expression changes were analyzed using both a traditional analysis of variance approach followed by pathway enrichment analysis and a pathway-based benchmark dose (BMD) analysis approach. Pathways related to glutathione biosynthesis and metabolism were the primary pathways consistent with cross-species differences in tumor incidence and transcriptional BMD values for the pathway were more similar to differences in tumor response than were estimated target tissue dose surrogates based on the total amount of chloroprene metabolized per unit mass of lung tissue per day. The closer correspondence of the transcriptional changes with the tumor response are likely due to their reflection of the overall balance between metabolic activation and detoxication reactions whereas the current tissue dose surrogate reflects only oxidative metabolism. Female mice (B6C3F1/Crl) were exposed to chloroprene (CAS 126-99-8) by whole-body inhalation exposure at 0, 0.3, 2, 13, or 90 ppm. Exposures were performed for 6 hr/day, 5 days per week. The animals were sacrified at 5 days or 19 days (15 exposure days) post initiation of exposure. The right lung was excised and gene expression microarray analysis was performed using Affymetrix Mouse 430_2 arrays. Female rats (F344/NCrl) were exposed to chloroprene (CAS 126-99-8) by whole-body inhalation exposure at 0, 5, 30, 90, or 200 ppm. Exposures were performed for 6 hr/day, 5 days per week. The animals were sacrified at 5 days or 19 days (15 exposure days) post initiation of exposure. The right lung was excised and gene expression microarray analysis was performed using Affymetrix Rat 230_2 arrays.

Project description:The primary goal of toxicology and safety testing is to identify agents that have the potential to cause adverse effects in humans. Unfortunately, many of these tests have not changed significantly in the past 30 years and most are inefficient, costly, and rely heavily on the use of animals. The rodent cancer bioassay is one of these safety tests and was originally established as a screen to identify potential carcinogens that would be further analyzed in human epidemiological studies. Today, the rodent cancer bioassay has evolved into the primary means to determine the carcinogenic potential of a chemical and generate quantitative information on dose-response behavior in chemical risk assessments. Due to the resource-intensive nature of these studies, each bioassay costs $2 to $4 million and takes over three years to complete. Over the past 30 years, only 1,468 chemicals have been tested in a rodent cancer bioassay. By comparison, approximately 9,000 chemicals are used by industry in quantities greater than 10,000 lbs and nearly 90,000 chemicals have been inventoried by the U.S. Environmental Protection Agency as part of the Toxic Substances Control Act. Given the disparity between the number of chemicals tested in a rodent cancer bioassay and the number of chemicals used by industry, a more efficient and economical system of identifying chemical carcinogens needs to be developed. Experiment Overall Design: Five-week old female B6C3F1 mice were exposed for 13 weeks in the following dose groups: 1) 1,5-Naphthalenediamine, CAS No. 2243-62-1, feed, 2000 ppm, positive lung carcinogen; 2) 2,3-Benzofuran, CAS No. 271-89-6, gavage, 240 mg/kg, positive lung carcinogen; 3) 2,2-Bis(bromomethyl)-1,3-propanediol, CAS No. 3296-90-0, feed, 1250 ppm, positive lung carcinogen; 4) N-Methylolacrylamide, CAS No. 924-42-5, gavage (water), 50 mg/kg, positive lung carcinogen; 5) 1,2-Dibromoethane, CAS No. 106-93-4, gavage (corn oil), 62 mg/kg, positive lung carcinogen; 6) Coumarin, CAS No. 91-64-5, gavage (corn oil), 200 mg/kg, positive lung carcinogen; 7) Benzene, CAS No. 71-43-2, gavage (corn oil), 100 mg/kg, positive lung carcinogen; 8) N-(1-naphthyl)ethylenediamine dihydrochloride, CAS No. 1465-25-4, feed, 2000 ppm, negative lung carcinogen; 9) Pentachloronitrobenzene, CAS No. 82-68-8, feed, 8187 ppm, negative lung carcinogen; 10) 4-Nitroanthranilic acid, CAS No. 619-17-0, feed, 10000 ppm, negative lung carcinogen; 11) 2-Chloromethylpyridine hydrochloride, CAS No. 6959-47-3, gavage (water), 250 mg/kg, negative lung carcinogen; 12) Diazinon, CAS No. 333-41-5, feed, 200 ppm, negative lung carcinogen; 13) Malathion, CAS No. 121-75-5, feed, 16000 ppm, negative lung carcinogen; 14) Corn oil control, gavage; 15) Water control, gavage; 16) Rodent diet control, feed. Feed animals were exposed 7 days/week and gavage animals were exposed 5 days/week (5 ml/kg). After 13 weeks, animals were euthanized and lungs were collected. The right lobe was used for microarray analysis. Microarray analysis was performed on the lungs of three to four mice per treatment group.

Project description:Concentration- and time-dependent genomic changes in the mouse urinary bladder following exposure to arsenate in drinking water for up to twelve weeks. Inorganic arsenic (Asi) is a known human bladder carcinogen. The objective of this study was to examine the concentration dependence of the genomic response to Asi in the urinary bladders of mice. C57BL/6J mice were exposed for 1 or 12 weeks to arsenate in drinking water at concentrations of 0.5, 2, 10, and 50 mg As/L. Urinary bladders were analyzed using gene expression microarrays. A consistent reversal was observed in the direction of gene expression change: from predominantly decreased expression at 1 week to predominantly increased expression at 12 weeks. These results are consistent with evidence from in vitro studies of an acute adaptive response that is suppressed on longer exposure due to down-regulation of Fos. Pathways with the highest enrichment in gene expression changes were associated with epithelial-to-mesenchymal transition, inflammation, and proliferation. Benchmark dose (BMD) analysis determined that the lowest median BMD values for pathways were above 5 mg As/L, despite the fact that pathway enrichment was observed at the 0.5 mg As/L exposure concentration. This disparity may result from the non-monotonic nature of the concentration-responses for the expression changes of a number of genes, as evidenced by the much fewer gene expression changes at 2 mg As/L compared to lower or higher concentrations. Pathway categories with concentration-related gene expression changes included cellular morphogenesis, inflammation, apoptosis/survival, cell cycle control, and DNA damage response. The results of this study provide evidence of a concentration-dependent transition in the mode of action for the subchronic effects of Asi in mouse bladder cells in the vicinity of 2 mg Asi/L. Female C57Bl/J mice will be exposed to COLD Arsenate in drinking water. One week interium sac on 7/18/06. 100 samples including liver, lung, kidney and bladder. Bladder will be analyzed with microarrays, 24 samples. Twelve week terminal sac on 10/05/06. 75 total samples including lung, kidney, and bladder. Bladdler will be analyzed by microarray, 25 samples. Drinking water containing As will be prepared weekly with monitoring to determine amount used by mice. Following tissues will be available for genomic study: Bladder, liver, lung, and kidney.

Project description:The process for evaluating chemical safety is inefficient, costly, and animal intensive. There is growing consensus that the current process of safety testing needs to be significantly altered to improve efficiency and reduce the number of untested chemicals. In this study, the use of short-term gene expression profiles was evaluated for predicting the increased incidence of mouse lung tumors. Animals were exposed to a total of 26 diverse chemicals with matched vehicle controls over a period of three years. Upon completion, significant batch-related effects were observed. Adjustment for batch effects significantly improved the ability to predict increased lung tumor incidence. For the best statistical model, the estimated predictive accuracy under honest five-fold cross-validation was 79.3% with a sensitivity and specificity of 71.4 and 86.3%, respectively. A learning curve analysis demonstrated that gains in model performance reached a plateau at 25 chemicals, indicating that the size of the current data set was sufficient to provide a robust classifier. The classification results showed a small subset of chemicals contributed disproportionately to the misclassification rate. For these chemicals, the misclassification was more closely associated with genotoxicity status than efficacy in the original bioassay. Statistical models were also used to predict dose-response increases in tumor incidence for methylene chloride and naphthalene. The average posterior probabilities for the top models matched the results from the bioassay for methylene chloride. For naphthalene, the average posterior probabilities for the top models over-predicted the tumor response, but the variability in predictions were significantly higher. The study provides both a set of gene expression biomarkers for predicting chemically-induced mouse lung tumors as well as a broad assessment of important experimental and analysis criteria for developing microarray-based predictors of safety-related endpoints. Experiment Overall Design: Five-week-old female B6C3F1 mice were exposed for 13 weeks to 26 chemicals. The chemical and dose information are provided with the individual sample annotations. With each chemical treatment, a matched vehicle control group was run concurrently with the exposure. A subset of two chemicals, methylene chloride and naphthalene, were performed in a five-point dose response with a matched purified air control group. The concentrations for these exposures overlapped those in the original cancer bioassay. Gavage exposures were administered 5 days per week and feed exposures were provided 7 days per week. For inhalation exposures, mice were exposed 6 hr per day, 5 days per week. After 13 weeks, animals were euthanized and lungs were collected. The right lobe was used for microarray analysis. Microarray analysis was performed on the lungs of three to four mice per treatment group.

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Temporal Concordance between Apical and Transcriptional Points-of-Departure for Chemical Risk Assessment

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