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Gene expression microarray analysis of rat nasal tissue with time and dose following formaldehyde inhalation

ABSTRACT: Formaldehyde (FA), an endogenous cellular aldehyde, is a rat nasal carcinogen. In this study, concentration- and exposure-duration transitions in FA mode of action (MOA) were examined with pharmacokinetic (PK) modeling for tissue formaldehyde acetal (FAcetal) and glutathione (GSH) and with histopathology and gene expression studies for tissue responses in nasal epithelium from rats exposed to 0, 0.7, 2, 6, 10 or 15 ppm FA 6 hr/day for 1, 4 or 13 weeks. The study had two goals. The first goal was to develop a basic PK model to estimate various forms of tissue formaldehyde and tissue glutathione (GSH). The second goal was to compare histopathology and gene expression changes in nasal tissues caused by inhalation of FA with changes in tissue FAcetal and free GSH calculated from the PK model. Patterns of gene expression varied with concentration and with duration. At 0.7 and 2 ppm, sensitive response genes (SRGs) - associated with cellular stress, thiol transport/reduction, inflammation, and cell proliferation - were similarly upregulated at all exposure durations. At 6 ppm and greater, gene expression changes showed enrichment of pathways involved in cell cycle, DNA repair, and apoptosis processes. ERBB, EGFR, WNT, TGF-β, Hedgehog, and Notch signaling were also enriched in differentially expressed genes. Benchmark doses (BMDs) for genes in significantly enriched pathways were lower at 13 weeks than at 1 or 4-week. The transcriptional and histological changes corresponded to PK model-predicted changes in free GSH at 0.7 and 2 ppm and in FAcetal at 6 ppm. DNA-replication stress, enhanced proliferation, metaplasia, and stem cell-niche activation appear to be associated with FA carcinogenesis at 6 ppm and above. Dose dependencies in MOA, the presence of high physiological FAcetal, and non-linear FAcetal/GSH tissue kinetics indicate that FA concentrations below 150 ppb (and probably any concentrations below irritant levels, i.e., ~ 1 ppm) would not increase cancer risks of inhaled FA in the nose or any other tissue. Closer examination of dose response relationships for endogenous compound toxicity could help guide biologically relevant approaches for chemical risk assessment.

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE23179 | GEO | 2010/07/28

SECONDARY ACCESSION(S): PRJNA131653

REPOSITORIES: GEO

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Project description:Formaldehyde (FA), an endogenous cellular aldehyde, is a rat nasal carcinogen. In this study, concentration- and exposure-duration transitions in FA mode of action (MOA) were examined with pharmacokinetic (PK) modeling for tissue formaldehyde acetal (FAcetal) and glutathione (GSH) and with histopathology and gene expression studies for tissue responses in nasal epithelium from rats exposed to 0, 0.7, 2, 6, 10 or 15 ppm FA 6 hr/day for 1, 4 or 13 weeks. The study had two goals. The first goal was to develop a basic PK model to estimate various forms of tissue formaldehyde and tissue glutathione (GSH). The second goal was to compare histopathology and gene expression changes in nasal tissues caused by inhalation of FA with changes in tissue FAcetal and free GSH calculated from the PK model. Patterns of gene expression varied with concentration and with duration. At 0.7 and 2 ppm, sensitive response genes (SRGs) - associated with cellular stress, thiol transport/reduction, inflammation, and cell proliferation - were similarly upregulated at all exposure durations. At 6 ppm and greater, gene expression changes showed enrichment of pathways involved in cell cycle, DNA repair, and apoptosis processes. ERBB, EGFR, WNT, TGF-β, Hedgehog, and Notch signaling were also enriched in differentially expressed genes. Benchmark doses (BMDs) for genes in significantly enriched pathways were lower at 13 weeks than at 1 or 4-week. The transcriptional and histological changes corresponded to PK model-predicted changes in free GSH at 0.7 and 2 ppm and in FAcetal at 6 ppm. DNA-replication stress, enhanced proliferation, metaplasia, and stem cell-niche activation appear to be associated with FA carcinogenesis at 6 ppm and above. Dose dependencies in MOA, the presence of high physiological FAcetal, and non-linear FAcetal/GSH tissue kinetics indicate that FA concentrations below 150 ppb (and probably any concentrations below irritant levels, i.e., ~ 1 ppm) would not increase cancer risks of inhaled FA in the nose or any other tissue. Closer examination of dose response relationships for endogenous compound toxicity could help guide biologically relevant approaches for chemical risk assessment. Eight week old male F344/CrlBR rats were exposed to formaldehyde through whole body inhalation. Whole-body exposures were performed at doses of 0, 0.7, 2, 6, 10, and 15 ppm (6 hours per day, 5 days per week). Inhalation animals were sacrified at 1, 4, and 13 weeks following initiation of exposure. Following sacrifice, tissue from the Level II region of the nose was dissected and digested with a mixture of proteases to remove the epithelial cells. The epithelial cells acquired from this section of the nose consisted primarily of transitional epithelium with some respiratory epithelium. Gene expression microarray analysis was performed on the epithelial cells.

Project description:41 volunteers (male non-smokers) were exposed to formaldehyde (FA) vapors for 4 h per day over a period of 5 working days under strictly controlled conditions. For each exposure day, different exposure concentrations were used in a random order ranging from 0 up to 0.7 ppm. At concentrations of 0.3 ppm and 0.4 ppm, four peaks of 0.6 or 0.8 ppm for 15 min each were applied. During exposure, subjects had to perform bicycle exercises (about 80 W) four times for 15 min. Blood samples, exfoliated nasal mucosa cells and nasal biopsies were taken before the first and after the last exposure. Nasal epithelial cells were additionally sampled 1, 2 and 3 weeks after the end of the exposure period. The alkaline comet assay, the sister chromatid exchange (SCE) test and the cytokinesis-block micronucleus test (CBMNT) were performed with blood samples. The micronucleus test (MNT) was also performed with exfoliated nasal mucosa cells. The expression (mRNA level) of the GSH-dependent formaldehyde dehydrogenase (FDH, identical to alcohol dehydrogenase 5; ADH5; EC 1.2.1.46) was measured in blood samples by quantitative real-time RT-PCR with TaqMan probes. DNA microarray analyses using a full-genome human microarray were performed on blood samples and nasal biopsies of selected subgroups with the highest FA exposure at different days. None of the tests performed showed a biologically significant effect related to FA exposure. Under the experimental conditions of this study, inhalation of FA did not lead to genotoxic effects in peripheral blood cells and nasal mucosa and had no effect on the expression of the FDH gene. Inhalation of FA also did not cause biologically relevant alterations in the expression of genes in a microarray analysis with nasal biopsies and peripheral blood cells. Gene expression analysis of nasal biopsies and blood samples before and after inhalation of 0.7ppm formaldehyde (0 h, 24 h, or 72 h before sampling), and of blood cells before and after exposure to 200µM formaldehyde for 4 hours.

Project description:Formaldehyde, an important industrial chemical, is used for multiple commercial purposes throughout the industrialized world. This simple, one carbon aldehyde is a natural metabolite formed in cells throughput the body. However, it is also a rodent nasal carcinogen, when inhaled by rats every day for two-years at irritant concentrations. High tumor incidences occur at concentration of 10 ppm and above; no tumors are observed at concentrations below 6.0 ppm. The US Environmental Protection Agency (US EPA) is now (2007) conducting a risk assessment to try to evaluate possible cancer risks for much lower levels of human exposure. Sensitive methods are needed to evaluate tissue responses below those concentrations that are clearly irritant or carcinogenic. This microarray study was undertaken to evaluate the mode of action for nasal responses to inhaled formaldehyde in Fisher 344 rats over a range of exposure concentrations. The range of concentrations used spanned those at which virtually no tissue responses were observed (0.7 ppm) to those that represent the highest concentration in the cancer studies (15 ppm) that produced nasal tumors in half the exposed group of rats. The study identified doses at which there were no statistically significant changes in gene expression; intermediate doses with changes in a small number of genes not easily grouped by function; and then concentrations where changes were consistent with irritation and cell stress responses. Experiment Overall Design: Eight week old male F344/NCrl rats were exposed to formaldehyde through either instillation or inhalation. For animals exposed via instillation, 40 ul per nostril of 400 mM formaldehyde was instilled intranasally. Vehicle control animals were instilled with 40 ul per nostril of distilled water. All animals exposed via instillation were sacrificed 6 hours post-exposure. For animals exposed via inhalation, whole-body exposures were performed at doses of 0, 0.7, 2, 6, and 15 ppm (6 hours per day, 5 days per week). Inhalation animals were sacrified at 6 hours, 24 hours, 5 days, and 19 days following initiation of exposure except for the 15 ppm concentration which was sacrificed at only the 6 hour time point. Following sacrifice, tissue from the Level II region of the nose was dissected and digested with a mixture of proteases to remove the epithelial cells. The epithelial cells scquired from this section of the nose consisted primarily of transitional epithelium with some respiratory epithelium. Microarray analysis was performed on the epithelial cells.

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Gene expression microarray analysis of rat nasal tissue with time and dose following formaldehyde inhalation

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