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Toxicological information

Genetic toxicity: in vivo

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Administrative data

Endpoint:
genetic toxicity in vivo, other
Remarks:
gene expression
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Data source

Reference
Reference Type:
publication
Title:
Formaldehyde: Integrating Dosimetry, Cytotoxicity, and Genomics to Understand Dose-Dependent Transitions for an Endogenous Compound
Author:
Andersen, M.E. et al.
Year:
2010
Bibliographic source:
Tox. Sci. 118(2), 716–731

Materials and methods

Principles of method if other than guideline:
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 in nasal epithelium from rats exposed to 0, 0.7, 2, 6, 10, or 15 ppm FA 6 h/day for 1, 4, or 13 weeks.
GLP compliance:
not specified

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
other: no additional information
Specific details on test material used for the study:
Name of test material (as cited in study report): formaldehyde

Test animals

Species:
rat
Strain:
Fischer 344
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories, Inc. (Wilmington, MA or Kingston, NY).
- Age at study initiation: 6-7 weeks
- Acclimation period: ca 2 weeks

Administration / exposure

Route of administration:
inhalation: vapour
Details on exposure:
Two 13-week inhalation exposure studies were conducted. Rats were whole-body exposed to target vapor concentrations of 0 (control), 0.7, 2, 6, 10, or 15 ppm FA in either 8 m3 (first 13-week study) or 1 m3 (second 13-week study) stainless steel and glass chambers. Controls were exposed to filtered air only. Chambers were provided with air at a flow rate of ~12 to 15 air changes per hour, and the airflow rate was monitored and recorded.
Test atmospheres were generated by slowly vaporizing solid paraformaldehyde in stainless steel pans of various sizes in sealed stainless steel canisters in an oven. Nitrogen flowed through the stainless steel canister and carried vaporized FA into the charcoal-HEPA-filtered air supplying each chamber. Atmosphere concentrations were monitored every 30 min during the 6-h exposure period, using a calibrated infrared (IR) analyzer .
Duration of treatment / exposure:
6 h/day, for 1, 4, or 13 weeks
Frequency of treatment:
5 days/week
Doses / concentrationsopen allclose all
Dose / conc.:
0.7 ppm (analytical)
Dose / conc.:
2 ppm (analytical)
Dose / conc.:
6 ppm (analytical)
Dose / conc.:
10 ppm (analytical)
Dose / conc.:
15 ppm (analytical)
No. of animals per sex per dose:
For the cell proliferation and histopathology study: 8 per dose per time period.
For the gene expression, cytokines, hematology, and bone marrow evaluation: 15 per dose per time point.
Control animals:
yes

Examinations

Tissues and cell types examined:
Nasal epithelium

Results and discussion

Test results
Genotoxicity:
other: Dose dependencies in MOA, high background FAcetal, and nonlinear FAcetal/GSH tissue kinetics indicate that FA concentrations < 1 or 2 ppm would not increase risk of cancer in the nose or any other tissue or affect FA homeostasis within epithelial cells.

Any other information on results incl. tables

Cell proliferation: Clear dose-response trends at all three exposure durations with increases seen at 6, 10, and 15 ppm but not at the two lower exposure concentrations.

 

Histopathology: Treatment-related nasal lesions (predominantly inflammation, squamous cell metaplasia, and epithelial hyperplasia) were found in the respiratory/transitional epithelium in rats exposed to 2 ppm FA or higher.

At higher exposure concentrations >6 ppm and especially the 1-week exposure, there was erosion or ulceration of respiratory epithelia and/or necrosis of underlying structures. The incidence of the lesions was related to the inhaled concentration and inversely related to the exposure duration; with longer exposure, the more robust squamous epithelium showed less erosion than did the respiratory epithelium it had replaced.

 

Gene Expression Profiling: The total number of genes that was significantly altered across all concentrations and durations was 2197, but patterns of gene expression varied with exposure concentration and duration. Although at 13 weeks the numbers of genes significantly up- and downregulated were higher than at 1-week and 4-week exposure, no grouping of genes appeared to be uniquely associated with this longer duration, as had been observed at shorter exposures.

Enrichment analysis was performed on the highest three concentrations at all exposure durations and for the up- and downregulated gene groupings at 1 and 4 weeks, and indicated a diverse suite of enriched pathways. The top 10 of these pathways includes Wnt, TGF-beta, Erbb and Hedgehog signalling, as well as pathways related to DNA repair and cell cycle. At 10 ppm, 8 of 10 of the top pathways were cell cycle related with the two others related to DNA damage and Erbb signaling. At 15 ppm, cell cycle and DNA damage were represented; however, cell adhesion and immune response pathways were also present.

At the 1-week 15 ppm exposure concentration, a widespread activation of various immune response pathways likely associated with an inflammatory response following cytotoxicity was observed. Benchmark doses for significantly enriched pathways were lowest at 13 weeks. Seven genes, in previous studies found to be upregulated genes at lower exposure concentrations, were combined in a ‘‘Sensitive Response Genes’’-grouping (SRG) and had the lowest BMD of 1 ppm.

 

PK analysis: The PK analysis showed that the lower two inhaled FA concentrations (0.7 and 2 ppm) would be characterized by only minor changes in cellular GSH and intracellular FAcetal. Above 4 ppm, FAcetal increases with a steeper dose response and free GSH is reduced to much more significant degree.

Transcriptional and histological changes corresponded to the dose ranges in which the PK model predicted significant reductions in free GSH and increases in FAcetal. Genomic changes at 0.7–2 ppm likely represent changes in extracellular FAcetal and GSH. DNA replication stress, enhanced proliferation, squamous metaplasia, and stem cell niche activation appear to be associated with FA carcinogenesis. At 2 ppm, sensitive response genes (SRGs)—associated with cellular stress, thiol transport/reduction, inflammation, and cell proliferation—were upregulated at all exposure durations. Dose dependencies in MOA, high background FAcetal, and nonlinear FAcetal/GSH tissue kinetics indicate that FA concentrations below 1 or 2 ppm would not increase risk of cancer in the nose or any other tissue or affect FA homeostasis within epithelial cells.

Applicant's summary and conclusion