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Toxicological information

Genetic toxicity: in vivo

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Administrative data

Endpoint:
in vivo mammalian cell study: DNA damage and/or repair
Remarks:
Type of genotoxicity: DNA damage and/or repair
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: GLP-compliant non-guideline study, available as unpublished report, no restrictions, fully adequate for assessment.

Data source

Referenceopen allclose all

Reference Type:
study report
Title:
Unnamed
Year:
2009
Reference Type:
other: manuscrpit
Title:
Unnamed
Year:
2006

Materials and methods

Test guideline
Qualifier:
no guideline available
Principles of method if other than guideline:
The tandem mass spectrometric detection was done in the Selected Reaction Monitoring (SRM) mode. The SRM transitions used were m/z 210 to 152 and m/z 214 to 156 for hydroxypropylguanine (N7-HPG) and its [13C4]–labeled internal standard, respectively.
Apurinic/apyrimidinc (AP) sites in DNA were measured following a procedure reported by: Nakamura, J, and Swenberg, JA. 1999. Endogenous apurinic/apyrmidinic sites in genomic DNA of mammalian tissues. Cancer Res. 59:2522-2526.
GLP compliance:
yes (incl. QA statement)
Remarks:
The Dow chemical company Midland, Michigan 48674
Type of assay:
other: DNA adducts and Apurinic/apyrimidinc (AP) sites in DNA

Test material

Constituent 1
Chemical structure
Reference substance name:
Methyloxirane
EC Number:
200-879-2
EC Name:
Methyloxirane
Cas Number:
75-56-9
Molecular formula:
C3H6O
IUPAC Name:
1,2-Epoxypropane
Details on test material:
- Name of test material (as cited in study report): propylene oxide (PO), supplied by Sigma-Aldrich, St. Louis, Missouri
- Physical state: Clear Liquid
- Analytical purity: 99.9% by Liquid chromatography

Test animals

Species:
rat
Strain:
Fischer 344
Sex:
male
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Charles River Lab. (Raleigh, North Carolina)
- Age at study initiation: 9-10 weeks
- Assigned to test groups randomly: yes
- Housing: one per cage
- Diet : e.g. ad libitum
- Water: e.g. ad libitum
- Acclimation period: at least one week


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21-25
- Humidity (%): 40-68
- Air changes (per hr): 12-15 times
- Photoperiod (hrs dark / hrs light): 12/12


Administration / exposure

Route of administration:
inhalation: vapour
Vehicle:
none
Details on exposure:
Whole body exposure chambers (Rochester-style).
The various concentrations of PO were generated using the glass J-tube method (Miller et al., 1980). Liquid test material was pumped into the glass J-tube assemblies (1 per exposure chamber) and vaporized by the flow of nitrogen gas passing through the bead bed of the glass J-tube. The nitrogen was heated as needed with a flameless heat torch (FHT-4, Master Appliance Corporation, Racine, Wisconsin) to the minimum extent necessary to vaporize the test material. All chambers, including the 0 ppm (control) chamber received the same amount (20 liters per minute) of supplemental nitrogen
(carrier gas). The minimum amount of nitrogen necessary to reach the desired chamber concentrations was used. The generation system was electrically grounded and the Jtubes were changed as needed. The vaporized test material and carrier gas were mixed and diluted with supply air to achieve the desired test chamber concentration.

The animals were exposed to filtered air or PO vapors in 4 cubic meter stainless steel and glass Rochester-type whole-body exposure chambers [1.5 meters (m) x 1.5 m wide x 1.3 m deep with a pyramidal top and bottom]. Chamber airflow was maintained at a flow rate sufficient to provide the normal concentration of oxygen to the animals and 9-11 calculated air changes per hour. The chambers were operated at a slightly negative pressure, relative to the surrounding area. Animals were singly housed to minimize crowding during the exposure.

The chamber concentrations of PO, measured approximately in the center of the breathing zone of the animals, were determined at least once per hour with a Miran 1A infrared (IR) spectrophotometer (Foxboro/Wilks, South Norwalk, Connecticut) and reported by a strip chart recorder. The IR spectrophotometer was calibrated and a standard curve was compiled prior to and at the end of the study, using air standards prepared by vaporizing measured volumes of PO into Tedlar® sample bags (Series 233, SKC, Eighty Four, Pennsylvania) along with the metered volumes of dry, compressed air.
Duration of treatment / exposure:
6hr/day
Frequency of treatment:
5 days/ week for 4 consecutive weeks
Post exposure period:
none
Doses / concentrations
Remarks:
Doses / Concentrations:
0, 50, 100, 200 and 400 ppm
Basis:
nominal conc.
close to analytical concentrations
No. of animals per sex per dose:
16/exposure level
Control animals:
yes, concurrent no treatment

Examinations

Tissues and cell types examined:
nose, respiratory epithelium, liver, spleen and lung.
Details of tissue and slide preparation:
DNA was isolated from liver, spleen, and lung by the Gentra Puregene System.
The DNA from nasal respiratory epithelium was isolated by phenol/chloroform extraction
Evaluation criteria:
Quantitation was based on comparisons to internal standard DNA containing known amounts of AP sites, calibrated with DNA from Kubo et al. (6).

Calibration curves were generated by using the standard solutions prepared by spiking varying amounts of 7-HPG into the solutions that contained a constant amount of internal standard. Solvent control was applied per sample set in order to avoid contamination of regents.
Statistics:
AP site measurement
Based on Dunnett’s multiple comparisons analysis.

Results and discussion

Test resultsopen allclose all
Sex:
male
Genotoxicity:
other: A dose-related increase for 7-HPG (a biomarker of exposure) was seen from 50 ppm onward, the highest levels in the nasal repiratory epithelium.
Toxicity:
yes
Remarks:
reduced bw gain at the highest dose only; 400 ppm
Vehicle controls validity:
not applicable
Negative controls validity:
valid
Positive controls validity:
not applicable
Sex:
male
Genotoxicity:
other: no significant differences in the number of AP sites in DNA from nasal respiratory epithelium
Toxicity:
yes
Remarks:
reduced bw gain at the highest dose only; 400 ppm
Vehicle controls validity:
not applicable
Negative controls validity:
valid
Positive controls validity:
not applicable
Additional information on results:
For rats, the N7-HPG adducts at the 50 ppm PO exposure concentration and the linear dose-response relationship was noted.

AP site determination found that there were no significant differences in the number of AP sites in DNA from nasal respiratory epithelium, across the dose groups (Table 2 p>0.05).

Any other information on results incl. tables

Clearly the target tissue, nasal repiratory epithelium, receives the highest dose of N7-HPG, as expected for the site-of-contact tissue.

Exposure to PO did not cause an increase in AP sites in respiratory nasal mucosa, despite the high number of 7-HPG adducts. HPG is not considered to be a promutagenic DNA adduct. However, it is chemically unstable, resulting in chemical depurination and the formation of an AP site. The fact that AP sites were not increased with increasing exposure demonstrates that AP sites resulting from such chemical depurination do not lead to unbalanced DNA repair.

Applicant's summary and conclusion