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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: Comparable to guideline study with acceptable restrictions.

Data source

Reference
Reference Type:
publication
Title:
Assessment of unscheduled and replicative DNA synthesis in hepatocytes treated in vivo and in vitro with unleaded gasoline or 2,2,4 - trimethylpentane
Author:
Loury, D.J. et al.
Year:
1986
Bibliographic source:
Toxicology and Applied Pharmacology 85(1): 11-23

Materials and methods

Test guideline
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 486 (Unscheduled DNA Synthesis (UDS) Test with Mammalian Liver Cells in vivo)
Deviations:
yes
Remarks:
- limited documentation
GLP compliance:
not specified
Type of assay:
unscheduled DNA synthesis

Test material

Constituent 1
Chemical structure
Reference substance name:
2,2,4-trimethylpentane
EC Number:
208-759-1
EC Name:
2,2,4-trimethylpentane
Cas Number:
540-84-1
Molecular formula:
C8H18
IUPAC Name:
2,2,4-trimethylpentane
Details on test material:
- Name of test material (as cited in study report): 2,2,4-trimethylpentane
- Analytical purity: >99%

Test animals

Species:
rat
Strain:
Fischer 344
Sex:
male
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories (Kingston, N.Y.)
- Weight at study initiation: 200-300 g
- Assigned to test groups randomly: yes
- Fasting period before study: no
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum


ENVIRONMENTAL CONDITIONS
- Temperature (°C): controlled
- Humidity (%): controlled
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:
oral: gavage
Vehicle:
- Vehicle(s)/solvent(s) used: none
Duration of treatment / exposure:
one single dose
Frequency of treatment:
sinlge treatment
Post exposure period:
2, 12, 24 and 48 hours after dosing
Doses / concentrations
Remarks:
Doses / Concentrations:
500 mg/kg
Basis:
nominal conc.
No. of animals per sex per dose:
3 males/ time period
Control animals:
yes
Positive control(s):
dimethylnitrosamine (DMN), dissolved in water
- Route of administration: orally
- Doses / concentrations: 10 mg/kg

Examinations

Tissues and cell types examined:
hepatocytes
Details of tissue and slide preparation:
see "any other information on materials and methods"
Statistics:
One-way analysis of variance was performed on UDS and S-phase data with multiple treatment groups. S-phase data were adjusted by square root transformation. Treatment means were compared to control means by Dunnett's multiple comparison test. Level of significance was <0.05.

Results and discussion

Test results
Key result
Sex:
male
Genotoxicity:
negative
Remarks:
TMP did not induce unscheduled DNA synthesis in hepatocyte cultures from rats treated in vivo.
Toxicity:
no effects
Remarks:
Mean cell viabilities in preparations of hepatocytes were: 84 % at 2-12 hours after administration of 500 mg/kg TMP.
Vehicle controls validity:
not applicable
Negative controls validity:
valid
Positive controls validity:
valid
Additional information on results:
see "Remarks on results"

Any other information on results incl. tables

Mean cell viabilities in preparations of hepatocytes were: 85 % at 24 hours after administration of water (negative control) and 84 % at 2-12 hours after administration of 500 mg/kg TMP.

No increase in UDS expressed as increase in NG or number of cells in repair was observed in hepatocytes isolated from male rats at 2, 12, 24, or 48 hours post-dose. A strong response was elicited by the DMN positive control, as expected.

Autoradiographic preparations of hepatocytes isolated from rats 24 hr after treatment with TMP revealed a significant increase in the number of cells in S phase (2.1% vs 0.35% in controls); this value dropped back to 0.55% at 48 hours. TMP also significantly increased RDS in mice at 24 hours; no 48 hour values were presented. However low serum alanine transaminase activity were observed at 24 and 48 hours after a single treatment with 500 mg/kg TMP indicating that TMP induced little if any hepatocellular necrosis which could trigger regenerative cell proliferation.

Following 11 consecutive daily treatments with 100 mg/kg/day TMP, a significant increase (p<0.05) in rat hepatic concentration of DNA (mg/g liver) was seen but the total hepatic DNA content per rat was comparable to controls. Liver weight relative to body weight was also comparable to controls. The demonstrated increase in RDS suggests that TMP may stimulate additive rather than regenerative cell proliferation but not of sufficient magnitude to significantly increase the total DNA content of the liver.

TMP was administered at a single 500 mg/kg concentration to evaluate UDS and RDS in conjunction with a multidose study for unleaded gasoline. When RDS was observed, a liver DNA content determination was performed in rats with treatment over 11 days to determine the type of proliferative response.

Applicant's summary and conclusion

Conclusions:
Interpretation of results: negative

Based on this study design 2, 2, 4- trimethylpentane does not induce unscheduled DNA synthesis in vivo by unchanged application via gavage.
Executive summary:

Based on this study design 2, 2, 4- trimethylpentane does not induce unscheduled DNA synthesis in vivo by unchanged application via gavage.