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Toxicological information

Genetic toxicity: in vivo

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Administrative data

Endpoint:
in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus
Type of information:
experimental study
Adequacy of study:
key study
Study period:
February 19, 1991
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
A standard NTP (National Toxicology Program) protocol.

Data source

Referenceopen allclose all

Reference Type:
publication
Title:
Unnamed
Year:
1991
Reference Type:
publication
Title:
Unnamed
Year:
1999

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)
Deviations:
yes
Remarks:
(no positive control was performed)
GLP compliance:
not specified
Type of assay:
other: micronucleus assay

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): Methyl Ethyl Ketoxime

Test animals

Species:
mouse
Strain:
B6C3F1
Sex:
male/female

Administration / exposure

Route of administration:
oral: drinking water
Vehicle:
- Vehicle(s)/solvent(s) used: water
Duration of treatment / exposure:
13 weeks.
Frequency of treatment:
Daily.
Doses / concentrationsopen allclose all
Dose / conc.:
0 ppm
Remarks:
nominal
Dose / conc.:
625 ppm
Remarks:
nominal
Dose / conc.:
1 250 ppm
Remarks:
nominal
Dose / conc.:
2 500 ppm
Remarks:
nominal
Dose / conc.:
5 000 ppm
Remarks:
nominal
Dose / conc.:
10 000 ppm
Remarks:
nominal
Dose / conc.:
0 mg/kg bw/day (actual dose received)
Remarks:
males and females
Dose / conc.:
110 mg/kg bw/day (actual dose received)
Remarks:
males
Dose / conc.:
200 mg/kg bw/day (actual dose received)
Remarks:
males
Dose / conc.:
515 mg/kg bw/day (actual dose received)
Remarks:
males
Dose / conc.:
755 mg/kg bw/day (actual dose received)
Remarks:
males
Dose / conc.:
1 330 mg/kg bw/day (actual dose received)
Remarks:
males
Dose / conc.:
145 mg/kg bw/day (actual dose received)
Remarks:
females
Dose / conc.:
340 mg/kg bw/day (actual dose received)
Remarks:
females
Dose / conc.:
630 mg/kg bw/day (actual dose received)
Remarks:
females
Dose / conc.:
1 010 mg/kg bw/day (actual dose received)
Remarks:
females
Dose / conc.:
3 170 mg/kg bw/day (actual dose received)
Remarks:
females
No. of animals per sex per dose:
5 animals per sex per dose.
Control animals:
yes, concurrent vehicle
Positive control(s):
none;

Examinations

Tissues and cell types examined:
Mouse peripheral blood erythrocytes
Details of tissue and slide preparation:
At the end of the 13-week drinking water study, blood samples were obtained from male and female mice. Smears were immediately prepared and fixed in absolute methanol. The methanol-fixed slides were stained with a chromatin-specific fluorescent dye (acridine orange) and coded. Slides were scanned to determine the frequency of micronuclei in 2,000 normochromatic eythrocytes (NCEs) in each of 5 animals per exposure group
Evaluation criteria:
An individual trial is considered positive if the trend test P value is less than or equal to 0.025 or if the P value for any single exposure group is less than or equal to 0.025 divided by the number of exposure groups. A final call of positive for micronucleus induction is preferably based on reproducibly positive trials. Results of the 13-week studies were accepted without repeat tests, because additional test data could not be obtained. Ultimately, the final call is determined by the scientific staff after considering the results of statistical analyses, the reproducibility of any effects observed, and the magnitudes of those effects.
Statistics:
The frequency of micronucleated cells among NCEs was analyzed by a statistical software package that tested for increasing trend over exposure groups with a one-tailed Cochran-Armitage trend test, followed by pairwise comparisons between each exposure group and the control group In the presence of excess binomial variation, as detected by a binomial dispersion test, the binomial variance of the Cochran-Armitage test was adjusted upward in proportion to the excess variation

Results and discussion

Test results
Key result
Sex:
male/female
Genotoxicity:
negative
Remarks:
(up to 10000 ppm)
Toxicity:
not specified
Vehicle controls validity:
valid
Negative controls validity:
not examined
Positive controls validity:
not examined

Any other information on results incl. tables

Frequency of Micronuclei in Peripheral Blood Erythrocytes of Mice Following Treatment with Methyl Ethyl Ketoxime in Drinking Water for 13 Weeks:

A79779 -1

Start Date

Sample Collection Time

Sex

Cell

Methodology Used

Dosing Regimen

Route

Trend Test P-Value

02/19/1991

0 Hours

Female

NCE

Slide Scoring

WATER x 93, 93 Days

Dosed-Water

0.998

Dose (ppm)

Number of Animals Scored

Mean MN-NCE/1000 NCE ± SEM

Pairwise P

Vehicle Control

Water

 0         

5

2.00 ± 0.35

 

Test Chemical

Methyl ethyl ketoxime

625         

5

2.10 ± 0.58

0.4379

1250         

5

3.00 ± 0.42

0.0784

2500         

5

2.90 ± 0.89

0.0990

5000         

5

1.90 ± 0.37

0.5637

10000         

5

0.80 ± 0.34

0.9884

A79779 -2

Start Date

Sample Collection Time

Sex

Cell

Methodology Used

Dosing Regimen

Route

Trend Test P-Value

02/19/1991

0 Hours

Male

NCE

Slide Scoring

WATER x 92, 92 Days

Dosed-Water

1.000

Dose (ppm)

Number of Animals Scored

Mean MN-NCE/1000 NCE ± SEM

Pairwise P

Vehicle Control

Water

0

5

4.80 ± 0.68

Test Chemical

Methyl ethyl ketoxime

625

5

4.50 ± 0.76

0.6224

1250

5

4.00 ± 0.16

0.8036

2500

5

3.70 ± 0.34

0.8841

5000

5

1.40 ± 0.37

10.000

10000

5

1.60 ± 0.19

10.000

NCE=normochromatic erythrocyte

Applicant's summary and conclusion

Conclusions:
No increase in the frequency of micronucleated normochromatic erythrocytes was observed in the peripheral blood of male or female mice administered methyl ethyl ketoxime via drinking water at concentrations from 625 to 10000 ppm for 13 weeks.
Executive summary:

A Mammalian Erythrocyte Micronucleus Test was performed on methyl ethyl ketoxima according to NTP's standard protocol (test method similar to OECD Guideline 474). 5 mice per sex and per dose were exposed to test item at 0 (control, water), 625, 1250, 2500, 5000 and 10000 ppm (0, 110, 200, 515, 755, 1330 mg/kg bw/day males and 0, 145, 340, 630, 1010, 3170 mg/kg bw/day females) for 13 weeks by drinking water. At the end of the exposure, blood samples were obtained from male and female mice, smears were prepared, fixed in absolute methanol and stained with a chromatin-specific fluorescent dye (acridine orange). Slides were scanned to determine the frequency of micronuclei in 2000 normochromatic eythrocytes (NCEs) in each of 5 animals per exposure group. No increase in the frequency of micronucleated normochromatic erythrocytes was observed in the peripheral blood of male or female mice administered methyl ethyl ketoxime via drinking water at concentrations from 625 to 10000 ppm (1130 mg/kg bw/day males and 3170 mg/kg bw/day females) for 13 weeks. The percentage of normochromatic erythrocytes among the population of circulating erythrocytes was markedly decreased at the highest dose tested in male and female mice.