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Administrative data

Endpoint:
in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus
Type of information:
experimental study
Adequacy of study:
weight of evidence
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:
Unnamed
Year:
2007

Materials and methods

Test guideline
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)
GLP compliance:
yes
Type of assay:
mammalian erythrocyte micronucleus test

Test material

Constituent 1
Chemical structure
Reference substance name:
Sodium bromate
EC Number:
232-160-4
EC Name:
Sodium bromate
Cas Number:
7789-38-0
Molecular formula:
BrHO3.Na
IUPAC Name:
sodium bromate

Test animals

Species:
mouse
Strain:
other: genitically modified: Tg.AC hemizygous, p53 haploinsufficient
Sex:
male/female
Details on test animals or test system and environmental conditions:
TEST ANIMALS:
Male and female FVB/N-TgN(v-Ha-ras) (Tg.AC) hemizygous (Tg.AC hemizygous) and B6.129-Trp53tmlBrd (N5) haploinsufficient (p53 haploinsufficient) mice were obtained from Taconic Laboratory Animals and Services (Germantown, NY) for use in the 26-, 27-, 39-, and 43-week studies. Tg.AC hemizygous mice were quarantined for 16 days before the beginning of the dermal studies and for 13 days before the beginning of the drinking water studies; p53 haploinsufficient mice were quarantined for 14 days before the beginning of the drinking water studies. Five male and five female mice per strain were randomly selected for parasite evaluation and gross observation of disease. Tg.AC hemizygous mice were 6 weeks old and p53 haploinsufficient mice were 6 to 8 weeks old at the beginning of the studies. Blood samples were collected from five male and five female sentinel mice per strain and study group at 4 and 26 weeks, from five male and five female mice from the highest surviving groups at 39 or 43 weeks, and from moribund mice in the 43-week drinking water studies.

ANIMAL MAINTENANCE:
Mice were housed individually and feed and water were available ad libitum. Water consumption was measured weekly by cage during the drinking water studies. Cages and racks were rotated every two weeks.

Administration / exposure

Route of administration:
other: dermal and oral via drinking water
Vehicle:
- Vehicle(s)/solvent(s) used:
Dermal application :40% USP-grade 95% ethanol/60% water
Drinking water: tap water
Duration of treatment / exposure:
26 weeks (dermal route); 27 weeks (drinking water)
Frequency of treatment:
daily
Doses / concentrationsopen allclose all
Dose / conc.:
0 mg/kg bw/day
Remarks:
dermal route
Dose / conc.:
64 mg/kg bw/day
Remarks:
dermal route
Dose / conc.:
128 mg/kg bw/day
Remarks:
dermal route
Dose / conc.:
256 mg/kg bw/day
Remarks:
dermal route
Dose / conc.:
0 mg/L drinking water
Remarks:
oral route
Dose / conc.:
80 mg/L drinking water
Remarks:
oral route
Dose / conc.:
400 mg/L drinking water
Remarks:
oral route
Dose / conc.:
800 mg/L drinking water
Remarks:
oral route
No. of animals per sex per dose:
15
Control animals:
yes, concurrent vehicle
Positive control(s):
12-O-Tetradecanoylphorbol-13-acetate (TPA)

Examinations

Tissues and cell types examined:
Peripheral blood erythrocytes
Details of tissue and slide preparation:
At the end of the 26- and 27-week studies, peripheral 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 acridine orange and coded. Slides were scanned to determine the frequency of micronuclei in 2,000 normochromatic erythrocytes (NCEs) in each of up to 15 animals per group. In addition, the percentage of polychromatic erythrocytes (PCEs) in a population of 1,000 erythrocytes was determined as a measure of bone marrow toxicity.
Statistics:
The results were tabulated as the mean of the pooled results from all animals within a treatment group plus or minus the standard error of the mean. The frequency of micronucleated cells among NCEs was analyzed by a statistical software package that tested for increasing trend over dose or exposure groups with a one-tailed Cochran-Armitage trend test, followed by pairwise comparisons between each dosed or exposed group and the control group (ILS, 1990).

Results and discussion

Test results
Key result
Sex:
male/female
Genotoxicity:
positive
Remarks:
Significant increases in micronucleated normochromatic erythrocytes (MN-NCE) were seen in Tg.AC hemizygous and p53 deficient mice.
Toxicity:
yes
Remarks:
Significant increases in the percentage of polychromatic erythrocytes among total erythrocytes were observed in Tg.AC hemizygous mice exposed via drinking water and dermally with NaBrO3.
Vehicle controls validity:
valid
Remarks:
only dermal route
Negative controls validity:
valid
Remarks:
only oral route
Positive controls validity:
valid
Additional information on results:
The genotoxic effects of sodium bromate was evaluated in a peripheral blood micronucleus assays on genetically modified (Tg.AC hemizygous and p53 haploinsufficient) mice (n= 10-15 per sex/dose).
Tg.AC hemizygous mice were treated dermally and orally (via drinking water); p53 haploinsufficient mice were exposed only through drinking water.
Sodium bromate exposure resulted in significantly increased frequencies of micronucleated erythrocytes in male and female Tg.AC hemizygous and p53 haploinsufficient mice administered the chemical in drinking water for 27 weeks or by dermal application for 26 weeks (Tg.AC hemizygous only). In all three micronucleus tests, a clear dose response was observed in male and female mice. Furthermore, significant increases in the percentage of polychromatic erythrocytes among total erythrocytes were observed in male and female Tg.AC hemizygous mice exposed via drinking water and in male Tg.AC hemizygous mice dosed dermally with sodium bromate. While, the percentage of polychromatic erythrocytes was not significantly altered in male or female p53 deficient mice.

Applicant's summary and conclusion

Conclusions:
Under the experimental conditions reported, sodium bromate induced a significant increase in the frequency of micronucleated erythrocytes in all Tg.AC hemizygotes and p53 haploinsufficient mice. Therefore, sodium bromate is considered to be mutagenic in the mammalian erythrocyte micronucleus test. However, in the carcinogenicity study reported in this publication, sodium bromate (> 99 % purity), did not show evidence of carcinogenic activity.
Executive summary:

Three in vivo micronucleus tests in genetically modified mice were conducted by the National Toxicology Program (NTP) to assess the mutagenicity of sodium bromate (> 99 % purity) in peripheral blood cells derived from the bone marrow of the tested animals.

The genetically modified Tg.AC hemizygous mice (n= 15 per sex/dose) were treated by dermal application for 26 weeks or in drinking water for 27 weeks with sodium bromate at doses of 0, 64, 128 or 256 mg/kg bw (dermal route) or 0, 80, 400 or 800 mg/L (drinking water). p53 haploinsufficient mice (n= 15 per sex/dose) were were exposed to drinking water containing 0, 80, 400 or 800 mg/L sodium bromate for 27 weeks.

Sodium bromate exposure resulted in significantly increased frequencies of micronucleated erythrocytes in male and female Tg.AC hemizygous and p53 haploinsufficient mice. In all three in vivo micronucleus tests, a clear dose response was observed in male and female mice. Furthermore, significant increases in the percentage of polychromatic erythrocytes among total erythrocytes were observed in male and female Tg.AC hemizygous mice exposed via drinking water and in male Tg.AC hemizygous mice dosed dermally with sodium bromate. While, the percentage of polychromatic erythrocytes was not significantly altered in male or female p53 deficient mice.

Under the experimental conditions reported, sodium bromate induced a significant increase in the frequency of micronucleated erythrocytes in male and female mice Tg.AC hemizygotes and p53 haploinsufficient mice. Therefore, sodium bromate is considered to be mutagenic in the mammalian erythrocyte micronucleus test. However, in the carcinogenicity study reported in this publication, sodium bromate (> 99 % purity), did not show evidence of any carcinogenic activity. Thus, in an overall assessment of the entire data set, it is not possible to conclude on the classification for genotoxicity of sodium bromate (inconclusive).