lambda4-cerium(4+) zirconium(4+) tetraoxidandiide

Genetic toxicity: in vivo

Administrative data

Endpoint:

in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus

Remarks:

Type of genotoxicity: chromosome aberration

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

Not specified

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: GLP OECD TG 474-compliant study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1993

Report date:

1993

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)

Deviations:

no

GLP compliance:

yes

Type of assay:

micronucleus assay

Test material

Test material information

Constituent 1

Reference substance name:

Cerium dioxide

EC Number:

215-150-4

EC Name:

Cerium dioxide

Cas Number:

1306-38-3

Molecular formula:

CeO2

IUPAC Name:

cerium dioxide

Test animals

Species:

mouse

Strain:

Swiss

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Iffa Credo, 69210 L'Arbresle France
- Age at study initiation: 5 weeks old
- Weight on day of dosing: 30 - 34 g (males) / 23 - 29 g (females)
- Housing: by groups of 5 of the same sex in polycarbonate cages with stainless steel lid
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 5 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21 +/- 2
- Humidity (%): 50 +/- 20
- Air changes (per hr): filtered and non-recycled fresh air
- Photoperiod (hrs dark / hrs light): 12 / 12


IN-LIFE DATES: Not specified

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

- Vehicle used: 1% carboxymethylcellulose solution
- Justification for choice of solvent/vehicle: appropriate to oral suspensions
- Concentration of test material in vehicle: 100 mg/mL
- Amount of vehicle: 20 mL/kg bw
- Lot/batch no. (if required): Sigma 58C-0156

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: Immediately before use, by putting the test substance in suspension

Duration of treatment / exposure:

Single administration

Frequency of treatment:

Single administration

Post exposure period:

24 hours (test substance, negative control, positive control) and 48 hours (test substance, negative control)

Doses / concentrations

Remarks:

Doses / Concentrations:
2000 mg/kg bw
Basis:
other: nominal

No. of animals per sex per dose:

5

Control animals:

yes, concurrent vehicle

Positive control(s):

- Nature: cyclophosphamide
- Justification for choice of positive control: not provided
- Route of administration: Oral (gavage)
- Dose: 50 mg/kg bw

Examinations

Tissues and cell types examined:

Femur bone marrow erythrocytes

Details of tissue and slide preparation:

- Femur bone marrow eluted out with fetal calf serum and cell suspension centrifuged
- Supernatant removed and cells in sediment resuspended by shaking
- One drop of cell suspension spread on a coded slide
- Slides air-dried and stained by May-Grünwald Giemsa
- Two slides prepared per animal but only one used for scoring

Evaluation criteria:

- 2000 polychromatic erythrocytes scored for micronuclei per animal
- Ratio between polychromatic and normochromatic erythrocytes (PE/NE ratio) calculated by scoring 1000 erythrocytes per animal
- Substance considered clastogenic if statistical increase in mean number of micronucleated polychromatic erythrocytes for at least one of the sampling time compared to negative controls and this increase doubles the number of micronucleated polychromatic erythrocytes in the test facility's historical data (1.4 +/- 0.6 per thousand)

Statistics:

- Intergroup comparison of mean numbers of micronucleated polychromatic erythrocytes using Kastenbaum and Bowman's test (5% significance level)
- Intergroup comparison of PE/NE ratios using Student's t test

Results and discussion

Test results

Sex:

male/female

Genotoxicity:

negative

Remarks:

at 2000 mg/kg bw (nominal)

Toxicity:

no effects

Vehicle controls validity:

valid

Negative controls validity:

valid

Positive controls validity:

valid

Additional information on results:

RESULTS OF RANGE-FINDING STUDY
No clinical signs in 3 males and 3 females given a single oral dose of 2000 mg/kg bw.


RESULTS OF DEFINITIVE STUDY
See summary table below.

Any other information on results incl. tables

Mean number of micronucleated polychromatic erythrocytes and PE/NE ratio:

Time of sacrifice (hours post dosing)	Group	Number of polychromatic erytrocytes / 1000 polychromatic erythrocytes(mean +/- standard deviation)	PE/NE ratio(mean +/- standard deviation)
24	Vehicle	1.9 +/- 1.0	1.0 +/- 0.2
	Test substance	2.4 +/- 1.3	1.1 +/- 0.2
	Cyclophosphamide	56.6 +/- 10.4 ***	0.8 +/- 0.1 *
48	Vehicle	1.7 +/- 1.6	1.0 +/- 0.2
	Test substance	2.9 +/- 1.3	1.1 +/- 0.3

*** p < 0.001       * p < 0.05

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): negative at 2000 mg/kg bw
No evidence of clastogenicity in this mouse bone marrow micronucleus assay at the limit dose of 2000 mg/kg

Executive summary:

The clastogenic potential of Cerium Oxide was tested in an oral mouse bone marrow micronucleus assay. Swiss OF1 5-week old mice (5/sex per group) were given a single oral administration of 2000 mg/kg Cerium Oxide by gavage. Two test substance-treated groups, two vehicle (1% carboxymethylcellulose)-treated control groups and one positive control (cyclophosphamide) group were used. Euthanasia was performed 24 and 48 hours after dosing for substance-treated and negative control groups. Positive controls were euthanasied 24 hours after dosing. For each animal, 2000 polychromatic erythrocytes from femur bone marrow were microscopically examined for micronuclei. The polychromatic to normochromatic erythrocytes (PE/NE) ratio was determined from 1000 erythrocytes per mouse.

At both sampling times, there were no statistical differences from negative control values in the number of micronucleated polychromatic erythrocytes and the PE/NE ratio from substance-treated animals.

An appropriate reference mutagen used as positive control showed a significant increase in micronucleated polychromatic erythrocytes together with a significant decrease in the PE/NE ratio, indicating that the test was sensitive and valid.

Therefore, Cerium Oxide did not induce cytogenetic damage in this micronucleus test in mice treated by the oral route at the limit dose of 2000 mg/kg.

This study is classified as acceptable. It satisfies the OECD 474 guideline requirements on Mammalian Erythrocyte Micronucleus Test.