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Administrative data

Endpoint:
in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus
Remarks:
in B6C3F mice
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
positive control is lacking as well as any information related to the effect on P/N

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1995

Materials and methods

Test guideline
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)
Version / remarks:
Detailed discussion of this assay is given by Mc Gregor et al. (1990). Instead of one or two exposures to the test agent, followed by sampling at two or three postexposure times to obtain a sample near the time of transient peak of micronucleated polychromatic erythrocytes, a repeated dose schedule with a single sample taken at steady state (reached within 2 to 3 days in RNA-positive reythrocytes to 5-6 weeks in RNA-negative erythroytes) is preferred. It was demonstrated that frequencies of micronucleated RNA-positive (PCEs) and RNA-negative erythrocytes in blood and bone marrow come to steady state during ‚continuous’ exposure via diet, drinking water or during repeated daily exposures to test agents by i.p. injection, gavage or inhalation.

Deviations from the EC Method: tested doses are not related to maximum tolerated dose or that producing some cytotoxicity. However, highest exposure dose is near the recommended limit dose of 1000 mg/kg b.w. per day. Blood samples are used instead of bone marrow samples. However, according to the investigations results of Mc Gregor et al. (1990) on several substances, the used procedure should allow adequate testing as well.

GLP compliance:
yes
Remarks:
in compliance with US Food and Drug Administration Good Laboratory Practices Regulations (21 CFR, Part 58).
Type of assay:
mammalian erythrocyte micronucleus test

Test material

Constituent 1
Chemical structure
Reference substance name:
Cadmium oxide
EC Number:
215-146-2
EC Name:
Cadmium oxide
Cas Number:
1306-19-0
Molecular formula:
CdO
IUPAC Name:
oxocadmium
Details on test material:
-Name of the test material: CdO
SOURCE: Lot 110383 from Johnson Matthey Aesar Group (Seabrook, NH).
PURITY: Purity : 99.4 % ( 0.6 % )
Impurities : 400 ppm chlorine, all other impurities detected totaled less than 263 ppm

Test animals

Species:
mouse
Strain:
B6C3F1
Sex:
male/female
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Simonsen Laboratories (Gilroy, CA)
- Age at study initiation: : 6 wk old
- Weight at study initiation: no information
- Housing: in individual cages within the exposure chambers
- Diet : NIH-07 Open Formula Diet (Zeigler Brothers, Inc., Gardners, PA) in pellet form
- Water : City water (Richland, WA), ad libitum
- Acclimation period: 12-15 d


ENVIRONMENTAL CONDITIONS
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:
inhalation: aerosol
Vehicle:
none
Details on exposure:
TYPE OF INHALATION EXPOSURE: whole body

Duration of treatment / exposure:
for 12 exposure days or 13 weeks
Frequency of treatment:
exposure for 6 hours plus T90 per day, 5 days per week, except weekends and holidays, for 12 exposure days or 13 weeks
Doses / concentrationsopen allclose all
Dose / conc.:
0 mg/m³ air
Remarks:
For the 2 and 13 weeks studies
Dose / conc.:
0.025 mg/m³ air
Remarks:
For the 13 weeks study
Dose / conc.:
0.05 mg/m³ air
Remarks:
For the 13 weeks study
Dose / conc.:
0.1 mg/m³ air
Remarks:
For the 13 weeks study
Dose / conc.:
0.25 mg/m³ air
Remarks:
For the 13 weeks study
Dose / conc.:
1 mg/m³ air
Remarks:
For the 13 weeks study
Dose / conc.:
0.1 mg/m³ air
Remarks:
For the 2 weeks study
Dose / conc.:
1 mg/m³ air
Remarks:
For the 2 weeks study
Dose / conc.:
3 mg/m³ air
Remarks:
For the 2 weeks study
Dose / conc.:
10 mg/m³ air
Remarks:
For the 2 weeks study
Dose / conc.:
0.3 mg/m³ air
Remarks:
For the 2 weeks study
No. of animals per sex per dose:
Groups of 5 mice of each sex for the 2 weeks treatment
Groups of 10 mice of each sex for the 13 weeks treatment
Control animals:
yes, concurrent no treatment
Positive control(s):
none

Examinations

Tissues and cell types examined:
blood
Details of tissue and slide preparation:
SAMPLING TIMES and NUMBER of SAMPLES: once, at the end of the 13 week study

TISSUE PREPARATION: Blood samples were obtained from B6C3F1 mice at the end of the 13-week study. Smears were immediately prepared, fixed in absolute methanol, stained with acridine orange (a chromatin-specific fluorescent dye), and coded. The slides were scanned to determine the frequency of micronuclei and criteria of Schmid (1976) were used to define micronuclei.

CELL STAINING: Acridine Orange

SCORING: 2,000 normochromatic erythrocytes (NCEs) in each of five male and five female mice per exposure concentration
Evaluation criteria:
the criteria of Schmid (1976) were used to define micronuclei
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 normochromatic erythrocytes was analyzed by a statistical software package that tested 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 (Margolin et al., 1990). 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 varaition. In the micronucleus test, an individual trial was considered positive if the trend test P-value was less than or equal to 0.025 or the P-value for any single exposure group was less than or equal to 0.025 or the P-value for any single exposure group was less than or equal to 0.025 divided by the number of exposure groups. A final call of positive for micronucleaus induction is prefereably based on reproducible positive trials. Ultimately, the final call was determmined by the scientific staff after considering the results of statistical analyses, reproducibility of any effects observed, and the magnitudes of those effects.

Results and discussion

Test results
Sex:
male/female
Genotoxicity:
negative
Toxicity:
not specified
Vehicle controls validity:
not specified
Negative controls validity:
valid
Positive controls validity:
not specified

Any other information on results incl. tables

The frequency of micronuclei in peripheral blood erythrocytes of mice following treatment with CdO by inhalation for 13 weeks, are given below.

The results are tabulated as the mean of the pooled results from all animals within a treatment group, plus or minus the standard error of the mean.

 

Concentration (mgCdO/m3)

Micronucleated NCEs/1000 NCEs (mean ± standard error)

Male

Air

 

0.025

0.050

0.100

0.250

1.000

3.5 ±0.4

 

2.8 ± 0.3

3.7 ± 0.6

3.1 ± 0.9

3.1 ± 0.4

4.3 ± 0.6

Female

Air

 

0.025

0.050

0.100

0.250

1.000

2.1 ± 0.2

 

2.1 ± 0.4

2.2 ± 0.3

2.1 ± 0.3

2.7 ± 0.4

2.7 ± 0.3

Applicant's summary and conclusion

Conclusions:
Inhalation exposure to cadmium oxide (0.025-1 mg/m3) for 13 weeks did not result in increased frequencies in micronucleated erythrocytes in peripheral blood of male or female B6C3F1 mice.
Remark: There is however a concern that the bone marrow was not adequately exposed given the unknown effect on the P/N ratio and lack of information regards other indications of systemic toxicity. The (limited) toxicokinetic information following inhalation exposure indicates absorption of CdO into the blood, presumably leading to exposure of the bone marrow. Thus it can be reasonably assumed that the bone marrow was exposed to CdO and the negative result is relatively reliable.
Executive summary:

Dunnick (1995) treated male and female B6C3F1 mice with cadmium oxide (0.025, 0.05, 0.1, 0.25, 1 mg/m³) for 13 week to determine the frequency of micronucleated erythrocytes in peripheral blood of these animals..

At the end of the 13-week study, smears were prepared and slides were scanned to determine the frequency of micronuclei in 2,000 normochromatic erythrocytes in each of five male and five female mice per exposure concentration

Inhalation exposure to cadmium oxide (0.025-1 mg/m3) for 13 weeks did not result in increased frequencies in micronucleated erythrocytes in peripheral blood of male or female B6C3F1 mice.

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