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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
Remarks:
Type of genotoxicity: chromosome aberration
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: study according to OECD guideline and GLP

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2010
Report Date:
2010

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to
Guideline:
OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)
Qualifier:
according to
Guideline:
EU Method B.12 (Mutagenicity - In Vivo Mammalian Erythrocyte Micronucleus Test)
Qualifier:
according to
Guideline:
EPA OPPTS 870.5395 (In Vivo Mammalian Cytogenetics Tests: Erythrocyte Micronucleus Assay)
GLP compliance:
yes (incl. certificate)
Type of assay:
micronucleus assay

Test material

Reference
Name:
Unnamed
Type:
Constituent

Test animals

Species:
mouse
Strain:
NMRI
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River
- Age at study initiation: 5-8 weeks
- Weight at study initiation: 28.15 g
- Assigned to test groups randomly: yes, according to a randomization plan prepared with an appropriate computer program
- Housing: single in Makrolon cages, type M II
- Diet (e.g. ad libitum): standardized pellet feed (Maus/Ratte Haltung "GLP", Provimi Kliba SA, Kaiseraugst, Switzerland)
- Water (e.g. ad libitum): drinking water from bottles, ad libitum
- Acclimation period: 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20-24
- Humidity (%): 30-70
- Air changes (per hr): fully air conditioned rooms with central air conditioning
- Photoperiod (hrs dark / hrs light): 12:12

Administration / exposure

Route of administration:
oral: gavage
Vehicle:
- Vehicle(s)/solvent(s) used: DMSO/corn oil (ratio 2:3)
- Justification for choice of solvent/vehicle: limited solubility of test substance in water and better volume for administration
- Amount of vehicle (if gavage or dermal): 10 ml/kg bw
Duration of treatment / exposure:
once
Frequency of treatment:
once
Post exposure period:
24 and 48 hours
Doses / concentrationsopen allclose all
Remarks:
Doses / Concentrations:
375 mg/kg bw
Basis:
actual ingested
Remarks:
Doses / Concentrations:
750 mg/kg bw
Basis:
actual ingested
Remarks:
Doses / Concentrations:
1500 mg/kg bw
Basis:
actual ingested
No. of animals per sex per dose:
5
Control animals:
yes, concurrent vehicle
Positive control(s):
- cyclophosphamide (CPP): 20 mg/kg bw
- vincristine sulfate (VCR): 0.15 mg/kg bw

Examinations

Tissues and cell types examined:
- Clinical examinations: After treatment up to the time of sacrifice, the animals were examined for any clinically evident signs of toxicity several times.
- Preparation of the bone marrow: The bone marrow was prepared according to the method described by Schmid and Salamone et al.
- MICROSCOPIC EVALUATION
In general, 2 000 polychromatic erythrocytes (PCE) were evaluated for the occurrence of micronuclei from each animal of every test group, so in total 10 000 PCEs were scored per test group. The normochromatic erythrocytes (= normocytes / NCE) were also scored. The following parameters were recorded:
• Number of polychromatic erythrocytes
• Number of polychromatic erythrocytes containing micronuclei
The increase in the number of micronuclei in polychromatic erythrocytes of treated animals as compared with the vehicle control group provides an index of a chromosome-breaking (clastogenic) effect or damage of the mitotic apparatus (aneugenic activity) of the test substance administered.
• Number of normochromatic erythrocytes
• Number of normochromatic erythrocytes containing micronuclei
The number of micronuclei in normochromatic erythrocytes at the early sacrifice interval shows the situation before test substance administration and may serve as a control value. A test substance induced increase in the number of micronuclei in normocytes may be found with an increase in the duration of the sacrifice interval.
• Ratio of polychromatic to normochromatic erythrocytes
An alteration of this ratio indicates that the test substance actually reached the bone marrow, means the target determined for genotoxic effects.
• Number of small micronuclei (d < D/4) and of large micronuclei (d ≥ D/4)
[d = diameter of micronucleus, D = cell diameter]
The size of micronuclei may indicate the possible mode of action of the test substance, i.e. a clastogenic effect (d < D/4) or a spindle poison effect (d ≥ D/4).
Slides were coded before microscopic analysis.
Details of tissue and slide preparation:
Preparation of the bone marrow
- The animals were anesthetized with isoflurane and afterwards sacrificed by cervical dislocation. Then the two femora were prepared by dissection and removing all soft tissues.
- After cutting off the epiphyses, the bone marrow was flushed out of the diaphysis into a centrifuge tube using a cannula filled with fetal calf serum (FCS) which was preheated up to 37°C (about 2 mL/femur).
- The suspension was mixed thoroughly with a pipette and centrifuged at 300 x g for 5 minutes. The supernatant was removed and the precipitate was resuspended in about 50 μL fresh FCS.
- One drop of this suspension was dropped onto clean microscopic slides, using a Pasteur pipette. Smears were prepared using slides with ground edges. The preparations were dried in the air and subsequently stained.

Staining of the slides
- The slides were stained with eosin and methylene blue (modified May-Grünwald solution or Wrights solution) for about 5 minutes.
- After briefly rinsing in purified water, the preparations were soaked in purified water for about 2 - 3 minutes.
- Subsequently, the slides were stained with Giemsa solution (15 mL Giemsa plus 185 mL purified water) for about 15 minutes.
- After rinsing twice in purified water and clarifying in xylene, the preparations were mounted in Corbit-Balsam.
Evaluation criteria:
Acceptance criteria
The mouse micronucleus test is considered valid if the following criteria are met:
• The quality of the slides must allow the evaluation of a sufficient number of analyzable
cells; i. e. ≥ 2 000 PCEs per animal and a clear differentiation between PCEs and NCEs.
• The ratio of PCEs/NCEs in the concurrent vehicle control animals has to be within the normal range for the animal strain selected.
• The number of cells containing micronuclei in vehicle control animals has to be within the range of the historical vehicle control data both for PCEs and for NCEs.
• The two positive control substances have to induce a distinct increase in the number of PCEs containing small and/or large micronuclei within the range of the historical positive control data or above.

Assessment criteria
A finding is considered positive if the following criteria are met:
• Statistically significant and dose-related increase in the number of PCEs containing micronuclei.
• The number of PCEs containing micronuclei has to exceed both the concurrent vehicle control value and the range of the historical vehicle control data.
A test substance is considered negative if the following criteria are met:
• The number of cells containing micronuclei in the dose groups is not statistically significant increased above the concurrent vehicle control value and is within the range of the historical vehicle control data.
Statistics:
The statistical evaluation of the data was carried out using the program system MUKERN (BASF SE). The asymptotic U test according to MANN-WHITNEY (modified rank test according to WILCOXON) was carried out to clarify the question whether there are statistically significant differences between the untreated control group and the treated dose groups with regard to the micronucleus rate in polychromatic erythrocytes. The relative frequencies of cells containing micronuclei of each animal were used as a criterion for the rank determination for the U test. Statistical significances were identified as follows:
* p ≤ 0.05
** p ≤ 0.01
However, both biological relevance and statistical significance were considered together.

Results and discussion

Test results
Sex:
male
Genotoxicity:
negative
Toxicity:
yes
Remarks:
piloerection and hunched posture in high dose
Vehicle controls validity:
valid
Positive controls validity:
valid
Additional information on results:
According to the results of the present study, there are no statistical significances or biologically relevant differences in the frequency of erythrocytes containing micronuclei either between the vehicle control groups and the three dose groups (375 mg/kg, 750 mg/kg and 1 500 mg/kg) or between the two sacrifice intervals (24 and 48 hours). The number of normochromatic or polychromatic erythrocytes containing small micronuclei (d < D/4) or large micronuclei (d ≥ D/4) did not deviate from the vehicle control values at any of the sacrifice intervals and was within the historical vehicle control data range.
In this study, after single oral administration of the vehicle DMSO/corn oil the ratio of PCEs/NCEs in the vehicle control animals at both sacrifice intervals was within the normal range for the animal strain selected. Besides the number of cells containing micronuclei in these vehicle control animals was within the range of the historical vehicle control data both for PCEs and for NCEs.
In addition, both positive control substances, cyclophosphamide and vincristine sulfate, induced a statistically significant increase in the number of PCEs containing small and/or large micronuclei within the range of the historical positive control data or above.

Any other information on results incl. tables

Summary table – Induction of Micronuclei in bone marrow cells

Test group

Sacrificeinterval

[hrs]

AnimalNo.

Micronuclei in PCE

Numberof NCEc

totala[‰]

largeb[‰]

Vehicle control

DMSO/corn oil

24

5

2.4

0.1

3 505 

Test substance

375 mg/kg bw.

24

5

1.3

0.0

3 490

Test substance

750 mg/kg bw.

24

5

1.3

0.0

3188

Test substance

1 500 mg/kg bw.

24

5

1.4

0.0

3 699

Positive control

cyclophosphamide

20 mg/kg bw.

24

5

13.7**

0.1

4 076

Positive control

vincristine sulfate

0.15 mg/kg bw.

24

5

47.9**

14.7**

5 879

Vehicle control

DMSO/corn oil

48

5

1.3

0.0

4 630

Test substance

1 500 mg/kg bw.

48

5

1.3

0.0

4 078

 

PCE = polychromatic erythrocytes

NCE = normochromatic erythrocytes

bw. = body weight

 

a= sum of small and large micronuclei

b= large micronuclei (indication for spindle poison effect)

c= number of NCEs observed when scoring 10 000 PCEs

 

* = p ≤ 0.05

** = p ≤ 0.01

Applicant's summary and conclusion

Conclusions:
Interpretation of results (migrated information): negative
According to the aouthors, under the experimental conditions chosen here, the test substance has no chromosome-damaging (clastogenic) effect nor does it lead to any impairment of chromosome distribution in the course of mitosis (aneugenic activity) in bone marrow cells of NMRI mice in vivo.