thiourea; thiocarbamide

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:

experimental study

Adequacy of study:

weight of evidence

Study period:

February 1979

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1979

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)

Deviations:

yes

Remarks:

400 instead of 200 erythrocytes were examined

GLP compliance:

no

Type of assay:

micronucleus assay

Test material

Test material information

Constituent 1

Reference substance name:

Thiourea

EC Number:

200-543-5

EC Name:

Thiourea

Cas Number:

62-56-6

Molecular formula:

CH4N2S

IUPAC Name:

thiourea

Test material form:

solid: particulate/powder

Test animals

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Central institute for the breeding of laboratory animals TNO, Zeist
- Age at study initiation: 4-5 weeks
- Assigned to test groups randomly: the animals were assigned to three test groups of 5 males and 5 females according body weight
- Fasting period before study: deprivation of food for 14-15 h
- Housing: screen bottom cages
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: yes

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 24+/-1°C
- Humidity (%): 40-60 %
- Air changes (per hr): no data. air conditioned rooms
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

- Vehicle(s)/solvent(s) used: water
- Justification for choice of solvent/vehicle:
- Concentration of test material in vehicle: 350 mg/kg bw in 5 mL water per kg bw

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: freshly prepared immediately before treatment of the animals

Duration of treatment / exposure:

The test samples were administered twice with an interval of 24 h. 6 hours after the last treatment the animals were killed.

Frequency of treatment:

twice

Post exposure period:

6 hours

Doses / concentrations

Dose / conc.:

350 mg/kg bw/day (nominal)

Remarks:

Basis: nominal in water

No. of animals per sex per dose:

5 males and 5 females

Control animals:

yes, concurrent vehicle

Positive control(s):

2,3,5-tris-ethyleneiminobenzoquinone (Trenimon; Bayer) was used as a solution in physiological saline
- Justification for choice of positive control(s): no data
- Route of administration: oral
- Doses / concentrations: 0.0625 mg/kg body weight

Examinations

Tissues and cell types examined:

bone marrow of the femora; erythrocytes

Details of tissue and slide preparation:

The bone marrow of the femora was flushed into centrifuge tubescontaining foetal calf serum and centrifuged. The excess serum was removed. The cells were than resuspended by mixing gently with a pasteur pipette. A drop was placed on a slide cleaned with methanol overnight and spread with a haemocytometer cover glass. Five slides were prepared of each animal. The smears were air dried, fixed in methanol and stained according to May-Grünwald.

Results and discussion

Test results

Key result

Sex:

male/female

Genotoxicity:

negative

Toxicity:

not examined

Vehicle controls validity:

valid

Negative controls validity:

valid

Positive controls validity:

valid

Additional information on results:

RESULTS OF RANGE-FINDING STUDY
The dose-levels used in the present study were based on acute oral LD50 of the test material for rats (CIVO letters 29/12/75)

RESULTS OF DEFINITIVE STUDY
- Induction of micronuclei (for Micronucleus assay): Oral administration of thiourea did not affect the incidence of micronucleated erythrocytes
- Ratio of PCE/NCE (for Micronucleus assay):Oral administration of thiourea did not affect the ratio of poly and normochromatic erythrocytes
- Appropriateness of dose levels and route:
- Statistical evaluation: standard deviations were determined

Any other information on results incl. tables

No mortality or abnormalities of condition or behaviour, attributable to treatment were observed in any of the animals during the exposure period.

 

 

Table 1: Average body weights of groups of 5 rats

Group No	Treatment/kg body weight	Average body weight +/- SD
		males	females
390	2x5mL distilled water	99+/-3	79+/-7
392	2x5 mL 7% Thioharnstoff	96+/-4	81+/-5

 

 

 

Table 2: Mean numbers of micronucleated erythrocytes and percentage polychromatic erythrocytes in bone marrow of rats

Treatment	Sex	Incidence of micronucleated cells per 2000 erythrocytes per rat		Percentage polychromatic erythrocytes +/-SD
		mean	range
Vehicle control	Male	4.4	2-7	74.2+/-3.5
Thioharnstoff	Male	5.4	4-8	72.0+/-3.7
Vehicle control	Female	5.0	2-8	63.8+/-5.1
Thioharnstoff	female	4.0	4-6	62.9+/-3.5

Applicant's summary and conclusion

Conclusions:

Interpretation of results: negative
Thiourea did no increase the frequency of micronucleated polychromatic erythrocytes in bone marrow. In this study thiourea did not reveal any evidence for mutagenic activity.

Executive summary:

In a Wistar rats bone marrow micronucleus assay, 5 male and 5 female animals per dose were treated by oral gavage with Thiourea (7 % a.i.) at doses of 0 and 350 mg/kg bw. Bone marrow cells were harvested at 6 hours post-treatment. The vehicle was water. There were no signs of toxicity during the study. Thiourea was tested at an adequate dose based on the results of an oral acute toxicity test. The positive control induced the appropriate response. There was not a significant increase in the frequency of micronucleated polychromatic erythrocytes in bone marrow after any treatment time. This study is classified as acceptable. This study satisfies the requirement for Test Guideline OECD 474 for in vivo cytogenetic mutagenicity data.