thiourea; thiocarbamide

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vivo

Description of key information

Thiourea did not induce gene mutation in bacteria, but mixed results were obtained in assays in mammalian cells. It consistently induced chromosomal recombination in yeast and insects and induced mammalian cell transformation. Thiourea did not induce genotoxicity in an in vivo micronucleus test.

Link to relevant study records

Reference

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:

other: Comparable to guideline study with acceptable restrictions

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

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

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

Remarks:

Doses / Concentrations:
350 mg/kg body weight
Basis:
nominal in water

Remarks:

Doses / Concentrations:
7 % Thiourea
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

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.

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

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

Conclusions:

Interpretation of results (migrated information): 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.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Additional information

Additional information from genetic toxicity in vivo:

Thiourea did not induce gene mutation in bacteria, but mixed results were obtained in mammalian cells. It consistently induced chromosomal recombination in yeast and insects and induced mammalian cell transformation. Thiourea is reported to elicit cytotoxicity in mammalian cell cultures. In several in vitro tests cytotoxicic effects have not been reported making it difficult to verify any positive result. Thiourea did not induce genotoxicity in an in vivo micronucleus test in rats.

Based on the available data the MAK commission concluded in 1990 that Thiourea is weak genotoxic. The WHO/IPCS concluded in 2003 that thiourea is not considered to be a genotoxic carcinogen and that the development of thiourea-induced thyroid tumours may involve inhibition of peroxidase in the thyroid gland, leading to decreased thyroid hormone production and increased proliferation as a result of an increase in the secretion of thyroid-stimulating hormone.

Based on the overall assessment of the available data Thiourea is not considered being genotoxic. This is in agreement with the WHO/IPCS conclusion (2003).

Andrae (1989) tested the Thiourea metabolite FASA (formamidine sulfinate) for its genotoxic effects on V79 hepatocytes of rats. FASA is formed enzymatically by FMO (FAD-dependent monooxygenase) and is inducing several genotoxic effects like induction of gene mutation, micronuclei formation and DNA repair. The author concluded that FASA would be responsible for the genotoxic effects elicited by thiourea if it would be formed in vivo, which was not verified in this study.

The results obtained in the PhD thesis of Timme Madlon (1998) on "Studies on the mechanism and significance of thiourea genotoxicity in mammalian cells in vitro and in vivo – The genotoxicity and metabolism of thiourea in human thyroid follicle cells" showed that thiourea was marginally genotoxic to human thyroid follicle cells. The genotoxicity was indicated by a slight increase in the frequency of DNA strand breaks in the cells and possibly due to slight auto oxidation of thiourea to electrophilic S oxygenated products. The investigations yielded no indication of organ-specific metabolic activation of thiourea in thyrocytes. It can therefore be assumed that human exposure to thiourea is not associated with a relevant risk of thyroid tumours due to genotoxic effects.

The following tables summarize several of the available test reports, some are not included as individual IUCLID study records, but to emphasise the amount of available, ambiguous data.

Genotoxicity and related endpoints: in vitro

Table1: summary of available studies on genotoxicity in vitro

Endpoint	Results and references
	Species, strain	Result	Metabolic activation	Reference
Genotoxicity and related endpoints:in vitro
Gene mutation	Salmonella typhimuriumTA 97	Negative	+/-	Brams et al. 1987 Zeiger et al. 1988
	Salmonella typhimuriumTA1535, TA100, TA1537, TA1538, TA98	Negative	+/-	Korte und Greim, 1981 Brusick, 1977
	Salmonella typhimuriumTA 98	Negative	+/-	Simmon 1979a* Dunkel et al. 1984* Brams et al. 1987 Zeiger et al. 1988
	Salmonella typhimuriumTA 100	Negative	+/-	Simmon 1979a* Yamaguchi 1980* Dunkel et al. 1984* Brams et al. 1987 Zeiger et al. 1988
	Salmonella typhimuriumTA1535	Negative	+/-	Simmon 1979a* Rozenkranz and Poirier 1979* Dunkel et al. 1984* Zeiger et al. 1988
	Salmonella typhimuriumTA1535/pSK1002 umu test	Negative	+/-	Nakamura et al. 1987
	Salmonella typhimuriumTA1537	Negative	+/-	Simmon 1979°* Dunkel et al. 1984*
	Salmonella typhimuriumTA1538	Negative	+/-	Rozenkranz and Poirier 1979* Simmon 1979a* Dunkel et al. 1984*
	Escherichia coli SOS repair	Negative	+/-	Brams et al. 1987 Kevekordes et al. 1999*
	Escherichia coliWP2uvrA	Negative	+/-	Dunkel et al. 1984*
	Escherichia colipol A	Negative	+	Rosenkranz and Poirier 1979* McCarroll et al. 1981
			-	McCarroll et al. 1981
	Escherichia coliuvr/rec strains	Positive	-	Hellmér and Bolcsfoldi 1992
		Negative	+	Hellmér and Bolcsfoldi 1992
	Escherichia coliK12	Negative	+	Mamber et al. 1984*
		Not tested	-	Mamber et al. 1984*
	Escherichia coliRK	Negative	+/-	Hayes et al. 1984*
	Aspergillus nidulans	Negative	-	Crebelli et al. 1986
	Saccharamyces cerevisiae	Positive	-	Schiestl et al. 1989 Galli and Schiestl 1995, 1996, 1998*
			+	Galli and Schiestl 1998* Egilsson et al. 1979* Wilkie and Gooneskera 1980*
		ambigous	+/-	Zoushu, 1989
	Saccharamyces cerevisiaetrp locus	Positive	+	Morita et al. 1989
		Negative	-	Morita et al. 1989
	Saccharamyces cerevisiaeD7 trp locus	Positive	Not indicated	Jiang et al. 1989*
	Drosophila melanogaster	Positive	-	Batiste-Alentorn et al. 1991*
		Weakly positive	-	Vogel & Nivard 1993*
		Inconclusive	-	Batiste-Alentorn et al. 1994, 1995*
		Negative	-	Rodriguez-Arnaiz 1997*
	Mouse L5178Y cells	Weakly positive	+	Caspary 1988 Wangenheim and Bolcsfoldi 1988
			-	Wangenheim and Bolcsfoldi 1988
		Negative	+	Mitchell et al. 1988*
			-	Mitchell et al. 1988* Myhr and Caspary 1988*
	Chinese hamster ovary cells (V79),hprtlocus	Negative	-	Bradley et al. 1982*
		Positive	+/-	Ziegler-Skylakakis et al. 1985*
	Chinese hamster ovary cells (V79), cell sub-line Sp5	Negative	-	Helleday et al. 1998*
Sister chromatid exchange	Chinese hamster V79 cells	Negative	-	Bradley et al. 1982*
	Chinese hamster Ovary (CHO)	Positive	+/-	TNO 1978; de Raat
Unscheduled DNA synthesis	Rat liver cells	Weakly positive	-	Ziegler-Skylakakis et al. 1985*
	Rat liver cells	Negative	-	Lonati-Galligani et al. 1983* Fautz et al. 1991
Mitotic recombination	Saccharamyces cerevisiaeD3	Negative	+/-	Simmon 1979b*
Recombination	Transformed human lymphoblastoid GM6804 cells	Positive	-	Aubrecht et al. 1995*
Micronucleus formation	Syrian hamster embryo cells	Positive	-	Fritzenschaf et al. 1993
	Chinese hamster V79	Weakly positive		Ziegler-Skylakakis et al. 1998*
DNA strand breaks	Rat hepatocytesin vitro	Positive	-	Sina et al. 1983*
	Rat hepatocytesin vitro	Negative	-	Fautz et al. 1991
Cell transformation	Syrian hamster embryo cells	Positive	-	Pienta et al. 1977*
	Rauscher virus-infected rat embryo cells	Positive	-	Dunkel et al. 1981*
	Bovine papilloma virus DNA-enhanced C3H10T1/2 cells	Weakly positive	-	Kowalski et al. 2000*
DNA synthesis inhibition	Human fibroblast cells	Positive	-	Painter 1977*

* studies referred to in IPCS 2003, Health Canada 2008, IARC 2001, or MAK 1990

 

Genotoxicity and related endpoints: in vivo

Table2: summary of available studies on genotoxicity in vivo

Endpoint	Results and references
	Species, strain	Result	Metabolic activation	Reference
Gene mutation	Drosophila melanogaster	Positive	n.a.	Batiste-Alentorn et al. 1991
	Drosophila melanogaster	Weakly Positive	n.a.	Vogel and Nivard 1993
	Drosophila melanogaster	Negative	n.a.	Rodriguez-Arnaiz 1997
	Drosophila melanogaster	Inconclusive	n.a.	Batiste-Alentorn et al. 1994, 1995*
Micronucleus test	Rats treated with two successive oral doses within 24 hours	Negative	n.a.	TNO 1979b

Justification for selection of genetic toxicity endpoint
mammalian in vivo micronucleus test similar to OECD 474

Justification for classification or non-classification

Thiourea did not induce gene mutation in bacteria, but mixed results were obtained in assays in mammalian cells. It consistently induced chromosomal recombination in yeast and insects and induced mammalian cell transformation. Based on the overall assessment of available data the test item is not considered a mutagen.