N,N''-methylenebis[N'-[3-(hydroxymethyl)-2,5-dioxoimidazolidin-4-yl]urea]

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vivo

Description of key information

In vitro gene mutation:

- overall negative (limited indication of possible weak activity) in a bacterial assay.

In vitro cytogenetics:

- negative in a mammalian cell chromosome aberration  assay.

Studies performed with a close chemical analogue:

- in vitro positive in a mouse lymphoma cell mutation assay

- in vivo negative in a mouse bone marrow micronucleus study

- in vivo negative in a rat liver UDS study.

Link to relevant study records

Reference

Endpoint:

in vivo mammalian cell study: DNA damage and/or repair

Remarks:

Type of genotoxicity: DNA damage and/or repair

Type of information:

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

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Read-across from Klimisch 1 study performed on a close structural analogue which is manufactured in the same way (reaction of formaldehyde with a modified urea) and reacts with water in the same way (hydrolysis releasing formaldehyde) as the registered substance

Qualifier:

according to guideline

Guideline:

OECD Guideline 486 (Unscheduled DNA Synthesis (UDS) Test with Mammalian Liver Cells in vivo)

GLP compliance:

yes

Type of assay:

unscheduled DNA synthesis

Species:

rat

Strain:

Wistar

Sex:

male

Details on test animals or test system and environmental conditions:

Approximately 7 weeks of age, 194-253g bodyweight at study start (main UDS test).

Route of administration:

oral: gavage

Vehicle:

Aqueous 0.25% methylcellulose

Details on exposure:

Single oral dosing at 10 ml/kg dose volume.

Post exposure period:

Animals terminated 12-14h (experiment1) or 2-4h (experiment 2) post-dose.

Remarks:

Doses / Concentrations:
800 and 2000 mg/kg
Basis:
actual ingested
dosages selected following a preliminary toxicity test in which 3M, 3F dosed at 2000 mg/kg showed little sign of toxicity over 2 days.

No. of animals per sex per dose:

Experiment 1 (12-14h termination): 4M, 4F
Experiment 2 (2-4h termination): 4M, 4F.

Control animals:

yes, concurrent vehicle

Positive control(s):

Yes: 2-acetylaminofluorine (experiment 1), dimethylnitrosamine (experiment 2).

Tissues and cell types examined:

Hepatocytes

Details of tissue and slide preparation:

Hepatocytes collected by liver perfusion at termination and allowed to attach to coverslips in multiwell plates, then radiolabelled by addition of 3H thymidine. Cells then fixed, washed and dipped for autoradiography.

Evaluation criteria:

100 cells/animal (where possible) were scored for nuclear and cytoplasmic grain counts and net nuclear grain count (NNG) was determined. Cells showing S-phase synthesis, seen as heavily labelled nuclei, were excluded.
Positive result criteria: NNG >0 with 20% or more of cells responding, test >vehicle controls for NNG and % cells in repair.

Sex:

male

Genotoxicity:

negative

Toxicity:

no effects

Remarks:

no significant adverse reactions were seen up to termination

Vehicle controls validity:

valid

Positive controls validity:

valid

Additional information on results:

Cell viabilities in test and control groups werewithin the range 55-76%.

NNG counts in all test group animals were <0: group mean values were -1.2 to -2.4. No more than 0.7% of cells were seen to be repairing DNA in any test group.

Conclusions:

Interpretation of results (migrated information): negative
Single oral administration of the tested analogue at a dosage approaching the rat acute oral LD50 reported by others produced no evidence of DNA damage (as indicated by UDS) in this study. Based on the close similarity of chemical structure and properties, it is predicted that the registered substance will show a similar absence of in vivo genotoxicity.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Additional information

Additional information from genetic toxicity in vivo:

Although a possible indication of weak activity was seen in a bacterial mutagenicity test, this study was concluded overall negative.

Negative results for both gene and chromosomal mutation in vitro were confirmed by read-across from negative in vivo test results on a close chemical analogue (manufactured similarly and also a formaldehyde donor).

Although the close analogue has shown activity in one type of in vitro assay in which the registered substance has not been tested, this

mouse lymphoma mutation assay:

- has been shown to detect both point or gene mutations (seen as large size mutant colonies) and larger-scale, chromosomal events (seen as small size mutant colonies)

- has been shown to have a relatively low specificity for detection of carcinogens (39.0 or 57.8% according to two expert reviews cited in the EFSA draft "Scientific opinion on genotoxicity testing strategies applicable to food and feed safety assessment", 2011).

Neither chromosomal disruption (clastogenesis or aneuploidy leading to micronucleus formation in bone marrow cells) nor DNA damage (leading to repair in liver cells) were detected when rodents were given a high oral dose of the analogue.

Justification for selection of genetic toxicity endpoint

Both in vitro and in vivo studies are available.  The selected in vivo UDS study performed on a close chemical analogue gave clearly negative results after single oral administration of test substance at a dosage approaching the acute oral LD50 value reported by others.

Justification for classification or non-classification

Based on the clearly negative results obtained with the registered substance in vitro plus the similarly negative results obtained when the close chemical analogue was tested in vivo (in assays addressing different genotoxicity endpoints), it is concluded that no concerns are raised regarding possible germ cell mutation in humans. Therefore no classification of the substance is warranted.