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Key value for chemical safety assessment

Genetic toxicity in vivo

Description of key information
Studies of bacterial mutation, mammalian cell mutation and mammalian cell cytogenicity are available in vitro. A study of micronucleus induction in the mouse in vivo is also available.
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:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Research paper. Study well documented meeting generally accepted scientific principles.
Qualifier:
no guideline followed
Principles of method if other than guideline:
Method: other: Wargovich et al, J Natl Cancer Inst 71, 133-137 (1983)
GLP compliance:
not specified
Type of assay:
micronucleus assay
Species:
mouse
Strain:
other: C57BL/6J
Sex:
female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles river, Calco, Como Italy
- Age at study initiation: no information
- Weight at study initiation: 17-18 g
- Assigned to test groups randomly: no information
- Fasting period before study: 12 h, or not fasted
- Diet (e.g. ad libitum): ad libitum for non-fasting animals
- Water (e.g. ad libitum): ad libitum (after treatment)
Route of administration:
other: oral gavage or intrarectal
Vehicle:
- Vehicle(s)/solvent(s) used: saline
- Amount of vehicle (if gavage or dermal): 0.2 ml
Details on exposure:
PREPARATION OF DOSING SOLUTIONS: no details


Duration of treatment / exposure:
24 hours
Frequency of treatment:
Single treatment
Post exposure period:
24 hours
Remarks:
Doses / Concentrations:
2, 6.5 and 13 mg Fe/kg
Basis:

No. of animals per sex per dose:
4-9 female animals per dose
Control animals:
yes
Positive control(s):
- 2-amino-3-methylimidazo(4,5-f)quinoline) (IQ)
- Justification for choice of positive control(s): IQ is a genotoxic chemical with specific intestinal action.
- Route of administration: orally to non-fasting mice
- Doses / concentrations: 100 and 200 mg/kg bw
Tissues and cell types examined:
Samples of forestomach, duodenum and colon were taken following oral administration and colon samples after intrarectal administration
Details of tissue and slide preparation:
CRITERIA FOR DOSE SELECTION: The lowest dose tested was equivalent to a therapeutic dose in iron deficiency anaemia.

DETAILS OF SLIDE PREPARATION: colon and duodenum where opened longitudinally and rolled. The forestomach was excised. Specimens were fixed in 10% buffered formalin and processed for histology. Slides with 5 micron thick paraffin sections were stained with Feulgen-fast green.

METHOD OF ANALYSIS:
Slides were examined and scored for a) micronuclei defined as nuclear fragments not larger than ¼ -1/3 of the diameter of the primary nucleus b) nuclear aberrations comprised of micronuclei, pyknotic nuclei, cytolysosomes and disintegrated nuclei. The forestomach was analysed by observing around 400 mucosal cells per animal. Mucosal cells lining 20 crypts for colon and 5 crypts for duodenum were analysed per animal beginning from the anal end of the colon and the pyloric end of the duodenum.
Evaluation criteria:
Evaluation criteria are not described.
Statistics:
No statistical evaluation was described.
Sex:
female
Genotoxicity:
negative
Toxicity:
yes
Vehicle controls validity:
valid
Negative controls validity:
not applicable
Positive controls validity:
valid
Additional information on results:
The reference compound IQ caused an increase of nuclear aberrations and micronuclei, results being presented for effects in the colon.  Ferrous sulphate did not significantly increase the incidence of micronuclei in the stomach, duodenum or colon following oral 
administration to fasting or non-fasting mice.  In the colon nuclear aberrations indicating toxicity were increased in fasting and non-fasting mice receiving oral ferrous sulphate.  Following intrarectal administration ferrous sulfate showed slight  toxicity to the colon producing a slight but statistically 
significant (p<0.01) increase in micronuclei and in chromosome aberrations.  The authors consider that the iron salts do not appear to have a significant genotoxic effect on the gastrointestinal tract and that the toxic effects are 
due to generalized toxicity rather than a genotoxic  effect.

The reference compound IQ caused an increase of nuclear aberrations and micronuclei, results being presented for effects in the colon. Ferrous sulphate did not significantly increase the incidence of micronuclei in the stomach, duodenum or colon following oral administration to fasting or non-fasting mice. In the colon nuclear aberrations indicating toxicity were increased in fasting and non-fasting mice receiving oral ferrous sulphate. 

Following intrarectal administration ferrous sulfate showed slight toxicity to the colon producing a slight but statistically significant (p<0.01) increase in micronuclei and in chromosome aberrations. 

The authors consider that the iron salts do not appear to have a significant genotoxic effect on the gastrointestinal tract and that the toxic effects are due to generalized toxicity rather than a genotoxic effect.

Conclusions:
Interpretation of results (migrated information): negative
Ferrous sulphate is not considered to have a significant genotoxic effect on the mouse gastrointestinal tract as measured by induction of micronuclei. An increased incidence of nuclear aberrations was considered evidence of general toxicity rather than mutagenic activity.
Executive summary:

 This study was undertaken to assess the effects of iron status on the gastrointestinal tract using the nuclear aberrations assay of Wargovich, Medline and Bruce, 1983. 

The current authors interpreted the results by differentiating between micronuclei and nuclear aberrations considering that micronuclei are a specific sign of genetic damage while nuclear aberrations are more unspecific effects related to cellular toxicity. This was because nuclear aberrations may also be associated with substances acting through non-genotoxic mechanisms.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (negative)

Additional information

Additional information from genetic toxicity in vivo:

Read-across data are available for the substance iron sulphate. A negative response was obtained in an Ames test (MHLW, 2003); however positive responses were seen in a study of mammalian cell mutation (Dunkel, 1999) and in a study of mammalian cell cytogenicity (MHLW, 2003). No clear evidence for the induction of micronuclei was seen in the mouse (Bianchini, 1988); a positive response was seen only at levels causing cytotoxicity. It is concluded that iron sulphate (and therefore iron trinitrate, by read-across) is not genotoxic in vivo.


Justification for selection of genetic toxicity endpoint
A weight of evidence approach is used: the battery of available in vitro and in vivo genotoxicity investigations lead to an overall conclusion for mutagenicity

Justification for classification or non-classification

Classification for genetic toxicity is not proposed in the absence of any evidence of genetic toxicity in vivo.