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Genetic toxicity: in vitro

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Administrative data

Endpoint:
in vitro gene mutation study in bacteria
Remarks:
Type of genotoxicity: gene mutation
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2016
Report Date:
2016

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 471 (Bacterial Reverse Mutation Assay)
GLP compliance:
yes (incl. certificate)
Type of assay:
bacterial reverse mutation assay

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
impurity
Test material form:
liquid

Method

Species / strain
Species / strain / cell type:
S. typhimurium TA 1535, TA 1537, TA 98, TA 100 and E. coli WP2
Metabolic activation:
with and without
Metabolic activation system:
S9-mix from male Wistar rats livers (received 80 mg/kg b.w. phenobarbital i.p. and β-naphthoflavone orally each on three consecutive days)
Test concentrations with justification for top dose:
Experiment 1: 0; 33; 100; 333; 1000; 2500 and 5000 μg/plate; (Standard plate test with and without S9 mix) all strains
Experiment 2: 0; 10; 33; 100; 333; 1000 and 2500 μg/plate; (Standard plate test without S9 mix) TA 1537
Experimant 3: 0; 10; 33; 100; 333; 1000 and 2500 μg/plate; (Preincubation test with and without S9 mix) all strains
Vehicle / solvent:
- Vehicle(s)/solvent(s) used: DMSO
To achieve a clear solution of the test substance in the vehicle, the test substance preparation was shaken thoroughly. The further concentrations were diluted according to the planned doses. All test substance formulations were prepared immediately before administration.
Controls
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
Positive controls:
yes
Positive control substance:
4-nitroquinoline-N-oxide
9-aminoacridine
other: 2-aminoanthracene; N-methyl-N'-nitro-N-nitrosoguanidine; 4-nitro-o-phenylenediamine
Details on test system and experimental conditions:
METHOD OF APPLICATION: in medium
Both tests: In each experiment 3 Test plates per dose control used.

Standard plate test
• Salmonella typhimurium
Test tubes containing 2-mL portions of soft agar (overlay agar), which consists of 100 mL agar (0.8% [w/v] agar + 0.6% [w/v] NaCl) and 10 mL amino acid solution (minimal amino acid solution for the determination of mutants: 0.5 mM histidine + 0.5 mM biotin) were kept in a water bath at about 42 - 45°C, and the remaining components were added in the following order:
0.1 mL test solution or vehicle (negative control)
0.1 mL fresh bacterial culture
0.5 mL S9 mix (with metabolic activation)
or
0.5 mL phosphate buffer (without metabolic activation)
After mixing, the samples were poured onto Minimal glucose agar plates (Moltox Molecular Toxicology, Inc.; Boone, NC 28607; USA) within approx. 30 seconds. After incubation at 37°C for 48 – 72 hours in the dark, the bacterial colonies (his+ revertants) were counted. The colonies were counted using the Sorcerer Image Analysis System with the software program Ames Study Manager (Perceptive Instruments Ltd., Haverhill, UK). Colonies were counted manually, if precipitation of the test substance hinders the counting using the Image Analysis System.
• Escherichia coli
Test tubes containing 2-mL portions of soft agar (overlay agar), which consists of 100 mL agar (0.8% [w/v] agar + 0.6% [w/v] NaCl) and 10 mL amino acid solution (minimal amino acid solution for the determination of mutants: 0.5 mM tryptophan) were kept in a water bath at about 42 - 45°C, and the remaining components were added in the following order:
0.1 mL test solution or vehicle (negative control)
0.1 mL fresh bacterial culture
0.5 mL S9 mix (with metabolic activation)
or
0.5 mL phosphate buffer (without metabolic activation)
After mixing, the samples were poured onto Minimal glucose agar plates (Moltox Molecular Toxicology, Inc.; Boone, NC 28607; USA) within approx. 30 seconds. After incubation at 37°C for 48 – 72 hours in the dark, the bacterial colonies (trp+ revertants) were counted. The colonies were counted using the Sorcerer Image Analysis System with the software program Ames Study Manager (Perceptive Instruments Ltd., Haverhill, UK). Colonies were counted manually, if precipitation of the test substance hinders the counting using the Image Analysis System.

Preincubation Test
The experimental procedure was based on the method described by Yahagi et al. (7) and Matsushima et al. (8).
0.1 mL test solution or vehicle, 0.1 mL bacterial suspension and 0.5 mL S9 mix (with metabolic activation) or phosphate buffer (without metabolic activation) were incubated at 37°C for the duration of about 20 minutes using a shaker. Subsequently, 2 mL of soft agar was added and, after mixing, the samples were poured onto the agar plates within approx. 30 seconds.
After incubation at 37°C for 48 – 72 hours in the dark, the bacterial colonies were counted. The colonies were counted using the Sorcerer Image Analysis System with the software program Ames Study Manager (Perceptive Instruments Ltd., Haverhill, UK). Colonies were counted manually, if precipitation of the test substance hindered the counting using the Image Analysis System.

Positive controls
The following positive controls were used to check the mutability of the bacteria and the activity of the S9 mix:
With S9 mix
• 2-aminoanthracene (2-AA) ; 2.5 μg/plate, TA 1535, TA 100, TA 1537, TA 98; 60 μg/plate, dissolved in DMSO, Escherichia coli WP2 uvrA
Without S9 mix
• N-methyl-N'-nitro-N-nitrosoguanidine (MNNG); 5 μg/plate TA 1535, TA 100
• 4-nitro-o-phenylenediamine (NOPD); 10 μg/plate TA 98
• 9-aminoacridine (AAC); 100 μg/plate TA 1537
• 4-nitroquinoline-N-oxide; 5 μg/plate E. coli WP2 uvrA


Evaluation criteria:
The test substance was considered positive in this assay if the following criteria were met:
• A dose-related and reproducible increase in the number of revertant colonies, i.e. at least doubling (bacteria strains with high spontaneous mutation rate, like TA 98, TA 100 and E.coli WP2 uvrA) or tripling (bacteria strains with low spontaneous mutation rate, like TA 1535 and TA 1537) of the spontaneous mutation rate in at least one tester strain either without S9 mix or after adding a metabolizing system.
A test substance was generally considered non-mutagenic in this test if:
• The number of revertants for all tester strains were within the range of the historical negative control data under all experimental conditions in at least two experiments carried out independently of each other.

Results and discussion

Test results
Species / strain:
S. typhimurium TA 1535, TA 1537, TA 98, TA 100 and E. coli WP2
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Additional information on results:
SOLUBILITY: No precipitation of the test substance was found with and without S9 mix.
TOXICITY: A bacteriotoxic effect was observed depending on the strain and test conditions from about 333 μg/plate onward.
MUTAGENICITY:
A relevant increase in the number of his+ or trp+ revertants (factor ≥ 2: TA 100, TA 98 and E.coli WP2 uvrA or factor ≥ 3: TA 1535 and TA 1537) was not observed in the standard plate test or in the preincubation test either without S9 mix or after the addition of a metabolizing system.
Remarks on result:
other: all strains/cell types tested
Remarks:
Migrated from field 'Test system'.

Any other information on results incl. tables

For detailed result tables see attached document.

Applicant's summary and conclusion

Conclusions:
Interpretation of results (migrated information):
negative

Thus, under the experimental conditions of this study, the test substance 2,2’-dimethyl-4,4’- methylenebis(cyclohexylamine) is not mutagenic in the Salmonella typhimurium/Escherichia coli reverse mutation assay in the absence and the presence of metabolic activation.