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Administrative data

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

2 -Methylbutryric acid did not induce gene mutations in a bacterial reverse mutation assay (Ames Assay) with and without metabolic activation up to the highest concentration tested (5000 µg/plate).

Link to relevant study records
Reference
Endpoint:
in vitro gene mutation study in bacteria
Remarks:
Type of genotoxicity: gene mutation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
15. Aug 2017 to 30. Aug. 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reference:
Composition 0
Qualifier:
according to
Guideline:
OECD Guideline 471 (Bacterial Reverse Mutation Assay)
Version / remarks:
July 21, 1997
Qualifier:
according to
Guideline:
EU Method B.13/14 (Mutagenicity - Reverse Mutation Test Using Bacteria)
Version / remarks:
May 30, 2008
GLP compliance:
yes
Type of assay:
bacterial reverse mutation assay
Test material information:
Composition 1
Species / strain:
S. typhimurium TA 1535, TA 1537, TA 98 and TA 100
Additional strain characteristics:
not applicable
Metabolic activation:
with and without
Metabolic activation system:
Phenobarbital/β-naphthoflavone induced rat liver S9
Species / strain:
E. coli WP2 uvr A
Additional strain characteristics:
not applicable
Metabolic activation:
with and without
Metabolic activation system:
Phenobarbital/β-naphthoflavone induced rat liver S9
Test concentrations with justification for top dose:
Pre-Experiment/Experiment I: 3; 10; 33; 100; 333; 1000; 2500; and 5000 μg/plate
Experiment II: 33; 100; 333; 1000; 2500; and 5000 μg/plate
Top dose according to guideline
Vehicle:
DMSO (purity > 99%)
Negative controls:
no
Solvent controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: TA 1535, TA 100: sodium azide, TA 1537, TA 98: 4-nitro-o-phenylene-diamine, WP2 uvrA: methyl methane sulfonate
Remarks:
without metabolic activation
Negative controls:
no
Solvent controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: 2-aminoanthracene
Remarks:
all strains with metabolic activation
Details on test system and conditions:
METHOD OF APPLICATION: plate incorporation test (experiment I) and the pre-incubation test (experiment II)

DURATION
- Preincubation period: at 37 °C for 60 minutes (experiment II)
- Exposure duration: at least 48 h

NUMBER OF REPLICATIONS: triplicates for each dose


DETERMINATION OF CYTOTOXICITY
- Method: relative total growth (background growth)
Rationale for test conditions:
Conditions according to guideline
Evaluation criteria:
A test item is considered as a mutagen if a biologically relevant increase in the number of revertants exceeding the threshold of twice (strains TA 98, TA 100, and WP2 uvrA) or thrice (strains TA 1535 and TA 1537) the colony count of the corresponding solvent control is observed.
A dose dependent increase is considered biologically relevant if the threshold is exceeded at more than one concentration.
An increase exceeding the threshold at only one concentration is judged as biologically relevant if reproduced in an independent second experiment.
A dose dependent increase in the number of revertant colonies below the threshold is regarded as an indication of a mutagenic potential if reproduced in an independent second experiment. However, whenever the colony counts remain within the historical range of negative and solvent controls such an increase is not considered biologically relevant.
Statistics:
not perfrormed
Key result
Species / strain:
S. typhimurium TA 1535
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity:
no
Vehicle controls valid:
yes
Negative controls valid:
not examined
Positive controls valid:
yes
Key result
Species / strain:
S. typhimurium TA 1537
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity:
no
Vehicle controls valid:
yes
Negative controls valid:
not examined
Positive controls valid:
yes
Key result
Species / strain:
S. typhimurium TA 98
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity:
no
Vehicle controls valid:
yes
Negative controls valid:
not examined
Positive controls valid:
yes
Key result
Species / strain:
S. typhimurium TA 100
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity:
no
Vehicle controls valid:
yes
Negative controls valid:
not examined
Positive controls valid:
yes
Key result
Species / strain:
E. coli WP2 uvr A
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity:
no
Vehicle controls valid:
yes
Negative controls valid:
not examined
Positive controls valid:
yes
Additional information on results:
No precipitation of the test item occurred up to the highest investigated dose.
Conclusions:
Under the conditions of this bacterial mutagenicity assay, the test item was not mutagenic
Executive summary:

This study was performed to investigate the potential of 2-methylbutyric acid to induce gene mutations according to the plate incorporation test (experiment I) and the pre-incubation test (experiment II) using the Salmonella typhimurium strains TA 1535, TA 1537, TA 98, TA 100, and the Escherichia coli strain WP2 uvrA.

The assay was performed in two independent experiments both with and without liver microsomal activation. Each concentration, including the controls, was tested in triplicate. The test item was tested at the following concentrations:

Pre-Experiment/Experiment I: 3; 10; 33; 100; 333; 1000; 2500; and 5000 μg/plate

Experiment II: 33; 100; 333; 1000; 2500; and 5000 μg/plate

No precipitation of the test item occurred up to the highest investigated dose.

The plates incubated with the test item showed normal background growth up to 5000 μg/plate with and without S9 mix in all strains used.

No toxic effects, evident as a reduction in the number of revertants (below the indication factor of 0.5), occurred in all strains with and without metabolic activation.

No substantial increase in revertant colony numbers of any of the five tester strains was observed following treatment with 2-methylbutyric acid at any dose level, neither in the presence nor absence of metabolic activation (S9 mix). There was also no tendency of higher mutation rates with increasing concentrations in the range below the generally acknowledged border of biological relevance.

Appropriate reference mutagens were used as positive controls and showed a distinct increase of induced revertant colonies.

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

Genetic toxicity in vivo

Endpoint conclusion
Endpoint conclusion:
no study available

Mode of Action Analysis / Human Relevance Framework

In the absence of information on species specific effects or metabolism the results are regarded as relevant for humans.

Additional information

The potential of 2-methylbutyric acid to induce gene mutations according to GLP and OECD TG 471 was investigated in a plate incorporation test (experiment I) and a pre-incubation test (experiment II) using the Salmonella typhimurium strains TA 1535, TA 1537, TA 98, TA 100, and the Escherichia coli strain WP2 uvrA. The test item was tested at concentrations up to 5000 µg/plate with and without metabolic activation.

No substantial increase in revertant colony numbers of any of the five tester strains was observed following treatment with 2-methylbutyric acid at any dose level, neither in the presence nor absence of metabolic activation (S9 mix). There was also no tendency of higher mutation rates with increasing concentrations in the range below the generally acknowledged border of biological relevance.

Appropriate reference mutagens were used as positive controls and showed a distinct increase of induced revertant colonies.

Justification for classification or non-classification

Based on the negative results of a bacterial reverse mutation assay it is concluded that 2-methylbutyric acid has not to be classified as mutagenic according to Regulation (EC) no 1272/2008.