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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
Study period:
02 July 2014 to 11 August 2014
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Study conducted to GLP in accordance with recognised guideline. There were no deviations (unplanned changes) from the study plan.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2014
Report Date:
2015

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to
Guideline:
JAPAN: Guidelines for Screening Mutagenicity Testing Of Chemicals
Deviations:
no
Qualifier:
according to
Guideline:
EU Method B.13/14 (Mutagenicity - Reverse Mutation Test Using Bacteria)
Deviations:
no
Qualifier:
according to
Guideline:
OECD Guideline 471 (Bacterial Reverse Mutation Assay)
Deviations:
no
Qualifier:
according to
Guideline:
EPA OPPTS 870.5100 - Bacterial Reverse Mutation Test (August 1998)
Version / remarks:
OPPTS harmonised guidelines
Deviations:
no
GLP compliance:
yes (incl. certificate)
Type of assay:
bacterial reverse mutation assay

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
other: light brown viscous liquid
Details on test material:
- Purity: 100%
- Physical state/Appearance: Light brown viscous liquid
- Storage Conditions: Room temperature in the dark
- No correction was made for purity.
- The test item was immiscible in sterile distilled water, dimethyl sulphoxide and dimethyl formamide at 50 mg/mL, and acetone at 100 mg/mL but was fully miscible in tetrahydrofuran at 200 mg/mL in solubility checks performed in-house.
- Tetrahydrofuran was selected as the vehicle.
- The test item was accurately weighed and approximate half-log dilutions prepared in tetrahydrofuran by mixing on a vortex mixer on the day of each experiment. All formulations were used within four hours of preparation and were assumed to be stable for this period.
- Analysis for concentration, homogeneity and stability of the test item formulations is not a requirement of the test guidelines and was, therefore, not determined. This is an exception with regard to GLP and has been reflected in the GLP compliance statement.
- Prior to use, the solvent was dried to remove water using molecular sieves i.e. 2 mm sodium alumino-silicate pellets with a nominal pore diameter of 4 x 10-4 microns.

Method

Target gene:
Not required
Species / strainopen allclose all
Species / strain / cell type:
S. typhimurium TA 1535, TA 1537, TA 98 and TA 100
Details on mammalian cell type (if applicable):
Non-mammalian study
Species / strain / cell type:
E. coli WP2 uvr A
Details on mammalian cell type (if applicable):
Non-mammalian study
Metabolic activation:
with and without
Metabolic activation system:
phenobarbitone/β-naphthoflavone induced rat liver S9
Test concentrations with justification for top dose:
Experiment 1: Range-finding test: 1.5, 5, 15, 50, 150, 500, 1500 and 5000 µg/plate

Experiment 2: Main test: 50, 150, 500, 1500 and 5000 µg/plate
Vehicle / solvent:
- Vehicle(s)/solvent(s) used: Tetrahydrofuran
- Justification for choice of solvent/vehicle: The substance was not misicible in water, DMSO or Acetone
Controlsopen allclose all
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
Remarks:
Concurrent - Tetrahydrofuran
True negative controls:
yes
Positive controls:
yes
Positive control substance:
N-ethyl-N-nitro-N-nitrosoguanidine
Remarks:
2, 3, 5 µg/plate respectively for WP2uvrA, TA100, TA1535
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
Remarks:
Concurrent - Tetrahydrofuran
True negative controls:
yes
Positive controls:
yes
Positive control substance:
9-aminoacridine
Remarks:
80 µg/plate for TA1537
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
Remarks:
Concurrent - Tetrahydrofuran
True negative controls:
yes
Positive controls:
yes
Positive control substance:
4-nitroquinoline-N-oxide
Remarks:
0.2 µg/plate for TA98
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
Remarks:
Concurrent - Tetrahydrofuran
True negative controls:
yes
Positive controls:
yes
Positive control substance:
other: 2-Aminoanthracene
Remarks:
1, 2, 10 µg/plate for TA100, TA1535&TA1537, WP2uvrA respectively
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
Remarks:
Concurrent - Tetrahydrofuran
True negative controls:
yes
Positive controls:
yes
Positive control substance:
benzo(a)pyrene
Remarks:
5 µg/plate for TA98
Details on test system and experimental conditions:
METHOD OF APPLICATION: in agar (plate incorporation) at multiple dose levels, in triplicate, both with and without the addition of a rat liver homogenate metabolising system (10% liver S9 in standard co-factors).

RANGE FINDING
Dose selection
The test item was tested using the following method. The maximum concentration was 5000 µg/plate (the maximum recommended dose level). Eight concentrations of the test item (1.5, 5, 15, 50, 150, 500, 1500 and 5000 µg/plate) were assayed in triplicate against each tester strain, using the direct plate incorporation method.
Without Metabolic Activation
0.025 mL of the appropriate concentration of test item or 0.1 mL of solvent or appropriate positive control was added to 2 mL of molten trace amino-acid supplemented media containing 0.1 mL of one of the bacterial strain cultures and 0.5 mL of phosphate buffer. These were then mixed and overlayed onto a Vogel-Bonner agar plate. Negative (untreated) controls were also performed on the same day as the mutation test. Each concentration of the test item, appropriate positive, vehicle and negative controls, and each bacterial strain, was assayed using triplicate plates.
With Metabolic Activation
The procedure was the same as described previously (see 3.5.1.2) except that following the addition of the test item formulation and bacterial culture, 0.5 mL of S9-mix was added to the molten trace amino-acid supplemented media instead of phosphate buffer.
Incubation and Scoring
All of the plates were incubated at 37 °C +/- 3 °C for approximately 48 hours and scored for the presence of revertant colonies using an automated colony counting system. The plates were viewed microscopically for evidence of thinning (toxicity).

MAIN TEST
Dose selection
The dose range used for the main test was determined by the results of the range-finding test and was 50 to 5000 µg/plate.
Seven test item dose levels were selected in Experiment 2 in order to achieve both four non-toxic dose levels and the potential toxic limit of the test item following the results from the first mutation test.
Without Metabolic Activation
The procedure was the same as described previously
With Metabolic Activation
The procedure was the same as described previously
Incubation and Scoring
All of the plates were incubated at 37 °C +/- 3 °C for approximately 48 hours and scored for the presence of revertant colonies using an automated colony counting system. The plates were viewed microscopically for evidence of thinning (toxicity).

DURATION
- Preincubation period: N/A
- Exposure duration: Approximately 48 hours
- Expression time (cells in growth medium): N/A
- Selection time (if incubation with a selection agent): N/A
- Fixation time (start of exposure up to fixation or harvest of cells): N/A


SELECTION AGENT (mutation assays): NDA
SPINDLE INHIBITOR (cytogenetic assays): N/A
STAIN (for cytogenetic assays): N/A


NUMBER OF REPLICATIONS: 3 replicates of each strain at each concentration both in the presence and absence of S9

NUMBER OF CELLS EVALUATED:
All strains 0.9 to 9 * 10>9

DETERMINATION OF CYTOTOXICITY
- Method: N/A

OTHER EXAMINATIONS:
N/A


OTHER:
Prior to use, the master strains were checked for characteristics, viability and spontaneous reversion rate (all were found to be satisfactory). The amino acid supplemented top agar and the S9-mix used in both experiments was shown to be sterile. The test item formulation was also shown to be sterile. These data are not given in the report.
In order to select appropriate dose levels for use in the main test, a preliminary assay was carried out to determine the toxicity of the test material.

All tester strain cultures should exhibit a characteristic number of spontaneous revertants per plate in the vehicle and untreated controls (negative controls). Acceptable ranges are presented as follows:
TA1535: 7 to 40
TA100: 60 to 200
TA1537: 2 to 30
TA98: 8 to 60
WP2uvrA: 10 to 60
Evaluation criteria:
There are several criteria for determining a positive result. Any, one, or all of the following can be used to determine the overall result of the study:
1 . A dose-related increase in mutant frequency over the dose range tested (De Serres and Shelby, 1979).
2. A reproducible increase at one or more concentrations.
3. Biological relevance against in-house historical control ranges.
4. Statistical analysis of data as determined by UKEMS (Mahon et al, 1989).
5. Fold increase greater than two times the concurrent solvent control for any tester strain (especially if accompanied by an out-of-historical range response (Cariello and Piegorsch, 1996)).
A test item will be considered non-mutagenic (negative) in the test system if the above criteria are not met.
Although most experiments will give clear positive or negative results, in some instances the data generated will prohibit making a definite judgment about test item activity. Results of this type will be reported as equivocal.
Statistics:
MAHON, G.A.T., et al (1989). Analysis of data from microbial colony assays. In: KIRKLAND D.J., (eds.). Statistical Evaluation of Mutagenicity Test Data: UKEMS sub-committee on guidelines for mutagenicity testing. Cambridge University Press Report, pp. 26-65.

Results and discussion

Test resultsopen allclose all
Species / strain:
S. typhimurium TA 1535, TA 1537, TA 98 and TA 100
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
Species / strain:
E. coli WP2 uvr A
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
Remarks on result:
other: all strains/cell types tested
Remarks:
Migrated from field 'Test system'.

Any other information on results incl. tables

The maximum dose level of the test item in the first mutation test was selected as the maximum recommended dose level of 5000 µg/plate. In the first mutation test there was no visible reduction in the growth of the bacterial background lawns noted at any dose level, either in the presence or absence of S9-mix. Consequently the same maximum dose level was used in the second mutation test. Similarly there was no visible reduction in the growth of the bacterial backgroiund lawn at any dose level, either in the presence or absence of metabolic activation, in the second mutation test. A test item precipitate (globular in appearance) was observed under an inverted microscope at 1500 µg/plate and by eye at 5000 µg/plate, this observation did not prevent the scoring of revertant colonies.

There were no significant increases in the frequency of revertant colonies recorded for any of the bacterial strains, with any dose of the test item, either with or without S9-mix in the first mutation test. Similarly, no significant increases in the frequency of revertant colonies were recorded for any of the bacterial strains, with any dose of the test item, either with or without S9-mix in the second mutation test.

All of the positive control chemicals used in the test induced marked increases in the frequency of revertant colonies thus confirming the activity of the S9-mix and the sensitivity of the bacterial strains.

Applicant's summary and conclusion

Conclusions:
Interpretation of results (migrated information):
negative

The test item was considered to be non-mutagenic under the conditions of this test.
Executive summary:

Introduction

The test method was designed to be compatible with the guidelines for bacterial mutagenicity testing published by the major Japanese Regulatory Authorities including METI, MHLW and MAFF, the OECD Guidelines for Testing of Chemicals No. 471 "Bacterial Reverse Mutation Test", Method B13/14 of Commission Regulation (EC) number 440/2008 of 30 May 2008 and the USA, EPA OCSPP harmonized guideline - Bacterial Reverse Mutation Test.

Methods

Salmonella typhimurium strains TAl53 5, TA1537, TA98 and TAl00 and Escherichia coli strain WP2uvrA were treated with the test item using the Ames plate incorporation method at up to eight dose levels, in triplicate, both with and without the addition of a rat liver homogenate metabolizing system (10% liver S9 in standard co—factors). The dose range for the range-finding test was predetermined and was 1.5 to 5000 µg/plate. The experiment was repeated on a separate day using fresh cultures of the bacterial strains and fresh test item formulations. The dose range was amended, following the results of the range-findi ng test, and was 50 to 5000 µg/plate.

Seven test item dose levels were selected in the main test in order to achieve both four non-toxic dose levels and the potential toxic limit of the test item following the results from the first mutation test.

Results

The vehicle (tetrahydrofuran) control plates gave counts of revertant colonies within the normal range. All of the positive control chemicals used in the test induced marked increases in the frequency of revertant colonies, both with or without metabolic activation. Thus, the sensitivity of the assay and the efficacy of the S9-mix were validated.

The maximum dose level of the test item in the first mutation test was selected as the maximum recommended dose level of 5000 µg/plate. In the first mutation test there was no visible reduction in the growth of the bacterial background lawns noted at any dose level, either in the presence or absence of S9-mix. Consequently the same maximum dose level was used in the second mutation test.

Results from the second mutation test showed the test item inducing no toxicity. A test item precipitate (globular in appearance) was observed under an inverted microscope at 1500 µg/plate and by eye at 5000 µg/plate, this observation did not prevent the scoring of revertant colonies.

There were no significant increases in the frequency of revertant colonies recorded for any of the bacterial strains, with any dose of the test item, either with or without S9-mix in the first mutation test. Similarly, no significant increases in the frequency of revertant colonies were recorded for any of the bacterial strains, with any dose of the test item, either with or without S9-mix in the second mutation test.

Conclusion

The test substance was considered to be non-mutagenic under the conditions of this test.