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Genetic toxicity: in vitro

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Administrative data

Endpoint:
in vitro gene mutation study in bacteria
Type of information:
experimental study
Adequacy of study:
key study
Study period:
22 to 29 March 2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
conducted under GLP conditions

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2018
Report date:
2018

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to guideline
Guideline:
OECD Guideline 471 (Bacterial Reverse Mutation Assay)
Version / remarks:
1997
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method B.13/14 (Mutagenicity - Reverse Mutation Test Using Bacteria)
Version / remarks:
2008
Deviations:
no
GLP compliance:
yes
Type of assay:
bacterial reverse mutation assay

Test material

Constituent 1
Chemical structure
Reference substance name:
4-(dodecylthio)-4-methylpentan-2-one
Cas Number:
855737-35-8
Molecular formula:
C18H36OS
IUPAC Name:
4-(dodecylthio)-4-methylpentan-2-one
Test material form:
liquid

Method

Target gene:
Histidine
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:
Rat liver microsomal enzymes (S9 homogenate) was obtained from Trinova Biochem GmbH,Giessen, Germany and was prepared from male Sprague Dawley rats that had been injected intraperitoneal with Aroclor 1254 (500 mg/kg body weight).
Each S9 batch is characterized with the mutagens Benzo-(a)-pyrene and 2-aminoanthracene, which require metabolic activation, in tester strain TA100 at concentrations of 5 μg/plate and 2.5 μg/plate, respectively.

S9-mix was prepared immediately before use and kept refrigerated. S9-mix contained per 10 mL: 30 mg NADP (Randox Laboratories Ltd., Crumlin, United Kingdom) and 15.2 mg glucose-6-phosphate (Roche Diagnostics, Mannheim, Germany) in 5.5 mL or 5.0 mL Milli-Q water (first or second experiment respectively) (Millipore Corp., Bedford, MA., USA); 2 mL 0.5 M sodium phosphate buffer pH 7.4; 1 mL 0.08 M MgCl2 solution (Merck); 1 mL 0.33 M KCl solution (Merck). The above solution was filter (0.22 μm)-sterilized. To 9.5 mL of S9-mix components 0.5 mL S9-fraction was added (5% (v/v) S9-fraction) to complete the S9-mix in the first experiment and to 9.0 mL of S9-mix components 1.0 mL S9-fraction was added (10% (v/v) S9-fraction) to complete the S9-mix in the second experiment.
Test concentrations with justification for top dose:
In the first experiment, seven concentrations of the test item, 5.4, 17, 52, 164, 512, 1600 and 5000 μg/plate were tested in triplicate in the tester strains TA1535, TA1537, TA98, TA100 and WP2uvrA.
Based on the results of the first mutation assay, five doses (increasing with approximately half-log steps) of the test item were selected and tested in triplicate in each strain in the second experiment.
The highest concentration of the test item used in the second mutation assay was 5 mg/plate.
Vehicle / solvent:
Ethanol
Controls
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
4-nitroquinoline-N-oxide
2-nitrofluorene
sodium azide
methylmethanesulfonate
other: ICR-191 and 2-aminoanthracene
Details on test system and experimental conditions:
Test system: Salmonella typhimurium bacteria and Escherichia coli bacteria
Source: Trinova Biochem GmbH, Germany (Master culture from Dr.Bruce N. Ames) (TA1535, TA1537, TA98, TA100) and (Master culture from The National Collections of Industrial and Marine Bacteria, Aberdeen, UK) (WP2uvrA)

Cell culture:
- Preparation of bacterial cultures: Samples of frozen stock cultures of bacteria were transferred into enriched nutrient broth (Oxoid LTD, Hampshire, England) and incubated in a shaking incubator (37°C, 150 rpm), until the cultures reached an optical density of 1.0 ± 0.1 at 700 nm (109 cells/mL). Freshly grown cultures of each strain were used for testing.
- Agar plates: Agar plates (ø 9 cm) containing 25 mL glucose agar medium. Glucose agar medium contained per liter: 18 g purified agar (Oxoid LTD) in Vogel-Bonner Medium E, 20 g glucose (Fresenius Kabi, Bad Homburg, Germany). The agar plates for the test with the Salmonella typhimurium strains also contained 12.5 μg/plate biotin (Merck) and 15 μg/plate histidine (Sigma) and the agar plates for the test with the Escherichia coli strain contained 15 μg/plate tryptophan (Sigma).
- Top agar: Milli-Q water containing 0.6% (w/v) bacteriological agar (Oxoid LTD) and 0.5% (w/v) sodium chloride (Merck) was heated to dissolve the agar. Samples of 3 mL top agar were transferred into 10 mL glass tubes with metal caps. Top agar tubes were autoclaved for 20 min at 121 ± 3°C.
- Environmental conditions: All incubations were carried out in a controlled environment at a temperature of 37.0 ± 1.0°C (actual range 36.3 - 38.3°C). The temperature was continuously monitored throughout the experiment. Due to addition of plates (which were at room temperature) to the incubator or due to opening and closing the incubator door, temporary deviations from the temperature may occur. Based on laboratory historical data these deviations are considered not to affect the study integrity.

Experimental procedure:
The test item was tested both in the absence and presence of S9-mix in each strain, in two independent experiments.
The vehicle control and relevant positive controls were concurrently tested in each strain in the presence and absence of S9-mix.
Top agar in top agar tubes was melted by heating to 45 ± 2°C. The following solutions were successively added to 3 mL molten top agar: 0.1 mL of a fresh bacterial culture (109 cells/mL) of one of the tester strains, 0.1 mL of a dilution of the test item in ethanol, and either 0.5 mL S9-mix (in case of activation assays) or 0.5 mL 0.1 M phosphate buffer (in case of non-activation assays). The ingredients were mixed on a Vortex and the content of the top agar tube was poured onto a selective agar plate. After solidification of the top agar, the plates were inverted and incubated in the dark at 37.0 ± 1.0 °C for 48 h. After this period
revertant colonies (histidine independent for Salmonella typhimurium bacteria and tryptophan independent for Escherichia coli) were counted.

Colony counting:
The revertant colonies were counted automatically with the Sorcerer Colony Counter. Plates with sufficient test item precipitate to interfere with automated colony counting were counted manually. Evidence of test item precipitate on the plates and the condition of the bacterial background lawn were evaluated when considered necessary, macroscopically and/or microscopically by using a dissecting microscope.
Rationale for test conditions:
Recommended test system in international guidelines (e.g. OECD, EC and METI).
Evaluation criteria:
A test item is considered negative (not mutagenic) in the test if:
a) The total number of revertants in tester strain TA100 or WP2uvrA is not greater than two (2) times the concurrent vehicle control, and the total number of revertants in tester strains TA1535, TA1537 or TA98 is not greater than three (3) times the concurrent vehicle control.
b) The negative response should be reproducible in at least one independently repeated experiment.

A test item is considered positive (mutagenic) in the test if:
a) The total number of revertants in tester strain TA100 or WP2uvrA is greater than two (2) times the concurrent control, or the total number of revertants in tester strains TA1535, TA1537 or TA98 is greater than three (3) times the concurrent vehicle control.
b) In case a positive response will be repeated, the positive response should be reproducible in at least one independently repeated experiment.
Statistics:
A statistical analysis of the data is not required.

Results and discussion

Test results
Key result
Species / strain:
other: 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
Positive controls validity:
valid
Additional information on results:
All bacterial strains showed negative responses over the entire dose-range, i.e. no significant dose-related increase in the number of revertants in two independently repeated experiments.
The negative and strain-specific positive control values were within the laboratory historical control data ranges indicating that the test conditions were adequate and that the metabolic activation system functioned properly.

Results of second mutation experiment:
Precipitate:
Precipitation of the test item on the plates was observed at the start of the incubation period at concentrations of 512 μg/plate and upwards and at 1600 and 5000 μg/plate at the end of the incubation period.

Toxicity:
The bacterial background lawn was not reduced at any of the concentrations tested and no biologically relevant decrease in the number of revertants was observed.
In tester strain TA1537 (absence of S9-mix), a fluctuation in the number of revertant colonies below the laboratory historical control data range was observed. However, since no doserelationship was observed, this reduction is not considered to be caused by toxicity of the test item. It is more likely this reduction is caused by incidental fluctuation in the number of revertant colonies.

Mutagenicity:
No increase in the number of revertants was observed upon treatment with GR-87-7596 under all conditions tested.

Any other information on results incl. tables

First main experiment results:

Precipitate:

Precipitation of the test item on the plates was observed at the start of the incubation period at concentrations of 512 μg/plate and upwards and at 5000 μg/plate at the end of the incubation period.

Toxicity:

To determine the toxicity of the test item, the reduction of the bacterial background lawn, the increase in the size of the microcolonies and the reduction of the revertant colonies were examined.

No reduction of the bacterial background lawn and no biologically relevant decrease in the number of revertants were observed.

Mutagenicity:

No increase in the number of revertants was observed upon treatment with GR-87-7596 under all conditions tested.

Applicant's summary and conclusion

Conclusions:
In conclusion, based on the results of this study it is concluded that GR-87-7596 is not mutagenic in the Salmonella typhimurium reverse mutation assay and in the Escherichia coli reverse mutation assay.
Executive summary:

The objective of this study was to determine the potential of GR-87-7596 and/or its metabolites to induce reverse mutations at the histidine locus in several strains of Salmonella typhimurium (S. typhimurium; TA98, TA100, TA1535, and TA1537), and at the tryptophan locus of Escherichia coli (E. coli) strain WP2uvrA in the presence or absence of an exogenous mammalian metabolic activation system (S9-mix).

The study procedures described in this report were based on the most recent OECD, EC and METI guidelines.

Batch 4 of GR-87-7596 was a yellow liquid. The vehicle of the test item was ethanol.

In the first mutation assay, the test item was tested up to concentrations of 5000 μg/plate in the absence and presence of 5% (v/v) S9-mix. The test item precipitated on the plates at the dose level of 5000 μg/plate. The bacterial background lawn was not reduced at any of the concentrations tested and no biologically relevant decrease in the number of revertants was observed.

In the second mutation assay, the test item was tested up to concentrations of 5000 μg/plate in the absence and presence of 10% (v/v) S9-mix. The test item precipitated on the plates at dose levels of 1600 and 5000 μg/plate. The bacterial background lawn was not reduced at any of the concentrations tested and no decrease in the number of revertants was observed.

GR-87-7596 did not induce a significant dose-related increase in the number of revertant (His+) colonies in each of the four tester strains (TA1535, TA1537, TA98 and TA100) and in the number of revertant (Trp+) colonies in tester strain WP2uvrA both in the absence and presence of S9-metabolic activation. These results were confirmed in an independently repeated experiment.

In this study, the negative and strain-specific positive control values were within the laboratory historical control data ranges indicating that the test conditions were adequate and that the metabolic activation system functioned properly.

In conclusion, based on the results of this study it is concluded that GR-87-7596 is not mutagenic in the Salmonella typhimurium reverse mutation assay and in the Escherichia coli reverse mutation assay.