2-acetyl-3-(4-hexadecoxyphenyl)-1,4-benzoquinone

Genetic toxicity: in vitro

Administrative data

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2018

Report date:

2018

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Version / remarks:

July 21, 1997

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method B.13/14 (Mutagenicity - Reverse Mutation Test Using Bacteria)

Version / remarks:

31 May 2008

Deviations:

no

GLP compliance:

yes

Type of assay:

bacterial reverse mutation assay

Test material

Test material information

Constituent 1

Reference substance name:

2-acetyl-3-(4-hexadecoxyphenyl)-1,4-benzoquinone

EC Number:

947-565-8

Molecular formula:

C30 H42 O4

IUPAC Name:

2-acetyl-3-(4-hexadecoxyphenyl)-1,4-benzoquinone

Method

Species / strain

Species / strain / cell type:

S. typhimurium TA 1535, TA 1537, TA 98, TA 100 and E. coli WP2

Remarks:

E. coli WP2uvrA

Metabolic activation:

with and without

Metabolic activation system:

S9-mix

Test concentrations with justification for top dose:

Dose-range finding test: Eight concentrations, 1.7, 5.4, 17, 52, 164, 512, 1600 and 5000 μg/plate
First mutation experiment: 17, 52, 164, 512, 1600 and 5000 μg/plate., based on the results of the dose-range finding test.
Second mutation experiment: 16, 31, 63, 125, 500 and 2000 μg/plate., based on the results of the dose-range finding test.

Vehicle / solvent:

A solubility test was performed based on visual assessment. The test item could not be dissolved in Milli-Q water, DMSO, ethanol, hexane or acetone. The test item formed a red homogenous suspension in dimethylformamide (DMF) at 25 mg/mL.

Controls

Controls 1

Negative solvent / vehicle controls:

yes

Positive controls:

yes

Positive control substance:

4-nitroquinoline-N-oxide

2-nitrofluorene

sodium azide

methylmethanesulfonate

other: Acridine Mutagen ICR 191

Remarks:

without metabolic activation

Controls 2

Negative solvent / vehicle controls:

yes

Positive controls:

yes

Positive control substance:

other: 2-aminoanthracene

Remarks:

with metabolic activation

Details on test system and experimental conditions:

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 ± 1°C, 150 rpm), until the cultures reached an optical density of 1.0 ± 0.1 at 700 nm (10^9 cells/ml). Freshly grown cultures of each strain were used for a test.
Agar plates: Agar plates (ø 9 cm) contained 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 34.5 - 38.0 °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.

Metabolic Activation System
S9-Fraction: Rat liver microsomal enzymes (S9 homogenate) were obtained from Trinova Biochem GmbH, Giessen, Germany and were prepared from male Sprague Dawley rats that had been injected intraperitoneally with Aroclor 1254 (500 mg/kg body weight).
Each S9 batch was characterized with the mutagens benzo-(a)-pyrene (Sigma) and 2-aminoanthracene, which require metabolic activation, in tester strain TA100 at concentrations of 5 μg/plate and 2.5 μg/plate, respectively.
Preparation of S9-Mix: S9-mix was prepared immediately before use and kept on ice. 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 Milli-Q water (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.

TEST DESIGN

Dose-range Finding Test
Selection of an adequate range of doses was based on a dose-range finding test with the strains TA100 and WP2uvrA, both with and without 5% (v/v) S9-mix. Eight concentrations, 1.7, 5.4, 17, 52, 164, 512, 1600 and 5000 µg/plate were tested in triplicate. The highest concentration of V134434 used in the subsequent mutation assays was 5000 µg/plate or the level at which the test item exhibited limited solubility.

Mutation Assay
All mutation experiments were performed following the direct plate method. At least five different doses (increasing with approximately half-log steps) of the test item were tested in triplicate in each strain. The above mentioned dose-range finding study with the two tester strains TA100 and WP2uvrA, is reported as a part of the first mutation experiment. In the second part of this experiment, the test item was tested both in the absence and presence of 5% (v/v) S9-mix in the tester strains TA1535, TA1537 and TA98. In a follow-up experiment with additional parameters, the test item was tested both in the absence and presence of 10% (v/v) S9-mix in all tester strains.
The negative control (vehicle) 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, 0.05 to 0.2 mL of a dilution of the test item in DMF, 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 ± 4 h. After this period revertant colonies (histidine independent (His+) for Salmonella typhimurium bacteria and tryptophan independent (Trp+) 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:

Guideline test conditions.

Evaluation criteria:

In addition to the criteria stated below, any increase in the total number of revertants should be evaluated for its biological relevance including a comparison of the results with the historical control data range.
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 control, and the total number of revertants in tester strains TA1535, TA1537 or TA98 is not greater than three (3) times the concurrent control.
b) The negative response should be reproducible in at least one follow up 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 control.
b) In case a repeat experiment is performed when a positive response is observed in one of the tester strains, the positive response should be reproducible in at least one follow up experiment.

Statistics:

No formal hypothesis testing was done.

Results and discussion

Test results

Test results 1

Species / strain:

S. typhimurium TA 100

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

Positive controls validity:

valid

Test results 2

Species / strain:

S. typhimurium TA 1535

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not examined

Positive controls validity:

valid

Test results 3

Species / strain:

S. typhimurium TA 1537

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not examined

Positive controls validity:

valid

Test results 4

Species / strain:

S. typhimurium TA 98

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Remarks:

only cytotoxic in the absence of S9-mix

Vehicle controls validity:

valid

Untreated negative controls validity:

not examined

Positive controls validity:

valid

Test results 5

Species / strain:

E. coli WP2 uvr A

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not examined

Positive controls validity:

valid

Additional information on results:

All bacterial strains showed no response over the entire dose-range, i.e. no significant dose-related increase in the number of revertants in two experiments.
The negative 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.
The 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, except the response for WP2uvrA in the presence of S9-mix in the second experiment. The purpose of the positive control is as a reference for the test system, where a positive response is required to check if the test system functions correctly. Since the value was above the historical control data range, this deviation in the mean plate count of the positive control had no effect on the results of the study.

Applicant's summary and conclusion

Conclusions:

In conclusion, based on the results of this study it is concluded that V134434 is not mutagenic in the Salmonella typhimurium and in the Escherichia coli reverse mutation assay.

Executive summary:

The objective of this study was to determine the potential of V134434 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). 

The study procedures described in this report were based on the most recent OECD 471 (1997) and EC B.13/14(2008) guidelines.

Batch v134434/CA of V134434 was an orange-red powder. The vehicle of the test item was dimethylformamide (DMF).

In the dose-range finding test, the test item was tested with the direct plate method up to concentrations of 5000 µg/plate in the absence and presence of S9-mix in the strains TA100 and WP₂uvrA. V134434 precipitated on the plates at dose levels of 1600 and 5000 μg/plate. No cytotoxicity was observed: 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. Results of this dose-range finding test were reported as part of the first mutation assay.

Based on the results of the dose-range finding test, the test item was tested in the first mutation assay with the direct plate method at a concentration range of 17 to 5000 µg/plate in the absence and presence of 5% (v/v) S9-mix in the tester strains TA1535, TA1537 and TA98. V134434 precipitated on the plates at dose levels of 512 μg/plate and higher. V134434 was not cytotoxic at the concentrations tested: 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 a follow-up experiment of the assay with additional parameters, the test item was tested with the direct plate method at a concentration range of 16 to 2000 µg/plate in the absence and presence of 10% (v/v) S9-mix in the tester strains TA1535, TA1537, TA98, TA100 and WP₂uvrA. The test item precipitated on the plates at dose levels of 500 μg/plate and higher. Cytotoxicity was only observed in tester strain TA98 in the absence of S9-mix at the highest tested concentration.   

V134434 did not induce a dose-related increase in the number of revertant (His⁺) colonies in any of the four tester strains (TA1535, TA1537, TA98 and TA100) nor in the number of revertant (Trp⁺) colonies in the tester strain WP₂uvrA, both in the absence and presence of S9-metabolic activation. These results were confirmed in a follow-up experiment.

In this study, acceptable responses were obtained for the negative and strain-specific positive control items 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 V134434 is not mutagenic in the Salmonella typhimurium reverse mutation assay and in the Escherichia coli reverse mutation assay.