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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:
October 26 - December 12, 2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Justification for type of information:
Justification of concentrations:
Selection of the concentration range was done on the basis of a Solubility Test and a Concentration Range Finding Test (Informatory Toxicity Test).

Data source

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

Materials and methods

Test guideline
Qualifier:
according to guideline
Guideline:
OECD Guideline 471 (Bacterial Reverse Mutation Assay)
Version / remarks:
July, 1997
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Type of assay:
bacterial reverse mutation assay

Test material

Constituent 1
Reference substance name:
Carbonic acid disodium salt, reaction products with aniline, 4-nitrobenzenamine, p-phenylenediamine, sodium sulfide, sulfur and p-toluidine
EC Number:
290-904-3
EC Name:
Carbonic acid disodium salt, reaction products with aniline, 4-nitrobenzenamine, p-phenylenediamine, sodium sulfide, sulfur and p-toluidine
Cas Number:
90268-98-7
Molecular formula:
Molecular formula is not available
IUPAC Name:
Carbonic acid disodium salt, reaction products with aniline, 4-nitrobenzenamine, p-phenylenediamine, sodium sulfide, sulfur and p-toluidine
Test material form:
solid: particulate/powder
Details on test material:
Test item: Yellow 22
Appearance: ocher clay, solid
CAS No. 90268-98-7
EC No. 290-904-3
Storage: room temperature

Method

Target gene:
In addition to histidine and tryptophan mutation, each strain has additional mutations which enhance its sensitivity to mutagens. The uvrB (uvrA) strains are defective in excision repair. It causes the strains to be more sensitive to the mutagenic and lethal effects of a wide variety of mutagens because they cannot repair DNA damages. rfa mutation increases the permeability of the bacterial lipopolysaccharide wall for larger molecules. The plasmid pKM101 (TA98, TA100) carries the muc+ gene which participates in the error-prone "SOS" DNA repair pathway induced by DNA damage. This plasmid also carries an ampicillin resistance transfer factor (R-factor) which is used to identify its presence in the cell. The Escherichia coli strain used in this test (WP2uvrA) is also defective in DNA excision repair.
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:
cofactor-supplemented post-mitochondrial fraction: S9
Test concentrations with justification for top dose:
The concentrations investigated in the Initial and Confirmatory Mutation Tests:
5000, 1600, 500, 160, 50, 16 and 5 µg/plate.
(reported as corrected concentrations considering the dye content of the test item)
Vehicle / solvent:
Name: Dimethyl sulfoxide (DMSO)
Supplier: SIGMA-ALDRICH
Batch Numbers: SZBF3070V and SZBG0830V
Retest date: 18 October 2018 and 08 March 2019
Storage: Room temperature
Controls
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
True negative controls:
yes
Positive controls:
yes
Positive control substance:
9-aminoacridine
sodium azide
methylmethanesulfonate
other: 4-Nitro-1,2-phenylenediamine, NPD;2-aminoanthracene, 2AA
Details on test system and experimental conditions:
Tester strains: Salmonella typhimurium TA98, TA100, TA1535, TA1537 and Escherichia coli WP2 uvrA were obtained from:
Supplier: Trinova Biochem GmbH ;Manufacturer: MOLTOX INC., P.O. BOX 1189; BOONE, NC 28607 USA.
Frozen stock cultures were prepared from the disc cultures.

Storage of Tester Strains
The strains are stored at -80 ± 10ºC in the Laboratory of TOXI-COOP ZRT. in the form of lyophilized discs and in frozen permanent copies. Frozen permanent cultures of the tester strains are prepared from fresh, overnight cultures to which DMSO (8 % (v/v)) is added as a cryoprotective agent.

Confirmation of Phenotypes of Tester Strains
The phenotypes of the tester strains used in the bacterial reverse mutation assays with regard to membrane permeability (rfa), UV sensitivity (uvrA and uvrB), ampicillin resistance (amp), as well as spontaneous mutation frequencies are checked regularly according to Ames et al.
Established procedures (Standard Operating Procedures) for the preparations of each batch of frozen stock culture and raw data and reports of phenotype confirmation are stored in the Laboratory of TOXI-COOP ZRT.

Spontaneous Reversion of Tester Strains
Each tester strain reverts spontaneously at a frequency that is characteristic for the strain. Spontaneous reversions of the test strains to histidine or tryptophan prototrophs are measured routinely in mutagenicity experiments and expressed as the number of spontaneous revertants per plate.
Procedure for Bacterial Cultures
The frozen bacterial cultures were thawed at room temperature and 200 µL inoculum was used to inoculate each 50 mL of Nutrient Broth No. 2 for the overnight cultures in the assay. The cultures were incubated for approximately 11-13 hours in a 37oC Benchtop Incubator Shaker.
Viability and the Cell Count of the Testing Bacterial Cultures
The viability of each testing culture was determined by plating 0.1 mL of the 10-5, 10-6, 10-7 and 10-8 dilutions of cultures on nutrient agar plates The viable cell number of the cultures was determined by manual colony counting.
Media
The Minimal Glucose Agar (MGA) Plates
Ready-to-use minimal glucose agar (MGA) plates were used in the study. The origin of the ready-to use MGA plates:
Supplier: VWR International;
Manufacturer: Merck Life Science GmbH, Germany.
Certificates of Analysis* were obtained from the supplier.
Typical composition (g/1000 mL) of MGA plates:
Glucose 20.0 g
Magnesium sulfate 0.2 g
Citric acid 2.0 g
di-Potassium hydrogenphosphate 10.0 g
Sodium ammonium hydrogenphosphate 3.5 g
Agar agar 13.0 g
* Batch No.: 140149; Expiry date: 26 December 2016; (used in the Informatory Toxicity Test)
139475; Expiry date: 13 November 2016; (used in the Initial and Confirmatory Mutation Tests)

Nutrient Broth No. 2

Nutrient broth No. 2. 25.0 g
Ultrapure water ad 1000.0 mL
Sterilization for 20 minutes was performed at 121˚C in an autoclave.

Nutrient Agar 20.0 g
Ultrapure water ad 1000.0 mL
Sterilization for 20 minutes was performed at 121˚C in an autoclave.
Top Agar for Salmonella typhimurium Strains
Agar solution:
Agar Bacteriological 4.0 g
NaCl 5.0 g
Ultrapure water ad 1000.0 mL
Sterilization for 20 minutes was performed at 121˚C in an autoclave.

Histidine – Biotin solution (0.5 mM):
D-Biotin 122.2 mg
L-Histidine•HCl H2O 104.8 mg
Ultrapure water ad 1000.0 mL
Sterilization was performed by filtration through a 0.22 µm membrane filter.

Complete Top Agar for Salmonella typhimurium strains:
Histidine – Biotin solution (0.5 mM) 100.0 mL
Agar solution 900.0 mL

Top Agar for Escherichia coli Strain

Tryptophan solution (2 mg/mL):
L-Tryptophan 2000.0 mg
Ultrapure water ad 1000.0 mL
Sterilization was performed by filtration through a 0.22 µm membrane filter.

Complete Top Agar for Escherichia coli strain:
Nutrient Broth by 5.4.2 50.0 mL
Tryptophan solution (2 mg/mL) 2.5 mL
Agar solution by 5.4.4 947.5 mL

Metabolic Activation System

The test bacteria were also exposed to the test item in the presence of an appropriate metabolic activation system, which is a cofactor-supplemented post-mitochondrial fraction (S9).

Rat Liver S9 Fraction

The S9 fraction of Phenobarbital (PB) and β-naphthoflavone (BNF)-induced rat liver was provided by Trinova Biochem GmbH (Rathenau Str. 2; D-35394 Giessen, Germany; Manufacturer: MOLTOX INC., P.O. BOX 1189; BOONE, NC 28607 USA).

The Quality Control & Production Certificate of each lot of S9 was obtained from the supplier. The original Quality Control & Production Certificates of rat liver S9 are stored in the Laboratory of TOXI-COOP ZRT. The copies of the quality control certificates of the used S9 lots are given in Appendix VIII. The following lots of the S9 were applied:
Lot Number: 3647; Expiry date: June 09, 2018; Protein content: 40.2 mg/mL
(used in the Informatory Toxicity Test);
Lot Number: 3662; Expiry date: July 07, 2018; Protein content: 40.5 mg/mL
(used in all experimental phases of the study).

The S9 Mix (with Rat Liver S9)

Salt solution for S9 Mix Final concentration in S9 Mix
NADP Na 7.66 g 4 mM
D-glucose-6 phosphate Na 3.53 g 5 mM
MgCl2 1.90 g 8 mM
KCl 6.15 g 33 mM
Ultrapure water ad 1000 mL
Sterilized by filtration through a 0.22 µm membrane filter.

The complete S9 Mix was freshly prepared containing components as follows:
Ice cold 0.2 M sodium phosphate-buffer, pH 7.4 500 mL
Rat liver homogenate (S9) 100 mL
Salt solution for S9 Mix 400 mL
The S9 Mix (containing 10 % S9) was kept in an ice bath before it was added to the culture medium.

Sodium Phosphate Buffer (0.2 M, pH 7.4)

Solution A:
Na2HPO4 x 12H2O 71.63 g
Ultrapure water ad 1000 mL
Solution B:
NaH2PO4 x H2O 27.6 g
Ultrapure water ad 1000 mL

Solution A 880 mL
Solution B 120 mL*
* The components were mixed in the above ratio; thereafter the pH was checked and corrected. The correction was performed with admixture of the solution A or B.
After the pH setting the sterilization was performed by filtration through a 0.22 µm membrane filter.
Rationale for test conditions:
Justification of concentrations:
Choice of the concentrations was done on the basis of a Solubility Test and a concentration Range Finding Test (Informatory Toxicity Test).
Based on the solubility test, the stock solution with a concentration of 50 mg/mL was prepared in the vehicle and diluted in at least 6 steps by factor of approximately √10.
The revertant colony numbers and the inhibition of the background lawn of auxotrophic cells of two of the tester strains (Salmonella typhimurium TA98, TA100) were determined at the concentrations of 5000, 1600, 500, 160, 50, 16 and 5 µg/plate of the test item.
The revertant colony numbers of vehicle control plates in both strains with and without S9 Mix were in line with the corresponding historical control data ranges. The positive control treatments showed the expected, biological relevant increases in induced revertant colonies in both tester strains.
Evaluation criteria:
The colony numbers on the controls (untreated, vehicle, positive) and the test plates were determined (counted manually), the mean values and appropriate standard deviations and mutation rates were calculated.
A test item is considered mutagenic if:
- a dose–related increase in the number of revertants occurs and/or;
- a reproducible biologically relevant positive response for at least one of the dose groups occurs in at least one strain with or without metabolic activation.

An increase is considered biologically relevant if:
- in strain Salmonella typhimurium TA100 the number of reversions is at least twice as high as the reversion rate of the vehicle control,
- in strain Salmonella typhimurium TA98, TA1535, TA1537 and Escherichia coli WP2 uvrA the number of reversions is at least three times higher than the reversion rate of the vehicle control.

According to the guidelines, the biological relevance of the results is the criterion for the interpretation of results, a statistical evaluation of the results is not regarded as necessary.

Criteria for a Negative Response:
A test item is considered non-mutagenic if it produces neither a dose-related increase in the number of revertants nor a reproducible biologically relevant positive response at any of the dose groups, with or without metabolic activation.
Statistics:
The mean values and appropriate standard deviations and mutation rates were calculated by EXCEL software.

Results and discussion

Test resultsopen allclose all
Key result
Species / strain:
S. typhimurium TA 98
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 100
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Key result
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:
valid
Positive controls validity:
valid
Key result
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:
valid
Positive controls validity:
valid
Key result
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:
valid
Positive controls validity:
valid
Additional information on results:
No substantial increases were observed in revertant colony numbers of any of the five test strains following treatment at any concentration level, either in the presence or absence of metabolic activation (S9 Mix) in the performed experiments.
In the performed experiments, sporadically increased revertant colony numbers were observed. These increases did not show a dose-response relationship, were of minor intensity, and all of the increases remained far below the biologically relevant thresholds for being positive. The obtained increases were therefore considered as biologically not relevant, being in the range of the biological variability of the applied test system.
The highest revertant colony number increase was observed in the Initial Mutation Test (Plate Incorporation Test) in S. typhimurium TA98 strain at 160 μg/plate, in the absence of metabolic activation ( S9). This value however remained in the range of the corresponding vehicle historical control data and additional concentration related increase in revertant colony counts was not noticed. The mutation rate was 2.14, which was far below the genotoxicological threshold for being positive.
In the Initial and Confirmatory Mutation Tests, unequivocal inhibitory effect of the test item on bacterial growth was observed. In the Initial Mutation Test inhibitory effect of the test item was observed in the S. typhimurium TA1537 strain only, in the absence and also in the presence of exogenous metabolic activation. In the Confirmatory Mutation Test unequivocal inhibition was noticed in all examined Salmonella typhimurium strains, mostly in the absence of exogenous metabolic activation. The cytotoxicity was indicated by absent or decreased revertant colony counts (some of them below the corresponding historical control data ranges) and/or affected background lawn development: reduced or slightly reduced background lawn. For the cytotoxicity tendency (it did not show a clear dose-dependent tendency), the effect of precipitate formation was supposed. The cytotoxicity results are summarized in Table 7. The table contains the unequivocal results where the obtained revertant colony numbers were below the vehicle (in some cases below the corresponding historical control data ranges), and/or affected background lawn development occurred. All of the further observed lower revertant colony numbers (when compared to the revertant colony numbers of the corresponding vehicle control) remained in the range of the biological variability of the applied test system.
In general, 500 µg/plate was considered as lowest concentration showing cytotoxicity.

When evaluated by naked eye, non-interfering test item precipitate was noticed after about 48 hours incubation on the plates in the examined strains at the concentration of 5000 µg/plate in absence and in the presence of S9 following the plate incorporation and pre-incubation procedures.
For confirmation of manual evaluations (made by naked eye) all of the plates were checked for colony and background lawn development by microscope at 40X magnification. At this magnification test item particles were noticed down to and including the concentration of 50 µg/plate (±S9 Mix), following the plate incorporation test and down to and including the concentration of 16 µg/plate (±S9 Mix) following the pre-incubation procedure.

Any other information on results incl. tables

Summary of the Inhibitory Tendencies in the Initial and Confirmatory Mutation Tests

Initial Mutation Test

Concentrations

(µg/plate)

Salmonella typhimurium

Escherichia coliWP2uvrA

TA98

TA100

TA1535

TA1537

‑S9

+S9

‑S9

+S9

‑S9

+S9

‑S9

+S9

‑S9

+S9

5000

< B

< B

1600

SB

SB

500

SB

SB

160

50

16

5

Confirmatory Mutation Test

Concentrations

(µg/plate)

Salmonella typhimurium

Escherichia coliWP2uvrA

TA98

TA100

TA1535

TA1537

‑S9

+S9

‑S9

+S9

‑S9

+S9

‑S9

+S9

‑S9

+S9

5000

SB

<< 

SB

SB

<< B

1600

< SB

SB

< SB

<< B

500

< SB

<< SB

< SB

B0

160

50

16

5

<:         Revertant colony numbers below the vehicle control data range

<<:      Revertant colony numbers below the vehicle and historical control data ranges

B:         Reduced background lawn development

SB:        Slightly reduced background lawn development

B0:        Reduced background lawn development and absent revertant colonies

 

Applicant's summary and conclusion

Conclusions:
The test item has no mutagenic activity on the applied bacterium tester strains under the test conditions used in this study.
Executive summary:

The test item dissolved in DMSO was tested with regard to a potential mutagenic activity using the Bacterial Reverse Mutation Assay. The experiments were carried out using histidine-requiring auxotroph strains of Salmonella typhimurium (Salmonella typhimuriumTA98, TA100, TA1535 and TA1537), and the tryptophan-requiring auxotroph strain of Escherichia coli (Escherichia coliWP2uvrA) in the presence and absence of a post mitochondrial supernatant (S9) prepared from livers of Phenobarbital/b-naphthoflavone-induced rats.

The study included a Preliminary Solubility Test, a Preliminary Concentration Range Finding Test (Informatory Toxicity Test), an Initial Mutation Test (Plate Incorporation Test), and a Confirmatory Mutation Test (Pre-Incubation Test. The following concentrations of the test item were prepared and investigated in the Initial and Confirmatory Mutation Tests (reported as corrected concentrations considering the dye content of the test item)

: 5000;1600; 500; 160; 50; 16 and 5 µg/plate. The selection of the concentration range was based on the recommendations in OECD 471 guideline. In the Initial Mutation Test inhibitory effect of the test item was observed in the S. typhimuriumTA1537 strain in the absence and also in the presence of exogenous metabolic activation. In the Confirmatory Mutation Test unequivocal inhibition was noticed in all examined Salmonella typhimurium strains, mostly in the absence of exogenous metabolic activation. The inhibitory effect was indicated by absent or decreased revertant colony counts (some of them below the corresponding historical control data ranges) and affected background lawn development: reduced or slightly reduced background lawn. In general, 500 µg/plate was considered as lowest concentration showing cytotoxicity. The revertant colony numbers of vehicle control (dimethyl sulfoxide (DMSO) plates with and without S9 Mix demonstrated the characteristic mean number of spontaneous revertants that was in line with the corresponding historical control data ranges.

The reference mutagen treatments (positive controls) showed the expected, biological relevant increases (more than 3-fold increase)in induced revertant colonies and the number of revertants fell in the corresponding historical control ranges, thereby meeting the criteria for the positive control in all experimental phases, in all tester strains. No biologically relevant increases were observed in revertant colony numbers of any of the five test strains following treatment with the test item at any concentration level, either in the presence or absence of metabolic activation (S9 Mix) in the performed experiments.

In conclusion, the test item has no mutagenic activity on the applied bacterium tester strains.