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

Test material

Constituent 1
Chemical structure
Reference substance name:
2-[4-[(hexahydro-2,4,6-trioxo-5-pyrimidyl)azo]phenyl]-6-methylbenzothiazole-7-sulphonic acid, compound with 2,2',2''-nitrilotris[ethanol] (1:1)
EC Number:
265-314-4
EC Name:
2-[4-[(hexahydro-2,4,6-trioxo-5-pyrimidyl)azo]phenyl]-6-methylbenzothiazole-7-sulphonic acid, compound with 2,2',2''-nitrilotris[ethanol] (1:1)
Cas Number:
65036-46-6
Molecular formula:
C18H13N5O6S2.C6H15NO3
IUPAC Name:
2-[4-[(hexahydro-2,4,6-trioxo-5-pyrimidyl)azo]phenyl]-6-methylbenzothiazole-7-sulphonic acid, compound with 2,2',2''-nitrilotris[ethanol] (1:1)
Test material form:
liquid

Method

Target gene:
Histidine operon
Species / strain
Species / strain / cell type:
S. typhimurium TA 1535, TA 1537, TA 98, TA 100 and TA 102
Details on mammalian cell type (if applicable):
Tester strains TA 98, TA 1535 and TA 102 were obtained from MOLTOX, INC., NC 28607, USA. Tester strains TA 100 and TA 1537 were obtained from Xenometrix AG, Switzerland. They were stored as stock cultures in ampoules with nutrient broth (OXOID) supplemented with DMSO (approx. 8% v/v) over liquid nitrogen.
All Salmonella strains contain mutations in the histidine operon, thereby imposing a requirement for histidine in the growth medium. They contain the deep rough (rfa) mutation, which deletes the polysaccharide side chain of the lipopolysaccharides of the bacterial cell surface. This increases cell permeability of larger substances. The other mutation is a deletion of the uvrB gene coding for a protein of the DNA nucleotide excision repair system resulting in an increased sensitivity in detecting many mutagens. This deletion also includes the nitrate reductase (chl) and biotin (bio) genes (bacteria require biotin for growth).
The tester strains TA 98, TA 100 and TA 102 contain the R-factor plasmid, pkM101. These strains are reverted by a number of mutagens that are detected weakly or not at all with the non R-factor parent strains. pkM101 increases chemical and spontaneous mutagenesis by enhancing an error-prone DNA repair system which is normally present in these organisms [12], [15].
The properties of the S. typhimurium strains with regard to membrane permeability, ampicillin- and tetracycline-resistance as well as normal spontaneous mutation rates are checked regularly according to Ames et al. [7]. In this way it is ensured that the experimental conditions set up by Ames are fulfilled.

Samples of each tester strain were grown by culturing for 12 h at 37 °C in Nutrient Broth to the late exponential or early stationary phase of growth (approx. 109 cells/mL). A solution of 125 µL ampicillin (10 mg/mL) (TA 98, TA 100, TA 102) was added in order to retain the phenotypic characteristics of the strain.
Additional strain / cell type characteristics:
not applicable
Metabolic activation:
with and without
Metabolic activation system:
Rat and hamster liver S9 homogenate
Test concentrations with justification for top dose:
0.00316, 0.0100, 0.0316, 0.100, 0.316, 1.0, 2.5 and 5.0 µL/plate
Controls
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
sodium azide
congo red
methylmethanesulfonate
other: 4-nitro-o-phenylene-diamine, 2-aminoanthracene
Details on test system and experimental conditions:
METHOD OF APPLICATION: plate incorporation test with rat liver (experiment I) and the pre-incubation test with hamster liver (experiment II)

DURATION
- Preincubation period: 30 min. at 30 °C.
- Exposure duration: After solidification the plates were inverted and incubated at 37 °C for at least 48 h in the dark.

NUMBER OF REPLICATIONS: Each assay was conducted with and without metabolic activation. The concentrations, including the controls, were tested in triplicate. The following concentrations of the test item were prepared and used in the experiments:
0.0316, 0.100, 0.316, 1.0, 2.5 and 5.0 µL/plate

DETERMINATION OF CYTOTOXICITY :
No precipitation of the test item was observed in any tester strain used in experiment I and II (with and without metabolic activation).
No toxic effects of the test item were noted in any of the five tester strains used up to the highest dose group evaluated (with and without metabolic activation) in experiment I and II, with one exception: In experiment II in tester strain TA 1537 toxic effects of the test item were observed at a concentration of 5.0 µL/plate (with metabolic activation).
Evaluation criteria:
The Mutation Factor is calculated by dividing the mean value of the revertant counts by the mean values of the solvent control (the exact and not the rounded values are used for calculation).
A test item is considered as mutagenic if:
- a clear and dose-related increase in the number of revertants occurs and/or
- a biologically relevant positive response for at least one of the dose groups occurs
in at least one tester strain with or without metabolic activation.
A biologically relevant increase is described as follows:
- if in tester strains TA 98, TA 100 and TA 102 the number of reversions is at least twice as high
- if in tester strains TA 1535 and TA 1537 the number of reversions is at least three times higher
than the reversion rate of the solvent control [11].
According to OECD 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.
A test item producing neither a dose related increase in the number of revertants nor a reproducible biologically relevant positive response at any of the dose groups is considered to be non-mutagenic in this system
A test is considered acceptable if for each strain:
- the bacteria demonstrate their typical responses to ampicillin (TA 98, TA 100, TA 102)
- the negative control plates (A. dest.) with and without S9 mix are within the following ranges (mean values of the spontaneous reversion frequency are within the historical control data range (2014 -2016)):

- S9 + S9 (rat liver)
min max min max
TA 98 11 58 15 59
TA 100 49 155 62 160
TA 1535 4 41 3 38
TA 1537 3 35 3 36
TA 102 141 472 157 586
- corresponding background growth on negative control, solvent control and test plates is observed
- the positive controls show a distinct enhancement of revertant rates over the control plate
- at least five different concentrations of each tester strain are analysable.
Statistics:
Not necessary

Results and discussion

Test resultsopen allclose all
Key result
Species / strain:
S. typhimurium TA 98
Remarks:
Experiment I (plate encorporation)
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity nor precipitates, but tested up to recommended limit concentrations
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 100
Remarks:
Experiment I (plate encorporation)
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity nor precipitates, but tested up to recommended limit concentrations
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 1535
Remarks:
Experiment I (plate encorporation)
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity nor precipitates, but tested up to recommended limit concentrations
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 1537
Remarks:
Experiment I (plate encorporation)
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity nor precipitates, but tested up to recommended limit concentrations
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 102
Remarks:
Experiment I (plate encorporation)
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity nor precipitates, but tested up to recommended limit concentrations
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 98
Remarks:
Experiment II (pre-incubation)
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity nor precipitates, but tested up to recommended limit concentrations
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
not valid
Remarks:
Congo red gave a lower mutation factor of 1.9 in this experiment.
Key result
Species / strain:
S. typhimurium TA 100
Remarks:
Experiment II (pre-incubation)
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity nor precipitates, but tested up to recommended limit concentrations
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 1535
Remarks:
Experiment II (pre-incubation)
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity nor precipitates, but tested up to recommended limit concentrations
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 1537
Remarks:
Experiment II (pre-incubation)
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Remarks:
Cytotoxicity observed at highest dose tested (with metabolic activation only)
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 102
Remarks:
Experiment II (pre-incubation)
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
Additional information on results:
The test item Direct Yellow 147 was investigated for its potential to induce gene mutations according to the plate incorporation test with rat liver S9 (experiment I) and the pre-incubation test with hamster liver S9 (experiment II) using Salmonella typhimurium strains TA 98, TA 100, TA 1535, TA 1537 and TA 102.
In two independent experiments several concentrations of the test item were used. Each assay was conducted with and without metabolic activation. The concentrations, including the controls, were tested in triplicate. The following concentrations of the test item were prepared and used in the experiments:
0.0316, 0.100, 0.316, 1.0, 2.5 and 5.0 µL/plate
No precipitation of the test item was observed in any tester strain used in experiment I and II (with and without metabolic activation).
No toxic effects of the test item were noted in any of the five tester strains used up to the highest dose group evaluated (with and without metabolic activation) in experiment I and II, with one exception: In experiment II in tester strain TA 1537 toxic effects of the test item were observed at a concentration of 5.0 µL/plate (with metabolic activation).
No biologically relevant increases in revertant colony numbers of any of the five tester strains were observed following treatment with Direct Yellow 147 at any concentration level, neither in the presence nor absence of metabolic activation in experiment I and II.
All criteria of validity were met. The reference mutagens induced a distinct increase of revertant colonies indicating the validity of the experiments. Only in experiment II, in tester strain TA 98 (with metabolic activation) a low mutation factor for Congo Red was found (1.9). Nevertheless, compared to the mutation factors found with the test item concentrations the increase can be considered as distinct. Moreover, the result is only slight below the threshold value of 2.0. Thus, this effect was regarded as not biologically relevant and it did not influence the quality or integrity of the present study.

Applicant's summary and conclusion

Conclusions:
In conclusion, it can be stated that during the described mutagenicity test and under the experimental conditions reported, Direct Yellow 147 did not cause gene mutations by base pair changes or frameshifts in the genome of the tester strains used.
Therefore, Direct Yellow 147 is considered to be non-mutagenic in this bacterial reverse mutation assay.
Executive summary:

The registered substance is not mutagenic in a valid bacterial cell gene mutation assay according to OECD 471.

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