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Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

Based on the results obtained in this study, it is concluded that beta-amylase, batch PPY36295 did not show any evidence of mutagenic activity when tested under the conditions applied in this bacterial reverse mutation test, in concentrations up to 5000 μg TOS/mL in the presence and absence of S9.

Link to relevant study records
Reference
Endpoint:
in vitro gene mutation study in bacteria
Type of information:
experimental study
Adequacy of study:
key study
Study period:
09-04-2014 to 11-07-2014
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 471 (Bacterial Reverse Mutation Assay)
Version / remarks:
July 1997.
Deviations:
no
GLP compliance:
yes
Type of assay:
bacterial reverse mutation assay
Target gene:
Histidine and tryptophan locus in the genome of five strains of bacteria.
Species / strain / cell type:
S. typhimurium TA 1535, TA 1537, TA 98 and TA 100
Species / strain / cell type:
E. coli WP2 uvr A pKM 101
Metabolic activation:
with and without
Metabolic activation system:
S-9 mix from Aroclor 1254-induced rat liver
Test concentrations with justification for top dose:
Preliminary test: No preliminary trials were carried out.
Six concentrations of the test item (156, 313, 625, 1250, 2500, 5000 μg TOS/mL)
Vehicle / solvent:
Vehicle for enzyme: Purified water.
Justification for choice of solvent/vehicle: Substance is water-soluble and any human exposure will be in aqueous solutions.
Solvent for the positive control: DMSO
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
2-nitrofluorene
other: Acridine mutagen (ICR-191), 1-Methyl-3-Nitro-N-NitroGuanidine, 2-Aminoanthracene
Details on test system and experimental conditions:
METHOD OF APPLICATION: Preincubation in suspension, followed by plating on agar plates (treat and plate method)
- Cell density at seeding (if applicable): Overnight culture of approximately 1x 10^9 cells/mL

DURATION
- Exposure duration, pre-incubation: The incubation mixtures were incubated with shaking at 37 ± 1 °C for 3 hours (treat and plate).
- Incubation time (selective incubation): about 72 hours

NUMBER OF REPLICATIONS: 3

DETERMINATION OF CYTOTOXICITY
- Method: Viable cell count and observation of the bacterial background lawn. 0.1 mL aliquots of a 10^6 dilution of each bacterial suspension were poured on to minimal glucose agar plates in duplicates. The plates were inverted and incubated at 37 ± 2°C for about 72 hours and scored.
Evaluation criteria:
The test substance was considered as positive when it has induced at least a doubling in the mean number of revertant colonies per plate compared to the appertaining solvent control in one or more of the strains, in the presence or absence of S9 mix, if this response is dose related (at least 3 doses) and reproducible. In case of a dose related and reproducible numerical increase, which is below a doubling but at least 50% higher than the solvent control, the result is considered as equivocal and needs further clarification.
Statistics:
Not performed.
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:
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 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:
cytotoxicity
Remarks:
in the absence of S9
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Key result
Species / strain:
E. coli WP2 uvr A pKM 101
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:
TEST-SPECIFIC CONFOUNDING FACTORS
- Water solubility: Yes
- Precipitation: Precipitation is a concentration limiting factor, but no issues were reported in this study.
- Definition of acceptable cells for analysis: Viability and gene type control

HISTORICAL CONTROL DATA
- Positive historical control data: Yes
- Negative (solvent/vehicle) historical control data: Yes

In experiment 2 with TA1537 treated at 1250 μg TOS/mL in the absence of S9 mix, an increase only just exceeding 50% of the solvent control was seen. However, no obvious dose relationship was present and the increase was not reproduced in experiment 1. Therefore this increase is considered to be of no biological importance.

The test substance was slightly toxic to some of the bacterial strains at the one to three highest dose levels, most pronounced with TA100 in the absence of S9 mix, as seen by reductions in the viable cell counts, accompanied by minor reductions in the revertant colony counts.

Conclusions:
Based on the results obtained in this study, it was concluded that beta-amylase, batch PPY36295 did not show any evidence of mutagenic activity when tested under the conditions applied in this bacterial reverse mutation test, in concentrations up to 5000 μg TOS/mL in the presence and absence of S9.
Executive summary:

Beta-amylase, batch PPY36295 was examined for mutagenic activity in the bacterial reverse mutation assay using Salmonella typhimurium strain TA1535, TA100, TA1537, TA98 and Escherichia coli WP2uvrApKM101. Crude enzyme preparations, like the present test substance contain the free amino acids histidine and tryptophan, most often in an amount, which exceeds the critical concentration for incorporation in the direct standard assay. To overcome this problem all strains were exposed to the test substance in liquid culture ("treat and plate assay"). Bacteria were exposed to 6 doses of the test substance in a phosphate buffered nutrient broth for 3 hours with 5 mg TOS/L as the highest concentration. After incubation the test substance was removed by centrifugation prior to plating.

The study was conducted with and without the metabolic activation system S9 - a liver preparation from male rats, pre-treated with Aroclor 1254, and the co-factors required for mixed function oxidase activity (S9 mix). All results were confirmed by conducting two complete and independent experiments. The test substance contains an abundance of various nutrients, and composes a rich growth medium to the test bacteria. These circumstances are reflected in the present study.

The test substance was slightly toxic to some of the bacterial strains at the one to three highest dose levels, as seen by reductions in the viable cell counts accompanied by minor reductions in the revertant colony counts. No treatments of any of the S. typhimurium and E. coli strains with the test substance resulted in any increases in the number of revertant colonies that meet the criteria for a positive or equivocal response.

Based on the results obtained in this study, it was concluded that beta-amylase, batch PPY36295 did not show any evidence of mutagenic activity when tested under the conditions applied in this bacterial reverse mutation test, in concentrations up to 5000 μg TOS/mL in the presence and absence of S9.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (negative)

Additional information

Justification for classification or non-classification

Not classified.