N-(tri(hydroxymethyl)methyl)glycine

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:

2017-09-29 to 2018-02-01

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:

adopted 21 July 1997

Deviations:

no

GLP compliance:

yes

Type of assay:

bacterial reverse mutation assay

Test material

Test material information

Constituent 1

Reference substance name:

N-(tri(hydroxymethyl)methyl)glycine

EC Number:

227-193-6

EC Name:

N-(tri(hydroxymethyl)methyl)glycine

Cas Number:

5704-04-1

Molecular formula:

C6H13NO5

IUPAC Name:

2-{[1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl]amino}acetic acid

Test material form:

solid: particulate/powder

Details on test material:

- Batch No.: 74944923
- CAS No.: 5704-04-1
- Purity: 100.2%
- Physical State: white powder
- Storage Conditions: room temperature
- Expiry Date: 2018-06-15 (retest date)

Method

Target gene:

- Salmonella typhimurium: histidine
- Escherichia coli: tryptophan

Species / strain

Species / strain / cell type:

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

Details on mammalian cell type (if applicable):

CELLS USED
- Source of cells:
Trinova Biochem GmbH, Germany [Master culture from Dr. Bruce N. Ames (TA1535: 2016, TA1537: 2015, TA98: 2017, TA100: 2016; and Master culture from The National Collections of Industrial and Marine Bacteria, Aberdeen, UK (WP2uvrA: 2008)]

MEDIA USED:
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.

Metabolic activation:

with and without

Metabolic activation system:

S9 mix

Test concentrations with justification for top dose:

Selection of an adequate range of doses was based on a dose-range finding test with the strains TA100 and the WP2uvrA, both with and without 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 Tricine used in the subsequent mutation assay was 5000 µg/plate. At least five different doses (increasing with approximately half-log steps) of the test item were tested in triplicate in each strain in the absence and presence of S9-mix. The first experiment was a direct plate assay and the second experiment was a pre-incubation assay. The negative control (vehicle) and relevant positive controls were concurrently tested in each strain in the presence and absence of S9-mix.

Vehicle / solvent:

- Vehicle(s)/solvent(s) used: Milli-Q water

Controls

Controls 1

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

Remarks:

water

True negative controls:

no

Positive controls:

yes

Positive control substance:

sodium azide

Remarks:

TA1535 (5 µg/plate), -S9

Controls 2

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

Remarks:

water

True negative controls:

no

Positive controls:

yes

Positive control substance:

other: ICR-191

Remarks:

TA1537 (2.5 µg/plate), -S9, only direct plate assay

Controls 3

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

Remarks:

water

True negative controls:

no

Positive controls:

yes

Positive control substance:

2-nitrofluorene

Remarks:

TA1537 (15 µg/plate), -S9, only pre-incubation assay

Controls 4

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

Remarks:

water

True negative controls:

no

Positive controls:

yes

Positive control substance:

2-nitrofluorene

Remarks:

TA98 (10 µg/plate), -S9

Controls 5

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

Remarks:

water

True negative controls:

no

Positive controls:

yes

Positive control substance:

methylmethanesulfonate

Remarks:

TA100 (650 µg/plate), -S9

Controls 6

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

Remarks:

water

True negative controls:

no

Positive controls:

yes

Positive control substance:

4-nitroquinoline-N-oxide

Remarks:

WP2uvrA (10 µg/plate), -S9

Controls 7

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

Remarks:

water

True negative controls:

no

Positive controls:

yes

Positive control substance:

other: 2-aminoanthracene

Remarks:

All strains, +S9; TA1535 and TA1537 (2.5 µg/plate), TA98 (1 µg/plate); TA100 (1 µg/plate direct plate assay, 5 µg/plate pre-incubation assay); WP2uvrA (15 µg/plate)

Details on test system and experimental conditions:

Experimental 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 the WP2uvrA, both with and without 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 Tricine used in the subsequent mutation assay was 5000 µg/plate. At least five different doses (increasing with approximately half-log steps) of the test item were tested in triplicate in each strain in the absence and presence of S9-mix. The first experiment was a direct plate assay and the second experiment was a pre-incubation assay. The negative control (vehicle) and relevant positive controls were concurrently tested in each strain in the presence and absence of S9-mix.

First Experiment: Direct Plate Assay:
The above mentioned dose-range finding study with two tester strains is reported as a part of the direct plate assay. In the second part of this experiment, the test item was tested both in the absence and presence of S9-mix in the tester strains TA1535, TA1537 and TA98. 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 (10^9 cells/mL) of one of the tester strains, 0.1 mL of a dilution of the test item in Milli-Q water or control solution 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.

Second Experiment: Pre-Incubation Assay
The test item was tested both in the absence and presence of S9-mix in all tester strains. Top agar in top agar tubes was melted by heating to 45 ± 2 °C. The following solutions were pre-incubated for 30 ± 2 minutes by 70 rpm at 37 ± 1 °C, 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), 0.1 mL of a fresh bacterial culture (10^9 cells/mL) of one of the tester strains, 0.1 mL of a dilution of the test item in Milli-Q water or control solution. After the pre-incubation period the solutions were added to 3 mL molten top agar. 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.

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.

Results and discussion

Test results

Key result

Species / strain:

other: TA1535, TA1537, TA98, TA100, WP2uvrA

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:

TEST-SPECIFIC CONFOUNDING FACTORS
- Precipitation: Precipitation of Tricine on the plates was not observed at the start or at the end of the incubation period.

RANGE-FINDING/SCREENING STUDIES:
Tricine was initially tested in the tester strains TA100 and WP2uvrA as a dose-range finding test with concentrations of 1.7, 5.4, 17, 52, 164, 512, 1600 and 5000 µg/plate in the absence and presence of S9-mix. Based on the results of the dose-range finding test, the following dose-range was selected for the mutation assay with the tester strains, TA1535, TA1537 and TA98 in the absence and presence of S9-mix: 52, 164, 512, 1600 and 5000 μg/plate

TOXICITY:
No reduction of the bacterial background lawn and no biologically relevant decrease in the number of revertants were observed in experiment I and II.

Remarks on result:

other:

Remarks:

Experiment 1: Direct plate

Applicant's summary and conclusion

Conclusions:

Under the experimental conditions reported, the test item did not cause gene mutations in an Ames Test conducted according to OECD 471. Therefore, the test item is considered to be non-mutagenic in this bacterial reverse gene mutation assay.

Executive summary:

In a bacterial reverse gene mutation assay conducted according to OECD guideline 471, strains TA98, TA100, TA1535 and TA1537 of Salmonella typhimurium and E. coli strain WP2uvrA were exposed to Tricine (100.2% purity) in water at concentrations of up to 5000 µg/plate in the presence and absence of mammalian metabolic activation. The positive controls induced the appropriate responses in the corresponding strains. There was no evidence of induced mutant colonies over background in all tester strains in both experiments (plate incorporation and pre-incubation). Based on the results, the test item is considered to be non-mutagenic in the bacterial reverse gene mutation assay.

This study is classified as acceptable. This study satisfies the requirement for Test Guideline OPPTS 870.51001; OECD 471 for in vitro mutagenicity (bacterial reverse gene mutation) data.