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Toxicological information

Skin sensitisation

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Administrative data

Endpoint:
skin sensitisation: in vitro
Type of information:
experimental study
Adequacy of study:
key study
Study period:
15 Dec 2020 to 21 Jan 2021
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2021
Report date:
2021

Materials and methods

Test guideline
Qualifier:
according to guideline
Guideline:
OECD Guideline 442D (In Vitro Skin Sensitisation: ARE-Nrf2 luciferase KeratinoSens™ test method)
Version / remarks:
2018
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Type of study:
ARE-Nrf2 luciferase KeratinoSens™ test method

Test material

Constituent 1
Reference substance name:
Polysulfides, di-tert-nonyl
EC Number:
270-336-2
EC Name:
Polysulfides, di-tert-nonyl
Cas Number:
68425-16-1
Molecular formula:
C78H110O6S5
IUPAC Name:
bis(1,1,2,3,3-pentamethylbutyl)trisulfane
Test material form:
liquid

In vitro test system

Details of test system:
Keratinoses transgenic cell line [442D]
Details on the study design:
PREPARATION OF TEST SOLUTIONS
- Preparation of the test chemical stock solution: the test item was dissolved in ethanol at 40 mg/mL
- Preparation of the test chemical serial dilutions from the stock solution: 11 spike solutions in ethanol were prepared (2-fold in the first experiment and 1.5-fold dilution series in the second, third and fourth experiment). The stock and spike solutions were diluted 100-fold with exposure medium. These solutions were diluted 4-fold with exposure medium in the assay to give the final test concentrations.
- Preparation of the positive controls: The positive control used in the case of KeratinoSensTM is ethylene dimethacrylate glycol (EDMG, Sigma, Zwijndrecht, The Netherlands), for which a 2-fold dilution series ranging from 0.78 to 25 mM were prepared in DMSO and diluted as described in paragraph 4.4.1, so that the final concentration of the positive control ranges from 7.8 to 250 μM (final concentration DMSO of 1%). All concentrations of the positive control were tested in triplicate. The formulation of the positive control was used in studies performed concurrently.
- Preparation of the solvent, vehicle and negative controls: The vehicle control was 0.25% ethanol and the negative control was 1% DMSO, both in exposure medium. Eighteen wells were tested per plate per vehicle control. On each plate three blank wells were tested (no cells and no treatment).
- Stable dispersion obtained: The test item precipitated at dose levels of 25, 8.8, 13 and 13 μg/mL and upwards in experiment 1, 2, 3 and 4, respectively at the start and end of the incubation period in the 96-well plates.

DOSE RANGE FINDING ASSAY:
- Highest concentration used : 100 µg/ml
- Solubility in solvents : The test item could not be dissolved in Milli-Q water or in DMSO at a concentration of 40 mg/mL. The test item was suspended in ethanol to a final concentration of 160 mg/mL (yellow suspension which precipitated quickly into an emulsion). The test item was suspended in ethanol to a final concentration of 80 mg/mL (yellow suspension). The stock solution was treated with ultrasonic waves to obtain a homogeneous suspension.
- Solubility in incubation medium : The 100-fold dilution in DMEM glutamax of 160 and 80 mg/mL showed moderate precipitate and were therefore not suitable to test. The 100-fold dilution of the 40 mg/mL ethanol stock showed slight precipitation. This concentration was selected as highest concentration for the main assay (limit of solubility).
- Cytotoxicity assessment performed : no
- Final concentration range selected on basis of: limit of solubility

APPLICATION OF THE TEST CHEMICAL AND CONTROL SUBSTANCES
- Number of replicates : 3
- Number of repetitions: 4
- Test chemical concentrations : of 100, 50, 25, 13, 6.3, 3.1, 1.6, 0.78, 0.39, 0.2, 0.1 and 0.05 μg/mL (final concentration ethanol of 0.25%) in the first experiment and 100, 67, 44, 30, 20, 13, 8.8, 5.9, 3.9, 2.6, 1.7 and 1.2 μg/mL (final concentration ethanol of 0.25%) in the second, third and fourth experiment. Test item concentrations were used within 3 hours after preparation.
- Application procedure : Four experiments, duplicate plates, 25-fold diluted test chemical and control items. Three wells per plate were left empty (no cells and no treatment) to assess background values. Initially, experiment 1 was terminated due to infections. In addition, experiment 3 did not pass all the acceptability criteria and therefore this experiment was repeated. In total 4 valid experiments were performed.
- Exposure time : 48 hours ± 1 hour
- Study evaluation and decision criteria used :
The prediction is considered positive if the following 4 conditions are all met in 2 of 2 or in the same 2 of 3 repetitions, otherwise the KeratinoSensTM prediction is considered negative:
1. The Imax is equal or higher than (≥) 1.5 fold and statistically significantly different as compared to the vehicle (negative) control (as determined by a two-tailed, unpaired Student’s t-test);
2. The cellular viability is higher than (>) 70% at the lowest concentration with induction of luciferase activity ≥ 1.5 fold (i.e. at the EC₁.₅ determining concentration);
3. The Imax value is less than (<) 1000 μM (or < 200 μg/mL for test chemicals with no defined MW);
4. There is an apparent overall dose-response for luciferase induction.
Negative results obtained with concentrations <1000 μM or 200 μg/mL and which do not reach cytotoxicity (< 70% viability) at the maximal tested concentration should be considered as inconclusive.
- Description on study acceptance criteria :
• The luciferase activity induction obtained with the positive control, ethylene dimethacrylate glycol, should be statistically significant above the threshold of 1.5 in at least one of the tested concentrations (from 7.8 to 250 μM).
• The EC₁.₅ of the positive control should be within two standard deviations of the historical mean. Moreover, the induction for ethylene dimethacrylate glycol at 250 μM should be higher than 2-fold. If the latter criterion is not fulfilled, the dose-response of ethylene dimethacrylate glycol should be carefully checked, and tests may be accepted only if there is a clear dose-response with increasing luciferase activity induction at increasing concentrations for the positive control.
• Finally, the average coefficient of variation of the luminescence reading for the vehicle control DMSO, and, if applicable, Milli-Q or ethanol, should be below 20% in each repetition which consists of 18 wells. If the variability is higher, a maximum of three of the eighteen wells may be excluded based on the Dixon’s Q-test. If the variability is still higher, the results should be discarded.

SEEDING AND INCUBATION
- Seeding conditions (passage number and seeding density) : passage number: P+5, P+7, P+8 and P+10 in experiment 1, 2, 3 and 4, respectively. Seeding density: 10,000 cells/well in duplicate 96-well plates. One plate was used for the luciferase activity measurements, and one parallel replicate was used for the MTT cell viability assay.
- Incubation conditions : 37±1.0°C in the presence of 5% CO²
- Precipitation noted : at start and end of exposure period at 25 μg/mL (Expt. 1), 8.8 μg/mL (Expt 2) and 13 μg/mL (Expt 3 and 4)

LUCIFERASE ACTIVITY MEASUREMENTS
- Choice of luminometer with demonstration of appropriate luminescence measurements based on control test : TECAN Infinite® M200 Pro Plate Reader (integration time 2 minutes)
- Plate used :96-well plates
- Lysate preparation : The Steady-Glo Luciferase Assay Buffer (10 mL) and Steady-Glo Luciferase Assay Substrate (lyophilized) from Promega (Leiden, The Netherlands) were mixed together. The assay plates were removed from the incubator and the medium is removed. Then 200 μL (100 in Experiment 2) of the Steady-Glo Luciferase substrate solution (prior to addition 1:1 mixed with exposure medium) was added to each well. The plates were shaken for at least 5 minutes at room temperature. The lower volume was considered to have no effect on the outcome as the reagent is added only for luminescence readings and the solvent and positive controls fulfill the criteria.

DATA EVALUATION
- Cytotoxicity assessment : medium was replaced after the 48 hour exposure time with fresh DMEM Glutamax containing MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, Thiazolyl blue tetrazolium bromide; CAS No. 298-93-1; Sigma, Zwijndrecht, The Netherlands) and cells were incubated for 3 - 4 hours at 37°C ± 1.0°C in the presence of 5% CO2. The MTT medium was then removed and cells were lysed overnight by adding 10% SDS solution (Sigma, Zwijndrecht, The Netherlands) to each well. After shaking, the absorption was measured at 570 nm with the TECAN Infinite® M200 Pro Plate Reader.
- Prediction model used : See evaluation criteria above and prediction model Figure attached.


Vehicle / solvent control:
other: ethanol and DMSO
Negative control:
other: DMSO
Positive control:
EGDMA (120 M) [442D]

Results and discussion

Positive control results:
A dose-related induction of luciferase activity was observed in all experiments:
Experiment 1: Iₘₐₓ 2.45, EC₁.₅ 46 µM
Experiment 2: Iₘₐₓ 2.66, EC₁.₅ 104 µM
Experiment 3: Iₘₐₓ 3.72, EC₁.₅ 35 µM
Experiment 4: Iₘₐₓ 3.84, EC₁.₅ 49 µM

In vitro / in chemico

Resultsopen allclose all
Key result
Group:
test chemical
Run / experiment:
run/experiment 1
Parameter:
EC 1.5 [442D]
Value:
29 µM
Cell viability:
The test item showed no toxicity
Vehicle controls validity:
valid
Negative controls validity:
valid
Positive controls validity:
valid
Remarks on result:
positive indication of skin sensitisation
Remarks:
Dose-related induction of luciferase activity
Key result
Group:
test chemical
Run / experiment:
run/experiment 1
Parameter:
Imax [442D]
Remarks:
Imax is unitless
Value:
2.84 %
Cell viability:
The test item showed no toxicity
Vehicle controls validity:
valid
Negative controls validity:
valid
Positive controls validity:
valid
Remarks on result:
positive indication of skin sensitisation
Remarks:
Dose-related induction of luciferase activity
Group:
test chemical
Run / experiment:
run/experiment 2
Parameter:
EC 1.5 [442D]
Value:
1.1 µM
Cell viability:
Toxicity was observed
Vehicle controls validity:
valid
Negative controls validity:
valid
Positive controls validity:
valid
Remarks on result:
positive indication of skin sensitisation
Remarks:
response was biphasic and non dose related response
Group:
test chemical
Run / experiment:
run/experiment 2
Parameter:
Imax [442D]
Remarks:
Imax is unitless
Value:
1.87 %
Cell viability:
Toxicity was observed
Vehicle controls validity:
valid
Negative controls validity:
valid
Positive controls validity:
valid
Remarks on result:
positive indication of skin sensitisation
Remarks:
response was biphasic and non dose related response
Group:
test chemical
Run / experiment:
run/experiment 2
Parameter:
IC30 [442D]
Value:
47 mM
Group:
test chemical
Run / experiment:
run/experiment 2
Parameter:
IC50 [442D]
Value:
86 mM
Group:
test chemical
Run / experiment:
run/experiment 3
Parameter:
Imax [442D]
Remarks:
Imax is unitless
Value:
1.38 %
Cell viability:
The test item showed no toxicity.
Vehicle controls validity:
valid
Negative controls validity:
valid
Positive controls validity:
valid
Remarks on result:
no indication of skin sensitisation
Key result
Group:
test chemical
Run / experiment:
other: run/experiment 4
Parameter:
EC 1.5 [442D]
Value:
6.8 µg/mL
Cell viability:
The test item showed no toxicity
Vehicle controls validity:
valid
Negative controls validity:
valid
Positive controls validity:
valid
Remarks on result:
positive indication of skin sensitisation
Remarks:
Dose-related induction of luciferase activity
Key result
Group:
test chemical
Run / experiment:
other: run/experiment 4
Parameter:
Imax [442D]
Remarks:
Imax is unitless
Value:
2.76 %
Cell viability:
No test item toxicity was observed
Vehicle controls validity:
valid
Negative controls validity:
valid
Positive controls validity:
valid
Remarks on result:
positive indication of skin sensitisation
Remarks:
Dose-related induction of luciferase activity
Group:
other: positive control
Run / experiment:
run/experiment 1
Parameter:
EC 1.5 [442D]
Value:
46 µM
Group:
other: positive control
Run / experiment:
run/experiment 1
Parameter:
Imax [442D]
Remarks:
Imax is unitless
Value:
2.45 %
Group:
other: positive control
Run / experiment:
run/experiment 2
Parameter:
EC 1.5 [442D]
Value:
1.4 µM
Group:
other: positive control
Run / experiment:
run/experiment 2
Parameter:
Imax [442D]
Remarks:
Imax is unitless
Value:
2.66 %
Group:
other: positive control
Run / experiment:
run/experiment 3
Parameter:
EC 1.5 [442D]
Value:
35 µM
Group:
other: positive control
Run / experiment:
run/experiment 3
Parameter:
Imax [442D]
Remarks:
Imax is unitless
Value:
3.72 %
Group:
other: positive control
Run / experiment:
other: run/experiment 4
Parameter:
EC 1.5 [442D]
Value:
49 µM
Group:
other: positive control
Run / experiment:
other: run/experiment 4
Parameter:
Imax [442D]
Remarks:
Imax is unitless
Value:
3.84 %
Outcome of the prediction model:
positive [in vitro/in chemico]
Other effects / acceptance of results:
OTHER EFFECTS:
- Visible damage on test system: no

DEMONSTRATION OF TECHNICAL PROFICIENCY: no information

ACCEPTANCE OF RESULTS:
- Acceptance criteria met for negative control: yes
- Acceptance criteria met for positive control: yes
- Acceptance criteria met for reference controls A to C: historical control data are presented in summary, and duplicate vehicle control data are given in the report but data for reference controls are not given.
- Acceptance criteria met for variability between replicate measurements: yes
- Range of historical values if different from the ones specified in the test guideline: yes

Any other information on results incl. tables

Experiment 1

•Precipitation was observed at the start and end of the incubation period in the 96-well plates at concentrations of 25 μg/mL and upwards.

•The test item showed no toxicity. The viability of the cells was higher than 70% at all test concentrations and therefore no IC₃₀ and IC₅₀ values could be calculated.

•A dose related luminescence activity induction was observed after treatment with the test item. The Imax was 2.84 and the EC₁.₅ 29 μg/mL.

•The positive control ethylene dimethacrylate glycol caused a dose related induction of the luciferase activity. The Imax was 2.45 and the EC₁.₅ 46 μM.

Experiment 2

•Precipitation was observed at the start and end of the incubation period in the 96-well plates at concentrations of 8.8 μg/mL and upwards.

•The test item showed toxicity. The calculated IC₃₀ was 47 μg/mL and the calculated IC₅₀ was 86 μg/mL.

•An induction was observed after treatment with the test item. The Imax was 1.87 and the EC₁.₅1.1 μg/mL.

•The positive control ethylene dimethacrylate glycol caused a dose related induction of the luciferase activity. The Imax was 2.66 and the EC₁.₅ 104 μM.

Experiment 3

•Precipitation was observed at the start and end of the incubation period in the 96-well

plates at concentrations of 13 μg/mL and upwards.

•The test item showed no toxicity. The viability of the cells was higher than 70% at all test

concentrations and therefore no IC₃₀ and IC₅₀ values could be calculated.

•No luminescence activity induction compared to the vehicle control was observed at any

of the test concentrations after treatment with the test item. The Imax was 1.38 and

therefore no EC₁.₅ could be calculated.

•The positive control ethylene dimethacrylate glycol caused a dose related induction of

the luciferase activity. The Imax was 3.72 and the EC₁.₅ 35 μM.

Experiment 4

•Precipitation was observed at the start and end of the incubation period in the 96-well

plates at concentrations of 13 μg/mL and upwards.

•The test item showed no toxicity. The viability of the cells was higher than 70% at all test

concentrations and therefore no IC₃₀ and IC₅₀ values could be calculated.

•A dose related luminescence activity induction was observed after treatment with the test

item. The Imax was 2.76 and the EC₁.₅ 6.8 μg/mL.

•The positive control ethylene dimethacrylate glycol caused a dose related induction of

the luciferase activity. The Imax was 3.84 and the EC₁.₅ 49 μM.

All tests passed the acceptance criteria:

•The luciferase activity induction obtained with the positive control, Ethylene

dimethacrylate glycol, was statistically significant above the threshold of 1.5-fold in at

least one concentration.

•The EC₁.₅ of the positive control was within two standard deviations of the historical

mean (46 μM, 104 μM, 35 μM and 49 μM in experiment 1, 2, 3 and 4, respectively). A

dose response was observed and the induction at 250 μM was higher than 2-fold (2.45-

fold, 2.66-fold, 3.72-fold and 3.84-fold in experiment 1, 2, 3 and 4, respectively).

•The average coefficient of variation of the luminescence reading for the vehicle

(negative) control ethanol was below 20% (8.5%, 9.2%, 6.6% and 10% in experiment 1,

2, 3 and 4, respectively).

•Finally, the average coefficient of variation of the luminescence reading for the vehicle

(negative) control DMSO was below 20% (6.9%, 14%, 5.4% and 13% in experiment 1,

2, 3 and 4, respectively).

Applicant's summary and conclusion

Interpretation of results:
Category 1 (skin sensitising) based on GHS criteria
Conclusions:
In a study conducted according to OECD 442D and in compliance with GLP using the ARE-Nrf2 luciferase KeratinoSens™ test method, di-tert-nonyl polysulfides induced luciferase activation in three out of four experiments (EC₁.₅ values of 29, 104 and 6.8, Imax values 2.84, 1.87, and 2.76 in experiments 1, 2 and 4). In two of the four experiments (1 and 4) the results were concordant: the responses were dose-related, and no toxicity was observed, in experiment 2 the response was biphasic and no toxicity was observed so it was concluded that the test substance is positive under the conditions of the study.
Executive summary:

The ability of the test item to activate the antioxidant/electrophile responsive element (ARE)-dependent pathway was examined with the aid of luciferase in the KeratinoSens™ cell line in an assay conducted according to OECD 442D and in compliance with GLP.

The test item was dissolved in ethanol at 40 mg/mL. From this stock 11 spike solutions in ethanol were prepared. The stock and spike solutions were diluted 400-fold in the assay resulting in test concentrations of 0.05 – 100 μg/mL (2-fold dilution series) in the first experiment and resulting in test concentrations of 1.2 – 100 μg/mL (1.5-fold dilution series) in the second, third and fourth experiment. A more narrow dose-response analysis was performed using a lower dilution factor of 1.5-fold to investigate the induction at 100 μM in experiment 1 in more detail. The highest test concentration was considered to be the limit of solubility. The test item precipitated at concentrations of 25, 8.8, 13 and 13 μg/mL and upwards in experiment 1, 2, 3 and 4, respectively. Four independent experiments were performed.

In the first experiment, the test item showed no toxicity (no IC30 and IC50 value). A biologically relevant, dose-related induction of the luciferase activity (EC1.5 value of 29 μg/mL) was measured. The maximum luciferase activity induction (Imax) was 2.84-fold leading to an individual run conclusion of positive since positive results (>1.5-fold induction) were observed at test concentrations < 200 μg/mL with a cell viability of >70% compared to the vehicle control.

In the second experiment, the test item showed toxicity (IC30 value of 47 μg/mL and IC50 value of 86 μg/mL). An induction of the luciferase activity (EC1.5 value of 1.1 μg/mL) was measured. The maximum luciferase activity induction (Imax) was 1.87-fold leading to an individual run conclusion of positive since positive results (>1.5-fold induction) were observed at test concentrations < 200 μg/mL with a cell viability of >70% compared to the vehicle control. However, a biphasic non dose related response was observed.

Since the first two experiments were not concordant, a third experiment was performed to provide a final conclusion.

In the third experiment, the test item showed no toxicity (no IC30 and IC50 value) and no biologically relevant induction of the luciferase activity (no EC1.5 value) was measured at any of the test concentrations. The maximum luciferase activity induction (Imax) was 1.38-fold leading to an individual run conclusion of inconclusive in the KeratinoSensTM assay since negative results (<1.5-fold induction) were observed at test concentrations at test concentrations < 200 μg/mL with a cell viability of >70% compared to the vehicle control.

Since the third experiment does not give a decisive answer, a fourth experiment was performed to provide a final conclusion.

In the fourth experiment, the test item showed no toxicity (no IC30 and IC50 value). A biologically relevant, dose-related induction of the luciferase activity (EC1.5 value of 6.8 μg/mL) was measured. The maximum luciferase activity induction (Imax) was 2.76-fold leading to an individual run conclusion of positive since positive results (>1.5-fold induction) were observed at test concentrations < 200 μg/mL with a cell viability of >70% compared to the vehicle control.

Overall, positive results (>1.5-fold induction) were observed at test concentrations < 200 μg/mL with a cell viability of >70% compared to the vehicle control in three out of four experiments (one individual run was biphasic but positive nonetheless).

It was concluded that di-tert-nonyl polysulfides (TNPS 537) is positive (activation of the antioxidant/electrophile responsive element (ARE)-dependent pathway in keratinocytes) under the experimental conditions.