Tributylethylammonium ethyl sulphate

Skin sensitisation

Administrative data

Endpoint:

skin sensitisation: in chemico

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

16 October 2017 - 24 November 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

The validated in chemico skin sensitization test is the DPRA assay, which is recommended in international guidelines (e.g. OECD) and mentioned in the ECHA guidance as the in chemico test to be performed as part of weight of evidence.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2017

Report date:

2017

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 442C (In Chemico Skin Sensitisation: Direct Peptide Reactivity Assay (DPRA))

Version / remarks:

4 February 2015

Deviations:

no

GLP compliance:

yes

Type of study:

direct peptide reactivity assay (DPRA)

Justification for non-LLNA method:

A validated in chemico skin sensitization test is the DPRA assay, which is recommended in international guidelines (e.g. OECD) and mentioned in the ECHA guidance as one of the non-animal tests to be performed as part of weight of evidence.

Test material

Test material information

Constituent 1

Reference substance name:

Tributylethylammonium ethyl sulphate

EC Number:

268-329-4

EC Name:

Tributylethylammonium ethyl sulphate

Cas Number:

68052-51-7

Molecular formula:

C14H32N . C2H5O4S (or C16H37NO4S)

IUPAC Name:

tributyl(ethyl)azanium ethyl sulfate

impurity 1

Reference substance name:

Water

EC Number:

231-791-2

EC Name:

Water

Cas Number:

7732-18-5

Molecular formula:

H2O

IUPAC Name:

Dihydrogen oxide

Test material form:

solid

Details on test material:

- Physical appearance: off white solid
- Storage conditions: at room temperature

In chemico test system

Details on the study design:

TEST ITEM PREPARATION
Solubility of the test item in an appropriate solvent was assessed before performing the DPRA. An appropriate solvent dissolved the test item completely, i.e. by visual inspection the solution had to be not cloudy nor have noticeable precipitate. The following solvents were evaluated: acetonitrile (ACN), Milli-Q water (MQ) and MQ/ACN (1:1, v/v).
Test item stock solutions were prepared freshly for each reactivity assay.
For both the cysteine and lysine reactivity assay 53.06 mg of test item was pre-weighed into a clean amber glass vial and dissolved, just before use, in 1563 µL MQ to obtain a 100 mM solution. Visual inspection of the forming of a clear solution was considered sufficient to ascertain that the test item was dissolved. The test item, positive control and peptide samples were prepared less than 4 hours before starting the incubation of the cysteine (cys) or lysine (lys) reactivity assay, respectively.

TEST SYSTEM
Synthetic peptides containing cysteine (SPCC) (Ac-RFAACAA-COOH) or synthetic peptides containing lysine (SPCL) (Ac-RFAAKAA-COOH). The molecular weight is 750.9 g/mol for SPCC and 775.9 g/mol for SPCL. Rationale: Recommended test system in the international OECD guideline for DPRA studies.
Source: JPT Peptide Technologies GmbH, Berlin, Germany.
Storage: The peptides were stored in the freezer (≤-15°C) for a maximum of 6 months.
Incubation: After preparation, the samples (reference controls, calibration solutions, co-elution control, positive controls and test item samples) were placed in an incubator at 25±2.5°C. After incubation, the samples were transferred to the autosampler. The incubation time between placement of the samples in the incubator and analysis of the first cysteine and lysine sample was 24.5 hours and 24 hours, respectively. The time between the first and the last injection of a cysteine or lysine sequence, respectively, did not exceed 30 hours.
Prior to HPLC-PDA analysis the samples were visually inspected for precipitation.

analysis: All samples were analyzed according to the HPLC-PDA method presented in Table 1. (See 'other information on materials and methods').
The HPLC sequences of the cysteine and lysine reactivity assay for the test item are presented in Table 2. (See 'other information on materials and methods').

POSITIVE CONTROL
Cinnamic aldehyde
- Purity: 98.4%
- Batch: MKBP1014V
- Expiry of batch: 31 May 2018

DATA EVALUATION
The concentration of SPCC or SPCL was photometrically determined at 220 nm in each sample by measuring the peak area of the appropriate peaks by peak integration and by calculating the concentration of peptide using the linear calibration curve derived from the standards.
The Percent Peptide Depletion was determined in each sample by measuring the peak area and dividing it by the mean peak area of the relevant reference controls C according to the following formula:
Percent Peptide Depletion= [1-(Peptide Peak Area in Replicate Injection (at 220 nm)/Mean Peptide Peak Area in Reference Controls (at 220 nm))]x100

In addition, the absorbance at 258 nm was determined in each sample by measuring the peak area of the appropriate peaks by peak integration. The ratio of the 220 nm peak area and the 258 nm peak was used as an indicator of co-elution. For each sample, a ratio in the range of 90%< mean area ratio of control samples <110% gives a good indication that co-elution has not occurred.

DATA INTERPRETATION
The mean Percent Cysteine Depletion and Percent Lysine Depletion were calculated for the test item. Negative depletion was considered as “0” when calculating the mean. By using the Cysteine 1:10 / Lysine 1:50 prediction model (see Table 3), the threshold of 6.38% average peptide depletion was used to support the discrimination between a skin sensitizer and a non-sensitizer.

Results and discussion

In vitro / in chemico

Results

Results 1

Run / experiment:

other: Cysteine Reactivity Assay

Parameter:

other: Mean SPCC depletion(%)

Value:

0.8

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Remarks:

CV between reference controls: 1.6%

Positive controls validity:

valid

Remarks:

Mean percentage SPCC: 78.7% ±1.1%

Remarks on result:

other: SD: 6%

Results 2

Run / experiment:

other: Lysine Reactivity Assay

Parameter:

other: Mean SPCL depletion (%)

Value:

1

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Remarks:

CV between reference controls: 2%

Positive controls validity:

valid

Remarks:

Mean percentage SPCL: 50 ± 2.2%

Remarks on result:

other: SD: 0.8%

Other effects / acceptance of results:

No precipitation or co-elution occured during the tests.
See Table 4 & 5 "any other information on results incl. tables" for acceptibility criteria.

Any other information on results incl. tables

Table 4: Acceptability of the Direct Peptide Reactivity Assay (DPRA)

	Cysteine reactivity assay		Lysine reactivity assay
	Acceptability criteria	Results for SPCC	Acceptability criteria	Results for SPCL
Correlation coefficient (r^2) standard calibration curve	>0.99	0.996	>0.99	0.998
Mean peptide concentration RC-A samples (mM)	0.50 ± 0.05	0.501 ± 0.009	0.50 ± 0.05	0.488 ± 0.002
Mean peptide concentration RC-C samples (mM)	0.50 ± 0.05	0.502 ± 0.013	0.50 ± 0.05	0.482 ± 0.009
Mean peptide concentration RC-Cwatersamples (mM)	0.50 ± 0.05	0.497 ± 0.006	0.50 ± 0.05	0.477 ± 0.006
CV (%) for RC samples B and C	<15.0	1.7	<15.0	2.0
Mean peptide depletion cinnamic aldehyde (%)	60.8-100	73.7	40.2-69.0	50.4
SD of peptide depletion cinnamic aldehyde (%)	<14.9	0.2	<11.6	2.2
SD of peptide depletion for  the test item (%)	<14.9	0.6	<11.6	0.8

RC = Reference Control; CV = Coefficient of Variation; SD = Standard Deviation.

Table 5: SPCC and SPCL Depletion, DPRA Prediction and Reactivity Classification for the Test Item

Test item	SPCC depletion		SPCL depletion		Mean of SPCC and SPCL depletion	DPRA prediction and     reactivity classification
	Mean	± SD	Mean	± SD		Cysteine 1:10 / Lysine 1:50 prediction model
TBEAES DRY	0.8%	±0.6%	1.0%	±0.8%	0.9%	Negative: No or minimal reactivity

SD = Standard Deviation.

Applicant's summary and conclusion

Interpretation of results:

study cannot be used for classification

Remarks:

(study is part of a weight of evidence approach and is not used for classification on its own)

Conclusions:

In a DPRA study performed according to OECD TG 442C and in accordance with GLP principles, TBEAES was considered negative and classified in the "No or minimal reactivity class” when using the Cysteine 1:10 / Lysine 1:50 prediction model.

Executive summary:

In an in chemico study, performed according to OECD guideline 442C and in accordance with GLP principles, the reactivity of TBEAES DRY towards model synthetic peptides containing either cysteine (SPCC) or lysine (SPCL) was determined to assign the test chemical to one of four reactivity classes used to support the discrimination between skin sensitisers and non skin sensitisers.

Following incubation of the test substance with either SPCC or SPCL, the relative peptide concentration was determined by High-Performance Liquid Chromatography (HPLC) with gradient elution and photodiode array (PDA) detection at 220 nm and 258 nm. SPCC and SPCL Percent Depletion Values were calculated and used in the prediction model.

MQ water was found to be an appropriate solvent to dissolve the test substance, and was therefore used in this DPRA study. Cinnamic aldehyde was used as a positive control. No precipitation was observed.

The validation parameters, i.e. calibration curve, mean concentration of Reference Control (RC) samples, the CV for RC samples, the mean percent peptide depletion values for the positive control with its standard deviation value and the standard deviation value of the peptide depletion for the test item, were all within the acceptability criteria for the DPRA. Therefore, the study was considered to be valid. No co-elution of the test item with SPPC or SPCL was observed.

In the cysteine reactivity assay the test item showed 0.8% SPCC depletion while in the lysine reactivity assay the test item showed 1.0% SPCL depletion. The mean of the SPCC and SPCL depletion was 0.9% and as a result the test item was considered to be negative in the DPRA and classified in the “no or minimal reactivity class” when using the Cysteine 1:10 / Lysine 1:50 prediction model.