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Toxicological information

Skin sensitisation

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Administrative data

Endpoint:
skin sensitisation: in chemico
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2017-11-23 to 2018-01-20
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 guidelineopen allclose all
Qualifier:
according to
Guideline:
OECD Guideline 442C (In Chemico Skin Sensitisation: Direct Peptide Reactivity Assay (DPRA))
Qualifier:
according to
Guideline:
other: Direct Peptide Reactivity Assay (DPRA) for Skin Sensitization Testing, DB-ALM Protocol n°154, January 12, 2013
GLP compliance:
yes (incl. certificate)
Remarks:
Bayerisches Landesamt für Gesundheit und Lebensmittelsicherheit, München, Germany
Type of study:
other: (in chemico) reactivity against synthetic peptides with a thiol or amino group

Test material

Reference
Name:
Unnamed
Type:
Constituent

In chemico test system

Details on study design:
The in chemico direct peptide reactivity assay (DPRA) enables detection of the sensitising potential of a test item by quantifying the reactivity of test chemicals towards synthetic peptides containing either lysine or cysteine.

Results and discussion

Positive control results:
The 100 mM stock solution of the positive control (cinnamic aldehyde) showed high reactivity towards the synthetic peptides. The mean depletion of both peptides was 65.38%.

In vitro / in chemico

Resultsopen allclose all
Key result
Parameter:
other: mean peptide depletion [%]
Run / experiment:
cysteine run
Value:
0.55
Vehicle controls validity:
valid
Negative controls validity:
valid
Positive controls validity:
valid
Key result
Parameter:
other: mean peptide depletion [%]
Run / experiment:
lysine run
Value:
0.37
Vehicle controls validity:
valid
Negative controls validity:
valid
Positive controls validity:
valid
Other effects / acceptance of results:
Acceptance Criteria

The run meets the acceptance criteria if:
- the standard calibration curve has a r² > 0.99,
- the mean percent peptide depletion (PPD) value of the three replicates for the positive control is
between 60.8% and 100% for the cysteine peptide and the maximum standard deviation (SD) for the
positive control replicates is < 14.9%,
- the mean percent peptide depletion (PPD) value of the three replicates for the positive control is
between 40.2% and 69.0% for the lysine peptide and the maximum SD for the positive control
replicates is < 11.6%,
- the mean peptide concentration of the three reference controls A replicates is 0.50 ± 0.05 mM,
- the coefficient of variation (CV) of peptide peak areas for the six reference control B replicates and three reference control C replicates in acetonitrile is < 15.0%.

The results of the test item meet the acceptance criteria if:
- the maximum standard deviation (SD) for the test chemical replicates is < 14.9% for the cysteine
percent depletion (PPD),
- the maximum standard deviation (SD) for the test chemical replicates is < 11.6% for the lysine
percent depletion (PPD),
- the mean peptide concentration of the three reference controls C replicates in the appropriate solvent is 0.50 ± 0.05 mM.

Both peptide runs and the test item results met the acceptance criteria of the test.

Any other information on results incl. tables

Cysteine and Lysine Values of the Calibration Curve

Sample

Cysteine Peptide

Lysine Peptide

Peak Area
at 220 nm

Peptide Concentration [mM]

Peak Area
at 220 nm

Peptide Concentration [mM]

STD1

17.8700

0.5340

4254.6284

0.5340

STD2

9.0120

0.2670

2161.7087

0.2670

STD3

4.5180

0.1335

1051.8925

0.1335

STD4

2.2520

0.0667

525.2503

0.0667

STD5

1.1010

0.0334

260.5259

0.0334

STD6

0.5300

0.0167

130.8325

0.0167

STD7

0.0000

0.0000

0.0000

0.0000

Depletion of the Cysteine Peptide

Cysteine Peptide

Sample

Peak Area
at 220 nm

Peptide Conc. [mM]

Peptide Depletion [%]

Mean Peptide Depletion [%]

SD of Peptide Depletion [%]

CV of Peptide Depletion [%]

Positive Control

4.4470

0.1325

74.33

74.15

0.18

0.25

4.4770

0.1334

74.15

4.5100

0.1344

73.96

Test Item

16.9410

0.5052

0.26

0.55

0.25

46.16

16.8690

0.5031

0.68

16.8640

0.5029

0.71

Depletion of the Lysine Peptide

Lysine Peptide

Sample

Peak Area
at 220 nm

Peptide Conc. [mM]

Peptide Depletion [%]

Mean Peptide Depletion [%]

SD of Peptide Depletion [%]

CV of Peptide Depletion [%]

Positive Control

1675.9452

0.2100

57.93

56.62

1.13

2.00

1753.5808

0.2197

55.98

1754.5223

0.2198

55.95

Test Item

4019.5232

0.5032

0.26

0.37

0.13

35.68

4016.2871

0.5028

0.34

4009.0984

0.5019

0.52

Prediction Model 1

Cysteine 1:10/ Lysine 1:50 Prediction Model 1

Mean Cysteine andLysine PPD

Reactivity Class

DPRA Prediction²

0.00% PPD 6.38%

 No or Minimal Reactivity

Negative

6.38% < PPD 22.62%

Low Reactivity

Positive

22.62% < PPD 42.47%

Moderate Reactivity

42.47% < PPD 100%

High Reactivity

1 The numbers refer to statistically generated threshold values and are not related to the precision of the measurement.

2 DPRA predictions should be considered in the framework of an IATA.

Prediction Model 2

Cysteine 1:10 Prediction Model

Cysteine PPD

ReactivityClass

DPRA Predictio

0.00% PPD 13.89%

No or Minimal Reactivity

Negative

13.89% < PPD 23.09%

Low Reactivity

Positive

23.09% < PPD 98.24%

Moderate Reactivity

98.24% < PPD 100%

High Reactivity

Categorization of the Test Item

Prediction Model

Prediction Model 1
(Cysteine Peptide and Lysine Peptide / Ratio: 1:10 and 1:50)

Prediction Model 2
(Cysteine Peptide / Test Item Ratio: 1:10)

Test Substance

Mean Peptide Depletion [%]

Reactivity Category

Prediction

Mean Peptide Depletion [%]

Reactivity Category

Prediction

Test Item

--

--

--

0.55

Minimal Reactivity

negative

Positive Control

65.38

High Reactivity

positive

74.15

Moderate Reactivity

positive

Applicant's summary and conclusion

Interpretation of results:
study cannot be used for classification
Conclusions:
In this study under the given conditions the test item showed minimal reactivity towards the cysteine peptide. Due to the observed precipitation the prediction
model does not apply and a prediction cannot be made.
The data generated with this test should be considered in the context of integrated approached such as IATA, combining the result with other complementary
information, e.g. derived from in vitro assays addressing other key events of the skin sensitisation AOP.
Executive summary:

In the present study the test item was dissolved in DMF, based on the results of the pre-experiments. A maximum solubility of 37.5 mM was determined. However, in the main experiments stock solutions of 100 mM were prepared accidentally. It is assumed that not the whole amount of test item was dissolved. Since with this concentration the highest possible concentration was guaranteed, the experiments were not repeated. For reasons of simplicity the concentrations of the stock solutions are reported as 100 mM. Based on a molecular weight of 348.47 g/mol a 100 mM stock solution was prepared. The test item solutions were tested by incubating the samples with the peptides containing either cysteine or lysine for 24 ± 2 h at 25 ± 2.5 °C. Subsequently samples were analysed by HPLC.

For the 100 mM stock solution of the test item precipitation was observed when diluted with the cysteine peptide solution. After the 24 h ± 2 h incubation period but prior to the HPLC analysis samples were inspected for precipitation, turbidity or phase separation. Precipitation was observed for the samples of the test item (including the co-elution control). Samples were centrifuged prior to the HPLC analysis.

For the 100 mM stock solution of the test item precipitation was observed when diluted with the lysine peptide solution. After the 24 h ± 2 h incubation period but prior to the HPLC analysis samples were inspected for precipitation, turbidity or phase separation. Precipitation was observed for the samples of the test item (including the co-elution control). Samples were centrifuged prior to the HPLC analysis. Phase separation was observed for the co-elution control of the positive control sample.

A minor co-elution of the test item with the lysine peptide peak was observed. Therefore, the given peak areas and corresponding peptide values can only be considered as an estimation of the peptide depletion and were not used for evaluation. The 100 mM stock solution of the test item showed minimal reactivity towards the cysteine peptide (0.55%). According to the evaluation criteria in the guideline, if a precipitation or phase separation is observed after the incubation period, peptide depletion may be underestimated and a conclusion on the lack of reactivity cannot be drawn with sufficient confidence in case of a negative result. Due to the observed precipitation in the cysteine experiment no prediction can be made.

The 100 mM stock solution of the positive control (cinnamic aldehyde) showed high reactivity towards the synthetic peptides. The mean depletion of both peptides was 65.38%.