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Skin sensitisation

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skin sensitisation: in vitro
Type of information:
experimental study
Adequacy of study:
weight of evidence
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference Type:
study report
Report Date:

Materials and methods

Test guideline
according to
OECD Guideline 442C (In Chemico Skin Sensitisation: Direct Peptide Reactivity Assay (DPRA))
GLP compliance:
yes (incl. certificate)
Type of study:
direct peptide binding assay

Test material

Test material form:

In vitro test system

Details on study design:
Experimental procedure of the DPRA:
The test substance was dissolved in a suitable vehicle. Three samples of the test substance were incubated with each peptide. Additionally, triplicates of the concurrent vehicle control (=NC) were incubated with the peptides. The remaining non-depleted peptide concentration was determined thereafter by HPLC with gradient elution and UV-detection at 220 nm. In addition, calibration samples of known peptide concentration, prepared from the respective peptide stock solution used for test-substance incubation, were measured in parallel with the same analytical method.

Test substance solubility:
Prior to the assay the solubility of the test substance at a concentration of 100 mM was tested. A suitable non-reactive, water-miscible solvent which dissolves the test substance completely (no visible precipitation or cloudyness of the test-substance preparation) should be used. The preferred solvent was acetonitrile. When not soluble in acetonitrile solutions in water, isopropanol, acetone, propanol, methanol or mixtures of these solvents were tried.

Preparation of peptide stock solutions:
Peptide stock solutions in a concentration of 0.667 mM were prepared in pH 7.5 phosphate buffer (C-containing peptide) or pH 10.2 ammonium acetate buffer (K-containing peptide). The peptide stock solution was used for preparing the calibration samples and the test substance and control samples.

Preparation of the test-substance samples:
The samples were prepared in triplicates for each peptide according to the pipetting scheme given below. The samples were prepared in suitable tubes, capped tightly and incubated at 25°C ± 2.5°C in the dark for 24 ± 2 hours. Visual inspection for solubility was performed directly after sample preparation and prior to HPLC analysis. Unsolved samples were centrifuged and/or filtrated prior to injection into the HPLC in order to remove any unsolved particles. The HLPC analysis of the batch of samples started about 24 hours after sample preparation and the analysis time itself did not exceed 30 hours.

Preparation of the vehicle controls:
Several vehicle controls were prepared in triplicates in the same way as the test-substance samples described above but with the vehicle (acetonitrile) instead of the test substance: One set (set A) was analyzed together with the calibration samples without incubation and serves as a performance control. Another three sets (two sets B and set C) were prepared and incubated with the samples. Sets B were placed at the very start and ending of the sample list and serve as stability control of the peptide over the analysis time. Set C was analyzed with the samples and serves for calculation of the peptide depletion of any chemical formulated in the vehicle.

Preparation of the co-elution control:
One sample per peptide was prepared in the same way as the test-substance samples described above but without the peptides. Instead the respective peptide buffer was used. The samples were analyzed together with the calibration samples. Samples which were visually turbid or display precipitates were centrifuged and/or filtrated prior to injection into the HPLC in order to remove any unsolved particles.

Synthetic peptides: (DPRA)
Cysteine- (C-) containing peptide: Ac-RFAACAA-COOH (MW=751.9 g/mol)
Lysine- (K-) containing peptide: Ac-RFAAKAA-COOH (MW=776.2 g/mol)
The peptides are custom material (Supplier: GenScript, Piscataway, NJ, USA and RS Synthesis, Louisville KY, USA) containing phenylalanine to aid in detection and either cysteine or lysine as the reactive center.

Controls for the DPRA
Negative control (NC): vehicle control = acetonitrile
Positive control (PC): Ethylene glycol dimethacrylate (EGDMA; CAS-no. 97-90-5), prepared as a 50 mM solution in acetonitrile.
Co-elution control (SK): Sample prepared of the respective peptide buffer and the test substance but without peptide.

Results and discussion

In vitro / in chemico

other: mean peptide depletion (%)
Remarks on result:
other: show low chemical reactivity

Any other information on results incl. tables

The test substance was dissolved in acetonitrile at a concentration of 100 mM. The samples of the test substance with the peptides were solutions at the time of preparation. Visual observation after the 24-hour incubation time did not reveal precipitates in any samples of the test substance with the peptides.

No co-elution of test substance and peptides was present.

The mean C-peptide depletion, caused by the test substance was determined to be 31.92%.

The mean K-peptide depletion, caused by the test substance was determined to be 1.70%.

Thus, the mean peptide depletion was calculated to be 16.81%.

Applicant's summary and conclusion

Based on the observed results and applying the cysteine 1:10 / lysine 1:50 prediction model it was concluded that 1,1-diethoxyethane shows low chemical reactivity in the DPRA under the test conditions chosen.