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Description of key information

In vitro (Skin Sensitisation Test Battery):

The objective was to assess the skin sensitizing potential of 1,1-diethoxyethane. A combination of the following three in vitro methods, addressing key events of the adverse outcome pathway (AOP) for skin sensitization (OECD, 2012) as defined by the OECD, were part of this in vitro Skin Sensitization Turnkey Testing Strategy:

• protein reactivity (DPRA),

• activation of keratinocytes (LuSens), and

• activation of dendritic cells (h-CLAT).

DPRA: The reactivity of 1,1-diethoxyethane towards synthetic cysteine (C)- or lysine (K)-containing peptides was evaluated in the Direct Peptide Reactivity Assay (DPRA). For this purpose, the test substance was incubated with synthetic peptides for ca. 24 hours at ca. 25°C and the remaining non-depleted peptide concentrations were determined by high performance liquid chromatography (HPLC) with gradient elution and UV-detection at 220 nm. The test substance was dissolved at 100 mM in acetonitrile. Three samples of the test substance were incubated with each peptide in ratios of 1:10 (for C-containing peptide) or 1:50 (for K-containing peptide). Additionally, triplicates of the concurrent vehicle control (= VC) were incubated with the peptides. Additionally, triplicates of the concurrent vehicle control (= NC) were incubated with the peptides. Further, in order to detect possible interference of the test substance with the peptides, a co-elution control was performed and the samples were analyzed by measuring UV absorbance at 258 nm in order to calculate the area ratio 220 nm / 258 nm.

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%. 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.

LuSens: The keratinocyte activating potential of test substance 1,1-diethoxyethane was evaluated in the LuSens assay. For this purpose, the test substance was incubated with a luciferase reporter cell line (LuSens cells) for ca. 48 hours at 37°C and antioxidant response element (ARE) dependent luciferase activity was measured in a luminometer. In order to determine the concentrations suitable for the main experiment a pre-test (non-GLP) was performed. Cells were exposed to several concentrations of the test substance and cytotoxicity was determined by MTT assay. No cytotoxicity was observed. In the main test luciferase activity was measured after 48-hour exposure. In parallel a MTT assay was performed to assess cytotoxicity of the test substance. A total of 3 valid experiments were performed. One further experiment was conducted but was invalid for not meeting acceptance criteria and is not included in the report. The test substance was soluble in 4% DMSO in culture medium 3 (4 x stock preparations) and in 1% DMSO in culture medium 3 (final concentrations). No precipitates were noticed in any concentration after 48 hours. Calculation of an EC1.50 (the concentration resulting in a 1.50-fold luciferase induction) was not applicable due to the overall negative result of the study. In summary, after 48 hours of exposure to test substance 1,1-diethoxyethane luciferase activity in LuSens cells was not induced in at least two consecutive concentrations with statistical significance affording at least 70% viability in at least two independent experiments. From this it has to be concluded that test substance 1,1-diethoxyethane does not have a keratinocyte activating potential.

h-CLAT: The potential of test substance 1,1-diethoxyethane to induce the cell membrane markers CD86 and CD54 expression was evaluated in the Human Cell Line Activation Test (h-CLAT). For this purpose, the test substance was incubated with human monocytic leukemia cell line THP-1 for ca. 24 hours at 37°C and membrane marker expression (CD86 / CD54) was measured by flow cytometry. In order to determine the concentrations suitable for the main experiment a pre-test (non-GLP) was performed. Cells were exposed to several concentrations of the test substance and cytotoxicity was determined thereafter by propidium iodide (PI) intercalation into the DNA. The CV75 value (= estimated concentration that affords 75% cell viability) was determined by linear regression from the concentration-response curve to be 2514 μg/mL. In the main test after 24-hour exposure THP-1 cells were stained with FITC labeled anti-human-CD86/ anti-human-CD54 antibody and propidium iodide and the fluorescence intensity was analyzed using flow cytometry. A total of 2 valid experiments were performed. A further experiment was performed but not evaluable due to a technical error and is not included in the report. At concentrations used in the main experiment the test substance was soluble in culture medium (2 x stock preparations and final concentrations). After 24 hours, the highest concentration was unsolved, only. The EC150% (the concentration resulting in a RFI of 150%) for CD86 was calculated to be 2293 μg/mL (experiment 2). The EC200% (the concentration resulting in a RFI of 200%) for CD54 was calculated to be 1911 μg/mL (experiment 2).

Calculation of an EC150%/EC200% was not applicable for the 3rd experiment as fold inductions above 150%/200% were obtained in the lowest tested concentrations, respectively. In summary, after 24 hours of exposure to test substance 1,1-diethoxyethane CD86 and CD54 expression was induced in THP-1 cells affording at least 50% viability in at least two independent experiments. From this it has to be concluded that test substance 1,1 -diethoxyethane induces dendritic cell activation.

Test Method

Test Result

Test Evaluation

Direct Peptide Reactivity

Assay (DPRA)

16.81% mean peptide depletion (31.92%

cysteine-peptide depletion; 1.70% lysinepeptide

depletion).

Positive

Keratinocyte Activation

Assay - LuSens

In at least two independent experiments no biologically relevant ARE-dependent

luciferase activity induction was observed.a

Negative

Dendritic Cell Line

Activation Assay Human

Cell Line Activation Test

(h-CLAT)

In at least two independent experiments an induction of the expression of CD86

(above 150%) and CD54 (above 200%) were observed at sufficiently non-cytotoxic (cell viability ≥ 50%) concentration.

Positive

Based on the results and applying the evaluation criteria, 1,1-diethoxyethane is peptide reactive, does not activate keratinocytes and activates dendritic cells. Applying the evaluation criteria is predicted to be a skin sensitizer.

 

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Referenceopen allclose all

Endpoint:
skin sensitisation: in vitro
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 442C (In Chemico Skin Sensitisation: Direct Peptide Reactivity Assay (DPRA))
GLP compliance:
yes (incl. certificate)
Type of study:
direct peptide binding assay
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.
Parameter:
other: mean peptide depletion (%)
Value:
16.81
Remarks on result:
other: show low chemical reactivity

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%.

Conclusions:
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.
Endpoint:
skin sensitisation: in vitro
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
other: OECD Guideline 442 E (In (Vitro skin Sensitization: human Cell Line Activation Test (h-CLAT))
GLP compliance:
yes (incl. certificate)
Type of study:
activation of dendritic cells
Details on study design:
Experimental procedure of the h-CLAT:
Preparation of the cells:
THP-1 cells from the working cell bank were thawed and cultured in suspension using complete RPMI 1640 medium supplemented with 10% fetal bovine serum (heat inactivated), 100 U/mL penicillin, 100 μg/mL streptomycin and 0.05 mM 2-mercaptoethanol under standard culture conditions (37°C, ca. 5% CO2, ≥ 90% relative humidity) until for 5 passages but not longer than passage 30 prior to testing. Prior to use of the cells for a study, a reactivity check was performed with each new-thawed cells, as proposed in the OECD test guideline, using Nickel(II)sulfate hexahydrate, lactic acid and 1- chloro-2,4-dinitrobenzene in order to demonstrate qualification of the cells for the assay. For substance incubation, cells were seeded in 24-well plates (500 μL of 2.0 x 106 cells/mL cell suspensions). Two independent, valid experiments were performed. In each experiment, duplicates of each test-substance concentration were tested.

Test-substance application:
Treatment was performed by adding 500 μL of test-substance preparation to the cells, thus diluting the 2x concentrated test-substance preparations to their final concentration and the cells to 1.0 x 106 cells/mL. After test-substance application the plates were sealed with semipermeable plate sealers in order to prevent evaporation of the test substance. The plates were placed into the incubator under standard culture conditions for the exposure period of 24 ± 0.5 hours.

Visual inspections:

Each test-substance concentration was visually inspected directly after application and after the exposure period of 24 ± 0.5 hours in order to detect test-substance precipitates.

Cell staining and flow cytometric analysis:
After visual inspection the cells were transferred into safe-lock tubes, collected by centrifugation and washed twice with 1 mL buffer. Cells were incubated with 600 μL of 0.01% Globulins Chon fraction II,III at 4°C for 15 min to block FC receptors (FcR). After FcR blocking, cells of each treatment condition were divided into 3 aliquots (approximately 0.3 x 106 cells/180 μL/group) in 96-well microtiter plates. Cells were centrifuged, supernatant was discarded and 50 μL working antibody solution was added to each pellet.
Cell staining was performed at 4°C for ca. 30 min in the dark. After staining the cells were washed twice with 200 μL buffer and finally re-suspended in 200 μL buffer. Before analysis in flow cytometer the cells were stained with 5 μL of PI (50 μg/mL diluted in buffer) to yield a final concentration of 1.22 μg/mL PI.

Controls for the h-CLAT
Negative control (NC): Lactic acid (LA, CAS no.: 50-21-5), 1000 μg/mL in culture medium
Positive control (PC): 1-chloro-2,4-dinitrobenzene (DNCB, CAS no.: 97-00-7), 4.0 μg/mL in 0.2% DMSO in culture medium
Vehicle control (VC): culture medium
Isotype control: In order to help distinguish non-specific (“background”) staining from specific antibody staining each test-substance concentration and control is additionally incubated with mouse IgG1.

h-CLAT:
Cell line: THP-1 cells
The human monocytic leukemia cell line was obtained from “American Type Culture Collection, Manassas, USA” (ATCC, TIB-202).
Remarks on result:
other: induces dendritic cell activation

At concentrations used in the main experiment the test substance was soluble in culture medium (2 x stock preparations and final concentrations). After 24 hours, the highest concentration was unsolved, only.

The EC150% (the concentration resulting in a RFI of 150%) for CD86 was calculated to be 2293 μg/mL (experiment 2). The EC200% (the concentration resulting in a RFI of 200%) for CD54 was calculated to be 1911 μg/mL (experiment 2).

Calculation of an EC150%/EC200% was not applicable for the 3rd experiment as fold inductions above 150%/200% were obtained in the lowest tested concentrations, respectively. In summary, after 24 hours of exposure to test substance 1,1-diethoxyethane CD86 and CD54 expression was induced in THP-1 cells affording at least 50% viability in at least two independent experiments. From this it has to be concluded that test substance 1,1 -diethoxyethane induces dendritic cell activation.

Conclusions:
From this it has to be concluded that the test substance 1,1.diethoxyethane induces dendritic cell activation.
Endpoint:
skin sensitisation: in vitro
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 442D (In Vitro Skin Sensitisation: ARE-Nrf2 Luciferase Test Method)
GLP compliance:
yes (incl. certificate)
Type of study:
activation of keratinocytes
Details on study design:
Experimental procedure of the LuSens
Preparation of the cells:
LuSens cells from the working cell bank were thawed and cultured using culture medium 1, under standard culture conditions (37°C, ca. 5% CO2, ≥ 90% relative humidity) for at least passage ≥5 but not longer than 15 passages prior to testing. Before substance incubation, cells were seeded in 96-well microtiter plates (120 μL of 0.83 x 105 cells/mL cell suspension), using culture medium 2 for incubation for ca. 24 hours. Three independent, valid experiments were performed. In each experiment, three replicates of each test-substance concentration were tested.

Test-substance application for MTT and luciferase assay:
After cell adaption for ca. 24 hours culture medium 2 was aspirated and replaced with 150 μL culture medium 3. The test substance was prepared as described in section 3.5.2. Each preparation of the dilution plate was then applied in a ratio of 1:4 (50 μL) to the cells (final DMSO concentration in the test medium = 1%).After test-substance application the plates were sealed with semi-permeable plate sealers in order to prevent evaporation of the test substance. The plates were placed into the incubator under standard culture conditions for the exposure period of 48 ± 1 hours. For the luciferase assay a white plate (luminescence compatible plate) was used. In addition, a clear plate was treated in parallel for the determination of cell viability.

Visual inspections:
Each test-substance concentration was visually inspected directly after application and after the exposure period of 48 ± 1 hours in order to detect test-substance precipitates.

Luciferase assay:
After visual inspection of the cells, the supernatant was aspirated from the white assay plate and discarded. The cells were washed twice with 300 μL PBS (with Ca2+/Mg2+). Subsequently 200 μL of One-Glo-preparation (= 100 μL One-Glo- Mix and 100 μL PBS (without Ca2+/Mg2+)) per well was added and cells were shaken on a plate shaker for ca. 10 min at room temperature in darkness. After the incubation the luminescence was measured in the luminometer.

Cell viability assay MTT:
Cell culture medium was aspirated from all wells. Thereafter 200 μL of a 0.5 mg/mL thiazolyl blue tetrazolium bromide (MTT) solution (prepared 1:10 from a 5 mg/mL (MTT) stock solution in PBS (without Ca2+/Mg2+) and culture medium 3) was added to each well of the 96-well microtiter plate and incubated for at least further 2 hours in the incubator. For analysis, medium was aspirated and cells were lysed by adding 100 μL of lysis solution (99.6 mL DMSO; 10 g sodium dodecyl sulfate, SDS; and 0.4 mL glacial acetic acid). Absorbance was measured at 570 nm with reference wavelength 690 nm using a spectral-photometer.

LuSens:
Cell line: LuSens
Human transgenic keratinocyte cell line derived from HaCaT cells, prepared in collaboration with Christoph J. Wruck, RWTH Aachen, Germany.
Controls for the LuSens
Negative control (NC): DL-Lactic acid (LA, CAS no.: 50-21-5), 5000 μM (= 450 μg/mL) in 1% DMSO in culture medium 3
Positive control (PC): Ethylene glycol dimethacrylate (EGDMA, CAS no.: 97-90-5), 90.8 μM (= 18 μg/mL) in 1% DMSO in culture medium 3
Vehicle control (VC): 1% DMSO in culture medium 3
Blank control: culture medium 3 without cells
Basal control: culture medium 3 with cells
Remarks on result:
other: does not habe a keratinocyte activating potential

In the main test luciferase activity was measured after 48-hour exposure. In parallel a MTT assay was performed to assess cytotoxicity of the test substance. A total of 3 valid experiments were performed. One further experiment was conducted but was invalid for not meeting acceptance criteria and is not included in the report. The following results were observed: The test substance was soluble in 4% DMSO in culture medium 3 (4 x stock preparations) and in 1% DMSO in culture medium 3 (final concentrations). No precipitates were noticed in any concentration after 48 hours.

Calculation of an EC1.50 (the concentration resulting in a 1.50-fold luciferase induction) was not applicable due to the overall negative result of the study.

In summary, after 48 hours of exposure to test substance 1,1-diethoxyethane luciferase activity in LuSens cells was not induced in at least two consecutive concentrations with statistical significance affording at least 70% viability in at least two independent experiments. From this it has to be concluded that test substance 1,1-diethoxyethane does not have a keratinocyte activating potential.

Conclusions:
Based on the observed results and applying the evaluation criteria, 2-Phenylethylamine does not activate keratinocytes.
Endpoint conclusion
Endpoint conclusion:
adverse effect observed (sensitising)
Additional information:

In vitro studies covering three key steps of the adverse outcome pathway for skin sensitization as identified by the OECD (OECD Publication No.168; ENV/JM/MONO(2012)10) were performed. These study types have initially undergone in-house validation using 54 substances (Bauch et al., 2012 Regul Toxicol Pharmacol. 63: 489-504). Recently, a validation performed with 213 substances has been published (Urbisch et al. 2015 Regul Toxicol Pharmacol. 71: 337-351).

Based on the results of the in house validation (Bauch et al., 2012 Regul Toxicol Pharmacol. 63: 489-504) the predictive capacity of the evaluation scheme using DPRA (peptide reactivity), LuSens/KeratinoSens™ (keratinocyte activation) and (m)MUSST/h-CLAT (dendritic cell activation) is comparable to that of the local lymph node assay. This was confirmed in the validation study with more substances (Urbisch 2015): When compared to the sensitization potential of the substances in humans, the classification based on an evaluation scheme using results obtained from the DPRA, LuSens and mMUSST had a sensitivity of 90%, a specificity of 90% and an accuracy of 90%.

 

In the evaluation scheme used here any two of the three test results determine the overall classification, i.e. any two positive test results drive the prediction of a sensitizer, while any two negative test results drive the prediction of a test substance to be a non-sensitizer (Bauchet al. 2012; Table 1). If two assays (DPRA ,LuSens or KeratinoSens, MUSST or h-CLAT) yield concordant results, the result of the third assay is not necessarily required to determine the overall outcome of the evaluation scheme.

 

Table 1: Decision matrix for combinations of DPRA, LuSens/KeratinoSens and MUSST/ h-CLAT assays.

DPRA

LuSens/

KeratinoSensTM

MUSST/

h-CLAT

Test battery evaluation

positive

positive

positive

sensitizer

positive

positive

negative

sensitizer

positive

negative

positive

sensitizer

positive

negative

negative

non-sensitizer

negative

positive

positive

sensitizer

negative

positive

negative

non-sensitizer

negative

negative

positive

non-sensitizer

negative

negative

negative

non-sensitizer

Each individual assay was performed under GLPand the cell based assays LuSens consisted of at least two independent experiments. Positive and negative controls were included in each experiment and confirmed the functionality and validity of the individual assays. The DPRA and the keratinocyte activation assay follow the procedures of the respective OECD testing guidelines (OECD 442C and D). An OECD testing guideline for the dentritic cell activation assay is under preparation.

The test battery applicability is limited when testing substances insoluble in the commonly used vehicles and highly volatile substances. Substances susceptible to base-catalyzed hydrolysis cannot be evaluated reliably for binding to lysine as the incubation is performed at pH 10.2. Also substances that interfere with the experimental measurements (e.g., co-elution with the peptide in the DPRA-assay) are not or only partially suitable for testing using in vitro methods. The substance under evaluation did not have any of the above mentioned limitations and the outcome of this assay is therefore considered adequate for hazard identification for the endpoint of skin sensitization.

Sensitization involves a number of key steps in order to take place, and can be described in terms of an adverse outcome pathway (AOP). These include reactivity with skin proteins (peptide reactivity), activation of skin cells (keratinocyte activation) and immune cells (dendritic cell activation). The studies carried out for this substance address these three key steps. The results are then used in a predefined evaluation scheme to determine hazard classification as a sensitizer by a weight-of-evidence approach.

Respiratory sensitisation

Endpoint conclusion
Endpoint conclusion:
no study available

Justification for classification or non-classification

Classification, Labelling, and Packaging Regulation (EC) No 1272/2008

The available experimental test data are reliable and suitable for classification purposes under Regulation (EC) No 1272/2008, as amended for the eighth time in Regulation (EU) No 2016/218. As a result the substance is considered to be classified as skin sensitising cat. 1 (H317).