Diethyl ethoxymethylenemalonate

Skin irritation / corrosion

Administrative data

Endpoint:

skin corrosion: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2017-08-22 to 2017-08-28

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

Well documented GLP study performed according to OECD guideline 439 and EU method B.46. There were no deviations from the study plan.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2017

Report date:

2017

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 439 (In Vitro Skin Irritation: Reconstructed Human Epidermis Test Method)

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method B.46 (In Vitro Skin Irritation: Reconstructed Human Epidermis Model Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test material

Test material information

Constituent 1

Reference substance name:

Diethyl ethoxymethylenemalonate

EC Number:

201-725-7

EC Name:

Diethyl ethoxymethylenemalonate

Cas Number:

87-13-8

Molecular formula:

C10H16O5

IUPAC Name:

diethyl ethoxymethylenemalonate

Test material form:

liquid

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: JC170405
- Expiration date of the lot/batch: 2018-04-12 (retest date)
- Purity test date: no data

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: at room temperature

TREATMENT OF TEST MATERIAL PRIOR TO TESTING
- Treatment of test material prior to testing: none, the liquid test item was applied undiluted directly on top of the tissue.

In vitro test system

Test system:

human skin model

Remarks:

of human-derived epidermal keratinocytes

Source species:

human

Cell type:

non-transformed keratinocytes

Source strain:

other: not applicable

Justification for test system used:

In the interest of sound science and animal welfare, a sequential testing strategy is recommended to minimise the need of in vivo testing. One of the validated in vitro skin irritation tests is the EPISKIN test, which is recommended in international guidelines (e.g. OECD and EC)

Vehicle:

unchanged (no vehicle)

Details on test system:

RECONSTRUCTED HUMAN EPIDERMIS (RHE) TISSUE
- Model used: EPISKIN Small model (EPISKIN-SMTM, 0.38 cm²) supplied by SkinEthic Laboratories, Lyon, France
- Tissue batch number(s): 17-EKIN-034
- This model is a three-dimensional human epidermis model, which consists of adult human-derived epidermal keratinocytes which have been seeded on a dermal substitute consisting of a collagen typ e I matrix coated with type IV collagen. The keratinocytes were cultured for 13 days, which results in a highly differentiated and stratified epidermis model comprising the main basal, supra basal, spinous a nd granular layers and a functional stratum corneum.
- On the day of receipt the tissues were transferred to 12-well plates and preincubated with prewarmed Maintenance Medium for 68 hours at 37°C.
- Twenty five µl of the undiluted test item was added into 12-well plates on top of the skin tissues.

TEMPERATURE USED FOR TEST SYSTEM
- Temperature used during treatment / exposure: room temperature
- Temperature of post-treatment incubation (if applicable): 37°C
- All incubations, with the exception of the test item incubation of 15 minutes at room temperature, were carried out in a controlled environment, in which optimal conditions were a humid atmosphere of 80 - 100% (actual range 66 - 93%), containing 5.0 ± 0.5% CO2 in air in the dark at 37.0 ± 1.0°C (actual range 36.3 - 37.4°C).
- Temperature and humidity were continuously monitored throughout the experiment. The CO2 percentage was monitored once on each working day. Temporary deviations from the temperature, humidity and CO2 percentage may occur due to opening and closing of the incubator door. Based on laboratory historical data these deviations are considered not to affect the study integrity.

REMOVAL OF TEST MATERIAL AND CONTROLS
- After the exposure period of 15 ± 0.5 minutes at room temperature, the tissues were washed with phosphate buffered saline (PBS) to remove residual test item. After rinsing the cell culture inserts were each dried carefully and moved to a new well on 2 mL pre-warmed maintenance medium until all tissues were dosed and rinsed. Subsequently the skin tissues were incubated for 42 hours at 37°C.

MTT DYE USED TO MEASURE TISSUE VIABILITY AFTER TREATMENT / EXPOSURE
- After incubation, cell culture inserts were dried carefully to remove excess medium and were transfer red into a 12-wells plate prefilled with 2 mL MTT-medium (0.3 mg/mL). The tissues were in cubated for 3 hours at 37°C. After incubation the tissues were placed on blotting paper to dry the tissues. Total biopsy was made by using a biopsy punch. Epidermis was separated from the collagen matrix and both parts were placed in prelabeled microtubes and extracted with 500 µL isopropanol (Merck, Darmstadt, Germany). Tubes were stored refrigerated and protected from light for approximately 68 hours. The amount of extracted formazan was determined spectrophotometrically at 570 nm in duplicate with the TECAN Infinite® M200 Pro Plate Reader.
- Cell viability was calculated for each tissue as a percentage of the mean of the negative control tissues. Skin irritation potential of the test item was classified according to remaining cell viability following exposure of the test item.
- Test for reduction of MTT by test item: A test item may interfere with the MTT endpoint if it is coloured and/or it is able to directly reduce MTT. The cell viability measurement is affected only if the test item is present on the tissues when the MTT viability test is performed. The test item was checked for possible direct MTT reduction and colour interference in the Skin corrosion test using EpiDerm as a skin model (project 514804). Because solutions turned blue / purple and a blue / purple precipitate was observed it was concluded that the test item is able to directly reduce the MTT.


FUNCTIONAL MODEL CONDITIONS WITH REFERENCE TO HISTORICAL DATA
- Viability (≥ 19.5%): 23.0 +/-0.3% (CV =1.4%)
- Barrier function (IC50 determination, ≥ 1.5 mg/mL): 2.1 mg/mL
- Morphology: well-differentiated epidermis consisting of a basal layer, several spinous and granular layers and a thick stratum corneum.
- Contamination:
- on blood of the same donors, the following was verified: the absence of HIV1 and 2 antibodies, the absence of hepatitis C antibodies, the absence of hepatitis B antigen HBs;
- on epidermal cells of the same donors, the following was verified: the absence of bacteria, fungus and mycoplasma.
- Expiration date: 2017-08-28

CONTROL TISSUES USED IN CASE OF MTT DIRECT INTERFERENCE
- Fresh tissues / killed tissues: In addition to the normal 15-min procedure, two killed tissues treated with test item and two killed non treated tissues from the same batch were used for the cytotoxicity evaluation with MTT.
- Procedure used to prepare the killed tissues (if applicable): Living epidermis was transferred to 12 well plates and incubated with 2 ml Milli-Q for 48 ± 1 hours. After incubation, killed epidermis was stored at ≤ -15°C. Killed tissues were thawed by placing them for 1 hour at room temperature in 12 well plates on 2 ml maintenance medium. Further use of killed tissues was similar to living tissues.
- N. of replicates: 2 replicates
- Lot no.: 17-EKIN-032
- Method of calculation used: Non specific MTT reduction (NSMTT) was calculated. NSMTT is the difference between the OD of untreated killed tissues (ODku) and test item treated killed tissues (ODkt) expressed as percentage of the mean of the negative control tissues (ODnc).
NSMTT = [(ODkt – ODku)/ODnc] * 100
NSMTT should be ≤30% relative to the negative control OD. If the NSMTT is >50%, the chemical must be considered as incompatible with the test.
True MTT metabolic conversion (TODtt) is the difference between the OD of test item treated viable tissues (ODtv) and the difference between ODkt and ODku.
TODtt = [ODtv – (ODkt-ODku)]
The relative viability of these tissues is the true MTT metabolic conversion (TODtt) as a percentage of the mean of the negative control tissues.
% viability = [TODtt/ODnc] * 100
In case the NSMTT ≤ 0.0, there is no need to calculate the TODtt. The % viability will be calculated according to the protocol.

NUMBER OF INDEPENDENT TEST SEQUENCES / EXPERIMENTS TO DERIVE FINAL PREDI CTION: 1

INTERPRETATION
- A test item is considered to be irritant in the skin irritation test (category 2) if: the relative mean tissue viability of three individual tussues after 15 minutes of exposure to the test item and 42 hours of post incubation is ≤ 50% of the mean viability of the negative controls.
- A test item is considered to be non-irritant in the in vitro skin irritation test (no category) if the relative mean tissue viability after 15 minutes of exposure to the test item and 42 hours of post incubation is > 50% of the mean viability of the negative controls.

Control samples:

yes, concurrent negative control

yes, concurrent positive control

Amount/concentration applied:

TEST MATERIAL
- Amount(s) applied (volume or weight with unit): 25 µL

NEGATIVE CONTROL (PBS)
- Amount(s) applied (volume or weight): 25 µL

POSITIVE CONTROL (5% SDS)
- Amount(s) applied (volume or weight): 25 µL

Duration of treatment / exposure:

15 +/- 0.5 minutes (the positive control was re-spread after 7 minutes contact time)

Duration of post-treatment incubation (if applicable):

42 hours

Number of replicates:

3 replicates per test item together with negative and positive controls

Results and discussion

In vitro

Results

Results 1

Irritation / corrosion parameter:

% tissue viability

Remarks:

mean tissue viability

Run / experiment:

1

Value:

18

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Positive controls validity:

valid

Remarks on result:

other: range: 9.4 to 28%

Remarks:

SD: +/- 9.6

Results 2

Irritation / corrosion parameter:

other: mean optical density

Run / experiment:

1

Value:

0.172

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Positive controls validity:

valid

Remarks on result:

other: range: 0.089 to 0.269

Remarks:

SD: +/- 0.091

Other effects / acceptance of results:

mean tissue viability (percentage of control):
negative control: 100 +/- 5.3
positive control: 15 +/- 5.6

mean optical density:
negative control: 0.947 +/- 0.050
positive control: 0.146 +/- 0.053

Interpretation:
The viabilities of all replicates were within one category.

Results:
The test item was checked for possible direct MTT reduction and colour interference in the Skin corrosion test using EpiDerm as a skin model (project 514804). Because a color change was observed by adding MTT-medium it was concluded that the test item did interact with the MTT endpoint.
In addition to the normal procedure, three killed tissues treated with test item and three killed non treated tissues were used for the cytotoxicity evaluation with MTT.
The non-specific reduction of MTT by the test item was -4.2% of the negative control tissues. Since the NSMTT was <0.0, there was no need to correct OD values of the living tissues.

The relative mean tissue viability obtained after 15 ± 0.5 minutes treatment with the test item compa red to the negative control tissues was 18% (9.4 to 28%). Since the mean relative tissue viability for the test item was below 50% it is considered to be irritant.

The positive control had a mean cell viability after 15 ± 0.5 minutes exposure of 15% (9.2 to 20%). The absolute mean OD570 of the negative control tissues was within 0.6 and 1.5. The standard deviation values of the percentage viability of three tissues treated identically were 5.3%, 5.6% and 9.6% for the negative, positive control and the test item respectively, indicating that the test system functioned properly.

Applicant's summary and conclusion

Interpretation of results:

Category 2 (irritant) based on GHS criteria

Conclusions:

It is concluded that the test is valid and that the test item is irritant in the in vitro skin irritation test under the experimental conditions described and should be classified category 2 according to the Globally Harmonized System of Classification and Labeling of Chemicals (GHS) of the United Nations based on this test and the in vitro skin corrosion study (project 514804).