ethyl N,S-bis(4-oxo-4-(2,6,6-trimethylcyclohex-3-en-1-yl)butan-2-yl)cysteinate

Skin irritation / corrosion

Administrative data

Endpoint:

skin irritation: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

19 March 2018 to 26 March 2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

conducted under GLP conditions

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2018

Report date:

2018

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)

Version / remarks:

2015

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

2012

Deviations:

no

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

ethyl N,S-bis(4-oxo-4-(2,6,6-trimethylcyclohex-3-en-1-yl)butan-2-yl)cysteinate

EC Number:

866-600-7

Cas Number:

2173997-41-4

Molecular formula:

C31H51NO4S

IUPAC Name:

ethyl N,S-bis(4-oxo-4-(2,6,6-trimethylcyclohex-3-en-1-yl)butan-2-yl)cysteinate

Test material form:

liquid

In vitro test system

Test system:

human skin model

Source species:

human

Cell type:

non-transformed keratinocytes

Justification for test system used:

In the interest of sound science and animal welfare, a sequential testing strategy is recommended to minimize 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:

Test system: EPISKIN Small ModelTM (EPISKIN-SMTM, 0.38 cm2, Batch no.: 18-EKIN-012
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 type 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 and granular layers and a functional stratum corneum.

Source
SkinEthic Laboratories, Lyon, France

Experimental design:
- Test for the Interference of the Test Item with the MTT Endpoint: A test item may interfere with the MTT endpoint if it is colored 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.
- Test for Color Interference by the Test Item: GR-87-0307 was checked for possible color interference before the study was started. Some non-colored test items may change into colored items in aqueous conditions and thus stain the skin tissues during the exposure. To assess the color interference, 10 µL of GR-87-0307 was added to 90 µL Milli-Q water. The mixture was mixed for approximately 15 minutes. A negative control, 10 µL Milli-Q water was tested concurrently. At the end of the shaking period a color check was performed.
- Test for Reduction of MTT by the Test Item: GR-87-0307 was checked for possible direct MTT reduction before the study was started. To assess the ability of the test item to reduce MTT, 25 µL of the test item was added to 2 mL MTT solution (0.3 mg/mL in PBS). The mixture was incubated for 3 hours at 37°C. A negative control, 25 µL sterile Milli-Q water was tested concurrently. At the end of the incubation period a color check was performed.
- Test system set up: On the day of receipt the tissues were transferred to 12-well plates and pre-incubated with pre-warmed Maintenance Medium for 21 hours at 37°C. Maintenance medium and Assay medium were supplied by Skinethic Laboratories, Lyon, France.

Killed tissues (EPISKIN-SMTM, 0.38 cm2, Lot no.: 17-EKIN-040 and 18-EKIN-010). 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.

MTT medium:
MTT concentrate (Sigma Aldrich, Zwijndrecht, The Netherlands; 3 mg/mL in PBS) diluted (10x) in Assay medium (final concentration 0.3 mg/mL).

Environmental conditions:
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 58 - 84%), containing 5.0 ± 0.5% CO2 in air in the dark at 37.0 ± 1.0°C (actual range 36.8 – 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.

Application/Treatment of the test item:
The test was performed on a total of 3 tissues per test item together with negative and positive controls. Twenty five µL of the undiluted test item was added into 12-well plates on top of the skin tissues. Three tissues were treated with 25 µL PBS (negative control) and 3 tissues with 25 µL 5% SDS (positive control) respectively. The positive control was re-spread after 7 minutes contact time.
Since the test item reacted with the MTT medium, in addition three killed tissues treated with test item and three killed untreated tissues were used for the cytotoxicity evaluation with MTT.
After the exposure period of 15 ± 0.5 minutes at room temperature, the tissues were washed with phosphate buffered saline 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.

Cell viability measurement:
After incubation, cell culture inserts were dried carefully to remove excess medium and were transferred into a 12-wells plate prefilled with 2 mL MTT-solution (0.3 mg/mL in PBS). The tissues were incubated for 3 h 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 pre-labeled microtubes and extracted with 500 µL isopropanol (Merck, Darmstadt, Germany). Tubes were stored refrigerated and protected from light for 68 hours. The amount of extracted formazan was determined spectrophotometrically at 570 nm in duplicate with the TECAN Infinite® M200 Pro Plate Reader.

Analysis:
Calculation of Cell Viability:
Optical Density readings were transferred into Microsoft Excel to allow further calculations to be performed.
The corrected OD (ODc) for each sample or control was calculated by subtracting the value of the blank mean (ODbl) (well with solvent) from each reading (ODraw).
ODc = ODraw – ODbl
The OD value representing 100% cell viability is the average OD of the negative controls (ODlt_u+MTT).
The %Viability for each sample and positive control is calculated as follows:
%Viability = (ODc/mean ODlt_u+MTT) * 100

MTT interacting test items:
Nonspecific MTT reduction (NSMTT) was calculated. NSMTT is the difference between the mean OD of the untreated killed tissues (ODkt_u+MTT) and test item treated killed tissues (ODkt_t+MTT) expressed as percentage of the mean of the negative control tissues (ODlt_u+MTT).
%NSMTT = [(ODkt_t+MTT – ODkt_u+MTT)/ mean ODlt_u+MTT] * 100
True tissue viability is calculated as the difference between the living test item treated tissues incubated with MTT medium (ODlt_t+MTT) and the difference between ODkt_t+MTT and ODkt_u+MTT.
OD= ODlt_t+MTT – (ODkt_t+MTT-ODkt_u+MTT)
%Viability = [OD/ mean ODlt_u+MTT] * 100
In case the %NSMTT ≤ 0.0, there is no need to correct for interference of the test item.

Control samples:

yes, concurrent negative control

yes, concurrent positive control

Amount/concentration applied:

- 25 µL of undiluted test item
- 25 µL PBS for negative control
- 25 µL 5% SDS for positive control

Duration of treatment / exposure:

15 +/- 5 minutes

Duration of post-treatment incubation (if applicable):

42 hours at 37°C

Number of replicates:

Triplicate tissues for test item, negative and positive controls

Results and discussion

In vitro

Results

Irritation / corrosion parameter:

% tissue viability

Run / experiment:

15 +/- 0.5 minutes exposure period and 42 hour post incubation period

Value:

72

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Positive controls validity:

valid

Remarks on result:

no indication of irritation

Other effects / acceptance of results:

The net OD of the treated killed tissues was subtracted from the ODs of the test item treated viable tissues.
Skin irritation is expressed as the remaining cell viability after exposure to the test item. The relative mean tissue viability obtained after 15 ± 0.5 minutes treatment with GR-87-0307 compared to the negative control tissues was 72%. Since the mean relative tissue viability for GR-87-0307 was above 50% after 15 ± 0.5 minutes treatment GR-87-0307 is considered to be non-irritant.
The positive control had a mean cell viability of 13% after 15 ± 0.5 minutes exposure. The absolute mean OD570 (optical density at 570 nm) of the negative control tissues was within the laboratory historical control data range. The standard deviation value of the percentage viability of three tissues treated identically was ≤ 11%, indicating that the test system functioned properly.

Applicant's summary and conclusion

Interpretation of results:

GHS criteria not met

Conclusions:

In conclusion, GR-87-0307 is non-irritant in the in vitro skin irritation test under the experimental conditions described in this report and should not be classified.

Executive summary:

The objective of this study was to evaluate GR-87-0307 for its ability to induce skin irritation on a human three dimensional epidermal model (EPISKIN Small model (EPISKIN-SMTM)). The possible skin irritation potential of GR-87-0307 was tested through topical application for 15 minutes.

The study procedures described in this report were based on the most recent OECD and EC guidelines.

Batch 8 of GR-87-0307 was a pale yellow to yellow liquid. GR-87-0307 was applied undiluted (25 µL directly on top of the skin tissue for 15 ± 0.5 minutes. After a 42 hour post- incubation period, determination of the cytotoxic (irritancy) effect was performed.

Cytotoxicity is expressed as the reduction of mitochondrial dehydrogenase activity measured by formazan production from MTT at the end of the treatment.

GR-87-0307 did interact with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT). In addition to the normal procedure, three killed tissues treated with test item and three killed untreated tissues were used for the cytotoxicity evaluation with MTT. The non- specific reduction of MTT by GR-87-0307 was 12.9% of the negative control tissues. The net OD of the treated killed tissues was subtracted from the ODs of the test item treated viable tissues.

Skin irritation is expressed as the remaining cell viability after exposure to the test item. The relative mean tissue viability obtained after 15 ± 0.5 minutes treatment with GR-87-0307 compared to the negative control tissues was 72%. Since the mean relative tissue viability for GR-87-0307 was above 50% after 15 ± 0.5 minutes treatment GR-87-0307 is considered to be non-irritant.

The positive control had a mean cell viability of 13% after 15 ± 0.5 minutes exposure. The absolute mean OD570(optical density at 570 nm) of the negative control tissues was within the laboratory historical control data range. The standard deviation value of the percentage viability of three tissues treated identically was ≤ 11%, indicating that the test system functioned properly.

In conclusion, GR-87-0307 is non-irritant in the in vitro skin irritation test under the experimental conditions described in this report and should not be classified.