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Toxicological information

Skin irritation / corrosion

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Administrative data

Endpoint:
skin corrosion: in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2017-12-04 - 2018-02-08
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 guideline
Qualifier:
according to
Guideline:
OECD Guideline 431 (In Vitro Skin Corrosion: Reconstructed Human Epidermis (RHE) Test Method)
Deviations:
no
GLP compliance:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Test material form:
liquid

In vitro test system

Test system:
human skin model
Source species:
human
Cell type:
non-transformed keratinocytes
Cell source:
other: not specified (adult donors)
Justification for test system used:
The corrosivity potential of a chemical may be predicted by measurement of its cytotoxic effect, as reflected in the MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, Thiazolyl blue; CAS number 298-93-1] assay, on EPISKINTM(SM) reconstituted human epidermis. This method is approved by international regulatory agencies as a replacement for the identification of irritants / corrosives in the in vivo Rabbit skin assay (OECD No. 404) and is specifically approved as a replacement for the in vivo skin corrosivity test within OECD No. 431.
Vehicle:
unchanged (no vehicle)
Details on test system:
RECONSTRUCTED HUMAN EPIDERMIS (RHE) TISSUE
- Model used: EPISKINTM(SM)
- Tissue batch number(s): 17-EKIN-050
- Production date: 12 December 2017
- Shipping date: not specified
- Delivery date: not specified
- Date of initiation of testing: 14 December 2017

TEMPERATURE USED FOR TEST SYSTEM
- Temperature used during treatment / exposure: room temperature (22.4-25.1°C)
- Temperature of post-treatment incubation: N/A

REMOVAL OF TEST MATERIAL AND CONTROLS
-Volume and number of washing steps: one washing with PBS solution
- Observable damage in the tissue due to washing: no
- Modifications to validated SOP: no

MTT DYE USED TO MEASURE TISSUE VIABILITY AFTER TREATMENT / EXPOSURE
- MTT concentration: 0.3 mg/mL MTT
- Incubation time: 3 hours (±15 minutes)
- Spectrophotometer: Thermo Fisher Scientific
- Wavelength: 570 nm.
- Filter: not specified
- Filter bandwidth: not specified
- Linear OD range of spectrophotometer: The proper status of the instrument was verified by measuring a Verification plate (Manufacturer: Thermo Fisher Scientific, Catalogue Number: 24072800, Serial
Number: 0920-14, Date of calibration: 22 August 2016, calibration is valid until August 2018) at the required wavelength on each day before use.

FUNCTIONAL MODEL CONDITIONS WITH REFERENCE TO HISTORICAL DATA
- Quality control: The quality of the final product is assessed by undertaking a MTT cell viability test and a cytotoxicity test with sodium dodecylsulphate (SDS). These quality control experiments were conducted at SkinEthic laboratories (supplier of the EpiSkinTM(SM) Test Kits used in the present study) .
- Contamination: All biological components of the epidermis and the kit culture medium have been tested for the presence of viruses, bacteria and mycoplasma.


NUMBER OF REPLICATE TISSUES: Two replicates for test item were used. Two negative controls and two positive controls were also run in this assay.

CONTROL TISSUES USED IN CASE OF MTT DIRECT INTERFERENCE
- Fresh tissues
- Procedure used to prepare the killed tissues (if applicable): N/A
- N. of replicates : duplicate
- Method of calculation used: Non specific MTT reduction calculation (NSMTT%):
NSMTT% = [(ODKT- ODKNC) / ODNC] × 100
ODKNC: negative control treated killed tissues OD
ODKT: test item treated killed tissues OD
ODNC: negative control OD


NUMBER OF INDEPENDENT TEST SEQUENCES / EXPERIMENTS TO DERIVE FINAL PREDICTION: one

PREDICTION MODEL / DECISION CRITERIA:
The cut-off value of 35% and classification method was validated in an international validation study of this kit (Fentem, 1998).
For 2 disks:
If both disks have mean viability of ≥35% = Non Corrosive
If both disks have mean viability of <35% = Corrosive (at the corresponding incubation period)
Control samples:
yes, concurrent negative control
yes, concurrent positive control
yes, concurrent MTT non-specific colour control
Amount/concentration applied:
The test item was applied as supplied, no formulation was required.
The Assay Medium was pre-warmed to 37°C. The appropriate number of wells in an assay plate was filled with the pre-warmed medium (2 mL per well). The epidermis units were placed with the media below them, whereby each epidermis was in contact with the medium in the corresponding well underneath. Two epidermis units were used for each test or control materials.
- ~95 mg of test item was applied evenly to the epidermal surface of each of two test units and each additional control skin units and then 100 μL physiological saline was added to the test item to ensure good contact with the epidermis.
- 50 μL of physiological saline was added to each of the two negative control skin units.
- 50 μL of glacial acetic acid was added to each of the two positive control skin units.
Duration of treatment / exposure:
The plates with the treated epidermis units were incubated for 4 hours (±10 min) at room temperature (22.4-25.1°C) covered with the plate lids.
Duration of post-treatment incubation (if applicable):
Rinsing:
After the incubation time (4 hours), all test item treated tissues or also the positive control tissues were removed and rinsed thoroughly with PBS solution to remove all the remaining test or positive control material from the epidermal surface. Likewise, negative control tissues were processed accordingly.
The rest of the PBS was removed from the epidermal surface using a pipette (without touching the epidermis).

MMT test:
MTT solution (2 mL of 0.3 mg/mL MTT working solution) was added to each well below the skin units (except of the two living colour control units). The lid was replaced and the plate incubated at 37°C in an incubator with 5% CO2 in a >95% humidified atmosphere for 3 hours (±15 minutes), protected from light.

Formazan extraction:
At the end of incubation with MTT a formazan extraction was undertaken. A disk of epidermis was cut from each skin unit (this procedure involved the maximum area of the disk) using a biopsy punch (supplied as part of the kit). The epidermis was separated
with the aid of forceps and both parts (epidermis and collagen matrix) were placed into a tube containing 500 μL acidified isopropanol (one tube corresponded to one well of the assay plate).
The capped tubes were thoroughly mixed by using a vortex mixer to achieve a good contact of all of the material and the acidified isopropanol, and then incubated overnight at room temperature protected from light with gentle agitation (~150 rpm) for formazan
extraction.
A blank sample containing 2 mL of acidified isopropanol was processed in parallel.

Cell viability measurement:
Following the formazan extraction, 2×200 μL sample from each tube were placed into the wells of a 96-well plate (labelled appropriately). The OD (optical density or absorbance) of the samples was measured using a plate reader at 570 nm. The mean of 6 wells of acidified isopropanol solution (200 μL/well) was used as blank.
Number of replicates:
In this assay, two replicates for test item were used. Two negative controls and two positive controls were also run in this assay. Furthermore, as the test item was coloured, two additional test item-treated living tissues were used for the non specific OD evaluation.

Results and discussion

In vitro

Results
Irritation / corrosion parameter:
% tissue viability
Value:
94.3
Vehicle controls validity:
not applicable
Negative controls validity:
valid
Positive controls validity:
valid
Other effects / acceptance of results:
- OTHER EFFECTS:
- Visible damage on test system: After receipt, the two indicators of the delivered kit were checked. Based on the observed colours, the epidermis units were in proper conditions.
- Direct-MTT reduction: As no colour change was observed after three hours of incubation of the test item in MTT solution, thus the test material did not interact with MTT.
- Colour interference with MTT: As the test item was coloured, two additional test item-treated living tissues were used for the non-specific OD evaluation. The mean optical density (measured at 570 nm) of these tissues was determined as 0.006, Non Specific Colour % (NSCliving%) was calculated as 0.8%. This is below the threshold of 5%, therefore correction due to colouring potential was not necessary.

ACCEPTANCE OF RESULTS:
- Acceptance criteria met for negative control: The mean OD value of the two negative control tissues was in the recommended range (0.826).
- Acceptance criteria met for positive control: The two positive control treated tissues showed 1.0% viability demonstrating the proper performance of the assay.
- Acceptance criteria met for variability between replicate measurements: The difference of viability between the two test item-treated tissue samples in the MTT assay was 8.9%. The difference of viability between the two negative control tissue samples in the MTT assay was 7.9 %.
- Range of historical values if different from the ones specified in the test guideline:N/A

Any other information on results incl. tables

Validity of the test:

After receipt, the two indicators of the delivered kit were checked. Based on the observed colours, the epidermis units were in proper conditions.

The mean OD value of the two negative control tissues was in the recommended range (0.826).

The two positive control treated tissues showed 1.0% viability demonstrating the proper performance of the assay.

The difference of viability between the two test item-treated tissue samples in the MTT assay was 8.9%.

The difference of viability between the two negative control tissue samples in the MTT assay was 7.9 %.

The mean OD value of the blank samples (acidified isopropanol) was 0.048.

All these parameters were within acceptable limits and therefore the study was considered to be valid.

Additional controls:

As no colour change was observed after three hours of incubation of the test item in MTT solution, thus the test material did not interact with MTT. Therefore, additional controls and data calculations were not necessary to exclude the false estimation of viability.

As the test item was coloured, two additional test item-treated living tissues were used for the non-specific OD evaluation. The mean optical density (measured at 570 nm) of these tissues was determined as 0.006, Non Specific Colour % (NSCliving%) was calculated as 0.8% . This is below the threshold of 5%, therefore correction due to colouring potential was not necessary.

Applicant's summary and conclusion

Interpretation of results:
GHS criteria not met
Conclusions:
In this in vitro EPISKIN™(SM) model test with Sopromine 1686, the results indicate that the test item is non-corrosive to the skin.
Executive summary:

An in vitro skin corrosivity test of Sopromine 1686 test item was performed in a reconstructed human epidermis model. EPISKINTM(SM) is designed to predict and classify the corrosive potential of chemicals by measuring its cytotoxic effect as reflected in the MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. The corrosivity of the test item was evaluated according to the OECD No. 431 guideline.

Disks of EPISKINTM(SM) (two units) were treated with Sopromine 1686 test item and incubated for 4 hours at room temperature. Exposure of test material was terminated by rinsing with Phosphate Buffered Saline solution. The viability of each disk was assessed by incubating the tissues for 3 hours with MTT solution. The precipitated formazan crystals were then extracted using acidified isopropanol and quantified

spectrophotometrically.

Physiological saline (0.9% (w/v) NaCl solution) and glacial acetic acid treated epidermis were used as negative and positive controls, respectively (two units / control).

Two additional disks were used to provide an estimate of colour contribution (NSCliving%) from the test item. For each treated tissue viability was expressed as a % relative to the negative control. If the mean relative viability after 4 hours of exposure is below 35% of the negative control, the test item is considered to be corrosive to skin.

Following exposure with Sopromine 1686, the mean cell viability was 94.3% compared to the negative control. This is above the threshold of 35%, therefore the test item was considered as being non-corrosive. The experiment met the validity criteria, therefore the study was considered to be valid.

In conclusion, in this in vitro EPISKIN™(SM) model test with Sopromine 1686 (Batch number: 3900075), the results indicate that the test item is non-corrosive to the skin.