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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:
02 September 2016 to 03 September 2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2017
Report date:
2017

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to guideline
Guideline:
OECD Guideline 431 (In Vitro Skin Corrosion: Reconstructed Human Epidermis (RHE) Test Method)
Version / remarks:
2015
Deviations:
no
Qualifier:
according to guideline
Guideline:
other: EU Method B.40 bis
Version / remarks:
2880
Deviations:
no
GLP compliance:
yes (incl. QA statement)

Test material

Constituent 1
Chemical structure
Reference substance name:
2-ethylhexyl 4-(dimethylamino)benzoate
EC Number:
244-289-3
EC Name:
2-ethylhexyl 4-(dimethylamino)benzoate
Cas Number:
21245-02-3
Molecular formula:
C17H27NO2
IUPAC Name:
2-ethylhexyl 4-(dimethylamino)benzoate
Test material form:
liquid

In vitro test system

Test system:
human skin model
Source species:
human
Cell type:
non-transformed keratinocytes
Vehicle:
unchanged (no vehicle)
Details on test system:
RECONSTRUCTED HUMAN EPIDERMIS (RHE) TISSUE
- Model used: EpiDerm™ Tissues (0.63 cm2)
- Supplier: MatTek
- Tissue batch number(s): Lot no.: 23352
- Storage conditions of tissues: The sealed 24 well plate was stored in a refrigerator until use

TEMPERATURE USED FOR TEST SYSTEM
- Temperature used during treatment / exposure: 37 °C
- Temperature of post-treatment incubation (if applicable): 37 °C

REMOVAL OF TEST MATERIAL AND CONTROLS
-Volume and number of washing steps: Rinsing was achieved by filling and emptying each tissue under a constant soft stream of DPBS to gently remove any residual test material. Excess DPBS was removed by blotting the bottom of the tissue insert with tissue paper. Each tissue was placed into the prepared holding plate until all tissues were rinsed. They were then blotted and transferred to the 24-well plate prepared for MTT loading.

MTT DYE USED TO MEASURE TISSUE VIABILITY AFTER TREATMENT / EXPOSURE
- MTT concentration: 1.0 mg/mL
- Incubation time: 3 hours
- Spectrophotometer: Anthos 2001 microplate reader
- Wavelength: 562 nm

NUMBER OF REPLICATE TISSUES: 2

TEST FOR DIRECT MTT REDUCTION BY THE TEST MATERIAL
A test material may interfere with the MTT endpoint if it was able to directly reduce MTT and at the same time was present on or in the tissues when the MTT viability test was performed. To identify this possible interference, the test material was checked for the ability to directly reduce MTT. 50 µL of the test material was added to 1 mL of a freshly prepared 1.0 mg/mL MTT solution. The solution was incubated in the dark at 37 °C, 5 % CO2 for 60 minutes. Untreated MTT solution was tested concurrently to act as a control. If the MTT solution containing the test material turns blue/purple relative to the control, the test material was presumed to have reduced the MTT.

ASSESSMENT OF COLOUR INTERFERENCE WITH THE MTT ENDPOINT
The test material may interfere with the MTT endpoint if it is coloured; the MTT assay is affected only if the test material is present in the tissues when the MTT viability assay is performed. 50 µL of test material was added to 300 µL of sterile water, the solution was incubated in the dark at 37 °C, 5% CO2 for 60 minutes. A visual assessment of the colour was then made.

MAIN TEST
-Pre-Incubation
0.9 mL of pre-warmed assay medium was pipetted into the appropriate wells of two pre-labelled 6-well plates for both the 3- and 60-minute exposure periods. EpiDerm™ tissues were transferred into the 6-well plates containing the assay medium. The 6-well plates containing the EpiDerm™ samples were pre-incubated (37 °C, 5 % CO2) for approximately 1 hour before dosing.

- Application of Test Material and Rinsing
Before pre-incubation was complete, a 24-well plate was prepared for use as a “holding plate” for both the 3- and 60-minute exposure periods. This plate was used to maintain the viability of the tissue inserts between rinsing following chemical exposure and MTT loading. Another 24-well plate was prepared for the MTT loading. 300 µL of either pre-warmed assay medium (holding plate) or MTT medium (MTT loading plate) was dispensed into each well. The two plates were placed into the incubator until required. After pre-incubation of the EpiDerm™ tissues, the medium was aspirated and replaced with 0.9 mL of fresh assay medium. The 6-well plate for the 3-minute exposure period was returned to the incubator, while the other was being dosed for the 60-minute exposure. For the 60-minute exposure period, 50 µL of sterile distilled water (negative control) was added to the first two tissues. The tissues were dosed at regular intervals to allow for the time taken to rinse each tissue following exposure and to ensure that each tissue gets an equal exposure time. 50 µL of the test material and 50 µL of 8.0 N Potassium Hydroxide (positive control) were also applied to the corresponding tissues in turn. The plate was returned to the incubator (37 °C, 5 % CO2) for the 60-minute exposure period.
When dosing for the 60-minute exposure period was complete, the same procedure was repeated for the 3-minute exposure period. Asthe exposure time was so short, the tissues were dosed at regular intervals to ensure that each tissue received an equal exposure time and to allow for the time taken to rinse each tissue following exposure. The plate was incubated (37 °C, 5 % CO2) for 3 hours. Once the 60-minute exposure period was complete, the same rinsing and MTT loading procedure was repeated.
After the 3-Hour MTT incubation was complete, the inserts were blotted and transferred to labelled 24-well plates for MTT extraction. 2 mL of MTT extractant (isopropanol) was used to completely immerse each insert and the plate was covered with plate sealer to prevent isopropanol evaporation. The plates stood overnight at room temperature, to allow extraction to proceed.

-Absorbance/Optical Density Measurements
After extraction, each tissue was pierced with a pipette fitted with a 1000 µL tip and the extraction solution was forced vigorously up and down to form a homogenous solution. 3 x 200 µL aliquots of the extract were transferred to the appropriate wells of a pre-labelled 96-well plate. 200 µL of isopropanol alone was added to the three wells designated as blanks. Absorbency at 562nm (OD562) of each well was measured using the Anthos 2001 microplate reader.

-Quantitative MTT Assessment (percentage tissue viability)
The corrosivity potential of the test material was predicted from the relative mean tissue viabilities obtained after the 3 and 60-minute exposure periods, compared to the mean of the negative control tissues (n = 2) treated with sterile distilled water. The relative mean viabilities were calculated in the following way:
Relative mean viability (%) = (mean OD562 of test material / mean OD562 of negative control) x 100

QUALITY CRITERIA
The results of the assay are considered acceptable if the following assay acceptance criteria are achieved:
-Negative Control
The absolute OD562 of the negative control treated tissues in the MTT-test is an indicator of tissue viability obtained in the testing laboratory after the shipping and storing procedure and under specific conditions of the assay. The mean OD562 of the two negative control tissues should be = 0.8 and = 2.8 for each exposure time, which ensures that the tissue viability meets the acceptance criteria.
-Positive Control
An assay meets the acceptance criterion if mean relative tissue viability of the 60 minute positive control is <15 %.
-Coefficient of Variation
In the range 20 and 100 % viability, the Coefficient of Variation between tissue replicates should be = 30 %.
Control samples:
yes, concurrent negative control
yes, concurrent positive control
Amount/concentration applied:
TEST MATERIAL
- Amount(s) applied (volume or weight with unit): 50 µL
Duration of treatment / exposure:
3 minutes and 60 minutes of exposure
Duration of post-treatment incubation (if applicable):
3 hours with MTT
Number of replicates:
2

Results and discussion

In vitro

Resultsopen allclose all
Irritation / corrosion parameter:
% tissue viability
Run / experiment:
3 minute exposure time
Value:
97.7
Vehicle controls validity:
not applicable
Negative controls validity:
valid
Positive controls validity:
valid
Irritation / corrosion parameter:
% tissue viability
Run / experiment:
60 minute exposure time
Value:
99.3
Vehicle controls validity:
not applicable
Negative controls validity:
valid
Positive controls validity:
valid
Other effects / acceptance of results:
The MTT solution containing the test material did not become coloured. This was taken to indicate the test material did not reduce MTT.
The solution containing the test material did not become coloured. This was taken to indicate the test material did not have the potential to cause colour interference.

QUALITY CRITERIA
The mean OD562 for the negative control treated tissues was 1.727 for the 3-minute exposure period and 1.603 for the 60-Minute exposure period. The negative control acceptance criteria were therefore satisfied.
The relative mean tissue viability for the positive control treated tissues was 4.8 % relative to the negative control following the 60-minute exposure period. The positive control acceptance criterion was therefore satisfied.
In the range 20 to 100 % viability the Coefficient of Variation between the two tissue replicates of each treatment group did not exceed 30 %. The acceptance criterion was therefore satisfied.

Any other information on results incl. tables

Table 1: Relative mean viabilities for each treatment group

Exposure Period

Percentage viability

Negative control

Positive control

Test material

3 minutes

100*

5.1

97.7

60 minutes

100*

4.8

99.3

*The mean viability of the negative control tissues is set at 100 %

Applicant's summary and conclusion

Interpretation of results:
other: Not corrosive in accordance with EU criteria
Conclusions:
Under the conditions of this study, the test material was determined to be non-corrosive.
Executive summary:

The corrosivity potential of the test material was determined in accordance with the standardised guidelines OECD 431 and EU Method B.40 bis using the EpiDerm™ Human Skin Model under GLP conditions.

Duplicate tissues were treated with the test material for exposure periods of 3 and 60 minutes and negative and positive control groups were also treated for each exposure period. At the end of the exposure period the test material was rinsed from each tissue before each tissue was taken for MTT-loading. After MTT loading each tissue was placed in 2 mL Isopropanol for MTT extraction. At the end of the formazan extraction period, each well was mixed thoroughly and triplicate 200 µL samples were transferred to the appropriate wells of a pre-labelled 96-well plate. The optical density (OD) was measured at 562 nm (OD562).

The percentage viability of the skin after exposure to the test material was 97.7 and 99.3 % after 3 and 6 minute exposures, respectively.

The quality criteria required for acceptance of results in the test were satisfied and the test was therefore considered to be valid.

Under the conditions of this study, the test material was determined to be non-corrosive.