Registration Dossier

Administrative data

Endpoint:
skin irritation: in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
key study
Study period:
8 December 2009 to 14 December 2009
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study conducted to GLP in accordance with generally accepted scientific principles, possibly with incomplete reporting or methodological deficiencies, which do not affect the quality of the relevant results.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2010
Report Date:
2010

Materials and methods

Test guideline
Qualifier:
no guideline available
Principles of method if other than guideline:
The purpose of this test was to evaluate the skin irritation potential of the test material using the EPISKIN™ reconstituted human epidermis model after a treatment period of 15 minutes followed by a post-exposure incubation period of 42 hours. The principle of the assay was based on the measurement of cytotoxicity in reconstituted human epidermal cultures following topical exposure to the test material by means of the colourimetric MTT reduction assay. Cell viability is measured by enzymatic reduction of the yellow MTT tetrazolium salt (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide) to a blue formazan salt (within the mitochondria of viable cells) in the test material treated tissues relative to the negative controls. The concentration of the inflammatory mediator IL-1alpha in the culture medium retained following the 42 hour post-exposure incubation period is also determined for test materials which are found to be borderline non-irritant based upon the MTT reduction endpoint. This complimentary end-point will be used to either confirm a non-irritant result or will be used to override the non-irritant result.
GLP compliance:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent

Test animals

Species:
other: reconstituted human epidermis
Strain:
other: not applicable
Details on test animals and environmental conditions:
Not applicable as the test was performed in vitro.

Test system

Type of coverage:
other: test material applied directly
Preparation of test site:
other: moistened with sterile distilled water
Vehicle:
unchanged (no vehicle)
Controls:
not required
Amount / concentration applied:
TEST MATERIAL
- Amount(s) applied (volume or weight with unit): 10 ± 2 mg

VEHICLE
- Amount(s) applied (volume or weight with unit): The epidermis surface had previously been moistened with 5 µl of sterile distilled water to improve contact between the solid test material and the epidermis.
Duration of treatment / exposure:
15 minutes
Observation period:
Not applicable
Number of animals:
Not applicable; the test was conducted in vitro. Three replicate test tissues were used for this study.
Details on study design:
Pre-Test

Assessment of Direct Test Material Reduction of MTT

MTT dye metabolism, cell viability assay

The MTT assay, a colourimetric method of determining cell viability, is based on reduction of the yellow tetrazolium salt (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide) to a purple formazan dye by mitochondrial succinate dehydrogenase in viable cells.

Assessment of Direct Test Material Reduction of MTT

One limitation of the assay is possible interference of the test substance with MTT. A test substance may directly reduce MTT, thus mimicking dehydrogenase activity of the cellular mitochondria. This property of the test substance is only a problem, if at the time of the MTT test (after rinsing) there are still sufficient amounts of the test substance present on or in the tissues. In this case, the true metabolic MTT reduction and the false direct MTT reduction can be differentiated and quantified by the procedure described as follows:

Test for Direct MTT Reduction

As specified, a test substance may interfere with the MTT endpoint, if it is able to directly reduce MTT and at the same time is present on or in the tissues when the MTT viability test is performed. To identify this possible interference, each test substance is checked for the ability to directly reduce MTT according to the following procedure:

10 mg of the test material was added to 2 ml of a 0.3 mg/ml TT solution freshly prepared in assay medium. The solution was incubated in the dark at 37°C, 5% CO2 in air for 3 hours. Untreated MTT solution was used as a control.

If the MTT solution containing the test substance turns blue/purple, the test substance is presumed to have reduced the MTT.

Pre-Incubation (Day 0: tissue arrival)

2 ml of maintenance medium, warmed to approximately 37°C, was pipetted into the first column of 3 wells of a pre-labelled 12-well plate. Each epidermis unit was transferred into the maintenance medium filled wells (3 units per plate). A different 12-well plate was used for the test material and each control material. The tissues were incubated at 37°C, 5% CO2 in air for at least 24 hours.

Main Test

Application of Test Material and Rinsing (Day 1)

2 ml of maintenance medium, warmed to approximately 37°C, was pipetted into the second column of 3 wells of the 12-well plate.

Triplicate tissues were treated with the test material for an exposure period of 15 minutes. The test material was applied topically to the corresponding tissues ensuring uniform covering. 10 ± 2 mg of the test material was applied to the epidermis surface. The epidermis surface had previously been moistened with 5 µl of sterile distilled water to improve contact between the solid test material and the epidermis. Triplicate tissues treated with 10 µl of PBS (Dulbecco's Phosphate Buffered Saline) served as the negative controls and triplicate tissues treated with 10 µl of SDS (Sodium Dodecyl Sulphate) 5% w/v served as the positive controls. To ensure satisfactory contact with the positive control material the SDS solution was spread over the entire surface of the epidermis using a pipette tip (taking particular care to cover the centre). After 7 minutes contact time the SDS solution was re-spread with a pipette tip to maintain the distribution of the SDS for the remainder of the contact period. The plate(s) were kept in the biological safety cabinet at room temperature for 15 ± 0.5 minutes.

At the end of the exposure period, each tissue was removed from the well using forceps and rinsed using a wash bottle containing PBS with Ca++ and Mg++. Rinsing was achieved by filling and emptying each tissue insert for approximately 40 seconds using a constant soft stream of PBS to gently remove any residual test material. The rinsed tissues were transferred to the second column of 3 wells containing 2 ml of maintenance medium in each well. The rinsed tissues were incubated at 37°C, 5% CO2 in air for approximately 42 hours.

MTT Loading/Formazan Extraction (Day 3)

Following the 42-hour post-exposure incubation period each 12-well plate was placed onto a plate shaker for 15 ± 2 minutes to homogenise the released mediators in the maintenance medium. 1.6 ml of the maintenance medium from beneath each tissue was transferred to pre-labelled micro tubes and stored in a freezer at -14 to -30°C for possible inflammatory mediator determination.

2 ml of a 0.3 mg/ml MTT solution, freshly prepared in assay medium, was pipetted into the third column of 3 wells of the 12 well plate(s). The tissues were transferred to the MTT filled wells, being careful to remove any excess maintenance medium from the bottom of the tissue insert by blotting on absorbent paper. The tissues were incubated for 3 hours at 37°C, 5% CO2 in air. At the end of the 3 hour incubation period each tissue was placed onto absorbent paper to dry. The tissues were examined and the degree of MTT staining evaluated (qualitative evaluation of cell viability) using the MTT Visual Scoring scheme. Following qualitative evaluation of tissue viability a total biopsy of the epidermis was made using the EPISKIN™ biopsy punch. The epidermis was carefully separated from the collagen matrix using forceps and both parts (epidermis and collagen matrix) placed into labelled 1.5 ml micro tubes containing 500 µl of acidified isopropanol, ensuring that both the epidermis and collagen matrix were fully immersed. Each tube was plugged to prevent evaporation and mixed thoroughly on a vortex mixer. The tubes were refrigerated at 1 to 10°C until Day 6 of the experiment, allowing the extraction of formazan crystals out of the MU-loaded tissues.

Absorbance/Optical Density Measurements (Day 6)
At the end of the formazan extraction period each tube was mixed thoroughly on a vortex mixer to produce a homogenous coloured solution.

For each tissue, duplicate 200 µl samples were transferred to the appropriate wells of a pre-labelled 96-well plate. 200 µl of acidified isopropanol alone was added to the two wells designated as 'blanks'. The optical density was measured (quantitative viability analysis) at 540 nm (without a reference filter) using the Anthos 2001 microplate reader.

Results and discussion

In vitro

Results
Irritation / corrosion parameter:
other: other: mean % viability
Value:
109.4
Remarks on result:
other:
Remarks:
Basis: mean. Time point: Day 6. Max. score: 119.4. Reversibility: other: not applicable. Remarks: In vitro result using the EPISKIN reconstituted human epidermis model. (migrated information)

In vivo

Irritant / corrosive response data:
Direct MTT Reduction
The MTT solution containing the test material did not turn blue/purple which indicated that the test material did not directly reduce MTT.

Test Material, Positive Control Material and Negative Control Material
The relative mean viability of the test material treated tissues was 109.4% after a 15-minute exposure.
Following the 15-minute exposure the test material treated tissues appeared blue which was considered indicative of viable tissue.

Quality Criteria
The relative mean tissue viability for the positive control treated tissues was <=40% relative to the negative control treated tissues and the standard deviation value of the percentage viability was <=20%. The positive control acceptance criterion was therefore satisfied.
The mean OD540 for the negative control treated tissues was >=0.6 and the SD value of the percentage viability was <=20%. The negative control acceptance criterion was therefore satisfied.
Other effects:
None reported

Any other information on results incl. tables

Mean OD540Values and Percentage Viabilities for the Negative Control Material, Positive Control Material and Test Material

Material

OD540of tissue

Mean OD540of triplicate tissue

± SD of OD540

Relative individual tissue viability (%)

Relative mean viability (%)

± SD of Relative mean viability (%)

Negative Control Material

0.834

0.821

0.122

101.6

100*

1.48

0.818

99.6

0.810

98.7

Positive Control Material

0.042

0.046

0.007

5.1

5.6

0.90

0.041

5.0

0.054

6.6

Test Material

0.980

0.898

0.076

119.4

109.4

9.30

0.886

107.9

0.829

101.0

SD = Standard deviation

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

Qualitative Evaluation of Tissue Viability (MTT uptake visual evaluation) 

Material

Tissue 1

Tissue 2

Tissue 3

Negative Control Material

-

-

-

Positive Control Material

++

++

++

Test Material

-

-

-

MTT visual scoring scheme

- = blue tissue (viable)

+ = blue/white tissue (semi-viable)

++ = tissue is completely white (dead)

Applicant's summary and conclusion

Interpretation of results:
not irritating
Remarks:
Migrated information Criteria used for interpretation of results: other: no direct reduction of MTT and colour of treated tissues after treatment period.
Conclusions:
The test material was considered to be Non-Irritant.
Executive summary:

Method: The purpose of this test was to evaluate the skin irritation potential of the test material using the EPISKIN™ reconstituted human epidermis model after a treatment period of 15 minutes followed by a post-exposure incubation period of 42 hours.

Triplicate tissues were treated with the test material for an exposure period of 15 minutes. At the end of the exposure period each tissue was rinsed before incubating for approximately 42 hours. At the end of the post-exposure incubation period each tissue was taken for MIT-loading. The maintenance medium from beneath each tissue was transferred to pre-labelled micro tubes and stored in a freezer for possible inflammatory mediator determination. After MTT loading a total biopsy of each epidermis was made and placed into micro tubes containing acidified isopropanol for extraction of formazan crystals out of the MTT-loaded tissues.

At the end of the formazan extraction period each tube was mixed thoroughly and duplicate 200 pl samples were transferred to the appropriate wells of a pre-labelled 96-well plate. The optical density was measured at 540 nm. Data are presented in the form of percentage viability (MTT reduction in the test material treated tissues relative to negative control tissues).

Results: The relative mean viability of the test material treated tissues was 109.4% after a 15-minute exposure.

Quality criteria: The quality criteria required for acceptance of results in the test were satisfied.

Conclusion: The test material was considered to be Non-Irritant.