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Eye irritation

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eye irritation: in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
key study
Study period:
October 2017 - February 2018
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference Type:
study report
Report Date:

Materials and methods

Test guidelineopen allclose all
according to
OECD Guideline 492 (Reconstructed Human Cornea-like Epithelium (RhCE) Test Method for Identifying Chemicals Not Requiring Classification and Labelling for Eye Irritation or Serious Eye Damage)
Version / remarks:
July, 2015
according to
other: MatTek Corporation Protocol: EpiOcular™ Eye Irritation Test (OCL-200-EIT) for the prediction of acute ocular irritation of chemicals; for use with MatTek Corporation’s Reconstructed Human EpiOcular™ Model
Version / remarks:
29 June 2015
GLP compliance:
yes (incl. certificate)
Hess. Ministerium für Umwelt, Klimaschutz, Landwirtschaft und Verbraucherschutz, Wiesbaden, Germany

Test material


Test animals / tissue source

other: Human Cornea Model
Details on test animals or tissues and environmental conditions:
EpiOcular™ kits and MTT-100 kits are purchased from MatTek Corporation (82105 Bratislava, Slovakia). The EpiOcular™ tissue consists of normal, human-derived epidermal keratinocytes which have been cultured to form a stratified squamous epithelium similar to that found in the human cornea. It consists of highly organized basal cells which progressively flatten out as the apical surface of the tissue is approached, analogous to the normal in vivo corneal epithelium. The EpiOcular™ tissues (surface 0.6 cm²) are cultured on specially prepared cell culture inserts (MILLICELL, 10 mm diameter).
EpiOcular™ tissues were shipped at 2 - 8 °C on medium-supplemented agarose gels in a 24-well plate on Tuesday. On day of receipt of the EpiOcular™ tissues, the equilibration step (15 minutes at room temperature in the 24-well shipping container) started. 1.0 mL of the medium was aliquoted into the appropriate wells of pre-labeled 6-well plates.
Each 24-well shipping container was removed from its plastic bag under sterile conditions and its surface disinfected by wiping with 70% isopropanol- or ethanol-soaked tissue paper. The sterile gauze was removed and each tissue was inspected for air bubbles between the agarose gel and insert. The tissues were carefully removed from the 24-well shipping containers using sterile forceps. Any agarose adhering to the inserts was removed by gentle blotting on sterile filter paper or gauze. The insert was then transferred aseptically into the 6-well plates and pre-incubated at standard culture conditions for one hour in the Assay Medium. After one hour, the Assay Medium was replaced by 1 mL fresh Assay Medium at 37 °C and the EpiOcular™ tissues were incubated at standard culture conditions overnight (16 -24 hours).

- RhCE tissue construct used, including batch number: EpiOcular™ (MatTek Corporation, Bratislava, Slovakia), Lot No.: 27012
- Tissue viability: The quality of the final product was assessed by undertaking an MTT cell viability test. The determined OD (540 - 570 nm) was 1.504 ± 0.057 (acceptance criteria: 1.1 - 3.0).
- Barrier function: The barrier function was assessed by determination of the exposure time required to reduce tissue viability by 50% (ET-50) upon application of 100 µL of 0.3% Triton X-100. The ET-50 value was determined to be 14.5 min (acceptance criteria: 12.2 - 37.5 min).
- Contamination: The cells used to produce the EpiOcular tissue were screened for the presence of viruses, bacteria, yeast and other fungi.

Test system

unchanged (no vehicle)
yes, concurrent positive control
yes, concurrent negative control
Amount / concentration applied:
- Amount applied: 50 mg

- Amount applied: 50 µL

- Amount applied: 50 µL
Duration of treatment / exposure:
6 h
Duration of post- treatment incubation (in vitro):
25 min immersion incubation after rinsing, followed by 18 h incubation in humidified atmosphere
Number of animals or in vitro replicates:
Details on study design:
Assessment of Direct MTT Reduction by the Test Item:
Test items may have the ability to directly reduce MTT and to form a blue/purple reaction product which could have an impact on the quantitative MTT measurement. Therefore, it was necessary to assess this ability for the test item prior to conducting any assays with viable tissues. For this purpose approximately 50 mg of the test item were added to a 1 mL of a 1.0 mg/mL MTT solution (in DMEM) in a glass tube and the mixture was incubated in the dark at 37 ± 1.5 °C in a humidified atmosphere of 5 ± 0.5% CO2 in air for three hours. A control (50 μL of deionised water in 1 mL of 1.0 mg/mL MTT solution) was run concurrently. If the MTT solution colour turned blue/purple, the test item was presumed to have reduced the MTT. Since the MTT solution colour did not turn blue/purple, the test item was not presumed to be a MTT reducer, and an additional test with freeze-killed tissues was not necessary.

Assessment of Coloured or Staining Materials:
Coloured test items or test items which become coloured after application to the tissues may interfere with the quantitative photometric MTT measurement, if the colourant binds to the tissue and is extracted together with MTT. Therefore, each test item has to be checked for its colouring properties. Since the test item was non-coloured, additional tests had to be performed to assess, if it becomes coloured after contact with water or isopropanol. For this purpose each approximately 50 mg of the test item was added to 1.0 mL of water and to 2 mL isopropanol in a glass tube. The water mixture was incubated in the dark at 37 ± 1.5 °C in a humidified atmosphere of 5 ± 0.5% CO2 in air for one hour, the isopropanol mixture for 3 hours at room temperature.Since the test item did not become coloured either in water or isopropanol, it was not considered as possibly interacting with the MTT measurement and an additional test with viable tissues (with medium instead of MTT addition) did not have to be performed.

Experimental Performance:
After the overnight incubation, the tissues were pre-wetted with 20 μL of Ca2+Mg2+free-DPBS. The tissues were incubated at standard culture conditions for 30 minutes. After the 30 minute Ca2+Mg2+free-DPBS pre-treatment, the test and control item were tested by applying approximately 50 mg (test item) or 50 μL (controls) topically on the EpiOcular™ tissues. The tissues were incubated at standard culture conditions (37 ± 1.5 °C, 5 ± 0.5% CO2, 95% RH) for 6 hours. At the end of the 6 hours treatment time, the test item was removed by extensively rinsing the tissues with Ca2+Mg2+-free DPBS (brought to room temperature). Three clean beakers containing a minimum of 100 mL each of Ca2+Mg2+-free DPBS were used per test item. The test item utilized a different set of three beakers. The inserts containing the tissue were lifted out of the medium by grasping the upper edge of the plastic "collar" with fine forceps. To assure throughput, the tissues were rinsed two at a time by holding replicate inserts together by their collars using forceps. The test or control items were decanted from the tissue surface onto a clean absorbent material (paper towel, gauze, etc.) and the cultures dipped into the first beaker of DPBS, swirled in a circular motion in the liquid for approximately 2 seconds, lifted out so that the inserts are mostly filled with DPBS, and the liquid was decanted back into the container. This process was performed two additional times in the first beaker. The culture was then be rinsed in the second and third beakers of DPBS three times each in the same fashion. Finally, any remaining liquid was decanted onto the absorbent material. Decanting was most efficiently performed by rotating the insert to approximately a 45° angle (open end down) and touching the upper lip to the absorbent material (to break the surface tension). After rinsing, the tissues were immediately transferred to and immersed in 5 mL of previously-warmed assay medium (room temperature) in a pre-labelled 12-well plate for a 25 minutes immersion incubation (post-soak) at room temperature. This incubation in assay medium was intended to remove any test item or control absorbed into the tissue. At the end of the post-soak immersion, each insert was removed from the assay medium, the medium was decanted off the tissue, and the insert was blotted on absorbent material and transferred to the appropriate well of the pre-labelled 6-well plate containing 1 mL of warm assay medium. The tissues were incubated for 18 hours at 37 ± 1.5 °C in a humidified atmosphere of 5 ± 0.5% CO2 (post-treatment incubation).

MTT Assay:
At the end of the post-treatment incubation, each insert was removed from the 6-well plate and gently blotted on absorbent material. The tissues were placed into the 24-well plate containing 0.3 mL of MTT solution. Once all the tissues were placed into the 24-well plate, the plate was incubated for 180 minutes at standard culture conditions. Inserts were removed from the 24-well plate after 180 minutes; the bottom of the insert was blotted on absorbent material, and then transferred to a pre-labelled 6-well plate containing 2 mL isopropanol in each well so that no isopropanol is flowing into the insert. The plates were sealed with parafilm (between the plate cover and upper edge of the wells) or a standard plate sealer, and were immediately extracted (shaken for 2 to 3 hours at room temperature). For this procedure it was necessary to seal the plates particularly thorough since a higher evaporation rate had to be expected due to the larger surface of wells in 6-well plates. The extract solution was mixed and two 200 μL aliquots were transferred to the appropriate wells of a pre-labelled 96-well plate(s). The absorbance at 570 nm (OD570) of each well was measured with a plate reader (Versamax® Molecular Devices, 85737 Ismaning, Germany, Software Softmax Pro Enterprise, version 4.7.1). No reference wavelength measurement was used.

Acceptability of the Assay:
The results are acceptable according to MatTek Protocol, if:
1) The negative control OD is > 0.8 and < 2.5,
2) The mean relative viability of the positive control is below 50% of the negative control viability.
3) The difference of viability between the two relating tissues of a single test item is < 20% in the same run (for positive and negative control tissues and tissues of test items). This applies also to the freeze-killed tissues (items and negative control) and the additional viable tissues (without MTT addition) which are calculated as percent values related to the viability of the relating negative control.

Results and discussion

In vitro

Irritation parameter:
other: cell viability (relative absorbance value)
Run / experiment:
Vehicle controls valid:
not examined
Negative controls valid:
Positive controls valid:
Remarks on result:
positive indication of irritation
Other effects / acceptance of results:
- Acceptance criteria met for negative control: The negative control OD is > 0.8 and < 2.5 (1.494 and 1.569)
- Acceptance criteria met for positive control: The mean relative viability of the positive control is below 50% of the negative control viability (28.6%)
- The difference of viability between the two relating tissues of a single item is < 20% (values between 0.3% and 2.7%) in the same run (for positive and negative control tissues and tissues of single test items)

In vivo

Irritant / corrosive response data:
Relevant irritating effects were observed following 6 hours incubation with the test item. The mean relative absorption value of the tissues corresponding to the cornea viability decreased to 2.8% compared with the value of the negative control (threshold for irritancy: ≤ 60%)

Any other information on results incl. tables

Table 2: Results after treatment for 6 hours with the test item and the controls

Treatment Group

Tissue No.

OD 570 nm Well 1

OD 570 nm Well 2

Mean OD of 2 Wells

Mean OD

of 2 Wells blank




of Treatment Group

blank corrected

Rel. Viability [%] Tissue 1, 2

Absolute Value of the Difference of Rel.Viability Tissue 1,2[%]

Mean Rel. Viability







Negative Control
















Positive Control
















Test Item
















Applicant's summary and conclusion

Interpretation of results:
other: Eye irritating potential according to OECD TG 492
This in vitro study was performed to assess the eye irritation potential of the test item by means of the Human Cornea Model Test according to OECD 492. The cornea viability decreased to 2.8 %, therefore an eye irritation cannot be excluded.
Executive summary:

This in vitro study was performed to assess the eye irritation potential of the test item by means of the Human Cornea Model Test according to OECD 492 and GLP. The test item did not prove to be an MTT reducer in the MTT pre-test. Also, its intrinsic colour was not intensive and it did not prove to dye water or isopropanol in the colour interference pre-test. Therefore, additional tests with freeze-killed tissues or viable tissues (without MTT addition) did not have to be performed. Each 50 mg of the test item were applied to each of duplicate tissue for 6 hours. Each 50 μL of the negative control (deionised water) and of the positive control (methyl acetate) were also applied to duplicate tissues each. After treatment with the negative control the absorbance values were well within the required acceptability criterion of OD > 0.8 and < 2.5, thus showing the quality of the tissues. Treatment with the positive control induced a decrease below 50% viability compared with the negative control value in the relative absorbance, thus ensuring the validity of the test system. The difference of viability between the two relating tissues was < 20% in the same run (for test item tissues, positive and negative control tissues). Irritating effects were observed following incubation with the test item. Compared with the value of the negative control, the relative mean absorption value corresponding to the viability of the tissues decreased below 60% (2.8%). In conclusion, it can be stated that in this study and under the experimental conditions reported, the test substance possesses an eye irritating potential.