1,1'-[ethane-1,2-diylbis(thio)]bisbenzene

Eye irritation

Administrative data

Endpoint:

eye irritation: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

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 guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 437 (Bovine Corneal Opacity and Permeability Test Method for Identifying i) Chemicals Inducing Serious Eye Damage and ii) Chemicals Not Requiring Classification for Eye Irritation or Serious Eye Damage)

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

1,1'-[ethane-1,2-diylbis(thio)]bisbenzene

EC Number:

210-723-5

EC Name:

1,1'-[ethane-1,2-diylbis(thio)]bisbenzene

Cas Number:

622-20-8

Molecular formula:

C14H14S2

IUPAC Name:

1,1'-(ethane-1,2-diyldisulfanediyl)dibenzene

Details on test material:

The test substance is identified as 1,1'-[ethane-1,2-diylbis(thio)]bisbenzene. The purity is 100%. The physical state/appearance of material is white solid. The expiry date of material is 13 February 2019. The substance can be stored at room temperature in the dark conditions.

Test animals / tissue source

Species:

cattle

Strain:

not specified

Details on test animals or tissues and environmental conditions:

SOURCE OF BOVINE EYES
Eyes from adult cattle (typically 12 to 60 months old) were obtained from a local abattoir as a by-product from freshly slaughtered animals. The eyes were excised by an abattoir employee after slaughter, and were placed in Hanks’ Balanced Salt Solution (HBSS) supplemented with antibiotics (penicillin at 100 IU/mL and streptomycin at 100 µg/mL). They were transported to the test facility over ice packs on the same day of slaughter. The corneas were prepared immediately on arrival.

PREPARATION OF CORNEAS
All eyes were macroscopically examined before and after dissection. Only corneas free of damage were used.

The cornea from each selected eye was removed leaving a 2 to 3 mm rim of sclera to facilitate handling. The iris and lens were peeled away from the cornea. The isolated corneas were immersed in a dish containing HBSS until they were mounted in Bovine Corneal Opacity and Permeability (BCOP) holders.

The anterior and posterior chambers of each BCOP holder were filled with complete Eagle’s Minimum Essential Medium (EMEM) without phenol red and plugged. The holders were incubated at 32 ± 1 ºC for 60 minutes. At the end of the incubation period each cornea was examined for defects. Only corneas free of damage were used.

SELECTION OF CORNEAS AND OPACITY READING
The medium from both chambers of each holder was replaced with fresh complete EMEM. A pre-treatment opacity reading was taken for each cornea using a calibrated opacitometer
(Annex 1). The average opacity for all corneas was calculated. Three corneas were randomly allocated to the negative control. Three corneas were also allocated to the test item and three corneas to the positive control item.

TREATMENT OF CORNEAS
The EMEM was removed from the anterior chamber of the BCOP holder and the test item or control items were applied to the cornea. Approximately 0.650 g of the solid test item was found to adequately cover the corneal surface. 0.75ml of each control item was applied to the appropriate corneas. The holders were gently tilted back and forth to ensure a uniform application of the item over the entire cornea. Each holder was incubated, anterior chamber uppermost, at 32 ± 1 ºC for 240 minutes.

APPLICATION OF SODIUM FLUORESCEIN
Following the opacity measurement the permeability of the corneas to sodium fluorescein was evaluated. The medium from the anterior chamber was removed and replaced with 1 mL of sodium fluorescein solution (5 mg/mL). The dosing holes were plugged and the holders incubated, anterior chamber uppermost, at 32 ± 1 ºC for 90 minutes.

PERMEABILITY DETERMINATIONS
After incubation the medium in the posterior chamber of each holder was decanted and retained.
360 µL of media representing each cornea was dispensed into the appropriate wells of a pre-labeled 96-well plate. The optical density was measured (quantitative viability analysis) at 492 nm (without a reference filter) using the Labtech LT-4500 microplate reader.

HISTOPATHOLOGY
The corneas were retained after testing for possible conduct of histopathology. Each cornea was placed into a pre-labeled tissue cassette fitted with a histology sponge to protect the endothelial surface. The cassette was immersed in 10% neutral buffered formalin.

Test system

Vehicle:

unchanged (no vehicle)

Controls:

yes, concurrent positive control

yes, concurrent negative control

Amount / concentration applied:

0.75 Ml

Number of animals or in vitro replicates:

3

Details on study design:

Results from the two test method endpoints, opacity and permeability, were combined in an empirically derived formula to generate an In Vitro Irritancy Score.

OPACITY MEASUREMENT
The change in opacity for each cornea (including the negative control) was calculated by subtracting the initial opacity reading from the final opacity reading. These values were then corrected by subtracting the average change in opacity observed for the negative control corneas. The mean opacity value of each treatment group was then calculated by averaging the corrected opacity values of each cornea for that treatment group.

PERMEABILITY MEASUREMENT
The corrected OD492 was calculated by subtracting the mean OD492 of the negative control corneas from the OD492 value of each treated cornea. The OD492 value of each treatment group was calculated by averaging the corrected OD492 values of the treated corneas for the treatment group.

IN VITRO IRRITANCEY SCORE
The following formula was used to determine the In Vitro Irritancy Score:

In Vitro Irritancy Score = mean opacity value + (15 x mean permeability OD492 value)

Additionally, the opacity and permeability values were evaluated independently to determine whether the test item induced a response through only one of the two endpoints.

VISUAL OBSERVATIONS
The condition of the cornea was visually assessed post treatment.

DATA INTERPRETATION
The test item was classified according to the following prediction model:

IVIS CLASSIFICATION
below 3 no category. Not requiring classificatio to UN GHS or EU CLP
between 3 and 55 No prediction of eye irritation can be made
greater than 55 Category 1 (UN GHS or EU CLP (causes serius eye damage)

CRITERIA FOR AN ACCEPTABLE TEST
For an acceptable test the following positive control criterion should be achieved:

20% w/v Imidazole was used for positive control purposes. The test was acceptable if the positive control produced an In Vitro Irritancy Score which fell within two standard deviations of the historical mean during 2016 for this testing facility. Therefore the In Vitro Irritancy Score should fall within the range of 65.1 to 123.3.

For an acceptable test the following negative control criteria should be achieved:

Sodium chloride 0.9% w/v was used for negative control purposes. The test was acceptable if the negative control produced an In Vitro Irritancy Score which is less than or equal to the upper limit for background opacity and permeability values during 2016 for bovine corneas treated with the respective negative control. When testing solids the negative control limit for opacity should be ≤2.4 and for permeability ≤0.072.

REFERENCE ITEM PREPARATION
The negative control item, sodium, chloride 0.9% w.v, was used as supplied.
The positive control item, Imidazole, was used as a 20% w/v solution in sodium chloride 0.9% w/v.

Results and discussion

In vitro

Results

Irritation parameter:

in vitro irritation score

Value:

0.4

Negative controls validity:

valid

Positive controls validity:

valid

Applicant's summary and conclusion

Interpretation of results:

other: No category. Not requiring classification to UN GHS or EU CLP

Conclusions:

No category. Not requiring classification to UN GHS or EU CLP.

Executive summary:

The purpose of this test was to determine whether a test item, 1,1'-[ethane-1,2-diylbis(thio)]bisbenzenethat can induce serious eye damage and to identify test items not requiring classification for eye irritation or serious eye damage.  The Bovine Corneal Opacity and Permeability (BCOP) test method is an organotypic model that provides short-term maintenance of normal physiological and biochemical function of the bovine cornea in vitro.  In this test method, damage by the test item is assessed by quantitative measurements of changes in corneal opacity and permeability.

The test method can correctly identify test items (both chemicals and mixtures) inducing serious eye damage as well as those not requiring classification for eye irritation or serious eye damage, as defined by the United Nations (UN) Globally Harmonized System of Classification and Labelling of Items (GHS) and EU Classification, Labelling and Packaging (CLP) of chemicals (Regulation (EC) No 1272/2008), and it was therefore endorsed as scientifically valid for both purposes.  Test items inducing serious eye damage are classified as UN GHS and EU CLP Category 1.  Items not classified for eye irritation or serious eye damage are defined as those that do not meet the requirements for classification as UN GHS/EU CLP Category 1 or 2 (2A or 2B), i.e. they are referred to as UN GHS/EU CLP No Category.

The test item was applied neat for 240 minutes.  Negative and positive control items were tested concurrently.  The two endpoints, decreased light transmission through the cornea

(opacity) and increased passage of sodium fluorescein dye through the cornea (permeability) were combined in an empirically derived formula to generate an In Vitro Irritancy Score

(IVIS). The IVIS scores for the test item, the negative control and the positive control were 0.4, 0.7, and 101.4, respectively. These data indicate that the criteria for evaluation of eye irritancy were met, and the test item is not requiring classification for eye irritancy under either UN GHS or EU CLP.