Sodium iodate

Eye irritation

Administrative data

Endpoint:

eye irritation: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

05 March 2018 to 27 March 2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2018

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)

Version / remarks:

2017

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Sodium iodate

EC Number:

231-672-5

EC Name:

Sodium iodate

Cas Number:

7681-55-2

Molecular formula:

HIO3.Na

IUPAC Name:

sodium iodate

Test material form:

solid: particulate/powder

Details on test material:

- Appearance: white powder
- Storage conditions: at room temperature

Test animals / tissue source

Species:

cattle

Strain:

not specified

Details on test animals or tissues and environmental conditions:

SOURCE OF COLLECTED EYES
- Source: Bovine eyes from young cattle were obtained from the slaughterhouse (Vitelco, -'s Hertogenbosch, The Netherlands), where the eyes were excised by a slaughterhouse employee as soon as possible after slaughter.
- Storage, temperature and transport conditions of ocular tissue: Eyes were collected and transported in physiological saline in a suitable container under cooled conditions.

Test system

Vehicle:

unchanged (no vehicle)

Controls:

yes, concurrent positive control

yes, concurrent negative control

Amount / concentration applied:

TEST MATERIAL
- Amount(s) applied: 424.8 - 462.7 mg

Duration of treatment / exposure:

240 ± 10 minutes

Duration of post- treatment incubation (in vitro):

90 ± 5 minutes with sodium fluorecein

Number of animals or in vitro replicates:

3 replicates for each condition (test material, negative control and positive control)

Details on study design:

SELECTION AND PREPARATION OF CORNEAS
The eyes were checked for unacceptable defects, such as opacity, scratches, pigmentation and neovascularisation by removing them from the physiological saline and holding them in the light. Those exhibiting defects were discarded.
The isolated corneas were stored in a petri dish with cMEM (Earle’s Minimum Essential Medium containing 1 % (v/v) L-glutamine (Life Technologies) and 1 % (v/v) Foetal Bovine Serum. The isolated corneas were mounted in a corneal holder (one cornea per holder) of BASF with the endothelial side against the O-ring of the posterior half of the holder. The anterior half of the holder was positioned on top of the cornea and tightened with screws. The compartments of the corneal holder were filled with cMEM of 32 ± 1 °C. The corneas were incubated for the minimum of 1 hour at 32 ± 1 °C.

QUALITY CHECK OF THE ISOLATED CORNEAS
After the incubation period, the medium was removed from both compartments and replaced with fresh cMEM. Opacity determinations were performed on each of the corneas using an opacitometer. The opacity of each cornea was read against a cMEM filled chamber, and the initial opacity reading thus determined was recorded. Corneas that had an initial opacity reading higher than 7 were not used.

NUMBER OF REPLICATES
Three corneas were selected at random for each treatment group.

NEGATIVE CONTROL USED : physiological saline

POSITIVE CONTROL USED : 20 % (w/v) Imidazole solution prepared in physiological saline

TREATMENT METHOD
Initially, this experiment was rejected since some of the acceptability criteria were not met. A repeat experiment was performed.
The medium from the anterior compartment was removed and 750 µL of the negative control and positive control were introduced onto the epithelium of the cornea. The test material was weighed in a bottle and applied directly on the corneas in such a way that the cornea was completely covered (424.8 to 462.7 mg).The holder was slightly rotated, with the corneas maintained in a horizontal position, to ensure uniform distribution of the solutions over the entire cornea. Corneas were incubated in a horizontal position for 240 ± 10 minutes at 32 ± 1 °C.

REMOVAL OF TEST SUBSTANCE
After the incubation the solutions and the test material were removed and the epithelium was washed at least three times with MEM with phenol red. Possible pH effects of the test material on the corneas were recorded. Each cornea was inspected visually for dissimilar opacity patterns. The medium in the posterior compartment was removed and both compartments were refilled with fresh cMEM and the opacity determinations were performed.

OPACITY MEASUREMENT
The opacity of a cornea was measured by the diminution of light passing through the cornea. The light was measured as illuminance (I = luminous flux per area, unit: lux) by a light meter.
The opacity value (measured with the device OP-KIT) was calculated according to:
Opacity = [(I0/I) - 0.9894] / 0.0251
With I0 the empirically determined illuminance through a cornea holder but with windows and medium, and I the measured illuminance through a holder with cornea.
The change in opacity for each individual cornea (including the negative control) was calculated by subtracting the initial opacity reading from the final post-treatment reading. The corrected opacity for each treated cornea with the test material or positive control was calculated by subtracting the average change in opacity of the negative control corneas from the change in opacity of each test material or positive control treated cornea.
The mean opacity value of each treatment group was calculated by averaging the corrected opacity values of the treated corneas for each treatment group.

APPLICATION OF SODIUM FLUORESCEIN
Following the final opacity measurement, permeability of the cornea to Na-fluorescein was evaluated.
The medium of both compartments (anterior compartment first) was removed. The posterior compartment was refilled with fresh cMEM. The anterior compartment was filled with 1 mL of 5 mg Na-fluorescein/mL cMEM solution. The holders were slightly rotated, with the corneas maintained in a horizontal position, to ensure uniform distribution of the sodium-fluorescein solution over the entire cornea. Corneas were incubated in a horizontal position for 90 ± 5 minutes at 32 ± 1 °C.

PERMEABILITY DETERMINATIONS
After the incubation period, the medium in the posterior compartment of each holder was removed and placed into a sampling tube labelled according to holder number. 360 µL of the medium from each sampling tube was transferred to a 96-well plate. The optical density at 490 nm (OD490) of each sampling tube was measured in triplicate using a microplate reader. Any OD490 that was 1.500 or higher was diluted to bring the OD490 into the acceptable range (linearity up to OD490 of 1.500 was verified before the start of the experiment). OD490 values of less than 1.500 were used in the permeability calculation.
The mean OD490 for each treatment was calculated using cMEM corrected OD490 values. If a dilution has been performed, the OD490 of each reading of the positive control and the test item was corrected for the mean negative control OD490 before the dilution factor was applied to the reading.

SCORING SYSTEM: In Vitro Irritancy Score (IVIS)
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 material induced a response through only one of the two endpoints.

DATA INTERPRETATION
The test material was classified according to the following:
- IVIS ≤ 3 = Not classified for irritation
- IVIS > 3; ≤ 55 = No prediction can be made
- IVIS > 55 = Category 1, H318: Causes serious eye damage

ACCEPTABILITY OF THE ASSAY
The assay is considered acceptable if:
- The positive control gives an in vitro irritancy score that falls within two standard deviations of the current historical mean.
- The negative control responses should result in opacity and permeability values that are less than the upper limits of the laboratory historical range.

Results and discussion

In vitro

Results

Results 1

Irritation parameter:

in vitro irritation score

Run / experiment:

Experiment 1

Value:

22

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Positive controls validity:

valid

Results 2

Irritation parameter:

in vitro irritation score

Run / experiment:

Experiment 2

Value:

1.2

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Positive controls validity:

valid

Other effects / acceptance of results:

TEST MATERIAL
The corneas treated with the test material showed opacity values ranging from -1.5 to 1.1 and permeability values ranging from 1.060 to 2.146. The corneas were slightly translucent after the 240 minutes of treatment with the test material. No pH effect of the test material was observed on the rinsing medium. Hence, the in vitro irritancy scores ranged from 17 to 32 after 240 minutes of treatment with the test material.
In the second experiment, the corneas treated with the test material showed opacity values ranging from -2.5 to -1.9 and permeability values ranging from 0.065 to 0.541. The corneas were clear after the 240 minutes of treatment with the test material. No pH effect of the test material was observed on the rinsing medium. Hence, the in vitro irritancy scores ranged from -1.0 to 5.6 after 240 minutes of treatment with the test material.

POSITIVE AND NEGATIVE CONTROLS
In the first test, the individual in vitro irritancy scores for the negative controls ranged from 1.8 to 5.3. One of the negative control eyes was excluded from the analysis since the opacity was above the historical data base which resulted in an IVIS outside the historical data base. Since the mean of the two remaining eyes completely met the criteria and the test material results were not influenced by this result, this was not considered to affect the study outcome. The individual positive control in vitro irritancy scores ranged from 162 to 166. The corneas treated with the positive control were turbid after the 240 minutes of treatment.
Since one of the negative controls was excluded an additional test was performed.
In the second experiment, the individual in vitro irritancy scores for the negative controls ranged from 3.2 to 5.9. The individual positive control in vitro irritancy scores ranged from 111 to 146. The corneas treated with the positive control were turbid after the 240 minutes of treatment.

Any other information on results incl. tables

Table 1: Summary of opacity, permeability and in vitro irritancy scores - Experiment 1

Treatment	Mean Opacity	Mean Permeability	Mean In Vitro Irritancy Score
Negative control	2.7	0.055	3.6
Positive control	131	2.161	164
Test material	-0.3	1.488	22

Table 2: Summary of opacity, permeability and in vitro irritancy scores - Experiment 2

Treatment	Mean Opacity	Mean Permeability	Mean In Vitro Irritancy Score
Negative control	4.6	0.021	4.9
Positive control	96	2.515	133
Test material	-2.2	0.226	1.2

Applicant's summary and conclusion

Interpretation of results:

other: According to EU criteria, no prediction on eye irritation can be made

Conclusions:

Under the conditions of the study no prediction of eye irritation can be made.

Executive summary:

The potential of the test material to cause eye irritation was investigated in accordance with the standardised guideline OECD 437, under GLP conditions.

During the study eyes from slaughtered cattle were treated with 424.8 to 462.7 mg test material. Positive and negative controls 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).

In the first test, the negative control responses for opacity and permeability were less than the upper limits of the laboratory historical range indicating that the negative control did not induce irritancy on the corneas (after exclusion of one outlioer).  The mean in vitro irritancy score of the positive control (20 % (w/v) imidazole) was 164 and within two standard deviations of the current historical positive control mean.  It was therefore concluded that the test conditions were adequate and that the test system functioned properly.  

The test material induced ocular irritation through one endpoint, resulting in a mean in vitro irritancy score of 22 after 4 hours of treatment.

In conclusion, since the test material induced an IVIS > 3 ≤ 55, no prediction on the classification can be made.  

Since one of the negative controls was excluded an additional test was performed.

In the second experiment, the mean negative control responses for opacity and permeability were less than the upper limits of the laboratory historical range indicating that the negative control did not induce irritancy on the corneas. The mean in vitro irritancy score of the positive control (20% (w/v) imidazole) was 133 and within two standard deviations of the current historical positive control mean. It was therefore concluded that the test conditions were adequate and that the test system functioned properly.

The mean in vitro irritancy score was 1.2 after 240 minutes of treatment with the test material. Since the results for the test material were spread over 2 categories (-0.9, 5.6 and -1.0, respectively), no prediction about the category could be made.  

In conclusion, since the test material induced irritancy through the endpoint permeability, no prediction on the classification can be made.

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