(±)-neomenthol

Eye irritation

Administrative data

Endpoint:

eye irritation: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

6 Feb 2015

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2015

Report date:

2015

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 437 (Bovine Corneal Opacity and Permeability Test Method for Identifying Ocular Corrosives and Severe Irritants)

Version / remarks:

2013

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Hess. Ministerium für Umwelt, Energie, Landwirtschaft und Verbraucherschutz, Wiesbaden, Germany

Test material

Test material information

Constituent 1

Reference substance name:

L-menthol

EC Number:

218-690-9

EC Name:

L-menthol

Cas Number:

2216-51-5

Molecular formula:

C10H20O

IUPAC Name:

(1R,2S,5R)-2-isopropyl-5-methyl-cyclohexanol

Test animals / tissue source

Species:

cattle

Strain:

not specified

Details on test animals or tissues and environmental conditions:

TEST METHOD
The bovine corneal opacity and permeability (BCOP) test method is designed to measure the opacity of the cornea by quantifying the ability of light to pass through it.The permeability, as a result of the irritation potential of the test item, is determined using sodium fluorescein solution. The comparison of the opacity before and after the exposure to the test item and the determination of the permeability after the treatment provide an indication of the damaging effect of the test item. For this purpose the induction of opacity and increased permeability in an isolated bovine cornea after application of the test item was measured. The results of both criteria were combined. The resulting in vitro irritation factor (IVIS) was compared with the classification "no category (GHS)", "no prediction can be made", and "serious eye damaging" (CLP/EPA/GHS (Cat 1)).

IDENTIFICATION OF THE SOURCE OF THE EYES, STORAGE AND TRANSPORT CONDITIONS
- Source: Schlachthof Bensheim, Bensheim, Germany
- Donor animals: at least 9 month old
- Time interval prior to initiating testing: The corneae were isolated on the same day after delivery of the eyes. The cornea were directly used in the BCOP test on the same day.
- Transport medium and temperature conditions: Hank's Buffered Salt Solution (HBSS) supplemented with penicillin/streptomycin at ambient temperature.

PREPARATION OF THE EYES (BEFORE EXPOSURE)
- Eyes free of defects (scratches, neovascularisation, pigmentation, opacity): yes
- Dissection of the eyes and treatment: The cornea was carefully removed from the eye using scalpel and rounded scissors. A rim of about 2 mm of tissue (sclera) was left for stability and handling of the isolated cornea. Each cornea was mounted in a specially designed cornea holder.
- Description of the cornea holder: The cornea holder consists of anterior and posterior compartments, which interface with the epithelial and endothelial sides of the cornea, respectively.
- Test medium used in the cornea holder: The incubation medium consisted of MEM, supplemented with 1.1 g/500 mL sodium bicarbonate, 5 mL/500 mL L-glutamine, 100 U/mL penicillin and 100 µg/mL streptomycin. Immediately before starting the test, MEM was supplemented with 1% fetal calf serum.
- Equilibration time: 1 h at 32 ± 1°C
- Quality check of the equilibrated corneas: At the end of the equilibration period, the basal opacity was determined (t0). Each cornea with a value of the basal opacity >7 was discarded.

DETERMINATION OF THE INITIAL OPACITY
- Method: Corneal opacity was determined by the amount of light transmission passing through the cornea via an opacitometer.
- Specification of the device: OP_KiT opacitometer (Electro Design, France)

Test system

Vehicle:

physiological saline

Controls:

other: number of eyes for the negative control: 3; number of eyes for the positive control: 3

Amount / concentration applied:

TEST MATERIAL
- Amount applied: 0.75 mL
- Concentration: 20% (with large particles) (w/v) in saline
After preparation of the 20% solution (with large particles) it was taken for 20 min in the ultrasonic bath. The test item could not be suspended homogeneously.

POSITIVE SUBSTANCE
- 10% (w/v) benzalkonium chloride in saline
- Amount applied in the test: 0.75 mL

NEGATIVE CONTROL/VEHICLE
- 0.9% NaCl (w/v) solution in deionised water (saline)
- Amount applied: 0.75 mL

Duration of treatment / exposure:

240 min at 32 ± 1°C

Observation period (in vivo):

Not applicable

Number of animals or in vitro replicates:

number of eyes for the test item: 3

Details on study design:

TEST CONDITIONS
- Short description of the method used: The endothelial side of the cornea was positioned against the sealing ring (O-ring) of the posterior part of the holder. The cornea was gently flattened over the O-ring but stretching was avoided. The anterior part of the holder was positioned on the top of the cornea and fixed in place with screws. Both compartments of the holder were filled with incubation medium. The posterior compartment was filled first to return the cornea to its natural convex position. The anterior compartment received the test item or the controls on the surface of the corneae. The corneae were incubated in a horizontal position at 32 ± 1 °C in the water-bath for 240 minutes.

POST-EXPOSURE TREATMENT
- Removal of the test substance: The test item was rinsed off from the application side with saline. However, the test item could not be rinsed off completely from the cornea. Some residue was visible after intensive rinsing.

DETERMINATION OF THE FINAL OPACITY
- Method: Corneal opacity was determined by the amount of light transmission through the cornea via an opacitometer.
- Time of determination: Directly after refilling fresh incubation medium in the anterior compartment the final opacity was measured (t240).
- Specification of the device: OP_KiT opacitometer (Electro Design, France)

DETERMINATION OF THE CORNEAL PERMEABILITY:
- Method: After the final opacity measurement was performed, the incubation medium was removed from the anterior compartment and replaced by sodium fluorescein solution. Corneae were incubated again in horizontal position for 90 ± 10 min in a water-bath at 32 ± 1 °C. The amount of sodium fluorescein that crosses into the posterior chamber was quantitatively measured with a spectrophotometer as optical density at 490 nm (OD490).
- Amount and concentration of the dye: 1 mL sodium fluorescein solution (0.5% (w/v); dissolved in HBSS)
- Incubation time: 90 ± 10 min at 32 ± 1 °C
- Treatment for measuring: Complete medium from the posterior compartment was removed, well mixed, transferred into a 96 well plate and OD490 was determined.
- Specification of the spectrophotometer: Versamax Molecular Devices

Results and discussion

In vitro

Results

Irritation parameter:

in vitro irritation score

Run / experiment:

240 min

Value:

6.86

Vehicle controls validity:

valid

Negative controls validity:

valid

Positive controls validity:

valid

In vivo

Irritant / corrosive response data:

With the negative control (0.9% (w/v) NaCl solution in deionised water) neither an increase of opacity nor permeability of the corneae could be observed.
The positive control (10% (w/v) benzalkonium chloride in saline) showed clear opacity of the corneae corresponding to a classification as serious eye damaging.
Relative to the negative control, the test item caused any slight increase of the corneal opacity but not of the permeability. The calculated mean IVIS was 6.86. In the calculation, only two treated bovine eyes of three were included because the values of one eye were considered as outliers. Based on the experimental results the test substance is not classified as corrosive (Eye Cat. 1) but no prediction for the damage hazard can be made.

Any other information on results incl. tables

Table 1: Results after 240 min incubation time

Test group	Opacity value = Difference (t240-t0) of Opacity		Permeability at 490 nm (OD490)		IVIS	Mean IVIS
		Mean		Mean
Negative control	0	0.00	0.063	0.063	0.95	0.95
	0		0.065		0.98
	0		0.061		0.92
Positive control	96.00*		0.045*		96.68	101.85
	90.00*		0.041*		90.62
	118.00*		0.017*		118.26
Test substance	7.00*		0.873*		20.10
	7.00*		0.046*		7.69	6.86
	5.00*		0.068*		6.02

*corrected values

grey shaded groups were not included in calculation because the values are outliers

Applicant's summary and conclusion

Interpretation of results:

other: non-corrosive

Remarks:

according to Regulation (EC) No 1272/2008

Conclusions:

The corneal damage potential of the test substance was assessed in the BCOP assay using three fresh bovine corneae. The calculated mean IVIS was 6.86 (only two treated bovine eyes were included, the third was considered as outlier). According to OECD 437 the test item's hazard for eye damaging cannot be predicted but the test item is not classified as Eye Cat. 1.