6-tert-butyl-1,1-dimethylindan-4-yl methyl ketone

Endpoint summary

Description of key information

Skin corrosion: Not corrosive in absence of skin and eye irritation

Skin irritation (OECD TG 439): Not skin irritating

Eye irritation (OECD TG 438) Isolated Chicken Eye test: Not eye irritating

Key value for chemical safety assessment

Skin irritation / corrosion

Link to relevant study records

Reference

Endpoint:

skin irritation: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

23 November 2016 to 13 January 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 439 (In Vitro Skin Irritation: Reconstructed Human Epidermis Test Method)

Version / remarks:

Original Guideline adopted July 28, 2015

GLP compliance:

yes (incl. QA statement)

Test system:

human skin model

Source species:

human

Cell type:

other: normal, human-derived epidermal keratinocytes

Cell source:

other: SkinEthic Laboratories (69007 Lyon, France)

Vehicle:

water

Remarks:

The test item tissues were wetted with 5 µL of deionised water before applying the test item.

Details on test system:

TEST SYSTEM: human skin model EpiSkin™
EpiSkin™ Kit
Supplier: SkinEthic Laboratories (69007 Lyon, France)
Date received: 10 January 2017
EpiSkin™ Kit Lot No.: 17-EKIN-002

The EpiSkin™ tissue consists of normal, human-derived epidermal keratinocytes which have been cultured to form a multilayered, highly differentiated model of the human epidermis. It consists of organized basal, spinous and granular layers, and a multi-layered stratum corneum containing intercellular lamellar lipid layers arranged in patterns analogous to those found in vivo. The EpiSkin™ tissues (surface 0.38 cm2) are cultured on specially prepared cell culture inserts.
EpiSkin™ tissues were shipped at ambient temperature on medium-supplemented agarose gels in a 12-well plate and reached Envigo CRS GmbH on 10 January 2017. On the day of experiment the pre-incubation phase of the EpiSkin™ tissues started.

Test for Direct MTT Reduction and Colour Interference:
Prior to the start of the test, the test item’s colour interference potential had to be evaluated. For this purpose the test item (approximately 10 mg) was mixed with 90 µL of deionised water in a pre-experiment. The test item/water mixture was gently shaken for 15 minutes at room temperature.
The colour of the test item/water mixture did not change during the incubation period compared with the colour of the pure test item. Therefore, an additional test with viable tissues (without MTT addition) was not necessary.
For correct interpretation of results it is necessary to assess the ability of the test item to directly reduce MTT. To test for this ability approximately 10 mg of the test item was added to 2 mL of MTT solution (0.3 mg/mL) and the mixture will be incubated in the dark at 37 ± 1.5 °C (5 ± 0.5% CO2) for 3 hours. MTT solution with 10 µL of DMEM was used as the control.
Since the colour did not turn blue/purple, the test item was not considered to be a MTT reducer.

Pre-warming of EpiSkin™ Tissues:
Under sterile conditions using sterile forceps, the inserts were transferred into 12-well plates containing the pre-warmed (37 ± 1.5 °C) maintenance medium. The EpiSkin™ tissues were incubated for about 22.5 hours.

Treatment:
The test item tissues were wetted with 5 µL of deionised water. The negative control, positive control and the test item were added into the insert atop the concerning EpiSkin™ triplicate tissues. The 12-well plates were treated for 15 minutes.
After the end of the treatment interval the inserts were immediately removed from the 12-well plate. The tissues were gently rinsed with PBS to remove any residual test material. Excess PBS was removed by gently shaking the inserts and blotting the bottom with blotting paper. The inserts were placed in the plates with 2 mL maintenance medium. The tissues were incubated for approximately 42 hours at 37 ± 1.5 °C, 5 ± 0.5% CO2.

IL-1 α Immunoassay:
Samples of all treatment groups were taken from the wells. The plates were shaken for approximately 15 minutes to homogenise the released mediators in the medium before sampling. At least 1.6 mL medium from each well was taken and was stored in the freezer at –20 °C. Since the results derived from the MTT assay were not unclear or borderline, the IL-1 α concentration in the medium was not determined and the taken samples will be discarded after report finalization.

MTT Assay:
A 12-well plate was filled with 2 mL assay medium containing 0.3 mg/mL MTT per well.
After the 42 ± 1 hour incubation period was completed for all tissues the cell culture inserts were transferred from the holding plates to the MTT-plates. After a 3 hour incubation period (37 ± 1.5 °C, 5 ± 0.5% CO2) MTT solution was rinsed three times with PBS and the tissues were blotted. Tissue samples were cut out of the inserts with a biopsy punch and transferred into plastic vials. The tissue samples were immersed into extractant solution by gently pipetting 0.5 mL extractant solution (isopropanol containing 0.04 N HCl) into each vial. The tissue samples were completely covered by isopropanol. The formazan salt was extracted for nearly 3 hours while shaking at room temperature.
Per tissue sample 2 x 200 µL aliquots of the formazan extract were transferred into a 96-well flat bottom microtiter plate. Isopropanol was used for blank measurement. OD was read in a microplate reader (Versamax® Molecular Devices, 85737 Ismaning, Germany, version 4.7.1) with 570 nm filter. Mean values were calculated from the 2 wells per tissue sample.

DATA EVALUATION:
The mean OD of the three tissues per group (negative control, positive control and test item) was calculated after blank correction. The mean OD of the negative control corresponds to 100% tissue viability in the current test. For each individual tissue treated with the test item or the positive control the individual relative tissue viability is calculated according to the following formula:
Relative viability (%) = (OD test item or positive control / mean OD negative control) *100
For the test item and the positive control, the mean relative viability +/- rel. standard deviation of the three individual tissues was calculated and used for classification according to the following prediction model:
in vitro result : in vivo prediction
mean tissue viability =< 50%: irritant
mean tissue viability > 50%: non-irritant

Acceptability of the Assay:
The absolute OD 570 nm of the negative control tissues in the MTT test is an indicator of tissue viability obtained after the shipping and storing procedure and under specific conditions of the assay. Tissue viability is meeting the acceptance criterion if the mean OD of the three tissues is >= 0.6 till <= 1.5.
The rel. standard deviations between tissues of the same treatment group should be <= 18%.
An assay is meeting the acceptance criterion if mean relative tissue viability of the positive control is <= 40%.
The data of the quality control (determined by SkinEthic Laboratories, 69007 Lyon, France) of the respective EpiSkin™ lot is mentioned in the report (the acceptance limit of the IC50 should be between 1.5 and 3.0 mg/mL after 18 hours treatment with SLS).
The historical data (means, rel. standard deviation, and ranges) of the positive control as well as the negative control obtained with the EpiSkin™ model at Envigo CRS GmbH are mentioned in the report.

Control samples:

yes, concurrent negative control

yes, concurrent positive control

Amount/concentration applied:

approximately 10 mg test item:
5 µL of deionised water were topically applied to the epidermal surface in order to improve further contact between the solid and the epidermis. Each approximately 10 mg of the test item were applied to and spread on the wetted triplicate tissues.

Duration of treatment / exposure:

15 minutes

Duration of post-treatment incubation (if applicable):

approximately 42 hours

Number of replicates:

3

Irritation / corrosion parameter:

other: Mean relative tissue viability (%)

Value:

115.2

Negative controls validity:

valid

Positive controls validity:

valid

Remarks on result:

no indication of irritation

Other effects / acceptance of results:

- OTHER EFFECTS:
- Colour interference: The optical pre-experiment (colour interference pre-experiment) to investigate the test item’s colour change potential in water did not lead to a change in colour.
- Direct-MTT reduction: Optical evaluation of the MTT-reducing capacity of the test item after 3 hour incubation with MTT-reagent did not show blue colour.

The test item did not reduce MTT (test for direct MTT reduction), and it did not change colour when mixed with deionised water (test for colour interference). Consequently, additional tests with freeze-killed or viable tissues were not necessary.

DEMONSTRATION OF TECHNICAL PROFICIENCY:
Quality control data (determined by SkinEthic Laboratories, 69007 Lyon, France) of the respective EpiSkinTM lot: the acceptance limit of the IC50 should be between 1.5 and 3.0 mg/mL after 18 hours treatment with SLS (actual value: 2.2 mg/mL)

ACCEPTANCE OF RESULTS:
- Acceptance criteria met for negative control: The absolute OD 570 nm of the negative control tissues in the MTT test is an indicator of tissue viability obtained after the shipping and storing procedure and under specific conditions of the assay. Tissue viability is meeting the acceptance criterion if the mean OD of the three tissues is >= 0.6 till <= 1.5 (actual value: 1.053).
- Acceptance criteria met for positive control: An assay is meeting the acceptance criterion if mean relative tissue viability of the positive control is <= 40% (actual: 8.1%).
- Acceptance criteria met for variability between replicate measurements: The rel. standard deviations between tissues of the same treatment group should be <= 18% (actual: <= 15.9%).
- Range of historical values: The actual values for the positive and negative control lie within the Envigo CRS GmbH historical data.

IL-1 α Immunoassay:

Since the results derived from the MTT assay were not unclear or borderline, the IL-1 α concentration in the medium was not determined.

Results after treatment with the test item and controls:

Test Group	Absorbance 570 nm Tissue 1*	Absorbance 570 nm Tissue 2*	Absorbance 570 nm Tissue 3*	Mean Absorbance of 3 Tissues	Stand. Dev.	Relative Absorbance [%] Tissue 1, 2 + 3**	Relative Standard Deviation [%]***	Rel. Absorbance [% of Negative Control]****
Negative Control	1.111	1.094	0.954	1.053	0.086	105.5 103.9 90.6	8.2	100.0
Positive Control	0.074	0.082	0.101	0.086	0.014	7.0 7.8 9.6	15.9	8.1
Test Item	1.178	1.222	1.242	1.214	0.033	111.8 116.0 117.9	2.7	115.2

* Mean of two replicate wells after blank correction

** Relative absorbance per tissue [rounded values]: (100 * (absorbance tissue)) / mean absorbance negative control

*** Rel. standard deviation: (Standard deviation absorbance / mean absorbance of 3 tissues) * 100

**** Relative absorbance per treatment group [rounded values]: (100 * (mean absorbance test item)) / mean absorbance negative control

Interpretation of results:

other: not classified, criteria not met

Remarks:

according to EU CLP Regulation (EC) No. 1272/2008 and its amendments.

Conclusions:

The relative mean tissue viability obtained after 15 minutes treatment with the substance compared to the negative control tissues was 115.2%. The relative tissue viability was not reduced, the value is above the threshold for irritancy of <= 50%. Therefore, the test item is not considered to be a skin irritant under the conditions of this study.

Executive summary:

The possible skin irritation potential of the substance was tested in compliance with OECD TG 439 and GLP principles. Three tissues of the human skin model EpiSkin™ were topically applied with 5 µL deionized water in order to improve contact between the solid test item and the epidermis. Each approximately 10 mg of the solid test item were applied to and spread on the wetted triplicate tissues. In addition, triplicate tissues were applied with 10 µL of the negative control (deionised water) or the positive control (5% Sodium lauryl sulfate). Each three tissues of the human skin model EpiSkin™ were treated with the test item, the negative or the positive control for 15 minutes. After approximately 42 hour post-exposure incubation period, determination of the cell viability was performed. Cell viability is measured by dehydrogenase conversion of MTT [3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl-tetrazoliumbromide], in cell mitochondria, into a blue formazan salt that is quantitatively measured after extraction from tissues. The percent reduction of cell viability in comparison with untreated negative controls is used to predict skin irritation potential. The validity criteria for the positive and negative control were met. The relative mean tissue viability obtained after 15 minutes treatment with the substance compared to the negative control tissues was 115.2%. This value is above the threshold for irritancy of <= 50%. Therefore, the test item is not considered to be a skin irritant under the conditions of this study.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not irritating)

Eye irritation

Link to relevant study records

Reference

Endpoint:

eye irritation: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

14-11-2016 to 14-12-2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 438 (Isolated Chicken Eye 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 (incl. QA statement)

Remarks:

Triskelion B.V., Utrechtseweg 48, 3700 AV, Zeist

Species:

other: eyes of male or female chickens (ROSS, spring chickens)

Details on test animals or tissues and environmental conditions:

SOURCE OF COLLECTED EYES
- Source: Slaughterhouse v.d. Bor, Nijkerkerveen, The Netherlands
- Characteristics of donor animals: Approximately 7 weeks old, male or female chickens, body weight range approximately 1.5-2.5 kg, were used as eye donors.
- Storage, temperature and transport conditions of ocular tissue: Heads of the animals were cut off immediately after sedation of the animals by electric shock and incision of the neck for bleeding, and before they reached the next station on the process line. The heads were placed in small plastic boxes on a bedding of paper tissues moistened with isotonic saline. Next, they were transported to the testing facility. During transportation, the heads were kept at ambient temperature.
- Time interval prior to initiating testing: Within 2 hours after kill, eyes were carefully dissected and placed in a superfusion apparatus.
- Indication of any existing defects or lesions in ocular tissue samples: No
- Indication of any antibiotics used: No

Vehicle:

unchanged (no vehicle)

Details on study design:

SELECTION AND PREPARATION OF ISOLATED EYES
Within 2 hours after kill, eyes were carefully dissected and placed in a superfusion apparatus using the following procedure: First the eye-lids were carefully removed without damaging the cornea and a small drop of Fluorescein sodium 2.0% w/v was applied to the corneal surface for a few seconds and subsequently rinsed off with isotonic saline at ambient temperature. Next, the head with the fluorescein-treated cornea was examined with a slit-lamp microscope (Slit-lamp 900 BP, Haag-Streit AG, Liebefeld-Bern, Switzerland) to ensure that the cornea was not damaged. If undamaged (e.g., fluorescein retention and corneal opacity scores of ≤ 0.5), the eye was further dissected from the head without damaging the eye or cornea. Care was taken to remove the eye-ball from the orbit without cutting off the optical nerve too short. The enucleated eye was placed in a stainless steel clamp with the cornea positioned vertically and transferred to a chamber of the superfusion apparatus. The clamp holding the eye was positioned in such a way that the entire cornea was supplied with isotonic saline from a bent, stainless steel tube, at a target rate of 0.10-0.15 mL/min. The chambers of the superfusion apparatus as well as the saline were temperature controlled at approximately 32 °C (water pump set at 36.4 °C). After placing in the superfusion apparatus, the eyes were examined again with the slit-lamp microscope to ensure that they were not damaged. Corneal thickness was measured using the Depth Measuring Attachment No. I for the Haag-Streit slit-lamp microscope, set at 0.095 mm. An accurate measurement was taken at the corneal apex of each eye. Eyes with a corneal thickness deviating more than 10% of the average corneal thickness of the eyes, eyes showing opacity (score higher than 0.5), or were unacceptably stained with fluorescein (score higher than 0.5) indicating the cornea to be permeable, or eyes that showed any other signs of damage, were rejected as test eyes and replaced.

EQUILIBRATION AND BASELINE RECORDINGS
Each eye provided its own baseline values for corneal swelling, corneal opacity and fluorescein retention. For that purpose, after an equilibration period of 45-60 minutes, the corneal thickness of the eyes was measured again to determine the zero reference value for corneal swelling calculations.

NUMBER OF REPLICATES
Negative control: 1
Positive control: 3
Test group: 3

NEGATIVE CONTROL USED
Physiological saline

POSITIVE CONTROL USED
NaOH

APPLICATION DOSE AND EXPOSURE TIME
30 mg (or 30 μL physioligical saline) for 10 seconds

OBSERVATION PERIOD
240 minutes

REMOVAL OF TEST SUBSTANCE
- Volume and washing procedure after exposure period: 20 mL saline. After rinsing, each eye in the holder was returned to its chamber.
- Indicate any deviation from test procedure in the Guideline: none

METHODS FOR MEASURED ENDPOINTS:
- Corneal opacity: Slit-lamp microscope examination
- Damage to epithelium based on fluorescein retention: Slit-lamp microscope examination
- Swelling: measured with optical pachymeter on a slit-lamp microscope; slit-width setting: set at 0.095 mm
- Others: After the final examination, the test substance treated eyes, the negative and positive control eyes were preserved in a neutral aqueous phosphate-buffered 4% solution of formaldehyde. The corneas were embedded in paraffin wax, sectioned at ca 4 μm and stained with PAS (Periodic Acid-Schiff). The microscopic slides were subjected to histopathological examination.

SCORING SYSTEM:
Defined scoring scales were used for each parameter to define the severity of effects into four categories (I-IV).
- Mean corneal swelling (%): According to OECD 438 guideline. Examination of the eyes after 0, 30, 75, 120, 180, and 240 minutes
- Mean maximum opacity score: According to OECD 438 guideline. Examination of the eyes after 0, 30, 75, 120, 180, and 240 minutes
- Mean fluorescein retention score at 30 minutes post-treatment: According to OECD 438 guideline.

DECISION CRITERIA: According to OECD 438 guideline

Irritation parameter:

percent corneal swelling

Run / experiment:

slit-lamp examination

Value:

0

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Positive controls validity:

valid

Remarks on result:

other: maximum mean values

Irritation parameter:

cornea opacity score

Run / experiment:

slit-lamp examination

Value:

0

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Positive controls validity:

valid

Remarks on result:

other: maximum mean values

Irritation parameter:

fluorescein retention score

Run / experiment:

slit-lamp examination

Value:

0

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Positive controls validity:

valid

Other effects / acceptance of results:

Slit-lamp examination: The test substance did not cause any corneal effects. The negative control eye did not show any corneal effect and demonstrated that the general conditions during the tests were adequate. The positive control NAOH caused severe corneal effects and demonstrated the ICE test valid to detect severe eye irritants.

Microscopic examination of the corneas treated with the test substance did not reveal any abnormalities. Microscopic examination of the cornea treated with the negative control (saline) did not reveal any abnormalities. Microscopic examination of the corneas treated with the positive control NAOH revealed severe erosion and severe necrosis of the epithelium, stromal and endothelial necrosis.

Interpretation of results:

other: Not classified, criteria not met

Remarks:

according to EU CLP Regulation (EC) No. 1272/2008 and its amendments.

Conclusions:

Under the test conditions (OECD 438 and GLP) the test substance is not considered to be an eye irritant.

Executive summary:

In accordance to OECD guideline 438 and GLP, the test substance was examined for its in vitro eye irritating potential using the Isolated Chicken Eye (ICE) Test. In the ICE test, 3 eyes were exposed to 30 mg test substance for 10 seconds. In addition, one negative control eye (30 µL saline) and three positive control eyes (30 mg sodium hydroxide (NaOH)) were tested. After the exposure the eyes were rinsed with 20 mL saline and were examined at approximately 0, 30, 75, 120, 180, and 240 minutes after treatment. The test substance did not cause any corneal effects. The negative control eye did not show any corneal effect and demonstrated that the general conditions during the tests were adequate. The positive control NaOH caused severe corneal effects and demonstrated the ICE test valid to detect severe eye irritants. Microscopic examination of the corneas treated with the test substance did not reveal any abnormalities. Microscopic examination of the cornea treated with the negative control (saline) did not reveal any abnormalities. Microscopic examination of the corneas treated with the positive control NAOH revealed severe erosion and severe necrosis of the epithelium, stromal and endothelial necrosis. Based on these results, the test substance is considered to be not eye irritating.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not irritating)

Additional information

Skin irritation:

The possible skin irritation potential of the substance was tested in compliance with OECD TG 439 and GLP principles. Three tissues of the human skin model EpiSkin™ were topically applied with 5 µL deionized water in order to improve contact between the solid test item and the epidermis. Each approximately 10 mg of the solid test item were applied to and spread on the wetted triplicate tissues. In addition, triplicate tissues were applied with 10 µL of the negative control (deionised water) or the positive control (5% Sodium lauryl sulfate). Each three tissues of the human skin model EpiSkin™ were treated with the test item, the negative or the positive control for 15 minutes. After approximately 42 hour post-exposure incubation period, determination of the cell viability was performed. Cell viability is measured by dehydrogenase conversion of MTT [3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl-tetrazoliumbromide], in cell mitochondria, into a blue formazan salt that is quantitatively measured after extraction from tissues. The percent reduction of cell viability in comparison with untreated negative controls is used to predict skin irritation potential. The validity criteria for the positive and negative control were met. The relative mean tissue viability obtained after 15 minutes treatment with the substance compared to the negative control tissues was 115.2%. This value is above the threshold for irritancy of <= 50%. Therefore, the test item is not considered to be a skin irritant under the conditions of this study.

Eye irritation:

In accordance to OECD guideline 438 and GLP, the test substance was examined for its in vitro eye irritating potential using the Isolated Chicken Eye (ICE) Test. In the ICE test, 3 eyes were exposed to 30 mg test substance for 10 seconds. In addition, one negative control eye (30 µL saline) and three positive control eyes (30 mg sodium hydroxide (NaOH)) were tested. After the exposure the eyes were rinsed with 20 mL saline and were examined at approximately 0, 30, 75, 120, 180, and 240 minutes after treatment. The test substance did not cause any corneal effects. The negative control eye did not show any corneal effect and demonstrated that the general conditions during the tests were adequate. The positive control NaOH caused severe corneal effects and demonstrated the ICE test valid to detect severe eye irritants. Microscopic examination of the corneas treated with the test substance did not reveal any abnormalities. Microscopic examination of the cornea treated with the negative control (saline) did not reveal any abnormalities. Microscopic examination of the corneas treated with the positive control NAOH revealed severe erosion and severe necrosis of the epithelium, stromal and endothelial necrosis. Based on these results, the test substance is considered to be not eye irritating.

Justification for classification or non-classification

Based on the negative results in the skin and eye irritation tests the substance does not need to be classified for these endpoints according to EU CLP Regulation (EC) No. 1272/2008 and its amendments.