(4E)-5-cyclohexyl-2,4-dimethylpent-4-enal

Skin irritation / corrosion

Administrative data

Endpoint:

skin irritation: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

11-04-2018 to 16-04-2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Guideline study performed under GLP. All relevant validity criteria were met.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2018

Report date:

2018

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method B.46 (In Vitro Skin Irritation: Reconstructed Human Epidermis Model Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

inspected: July 2017 ; signature: November 2017

Test material

Test material information

Constituent 1

Reference substance name:

(4E)-5-cyclohexyl-2,4-dimethylpent-4-enal

EC Number:

947-579-4

Cas Number:

1449104-34-0

Molecular formula:

C13H22O

IUPAC Name:

(4E)-5-cyclohexyl-2,4-dimethylpent-4-enal

Test material form:

liquid

Details on test material:

- Physical state: Liquid
- Storage condition of test material: approximately 4ºC, in the dark, under nitrogen
- Other: colourless

In vitro test system

Test system:

human skin model

Remarks:

EPISKIN TM Small Model

Source species:

human

Cell type:

non-transformed keratinocytes

Cell source:

foreskin from a single donor

Vehicle:

unchanged (no vehicle)

Details on test system:

RECONSTRUCTED HUMAN EPIDERMIS (RHE) TISSUE
- Model used: EPISKIN TM Small Model
- Tissue batch number(s): Lot no.: 18-EKIN-015
- Production date: Not reported.
- Shipping date: Not reported.
- Delivery date: 10-04-2018 ; day prior to test initiation (ca. 24 hours)
- Date of initiation of testing: ca. 11-04-2018

TEMPERATURE USED FOR TEST SYSTEM
- Temperature used during treatment / exposure: 37 °C, 5% CO2
- Temperature of post-treatment incubation (if applicable): 37 °C, 5% CO2

REMOVAL OF TEST MATERIAL AND CONTROLS
- Volume and number of washing steps: At the end of the exposure period, each tissue was removed from the well using forceps and rinsed using a wash bottle containing DPBS with Ca++ and Mg++. Rinsing was achieved by filling and emptying each tissue insert for approximately 40 seconds using a constant soft stream of DPBS to gently remove any residual test item. The rinsed tissues were transferred to the second column of 3 wells containing 2 mL of maintenance medium in each well. The rinsed tissues were incubated at 37 °C, 5% CO2 in air for 42 hours. Following the 42-Hour post-exposure incubation period each 12-well plate was placed onto a plate shaker for 15 minutes to homogenize the released mediators in the maintenance medium. 1.6 mL of the maintenance medium from beneath each tissue was transferred to pre-labelled micro tubes and stored in a freezer at -14 to -30 ºC for possible inflammatory mediator determination. The tissues were then processed for MTT-loading and 3 hour incubation at 37 °C, 5% CO2.
- Observable damage in the tissue due to washing: Not applicable.
- Modifications to validated SOP: Not applicable.

MTT DYE USED TO MEASURE TISSUE VIABILITY AFTER TREATMENT / EXPOSURE
- MTT concentration: 0.3 mg/mL MTT solution prepared in assay medium
- Incubation time: The plate was incubated (37 °C, 5% CO2) for 3 hours.
- Spectrophotometer: Labtech LT-4500 microplate reader
- Wavelength: 570 nm (OD570)
- Filter: Without reference filter
- Filter bandwidth: No reported.
- Linear OD range of spectrophotometer: Not reported.

FUNCTIONAL MODEL CONDITIONS WITH REFERENCE TO HISTORICAL DATA
- Viability: Within NC and PC historic control ranges presented within the report.
- Barrier function: See above.
- Morphology: See above.
- Contamination: Not applicable.
- Reproducibility: The relative mean tissue viability for the positive control treated tissues was 5.6% relative to the negative control following the 15-minute exposure/42-hour incubation period. With standard deviation of 4.0%. The positive control acceptance criterion was therefore satisfied. The negative control triplicate treated tissues mean OD570 was 0.787 and the standard deviation of viability was 11.9%. The acceptance criterion was therefore satisfied. The test item triplicate treated tissues viability standard deviation was 5.0%. The mean OD570 for both the negative and positive controls were within the historical control ranges.
- Other: As an additional quality control step, the results of the assay are compared to the historical ranges for negative and positive controls generated by the testing laboratory to confirm the functioning of the test system.

NUMBER OF REPLICATE TISSUES: Three (3), triplicate

CONTROL TISSUES USED IN CASE OF MTT DIRECT INTERFERENCE
- Fresh tissues / killed tissues: In the pretest for colour interference: the solution containing the test item was colourless. It was therefore unnecessary to run colour correction tissues. In the pre-test for direct MTT reduction: The MTT solution containing the test item did not turn blue or purple which indicated that the test item did not directly reduce MTT. It was unnecessary to run killed tissues.
- Procedure used to prepare the killed tissues (if applicable): Not applicable.
- N. of replicates : Not applicable.
- Method of calculation used: Not applicable.
- Other: In the assessment of Colour Interference with the MTT endpoint, the solution containing the test item did not become coloured. This was taken to indicate the test item did not have the potential to cause colour interference.

NUMBER OF INDEPENDENT TEST SEQUENCES / EXPERIMENTS TO DERIVE FINAL PREDICTION: One (n=1)

PREDICTION MODEL / DECISION CRITERIA (choose relevant statement)
- The test substance is considered to be irritating to skin if e.g. the viability after 15-minutes exposure / 42-hours incubation is less than or equal to 50%,.
- The test substance is considered to be non-irritating to skin if e.g. the viability after 15-minutes exposure / 42-hours incubation is greater than 50%.
- Cut off points in accordance with OECD TG 439 and the GHS and CLP Classification systems.
- Skin irritation is expressed as the remaining cell viability after exposure to the test substance at exposure times 15-minutes / 42-hours incubation. Where necessary, direct MTT reduction, colour interference was completed.

OTHER:
EpiSkin RHE Model (Lot no.: 15-EKIN-015). The principle of the assay is based on the measurement of cytotoxicity in reconstructed human epidermal cultures following topical exposure to the test item by means of the colorimetric MTT reduction assay. Cell viability is measured by enzymatic reduction of the yellow MTT tetrazolium salt. to a blue formazan salt (within the mitochondria of viable cells) in the test item treated tissues relative to the negative controls. As a complimentary endpoint the concentration of the inflammatory mediator IL-1α in the culture medium retained following the 42-Hour post-exposure incubation period may also be determined for test items which are found to be borderline non-irritant based upon the MTT reduction endpoint. The EPISKINTM model is a three-dimensional reconstructed human epidermis model consisting of adult human-derived epidermal keratinocytes seeded on a dermal substitute consisting of a collagen type I matrix coated with type IV collagen. A highly differentiated and stratified epidermis model is obtained after a 13-Day culture period comprising of the main basal, supra basal, spinous and granular layers and a functional stratum corneum. Pre-test checks for Direct MTT reduction and Colour Interference were completed.

Preincubation:
Before removal from the transport plate each tissue was inspected for any air bubbles between the agarose gel and the insert. 2 mL of maintenance medium, warmed to approximately 37 °C, was pipetted into the first column of 3 wells of a pre-labelled 12-well plate. Each epidermis unit was transferred into the maintenance medium filled wells (3 units per plate). A different 12-well plate was used for the test item and each control item. The tissues were incubated at 37 °C, 5% CO2 in air overnight.

Application of test item and rinsing:
2 mL of maintenance medium, warmed to approximately 37 °C, was pipetted into the second column of 3 wells of the 12-well plate. Triplicate tissues were treated with the test item for an exposure period of 15 minutes. The test item was applied topically to the corresponding tissues ensuring uniform covering. 10 μL (26.3 μL/cm2) of the test item was applied to the epidermis surface. Triplicate tissues treated with 10 μL of DPBS served as the negative controls and triplicate tissues treated with 10 μL of SDS 5% w/v served as the positive controls. At the end of the exposure period, each tissue was removed from the well using forceps and rinsed using a wash bottle containing DPBS with Ca++ and Mg++. Rinsing was achieved by filling and emptying each tissue insert for approximately 40 seconds using a constant soft stream of DPBS to gently remove any residual test item. The rinsed tissues were transferred to the second column of 3 wells containing 2 mL of maintenance medium in each well. The rinsed tissues were incubated at 37 °C, 5% CO2 in air for 42 hours.
The tissues were subsequently placed into was placed onto a plate shaker for 15 minutes to homogenize the released mediators in the maintenance medium. 1.6 mL of the maintenance medium from beneath each tissue was transferred to pre-labelled micro tubes and stored in a freezer at -14 to -30 ºC for possible inflammatory mediator determination. Following 42 hour post exposure incubation the treated plates were then tested for MTT formazan extraction.

Control samples:

yes, concurrent negative control

yes, concurrent positive control

Amount/concentration applied:

TEST MATERIAL
- Amount(s) applied (volume or weight with unit): 10 µl
- Concentration (if solution): undiluted

VEHICLE
- Amount(s) applied (volume or weight with unit): Not applicable.
- Concentration (if solution): Not applicable.
- Lot/batch no. (if required): Not applicable.
- Purity: Not applicable.

NEGATIVE CONTROL
- Amount(s) applied (volume or weight): 10 µl ; Dulbecco’s Phosphate Buffered Saline (DPBS) with Ca++ and Mg++
- Concentration (if solution): Tested as supplied (undiluted).

POSITIVE CONTROL
- Amount(s) applied (volume or weight): 10 µl ; The positive control item, Sodium dodecyl sulphate (SDS), was prepared as a 5% w/v aqueous solution. The positive control was formulated within 2 hours of being applied to the test system.
- Concentration (if solution): 5%

Duration of treatment / exposure:

Tissues were treated with the test item for 15 minutes and then washed with DPBS with Ca++ and Mg++ to remove residual test item.
Positive control: SDS (5% w/v) was respread after 7 minutes contact time to maintain distribution of the SDS - for the remainder of the contact period. This was not deemed necessary in the negative control or test item definitive test group.

Duration of post-treatment incubation (if applicable):

Subsequently the skin tissues were incubated for 42 hours at 37°C. Then 3 hours incubation prior to and/or MTT loading and Formazan extraction.

Number of replicates:

Triplicate (n=3) ; treatment and concurrent negative control and positive control groups

Results and discussion

In vitro

Results

Irritation / corrosion parameter:

other: other: mean tissue viability

Value:

86.9

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Positive controls validity:

valid

Remarks on result:

other:

Remarks:

Basis: mean. Time point: 15 minute exposure. Reversibility: no data. Remarks: n=3; SD = 5.0% ; Score in terms of percentage of negative control.

Other effects / acceptance of results:

- OTHER EFFECTS:
- Visible damage on test system: None reported.
- Direct-MTT reduction: Screened prior to test. Not applicable.
- Colour interference with MTT: Screened prior to test. Not applicable.

DEMONSTRATION OF TECHNICAL PROFICIENCY: The laboratory has previously demonstrated technical proficiency. Also see historic control data.

ACCEPTANCE OF RESULTS:
- Acceptance criteria met for negative control: Yes.
- Acceptance criteria met for positive control: Yes.
- Acceptance criteria met for variability between replicate measurements: Yes.
- Range of historical values if different from the ones specified in the test guideline: Historic Control Data are presented in the full study report. All values for the control groups were within the ranges of the current Historic Control Data.

Any other information on results incl. tables

Table 1. Mean absorption and tissue viability in the in vitro skin irritation test with the test item

Item	OD570 of tissues	Mean OD570 of triplicate tissues	± SD of OD570	Relative individual tissue viability (%)	Relative mean viability (%)	± SD of Relative mean viability (%)
Negative Control Item	0.872	0.787	0.093	110.8	100*	11.9
	0.687			87.3
	0.803			102.0
Positive Control Item	0.080	0.044	0.031	10.2	5.6	4.0
	0.029			3.7
	0.024			3.0
Test Item	0.645	0.684	0.040	82.0	86.9	5.0
	0.724			92.0
	0.682			86.7

OD = Optical Density

SD = Standard deviation

* = The mean viability of the negative control tissues is set at 100%

Applicant's summary and conclusion

Interpretation of results:

GHS criteria not met

Remarks:

Criteria used for interpretation of results: EU

Conclusions:

Under the conditions of this in vitro study, the test item is not considered to be irritating to skin.

Executive summary:

The study was performed to OECD TG 439 and EU Method B.46 under GLP to assess the skin irritation potential of the test item using a human three dimensional epidermal model (EPISKIN Small Model). Triplicate tissues were treated with the test item for an exposure period of 15 minutes. At the end of the exposure period each tissue was rinsed before incubating for 42 hours. At the end of the post-exposure incubation period each tissue was taken for MTT-loading. The maintenance medium from beneath each tissue was transferred to pre-labelled micro tubes and stored in a freezer for possible inflammatory mediator determination. After MTT-loading a total biopsy of each epidermis was made and placed into micro tubes containing acidified isopropanol for extraction of formazan crystals out of the MTT-loaded tissues. At the end of the formazan extraction period each tube was mixed thoroughly and duplicate 200 μL samples were transferred to the appropriate wells of a pre-labelled 96-well plate. The optical density was measured at 570 nm. Data are presented in the form of percentage viability (MTT reduction in the test item treated tissues relative to negative control tissues). The relative mean viability of the test item treated tissues was 86.9% after the 15-Minute exposure period and 42-Hours post-exposure incubation period. The standard deviation calculated from individual tissue viabilities of the three identically test item treated tissues was 5.0%. The mean OD570 for the negative control treated tissues was 0.787 and the standard deviation value of the viability was 11.9%. The negative control acceptance criteria were therefore satisfied. The relative mean tissue viability for the positive control treated tissues was 5.6% relative to the negative control treated tissues and the standard deviation value of the viability was 4.0%. The positive control acceptance criteria were therefore satisfied. All acceptance criteria were considered to be met. Under the conditions of this study, the test item is not considered to be irritating to the skin.