1,3-diethyl-2,4-diisocyanato-5-methylbenzene

Skin irritation / corrosion

Administrative data

Endpoint:

skin irritation: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2017-07-17 - 2017-10-06 (experimental phase)

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

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)

Version / remarks:

OECD Guideline for the testing of Chemicals 439: In Vitro Skin Irritation: Reconstructed Human Epidermis Test Method (Original Guideline adopted July 28, 2015), and as described in detail in the Protocol for: In Vitro EpiDermTM Skin Irritation Test (EPI-200-SIT) for use with MatTek Corporation’s Reconstructed Human Epidermal Model EpiDerm (EPI-200).

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

Based on a “Statement on the Scientific Validity of In Vitro Tests for Skin Irritation” of the European Commission (November 2008), official acceptance of the test method in the EU was achieved and implemented in EU, 2008a, Council Regulation (EC) No 440/2008 of 30 May 2008 laying down test methods pursuant to EC Regulation No 1907/2006 of the European Parliament and of the Council on REACH; 1st ATP 2009: EC Regulation No 761/2009 of 23 July 2009 amending, for the purpose of its ATP, EC Regulation No 440/2008 laying down test methods pursuant to EC Regulation No 1907/2006 of the European Parliament and of the Council on REACH, section B46.

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test material

Test material information

Constituent 1

Reference substance name:

1,3-diethyl-2,4-diisocyanato-5-methylbenzene

EC Number:

813-050-0

Cas Number:

2162-70-1

Molecular formula:

C13H14N2O2

IUPAC Name:

1,3-diethyl-2,4-diisocyanato-5-methylbenzene

impurity 1

Reference substance name:

1,3-diisocyanato-4,6-diethyl-2-methyl-benzene

Cas Number:

93187-13-4

Molecular formula:

C13H14N2O2

IUPAC Name:

1,3-diisocyanato-4,6-diethyl-2-methyl-benzene

impurity 2

Reference substance name:

unknown impurities

IUPAC Name:

unknown impurities

Test material form:

liquid

Remarks:

light yellow

Details on test material:

Analytical purity: 87.2 % CAS 2162-70-1 (99.8 % isomeric mixture)
- Isomers composition:
87.2% 3,5-Diethyltoluene-2,4-diisocyanate
12.6% 3,5-Diethyltoluene 2,6-diisocyanate

In vitro test system

Test system:

human skin model

Source species:

human

Cell type:

non-transformed keratinocytes

Cell source:

other: not stated

Source strain:

other: not applicable

Details on animal used as source of test system:

SOURCE ANIMAL
human donors

Justification for test system used:

Dermal irritation is generally defined as "the production of reversible inflammatory changes in the skin". The potential for chemical induced skin irritation is an important consideration in establishing procedures for the safe handling, packing and transport of chemicals. It is usually determined in vivo in the Draize rabbit skin irritation test as described in OECD guideline 404. Because systemic reactions play a minor role in modulating local skin toxicity potential of chemicals, skin irritation potential may be predicted by in vitro systems, provided they are sufficiently complex to mimic human skin barrier and cell reactivity. In an international prevalidation study performed by ECVAM, the in vitro skin irritation test using the human skin model EpiDerm™ and EpiSkin™ and measurement of cell viability by dehydrogenase conversion of MTT into a blue formazan salt have turned out as a sufficiently promising predictor for skin irritancy potential.

Vehicle:

unchanged (no vehicle)

Details on test system:

RECONSTRUCTED HUMAN EPIDERMIS (RHE) TISSUE
- Model used: Epi-200 SIT kits and MTT-100 assay diluent were purchased from MatTek Corporation (82105 Bratislava, Slovakia). The EpiDerm™ 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 EpiDerm™ tissues (surface 0.6 cm²) are cultured on specially prepared cell culture inserts (MILLICELLs, 10 mm diameter).
- Tissue batch number(s): 25847
- Production date: 2017-10-03
- Delivery date: EpiDerm™ tissues were shipped with cool packs on medium-supplemented agarose gels in a 24-well plate and reached on 04 October 2017.
- Date of initiation of testing: On day of receipt the pre-incubation phase of the EpiDerm™ tissues started.

TEMPERATURE USED FOR TEST SYSTEM
- Temperature used during treatment / exposure: 20 – 25 °C (treatment); 37 ± 1.5 °C (incubator)

REMOVAL OF TEST MATERIAL AND CONTROLS
-Volume and number of washing steps: After the end of the treatment interval the inserts were removed immediately from the 6-well plate and tissues were gently rinsed with DPBS at least 15 times in order to remove any residual test material.
- Observable damage in the tissue due to washing: none stated
- Modifications to validated SOP: none stated; but the following deviation from study plan occurred: The pre-incubation phase was shortened to 1 hour instead of 1 + 18 hours as described in the study plan. The quality of the tissues was not affected, because the acceptance criteria for the test method were clearly fulfilled, positive and negative controls gave the appropriate response, and the OD values were within the historically established boundaries.

MTT DYE USED TO MEASURE TISSUE VIABILITY AFTER TREATMENT / EXPOSURE
- MTT concentration: On the day of testing the MTT concentrate was diluted with the MTT diluent (1 mg/mL). The 24-well plates were prepared before the end of the tissue pre-warming period. A volume of 300 µL of the MTT solution was added to each well and the plates were kept in an incubator (37 ± 1.5 °C, 5 ± 0.5 % CO2) until further use.
- Incubation time: After the approximately 42-hours incubation period was completed for all tissues and exposure groups, 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), the tissues were rinsed three times with DPBS, and carefully dried with blotting paper. The tissues were transferred into new 24-well plates containing 2 mL of extractant solution (isopropanol) in each well ensuring that the tissues are completely covered. The 24-well plate was sealed to inhibit the isopropanol evaporation.
The formazan salt was extracted for about 2 hours while shaking at room temperature.
After the extraction period was completed, the inserts were pierced with an injection needle to allow the extract to run into the well from which the insert was taken. Afterwards the insert was discarded. The 24-well plates were placed on a shaker for 15 minutes until the solution was homogeneous in colour.
- Spectrophotometer / Wavelength / Filter: Per each tissue, 3 x 200 µL aliquots of the blue formazan solution were transferred into a 96-well flat bottom microtiter plate from the 15 minutes exposure. OD was read in a microplate reader (Versamax® Molecular Devices, Softmax Pro Enterprise, version 4.7.1) with a 570 nm filter. Mean values were calculated from the 3 wells per tissue.

FUNCTIONAL MODEL CONDITIONS WITH REFERENCE TO HISTORICAL DATA
- Viability: See below, historical control data; 1.311 ± 0.083 (1.0 – 3.0)
- Barrier function: 8.10 h (4.77 – 8.72 h)
- Contamination: sterile

NUMBER OF REPLICATE TISSUES: triplicates

CONTROL TISSUES USED IN CASE OF MTT DIRECT INTERFERENCE
Since the MTT solution did not turn blue/purple in the Test for Direct MTT Reduction and Colour Interference, the test item was not considered to reduce MTT and an additional test with freeze-killed tissues did not have to be performed.

NUMBER OF INDEPENDENT TEST SEQUENCES / EXPERIMENTS TO DERIVE FINAL PREDICTION: 1

PREDICTION MODEL / DECISION CRITERIA (choose relevant statement)
An irritation potential of a test item leading to H315 (according to regulation (EC) 1272/2008), and GHS category 2 according to UN GHS (published 2003, last (6th) revision 2015) is recommended if the mean relative tissue viability of three individual tissues is reduced ≤ 50% of the negative control after incubation with the test item for 60 min in total.

Control samples:

yes, concurrent negative control

other: yes, concurrent positive control

Amount/concentration applied:

TEST MATERIAL
- Amount(s) applied (volume or weight with unit): 30 μL (47 μL/cm² according to guideline) of the undiluted test item was dispensed directly atop the EpiDerm™ tissue and spread to match the surface of the tissue for a complete treatment time of 60 minutes.
- Concentration (if solution): undiluted

NEGATIVE CONTROL
- Amount(s) applied (volume or weight): 30 µl DPBS (Gibco)

POSITIVE CONTROL
- Amount(s) applied (volume or weight): 30 µl 5% SLS solution in deionised water (MatTek)

Duration of treatment / exposure:

60 min

Duration of post-treatment incubation (if applicable):

After the end of the treatment interval the inserts were removed immediately from the 6-well plate and tissues were gently rinsed with DPBS at least 15 times in order to remove any residual test material. After the rinsing the inserts were submerged in DPBS at least three times. Afterwards the inserts were once again rinsed with sterile DPBS from the inside and the outside. Excess DPBS was removed by gently shaking the inserts and blotting the bottom with sterile blotting paper. The tissues were then transferred into new 6-well plates with 0.9 mL of fresh assay medium in the upper row. The inserts were placed in the prepared holding plate. Tissues were incubated for about 24 hours at 37 ± 1.5 °C, 5 ± 0.5 % CO2. After incubation medium will be changed (0.9 mL of pre-warmed fresh medium). Thereafter tissues were incubated for another 18 hours at 37 ± 1.5 °C, 5 ± 0.5 % CO2. The complete incubation time was about 42 hours.

Number of replicates:

1 run, each three replicate tissues

Results and discussion

In vitro

Results

Irritation / corrosion parameter:

% tissue viability

Run / experiment:

mean of three replicates

Value:

103.8

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Positive controls validity:

valid

Remarks on result:

no indication of irritation

Other effects / acceptance of results:

- OTHER EFFECTS:
- Visible damage on test system:
- Direct-MTT reduction: none
- Colour interference with MTT: none
The optical pre-experiment (colour interference pre-experiment) to investigate the test item’s colour change potential in water did not led to a change in colour.
Optical evaluation of the MTT-reducing capacity of the test item after 1 hour incubation with MTT-reagent did not show blue/purple colour.
The test item passed the MTT- and the Colour Interference pre-tests.

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

The relative standard deviations between the % variability values of the test item, the positive and negative controls in the main test were below 11% (threshold of the "OECD Guideline for the Testing of Chemicals 439: In vitro Skin Irritation: Reconstructed Human Epidermis Test Method”: < 18%), thus ensuring the validity of the study.

Applicant's summary and conclusion

Interpretation of results:

GHS criteria not met

Conclusions:

The study was conducted under GLP according to OECD guideline 439 on the registered substance itself. The method is to be considered scientifically reasonable with no deficiencies in documentation or any deviations, the validity criteria are fulfilled, positive and negative controls gave the appropriate response. Hence, the results can be considered as reliable to assess the irritating potential of the test substance to the skin in vitro. The relative mean tissue viability obtained after 60 minutes treatment with the test item compared to the negative control tissues was 103.8%. Since the mean relative tissue viability for the test item was above 50% the test item is considered to be non-irritant. It is concluded that this test is valid and that 3,5-Diethyltoluene-2,4-diisocyanate is non-irritant in the in vitro skin irritation test under the experimental conditions described in this report and should not be classified according to the Globally Harmonized System of Classification and Labeling of Chemicals (GHS) of the United Nations.

Executive summary:

This in vitro study was performed according to OECD 439 under GLP to assess the irritation potential of 3,5-Diethyltoluene-2,4-diisocyanate by means of the Human Skin Model Test.

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). Also its intrinsic colour was not intensive. Consequently, additional tests with freeze-killed or viable tissues were not necessary.

Each three tissues of the human skin model EpiDerm™ were treated with the test item, the negative control (DPBS) or the positive control (5% SLS) for 60 minutes.

After treatment with the negative control the absorbance values were well within the required range of the acceptability criterion of mean OD³0.8 and ≤ 2.8 for the 60 minutes treatment interval, thus assuring the quality of the tissues.

Treatment with the positive control induced a sufficient decrease in the relative absorbance as compared to the negative control for the 60 minutes treatment interval, and thus assuring the validity of the test system.

After treatment with the test item 3,5-Diethyltoluene-2,4-diisocyanate the mean relative absorbance value was 103.8% compared to the relative absorbance value of the negative control. This value is above the threshold for irritancy of ≤ 50%. Therefore, the test item is not considered to possess an irritant potential.

In conclusion, it can be stated that in this study and under the experimental conditions reported, 3,5-Diethyltoluene-2,4-diisocyanate is not irritant to skin.