Ethyl 2,6,6-trimethylcyclohexa-1,3-ene-1-carboxylate

Skin sensitisation

Administrative data

Endpoint:

skin sensitisation: in vivo (LLNA)

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2015

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Guideline study performed under GLP.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2015

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 429 (Skin Sensitisation: Local Lymph Node Assay)

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method B.42 (Skin Sensitisation: Local Lymph Node Assay)

Deviations:

no

Test guideline 3

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.2600 (Skin Sensitisation)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

inspected March 2013; signature: May 2013

Type of study:

mouse local lymph node assay (LLNA)

Test material

Test material information

Constituent 1

Reference substance name:

Ethyl 2,6,6-trimethylcyclohexa-1,3-ene-1-carboxylate

EC Number:

252-335-9

EC Name:

Ethyl 2,6,6-trimethylcyclohexa-1,3-ene-1-carboxylate

Cas Number:

35044-59-8

Molecular formula:

C12H18O2

IUPAC Name:

ethyl 2,6,6-trimethylcyclohexa-1,3-diene-1-carboxylate

Details on test material:

- Physical state: Liquid.
- Storage condition of test material: At room temperature protected from light.
- Other: Colourless liquid

In vivo test system

Test animals

Species:

mouse

Strain:

other: CBA/J strain, inbred, SPF-Quality

Sex:

female

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: recognised animal supplier
- Age at study initiation: approx. 10 weeks old
- Weight at study initiation: 19 - 23 grams; Body weight variation was within +/- 20% of the sex mean.
- Housing: Group housed, in labelled Makrolon cages sterilised sawdust as bedding material, paper and shelters as cage enrichment. On Day 6, the animals were group housed in Makrolon MII type cages with a sheet of paper instead of sawdust and cage enrichment.
- Diet: Free access to pelleted rodent diet
- Water: mains tap water ad libitum
- Acclimation period: at least 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18 - 24
- Humidity (%): 40 - 70
- Air changes (per hr): 10
- Photoperiod: 12 hours light / 12 hours dark

Study design: in vivo (LLNA)

Vehicle:

acetone/olive oil (4:1 v/v)

Concentration:

- Preliminary test: Initially, two test substance concentrations were tested; a 50% and 100% concentration. The highest concentration was the maximum concentration as required in the test guidelines (undiluted for liquids).
- Main test: 0% (vehicle control), 10% 25, 50 and 100% (undiluted). Test concentrations were determined from the results of the preliminary test. Based on the results, in order to achieve more information, an additional group of animals was treated with a 10% test substance concentration together with a concurrent vehicle control group.

No. of animals per dose:

Preliminary test: Two per concentration: 50% and 100%.
Main test: 5 mice per dose group 0% (vehicle control), 10%, 25, 50 and 100%

Details on study design:

RANGE FINDING TESTS:
A pre-screen test was conducted in order to select the highest test substance concentration to be used in the main study. In principle, this highest concentration should cause no systemic toxicity, may give well-defined irritation at most (maximum grade 2 and/or an increase in ear thickness < 25%) and is the highest possible concentration that can technically be applied. Two test substance concentrations were tested; a 50% and 100% concentration. The highest concentration was the maximum concentration as required in the test guidelines (undiluted for liquids). The test system, procedures and techniques were identical to those used in the main study except that the assessment of lymph node proliferation and necropsy were not performed. Two young adult animals per concentration were selected. Each animal was treated with one concentration on three consecutive days. Ear thickness measurements were conducted using a digital thickness gauge on prior to dosing on Day 1, 1-hour post application of test item on Days 1, 2 and 3 and on Days 4, 5 and 6.

MAIN STUDY
ANIMAL ASSIGNMENT AND TREATMENT
- Criteria used to consider a positive response: Following excision of the nodes. The individual SI is the ratio of the DPM/animal compared to DPM/vehicle control group. If the results indicate a SI ≥ 3, the test substance may be regarded as a skin sensitizer.

TREATMENT PREPARATION AND ADMINISTRATION:
Three groups of five animals were treated with one test substance concentration per group. The highest test substance concentration was selected from the pre-screen test. One group of five animals was treated with vehicle (and a further group for the additional dose as control).
- Induction: The dorsal surface of both ears was topically treated (25 μL/ear) with the test substance concentration, at approximately the same time on each day. The concentrations were stirred with a magnetic stirrer immediately prior to dosing. The control animals were treated in the same way as the experimental animals, except that the vehicle was administered instead of the test substance.
- Node excision: Each animal was injected via the tail vein with 0.25 mL of sterile phosphate buffered saline (PBS) containing 20 μCi of 3H-methyl thymidine. After approximately five hours, all animals were killed by intraperitoneal injection (0.2 mL/animal) with Euthasol® 20%. The draining (auricular) lymph node of each ear was excised. The relative size of the nodes (as compared to normal) was estimated by visual examination and abnormalities of the nodes and surrounding area were recorded. The nodes were pooled for each animal in approximately 3 mL PBS.
- Tissue processing and radioactivity measurements: A single cell suspension of lymph node cells (LNC) was prepared in PBS by gentle separation through stainless steel gauze (diameter 125 μm). LNC were washed twice with an excess of PBS by centrifugation at 200g for 10 minutes at 4ºC. To precipitate the DNA, the LNC were exposed to 5% trichloroacetic acid (TCA) and stored in the refrigerator until the next day. Precipitates were recovered by centrifugation, resuspended in 1 mL TCA and transferred to 10 mL of Ultima Gold cocktail as the scintillation fluid. Radioactive measurements were performed using a scintillation counter. Counting time was to a statistical precision of ± 0.2% or a maximum of 5 minutes whichever came first. The scintillation counter was programmed to automatically subtract background and convert Counts Per Minute (CPM) to Disintegrations Per Minute (DPM).

Observations:
- Mortality/Viability: Twice daily.
- Bodyweights: On Day 1 (pre-dose) and Day 6 (prior to necropsy).
- Clinical Observations: Twice daily (pre- and post-dosing) on Days 1-3. Once daily on Days 4-6 (on Days 1-3 between 3 and 4 hours after dosing).
- Irritation: Twice daily (pre- and post-dosing) on Days 1-3. Once daily on Days 4-6 (on Days 1-3 within 1 hour after dosing) according to the following numerical scoring system. Furthermore, a description of all other (local) effects was recorded.
- Ear Thickness: Measurements were conducted in the pre-screen test and in the main study. A digital thickness gauge was used to measure the ear thickness of each ear prior to dosing on Day 1, 1-hour post application of test substance on Days 1, 2 and 3 and on Days 4, 5 and 6 in order to monitor for any changes in ear thickness.

Positive control substance(s):

hexyl cinnamic aldehyde (CAS No 101-86-0)

Results and discussion

Positive control results:

In a separate 'positive control study' performed according to OECD 429 during November 2014, the sensitivity of the strain of mouse used in this study was assessed using the known sensitiser, α-hexylcinnamaldehyde. The positive control was tested at concentrations 5, 10 and 25% in Acetone/Olive oil (4:1 v/v). The highest concentration tested showed a Stimulation Index (SI) of 3.7 ± 1.1 (at 25% v/v) and met the criteria for a 'positive' result. An EC3 value of 9.8% was calculated using linear interpolation. The calculated EC3 value was found to be in the acceptable range of 4.8 and 19.5%. The results of the 6 monthly HCA reliability checks of the recent years were 14.4, 16.5, 14.5, 13.4, 14.1 and 17.3%

In vivo (LLNA)

Results

Results 1

Parameter:

SI

Remarks on result:

other: See table below

Results 2

Parameter:

other: disintegrations per minute (DPM)

Remarks on result:

other: See table below

Any other information on results incl. tables

In the preliminary screening test: No irritation and no signs of systemic toxicity were observed in any of the animals examined. Variations in ear thickness during the observation period were less than 25% from Day 1 pre-dose values. Based on these results, the highest test substance concentration selected for the main study was a 100% concentration.

 

In the main test:

No irritation of the ears was observed in any of the animals examined. Variations in ear thickness during the observation period were less than 25% from Day 1 pre-dose values for the initially treated animals. No ear thickness measurements were conducted in the additional groups. No mortality occurred and no clinical signs of systemic toxicity were observed in the animals of the main study, except for the turbid left eye, observed for one vehicle control animal on Day 6. Body weights and body weight gain of experimental animals remained in the same range as controls over the study period. All auricular lymph nodes of the animals of the experimental and control groups were considered normal in size. No macroscopic abnormalities of the surrounding area were noted for any of the animals.

 

The radioactive disintegrations per minute (dpm) and stimulation index (SI) are given in the table below. The SI values calculated for the substance concentrations 25, 50 and 100% were 4.4, 7.0 and 7.2, respectively. The data showed a dose-response and an EC3 value (the estimated test substance concentration that will give a SI =3) of 25.7 % was calculated. In order to achieve more information regarding the SI=3 value, an additional group of animals was treated with a 10% test substance concentration together with a concurrent vehicle control group. Mean disintegrations per minute (dpm) for the additional group and control are presented below. The SI value calculated for the 10% concentration was 1.5.

 

Table 1. Results from the definitive test

Group	TS (%) #1	Number	Size nodes #2		DPM / animal #3	mean			mean
			left	right		DPM ± SEM #4			SI ± SEM
1	0	1	n	n	171	234	±	23	1.0	±	0.1
		2	n	n	255
		3	n	n	303
		4	n	n	241
		5	n	n	200
2	25	6	n	n	1749	1028	±	222	4.4	±	1.0
		7	n	n	1231
		8	n	n	579
		9	n	n	1030
		10	n	n	552
3	50	11	n	n	2182	1637	±	269	7.0	±	1.3
		12	n	n	1614
		13	n	n	2301
		14	n	n	1086
		15	n	n	1003
4	100	16	n	n	2396	1695	±	370	7.2	±	1.7
		17	n	n	2697
		18	n	n	723
		19	n	n	1209
		20	n	n	1451
Additional Groups
5	0	21	n	n	161	593	±	169	1.0	±	0.4
		22	n	n	344
		23	n	n	1030
		24	n	n	490
		25	n	n	940
6	10	26	n	n	1218	890	±	145	1.5	±	0.5
		27	n	n	729
		28	n	n	627
		29	n	n	1263
		30	n	n	614

#1. TS = test substance (% w/w).

#2. Relative size auricular lymph nodes (-, -- or ---: degree of reduction, +,++ or +++: degree of enlargement, n: considered to be normal).

#3. DPM = Disintegrations per minute

#4. SEM = Standard Error of the Mean

Applicant's summary and conclusion

Interpretation of results:

sensitising

Remarks:

Migrated information Criteria used for interpretation of results: EU

Conclusions:

Under the conditions of this study the test material is considered to be sensitising to skin with EC3 of 17.8%.

Executive summary:

The study was performed to OECD TG 429 under GLP to assess the skin sensitisation potential of the test material in the CBA/J strain mouse following topical application to the dorsal surface of the ear. In a preliminary screening test mice were treated by daily application of 25 μl of the test substance at 50% and 100% v/v in acetone/olive oil 4:1 to the dorsal surface of each ear for three consecutive days (Days 1, 2, 3). The mice was observed twice daily and local skin irritation was scored daily. Any clinical signs of toxicity, if present, were also recorded. The bodyweight was recorded on Day 1 (prior to dosing) and on Day 6. Ear thickness measurements were conducted using a digital thickness gauge on prior to dosing on Day 1, 1-hour post application of test item on Days 1, 2 and 3 and on Days 4, 5 and 6. A mean ear thickness increase of equal to or greater than 25% and/or well-defined irritation at the most (maximum grade 2) was considered to indicate excessive irritation and limited biological relevance to the endpoint of sensitisation. No irritation or signs of systemic toxicity were observed. Variations in ear thickness during the observation period were less than 25% from Day 1 pre-dose values. Based on the preliminary test, the concentrations selected for the main test were 0%, 25%, 50% and 100% v/v. In the main test, three groups of five female CBA/J mice were treated with test substance concentrations of 25, 50 or 100% w/w on three consecutive days, by open application on the ears. Five vehicle control animals were similarly treated, but with vehicle alone (Acetone/Olive oil (4:1 v/v)). Following the results an additional group of 10% and a parallel control group were completed to obtain more information. No irritation of the ears was observed in any of the animals examined. Variations in ear thickness during the observation period were less than 25% from Day 1 pre-dose values for the initially treated animals. No ear thickness measurements were conducted in the additional groups. No mortality occurred and no clinical signs of systemic toxicity were observed in the animals of the main study, except for the turbid left eye, observed for one vehicle control animal on Day 6. Body weights were within the range seen for historic control animals. The auricular lymph nodes in all dose levels were considered normal in size. No macroscopic abnormalities of the surrounding area were noted for any of the animals. Mean DPM/animal values for the experimental groups treated with test substance concentrations 25, 50 and 100% were 1028, 1637 and 1695 DPM, respectively. The mean DPM/animal value for the vehicle control group was 234 DPM. The SI values calculated for the substance concentrations 25, 50 and 100% were 4.4, 7.0 and 7.2, respectively. In order to achieve more information regarding the SI=3 value, an additional group of animals was treated with a 10% test substance concentration together with a concurrent vehicle control group. A mean DPM/animal value of 890 DPM was calculated for the 10% group. A mean DPM/animal value of 593 DPM was calculated for the vehicle control group. The SI value calculated for the 10% concentration was 1.5. The data showed a dose-response and an EC3 value of 17.8 % was calculated. Under the conditions of this study, the test substance would be considered to be classified as skin sensitizer (category 1B) under Regulation (EC) No 1272/2008.