Trimethoxy(methyl)silane

Skin sensitisation

Administrative data

Endpoint:

skin sensitisation: in vivo (LLNA)

Type of information:

experimental study

Adequacy of study:

key study

Study period:

05 Jan 2021 - 10 Feb 2021

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2021

Report date:

2021

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

2010

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of study:

mouse local lymph node assay (LLNA)

Test material

Test material information

Constituent 1

Reference substance name:

Trimethoxy(methyl)silane

EC Number:

214-685-0

EC Name:

Trimethoxy(methyl)silane

Cas Number:

1185-55-3

Molecular formula:

C4H12O3Si

IUPAC Name:

trimethoxy(methyl)silane

Test material form:

liquid

In vivo test system

Test animals

Species:

mouse

Strain:

CBA

Remarks:

CBA/J

Sex:

female

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: Janvier, Le Genest-Saint-Isle, France
- Females (if applicable) nulliparous and non-pregnant: yes
- Age at study initiation: approximately 11 weeks old
- Weight at study initiation: 20.6 to 25.0 g.
- Housing: up to 5 animals of the same sex and same dosing group together
- Diet (e.g. ad libitum): Pelleted rodent diet, ad libitum
- Water (e.g. ad libitum): Municipal tap-water, ad libitum
- Acclimation period: at least 5 days
- Indication of any skin lesions: Before the initiation of dosing, a health inspection was performed, and any assigned animal considered unsuitable for use in the study were replaced by alternate animals.

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22°C
- Humidity (%): 39 to 42%
- Air changes (per hr): Ten or greater air changes per hour with 100% fresh air
- Photoperiod (hrs dark / hrs light): 12 hour light/12 hour dark cycle

- IN-LIFE DATES: From: 20 Jan 2021 To: 08 Feb 2021

Study design: in vivo (LLNA)

Vehicle:

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

Concentration:

0, 10, 25 and 50 % w/w

No. of animals per dose:

5

Details on study design:

PRE-SCREEN TESTS:
- Compound solubility: two test concentrations were tested - 25% and 50%. The highest concentration was the maximum concentration that could technically be applied.
- Irritation: very slight irritation at 25% and 50% concentration
- Systemic toxicity: no effects indicative of systemic toxicity
- Ear thickness measurements: yes
- Erythema scores: very slight irritation observed

MAIN STUDY

ANIMAL ASSIGNMENT AND TREATMENT
- Name of test method: Skin Sensitization: Local Lymph Node Assay
- Criteria used to consider a positive response: Disintegrations Per Minute (DPM) values are presented for each animal and for each dose group. A Stimulation Index (SI) is calculated for each group using the individual SI values. The individual SI is the ratio of the DPM/animal compared to the DPM/vehicle control group mean. If the results indicate a SI ≥ 3, the test item may be regarded as a skin sensitiser. Consideration was given to the EC3 value (the estimated test item concentration that will give a SI =3).


TREATMENT PREPARATION AND ADMINISTRATION:
- Preparation of test item - Test item dosing formulations (w/w) were homogenized to visually acceptable levels at appropriate concentrations to meet dose level requirements. The dosing formulations were prepared daily and dosed within 4 hours after adding the vehicle to the test item. The dosing formulations were kept at room temperature until dosing. The dosing formulations were stirred until and during dosing.
- Induction - The dorsal surface of both ears was topically treated (25 μL/ear) with the test item on days 1, 2 and 3, at approximately the same time on each day. The control animals were treated in the same way as the experimental animals, except that the vehicle was administered instead of the test item.
- Excision of the Nodes - On day 6, 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 five hours, all animals were euthanised and 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 PBS.
- Tissue Processing for Radioactivity - On day 6, following excision of the nodes, a single cell suspension of lymph node cells (LNC) was prepared in PBS by gentle separation through stainless steel gauze (maze size: 200 µm, diameter: ± 1.5 cm). 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 then stored in the refrigerator until the next day.
- Radioactivity measurements - On day 7, precipitates were recovered by centrifugation, resuspended in 1 mL TCA and transferred to 10 mL scintillation fluid. Radioactivity measurements were performed using a Packard 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).

Positive control substance(s):

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

Results and discussion

Positive control results:

The six-month reliability check with Alpha-Hexylcinnamaldehyde indicates that the Local Lymph Node Assay as performed at Charles River Den Bosch is an appropriate model for testing for contact hypersensitivity. The SI values calculated for the item concentrations 5, 10 and 25% were 2.1, 3.6 and 9.0 respectively. An EC3 value of 8.0% was calculated using linear interpolation.

In vivo (LLNA)

Results

Results 1

Key result

Parameter:

SI

Value:

0.6

Test group / Remarks:

10 % w/w

Results 2

Key result

Parameter:

SI

Value:

0.6

Test group / Remarks:

25 % w/w

Results 3

Key result

Parameter:

SI

Value:

0.7

Test group / Remarks:

50 % w/w

Cellular proliferation data / Observations:

CELLULAR PROLIFERATION DATA : 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.

DETAILS ON STIMULATION INDEX CALCULATION : Mean DPM/animal values for the experimental groups treated with test item concentrations 10, 25 and 50% were 472, 460 and 531 DPM, respectively. The mean DPM/animal value for the vehicle control group was 734 DPM. The SI values calculated for the test item concentrations 10, 25 and 50% were 0.6, 0.6 and 0.7, respectively.

EC3 CALCULATION : The EC3 value (the estimated test item concentration that will give a SI =3) (if any) exceeds 50%.

CLINICAL OBSERVATIONS: No mortality occurred and no clinical signs of systemic toxicity were observed in the animals.

BODY WEIGHTS: Body weights and body weight gain of experimental animals remained in the same range as controls over the study period, except for one animal dosed at 10%, which showed slight body weight loss (-10%), as there were no corroborative findings for these animals, it was considered that the results for these animals were not affected.

Any other information on results incl. tables

See attachment for data tables.

Applicant's summary and conclusion

Interpretation of results:

GHS criteria not met

Conclusions:

In the skin sensitisation local lymph node assay, conducted according to OECD Test Guideline 429 and in compliance with GLP, the SI values calculated for trimethoxy(methyl)silane were lower than 3, indicating that the test material is not a skin sensitiser.