Methyl-tris acetonoximo-silane

Endpoint summary

Description of key information

No data are available to assess the skin sensitisation potential of the target substance Methyl-tris acetonoximo-silane. Thus, available data from the source substance WASOX-MMAC2 was used in a read-across approach. In a dermal sensitisation study conducted according to OECD 429 with "WASOX-MMAC2" suspended in AOO (4:1 v/v acetone/olive oil), young adult female CBA/CaOlaHsd mice (5 per dose group) were tested at concentrations of 25% (v/v), 50% (v/v) and 100% (undiluted) in a local lymph node assay (LLNA). There was no mortality nor clinical observations nor effects on body weights observed. None of the tested concentrations of the test substance reached the stimulation index (SI) threshold of 3. Therefore, no EC3 value could be determined. Application of the positive control substance hexyl cinnamic aldehyde (25%) resulted in a SI of 10.2. This result proves the sensitivity of the strain of animals used and the reliability of the experimental technique.

Based on the results from the source substance, the target substance can be considered as non-sensitising to the skin.

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Endpoint:

skin sensitisation: in vivo (LLNA)

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

The source compound WASOX-MMAC2 (A mixture of: propan-2-one-O,O'-(methoxymethylsilandiyl)dioxime; propan-2-one-O-(dimethoxymethylsilyl)oxime; propan-2-one-O,O',O''-(methylsilantriyl)trioxime; EC No. 460-110-3) is considered a suitable read across partner for the target substance MAC (CAS 2594-75-4). This read-across is based on the hypothesis that source and target substances have similar toxicological properties because:

- structural similarity of the target and the source substances (the presence or absence of additional functional groups or substituents that could influence the behaviour of a chemical),

- similarity in physico-chemical profile of the source and target substances (rapid decomposition in water under cleavage of the same substance (acetone oxime)).

Both substances are similar in terms of the substitution pattern at the silicon atom (i.e. acetoneoximo and methyl group(s)). Both substances exhibit consequently similar physico-chemical properties (rapid decomposition in water, decomposition upon heating to determine boiling point).

Reason / purpose for cross-reference:

read-across source

Vehicle:

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

Concentration:

25, 50 and 100%

No. of animals per dose:

5

Details on study design:

MAIN STUDY
The test substance was administered in 3 concentrations to the dorsal surfaces of the ears of the animals of the test substance groups. In a manner identical to that of animals in the treatment groups animals of one negative control group and one positive control group were treated with AOO and HCA respectively. Each animal was treated for 3 consecutive days. 3 days after the last administration the proliferation of the Iymphocytes of the draining Iymph nodes was measured by the determination of the amounts of incorporated 3HTdR.

Administration of the test substance:
Route of Administration: epicutaneous administration to the dorsal surface of each ear
Administration volume: 25 µL

Incorporation of 3H-methyl thymidine in vivo:
5 days after the first topical administration, each animal received 20 µCi 3HTdR by slow intravenous administration. The injection solution containing nominal 80 µCi/mL 3HTdR was prepared by the dilution of 1.152 mL 3HTdR (amersham pharmacia biotech, Kat. Nr.:TRA 310, batch 315, specific activity 2.0 Ci/mmol, radioactive concentration 1 mCi/mL, radiochemical purity 98.6%, thymine content 0.2%) with 13.248 mL PBS. Several minutes prior to 3HTdR administration the animals were kept restrained in Plexiglas-tubes and the tail veins were visualised by placing the tails in warm water. Then 250 µL of the injection solution were intravenously administered to each animal.

Preparation of single cell suspensions and determination of incorporated 3H-methyl thymidine:
Approximately 5 hours after 3HTdR injection all animals were sacrificed by carbon dioxide asphyxiation and the draining auricular lymph nodes were rapidly excised. The Iymph nodes of each group were pooled in PBS. A single cell suspension (SCS) of Iymphnode cells (LNC) nwas prepared by gentle mechanical disaggregation of the pooled Iymph nodes through a 70 µm cell strainer. The SCSs were then transferred into centrifuge tubes and LNC were pelleted by centrifugation (4 °C, max. 200 g, 10 min). Afterwards supernatants were removed by aspiration. Then the LNC were resuspended and washed twice with PBS. After the final washing the supernatants were removed leaving just a small volume < 0.5 mL) and
macromolecules were precipitated by incubation with 5 % trichloroacetic acid (TCA) at 4 °C overnight. Each precipitate was pelleted by centrifugation (4 °C, max. 200 g, 10min) and resuspended in 1 mL TCA. This suspension was transferred into scintillation vials containing 10 mL scintillation cocktail (Packard Bioscience: Ultima Gold, Bestellnr. 6013329) and 3HTdR incorporation was determined with a ß-scintillation counter.

INVESTIGATIONS
General observations: All animals were observed at least once daily for behavioural changes or signs of toxicity
Body masses: The body mass of each animal was recorded on Days 1 and 6
Skin reactions: The application sites were visually checked for local irritations once a day from Days 1-6.

Positive control substance(s):

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

Statistics:

Calculation of the stimulation indices (Sls):
Results are presented as test/control ratio (Stimulation index), calculated as dpm test group/dpm negative control group.
(dpm = disintegrations per minute, corrected by the subtraction of the background)

Positive control results:

Application of 25% HCA in AOO resulted in an SI of 10.2. This result proves the sensitivity of the strain of animals used and the reliability of the experimental technique.

Key result

Parameter:

SI

Value:

1

Test group / Remarks:

25%

Remarks on result:

other: no indication of sensitisation

Key result

Parameter:

SI

Value:

0.8

Test group / Remarks:

50%

Remarks on result:

other: no indication of sensitisation

Key result

Parameter:

SI

Value:

0.7

Test group / Remarks:

100%

Remarks on result:

other: no indication of sensitisation

Cellular proliferation data / Observations:

DETAILS ON STIMULATION INDEX CALCULATION : The SIs of the test substance groups were between 0.7 and 1. For detailed results please refer to table 1 in box "Any other information on results incl. tables".

SKIN REACTIONS: No local skin irritations were observed at the application sites of all animals of all test substance groups and both control groups throughout the whole study.

MORTALITY: No mortality occurred

GENERAL OBSERVATIONS: One animal of the high dose group had reduced motoric activities on Day 6. In all other animals no abnormal behaviour or clinical signs were detected during the experiment.

BODY MASS: Body masses and body mass gains of all animals were in the range to be expected from animals of the same strain, sex and age.

Table 1: DPM results and calculated SIs

Test group	DPM	SI
Negative control	4197	1
Low dose	4217	1.0
Mid dose	3536	0.8
High dose	2919	0.7
Positive control	42767	10.2

Rationale for selection of the concentrations:

In a range finding study the test substance as it is (100%) was administered to two animals. In this study the animals were treated in the same manner as in a main study with 25 µL test substance on the dorsum of each ear on three consecutive days. None of the animals showed overt systemic toxicity, excessive local skin irritation or an increase in ear thickness in the range finding study. Therefore, 100% was chosen as highest test substance concentration and ear thickness measurement was not performed in the main study.

Interpretation of results:

GHS criteria not met

Conclusions:

The test substance "WASOX-MMAC2" is not sensitizing under the conditions of this LLNA study (OECD 429).

Executive summary:

In a dermal sensitization study conducted according to OECD 429 with "WASOX-MMAC2" suspended in AOO (4:1 v/v acetone/olive oil), young adult female CBA/CaOlaHsd mice (5 per dose group) were tested at concentrations of 25% (v/v), 50% (v/v) and 100% (undiluted) in a local lymph node assay (LLNA). There was no mortality nor clinical observations nor effects on body weights observed. None of the tested concentrations of the test substance reached the stimulation index (SI) threshold of 3. Therefore, no EC3 value could be determined. Application of the positive control substance hexyl cinnamic aldehyde (25%) resulted in a SI of 10.2. This result proves the sensitivity of the strain of animals used and the reliability of the experimental technique. In this study, the test substance is not a dermal sensitizer.

This information is used in a read-across approach in the assessment of the target substance.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

No data are available to assess the skin sensitisation potential of the target substance Methyl-tris acetonoximo-silane. Thus, available data from the source substance WASOX-MMAC2 was used in a read-across approach. In a dermal sensitisation study conducted according to OECD 429 with "WASOX-MMAC2" suspended in AOO (4:1 v/v acetone/olive oil), young adult female CBA/CaOlaHsd mice (5 per dose group) were tested at concentrations of 25% (v/v), 50% (v/v) and 100% (undiluted) in a local lymph node assay (LLNA). There was no mortality nor clinical observations nor effects on body weights observed. None of the tested concentrations of the test substance reached the stimulation index (SI) threshold of 3. Therefore, no EC3 value could be determined. Application of the positive control substance hexyl cinnamic aldehyde (25%) resulted in a SI of 10.2. This result proves the sensitivity of the strain of animals used and the reliability of the experimental technique.

Based on the results from the source substance, the target substance can be considered as non-sensitising to the skin.

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

In a dermal sensitisation study according to OECD 429, female mice were tested negative for the source substance WASOX-MMAC2. Based on the results from the read-across partner, no classification of the target substance Methyl-tris acetonoximo-silane is warranted.