Amino functional alkoxysilanes

Endpoint summary

Description of key information

In the key in vivo skin sensitisation study, conducted according to OECD Test Guideline 406 (Buehler test) and in compliance with GLP, trimethoxy(methyl)silane and its reaction products with [3-(2,3-epoxypropoxy)propyl]trimethoxysilane and 3-(trimethoxysilyl)propylamine (EC 945 -567 -3) was concluded to be not sensitising to skin (Eurofins Munich / BSL Munich, 2020).

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Endpoint:

skin sensitisation: in vivo (non-LLNA)

Type of information:

experimental study

Adequacy of study:

key study

Study period:

20th of November 2019 to 20th of February 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 406 (Skin Sensitisation)

Version / remarks:

Adopted the 17th of July 2003

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of study:

Buehler test

Justification for non-LLNA method:

An LLNA study was not performed because the test method is not considered to be suitable for substances that contain silicon.
Buehler test was selected based on that in vitro methods for assessing sensitisation potential are available but cannot yet fully substitute the animal tests. The sensitivity and reliability of the experimental technique is assessed on a regular basis using mercaptobenzothiazole, which is recommended by the OECD 406 and is known to have moderate skin sensitisation properties.

Species:

guinea pig

Strain:

other: Crl:HA

Sex:

male

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: Charles River, 97633 Sulzfeld, Germany
- Females nulliparous and non-pregnant: N/a
- Microbiological status of animals, when known: Not specified
- Age at study initiation: Approximately 5-6 weeks
- Weight at study initiation: 343 - 387 grams
- Housing: Semi barrier in an air-conditioned room.
- Diet: Autoclaved hay and Altromin 3122 maintenance diet for guinea pigs, rich in crude fibre, ad libitum .
- Water: Tap water, ad libitum.
- Acclimation period: At least 5 days
- Indication of any skin lesions: None reported

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 3 °C
- Humidity (%): 55 ± 10%
- Air changes (per hr): At least 10 x / hour
- Photoperiod (hrs dark / hrs light): 12 hours light / 12 hours dark
- IN-LIFE DATES: From: not reported To: 20th of February 2020

Route:

epicutaneous, occlusive

Vehicle:

other: acetone, extra dry

Concentration / amount:

100%

Day(s)/duration:

Occlusive dressing kept in contact with the skin for 6 hours; induction was repeated once a week for three consecutive weeks.

Adequacy of induction:

highest concentration used causing mild-to-moderate skin irritation and well-tolerated systemically

No.:

#1

Route:

epicutaneous, occlusive

Vehicle:

other: acetone

Concentration / amount:

100%

Day(s)/duration:

Occlusive dressing kept in contact with the skin for 6 hours.

Adequacy of challenge:

highest non-irritant concentration

No. of animals per dose:

20

Details on study design:

RANGE FINDING TESTS: 5 animals were used. The adequate concentrations for the induction and challenge was determined by a preliminary test with different concentrations. The test item was applied topically at 5 different concentrations (25%; 50%; 75%; 90% or 100%, each diluted with the vehicle acetone) to the flanks of the animals for 6 hours using occlusive dressings. Based on the gained result of this preliminary test, a concentration of 100% for the dermal induction and 100% for the challenge application respectively was used.

MAIN STUDY
A. INDUCTION EXPOSURE
- No. of exposures: 3 exposures
- Exposure period: 3 weeks
- Test groups: Test groups treated with 100% of the test substance.
- Control group: The negative control was a dry gauze patch (since the test item was applied undiluted)
- Site: Flanks
- Frequency of applications: Once a week
- Duration: 6 hours
- Concentrations: 100% test substance

B. CHALLENGE EXPOSURE
- No. of exposures: One
- Day(s) of challenge: 14 days after the last induction
- Exposure period: 6 hours
- Test groups: The right flanks of 20 animals were treated with 0.5 mL of 100% test item in acetone.
- Control group: The left flanks of 10 animals were treated with 0.5 mL of acetone only.
- Site: Both flanks
- Concentrations: 100% test item in acetone.
- Evaluation (hr after challenge): At 24 and 48 hours.

Challenge controls:

A dry patch was applied to an area of approximately 2.5 x 2.5 cm on the left flank at an untreated site (intraspecific control) and was held in contact with the help of an occlusive dressing for 6 hours for the negative control.

Positive control substance(s):

yes

Remarks:

2-mercaptobenzothiazole

Positive control results:

The sensitisation rate after application of the positive control substance 2-mercaptobenzothiazole (25% in vaseline) was 90%, confirming the reliability of the test system.

Key result

Reading:

1st reading

Hours after challenge:

24

Group:

test chemical

Dose level:

100% in acetone

No. with + reactions:

0

Total no. in group:

20

Remarks on result:

no indication of skin sensitisation

Key result

Reading:

2nd reading

Hours after challenge:

48

Group:

test chemical

Dose level:

100% in acetone

No. with + reactions:

0

Total no. in group:

20

Remarks on result:

no indication of skin sensitisation

Key result

Reading:

1st reading

Hours after challenge:

24

Group:

negative control

Dose level:

0%

No. with + reactions:

0

Total no. in group:

10

Remarks on result:

no indication of skin sensitisation

Key result

Reading:

2nd reading

Hours after challenge:

48

Group:

negative control

Dose level:

0%

No. with + reactions:

0

Total no. in group:

10

Remarks on result:

no indication of skin sensitisation

Reading:

1st reading

Hours after challenge:

24

Group:

positive control

Dose level:

2-mercaptobenzothiazole

No. with + reactions:

18

Total no. in group:

20

Clinical observations:

90% of positive control animals showed skin sensitisation

Remarks on result:

positive indication of skin sensitisation

Reading:

2nd reading

Hours after challenge:

48

Group:

positive control

Dose level:

2-mercaptobenzothiazole

No. with + reactions:

16

Total no. in group:

20

Clinical observations:

80% of positive control animals showed skin sensitisation

Remarks on result:

positive indication of skin sensitisation

Table 1: Frequency of Sensitisation in Positive-Control Animals

20 animals used for positive-control group

Group / Time of Observation	E0	E1	E2	E3	O0	O1	O2	O3	Sensitised Animals (%)
C/24	10	0	0	0	10	0	0	0	0
C/48	10	0	0	0	10	0	0	0	0
T/24	2	18	0	0	20	0	0	0	90
T/48	4	12	4	0	20	0	0	0	80

E0–E3 = erythema grade 0–3; O0–O3 = oedema grade 0–3; 0–20 = number of animals T = test group (2-mercaptobenzothiazole: 25% in vaseline); C = control group; 24/ 48 = 24/48 hours after end of challenge treatment

Table 2: Individual Grading of Reactions after Challenge

	Negative-Control Group
Animal No.	Conc. %	24 hoursafter patch removal				48 hoursafter patch removal
		Test Item		Control		Test Item		Control
		E	O	E	O	E	O	E	O
21	0	0	0	0	0	0	0	0	0
22		0	0	0	0	0	0	0	0
23		0	0	0	0	0	0	0	0
24		0	0	0	0	0	0	0	0
25		0	0	0	0	0	0	0	0
26		0	0	0	0	0	0	0	0
27		0	0	0	0	0	0	0	0
28		0	0	0	0	0	0	0	0
29		0	0	0	0	0	0	0	0
30		0	0	0	0	0	0	0	0
	Test Group
Animal No.	Conc. %	24 hoursafter patch removal				48 hoursafter patch removal
		Test Item		Control		Test Item		Control
		E	O	E	O	E	O	E	O
1	100	0	0	0	0	0	0	0	0
2		0	0	0	0	0	0	0	0
3		0	0	0	0	0	0	0	0
4		0	0	0	0	0	0	0	0
5		0	0	0	0	0	0	0	0
6		0	0	0	0	0	0	0	0
7		0	0	0	0	0	0	0	0
8		0	0	0	0	0	0	0	0
9		0	0	0	0	0	0	0	0
10		0	0	0	0	0	0	0	0
11		0	0	0	0	0	0	0	0
12		0	0	0	0	0	0	0	0
13		0	0	0	0	0	0	0	0
14		0	0	0	0	0	0	0	0
15		0	0	0	0	0	0	0	0
16		0	0	0	0	0	0	0	0
17		0	0	0	0	0	0	0	0
18		0	0	0	0	0	0	0	0
19		0	0	0	0	0	0	0	0
20		0	0	0	0	0	0	0	0

E = erythema; O = oedema; 0 – 3 = grade

 

Interpretation of results:

GHS criteria not met

Conclusions:

In the in vivo skin sensitisation study, conducted according to OECD Test Guideline 406 and in compliance with GLP, the test material was concluded to not be sensitising to skin. Positive and negative controls were included and gave the expected results.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

The key in vivo skin sensitisation study with trimethoxy(methyl)silane and its reaction products with [3-(2,3-epoxypropoxy)propyl]trimethoxysilane and 3-(trimethoxysilyl)propylamine was conducted according to OECD Test Guideline 406 and in compliance with GLP.

At induction, three epicutaneous occlusive applications of 100% of the test material were applied to the flanks of 20 test guinea pigs for six hours. This was in total repeated three times for three consecutive weeks. Following each application, each guinea pig was examined for dermal reactions. At challenge (14 days after the last topical induction application), 0.5 mL of 100% of the test material in acetone was applied topically to the right flank of each test animal and kept in contact with the skin for six hours under occlusive dressing. Dermal reactions were evaluated at 24 and 48 hours after removal of the test material. Changes in body weight were recorded prior to administration and at the end of the observation period. All animals were observed for signs of toxicity at least once daily during the test period. Positive and negative controls were included and provided expected results. No evidence of sensitisation occurred; the percentage of affected animals was 0%. Moreover, no systemic toxicity was observed throughout the study and no mortality occurred in any animals. The body weight development of all animals was within the range of variation for this strain. Consequently, it was concluded that the test substance is not sensitising to skin (Eurofins Munich / BSL Munich, 2020).

The current accepted and preferred method for skin sensitisation testing when in vitro testing is not possible according to the REACH legislation (EC no 1907/2006) and CLP Regulation (EC No 1272/2008) is the murine local lymph node assay (LLNA). There is also a question regarding the reliability of the LLNA for silicon-based substances, which means that conducting such a study would not add weight to the database for a positive or negative outcome and therefore, will not make any contribution to the protection of human health. OECD Test Guideline 429 acknowledges the limits of the LLNA, and states that there are instances where ‘test substance classes or substances containing functional groups shown to act as potential confounders’ make the use of guinea pig tests more appropriate. It is concluded that the LLNA is not applicable where the properties of the test material cause interference in the accuracy of the LLNA (OECD 2002). The statement in the OECD TG 429 is given with reference to the findings of Basketteret al. (2009a), who demonstrated false positives in silicone based substances which had previously been demonstrated to be non-sensitisers in the guinea pig maximisation test (GPMT). The importance of available evidence from guinea pig results, consideration of chemical reactivity, epidermal bioavailability and clinical and experimental human data are emphasised as central to reaching appropriate regulatory decisions for substances which have been shown to fall outside the specificity of the LLNA (Basketteret al., 2009b). The non-applicability of the LLNA for silicone based substances has also been demonstrated by Petryet al.(2012). The sensitisation potential of polyfunctional silicone materials was tested in a comparative study investigating the GPMT and the LLNA assays, which found the five tested substances to be negative in the GPMT whereas they were concluded to be weak to moderate skin sensitisers in the LLNA (Petryet al.,2012).

Basketter D, Ball N, Cagen S, Carillo JC, Certa H, Eigler D, Garcia C, Esch H, Graham C, Haux C, Kreiling R, Mehling A (2009a). Application of weight of evidence approach to assessing discordant sensitisation datasets: implication for REACH. Reg. Toxicol. Pharmacol.,55, 90-96.

 

Basketter D, McFadden JF, Gerberick F, Cockshott A, Kimber I (2009b) Nothing is perfect, not even the local lymph node assay: a commentary and the implications for REACH.Contact Dermatitis, 60, 65-69.

 

Petry, T., Bosch, A., Coste, X., Dupuis, V., Eigler, D., Germain, P. (2012). An assessment of the skin sensitisation hazard of a group of polyfunctional silicones using a weight of evidence approach. Regulatory Toxicology and Pharmacology, 64, 305 -314.

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Based on the available skin sensitisation data, no classification for skin sensitisation is required for trimethoxy(methyl)silane and its reaction products with [3-(2,3-epoxypropoxy)propyl]trimethoxysilane and 3-(trimethoxysilyl)propylamine according to Regulation (EC) No 1272/2008.