4,4,19,19-tetraethoxy-3,20-dioxa-8,15-dithia-4,19-disiladocosaneand S-(6-{[3-(triethoxysilyl)propyl]thio}hexyl) ethanethioate

Skin irritation / corrosion

Administrative data

Endpoint:

skin irritation: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

February 2020 - October 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2020

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 431 (In Vitro Skin Corrosion: Reconstructed Human Epidermis (RHE) Test Method)

Version / remarks:

18 June 2019, corrected 26 June 2020

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test material

Test material information

Constituent 1

Reference substance name:

4,4,19,19-tetraethoxy-3,20-dioxa-8,15-dithia-4,19-disiladocosane and S-(6-{[3-(triethoxysilyl)propyl]thio}hexyl) ethanethioate

EC Number:

951-696-6

Molecular formula:

C17H36O4S2Si and C24H54O6S2Si2

IUPAC Name:

4,4,19,19-tetraethoxy-3,20-dioxa-8,15-dithia-4,19-disiladocosane and S-(6-{[3-(triethoxysilyl)propyl]thio}hexyl) ethanethioate

Test material form:

liquid

In vitro test system

Test system:

human skin model

Source species:

human

Cell type:

non-transformed keratinocytes

Cell source:

other: The EpiDerm tissues were provided as kits (e.g. EPI-200-SIT, MatTek)

Source strain:

other: not applicable

Details on animal used as source of test system:

not applicable

Justification for test system used:

This test uses the EpiDerm™ reconstructed human epidermis model (MatTek) which consists of normal human epidermal keratinocytes (NHEK) and therefore represents in vitro the target organ of the species of interest and closely mimics the biochemical and physiological properties of the upper parts of the human skin, i.e. the epidermis.

Vehicle:

unchanged (no vehicle)

Details on test system:

Upon receipt of the EpiDermTM, the tissues were inspected visually and transferred into 6-well plates containing 0.9 mL assay medium per well. The surface was dried using a sterile cotton tip and the plates were incubated in a humidified incubator at 37  1 °C, 5.0% CO2 for 60 ± 5 min. Subsequently the tissues were transferred into new wells containing 0.9 mL pre-warmed assay medium per well and were incubated for 18 ± 3 h in a humidified incubator at 37  1 °C, 5.0% CO2.
After this pre-incubation the tissues were treated with each dose group in triplicate, starting with the negative control. Start time was recorded with dosing of the first tissue and occurred sequentially for the other tissues, e.g. in one-minute intervals. After dosing of all tissues, all plates were incubated for 25 ± 1 min under the sterile flow and for the remaining time of 35 ± 1 min transferred to the incubator. Then the tissues were washed by filling and emptying the inserts 15 times with DPBS using a constant stream in about 1.5 cm distance from the tissue surface, this process also occurred sequentially, e.g. in one-minute intervals. Subsequently, the inserts were completely submerged three times in 150 mL DPBS and shaken to remove rests of the test item. Finally, the inserts were rinsed once from the inside and the outside with sterile DPBS. Excess DPBS was removed by blotting the bottom with blotting paper. The inserts were placed in prepared new 6-well plates containing 0.9 mL pre-warmed fresh assay medium per well and the tissue surface was dried using a sterile cotton tip. The plates were post-incubated at 37  1 °C, 5.0% CO2, humidified to 95%, for 24  2 h. Following this incubation the tissues were transferred to new wells containing 0.9 mL fresh assay medium and incubated for additional 18 ± 2 h.
After this post-incubation period the bottom of the inserts were blotted on sterile blotting paper and the inserts were transferred in a prepared 24-well plate containing 300 µL pre-warmed MTT medium. This plate was incubated for 3 h  5 min at 37  1 °C, 5.0% CO2, humidified to 95%.
After the MTT incubation period, the tissues were rinsed three times with DPBS and afterwards placed on blotting paper to dry. The tissues were transferred into 12-well plates and immersed in 2 mL isopropanol, sealed to inhibit evaporation. Extraction was carried out protected from light at room temperature for at least 2 h with gentle shaking on a plate shaker.
Before using the extracts, the plate had been shaken for at least 15 min on a plate shaker and the inserts were pierced with an injection needle. The extract was pipetted up and down 3 times before 2 x 200 µL aliquots per each tissue were transferred into a 96-well plate. OD was measured at 570 nm with a filter band pass of maximum ± 30 nm without reference wavelength in a plate spectrophotometer using isopropanol as a blank.

Control samples:

yes, concurrent negative control

yes, concurrent positive control

Amount/concentration applied:

Dose Groups
1. Negative control 30 µL DPBS
2. Positive control 30 µL 5% SDS solution
3. Test Item 30 µL (undiluted)
The test was performed on a total of 3 tissues per dose group

Duration of treatment / exposure:

60 min

Duration of post-treatment incubation (if applicable):

42 h post-incubation period and immediate determination of cytotoxic effects via MTT reduction assay.

Number of replicates:

3 tissues per dose group

Results and discussion

In vitro

Results

Irritation / corrosion parameter:

% tissue viability

Value:

97.2

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:

Irritant potential of the test item was predicted from the relative mean tissue viabilities obtained compared to the corresponding negative control tissues concurrently treated with DPBS.
The mixture of 30 µL test item per 1 mL MTT medium showed reduction of MTT compared to the solvent. The mixture turned blue/purple.
For quantitative correction of results, two killed tissues were treated with 30 µL of the test item (KT) and two killed tissues were left untreated as a control (KU), respectively. NSMTT was calculated relative to the negative control of living tissues (NC) according to the following formula:
NSMTT [%] = [(ODKT - ODKU)/ODNC] * 100 = 1.2
Mean ODKT = 0.063
Mean ODKU = 0.043
Mean ODNC = 1.679
NSMTT was ≤ 30% (1.2%) relative to the negative control of living epidermis, the true MTT metabolic conversion (TODTT) of the test item treated living tissues TM was therefore corrected according to the following formula:
TODTT = ODTM – (ODKT – ODKU) = 1.632
The mixture of 30 µL of the test item per 300 µl aqua dest. and per 300 µL isopropanol showed no colouring detectable by unaided eye-assessment. Therefore, NSC equaled 0%.
The test item showed no irritant effects. The mean relative tissue viability (% negative control) was > 50% (97.2%, NSMTT-corrected) after 60 min treatment and 42 h post-incubation.
The controls confirmed the validity of the study. The mean absolute OD570 of the three negative control tissues was  0.8 and ≤ 2.8 (1.724). The mean relative tissue viability (% negative control) of the positive control was < 20% (4.4%). Standard deviation of viability of replicate tissues of all dose groups was ≤ 18% (0.5% - 17.6%).

Any other information on results incl. tables

Table 1. Result of the Test Item Reaction mass of S-(6-((3-(triethoxysilyl)propyl)thio)hexyl)ethylthioester and Hexamethylene-1,6-dithio-bis((3-triethoxysilyl)propane)

Name	Negative Control					Positive Control					Test Item
Tissue	1	2		3		1		2		3	1	2	3
Absolute OD570	1.839	1.935		1.369		0.114		0.114		0.128	1.745	1.845	1.454
	1.847	1.949		1.406		0.112		0.122		0.130	1.781	1.882	1.476
Mean Absolute OD570	1.724****					0.120					1.697
OD570 (Blank Corrected)	1.794	1.889		1.323		0.068		0.068		0.082	1.700	1.799	1.408
	1.802	1.904		1.360		0.067		0.076		0.085	1.735	1.837	1.430
Mean OD570of the Duplicates (Blank Corrected)	1.798	1.896		1.342		0.067		0.072		0.084	1.717	1.818	1.419
Total Mean OD570of the 3 Replicate Tissues (Blank Corrected)	1.679*					0.074					1.652
TODTT	-					-					1.632
SD of Mean OD570of the 3 Replicate Tissues (Blank Corrected)	0.296					0.008					0.207
Relative Tissue Viabilities [%]	107.1		113.0		79.9	4.0	4.3		5.0		102.3	108.3	84.5
Mean Relative Tissue Viability [%]	100.0					4.4**					98.4
Mean Relative Tissue Viability [%] – NSMTT Corrected	-					-					97.2
SD of Relative Tissue Viability [%]^***	17.6					0.5					12.4
CV [% Viabilities]	17.6					11.1					12.6

 

^*     Blank-corrected mean OD₅₇₀of the negative control corresponds to 100% absolute tissue viability.

^**   Mean relative tissue viability of the three positive control tissues is < 20%.

^***  Standard deviation (SD) obtained from the three concurrently tested tissues is≤ 18%.

^**** The mean absolute OD₅₇₀of the negative control is≥ 0.8 and ≤ 2.8.

  Table 2. Result of the NSMTT control

Name	KU		KT		Negative Control
Tissue	1	2	1	2	1	2	3
Absolute OD570	0.090	0.088	0.121	0.096	1.839	1.935	1.369
	0.089	0.088	0.122	0.096	1.847	1.949	1.406
OD570 (Blank Corrected)	0.044	0.043	0.075	0.050	1.794	1.889	1.323
	0.044	0.043	0.076	0.050	1.802	1.904	1.360
Mean OD570of the Duplicates (Blank Corrected)	0.044	0.043	0.076	0.050	1.798	1.896	1.342
Total Mean OD570of the 2 or 3 Replicate Tissues (Blank Corrected)	0.043		0.063		1.679
SD of Mean OD570of the 2 or 3 Replicate Tissues (Blank Corrected)	0.001		0.018		0.296
NSMTT [%]	1.2				-
Relative Tissue Viability [%]	-				107.1	113.0	79.9
Mean Relative Tissue Viability [%]	-				100.0
SD of Relative Tissue Viability [%]	-				17.6
CV [% Viabilities]	-				17.6

Table3:  Quality Criteria

	Value	Cut off	pass/fail
Mean Absolute OD570 nmNC	1.724	0.8 ≤ NC ≤2.8	pass
Mean Relative Viability [%] PC	4.4	< 20%	pass
SD Viability[%]	0.5 – 17.6	≤ 18%	pass

Applicant's summary and conclusion

Interpretation of results:

GHS criteria not met

Conclusions:

In this study under the given conditions the test item showed no irritant effects. The relative mean tissue viability after 60 min of exposure and 42 h post-incubation was > 50%. The test item is therefore classified as “non-irritant” in accordance with UN GHS “No Category”.