3-[[2-(acetyloxy)ethyl][4-[(4-nitrophenyl)azo]phenyl]amino]propiononitrile

Endpoint summary

Description of key information

Not skin sensitising.

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

As no data on target substance was available, skin sensitising potential was assessed using a read across approach. Similar Substance 01 was used as read across substance and further details were reported in section 13.

Available data on Similar Substance 01 was used in a weight of evidence approach.

Similar Substance 01 was tested according to OECD guideline 429 (local lymph node assay). Male mice were exposed to test substance at concentrations of 0, 3, 10 and 30 % in acetone. Negative and positive controls were valid. The isotope (3H-methyl thymidine) incorporation in lymph nodes was increased by less than a threefold at all concentrations of test substance. Therefore, test substance was considered to be not sensitising to mouse skin.

In addition, a study on Similar Substance 01 was available in literature. Modified protocols of the Local Lymph Node Assay i.e. sensitisation and sensitisation-challenge protocols were applied. Female NMRI mice were exposed to test substance at concentrations of 10 and 30 % in DMSO, using DMSO alone as negative control. In the sensitisation protocol, 25 µl of test substance solution were applied for 3 consecutive days. 48 h after the last exposure, mice were euthanised, ear thickness was measured, draining auricular lymph nodes were excised and weighed, and cell suspensions were prepared to count the number of cells.

In the sensitisation-challenge protocol, 50 µl test solution were applied once daily on days 1 - 3; mice remained untreated on days 4 - 14 and were then challenged with 25 µl of test solution on days 15 - 17. 48 h after the last exposure, mice were euthanised, ear thickness was measured, draining auricular lymph nodes were excised and weighed, and cell suspensions were prepared to count the number of cells.

Lymphocyte subpopulations (T-cells and B-cells, CD69 and 1A epitopes) were also analysed by flow cytometry. Compared to controls, test substance did not induce any changes regarding lymph node weight and cellularity, ear thickness, or lymphocytes subpopulations.

In both protocols, test substance was considered not sensitizing to mouse skin.

A study on Similar Substance 01 according to OECD guideline 406 was conducted on female guinea-pigs.

A pre-test was run to identify a maximally tolerated concentration suitable for the induction phase of the main study and a suitable non-irritant concentration, by topical route of administration, for the challenge phase.

In the main study, intradermal induction was carried out with a 5 % dilution of test substance in bi-distilled water and in an emulsion with Freund's Complete Adjuvant (FCA) / physiological saline; epidermal induction was conducted under occlusion (clipped, shaved skin) with test substance at 50 % in bi-distilled water. Approximately 22 h prior to the epidermal induction, test sites were pretreated with a 10 % SLS solution in paraffinum perliquidum. Two weeks after the epidermal induction application, challenge was completed by epidermal application of test substance at 50 % in bi-distilled water under occlusive dressing (clipped, shaved skin). Animals of control group were induced with bi-distilled water and FCA/physiological saline, pretreated with 10 % SLS and challenged similarly to those of test group. Cutaneous reactions, i.e. erythema, eschar and oedema formation were evaluated at 24 and 48 h after removal of the dressing. Mortality, symptoms of systemic toxicity, and body weights were also investigated.

A normal development of the expected local symptoms was observed in the animals of the control and test group during the intradermal induction phase. After challenge, no reactions were seen in control groups. Positive reactions were seen in all animals at the 24 and 48 h readings when treated with test substance at 50 % in bi-distilled water.

Due to conflicting evidences with different test types and samples, the following issues were taken into account in drawing a conclusion on the skin sensitising potential:

- in LLNAs, either a test sample with high purity (92 %) or a commercial sample with low purity (30 -35 %) gave no sensitising effects

- test sample used for in GPMT has a purity of 42.3 % only with unknown composition

- the use of SLS causes often false positive results in the GPMT

- in GPMT, treated areas were depilated with Veet Cream to remove the red staining of test substance which prevented erythema evaluation, but such cream may cause sensitising effects

On these bases, the GPMT result was considered as not representative of a toxic potential of the substance and it was excluded from the assessment.

Accordingly, the substance was taken as not skin sensitising.

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Category 1

Substances shall be classified as skin sensitizers in category 1 where data are not sufficient for sub-categorisation in accordance with the following criteria:

(a) if there is evidence in humans that the substance can lead to sensitisation by skin contact in a substantial number of persons; or

(b) if there are positive results from an appropriate animal test.

As for LLNA, a stimulation index ≥ 3 is considered as a positive response.

Subcategorisation is done as follows:

Sub-category 1A

Substances showing a high frequency of occurrence in humans and/or a high potency in animals can be presumed to have the potential to produce significant sensitisation in humans. Severity of reaction may also be considered.

Specific criteria: EC3 value ≤ 2 %

Sub-category 1B

Substances showing a low to moderate frequency of occurrence in humans and/or a low to moderate potency in animals can be presumed to have the potential to produce sensitisation in humans. Severity of reaction may also be considered.

Specific criteria: EC3 value > 2 %

Based on data derived from LLNAs, none concentration produced a stimulation index of 3, thus no EC3 value could be derived and no classification applied according to the CLP Regulation (EC 1272/2008).