2,2'-[azobis(1-methylethylidene)]bis[4,5-dihydro-1H-imidazole dihydrochloride

Skin sensitisation

Administrative data

Endpoint:

skin sensitisation: in vivo (LLNA)

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2014

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

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

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:

2,2'-[azobis(1-methylethylidene)]bis[4,5-dihydro-1H-imidazole dihydrochloride

EC Number:

248-655-3

EC Name:

2,2'-[azobis(1-methylethylidene)]bis[4,5-dihydro-1H-imidazole dihydrochloride

Cas Number:

27776-21-2

Molecular formula:

C12H22N6.2ClH

IUPAC Name:

2,2'-[azobis(1-methylethylidene)]bis[4,5-dihydro-1H-imidazole dihydrochloride

Test material form:

solid: flakes

In vivo test system

Test animals

Species:

mouse

Strain:

CBA/Ca

Sex:

female

Study design: in vivo (LLNA)

Vehicle:

other: Ethanol/water (3+7, v/v)

Concentration:

Low Dose: 5 %
Mid Dose: 10 %
High Dose: 25 %

No. of animals per dose:

5

Details on study design:

Each test group of mice was treated by (epidermal) topical application to the dorsal surface of each ear with test item concentrations of 5, 10, and 25 % in ethanol/water (3+7, v/v). The application volume, 25 μL/ear/day, was spread over the entire dorsal surface of each ear once daily for three consecutive days. A further group of mice (control animals) was treated with an equivalent volume of the relevant vehicle alone (control animals).

Positive control substance(s):

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

Results and discussion

In vivo (LLNA)

Results

Results 1

Parameter:

SI

Value:

1

Test group / Remarks:

Vehicle Control Group (ethanol/water (3+7, v/v))

Results 2

Parameter:

SI

Value:

0.99

Test group / Remarks:

5 % Azo Initiator VA044

Results 3

Parameter:

SI

Value:

0.96

Test group / Remarks:

10 % Azo Initiator VA044

Results 4

Parameter:

SI

Value:

0.96

Test group / Remarks:

25 % Azo Initiator VA044

Applicant's summary and conclusion

Interpretation of results:

GHS criteria not met

Conclusions:

The test item Azo Initiator VA044 was not a skin sensitiser under the test conditions of this study.

Executive summary:

In order to study a possible skin sensitising potential of Azo Initiator VA044, three groups each of five female mice were treated once daily with the test item at concentrations of 5, 10, and 25 % in ethanol/water (3+7, v/v) by topical application to the dorsum of each ear for three consecutive days. The test item could be either suspended (25 %) or dissolved (10 + 5 %) in the vehicle. The appropriateness of the used concentrations was previously assessed by a pre-experiment.

A control group of five mice was treated with the vehicle ethanol/water (3+7, v/v) only. Five days after the first topical application the mice were injected intravenously into a tail vein with radio-labelled thymidine (3H-methyl thymidine). Approximately five hours after intravenous injection, the mice were sacrificed, the draining auricular lymph nodes excised, pooled per animal and immediately weighed. Furthermore, after excision of the lymph nodes, both ears of the mice were punched at the apical area using a biopsy punch and were immediately weighed pooled per animal using an analytical balance. Afterwards single cell suspensions of lymph node cells were prepared from pooled lymph nodes per animal. An aliquot of each cell suspension was used for determination of lymph node cell count. Subsequently the suspensions were washed and incubated with trichloroacetic acid overnight. The proliferative capacity of pooled lymph node cells was determined by the incorporation of 3H-methyl thymidine measured in a β-scintillation counter.

The animals did neither show any signs of systemic toxicity nor local skin effects during the course of the study and no cases of mortality were observed. A statistically significant increase in ear weights was observed in the mid and the high dose group in comparison to the vehicle control group (p < 0.05) For BALB/c mice, a cut-off value of 1.1 for the ear weight index was reported for a positive response regarding ear skin irritation (see Ref. 9). None of the indices determined for the test item treated groups exceeded this threshold.

A test item is regarded as a sensitiser in the LLNA if exposure to one or more test item concentration results in a 3-fold or greater increase in incorporation of 3HTdR compared with concurrent controls, as indicated by the Stimulation Index (S.I.). The estimated test item concentration required to produce a S.I. of 3 is referred to as the EC3 value.

For BALB/c mice, a cut-off value of 1.1 for the ear weight index was reported for a positive response regarding ear skin irritation. None of the indices determined for the test item treated groups exceeded this threshold. A test item is regarded as a sensitiser in the LLNA if exposure to one or more test item concentration results in a 3-fold or greater increase in incorporation of 3HTdR compared with concurrent controls, as indicated by the Stimulation Index (S.I.). The estimated test item concentration required to produce a S.I. of 3 is referred to as the EC3 value.

In this study Stimulation Indices (S.I.) of 0.99, 0.96, and 0.96 were determined with the test item at concentrations of 5, 10, and 25% in ethanol/water (3+7, v/v), respectively. A dose response was not observed.

A statistically significant and biologically relevant increase in DPM values, lymph node weight or –cell count was not obtained in any group in comparison to the vehicle control group (p<0.05). Moreover, the cut-off value for a positive response regarding the lymph node cell count index reported for BALB/c mice was not exceeded in any of the test item groups. The EC3 value could not be calculated, since none of the tested concentrations induced a S.I. greater than the threshold value of 3.