N-(2-ethylhexyl)-1-[[2-methyl-4-[(2-methylphenyl)azo]phenyl]azo]naphthalen-2-amine

Skin sensitisation

Administrative data

Endpoint:

skin sensitisation: in vivo (LLNA)

Type of information:

experimental study

Adequacy of study:

key study

Study period:

24.10.2012 - 6.11.2012

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2012

Report date:

2012

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

EU Method B.42 (Skin Sensitisation: Local Lymph Node Assay)

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

GLP compliance:

yes

Type of study:

mouse local lymph node assay (LLNA)

Test material

Test material information

Constituent 1

Reference substance name:

N-(2-ethylhexyl)-1-[[2-methyl-4-[(2-methylphenyl)azo]phenyl]azo]naphthalen-1-amine

EC Number:

260-124-8

EC Name:

N-(2-ethylhexyl)-1-[[2-methyl-4-[(2-methylphenyl)azo]phenyl]azo]naphthalen-1-amine

Cas Number:

56358-09-9

Molecular formula:

C32H37N5

IUPAC Name:

N-(2-ethylhexyl)-1-({2-methyl-4-[(2-methylphenyl)diazenyl]phenyl}diazenyl)-1,2-dihydronaphthalen-2-amine

Details on test material:

- Name of test material (as cited in study report): Solvent Red 19E
- Physical state: dark viscous liquid/borderline waxy solid
- Analytical purity: 90% (w/w)
- Impurities (identity and concentrations): Solvent Red24 (CAS 85-83-6) 2% (w/w)
- Lot/batch No.: S2409
- Expiration date of the lot/batch: unlisted
- Storage condition of test material: in tightly closed container in dark and well ventilated place at room temperature

In vivo test system

Test animals

Species:

mouse

Strain:

Balb/c

Sex:

female

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: breeding farm VELAZ s.r.o., Koleč u Kladna, Czech Republic
- Age at study initiation: 8 to 10 weeks
- Weight at study initiation: 16.50 – 19.66 g
- Housing: Maximum six in macrolon cages with sterilized softwood shavings
- Diet (e.g. ad libitum): Pelleted standard diet for experimental animals ad libitum
- Water (e.g. ad libitum): Drinking tap water ad libitum
- Acclimation period: At least 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20.4 – 21.6 °C
- Relative humidity (%): 30-70 %
- Air changes (per hr): Approximately 15 air changes per hour
- Photoperiod (hrs dark / hrs light): 12 hours light/dark cycle

STUDY TIME SCHEDULE
Animal arrival/ start of acclimatization: 16.10.2012
Pilot experiment: 24.10.12 - 29.10.2012
Main study:
First day of administration: 31.10.2012
End of treatment period: 02.11.2012
Application of radionuclide and necropsy: 05.11.2012

Study design: in vivo (LLNA)

Vehicle:

other: DAE 433 - mixture of 40 % dimethylacetamide, 30 % acetone and 30 % ethanol

Concentration:

Concentrations in formulation:
50 % (w/v) - 500 mg/mL
5 % (w/v) - 50 mg/mL
0.5 % (w/v) - 5 mg/mL

No. of animals per dose:

5 females

Details on study design:

PILOT EXPERIMENT
The pilot experiment was conducted under the conditions identical to the main study, except assessment of lymph node proliferation. The appropriate dilution of the test substance (50 %, 5 %, 0.5 % w/v) was applied to three animals in volume 25 µl to the dorsum of each ear once a day morning for 3 consecutive days. Both ears of each mouse was observed for erythema and scored and subsequently thickness was measured using digital thickness gauge

MAIN STUDY
ANIMAL ASSIGNMENT AND TREATMENT
Animals were subjected to a clinical examination (health check) shortly after arrival. No clinical changes were recorded.
Study animals were randomly allocated to the dose groups manually and assigned animal numbers.

TREATMENT PREPARATION AND ADMINISTRATION:
Dosage volume: 25 μL / ear / animal
Preparation for administration: The suspensions were prepared before the start of application by mixing on magnetic stirrer and then were still mixed during application.
Frequency of preparation: On each day immediately before administration.

IN VIVO EXAMINATION
- mortality
- clinical observation
- body weight

POST MORTEM INVESTIGATIONS
- ears weights
- incorporation of 3H-methyl thymidine

DATA ANALYSIS
Mean values and standard deviations of ears weight and incorporation of 3H-methyl thymidine were computed for the test item groups and for the positive as well as the vehicle control group. Stimulation index (for incorporation of 3H-methyl thymidine) was calculated by dividing mean values from the test substance groups and the positive control group by the corresponding mean value of the vehicle control group. The index for the vehicle control group was set at 1 by definition.

Positive control substance(s):

other: Dinitrochlorobenzene (DNCB)

Statistics:

For statistical calculations the software Statgraphic ® Centurion (version XV, USA) was used. Statistical evaluation of measured parameters was performed at first by applying the non-parametric Kruskal-Wallis test for the comparison of the measured effect in all treatment groups with the vehicle control group, as global test, and then the non-parametric two-group Mann-Whitney rank test (probability level 0.05) for all two-group comparisons.

Results and discussion

Positive control results:

The positive control substance DNCB produced positive LLNA response at an exposure level expected to give an increase in the Stimulation Index SI ≥ 3 over the negative control group, which was in congruence with the expected mode of action of a contact allergen. The positive control also elicited a reaction pattern with statistically significant increase in ear weight. These results demonstrate that the method performed in conditions of our laboratory has sufficient reliability.

In vivo (LLNA)

Results

Results 1

Key result

Parameter:

SI

Value:

8.35

Test group / Remarks:

50 %

Remarks on result:

other: see Remark

Remarks:

The test substance at the highest dose level caused a dose dependent increase in radioisotope incorporation into the DNA of dividing lymphocytes.

Results 2

Key result

Parameter:

SI

Value:

3.27

Test group / Remarks:

5 %

Remarks on result:

other:

Remarks:

The test substance at the highest dose level caused a dose dependent increase in radioisotope incorporation into the DNA of dividing lymphocytes

Results 3

Key result

Parameter:

SI

Value:

1.64

Test group / Remarks:

0.5 %

Remarks on result:

other:

Remarks:

0.5% is below the threshold

Results 4

Parameter:

other: DPM

Value:

943.17

Test group / Remarks:

50 %

Results 5

Parameter:

other: DPM

Value:

369.29

Test group / Remarks:

5 %

Results 6

Parameter:

other: DPM

Value:

184.83

Test group / Remarks:

0.5 %

Any other information on results incl. tables

Summary table

Group	Radioisotope incorporation		Ear weight
	Mean DPM	SI	Mean (mg)
NC	112.89	1.00	24.10
PC	890.38	7.89+	34.84*
50%	943.17	8.35+	46.34*
5%	369.29	3.27+	26.08*
0.5%	184.83	1.64	25.04

Figures with asterisk * = values statistically significant on probability level < 0.05 (Mann-Whitney test)

Figures with cross + = values ≥ 3 

DISCUSSION

The animals exposed to the test substance showed no clinical symptoms of intoxication throughout the experiment. The skin reaction could not be evaluated because the test substance caused marked colouration of skin.

 

The test substance Solvent Red 19E showed a tendency to increase ear weight with relation to the dose. Statistically significant increase of ear weight was recorded in animals at the highest and the middle dose level (50%, 5% test substance concentrations). The test substance showed a tendency to form residues. Residues of the test substance on the ears could cause this weight increase. With respect to the results of the study No. 188/12/4 – Histopathological examination it could not be excluded possibility of irritating effect.

Applicant's summary and conclusion

Interpretation of results:

sensitising

Conclusions:

The test material elicited a sensitising response in LLNA assay and therefore could be a contact allergen in mice.

Executive summary:

The test material was assessed for skin sensitisation potential according to the Method B.42 – Skin Sensitisation: Local Lymph Node Assay, Council Regulation (EC) No.640/2012, and OECD Test Guideline 429.

In this study the contact allergenic potential was evaluated after topical application to female BALB/c mice. Five mice per group were exposed on the dorsum of both ears once a day by test substance and control substances during 3 consecutive days. Primary proliferation of lymphocytes in the lymph node draining the site of application was evaluated using radioactive labelling of proliferating cells. The ratio of the proliferation in treated groups to that in vehicular controls, termed the Stimulation Index, was determined.

The evaluation of ear weight was performed for elimination of false positive findings with certain skin irritants.

Concentrations of test substance in vehicle (DAE 433): 50%, 5%, 0.5% (w/v) The animals exposed to the test substance at all concentrations showed no pathological and no other negative clinical symptoms of intoxication throughout the experiment. The test substance caused marked colouration of skin on dorsum of both ears of animals so the assessment of erythema and other skin reactions could not be evaluated.

There was no significant difference in body weight increment of all groups in comparison to the vehicle control.

The positive control substance DNCB (concentration 0.5 % (w/v) elicited a reaction pattern with statistically significant increase in Stimulation Index of cell proliferation and of ear weight, which was in congruence with his expected mode of action as a contact allergen.

The test substance showed a tendency to increased ear weight in the highest and the middle of concentrations tested. Residues of the test substance on the ears could cause this weight increase.

Comparison of Stimulation Indexes between all treated groups and control vehicle group revealed that the test substance caused a significant and dose dependent increase in radioisotope incorporation into the DNA of dividing lymphocytes. The Stimulation Index of the highest treated group (50% w/v) was 8.35 and of the middle treated group 3.27.