4,6-bis(octylthiomethyl)-o-cresol

Endpoint summary

Description of key information

In the key study, only 10% (2 out of 20 guinea pigs) of test animals were positive after challenge exposures with the test article. In the supporting study, only 5 % (1 out of 20 guinea pigs) of tested animals produced evidence of skin sensitisation (delayed contact hypersensitivity). Based on the CLP evaluation criteria, the evaluation "sensitizing" is warranted when at least 30 % of the test animals exhibit positive skin reactions in an adjuvant test. Therefore, in line with the above arguments, the test article is considered not sensitizing after skin contact.

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

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 in 1981)

Deviations:

no

GLP compliance:

yes

Type of study:

guinea pig maximisation test

Justification for non-LLNA method:

A valid guinea pig maximization study is available, an additional LLNA is not necessary

Species:

guinea pig

Strain:

Dunkin-Hartley

Sex:

male/female

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: Iffa Credo (Les Oncins - 69210 L'Arbresle - France), Bantin and Kingman (Aldbrough Hull - HU 11 1QE - Great Britain), David Hall (Burton on Trent - DE 13 8RJ - Great Britain), Shamrock Bloservcles (12, route de Saint Come - 7895C Garabals - France)
- Age at study initiation: no data
- Weight at study initiation: 330-500 g
- Housing: in groups of 5 (or of 2 for the preliminary studies) in polystyrene cages
- Diet: ad libitum; Guinea-pig complete pelleted maintenance food (Extra Labo formule "C.15.50" - Ets. Pletrement, Sainte Colorabe - 77650 Longueville, France).
- Water: ad libitum; softened and filtered drinking water (15 µl) (automatic watering system). Bacteriological and chemical controls were performed every six months
- Acclimation period: at least 5 days
- Rationale for choice: the guinea-pig is the most sensitive species for the evaluation of the allergenic potential. Historically, this species is often used a lot for this type of studies and is the species of choice of the various regulatory authorities.

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20 ± 3
- Humidity (%): 30 -70
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12/12

Route:

intradermal

Vehicle:

other: Vaseline Codex: lot 653 (Laboratoires Aguettant - 1 avenue Carteret, Lyon - France)

Concentration / amount:

100%

Adequacy of induction:

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

Route:

epicutaneous, occlusive

Vehicle:

other: Vaseline Codex: lot 653 (Laboratoires Aguettant - 1 avenue Carteret, Lyon - France)

Concentration / amount:

100%

Day(s)/duration:

48 hours

Adequacy of induction:

non-irritant substance, but skin pre-treated with 10% SDS

No.:

#1

Route:

epicutaneous, occlusive

Vehicle:

other: Vaseline Codex: lot 653 (Laboratoires Aguettant - 1 avenue Carteret, Lyon - France)

Concentration / amount:

100%

Day(s)/duration:

24 hours

Adequacy of challenge:

highest non-irritant concentration

No. of animals per dose:

Preliminary test: total of 12 animals (2 males + 2 females)/intradermal induction, topical induction and challenge
Test group : 10 males + 10 females. An additional 1 male and 1 female were treated as satellites to allow for possible non treatment-related mortality
Control group: 10 males and 10 females

Details on study design:

RANGE FINDING TESTS
Intradermal Injection
- Number of animals: 2 male + 2 females
- Concentrations: 10 and 50% in Vaseline codex or 100%
- Methodology: same as in main study

Epicutaneous induction exposure:
- Number of animals: 2 male + 2 females
- Concentrations: 50% in Vaseline codex and 100%
- Methodology: same as in main study
- Evaluation (hr after removal of patch): 1 hour

Challenge
- Site/area: Back/ 8 cm2
- Number of animals: 2 male + 2 females
- Concentrations: 50% in Vaseline codex and 100%
- Method: same as in main study
- Evaluation (hr after removal of patch): 24 and 48

MAIN STUDY
A. INDUCTION EXPOSURE
Intradermal Injection
- Site/Area: Back (scapular region)/2 x 4 cm
- No. of injections/animal: 6 injections in pairs each.
- Test substance group: Freund's complete adjuvant blended (1:1, v/v) in 0.9 % NaCl
- Test substance group: undiluted test article
- Test substance group: Freund's complete adjuvant blended (1:1, v/v) in 0.9 % NaCl + undiluted test article
- Control group : Freund's complete adjuvant blended (1:1, v/v) with 0.9 % NaCl
- Control group: Vehicle.
- Control group : Freund's complete adjuvant blended (1:1, v/v) with 0.9 % NaCl + vehicle
- Volume per injection: 0.1 ml/animal
- Evaluation (hr after injection): 24 and 48

Epicutaneous induction exposure:
- Time schedule: 8 days after intradermal induction
- Site: same as intradermal injections (site was pretreated 24 hours before with 0.5 ml per site of 10% w/w sodium lauryl sulphate in Vaseline codex paraffin)
- Area of application: 2 x 4 cm
- Concentrations: undiluted test article (test group), and vehicle (control group)
- Volume applied: 0.5ml/animal
- Type of coverage: occlusive (a 3 x 5 cm waterproof and hypoallergenic adhesive plaster (Blenderm: 3M, Laboratoire des Professions Hedlcales - 10, rue Gabriel Crle - 92210 Malakoff - France). Reinforcement was performed with 4 cm wide linen adhesive tapes applied on hydrophilic gauze
- Duration: 48 hours
- Evaluation (hr after challenge): directly after removal of patch

B. CHALLENGE EXPOSURE (identical treatment for treated and control animals)
- Time schedule: 11 days after end of topical induction
- Site: left flank (test article) and right flank (vehicle)
- Area of application: 2 x 2 cm
- Concentrations: undiluted
- Volume applied: 0.5 ml/animal
- Type of coverage: occlusive (hypoallergenic adhesive plaster (H-IFT - Urgo : Laboratoire de Pansements et d'Hygiene - 42, rue de Longvic - 21300 Chenove - France). Reinforcement was performed with 4 cm wide linen adhesive tapes applied on hydrophilic gauze
- Duration: 24 hours
- Evaluation (hr after challenge): 24 and 48 hours after termination of exposure. Histopathological examination of the skin was performed for all the animals which showed doubtful reactions after macroscopical examination at 24 and 48 hours.

Positive control substance(s):

yes

Remarks:

The sensitivity of the test was evaluated in the test laboratory with known sensitizers as well as known non sensitizers (Dihydrocoumarin, Paraphenylenediamine, Formalin, Penicillin G, Benzocaine, Propylene Glycol).

Reading:

1st reading

Hours after challenge:

24

Group:

negative control

Dose level:

undiluted

No. with + reactions:

0

Total no. in group:

19

Reading:

2nd reading

Hours after challenge:

48

Group:

negative control

Dose level:

undiluted

No. with + reactions:

0

Total no. in group:

19

Reading:

1st reading

Hours after challenge:

24

Group:

test chemical

Dose level:

undiluted

No. with + reactions:

2

Total no. in group:

20

Reading:

2nd reading

Hours after challenge:

48

Group:

test chemical

Dose level:

undiluted

No. with + reactions:

2

Total no. in group:

20

PRELIMINARY TEST

Intradermal induction:

At the 24 hour observation time point, the intradermal injection of the undiluted test article (erythema score = 2 (2/4 animals); erythema score = 1 (2/4 animals)) as well as 50% in vaseline (erythema score = 1 (3/4 animals); erythema score = 2 (1/4 animals) caused slight to moderate skin irritations in 4 guinea pigs. At the 48 hour observation point, the intradermal injection of the undiluted test article (erythema score = 2 (4/4 animals) as well as 50% in vaseline (erythema score = 1 (4/4 animals)) caused slight to moderate skin irritations in 4 guinea pigs. A slight skin irritation (erythema score = 1) was seen in only 1/4 guinea pigs at the 24 hour observation time with 10% of the test article in vaseline.

Topical induction:

Only one out of 4 treated animals had a slight erythema after treatment with the undiluted test article (erythema score = 1) or with 50% test article in vaseline (erythema score = 1).

Challenge

No skin irritation was recorded in all 4 animals. On the basis of these results, the undiluted test substance was applied in the main study.

MAIN STUDY

In the control animals, slight desquamation was seen in 4/19 surviving animals at the 48 hour examination following challenge exposures. One female guinea pig died. There was slight desquamation at the site application in the dead control animal. In the treatment group, slight desquamation was evident in 8/20 animals at the 48 hour examination. At the 24 hour examination, no desquamation was seen in any animals, however, 5/20 guinea pigs had an erythema score of 1. At the 48 hour examination, 5 additional guinea pigs had an erythema score of 1. Histopathological biopsies of the cutaneous tissues confirmed a positive skin irritation only in 2 of the10 questionable cases making a total of 2/20 animals (5%) positive for "delayed hypersensitivity". Two cases of mortality were recorded in the treatment group. These animals were replaced with the satellite animals which had undergone simultaneous identical treatment.

POSITIVE CONTROL

The sensitivity of this method was evaluated in the test laboratory using various substances known for their sensitizing potential (or their innocuity). The results obtained are presented in the following table:

Table 1: List of substances tested in the laboratory

Test substance	Results with Histology (% of sensitized animals)
Dihydrocoumarin	100
Paraphenylenediamine	55
Formalin	70
Penicillin G	70
Benzocaine	45
Propylene Glycol	0

Interpretation of results:

GHS criteria not met

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

In the key study, the potential of the test article to cause "delayed contact hypersensitivity" after dermal contact was appraised in a maximization test with Dunkin-Hartley Guinea Pigs pursuant to OECD TG 406 and GLP guidelines. Intradermal and topical induction (occlusive; 48 hours) as well as challenge exposures (epicutaneous occlusive; 24 hours) were performed with the undiluted test article. The control and test groups consisted of 20 animals each. Evaluation of the skin reactions were performed 24 and 48 hours after challenge according to the Draize method in conjunction with histological biopsies for the confirmation of questionable results. After challenge, only 2 out of 20 guinea pigs were positively identified to exhibit evidence of "delayed contact hypersensitivity". All animals of the control group did not show evidence of "delayed contact hypersentisation" (0/19; one animal died). The sensitivity of the assay was ascertained using positive controls which elicited the expected results e.g. Dihydrocoumarin.

In support of the findings of the key study are the results of a dermal sensitisation study performed according to OECD Guideline 406 and GLP standards, in which Pirbright guinea pigs were used. The control and test groups consisted of 20 animals each. Intradermal inductions were performed with 1% of the test article in Freund's complete adjuvant (FCA) mixed with physiological saline. Topical inductions were carried out under occlusive conditions for 48 hours with 30% of the test article in Vaseline. Challenge exposures were performed epicutaneously (occlusive; 24 hours) with 3% of the test article in Vaseline. Only 10 animals of the control group were challenged with the test article. Evaluation of the skin reactions was performed according to Draize 24 and 48 hours after challenge. Evaluations indicated very slight erythema in 7 animals at the 24 hour examination and in 6 animals at the 48 hour examination. In a re-challenge of the same animals performed 1 week after the standard challenge, only 1 animal had skin irritating reactions, indicating that most of the reactions observed after the first challenge application were nonspecific as it may happen in adjuvant treated animals. All animals of the control group were negative for being sensitised (0/10). The sensitivity of the assay was ascertained every six months with Paraphenylene-diamine or Potassium-dichromate.

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information:

No information is availabel on respiratory sensitization.

Justification for classification or non-classification

Classification, Labeling, and Packaging Regulation (EC) No. 1272/2008

The available experimental test data are reliable and suitable for the purpose of classification under Regulation 1272/2008. Based on the criteria laid down in Regulation (EC) No. 1272/2008 classification as a skin sensitizer is not warranted.