(4S)-1-methyl-4-(6-methylhepta-1,5-dien-2-yl)cyclohexene

Endpoint summary

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion

Additional information:

No key study for skin sensitization is available for beta-bisabolene.

In a skin sensitization study (LLNA according to OECD TG 429, GLP), a mixture was tested, that contained different isomers of Bisabolene as main components (i.e. alpha-, gamma-Bisabolene) with high structural similarity to beta-Bisabolene as well as beta-biabolene, which was also present at lower concentrations in the test substance applied (RCC 2002; 845134).

 

Four groups of 4 female CBA/CaOlaHsd mice were each treated with BISABOLENE at concentrations of 0.1%, 1%, 10 % (w/v) in ethanol: water. 7:3 (v/v) and 100 % (undiluted) by topical application to the dorsum of each ear lobe (left and right) on three consecutive days. A control group of 4 mice was treated with the vehicle (ethanol:water, 7:3 (v/v)) only. Five days after the first topical application the mice were injected intravenously into a tail vein with radiolabelled thymidine (3H-methyl thymidine). Approximately 5 hours after intravenous injection, the mice were sacrificed, the draining auricular lymph nodes excised and pooled per group. Single cell suspensions of lymph node cells were prepared from pooled lymph nodes which were washed subsequently 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 beta-scintillation counter.

All treated animals survived the scheduled study period and no test item-related clinical signs were observed in all animals with the exception of the 100 % (undiluted) group, showing moderate to slight swelling and slight general erythema at the dosing sites of both ears in all mice of the respective dose group.

Stimulation indices of 0.4, 0.8, 3.4 and 13.5 were determined with BISABOLENE at concentrations of 0.1%, 1%, 10% and 100%, respectively. Accordingly, BISABOLENE was found to be a non-sensitizer when tested up to 1 % (w/v) in ethanol:water, 7:3 (v/v) but showed an allergenic potency when tested at concentrations of 10 % (w/v) in ethanol: water, 7:3 (v/v) and 100 % (undiluted). The EC3 value derived was 8.6 %.

Overall, the mixture of different isomers of Bisabolene was found to be a skin sensitizer in the LLNA in mice under the chosen testing conditions.

 

Beta-Bisabolene was assessed in a QSAR model (i.e. the Skin sensitization GHS v.02.04 model)  using the OASIS TIMES v.2.31.2 platform. The target chemical beta-Bisabolene is not active as parent but gets activated as a result of autoxidation reactions and thus, it is predicted as skin sensitizer sub-category 1B (according to GHS classification). The active autoxidation products are interacting with skin proteins via the following mechanisms of action:

1. Radical reaction >> Free radical formation >> Hydroperoxides


2. Nucleophilic addition >> Addition to carbon-hetero double bonds >> Ketones

When considering the data available for Bisabolene isomers and the in silico (QSAR) data for beta-Bisabolene in a weight of evidence approach, beta-Bisabolene is considered to be a skin sensitizer. 

 

In a human maximization test with limited documentation, 10% Bisabolene (unknown isomer composition) in petrolatum was applied under occlusion to the same sites on the volar aspects of the forearms of 21 male volunteers for 5 alternate day 48 hours periods (RIFM 1974; 08/27B). Patch sites were pretreated for 24 hours with 5% aqueous SLS under occlusion for the initial patch only. Following a 10-14 day rest period, challenge patches with the test substance were applied under occlusion to fresh sites for 48 hours. Challenge applications were preceeded by 30 min applications of 2% aqueous SLS under occlusion on the left side of the back whereas the test item was applied without SLS treatment on the right side. Additional SLS controls were placed on the left and petrolatum on the right site. Very little evidence of irritation was produced after the SLS pretreated challenge patch application (1 subject with a +/- reaction only) and no skin reactions were observed after removal of the challenge patch (and 24h later) without SLS pretreatment in any of the volunteers tested. Thus, no evidence of contact sensitization was found for the test item.

In conclusion, 10% Bisabolene in petrolatum produced no reactions, that were considered allergic to the 21 subjects tested.

Respiratory sensitisation

Endpoint conclusion

Additional information:

No data available

Justification for classification or non-classification

The present data on dermal sensitization fulfill the criteria laid down in regulation (EU) 1272/2008, and therefore, a classification with "Skin sensitisation" (Category 1B) is warranted.