1-cyclohexylethyl butyrate

Endpoint summary

Description of key information

Skin sensitisation Veilex 1 (based on read across): Negative

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

Study period:

Study initiated: end fo March 1981 and reporting 30th April

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 406 (Skin Sensitisation)

GLP compliance:

no

Type of study:

guinea pig maximisation test

Justification for non-LLNA method:

Currently no LLNA study is available for assessment. The Guinea Pig Maximization Test (GPMT) has been carried out as an animal test to predict human sensitization for over a decade and is recommended by international test guidelines such as OECD.

Species:

guinea pig

Strain:

Dunkin-Hartley

Sex:

male

Details on test animals and environmental conditions:

Animals were housed in suspended cages with wire mesh floors, with free access to tap water and Vitamin C-enriched Guiney-pig Diet Standard F.D.I. No 803189W. Hay was given once a week.
Animal room temperature was 21oC and the air exchange was maintained at 15 air changes/hour
Lighting was controlled using a 12 hour light/dark cycle.

Route:

intradermal and epicutaneous

Vehicle:

paraffin oil

Concentration / amount:

Intradermal injection were in 1% v/v liquid paraffin

Route:

epicutaneous, occlusive

Vehicle:

paraffin oil

Concentration / amount:

Intradermal injection were in 1% v/v liquid paraffin

No. of animals per dose:

15 test animals and 15 control animals

Details on study design:

A 4x6 cm area of dorsal skin on the scapular region of the guiney-pig was clipped free of hair with electric clippers. Three pairs of intradermal injections were made simulataneously into this area. Injections were as follows: 1) Freund's complete adjuvant was diluted with an equal volume of water for injection; 2) Cyclocitronellene acetate 10% v/v in liquid paraffin and; 3) Cyclocitronellene 10% in a 50:50 mixture of Freund's adjuvant and liquid paraffin.
Topical application One week after the injections, the same 4x6 cm interscapular area was clipped and shaved free of hair. A 2x4 cm patch of Whatmen No 3 mm paper was saturated with cyclocitronellene acetate as supplied (100%). The patch was placed on the skin and covered by a length of impermeable plastic adhesive tape (5 cm width 'Blenderm'). This in turn was firmly secured by elastic adhesive bandage ('Elastoplast' of 5 cm width) wound around the torso of the animal and fixed with 'Sleek" impervious plastic adhesive tape. The dressing was left in place for 4h hours.
The control animals were treated similarly but with the exception that the test compound was omitted from the intradermal injection and the topical application.

Challenge controls:

Challenge applications were applied 2 weeks after last exposure using 20 and 10% in liquid paraffin. The challenge sites were evaluated 24, 48 and 72 hours after removal of the patches

Positive control substance(s):

no

Reading:

1st reading

Hours after challenge:

24

Group:

test chemical

Dose level:

0.2 mL and 20%

No. with + reactions:

3

Total no. in group:

14

Clinical observations:

Localised dermal reaction (restricted to a small area)

Remarks on result:

other: Reading: 1st reading. . Hours after challenge: 24.0. Group: test group. Dose level: 0.2 mL and 20%. No with. + reactions: 3.0. Total no. in groups: 14.0. Clinical observations: Localised dermal reaction (restricted to a small area).

Reading:

2nd reading

Hours after challenge:

48

Group:

test chemical

Dose level:

0.2 mL and 20%

No. with + reactions:

4

Total no. in group:

14

Clinical observations:

Localised dermal reaction (restricted to a small area)

Remarks on result:

other: Reading: 2nd reading. . Hours after challenge: 48.0. Group: test group. Dose level: 0.2 mL and 20%. No with. + reactions: 4.0. Total no. in groups: 14.0. Clinical observations: Localised dermal reaction (restricted to a small area).

Reading:

other: 3rd reading

Hours after challenge:

72

Group:

test chemical

Dose level:

0. 2 ml and 20%

No. with + reactions:

2

Total no. in group:

14

Clinical observations:

dryness and sloughing of the epidermis

Remarks on result:

other: Reading: other: 3rd reading. . Hours after challenge: 72.0. Group: test group. Dose level: 0. 2 ml and 20%. No with. + reactions: 2.0. Total no. in groups: 14.0. Clinical observations: dryness and sloughing of the epidermis.

Reading:

1st reading

Hours after challenge:

24

Group:

negative control

Dose level:

0.2 ml and 20%

No. with + reactions:

4

Total no. in group:

14

Clinical observations:

Localised dermal reaction (restricted to a small area)

Remarks on result:

other: Reading: 1st reading. . Hours after challenge: 24.0. Group: negative control. Dose level: 0.2 ml and 20%. No with. + reactions: 4.0. Total no. in groups: 14.0. Clinical observations: Localised dermal reaction (restricted to a small area).

Reading:

2nd reading

Hours after challenge:

48

Group:

negative control

Dose level:

0.2 ml and 20%

No. with + reactions:

3

Total no. in group:

14

Clinical observations:

Localised dermal reaction (restricted to a small area)

Remarks on result:

other: Reading: 2nd reading. . Hours after challenge: 48.0. Group: negative control. Dose level: 0.2 ml and 20%. No with. + reactions: 3.0. Total no. in groups: 14.0. Clinical observations: Localised dermal reaction (restricted to a small area).

Reading:

other: 3rd reading

Hours after challenge:

72

Group:

negative control

Dose level:

0.2 ml and 20%

No. with + reactions:

3

Total no. in group:

14

Clinical observations:

Localised dermal reaction (restricted to a small area) and one animal showed dryness and sloughing of the epidermis

Remarks on result:

other: see Remark

Remarks:

Reading: other: 3rd reading. . Hours after challenge: 72.0. Group: negative control. Dose level: 0.2 ml and 20%. No with. + reactions: 3.0. Total no. in groups: 14.0. Clinical observations: Localised dermal reaction (restricted to a small area) and one animal showed dryness and sloughing of the epidermis.

Animals	Skin reaction	Scores						Result
Scoring after (hours Challenge concentrations		24 10%	24h 20%	48 10	48 20	72 10	72 20
Controls		7/14	4/14	6/14	3/14	5/14	3/14	-
Test animals	Reaction*	4/14	3/14	5/14	3/14	5/14	0/14	-

*Skin reaction mainly consisted of localised dermal reactions (restriction to small area of the challenge site)

Interpretation of results:

other: not sensitising

Remarks:

according to the CLP Regulation (EC) 1272/2008

Conclusions:

Under the results of this study the test substance is not sensitising

Executive summary:

In a Maximisation test (OECD TG 406), with intradermal concentrations of 10% and challenge concentrations of 10 and 20% the skin sensitisation of the substance was investigated. In the test animals and controls localised dermal reactions were seen, which were thought to be related to skin irritation rather than sensitisation because the number and frequency of the findings were similar in the treated groups and the test animals. Therefore the substance is not considered skin sensitising.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

The skin sensitization of Veilex #1 (CAS #63449-88-7) using read across from substance CP Acetate (CAS #25225-10-9) and Veilex #2 (CAS #13487-27-9)

Introduction and hypothesis for the analogue approach

Veilex #1 has acyclohexylethyl backbonewith anbutyrate estergroup attached. For this substance no skin sensitization data are available. In accordance with Article 13 of REACH, lacking information should be generated whenever possible by means other than vertebrate animal tests, i. e. applying alternative methods such as in vitro tests, QSARs, grouping and read-across. For assessing the sensitizing potential of Veilex #1 the analogue approach is selected because for a closely related analogue, CP Acetate, sensitization information is available which can be used for read across. Furthermore, there is supporting information available of a second analogue, Veilex #2.

Hypothesis: Veilex #1 has similar sensitization potential compared to CP Acetate as thetwo methyl groups attached to the meta-position of the cyclohexylethyl backbone and the acetate ester instead of a butyrate ester in CP Acetate are not expected to influence the sensitization potential.

Available information:For Veilex #1 a well conducted HRIPT was conducted with the neat test material (reliability 2). In this study no skin sensitization was observed. More information is available from the source chemicals to cover the skin sensitization endpoint for Veilex #1. For the key source chemical CP Acetate a well conducted Maximisation test (OECD TG 406), with intradermal concentrations of 10% and challenge concentrations of 10 and 20% was conducted (reliability 2). Furthermore a HRIPT is available for CP Acetate performed with a concentration of 25% (reliability 2). In both tests CP Acetate was not skin sensitizing. These results are supported by an HRIPT conducted with Veilex #2 (reliability 4). In this study the neat test material also did not induce skin sensitization.

Target chemical and source chemical(s)

Chemical structures of the target chemical and the source chemicals are shown in the data matrix, including physico-chemical properties and toxicological information, thought relevant for sensitization, of all substances.

Purity / Impurities

Veilex #1 is a mono-constituent presenting a purity of close to 100%. Also CP Acetate has a purity close to 100% and therefore the impurities will not be relevant for the read across justification.

Analogue approach justification

According to Annex XI 1.5 read across can be used to replace testing when the similarity can be based on a common backbone and a common functional group.The analogue is selected from a group of cyclohexyl-esters e.g. acetates, which are generally negative for skin sensitisation (Belsito et al., 2008) and CP Acetate being the most similar in structure (ECHA guidance, 2015, RAAF).

Structural similarities and difference:Veilex #1 as well as the structural analogues have a common cyclohexylethyl backbone. CP Acetate, has two methyl groups attached to the meta position of the cyclohexylethyl backbone, while Veilex #1 and Veilex #2 do not have additional substituents. An acetate ester is attached to the cyclohexylethyl backbone of CP Acetate and Veilex #2, while Veilex #1 has a butyrate ester attached.These differences between the target and source chemicals are not expected influence significantly the sensitising potential of thesechemicals.

Toxico-kinetic similarities and differences:

Absorption:Veilex #1, CP Acetate and Veilex #2 have similar molecular weight and physico-chemical properties indicating similar absorption characteristics. The liquid state, molecular weight (170.3 - 198.3 g/mol)and log Kow (Ca. 3.2 – 5.2) indicate that Veilex #1 and its source chemicals are likely to be dermally absorbed to a significant extent.

Metabolism:Although metabolism is of lesser importance for local effects compared to systemic effects some local metabolism in the skin could occur. It can be anticipated that Veilex #1 will metabolise by carboxyl-esterases to butanoic acid (CAS #107-92-6) and 1-cyclohexylethanol (CAS #1193-81-3) while Veilex #2 will metabolise to acetic acid (CAS #64-19-7) and 1-cyclohexylethanol. CP Acetate will metabolise to 1-(3,3-dimethylcyclohexyl)ethanol (CAS#25225-09-6) and acetic acid.

 

Fig. 1 The metabolisation pathway of Veilex #1 and Veilex #2 and CP Acetate.

Similarities in results for toxicological endpoints between the target and the source chemical(s)

Most relevant are the similarities between the local effects of the target and source chemicals since skin sensitization is a local effect. Veilex #1, Veilex #2 and CP Acetate are not skin irritating.

Uncertainty of the prediction:There is no remaining uncertainty, in view of similarities in structure, toxico-kinetic profile (absorption and metabolism) and reactivity profile between the substances. For skin sensitization two main causes for induction are known. Skin sensitization is caused by covalent binding between the negatively charged skin proteins and the positively charged carbon-atom in the molecular structure due to adjacent electrophilic substructures such as oxygen atoms. This covalent binding between these two is the onset of an immunological reaction as presented in ECHA’s R.7.3.4.1. This onset can also be caused by radicals. Radical formation may be caused by hydroperoxides and peroxides: R-O-OH bonds or R1-O-O-R2 bonds, respectively. For Veilex #1 and its source chemicals the carbon-ester would be the potential site for attack for proteins in the skin. Due to the limitedly positively charged carbon of this ester, the proteins will not bind (sufficiently) to cause an immunological reaction. This is because of the absence of additional electrophilic activating groups on the alpha or beta position of the ester e.g. no halogens and no double or triple bonds.

In addition, there are no structural alerts regarding sensitization for the target chemical, source chemicals and their metabolites (Toxtree V2.6.13 and OECD toolbox V3.3.0.132). Therefore, read across is justified. Application of the RAAF criteria a quality score 5 can be assigned (ECHA, 2015).

Data matrix

The relevant information on physico-chemical properties and toxicological characteristics are presented in the Data matrix, see below.

Conclusions on hazard assessment and Classification and labelling.

Veilex #1 has been shown not to have skin sensitizing properties in humans. This absence of skin sensitization is confirmed with animal data from Veilex #2 and CP Acetate and with in silico data. Therefore Veilex #1 has no skin sensitization properties.

Final conclusion on hazard and C&L

Veilex #1 is not skin sensitizing. Classification and labeling is not needed for this endpoint according to CLP Regulation (EC) No. 1272/2008 and its updates.

 

Data matrix for the read across to Veilex #1, Veilex #2, and CP Acetate

Common names	Veilex #1 (CP Butyrate)	Veilex #2	CP Acetate
Chemical structures
CAS no	63449-88-7	13487-27-9	25225-10-9
Empirical formula	C12H22O2	C10H18O2	C12H22O2
Physico-chemical data
Molecular weight	198.304	170.25	198.304
Physical state	liquid	liquid	liquid
Melting point,^oC	< -20	< -20	13.46 (EpiSuite)
Boiling point,^oC	246.5	215.7	>204 (EpiSuite)
Vapour pressure, Pa	6.5 at 24 °C	38.5 at 24 °C	6.7 (EpiSuite)
Water solubility, mg/L	23.8 at 24 °C	43 at 24 °C	7.462 (EpiSuite)
Log Kow	5.2 at 20 °C	3.2 at 25 °C	4.42 (EpiSuite)
Human health endpoints
Skin irritation	No irritation OECD TG 404 (IFF, 1977)	No irritation (IFF, 1977	No irritation(IFF, 1983)
Skin sensitisation	Read across from CP Acetate and Veilex #2   No sensitization HRIPT (concentration 100%)(IFF, 1976)	Read across from CP Acetate and Veilex #1   No sensitization HRIPT (concentration 100%)(IFF, 1977)	Not a sensitizer in a Maximisation test (IFF/BBA, 1981)   No sensitization HRIPT (concentration 25%)

 

References

Belsito, D., Bickers, D., Bruze, M., Calow, P., Greim, H., Hanifin, J.M., Rogers, A.E., Saurat, J.H., Sipes, I.G., Tagami, H., RIFM Expert Panel, 2008, A toxicologic and dermatologic assessment of cyclic acetates when used as fragrance ingredients, Food and Chem. Toxicol., 46, S1-27.

Justification for classification or non-classification

In view of the negative result obtained with read across substance CP acetate in the maximisation study and supported by the negative results obtained with HRIPT studies with the test substance and read across substances Veilex 2 and CP Acetate, the substance does not need to be classified for skin sensitisation according to EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008.