5,9-dimethyl-4,8-decadienal

Endpoint summary

Description of key information

Skin sensitisation (read across from Profarnesal, which was tested in an OECD TG 429): sensitising

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Reference 1

Endpoint:

skin sensitisation: in vivo (LLNA)

Type of information:

experimental study

Adequacy of study:

key study

Study period:

08 September, 2015 - 09 December, 2015

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

read-across: supporting information

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

2010

Deviations:

no

GLP compliance:

yes

Type of study:

mouse local lymph node assay (LLNA)

Species:

mouse

Strain:

other: CBA/Jcr

Sex:

female

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: Harlan Sprague-Dawley; Indianapolis, IN
- Age at study initiation: 8 weeks
- Weight at study initiation: 18.8 - 24.0 g (on initial dose day)
- Housing: One to five animals in polycarbonate box with bedding.
- Diet: Free access to PMI Feeds Inc. TM Formulab #5008
- Water: Free access to municipal water
- Acclimation period: 5 days.

ENVIRONMENTAL CONDITIONS (target ranges)
- Temperature (°C): 20 - 23
- Humidity (%): 30 - 94
- Air changes (per hr): 10+
- Photoperiod (hrs dark / hrs light): 12/12

Vehicle:

acetone/olive oil (4:1 v/v)

Concentration:

Undiluted test item or the test item at concentrations of 25% or 50% v/v in vehicle.

No. of animals per dose:

5

Details on study design:

A range finding test was not conducted for this study.

TREATMENT PROCEDURES:
TOPICAL APPLICATION:
On Days 1, 2 and 3, each test animal in its group received an open application of 25 μL of appropriate dilution (25 or 50%) of test item in vehicle, or l 00% test item, to the dorsum of both ears. The vehicle control group (5 females) was treated the same way as test animals, but with vehicle alone instead of test item. The positive control group (5 females) was treated with 100% alpha-hexylcinnamaldehyde. All test and control animals were given a two-day rest period on Days 4 and 5.

ADMINISTRATION OF 3H-METHYL THYMIDINE:
On Day 6 of the study, all test and control animals were injected in the tail vein with 250 μL of 0.01 M phosphate-buffered saline (PBS; Sigma, Lot SLBJS 11 OV, Exp Jun 2024), pH 7.4 at 25°C per manufacturer, containing 20 μCi of [methyl-3H] Thymidine (PerkinElmer, Lot 201511, Exp 6 Nov 16). Five hours after injection, animals were sacrificed with an overdose of C02, the draining auricular lymph nodes excised and pairs from each individual animal processed.

DETERMINATION OF INCORPORATED 3HTdR:
A single cell suspension was prepared by gentle mechanical disintegration through 200 mesh stainless steel gauze. Cells were washed twice with an excess of PBS and precipitated with 5% trichloroacetic acid (TCA; Ricca, Lot 250882311511892, Exp Jul/Nov 20 16) at 4°C for 18 hours. The pellets were resuspended in 1 mL of TCA and transferred to 10 mL of scintillation fluid. Incorporation of tritiated thymidine was measured by liquid scintillation counting as disintegrations per minute (DPM) from paired lymph nodes of each animal, and mean DPM/animal was calculated for each group. Background DPM values, determined by blanks, are automatically subtracted by the scintillation counter.

OBSERVATIONS:
Individual body weights were recorded on Day 1 prior to dosing, and Day 6, prior to injection. All test and control animals were observed daily for clinical signs of toxicity and any excessive irritation at the test site.

Positive control substance(s):

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

Statistics:

A one-way parametric analysis of variance (ANOVA) with Dunnett's Multiple Comparisons Test, using GraphPad InStat version 3.06 for Windows 95, GraphPad Software, San Diego California USA, was performed on DPM counts.

Positive control results:

The positive control item, hexyl cinnamic aldehyde, gave a Stimulation Index of 5.2 when tested at a concentration of 100% v/v in acetone/olive oil 4:1.

Parameter:

SI

Remarks on result:

other: The SI values calculated for the substance concentrations 25, 50, and 100% were 1.9, 3.5 and 3.4, respectively.

Key result

Parameter:

EC3

Remarks:

%

Value:

42.3

Parameter:

other: NOEC %

Value:

25

Results:

Animal group	Test item concentration	Average DPM count per mouse	Number of mice in group	Test/vehicle control ratio (SI)
Vehicle control	NA	2405	5	NA
Test group I	25%	4649	5	1.9
Test group II	50%	8368	5	3.5
Test group III	100%	8274	5	3.4
Positive control	NA	12508	4	5.2

VIABILITY / MORTALITY:

One Positive Control animal was found dead following Day 6 injection.

CLINICAL SIGNS:

All animals appeared normal for the duration of the study.

BODY WEIGHTS:

Four of both Test Group II and III animals lost or failed to gain weight during the study; some animals in both control groups also lost weight.

Interpretation of results:

other: Skin sensitising (category 1B)

Remarks:

According to Regulation (EC) No. 1272/2008 and its amendments.

Conclusions:

The SI values calculated for the substance concentrations 25, 50 and 100% were 1.9, 3.5 and 3.4, respectively. These results show that the test substance could elicit a SI ≥ 3. An EC3 has been derived resulted in an EC3 of 42.3%. A NOEC of 25% is derived. The test substance was considered to be a sensitiser under the conditions of the test.

Executive summary:

The skin sensitisation potential of the substance has been tested according to OECD TG 429 and GLP principles. At 25, 50 and 100% the substance showed SI values of 1.9, 3.5 and 3.4, respectively. Reliable negative and positive controls were included. All animals appeared normal for the duration of the study.

These results show that the test substance could elicit a SI ≥ 3. An EC3 has been derived resulted in an EC3 of 42.3%. A NOEC of 25% is derived.

Based on the results, the substance is considered to be a skin sensitiser.

Reference 2

Endpoint:

skin sensitisation, other

Remarks:

Read-across

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: The information is derived from read across

Justification for type of information:

Executive summary: The skin sensitization of Geraldehyde is assessed by using read across from Profarnesal (CAS 54082-68-7) resulting in presence of skin sensitization for Geraldehyde. Full details are provided in the study record. Structural similarity and differences: The structures of the source and target chemicals are very similar, which can already be seen from the chemical names: 2,6,10-trimethylundeca-5,9-dienal (Profarnesal) and 5,9-dimethyldeca-4,8-dienal (Geraldehyde); both have a C10 or C11 backbone with two isolated double bonds (terpenoid fragments) and two or three methyl groups along this alkyl chain. Both substances are aldehydes and these functional groups are considered to be mainly responsible for the skin sensitizing potential. Toxico-kinetic relevant for skin sensitization: The dermal bioavailability can be assessed using the molecular weight, appearance and physico-chemical properties of both substances. Both substances are liquids. The 2Cs longer alkyl chain of Profarnesal results in a somewhat higher log Kow and lower water solubility compared to Geraldehyde, but this will not significantly change the dermal bioavailability also because both substances are liquids. Toxico-dynamics: Both substances are alkyl aldehydes and these aldehydes are predicted to have similar reactivity. The terpenoid functionality present in both substances is prone to auto oxidation and thus hydrogen peroxide formation. The presence of these groups results in similar reactivity. Remaining uncertainties: There is no remaining uncertainty as presented in the reasoning above.

Reason / purpose for cross-reference:

read-across source

Parameter:

SI

Remarks on result:

other: The SI values calculated for the substance concentrations 25, 50, and 100% were 1.9, 3.5 and 3.4, respectively.

Key result

Parameter:

EC3

Remarks:

%

Value:

42.3

Parameter:

other: NOEC %

Value:

25

Interpretation of results:

other: Skin sensitising (category 1B)

Remarks:

According to Regulation (EC) No. 1272/2008 and its amendments.

Conclusions:

Based on the data available it can be concluded that the substance is a skin sensitiser.

Reference 3

Endpoint:

skin sensitisation: in vitro

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (sensitising)

Additional information:

The skin sensitization is based on read across to Profarnesal. First the study with the analogue is described and thereafter the read across justification is presented.

LLNA test:

The skin sensitisation potential of the read-across substance Profarnesal has been tested according to OECD TG 429 and GLP principles. At 25, 50 and 100% the substance showed SI values of 1.9, 3.5 and 3.4, respectively. Reliable negative and positive controls were included. All animals appeared normal for the duration of the study.

These results show that the test substance could elicit a SI ≥ 3. An EC3 has been derived resulted in an EC3 of 42.3%. A NOEC of 25% is derived.

Geraldehyde and its (non)-sensitising potential using read across fromProfarnesal (CAS 54082-68-7)

 

Introduction and hypothesis for the read across

Geraldehyde is an alkyl aldehyde, with two double bonds in its chain and methyl groups attached to this chain. For Geraldehyde limited skin sensitisation data are available, which are not sufficient to make a decision for this endpoint. Therefore, additional information is used in accordance with Article 13 of REACH where it is said thatlacking information should be generated whenever possible by means other than vertebrate animal tests, i.e. applying alternative methods such as in vitro tests, SARs, grouping and read-across.

Hypothesis:Geraldehydeis expected to have the same sensitising properties and potency as Profarnesal.

Available experimental information: For the target substance, Geraldehyde, a Buehler test is available, but the results of the study are equivocal, therefore the results of the study cannot be used to cover the skin sensitisation endpoint.Forthe source chemical,Profarnesal, a well conducted LLNA test (OECD TG 429, K1) is available, showing the presence of skin sensitising potential. For Profarnesal also a negative GPMT is available (minimally documented, likely K2), which did not result in skin sensitization at 50%. The LLNA method is currently the preferred method and therefore the results of this method will be used.

 

Target and Source chemical(s):

The target is Geraldehyde, and the source is Profarnesal. The information on the target and source substances, together with their physico-chemical properties,is presented in the data matrix below.

 

Purity / Impurities:

Geraldehyde is a mixture of E- and Z-isomer with a ratio of 42:56%.The purity, the constituents and impurities indicate a similar sensitization potential. The impurities are all below < 10%.

 

Analogue justification

According to REACH Annex XI, an analogue approach and structural alert information can be used to replace testing when information from different sources provides sufficient evidence to conclude that this substance has or does not have a particular dangerous property. The result derived should be applicable for C&L and/or risk assessment and be presented with adequate and reliable documentation.

 

Analogue selection:

According to ECHA guidance (RAAF, 2015), a clear documentation is needed on the selection of potential source substances.In order to identify possible RA candidates, RIFM database and OECD QSAR toolbox were used for search of analogues.From all identified analogues, Profarnesal is the most similar to Geraldehyde with a Tanimoto similarity of 75% and has reliable skin sensitization data.

 

Structural similarity and differences:

·        The structures of the source and target chemicals are very similar,which can already be seen from the chemical names: 2,6,10-trimethylundeca-5,9-dienal (Profarnesal) and 5,9-dimethyldeca-4,8-dienal (Geraldehyde); both have a C10 or C11 backbone with two isolated double bonds (terpenoid fragments) and two or three methyl groupsalong this alkyl chain;

·        Both substances are aldehydes and these functional groups are considered to be mainly responsible for the skin sensitizing potential.

Toxico-kinetic relevant for skin sensitization:

·        The dermal bioavailability can be assessed using the molecular weight, appearance and physico-chemical properties of both substances. Both substances are liquids. The 2Cs longer alkyl chain of Profarnesal results in a somewhat higher log Kow and lower water solubility compared to Geraldehyde, but thiswill not significantly change the dermal bioavailability also because both substances are liquids.

Toxico-dynamics:

·        Both substances are alkyl aldehydes and these aldehydes are predicted to have similar reactivity. The terpenoid functionality present in both substances is prone to auto oxidation and thus hydrogen peroxide formation. The presence of these groups results in similar reactivity.

Remaining uncertainties:

There is no remaining uncertaintyas presented in the reasoning above.

 

Conclusions per endpoint for C&L

Profarnesal is skin sensitising in a reliable LLNA with an EC3 of 42%. Based on read across also Geraldehyde is expected to have an EC3 of 42%.Therefore, Geraldehyde is sensitizing, and it needs to be classified and labelled for sensitisation with category 1B according to EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008.

 

Data matrix Information on Geraldehyde and Profarnesal important for assessment of skin sensitising properties

 

CHEMICAL NAME	Geraldehyde (target)	Profarnesal (source)
CAS	762-26-5	54082-68-7
Molecular structure
Empirical formula	C12H20O	C14H24O
Molecular weight	180.91	208.35
Physico-chemical properties
Appearance	Liquid	Liquid
Vapour pressure at 25˚C (Pa)	2.96 at 25°C (EpiSuite) 2.22 at 24°C (measured)	0.83 at 25°C (EpiSuite)
Water solubility at 20˚C (mg/L)	9 (from Log Kow; EpiSuite) 52.2 mg/l at 24°C (measured)	1 (from Log Kow; EpiSuite)
Log Kow	4.4 (EpiSuite) 4.4 (measured)	5.3 (EpiSuite)
Human health
Skin sensitisation animal test	No relevant data (equivocal Buehler test and two HRIPT studies, both negative at 1%) Read-across from Profarnesal	GPMT: 50%- not sensitizer LLNA: EC3 = 42.3% (Symrise, 2016; GLP, OECD 429, K1)

Justification for classification or non-classification

Based on the results of the read-across substance, the substance is considered to be a sensitiser and should be classified as skin sensitizer (Category 1B) and labeled with H317: May cause an allergic skin reaction according to Regulation (EC) No. 1272/2008 and its amendments.