3,7-dimethyloct-1-en-3-yl acetate

Skin sensitisation

Administrative data

Endpoint:

skin sensitisation: in chemico

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

15 June 2015 to 29 June 2015

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2015

Report date:

2015

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 442C (In Chemico Skin Sensitisation Assays addressing the Adverse Outcome Pathway key event on covalent binding to proteins)

Version / remarks:

04 February 2015

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of study:

direct peptide reactivity assay (DPRA)

Test material

Test material information

Constituent 1

Reference substance name:

3,7-dimethyloct-1-en-3-yl acetate

EC Number:

269-847-3

EC Name:

3,7-dimethyloct-1-en-3-yl acetate

Cas Number:

68345-17-5

Molecular formula:

C12H22O2

IUPAC Name:

3,7-dimethyloct-1-en-3-yl acetate

Test material form:

liquid

In chemico test system

Details of test system:

cysteine peptide, (Ac-RFAACAA-COOH)

Details on the study design:

PREPARATION OF TEST SOLUTIONS
Co-elution control samples preparation
For the co-elution control with cysteine peptide: 50 μL of test item formulation was incubated with 750 μL of cysteine peptide dilution buffer (without cysteine peptide) and 200 μL of acetonitrile.
For the co-elution control with lysine peptide: In parallel, 250 μL of test item formulation was incubated with 750 μL of lysine peptide dilution buffer (without lysine peptide).

Reference control samples preparation
Reference control A and B samples: In a vial, acetonitrile was added to a volume of peptide solution (cysteine or lysine) to achieve a nominal concentration of 0.500 mM.

Reference control C samples
Reference control C samples were prepared for each solvent used to dissolve the test and positive control items.
For the reference control C prepared with cysteine peptide:
50 μL of vehicle (acetonitrile) was incubated with 750 μL of cysteine peptide solution (at 0.667 mM in phosphate buffer at pH 7.5) and 200 μL of acetonitrile.
For the reference control C prepared with lysine peptide:
In parallel, 250 μL of vehicle (acetonitrile) was incubated with 750 μL of lysine peptide solution (at 0.667 mM in ammonium acetate buffer at pH 10.2).

Cinnamaldehyde (positive control) depletion control samples preparation
For the reactivity of cinnamaldehyde with cysteine peptide:
50 μL of cinnamaldehyde at 100 mM in acetonitrile was incubated with 750 μL of cysteine peptide solution (at 0.667 mM in phosphate buffer at pH 7.5) and 200 μL of acetonitrile.
For the reactivity of cinnamaldehyde with lysine peptide:
In parallel, 250 μL of cinnamaldehyde at 100 mM in acetonitrile was incubated with 750 μL of lysine peptide solution (at 0.667 mM in ammonium acetate at pH 10.2).

Test item samples preparation
For the reactivity of test item with cysteine peptide:
50 μL of test item formulation was incubated with 750 μL of cysteine peptide solution (at 0.667 mM in phosphate buffer at pH 7.5) and 200 μL of acetonitrile.
For the reactivity of test item with lysine peptide:
In parallel, 250 μL of test item formulation was incubated with 750 μL of lysine peptide solution (at 0.667 mM in ammonium acetate at pH 10.2).


INCUBATION
All samples (co-elution controls, reference controls, test item and positive control samples) were then incubated during 24 (± 2) hours with cysteine peptide or during approximately 27 hours with lysine peptide at 25°C and protected from light before injection onto the HPLC/UV system. At the end of the incubation period, a visual inspection of the samples was performed prior to HPLC analysis.
As precipitates and/or micelles were observed in the co-elution and test item samples incubated with the cysteine and lysine peptides, these vials were centrifuged at 400 g for a period of 5 minutes at room temperature to force precipitate to the bottom of the vial. Only supernatants were then injected onto the HPLC/UV system.
Although precipitates were observed in the reference and positive control samples incubated with the cysteine and lysine peptides, these vials were not centrifuged at 400 g for a period of 5 minutes at room temperature since precipitates were already observed at the bottom of the vial. Only supernatants were injected onto the HPLC/UV system.


DATA EVALUATION
The study samples were assayed in batches using HPLC/UV analysis. The concentration of cysteine or lysine peptide was photometrically determined at 220 nm.

Vehicle / solvent:

acetonitrile

Positive control:

cinnamic aldehyde

Results and discussion

Positive control results:

The positive control depletion values for cysteine and lysineldepletion are within the ranges of the acceptance criteria.

In vitro / in chemico

Results

Results 1

Key result

Group:

test chemical

Run / experiment:

mean

Parameter:

lysine depletion

Value:

0 %

At concentration:

100 mM

Vehicle controls validity:

valid

Negative controls validity:

not examined

Positive controls validity:

valid

Results 2

Key result

Group:

test chemical

Run / experiment:

mean

Parameter:

cysteine depletion

Value:

0 %

At concentration:

100 mM

Vehicle controls validity:

valid

Negative controls validity:

not examined

Positive controls validity:

valid

Outcome of the prediction model:

no or minimal reactivity [in chemico]

Other effects / acceptance of results:

ACCEPTANCE OF RESULTS:
- Acceptance criteria met for positive control: yes
- Acceptance criteria met for reference controls A to C: yes
- Acceptance criteria met for co-elution controls (Lysine and Cysteine): yes
- Acceptance criteria met for variability between replicate measurements: yes

Any other information on results incl. tables

 

Since precipitates and/or micelles were observed at the end of the incubation with the peptides, the peptide depletion may be underestimated. Therefore, the conclusion on the lack of reactivity cannot be drawn with sufficient confidence. However, precipitates were observed in the positive control samples as well.

 

Table 1: Peptide Depletion

Sample	Cysteine peptide depletion (%)	Lysine peptide depletion (%)	Mean Depletion (%)
Positive control	72.24	54.92	63.20
	73.14	53.92
	71.20	53.78
DMOE-Ac	-2.60	-1.39	0
	-1.98	-0.90
	-3.47	-1.56

 

Applicant's summary and conclusion

Interpretation of results:

other: This study alone is not sufficient to decide on the classification of a substance as skin sensitiser.

Conclusions:

The negative Direct Peptide Reactivity Assay (DPRA)-result can be used as part of a testing battery (including e.g. h-CLAT (human cell line activation test), ARE-Nrf2 luciferase test method) based on the OECD adverse outcome pathway (AOP) for the assessment of the skin sensitisation potential of chemicals.

Executive summary:

The reactivity of the test item was evaluated in chemico by monitoring peptide depletion following a 24-hour contact between the test item and synthetic cysteine and lysine peptides. The method consisted of the incubation of a diluted solution of cysteine or lysine with the test item for 24 hours. At the end of the incubation, the concentrations of residual peptides were evaluated by HPLC with Ultra-Violet detection at 220 nm. Peptide reactivity was reported as percent depletion based on the peptide peak area of the replicate injection and the mean peptide peak area in the three relevant reference control C samples (in the appropriate solvent).

The test item was dissolved at 100 mM in acetonitrile. The acceptance criteria for the calibration curve samples, the reference and positive controls as well as for the study samples were satisfied. The study was therefore considered to be valid. Analysis of the chromatograms of the co-elution samples indicated that the test item did not co-elute with either the lysine or the cysteine peptides. As a result, the mean percent depletion values were calculated for each peptide. For both peptides, the mean depletion value was set to 0 due to negative percentage depletion value. The mean of the percent cysteine and percent lysine depletions was therefore equal to 0%. Accordingly, the test item was considered to have no/minimal peptide reactivity. Therefore, the DPRA prediction would be considered as negative. Since precipitates and/or micelles were observed at the end of the incubation with the peptides, the peptide depletion may be underestimated. Therefore, the conclusion on the lack of reactivity cannot be drawn with sufficient confidence. However, precipitates were observed in the positive control samples as well.

As a conclusion, under the experimental conditions of this study, the test item Dimethyl Octenyl Acetate (DMOE-Ac) was considered to have no/minimal peptide reactivity, though with limitations due to presence of precipitates and/or micelles at the end of the incubation with peptides in test item samples.