Geranyl formate

Endpoint summary

Description of key information

Skin sensitisation (OECD 442C and OECD 442E): positive for key events peptide reactivity and activation of dendritic cells

Skin sensitisation (OECD 442B): sensitising

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Reference 1

Endpoint:

skin sensitisation: in vitro

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

8 Aug - 1 Sep 2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: OECD Guideline 442E (In Vitro Skin Sensitisation: human Cell Line Activation Test)

Version / remarks:

July 2016

Deviations:

yes

Remarks:

cytotoxicity measurement and estimation of the CV75 value was performed by XTT test instead of flow cytometry

GLP compliance:

yes (incl. QA statement)

Remarks:

Hess. Ministerium für Umwelt, Klimaschutz, Landwirtschaft und Verbraucherschutz, Wiesbaden, Germany

Type of study:

activation of dendritic cells

Details on the study design:

TEST CELL LINE
- Strain: THP-1 cells (human monocytic leukemia cell line)
- Source: American Type Culture Collection
- Passage number: 7 - 10 (XTT test); 15 - 16 (h-CLAT)

CELL CULTURE CONDITIONS
- Type and identity of media: RPMI-1640 supplemented with 10% (v/v) FBS, 100 U/mL penicillin, 100 µg/mL streptomycin, 0.05 mM 2-mercaptoethanol, 4.5 g/L glucose, 1% (v/v) pyruvate and 1% (v/v) L-glutamine
- Temperature (°C): 37 ± 1.5
- CO2 (%): 5.0 ± 0.5

DOSE FINDING ASSAY BY CYTOTOXICITY MEASUREMENT (XTT TEST)
The doses investigated in the main experiment (h-CLAT) were determined with a XTT test. The XTT test is a method to investigate the cytotoxicity of a test substance. The test is based on the cleavage of the yellow tetrazolium salt, sodium 3'-(1-phenylaminocarbonyl)-(3,4 - tetrazolium)-bis-(4–methoxy-6-nitro)-benzenesulfonic acid hydrate (XTT), to form an orange water soluble formazan dye by dehydrogenase activity in active mitochondria. Two independent cytotoxicity experiments were performed with different cell cultures and on different days to obtain a reliable concentration showing 75% cell viability (CV75).

CONTROLS
Negative Control
- Substance: culture medium
Vehicle control
- Substance: dimethyl sulfoxide (DMSO)
- Concentration: 0.2 - 0.5%

EXPOSURE CONDITIONS
- Exposure duration: 24 ± 1 h

TEST CONCENTRATIONS
- Justification for top dose: The test substance was soluble in DMSO up to and including 500 µg/mL as tested by a solubility test.
3.91, 7.81, 15.63, 31.25, 62.5, 125, 250 and 500 µg/mL (XTT 1 and 2)

NUMBER OF REPLICATIONS: septuplicates per concentration in two independent experiments

MEASUREMENT
- Device: microplate reader (Versamax Molecular Devices)
- Wavelength: 450 nm
- Reference wavelength: 690 nm

EVALUATION CRITERIA
A decrease in number of living cells results in a decrease in the overall activity of mitochondrial dehydrogenases in the sample. This decrease directly correlates to the amount of orange formazan formed, as monitored by the absorbance. The relative absorbance as compared to the solvent control is calculated using the formula:
Relative absorbance = 100 x [(mean absorbance test substance) - (absorbance blank)] / [(mean absorbance vehicle control) - (absorbance blank)]

To calculate the concentration of test substance needed to reduce the relative absorbance to 75% of the vehicle control (CV75) the following formula is used:
CV75 = Conc. > 75 - ([(Conc. > 75) - (Conc. < 75)] x [(% > 75) - 75] / [(% > 75) - (% < 75)])
a) Conc. > 75: max. measured concentration with the % of vehicle control > 75%
b) Conc. < 75: min. measured concentration with the % of vehicle control < 75%
c) % > 75: relative absorbance at a) in %
d) % < 75: relative absorbance at b) in %

ACCEPTANCE CRITERIA
The XTT test is considered to be acceptable if it meets the following criteria:
- mean absorbance of the negative control is ≥ 0.5
- mean viability of the vehicle control is ≥ 70%

h-CLAT (MAIN STUDY)
The h-CLAT method is an in vitro method which quantifies changes of cell surface marker expression (CD86 and CD54) on a human cell line, THP-1 cells, following 24 h exposure to the test substance. The changes of surface marker expression are measured by flow cytometry following cell staining with fluorescein isothiocyanate (FITC)-labelled antibodies. The relative fluorescence intensity of surface markers compared to solvent control are calculated and used in the prediction model to support the discrimination between sensitisers and non-sensitisers.

CONTROLS
Negative Control
- Substance: culture medium
Vehicle control
- Substance: dimethyl sulfoxide (DMSO)
- Concentration: 0.2%
Positive control
- Substance: 2,4-dinitrochlorobenzene (DNCB) in DMSO
- Concentration: 2 and 3 µg/mL

EXPOSURE CONDITIONS
- Exposure duration: 24 ± 1 h

TEST CONCENTRATIONS
- Justification for top dose: Since a CV75 value could not be determined the highest soluble test substance concentration was multiplied with 1.2 (600 µg/mL)
167, 201, 241, 289, 347, 417, 500 and 600 µg/mL

NUMBER OF REPLICATIONS: at least in triplicates for the different stainings in two independent experiments

STAINING
- Antibodies: FITC anti-CD54 (Clone: Fun-1); FITC anti-CD86 (Clone: 6.5B5); FITC mouse IgG1 (isotype control)
- Temperature: 2 - 8 °C
- Duration: 30 ± 5 min

MEASUREMENT
- Device: flow cytometer FACSCalibur (Becton Dickinson)

EVALUATION CRITERIA
The relative fluorescence intensity (RFI) is used as an indicator of CD86 and CD54 expression, and is calculated as follows for each concentration:
RFI (%) = [(MFI of test substance treated cells) - (MFI of test substance isotype control cells) / (MFI of vehicle control cells) - (MFI of vehicle isotype control cells)] x 100
MFI: geometric mean fluorescence intensity (GeoMean)

The cell viability is calculated as follows for each concentration:
Cell viability (%) = (mean cytotox of vehicle control cells) / (mean cytotox of test substance treated cells) x 100
Where the mean cytotox is the mean of GeoMean (7-AAD) isotype control, GeoMean (7-AAD) CD54 and GeoMean (7-AAD) CD86.

The test substance is tested in 2 independent runs. If the RFI of CD86 is ≥ 150% or if the RFI of CD54 is ≥ 200% in both independent run data, the test substance is considered to be a sensitizer. Otherwise it is considered to be a non-sensitizer. In case of different results in both runs, a third run has to be performed. If the RFI of CD86 is ≥ 150% at any dose in at least 2 of 3 independent run data, or if the RFI of CD54 is ≥ 200% in at least 2 of 3 independent run data, the test substance is considered to be a sensitizer. Otherwise it is considered to be a non-sensitizer.

ACCEPTANCE CRITERIA
The study is considered as valid, if the following criteria are met:
- Cell viability of negative control is adjusted to 100% and the cell viability of the vehicle control should be more than 90% in comparison to the negative control.
- In the positive control, RFI values of both CD86 and CD54 should exceed the positive criteria (CD86 ≥ 150% and CD54 ≥ 200%) and the cell viability should be > 50%.
- In the vehicle control, RFI values compared to the negative control of both CD86 and CD54 should not exceed the positive criteria (CD86 ≥ 150% and CD54 ≥ 200%).
- For negative and vehicle controls, the MFI ratio of CD86 and CD54 to isotype control should be > 105%.
- For the test substance resulting in negative outcome, the cell viability at the 1.2 × CV75 value should be less than 90%. If the cell viability at the 1.2 × CV75 value is more than 90% for a positive tested test substance, the data will be acceptable. If 5 mg/mL in saline, 1 mg/mL in DMSO or the highest soluble dose will be used as the maximal test concentration instead of CV75-based dose, the data for test substance are accepted independent by the cell viability.
- The cell viability of at least 4 doses in each experiment should be ≥50%.

Run / experiment:

other: 24 h incubation

Parameter:

other: relative fluorescence intensity of CD54 (%)

Value:

200

Vehicle controls validity:

valid

Negative controls validity:

valid

Positive controls validity:

valid

Run / experiment:

other: 24 h incubation

Parameter:

other: relative fluorescence intensity of CD86 (%)

Value:

150

Vehicle controls validity:

valid

Negative controls validity:

valid

Positive controls validity:

valid

Other effects / acceptance of results:

ADDITIONAL INFORMATION ON CYTOTOXICITY:
XTT test
Cytotoxic effects were not observed following incubation with the test substance up to the highest soluble concentration (500 µg/mL). The viability of the cells spaced within a range of 77.90 to 189.62% in the first experiment and within a range of 84.03 to 98.30% in the second experiment (threshold of cytotoxicity: < 75%). Due to the lack of cytotoxicity, a CV75 value could not be calculated.
h-CLAT
The cell viability was not negatively affected (viability > 80%) in both independent experiments.

ACCEPTANCE OF RESULTS:
- Acceptance criteria met for vehicle control: In the vehicle control, RFI values compared to the negative control of both CD86 and CD54 did not exceed the positive criteria (CD86 ≥150% and CD54 ≥200%).
- Acceptance criteria met for positive control: The RFI values of the positive control for CD86 and CD54 exceeded the positive criteria (CD86 >150% and CD54 >200%) and the cell viability was >50%.

Table 1: Results of the first XTT test

	Concentration [µg/mL]	Mean absorbance*	Blank	Absorbance in % of vehicle control**
Medium control	-	0.891 ± 0.067	0.260	91.47
Vehicle control	-	0.937 ± 0.059	0.247	100.00
Test substance	3.91	0.874 ± 0.030	0.255	89.62
	7.81	0.807 ± 0.032	0.257	79.67
	15.63	0.868 ± 0.051	0.256	88.50
	31.25	0.844 ± 0.049	0.257	85.03
	62.5	0.830 ± 0.055	0.246	84.53
	125	0.789 ± 0.040	0.252	77.90
	250	0.791 ± 0.021	0.251	78.17
	500	0.813 ± 0.037	0.260	80.05

*: mean absorbance (absolute) of 7 wells

**: relative absorbance

 

Table 2: Results of the second XTT test

	Concentration [µg/mL]	Mean absorbance*	Blank	Absorbance in % of vehicle control**
Medium control	-	0.860 ± 0.022	0.256	116.47
Vehicle control	-	0.775 ± 0.060	0.256	100.00
Test substance	3.91	0.757 ± 0.030	0.247	98.30
	7.81	0.732 ± 0.039	0.250	92.84
	15.63	0.722 ± 0.036	0.252	90.63
	31.25	0.735 ± 0.016	0.250	93.49
	62.5	0.713 ± 0.033	0.254	88.56
	125	0.689 ± 0.045	0.254	84.03
	250	0.694 ± 0.025	0.248	86.09
	500	0.689 ± 0.052	0.248	85.17

*: mean absorbance (absolute) of 7 wells

**: relative absorbance

Table 3. Results of the first h-CLAT run

	Concentration [µg/mL]	Antibody / ISO	MFI GeoMean (FITC)	MFI - ISO	Csto(Geo) GeoMean (7-AAD)	Mean Cyto	RFI (%)	Viability (%)
Medium control	-	ISO	2.17	-	2.29	2.0	-	100.0
		CD54	2.85	0.68	2.15		100.0
		CD86	5.38	3.21	1.67		100.0
Vehicle control	-	ISO	2.09	-	2.39	2.0	-	100.0
		CD54	3.12	1.03	2.03		100.0
		CD86	5.24	3.15	1.64		100.0
Positive control	2	ISO	2.28	-	2.62	2.0	-	100.8
		CD54	8.47	6.19	1.81		601.0*
		CD86	9.96	7.68	1.58		243.8*
	3	ISO	2.33	-	2.84	2.1	-	96.8
		CD54	8.21	5.88	1.83		570.9*
		CD86	11.03	8.70	1.59		276.2*
Test substance	167	ISO	2.35	-	2.61	2.1	-	94.1
		CD54	4.30	1.95	2.09		189.3
		CD86	6.35	4	1.74		127.0
	201	ISO	2.43	-	2.75	2.2	-	90.7
		CD54	4.60	2.17	2.19		210.7*
		CD86	6.95	4.52	1.74		143.5
	241	ISO	2.53	-	2.82	2.3	-	89.0
		CD54	4.54	2.01	2.28		195.1
		CD86	7.53	5	1.71		158.7*
	289	ISO	2.42	-	2.49	2.0	-	100.2
		CD54	4.47	2.05	2.01		199.0
		CD86	6.74	4.32	1.55		137.1
	347	ISO	2.30	-	2.37	2.0	-	103.2
		CD54	4.18	1.88	1.94		182.5
		CD86	6.45	4.15	1.56		131.7
	417	ISO	2.42	-	2.61	2.1	-	95.7
		CD54	4.55	2.13	2.06		206.8*
		CD86	7.01	4.59	1.66		145.7
	500	ISO	2.54	-	2.89	2.3	-	88.7
		CD54	4.93	2.39	2.36		232.0*
		CD86	8.96	6.42	1.58		203.8*
	600	ISO	2.58	-	2.86	2.3	-	86.2
		CD54	5.22	2.64	2.36		256.3*
		CD86	8.18	5.60	1.81		177.8*

*: RFI value of CD86 or CD54 exceeded the criteria for a positive response (CD86 ≥ 150% and CD54 ≥ 200%).

 

Table 4. Results of the second h-CLAT run

	Concentration [µg/mL]	Antibody / ISO	MFI GeoMean (FITC)	MFI - ISO	Csto(Geo) GeoMean (7-AAD)	Mean Cyto	RFI (%)	Viability (%)
Medium control	-	ISO	2.16	-	2.1	1.8	-	100
		CD54	2.89	0.73	1.80		100.0
		CD86	4.45	2.29	1.55		100.0
Vehicle control	-	ISO	2.14	-	1.91	1.7	-	100.0
		CD54	2.91	0.77	1.79		100.0
		CD86	4.73	2.59	1.51		100.0
Positive control	2	ISO	2.69	-	2.39	1.9	-	91.6
		CD54	5.94	3.25	1.88		422.1*
		CD86	9.44	6.75	1.42		260.6*
	3	ISO	2.74	-	2.86	2.1	-	83.1
		CD54	6.66	3.92	1.94		509.1*
		CD86	12.27	9.53	1.47		368.0*
Test substance	84	ISO	2.71	-	2.05	1.8	-	99.0
		CD54	4.32	1.61	1.79		209.1*
		CD86	6.75	4.04	1.42		156.0*
	100	ISO	2.71	-	2.00	1.7	-	100.6
		CD54	4.16	1.45	1.78		188.3
		CD86	6.85	4.14	1.4		159.8*
	121	ISO	2.73	-	2.11	1.8	-	97.4
		CD54	4.48	1.75	1.85		227.3*
		CD86	7.43	4.7	1.39		181.5*
	145	ISO	2.77	-	2.2	1.9	-	92.2
		CD54	4.39	1.62	2.02		210.4*
		CD86	7.48	4.71	1.43		181.9*
	174	ISO	2.65	-	2.2	1.9	-	91.1
		CD54	4.46	1.81	1.93		235.1*
		CD86	6.17	3.52	1.59		135.9
	208	ISO	2.73	-	2.25	1.9	-	91.9
		CD54	4.45	1.72	1.97		223.4*
		CD86	7.86	5.13	1.45		198.1*
	250	ISO	2.71	-	2.24	1.9	-	90.9
		CD54	4.27	1.56	1.99		202.6*
		CD86	6.75	4.04	1.50		156.0*
	300	ISO	2.88	-	2.61	2.2	-	80.3
		CD54	5.53	2.65	2.27		344.2*
		CD86	8.14	5.26	1.61		203.1*

*: RFI value of CD86 or CD54 exceeded the criteria for a positive response (CD86 ≥150% and CD54

Interpretation of results:

other: activation of dendritic cells positive according to OECD 442E

Conclusions:

Under the conditions of the Human Cell Line Activation Test the test substance increased the expression of both cell surface markers, CD54 and CD86, which is associated with the process of activation of monocytes and dendritic cells. Based on this result, the h-CLAT prediction is considered positive for skin sensitisation.

Executive summary:

Dendritic cell response of the test substance was investigated ina Human Cell Line Activation Test (h-CLAT) according to OECD Guideline 442E and in compliance with GLP (2016). The test substance increased the expression of the cell surface marker CD54 and CD86to greater than 200% and 150%, respectively in two independent experiments.Thus, the h-CLAT predictionfor activation of dendritic cellsis considered positive.

Reference 2

Endpoint:

skin sensitisation: in chemico

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

18 - 25 Aug 2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 442C (In Chemico Skin Sensitisation: Direct Peptide Reactivity Assay (DPRA))

Version / remarks:

2015

Deviations:

yes

Remarks:

No information on stability, precision and co-elution controls provided. No information on stability/solubility of test substance after preparation of peptide depletion samples and after 22 h incubation.

GLP compliance:

yes (incl. QA statement)

Remarks:

THE DEPARTMENT OF HEALTH OF THE GOVERNMENT OF THE UNITED KINGDOM, UK

Type of study:

direct peptide reactivity assay (DPRA)

Details on the study design:

TEST METHOD
The DPRA is an in chemico test system proposed to address the molecular initiating event of the skin sensitisation adverse outcome pathway, namely protein reactivity, by substance towards model synthetic peptides containing either lysine or cysteine. The DPRA quantifies the free concentration of cysteine- or lysine-containing peptide following incubation with the test substance. Relative peptide concentration is measured by HPLC with gradient elution and UV detection at 220 nm. Cysteine- and lysine peptide percent depletion values are then calculated and used in the prediction model which allows assigning the test substance to one of four reactivity classes used to support the discrimination between sensitisers and non-sensitisers.

TEST SYSTEM
- Supplier: AnaSpec
- Synthetic cysteine-containing peptide:
Alternative name: Ac-RFAACAA-OH
Batch number: 1556171
Molecular weight: 751.5 g/L
Purity: 95%
Expiry date: 5 years
- Synthetic lysine-containing peptide:
Alternative name: Ac-RFAAKAA-OH
Batch number: 1556172
Molecular weight: 776 g/L
Purity: 90 - 95%
Expiry date: 5 years

SOLVENT CONTROL AND ASSESSMENT OF TEST ITEM SOLUBILITY
- Substance: acetonitrile
- The solubility of the test item in acetonitril was assessed at a concentration of 100 mM.

POSITIVE CONTROL
- Substance: cinnamic aldehyde
- Batch number: MKBR2427V
- Purity: > 95%
- Expiry date: Feb 2019
- The positive control was prepared at a concentration of 100 mM.

STABILITY AND PRECISION CONTROL
Stability and precision controls of both peptides were prepared at a concentration of 0.5 mM.

PEPTIDE STOCK SOLUTION PREPARATION
Cysteine-containing peptide:
- Solvent: phosphate buffer (pH 7.5)
- Concentration: 0.667 mM
Lysine-containing peptide:
- Solvent: ammonium acetate buffer (pH 10.2)
- Concentration: 0.667 mM

INCUBATION CONDITIONS OF THE TEST SUBSTANCE WITH THE PEPTIDE SOLUTIONS
- Peptide to test substance ratios: Cysteine-containing peptide: 1:10 (0.5 mM peptide, 5 mM test substance/positive control); Lysine-containing peptide: 1:50 (0.5 mM peptide, 25 mM test substance/positive control)
- Temperature used during treatment / exposure: 25 °C
- Duration of treatment / exposure: at least 22 h prior to initiation of the analysis run

NUMBER OF REPLICATES
for each peptide in triplicates for treatment and control

HIGH PERFORMANCE LIQUID CHROMATOGRAPHY
- Specification of the device: Waters Alliance 2695 separation module and 2487 dual wavelength detector
- Column: Agilent Zorbax SB C18, 3.5 µm, 100 x 2.1 mm with guard column Phenomenex AJO4286
- HPLC mobile phase:
A: 0.1% (v/v) trifluoracetic acid in deionised water
B: 0.085% (v/v) trifluoracetic acid in acetonitrile
- Flow: 0.35 mL/min
- Gradient:
Time (min): 0, 20, 21, 23, 23.5, 30
% B: 10, 25, 90, 90, 10, 10
- Detector wavelength: 220 nm
- Column temperature: 30 °C

Run / experiment:

other: ≥ 22 h incubation

Parameter:

other: % depletion of cystein-containing peptide

Remarks:

(mean of 3 replicates)

Value:

5.87

Vehicle controls validity:

valid

Negative controls validity:

not specified

Positive controls validity:

valid

Run / experiment:

other: ≥ 22 h incubation

Parameter:

other: % depletion of lysine-containing peptide

Remarks:

(mean of 3 replicates)

Value:

7.19

Vehicle controls validity:

valid

Negative controls validity:

not specified

Positive controls validity:

valid

Run / experiment:

other: ≥ 22 h incubation

Parameter:

other: % overall mean depletion

Value:

6.53

Vehicle controls validity:

not applicable

Negative controls validity:

not applicable

Positive controls validity:

not applicable

Other effects / acceptance of results:

TEST-SPECIFIC CONFOUNDING FACTORS
- Other confounding effects: No co-elution of the test substance occurred during the assay. Small micro droplets were observed in both the incubated Cysteine and Lysine peptide samples indicative of potential phase separation. As the test item is present in excess in the both incubation samples (and peaks attributed to the test item were observed in both assays) relative to the amount of peptide present then enough test item is considered to have remained in solution so as to ensure that results are valid and hence there is no impact on the data reported. The solubility of the test substance in acetonitrile at a nominal concentration of 100 mM was confirmed.

ACCEPTANCE OF RESULTS:
All analytical acceptance criteria for each peptide were met.

Table 5. Mean peptide depletion of cysteine-containing peptide.

	Peak area (µV.sec)	Peptide concentration (µg/mL)*	Peptide depletion (%)**	Mean depletion ± CV (%)
Test substance	837277	355.83	6.08	5.87 ± 0.44
	836818	355.64	6.13
	843405	358.43	5.39
Positive control	240892	102.84	73.0	72.9 ± 0.53
	241472	103.09	72.9
	243345	103.88	72.7

 CV: Coefficient of Variation

*: Samples prepared at a concentration of 376 μg/mL (0.5 mM)

**: Calculated against a mean reference control peak area of 891480 μV.sec (n=6)

Table 6. Mean peptide depletion of lysine-containing peptide.

	Peak area (µV.sec)	Peptide concentration (µg/mL)*	Peptide depletion (%)**	Mean depletion ± CV (%)
Test substance	691227	355.31	8.76	7.19 ± 2.41
	695708	357.62	8.17
	722519	371.41	4.63
Positive control	317975	163.34	58.0	57.5 ± 1.09
	324749	166.82	57.1
	322828	165.83	57.4

CV: Coefficient of Variation

*: Samples prepared at a concentration of 388 μg/mL (0.5 mM)

**: Calculated against a mean reference control peak area of 757580 μV.sec (n=6)                            

 

 

Interpretation of results:

other: positive for peptide reactivity (low reactivity) according to OECD 442C

Conclusions:

Under the conditions of the Direct Peptide Reactivity Assay the test substance showed low peptide reactivity.

Executive summary:

In the study,the protein reactivity of the test substance was investigated in a Direct Peptide Reactivity Assay according to OECD Guideline 442C and in compliance with GLP (2017).The overall mean percent cysteine and lysine depletion is 6.53 and therefore the test substance is allocated to the “low reactivity” class (mean % depletion > 6.38 ≤ 22.62).

Reference 3

Endpoint:

skin sensitisation: in vivo (LLNA)

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

19 Jan - 25 May 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 442B (Skin Sensitization: Local Lymph Node Assay: BrdU-ELISA)

Version / remarks:

adopted 22 Jul 2010

Deviations:

no

GLP compliance:

yes

Type of study:

mouse local lymph node assay (LLNA): BrdU-ELISA

Species:

mouse

Strain:

other: CBA/N

Sex:

female

Details on test animals and environmental conditions:

TEST ANIMALS
- Females nulliparous and non-pregnant: not specified
- Microbiological status of animals, when known: SPF
- Age at study initiation: 9 weeks
- Weight at study initiation: 18.3 - 21.2 g (dose range finding study; DRF), 17.1 - 22.2 g (main study)
- Housing: 2 - 3 animals per cage in polysulfone cages (200Wx320Dx140H mm)
- Diet: Teklad Certified Irradiated Global 18% Protein Rodent Diet 2918C (Envigo RMS, Inc., USA), ad libitum
- Water: public tap water (filtered and irradiated by UV light), ad libitum
- Acclimation period: 4 - 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20.5 - 24.1 (DRF), 20.6 - 23.6 (main study)
- Humidity (%): 39.9 - 56.0 (DRF), 40.7 - 54.8 (main study)
- Air changes (per hr): 10 - 15
- Photoperiod (hrs dark / hrs light): 12 / 12

Vehicle:

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

Concentration:

Dose range finding study: 5, 10, 25, 50 and 100 % (w/v)
Main study: Set 1: 25, 50 and 100 % (w/v); Set 2: 0.1, 1 and 10 % (w/v)

No. of animals per dose:

5

Details on study design:

RANGE-FINDING STUDY: Two animals were observed per dose group. All mice were observed daily for any clinical signs of systemic toxicity or local irritation at the application site. Body weights were recorded prior to dosing (Day 1) and on the day of necropsy (Day 6). Both ears of each mouse were observed for erythema and scored using erythema score. Ear thickness measurement was taken using a thickness gauge on Day 1 (pre-dose), Day 3 and Day 6. Additionally, on Day 6, ear weight was determined by balance
- Dose selction: Dose selection was based on the consecutive doses and dose levels were selected from a series of appropriate concentrations of such as 100, 50, 25, 10 and 5%.
- Compound solubility: The test substance was dissolved in AOO in a preliminary solubility test. Therefore, AOO was utilized as vehicle for this study.
- Irritation: no
- Systemic toxicity: no
- Ear thickness measurements: not specified
- Erythema scores: not specified

MAIN STUDY: Based on the result of the dose range finding study, the high dose level for the main study was selected at 100%. Two additional low dose levels (25 and 50%) and a positive and negative control were tested in the main study.

ANIMAL ASSIGNMENT AND TREATMENT
- Name of test method: ELISA BrdU
- Criteria used to consider a positive response: A stimulation index (SI) was calculated for each group using the BrdU labelling index of each test group divided by the BrdU labelling index of the vehicle control group. SI < 1.6 is considered as negative result. SI ≥ 1.6 is considered as positive result.

The EC1.6 value was used to classify the test substance according to ECETOC Potency classification as follows:
EC1.6 Value (%) ≥ 10 to ≤ 100 -> Weak
EC1.6 Value (%) ≥ 1 to ≤ 10 -> Moderate
EC1.6 Value (%) ≥ 0.1 to ≤ 1 -> Strong
EC1.6 Value (%) < 0.1 -> Extreme
Ryan et al. Extrapolating local lymph node assay EC3 values to estimate relative sensitizing potency. Cutaneous and Ocular Toxicology, 2007, 26: 135-145.

TREATMENT PREPARATION AND ADMINISTRATION: A volume of 25 μL was applied to the dorsum of both ears of all animals daily for three consecutive days. Two days after the third application on Day 5, an intraperitoneal injection of 0.5 mL (5 mg/mouse) of BrdU solution (10 mg/mL) was made. Approximately 24 h after BrdU injection, the mice were sacrificed by CO2 gas and draining auricular lymph nodes from each mouse ear were excised and processed separately in phosphate buffered saline for each animal. A single cell suspension was prepared by separation through a nylon mesh. In each case, the target volume of the cell suspension was adjusted to the determined optimized volume. The optimized volume was based on the mean absorbance within 0.1 - 0.2 in the negative control group. BrdU was measured by ELISA using a commercial kit. Briefly, 100 µL of the lymph node cell suspension was added to the wells of a microplate in triplicate. After fixation and denaturation of the cell suspension, anti-BrdU antibody was added to each well. Subsequently, anti-BrdU antibody was removed by washing and the substrate solution was added. Absorbance was measured at 370 nm with a reference wavelength of 492 nm.

Negative control animals were dosed with the vehicle, acetone/olive oil solution.

Positive control substance(s):

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

Statistics:

Statistical analysis was conducted using a statistical program (version 9.3, SAS Institute Inc., U.S.A.) for the data including body weight, erythema score, ear thickness, ear weight and stimulation index.
Bartlett’s test was employed on homogeneity of variance (significance level: 0.05) for body weights, ear thickness, ear weight and stimulation index data. One-way analysis of variance (ANOVA) was employed on homogeneous data. Dunnett’s t-test was applied for multiple comparisons (significance levels: 0.05 and 0.01, one-tailed) between the negative control group and each of the test substance groups or positive substance group. Since it was not significant, Kruskal-Wallis test was employed on heterogeneous data and Steel’s test was applied for multiple comparisons (significance levels: 0.05 and 0.01, one-tailed) between the negative control group and each of the test substance groups or positive substance group.
Kruskal-Wallis test for the erythema score was employed on heterogeneous data, and Steel’s test was applied for multiple comparisons (significance levels: 0.05 and 0.01, one-tailed) between the negative control group and each of the test substance groups or positive substance group.

Positive control results:

Body weights: Set 1: In the positive control group at 25%, the mean body weight was in the range of 19.4 -19.6 g. There were no significant differences when compared to the negative control group. Set 2: In the positive control group at 25%, the mean body weight was in the range of 19.3–19.9 g. There were no significant differences when compared to the negative control group.
Erythema scores: Set 1: In the positive control group at 25%, the mean erythema score was in the range of 0 - 2. There were significant increases when compared to the negative control group (p<0.05: Day 3, p<0.01: Days 4, 5 and 6). Set 2: In the positive control group at 25%, the mean erythema score was in the range of 0–1. There were significant increases when compared to the negative control group (p<0.05: Days 4 and 5, p<0.01: Day 6).
Ear thickness: Set 1: In the positive control group at 25%, the mean ear thickness was in the range of 0.19 - 0.22 mm. There were significant increases when compared to the negative control group (p<0.05: Day 6). Set 2: In the positive control group at 25%, the mean ear thickness was in the range of 0.19 - 0.20 mm. There were significant increases when compared to the negative control group (p<0.01: Day 6).
Ear weights: Set 1: In the positive control group at 25%, the mean ear weight was 13.8 mg. There were no significant differences when compared to the negative control group. Set 2: In the positive control group at 25%, the mean ear weight was 14.3 mg. There was a significant increase when compared to the negative control group (p<0.05).

Parameter:

SI

Value:

0.83

Test group / Remarks:

0.1%

Remarks on result:

other: Set 2

Parameter:

SI

Value:

0.87

Test group / Remarks:

1%

Remarks on result:

other: Set 2

Parameter:

SI

Value:

0.85

Test group / Remarks:

10%

Remarks on result:

other: Set 2

Parameter:

SI

Value:

2.39

Test group / Remarks:

25%

Remarks on result:

other: Set 1

Parameter:

SI

Value:

2.47

Test group / Remarks:

50%

Remarks on result:

other: Set 1

Parameter:

SI

Value:

3.84

Test group / Remarks:

100%

Remarks on result:

other: Set 1

Cellular proliferation data / Observations:

IRRITATION, EAR THICKNESS AND EAR WEIGHTS:
- Erythema Score: Set 1: In the negative control group, the mean erythema score was 0 from Day 1 to Day 6 after dosing.
In the test substance groups at 25, 50 and 100%, the mean erythema scores were in the ranges of 0–0, 0–0 and 0–1, respectively. There were significant increases when compared to the negative control group (p<0.01: Days 5 and 6 (100%)).
Set 2: In the negative control group, the mean erythema score was 0 from Day 1 to Day 6 after dosing.
In the test substance groups at 0.1, 1 and 10%, the mean erythema scores were in the ranges of 0–0, 0–0 and 0–0, respectively. There were no significant differences when compared to the negative control group.

- Ear thickness: Set 1: In the negative control group, the mean ear thickness was in the range of 0.19–0.20 mm from Day 1 to Day 6 after dosing.
In the test substance groups at 25, 50 and 100%, the mean ear thickness was in the ranges of 0.19–0.20, 0.19–0.20 and 0.19–0.21 mm, respectively. There were significant increases when compared to the negative control group (p<0.05: Day 6 (100%)).
Set 2: In the negative control group, the mean ear thickness was in the range of 0.19–0.19 mm from Day 1 to Day 6 after dosing.
In the test substance groups at 0.1, 1 and 10%, the mean ear thickness was in the ranges of 0.19–0.19, 0.19–0.19 and 0.19–0.19 mm, respectively. There were no significant differences when compared to the negative control group.

- Ear weights: Set 1: In the negative control group, the mean ear weight was 13.2 mg.
In the test substance groups at 25, 50 and 100%, the mean ear weights were 13.4, 13.1 and 13.6 mg, respectively. There were no significant differences when compared to the negative control group.
Set 2: In the negative control group, the mean ear weight was 12.8 mg.
In the test substance groups at 0.1, 1 and 10%, the mean ear weights were 12.9, 13.5 and 13.0 mg, respectively. There was a significant increase when compared to the negative control group (p<0.05: 1%).


DETAILS ON STIMULATION INDEX CALCULATION: EC1.6 =c+[(1.6-d)/(b-d)] x (a-c)
a = The dose concentration with higher SI
b = The higher SI value
c = The dose concentration with lower SI
d = The lower SI value

Three concentrations showed SI of <1.6, and EC1.6 was calculated to be 25.7%

CLINICAL OBSERVATIONS: Set 1 and 2: There were no abnormal clinical signs or deaths in any dosing group during the observation period.

BODY WEIGHTS: Set 1: In the negative control group, the mean body weight was in the range of 19.3–20.6 g from Day 1 to Day 6 after dosing.
In the test substance groups at 25, 50 and 100%, the mean body weights were in the ranges of 19.4– 19.9, 19.5–20.2 and 19.2–19.5 g, respectively. There were no significant differences when compared to the negative control group.
Set 2: In the test substance groups at 0.1, 1 and 10%, the mean body weights were in the ranges of 19.5– 19.6, 19.4–20.3 and 19.6–19.8 g, respectively. There were no significant differences when compared to the negative control group.
In the positive control group at 25%, the mean body weight was in the range of 19.3–19.9 g. There were no significant differences when compared to the negative control group.

Interpretation of results:

other: Skin Sens Cat 1B according to Regulation (EC) No 1272/2008

Conclusions:

Under the conditions of the local lymph node assay, the test substance revealed a SI > 1.6 at 25%, 50% and 100% in acetone:olive oil (4:1, v/v). Consequently, the EC1.6 was calculated to be 25.7%. Therefore, the test substance is considered to be a weak sensitiser.

Executive summary:

The skin sensitisation potential of the test substance was investigated in vivo by a LLNA test using the BrdU ELISA method according to OECD Guideline 442B in compliance with GLP (2017). Treatment of CBA/N mice with the test substance revealed stimulation indices of 0.83, 0.87, 0.85, 2.39, 2.47 and 3.84 at concentrations of 0.1, 1, 10, 25, 50 and 100%, respectively. EC1.6 value was calculated to be 25.7. The test substance is therefore considered to be a weak skin sensitiser.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (sensitising)

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information:

In vitro:

Dendritic cell response of the test substance was investigated in a Human Cell Line Activation Test (h-CLAT) according to OECD Guideline 442E and in compliance with GLP (2016). The test substance increased the expression of the cell surface marker CD54 and CD86 to greater than 200% and 150%, respectively in two independent experiments. Thus, the h-CLAT prediction for activation of dendritic cells is considered positive.

In a second study, the protein reactivity of the test substance was investigated in a Direct Peptide Reactivity Assay according to OECD Guideline 442C and in compliance with GLP (2017). The overall mean percent cysteine and lysine depletion is 6.53 and therefore the test substance is allocated to the “low reactivity” class (mean % depletion > 6.38 ≤ 22.62).

In vivo:

In a next step, the skin sensitisation potential of the test substance was further investigated in vivo by a LLNA test using the BrdU ELISA method according to OECD Guideline 442B in compliance with GLP (2017). Treatment of CBA/N mice with the test substance revealed stimulation indices of 0.83, 0.87, 0.85, 2.39, 2.47 and 3.84 at concentrations of 0.1, 1, 10, 25, 50 and 100%, respectively. EC1.6 value was calculated to be 25.7. The test substance is therefore considered to be a weak skin sensitiser.

Conclusion:

Based on two positive results in the in vitro test battery according to the Adverse Outcome Pathway defined for skin sensitisation and a positive result in the LLNA, the test substance is considered to be a weak skin sensitiser.

Justification for classification or non-classification

The available data on skin sensitisation meet the criteria for classification according to Regulation (EC) 1272/2008, and is therefore classified as skin sensitiser Category 1B (H317).