Bis(α,α-dimethylbenzyl) peroxide

Skin sensitisation

Administrative data

Endpoint:

skin sensitisation: in vivo (LLNA)

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2009-12-10 to 2010-03-29

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2010

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

24 April 2002

Deviations:

yes

Remarks:

see box " Principles of method if other than guideline"

Principles of method if other than guideline:

The purpose of this study was to determine the sensitising potential of Dicumyl peroxide in the local lymph node assay in mice. The study was performed according to OECD 429, however not employing the use of radioactive labelling to measure cell proliferation, as the radioactive method proposed by the OECD guideline led to problems in various EU laboratories: such as (i) practical difficulties/complexity of the test, in particular the radiochemical steps, which sometimes resulted in loss of specimen/activity; this in turn led to variability in the results and to a poor reproducibility and (ii) radiation protection issues. However, the OECD guideline allows other endpoints for assessment of proliferation in form of lymph node cell counts and lymph node weights if justification and appropriate
scientific support exist showing the validity of this method. The alternative method used for the study employing the lymph node weight and lymph node cell count to assess proliferation has been established by an European inter-laboratory validation exercise, as described in the two publications by Ehling et al. 2005a and 2005b. In addition, the acute inflammatory skin reaction is measured by ear weight determination of circular biopsies of the ears and ear thickness measurements on test day 1 and test day 4 to identify skin irritation properties of the test item. Stimulation indices were calculated for the lymph node cell count, lymph node weight, ear weight and ear thickness by dividing the average values per group of the test item treated animals by the vehicle treated ones. Values above 1.4 (lymph node cell count to identify sensitisation) or 1.1 (ear weight to identify irritation) are considered positive (these values were fixed empirically during the inter-laboratory validation of this method (Ehling et al. 2005a and 2005b).

GLP compliance:

yes (incl. QA statement)

Type of study:

mouse local lymph node assay (LLNA)

Test material

Test material information

Constituent 1

Reference substance name:

Bis(α,α-dimethylbenzyl) peroxide

EC Number:

201-279-3

EC Name:

Bis(α,α-dimethylbenzyl) peroxide

Cas Number:

80-43-3

Molecular formula:

C18H22O2

IUPAC Name:

1,1'-(dioxydipropane-2,2-diyl)dibenzene

Details on test material:

- Name of test material (as cited in study report): Dicumylperoxide
- Molecular formula (if other than submission substance): C18H22O2
- Substance type: white crystalline powder
- Physical state: solid
- Analytical purity: 99.5% (based on CoA)
- Purity test date: 07.12.2009
- Lot/batch No.: 44229 (receipt no.)

In vivo test system

Test animals

Species:

mouse

Strain:

CBA

Sex:

female

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories
- Age at study initiation: 12 weeks
- Weight at study initiation: 20-25 g
- Housing: singly in MAKROLON cages (type III)
- Diet (e.g. ad libitum): ssniff R/m-H V1534, ad libitum
- Water (e.g. ad libitum): tap water ad libitum
- Acclimation period: at least 5 d

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 +/- 3°C
- Humidity (%): 55 +/- 15%
- Air changes (per hr): Not reported
- Photoperiod (hrs dark / hrs light): 12 / 12

Study design: in vivo (LLNA)

Vehicle:

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

Remarks:

given in report as (3+1, v/v)

Concentration:

10%, 25%, and 50% (w/w) in 25 µL

No. of animals per dose:

6 females

Details on study design:

RANGE FINDING TESTS:
perfomed with 1 animal each at 10, 25 and 50% (25 µL/ear)

MAIN STUDY
ANIMAL ASSIGNMENT AND TREATMENT
- Name of test method: LLNA
- Criteria used to consider a positive response: Index for lymph node cell count above 1.4 and index for ear weight above 1.1

Positive control substance(s):

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

Statistics:

Mann & Whitney U-test , concentration-response-relationship examined by linear regression analysis using Pearsons's correlation coefficient.

Results and discussion

Positive control results:

The positive control revealed a significant increase in lymph node cell count above the threshold of 1.4. Therefore, the test was considered valid.

In vivo (LLNA)

Results

Results 1

Parameter:

SI

Remarks:

Mean of six animals

Value:

1

Test group / Remarks:

Negative control

Results 2

Key result

Parameter:

SI

Remarks:

Mean of six animals

Value:

1.086

Test group / Remarks:

10%

Remarks on result:

other: The simulation index for lymph node cell count did not exceed the threshold of 1.4. Hence, the test item is classified as not sensitising.

Results 3

Key result

Parameter:

SI

Remarks:

Mean of six animals

Value:

1.339

Test group / Remarks:

25%

Remarks on result:

other: The simulation index for lymph node cell count did not exceed the threshold of 1.4. Hence, the test item is classified as not sensitising.

Results 4

Key result

Parameter:

SI

Remarks:

Mean of six animals

Value:

1.384

Test group / Remarks:

50%

Remarks on result:

other: The simulation index for lymph node cell count did not exceed the threshold of 1.4. Hence, the test item is classified as not sensitising.

Results 5

Parameter:

SI

Value:

1.764

Test group / Remarks:

Positive control

Remarks on result:

other: The positive control group caused an increase in lymph node cell count above the threshold of 1.4.

Any other information on results incl. tables

 Table 1: Stimulation indices

Parameter	Group 1, negative control	Group 2, 10%	Group 3, 25%	Group 4, 50%	Group 5, positive control
Lymph node cell count	1	0.086	1.339	1.384	1.764*
Lymph node weight	1	1.400	1.909*	1.954*	2.127*
Ear weight	1	0.949	0.916*	0.888*	0.762*
Ear thickness	1	1.032	1.036	1.044	1.104

*: sign. at p< 0.01

 

Applicant's summary and conclusion

Interpretation of results:

GHS criteria not met

Conclusions:

The result of the LLNA test perfomed with dicumyl peroxide revealed that dicumyl peroxide is not senstizing to skin.

Executive summary:

In a dermal sensitisation test conducted according to OECD 429, female CBA mice (six/group) were treated with concentrations of 10, 25 and 50% test item in acetone/olive oil (3 +1 v/v). No changes in behaviour were observed in any of the treated animals.The result of the LLNA test indicated, that dicumyl peroxide is not sensitizing to skin when tested at concentration up to 50%.