Bis(2,4-dichlorobenzoyl) peroxide

Endpoint summary

Description of key information

A key study was performed to assess the skin sensitisation potential of the test item in the CBA/Ca strain mouse following topical application to the dorsal surface of the ear. The method was designed to be compatible with the following: (1) OECD Guideline for the Testing of Chemicals No. 429 "Skin Sensitisation: Local Lymph Node Assay" (adopted 22 July 2010), and (2) Method B42 Skin Sensitisation (Local Lymph Node Assay) of Commission Regulation (EC) No. 440/2008.

Conclusion. At concentrations 5, 10, and 25% (w/w) in 1% pluronic L92 in distilled water, the resulting stimulation indices were all positive (18.65, 13.79, and 22.71, respectively). As there was no clear dose-response, it was not possible to determine the EC₃value. The test item was considered to be a sensitiser under the conditions of the test. 

Migrated from Short description of key information:
The test material is shown to be a strong skin sensitiser in the LLNA test in rats.

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:

Between 10 May 2012 and 24 May 2012

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method B.42 (Skin Sensitisation: Local Lymph Node Assay)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

No analysis was carried out to determine the homogeneity, concentration or stability of the test item formulation. This exception is considered not to affect the purpose or integrity of the study.

Type of study:

mouse local lymph node assay (LLNA)

Species:

mouse

Strain:

other: CBA/Ca (CBA/CaOlaHsd)

Sex:

female

Details on test animals and environmental conditions:

Female CBA/Ca (CBA/CaOlaHsd) strain mice were supplied by Harlan Laboratories UK Ltd., Oxon, UK. On receipt the animals were randomly allocated to cages. The animals were nulliparous and non pregnant. After an acclimatisation period of at least five days the animals were selected at random and given a number unique within the study by indelible ink marking on the tail and a number written on a cage card. At the start of the study the animals were in the weight range of 15 to 23 g, and were eight to twelve weeks old.
The animals were individually housed in suspended solid floor polypropylene cages furnished with softwood woodflakes. Free access to mains tap water and food (2014C Teklad Global Rodent diet supplied by Harlan Laboratories UK Ltd., Oxon, UK) was allowed throughout the study.
The temperature and relative humidity were controlled to remain within target ranges of 19 to 25°C and 30 to 70%, respectively. Any occasional deviations from these targets were considered not to have affected the purpose or integrity of the study. The rate of air exchange was approximately fifteen changes per hour and the lighting was controlled by a time switch to give twelve hours continuous light (06.00 to 18.00) and twelve hours darkness.
The animals were provided with environmental enrichment items which were considered not to contain any contaminant of a level that might have affected the purpose or integrity of the study.

Vehicle:

other: 1% pluronic L92 in distilled water

Concentration:

25%, 10% or 5% w/w in 1% pluronic L92 in distilled water

No. of animals per dose:

Groups of five mice were treated

Details on study design:

Preliminary Screening Test
Using available information regarding the systemic toxicity/irritancy potential of the test item, a preliminary screening test was performed using one mouse. The mouse was treated by daily application of 25 µl of the test item at a maximum attainable concentration of 25% w/w in 1% pluronic L92 in distilled water, to the dorsal surface of each ear for three consecutive days (Days 1, 2, 3). The mouse was observed twice daily on Days 1, 2 and 3 and once daily on Days 4, 5 and 6. Local skin irritation was scored daily according to the scale included as Appendix 4. Any clinical signs of toxicity, if present, were also recorded. The bodyweight was recorded on Day 1 (prior to dosing) and on Day 6.
The thickness of each ear was measured using an Oditest micrometer (Dyer, PA), pre dose on Day 1, post dose on Day 3 and on Day 6. Any changes in the ear thickness were noted. Mean ear thickness changes were calculated between Days 1 to 3 and Days 1 to 6. A mean ear thickness increase of equal to or greater than 25% was considered to indicate excessive irritation and limited biological relevance to the endpoint of sensitisation.
Main Test
Test Item Administration
Groups of five mice were treated with the test item at concentrations of 25%, 10% or 5% w/w in 1% pluronic L92 in distilled water. The preliminary screening test suggested that the test item would not produce systemic toxicity or excessive local irritation at the highest suitable concentration. The mice were treated by daily application of 25 µl of the appropriate concentration of the test item to the dorsal surface of each ear for three consecutive days (Days 1, 2, 3). The test item formulation was administered using an automatic micropipette and spread over the dorsal surface of the ear using the tip of the pipette.
A further group of five mice received the vehicle alone in the same manner.
3H-Methyl Thymidine Administration
Five days following the first topical application of the test item or vehicle (Day 6) all mice were injected via the tail vein with 250 µl of phosphate buffered saline (PBS) containing 3H methyl thymidine (3HTdR:80µCi/ml, specific activity 2.0 Ci/mmol, ARC UK Ltd) giving a total of 20 µCi to each mouse.
Observations
Clinical Observations: All animals were observed twice daily on Days 1, 2 and 3 and on a daily basis on Days 4, 5 and 6. Any signs of toxicity or signs of ill health during the test were recorded.
Bodyweights: The bodyweight of each mouse was recorded on Day 1 (prior to dosing) and Day 6 (prior to termination).
Terminal Procedures
Termination: Five hours following the administration of 3HTdR all mice were killed by carbon dioxide asphyxiation followed by cervical separation. For each individual animal of each group the draining auricular lymph nodes were excised and processed. For each individual animal 1 ml of PBS was added to the lymph nodes.
Preparation of Single Cell Suspension: A single cell suspension of the lymph node cells for each individual animal was prepared by gentle mechanical disaggregation through a 200 mesh stainless steel gauze. The lymph node cells were rinsed through the gauze with 4 ml of PBS into a petri dish labelled with the project number and dose concentration. The lymph node cells suspension was transferred to a centrifuge tube. The petri dish was washed with an additional 5 ml of PBS to remove all remaining lymph node cells and these were added to the centrifuge tube. The lymph node cells were pelleted at 1400 rpm (approximately 190 g) for ten minutes. The pellet was resuspended in 10 ml of PBS and re-pelleted. To precipitate out the radioactive material, the pellet was resuspended in 3 ml of 5% Trichloroacetic acid (TCA).
Determination of 3HTdR Incorporation: After approximately eighteen hours incubation at approximately 4°C, the precipitates were recovered by centrifugation at 2100 rpm (approximately 450 g) for ten minutes, resuspended in 1 ml of TCA and transferred to 10 ml of scintillation fluid (Optiphase 'Trisafe'). 3HTdR incorporation was measured by ß scintillation counting. The "Poly QTM" vials containing the samples and scintillation fluid were placed in the sample changer of the scintillator and left for approximately twenty minutes. The purpose of this period of time in darkness was to reduce the risk of luminescence, which has been shown to affect the reliability of the results. After approximately twenty minutes, the vials were shaken vigorously. The number of radioactive disintegrations per minute was then measured using the Beckman LS6500 scintillation system (Beckman Instruments Inc, Fullerton, CA, USA).

Positive control substance(s):

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

Statistics:

Data was processed to give group mean values for disintegrations per minute and standard deviations where appropriate. Individual and group mean disintegrations per minute values were assessed for dose response relationships by analysis of homogeneity of variance followed by one way analysis of variance (ANOVA). In the event of a significant result from the ANOVA, pairwise comparisons were performed between control and treated groups. For homogenous datasets Dunnett’s Multiple Comparison test was used and for non homogenous datasets Dunnett’s T3 Multiple Comparison Method was used.
Probability values (p) are presented as follows:
P<0.001 ***
P<0.01 **
P<0.05 *
P>0.05 (not significant)

Positive control results:

Appendix 1 Current Positive Control Study for the Local Lymph Node Assay
Introduction. A study was performed to assess the sensitivity of the strain of mouse used at these laboratories to a known sensitiser. The methodology for the LLNA is detailed in the OECD Guideline for the Testing of Chemicals No. 429 and Method B.42 of Commission Regulation (EC) No. 440/2008. The study described in this document is based on these test methods but has been refined in order to reduce the number of animals required. The reduced LLNA (rLLNA) has been endorsed by the non Commission members of the European Centre for the Validation of Alternative Methods (ECVAM) Scientific Advisory Committee (ESAC) at its 26th meeting held on 26 – 27 April 2007 at ECVAM, Ispra, Italy.
Test Item: α Hexylcinnamaldehyde, tech., 85%
Project number: 41103440
Study dates: 01 December 2011 to 07 December 2011
Methods. A group of five animals was treated with 50 µl (25 µl per ear) of α Hexylcinnamaldehyde, tech., 85% as an emulsion in 1% pluronic L92 in distilled water at a concentration of 25% v/v. A further control group of five animals was treated with 1% pluronic L92 in distilled water alone.
Results. The Stimulation Index expressed as the mean radioactive incorporation for the treatment group divided by the mean radioactive incorporation of the vehicle control group is as follows:
Concentration (% v/v) in
1% pluronic L92 in distilled water Stimulation Index Result
25 7.86 Positive
Conclusion. α Hexylcinnamaldehyde, tech., 85% was considered to be a sensitiser under the conditions of the test.

Parameter:

SI

Value:

18.65

Variability:

SD: +/- 4.17

Test group / Remarks:

5 %w/w

Parameter:

SI

Value:

13.79

Variability:

SD: +/- 4.64

Test group / Remarks:

10 %w/w

Parameter:

SI

Value:

22.71

Variability:

SD: +/- 3.14

Test group / Remarks:

25 %w/w

Interpretation of Results The proliferation response of lymph node cells was expressed as the number of radioactive disintegrations per minute per animal and as the ratio of ³HTdR incorporation into lymph node cells of test nodes relative to that recorded for the control nodes (Stimulation Index).

The test item will be regarded as a sensitiser if at least one concentration of the test item results in a threefold or greater increase in ³HTdR incorporation compared to control values. Any test item failing to produce a threefold or greater increase in ³HTdR incorporation will be classified as a "non‑sensitiser".

Preliminary Screening Test

Clinical observations, bodyweight and mortality data are given in Table 1 and local skin irritation is given in Table 2. The ear thickness measurements and mean ear thickness changes are given in Table 3.

No signs of systemic toxicity, visual local skin irritation or irritation indicated by anequal to or greater than 25% increase in mean ear thicknesswere noted.

Based on this information the dose levels selected for the main test were 25%, 10% and 5% w/w in 1% pluronic L92 in distilled water.

Main Test

Estimation of the Proliferative Response of Lymph Node Cells

The radioactive disintegrations per minute per animal and the stimulation index are given in Table 4.

The Stimulation Index expressed as the mean radioactive incorporation for each treatment group divided by the mean radioactive incorporation of the vehicle control group are as follows:

Concentration (%w/w) in 1% pluronic L92 in distilled water	Stimulation Index	Result
5	18.65	Positive
10	13.79	Positive
25	22.71	Positive

As there was no clear dose-response, it was not possible to determine the EC₃value.

Clinical Observations and Mortality Data

Individual clinical observations and mortality data for test and control animals are given in Table 5.

There were no deaths. No signs of systemic toxicity were noted in the test or control animals during the test.

Bodyweight

Individual bodyweights and bodyweight changes for test and control animals are given in Table 6.

Bodyweight changes of the test animals between Day 1 and Day 6 were comparable to those observed in the corresponding control group animals over the same period.

Table 1              Clinical Observations, Bodyweight and Mortality Data – Preliminary Screening Test

Concentration (% w/w) in 1% pluronic L92in distilled water	Animal Number	Bodyweight (g)		Day
				1		2		3		4	5	6
		Day 1	Day 6	Pre-Dose	Post Dose	Pre-Dose	Post Dose	Pre-Dose	Post Dose
25	S-1	19	20	0	0	0	0	0	0	0	0	0

0=     No signs of systemic toxicity

Table 2              Local Skin Irritation – Preliminary Screening Test

Concentration (% w/w) in 1% pluronic L92in distilled water

Animal Number

Local Skin Irritation

Day 1

Day 2

Day 3

Day 4

Day 5

Day 6

left

right

left

right

left

right

left

right

left

right

left

right

25

S-1

0

0

0

0

0

0

0

0

0

0

0

0

Table 3              Measurement of Ear Thicknessand Mean Ear Thickness Changes – Preliminary Screening Test

Concentration (% w/w) in 1% pluronic L92in distilled water	Animal Number	Ear Thickness Measurement (mm)
		Day 1		Day 3		Day 6
		pre‑dose		post dose
		left	right	left	right	left	right
25	S-1	0.230	0.225	0.245	0.240	0.235	0.245
overall mean (mm)		0.228		0.243		0.240
overall mean ear thickness change (%)		na		6.593		5.495

na=     Not applicable

Table 4              Individual Disintegrations per Minute and Stimulation Indices

Concentration (% w/w) in 1% pluronic L92 in distilled water	Animal Number	dpm/ Animal^a	Mean dpm/Animal (Standard Deviation)	Stimulation Index^b	Result
Vehicle	1-1	844.86	1443.85 (±622.96)	na	na
	1-2	1831.28
	1-3	2342.17
	1-4	1118.24
	1-5	1082.71
5	2-1	17158.52	26928.79*** (±6021.10)	18.65	Positive
	2-2	25361.63
	2-3	30724.71
	2-4	29241.11
	2-5	32157.98
10	3-1	19981.32	19911.53*** (±6697.10)	13.79	Positive
	3-2	29463.69
	3-3	17047.43
	3-4	21876.70
	3-5	11188.50
25	4-1	27463.60	32796.10*** (±4540.11)	22.71	Positive
	4-2	38799.19
	4-3	29677.77
	4-4	35641.39
	4-5	32398.55

dpm=Disintegrations per minute

a=     Total number of lymph nodes per animal is 2

b=     Stimulation Index of 3.0 or greater indicates a positive result

na=     Not applicable

***=   Significantly different from control group p<0.001

Table 5              Individual Clinical Observations and Mortality Data

Concentration (% w/w) in 1% pluronic L92in distilled water	Animal Number	Day 1		Day 2		Day 3		Day 4	Day 5	Day 6
		Pre-Dose	Post Dose	Pre-Dose	Post Dose	Pre-Dose	Post Dose
Vehicle	1-1	0	0	0	0	0	0	0	0	0
	1-2	0	0	0	0	0	0	0	0	0
	1-3	0	0	0	0	0	0	0	0	0
	1-4	0	0	0	0	0	0	0	0	0
	1-5	0	0	0	0	0	0	0	0	0
5	2-1	0	0	0	0	0	0	0	0	0
	2-2	0	0	0	0	0	0	0	0	0
	2-3	0	0	0	0	0	0	0	0	0
	2-4	0	0	0	0	0	0	0	0	0
	2-5	0	0	0	0	0	0	0	0	0
10	3-1	0	0	0	0	0	0	0	0	0
	3-2	0	0	0	0	0	0	0	0	0
	3-3	0	0	0	0	0	0	0	0	0
	3-4	0	0	0	0	0	0	0	0	0
	3-5	0	0	0	0	0	0	0	0	0
25	4-1	0	0	0	0	0	0	0	0	0
	4-2	0	0	0	0	0	0	0	0	0
	4-3	0	0	0	0	0	0	0	0	0
	4-4	0	0	0	0	0	0	0	0	0
	4-5	0	0	0	0	0	0	0	0	0

0=      No signs of systemic toxicity

Table 6              Individual Bodyweights and Bodyweight Changes

Concentration (% w/w) in 1% pluronic L92 in distilled water	Animal Number	Bodyweight (g)		Bodyweight Change (g)
		Day 1	Day 6
Vehicle	1-1	23	21	-2
	1-2	20	20	0
	1-3	22	21	-1
	1-4	19	20	1
	1-5	19	19	0
5	2-1	19	20	1
	2-2	19	20	1
	2-3	20	20	0
	2-4	21	22	1
	2-5	19	18	-1
10	3-1	23	22	-1
	3-2	19	19	0
	3-3	21	21	0
	3-4	20	18	-2
	3-5	21	20	-1
25	4-1	21	20	-1
	4-2	21	20	-1
	4-3	18	19	1
	4-4	20	19	-1
	4-5	21	21	0

Interpretation of results:

sensitising

Remarks:

Migrated information

Conclusions:

The test item was considered to be a sensitiser under the conditions of the test.

Executive summary:

Introduction. A study was performed to assess the skin sensitisation potential of the test item in the CBA/Ca strain mouse following topical application to the dorsal surface of the ear. The method was designed tobe compatible withthe following:

OECD Guideline for the Testing of Chemicals No. 429 "Skin Sensitisation: Local Lymph Node Assay" (adopted 22 July 2010)

Method B42 Skin Sensitisation (Local Lymph Node Assay) of Commission Regulation (EC) No. 440/2008

Methods. Following a preliminary screening test in which no clinical signs of toxicity were noted at a maximum attainable concentration of 25% w/w, this concentration was selected as the highest dose investigated in the main test of the Local Lymph Node Assay. Three groups, each of five animals, were treated with 50 µl (25 µl per ear) of the test item as an emulsion in 1% pluronic L92 in distilled water at concentrations of 25%, 10% or 5% w/w. A further group of five animals was treated with 1% pluronic L92 in distilled wateralone.

Results. The Stimulation Index expressed as the mean radioactive incorporation for each treatment group divided by the mean radioactive incorporation of the vehicle control group are as follows:

Concentration (% w/w) in 1% pluronic L92 in distilled water	Stimulation Index	Result
5	18.65	Positive
10	13.79	Positive
25	22.71	Positive

As there was no clear dose-response, it was not possible to determine the EC₃value.

Conclusion. The test item was considered to be a Category 1 sensitiser under the conditions of the test

Reference 2

Endpoint:

skin sensitisation: in vitro

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

an in vitro skin sensitisation study does not need to be conducted because adequate data from an in vivo skin sensitisation study are available

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (sensitising)

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

At all concentrations tested, the test item was positive in a key study. As there was no clear dose-response, it was not possible to determine the EC₃value. The test item was considered to be a Category 1, strong skin sensitiser under the conditions of the test.