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Description of key information

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records
Reference
Endpoint:
skin sensitisation: in vivo (LLNA)
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
05 December 2013 to21 January 2014
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Study conducted to approved guidelines and in compliance with GLP
Qualifier:
according to
Guideline:
OECD Guideline 429 (Skin Sensitisation: Local Lymph Node Assay)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method B.42 (Skin Sensitisation: Local Lymph Node Assay)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Remarks:
Copy of scertificate of compliance form UK GLP Monitoring Authority included in report
Type of study:
mouse local lymph node assay (LLNA)
Species:
mouse
Strain:
other: CBA/Ca
Sex:
female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: UK
- Age at study initiation: 9-11 weeks
- Weight at study initiation: 18-20.3 g
- Housing:2 per cage
- Diet (e.g. ad libitum):ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: >6 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 19-23 deg C
- Humidity (%): 40-70%
- Air changes (per hr):
- Photoperiod (hrs dark / hrs light):12 h dark/12 h light

IN-LIFE DATES: From: 11 December 21013 To:20 January 2014
Vehicle:
acetone/olive oil (4:1 v/v)
Concentration:
as supplied and then 50% and 25% of "as supplied" solution
No. of animals per dose:
4
Details on study design:
The results of the preliminary investigations indicated that ‘as supplied’ was a suitable high
concentration for administration in the main phase of the study. The low and intermediate
concentrations were selected from the concentration series given in regulatory guidelines and
the concentrations administered on the main study were:
25, 50% v/v in AOO and ‘as supplied’
The positive control group received 25% v/v hexylcinnamic aldehyde in AOO based on
previous experience at this laboratory.

Main phase
Groups of four mice were treated at one of three concentrations of the test substance. The
mice were treated by daily application of 25 L of the appropriate concentration of the test
substance to the dorsal surface of each ear for three consecutive days (Days 1-3). The test
substance was applied to the dorsal surface of each ear using an automatic micropipette and
was spread over the entire dorsal surface of the ear using the tip of the pipette. Further
groups of four mice received the vehicle alone or the positive control substance in the same
manner and a sham control group

Administration of 3H-methyl Thymidine
In the main phase of the study, five days following the first topical application of test
substance (Day 6) all mice were injected via the tail vein with 250 L of phosphate buffered
saline containing 3H-methyl Thymidinea (3HTdR: 80 Ci/mL) giving a nominal 20 Ci to
each mouse. The injection into the tail vein was carried out using a plastic syringe and needle
after the mouse had been heated in a warming chamber
Positive control substance(s):
hexyl cinnamic aldehyde (CAS No 101-86-0)
Statistics:
None stated
Parameter:
SI
Remarks on result:
other: see Remark
Remarks:
The SI (test/control ratios) obtained for 25, 50% v/v and ‘as supplied’ 3-Phenylpropyl benzoate were 0.9, 1.6 and 6.3 respectively. As a SI of 3 or more was recorded for the highest concentration tested (as supplied), 3-Phenylpropyl benzoate was considered to have the potential to cause skin sensitization. Based on the results of this study the EC3 value is calculated to be 64.9% v/v. The SI for the positive control substance hexyl cinnamic aldehyde (HCA) was 6.5 which demonstrates the validity of this study.
Parameter:
other: disintegrations per minute (DPM)
Remarks on result:
other: see Remark
Remarks:
Group 2 Sham control: 1593.70 dpm and 199.21 dpm/node Group 3 vehicle: 1870.80 dpm and 233.85 dpm/node Group 4 25% v/v: 1698.00 dpm and 212.25 dpm/node Group 5 50% v/v: 3046.50 dpm and 380.81 dpm/node Group 6 "as supplied" 10060.30 dpm and 1257.54 dpm/node Group 7 HCA 25% v/v 12252.40 dpm and 1531.55 dpm/node
Interpretation of results:
sensitising
Remarks:
Migrated information Criteria used for interpretation of results: EU
Conclusions:
3-Phenylpropyl benzoate is regarded as a weak skin sensitizer. The EC3 value was calculated to be 64.9% v/v.
Executive summary:

The SI (test/control ratios) obtained for 25, 50% v/v and ‘as supplied’ 3-Phenylpropyl benzoate were 0.9, 1.6 and 6.3 respectively. As a SI of 3 or more was recorded for the highest concentration tested (as supplied), 3-Phenylpropyl benzoate was considered to have the potential to cause skin sensitization. Based on the results of this study the EC3 value is calculated to be 64.9% v/v. The SI for the positive control substance hexyl cinnamic aldehyde (HCA) was 6.5 which demonstrates the validity of this study.

3-Phenylpropyl benzoate is regarded as a potential skin sensitizer

Endpoint conclusion
Endpoint conclusion:
adverse effect observed (sensitising)
Additional information:

A weight of evidence assessment of the skin sensitization hazard of 3-PPB (Earl, 2015 see attached document below) has been generated to ensure that the correct decision is taken on the classification of 3-PPB as a skin sensitiser/non sensitiser. The report contains a review of LLNA accuracy of predictions, physicochemical and hazard data of the substance, its metabolites and impurities and closely related substances and computational prediction tools to detect skin sensitisation structural alerts. It was concluded on the basis of this weight of evidence that 3-PPB does not have significant skin sensitisation potential and should not be classified as a skin sensitizer.


Migrated from Short description of key information:
A LLNA study performed with 3-PPB is available and shows a weak positive response with the undiluted 3-PPB and a EC3 value of 64.9%. The results of the computational prediction tool DEREK used to interogate the skin sensitisation potential of 3-PPB and its analogue benzyl benzoate are also available and generated no structural alerts for 3-PPB but Alert 719 for benzyl benzoate.

Justification for selection of skin sensitisation endpoint:
One valid study performed to GLP and current guidelines

Respiratory sensitisation

Endpoint conclusion
Endpoint conclusion:
no study available

Justification for classification or non-classification

A LLNA study performed with 3-PPB is available and shows a weak positive response with the undiluted 3-PPB and a EC3 value of 64.9%, therefore 3 -phenyl propyl benzoate could be classified as a skin sensitiser 1B ( EC3 value > 2 %) according to EU Regulation 1272/2008. However the possibility for the LLNA result with 3-PPB to be a false positive was assessed in a weight of evidence approach described in the expert judgement report attached below (Earl, 2015). Like all hazard identification tests the LLNA has been associated with some false positive reactions. A brief review of the available literature identified several examples of substances which have been identified as false positives in the LLNA.   The comparison of 3-PPB with structurally similar substances showed a trend in structural alerts for skin sensitization using publicly available commonly used expert systems with the shorter alkyl chain between the 2 aromatic rings producing structural alerts in benzyl benzoate and phenyl benzoate. However, neither 3-PPB nor its likely metabolites are predicted to be skin sensitisers and experimental in vivo data obtained in LLNAs or in human studies with 3-PPB structural analogues demonstrated a weak or no sensitising effect. The weak positive response with only the undiluted 3-PPB applied (lower concentrations were negative) highlighted the possibility that the LLNA result for 3-PPB was either a false positive or there was an impurity in the substance that was tested which triggered the response. In view of the product analysis result which showed that the tested batch was 99.1% pure and the evaluation of the skin sensitization information on the typical range of product impurities/constituents, there was insufficient evidence to conclude the presence of a sensitising impurity in the tested product. The evidence supports the conclusion that the positive result for 3-PPB in the LLNA is likely to be a false positive.  Given the consistent evidence of lack of hazard from similar structures and metabolites of 3-PPB, the weight of evidence leads to the conclusion that 3-PPB is not a hazard for skin sensitization. Therefore no classification is proposed.