Phenyl 4-hydroxybenzoate

Endpoint summary

Description of key information

The skin sensitisation potential of the target substance phenylparaben was evaluated in a weight-of-evidence approach. Based on the results from an in vitro skin sensitisation assay, namely the loose-fit coculture-based sensitisation assay (LCSA), the test item phenylparaben must be considered as moderate skin-sensitiser based on the expression of the surface marker CD86.

Further evidence of the positive skin sensitisation potential of the target substance was predicted by QSAR, using the Skin Sensitization model CAESAR 2.1.6, which is implemented in the QSAR tool VEGA (version 1.2.4.). Phenylparaben is predicted to be a skin sensitizer. As a conclusion based on an assessment of the available data in a weight-of-evidence approach, the target substance must be considered as a skin-sensitiser. The classification of the target substance as skin sensitizer is also further supported by the QSAR Toolbox (Version 4.0), which revealed a positive structural alert for protein binding: Acylation (Protein Binding by OASIS v1.4 and Protein Binding by OECD).

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Reference 1

Endpoint:

skin sensitisation, other

Remarks:

in silico

Type of information:

(Q)SAR

Adequacy of study:

supporting study

Study period:

2017-09-04

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model, but not (completely) falling into its applicability domain, with adequate and reliable documentation / justification

Justification for type of information:

1. SOFTWARE
VEGA QSAR Models

2. MODEL (incl. version number)
Skin Sensitization model (CAESAR) 2.1.6
Core version: 1.2.4

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
Compound SMILES: O=C(Oc1ccccc1)c2ccc(O)cc2

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
- Defined endpoint: skin sensitization activity

5. APPLICABILITY DOMAIN
Global AD Index
AD index = 0.95
Explanation: the predicted compound is into the Applicabilty Domain of the model

Similar molecules with known experimental value
Similarity index = 0.903
Explanation: strongly similar compounds with known experimental value in the training set have been found.

Accuracy of prediction for similar molecules
Accuracy index = 1
Explanation: accuracy of prediction for similar molecules found in the training set is good.

Concordance for similar molecules
Concordance index = 1
Explanation: similar molecules found in the training set have experimental values that agree with the predicted value.

Model's descriptors range check
Descriptors range check = True
Explanation: descriptors for this compound have values inside the descriptor range of the compounds of the training set.

Atom Centered Fragments similarity check
ACF index= 1
Explanation: all atom centered fragment of the compound have been found in the compounds of the training set.

Interpretation of results:

Category 1 (skin sensitising) based on GHS criteria

Conclusions:

Phenyl 4-hydroxybenzoate is predicted to be a sensitizer.

Executive summary:

The test item was predicted to be a senitiser in the VEGA QSAR model. Strongly similar compounds with known experimental value were found in the training set (Similarity index = 0.903), and similar molecules found in the training set had experimental values that agree with the predicted value. The descriptors for the compound had values inside the descriptor range of the compounds of the training set and the accuracy of prediction for similar molecules found in the training set was considered good. Overall, the QSAR prediction is considered supporting evidence for a sensitising potential of the test item.

Reference 2

Endpoint:

skin sensitisation: in vitro

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Qualifier:

no guideline followed

Principles of method if other than guideline:

In the publication the results after conducting the loose-fit coculture-based sensitisation assay (LSCA) were provided. The coculture of primary human keratinocytes and allogenic dendritic cell-related cells (DC-rc) were used to emulate the in vivo situation of human skin.

GLP compliance:

not specified

Remarks:

Study is published and it is not further specified, if the GLP did apply

Type of study:

activation of dendritic cells

Specific details on test material used for the study:

- Source: TCI Deutschland GmbH, Eschborn, Germany

Details on the study design:

Skin sensitisation (In vitro test system) - Details on study design:
Keratinocytes were isolated from skin which was received as residual material from plastic surgery. PBMCs were enriched from buffy coats by density centrifugation. Cells were cocultured in serum-free KGM-2 (PromoCell, Heidelberg, Germany) on 12-well cell culture plates. Increasing concentrations of test substances were tested until significant cytotoxicity or decreased solubility occurred. Viability of cells was measured by 7-AAD staining. Each substance was tested with three different DC-rc/KC-donor pairs to account for interindividual variability. TNBS at a concentration of 100 µmol/L served as positive control.

FACS ANALYSIS:
FACS analysis was performed on a FACS Calibur flow cytometer (BD Biosciences). Cells were gated to a distinct population of DC-rc according to their scatter properties. Of three cell populations to be seen in a scatter dot plot, one is CD14+, one CD4+CD8+ and one CD86+. The latter is considered to be the DC-rc population and is therefore gated. The experiments were assumed to be reliable, when the addition of TNBS led to an at least 1.4-fold increase in CD86 expression compared to zero controls. Relative upregulation of CD86-expression was calculated by the following equation: MFI (CD86 of treated cells)/MFI (CD86 of vehicle control). 7-AAD staining was used to determine and exclude dead cells from the calculation. Dose-effect relationships for relative CD86-expression and viability as well as EC50 values were determined using GraphPadPrism software.

Categorisation:
For categorisation of sensitising potency, the substance concentration which led to a half-maximal increase in CD86-expression (EC50 sens) was assessed. Substances were categorized as follows: half-maximal increase in CD86-expression <12.5 µM: extreme; <50 µM: strong; <100 µM: moderate and >100 µM: weak. Substances failing to elicit significant rise in CD86-expression up to the maximum test concentration were deemed non-sensitisers.
Likewise, categorisation of irritative potency is based on the concentration that resulted in cell death of 50% (EC50vit) of DC-rc as compared to vehicle controls. Substances eliciting 50% cell death at concentrations below 50 µM were considered to be irritative. Those with an EC50vit value from 50 to 1000 µM were considered to be weakly irritative. Substances that did not reach the 50% threshold or with EC50(vit) values above 1000 µM were rated as non-irritative.

Key result

Run / experiment:

other: mean of triplicates

Parameter:

other: EC50sens (µmol/L)

Value:

69.23

Vehicle controls validity:

not specified

Negative controls validity:

not specified

Positive controls validity:

valid

Remarks on result:

positive indication of skin sensitisation

Other effects / acceptance of results:

Based on a EC50sens value of 69.23 µmol/L the test substance can be considered as moderate skin sensitising. The EC50vit was 416.17 µmol/L, indicating that the substance is weakly irritative.

Interpretation of results:

Category 1 (skin sensitising) based on GHS criteria

Conclusions:

Based on the results from an in vitro skin sensitisation assay, namely the loose-fit coculture-based sensitisation assay (LCSA), the test item phenylparaben must be considered as moderate skin-sensitiser.

Executive summary:

In a loose-fit coculture-based sensitisation assay (LCSA), keratinocytes were isolated from skin which was received as residual material from plastic surgery. PBMCs were enriched from buffy coats by density centrifugation. Cells were cocultured in serum-free KGM-2 (PromoCell, Heidelberg, Germany) on 12-well cell culture plates. Each substance was tested with three different DC-rc/KC-donor pairs to account for interindividual variability. TNBS at a concentration of 100 µmol/L served as positive control. Dose-effect relationships for relative CD86-expression and viability as well as EC50 values were determined using GraphPadPrism software. Based on a EC50sens value of 69.23 µmol/L, can the test substance be considered as moderate skin sensitising. The EC50vit was 416.17 µmol/L, indicating that the substance is weakly irritative.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (sensitising)

Additional information:

The skin sensitisation potential of the target substance phenylparaben was evaluated in a weight-of-evidence approach. Based on the results from an in vitro skin sensitisation assay, namely the loose-fit coculture-based sensitisation assay (LCSA), the test item phenylparaben must be considered as moderate skin-sensitiser based on the expression of the surface marker CD86.

Further evidence of the positive skin sensitisation potential of the target substance was predicted by QSAR, using the Skin Sensitization model CAESAR 2.1.6, which is implemented in the QSAR tool VEGA (version 1.2.4.). Phenylparaben is predicted to be a skin sensitizer. As a conclusion based on an assessment of the available data in a weight-of-evidence approach, the target substance must be considered as a skin-sensitiser. The classification of the target substance as skin sensitizer is also further supported by the QSAR Toolbox (Version 4.0), which revealed a positive structural alert for protein binding: Acylation (Protein Binding by OASIS v1.4 and Protein Binding by OECD).

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Based on the available data, classification as H317, Skin Sens 1 is warranted for the target substance.