N-butyl 4-oxopentanoate

Endpoint summary

Description of key information

non-skin sensitiser

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

The sensitising potential of the test item was assessed in the in vitro assay by quantifying changes in the expression level of the two cell surface markers CD86 and CD54, which are associated with the process of activation of monocytes and dendritic cells. The test was performed according to the OECD Guideline 442E. Two valid experiments with a treatment period of 24 hours were performed. In the experiments, the highest nominal applied concentration (1000 µg/ml) was chosen based on the results obtained in the pre-test. A geometric series (factor 1.2) of 7 dilutions thereof was prepared and tested. As solvent control for the test item, DMSO was used in a final concentration of 0.2 % in culture medium. As positive control, DNCB was used. Prior to the study, the cells used in the experiments were checked in a reactivity check and were found to be suitable for the experiments. All acceptance criteria were met and therefore, the study was considered valid. In both experiments all of the tested concentrations of the test item didn´t show any cytotoxicity. The RFI of CD86 was not ≥ 150 % as well as the RFI of CD54 was not ≥ 200 % at any tested concentration. Therefore, in accordance with the classification criteria the result of this study is negative. In conclusion, it can be stated that under the experimental conditions of this study, the test item, was negative in the h-CLAT and is therefore considered not to have the potential to activate dendritic cells.

In another study, the potential of the Similar Substance 02 (Justification for Read Across is given in Section 13 of IUCLID) to activate the Nrf2 transcription factor (sensitizing potential) was evaluated by using the LuSens cell line according to the OECD Guideline 442D and EU Method B60.

The assay included a cytotoxicity range finder test (CRFT) and two independent experiments (experiment I and II) with a treatment period of 48 h. In the experiments, the highest nominal applied concentration (2000 μM) was chosen based on the results obtained in the CRFT. A geometric series (factor 1.2) of eleven dilutions thereof was prepared. Precipitation of the test item was not visible in any of the experiments. DMSO was used as solvent control and medium no. 3 as growth control (blank medium control). Lactic acid (5000 μM) was used as negative control and EGDMA (120 μM) as positive control. No substantial and reproducible dose-dependent increase in luciferase induction equal or above 1.5 fold was observed in both experiments up to the maximal tested concentration of the test item. The test item, was negative and is therefore considered not to have the potential to activate the Nrf2 transcription factor.

Considering the results of both in vitro studies, in a weight-of-evidence approach, the substance has no skin sensitisation potential.

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

According to the CLP Regulation (EC) No. 1272/2008:

Annex I: 3.4.2.2. Skin Sensitisers Annex I: 3.4.2.2.1. Hazard categories

Annex I: 3.4.2.2.1.1. Skin sensitisers shall be classified in Category 1 where data are not sufficient for sub-categorisation.

Annex I: 3.4.2.2.1.2. Where data are sufficient a refined evaluation according to section 3.4.2.2.1.3 allows the allocation of skin sensitisers into sub-category 1A, strong sensitisers, or sub-category 1B for other skin sensitisers.

Annex I: 3.4.2.2.1.3. Effects seen in either humans or animals will normally justify classification in a weight of evidence approach for skin sensitisers as described in section 3.4.2.2.2. Substances may be allocated to one of the two sub-categories 1A or 1B using a weight of evidence approach in accordance with the criteria given in Table 3.4.2 and on the basis of reliable and good quality evidence from human cases or epidemiological studies and/or observations from appropriate studies in experimental animals according to the guidance values provided in sections 3.4.2.2.2.1 and 3.4.2.2.3.2 for sub-category 1A and in sections 3.4.2.2.2.2 and 3.4.2.2.3.3 for sub-category 1B.

Based on the OECD442D and OECD442E results the substance does not activate the dendritic cells,does not have the potential to bind to peptides/protein nor can activate the Nrf2 transcription factor and thus does not satisfy the key event 2 and key event 3. No experimental data is available for the evaluation of the key event 1 (Peptide/protein binding capacity), however, based on the QSAR Toolbox v.4.0 for Protein binding potency Lys and Cys, the substance is not reactive. According to the Guidance on the CLP criteria (ECHA, version 5.0, July 2017) validatedin vitro/in chemicomethods exist with the aim to identify a sensitising potential of a chemical. These include OECD TG442C (Peptide/protein binding), TG442D (keratinocyte response) and TG 442E (monocytic/dendritic cell response). Thein vitro/in chemicotests are not regarded as stand alone tests and the result from such a test should be used together with other data in an overall WoE assessment. Further, at present there is no agreed strategy on how to usein vitro/in chemicomethods for direct estimation of sensitising potency, but data from such tests can be used in a WoE assessment together with other data in order to assess skin sensitisation potency. According to Chapter R7a-Endpoint specific guidance (ECHA, version 16, July 2017) if information from test method(s) addressing one or two of the key events in column 1 already allows classification and risk assessment according to point 8.3, studies addressing the other key event(s) need not be conducted.

As per Bauch (2012) statistics revealed that the h-CLAT assay has a sensitivity of 75 % or 72 %, a specificity of 77 % or 76 %, and an overall accuracy of 76 % or 74 % when compared to human data or the LLNA, respectively. Thein chemicomethod offered a sensitivity of 89 % or 81 %, a specificity of 82 % or 76 % and an overall accuracy of 86 % or 79 % when compared to human data or the LLNA, respectively. For the LuSens assay, the statistics estimated a sensitivity of 89 % or 81 %; a specificity of 77 % or 71 % and an overall accuracy of 84 % or 77 % when compared to the human data or LLNA, respectively. It seems that h-CLAT sensitivity is slightly lower than the one of the other two in vitro methods used.

Two out of three in vitro tests result negative; the QSAR Toolbox did not identify any alert for skin sensitisation for the key event 1.

Based on the above considerations, the substance is considered to be non-sensitiser and thus a classification for skin sensitisation as per the CLP Regulation (EC) No.1272/2008 is not attributed.

Bauch C, Kolle S.N, Ramirez T, Eltze T, Fabian E, Mehling A, Teubner W, van Ravenzwaay B, Landsiedel R. Putting the parts together: Combining in vitro methods to test for skin sensitizing potentials. Regulatory Toxicology and Pharmacology 63 (2012) 489–504v