Platinum dioxide

Endpoint summary

Description of key information

Platinum dioxide was non-sensitising in a mouse local lymph node assay (LLNA), conducted according to OECD Test Guideline 442B and to GLP (Haferkorn 2019 ).

 

No respiratory tract sensitisation data are available.

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Endpoint:

skin sensitisation: in vitro

Data waiving:

study technically not feasible

Justification for data waiving:

an in vitro skin sensitisation study does not need to be conducted because the available in vitro test methods are not applicable for the substance and therefore an in vivo skin sensitisation study was conducted

Justification for type of information:

Compound name Molecular formula CAS number Skin sensitisation classification
Platinum dioxide PtO2 1314-15-4 Not Classified

Adhering to ECHA “How to use new or revised in vitro test methods to address skin sensitisation”1 If a conclusion on classification cannot be made based on existing information or the column 2 adaptation criteria cannot be applied, the following information in chemico/in vitro test(s) addressing each of the following key events needs to be performed:
1) molecular interaction with skin proteins- OECD (2018), Test method EU B.59 / OECD TG 442C – Direct Peptide Reactivity Assay (DPRA)2
2) inflammatory responses in keratinocyte- OECD (2018), Test No. 442D: In Vitro Skin Sensitisation ARE-Nrf2 Luciferase Test Method4
3) activation of dendritic cells - OECD (2018), Test No. 442E: In Vitro Skin Sensitisation: In Vitro Skin Sensitisation assays addressing the Key Event on activation of dendritic cells on the Adverse Outcome Pathway for Skin Sensitisation5
After these steps, no new in vivo test is necessary unless the in chemico/in vitro tests available are not applicable for the test substance.

Applicability of available in vitro assays
- the assays OECD442 (C, D and E) all have their limitations as in vitro methods inorganic salts containing a metal ion, primarily because metals act via a different adverse outcome pathway as the IATA is built on. The IATA adverse outcome pathway is initiated by covalent binding to proteins, whereas metals and metal substances interact by different mechanisms with cell structures (e.g. formation of coordination complexes)
- the DPRA (OECD 442C) assay measures peptide (cysteine and lysine) depletion as an indirect indicator of peptide reactivity. The OECD TG states that “this test guideline is not applicable for the testing of metal compounds since they are known to react with proteins with mechanisms other than covalent binding”. Consequently, we can not reliably use this system.
- the OECD 442D ARE-Nrf2 Luciferase Test shows an unknown capacity to correctly identify moderate and weak sensitisers. Further, chemicals activating the Keap1-Nrf2-ARE pathway by other mechanisms than covalent binding to cysteine residues of the Keap1-protein (i.e. electrophilic/oxidative stress) might lead to false positive results in the test – oxidative stress is a common effect caused by metal substances.
- in the OECD 442E h-CLAT assay validation studies, only two metal substances (nickel chloride and beryllium sulfate) which are known sensitisers were tested. Beryllium sulfate showed inconsistent results, whereas nickel chloride showed a positive result in the h-CLAT test. ECVAM stated that some substances, including metal salts, might be excluded from the empirical applicability domain, but to confirm this statement further testing on the applicability domain is required.
As the available in chemico/in vitro methods, as specified above, provide information only on one mechanistic event, i.e. key event from the AOP, combinations of the methods are needed and should be used within a weight-of-evidence approach to conclude on the skin sensitisation hazard potential. Information that may complement the weight-of-evidence may be derived from test methods addressing other biological mechanisms based on skin sensitisation or non-testing methods, e.g. read-across or in silico approaches.

Read-across / in silico approaches
Currently, computational methods are generally not applicable to metals. Their predictivity and applicability are limited by the quality and quantity of available human, animal, and non-animal data.7

OECD Toolbox
The substances in question do not fall within the QSAR toolbox applicability domain and therefore QSAR toolbox cannot be used in this instance to help predict the skin sensitisation potency of the substances.

In vitro WoE (Weight of evidence) approach
The OECD accepted weight-of-evidence approach according to their Guidance Document on the Reporting of Defined Approaches and Individual Information Sources to be Used within Integrated Approaches to Testing and Assessment (IATA) for Skin Sensitisation3 is to use an AOP - based "2 out of 3" weight-of-evidence (WoE)/ integrated testing strategy (ITS) approach to skin hazard identification ("2 out of 3 – Sens ITS"; BASF).
Due to lack of appropriate in vitro assays for metals this weight-of-evidence approach (as seen in “Applicability of available in vitro assays” headed section) cannot be applied.

Hazard and risk assessment
There is also a difficulty in the use of in vitro methods for hazard and risk assessment purposes.
- the classification criteria in regulation 1272/20088 do not provide guidance on how to interpret the outcome of the in vitro assays
- section 8.3, column 1 of the REACH regulation states that testing shall allow “a conclusion whether the substance is a skin sensitiser and whether it can be presumed to have the potential to produce significant sensitisation in humans (Cat. 1A), and risk assessment, where required.” Section 8.3.1, column 2 foresees that “the(se) test(s) do not need to be conducted if the available in vitro/in chemico test methods are not applicable for the substance or are not adequate for classification and risk assessment according to point 8.3.”. In the absence of clear classification criteria for the in vitro systems, one may conclude that the data is not adequate for classification and risk assessment.

Potency assessment for classification purposes
In Vitro methods are available to address the endpoint of skin sensitisation as described in OECD IATA guidance Document 256¬3 & ECHA 2018 “How to use new or revised in vitro test methods to address skin sensitisation”1, although these methods are not currently suitable to establish skin sensitisation potency.
“Currently, there is no generally approved and/or validated way how to combine results obtained from in chemico and in vitro methods to assess the skin sensitisation potency. Some approaches on how to combine the in vitro data have been described in the ECHA Guidance (Appendix r.7.3-4) and in the OECD guidance Document 256, Annex 1. Due to this, an OECD project has been launched in 2107 to assess how in vitro data obtained from these three key events and other data can be combined to conclude on the skin sensitisation potency classification with a defined approach.1”
Therefore, to establish skin sensitisation potency, which is required for registration, in vitro testing is also not appropriate.

Suggested Platinum dioxide skin sensitisation testing
As the ECHA guidance for new or revised in vitro test methods to address skin sensitisation as discussed above has been deemed not appropriate for Platinum dioxide, it is advised to conduct the following assay in order to establish skin sensitisation potential of the compounds for hazard classification and risk assessment purposes:
Skin Sensitisation: Local Lymph Node Assay: BrdU-ELISA, OECD 442B (2010)6

References
1 ECHA (2018), “How to use new or revised in vitro test methods to address skin sensitisation” https://echa.europa.eu/documents/10162/21650280/oecd_test_guidelines_skin_sensitisation_en.pdf
2 OECD (2015), Test No. 442C: In Chemico Skin Sensitisation: Direct Peptide Reactivity Assay (DPRA), OECD Guidelines for the Testing of Chemicals, Section 4, OECD Publishing, Paris, https://doi.org/10.1787/9789264229709-en.
3 OECD (2017), Guidance Document on the Reporting of Defined Approaches and Individual Information Sources to be Used within Integrated Approaches to Testing and Assessment (IATA) for Skin Sensitisation, OECD Series on Testing and Assessment, No. 256, OECD Publishing, Paris, https://doi.org/10.1787/9789264279285-en.
4 OECD (2018), Test No. 442D: In Vitro Skin Sensitisation: ARE-Nrf2 Luciferase Test Method, OECD Guidelines for the Testing of Chemicals, Section 4, OECD Publishing, Paris, https://doi.org/10.1787/9789264229822-en.
5 OECD (2018), Test No. 442E: In Vitro Skin Sensitisation: In Vitro Skin Sensitisation assays addressing the Key Event on activation of dendritic cells on the Adverse Outcome Pathway for Skin Sensitisation, OECD Guidelines for the Testing of Chemicals, Section 4, OECD Publishing, Paris, https://doi.org/10.1787/9789264264359-en.
6 OECD (2018), Test No. 442B: Skin Sensitization: Local Lymph Node Assay: BrdU-ELISA or –FCM, OECD Guidelines for the Testing of Chemicals, Section 4, OECD Publishing, Paris, https://doi.org/10.1787/9789264090996-en.
7 Wilm, A., Kühnl, J. and Kirchmair, J., 2018. Computational approaches for skin sensitization prediction. Critical reviews in toxicology, 48(9), pp.738-760.
8 Regulation (EC) No 1272/2008 of the European Parliament and of the Council of 16 December 2008 on classification, labelling and packaging of substances and mixtures, amending and repealing Directives 67/548/EEC and 1999/45/EC, and amending Regulation (EC) No 1907/2006

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

No relevant human skin sensitisation data were identified.

In vitro testing for skin sensitisation is not possible. Therefore, an in vivo assay has been performed.

The skin sensitising potential of platinum dioxide,hydrate has been assessed in a GLP mouse local lymph node assay (LLNA): BrdU-ELISA, conducted according to OECD Test Guideline 442B. Following a preliminary range-finding study to assess irritancy, female mice CBA/JN mice (5/group) were treated topically with 0, 5, 10 and 25% test item (in propylene glycol) on three consecutive days.There was no treatment on test days 4, 5 and 6.On day 6, cell proliferation in the local lymph nodes was measured by incorporation of injected 5-bromo-2-deoxyuridine (BrdU) using ELISA.The cell proliferation in the local lymph nodes was determined by measuring the BrdU content with BrdU-ELISA and the values obtained were used to calculate Stimulation Indices (SI).

The stimulation indices of the test item treated groups calculated for the BrdU labelling index did not exceed the threshold value of 1.6. Hence, there was no clear evidence of cell proliferation and the test item is classified as not skin sensitising.

There were no deaths and no systemic clinical signs or effects on body weights were observed during the study. The ear weight (punch biopsies) and the difference of ear thickness on test day 3 and test day 6 compared to the vehicle control were not or only slightly increased, i.e. no skin irritating properties were noted.

Treatment with the positive control item caused a statistically significant increase in the BrdU labelling index, compared to the negative control, and a Stimulation Index in excess of the threshold value of 1.6. Therefore, the study can be regarded as valid.

In conclusion, under the present test conditions, the test item platinum dioxide,hydrate did not reveal any skin sensitising properties in the local lymph node assay: BrdU-ELISA.

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information:

No respiratory tract sensitisation data are available. A new study was not conducted as no standard and validated test method is available and it is not a REACH Standard Information Requirement.

Justification for classification or non-classification

Based on the results of the available and reliable

mouse local lymph node assay (LLNA): BrdU-ELISA conducted according to OECD Test Guideline 442B and under GLP, platinum dioxide

does not warrant classification for skin sensitisation, according to EU CLP criteria (EC 1272/2008).