Within the skin sensitisation adverse outcome pathway, the first key event is based on the premise that a chemical can become a skin sensitiser via interaction with skin proteins, forming a hapten that is recognised by cells of the immune system and triggers a response.

Testing novel chemicals and formulations for this Molecular Initiating Event (MIE), haptenation, is an essential aspect of skin sensitisation safety testing and risk assessment. Our GLP Direct Peptide Reactivity Assay (DPRA), enables our clients to quickly determine if their chemicals present these challenges, and generate data opposite the MIE stage of the sensitisation AOP.

You can find out more about our DPRA service here: https://lnkd.in/dyVENpn

The use of the OECD 442C Direct Peptide Reactivity Assay (DPRA) is a key first stage in determining whether a chemical (mono- or multi-constituent), product or formulation presents a skin sensitisation safety concern. The DRPA focusses on the detection of test substances that covalently bind peptides in the skin, creating a hapten, which triggers downstream events in the AOP. This molecular initiating event is then linked to subsequent activation of Key Stage 2 (keratinocyte activation and inflammation covered by OECD 442D, KeratinoSens™), Key Stage 3 (dendritic cell activation, OECD 442E, h-CLAT) and Key Stage 4 (T-cell activation, OECD 442A, LLNA in vivo test). As DPRA detects the MIE, it is a critical aspect of understanding whether a test substance presents sensitisation toxicological risk.

The DPRA uses HPLC techniques, where the test substance is mixed with either cystine or lysine peptides. These mixtures are then analysed to assess depletion of the cystine or lysine peptide from the HPLC read-out compared to the calibration curve for each peptide in absence of test substance. Controls are included to mitigate the impact of co-elution or chemical interference effects. A substance demonstrating clear depletion of either peptide in this method presents is a strong indication of potential skin sensitisation hazard. Our laboratory has established proficiency for this method, with correct classification of all substances as sensitisers or non-sensitisers as per the OECD 442C guideline (see here https://gentronix.co.uk/services/skin-sensitisation/direct-peptide-reactivity-assay).

When combined with either KeratinoSens™ OECD 442D and/or h-CLAT OECD 442E studies, the data generated in DPRA can be supplemented to either confirm that the test substance presents a human skin sensitisation safety issue (positive result in at least 2 of the 3 tests) or, that it may not be considered as being of skin sensitisation risk (negative findings in both of the follow-up KeratinoSens™ and h-CLAT studies).

Our team of skin sensitisation scientists are experienced in supporting clients generate GLP study data in OECD 442C DPRA and the other supporting endpoints. Working with our clients we can optimise formulation approaches, interpret study findings, and advise on testing strategies to manage DPRA positive results.