The Direct Peptide Reactivity Assay (DPRA) is an in chemico skin sensitisation test, which addresses the molecular initiating event in the Adverse Outcome Pathway (AOP), which is mediated by a covalent binding of the potential skin sensitiser to cysteine or lysine residues on proteins. A skin sensitiser is a substance that will lead to an allergic response following repeated skin contact as defined by the United Nations Globally Harmonized System of Classification and Labelling of Chemicals (UN GHS).
In the DPRA assay, fixed amounts of either a cysteine- or a lysine-containing peptide is incubated with the test chemical for 24 hours at 22.5-30°C. A reaction of the test chemical with the peptide will lead to a depletion of the amount of the original (non-reacted) amount of peptide in the reaction mixture. The relative extent of this depletion (determined by UV-VIS HPLC analysis at 220 nm) allows the assigning the test chemical to one of reactivity classes used to support the discrimination between sensitisers and non-sensitisers.
Typical examples of standard curves for the Cysteine and Lysine peptides used in DPRA tests.