Prediction of skin sensitization potency sub-categories using peptide reactivity data

- Assigning skin sensitizers to CLP/GHS potency sub-categories 1A or 1B
- Three methods, which are based on reactivity, were assessed.
- The standard DPRA was not sufficiently accurate.
- The quantitative DPRA achieved an accuracy of 83% (n = 36) compared to LLNA data.
- The kinetic DPRA achieved a high accuracy of 92% compared to LLNA data (n = 38).

While the skin sensitization hazard of substances can already be identified using non-animal methods, the classification of potency sub-categories GHS-1A and 1B is still challenging. Potency can be measured by the dose at which an effect is observed; since the protein-adduct formation is determining the dose of the allergen in the skin, peptide reactivity was used to assess the potency.The Direct Peptide Reactivity Assay (DPRA; one concentration and reaction-time) did not sufficiently discriminate between sub-categories 1A and 1B (56% accuracy compared to LLNA data, n = 124). An extended protocol termed 'quantitative DPRA' (three concentrations and one reaction-time), discriminated sub-categories GHS 1A and 1B with an accuracy of 81% or 57% compared to LLNA (n = 36) or human (n = 14) data, respectively. The analysis of the Cys-adducts was already sufficient; additional analysis of Lys-adducts did not improve the predictivity. An additional modification, the 'kinetic DPRA' (several concentrations and reaction-times) was used to approximate the rate constant of Cys-peptide-adduct formation. 35 of 38 substances were correctly assigned to the potency sub-categories (LLNA data), and the predictivity for 14 human data was equally high.These results warrant the kinetic DPRA for further validation in order to fully replace in vivo testing for assessing skin sensitization including potency sub-classification.

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