Development of a peptide reactivity assay for screening botanicals and natural substances: Proof of concept studies.

Consumer products containing botanicals or natural substances (BNS) are often preferred because there is a perception that 'natural' is safe. As with any product ingredient, a thorough safety assessment must be conducted, including a determination of skin sensitization potential. A modification of the Peroxidase Peptide Reactivity Assay (PPRA) was explored for screening BNS (B-PPRA) for their reactivity to a model cysteine peptide. The PPRA incorporates a horseradish peroxidase‑hydrogen peroxide (+HRP/P) oxidation system for the activation of potential pre- and pro-haptens. BNS test materials contained <2% botanical constituent in either glycerin/water or propylene glycol/water. Stock solutions prepared in acetonitrile were diluted to 8 working concentrations. Direct reactivity was determined in reaction mixtures containing peptide and deferoxamine in potassium phosphate buffer. Enzyme-mediated reactivity determinations were performed with addition of +HRP/P. Initial studies demonstrated that results were reproducible and impact of carrier low. To determine the sensitivity of the assay, experiments were conducted with chamomile extract spiked with three sensitizers. Peptide depletion was observed in the +HRP/P reaction mixtures with isoeugenol spikes as low as 0.05%. The B-PPRA shows promise as a screening method for skin sensitization potential and could become part of a framework for the skin sensitization safety assessment of BNS. • Botanical natural substances (BNS) are preferred in consumer products as there is a perception that 'natural' is safe. • A safety assessment, including skin sensitization evaluation, must be conducted also for BNS containing products. • The Peroxidase Peptide Reactivity Assay (PPRA) was adapted for screening BNS semi quantitively for their reactivity. • The proof-of-concept studies with 6 BNS demonstrated reproducibility, low carrier impact and sufficient sensitivity. • A framework for skin sensitization safety assessment of BNS using B-PPRA will be developed. [ABSTRACT FROM AUTHOR]