Skin sensitisation to fragrance hydroperoxides: interplay between dendritic cells, keratinocytes and free radicals.

Skin sensitisation to hydroperoxides (R-OOHs) of the commonly used fragrance terpenes limonene, linalool and citronellol is frequently reported. R-OOHs are believed to initiate the process leading to sensitisation and allergic contact dermatitis (ACD) through mechanisms involving radical intermediates. Thus, radical intermediates, keratinocytes and dendritic cells (DC) may act in concert to initiate the process.To evaluate individual DC activation profiles in the context of keratinocytes by R-OOHs with regard to frequency, specificity and magnitude of upregulation.2D and 3D cocultures with keratinocytes/reconstructed human epidermis (RHE) and DC to evaluate cell surface levels of the costimulatory molecules CD86, CD80 and the adhesion molecule CD54 on cocultured DC. Analysis of radical formation from limonene hydroperoxides in RHE by EPR-ST.R-OOHs induce donor-dependent DC activation. Major differences were found between the limonene-OOHs. Limonene-1-OOH was stronger with respect to both, frequency and magnitude of responses. Using a 3D coculture model, no DC activation was detected after topical application of 0.2% limonene-OOHs (20 µg/cm2 ), while 1.2% limonene-1-OOH or 2% limonene-2-OOH induced DC activation. Furthermore, we demonstrated differences in the formed carbon and oxygen radicals from the limonene-OOHs using RHE, mimicking what may happen in vivo.We report clear individual differences in DC maturation by the most important hydroperoxides. Both, response rates and magnitude of response indicate that very small structural alterations in the hydroperoxides are translated into specific DC responses. In addition, we provide more insights into the amounts of hydroperoxides that are able to activate DC and induce sensitisation.

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