Terpene Hydroperoxides as Lipid Peroxidation Inducers: Biomimetic and HaCaT Cell Studies in Allergic Contact Dermatitis.

BACKGROUND: Terpene hydroperoxides are oxidation products of fragrance terpenes commonly found in cosmetic and household products. They are moderate to strong contact allergens associated with allergic contact dermatitis (ACD). Through the cleavage of their oxygen-oxygen bond, they have the potential to induce lipid peroxidation (LPO). However, the role of oxidised lipids in the context of ACD is largely unexplored. OBJECTIVES: Herein, the capacity of terpene hydroperoxides derived from linalool (Lin-6/7-OOH), geraniol (Ger-6/7-OOH), and limonene (Lim-2-OOH) to induce LPO was evaluated using liposomes in a biomimetic metal-catalysed oxidation system. LPO products were identified and quantified by liquid chromatography-mass spectrometry (LC-MS) and Tandem MS (MS/MS). The C11-BODIPY(581/591) ratio-fluorescence probe was also used to assess the capacity of terpene hydroperoxides to cause LPO in vitro using a human epidermal keratinocyte cell line (HaCaT). RESULTS: LC-MS/MS analysis identified 14 LPO products (long-chain and short-chain) formed under metal-catalysed oxidation mediated by terpene hydroperoxides. All hydroperoxides tested at 50 mM caused significant LPO, with Lim-2-OOH exhibiting exceptionally high oxidising potential. The C11-BODIPY(581/591) ratio-fluorescence assay also revealed higher oxidation associated with Lim-2-OOH. CONCLUSIONS: This work shows the ability of terpene hydroperoxide allergens to cause LPO, raising the possibility that LPO products may act as effectors in the pathogenesis of ACD.