Squalene is one of the main skin targets of environmental oxidative factors. Squalene by-products, mostly under peroxidized forms, are key mediators of skin reactions (comedogenesis, inflammation and wrinkling) to extrinsic stressors. However, the skin hydrolipid mantel is a relevant source of several other peroxidated intermediates also leading to many adverse effects. We first developed a lipid mix containing oleic acid 27.3%, behenic acid 4.5%, triolein 25.5%, oleyl stearate 23.5%, squalene 11.1% and cholesterol 8.1%, close to the composition found in cutaneous stratum corneum. We then exposed the artificial lipid mix and squalene alone to cigarette smoke (3R4F, University of Kentucky, UK) using a homemade pollution box. Finally, we applied the oxidized lipids onto reconstructed epidermis 3D cultures to investigate the epidermal response. By measuring the peroxide index, we confirmed that cigarette smoke induced oxidation of both artificial lipid mix and squalene alone. We showed oxidized squalene provoked no cell mortality in 3D cultures which exhibited a proper epidermal morphology. In contrast, cell viability of 3D cultures dropped to 44% in presence of the oxidized lipid mix and pyknotic nuclei were found within the reconstructed epidermis. Finally, we highlighted the triggering of an inflammatory response, mainly composed of chemokines, only in oxidized lipid mix-treated 3D cultures. Although oxidized squalene is described as the marker of environmental pollution studies, oxidization of artificial lipid mix really appears to be a more reliable process compared with other pollution-induced skin assaults. From an applied point of view, the oxidization of artificial lipid mix appears to be a realistic model for assessing active ingredient efficacy aiming at preventing – or protecting – such oxidation-induced chemical alterations.

Use of artificial lipid mix as a new method to test efficacy of active ingredients directed towards skin protection. Comparison with the reference lipid squalene