Skin surface lipids photo-oxidation: A vibrational spectroscopy study

Skin surface lipid (SSL) film is a mixture of sebum and epidermal lipids protecting the skin from the effects of the environment such as solar radiation. SSLs are a suitable target and scavenger for all reactive oxygen species (ROS) generated in the skin. In the SSLs, vitamin E has been identified as one of the main antioxidants that can capture ROS. This paper is the third part of a global study that evaluates the effect of solar radiation on the lipid classes that constitute SSLs. In the first two parts, the effect of solar radiation on fatty acids and triglycerides was studied using vibrational spectroscopy. In this part, the effect on the other lipid classes such as squalene (SQ), cholesterol (Chol), and wax ester (WE) (Palmitoleyl Palmitate) was studied and then the behavior of vitamin E under solar radiation was monitored. Finally, SSLs were irradiated and analyzed using vibrational spectroscopy and HT-GC/MS to respectively follow the oxidation process and to identify the first target of solar radiation in SSLs. When irradiated alone, SQ oxidation process was detectable only after 2430 J/cm(2) dose. Similar observations were obtained for vitamin E (after 1620 J/cm(2)). No changes were observed on the cholesterol and on the wax ester (Palmitoleyl Palmitate). In contrast, when extracted human SSLs film was irradiated, the more marked modifications were observed on SQ. This confirmed the antioxidant role of SQ by scavenging free radicals generated from the oxidation of polyunsaturated fatty acids (PUFA).