Relationship between changes in skin lipids by ultraviolet exposure and the cell toxicity

Abstract

The oxidative decomposition of skin lipids by UV exposure and its cell toxicity were studied in vivo and in vitro, using guinea pigs, to investigate the role of oxidative damage in cell membranes and mitochondria in nuclear genome DNA damage resulting in skin cell death by ultraviolet (UV) exposure. Two new methods were developed for this research: selective methylation by trimethylsilyldiazomethane (TMSCHN2) of free fatty acids in crude skin lipids for gas chromatography-mass spectrometry (GC-MS) analysis, and the improvement of the thiobarbituric acid (TBA) reaction for lipid peroxide analysis, which was obtained by adding 0.01% BHT and 1 mM EDTA, an antioxidant additive, into the reaction system described by Ohkawa. The following findings were noted: 1. Using an optical microscope, the infiltration of inflammatory cells such as neutrophils, lymphocytes and monocytes was noted after skin tissue was exposed to UV. 2. The increase of lipid peroxide in exposed areas was small. In the epidermis the increase was about 2 times higher than the non-exposed areas. 3. The fragments of lipid were generated in accordance with the increase of free fatty acids (C16:0, C18:1,:2, C18:0) in the surface of the exposed skin by GC-MS precise assay, and the level of 7-dehydrocholesterol was decreased. 4. The skin homogenate received peroxidation by ultraviolet more easily than living skin, and its peroxidation was inhibited with fat-soluble antioxidative agents such as flavonoids, BHT, BHA, and vitamin E and the metal chelating agent such as Fenton reaction inhibitor as expected; however, it was promoted by water soluble antioxidative agents such as glutathione and vitamin C, which are useful to the human body. 5. Steroids and nonsteroidal anti-inflammatory drugs (NSAIDs) such as indomethacin and aspirin, had no inhibitory effect on lipid peroxidation by ultraviolet as properties of chemicals.