[55] Noninvasive techniques for measuring oxidation products on the surface of human skin

Oxidative stress is defined as the result of an imbalance between prooxidants and antioxidants in living cells. This imbalance leads to molecular damage (peroxidation of lipids, metal-catalyzed carbonylation of proteins, and oxidative damage to DNA) as well as to modifications in cellular morphology (zeiosis, modification of chromatin structure) and tissue alterations. One way to illustrate the physiological consequences of oxidative stress imposed on human skin and the relevance of antioxidants is to analyze histology sections before and after an oxidative stress in the presence or absence of antioxidants. Morphological modifications of the ultraviolet-exposed epidermis are remarkable, particularly the loss of cell-to-cell contact and intercellular spongiosis. Protection afforded by the antioxidants against these morphological changes is nearly complete. However, histology methods are invasive and impractical for studies involving large cohorts of volunteers. Noninvasive techniques are therefore preferred for the analysis of the molecular consequences of the oxidative stresses induced by UVA, singlet oxygen, or ozone. For example, one might be interested in learning about the formation of oxidation products on the surface or in the different layers of the epidermis exposed to these environmental factors and its inhibition by antioxidants. This chapter describes some methodologies for investigating the effects of prooxidants and antioxidants on human epidermis.