DEPLETION OF HUMAN STRATUM-CORNEUM VITAMIN-E - AN EARLY AND SENSITIVEIN-VIVO MARKER OF UV INDUCED PHOTOOXIDATION

As the outermost barrier of the body, the stratum corneum (SC) is freq uently and directly exposed to a pro-oxidative environment, including ultraviolet solar radiation (UVR). Therefore, we hypothesized that the SC is susceptible to WR induced depletion of vitamin E, the major lip ophilic antioxidant. To test this, we investigated (i) the susceptibil ity of SC tocopherols to solar simulated UVR in hairless mice, (ii) th e baseline levels and distribution patterns of tocopherols in human SC , and (iii) the impact of a suberythemogenic dose of solar simulated W R on human SC tocopherols. SC tocopherol levels were measured by high performance liquid chromotography analysis of SC extracts from tape st rippings. In murine SC, overall tocopherol concentrations were determi ned, whereas in human SC, 10 consecutive layers were analyzed for each individual. The results on SC tocopherols demonstrated (i) their conc entration dependent depletion by solar simulated UVR in hairless mice; (ii) a gradient distribution within untreated human SC, with the lowe st levels at the surface (alpha-tocopherol 6.5 +/- 1.4 pmol per mg, an d gamma-tocopherol 2.2 +/- 1.3 pmol per mg) and the highest levels in the deepest layers (alpha-tocopherol 76 +/- 12 pmol per mg, and gamma- tocopherol 7.9 +/- 3.7 pmol per mg, n = 10; p < 0.0001); and (iii) the depletion of tocopherols in human SC by a single suberythemogenic dos e of solar simulated WR (alpha-tocopherol by 45%, and gamma-tocopherol by 35% as compared with controls; n = 6; both p < 0.01). These result s demonstrate that the SC is a remarkably susceptible site for UVR ind uced depletion of vitamin E.