Retinol and retinyl ester epidermal pools are not identically sensitive toUVB irradiation and anti-oxidant protective effect

Background: UV irradiation can deplete epidermal vitamin A, thus the hypoth esis that UV-induced depletion of vitamin A in sun-exposed skin is involved in the pathogenesis of skin cancers and skin ageing. Objectives: In this s tudy we addressed two questions: (1) Are retinol (ROL) and retinyl esters ( RE) - the two predominant forms of vitamin A - equally sensitive to the act ion of UVB, and (2) could the depletion be prevented by antioxidants? Metho ds: Hairless mice were irradiated with a single UVB dose, corresponding to the maximum of ROL and RE absorption. Retinoid content, enzyme activities c atalysing the esterification of ROL (ARAT and LRAT) and the hydrolysis of R E (REH), as well as retinol-binding protein (CRBP-1) expression were determ ined in the epidermis. Results: A single UVB dose induced a rapid, dose-dep endent decrease in both ROL and RE in the epidermis of hairless mice, with partial replenishment after 24 h. The dose-response curve for ROL showed a high sensitivity to UV at doses not exceeding 200 mJ/cm(2), followed by a p lateau, whereas RE underwent a continuous dose-dependent decrease at UVB do ses up to 1 J/cm(2). A topical anti-oxidant mixture containing 0.5% ascorba te, 0.25% tocopherol and 0.25% melatonin failed to protect epidermal RE fro m UVB-induced depletion, whereas it did prevent ROL depletion. ARAT and REH , as well as CRBP-1, were not affected by UVB in these conditions. Conclusi on: Vitamin A storage in the epidermis comprises two forms, ROL and RE, tha t do not show similar sensitivity to acute UVB exposure. ROL stores compris e a UVB-resistant (possibly by CRBP) portion and a UVB-sensitive portion th at can be protected by anti-oxidants. RE stores do not show such a pattern. Copyright (R) 2000 S. Karger AG. Basel.