Retinol and Retinyl Ester Epidermal Pools Are Not Identically Sensitive to UVB Irradiation and Anti-Oxidant Protective Effect

Abstract

Background: UV irradiation can deplete epidermal vitamin A, thus the hypothesis 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 study we addressed two questions: (1) Are retinol (ROL) and retinyl esters (RE) – the two predominant forms of vitamin A – equally sensitive to the action of UVB, and (2) could the depletion be prevented by anti-oxidants? Methods: Hairless mice were irradiated with a single UVB dose, corresponding to the maximum of ROL and RE absorption. Retinoid content, enzyme activities catalysing the esterification of ROL (ARAT and LRAT) and the hydrolysis of RE (REH), as well as retinol-binding protein (CRBP-1) expression were determined in the epidermis. Results: A single UVB dose induced a rapid, dose-dependent 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/cm², followed by a plateau, whereas RE underwent a continuous dose-dependent decrease at UVB doses up to 1 J/cm². A topical anti-oxidant mixture containing 0.5% ascorbate, 0.25% tocopherol and 0.25% melatonin failed to protect epidermal RE from 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. Conclusion: Vitamin A storage in the epidermis comprises two forms, ROL and RE, that do not show similar sensitivity to acute UVB exposure. ROL stores comprise a UVB-resistant (possibly by CRBP) portion and a UVB-sensitive portion that can be protected by anti-oxidants. RE stores do not show such a pattern.

Isomerization of 11-cis- Retinoids to All-trans-retinoids in Vitro and in Vivo

“…One investigation of UV light exposure on hairless mice found that it greatly reduced the concentrations of retinyl esters, although all-trans-retinol was largely unaffected. This suggested that retinoid-binding proteins such as CRBP I protect all-trans-retinol from the damaging effects of UV light (64,65). Although more recent work has suggested that CRBP's primary role in UV-mediated damage is more related to retinoid mobilization in response to the light-induced injury (66), other studies of UV exposure to human skin and to Gecko lens further support the protective role of CREB I (64,67).…”

Decreased Oxidative State in Non-Lesional Skin of Atopic Dermatitis

“…The whole processing of α-tocopherol extraction was performed at a cool temperature (4°C) as described previously for the retinoid assay [13]. Epidermis was minced with scissors in 1.92 ml extraction buffer, then epidermis or collected squames were homogenised by using a Polytron PT 3100 homogeniser in 1.92 ml extraction buffer.…”

“…The homogenate was sonicated for 10 s at a low power (50 W) and centrifuged for 10 min at 12,000 g , then the supernatant was extracted with 4 ml hexane. The hexane fraction was evaporated to dryness under nitrogen flux, then the sample was reconstituted in 100 µl methanol, before being injected into the HPLC [13]. α-Tocopherol was detected by fluorescence (excitation: 292 nm; emission: 330 nm), and retinyl acetate (internal standard) was detected by UV absorption at 325 nm.…”

In Vitro Assessment of the Tolerance Profile, the Metabolism and the Potential Depigmenting Activity of New Retinoid Derivatives

“…Retinoids were applied at 10 µM for 4, 24 or 96 hours in BDVII keratinocytes or B16 melanocytes, then the cells were lysed and harvested by sonication in 50 mM acetate buffer pH 4, and intracellular retinoids were analysed by high performance liquid chromatography (HPLC) and UV detection as described ( Table 1) [17]. Results shown in Figs. (2-5) are expressed as (pmol retinoid/mg protein) and represent the means of duplicate experiments performed in the same series of culture.…”