Abstract
We have previously reported that photoirradiation of retinyl palmitate (RP), a storage and ester form of vitamin A (retinol), with UVA light resulted in the formation of photodecomposition products, generation of reactive oxygen species, and induction of lipid peroxidation. In this paper, we report our results following the photoirradiation of RP in ethanol by an UV lamp with approximately equal UVA and UVB light. The photodecomposition products were separated by reversed-phase HPLC and characterized spectroscopically by comparison with authentic standards. The identified products include: 4-keto-RP, 11-ethoxy-12-hydroxy-RP, 13-ethoxy-14-hydroxy-RP, anhydroretinol (AR), and trans- and cis-15-ethoxy-AR. Photoirradiation of RP in the presence of a lipid, methyl linoleate, resulted in induction of lipid peroxidation. Lipid peroxidation was inhibited when sodium azide was present during photoirradiation which suggests free radicals were formed. Our results demonstrate that, similar to irradiation with UVA light, RP can act as a photosensitizer leading to free radical formation and induction of lipid peroxidation following irradiation with UVB light.
Highlights
Retinyl palmitate (RP) (Figure 1) is an ester and the storage form of vitamin A (Figure 1) which is required in many essential biological processes, including regulation of epidermal cell growth, normal cell differentiation, and cell maintenance [1, 2]
For structural identification of the photodecomposition products, photoirradiation of RP with UVA light under similar conditions as previously reported (7) was performed in parallel and the resulting HPLC profile is shown in Figure 3 (Panel A)
The profiles of the photodecomposition products formed from photoirradiation of RP with the high output UVB light source and the high output UVA light source can be compared
Summary
Retinyl palmitate (RP) (Figure 1) is an ester and the storage form of vitamin A (retinol) (Figure 1) which is required in many essential biological processes, including regulation of epidermal cell growth, normal cell differentiation, and cell maintenance [1, 2]. The number of cosmetic products containing RP has increased rapidly in the last two decades, with more than 700 RP-containing cosmetic products in the U.S market in 2004 [4]. The individuals using these products are unavoidably exposed to sunlight. We have confirmed the above hypothesis and demonstrated that photoirradiation of RP with UVA light generated several photodecomposition products, and formed superoxide and singlet oxygen [7, 8]. We have shown that photoirradiation of RP with UVA light in the presence of a lipid, methyl linoleate, resulted in the formation of ROS-induced lipid peroxidation [8]
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