Photoreaction, Phototoxicity, and Photocarcinogenicity of Retinoids

Abstract

Sunlight is a human carcinogen. Many retinoid-containing cosmetics are used to protect damages caused by sunlight irradiation. Since retinol is thermally unstable and retinyl palmitate (RP) s relatively more stable, RP is also widely used as an ingredient in cosmetic formulations. In general, little is known about the photodecomposition of retinoids and the toxicity of retinoids and their photodecomposition products on the skin's responses to sunlight. This review focuses on the update information on photoreactions, phototoxicity, and photocarcinogenicity of the natural retinoids including retinol, retinal, retinoid acid (RA), retinyl acetate, and RP.

Superoxidation of Bisretinoids

“…The oxidized products often show biological activity and are responsible for various aromas and tastes of food 2. 3 Identification of the oxygenated products is complicated by the fact that the initial species are reactive dioxetanes, peroxides, epoxides, and endoperoxides that can undergo secondary reactions and rearrangements upon chromatographic separation and identification 2. 3 Furthermore, various cis / trans , stereo‐, and regioisomers are often obtained.…”

“…The polyenes 1 a – k react readily with singlet oxygen 2. 3 Reactions with oxygen can be initiated by light, in the presence or absence of a photosensitizer, or by autoxidation 3.…”

Reappraising the phototoxicity of tretinoin: a report of four controlled clinical trials

“…With multiple conjugated double bonds, retinoids are susceptible to a range of photochemical reactions, including isomerization, dimerization, and oxidation. The extent to which these reactions take place in a topically applied product depends on the vehicle, retinoid concentration, exposure time, dosage, and wavelength of the light (1).…”

“…However, a photoreactive chemical is not necessarily phototoxic or photosensitizing. Phototoxic chemicals are those which meet all of the following criteria: (i) they are toxic to organisms or cells in the presence of light, (ii) the toxic effect does not occur in the absence of light, and (iii) there are no toxic effects when the test organisms or cells are not treated with the chemical and photoirradiation at the same time (1).…”

Superoxidation of Bisretinoids

“…3 Reactions with oxygen can be initiated by light, in the presence or absence of a photosensitizer, or by autoxidation 3. The oxidized products often show biological activity and are responsible for various aromas and tastes of food 2. 3 Identification of the oxygenated products is complicated by the fact that the initial species are reactive dioxetanes, peroxides, epoxides, and endoperoxides that can undergo secondary reactions and rearrangements upon chromatographic separation and identification 2.…”