Photosensitizers are activated by light to change themselves or to transfer the light energy to other surrounding molecules to induce chemical or physical changes. Riboflavin is a well-known photosensitizer and is photolyzed under light into lumichrome (LC) and lumiflavin (LF), whose photo-reactivity has not been clearly elucidated. Therefore, in the present study, photosensitizing properties and bioactivities of riboflavin and its photo-degradation products were investigated.
The riboflavin has widely been used as a cosmetic agent for skin conditioning. First, photosensitizing activity of the cosmetic nutrients including vitamins (β-carotene, ascorbic acid, riboflavin, niacin, pantothenic acid, pyridoxine, menadione) and nucleotides (adenosine, guanosine), and their interaction with riboflavin under light (1800 lx, 25℃) were evaluated using three photosensitizing activity evaluation systems. Among the cosmetic nutrients tested, only riboflavin showed a prominent photosensitizing activity in all assay systems using TTC and MTT formazan probes or 2'-7'dichlorofluorescin (DCFH) probe. Under light, formazan decolorization by riboflavin was accelerated in the presence of pantothenic acid and pyridoxine. DCF fluorescence through reactive oxygen species (ROS) formation by riboflavin was also enhanced in the presence of pyridoxine and folic acid. The results indicate that photosensitizing activity of riboflavin as a cosmetic compound and effects of the interaction among the cosmetic nutrients needs to be carefully considered when applied in light-exposed skin.
Riboflavin, an essential vitamin, is also contained in the cell culture medium. Many cell culture experiments have been performed under light, especially for evaluating properties of photodynamic or cosmetic agents. In this study, photo-reactivity and cytotoxic effects of different culture media including regular DMEM (P-D), phenol red free DMEM (PF-D), and phenol red and riboflavin free DMEM (PRF-D) on the keratinocyte were evaluated. Significant amounts of ROS were generated from the media under irradiation of fluorescent light (FL), white, and blue LED; it was not observed under red and green LED. Higher levels of ROS were produced in PF-D than one containing phenol red under light. ROS generation was not observed in riboflavin-free medium. Cytotoxic effect on keratinocyte (HaCaT) was more pronounced in PF-D than in P-D. The phototoxicity of HaCaT was also enhanced according to increase of treated media volume, light-intensity, and irradiation time. The results indicate that regular media components including riboflavin and phenol red could interfere with the cell experiments using the light irradiation process.
Riboflavin and its photo-degradation products, LC and LF, all of which have a light-sensitive isoalloxazine structure. In this study, photosensitizing properties of riboflavin and its photo-degradation products were investigated. In addition, the effect of chlorogenic acid (CGA) on the riboflavin-induced phototoxicity was also evaluated. Riboflavin showed the strongest photosensitizing and photo-oxidation activity as compared to LC and LF. Riboflavin, however, inhibited the Fenton reaction-induced lipid oxidation even under light since its Fe2+ chelating activity was enhanced under light. LC also promoted lipid oxidation potently under fluorescent light (4000 lx, 2h). LC and LF did not inhibited the Fenton reaction-induced lipid peroxidation. Riboflavin induced the most potent photo-toxicity in both HaCaT and HDF. Riboflavin also increased the levels of pro-inflammatory cytokines, IL-1β, IL-6, and IL-8 in HaCaT under light (2000 lx, 1h). Chlorogenic acid, a polyphenolic ROS scavenger, alleviated riboflavin-induced photosensitizing activity and photo-toxicity. These results indicate that riboflavin and its photo-degradation products could cause photo-damages in the skin through promoting lipid peroxidation and inducing inflammatory and cytotoxic processes and CGA could inhibit the process.