Carotenoids have been traditionally used as spices and colorants and showed various physiological activities. Carotenoids have a chromophore through more than 4 conjugated polyenes, which gives them yellow color, and acts as a co-pigment during photosynthesis in plants. In mammal, carotenoids are obtained by ingestion of food, and metabolized either by catrotenoid oxygenase or by non-enzymatic reactions. Carotenoid metabolites are accumulated in plasma, skin, and retina. They regulate immune activity and have photoprotective functions. However, it is possibile that carotenoids exhibit the photosensitizing property due to their chromophore. In this study, the photo-reactivity of dietary carotenoids including norbixin, bixin, crocin as well as lutein, and changes in their physiological activities through interaction with light were studied.
Annatto, a dietary pigment obtained from the seeds of the Achiote tree (Bixa Orellana), contains the apocarotenoids, bixin and norbixin. Crocin gives the red color of saffron crocus (Crocus sativus), and lutein is abundantly present in plants and yolks and classified as the xanthophylls, an oxygen containing carotenoid. Lutein was the most unstable under fluorescent light (FL) and blue LED in distilled water (DW), and maximum absorptivity calculated according to Fieser-Kuhn rule showed the highest value in the order of lutein, bixin, norbixin, and crocin. Photosensitizing activities of the carotenoids were analyzed under 5 light sources (FL, white, red, green, blue LED) with an intensity of 10 W/㎡ using the MTT formazan, NBT and DCFH as a probe. Annatto and crocin showed a photosensitizing property by inducing MTT formazan discoloration. Bixin displayed the most potent reduction of NBT, regardless of the presence of methionine, whereas crocin did not induce the reduction. Annatto showed the increase of DCF fluorescence in a light intensity- and concentration-dependent manner indicating that it produced reactive oxygen species (ROS) under light due to its photosensitivity. The changes in chemical stability and antioxidant activity of annatto by light irradiation were also studied. Annatto was more stable in DMSO than DW, and the decrease in norbixin level was much more pronounced than the decrease in color intensity of annatto. Annatto induced lipid peroxidation under light exposure condition. Additionally, ABTS radical scavenging activity, oxygen radical antioxidant capacity, and ferric reducing activity of annatto were significantly reduced by light irradiation. Annatto, however, inhibited lipid peroxidation induced by the Fenton reaction in a concentration-dependent manner and a metal chelating activity of annatto played an important role for the inhibition.
Carotenoids could control inflammatory processes and have shown protective effects on skin damages. The effects of four carotenoids on proliferation, melanogenesis, and inflammation in skin cell, and monocyte differentiation were also investigated. As a result of treating each carotenoid on 3 types of skin cells including keratinocyte (HaCaT), fibroblast (HDF), and mouse melanoma (B16F10), annatto and bixin induced the proliferation of HDF, whereas lutein inhibited. Long-term treatment annatto and bixin for 7 days using the colony formation assay showed the growth inhibition of keratinocyte, whereas the mean area of colony treated with lutein was increased. Significant enhancement of melanogenesis in the melanoma treated with lutein was observed; it was possibly because lutein metabolite promoted the formation of eumelanin through depleting thiol compounds in cells. The carotenoids decreased mRNA levels of the pro-inflammatory cytokines including TNF-α, IL-1β, and IL-8 in PMA-stimulated inflammation of HaCaT. The monocyte (THP-1) differentiation induced by PMA was also inhibited by the carotenoids, and lutein showed the highest effect. LPS-induced COX-2 levels in differentiated THP-1 were decreased by annatto and bixin, whereas lutein increased the level. The growth of HDF was inhibited by the culture media from LPS-stimulated THP-1 only pretreated with lutein.