Carotenoids in Photooxidative Stress

Carotenoids are secondary plant constituents and more than 700 different compounds have been identified. They are synthesized by plants, where they serve as colorants for fruits and leaves, bacteria, fungi and algae. In nature carotenoids are important biological compounds due to their provitamin A activity, antioxidant properties and accessory functions in the light harvesting system of plants. Considerable amounts of carotenoids are ingested with the diet and accumulate in the human organism. α- and β- carotene, β- cryptoxanthin, lutein, zeaxanthin and lycopene are the major carotenoids in human blood and tissues. Based on their structural features carotenoids are suitable compounds for photoprotection in humans. They may act as ultraviolet (UV) absorbers and dietary antioxidants capable of scavenging reactive intermediates generated under the condition of photooxidative stress. Photooxidative stress is involved in processes of photoageing, photocarcinogenesis and plays a major role in the pathogenesis of photodermatoses. Intervention studies with β- carotene and lycopene supplements or diets rich in those carotenoids have shown that these molecules contribute to systemic photoprotection ameliorating UVinduced erythema. In- vitro data provide evidence that also other carotenoids are efficient photoprotectors, for example lutein and the structurally unusual phenolic polyene 3,3'- dihydroxyisorenieratene.