Lycopene as the most efficient biological carotenoid singlet oxygen quencher

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Abstract

Lycopene, a biologically occurring carotenoid, exhibits the highest physical quenching rate constant with singlet oxygen (kq = 31 X 10(9) M-1 s-1), and its plasma level is slightly higher than that of beta-carotene (kq = 14 X 10(9) M-1 s-1). This is of considerable general interest, since nutritional carotenoids, particularly beta-carotene, and other antioxidants such as alpha-tocopherol (kq = 0.3 X 10(9) M-1 s-1) have been implicated in the defense against prooxidant states; epidemiological evidence reveals that such compounds exert a protective action against certain types of cancer. Also, albumin-bound bilirubin is a known singlet oxygen quencher (kq = 3.2 X 10(9) M-1 s-1). Interestingly, those compounds with low kq values occur at higher plasma levels. When these differences are taken into account, the singlet oxygen quenching capacities of lycopene (0.7 microM in plasma), beta-carotene (0.5 microM in plasma), albumin-bound bilirubin (15 microM in plasma), and alpha-tocopherol (22 microM in plasma) are of comparable magnitude.

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The human diet contains a great variety of natural mutagens and carcinogens, as well as many natural antimutagens and anticarcinogens. Many of these mutagens and carcinogens may act through the generation of oxygen radicals. Oxygen radicals may also play a major role as endogenous initiators of degenerative processes, such as DNA damage and mutation (and promotion), that may be related to cancer, heart disease, and aging. Dietary intake of natural antioxidants could be an important aspect of the body's defense mechanism against these agents. Many antioxidants are being identified as anticarcinogens. Characterizing and optimizing such defense systems may be an important part of a strategy of minimizing cancer and other age-related diseases.

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P A Cerutti (1985)

There is convincing evidence that cellular prooxidant states--that is, increased concentrations of active oxygen and organic peroxides and radicals--can promote initiated cells to neoplastic growth. Prooxidant states can be caused by different classes of agents, including hyperbaric oxygen, radiation, xenobiotic metabolites and Fenton-type reagents, modulators of the cytochrome P-450 electron-transport chain, peroxisome proliferators, inhibitors of the antioxidant defense, and membrane-active agents. Many of these agents are promoters or complete carcinogens. They cause chromosomal damage by indirect action, but the role of this damage in carcinogenesis remains unclear. Prooxidant states can be prevented or suppressed by the enzymes of the cellular antioxidant defense and low molecular weight scavenger molecules, and many antioxidants are antipromoters and anticarcinogens. Finally, prooxidant states may modulate the expression of a family of prooxidant genes, which are related to cell growth and differentiation, by inducing alterations in DNA structure or by epigenetic mechanisms, for example, by polyadenosine diphosphate-ribosylation of chromosomal proteins.