Lycopene actions/effects

Three major types of research have emerged (Levy et al., 1995) epidemiological studies involving patients with various malignancies, studies on the direct effect of lycopene on the proliferation of various tumors in cell lines and in animal models, and studies on the biochemical and immunological mechanisms of lycopene action. 

There are various factors in the effectiveness of the antioxidant action. Among these are the presence of oxygenated functional groups in the stmcture of the pigment," the conditions of the medium where the pigment acts," " and the nature of the prooxidant substance." Any of these factors may cause a self-oxidizing effect in place of the expected antioxidant beneficial one. Nevertheless, different in vitro and in vivo studies have concluded that the antioxidant action of pigments such as p-carotene and lycopene is effective. 

Fruifs and vegetables also contain ofher bioactive substances such as polyphenols (including well-known pigments anthocyanins, flavonols) and non-provitamin A carotenoids (mainly lycopene, lutein, and zeaxanthin) that may have protective effects on chronic diseases. Polyphenols and carotenoids are known to display antioxidant activities, counteracting oxidative alterations in cells. Besides these antioxidant properties, these colored bioactive substances may exert other actions on cell signaling and gene expression. 

Evidence is now being obtained that suggests that lycopene may have direct stimulatory effects on the response of the immune system. This may involve an antioxidant action, and it could form the basis of a protective action against cancer and also against human immunodifiency virus (HIV) and acquired immune deficiency syndrome (AIDS). The free radical quenching constant of lycopene was found to be more than double that of [3-carotene and 10 times more than that of a-tocopherol, which makes lycopene s presence in the diet of considerable interest (Di Mascio et al., 1989,1991 Conn et al., 1991 Devasagayam et al., 1992 Ribaya-Mercado et al., 1995). 

Chapter 12 summarizes the role of dietary phytochemicals, especially those from fruits, herbs, and spices, in the prevention of cardiovascular disease. Chapter 13 is devoted to the effects and mecharusms of action of resveratrol, a polyphenolic phytoalexin that has received considerable publicity. The same is tine of lycopene, the topic of Chapter 14, which occurs in especially high levels in fresh and processed tomatoes. Consideration is given in Chapter 15 to the effects of oltipraz on phase 1 and 2 xenobiotic-metabolizing enzymes this draws together nutritional, clinical, and pharmacological investigation and provides some pointers for the future. These are elaborated upon in Chapter 16, which addresses research directions, challenges, and opportunities. 

Farombi and Burton, examined the effects of several carotenoids on autoxidized triglycerides and concluded that potential prooxidant effects could occur at high concentrations. Moreover, Henry et al., suggested that at concentrations >500 ppm both P-carotene and lycopene acted as prooxidants by decreasing the induction time significantly, during the heat catalyzed oxidation of safflower seed oil. Several studies have shown that the presence of primary antioxidants and especially tocopherols stabilize carotenoids so they exhibit synergistic antioxidant character, instead of the prooxidant action that carotenoids would present individually. 

Chemical synthesis has a major part to play in the sophisticated interdisciplinary studies that are now needed to study the biological functions and actions of carotenoids, and the interactions of carotenoids with other molecules such as proteins. Essential roles in photosynthesis have been discovered for several different carotenoids, including specific geometrical isomers. Synthesis is able to provide the pure and, when appropriate, isotopically labelled carotenoids that are required for reconstitution studies, investigation of photochemistry, etc. In the field of medicine it is now clear that the provitamin A activity of p,p-carotene (3) may not be the only beneficial effect of carotenoids. Several carotenoids found in the human diet, especially lycopene (31), lutein (133) and zeaxanthin (119), could also be important in giving protection against serious disorders such as cancer, heart disease, and degenerative eye diseases. Characterization of these effects and elucidation of the mechanisms involved require substantial quantities (g to kg) of pure carotenoids these materials can only be produced by chemical synthesis. 

The presence of oxygenated functional groups also modifies the bioavailability of these compounds. It has been demonstrated recently that some ketocarotenoids are more rapidly absorbed and metabolized than other carotenes such as, for instance, lycopene. These xanthophylls do not present provitamin A activity, but their antioxidant action is more effective than that of p-carotene. The incorporation of the carotenoid pigments into cell structures is affected by the pigment stmcture and the presence of functional groups that may modify the interaction with other molecules. Such stmcture, as mentioned above, determines the effectiveness of the pigment s action. 

As an action independent of their conversion into vitamin A, both nutritionally active and nutritionally inactive carotenoids (e.g. zeaxanthin, lutein and lycopene) may have protective effects in reducing oxidative stress and some forms of chronic disease [56-60]. The extent to which carotenoid ingestion affects the onset of chronic disease in humans, however, is still unclear. 

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