Synergistic anti-oxidative effects of lycopene with other bioactive compounds

Lycopene belongs to the carotenoid family, which has more than 700 members. In human serum, only 14 caroteinoids have been identified, and, among these, lycopene was the most abundant. Lycopene is regarded as one of the most efficient singlet oxygen quencher and peroxyl radical scavenger of all the carotenoids and may represent an important defense mechanism in the human body. Singlet oxygen and free radicals can cause biological damage to important macromolecules and membrane constituents, and the presence of natural antioxidants may help to control these degradative reactions. The oxidation of low density lipoproteins (LDL) has been implicated in the development of atherosclerosis which makes the antioxidants that protect LDL potential antiatherogenic agents. There is growing evidence that certain combinations of natural antioxidants have synergistic antioxidant activity, that is, the actual inhibitory activity of the mixture is greater than the additive activities of the individual antioxidants. Lycopene on its own can retard the oxidation of LDL, but in combination with vitamin E, a synergistic effect is observed. There is clear evidence that lycopene in association with alpha-tocopherol synergistically inhibits the proliferation of two prostate carcinoma cell lines. Polyphenols are very potent antioxidants found in tomatoes and many other fruits, vegetables, and herbs. The polyphenols glabridin, rosmarinic acid, and carnosic acid, when used in combination with lycopene, inhibited the oxidation of LDL to a greater extent than the additive values by 32%, 32%, and 15%, respectively. Extracts and powders containing mixtures of antioxidants also showed synergism. Tomato oleoresin produced a 5-fold increase in antioxidant activity against LDL oxidation when compared to pure lycopene at the same concentration. A 33% increase in LDL inhibition was observed when lycopene was used with garlic powder. Of the six major carotenoids found in human blood and tissue, lycopene plus lutein produced the greatest synergistic effect against oxidation of multilamellar liposomes. It also has been shown that low concentrations of 1,25-dihydroxylvitamin D3 and lycopene synergistically inhibit cell proliferation and differentiation in HL-60 leukemic cells. A number of hypotheses have been put forward to explain the synergistic effects between lycopene and other natural antioxidants. It has been suggested that the synergistic effects may be related to their physicochemical properties and or their location within the biomembrane or LDL particle, that one antioxidant is able to regenerate the second antioxidant; or that vitamin E and lycopene affect different signal transduction pathways leading to the synergistic inhibition of cell proliferation.