Lutein antioxidant

Most carotenoids have no pro-vitamin A activity with the notable exceptions of P-carotene, and to a lesser extent a-carotene and P-cryptoxanthin. They act as macular pigments (lutein and zeaxanthin) and they have antioxidant and biochemical properties other than pro-vitamin A activity. 

It has been established that carotenoid structure has a great influence in its antioxidant activity for example, canthaxanthin and astaxanthin show better antioxidant activities than 3-carotene or zeaxanthin. 3- 3 3-Carotene also showed prooxidant activity in oil-in-water emulsions evaluated by the formation of lipid hydroperoxides, hexanal, or 2-heptenal the activity was reverted with a- and y-tocopherol. Carotenoid antioxidant activity against radicals has been established. In order of decreasing activity, the results are lycopene > 3-cryptoxanthin > lutein = zeaxanthin > a-carotene > echineone > canthaxanthin = astaxanthin. ... 

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. 

The lag-phase measurement at 234 nm of the development of conjugated dienes on copper-stimulated LDL oxidation is used to define the oxidation resistance of different LDL samples (Esterbauer et al., 1992). During the lag phase, the antioxidants in LDL (vitamin E, carotenoids, ubiquinol-10) are consumed in a distinct sequence with a-tocopherol as the first followed by 7-tocopherol, thereafter the carotenoids cryptoxanthin, lycopene and finally /3-carotene. a-Tocopherol is the most prominent antioxidant of LDL (6.4 1.8 mol/mol LDL), whereas the concentration of the others 7-tocopherol, /3-carotene, lycopene, cryptoxanthin, zea-xanthin, lutein and phytofluene is only 1/10 to 1/300 of a-tocopherol. Since the tocopherols reside in the outer layer of the LDL molecule, protecting the monolayer of phospholipids and the carotenoids are in the inner core protecting the cholesterylesters, and the progression of oxidation is likely to occur from the aqueous interface inwards, it seems reasonable to assign to a-tocopherol the rank of the front-line antioxidant. In vivo, the LDL will also interact with the plasma water-soluble antioxidants in the circulation, not in the artery wall, as mentioned above. 

Richer S, Stiles W, Statkute L, Pulido J, Frankowski J, Rudy D, Pei K, Tsipursky M, and Nyland J (2004), Double-masked, placebo-controlled, randomized trial of lutein and antioxidant supplementation in the intervention of atrophic age-related macular degeneration The Veterans LAST study (lutein antioxidant supplementation trial), Optometry 75 216-30. 

The contribution of lutein and zeaxanthin to the risk reduction of AMD is mainly based on two properties of the xanthophylls one is their blue-light absorption and the other is their antioxidant... 

As mentioned previously, the ability of carotenoids to inhibit oxidative stress was tested in vitro in many different cell types. In the retina only lutein and zeaxanthin accumulate in sufficient concentrations to exert direct antioxidant effects, therefore our further discussion of these antioxidant effects will be focused mainly on those two xanthophylls. 

Altogether, studies in cultured RPE indicate that lutein and zeaxanthin may provide antioxidant protection in the RPE but more research is required to determine the exact mechanisms responsible for the observed protective effects or the lack thereof. 

In most assays designed to study antioxidant action of carotenoids, the effects of carotenoids were followed for a relatively short periods of time, while carotenoids were still present at substantial concentrations. Carotenoids, such as [1-carotene, lutein, and zeaxanthin, undergo rapid degradation upon exposure to oxidants or irradiation with ultraviolet and visible light (Ojima et al 1993 Siems et al 1999, 2005). 

One possible mechanism responsible for cooperative action of antioxidants is reduction of a semi-oxidized carotenoid by another antioxidant. Carotenoid cation radicals can be reduced, and therefore recycled to the parent molecule, by a-tocopherol, ascorbate, and melanins (Edge et al., 2000b El-Agamey et al., 2004b) (Figure 15.5). Interestingly, lycopene can reduce radical cations of other carotenoids, such as astaxanthin, (3-carotene, lutein, and zeaxanthin (Edge et al., 1998). 

Reboul, E, Thap, S, Toumiaire, F, Andre, M, Juhel, C, Morange, S, Amiot, MJ, Lairon, D, and Borel, P, 2007b. Differential effect of dietary antioxidant classes (carotenoids, polyphenols, vitamins C and E) on lutein absorption. Br J Nutr 97, 440-446. 

---