Lutein, structure

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. ... 

Batista, A.P. et al., Phycocyanin and Lutein colored food emulsions relation between pigment concentration and structural properties, in Proceedings of 3rd International Congress on Pigments in Food, Le Berre, Qnunper, France, 2004, 118. 

In several studies of toxicity, no adverse effects were documented in monkeys or humans. Taking into account data showing that lutein was not genotoxic, had no structural alert, did not exhibit tumor-promoting activity, and is a natural component of the body (the eye), the Scientific Steering Committee concluded there was no need for a study of carcinogenicity. 

Lutein has some structural similarities to P-carotene, reported to enhance the development of lung cancer when given in supplement form to heavy smokers. The available data indicate that lutein in food would not be expected to have this effect. The committee was unable to assess whether lutein in the form of supplements would produce the reported effect in heavy smokers. 

Castelli, F., S. Caruso, and N. Giuffrida. 1999. Different effects of two structurally similar carotenoids, lutein and beta-carotene, on the thermotropic behaviour of phosphatidylcholine liposomes. Calorimetric evidence of their hindered transport through biomembranes. Thermochim. Acta 327 125-131. 

Sujak, A., J. Gabrielska, W. Grudzinski, R. Bore, P. Mazurek, and W.I. Gruszecki. 1999. Lutein and zeaxanthin as protectors of lipid membranes against oxidative damage The structural aspects. Arch. Biochem. Biophys. 371 301-317. 

Douillard R, Burghoffer C, and Costes C. 1982. Structure excitonique de complexes hydroethanoliques de la luteine et de la zeaxanthine. Physiologie Vegetale 20 123-136. 

Figure 4.7 shows the structures of important carotenoids (all-E) lutein, (all-E) zeaxanthin, (all-E) canthaxanthin, (all-E) p-carotene, and (all-E) lycopene. Employing a self-packed C30 capillary column, the carotenoids can be separated with a solvent gradient of acetone water=80 20 (v/v) to 99 1 (v/v) and a flow rate of 5 pL min, as shown in Figure 4.8 (Putzbach et al. 2005). The more polar carotenoids (all-E) lutein, (all-E) zeaxanthin, and (all-E) canthaxanthin elute first followed by the less polar (all-E) p-carotene and the nonpolar (all-E) lycopene. Figure 4.9 shows the stopped-flow II NMR spectra of these five carotenoids. The chromatographic run was stopped when the peak maximum of the compound of interest reached the NMR probe detection volume.

FIGURE 4.7 Structures of important carotenoids (all-E) lutein, (all-/ ) zeaxanthin, (all-E) canthaxanthin, (all-E) P-carotene, and (all-E) lycopene. 

The structure of the major trimeric LHCII complex has been recently obtained at 2.72 A (Figure 7.3) (Liu et al., 2004). It was revealed that each 25kDa protein monomer contains three transmembrane and three amphiphilic a-helixes. In addition, each monomer binds 14 chlorophyll (8 Chi a and 6 Chi b) and 4 xanthophyll molecules 1 neoxanthin, 2 luteins, and 1 violaxanthin. The first three xanthophylls are situated close to the integral helixes and are tightly bound to some amino acids by hydrogen bonds to hydroxyl oxygen atoms and van der Waals interactions to chlorophylls, and hydrophobic amino acids such as tryptophan and phenylalanine. 

Neoxanthin and the two lutein molecules have close associations with three transmembrane helixes, A, B, and C, forming three chlorophyll-xanthophyll-protein domains (Figure 7.5). Considering the structure of LHCII complex in terms of domains is useful for understanding how the antenna system works, and the functions of the different xanthophylls. Biochemical evidence suggests that these xanthophylls have a much stronger affinity of binding to LHCII in comparison to violaxanthin... 

FIGURE 7.7 (a) Structure of the LHCII trimer showing lutein 2 from the monomer 1 (monl) interacting with... 

A close analysis of the trimers order in the crystal revealed that the exposed part of neoxanthin molecule is completely free from interactions with any protein or pigment components (Pascal et al., 2005). In addition, an examination of the neoxanthin configuration, taken from the structure of LHCII, points toward strong distortion of the d.v-end of the molecule (Figure 7.9). This fact suggests that the twist most likely occurs within the protein interior, implying that some movement in the LHCII monomer must take place during the transition into dissipative state. Apparently, this movement affects not only lutein 1, as previously discussed, but also neoxanthin. 

The v4 region enhancement and structure in the resonance Raman spectra of xanthophylls reviewed in this chapter shows that it can be used for the analysis of carotenoid-protein interactions. Figure 7.8 summarizes the spectra for all four major types of LHCII xanthophylls. Lutein 2 possesses the most intense and well-resolved v4 bands. The spectrum for zeaxanthin is very similar to that of lutein with a slightly more complex structure. This similarity correlates with the structural similarity between these pigments. It is likely that they are both similarly distorted. The richer structure of zeaxanthin spectrum may be explained by the presence of the two flexible P-end rings... 

FIGURE 13.2 Chemical formulas of macular xanthophylls. It can be noted that the chemical structures of (meso)-zeaxanthin and lutein differ only by the position of a single double bond. 

The observation that lutein and zeaxanthin occur in the highest concentration in the macula soon raised expectations that the macular xanthophylls may be essential in maintaining structure and function of the retina by contributing not only to risk reduction of macular diseases but also to improving visual performance of the healthy eye, which was the original hypothesis to explain the presence of the macular yellow pigment as mentioned previously. 

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