Xanthophyll, effect

Allenic groups — Neoxanthin, a xanthophyll found in many foods, has an allenic group at the C-6,7,8 position where the two double bonds are perpendicular to each other, and the C-7,8 double bond coplanar with the polyene chain contributing effectively to the chromophore since the C-6,7 bond is in a different plane, it makes no contribution. Therefore, neoxanthin, despite its 10 conjugated double bonds, has a UV-Vis spectrum similar to that of a conjugated nonaene such as violaxanthin. 

Although these studies were designed to look for ocular effects, no adverse effects of these xanthophylls were reported where clinical or biochemical parameters were also examined. 

Recently, due to increased interest in membrane raft domains, extensive attention has been paid to the cholesterol-dependent liquid-ordered phase in the membrane (Subczynski and Kusumi 2003). The pulse EPR spin-labeling DOT method detected two coexisting phases in the DMPC/cholesterol membranes the liquid-ordered and the liquid-disordered domains above the phase-transition temperature (Subczynski et al. 2007b). However, using the same method for DMPC/lutein (zeaxanthin) membranes, only the liquid-ordered-like phase was detected above the phase-transition temperature (Widomska, Wisniewska, and Subczynski, unpublished data). No significant differences were found in the effects of lutein and zeaxanthin on the lateral organization of lipid bilayer membranes. We can conclude that lutein and zeaxanthin—macular xanthophylls that parallel cholesterol in its function as a regulator of both membrane fluidity and hydrophobicity—cannot parallel the ability of cholesterol to induce liquid-ordered-disordered phase separation. 

FIGU RE 10.13 Schematic drawing of the distribution of xanthophyll molecules between raft domain (DRM) and bulk domain (DSM) in lipid bilayer membranes. For this illustration, the xanthophyll partition coefficient between domains is the same as obtained experimentally for raft-forming mixture. However, to better visualize the observed effect in the drawing, the number of lipid molecules was decreased and the total number of xanthophyll molecules was increased about 10 times. (From Wisniewska, A. and Subczynski, W.K., Free Radio. Biol. Med., 40, 1820, 2006. With permission.)... 

Johnson, E. J., M. Neuringer et al. (2005). Nutritional manipulation of primate retinas. III. Effects of lutein or zeaxanthin supplementation on adipose and retina of xanthophyll-free monkeys. Invest. Ophthalmol. Vis. Sci. 46(2) 692-702. 

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. 

It has been shown in many studies that protective effects of carotenoids can be observed only at small carotenoid concentrations, whereas at high concentrations carotenoids exert pro-oxidant effects via propagation of free radical damage (Chucair et al., 2007 Lowe et al., 1999 Palozza, 1998, 2001 Young and Lowe, 2001). For example, supplementation of rat retinal photoreceptors with small concentrations of lutein and zeaxanthin reduces apoptosis in photoreceptors, preserves mitochondrial potential, and prevents cytochrome c release from mitochondria subjected to oxidative stress induced by paraquat or hydrogen peroxide (Chucair et al., 2007). However, this protective effect has been observed only at low concentrations of xanthophylls, of 0.14 and 0.17 pM for lutein and zeaxanthin, respectively. Higher concentrations of carotenoids have led to deleterious effects (Chucair et al., 2007). 

Lutein and zeaxanthin seem to exert distinct effects on distribution of the RPE cells in the retina (Leung et al., 2004). In animal studies, Leung and colleagues demonstrated that animals supplemented with either lutein and zeaxanthin on a low n-3 fatty acid diet had a lower RPE cell density than unsupplemented animals on the same diet (Leung et al., 2004). The authors suggested that macular xanthophylls could stimulate the movement of RPE cells away from the central retina (Leung et al., 2004). 

The involvement of mitochondria in the pro-apoptotic effects of carotenoids has been clearly demonstrated by the fact that P-carotene induces the release of cytochrome c from mitochondria and alters the mitochondrial membrane potential (Aym) in different tumor cells (Palozza et al., 2003a). Moreover, the highly polar xanthophyll neoxanthin has been reported to induce apoptosis in colon cancer cells by a mechanism that involves its accumulation into the mitochondria and a consequent loss of mitochondrial transmembrane potential and releas of cytochrome c and apoptosis-inducing factor (Terasaki et al., 2007). 

Xanthophyll esters are common in fruits and vegetables. Few data exist regarding the effect of carotenoid esterification on carotenoid bioavailability. Xanthophyll esters are readily broken in the human intestine (West and Castenmiller 1998 Breithaupt and others 2003 Faulks and Southon 2005). Chitchumroonchokchai and Failla (2006) demonstrated that hydrolysis of zeaxanthin esters increases zeaxanthin bioavailability. Wingerath and others (1995) did not find (3-cryptoxanthin esters in chylomicrons from humans fed with tangerine juice. Herbst and others (1997) demonstrated that lutein diesters are more bioavailable than free lutein. However, the question of whether the free or the esterified form is more bioavailable to humans is still an ongoing discussion. 

The composition and amount of pigments in marine environments have also been vigorously investigated. Thus, on RP-HPLC method has been developed for the study of the effect of variable irradiance on the xanthophyll cycle of the seagrass Zostera marina. Extraction of pigments from seagrass was carried out by grinding the samples with acid-washed sand in the presence of 1 ml of 90 per cent acetone and the liquid phase was... 

The photoprotection hypothesis for anthocyanins is attractive because it can explain why red-leafed plants occur across such diverse environments. In the tropics, for example, anthocyanins in flushing red leaves may provide a critical photoprotective role to the nascent chloroplasts until adequate levels of xanthophylls have been synthesized. In the understorey, anthocyanins might protect shade-acclimated plants from the effects of sunflecks, which can be 2000-fold brighter than the usual light level, or canopy gaps caused by tree blowdown. A photoprotective function of anthocyanins would also benefit leaves in... 

The limits of detection for carotenoids using FAB-MS and LSIMS are not as low as with most other ionization techniques (Schmitz et al., 1992). Therefore, >10 pmol of each carotenoid should be loaded onto the direct insertion probe per analysis. The matrix, 3-nitrobenzyl alcohol, has been effective in facilitating the ionization of all types of carotenoids. However, more polar matrices such as glycerol or thioglycerol might be useful for the FAB-MS or LSIMS analysis of polar xanthophylls such as astaxanthin. Because glycerol and thioglycerol are poor solvents for hydrophobic compounds, they are unlikely to solvate and thus facilitate the ionization of the nonpolar carotenes such as (3-carotene. 

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