Carotenoids metabolites

The availability of precursor IPP may ultimately be most influential over accumulation of carotenoid metabolites. While over-expression of DXS and DXR in color complementation systems leads to hyperaccumulation of carotenoids (discussed in Section 5.3.3.3), over-expression of plant Dxs genes has not always been effective. Over-expression of DXS resulted in increased carotenoid accumulation in transgenic tomato and Arabidopsis, but over-expression of daffodil DXS in rice endosperm did not increase pigment accumulation. ... 

Bhosale, P, Zhao da, Y, Serban, B, and Bernstein, PS, 2007b. Identification of 3-methoxyzeaxanthin as a novel age-related carotenoid metabolite in the human macula. Invest Ophthalmol Vis Sci 48, 1435-1440. 

The identification of lycopene metabolites in vitro and in vivo raises the question as to whether lycopene metabolites, similar to other carotenoid metabolites, which can possess either more or less activity than the parent compound or have entirely different functions (Wang 2004), may contribute, at least in part, to the biological functions ascribed to lycopene. 

As in many fields of research, new tools and techniques for measuring carotenoids in various systems are critical to support research progress. Several chapters discuss new methodologies to measure carotenoids (see Chapter 4), carotenoid metabolites/radicals (see Chapter 9), or carotenoids in vivo in complex biological systems, especially in the human eye (e.g., see Chapters 5 and 6). Other chapters describe the oxygenase enzymes that are essential components of carotenoid metabolism to active metabolites (see Chapter 19). The study of active metabolites includes the in-depth evaluation of carotenoid cleavage products (see Chapter 11) and carotenoid radicals (see Chapter 14) that may account for some of the biological actions observed for these unique substances. 

The accurate mass capabilities of Time-of-Flight (TOF) are useful in determining the composition of new carotenoids or carotenoid metabolites which have not previously been identified (Mercadante et ah, 1997 Lakshminarayana et ah, 2008 Kopec et ah, 2010). In addition, a TOF chamber (interfaced with MALDI or an ESI ion source) is often used with a targeted metabolomics approach, where determining the exact mass of a mixture of components is important to successfully differentiate carotenoids from a high level of background ions (Fraser et ah, 2007 Chu et ah, 2011). 

AMS is a special type of MS that has been used to determine various parameters of carotenoid absorption, distribution, and metabolism, and the basics of this technique have been reviewed by Buchholz et al. (2000). A radio-labeled carotenoid (generally labeled with " C) is fed to a subject, and biological sample or expired air are collected. Samples may be analyzed directly, or first extracted and analyzed by HPLC, where fractions containing the putative isotopically labeled parent carotenoid(s) and/or carotenoid metabolites are collected. 

Techniques used to identify new carotenoids are also employed to identify carotenoid metabolites in various photosynthetic organisms, as well as animals and humans. A new metabolite might be identified in a food or biological extract by HPLC-PDA, with the observation of a new peak with a UVA is spectrum similar to a carotenoid, or which produces an MS fragment similar to other known carotenoids. Alternatively, the metabolism may be induced in vitro by creating ideal biological conditions for generating metabolites (with intestinal mucosa, for example dos Anjos Ferreira et ah, 2004). 

These types of technique have been employed to identify a number of carotenoids in multiple types of samples. Recently GC-MS and authentic standards were used to identify volatile carotenoid metabolites from plant tissues (Vogel et ah, 2008) and numerous studies have identified P-carotene metabolites in animals and humans using a variety of analytical techniques (Hu et ah, 2006 Ho et ah, 2007). These techniques have also been used to identify lycopene metabolites in both foods and biological samples (Khachik et ah, 1997 Bouvier et ah, 2003 Kopec et ah, 2010) and the metabolism of lutein, zeaxanthin, and P-cryptox-anthin (Bernstein et ah, 2001 Prasain et ah, 2005 Mein et ah, 2011). 

If history is any guide, then we foresee great potential for growth in the field of carotenoid analysis in the coming years. Sample preparation methods that quickly and effectively break down and remove sample matrix while preserving carotenoids intact will improve the accuracy of both parent carotenoid and carotenoid metabolite identification and quantitation. 

The synthesis of optically active carotenoidshas been extended to include the preparation of important possible carotenoid metabolites such as (4-)-abscisic acid (126), (-)-xanthoxin (127), (-)-loliolide (128), (-)-actinidiolide (130), and (-)-dihydroactinidiolide (129), all from one starting compound... 

Furthermore, many carotenoid metabolites exist that have distinct functions. One such example shown in Fig. 3 is retinal, the chromophore of visual pigments (rhodopsins) and the light-driven proton pump, bacteriorhodopsin. Other examples are the plant hormone, abscisic acid, or volatile compounds that contribute to the fragrance of roses, for example. 

With regard to the metabolism of primary carotenoid degradation p ucts, recent results obtained by Tang and Suga (57) have indicated a two-step mechanism for the conversion of the primary carotenoid metabolite B-ionone 1 to 14 in Nicotiana tabacum plant cells (cf. Fig. 4). These results revealed, that first of all, the side-chain double bond is hydrogenated by the action of carvone reductase (co-factor NADH), before the carbonyl function is enzymatically reduced in the second step. Importantly, the enantioselectivity of the latter reductase is decisive for the enantiomeric composition in fruits as outlined for theaspirane formation from the labile precursor diol 12 (cf. Fig. 5). The formation of vitispiranes 10, edulans 11 and related Ci3-norisoprenoids (29,30) is known to proceed via similar mechanisms. 

Fig. 4 Biotransformation of the primary carotenoid metabolite B-ionone 1 into...

Today the total synthesis of a carotenoid for structure elucidation is often no longer necessary because of advances in high resolution spectroscopic methods but, when only small amounts of a new natural carotenoid, metabolite or degradation product are available, full spectroscopic characterization may not be possible, and total synthesis of the proposed structure then becomes indispensable, especially to establish its stereochemistry. 

Carotenoids in Photosynthesis Photoresponses in Plants Carotenoids and Vision Development in animals Pigmentation in Animals Pigmentation of Flowers and Fruits Uses of Carotenoids Metabolites of Carotenoids Plant Growth-Regulating Compounds Carotenoids Metabolites as Fungal Pheromones References... 

Some carotenoid metabolites apparently arise during the processing of plant material [e.g., (3S, 5R, 6S)-3-hydroxy-5,6-epoxy-5,6-dihydro-P"ionol (30), 3-oxoactinidiol (31), and l-(2,3,6-trimethylphenyl)-but-2-ene-l-one (32)] are formed during curing of tobacco (Fig. 26.15). These compounds are related to p-damascenone (33) and the aromatic carotenoids. 

Several carotenoid metabolites have important functions. The most important of these to consider is vitamin A, which is a metabolite of /8-carotene. This compound plays a key role in vision and in other biological reactions. The role of vitamin A in animals has been reviewed by Pitt (1971). Trisporic acid, also a metabolite of j8-carotene, is important in sexual reproduction in Mucorales, a group of fungi (Bu Lock et al., 1976). Sporopol-lenin, found in the outer layer (exine) of both spores and pollen, is considered a carotenoid polymer (Krinsky, 1971). It has been proposed that abscisic acid, an important plant growth regulator, may be a carotenoid metabolite, but a direct biosynthetic pathway from GGPP seems more probable (Burden and Taylor, 1976). 

The most important carotenoid metabolites in animals are the vitamins A vitamin Aj (4.131), its 3,4-didehydro-derivative (vitamin A2), retinaldehyde (4.130) and its 3,4-didehydro-derivative. These vitamins are the basis of rhodopsin and other visual pigments. Retinaldehyde is formed by oxidative cleavage of jS-carotene via the peroxide (4.129) and the reaction is catalysed by an enzyme in the intestinal mucosa. 

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