Zeaxanthin

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Zeaxanthin
Structural formula of zeaxanthin
Space-filling model of the zeaxanthin molecule
Names
IUPAC name
4-[18-(4-hydroxy-2,6,6-trimethyl-1-cyclohexenyl)-3,7,12,16-tetramethyl-octadeca-1,3,5,7,9,11,13,15,17-nonaenyl]-3,5,5-trimethyl-cyclohex-3-en-1-ol
Other names
β,β-carotene-3,3'-diol
Identifiers
144-68-3 YesY
3D model (Jmol) Interactive image
ChEBI CHEBI:27547 YesY
ChemSpider 4444421 YesY
ECHA InfoCard 100.005.125
E number E161h (colours)
PubChem 5280899
UNII CV0IB81ORO YesY
Properties
C40H56O2
Molar mass 568.88 g/mol
Appearance orange-red
Melting point 215.5 °C (419.9 °F; 488.6 K)
insol.
Related compounds
Related compounds
lutein
xanthophyll
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
YesY verify (what is YesYN ?)
Infobox references

Zeaxanthin is one of the most common carotenoid alcohols found in nature. It is important in the xanthophyll cycle. Synthesized in plants and some micro-organisms, it is the pigment that gives paprika (made from bell peppers), corn, saffron, wolfberries, and many other plants and microbes their characteristic color.[1][2]

The name (pronounced zee-uh-zan'-thin) is derived from Zea mays (common yellow maize corn, in which zeaxanthin provides the primary yellow pigment), plus xanthos, the Greek word for "yellow" (see xanthophyll).

Xanthophylls such as zeaxanthin are found in highest quantity in the leaves of most green plants, where they act to modulate light energy and perhaps serve as a non-photochemical quenching agent to deal with triplet chlorophyll (an excited form of chlorophyll) which is overproduced at high light levels during photosynthesis.

Animals derive zeaxanthin from a plant diet.[2] Zeaxanthin is one of the two primary xanthophyll carotenoids contained within the retina of the eye. Within the central macula, zeaxanthin is the dominant component, whereas in the peripheral retina, lutein predominates.

Zeaxanthin supplements are typically taken on the supposition of supporting eye health. Although there are no reported side effects from taking zeaxanthin supplements, this possible benefit remains scientifically unproven, despite extensive ongoing research to define dietary or supplemental effects of zeaxanthin and lutein.[3][4][5]

As a food additive, zeaxanthin is a food dye with E number E161h.

Isomers and macular uptake[edit]

Lutein and zeaxanthin have identical chemical formulas and are isomers, but they are not stereoisomers. The only difference between them is in the location of the double bond in one of the end rings. This difference gives lutein three chiral centers whereas zeaxanthin has two. Because of symmetry, the (3R,3'S) and (3S,3'R) stereoisomers of zeaxanthin are identical. Therefore, zeaxanthin has only three stereoisomeric forms. The (3R,3'S) stereoisomer is called meso-zeaxanthin.

The principal natural form of zeaxanthin is (3R,3'R)-zeaxanthin. The macula mainly contains the (3R,3'R)- and meso-zeaxanthin forms, but it also contains much smaller amounts of the third (3S,3'S) form.[6] Evidence exists that a specific zeaxanthin-binding protein recruits circulating zeaxanthin and lutein for uptake within the macula.[7]

Due to the commercial value of carotenoids, their biosynthesis has been studied extensively in both natural products and non-natural (heterologous) systems such as the bacteria Escherichia coli and yeast Saccharomyces cerevisiae. Zeaxanthin biosynthesis proceeds from beta-carotene via the action of a single protein, known as a beta-carotene hydroxylase, that is able to add a hydroxyl group (-OH) to carbon 3 and 3' of the beta-carotene molecule. Zeaxanthin biosynthesis therefore proceeds from beta-carotene to zeaxanthin (a di-hydroxylated product) via beta-cryptoxanthin (the mono hydroxylated intermediate). Although functionally identical, several distinct beta-carotene hydroxylase proteins are known. Due to the nature of zeaxanthin, relative to astaxanthin (a carotenoid of significant commercial value) beta-carotene hydroxylase proteins have been studied extensively.[8]

Relationship with diseases of the eye[edit]

Several observational studies have provided preliminary evidence for high dietary intake of foods including zeaxanthin with lower incidence of age-related macular degeneration (AMD), most notably the Age-Related Eye Disease Study.[9][10]

In general, however, there remains insufficient evidence to assess the effectiveness of dietary or supplemental zeaxanthin or lutein in treatment or prevention of AMD, or the formation or progression of cataracts.[2][9][11] Any benefit is more likely to be apparent in subpopulations of individuals exposed to high oxidative stress, such as heavy smokers, alcoholics or those with poor nutrition.[12]

In 2005, the US Food and Drug Administration rejected a Qualified Health Claims application by Xangold, citing insufficient evidence supporting the use of a zeaxanthin-containing supplement in prevention of AMD.[13]

Natural occurrence[edit]

Zeaxanthin is the pigment that gives paprika (made from bell peppers), corn, saffron, wolfberries, and many other plants their characteristic color.[2] Spirulina is also a rich source and can serve as a dietary supplement.[14] Zeaxanthin breaks down to form picrocrocin and safranal, which are responsible for the taste and aroma of saffron.[15]

Foods containing the highest amounts of lutein and zeaxanthin are dark green leaf vegetables, such as kale, spinach, turnip greens, collard greens, romaine lettuce, watercress, Swiss chard and mustard greens.[2][16]

Safety[edit]

An acceptable daily intake level for zeaxanthin was proposed as 0.75 mg/kg  of body weight/day, or 53 mg/day for a 70 kg adult.[17] In humans, an intake of 20 mg/day for up to six months had no adverse effects.[17]

References[edit]

  1. ^ Encyclopedia.com. "Carotenoids". Retrieved 6 May 2012. 
  2. ^ a b c d e "Lutein + Zeaxanthin Content of Selected Foods". Linus Pauling Institute, Oregon State University, Corvallis. 2014. Retrieved 20 May 2014. 
  3. ^ Age-Related Eye Disease Study 2 Research Group (2013). "Lutein + zeaxanthin and omega-3 fatty acids for age-related macular degeneration: The Age-Related Eye Disease Study 2 (AREDS2) randomized clinical trial". JAMA. 309 (19): 2005–15. doi:10.1001/jama.2013.4997. PMID 23644932. 
  4. ^ Pinazo-Durán, M. D.; Gómez-Ulla, F; Arias, L; Araiz, J; Casaroli-Marano, R; Gallego-Pinazo, R; García-Medina, J. J.; López-Gálvez, M. I.; Manzanas, L; Salas, A; Zapata, M; Diaz-Llopis, M; García-Layana, A (2014). "Do Nutritional Supplements Have a Role in Age Macular Degeneration Prevention?". Journal of Ophthalmology. 2014: 901686. doi:10.1155/2014/901686. PMC 3941929Freely accessible. PMID 24672708. 
  5. ^ Koo, E; Neuringer, M; Sangiovanni, J. P. (2014). "Macular xanthophylls, lipoprotein-related genes, and age-related macular degeneration". American Journal of Clinical Nutrition. 100 (Supplement 1): 336S–346S. doi:10.3945/ajcn.113.071563. PMID 24829491. 
  6. ^ Nolan, J. M.; Meagher, K; Kashani, S; Beatty, S (2013). "What is meso-zeaxanthin, and where does it come from?". Eye. 27 (8): 899–905. doi:10.1038/eye.2013.98. PMC 3740325Freely accessible. PMID 23703634. 
  7. ^ Li, B; Vachali, P; Bernstein, P. S. (2010). "Human ocular carotenoid-binding proteins". Photochemical & Photobiological Sciences. 9 (11): 1418–25. doi:10.1039/c0pp00126k. PMC 3938892Freely accessible. PMID 20820671. 
  8. ^ Scaife, Mark A.; Ma, Cynthia A.; Ninlayarn, Thanyanun; Wright, Phillip C.; Armenta, Roberto E. (22 May 2012). "Comparative Analysis of β-Carotene Hydroxylase Genes for Astaxanthin Biosynthesis". Journal of Natural Products. 75 (6): 120522090507004. doi:10.1021/np300136t. PMID 22616944. 
  9. ^ a b Krishnadev N, Meleth AD, Chew EY (May 2010). "Nutritional supplements for age-related macular degeneration". Current Opinion in Ophthalmology. 21 (3): 184–9. doi:10.1097/ICU.0b013e32833866ee. PMC 2909501Freely accessible. PMID 20216418. 
  10. ^ SanGiovanni JP, Chew EY, Clemons TE, et al. (September 2007). "The relationship of dietary carotenoid and vitamin A, E, and C intake with age-related macular degeneration in a case-control study: AREDS Report No. 22". Archives of Ophthalmology. 125 (9): 1225–1232. doi:10.1001/archopht.125.9.1225. PMID 17846363. 
  11. ^ Chong EW, Wong TY, Kreis AJ, Simpson JA, Guymer RH (October 2007). "Dietary antioxidants and primary prevention of age related macular degeneration: systematic review and meta-analysis". BMJ (Clinical Research Ed.). 335 (7623): 755. doi:10.1136/bmj.39350.500428.47. PMC 2018774Freely accessible. PMID 17923720. 
  12. ^ Fernandez MM, Afshari NA (January 2008). "Nutrition and the prevention of cataracts". Current Opinion in Ophthalmology. 19 (1): 66–70. doi:10.1097/ICU.0b013e3282f2d7b6. PMID 18090901. 
  13. ^ "Letter of Denial - Xangold Lutein Esters, Lutein, or Zeaxanthin and Reduced Risk of Age-related Macular Degeneration or Cataract Formation (Docket No. 2004Q-0180". US FDA, Qualified Health Claims. 19 December 2005. 
  14. ^ Yu, B.; Wang, J.; Suter, P. M.; Russell, R. M.; Grusak, M. A.; Wang, Y.; Wang, Z.; Yin, S.; Tang, G. (2012). "Spirulina is an effective dietary source of zeaxanthin to humans". British Journal of Nutrition. 108 (4): 611–619. doi:10.1017/S0007114511005885. PMID 22313576. 
  15. ^ Frusciante, Sarah; Diretto, Gianfranco; Bruno, Mark; Ferrante, Paola; Pietrella, Marco; Prado-Cabrero, Alfonso; Rubio-Moraga, Angela; Beyer, Peter; Gomez-Gomez, Lourdes (2014-08-19). "Novel carotenoid cleavage dioxygenase catalyzes the first dedicated step in saffron crocin biosynthesis". Proceedings of the National Academy of Sciences. 111 (33): 12246–12251. doi:10.1073/pnas.1404629111. ISSN 0027-8424. PMC 4143034Freely accessible. PMID 25097262. 
  16. ^ "Foods highest in lutein-zeaxanthin per 100 grams". Conde Nast for the USDA National Nutrient Database, release SR-21. 2014. Retrieved 23 December 2015. 
  17. ^ a b Edwards JA (2016). "Zeaxanthin: Review of Toxicological Data and Acceptable Daily Intake". Journal of Ophthalmology. 2016: 3690140. doi:10.1155/2016/3690140. PMC 4738691Freely accessible. PMID 26885380. Retrieved 2016-07-23.
    • In their evaluation of the safety of synthetic zeaxanthin as a Novel Food, the EFSA NDA Scientific Panel [37] applied a 200-fold safety factor to this NOAEL to define an ADI of 0.75 mg/kg bw/day, or 53 mg/day for a 70 kg adult.
    • Formulated zeaxanthin was not mutagenic or clastogenic in a series of in vitro and in vivo tests for genotoxicity.
    • Information from human intervention studies also supports that an intake higher than 2 mg/day is safe, and an intake level of 20 mg/day for up to 6 months was without adverse effect.