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BETA CAROTENE.
Term Paper ID:24884
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Essay Subject:
Structure, chemistry, biological activity, focusing on antioxidant & anti-carcinogenic properties in animal systems.... More...
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7 Pages / 1575 Words
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Paper Abstract:
Structure, chemistry, biological activity, focusing on antioxidant & anti-carcinogenic properties in animal systems.
Paper Introduction:
Beta Carotene
The carotenoids as a group, and specifically the beta carotenes, are known to serve a variety of functions in living cells. Presented here is an overview of the structure, chemistry, and biological activity of beta carotene, with emphasis on its capacity as an antioxidant and anti-carcinogen in animal systems.
Beta carotene is a member of a class of pigments called carotenoids, which occur naturally in plants and are found as well in animals. A precursor of vitamin A, also called provitamin A, it is found as an orange-red pigment in terrestrial plants, algae and some marine mammals. After purification, it appears as ruby-red crystals, easily oxidized on contact with air, with MP 184 degrees, MW 536.44. It is insoluble in water, slightly soluble in alcohol, soluble in chloroform, carbon disulfide, ether and benzene. Its pla
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66:13 1-2; 1997.12. Ann.Rev. Aprecursor of vitamin A, also called provitamin A, it is found as an orange-red pigment in terrestrial plants, algae and some marine mammals. Carcinogenesis. In a very extensive review of the actions of carotenoids inbiological systems, Krinsky (5) observes that while carotenoids were firstisolated from carrots by Wackenroder in 1831, they did not reach prominenceas legitimate study until after 1952. J. J.Cancer. The vitamin book. U. 12th ed.Van Nostrand Reinhold; 1993. 15:561-565; 1975. Med. PrimaPublishing; 1996.13. In addition, exposure to or formation of free-radicals in cells has been implicated in the pathogenesis of cancer (4,5).While essential for life, oxygen in cells promotes the formation of free-radicals which can dammage cell tissue and function; it is at the level ofinhibition of free-radical formation that beta carotene exercises itsprotective role. Canad. Leo, M.; Aleynik. S. Fund. In a study where baboons weregiven alcohol to simulate alcoholism, Mezey (11) reports that usingsupplemental retinoids in an attempt to correct deficient hepatic vitamin Aconcentrations damaged liver mitochondria and produced hepaticinflammation. Am. Lodish, H.; Baltimore, D.; Berk, A.; Zipursky, S.; Matsudaira,P.; Darnell, J. Absorption, metabolism, and transport of carotenoids.FASEB J. 12(2):4-11; 1998. In plants, beta carotene's absorption spectrum matches the actionspectrum of photosynthesis, indicating the pigment is integral in thisprocess. 9. Freeman and Sons; 1995.1 . Pung, A.; Rundhaug, J.; Yoshikawa, C.; Bertram, J. The functional differences betweenthe activities of beta carotene and its metabolic end-products, and themechanisms of the selective process controlling differential uptake and useof carotenoids invites study. The enzymatic cleavage of beta carotene: stillcontroversial. Mezey, E. Stahl, W.; Nicolai, S.; Briviba, K.; Hanusch, M.; Broszeit, G.;Peters, M.; Martin, H.; Sies, H. 4. (16) cites numerous examples ofthe anti-carcinogenic properties of carotenoids, with emphasis on mediationof oxygen-induced toxicity and genotoxicity. Arch.Int. (4) showed that the mechanism ofprotection was more likely localized at the colon epithelium rather thanrelated to simple blood plasma concentrations, indicating a site-specificeffect of beta carotene as an antioxidant. W.H. Nutr.Rev. Pharmacopeia. Beta carotene is a member of a class of pigments called carotenoids,which occur naturally in plants and are found as well in animals. 5. Am. 2nd ed. Tumors can impair free gap junctioncommunication between cells; these authors suggest that beta carotene, evenin synthetic forms, efficiently induces gap junction formation, and thatthe ring size of the molecule is important in determining its activeproperties. Rev. 53(5):134-7; 1995.25. Diet and Cancer. The USP guide to vitamins and minerals.Avon Books; 1996.23. Appl. The role of beta carotene in influencing heart disease has yet to bedefined. The 'dual-face' of this compound has also beenevaluated in instances of liver pathology. These authors havesuggested that these compounds regulate genetic repair at the level ofbenzo[a]pyrene-induced DNA adducts. The contributing role that beta carotene plays with regard tothe activity of other antioxidants, such as tocopherol and ascorbic acid,also deserves more attention. Little is known about the theabsorption and use of non-provitamin A but related carotenoids and theirrelationship to the biological activity of beta carotene. 2. 6. Dietary vitamin A and human lung cancer. 114(1-2):231-2;1997. Torsell, K. Vitamin A and beta carotene influence thelevel of benzo[a]pyrene-induced DNA adducts and DNA repair activiitesin hamster tracheal epithelium in organ culture. Additional work has revealedthat beta carotene, exclusive of the presence of other antioxidants such asalpha tocopherol and apparently in a manner unrelated to its antioxidantabilities, can "up-regulate" the expression of at least one generesponsible for the production of a key component in gap junction formation(25). 18(1):89-92; 1997.21. Biol. The first recognized fat-soluble vitamin, vitamin Awas first chemically characterized by two independent studies in 193 (12:19), each of which correlated the reversal of poor growth and eyeproblems in fat-starved animals with the addition of butter and cod liveroil to their diet. 3rd ed. Silverman, H. Is there a role for antioxidant vitamins inthe prevention of cardiovascular diseases? Beta carotene: friend or foe? Additional oxidationresults in apocarotenoic acids which ultimately yield retinoic acid viamitochondrial beta-oxidation. Omaye, S.; Krinsky, N.; Kagan, V.; Mayne, S.; Liebler, D.;Bidlack, W. The protectiverole of dietary antioxidants against free radical formation in anaerobeswith continued exposure to oxygen. The carotenoids as a class and beta carotene specifically serve avariety of important biological and chemical functions in both plants andanimals. Beta Carotene The carotenoids as a group, and specifically the beta carotenes, areknown to serve a variety of functions in living cells. Nutr. The role of beta carotene in in vivoimmune system functions is less clear. Short- and long-term beta carotenesupplementation do not influence T-cell-mediated immunity in healthyelderly patients. 153:2149-2154; 1993.19. Literature Cited 1. Healso cites this compound's ability to protect against smoking-relatedintraepithelial neoplasia but notes that beta carotene may increase risk oflung cancer in very heavy, chronic smokers. Lohn, E.; Yusuf, S. (2 ), who suggest that antioxidant effectiveness is dependent on betacarotene's ability to intercept with reactive oxygen species that maypotentially damage DNA. Retinoids and alcoholic liver disease. Nutr. Lewis, R. Actions of carotenoids in biological systems. J. Presented here is anoverview of the structure, chemistry, and biological activity of betacarotene, with emphasis on its capacity as an antioxidant and anti-carcinogen in animal systems. Charleux, J-L. Your Patient & Fitness. 7. Krinsky, N. This "quenching" capacity deactivates such entities as singletmolecular oxygen and peroxyl radicals. Biological activities of natural andsynthetic carotenoids. Bjelke, E. There is near symmetry around the middle C15,15' bond(12) and fission at this point produces two molecules of vitamin A- retinolor retinal (22), R=CH2 and CHO respectively. 13:4 7-33.17. Betacarotene and canthaxanthin inhibit chemically- and physically-inducedneoplastic transformation in 1 T1/2 cells. Murray, M. Beta carotene may also bemetabolized to a series of shortened carbonyls. Zhang, L.-X.; Cooney, R.; Bertram, J. Clin. This group of compounds, includingbeta carotene, exhibits many activities in cell functions, one of the bestdocumented being that of antioxidant and free-radical scavenging. Many cellregulatory events (i.e., protein phosphorylation, site-specifictranscription factor binding on DNA) are sensitive or driven by oxidant-antioxidant status (13). of Cardiol.13(1 ):957-65; 1997.11. Radic. 54(11)S1 9-S114; 1996. It is insoluble in water,slightly soluble in alcohol, soluble in chloroform, carbon disulfide, etherand benzene. Nutr. Taylor and Francis; 1997.22. While deficiencies in vitamin A havebeen linked to increased mortality in immuno-compromised patients (8),additional supplementation of beta carotene to the diet of healthy elderlypatients had neither enhancing nor suppressive effects on these patient's T-cell-mediated functions (17). As a result of important changes in experimental scope design, therole of beta carotene in the progression of certain cancers and pathologyhas recently become less clear, and increases in mortality or a lack ofsubstantiated effect have been reported. Protection by betacarotene and related compounds against oxygen-mediated cytotoxicity andgenotoxicity. Additional mechanisms by which cells resist malignancy include activerepair of molecules at the gene level. Am. A related study in rats given alcohol and provitamin Asupplements showed that beta carotene acted as a toxin, by potentiatingeven more the expected hepatotoxicity of alcohol in liver (7). 8. Carotenoids up- regulateconnexin 43 gene expression independent of pro- vitamin A or antioxidantproperties. Cancer Letters. Hirayama, T. In an in-vitro study relating dietary beta carotene torisk of colonic cancer, Kemble et al. The biosynthesis in plants parallels that of squalene, with tail-to-tail coupling of geranylgeranyl pyrophosphates producing the C4 terpenesor carotenes, yellow-red conjugated polyphene pigments (21:3 ). Clin. J. Lazar, J.; Yiachos, G. They further note that the antioxidant abilities ofcarotenoids is highly variable in vivo, being dependent on differences instructure, in vivo interactions and the influence of environment. It has been suggested that beta carotene provides protectionagainst cardiovascular disease (CAD)--but only in smokers (2). 4 (2):163-174; 1997.14. In this way, it may extend the range of lightthat can be absorbed and used by plants in photosynthesis. 1 :542-551; 1996.15. Scientific AmericanBooks. Natural product chemistry: a mechanistic, biosyntheticand ecological approach. In a study of the dietary habits of over 265, Japanese,Hirayama (3) also showed that risks for a variety of cancers, includingstomach and cervical, were powerfully influenced by diet, especially withregard to inclusion of the "carotin", as it occurred naturally in thecarrots, spinach, green peppers, pumpkins, and turnip leaves eaten by thestudy participants. Afterpurification, it appears as ruby-red crystals, easily oxidized on contactwith air, with MP 184 degrees, MW 536.44. Cleavage and the production of intermediaryforms, particularly apocarotenals, is not yet well understood and may havesignificance for biological activity. Rousseau, E.; Davison, A.; Dunn, B. A recent review by Rousseau et al. Bantam; 1985.2 . 1:67-81; 1979. Int. Cancer. Its plant sources include vegetables with dark, green leaves,carrots, pumpkins, certain fruits such as canteloupe, and wild vegetation.Current derivation techniques include extraction from carrots and palm oil,concentration by chromatographic processes from alfalfa, and separationfollowing the fermentation of corn and soybean oils (8:226). Possible means by which betacarotene acts as a cancer preventive have also been described by Stahl etal. Wolf, G. 52:57 7- 12; 1992. Carotenoids are transported in plasma by lipoproteins, but themeans of differential distribution in terms of tissue uptake andmaintenance is unclear. 66:1461-91; 1997. Whenwater-dispersible beadlets of beta carotene and canthaxanthin were added toC3H/1 T1/2 cells in culture, Pung et al. Clin.Nutr. Can antioxidants reduce the risk ofcoronary artery disease? Increased mortality associated with vitamin Adeficiency during human immunodeficiency virus Type I infection. 9:1533-39; 1988.16. It was shown by Wolterbeek et al.(23) that both vitamin A and beta carotene enhance the ability of the DNAfound in hamster tracheal epithelium to repair itself. by Hippocrates, who observed that night blindness could bealleviated by his suggested ingestion of beef liver (a rich source ofvitamin A) (19:155). Med. Cancer Res. (13) have proposed that the polyene chain is most likelyresponsible for beta carotene's ability to act as an antioxidant and free-radical scavenger. Omaye (13) emphasizes that thebiological processes by which beta carotene act as either protectant ortoxin are not well known at this time. In supplemented smokers, whilegreater risk is correlated with greater smoking intensity, current smokershave the highest rates and former smokers show a reduced incidence in lungcancer. Free. Carcin. Parker, R. S.; Aleynik, M.; Lieber, C. Santos, M.; Leka, L. Encyclopedia of nutritional supplements. In addition, these authors proposethat the antioxidant capabilities exhibited by beta carotene may operateindependently of one another. J. Molecular Biology. Hawley's Condensed Chemical Dictionary. 13:561-87; 1993. Charleux (2) provides manyinstances of carotenoid activity, including its role in the inhibition ofneoplastic transformation, regression of cervical dysplasia, and thereduction in risk of cataracts and age-related macular degeneration. Cancer Letters.91(2):2 5-214; 1995.24. Beta carotenebeadlets potentiate hepatotoxicity of alcohol. In animals, beta carotene is taken up by passive diffusion across theintestinal mucosa, the site where initial central cleavage and metabolismoccurs (14). Nutr. A very early study by Bjelke (1)demonstrated the ability of vitamin A to modify the expression of pulmonarycarcinogens in male smokers and provided some the earliest evidence for theability of beta carotene and vitamin A to scavenge free-radicals in vivo.This study of more than 8, smokers over five years found strongcorrelations of lowered lung cancer rates associated with the ingestion ofvitamin A. (15) report that both substancesdecreased the extent of malignant transformation normally induced bycarcinogenic chemical or x-ray treatments. The precise means by which the enzymaticcleavage of beta carotene occurs in vivo is still controversial and thesignificance of reported frequent excentric cleavage is not known (24). The pigment absorbs light at wavelengths other than those used bychlorophyll b or a (9:783). 66:917-24; 1997.18. In addition, moreneeds to be done to elucidate the specificity of such compounds to thetissues where they exert their biological activity, and how localization ismaintained. Beta carotene is transformed in the liver to vitamin A, which isnecessary to maintain skin, mucous membranes, and the function of visualpurple, a pigment in the primate fovea required for night vision (22:157).Associations of vitamin A ingestion with improved health were reported in15 B.C. Thisvariability of expression may also be due in part to genetic factors. Tox. Semba, R. 3. Omaye et al. It is not known whether risk in heavy smokers using beta caroteneis mediated by nicotine metabolic routes or is somehow a result ofcompetition between the provitamin and other cancer-producing substances.Cigarette smoking is a highly oxidative process, which may result incarotenoid degradation and the formation of more destructive pro-oxidantradicals in lung tissue. Beta carotene, vitamin C and vitamin E. Kemble, R.; Glass, H.; Hillman, K.; Ratcliffe, B. Additionalrecent studies using clinical trials have found little or no substantiationof prior reports of the ability of beta carotene to prevent heart disease(6,1 ). Wolterbeek, A.; Roggeband, R.; van Moorsel, C,; Baan, R.; Koeman,J.; Feron, v.; Rutten, A. Acylcopropanoid prehytoene forms first, re-arranging either assisted byNADPH to lycopersene or to cis- or trans- phytoene, with additionaldehydrogenations. Nutr. In the case of animal systems, it is premature to conclude thatbeta carotene has only one role in the expression of cancers and diseases,and additional work needs to be done.
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